title: New emerging role of protein-tyrosine phosphatase 1B in the regulation of glycogen metabolism in basal and TNF-α-induced insulin-resistant conditions in an immortalised muscle cell line isolated from mice.
abstract: OBJECTIVE
  Protein-tyrosine phosphatase 1B (PTP1B) negatively regulates insulin action, promoting attenuation of the insulin signalling pathway. The production of this phosphatase is enhanced in insulin-resistant states, such as obesity and type 2 diabetes, where high levels of proinflammatory cytokines (TNF-α, IL-6) are found. In these metabolic conditions, insulin action on glycogen metabolism in skeletal muscle is greatly impaired. We addressed the role of PTP1B on glycogen metabolism in basal and insulin-resistant conditions promoted by TNF-α.
  
  
  METHODS
  We studied the effect of TNF-α in the presence and absence of insulin on glycogen content and synthesis, glycogen synthase (GS) and glycogen phosphorylase (GP) activities and on glycogen synthesis and degradation signalling pathways. For this purpose we used immortalised cell lines isolated from skeletal muscle from mice lacking PTP1B.
  
  
  RESULTS
  Absence of PTP1B caused activation of GS and GP with a net glycogenolytic effect, reflected in lower amounts of glycogen and activation of the glycogenolytic signalling pathway, with higher rates of phosphorylation of cyclic adenosine monophosphate-dependent kinase (PKA), phosphorylase kinase (PhK) and GP phosphorylation. Nevertheless, insulin action was strongly enhanced in Ptp1b (also known as Ptpn1)(-/-) cells in terms of glycogen content, synthesis, GS activation rates and GS Ser641 dephosphorylation. Treatment with TNF-α augmented the activity ratios of both GS and GP, and impaired insulin stimulation of glycogen synthesis in wild-type myocytes, whereas Ptp1b (-/-) myocytes restored this inhibitory effect. We report a glycogenolytic effect of TNF-α, as demonstrated by greater activation of the degradation signalling cascade PKA/PhK/GP. In our model, this effect is mediated by the activation of PKA.
  
  
  CONCLUSIONS
  We provide new data about the role of PTP1B in glycogen metabolism and confirm the beneficial effect that absence of the phosphatase confers against an insulin-resistant condition.
authors.affiliation: Department of Biochemistry and Molecular Biology II, Faculty of Pharmacy, Universidad Complutense de Madrid, 28040 Madrid, Spain. marialon@farm.ucm.es
authors.forename: M
authors.initials: M
authors.lastname: Alonso-Chamorro
authors.forename: I
authors.initials: I
authors.lastname: Nieto-Vazquez
authors.forename: M
authors.initials: M
authors.lastname: Montori-Grau
authors.forename: A M
authors.initials: AM
authors.lastname: Gomez-Foix
authors.forename: S
authors.initials: S
authors.lastname: Fernandez-Veledo
authors.forename: M
authors.initials: M
authors.lastname: Lorenzo
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D006003:Glycogen / Q000378:metabolism*; D024981:Glycogen Phosphorylase / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D047468:Immunoprecipitation; D007328:Insulin / Q000494:pharmacology; D051379:Mice; D008817:Mice, Mutant Strains; D010764:Phosphorylase Kinase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1 / Q000235:genetics / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D007328:Insulin; D014409:Tumor Necrosis Factor-alpha; D006003:Glycogen; D024981:Glycogen Phosphorylase; D006006:Glycogen Synthase; D010764:Phosphorylase Kinase; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1