NFAT regulates insulin gene promoter activity in response to synergistic pathways induced by glucose and glucagon-like peptide-1.
Currently there is intense interest to define the mechanism of action of glucagon-like peptide-1 (GLP-1) in regulating beta-cell function, including insulin gene transcription. In this study, GLP-1 (100 nmol/l), in the presence of glucose (11 mmol/l), induced a similar71-fold increase in insulin gene promoter activity in INS-1 pancreatic beta-cells, an effect that was an order of magnitude larger than with either stimulant alone. The response to GLP-1 was mimicked by forskolin and largely inhibited by the protein kinase A (PKA) inhibitors, H89 and myristoylated PKI(14--22) amide, indicating partial mediation via a cAMP/PKA pathway. Significantly, the actions of both GLP-1 and forskolin were abolished by the selective Ca(2+)/calmodulin-dependent phosphatase 2B (calcineurin) inhibitor, FK506, as well as by the chelation of intracellular Ca(2+) by BAPTA (bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate). Glucose and GLP-1 also synergistically activated NFAT (nuclear factor of activated T-cells)-mediated transcription from a minimal promoter construct containing tandem NFAT consensus sequences. Furthermore, two-point base pair mutations in any of the three identified NFAT sites within the rat insulin I promoter resulted in a significant reduction in the combined effect of glucose and GLP-1. These data suggest that the synergistic action of glucose and GLP-1 to promote insulin gene transcription is mediated through NFAT via PKA- and calcineurin-dependent pathways in pancreatic beta-cells.
Lawrence
Michael C
MC
Department of Molecular Biology and Immunology, University of North Texas Health Science Center at Fort Worth, Texas 76107-2699, USA.
Bhatt
Harshika S
HS
Easom
Richard A
RA
D000818:Animals; D019703:Calcineurin / Q000502:physiology; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000235:genetics*; D007515:Islets of Langerhans / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D010446:Peptide Fragments / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011498:Protein Precursors / Q000494:pharmacology*; D051381:Rats; D013449:Sulfonamides; D016559:Tacrolimus / Q000494:pharmacology; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects
D065095:Calcineurin Inhibitors; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D007328:Insulin; D007546:Isoquinolines; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D010446:Peptide Fragments; D011498:Protein Precursors; D013449:Sulfonamides; D014157:Transcription Factors; D005576:Colforsin; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D019703:Calcineurin; D005947:Glucose; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D002118:Calcium; D016559:Tacrolimus