Abstract LB-185: Oxidative damage targets complexes containing DNA methyltransferases, SIRT1 and polycomb members to promoter CpG islands

Abstract

Abstract A key question in cancer epigenetics is how cancers of multiple types simultaneously acquire global losses and gains of DNA methylation. The increases often occur in promoter CpG islands and can be associated with transcriptional inactivation of key tumor suppressor genes. Here we demonstrate a molecular response to oxidative damage, a key factor in cancer risk states, which could help explain the gains and losses of DNA methylation that occur during tumor progression. Within 30 minutes of exposing cells to the reactive oxygen species, hydrogen peroxide (H2O2), the major maintenance enzyme for DNA methylation, DNMT1, becomes notably more tightly bound to chromatin. Concomitantly, DNMT1 targets SIRT1 to chromatin and both proteins become part of a large multi-protein complex(es) which also contains the de novo DNA methyltransferase, DNMT3B. This oxidative damage-induced complex also contains specific polycomb group members, which, in the context of SIRT1, define the Polycomb Repressive Complex 4 (PRC4), previously found only in embryonic and adult stem cells and cancer cells. By examining chromatin on a genome-wide scale, we demonstrate that H2O2 treatment preferentially damages GC-rich regions of DNA. This damage causes a shift in localization of the above complex(es) from non-GC-rich to GC-rich regions of the genome including promoter CpG islands of which some are DNA hypermethylated in cancer cells. Additionally, this treatment causes a decrease in nascent RNA transcript levels of these genes that have oxidative damage-induced enrichment of the silencing complex in their CpG island-containing promoters. Thus, oxidative damage induces formation and localization of a silencing complex that may in part explain cancer specific aberrant losses and gains in DNA methylation associated with gene transcriptional silencing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-185. doi:10.1158/1538-7445.AM2011-LB-185