MEK5 and ERK5 are mediators of the pro-myogenic actions of IGF-2.
During the differentiation of muscle satellite cells, committed myoblasts respond to specific signalling cues by exiting the cell cycle, migrating, aligning, expressing muscle-specific genes and finally fusing to form multinucleated myotubes. The predominant foetal growth factor, IGF-2, initiates important signals in myogenesis. The aim of this study was to investigate whether ERK5 and its upstream MKK activator, MEK5, were important in the pro-myogenic actions of IGF-2. ERK5 protein levels, specific phosphorylation and kinase activity increased in differentiating C2 myoblasts. ERK5-GFP translocated from the cytoplasm to the nucleus after activation by upstream MEK5, whereas phospho-acceptor site mutated (dominant-negative) ERK5AEF-GFP remained cytoplasmic. Exogenous IGF-2 increased MHC levels, myogenic E box promoter-reporter activity, ERK5 phosphorylation and kinase activity, and rapidly induced nuclear localisation of ERK5. Transfection with antisense Igf2 decreased markers of myogenesis, and reduced ERK5 phosphorylation, kinase and transactivation activity. These negative effects of antisense Igf2 were rescued by constitutively active MEK5, whereas transfection of myoblasts with dominant-negative MEK5 blocked the pro-myogenic action of IGF-2. Our findings suggest that the MEK5-ERK5 pathway is a novel key mediator of IGF-2 action in myoblast differentiation.
Carter
Emma J
EJ
Molecular Signalling, The Babraham Institute, Babraham Research Campus, Cambridge, UK.
Cosgrove
Ruth A
RA
Gonzalez
Ivelisse
I
Eisemann
Joan H
JH
Lovett
Fiona A
FA
Cobb
Laura J
LJ
Pell
Jennifer M
JM
D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000378:metabolism*; D048671:MAP Kinase Kinase 5 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D048054:Mitogen-Activated Protein Kinase 7 / Q000235:genetics / Q000378:metabolism*; D024510:Muscle Development; D032446:Myoblasts / Q000166:cytology / Q000201:enzymology; D010766:Phosphorylation; D021381:Protein Transport; D051381:Rats; D015398:Signal Transduction; D015533:Transcriptional Activation
D007335:Insulin-Like Growth Factor II; D048054:Mitogen-Activated Protein Kinase 7; D048671:MAP Kinase Kinase 5