Effects of p38 inhibition on p21WAF1, myogenin and MyoD expression. (A and B) RD cells were left untreated, treated with TPA or U0126 or pre-treated with 5 μM SB 203580 for 1 hour and then left untreated or treated with TPA or U0126 for the times indicated. Immunoblots of total lysates were performed using specific antibodies recognising p21WAF1 and α-tubulin (A) and pRb (B). Densitometric analysis of bands provided quantification expressed as the ratio of amount of p21WAF1 versus α-tubulin amount. (C) Northern blot analysis of p21WAF1, myogenin and MyoD expression in RD cells left untreated or treated with U0126 in the absence or in the presence of SB 203580 for the times indicated. The GAPDH mRNA levels are shown. The data shown are representative of three independent experiments for A and B and two for C.