title: PKC alpha is activated but not required during glucose-induced insulin secretion from rat pancreatic islets.
abstract: The role of protein kinase C (PKC) in glucose-stimulated insulin secretion (GSIS) is controversial. Using recombinant adenoviruses for overexpression of PKC alpha and PKC delta, in both wild-type (WT) and kinase-dead (KD) forms, we here demonstrate that activation of these two PKCs is neither necessary nor sufficient for GSIS from batch-incubated, rat pancreatic islets. In contrast, responses to the pharmacologic activator 12-O-tetradecanoylphorbol-13-acetate (TPA) were reciprocally modulated by overexpression of the PKC alpha WT or PKC alpha KD but not the corresponding PKC delta adenoviruses. The kinetics of the secretory response to glucose (monitored by perifusion) were not altered in either cultured islets overexpressing PKC alpha KD or freshly isolated islets stimulated in the presence of the conventional PKC (cPKC) inhibitor Go6976. However, the latter did inhibit the secretory response to TPA. Using phosphorylation state-specific antisera for consensus PKC phosphorylation sites, we also showed that (compared with TPA) glucose causes only a modest and transient functional activation of PKC (maximal at 2-5 min). However, glucose did promote a prolonged (15 min) phosphorylation of PKC substrates in the presence of the phosphatase inhibitor okadaic acid. Overall, the results demonstrate that glucose does stimulate PKC alpha in pancreatic islets but that this makes little overall contribution to GSIS.
authors.affiliation: Garvan Institute of Medical Research, St. Vincents Hospital, and Department of Medicine, University of New South Wales, Sydney, Australia.
authors.forename: Lee
authors.initials: L
authors.lastname: Carpenter
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Mitchell
authors.forename: Zheng Z
authors.initials: ZZ
authors.lastname: Xu
authors.forename: Philip
authors.initials: P
authors.lastname: Poronnik
authors.forename: Gerald W
authors.initials: GW
authors.lastname: Both
authors.forename: Trevor J
authors.initials: TJ
authors.lastname: Biden
mesh_terms: D000256:Adenoviridae / Q000201:enzymology / Q000235:genetics; D000818:Animals; D004789:Enzyme Activation; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D023421:Models, Animal; D019319:Okadaic Acid / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
chemical_list: D007328:Insulin; D011994:Recombinant Proteins; D019319:Okadaic Acid; C497260:Prkcd protein, rat; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate