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.