Data from ERG/AKR1C3/AR Constitutes a Feed-Forward Loop for AR Signaling in Prostate Cancer Cells

Abstract

<div>Abstract<p><b>Purpose:</b> 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 <i>TMPRSS2–ERG</i> fusions regulate androgen biosynthetic enzyme (ABE) gene expression and the production of androgens, which contributes to the development of CRPC.</p><p><b>Experimental design:</b> 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 gene microarray databases, to determine ERG regulation of androgen synthesis.</p><p><b>Results:</b> We found that ERG regulated the expression of the ABE AKR1C3 in prostate cancer cells via direct binding to the <i>AKR1C3</i> gene. Knockdown of ERG resulted in reduced AKR1C3 expression, which caused a reduction in both DHT synthesis and PSA expression in VCaP prostate cancer cells treated with 5α-androstanedione (5α-Adione), a DHT precursor metabolite. Immunohistochemical staining revealed that ERG was coexpressed with AKR1C3 in prostate cancer tissue samples.</p><p><b>Conclusions:</b> These data suggest that AKR1C3 catalyzes the biochemical reduction of 5α-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 CRPC may help to stratify <i>TMPRSS2–ERG</i> fusion-positive prostate cancer patients in the clinic for anti–androgen receptor–driven therapies; and AKR1C3 may serve as a valuable therapeutic target in the treatment of CRPC. <i>Clin Cancer Res; 21(11); 2569–79. ©2015 AACR</i>.</p></div>