MiR-185 attenuates androgen receptor function in prostate cancer indirectly by targeting bromodomain containing 8 isoform 2, an androgen receptor co-activator

Objectives: Aberrant androgen receptor (AR) signaling functions are implicated in prostate cancer (PCa) pathogenesis. Here, we studied interactions between miR-185 and the bromodomain containing 8 isoform 2 (BRD8 ISO2) to investigate indirect mechanisms of miR-185 with respect to AR function through BRD8 ISO2 in PCa. Methods: Putative miRNA response element (MRE) of miR-185 in 3'-untranslated region (3'-UTR) of BRD8 ISO2 mRNA was predicted by software and confirmed using dual-luciferase assays and Ago2 immunoprecipitation. BRD8 and AR expression were determined by qRT-PCR and Western blot in PCa cells and tissues. MMTV-Fluc reporter plasmids and dual-luciferase assays were used to evaluate AR activity. Results: MRE prediction, dual-luciferase assays and Ago2 immunoprecipitation confirmed that miR-185 is capable of binding the 3'-UTR of BRD8 ISO2 mRNA. QRT-PCR and Western blot indicated that BRD8 ISO2 expression is decreased by miR-185 mimic transfection while increased by miR-185 inhibitor transfection. MMTV-Fluc reporter assays revealed that miR-185 can attenuate AR function by suppressing BRD8 ISO2. Additionally, Pearson's correlation analyses confirmed that BRD8 ISO2 mRNA expression is inversely correlated with miR-185 expression in clinical specimens. Conclusion: In addition to suppression of AR expression, miR-185 can attenuate AR function indirectly by suppressing BRD8 ISO2. MiR-185 and BRD8 ISO2 may be possible therapeutic targets for PCa treatment. (C) 2016 Elsevier Ireland Ltd. All rights reserved.