Transcriptional Regulation of PRKAR2B by MiR-200b-3p/200c-3p and XBP1 in Human Prostate Cancer

The cyclic adenosine monophosphate (cAMP)-activated protein kinase A (PKA) pathway is profoundly implicated in Prostate cancer (PCa) progression. Previously, we showed that PRKAR2B, the type II-beta regulatory subunit of PKA, is highly expressed in castration-resistant prostate cancer (CRPC) and can induce epithelial-mesenchymal transition by activating Wnt/β-catenin signaling in PCa cells. However, the molecular mechanism of dysregulated PRKAR2B expression pattern is still largely unknown. In this study, we found that the mutation, copy number alteration, and methylation status of PRKAR2B gene have no correlation with its expression level in PCa. Then, we identified two microRNAs (miR-200b-3p and miR-200c-3p) to be critical regulators of PRKAR2B expression in PCa. Notably, miR-200b-3p and miR-200c-3p expression were significantly downregulated in metastatic CRPC and negatively correlated with the expression level of PRKAR2B in PCa tissues. Moreover, we characterized X-Box Binding Protein 1 (XBP1) as a key transcription factor responsible for PRKAR2B expression in PCa. Importantly, miR-200b-3p/200c-3p or XBP1 knockdown inhibited PCa cell proliferation and promoted cell apoptosis and these inhibitory roles could be largely restored by PRKAR2B, suggesting that PRKAR2B is a functional mediator of miR-200b-3p, miR-200c-3p, and XBP1 in PCa. Collectively, our study firstly identified miR-200b-3p/200c-3p and XBP1 as the critical upstream regulators of PRKAR2B in PCa and provided novel insights to PRKAR2B-driven PCa progression.