DHT Selectively Reverses Smad3-Mediated/TGF-β-Induced Responses through Transcriptional Down-Regulation of Smad3 in Prostate Epithelial Cells

Androgens suppress TGF-beta responses in the prostate through mechanisms that are not fully explored. We have recently reported that 5 alpha-dihydrotestosterone (DHT) suppresses the ability of TGF-beta to inhibit proliferation and induce apoptosis of prostatic epithelial cells and provided evidence that such suppression was fueled by transcriptional down-regulation of TGF-beta receptor II (T beta RII). We now show that androgen receptor (AR) activated by DHT suppresses the TGF-beta-induced phosphorylation of Sma- and Mad-related protein (Smad) 3 in LNCaP cells overexpressing T beta RII under the control of a cytomegalovirus promoter, which is not regulated by DHT, suggesting that transcriptional repression of T beta RII alone does not fully account for the impact of DHT on TGF-beta responses. Instead, we demonstrate that such suppression occurs through loss of total Smad3, resulting from transcriptional suppression of Smad3. We provide evidence that DHT down-regulates the promoter activity of Smad3 in various prostate cancer cell lines, including NRP-154+AR, DU145+AR, LNCaP, and VCaP, at least partly through androgen-dependent inactivation of Sp1. Moreover, we show that overexpression of Smad3 reverses the ability of DHT to protect against TGF-beta-induced apoptosis in NRP-154+AR, supporting our model that loss of Smad3 by DHT is involved in the protection against TGF-beta-induced apoptosis. Together, these findings suggest that deregulated/enhanced expression and activation of AR in prostate carcinomas may intercept the tumor suppressor function of TGF-beta through transcriptional suppression of Smad3, thereby providing new mechanistic insight into the development of castration-resistant prostate cancer. (Molecular Endocrinology 24: 2019-2029, 2010)