PROTEASE ACTIVATION IS REQUIRED FOR GLUCOCORTICOID-INDUCED APOPTOSIS IN CHRONIC LYMPHOCYTIC LEUKEMIC LYMPHOCYTES

Recent work has demonstrated that glucocorticoids, nucleoside analogue s, and other cancer chemotherapeutics induce apoptosis in chronic lymp hocytic leukemia (CLL) cells. In this study, we investigated the invol vement of protease activation in these responses using selective pepti de inhibitors of the interleukin-lp converting enzyme (ICE)/caspase fa mily and a Ca2+-activated protease we recently implicated in thymocyte apoptosis, Apoptosis was associated with proteolytic cleavage of poly (adenosine diphosphate [ADP]-ribose) polymerase (PARR) and increased c aspase protease activity, and cell-permeant caspase antagonists [zVAD( OMe)fmk and Boc-D(OBzl)cmk] blocked apoptosis in response to the gluco corticoid methylprednisolone or the nucleoside analogue fludarabine, i ndicating that caspase activation was required for these responses, Ho wever, a peptide-based inhibitor of the Ca2+-dependent lamin protease (zAPFcmk) also completely suppressed DNA fragmentation and the cleavag e of lamin B-1. Strikingly, treatment of cells with zAPFcmk alone led to characteristic PARP cleavage, depletion of the precursor forms of t wo ICE family proteases (CPP32 and ICH-1), and phosphatidylserine expo sure, suggesting that blockade of the lamin protease led to activation of the ICE family. Our results implicate the lamin protease as a targ et for Ca2+ during chemotherapy-induced apoptosis in CLL lymphocytes, and they identify a novel functional interaction between the protease and members of the ICE family. (C) 1997 by The American Society of Hem atology.