Progression of hypermethylation of the p16(INK4A) gene from normal liver to nontumorous liver and hepatocellular carcinoma: an evaluation using quantitative PCR analysis.

The aim of this study was to determine to what extent hypermethylation of the p16(INK4A) (p16) gene promoter is increased in nontumorous liver tissues compared with in normal liver, using two quantitative methylation-specific polymerase chain reaction (MS-PCR) methods and a bisulfite sequencing method. Methylation of the p16 gene was detected more frequently in nontumorous liver than in normal liver using the TaqMan PCR method. Methylation indices also were significantly higher in nontumorous than in normal liver. However, the bisulfite sequencing method did not detect significantly more methylation of the p16 gene in nontumorous than normal liver, nor was there a significant difference in the level of p16 mRNA. There may be a greater proportion of cells which contain methylated p16 in nontumorous than in normal liver. However, the difference was so small that the functional relevance to hepatocarcinogenesis remains elusive.