Abstract
Cobalt promotes apoptosis in multiple cell systems, however, the molecular mechanisms that influence cobalt-induced apoptosis are not fully understood. We investigated mechanisms of cobalt chloride induced apoptosis in HCT116 colorectal cancer cells. Cobalt chloride induced dose dependent apoptosis in HCT116 cells (250-750 muM) which, at higher concentrations (500-750 muM), was associated with an increase in the expression of the Bcl-2-related Mcl-1 survival protein. Cobalt chloride caused the accumulation of higher molecular weight ubiquitin-conjugates of Mcl-1 in intact HCT116 cells and inhibited the activity of the trypsin-like site of the 20S proteasome in an in vitro assay. Although siRNA-mediated knockdown of Mcl-1 increased apoptosis in HCT116 cells, the combination of Mcl-1 siRNA and cobalt chloride induced very high levels of cell killing. Therefore, inhibition of the proteasome by cobalt chloride leads to the accumulation of Mcl-1 which acts to limit cobalt chloride induced apoptosis.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Antimutagenic Agents / pharmacology
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Apoptosis / drug effects
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Apoptosis / physiology*
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Apoptosis Regulatory Proteins / drug effects
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Apoptosis Regulatory Proteins / metabolism
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Binding Sites / drug effects
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Binding Sites / physiology
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Carcinoma / drug therapy
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Carcinoma / metabolism*
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Carcinoma / physiopathology
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Cell Line, Tumor
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Cell Survival / drug effects
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Cell Survival / physiology
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Cobalt / pharmacology*
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Colorectal Neoplasms / drug therapy
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Colorectal Neoplasms / metabolism*
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Colorectal Neoplasms / physiopathology
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Dose-Response Relationship, Drug
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Down-Regulation / drug effects
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Down-Regulation / genetics
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Feedback, Physiological / drug effects
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Feedback, Physiological / genetics
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Humans
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Hypoxia-Inducible Factor 1, alpha Subunit / genetics
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Hypoxia-Inducible Factor 1, alpha Subunit / metabolism
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Myeloid Cell Leukemia Sequence 1 Protein
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Proteasome Endopeptidase Complex / drug effects
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Proteasome Endopeptidase Complex / metabolism*
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Proto-Oncogene Proteins c-bcl-2 / drug effects
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Proto-Oncogene Proteins c-bcl-2 / genetics
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Proto-Oncogene Proteins c-bcl-2 / metabolism*
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RNA Interference / physiology
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RNA, Small Interfering
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Ubiquitination / drug effects
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Ubiquitination / physiology
Substances
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Antimutagenic Agents
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Apoptosis Regulatory Proteins
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HIF1A protein, human
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Hypoxia-Inducible Factor 1, alpha Subunit
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Myeloid Cell Leukemia Sequence 1 Protein
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Proto-Oncogene Proteins c-bcl-2
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RNA, Small Interfering
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Cobalt
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Proteasome Endopeptidase Complex
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cobaltous chloride