Involvement of ROS and ASK1 in denbinobin-induced JNK activation in A549 cells. Cells were pretreated with 1 mM NAC or 100 μM GSH (A) or transiently transfected with pcDNA or ASK1DN for 6 h (B) before incubation with 20 μM denbinobin for 30 min. Cells were then harvested and subjected to immunoblotting for JNK phosphorylation as described in "Materials and methods". Equal loading in each lane is shown by the similar intensities of JNK. Compiled results are shown in the lower panel. Each column represents the mean ± S.E.M. of at least three independent experiments. * p < 0.05, compared to the denbinobin group.