title: Methylation profile of the MLH1 promoter region and their relationship to colorectal carcinogenesis.
abstract: Methylation of the MLH1 promoter region has been suggested to be a principal mechanism of gene inactivation in sporadic microsatellite instability (MSI)-positive colorectal carcinoma. Recently, we have shown a novel methylation profile of the MLH1 promoter region (i.e., full, partial, and no methylation), among which full methylation was strongly associated with MSI. In this study, to confirm whether methylation requires the involvement of both alleles, we studied the MLH1 promoter region concerning the methylation profile and allelic loss. Furthermore, we studied correlations of methylation profiles with genetic alternations such as loss of heterozygosity (LOH) of the TP53 locus and KRAS mutation. Eighty-eight tumors were classified as full (n = 14), partial (n = 26), and no methylation (n = 48). Full methylation was observed in 78% (14/18) of high-frequency MSI, in which all CpG sites in the promoter region were methylated. Full methylation differed significantly from partial methylation regarding absence of TP53 LOH (0/12) and KRAS mutation (0/14). In cases with full methylation, we could show biallelic methylation by use of a single-base nucleotide polymorphism in the promoter. However, this did not accompany LOH of the MLH1 locus. In contrast, there were no significant differences in molecular features between partial and no methylation, except for low frequencies of LOH of the MLH1 locus (P = 0.02). In conclusion, biallelic extensive methylation of the MLH1 promoter region plays a significant role in gene inactivation and is independent of KRAS mutation and TP53 LOH.
authors.affiliation: Department of Surgery, Jichi Medical School, Tochigi, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Miyakura
authors.forename: Kokichi
authors.initials: K
authors.lastname: Sugano
authors.forename: Fumio
authors.initials: F
authors.lastname: Konishi
authors.forename: Noriko
authors.initials: N
authors.lastname: Fukayama
authors.forename: Seiji
authors.initials: S
authors.lastname: Igarashi
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Kotake
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsui
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Koyama
authors.forename: Masato
authors.initials: M
authors.lastname: Maekawa
authors.forename: Hideo
authors.initials: H
authors.lastname: Nagai
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D017668:Age of Onset; D000368:Aged; D002352:Carrier Proteins; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D020868:Gene Silencing; D016158:Genes, p53 / Q000235:genetics; D006801:Humans; D019656:Loss of Heterozygosity / Q000235:genetics; D008297:Male; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009154:Mutation / Q000235:genetics; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics*; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004273:DNA, Neoplasm; C117307:KRAS protein, human; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D000070957:MutL Protein Homolog 1; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins