title: Involvement of FADD and caspase-8 signalling in detachment-induced apoptosis.
abstract: Detachment of most untransformed adherent cells from the extracellular matrix promotes apoptosis, in a process termed anoikis [1] [2]. The death signalling mechanisms involved in this process are not known, although adhesion or transformation by ras oncogenes have been shown to protect epithelial cells from apoptosis through activation of phosphatidylinositol 3-kinase and protein kinase B (PKB/Akt) [3]. Here we show that detachment-induced apoptosis (anoikis) is blocked by the expression of a dominant-negative form of FAS-associated death domain protein (FADD) in a number of untransformed epithelial cell lines. Because the soluble extracellular domains of the death receptors CD95, DR4 and DR5 failed to block anoikis, we conclude that ligand-dependent activation of these death receptors is not involved in this process. Detachment induced strong activation of caspase 8 and caspase 3. Detachment-induced caspase-8 activation did not require the function of downstream caspases but was blocked by overexpression of the anti-apoptotic proteins Bcl-2 or Bcl-X(L). We propose that caspase-8 activation is the initiating event in anoikis, which is subsequently subject to a positive-feedback loop involving mitochondrial events.
authors.affiliation: Signal Transduction Laboratory Imperial Cancer Research Fund 44 Lincoln's Inn Fields, London, WC2A 3PX, UK.
authors.forename: M
authors.initials: M
authors.lastname: Rytömaa
authors.forename: L M
authors.initials: LM
authors.lastname: Martins
authors.forename: J
authors.initials: J
authors.lastname: Downward
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D029681:Arabidopsis Proteins; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000502:physiology*; D002448:Cell Adhesion / Q000502:physiology*; D002460:Cell Line; D003374:Coumarins / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004285:Dogs; D004789:Enzyme Activation / Q000187:drug effects; D004847:Epithelial Cells / Q000166:cytology; D005109:Extracellular Matrix / Q000502:physiology; D044943:Fatty Acid Desaturases / Q000502:physiology*; D007668:Kidney; D009842:Oligopeptides / Q000378:metabolism / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D051020:bcl-X Protein; D019014:fas Receptor / Q000502:physiology
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D029681:Arabidopsis Proteins; D061945:Caspase Inhibitors; D003374:Coumarins; D015853:Cysteine Proteinase Inhibitors; D009842:Oligopeptides; D019253:Proto-Oncogene Proteins c-bcl-2; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; C105190:TNFRSF10A protein, human; C505639:TNFRSF10B protein, human; D051020:bcl-X Protein; C106566:benzyloxycarbonyl-aspartyl-glutamyl-valyl-aspartyl-7-amino-4-trifluoromethylcoumarin; C403753:benzyloxycarbonyl-isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone; C403754:benzyloxycarbonyl-leucyl-glutamyl-histidyl-aspartic acid fluoromethyl ketone; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; D044943:Fatty Acid Desaturases; C084083:Fad7 protein, Arabidopsis; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases