DNA Methylation and its Role in Carcinogenesis
Gene methylation is a control mechanism that regulates gene expression in DNA. Gene methylation occurs when a methyl group is added to one of the four building blocks of DNA, a cytosine, as demonstrated in Figure 1.
Figure 1: Cytosine methylation
The regulatory regions of active genes are sensitive to methylation. In normal cells, these promoter regions are regulated, as necessary, by the methylation process. In several diseases however, the promoter regions can be abnormally, or hyper-methylated, in which case their function remains blocked and the proteins they code for are not produced, as demonstrated in Figure 2. Such abnormal methylation of relevant genes such as tumor suppressor genes is associated with the presence and development of most cancers.
Figure 2. Methylation of promoter gene regions blocks gene expression and protein production
The pattern of gene hyper-methylation in tumor cells is often specific to the tissue of origin and can be used to improve cancer detection, assess cancer aggressiveness, and predict a tumor’s response to therapy.