Abstract IA20: DNA methylation and nucleosome repositioning in cancer

Abstract

Abstract Epigenetic processes are reinforced by interactions between covalent chromatin marks such as DNA methylation, histone modifications, and variants. These marks ultimately specify the locations of nucleosomes particularly with respect to transcriptional start sites and in regulatory regions. Understanding how the epigenome functions therefore requires a coordinated approach so that the mechanisms by which the chemical modifications interact with nucleosomal remodeling machines are achieved to ensure epigenetic inheritance and control of gene expression. We have developed a new methodology to simultaneously map nucleosomal positioning and DNA methylation on individual molecules of DNA. We used this nucleosomal mapping technology to ascertain alterations in nucleosomal positioning during the abnormal silencing of genes by promoter hypermethylation. These experiments show that the methylation of CpG islands at the transcriptional start sites of key tumor suppressor genes results in the stable placement of nucleosomes at the transcription start site. Inhibition of DNA methylation by 5-azanucleoside treatment results in an immediate inhibition of DNA methylation and a sequence of downstream events which ultimately result in the eviction of the nucleosomes from the transcription start site and the activation of gene expression. Interestingly this process requires the insertion of the histone variant H2AZ downstream and upstream of the transcriptional start site for full gene activation to occur. Thus inhibition of DNA methylation by these drugs which are used to treat myelodysplastic syndrome results not only in the removal of DNA methylation but in the resetting of chromatin to an active state. Genes activated in this way often undergo resilencing when the drug is removed so that understanding the precise nature of these alterations is essential in the design of the next generation of epigenetic therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr IA20.