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Androgen receptor and its splice variant, AR-V7, differentially induce mRNA splicing in prostate cancer cells.

ABSTRACT: Prostate cancer (PCa) is dependent on the androgen receptor (AR). Advanced PCa is treated with an androgen deprivation therapy-based regimen; tumors develop resistance, although they typically remain AR-dependent. Expression of constitutively active AR variants lacking the ligand-binding domain including the variant AR-V7 contributes to this resistance. AR and AR-V7, as transcription factors, regulate many of the same genes, but also have unique activities. In this study, the capacity of the two AR isoforms to regulate splicing was examined. RNA-seq data from models that endogenously express AR and express AR-V7 in response to doxycycline were used. Both AR isoforms induced multiple changes in splicing and many changes were isoform-specific. Analyses of two endogenous genes, PGAP2 and TPD52, were performed to examine differential splicing. A novel exon that appears to be a novel transcription start site was preferentially induced by AR-V7 in PGAP2 although it is induced to a lesser extent by AR. The previously described AR induced promoter 2 usage that results in a novel protein derived from TPD52 (PrLZ) was not induced by AR-V7. AR, but not AR-V7, bound to a site proximal to promoter 2, and induction was found to depend on FOXA1.

SUBMITTER: Rana M

PROVIDER: S-EPMC7809134 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Androgen Receptor splice variant V7 (AR-V7) mediates AR signalling in castration resistant prostate cancer (CRPC)

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Androgen Receptor Variant AR-V9 Is Coexpressed with AR-V7 in Prostate Cancer Metastases and Predicts Abiraterone Resistance.

Project description:Purpose: Androgen receptor (AR) variant AR-V7 is a ligand-independent transcription factor that promotes prostate cancer resistance to AR-targeted therapies. Accordingly, efforts are under way to develop strategies for monitoring and inhibiting AR-V7 in castration-resistant prostate cancer (CRPC). The purpose of this study was to understand whether other AR variants may be coexpressed with AR-V7 and promote resistance to AR-targeted therapies.Experimental Design: We utilized complementary short- and long-read sequencing of intact AR mRNA isoforms to characterize AR expression in CRPC models. Coexpression of AR-V7 and AR-V9 mRNA in CRPC metastases and circulating tumor cells was assessed by RNA-seq and RT-PCR, respectively. Expression of AR-V9 protein in CRPC models was evaluated with polyclonal antisera. Multivariate analysis was performed to test whether AR variant mRNA expression in metastatic tissues was associated with a 12-week progression-free survival endpoint in a prospective clinical trial of 78 CRPC-stage patients initiating therapy with the androgen synthesis inhibitor, abiraterone acetate.Results: AR-V9 was frequently coexpressed with AR-V7. Both AR variant species were found to share a common 3' terminal cryptic exon, which rendered AR-V9 susceptible to experimental manipulations that were previously thought to target AR-V7 uniquely. AR-V9 promoted ligand-independent growth of prostate cancer cells. High AR-V9 mRNA expression in CRPC metastases was predictive of primary resistance to abiraterone acetate (HR = 4.0; 95% confidence interval, 1.31-12.2; P = 0.02).Conclusions: AR-V9 may be an important component of therapeutic resistance in CRPC. Clin Cancer Res; 23(16); 4704-15. ©2017 AACR.

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Constitutively active androgen receptor splice variants AR-V3, AR-V7 and AR-V9 are co-expressed in castration-resistant prostate cancer metastases.

Project description:BACKGROUND:A significant subset of prostate cancer (PC) patients with a castration-resistant form of the disease (CRPC) show primary resistance to androgen receptor (AR)-targeting drugs developed against CRPC. As one explanation could be the expression of constitutively active androgen receptor splice variants (AR-Vs), our current objectives were to study AR-Vs and other AR aberrations to better understand the emergence of CRPC. METHODS:We analysed specimens from different stages of prostate cancer by next-generation sequencing and immunohistochemistry. RESULTS:AR mutations and copy number variations were detected only in CRPC specimens. Genomic structural rearrangements of AR were observed in 5/30 metastatic CRPC patients, but they were not associated with expression of previously known AR-Vs. The predominant AR-Vs detected were AR-V3, AR-V7 and AR-V9, with the expression levels being significantly higher in CRPC cases compared to prostatectomy samples. Out of 25 CRPC metastases that expressed any AR variant, 17 cases harboured expression of all three of these AR-Vs. AR-V7 protein expression was highly heterogeneous and higher in CRPC compared to hormone-naïve tumours. CONCLUSIONS:AR-V3, AR-V7 and AR-V9 are co-expressed in CRPC metastases highlighting the fact that inhibiting AR function via regions common to all AR-Vs is likely to provide additional benefit to patients with CRPC.

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Role of Circulating Tumor Cells (CTC), Androgen Receptor Full Length (AR-FL) and Androgen Receptor Splice Variant 7 (AR-V7) in a Prospective Cohort of Castration-Resistant Metastatic Prostate Cancer Patients.

Project description:Circulating tumor cells (CTC), androgen receptor full-length (AR-FL), and androgen receptor splice variant 7 (AR-V7) are prognostic in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC). AR-V7 seems to predict resistance to androgen-receptor signaling inhibitors (ARSi). We assessed the association of CTC, AR-FL, and AR-V7 with prostate-specific antigen (PSA) response and overall survival (OS). We used a modified AdnaTest CTC-based AR-FL and AR-V7 mRNA assay. Chi-square test, Fisher Exact test, Kaplan-Meier method, log-rank test, Cox proportional hazards models were used as appropriate. We enrolled 39 mCRPC pts, of those 24 started a first-line treatment for mCRPC (1L subgroup) and 15 had received at least two lines for mCRPC (>2L subgroup). CTC, AR-FL, and AR-V7 were enriched in >2L compared to 1L subgroup. Detection of these biomarkers was associated with a lower percentage of biochemical responses. Only 1/7 AR-V7+ pts had a PSA response and received cabazitaxel. Median OS was 4.7 months (95% CI 0.6-8.9) in AR-V7+ pts and not reached in AR-V7- pts. AR-V7 was the only variable with prognostic significance in the Cox model. AR-V7, CTC, and AR-FL are associated with advanced mCRPC and AR-V7+ predicts for shorter OS.

| S-EPMC6770005 | biostudies-literature

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