We previously showed that cepharanthine (CEP), a biscoclaurine alkaloid, induces caspase-dependent and Fas-independent apoptosis in Jurkat and K562 human leukemia cells. In the present study, we investigated the effect of CEP on three groups of human mitogen-activated protein kinases (MAPKs) in relation to CEP-induced apoptosis. CEP, at the concentration required for and at the time of induction of apoptosis, activated MAPKs p38 in both Jurkat and K562 cells and activated extracellular signal-regulated kinases (ERKs) only in K562 cells. However, CEP treatment did not trigger c-Jun NH(2)-terminal kinases (JNKs) activation. CEP increased the expression and phosphorylation levels of c-Jun and ATF-2 transcription factors. zVAD-fmk, a general caspase inhibitor, did not inhibit CEP-triggered p38 activation in Jurkat and K562 cells or ERK activation in K562 cells. Unexpectedly, pretreatment with a specific p38 inhibitor, SB203580, promoted CEP-induced apoptosis and caspase activation in Jurkat and K562 cells, whereas pretreatment with an MEK-1 inhibitor PD98059 inhibited CEP-induced apoptosis and caspase activation in K562 cells. A selective tyrosine kinase inhibitor, herbimycin A, which completely inhibited CEP-triggered ERKs activation, clearly promoted CEP-induced c-Jun expression and phosphorylation. Our results suggest that each of the three groups of MAP family members is uniquely involved in the CEP-mediated signal cascades in two different leukemia cell lines for inducing/regulating caspase activation and DNA fragmentation.