Identification of an insulin-responsive element in the promoter of the human gene for insulin-like growth factor binding protein-1.
Insulin inhibits the hepatic transcription of insulin-like growth factor binding protein-1 (IGFBP-1). In the present studies, human HEP G2 hepatoma cells were transiently transfected with human IGFBP-1 gene promoter constructs in order to identify cis elements and trans-acting factors that confer the insulin effect. Transfections of IGFBP-1 promoter deletion constructs localized an insulin responsive element (IRE) between approximately 140- and approximately 103-base pair (bp) 5' to the mRNA capsite. This region contains a 25-bp sequence which is 100% conserved in the rat IGFBP-1 promoter and which has two AT-rich, 8-bp elements exhibiting dyad symmetry. Site-directed mutagenesis of both elements in the same 1205-bp IGFBP-1 promoter construct abolished the inhibitory effect of insulin on promoter activity. Also, the native but not the mutant IGFBP-1 IRE conferred the inhibitory effect of insulin to the heterologous thymidine kinase promoter. Gel mobility shift assays identified a DNA binding activity which specifically binds the native IGFBP-1 IRE and which is not altered by prior insulin treatment. The IGFBP-1 IRE sequence is similar to those of functionally mapped IREs from other gene promoters, suggesting that this common IRE and the protein(s) which it binds confer the insulin effect to a number of insulin-sensitive genes.
Suwanickul
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A
Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030.
Morris
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SL
Powell
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D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D004247:DNA; D006801:Humans; D007328:Insulin / Q000502:physiology*; D018970:Insulin-Like Growth Factor Binding Protein 1; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic; D013937:Thymidine Kinase / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D004247:DNA; D013937:Thymidine Kinase