title: The Fas death signaling pathway connecting reactive oxygen species generation and FLICE inhibitory protein down-regulation.
abstract: Fas-mediated apoptosis plays an important role in normal tissue homeostasis, and disruption of this death pathway contributes to many human diseases. Induction of apoptosis via Fas activation has been associated with reactive oxygen species (ROS) generation and down-regulation of FLICE inhibitory protein (FLIP); however, the relationship between these two events and their role in Fas-mediated apoptosis are unclear. We show herein that ROS are required for FLIP down-regulation and apoptosis induction by Fas ligand (FasL) in primary lung epithelial cells. ROS mediate the down-regulation of FLIP by ubiquitination and subsequent degradation by proteasome. Inhibition of ROS by antioxidants or by ectopic expression of ROS-scavenging enzymes glutathione peroxidase and superoxide dismutase effectively inhibited FLIP down-regulation and apoptosis induction by FasL. Hydrogen peroxide is a primary oxidative species responsible for FLIP down-regulation, whereas superoxide serves as a source of peroxide and a scavenger of NO, which positively regulates FLIP via S-nitrosylation. NADPH oxidase is a key source of ROS generation induced by FasL, and its inhibition by dominant-negative Rac1 expression or by chemical inhibitor decreased the cell death response to FasL. Taken together, our results indicate a novel pathway of FLIP regulation by an interactive network of reactive oxygen and nitrogen species that provides a key mechanism of apoptosis regulation in Fas-induced cell death and related apoptosis disorders.
authors.affiliation: Pathology and Physiology Research Branch, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.
authors.forename: Liying
authors.initials: L
authors.lastname: Wang
authors.forename: Neelam
authors.initials: N
authors.lastname: Azad
authors.forename: Lalana
authors.initials: L
authors.lastname: Kongkaneramit
authors.forename: Fei
authors.initials: F
authors.lastname: Chen
authors.forename: Yongju
authors.initials: Y
authors.lastname: Lu
authors.forename: Bing-Hua
authors.initials: BH
authors.lastname: Jiang
authors.forename: Yon
authors.initials: Y
authors.lastname: Rojanasakul
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000276:immunology; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000037:antagonists & inhibitors* / Q000502:physiology; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000276:immunology; D002478:Cells, Cultured; D015536:Down-Regulation / Q000276:immunology*; D053222:Fas Ligand Protein / Q000502:physiology; D006801:Humans; D008168:Lung / Q000166:cytology / Q000201:enzymology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000166:cytology / Q000201:enzymology / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology*; D019014:fas Receptor / Q000378:metabolism / Q000502:physiology*
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D017382:Reactive Oxygen Species; D019014:fas Receptor; D020169:Caspases