Abstract
Previously we reported that both human TNFR1 and TNFR2 mediate TNF-induced apoptosis in the transfected rat/mouse T cell hybridoma PC60. We show here that TNFR2-mediated apoptosis in PVC60 cells can be blocked by the broad-spectrum caspase inhibitor zVAD-fmk, the caspase-8 inhibitor zIETD-fmk and by CrmA, a viral inhibitor of caspase-1 and caspase-8. This suggests an involvement of caspase-8 in TNFR2-mediated apoptosis. The upstream adaptor of caspase-8, FADD, is also involved in TNFR2-induced cell death, since transient overexpression of a dominant negative deletion mutant of FADD inhibited apoptosis induced by this receptor. TNFR2-induced apoptosis is independent of endogenous TNF or other death-inducing ligand production and subsequent activation of TNFR1 or other death receptors. Furthermore, TNFR2 stimulation does not enhance sensitivity for a subsequent TNFR1-induced apoptotic signal, as has been reported for Jurkat cells. TRAF2 downregulation, which has been proposed as the mechanism by which TNFR2 enhances TNFR1 signaling, was observed in PC60 cells, but the TNRF1 signal was not modulated. These data confirm the capacity of TNFR2 to generate an apoptotic cell death signal independent of TNFR1.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing / genetics
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Adaptor Proteins, Signal Transducing / physiology*
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Animals
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Apoptosis / drug effects
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Apoptosis / physiology*
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Caspase 8
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Caspase Inhibitors
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Caspases / metabolism*
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Cell Survival / drug effects
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Cycloheximide / pharmacology
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Cysteine Proteinase Inhibitors / pharmacology
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Fas-Associated Death Domain Protein
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Humans
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Hybridomas
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Mice
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Mutation / genetics
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Rats
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Receptors, Tumor Necrosis Factor, Type I / antagonists & inhibitors
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Receptors, Tumor Necrosis Factor, Type I / genetics
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Receptors, Tumor Necrosis Factor, Type I / physiology
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Receptors, Tumor Necrosis Factor, Type II / genetics
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Receptors, Tumor Necrosis Factor, Type II / physiology*
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T-Lymphocytes / drug effects
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T-Lymphocytes / physiology*
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TNF Receptor-Associated Factor 2 / metabolism
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Transfection
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Tumor Necrosis Factor-alpha / pharmacology
Substances
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Adaptor Proteins, Signal Transducing
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Caspase Inhibitors
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Cysteine Proteinase Inhibitors
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FADD protein, human
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Fadd protein, mouse
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Fadd protein, rat
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Fas-Associated Death Domain Protein
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Receptors, Tumor Necrosis Factor, Type I
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Receptors, Tumor Necrosis Factor, Type II
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TNF Receptor-Associated Factor 2
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Tumor Necrosis Factor-alpha
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Cycloheximide
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CASP8 protein, human
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Casp8 protein, mouse
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Casp8 protein, rat
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Caspase 8
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Caspases