Extensive but hemiallelic methylation of the hMLH1 promoter region in early-onset sporadic colon cancers with microsatellite instability.
OBJECTIVE
Methylation of the hMLH1 promoter region is frequently observed in microsatellite instability (MSI)-positive sporadic colorectal carcinomas. We studied hMLH1 promoter methylation in peripheral blood lymphocytes of 87 index patients representing 29 cases of hereditary nonpolyposis colorectal cancers (HNPCCs), 28 cases of atypical HNPCCs, and 30 sporadic cases of the development of early-onset colorectal carcinomas or multiple primary cancers.


METHODS
Methylation of the hMLH1 promoter region was analyzed by Na-bisulfite polymerase chain reaction/single-strand conformation polymorphism analysis or methylation-specific polymerase chain reaction. MSI, allelic status of the hMLH1 locus, and loss of hMLH1 protein expression were examined in cases for which tumor tissues were available.


RESULTS
Extensive methylation of the hMLH1 promoter was detected in peripheral blood lymphocytes of 4 of 30 patients with sporadic early-onset colon cancer, among whom multiple primary cancers (1 colon and 1 endometrial cancer) developed in 2 cases. This methylation was not detected in analyses of HNPCC or atypical HNPCC groups or healthy control subjects. MSI was positive, and extensive methylation was detected in both cancers (colon and endometrial cancer) and normal tissues (colon, gastric mucosa, endometrium, and bone marrow) in all of the examined cases (3 of 3). Analysis of a polymorphic site in the hMLH1 promoter in 2 informative cases showed that methylation was hemiallelic. In 1 case, the unmethylated allele was lost in the colon cancer but not in the metachronous endometrial cancer.


CONCLUSIONS
Constitutive, hemiallelic methylation of the hMLH1 promoter region was shown to be associated with carcinogenesis in sporadic, early-onset MSI-positive colon cancers.
Miyakura
Yasuyuki
Y
Oncogene Research Unit/Cancer Prevention Unit, Tochigi Cancer Center Research Institute, Tochigi, Japan.
Sugano
Kokichi
K
Akasu
Takayuki
T
Yoshida
Teruhiko
T
Maekawa
Masato
M
Saitoh
Soh
S
Sasaki
Hideyuki
H
Nomizu
Tadashi
T
Konishi
Fumio
F
Fujita
Shin
S
Moriya
Yoshihiro
Y
Nagai
Hideo
H
D048868:Adaptor Proteins, Signal Transducing; D000483:Alleles; D002352:Carrier Proteins; D003106:Colon / Q000502:physiology; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D019175:DNA Methylation; D006801:Humans; D007150:Immunohistochemistry; D018895:Microsatellite Repeats; D000070957:MutL Protein Homolog 1; D009154:Mutation / Q000235:genetics; D009363:Neoplasm Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D018807:Polymorphism, Single-Stranded Conformational; D011401:Promoter Regions, Genetic / Q000235:genetics*; D013997:Time Factors
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1