title: The nitrosated bile acid DNA lesion O6-carboxymethylguanine is a substrate for the human DNA repair protein O6-methylguanine-DNA methyltransferase.
abstract: The consumption of red meat is a risk factor in human colorectal cancer (CRC). One hypothesis is that red meat facilitates the nitrosation of bile acid conjugates and amino acids, which rapidly convert to DNA-damaging carcinogens. Indeed, the toxic and mutagenic DNA adduct O(6)-carboxymethylguanine (O(6)-CMG) is frequently present in human DNA, increases in abundance in people with high levels of dietary red meat and may therefore be a causative factor in CRC. Previous reports suggested that O(6)-CMG is not a substrate for the human version of the DNA damage reversal protein O(6)-methylguanine-DNA methyltransferase (MGMT), which protects against the genotoxic effects of other O(6)-alkylguanine lesions by removing alkyl groups from the O(6)-position. We now show that synthetic oligodeoxyribonucleotides containing the known MGMT substrate O(6)-methylguanine (O(6)-MeG) or O(6)-CMG effectively inactivate MGMT in vitro (IC50 0.93 and 1.8 nM, respectively). Inactivation involves the removal of the O(6)-alkyl group and its transfer to the active-site cysteine residue of MGMT. O(6)-CMG is therefore an MGMT substrate, and hence MGMT is likely to be a protective factor in CRC under conditions where O(6)-CMG is a potential causative agent.
authors: Centre for Occupational and Environmental Health, Faculty of Medical & Human Sciences, University of Manchester, Manchester M13 9PL, UK.
authors: Pattama
authors: P
authors: Senthong
authors: Christopher L
authors: CL
authors: Millington
authors: Oliver J
authors: OJ
authors: Wilkinson
authors: Andrew S
authors: AS
authors: Marriott
authors: Amanda J
authors: AJ
authors: Watson
authors: Onrapak
authors: O
authors: Reamtong
authors: Claire E
authors: CE
authors: Eyers
authors: David M
authors: DM
authors: Williams
authors: Geoffrey P
authors: GP
authors: Margison
authors: Andrew C
authors: AC
authors: Povey
mesh_terms: D001483:Base Sequence; D001647:Bile Acids and Salts / Q000378:metabolism / Q000502:physiology; D020134:Catalytic Domain; D015179:Colorectal Neoplasms / Q000201:enzymology; D018736:DNA Adducts / Q000235:genetics / Q000378:metabolism*; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors / Q000737:chemistry*; D045643:DNA Repair Enzymes / Q000037:antagonists & inhibitors / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry; D019204:GTP-Binding Proteins; D006147:Guanine / Q000031:analogs & derivatives* / Q000737:chemistry*; D006801:Humans; D008565:Membrane Proteins; D008780:Methyltransferases / Q000037:antagonists & inhibitors / Q000737:chemistry; D008970:Molecular Weight; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry*
chemical_list: D001647:Bile Acids and Salts; D018736:DNA Adducts; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D009838:Oligodeoxyribonucleotides; D025521:Tumor Suppressor Proteins; D006147:Guanine; D015254:DNA Modification Methylases; D008780:Methyltransferases; C515491:MGMT protein, human; C067511:Ogt protein, E coli; C440006:ATL1 protein, human; D019204:GTP-Binding Proteins; D045643:DNA Repair Enzymes