Genome-wide analysis of mouse intestinal adenoma identifies early steps in the formation of cancer-specific DNA methylation patterns. Mus musculus

Aberrant CpG methylation is a universal trait of cancer cell genomes and can result in epigenetic modulation of gene activity; however, at which stages tumour-specific epigenetic patterns arise is unknown. Here, we analyse the methylome of APCM in mouse intestinal adenoma as a model of intestinal cancer initiation, and inventory a map of over 13,000 adenoma-specific recurrent differentially methylated regions (DMRs). We find that multiple genes coding for Polycomb proteins are upregulated in adenoma, and concomitantly, hypermethylated DMRs form preferentially at Polycomb target sites. We establish that DMRs are absent from proliferating intestinal epithelial cells or intestinal stem cells, and thus arise de novo after loss of APC. Importantly, a core set of DMRs is conserved in human colon cancer, defining a class of early epigenetic alterations that are distinct from known sets of epigenetically silenced tumour suppressors. The data presented suggests a sequence of events that leads to an altered methylome of colon cancer cells, and may allow more specific selection of clinical epigenetic biomarkers. Overall design: Analysis of the methylome and RNA expression in adenoma of Apc-Min/+ mutant mice and of normal intestine in Apc-Min/+ and Apc-+/+ wild type mice.