title: Mitochondria-dependent caspase-9 activation is necessary for antigen receptor-mediated effector caspase activation and apoptosis in WEHI 231 lymphoma cells.
abstract: Engagement of the B cell Ag receptor (BCR) on immature B cells leads to growth arrest followed by apoptosis. Concomitant signaling through CD40 sustains proliferation and rescues the cells from apoptosis. Previously, we have shown that cross-linking CD40 on B cells stimulates the expression of A1, an antiapoptotic member of the Bcl-2 family, and that transduction of the murine B lymphoma line WEHI 231, a model for immature B cells, with A1 protected the cells against BCR-induced apoptosis. Here we demonstrate that A1 strongly interferes with activation of caspase-7, the major effector caspase activated after BCR cross-linking on WEHI 231 lymphoma cells. The pathway leading to activation of the effector caspase cascade including caspase-7 is unclear. Using retrovirally transduced WEHI 231 cell populations, we show that a catalytically inactive mutant of caspase-7 is cleaved almost as efficiently as the wild-type form, arguing against autocatalysis as the sole activating process. In contrast, overexpression of catalytically inactive caspase-9 strongly interferes with caspase-7 processing, poly(ADP-ribose) polymerase cleavage, and DNA laddering, suggesting a role for caspase-9 and hence for the mitochondrial pathway. The importance of the mitochondrial/caspase-9 pathway for BCR-triggered apoptosis is highlighted by our finding that both A1 and the mutant caspase-9 attenuate BCR-induced apoptosis. Thus, our data suggest that the BCR-mediated apoptotic signal in immature B cells spreads via a mitochondrial/caspase-9 pathway.
authors.affiliation: Institute for Virology and Immunobiology, University of Würzburg, Würzburg, Germany.
authors.forename: Marco J
authors.initials: MJ
authors.lastname: Herold
authors.forename: Andreas W
authors.initials: AW
authors.lastname: Kuss
authors.forename: Christa
authors.initials: C
authors.lastname: Kraus
authors.forename: Ingolf
authors.initials: I
authors.lastname: Berberich
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000276:immunology*; D053179:Caspase 7; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D053938:DNA Fragmentation / Q000235:genetics / Q000276:immunology; D004789:Enzyme Activation / Q000235:genetics / Q000276:immunology; D006801:Humans; D008024:Ligands; D016393:Lymphoma, B-Cell / Q000201:enzymology* / Q000235:genetics / Q000276:immunology* / Q000473:pathology; D051379:Mice; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D010446:Peptide Fragments / Q000378:metabolism; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000235:genetics / Q000276:immunology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D011947:Receptors, Antigen, B-Cell / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D014161:Transduction, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D061945:Caspase Inhibitors; D008024:Ligands; D010446:Peptide Fragments; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D011947:Receptors, Antigen, B-Cell; D011065:Poly(ADP-ribose) Polymerases; C505520:CASP7 protein, human; C506433:CASP9 protein, human; C505524:Casp7 protein, mouse; C506434:Casp9 protein, mouse; D053179:Caspase 7; D053453:Caspase 9; D020169:Caspases