title: Distinct and opposing roles for the phosphatidylinositol 3-OH kinase catalytic subunits p110α and p110β in the regulation of insulin secretion from rodent and human beta cells.
abstract: OBJECTIVE
  Phosphatidylinositol 3-OH kinases (PI3Ks) regulate beta cell mass, gene transcription, and function, although the contribution of the specific isoforms is unknown. As reduced type 1A PI3K signalling is thought to contribute to impaired insulin secretion, we investigated the role of the type 1A PI3K catalytic subunits α and β (p110α and -β) in insulin granule recruitment and exocytosis in rodent and human islets.
  
  
  METHODS
  The p110α and p110β subunits were inhibited pharmacologically or by small hairpin (sh)RNA-mediated knockdown, and were directly infused or overexpressed in mouse and human islets, beta cells and INS-1 832/13 cells. Glucose-stimulated insulin secretion (GSIS), single-cell exocytosis, Ca(2+) signalling, plasma membrane granule localisation, and actin density were monitored.
  
  
  RESULTS
  Inhibition or knockdown of p110α increased GSIS. This was not due to altered Ca(2+) responses, depolymerisation of cortical actin or increased cortical granule density, but to enhanced Ca(2+)-dependent exocytosis. Intracellular infusion of recombinant PI3Kα (p110α/p85β) blocked exocytosis. Conversely, knockdown (but not pharmacological inhibition) of p110β blunted GSIS, reduced cortical granule density and impaired exocytosis. Exocytosis was rescued by direct intracellular infusion of recombinant PI3Kβ (p110β/p85β) even when p110β catalytic activity was inhibited. Conversely, both the wild-type p110β and a catalytically inactive mutant directly facilitated exocytosis.
  
  
  CONCLUSIONS
  Type 1A PI3K isoforms have distinct and opposing roles in the acute regulation of insulin secretion. While p110α acts as a negative regulator of beta cell exocytosis and insulin secretion, p110β is a positive regulator of insulin secretion through a mechanism separate from its catalytic activity.
authors.affiliation: Department of Pharmacology, University of Alberta, Edmonton, AB, Canada T6G 2E1.
authors.forename: J
authors.initials: J
authors.lastname: Kolic
authors.forename: A F
authors.initials: AF
authors.lastname: Spigelman
authors.forename: G
authors.initials: G
authors.lastname: Plummer
authors.forename: E
authors.initials: E
authors.lastname: Leung
authors.forename: C
authors.initials: C
authors.lastname: Hajmrle
authors.forename: T
authors.initials: T
authors.lastname: Kin
authors.forename: A M J
authors.initials: AM
authors.lastname: Shapiro
authors.forename: J E
authors.initials: JE
authors.lastname: Manning Fox
authors.forename: P E
authors.initials: PE
authors.lastname: MacDonald
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D020134:Catalytic Domain; D002462:Cell Membrane / Q000378:metabolism; D058543:Class Ia Phosphatidylinositol 3-Kinase / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008875:Middle Aged; D020033:Protein Isoforms / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D004791:Enzyme Inhibitors; D007328:Insulin; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D058543:Class Ia Phosphatidylinositol 3-Kinase