Abstract A23: Repression of Id4 (inhibitor of DNA binding 4) by the polycomb group protein EZH2 in prostate cancer

Abstract

Abstract Introduction: Inhibitor of DNA binding/differentiation protein 4 (Id4) is dominant negative regulator of basic helix loop helix (bHLH) family of transcription factors. Id4 shares the homology of HLH domain with other Ids and lack the basic DNA binding region. Unlike Id1, Id2 and Id3, Id4 acts as a tumor suppressor in prostate cancer by attenuating cell proliferation and promote apoptosis. We have previously shown that decreased Id4 expression in prostate cancer is due to its promoter hypermethylation. In this study we investigated the molecular mechanism by which Id4 promoter is hypermethylated. Here, we demonstrate that Id4 promoter methylation is initiated by EZH2 dependent tri-methylation of histone 3 at lysine 27 (H3K27me3). Experimental procedures: Id4 protein expression was analyzed on human prostate adenocarcinoma samples by Immunohistochemistry and prostate cancer cell lines (LNCaP, C81 and DU145) by Western blot. EZH2 was silenced in DU145 cells and confirmed through western blot and Immunocytochemistry. Chromatin Immunoprecipitation (ChIP) was performed with IgG, RNA polymerase, EZH2 and H3K27Me3 antibodies in both prostate cancer cell lines and prostate cancer tissue samples. Results: IHC demonstrated decreased Id4 protein expression in human prostate tissue samples whereas higher nuclear Id4 expression was found in normal prostate tissues. Re-expression of Id4 in EZH2 silenced Du145 demonstrated that Id4 is regulated in an EZH2 dependent manner. ChIP data on prostate cancer samples and cell lines suggested EZH2 occupancy and H3K27Me3 marks in the Id4 promoter region in cell lines and prostate cancer tissue specimens. Conclusions: Id4 appears as a potential tumor suppressor gene that is epigenetically silenced during prostate cancer development. H3K27Me3 marks and EZH2 occupancy suggest a PRC2 dependent mechanism in Id4 promoter silencing in prostate cancer. Acknowledgement: The research was supported by NIH/NCI-RO1CA128914 and in part by NIH/NCRR/RCMI G12RR03062 Citation Format: Swathi Chinaranagari, Pankaj Sharma, Jaideep Chaudhary. Repression of Id4 (inhibitor of DNA binding 4) by the polycomb group protein EZH2 in prostate cancer. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr A23.