THE ROLE OF BCL-X(L) IN CD40-MEDIATED RESCUE FROM ANTI-MU-INDUCED APOPTOSIS IN WEHI-231 B-LYMPHOMA-CELLS

The phenotypically immature B cell lymphoma WEHI-231 undergoes apoptot ic cell death when cultured with anti-immunoglobulin (Ig) antibodies, via a bcl-2-independent mechanism. We have therefore studied the role of the bcl-2-related protein bcl-x in controlling cell death in WEHI-2 31. We find that overexpression of the long form of bcl-x (bcl-x(L)) r enders these cells refractory to anti-Ig-induced cell death. Stimulati on of WEHI-231 via CD40 has similar protective effects. We show here t hat ligation of CD40 rapidly induces the appearance of the bcl-x(L) pr otein in WEHI-231, while stimulation via sIgM, sIgD, CD5 or CD45 recep tors, or with phorbol esters plus ionomycin does not. WEHI-231 cells a lso rapidly undergo massive apoptosis following culture with thapsigar gin, a specific inhibitor of the Ca2+-ATPase of the endoplasmic reticu lum: this is also reversed by anti-CD40, or by overexpression of bcl-x (L). We, therefore, conclude that bcl-x(L) plays a key role in the reg ulation of antigen receptor-mediated apoptosis via CD40 in WEHI-231. I n addition, the fact that this protein is not induced in WEHI-231 in r esponse to phorbol dibutyrate plus ionomycin points to a fundamental s ignaling defect in these cells, which could conceivably be a reflectio n of their immature, apoptosis-susceptible phenotype.