Abstract B39: Methylation of BRCA2 gene promoter CpG units through ZAR2-dependent DNMT1 recruitment

Abstract

Abstract BRCA2 gene expression is stringently regulated during the cell cycle. BRCA2 expression is proportional to the rate of cell proliferation. Looking at the human BRCA2 gene minimal promoter sequence we found that it has over 45 CpG units which could be potentially methylated regulating the recruitment of different transcription factors affecting BRCA2 gene expression. We discovered that BRCA2 gene promoter has bi-directional activity and the product of the reverse activity (a ZAR1-like protein, we named ZAR2) silences the forward promoter (for BRCA2). ZAR2 is a C4-type zinc finger-containing transcription factor that regulates BRCA2 in a cell cycle dependent manner. We found that ZAR2 enters the nucleus of the G0/G1 cells binds to the promoter of BRCA2 and silences the BRCA2 gene expression. ZAR2 has a dsRNA binding domain. We report here that BRCA2 gene promoter, through its bidirectional activity, produces two partially overlapping transcripts (BRCA2 and ZAR2) in the breast cells forming a 111 bp RNA duplex. We postulate that endogenous transcriptional gene silencing RNAs (tgsRNAs) against BRCA2 gene promoter are thus formed from the overlapping RNA duplex in the cell nucleus. These tgsRNAs in turn contribute towards promoter methylation. Our data suggest that ZAR2 upon binding to the tgsRNAs binds to specific locations of BRCA2 gene promoter and recruits DNMT1 which in turn perform CpG methylation. This study will contribute towards the understanding of the epigenetic regulation of BRCA2 gene expression in different cell cycle stages as well as in sporadic cases of breast and other cancer. Supported in part by the DOD-CDMRP IDEA Grants BC990678 and BC050641 to GC and MeTRC pilot project grant 1U54RR026140-01 to SM Citation Format: Smita Misra, Mukul K. Mittal, Sheetal V. Khedkar, Gautam Chaudhuri. Methylation of BRCA2 gene promoter CpG units through ZAR2-dependent DNMT1 recruitment. [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 B39.