Raf-1 sets the threshold of Fas sensitivity by modulating Rok-alpha signaling.
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.
Piazzolla
Daniela
D
Max F. Perutz Laboratories, Department of Microbiology and Immunobiology, Campus Vienna Biocenter, 1030 Vienna, Austria.
Meissl
Katrin
K
Kucerova
Lucia
L
Rubiolo
Cristina
C
Baccarini
Manuela
M
D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism; D053418:Death Domain Receptor Signaling Adaptor Proteins; D004305:Dose-Response Relationship, Drug; D047108:Embryonic Development / Q000502:physiology; D005347:Fibroblasts / Q000378:metabolism; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D005804:Genes, Lethal; D047908:Intracellular Signaling Peptides and Proteins; D008099:Liver / Q000196:embryology / Q000378:metabolism; D008566:Membranes / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains / Q000196:embryology / Q000378:metabolism; D008954:Models, Biological; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism*; D012680:Sensitivity and Specificity; D015398:Signal Transduction; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins / Q000378:metabolism; D054460:rho-Associated Kinases; D000099149:Ezrin
D003598:Cytoskeletal Proteins; D053418:Death Domain Receptor Signaling Adaptor Proteins; D047908:Intracellular Signaling Peptides and Proteins; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D018124:Receptors, Tumor Necrosis Factor; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins; D054460:rho-Associated Kinases; D000099149:Ezrin