Glucagon gene G3 enhancer: evidence that activity depends on combination of an islet-specific factor and a winged helix protein.
The peptide hormone glucagon is expressed in A cells of the pancreatic islets due to an interaction between multiple regulatory elements within the 5'-flanking region of its gene directing glucagon gene transcription. An A-cell-specific enhancer-like element in the rat glucagon gene, G3, contains two domains, both of which are necessary for G3 activity. Domain A of the G3 element comprises a sequence motif, PISCES, that is also found in control elements of the rat insulin I and somatostatin genes exhibiting cell-specific transcriptional activities distinct from G3. In this study, the nuclear proteins binding to domain B of G3 were characterized. In electrophoretic mobility shift assays using nuclear extracts from a glucagon-producing islet cell line, it was observed that the binding specificity of G3-domain-B-binding proteins is related to that of winged helix proteins supporting the hypothesis that the proteins binding to domain B of G3 may belong to the winged helix protein family of transcription factors. The overexpression of a dominant-negative winged helix protein mutant (derived from HNF-3) virtually abolished the transcriptional activity of G3 in a glucagon-expressing islet cell line. These results suggest that the unique A-cell-specific basal transcriptional activity of the glucagon G3 element depends on a combination of at least two proteins, the islet specific PISCES-binding protein and a more widely expressed winged helix protein.
Diedrich
T
T
Department of Molecular Pharmacology, University of Göttingen, Germany.
Fürstenau
U
U
Knepel
W
W
D001665:Binding Sites; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic / Q000502:physiology*; D005786:Gene Expression Regulation; D005934:Glucagon / Q000096:biosynthesis / Q000235:genetics*; D015292:Glycoprotein Hormones, alpha Subunit / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007515:Islets of Langerhans / Q000378:metabolism / Q000502:physiology*; D009687:Nuclear Proteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000502:physiology; D017433:Protein Structure, Secondary; D012680:Sensitivity and Specificity; D014157:Transcription Factors / Q000378:metabolism* / Q000502:physiology
D004268:DNA-Binding Proteins; D015292:Glycoprotein Hormones, alpha Subunit; D009687:Nuclear Proteins; D014157:Transcription Factors; D004247:DNA; D005934:Glucagon