Normal hepatocytes express very few class I major histocompatibility complex (MHC I) molecules, but MHC I expression is elevated in hepatitis B virus (HBV) infection. We report here that hepatoblastoma cells with replicating HBV genomes express three- to fourfold-higher levels of MHC I protein and mRNA than do parent cells without HBV DNA. Transient transfection assays demonstrated that the HBV X protein trans activated transcription from an MHC I promoter and allowed identification of cis elements important for trans activation.
