Characterization of hepatitis B virus X variants that are integrated and expressed in human hepatocellular carcinomas

This chapter discusses hepatitis B virus X protein (HBX) that has been implicated in the transactivation of diverse cellular genes and possibly the pathogenesis of human hepatocellular carcinoma (HCC). The characterization of HBX variants from hepatitis B virus (HBV)-related human HCC is described in the chapter. Mutations and deletions are identified in well-defined functional domains of HBX essential for transactivation and Kunitz-like serine protease inhibitor activities. Genomic Southern blot analysis described in the chapter reveals that HBX sequences were integrated into the host chromosomes of HCC tissues. Analysis using reverse transcriptase-based polymerase chain reaction (RT-PCR) indicates that these integrated HBX genes were expressed in the HCC tissues. A novel in vitro HBX activity assay based on color changes is indicative of the J galactosidase enzyme activity. Conducted in wheat germ lysates, the transactivating function of either wild type or mutant HBX protein was measured through its interaction with the rarly growth response factor 1 (Egr-1) that controls the P-galactosidase gene. Analysis of HBX deletion mutants using this assay may shed new insights on the significance of various mutations occurring in HCC-associated HBX.