Caspases mediate tumor necrosis factor-alpha-induced neutrophil apoptosis and downregulation of reactive oxygen production.
Tumor necrosis factor-alpha (TNF-alpha) exerts two separate effects on neutrophils, stimulating effector functions while simultaneously inducing apoptosis. We examined here the involvement of caspases in neutrophil apoptosis and the effect of TNF-alpha-induced apoptosis on reactive oxygen production. Immunoblotting and affinity labeling showed activation of caspase-8, caspase-3, and a caspase with a large subunit of 18 kD (T18) in TNF-alpha-treated neutrophils. Active caspase-6 and -7 were not detectable in this cell type. Caspase-8 activated caspase-3 and T18 in neutrophil cytoplasmic extracts. zVAD-fmk blocked neutrophil apoptosis, in parallel with the inhibition of caspase activation. TNF-alpha-induced caspase activation was accompanied by a decrease in the ability of neutrophils to release superoxide anion. Conversely, TNF-alpha treatment in the presence of zVAD-fmk caused a prolonged augmentation of superoxide release. Granulocyte-macrophage colony-stimulating factor inhibited TNF-alpha-induced caspase activation and apoptosis, while reversing the diminution in superoxide release. These observations not only suggest that a caspase cascade mediates apoptotic events and downregulates oxygen radical production in TNF-alpha-treated neutrophils, but also raise the possibility that suppression of caspase activation with enhanced proinflammatory actions of TNF-alpha may underlie the pathogenesis of inflammatory diseases.
Yamashita
K
K
Department of Hematology and Oncology, Clinical Sciences for Pathological Organs, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Takahashi
A
A
Kobayashi
S
S
Hirata
H
H
Mesner
P W
PW
Kaufmann
S H
SH
Yonehara
S
S
Yamamoto
K
K
Uchiyama
T
T
Sasada
M
M
D000328:Adult; D000345:Affinity Labels; D017209:Apoptosis; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D004357:Drug Synergism; D004789:Enzyme Activation; D006801:Humans; D015151:Immunoblotting; D009504:Neutrophils / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D000345:Affinity Labels; D011500:Protein Synthesis Inhibitors; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D013481:Superoxides; D003513:Cycloheximide; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases