Regulation of Apoptosis by Caspases

Caspases are a family of cysteine proteases that play important roles in regulating apoptosis, a genetically encoded cellular suicide mechanism. To determine the mechanism by which caspases regulate apoptosis. We carried out a screen to identify substrates of caspases using small pool expression cloning method. We have screened l700 pools which contains approximately 70,000 cDNA clones. From such screening, we identified more than 60 caspase substrates, 10 of which have been verified to be cleaved in vivo during apoptosis. Of these substrates, 24 have not been previously identified or have no assigned function. During the last granting period, we concentrated on characterization of one of the substrates, Bid, which was originally identified as the Bcl-2 interacting protein. We found that Bid is a specific substrate for caspase-8 and is cleaved during Eas and TNF induced apoptosis. Cleaved Bid acts as an intracellular signal transducer from cytoplasmic membrane to mitochondria to induce cytochrome c release. We have also collaborated with Dr. Gerhard Wagner 5 lab to determine the NMR solution structure of Bid which revealed the structure basis of Bid 5 action in inducing mitochondrial damage. These works have been published in two papers in Cell.