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.
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.


CONCLUSIONS
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.
Kanoh
Yoshinori
Y
Research Service, James A. Haley Veterans Administration Medical Center and Department of Internal Medicine, University of South Florida College of Medicine, Tampa, Florida 33612, USA.
Sajan
Mini P
MP
Bandyopadhyay
Gautam
G
Miura
Atsushi
A
Standaert
Mary L
ML
Farese
Robert V
RV
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology*; D004041:Dietary Fats / Q000008:administration & dosage; D004789:Enzyme Activation / Q000187:drug effects; D005947:Glucose / Q000008:administration & dosage; D007328:Insulin / Q000494:pharmacology*; D007527:Isoenzymes; D018482:Muscle, Skeletal / Q000201:enzymology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D000099293:Protein Kinase C-lambda; D000099221:Protein Kinase C zeta
D064413:3-Phosphoinositide-Dependent Protein Kinases; D004041:Dietary Fats; D005947:Glucose; D007328:Insulin; D007527:Isoenzymes; D019869:Phosphatidylinositol 3-Kinases; D018129:Phosphatidylinositol Phosphates; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D000099293:Protein Kinase C-lambda; D000099221:Protein Kinase C zeta; C060974:phosphatidylinositol 3,4,5-triphosphate