Liver-specific enhancer II is the target for the p53-mediated inhibition of hepatitis B viral gene expression.
Here, we established the inhibitory mechanism of p53 on hepatitis B viral gene expression using HepG2 cells. Our results are as follows. First, p53 down-regulated the activities of all four promoters of hepatitis B virus (HBV), suggestive of the presence of a common element mediating the p53-dependent transcriptional repression. Second, employing the 5'-deletion constructs of the pregenomic/core promoter, the liver-specific enhancer II region was localized as a target for the p53-mediated transcriptional repression. Third, in a detailed analysis of the enhancer II region, the 5'-proximal 31-base pair region was defined as a p53-repressible element. Throughout the study, p53-mediated repression was rescued upon coexpression of the X-gene product, HBx. Finally, in an electrophoretic mobility shift assay, the defined p53-repressible element did not bind purified p53 directly, but shifted three bands in HepG2 nuclear extract, two of which was supershifted upon addition of p53 monoclonal antibody. These results display a novel mechanism of p53-dependent transcriptional repression in which p53 negatively regulates the viral-specific DNA enhancer through protein to protein interaction with an enhancer-binding protein. At the same time, the results indicate that p53 plays a defensive role against HBV by transcriptionally repressing the HBV core promoter through liver-specific enhancer II and HBx is required to counteract this inhibitory function of p53.
Signal Transduction Laboratory, Mogam Biotechnology Research Institute, 341 Pojungri, Koosungmyon, Yongingoon, Kyunggido 449-910, Korea.
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D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000032:analysis; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D015967:Gene Expression Regulation, Viral / Q000235:genetics; D017930:Genes, Reporter / Q000235:genetics; D005814:Genes, Viral / Q000235:genetics; D006515:Hepatitis B virus / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000502:physiology*; D009363:Neoplasm Proteins / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D012097:Repressor Proteins / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics; D014162:Transfection / Q000235:genetics; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D017361:Viral Nonstructural Proteins / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C110719:LAMTOR5 protein, human; D009363:Neoplasm Proteins; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; D017361:Viral Nonstructural Proteins