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.
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.
Shen
Wei-Hua
WH
Herman B Wells Center for Pediatric Research, Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana, USA.
Boyle
David W
DW
Wisniowski
Paul
P
Bade
Aashia
A
Liechty
Edward A
EA
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
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