Acetoxycycloheximide (E-73) rapidly induces apoptosis mediated by the release of cytochrome c via activation of c-Jun N-terminal kinase

Cycloheximide (CHX) is an inhibitor of protein synthesis and commonly used to modulate death receptor-mediated apoptosis or to induce apoptosis in a number of normal and transformed cells. In this study we show that a close structural derivative of CHX, acetoxycycloheximide (E-73) induced rapid processing of procaspases and subsequent apoptosis with much higher efficacy than CHX in human leukemia Jurkat T cells. E-73 induced the release of cytochrome c from mitochondria even in the presence of the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethyl ketone. The Bcl-2 family protein Bcl-x(L) suppressed cytochrome c release as well as processing of procaspases-3, -8, and -9 in E-73-treated cells. In Jurkat T cells transfected with the caspase-8 modulator FLIP(L), E-73 still induced activation of procaspase-3 and subsequent apoptosis, suggesting that the caspase-8 activity is dispensable for apoptosis. In contrast to CHX, E-73 drastically induced activation of extracellular signal-regulated kinase, c-Jun N-terminal kinase (JNK), and p38 MAP kinase. Inhibitory profiles of small-molecular kinase inhibitors revealed that JNK activation was critical for induction of cytochrome c release in E-73-induced apoptosis. Thus, our present results demonstrate that E-73, unlike CHX, induces strong activation of the JNK pathway and triggers rapid apoptosis mediated by the release of cytochrome c.