Ectopic expression of the beta-cell specific transcription factor Pdx1 inhibits glucagon gene transcription
| Autor: | Philippe A. Halban, Beate Ritz-Laser, Benoit R. Gauthier, Jacques Philippe, Didier Trono, Aline Mamin, Anne Estreicher, Frédéric Ris, Thierry Brun, Patrick Salmon |
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| Rok vydání: | 2003 |
| Předmět: |
endocrine system
Transcription Genetic endocrine system diseases Endocrinology Diabetes and Metabolism Genetic Vectors Molecular Sequence Data Glucagonoma Biology Transfection digestive system Glucagon Alpha cell Cell Line Islets of Langerhans Cricetinae Internal Medicine medicine Animals Humans Insulin Northern blot Homeodomain Proteins/genetics/metabolism Transcription factor Trans-Activators/ genetics/metabolism Glucagon-like peptide 1 receptor ddc:616 Homeodomain Proteins Transcription Genetic/ genetics Binding Sites Base Sequence Mesocricetus Insulin/genetics medicine.disease Molecular biology Islets of Langerhans/physiology Glucagon/ genetics Oligodeoxyribonucleotides Organ Specificity Trans-Activators PDX1 Ectopic expression |
| Zdroj: | Diabetologia, Vol. 46, No 6 (2003) pp. 810-821 |
| ISSN: | 1432-0428 0012-186X |
| DOI: | 10.1007/s00125-003-1115-7 |
| Popis: | AIMS/HYPOTHESIS: The transcription factor Pdx1 is required for the development and differentiation of all pancreatic cells. Beta-cell specific inactivation of Pdx1 in developing or adult mice leads to an increase in glucagon-expressing cells, suggesting that absence of Pdx1could favour glucagon gene expression by a default mechanism. METHOD: We investigated the inhibitory role of Pdx1 on glucagon gene expression in vitro. The glucagonoma cell line InR1G9 was transduced with a Pdx1-encoding lentiviral vector and insulin and glucagon mRNA levels were analysed by northern blot and real-time PCR. To understand the mechanism by which Pdx1 inhibits glucagon gene expression, we studied its effect on glucagon promoter activity in non-islet cells using transient transfections and gel-shift analysis. RESULTS: In glucagonoma cells transduced with a Pdx1-encoding lentiviral vector, insulin gene expression was induced while glucagon mRNA levels were reduced by 50 to 60%. In the heterologous cell line BHK-21, Pdx1 inhibited by 60 to 80% the activation of the alpha-cell specific element G1 conferred by Pax-6 and/or Cdx-2/3. Although Pdx1 could bind three AT-rich motifs within G1, two of which are binding sites for Pax-6 and Cdx-2/3, the affinity of Pdx1 for G1 was much lower as compared to Pax-6. In addition, Pdx1 inhibited Pax-6 mediated activation through G3, to which Pdx1 was unable to bind. Moreover, a mutation impairing DNA binding of Pdx1 had no effect on its inhibition on Cdx-2/3. Since Pdx1 interacts directly with Pax-6 and Cdx-2/3 forming heterodimers, we suggest that Pdx1 inhibits glucagon gene transcription through protein to protein interactions with Pax-6 and Cdx-2/3. CONCLUSION/INTERPRETATION: Cell-specific expression of the glucagon gene can only occur when Pdx1 expression extinguishes from the early alpha cell precursor. |
| Databáze: | OpenAIRE |
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