Integrity of p53 in hepatitis B x antigen-positive and -negative hepatocellular carcinomas

Inactivation of the tumor suppressor p53 seems to be important to the pathogenesis of hepatocellular carcinoma (HCC) associated with chronic hepatitis B virus infection. Although this inactivation may be due to mutations in the p53 gene, recent evidence suggests that the hepatitis B virus-encoded X antigen (HBxAg) binds to and inactivates wild-type p53. Hence, experiments were designed to test the hypothesis that there is a low frequency of p53 mutations in HBxAg-positive HCC. HBxAg and p53 were assayed by immunohistochemistry (IHC) in HCC and nontumor liver from 16 Chinese patients, half of whom were hepatitis B surface antigen carriers. HBxAg was detectable in tumor and/or nontumor cells from all patients by IHC; six of these samples also had detectable p53. To determine whether p53 detection by IHC, and hence stabilization, is associated with mutation, sequencing of p53 exons 5-8 was performed with each patient sample. Wild-type sequences were found in 13 of 16 HBxAg-positive cases (81%). Hence, HBxAg is a common marker of HCC that correlates with the persistence of wild-type p53 among both carriers and noncarriers. The low frequency of p53 mutations in HCC in these patients implies that p53 inactivation may occur predominantly by complex formation with HBxAg.