Androgen Receptor Function In Prostate Cancer Research Articles

Abstract 6285: Defining androgen receptor function and the effects of PARP inhibition in BRCA1/2-deficient vs. proficient prostate cancer

Abstract Mutation or loss of the tumor suppressor genes BRCA1 and BRCA2 promotes the development of aggressive prostate cancer with poor outcomes and a high risk of metastatic relapse. Approximately 15% of metastatic prostate tumors are BRCA1/2-deficient. These tumors are frequently resistant to standard-of-care treatments that block androgen receptor (AR) function, although the mechanisms underlying this effect remain unclear. PARP inhibitors are synthetically lethal with BRCA1/2-deficiency and are commonly used as a late-line treatment in metastatic prostate cancer; however, both preclinical and clinical data have provided conflicting results on whether PARP inhibitors can be effective in BRCA1/2-proficient prostate tumors. BRCA1, BRCA2, PARP-1, and PARP-2 all have proposed roles in regulating transcription and the chromatin landscape. We therefore hypothesized that loss of BRCA1, BRCA2, and/or inhibition of PARP modulates AR function through changes in global chromatin structure and transcriptional pathways. We used patient-derived xenograft models and next-generation sequencing techniques to profile AR function in BRCA1/2-deficient vs. proficient prostate tumors. We found that loss of BRCA1 and BRCA2 is associated with chromatin accessibility changes, and differentially accessible regions correlate with DNA binding motifs for AR and AR cofactors. ChIP-seq for AR in these tumors demonstrated that BRCA1/2-deficiency is associated with an altered AR cistrome and a global decrease in AR genomic binding. Corresponding RNA-seq data confirmed a downregulated androgen response in BRCA1/2-deficient tumors. In cell line models, inhibition of PARP1 and PARP1/2 inhibited AR-driven transcription. Combining PARP inhibition with either androgen deprivation or the AR antagonist enzalutamide dampened the growth-inhibitory effects of PARP inhibitor treatment. Together, these results indicate that BRCA1/2-deficiency and PARP inhibition modulate AR function in prostate cancer. Citation Format: Nicole A. Traphagen, Esme Wheeler, Rong Li, Xintao Qiu, Myles Brown. Defining androgen receptor function and the effects of PARP inhibition in BRCA1/2-deficient vs. proficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6285.

Abstract LB038: Identification of androgen receptor co-chaperone interactors implicated in castration resistant prostate cancer

Abstract Background: Prostate cancer (PCa) is the most common non-cutaneous cancer afflicting men, both in the United States and worldwide. Aberrant molecular signaling mechanisms mediated by the Androgen Receptor (AR) are attributed as the main culprits for the initiation and progression of PCa, and research efforts have focused on developing strategies to directly target the AR. In an alternative approach, molecular chaperones that are critical for the maturation and signaling of the AR have emerged as potential therapeutic targets. Our lab has demonstrated the potential of inhibitors that target AR cochaperones, FKBP51 and FKBP52, in PCa cells. Previously, FKBP51 and FKBP52 have been shown to play a role in cell proliferation and survival, steroid hormone receptor maturation, and other mechanisms highly implicated in prostate carcinogenesis. Therefore, it is imperative to understand the protein-protein interactions that regulate FKBP51 and FKBP52-mediated AR function in PCa. We hypothesize that unknown interactors cooperate with FKBP51 and FKBP52 to promote PCa progression via the AR signaling pathways. Here, we performed a series of experiments aimed to identify and characterize auxiliary proteins influencing FKBP51- and FKBP52-mediated AR activity. Ultimately, our goal is to define novel protein interactions involved in AR-mediated PCa progression for therapeutic intervention. Methods: We implemented tandem affinity purification followed by mass spectrometry analysis in 22RV1 PCa cells using FKBP51 and FKBP52 as bait. The spectral counts of proteins identified were then used to analyze protein-protein interactions through the IDEP workflow software. Gene Ontology (GO) term enrichment analysis was used to generate a STRING interaction network. Protein interactions of interest were then validated via reciprocal immunoprecipitations. Results: This interactome analysis resulted in 353 IDs for FKBP51 and FKBP52 interactors. Heatmaps representing top 100 interactors were generated for both bait proteins. Members of the peroxiredoxin family, implicated in development of PCa and resistance to treatment, are among the top candidates of interest resulting from this interactome. Conclusion: This analysis aims to provide important insights into the androgen signaling milieu, which can be applied in the development of novel treatments targeting AR interacting partners in PCa progression. This study contributes to the growing list of functionally diverse proteins that help modulate AR transcriptional activity, and supports the idea that AR signaling is dynamic with numerous molecules involved in the aberrant activation of AR in prostate-tumor cells Citation Format: Olga B. Soto, Abhijeet R. Patil, Sourav Roy, Marc B. Cox. Identification of androgen receptor co-chaperone interactors implicated in castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB038.

Modulation of Androgen Receptor by FOXA1 and FOXO1 Factors in Prostate Cancer

Androgens and the androgen receptor (AR) are essential for growth and differentiation of the normal prostate gland as well as proliferation and survival of prostate cancer (PCa). Increasing evidence suggests that reactivation of the AR plays a pivotal role in disease progression to castration-resistant PCa (CRPC). Forkhead box (FOX) factors exert two distinct effects on AR function in PCa. The A-class of FOX proteins, especially FOXA1, functions as a pioneer factor to facilitate AR transactivation and PCa growth. In contrast, the O-class of FOX proteins such as FOXO1 and FOXO3, which are downstream effectors of the PTEN tumor suppressor, inhibit the transcriptional activity of either full-length AR or constitutively active splice variants of AR in a direct or indirect manner in PCa. FOXO1 also contributes to taxane-mediated inhibition of the AR and CRPC growth. Therefore, FOX family members not only have a tight relationship with AR, but also represent a pivotal group of proteins to be targeted for PCa therapy. The present review focuses primarily on recent advances in the epigenetic, mechanistic and clinical relevant aspects of regulation of the AR by FOXA1 and FOXO1 factors in PCa.

Abstract 1206: Evaluation of androgen receptor function index (ARFI) in prostate cancer.

Abstract Introduction: Initially prostate cancer is driven by the male hormone androgen through the androgen receptor (AR). However, in some cases androgen receptor is functionally altered at late stages of tumorigenesis. Early knowledge of androgen receptor dysfunctions may assist in patient stratification for emerging therapeutic strategies. Although AR function can be altered by numerous mechanisms, the net effect of these changes is reflected in defective transcription factor functions of the AR. To develop readouts for AR function in prostate cancer we have evaluated the expression of a functionally relevant panel of AR-regulated genes in a prostate cancer cell culture model and in whole-mounted prostate tumor tissues. Methods: In the VCaP cell culture model of prostate cancer that endogenously express, AR, TMPRSS2-ERG fusion (ERG), KLK3 (PSA), NKX3.1, PMEPA1, ODC1 and AMD1 genes we have evaluated the dose and time kinetics of these AR regulated genes in response to androgen (R1881) treatment at protein and mRNA levels. Radical prostatectomy specimens representing favorable or poor prognostic cases were selected for the study. Each prostate was fixed, sectioned and immunohistochemical (IHC) staining on adjacent four-micron sections of the whole-mounted blocks were performed by using mouse monoclonal anti-AR, anti-ERG antibody (clone 9FY), rabbit polyclonal anti-PSA and anti-NKX3.1 antibodies. IHC intensities were scored and the final score was determined after multiplying the intensity score and percentage of positively stained area in the respective lesions. Results: Towards defining the expression levels of AR regulated genes in prostate cancer cells we have evaluated and confirmed the androgen dose and time kinetic response of endogenously expressed KLK3(PSA), PMEPA1, NKX3.1, ODC1, AMD1 and TMPRSS2-ERG (ERG) genes in VCaP cell culture model. Assessment of AR dysfunction by the immunohistochemical evaluation of AR regulated genes in whole-mounted prostate cancer specimens showed reduced expression of AR regulated genes in a sub-set of prostate cancer cases with notable inter- and intratumoral heterogeneity. Conclusions: Androgen regulation of examined genes was confirmed in VCaP prostate cancer cell culture model. Assessment of AR, ERG, NKX3.1 and PSA protein levels by IHC indicated reduced expression of AR-regulated genes in a subset of the cases. The analysis revealed inter- and intratumoral heterogeneity, as well as, challenges in the quantitative assessment of IHC. The observed readouts of AR dysfunction may provide a new tool for improved prognostic accuracy and patient stratification at early stages of prostate cancer treatment. Citation Format: Albert Dobi, Denise Young, Wei Huang, Lakshmi Ravindranth, Shashwat Sharad, Hua Li, Gyorgy Petrovics, David G. McLeod, Isabell Sesterhenn, Shiv Srivastava. Evaluation of androgen receptor function index (ARFI) in prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1206. doi:10.1158/1538-7445.AM2013-1206

Dual role of FoxA1 in androgen receptor binding to chromatin, androgen signalling and prostate cancer

High androgen receptor (AR) level in primary tumour predicts increased prostate cancer-specific mortality. However, the mechanisms that regulate AR function in prostate cancer are poorly known. We report here a new paradigm for the forkhead protein FoxA1 action in androgen signalling. Besides pioneering the AR pathway, FoxA1 depletion elicited extensive redistribution of AR-binding sites (ARBs) on LNCaP-1F5 cell chromatin that was commensurate with changes in androgen-dependent gene expression signature. We identified three distinct classes of ARBs and androgen-responsive genes: (i) independent of FoxA1, (ii) pioneered by FoxA1 and (iii) masked by FoxA1 and functional upon FoxA1 depletion. FoxA1 depletion also reprogrammed AR binding in VCaP cells, and glucocorticoid receptor binding and glucocorticoid-dependent signalling in LNCaP-1F5 cells. Importantly, FoxA1 protein level in primary prostate tumour had significant association to disease outcome; high FoxA1 level was associated with poor prognosis, whereas low FoxA1 level, even in the presence of high AR expression, predicted good prognosis. The role of FoxA1 in androgen signalling and prostate cancer is distinctly different from that in oestrogen signalling and breast cancer.

Inhibition of HER-2/neu Kinase Impairs Androgen Receptor Recruitment to the Androgen Responsive Enhancer

Advanced prostate cancer invariably recurs despite androgen deprivation therapy. The androgen receptor (AR) likely plays a key role in this progression and in the continued survival and proliferation of prostate cancer cells in the low androgen environment. Cross-talk with growth factor receptors, such as epidermal growth factor receptor (EGFR) family, has been postulated as a potential mechanism to activate AR in recurrent prostate cancer. We have investigated the role of HER-2/neu (ErbB-2) tyrosine kinase in AR function by characterizing the effect of inhibiting endogenous HER-2 activity in LNCaP cells. We used two independent methods, expression of intracellular single-chain antibody against HER-2 and treatment with a novel dual EGFR/HER-2 kinase inhibitor GW572016 (lapatinib). Expression of intracellular HER-2 antibody scFv-5R and treatment with GW572016 inhibited HER-2 signaling. This HER-2 inhibition led to impairment of AR-mediated functions, such as androgen-stimulated growth and the induction of endogenous prostate-specific antigen (PSA) mRNA and protein. Androgen-stimulated recruitment of AR and histone acetylation at the androgen responsive enhancer of the PSA gene, detected by chromatin immunoprecipitation analysis, were impaired by HER-2 inhibition. GW572016 was more potent in its ability to inhibit PSA expression and AR recruitment and histone acetylation than the EGFR-selective kinase inhibitor ZD1839 (gefitinib), consistent with the HER-2 kinase playing the major role in AR regulation. These results show that HER-2 signaling is required for optimal transcriptional activity of AR in prostate cancer cells and suggest that HER-2 inhibition may provide a novel strategy to disrupt AR function in prostate cancer.

TR2 orphan receptor functions as negative modulator for androgen receptor in prostate cancer cells PC-3.

Both androgen receptor (AR) and orphan receptor TR2 (TR2) belong to the steroid nuclear receptor superfamily and are expressed in prostate cancer tissue and cell lines. AR has been known to be involved in prostate proliferation and prostate cancer progression. AR binds to androgen response elements and regulates target gene expression via a mechanism involving coregulators. However, the function of TR2 in prostate and prostate cancer and the relationship between TR2 and AR in the prostate cancer is unclear. Transient transfection and CAT reporter gene assays were employed to assess AR-mediated transactivation. The expression level of prostate specific antigen (PSA) was measured by Northern blot analysis. The interaction between AR and TR2 was assessed by glutathione-S-transferase (GST) pull-down assay and mammalian two-hybrid system assay. Orphan nuclear receptor TR2 suppressed androgen-mediated transactivation in prostate cancer PC-3 cells, and over-expression of TR2 suppressed PSA expression. The suppression of AR mediated transactivation by TR2 is not due to competition for the limited coregulator availability by these two receptors, but possibly through the interaction between TR2 and AR nuclear receptors. TR2 may function as a negative modulator to suppress AR function in prostate cancer. Further studies on how to control TR2 function may result in the ability to modulate AR function in prostate cancer.

The role of the androgen receptor in prostate cancer.

Androgens are important not only for the development and function of the normal prostate gland, but also for the maintenance of prostate cancer (PCa) cells. The biological function of androgens is exerted by activation of the transcriptional activity of the androgen receptor (AR). The function of the AR in the prostate is largely dependent on AR protein levels and structural integrity of the protein and other transcription activation factors. Based upon the clinical findings that androgen ablation therapy-resistant PCa still expresses AR and the androgen-regulated gene, prostate-specific antigen, a concept is developing that the androgen receptor iscritical for androgen-refractory prostate cancer cells. Indeed, because of the alterations detected in the AR gene, many noncognate activators, including estrogen, progesterone, peptide growth factors, and cytokines, are able to induce transactivation of the AR under androgen-depleted conditions. Also, transactivational activity of the AR is often modulated by crosstalk between the AR and other signaling pathways in cancerous prostatic cells. Dysregulation of AR function in prostate cancer results in an abnormal profile of AR-regulated genes, which include cell cycle regulators, transcription factors, and those proteins important for cell survival, lipogenesis, and secretion. Thus in this review we will evaluate the significance of the AR in the development and progression of prostate cancer.