ACTR/AIB1/SRC-3 and androgen receptor control prostate cancer cell proliferation and tumor growth through direct control of cell cycle genes

BACKGROUND: Co-factor ACTR is frequently overexpressed and/or amplified in multiple types of tumors. The mechanism of its function in prostate cancer (CaP) is still unclear. METHODS: The effects of ACTR and androgen receptor (AR) depletion on cell proliferation and gene expression and their functions were analyzed in a panel of androgen-dependent and -independent CaP cells and CWR22 xenograft. RESULTS: ACTR and AR, but not TIF2, are required for proliferation of androgen-dependent and -independent cells, and for tumor growth. While AR depletion inhibited the expression of cyclin D1, cyclin B, and cdc2, ACTR depletion reduced the expression of cyclin E and cdk2. In response to serum stimulation, AR and ACTR are recruited to the corresponding target gene promoters to activate their expression in androgen-independent manner. CONCLUSION: These findings suggest that AR and ACTR may play important roles in androgen ablation resistance by controlling key cell cycle gene expression.     

Longitudinal analysis of androgen deprivation of prostate cancer cells identifies pathways to androgen independence

BACKGROUND: Following androgen ablation therapy, the majority of prostate cancer patients develop treatment resistance with a median time of 18-24 months to disease progression. METHODS: To identify molecular targets that promote prostate cancer cell survival and contribute to androgen independence, we evaluated changes in LNCaP cell gene expression during 12 months of androgen deprivation. At time points reflecting critical growth and phenotypic changes, we performed Affymetrix expression array analysis to examine the effects of androgen deprivation during the acute response, during the period of apparent quiescence, and following the emergence of a highly proliferative, androgen-independent prostate cancer cell phenotype (LNCaP-AI). RESULTS: We discovered alterations in gene expression for molecules associated with promoting prostate cancer cell growth and survival, and regulating cell cycle progression and apoptosis. Additionally, expression of AR co-regulators, adrenal androgen metabolizing enzymes, and markers of neuroendocrine disease were significantly altered. CONCLUSIONS: These findings contribute greatly to our understanding of androgen-independent prostate cancer. The value of this longitudinal approach lies in the ability to examine gene expression changes throughout the adaptive response to androgen deprivation; it provides a more dynamic illustration of genes which contribute to disease progression in addition to specific genes which constitute an androgen-independent phenotype.     

Involvement of arginine methyltransferase CARM1 in androgen receptor function and prostate cancer cell viability

BACKGROUND: Androgen receptor (AR) may play a role in prostate cancer progression. Coactivator-associated arginine methyltransferase (CARM1) catalyzes methylation of histone H3 at Arg-17. METHODS: Immunohistochemistry of CARM1 was performed on primary prostate cancer specimens. CARM1 recruitment and histone methylation was analyzed by chromatin immunoprecipitation. The effect of CARM1 overexpression or CARM1 knockdown was assessed on reporter assays, cell proliferation, apoptosis, and endogenous androgen target gene expression. RESULTS: CARM1 expression was increased in the nucleus of castration-resistant, but not androgen-stimulated prostate cancer. Androgen stimulation led to CARM1 recruitment and methylation of histone H3 at androgen responsive enhancers. Overexpression of CARM1 stimulated and CARM1 knockdown inhibited AR reporter activity. CARM1 knockdown inhibited cell proliferation and induced apoptosis. CARM1 knockdown inhibited androgen-dependent prostate specific antigen (PSA) and hK2 mRNA expression. CONCLUSIONS: CARM1 is essential for AR function and may play a role in prostate cancer progression. CARM1 may represent a novel therapeutic target in prostate cancer.     

前列腺癌雄激素依赖转化后细胞内雄激素受体表达变化的研究

目的：探讨雄激素受体（AR）在前列腺癌雄激素依赖特性转化过程中的作用。方法：对33例晚期前列腺癌患者进行雄激素阻断治疗并作长时间随访,其间有18例发生了雄激素依赖转化．15例未发生雄激素依赖转化。采用免疫组织化学及RT—PCR法测定18例患者雄激素依赖转化前后及15例患者雄激素阻断治疗前后癌细胞内AR蛋白及AR基因的表达情况。结果：18例患者雄激素依赖转化前后AR蛋白及AR基因的表达分别为（1．33±0．97VS3．11±0．76）和（28．41±3．38Ct vs 36．73±1．81Ct）,两者之间差异有统计学意义（P〈0．01）;15例患者雄激素阻断治疗前后AR蛋白及AR基因的表达分别为（1．47±0．83 vs 1．40±0．99）和（29．50±3．08Ct vs29．14±3．23Ct）,两者之间差异无统计学意义（P〉0．05）。结论：AR基因及AR蛋白表达增强是前列腺癌雄激素依赖转化的原因之一。     

Molecular alterations associated with LNCaP cell progression to androgen independence

BACKGROUND: There is no effective therapy currently available for androgen-independent (AI) prostate cancer (CaP). This is largely due to lack of information about the molecular mechanisms by which androgen-dependent tumor cells progress to androgen independence. In this study, we investigated molecular alterations occurring in AI LNCaP cells. METHODS: We established and characterized three AI LNCaP sublines that exhibited a wide range of cytogenetic alterations. In order to understand why androgen-sensitive LNCaP cells can survive in an androgen-deprived environment, we analyzed the expression of signaling proteins associated with proliferation and survival of AI cells. In addition, gene expression profiling was performed to gain insight into molecular alterations in these LNCaP sublines. RESULTS: These LNCaP sublines exhibited heightened levels of androgen receptor (AR), HER2, MAPK, serine 473-phosphorylated Akt, and Bcl-2, implicating these proteins as mediators of AI growth. Gene expression profiling identified a common set of 66 genes that were differentially expressed in all three sublines compared to the parental LNCaP cells. Of these, 32 were apparently androgen regulated, while the remainder comprised an expression signature specific for androgen independence. CONCLUSION: We have developed AI LNCaP cell models and identified several genes that are specifically expressed in these models. Elucidating the relative importance of these genetic changes will help define the molecular mechanism by which CaP progresses to androgen independence.     

Estrogen signaling and disruption of androgen metabolism in acquired androgen-independence during cadmium carcinogenesis in human prostate epithelial cells

BACKGROUND: Lethal prostate cancers often become androgen-independent due to androgen receptor (AR) overexpression. The role of cadmium in prostate tumor progression was determined. METHODS: Control and cadmium-transformed prostate epithelial cells (CTPE) were compared for steroid-induced proliferation, steroid receptor expression, and androgen metabolism. RESULTS: CTPE cells showed rapid proliferation in complete medium and sustained proliferation in steroid-reduced medium. Androgens stimulated significantly less cell proliferation and AR-related genes expression in CTPE cells. 5alpha-Dihydrotestosterone increased PSA expression more effectively in control cells. Flutamide reduced 5alpha-dihydrotestosterone-stimulated growth less effectively in CTPE cells compared to control. CTPE cells showed decreased p27 expression. Estrogen receptors were overexpressed and estradiol markedly stimulated proliferation in CTPE cells. In CTPE cells 5alpha-aromatase was markedly increased, while 5alpha-reductase was decreased. CONCLUSIONS: Cadmium-induced malignant transformation stimulates androgen independence, unrelated to AR expression or activity. Increased estrogen receptor and 5alpha-aromatase expression suggest estrogen signaling may be critical to this process.     

PC-3 cells with enhanced androgen receptor signaling: a model for clonal selection in prostate cancer

BACKGROUND: Two sublines of the human prostate cancer cell line, PC-3, which is widely used as a model of prostate cancer progression, have been reported: PC-3(AR-) that do not express androgen receptor (AR), and PC-3AR+ that have measurable AR RNA but little protein. METHODS: We assayed the geneotype, karyotype, AR expression, and physical characteristics of the two PC-3 sublines, and compared their ability to elicit a transactivation response from ectopic AR in the presence and absence of specific AR coregulators. RESULTS: PC-3(AR-) and PC-3AR+ cells are genotypically and karyotypically similar, but exhibit salient differences in their morphology, growth rate, and expression of AR RNA. Whereas endogenous AR expression in PC-3AR+ cells does not result in sufficient protein to confer androgen responsiveness in culture, ectopic AR consistently elicited a much greater transactivation response in PC-3AR+ than in PC-3(AR-) cells, without altered sensitivity to activation by native ligand or AR coregulators including GRIP1, BRCA1, and Zac1. Moreover, phenotypic differences of AR variants implicated in prostate cancer susceptibility and progression were only observed in PC-3AR+ cells. Higher levels of known AR coregulator proteins detected in PC-3AR+ compared with PC-3(AR-) cells likely contribute to these differences. CONCLUSIONS: These studies provide new evidence that the androgen-signaling axis can be sensitized in prostate cancer cells, and have important implications for the analysis and interpretation of AR structure and function in in vitro cell systems.     

Androgen deprivation therapy for prostate cancer: current status and future prospects

Androgens play a major role in promoting the development and progression of prostate cancer. As a result, androgen ablation or blockade of androgen action through the androgen receptor (AR) has been the cornerstone of treatment of advanced prostate cancer. Different strategies involving this hormonal therapy produce a significant clinical response in most of the patients, but most responders eventually lose dependency, resulting in mortality. Thus, whether hormonal therapy contributes to the improvement of overall survival rates, especially in patients with advanced prostate cancer, remains controversial. However, patients with advanced disease clearly have a benefit from androgen deprivation-based treatment for palliating their symptoms and for improving the quality of their lives. In order to improve overall survival, novel treatment strategies that prolong the androgen-dependent state and that are useful for androgen-independent disease based on specific molecular mechanisms need to be identified.     

Different profiles of neuroendocrine cell differentiation evolve in the PC-310 human prostate cancer model during long-term androgen deprivation

BACKGROUND: Neuroendocrine (NE) cells are androgen-independent cells and secrete growth-modulating peptide hormones via a regulated secretory pathway (RSP). We studied NE differentiation after long-term androgen withdrawal in the androgen-dependent human prostate cancer xenograft PC-310. METHODS: Tumor-bearing nude mice were killed at 0, 2, 5, 7, 14, 21, 47, 84, and 154 days after castration. The half-life of the PC-310 tumor was 10 days, with a stable residual tumor volume of 30--40% after 21 days and longer periods of androgen deprivation. RESULTS: Proliferative activity and prostate-specific antigen serum levels decreased to zero after castration, whereas cell-cycle arrest was manifested by increased p27(kip1) expression. A temporary downregulation of androgen receptor (AR) expression was noted after androgen deprivation. The expression of chromogranin A, secretogranin III, and secretogranin V (7B2) increased 5 days after castration and later. Subsequently, pro-hormone convertase 1 and peptidyl alpha--amidating monooxygenase as well as vascular endothelial growth factor were expressed from 7 days after castration on. Finally, such growth factors as gastrin-releasing peptide and serotonin were expressed in a small part of the NE cells 21 days after castration, but strong expression was induced late during androgen deprivation, that is, 84 and 154 days after castration, respectively. CONCLUSIONS: Androgen deprivation of the NE-differentiated PC-310 model induced the formation of NE-differentiated AR(minus sign) and non-NE AR(+) tumor residues. The NE-differentiated cells actively produced growth factors via an RSP that may lead to hormone-refractory disease. The dormant non-NE AR(+) tumor cells were shown to remain androgen sensitive even after long-term androgen deprivation. In the PC-310 xenograft, time-dependent NE differentiation and subsequent maturation were induced after androgen depletion. The androgen-dependent PC-310 xenograft model constitutes an excellent model for studying the role of NE cells in the progression of clinical prostate cancer.     

Mechanisms of prostate cancer recurrence

Androgen-deprivation therapy is often the first choice of several therapeutic procedures for advanced prostate cancer. However, despite an initial response to androgen-deprivation therapy, the cancer eventually progresses from an androgen-dependent to an androgen-independent phenotype. Molecular mechanism of development to androgen-independence and recurrence during androgen-deprivation therapy remain unclear. The observation that heterogeneity of AR expression in prostate cancer correlates with malignancy suggests that androgen responsiveness plays an important key role in the progression of prostate cancer. Therefore, it is very important to consider the role of AR and mechanisms of relapse when we treat androgen-independent prostate cancer.     

1alpha,25-Dihydroxyvitamin D3 down-regulates expression of prostate specific membrane antigen in prostate cancer cells

BACKGROUND: Prostate specific membrane antigen (PSMA) expression correlates with prostate cancer grade and is increased in hormone-refractory prostate cancer. The increased expression of PSMA following androgen deprivation therapy may be a consequence of the down-regulation of PSMA expression by androgen. Moreover, 1alpha,25-dihydroxyvitamin D3 (1,25-VD) has been shown to suppress prostate cancer progression as well as cell motility and invasion. Since PSMA is positively correlated with both of these characteristics, we hypothesized that 1,25-VD would regulate PSMA expression. METHODS: LNCaP prostate cancer cells were treated with 1,25-VD, followed by analysis of cell surface PSMA expression. The PSMA enhancer, located within the third intron of the PSMA gene, was cloned into a reporter vector and regulation by 1,25-VD was investigated. The role of the androgen receptor (AR) in 1,25-VD mediated suppression of PSMA expression was examined using Casodex and AR specific siRNA. RESULTS: Surface expression of PSMA was significantly decreased in a dose-dependent manner by 10 nM 1,25-VD or greater. Regulation by 1,25-VD occurred at the level of the PSMA enhancer. Over-expression of the vitamin D receptor (VDR) also decreased expression of PSMA. Additionally, suppression of AR translation using siRNA technology blocked the suppressive effect of 1,25-VD on PSMA expression, however inhibition of PSMA expression by 1,25-VD occurred in the absence of androgens. CONCLUSIONS: Suppression of PSMA by 1,25-VD occurs at the level of the PSMA enhancer and is elevated by over-expression of the VDR. This regulation involves the AR, but is not dependent on the presence of androgens.     

Expression and somatic mutation on androgen receptor gene in prostate cancer

BACKGROUND: Lack of androgen receptor (AR) expression or mutation on the AR gene creates the tendency for androgen independence and progression of prostate cancer. However, the association between the progression and AR expression or mutations is still controversial. In this study, we evaluated the prognostic significance of AR expression and mutations in prostate cancers. METHODS: Forty-two prostate adenocarcinomas and three lymph node metastatic lesions sampled prior to hormonal therapy were included in this study; AR expression was analyzed immunohistochemically using an antibody against AR and the result was scored as the percentage of AR-positive tumor cells in the total tumor cells. Polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP) analysis and DNA sequencing were used to detect AR mutations. RESULTS: Our study revealed the average AR expression in the prostate adenocarcinoma was 52.2 +/- 27.1%, which was significantly lower than that in the adjacent non-tumorous prostate tissue (68.3 +/- 18.3% in average) (P < 0.001). A significant correlation was obtained between progression-free survival and AR expression (P < 0.01). By SSCP analysis, three silent mutations (T649T, E709E and E711E) were detected in three separate prostate carcinomas. CONCLUSION: : We conclude that AR expression is a useful prognostic indicator for tumor progression. Androgen receptor mutation may be an uncommon molecular event in untreated prostate cancer in Japanese men.