Apoptosis via the B cell antigen receptor requires Bax translocation and involves mitochondrial depolarization, cytochrome C release, and caspase-9 activation.
Various routes to apoptosis can be active during B cell development. In a model system of mature B cells, differences in caspase-3 processing have suggested that antigen receptor (BCR)-mediated apoptosis may involve a zVAD-insensitive initiator protease(s). In search of the events leading to caspase-3 activation, we now establish that both CD95- and BCR-mediated apoptosis depend on Bax activation and cytochrome C (cytC) release. Nevertheless, the timing and caspase-dependence of mitochondrial membrane depolarization differed considerably after CD95- or BCR-triggering. To delineate events subsequent to cytC release, we compared apoptosis induced via BCR triggering and via direct mitochondrial depolarization by CCCP. In both cases, partial processing of caspase-3 was observed in the presence of zVAD. By expression in 293 cells we addressed the potential of candidate initiator caspases to function in the presence of zVAD, and found that caspase-9 efficiently processed caspase-3, while caspase-2 or -8 were inactive. Finally, retroviral expression of dominant-negative caspase-9 inhibited both CD95- and BCR-mediated apoptosis. In conclusion, we obtained no evidence for involvement of a BCR-specific protease. Instead, our data show for the first time that the BCR-signal causes Bax translocation, followed by mitochondrial depolarization, and cytC release. Subsequent caspase-9 activation can solely account for events further downstream.
Eldering
Eric
E
Department of Experimental Immunology, Academical Medical Centre, Amsterdam, The Netherlands. e.eldering@amc.uva.nl
Mackus
Wendelina J M
WJ
Derks
Ingrid A M
IA
Evers
Ludo M
LM
Beuling
Esther
E
Teeling
Peter
P
Lens
Susanne M A
SM
van Oers
Marinus H J
MH
van Lier
René A W
RA
D000941:Antigens / Q000276:immunology; D017209:Apoptosis / Q000187:drug effects; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D045304:Cytochromes c / Q000378:metabolism*; D004789:Enzyme Activation; D005799:Genes, Dominant / Q000235:genetics; D006801:Humans; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism*; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D011947:Receptors, Antigen, B-Cell / Q000276:immunology / Q000378:metabolism*; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000378:metabolism
D000941:Antigens; C494826:BAX protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011947:Receptors, Antigen, B-Cell; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D045304:Cytochromes c; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases