Acute inhibition of PI3K-PDK1-Akt pathway potentiates insulin secretion through upregulation of newcomer granule fusions in pancreatic β-cells

PLoS One. 2012;7(10):e47381. doi: 10.1371/journal.pone.0047381. Epub 2012 Oct 15.

Abstract

In glucose-induced insulin secretion from pancreatic β-cells, a population of insulin granules fuses with the plasma membrane without the typical docking process (newcomer granule fusions), however, its mechanism is unclear. In this study, we investigated the PI3K signaling pathways involved in the upregulation of newcomer granule fusions. Acute treatment with the class IA-selective PI3K inhibitors, PIK-75 and PI-103, enhanced the glucose-induced insulin secretion. Total internal reflection fluorescent microscopy revealed that the PI3K inhibitors increased the fusion events from newcomer granules. We developed a new system for transfection into pancreatic islets and demonstrated the usefulness of this system in order for evaluating the effect of transfected genes on the glucose-induced secretion in primary cultured pancreatic islets. Using this transfection system together with a series of constitutive active mutants, we showed that the PI3K-3-phosphoinositide dependent kinase-1 (PDK1)-Akt pathway mediated the potentiation of insulin secretion. The Akt inhibitor also enhanced the glucose-induced insulin secretion in parallel with the upregulation of newcomer granule fusions, probably via increased motility of intracellular insulin granules. These data suggest that the PI3K-PDK1-Akt pathway plays a significant role in newcomer granule fusions, probably through an alteration of the dynamics of the intracellular insulin granules.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Furans / pharmacology
  • Glucose / pharmacology
  • Hydrazones / pharmacology
  • Insulin / metabolism*
  • Insulin Secretion
  • Insulin-Secreting Cells / metabolism*
  • Mice
  • Phosphatidylinositol 3-Kinases / genetics
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoinositide-3 Kinase Inhibitors
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins c-akt / genetics
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Pyridines / pharmacology
  • Pyrimidines / pharmacology
  • Pyruvate Dehydrogenase Acetyl-Transferring Kinase
  • Secretory Vesicles / drug effects
  • Signal Transduction / drug effects
  • Sulfonamides / pharmacology
  • Up-Regulation / drug effects

Substances

  • Furans
  • Hydrazones
  • Insulin
  • PI103
  • PIK 75
  • Pdk1 protein, mouse
  • Phosphoinositide-3 Kinase Inhibitors
  • Pyridines
  • Pyrimidines
  • Pyruvate Dehydrogenase Acetyl-Transferring Kinase
  • Sulfonamides
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Glucose

Grant support

This research was supported by grants from the Grants-in-Aid for Scientific Research (KAKENHI), Japan Society for Promotion of Science B-20390260, 23113724, 20570189), Research Foundation for Opto-Science and Technology, Novo Nordisk Pharma, and Kyorin University School of Medicine Collaboration Project. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.