The Novel Direct AR Target Gene Annexin A2 Mediates Androgen-Induced Cellular Senescence in Prostate Cancer Cells

Clinical trials for prostate cancer (PCa) patients have implemented the bipolar androgen therapy (BAT) that includes the treatment with supraphysiological androgen level (SAL). SAL treatment induces cellular senescence in tumor samples of PCa patients and in various PCa cell lines, including castration-resistant PCa (CRPC), and is associated with enhanced phospho-AKT levels. Using an AKT inhibitor (AKTi), the SAL-mediated cell senescence is inhibited. Here, we show by RNA-seq analyses of two human PCa cell lines, that annexin A2 (ANXA2) expression is induced by SAL and repressed by co-treatment with AKTi. Higher ANXA2 expression is associated with better survival of PCa patients and suggests that ANXA2 is part of SAL-mediated tumor suppressive activity. ChIP-seq revealed that AR is recruited to the intronic regions of ANXA2 gene suggesting that ANXA2 is a novel direct AR target gene. Knockdown of ANXA2 shows that SAL-induced cellular senescence is mediated by ANXA2 and enhances the levels of phospho-AKT indicating an interaction between the AR, ANXA2 and AKT. Notably, we found that the level of heat shock protein HSP27, known to interact with ANXA2, is associated with cellular senescence. HSP27 level is induced by SAL but the induction is blunted by knockdown of ANXA2 suggesting a novel ANXA2-HSP27 pathway in PCa. This was confirmed using an HSP27 inhibitor that reduced the SAL-induced cellular senescence levels suggesting that ANXA2 upregulates HSP27 to mediate AR-signaling in SAL-induced cellular senescence. Thus, the data indicate ANXA2-HSP27 cross-talk as novel factors in the signaling by the AR-AKT pathway to mediate cellular senescence.