Ca2+ signaling and gene transcription in glucose-stimulated insulinoma cells.
Glucose stimulation induces expression of the transcription factors Egr-1 and c-Jun as well as phosphorylation of CREB and c-Jun in insulinoma cells. The activator protein-1 (AP-1) binding sites within the c-Jun promoter, the serum response elements (SREs) within the Egr-1 promoter, and cyclic AMP response elements (CREs) function as glucose responsive element. Glucose-induced transcriptional regulation was attenuated by inhibition of L-type Ca(2+) channels, or chelating cytoplasmic Ca(2+). It has been proposed that a rise in nuclear Ca(2+) is required for CREB-mediated transcription of CRE-regulated genes, while elevated cytoplasmic Ca(2+) levels trigger an upregulation of SRE-containing genes. Here, we show that a rise in cytoplasmic Ca(2+) is required for AP-1, CRE, and SRE mediated transcription in glucose-stimulated insulinoma cells. Buffering Ca(2+) in the nucleus or the endoplasmic reticulum had no inhibitory effect upon transcription. However, overexpression of the mitochondrial protein Fis-1 or inhibition of the GTPase Drp-1 impaired glucose-stimulated gene transcription in insulinoma cells, suggesting that the mitochondria play an important role in regulating Ca(2+) mediated gene transcription. The extracellular signal-regulated protein kinase functions as an essential link connecting glucose stimulation, the rise in cytoplasmic Ca(2+), and enhanced transcription in insulinoma cells.
Department of Medical Biochemistry and Molecular Biology, University of Saarland Medical Center, Homburg, Germany.
Isabelle
I
Müller
Peter
P
Lipp
Gerald
G
Thiel
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D050882:CREB-Binding Protein / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D045744:Cell Line, Tumor; D064550:Death-Associated Protein Kinases; D051766:Early Growth Response Protein 1 / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D007340:Insulinoma / Q000378:metabolism / Q000473:pathology; D048031:JNK Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051381:Rats; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*; D015854:Up-Regulation
D051017:Apoptosis Regulatory Proteins; D020746:Calcium Channels, L-Type; D051766:Early Growth Response Protein 1; C486110:Egr1 protein, rat; C503403:Fis1 protein, rat; D024101:Mitochondrial Proteins; D018808:Transcription Factor AP-1; D050882:CREB-Binding Protein; D064550:Death-Associated Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D005947:Glucose; D002118:Calcium