Bryostatin and CD40-ligand enhance apoptosis resistance and induce expression of cell survival genes in B-cell chronic lymphocytic leukaemia

Modulating signal transduction pathways represents a promising approach for altering the biological behaviour of haemopoietic malignancies. B-cell chr onic lymphocytic leukaemia (B-CLL) cells were treated in vitro with CD40-li gand (CD40L) (CD154) or the protein kinase C modulator Bryostatin-1, explor ing the effects on: (a) sensitivity to apoptosis induction by chemotherapeu tic drugs (fludarabine, dexamethasone) or anti-Fas antibody; (b) expression of apoptosis-regulatory proteins (Bcl-2, Bcl-X, Mcl-1, Bar, Bak, BAG-1, Fl ip, XIAP); (c) expression of cell surface co-stimulatory antigens (CD80 [B7 .1]: CD54 [ICAM-1]; CD70); and (d) expression of immune modulatory receptor s (CD27, CD40, CD95 [Fas]), CD40L and Bryostatin decreased both spontaneous and drug-induced apoptosis in most B-CLL specimens tested. Apoptosis resis tance was associated with CD40L- and Bryostatin-induced elevations in the a nti-apoptotic Bcl-2 family protein Mcl-1. CD40L also induced striking incre ases in the levels of the anti-apoptotic protein Bcl-X-L in B-CLLs. CD40L s timulated increases in the surface expression of CD40, CD54, CD69, CD70, CD 80 and CD95, whereas Bryostatin induced expression of CD40, CD54, CD69 and CD95 but not the co-stimulatory molecules CD70 and CD80. Despite elevations in the expression of CD95 (Fas), anti-Fas antibodies failed to induce apop tosis of CD40L- and Bryostatin-treated B-CLL cells. This Fas-resistance was associated with increased expression of the Fas-antagonist Flip in CD40L-t reated, and with elevations in the caspase inhibitor XIAP in Bryostatin-tre ated B-CLLs. The potential anti-apoptotic properties of CD40L and Bryostati n should be taken into consideration when employing these agents in clinica l trials involving patients with B-CLL.