Overexpression of cyclin A and p53 in hepatocellular carcinomas. Wild P53 downregurate cyclin a promoter activity

Abstract

Backround: The p16 INK4a tumor suppressor gene induces a cell cycle G1 arrest. It is the second most commonly inactivated gene identified in human cancers after p53. The p16 gene has been shown to be inactivated in nearly all human colon cancer cell lines and half of colon cancers and adenomas. While the p16 gene has been demonstrated to be inactivated primarily by promoter DNA methylation in hepatocellular carcinomas, there have been no studies examining p16 expression in premalignant liver lesions . Design: 17 macroregenerative and dysplastic nodules and 2 hepatocellular carcinomas from 15 hepatectomy specimens in patients undergoing transplantation for hepatitis C cirrhosis were examined by immunohistochemistry and methylation sensitive polymerase chain reaction (PeR). The nodules were less than 2 cm in diameter and clinically undetected . Sections were stained with anti-human pl6 monoclonal antibody . Human sporadic colon adenocarcinomas served as positive controls . Staining for p16 was considered positive if nuclear staining was greater than cytoplasmic staining. Methylation sensitive PCR was performed on bisulfite-treated DNA extracted from microdissected paraffin sections. Results: No nuclear staining was detected in the macroregenerative or dysplastic nodules. Two nodules demonstrated weak cytoplasmic staining . The surrounding cirrhotic liver showed cytoplasmic and no nuclear staining . Bile ductules at the margins of the nodules showed positive staining and served as internal positive controls. The 2 hepatocellular carcinomas showed a distinct lack of nuclear or cytoplasmic staining. Negative controls lacked cytoplasmic and nuclear staining. One hepatocellular carcinoma and two macroregenerative nodules had methylated p16 gene promoters , while two of the surrounding cirrhotic liver samples had unmethylated pl6 gene promoters. One macroregenerative nodule also showed evidence of both methylated and unmethylated pl6 forms. Conclusions: In patients with hepatitis C, clinically undetected macroregenerative and dysplastic nodules show an absence of pl6 staining. It is likely that pl6 gene methylation is responsible for suppression ofpl6 expression in these nodules. This supports previous observations that a high percentage of hepatocellular carcinomas have inactive p16 genes and suggests that p16 inactivation occurs early in liver tumor progression.