title: Hepatitis B virus X gene expression is activated by X protein but repressed by p53 tumor suppressor gene product in the transient expression system.
abstract: Hepatitis B virus (HBV) X gene is known to exhibit a transcriptional activation function and is considered to play a major role in hepatocarcinogenesis. We determined a 20-bp promoter element for the HBV X gene transcription and found a binding protein to this promoter element, designated as an X-PBP. We then examined the effects of HBV X protein and p53 tumor suppressor gene product on X gene transcription from the 20-bp promoter element using the transient expression technique. Activity of the X gene promoter was stimulated by X protein expression, but, in contrast, was repressed by transfected normal p53 gene. On the other hand, mutant p53 gene product exhibited no repression. Moreover, the p53 repression of X gene transcription was canceled by X protein coexpression. Thus, the effects of X protein and normal p53 product appear to be mutually antagonistic in the regulation of X gene expression. However, mutated promoter elements which failed to bind to X-PBP still responded to X protein or p53, indicating that the process of X transactivation or p53 repression may be independent of X-PBP binding to the promoter element. Our data suggest that X protein could disrupt function of normal p53 protein in X gene-transfected cells.
authors.affiliation: Department of Gene Research, Cancer Institute (JFCR), Tokyo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Takada
authors.forename: N
authors.initials: N
authors.lastname: Kaneniwa
authors.forename: N
authors.initials: N
authors.lastname: Tsuchida
authors.forename: K
authors.initials: K
authors.lastname: Koike
mesh_terms: D001483:Base Sequence; D004279:DNA, Viral / Q000235:genetics; D015967:Gene Expression Regulation, Viral; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D004279:DNA, Viral; D012097:Repressor Proteins; D015534:Trans-Activators; D016159:Tumor Suppressor Protein p53; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein