Figure 3

Schematic of methylation and hydroxymethylation patterns in normal and cancer cells. In normal cells, unmethylated cytosines are located in CpG islands and promoters of actively transcribed genes, whereas promoters of repressed genes are mainly composed of 5-methylcytosine (5-mC). 5-hydroxymethylcytosines (5-hmCs) are frequent in cis-regulatory elements such as enhancers, in low CpG content regions, and within gene bodies of transcribed genes. A global hypermethylation phenotype, with respect to normal tissue, is usually associated with tumoral transformation, including repressed tumor suppressor gene promoters. Hypomethylation can, however, be observed locally, in oncogene promoters, for example. Cancer cells present a global decrease of 5-hmC and local redistribution of this mark towards some oncogene promoters. C, cytosine; TSG, tumor suppressor gene.