Tumor necrosis factor (TNF)-alpha activates c-raf-1 kinase via the p55 TNF receptor engaging neutral sphingomyelinase.
TNF-alpha mediates proliferation, functional activation and apoptotic death of cells depending upon its concentration and target cell type. The signaling pathways used by TNF-alpha to mount these responses are, at present, not completely understood. We report here that TNF-alpha promotes dose- and time-dependent phosphorylation and activation of the c-raf-1 kinase engaging the type I p55 TNF receptor (TNF-R). c-raf-kinase activation was duplicated by an agonistic monoclonal antibody directed against the p55 TNF-R. Moreover, ectopic expression of the human p55 TNF-R in murine pre-B 70Z/3 cells was sufficient to confer c-raf-1-kinase activation by human TNF-alpha. By inhibiting intracellular activation of acidic sphingomyelinase (SMase) and by using deleted forms of the type I TNF-R it was shown that the neutral, but not the acidic SMase, participated in TNF-alpha-mediated phosphorylation and activation of the c-raf kinase. TNF-alpha-induced transcriptional activation of a heterologous promoter construct harboring the AP-1 binding site was also mediated by the type I p55 TNF-R. In this case the initiation of transcription required the same cytoplasmic domain as that responsible for activation of c-raf-1 kinase and was liberated in the presence of a dominant negative mutant of c-raf-1.
Belka
C
C
Abteilung für Medizinische Onkologie und Angewandte Molekularbiologie, Freie Universität Berlin, Germany.
Wiegmann
K
K
Adam
D
D
Holland
R
R
Neuloh
M
M
Herrmann
F
F
Krönke
M
M
Brach
M A
MA
D000818:Animals; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D002478:Cells, Cultured; D004789:Enzyme Activation; D005347:Fibroblasts; D017930:Genes, Reporter; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051379:Mice; D009000:Monocytes; D009154:Mutation / Q000502:physiology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D018124:Receptors, Tumor Necrosis Factor / Q000096:biosynthesis / Q000276:immunology / Q000502:physiology*; D047888:Receptors, Tumor Necrosis Factor, Type I; D015398:Signal Transduction / Q000502:physiology*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D011518:Proto-Oncogene Proteins; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; D014409:Tumor Necrosis Factor-alpha; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D013108:Sphingomyelin Phosphodiesterase