NOVEL SERPENTINE TRANSMEMBRANE ANTIGENS EXPRESSED IN HUMAN CANCERS AND USES THEREOF

Abstract: Described is a novel family of cell surface serpentine transmembrane antigens. Two of the proteins in this family are exclusively or predominantly expressed in the prostate, as well as in prostate cancer, and thus members of this family have been termed "STEAP" (<u>S</u>ix <u>T</u>ransmembrane <u>E</u>pithelial <u>A</u>ntigen of the <u>P</u>rostate). Four particular human STEAPs are described and characterized herein. The human STEAPs exhibit a high degree of structural conservation among them but show no significant structural homology to any known human proteins. The prototype member of the STEAP family, STEAP-1, appears to be a type IIIa membrane protein expressed predominantly in prostate cells in normal human tissues. Structurally, STEAP-1 is a 339 amino acid protein characterized by a molecular topology of six transmembrane domains and intracellular N- and C- termini, suggesting that it folds in a "serpentine" manner into three extracellular and two intracellular loops. STEAP-1 protein expression is maintained at high levels across various stages of prostate cancer. Moreover, STEAP-1 is highly over-expressed in certain other human cancers.

Description: NOVEL SERPENTINE TRANSMEMBRANE ANTIGENS EXPRESSED IN HUMAN CANCERS AND USES THEREOF This application claims the benefit of United States patent application number 09/455,486, filed December 6, 1999. FIELD OF THE INVENTION The invention described herein relates to a family of novel genes and their encoded proteins and tumor antigens, termed STEAPs, and to diagnostic and therapeutic methods and compositions useful in the management of various cancers, particularly including prostate cancer, colon cancer, bladder cancer, lung cancer, ovarian cancer and pancreatic cancer. BACKGROUND OF THE INVENTION Cancer is the second leading cause of human death next to coronary disease. Worldwide, millions of people die from cancer every year. In the United States alone, cancer causes the death of well over a half-million people annually, with some 1.4 million new cases diagnosed per year. While deaths from heart disease have been declining significantly, those resulting from cancer generally are on the rise. In the early part of the next century, cancer is predicted to become the leading cause of death. Worldwide, several cancers stand out as the leading killers. In particular, carcinomas of the lung, prostate, breast, colon, pancreas, and ovary represent the primary causes of cancer death. These and virtually all other carcinomas share a common lethal feature. With very few exceptions, metastatic disease from a carcinoma is fatal. Moreover, even for those cancer patients who initially survive their primary cancers, common experience has shown that their lives are dramatically altered. Many cancer patients experience strong anxieties driven by the awareness of the potential for recurrence or treatment failure. Many cancer patients experience physical debilitations following treatment. Many cancer patients experience a recurrence. Worldwide, prostate cancer is the fourth most prevalent cancer in men. In North America and Northern Europe, it is by far the most common male cancer and is the second leading cause of cancer death in men. In the United States alone, well over 40,000 men die annually of this disease - second only to lung cancer. Despite the magnitude of these figures, there is still no effective treatment for metastatic prostate cancer. Surgical prostatectomy, radiation therapy, hormone ablation therapy, and chemotherapy continue to be the main treatment modalities. Unfortunately, these treatments are ineffective for many and are often associated with undesirable consequences. On the diagnostic front, the lack of a prostate tumor marker that can accurately detect early-stage, localized tumors remains a significant limitation in the management of this disease. Although the serum PSA assay has been a very useful tool, its specificity and general utility is widely regarded as lacking in several important respects. Progress in identifying additional specific markers for prostate cancer has been improved by the generation of prostate cancer xenografts that can recapitulate different stages of the disease in mice. The LAPC (Los Angeles Prostate Cancer) xenografts are prostate cancer xenografts that have survived passage in severe combined immune deficient (SCID) mice and have exhibited the capacity to mimic disease progression, including the transition from androgen dependence to androgen independence and the development of metastatic lesions (U.S. Patent No. 6,107,540; Klein et al, 1997, Nat. Med.3:402). More recently identified prostate cancer markers include PCTA-1 (Su et al., 1996, Proc. Natl. Acad. Sci. USA 93: 7252), prostate stem cell antigen (PSCA) (Reiter et al., 1998, Proc. Natl. Acad. Sci. USA 95: 1735), and STEAP (Hubert et al., 1999, Proc. Natl. Acad. Sci. USA 96: 14523). While previously identified markers such as PSA, PSM, PCTA and PSCA have facilitated efforts to diagnose and treat prostate cancer, there is need for the identification of additional markers and therapeutic targets for prostate and related cancers in order to further improve diagnosis and therapy. SUMMARY OF THE INVENTION The present invention relates to a novel family of cell surface serpentine transmembrane antigens. Two of the proteins in this family are exclusively or predominantly expressed in the prostate, as well as in prostate cancer, and thus members of this family have been termed "STEAP" (Six Transmembrane Epithehal Antigen of the Prostate). Four particular human STEAPs are described and characterized herein. The human STEAPs exhibit a high degree of structural conservation among them but show no significant structural homology to any known human proteins The prototype member of the STEAP family, STEAP-1, appears to be a type Ilia membrane protein expressed predominantly in prostate cells in normal human tissues. Structurally, STEAP-1 is a 339 amino acid protein characterized by a molecular topology of six transmembrane domains and intracellular N- and C- termini, suggesting that it folds in a "serpentine" manner into three extracellular and two intracellular loops STEAP-1 protein expression is maintained at high levels across various stages of prostate cancer Moreover, STEAP-1 is highly over-expressed in certain other human cancers. In particular, cell surface expression of STEAP-1 has been definitively confirmed in a variety of prostate and prostate cancer cells, lung cancer, bladder cancer cells and colon cancer cells. These characteristics indicate that STEAP-1 is a specific cell-surface tumor antigen expressed at high levels in prostate, bladder, colon, and other cancers. A second member of the family, STEAP-2, is a 454 amino acid protein with a predicted molecular topology similar to that of STEAP-1. STEAP-2, kke STEAP-1, is prostate-specific in normal human tissues and is also expressed in prostate cancer Alignment of the STEAP-2 and STEAP-1 ORFs shows 54.9% identity over a 237 amino acid residue overlap, and the locations of the six putative transmembrane domains in STEAP-2 coincide with the locations of the transmembrane domains in STEAP-1 (FIG. 1 A-B). STEAP-3 and STEAP-4 are also described herein. These are also structurally related, and show unique expression profiles. In particular, STEAP-3 and STEAP-4 appear to show a different tissue restriction patterns. An amino acid sequence alignment of all four STEAPs is shown in FIG. 11 A-B. The invention provides polynucleotides corresponding or complementary to all or part of the STEAP gene as described herein, mRNAs, and/or coding sequences, preferably in isolated form, including polynucleotides encoding STEAP proteins and fragments thereof, DNA, RNA, DNA/RNA hybrid, and related molecules, polynucleotides or oligonucleotides complementary to the STEAP gene or mRNA sequences or parts thereof, and polynucleotides or oligonucleotides which hybridize to the STEAP gene, mRNAs, or to STEAP-encoding polynucleotides Also provided are means for isolating cDNAs and the genes encoding STEAP. Recombinant DNA molecules containing STEAP polynucleotides, cells transformed or transduced with such molecules, and host vector systems for the expression of STEAP gene products are also provided. The invention further provides STEAP proteins and polypeptide fragments thereof. The invention further provides antibodies that bind to STEAP proteins and polypeptide fragments thereof, including polyclonal and monoclonal antibodies, murine and other mammalian antibodies, chimeric antibodies, humanized and fully human antibodies, and antibodies labeled with a detectable marker, and antibodies conjugated to radionuchdes/radioisotopes, toxins or other therapeutic compositions. The invention further provides methods for detecting the presence of STEAP polynucleotides and proteins in various biological samples, as well as methods for identifying cells that express a STEAP. The invention further provides various therapeutic compositions and strategies for treating prostate and other cancers, including particularly, antibody, vaccine and small molecule therapy.. The invention further provides methods for detecting the presence of STEAP polynucleotides and proteins in various biological samples, as well as methods for identifying cells that express STEAP. The invention further provides various therapeutic compositions and strategies, including particularly, antibody, vaccine and small molecule therapy, for treating cancers of the prostate The extracellular nature of this protein presents a number of therapeutic approaches using molecules that target STEAP and its function, as well as molecules that target other proteins, factors and ligands that interact with STEAP These therapeutic approaches include antibody therapy with anti-STEAP antibodies, small molecule therapies, and vaccine therapies. In addition, given its up- regulated expression in prostate cancer, STEAP is useful as a diagnostic, staging and/ or prognostic marker for prostate cancer and, similarly, may be a marker for other cancers expressing this protein. In particular, STEAP-1 provides an excellent marker for identifying prostate cancer metastases. BRIEF DESCRIPTION OF THE FIGURES FIG. 1. STEAP-1 structure. 1A-B: Nucleotide and deduced amino acid sequences of STEAP-1 (8P1B4) clone 10 cDNA (SEQ ID NOS. 1 and 2, respectively). The start methionine is indicated in bold at amino acid residue position 1 and six putative transmembrane domains are indicated in bold and are underlined. IC: Schematic representation of STEAP-1 transmembrane orientation; amino acid residues bordering the predicted extracellular domains are indicated and correspond to the numbering scheme of FIG. 1A-B. ID: G/C rich 5' non-coding sequence of the STEAP-1 gene (SEQ ID NO: 3) as determined by overlapping sequences of clone 10 and clone 3. FIG. 2. Predominant expression of STEAP-1 in prostate tissue. First strand cDNA was prepared from 16 normal tissues, the LAPC xenografts (4AD, 4AI and 9AD) and HeLa cells. Normalization was performed by PCR using primers to actin and GAPDH. Semi-quantitative PCR, using primers derived from STEAP-1 (8P1D4) cDNA (FIG. 1 A-B), shows predominant expression of STEAP-1 in normal prostate and the LAPC xenografts. The following primers were used to amplify STEAP-1: 8P1D4.1 5' ACTTTGTTGATGACCAGGATTGGA 3' (SEQ ID NO: 4) 8P1D4.2 5' CAGAACTTCAGCACACACAGGAAC 3' (SEQ ID NO: 5). FIG. 2A. Lanes are as follows: 1 brain; 2 prostate; 3 LAPC-4 AD; 4 LAPC-4 Al; 5 LAPC-9 AD; 6 HeLa; 7 murine cDNA; 8 negative control. FIG. 2B. Lanes are as follows: 1 brain; 2 heart; 3 kidney; 4 liver; 5 lung; 6 pancreas; 7 placenta; 8 skeletal muscle. FIG. 2C. Lanes are as follows: 1 colon; 2 ovary; 3 leukocytes; 4 prostate; 5 small intestine; 6 spleen; 7 testis; 8 thymus. FIG. 3. Northern blot analyses of STEAP-1 expression in various normal human tissues and prostate cancer xenografts, showing predominant expression of STEAP-1 in prostate tissue. FIG. 3A Two multiple tissue northern blots (Clontech) were probed with a full length STEAP cDNA clone 10 (FIG. 1A-B). Size standards in kilobases (kb) are indicated on the side. Each lane contains 2 μg of mRNA that was normalized by using a β-actin probe. Al brain; A2 amygdala; A3 caudate nucleus; A4 cerebellum, A5 cerebral cortex; A6 frontal lobe; A7 hippocampus; A8 medulla oblongata; Bl occipital lobe; B2 putamen; B3 substantia nigra; B4 temporal lobe; B5 thalamus; B6 sub-thalamic nucleus; B7 spinal cord; Cl heart, C2 aorta; C3 skeletal muscle; C4 colon, C5 bladder; C6 uterus; C7 prostate; C8 stomach; DI testis; D2 ovary; D3 pancreas; D4 pituitary gland; D5 adrenal gland; D6 thyroid gland; D7 salivary gland; D8 mammary gland; El kidney; E2 liver; E3 small intestine; E4 spleen; E5 thymus ; E6 peripheral leukocytes, E7 lymph node; E8 bone marrow; FI appendix; F2 lung; F3 trachea; F4 placenta; Gl fetal brain; G2 fetal heart; G3 fetal kidney; G4 fetal liver; G5 fetal spleen; G6 fetal thymus; G7 fetal lung. FIG. 3B: Multiple tissue RNA dot blot (Clontech, Human Master Blot cat# 7770-1) probed with STEAP-1 cDNA clone 10 (FIG. 1A-B), showing approximately five-fold greater expression in prostate relative to other tissues with significant detectable expression. FIG 4A-B. Nucleotide sequence (SEQ ID NO: 6) of STEAP-1 GTH9 clone corresponding to the 4 kb message on northern blots (FIG. 3A). The sequence contains an intron of 2399 base pairs relative to the STEAP-1 clone 10 sequence of FIG. 1A-B; coding regions are nucleotides 96-857 and 3257- 3510 (indicated in bold). The start ATG is in bold and underlined, the STOP codon is in bold and underlined, and the intron-exon boundaries are underlined. FIG. 5. Expression of STEAP-1 in prostate and multiple cancer cell lines and prostate cancer xenografts. Xenograft and cell line filters were prepared with 10 μg of total RNA per lane. The blots were analyzed using the STEAP-1 clone 10 as probe All RNA samples were normalized by ethidium bromide staining and subsequent analysis with a β-actin probe FIG. 5A- Expression in various cancer cell lines and xenografts and prostate. Lanes as follows: (1) PrEC cells, (2) normal prostate tissue, (3) LAPC-4 AD xenograft, (4) LAPC-4 Al xenograft, (5) LAPC-9 AD xenograft, (6) LAPC-9 Al xenograft, (7) LNCaP ceUs, (8) PC-3 cells, (9) DU145 cells, (10) PANC-1 cells, (11) BxPC-3 cells, (12) HPAC ceUs, (13) Capan-1 cells, (14) CACO-2 cells, (15) LOVO cells, (16) T84 cells, (17) COLO-205 cells, (18) KCL-22 cells (acute lymphocytic leukemia, ALL), (19) HT1197 ceUs, (20) SCABER cells, (21) UM-UC-3 cells, (22) TCCSUP cells, (23) J82 cells, (24) 5637 cells, (25) RD-ES cells (Ewing sarcoma, EWS), (26) CAMA-1 cells, (27) DU4475 cells, (28) MCF-7 cells, (29) MDA-MB-435s cells, (30) NTERA-2 cells, (31) NCCIT cells, (32) TERA-1 cells, (33) TERA-2 cells, (34) A431 cells, (35) HeLa ceUs, (36) OV-1063 cells, (37) PA-1 cells, (38) SW 626 cells, (39) CAOV-3 cells. FIG. 5B: The expression of STEAP-1 in subcutaneously (sc) grown LAPC xenografts compared to the expression in LAPC-4 and LAPC-9 xenografts grown in the tibia (it) of mice. FIG. 6A-B. Western blot analysis of STEAP-1 protein expression in tissues and multiple cell lines. Western blots of cell lysates prepared from prostate cancer xenografts and cell lines were probed with a polyclonal anti-STEAP-1 antibody preparation. The samples contain 20 μg of protein and were normalized with anti-Grb-2 probing of the western blots. FIG. 7A-B. Cell surface biotinylation of STEAP-1. FIG. 7A: Cell surface biotinylation of 293T cells transfected with vector alone or with vector containing cDNA encoding 6Hιs-tagged STEAP-1. Cell lysates were lmmunoprecipitated with specific antibodies, transferred to a membrane and probed with horseradish peroxidase- con j ugated streptavidin. Lanes 1 -4 and 6 correspond to immunoprecipitates from lysates prepared from STEAP-1 expressing 293T cells. Lanes 5 and 7 are immunoprecipitates from vector transfected cells. The lmmunoprecipitations were performed using the following antibodies: (1) sheep non-immune, (2) anti-Large T antigen, (3) anti- CD71 (transferrin receptor), (4) anti-His, (5) anti-His, (6) anti-STEAP-1, (7) anti-STEAP-1. FIG. 7B: Prostate cancer (LNCaP, PC-3, DU145), bladder cancer (UM-UC-3, TCCSUP) and colon cancer (LOVO, COLO) cell lines were either biotmylated (+) or not (-) prior to lysis. Western blots of streptavidin-gel purified proteins were probed with anti- STEAP-1 antibodies. Molecular weight markers are indicated in ktlodaltons (kD). FIG 8 Immunohistochemical analysis of STEAP-1 expression using anti- STEAP-1 polyclonal antibody. Tissues were fixed in 10% formalin and embedded in paraffin. Tissue sections were stained using anti-STEAP-1 polyclonal antibodies directed towards the N-terminal peptide. FIG. 8A: LNCaP cells probed in the presence of N- terminal STEAP-1 peptide 1, FIG. 8B: LNCaP plus non specific peptide 2, FIG. 8C: normal prostate tissue, FIG. 8D: grade 3 prostate carcinoma, FIG. 8E: grade 2, Gleason 7 prostate carcinoma, FIG. 8F: LAPC-9 AD xenograft, FIG. 8G: normal bladder, FIG. 8H: normal colon. All images are at 400x magnification. FIG. 9A-D. Nucleotide (SEQ ID NO: 7) and deduced amino acid (SEQ ID NO: 8) sequences of STEAP-2 (98P4B6) clone GTD3 cDNA. The start methionine and Kozak sequence are indicated in bold, and the putative transmembrane domains are underlined in bold. The 5' UTR exhibits a high GC content of 72%. FIG. 10A-E Nucleotide (SEQ ID NO 9) and deduced amino acid (SEQ ID NO: 10) sequences of STEAP-3. Kozak region is in bold. FIG. 10F. Nucleotide sequences (SEQ ID NOS: 11-14, respectively) of dbEST database entries corresponding to additional STEAP family members obtained by searching with the protein sequence of STEAP-1. FIG. 11. Primary structural comparisons of STEAP family proteins: FIG. 11 A-B Amino acid sequence alignment of STEAPs 1-4 (SEQ ID NOS: 2, 8, 10 and 15, respectively) using PIMA program (PIMA 1.4 program at Internet address:<http:\\dot.ιmgen.bcm.tmc.edu:9331 html>); transmembrane domains identified by the SOSUI program (available at Internet address www.tuat.ac. j p\~nntaku\adv_sosui\submit.html) are in bold. PIMA maximal linkage clustering results shown; identical residues shown in bold. FIG. l lC. Amino acid sequence alignment of STEAP-1 (8P1D4 clone 10; SEQ ID NO: 2) and STEAP-2 (98P4B6 clone GTD3; SEQ ID NO 8) sequences. The alignment was performed using the SIM alignment program of the Baylor College of Medicine Search Launcher Web site. Transmembrane domains are indicated in boldface. The results show a 54.9% identity in a 237 residues overlap (Score: 717 0; Gap frequency: 0.0%). FIG. 1 ID. Am o acid sequence alignment of STEAP-1 (SEQ ID NO: 2) and STEAP-3 (98P4B6 clone GTD3, SEQ ID NO: 10) sequences. Identical residues indicated with asterisks SIM results- 40.9% identity in 264 residues overlap; Score: 625.0; Gap frequency: 0.0%. FIG. 1 IE. Amino acid sequence alignment of STEAP-2 (SEQ ID NO- 8) and STEAP-3 (98P4B6 clone GTD3; SEQ ID NO: 10) sequences. Identical residues indicated with asterisks. SIM results: 47.8% identity in 416 residues overlap; Score- 1075.0; Gap frequency: 0.2%. FIG. 12. Expression of STEAP-3 mRNA in normal tissues by northern blot (FIG. 12A-B) and RT-PCR (FIG 12B). For RT-PCR analysis, first strand cDNA was prepared from 16 normal tissues. Normalization was performed by PCR using primers to actin and GAPDH. Semi-quantitative PCR, using primers to All 39607, shows predominant expression of All 39607 m placenta and prostate after 25 cycles of amplification The following primers were used to amplify AI139607: All 39607.1 5' TTAGGACAACTTGATCACCAGCA 3' (SEQ ID NO: 16) AI139607.2 5' TGTCCAGTCCAAACTGGGTTATTT 3' (SEQ ID NO: 17). FIG 12A. Lanes are as follows (from left to right): Panel 1- heart, brain, placenta, lung, hver, skeletal muscle, kidney and pancreas; Panel 2: spleen, thymus, prostate, testis, ovary, small intestine, colon and white blood cells FIG. 12B Lanes are as follows: 1 brain, 2 heart; 3 kidney; 4 hver; 5 lung, 6 pancreas; 7 placenta; 8 skeletal muscle. FIG. 12C. Lanes are as follows: 1 colon; 2 ovary; 3 leukocytes; 4 prostate; 5 small intestine; 6 spleen; 7 testis; 8 thymus. FIG. 13 Predominant expression of STEAP-4/R80991 m hver. First strand cDNA was prepared from 16 normal tissues. Normalization was performed by PCR usmg primers to actin and GAPDH. Semi-quantitative PCR, usmg primers to R80991, shows predommant expression of R80991 in hver after 25 cycles of amphfication. The following primers were used to amplify R80991: R80991.1 5' AGGGAGTTCAGCTTCGTTCAGTC 3' (SEQ ID NO: 18) R80991.2 5' GGTAGAACTTGTAGCGGCTCTCCT 3' (SEQ ID NO: 19). FIG. 13A. Lanes are as follows. 1 brain; 2 heart; 3 kidney; 4 hver; 5 lung; 6 pancreas; 7 placenta; 8 skeletal muscle. FIG. 13B. Lanes are as follows: 1 colon, 2 ovary; 3 leukocytes; 4 prostate; 5 small intestine; 6 spleen; 7 testis; 8 thymus FIG. 14. Predominant expression of STEAP-2 (98P4B6) in prostate tissue. First strand cDNA was prepared from 8 normal tissues, the LAPC xenografts (4AD, 4AI and 9AD) and HeLa cells. Normahzation was performed by PCR usmg primers to actin and GAPDH. Semi-quantitative PCR, usmg primers to 98P4B6, shows predommant expression of 98P4B6 in normal prostate and the LAPC xenografts. The following primers were used to amplify STEAP II: 98P4B6.1 5' GACTGAGCTGGAACTGGAATTTGT 3' (SEQ ID NO- 20) 98P4B6.2 5' TTTGAGGAGACTTCATCTCACTGG 3' (SEQ ID NO: 21). FIG. 14A. Lanes are as follows: 1 brain; 2 prostate; 3 LAPC-4 AD; 4 LAPC-4 Al; 5 LAPC-9 AD; 6 HeLa; 7 murine cDNA; 8 negative control. FIG. 14B. Lanes are as follows: 1 colon; 2 ovary; 3 leukocytes; 4 prostate; 5 small intestine; 6 spleen; 7 testis; 8 thymus. FIG. 15. Expression of the prostate-specific STEAP-2/98P4B6 gene in normal tissues and in prostate cancer xenografts determined by Northern blot analysis. Human normal tissue filters (A and B) were obtained from CLONTECH and contain 2 μg of mRNA per lane. Xenograft filter (C) was prepared with 10 μg of total RNA per lane. The blots were analyzed usmg the SSH derived 98P4B6 clone as probe. All RNA samples were normalized by ethidium bromide staining. FIG. 15A. Lanes are as follows: 1 heart; 2 bram; 3 placenta; 4 lung; 5 hver; 6 skeletal muscle; 7 kidney; 8 pancreas. FIG. 15B. Lanes are as follows: 1 spleen; 2 thymus; 3 prostate; 4 testis; 5 ovary; 6 small intestine; 7 colon; 8 leukocytes. FIG. 15C. Lanes are as follows: 1 prostate; 2 LAPC-4 AD; 3 LAPC-4 Al; 4 LAPC-9 AD; LAPC-9AI. FIG. 16. Expression of STEAP-2 m prostate and select cancer cell lines as determined by Northern blot analysis. Xenograft and cell lme filters were prepared with 10 μg total RNA per lane. The blots were analyzed usmg an SSH derived 98P4B6 clone as probe. All RNA samples were normalized by ethidium bromide staining. Lanes are as follows: 1 prostate; 2 LAPC-4 AD; 3 LAPC-4 Al; 4 LAPC-9 AD; 5 LAPC-9 Al; 6 TsuPrl; 7 DU145; 8 LNCaP; 9 PC-3; 10 LAPC-4 CL; 11 PrEC; 12 HT1197; 13 SCaBER; 14 UM-UC-3; 15 TCCSUP; 16 J82; 17 5637; 18 RD-ES; 19 293T; 20 PANC-1; 21 BxPC-3; 22 HPAC; 23 Capan-1; 24 LSI 80; 25 SK-CO-1; 26 CaCo-2; 27 LoVo; 28 T84; 29 Colo-205; 30 BT-20, 31 CAMA-1; 32 DU4475; 33 MCF-7; 34 MDA-MB-435s; 35 NTERA-2; 36 NCCIT; 37 TERA-1; 38 TERA-2; 39 A431; 40 HeLa; 41 OV-1063; 42 PA-1; 43 SW626; 44 CAOV-3. FIG. 17. Chromosomal localization of STEAP family members. The chromosomal localizations of the STEAP genes described herem were determined usmg the GeneBrιdge4 radiation hybrid panel (Research Genetics, Huntsvύle Al). The mapping for STEAP-2 and All 39607 was performed usmg the Stanford G3 radiation hybrid panel (Research Genetics, Huntsville Al). FIG. 18. Schematic representation of Intron-Exon boundaries within the ORF of human STEAP-1 gene A total of 3 lntrons (l) and 4 exons (e) were identified. FIG. 19. Zooblot southern analysis of STEAP-1 gene in various species. Genomic DNA was prepared from several different organisms including human, monkey, dog, mouse, chicken and Drosophila. Ten micrograms of each DNA sample was digested with EcoRI, blotted onto nitrocellulose and probed with a STEAP-1 probe. Size standards are indicated on the side m kilobases (kb). FIG. 20. Southern blot analysis of mouse BAC with a STEAP-1 probe. DNA was prepared from human cells to isolate genomic DNA and from a mouse BAC clone (12P11) that contains the mouse STEAP gene. Each DNA sample was digested with EcoRI, blotted onto nitrocellulose and probed. Eight micrograms of genomic DNA was compared to 250 ng of mouse BAC DNA. Lanes are as follows: (1) 1 kb ladder; (2) human female genomic; (3) 12P11 BAC mus; (4) human female genomic; (5) 12P11 BAC mus, (6) 3T3 FIG. 21A. Irnmunohistochemical staining usmg a sheep polyclonal antibody directed agamst STEAP-1 and showmg pericellular staining m a bladder cancer specimen. FIG 21B. Immunohistochemical staining usmg a sheep polyclonal antibody directed agamst STEAP-1 and showmg pericellular staining m a second bladder cancer specimen. FIG 21 C. Immunohistochemical staining usmg a sheep polyclonal antibody directed agamst STEAP-1 and showmg pericellular staining in a lung cancer specimen. FIG 21D. Immunohistochemical staining usmg a sheep polyclonal antibody directed agamst STEAP-1 and showmg pericellular staining m a second lung cancer specimen. FIG. 22A. STEAP-2 expression in normal prostate shown by RNA in situ hybridization with an antisense probe. FIG. 22B. STEAP-2 expression in normal prostate by RNA m situ hybridization usmg a sense probe as control. FIG 23A. STEAP-2 expression in prostate cancer shown by RNA m situ hybridization with an antisense probe. FIG. 23B STEAP-2 expression m prostate cancer control for RNA m situ hybridization usmg a sense probe. FIG. 24. Expression of STEAP-2 m various cancer tissues as examined usmg RT-PCR. Lane 1 represents a sample from an LAPC4 AD xenograft; lane 2 is LAPC9 AD xenograft; lane 3 is LAPC9 AD 2 xenograft (grown with human bone explant); lane 4 is LAPC9 AD IT (grown lntratibially); lane 5 is pooled tissue from colon cancer patients; lane 6 is pooled tissue from lung cancer patients, M represents a marker lane, lane 7 is patient normal prostate tissue, lane 8 is patient prostate cancer tissue; lane 9 is pooled tissue from kidney cancer patients; lane 10 is pooled tissue from bladder cancer patients; lane 11 is HeLa cells; and lane 12 is a water blank. FIG. 25. RNA dot blot analysis of STEAP-2 expression in 76 normal tissues, showing prostate-specific expression. RNA tissue sources: Al whole brain; A2 cerebellum, left; A3 substantia nigra; A4 heart; A5 esophagus; A6 colon, transverse; A7 kidney; A8 lung; A9 liver; A10 HL60, leukemia; Al l fetal brain; Bl cerebral cortex; B2 cerebellum, right; B3 accumbens nucleus; B4 aorta; B5 stomach; B6 colon, descending; B7 skeletal muscle; B8 placenta; B9 pancreas; BIO HeLa, S3; Bl lfetal heart; Cl frontal lobe; C2 corpus callosum; C3 thalamus; C4 atrium, left; C5 duodenum; C6 rectum; C7 spleen; C8 bladder; C9 adrenal gland; CIO K562, leukemia; Cll fetal kidney; DI parietal lobe; D2 amygdala; D3 pituitary gland; D4 atrium, right; D5 jejunum; D6 blank; D7 thymus; D8 uterus; D9 thyroid gland; D10 MOLT-4, leukemia; DI 1 fetal liver; El occipital lobe; E2 caudate nucleus; E3 spinal cord; E4 ventricle, left; E5 ileum; E6 blank; E7 leukocytes; E8 prostate; E9 salivary gland; E10 RAJI, lymphoma; Ell fetal spleen; FI temporal lobe; F2 hippocampus; F3 blank; F4 ventricle, right; F5 ileocecum; F6 blank; F7 lymph node; F8 testis; F9 mammary gland; F10 DAUDI, lymphoma; Fll fetal thymus; Gl paracentral gyrus; G2 medulla oblongata; G3 blank; G4 interventricular septum; G5 appendix; G6 blank; G7 bone marrow; G8 ovary; G9 blank; Gl 0 SW480, colon cancer; Gil fetal lung; HI pons; H2 putamen; H3 blank; H4 apex of the heart; H5 colon, ascending; H6 blank; H7 trachea; H8 blank; H9 blank; H10 A549, lung cancer; Hll blank. FIG. 26. Western blot with anti-phosphotyrosine (4G10 mAb) showing that expression of STEAP-2 in PC3 cells is sufficient to induce phosphorylation of various proteins on tyrosine residues, including pi 50, pi 20 and p75. An overlay using anti-Grb2 Ab shows that the gel was equally loaded. FIG. 27A. Western blot using anti-phospho-p38 showing that expression of STEAP-1 or STEAP-2 in PC3 cells activates the p38 kinase, as compared to PC3-neo controls. TNF-NaSal and NaSal, known p38 activators, served as positive controls. FIG. 27B. Western blot, as in FIG. 27A, using anti-p38 to demonstrate equal protein loading on the gels. FIG. 28A Western blot usmg anti-phospho-ERK to examine activation of the ERK pathway in 1% FBS. PC3 cells expressmg Ras (positive control), STEAP-1, STEAP-2, or neo (negative control), were grown m 1% FBS. The results show that, while expression of the neo control gene has no effect on ERK phosphorylation, expression of STEAP-1 and STEAP-2 mduces ERK phosphorylation. An anti-ERK antibody was used to confirm the presence of ERK m all lanes. FIG. 28B. Western blot usmg anti-phospho-ERK to examine activation of the ERK pathway in 0.1% and 10% FBS. PC3 cells expressmg STEAP-1 or neo (negative control), were grown m either 0.1% or 10% FBS. The results confirm that expression of STEAP-1 is sufficient to mduce activation of the ERK signaling cascade. FIG. 29. Signaling in PC3-STEAP-1 cells mediated by odorants. FIG. 29A. Anti-phosphotyrosine western blot of PC3 cells, stably expressmg neo, were grown overnight m 0.1% FBS to allow for receptor occupancy, and then treated with citralva, ethylvantlhn or IBMP. Treatment with 10% FBS was used as a control. FIG. 29B. Anti-phosphotyrosine western blot of PC3 cells, stably expressmg STEAP-1, were treated as described for FIG. 29A. The results show that citralva and ethylvanillin specifically mduce the phosphorylation of pl36-140 m PC3-STEAP-1 cells. In addition, citralva mduces the de novo phosphorylation of a protem at 160-200kDa. FIG. 30. Activation of the ERK cascade by odorants. Anti-ERK western blot of PC3 cells, stably expressmg either neo or STEAP-1, were grown overmght m 0.1% FBS. Cells were then treated with citralva for 5 mm. Treatment with 10% FBS was used as a control. Whole cell lysates were analyzed usmg anti-phospho-ERK. The results show that citralva mduces the phosphorylation of ERK, and therefore activation of the ERK pathway, in a STEAP-1 specific manner. FIG. 31 A. Anti-STEAP-1 lmmunohistochemistry analysis on the LAPC-9 orthotopic prostate cancer tumor (magmfication 200X). CeUs expressmg STEAP-1 show permuclear staining. FIG. 31 B Anti-STEAP-1 lmmunohistochemistry analysis on the LAPC-9 lymph node metastasis (magmfication 400X). Cells expressmg STEAP-1 show permuclear staining FIG. 31C-D Anti-STEAP-1 lmmunohistochemistry analysis on the LAPC-9 lung metastasis (magmfication 800X). CeUs expressmg STEAP-1 show permuclear staining. FIG. 31E-F. Anti- PSA lmmunohistochemistry analysis on a LAPC-9 prostate cancer lung micrometastasis (magmfication 800X). CeUs expressmg PSA show permuclear staining. FIG. 32A. Immunohistochemical detection of STEAP-1 showmg mtense penceUular staining in lymph node metastasis of a human patient. FIG 32B. Immunohistochemical detection of STEAP-1 showmg mtense penceUular staining m bone metastasis of a human patient. FIG. 33. Western blot showmg that anti-STEAP-1 murine pAb recognizes STEAP-1 protein m engineered ceU lines and endogenous STEAP-1 protem m LNCaP ceUs. Lysates of LNCaP ceUs and 293T ceUs transfected with either pcDNA 3.1 MYC/HIS tagged STEAP-1 or neo empty vector, and RATl ceUs engineered to express STEAP-1 or a neo control gene, were separated by SDS-PAGE and transferred to nitroceUulose. The blot was then subjected to anti-STEAP western analysis usmg a 1:1000 dilution of serum from mice immunized with a GST-STEAP-1 fusion protem. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel family of ceU surface serpentine transmembrane antigens Two of the protems m this family are exclusively or predominantly expressed in the prostate, as weU as m prostate cancer, and thus members of this family have been termed "STEAP" (Six Transmembrane Epithehal Antigen of the Prostate) Four particular human STEAPs are described and characterized herem. The human STEAPs exhibit a high degree of structural conservation among them but show no significant structural homology to any known human protems The present invention relates to methods and compositions for the diagnosis and therapy of prostate and other cancers, which methods utilize isolated polynucleotides corresponding to human STEAP genes, protems encoded by the STEAP genes and fragments thereof, and antibodies capable of specificaUy recognizing and binding to STEAP protems. Unless otherwise defined, aU terms of art, notations and other scientific terminology used herem are mtended to have the meanings commonly understood by those of skiU m the art to which this invention pertains. In some cases, terms with commonly understood meanings are defined herem for clarity and/or for ready reference, and the inclusion of such definitions herem should not necessarily be construed to represent a substantial difference over what is generaUy understood in the art. The techmques and procedures described or referenced herein are generaUy weU understood and commonly employed usmg conventional methodology by those skiUed in the art, such as, for example, the widely utilized molecular cloning methodologies described m Sambrook et al , Molecular Cloning A Laboratory Manual 2nd edition (1989) Cold Spring Harbor Laboratory Press, Cold Sprmg Harbor, N.Y. As appropriate, procedures involving the use of commerciaUy available kits and reagents are generaUy carried out m accordance with manufacturer defined protocols and/or parameters unless otherwise noted. As used herem, the terms "advanced prostate cancer", "locaUy advanced prostate cancer", "advanced disease" and "locaUy advanced disease" mean prostate cancers that have extended through the prostate capsule, and are meant to mclude stage C disease under the American Urological Association (AUA) system, stage Cl - C2 disease under the Whitmore-Jewett system, and stage T3 - T4 and N+ disease under the TNM (tumor, node, metastasis) system In general, surgery is not recommended for patients with locaUy advanced disease, and these patients have substantiaUy less favorable outcomes compared to patients havmg climcaUy localized (organ-confined) prostate cancer. LocaUy advanced disease is clinicaUy identified by palpable evidence of induration beyond the lateral border of the prostate, or asymmetry or induration above the prostate base. LocaUy advanced prostate cancer is presently diagnosed pathologicaUy foUowmg radical prostatectomy if the tumor mvades or penetrates the prostatic capsule, extends into the surgical margin, or mvades the seminal vesicles. As used herem, the terms "metastatic prostate cancer" and "metastatic disease" mean prostate cancers that have spread to regional lymph nodes or to distant sites, and are meant to mclude stage D disease under the AUA system and stage TxNxM+ under the TNM system. As is the case with locaUy advanced prostate cancer, surgery is generaUy not indicated for patients with metastatic disease, and hormonal (androgen ablation) therapy is the preferred treatment modahty. Patients with metastatic prostate cancer eventuaUy develop an androgen-refractory state withm 12 to 18 months of treatment initiation, and approximately half of these patients die withm 6 months thereafter. The most common site for prostate cancer metastasis is bone. Prostate cancer bone metastases are, on balance, characteristicaUy osteoblastic rather than osteolytic (ι.e., resulting m net bone formation). Bone metastases are found most frequently m the spme, foUowed by the femur, pelvis, rib cage, skuU and humerus. Other common sites for metastasis mclude lymph nodes, lung, hver and bram. Metastatic prostate cancer is typicaUy diagnosed by open or laparoscopic pelvic lymphadenectomy, whole body radionuchde scans, skeletal radiography, and/or bone lesion biopsy. As used herem, the term "polynucleotide" means a polymeric form of nucleotides of at least 10 bases or base pairs m length, either ribonucleotides or deoxynucleotides or a modified form of either type of nucleotide, and is meant to mclude smgle and double stranded forms of DNA. As used herem, the term "polypeptide" means a polymer of at least 10 ammo acids. Throughout the specification, standard three letter or smgle letter designations for ammo acids are used. As used herein, the terms "hybridize", "hybridizing", "hybridizes" and the like, used in the context of polynucleotides, are meant to refer to conventional hybridization conditions, preferably such as hybridization in 50% formamide/6XSSC/0.1% SDS/100 μg/ml ssDNA, in which temperatures for hybridization are above 37°C and temperatures for washing in 0.1XSSC/0.1% SDS are above 55°C, and most preferably to stringent hybridization conditions. "Stringency" of hybridization reactions is readily determinable by one of ordinary skill in the art, and generaUy is an empirical calculation dependent upon probe length, washing temperature, and salt concentration. In general, longer probes require higher temperatures for proper annealing, whUe shorter probes need lower temperatures. Hybridization generaUy depends on the ability of denatured DNA to reanneal when complementary strands are present in an environment below their melting temperature. The higher the degree of desired homology between the probe and hybridizable sequence, the higher the relative temperature that can be used. As a result, it foUows that higher relative temperatures would tend to make the reaction conditions more stringent, whUe lower temperatures less so. For additional deta s and explanation of stringency of hybridization reactions, see Ausubel et al., Current Protocols in Molecular Biology, WUey Interscience Publishers, (1995). "Stringent conditions" or "high stringency conditions", as defined herein, may be identified by those that: (1) employ low ionic strength and high temperature for washing, for example 0.015 M sodium chloride/0.0015 M sodium citrate/0.1% sodium dodecyl sulfate at 50°C; (2) employ during hybridization a denaturing agent, such as formamide, for example, 50% (v/v) formamide with 0.1% bovine serum albumin/0.1% FicoU/0.1% ρolyvinylpyrroHdone/50mM sodium phosphate buffer at pH 6.5 with 750 mM sodium chloride, 75 mM sodium citrate at 42°C; or (3) employ 50% formamide, 5 x SSC (0.75 M NaCl, 0.075 M sodium citrate), 50 mM sodium phosphate (pH 6.8), 0.1% soclium pyrophosphate, 5 x Denhardt's solution, sonicated salmon sperm DNA (50 μg/ml), 0.1% SDS, and 10% dextran sulfate at 42°C, with washes at 42°C in 0.2 x SSC (sodium chloride/sodium, citrate) and 50% formamide at 55°C, foUowed by a high-stringency wash consisting of 0.1 x SSC containing EDTA at 55°C. "Moderately stringent conditions" may be identified as described by Sambrook et al., Molecular Cloning: A Laboratory Manual, New York: Cold Spring Harbor Press, 1989, and mclude the use of washing solution and hybridization conditions (e.g., temperature, ionic strength and %SDS) less stringent than those described above. An example of moderately stringent conditions is overnight incubation at 37°C in a solution comprising- 20% formamide, 5 x SSC (150 mM NaCl, 15 mM tnsodium citrate), 50 mM sodium phosphate (pH 7.6), 5 x Denhardt's solution, 10% dextran sulfate, and 20 mg/ml denatured sheared salmon sperm DNA, foUowed by washing the filters m i x SSC at about 37-50°C. The skiUed artisan wiU recognize how to adjust the temperature, ionic strength, etc. as necessary to accommodate factors such as probe length and the like. In the context of ammo acid sequence comparisons, the term "identity" is used to express the percentage of amino acid residues at the same relative positions that are the same. Also in this context, the term "homology" is used to express the percentage of ammo acid residues at the same relative positions that are either identical or are simύar, usmg the conserved ammo acid catena of BLAST analysis, as is generaUy understood m the art. For example, % identity values may be generated by WU-BLAST-2 (Altschul et al., Methods m Enzymology, 266: 460-480 (1996): http://blast.wustl/edu/blast/ README.html). Further details regarding ammo acid substitutions, which are considered conservative under such cnteria, are provided below. Additional definitions are provided throughout the subsections that foUow. STEAP POLYNUCLEOTIDES One aspect of the invention provides polynucleotides corresponding or complementary to aU or part of a STEAP gene, mRNA, and/or coding sequence, preferably in isolated form, mcluding polynucleotides encoding a STEAP protem and fragments thereof, DNA, RNA, DNA/RNA hybrid, and related molecules, polynucleotides or oligonucleotides complementary to a STEAP gene or mRNA sequence or a part thereof, and polynucleotides or oligonucleotides that hybndize to a STEAP gene, mRNA, or to a STEAP encoding polynucleotide (coUectively, "STEAP polynucleotides"). As used herem, STEAP genes and protems are meant to mclude the STEAP-1, STEAP-2 and STEAP-3 genes and protems, and the gene and protem corresponding to GenBank Accession number R80991 (STEAP-4), and the genes and proteins corresponding to other STEAP proteins and structuraUy simUar variants of the foregoing. Such other STEAP proteins and variants wiU generaUy have coding sequences that are highly homologous to the STEAP coding sequence, and preferably wiU share at least about 50% amino acid identity and at least about 60% amino acid homology (using BLAST criteria), more preferably sharing 70% or greater homology (using BLAST criteria). The STEAP farmly member gene sequences described herein encode STEAP proteins sharing unique highly conserved amino acid sequence domains which distinguish them from other proteins. Proteins which include one or more of these unique highly conserved domains may be related to the STEAP famUy members or may represent new STEAP proteins. Referring to FIG. 11 A-B, which is an amino acid sequence alignment of the fuU STEAP-1, STEAP-2, and STEAP-3 protein sequences as weU as the partial STEAP-4 sequence, it is clear that the STEAPs are closely related at the structural level. Referring to FIG. 11C, which is an amino acid sequence aUgnment of the fuU STEAP-1 and STEAP-2 protein sequences, close structural conservation is apparent, particularly in the predicted transmembrane domains. The STEAP-1 and STEAP-2 sequences share 54.9% identity over a 237 amino acid overlap. Additional amino acid sequence alignments between the STEAPs are shown in FIGS. 11D and HE. These alignments show that STEAP-1 and STEAP-3 are 40.9% identical over a 264 amino acid region, whUe STEAP-2 and STEAP-3 are 47.8% identical over a 416 amino acid region. A STEAP polynucleotide may comprise a polynucleotide having the nucleotide sequence of human STEAP-1 as shown in FIG. 1 A-B, the nucleotide sequence of human STEAP-2 as shown in FIG. 9A-D, the nucleotide sequence of human STEAP-3 as shown in FIG. 10A-E, or the nucleotide sequence of STEAP-4 as shown in FIG. 10F, or a sequence complementary thereto, or a polynucleotide fragment of any of the foregoing. Another embodiment comprises a polynucleotide which encodes the human STEAP-1, STEAP-2, STEAP-3 or STEAP-4 protein amino acid sequences, a sequence complementary thereto, or a polynucleotide fragment of any of the foregoing. Another embodiment comprises a polynucleotide which is capable of hybridizing under stringent hybridization conditions to the human STEAP-1 cDNA shown in FIG. 1A-B, the human STEAP-2 cDNA shown m FIG. 9A-D, the human STEAP-3 cDNA shown m FIG 10A-E, or the STEAP-4 as shown m FIG. 10F, or to a polynucleotide fragment thereof. Typical embodiments of the invention disclosed herem mclude STEAP polynucleotides encoding specific portions of a STEAP mRNA sequence such as those that encode the protem and fragments thereof. For example, representative embodiments of the invention disclosed herem mclude: polynucleotides encoding about ammo acid 1 to about amino acid 10 of a STEAP protem shown m Figure 11 A-B, polynucleotides encodmg about amino acid 20 to about ammo acid 30 of a STEAP protem shown m Figure 11 A-B, polynucleotides encoding about ammo acid 30 to about ammo acid 40 of a STEAP protem shown m Figure 11 A-B, polynucleotides encoding about amino acid 40 to about ammo acid 50 of a STEAP protem shown m Figure 11A- B, polynucleotides encodmg about ammo acid 50 to about ammo acid 60 of a STEAP protem shown m Figure 11 A-B, polynucleotides encoding about ammo acid 60 to about ammo acid 70 of a STEAP protem shown m Figure 11A-B, polynucleotides encodmg about ammo acid 70 to about ammo acid 80 of a STEAP protem shown m Figure 11A- B, polynucleotides encoding about ammo acid 80 to about amino acid 90 of a STEAP protem shown in Figure 11 A-B and polynucleotides encoding about ammo acid 90 to about amino acid 100 of a STEAP protem shown m Figure 11 A-B, etc. FoUowmg this scheme, polynucleotides (of at least 10 ammo acids) encodmg further portions of the ammo acid sequence of a STEAP protem are typical embodiments of the invention. Such portions of a STEAP protem mclude ammo acids 100-339 of a STEAP-1 protem shown in Figure 11 A-B, or amino acids 100-454 of a STEAP-2 protem shown in Figure 11 A-B, or ammo acids 100-459 of a STEAP-3 protem shown m Figure 11 A-B, and ammo acids 100-133 of a STEAP-4 protem shown m Figure 11A-B. Polynucleotides encoding larger portions of the STEAP protem are also contemplated. For example polynucleotides encoding from about ammo acid 1 (or 20 or 30 or 40 etc.) to about am o acid 20, (or 30, or 40 or 50 etc.) of a STEAP protem shown in Figure 11A-B may be generated by a variety of techniques weU known m the art. Additional lUustrative embodiments of the invention disclosed herem mclude STEAP polynucleotide fragments encodmg one or more of the biological motifs contained within the STEAP protem sequence In one embodiment, typical polynucleotide fragments of the invention can encode one or more of the regions of STEAP that exhibit homology to other STEAP family members, such as one or more of the transmembrane domains. In another embodiment of the invention, typical polynucleotide fragments can encode sequences that are unique to one or more STEAP alternative splicing variants. In yet another embodiment, typical polynucleotide fragments can encode an immunogenic portion of a STEAP protem. One example of an immunogenic portion of a STEAP protem is ammo acid residues 14 through 28 of the STEAP-1 ammo acid sequence as shown m FIG. 1A-B (WKMKPRRNLEEDDYL; SEQ ID NO: 22). The polynucleotides of the preceding paragraphs have a number of different specific uses. As STEAPs are differentiaUy expressed m prostate and other cancers, these polynucleotides may be used m methods assessmg the status of STEAP gene products m normal versus cancerous tissues. TypicaUy, polynucleotides encodmg specific regions of a STEAP protem may be used to assess the presence of perturbations (such as deletions, msertions, pomt mutations etc.) m specific regions of the STEAP gene products. Exemplary assays mclude both RT-PCR assays as weU as single-strand conformation polymorphism (SSCP) analysis (see e.g. Marrogi et al., J. Cutan. Pathol. 26(8): 369-378 (1999), both of which utilize polynucleotides encoding specific regions of a protem to examine these regions within the protem. Assays and methods for analyzmg sequences to detect smgle nucleotide polymorphisms are also available (Inzarry, et al, 2000, Nature Genetics 26(2):223-236. Other specificaUy contemplated embodiments of the invention disclosed herem are genomic DNA, cDNAs, nbozymes, and antisense molecules, including morpholino anti- sense molecules, as weU as nucleic acid molecules based on an alternative backbone or mcluding alternative bases, whether denved from natural sources or synthesized. For example, antisense molecules can be RNAs or other molecules, mcluding peptide nucleic acids (PNAs) or non-nucleic acid molecules such as phosphorothioate derivatives, that specificaUy bmd DNA or RNA m a base pair-dependent manner. A skiUed artisan can readύy obtain these classes of nucleic acid molecules usmg the STEAP polynucleotides and polynucleotide sequences disclosed herem. Antisense technology entails the administration of exogenous oligonucleotides that bmd to a target polynucleotide located within the ceUs. The term "antisense" refers to the fact that such oligonucleotides are complementary to their mtraceUular targets, e.g, STEAP. See for example, Jack Cohen, OLIGODEOXYNUCLEOTIDES, Antisense Inhibitors of Gene Expression, CRC Press, 1989; and Synthesis 1T-5 (1988). The STEAP antisense oligonucleotides of the present invention mclude denvatives such as S-ohgonucleotides (phosphorothioate denvatives or S-ohgos, see, Jack Cohen, supra), which exhibit enhanced cancer ceU growth inhibitory action. S-ohgos (nucleoside phosphorothioates) are lsoelectronic analogs of an ohgonucleotide (O-okgo) in which a nonbridgmg oxygen atom of the phosphate group is replaced by a sulfur atom. The S- ohgos of the present invention may be prepared by treatment of the corresponding O- ohgos with 3H-l,2-benzodιthιol-3-one-l,l -dioxide, which is a sulfur transfer reagent. See Iyer, R. P. et al, J. Org. Chem. 55-4693-4698 (1990); and Iyer, R. P. et al, J. Am. Chem. Soc. 112:1253-1254 (1990), the disclosures of which are fuUy incorporated by reference herem. Additional STEAP antisense oligonucleotides of the present invention mclude morphohno antisense oligonucleotides known m the art (see e.g. Partridge et al , 1996, Antisense & Nucleic Acid Drug Development 6: 169-175). The STEAP antisense oligonucleotides of the present invention typicaUy may be RNA or DNA that is complementary to and stably hybridizes with the first 100 N- termtnal codons or last 100 C-terminal codons, or overlappmg with the ATG start site, of the STEAP genome or the corresponding mRNA. While absolute complementarity is not required, high degrees of complementarity are preferred. Use of an ohgonucleotide complementary to this region aUows for the selective hybridization to STEAP mRNA and not to mRNA specifying other regulatory subumts of protem kinase. Preferably, the STEAP antisense oligonucleotides of the present invention are a 15 to 30-mer fragment of the antisense DNA molecule having a sequence that hybndizes to STEAP mRNA. OptionaUy, STEAP antisense ohgonucleotide is a 30-mer ohgonucleotide that is complementary to a region m the first 10 N-terminal codons and last 10 C-termmal codons of STEAP. Alternatively, the antisense molecules are modified to employ nbozymes m the inhibition of STEAP expression. L. A. Couture & D. T. Stinchcomb; Trends Genet 12: 510-515 (1996). Further specific embodiments of this aspect of the invention mclude primers and primer pairs, which aUow the specific amphfication of the polynucleotides of the invention or of any specific parts thereof, and probes that selectively or specificaUy hybridize to nucleic acid molecules of the invention or to any part thereof. Probes may be labeled with a detectable marker, such as, for example, a radioisotope, fluorescent compound, bioluminescent compound, a chemUuminescent compound, metal chelator or enzyme. Such probes and primers can be used to detect the presence of a STEAP polynucleotide in a sample and as a means for detecting a ceU expressing a STEAP protein. Examples of such probes include polypeptides comprising aU or part of a human STEAP cDNA sequence shown in Fig. 1A-B (SEQ ID NO: 1), FIG. 9A-D (SEQ ID NO: 7) or Fig. 10A-E (SEQ ID NO: 9). Examples of primer pairs capable of specificaUy ampUfying STEAP mRNAs are also described in the Examples that foUow. As will be understood by the skiUed artisan, a great many different primers and probes may be prepared based on the sequences provided in herein and used effectively to amplify and/or detect a STEAP mRNA. As used herein, a polynucleotide is said to be "isolated" when it is substantiaUy separated from contaminant polynucleotides that correspond or are complementary to genes other than the STEAP gene or that encode polypeptides other than STEAP gene product or fragments thereof. A skiUed artisan can readily employ nucleic acid isolation procedures to obtain an isolated STEAP polynucleotide. The STEAP polynucleotides of the invention are useful for a variety of purposes, including but not limited to their use as probes and primers for the amplification and/or detection of the STEAP gene(s), mRNA(s), or fragments thereof; as reagents for the diagnosis and/or prognosis of prostate cancer and other cancers; as tools for identifying molecules that inhibit calcium entry specificaUy into prostate ceUs; as coding sequences capable of directing the expression of STEAP polypeptides; as tools for modulating or inhibiting the expression of the STEAP gene(s) and/or translation of the STEAP transcript(s); and as therapeutic agents. MOLECULAR AND BIOCHEMICAL FEATURES OF THE STEAPs The invention relates to a novel fairάly of proteins, termed STEAPs. Four STEAPs are specificaUy described herein by way of structural, molecular and biochemical features. As is further described in the Examples which foUow, the STEAPs have been characterized in a variety of ways. For example, analyses of nucleotide coding and amino acid sequences were conducted in order to identify conserved structural elements withm the STEAP family. Extensive RT-PCR and Northern blot analyses of STEAP mRNA expression were conducted m order to estabhsh the range of normal and cancerous tissues expressmg the vanous STEAP messages. Western blot, immunohistochemical and flow cytometric analyses of STEAP protem expression were conducted to determine protem expression profiles, ceU surface localization and gross molecular topology of STEAP. The prototype member of the STEAP family, STEAP-1, is a six-transmembrane ceU surface protem of 339 ammo acids with no identifiable homology to any known human protem. The cDNA nucleotide and deduced ammo acid sequences of human STEAP-1 are shown m FIG. 1A-B. A gross topological schematic of the STEAP-1 protem mtegrated withm the ceU membrane is shown m FIG. IB. STEAP-1 expression is predominantly prostate-specific m normal tissues. SpecificaUy, extensive analysis of STEAP-1 mRNA and protem expression m normal human tissues shows that STEAP-1 protem is predominantly expressed in prostate and, to a far smaUer degree, m bladder. STEAP-1 mRNA is also relatively prostate specific, with only very low level expression detected m a few other normal tissues. In cancer, STEAP-1 mRNA and protem is consistently expressed at high levels m prostate cancer (including androgen-dependent and androgen-independent tumors) and during aU stages of the disease. STEAP-1 is also expressed m other cancers. SpecificaUy, STEAP-1 mRNA is expressed at very high levels in bladder, colon, pancreatic, and ovarian cancer (as weU as other cancers). In addition, ceU surface expression of STEAP-1 protein has been estabhshed in prostate, bladder, lung and colon cancers. Therefore, STEAP-1 has aU of the hallmark charactenstics of an exceUent diagnostic and therapeutic target for the treatment of certam cancers, including particularly prostate, colon and bladder carcmomas. A second member of the famUy, STEAP-2, is a 454 amino acid protem encoded by a distinct gene and having a predicted molecular topology similar to that of STEAP-1. The cDNA nucleotide and deduced ammo acid sequences of STEAP-2 are shown m FIG. 9A-D. Ammo acid alignment of the STEAP-1 and STEAP-2 sequences show a high degree of structural conservation (54.9% identity over a 237 ammo acid residue overlap, and the locations of the six putative transmembrane domams m STEAP-1 and STEAP-2 comcide (FIGS. 11 A-B, 11C). Structural homology between these STEAP-1 and STEAP-2 is highest m the regions spanned by the first putative extraceUular loop to the fifth transmembrane domain. However, some significant structural differences between STEAP-1 and STEAP-2 are apparent. For example, STEAP-2 exhibits a 205 a.a. long mtraceUular N-termmus (compared to 69 a.a. m STEAP-1) and a short 4 a.a. lntraceUular C-terminus (compared to 26 a.a m STEAP-1). In addition, both the STEAP-1 and STEAP-2 genes are located on chromosome 7, but on different arms. These differences could imply significant differences in function and/or interaction with mtraceUular signaling pathways. STEAP-2 is expressed only m normal prostate among human tissues tested (FIGS. 14 and 15) and is also expressed m prostate cancer (FIG. 15), and thus shows some similarity m expression profile to STEAP-1. However, STEAP-2 exhibits a different mRNA expression profile relative to STEAP-1 in prostate cancer samples (compare FIGS. 3 and 15) and m other non-prostate cancers tested (compare FIGS. 5 and 16). These differences in the expression profiles of STEAP-1 and STEAP-2 suggest that they are differentiaUy regulated STEAP-3 and STEAP-4 appear to be closely related to both STEAP-1 and STEAP-2 on a structural level, and both appear to be transmembrane protems as weU. STEAP-3 is more related to STEAP-2 (47.8% identity) than to STEAP-1 (40.9% identity). STEAP-3 and STEAP-4 show unique expression profiles. STEAP-3, for example, appears to have an expression pattern which is predominantly restricted to placenta and, to a smaUer degree, expression is seen m prostate but not m other normal tissues tested. STEAP-4 seems to be expressed predominantly m hver by RT-PCR analysis. Neither STEAP-3 nor STEAP-4 appear to be expressed m prostate cancer xenografts which exhibit high level STEAP-1 and STEAP-2 expression. The STEAP protems exhibit charactenstics of protems mvolved m ceU signaling pathways. SpecificaUy, STEAP-1 and STEAP-2, when expressed in PC3 ceUs, activate phosphorylation of p38, a protem mvolved m the MAPK signaling cascade. In addition, STEAP-2 expression mduces tyrosine phosphorylation, and STEAP-1 mediates activation of tyrosine kinase m odorant-treated ceUs. These findings support the use of STEAP-related molecules and ceUs modified to express STEAP m high throughput assays to identify molecules capable of altermg ceUular signaling pathways, leadmg to the identification of novel therapeutic agents In one embodiment, the assay identifies molecules capable of inhibiting STEAP function, which molecules are thereby capable of modulating the progression of cancer or other disease associated with dysregulated ceU growth. Three of the four STEAPs described herem map to human chromosome 7 (STEAP-1, -2 and 3). Interestingly, STEAP-1 maps withm 7p22 (7p22.3), a large region of aUehc gam reported for both primary and recurrent prostate cancers (Visakorpi et al, 1995 Cancer Res. 55: 342, Nupponen et al, 1998 Amencan J. Pathol. 153: 141), suggesting that up-regulation of STEAP-1 m cancer might mclude genomic mechanisms. In addition, both STEAP-2 and STEAP-3 locate to chromosome 7q21, suggesting that these two genes arose by gene duplication. Other ceU surface molecules that contain six transmembrane domams mclude ion channels (DoUy and Parce j , 1996 J Bioenerg Biomembr 28:231) and water channels or aquaporins (Reizer et al, 1993 Cnt Rev Biochem Mol Biol 28:235). Structural studies show that both types of molecules assemble to tetramenc complexes to form functional channels (Christie, 1995, Clin Exp Pharmacol Physiol 22:944, Walz et al, 1997 Nature 387:624, Cheng et al, 1997 Nature 387:627). Immunohistochemical stammg of STEAP-1 m the prostate gland seems to be concentrated at the ceU-ceU boundanes, with less staining detected at the lumenal side. This may suggest a role for STEAP-1 in tight- junctions, gap-junctions, ceU communication, adhesion or as a transporter protem. To test these possibilities, xenopus oocytes (or other ceUs) expressmg STEAP may be analyzed using voltage-clamp and patch-clamp experiments to determine if STEAP functions as an ion-channel. Oocyte ceU volume may also be measured to determine if STEAP exhibits water channel properties. If STEAPs function as channel or gap-junction protems, they may serve as exceUent targets for inhibition usmg, for example, antibodies, smaU molecules, and polynucleotides capable of inhibiting expression or function. The restncted expression pattern in normal tissue, and the high levels of expression in cancer tissue suggest that mterfermg with STEAP function may selectively kiU cancer ceUs. Smce the STEAP gene family is predominantly expressed in epithehal tissue, it seems possible that the STEAP protems function as ion channels, transport protems or gap-junction protems in epithehal ceU function Ion channels have been implicated m proliferation and mvasiveness of prostate cancer ceUs (Lalani et al, 1997, Cancer Metastasis Rev 16:29). Both rat and human prostate cancer ceUs contain sub-population of ceUs with higher and lower expression levels of sodium channels. Higher levels of sodium channel expression correlate with more aggressive invasiveness in vitro (Smith et al, 1998, FEBS Lett. 423:19). Sim arly, it has been shown that a specific blockade of sodium channels inhibits the invasiveness of PC-3 ceUs in vitro (Laniado et al, 1997, Am. J. Pathol. 150:1213), while specific inhibition of potassium channels in LNCaP ceUs inhibited ceU proHferation (Skryma et al, 1997, Prostate 33:112). These reports suggest a role for ion channels in prostate cancer and also demonstrate that smaU molecules that inhibit ion channel function may interfere with prostate cancer proliferation. ISOLATION OF STEAP-ENCODING NUCLEIC ACID MOLECULES The STEAP cDNA sequences described herein enable the isolation of other polynucleotides encoding STEAP gene product(s), as weU as the isolation of polynucleotides encoding STEAP gene product homologues, alternatively spliced isoforms, aUehc variants, and mutant forms of the STEAP gene product. Various molecular cloning methods that can be employed to isolate full length cDNAs encoding a STEAP gene are weU known (See, for example, Sambrook, J. et al. Molecular Cloning: A Laboratory Manual, 2d edition. Cold Spring Harbor Press, New York, 1989; Current Protocols in Molecular Biology. Ausubel et al, Eds, WUey and Sons, 995). For example, lambda phage cloning methodologies may be conveniently employed, using commerciaUy ava able cloning systems (e.g. Lambda ZAP Express, Stratagene). Phage clones containing STEAP gene cDNAs may be identified by probing with labeled STEAP cDNA or a fragment thereof. For example, in one embodiment, a STEAP cDNA or a portion thereof can be synthesized and used as a probe to retrieve overlapping and full length cDNAs corresponding to a STEAP gene. The STEAP gene itself may be isolated by screening genomic DNA hbraries, bacterial artificial chromosome hbraries (BACs), yeast artificial chromosome hbraries (YACs), and the like, with STEAP DNA probes or primers. RECOMBINANT DNA MOLECULES AND HOST-VECTOR SYSTEMS The invention also provides recombinant DNA or RNA molecules containing a STEAP polynucleotide, including but not limited to phages, plasmids, phagemids, cosmids, YACs, BACs, as weU as various viral and non-viral vectors weU known in the art, and ceUs transformed or transfected with such recombmant DNA or RNA molecules. As used herem, a recombmant DNA or RNA molecule is a DNA or RNA molecule that has been subjected to molecular manipulation m vitro Methods for generating such molecules are weU known (see, for example, Sambrook et al, 1989, supra). The invention further provides a host-vector system comprismg a recombmant DNA molecule containing a STEAP polynucleotide withm a suitable prokaryotic or eukaryotic host ceU. Examples of suitable eukaryotic host ceUs mclude a yeast ceU, a plant ceU, or an animal ceU, such as a mammahan ceU or an sect ceU (e.g, a baculovirus- mfectible ceU such as an Sf9 ceU). Examples of suitable mammahan ceUs mclude various prostate cancer ceU lines such LNCaP, PC-3, DU145, LAPC-4, TsuPrl, other transferable or transducible prostate cancer ceU lines, as weU as a number of mammahan ceUs routinely used for the expression of recombmant protems (e.g, COS, CHO, 293, 293T ceUs). More particularly, a polynucleotide comprismg the coding sequence of a STEAP may be used to generate STEAP proteins or fragments thereof usmg any number of host vector systems routinely used and widely known m the art. A wide range of host vector systems suitable for the expression of STEAP protems or fragments thereof are available, see for example, Sambrook et al, 1989, supra; Current Protocols m Molecular Biology, 1995, supra). Preferred vectors for mammahan expression mclude but are not hmited to pcDNA 3.1 myc-His-tag (Invittogen) and the retroviral vector pSRαtkneo (MuUer et al, 1991, MCB 11:1785). Usmg these expression vectors, STEAP may be preferably expressed m several prostate cancer and non-prostate ceU lines, including for example 293, 293T, rat-1, 3T3, PC-3, LNCaP and TsuPrl. The host vector systems of the invention are useful for the production of a STEAP protem or fragment thereof. Such host-vector systems may be employed to study the functional properties of STEAP and STEAP mutations. Protems encoded by the STEAP genes, or by fragments thereof, wiU have a variety of uses, including but not limited to generating antibodies and in methods for identifying hgands and other agents and ceUular constituents that bmd to a STEAP gene product. Antibodies raised agamst a STEAP protem or fragment thereof may be useful m diagnostic and prognostic assays, imaging methodologies (mcluding, particularly, cancer imaging), and therapeutic methods in the management of human cancers characterized by expression of a STEAP protein, including but not limited to cancer of the prostate. Various immunological assays useful for the detection of STEAP proteins are contemplated, including but not limited to various types of radioimmunoassays, enzyme- linked i munosorbent assays (ELISA), enzyme-linked immunofluorescent assays (ELIFA), immunocytochemical methods, and the like. Such antibodies may be labeled and used as immunological imaging reagents capable of detecting prostate ceUs (e.g, in radioscintigraphic imaging methods). STEAP proteins may also be particularly useful in generating cancer vaccines, as further described below. STEAP PROTEINS Another aspect of the present invention provides various STEAP proteins and polypeptide fragments thereof. As used herein, a STEAP protein refers to a protein that has or includes the amino acid sequence of human STEAP-1 as provided in FIG. 1 A-B, human STEAP-2 as provided in FIG. 9A-D, human STEAP-3 as provided in FIG. 1 OA-E, the amino acid sequence of other mammahan STEAP homologs (e.g., STEAP-4) and variants, as weU as aUelic variants and conservative substitution mutants of these proteins that have STEAP biological activity, to the extent that such variants and homologs can be isolated/generated and characterized without undue experimentation foUowing the methods outlined below. Fusion proteins that combine parts of different STEAP proteins or fragments thereof, as weU as fusion proteins of a STEAP protein and a heterologous polypeptide, are also included. Such STEAP proteins will be coUectively referred to as the STEAP proteins, the proteins of the invention, or STEAP. As used herein, the term "STEAP polypeptide" refers to a polypeptide fragment or a STEAP protein of at least 10 amino acids, preferably at least 15 amino acids. A specific embodiment of a STEAP protein comprises a polypeptide having the amino acid sequence of human STEAP-1 as shown in FIG. 1A-B. Another embodiment of a STEAP protein comprises a polypeptide containing the STEAP-2 amino acid sequence as shown in FIG. 9A-D. Another embodiment comprises a polypeptide containing the STEAP-3 amino acid sequence of shown in FIG. 10A-E. Yet another embodiment comprises a polypeptide containing the partial STEAP-4 amino acid sequence of shown in FIG. 11 A-B. In general, naturaUy occurring aUehc vanants of human STEAP will share a high degree of structural identity and homology (e.g, 90% or more identity). TypicaUy, aUehc variants of the STEAP protems will contain conservative amino acid substitutions within the STEAP sequences descnbed herem or will contain a substitution of an ammo acid from a corresponding position in a STEAP homologue. One class of STEAP aUehc variants wiU be protems that share a high degree of homology with at least a smaU region of a particular STEAP ammo acid sequence, but wiU further contain a radical departure from the sequence, such as a non-conservative substitution, truncation insertion or frame shift. Conservative ammo acid substitutions can frequently be made m a protem without altermg either the conformation or the function of the protein. Such changes mclude substituting any of isoleucine (I), valine (V), and leucme (L) for any other of these hydrophobic ammo acids; aspartic acid (D) for glutamic acid (E) and vice versa; glutamine (Q) for asparagine (N) and vice versa; and serine (S) for threonine (T) and vice versa. Other substitutions can also be considered conservative, depending on the environment of the particular ammo acid and its role m the three-dimensional structure of the protem. For example, glycme (G) and alanine (A) can frequendy b interchangeable, as can alanine (A) and vahne (V). Methionine (M), which is relatively hydrophobic, can frequently be mterchanged with leucme and isoleucine, and sometimes with vahne. Lysme (K) and arginine (R) are frequendy mterchangeable m locations m which the significant feature of the ammo acid residue is its charge and the differing pK's of these two ammo acid residues are not significant. StiU other changes can be considered "conservative" m particular environments. STEAP protems, mcluding vanants, comprise at least one epitope m common with a STEAP protein hav g an ammo acid sequence shown m Fig. 11 A-B, such that an antibody that specificaUy bmds to a STEAP protem or vanant wiU also specificaUy bmd to the STEAP protem havmg an am o acid sequence shown m Fig. 11 A-B. One class of STEAP protem vanants shares 90% or more identity with an amino acid sequence of Fig. 11 A-B. A more specific class of STEAP protem variants compnses an extraceUular protem SCP motif as descnbed above. Preferred STEAP protem vanants are capable of exhibiting one or more of the defensin functions described herem, including, for example, the ability to mduce tumor death or to chemoattract and/or mduce migration of ceUs STEAP protems may be embodied m many forms, preferably m isolated form. As used herein, a protem is said to be "isolated" when physical, mechanical or chemical methods are employed to remove the STEAP protem from ceUular constituents that are normaUy associated with the protem. A skiUed artisan can readily employ standard purification methods to obtam an isolated STEAP protem. A purified STEAP protem molecule wiU be substantiaUy free of other protems or molecules that impair the binding of STEAP to antibody or other ligand. The nature and degree of isolation and purification wiU depend on the mtended use. Embodiments of a STEAP protem mclude a purified STEAP protem and a functional, soluble STEAP protem. In one form, such functional, soluble STEAP protems or fragments thereof retain the ability to bmd antibody or other hgand. The invention also provides STEAP polypeptides comprismg biologicaUy active fragments of the STEAP ammo acid sequence, such as a polypeptide corresponding to part of the ammo acid sequences for STEAP-1 as shown m FIG. 1A-B, STEAP-2 as shown m FIG. 9A-D, STEAP-3 as shown m FIG. 10A-E, or STEAP-4 as shown m FIG. 11 A-B Such polypeptides of the invention exhibit properties of a STEAP protem, such as the ability to ehcit the generation of antibodies which specificaUy bmd an epitope associated with a STEAP protem. Polypeptides compnsmg ammo acid sequences which are unique to a particular STEAP protem (relative to other STEAP protems) may be used to generate antibodies which wiU specificaUy react with that particular STEAP protem. For example, referring to the ammo acid alignment of the STEAP structures shown in FIGS. 11A-E, the skiUed artisan wiU rea hly appreciate that each molecule contains stretches of sequence unique to its structure. These unique stretches can be used to generate antibodies specific to a particular STEAP. Similarly, regions of conserved sequence may be used to generate antibodies that may bmd to multiple STEAPs. Embodiments of the invention disclosed herem mclude a wide variety of art accepted variants of STEAP protems such as polypeptides havmg ammo acid msertions, deletions and substitutions. STEAP vanants can be made usmg methods known m the art such as site-directed mutagenesis, alanine scanning, and PCR mutagenesis. Site- directed mutagenesis [Carter et al, Nucl. Adds Res., 13Λ33 (1986); ZoUer et al, Nucl. Adds Res., 10:6481 (1987)], cassette mutagenesis [WeUs et al. Gene, 34:315 (1985)], restriction selection mutagenesis [WeUs et al, Philos. Trans. R. Soc. London SerA, 317:415 (1986)] or other known techniques can be performed on the cloned DNA to produce the STEAP variant DNA. Scanning amino acid analysis can also be employed to identify one or more amino acids along a contiguous sequence. Among the preferred scanning amino acids are relatively smaU, neutral amino acids. Such amino acids include alanine, glycine, serine, and cysteine. Alanine is typicaUy a preferred scanning amino acid among this group because it eliminates the side-chain beyond the beta-carbon and is less likely to alter the main-chain conformation of the variant. Alanine is also typicaUy preferred because it is the most common amino acid. Further, it is frequendy found in both buried and exposed positions [Creighton, The Proteins, (W.H. Freeman & Co, N.Y.); Chothia, J. Mol. Biol, 150:1 (1976)]. If alanine substitution does not yield adequate amounts of variant, an isosteric amino acid can be used. As discussed above, embodiments of the claimed invention include polypeptides containing less than the full amino acid sequence of a STEAP protein shown in Figure 11 A-B. For example, representative embodiments of the invention disclosed herein include polypeptides consisting of about amino acid 1 to about amino acid 10 of a STEAP protein shown in Figure 11 A-B, polypeptides consisting of about amino acid 20 to about amino acid 30 of a STEAP protein shown in Figure 11 A-B, polypeptides consisting of about amino acid 30 to about amino acid 40 of a STEAP protein shown in Figure 11 A-B, polypeptides consisting of about amino acid 40 to about amino acid 50 of a STEAP protein shown in Figure 11 A-B, polypeptides consisting of about amino acid 50 to about amino acid 60 of a STEAP protein shown in Figure 11 A-B, polypeptides consisting of about amino acid 60 to about amino acid 70 of a STEAP protein shown in Figure 11 A-B, polypeptides consisting of about amino acid 70 to about amino acid 80 of a STEAP protein shown in Figure 11 A-B, polypeptides consisting of about amino acid 80 to about amino acid 90 of a STEAP protein shown in Figure 11 A-B and polypeptides consisting of about amino acid 90 to about amino acid 100 of a STEAP protein shown in Figure 11 A-B, etc. FoUowing this scheme, polypeptides consisting of portions of the amino acid sequence of amino acids 100-339 of a STEAP-1 protein shown in Figure 11A-B, or amino acids 100-454 of a STEAP-2 protein shown in Figure 11A-B, or amino acids 100-459 of a STEAP-3 protein shown in Figure 11 A-B, or amino acids 100-133 of a STEAP-4 protein shown in Figure 11 A-B, are typical embodiments of the invention. Polypeptides consisting of larger portions of the STEAP protein are also contemplated. For example polypeptides consisting of about amino acid 1 (or 20 or 30 or 40 etc.) to about amino acid 20, (or 30, or 40 or 50 etc.) of a STEAP protein shown in Figure 11 A- B may be generated by a variety of techniques weU known in the art. Additional iUustrative embodiments of the invention disclosed herein include STEAP polypeptides containing the amino acid residues of one or more of the biological motifs contained within a STEAP polypeptide sequence as shown in Fig. 11 A-B. STEAP polypeptides containing one or more of these motifs or other select regions of interest described herein wiU typicaUy include an additional 5 to 25 or more amino acid residues of adjacent STEAP protein sequence on one or both sides of the selected motif (s). In one embodiment, typical polypeptides of the invention can contain one or more of the regions of STEAP that exhibit homology to one or more other STEAP proteins. In another embodiment, typical polypeptides of the invention can contain one or more immunogenic portions of a STEAP protein. One example of an immunogenic portion of a STEAP protein is amino acid residues 14 through 28 of the STEAP-1 amino acid sequence as shown in FIG. 1A-B (WKMKPRRNLEEDDYL; SEQ ID NO: 22). In another embodiment, typical polypeptides of the invention can contain one or more predicted HLA-A2 binding peptides such as amino acids 165-173 of STEAP-1, amino acids 86-94 of STEAP-1, amino acids 262-270 of STEAP-1, amino acids 302-310 of STEAP-1, amino acids 158-166 of STEAP-1, amino acids 227-235 of STEAP-2, amino acids 402-410 of STEAP-2, amino acids 307-315 of STEAP-2, amino acids 306-314 of STEAP-2, and amino acids 100-108 of STEAP-2. In another embodiment, typical polypeptides of the invention consist of aU or part of a fragment of STEAP-2, such as amino acids 1-245, 2-204, 121-454, 153-165, 182-454, 183-387, 276-453, 345-358, or 419- 454 of the STEAP-2 protein shown in FIG. 8. Related embodiments of these inventions include polypeptides containing combinations of the different motifs discussed above with preferable embodiments being those that contain no insertions, deletions or substitutions either within the motifs or the intervening sequences of these polypeptides. STEAP polypeptides can be generated using standard peptide synthesis technology or using chemical cleavage methods weU known in the art based on the ammo acid sequences of the human STEAP protems disclosed herem. Alternatively, recombmant methods can be used to generate nucleic acid molecules that encode a polypeptide fragment of a STEAP protem. In this regard, the STEAP-encoding nucleic acid molecules descnbed herem provide means for generating defined fragments of STEAP proteins. STEAP polypeptides are particularly useful m generating and charactenzmg domain specific antibodies (e.g, antibodies recognizing an extraceUular or mtraceUular epitope of a STEAP protem), m identifying agents or ceUular factors that bmd to STEAP or a particular structural domam thereof, and m various therapeutic contexts, mcluding but not limited to cancer vaccmes. STEAP polypeptides containing particularly interesting structures can be predicted and/or identified usmg vanous analytical techmques weU known m the art, mcluding, for example, the methods of Chou-Fasman, Garnier-Robson, Kyte-Doohtde, Eisenberg, Karplus-Schultz or Jameson- Wolf analysis, or on the basis of immunogenicity. Fragments contaimng such structures are particularly useful in generating subunit specific anti-STEAP antibodies or m identifying ceUular factors that bmd to STEAP. In a specific embodiment descnbed m the examples that foUow, a secreted form of STEAP may be conveniendy expressed m 293T ceUs transfected with a CMV-dnven expression vector encoding STEAP with a C-terminal 6XHιs and MYC tag (pcDNA3.1/mycHIS, Invitrogen). The secreted HIS-tagged STEAP m the culture media may be punfied usmg a mckel column and standard techmques. Alternatively, an AP-tag system may be used Various constructs for expression of STEAP are descnbed in the examples below. Modifications of STEAP such as covalent modifications are mcluded within the scope of this invention. One type of covalent modification includes reacting targeted am o acid residues of an STEAP polypeptide with an orgamc denvatizmg agent that is capable of reacting with selected side chains or the N- or C- terminal residues of the STEAP. Another type of covalent modification of the STEAP polypeptide mcluded within the scope of this invention compnses altermg the native glycosylation pattern of the polypeptide. "Altermg the native glycosylation pattern" is mtended for purposes herem to mean deleting one or more carbohydrate moieties found m native sequence STEAP (either by removing the underlymg glycosylation site or by deleting the glycosylation by chemical and/or enzymatic means), and/or adding one or more glycosylation sites that are not present m the native sequence STEAP. In addition, the phrase mcludes qualitative changes m the glycosylation of the native protems, involving a change m the nature and proportions of the various carbohydrate moieties present Another type of covalent modification of STEAP comprises linking the STEAP polypeptide to one of a vanety of nonprotemaceous polymers, e.g, polyethylene glycol (PEG), polypropylene glycol, or polyoxyalkylenes, in the manner set forth in U.S. Patent Nos. 4,640,835; 4,496,689; 4,301,144; 4,670,417; 4,791,192 or 4,179,337. The STEAP of the present invention may also be modified m a way to form a chimeric molecule comprising STEAP fused to another, heterologous polypeptide or ammo acid sequence. In one embodiment, such a chimeric molecule comprises a fusion of the STEAP with a polyhistidine epitope tag, which provides an epitope to which immobilized mckel can selectively bmd. The epitope tag is generaUy placed at the amino- or carboxyl- terminus of the STEAP. In an alternative embodiment, the chimeric molecule may comprise a fusion of the STEAP with an immunoglobulin or a particular region of an lmmunoglobultn. For a bivalent form of the chimenc molecule (also referred to as an "immunoadhesin"), such a fusion could be to the Fc region of an IgG molecule. The Ig fusions preferably mclude the substitution of a soluble (transmembrane domain deleted or inactivated) form of an STEAP polypeptide m place of at least one vanable region withm an Ig molecule. In a particularly preferred embodiment, the immunoglobulin fusion mcludes the hmge, CH2 and CH3, or the hinge, CHI, CH2 and CH3 regions of an IgGl molecule. For the production of immunoglobulin fusions see also US Patent No. 5,428,130 issued June 27, 1995. STEAP ANTIBODIES Another aspect of the invention provides antibodies that bmd to STEAP protems and polypeptides. The most preferred antibodies wiU selectively bind to a STEAP protem and wiU not bmd (or wiU bmd weakly) to non-STEAP protems and polypeptides. Anti-STEAP antibodies that are particularly contemplated mclude monoclonal and polyclonal antibodies as weU as fragments containing the antigen- binding domain and/or one or more complementanty determining regions of these antibodies. As used herem, an antibody fragment is defined as at least a portion of the variable region of the immunoglobulin molecule that bmds to its target, ι.e, the antigen bmdmg region. For some applications, it may be desirable to generate antibodies which specificaUy react with a particular STEAP protem and/or an epitope within a particular structural domain. For example, preferred antibodies useful for cancer therapy and diagnostic imaging purposes are those which react with an epitope an extraceUular region of the STEAP protem as expressed in cancer ceUs. Such antibodies may be generated by usmg the STEAP protems descnbed herem, or usmg peptides denved from predicted extraceUular domains thereof, as an immunogen. In this regard, with reference to the STEAP-1 protem topological schematic shown m FIG IB, regions m the extraceUular loops between the indicated transmembrane domains may be selected as used to design appropnate rmmunogens for raising extraceUular-specific antibodies. STEAP antibodies of the invention may be particularly useful m prostate cancer therapeutic strategies, diagnostic and prognostic assays, and imaging methodologies. Siπularly, such antibodies may be useful m the treatment, diagnosis, and/or prognosis of other cancers, to the extent STEAP is also expressed or overexpressed in other types of cancer The invention provides various immunological assays useful for the detection and quantification of STEAP and mutant STEAP protems and polypeptides. Such assays generaUy comprise one or more STEAP antibodies capable of recognizing and bmdmg a STEAP or mutant STEAP protem, as appropnate, and may be performed withm various immunological assay formats weU known m the art, mcluding but not limited to various types of radioimmunoassays, enzyme- nked immunosorbent assays (ELI SA), enzyme-hnked lmmunofluorescent assays (ELIFA), and the like. In addition, immunological imaging methods capable of detecting prostate cancer are also provided by the invention, including but limited to radioscintigraphic imaging methods usmg labeled STEAP antibodies. Such assays may be used cli caUy m the detection, monitoring, and prognosis of prostate cancer, particularly advanced prostate cancer. STEAP antibodies may also be used m methods for punfymg STEAP and mutant STEAP protems and polypeptides and for isolating STEAP homologues and related molecules. For example, m one embodiment, the method of punfymg a STEAP protem comprises incubating a STEAP antibody, which has been coupled to a solid matrix, with a lysate or other solution containing STEAP under conditions which permit the STEAP antibody to bind to STEAP; washing the solid matrix to eliminate impurities; and eluting the STEAP from the coupled antibody. Other uses of the STEAP antibodies of the invention include generating anti-idiotypic antibodies that mimic the STEAP protein. STEAP antibodies may also be used therapeuticaUy by, for example, modulating or inhibiting the biological activity of a STEAP protein or targeting and destroying cancer ceUs expressing a STEAP protein. Antibody therapy of prostate and other cancers is more specificaUy described in a separate subsection below. Various methods for the preparation of antibodies are weU known in the art. For example, antibodies may be prepared by immunizing a suitable mammahan host using a STEAP protein, peptide, or fragment, in isolated or immunoconjugated form (Antibodies: A Laboratory Manual, CSH Press, Eds, Harlow, and Lane (1988); Harlow, Antibodies, Cold Spring Harbor Press, NY (1989)). Examples of protein immunogens include recombinant STEAP (expressed in a baculovirus system, mammalian system, etc.), STEAP extraceUular domain or extraceUular loops of STEAP protein conjugated to one or more antibody constant regions, AP-tagged STEAP, etc. In addition, fusion proteins of STEAP may also be used, such as a fusion of STEAP with GST, maltose- binding protein (MBP), green fluorescent protein (GFP), HisMax-TOPO or MycHis (see Examples below). In a particular embodiment, a GST fusion protein comprising aU or most of an open reading frame amino acid sequence as shown in Fig. 11 A-B may be produced and used as an immunogen to generate appropriate antibodies. CeUs expressing or overexpressing STEAP may also be used for imn unizations. SimUarly, any ceU engineered to express STEAP may be used. Such strategies may result in the production of monoclonal antibodies with enhanced capacities for recognizing endogenous STEAP. Another useful immunogen comprises STEAP peptides linked to the plasma membrane of sheep red blood ceUs. The amino acid sequences of STEAP proteins as shown in Fig. 11A-B may be used to select specific regions of a STEAP protein for generating antibodies. For example, hydrophobicity and hydrophuicity analyses of the STEAP amino acid sequence may be used to identify hydrophilic regions in the STEAP structure. Regions of the STEAP protein that show immunogenic structure, as weU as other regions and domains, can readily be identified using various other methods known in the art, such as Chou- Fasman, Gamier Robson, Kyte-Doolittle, Eisenberg, Karplus-Schultz or Jameson- Wolf analysis. Peptides of STEAP predicted to bind HLA-A2 may be selected for the generation of antibodies or used to generate a CTL response. Such predicted HLN-A2 binding peptides include, but are not limited to, amino acids 165-173 of STEAP-1, amino acids 86-94 of STEAP-1, amino acids 262-270 of STEAP-1, amino acids 302-310 of STEAP-1, amino acids 158-166 of STEAP-1, amino acids 227-235 of STEAP-2, amino acids 402-410 of STEAP-2, amino acids 307-315 of STEAP-2, amino acids 306- 314 of STEAP-2, and amino acids 100-108 of STEAP-2. As discussed in the examples below, immunogenicity has been demonstrated with STEAP, which was used to generate polyclonal and monoclonal antibodies using rabbits and mice, respectively. This B ceU response (antibody production) is the result of an initial T ceU response elicited by the immunogenic portions of STEAP. Methods for preparing a protein or polypeptide for use as an immunogen and for preparing immunogenic conjugates of a protein with a carrier such as BSA, KLH, or other carrier proteins are weU known in the art. In some circumstances, direct conjugation using, for example, carbodiimide reagents may be used; in other instances linking reagents such as those supplied by Pierce Chemical Co, Rockford, IL, may be effective. Administration of a STEAP immunogen is conducted generaUy by injection over a suitable period and with use of a suitable adjuvant, as is generaUy understood in the art. During the imrnunization schedule, titers of antibodies can be taken to determine adequacy of antibody formation. STEAP monoclonal antibodies are preferred and may be produced by various means weU known in the art. For example, immortalized ceU lines which secrete a desired monoclonal antibody may be prepared using the standard hybridoma technology of Kohler and MUstein or modifications which immortalize producing B ceUs, a is generaUy known. The immortalized ceU lines secreting the desired antibodies are screened by immunoassay in which the antigen is the STEAP protein or STEAP fragment. When the appropriate immortalized ceU culture secreting the desired antibody is identified, the ceUs may be expanded and antibodies produced either from in vitro cultures or from ascites fluid. The antibodies or fragments may also be produced, using current technology, by recombinant means. Regions that bind specificaUy to the desired regions of the STEAP protein can also be produced in the context of chimeric or CDR grafted antibodies of multiple species origin. Humanized or human STEAP antibodies may also be produced and are preferred for use in therapeutic contexts. Methods for humanizing murine and other non-human antibodies by substituting one or more of the non-human antibody CDRs for corresponding human antibody sequences are weU known (see for example, Jones et al, 1986, Nature 321: 522-525; Riechmann et al, 1988, Nature 332: 323-327; Verhoeyen et al, 1988, Science 239:1534-1536). See also, Carter et al, 1993, Proc. Nat'l Acad. Sci. USA 89: 4285 and Sims et al, 1993, J. Immunol. 151: 2296. Methods for producing fully human monoclonal antibodies include phage display and transgenic animal technologies (for review, see Vaughan et al, 1998, Nature Biotechnology 16: 535- 539). Fully human STEAP monoclonal antibodies may be generated using cloning technologies employing large human Ig gene combinatorial hbraries (i.e, phage display) (Griffiths and Hoogenboom, Building an in vitro immune system: human antibodies from phage display hbraries. In: Protein Engineering of Antibody Molecules for Prophylactic and Therapeutic Applications in Man. Clark, M. (Ed.), Nottingham Academic, pp 45-64 (1993); Burton and Barbas, Human Antibodies from combinatorial hbraries. Id, pp 65-82). Fully human STEAP monoclonal antibodies may also be produced using transgenic mice engineered to contain human immunoglobulin gene loci as described in U.S. Patent No. 6,150,584 and in PCT Patent Application W098/24893, pubhshed December 3, 1997 (see also, Jakobovits, 1998, Exp. Opin. Invest. Drugs 7(4): 607-614). This method avoids the in vitro manipulation required with phage display technology and efficiendy produces high affinity authentic human antibodies. Reactivity of STEAP antibodies with a STEAP protein may be estabhshed by a number of weU known means, including western blot, immunoprecipitation, ELISA, and FACS analyses using, as appropriate, STEAP proteins, peptides, STEAP expressing ceUs or extracts thereof. A STEAP antibody or fragment thereof of the invention may be labeled with a detectable marker or conjugated to a second molecule, such as a cytotoxin or other therapeutic agent, and used for targeting the second molecule to a STEAP positive ceU (Vitetta, E.S. et al, 1993, Immunotoxin therapy, in DeVita, Jr., V.T. et al, eds. Cancer: Principles and Practice of Oncology, 4th ed, J.B. Lippincott Co, Philadelphia, 2624- 2636). Examples of cytotoxic agents include, but are not limited to ricin, ricin A-chain, doxorubicin, maytansinoids, daunorubicin, taxol, ethidium bromide, mitomycin, etoposide, tenoposide, vincristine, vinblastine, colchicine, dihydroxy anthracin dione, actinomycin, diphtheria toxin, Pseudomonas exotoxin (PE) A, PE40, abrin, abrin A chain, modeccin A chain, alpha-sarcin, gelonin, mitogellin, retstrictocin, phenomycin, enomycin, curicin, crotin, cahcheamicin, sapaonaria officinahs inhibitor, and glucocorticoid and other chemotherapeutic agents, as weU as radioisotopes such as 212 Bi, 131 I, 131 In, 90 Y, and 186 Re. Suitable detectable markers include, but are not limited to, a radioisotope, a fluorescent compound, a bioluminescent compound, chemUutninescent compound, a metal chelator or an enzyme. Antibodies may also be conjugated to an anti- cancer pro-drug activating enzyme capable of converting the pro-drug to its active form. See, for example, US Patent No. 4,975,287. Further, bi-specific antibodies specific for two or more STEAP epitopes may be generated using methods generaUy known in the art. Further, antibody effector functions may be modified to enhance the therapeutic effect of STEAP antibodies on cancer ceUs. For example, cysteine residues may be engineered into the Fc region, permitting the formation of interchain disulfide bonds and the generation of homodimers which may have enhanced capacities for internaUzation, ADCC and/or complement mediated ceU killing (see, for example, Caron et al, 1992, J. Exp. Med. 176: 1191-1195; Shopes, 1992, J. Immunol. 148: 2918-2922). Homodimeric antibodies may also be generated by cross-linking techniques known in the art (e.g., Wolff et al. Cancer Res. 53: 2560-2565). STEAP TRANSGENIC ANIMALS Nucleic acids that encode STEAP or its modified forms can also be used to generate either transgenic animals or "knock out" animals which, in turn, are useful in the development and screening of therapeuticaUy useful reagents. A transgenic animal (e.g, a mouse or rat) is an animal having ceUs that contain a transgene, which transgene was introduced into the animal or an ancestor of the animal at a prenatal, e.g, an embryonic stage. A transgene is a DNA that is integrated into the genome of a ceU from which a transgenic animal develops. In one embodiment, cDNA encoding STEAP can be used to clone genomic DNA encoding STEAP in accordance with established techniques and the genomic sequences used to generate transgenic animals that contain ceUs that express DNA encoding STEAP. Methods for generating transgenic animals, particularly animals such as mice or rats, have become conventional in the art and are described, for example, in U.S. Patent Nos. 4,736,866 and 4,870,009. TypicaUy, particular ceUs would be targeted for STEAP transgene incorporation with tissue-specific enhancers. Transgenic animals that include a copy of a transgene encoding STEAP introduced into the germ line of the animal at an embryonic stage can be used to examine the effect of increased expression of DNA encoding STEAP. Such animals can be used as tester animals for reagents thought to confer protection from, for example, pathological conditions associated with its overexpression. In accordance with this facet of the invention, an animal is treated with the reagent and a reduced incidence of the pathological condition, compared to untreated animals bearing the transgene, would indicate a potential therapeutic intervention for the pathological condition. Alternatively, non-human homologues of STEAP can be used to construct a STEAP "knock out" animal that has a defective or altered gene encoding STEAP as a result of homologous recombination between the endogenous gene encoding STEAP and altered genomic DNA encoding STEAP introduced into an embryonic ceU of the animal. For example, cDNA encoding STEAP can be used to clone genomic DNA encoding STEAP in accordance with established techniques. A portion of the genomic DNA encoding STEAP can be deleted or replaced with another gene, such as a gene encoding a selectable marker that can be used to monitor integration. TypicaUy, several ldlobases of unaltered flanking DNA (both at the 5' and 3' ends) are included in the vector (see e.g, Thomas and Capecchi, 1987, CeU 51:503 for a description of homologous recombination vectors). The vector is introduced into an embryonic stem ceU line (e.g, by electroporation) and ceUs in which the introduced DNA has homologously recombined with the endogenous DNA are selected (see e.g, Li et al, 1992, CeU 69:915). The selected ceUs are then injected into a blastocyst of an animal (e.g, a mouse or rat) to form aggregation chimeras (see e.g, Bradley, in Teratocaranomas and Embryomc Stem Cells: A Practical Approach, E. J. Robertson, ed, IRL, Oxford, 1987, pp. 113-152). A chimeric embryo can then be implanted mto a suitable pseudopregnant female foster animal and the embryo brought to term to create a "knock out" animal. Progeny harbormg the homologously recombmed DNA m their germ ceUs can be identified by standard techmques and used to breed animals m which aU ceUs of the animal contam the homologously recombined DNA. Knockout animals can be characterized for mstance, for their ability to defend agamst certain pathological conditions and for their development of pathological conditions due to absence of the STEAP polypeptide. MONITORING THE STATUS OF STEAP AND ITS PRODUCTS Assays that evaluate the status of a STEAP gene and STEAP gene products m an individual may provide information on the growth or oncogenic potential of a biological sample from this individual. For example, because STEAP mRNA is so highly expressed m prostate, and not in most normal tissue, and because its expression is associated with certain cancers, assays that evaluate the relative levels of STEAP mRNA transcnpts or protems m a biological sample may be used to diagnose a disease associated with STEAP dysregulation, such as cancer or benign prostatic hyperplasia (BPH), and may provide prognostic information useful m defining appropnate therapeutic options. Similarly, assays that evaluate the mtegnty STEAP nucleotide and ammo acid sequences in a biological sample, may also be used in this context. The finding that STEAP mRNA is expressed m prostate and other cancers, and not in most normal tissue, provides evidence that this gene is associated with dysregulated ceU growth and therefore identifies this gene and its products as targets that the skiUed artisan can use to evaluate biological samples from mdividuals suspected of having a disease associated with STEAP dysregulation. In another example, because the expression of STEAP is normaUy restncted to prostate, one can also evaluate biological samples taken from other tissues to detect STEAP expression as an indication of metastasis. For example, as shown m Figure 31A-F, antibodies directed to STEAP-1 provide a supenor marker for detection of metastases, as compared to the conventional prostate cancer marker, PSA. Such a marker can be useful both m evaluation tissue biopsies and as part of in vivo imaging strategies. In this context, the evaluation of the expression status of STEAP gene and its products can be used to gain information on the disease potential of a tissue sample. The terms "expression status" in this context is used to broadly refer to the variety of factors involved in the expression, function and regulation of a gene and its products such as the level of mRNA expression, the integrity of the expressed gene products (such as the nucleic and amino acid sequences) and transcriptional and translational modifications to these molecules. The expression status of STEAP may provide information useful for predicting susceptibility to particular disease stages, progression, and/ or tumor aggressiveness. The invention provides methods and assays for determining STEAP expression status and diagnosing cancers that express STEAP, such as cancers of the prostate. STEAP expression status in patient samples may be analyzed by a number of means weU known in the art, including without limitation, i ninunohistochemical analysis, in situ hybridization, RT-PCR analysis on laser capture micro-dissected samples, western blot analysis of clinical samples and ceU lines, and tissue array analysis. Typical protocols for evaluating the expression status of the STEAP gene and gene products can be found, for example in Current Protocols In Molecular -Biology, Units 2 [Northern Blotting], 4 [Southern Blotting], 15 [Immunoblotting] and 18 [PCR Analysis], Frederick M. Ausubul et al. eds, 1995. In one aspect, the invention provides methods for monitoring STEAP gene products by determining the status of STEAP gene products expressed by ceUs in a test tissue sample from an individual suspected of having a disease associated with dysregulated ceU growth (such as hyperplasia or cancer) and then comparing the status so determined to the status of STEAP gene products in a corresponding normal sample, the presence of aberrant or altered status of STEAP gene products in the test sample relative to the normal sample providing an indication of the presence of dysregulated ceU growth within the ceUs of the individual. The invention additionaUy provides methods of examining a biological sample for evidence of dysregulated ceUular growth. In one embodiment, the method comprises comparing the status of STEAP in the biological sample to the status of STEAP in a corresponding normal sample, wherein alterations in the status of STEAP in the biological sample are associated with dysregulated ceUular growth. The status of STEAP in the biological sample can be evaluated by, for example, exarriining levels of STEAP mRNA expression or levels of STEAP protein expression. In one embodiment, an alteration in the status of STEAP is identified by the presence of STEAP expressing ceUs in a biological sample from a tissue in which STEAP expressing ceUs are normaUy absent. In another aspect, the invention provides assays useful in deten_aining the presence of cancer in an individual, comprising detecting a significant increase in STEAP mRNA or protein expression in a test ceU or tissue sample relative to expression levels in the corresponding normal ceU or tissue. The presence of STEAP mRNA may, for example, be evaluated in tissue samples including but not limited to colon, lung, prostate, pancreas, bladder, breast, ovary, cervix, testis, head and neck, brain, stomach, bone, etc. The presence of significant STEAP expression in any of these tissues may be useful to indicate the emergence, presence and/or severity of these cancers or a metastasis of cancer originating in another tissue, since the corresponding normal tissues do not express STEAP mRNA or express it at lower levels. In a related embodiment, STEAP expression status may be determined at the protein level rather than at the nucleic acid level. For example, such a method or assay would comprise determining the level of STEAP protein expressed by ceUs in a test tissue sample and comparing the level so determined to the level of STEAP expressed in a corresponding normal sample. In one embodiment, the presence of STEAP protein is evaluated, for example, using immunohistochemical methods. STEAP antibodies or binding partners capable of detecting STEAP protein expression may be used in a variety of assay formats weU known in the art for this purpose. As shown in the accompanying examples, STEAP immunoreactivity is associated with prostate, bladder and lung cancer, as weU as BPH and prostate cancer metastases. In other related embodiments, one can evaluate the integrity STEAP nucleotide and amino acid sequences in a biological sample in order to identify perturbations in the structure of these molecules such as insertions, deletions, substitutions and the like. Such embodiments are useful because perturbations in the nucleotide and amino acid sequences are observed in a large number of proteins associated with a growth dysregulated phenotype (see e.g. Marrogi et al, J. Cutan. Pathol. 26(8): 369-378 (1999)). In this context, a wide variety of assays for observing perturbations in nucleotide and amino acid sequences are weU known in the art. For example, the size and structure of nucleic acid or amino acid sequences of STEAP gene products may be observed by the northern, Southern, western, PCR and DNA sequencing protocols discussed herein. In addition, other methods for observing perturbations in nucleotide and amino acid sequences such as single strand conformation polymorphism analysis are weU known in the art (see e.g. U.S. Patent Nos. 5,382,510 and 5,952,170). In another embodiment, one can examine the methylation status of the STEAP gene in a biological sample. Aberrant demethylation and/or hypermethylation of CpG islands in gene 5' regulatory regions frequently occurs in immortalized and transformed ceUs and can result in altered expression of various genes. For example, promoter hypermethylation of the pi-class glutathione S-transferase (a protein expressed in normal prostate but not expressed in >90% of prostate carcinomas) appears to permanently silence transcription of this gene and is the most frequendy detected genomic alteration in prostate carcinomas (De Marzo et al, 1999, Am. J. Pathol. 155(6): 1985-1992). In addition, this alteration is present in at least 70% of cases of high-grade prostatic intraepithelial neoplasia (PIN) (Brooks et al, 1998, Cancer Epidemiol. Biomarkers Prev, 7:531-536). In another example, expression of the LAGE-I tumor specific gene (which is not expressed in normal prostate but is expressed in 25-50% of prostate cancers) is induced by deoxy-azacytidine in lymphoblastoid ceUs, suggesting that tumoral expression is due to demethylation (Lethe et al, 1998, Int. J. Cancer 76(6): 903-908). In this context, a variety of assays for examining methylation status of a gene are weU known in the art. For example, one can utilize in Southern hybridization approaches methylation-sensitive restriction enzymes which can not cleave sequences that contain methylated CpG sites in order to assess the overaU methylation status of CpG islands. In addition, MSP (methylation specific PCR) can rapidly profile the methylation status of aU the CpG sites present in a CpG island of a given gene. This procedure involves initial modification of DNA by sodium bisulfite (which wiU convert aU unmethylated cytosines to uradl) foUowed by amphfication using primers specific for methylated versus unmethylated DNA. Protocols involving methylation interference can also be found for example in Current Protocols In Molecular Biology, Units 12, Frederick M. Ausubel et al. eds, 1995. In another related embodiment, the invention provides assays useful in determining the presence of cancer in an individual, comprising detecting a significant change in the STEAP alternative sphce variants expressed in a test ceU or tissue sample relative to expression levels in the corresponding normal ceU or tissue. The monitoring of alternative sphce variants of STEAP is useful because changes in the alternative splicing of proteins is suggested as one of the steps in a series of events that lead to the progression of cancers (see e.g. Carstens et al, Oncogene 15(250: 3059-3065 (1997)). Gene amphfication provides an additional method of assessing the status of STEAP. Gene amphfication may be measured in a sample direcdy, for example, by conventional Southern blotting, northern blotting to quantitate the transcription of mRNA [Thomas, Proc. Natl. Acad. Sci. USA, 77:5201-5205 (1980)], dot blotting (DNA analysis), or in situ hybridization, using an appropriately labeled probe, based on the sequences provided herein. Alternatively, antibodies may be employed that can recognize specific duplexes, including DNA duplexes, RNA duplexes, and DNA -RNA hybrid duplexes or DNA -protein duplexes. The antibodies in turn may be labeled and the assay may be carried out where the duplex is bound to a surface, so that upon the formation of duplex on the surface, the presence of antibody bound to the duplex can be detected. In addition to the tissues discussed above, peripheral blood may be conveniently assayed for the presence of cancer ceUs, including but not limited to prostate cancers, using RT-PCR to detect STEAP expression. The presence of RT-PCR amplifiable STEAP mRNA provides an indication of the presence of the cancer. RT-PCR detection assays for tumor ceUs in peripheral blood are currently being evaluated for use in the diagnosis and management of a number of human solid tumors. In the prostate cancer field, these include RT-PCR assays for the detection of ceUs expressing PSA and PSM (Verkaik et al, 1997, Urol. Res. 25: 373-384; Ghossein et al, 1995, J. Clin. Oncol. 13: 1195-2000; Heston et al, 1995, Clin. Chem. 41: 1687-1688). RT-PCR assays are weU known in the art. A related aspect of the invention is directed to predicting susceptibility to developing cancer in an individual. In one embodiment, a method for predicting susceptibility to cancer comprises detecting STEAP mRNA or STEAP protein in a tissue sample, its presence indicating susceptibility to cancer, wherein the degree of STEAP mRNA expression present is proportional to the degree of susceptibility. In a specific embodiment, the presence of STEAP in prostate tissue is examined, with the presence of STEAP in the sample providing an indication of prostate cancer susceptibility (or the emergence or existence of a prostate tumor). In a closely related embodiment, one can evaluate the lntegnty STEAP nucleotide and ammo acid sequences m a biological sample in order to identify perturbations in the structure of these molecules such as msertions, deletions, substitutions and the like, with the presence of one or more perturbations m STEAP gene products m the sample providing an indication of cancer susceptibility (or the emergence or existence of a tumor). Yet another related aspect of the invention is directed to methods for gauging tumor aggressiveness. In one embodiment, a method for gauging aggressiveness of a tumor compnses determining the level of STEAP mRNA or STEAP protem expressed by ceUs in a sample of the tumor, comparing the level so determined to the level of STEAP mRNA or STEAP protem expressed in a conespondmg normal tissue taken from the same mdividual or a normal tissue reference sample, wherem the degree of STEAP mRNA or STEAP protem expression m the tumor sample relative to the normal sample indicates the degree of aggressiveness. In a specific embodiment, aggressiveness of prostate tumors is evaluated by determining the extent to which STEAP is expressed m the tumor ceUs, with higher expression levels indicating more aggressive tumors. In a closely related embodiment, one can evaluate the lntegnty STEAP nucleotide and ammo acid sequences in a biological sample m order to identify perturbations m the structure of these molecules such as msertions, deletions, substitutions and the like, with the presence of one or more perturbations indicating more aggressive tumors. Yet another related aspect of the invention is directed to methods for observing the progression of a malignancy m an mdividual over time. In one embodiment, methods for observing the progression of a malignancy m an mdividual over time compnse detenriining the level of STEAP mRNA or STEAP protem expressed by ceUs in a sample of the tumor, comparing the level so determined to the level of STEAP mRNA or STEAP protem expressed m an equivalent tissue sample taken from the same mdividual at a different time, wherem the degree of STEAP mRNA or STEAP protem expression m the tumor sample over time provides information on the progression of the cancer. In a specific embodiment, the progression of a cancer is evaluated by determining the extent to which STEAP expression in the tumor cells alters over time, with higher expression levels indicating a progression of the cancer. In a closely related embodiment, one can evaluate the integrity STEAP nucleotide and amino acid sequences in a biological sample in order to identify perturbations in the structure of these molecules such as insertions, deletions, substitutions and the like, with the presence of one or more perturbations indicating a progression of the cancer. The above diagnostic approaches may be combined with any one of a wide variety of prognostic and diagnostic protocols known in the art. For example, another embodiment of the invention disclosed herein is directed to methods for observing a coincidence between the expression of STEAP gene and STEAP gene products (or perturbations in STEAP gene and STEAP gene products) and a factor that is associated with mahgnancy as a means of diagnosing and prognosticating the status of a tissue sample. In this context, a wide variety of factors associated with mahgnancy may be utilized such as the expression of genes otherwise associated with mahgnancy (including PSA, PSCA and PSM expression) as weU as gross cytological observations (see e.g. Bocking et al, 1984, Anal. Quant. Cytol. 6(2):74-88; Epstein, 1995, Hum. Pathol. 1995 Feb;26(2):223-9; Thorson et al, 1998, Mod. Pathol. 11(6):543-51; Baisden et al, 1999, Am. J. Surg. Pathol. 23(8):918-24). Methods for observing a coincidence between the expression of STEAP gene and STEAP gene products (or perturbations in STEAP gene and STEAP gene products) and an additional factor that is associated with mahgnancy are useful, for example, because the presence of a set or consteUation of specific factors that coincide provides information crucial for diagnosing and prognosticating the status of a tissue sample. In a typical embodiment, methods for observing a coincidence between the expression of STEAP gene and STEAP gene products (or perturbations in STEAP gene and STEAP gene products) and a factor that is associated with mahgnancy entaUs detecting the overexpression of STEAP mRNA or protein in a tissue sample, detecting the overexpression of PSA mRNA or protein in a tissue sample, and observing a coincidence of STEAP mRNA or protein and PSA mRNA or protein overexpression. In a specific embodiment, the expression of STEAP and PSA mRNA in prostate tissue is examined. In a preferred embodiment, the coincidence of STEAP and PSA mRNA overexpression in the sample provides an indication of prostate cancer, prostate cancer susceptibility or the emergence or existence of a prostate tumor. Methods for detecting and quantifying the expression of STEAP mRNA or protein are described herein and use standard nucleic acid and protein detection and quantification technologies weU known in the art. Standard methods for the detection and quantification of STEAP mRNA include in situ hybridization using labeled STEAP riboprobes, northern blot and related techniques using STEAP polynucleotide probes, RT-PCR analysis using primers specific for STEAP, and other amphfication type detection methods, such as, for example, branched DNA, SISBA, TMA and the like. In a specific embodiment, semi- quantitative RT-PCR may be used to detect and quantify STEAP mRNA expression as described in the Examples that foUow. Any number of primers capable of amplifying STEAP may be used for this purpose, including but not limited to the various primer sets specificaUy described herein. Standard methods for the detection and quantification of protein may be used for this purpose. In a specific embodiment, polyclonal or monoclonal antibodies specificaUy reactive with the wUd-type STEAP protein may be used in an immunohistochemical assay of biopsied tissue. Antibodies directed against STEAP protein can also be used to detect STEAP in a patient specimen (e.g, blood, urine, semen or other sample) using conventional techniques such as fluorescence-activated ceU sorting (FACS) and/or ELISA. IDENTIFYING MOLECULES THAT INTERACT WITH STEAP The STEAP protein sequences disclosed herein aUow the skilled artisan to identify proteins, smaU molecules and other agents that interact with STEAP and pathways activated by STEAP via any one of a variety of art accepted protocols. For example one can utilize one of the variety of so-caUed interaction trap systems (also referred to as the "two-hybrid assay"). In such systems, molecules that interact reconstitute a transcription factor and direct expression of a reporter gene, the expression of which is then assayed. Typical systems identify protein-protein interactions in vivo through reconstitution of a eukaryotic transcriptional activator and are disclosed for example in U.S. Patent Nos. 5,955,280, 5,925,523, 5,846,722 and 6,004,746. Alternatively one can identify molecules that interact with STEAP protein sequences by screening peptide hbraries. In such methods, peptides that bind to selected receptor molecules such as STEAP are identified by screening hbraries that encode a random or controUed coUection of amino acids. Peptides encoded by the hbraries are expressed as fusion proteins of bacteriophage coat proteins, and bacteriophage particles are then screened against the receptors of interest. Peptides having a wide variety of uses, such as therapeutic or diagnostic reagents, may thus be identified without any prior information on the structure of the expected ligand or receptor molecule. Typical peptide hbraries and screening methods that can be used to identify molecules that interact with STEAP protein sequences are disclosed for example in U.S. Patent Nos. 5,723,286 and 5,733,731. Alternatively, ceU lines expressing STEAP can be used to identify protein-protein interactions mediated by STEAP. This possibility can be examined using immunoprecipitation techniques as shown by others (HamUton BJ, et al. Biochem. Biophys. Res. Commun. 1999, 261:646-51). TypicaUy STEAP protein can be imrnunoprecipitated from STEAP expressing prostate cancer ceU lines using anti-STEAP antibodies. Alternatively, antibodies against His-tag can be used in a ceU line engineered to express STEAP (vectors mentioned above). The imrnunoprecipitated complex can be examined for protein association by procedures such as western blotting, 35 S-methionine labeling of proteins, protein microsequencing, sUver staining and two dimensional gel electrophoresis. SmaU molecules that interact with STEAP can be identified through related embodiments of such screening assays. For example, smaU molecules can be identified that interfere with STEAP function, including molecules that interfere with STEAP's ability to bind to ceUs and/or to modulate tumor formation, progression, migration and/or apoptosis. Typical methods are discussed for example in U.S. Patent No. 5,928,868 and include methods for forming hybrid ligands in which at least one hgand is a smaU molecule. In an iUustrative embodiment, the hybrid hgand is introduced into ceUs that in turn contain a first and a second expression vector. Each expression vector includes DNA for expressing a hybrid protein that encodes a target protein linked to a coding sequence for a transcriptional module. The ceUs further contains a reporter gene, the expression of which is conditioned on the proximity of the first and second hybrid proteins to each other, an event that occurs only if the hybrid hgand binds to target sites on both hybrid proteins. Those ceUs that express the reporter gene are selected and the unknown smaU molecule or the unknown hybrid protein is identified. A typical embodiment of this invention consists of a method of screening for a molecule that interacts with a STEAP amino acid sequence shown in Fig. 11 A-B, comprising the steps of contacting a population of molecules with the STEAP amino acid sequence, aUowing the population of molecules and the STEAP amino acid sequence to interact under conditions that facilitate an interaction, determining the presence of a molecule that interacts with the STEAP amino acid sequence and then separating molecules that do not interact with the STEAP amino acid sequence from molecules that do interact with the STEAP amino acid sequence. In a specific embodiment, the method further includes purifying a molecule that interacts with the STEAP amino acid sequence. In a preferred embodiment, the STEAP amino acid sequence is contacted with a library of peptides. Additional assays for identifying molecules that modulate STEAP function are described in the Examples that foUow. The invention additionaUy provides a method of screening for a molecule that modulates the activity of STEAP or a STEAP-related pathway. The method comprises contacting a molecule with a ceU that expresses a STEAP protein and deterrriining the activity of STEAP or a STEAP-related pathway. The determining can be via use of one of the phosphorylation assays described in the examples that foUow, such as western blotting with an antibody directed to a phosphorylated signaling molecule. Alterations in the phosphorylation of the signaling molecule indicate a candidate molecule that modulates the activity of STEAP or a STEAP-related pathway. THERAPEUTIC METHODS AND COMPOSITIONS The identification of STEAP as a prostate cancer protein opens a number of therapeutic approaches to the treatment of prostate and other STEAP-associated cancers. As discussed above, STEAP is a transmembrane protein, and its interaction with other ceUs and molecules likely plays a role in the regulation of the prostate environment and the initiation, development and/or progression of cancer. STEAP can be targeted for therapy via approaches aimed at inhibiting activity of the STEAP protein, inhibiting the binding or association of STEAP protein with other ceUs and molecules, inhibiting transcription or translation of STEAP, and/or via the use of cancer vaccines based on STEAP. The therapeutic strategy can thus be designed to inhibit a function of the molecule or to target the STEAP molecule itself. The expression profile of STEAP is reminiscent of the MAGEs, PSA and PMSA, which are tissue-specific genes that are up-regulated in melanomas and other cancers (Van den Eynde and Boon, Int J Clin Lab Res. 27:81-86, 1997). Due to their tissue- specific expression and high expression levels in cancer, these molecules are currendy being investigated as targets for cancer vaccines (Durrant, Anticancer Drugs 8:727-733, 1997; Reynolds et al, Int J Cancer 72:972-976, 1997). The expression pattern of STEAP provides evidence that it is likewise an ideal target for a cancer vaccine approach to prostate cancer, as its expression is not detected in most normal tissues. Accordingly, therapeutic approaches targeting particular motifs of STEAP, or aimed at inhibiting the activity of the STEAP protein, are expected to be useful for patients suffering from prostate cancer and other cancers expressing STEAP. The therapeutic approaches aimed at inhibiting the activity of the STEAP protein generaUy faU into two classes. One class comprises various methods for inhibiting the binding or association of the STEAP protein with its binding partner or with other proteins. Another class comprises a variety of methods for inhibiting the transcription of the STEAP gene or translation of STEAP mRNA. STEAP as a Target for Antibody-Based Therapy The ceU surface nature and expression profiles of the STEAPs in cancers including prostate cancer indicate that they are promising targets for antibody therapy of prostate and other cancers expressing STEAPs. The experimental results described in the Examples herein provide compelling evidence that STEAP-1 and STEAP-2 are strongly expressed uniformly over the surface of glandular epithelial ceUs within prostate and prostate cancer ceUs. In particular, immunohistochemical analysis results show that the surface of human prostate epithehal ceUs (normal and cancer) appear to be uniformly coated with STEAP-1. Biochemical analysis confirms the ceU surface localization of STEAP-1 initiaUy suggested by its putative 6-transmembrane primary structural elements and by the periceUular staining plainly evident by imrnunohistochemical staining. STEAP-1 and STEAP-2 are uniformly expressed at high levels over the surface of prostate glandular epithelia, an ideal situation for immunotherapeutic intervention strategies that target extraceUular STEAP epitopes. Systemic administration of STEAP- immunoreactive compositions would be expected to result in extensive contact of the composition with prostate epithehal ceUs via binding to STEAP extraceUular epitopes. Moreover, given the near absence of STEAP-1 protein expression in normal human tissues, there is ample reason to expect exquisite sensitivity without toxic, non-specific and/ or non- target effects caused by the binding of the immunotherapeutic composition to STEAP-1 on non-target organs and tissues. In addition to the high level expression of STEAP-1 in prostate and prostate cancer ceUs, STEAP-1 appears to be substantiaUy over-expressed in a variety of other human cancers, including bladder, lung, colon, pancreatic and ovarian cancers. In particular, high level STEAP-1 mRNA expression is detected in aU tested prostate cancer tissues and ceU lines, and in most of the pancreatic, colon, and bladder cancer ceU lines tested. High level expression of STEAP-1 is also observed in some ovarian cancer ceU lines. Lower level expression is observed in some breast, testicular, and cervical cancer ceU lines. Very high level expression is also detected in a Ewing sarcoma ceU line. Apphcants have shown that ceU surface STEAP-1 protein is expressed in bladder, lung and colon cancers, while there is no detectable ceU surface (or intraceUular) STEAP-1 protein in normal colon and low expression in normal bladder. Antibodies specificaUy reactive with extraceUular domains of STEAP-1 may be useful to treat these cancers systemicaUy, either as toxin or therapeutic agent conjugates or as naked antibodies capable of inhibiting ceU proliferation or function. STEAP-2 protein is also expressed in prostate cancer, and in other cancers as weU, including colon and lung cancers. STEAP-2 mRNA analysis by RT-PCR and northern blot show that expression is restricted to prostate in normal tissues, is also expressed in some prostate, pancreatic, colon, testicular, ovarian and other cancers. Therefore, antibodies reactive with STEAP-2 may be useful in the treatment of prostate and other cancers. SimUarly, the expression of STEAP-3 and STEAP-4 (as weU as other STEAPs) may be associated with some cancers. Thus antibodies reactive with these STEAP family member proteins may also be useful therapeuticaUy. STEAP antibodies may be introduced into a patient such that the antibody binds to STEAP on the cancer ceUs and mediates the destruction of the ceUs and the tumor, inhibits the growth of the ceUs or the tumor, and/or eliminates STEAP function in the primary tumor, in circulating micrometastases, and/or in estabhshed metastases. The degree of tumor vascularization may provide guidance on which delivery approach is recommended. SimUarly, the grade and/or stage of disease would be expected to provide useful information in this regard. For example, a higher grade, more advanced tumor may be more likely to seed metastases, suggesting systemic administration in order to treat or prevent the emergence of metastases. Mechanisms by which such antibodies exert a therapeutic effect may include complement-mediated cytolysis, antibody-dependent ceUular cytotoxicity, modulating the physiologic function of STEAP, inhibiting ligand binding or signal transduction pathways, modulating tumor ceU differentiation, altering tumor angiogenesis factor profiles, and/or by inducing apoptosis. STEAP antibodies conjugated to toxic or therapeutic agents may also be used therapeuticaUy to dehver the toxic or therapeutic agent directly to STEAP-bearing tumor ceUs. Cancer immunofherapy using anti-STEAP antibodies may foUow the teachings generated from various approaches that have been successfully employed in the treatment of other types of cancer, including but not limited to colon cancer (Arlen et al, 1998, Crit. Rev. Immunol. 18:133-138), multiple myeloma (Ozaki et al, 1997, Blood 90:3179-3186; Tsunenari et al, 1997, Blood 90:2437-2444), gastric cancer (Kasprzyk et al, 1992, Cancer Res. 52:2771-2776), B-ceU lymphoma (Funakoshi et al, 1996, J. Immunother. Emphasis Tumor Immunol. 19:93-101), leukemia (Zhong et al, 1996, Leuk. Res. 20:581-589), colorectal cancer (Moun et al, 1994, Cancer Res. 54:6160-6166); Velders et al, 1995, Cancer Res. 55:4398-4403), and breast cancer (Shepard et al, 1991, J. Clin. Immunol. 11:117-127). Some therapeutic approaches involve conjugation of naked antibody to a toxin, such as the conjugation of 131 I to anti-CD20 antibodies (e.g, Bexxar, Coulter Pharmaceutical), whUe others involve co-aclministration of antibodies and other therapeutic agents, such as Herceptin™ (trastuzumab) with pachtaxel (Genentech, Inc.). For treatment of prostate cancer, for example, STEAP antibodies can be administered in conjunction with radiation, chemotherapy or hormone ablation. Although STEAP antibody therapy may be useful for aU stages of cancer, antibody therapy may be particularly appropriate in advanced or metastatic cancers. Treatment with the antibody therapy of the invention may be indicated for patients who have received previously one or more chemotherapy, whUe combining the antibody therapy of the invention with a chemotherapeutic or radiation regimen may be preferred for patients who have not received chemotherapeutic treatment. AdditionaUy, antibody therapy may enable the use of reduced dosages of concomitant chemotherapy, particularly for patients who do not tolerate the toxicity of the chemotherapeutic agent very weU. It may be desirable for some cancer patients to be evaluated for the presence and level of STEAP expression, preferably using immunohistochemical assessments of tumor tissue, quantitative STEAP imaging, or other techniques capable of rehably indicating the presence and degree of STEAP expression. Immunohistochemical analysis of tumor biopsies or surgical specimens may be preferred for this purpose. Methods for immunohistochemical analysis of tumor tissues are weU known in the art. Anti-STEAP monoclonal antibodies useful in treating prostate and other cancers include those that are capable of initiating a potent immune response against the tumor and those that are capable of direct cytotoxicity. In this regard, anti-STEAP monoclonal antibodies (mAbs) may ehcit tumor ceU lysis by either complement-mediated or antibody-dependent ceU cytotoxicity (ADCC) mechanisms, both of which require an intact Fc portion of the immunoglobulin molecule for interaction with effector ceU Fc receptor sites or complement proteins. In addition, anti-STEAP mAbs that exert a direct biological effect on tumor growth are useful in the practice of the invention. Potential mechanisms by which such direcdy cytotoxic mAbs may act include inhibition of ceU growth, modulation of ceUular differentiation, modulation of tumor angiogenesis factor profiles, and the induction of apoptosis. The mechanism by which a particular anti- STEAP mAb exerts an anti-tumor effect may be evaluated using any number of in vitro assays designed to determine ADCC, ADMMC, complement-mediated ceU lysis, and so forth, as is generaUy known in the art. The anti-tumor activity of a particular anti-STEAP mAb, or combination of anti- STEAP mAbs, may be evaluated in vivo using a suitable animal model. For example, xenogenic prostate cancer models wherein human prostate cancer explants or passaged xenograft tissues are introduced into immune compromised animals, such as nude or SCID mice, are appropriate in relation to prostate cancer and have been described (U.S. Patent No. 6,107,540; Klein et al, 1997, Nature Medicine 3: 402-408). For Example, PCT Patent Application WO98/16628, Sawyers et al, published April 23, 1998, describes various xenograft models of human prostate cancer capable of recapitulating the development of primary tumors, micrometastasis, and the formation of osteoblastic metastases characteristic of late stage disease. Efficacy may be predicted using assays which measure inhibition of tumor formation, tumor regression or metastasis, and the like. The use of murine or other non-human monoclonal antibodies, or human/mouse chimeric mAbs may induce moderate to strong immune responses in some patients. In some cases, this wiU result in clearance of the antibody from circulation and reduced efficacy. In the most severe cases, such an immune response may lead to the extensive formation of immune complexes that, potentiaUy, can cause renal faUure. Accordingly, preferred monoclonal antibodies used in the practice of the therapeutic methods of the invention are those that are either fuUy human or humanized and that bind specificaUy to the target STEAP antigen with high affinity but exhibit low or no antigenicity in the patient. Therapeutic methods of the invention contemplate the administration of single anti-STEAP mAbs as weU as combinations, or cocktaUs, of different mAbs. Such mAb cocktaUs may have certain advantages inasmuch as they contain mAbs that target different epitopes, exploit different effector mechanisms or combine direcdy cytotoxic mAbs with mAbs that rely on immune effector functionality. Such mAbs in combination may exhibit synergistic therapeutic effects. In addition, the administration of anti-STEAP mAbs may be combined with other therapeutic agents, including but not limited to various chemotherapeutic agents, androgen-blockers, and immune modulators (e.g, IL-2, GM-CSF). The anti-STEAP mAbs may be administered in their "naked" or unconjugated form, or may have therapeutic agents conjugated to them. The anti-STEAP monoclonal antibodies used in the practice of the method of the invention may be formulated into pharmaceutical compositions comprising a carrier suitable for the desired delivery method. Suitable carriers include any material which when combined with the anti-STEAP mAbs retains the anti-tumor function of the antibody and is non-reactive with the subject's immune systems. Examples include, but are not limited to, any of a number of standard pharmaceutical carriers such as sterUe phosphate buffered saline solutions, bacteriostatic water, and the like. The anti-STEAP antibody formulations may be acirninistered via any route capable of delivering the antibodies to the tumor site. PotentiaUy effective routes of administration include, but are not limited to, intravenous, intraperitoneal, intramuscular, intratumor, intradermal, and the like. The preferred route of administration is by intravenous injection. A preferred formulation for intravenous injection comprises the anti-STEAP mAbs in a solution of preserved bacteriostatic water, sterUe unpreserved water, and/or diluted in polyvinylchloride or polyethylene bags containing 0.9% sterUe Sodium Chloride for Injection, USP. The anti-STEAP mAb preparation may be lyophilized and stored as a sterUe powder, preferably under vacuum, and then reconstituted in bacteriostatic water containing, for example, benzyl alcohol preservative, or in sterile water prior to injection. Treatment wiU generaUy involve the repeated administration of the anti-STEAP antibody preparation via an acceptable route of administration such as intravenous injection (TV), typicaUy at a dose in the range of about 0.1 to about 10 mg/kg body weight. Doses in the range of 10-500 mg mAb per week may be effective and weU tolerated. Based on clinical experience with the Herceptin mAb in the treatment of metastatic breast cancer, an initial loading dose of approximately 4 mg/kg patient body weight IV foUowed by weekly doses of about 2 mg/kg IV of the anti- STEAP mAb preparation may represent an acceptable dosing regimen. Preferably, the initial loading dose is administered as a 90 minute or longer infusion. The periodic maintenance dose may be administered as a 30 minute or longer infusion, provided the initial dose was weU tolerated. However, as one of skiU in the art wiU understand, various factors wiU influence the ideal dose regimen in a particular case. Such factors may include, for example, the binding affinity and half hfe of the mAb or mAbs used, the degree of STEAP overexpression in the patient, the extent of circulating shed STEAP antigen, the desired steady-state antibody concentration level, frequency of treatment, and the influence of chemotherapeutic agents used m combination with the treatment method of the invention. OptimaUy, patients should be evaluated for the level of circulating shed STEAP antigen in serum in order to assist m the determination of the most effective dosmg regimen and related factors. Such evaluations may also be used for monitoring purposes throughout therapy, and may be useful to gauge therapeutic success m combination with evaluating other parameters (such as serum PSA levels m prostate cancer therapy). Inhibition of STEAP Protein Function The invention mcludes various methods and compositions for inhibiting the bmdmg of STEAP to its bmd g partner or hgand, or its association with other protem(s) as weU as methods for inhibiting STEAP function. Inhibition of STEAP With Recombinant Proteins In one approach, recombinant molecules that are capable of bmdmg to STEAP thereby preventing STEAP from accessing/binding to its bmdmg partner(s) or associating with other protem(s) are used to inhibit STEAP function. Such recombmant molecules may, for example, contain the reactive part(s) of a STEAP specific antibody molecule. In a particular embodiment, the STEAP binding domam of a STEAP bmdmg partner may be engineered mto a dimenc fusion protem compnsmg two STEAP hgand bmdmg domams linked to the Fc portion of a human IgG, such as human IgGl . Such IgG portion may contain, for example, the CH2 and C H 3 domams and the hmge region, but not the CHI domam. Such dimenc fusion protems may be administered in soluble form to patients suffermg from a cancer associated with the expression of STEAP, mcludmg but not limited to prostate cancer, where the dimenc fusion protem specificaUy bmds to STEAP thereby blocking STEAP interaction with a bmdmg partner and/or modulating STEAP function. Such dimenc fusion protems may be further combined mto multimenc protems usmg known antibody linking technologies. Inhibition of STEAP With Intracellular Antibodies In another approach, recombmant vectors encoding smgle chain antibodies that specificaUy bmd to STEAP may be introduced mto STEAP expressmg ceUs via gene transfer technologies, wherem the encoded smgle cham anti-STEAP antibody is expressed mtraceUularly, bmds to STEAP protem, and thereby inhibits its function. Methods for engineering such mtraceUular smgle cham antibodies are weU known. Such mtraceUular antibodies, also known as "intrabodies", may be specificaUy targeted to a particular compartment withm the ceU, providing control over where the inhibitory activity of the treatment wiU be focused. This technology has been successfully apphed m the art (for review, see Richardson and Marasco, 1995, TIBTECH vol. 13). Intrabodies have been shown to virtuaUy eliminate the expression of otherwise abundant ceU surface receptors. See, for example, Richardson et al, 1995, Proc. Nad. Acad. Sci. USA 92: 3137-3141; Beerh et al, 1994, J. Biol. Chem. 289: 23931-23936; Deshane et al, 1994, Gene Ther. 1: 332-337. Single cham antibodies comprise the vanable domams of the heavy and light cham jomed by a flexible hnker polypeptide, and are expressed as a smgle polypeptide. OptionaUy, smgle chain antibodies may be expressed as a smgle chain vanable region fragment joined to the hght cham constant region. WeU known mtraceUular trafficking signals may be engineered mto recombinant polynucleotide vectors encodmg such smgle cham antibodies m order to precisely target the expressed lntrabody to the desired mtraceUular compartment. For example, intrabodies targeted to the endoplasmic reticulum (ER) may be engineered to incorporate a leader peptide and, OptionaUy, a C- terminal ER retention signal, such as the KDEL ammo acid motif. Intrabodies mtended to exert activity in the nucleus may be engineered to mclude a nuclear localization signal. Lipid moieties may be jomed to intrabodies m order to tether the mtrabody to the cytosohc side of the plasma membrane. Intrabodies may also be targeted to exert function m the cytosol. For example, cytosohc intrabodies may be used to sequester factors within the cytosol, thereby preventing them from bemg transported to their natural ceUular destination. In one embodiment, STEAP intrabodies are designed to bmd specificaUy to a particular STEAP domain. For example, cytosohc intrabodies that specificaUy bmd to the STEAP protem may be used to prevent STEAP related molecules from gaining access to the nucleus, thereby preventing it from exerting any biological activity withm the nucleus. In order to direct the expression of such intrabodies specificaUy to particular tumor ceUs, the transcription of the intrabody may be placed under the regulatory control of an appropriate tumor-specific promoter and/ or enhancer. In order to target intrabody expression specificaUy to prostate, for example, the PSA promoter and/or promoter/enhancer may be utilized (See, for example, U.S. Patent No. 5,919,652). Inhibition of STEAP Transcription or Translation Withm another class of therapeutic approaches, the invention provides vanous methods and compositions for inhibiting the transcnption of the STEAP gene. Similarly, the invention also provides methods and compositions for inhibiting the translation of STEAP mRNA mto protem. In one approach, a method of inhibiting the transcnption of the STEAP gene comprises contacting the STEAP gene with a STEAP antisense polynucleotide. In another approach, a method of inhibiting STEAP mRNA translation comprises contacting the STEAP mRNA with an antisense polynucleotide. In another approach, a STEAP specific nbozyme may be used to cleave the STEAP message, thereby inhibiting translation. Such antisense and nbozyme based methods may also be directed to the regulatory regions of the STEAP gene, such as the STEAP promoter and/or enhancer elements. SimUarly, protems capable of inhibiting a STEAP gene transcription factor may be used to inhibit STEAP mRNA transcription. The vanous polynucleotides and compositions useful m the aforementioned methods have been descnbed above. The use of antisense and nbozyme molecules to inhibit transcnption and translation is weU known in the art. Other factors that inhibit the transcription of STEAP through interfering with STEAP transcnptional activation may also be useful for the treatment of cancers expressmg STEAP. SimUarly, factors that are capable of interfering with STEAP processmg may be useful for the treatment of cancers expressmg STEAP. Cancer treatment methods utilizing such factors are also withm the scope of the invention. General Considerations for Therapeutic Strategies Gene transfer and gene therapy technologies may be used for delivering therapeutic polynucleotide molecules to tumor ceUs synthesizing STEAP (i.e, antisense, ribozyme, polynucleotides encoding intrabodies and other STEAP inhibitory molecules). A number of gene therapy approaches are known in the art. Recombinant vectors encoding STEAP antisense polynucleotides, ribozymes, factors capable of interfering with STEAP transcription, and so forth, may be delivered to target tumor ceUs using such gene therapy approaches. The above therapeutic approaches may be combined with any one of a wide variety of chemotherapy or radiation therapy regimens. These therapeutic approaches may also enable the use of reduced dosages of chemotherapy and/or less frequent administration, particularly in patients that do not tolerate the toxicity of the chemotherapeutic agent weU. The anti-tumor activity of a particular composition (e.g, antisense, ribozyme, intrabody), or a combination of such compositions, may be evaluated using various in vitro and in vivo assay systems. In vitro assays for evaluating therapeutic potential include ceU growth assays, soft agar assays and other assays indicative of tumor promoting activity, binding assays capable of deterrnining the extent to which a therapeutic composition wiU inhibit the binding of STEAP to a binding partner, etc. In vivo, the effect of a STEAP therapeutic composition may be evaluated in a suitable animal model. For example, xenogeneic prostate cancer models wherein human prostate cancer explants or passaged xenograft tissues are introduced into immune compromised animals, such as nude or SCID mice, are appropriate in relation to prostate cancer and have been described (Klein et al, 1997, Nature Medicine 3: 402-408). For example, PCT Patent Application WO98/16628, Sawyers et al, published April 23, 1998, describes various xenograft models of human prostate cancer capable of recapitulating the development of primary tumors, micrometastasis, and the formation of osteoblastic metastases characteristic of late stage disease. Efficacy may be predicted using assays that measure inhibition of tumor formation, tumor regression or metastasis, and the like. See, also, the Examples below. In vivo assays that qualify the promotion of apoptosis may also be useful in evaluating potential therapeutic compositions. In one embodiment, xenografts from bearing mice treated with the therapeutic composition may be examined for the presence of apoptotic foci and compared to untreated control xenograft-bearing mice. The extent to which apoptotic foci are found in the tumors of the treated mice provides an indication of the therapeutic efficacy of the composition. The therapeutic compositions used in the practice of the foregoing methods may be formulated into pharmaceutical compositions, including vaccine compositions, comprising a carrier suitable for the desired delivery method. Suitable carriers include any material that when combined with the therapeutic composition retains the anti- tumor function of the therapeutic composition and is non-reactive with the patient's immune system. Examples include, but are not limited to, any of a number of standard pharmaceutical carriers such as sterUe phosphate buffered saline solutions, bacteriostatic water, and the like (see, generaUy, Remington's Pharmaceutical Sciences 16 th Edition, A. Osal, Ed, 1980). Therapeutic formulations may be solubilized and administered via any route capable of delivering the therapeutic composition to the tumor site. PotentiaUy effective routes of administration include, but are not limited to, intravenous, parenteral, intraperitoneal, intramuscular, intratumor, intradermal, intraorgan, orthotopic, and the like. A preferred formulation for intravenous injection comprises the therapeutic composition in a solution of preserved bacteriostatic water, sterUe unpreserved water, and/or diluted in polyvinylchloride or polyethylene bags containing 0.9% sterile Sodium Chloride for Injection, USP. Therapeutic protein preparations may be lyophihzed and stored as sterUe powders, preferably under vacuum, and then reconstituted in bacteriostatic water containing, for example, benzyl alcohol preservative, or in sterile water prior to injection. Dosages and administration protocols for the treatment of cancers using the foregoing methods wiU vary with the method and the target cancer and wiU generaUy depend on a number of other factors appreciated in the art. CANCER VACCINES The invention further provides cancer vaccines comprising a STEAP protem or fragment thereof, as weU as DNA based vaccines. In view of the prostate- and tumor- restricted expression of STEAP, STEAP cancer vaccines are expected to be effective at specificaUy preventing and/or treating STEAP expressing cancers without creating nonspecific effects on non-target tissues. The use of a tumor antigen in a vaccine for generating humoral and ceU-mediated immunity for use in anti-cancer therapy is weU known in the art and has been employed in prostate cancer using human PSMA and rodent PAP immunogens (Hodge et al, 1995, Int. J. Cancer 63: 231-237; Fong et al, 1997, J. Immunol. 159: 3113-3117). Such methods can be readUy practiced by employing a STEAP protein, or fragment thereof, or a STEAP-encoding nucleic acid molecule and recombinant vectors capable of expressing and appropriately presenting the STEAP immunogen. For example, viral gene delivery systems may be used to dehver a STEAP-encoding nucleic acid molecule. Various viral gene delivery systems that can be used in the practice of this aspect of the invention include, but are not limited to, vaccinia, fowlpox, canarypox, adenovirus, influenza, poliovirus, adeno-associated virus, lentivirus, and sindbus virus (Restifo, 1996, Curr. Opin. Immunol. 8: 658-663). Non-viral delivery systems may also be employed by using naked DNA encoding a STEAP protein or fragment thereof introduced into the patient (e.g, intramuscularly) to induce an anti-tumor response. In one embodiment, the full-length human STEAP cDNA may be employed. In one embodiment, a STEAP cancer vaccine is based on the identification of immunogenic peptides within a STEAP amino acid sequence shown in Fig. 11A-B. As discussed further in the examples below, STEAPs have been shown to induce T and B ceU responses. STEAP-l and STEAP-2 polypeptides have been used to generate an immune response in mice and rabbits for the production of monoclonal and polyclonal antibodies. Thus, specific portions of STEAP, and polynucleotides encoding these portions, may be selected for the production of a cancer vaccine. One example of such a portion of a STEAP protein is amino acid residues 14 through 28 of the STEAP-1 amino acid sequence as shown in FIG. 1A-B (WKMKPRRNLEEDDYL; SEQ ID NO: 22). In another embodiment, STEAP nucleic acid molecules encoding specific cytotoxic T lymphocyte (CTL) epitopes may be employed. CTL epitopes can be determined using specific algorithms (e.g, Epimer, Brown University) to identify peptides within a STEAP protein that are capable of optimaUy binding to specified HLA aUeles. One suitable -dgofithm is the HLA Peptide Motif Search algorithm avaUable at the Bioinformatics and Molecular Analysis Section (BIMAS) web site (http://b_rnas.dcrt.nih.gov/). This algorithm is based on binding of specific peptide sequences in the groove of HLA Class I molecules and specificaUy HLA-A2 (Falk et al, 1991, Nature 351:290-6; Hunt et al, 1992, Science 255:1261-3; Parker et al, 1992, J. Immunol. 149:3580-7; Parker et al, 1994, J. Immunol. 152:163-75). The HLA Peptide Motif Search algorithm aUows location and ranking of 8- mer, 9-mer, and 10-mer peptides from a complete protein sequence for predicted binding to HLA-A2 as weU as other Class I molecules. Most HLA-A2 binding peptides are 9-mers, favorably containing a leucine at position 2 and a valine or leucine at position 9 (Parker et al, 1992, J. Immunol. 149:3580-7). Actual binding of peptides to HLA-A2 can be evaluated by stabilization of HLA-A2 expression on the antigen processing defective ceU line T2 (Xue et al, 1997, Prostate 30:73-8; Peshwa et al, 1998, Prostate 36:129-38). Immunogenicity of specific peptides can be evaluated in vitro by stimulation of CD8+ CTL in the presence of dendritic ceUs (Xue et al.; Peshwa et al, supra). Specific STEAP peptides predicted to bind HLA-A2 and preferred for use in cancer vaccines include peptides conesponding to amino acids 165-173 of STEAP-1, amino acids 86-94 of STEAP-1, amino acids 262-270 of STEAP-1, amino acids 302-310 of STEAP-1 , amino acids 158-166 of STEAP-1 , amino acids 227-235 of STEAP-2, amino acids 402-410 of STEAP-2, amino acids 307-315 of STEAP-2, amino acids 306- 314 of STEAP-2, and amino acids 100-108 of STEAP-2. Various ex vivo strategies may also be employed. One approach involves the use of dendritic ceUs to present STEAP antigen to a patient's immune system. Dendritic ceUs express MHC class I and II, B7 co-stimulator, and IL-12, and are thus highly specialized antigen presenting ceUs. In prostate cancer, autologous dendritic ceUs pulsed with peptides of the prostate-specific membrane antigen (PSMA) are being used in a Phase I clinical trial to stimulate prostate cancer patients' immune systems (Tjoa et al, 1996, Prostate 28: 65-69; Murphy et al, 1996, Prostate 29: 371-380). Dendritic ceUs can be used to present STEAP peptides to T ceUs in the context of MHC class I and II molecules. In one embodiment, autologous dendritic ceUs are pulsed with STEAP peptides capable of binding to MHC molecules. In another embodiment, dendritic ceUs are pulsed with the complete STEAP protem. Yet another embodiment mvolves engmeermg the overexpression of the STEAP gene m dendntic ceUs usmg vanous implementing vectors known m the art, such as adenovirus (Arthur et al, 1997, Cancer Gene Ther. 4: 17-25), retrovirus (Henderson et al, 1996, Cancer Res. 56: 3763-3770), lentivirus, adeno-associated virus, DNA transfection (Ribas et al, 1997, Cancer Res. 57: 2865-2869), and tumor-derived RNA transfection (Ashley et al, 1997, J. Exp. Med. 186: 1177-1182). CeUs expressmg STEAP may also be engineered to express immune modulators, such as GM-CSF, and used as immunizing agents. Anti-idiotypic anti-STEAP antibodies can also be used m anti-cancer therapy as a vaccme for inducing an immune response to ceUs expressmg a STEAP protem. SpecificaUy, the generation of anti-idiotypic antibodies is weU known in the art and can readily be adapted to generate anti-idiotypic anti-STEAP antibodies that mimic an epitope on a STEAP protem (see, for example, Wagner et al, 1997, Hybndoma 16: 33-40, Foon et al, 1995, J Clm Invest 96: 334-342; Herlyn et al, 1996, Cancer Immunol Immunother 43: 65-76). Such an anti-idiotypic antibody can be used in cancer vaccme strategies. Genetic immunization methods may be employed to generate prophylactic or therapeutic humoral and ceUular immune responses directed agamst cancer ceUs expressmg STEAP. Constructs compnsmg DNA encoding a STEAP protem/irnmunogen and appropnate regulatory sequences may be injected direcdy mto muscle or skm of an individual, such that the ceUs of the muscle or skm take up the construct and express the encoded STEAP protem/i mimogen. Expression of the STEAP protem immunogen results m the generation of prophylactic or therapeutic humoral and ceUular immunity agamst prostate and other STEAP-expressmg cancers. Vanous prophylactic and therapeutic genetic immunization techmques known in the art may be used (for review, see information and references pubhshed at Internet address www.genweb.com). DIAGNOSTIC COMPOSITIONS AND KITS For use in the diagnostic and therapeutic applications descnbed or suggested above, kits are also provided by the invention. Such kits may compnse a earner means bemg compartmentalized to receive m close confinement one or more contamer means such as vials, tubes, and the like, each of the contamer means compnsmg one of the separate elements to be used in the method. For example, one of the container means may comprise a probe that is or can be detectably labeled. Such probe may be an antibody or polynucleotide specific for a STEAP protein or a STEAP gene or message, respectively. Where the kit utilizes nucleic acid hybridization to detect the target nucleic acid, the kit may also have containers containing nucleotide(s) for amphfication of the target nucleic acid sequence and/or a container comprising a reporter-means, such as a biotin-binding protein, such as avidin or streptavidin, bound to a reporter molecule, such as an enzymatic, florescent, or radioisotope label. The kit of the invention wiU typicaUy comprise the container described above and one or more other containers comprising materials desirable from a commercial and user standpoint, including buffers, dUuents, filters, needles, syringes, and package inserts with instructions for use. A label may be present on the on the container to indicate that the composition is used for a specific therapy or non-therapeutic application, and may also indicate directions for either in vivo or in vitro use, such as those described above. Accordingly, the invention also provides diagnostic compositions comprising STEAP-related molecules. Such molecules include the various STEAP polynucleotides, primers, probes, proteins, fragments, antibodies described herein. The molecules included in the diagnostic composition may OptionaUy be labeled with a detectable marker. STEAP diagnostic compositions may further comprise appropriate buffers, dUuents, and other ingredients as desired. EXAMPLES Various aspects of the invention are further described and iUustrated by way of the several examples that foUow, none of which are intended to limit the scope of the invention. Example 1: SSH-Generated Isolation of cDNA Fragment of the STEAP Gene Materials and Methods LAPC Xenografts: LAPC xenografts were obtained from Dr. Charles Sawyers (UCLA) and generated as described (Klein et al, 1997, Nature Med. 3: 402-408; Craft et al, 1999, Cancer Res. 59: 5030-5036). Androgen dependent and independent LAPC-4 xenografts (LAPC-4 AD and Al, respectively) and LAPC-9 xenografts (LAPC-9 AD and Al, respectively) were grown in intact male SCID mice or in castrated males, respectively, and were passaged as smaU tissue chunks in recipient males. LAPC-4 Al xenografts were derived from LAPC-4 AD tumors and LAPC-9 Al xenografts were derived from LAPC- 9 AD tumors. To generate the Al xenografts, male mice bearing LAPC AD tumors were castrated and maintained for 2-3 months. After the LAPC tumors re-grew, the tumors were harvested and passaged in castrated males or in female SCID mice. LAPC-4 AD xenografts were grown intratibiaUy as foUows. LAPC-4 AD xenograft tumor tissue grown subcutaneously was minced into 1-2 mm 3 sections whUe the tissue was bathed in IX Iscoves medium, minced tissue was then centrifuged at 1.3K rpm for 4 minutes, the supernatant was resuspended in 10 ml ice cold IX Iscoves medium and centrifuged at 1.3K rpm for 4 minutes. The peUet was then resuspended in IX Iscoves with 1% pronase E and incubated for 20 minutes at room temperature with mUd rocking agitation foUowed by incubation on ice for 2-4 minutes. FUtrate was centrifuged at 1.3K rmp for 4 minutes, and the pronase was removed from the aspirated peUet by resuspending in 10 ml Iscoves and re-centrifuging. Clumps of ceUs were then plated in PrEGM medium and grown overnight. The ceUs were then harvested, filtered, washed 2X RPMI, and counted. Approximately 50,000 ceUs were mixed with and equal volume of ice-cold Matrigel on ice, and surgicaUy injected into the proximal tibial metaphyses of SCID mice via a 27 gauge needle. After 10-12 weeks, LAPC-4 tumors growing in bone marrow were recovered. CeU Lines and Tissues: Human ceU lines (e.g, HeLa) were obtained from the ATCC and were maintained in DMEM with 5% fetal calf serum. Human tissues for RNA and protein analyses were obtained from the Human Tissue Resource Center (HTRC) at the UCLA (Los Angeles, CA) and from QualTek, Inc. (Santa Barbara, CA). RNA Isolation: Tumor tissue and ceU lines were homogenized in Trizol reagent (Life Technologies, Gibco BRL) using 10 ml/ g tissue or 10 ml/ 10 8 ceUs to isolate total RNA. Poly A RNA was purified from total RNA using Qiagen's Ohgotex mRNA Mini and Midi kits. Total and mRNA were quantified by spectrophotometric analysis (O.D. 260/280 nm) and analyzed by gel electrophoresis. Oligonucleotides : The foUowing HPLC purified oligonucleotides were used. DPNCDN (cDNA synthesis primer): 5'TTTTGATCAAGCTT 3 o3' (SEQ ID NO: 23) Adaptor 1: 5'CTAATACGACTCACTATAGGGCTCGAGCGGCCGCCCGGGCAG3' 3'GGCCCGTCCTAG5' (SEQ ID NO: 24,25) Adaptor 2: 5'GTAATACGACTCACTATAGGGCAGCGTGGTCGCGGCCGAG3' 3'CGGCTCCTAG5' (SEQ ID NO: 26,27) PCR primer 1 : 5'CTAATACGACTCACTATAGGGC3' (SEQ ID NO: 28) Nested primer (NP)1: 5TCGAGCGGCCGCCCGGGCAGGA3' (SEQ ID NO: 29) Nested primer (NP)2: 5ΑGCGTGGTCGCGGCCGAGGA3' (SEQ ID NO: 30) Suppression Subtractive Hybridization: Suppression Subtractive Hybridization (SSH) was used to identify cDNAs corresponding to genes which may be up-regulated in androgen dependent prostate cancer compared to benign prostatic hyperplasia (BPH). Double stranded cDNAs corresponding to the LAPC-4 AD xenograft (tester) and the BPH tissue (driver) were synthesized from 2 μg of poly(A)+ RNA isolated from xenograft and BPH tissue, as described above, using CLONTECH's PCR-Select cDNA Subtraction Kit and 1 ng of ohgonucleotide RSACDN as primer. First- and second- strand synthesis were carried out as described in the Kit's user manual protocol (CLONTECH Protocol No. PT1117-1, Catalog No. K1804-1). The resulting cDNA was digested with Rsa I for 3 hrs. at 37°C. Digested cDNA was extracted with phenol/chloroform (1:1) and ethanol precipitated. Driver cDNA (BPH) was generated by combining in a 4 to 1 ratio Rsa I digested BPH cDNA with digested cDNA from mouse hver, in order to ensure that murine genes were subtracted from the tester cDNA (LAPC-4 AD). Tester cDNA (LAPC-4 AD) was generated by dUuting 1 μl of Rsa I digested LAPC-4 AD cDNA (400 ng) m 5 μl of water. The chluted cDNA (2 μl, 160 ng) was then hgated to 2 μl of adaptor 1 and adaptor 2 (10 μM), in separate ligation reactions, in a total volume of 10 μl at 16°C overnight, using 400 u of T4 DNA hgase (CLONTECH). Ligation was terminated with 1 μl of 0.2 M EDTA and heating at 72°C for 5 min. The first hybridization was performed by adding 1.5 μl (600 ng) of driver cDNA to each of two tubes containing 1.5 μl (20 ng) adaptor 1- and adaptor 2- hgated tester cDNA. In a final volume of 4 μl, the samples were overlayed with mineral oU, denatured in an MJ Research thermal cycler at 98°C for 1.5 minutes, and then were aUowed to hybridize for 8 hrs at 68°C. The two hybridizations were then mixed together with an additional 1 μl of fresh denatured driver cDNA and were aUowed to hybridize overnight at 68°C. The second hybridization was then diluted in 200 μl of 20 mM Hepes, pH 8.3, 50 mM NaCl, 0.2 mM EDTA, heated at 70°C for 7 min. and stored at -20°C. PCR Amplification. Cloning and Sequencing of Gene Fragments Generated from SSH: To amplify gene fragments resulting from SSH reactions, two PCR amplifications were performed. In the primary PCR reaction 1 μl of the chluted final hybridization mix was added to 1 μl of PCR primer 1 (10 μM), 0.5 μl dNTP mix (10 μM), 2.5 μl 10 x reaction buffer (CLONTECH) and 0.5 μl 50 x Advantage cDNA polymerase Mix (CLONTECH) in a final volume of 25 μl. PCR 1 was conducted using the foUowing conditions: 75°C for 5 min, 94°C for 25 sec, then 27 cycles of 94°C for 10 sec, 66°C for 30 sec, 72°C for 1.5 min. Five separate primary PCR reactions were performed for each experiment. The products were pooled and diluted 1:10 with water. For the secondary PCR reaction, 1 μl from the pooled and chluted primary PCR reaction was added to the same reaction mix as used for PCR 1, except that primers NP1 and NP2 (10 μM) were used instead of PCR primer 1. PCR 2 was performed using 10-12 cycles of 94°C for 10 sec, 68°C for 30 sec, 72°C for 1.5 minutes. The PCR products were analyzed using 2% agarose gel electrophoresis. The PCR products were inserted into pCR2.1 using the T/A vector cloning kit (Invittogen). Transformed E. coh were subjected to blue/white and ampicillin selection. White colonies were picked and arrayed into 96 weU plates and were grown in liquid culture overnight. To identify inserts, PCR amphfication was performed on 1 ml of bacterial culture using the conditions of PCR1 and NP1 and NP2 as primers. PCR products were analyzed using 2% agarose gel electrophoresis. Bacterial clones were stored in 20% glycerol in a 96 weU format. Plasmid DNA was prepared, sequenced, and subjected to nucleic acid homology searches of the GenBank, dbEST, and NCI-CGAP databases. RT-PCR Expression Analysis: First strand cDNAs were generated from 1 μg of mRNA with oligo (dT)12-18 priming using the Gibco-BRL Superscript Preamphfication system. The manufacturers protocol was used and included an incubation for 50 min at 42°C with reverse transcriptase foUowed by RNase H treatment at 37°C for 20 min. After completing the reaction, the volume was increased to 200 μl with water prior to normahzation. First strand cDNAs from 16 different normal human tissues were obtained from Clontech. Normahzation of the first strand cDNAs from multiple tissues was performed by using the primers 5'atatcgccgcgctcgtcgtcgacaa3' (SEQ ID NO: 31) and 5'agccacacgcagctcattgtagaagg 3' (SEQ ID NO: 32) to amplify β-actin. First strand cDNA (5 μl) was amplified in a total volume of 50 μl containing 0.4 μM primers, 0.2 μM each dNTPs, 1XPCR buffer (Clontech, 10 mM Tris-HCL, 1.5 mM MgCl 2 , 50 mM KC1, pH8.3) and IX Klentaq DNA polymerase (Clontech). Five μl of the PCR reaction was removed at 18, 20, and 22 cycles and used for agarose gel electrophoresis. PCR was performed usmg an MJ Research thermal cycler under the foUowmg conditions- initial denaturation was at 94°C for 15 sec, foUowed by a 18, 20, and 22 cycles of 94°C for 15, 65°C for 2 mm, 72°C for 5 sec A final extension at 72°C was earned out for 2 mm. After agarose gel electrophoresis, the band intensities of the 283 bp β-actin bands from multiple tissues were compared by visual mspection. DUution factors for the first sttand cDNAs were calculated to result m equal β-actin band intensities m aU tissues after 22 cycles of PCR. Three rounds of normalization were required to achieve equal band intensities m aU tissues after 22 cycles of PCR To determine expression levels of the 8P1D4 gene, 5 μl of normalized first strand cDNA was analyzed by PCR usmg 25, 30, and 35 cycles of amphfication usmg the foUowmg primer pairs: 5' ACT TTG TTG ATG ACC AGG ATT GGA 3' (SEQ ID NO: 4) 5' CAG AAC TTC AGC ACA CAC AGG AAC 3' (SEQ ID NO: 5) Semi quantitative expression analysis was achieved by comparmg the PCR products at cycle numbers that give hght band intensities. Results Several SSH experiments were conduced as descnbed m the Matenals and Methods, supra, and led to the isolation of numerous candidate gene fragment clones. AU candidate clones were sequenced and subjected to homology analysis agamst aU sequences m the major pubhc gene and EST databases m order to provide information on the identity of the corresponding gene and to help guide the decision to analyze a particular gene for differential expression. In general, gene fragments which had no homology to any known sequence m any of the searched databases, and thus considered to represent novel genes, as weU as gene fragments showmg homology to previously sequenced expressed sequence tags (ESTs), were subjected to differential expression analysis by RT-PCR and/or Northern analysis. One of the cDNA clones, designated 8P1D4, was 436 bp m length and showed homology to an EST sequence m the NCI-CGAP tumor gene database. The full length cDNA encoding the 8P1D4 gene was subsequendy isolated using this cDNA and renamed STEAP-1. The 8P1D4 cDNA nucleotide sequence corresponds to nucleotide residues 150 through 585 in the STEAP-1 cDNA sequence as shown in FIG. 1A-B. Another clone, designated 28P3E1, 561 bp in length showed homology to a number of EST sequences in the NCI-CGAP tumor gene database or in other databases. Part of the 28P3E1 sequence (356 bp) is identical to an EST derived from human fetal tissue. After the full length STEAP-1 cDNA was obtained and sequenced, it became apparent that this clone also corresponds to STEAP-1 (more specificaUy, to residues 622 through the 3' end of the STEAP-1 nucleotide sequence as shown in FIG. 1A-B). Differential expression analysis by RT-PCR using primers derived from the 8P1D4 cDNA clone showed that the 8P1D4 (STEAP-1) gene is expressed at approximately equal levels in normal prostate and the LAPC-4 and LAPC-9 xenografts (FIG. 2, panel A). Further RT-PCR expression analysis of first strand cDNAs from 16 normal tissues showed greatest levels of 8P1D4 expression in prostate. SubstantiaUy lower level expression in several other normal tissues (i.e, colon, ovary, smaU intestine, spleen and testis) was detectable only at 30 cycles of amphfication in brain, pancreas, colon and smaU intestine (FIG. 2, panels B and C). Example 2: Isolation of Full Length STEAP-1 Encoding cDNA The 436 bp 8P1D4 gene fragment (Example 1) was used to isolate additional cDNAs encoding the 8P1D4/STEAP-1 gene. Briefly, a normal human prostate cDNA library (Clontech) was screened with a labeled probe generated from the 436 bp 8P1D4 cDNA. One of the positive clones, clone 10, is 1195 bp in length and encodes a 339 amino acid protein having nucleotide and encoded amino acid sequences bearing no significant homology to any known human genes or proteins (homology to a rat Kidney Injury Protein recendy described in International Application WO98/53071). The encoded protein contains at least 6 predicted transmembrane motifs implying a ceU surface orientation (see FIG. 1A-B, predicted transmembrane motifs underlined). These structural features led to the designation "STEAP", for "Six Transmembrane Epithehal Antigen of the Prostate". Subsequent identification of additional STEAP proteins led to the re-designation of the 8P1D4 gene product as "STEAP-1". The STEAP-1 cDNA and encoded amino acid sequences are shown in FIG. 1A-B and correspond to SEQ ID NOS: 1 and 2, respectively. STEAP-1 cDNA clone 10 was deposited with the American Type Culture CoUection ("ATCC") (10801 University Blvd., Manassas, VA 20110-2209 USA) as plasmid 8P1D4 clone 10.1 on August 26, 1998 as ATCC Accession Number 98849. The STEAP-1 cDNA clone can be excised therefrom using EcoRI/Xbal double digest (EcoRI at the 5'end, Xbal at the 3'end). Example 3: STEAP-1 Gene and Protein Expression Analysis In order to begin to characterize the biological characteristics of STEAP-1, an extensive evaluation of STEAP-1 mRNA and STEAP-1 protein expression across a variety of human tissue specimens was undertaken. This evaluation included Northern blot, Western blot and immunohistochemical analysis of STEAP-1 expression in a large number of normal human tissues, human prostate cancer xenografts and ceU lines, and various other human cancer ceU lines. Example 3A: Northern Blot Analysis of STEAP-1 mRNA Expression in Normal Human Tissues Initial analysis of STEAP-1 mRNA expression in normal human tissues was conducted by northern blotting two multiple tissue blots obtained from Clontech (Palo Alto, California), comprising a total of 16 different normal human tissues, using labeled STEAP-1 clone 10 as a probe. RNA samples were quantitatively normalized with a β- actin probe. The results are shown in FIG. 3A. The highest expression level was detected in normal prostate, with an approximately 5-10 fold lower level of expression detected in colon and hver. These northern blots showed two transcripts of approximately 1.4 kb and 4.0 kb, the former of which corresponds to the full length STEAP-1 clone 10 cDNA, which encodes the entire STEAP-1 open reading frame. The larger transcript was separately cloned as a 3627 bp cDNA from a normal prostate library, the sequence of which contains a 2399 bp intron (FIG. 4). This initial analysis was extended by using the STEAP-1 clone 10 probe to analyze an RNA dot blot matrix of 37 normal human tissues (Clontech, Palo Alto, CA; Human Master Blot™). The results are shown in FIG. 3B and show strong STEAP-1 expression only in prostate. Very low level STEAP-1 RNA expression was detected in hver, lung, trachea and fetal hver tissue, at perhaps a 5-fold lower level compared to prostate. No expression was detected in any of the remaining tissues. Based on these analyses, significant STEAP-1 expression appears to be prostate specific in normal tissues. Example 3B: Northern Blot Analysis of STEAP-1 mRNA Expression in Prostate Cancer Xenografts and Cell Lines To analyze STEAP-1 expression in human cancer tissues and ceU lines, RNAs derived from human prostate cancer xenografts and an extensive panel of prostate and non-prostate cancer ceU lines were analyzed by Northern blot using STEAP-1 cDNA clone 10 as probe. AU RNA samples were quantitatively normahzed by ethidium bromide staining and subsequent analysis with a labeled β— actin probe. The results, presented in FIG. 5, show high level STEAP-1 expression in aU the LAPC xenografts and aU of the prostate cancer ceU lines. Expression in the LAPC-9 xenografts was higher compared to the LAPC-4 xenografts, with no significant difference observed between androgen-dependent and androgen-independent subhnes (FIG. 5A). Expression in the LAPC-4 xenografts was comparable to expression in normal prostate. Lower levels of expression were detected in PrEC ceUs (Clonetics), which represent the basal ceU compartment of the prostate. Analysis of prostate cancer ceU lines showed highest expression levels in LNCaP, an androgen dependent prostate carcinoma ceU line. Significant expression was also detected in the androgen- independent ceU lines PC-3 and DU145. High levels of STEAP expression were also detected in LAPC-4 and LAPC-9 tumors that were grown within the tibia of mice as a model of prostate cancer bone metastasis (FIG. 5B). Significandy, very strong STEAP-1 expression was also detected in many of the non-prostate human cancer ceU lines analyzed (FIG. 5A). Particularly high level expression was observed in RD-ES ceUs, an Ewing sarcoma (EWS) derived ceU line. AdditionaUy, very high level expression was also detected in several of the colon cancer ceU lines (e.g, CaCo-2, LoVo, T84 and Colo-205), bladder carcinoma ceU lines (e.g, SCABER, UM-UC-3, TCCSUP and 5637), ovarian cancer ceU lines (e.g, OV-1063 and SW 626) and pancreatic cancer ceU lines (e.g, HPAC, Capan-1, PANC-1 and BxPC-3). These results, combined with the absence of strong expression in the corresponding normal tissues (FIG. 3), indicate that STEAP-1 may be generaUy up-regulated in these types (as weU as other types) of human cancers. Example 3C: Western Blot Analysis of STEAP-1 Protein Expression in Prostate and Other Cancers A 15 mer peptide corresponding to amino acid residues 14 through 28 of the STEAP-1 amino acid sequence as shown in FIG. 1A-B (WKMKPRRNLEEDDYL; SEQ ID NO: 22) was synthesized and used to immunize sheep for the generation of sheep polyclonal antibodies towards the amino-terminus of the protein (anti-STEAP-1) as foUows. The peptide was conjugated to KLH (keyhole limpet hemocyanin). The sheep was initiaUy immunized with 400 μg of peptide in complete Freund's adjuvant. The animal was subsequentiy boosted every two weeks with 200 μg of peptide in incomplete Freund's adjuvant. Anti-STEAP antibody was affinity-purified from sheep serum using STEAP peptide coupled to affigel 10 (Bio Rad). Purified antibody is stored in phosphate- buffered saline with 0.1% sodium azide. To test antibody specificity, the cDNA of STEAP-1 was cloned into a retroviral expression vector (pSRαtkneo, MuUer et al, 1991, MCB 11:1785). NIH 3T3 ceUs were infected with retroviruses encoding STEAP-1 and were selected in G418 for 2 weeks. Western blot analysis of protein extracts of infected and uninfected NIH 3T3 ceUs showed expression of a protein with an apparent molecular weight of 36 kD only in the infected ceUs (FIG. 6, lanes marked "3T3 STEAP" AND "3T3"). The anti-STEAP-1 polyclonal antibody was used to probe western blots of ceU lysates prepared from a variety of prostate cancer xenograft tissues, prostate cancer ceU lines and other non-prostate cancer ceU lines. Protein samples (20μg each) were quantitatively normahzed by probing the blots with an anti-Grb-2 antibody. The results are shown in FIG. 6. STEAP-1 protein was detected in aU of the LAPC prostate cancer xenografts, aU of the prostate cancer ceU lines, a primary prostate cancer specimen and its matched normal prostate control. Highest STEAP-1 protein expression was detected in the LAPC-9 xenograft and in LNCaP ceUs, in agreement with the northern blot analysis described immediately above. High level expression was also observed in the bladder carcinoma ceU line UM-UC-3. Expression in other cancer ceU lines was also detectable (FIG. 6). Example 3D: Immunohistochemical Analysis of STEAP-1 Protein Expression in Prostate Tumor Biopsy and Surgical Specimens To determine the extent of STEAP-1 protein expression in clinical materials, tissue sections were prepared from a variety of prostate cancer biopsies and surgical samples for immunohistochemical analysis." Tissues were fixed in 10% formalin, embedded in paraffin, and sectioned according to standard protocol. Formalin-fixed, paraffin-embedded sections of LNCaP ceUs were used as a positive control. Sections were stained with a sheep anti-STEAP-1 polyclonal antibody directed against a STEAP-1 N-terminal epitope (as described immediately above). LNCaP sections were stained in the presence of an excess amount of the STEAP-1 N-terminal peptide immunogen used to generate the polyclonal antibody (peptide 1) or a non-specific peptide derived from a distinct region of the STEAP-1 protein (peptide 2; YQQVQQNKEDAWIEH; SEQ ID NO: 33). The results are shown in FIG. 8. LNCaP ceUs showed uniformly strong periceUular staining in aU ceUs (FIG. 8B). Excess STEAP N-terminal peptide (peptide 1) was able to competitively inhibit antibody staining (FIG. 8A), whUe peptide 2 had no effect (FIG. 8B). SimUarly, uniformly sttong periceUular staining was seen in the LAPC-9 (FIG. 8F) and LAPC-4 prostate cancer xenografts. These results are clear and suggest that the staining is STEAP specific. Moreover, these results show localization of STEAP to the plasma membrane, corroborating the biochemical findings presented in Example 4 below. The results obtained with the various clinical specimens are show in FIG. 8C (normal prostate tissue), FIG. 8D (grade 3 prostatic carcinoma), and FIG. 8E (grade 4 prostatic carcinoma), and are also included in the summarized results shown in Table 1. Light to strong staining was observed in the glandular epithelia of aU prostate cancer samples tested as weU as in aU samples derived from normal prostate or benign disease (e.g, BPH). The signal appears to be strongest at the ceU membrane of the epithehal ceUs, especiaUy at the ceU-ceU junctions (FIG. 8C-E) and is also inhibited with excess STEAP N-tern inal peptide 1. Some basal ceU staining is also seen in normal prostate (FIG. 8C), which is more apparent when examining attophic glands. STEAP-1 seems to be expressed at aU stages of prostate cancer since lower grades (FIG. 8D), higher grades (FIG. 8E) and metastatic prostate cancer (represented by LAPC-9; FIG. 8F; See also human patient metastases shown in FIG. 32A-B) aU exhibit sttong staining. Immunohistochemical staining of a large panel of normal non-prostate tissues showed no detectable STEAP-1 expression in most of these normal tissues (Table 1). Normal bladder exhibited low levels of ceU surface staining in the transitional epithelium (FIG. 8G). Pancreas, stomach, uterus, faUopian tubes and pituitary showed low levels of cytoplasmic staining (Table 1). It is unclear whether the observed cytoplasmic staining is specific or is due to non-specific binding of the antibody, since northern blotting showed htde to no STEAP-1 expression in pancreas (FIG. 3). These results indicate that ceU surface expression of STEAP-1 in normal tissues appears to be restricted to prostate and bladder. Table 1; Immunohistochemical Staining of Human Tissues With Anti-STEAP-1 Sheep Polyclonal Antibody Staining Intensity Tissues* None CerebeUum, cerebral cortex, spinal cord, heart, skeletal muscle (2), artery, thymus, spleen (4), bone marrow, lymph node (3), lung (8), hver (4), Ueum, kidney (2), testis (2), ovary, placenta, breast, adrenal gland (2), thyroid gland (2), skin (2) Light Cytoplasmic Ureter, bladder cancer (2/5), colon (4/7), colon cancer (4/7), faUopian tubes (2), pituitary gland, pancreas, stomach (1/2), uterus (1/2) Light Membrane Prostate cancer bone marrow metastasis (1/6), prostate cancer lymph node metastasis (1/5), lung cancer (1/6) Moderate to Strong Prostate (7/7), BPH (5/5), prostate cancer (20/20)**, Membrane prostate cancer lymph node metastasis (4/5), prostate cancer bone marrow metastasis (5/6), bladder (2/5), bladder cancer (3/5), lung cancer (3/6) *In cases where more than one sample was analyzed per tissue, the number in parenthesis indicates how many samples showed positive staining/total analyzed. **Prostate cancer grades varied from 3 to 5 and Gleason scores of 7 to 10. Example 3E: Immunohistochemical Analysis of STEAP-1 Protein Expression in Bladder and Lung Cancer To detenriine the extent of STEAP-1 protein expression in other cancers, tissue from bladder and lung cancer clinical specimens were subjected to immunohistochemical analysis using the polyclonal antibody and methods as described in Example 3D. The results, shown in Figures 21A-D, reveal a periceUular staining pattern simUar to that observed with prostate cancer tissue. Example 4: Biochemical Characterization of STEAP-1 Protein To initiaUy characterize the STEAP-1 protein, cDNA clone 10 was cloned into the pcDNA 3.1 Myc-His plasmid (Invittogen), which encodes a 6His tag at the carboxyl- terminus, transfected into 293T ceUs, and analyzed by flow cytometry using anti-His monoclonal antibody (His-probe, Santa Cruz) as weU as the anti-STEAP-1 polyclonal antibody described above. Staining of ceUs was performed on intact ceUs as weU as permeabihzed ceUs. The results indicated that only permeabilized ceUs stained with both antibodies, suggesting that both terrnini of the STEAP-1 protein are localized inttaceUularly. It is therefore possible that one or more of the STEAP-1 protein termini are associated with intraceUular organeUes rather than the plasma membrane. To determine whether STEAP-1 protein is expressed at the ceU surface, intact STEAP-1 -transfected 293T ceUs were labeled with a biotinylation reagent that does not enter hve ceUs. STEAP-1 was then imrnunoprecipitated from ceU extracts using the anti- His and anti-STEAP antibodies. SV40 large T antigen, an intraceUular protein that is expressed at high levels in 293T ceUs, and the endogenous ceU surface ttansferrin receptor were imrnunoprecipitated as negative and positive controls, respectively. After immunoprecipitation, the proteins were transferred to a membrane and visualized with horseradish peroxidase-conjugated streptavidin. The results of this analysis are shown in FIG. 7. Only the ttansferrin receptor (positive control) and STEAP-1 were labeled with biotin, whUe the SV40 large T antigen (negative conttol) was not detectably labeled (FIG. 7A). Since only ceU surface proteins are labeled with this technique, it is clear from these results that STEAP-1 is a ceU surface protein. Combined with the results obtained from the flow cytometric analysis, it is clear that STEAP-1 is a ceU surface protein with intraceUular amino- and carboxyl- termini. Furthermore, the above results together with the STEAP-1 secondary structural predictions, shows that STEAP-1 is a type Ilia membrane protein with a molecular topology of six potential transmembrane domains, 3 extraceUular loops, 2 intraceUular loops and two intraceUular termini. A schematic representation of STEAP-1 protein topology relative to the ceU membrane is shown in FIG. IB. In addition, prostate, bladder and colon cancer ceUs were direcdy analyzed for ceU surface expression of STEAP-1 by biotinylation studies. Briefly, biotmylated ceU surface proteins were affinity purified with stteptavidin-gel and probed with the anti- STEAP-1 polyclonal antibody described above. Western blotting of the streptavidin purified proteins clearly show ceU surface biotinylation of endogenous STEAP-1 in aU prostate (LNCaP, PC-3, DU145), bladder (UM-UC-3, TCCSUP) and colon cancer (LoVo, Colo) ceUs tested, as weU as in NIH 3T3 ceUs infected with a STEAP-1 encoding rettovirus, but not in non-expressing NIH 3T3 ceUs used as a negative control (FIG. 7B). In a further negative conttol, STEAP-1 protein was not detected in streptavidin precipitates from non-biotinylated STEAP expressing ceUs (FIG. 7B). Example 5: Constructs for Recombinant Expression of STEAP-1 pGEX Constructs To express STEAP-1 in bacterial ceUs, portions of STEAP-1 were fused to the Glutathione S-ttansferase (GST) gene by cloning into pGEX-6P-l(Amersham Pharmacia Biotech, NJ). AU constructs were made to generate recombinant STEAP-1 protein sequences with GST fused at the N-terminus and a six histidine epitope at the C- terminus. The six histidine epitope tag was generated by adding the histidine codons to the cloning primer at the 3' end of the ORF. A PreScission™ recognition site permits cleavage of the GST tag from STEAP-1. The ampicillin resistance gene and pBR322 origin permits selection and maintenance of the plasmid in E. coli. The foUowing fragments of STEAP-1 were cloned into pGEX-6P-l: Amino acids 148 to 251; amino acids 144 to 339; amino acids 39 to 253; amino acids 70 to 136; amino acids 254 to 313. And into pGEX-4T: Amino acids 2 to 247; amino acids 135-318; and amino acids 144-339. Exemplary additional constructs that can be made in pGEX-6P-l spanning the foUowing regions of the STEAP-1 protein include: Amino acids 1 to 339; amino acids 1 to 144. pcDNA3.1/MycHis Construct To express STEAP-1 in mammahan ceUs, the 1,017 bp STEAP-1 ORF (with ttanslational start Kozak consensus) was cloned into pcDNA3.1/MycHis_Version B (Invittogen, Carlsbad, CA). Protein expression is driven from the cytomegalovirus (CMV) promoter. The recombinant protein has the myc and six histidines fused to the C-terminus. The pcDNA3.1/M cHis vector also contains the bovine growth hormone (BGH) polyadenylation signal and transcription termination sequence to enhance mRNA stability along with the SV40 origin for episomal replication and simple vector rescue in ceU lines expressing the large T antigen. The Neomycin resistance gene aUows for selection of mammalian ceUs expressing the protein and the ampicillin resistance gene and ColEl origin permits selection and maintenance of the plasmid in E. coli. pSRa Constructs To generate mammalian ceU lines expressing STEAP-1 constitutively, the 1,017 bp ORF (with ttanslational start Kozak consensus) was cloned into pSRa constructs. Amphotropic and ecotropic retroviruses are generated by transfection of pSRa constructs into the 293T-10A1 packaging line or co-ttansfection of pSRa and a helper plasmid (φ— ) in 293 ceUs, respectively. The rettovirus can be used to mfect a vanety of mammahan ceU lines, resulting m the integration of the cloned gene, STEAP-1, mto the host ceU lines. Protem expression is driven from a long terminal repeat (LTR). The Neomycm resistance gene aUows for selection of mammahan ceUs expressmg the protem and the ampicillin resistance gene and ColEl origin permits selection and mamtenance of the plasmid m E. coli. Additional pSRa constructs were made that fused the FLAG tag to the C and N-terminus to aUow detection usmg anti-FLAG antibodies. The FLAG sequence 5' gat tac aag gat gac gac gat aag 3' (SEQ ID NO: 34) were added to cloning primer at the 3' end of the ORF. Another pSRa construct was made that contained ammo acids 182 to 454. This truncated form of the STEAP-1 protem wiU help determine the function of the long extraceUular N-Terminal region. An Additional pSRa construct is bemg made to produce a myc/6 HIS fusion protem of the full length STEAP-1 protem. Example 6: Identification and Structural Analysis of Other Human STEAPs STEAP-1 has no homology to any known human genes. In an attempt to identify additional genes that are homologous to STEAP-1, the protem sequence of STEAP-1 was used as an electronic probe to identify famUy members m the pubhc EST (expression sequence tag) database (dbEST). Usmg the "tblastn" function m NCBI (National Center for Biotechnology Information), the dbEST database was quened with the STEAP-1 protem sequence. This analysis revealed additional putative STEAP-1 homologues or STEAP famUy members, as further descnbed below. In addition, SSH cloning experiments also identified a STEAP-1 related cDNA fragment, clone 98P4B6. This clone was isolated from SSH cloning usmg normal prostate cDNA as tester and LAPC-4 AD cDNA as driver. A larger partial sequence of the 98P4B6 clone was subsequendy isolated from a normal prostate library; this clone encodes an ORF of 173 ammo acids with close homology to the primary structure of STEAP-1, and thus was designated STEAP-2. A full length STEAP-2 cDNA of 2454 bp was isolated from a prostate library. The STEAP-2 nucleotide and encoded ORF ammo acid sequences are shown m FIG. 9A-D. An ammo acid ahgnment of the STEAP-1 and partial STEAP-2 primary structures is shown m FIGS. 11 A-B and 11C. STEAP-1 and - 2 share 61% identity over their 171 ammo acid residue overlap (FIG. 11C). The STEAP- 2 cDNA has been deposited with the American Type Culture CoUection ("ATCC"; 10801 University Blvd., Manassas, VA 20110-2209 USA) as plasmid 98P4B6-GTD3 on July 2, 1999 as ATCC Accession Number PTA-311. The STEAP-2 cDNA (98P4B6-GTD3) contains a 355 bp 5'UTR (untranslated region) that is 72% GC rich, suggesting that it contains ttanslational regulatory elements. The cDNA encodes an open reading frame (ORF) of 454 amino acids (a.a.) with six potential transmembrane domains. This is in contrast to STEAP-1, which is 339 a.a. in length. Ahgnment with STEAP-1 demonstrates 54.9% identity over a 237 amino acid overlap. Interestingly, the locations of the six putative transmembrane domains in STEAP-2 coincide with the locations of the transmembrane domains in STEAP-1 (see ahgnment). The homology of STEAP-2 with STEAP-1 is highest in the regions spanned by the first putative extraceUular loop to the fifth transmembrane domain. This analysis and the sequence of STEAP-2 suggest some significant differences between STEAP-1 and STEAP-2: STEAP-2 exhibits a 205 a.a. long intraceUular N-terminus (compared to 69 a.a. in STEAP-1) and a short 4 a.a. intraceUular C-terminus (compared to 26 a.a. in STEAP-1). These differences could imply significant differences in function and/or interaction with intraceUular signaling pathways. To identify a unique mouse EST corresponding to STEAP-2, the unique N-terminus of STEAP-2 was used to query the dbEST database. One mouse EST was isolated (AI747886, mouse kidney) that may be used in the identification of mouse STEAP-2 and in expression analysis of STEAP-2 in mouse. Two ESTs encoding ORFs bearing close homology to the STEAP-1 and STEAP-2 sequences were also identified by electronic probing with the STEAP-1 protein sequence. These ESTs (AI139607 and R80991) were provisionaUy designated STEAP-3 and STEAP-4. A full length cDNA encoding STEAP-3 was subsequendy cloned, and its nucleotide and deduced amino acid sequences are shown in FIG. 10A-E. The STEAP-3 cDNA has been deposited with the American Type Culture CoUection ("ATCC"; 10801 University Blvd., Manassas, VA 20110-2209 USA) on December 8, 1999 as plasmid pSTEAP-3 EBB4 as ATCC Accession Number PTA-1033. The nucleotide sequences of the ESTs corresponding to the STEAPs are reproduced in FIG. 10F. An amino acid ahgnment of the structures of STEAP-1, STEAP-2, STEAP-3 and the partial sequence of the putative STEAP-4 is shown in FIG. 11A-B. This ahgnment shows a close structural simUarity between aU four STEAP famUy proteins, particularly in the predicted transmembrane domains. As indicated above, STEAP-1 and STEAP-2 demonstrate 54.9% identity over a 237 amino acid overlap. STEAP-1 and STEAP-3 are 40.9% identical over a 264 amino acid region, whUe STEAP-2 and STEAP-3 are 47.8% identical over a 416 amino acid region. Example 7: Constructs for Recombinant Expression of STEAP-2 pGEX Constructs To express STEAP-2 in bacterial ceUs, portions of STEAP-2 were fused to the Glutathione S-ttansferase (GST) gene by cloning into pGEX-6P-l(Amersham Pharmacia Biotech, NJ). AU constructs were made to generate recombinant STEAP-2 protein sequences with GST fused at the N-terminus and a six histidine epitope at the C- terminus. The six histidine epitope tag was generated by adding the histidine codons to the cloning primer at the 3' end of the ORF. A PreScission™ recognition site permits cleavage of the GST tag from STEAP-2. The ampicillin resistance gene and pBR322 origin permits selection and maintenance of the plasmid in E. coli. The foUowing fragments of STEAP-2 were cloned into pGEX-6P-l: Amino acids 287 to 390; amino acids 285 to 454; amino acids 193 to 454. Additional exemplary constructs that can be made in pGEX-6P-l spanning the foUowing regions of the STEAP-2 protein include: Amino acids 1 to 193; amino acids 1 to 454. And in pGEX-4T: Amino acids 2-204; 183-387; and 276-453. pCRIl Construct To generate sense and anti-sense riboprobes for RNA in situ investigations, a pCRII construct was generated using bp 367 to 877 of the GTD3 STEAP-2 cDNA. The pCRII vector has Sp6 and T7 promoters flanking the insert to drive the production of STEAP-2 RNA riboprobes which were used in RNA in situ hybridization experiments. pcDNA4/HιsMax-TOPO Construct To express STEAP-2 in mammahan ceUs, the 1,362 bp STEAP-2 ORF was cloned into pcDNA4/HisMax-TOPO Version A (cat# K864-20, Invittogen, Carlsbad, CA). Protein expression is driven from the cytomegalovirus (CMV) promoter and the SP163 ttanslational enhancer. The recombinant protein has Xpress™ and six histidine epitopes fused to the N-terminus. In addition to this construct containing only the 1,362 bp ORF an additional construct was made with the C-temiinus of the recombinant protein containing a 28 amino acid fusion resulting from vector sequences prior to the termination codon. The pcDNA4/HisMax-TOPO vector also contains the bovine growth hormone (BGH) polyadenylation signal and transcription termination sequence to enhance mRNA stability along with the SV40 origin for episomal replication and simple vector rescue in ceU lines expressing the large T antigen. The Zeocin resistance gene aUows for selection of mammalian ceUs expressing the protein and the ampicillin resistance gene and ColEl origin permits selection and maintenance of the plasmid in E. coli. pcDNA . l/M cHιs Construct To express STEAP-2 in mammahan ceUs, the 1,362 bp STEAP-2 ORF (with start Kozak consensus) was cloned into pcDNA3.1/MycHis.Version A (Invittogen, Carlsbad, CA). Protein expression is driven from the cytomegalovirus (CMV) promoter. The recombinant protein has the myc and six histidines fused to the C-terminus. The pcDNA3.1/MycHis vector also contains the bovine growth hormone (BGH) polyadenylation signal and transcription termination sequence to enhance mRNA stability along with the SV40 origin for episomal replication and simple vector rescue in ceU lines expressing the large T antigen. The neomycin resistance gene aUows for selection of mammahan ceUs expressing the protein and the ampicillin resistance gene and ColEl origin permits selection and maintenance of the plasmid in E. coli. Additional pcDNA3.1/MycHis constructs were generated using STEAP-2 amino acids 6 to 454, 121-454 and 182-454. pBlueBacHIS2a To express STEAP-1 m SF9 msect ceUs, the STEAP-1 ORF was cloned mto pBlueBacHIS2A (Invittogen, California). Protem expression is dnven under the polyhedrm promoter N-termtnus poly HIS and Xpress tags aUow for detection and purification of the recombinant STEAP-1 protem. A C-terminus enterokinase recognition site aUows for cleavage of these tags. The ampicillin resistance gene and ColEl ongm permits selection and mamtenance of the plasmid m E. coh. FoUowmg co transfection with AcMNPV DNA, a homologous recombination event occurs between these sequences resulting in a recombmant virus carrying the gene of interest and the polyhedrm. A variety of restnction enzyme sites for simphfied subclonmg are present In addition, a reporter gene (b-galactosidase) conveniendy identifies recombmant plaques, to eliminate tedious plaque screening. pcDNA3. lCT-GFP-TOPO Construct To express STEAP-2 m mammahan ceUs and to aUow detection of the recombinant protein usmg fluorescence, the 1 ,362 bp ORF (with start Kozak consensus) was cloned mto pcDNA3.1CT-GFP-TOPO (Invittogen, CA). Protem expression is driven from the cytomegalovirus (CMV) promoter. The recombinant protem has the Green Fluorescent Protem (GFP) fused to the C-terminus facilitating non-mvasive, m vivo detection and ceU biology studies. The pcDNA3.1/MycHιs vector also contams the bovme growth hormone (BGH) polyadenylation signal and transcnption termination sequence to enhance mRNA stability along with the SV40 origin for episomal replication and simple vector rescue m ceU lines expressmg the large T antigen. The neomycin resistance gene aUows for selection of mammahan ceUs expressmg the protem and the ampicilhn resistance gene and ColEl ongm permits selection and mamtenance of the plasmid m E. coh An additional construct with a N-terminal GFP fusion is bemg made m pcDNA3.1NT-GFP-TOPO spanning the entire length of the STEAP-2 protem. pSRa Constructs To generate mammahan ceU lines expressmg STEAP-2 constitutively, the 1362 bp ORF was cloned mto pSRa constructs. Amphotropic and ecotropic retroviruses are generated by transfection of pSRa constructs mto the 293T-10A1 packaging line or co- transfection of pSRa and a helper plasmid (φ-) m 293 ceUs, respectively. The rettovirus can be used to infect a variety of mammahan ceU lines, resulting m the integration of the cloned gene, STEAP-2, mto the host ceU-hnes. Protem expression is dnven from a long terminal repeat (LTR). The neomycm resistance gene aUows for selection of mammahan ceUs expressmg the protem and the ampicilhn resistance gene and ColEl ongm permits selection and mamtenance of the plasmid m E. coh. Additional pSRa constructs were made that fused the FLAG tag to the C and N-terminus to aUow detection usmg anti- FLAG antibodies. The FLAG sequence 5' gat tac aag gat gac gac gat aag 3' (SEQ ID NO: 34) was added to cloning primer at the 3' end of the ORF. Another pSRa construct was made that contained ammo acids 182 to 454. This truncated form of the STEAP-2 protem wiU help determine the function of the long extraceUular N-Terminal region. In addition, a pSRa construct can be made to produce a myc/6 HIS fusion protem of the full length STEAP protem. Example 8: Expression Analysis of STEAP-2 and Other Human STEAP Family Members Example 8A: Tissue Specific Expression of STEAP Family Members in Normal Human Tissues RT-PCR analysis of STEAP-2 shows expression m aU the LAPC prostate cancer xenografts and m normal prostate (FIG. 14, panel A). Analysis of 8 normal human tissues shows prostate-specific expression after 25 cycles of amphfication (FIG. 14, panel B). Lower level expression in other tissues was detected only after 30 cycles of amphfication. Northern blotting for STEAP-2 shows a pattern of 2 ttanscnpts (approximately 3 and 8 kb m size) expressed only m prostate (and at significantiy lower levels m the LAPC xenografts), with no detectable expression m any of the 15 other normal human tissues analyzed (FIG. 15, panel C). Thus, STEAP-2 expression m normal human tissues appears to be highly prostate-specific. Expression analysis of STEAP famUy members m normal tissues was performed by Northern blot and/or RT-PCR. AU STEAP famUy members appeared to exhibit tissue restricted expression patterns. STEAP-3/AI139607 expression is shown in FIG. 12A (Northern) and FIG. 12B (RT-PCR). STEAP-4/R80991 expression is shown in FIG. 13. Example 8B: Expression of STEAP-2 in Various Cancer Cell Lines The RT-PCR results above suggested that the different STEAP famUy members exhibit different tissue expression patterns. Interestingly, STEAP-2, which appears very prostate-specific, seems to be expressed at lower levels in the LAPC xenografts. This is in contrast to STEAP-1, which is highly expressed in both normal and malignant prostate tissue. To better characterize this suggested difference in the STEAP-2 prostate cancer expression profile (relative to STEAP-1), Northern blotting was performed on RNA derived from the LAPC xenografts, as weU as several prostate and other cancer ceU lines, using a STEAP-2 specific probe (labeled cDNA clone 98P4B6). The results are shown in FIG. 16 and can be summarized as foUows. STEAP-2 is highly expressed in normal prostate and in some of the prostate cancer xenografts and ceU lines. More particularly, very sttong expression was observed in the LAPC-9 AD xenograft and the LNCaP ceUs. Significandy attenuated or no expression was observed in the other prostate cancer xenografts and ceU lines. Very sttong expression was also evident in the Ewing Sarcoma ceU line RD-ES. Unlike STEAP-1, which is highly expressed in cancer ceU lines derived from bladder, colon, pancreatic and ovarian tumors, STEAP-2 showed low to non- detectable expression in these same ceU lines (compare with FIG. 5). Interestingly, STEAP-2 was also non-detectable in PrEC ceUs, which are representative of the normal basal ceU compartment of the prostate. These results suggests that expression of STEAP-1 and STEAP-2 are differentiaUy regulated. WhUe STEAP-1 may be a gene that is generaUy up-regulated in cancer, STEAP-2 may be a gene that is more restricted to normal prostate and prostate cancer. Example 8C: Analysis of in Situ Expression of STEAP-2 RNA in Normal Prostate and Prostate Cancer The expression of STEAP-2 RNA was evaluated using in situ hybridization with a labeled antisense probe and using a labeled sense probe as conttol. AU four of four normal prostate tissue specimens examined were positive for STEAP (Figures 22A-B) Likewise, five of five prostate cancer tissue specimens were positive usmg STEAP RNA in situ hybridization (Figures 23A-B) A PIN specimen and a sample of LNCaP ceUs that were examined were positive as weU. Example 8D: Analysis of STEAP-2 Expression in Cancer Tissues The expression of STEAP-2 m vanous cancer tissues was examined usmg RT- PCR. The results are shown m Figure 24, m which lane 1 represents a sample from an LAPC4 AD xenograft; lane 2 is LAPC9 AD xenograft; lane 3 is LAPC9 AD 2 xenograft (grown with human bone explant), lane 4 is LAPC9 AD IT (grown mttatibiaUy), lane 5 is pooled tissue from colon cancer patients, lane 6 is pooled tissue from lung cancer patients; M represents a marker lane; lane 7 is patient normal prostate tissue; lane 8 is patient prostate cancer tissue; lane 9 is pooled tissue from kidney cancer patients; lane 10 is pooled tissue from bladder cancer patients; lane 11 is HeLa ceUs; and lane 12 is a water blank. The highest expression is found m the three LAPC9 AD xenografts High expression is observed m the LAPC4 AD xenograft as weU, and m normal prostate and lung cancer. Significant expression was detected also in colon and bladder cancer. Lower expression was detected m prostate and kidney cancer patient samples. Example 8E: Analysis of STEAP-2 Expression in Normal Tissues The expression of STEAP-2 m 76 normal human tissues was examined usmg a dot blot analysis of RNA samples. As shown m Figure 25, STEAP-2 is expressed at very high levels only m normal prostate. Example 9: Chromosomal Localization of STEAP Genes The chromosomal localization of STEAP-1 was determined usmg the GeneBndge 4 Human/Hamster radiation hybnd (RH) panel (Walter et al, 1994, Nat. Genetics 7.22) (Research Genetics, HuntsvtUe Al), whUe STEAP-2 and the STEAP homologues were mapped usmg the Stanford G3 radiation hybnd panel (Stewart et al, 1997, Genome Res. 7:422). The foUowing PCR primers were used for STEAP-1: 8P1D4.1 5' ACTTTGTTGATGACCAGGATTGGA 3' (SEQ ID NO: 4) 8P1D4.2 5' CAGAACTTCAGCACACACAGGAAC 3' (SEQ ID NO: 5) The resulting STEAP-1 mapping vector for the 93 radiation hybrid panel DNAs (2100000201101010001000000101110101221000111001110110101000100010001010010 21000001111001010000), and the mapping program avaUable at the internet address <http://www-genome.wi.mit.edu/cgi-bin/contig/rhmapper.pl>, localized the STEAP-1 gene to chromosome 7p22.3, telomeric to D7S531. The foUowing PCR primers were used for 98P4B6/STEAP-2: 98P4B6.1 5' GACTGAGCTGGAACTGGAATTTGT 3' (SEQ ID NO: 20) 98P4B6.2 5' TTTGAGGAGACTTCATCTCACTGG 3' (SEQ ID NO: 21) The resulting vector (0000010010000000000000000000000010010000000000100 0100000000000001000010101010010011), and the mapping program avaUable at the internet ad(hess<httρ://www-shgc.stanford.edu/l^/rhserverforιτ_new.html> maps the 98P4B6 (STEAP-2) gene to chromosome 7q21. The foUowing PCR primers were used for All 39607: AI139607.1 5' TTAGGACAACTTGATCACCAGCA 3' (SEQ ID NO: 16) All 39607.2 5'TGTCCAGTCCAAACTGGGTTATTT3' (SEQ ID NO: 17) The resulting vector (0000000010000000000000000000100010000020000000100 0100000001000000100010001010000010), and the mapping program avaUable at the internet address <http://www-shgc.stanford.edu/l^/rhseιrverfonr_new.htinl>, maps All 39607 to chromosome 7q21. The foUowing PCR primers were used for R80991: R80991.3 5' ACAAGAGCCACCTCTGGGTGAA 3' (SEQ ID NO: 35) R80991.4 5' AGTTGAGCGAGTTTGCAATGGAC 3' (SEQ ID NO: 36) The resulting vector (0000000000020000102000000001000000000000000000 0010000000001000011100000001001000001), and the mapping program avaUable at the internet address <http://www-shgc.stanford.edu/RH/rhserverformnew.httnl> maps R80991 to chromosome 2ql4-q21, near D2S2591. In summary, the above results show that three of the putative human STEAP famUy members localize to chromosome 7, as is schematicaUy depicted in FIG. 17. In particular, the STEAP-1 gene localizes to the far telomeric region of the short arm of chromosome 7, at 7p22.3, whUe STEAP-2 and All 39607 localize to the long arm of chromosome 7, at 7q21 (FIG. 17). R80991 maps to chromosome 2ql4-q21. Example 10: Identification of Intron-Exon Boundaries of STEAP-1 Genomic clones for STEAP-1 were identified by searching GenBank for BAC clones containing STEAP-1 sequences, resulting in the identification of accession numbers AC004969 (PAC DJ1121E10) and AC005053 (BAC RG041D11). Using the sequences derived from the PAC and BAC clones for STEAP the intron-exon boundaries were defined (FIG. 18). A total of 4 exons and 3 inttons were identified within the coding region of the STEAP gene. Knowledge of the exact exon-intton structure of the STEAP-1 gene may be used for designing primers within inttonic sequences which in turn may be used for genomic amphfication of exons. Such amphfication permits single-stranded conformational polymorphism (SSCP) analysis to search for polymorphisms associated with cancer. Mutant or polymorphic exons may be sequenced and compared to wUd type STEAP. Such analysis may be useful to identify patients who are more susceptible to aggressive prostate cancer, as weU as other types of cancer, particularly colon, bladder, pancreatic, ovarian, cervical and testicular cancers. Southern blot analysis shows that the STEAP-1 gene exists in several species including mouse (FIG. 19). Therefore, a mouse BAC library (Mouse ES 129-V release I, Genome Systems, FRAC-4431) was screened with the human cDNA for STEAP-1 (clone 10, Example 2). One positive clone, 12P11, was identified and confirmed by southern blotting (FIG. 20). The intron-exon boundary information for human STEAP may be used to identify the mouse STEAP-1 coding sequences. The mouse STEAP-1 genomic clone may be used to study the biological role of STEAP-1 during development and tumorigenesis. SpecificaUy, the mouse genomic STEAP-1 clone may be inserted into a gene knock-out (K/O) vector for targeted disruption of the gene in mice, using methods generaUy known in the art. In addition, the role of STEAP in metabolic processes and epithehal ceU function may be elucidated. Such K/O mice may be crossed with other prostate cancer mouse models, such as the TRAMP model (Greenberg et al, 1995, PNAS 92:3439), to determine whether STEAP influences the development and progression of more or less aggressive and metastatic prostate cancers. Example 11: Predicted HLA-A2 Binding Peptides of STEAP-1 and STEAP-2 The complete amino acid sequences of the STEAP-1 and STEAP-2 proteins were entered into the HLA Peptide Motif Search algorithm found in the Bioinformatics and Molecular Analysis Section (BIMAS) Web site (http://bimas.dcrt.nih.gov/). The HLA Peptide Motif Search algorithm was developed by Dr. Ken Parker based on binding of specific peptide sequences in the groove of HLA Class I molecules and specificaUy HLA-A2 (Falk et al, 1991, Nature 351: 290-6; Hunt et al, 1992, Science 255:1261-3; Parker et al, 1992, J. Immunol. 149:3580-7; Parker et al, 1994, J. Immunol. 152:163-75). This algorithm aUows location and ranking of 8-mer, 9-mer, and 10-mer peptides from a complete protein sequence for predicted binding to HLA-A2 as weU as other HLA Class I molecules. Most HLA-A2 binding peptides are 9-mers favorably containing a leucine (L) at position 2 and a valine (V) or leucine (L) at position 9. The results of STEAP-1 and STEAP-2 predicted binding peptides are shown in Table 2 below. For both proteins the top 5 ranking candidates are shown along with their location, the amino acid sequence of each specific peptide, and an estimated binding score. The binding score corresponds to the estimated half-time of dissociation of complexes containing the peptide at 37°C at pH 6.5. Peptides with the highest binding score (ie. 10776.470 for STEAP-1 peptide 165; 1789.612 for STEAP-2 peptide 227) are predicted to be the most tighdy bound to HLA Class I on the ceU surface and thus represent the best immunogenic targets for T-ceU recognition. Actual binding of peptides to HLA-A2 can be evaluated by stabilization of HLA-A2 expression on the antigen-processing defective ceU line T2 (Refs. 5,6). Immunogenicity of specific peptides can be evaluated in vitto by stimulation of CD8+ cytotoxic T lymphocytes (CTL) in the presence of dendritic ceUs (Xue et al, 1997, Prostate 30:73-8; Peshwa et al, 1998, Prostate 36:129-38). Table 2: Predicted Binding of STEAP-1 and STEAP-2 Peptide Sequences With Highest Affinity for HLA-A2 Example 12: STEAP-2 Induction of Tyrosine Phosphorylation of Cellular Proteins Multi-ttansmembrane proteins have the ability to transmit signal from the membrane and initiate signaling cascades that regulate a variety of downstream events, including gene expression, ceUular differentiation, migration and prohferation (Biochim. Biophys. Acta 1997; 1348:56-62, J. Virol. 1995; 69:675-83). In order to determine the involvement of STEAP-1 and STEAP-2 in downstream signaling events, the effect of STEAP-1 and STEAP-2 on tyrosine phosphorylation of PC3 ceUs was investigated (Figure 26). PC3 ceUs, stably expressing neo, STEAP-1, or STEAP-2 were grown overnight in 1% fetal bovine serum (FBS) to reduce receptor occupancy and background activity. The ceUs were then incubated for 5 minutes in the presence of either 1% or 10% FBS, lysed and analyzed by western blotting with anti-phosphotyrosine (4G10 mAb). An overlay using anti-Grb2 Ab was used to show that the gel was equaUy loaded. The results (Figure 26) show that expression of STEAP-2 in PC3 ceUs induces the phosphorylation of several proteins on tyrosine residues, including pi 50, pi 20 and p75. In contrast, expression of STEAP-1 induced the de-phosphorylation of pi 50. Several of the phosphotylated proteins correspond to known signaling proteins, indicating that STEAP-1 and STEAP-2 may be controlling the activation of specific signaling cascades. Example 13: STEAP-1- and STEAP-2- Mediated Activation of MAPK Cascades Several multi-transmembrane proteins induce specific biological responses by activating protein kinase cascades, including the MAPK pathways (Curr. Med. Chem. 2000; 7:911-43, Life Sci. 2000; 67:335-6, Biol. Chem. 2000; 275:4660-9). In order to determine whether expression of STEAP-1 and STEAP-2 is sufficient to regulate specific signaling pathways not otherwise active in resting PC3 ceUs, the effect of these genes on the activation of the p38 MAPK cascade was investigated in the prostate cancer ceU line PC3 (Figure 27A-B). Activation of the p38 kinase is dependent on its phosphorylation on tyrosine and serine residues. Phosphotylated p38 can be distinguished from the non- phosphorylated state by a Phospho-p38 mAb. This phospho-specific Ab was used to study the phosphorylation state of p38 in engineered PC3 ceU lines. PC3 ceUs stably expressing STEAP-1, STEAP-2 or neo were grown overnight in either 1% or 10% FBS. Whole ceU lysates were analyzed by western blotting. PC3 ceUs treated with the known p38 activators, NaSal or TNF, were used as a positive conttol. The results show that whUe expression of the conttol neo gene has no effect on p38 phosphorylation, expression of STEAP-1 and STEAP-2 in PC3 ceUs is sufficient to induce the activation of the ρ38 pathway (Figure 27A). The results were verified using western blotting with an anti-p38 Ab, which shows equal protein loading on the gels (Figure 27B). In another set of experiments, the sufficiency of expression of STEAP-1 or STEAP-2 in the prostate cancer ceU line PC3 to activate the mitogenic MAPK pathway, namely the ERK cascade, was examined (Figure 28A-B). Activation of ERK is dependent on its phosphorylation on tyrosine and serine residues. Phosphotylated ERK can be distinguished from the non-phosphorylated state by a Phospho-ERK mAb. This phospho-specific Ab was used to study the phosphorylation state of ERK in engineered PC3 ceU lines. PC3 ceUs, expressing an activated form of Ras, were used as a positive control. The results show that whUe expression of the conttol neo gene has no effect on ERK phosphorylation, expression of STEAP-2 in PC3 ceUs is sufficient to induce at least a 3-fold increase in ERK phosphorylation (Figure 28A). Expression of STEAP-1 also induced some ERK phosphorylation in PC3 ceUs grown in 1% FBS. These results were verified using anti-ERK western blotting (Figure 28A) and confirm the activation of the ERK pathway by STEAP-1 and STEAP-2. Since FBS contains several components that may contribute to receptor- mediated ERK activation, we examined the effect of STEAP-1 in low and optimal levels of FBS. PC3 ceUs expressing neo or STEAP-1 were grown in either 0.1% or 10% FBS overnight. The ceUs were analyzed by anti-Phospho-ERK western blotting. This experiment shows that STEAP-1 induces the phosphorylation of ERK in 0.1% FBS, and confirms that expression of STEAP-1 is sufficient to induce activation of the ERK signaling cascade in the absence of additional stimuli. Example 14: Ligand-mediated activation of STEAP-1 Several factors have been shown to activate multi-ttansmembrane proteins and mediate downstream signaling events, including ions, leukotrienes, hpophosphatidic acid, etc. (CeU Biochem. Biophys. 1999; 30:213-42). One group of compounds known to activate multi-ttansmembrane proteins are odorants (Neuron 2000; 25:503-4). In this example, 3 classes of odorants were screened for their ability to induce the activation of tyrosine kinase-mediated signaling in PC3 ceUs (Figure 29). PC3 ceUs, stably expressing neo or STEAP-1 were grown overnight in 0.1% FBS to aUow for receptor occupancy. The ceUs were then treated for 5 min with the indicated concentrations (0.1-10 μM) of citralva, ethylvanillin or IBMP. Treatment with 10% FBS was used as a conttol. Whole ceU lysates (20 μg) generated from the different treatment conditions were separated by SDS-PAGE and analyzed by anti-phosphotyrosine western blotting. This experiment shows that, whUe aU 3 classes of odorant induce some tyrosine phosphorylation in PC3-STEAP-1 ceUs, only IBMP had a measurable effect on the phosphorylation of PC3-neo ceUs that do not express the STEAP-1 gene. Moreover both citralva and ethylvaniUin induced an increase in the phosphorylation of pi 36-140 and p200-210 in PC3-STEAP-1 ceUs in a STEAP-1 specific manner. In addition, citralva induced the de novo phosphorylation of a protein at 160-200kDa. The results demonstrate that STEAP-1 is mediating the activation of tyrosine kinase pathways in odorant treated ceUs. The finding that citralva induced the tyrosine phosphorylation of proteins in a STEAP-1 mediated manner suggests that STEAP-1 may initiate the activation of one or more signaling cascades. In order to identify potential signaling cascade associated with odorant activation of STEAP-1, the effect of odorants on the activation of the MAPK cascade was studied in PC3 ceUs (Figure 30). PC3 ceUs, stably expressing either neo or STEAP-1, were grown overnight in 0.1% FBS. CeUs were then treated with citralva for 5 min. Treatment with 10% FBS was used as a control. As observed using phospho- specific mAb (anti-phospho-ERK), citralva activated the ERK pathway in a STEAP-2 specific manner. These results also confirm the findings described in Figures 27-28, that expression of STEAP-1 alone is sufficient to induce the activation of the ERK pathway. Example 15: Identification of Potendal Signal Transduction Pathways To confirm that STEAP direcdy or indirecdy activates known signal transduction pathways in ceUs and to delineate STEAP-mediated downstream events, luciferase (luc) based transcriptional reporter assays are carried out in ceUs expressing STEAP. These transcriptional reporters contain consensus binding sites for known transcription factors which he downstream of weU characterized signal transduction pathways. The reporters and examples of their associated transcription factors, signal transduction pathways, and activation stimuli are hsted below. 1. NFkB-luc, NFkB/Rel; Ik-kinase/SAPK; growth/apoptosis/sttess 2. SRE-luc, SRF/TCF/ELKl; MAPK/SAPK; growth/ differentiation 3. AP-l-luc, FOS/JUN; MAPK/SAPK/PKC; growth/apoptosis/sttess 4. ARE-luc, androgen receptor; steroids/MAPK; growth/differentiation/apoptosis 5. p53-luc, p53; SAPK; growth/differentiation/apoptosis 6. CRE-luc, CREB/ATF2; PKA/p38; growth/apoptosis/sttess STEAP -mediated effects may be assayed in ceUs showing mRNA expression. Luciferase reporter plasmids may be introduced by lipid mediated transfection (TFX-50, Promega). Luciferase activity, an indicator of relative transcriptional activity, is measured by incubation of ceUs extracts with luciferin substrate and luminescence of the reaction is monitored in a luminometer. Example 16: In Vitro Assays of STEAP Function The expression profile of STEAP in prostate cancer suggests a functional role in tumor initiation, progression and/or maintenance. STEAP function can be assessed in mammahan ceUs using in vitto approaches. For mammahan expression, STEAP can be cloned into a number of appropriate vectors, including pcDNA 3.1 myc-His-tag and the retroviral vector pSRαtkneo (MuUer et al, 1991, MCB 11:1785). Using such expression vectors, STEAP can be expressed in several cancer ceU lines, including for example PC-3, NIH 3T3, LNCaP and 293T. Expression of STEAP can be monitored using anti- STEAP antibodies. Mammahan ceU lines expressing STEAP can be tested in several in vitto and in vivo assays, including ceU prohferation in tissue culture, activation of apoptotic signals, primary and metastatic tumor formation in SCID mice, and in vitto invasion using a membrane invasion culture system (MICS) (Welch et al. ,Int. J. Cancer 43: 449-457). STEAP ceU phenotype is compared to the phenotype of ceUs that lack expression of STEAP. In addition, ceUs treated with and without exogenously added STEAP protein may be analyzed for altered growth parameters. CeU lines expressing STEAP can also be assayed for alteration of invasive and migratory properties by measuring passage of ceUs through a matrigel coated porous membrane chamber (Becton Dickinson). Passage of ceUs through the membrane to the opposite side is monitored using a fluorescent assay (Becton Dickinson Technical BuUetin #428) using calcein-Am (Molecular Probes) loaded indicator ceUs. CeU lines analyzed include parental and STEAP overexpressing PC3, 3T3 and LNCaP ceUs. To assay whether STEAP has chemoatttactant properties, parental indicator ceUs are monitored for passage through the porous membrane toward a gradient of STEAP conditioned media compared to conttol media. This assay may also be used to qualify and quantify specific neutralization of the STEAP induced effect by candidate cancer therapeutic compositions. In order to estabhsh whether STEAP binds to ceUular proteins expressed in prostate cancer ceUs and other cancer ceUs or normal ceUs, two approaches may be taken. In the first approach, in vitto assay for recombinant HIS-tagged STEAP binding to various ceU lines are used. In another approach, a recombinant alkaline phosphatase- STEAP fusion protein is generated using the AP-TAG system from GenHunter Corporation (NashviUe, TN, cat# Q202), and the AP-TAG fusion used to test STEAP binding to a variety of prostate cancer ceU lines as described (Cheng and Flanagan, 1994, CeU 79:157-168). After washing the ceUs and adding the AP substtate BCIP, which forms an insoluble blue precipitate upon dephosphorylation, STEAP binding is determined by identifying ceUs staining blue under the light microscope. Various cancer ceU lines can be examined, including without limitation, various prostate cancer ceU lines (e.g, LNCaP, PC-3, DU145, TSUPR, LAPC4). Other ceU lines such as PREC prostate ceU line, 293T, PIN ceUs, and NIH 3T3, etc. may also be examined. AdditionaUy, the LAPC and other prostate cancer xenografts may be tested. Equilibrium dissociation rate constants may be calculated to evaluate the strength of the binding interaction. In addition, the number of ceU surface receptors per ceU can be determined. CeU lines or tissues with the highest binding capacity for STEAP would be preferred for cloning a STEAP binding partner. In another functional assay, NIH-3T3 ceUs stably expressing STEAP can be analyzed for their ability to form colonies in soft agar. In these experiments, ceUs used in such procedures (e.g. NIH-3T3 ceUs), can be transfected to stably express STEAP or neo or activated-Ras (as the test gene, the negative and the positive controls, respectively) in order to assess the ttansfonriing capabilities of STEAP. TypicaUy experiments are performed in duplicate and the assays are evaluated approximately 4 weeks after ceU plating. Where experimental observations demonstrate that STEAP induces an increase in colony formation relative to a negative conttol (e.g. neo) such results indicate that STEAP has significant transforming capabilities. Example 17: In Vivo Assay for STEAP Tumor Growth Promotion The effect of the STEAP protein on tumor ceU growth may be evaluated in vivo by gene overexpression in tumor-bearing mice. For example, SCID mice can be injected subcutaneously on each flank with 1 x 10 6 of a prostate ceU line containing tkNeo empty vector or STEAP. At least two sttategies may be used: (1) Constitutive STEAP expression under regulation of an LTR promoter, and (2) Regulated expression under control of an inducible vector system, such as ecdysone, tet, etc. Tumor volume is then monitored at the appearance of palpable tumors and foUowed over time to determine if STEAP expressing ceUs grow at a faster rate. AdditionaUy, mice may be implanted with 1 x 10 5 of the same ceUs orthotopicaUy to determine if STEAP has an effect on local growth in the target tissue (i.e, prostate) or on the ability of the ceUs to metastasize, specificaUy to lungs, lymph nodes, hver, bone marrow, etc. The effect of STEAP on bone tumor formation and growth may be assessed by injecting prostate tumor ceUs inttatibiaUy, as described in Example 1. These assays are also useful to determine the STEAP inhibitory effect of candidate therapeutic compositions, such as for example, STEAP antibodies, STEAP antisense molecules and ribozymes. Example 18: Detection of Prostate Cancer Metastases in Mice and Humans Using Anti-STEAP-1 Polyclonal Antibodies Mice STEAP-1 iminunohistochemical analysis was performed on 4 μm formalin-fixed tissues derived from mice bearing orthotopic LAPC-9 prostate cancer tumors and their derived lung and lymph node metastases. Serial lung sections were tested using anti- STEAP-1 sheep polyclonal antibody and anti-PSA rabbit polyclonal antibody (pAb). Microscopic examination of stained tissue was used to detect LAPC-9 prostate cancer ceUs, and the results are shown in Figures 31A-F. The anti-STEAP-1 sheep pAb readUy detected human prostate cancer ceUs in the mouse prostate (Figure 31A), as weU as in metastases to lymph nodes (Figure 31B) and lung (Figure 31C-D). Both smaU (Figure 31C) and large (Figure 3 ID) micrometastases to the lung were readUy detected using the anti-STEAP-1 pAb. To confirm that the lung metastases were of prostate cancer origin, immunohistochemistry on serial lung sections was performed using the anti-PSA pAb (Figure 31E-F). The sttong ceU surface staining observed with the anti-STEAP-1 pAb aUows for easier detection of micrometastases as compared to the use of the anti-PSA polyclonal antibody. Humans The STEAP-1 polyclonal Ab was used in a simUar immunohistochemical assay of metastatic prostate cancer specimens from human patients. High expression of STEAP- 1 was detected in both the lymph node and bone metastases studied. As shown in Figures 32A (lymph node metastasis) and 32B (bone metastasis), intense periceUular staining is observed in these human patient samples, confirming that STEAP-1 is an exceUent marker for the detection of metastatic prostate cancer. Example 19: STEAP-1. STEAP-2 and STEAP-3 Extracellular Loop-Fc Fusion Constructs To express and secrete the extraceUular loops of STEAP-1, STEAP-2, and STEAP-3 into conditioned media of mammahan ceU lines, fragments of these genes can be cloned into the pFc vector to generate C-terminal fusions of the human IgGl Fc region. The pFc vector was generated by cloning human immunoglobulin Gl , Fc (bases 74-768 of GenBank accession X70421) proceeded by the IgA protease cleavage site (Roche, Cat 1461265) coded by 5' cctcgacctccaacaccgggg 3' (SEQ ID NO: 47) into pTag-5 (GenHunter Corp. NashviUe, TN) using Xhol and Apal. This construct generates an IgGl Fc fusion at the C-terminus of STEAP-1, STEAP-2 and STEAP-3 extraceUular regions whUe fusing the IgGK signal sequence to N-terminus. The resulting recombinant proteins are optimized for secretion into the media of ttansfected mammalian ceUs and can be used to identify proteins such as hgands or receptors that interact with the STEAP-1, STEAP-2, and STEAP-3 protein. These protein fusions can also be used as immunogen to generate antibodies. Protein expression is driven from the CMV promoter. The Zeosin resistance gene aUows for selection of mammalian ceUs expressing the protein and the ampicillin resistance gene permits selection of the plasmid in E. coh. The foUowing extraceUular loops of the STEAP-1, STEAP-2, and STEAP-3 proteins are suitable for cloning into pFc: STEAP-1 revihplatshqqyfykipUv (SEQ ID NO: 37) rrsyrykllnwayqqvqqnkedawiehdvwrmei (SEQ ID NO: 38) widikqfvwytpptf (SEQ ID NO: 39) STEAP-2 ysfvrdvihpyarnqqsdfykipiei (SEQ ID NO: 40) rrserylflnmayqqvhanienswneeevwrie (SEQ ID NO: 41) krafeeeyyrfy (SEQ ID NO: 42) STEAP-3 ypyvyekkdntfrmaisipnrifp (SEQ ID NO: 43) yyvrwrlgnltvtqailkkenpfstssawlsdsy (SEQ ID NO: 44) Example 20: Generation of Polyclonal Antibodies to STEAP-2 Three immunogens were used to generate antibodies specific to STEAP-2. Two immunogens were peptides encoding amino acids 153-165 (ALQLGPKDASRQV; SEQ ID NO: 45) and amino acids 345-358 (lENSWNEEEVWRIE; SEQ ID NO: 46) of the STEAP-2 protein sequence. The first peptide resides in the N-terminus of STEAP-2, which is intraceUular using the membrane topology prediction program SOSUI. The latter peptide resides in the region between transmembrane domains 3 and 4, and this region is predicted to encode the second of 3 extraceUular loops. A third immunogen was a glutathione-S-transferase (GST) fusion protein encompassing amino acids 2-204 of the STEAP-2 protein sequence. The recombinant GST-STEAP-2 fusion protein was purified from induced bacteria by glutathione-sepharose affinity chromatography. In addition to the above antigens, peptides encoding other regions of the STEAP-2 protein, or bacterial and baculovirus virus produced proteins encoding either full length or partial sequences of the STEAP-2 protein, are use to generate a variety of STEAP-2 specific antibodies. These antibodies are directed to regions that may modulate STEAP-2 function. Generation of poyl clonal antibodies (pAbs) To generate pAbs to STEAP-2, the purified GST-fusion protein and the peptides coupled to Keyhole limpet hemacyanin (KLH) were used to immunize individual rabbits as foUows. The rabbits were immunized with 200 μg of fusion protein or KLH-peptide antigen mixed in complete Freund's adjuvant. The rabbits were then injected every two weeks with 200 μg of immunogen in incomplete Freund's adjuvant. Test bleeds were taken approximately 7-10 days foUowing each immunization. The titer of peptide 153- 165 antiserum was at least 25,000 and of peptide 345-358 antiserum at least 10,000 as determined by ELISA to the respective immunogens. The titer of the GST-fusion serum was at least 300,000. Peptide antiserum is affinity purified by passage of the serum over an affinity column composed of the respective peptide covalendy coupled to Affigel matrix (BioRad). Serum raised to the GST- fusion is semi-purified first by removal of GST-reactive antibodies by passage over a GST affinity column. STEAP-2 specific antibody is then isolated by passage over a GST-STEAP-2 affinity column. Alternatively, STEAP-2 specific antisera is isolated by affinity chromatography using a maltose binding protein (MBP) -STEAP-2 fusion protein encoding the same amino acids Example 21: Generation of Monoclonal Antibodies to STEAP Proteins To generate mAbs to STEAP-1, STEAP-2, STEAP-3, or STEAP-4 proteins, Balb C mice are immunized inttaperitoneaUy with 20-50 μg of KLH-coupled peptide or with bacterial recombinant polypeptides, such as GST-fusion proteins, encoding regions of the respective STEAP member protein sequence mixed in complete Freund's adjuvant. Mice are then subsequendy immunized every 2-4 weeks with 20-50 μg of immunogen mixed in Freund's incomplete adjuvant. Alternatively, Ribi adjuvant is used for initial immunizations. Test bleeds are taken 7-10 days foUowing immunization to monitor titer and specificity of the immune response. Serum from mice immunized with a GST-fusion protein encompassing amino acids 148-251 of STEAP-1 attained a titer of at least 8X10 6 as determined by ELISA and specificaUy recognized STEAP-1 protein by western blot (Figure 33). Once appropriate reactivity and specificity are obtained as determined by ELISA, western blotting, and flow cytometry analyses, fusion and hybridoma generation is then carried out using established procedures weU known in the art (Harlow and Lane, 1988). Figure 33 is a western blot showing that anti-STEAP-1 murine pAb recognizes STEAP-1 protein in engineered ceU lines and endogenous STEAP-1 protein in LNCaP ceUs. Lysates of LNCaP ceUs and 293T ceUs ttansfected with either pcDNA 3.1 MYC/HIS tagged STEAP-1 or neo empty vector, and RATl ceUs engineered to express STEAP-1 or a neo conttol gene, were separated by SDS-PAGE and transferred to nitroceUulose. The blot was then subjected to anti-STEAP western analysis using a 1:1000 dUution of serum from mice immunized with a GST-STEAP-1 fusion protein. Alternative antigens and immunization sttategies are also used to generate mAbs with specific reactivity and specificity to various regions of the STEAP proteins. Such antigens may include baculovirus produced recombinant proteins or mammalian expressed and secreted human IgG FC-fusion proteins encoding various regions of each STEAP famUy member protein sequence, such as predicted extraceUular domains. A ceU based immunization sttategy is also used in which the cDNA of a STEAP famUy member is overexpressed in ceUs such as NIH3T3 mouse fibroblasts or 300.19 murine pre-B ceUs and whole ceUs or membrane preparations from these ceUs are used as immunogen. In addition, a DNA-based irrimunization protocol in which a mammahan expression vector encoding the STEAP-1 or STEAP-2 cDNA such as pcDNA 3.1 is used to immunize mice by direct injection of the plasmid DNA. This protocol is used either alone or in combination with protein and/or ceU-based immunization sttategies. Throughout this application, various publications are referenced. The disclosures of these publications are hereby incorporated by reference herein in their entireties. The present invention is not to be limited in scope by the embodiments disclosed herein, which are intended as single iUusttations of individual aspects of the invention, and any that are functionaUy equivalent are within the scope of the invention. Various modifications to the models and methods of the invention, in addition to those described herein, wiU become apparent to those skiUed in the art from the foregoing description and teachings, and are simUarly intended to faU within the scope of the invention. Such modifications or other embodiments can be practiced without departing from the true scope and spirit of the invention. Applicant's or agent's file International application No reference number 29 17WOI1 INDICATIONS RELATING TO A DEPOSITED MICROORGANISM (PCT Rule I3bιs) A. The indications made belowrelate to the microorganismreferred to in the description on page 75 , lιne 4-6 B. IDENTIFICATIONOFDEPOSΓΓ Furtherdeposits are identified on an additional sheet Name of depositary institution American Type Culture Collection Address of depositary institution (including postal code and country) 10801 University Boulevard Manassas, Virginia 20110-2209 United States of America Date of deposit AccessionNumber 26 August 1998 (26 08 98) 98849 C. ADDITIONAL INDICATIONS (leave blank if not applicable) This information is continued on an additional sheet | | D. DESIGNATED STATES FOR WHICH INDICATIONS ARE MADE (if the indications are nolfor all designated Stales) E. SEPARATE FURNISHING OF INDICATIONS fleaveblankifnot applicable) The indications listed below will be submitted to the International Bureau later (specify the general nature of Ihe indications e g "Accession Number of Deposit") For International Bureau use only | | This sheet was received by the International Bureau on Authorized officer Form PCT/RO/134 (July 199 2 ) Applicant s or agent's file International application No reference number I 29 17WOI1 INDICATIONS RELATING TO A DEPOSITED MICROORGANISM A. The indications made belowrelate to the microorganism referred to in the description on page 84 . line 1-3 B. IDENTIFICATIONOFDEPOSIT Further deposits are identified on an additional sheet Name of depositary institution American Type Culture Collection Address of depositary institution (including postal code and country) 10801 University Boulevard Manassas, Virginia 20110-2209 United States of America Date of deposit Accession Number 02 July 1999 (02.07.99) PTA-311 C. ADDITIONAL INDICATIONS fleaveblankifnot applicable) This information is continued on an additional sheet | | D. DESIGNATED STATES FOR WHICH INDICATIONS ARE MADE (if the indications are not for all designated States) E. SEPARATE FURNISHING OF INDICATIONS (leaveblankif not applicable) The indications listed below will be submitted to the International Bureau later (specijy the general nature oflhe indications eg "Accession Number of Deposit") For International Bureau use only | | This sheet wasreceivedby the International Bureau on Authorized officer Form PCT RO/13 (July 1992) Applicant's or agent's file International application No. I reference number 129 17WOI1 INDICATIONS RELATING TO A DEPOSITED MICROORGANISM (PCT Rule ttbis) The indications made belowrelate to the microorganism referred to in the description on page §4 , ime 27-29 B. IDENTIFTCATIONOFDEPOSIT Further deposits are identified on an additional sheet \jζ\ Name of depositary institution American Type Culture Collection Address of depositary institution (including postal code and country) 10801 University Boulevard Manassas, Virginia 20110-2209 United States of America Dateof deposit Accession Number 08 December 1999 (08.12.99) PTA-1033 C. ADDITIONAL INDICATIONS (leave blank if not applicable) This information is continued on an additional sheet | | D. DESIGNATED STATES FOR WHICH INDICATIONS ARE MADE (if the indicationsarenotforalldesignatedStates) E. SEPARATEFURNISHINGOFINDICATIONS f7ecvefe;α«iι/«ofαpp/ιcα6/e) The indications listed below will be submitted to the International Bureau later (specify the general nature of Ihe indications eg, "Accession Number of Deposit") Forlntemational Bureau use only j I This sheet was receivedby the International Bureau on Authoπzed officer

Claims: CLAIMS: 1. A STEAP-2 protein having an amino acid sequence shown in FIG. 9A-D (SEQ ID NO: 8). 2. A STEAP-2 polypeptide that includes at least 10 contiguous amino acids of an amino acid sequence selected from the group consisting of amino acids 1-245, 2- 204, 100-108, 121-454, 153-165, 182-454, 183-387, 227-235, 276-453, 306-314, 307-315, 345-358, 402-410, and 419-454 of the amino acid sequence shown in FIG. 9A-D (SEQ ID NO: 8). 3. A polypeptide comprising an amino acid sequence which is at least 90% identical to the amino acid sequence shown in FIG. 9A-D (SEQ ID NO: 8) over its entire length. 4. A polynucleotide selected from the group consisting of (a) a polynucleotide having the sequence as shown in FIG. 9A-D (SEQ ID NO: 7), wherein T can also be U; (b) a polynucleotide encoding a STEAP-2 polypeptide whose sequence is encoded by the cDNA contained in plasmid 98P4B6-GTD3 as deposited with American Type Culture Collection as Accession No. PTA-311; (c) a polynucleotide encoding the STEAP-2 protein of claim 1 ; and (d) a polynucleotide which is fully complementary to a polynucleotide of (a)-(c). 5. A polynucleotide that encodes the fragment of claim 2. 6. A recombinant expression vector which contains a polynucleotide according to claim 4 or 5. 7. A host cell which contains an expression vector according to claim 6. 8. A polynucleotide according to claim 4 or 5 which is labeled with a detectable marker. 9. A process for producing a STEAP-2 protein comprising culturing a host cell of claim 7 under conditions sufficient for the production of the polypeptide and recovering the STEAP-2 protein from the culture. 10. An antibody or fragment thereof which specifically binds to an epitope within amino acids 1-245, 2-204, 100-108, 121-454, 153-165, 182-454, 183-387, 227-235, 276-453, 306-314, 307-315, 345-358, 402-410, or 419-454 of the STEAP-2 protein of claim 1. 11. The antibody or fragment thereof of claim 10 which is monoclonal. 12. A recombinant protein comprising the antigen binding region of a monoclonal antibody of claim 11. 13. The antibody or fragment thereof of claim 10 or 11, or the recombinant protein of claim 12, which is labeled with a detectable marker. 14. The antibody or fragment thereof or recombinant protein of claim 13, wherein the detectable marker comprises a radioisotope, metal chelator, enzyme or fluorescent, bioluminescent or cherniluminescent compound. 15. The antibody fragment of claim 13, which is an Fab, F(ab')2, Fv or Sfv fragment. 16. The antibody or fragment thereof of any one of claims 10, 11, 13 or 14, which is a human antibody. 17. The antibody of any one of claims 10, 11, 13 or 14, which comprises murine antigen binding region residues and human antibody residues. 18. A transgenic animal producing a monoclonal antibody of claim 11. 19. A hybridoma producing a monoclonal antibody of claim 11. 20. A single chain monoclonal antibody that comprises the variable domains of the heavy and light chains of a monoclonal antibody of claim 11. 21. A vector comprising a polynucleotide encoding a single chain monoclonal antibody of claim 20. 22 The monoclonal antibody or fragment thereof of claim 11 which is conjugated to a toxin, a radioisotope or a therapeutic agent. 23. The monoclonal antibody or fragment thereof of claim 22, wherein the toxin comprises ricin, ricin A-chain, doxorubicin, daunorubicin, a maytansinoid, taxol, ethidium bromide, mitomycin, etoposide, tenoposide, vincristine, vinblastine, colchicine, dihydroxy anthracin dione, actinomycin, diphtheria toxin, Pseudomonas exotoxin (PE) A, PE40, abrin, abrin A chain, modeccin A chain, alpha-sarcin, gelonin, mitogellin, retstrictocin, phenomycin, enomycin, cuncin, crotin, cahcheamicin, sapaonaria officinalis inhibitor, or a glucocorticoid. 24. The monoclonal antibody or fragment thereof of claim 22, wherein the radioisotope comprises 212 Bι, 131 I, 131 In, 90 Y, or 186 Re. 25 An assay for detecting the presence of a STEAP-2 protein in a biological sample comprising contacting the sample with an antibody of claim 13, and detecting the binding of STEAP-2 protein in the sample thereto. 26. An assay for detecting the presence of a STEAP-2 polynucleotide in a biological sample, comprising: (a) contacting the sample with a polynucleotide probe which specifically hybridizes to a polynucleotide of claim 4; and (b) detecting the presence of a hybridization complex formed by the hybridization of the probe with STEAP-2 polynucleotide in the sample, wherein the presence of the hybridization complex indicates the presence of STEAP-2 polynucleotide within the sample. 27. An assay for detecting the presence of STEAP-2 mRNA in a biological sample comprising: (a) producing cDNA from the sample by reverse transcription using at least one primer; (b) amplifying the cDNA so produced using STEAP-2 polynucleotides as sense and antisense primers to amplify STEAP-2 cDNAs therein; (c) detecting the presence of the amplified STEAP-2 cDNA, wherein the STEAP-2 polynucleotides used as the sense and antisense primers are capable of amplifying the polynucleotide shown in FIG. 9A-D (SEQ ID NO: V). 28. A pharmaceutical composition comprising an antibody or fragment thereof according to claim 10, 11, 15, 16 or 17, a STEAP-2 protein according to claim 1 or 2, or a STEAP-2 polynucleotide according to claim 4 or 5, and a physiologically acceptable carrier. 29. A vaccine composition comprising a STEAP-2 protein according to claim 1 or 2, or a STEAP-2 polynucleotide according to claim 4 or 5, and a physiologically acceptable carrier. 30. A method of inhibiting the development or progression of a cancer expressing STEAP-2 in a patient, comprising administering to the patient an effective amount of the vaccine composition of claim 29. 31. A method of inhibiting the growth of cells expressing STEAP-2 in a patient, comprising administering to the patient an effective amount of the vaccine composition of claim 29. 32. A method of killing cells that express STEAP-2 in a patient, comprising administering to the patient an effective amount of the vaccine composition of claim 29. 33. A method of treating a patient with a cancer that expresses STEAP-2, which comprises administering to said patient a vector encoding a single chain monoclonal antibody that comprises the variable domains of the heavy and light chains of a monoclonal antibody that specifically binds to a STEAP-2 protein of claim 2, such that the vector delivers the single cham monoclonal antibody coding sequence to the cancer cells and the encoded smgle cham antibody is expressed lntracellularly therein. 34. A method of inhibiting growth of cells that express STEAP-2, which comprises administering to said patient a vector encodmg a smgle cham monoclonal antibody that comprises the variable domains of the heavy and light chains of a monoclonal antibody that specifically bmds to a STEAP-2 protem of claim 2, such that the vector delivers the smgle cham monoclonal antibody coding sequence to the cancer cells and the encoded smgle cham antibody is expressed lntracellularly therein. 35. A method of killing cells that express STEAP-2, which comprises adrnimstermg to said patient a vector encoding a smgle chain monoclonal antibody that comprises the variable domams of the heavy and light chains of a monoclonal antibody that specifically bmds to a STEAP-2 protem of claim 2, such that the vector delivers the smgle cham monoclonal antibody coding sequence to the cancer cells and the encoded smgle cham antibody is expressed lntracellularly therein. 36. A STEAP-3 protem havmg an ammo acid sequence shown in FIG. 10A-E (SEQ ID NO: 10). 37. A polypeptide of at least 10 contiguous amino acids of the protem of claim 36. 38. A polypeptide comprismg an am o acid sequence which is at least 90% identical to the ammo acid sequence shown m FIG. 10A-E (SEQ ID NO: 10) over its entire length. 39. A polynucleotide selected from the group consisting of (a) a polynucleotide havmg the sequence as shown in FIG. 10A-E (SEQ ID NO: 9), wherem T can also be U; (b) a polynucleotide encoding the STEAP-3 protem of claim 1 ; and (c) a polynucleotide which is fully complementary to a polynucleotide of (a) or (b). 40. An antibody or fragment thereof which specifically binds to the STEAP-3 protein of claim 36. 41. The antibody or fragment thereof of claim 40 which is monoclonal. 42. A recombinant protein comprising the antigen binding region of a monoclonal antibody of claim 41. 43. The antibody or fragment thereof of claim 40 or 41 which is labeled with a detectable marker. 44. The antibody or fragment thereof or recombinant protein of claim 43, wherein the detectable marker comprises a radioisotope, metal chelator, enzyme or fluorescent, bioluminescent or cherniluminescent compound. 45. The monoclonal antibody or fragment thereof of claim 41 which is conjugated to a toxin, a radioisotope or a therapeutic agent. 46. The monoclonal antibody or fragment thereof of claim 41, wherein the toxin comprises ricin, ricin A-chain, doxorubicin, daunorubicin, a maytansinoid, taxol, ethidium bromide, mitomycin, etoposide, tenoposide, vincristine, vinblastine, colchicine, dihydroxy anthracin dione, actinomycin, diphtheria toxin, Pseudomonas exotoxin (PE) A, PE40, abrin, abrin A chain, modeccin A chain, alpha-sarcin, gelonin, mitogellin, retstrictocin, phenomycin, enomycin, curicin, crotin, calicheamicin, sapaonaria officinalis inhibitor, or a glucocorticoid. 47. The monoclonal antibody or fragment thereof of claim 41, wherein the radioisotope comprises 2l2 Bi, l3l I, 13l In, 90 Y, or 186 Re. 48. The antibody fragment of claim 41, which is an Fab, F(ab')2, Fv or Sfv fragment. 49. The antibody or fragment thereof of any one of claims 40, 41, and 43-48, which is a human antibody. 50. The antibody or fragment thereof of any one of claims 40, 41 , and 43-48, which comprises murine antigen binding region residues and human antibody residues. 51. A transgenic animal producing a monoclonal antibody of claim 41. 52. A hybridoma producing a monoclonal antibody of claim 41. 53. A single chain monoclonal antibody that comprises the variable domains of the heavy and light chains of a monoclonal antibody of claim 41. 54. A vector comprising a polynucleotide encoding a single chain monoclonal antibody of claim 53. 55. An assay for detecting the presence of a STEAP-3 protein in a biological sample comprising contacting the sample with an antibody of claim 43 or 44, and detecting the binding of STEAP-3 protein in the sample thereto. 56. An assay for detecting the presence of a STEAP-3 polynucleotide in a biological sample, comprising (a) contacting the sample with a polynucleotide probe which specifically hybridizes to a polynucleotide of claim 39 or its complement; and (b) detecting the presence of a hybridization complex formed by the hybridization of the probe with STEAP-3 polynucleotide in the sample, wherein the presence of the hybridization complex indicates the presence of STEAP-3 polynucleotide within the sample. 57. An assay for detecting the presence of STEAP-3 mRNA in a biological sample comprising: (a) producing cDNA from the sample by reverse transcription using at least one primer; (b) amplifying the cDNA so produced using STEAP-3 polynucleotides as sense and antisense primers to amplify STEAP-3 cDNAs therein; (c) detecting the presence of the amplified STEAP-3 cDNA, wherein the STEAP-3 polynucleotides used as the sense and antisense primers are capable of amplifying the polynucleotide of FIG. 10A-E (SEQ ID NO: 9). 58. A pharmaceutical composition comprising an antibody or fragment thereof or recombinant protein of any one of claims 40-50, a STEAP-3 protein according to claim 36, or a STEAP-3 polynucleotide according to claim 39, and a physiologically acceptable carrier.

Inventors: AFAR DANIEL E H, FARIS MARY, HUBERT RENE S, JAKOBOVITS AYA, MITCHELL STEVE CHAPPELL, RAITANO ARTHUR B, SAFFRAN DOUGLAS C, AFAR, DANIEL, E., H., FARIS, MARY, HUBERT, RENE, S., JAKOBOVITS, AYA, MITCHELL, STEVE, CHAPPELL, RAITANO, ARTHUR, B., SAFFRAN, DOUGLAS, C.
Applicants: UROGENESYS INC, UROGENESYS, INC.
Application year: 2000
Main classification: C07K14
IPC codes: A01K67, A61K35, A61K38, A61K39, A61K48, A61K51, A61P35, A61P43, C07K14, C07K16, C07K19, C12N1, C12N5, C12N15, C12P21, C12Q1, G01N33