CLEAVAGE OF CPP32 BY GRANZYME-B REPRESENTS A CRITICAL ROLE FOR GRANZYME-B IN THE INDUCTION OF TARGET-CELL DNA FRAGMENTATION

Cytotoxic T lymphocytes (CTLs) are able to recognize and destroy targe t cells bearing foreign antigen using one of two distinct mechanisms: granule- or Fas-mediated cytotoxicity. The exact mechanisms involved i n the induction of apoptotic cell death remain elusive; however, it se ems likely that a family of cysteine proteases related to interleukin- 1 beta converting enzyme are involved. One family member, CPP32, has b een identified as an intracellular substrate for granzyme B, a CTL-spe cific serine protease responsible for the early induction of target ce ll DNA fragmentation. Here we use cytolytic cells from granzyme B-defi cient mice to confirm that cleavage and activation of CPP32 represents a nonredundant role for granzyme B and that this activation plays a r ob in the induction of DNA fragmentation in target cells, a signature event for apoptotic cell death. A peptide inhibitor of CPP32-like prot eases confirmed the function of these enzymes in fragmentation. Cr-51 release was not suppressed under these conditions, suggesting that gra nzyme B cleavage of CPP32 is primarily involved in the induction of DN A fragmentation and not membrane damage during CTL-induced apoptosis.