Divergent signalling via APO-1/Fas and the TNF receptor, two homologous molecules involved in physiological cell death.
Tumor necrosis factor receptor (TNF-R) and APO-1/Fas (CD95) are members of the tumor necrosis factor/nerve growth factor receptor superfamily involved in various forms of physiological cell death. Due to the structural homology between these receptors and their ligands, it has been suggested that APO-1/Fas and TNF-R kill cells by similar mechanisms. Here, we compared the killing pathways mediated by each receptor molecule in TNF-sensitive L929 cells stably transfected with APO-1/Fas cDNA. Morphological analysis revealed that TNF-induced cell death resembles necrosis, while APO-1/Fas-mediated cell killing shows an apoptotic pattern, evident by the appearance of membrane blebbing, nuclear condensation and non-random DNA degradation. Studies with inhibitors of several intracellular pathways further demonstrate that the mechanisms of TNF- and APO-1/Fas-mediated cell killing are substantially different. TNF cytotoxicity is mediated by reactive oxygen intermediates generated during mitochondrial respiration. However, these mediators are not involved in APO-1/Fas-mediated cell death as neither mitochondrial inhibitors nor antioxidants exert a protecting effect. Moreover, several inhibitors of calcium metabolism, ADP ribosylation and phospholipase action suppress TNF cytotoxicity, but not APO-1/Fas-mediated apoptosis. Additional differences between the two molecules were observed at the transcriptional level. Whereas transcription factor NF-kappa B was readily activated by TNF, activation was not induced by triggering APO-1/Fas. These data suggest that the two molecules, though structurally related, utilize distinct signal transduction pathways, even in a single cell type. Hence, cells may undergo different programs of cell death depending on the activating stimulus.
Schulze-Osthoff
K
K
Division of Immunochemistry, Deutsches Krebsforschungszentrum, D-69120 Heidelberg, Germany.
Krammer
P H
PH
Dröge
W
W
D000818:Animals; D000954:Antigens, Surface / Q000502:physiology*; D017209:Apoptosis / Q000502:physiology; D001483:Base Sequence; D002118:Calcium / Q000502:physiology; D016923:Cell Death / Q000502:physiology*; D002460:Cell Line; D048429:Cell Size / Q000502:physiology; D004247:DNA / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000502:physiology; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D018124:Receptors, Tumor Necrosis Factor / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D014407:Tumor Cells, Cultured; D019014:fas Receptor
D000954:Antigens, Surface; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D016328:NF-kappa B; D018124:Receptors, Tumor Necrosis Factor; D019014:fas Receptor; D004247:DNA; D002118:Calcium