Oleate-induced decrease in hepatocyte insulin binding is mediated by PKC-delta.
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.
Chen
Shu
S
Department of Physiology, University of Toronto, Toronto, Ont., Canada M5S 1A8.
Lam
Tony K T
TK
Park
Edward
E
Burdett
Elena
E
Wang
Penny Y T
PY
Wiesenthal
Stephanie R
SR
Lam
Loretta
L
Tchipashvili
Vaja
V
Fantus
I George
IG
Giacca
Adria
A
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
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