Fig. 3.

IL-1β induces JNK and ERK1/2 phosphorylation. To determine the time course in which IL-1β activates two of the classical MAPK pathways in muscle progenitors, we treated C₂C₁₂ myoblasts with IL-1β (1 ng/ml) for 0, 5, 10, 15, 30, or 60 min. Phosphorylation of ERK1/2 and JNK was determined by probing membranes with monoclonal antibodies against phospho-ERK1/2 and polyclonal antibodies against phospho-JNK. Membranes were then stripped and reprobed with an anti-α-tubulin-specific antibody to ensure that equal amounts of protein for each sample were loaded into the SDS-PAGE gels and subsequently transferred to polyvinylidene difluoride (PVDF) membranes. Densitometric summaries were calculated as ratios of phosphorylated ERK1/2 and JNK to α-tubulin. A: densitometric summary of 7 independent experiments demonstrated that IL-1β induced an increase in ERK1/2 phosphorylation at 10 min and that this increase was sustained through 15 min. B: similarly, a densitometric summary of 4 independent experiments indicated that phosphorylation of JNK also required a 10-min induction period in muscle progenitors, but this signal diminished less rapidly than that for P-ERK1/2. *P < 0.05; **P < 0.01.