Protein kinase C-zeta as a downstream effector of phosphatidylinositol 3-kinase during insulin stimulation in rat adipocytes. Potential role in glucose transport.
Insulin provoked rapid increases in enzyme activity of immunoprecipitable protein kinase C-zeta (PKC-zeta) in rat adipocytes. Concomitantly, insulin provoked increases in 32P labeling of PKC-zeta both in intact adipocytes and during in vitro assay of immunoprecipitated PKC-zeta; the latter probably reflected autophosphorylation, as it was inhibited by the PKC-zeta pseudosubstrate. Insulin-induced activation of immunoprecipitable PKC-zeta was inhibited by LY294002 and wortmannin; this suggested dependence upon phosphatidylinositol (PI) 3-kinase. Accordingly, activation of PI 3-kinase by a pYXXM-containing peptide in vitro resulted in a wortmannin-inhibitable increase in immunoprecipitable PKC-zeta enzyme activity. Also, PI-3,4-(PO4)2, PI-3,4,5-(PO4)3, and PI-4,5-(PO4)2 directly stimulated enzyme activity and autophosphoralytion in control PKC-zeta immunoprecipitates to levels observed in insulin-treated PKC-zeta immunoprecipitates. In studies of glucose transport, inhibition of immunoprecipitated PKC-zeta enzyme activity in vitro by both the PKC-zeta pseudosubstrate and RO 31-8220 correlated well with inhibition of insulin-stimulated glucose transport in intact adipocytes. Also, in adipocytes transiently expressing hemagglutinin antigen-tagged GLUT4, co-transfection of wild-type or constitutive PKC-zeta stimulated hemagglutinin antigen-GLUT4 translocation, whereas dominant-negative PKC-zeta partially inhibited it. Our findings suggest that insulin activates PKC-zeta through PI 3-kinase, and PKC-zeta may act as a downstream effector of PI 3-kinase and contribute to the activation of GLUT4 translocation.
Standaert
M L
ML
J. A. Haley Veterans' Hospital Research Service and Departments of Internal Medicine and Biochemistry/Molecular Biology, University of South Florida College of Medicine, Tampa, Florida 33612, USA.
Galloway
L
L
Karnam
P
P
Bandyopadhyay
G
G
Moscat
J
J
Farese
R V
RV
D017667:Adipocytes / Q000502:physiology*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002867:Chromones / Q000494:pharmacology; D003847:Deoxyglucose / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D007211:Indoles / Q000494:pharmacology; D007328:Insulin / Q000502:physiology*; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D013997:Time Factors; D000077191:Wortmannin; D000099221:Protein Kinase C zeta
D000730:Androstadienes; D002867:Chromones; D003847:Deoxyglucose; D004791:Enzyme Inhibitors; D005947:Glucose; D007211:Indoles; D007328:Insulin; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D000077191:Wortmannin; D000099221:Protein Kinase C zeta; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C064758:Ro 31-8220