title: PI3 kinases p110α and PI3K-C2β negatively regulate cAMP via PDE3/8 to control insulin secretion in mouse and human islets.
abstract: OBJECTIVE
  Phosphatidylinositol-3-OH kinase (PI3K) signalling in the endocrine pancreas contributes to glycaemic control. However, the mechanism by which PI3K modulates insulin secretion from the pancreatic beta cell is poorly understood. Thus, our objective was two-fold; to determine the signalling pathway by which acute PI3K inhibition enhances glucose-stimulated insulin secretion (GSIS) and to examine the role of this pathway in islets from type-2 diabetic (T2D) donors.
  
  
  METHODS
  Isolated islets from mice and non-diabetic or T2D human donors, or INS 832/13 cells, were treated with inhibitors of PI3K and/or phosphodiesterases (PDEs). The expression of PI3K-C2β was knocked down using siRNA. We measured insulin release, single-cell exocytosis, intracellular Ca(2+) responses ([Ca(2+)]i) and Ca(2+) channel currents, intracellular cAMP concentrations ([cAMP]i), and activation of cAMP-dependent protein kinase A (PKA) and protein kinase B (PKB/AKT).
  
  
  RESULTS
  The non-specific PI3K inhibitor wortmannin amplifies GSIS, raises [cAMP]i and activates PKA, but is without effect in T2D islets. Direct inhibition of specific PDE isoforms demonstrates a role for PDE3 (in humans and mice) and PDE8 (in mice) downstream of PI3K, and restores glucose-responsiveness of T2D islets. We implicate a role for the Class II PI3K catalytic isoform PI3K-C2β in this effect by limiting beta cell exocytosis.
  
  
  CONCLUSIONS
  PI3K limits GSIS via PDE3 in human islets. While inhibition of p110α or PIK-C2β signalling per se, may promote nutrient-stimulated insulin release, we now suggest that this signalling pathway is perturbed in islets from T2D donors.
authors.affiliation: Department of Pharmacology, and the Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, T6G 2E1, Canada. Electronic address: jkolic@ualberta.ca.
authors.forename: Jelena
authors.initials: J
authors.lastname: Kolic
authors.affiliation: Department of Pharmacology, and the Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, T6G 2E1, Canada.
authors.forename: Jocelyn E
authors.initials: JE
authors.lastname: Manning Fox
authors.affiliation: Department of Medicine, State University of New York, Upstate Medical University, Syracuse, NY 13210, USA.
authors.forename: Oleg G
authors.initials: OG
authors.lastname: Chepurny
authors.affiliation: Department of Pharmacology, and the Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, T6G 2E1, Canada.
authors.forename: Aliya F
authors.initials: AF
authors.lastname: Spigelman
authors.affiliation: Department of Pharmacology, and the Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, T6G 2E1, Canada.
authors.forename: Mourad
authors.initials: M
authors.lastname: Ferdaoussi
authors.affiliation: BIOLOG Life Science Institute, 28199 Bremen, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Schwede
authors.affiliation: Department of Medicine, State University of New York, Upstate Medical University, Syracuse, NY 13210, USA; Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, NY 13210, USA.
authors.forename: George G
authors.initials: GG
authors.lastname: Holz
authors.affiliation: Department of Pharmacology, and the Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, T6G 2E1, Canada.
authors.forename: Patrick E
authors.initials: PE
authors.lastname: MacDonald
keywords: Beta cells; Insulin secretion; PDE; PI3K; T2D; cAMP