title: Calcium influx into MIN6 insulinoma cells induces expression of Egr-1 involving extracellular signal-regulated protein kinase and the transcription factors Elk-1 and CREB.
abstract: Glucose induces many changes in the transcriptional pattern of beta-cells derived from the endocrine pancreas. The zinc finger protein Egr-1 belongs to the transcription factors that are activated in glucose-treated beta-cells. Egr-1 expression is additionally induced by treatment of MIN6 pancreatic beta-cells with tolbutamide, a compound that triggers a closure of ATP-dependent potassium channels, K(ATP), in the plasma membrane or by KCl that depolarizes the cell membrane. Stimulation with glucose, tolbutamide or KCl induces a Ca2+ influx into the beta-cells via L-type Ca2+ channels. Accordingly, incubation of the cells with the L-type Ca2+ channel blocker nifedipine or the acetoxymethylester of the cytosolic Ca2+ chelator BAPTA prevented Egr-1 expression. Moreover, diacylgycerol-dependent protein kinase C isoenzymes and activation of extracellular signal-regulated protein kinase (ERK) are required for glucose-, tolbutamide- and KCl-induced Egr-1 expression. The signaling cascade was blocked by MAP kinase phosphatase-1 (MKP-1) overexpression that dephosphorylated ERK in the nucleus. Stimulation of beta-cells by glucose, tolbutamide and KCl induced the phosphorylation of the transcription factors Elk-1 and CREB. ChIP experiments revealed that phosphorylated Elk-1 and CREB bound under physiological conditions to the Egr-1 gene. Lentiviral-mediated expression of dominant-negative mutants of Elk-1 or CREB interfered with glucose-, tolbutamide- and KCl-induced upregulation of Egr-1 biosynthesis. Together, these data indicate that stimulus-induced transcription of the Egr-1 gene in beta-cells requires combinatorial regulation by Elk-1 and CREB following activation of ERK. The newly synthesized Egr-1 is biologically active and binds under physiological conditions to the genes encoding basic fibroblast growth factor, tumor necrosis factor alpha, transforming growth factor beta and PTEN.
authors.affiliation: Department of Medical Biochemistry and Molecular Biology, Building 44, University of Saarland Medical Center, D-66421 Homburg, Germany.
authors.forename: Sabine I
authors.initials: SI
authors.lastname: Mayer
authors.forename: Gerald
authors.initials: G
authors.lastname: Thiel
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism*; D054638:Dual Specificity Phosphatase 1 / Q000235:genetics / Q000378:metabolism; D051766:Early Growth Response Protein 1 / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D044127:Epigenesis, Genetic; D066246:ErbB Receptors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000235:genetics; D005947:Glucose / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000378:metabolism; D007340:Insulinoma; D051379:Mice; D051059:PTEN Phosphohydrolase / Q000235:genetics; D011189:Potassium Chloride / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D050801:Ternary Complex Factors / Q000378:metabolism; D014044:Tolbutamide / Q000378:metabolism; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000235:genetics; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics; D050807:ets-Domain Protein Elk-1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D051766:Early Growth Response Protein 1; D007004:Hypoglycemic Agents; D050801:Ternary Complex Factors; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha; D050807:ets-Domain Protein Elk-1; D016222:Fibroblast Growth Factor 2; D011189:Potassium Chloride; D014044:Tolbutamide; D066246:ErbB Receptors; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D054638:Dual Specificity Phosphatase 1; C517020:Dusp1 protein, mouse; D051059:PTEN Phosphohydrolase; D005947:Glucose; D002118:Calcium