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

Endocrinology. 2001 May;142(5):1820-7. doi: 10.1210/endo.142.5.8128.

Abstract

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.

MeSH terms

  • Animals
  • Biological Transport / drug effects
  • Cell Nucleus / metabolism*
  • Cyclic AMP / physiology*
  • Cyclic AMP-Dependent Protein Kinases / physiology*
  • Cycloheximide / pharmacology
  • Cytoplasm / metabolism*
  • Glucagon / pharmacology*
  • Glucagon-Like Peptide 1
  • Glucose / pharmacology
  • Homeodomain Proteins*
  • Insulin / genetics
  • Insulin / metabolism
  • Insulin Secretion
  • Isoquinolines / pharmacology
  • Peptide Fragments / pharmacology*
  • Promoter Regions, Genetic
  • Protein Precursors / pharmacology*
  • RNA, Messenger / analysis
  • Rats
  • Sulfonamides*
  • Trans-Activators / genetics
  • Trans-Activators / metabolism*
  • Tumor Cells, Cultured

Substances

  • Homeodomain Proteins
  • Insulin
  • Isoquinolines
  • Peptide Fragments
  • Protein Precursors
  • RNA, Messenger
  • Sulfonamides
  • Trans-Activators
  • pancreatic and duodenal homeobox 1 protein
  • Glucagon-Like Peptide 1
  • Glucagon
  • Cycloheximide
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases
  • Glucose
  • N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide