Activation of p38 and c-Jun N-terminal kinase pathways and induction of apoptosis by chelerythrine do not require inhibition of protein kinase C

Chelerythrine, a natural benzophenanthridine alkaloid, has been reported to mediate a variety of biological activities, including inhibition of protein kinase C (PKC). Here we report that chelerythrine induced time- and dose-dependent activation of JNK1 and p38 in HeLa cells, which was mediated the upstream kinases, MEKK1 and MKK4. However, treatment with two other potent and selective PKC inhibitors, GF-109203X and G?6983, or down-regulation of PKC activity by prolonged treatment with phorbol 12-myristate 13-acetate had no effect on JNK1 and p38 activities. Furthermore, under the conditions where JNK1 and p38 were activated, we did not observe any significant inhibitory effect of chelerythrine on the activities of PKC isozymes present in HeLa cells. Interestingly, pretreatment with the antioxidants, N-acetyl-L-cysteine, dithiothreitol, and glutathione, impaired chelerythrine-induced JNK1 and p38 activation. In addition, chelerythrine induced apoptosis that was blocked by the antioxidants and the dominant-negative mutants of MEKK1, MKK4, JNK1, and p38. Together, these results uncover a novel biochemical property of chelerythrine, i.e. activation of MEKK1- and MKK4-dependent JNK1 and p38 pathways through an oxidative stress mechanism, which mediate the induction of apoptosis, but are independent of PKC inhibition.