Previous studies on skeletal muscle differentiation showed that myogenesis is regulated by extracellular signal-regulated kinases (ERK-1/-2) and p38 mitogen activated kinase (MAPK) pathways. Present study shows that c-Jun NH(2)-terminal protein kinase (JNK) activities were up regulated during skeletal muscle differentiation in rat skeletal muscle L6E9 cells, as determined by Western immunoblot of differentiating cells probed with anti-phospho-JNK antibody. Inhibition of JNK activities by JNK inhibitor II drastically inhibited differentiation as determined by decreased myosin, myogenin expression and creatine kinase activity. The inhibition of the differentiation was regulated by apoptosis as determined by the detection of poly(ADP-ribose) polymerase (PARP) cleavage, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) positive cells when JNK activities were inhibited. Apoptosis was accompanied by marked expression and activation of c-Jun and p53 transcription factors. Taken together, our results indicate that basal JNK activities are essential for regulating skeletal muscle differentiation, and inhibition of JNK activation affects myogenesis by apoptosis dependent on c-Jun and p53 transcription factors.
