FLICE, A NOVEL FADD-HOMOLOGOUS ICE CED-3-LIKE PROTEASE, IS RECRUITED TO THE CD95 (FAS/APO-1) DEATH-INDUCING SIGNALING COMPLEX/

To identify CAP3 and CAP4 components of the CD95 (Fas/APO-1) death-ind ucing signaling complex, we utilized nano-electrospray tandem mass spe ctrometry, a recently developed technique to sequence femtomole quanti ties of polyacrylamide gel-separated proteins. Interestingly, CAP4 enc odes a novel 55 kDa protein, designated FLICE, which has homology to b oth FADD and the ICE/CED-3 family of cysteine proteases. FLICE binds t o the death effector domain of FADD and upon overexpression induces ap optosis that is blocked by the ICE family inhibitors, CrmA and z-VAD-f mk. CAP3 was identified as the FLICE prodomain which likely remains bo und to the receptor after proteolytic activation. Taken together, this is unique biochemical evidence to link a death receptor physically to the proapoptotic proteases of the ICE/CED-3 family.