title: Go-6976 reverses hyperglycemia-induced insulin resistance independently of cPKC inhibition in adipocytes.
abstract: Chronic hyperglycemia induces insulin resistance by mechanisms that are incompletely understood. One model of hyperglycemia-induced insulin resistance involves chronic preincubation of adipocytes in the presence of high glucose and low insulin concentrations. We have previously shown that the mTOR complex 1 (mTORC1) plays a partial role in the development of insulin resistance in this model. Here, we demonstrate that treatment with Go-6976, a widely used "specific" inhibitor of cPKCs, alleviates hyperglycemia-induced insulin resistance. However, the effects of mTOR inhibitor, rapamycin and Go-6976 were not additive and only rapamycin restored impaired insulin-stimulated AKT activation. Although, PKCα, (but not -β) was abundantly expressed in these adipocytes, our studies indicate cPKCs do not play a major role in causing insulin-resistance in this model. There was no evidence of changes in the expression or phosphorylation of PKCα, and PKCα knock-down did not prevent the reduction of insulin-stimulated glucose transport. This was also consistent with lack of IRS-1 phosphorylation on Ser-24 in hyperglycemia-induced insulin-resistant adipocytes. Treatment with Go-6976 did inhibit a component of the mTORC1 pathway, as evidenced by decreased phosphorylation of S6 ribosomal protein. Raptor knock-down enhanced the effect of insulin on glucose transport in insulin resistant adipocytes. Go-6976 had the same effect in control cells, but was ineffective in cells with Raptor knock-down. Taken together these findings suggest that Go-6976 exerts its effect in alleviating hyperglycemia-induced insulin-resistance independently of cPKC inhibition and may target components of the mTORC1 signaling pathway.
authors.affiliation: The Departments of Biochemistry and Molecular Biology and Medicine, Division Diabetes, Endocrinology and Medical Genetics, Medical University of South Carolina, Charleston, South Carolina, United States of America.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Robinson
authors.affiliation: The Department of Clinical Biochemistry, University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, United Kingdom.
authors.forename: Krisztina
authors.initials: K
authors.lastname: Hegyi
authors.affiliation: The Department of Medicine and the Stony Brook Cancer Center, Stony Brook University, Stony Brook, New York, United States of America.
authors.forename: Yusuf A
authors.initials: YA
authors.lastname: Hannun
authors.affiliation: The Departments of Biochemistry and Molecular Biology and Medicine, Division Diabetes, Endocrinology and Medical Genetics, Medical University of South Carolina, Charleston, South Carolina, United States of America.
authors.forename: Maria G
authors.initials: MG
authors.lastname: Buse
authors.affiliation: The Department of Clinical Biochemistry, University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, United Kingdom.
authors.forename: Jaswinder K
authors.initials: JK
authors.lastname: Sethi
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000201:enzymology; D000818:Animals; D002227:Carbazoles / Q000008:administration & dosage*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D006943:Hyperglycemia / Q000235:genetics* / Q000473:pathology; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance / Q000235:genetics*; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes / Q000235:genetics; D051571:Protein Kinase C-alpha / Q000096:biosynthesis; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000235:genetics
chemical_list: D002227:Carbazoles; D007328:Insulin; D046912:Multiprotein Complexes; C081021:Go 6976; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D051571:Protein Kinase C-alpha