Androgen-regulated gene expressed in prostate tissue

This invention relates to androgen-regulated nucleic acids, a polynucleotide array containing these androgen-regulated nucleic acids, and methods of using the polynucleotide array in the diagnosis and prognosis of prostate cancer.

FIELD OF THE INVENTION

The present invention relates to the quantitative evaluation of gene expression. More particularly, the present invention relates to novel, androgen-regulated nucleic acids, polynucleotide arrays containing these nucleic acids, and methods of using the array in the evaluation of hormone-related cancers, such as prostate cancer.

BACKGROUND

Prostate cancer (CaP) is the most common malignancy in American men and second leading cause of cancer mortality (1). Serum-prostate specific antigen (PSA) tests have revolutionized the early detection of CaP (2). Although PSA has revolutionized early detection of prostate cancer, there is still a very high false positive rate. The increasing incidence of CaP has translated into wider use of radical prostatectomy as well as other therapies for localized disease (3-5). The wide spectrum of biologic behavior (6) exhibited by prostatic neoplasms poses a difficult problem in predicting the clinical course for the individual patient (3-5). Traditional prognostic markers such as grade, clinical stage, and pretreatment PSA have limited prognostic value for individual men (3-5). A more reliable technique for the evaluation and prognostic of CaP is desirable.

Molecular studies have shown a significant heterogeneity between multiple cancer foci present in a cancerous prostate gland (7,8). These studies have also documented that the metastatic lesion can arise from cancer foci other than those present in dominant tumors (7). Approximately 50-60% of patients treated with radical prostatectomy for localized prostate carcinomas are found to have microscopic disease that is not organ-confined, and a significant portion of these patients relapse (9). Therefore, identification and characterization of genetic alterations defining CaP onset and progression is crucial in understanding the biology and clinical course of the disease.

Despite recent intensive research investigations, much remains to be learned about specific molecular defects associated with CaP onset and progression (6, 10-15). Alterations of the tumor suppressor gene p53, bcl-2 and the androgen receptor (AR), are frequently reported in advanced CaP (6, 10-15). However, the exact role of these genetic defects in the genesis and progression of CaP is poorly understood (6, 10-15). Recent studies have shown that the focal p53 immunostaining or bcl-2 immunostaining in radical prostatectomy specimens were independent prognostic markers for cancer recurrence after surgery (16-19). Furthermore, the combination of p53 and bcl-2 alterations was a stronger predictor of cancer recurrence after radical prostatectomy (18).

The roles of several new chromosome loci harboring putative proto-oncogenes or tumor suppressor genes are being currently evaluated in CaP (7-13). High frequency of allelic losses on 8p21-22, 7q31.1, 10q23-25 and 16q24 loci have been shown in CaP (6, 10-15). PTEN1/MMAC1, a recently discovered tumor suppressor gene on chromosome 10q25, is frequently altered in advanced CaP (20, 21). Gains of chromosome 8q24 harboring c-myc and prostate stem-cell antigen (PSCA) genes have also been shown in prostate cancer (22, 23). Studies utilizing comparative genomic hybridization (CGH) have shown frequent losses of novel chromosomal loci including 2q, 5q and 6q and gains of 11p, 12q, 3q, 4q and 2p in CaP (24, 25). The inventors have recently mapped a 1.5 megabase interval at 6q16-21 which may contain the putative tumor suppressor gene involved in a subset of prostate tumors. The risk for 6q LOH to non-organ confined disease was five fold higher than for organ confined disease (26). Chromosome regions, 1q24-25 and Xq27-28 have been linked to familial CaP (27, 28).

It is evident that multiple molecular approaches need to be explored to identify CaP-associated genetic alterations. Emerging strategies for defining cancer specific genetic alterations and characterizing androgen regulated genes in rat prostate and LNCaP human prostate cancer cell models include, among others, the study of global gene expression profiles in cancer cells and corresponding normal cells by differential display (DD) (29) and more recent techniques, such as serial amplification of gene expression (SAGE) (30) and DNA micro-arrays (31; U.S. Pat. Nos. 5,744,305 and 5,837,832 which are herein incorporated by reference) followed by targeted analyses of promising candidates. Our laboratory has also employed DD, SAGE and DNA microarrays to study CaP associated gene expression alterations (32-33). Each of these techniques, however, is limited. The number of transcripts that can be analyzed is the major limitation encountered in subtractive hybridization and differential display approaches. Furthermore, while cDNA microarray approaches can determine expression of a large number of genes in a high throughput manner, the current limitations of cDNA arrays include the presence of specific arrays used for analyses and the inability to discover novel genes.

While alterations of critical tumor-suppressor genes and oncogenes are important in prostate tumorogenesis, it is also recognized that hormonal mechanisms play equally important roles in prostate tumorogenesis. The cornerstone of therapy in patients with metastatic disease is androgen ablation, commonly referred to as hormonal therapy (34), which is dependent on the inhibition of androgen signaling in prostate cancer cells. Androgen ablation can be achieved, for example, by orchiectomy, by the administration of estrogen, or more recently by one of the luteinizing hormone-releasing hormone agonists. Recent clinical trials have demonstrated the efficacy of combining an antiandrogen to orchiectomy or a luteinizing hormone-releasing hormone to block the remaining androgens produced by the adrenal glands. Although approximately 80% of patients initially respond to hormonal ablation, the vast majority of patients eventually relapse (35), presumably due to neoplastic clones of cells which become refractory to this therapy.

Alterations of the androgen receptor gene by mutations in the hormone binding domain of the AR or by amplification of the AR gene have been reported in advanced stages of CaP. Much remains to be learned, however, about the molecular mechanisms of the AR-mediated cell signaling in prostate growth and tumorogenesis (36-43). Our earlier studies have also described mutations of the AR in a subset of CaP (40). Mutations of the AR are reported to modify the ligand (androgen) binding of the AR by making the receptor promiscuous, so that it may bind to estrogen, progesterone, and related molecules, in addition to the androgens (36,38,42). Altered ligand binding specificity of the mutant AR may provide one of the mechanisms for increased function in cancer cells. Amplifications of the AR gene in hormone-refractory CaP represent yet another scenario where increase in AR function is associated with tumor progression (44,45).

Several growth factors commonly involved in cell proliferation and tumorogenesis, e.g., IGF1, EGF, and others, have been shown to activate the transcription transactivation functions of the AR (46). The co-activator of the AR transcription factor functions may also play a role in prostate cancer (47). Recent studies analyzing expression of the androgen-regulated genes (ARGs) in hormone sensitive and refractory CWR22 nude mice xenograft models (48) have also shown expression of several androgen regulated genes in AR positive recurrent tumors following castration, suggesting activation of AR in these tumors (49).

In addition to the alterations of the androgen signaling pathway(s) in prostate tumor progression, androgen mechanisms are suspected to play a role in the predisposition to CaP. Prolonged administration of high levels of testosterone has been shown to induce CaP in rats (50-52). Although recent evidence suggests an association of androgen levels and risk of CaP, this specific observation remains to be established. (53). An independent line of investigations addressing the length of inherited polyglutamine (CAG) repeat sequence in the AR gene and CaP risk have shown that men with shorter repeats were at high risk of distant metastasis and fatal CaP (54,55). Moreover, the size distribution of AR CAG repeats in various ethnic groups has also suggested a possible relationship of shorter CAG repeats and increased prostate cancer risks in African-American men (56,57). Biochemical experiments evaluating AR-CAG repeat length and in vitro transcription transactivation functions of the AR revealed that AR with shorter CAG repeats possessed a more potent transcription trans-activation activity (58). Thus, molecular epidemiologic studies and biochemical experimentation suggest that gain of AR function, consequently resulting in transcriptional transactivation of downstream targets of the AR gene, may play an important role in CaP initiation. However, downstream targets of AR must be defined in order to understand the biologic basis of these observations.

The biologic effects of androgen on target cells, e.g., prostatic epithelial cell proliferation and differentiation as well as the androgen ablation-induced cell death, are likely mediated by transcriptional regulation of ARGs by the androgen receptor (reviewed in 59). Abrogation of androgen signaling resulting from structural changes in the androgen gene or functional alterations of AR due to modulation of AR functions by other proteins would have profound effects on transcriptional regulation of genes regulated by AR and, thus, on the growth and development of the prostate gland, including abnormal growth characterized by benign prostatic hyperplasia and prostatic cancer. The nature of ARGs in the context of CaP initiation and progression, however, remains largely unknown. Since forced proliferation of the AR prostate cancer cells lacking AR induces cell-death related phenotypes (60), the studies utilizing AR expression via heterologous promoters in cell cultures have failed to address the observations relating to gain of AR functions and prostate cancer progression. Moreover, suitable animal models to assess gain of AR functions do not exist. Therefore, the expression profile of androgen responsive genes (ARGs) has potential to serve as read-out of the AR signaling status. Such a read-out may also define potential biomarkers for onset and progression of those prostate cancers which may involve abrogation of the androgen signaling pathway. Furthermore, functional analysis of androgen regulated genes will help understand the biochemical components of the androgen signaling pathways.

SUMMARY OF THE INVENTION

The present invention relates to the identification and characterization of a novel androgen-regulated gene that exhibits abundant expression in prostate tissue. The novel gene has been designated PMEPA1. The invention provides the isolated nucleotide sequence of PMEPA1 or fragments thereof and nucleic acid sequences that hybridize to PMEPA1. These sequences have utility, for example, as markers of prostate cancer and other prostate-related diseases, and as targets for therapeutic intervention in prostate cancer and other prostate-related diseases. The invention further provides a vector that directs the expression of PMEPA1, and a host cell transfected or transduced with this vector.

In another embodiment, the invention provides a method of detecting prostate cancer cells in a biological sample, for example, by using nucleic acid amplification techniques with primers and probes selected to bind specifically to the PMEPA1 sequence.

In another aspect, the invention relates to an isolated polypeptide encoded by the PMEPA1 gene or a fragment thereof, and antibodies generated against the PMEPA1 polypeptide, peptides, or portions thereof, which can be used to detect, treat, and prevent prostate cancer.

The present invention also relates to a polynucleotide array comprising (a) a planar, non-porous solid support having at least a first surface; and (b) a first set of polynucleotide probes attached to the first surface of the solid support, where the first set of polynuceotide probes comprises polynucleotide sequences derived from genes that are up-regulated, such as PMEPA1, or down-regulated in response to androgen, including genes downstream of the androgen receptor gene and genes upstream of the androgen receptor gene that modulate androgen receptor function. In another embodiment of the invention the polynucleotides immobilized on the solid support include genes that are known to be involved in testosterone biosynthesis and metabolism. In another embodiment of the invention the oligonucleotides immobilized on the solid support include genes whose expression is altered in prostate cancer or is specific to prostate tissue.

In another embodiment, the invention provides a method for the diagnosis or prognosis of prostate cancer, comprising (a) hybridizing nucleic acids of a target cell of a patient with a polynucleotide array, as described above, to obtain a first hybridization pattern, where the first hybridization pattern represents an expression profile of androgen-regulated genes in the target cell; (b) comparing the first hybridization pattern of the target cell to a second hybridization pattern, where the second hybridization pattern represents an expression profile of androgen-regulated genes in prostate cancer, and (c) diagnosing or prognosing prostate cancer in the patient.

Thus, a first aspect of the present invention is directed towards a method for analysis of radical prostatectomy specimens for the expression profile of those genes involved in androgen receptor-mediated signaling. In a preferred embodiment, computer models may be developed for the analysis of expression profiles. Another aspect of the invention is directed towards a method of correlating expression profiles with clinico-pathologic features. In a preferred embodiment, computer models to identify gene expression features associated with tumor phenotypes may be developed. Another aspect of the invention is directed towards a method of distinguishing indolent prostate cancers from those with a more aggressive phenotype. In a preferred embodiment, computer models to such cancers may be developed. Another aspect of the invention is directed towards a method of analyzing tumor specimens of patients treated by radical prostate surgery to help define prognosis. Another aspect of the invention is directed towards a method of screening candidate genes for the development of a blood test for improved prostate cancer detection. Another aspect of the invention is directed towards a method of identifying androgen regulated genes that may serve as biomarkers for response to treatment to screen drugs for the treatment of advanced prostate cancer.

This invention is further directed to a method of identifying an expression profile of androgen-regulated genes in a target cell, comprising hybridizing the nucleic acids of the target cell with a polynucleotide array, as described above, to obtain a hybridization pattern, where the hybridization pattern represents the expression profile of androgen-regulated genes in the target cell.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method useful in the diagnosis and prognosis of prostate cancer. An aspect of the invention provides a method to identify ARGs, such as PMEPA1, that exhibit stable transcriptional induction/repression in response to androgen and have potential as surrogate markers of the status of the androgen signaling in normal and cancerous epithelial cells of prostate.

A second aspect of the invention provides for use of the expression profiles resulting from these methods in diagnostic methods, including, but not limited to, characterizing the treatment response to hormonal therapy, correlating expression profiles with clinico-pathologic features, distinguishing indolent prostate cancers from those with a more aggressive phenotype, analyzing tumor specimens of patients treated by radical prostate surgery to help define prognosis, screening candidate genes for the development of a polynucleotide array for use as a blood test for improved prostate cancer detection, and identifying androgen regulated genes that may serve as biomarkers for response to treatment to screen drugs for the treatment of advanced prostate cancer.

As will be readily appreciated by persons having skill in the art, these gene sequences and ESTs described herein can easily be synthesized directly on a support, or pre-synthesized polynucleotide probes may be affixed to a support as described, for example, in U.S. Pat. Nos. 5,744,305, 5,837,832, and 5,861,242, each of which is incorporated herein by reference. Furthermore, such arrays may be made in a wide number of variations, combining, probes derived from sequences identified by the inventors as up-regulated or down-regulated in response to androgen and listed in Table 3 (genes and ESTs derived from the inventors' SAGE library that are up-regulated and down-regulated by androgens) with any of the sequences described in Table 4 (candidate genes and ESTs whose expression are potentially prostate specific or restricted), Table 5 (previously described genes and ESTs, including those associated with androgen signaling, prostate specificity, prostate cancer, and nuclear receptors/regulators with potential interaction with androgen receptors), Table 6 (genes and ESTs identified from the NIH CGAP database that are differentially expressed in prostate cancer), Table 7 (androgen regulated genes and ESTs derived from the CPDR Genome Systems ARG Database) and Table 8 (other genes associated with cancers). Tables 3-8 are located at the end of the specification at the end of the Detailed Description section and before the References. In Table 3, genes in bold type are known androgen-regulated genes based on Medline Search. In Table 4, genes in bold type are known prostate-specific genes.

Such arrays may be used to detect specific nucleic acid sequences contained in a target cell or sample, as described in U.S. Pat. Nos. 5,744,305, 5,837,832, and 5,861,242, each of which is incorporated herein by reference. More specifically, in the present invention, these arrays may be used in methods for the diagnosis or prognosis of prostate cancer, such as by assessing the expression profiles of genes, derived from biological samples such as blood or tissues, that are up-regulated and down-regulated in response to androgen or otherwise involved in androgen receptor-mediated signaling. In a preferred embodiment, computer models may be useful in methods to screen drugs for the treatment of advanced prostate cancer. In these screening methods, the polynucleotide arrays are used to analyze how drugs affect the expression of androgen-regulated genes that are involved in prostate cancer.

SAGE analysis. The SAGE technology is based on three main principles: 1) A short sequence tag (10-11 bp) is generated that contains sufficient information to identify a transcript, thus, each tag represents a signature sequence of a unique transcript; 2) many transcript tags can be concatenated into a single molecule and then sequenced, revealing the identity of multiple tags simultaneously; 3) quantitation of the number of times a particular tag is observed provides the expression level of the corresponding transcript (30). The schematic diagram and the details of SAGE procedure can be obtained from the web site: www.genzyme.com/SAGE.

About fifty percent of SAGE tags identified by the inventors represent ESTs which need to be further analyzed for their protein coding capacity. The known genes up-regulated or down-regulated by four-fold (p<0.05) were broadly classified on the basis of the biochemical functions. SAGE tag defined ARGs were grouped under following categories: transcriptional regulators; RNA processing and translation regulators; protein involved in genomic maintenance and cell cycle; protein trafficking/chaperone proteins; energy metabolism, apoptosis and redox regulators; and signal transducers. As determined by PubMed database searches, a majority of genes listed in FIG. 3 have not been described as androgen regulated before. This is the first comprehensive list of the functionally defined genes regulated by androgen in the context of prostatic epithelial cells.

Although promising candidate ARGs have been identified using these approaches, much remains to be learned about the complete repertoire of these genes. SAGE provides both quantitative and high throughput information with respect to global gene expression profiles of known as well as novel transcripts. We have performed SAGE analysis of the ARGs in the widely studied hormone responsive LNCaP prostate cancer cells treated with and without synthetic androgen, R1881. Of course, this SAGE technique could be repeated with hormones other than R1881, including other synthetic or natural androgens, such as dihydroxytestosterone, to potentially obtain a slightly different ARG expression panel. A goal of the inventors was to identify highly induced and repressed ARGs in LNCaP model which may define a panel of surrogate markers for the status androgen signaling in normal as well as cancerous prostate. Here, we report identification and analyses of a comprehensive database of SAGE tags corresponding to well-characterized genes, expressed sequence tags (ESTs) without any protein coding information and SAGE tags corresponding to novel transcripts. This is the first report describing a quantitative evaluation of the global gene expression profiles of the ARGs in the context of prostatic cancer cells by SAGE. We have further defined the ARGs on the basis of their known biologic/biochemical functions. Our study provides quantitative information on about 23,000 transcripts expressed in LNCaP cells, the most common cell line used in prostate cancer research. Finally, comparison of the LNCaP SAGE tag library and 35 SAGE tag libraries representing diverse cell type/tissues have unraveled a panel of genes whose expression are prostate specific or prostate abundant. Utilizing the LNCaP prostate cancer cells, the only well-characterized androgen responsive prostatic epithelial cells (normal or cancerous), we have identified a repertoire of androgen regulated genes by SAGE.

Utilizing cell-culture systems and cell-signaling agents or exogenous expression of p53 and APC genes, SAGE technology has identified novel physiologically relevant transcriptional target genes which have unraveled new functions of p53 and APC genes (61-64). Our analysis of ARGs has provided identification and quantitative assessment of induction or repression of a global expression profile of ARGs in LNCaP cells. ARGs resulting from the mutational defects of the AR and those ARGs unaffected by AR mutations may be identified in this model system. Subsequent androgen regulation analysis of the selected ARGs in AR-positive, primary cultures of normal prostatic epithelial cells, and ARGs expression analysis in normal and tumor tissues will clarify normal or abnormal regulation of these ARGs. A panel of highly inducible/repressible ARGs identified by the inventors may provide bio-indicators of the AR transcription factor activity in physiologic context. These AR Function Bio-indicators (ARFBs) are useful in assessing the risk of CaP onset and/or progression. Moreover, identification or ARGs may also help in defining the therapeutic targets which could lead to effective treatment for hormone refractory cancer, currently a frustrating stage of the disease with limited therapeutic options.

Characterization of a SAGE-defined EST that exhibited the highest level of induction in LNCaP cells responding to R1881 led to the discovery of a novel, androgen-induced gene PMEPA1, which encodes a polypeptide with a type 1 b transmembrane domain. A Protein sequence similarity search showed homology to C18 or f1, a novel gene located on chromosome 18 that is mainly expressed in brain with multiple transcriptional variants (Yoshikawa et al., 1998). In addition to the sequence similarity, PMEPA1 also shares other features with C18 or f1, e.g., similar size of the predicted protein and similar transmembrane domain as the 1 isoform of C18 or f1. Therefore, it is likely that other isoforms of PMEPA1 may exist.

Database searches showed that the PMEPA1 sequence matched to genomic clones RP5-1059L7 and 718J7 which were mapped to chromosome 20q13.2-13.33. Gain of 20q has been observed in many cancer types, including prostate, bladder, melanoma, colon, pancreas and breast (Brothman et al., 1990; Richter et al., 1998; Bastian et al, 1998; Korn et al., 1999; Mahlamaki et al., 1997; Tanner et al., 1996). Chromosome 20q gain was also observed during immortalization and may harbor genes involved in bypassing senescence (Jarrard et al., 1999; Cuthill et al, 1999). A differentially expressed gene in hormone refractory CaP, UEV-1, mapped to 20q13.2 (Stubbs et al., 1999). These observations indicate that one or several genes on chromosome 20q may be involved in prostate or other cancer progression. Although we did not observe increased expression of PMEPA1 in primary prostate tumors, increased PMEPA1 expression was noted in recurrent cancers of CWR22 xenograft.

PMEPA1 expression is upregulated by androgens in a time- and concentration-specific manner in LNCaP cells. This observation underscores the potential of measuring PMEPA1 expression as one of the surrogate markers of androgen receptor activity in vivo in the epithelial cells of prostate tissue. Prostate cancer is androgen dependent and its growth in prostate is mediated by a network of ARGs that remains to be fully characterized. Most prostate cancers respond to androgen withdrawal but relapse after the initial response (Koivisto et al., 1998). The growth of the relapsed tumors is androgen independent even though tumors are positive for the expression of the AR (Bentel et al., 1996).

One of the hypotheses of how cancer cells survive and grow in the low androgen environment is the sensitization or the activation of the AR pathway (Jenster et al., 1999). Studies have shown increased expression of the ARGs or amplification of AR in androgen independent prostate cancer tissues (Gregory et al., 1998; Lin et al., 1999). We have observed that PMEPA1 was expressed in all CWR22R tumors and increased expression in three of four compared with CWR22 tumor. Our data support the concept that normally AR-dependent pathways remain activated, despite the absence of androgen in androgen-independent prostate cancer. There are only limited studies that have addressed whether ARGs play a role in the transition from androgen dependent tumor to androgen independent tumors. The high level of expression only in the prostate gland indicates that PMEPA1 might have important roles related to prostate cell biology or physiology. On the basis of homology of PMEPA1 to C18 or f1 it is tempting to suggest that the PMEPA1 may belong to family of proteins involved in the binding of calcium and LDL.

Characterization of genes like PMEPA1 is a step forward in the definition of the network of androgen regulated genes in prostate biology and tumorigenesis. In addition, ARGs, including PMEPA1, can be used as biomarkers of AR function readout in the subset of prostate cancers that may involve abrogation of androgen signaling. Furthermore, the newly defined ARGs have potential to identify novel targets in therapy of hormone refractory prostate cancer.

The nucleic acid molecules encompassed in the invention include the following PMEPA1 nucleotide sequence:

The amino acid sequences of the polypeptides encoded by the PMEPA1 nucleotide sequences of the invention include:

The discovery of the nucleic acids of the invention enables the construction of expression vectors comprising nucleic acid sequences encoding polypeptides; host cells transfected or transformed with the expression vectors; isolated and purified biologically active polypeptides and fragments thereof; the use of the nucleic acids or oligonucleotides thereof as probes to identify nucleic acid encoding proteins having PMEPA1-like activity; the use of single-stranded sense or antisense oligonucleotides from the nucleic acids to inhibit expression of polynucleotides encoded by the PMEPA1 gene; the use of such polypeptides and fragments thereof to generate antibodies; the use of the antibodies to purify PMEPA1 polypeptides; and the use of the nucleic acids, polypeptides, and antibodies of the invention to detect, prevent, and treat prostate cancer (e.g., prostatic intraepithelial neoplasia (PIN), adenocarcinomas, nodular hyperplasia, and large duct carcinomas) and prostate-related diseases (e.g., benign prostatic hyperplasia).

NUCLEIC ACID MOLECULES

In a particular embodiment, the invention relates to certain isolated nucleotide sequences that are free from contaminating endogenous material. A nucleotide sequence refers to a polynucleotide molecule in the form of a separate fragment or as a component of a larger nucleic acid construct. The nucleic acid molecule has been derived from DNA or RNA isolated at least once in substantially pure form and in a quantity or concentration enabling identification, manipulation, and recovery of its component nucleotide sequences by standard biochemical methods (such as those outlined in (Sambrook et al., Molecular Cloning: A Laboratory Manual , 2nd ed., Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1989)). Such sequences are preferably provided and/or constructed in the form of an open reading frame uninterrupted by internal non-translated sequences, or introns, that are typically present in eukaryotic genes. Sequences of non-translated DNA can be present 5 or 3 from an open reading frame, where the same do not interfere with manipulation or expression of the coding region.

Nucleic acid molecules of the invention include DNA in both single-stranded and double-stranded form, as well as the RNA complement thereof. DNA includes, for example, cDNA, genomic DNA, chemically synthesized DNA, DNA amplified by PCR, and combinations thereof. Genomic DNA may be isolated by conventional techniques, e.g., using the cDNA of SEQ ID NO:1, or a suitable fragment thereof, as a probe.

The DNA molecules of the invention include full length genes as well as polynucleotides and fragments thereof. The full length gene may also include the N-terminal signal peptide. Other embodiments include DNA encoding a soluble form, e.g., encoding the extracellular domain of the protein, either with or without the signal peptide.

The nucleic acids of the invention are preferentially derived from human sources, but the invention includes those derived from non-human species, as well.

Preferred Sequences

The particularly preferred nucleotide sequence of the invention is SEQ ID NO:2, as set forth above. The sequence of amino acids encoded by the DNA of SEQ ID NO:2 is shown in SEQ ID NO:3.

Additional Sequences

Due to the known degeneracy of the genetic code, where more than one codon can encode the same amino acid, a DNA sequence can vary from that shown in SEQ ID NO:2, and still encode a polypeptide having the amino acid sequence of SEQ ID NO:3. Such variant DNA sequences can result from silent mutations (e.g., occurring during PCR amplification), or can be the product of deliberate mutagenesis of a native sequence.

The invention thus provides isolated DNA sequences encoding polypeptides of the invention, selected from: (a) DNA comprising the nucleotide sequence of SEQ ID NO:2; (b) DNA encoding the polypeptide of SEQ ID NO:3; (c) DNA capable of hybridization to a DNA of (a) or (b) under conditions of moderate stringency and which encodes polypeptides of the invention; (d) DNA capable of hybridization to a DNA of (a) or (b) under conditions of high stringency and which encodes polypeptides of the invention, and (e) DNA which is degenerate as a result of the genetic code to a DNA defined in (a), (b), (c), or (d) and which encode polypeptides of the invention. Of course, polypeptides encoded by such DNA sequences are encompassed by the invention.

As used herein, conditions of moderate stringency can be readily determined by those having ordinary skill in the art based on, for example, the length of the DNA. The basic conditions are set forth by (Sambrook et al., Molecular Cloning: A Laboratory Manual , 2ed. Vol. 1, pp. 1.101-104, Cold Spring Harbor Laboratory Press, (1989)), and include use of a prewashing solution for the nitrocellulose filters 5 SSC, 0.5% SDS, 1.0 mM EDTA (pH 8.0), hybridization conditions of about 50% formamide, 6 SSC at about 42 C. (or other similar hybridization solution, such as Stark's solution, in about 50% formamide at about 42 C.), and washing conditions of about 60 C., 0.5 SSC, 0.1% SDS. Conditions of high stringency can also be readily determined by the skilled artisan based on, for example, the length of the DNA. Generally, such conditions are defined as hybridization conditions as above, and with washing at approximately 68 C., 0.2 SSC, 0.1% SDS. The skilled artisan will recognize that the temperature and wash solution salt concentration can be adjusted as necessary according to factors such as the length of the probe.

Also included as an embodiment of the invention is DNA encoding polypeptide fragments and polypeptides comprising inactivated N-glycosylation site(s), inactivated protease processing site(s), or conservative amino acid substitution(s), as described below.

In another embodiment, the nucleic acid molecules of the invention also comprise nucleotide sequences that are at least 80% identical to a native sequence. Also contemplated are embodiments in which a nucleic acid molecule comprises a sequence that is at least 90% identical, at least 95% identical, at least 98% identical, at least 99% identical, or at least 99.9% identical to a native sequence.

The percent identity may be determined by visual inspection and mathematical calculation. Alternatively, the percent identity of two nucleic acid sequences can be determined by comparing sequence information using the GAP computer program, version 6.0 described by (Devereux et al., Nucl. Acids Res ., 12:387 (1984)) and available from the University of Wisconsin Genetics Computer Group (UWGCG). The preferred default parameters for the GAP program include: (1) a unary comparison matrix (containing a value of 1 for identities and 0 for non-identities) for nucleotides, and the weighted comparison matrix of (Gribskov and Burgess, Nucl. Acids Res ., 14:6745 (1986)), as described by (Schwartz and Dayhoff, eds., Atlas of Protein Sequence and Structure , National Biomedical Research Foundation, pp. 353-358 (1979)); (2) a penalty of 3.0 for each gap and an additional 0.10 penalty for each symbol in each gap; and (3) no penalty for end gaps. Other programs used by one skilled in the art of sequence comparison may also be used.

The invention also provides isolated nucleic acids useful in the production of polypeptides. Such polypeptides may be prepared by any of a number of conventional techniques. A DNA sequence encoding a PMEPA1 polypeptide, or desired fragment thereof may be subcloned into an expression vector for production of the polypeptide or fragment. The DNA sequence advantageously is fused to a sequence encoding a suitable leader or signal peptide. Alternatively, the desired fragment may be chemically synthesized using known techniques. DNA fragments also may be produced by restriction endonuclease digestion of a full length cloned DNA sequence, and isolated by electrophoresis on agarose gels. If necessary, oligonucleotides that reconstruct the 5 or 3 terminus to a desired point may be ligated to a DNA fragment generated by restriction enzyme digestion. Such oligonucleotides may additionally contain a restriction endonuclease cleavage site upstream of the desired coding sequence, and position an initiation codon (ATG) at the N-terminus of the coding sequence.

The well-known polymerase chain reaction (PCR) procedure also may be used to isolate and amplify a DNA sequence encoding a desired protein fragment. Oligonucleotides that define the desired termini of the DNA fragment are employed as 5 and 3 primers. The oligonucleotides may additionally contain recognition sites for restriction endonucleases, to facilitate insertion of the amplified DNA fragment into an expression vector. PCR techniques are described in (Saiki et al., Science , 239:487 (1988)); (Wu et al., Recombinant DNA Methodology , eds., Academic Press, Inc., San Diego, pp. 189-196 (1989)); and (Innis et al., PCR Protocols: A Guide to Methods and Applications , eds., Academic Press, Inc. (1990)).

POLYPEPTIDES AND FRAGMENTS THEREOF

The invention encompasses polypeptides and fragments thereof in various forms, including those that are naturally occurring or produced through various techniques such as procedures involving recombinant DNA technology. Such forms include, but are not limited to, derivatives, variants, and oligomers, as well as fusion proteins or fragments thereof.

Polypeptides and Fragments Thereof

The polypeptides of the invention include full length proteins encoded by the nucleic acid sequences set forth above. Particularly preferred polypeptides comprise the amino acid sequence of SEQ ID NO:3.

The polypeptides of the invention may be membrane bound or they may be secreted and thus soluble. Soluble polypeptides are capable of being secreted from the cells in which they are expressed. In general, soluble polypeptides may be identified (and distinguished from non-soluble membrane-bound counterparts) by separating intact cells which express the desired polypeptide from the culture medium, e.g., by centrifugation, and assaying the medium (supernatant) for the presence of the desired polypeptide. The presence of polypeptide in the medium indicates that the polypeptide was secreted from the cells and thus is a soluble form of the protein.

In one embodiment, the soluble polypeptides and fragments thereof comprise all or part of the extracellular domain, but lack the transmembrane region that would cause retention of the polypeptide on a cell membrane. A soluble polypeptide may include the cytoplasmic domain, or a portion thereof, as long as the polypeptide is secreted from the cell in which it is produced.

In general, the use of soluble forms is advantageous for certain applications. Purification of the polypeptides from recombinant host cells is facilitated, since the soluble polypeptides are secreted from the cells. Further, soluble polypeptides are generally more suitable for intravenous administration.

The invention also provides polypeptides and fragments of the extracellular domain that retain a desired biological activity. Such a fragment may be a soluble polypeptide, as described above.

Also provided herein are polypeptide fragments comprising at least 20, or at least 30, contiguous amino acids of the sequence of SEQ ID NO:3. Fragments derived from the cytoplasmic domain find use in studies of signal transduction, and in regulating cellular processes associated with transduction of biological signals. Polypeptide fragments also may be employed as immunogens, in generating antibodies.

Variants

Naturally occurring variants as well as derived variants of the polypeptides and fragments are provided herein.

Variants may exhibit amino acid sequences that are at least 80% identical. Also contemplated are embodiments in which a polypeptide or fragment comprises an amino acid sequence that is at least 90% identical, at least 95% identical, at least 98% identical, at least 99% identical, or at least 99.9% identical to the preferred polypeptide or fragment thereof. Percent identity may be determined by visual inspection and mathematical calculation. Alternatively, the percent identity of two protein sequences can be determined by comparing sequence information using the GAP computer program, based on the algorithm of (Needleman and Wunsch, J. Mol. Bio ., 48:443 (1970)) and available from the University of Wisconsin Genetics Computer Group (UWGCG). The preferred default parameters for the GAP program include: (1) a scoring matrix, blosum62, as described by (Henikoff and Henikoff Proc. Natl. Acad. Sci. USA , 89:10915 (1992)); (2) a gap weight of 12; (3) a gap length weight of 4; and (4) no penalty for end gaps. Other programs used by one skilled in the art of sequence comparison may also be used.

The variants of the invention include, for example, those that result from alternate mRNA splicing events or from proteolytic cleavage. Alternate splicing of mRNA may, for example, yield a truncated but biologically active protein, such as a naturally occurring soluble form of the protein. Variations attributable to proteolysis include, for example, differences in the N- or C-termini upon expression in different types of host cells, due to proteolytic removal of one or more terminal amino acids from the protein (generally from 1-5 terminal amino acids). Proteins in which differences in amino acid sequence are attributable to genetic polymorphism (allelic variation among individuals producing the protein) are also contemplated herein.

Additional variants within the scope of the invention include polypeptides that may be modified to create derivatives thereof by forming covalent or aggregative conjugates with other chemical moieties, such as glycosyl groups, lipids, phosphate, acetyl groups and the like. Covalent derivatives may be prepared by linking the chemical moieties to functional groups on amino acid side chains or at the N-terminus or C-terminus of a polypeptide. Conjugates comprising diagnostic (detectable) or therapeutic agents attached thereto are contemplated herein, as discussed in more detail below.

Other derivatives include covalent or aggregative conjugates of the polypeptides with other proteins or polypeptides, such as by synthesis in recombinant culture as N-terminal or C-terminal fusions. Examples of fusion proteins are discussed below in connection with oligomers. Further, fusion proteins can comprise peptides added to facilitate purification and identification. Such peptides include, for example, poly-His or the antigenic identification peptides described in U.S. Pat. No. 5,011,912 and in (Hopp et al., Bio/Technology , 6:1204 (1988)). One such peptide is the FLAG peptide, Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys, (SEQ ID NO:4) which is highly antigenic and provides an epitope reversibly bound by a specific monoclonal antibody, enabling rapid assay and facile purification of expressed recombinant protein. A murine hybridoma designated 4E11 produces a monoclonal antibody that binds the FLAG peptide in the presence of certain divalent metal cations, as described in U.S. Pat. No. 5,011,912, hereby incorporated by reference. The 4E11 hybridoma cell line has been deposited with the American Type Culture Collection under accession no. HB 9259. Monoclonal antibodies that bind the FLAG peptide are available from Eastman Kodak Co., Scientific Imaging Systems Division, New Haven, Conn.

Among the variant polypeptides provided herein are variants of native polypeptides that retain the native biological activity or the substantial equivalent thereof. One example is a variant that binds with essentially the same binding affinity as does the native form. Binding affinity can be measured by conventional procedures, e.g., as described in U.S. Pat. No. 5,512,457 and as set forth below.

Variants include polypeptides that are substantially homologous to the native form, but which have an amino acid sequence different from that of the native form because of one or more deletions, insertions or substitutions. Particular embodiments include, but are not limited to, polypeptides that comprise from one to ten deletions, insertions or substitutions of amino acid residues, when compared to a native sequence.

A given amino acid may be replaced, for example, by a residue having similar physiochemical characteristics. Examples of such conservative substitutions include substitution of one aliphatic residue for another, such as Ile, Val, Leu, or Ala for one another; substitutions of one polar residue for another, such as between Lys and Arg, Glu and Asp, or Gln and Asn; or substitutions of one aromatic residue for another, such as Phe, Trp, or Tyr for one another. Other conservative substitutions, e.g., involving substitutions of entire regions having similar hydrophobicity characteristics, are well known.

Similarly, the DNAs of the invention include variants that differ from a native DNA sequence because of one or more deletions, insertions or substitutions, but that encode a biologically active polypeptide.

The invention further includes polypeptides of the invention with or without associated native-pattern glycosylation. Polypeptides expressed in yeast or mammalian expression systems (e.g., COS-1 or COS-7 cells) can be similar to or significantly different from a native polypeptide in molecular weight and glycosylation pattern, depending upon the choice of expression system. Expression of polypeptides of the invention in bacterial expression systems, such as E. coli , provides non-glycosylated molecules. Further, a given preparation may include multiple differentially glycosylated species of the protein. Glycosyl groups can be removed through conventional methods, in particular those utilizing glycopeptidase. In general, glycosylated polypeptides of the invention can be incubated with a molar excess of glycopeptidase (Boehringer Mannheim).

Correspondingly, similar DNA constructs that encode various additions or substitutions of amino acid residues or sequences, or deletions of terminal or internal residues or sequences are encompassed by the invention. For example, N-glycosylation sites in the polypeptide extracellular domain can be modified to preclude glycosylation, allowing expression of a reduced carbohydrate analog in mammalian and yeast expression systems. N-glycosylation sites in eukaryotic polypeptides are characterized by an amino acid triplet Asn-X-Y, wherein X is any amino acid and Y is Ser or Thr. Appropriate substitutions, additions, or deletions to the nucleotide sequence encoding these triplets will result in prevention of attachment of carbohydrate residues at the Asn side chain. Alteration of a single nucleotide, chosen so that Asn is replaced by a different amino acid, for example, is sufficient to inactivate an N-glycosylation site. Alternatively, the Ser or Thr can by replaced with another amino acid, such as Ala. Known procedures for inactivating N-glycosylation sites in proteins include those described in U.S. Pat. No. 5,071,972 and EP 276,846, hereby incorporated by reference.

In another example of variants, sequences encoding Cys residues that are not essential for biological activity can be altered to cause the Cys residues to be deleted or replaced with other amino acids, preventing formation of incorrect intramolecular disulfide bridges upon folding or is renaturation.

Other variants are prepared by modification of adjacent dibasic amino acid residues, to enhance expression in yeast systems in which KEX2 protease activity is present. EP 212,914 discloses the use of site-specific mutagenesis to inactivate KEX2 protease processing sites in a protein. KEX2 protease processing sites are inactivated by deleting, adding or substituting residues to alter Arg-Arg, Arg-Lys, and Lys-Arg pairs to eliminate the occurrence of these adjacent basic residues. Lys-Lys pairings are considerably less susceptible to KEX2 cleavage, and conversion of Arg-Lys or Lys-Arg to Lys-Lys represents a conservative and preferred approach to inactivating KEX2 sites.

PRODUCTION OF POLYPEPTIDES AND FRAGMENTS THEREOF

Expression, isolation and purification of the polypeptides and fragments of the invention may be accomplished by any suitable technique, including but not limited to the following:

Expression Systems

The present invention also provides recombinant cloning and expression vectors containing DNA, as well as host cell containing the recombinant vectors. Expression vectors comprising DNA may be used to prepare the polypeptides or fragments of the invention encoded by the DNA. A method for producing polypeptides comprises culturing host cells transformed with a recombinant expression vector encoding the polypeptide, under conditions that promote expression of the polypeptide, then recovering the expressed polypeptides from the culture. The skilled artisan will recognize that the procedure for purifying the expressed polypeptides will vary according to such factors as the type of host cells employed, and whether the polypeptide is membrane-bound or a soluble form that is secreted from the host cell.

Any suitable expression system may be employed. The vectors include a DNA encoding a polypeptide or fragment of the invention, operably linked to suitable transcriptional or translational regulatory nucleotide sequences, such as those derived from a mammalian, microbial, viral, or insect gene. Examples of regulatory sequences include transcriptional promoters, operators, or enhancers, an mRNA ribosomal binding site, and appropriate sequences which control transcription and translation initiation and termination. Nucleotide sequences are operably linked when the regulatory sequence functionally relates to the DNA sequence. Thus, a promoter nucleotide sequence is operably linked to a DNA sequence if the promoter nucleotide sequence controls the transcription of the DNA sequence. An origin of replication that confers the ability to replicate in the desired host cells, and a selection gene by which transformants are identified, are generally incorporated into the expression vector.

In addition, a sequence encoding an appropriate signal peptide (native or heterologous) can be incorporated into expression vectors. A DNA sequence for a signal peptide (secretory leader) may be fused in frame to the nucleic acid sequence of the invention so that the DNA is initially transcribed, and the mRNA translated, into a fusion protein comprising the signal peptide. A signal peptide that is functional in the intended host cells promotes extracellular secretion of the polypeptide. The signal peptide is cleaved from the polypeptide upon secretion of polypeptide from the cell.

Suitable host cells for expression of polypeptides include prokaryotes, yeast or higher eukaryotic cells. Mammalian or insect cells are generally preferred for use as host cells. Appropriate cloning and expression vectors for use with bacterial, fungal, yeast, and mammalian cellular hosts are described, for example, in (Pouwels et al., Cloning Vectors: A Laboratory Manual , Elsevier, N.Y., (1985)). Cell-free translation systems could also be employed to produce polypeptides using RNAs derived from DNA constructs disclosed herein.

Prokaryotic Systems

Prokaryotes include gram-negative or gram-positive organisms. Suitable prokaryotic host cells for transformation include, for example, E. coli, Bacillus subtilis, Salmonella typhimurium , and various other species within the genera Pseudomonas, Streptomyces, and Staphylococcus. In a prokaryotic host cell, such as E. coli , a polypeptide may include an N-terminal methionine residue to facilitate expression of the recombinant polypeptide in the prokaryotic host cell. The N-terminal Met may be cleaved from the expressed recombinant polypeptide.

Expression vectors for use in prokaryotic host cells generally comprise one or more phenotypic selectable marker genes. A phenotypic selectable marker gene is, for example, a gene encoding a protein that confers antibiotic resistance or that supplies an autotrophic requirement. Examples of useful expression vectors for prokaryotic host cells include those derived from commercially available plasmids such as the cloning vector pBR322 (ATCC 37017). pBR322 contains genes for ampicillin and tetracycline resistance and thus provides simple means for identifying transformed cells. An appropriate promoter and a DNA sequence are inserted into the pBR322 vector. Other commercially available vectors include, for example, pKK223-3 (Pharmacia Fine Chemicals, Uppsala, Sweden) and pGEM1 (Promega Biotec, Madison, Wis., USA).

Promoter sequences commonly used for recombinant prokaryotic host cell expression vectors include -lactamase (penicillinase), lactose promoter system (Chang et al., Nature 275:615 (1978); and (Goeddel et al., Nature 281:544 (1979)), tryptophan (trp) promoter system (Goeddel et al., Nucl. Acids Res . 8:4057 (1980); and EP-A-36776) and tac promoter (Maniatis, Molecular Cloning: A Laboratory Manual , Cold Spring Harbor Laboratory, p. 412 (1982)). A particularly useful prokaryotic host cell expression system employs a phage P L promoter and a cI857ts thermolabile repressor sequence. Plasmid vectors available from the American Type Culture Collection which incorporate derivatives of the P L promoter include plasmid pHUB2 (resident in E. coli strain JMB9, ATCC 37092) and pPLc28 (resident in E. coli RR1, ATCC 53082).

Yeast Systems

Alternatively, the polypeptides may be expressed in yeast host cells, preferably from the Saccharomyces genus (e.g., S. cerevisiae ). Other genera of yeast, such as Pichia or Kluyveromyces, may also be employed. Yeast vectors will often contain an origin of replication sequence from a 2 yeast plasmid, an autonomously replicating sequence (ARS), a promoter region, sequences for polyadenylation, sequences for transcription termination, and a selectable marker gene. Suitable promoter sequences for yeast vectors include, among others, promoters for metallothionein, 3-phosphoglycerate kinase (Hitzeman et al., J. Biol. Chem . 255:2073 (1980)) or other glycolytic enzymes (Hess et al., J. Adv. Enzyme Reg . 7:149 (1968)); and (Holland et al., Biochem. 17:4900 (1978)), such as enolase, glyceraldehyde-3-phosphate dehydrogenase, hexokinase, pyruvate decarboxylase, phosphofructokinase, glucose-6-phosphate isomerase, 3-phosphoglycerate mutase, pyruvate kinase, triosephosphate isomerase, phosphoglucose isomerase, and glucokinase. Other suitable vectors and promoters for use in yeast expression are further described in (Hitzeman, EPA-73,657). Another alternative is the glucose-repressible ADH2 promoter described by (Russell et al., J. Biol. Chem . 258:2674 (1982)) and (Beier et al., Nature 300:724 (1982)). Shuttle vectors replicable in both yeast and E. coli may be constructed by inserting DNA sequences from pBR322 for selection and replication in E. coli (Amp r gene and origin of replication) into the above-described yeast vectors.

The yeast -factor leader sequence may be employed to direct secretion of the polypeptide. The -factor leader sequence is often inserted between the promoter sequence and the structural gene sequence. See, e.g., (Kurjan et al., Cell 30:933 (1982)) and (Bitter et al., Proc. Natl. Acad. Sci. USA 81:5330 (1984)). Other leader sequences suitable for facilitating secretion of recombinant polypeptides from yeast hosts are known to those of skill in the art. A leader sequence may be modified near its 3 end to contain one or more restriction sites. This will facilitate fusion of the leader sequence to the structural gene.

Yeast transformation protocols are known to those of skill in the art. One such protocol is described by (Hinnen et al., Proc. Natl. Acad. Sci. USA 75:1929 (1978)). The Hinnen et al. protocol selects for Trp transformants in a selective medium, wherein the selective medium consists of 0.67% yeast nitrogen base, 0.5% casamino acids, 2% glucose, 10 mg/ml adenine and 20 mg/ml uracil.

Yeast host cells transformed by vectors containing an ADH2 promoter sequence may be grown for inducing expression in a rich medium. An example of a rich medium is one consisting of 1% yeast extract, 2% peptone, and 1% glucose supplemented with 80 mg/ml adenine and 80 mg/ml uracil. Derepression of the ADH2 promoter occurs when glucose is exhausted from the medium.

Mammalian or Insect Systems

Mammalian or insect host cell culture systems also may be employed to express recombinant polypeptides. Bacculovirus systems for production of heterologous proteins in insect cells are reviewed by (Luckow and Summers, Bio/Technology , 6:47 (1988)). Established cell lines of mammalian origin also may be employed. Examples of suitable mammalian host cell lines include the COS-7 line of monkey kidney cells (ATCC CRL 1651) (Gluzman et al., Cell 23:175 (1981)), L cells, C127 cells, 3T3 cells (ATCC CCL 163), Chinese hamster ovary (CHO) cells, HeLa cells, and BHK (ATCC CRL 10) cell lines, and the CV1/EBNA cell line derived from the African green monkey kidney cell line CV1 (ATCC CCL 70) as described by (McMahan et al., EMBO J ., 10: 2821 (1991)).

Established methods for introducing DNA into mammalian cells have been described (Kaufman, R. J., Large Scale Mammalian Cell Culture , pp. 15-69 (1990)). Additional protocols using commercially available reagents, such as Lipofectamine lipid reagent (Gibco/BRL) or Lipofectamine-Plus lipid reagent, can be used to transfect cells (Felgner et al., Proc. Natl. Acad. Sci. USA 84:7413-7417 (1987)). In addition, electroporation can be used to transfect mammalian cells using conventional procedures, such as those in (Sambrook et al., Molecular Cloning. A Laboratory Manual , 2 ed. Vol. 1-3, Cold Spring Harbor Laboratory Press (1989)). Selection of stable transformants can be performed using methods known in the art, such as, for example, resistance to cytotoxic drugs. (Kaufman et al., Meth. in Enzymology 185:487-511 (1990)), describes several selection schemes, such as dihydrofolate reductase (DHFR) resistance. A suitable host strain for DHFR selection can be CHO strain DX-B11, which is deficient in DHFR (Urlaub and Chasin, Proc. Natl. Acad. Sci. USA 77:4216-4220 (1980)). A plasmid expressing the DHFR cDNA can be introduced into strain DX-B11, and only cells that contain the plasmid can grow in the appropriate selective media. Other examples of selectable markers that can be incorporated into an expression vector include cDNAs conferring resistance to antibiotics, such as G418 and hygromycin B. Cells harboring the vector can be selected on the basis of resistance to these compounds.

Transcriptional and translational control sequences for mammalian host cell expression it vectors can be excised from viral genomes. Commonly used promoter sequences and enhancer sequences are derived from polyoma virus, adenovirus 2, simian virus 40 (SV40), and human cytomegalovirus. DNA sequences derived from the SV40 viral genome, for example, SV40 origin, early and late promoter, enhancer, splice, and polyadenylation sites can be used to provide other genetic elements for expression of a structural gene sequence in a mammalian host cell. Viral early and late promoters are particularly useful because both are easily obtained from a viral genome as a fragment, which can also contain a viral origin of replication (Fiers et al., Nature 273:113 (1978)); (Kaufman, Meth. in Enzymology (1990)). Smaller or larger SV40 fragments can also be used, provided the approximately 250 bp sequence extending from the Hind III site toward the Bgl I site located in the SV40 viral origin of replication site is included.

Additional control sequences shown to improve expression of heterologous genes from mammalian expression vectors include such elements as the expression augmenting sequence element (EASE) derived from CHO cells (Morris et al., Animal Cell Technology , pp. 529-534 and PCT Application WO 97/25420 (1997)) and the tripartite leader (TPL) and VA gene RNAs from Adenovirus 2 (Gingeras et al., J. Biol. Chem . 257:13475-13491 (1982)). The internal ribosome entry site (IRES) sequences of viral origin allows dicistronic mRNAs to be translated efficiently (Oh and Sarnow, Current Opinion in Genetics and Development 3:295-300 (1993)); (Ramesh et al., Nucleic Acids Research 24:2697-2700 (1996)). Expression of a heterologous cDNA as part of a dicistronic mRNA followed by the gene for a selectable marker (e.g. DHFR) has been shown to improve transfectability of the host and expression of the heterologous cDNA (Kaufman, Meth. in Enzymology (1990)). Exemplary expression vectors that employ dicistronic mRNAs are pTR-DC/GFP described by (Mosser et al., Biotechniques 22:150-161 (1997)), and p2A5I described by (Morris et al., Animal Cell Technology , pp. 529-534 (1997)).

A useful high expression vector, pCAVNOT, has been described by (Mosley et al., Cell 59:335-348 (1989)). Other expression vectors for use in mammalian host cells can be constructed as disclosed by (Okayama and Berg, Mol. Cell. Biol . 3:280 (1983)). A useful system for stable high level expression of mammalian cDNAs in C127 murine mammary epithelial cells can be constructed substantially as described by (Cosman et al., Mol. Immunol . 23:935 (1986)). A useful high expression vector, PMLSV N1/N4, described by (Cosman et al., Nature 312:768 (1984)), has been deposited as ATCC 39890. Additional useful mammalian expression vectors are described in EP-A-0367566, and in WO 91/18982, incorporated by reference herein. In yet another alternative, the vectors can be derived from retroviruses.

Another useful expression vector, pFLAG , can be used. FLAG technology is centered on the fusion of a low molecular weight (1 kD), hydrophilic, FLAG marker peptide to the N-terminus of a recombinant protein expressed by pFLAGO expression vectors. pDC311 is another specialized vector used for expressing proteins in CHO cells. pDC311 is characterized by a bicistronic sequence containing the gene of interest and a dihydrofolate reductase (DHFR) gene with an internal ribosome binding site for DHFR translation, an expression augmenting sequence element (EASE), the human CMV promoter, a tripartite leader sequence, and a polyadenylation site.

Purification

The invention also includes methods of isolating and purifying the polypeptides and fragments thereof.

Isolation and Purification

The isolated polypeptides or fragments thereof encompassed by this invention are polypeptides or fragments that are not in an environment identical to an environment in which it or they can be found in nature. The purified polypeptides or fragments thereof encompassed by this invention are essentially free of association with other proteins or polypeptides, for example, as a purification product of recombinant expression systems such as those described above or as a purified product from a non-recombinant source such as naturally occurring cells and/or tissues.

In one preferred embodiment, the purification of recombinant polypeptides or fragments can be accomplished using fusions of polypeptides or fragments of the invention to another polypeptide to aid in the purification of polypeptides or fragments of the invention.

With respect to any type of host cell, as is known to the skilled artisan, procedures for purifying a recombinant polypeptide or fragment will vary according to such factors as the type of host cells employed and whether or not the recombinant polypeptide or fragment is secreted into the culture medium.

In general, the recombinant polypeptide or fragment can be isolated from the host cells if not secreted, or from the medium or supernatant if soluble and secreted, followed by one or more concentration, salting-out, ion exchange, hydrophobic interaction, affinity purification or size exclusion chromatography steps. As to specific ways to accomplish these steps, the culture medium first can be concentrated using a commercially available protein concentration filter, for example, an Amicon or Millipore Pellicon ultrafiltration unit. Following the concentration step, the concentrate can be applied to a purification matrix such as a gel filtration medium. Alternatively, an anion exchange resin can be employed, for example, a matrix or substrate having pendant diethylaminoethyl (DEAE) groups. The matrices can be acrylamide, agarose, dextran, cellulose or other types commonly employed in protein purification. Alternatively, a cation exchange step can be employed. Suitable cation exchangers include various insoluble matrices comprising sulfopropyl or carboxymethyl groups. In addition, a chromatofocusing step can be employed. Alternatively, a hydrophobic interaction chromatography step can be employed. Suitable matrices can be phenyl or octyl moieties bound to resins. In addition, affinity chromatography with a matrix which selectively binds the recombinant protein can be employed. Examples of such resins employed are lectin columns, dye columns, and metal chelating columns. Finally, one or more reversed-phase high performance liquid chromatography (RP-HPLC) steps employing hydrophobic RP-HPLC media, (e.g., silica gel or polymer resin having pendant methyl, octyl, octyldecyl or other aliphatic groups) can be employed to further purify the polypeptides. Some or all of the foregoing purification steps, in various combinations, are well known and can be employed to provide an isolated and purified recombinant protein.

It is also possible to utilize an affinity column comprising a polypeptide-binding protein of the invention, such as a monoclonal antibody generated against polypeptides of the invention, to affinity-purify expressed polypeptides. These polypeptides can be removed from an affinity column using conventional techniques, e.g., in a high salt elution buffer and then dialyzed into a lower salt buffer for use or by changing pH or other components depending on the affinity matrix utilized, or be competitively removed using the naturally occurring substrate of the affinity moiety, such as a polypeptide derived from the invention.

In this aspect of the invention, polypeptide-binding proteins, such as the anti-polypeptide antibodies of the invention or other proteins that may interact with the polypeptide of the invention, can be bound to a solid phase support such as a column chromatography matrix or a similar substrate suitable for identifying, separating, or purifying cells that express polypeptides of the invention on their surface. Adherence of polypeptide-binding proteins of the invention to a solid phase contacting surface can be accomplished by any means, for example, magnetic microspheres can be coated with these polypeptide-binding proteins and held in the incubation vessel through a magnetic field. Suspensions of cell mixtures are contacted with the solid phase that has such polypeptide-binding proteins thereon. Cells having polypeptides of the invention on their surface bind to the fixed polypeptide-binding protein and unbound cells then are washed away. This affinity-binding method is useful for purifying, screening, or separating such polypeptide-expressing cells from solution. Methods of releasing positively selected cells from the solid phase are known in the art and encompass, for example, the use of enzymes. Such enzymes are preferably non-toxic and non-injurious to the cells and are preferably directed to cleaving the cell-surface binding partner.

Alternatively, mixtures of cells suspected of containing polypeptide-expressing cells of the invention first can be incubated with a biotinylated polypeptide-binding protein of the invention. Incubation periods are typically at least one hour in duration to ensure sufficient binding to polypeptides of the invention. The resulting mixture then is passed through a column packed with avidin-coated beads, whereby the high affinity of biotin for avidin provides the binding of the polypeptide-binding cells to the beads. Use of avidin-coated beads is known in the art. See (Berenson, et al., J. Cell. Biochem ., 10D:239 (1986)). Wash of unbound material and the release of the bound cells is performed using conventional methods.

The desired degree of purity depends on the intended use of the protein. A relatively high degree of purity is desired when the polypeptide is to be administered in vivo, for example. In such a case, the polypeptides are purified such that no protein bands corresponding to other proteins are detectable upon analysis by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). It will be recognized by one skilled in the pertinent field that multiple bands corresponding to the polypeptide may be visualized by SDS-PAGE, due to differential glycosylation, differential post-translational processing, and the like. Most preferably, the polypeptide of the invention is purified to substantial homogeneity, as indicated by a single protein band upon analysis by SDS-PAGE. The protein band may be visualized by silver staining, Coomassie blue staining, or (if the protein is radiolabeled) by autoradiography.

PRODUCTION OF ANTIBODIES

Antibodies that are immunoreactive with the polypeptides of the invention are provided herein. Such antibodies specifically bind to the polypeptides via the antigen-binding sites of the antibody (as opposed to non-specific binding). Thus, the polypeptides, fragments, variants, fusion proteins, etc., as set forth above may be employed as immunogens in producing antibodies immunoreactive therewith. More specifically, the polypeptides, fragment, variants, fusion proteins, etc. contain antigenic determinants or epitopes that elicit the formation of antibodies.

These antigenic determinants or epitopes can be either linear or conformational (discontinuous). Linear epitopes are composed of a single section of amino acids of the polypeptide, while conformational or discontinuous epitopes are composed of amino acids sections from different regions of the polypeptide chain that are brought into close proximity upon protein folding (C. A. Janeway, Jr. and P. Travers, Immuno Biology 3:9, Garland Publishing Inc., 2nd ed. (1996)). Because folded proteins have complex surfaces, the number of epitopes available is quite numerous; however, due to the conformation of the protein and steric hinderances, the number of antibodies that actually bind to the epitopes is less than the number of available epitopes (C. A. Janeway, Jr. and P. Travers, Immuno Biology 2:14, Garland Publishing Inc., 2nd ed. (1996)). Epitopes may be identified by any of the methods known in the art.

Thus, one aspect of the present invention relates to the antigenic epitopes of the polypeptides of the invention. Such epitopes are useful for raising antibodies, in particular monoclonal antibodies, as described in more detail below. Additionally, epitopes from the polypeptides of the invention can be used as research reagents, in assays, and to purify specific binding antibodies from substances such as polyclonal sera or supernatants from cultured hybridomas. Such epitopes or variants thereof can be produced using techniques well known in the art such as solid-phase synthesis, chemical or enzymatic cleavage of a polypeptide, or using recombinant DNA technology.

As to the antibodies that can be elicited by the epitopes of the polypeptides of the invention, whether the epitopes have been isolated or remain part of the polypeptides, both polyclonal and monoclonal antibodies may be prepared by conventional techniques. See, for example, (Kennet et al., Monoclonal Antibodies, Hybridomas: A New Dimension in Biological Analyses , eds., Plenum Press, N.Y. (1980); and Harlow and Land, Antibodies: A Laboratory Manual , eds., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., (1988)).

Hybridoma cell lines that produce monoclonal antibodies specific for the polypeptides of the invention are also contemplated herein. Such hybridomas may be produced and identified by conventional techniques. One method for producing such a hybridoma cell line comprises immunizing an animal with a polypeptide; harvesting spleen cells from the immunized animal; fusing said spleen cells to a myeloma cell line, thereby generating hybridoma cells; and identifying a hybridoma cell line that produces a monoclonal antibody that binds the polypeptide. The monoclonal antibodies may be recovered by conventional techniques.

The monoclonal antibodies of the present invention include chimeric antibodies, e.g., humanized versions of murine monoclonal antibodies. Such humanized antibodies may be prepared by known techniques and offer the advantage of reduced immunogenicity when the antibodies are administered to humans. In one embodiment, a humanized monoclonal antibody comprises the variable region of a murine antibody (or just the antigen binding site thereof) and a constant region derived from a human antibody. Alternatively, a humanized antibody fragment may comprise the antigen binding site of a murine monoclonal antibody and a variable region fragment (lacking the antigen-binding site) derived from a human antibody. Procedures for the production of chimeric and further engineered monoclonal antibodies include those described in (Riechmann et al., Nature 332:323 (1988), Liu et al., PNAS 84:3439 (1987), Larrick et al., Bio/Technology 7:934 (1989), and Winter and Harris, TIPS 14:139 (May 1993)). Procedures to generate antibodies transgenically can be found in GB 2,272,440, U.S. Pat. Nos. 5,569,825 and 5,545,806 and related patents claiming priority therefrom, all of which are incorporated by reference herein.

Antigen-binding fragments of the antibodies, which may be produced by conventional techniques, are also encompassed by the present invention. Examples of such fragments include, but are not limited to, Fab and F(ab ) 2 fragments. Antibody fragments and derivatives produced by genetic engineering techniques are also provided.

In one embodiment, the antibodies are specific for the polypeptides of the present invention and do not cross-react with other proteins. Screening procedures by which such antibodies may be identified are well known, and may involve immunoaffinity chromatography, for example.

The following examples further illustrate preferred aspects of the invention.

Cell Culture and Androgen Stimulation

LNCaP cells (American Type Culture Collection, Rockville, Md.) were used for SAGE analysis of ARGs. LNCaP cells were maintained in RPMI 1640 (Life Technologies, Inc., Gaithersburg, Md.) supplemented with 10% fetal bovine serum (FBS, Life Technologies, Inc., Gaithersburg, Md.) and experiments were performed on cells between passages 20 and 30. For the studies of androgen regulation, charcoal/dextran stripped androgen-free FBS (cFBS, Gemini Bio-Products, Inc., Calabasas, Calif.) was used. LNCaP cells were cultured first in RPMI 1640 with 10% cFBS for 5 days and then stimulated with 10-8 M of non-metabolizable androgen analog, R1881 (DUPONT, Boston, Mass.) for 24 hours. LNCaP cells identically treated but without R1881 treatment served as control. Cells were harvested at indicated time and polyA RNA was double-selected with Fast Track kit (Invitrogene). The quality of polyA was checked by Northern hybridization analysis.

SAGE Analysis

Two SAGE libraries (library LNCaP-C and library LNCaP-T) were generated according to the procedure described previously Velculescu et al., (30). Briefly, biotinylated oligo dT primed cDNA was prepared from five micrograms of polyA RNA from R1881 treated and control LNCaP cells and biotinylated cDNA was captured on strepravidin coated magnetic beads (Dynal Corporation, Mich.). cDNA bound to the magnetic beads were digested by NlaIII followed by ligation to synthetic linkers containing a site for anchoring enzyme, NlaIII and a site for tagging enzyme BsmF1. The restriction digestion of ligated products with BsmF1 resulted in the capture of 10-11 bp sequences termed as tags representing signature sequence of unique cDNAs. A multi-step strategy combining ligation, PCR, enzymatic digestion and gel purification yielded two tags linked together termed as ditags. Ditags were concatamerized, purified and cloned in plasmid pZero cloning vector (Invitrogen, Calif.). The clones containing concatamers were screened by PCR and sequenced. The sequence and the occurrence of each of the SAGE tags was determined using the SAGE software kindly provided by Dr. Kenneth W. Kinzler (Johns Hopkins University School of Medicine, Baltimore, Md.). All the SAGE tags sequences were analyzed for identity to DNA sequence in GenBank (National Center for Biotechnology Information, Bethesda, Md., USA). The relative abundance of each transcript was determined by dividing the number of individual tags by total tags in the library. The copy number of each gene was calculated assuming there are approximately 300,000 transcripts in a cell (Zhang et al., 1997). The differentially expressed SAGE tags were determined by comparing the frequency of occurrence of individual tags in the two libraries obtained from the control (library LNCaP-C) and R1881 treated LNCaP cells (library LNCaP-T). The results were analyzed with t test, and p<0.05 was considered as a statistically significant difference for a specific tag between these two libraries.

Kinetics of Androgen Regulation ARGs Defined by SAGE Analysis

LNCaP cells were cultured in RPMI 1640 with 10% cFBS for 5 days, then stimulated with R1881 at 10-10, 10-8, and 10-6 M for 1, 3, 12, 24, 72, 120, 168, and 216 hours. LNCaP cells identically treated but without R1881 served as control. The cells were harvested at indicated time and polyA RNA was prepared as described as above. The polyA RNA was fractionated (2 g/lane) by running through 1% formaldehyde-agarose gel and transferred to nylon membrane. The cDNA probes of several ARGs were labeled with 32P-dCTP by random priming (Stratagene Cloning Systems, La Jolla, Calif.). The nylon membranes were prehybridized for 2 hrs in hybridization buffer (10 mM Tris-HCl, pH 7.5, 10% Dextran sulfate, 40% Formamide, 5 SSC, 5 Denhardt's solution and 0.25 mg/ml salmon sperm DNA) and hybridized to the 32P labeled probes (1 106 cpm/ml) in the same buffer at 40 C. for 12-16 hrs. Blots were washed twice in 2 SSC/0.1% SDS for 20 min at room temperature followed by two high-stringency wash with 0.1 SSC/0.1% SDS at 50 C. for 20 min. Nylon membranes were exposed to X-ray film for autoradiography.

ARGs Expression Pattern in Cwr22 Model

CWR22 (androgen dependent) and CWR22R (androgen relapsed) tumor specimens were kindly provided by Dr. Thomas Pretlow (Case Western Reserve University School of Medicine). The tissue samples were homogenized and polyA RNA was extracted with Fast Track kit (Invitrogen) following manufacture's protocol. Northern blots were prepared as described in Example 3 and were hybridized with 32P labeled probes of the cDNA of interest.

Analysis of SAGE tag libraries from R1881 treated LNCaP cells. LNCaP cells were maintained in androgen deprived growth media for five days and were treated with synthetic androgen R1881 (10 nm) for 24 hours. Since a goal of the inventors was to identify androgen signaling read-out transcripts, we chose conditions of R1881 treatment of LNCaP cells showing a robust and stable transcriptional induction of well-characterized prostate-specific androgen regulated genes, prostate-specific antigen (PSA) and NKX3.1 genes. A total of 90,236 tags were derived from the two SAGE libraries. Of 90,236 tags, 6,757 tags corresponded to linker sequences, and were excluded from further analysis. The remaining 83,489 tags represented a total of 23,448 known genes or ESTs and 1,655 tags did not show any match in the GeneBank data base. The relative abundance of the SAGE tags varied between 0.0011% and 1.7%. Assuming that there are 18,000 transcripts per cell type and there are about 83,489 anticipated total transcripts, the estimated abundance of transcripts will be 0.2-308 copies per cell. This calculation indicated that single copy genes had high chance to be recognized by SAGE analysis in this study. The distribution of transcripts by copy number suggests that the majority (above 90%) of the genes in our analysis are expressed at 1 or 2 copies level/cell. A total of 46,186 and 45,309 tags were analyzed in the control (C) and R1881 (T) groups respectively. Unique SAGE tags corresponding to known genes, expressed sequence tags (ESTs) and novel transcripts were 15,593 and 15,920 in the control and androgen treated groups respectively. About 94% of the unique SAGE tags in each group showed a match to a sequence in the gene bank and 6% SAGE tags represented novel transcripts. The most abundant SAGE tags in both control and androgen treated LNCaP cells represented proteins involved in cellular translation machinery e.g., ribosomal proteins, translation regulators, mitochondrial proteins involved in bio-energetic pathways.

Analysis of the ARGs Defined by SAGE Tags

Of about 15,000 unique tags a total of 136 SAGE tags were significantly up-regulated in response to R1881 whereas 215 SAGE tags were significantly down-regulated (p<0.05). It is important to note that of 15,000 expressed sequences only 1.5% were androgen responsive suggesting that expression of only a small subset of genes are regulated by androgen under our experimental conditions. The ARGs identified by the inventors are anticipated to represent a hierarchy, where a fraction of ARGs are directly regulated by androgens and others represent the consequence of the activation of direct down-stream target genes of the AR. Comparison of SAGE tags between control and R1881 also revealed that 74 SAGE tags were significantly up-regulated (p<0.05) by four-fold and 120 SAGE tags were significantly (p<0.05) down-regulated. Two SAGE tags corresponding to the PSA gene sequence exhibited highest induction (16 fold) between androgen treated (T) and control (C) groups. Another prostate specific androgen regulated gene, NKX3.1 was among significantly up-regulated ARGs (8 fold). Prostate specific membrane antigen (PSMA) and Clusterin known to be down-regulated by androgens were among the SAGE tags exhibiting decreased expression in response to androgen (PSMA, 4 fold; Clusterin, fold). Therefore, identification of well characterized up-regulated and down-regulated ARGs defined by SAGE tags validates the use of LNCaP experimental model for defining physiologically relevant ARGs in the context of prostatic epithelial cells. It is important to note that about 90% of up-regulated ARGs and 98% of the down-regulated ARGs defined by our SAGE analysis were not known to be androgen-regulated before.

Identification of Prostate Specific/Abundant Genes

LNCaP C/T-SAGE tag libraries were compared to a bank of 35 SAGE tag it libraries (http://www.ncbi.nlm.nih.gov/SAGE/) containing 1.5 million tags from diverse tissues and cell types. Our analysis revealed that known prostate specific genes e.g., PSA and NKX3.1 were found only in LNCaP SAGE tag libraries (this report and one LNCaP SAGE,library present in the SAGE tag bank). We have extended this observation to the other candidate genes and transcripts. On the basis of abundant/unique expression of the SAGE tag defined transcripts in LNCaP SAGE tag libraries relative to other libraries, we have now identified several candidate genes and ESTs whose expression are potentially prostate specific or restricted (Table 4). The utility of such prostate-specific genes includes: (a) the diagnosis and prognosis of CaP (b) tissue specific targeting of therapeutic genes (c) candidates for immunotherapy and (d) defining prostate specific biologic functions.

Genes with defined functions showing at least five fold up or down-regulation (p<0.05) were broadly classified on the basis of their biochemical function, since our results of Northern analysis of representative SAGE derived ARGs at 5-fold difference showed most reproducible results. Table 9, presented at the end of this specification immediately preceding the References section, represents the quantitative expression profiles of a panel of functionally defined ARGs in the context of LNCaP prostate cancer cells. ARGs in the transcription factor category include proteins involved in the general transcription machinery e.g., KAP1/TIF , CHD4 and SMRT (Douarin et al., 1998; Xu et al., 1999) have been shown to participate in transcriptional repression. The mitochondrial transcription factor 1 (mtTF1) was induced by 8 fold in response to R1881. A recent report describes that another member of the nuclear receptor superfamily, the thyroid hormone receptor, also up-regulates a mitochondrial transcription factor expression through a specific co-activator, PGC-1 (Wu et al., 1999). As shown in Table 9 a thyroid hormone receptor related gene, ear-2 (Miyajima et al., 1998) was also upregulated by R1881. It is striking to note that expression of four NKX3.1 (He et al., 1997), HOX B13 (Sreenath et al., 1999), mtTF1 and PDEF (Oettgen et al., 2000) of the eight transcription regulators listed in Table 9 appear to be prostate tissue abundant/specific based on published reports as well as our analysis described above.

ARGs also include a number of proteins involved in cellular energy metabolism and it is possible that some of these enzymes may be transcriptionally regulated by mtTF1. Components of enzymes involved in oxidative decaboxylation: dihydrolipoamide succinyl transferase (Patel it et al., 1995), puruvate dehydrogenase E-1 subunit (Ho et al., 1989), and the electron tansport chain: NADH dehydrogenase 1 beta subcomplex 10 (Ton et al., 1997) were upregulated by androgen. VDAC-2 (Blachly-Dyson et al., 1994), a member of small pore forming proteins of the outer mitochondrial membrane and which may regulate the transport of small metabolites necessary for oxidative-phosphorylation, was also up regulated by androgen. Diazepam binding protein (DBI), a previous reported ARG (Swinnen et al., 1996), known to be associated with the VDAC complex and implicated in a multitude of functions including modulation of pheripheral benzodiaepine receptor, acyl-CoA metabolism and mitochondrial steroidogenesis (Knudsen et. al., 1993) were also induced by androgen in our study. A thioredoxin like protein (Miranda-Vizuete et al., 1998) which may function in modulating the cellular redox state was down regulated by androgen. In general, it appears that modulation of ARGs involved in regulating cellular redox status and energy metabolism may effect reactive oxygen species concentrations.

A number of cell proliferation associated proteins regulating cell cycle, signal transduction and cellular protein trafficking were upregulated by androgen, further supporting the role of androgens in survival and growth of prostatic epithelial cells. Androgen regulation of two proteins: XRCC2 (Cartwright et al., 1998) and RPA3 (Umbricht et al., 1993) involved in DNA repair and recombination is a novel and interesting finding. Induction of these genes may represent a response to DNA damage due to androgen mediated pro-oxidant shift, or these genes simply represent components of genomic surveillance mechanisms stimulated by cell proliferation. The androgen induction of a p53 inducible gene, PIG 8 (Umbricht et al., 1997), is another intriguing finding as the mouse homolog of this gene, ei24 (Gu et al., 2000), is induced by etoposide known to generate reactive oxygen species. In addition, components of protein kinases modulated by adenyl cyclase, guanyl cyclase and calmodulin involved in various cellular signal transduction stimuli were also regulated by androgen.

Gene expression modulations in RNA processing and translation components is consistent with increased protein synthesis expected in cells that are switched to a highly proliferative state. Of note is nucleolin, one of the highly androgen induced genes (12 fold) t which is an abundant nucleolar protein associating with cell proliferation and plays a direct role in the biogenesis, processing and transport of ribosomes to the cytoplasm (Srivastava and Pollard, 1999). Another androgen up-regulated gene, exportin, a component of the nuclear pore, may be involved in the shuttling of nucleolin. Androgen regulation of SiahBP1 (Page-McCaw et al., 1999), GRSF-1 (Qian and Wilusz, 1994) and PAIP1 (Craig et al., 1998) suggests a role of androgen signaling in the processing of newly transcribed RNAs. Two splicesosomal genes, snRNP-G and snRNP-E coding for small ribo-nucleoproteins were down-regulated by androgen. The unr-interacting protein, UNRIP (Hunt et al., 1999) which is involved in the direct ribosome entry of many viral and some cellular mRNAs into the translational pathway, was the most down-regulated gene in response to androgen.

Quantitative evaluation of gene expression profiles by SAGE approach have defined yeast transcriptome (Velculescu et al., 1997) and have identified critical genes in biochemical pathways regulated by p53 (Polyak et al., 1997), x-irradiation (Hermeking et al., 1997) and the APC gene (Korinek et al., 1997). Potential tumor biomarkers in colon (Zhang et al., 1997), lung (Hibi et al., 1998), and breast (Nacht et al., 1999) cancers and genes regulated by other cellular stimuli (Waard et al., 1999; Berg et al., 1999) have also been identified by SAGE. SAGE technology has enabled us to develop the first quantitative database of androgen regulated transcripts. Comparison of our SAGE tag libraries to the SAGE TagBank has also revealed a number of new candidate genes and ESTs whose expression is potentially abundant or specific to the prostate. We have also identified a large number of transcripts not previously defined as ARGs.

A great majority of functionally defined genes that were modulated by androgen in our experimental system appear to promote cell proliferation, cell survival, gain of energy and increased oxidative reactions shift in the cells. However, a substantial fraction of these ARGs appears to be androgen specific since they do not exhibit appreciable change in their expression in other studies examining cell proliferation associated genes (Iyer et al., 1999, genome-www.stanford.edu/serum) or estrogen regulated genes in MCF7 cells (Charpentier et al., 2000). The interesting experimental observation of Ripple et al., (Ripple et al., 1997) showing a prooxidant-antioxidant shift induced by androgen in prostate cancer cells is supported by our identification of specific ARGs (upregulation of enzymes involved in oxidative reactions, thioredoxin like protein) that may be involved in the induction of oxidative stress by androgen.

Characterization of the Androgen-Regulated Gene PMEPA1

cDNA library screening and Sequencing of cDNA clone. One of the SAGE tags (14 bp) showing the highest induction by androgen (29-fold) exhibited homology to an EST in the GenBank EST database. PCR primers (5 GGCAGAACACTCCGCGCTTCTTAG3 (SEQ ID NO.5) and 5 CAAGCTCTCTTAGCTTGTGCATTC3 (SEQ ID NO.6)) were designed based on the EST sequence (accession number AA310984). RT-PCR was performed using RNA from R1881 treated LNCaP cells and the co-identity of the PCR product to the EST was confirmed by DNA sequencing. Using the PCR product as probe, the normal prostate cDNA library was screened through the service provided by Genome Systems (St. Louis, Mo.). An isolated clone, GS 22381 was sequenced using the 310 Genetic Analyzer (PE Applied Biosystems, Foster Calif.) and 750 bp of DNA sequence was defined, which included 2/3 of the coding region of PMEPA1. A GenBank search with PMEPA1 cDNA sequence revealed one EST clone (accession number AA088767) homologous to the 5 region of the PMEPA1 sequence. PCR primers were designed using the EST clone (5 primer) and PMEPA 1 (3 primer) sequence. cDNA from LNCaP cells was PCR amplified and the PCR product was sequenced using the PCR primers. The sequences were verified using at least two different primers. A contiguous sequence of 1,141 bp was generated by these methods.

Kinetics of androgen regulation of PMEPA1 expression in LNCaP cells. LNCaP cells (American Type Culture Collection, ATCC, Rockville Md.) were maintained in RPMI 1640 media (Life Technologies, Inc., Gaithersburg, Md.) supplemented with 10% fetal bovine serum (FBS, Life Technologies, Inc., Gaithersburg, Md.) and experiments were performed on cells cultured between passages 20 and 30. For the studies of androgen regulation, charcoal/dextran stripped androgen-free FBS (cFBS, Gemini Bio-Products, Inc., Calabasas, Calif.) was used. LNCaP cells were cultured first in RPMI 1640 with 10% cFBS for 5 days, and then stimulated with R1881 (DUPONT, Boston, Mass.) at 10 10 M and 10 8 M for 3, 6, 12 and 24 hours. LNCaP cells identically treated but without R1881 served as control. To study the effects of androgen withdrawal on PMEPA1 gene expression, LNCaP cells were cultured in RPMI 1640 with 10% cFBS for 24, 72 and 96 hours. Poly A RNA samples derived from cells treated with or without R1881 were extracted at indicated time points with a Fast Track mRNA extraction kit (Invitrogen, Carlsbad, Calif.) following the manufacturer's protocol. Poly A RNA specimens (2 g/lane) were electrophoresed in a 1% formaldehyde-agarose gel and transferred to a nylon membrane. Two PMEPA1 probes used for Northern blots analysis were (a) cDNA probe spanning nucleotides 3-437 of PMEPA1 cDNA sequence (See Table 1) and (b) 71-mer oligonucleotide between nucleotides 971 to 1,041 of PMEPA1 cDNA sequence (See Table 1).

The cDNA probe was generated by RT-PCR with primers 5 CTTGGGTTCGGGTGAAAGCGCC 3 (SEQ ID NO.7) (sense) and 5 GGTGGGTGGCAGGTCGATCTCG 3 (SEQ ID NO.8) (antisense). PMEPA1 oligonucleotide and cDNA probes and glyceraldehyde phosphate dehydrogenase gene (GAPDH) cDNA probe were labeled with 32 P-dCTP using 3 end tailing for oligonucleotides (Promega, Madison, Wis.) and random priming for cDNA (Stratagene, La Jolla, Calif.). The nylon membranes were treated with hybridization buffer (10 mM Tris-HCl, pH 7.5, 10% Dextran sulfate, 40% Formamide, 5 SSC, 5 Denhardt's solution and 0.25 mg/ml salmon sperm DNA) for two hours followed by hybridization in the same buffer containing the 32 P labeled probes (1 10 6 cpm/ml) for 12-16 hrs at 40 C. Blots were washed twice in 2 SSC/0.1% SDS for 20 min at room temperature followed by two high-stringency washes with 0.1 SSC/0.1% SDS at 58 C. for 20 min. Nylon membranes were exposed to X-ray film for autoradiography. The bands on films were then quantified with NIH-Image processing software.

PMEPA1 expression analysis in CWR22 tumors. CWR22 is an androgen-dependent, serially transplantable nude mouse xenograft derived from a primary human prostate cancer. Transplanted CWR22 tumors are positive for AR and the growth of CWR22 is androgen dependent. CWR22 tumors regress initially upon castration followed by a relapse. The recurrent, CWR22 tumors (CWR22R) express AR, but the growth of these tumors become androgen-independent (Gregory et al., 1998; Nagabhushan et al., 1996). One CWR22 and four CWR22R tumor specimens were kindly provided by Dr. Thomas Pretlow's laboratory (Case Western Reserve University School of Medicine). Tumor tissues were homogenized and poly A RNA were extracted as above. PolyA RNA blots were made and hybridized as described above.

PMEPA1 expression analysis in multiple human tissues and cell lines. Multiple Tissue Northern blots containing mRNA samples from 23 human tissues and Master Dot blots containing mRNA samples from 50 different human tissues were purchased from ClonTech (Palo Alto, Calif.). The blots were hybridized with PMEPA1 cDNA and oligo probes, as described above. The expression of PMEPA1 in normal prostate epithelial cells (Clonetics, San Diego, Calif.), prostate cancer cells PC3 (ATCC) and LNCaP cells and breast cancer cells MCF7 (ATCC) was also analyzed by northern blot.

In situ hybridization of PMEPA1 in prostate tissues. A 430 bp PCR fragment (PCR sense primer: 5 CCTTCGCCCAGCGGGAGCGC 3 , (SEQ ID NO.9) PCR antisense primer 5 CAAGCTCTCTTAGCTTGTGCATTC3 (SEQ ID NO.10) was amplified from cDNA of LNCaP cells treated by R1881 and was cloned into a PCR-blunt II-TOPO vector (Invitrogen, Carlsbad, Calif.). Digoxigenin labeled antisense and sense riboprobes were synthesized using an in vitro RNA transcription kit (Boehringer Mannheim, GMbH, Germany) and a linearized plasmid with PMEPA1 gene fragment as templates. Frozen normal and malignant prostate tissues were fixed in 4% paraformaldehyde for 30 min. Prehybridization and hybridization were performed at 55 C. After hybridization, slides were sequentially washed with 2 SSC at room temperature for 30 min, 2 SSC at 58 C. for 1 hr and 0.1 SSC at 58 C. for 1 hr. Antibody against digoxygenin was used to detect the signal and NBT/BCIP was used as substrate for color development (Boehringer Mannheim, GMbH, Germany). The slides were evaluated under an Olympus BX-60 microscope.

Full-length PMEPA1 Coding Sequence and Chromosomal Localization

Analysis of the 1,141 bp PMEPA1 cDNA sequence (SEQ ID NO.1) revealed an open reading frame of 759 bp nucleotides (SEQ ID NO.2) encoding a 252 amino acid protein (SEQ ID NO.3) with a predicted molecular mass of 27.8 kDa, as set forth below in Table 1.

A GenBank search revealed a sequence match of PMEPA1 cDNA to two genomic clones, RP5-1059L7 (accession number AL121913 in the GenBank/htgc database) and 718J7 (accession number AL035541 in the GenBank/nr database). These two clones mapped to Chromosome 20q13.2-13.33 and Chromosome 20q13.31-13.33. This information provided evidence that PMEPA1 is located on chromosome 20q13.

The intron/exon juctions of PMEPA1 gene were determined based on the comparison of the sequences of PMEPA1 and the two genomic clones. A protein motif search using ProfileScan (http://www.ch.embnet.org/cgi-bin/TMPRED) indicated the existence of a type Ib transmembrane domain between amino acid residues 9 to 25 of the PMEPA1 sequence. Another GenBank search further revealed that the PMEPA1 showed homology (67% sequence identity and 70% positives at protein level) to a recently described novel cDNA located on chromosome 18 (accession number NM 004338) (Yoshikawa et al., 1998), as set forth below in Table 2. In addition to the sequence similarity, PMEPA1 also shares other features with C18 or f1, e.g., similar size of the predicted protein and similar transmembrane domain as the 1 isoform of it C18 or f1.

Northern hybridization revealed two transcripts of 2.7 kb and 5 kb using either PMEPA1 cDNA or oligo probe. The signal intensity of bands representing these two transcripts was very similar on the X-ray films of the northern blots. RT-PCR analysis of RNA from LNCaP cells with four pairs of primers covering different regions of PMEPA1 protein coding region revealed expected size of bands from PCR reactions, suggesting that two mRNA species on northern blot have identical sequences in the protein coding region and may exhibit differences in 5 and/or 3 non-coding regions. However, the exact relationship between the two bands remains to be established. Analysis of multiple northern blots containing 23 human normal tissues revealed the highest level of PMEPA1 expression in prostate tissue. Although other tissues expressed PMEPA1,their relative expression was significantly lower as compared to prostate (FIG. 1 ). In situ RNA hybridization analysis of PMEPA1 expression in prostate tissues revealed abundant expression in the glandular epithelial compartment as compared to the stromal cells. However, both normal and tumor cells in tissue sections of primary tumor tissues revealed similar levels of expression.

Androgen Dependent Expression of PMEPA1

As discussed above, PMEPA1 was originally identified as a SAGE tag showing the highest fold induction (29-fold) by androgen. Androgen depletion of LNCaP cells resulted in decreased expression of PMEPA1. Androgen supplementation of the LNCaP cell culture media lacking androgen caused induction of both 2.7 and 5.0 bp RNA species of PMEPA1 in LNCaP cells in a dose and time dependent fashion (FIG. 2 A). Basal level of PMEPA1 expression was detected in normal prostatic epithelial cell cultures and androgen-dependent LNCaP cells cultured in regular medium. PMEPA1 expression was not detected in AR negative CaP cells, PC3 or in the breast cancer cell line, MCF7 (FIG. 2 B). Evaluation of PMEPA1 expression in androgen sensitive and androgen refractory tumors of CWR 22 prostate cancer xenograft model

Previous studies have described increased expression of ARGs in the hormone refractory CWR22R variants of the CWR22 xenograft, suggesting the activation of AR mediated cell signaling in relapsed CWR22 tumors following castration. The androgen sensitive CWR22 tumor expressed detectable level of PMEPA1 transcripts. However, three of the four CWR22R tumors exhibited increased PMEPA1 expression (FIG. 3 ).

The specification is most thoroughly understood in light of the teachings of the references cited within the specification which are hereby incorporated by reference. The embodiments within the specification provide an illustration of embodiments of the invention and should not be construed to limit the scope of the invention. The skilled artisan readily recognizes that many other embodiments are encompassed by the invention.

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