Inhibition of mammalian target of rapamycin (mTOR) signalling in C2C12 myoblasts prevents myogenic differentiation without affecting the hyperphosphorylation of 4E-BP1.
Current accepted models suggest that hypophosphorylated 4E-binding protein (4E-BP1) binds to initiation factor 4E (eIF4E) to inhibit cap-dependent translation, a process readily reversed by its phosphorylation following activation of mammalian target of rapamycin (mTORC1) signalling. Myogenic differentiation in the C2C12 myoblast model system reflects a concerted and controlled activation of transcription and translation following the exit of cells from the cell cycle. Here we show that myogenic differentiation is associated with increased rates of translation, the up-regulation of both 4E-BP1 mRNA and protein levels and enhanced levels of eIF4E/4E-BP1 complex. Paradoxically, treatment of C2C12 myoblasts with an inhibitor of mTOR signalling (RAD001) which inhibits translation, promotes the hyperphosphorylation of 4E-BP1 on novel sites and prevents the increase in 4E-BP1 levels. In contrast, eIF4E appears to be under translational control with a significant delay between induction of mRNA and subsequent protein expression.
Willett
Mark
M
Department of Biochemistry, School of Life Sciences, University of Sussex, Falmer, Brighton BN19QG, UK.
Cowan
Joanne L
JL
Vlasak
Markete
M
Coldwell
Mark J
MJ
Morley
Simon J
SJ
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002460:Cell Line; D039642:Eukaryotic Initiation Factors; D000068338:Everolimus; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes; D024510:Muscle Development; D032446:Myoblasts / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011506:Proteins; D015398:Signal Transduction; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C499527:Eif4ebp1 protein, mouse; D039642:Eukaryotic Initiation Factors; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D011506:Proteins; D014157:Transcription Factors; D000068338:Everolimus; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus