Abstract
Sulforaphane is a chemopreventive agent present in various cruciferous vegetables, including broccoli. Here, we show that treatment with tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) in combination with subtoxic doses of sulforaphane significantly induces rapid apoptosis in TRAIL-resistant hepatoma cells. Neither TNF-alpha- nor Fas-mediated apoptosis was sensitized in hepatoma cells by cotreatment with sulforaphane, suggesting that sulforaphane can selectively sensitize cells to TRAIL-induced apoptosis but not to apoptosis mediated by other death receptors. We found that sulforaphane treatment significantly up-regulated mRNA and protein levels of DR5, a death receptor of TRAIL. This was accompanied by an increase in the generation of reactive oxygen species (ROS). Pretreatment with N-acetyl-l-cysteine and overexpression of catalase inhibited sulforaphane-induced up-regulation of DR5 and almost completely blocked the cotreatment-induced apoptosis. Furthermore, the sulforaphane-mediated sensitization to TRAIL was efficiently reduced by administration of a blocking antibody or small interfering RNAs for DR5. These results collectively indicate that sulforaphane-induced generation of ROS and the subsequent up-regulation of DR5 are critical for triggering and amplifying TRAIL-induced apoptotic signaling. We also found that sulforaphane can sensitize both Bcl-xL- and Bcl-2-overexpressing hepatoma cells to TRAIL-induced apoptosis, indicating that treatment with a combination of TRAIL and sulforaphane may be a safe strategy for treating resistant hepatomas.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Antineoplastic Combined Chemotherapy Protocols / pharmacology*
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Apoptosis / drug effects
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Apoptosis Regulatory Proteins / administration & dosage
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Apoptosis Regulatory Proteins / pharmacology*
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Carcinoma, Hepatocellular / drug therapy*
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Carcinoma, Hepatocellular / genetics
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Carcinoma, Hepatocellular / metabolism
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Cell Line, Tumor
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Drug Screening Assays, Antitumor
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Drug Synergism
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Hepatocytes / drug effects
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Hepatocytes / metabolism
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Humans
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Inhibitor of Apoptosis Proteins / biosynthesis
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Isothiocyanates
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Liver Neoplasms / drug therapy*
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Membrane Glycoproteins / administration & dosage
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Membrane Glycoproteins / pharmacology*
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Promoter Regions, Genetic / drug effects
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Proto-Oncogene Proteins c-bcl-2 / biosynthesis
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Rats
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Reactive Oxygen Species / metabolism*
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Receptors, TNF-Related Apoptosis-Inducing Ligand
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Receptors, Tumor Necrosis Factor / biosynthesis
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Receptors, Tumor Necrosis Factor / genetics
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Receptors, Tumor Necrosis Factor / metabolism*
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Sulfoxides
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TNF-Related Apoptosis-Inducing Ligand
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Thiocyanates / administration & dosage
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Thiocyanates / pharmacology*
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Transcriptional Activation / drug effects
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Tumor Necrosis Factor-alpha / administration & dosage
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Tumor Necrosis Factor-alpha / pharmacology*
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Up-Regulation
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bcl-X Protein / biosynthesis
Substances
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Apoptosis Regulatory Proteins
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BCL2L1 protein, human
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Inhibitor of Apoptosis Proteins
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Isothiocyanates
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Membrane Glycoproteins
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Proto-Oncogene Proteins c-bcl-2
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Reactive Oxygen Species
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Receptors, TNF-Related Apoptosis-Inducing Ligand
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Receptors, Tumor Necrosis Factor
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Sulfoxides
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TNF-Related Apoptosis-Inducing Ligand
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TNFRSF10B protein, human
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TNFSF10 protein, human
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Thiocyanates
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Tnfrsf10b protein, rat
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Tnfsf10 protein, rat
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Tumor Necrosis Factor-alpha
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bcl-X Protein
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sulforaphane