Aberrant TGF-β Signaling Drives Castration-Resistant Prostate Cancer in a Male Mouse Model of Prostate Tumorigenesis

The androgen receptor (AR) plays a critical role as a driver of castration-resistant prostate cancer (CRPC). Our previous studies demonstrated that disruption of transforming growth factor-beta (TGF-beta) signaling via introduction of dominant-negative transforming growth factor-beta type II receptor (DNTGF beta RII) in the prostate epithelium of transgenic adenocarcinoma of the prostate mice accelerated tumor. This study investigated the consequences of disrupted TGF-beta signaling on prostate tumor growth under conditions of castration-induced androgen deprivation in the preclinical model of DNTGF beta RII. Our results indicate that in response to androgen deprivation therapy (ADT) the proliferative index in prostate tumors from DNTGF beta RII mice was higher compared with prostate tumors from TGF beta RII wild-type (WT) mice, whereas there was a reduced incidence of apoptosis in tumors from DNTGF beta RII. Protein and gene expression profiling revealed that tumors from DNTGF beta RII mice exhibit a strong nuclear AR localization among the prostate tumor epithelial cells and increased AR messenger RNA after ADT. In contrast, TGF beta RII WT mice exhibited a marked loss in nuclear AR in prostate tumor acini (20 weeks), followed by a downregulation of AR and transmembrane protease serine 2 messenger RNA. There was a significant increase in nuclear AR and activity in prostate tumors from castrate DNTGF beta RII compared with TGF beta RII WT mice. Consequential to aberrant TGF-beta signaling, ADT enhanced expression and nuclear localization of Smad4 and beta-catenin. Our findings support that under castrate conditions, aberrant TGF-beta signaling leads to AR activation and beta-catenin nuclear localization, an adaptation mechanism contributing to emergence of CRPC. The work defines a potentially significant new targeting platform for overcoming therapeutic resistance in CRPC.