Essential interaction of Egr-1 at an islet-specific response element for basal and gastrin-dependent glucagon gene transactivation in pancreatic alpha-cells.
The peptide hormone gastrin is secreted from G cells of the gastric antrum and is the main inducer of gastric acid secretion via activation of its receptor the cholecystokinin 2 (CCK2) receptor. Both gastrin and CCK2 receptors are also transiently detected in the fetal pancreas and believed to exert growth/differentiation effects during endocrine pancreatic development. We demonstrated previously that whereas gastrin expression is extinguished in adult pancreas, CCK2 receptors are present in human glucagon-producing cells where their activation stimulates glucagon secretion. Based on these findings, we investigate in the present study whether gastrin regulates glucagon gene expression. To this aim, the CCK2 receptor was stably expressed into a glucagon-producing pancreatic islet cell line, and a glucagon-reporter fusion gene was transiently transfected in this new cellular model. We report that gastrin stimulates glucagon gene expression in glucagon-producing pancreatic cells. By using progressively 5'-increased sequences of the glucagon gene, gastrin responsiveness was located within the minimal promoter. Moreover, we clearly identified early growth response protein 1 (Egr-1) as an essential transcription factor interacting with the islet cell-specific G4 element. Egr-1 was shown to be essential for basal and gastrin-dependent glucagon gene transactivation. Furthermore, our results demonstrate that the MEK1/ERK1/2 pathway couples the CCK2 receptor to nuclearization and DNA binding of Egr-1. In conclusion, our data provide new information concerning the transcriptional regulation of the glucagon gene. Moreover they open new working hypothesis with reference to a potential role of gastrin in glucagon-producing pancreatic cells.
Leung-Theung-Long
Stéphane
S
Inserm U531, IFR31, Hospital Rangueil, 31059 Toulouse Cedex 9, France.
Roulet
Emmanuelle
E
Clerc
Pascal
P
Escrieut
Chantal
C
Marchal-Victorion
Sophie
S
Ritz-Laser
Beate
B
Philippe
Jacques
J
Pradayrol
Lucien
L
Seva
Catherine
C
Fourmy
Daniel
D
Dufresne
Marlène
M
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D015500:Chloramphenicol O-Acetyltransferase / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D006224:Cricetinae; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D051766:Early Growth Response Protein 1; D005755:Gastrins / Q000378:metabolism*; D005786:Gene Expression Regulation; D005934:Glucagon / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism / Q000502:physiology*; D007150:Immunohistochemistry; D007515:Islets of Langerhans / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D043887:Receptor, Cholecystokinin B / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D005755:Gastrins; D017874:Immediate-Early Proteins; D012333:RNA, Messenger; D043887:Receptor, Cholecystokinin B; D014157:Transcription Factors; D004247:DNA; D005934:Glucagon; D015500:Chloramphenicol O-Acetyltransferase