Moreover, we noted that pretreatment of PP2A inhibitor, okadaic acid, can rescue penfluridol-induced deactivation of ERK and JNK, and activation of caspase-3 in both HL-60 and MV4–11 cells (Fig. 3e and f), suggesting that the penfluridol-induced apoptotic effect in AML cells might be through induction of PP2A activation to negatively regulate ERK and JNK activities. This evidence concerns the gene MAPK8 and acute myeloid leukemia.