Abstract 1016: The androgen receptor splice variant AR-V7 associates with the glucocorticoid receptor following androgen blockade

Abstract

Expression of the constitutively active androgen receptor splice variant AR-V7 is associated with resistance to anti-androgen therapies and worse clinical outcomes in prostate cancer. Dimerization is a requirement for AR-V7 transcriptional activity, but whether that occurs through homodimerization or heterodimerization remains poorly understood. Because NR3C-family nuclear hormone receptors rely on a highly conserved D-box motif within the DNA-binding domain to mediate dimerization, we hypothesized that AR-V7 can heterodimerize with other NR3C-family nuclear hormone receptors, with a particular interest in the glucocorticoid receptor (GR). Like AR-V7, GR is upregulated in prostate cancer following androgen blockade, regulates canonical AR target genes, and is associated with resistance to anti-androgen therapies. Using NanoBRET technology in HEK293 cells, we found that AR-V7 interacts with liganded NR3C-family nuclear hormone receptors, including the full-length androgen receptor, the progesterone receptor, the mineralocorticoid receptor, and, most notably, GR. Using co-immunoprecipitation and proximity ligation assays, we demonstrate that AR-V7 associates with GR following androgen blockade in both the VCaP cell line and the CWR-22RV1 cell line, two models of prostate cancer that express endogenous AR-V7 and GR. Preliminary ChIP-Seq experiments in these cell lines suggest AR-V7 and GR chromatin occupancy at the same genomic sites in a ligand-dependent manner. Taken altogether, this data suggests AR-V7 can utilize GR as an alternative binding partner to initiate heterodimerization and transcriptional activation. Citation Format: Eric Bueter, David Hosfield, Erin McAuley, Phillip Selman, Geoffrey Greene, Suzanne D. Conzen, Russell Z. Szmulewitz. The androgen receptor splice variant AR-V7 associates with the glucocorticoid receptor following androgen blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1016.

Glucocorticoid receptor and androgen receptor-targeting therapy in patients with castration-resistant prostate cancer

“…Although evidence to support a direct relationship between AR-V7 and GR is limited, AR-V7 interacts with ligand-bound members of the NR3C-family of nuclear hormone receptors, including full-length AR and GR. One study showed AR-V7 and GR could occupy the same genomic sites in a ligand-dependent manner, suggesting that AR-V7 can utilize GR as an alternative binding partner to initiate heterodimerization transcriptional activation (30).…”