Glucagon-like peptide-1 causes pancreatic duodenal homeobox-1 protein translocation from the cytoplasm to the nucleus of pancreatic beta-cells by a cyclic adenosine monophosphate/protein kinase A-dependent mechanism.
Glucagon-like peptide-1 (GLP-1) enhances insulin secretion and synthesis. It also regulates the insulin, glucokinase, and GLUT2 genes. It mediates increases in glucose-stimulated insulin secretion by activating adenylyl cyclase and elevating free cytosolic calcium levels in the beta-cell. In addition, GLP-1 has been shown, both in vitro and in vivo, to be involved in regulation of the transcription factor, pancreatic duodenal homeobox-1 protein (PDX-1), by increasing its total protein levels, its translocation to the nucleus and its binding and resultant increase in activity of the insulin gene promoter in beta-cells of the pancreas. Here we have investigated the role of protein kinase A (PKA) in these processes in RIN 1046-38 cells. Three separate inhibitors of PKA, and a cAMP antagonist, inhibited the effects of GLP-1 on PDX-1. Furthermore, forskolin, (which stimulates adenylyl cyclase and insulin secretion), and 8-Bromo-cAMP, (an analog of cAMP which also stimulates insulin secretion), mimicked the effects of GLP-1 on PDX-1. These effects were also prevented by PKA inhibitors. Glucose-mediated increases in nuclear translocation of PDX-1 were not prevented by PKA inhibitors. Our results suggest that regulation of PDX-1 by GLP-1 occurs through activation of adenylyl cyclase and the resultant increase in intracellular cAMP, in turn, activates PKA, which ultimately leads to increases in PDX-1 protein levels and translocation of the protein to the nuclei of beta-cells.
Wang
X
X
Diabetes Section, Gerontology Research Center, National Institute on Aging, NIH, Baltimore, Maryland 21224, USA.
Zhou
J
J
Doyle
M E
ME
Egan
J M
JM
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002467:Cell Nucleus / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism*; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D005947:Glucose / Q000494:pharmacology; D018398:Homeodomain Proteins; D007328:Insulin / Q000235:genetics / Q000378:metabolism; D000078790:Insulin Secretion; D007546:Isoquinolines / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011498:Protein Precursors / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D013449:Sulfonamides; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D018398:Homeodomain Proteins; D007328:Insulin; D007546:Isoquinolines; D010446:Peptide Fragments; D011498:Protein Precursors; D012333:RNA, Messenger; D013449:Sulfonamides; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D003513:Cycloheximide; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D005947:Glucose; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide