Palmitate Induced Insulin Resistance by PKCtheta-Dependent Activation of mTOR/S6K Pathway in C2C12 Myotubes

Abstract

The underlying mechanism of palmitate-induced insulin resistance in skeletal muscle cells is obscure. In this study, we showed that palmitate inhibited the insulin signaling in C2C12 myotubes, accompanied with the enhanced phosphorylation of protein kinase C-theta (PKCΘ). The inhibitory effects of palmitate on the insulin signaling were diminished in PKCΘ- and mTOR (mammalian target of rapamycin)-deficient C2C12 myotubes, and C2C12 myotubes pre-treated with rapamycin. In addition, the phosphorylation of mTOR and p70 ribosomal S6 kinase (S6K) enhanced by palmitate was attenuated in PKCΘ-deficient C2C12 myotubes and in C2C12 myotubes treated with PKCΘ pseudosubstrate. Taken together, our results suggested that palmitate-induced insulin resistance in C2C12 myotubes is mediated by PKCΘ/mTOR/S6K pathway.

Key words

PKCΘ - mammalian target of rapamycin (mTOR) - p70 ribosomal S6 kinase (S6K) - insulin resistance - palmitic acid

References

• 1 Bell KS, Schmitz-Peiffer C, Lim-Fraser M. et al . Acute reversal of lipid-induced muscle insulin resistance is associated with rapid alteration in PKC-theta localization.  Am J Physiol Endocrinol Metab. 2000;  279 E1196-E1201
• 2 Coll T, Eyre E, Rodríguez-Calvo R. et al . Oleate reverses palmitate-induced insulin resistance and inflammation in skeletal muscle cells.  J Biol Chem. 2008;  283 11107-11116
• 3 Freeley M, Volkov Y, Kelleher D. et al . Stimulus-induced phosphorylation of PKC theta at the C-terminal hydrophobic-motif in human T lymphocytes.  Biochem Biophys Res Commun. 2005;  334 619-630
• 4 Gao Z, Wang Z, Zhang X. et al . Inactivation of PKCtheta leads to increased susceptibility to obesity and dietary insulin resistance in mice.  Am J Physiol Endocrinol Metab. 2007;  292 E84-E91
• 5 Gao Z, Zhang X, Zuberi A. et al . Inhibition of insulin sensitivity by free fatty acids requires activation of multiple serine kinases in 3T3-L1 adipocytes.  Mol Endocrinol. 2004;  18 2024-2034
• 6 Griffin ME, Marcucci MJ, Cline GW. et al . Free fatty acid-induced insulin resistance is associated with activation of protein kinase C theta and alterations in the insulin signaling cascade.  Diabetes. 1999;  48 1270-1274
• 7 Haasch D, Berg C, Clampit JE. et al . PKCtheta is a key player in the development of insulin resistance.  Biochem Biophys Res Commun. 2006;  343 361-368
• 8 Hirosumi J, Tuncman G, Chang L. et al . A central role for JNK in obesity and insulin resistance.  Nature. 2002;  420 333-336
• 9 Jové M, Planavila A, Sánchez RM. et al . Palmitate induces tumor necrosis factor-alpha expression in C2C12 skeletal muscle cells by a mechanism involving protein kinase C and nuclear factor-kappaB activation.  Endocrinology. 2006;  147 552-561
• 10 Kim JK, Fillmore JJ, Sunshine MJ. et al . PKC-Θ knockout mice are protected from fat-induced insulin resistance.  J Clin Invest. 2004;  114 823-827
• 11 Lallena MJ, Diaz-Meco MT, Bren G. et al . Activation of IkappaB kinase beta by protein kinase C isoforms.  Mol Cell Biol. 1999;  19 2180-2188
• 12 Mordier S, Iynedjian PB. Activation of mammalian target of rapamycin complex 1 and insulin resistance induced by palmitate in hepatocytes.  Biochem Biophys Res Commun. 2007;  362 206-211
• 13 Ono H, Pocai A, Wang Y. et al . Activation of hypothalamic S6 kinase mediates diet-induced hepatic insulin resistance in rats.  J Clin Invest. 2008;  118 2959-2968
• 14 Ragheb R, Shanab GM, Medhat AM. et al . Free fatty acid-induced muscle insulin resistance and glucose uptake dysfunction: evidence for PKC activation and oxidative stress-activated signaling pathways.  Biochem Biophys Res Commun. 2009;  389 211-216
• 15 Rivas DA, Yaspelkis 3rd BB, Hawley JA. et al . Lipid-induced mTOR activation in rat skeletal muscle reversed by exercise and 5'-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside.  J Endocrinol. 2009;  202 441-451
• 16 Schmitz-Peiffer C, Laybutt DR, Burchfield JG. et al . Inhibition of PKCepsilon improves glucose-stimulated insulin secretion and reduces insulin clearance.  Cell Metab. 2007;  6 320-328
• 17 Serra C, Federici M, Buongiorno A. et al . Transgenic mice with dominant negative PKC-theta in skeletal muscle: a new model of insulin resistance and obesity.  J Cell Physiol. 2003;  196 89-97
• 18 Tzatsos A, Kandror KV. Nutrients suppress phosphatidylinositol 3-kinase/Akt signaling via raptor-dependent mTOR-mediated insulin receptor substrate 1 phosphorylation.  Mol Cell Biol. 2006;  26 63-76
• 19 Um SH, Frigerio F, Watanabe M. et al . Absence of S6K1 protects against age- and diet-induced obesity while enhancing insulin sensitivity.  Nature. 2004;  431 200-205
• 20 Um SH, D'Alessio D, Thomas G. Nutrient overload, insulin resistance, and ribosomal protein S6 kinase 1, S6K1.  Cell Metab. 2006;  3 393-402
• 21 Vary TC, Goodman S, Kilpatrick LE. et al . Nutrient regulation of PKCepsilon is mediated by leucine, not insulin, in skeletal muscle.  Am J Physiol Endocrinol Metab. 2005;  289 E684-E694
• 22 Wang C, Liu M, Riojas RA. et al . Protein kinase C theta (PKCtheta)-dependent phosphorylation of PDK1 at Ser504 and Ser532 contributes to palmitate-induced insulin resistance.  J Biol Chem. 2009;  284 2038-2044
• 23 Wang L, Rolfe M, Proud CG. Ca(2+)-independent protein kinase C activity is required for alpha1-adrenergic-receptor-mediated regulation of ribosomal protein S6 kinases in adult cardiomyocytes.  Biochem J. 2003;  373 603-611

1 Equal contribution to paper

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