Androgen receptor and its splice variant, AR-V7, differentially regulate FOXA1 sensitive genes in LNCaP prostate cancer cells

Abstract

Prostate cancer (PCa) is an androgen-dependent disease, and tumors that are resistant to androgen ablation therapy often remain androgen receptor (AR) dependent. Among the contributors to castration-resistant PCa are AR splice variants that lack the ligand-binding domain (LBD). Instead, they have small amounts of unique sequence derived from cryptic exons or from out of frame translation. The AR-V7 (or AR3) variant is constitutively active and is expressed under conditions consistent with CRPC. AR-V7 is reported to regulate a transcriptional program that is similar but not identical to that of AR. However, it is unknown whether these differences are due to the unique sequence in AR-V7, or simply to loss of the LBD. To examine transcriptional regulation by AR-V7, we have used lentiviruses encoding AR-V7 (amino acids 1-627 of AR with the 16 amino acids unique to the variant) to prepare a derivative of the androgen-dependent LNCaP cells with inducible expression of AR-V7. An additional cell line was generated with regulated expression of AR-NTD (amino acids 1-660 of AR); this mutant lacks the LBD but does not have the AR-V7 specific sequence. We find that AR and AR-V7 have distinct activities on target genes that are co-regulated by FOXA1. Transcripts regulated by AR-V7 were similarly regulated by AR-NTD, indicating that loss of the LBD is sufficient for the observed differences. Differential regulation of target genes correlates with preferential recruitment of AR or AR-V7 to specific cis-regulatory DNA sequences providing an explanation for some of the observed differences in target gene regulation.

Nuclear Receptor Corepressor 1 Expression and Output Declines with Prostate Cancer Progression

“…To analyze whether NCOR1 regulates AR-V7 specific transcription, we measured EDN2 gene expression. As previously reported (17), EDN2 was induced specifically by AR-V7 and optimal induction required NCOR1 expression (Figure 4D). …”

“…We next tested whether the AR splice variant V7 can induce TARP expression and whether NCOR1 is required for TARP optimal induction using previously described LNCaP AR-V7/pLenti cell line inducibly expressing AR-V7 (17). As seen from Figure 4C, doxycycline induction of AR-V7 expression increased TARP expression levels and NCOR1 knockdown reduced AR and AR-V7 dependent induction of TARP.…”

“…LNCaP AR-V7/pLenti was described previously (17). Media was purchased from Life Technologies (Grand Island, NY).…”

SOCS3 Modulates the Response to Enzalutamide and Is Regulated by Androgen Receptor Signaling and CpG Methylation in Prostate Cancer Cells

“…To further investigate the effect of the androgen receptor on SOCS3 expression in CRPC, we performed experiments in presence of the constitutively active androgen receptor splice variant V7 which frequently contributes to the development of castration resistance (43,44). It is still a matter of debate, whether the AR-V7 variant has a different target gene specificity (39,45). Therefore, we investigated the influence of exogenous AR-V7 expression on SOCS3 expression in AR-V7-negative LNCaP cells.…”

A sting in the tail: the N-terminal domain of the androgen receptor as a drug target

“…ARv7 has been shown to differentially regulate FOXA1 sensitive genes in relevant PCa cell lines. Krause et al 40. generated LNCaP cell lines coexpressing doxycycline inducible ARv7 and an AR-NTD-DBD construct.…”