ACTIVATION OF HPAK65 BY CASPASE CLEAVAGE INDUCES SOME OF THE MORPHOLOGICAL AND BIOCHEMICAL-CHANGES OF APOPTOSIS

Apoptosis is a highly regulated form of cell death, characterized by d istinctive features such as cellular shrinkage and nuclear condensatio n. We demonstrate here that proteolytic activation of hPAK65, a p21-ac tivated kinase, induces morphological changes and elicits apoptosis, h PAK65 is cleaved both in vitro and irt vivo by caspases at a single si te between the N-terminal regulatory p21-binding domain and the C-term inal kinase domain. The C-terminal cleavage product becomes activated, with a kinetic profile that parallels caspase activation during apopt osis, This C-terminal hPAK65 fragment also activates the c-Jun N-termi nal kinase pathway in vivo. Microinjection or transfection of this tru ncated hPAK65 causes striking alterations in cellular and nuclear morp hology, which subsequently promotes apr,ptosis in both CHO and Hela ce lls. Conversely, apoptosis is delayed in cells expressing a dominant-n egative form of hPAK65, These findings provide a direct evidence that the activated form of hPAK65 generated by caspase cleavage is a proapo ptotic effector that mediates morphological and biochemical changes se en in apoptosis.