Expression of androgen receptor coregulators in prostate cancer.

PURPOSE: The androgen receptor (AR)-mediated signaling pathway seems to be essentially involved in the development and progression of prostate cancer. In vitro studies have shown that altered expression of AR coregulators may significantly modify transcriptional activity of AR, suggesting that these coregulators could also contribute to the progression of prostate cancer. Here, our goal was to assess alterations in the expression of the AR coregulators in prostate cancer in vivo. EXPERIMENTAL DESIGN: The expression of 16 AR coactivators and corepressors (SRC1, beta-catenin, TIF2, PIAS1, PIASx, ARIP4, BRCA1, AIB1, AIB3, CBP, STAT1, NCoR1, AES, cyclin D1, p300, and ARA24) was measured in prostate cancer cell lines, xenografts, and clinical prostate tumor specimens by using real-time quantitative reverse transcription-PCR. In addition, gene copy number of SRC1 was analyzed by fluorescence in situ hybridization. RESULTS: Both AR-positive and AR-negative cell lines and xenografts expressed the coregulators. Most of the coregulators studied were expressed at equal levels in benign prostatic hyperplasia and untreated and hormone-refractory carcinomas. However, the expression of PIAS1 and SRC1 was significantly (P = 0.048 and 0.017, respectively) lower in hormone-refractory prostate tumors than in untreated prostate tumors. No overexpression of the coregulators was found in the clinical material. Paradoxically, the SRC1 gene was found to be amplified and highly expressed in a LuCaP 70 prostate cancer xenograft. CONCLUSIONS: These findings suggest that the decreased expression of PIAS1 and SRC1 could be involved in the progression of prostate cancer. In addition, gene amplification of SRC1 in one of the xenografts implies that, in some tumors, genetic alteration of SRC1 may provide a growth advantage.

Amplification of the urokinase gene and the sensitivity of prostate cancer cells to urokinase inhibitors.

OBJECTIVES: To evaluate the frequency of the urokinase-type plasminogen activator (uPA) gene amplification and the sensitivity of prostate cancer cells to uPA inhibition, as we previously found one hormone-refractory prostate tumour with high-level amplification of the uPA (alias PLAU) gene, and also showed that a uPA inhibitor, amiloride, can effectively reduce the invasion potential of the PC-3 prostate cancer cell line. MATERIALS AND METHODS: Sixty-three locally recurrent hormone-refractory tumours and 78 hormone-refractory metastases from 29 patients who died from prostate cancer were analysed for uPA gene-copy number using fluorescence in situ hybridization. The Matrigel invasion assay was used to study the influence of uPA inhibitors on the invasive potential of prostate cancer cell lines. RESULTS: Of the locally recurrent hormone-refractory tumours, 21% had an increased copy number of uPA, but no high-level amplifications were found; 31% of the metastases had increased copy number and one high-level amplification of the uPA. Matrigel invasion assays with two specific uPA inhibitors, B428 and p-aminobenzamidine, showed that invasion of a prostate cancer cell line containing uPA gene amplification was inhibited by these small-molecule uPA inhibitors, while invasion of prostate cell lines without uPA gene amplification were not. CONCLUSION: These results suggest that selective inhibition of the uPA pathway in individuals whose tumours contain uPA gene amplification may provide therapeutic benefit.

Overexpression of EIF3S3 promotes cancer cell growth.

BACKGROUND: Amplification and overexpression of EIF3S3 gene has been demonstrated in breast and prostate cancer. Here, our goal was to study the effect of EIF3S3 on cell growth. METHODS: The effect of EIF3S3 on growth of NIH 3T3 murine fibroblasts as well as breast (SK-Br-3 and ZR-75-1) and prostate (PC-3 and LNCaP) cancer cell lines was examined by using transfection with inducible pTet-Off system and siRNAs. RESULTS: NIH 3T3 cells with overexpression of EIF3S3 grew significantly faster than cells transfected with empty vector and survived longer when grown in soft agar. The EIF3S3 overexpression was associated with increased fraction of cells in S-phase and with phosphorylation of retinoblastoma (Rb) protein. siRNA treatment inhibited significantly (P = 0.0022) the growth of all breast and prostate cancer cell lines studied. CONCLUSIONS: The results suggest that EIF3S3 regulates cell growth and viability, and that overexpression of the gene may provide growth advantage to the cancer cells.

Expression of ERalpha and ERbeta in prostate cancer.

BACKGROUND: It has been suggested that estrogens and their receptors (ERs) may be involved in the development and progression of prostate cancer. To elucidate the significance of these receptors, expression of both ERalpha and ERbeta was measured in benign and malignant prostate tumors, as well as in cell lines. METHODS: Expression of ERalpha and ERbeta was measured in prostate hyperplasia (BPH, n = 7), androgen-dependent (n = 30) as well as hormone-refractory (n = 12) prostate carcinomas, and in four prostate cancer cell lines (LNCaP, DU145, PC-3, and 22Rv1) using real-time quantitative RT-PCR. RESULTS: Only low-level expression of ERalpha was found in all tumor types and cell lines. The level of expression was similar to that observed in breast carcinomas found to be negative for ERalpha by immunohistochemistry. All cell lines showed low, but detectable, levels of ERbeta expression. The mean expression of ERbeta in the hormone-refractory carcinomas was about half that seen in BPH or the androgen-dependent carcinomas; however, the difference was not statistically significant. CONCLUSIONS: The data suggest it is unlikely that alterations in the expression of either ER are commonly involved in the progression of prostate cancer.

Expression and gene copy number analysis of ERBB2 oncogene in prostate cancer.

An anti-ERBB2 antibody, trastuzumab, has been shown to be highly efficient in the treatment of metastatic breast cancers overexpressing the ERBB2 gene. It has been suggested that overexpression and even amplification of ERBB2 may play a role in the development of prostate cancer. Here, we have analyzed gene copy number and expression of the ERBB2 gene in both androgen-dependent primary and metastatic tumors, as well as recurrent hormone-refractory tumors. The expression levels were compared to the expression of ERBB2 in breast cancers with or without ERBB2 gene amplification. Of 126 prostate tumors, chromogenic in situ hybridization (CISH) revealed only 1 case containing borderline (six to eight copies) amplifications of ERBB2. This hormone-refractory tumor, however, did not express ERBB2 protein. Immunohistochemical staining of ERBB2 protein was negative (0 or 1+ intensity) in all prostate samples (n = 124) analyzed. To quantitate the level of ERBB2 mRNA expression in prostate tumors (n = 34) and cell lines (n = 3), as well as in breast tumors (n = 30) and cell lines (n = 16), real-time reverse transcriptase-polymerase chain reaction (LightCycler) methodology was used. The expression level was similar in all prostate tumor types and corresponded to the level of expression in breast carcinomas without ERBB2 amplification. Breast tumors with ERBB2 amplification expressed, on average, approximately 20 times (P < 0.001) higher mRNA levels than prostate tumors or breast carcinomas without the gene amplification. In conclusion, the expression of ERBB2 in prostate cancer is relatively low, and is not altered during disease progression. Thus, it is unlikely that treatment modalities relying on the overexpression of ERBB2 gene will be useful in treating prostate cancer.