Methylation as a Cancer Switch

Courtesy of Richard Roberts, New England Biolabs

Reaction model: Methyltransferase (white) is methylating cyclic carbon 5 of a cytosine nucleotide.

The tenuous link between cancer and epigenetic changes, changes in gene expression without DNA mutations, has been strengthened by Joe Costello, assistant professor at the University of California, San Francisco, and colleagues (J.F. Costello et al., "Aberrant CpG-island methylation has non-random and tumour-type-specific patterns," Nature Genetics, 25:132-8, February 2000). They examined more than 1,000 CpG islands in 98 tumor samples for methylation patterns using restriction landmark genomic scanning (RLGS). The region of a gene that controls expression often contains short DNA sequences composed of cytosine (C) and guanine (G) nucleotides. Methylation of the C residue usually turns off gene expression. If the gene in question is a tumor suppressor, this may promote tumor formation. The researchers found that a significant fraction of all...