title: Selective depletion of human DNA-methyltransferase DNMT1 proteins by sulfonate-derived methylating agents.
abstract: 5-Methylcytosine residues in the DNA (DNA methylation) are formed from the transfer of the methyl group from S-adenosylmethionine to the C-5 position of cytosine by the DNA-(cytosine-5) methyltransferases (DNMTs). Although regional hypermethylation and global hypomethylation of the genome are commonly observed in neoplastic cells, how these aberrant methylation patterns occur remains unestablished. We report here that sulfonate-derived methylating agents, unlike N-methylnitrosourea or iodomethane, are potent in depleting DNMT1 proteins in human cells, in addition to their DNA-damaging properties. Their effects on cellular DNMT1 are time and dosage dependent but independent of cell type. Unlike gamma-irradiation, these agents apparently do not activate the p53/p21(WAF1) DNA damage response pathway to deplete the DNMT1 proteins because cells with wild-type, mutated, or inactivated p53 behave similarly. However, cell cycle analysis and protease assay studies strongly suggest that methylmethanesulfonate may activate a cellular protease to degrade DNMT1. These results explain why reported observations on the effect of alkylating agents on DNMT1 activities in human cells vary significantly and provide a crucial link to understand the mechanism behind genomic hypomethylation.
authors.affiliation: Chemical Carcinogenesis Laboratory, Institute of Molecular and Cell Biology, National University of Singapore, Singapore 117609, Republic of Singapore.
authors.forename: Linda Shyue-Huey
authors.initials: LS
authors.lastname: Chuang
authors.forename: Eileen Hwee-Hong
authors.initials: EH
authors.lastname: Tan
authors.forename: Hue-Kian
authors.initials: HK
authors.lastname: Oh
authors.forename: Benjamin F-L
authors.initials: BF
authors.lastname: Li
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism*; D019175:DNA Methylation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology / Q000528:radiation effects; D006801:Humans; D007700:Kinetics; D008741:Methyl Methanesulfonate / Q000494:pharmacology*; D009153:Mutagens / Q000494:pharmacology; D012697:Serine Endopeptidases / Q000378:metabolism; D013463:Sulfuric Acid Esters / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D000477:Alkylating Agents; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009153:Mutagens; D013463:Sulfuric Acid Esters; D016159:Tumor Suppressor Protein p53; D008741:Methyl Methanesulfonate; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619380:DNMT1 protein, human; D012697:Serine Endopeptidases; C028344:glutamyl endopeptidase; C007482:dimethyl sulfate