Activation of caspase-8 in drug-induced apoptosis of B-lymphoid cells is independent of CD95/Fas receptor-ligand interaction and occurs downstream of caspase-3.
The activation of caspase-8, a crucial upstream mediator of death receptor signaling, was investigated in epirubicin- and Taxol-induced apoptosis of B-lymphoma cells. This study was performed because the CD95/Fas receptor-ligand interaction, recruitment of the Fas-associated death domain (FADD) adaptor protein, and subsequent activation of procaspase-8 have been implicated in the execution of drug-induced apoptosis in other cell types. Indeed, active caspase-8 was readily detected after treatment of mature and immature B-lymphoid cells with epirubicin or Taxol. However, neither constitutive nor drug-induced expression of the CD95/Fas ligand was detectable in B-lymphoma cells. Furthermore, overexpression of a dominant-negative FADD mutant (FADDdn) did not block caspase-8 processing and subsequent DNA fragmentation, indicating that drug-induced caspase-8 activation was mediated by a CD95/Fas-independent mechanism. Instead, caspase-8 cleavage was slightly preceded by activation of caspase-3, suggesting that drug-induced caspase-8 activation in B-lymphoma cells is a downstream event mediated by other caspases. This assumption was confirmed in 2 experimental systems-zDEVD-fmk, a cell-permeable inhibitor of caspase-3-like activity, blocked drug-induced caspase-8 cleavage, and depletion of caspase-3 from cell extracts impaired caspase-8 cleavage after in vitro activation with dATP and cytochrome c. Thus, these data indicate that drug-induced caspase-8 activation in B-lymphoma cells is independent of death receptor signaling and is mediated by postmitochondrial caspase-3 activation.
Department of Hematology, Oncology and Tumor Immunology, University Medical Center Charité, Humboldt University of Berlin, Germany.
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T
Wieder
F
F
Essmann
A
A
Prokop
K
K
Schmelz
K
K
Schulze-Osthoff
R
R
Beyaert
B
B
Dörken
P T
PT
Daniel
D048868:Adaptor Proteins, Signal Transducing; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001853:Bone Marrow / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics / Q000494:pharmacology; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism / Q000494:pharmacology* / Q000502:physiology; D002648:Child; D015251:Epirubicin / Q000494:pharmacology; D053222:Fas Ligand Protein; D053200:Fas-Associated Death Domain Protein; D006801:Humans; D015151:Immunoblotting; D016393:Lymphoma, B-Cell / Q000473:pathology*; D008562:Membrane Glycoproteins / Q000378:metabolism* / Q000502:physiology; D017239:Paclitaxel / Q000494:pharmacology; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma; D014162:Transfection; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology
D048868:Adaptor Proteins, Signal Transducing; D000903:Antibiotics, Antineoplastic; D000970:Antineoplastic Agents; D002352:Carrier Proteins; C505533:FADD protein, human; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D053200:Fas-Associated Death Domain Protein; D008562:Membrane Glycoproteins; D019014:fas Receptor; D015251:Epirubicin; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D017239:Paclitaxel