Biology of Human Tumors ERG/AKR1C3/AR Constitutes a Feed-Forward Loop for AR Signaling in Prostate Cancer Cells

Purpose: Intratumoral androgen synthesis in prostate cancer contributes to the development of castration-resistant prostate cancer (CRPC). Several enzymes responsible for androgen biosynthesis have been shown to be overexpressed in CRPC, thus contributing to CRPC in a castrated environment. The TMPRSS2– ERG transcription factor has been shown to be present in primary prostate cancer tumors as well as CRPC tumors. We hypothesize that TMPRSS2–ERG fusions regulate androgen biosynthetic enzyme (ABE) gene expression and the production of androgens, which contributes to the development of CRPC. Experimental design: We used a panel of assays, including lentivirus transduction, gene expression, chromatin immunoprecipitation and sequencing, liquid chromatography-mass spectrometric quantitation, immunocytochemistry, immunohistochemistry, and bioinformatics analysis of genemicroarray databases, to determine ERG regulation of androgen synthesis. Results:We found that ERG regulated the expression of theABE AKR1C3 in prostate cancer cells via direct binding to the AKR1C3 gene. Knockdownof ERG resulted in reducedAKR1C3 expression, which caused a reduction in both DHT synthesis and PSA expression in VCaP prostate cancer cells treated with 5a-androstanedione (5a-Adione), a DHT precursor metabolite. Immunohistochemical staining revealed that ERG was coexpressed with AKR1C3 in prostate cancer tissue samples. Conclusions: These data suggest that AKR1C3 catalyzes the biochemical reduction of 5a-Adione to DHT in prostate cancer cells, and that ERG regulates this step through upregulation of AKR1C3 expression. Elucidation of ERG regulation of ABEs in CRPCmayhelp to stratifyTMPRSS2–ERG fusion-positive prostate cancer patients in the clinic for anti–androgen receptor–driven therapies; and AKR1C3may serve as a valuable therapeutic target in the treatment of CRPC. Clin Cancer Res; 1–11. 2015 AACR.