Inactivation of multiple targets by nitric oxide in CD95-triggered apoptosis

Nitric oxide (NO) plays an important anti-apoptotic role by inactivating bo th upstream and downstream apoptotic molecules. We now report that exogenou sly supplied NO protected Jurkat T cells from anti-CD95-stimulated apoptosi s. WE have recently shown that nitrosation of the activator protein-1 (AP-1 ) transcriptional factor is crucial for NO-mediated inhibition of cell deat h triggered by etoposide or ceramide. Since the inhibition of apoptosis by NO has been reported to involve AP-1, we evaluated its involvement in in CD 95-mediated cell death. Cross-linking of CD95 enhanced AP-1 DNA binding act ivity and AP-l-dependent CD95L transactivation, which were both significant ly reduced by different NO-donors compounds. However, AP-1 induction does n ot seem to significantly contribute to anti-wCD95-triggered apoptosis, as c ell death could not be prevented by using the recombinant Fas-fc fusion pro tein which inhibits the CD95/CD95L interaction. We observed that caspase 3- like activity was negatively modulated by several NO-donors in vitro and th at titratable thiol groups of purified caspases 3, 7, and 9 decreased in th e presence of NO-releasing compounds. In conclusion, we demonstrated that N O-mediated inhibition of other targets, possibly caspases, but not AP-1, is a crucial event responsible for protection against anti-CD95-stimulated ap optosis. Even though NO affects multiple molecular mechanisms, the relevant target for exerting the cellular effects, may vary among different models.