Requirement for Akt (Protein Kinase B) in Insulin-induced Activation of Glycogen Synthase and Phosphorylation of 4E-BP1 (PHAS-1)

Masafumi Takata,Wataru Ogawa,Tadahiro Kitamura,Yasuhisa Hino,Shoji Kuroda,Ko Kotani,Amira Klip,Anne-Claude Gingras,Nahum Sonenberg,Masato Kasuga

doi:10.1074/jbc.274.29.20611

Abstract

The roles of Akt (protein kinase B) and the atypical lambda isoform of protein kinase C (PKClambda), both of which act downstream of phosphoinositide 3-kinase, in the activation of glycogen synthase and phosphorylation of 4E-BP1 (PHAS-1) in response to insulin were investigated. A mutant Akt (Akt-AA) in which the phosphorylation sites targeted by growth factors are replaced by alanine was shown to inhibit insulin-induced activation of both Akt and glycogen synthase in L6 myotubes. Expression of a mutant Akt in which Lys179 in the kinase domain was replaced by aspartate also inhibited insulin-induced activation of glycogen synthase but had no effect on insulin activation of endogenous Akt. A kinase-defective mutant of PKClambda (lambdaDeltaNKD), which prevents insulin-induced activation of PKClambda, did not affect the activation of glycogen synthase by insulin. Insulin-induced phosphorylation of 4E-BP1 was inhibited by Akt-AA in Chinese hamster ovary cells. However, lambdaDeltaNKD had no effect on 4E-BP1 phosphorylation induced by insulin. These data suggest that Akt, but not PKClambda, is required for insulin activation of glycogen synthase and for insulin-induced phosphorylation of 4E-BP1.

Highlights

Insulin exerts a variety of effects on carbohydrate, lipid, and protein metabolism [1]
The activities of protein kinases belonging to the mitogen-activated protein (MAP) kinase superfamily, including those of extracellular signal-regulated kinase [17,18,19] and c-Jun NH2-terminal kinase [20] isozymes, are sensitive to blockers of PI 3-kinase in intact cells, suggesting that these enzymes participate in signaling downstream of PI 3-kinase
We have previously shown that a mutant Akt in which the sites of ligandinduced phosphorylation are replaced by alanine (Akt-AA) inhibits the activation of endogenous or transfected Akt by insulin, platelet-derived growth factor, or heat treatment in

Summary

Introduction

Insulin exerts a variety of effects on carbohydrate, lipid, and protein metabolism [1]. A mutant Akt (Akt-AA) in which the phosphorylation sites targeted by growth factors are replaced by alanine was shown to inhibit insulin-induced activation of both Akt and glycogen synthase in L6 myotubes.

Results

Conclusion