Study of CpG Methylation of the p16 and MGMT Promoter in Hepatocellular Carcinoma

Heo, Tae Gil; Shin, Sang Hyun; Chang, Yeo Goo; Hong, Seong Woo; Lee, Kyung Mi; Kim, Jeong Hyun; Kang, Yun Kyung; Paik, In Wook; Lee, Hyuck Sang

Abstract

PURPOSE
The aims of this study were to examine the methylation status of the p16 and MGMT promoters in hepatocellular carcinoma (HCC), and to evaluate the relationship between the loss of gene expression, the promoter methylation status and hepatocarcinogenesis. METHODS: We included 24 HCC tissues and their adjacent non-tumorous tissues and 5 normal liver tissues in our study, and all the specimens were obtained by hepatectomy. The methylation status of the p16 and MGMT promoter regions were evaluated by methylation-specific polymerase chain reaction (MSP) and quantitative analysis by using a Gel-pro analyzer (Media Cybernetics, CA, USA). We also analyzed the p16 and MGMT gene expressions by performing immunohistochemical staining of the HCC tissues. RESULTS: Methylation of the p16 promoter was detected in HCC (100%, 24/24) and the adjacent non-tumorous tissues (79.2%, 19/24), but not in the normal liver tissues. Methylation of the MGMT promoter was detected in the HCC (8.3%, 2/24) and the adjacent non-tumorous tissues (4.2%, 1/24), but not in the normal liver tissues. Methylation positive HCC samples showed the loss of p16 expression in 58.3% (14/24). The loss of the p16 expression in the HCC tissues was well correlated with the increased rate of p16 promoter methylation (p=0.009). When the p16 promoter methylation status of the HCC tissues was higher than that of the adjacent non-tumorous tissues, 77.8% of the cases showed the loss of the p16 expression (p=0.002). No correlation was observed between MGMT promoter methylation and the loss of the gene expression in the HCC tissues. CONCLUSION: These results suggest that methylation of the p16 promoter and the resulting loss of p16 protein expression are significant events in hepatocarcinogenesis, and further studies are needed to evaluate the relationship between the methylation of the MGMT promoter and HCC carcinogenesis.