Hepatocyte nuclear factor 1 alpha activates promoter 1 of the human insulin-like growth factor I gene via two distinct binding sites.
Expression of the human insulin-like growth factor I (hIGF-I) gene is regulated in a tissue- and developmental stage-specific manner. The hIGF-I gene has two promoters, P1 and P2. P1 is the more active promoter by far in adult liver, the main endocrine source of IGF-I. Recently, we described the involvement of the CAAT/enhancer binding protein family of liver-enriched transcription factors in the regulation of the expression of IGF-I in adult liver. In this study we report on the role of another family of liver-enriched transcription factors in the regulation of IGF-I expression. Hepatocyte nuclear factor 1 alpha (HNF-1 alpha) is shown to transactivate IGF-I P1 in transient transfection experiments performed in Hep3B cells. Bandshift experiments reveal that two distinct regions in P1, located 119 and 282 nucleotides upstream of the transcription start site, can bind HNF-1 alpha with relatively high affinity. Both HNF-1-binding sites are evolutionary well conserved, emphasizing the importance of HNF-1 in the regulation of the IGF-I gene expression. Mutational analysis of the binding sites indicates that both sites are essential for maximal stimulation of P1 by HNF-1 alpha, although the largest contribution stems from the more downstream of the two HNF-1-binding sites. The latter site completely overlaps the previously described CAAT/enhancer binding protein binding site in P1. The colocalization of the binding sites, to which binding of the respective factors seems to be mutually exclusive, is suggestive of a regulatory hotspot to which members of different transcription factor families may bind depending on developmental stage and nutritional status.
Nolten
L A
LA
Laboratory for Physiological Chemistry, Utrecht University, The Netherlands.
Steenbergh
P H
PH
Sussenbach
J S
JS
D000328:Adult; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D002461:Cell Line, Transformed; D002645:Chickens / Q000235:genetics; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins; D005786:Gene Expression Regulation / Q000187:drug effects*; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D008099:Liver / Q000378:metabolism; D008113:Liver Neoplasms / Q000473:pathology; D008322:Mammals / Q000235:genetics; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D009928:Organ Specificity; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012474:Salmon / Q000235:genetics; D013045:Species Specificity; D014157:Transcription Factors / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C496487:HNF1A protein, human; C496495:HNF1B protein, human; D051538:Hepatocyte Nuclear Factor 1-alpha; D009687:Nuclear Proteins; D014157:Transcription Factors; D051537:Hepatocyte Nuclear Factor 1; D051539:Hepatocyte Nuclear Factor 1-beta; D007334:Insulin-Like Growth Factor I