Abstract
FADD/MORT1 (The adaptor protein of Fas Associate Death Domain/Mediator of Receptor Induced Toxicity) is essential for signal transduction of death receptor signaling. We have previously shown that FADD is significantly up-regulated in TNFalpha/ActD induced apoptosis. Over-expression of FADD also induces death of lung cancer cells and primary hepatocytes. We hypothesize that the increase in detectable FADD levels require the proximal steps in apoptotic signaling and speculated that FADD would be redistributed in cells destined to undergo apoptosis. We show that monomeric non-phosphorylated FADD is up-regulated in hepatocytes treated with TNFalpha/ActD and that it accumulates in the cytoplasm. Nuclear phosphorylated FADD decreases with TNFalpha/ActD treatment. Dimeric FADD in the cytoplasm remains constant with TNFalpha/ActD. The change in FADD levels and distribution was dependent on caspase-3, caspase-8 activity and the presence of BID. Thus, changes in FADD levels and distribution are downstream of caspase activation and mitochondria changes that are initiated by the formation of the DISC complex. Changes in FADD levels and distribution may represent a novel feed-forward mechanism to propagate apoptosis signaling in hepatocytes.
MeSH terms
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Active Transport, Cell Nucleus / drug effects
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Active Transport, Cell Nucleus / physiology
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Animals
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Apoptosis / drug effects
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Apoptosis / physiology*
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BH3 Interacting Domain Death Agonist Protein / drug effects
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BH3 Interacting Domain Death Agonist Protein / metabolism*
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Caspase 3 / drug effects
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Caspase 3 / metabolism
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Caspase 8 / drug effects
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Caspase 8 / metabolism
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Caspases / drug effects
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Caspases / metabolism*
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Cytoplasm / drug effects
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Cytoplasm / metabolism
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Dactinomycin / pharmacology
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Death Domain Receptor Signaling Adaptor Proteins / drug effects
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Death Domain Receptor Signaling Adaptor Proteins / metabolism
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Fas-Associated Death Domain Protein / drug effects
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Fas-Associated Death Domain Protein / metabolism*
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Hepatocytes / drug effects
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Hepatocytes / metabolism*
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Humans
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Male
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Membrane Potential, Mitochondrial / drug effects
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Membrane Potential, Mitochondrial / physiology
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Mice
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Mice, Inbred C57BL
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Mice, Knockout
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Phosphorylation / drug effects
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Signal Transduction / drug effects
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Signal Transduction / physiology
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Tumor Necrosis Factor-alpha / drug effects
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Tumor Necrosis Factor-alpha / metabolism*
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Up-Regulation / drug effects
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Up-Regulation / physiology
Substances
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BH3 Interacting Domain Death Agonist Protein
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Bid protein, mouse
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Death Domain Receptor Signaling Adaptor Proteins
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Fadd protein, mouse
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Fas-Associated Death Domain Protein
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Tumor Necrosis Factor-alpha
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Dactinomycin
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Casp3 protein, mouse
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Caspase 3
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Caspase 8
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Caspases