show Abstracthide AbstractThe androgen receptor splice variant 7 (AR-V7) lacks the ligand-binding domain; is detected with increased frequency in advanced prostate cancer and is postulated to be one crucial mechanism for disease progression and therapeutic resistance to androgen deprivation in castration–resistant prostate cancer (CRPC). Targeting AR-V7 or unique downstream targets could provide novel therapeutic approaches for CRPC. Here, we report that, independent of ligand, AR-V7 binds not only to the androgen-responsive element (ARE) sites inducing canonical AR signaling but also to non-canonical target sites where ligand-stimulated full-length AR (AR-FL) does not bind. These AR-V7 “solo” binding sites are mainly found at gene promoters and are co-occupied by a zinc-finger transcription factor ZFX and the co-activator BRD4, both of which physically interact with AR-V7. Consequently, AR-V7 not only recapitulates AR-FL action without androgen but uniquely regulates transcripts correlating with AR-V7 expression in the TCGA prostate cancer cohort. Mechanistically, ZFX appears to function as a pioneer factor for AR-V7 at solo-binding sites and BRD4 inhibitors but not anti-androgens suppress AR-V7 action at solo-binding sites as well as AR-V7-dependent growth. Additionally, knockdown of ZFX, or two downstream targets uniquely co-activated by AR-V7 (ZNF32 and FZD6), also suppressed growth of AR-V7-dependent CRPC cells. AR-V7 directly activated genes differentiate tumor from normal prostate tissues and predict poor prognosis in patients. Thus AR-V7 has both canonical and non-canonical regulatory functions in CRPC, which may provide new therapeutic avenues. Overall design: mRNA profiles of knocking down AR-FL, AR-V7 or control vector in 22Rv1 cells were generated by deep-sequencing, in duplicate. mRNA profiles of knocking down ZFX or control vector in 22Rv1 cells were generated by deep-sequencing, in duplicate. mRNA profiles of 22Rv1 cells which were charcoal stripped for 3 days and then treated with vehicle, DHT, DHT plus MDV3100 or DHT plus JQ1 were generated by deep-sequencing, in duplicate. Examination of the genome-wide binding of full-length androgen receptor (AR-FL), AR-V7, Brd4 and ZFX in an castration-resistant prostate cancer cell line in the presence of different drug treatments.