Tumor suppressor gene

Details Tumor suppressor gene Tumor suppressor gene

1997-11-25

2003-06-24

Priebe, Scott D. (Department: 1632)

Chemistry: molecular biology and microbiology

Animal cell, per se ; composition thereof; process of...

C435S320100, C435S455000, C536S023100, C536S023500

Reexamination Certificate

active

06582956

ABSTRACT:

1. INTRODUCTION
The present invention relates to a novel tumor suppressor gene, referred to herein as SSeCKS, its encoded protein, and methods of use thereof. It is based, at least in part, on the discovery of a SSeCKS gene which encodes a substrate of protein kinase C that functions as both a mitogenic regulator as well as a tumor suppressor.
2. BACKGROUND OF THE INVENTION
The inactivation of several tumor suppressor gene families (for example, those encoding p53, Rb, and APC) as a result of mutation is acknowledged to contribute to oncogenicity of several types of human cancers (Levine, 1993, Ann. Rev. Biochem. 62:623-651). Many of these so-called class I tumor suppressor genes (Lee et al., 1991, Proc. Natl. Acad. Sci. U.S.A. 88:2825-2829) were identified and isolated following cumbersome pedigree and cytogenetic analyses (Sager, 1989, Science 246:1406-1412). Recently, another class of genes (class II) whose expression is known to be down-regulated in tumor cells has been shown by gene transfer techniques to encode potential tumor suppressors. These include nonmuscle &agr;-actinin, tropomyosin I, CLP, retinoic acid receptor &bgr;
1
, and interferon regulatory factor (Gluck et al., 1993, Proc. Natl. Acad Sci. U.S.A. 90:383-387; Hirada et al., 1993, Science 259:971-974; Hogel et al., 1993, Proc. Natl. Acad. Sci. U.S.A. 90:985-989; Mishra et al., 1994, J. Cell. Biochem. 18(Supp. C):171; Plasad et al., 1993, Proc. Natl. Acad. Sci. U.S.A. 90:7039-7043). Additional tumor suppressor gene families such as the maspin gene, rrg, and NO3 (Contente et al., 1993, Science 249:796-798; Ozaki et al., 1994, Cancer Res. 54:646-648; Zou et al., 1994, Science 263:526-529) were isolated by subtractive hybridization techniques designed to identify down-regulated genes. The ability of these genes to reverse an array of oncogenic phenotypes following gene transfer and over-expression supports the possibility for novel therapeutic modalities for cancer.
3. SUMMARY OF THE INVENTION
The present invention relates to a novel tumor suppressor gene, SSeCKS. It is based, at least in part, on the discovery of a gene, hitherto referred to as “322” (Lin et al., 1995, Mol. Cell. Biol. 15:2754-2762) but now referred to as SSeCKS, which was found to be down-regulated in certain transformed cells. Further, the SSeCKS gene product has been found to be a substrate of protein kinase C, and has been shown to act as a mitogenic regulator and as an inhibitor of the transformed phenotype.
In various embodiments, the present invention relates to the SSeCKS gene and protein, and in particular, to rat and human SSeCKS gene and protein. Furthermore, the present invention provides for the use of such genes and proteins in diagnostic and therapeutic methods.
4. BRIEF DESCRIPTION OF THE DRAWINGS
FIG.
1
. Northern blot analysis of SSeCKS RNA levels in NIH 3T3 cells versus NIH/v-src transformed cells.
FIG.
2
. Southern blot analysis showing that the decreased level of SSeCKS RNA in NIH/v-src cells is not due to gross deletion or translocation of the SSeCKS allele (A), and restriction map of SSeCKS (B).
FIG.
3
. Nucleic acid SEQ ID NO: 1 (top line, lower case letters) and deduced amino acid SEQ ID NO: 2 (lower line, capital letters) sequence of rat SSeCKS cDNA encoding an active truncated form of SSeCKS.
FIG.
4
. Northern blot analysis showing that the transcription of SSeCKS is suppressed relatively soon after the activation of a ts-src allele (A) or the addition of fetal calf serum (FCS) to starved rodent fibroblasts (B).
FIG.
5
. Northern blot analyses showing levels of SSeCKS transcripts in oncogene-transformed Rat-6 fibroblasts.
FIG.
6
. Results of in vitro transcription-translation of SSeCKS cDNA.
FIG.
7
. Proliferation of cells overexpressing SSeCKS (A and B).
FIG.
8
. “Zoo” Southern blot of SSeCKS probe to genomic DNA from various species.
FIG.
9
. Northern blot analysis showing tissue-specific expression of SSeCKS in mice.
FIG.
10
. Schematic diagram of SSeCKS protein.
FIG. 11A-I
. Nucleic acid SEQ IN NO: 3 sequence of rat cDNA encoding full-length SSeCKS and deduced amino acid sequence.
FIG.
12
. In vitro transcription and translation of SSeCKS. One &mgr;g of plasmid DNA encoding the full-length SSeCKS cDNA or a N-terminally truncated SSeCKS cDNA (clone 13.2.2) were incubated in a coupled T7 transcription/translation reaction (TNT; Promega) containing [
35
S]-methionine as described in section 7.1. One tenth of the labeled products were analyzed by SDS-PAGE followed by fluorography. Protein size markers are shown at left. Note that a shortened version of SSeCKS, synthesized from an internal ATG start site in clone 13.2.2, is not produced in the context of the upstream ATG start site in the full-length SSeCKS cDNA in in vitro reactions.
FIGS. 13A-C
. Glutathione S-transferase fusion constructs of SSeCKS domains. Secondary structural analysis of SSeCKS predicted a rod-like molecule with a high degree of hydrophilicity and amphipathic helices, and a concentration of Chou-Fasman turns (Chou and Fasman, 1978, Advances in Enzymology 47:45-147) from residues 400-900 (
13
B and
13
C). The turns in this region were not recognized by the Robson-Garnier algorithm (Garnier et al., 1978, J. Mol. Biol. 120:97-120), as shown in
13
C. Four concentrations of predicted PKC phosphorylation sites (
B
/
T
X
K
/
R
or
K
/
R
XX
S
/
T
) were also identified (
13
A, white boxes; numbered 1-4). The black bars (
13
A) indicate the sizes and names of GST-SSeCKS fusion constructs containing individual or combinations of the predicted PKC sites.
FIGS. 14A-B
. In vivo phosphorylation of SSeCKS by PKC. Confluent Rat-6 cells grown overnight in DEM lacking calf serum were starved of phosphate for 2 hours and then labeled for 4 hours with [
32
P]orthophosphate. At the end of the labeling period, some cells were treated with 200 nM PMA (lane b, 2 min; lanes c and d, 15 min) and the PKC-specific inhibitor, bis-indolylmaleimide (lane d, 30 min). SSeCKS protein was immunoprecipitated from equal aliquots (400 &mgr;g) of lysates from untreated (lane a) or treated cells (lanes b-d), and western blotted onto a PVDF membrane (
14
A).
14
B represents immunoblotting using rabbit anti-SSeCKS serum (showing equal amounts of SSeCKS protein loaded) whereas the upper panel represents autoradiography of the blotted protein (showing an increase in
32
PO
4
-labeling of SSeCKS following PMA treatment). The 280/290 kDa doublet (unresolved in this gel) is indicated by an arrow, and the minor 240 kDa form of SSeCKS can be detected in the upper panel. A better resolution of these SSeCKS species is shown in FIG.
22
.
FIGS. 15A-B
. In vitro phosphorylation of SSeCKS by PKC. GST and GST/322 fusion protein (see
FIG. 13
) were expressed and purified from bacteria as described in section 7.1 (
15
A). Five &mgr;g of the GST samples were added to PKC assays containing [32P]-&ggr;-ATP in the presence or absence of the PKC peptide inhibitor (19-36). The products were then bound to glutathione-Sepharose beads, precipitated and washed, and analyzed by SDS-PAGE and autoradiography (
15
B). Protein size markers are indicated on the appropriate sides. Radioactive labeling was detected in GST-322 (160 kDa) only.
FIGS. 16A-B
. Phospholipid preference for the in vitro phosphorylation of SSeCKS by PKC. Myelin basic protein, MBP (
16
A), GST-322 and GST proteins (
16
B) were phosphorylated in vitro as in
FIG. 15
, in the presence or absence of various lipids including phosphatidylserine (PS), phosphatidylcholine (PC) or phosphatidylinositol (PI). In some cases, excess PKC peptide inhibitor (19-36) was added as in FIG.
15
. The extent of labeling in the peptide substrates was determined by spotting the reaction products on phosphocellulose discs (Whatman), precipitating peptides with washes of 5% trichloroacetic acid, followed by scintillation counting.
FIGS. 17A-B
. Co-precipitation of SSeCKS with PKC.
17
A: GST-1322 fusion protein (see
FIG. 13
) was expressed and purified from bacteria as described in section 7.1.
17
B: RIPA lysates (1 mg pro

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