Raf-induced effects on the differentiation and apoptosis of skeletal myoblasts are determined by the level of Raf signaling: abrogation of apoptosis by Raf is downstream of caspase 3 activation.
We examined the effect of a constitutively active Raf protein (Raf-CAAX) on the differentiation and the coincident apoptosis of skeletal myoblasts. We found that a low level of Raf signaling leads to accelerated differentiation when compared to parental myoblasts, while a higher level of Raf signaling induces a transformed morphology and abrogates both differentiation and the coincident apoptosis. Raf signaling abrogates apoptosis without blocking the activation of caspase 3 and the subsequent cleavage of caspase 3 substrates. Eliminating the signal from Raf through MEK does not restore the ability to differentiate or to undergo apoptosis in the myoblasts with a high level of Raf signal, nor does it abrogate the accelerated differentiation observed in myoblasts with lower levels of Raf signal. Constitutive signaling through MEK is required, however, to maintain a transformed morphology. These results indicate that the effect of Raf on the differentiation and apoptosis of skeletal myoblasts is dictated by the level of Raf signaling, and that Raf signaling sufficient to abrogate the apoptosis coincident with differentiation does so downstream of caspase 3 signaling.
DeChant
Anne K
AK
Department of Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, Ohio, OH 44115, USA.
Dee
Keith
K
Weyman
Crystal M
CM
D020816:Amino Acid Motifs; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D048728:MAP Kinase Kinase Kinase 1; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism; D009132:Muscles / Q000196:embryology* / Q000473:pathology; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D018631:ras Proteins / Q000378:metabolism
D004791:Enzyme Inhibitors; D005419:Flavonoids; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D018631:ras Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one