SMYD3Promotes Prostate Tumorigenesis By Enhancing Androgen Receptor Expression

BackgroundAndrogen receptor (AR) is critical for prostate tumorigenesis and frequently overexpressed during prostate cancer (PCa) progression. Androgen-androgen receptor is the central signaling pathway in normal growth of the prostate gland and prostate carcinogenesis. When activated by binding of androgen ligands, AR becomes phosphorylated and translocates into the nucleus. There, AR binds to its binding motifs in the genome and activates transcription of its target genes, which is essential for prostate development and PCa progression. However, few studies addressed the epigenetic regulation of AR expression.Recent studies have shed light on the importance of epigenetic events in the carcinogenesis and progression of PCa including facilitation of AR signaling by histone-modifying enzymes. SET and MYND domain-containing protein3(SMYD3) is a histone methyltransferase (HMT). which recognizes and occupies the binding motif/s in the promoter region of its downstream target genes, and di-/tri-methylates H3-K4. thereby leading to transcriptional activation. Expression of SMYD3is undetectable or very weak in many types of normal human tissues, whereas overexpression of SMYD3has been shown to be associated with development and progression of colorectal. hepatocellular and breast cancer. And SMYD3is critical for these carcinomas.MethodsThe expression of SMYD3in PCa was determined using western blot analysis and immunohistochemistry. SMYD3was depleted with shRNA or siRNA in PCa cells. The impact of SMYD3depletion on cells was evaluated by cell proliferation assay, colony formation analysis, xenograft transplantation and apoptosis analysis. AR expression and promoter activity were evaluated with RT-qPCR, western blot analysis and luciferase reporter assay. The AR promoter associated with the Spl, SMYD3and histone modifications were assessed by chromatin immunoprecipitation.ResultsThe up-regulated SMYD3protein expression was observed in7of8prostate tumor tissues compared with their matched normal tissues by western blot analysis. A strong SMYD3staining was detected by immunohistochemistry in nucleus of PCa tissues in8of25(32%) cases and in cytoplasm in23of25(92%) cases, while benign prostate tissues showed weak immunostaining. Depletion of SMYD3by siRNA or shRNA inhibited PCa cell proliferation, colony formation, cell migration, invasion and xenograft tumor formation. Two functional SMYD3-binding motifs were identified in the AR promoter region and SMYD3directly trans-activates the AR gene. SMYD3induces chromatin remodeling in the AR promoter, followed by the increased Spl accumulation there, which was coupled with up-regulation of AR expression.Conclusion1. SMYD3expression was up-regulated in the majority of PCa.2. SMYD3depletion significantly suppressed tumor growth of PCa.3. SMYD3may induce the mobile phenotype of PCa cells, thereby contributing to invasion and metastasis of PCa.4. SMYD3Induces Chromatin Remodeling and other factors accumulate at the AR Promoter Region, which may induce prostate carcinogenesis jointly.