Defective activation of atypical protein kinase C zeta and lambda by insulin and phosphatidylinositol-3,4,5-(PO4)(3) in skeletal muscle of rats following high-fat feeding and streptozotocin-induced diabetes

• Published in: Endocrinology (Philadelphia) 2003-03, Vol.144 (3), p.947-954
• Main Authors: Kanoh, Yoshinori, Sajan, Mini P, Bandyopadhyay, Gautam, Miura, Atsushi, Standaert, Mary L, Farese, Robert V
• Format: Article
• Language: English
• Subjects: 3-Phosphoinositide-Dependent Protein Kinases; Animals; Diabetes Mellitus, Experimental - enzymology; Dietary Fats - administration & dosage; Enzyme Activation - drug effects; Glucose - administration & dosage; Insulin - pharmacology; Isoenzymes; Muscle, Skeletal - enzymology; Phosphatidylinositol 3-Kinases - metabolism; Phosphatidylinositol Phosphates - pharmacology; Phosphorylation; Protein Kinase C - metabolism; Protein-Serine-Threonine Kinases - metabolism; Rats; Rats, Sprague-Dawley
• ISSN: 0013-7227
• DOI: 10.1210/en.2002-221017

Insulin-stimulated glucose transport in skeletal muscle is thought to be effected at least partly through atypical protein kinase C isoforms (aPKCs) operating downstream of phosphatidylinositol (PI) 3-kinase and 3-phosphoinositide-dependent protein kinase-1 (PDK-1). However, relatively little is known about the activation of aPKCs in physiological conditions or insulin-resistant states. Presently, we studied aPKC activation in vastus lateralis muscles of normal chow-fed and high-fat-fed rats and after streptozotocin (STZ)-induced diabetes. In normal chow-fed rats, dose-dependent increases in aPKC activity approached maximal levels after 15-30 min of stimulation by relatively high and lower, presumably more physiological, insulin concentrations, achieved by im insulin or ip glucose administration. Insulin-induced activation of aPKCs was impaired in both high-fat-fed and STZ-diabetic rats, but, surprisingly, IRS-1-dependent and IRS-2-dependent PI 3-kinase activation was not appreciably compromised. Most interestingly, direct in vitro activation of aPKCs by PI-3,4,5-(PO(4))(3), the lipid product of PI 3-kinase, was impaired in both high-fat-fed and STZ-diabetic rats. Defects in activation of aPKCs by insulin and PI-3,4,5-(PO(4))(3) could not be explained by diminished PDK-1-dependent phosphorylation of threonine-410 in the PKC-zeta activation loop, as this phosphorylation was increased even in the absence of insulin treatment in high-fat-fed rats. 1) muscle aPKCs are activated at relatively low, presumably physiological, as well as higher supraphysiological, insulin concentrations; 2) aPKC activation is defective in muscles of high-fat-fed and STZ-diabetic rats; and 3) defective aPKC activation in these states is at least partly due to impaired responsiveness to PI-3,4,5-(PO(4))(3), apparently at activation steps distal to PDK-1-dependent loop phosphorylation.