Implication of calpain in caspase activation during B cell clonal deletion.
In the absence of costimulating signals, B cell receptor (BCR) crosslinking on immature B cells triggers the apoptotic cell death program. In the WEHI-231 B cell lymphoma model, anti-IgM crosslinking triggers activation of caspase-7 independently of caspase-8, followed by apoptosis. Two main mechanisms for caspase-7 activation have been proposed: (i) caspase-8 recruitment to death receptors (Fas or tumour necrosis factor); and (ii) changes in mitochondrial membrane permeability and cytochrome c release, which activate caspase-9. Here we report that caspase-7 activation induced by BCR crosslinking is independent of caspase-8 and cytochrome c translocation from mitochondria to the cytosol, as well as of mitochondrial depolarization. In addition, in a cell-free system, the S-100 fraction of anti-IgM-treated WEHI-231 cells induces a caspase activation pattern different from that activated by cytochrome c and dATP. We demonstrate that calpain specifically triggers activation and processing of caspase-7 both in vitro and in vivo, and that both processes are inhibited by calpain inhibitors. Furthermore, calpain activation is associated with decreased expression levels of calpastatin, which is upregulated by CD40 ligation. These data confirm a role for calpain during BCR crosslinking, which may be critical for cell deletion by apoptosis during B cell development and activation.
Ruiz-Vela
A
A
Department of Immunology Centro Nacional de Biotecnología, CSIC, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid, Spain. aruiz@cnb.uam.es
González de Buitrago
G
G
Martínez-A
C
C
D000818:Animals; D017209:Apoptosis; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D001483:Base Sequence; D019013:CD40 Antigens / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D053179:Caspase 7; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002474:Cell-Free System; D003432:Cross-Linking Reagents; D003574:Cytochrome c Group / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004789:Enzyme Activation; D007075:Immunoglobulin M / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism; D017634:Self Tolerance
D019013:CD40 Antigens; D003432:Cross-Linking Reagents; D003574:Cytochrome c Group; D017931:DNA Primers; D007075:Immunoglobulin M; D019253:Proto-Oncogene Proteins c-bcl-2; D011947:Receptors, Antigen, B-Cell; D002154:Calpain; C505524:Casp7 protein, mouse; D053179:Caspase 7; D020169:Caspases