title: MGMT methylation is associated primarily with the germline C>T SNP (rs16906252) in colorectal cancer and normal colonic mucosa.
abstract: O(6)-methylguanine DNA methyltransferase (MGMT) is a DNA repair protein that restores mutagenic O(6)-methylguanine to guanine. MGMT methylation is frequently observed in sporadic colorectal cancer and was recently correlated with the C>T allele at SNP rs16906252, within the transcriptional enhancer element of the promoter. MGMT methylation has also been associated with KRAS mutations, particularly G>A transitions. We studied 1123 colorectal carcinoma to define the molecular and clinicopathological profiles associated with MGMT methylation. Furthermore, we assessed factors contributing to MGMT methylation in the development of colorectal cancer by studying the allelic pattern of MGMT methylation using SNP rs16906252, and the methylation status of neighbouring genes within 10q26 in selected tumours and matched normal colonic mucosa. MGMT methylation was detected by combined bisulphite restriction analysis in 28% of tumours and was associated with a number of characteristics, including CDKN2A methylation, absent lymphovascular space invasion and KRAS mutations (but not specifically with KRAS G>A transitions). In a multivariate analysis adjusted for age and sex, MGMT methylation was associated with the T allele of SNP rs16906252 (P<0.0001, OR 5.5, 95% CI 3.8-7.9). Low-level methylation was detected by quantitative methylation-specific PCR in the normal colonic mucosa of cases, particularly those with a correspondingly methylated tumour, as well as controls without neoplasia, and this was also associated with the C>T SNP. We show that the T allele at SNP rs16906252 is a key determinant in the onset of MGMT methylation in colorectal cancer, whereas the association of methylation at MGMT and CDKN2A suggests that these loci may be targets of a common mechanism of epigenetic dysregulation.
authors.affiliation: School of Medical Sciences, University of NSW, Sydney, Australia.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Hawkins
authors.forename: James H-F
authors.initials: JH
authors.lastname: Lee
authors.forename: Justin J-L
authors.initials: JJ
authors.lastname: Wong
authors.forename: Chau-To
authors.initials: CT
authors.lastname: Kwok
authors.forename: Robyn L
authors.initials: RL
authors.lastname: Ward
authors.forename: Megan P
authors.initials: MP
authors.lastname: Hitchins
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001315:Australia; D002277:Carcinoma / Q000201:enzymology / Q000235:genetics* / Q000473:pathology / Q000601:surgery; D002879:Chromosomes, Human, Pair 10; D015179:Colorectal Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000473:pathology / Q000601:surgery; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics* / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000235:genetics* / Q000378:metabolism; D044127:Epigenesis, Genetic; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D018095:Germ-Line Mutation; D006801:Humans; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000201:enzymology*; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D016017:Odds Ratio; D010641:Phenotype; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D011446:Prospective Studies; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; D045643:DNA Repair Enzymes