Identification of Multiple Caenorhabditis elegansCaspases and Their Potential Roles in Proteolytic Cascades

Proteases of the caspase family play a central role in the execution of programmed cell death in all metazoans examined. The Caenorhabditis elegans caspase CED-3 is essential for programmed cell death in this organism. Three additional C. elegans caspase-related genes, csp-1 (caspase homolog-1), which encodes the csp-1A, csp-1B, and csp-1C RNA species; csp-2, which encodes the csp-2A and csp-2B RNA species; and csp-3 are identified. CSP-1A, CSP-1B, CSP-2A, and CSP-2B proteins are similar in sequence to caspase proproteins. CSP-1C is similar only to large caspase subunits, and CSP-3 is similar only to small caspase subunits. CSP-1B can be activated to become a cysteine protease by processing at internal aspartate residues. Activated CSP-1B can cleave the CSP-1B, CED-3, and CSP-2B proproteins, and activated CED-3 can cleave the CED-3 and CSP-2B proproteins. Inhibitor and synthetic substrate studies further suggest that activated CSP-1B and activated CED-3 have different substrate specificities. These results suggest that C. elegans encodes several caspases that might act in proteolytic cascades to regulate processes such as programmed cell death.