INVOLVEMENT OF CED-3 ICE PROTEASES IN THE APOPTOSIS OF B-CHRONIC LYMPHOCYTIC-LEUKEMIA CELLS/

B-chronic lymphocytic leukemia (B-CLL) is characterized by the accumul ation of long-lived B lymphocytes that express high levels of Bcl-2. W e examined the involvement of CED-3/ICE-like proteases in the apoptosi s of B-CLL cells. lane of the substrates of these proteases is poly(AD P [adenosine 5'-diphosphate]-ribose) polymerase (PARP). The effect of different factors that induce the apoptosis of B-CLL cells on the prot eolytic cleavage of PARP has been studied. Treatment of B-CLL cells wi th different concentrations of dexamethasone (1 to 1,000 mu mol/L) ind uced in a dose-dependent manner the cleavage of PARP. Dexamethasone in duced PARP cleavage after 12 hours of incubation, which was almost com plete at 48 hours. PARP cleavage during apoptosis of B-CLL cells was s tudied in cells from eight patients and a correlation was found betwee n cell viability and the degree of PARP cleavage. Incubation in vitro of B-CLL cells with fludarabine for 48 hours induced PARP cleavage in all the cases studied. protein kinase C (PKC) activation with 100 nmol /L TPA [12-O-tetradecanoylphorbol 13-acetate) or incubation with inter leukin-4 (10 ng/mL) prevented either dexamethasone- or fludarabine-ind uced proteolysis of PARP. Incubation of B-CLL cells with the CED-3/ICE -like protease inhibitor Z-VAD.fmk inhibited spontaneous and dexametha sone-induced PARP cleavage and DNA fragmentation in a dose-dependent m anner. Furthermore, Z-VAD.fmk prevented the cytotoxic effect of dexame thasone. These results indicate that CED-3/ICE-like proteases play an important role in the apoptosis of B-CLL cells. (C) 1997 by The Americ an Society of Hematology.