title: Folic acid, polymorphism of methyl-group metabolism genes, and DNA methylation in relation to GI carcinogenesis.
abstract: DNA methylation is the main epigenetic modification after replication in humans. DNA (cytosine-5)-methyltransferase (DNMT) catalyzes the transfer of a methyl group from S-adenosyl-L-methionine (SAM) to C5 of cytosine within CpG dinucleotide sequences in the genomic DNA of higher eukaryotes. There is considerable evidence that aberrant DNA methylation plays an integral role in carcinogenesis. Folic acid or folate is crucial for normal DNA synthesis and can regulate DNA methylation, and through this, it affects cellular SAM levels. Folate deficiency results in DNA hypomethylation. Epidemiological studies have indicated that folic acid protects against gastrointestinal (GI) cancers. Methylene-tetrahydrofolate reductase (MTHFR) and methionine synthase (MS) are the enzymes involved in folate metabolism and are thought to influence DNA methylation. MTHFR is highly polymorphic, and the variant genotypes result in decreased MTHFR enzyme activity and lower plasma folate level. Two common MTHFR polymorphisms, 677CT (or 677TT) and A1298C, and an MS polymorphism, A-->G at 2756, have been identified. Most studies support an inverse association between folate status and the rate of colorectal adenomas and carcinomas. During human GI carcinogenesis, MTHFR is highly polymorphic, and the variant genotypes result in decreased MTHFR enzyme activity and lower plasma folate level, as well as aberrant methylation.
authors.affiliation: Shanghai Institute of Digestive Disease, Shanghai Second Medical University Renji Hospital, 145 Shandong Zhong Road, Shanghai 200001, PR China.
authors.forename: Jing Yuan
authors.initials: JY
authors.lastname: Fang
authors.forename: Shu Dong
authors.initials: SD
authors.lastname: Xiao
mesh_terms: D019175:DNA Methylation; D005492:Folic Acid / Q000378:metabolism*; D005770:Gastrointestinal Neoplasms / Q000201:enzymology* / Q000235:genetics*; D006801:Humans; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics*; D011110:Polymorphism, Genetic
chemical_list: D005492:Folic Acid; D042965:Methylenetetrahydrofolate Reductase (NADPH2)