Feedback regulation of mitochondria by caspase-9 in the B cell receptor-mediated apoptosis.
During the germinal centre reaction (GC), B cells with non-functional or self-reactive antigen receptors are negatively selected by apoptosis to generate B cell repertoire with appropriate antigen specificities. We studied the molecular mechanism of Fas/CD95- and B cell receptor (BCR)-induced apoptosis to shed light on the signalling events involved in the negative selection of GC B cells. As an experimental model, we used human follicular lymphoma (FL) cell line HF1A3, which originates from a GC B cell, and transfected HF1A3 cell lines overexpressing Bcl-x(L), c-FLIP(long) or dominant negative (DN) caspase-9. Fas-induced apoptosis was dependent on the caspase-8 activation, since the overexpression of c-FLIP(long), a natural inhibitor of caspase-8 activation, blocked apoptosis induced by Fas. In contrast, caspase-9 activation was not involved in Fas-induced apoptosis. BCR-induced apoptosis showed the typical characteristics of mitochondria-dependent (intrinsic) apoptosis. Firstly, the activation of caspase-9 was involved in BCR-induced DNA fragmentation, while caspase-8 showed only marginal role. Secondly, overexpression of Bcl-x(L) could block all apoptotic changes induced by BCR. As a novel finding, we demonstrate that caspase-9 can enhance the cytochrome-c release and collapse of mitochondrial membrane potential (DeltaPsi(m)) during BCR-induced apoptosis. The requirement of different signalling pathways in apoptosis induced by BCR and Fas may be relevant, since Fas- and BCR-induced apoptosis can thus be regulated independently, and targeted to different subsets of GC B cells.
Eeva
J
J
Department of Clinical Microbiology, University of Kuopio, Kuopio, Finland. eeva@hytti.uku.fi
Nuutinen
U
U
Ropponen
A
A
Mättö
M
M
Eray
M
M
Pellinen
R
R
Wahlfors
J
J
Pelkonen
J
J
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000276:immunology* / Q000378:metabolism; D053181:Caspase 8 / Q000276:immunology / Q000378:metabolism; D053453:Caspase 9 / Q000276:immunology* / Q000378:metabolism; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D045304:Cytochromes c / Q000276:immunology / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D025461:Feedback, Physiological; D018858:Germinal Center / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007155:Immunologic Factors / Q000494:pharmacology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology / Q000276:immunology; D009842:Oligopeptides / Q000494:pharmacology; D011947:Receptors, Antigen, B-Cell / Q000276:immunology* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D051020:bcl-X Protein / Q000276:immunology* / Q000378:metabolism; D019014:fas Receptor / Q000819:agonists / Q000276:immunology / Q000378:metabolism
D000590:Amino Acid Chloromethyl Ketones; D000911:Antibodies, Monoclonal; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D007155:Immunologic Factors; D009842:Oligopeptides; D011947:Receptors, Antigen, B-Cell; D051020:bcl-X Protein; C110772:benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; D045304:Cytochromes c; D053181:Caspase 8; D053453:Caspase 9