Abstract
In many mammalian cell types, engagement of the TRAIL/Apo2L death receptors DR4 and DR5 alters mitochondrial physiology, thereby promoting the release of pro-apoptotic proteins normally contained within this organelle. A contemporary view of this process is that in so-called type II cells death receptor-activated caspase-8 cleaves the Bcl-2 family member Bid, which generates a truncated Bid fragment that collaborates with Bax, another Bcl-2 relative, to promote the release of mitochondrial factors necessary for activation of executioner caspases and apoptosis. Here we show that in some type II cells caspase-2 is necessary for optimal TRAIL-mediated cleavage of Bid. Down-regulation of caspase-2 using RNA interference significantly inhibited TRAIL-induced apoptosis. Analysis of the TRAIL proteolytic cascade following gene silencing of specific pathway components revealed that caspase-2 is necessary for efficient cleavage of Bid; however, caspase-2 proteolytic processing, which occurs downstream of Bax, is not necessary for its role in Bid cleavage.
MeSH terms
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Animals
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Apoptosis Regulatory Proteins
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Apoptosis*
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BH3 Interacting Domain Death Agonist Protein
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Blotting, Western
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Carrier Proteins / metabolism*
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Caspase 2
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Caspase 3
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Caspase 7
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Caspase 8
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Caspases / metabolism
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Caspases / physiology*
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Cell Death
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Cell Line
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Cell Survival
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Dose-Response Relationship, Drug
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Down-Regulation
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Enzyme Activation
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Etoposide / pharmacology
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Gene Silencing
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Humans
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Membrane Glycoproteins / metabolism*
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Mitochondria / metabolism
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Models, Biological
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-bcl-2*
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RNA Interference
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RNA, Small Interfering / metabolism
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Staurosporine / pharmacology
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TNF-Related Apoptosis-Inducing Ligand
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Tetrazolium Salts / pharmacology
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Thiazoles / pharmacology
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Time Factors
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Transfection
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Tumor Necrosis Factor-alpha / metabolism*
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bcl-2-Associated X Protein
Substances
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Apoptosis Regulatory Proteins
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BAX protein, human
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BH3 Interacting Domain Death Agonist Protein
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BID protein, human
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Carrier Proteins
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Membrane Glycoproteins
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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RNA, Small Interfering
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TNF-Related Apoptosis-Inducing Ligand
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TNFSF10 protein, human
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Tetrazolium Salts
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Thiazoles
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Tumor Necrosis Factor-alpha
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bcl-2-Associated X Protein
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Etoposide
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CASP3 protein, human
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CASP7 protein, human
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CASP8 protein, human
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Caspase 2
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Caspase 3
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Caspase 7
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Caspase 8
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Caspases
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thiazolyl blue
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Staurosporine