title: p53-mediated repression of alpha-fetoprotein gene expression by specific DNA binding.
abstract: Aberrant expression of the alpha-fetoprotein (AFP) gene is characteristic of a majority of hepatocellular carcinoma cases and serves as a diagnostic tumor-specific marker. By dissecting regulatory mechanisms through electromobility gel shift, transient-transfection, Western blot, and in vitro transcription analyses, we find that AFP gene expression is controlled in part by mutually exclusive binding of two trans-acting factors, p53 and hepatic nuclear factor 3 (HNF-3). HNF-3 protein activates while p53 represses AFP transcription through sequence-specific binding within the previously identified AFP developmental repressor domain. A single mutation within the DNA binding domain of p53 protein or a mutation of the p53 DNA binding element within the AFP developmental repressor eliminates p53-repressive effects in both transient-transfection and cell-free expression systems. Coexpression of p300 histone acetyltransferase, which has been shown to acetylate p53 and increase specific DNA binding, amplifies the p53-mediated repression. Western blot analysis of proteins present in developmentally staged, liver nuclear extracts reveal a one-to-one correlation between activation of p53 protein and repression of AFP during hepatic development. Induction of p53 in response to actinomycin D or hypoxic stress decreases AFP expression. Studies in fibroblast cells lacking HNF-3 further support a model for p53-mediated repression that is both passive through displacement of a tissue-specific activating factor and active in the presence of tissue-specific corepressors. This mechanism for p53-mediated repression of AFP gene expression may be active during hepatic differentiation and lost in the process of tumorigenesis.
authors.affiliation: Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, Ohio 45267-0524, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Lee
authors.forename: A J
authors.initials: AJ
authors.lastname: Crowe
authors.forename: M C
authors.initials: MC
authors.lastname: Barton
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism; D015687:Cell Hypoxia / Q000235:genetics; D004249:DNA Damage; D017931:DNA Primers / Q000235:genetics; D004273:DNA, Neoplasm / Q000235:genetics* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D051541:Hepatocyte Nuclear Factor 3-alpha; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D014018:Tissue Distribution; D014157:Transcription Factors; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D000509:alpha-Fetoproteins / Q000235:genetics*
chemical_list: D017931:DNA Primers; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C496499:FOXA1 protein, human; C496500:Foxa1 protein, mouse; D051541:Hepatocyte Nuclear Factor 3-alpha; D009687:Nuclear Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D000509:alpha-Fetoproteins