Competition between transcription factors HNF1 and HNF3, and alternative cell-specific activation by DBP and C/EBP contribute to the regulation of the liver-specific aldolase B promoter.
The aldolase B proximal promoter is controlled by at least five elements spanning from -190 to -103 bp with respect to the start site of transcription. From 5' to 3', we found: a negative DE element, an activating C/EBP-DBP binding site, a CCAAT box binding NFY that seems to play a negative role, and an activating element consisting of two overlapping binding sites for HNF-1 and HNF-3. Contransfection experiments of aldolase B/CAT constructs and of expression vectors for different transcription factors were carried out in human hepatoma Hep G2 cells. We found that DBP and HNF-1 are strong transactivators of the aldolase B promoter while C/EBP and vHNF-1 are only weak activators and HNF-3 alone does not modify such activity. Deletion of the distal negative element results in a similar transactivation by C/EBP and DBP, enhanced for the former and reduced for the latter. In hepatocytes in primary culture, the strong transactivator is C/EBP while DBP is essentially inactive. This tissue-specificity of C/EBP and DBP action could depend on interaction with tissue-specific proteins bound to a neighbouring site, probably DE. Finally, HNF3 behaves as a very strong anti-activator of the aldolase B promoter. It competitively antagonizes transactivation by HNF-1 and non-competitively transactivation by DBP. This negative effect of HNF-3 and tissue-specificity of the transactivation potential of DBP and C/EBP are unique features of the aldolase B promoter.
Institut Cochin de Genetique Moleculaire, U. 129 de l'INSERM, ICGM CHU Cochin, Paris, France.
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D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D022762:CCAAT-Enhancer-Binding Proteins; D006528:Carcinoma, Hepatocellular; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005634:Fructose-Bisphosphate Aldolase / Q000235:genetics*; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D006801:Humans; D008099:Liver; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D009928:Organ Specificity; D011401:Promoter Regions, Genetic / Q000502:physiology; D051381:Rats; D012045:Regulatory Sequences, Nucleic Acid / Q000502:physiology; D015534:Trans-Activators; D014157:Transcription Factors / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D022762:CCAAT-Enhancer-Binding Proteins; C063898:DBP protein, human; C485975:DBP protein, rat; D004268:DNA-Binding Proteins; C496487:HNF1A protein, human; C496495:HNF1B protein, human; D051538:Hepatocyte Nuclear Factor 1-alpha; C496489:Hnf1a protein, rat; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051537:Hepatocyte Nuclear Factor 1; D051539:Hepatocyte Nuclear Factor 1-beta; D005634:Fructose-Bisphosphate Aldolase