Note: Descriptions are shown in the official language in which they were submitted.
CA 022204~9 1997-11-27
W O ~C/10939 PCTnJS96/10002
Expression of Functional Verfebrate Phospholipases in Yeasf
~ Cross Refèrence to R~ t~Applications
This invention is a Continnzttion-in Part of U.S.S.N 08/431,632, filed on June 7,
1995.
Field of the Invention
This invention relates to functional expression of heterologous phospholipases in
yeast, the recombinant yeast cells, and methods for using the engineered cells, including,
inter alia, the identification of agonists and antagonists of signal transduction pathways which
involve phospholipases.
~ackground of the Invention
Eukaryotic phospholipases are known to be involved in cellular signal tr~n~cluction
processes important in regulation of cellular growth, dirrel~;llliation and secretory events in
numerous cell types. The binding of agonists to certain cell surface receptors leads to the
generation of a variety of sign~lin~ molecules which include phospholipid derived second
messengers. The phospholipid-derived second messengers mediate both transient and
sust~in~cl responses and are implicated in a wide variety of physiological responses including
growth regulation, immnn~ modulation and neulo~ mi~ion. Studies over the last two
decades indicate that membrane lipids serve as substrates for the variety of different
phospholipases that are responsible for the generation of phospholipid derived second
messengers. These include phosphatidylinositols (the substrate for phospholipase C
enzymes, see below), phosphatidylcholine, phosphatidylethanolamine, sphingolipids (e.g.
sphingomyelin, sphingosine, sphingosine phosphate and sphingosine phosphocholine). See
Dicheva and Irvine (1995) Cell 80:269-278 for a recent review.
There are at least five distinct types of phospholipase activities known to be
responsible for the generation of phospholipid second messengers, namely phospholipase A
(including phospholipases Al and A2), phospholipase B, phospholipase C, phospholipase D
and sphingomyelinase. The distinguishing feature of each of these phospholipases is the
substrate bond cleaved, and hence the second mec~l-ngers derived from a given phospholipid
-~ substrate.
PLAl and PLA2 (E.C.3.1.1.4) catalyze the release of fatty acids, in particular
35 arachidonic acid (AA), from the snl and sn2 positions of 1,2-diacylglycerol, 3-
phosphocholines, generating AA and lysophosphorylcholine (lyso-PC) respectively. AA, in
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-- 2 --
turn, has at least four known metabolic fates, namely, generation of proinfl~mm~tf-ry
eicosanoids (leukotrienes and prost~ n~1in~), reincorporation into existing membrane
phospholipids, reincorporation into soluble phospholipid metabolic pathways, and direct
secretion from cells. In addition, lyso-PC serves as the precursor for the production of lipid
5 second messengers like platelet activating factor (PAF). cDNA and genomic clones encoding
the pancreatic form of PLA2 have been isolated from a variety of eukaryotic sources
including bovine (Tanaka et al. 1987), rat (Ohara, O. et al. 1986 and 1990, and Kusunoki, et
al. 1990), dog (Kerfelec et al. 1986),and pig (Seilhamer et al. 1986). In addition to the
pancreatic PLA2 isofor~n, a variety of cellular PLA2 (cPLA2) isoforms have been isolated
10 from a wide variety of m~mm~ n tissues and cell tvpes including brain (Gray and
Strickland, 1982), liver (DeWinter et al. 1982), spleen (Terarnoto et al. 1983), macrophages
(Trotter and Smith (1986) Neurochem. Res. 11:349-361), leukocytes (Traynor and Authi
1981), and others (for a review see Ban Den Bosch, 1980). Clones for human (Clark et al.
1991; Sharp et al 1991) and murine (Clark et al. 1991) cPLA2 gene products have been
15 isolated and characterized. The 85kDa gene product encoded by these cDNAs is expressed in
cells types involved in the infl~mm~ ry response (neutrophils, platelets, monocytes and
macrophages) and its expression is regulated by, for example, tumor necrosis factor, IL-l,
TGF-,B, MCSF and glucocorticoids.
Phospholipase B (PLB) has been described in a variety of eukaryotic species from20 fungi to m~mm~ls. PLB isoforms have several catalytic properties including the release of
fatty acids from the snl and sn2 positions of phospholipids (as with PLAl and PLA2), the
release of fatty acids from lysopholipids, and in the yeast Saccharomyces cerevisiae,
acyltransferase activity that catalyzes the synthesis of phospholipids from lysophospholipids
(Kuwabara et al. 1989; G~ m~-Diagne 1989; and Lee et al. 1994). Genomic clones for
25 PLB-like enzymes have been isolated from several sources including S. cerevisiae (Lee et al.
1994) and Penicillium notatum (Masuda et al. 1991).
Phospholipase C enzymes (PLC; E.C. 3.1.4.3), of which there are at least four
subfamilies known as PLC-a, -~ , and -~ (For reviews, see F~hee et al. 1989, and Cook and
Wakelam 1992b) catalyze the hydrolysis of phosphatidylinositol (4,5) bisphosphate (PIP2) to
30 form two second messengers, inositol 1,4,5-trisphosphate (IP3) which is involved in the
mobilization of intracellular stores of calcium, and diacylglycerol ~DAG), which binds to and
activates selected isoforms of protein kinase C (PKC, E.C. 2.7.1.37). This class of enzymes,
and second messengers generated by them have been demonslrated to be linked to receptor
tyrosine kin~e~, G-protein coupled receptors and to MIRRs like the T-cell antigen receptor,
35 the B-cell antigen receptor and immunoglobulin Fc receptors
-
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Phospholipase D (PLD; E.C. 3.1.4.4) catalyzes the hydrolysis of phosphatidylcholines
to yield phosphatidic acid (PA) and free choline (see Bishop, Pachter and Pai 1992; and Cook
and W~kel~m, 1992a). While neither PA nor free choline has been shown to function as a
second messenger directly, it has been reported recently that PA or its lyso derivative, lyso-
5 PA, may function to stimulate hydrolysis of polyphosphoinositides, activation of PKC,inhibition of adenylyl cyclase and stimulation of DNA synthesis (Moolenaar et al, 1986;
Murayama and Ui, 1987, Van Corven et al, 1989; and Plevin et al, l991b. refs in Cook and
Wakelam, 1992b), as well as activate kinases directly in a manner similar to DAG (Eppand
and Stafford, 1990, and Bocckina and Exton, 1990, refs in Cook and Wakelarn, 1992b). In
10 addition, phosphatidic acid formed by the action of PLD can be converted to DAG by the
action of phosphatidic acid phosphohydrolase (E.C. 3.1.3.4), and thus serve as a secondary
reservoir for the production of DAG by PLC-independent mech~ni~ms (Bonser et al, 1989
cited in Divechia and Irvine 1995, review, and Cook and Wakelam, 1992b). cDNA clones
for phospholipase D have been isolated from a number of different species including
15 Arcanobacterium haemolyticum (Cuevas, W.A., and J.G.L. Songer, 1993), Corynebacterium
pseudotuberculosis (unpublished, GenBank Accession numbers L16586, L16587), Vibrio
damsela (unpu~lished, GenBank Accession number L16584) and human (Tsang et al. 1993)
Phospholipase C enzymes
Phospholipase C enzymes (PLC; E.C. 3.1.4.3) are intracellular enzymatic mediators
of a wide variety of cellular responses to extracellular stimuli. Binding of hormones, growth
factors, neurotransmitters, and other agonists to specific cell surface receptors initiates the
activation of PLC isozymes, which in turn result in the production of at least two well
characterized active second messengers, inositol-1,4,5-trisphophate (1,4,5-IP3) and sn-1,2-
diacylglycerol (DAG). 1,4,5-IP3 binds to a specific family of intracellular receptors
localized on modified portions of the endoplasmic reticulum that bears homology to the
ryanodine receptor family of intracellular calcium channels (the IP3 receptor family,
reviewed in Berridge, 1993). In addition to functioning as the IP3 receptor, these receptors
also function as IP3-sensitive calcium channels which cause release of intracellular stores of
calciurn upon liganding with IP3.
Increases in intracellular calcium, in turn, result in the transient or sustained activation
of a variety of cellular signaling pathways which include but are not limited to activation of
protein kinase C (PKC) isoforms, transcriptional activation through the Mitogen Activated
Protein Kinase (MAPK) and Jun Kinase (JNK) pathways, and mitogenesis. DAG, on the
other hand, forms a complex with phosphatidylserine and calcium and activates protein
kinase C (PKC) isozymes, which in turn activate signaling pathways by direct
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-- 4 --
phosphorylation of a variety of substrates which include adenylyl cyclases and RAF-l (P.J.
Parker et al, 1986, Coussens et al. 1986a, and Kolch et al. 1993).
The division of PLCs into four classes, a, ,B, ~, ~, originally corresponded to
immunologically distinct proteins of 56 kDa, 150 kDa, 145 kDa, and 85 kDa purified from
5 bovine brain (PLC-~ , and -~) and other tissues including liver, seminal vesicles or uterus
(PLC-a). (Described in Suh et al. 1986; and sllmm~ri7ed in A.J. Morris et al 1990). All of
these enzymes have similar catalytic properties in that they hydrolyze phosphatidyl inositol
(PI), phosphatidyl inositol 4-monophosphate (PIP) and phosphatidyl inositol-
4,5,bisphosphate (PIP2) in a calcium dependent manner, but not phosphatidylcholine,
10 phosphatidylserine or phosphatidylethanolamine. However, these immunologically distinct
isozymes are distinguishable in several regards, not the least of which is that they are all
unique gene products encoded by different genes, as discussed in further detail below. At
the enzymatic level, these enzymes differ with respect to both their catalytic properties and
their modes of regulation. With respect to divalent cation requirements for activity, for
15 exarnple, polyphosphoinositides are the ~ler~ d substrates for the PLC-,B and -~ classes at
low or physiological intracellular calcium concentrations, while PLC-~ isozymes prefer PI
and PIP2 at physiological intracellular calcium concentrations. The modes of regulation of
PLC isozymes also differ considerably with respect to one another. The PLC-~ isozymes are
activated in response to ligand binding to G-protein coupled receptors and are directly
20 stimulated by Ga and G13~ components of h~ tlillleric G-proteins. PLC-~ isozymes, on the
other hand, are activated directly by phosphorylation via receptor and non-receptor tyrosine
kinases. While little is known about the regulation of PLC-a activity in vivo or in viko,
recent studies of PLC-~ regulation suggest that it may be regulated by a novel class of
regulatory proteins (pl22-RhoGAP) that show similarity to the GTPase activating protein
25 homology region of bcr, display GAP activity towards RhoA, and bind to and directly
stimulate PLC-~l (Homma, Y., and Y. Emori, 1995).
Cloning of PLC isozymes
Molecular cloning studies have resulted in the identification of at least ten genes
30 encoding distinct PLC isozymes. Several PLC-a cDNA clones have been isolated from a
variety of sources including rat basophilic leukemia cells (Bennett et al. 1988), mouse
lymphocytes (Hempel and DeFranco, 1991), and bovine tissue (Hirano et al, GenBank
Accession number D16235). Four PLC-,(3 encoding cDNAs encoding subtypes -,B1-4 (Suh et
al 1988; Bahk et al. 1994; Park et al. 1992; Lee et al. 1993; and Kim et al. 1993) have been
35 reported. Two PLC-~ encoding cDNAs have been reported, which correspond to PLC-7rl and
-~2 subtypes (Emori et al. 1989; Suh, et al~ 1988; and Burgess et al. 1990). Three PLC-
~
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WO 96/40939 PCTAUS96/10002
-5-
encoding cDNAs encoding subtypes PLC-~1-3 have been published (reviewed in Cook and
Wakelam, 1 992b and Boyer et al, 1994).
Sequence Comparisons of PLCs
S The overall primary structural identity between PLC-,B isoforms is quite low (~ 30%
identity), in part explaining the differences in size among the (lirrele~lL isozymes and the lack
of immunological cross-reactivity observed with antisera and monoclonal antibodies
developed against the various purified isozymes. PLC-,B, -y,and -~ isozymes share
considerable sequence homology, however, in two regions, variously referred to as the X and
Y regions (Rhee et al, 1989) or regions I and II (Meldrum, et al. 1991). The X region is
approximately 150 amino acid residues in length, while the Y region is approximately 260
residues in length. Between classes, the X regions share approximately 50% identity, while
the Y regions share approximately 40% identity in pairwise comparisons amongst PLC-~
and -~ isozymes. Based on the high degree of conservation of these two domains among the
PLC-~, -y,and -â isozymes, it has been argued that these regions contribute to the catalytic
activity of these enzymes. An additional feature of the spacer region between the X and Y
regions is that in PLC-~3, and -~ classes, these regions are separated by 50-100 residues rich in
serine, threonine and acidic residues with no particular homology to known regulatory motifs,
while in the PLC-y class the X and Y regions are separated by more than 400 residues. This
region of the PLC-y isoforms encodes two src homology 2 (SH2) domains and one src
homology 3 (SH3) domain, which are not present in either PLC-,B or -~ enzymes. As
discussed below, the SH2 domains are involved in regulation of PLC-y activation by receptor
and non-receptor tyrosine kinases.
Sequence analysis of the PLC-a cDNA clones from a rat basophilic leukemia cell line
reveals considerable sequence divergence of this class of phospholipase C isozymes from the
PLC-,~, -y,and -~ isozymes. PLC-a encodes neither the highly conserved X or Y regions
found in all other PLC isoforrns nor SH2 or SH3 domains found in PLC-y isoforms.
Yeast PLC
In addition to the m~mm~ n PLC-,B isoforms discussed in the preceding sections,
various PLCs have been isolated from several other or~ni~m~ Of considerable importance
in this regard is the molecular cloning of the gene (PLCl ) encoding a protein with homology
to the PLC class of phospholipases from the yeast Saccharomyces cerevisiae (Yoko-O et al.
1993; Payne and Fitzgerald-Hayes, 1993; and Flick and Thorner, 1993). Sequence analysis
of the independently identified clones reveals first that all three clones are from the same
CA 022204~9 1997-11-27
WO 9~'10339 PCT~US96/10002
genetic locus and that the protein coded for by this gene most resembles m~mm~ n PLC-~
isozymes both with respect to size of the enzyme encoded by it and with respect to structural
features such as the relative distance between the X and Y domains, the size of the carboxyl
t~rmin~l extension beyond the Y domain, and the absence of SH2 and SH3 domains between
the X and Y motifs (t-his last point is to be expected as yeast show no evidence of
phosphotyrosine modifcation by biochemical analyses). Flick and Thorner (1993)
o~ ssed and purified this enzyme from yeast and demonstrated an associated
phospholipase C activity with divalent cation requirement and substrate ~lef~ ces that
resemble those of m~mm~ n PLC-~ isozymes. Finally, genetic analysis of S. cerevisiae
10 strains with deletions at the PLCl locus (plcl~) reveal a variety of conditionally lethal
phenotypes associated with the plcl ~ genotype, such as, sensitivity to high osmolarity, poor
growth on carbon sources other than glucose (i.e. galactose, raffinose, glycerol/ethanol),
temperature sensitive growth at elevated t~ p~ldllres (>35~C) and finally, chromosome
missegregation (~lick and Thorner, 1993, and Payne and Fitzgerald-Hayes, 1993).
Expression of Foreign Proteins in Yeast Cells
A wide variety of foreign proteins have been produced in S. cerevisiae, that remain in
the yeast cytoplasm or are directed through the yeast secretorv pathway (~ing.cm~n et al.
TIBTECH 5, 53 (1987). These proteins include, as examples, insulin-like growth factor
20 receptor (Steube et al. Eur. J. Biochem. 198, 651 (1991), influenza virus hem~gglutinin
(Jabbar et al. Proc. Natl. Acad. Sci. 82, 2019 (1985), rat liver cytochrome P-450 (Oeda et al.
DNA 4, 203 (1985) and functional m~mm~ n antibodies (Wood et al. Nature 314, 446(1985). Use of the yeast secretory pathway is ~l~r~ d since it increases the likelihood of
achieving faithful folding, glycosylation and stability of the foreign protein. Thus, expression
25 of heterologous proteins in yeast often involves fusion of the signal sequences encoded in the
genes of yeast secretory proteins (e.g., a-factor pheromone or the SUC2 [invertase] gene) to
the coding region of foreign protein genes.
A number of yeast ~ples~ion vectors have been designed to permit the constitutive or
regulated expression of foreign proteins. Constitutive promoters are derived from highly
30 expressed genes such as those encoding glycolytic enzymes like phosphoglycerate kinase
(PGKl) or alcohol dehydrogenase I (ADHl) and regulatable promoters have been derived
from a number of genes including the galactokinase (GAL 1) gene. In addition,
supersecreting yeast mutants can be derived; these strains secrete m~mm~ n proteins more
efficiently and are used as "production" strains to generate large quantities of biologically
35 active m~mm~ n proteins in yeast (Moir and Davidow, Meth. in Enzymol. 194, 491 (1991).
The following two reviews of the field are incorporated herein by reference in their entireties:
_
CA 022204~9 1997-ll-27
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--7--
"The Molecular and Cellular Biology of the Yeast. Saccharomyces, Genome dynamics,
Protein Synthesis, and Energetics." 1991. Edited by J.R.Broach, John Pringle and Elizabeth
Jones. Cold Spring Harbor Laboratory Press; "Guide to Yeast Genetics and Molecular
Biology" 1991. Methods in Enzymology vol. 194. Edited by Christine Guthrie and Gerald
R. Fink, Academic Press.
Several groups have ~Le~ ed to express phospholipases in yeasts. Yoko-o et al.,
((1993) Proc. Natl. Acad. Sci. USA 90:1804) claim to achieve complementation of a yeast
PLC defect with an uncoupled rat PLC~l. Yoko-o et al. report the cloning of PLC from S.
cerevisiae by PCR methodology using primers designed to incorporate sequences from two
10 conserved amino acid sequences found in the X-region of m~mm~ n PLC enzymes After
cloning the gene, they proceeded to make gene disruptions at the PLCl locus. Heterozygous
diploid transformant (PLCl/plcl ::HIS3) were sporulated and tetrad analyses were performed.
In the TYl background, all four spores were found to be viable at a range of temperatures
including 1 8~C, 30~C, and 37~C. In the TY4 background, Yoko-o et al. observed lethality at
15 30~Cin tetrad analyses. These phenotypes are in contradiction to those described herein, and
those reported by Flick and Thorner in the art, where conditional lethality at 37~C is
observed. This is important because it is not possible to measure complementation of a
growth defect under the nonselective conditions of the Yoko-o et al experiments. Thus,
Yoko-o et al. do not observe functional integration of the rat PLC~ into the yeast cell.
Arkin~t~ll et al ((1995) Mol. Cell. Biol. 15:1431) expressed a mz~mmz~ n platelet-
derived growth factor,B receptor and PLC~2 in Schizosaccharomyces pombe. Arkin~t~ll et al.
found that in cells coexpressing the mouse PDGF,B receptor and PLC~2, levels of
[3H]inositol phosphates in radioactively labeled yeast cells were increased. Coexpression of
c-src was also found to result in phospholipid hydrolysis. Because these experiments only
25 measure the immediate biochemical consequence of phospholipase C~ stimulation, this work
also fails to teach the functional integration of a m~mm~ n PLC~ into a yeast cell.
Brief Description of the Figures
Figure 1 is a graphic representation showing human phospholipases and Ga 16
30 complementation of the plcl growth defect on high salt medium: S cerevisiae strain
CY1630 ~MATa plcl~l::His3 ade2-101 his3~200 leu2~1 lys2-801 trpl~l ura3-52)
transformed with plasmids carrying each of the following as described in the text was
streaked out in sectors 1-6: (1) Gallp-rat PLC-,~l and GPAlp-Gal6; (2) CUPl-human PLC-
,32 and no G protein; (3) CUPl-human PLC-,B2 and GPAlp-Gai2-Q205L; (4) CUPl-human
35 PLC-~2 and GPAlp-GaS-Q227L; (5) CUPl-human PLC-,~2 and GPAlp-Gal6; (6) No PLC
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W O~6/10339 PCT~US96/10002
--8--
and GPA1-Gal6. In the figure the symbol (+) represents growth and (-) represents no
growth.
Summary of the Il2vention
The present invention relates to the functional expression of m~mm~ n
phospholipases in yeast cells. The use of the engineered yeast cells in identifying potential
inhibitors or activators of ~e m~mm~ n phospholipase, or of other proteins which belong to
a phospholipase signal tr~nc~ tion pathway, i.e., proteins which are naturally or artificially
"coupled" to the mslmm~ n phospholipase in the engineered yeast cell is also within the
scope of the invention. The te~n "coupled" here means that inhibition or inactivation of the
coupled protein results in inhibition or activation (not necessarily respectively) of the
phospholipase. The term coupled is meant to include both "natural" coupling of heterologous
.~ign~lin~ molecules into a yea~t signal transduction ~lhw~y and "artificial" coupling of
heterologous cisrn~ling molecules into a yeast p~lllw~y in a manner not normally operative in
yeast cells. Functional expression of human phospholipases is especially desirable.
In general, the yeast cells of the subject invention are characterized as in~ ing a
heterologous gene encoding a heterologous phospholipase C (PLC), e.g., a polypeptide
having a phospholipase C activity. In preferred embo-limentc, the PT C is a mannm~ n
PLC such as a human PLC. For example, the PLC can be a phospholipase selected from
the group consisting of PLCa's, PLC,B's, PLC~'s and PLCy's. Prefe~ed PLC's are of the ,13
subtype, such as PLC~ 1, PLC~2, PLC133 and PLC,134. In certain embo-limentc, theheterologous phospholipase C can be con~LuLiLiv~ly activated. This may occur by way of
mutations to the PLC itself which result in a higher level of activity, relative to the wild-
type protein, in the absence of cign~ling to the PLC. In other embodiments, the
constitutive activation of the PLC can occur due to overexpression and/or consitutively
activating mutations to upstream regulators of the PLC, such as receptors, G proteins and
the like.
In certain embodiments, the recombinant cell is characterized by the ability of the
heterologous PLC to hydrolyze phosphatidylinositol 4,5-bisphosphate. In other
embo-lim~ntc, the yeast cell has a loss-of-function mutation to an endogenous
phospholipase gene, giving it a first flet~-ct~hle phenotype, and the heterologous PLC
complements the loss-of-function mutation and confers a second cletect~hle phenotype on
the cell.
In preferred embo~lim~ntc, the heterologous PLC is functionally integrated in a
phospholipase-dependent signal ~dLhw~y of the cell For example, the heterlogous PLC
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WO 96/40939 PCTAUS96/10002
may complement a loss-of-function mutation of an endogenous phospholipase gene of the
yeast cell, e.g., the heterologous PLC may complement the plcl~ mutation. Expression of
the heterologous PLC may confer a phenotype to the host cell which is ~lete~t~hly
different than the phenotype of the host cell in the absence of the heterologous PLC
5 protein. For instance, compl~m~nt~tion of a loss-of-function mutation, such as the plcl~
mutation, by the heterologous PLC can rescue/overcome such phenotypes as temperature-
sensitivity and/or salt sensitivity. In certain embo~im~ms, the heterolgous PLC, via a
phospholipase-dependent signal pathway, can modulate such downstream effectors as
calcium mobilization and/or PKC activity.
Moreover, in those embo~im~ntc wherein the phospholipase-dependent signal
pathway modulates gene expression, the recombinant cell may also be ~ngineered to
include a reporter gene construct cont~ining a reporter gene in operative linkage with one or
more transcriptional regulatory elements responsive to the phospholipase-dependent signal
pathway, expression of the reporter gene providing the detectable signal. Exemplary reporter
15 genes encode a gene product that gives rise to a ~tect~hle signal, such as color,
fluoresc~nce, llln~in~scence, cell viability relief of a cell nutritional requirement, cell
growth, or drug resistance. In preferred embo~im~nts, the reporter gene encodes a gene
product selected from the group concicting of chloramphenicol acetyl transferase, beta-
galactosidase, luciferase, fluorescent protein, and alkaline phosphatase. In other
20 embodiments, the reporter gene encodes a gene product which confers the ability to grow
in the presence of a selective agent, e.g., canavanine.
In another embodiment the yeast cell further comprises a heterologous regulatoryprotein which is coupled to the phospholipase ~ign~ling pathway. e.g., the regulatory protein
modulates the activity of the heterologous PLC or is modulated by the PLC activity.
25 Exemplary regulatory proteins include, for example, G-protein heterotrimers; G a subunits;
G,B~ subunits; proteins known to interact functionally with PLC substrates (e.g., profilin,
gelsolin, cofilin, and alpha-actinin); and other effectors whose activity is dependent on PLC
activity (i.e., IP3 receptors/calcium channels, and IP3 or calcium sensitive enzyme activities
such as PKC or calcium/calmodulin kinase (CaM kinase)).
In another embodiment the yeast cell comprises a heterologous receptor or ion
- channel or other surface protein capable of transducing signals via the phospholipase-
dependent signal pathway, e.g., which is known to couple to PLC activity either directly or
via a regulatory protein. This aspect of the invention provides for more general readout
systems to assay modulation of the activity of a variety of different cellular cign~ling
components which effect phospholipase C activation. In a preferred embodiment, the host
cell further comprises a heterologous gene encoding a heterologous G-protein coupled
-
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- 10-
receptor. Preferred G-protein coupled receptors include chemoattractant peptide
receptors, neuropeptide receptords, cytokine, light receptors, neurotransmitter receptors,
cydic AMP receptors, and polypeptide hormone receptors. For example, the receptor may
be any one of: an alA-adrenergic receptor, an oclB-adrenergic receptor, an alC-adrenergic
5 receptor, an Ml AChR receptor, an M3 AChR receptor, an Ms AChR receptor, a D2
dopamine receptor, a D3 dopamine receptor, an Al adenosine receptor, a 5HTl-like receptor,
a SHTld-like receptor, a 5HTld beta receptor, a substance K (neurokinin A) receptor, a f-
Met-Leu-Phe (FMLP) receptor, an angiotensin II type 1 receptor, a mas proto-oncogene
receptor, an endothelin ETA receptor, an endothelin ETB receptor, a thrombin receptor, a
10 growth hormone-releasing hormone (GHRH) receptor, a vasoactive intestinal peptide
receptor, an oxytocin receptor, a SSTR3 receptor, an Luetinizing hormone/chorionic
gonadotropin (LH/CG) receptor, a thromboxane A2 receptor, a platelet-activating factor
(PAF) receptor, a CSa anaphylatoxin receptor, an Interleukin 8 (IL-B) IL-8RA receptor, an
IL-8RB receptor, a mip-l/RANTES receptor, a metabotropic ghltz~m~te mGluRl-5 receptor,
15 an ATP receptor, an amyloid protein precursor receptor, a bradykinin receptor, a
gonadotropin-releasing hormone receptor, a cholecystokinin receptor, an antidiuretic
hormone receptor, an adrenocorticotropic hormone II receptor, LTB4, LTD4 tachykinin
receptor, thyrotropin releasing hormone receptor, and oxytocin receptor. In other
embo~1iment~, the the receptor protein is a receptor tyrosine kinase.
In yet another embodiment, the recombinant cells are further engineered to include an
expressible recombinant gene encoding a heterologous test polypeptide. In preferred
embo~liment~7 such cells are provided as mixed culture collectively expressing a variegated
population of test polypeptides.
The present invention also relates to a rapid, reliable and effective assay for screening
and identifying pharmaceutically effective cornpounds that specifically interact with and
modulate the activity of a phospholipase. The subject assay enables rapid screening of large
numbers of test compounds to identifying those compounds which modulate, e.g., agonize or
antagonize, phospholipase bioactivity. In general, the assay is characterized by the use of the
recombinant cells described herein as engineered to express heterologous phospholipase
activities which produce, in the engineered cell, a detection signal. The ability of particular
test compounds contacted with the instant cells to modulate the phospholipase activity can be
scored for by detecting up or down-regulation of the detection signal. For example, second
messenger generation via the heterologous phospholipase activity can be measured directly.
Alternatively, the use of a reporter gene can provide a convenient readout. In any event, a
statistically significant change in the detection signal can be used to facilitate identification of
those compounds which are effectors of the phospholipase transducing activity.
.
CA 022204~9 1997-11-27
WO ~I/4C~39 PCT~US96/10002
In one embodiment, ~ere is provided an assay for identifying a modulator of a
phospholipase C activity, comprising the steps of: (i) com~cting the cell of claim 1 with a
test compound under conditions appropriate for cletecting an intracellular signal
tr~ncf~-lce~l via the phospholipase-dependent signal pathway; and (ii) measuring a level of
S signal tr~nc-~llce~ by the phospholipase-dependent signal pathway in the presence of the
test compound. A st~ticti~lly cignific~nt difference in the level of signal in the presence of
the test compound, e.g., increase or decrease relative to the absence of test compound,
indicates that the test compound is a modulator of the he~erologous phospholipase C
activity. The intr~ct~ r signal can be ~-otecte~l, for example, by expression of a reporter
10 gene operably linked to transcriptional regulatory el~m~ntc sensitive to the phospholipase-
dependent signal pathway. In other embodiments, the intracellular signal is (lete~tecl by
measuring products of the hydrolysis of phosphatidylinositol 4,5-bisphosphate; by
measuring Ca2+ mobilization; and/or by measuring the activation of a protein kinase such
as PKC. In yet other embo~lim~ms, the intr~cell~ r signal can be fletecte-3 by measuring a
15 change in phenotype conferred by the heterologous phospholipase, such as a change in
temperature sensitivity or NaCl sensitivity.
In a preferred embo-lim~nt, the assay makes use the ability of a heterologous PLC
to complement a loss-of-function mutation to an endogenous phospholipase activity. This
embodiment of the subject assay generally includes the steps of: (i) contacting the cell with
20 a test compound under conditions appropriate for ~ietecting one or both of the phenotypes
of the loss-of-function mutation or the complem~nte-l pheno~ype; and (ii) measuring the
level or degree of one or both of these phenotype in the presence of the test compound.
By comparing this measurement with a similar measurement made in the absence of the
test compound or the absence of the heterologous phospholipase C, the ability of the test
25 compound to alter the phenotype, relative to the absence of test compound or
phospholipase C, can be used to identify test compounds that are modulators of the
heterologous phospholipase C activity.
In yet another embodiment, the assay utilizes a cell which is further engineeredwith a reporter gene construct which is sensitive to a phospholipase-dependent signal
30 pathway from a heterologous PLC activity. Such assay formats generally include the steps
of: (i) contacting the cell with a test compound under conditions appropriate for
expression of the reporter gene; (ii) rletecting expression of the reporter gene in the
presence of the test compound; and (iii) comparing the level of reporter gene expression in
the presence of the test compound to the level of reporter gene expression in the absence
35 of the test compound or the absence of the heterologous phospholipase C. A statistically
~ignifie~nt difference in the level of reporter gene expression in the presence of the test
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compound, relative to the absence of test compound or phospholipase C, indicates that the
test compound is a modulator of the heterologous phospholipase C activity.
Still another embodiment of the assay provides a differential screening format for
identifying an agent which selectively inhibits a non-mamm~ n phospholipase C relative
5 to a m~mm~ n phospholipase. Such assay formats can include the steps of: (i) providing a
first ye~st cell cont~ining a non-m lmm~ n phospholipase gene; (ii) providing a second
yeast cell expressing a m~mm~ n phospholipase gene; (iii) cont~cting each of the first and
second yeast cells with a test compound; and (iv) cletecting or quantitating the activity of
the phospholipases of the first and second cell in the presence of the test compound. A
10 statistically greater decrease in the phospholipase activity of the first cell, relative to the
second cell, inr~ic~tes that the test compound selectively inhibits the non-m~mm~ n
phospholipase C. Such dirrele-lLial screening format can be used to identify inhibitors
which are selective for phospholipases of m~mm~ n pathogens relative to the hostmamm~ n phosphoIipase. For instance, the m~mm~ n PLC can be a human PLC, and
15 the non-m~mm~lian PLC can be derived from a human fungal pathogen, e.g. a pathogen
which causes a mycosis selected from a group consisting of candidiasis, aspergillosis,
mucormycosis, blastomycosis, geotrichosis, cryptococcosis, chromoblastomycosis,
penicilliosis, conidiosporosis, nocaidiosis, coccidioidomycosis, histoplasmosis,maduromycosis, rhinosporidosis, monoliasis, para-actinomycosis, and sporotrichosis. In
20 preferred embo~imt~ntc, the phospholipase of the first cell can be cloned from a human
pathogen selected from a group concicting of Candida albicans, Candida stellatoidea,
Candida tropicalis, Candida parapsi~osic, C~ndida kr~sei, Candida pse?~dotropicalis, Candida
quillermondii, Candida n~gosa, As~pergillusf~migat?~s, Aspergillusflavus, Aspergillusniger,
Aspergzllus nidulans, Aspergillus te~reus, Rhizopus awhiz~s, Rhizopus oryzae, Absidia
25 corymbifera, Absidia ramosa, and Mucor pusillus.
In any of the subject drug screening assays described herein, the assay can be carried
out, e.g., repeated, for a library of at least 100 different test compounds, though more
preferably at least 103, 104, 105, 106, or 107 different (variegated) compounds. The test
compound can be, to illuskate, peptides, nucleic acids, carbohydrates, small organic
30 molecules, natural product extracts, synthetic compounds, or a mixture of combinatorial
compounds.
The practice of the present invention will employ, unless otherwise indicated,
conventional techniques of cell biology, cell culture, molecular biology, transgenic biology,
microbiology, recombinant DNA, and immunology, which are within the skill of the art.
35 Such techniques are explained fully in the lil ldLul~. See, for example, Molecular CloningA
LaboratoryManual, 2nd Ed., ed. by Sambrook, Fritsch and Maniatis (Cold Spring Harbor
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13
Laboratory Press: 1989); DNA Cloning, Volumes I and II (D. N. Glover ed., 1985);Oligonucleotide Synthesis (M. J. Gait ed., 1984); Mullis et al. U.S. Patent No: 4,683,195;
Nucleic Acid Hybridization (B. D. Hames & S. J. Higgins eds. 1984); Transcription And
Translation (B D. Hames & S. J. Higgins eds. 1984); Immobili~ed Cells And Enzymes (IRL
Press, 1986); B. Perbal, A Practical Guide To Molecular Cloning (1984); the treatise,
Methods In Enzymology (~czlclemic Press, Inc., N.Y.); Methods In Enzymology, Vols. 154
and 155 (Wu et al. eds.), Immunochemical Methods In Cell And Molecular Biology (Mayer
and Walker, eds., Academic Press, London, 1987); Handbook Of Experimental Immunology,
Volumes I-IV (D. M. Weir and C. C. Blackwell, eds., 1986).
Detailed Descriptio~ of the I~2vention
Phospholipases C (PLC) are a family of enzymes which hydrolyze the sn-3
phosphodiester bond in membrane phospholipids producing diacylglycerol and a
phosphorylated polar head group. ~3mm~ n PLC enzymes exhibit specificity for the polar
head group which is hydrolyzed, i.e., phosphatidylcholine, phosphatidylinositol, etc.
Hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] by specific PLC
enzymes generates two second messenger molecules, diacylglycerol, a co-factor required for
activation of protein kinase C, and inositol 1,4,5-trisphosphate (IP3), a soluble second
messenger molecule which promotes the release of Ca2+ from intracellular stores (Berridge,
(1987) Ann. Rev. Biochem 56:159-193).
The importance of PLC activation in cell proliferation is evident from the fact that the
hydrolysis of PtdIns(4,5)P2 is one of the early events that follow the interaction of many
growth factors and mitogens with their respective receptors. However, the importance of
PLC activation is not restricted to proliferation; it is one of the most common transmembrane
25 ~ign~ling events elicited by receptors that regulate many other cellular processes, including
diLre,c;lltiation, metabolism, secretion, contraction, and sensory perception. Such PLC-
mediated transmembrane ~ign~ling events include, for example, sign~ling via receptor
tyrosine kinases and G protein coupled receptors.
Moreover, the diacylglycerol released may be further metabolized to free arachidonic
30 acid by sequential actions of diglycerol lipase and monoglycerol lipase. Thus, phospholipases
C are not only important enzymes in the generation of second messenger molecules, but may
serve an important role in making arachidonic acid available for eicosanoid biosynthesis in
select tissues.
The present invention is based on the development of yeast strains which express a
35 functional, heterologous phospholipase and makes available a rapid, effective assay for
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screening and identifying ph~rm~reutically effective compounds that specifically interact
with and modulate the activity of the heterologous phospholipase. As described herein, the
present invention provides a convenient format for discovering drugs which can be useful to
modulate cellular function, as well as to understand the ph~rm~fology of compounds that
5 specifically interact with phospholipases.
Before further description of the invention, certain terms employed in the
specification, examples and appended claims are, for convenience, collected here.
"Signal transduction" is the process by which chemical signals are relayed from the
cellular environment to cellular targets via the cell membrane, and may occur through one or
10 more mech~ni~m~, such as phosphorylation, activation of ;on channels, effector enzyme
activation via guanine nucleotide binding protein intermediates, activation of phospholipase,
and/or direct activation (or inhibition) of a transcriptional factor.
A "m~mm~ n phospholipase" is a protein which is either identical to an
phospholipase occurring naturally in a m~mmsll, or is a mutant which is substantially
15 homologous with such a m~mm~ n phospholipase and more similar in sequence to it than to
the yeast phospholipase. Related terms, such as "primate phospholipase", or "human
phospholipase", are analogously defined. A m~mm~ n phospholipase is "functionally
homologous" to a yeast protein if, either alone, or in concert with other exogenous proteins,
or after being modified by a drug, it is able to provide an phospholipase activity within the
20 engineered yeast cell. It is not necessary that it be as efficient as the yeast protein, however,
it is desirable that it have at least 10% of the activity of the analogous yeast protein.
An "activator" or "agonist" of a phospholipase is a substance which causes the
phospholipase to become more enzymatically active, e.g., elevates the rate at which
phospholipid hydroylsis occurs under particular conditions. The mode of action of the
25 activator may be direct, e.g., through binding the phospholipase, or indirect, e.g., through
binding another molecule which otherwise interacts with the phospholipase.
Conversely, an "inhibitor or antagonist" of an phospholipase is a substance which
causes the enzyme to become less active, and thereby reduces the rate or production of the
hydrolytic second messengers to a detectable degree. The reduction may be complete or
30 partial, and due to a direct or an indirect effect.
The term "phospholipase-dependent signal pathway" as used herein refers to a signal
transduction pathway including a phospholipase activity as a step in the transduction of the
intracellular signal. Such a signal transduction p~ w~y is meant to include components of a
pathway whose activity is modulated by a phospholipase, whether their activity is directly
35 modulated by the phospholipase or-indirectly modulated by the phospholipase or its second
~ =
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messengers. This term also includes components of the pathway which are "upstream" of the
phospholipase which regulate an activity of the phospholipase.
The term "functional integration" as used herein refers to the ability of an exogenous
phospholipase to function in a phospholipase-dependent signal transduction pathway such
S that a distal effect of a phospholipase activity can be cletermin~d, i.e., an activity regulated by
the products produced from phospholipase dependent phospholipid hydrolysis. Such distal
signaling effects can be observed in yeast expressing either a functional or mutant
phospholipase. Another example of functional integration is complementation by aheterologous phospholipase C of one of the pleiotropy of effects seen in phospholipase loss-
10 of-function yeast strains (e.g., reduced growth or NaCl sensitivity). Another assay of
functional complementation is the ability of the heterologous phospholipase to modulate gene
~ transcription. Yet another assay of functional integration is the reconstitution of regulated
phospholipase activity, i.e., phospholipase activity requiring stimulation, for example
phospholipase activity upon receptor-ligand activation or upon activation by a G protein
15 subunit or subunits. This term can also include functional integration of a phospholipase
into an endogenous yeast p~Lhw~y or a chimeric pathway including components not naturally
found in yeast cells.
The term "modulation of a phospholipase activity" in its various grammatical forms,
as used herein, cle~ipn~tec induction and/or potentiation, as well as inhibition of one or more
20 signal transduction pathways involving of a phospholipase. Such modulation may involve
effects of a compound directly on a phospholipase, or on a component of a signaltransduction pathway involving a phospholipase, for example upstream regulatory elements,
or downstream elements, including substrates.
The term "substantially homologous", when used in connection with amino acid
25 sequences, refers to sequences which are substantially identical to or similar in sequence,
giving rise to a homology in conformation and thus to similar biological activity. The term is
not intended to imply a common evolution of the sequences. Typically, "substantially
homologous" sequences are at least 50%, more preferably at least 80%, identical in sequence,
at least over any regions known to be involved in the desired activity. Most preferably, no
30 more than five residues, other than at the termini, are different. Preferably, the divergence in
- sequence, at least in the aforementioned regions, is in the form of "conservative
modifications".
The terms "protein", "polypeptide" and "peptide" are used interchangeably herein.
As used herein, "recombinant cells" include any cells that have been modified by the
35 introduction of heterologous DNA. Control cells include cells that are substantially identical
to the recombinant cells, but do not express one or more of the proteins encoded by the
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heterologous DNA, e.g., do not include or express one or more of the exogenous
phospholipase, regulatory protein, test polypeptide, or the reporter gene construct.
As used herein, the terms "heterologous DNA" or "heterologous nucleic acid" is
meant to include DNA that does not occur naturally as part of the genome in which it is
present or DNA which is found in a location or locations in the genome that differs from that
in which it occurs in nature. ~Ieterologous DNA is not endogenous to the cell into which it is
introduced, but has been obtained from another cell, i.e., is exogenous to the cell. Generally,
although not nect ~c~rily, such DNA encodes RNA and proteins that are not normally
produced by the cell in which it is expressed. Heterologous DNA may also be referred to as
10 foreign DNA. Any DNA that one of skill in the art would recognize or consider as
heterologous or foreign to the cell in which is expressed is herein encompassed by the term
heterologous DNA. Examples of heterologous DNA include, but are not limited to, DNA
that encodes a phospholipase, test polypeptides, regulatory proteins, reporter genes,
transcriptional and translational regulatory sequences, or selectable or traceable marker
15 proteins, such as a protein that confers drug resistance.
The terms "recombinant protein", "heterologous protein" and "exogenous protein" are
used interchangeably throughout the specification and refer to a polypeptide which is
produced by recombinant DNA techniques, wherein generally, DNA encoding the
polypeptide is inserted into a suitable ~p~ ion vector which is in turn used to transform a
20 host cell to produce the heterologous protein. That is, the polypeptide is expressed from a
heterologous nucleic acid.
A "heterologous phospholipase" refers to a non-yeast phospholipase enzyme, having a
phospholipase activity. For example, phospholipase C, in the presence of calcium, can
convert phosphatidyl inositol (PI), phosphatidyl inositol 4-monophosphate (PIP) or
25 phosphatidyl inositol (4,5) biphosphate (PIP2) into at least inositol 1,4,5 triphosphate (IP3)
and diacylglycerol (DAG).
An "endogenous, mutant phospholipase gene" as used herein refers to a yeast
phospholipase gene that encodes an endogenous, mutant or impaired yeast phospholipase
protein. For example, an endogenous, mutant phospholipase may have a deletion, insertion,
30 point mutation or other mutation that results in a conditional imp~irrnent or a constitutive
impairment, making them ideal for selection or complementation studies. An example of an
endogenous, mutant phospholipase gene is a deletion mutant in the S. cerevisiae PLC1 locus
~z71cl ). These mutants have several phenotypic differences from wildtype PLC l strains. plcl
strains are sensitive to high osmolarity (0.5M NaCl or 1.2M sorbitol) at 30~C and do not
35 grow well in the presence of carbon sources other than glucose (i.e. glycerol/ethanol,
raffinose, and galactose). Finally, plcl strains have a tt~ dLul~: sensitive phenotype; at
,
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temperatures above 35~C, plcl strains do not grow, while at temperatures below 35~C, they
grow, albeit slower than wildtype strains.
A "loss of function" mutation is one which leads to a change in the activity of a
phospholipase gene. Such a mutation may alter one or more of the coding sequence, the
S transcription, or the translation of an endogenous yeast phospholipase. Such a mutation will
lead to the lack of ~ e~ion of a yeast phospholipase, or the expression of an inactive yeast
phospholipase or a phospholipase of reduced activity.
As used herein, a "reporter gene construct" is a nucleic acid that includes a "reporter
gene" operatively linked to a transcriptional regulatory sequences. Transcription of the
10 reporter gene is controlled by these sequences. The activity of at least one or more of these
control sequences is directly or indirectly regulated by a signal transduction pathway
involving a phospholipase, e.g., is directly or indirectly regulated by a second me~s.?nper
produced by the phospholipase activity. The transcriptional regulatory sequences can include
a promoter and other regulatory regions, such as enhancer sequences, that modulate the
15 activity of the promoter, or regulatory sequences that modulate the activity or efficiency of
the RNA polymerase that recognizes the promoter, or regulatory sequences that are
recognized by effector molecules, including those that are specifically induced upon
activation of a phospholipase. For example, modulation of the activity of the promoter may
be effected by altering the RNA polymerase binding to the promoter region, or, alternatively,
20 by interfering with initiation of transcription or elongation of the mRNA. Such sequences are
herein collectively referred to as transcriptional regulatory elements or sequences. In
addition, the construct may include sequences of nucleotides that alter the stability or rate of
translation of the resulting mRNA in response to PLC second messages, thereby altering the
amount of reporter gene product.
25As used herein, a "heterologous regulatory protein" refers to a protein that regulates or
is coupled to a heterologous phospholipase. Such a regulatory protein may be upstream or
downstream of a phospholipase and is capable of mocl~ ting the activity of a phospholipase
or being modulated by the phospholipase. A preferred regulatory protein is a GTP binding
protein (G protein), which as used herein refers to heterotrimeric G proteins, G protein
30subunits thereof, e.g. a, ,B and r subunits, or a functional heterodimer (e.g. ,B~). A regulatory
protein as used herein may also be a receptor that modulates a signal transduction pathway
involving a phospholipase. Examples of ~l~f~ d regulatory receptors are those that directly
activate a phospholipase, such as the G protein coupled receptors, receptor tyrosine kinases
(~TK's), receptors that activate phospholipases via the activation of a non-receptor kin~es,
35such as those that signal via src kinases and the like. Other regulatory proteins can bind PIP2,
the ~lere,l~d substrate for many PLC isozymes (e.g. profilin, cofilin, gelsolin, and alpha-
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actinin) as discussed in Homma and Emori, 1995 and references therein. Regulatory
proteins are discussed in further detail below.
As used herein, "cell surface receptor" refers to molecules that occur on the surface of
cells, interact with the extracellular environment, and transmit or tr~n~d~lce the information
5 regarding the environment intracellularly in a manner that ultimately modulates transcription
of specific promoters, resulting in transcription of specific genes.
As used herein, "extracellular signals" include a molecule or a change in the
environment that is tran~ ced intracellularly via cell surface proteins that interact, directly
or indirectly, with the signal. An extracellular signal or effector molecule includes any
10 compound or substance that in some manner specifically alters the activity of a cell surface
protein. Examples of such signals include, but are not limited to, molecules such as ions,
acetylcholine, growth factors, and hormones, that bind to cell surface and/or intracellular
receptors and ion channels and modulate the activity of such receptors and channels.
Extracellular signals also include as yet unidentified substances that modulate a signal
15 transduction l~dLhWdy involving a phospholipase, and thereby influence intracellular
functions. Such extracellular signals are potential phslrm~cological agents that may be used
to treat specific ~ ce~ by mo-llll~tin~ phospholipase activity.
I. Ove~view of Assav
In vit~o testing is a preferred methodology in that it permits the design of high-
throughput screens: small quantities of large numbers of compounds can be tested in a short
period of time and at low expense. Optimally, animals are reserved for the latter stages of
compound evaluation and are not used in the discovery phase; the use of whole animals is
labor-intensive and extremely expensive. Microorg~ni~m~, to a much greater extent than
m~mm~ n cells and tissues, can be easily exploited for use in rapid drug screens. Yeast
provide a particularly attractive test system, extensive analysis of this organism has revealed
the conservation of structure and function of a variety of proteins active in basic cellular
processes in both yeast and higher eukaryotes.
As set out above, the present invention relates to recombinant yeast cells expressing a
heterologous phospholipase and the methods of using these cells to identify compounds
capable of mot1~ ting the signal transduction activity of such phospholipases. In general, the
subject assay is characterized by the use of recombinant cells which express a heterologous
phospholipase protein whose signal transduction activity can be modulated in therecombinant cell so as to generate a detectable signal. As described below, these cells may
35 (optionally) also express one or more of: (i) an ~ es~,ible recombinant gene encoding an
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exogenous test polypeptide from a polypeptide library, (iij a regulatory protein coupled to a
phospholipase activity, and (iii) a reporter construct.
The functional expression of a m~mm~ n phospholipase in yeast provides for the
design of inexpensive screens useful in the identification of modulators of the enzyme, the
5 activity which is required for the generation of a central sign~ling molecule in mzlmm~ n
cells. Any chemical entity, or combination of chemical entities, whether natural or synthetic,
may be screened for the ability to modulate the m~3mm~ n phospholipase. These
modulators may act directly on the enzyme to alter the activity of the enzyme, e.g., they can
competitively, noncompetitively, and/or allosterically potentiate or inhibit the enzyme's
10 activity, or may affect the ability of a regulatory protein to alter phospholipase activity.
In one embodiment, the engineered cell is used to screen for drugs which, like Ga or
in some cases G,~~y, can directly activate the phospholipase, or increase the activity of a
partially activated phospholipase. In certain embodiments a chimeric Ga or G~y may be
expressed for this purpose.
l S In a second embodiment, the engineered cell is used to screen for drugs which inhibit
m~mmz3li~n phospholipase. In this situation, the phospholipase must first be activated. This
can be done by engineering the cell to express Ga or G,~y, as a~lopl;ate. Alternatively, the
cell may be engineered to co-express both a G protein and a G protein coupled receptor, or
any other protein which regulates the activity of the phospholipase, and the receptor
20 stimulated either by extern~lly added ligand or by a co-expressed ligand. In either case, the
ligand is a known activator used merely to stimulate activation of the phospholipase, and the
drugs are screened for inhibition of this phospholipase.
In a third embodiment, the engineered cell is used to screen for drugs which inhibit or
activate phospholipase indirectly, e.g., by their action upon a regulatory protein, for example,
25 a G protein-coupled receptor. The receptor activates the G protein subunits which act on the
phospholipase. In this case, a compatible G protein-coupled receptor and a compatible G
protein would be provided with the m~mm~ n phospholipase in the same yeast cell.
The ability of particular test compounds to modulate the signal transduction activity
of the target phospholipase can be scored for by detecting up or down-regulation of the
30 detection signal. For example, second messenger generation (e.g. phospholipid hydrolysis,
Ca2+ mobilization or PKC activation) via a phospholipase-dependent signal pathway can be
measured directly. Alternatively, the use of a reporter gene can provide a convenient readout.
In any event, a statistically significant change in the detection signal can be used to facilitate
identification of those compounds which are effectors of the target phospholipase.
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By this method, test compounds which modulate phospholipase .~ign~ling can be
screened. If the test compound does not appear to induce the activity of the phospholipase,
the assay may be repeated and modified by the introduction of a step in which the
recombinant cell is first contacted with a known activator of the phospholipase, and the test
5 compound can be assayed for its ability to inhibit the activity of the phospholipase, e.g., to
identify phospholipase antagonists. Alternatively, the cell can be Pn~ineçred with an
activated phospholipase. In yet other embo-liment~, test compounds can be screened for
members which potentiate the response to a known activator of the phospholipase. In yet
another embodiment a phsopholipase or a phospholipase regulatory protein may be
10 constituatively active to facilitate screening for inhibitors of an activated phospholipase. For
example, constituatively active forms of the heterotrimeric Gq family members, such as Gl l
and G16 have been described, such as Ga qQ209L and Goc 16Q212L.
Overexpression these GTPase deficient activated alleles of Ga was found to
constitutively elevate basal phospholipase C activity, leading to persistent activation of cJun
NH2-terminal kinases (Heasley et al. 1996 Mol. Cell. Biol. 16:648, Heasley et al. 1996. J:
Biol. Chem. 271:349; Qian et al. 1994 J. Biol. Chem. 1994. 269:17417). In still a further
embodiment a con~ u~liv~ly actived form of a phospholipase activating receptor may be
expressed, such as an a 1 B-adrenergic receptor which has been mut~tP~l to render it
constituatively active (Perez et al. 1996. Mol. PharmacoZ. 49:112) or an altered form of the
20 formylmethionylleucylpheny~ nine receptor (Amatruda et al. 1995. J. Biol. Chem.
270:28010). In other embodiments the phospholipase itself may be expressed in aconstituatively activated form.
In a further embodiment, the subject reagent cells can be used to perform differential
screening assays, e.g., which can be used to identify a compound that selectively effects a
25 non-m~mm~ n (e.g. non-human) phospholipase. Such compounds, by selective inhibition,
can be used for treating or preventing a pathogen infection (e.g. viral, fungal, bacterial or
protozoan) in a m~mm~l (e.g. human). Preferred heterologous phospholipase enzymes for
performing differential screening assays against a mz~mm~ n phospholipase include
phospholipases from viral, fungal or protozoan pathogens. Examples of fungal pathogens
30 include fungi that cause Candidiasis, Aspergillosis, Mucorrnycosis, Blastomycosis,
Geotrichosis, Cryptococcosis, Chromoblastomycosis, Coccidioidomycosis, Conidiosporosis,
Histoplasmosis, Maduromycosis, Rhinosporidosis, ~ocaidiosis, Para-actinomycosis,Penicilliosis, Monoliasis, and Sporotrichosis.
In a further embodiment of a dirr~ ial screen, the ability of a compound to
35 modulate the activity of one phospholipase and not another phospholipase may be measured.
For example, compounds which are agonists or antagonists of PLC~ and not PLCy or are
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capable of mo~ ting PLC~2 and not PLC,B3 may be selected. In yet another embodiment
compounds which are capable of mo~llll~ting a heterologous phospholipase while not
affecting another member of a signal transduction protein which may or may not be a
member of a phospholipase pdLllwdy, such as PKC may be tested.
In developing the recombinant cells assays, it was recognized that a frequent result of
the activation of a phospholipase ~i~n~ling pathway was the transcriptional activation or
inactivation of specific genes, i.e., the activation of a phospholipase often ultimately leads to
a rapid and detectable change in the transcription or translation of a gene. Thus, transcription
of genes controlled by phospholipase-responsive transcriptional elements often reflects the
activity of the surface protein by virtue of transduction of an intracellular signal.
To illustrate, the intracellular signal that is tr~n~ ecl can be initiated by the specific
interaction of an extracellular signal, particularly a ligand, with a cell surface receptor which
is coupled to the phospholipase. This interaction sets in motion a cascade of intracellular
events, the ultimate consequence of which is a rapid and detectable change in the
transcription or translation of a gene. By selecting transcriptional regulatory sequences that
are responsive to the phospholipase-dependent intracellular signals and operatively linking
the selected promoters to reporter genes, whose transcription, translation or ultimate activity
is readily detectable and measurable, the transcription based assay provides a rapid indication
of whether a specific test compound influences intracellular transduction. Expression of the
reporter gene, thus, provides a valuable screening tool for the development of compounds
that act as agonists or antagonists of phospholipase activities.
Reporter gene based assays of this invention measure the end stage of the above
described cascade of events, e.g., transcriptional modulation and are thus ideal for assays in
which a heterologous phospholipase is functionally integrated into a signal transduction
pathway. Accordingly, in practicing one embodiment of the assay, a reporter gene construct
is inserted into the reagent cell in order to generate a detection signal dependent on 2nd
mes~t?ngers generated by the phospholipase activity. Typically, the reporter gene construct
will include a reporter gene in operative linkage with one or more transcriptional regulatory
elements responsive to the signal transduction activity of the target phospholipase, with the
level of expression of the reporter gene providing the phospholipase-dependent detection
signal. The amount of transcription from the reporter gene may be measured using any
method known to those of skill in the art to be suitable. For example, specific mRN~
expression may be detected using Northern blots or specific protein product may be
identified by a characteristic stain or an intrinsic activity. The amount of expression from the
reporter gene is then compared to the amount of expression in either the same cell in the
absence of the test compound or it may be compared with the amount of transcription in a
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substantially identical cell that lacks the target phospholipase. Any statistically or otherwise
significant difference in the amount of transcription indicates that the test compound has in
some manner altered the activity of the target phospholipase.
As described in fi~ther detail below, in ~l~rell~d embot1iment~ the gene product of
5 the reporter is detected by an intrinsic activity associated with that product. For instance, the
reporter gene may encode a gene product that, by enzymatic activity, gives rise to a detection
signal based on color, fluorescence, or lllminescence.
In other ~ler~ d embodiments, the reporter or marker gene provides a selective
growth advantage, e.g., the reporter gene may enhance cell viability, relieve a cell nutritional
10 requirement, and/or provide resistance to a drug.
In other embo-liment~, second messenger generation can be measured directly in the
detection step, such as mobilization of intracellular calcium or phospholipid metabolism are
quantitated, for instance, the products of phospholipid hydrolysis IP3 or DAG could be
measured For example, one of the downstream effects of PLC activation in m~mm~ n15 cells is Ca~ mobilization; because the te~- hings of the present invention demonstrate that a
m~mm~ n phospholipase can be functionally integrated into a yeast cell, it is likely that this
effect may be expected in yeast cells ~ S~illg functional, recombinant PLCs. Similarly, as
m~mm~ n PLC is known to modulate PKC via its second messenger products (including
DAG) functional expression of m~mm~ n PLCs in yeast may be expected to couple to other
20 signal pathway effectors including IP3-receptor, CaM kinase, calmodulin, PKA and PKC, or
other proteins which interact with the phospholipases.
Il. Host Cells
The host yeast cell of the present invention may be of any species which is cultivable
25 and in which an exogenous phospholipase can be moclnl~tt~l Suitable species include
Kluyverei lactis, Schizosaccharomyces pombe, and Ustilaqo maydis; Saccharomyces
cerevisiae is ~ d. Other yeast which can be used in practicing the present invention are
Neurospora crassa, Aspergillus niger, Aspergillus nidulans2 Pichia pastoris, Candida
tropicalis, and Hansenula polymorpha. The term "yeast", as used herein, includes not only
30 yeast in a strictly taxonomic sense, i.e., unicellular organisms, but also yeast-like
multicellular fungi or fil~mentous fungi.
The choice of ~plopl;ate host cell will also be influenced by the choice of detection
signal. For instance, reporter constructs, as described below, can provide a selectable or
screenable trait upon transcriptional activation (or inactivation) in response to a signal
35 transduction pathway coupled to the target receptor. The reporter gene may be an
-
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unmodified gene already in the host cell pathway, such as the genes responsible for growth
arrest in yeast. It may be a host cell gene that has been operably linked to a
"phospholipase-responsive" promoter. Alternatively, it may be a heterologous gene that has
been so linked Suitable genes and promoters are discussed below. Accordingly, it will be
S understood that to achieve selection or screening, the host cell must have an ~p~ iate
phenotype. For example, introducing a pheromone-responsive chimeric HIS3 gene into a
yeast that has a wild-type HIS3 gene would frustrate genetic selection. Thus, to achieve
nutritional selection, an auxotrophic strain will be desired.
"Inactivation", with respect to genes of the host cell, means that production of a
functional gene product is prevented or inhibited. Inactivation may be achieved by deletion of
the gene, mutation of the promoter so that expression does not occur, or mutation of the
coding sequence so that the gene product is inactive. Inactivation may be partial or total.
Accordingly, in certain embodiments it may be desirable to disrupt an endogenousyeast phospholipase to facilitate screening for an activity of a heterologous phospholipase.
The field of yeast genetics is advanced and techniques for disrupting yeast genes are known
in the art. For example, transplacement may be used to replace the endogenous yeast
phospholipase gene with a modified form, as described by Flick and Thorner in art. In the
case of yeast PLCl, aplc~l::HIS3 mutation can be created by replacing the internal PvuII
fragment of PLC1 (nucleotides +io69 to +1482) with HIS3, as follows. The 3.7-kb Eco RV
fragment cont~ining most of PLCl can be inserted into EcoRV-digested YCpS0 to (Rose et
al. 1987. Gene. 60:237) to yield pJF10, which can be cleaved with PvuII and ligated with the
2.1-kb PvuII fragment of pJJ215 that contains HIS3 (Jones and Prakash. 1990 Yeast 6:363).
In the rç~llltin~ plasmid (pJF18), HIS3 has replaced residues 357 to 494 of Plclp. The
plcl~ HIS3 allele can be introduced into yeast cells by DNA mediated transformation
(Rothstein. 1983. Methods Enzymol. 101:202) of two different his3/his3 diploid strains,
YPH501 (Sikorski and Heiter. 1989 Genetics 122:19) and W303 (Thomas and Rothstein
1989. Cell 56:619), using EcoRV-digested pJF18 and selecting for histidine prototrophy.
A plc1~2::LEU2 mutation can be created by replacing the HpaI-ClaI segment of
PLC1 (nucleotides +277 to ~2333) with LEU2, as follows. pJF58~ which consists of a 4.3-kb
Hind~lII fragment cont:~ining PLC1 inserted in pUCI9 can be digested with HpaI and ClaI
and incubated with the Klenow fragment of E coli DNA polymerase I. The resulting 5.4-kb
linearized vector can be gel purified and ligated with a 2.2 kb SalI-XhoI fragment cont~ining
LEU2 that can be excised from pJJ283 (Jones and Prakash, supra) and converted to flush
ends by treatment with Klenow enzyme, yielding pJF96. The plcl~2::LEU2 allele, which is
almost a complete deletion of the PLC1 gene, can be introduced into S. cerevisiae by DNA-
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mediated transformation of the leu2/leu2 diploid strain, YPH501, using HindIII-digested
pJF96 and selecting for leucine prototrophy.
Transplacement of the resident PLCI locus by the mutant allele on only one homolog
in each of the diploid transformants can be confirmed by restriction enzyme digestion and
5 Southern blot hybridization analysis (Sambrook et al. 1989. Molecular cloning: a laboratory
m~n~l, 2nd edition. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.). The
phenotype of asci from sporulated cultures of heterozygous plcl~/PLCl diploids may be
tPrmined as in the art.
Ideally, any . " ~ generated will have a selectable phenotype, such as, for example,
10 cessation of growth at 37~C, or failure to grow on a particular carbon source, will exhibit
sensitivity to hypertonic stress (e.g., to salt or sorbitol), or will fail to grow on medium
lacking a nitrogen source. In preferred embodiments a yeast cell expressing an endogenous
mutant PLC will be capable of growth under one set of experimental conditions and will fail
to grow or exhibit growth hllp~ ..ent under a second set of experimental conditions, i.e.,
15 would be conditionally lethal.
"Complement~tion", with respect to genes of the host ceil, means that at least partial
function of inactivated gene of the host cell is supplied by an exogenous nucleic acid. For
instance, yeast cells can be "m:~mmaliani7.?d", and even "hllmani7~d", by complementation of
receptor and signal tran~clllcfion proteins with mamm~ n homologs. To illustrate,
20 inactivation of a yeast phospholipase gene can be complemented, as described in the
appended examples, by expression of a human phospholipase gene.
The complementation of the plcl ~ ts phenotype observed with human PLC-132 and
Gaq family members can be used in a screening format to identify a variety of agonists and
antagonists directed to these functionally interacting proteins. PLC-,(3 agonists can be
25 identified in a screen for compounds that stimulate growth of plcl~ yeast strains expressing
PLC-~2 but not ~2~ple~ g any Gaq family Ga-subunit under non-permissive growth
conditions.plcl~ strains expressing wildtype yeast PLC1 could serve as an ~ liate
counterscreening strain. PLC-~ antagonists could be screened for in two formats. In the first
format, plcl~ yeast strains whose growth under non-permissive conditions is not dependent
30 upon co-expression of Gaq subunits (i.e. strains expressing m~mm~ n PLC-,Bl, -~2, or -,B3
on high copy plasmids) could be screened for compounds that block growth at 37~C or on
0.5M NaCl at 30~C but not at 30~C. An additional counterscreen for this format would be to
screen for compounds that block growth of the plcl ~ strains but not of PLC 1 strains under
non-permissive conditions. This counterscreen would serve to distinguish between35 compounds that act on fungal and mamm~lian PLC isoforms as opposed to those that act on
one or the other or both. In the second format, plcl ~ yeast strains whose growth under non-
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peImissive conditions is dependent upon co-expression of Go~q subunits (i.e. strains
expressing PLC-,~2 on a low copy plasmid) could be screened for loss of complementation
when contacted with compounds. This screen could in theory detect compounds that act
either by inhibiting PLC-isoforrns directly or by blocking the interaction between PLC-
~
5 isofo~ns and Gaq subunits or by blocking ~e activation of Gaq subunits. As a final exampleof the use of functional complement~tion in screening, it may be possible to construct yeast
strains in which the activation or inhibition of ~i~n~lin~ components downstream of PLC-,B
ca~ be scored ~lo~liately configured strains. For example, strains expressing both
m~mm~ n PLC-~ isoforms and PKC may be used to screen for compounds that modulate10 the activity of either PLC-13 isoforrns, PKC isofonns, or both.
Otkter complement~tions for use in the subject assay can be constructed wi~out any
undue experimentation. Indeed, numerous examples of yeast genetic complemen~:~tion with
m~mm~ n signal transduction proteins have been described in the art. For example, the
following table includes a list of some of the human genes which have been found to
complement of yeast genes (see also Tuendreich et al. 1994. Hum. Mol. Gen. 3:1509)
Table 2. Sequence similarity between Human cDNAs that complement S.
cerevisiae mutants and their correlate yeast proteins
GenBank BLASTX Yeast SwissProt
Human Gene Accession# P-value Mutant Accession # Reference
ARF5 M57567 I .OE-91 arf2 P 19146 Lee FJ. et al. (1992)
ARF5 M57567 1.4e-91 arfl P11076 Lee FJ. et al. (1992)
ARF6 M57763 3.1e-85 arf2 P19146 Lee FJ. et al. (1992)
ARF6 M57763 4.0e-84 arfl P11076 Lee FJ. et al. (1992)
mo~llllin D45887 7.7e-63 cmdl P06787 Davis TN. et al. (1989)
CBS L14577 9.4e-116 cys4 P32582 Kru~erWD.etal.(1994)
CCNDI M64349 NotDetected clnl P20437 Xion,aetal.(1991)
CCNDI M64349 NotDetected cln2 P20438 Xion~etal.(1991)
CCNDI M64349 Not Detected cln3 P13365 Xion~ et al. (1991)
CDC2 X05360 2.0e-130 cdc28 P00546 Ninomiva-Teuiietal.(1991)
CDC34 L22005 5.1e-38 cdc34 P14682 Plon et al. (1993)
CDK2 X61622 1.3e-137 cdc28 P00546 Elled~e et al. (1991)
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CDK3 X66357 1.3e-137 cdc28 P00546 Meverson et al. (1992)
CHK D10704 2.8e-20 ckil P20485 Hosaka et al. (1992)
CKSI X54941 8.7e-23 cksl P20486 Richardson HE~ et al. (1990)
CKS2 X54942 6 9e-14 cksl P20586 Richardson et al. (1990)
CSBPI L32563 7.2e-117 hogl P32485 K~lmaretal.(1995~
CYCI X06994 1.2e-98 cycl P00044 Tanaka Y. et al. (1988)
Cyclin E M73812 Not clnl P20437 Lew DJ. et al. (1991)
Detected
Cyclin E M73812 Not cln2 P20438 Lew DJ. et al. (1993)
Detected
Cyclin E M73812 Not cln3 P13365 Lew DJ. et al. (1991)
Detected
DHODH M94065 1.4e-5 ural P28272 Minet M. et al. (1992)
elF-2alpha M85294 8.3e-24 gcn2 P15442 Dever7Eetal.(1993)
elF-SA (elF-4D) M23419 1.6e-69 tifSlB P19211 S.,L~.~,lbc.~ .,. HG. et al. (1993)
elF-5A (elF-4D) M23419 1.7e-70 tifSlA P23301 S~ lln,~ ~.. HG. et al. (1993)
FLRN M59849 1.3e-120 nopl P15646 Jansen RP. et al. (1992)
G25K M35543 2.3e-108 cdc42 P19073 1~ ... S. et al. (1990)
G25K M35543 Not cdc24 P11433 M(~ S. et al. (1990)
Detected
GALK2 M84443 1.5e-64 gall P04385 Lee PT. et al. (1993)
GALT M96264 2.5e-85 gal7 P08431 Fridovich-Keil JL. et al. (1993)
GART X54199 2.0e-248 ade5, 7 P07244 Schild D. et al. (1990)
GART X54199 4.8e-12 ade8 P04161 Schild D. et al. (1990)
GBEI L07956 7.0e-290 glc3 P32775 ThonVJaal (1993)
GOS8 L13463 1.4e-1 get2 P11972 Siderovski DPetal. (1996)
GSPTI X17644 6.3e-165 get2 P05453 Hoshino S. et al. (1989)
HAP2 M59079 2.2e-23 hap2 P06774 Becker DM et al. (1991)
hFKB12 M80199 9.0e-43 rbpl P20081 Koltin Y. et al. (1991)
H-GRF55 S62035 6.2e-29 cdc25 P04821 Schwei~hofferF.etal.(l991)
HHR6A M74524 1.2e-73 rad6 P06104 KokenMHetal.(l991)
HHR6B M74525 6.7e-74 rad6 P06104 Koken MH. et al. (1991)
HMGCR M11058 1.0e-145 hrng2 P12684 Basson ME. et al. (1988)
SUBSTITUTE SHEET ~RULE 26)
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HMGCR M11058 4.6e-160 hmgl P13683 Basson ME. et al. (1988)
hRPB7.0 Z47727 3.9e-13 rpclO P40422 Sh~al~ i GV et al. (1995)
hRPB7.6 Z47728 3.9e-13 rpblO P22139 Shpakovski GV et al. (1995)
hRPB17 Z49199 I.Oe-23 rpb8 P20436 Shpakovski GV et al. (1995)
hRPB14.4 Z27113 2.8e-40 rpo26 P20435 Shpakovski GV et al. (1995)
LIGI M36067 2.3e-168 cdc9 P04819 Barnes DE. et al. (1990)
MGMT M29971 I.9e-8 mgt-l P26188 Xiac W. et al. (1995)
MSSI D11094 8.4e-211 cimS P33299 Ghislain M. et al. (1993)
MTTFI X64269 Not abf2 002486 Parisi MA. et al. (1993)
Detected
NFI M89914 I.5e-38 ira2 P19158 BallesterR.etal.(l990)
NMT M86707 9 7e-122 nmtl P14783 Duronio RJ. et al. (1992)
OAT M12267 9 7e-133 car2 P07991 Dou~herty KM. et al. (1993)
Oxidu.. du.,l~c S90469 6.7e-83 ncprl P16603 Eu)zster HP. et al. (1002
PDE4A M37744 Not pdel P22434 McHale et al. (1991)
Detected
PDE4A M37744 6.4e-15 pde2 P06776 McHale et al. (1991)
PDE7 L12052 Not pdel P22434 Michaeli T. et al. (1993)
Detected
PFKM M26066 1.9e-192 pfk P16861 Heinisch JJ. et al. (1993)
PYCRI M77836 4.9e-21 pro3 P32263 Dou~hertv KH. et al. (1993)
RCCI D00591 1.4e-13 srml P34760 Clark KL. et al. (1991)
(prp20)
SEC13r L09260 2.1e-116 secl3 004491 ShaywitzDA. etal. (1995)
snRMP Dl J03798 I.le-20 smdl 003260 Rvmond BC. et al. (1993)
SPT4 T50643 6.0e-19 spt4 P32914 Hartzo~ G. et al. (1996. submitted)
TOPI J03250 6.1e-195 topl P04786 Biornsti MA. et al. (1989)
TYMK L16991 4. Ie-47 cdc8 P06776 Su JY. et al. (1991)
UBCEPI M24507 4.5e-46 ubi3 P04839 Monia BP et al. (1990)
VDACI L06132 9 8e-15 porl P04840 Blachlv-Dvson E. et al. (1993)
VDAC2 L06328 2.8e-21 porl P04840 Blachlv-Dvson E. et al. (1993)
XPD X52221 2.9e-293 rad3 P06839 Guzder SN. et al. (1995)
SUBSTITUTE SHEET ~RULE 26)
~ ~ .
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Methods for introducing heterologous DNA into eukaryotic cells are well known inthe art and any such method may be used. In addition, cDNA encoding various
phospholipases and other of the recombinant proteins described herein are known to those of
skill in the art, or may be cloned by any method known to those of skill in the art. Generally,
ligating a polynucleotide coding sequence into a gene construct, such as an expression vector,
and tra~sforming or transfecting into hosts, either eukaryotic (yeast, avian, insect or
m~mm~ n) or prokaryotic (bacterial cells), are standard procedures used in producing other
well-known proteins, including sequences encoding exogenous receptor and peptidelibraries. Similar procedures, or modifications thereof, can be employed to prepare
recombinant reagent cells of the present invention by tissue-culture technology in accord with
the subject invention.
In general, it will be desirable that the vector be capable of replication in the host cell.
It may be a DNA which is integrated into the host genome, and thereafter is replicated as a
part of the chromosomal DNA, or it may be DNA which replicates autonomously, as in the
case of a plasmid. In the latter case, the vector will include an origin of replication which is
functional in the host. In the case of an integrating vector, the vector may include sequences
which facilitate integration, e.g., sequences homologous to host sequences, or encoding
integrases.
A number of vectors exist for the expression of recombinant proteins in yeast. For
instance, YEP24, YIP5, YEP51, YEP52, pYES2, and YRP17 are cloning and expressionvehicles useful in the introduction of genetic constructs into S cerevisiae (see, for example,
Broach et al. (1983) in Experimental Manipulation of Gene Expression, ed. M. Inouye
Ac~-lPmic Press, p. 83, incorporated by reference herein). These vectors can replicate in E.
coli due the presence of the pBR322 ori, and in S cerevisiae due to the replication
deterrnin~nt of the yeast 2 micron plasmid. In addition, drug resistance markers such as
ampicillin can be used.
Moreover, it will be understood that the expression of a gene in a yeast cell requires a
promoter which is functional in yeast. Suitable promoters include the promoters for
metallothionein, 3-phosphoglycerate kinase (Hitzeman et al., J. Biol. Chem. 255, 2073 (1980)
or other glycolytic euzymes (Hess et al., J. Adv En~yme Req. 7, 149 (1968); and Holland et
al. Biochemistry 17, 4900 (1978)), such as enolase, glyceraldehyde-3-phosphate
dehydrogenase, hexokin~ce, pyruvate decarboxylase, phospho-fructokinase,
glucose-6-phosphate isomerase, 3-phosphoglycerate mutase, pyruvate kinase,
triosephosphate isomerase, phospho-glucose isomerase, and glucokinase. Suitable vectors
and promoters for use in yeast expression are further described in R. Hitzeman et al., EPO
Publn. No. 73,657. Other promoters, which have the additional advantage of transcription
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controlled by growth conditions, are the promoter regions for alcohol dehydrogenase 2,
isocytochrome C, acid phosphzlt~e, degradative enzymes associated with nitrogen
metabolism, and the aforementioned metallothionein and glyceraldehyde-3-phosphate
dehydrogenase, as well as enzymes responsible for maltose and galactose utilization. Finally,
S promoters that are active in only one of the two haploid mating types may be ~ pl;ate in
certain circumstances. Among these haploid-specific promoters, the pheromone promoters
MFal and MFa 1 are of particular interest.
III. Phospholipases
As set out above, one aspect of the present invention encompasses the functionalexpression of a heterologous phospholipase in a yeast cell. A preferred phospholipase is
phospholipase C. Preferred PLCs for carrying out the subject screening assays include any
isotype of any of the four classes of phospholipases C (e g- a, ~1-4,1' 1&2 ,or ~1-3) The
phospholipases may be recombinant forms of vertebrate (e.g. m~mm~ n, such as bovine,
15 porcine, caprine, laprine, feline, canine, rodent, human or non-human primate), invertebrate
(e.g. insect), bacterial, non-bacterial or viral phospholipases. Preferred phospholipases of the
present invention are m~mm~ n, with particularly I~ler~ d phospholipases being of human
origin. Several human PLCs have also been cloned. For example, PLC (Genbank Accession
number ~14034), PLC1 (Genbank Accession number M37238), PLC~2 (Genbank Accessionnumber M95678; see also Park et al. J. Biol. Chem. 199Z. 267:16048) and PLC,B3 (Genbank
Accession number Z37566), see also Ohta, Matsui, Nazawa, La~,~l.;l~lL~ et al. (Genomics
(1995) 20:467:472); PLC,B4 (Genbank Accession number L41349) see also Alvarez et al.
(1995) Genomics 29:53), PLC~1 (Genbank Accession number U09117) see also Cheng et al
(1995) J. Biol. Chem 270:5495); PLC~ (Genbank Accession number M34667) see also
Burgess et al. (1990) Mol Cell Biol. 10:4770) and PLCo~ (Genbank accession number
D16234) see also Hirano et al. (1994) Biochem Biophys Res. Commun 204:375.
Moreover, the heterologous phospholipase need not be a naturally occurring protein,
rather, it may be a mutant form of a phospholipase. Preferably, the mutant is substantially
homologous to a naturally occurring phospholipase, or a mutant known to be functional.
Moreover, the structural gene encoding the phospholipase may be the wild-type
m:~mm~ n gene, or a modified gene. "Silent" modifications may be made to improveexpression, by, e.g., (1) elimin~ting secondary structures in the corresponding mRNA, or (2)
substituting codons ~l~r~llcd by yeast for codons that are not so preferred, or to facilitate
cloning, e.g., by introducing, deleting or modifying restriction sites. The gene may also be
modified so that a mutant phospholipase is encoded.
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Analysis of yeast codon usage indicates that there exists a preferred codon set
con~i~ting of the most abundant isoaccepting tRNAs present in yeast and that this pl~felled
set (25 out of the 61 possible coding triplets) is the sarne for all yeast proteins (Bennetzen and
Hall (1981) J. Biol. Chem. 257,3026-3031). The rapid translation rate required for abundant
proteins is believed to provide the selective pressure for the existence of the preferred set of
codons. As the extent of biased codon usage in specific genes correlates directly with the
level of gene expression (Hoekma et al. (1987) Mol. Cell. Biol. 7,2914-2924), experimental
strategies aimed at the expression of heterologous genes in yeast exploit the codon bias that
has been described for that organism (Sharp et al. (1986) Nuc. Acids Res. 14,5125-5143).
For in~t~nce, as described in details in the Exemplification, the amino termin~l seven
residues of PLC-,Bl and the amino terminal 21 residues of human PLC-132 can be mutated
using synthetic oligonucleotides to effect these changes. The nucleotide sequence of each
construct may be subsequently verified by dideoxynucleotide seq~lencing methods on both
DNA strands. Other desirable, conservative amino acid substitutions not specifically cited
here may be made to the phsopholipase sequence without any ~limini~hment of wild type
protein activity.
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IV. Other Re~ulatorv Proteins
In certain embo~liment~, the yeast cells of the present invention can be further~ engineered to express one or more regulatory proteins which regulate an exogenous
5 phospholipase. Preferred regulatory proteins are G-protein coupled receptors, G proteins,
receptor tyrosine kinases, and/or non-receptor kinases. Examples of other regulatory proteins
are proteins which bind to phospholipase substrates and influence the activity of a
phospholipase, such as profillin. Phospholipase regulatory proteins are described in detail
below.
A. G Protein-Coupled Receptors
One family of signal transduction c~cc~rles found in eukaryotic cells utilizes
h~le~ leric "G proteins." Transduction of growth signals by G protein-coupled receptors
has been demonstrated to include phospholipase-dependent pathways. For example, ~-type
15 PLC isoforms are activated by the heterotrimeric G protein subfamily Gq. The a-subunits of
Gq/~ 6, to further illustrate, specifically regulate PLC-,~1 and PLC-,~3, and the ,B/r-subunits
of the Gi subfamily interact with PLC-,B2. Agonist interaction with specific G protein-
coupled receptors causes the dissociation of Gq proteins into Ga and G ,s/r subunits and the
exchange of GDP bound to Ga for GTP. The resulting GTP-bound Ga subunit then activates
20 certain PLC isoforms, such as PLC,B's, by binding to the enzyme. G protein .~i~n~ling
systems include three components: a receptor, a GTP-binding protein (G protein), and an
intracellular target protein.
In their resting state, the G proteins, which consist of alpha (a), beta (O and gamma
(r) subunits, are complexed with the nucleotide guanosine diphosphate (GDP) and are in
25 contact with receptors. When a ligand engages the receptor, the receptor changes
conformation and this alters its interaction with the G protein. This spurs the a subunit to
release GDP, and the more abundant nucleotide guanosine triphosphate (GTP), replaces it,
thus activating the G protein. The G protein then dissociates to separate the a subunit from
the still complexed ~ and r subunits. The activated state lasts until the GTP is hydrolyzed to
~ 30 GDP by the intrinsic GTPase activity of the a subunit. Either the Ga subunit, or the G~r
complex, depending on the pathway, interacts with an effector such as a phospholipase. In
the instance of phospholipases, the enzyme in turn converts an inactive precursor molecule
into an active "second messenger," which may diffuse through the cytoplasm, triggering a
metabolic c~ le. Over time, the Ga converts the GTP to GDP, thereby inactivating itself.
35 The inactivated Ga may then reassociate with the G~y complex.
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Hundreds, if not thousands, of receptors tr~n~(1nce signals through heterotrimeric G
proteins, of which at least 17 distinct forms have been isolated. Although the greatest
variability has been seen in the a subunit, several different ~ and y structures have been
reported. There are, additionally, several different G protein-dependent effectors.
Most G protein coupled receptors are comprised oi~ a single protein chain that is
threaded through the plasma membrane seven times. Such receptors are often referred to as
seven transmembrane receptors (STRs). The following is a partial list of seven
transmembrane domain receptors that have been reported in the literature to be coupled to
phosphoinositide metabolism in cells and accordingly suitable for generating the subject
reagent cell: an alA-adrenergic receptor, an alB-adrenergic receptor, an alC-adrenergic
receptor, an Ml ACh receptor, an M3 ACh receptor, an M5 ACh receptor, a D2 dopamine
receptor, a D3 dopamine receptor, an Al adenosine receptor, a 5HT1-like receptor, a SHTld-
like receptor, a SHTld beta receptor, a substance K (neurokinin A) receptor, a f-Met-I,eu-Phe
(FMLP) receptor, an angiotensin II type 1 receptor, a mas proto-oncogene receptor, an
endothelin ETA receptor, an endothelin ETB receptor, a thrombin receptor, a growth
hormone-releasing hormone (GHRH) receptor, a vasoactive in~estinzll peptide receptor, an
oxytocin receptor, a SST3 receptor, an Ll1tini7ing hormone/chorionic gonadotropin (LH/CG)
receptor, a thromboxane A2 receptor, a platelet-activating factor (PAF) receptor, a C5a
anaphylatoxin receptor, an Interleukin 8 (IL-8), IL-8A receptor, an IL-8B receptor, a mip-
1/RANTES receptor, a metabotropic glutarnate mGlul-5 receptor, an ATP receptor, an
amyloid protein precursor -receptor, a bradykinin receptor, a gonadotropin-releasing hormone
receptor, a cholecystokinin receptor, an antidiuretic hormone receptor, an adrenocorticotropic
hormone II receptor, LTB4 receptor, LTD4 receptor, tachykinin receptor, thyrotropin
releasing hormone receptor, vasopressin receptor and oxytocin receptor Cloning references
for exemplary G protein coupled recepotors are provided in Table 1.
TABLE 1 HUMAN G PROTEIN-COUPLED SEVEN TRANSMEMBRANE
RECEPTORS: REFERENCES FOR CLONING
RECEPTOR REFERENCE
a1A-adrenergic receptor Bruno et al. (1991)
a1 g-adrenergic receptor Ramarao et al. (1992)
m1l~c~nnic receptors: Ml AChR, M2 AChR, Bonner et al (1987)
M3 AChR, Peralta et al. (1987)
M5 AChR Bonner et al. (1988)
D~ dopamine Grandy et al. (1989)1
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D3 dopamine Sokoloff et al. (1990)
Al adenosine Libert et al. (1992)
5-HTla Kobilka et al. (1987)
Fargin et al. (1988)
5-HTlb Hamblin et al. (1992)
Mochizuki et al. (1992)
5HT1-like Levy et al. (1992a)
5-HTld Levy et al. (1992b)
5HTld-like Hambln and Metcalf (1991)
5HTld beta Demchyshyn et al. (1992)
substance K (neurokinin A) Gerard, et al. (1991);
Takeda et al. (1991)
f-Met-Leu-Phe Boulay et al. (1991)
Murphy & McDermott (1991)
DeNardin et al. (1992)
angiotensin II type 1 Furuta et al. (1992)
mas proto-oncogene Young et al. (1986)
endothelin ETA Hayzer et al. (1992)
Hosoda et al. (1991)
endothelin ETB Nakamuta et al. (1991)
Ogawa et al. (1991)
thrombin Vu et al. (1991)
growth horrnone-releasing hormone (GHRH) Mayo (1992)
vasoactive intestinal peptide (VIP) Sreedharan et al. (1991)
oxytocin Kimura et al. (1992)
somatostatin Yamada et al. (1992a)
SSTR3 Yamada et al. (1992b)
Leutenizing hormone/chorionic gonadotrophin Minegish et al. (1990)
thromboxane A2 Hirata et al. (1991)
platelet-activating factor (PAF) Kunz et al. (1992)
- C5a anaphylatoxin Boulay et al. (1991)
Gerard and Gerard (1991)
~ IL-8RA Holmes et al. (1991)
IL-8RB - Murphy and Tiffany (1991)
MIP-1/RANTES Neote et al. (1993)
Murphy et al., in press
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metabotropic glnt~m~te mGluRl-6 Tanabe et al. (1992)
ATP Julius, David (unpub.)
amyloid protein precursor Kang et al. (1987)
Mita et al. (1988)
Lemaire et al. (1989)
bradykinin Hess et al. (1992)
gonadotropin-releasing hormone Chi et al. (1993)
cholecystokinin Pisegna et al. (1992)
antidiuretic hormone receptor Birnbaumer et al. (1992)
adrenocorticotropic hormone II Mountjoy et al. (1992)
Specific human G protein-coupled receptors for which genes have been isolated and
for which expression vectors could be constructed include those listed herein and others
known in the art. Thus, the gene would be operably linked to a promoter functional in the cell
to be en~in~ered and to a signal sequence that also functions in the cell. For example in the
case of yeast, suitable promoters include those derived from Ste2, Ste3 and ~all genes.
Suitable signal sequences include those of Ste2, Ste3 and of other genes which encode
proteins secreted by yeast cells. As appropriate, the yeast genome is preferably modified so
that it is unable to produce the yeast analog of the recombinant receptor in functional form.
B. G protein subunits
PLC-,(~ enzymes are activated in response to ligand binding to G-protein coupledreceptors by hormones, n~ul~ niLlel~, small molecules and other agonists. This occurs
via a pertussis toxin insensitive mech~ni~m mediated by members of the Gq family of Ga
subunits as well as via a pertussis toxin sensitive mechanism mediated by G-protein
complexes cont~inin~ Ga subunits of the Gi or Go family. With respect to activation of
PLC-,B enzymes by Gq family members, all members of the Gq family (q, 11, 14, 15, and 16)
have been demonstrated both in vitro and in cell culture systems to directly stim~ te the
catalytic activity of PLC-~ 32, and -,~3 and -134 enzymes (A.J. Morris et al 1990, and
references therein; Sternweis and Smrka, 1992, Wu et al. 1992, and Lee et al. 1992).
Members of other Ga subunit families (Gi, Go, Gt, Gz), on the other hand, do not directly
stimlll~te PLC-~ activity. The observation that in some cell types stimulation of PLC-~
enzymes is sensitive to pertussis toxin tre~tm~nt is now understood to be due to the direct
effect of G~3~ subunits on PLC-~ isozymes (sllmm~ri~d in Boyer et al. 1994, and Clapham
and Neer, 1993). Recent work from a number of laboratories has demonstrated that P~C-,B
isoforms (in particular PLC-,B2 and -~3) are sensitive to stimlll~tion directly by G,B~ subunits.
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Thus, G,By subunits derived from Gai or GaO-cont~ining heterotrimers could contribute to
the pertussis toxin sensitivity of PLC-,13 stimulation observed in whole cell systems in the
past. Certain of the regions of PLC-,13 isozymes that are required for activation by Ga or G,B
r subunits have been characterized. For instance, deletion mutations have shown that
S residues at the carboxyl terminll~ of PLC-~Bl (Wu et al, 1993) are crucial for interaction with
Ga subunits, while residues at the amino terrninll~ appear to be t~cs~nti~l for interaction with
G,'3r subunits, perhaps through binding of G,B~ subunits to a presumptive pleckstrin
homology present in the amino terminal 150 residues of PLC-,B2 (Inglese et al. 1995, and
references therein).
In certain embodiments of the invention it may be desirable to express both a
phospholipase and one or more exogenous G protein subunits, for example, a G protein a
subunit. If the exogenous G a subunit is not adequately coupled to the endogenous yeast
G,l~r or G protein coupled receptor, the Ga subunit may be modified to improve coupling.
These modifications often will take the form of mutations which, relative to interaction with
the receptor or G13~ complex, increase the resemblance of the Ga subunit to the yeast Ga
while decreasing its resemblance to the receptor-associated Ga. For example, a residue may
be changed so as to become identical to the corresponding yeast Ga residue, or to at least
belong to the same exchange group of that residue. After modification, the modified Ga
subunit might or might not be "substantially homologous" to the foreign and/or the yeast Ga
20 subunit.
The modifications are preferably concentrated in regions of the Ga which are likely
to be involved in one or both of receptor binding and G,13r binding. In some embo~liment~, the
modifications will take the form of replacing one or more segments of the receptor-associated
Ga with the corresponding yeast Ga segment(s), thereby forming a chimeric Ga subunit.
25 (For the purpose of the appended claims, the term "segment" refers to three or more
consecutive amino acids.) In other embo-liment~, point mutations may be sufficient.
This chimeric Ga subunit will interact with the endogenous receptor and the yeast
G~y complex, thereby permitting signal transduction to occur via a pathway which includes
the heterologous phospholipase. While use of the endogenous yeast G~r is preferred7 if a
30 foreign or chimeric G,Br capable of transducing the signal to the recombinant phospholipase
- may be used instead.
C. Tyrosine Kinases
Certain phospholipase, such as PLC-r enzymes, are activated directly in response to
35 phosphorylation of key tyrosine residues by both receptor and non-receptor tyrosine kinases
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(Surnmarized in Cook and Wakelam, 1992b). Examples of receptors which mediate PLCy
activation include those for epidermal growth factor (EGF), platelet-derived growth factor
(PDGF), fibroblast growth factor, platelet-derived growth factor (PDGF), fibroblast growth
factor (FGF), nerve growth factor (NGF), and erbB2 which have intrinsic tyriosine kinase
activity (Kumjian et al. (1991) J: Biol. Chem. 266:3973, Margolsis et al. 1989. Cell 57:1101;
~ei~Pnh~lder et al. 1989. Cell 57: 1109; Moh~mm~-li et al. l 9g 1. Mol. Cell. Biol. 11 :5068;
Stephens et al. 1994. ~euron 12:691). Other receptor systems which are devoid of intrinsic
enzymatic activity are also linked to PLC. These include receptors for a range of cytokines
(Boulton et al. 1994. ~ Biol. Chem. 269:11648), erythropoietin (Res et al. 1994. J Biol.
10 Chem. 269:19633), and thrombin (Guinebault et al. 1993. Biochem J. 292:851), as well as
multisubunit immune recognition receptors (MIRRs) such as membrane immunoglobulin M
and CD40 in B Iymphocytes (Coggeshall, et al. 1992. Proc. Natl. ~cad Sci. USA 89:5660;
Ren et al. 1994. J ~xp. Med 179:673), the T-cell antigen receptor (Park et al. 1991. Proc.
Natl. Acad. Sci. USA 88:5453; Weiss and Littman. 1994. Cell 76:253), the high-affinity
15 immunoglobulin E receptor in basophilic lellkemi~ cells (Li et al. 1992. Mol. Cell. Biol.
12:3176; Park et al. 1991. J~ Biol. Chem. 266:24237), and the immllnnglobulin G receptor in
monocytic cells (Liao et al. 1993. Biochem. Biophys. Res. Commun. 191: 1028). When the
receptor has no intrinsic tyrosine kinase activity, non-receptor protein tyrosine kinases
coupled to the receptor mediate the response, such as members of the Src and Syk/ZAP70
20 family, including lyn, syk and fyn (Liao et al. supra; Rhee et al. 1992. Adv. Second
Messenger Phosphoprotein Res. 26:35-61; Weiss and Littman, supra).
PLC-~ isozymes bind to specific autophosphorylated tyrosine residues within the
kinase domains of these PTKs via the SH2 domains present in the spacer region between the
PLC X and Y regions and the PLCs themselves become substrates for tyrosine
25 phosphorylation. Phosphorylation of specific tyrosine residues (Tyr783 and Tyrl254 on
PLC-~I and Tyr753 and Tyr759 on PLC-y2) by the receptor associated tyrosine kinase
activities in turn increases the catalytic activity of PLC-~ isozymes which results in increased
production of l ,4,5-IP3 and sn- l ,2-diacylglycerol (DAG).
30 D Other Regulatory Proleins
Yet other regulatory proteins may be coexpressed with a heterologous phospholipase
in yeast cells. Recent work has also focused on the interaction between cytoskeletal elements
and polyphosphoinositides. For example PtdIns(4,5)P2 has been found to bind to profilin.
(Vojtek et al. (1991) Cell 66:497). PIP2-binding proteins are known to bind actin and to
35 regulate its assembly in vivo, suggesting a possible role for PIP2 hydrolysis by PLC enzymes
in the regulation of cytoskeletal org~ni7~tion, volume regulation, and in other cellular
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functions related to the state of cytoskeletal assembly. Furthermore, Gol~lcçhmi~lt-Clermont
et al. (1991) Science 251:1231 demonstrated a role for profilin in regulating PI turnover in
vivo by showning that profilin-bound PIP2 was found to be resistant to cleavage by PLC-yl
except when the PLC-yl had been activated by tyrosine phosphorylation. Other exemplary
5 molecules which may regulate a phospholipase include profilin, gelsonin, cofilin, alpha-actin,
and villin. The binding sites for PtdIns(4,5)P 2 on gelsolin and villin have recently been
identified (Janmey et al.,(1992) J. Biol Chem 267:11818).
Recent studies of PLC-~ regulation suggest that it may be regulated by a novel class
of regulatory proteins (pl22-RhoGAP) that show similarity to the GTPase activating protein
10 homology region of bcr, display GAP activity towards RhoA, and bind to and directly
stimulate PLC-ol (Homma, Y., and Y. Emori, 1995) Other reports suggest that rho can
regulate PtdIns(4,5)P2 levels (Chong et al. (1994) Cell 79:507).
Also some PLCs such as PLC,~1 (Bernstein and Ross) have a GAP-like activity for
certain Gq family members. This activity serves to down regulate the activity of both the Gq
15 and the PLC itself.
Other exemplary regulatory proteins include: IP3 receptors, calcium ch~nnelc, DAG
protein kinase C (PKC), PKA3 (cAMP dependent protein kinase catalytic subunit), SOK1
(suppressor of PKA o~e~ ession), CMD1 (calmodulin, CMK1 (Calcium/calmodulin
dependent protein kinase), and CMK2 (calmodulin dependent protein kinase).
V. Drug Screening
In certain embo~liment.c, the assay is characterized by the use of recombinant cells to
sample a variegated compound library for phospholipase agonists and/or antagonists. In
l,lertlled embo~limentc, the reagent cells express a m~mm~ n phospholipase capable of
25 producing a detectable signal in the reagent cell.
In certain embo(1imentc, the reagent cell also produces the test compound which is
~being screened. For instance, the reagent cell can produce a test polypeptide, a test nucleic
acid and/or a test carbohydrate which is screened for its ability to modulate the mzlmm~ n
phospholipase activity. In such embodiments, a culture of such reagent cells will collectively
30 provide a variegated library of potential phospholipase effectors and those members of the
library which either agonize or antagonize the phospholipase function can be selected and
~ identified. Moreover, it will be apparent that the reagent cell can be used to detect agents
which directly alter the activity of the m~mm~ n phospholipase, or which act on some
target upstream or downstream of the mzlmm~ n phospholipase.
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In other embodiments, the test compound is exo~çenously added. In such
embodiments the test compound is contacted with the reagent cell. Exemplary compounds
which can be screened for activity include peptides, nucleic acids, carbohydrates, small
organic molecules, and natural product extract libraries. In such embodiments, both
S compounds which agonize or antagonize the phospholipase function can be selected and
identified. Moreover, it will be a~,~dlelll that the reagent cell can be used to detect agents
which directly alter the activity of the m~mm~ n phospholipase, or which act on some
target upstream or downstream of the m~rnm~ n phospholipase.
In still other embo~liment~7 the test compound is produced by cells which are
10 cocultured with the reagent cells expressing a m~mm~ n phospholipase.
,4. Screening and Selection: ,4ssays of Second Messenger Generation
When screening for bioactivity of peptides, intracellular second messenger generation
can be measured directly. Fxempl~ry assays for the direct measurement of phospholipase
15 generated second mes~ngers are provided below; other assays for the measurement of
second messengers generated in a signal transduction pathway involving a phospholipase will
be a~pa~ to those of skill in the art and may be substituted for the assays described below.
In one embodiment, the phospholipase enzymatic activity can be measured in yeastcell extracts. In other embodiments measurements of a detecting a phospholipase activity
20 are made using intact yeast cells.
Certain receptors stimul~t~ the activity of phospholipase C which stimlll~tes the
breakdown of phosphatidylinositol 4,5, bisphosphate to 1 ,4,5-IP3 (which mobilizes
intracellular Ca++) and diacylglycerol (DAG) (which activates protein kinase C). Inositol
lipids can be extracted and analyzed using standard lipid extraction techniques. DAG can
25 also be measured using thin-layer chromatography. Water soluble derivatives of all three
inositol lipids (IPI, IP2, IP3) can also be ~lu~lLi~t~d using radiolabelling techniques or
HPLC.
The mobilization of intracellular calcium or the inilux of calcium from outside the
cell can be measured using standard techniques. The choice of the appropriate calcium
30 indicator, fluorescent, bioluminescent, metallochromic, or Ca++-sensitive microelectrodes
depends on the cell type and the magnitude and time constant of the event under study (Borle
(1990) Environ Health Perspect 84:45-56). As an exemplary method of Ca++ detection,
cells could be loaded with the Ca++sensitive fluorescent dye fura-2 or indo-l, using standard
methods, and any change in Ca+~ measured using a fluorometer.
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The other product of PIP2 breakdown, DAG can also be produced from phosphatidyl
choline. The breakdown of this phospholipid in response to receptor-mediated .~ign~lin~ can
also be measured using a variety of radiolabelling techniques.
The activation of phospholipase A2 can easily be qll~ntit~tçd using known
5 techniques, including, for example, the generation of arachadonate in the cell.
In certain embodiments of the assay, it may be desirable to screen for changes in
cellular phosphorylation. The ability of compounds to modulate phospholipase activation
could be screened using colony immunoblotting (Lyons and Nelson (1984) Proc. Natl. Acad.
Sci. US,4 81 :7426-7430) using anti-phosphotyrosine. Reagents for p~lrO~llli~lg such assays
10 are commercially available, for example, phosphotyrosine specific antibodies which measure
increases in tyrosine phosphorylation and phospho-specific antibodies can be purchased
(New England Biolabs, Beverly, MA). Tests for phosphorylation could be useful to measure
the phosphorylation of proteins in response to the modulation of a phospholipase activity; it
is noted that protein phosphorylation need not be directly affected by the modulation in
15 phospholipase activity, but rather may amplify signals generated by the phospholipase.
Multi-kinase ç~c.~clçs allow not only signal amplification but also signal divergence to
multiple effectors that are often cell-type specific, allowing a growth factor to stimulate
mitosis of one cell and differentiation of another.
One such cascade is the MAP kinase pathway that appears to mediate both mitogenic,
20 differentiation and stress responses in different cell types. Stimulation of growth factor
receptors results in Ras activation followed by the sequential activation of c-Raf, MEK, and
p44 and p42 MAP kinases (ERKl and ERK2). Activated MAP kinase then phosphorylates
many key regulatory proteins, including p90RSK and Elk-l that are phosphorylated when
MAP kinase translocates to the nucleus. Homologous pathways exist in m~mm~ n and25 yeast cells. For instance, an ç~f nti~l part of the S. cerevisiae pheromone sign~lin~ pathway
is comprised of a protein kinase cascade composed of the products of the STEl l, STE7, and
FUS3/KSSl genes (the latter pair are distinct and functionally re~ n~l~nt). Accordingly,
phosphorylation and/or activation of members of this kinase cascade can be detected and
used to assay phospholipase modulation.
B. Complementation
Techniques to assay for complementation of a mutant endogenous yeast gene are well
known in the art; numerous assays exist for the selection of auxotrophs. For example, as
described in detail herein, conditional PLC1 mutations lead to a pleitropy of phenotypes
35 expressed in yeast under nonper-missive conditions and have been complemented by
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functional ~x~lc~sion of m~mm~ n PLCs. In one embodiment of the present assay it will be
possible to test for agonists and/or antagonists of a functionally integrated, exogenous
phospholipase by observing reversion to the original mutant phenotype. For example, yeast
may cease to display a telllpeldlure or NaCl sensitive phenotype upon expression of a
5 m~mm~ n PLC, and may revert to a temperature or NaCl sensitive phenotype upon
tre~tm~nt with an antagonist of the exogenous PLC.
C Screening and Selection Using Reporter Gene Constructs
Reporter gene based assays of this invention measure the end stage of the above
10 described cascade of events, e.g., transcriptional modulation. Accordingly, in practicing one
embodiment of the assay, a reporter gene construct is inserted into the reagent cell in order to
generate a detection signal dependent on phospholipase .ci~n~ling. Typically, the reporter
gene construct will include a reporter gene in operative linkage with one or more
transcriptional regulatory elements responsive to phospholipase signal modulation, with the
15 level of expression of the reporter gene providing the receptor-dependent detection signal. If
only one transcriptional regulatory element is included it must be a regulatable promoter. At
least one the selected transcriptional regulatory elements must be indirectly or directly
regulated by the activity of the heterologous phospholipase whereby activity of the
phospholipase can be monitored via transcription of the reporter genes.
Many reporter genes and transcriptional regulatory elements are known to those of
skill in the art and others may be identified or synthe~i7~tl by methods known to those of skill
in the art.
A reporter gene includes any gene that expresses a detectable gene product, which
may be RNA or protein. Preferred reporter genes are those that are readily detectable. The
reporter gene may also be included in the construct in the form of a fusion gene with a gene
that includes desired transcriptional regulatory sequences or exhibits other desirable
properties.
Examples of reporter genes include, but are not limited to CAT (chloramphenicol
acetyl transferase) (Alton and Vapnek (1979), Nature 282: 864-869) luciferase, and other
en_yme detection systems, such as beta-galactosidase; firefly luciferase (deWet et al. (1987),
Mol. Cell. Biol. 7:725-737); bacterial luciferase (Engebrecht and Silverman (1984), PNAS 1:
4154-4158; Baldwin et al. (1984), Biochemistry 23: 3663-3667), ~Ik~line phosphatase (Toh
et al. (1989) Eur. J. Biochem. 182: 231-238, Hall et al. (1983) J. Mol. Appl. Gen. 2: 101),
human placental secreted ~lk~line phosphatase (Cullen and Malim (1992~ Methods in
Enzymol. 216:362-368).
-
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Transcriptional control elements which may be included in a reporter gene construct
include, but are not limited to, promoters, enhancers, and repressor and activator binding
sites. Suitable transcriptional regulatory elements may be derived from the transcriptional
regulatory regions of genes whose expression is rapidly induced, generally within minlltes,
after modulation of a phospholipase. Examples of such genes include those which are
responsive to the second messengers generated upon phospholipase activation, such as Ca++,
cAMP, and others. One such gene is c-fos, an immediate early gene (see, Sheng et al. (1990)
Neuron 4: 477-485). Immediate early genes are genes that are rapidly induced upon binding
of a ligand to a cell surface protein. The characteristics of preferred genes from which the
10 transcriptional control elements are derived include, but are not limited to, low or
undetectable expression in quiescent cells, rapid induction at the transcriptional level within
minlltes of exkacellular simlll~tion, induction that is transient and independent of new protein
synthesis, subsequent shut-off of transcription requires new protein synthesis, and mRNAs
transcribed from these genes have a short half-life. It is not necessary for all of these
15 properties to be present.
The amount of transcription from the reporter gene may be measured using any
method known to those of skill in the art to be suitable. For example, specific mRNA
expression may be cl~tectc~l using Northern blots or specific protein product may be
identified by a characteristic stain or an intrinsic activity.
In preferred embo~liment~, the gene product of the reporter is detected by an intrinsic
activity associated with that product. For instance, the reporter gene may encode a gene
product that, by enzymatic activity, gives rise to a detection signal based on color,
fluorescence, or Illminescence.
The amount of expression from the reporter gene is then compared to the amount of
expression in either the same cell in the absence of the test compound or it may be compared
with the amount of transcription in a substantially identical cell that lacks heterologuos DNA,
such as the phospholipase. Any statistically or otherwise significant difference in the amount
of transcription indicates that the test compound has in some manner altered the activity of
the phospholipase.
In other pl~f~lled embodiments, the reporter or marker gene provides a selectionmethod such that cells in which the peptide is a ligand for the receptor have a growth
advantage. For example the reporter could enhance cell viability, e.g., by relieving a cell
nutritional requirement, and/or provide resistance to a drug. For example the reporter gene
could encode a gene product which confers the ability to grow in the presence of a
selective agent, e.g., canavanine.
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For example,use of the S cerevisiae plcl ~ allele as an endogenous mutant
phospholipase C gene provides a readout system, whereby functional complementation (i.e.
detection of the second detectable phenotype rather than the first detectable phenotype) can
be detected or quantitated by cell growth. However, growth systems suffer from their
5 "quantal" nature. Other readout systems, which provide a dirr~lellL detectable phenotype
when the endogenous, mutant phospholipase C is complemented by the expression ofheterologous phospholipase C may be more sensitive in a given range or may be more
convenient for automation. For example, a transcriptionally based readout may be ~rer~lled
because it is rapid (i.e. hours instead of days) and affords greater flexiblity both in terms of
10 types of readout and dynamic range of the readout. For example, by placing the bacterial
gene encoding lacZ under the control of the promoter sensitive to signals generated upon
activation of a phospholipase pathway can be detected in less than an hour by monitoring the
ability of permeabilized yeast to produce color from a chromogenic substrate. The rapidity of
such a readout would, in itself, be advantageous. And such a readout would be necessary to
15 monitor phospholipase activity under conditions where the yeast do not grow.
A transcriptional readout can be developed by identifying genes/promoters that are
positively or negatively regulated by the PLC1 locus (i.e. promoters that are up or down-
regulated in PLCl vs. plclA strains or in plcl~ strains expressing human PLC-,B2 plus Ga
16). These promoters can then be linked to a reporter gene. Alternatively, the reporter gene
20 can be expressed in response to a downstream phospholipase C signal molecule, such as IP3,
DAG, increased intracellular calcium levels or increased PKC activity.
For example, a transcriptional based readout can be constructed using yeast
expressing m~mm~ n PLC enzymes in the following mamler. CREB is a transcription
factor whose activity is regulated by phosphorylation at a particular serine (S133). When this
25 serine residue is phosphorylated, "phospho-CREB", binds to a recognition se~uence known
as a CRE (cAMP Responsive Element) found to the 5' of promotors known to be responsive
to elevated cAMP levels. Upon binding of phosphorylated CR~B to a CRE, transcription
from this promoter is increased. Phosphorylation of CREB is seen in response to both
increased cAMP levels and increased intracellular calciurn levels. Increased cAMP levels
30 result in activation of protein kinase A, which in turn phosphorylates CREB and leads to
binding to CRE and transcriptional activation. Increased intracellular calcium levels results
in activation of calcium/calmodulin responsive kinases (CaM kinases). Phosphorylation of
CREB by CaM kinase IV is effectively the sarne as phosphorylation of CREB by PKA, and
results in transcriptional activation of CRE cont~inin~ promotors.
Therefore, a transcriptional-based readout can be constructed in plcl~ yeast strains
expressing a m~mm~ n PLC enzyme, regulatory proteins (G a and/or G~y), if n~cees~ry,
_
-
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and/or a reporter gene (i.e. lacZ) whose expression is driven by a basal promoter containing
one or more CREs in the following manner. Changes in the intracellular concentration of
Ca~ (a result of alterations in the activity of the recombinant PLC) will result in changes in
the level of expression of the reporter gene if: a) CREB is also co-expressed in the cell, and
5 b) either the endogenous yeast CaM kinase will phosphorylate CREB in response to increases
in calcium or if an exogenously expressed CaM kinase IV is present in the same cell. In
other words, stimulation of PLC activity will result in phosphorylation of CREB and
increased transcription from the CRE-lacZ construct, while inhibition of PLC activity will
result in decreased transcription from the CRE-lacZ construct.
In one embodiment, the promoter is activated upon activation of the phospholipase,
in which case, for selection, the expression of the marker gene should result in a benefit to the
cell. A preferred marker gene is the imidazoleglycerol phosphate dehydratase gene (HIS3).
If a phospholipase responsive promoter is operably linked to a beneficial gene, the cells will
be useful in screening or selecting for phospholipase activators. If it is linked to a deleterious
15 gene, the cells will be useful in screening or selecting for inhibitors.
Alternatively, the promoter may be one which is repressed by phospholipase, thereby
preventing e2~le~ion of a product that is deleterious to the cell. With a phospholipase-
repressed promoter, one screens for agonists by linking the promoter to a deleterious gene,
and for antagonists, by linking it to a beneficial gene.
Repression may be achieved by operably linking a phospholipase-intlll~ ed promoter
to a gene encoding mRNA that is arltisense to at least a portion of the mRNA encoded by the
marker gene (whether in the coding or fl~nking regions), so as to inhibit translation of that
mRNA. Repression may also be obtained by linking a phospholipase induced promoter to a
gene encoding a DNA-binding repressor protein, and incorporating a suitable operator site
into the promoter or other suitable region of the marker gene.
In yeast, suitable positively selectable (beneficial) genes include the following:
URA3, LYS2, HIS3, LEU2, TRPl; ADEl,2,3,4,5, 7,8; ARGI, 3, 4, 5, 6, 8; HISl, 4, 5; ILVl, 2,
5; THRl, ~; TRP2, 3, 4, 5; LEUl, 4; MET2,3,4,8,9,14,16,19; UR~1,2,4,5,10; HOM3,6,
ASP3; CHOl; ARO 2, 7; CYS3; OLEl; IN01,2,4; PR01,3 Countless other genes are potential
selective markers. The above are involved in well-characterized biosynthetic pathways. The
imidazoleglycerol phosphate dehydratase (IGP dehydratase) gene (;~) is preferred because
it is both quite sensitive and can be selected over a broad range of expression levels. In the
simplest case, the cell is auxotrophic for histidine (requires histidine for growth) in the
absence of activation. Activation leads to synthesis of the enzyme and the cell becomes
prototrophic for histidine (does not require histidine). Thus the selection is for growth in the
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absence of hi~ti~line. Since only a few molecules per cell of IGP dehydratase are required for
histidine prototrophy, the assay is very sensitive.
In ~ro~liate assays, so-called counterselectable or negatively selectable genes may
be used. Suitable genes include: URA3 (orotidine-5'-phosphate decarboxylase, inhibits
S growth on 5-fluoroorotic acid), LYS2 (2-aminoadipate reductase; inhibits growth on
a-aminoadipate as sole nitrogen source), CYH2 (encodes ribosomal protein L29;
cycloheximide-sensitive allele is ~ minz-nt to resistant allele), CAN 1 (encodes arginine
permease; null allele confers resistance to the arginine analog canavanin), and other
recessive drug-resistant markers.
The marker gene may also be a screenable gene. The screened characteristic may be a
change in cell morphology, metabolism or other screenable features. Suitable markers include
beta-galactosidase (Xgal, C 1 2FDG, 3almon-gai, Magenta-Gal (latter two from Biosynth
Ag)), ~1kzl1ine phosphatase, horseradish peroxidase, exo-gluc~n~e (product of yeast exbl
gene, nonessential, secreted); luciferase; bacterial green fluorescent protein; (human
15 placental) secreted ~lk~line phosphatase (SEAP); and chlorarnphenicol transferase (CAT).
Some of the above can be engineered so that they are secreted (although not 13-galactosidase).
A p~r~llcd screenable marker gene is beta-galactosidase; yeast cells expressing the enzyme
convert the colorless substrate Xgal into a blue pigment. Again, the promoter may be
receptor-in(l~ e~l or receptor-inhibited.
D. Detection of Inhibi~ion or ~ctivation of Proteins Other Than Phospholipase
The present invention also facilitates the detection of inhibitors or activators of
proteins other than phospholipase provided that the yeast cell expresses or is engineered to
25 express the protein of interest in such a manner that it is functionally "coupled", directly or
indirectly, to the phospholipase.
For example, the yeast cells can also be used in more general readout systems for
modulation of the activity of a variety of different cellular sign~llin~ components which
regulate phospholipase activation, such as receptors, which are known to couple to
30 phospholipases, either directly, (e.g. the PDGF receptor) or via a regulatory protein (e.g. a G-
protein coupled receptor or tyrosine kinase coupled receptor); a G-protein hete~)Llilller; a G a
subunit; a G,13~ subunit; another protein known to interact functionally with a known
phospholipase substrate (e.g., profilin, gelsolin, cofilin, and alpha-actin); and other effectors
whose activity is dependent on phospholipase C activity (i.e., IP3 receptors/calcium chzlnnel~,
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other potential IP3 sensitive calcium channels, and other calcium sensitive enzyme activities
such as PKC or CaM kinase).
In a pl~f~ d embodiment the yeast cells of the present invention may be used to
identify drugs which modulate the activity of a m~mm~lian G protein-coupled receptor. In
5 this embodiment, the yeast cell is engineered to express a mamm~lian G protein-coupled
receptor.
E. Test Compounds
Exemplary compounds which can be screened for activity include peptides, nucleic10 acids, carbohydrates, small organic molecules, and natural product extract libraries.
One class of potential modulators of particular interest is the peptide class. The term
"peptide" is used herein to refer to a chain of two or more amino acids, with adjacent amino
acids joined by peptide (-NHCO-) bonds. Thus, the peptides of the present invention include
oligopeptides, polypeptides, and proteins. Preferably, the peptides of the present invention
are 2 to 200, more preferably 5 to 50, amino acids in length. The minimum peptide length is
chiefly dictated by the need to obtain sufficient potency as an activator or inhibitor. The
m~imllm peptide length is only a function of synthetic convenience once an active peptide is
identified.
Synthetic peptides are also of interest. By way of example, peptides based on the
calmodulin-binding domain of calmodulin-dependent phospholipases could serve as
modulators of phospholipase activity. In addition, peptides or molecules of any structure
which inhibit the interaction between the phospholipase and known endogenous modulators
of phospholipase activity are of interest. Known endogenous phospholipase modulators
include Ca2+, Ca2+/calmodulin, protein kinase C, protein kinase A, Gas, Gai, G~, and
adenosine.
When peptide drugs are being assayed, the yeast cells may be engineered to express
the peptides, rather than being exposed to the peptides simply by adding the peptides to the
culture medium. Peptide libraries are systems which simultaneously display, in a form which
permits interaction with a target, a highly diverse and numerous collection of peptides. These
peptides may be presented in solution (Houghten 1991), or Oll beads (Lam 1991), chips
(Fodor 1991), bacteria (Ladner USP 5,223,409), spores (Ladner USP '409), plasmids (Cull
1992) or on phage (Scott, Devlin, Cwirla, Felici, Ladner '409). Many of these systems are
limited in terms of the m~ x i ~ l l " length of the peptide or the composition of the peptide (e.g.,
Cys excluded). Steric factors, such as the proximity of a support, may hlLt:l~ele with binding.
Usually, the screening is for binding in vitro to an artificially presented target, not for
_
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activation or inhibition of a cellular signal tr~n~ tion pathway in a living cell. While a cell
surface receptor may be used as a target, the screening will not reveal whether the binding of
the peptide caused an allosteric change in the conformation of the receptor.
Ladner, USP 5,096,815 describes a method of identifying novel proteins or
polypeptides with a desired DNA binding activity. Semi-random ("variegated") DNAencoding a large number of dirre~ellL potential binding proteins is introduced, in expressible
form, into suitable host cells. The target DNA sequence is incorporated into a genetically
engineered operon such that the binding of the protein or polypeptide will prevent expression
of a gene product that is deleterious to the cell under selective conditions. Cells which
10 survive the selective conditions are thus cells which express a protein which binds the target
DNA. While it is taught that yeast cells may be used for testing, bacterial cells are preferred.
The interactions between the protein and the target DNA occur only in the cell, not in the
periplasm, and the target is a nucleic acid, not a protein.
Substitution of random peptide sequences for functional domains in cellular proteins
15 permits some (letermin~tion of the specific sequence requirements for the accomplishment of
function. Though the details of the recognition phenomena which operate in the localization
of proteins within cells remain largely unknown, the constraints on sequence variation of
mitochondrial targeting sequences and protein secretion signal sequences have been
elucidated using random peptides (Lemire et al., J. Biol. Chem. 264, 20206 (1989) and Kaiser
20 et al. Science 235, 312 (1987), respectively).
Yeast have been enginet?red to express foreign polypeptide variants to be tested as
potential antagonists of m~mm~ n receptors. Libraries encoding mutant glucagon
molecules were generated through random misincorporation of nucleotides during synthesis
of oligonucleotides co~ illg the coding sequence of m~mm~ n glucagon. These libraries
25 were expressed in yeast and culture broths from transformed cells were used in testing for
antagonist activity on glucagon receptors present in rat hepa~ocyte membranes (Smith et al.
1 993).
In one embodiment, the yeast cells are engineered to express a peptide library. A
"peptide library" is a collection of peptides of many different sequences (typically more than
30 1000 different sequences), which are prepared es~enti~lly simgrowthultaneously, in such a
way that, if tested ~im~lltz~neously for some activity, it is possible to characterize the
"positive" peptides. The peptide library of the present invention takes the form of a yeast cell
culture, in which e~nt~ y each cell expresses one, and usually only one, peptide of the
library. While the diversity of the library is m~imi~f -1 if each cell produces a peptide of a
35 different sequence, it is usually prudent to construct the library so there is some redl]n~l~ncy.
Moreover, each sequence should be produced at assayable levels.
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e::
The peptides of the library are encoded by a mixture of DNA molecules of dirrel~lt
sequence. Each peptide-encoding DNA molecule is ligated with a vector DNA molecule and
the resulting recombinant DNA molecule is introduced into a yeast cell. Since it is a matter
of chance which peptide-encoding DNA molecule is introduced into a particular cell, it is not
S predictable which peptide that cell will produce. However, based on a knowledge of the
manner in which the mixture was prepared, one may make certain statistical predictions about
the mixture of peptides in the peptide library.
It is convenient to speak of the peptides of the library as being composed of constant
and variable residues. If the nth residue is the same for all peptides of the library, it is said to
10 be constant. If the nth residues varies, depending on the peptide in question, the residue is a
variable one. The peptides of the library will have at least one, and usually more than one,
variable residue. A variable residue may vary among any of two to any of all twenty of the
genetically encoded amino acids, the range of possibilities may be different, if desired, for
each of the variable residues of the peptide. Moreover, the frequency of occurrence of the
15 allowed amino acids at particular residue positions may be the same or different. The peptide
may also have one or more constant residues.
There are two principal ways in which to prepare the required DNA mixture. In one
method, the DNAs are synth( ~i7~ ~1 a base at a time. When variation is desired, at a base
position dictated by the Genetic Code, a suitable mixture of nucleotides is reacted with the
20 nascent DNA, rather than the pure nucleotide reagent of conventional polynucleotide
synthesis.
The second method provides more exact control over the amino acid variation. First,
trinucleotide reagents are ~ red, each trinucleotide being a codon of one (and only one) of
the amino acids to be featured in the peptide library. When a particular variable residue is to
25 be synthesized, a mixture is made of the ~plup~;ate trinucleotides and reacted with the
nascent DNA.
Once the necessary "degenerate" DNA is complete, it must be joined with the DNA
sequences necessary to assure the expression of the peptide, as discussed in more detail
elsewhere, and the complete DNA construct must be introduced into the yeast cell.
VI. Periplasmic Secretion
The cytoplasm of the yeast cell is bounded by a lipid bilayer called the plasma
membrane. Between this plasma membrane and the cell wall is the periplasmic space.
Peptides secreted by yeast cells cross the plasma membrane through a variety of mech~ni~m~
35 and thereby enter the periplasmic space. The secreted peptides are then free to interact with
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other molecules that are present in the periplasm or displayed on the outer surface of the
plasma membrane. The peptides then either undergo re-uptake into the cell, diffuse through
the cell wall into the medium, or become degraded within the periplasmic space.
The peptide library may be secreted into the periplasm by one of two distinct
5 mech~ni~mc, depending on the nature of the expression system to which they are linked. In
one system, the peptide may be structurally linked to a yeast signal sequence, such as that
present in the a-factor precursor, which directs secretion through the endoplasmic reticulum
and Golgi apparatus. Since this is the same route that the receptor protein follows in its
journey to the plasma membrane, opportunity exists in cells expressing both the receptor and
10 the peptide library for a specific peptide to interact with the receptor during transit through
the secretory pathway. This has been postulated to occur in m~mm~ n cells exhibiting
autocrine activation. Such interaction would likely yield activation of the linked pheromone
response pathway during transit, which would still allow identification of those cells
expressing a peptide agonist.
An ~lt~rn~tive mech~ni~m for delivering peptides to the periplasmic space is to use
the ATP-dependent transporters of the STE6/MDR1 class. This transport pathway and the
signals that direct a protein or peptide to this pathway are not as well characterized as is the
endoplasmic reticulum-based secretory pathway. Nonetheless, these transporters ~p~llLly
can efficiently export certain peptides directly across the plasma membrane, without the
20 peptides having to transit the ER/Golgi pathway. We anticipate that at least a subset of
peptides can be secreted through this pathway by ~ hlg the library in context of the a-
factor prosequence and terminal tetrapeptide. The possible advantage of this system is that
the receptor and peptide do not come into contact until both are delivered to the ~?xt~rn~l
surface of the cell. Thus, this system strictly mimics the situation of an agonist or antagonist
25 that is normally delivered from outside the cell. Use of either of the described pathways is
within the scope of the invention.
The present invention does not require periplasmic secretion, or, if such secretion is
provided, any particular secretion signal or transport pathway.
30 VII. Pharmaceutical Preparations of Identified ~s~enfs
After identifying certain test compounds as potential modulators of the target
phospholipase activity, the practioner of the subject assay will continue to test the efficacy
and specificity of the selected compounds both in vitro and in vivo. Whether for subsequent
in vivo testing, or for ~(1mini.ctration to an animal as an approved drug, agents identified in the
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= -49-=
subject assay can be formulated in rh~rrnzl~eutical p~ dlions for in vivo ~1mini~tration to
an animal, preferably a human.
The subject compounds selected in the subject, or a ph~rrr-~çeutically acceptable salt
thereof, may accordingly be forrn~ ted for ~-lmini~tration with a biologically acceptable
5 medium, such as water, buffered saline, polyol (for example, glycerol, propylene glycol,
liquid polyethylene glycol and the like) or suitable mixtures thereof. The optimum
concentration of the active ingredient(s) in the chosen medium can be ~let~rrnined
empirically, according to procedures well known to medicinal chemists. As used herein,
"biologically acceptable medium" includes any and all solvents, dispersion media, and the
10 like which may be ~lopl;ate for the desired route of ~rlmini~tration of the ph~rm:~relltical
p-e~,~dlion. The use of such media for phz~rm~reutically active substances is known in the
art. Except insofar as any conventional media or agent is incompatible with the activity of
the compound, its use in the phslrmslceutical preparation of the invention is contemplated.
Suitable vehicles and their form~ tion inclusive of other proteins are described, for example,
15 in the book Remington's ph~rm~reutical Sciences (Remington's Ph~rrr-~elltical Sciences.
Mack Publishing Company, Easton, Pa., ~JSA 1985). These vehicles include injectable
"~eposit fon~ ions". Based on t~ a~ove, such ph~rm~eutical formulations include,although not exclusively, solutions or freeze-dried powders of the compound in association
with one or more pharmaceutically acceptable vehicles or diluents, and contained in buffered
20 media at a suitable pH and isosmotic with physiological fluids. In preferred embodiment, the
compound can be disposed in a sterile pl~ udlion for topical and/or systemic ~imini~tration
In the case of freeze-dried preparations, supporting excipients such as, but not exclusively,
mannitol or glycine may be used and ~lo~l;ate buffered solutions of the desired volume
will be provided so as to obtain adequate isotonic buffered solutions of the desired pH.
25 Similar solutions may also be used for the ph~rms~ceutical compositions of compounds in
isotonic solutions of the desired volume and include, but not exclusively, the use of buffered
saline solutions with phosphate or citrate at suitable concentrations so as to obtain at all times
isotonic ph~rm~eutical ~ dlions of the desired pH, (for example, neutral pH).
The present invention is further illustrated by the following examples, which should
not be construed as limiting in any way. The contents of all cited references (including
literature references, issued patents, published patent applications, and co-pending patent
applications) cited throughout this application are hereby expressly incorporated by reference.
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Exemplif cafion
Example 1. Development of Yeast Strains and Complementation Assays
Methods
A. Yeast Plasmids Which Express G Proteins
Expression Plasmids
All expression pl~mi<l~ are based upon the shuttle vectors originally described by
Sikorski and Hieter (R.S. Sikorski and P.Hieter (1989) A system of shuttle vectors and yeast
host strains designed for efficient manipulation of DNA in Saccharomyces cerevisiae.
Genetics 122: 19-27). The expression plasmids with the GPAl promoter (Cadus 1127), the
PGK promoter (Cadus 1447) and the CUPl promoter (Cadus 1725 and 1728) have been
described elsewhere (Cadus published Patent Application WO 94/23025 entitled "Yeast cells
engineered to produce pheromone system protein surrogates, and uses therefor).
Ga-subunits - Construction of Low Copy Expression Plasmids
The following full length G-protein encoding inserts: GaS, Gai2, Gai3, Gaq, Gal 1,
Go~16, GaOA, GaOB, Gal2, GNAZ, and activated alleles (GTPase-deficient) of GaS, Ga
i2, Gaq, and Gal6 (Wu et al. (1992); Wu et al (1993); Park et al (1992) and references
therein) were amplified by polymerase chain reaction using VENT polymerase, with cloning
sites added to the 5' and 3' ends of the coding regions. In all cases, the restriction site added
to the 5' end of the gene encoded a novel NcoI compatible overhang, while the restriction site
added to the 3' end of the gene encoded a novel XhoI compatible overhang. PCR products
were gel purified, restricted with the ~plopliate endonucleases, and cloned into NcoI/XhoI
cut Cadus 1127 (construction of this plasmid is described in Cadus patent application
W094/23025). Cadus 1127 is a low copy plasmid (CEN6 ARS4) in which heterologous
gene expression is driven by the GPAl promoter (-1400 to +1 of the native GPAl locus). A
novel NcoI site has been engineered into this vector such that the initiator methionine (at
position +l) is embedded in this site (CCATGG).
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All G-protein expression cassettes were constructed as described below for Gal6.Full length human Gal6 was arnplified from Cadus plasmid 1127 with Vent polymerase
(New England Biolabs) using 5' oligonucleotide KS9829 = 5'
GGGCGTCTCACATGGCCCGCTCGCTGACC 3 ' (in which a BsmB 1 site encoding a NcoI
5 overhang (CATG) has been introduced and is underlined) and 3' oligonucleotide KS9830 =
5' GGGCTCGAGCTGGGTCACAGCAGGTGGATC 3' (in which an XhoI site has been
introduced following the t(?rmin~tion codon (underlined). Template (100 ng) and primers (1
uM final concentrations) were added in the presence of lOx reaction buffer cont~inin~ 2 mM
MgSO4. Template was denatured at 94~C for 30 seconds in the presence of primers followed
10 byaddition of lul per l OOul reaction volurne of VENT polymerase. DNA was amplified in a
two stage amplification protocol: Stage 1 = 2 cycles of 94~C/ 30 seconds followed by
55~C130 seconds followed by 72~C/60 seconds; Stage 2 = 25 cycles of 94~C/ 30 seconds
followed by 60~C/30 seconds followed by 72~C/ 60 seconds. The amplified product was
purified by gel electrophoresis, cut with BsmBI and XhoI, and ligated to NcoI / XhoI cut and
15 phosphatase treated Cadus 1127 vector DNA. Recombinant clones were identified by colony
PCR using primers fl~nking the inserted Gal6 sequences, confirmed by restriction digestion,
and validated by dideoxynucleotide sequencing of the PCR product. Gaq and Gall
expressing plasmids were prepared in a similar fashion using the following oligonucleotide
primer pairs for amplification: Gaq - S' oligonucleotide = KS A14282 = 5'
20 GGGCGTCTCACATGACTCTGGAGTCCATCATG 3' (encoding an Esp3I site at the S'
end which leaves an NcoI overhang following cleavage with Esp3I or BsmBI) and 3'oligonucleotide = KS A 14283 = S'GGGCGTCTCCTCGAGGCACGGTTAGACCAG 3'
(encoding an Esp3I site at the 3' end that leaves an XhoI compatible overhang following
cleavage with Esp3I or BsmI). Gal 1 - 5' oligonucleotide = KS A14645
25 S'GGGGGTCTCCCATGACTCTGGAGT- CCATGATG3' (encoding a BsaI sites that
creates an NcoI compatible overhang following cleavage with BsaI) and 3' oligonucleotide =
KS A14285 = 5' GGGCTCGAGG-AAGCCTGGCCCT 3' (encoding a XhoI site).
Ga-subunits - High Copy ~xpression Plasmids
Full length G-protein encoding inserts were amplified by polymerase chain reaction
using VENT polymerase as described above, with cloning sites added to the S' and 3' ends of
the coding regions. In all cases, the restriction site added to the S' end of the gene encoded a
novel NcoI compatible overhang, while the restriction site added to the 3' end of the gene
encoded a novel XhoI ct-mp~tihle overhang. PCR products were gel purified, restricted with
the a~lopl;ate endonucleases, and cloned into NcoI/XhoI cut Cadus 1447. Cadus 1447 is a
high copy plasmid (2 micron origin of replication) in which heterologous gene expression is
,
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- 52 -
driven by the phosphoglycerol kinase (PGK) promoter. A novel NcoI site is present at the
initiator methionine, and a unique XhoI site is downstream from it. G-proteins cloned in this
manner include Go~S, Gaq, Gall, Gal6, GaOA, GaOB, Gal2, GNAZ, and activated
alleles (GTPase-deficient) of GaS, Gai2, Gaq, and Gal6.
Yeast Plasmids Which Express Phospholipase C Genes
PLC-~l
Rat PLC-~1 (Suh et al., (1988)) was cloned into Cadus 1725 (CUPp LEU2 CEN ARS
AmpR) and Cadus 1728 (CUPp LEU2 2 micron origin AmpR). In these expression vectors,
a minim~l CUPl promoter has been engineered to contain an initiator methionine codon
(ATG) imbedded in an NcoI site, so that cloning into the NcoI cut vector introduces the gene
of interest in frame into the NcoI site. The resulting plasmid, Cadus 1642 (Rat PLC-~ 1), was
cleaved with ApaLI and ligated to a duplex adapter encoding the amino terminal seven
15 residues of rat PLC-,Bl with yeast codon bias. The sequences of these oligonucleotides are:
Oligo A = 5' CATGGCTGGTGCTCAACCAGGTG 3' and Oligo B--5' TGCACACCTGG-
TTGAGCACCAGC 3'. Oligo B was kin~eecl with polynucleotide kinase prior to ~nne~ling
and ligation. Following ligation to ApaLI cut Cadus plasmid 1642, the ligation mixture was
treated with polynucleotide kinase, cleaved with BamHI and a 3.8 kb fragment with the entire
20 coding region of rat PLC-~1 was isolated by gel electrophoresis. This 3.8 kb PLC-,B1
fragment was then ligated to NcoI - BamHI cut Cadus 1725 and Cadus 1728. Plasmids
cont~ining inserts in the correct orientation were identified by colony PCR and verified by
restriction analysis and double-str~n~le~l DNA sequencing using Sequenase V2.0 (U.S.
Biochemicals).
PLC-~2
Human PLC-~2 (Park et al., (1992) was cloned into Cadus plasmid 1725 (CUPp
LEU2 CEN ARS AmpR) and Cadus 1728 (CUPp LEU2 2 micron origin AmpR). The
resulting plasmid, Cadus 1680 (Human PLC-~B2), was restricted with Eco47III and EcoRI to
30 completion and then treated with T4 polymerase to fill in the EcoRI overhang. The EcoRI-
bluntlEco47III cut plasmid was then ligated to a duplex adapter encoding the amino terminal
twenty-one residues of human PLC-~2 with yeast codon bias. The sequences of these are:
Oligo C = 5'CATGTCTTTGTTGAACCCAGTTTTGTTGCCACCAAAGGTTAAGGCTT-
ACTTGTCTCAAGGTGAGC 3'
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and Oligo D -5'GCTCACCTTGAGACAAGTAAGCCTTAACCTTTGGTGGCAACAAA-
ACTGGGTTCAACAAAGA3'.
Oligo D was treated with polynucleotide kinase prior to ~nne~ling to oligo C and ligation to
EcoRI-blunt/Eco47III cut Cadus 1680. Following ligation, the ligation mixture was treated
S with polynucleotide kinase to phosphorylate the NcoI overhang 2t the 5 ' end of the gene cLr.d
the 3.8kbfragment with the entire coding region of human PLC-~2 was purified by gel
electrophoresis. This 3.8kb ~agment has NcoI compatible overhangs at both t~rmini, and
was ligated to NcoI cut/ shrimp ~lk~line phosphatase treated Cadus 1725 and 1728.
Plasmids cont~ining insert in the correct orientation were identified by colony PCR and
10 verified by restriction analysis and double-stranded DNA sequencing using Sequenase V2Ø
Table 3
Yeast Strains
No. ~A~ Genobpe :'IAME PlGENE ~2 Name P2GENE
1630 a plc1*1::HIS3 ade2-101
his3 *200 leu2* 1 Iys2-801
trp I * I ura3-52
1632 a PLCI ade2-101 his3*200
leu2*1 Iys2-801 trpl*l
ura3-52'
1633 a plc1*2::LEU2 ade2-101
his3*200 leu2*1 Iys2-801
trp I * I ura3-52
1901 a plc1*2::LEU2 ade2-101 1443 URA3 2mu-ori
his3 *200 leu2* 1 Iys2-801 REP3 AmpR PGKp
trp I * I ura3 -52
1902 a plc1*2::LEU2 ade2-101 1460 URA3 CEN6 ARS4
his3 *200 leu2 * I Iys2-801 AmpR PGKp
trp I * I ura3-52
1903 a plc1*2::LEU2 ade2-101 GALlp PLCI URA3
his3*200 leu2*1 Iys2-801 1637 2mu-ori AmpR
trp I * I ura3-52
1904 a plcl*2::LEU2ade2-101 1639 GALlpratPLC-
his3*200 leu2*1 Iys2-801 betal URA3 CEN6
trp I * I ura3-52 ARS4 AmpR
2099 a plcl*2::LEU2ade2-101 1639 GALlpratPLC- 1127 TRPI CEN6ARS4
his3*2001eu2*1 Iys2-801 betal URA3CEN6 AmpRGPAlp
trp I * I ura3-51 ARS4 AmpR
2100 a plcl*2::LEU2ade2-101 J639 GALlpratPLC- 1179 TRPI CEN6ARS4
his3 *200 leu2* 1 Iys2-801 beta I URA3 CEN6 AmpR GPA I p
trp I * I ura3-52 ARS4 AmpR GPA I
- 2101 a plc1*2::LEu2 ade2-101 1639 GALlp rat PLC- 1181 TRPI CEN6 ARS4
his3*200 leu2*a Iys2-801 betal URA3 CEN6 AmpR GPAlpGaS
trp I * I ura3-52 ARS4 AmpR
2102 a plc1*2::LEU2 ade2-101 1639 GALlp ratPLC- 1606 trpl CEN6 ARS4
his3*200 leu2* 1 Iys2-801 - betal URA3 CEN6 AmpR GPA I Pga2
frp I * I ura3-52 ARS4 AmpR
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2103 a plcl *2::LEU2 ade2- 101 1639 GALI p rat PLC- 1617 TRPI CEN6 ARS4
his3 *200 leu2* 1 Iys2-801 beta I URA3 CEN6 AmpR GPA I p
trpl*l ura3-52 ARS4 AmpR Human
Gal6
2104 a PLCI*2::1eu2 ADE2-101 1639 GALlp ratPLC- 1685 TRPI CEN6 ARS4
HIS3*200 LEU2*1 LYSI- betal URA3 CEN6 AmpR GPAlp
801 . ARS4 AmpR Murine
TRP I * I URA3-52 Gaq
2105 a plc1*2::LEU2 DE2-101 1639 GALlpratPLC- 1749 TRPI CEN6ARS4
his3 *200 leu2* 1 Iys2-801 betal URA3 CEN6 AmpR GPA Ip
trpl*l ura3-52 ARS4AmpR Murine
Gaq
2106 a plc1*2::LEU2 ade2-101 1639 GALlp rat PLC- 1753 TRPI CEN6 ARS4
his3*2001eu2*1 Iys2-801 betal URA3 CEN6 AmpRGPAlp
trpl*l ura3-52 ARS4 AmpRq\ Human
Ga 16-Q212L
2107 a plcl*2::LEU2ade2-101 1639 GALlpratPLC- 1447 TRPI Imu-ori
his3*200 leu2*1 Iys2-801 betal URA3 CEN6 AmpR
trp I * I ura3-52 ARS4 AmpR PGKp
2108 a plcl*2::LEu2ade2-101 1639 GALlpratPLC- 1630 TRPI 2mu-ori
his3*200 leu2*1 Iys2-801 beta URA3 CEN6 AmpR
trpl * I ura3-52 ARS4 AmpR PGKp GaS
2110 a plcl*2::LEU2ade2-101 1639 GALlpratPLC- 1783 TRPI 2mu-ori
his3*200 leu2*1 Iys2-801 BETAI ura3 cen6 AmpR
trpl*l ura3-52 ars4 aMPr PGKp Murine Gaq
2111 a plc1*2::LEu2 ade2-101 1639 GALlp rat PLC- 1786 TRPI 2mu-ori
his3*200 leu2*1 Iys2-801 betal URA3 CEN6 AmpR
trp I * I ura3-52 ARS4 AmpR PGKp Human Ga
16
2112 a plcl*2::LEU2ade2-101 1639 GALlpratPLC- 1786 TRPI 2mu-ori
his3 *200 leu2*a Iys2-801 betal URA3 CEN6 AmpR
trpl*l ura3-52 ARS4 AmpR PGKp Human Ga
q-Q209L
2113 a plcl*2::LEU2ade2-101 1639 GALlpratPLC- 1786 TRPI 2mu-ori
his3*200 leu2*1 Iys2-801 betal URA3 CEN6 AmpR
trpl*l ura3-52 ARS4AmpR PGKpHuman Ga
116-Q212L
2945 a plc l * I ::HIS3 ade2-101 1725 LEU2 CEN6 ARSH4 1127 TRPI GPA I p
his3*200 leu2*1 Iys2-801 CUPI AmpR CEN6
trp I * I ura3-52 ARS4 AmpR
2946 a plcl*l::HIS3ade2-101 1728 LEU22m-oriREP3 1855 GPAlpBamHI
his3 *200 leu2* 1 Iys2-801 CUPI AmpR GPA-
trp I * I ura3-52 Ga 16 TRP I CEN6
ARS4 AmpR
2948 a plcl*l::HIS3 ade2-101 1728 LEU22mu-oriREP3 1855 GPAlpBamHI
his3*200 leu2*1 Iys2-801 CUPI AmpR GPA-
trp I * I ura3-52 Ga 16 TRP I CEN6
ARS4 AmpR
2950 a plcl*l::HIS3ade2-101 1639 GALlpratPLC- 1127 TRPI GPAlp
his3 *200 leu2* 1 Iys2-801 beta- I URA3 CEN CEN6
trpl * I ura3-52 ARS AmpR ARS4 AmpR
2952 a plcl*l::HlS3 ade2-101 1640 ADHlp rat PLC- 1855 GPAlp BamHI
his3*200 leu2*a Iys2-801 beta-l LEU2 2mu GPA-
trp I * I ura3-52 origin AmpR Ga 16 TRP I CEN6
ARS4 AmpR
CA 02220459 1997-11-27
W 096/40939 , PCTAUS96/10002
-55-
2954 a plcl*l::HlS3ade2-101 1922 CUPratPLC- 1127 TRP1 PAlpCEN6
his3*200 leu2*1 Iys2-801 betal LEU2 2mu-ori ARS4 AmpR
trp I * 1 ura3-52 REP3 AmpR
2956 a plc I * 1: :HIS3 ade2- 101 1922 CUP rat PLC- 1855 GPA 1 p BamHI
his3 *200 leu2* 1 Iys2-801 beta I LEU2 2mu- GPA-
trp I * I ura3-52 ori REP3 AmpR Ga 16 TRP I CEN6
ARS4 AmpR
2958 plcl*l::HIS3ade-2-101 1961 LEU2CEN6ARSH4 1127 TRPI GPAlp
a his3*200 leu2*1 Iys2-801 AmpRCUP-PLC- CEN6
trpl * I ura3-52 beta2 ARS4 AmpR
2962 plcl*l::HlS3 ade2-101 1961 LEU2 CEN6 ARSH4 1537 TRPI 2mu-ori
a his3*200 leu2*1 Iys2-801 AmpRCUP-PLC- REP3
trpl*l ura3-52 beta AmpRPGKp-
ratGasQ227L
2964 plcl*l::HlS3 ade2-101 1961 LEU2 CEN6 ARSH4 1617 GPAlp Human a
a his3*2001eu2*1 Iys2-801 AmpRCUP-PLC- 16
trpl*l ura3-52 beta2 TRPI CEN6 ARS4
AmpR
2966 plcl*l::HlS3 ade2-101 1961 LEU2 CEN6 ARSH4 1685 GPAlpMurineGaq
a his3*200 leu2*1 Iys2-801 AmpR CUP-PLC- TRPI CEN6 ARS4
trpl*l ura3-52 beta2 AmpR fl ori
2968 plcl*l::HlS3 ade2-101 1961 LEU2 CEN6 ARSH4 1752 GPAlp-Gaq-
a his3*200 leu2*1 Iys2-801 AmpRCUP-PLC- Q209L
trp 1 * I ura3-52 beta2 TRP I CEN6 ARS4
AmpR
2970 plcl*l::HlS3 ade2-101 1961 LEU2 CEN6 ARSH4 1783 GPAlp-Gal6-
a his3*200 leu2*1 Iys2-801 AmpRCUP-PLC- Q212L
trp I * I ura3-52 beta2 TRPI CEN6 ARS4
AmpR
2972 plcl*l::HlS3ade2-101 1961 LEU2CEN6ARSH4 1783 MurineGaq
a his3*200 leu2*1 Iys2-801 AmpRCUP-PLC- PGKp
trp I * I ura3-52 beta2 TRP I 2mu ori
REP3
AmpR
2974 plc I * 1: :HIS3 ade2- 101 1961 LEU2 CEN6 ARSH4 1786 PGKp Human a 16
a his3*200 leu2*1 Iys2-801 AmpR CUP-PLC- TRP1 2mu ori
trpl*l ura3-52 beta2 REP3
AmpR
2977 plc I * 1: :HIS3 ade2- 101 1961 LEU2 CEN6 ARSH4 1796 PGKp Human a 16-
a his3*200 leu2*1 Iys2-801 AmpR CUP-PLC- !212L 2mu ori
trpl*l ura3-52 beta2 REP3
AmpR
2979 plcl*l::HIS3 ade2-101 1961 LEU2 CEN6 ARSH4 1794 PGKp Murine Ga
a his3*2001eu2*1 Iys2-801 AmpRCUP-PLC0 1-
trpl*l ura3-52 beta2 Q209L TRPI 2mu
- REP3 AmpR
2981 plc I * 1: :HIS3 ade2- 101 1961 LEU2 CEN6 ARSH4 1850 PGKp Murine Ga
a his3*200 leu2*1 Iys2-801 AmpRCUP-PLC0 11
trpl*l ura3-52 beta2 TRPI 2mu-ori
REP3
AmpR fl ori
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WO ~/40:~39 PCT/US96/10002
- 56 -
3222 plcl*l::HIS3 ad~2-101 1961 LEU2 CEN6 ARSH4 1524 TRPI GPAlp-ratGo~ his3*200 leu2*1 Iys2-801 AmpR CUP-PLC- as-
trpl*l ura3-52 beta2 Q227L CEN6
ARS4
AmpR
3226 plcl*l::HIS3ade2-101 1961 LEU2CEN6ARSH4 1606 GPAlpHuman
a his3*200 leu2*1 Iys2-801 AmpR CUP-PLC- i~
trpl*l ura3-52 beta2 TRPI CEN6 ARS4
AmpR
3228 plcl*l::HIS3 ade2-101 1961 LEU2 CEN6 ARSH4 1612 GPAlp Human a
c~ his3*2001eu2*1 Iys2-801 AmpRCUP-PLC- i3
trpl * I ura3-52 beta~ TRPI CEN6 ARS4
AmpR
3230 plcl*l::HIS3 ae2-101 1961 LEU2 CEN6 ARSH4 1622 GPAlp Murine a his3*2001eu2*1 Iys2-801 AmpRCUP-PLC0 Oa
bpl*l ura3-52 beta2 TRPI CEN6ARS4
AmpR
3232 plcl*l::HIS3 ade2-101 1961 LEU2 CEN6 ARSH4 1623 GPAlp Murine aa his3*200 leu2*a Iys2-801 AmpR CUP-PLC- Ob
trpl*l ura3-52 beta2 TRPI CEN6 ARS4
AmpR
Biological Deposit
S.cerevisiae strain CY 2964 (plcl*l::HIS3 ade2-101 his3*200 leu2*1 lys2-801
trpl * 1 ura3-52 [LEU2 CEN6 ARS4 AmpR CUP-PLC-beta2], [GPAlp Human alphal 6 TRPlCEN6 ARS4 AmpR] was deposited with the American Type Culture Collection (Rockville,
Maryland) on June 5, 1995 and has been c~ ign~t.od with the ATCC Accession Number:
74345; and
S.cerevisiae strain CY 2954 (plcl*l::HIS3 ade2-101 his3*200 leu2*1 lys2-801
trpl*l ura3-52 [CUP RAT PLCbetal LEU2 2mu-ori REP3 AmpR], GPAlp TRP1 CEN6
ARS4 AmpR] was deposited with the American Type Culture Collection (Rockville,
Maryland) on June 5, 1995 and has been designated with the ATCC Accession Number:
74343.
PLCl ~ Yeast Strains and Complementation ~lssays
Yeast Transformations
All yeast transformation with the plcl~ strains (Flick and Thorner (1993) were done
using lithium acetate-based protocols and the Yeastmaker transformation kit (Clontech)
according to the manufacturer's specifications. In general, strains were grown up overnight
CA 022204~9 1997-11-27
W 096/40939 PCTAUS96/10002
-57-
at 30~C to late log phase and diluted the next morning to an OD600 = 0.2-0.3. Following 5
hours of growth at 30~C, cells were washed once in water and resuspended in lithium
acetate/TE such that the cells were concentrated 30-50 fold. To 100 ul of this suspension of
cells, carrier DNA (100 ug), and plasmid DNA (0.1 - 0.5 ug) were added. Cells and DNA
were then vortexed, PEG/lithium acetate/TE added, the suspension vortexed again, and the
suspension incubated at 30~C for 30 minutes. DMSO was then addedto a final concentration
of 10% was then added and the cells were heat shocked at 42~C for 15 minutes. Following
cooling on ice, the cells were centrifuged, the PEG con~ining supernatant was decanted, the
cells were resuspended in sterile TE and plated on selective plates.
Growth assays and alternative readouts
Standard media were used for the culture of yeast cells, and established procedures
were used for genetic manipulations (Rose, M.D., Winston, F., and P. Heiter (1990) Methods
in Yeast Genetics: A Laboratory Course Manual. Cold Spring Harbor Laboratory Press, Cold
Spring Harbor, NY). All yeast skains were grown under selective conditions on synthetic
medium supplemented with nutrients a~lo~l;ate for selection and m:~inten~nce of insertional
mutations and plasmids (Guthrie, C, and G.R. Fink (1991) Methods in Enzymology
Volumel94. Guide to Yeast Genetics and Molecular Biology, Academic Press, Inc.).Strains to be tested for suppression of plcl~ conditional lethal phenotypes were picked from
single colonies from selective Synthetic Complete (SC) plates and were then streaked onto
SC plates to single colonies and then grown for 48 to 72 hours under the following
conditions.
Permissive growth conditions:
SC / 2% Glucose / 30~C
Non-permissive growth conditions:
SC / 2% Glucose / 1.2 M Sorbitol / 30~C
SC / 2% Glucose / 0.5 M NaCl / 30~C
SC / 2% Glucose / 37~C
SC / 2% Glucose / 12M Sorbitol / 37~C
SC / 2% Glucose / 0.5 M NaCl / 37~C
The non-permissive conditions are listed above from least stringent to most stringent.
Cell growth was monitored visually by light microscopy using a Nikon phase contrast
- microscope and were photographed using the UVP digital image processing system.
Resul~s
GALl promoter driven PLC-~l does not complement the plcl mutant
-
CA 022204~9 1997-11-27
W O 96/40939 PCTAUS96/10002
phenotype
Initial attempts to complement the plcl ts and osmotic sensitivity phenotypes with
m~mm~ n PLC-~ isozymes were carried out using a rat PLC-~l construct driven by the
GAL 1 promoter (the sequence of this construct was verified by dideoxynucleotidesequencing) in Cadus yeast strains CY1630 (plcl~l::HIS3 ade2-101(Oc) his3-dlO0 leu2-dl
lys2-801 (Am) trpl-dl) and CY1633 (plc1~2::HIS3 ade2-101(Oc) his3-dlO0 leu2-dl lys2-
801 (Am) trpl-dl). In these ~x~ ents, no complementation was observed under
conditions in which the GALl promoter was either repressed (in the presence of glucose) or
when it was derepressed in the presence of low glucose and activated in the presence of
galactose. In control experiments using a GALl promoter driven PLCl cassette (Cadus
plasmid 1639) transformed into the same strain backgrounds (CY1630 and CY1633), both
the temperature sensitive and osmotic sensitivity phenotypes were complemented. These
negative results with the rat PLC-,Bl indicated that functional complementation of plcl
phenotypes requires more than ~ es~ion from the GALl promoter of the rat PLC-~l gene
alone.
Complementation Analysis with Ga subunits
Phospholipase-C ,13 dependent hydrolysis of phosphatidylinositol 4,5-bisphosphate
(PIP2) to form inositol 1,4,5, trisphosphate (IP3) and diacylglycerol (DAG) is stim~ tl ~l by
both Ga and G~ y subunits of heLe~ neric G-proteins. Stimulation of PLC-13 activity by G
a subunits is restricted to members ofthe Gq family that includes Gq, -11, -14, -15, and -16.
Ga subunits belonging to other families (-s, -i, and -12/13) do not sfim~ te PLC-,B dependent
hydrolysis of PIP2 . In several cell types, agonist dependent stimulation of IP3 and calciurn
mobilization have been shown to be partially sensitive to pertussis toxin. This observation
initially lead to speculation that Gi or Go could stimulate PLC-,13 activity. More recently the
pertussis toxin sensitive component of agonist dependent IP3 production has been shown to
be due to the ability of G,B y subunits to stimulate PLC-~ isoforrns directly.
In an effort to recapitulate G-protein dependent regulation of PLC-~ isoforms inyeast, a series of CY1630 derivatives were transformed with expression vectors coding for
m~mm~ n G-proteins and complementation of the plcl mutant phenotypes were scored.
Cadus yeast strains CY1901, CY1903 and CY1904 (all CY1630 derivatives cont~ining the
plcl~l::HIS3 allele) contain, respectively, Cadus plasmids 1443 (no PLC), 1637 (GALlp-rat
PLC-~l) or 1639 (GALlp-PLCl)(See Strain List, Table 2). While all three strains grow at
30~C on both synthetic complete and rich media, CY1904. harboring a GALlp-PLCl
expression cassette on a 2 micron plasmid, grows better than e-i.ner CY1901 (empty vector)
or CY1903 (harboring a GALlp-rat PLC-~l expression c~e~e ~n a 2 micron plasmid). At
CA 022204~9 1997-ll-27
W 096/40939 PCT~US96/10002
_ 59 _
non-permissive temperatures (>35~C), CY1901 and CY1903 failed to form colonies after 3
days in culture, while CY1904 forms large colonies.
CY1901, CY1903, and CY1904 (all haploid strains) were transformed by lithium
5 acetate transformation procedures (Clontech, as per manufacturer's recomm~n~l~tions) with a
panel of low-copy number (CEN ARS) Ga subunit expression plasmids coding for thefollowing genes under the transcriptional control of the GPAl upstream promoter: Cadus
plasmid 1127 (empty vector), 1179 (GPAl), 1181 (GaS), 1606 (Gai2), 1617 (Gal6), 1753
(Gal6-Q209L GTPase~ activated allele), 1685 (Gaq), and 1749 (Gaq-Q209L GTPase~
10 activated allele)(See Strain List, Table 1). Following transformation into the strains listed
above, isolated colonies were streaked to selective plates (-Ura, -Trp + glucose) and
. incubated at 30~C or at 37~C for up to 96 hours. While all strains cont~inin~ all
combinations of PLC expression vectors (1443, 1637, and 1639) and G-protein expression
vectors grew under permissive conditions (30~C), only those strains expressing the yeast
15 PLCl gene under the control of the GALl promoter grew at 37~C. Induction of the GALl
promoter by growth on low glucose/high galactose plates did not result in rescue of the ts
phenotypes of CY1901 or CY1903 derivatives, either. Even at times up to 96 hours post-
plating, there was no evidence of growth under non-permissive conditions for strains
harboring vectors expressing rat PLC-,Bl from the GALl promoter. These results indicate
20 that plasmids encoding the rat PLC-131 driven by the GALl promoter are not capable of
complementing the ts defect in plcl strains of yeast.
CUP-PLC-~ expression vectors
One possible explanation for the negative results described in the previous section is a
25 lack of expression or an inappropriate level of expression of rat PLC-,Bl from the GALl
promoter. A second potential difficulty presented with the GALl promoter relates to the
inability of plcl strains to utilitize galactose as a carbon source. If galactose utilization is
conlplolnised in these strains, then induction of galactose sensitive promoters like GALlp
and GAL 10p would also be compromised. To circumvent both of these potential problems,
30 the m~mm~ n PLC-,B isozymes were expressed from an inducible promoter whose
activation is not dependent on carbon sources other than glucose. Unlike other high level
constitutive promoters (i.e. PGK or ADHl), has not been associated with cellular toxicity.
This sort of toxicity has, in fact been reported in the literature by Flick and Thorner (1993)
with respect to overexpression of the yeast PLCl gene from the GALl promoter in the
35 presence of galactose. Flick and Thorner report that the growth of wildtype strains of yeast
that contained the PLCl gene under the control of the GALl promoter was col~lplulllised
CA 022204~9 1997-11-27
WO 96/40939 - PCTrUS96/10002
- 60 -
when the GALl promoter was in~ ce~l on galactose but not when it was repressed on
glucose-cont~ining media.
Four novel PLC-,I~ constructs were made, two encoding the rat PLC-,~l gene and two
encoding the human PLC-~2 gene each under the control of the CUPl promoter. In these
constructs, the nucleotide sequences of amino terminal regions of rat PLC-,~l and human
PLC-,B2 were altered to reflect a bias towards yeast codon usage instead of mz~mm~ n codon
usage. The amino terminal seven residues of PLC-~l and the amino ttsrmin~l 21 residues of
human PLC-132 were mutated using synthetic oligonucleotides to effect these changes. The
10 nucleotide sequence of each construct subsequently was verified by dideoxynucleotide
sequencing methods on both DNA strands.
Yeast Strain CY1630 was transformed with each of these pl~mifl~, as well as other
PLC constructs in which PLC isozymes are driven by the GALlp or ADHl promoters, in the
presence or absence of plasmids expressing various Ga subunits. Initial experiment~ tested
15 for complement~tion of the temperature sensitive (ts) phenotype associated with the plcl
genotype by human PLC-,B2 and rat PLC-~Bl in the presence of a hybrid Ga subunitcomposed of the amino t~:rmin~l 60% of the yeast GPAl subunit and the carboxyl terrnins~l
40% of the human Gal6 subunit (Gal6-Bam) This hybrid construct was chosen over avariety of other human Ga subunits for two reasons. First, in independent experiments it had
20 been demonstrated that this particular hybrid subunit is functionally expressed in yeast (i.e. it
couples to yeast G~ subunits and supresses activation of the pheromone response pathway in
gpal- strains). Second, the structural ~let~rmi~nt~ involved in effector activation by Ga
subunits are thought to map to residues in the carboxyl t~rmin~l portions of Ga subunits
(Berlot and Bourne (1992); Rarick et al. (1992); Artemeyer et al.(l993)).
Y1630 ( plcl) derivatives (See Strain List, Table 2) harboring combinations of
m~mm~ n PLC-~ isozymes and Ga subunits were first colony purified and then duplicate
sibs of each co-transformation assayed for growth at 30OC and 37OC in the presence or
absence of lOOuM CuS04. At 48 hours post-plating, all plcl strains, including those
30 cont~inin~ plasmids encoding rat PLC-,~l, grew at 30OC, albeit less well than strains CY1633
(PLC 1) or CY 1904 (plc 1 ~ HIS3 [GAL 1 p-PLC 1]). At non-permissive temperatures,
several differences could be observed between strains harboring m~mmz~ n PLC-~ isozymes
and those harboring empty vector by 48 hours post-plating. First, strains cont~ining high
copy versions (2 micron based) of rat-PLC-,Bl grew at 37OC regardless of the promoter
3~ driving expression of the PLC-,B isozyme, while strains cont~ining empty vector did not.
CY1630 derivatives cont~inin~ Cadus plasmid 1640 (ADHlp-rat PLC-131) or Cadus plasmid
CA 022204~9 1997-11-27
WO 9GM033g PCTAUS96/10002
- 61 -
1922 (CUP-human PLC-~l) formed small colonies within 48 hours at 370C, while CY1630
derivatives cont~ining Cadus 1443 (empty vector) did not.
Second, CY1630 derivatives co-transformed with a low copy (CEN ARS) plasmid
5 encoding CUP-human PLC-~2 and a low copy (CEN ARS) plasmid encoding the Gal 6-Bam
allele grew at both 300C and at 370C. Third, growth of CY1630 derivatives at 370C in this
assay was not due to expression of the Gal6-Bam allele alone as strains cont:~ininp the Ga
subunit variant alone in the absence of rat or human PLC-,B isozymes did not support growth
at 370C.
Finally, growth of CY1630 derivatives expressing m~mm~lian PLC isozymes was
unaffected by the addition of lOOuM CuS04 at 300C, while at 370C growth in the presence
of copper was less than growth in the absence of copper. This ~~ nl inhibition of growth
in the presence of copper at non-permissive temperatures may reflect toxicity due to
15 o~ x~l~ssion of phospholipase C enzymatic activity by analogy with the observations made
by Flick and Thorner on overexpression of PLC 1. These data represent the first
demonstration to our knowledge that expression of m~mm~ n PLC-~3 isozymes in yeast
could functionally complement defects in the PLCl allele of S. cerevisiae. These data also
demonstrate that members of the G-protein regulated PLC-,B family of phospholipase C
20 enzymes can functionally replace members of the PLC-delta family in yeast.
In an extension of these initial observations, a series of CY1630 derivatives were
constructed in which different combinations of m~rnm~ n PLC-13 isozymes and m~mm~ n
Ga subunits were co-expressed. The table of yeast strains (Table 2) lists the combinations
25 tested in growth complementation assays. Strains cont~inin~ any combination of Gq family
members (wildtype alleles of q, 11, 16 as well as GTPase-deficient alleles of q and 16) and
PLC-,B2 supported growth under non-permissive conditions. Go~ subunits from the GaS and
Gai families, on the hand, did not support growth of plc l ~ strains under restrictive
conditions. The Figure shows representative data. plcl~ strains expressing PLC-,~l under the
30 control of the CUP promoter grow under restrictive conditions regardless of the presence or
absence of Ga subunits.
-
Complementation of the temperature sensitive and NaCl-sensitive phenotype
associated with the plcl genotype was observed in two sets of circllm~t~nces. In PLCI~
35 strains cont~ining high copy plasmids encoding either rat PLC-,Bl (Plasmid 1922) or human
PLC-~2 (Plasmid 1964), growth at 370C did not require co-expression of a m~mm~ n Ga
subunit. These strains, therefore, display G-protein independent compl~ment~tion of the ts
CA 022204~9 1997-11-27
W O 96/40939 PCTnJS96/10002
-62-
defect. In strains cont~ining low copy plasmids encoding the human PLC-,132 allele (Plasmid
1961), growth at 370C required co-expression of a Ga subunit from the Gq farnily. plcl
strains cont~ining human PLC-~2 and Gq,-ll, or -16, either on low or high copy number
plasmids, all grew at 370C. Furthermore, strains expressing human PLC-,B2 and activated
forms of Gaq(Q209L) or Gal6(Q~12L) grew robustly at both 300C and 370C while strains
harboring human PLC-,B2 and an activated form of GaS (Q227L) failed to support growth at
370C. 3
Example 2. Complk".~,.lulion of fheyeast plcl mutation by human PLC-~3
Human PLC-~3 has been found to complement the temperature-sensitive and NaCI
sensitive phenotypes associated with the plcl genotype in yeast in a G-protein independent
15 fashion. These conclusions are based on the finding that expression of the human PLC-,~3 in
yeast strains with the plcl background under the control of the CUP promoter on either high
or low copy plasmids, results in growth on 0.5M NaCl or at elevated temperatures,
independent of the co-expression of Ga subunits of the Gq family (i.e. q, 11, 14, 15, or 16).
In this respect the char~çt~ri.~tics of the human PLC-~33 isoform expressed in yeast resemble
20 those of rat PLC-,~l in exhibiting G-protein independent growth under non-permissive
conditions, as distinct from the G-protein dependent growth phenotype of the human PLC-,132
isoform.
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CA 02220459 l997-ll-27
WO 96/~-939 -- PCT~US96/10002
-74-
All of the references and publications cited herein are hereby incorporated by
reference.
Equivalenfs
Those skilled in the art will recognize, or be able to ascertain using no more than
routine experimentation, many equivalents to the specific embot1iment~ of the invention
described herein. Such equivalents are intPn~le-l to be encompassed by the following claims.
CA 022204~9 l997-ll-27
WO 96/40939 PCT~U~96/10002
-75-
~u~ LISTING
(1) GENERAL INFORMATION:
(i) APPLICANT:
(A) NAME: Cadus Pharmaceutical Corporation.
(B) STREET: Old Saw Mill River Road
(C) CITY: Tarrytown
(D) STATE: NY
(E) COUNTRY: USA
(F) POSTAL CODE (ZIP): 10591
(G) TELEPXONE: (914) 345-3344
(H) TELEFAX: (914) 345-3565
(ii) TITLE OF lNv~N~l~lON: Functional Vertebrate Phospholipase C
in Ye2st
(iii) NUMBER OF SEQUENCES: 10
( iv) COMPUTER READABLE FORM:
(A) MEDIUM TYPE: Floppy disk
(B) COMPUTER: IBM PC compatible
(C) OPERATING SYSTEM: PC-DOS/MS-DOS
(D) SOFTWARE: ASCII (text)
(vi) PRIOR APPLICATION DATA:
(A) APPLICATION NUMBER: US 08/481,632
(B) FILING DATE: 07-~UN-1995
(2) INFORMATION FOR SEQ ID NO:l:
(i) ~u~ CHARACTERISTICS:
(A) LENGTH: 29 bases
(B) TYPE: nucleic acid
(c) STRANDEDNESS: single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:l:
GGGCGTCTCA CATGGCCCGC TCGCTGACC 29
(2) INFORMATION FOR SEQ ID NO:2:
(i) SEQUENCE CHARACTERISTICS:
(A) LENGTH: 30 bases
(B) TYPE: nucleic acid
(C) STRANDEDNESS: single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
CA 022204~9 l997-ll-27
W O 96/40939 PCTAUS96/10002
-76-
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:
GGGCTCGAGC TGGGTCACAG CAGGTGGATC 30
(2) INFORMATION FOR SEQ ID NO:3:
(i) SEQUENCE CHARACTERISTICS:
(A) LENGTH: 32 bases
(B) TYPE: nucleic acid
(C) STRANDEDNESS: single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:
20 GGGCGTCTCA CATGACTCTG GAGTCCATCA TG 32
(2) INFORMATION FOR SEQ ID NO:4:
(i) SEQUENCE CHARACTERISTICS:
(A) LENGTH: 30 bases
(B) TYPE: nucleic acid
(C) STR~Nn~nM~.~S: single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:
GGGCGTCTCC TCGAGGCACG GTTAGACCAG 30
(2) INFORMATION FOR SEQ ID NO:5:
(i) SEQUENCE CHARACTERISTICS:
(A) LENGTH: 32 bases
(B) TYPE: nucleic acid
(C) STRANDEDNESS: single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
(xi) ~yu~Nu~ DESCRIPTION: SEQ ID NO:5:
GGGGGTCTCC CATGACTCTG GAGTCCATGA TG 32
(2) INFORMATION FOR SEQ ID NO:6:
(i) ~yU~N~' CHARACTERISTICS:
CA 022204~9 1997-11-27
W O 96/40939 PCT~US96/10002
(A) LENGTH: 22 bases
(B) TYPE: nucleic acid
(C) STR~Nn~nNR~S: single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:
GGGCTCGAGG AAGCCTGGCC CT ~ 22
(2) INFORMATION FOR SEQ ID NO:7:
(i) SEQUENCE CHARACTERISTICS:
(A) LENGTH: 23 bases
(B) TYPE: nucleic acid
(C) STR~Nn~nNR~S: single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:
CATGGCTGGT GCTCAACCAG GTG 23
(2) INFORMATION FOR SEQ ID NO:8:
(i) SEQUENCE CHARACTERISTICS:
(A) LENGTH: 23 bases
(B) TYPE: nucleic acid
(C) STRANDEDNESS: single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
(Xi) ~ U~N~ DESCRIPTION: SEQ ID NO:8:
TGCACACCTG GTTGAGCACC AGC 23
(2) INFORMATION FOR SEQ ID NO:9:
(i) SEQUENCE CHARACTERISTICS:
(A) LENGTH: 65 bases
(B) TYPE: nucleic acid
(C) sTRA-NnRnNR~s single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
CA 02220459 l997-ll-27
W O9C/40~39 PCTAUS96/10002
-78-
(xi) SEQUENCE DESCRIPTION: SEQ ID NO:9:
CATGTCTTTG TTGAACCCAG r~ GCC ACCAAAGGTT AAGGCTTACT TGTCTCAAGG 60
TGAGC 65
(2) INFORMATION FOR SEQ ID NO:lO:
(i) SEQUENCE CHARACTERISTICS:
(A) LENGTH: 61 bases
(B) TYPE: nucleic acid
(C) STRANDEDNESS: single
(D) TOPOLOGY: linear
(ii) MOLECULE TYPE: cDNA
(xi ) SEQUENCE DESCRIPTION: SEQ ID NO:lO:
GCTCACCTTG AGACAAGTAA GCCTTAACCT TTGGTGGCAA CAAAACTGGG TTCAACA~AG 60
A ~ 61
