Methylation of hMLH1 promoter correlates with the gene silencing with a region-specific manner in colorectal cancer.
Microsatellite instability is present in over 80% of the hereditary non-polyposis colorectal carcinoma and about 15-20% of the sporadic cancer. Microsatellite instability is caused by the inactivation of the mismatch repair genes, such as primarily hMLH1, hMSH2. To study the mechanisms of the inactivation of mismatch repair genes in colorectal cancers, especially the region-specific methylation of hMLH1 promoter and its correlation with gene expression, we analysed microsatellite instability, expression and methylation of hMLH1 and loss of heterozygosity at hMLH1 locus in these samples. Microsatellite instability was present in 17 of 71 primary tumours of colorectal cancer, including 14 of 39 (36%) mucinous cancer and three of 32 (9%) non-mucinous cancer. Loss of hMLH1 and hMSH2 expression was detected in nine and three of 16 microsatellite instability tumours respectively. Methylation at CpG sites in a proximal region of hMLH1 promoter was detected in seven of nine tumours that showed no hMLH1 expression, while no methylation was present in normal mucosa and tumours which express hMLH1. However, methylation in the distal region was observed in all tissues including normal mucosa and hMLH1 expressing tumours. This observation indicates that methylation of hMLH1 promoter plays an important role in microsatellite instability with a region-specific manner in colorectal cancer. Loss of heterozygosity at hMLH1 locus was present in four of 17 cell lines and 16 of 54 tumours with normal hMLH1 status, while loss of heterozygosity was absent in all nine cell lines and nine tumours with abnormal hMLH1 status (mutation or loss of expression), showing loss of heterozygosity is not frequently involved in the inactivation of hMLH1 gene in sporadic colorectal cancer.
Deng
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Gastrointestinal Research Laboratory, 151M2 Veteran Affairs Medical Center, University of California, San Francisco, 4150 Clement Street, San Francisco, California, CA 94121, USA. guoren@itsa.ucsf.edu
Peng
E
E
Gum
J
J
Terdiman
J
J
Sleisenger
M
M
Kim
Y S
YS
D048868:Adaptor Proteins, Signal Transducing; D000483:Alleles; D002352:Carrier Proteins; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018899:CpG Islands; D019175:DNA Methylation; D017931:DNA Primers / Q000737:chemistry; D004273:DNA, Neoplasm / Q000235:genetics*; D004268:DNA-Binding Proteins; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D020868:Gene Silencing; D006801:Humans; D007124:Immunoenzyme Techniques; D019656:Loss of Heterozygosity; D018895:Microsatellite Repeats; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins; D016133:Polymerase Chain Reaction / Q000379:methods; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D017931:DNA Primers; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein