Abstract 4874: Epigenetic gene silencing is co-regulated by DNMT3B and polycomb-mediated histone modifications in human cancer

CpG-cytosine methylation, the only epigenetic modification in mammalian DNA, is established and maintained by three DNA methyltransferases (DNMT): DNMT1, DNMT3A, and DNMT3B. Although essential for development and differentiation, DNA methylation patterns are frequently disrupted in cancer and contribute directly to carcinogenesis. Recent studies linking polycomb group (PcG) repression complexes (PRC1 and PRC2) to the DNMTs have begun to shed light on how methylation is targeted. By comparing genes regulated by DNMT3B, which we identified in previous studies, with known polycomb group target genes, we chose a panel of genes co-regulated by DNMT3B and PRC1/PRC2 to test whether these criteria (DNMT & PcG co-regulation) could accurately identify novel targets of epigenetic silencing in human colon cancer. Using reverse transcription-PCR, bisulfite genomic sequencing, and pyrosequencing, we show that the majority of these genes are frequently silenced in colorectal cancer cell lines and primary tumors. We then analyzed the histone code, DNMT, and PRC1/PRC2 binding by chromatin immunoprecipitation at epigenetically silenced loci to reveal a novel link between DNMT3B and PRC1, which was further confirmed by siRNA knockdown assays. Specifically, loss of DNMT3B resulted in significant reductions in ubiquitinated histone H2A levels, a mark catalyzed by the RING2 subunit of PRC1. Taken together, these studies suggest that patterns of epigenetic modifiers and the histone code influence the propensity of a gene to become hypermethylated in cancer and that DNMT3B plays an important role in regulating PRC1 function. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4874.