Nitric oxide inhibits Fas-induced apoptosis.

The Fas antigen (CD95, APO-1) is a transmembrane cell surface receptor that mediates apoptosis of many cell types when bound by Fas ligand or cross-linked by agonist antibody. The cellular factors regulating Fas-induced apoptosis have not been well defined. Here we show that basal nitric-oxide synthase (NOS) activity in human leukocytes inhibits Fas-induced apoptosis via a cGMP-independent mechanism. Further, NOS inhibits Fas-induced cleavage of poly(ADP-ribose) polymerase by members of the caspase family of cysteine proteases. These data suggest that Fas activity is under the control of the NO signaling pathway. NOS regulating the function of this member of the tumor necrosis factor receptor family suggests a new role for nitric oxide (or related molecules) in the human immune response.