A, time course of MAPK activation by PEITC in HeLa cells. Cells were treated with 15 μM PEITC and harvested at the indicated times. Phosphorylation of JNK1/2, ERK1/2, and p38 was analyzed by Western Blotting with phospho-JNK, phospho-ERK, and phospho-p38 specific polyclonal antibodies. Total JNK, ERK, and p38 protein levels were also determined by Western Blot analysis using antibodies to the respective kinases. B, MAPKs activation is not involved in the PEITC-induced apoptosis in HeLa cells. Cells were pretreated with the MAPKs inhibitors (SP600125, U0126 and SB203580 for JNK, ERK and p38, respectively) for 1 h before the addition of 15 μM PEITC. After 24 h, the treated cells were harvested and assayed for caspase-3 activity with a colorimetric assay kit (top) and PARP cleavage assessed by Western Blot analysis using an anti-PARP monoclonal antibody (bottom).