Activation of serum response factor in the depolarization induction of Egr-1 transcription in pancreatic islet β-cells

E. Bernal-Mizrachi, B. Wice, H. Inoue, M. A. Permutt

Research output: Contribution to journalArticlepeer-review

59 Scopus citations


The results of the current studies define the major elements whereby glucose metabolism in islet β-cells leads to transcriptional activation of an early response gene in insulinoma cell lines and in rat islets. Glucose stimulation (2-20 mM) resulted in a 4-fold increase in Egr-1 mRNA at 30 min, as did the depolarizing agents KCl and tolbutamide. This response was inhibited by diazoxide and EGTA, indicating that β-cell depolarization and Ca2+ influx, respectively, are essential. Pharmacological inhibition of the Egr-1 induction by H89 (48%) and calmidazolium (35%), but not by mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1 and 2 or phosphatidylinositol 3-kinase inhibitors, implied that protein kinase A and Ca2+/calmodulin pathways are involved. Deletion mapping of the Egr-1 promoter revealed that the proximal -198 base pairs containing two serum response elements (SREs) and one cAMP-response element retained the depolarization response. Depolarization resulted in phosphorylation of cAMP-response element-binding protein, yet partial inhibition by a dominant negative cAMP-response element-binding protein, along with a robust response of a cAMP-response element-mutated Egr-1 promoter suggested the presence of a second Ca2+-responsive element. Depolarization activation of 5XSRE-LUC and serum response factor (SRF)-GAL4 constructs, along with activation of SRF-GAL4 by co-transfection with constitutively active calmodulin kinase IV and protein kinase A, and binding of Ser103-phosphorylated SRF in nuclear extracts, indicated that the SRE·SRF complexes contribute to the Ca2+-mediated transcriptional regulation of Egr-1. The results of the current experiments demonstrate for the first time SRE-dependent transcription and the role of SRF, a transcription factor known to be a major component of growth responses, in glucose-mediated transcriptional regulation in insulinoma cells.

Original languageEnglish (US)
Pages (from-to)25681-25689
Number of pages9
JournalJournal of Biological Chemistry
Issue number33
StatePublished - Aug 18 2000
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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