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It has been recognized that hypermethylation of the CpG island of the promoter region silences some genes as effectively as inactivation of the gene by mutations or deletions. Recently it has been found that the human ID4 gene, one of the ID family of the helix-loop-helix (HLH) transcription factors, did not significantly expressed in 82% and 30% in human gastric cancer cell lines and cancer tissues due to hypermethylation of the promoter region. Little is known, however, about the expression and hypermethylation status of ID4 in colorectal cancer cell lines and cancer tissues. To verify the expression and methylation status of ID4 gene in colorectal carcinogenesis, we checked promoter hypermethylation status by RT-PCR analysis and methylation specific PCR (MS-PCR) and sequencing analysis after sodium bisulfite modification in 32 colorectal cancer cell lines and 76 cancer tissues. We have also analyzed the hypermethylation status of hMLH1 gene and microsatellite instability status in cancer cell lines and cancer. Of 32 lines, ID4 expression was significantly reduced in 15 cell lines (47%) by RT-PCR. After sodium bisulfite modification and direct sequencing analysis, the promoter hypermethylation of ID4 was confirmed in 17 cell lines (17 out of 27 cell lines, 63%). Promoter hypermethylatoin of ID4 in colorectal cancer tissues and corresponding normal tissues was found in 63% and 1.3%, respectively. The promoter region of hMLH1 gene was hypermethylated in 31.2% in cancer cell lines and 29% in cancer tissues. There was no correlation between promoter hypermethylation of ID4 and hMLH1 gene, and hypermethylation of ID4 gene and microsatellite instability status. These results suggest that promoter hypermethylation of ID4 down-regulates its expression in colorectal carcinomas as well as gastric cancers and might play an important role the development and progression of human colorectal carcinomas.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]