Frequent hypermethylation of MLH1 promoter in normal endometrium of patients with endometrial cancers.
Silencing of the MLH1 gene by promoter hypermethylation is the mechanism underlying the microsatellite instability (MSI) phenotype in endometrial cancers. However, the profile of CpG methylation in a wide range of MLH1 promoters in endometrial cancers and in the normal endometrium is largely unknown. The present study investigates the region 700 bp upstream of MLH1 covering 48 CpG sites using bisulfite sequencing. Methylation status was classified as full (over 80% of CpGs are methylated), partial (10-80%) or nonmethylation (less than 10%). Of 56 endometrioid endometrial cancers, 16 (29%) were fully methylated, 14 (25%) were partially methylated and 26 (46%) were not methylated. Analyses of MLH1 by immunohistochemical means and of MSI revealed that the degree, rather than region-specific methylation of CpG islands is critical for decreased MLH1 expression and the MSI phenotype. Among 12 patients with methylated cancers, five (42%) patients contained methylated promoters in their normal endometria with profiles similar to those of cancer lesions, and these were associated with the MSI phenotype. In contrast, only one of 31 (3%) normal endometria from patients without endometrial malignancies harbored methylated promoters. These findings suggest that hypermethylation of the MLH1 promoter is frequent in the histologically normal endometrium adjacent to cancers, supporting the notion that hypermethylation of mismatch repair genes is the initial step that triggers various genetic events in endometrial carcinogenesis.
Kanaya
Taro
T
Department of Obstetrics and Gynecology, Kanazawa university School of Medicine, Kanazawa, Ishikawa 920-8641, Japan.
Kyo
Satoru
S
Maida
Yoshiko
Y
Yatabe
Noriyuki
N
Tanaka
Masaaki
M
Nakamura
Mitsuhiro
M
Inoue
Masaki
M
D048868:Adaptor Proteins, Signal Transducing; D020137:Base Pair Mismatch; D018269:Carcinoma, Endometrioid / Q000737:chemistry / Q000235:genetics*; D002352:Carrier Proteins; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D018899:CpG Islands; D019175:DNA Methylation; D004260:DNA Repair / Q000235:genetics; D004273:DNA, Neoplasm / Q000737:chemistry* / Q000235:genetics; D018900:Dinucleotide Repeats; D016889:Endometrial Neoplasms / Q000737:chemistry / Q000235:genetics*; D004717:Endometrium / Q000737:chemistry*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D018895:Microsatellite Repeats; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D010641:Phenotype; D011401:Promoter Regions, Genetic
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004273:DNA, Neoplasm; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1