Members of the CAAT/enhancer-binding protein, hepatocyte nuclear factor-1 and nuclear factor-1 families can differentially modulate the activities of the rat alpha-fetoprotein promoter and enhancer.
The promoter of the rat alpha-fetoprotein (AFP) gene, which makes the expression of the developmentally regulated AFP gene specific to the liver, is a putative target for transcription factors of the CAAT/enhancer-binding protein (C/EBP), hepatocyte nuclear factor-1 (HNF-1) and nuclear factor-1 (NF-1) families. We have evaluated the influence of these factors on the activity of the AFP promoter by transfection of HepG2 hepatoma cells with the appropriate expression vector plus a CAT plasmid under the control of the AFP promoter. A similar plasmid bearing the rat albumin promoter was used as a control. C/EBP alpha, C/EBP beta and D-binding protein (DBP) acted as trans-activators on the AFP promoter, whereas liver inhibitory protein (LIP), a truncated form of C/EBP beta, was a potent negative regulator of the promoter. C/EBP alpha also bound to and stimulated the activity of the AFP enhancer at -2.5 kb. Interestingly, HNF-1 beta was found to be more potent than HNF-1 alpha in activating the AFP promoter. This effect was specific, as it did not occur with the rat albumin promoter. HNF-1 beta, which is produced earlier than HNF-1 alpha during liver development, would thus have the greater influence on the AFP promoter in early development. Both HNF-1s allowed expression of the AFP promoter in cells of nonhepatic origin. Overexpression of NF-1 induced a specific decrease in the activity of the AFP promoter. This strongly suggests that competition between NF-1 and HNF-1 for binding to their overlapping binding sites on the AFP promoter is critical for modulating its activity. Thus changing combinations of these trans-acting factors may tightly modulate the AFP promoter activity in the course of liver development and carcinogenesis.
Bois-Joyeux
B
B
Centre de Recherche sur l'Endocrinologie Moléculaire et le Développement, CNRS UPR 1511, Meudon, France.
Danan
J L
JL
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D015870:Gene Expression; D005822:Genetic Vectors; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D006801:Humans; D008114:Liver Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D051839:NFI Transcription Factors; D009687:Nuclear Proteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D051381:Rats; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000378:metabolism; D051840:Y-Box-Binding Protein 1; D000509:alpha-Fetoproteins / Q000235:genetics*
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C496487:HNF1A protein, human; C496495:HNF1B protein, human; D051538:Hepatocyte Nuclear Factor 1-alpha; C496489:Hnf1a protein, rat; D051839:NFI Transcription Factors; D009687:Nuclear Proteins; D014157:Transcription Factors; D051840:Y-Box-Binding Protein 1; C070856:YBX1 protein, human; C486169:Ybx1 protein, rat; D000509:alpha-Fetoproteins; D051537:Hepatocyte Nuclear Factor 1; D051539:Hepatocyte Nuclear Factor 1-beta; D004247:DNA