Figure 3.

p38 and NF-κB activities are required for C2C12 myoblast differentiation and myotube formation. (A) Inhibition of p38 or NF-κB activity abrogates myoblast differentiation. C2C12 cells were cultured in DM for 24 h, in the absence or presence of the p38 inhibitor SB203580 or the NF-κB-inhibitor PDTC. Myogenin and α-actin expression was analyzed by Northern blotting by using the corresponding cDNA probes. Also, GAPDH mRNA expression was analyzed as internal loading control. (B) Muscle-specific promoter activity is abrogated by inhibition of p38 or NF-κB activity. C2C12 myoblasts were transiently transfected with the muscle-specific promoter-reporter plasmid MCK-Luc, together with an expression plasmid for the superepressor IκBα or with an empty vector and cultured in DM for 36, in the presence or absence of SB203580 or PDTC, respectively. Luciferase activities are expressed relative to the activity of MCK-Luc in DM, which was given a value of 100. Error bars represent the SE of the mean value. (C) Myoblast fusion is inhibited by p38 or NF-κB inhibitors. C2C12 cells were cultured for 3 d in the absence or presence of SB203580 or PDTC, and myoblast fusion was analyzed by examining the presence of plurinucleated myotubes.