Islet-specific proteins interact with the insulin-response element of the glucagon gene.
Glucagon gene expression is negatively regulated by insulin at the transcriptional level. G3, a DNA control element located in the 5'-flanking sequence of the rat glucagon gene mediates the inhibition of transcription, which occurs in response to insulin. We show here that two islet-specific protein complexes C1A and C1B, bind to the A domain of G3, which is critical for the insulin response. These two complexes bind to overlapping sequences of the A domain and display very similar binding specificities. Point mutations in the A domain that affect binding of C1A and C1B result in both decreased G3 enhancer activity and insulin-mediated inhibitory effects with a close correlation between diminution of binding and function. One of the two complexes, C1A, is similar or identical to B1, a protein complexes interacting with the upstream promoter element of the glucagon gene, G1, implicated in the A cell-specific expression of the glucagon gene. Our data indicate that islet-specific proteins are involved in glucagon gene regulation by insulin.
Philippe
J
J
Department of Genetics and Microbiology, University of Geneva Medical School, Switzerland.
Morel
C
C
Cordier-Bussat
M
M
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002417:Cattle; D002460:Cell Line; D006224:Cricetinae; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D005809:Genes, Regulator; D005934:Glucagon / Q000096:biosynthesis / Q000235:genetics*; D015292:Glycoprotein Hormones, alpha Subunit / Q000235:genetics; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental; D008647:Mesocricetus; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D016716:PC12 Cells; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D051381:Rats; D012045:Regulatory Sequences, Nucleic Acid; D012689:Sequence Homology, Nucleic Acid; D013004:Somatostatin / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014407:Tumor Cells, Cultured
D015292:Glycoprotein Hormones, alpha Subunit; D007328:Insulin; D009838:Oligodeoxyribonucleotides; D013004:Somatostatin; D004247:DNA; D005934:Glucagon