Fig. 1. TPA induces phosphorylation/activation of ERKs, JNKs and p38. The time course of ERK, JNK and p38 phosphorylations in RD cells, either untreated (C0, C2d and C5d) or treated with 10^-7 M TPA for different times (30 minutes to 5 days). Immunoblots of total lysate were performed using antibodies against phospho-active forms of MAPKs. Each blot was re-probed with antibodies that recognize total proteins. Densitometric analysis of bands, relative to both total and phosphorylated proteins, provided quantification (phospho-MAPK:total-MAPK) of TPA-induced ERK, JNK and p38 activation expressed as a fold increase over the control value arbitrarily set at 1. The data shown are representative of three independent experiments.