Death receptor recruitment of endogenous caspase-10 and apoptosis initiation in the absence of caspase-8.
Caspase-8 is believed to play an obligatory role in apoptosis initiation by death receptors, but the role of its structural relative, caspase-10, remains controversial. Although earlier evidence implicated caspase-10 in apoptosis signaling by CD95L and Apo2L/TRAIL, recent studies indicated that these death receptor ligands recruit caspase-8 but not caspase-10 to their death-inducing signaling complex (DISC) even in presence of abundant caspase-10. We characterized a series of caspase-10-specific antibodies and found that certain commercially available antibodies cross-react with HSP60, shedding new light on previous results. The majority of 55 lung and breast carcinoma cell lines expressed mRNA for both caspase-8 and -10; however, immunoblot analysis revealed that caspase-10 protein expression was more frequently absent than that of caspase-8, suggesting a possible selective pressure against caspase-10 production in cancer cells. In nontransfected cells expressing both caspases, CD95L and Apo2L/TRAIL recruited endogenous caspase-10 as well as caspase-8 to their DISC, where both enzymes were proteolytically processed with similar kinetics. Caspase-10 recruitment required the adaptor FADD/Mort1, and caspase-10 cleavage in vitro required DISC assembly, consistent with the processing of an apoptosis initiator. Cells expressing only one of the caspases underwent ligand-induced apoptosis, indicating that each caspase can initiate apoptosis independently of the other. Thus, apoptosis signaling by death receptors involves not only caspase-8 but also caspase-10, and both caspases may have equally important roles in apoptosis initiation.
Kischkel
F C
FC
Department of Molecular Oncology, Genentech, Inc., South San Francisco, California 94080, USA.
Lawrence
D A
DA
Tinel
A
A
LeBlanc
H
H
Virmani
A
A
Schow
P
P
Gazdar
A
A
Blenis
J
J
Arnott
D
D
Ashkenazi
A
A
D000595:Amino Acid Sequence; D017209:Apoptosis; D015153:Blotting, Western; D053455:Caspase 10; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007527:Isoenzymes / Q000276:immunology / Q000378:metabolism; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
D007527:Isoenzymes; D018124:Receptors, Tumor Necrosis Factor; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053455:Caspase 10; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; C506438:CASP10 protein, human