CASPASE ACTIVATION IS REQUIRED FOR NITRIC OXIDE-MEDIATED, CD95(APO-1 FAS)-DEPENDENT AND INDEPENDENT APOPTOSIS IN HUMAN NEOPLASTIC LYMPHOID-CELLS/

Nitric oxide (NO), an important effector molecule involved in immune r egulation and host defense, was shown to induce apoptosis in lymphoma cells. In the present report the NO donor glycerol trinitrate was foun d to induce apoptosis in Jurkat cells that are sensitive to CD95-media ted kill. In contrast, a CD95-resistant Jurkat subclone showed substan tial protection from apoptosis after exposure to NO. NO induced mRNA e xpression of CD95 (APO-1/Fas) and TRAIL/APO-2 ligands. Moreover, NO tr iggered apoptosis in freshly isolated human leukemic lymphocytes which were also sensitive to anti-CD95 treatment, The ability of NO to indu ce apoptosis was completely blocked by a broad-spectrum ICE (interleuk in-1 beta converting enzyme)-protease/caspase inhibitor and correlated with FLICE/caspase-8 activation. This activation was abrogated in som e neoplastic lymphoid cells but not in others by the inhibitor of prot ein synthesis cycloheximide. Our results were confirmed using an in vi tro experimental model of coculture of human lymphoid target cells wit h activated bovine endothelial cells generating NO as effecters. Furth ermore, the inhibition of endogenous NO production with the inducible NO synthase inhibitor N-G-monomethyl-L-arginine caused a complete abro gation of the apoptotic effect. Our data provide evidence that NO-indu ced apoptosis in human neoplastic lymphoid cells strictly requires act ivation of caspases, in particular FLICE, the most CD95 receptor-proxi mal caspase. Depending on the cell line tested this activation require d or was independent of the CD95 receptor/ligand system. (C) 1998 by T he American Society of Hematology.