Comprehensive analysis of promoter methylation and altered expression of hMLH1 in gastric cancer cell lines with microsatellite instability.
OBJECTIVE
Aberrant methylation of the promoter CpG island of hMLH1 is associated with gene silencing in colon cancer and gastric cancer with microsatellite instabilities (MSI). We analyzed the pattern of promoter methylation causing gene silencing.


METHODS
Comprehensive analysis of hMLH1 promoter was performed by bisulfite genomic sequencing in human gastric cancer cell lines. Altered expression of hMLH1 was examined by the immunocytochemical staining method and RT-PCR, and microsatellite instability was examined using two representative mononucleotide repeat microsatellite markers, BAT-25 and BAT-26.


RESULTS
As a result, MSI-positive gastric cancer cell lines were methylated extensively at the overall promoter region. MSI-negative gastric cancer cell lines - except in SNU-620 - were unmethylated completely at the overall promoter region including the more upstream region in contrast to colorectal cancer cell lines. Even though SNU-620 was methylated fully at the overall promoter region - except for partial methylation at the specific region (from -270 to -199) near the transcriptional start - hMLH1 protein was expressed.


CONCLUSIONS
Our data suggest that the methylation density of a specific region plays an important role in gene inactivation of hMLH1 and that the methylation status of the more upstream promoter region and exon 1 start region are not essential for gene inactivation.
Kang
Y-H
YH
Department of Pathology, Seoul National University College of Medicine, Seoul, South Korea.
Bae
S I
SI
Kim
W H
WH
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D017931:DNA Primers; D004273:DNA, Neoplasm / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D007150:Immunohistochemistry; D018895:Microsatellite Repeats / Q000235:genetics; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000096:biosynthesis*; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013274:Stomach Neoplasms / Q000235:genetics* / Q000473:pathology; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D017931:DNA Primers; D004273:DNA, Neoplasm; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1