Processing/activation of caspases, -3 and -7 and -8 but not caspase-2, in the induction of apoptosis in B-chronic lymphocytic leukemia cells

Abstract

Chlorambucil and prednisolone, two commonly used drugs in the treatment of chronic lymphocytic leukemia (CLL), induce apoptosis in CLL cells. We have investigated the involvement in this apoptotic cell death of caspases, which cleave critical cellular substrates thereby acting as the executioners of the apoptotic process. Induction of spontaneous or chlorambucil/ prednisolone-induced apoptosis of freshly isolated B-CLL cells in culture resulted in the activation of the 'effector' caspases, -3 and -7, but generally not of caspase-2. Activation of caspases-3 and -7 was accompanied by the proteolysis of the DNA repair enzyme, poly (ADP-ribose) polymerase. Induction of apoptosis was also accompanied by the processing of caspase-8, the extent of which varied between patients. Induction of apoptosis and processing of all the caspases was inhibited by the cell permeable caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethyl ketone (Z-VAD.fmk). Our results demonstrate a key role for the activation and processing of caspases in the execution phase of apoptosis in CLL cells. Apoptosis of CLL cells resulted in the selective activation of some but not all caspases. Our results suggest that the dysregulation of apoptosis observed in CLL may be due to the signalling leading to the activation of caspases rather than a deletion of pro-caspases. High levels of caspase-8 in CLL cells in conjunction with low levels of CD95 receptor may offer new therapeutic opportunities for the treatment of CLL.

High expression of Bfl‐1 contributes to the apoptosis resistant phenotype in B‐cell chronic lymphocytic leukemia

“…Recently, a role for caspase-2 upstream of the mitochondria in stressor DNA damage-induced apoptosis was reported. 48 King et al 49 failed to detect cleavage of caspase-2 in most B-CLL cells during spontaneous and chlorambucil-or prednisolone-induced apoptosis, but our results showing clear induction of caspase-2 transcripts suggest that the role and function of this caspase in B-CLL should be further studied.…”

CD5-induced apoptosis of B cells in some patients with chronic lymphocytic leukemia

“…Studies in B-CLL have indicated that in both spontaneous and drug-induced apoptosis, there is a lack of involvement of caspase-2, but processing of caspase-3 and 8. 41,42 Recently, survivin, which is a member of a family of inhibitors of apoptosis has also been shown to be a key regulator in this process. 43 The molecular mechanisms of CD5-mediated apoptosis in group II patients are currently under study in our laboratories.…”

Proteasome inhibitor-induced apoptosis of B-chronic lymphocytic leukaemia cells involves cytochrome c release and caspase activation, accompanied by formation of an ∼700 kDa Apaf-1 containing apoptosome complex

“…37 Peripheral blood samples, obtained after informed consent and with local ethical committee approval, were purified as previously described 23 except that T cells were removed using anti-CD3 Dynabeads (Dynal, Merseyside, UK). B-CLL cell purity was assessed by staining with anti-CD19/FITC and anti-CD5/RPE antibodies (Dako, Cambridge, UK) and analysed by flow cytometry.…”

“…[20][21][22][23] Although caspases play a key role in the execution phase of apoptosis, much less is known about the role of the proteasome in apoptosis. The 26 S proteasome, the major extra-lysosomal machinery for protein degradation, is responsible for the ATP-dependent degradation of proteins targeted for destruction by ubiquitin.…”