Insulin and insulin-like growth factor-I responsiveness and signalling mechanisms in C2C12 satellite cells: effect of differentiation and fusion

• Published in: Biochimica et biophysica acta Vol. 1355; no. 2; pp. 167 - 176
• Main Authors: Palmer, R M, Thompson, M G, Knott, R M, Campbell, G P, Thom, A, Morrison, K S
• Format: Journal Article
• Language: English
• Published: Netherlands 04.02.1997
• Subjects: Animals; Cell Differentiation; Cell Fusion; Cell Line; Cyclooxygenase Inhibitors - pharmacology; Glucose - metabolism; Insulin - pharmacology; Insulin-Like Growth Factor I - pharmacology; Mice; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; Phospholipase D - metabolism; Phospholipases A - antagonists & inhibitors; Phospholipases A2; Protein Biosynthesis; Protein Kinase C - antagonists & inhibitors; Protein-Serine-Threonine Kinases - metabolism; Receptor, IGF Type 1 - analysis; Receptor, Insulin - analysis; Ribosomal Protein S6 Kinases; RNA, Messenger - analysis; Signal Transduction; Type C Phospholipases - metabolism
• ISSN: 0006-3002; 0167-4889
• DOI: 10.1016/S0167-4889(96)00127-9

In proliferating C2C12 myoblasts, serum and physiological concentrations of insulin and IGF-I stimulated protein synthesis and RNA accretion. After fusion, the multinucleated myotubes remained responsive to serum but not to insulin or IGF-I, even though both insulin and type-I IGF receptor mRNAs increased in abundance. Protein synthetic responses to insulin and IGF-I in myoblasts were not inhibited by dexamethasone, ibuprofen or Ro-31-8220, thus phospholipase A2, cyclo-oxygenase and protein kinase C did not appear to be involved in the signalling mechanisms. Neither apparently were polyphosphoinositide-specific phospholipase C or phospholipase D since neither hormone increased inositol phosphate, phosphatidic acid, choline or phosphatidylbutanol production. Only the phosphatidylinositol-3-kinase inhibitor, wortmannin, and the 70 kDa S6-kinase inhibitor, rapamycin, wholly or partially blocked the effects of insulin and IGF-I on protein synthesis. 2-deoxyglucose uptake remained responsive to insulin and IGF-I after fusion and was also inhibited by wortmannin. The results suggest that the loss of responsiveness after fusion is not due to loss of receptors, but to the uncoupling of a post-receptor pathway, occurring after the divergence of the glucose transport and protein synthesis signalling systems, and that, if wortmannin acts at a single site, this is prior to that point of divergence.