Ceramide-induced killing of normal and malignant human lymphocytes is by anon-apoptotic mechanism

Synthetic ceramides induce apoptotic death of Jurkat and HL60 leukaemia cel l lines. By contrast we show here that ceramide induces non-apoptotic killi ng of malignant cells from patients with B-chronic lymphocytic leukaemia (B -CLL) and of normal B lymphocytes, The protein phosphatase inhibitor okadai c acid readily induces apoptosis of B-CLL cells, indicating that this death pathway is fully functional in these cells. The ability of ceramide to act ivate the apoptotic protease caspase 3 in HL60 cells but not in B-CLL cells , as well as the lack of correlation of ceramide-mediated killing of differ ent B-CLL isolates with expression of the apoptosis-regulating proteins bcl -2 and bax reinforce the conclusion that ceramide killing of B-CLL cells is by a non-apoptotic mechanism. Fludarabine treatment or gamma-irradiation o f B-CLL cells resulted in ceramide elevation and in killing by both apoptot ic and non-apoptotic mechanisms, suggesting that a ceramide-triggered non-a poptotic mechanism may play a role in the killing of these cells. Therefore , the results here show that ceramide can induce either apoptotic or non-ap optotic death, depending on the cellular conte it. The inability of synthet ic dihydroceramide to kill B-CLL cells or normal B lymphocytes suggests tha t non-apoptotic killing by ceramide is via interaction with a specific, but unidentified, cellular target.