Fatty acid and phorbol ester-mediated interference of mitogenic signaling via novel protein kinase C isoforms in pancreatic beta-cells (INS-1).
It is possible that activation of protein kinase C (PKC) isoforms by free fatty acids (FFA) plays a role in the failure of pancreatic beta-cell mass expansion to compensate for peripheral insulin resistance in the pathogenesis of type-2 diabetes. The effect of lipid moieties on activation of conventional (PKC-alpha and -beta1), novel (PKC-delta) and atypical (PKC-zeta) PKC isoforms was evaluated in an in vitro assay, using biotinylated neurogranin as a substrate. Oleoyl-Coenzyme A (CoA) and palmitoyl-CoA, but not unesterified FFA, significantly increased the activity of all PKC isoforms (P< or =0.05), particularly that for PKC-delta. It was found that FFA (0.4 mM oleate/complexed to 0.5% bovine serum albumin) inhibited IGF-I-induced activation of protein kinase B (PKB) in the pancreatic beta-cell line (INS-1), but this was alleviated in the presence of the general PKC inhibitor (Gö6850; 1 microM). To further investigate whether conventional or novel PKC isoforms adversely affect beta-cell proliferation, the effect of phorbol ester (phorbol 12-myristate 13-acetate; PMA)-mediated activation of these PKC isoforms on glucose/IGF-I-induced INS-1 cell mitogenesis, and insulin receptor substrate (IRS)-mediated signal transduction was investigated. PMA-mediated activation of PKC (100 nM; 4 h) reduced glucose/IGF-I mediated beta-cell mitogenesis (>50%; P< or =0.05), which was reversible by the general PKC inhibitor Gö6850 (1 microM), indicating an effect of PKC and not due to a non-specific PMA toxicity. PMA inhibited IGF-I-induced activation of PKB, correlating with inhibition of IGF-I-induced association of IRS-2 with the p85 regulatory subunit of phosphatidylinositol-3 kinase. However, in contrast, PMA activated the mitogen-activated protein kinases, Erk1/2. Titration inhibition analysis using PKC isoform inhibitors indicated that these PMA-induced effects were via novel PKC isoforms. Thus, FFA/PMA-induced activation of novel PKC isoforms can inhibit glucose/IGF-I-mediated beta-cell mitogenesis, in part by decreasing PKB activation, despite an upregulation of Erk1/2. Thus, activation of novel PKC isoforms by long-chain acyl-CoA may well contribute to decreasing beta-cell mass in the pathogenesis of type-2 diabetes, similar to their inhibition of insulin signal transduction which causes insulin resistance.
Wrede
C E
CE
Pacific Northwest Research Institute and Department of Pharmacology, University of Washington, Seattle, WA 98122, USA.
Dickson
L M
LM
Lingohr
M K
MK
Briaud
I
I
Rhodes
C J
CJ
D000098:Acetophenones / Q000494:pharmacology; D001578:Benzopyrans / Q000494:pharmacology; D002460:Cell Line; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology*; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D007515:Islets of Langerhans / Q000201:enzymology / Q000378:metabolism*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008301:Maleimides / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008934:Mitogens / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D000098:Acetophenones; D001578:Benzopyrans; D004791:Enzyme Inhibitors; D005230:Fatty Acids, Nonesterified; D007211:Indoles; D007527:Isoenzymes; D008301:Maleimides; D008934:Mitogens; D011518:Proto-Oncogene Proteins; D007334:Insulin-Like Growth Factor I; C085746:rottlerin; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate