NITRIC-OXIDE INHIBITS APO-1 FAS-MEDIATED CELL-DEATH/

Activation of the cysteine protease caspases, which are homologous to the product of Caenorhabditis elegans cell-death gene ced 3, is requir ed to mediate APO-1/Fas-induced apoptosis, We report here that nitric oxide (NO) released by exogenous NO donors, as well as NO endogenously derived by transfection with the inducible NO synthase, substantially suppresses APO-1/Fas-triggered cell death of Jurkat cells. The inhibi tory NO effect was independent of cGMP, because 8-bromo-cGMP did not i nfluence APO-1/Fas-mediated apoptosis, In contrast, NO interferes with the APO-1/Fas-induced stimulation of caspases. NO inhibits the proteo lytic cleavage of caspase-3 (CPP32) into its active subunits, thereby suppressing caspase-3 activity. In addition, NO potently inhibits apop tosis induction by overexpresssion of the death domain protein FADD or the immediate downstream target caspase-8, These results suggest that NO modulates the proteolytic cascade upstream of caspase-3. Indeed, N O specifically S-nitrosylates caspase-8 and caspase-1 and thereby may prevent activation of the proteolytic cascade. The NO-mediated increas e in the resistance toward induction of apoptosis may play a major rol e in mediating immune responses, as well as in the pathogenesis of aut oimmune diseases.