Abstract
Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted much attention because of its ability to kill tumour cells. In this study, we demonstrated that treatment of QGY-7703 cells with the combination of TRAIL and etoposide resulted in synergistic cytotoxic effects. In dissecting the mechanism underlying this synergistic effect, we found that treatment with etoposide alone resulted in the upregulation of Bax, while the level of truncated Bid (tBid) was unchanged. In contrast, while treatment with TRAIL alone significantly increased the level of tBid, the expression of Bax remained unaffected. The enhanced apoptosis was accompanied by an increased release of cytochrome c and second mitochondria-derived activator of caspase/direct IAP binding protein with low pI (DIABLO) from mitochondria, leading to the activation of cellular caspase-8, -9, -3 and -7, as well as poly ADP-ribose polymerase. This enhanced release of cytochrome c and second mitochondria-derived activator of caspase/DIABLO was inhibited by the general caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. The RT-PCR and Western blotting results demonstrated that the levels of both mRNA and protein for death receptor-4, death receptor-5 and decoy receptor-2 remained unchanged in response to etoposide, indicating that the synergistic effect of TRAIL and etoposide is not a result of increasing the expression for TRAIL receptors, but rather is associated with amplification of the mitochondrial signal pathway.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Antineoplastic Agents, Phytogenic / metabolism*
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Apoptosis / physiology*
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Apoptosis Regulatory Proteins
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BH3 Interacting Domain Death Agonist Protein
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Carcinoma / metabolism*
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Carrier Proteins / genetics
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Carrier Proteins / metabolism
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Caspases / metabolism
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Cell Survival
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Cytochrome c Group / metabolism
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Etoposide / metabolism*
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Humans
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Intracellular Signaling Peptides and Proteins
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Liver Neoplasms / metabolism*
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Membrane Glycoproteins / pharmacology*
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Mitochondrial Proteins / metabolism
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Models, Biological
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Proto-Oncogene Proteins / genetics
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Proto-Oncogene Proteins / metabolism*
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Proto-Oncogene Proteins c-bcl-2*
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Receptors, TNF-Related Apoptosis-Inducing Ligand
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Receptors, Tumor Necrosis Factor / genetics
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Receptors, Tumor Necrosis Factor / metabolism
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TNF-Related Apoptosis-Inducing Ligand
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Tumor Cells, Cultured
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Tumor Necrosis Factor-alpha / pharmacology*
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Tumor Suppressor Protein p53 / metabolism
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bcl-2-Associated X Protein
Substances
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Antineoplastic Agents, Phytogenic
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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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Cytochrome c Group
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DIABLO protein, human
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Intracellular Signaling Peptides and Proteins
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Membrane Glycoproteins
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Mitochondrial Proteins
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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Receptors, TNF-Related Apoptosis-Inducing Ligand
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Receptors, Tumor Necrosis Factor
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TNF-Related Apoptosis-Inducing Ligand
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TNFRSF10A protein, human
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TNFRSF10B protein, human
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TNFSF10 protein, human
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Tumor Necrosis Factor-alpha
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Tumor Suppressor Protein p53
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bcl-2-Associated X Protein
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Etoposide
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Caspases