ACTIVATION OF THE CPP32 PROTEASE IN APOPTOSIS INDUCED BY 1-BETA-D-ARABINOFURANOSYLCYTOSINE AND OTHER DNA-DAMAGING AGENTS

The response of human myeloid leukemia cells to treatment with 1-beta- arabinofuranosylcytosine (ara-C) includes the induction of apoptosis. Ara-C induced apoptosis is associated with proteolytic cleavage of pol y(ADP-ribose) polymerase (PARP) and protein kinase C (PKC) delta. Howe ver, the signals involved in this response are unknown, The present st udies show that ara-C treatment of U-937 cells is associated with indu ction of a protease activity that cleaves the tetrapeptides Ac-DEVD-pN A and Ac-DMQD-pNA found at the cleavage sites of PARP and PKC delta, r espectively. The ara-C-induced protease activity was sensitive to over expression of the anti-apoptotic protein Bcl-x(L) and the baculovirus protein p35. By contrast, overexpression of the cowpox virus protein C rmA blocked apoptosis induced by engagement of the Fas receptor but no t that induced by ara-C. CrmA overexpression also had no detectable ef fect on ara-C-induced cleavage of PKC delta. The results further show that ara-C induces activation of the CPP32 protease by a CrmA-insensit ive and p35-sensitive mechanism. Similar results were obtained with ci splatinum, etoposide, and camptothecin. These findings indicate that a ra-C and other DNA damaging agents activate a CrmA-insensitive apoptot ic pathway involving CPP32 and that these signals differ from those as sociated with apoptosis induced by the Fas receptor. (C) 1996 by The A merican Society of Hematology.