PROCESSING ACTIVATION OF CASPASES, CASPASE-3 AND CASPASE-7 AND CASPASE-8 BUT NOT CASPASE-2, IN THE INDUCTION OF APOPTOSIS IN B-CHRONIC LYMPHOCYTIC-LEUKEMIA CELLS/

Chlorambucil and prednisolone, two commonly used drugs in the treatmen t 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 o r chlorambucil/prednisolone-induced apoptosis of freshly isolated B-CL L cells in culture resulted in the activation of the 'effector' caspas es, -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 accompan ied by the processing of caspase-8, the extent of which varied between patients. Induction of apoptosis and processing of all the caspases w as inhibited by the cell permeable caspase inhibitor, benzyloxycarbony l-Val-Ala-Asp (OMe) fluoromethyl ketone (Z-VAD.fmk). Our results demon strate a key role for the activation and processing of caspases in the execution phase of apoptosis in CLL cells. Apoptosis of CLL cells res ulted in the selective activation of some but not all caspases. Our re sults 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 therape utic opportunities for the treatment of CLL.