Fig. 2. Specificity of the p38 and JNK inhibitors. (A) Cells were incubated with Fas-mAb for 1 hour in the absence (lane 2) or presence of PD169316 (lane 3), SP600125 (lane 4) or both (lane 5). Fas-induced increase in p38 activity was inhibited by PD169316 but not SP600125. (B) Phosphorylation of JUN by JNK was inhibited by SP600125 but was unaffected by PD169316. Inhibition of both kinases was observed only in cells treated with both inhibitors.