title: Modulation of insulin effects on phosphorylation of protein kinase B and glycogen synthesis by tumor necrosis factor-alpha in HepG2 cells.
abstract: The effects of tumor necrosis factor-alpha (TNF-alpha) on insulin-induced phosphorylation of protein kinase B-alpha (PKB-alpha) and downstream enzyme glycogen synthase kinase-3 beta (GSK-3 beta) was examined in HepG2 liver cells. The exogenous treatment of HepG2 cells with TNF-alpha for 1 h caused phosphorylation of Ser473 and Thr308 residues of PKB-alpha. The maximal phosphorylation (approximately 4-fold) was obtained with 1 ng/ml TNF-alpha and no further increase was observed with higher concentrations of this cytokine. The cells pretreated with TNF-alpha for 1 h followed by incubation with insulin (10 nM) showed near additive effect on phosphorylation of PKB-alpha and downstream enzyme GSK-3 beta. The long-term (4, 8, 24 h) exogenous treatment of cells with optimal (1 ng/ml) concentration of TNF-alpha also caused phosphorylation of PKB-alpha, albeit to a lesser degree. However, long-term pretreatments of cells with TNF-alpha reduced insulin-stimulated phosphorylation of PKB-alpha and GSK-3 beta. Short- and long-term preincubation of HepG2 cells with TNF-alpha also resulted in parallel changes in glycogen synthesis in the presence of insulin. In fact, long-term preincubation with TNF-alpha completely abolished the insulin-induced glycogen synthesis. These results suggest that short-term exposure to TNF-alpha augments insulin effects whereas long-term exposure causes insulin resistance in HepG2 cells.
authors.affiliation: Department of Biochemistry, College of Medicine, University of Saskatchewan, 107 Wiggins Road, Saskatoon, Saskatchewan, Canada, S7N 5E5.
authors.forename: Dhananjay
authors.initials: D
authors.lastname: Gupta
authors.forename: Ramji L
authors.initials: RL
authors.lastname: Khandelwal
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D006003:Glycogen / Q000096:biosynthesis*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013912:Threonine / Q000378:metabolism; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D007328:Insulin; D011518:Proto-Oncogene Proteins; D014409:Tumor Necrosis Factor-alpha; D013912:Threonine; D012694:Serine; D006003:Glycogen; C494918:AKT1 protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3