title: Overexpression of protein kinase C isoenzymes alpha, beta I, gamma, and epsilon in cells overexpressing the insulin receptor. Effects on receptor phosphorylation and signaling.
abstract: Chinese hamster ovary cells overexpressing the human insulin receptor were transfected with cDNAs encoding protein kinase C isoenzymes alpha, beta I, gamma, and epsilon as well as an inactive alpha. Overexpression of these protein kinase Cs did not affect expression of the insulin receptor or insulin-stimulated tyrosine phosphorylation of the receptor. However, in response to phorbol esters, cells overexpressing isoenzymes alpha, beta I, and gamma, but not epsilon or inactive alpha, exhibited 3-4-fold higher levels of insulin receptor phosphorylation. This increased phosphorylation occurred exclusively on serines and threonine. Tryptic peptide maps indicated that this phosphorylation was primarily on serines 1305/1306 and threonine 1348 as well as several other unidentified sites. This phorbol ester-stimulated phosphorylation did not inhibit activation of the insulin receptor kinase when the receptor was activated in situ but assayed in vitro. However, in cells overexpressing protein kinase C alpha, it did inhibit an in vivo monitor of the activation of the insulin receptor kinase, the insulin-stimulated increase in anti-phosphotyrosine-precipitable phosphatidylinositol 3-kinase activity. These results indicate that increased protein kinase C alpha activity can inhibit insulin-stimulated responses and support the hypothesis that excessive protein kinase C is involved in the insulin resistance observed in non-insulin-dependent diabetics.
authors.affiliation: Department of Pharmacology, Stanford University School of Medicine, California 94305.
authors.forename: J E
authors.initials: JE
authors.lastname: Chin
authors.forename: M
authors.initials: M
authors.lastname: Dickens
authors.forename: J M
authors.initials: JM
authors.lastname: Tavare
authors.forename: R A
authors.initials: RA
authors.lastname: Roth
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D006801:Humans; D007328:Insulin / Q000502:physiology; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D010449:Peptide Mapping; D010766:Phosphorylation; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D007328:Insulin; D007527:Isoenzymes; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D011493:Protein Kinase C