title: Treatment with TNF-alpha and IFN-gamma alters the activation of SER/THR protein kinases and the metabolic response to IGF-I in mouse c2c12 myogenic cells.
abstract: The aim of this study was to compare the effects of TNF-alpha, IL-1beta and IFN-gamma on the activation of protein kinase B (PKB), p70(S6k), mitogen-activated protein kinase (MAPK) and p90( rsk ), and on IGF-I-stimulated glucose uptake and protein synthesis in mouse C2C12 myotubes. 100 nmol/l IGF-I stimulated glucose uptake in C2C12 myotubes by 198.1% and 10 ng/ml TNF-alpha abolished this effect. Glucose uptake in cells differentiated in the presence of 10 ng/ml IFN-gamma increased by 167.2% but did not undergo significant further modification upon the addition of IGF-I. IGF-I increased the rate of protein synthesis by 249.8%. Neither TNF-alpha nor IFN-gamma influenced basal protein synthesis, but both cytokines prevented the IGF-I effect. 10 ng/ml IL-1beta did not modify either the basal or IGF-I-dependent glucose uptake and protein synthesis. With the exception of TNF-alpha causing an 18% decrease in the level of PKB protein, the cellular levels of PKB, p70(S6k), p42(MAPK), p44(MAPK) and p90( rsk ) were not affected by the cytokines. IGF-I caused the phosphorylation of PKB (an approximate 8-fold increase above the basal value after 40 min of IGF-I treatment), p42(MAPK) (a 2.81-fold increase after 50 min), and the activation of p70(S6k) and p90( rsk ), manifesting as gel mobility retardation. In cells differentiated in the presence of TNF-alpha or IFN-gamma, this IGF-I-mediated PKB and p70(S6k) phosphorylation was significantly diminished, and the increase in p42(MAPK) and p90( rsk ) phosphorylation was prevented. The basal p42(MAPK) phosphorylation in C2C12 cells treated with IFN-gamma was high and comparable with the activation of this kinase by IGF-I. Pretreatment of myogenic cells with IL-1beta did not modify the IGF-I-stimulated phosphorylation of PKB, p70(S6k), p42(MAPK) and p90( rsk ).
  
  
  CONCLUSIONS
  i) TNF-alpha and IFN-gamma, but not IL-1beta, if present in the extracellular environment during C2C12 myoblast differentiation, prevent the stimulatory action of IGF-I on protein synthesis. ii) TNF-alpha- and IFN-gamma-induced IGF-I resistance of protein synthesis could be associated with the decreased phosphorylation of PKB and p70(S6k). iii) The activation of glucose uptake in C2C12 myogenic cells treated with IFN-gamma is PKB independent. iv) The similar effects of TNF-alpha and IFN-gamma on the signalling and action of IGF-I on protein synthesis in myogenic cells could suggest the involvement of both of these cytokines in protein loss in skeletal muscle.
authors.affiliation: Department of Physiological Sciences, Faculty of Veterinary Medicine, Warsaw University of Life Sciences (SGGW), Nowoursynowska 159, 02-776, Warsaw, Poland. k_grzel_kow@poczta.fm
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Grzelkowska-Kowalczyk
authors.forename: Wioletta
authors.initials: W
authors.lastname: Wieteska-Skrzeczyńska
mesh_terms: D000818:Animals; D002460:Cell Line; D005947:Glucose / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology*; D053583:Interleukin-1beta / Q000494:pharmacology; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000201:enzymology* / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D053583:Interleukin-1beta; D014409:Tumor Necrosis Factor-alpha; D007334:Insulin-Like Growth Factor I; D007371:Interferon-gamma; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D005947:Glucose
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