ABSTRACT
AIM: To study the expression of HBV enhancer II by transcription factor COUP-TF1. METHODS: In order to study the regulation of HBV variants in the vicinity of the NRRE we cloned luciferase constructs containing the HBV enhancer II from variants and from HBV genotypes A and D and cotransfected them together with expression vectors for COUP-TF1 into HepG2 cells. RESULTS: Our findings show that enhancer II of HBV genotype A is also repressed by COUP-TF1. In contrast, two different enhancer II constructs of HBV genotype D were activated by COUP-TF1. The activation was independent of the NRRE because a natural variant with a deletion of nt 1763-1770 was still activated by COUP-TF1. CONCLUSION: Regulation of transcription of the HBV genome seems to differ among HBV genomes derived from different genotypes. These differences in transcriptional control among HBV genotypes may be the molecular basis for differences in the clinical course among HBV genotypes.
Subject(s)
COUP Transcription Factor I/genetics , Enhancer Elements, Genetic/genetics , Gene Expression Regulation, Viral/genetics , Hepatitis B virus/genetics , Base Sequence , Cell Line, Tumor , DNA, Viral/genetics , Electrophoretic Mobility Shift Assay , Gene Deletion , Genotype , Humans , Molecular Sequence Data , TransfectionABSTRACT
AIM: Hepatitis B virus protein X (HBx) has been shown to be weakly oncogenic in vitro. The transforming activities of HBx have been linked with the inhibition of several functions of the tumor suppressor p53. We have studied whether HBx may have different effects on p53 depending on the cell type. METHODS: We used the human hepatoma cell line HepG2 and the immortalized murine hepatocyte line AML12 and analyzed stably transfected clones which expressed physiological amounts of HBx. P53 was induced by UV irradiation. RESULTS: The p53 induction by UV irradiation was unaffected by stable expression of HBx. However, the expression of the cyclin kinase inhibitor p21(waf/cip/sdi) which gets activated by p53 was affected in the HBx transformed cell line AML12-HBx9, but not in HepG2. In AML-HBx9 cells, p21(waf/cip/sdi)-protein expression and p21(waf/cip/sdi) transcription were deregulated. Furthermore, the process of apoptosis was affected in opposite ways in the two cell lines investigated. While stable expression of HBx enhanced apoptosis induced by UV irradiation in HepG2-cells, apoptosis was decreased in HBx transformed AML12-HBx9. P53 repressed transcription from the HBV enhancer I, when expressed from expression vectors or after induction of endogenous p53 by UV irradiation. Repression by endogenous p53 was partially reversible by stably expressed HBx in both cell lines. CONCLUSION: Stable expression of HBx leads to deregulation of apoptosis induced by UV irradiation depending on the cell line used. In an immortalized hepatocyte line HBx acted anti-apoptotic whereas expression in a carcinoma derived hepatocyte line HBx enhanced apoptosis.
Subject(s)
Apoptosis/physiology , Gene Expression Regulation, Viral/physiology , Hepatocytes/pathology , Trans-Activators/metabolism , Animals , Apoptosis/genetics , Apoptosis/radiation effects , Cell Line , Cyclin-Dependent Kinase Inhibitor p21/genetics , Cyclin-Dependent Kinase Inhibitor p21/metabolism , Gene Expression Regulation, Neoplastic/physiology , Gene Expression Regulation, Neoplastic/radiation effects , Gene Expression Regulation, Viral/radiation effects , Hepatitis B/complications , Hepatoblastoma/genetics , Hepatoblastoma/metabolism , Hepatoblastoma/pathology , Hepatocytes/metabolism , Humans , Liver Neoplasms/genetics , Liver Neoplasms/metabolism , Liver Neoplasms/pathology , Mice , Trans-Activators/genetics , Tumor Suppressor Protein p53/genetics , Tumor Suppressor Protein p53/metabolism , Ultraviolet Rays , Viral Regulatory and Accessory ProteinsABSTRACT
BACKGROUND/AIMS: Epidemiological studies have shown that coinfection or superinfection with hepatitis B virus (HBV) and C virus (HCV) frequently leads to the suppression of hepatitis B virus replication. The mechanism of this phenomenon is still unclear. Shih et al. [J Virol 1993;67:5823] reported a direct suppression of HBV replication by the core protein of HCV. The target structure of HCV core protein in this system remained unclear. METHODS: As HCV core protein has been shown to influence expression from transcriptional elements, we studied whether HCV core protein altered the activity of the two HBV enhancers 1 and 2. Luciferase vectors for HBV enhancers 1 or 2 were cotransfected with expression constructs for HCV core protein in murine and human hepatocyte lines. RESULTS: Full-length HCV core protein suppressed the HBV enhancer 1 up to 11-fold, the enhancer 2 3-4-fold. Suppression of HBV enhancer 1 by HCV core from genotype 1b was stronger than by HCV core of genotypes 3a or 1a. Carboxyterminally truncated core proteins had lower or no suppression activity. CONCLUSIONS: These data suggest that HCV core protein may directly repress transcription of the HBV RNAs. This trans-repression may contribute to suppression of HBV replication in patients coinfected with both viruses.
