Ligation of CD40 rescues Ramos-Burkitt lymphoma B cells from calcium ionophore- and antigen receptor-triggered apoptosis by inhibiting activation of the cysteine protease CPP32/Yama and cleavage of its substrate PARP

The new and growing family of interleukin-1 beta-converting enzyme (ICE) cysteine proteases are now recognised to be major effecters of cellular death by apoptosis, Like other members of this family, the CPP32/Yama preform is activated by processing to its active heterodimeric enzyme or apopain when it likely contributes to the process of apoptosis by cleaving poly(ADP-ribose) polymerase (PARP) and thereby inhibiting much of its DNA repair activity, Apoptosis plays a fundamental role in the regulation of the immune system where it is involved in the selection of both T and B lymphocytes bearing antigen receptor (AgR) for non-self, Cells of the Ramos Epstein-Barr virus (EBV)-genome-negative Burkitt lymphoma (BL) B cell line (Ramos-BL) can be triggered into growth arrest and apoptosis by treating with the calcium ionophore ionomycin or by cross-linking their surface AgR with antibodies directed against immunoglobulin (Ig)M (anti-IgM). Ionomycin- and AgR-triggered growth arrest and apoptosis are arrested by signals transduced through the surface CD40 of Ramos-BL B cells, Both ionomycin and anti-IgM trigger activation of CPP32 and cleavage of PARP prior to the onset of apoptosis; this process is abrogated by treatment with anti-CD40 and is independent of Bcl-2 expression. A tripeptide inhibitor of ICE family cysteine proteases, Z-Val-Ala-Asp-fluoromethylketone (zVAD-frnk) inhibits ionomycin- and AgR-triggered CPP32 activation, PARP cleavage and apoptosis, but not growth arrest, in Ramos-BL B cells, Thus, in this report we demonstrate that in a physiological system, activation of endogenous members of the ICE family, including CPP32, and cleavage of the death substrate PARP act as major effecters of apoptotic death.