title: Oleate-induced decrease in hepatocyte insulin binding is mediated by PKC-delta.
abstract: We have previously shown that free fatty acids (FFA) impair hepatic insulin extraction in vivo and thus generate hyperinsulinemia, a suspected risk factor for atherosclerosis and cancer. Hepatic insulin extraction is a receptor-mediated event, which is initiated by hepatocyte insulin binding. In the present study, we investigated the effect of FFA on insulin binding in freshly isolated rat hepatocytes maintained at 10 mM glucose. Hepatocyte insulin binding decreased after 1 h exposure to oleate in a concentration-dependent manner reaching a maximum (35-40%) at 125 microM. Inhibition of FFA oxidation by >90% with the carnitine palmitoyltransferase I (CPT-I) inhibitor methylpalmoxirate (MP, 30 microM) did not prevent the effect of oleate. However, when hepatocytes were treated with the PKC inhibitor bisindolylmaleimide (BIM, 1 microM) the effect of oleate was abolished. Subcellular fractionation and immunoblotting of specific PKC isoforms revealed that oleate-induced hepatic PKC-delta membrane translocation, but did not translocate-epsilon, -theta, -alpha, -betaI and -betaII. These results indicate that PKC-delta activation mediated the FFA-induced decrease in hepatocyte insulin binding under our conditions, and thus provides a mechanistic basis for FFA-induced hyperinsulinemia.
authors.affiliation: Department of Physiology, University of Toronto, Toronto, Ont., Canada M5S 1A8.
authors.forename: Shu
authors.initials: S
authors.lastname: Chen
authors.forename: Tony K T
authors.initials: TK
authors.lastname: Lam
authors.forename: Edward
authors.initials: E
authors.lastname: Park
authors.forename: Elena
authors.initials: E
authors.lastname: Burdett
authors.forename: Penny Y T
authors.initials: PY
authors.lastname: Wang
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Wiesenthal
authors.forename: Loretta
authors.initials: L
authors.lastname: Lam
authors.forename: Vaja
authors.initials: V
authors.lastname: Tchipashvili
authors.forename: I George
authors.initials: IG
authors.lastname: Fantus
authors.forename: Adria
authors.initials: A
authors.lastname: Giacca
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004852:Epoxy Compounds / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D019301:Oleic Acid / Q000494:pharmacology*; D010084:Oxidation-Reduction / Q000187:drug effects; D011422:Propionates / Q000494:pharmacology; D051745:Protein Kinase C-delta / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D004852:Epoxy Compounds; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D007527:Isoenzymes; D011422:Propionates; D019301:Oleic Acid; D051745:Protein Kinase C-delta; D013755:Tetradecanoylphorbol Acetate; C017522:methyl 2-tetradecylglycidate