Epigenetics of colon cancer.

Accumulation of genetic and epigenetic alterations transforms normal colonic epithelial cells to adenocarcinoma cells. Genetic alterations include mutations in tumor suppressor genes and oncogenes, whereas epigenetic mechanisms are defined as heritable alterations in gene expression that is independent of changes in the primary DNA sequence. Role of epigenetic mechanisms in development and maintenance of organ- and tissue-specific gene expression is now realized. Disturbances in epigenetic landscape can lead to malignant cellular makeover, and these heritable changes are maintained through various cycles of cell division that renders cells to have discrete identity with similar genetic information. Epigenetic alterations in colorectal cancer (CRC) that transform colonic epithelial cells into adenocarcinoma cells include aberrant DNA methylation, chromatin modifications, and noncoding RNAs, especially microRNA expression. CpG island DNA methylation and aberrant methylation of genes drive the initiation and progression of CRC. Histone modifications impinge on chromatin structure and gene expression and thus play an important role in gene silencing in CRC. DNA hypermethylation also leads to downregulation and inappropriate expression of certain microRNAs that act like tumor suppressor genes. Determining the causes and roles of epigenetic instability in CRC pathogenesis will lead to effective prevention and therapeutic strategies for patients with CRC. Epigenetic drugs that underscore the reversible nature of epigenetic events have led the possibility of epigenetic therapy as a treatment option in CRC.