title: Insulin and IGF-I stimulate the formation of the eukaryotic initiation factor 4F complex and protein synthesis in C2C12 myotubes independent of availability of external amino acids.
abstract: The objective of this study was to investigate the effect of insulin and IGF-I on protein synthesis and translation initiation in C2C12 myotubes in nutrient-deprived Dulbecco's phosphate buffered saline (DPBS). The results showed that insulin and IGF-I increased protein synthesis by 62% and 35% respectively in DPBS, and the effect was not affected by rapamycin, but was blocked by LY294002. Insulin and IGF-I stimulated eukaryotic initiation factor 4E (eIF4E) binding protein (4EBP1) phosphorylation in a dose-dependent manner, and the stimulation was independent of availability of external amino acids. Both LY294002 and rapamycin blocked the insulin and IGF-I-induced increases in 4EBP1 phosphorylation. The results also showed that insulin and IGF-I were able to stimulate PKB/Akt phosphorylation, glycogen synthase kinase (GSK) 3beta phosphorylation and mTOR phosphorylation in DPBS. Insulin and IGF-I increased the amount of eIF4G associated with eIF4E in nutrient-deprived C2C12 myotubes. The amount of 4EBP1 associated with eIF4E was decreased after insulin or IGF-I stimulation. We conclude that in C2C12 myotubes, insulin and IGF-I may regulate protein synthesis and translation initiation independent of external amino acid supply via the phosphatidylinositol-3 kinase-PKB/Akt-mTOR pathway.
authors.affiliation: Herman B Wells Center for Pediatric Research, Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Wei-Hua
authors.initials: WH
authors.lastname: Shen
authors.forename: David W
authors.initials: DW
authors.lastname: Boyle
authors.forename: Paul
authors.initials: P
authors.lastname: Wisniowski
authors.forename: Aashia
authors.initials: A
authors.lastname: Bade
authors.forename: Edward A
authors.initials: EA
authors.lastname: Liechty
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D039562:Eukaryotic Initiation Factor-4F / Q000378:metabolism*; D039642:Eukaryotic Initiation Factors; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D013268:Stimulation, Chemical; D058570:TOR Serine-Threonine Kinases
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002867:Chromones; D039562:Eukaryotic Initiation Factor-4F; D039642:Eukaryotic Initiation Factors; D038362:Glycogen Synthase Kinase 3; D007004:Hypoglycemic Agents; D007166:Immunosuppressive Agents; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C499527:Eif4ebp1 protein, mouse; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546843:mTOR protein, mouse