The role of the Akt/PKB signaling in insulin action

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DESCRIPTION (provided by applicant): Type II Diabetes Mellitus is one of the most common diseases in the Western world, with prevalence ranging from 10-50% in elderly populations. An integral component of Type II diabetes mellitus is insulin resistance, i.e. the inability of maximal concentrations of the hormone to stimulate appropriately muscle glucose transport, suppression of hepatic glucose output and other physiological responses. A plausible strategy leading to the development of novel insulin-sensitizing drugs begins with the systematic analysis of insulin signaling. After over 30 years of intensive research in the pursuit of relevant protein kinases, Akt/PKB has emerged as the only serine/threonine protein kinases definitively established as a mediator of insulin's regulation of important metabolic targets. The activity of Akt/PKB depends on the lipid products of phosphotidylinositol 3'- kinase, an enzyme known to be required for virtually all of the metabolic actions of insulin. The Akt/PKB kinases represent a family of three closely related proteins that have been implicated in the regulation of processes as diverse as apoptosis, cell growth, cell cycle progression, differentiation and angiogenesis as well as metabolism. Recent work has shown that mice deficient in Akt2/PKBbeta mimic several features of diabetes, including insulin resistance in liver, muscle and adipose tissue. Interestingly, Akt1/PKBalpha null mice are absolutely normal metabolically, but are about 20% reduced in size. The differences in phenotype between Akt1/PKBalpha and Akt2/beta knockout mice are due to both to isoform-speciflc patterns of expression as well as distinct signaling properties intrinsic to the proteins. The underlying rationale of these proposed studies is that by investigating the biochemical basis of the preferential ability of Akt2/PKBbeta to signal to glucose transport, significant progress will be made in understanding the fundamental mechanism of insulin action. Specificity will be approached using several related strategies: 1) the domains of Akt/PKB conferring isoform specific signaling will be mapped by the use of chimeric proteins; 2) the two isoforms will be analyzed for differences in intracellular localization; and 3) a search will be conducted for Akt2-specific substrates. It is anticipated that these studies will significantly extend the knowledge of physiological insulin-independent signaling and ultimately lead to the identification of potential targets for therapeutic intervention in diabetes mellitus.