CLARP, A DEATH EFFECTOR DOMAIN-CONTAINING PROTEIN INTERACTS WITH CASPASE-8 AND REGULATES APOPTOSIS

We have identified and characterized CLARP, a caspase-like apoptosis-r egulatory protein. Sequence analysis revealed that human CLARP contain s two amino-terminal death effector domains fused to a carboxyl-termin al caspase-like domain, The structure and amino acid sequence of CLARP resemble those of caspase-8, caspase-10, and DCP2, a Drosophila melan ogaster protein identified in this study, Unlike caspase-8, caspase-10 , and DCP2, however, two important residues predicted to be involved i n catalysis were lost in the caspase-like domain of CLARP, Analysis wi th fluorogenic substrates for caspase activity confirmed that CLARP is catalytically inactive, CLARP was found to interact with caspase-8 bu t not with FADD/MORT-1, an upstream death effector domain-containing p rotein of the Fas and tumor necrosis factor receptor 1 signaling pathw ay, Expression of CLARP induced apoptosis, which was blocked by the vi ral caspase inhibitor p35, dominant negative mutant caspase-8, and the synthetic caspase inhibitor yloxycarbonyl-Val-Ala-Asp-(OMe)-fluoromet hylketone (zVAD-fmk). Moreover, CLARP augmented the killing ability of caspase-8 and FADD/MORT-1 in mammalian cells, The human clarp gene ma ps to 2q33, Thus, CLARP represents a regulator of the upstream caspase -8, which may play a role in apoptosis during tissue development and h omeostasis.