Activation of Elk-1, an Ets transcription factor, by glucose and EGF treatment of insulinoma cells.
Elk-1, a member of the ternary complex factor family of Ets domain proteins that bind serum response elements, is activated by phosphorylation in a cell-specific manner in response to growth factors and other agents. The purpose of the current study was to determine whether Elk-1 activation contributes to glucose-/depolarization-induced Ca(2+)-dependent induction of immediate early response genes in pancreatic islet beta-cells. The results of experiments in insulinoma (MIN6) cells demonstrated that Elk-1-binding sites (Ets elements) in the Egr-1 gene promoter contribute to transcriptional activation of the gene. Treatment with either epidermal growth factor (EGF), a known inducer of beta-cell hyperplasia, glucose, or KCl-induced depolarization resulted in Ser(383) phosphorylation and transcriptional activation of Elk-1 (4 +/- 0.3-, P = 0.003, 2.3 +/- 0.19-, P = 0.002, and 2.2 +/- 0.1- fold, P = 0.001 respectively). The depolarization response was inhibited by the Ca(2+) channel blocker verapamil and by the MEK inhibitor PD98059 (53 +/- 6 and 55 +/- 0.5%, respectively). EGF-induced activation of Elk-1 was also inhibited by PD98059 (60 +/- 5%). A dominant negative Ras produced partial inhibition (42%) of the depolarization-induced Elk-1 transcriptional activation. Transfection with a constitutively active Ca(2+)/calmodulin kinase IV plasmid also resulted in Elk-1 transcriptional activation. Experiments with p38, phosphatidylinositol 3-kinase, and protein kinase A inhibitors indicated that these pathways are not involved. We conclude that Elk-1 activation contributes to glucose-/depolarization-induced Ca(2+)-dependent induction of immediate early growth response genes in pancreatic islet beta-cells. Furthermore, the results demonstrated a convergence of nutrient- and growth factor-mediated signaling pathways on Elk-1 activation through induction of Ras/mitogen-activated protein kinase ERK-1 and -2. The role of these pathways in the glucose-induced proliferation of islet beta-cells can now be assessed.
Bernal-Mizrachi
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E
Division of Endocrinology, Diabetes, and Metabolism, Washington University School Of Medicine, St. Louis, Missouri 63110, USA. ebernal@im.wustl.edu
Wen
W
W
Srinivasan
S
S
Klenk
A
A
Cohen
D
D
Permutt
M A
MA
D015153:Blotting, Western; D004268:DNA-Binding Proteins; D004586:Electrophoresis; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D011905:Genes, ras / Q000235:genetics; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007340:Insulinoma / Q000378:metabolism* / Q000473:pathology; D008156:Luciferases / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D010957:Plasmids; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics*; D014162:Transfection; D050807:ets-Domain Protein Elk-1
D004268:DNA-Binding Proteins; C494112:ELK1 protein, human; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D004815:Epidermal Growth Factor; D008156:Luciferases; D019950:Mitogen-Activated Protein Kinase 1; D020928:Mitogen-Activated Protein Kinases; D005947:Glucose