Analysis of the signal transduction pathway of the transcription factor NF-κB activated by cytokines

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Acetoxycycloheximide (E-73) inhibits induction of the transcription factor NF-κB by TNF in the lung carcinoma A549 cells. Although E-73 failed to affect the expression of the adaptor proteins TRADD, RIP, and TRAF2, which are essential for activation of the NF-κB signaling pathway, the agent induced the downregulation of the cell-surface TNF receptor 1 via activation of p38 MAP kinase. By contrast, E-73 selectively induced caspase-dependent apoptosis and cytochrome c release from mitochondria in the human leukemia HL-60 and Jurkat T cells. E-73-induced cytochrome c release was blocked by the Bcl-2 family member Bcl-x_L and the JNK inhibitor SP600125, but was unaffected by the caspase inhibitor z-VAD-fmk and the p38 MAP kinase inhibitor SB203580. Thus, these data suggest that E-73 induces cytochrome c release from mitochondria through the JNK activation, thereby triggering the caspase cascade.The mycotoxin penicillic acid inhibited apoptosis by preventing activation of caspase-8, but not recruitment of caspase-8 into the Fas-FADD complex upon stimulation with Fas ligand (FasL). Penicillic acid inhibited the enzymatic activities of caspase-3, caspase-8, and casoase-9. However, penicillic acid weakly inhibited activation of caspase-3 and casoase-9 in staurosporine-treated cells, but did inhibit caspase-8 activation in FasL-treated cells, suggesting that penicillic acid selectively targets caspase-8 at the cellular level. Glutathione and cysteine suppressed the inhibitory effect of penicillic acid on caspase-8, and penicillic acid directly bound to the active center cysteine of caspase-8. These results demonstrate that penicillic acid inhibits FasL-induced apoptosis by blocking the self-processing of caspase-8.