Cyclin-dependent Kinase-5 Is a Key Molecule in Tumor Necrosis Factor-α-induced Insulin Resistance

Atsushi Nohara,Shuichi Okada,Kihachi Ohshima,Jeffrey E Pessin,Masatomo Mori

doi:10.1074/jbc.m111.231431

Abstract

The mechanism of TNF-α-induced insulin resistance has remained unresolved with evidence for down-regulation of insulin effector targets effects or blockade of proximal as well as distal insulin signaling events depending upon the dose, time, and cell type examined. To address this issue we examined the acute actions of TNF-α in differentiated 3T3L1 adipocytes. Acute (5-15 min) treatment with 20 ng/ml (~0.8 nm) TNF-α had no significant effect on IRS1-associated phosphatidylinositol 3-kinase. In contrast, TNF-α increased insulin-stimulated cyclin-dependent kinase-5 (CDK5) phosphorylation on tyrosine residue 15 through an Erk-dependent pathway and up-regulated the expression of the CDK5 regulator protein p35. In parallel, TNF-α stimulation also resulted in the phosphorylation and GTP loading of the Rho family GTP-binding protein, TC10α. TNF-α enhanced the depolymerization of cortical F-actin and inhibited insulin-stimulated glucose transporter-4 (GLUT4) translocation. Treatment with the MEK inhibitor, PD98059, blocked the TNF-α-induced increase in CDK5 phosphorylation and the depolymerization of cortical F-actin. Conversely, siRNA-mediated knockdown of CDK5 or treatment with the MEK inhibitor restored the impaired insulin-stimulated GLUT4 translocation induced by TNF-α. Furthermore, siRNA-mediated knockdown of p44/42 Erk also rescued the TNF-α inhibition of insulin-stimulated GLUT4 translocation. Together, these data demonstrate that TNF-α-mediated insulin resistance of glucose uptake can occur through a MEK/Erk-dependent activation of CDK5.

Highlights

Adipose tissue is composed of adipocytes embedded in a loose connective tissue meshwork containing adipocyte precursors, fibroblasts, immune cells, and various other cell types
In this study we demonstrate that TNF-␣ can acutely regulate CDK5-dependent phosphorylation of TC10␣ and thereby induce insulin resistance independent of IRS1-dependent signaling
Effect of TNF-␣ on IRS-1, Insulin Receptor Phosphorylation, and PI 3-Kinase Activity—It was previously reported that treatment of differentiated 3T3-L1 adipocytes with 20 ng/ml TNF-␣ for up to 6 h prevents secretion of other intrinsic adipokines such that any effects on insulin signaling can be directly attributable to the actions of TNF-␣ [20]

Summary

Introduction

Adipose tissue is composed of adipocytes embedded in a loose connective tissue meshwork containing adipocyte precursors, fibroblasts, immune cells, and various other cell types. Because of the dramatic rise in obesity and its metabolic sequelae during the past decades, adipose tissue gained tremendous scientific interest It is regarded as an active endocrine organ that, in addition to regulating fat mass and nutrient homeostasis, releases a large number of bioactive mediators (adipokines) modulating homeostasis, blood pressure, lipid and glucose metabolism, inflammation, and atherosclerosis. There are two major insulin signal pathways that are thought to regulate insulin-mediated GLUT42 translocation; one that is PI 3-kinase dependent and another that is PI 3-kinase-independent [6]. PDGF signaling that occurs independent of IRS1 was unable to rescue TNF-␣induced insulin resistance in either 3T3L1 adipocytes or L6 myotubes [17] Based upon these previous studies, we speculated the presence of an alternative pathway mediating TNF-␣induced insulin resistance. In this study we demonstrate that TNF-␣ can acutely regulate CDK5-dependent phosphorylation of TC10␣ and thereby induce insulin resistance independent of IRS1-dependent signaling

Methods

Results

Conclusion