Abstract
Regulation of the apoptotic threshold is of great importance in the homeostasis of both differentiating and fully developed organ systems. Triggering differentiation has been employed as a strategy to inhibit cell proliferation and accelerate apoptosis in malignant cells, in which the apoptotic threshold is often characteristically elevated. To better understand the mechanisms underlying differentiation-mediated regulation of apoptosis, we have studied death receptor responses during erythroid differentiation of K562 erythroleukemia cells, which normally are highly resistant to tumor necrosis factor (TNF) alpha-, FasL-, and TRAIL-induced apoptosis. However, upon hemin-mediated erythroid differentiation, K562 cells specifically lost their resistance to TNF-related apoptosis-inducing ligand (TRAIL), which efficiently killed the differentiating cells independently of mitochondrial apoptotic signaling. Concomitantly with the increased sensitivity, the expression of both c-FLIP splicing variants, c-FLIP(L) and c-FLIP(S), was downregulated, resulting in an altered caspase 8 recruitment and cleavage in the death-inducing signaling complex (DISC). Stable overexpression of both c-FLIP(L) and c-FLIP(S) rescued the cells from TRAIL-mediated apoptosis with isoform-specific effects on DISC-recruited caspase 8. Our results show that c-FLIP(L) and c-FLIP(S) potently control TRAIL responses, both by distinct regulatory features, and further imply that the differentiation state of malignant cells determines their sensitivity to death receptor signals.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Alternative Splicing
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Apoptosis / physiology*
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Apoptosis Regulatory Proteins
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CASP8 and FADD-Like Apoptosis Regulating Protein
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Carrier Proteins / genetics
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Carrier Proteins / metabolism*
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Caspase 8
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Caspase 9
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Caspases / metabolism
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Cell Differentiation / drug effects
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Cell Differentiation / physiology*
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Cytochrome c Group / metabolism
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Death Domain Receptor Signaling Adaptor Proteins
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Down-Regulation
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HL-60 Cells / metabolism
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HL-60 Cells / pathology
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Hemin / pharmacology
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Humans
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Intracellular Membranes
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Intracellular Signaling Peptides and Proteins*
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K562 Cells / metabolism
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K562 Cells / pathology*
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Membrane Glycoproteins / metabolism*
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Membrane Glycoproteins / pharmacology
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Membrane Potentials / drug effects
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Mitochondria / metabolism
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Protein Isoforms
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Proto-Oncogene Proteins c-bcl-2 / drug effects
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Proto-Oncogene Proteins c-bcl-2 / metabolism
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Receptors, TNF-Related Apoptosis-Inducing Ligand
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Receptors, Tumor Necrosis Factor / metabolism
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Signal Transduction
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TNF-Related Apoptosis-Inducing Ligand
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Tumor Necrosis Factor-alpha / metabolism*
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Tumor Necrosis Factor-alpha / pharmacology
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bcl-X Protein
Substances
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Apoptosis Regulatory Proteins
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BCL2L1 protein, human
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CASP8 and FADD-Like Apoptosis Regulating Protein
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CFLAR protein, human
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Carrier Proteins
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Cytochrome c Group
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Death Domain Receptor Signaling Adaptor Proteins
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Intracellular Signaling Peptides and Proteins
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Membrane Glycoproteins
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Protein Isoforms
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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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bcl-X Protein
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Hemin
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CASP8 protein, human
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CASP9 protein, human
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Caspase 8
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Caspase 9
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Caspases