The activity of the androgen receptor variant AR-V7 is regulated by FOXO1 in a PTEN-PI3K-AKT-dependent way

BACKGROUND The androgen receptor (AR) AR-V7 splice isoform is a constitutively active outlaw transcription factor. Transition of prostate cancer (PC) to the castration-resistant phenotype correlates with AR-V7 accumulation, suggesting that PC progression in patients refractory to conventional therapy is due to the activity of this AR isoform. The mechanism of AR-V7 constitutive activation is not known. METHODS We analyzed potential signaling pathways associated with AR-V7 constitutive activation in PTEN (-) PC-3 and LNCaP cells. We used transient and stable transfection, reporter gene assay, RNAi technology together with a number of kinase inhibitors to determine if AR-V7 activation is linked to a kinase-dependent signaling pathway. RESULTS In these cell lines, AR-V7 transcriptional activity was inhibited by LY294002, Wortmanin, and AKT inhibitor II. Analysis of the contributing mechanisms demonstrated the involvement of the Phosphatidylinositol 3-kinase (PI3K)-AKT-FOXO1 signaling pathway, and a significant reduction of AR-V7 constitutive activity under conditions of PTEN reactivation. CONCLUSIONS Our study identifies a pathway regulating AR-V7 constitutive activity and potential therapeutic targets for the treatment of castration-resistant PC. Prostate 73: 267277, 2013. (c) 2012 Wiley Periodicals, Inc.