Insulin antagonizes ischemia-induced Thr 172 phosphorylation of AMP-activated protein kinase α-subunits in heart via hierarchical phosphorylation of Ser 485/491

Abstract

Previous studies showed that insulin antagonizes AMP-activated protein kinase activation by ischemia and that protein kinase B might be implicated. Here we investigated whether the direct phosphorylation of AMP-activated protein kinase by protein kinase B might participate in this effect. Protein kinase B phosphorylated recombinant bacterially expressed AMP-activated protein kinase heterotrimers at Ser 485 of the α1-subunits. In perfused rat hearts, phosphorylation of the α1/α2 AMP-activated protein kinase subunits on Ser 485/Ser 491 was increased by insulin and insulin pretreatment decreased the phosphorylation of the α-subunits at Thr 172 in a subsequent ischemic episode. It is proposed that the effect of insulin to antagonize AMP-activated protein kinase activation involves a hierarchical mechanism whereby Ser 485/Ser 491 phosphorylation by protein kinase B reduces subsequent phosphorylation of Thr 172 by LKB1 and the resulting activation of AMP-activated protein kinase. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.