Study on the role of DNA methyltransferases in regulation of the expression of genes associated with the control of cell cycle

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To estimate the involvement of methylation in the down-regulation of the genes, APC, p16, FEZ1, KAI1, and survivine, wehich were associated with the regulation of cell cycle, we examined the expression revels of them and methyltransferases, DNMT1, DNMT3A, and DNMT3B, which were believed to be associated with carcinogenesis, in 8 cell lines, SAS, HSC-2, HSC-3, HSC-4, Ca9-22, OK-92, HO-1-u-1, and HO-1-N-1, which were derived from oral carcinoma, and clinical tissue samples of oral cancer. Additionally, restoration of the gene expression by 5-Aza-C, one of the demethylation agents, was examined. The hyper methylation of CDKN2A/p16 gene was detected in 24 (48.0%) of 50 oral squamous cell carcinoma cases (OSCC) and the restoration by 5-Aza-C was found in 6 (75.0%) of 8 cell lines. The down expression of APCgene was detected in 15 (30.0%) of 50cases, and hypermethylation of CPG island was found 12 (24.0%) of the all cases. Suppressed expression and hypermethylation of FEZ1gene was detected i … More n 11 (35.5%) and in 8 (25.8%) of 31 case, respectively. Out of the 31 cases, hypermethylation was detected and restoration of the gene expression by 5-Aza-C was found in all of the 8 cell lines. Silence or suppressed expression of KAI1 gene was detected in 84 of 101 OSCC cases. However, neither hypermethylation of CPG island of the promoter region nor restoration of the gene expression by 5-Aza-C was not found. The over-expression of surviving gene was detected in 58% of OSCC cases and in 37% of precancerous lesion, leukoplakia. On the other hand, the expression of surviving gene was not detected by RT-PCRin all of the 9 normal oral epitherium tissues and DNA methylation was confirmed by methylation specific PCR in 4 of the 9 normal specimens and the gene expression was restored by 5-Aza-Ctreatment in 2 of 8 cell lines. The over-expression of DNA methyltransferase, DNMTs ; DNMT1, DNMT3A, and DNMT3B, which were believed to be associated with carcinogenesis, were high frequently detected in OSCC. The rates of the expression of DNMTI, DNMT3A, and DNMT3B in OSCC were 72%, 56%, and 64%, respectively. There was no significant correlation between the expression levels and the situations of hypermethylation of the tumor suppressor and oncogenes examined and the expression levels of methyltransferases. Our data suggest that hypermethylation of the gene may be one of the major mechanisms for inactivation of the genes in oral carcinogenesis and that besides methyltransferases, some transcription factors involved in the suppression of gene expression might play an important roles in ora oncogenesis. Less