Treatment with IFN-gamma prevents insulin-dependent PKB, p70S6k phosphorylation and protein synthesis in mouse C2C12 myogenic cells.
The purpose of the present study was to examine the potential effect of IFN-gamma (interferon-gamma) on the cellular content and phosphorylation of PKB (protein kinase B), p70S6k (p70 S6 kinase) and MAPK (mitogen-activated protein kinase), and on the ability of insulin to stimulate the glucose uptake and protein synthesis in mouse C2C12 myotubes. Insulin (100 nmol/l) stimulated glucose uptake in C2C12 myotubes by 203.4%. Glucose uptake in cells differentiated in the presence of IFN-gamma (10 ng/ml) was increased by 165.8% and was not further significantly modified by the addition of insulin (183.4% of control value). Insulin increased the rate of protein synthesis by 198.8%. The basal rate of protein synthesis was not affected by IFN-gamma; however, this cytokine abolished the insulin effect. Cellular levels of PKB, p70S6k, p42MAPK and p44MAPK were not modified by IFN-gamma. Insulin caused the phosphorylation of PKB and the activation of p70S6k, but not p42MAPK and p44MAPK. In cells differentiated in the presence of IFN-gamma, the insulin-mediated PKB phosphorylation was significantly diminished, whereas the phosphorylation of p70S6k was completely prevented. Pretreatment of C2C12 myogenic cells with IFN-gamma led to the marked increase in p42MAPK phosphorylation. Exposure of C2C12 myoblasts to IFN-gamma impaired MyoD and myogenin expression and decreased the fusion index on the fifth day of differentiation. In conclusion, (i) IFN-gamma present in the extracellular environment during C2C12 myoblast differentiation prevents the stimulatory action of insulin on protein synthesis; (ii) IFN-gamma-induced insulin resistance of protein synthesis in myogenic cells can be associated with the decreased phosphorylation of PKB and p70S6k, as well as with the augmented basal phosphorylation of p42MAPK; (iii) this cytokine effect can be partly explained by alterations in the differentiation process.
Grzelkowska-Kowalczyk
Katarzyna
K
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
Wieteska-Skrzeczyńska
Wioletta
W
D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D007328:Insulin / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D017570:MyoD Protein / Q000378:metabolism; D018008:Myogenin / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D015398:Signal Transduction
D007328:Insulin; D017570:MyoD Protein; D018008:Myogenin; D007371:Interferon-gamma; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D019950:Mitogen-Activated Protein Kinase 1