B cell receptor cross-linking triggers a caspase-8-dependent apoptotic pathway that is independent of the death effector domain of Fas-associated death domain protein.
We have previously reported that B cell receptors, depending on the degree to which they are cross-linked, can promote apoptosis in various human B cell types. In this study, we show that B cell receptors can trigger two apoptotic pathways according to cross-linking and that these pathways control mitochondrial activation in human Burkitt's lymphoma cells. Whereas soluble anti-mu Ab triggers caspase-independent mitochondrial activation, cross-linked anti-mu Ab induces an apoptotic response associated with a caspase-dependent loss of mitochondrial transmembrane potential. This B cell receptor-mediated caspase-dependent mitochondrial activation is associated with caspase-8 activation. We show here that caspase-8 inhibitors strongly decrease cross-linking-dependent B cell receptor-mediated apoptosis in Burkitt's lymphoma BL41 cells. These inhibitors act upstream from the mitochondria as they prevented the loss of mitochondrial membrane potential observed in B cell receptor-treated BL41 cells. Caspase-8 activation in these cells was also evident from the detection of cleaved fragments of caspase-8 and the cleavage of specific substrates, including Bid. Our data show that cross-linked B cell receptors induced an apoptotic pathway involving sequential caspase-8 activation, loss of mitochondrial membrane potential, and the activation of caspase-9 and caspase-3. Cells expressing a dominant negative mutant of Fas-associated death domain protein were sensitive to cross-linked B cell receptor-induced caspase-8 activation and apoptosis; therefore, this caspase-8 activation was independent of the death effector domain of Fas-associated death domain protein.
Besnault
L
L
Institut National de la Santé et de la Recherche Médicale, Unité 131 and Unité 542, Clamart, France.
Schrantz
N
N
Auffredou
M T
MT
Leca
G
G
Bourgeade
M F
MF
Vazquez
A
A
D048868:Adaptor Proteins, Signal Transducing; D000888:Antibodies, Anti-Idiotypic / Q000378:metabolism; D000911:Antibodies, Monoclonal / Q000378:metabolism / Q000494:pharmacology; D017209:Apoptosis / Q000276:immunology*; D019013:CD40 Antigens / Q000276:immunology; D002352:Carrier Proteins / Q000502:physiology*; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism / Q000502:physiology*; D002999:Clone Cells; D004268:DNA-Binding Proteins / Q000502:physiology*; D053418:Death Domain Receptor Signaling Adaptor Proteins; D004789:Enzyme Activation / Q000276:immunology; D053200:Fas-Associated Death Domain Protein; D006801:Humans; D007106:Immune Sera / Q000494:pharmacology; D007425:Intracellular Membranes / Q000201:enzymology / Q000276:immunology; D047908:Intracellular Signaling Peptides and Proteins; D008564:Membrane Potentials / Q000276:immunology; D008928:Mitochondria / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011947:Receptors, Antigen, B-Cell / Q000276:immunology* / Q000378:metabolism* / Q000502:physiology; D012995:Solubility; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D019013:CD40 Antigens; D002352:Carrier Proteins; C116096:DEDD protein, human; D004268:DNA-Binding Proteins; D053418:Death Domain Receptor Signaling Adaptor Proteins; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D007106:Immune Sera; D047908:Intracellular Signaling Peptides and Proteins; D011947:Receptors, Antigen, B-Cell; C044203:anti-IgM; D019014:fas Receptor; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases