Abstract
Ablation of the Raf-1 protein causes fetal liver apoptosis, embryonic lethality, and selective hypersensitivity to Fas-induced cell death. Furthermore, Raf-1-deficient cells show defective migration as a result of the deregulation of the Rho effector kinase Rok-alpha. In this study, we show that the kinase-independent modulation of Rok-alpha signaling is also the basis of the antiapoptotic function of Raf-1. Fas activation stimulates the formation of Raf-1-Rok-alpha complexes, and Rok-alpha signaling is up-regulated in Raf-1-deficient cells. This leads to increased clustering and membrane expression of Fas, which is rescued both by kinase-dead Raf-1 and by interfering with Rok-alpha or its substrate ezrin. Increased Fas clustering and membrane expression are also evident in the livers of Raf-1-deficient embryos, and genetically reducing Fas expression counteracts fetal liver apoptosis, embryonic lethality, and the apoptotic defects of embryonic fibroblasts. Thus, Raf-1 has an essential function in regulating Fas expression and setting the threshold of Fas sensitivity during embryonic life.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Apoptosis / genetics
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Apoptosis / physiology
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Cells, Cultured
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Cytoskeletal Proteins / metabolism
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Death Domain Receptor Signaling Adaptor Proteins
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Dose-Response Relationship, Drug
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Embryonic Development / physiology
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Fibroblasts / metabolism
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Flow Cytometry
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Fluorescent Antibody Technique
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Genes, Lethal
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Intracellular Signaling Peptides and Proteins
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Liver / embryology
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Liver / metabolism
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Membranes / metabolism
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Mice
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Mice, Mutant Strains / embryology
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Mice, Mutant Strains / metabolism
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Models, Biological
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Protein Serine-Threonine Kinases / metabolism*
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Proto-Oncogene Proteins c-raf / genetics
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Proto-Oncogene Proteins c-raf / metabolism*
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Receptors, Tumor Necrosis Factor / metabolism*
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Sensitivity and Specificity
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Signal Transduction*
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Tumor Necrosis Factor Receptor-Associated Peptides and Proteins / metabolism
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rho-Associated Kinases
Substances
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Cytoskeletal Proteins
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Death Domain Receptor Signaling Adaptor Proteins
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Intracellular Signaling Peptides and Proteins
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Receptors, Tumor Necrosis Factor
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Tumor Necrosis Factor Receptor-Associated Peptides and Proteins
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ezrin
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-raf
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rho-Associated Kinases