Abstract 2303: MicroRNA-23b is a tumor suppressor and a useful prognostic biomarker in prostate cancer

Introduction and Objective: MicroRNAs are small noncoding RNAs that regulate the expression of >90% of all human genes, either inhibiting target mRNA translation or inducing its degradation. These genes are abnormally expressed in human malignancies, making their biological importance increasingly apparent. The main objective of this study was to investigate the role of miRNA-23b in prostate carcinogenesis and assess whether miR-23b has any prognostic implication in prostate cancer (PC). Methods: The methods employed in this study include quantitative-real time PCR; methylation specific quantitative-real time PCR; western blot; in-situ hybridization; fluorescence-activated cell sorting assays for cell cycle distribution and apoptosis; assays for cell viability, clonability, migration and invasiveness of prostate cancer cells. Luciferase reporter and mutational assays and in-vivo studies in nude mice were also performed. Results: The expression of miR-23b was significantly suppressed or silenced in human PC tissue samples and cell lines when compared with normal tissues and a non-malignant cell line. The mechanism of miR-23b silencing in PC was found to be due to hypermethylation that was reversed by 5Aza-deoxycitidine (5Aza) treatments. Lower expression of miR-23b also correlated with higher pathological stage and higher Gleason grade making it a useful prognostic biomarker in prostate cancer. Ectopic expression of miR-23b induced G0/G1 cell cycle arrest and apoptosis, suppressed cell proliferation, colony formation, migration, and invasion in prostate cancer cells. miR-23b exerted these functional effects by directly targeting the proto-oncogene Src kinase. Over-expression of miR-23b significantly suppressed the luciferase activity of reporter plasmid containing the 3′UTR sequences complementary to Src kinase, which was abolished by mutations in these 3′UTR regions. Genistein treatment also induced cell cycle arrest and apoptosis, and suppressed Src kinase expression at the protein level in prostate cancer cells. Genistein and miR-23b reduced the Src-regulated downstream ERK/AKT pathway molecules and also inhibited Src kinase and tumor cell growth in vivo. Conclusion: This is the first study demonstrating that i) miRNA-23b is silenced by CpG hypermethylation in PC; ii) miR-23b acts as a tumor suppressor and is a prognostic biomarker in PC; iii) genistein, a nontoxic chemopreventive agent induces the expression of miR-23b and iv) both genistein and miR-23b inhibited oncogenic Src kinase in-vitro and in-vivo. The use of RNAi is currently being implemented as a gene-specific approach for molecular medicine. By the same principle, it is possible that reexpression of silenced miR-23b by nontoxic chemopreventive agents may cause down-regulation of target oncogenes thereby leading to the development of novel therapeutic approaches for the treatment of prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2303. doi:1538-7445.AM2012-2303