CM1 Ligation Induces Apoptosis via Fas-FasL Interaction in Ramos Cells, but via Down-regulation of Bcl-2 and Subsequent Decrease of Mitochondrial Membrane Potential in Raji Cells

ABSTRACT

BACKGROUND: CM1 (Centrocyte/-blast Marker I) defined by a mAb developed against concanavalin-A activated PBMC, is expressed specifically on a subpopulation of centroblasts and centrocytes of human germinal center (GC) B cells. Burkitt lymphoma (BL) is a tumor consisting of tumor cells with the characteristics of GC B cell. Previously we reported that CM1 ligation with anti-CM1 mAb induced apoptosis in Ramos (IgM(high)) and Raji (IgM(low)) cells. METHODS & RESULTS: In the present study, we observed that CM1 ligation with anti-CM1 mAb induced Fas ligand and Fas expression in Ramos cells, but not in Raji cells. Furthermore, anti-Fas blocking antibody, ZB4, blocked CM1-mediated apoptosis effectively in Ramos cells, but not in Raji cells. Increased mitochondrial membrane permeabilization, which was measured by DiOC6, was observed only in Raji cells. In contrast to no significant change of Bax known as pro-apoptotic protein, anti-apoptotic protein Bcl-2 was significantly decreased in Raji cells. In addition, we observed that CM1 ligation increased release of mitochondrial cytochrome c and upregulated caspase-9 activity in Raji cells. CONCLUSION: These results suggest that apoptosis induced by CM1-ligation is mediated by Fas-Fas ligand interaction in Ramos cells, whereas apoptosis is mediated by down-regulation of Bcl-2 and subsequent decrease of mitochondrial membrane potential in Raji cells.