Writers, erasers, and readers of DNA and histone methylation marks

Changes in gene expression and activity underlie the formation of cancerous tumors. Historically, genetic alterations (deletions, point mutations, translocations, etc.) were believed to be the basis for tumor formation, but studies in recent years have demonstrated that epigenetic modifications, including the regulated addition of chemical groups to DNA and histones, also profoundly affect gene expression and thus cancer. Both chromatin compaction and gene expression are modulated by epigenetic modifications, which are deposited by specific enzymes (“writers”), and subsequently recognized by effector proteins (“readers”). Most epigenetic marks are reversible, and classes of enzymes (“erasers”) exist that remove these marks. The complex interplay of these three classes of proteins controls gene expression, and defects in this system contribute to cancer initiation and progression. This chapter introduces the key concepts surrounding these three types of proteins, focusing on writers, erasers, and readers of DNA and histone methylation marks.