JNK was activated by higher, but not lower, therapeutic concentrations of As₂O₃, in transfected Raji cells with or without GSTP1 expression. RV7 and RG20 cells were untreated or treated with 1 or 2 μM As₂O₃ for 24 hours (A) or 50 to 80 μM As₂O₃ for 2 hours (B). P-JNK, JNK, P-p38, and p38 were detected by Western blot analysis.