International Journal of Cancer, 01 July 2014, Vol.135(1), pp.19-26
The mediator complex is an evolutionary conserved key regulator of transcription of protein‐coding genes and an integrative hub for diverse signaling pathways. In this study, we investigated whether the mediator subunit MED15 is implicated in castration‐resistant prostate cancer (CRPC). MED15 expression and copy number/rearrangement status were assessed by immunohistochemistry (IHC) and fluorescence hybridization (FISH), respectively on 718 prostate cancer (PCa) specimens and sequenced by Sanger on a subset. Furthermore, SMAD3 phosphorylation, androgen receptor (AR) and proliferation markers were evaluated by IHC. In PCa cells, siRNA/shRNA knockdown of MED15 was followed by proliferation assays with/without dihydrotestosterone (DHT), and treatments with recombinant TGF‐β3. Our results show that is overexpressed in 76% of distant metastatic CRPC (CRPC) and 70% of local‐recurrent CRPC (CRPC), in contrast to low frequencies in androgen‐sensitive PCa, and no expression in benign prostatic tissue. Furthermore, overexpression correlates with worse clinical outcome thus defining a highly lethal phenotype. Moreover, TGF‐β signaling activation associates with overexpression in PCa tissues, and leads to increased expression of MED15 in PCa cells. MED15 knockdown effects phosphorylation and shuttling of p‐SMAD3 to the nucleus as well as TGF‐β‐enhanced proliferation. In PCa tissues, overexpression associates with overexpression/amplification and correlates with high proliferative activity. MED15 knockdown decreases both androgen‐dependent and ‐independent proliferation in PCa cells. Taken together, these findings implicate MED15 in CRPC, and as MED15 is evolutionary conserved, it is likely to emerge as a lethal phenotype in other therapeutic‐resistant diseases, and not restricted to our disease model. What's new? MED15, a subunit of the Mediator transcriptional regulator complex, has been implicated in castration‐resistant prostate cancer (CRPC). This study shows that 70 percent of local‐recurrent CRPCs and 76 percent of distant metastatic CRPCs overexpress MED15 and that MED15 overexpression defines a highly lethal phenotype. expression was found to be increased by TGF‐ß activation, such that MED15 knockdown affected TGF‐β signaling and TGF‐β‐enhanced proliferation. Knockdown also resulted in decreased androgen‐dependent and ‐independent proliferative activity. The findings, taken together with the evolutionary conservation of MED15, suggest that MED15 in CRPC may be a model of therapeutic‐resistant disease.
Med15 ; Castration‐Resistant ; Prostate Cancer ; Tgf‐Β