Mutation of PDK1 PH domain inhibits PKB/Akt leading to small size and insulin-resistance

MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland; College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland; Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland; Department of Physiology, University of Tübingen, Tübingen, Germany; Division of Pathology and Neurosciences, University of Dundee, Ninewells Hospital, Dundee; Department of Endocrinology and Metabolic Diseases, Leiden University Medical Center, Leiden, Netherlands; Division of Cell Biology and Immunology, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland

^* To whom correspondence should be addressed. Email: d.r.alessi{at}dundee.ac.uk.

	Abstract

PDK1 activates a group of kinases including PKB/Akt, S6K and SGK that mediate many of the effects of insulin as well as other agonists. PDK1 interacts with phosphoinositides through a PH-domain. To study the role of this interaction we generated knock-in mice expressing a mutant of PDK1 incapable of binding phosphoinositides. The knock-in mice are significantly small, insulin-resistant and hyperinsulinemic. Activation of PKB is markedly reduced in knock-in mice as a result of lower phosphorylation of PKB at Thr308, the residue phosphorylated by PDKThis results in the inhibition of downstream mTOR complex-1 and S6K1 signalling pathways. In contrast, activation of SGK1 or RSK, or stimulation of S6K1 induced by feeding, is unaffected by the PDK1-PH domain mutation. These observations establish the importance of the PDK1-phosphoinositide interaction in enabling PKB to be efficiently activated in an animal model. Our findings reveal how reduced activation of PKB isoforms impinges on downstream signalling pathways, causing diminution of size as well as insulin-resistance.