title: Cellular FLICE-like inhibitory protein deviates myofibroblast fas-induced apoptosis toward proliferation during lung fibrosis.
abstract: A prominent feature of fibrotic tissue in general and of lungs in particular is fibroblast proliferation and accumulation. In patients overcoming fibrosis, apoptosis limits this excessive cell growth. We have previously shown resistance to Fas-induced apoptosis of primary lung fibroblasts from mice with bleomycin-induced lung fibrosis, their escape from immune surveillance, and continued accumulation in spite of overexpression of the Fas death receptor. Cellular FLICE-like inhibitory protein (c-FLIP) is a regulator of cell death receptor-induced apoptosis in many cell types. We aimed to determine c-FLIP levels in myofibroblasts from fibrotic lungs and to directly assess c-FLIP's role in apoptosis and proliferation of primary lung myofibroblasts. c-FLIP levels were determined by apoptosis gene array, flow cytometry, Western blot, and immunofluorescence before and after down-regulation with a specific small interfering RNA. Apoptosis was assessed by caspase cleavage in Western blot and by Annexin V affinity labeling after FACS and tissue immunofluorescence. Proliferation was assessed by BrdU uptake, also using FACS and immunofluorescence. We show that myofibroblasts from lungs of humans with idiopathic pulmonary fibrosis and from bleomycin-treated versus normal saline-treated mice up-regulate c-FLIP levels. Using the animal model, we show that fibrotic lung myofibroblasts divert Fas signaling from apoptosis to proliferation and that this requires signaling by TNF receptor-associated factor (TRAF) and NF-κB. c-FLIP down-regulation reverses the effect of Fas activation, causing increased apoptosis, decreased proliferation, and diminished recruitment of TRAF to the DISC complex. This indicates that c-FLIP is essential for myofibroblast accumulation and may serve as a potential target to manipulate tissue fibrosis.
authors.affiliation: Lung Cellular and Molecular Laboratory, Institute of Pulmonary Medicine, Hadassah University Hospital, POB 12000, Jerusalem, Israel.
authors.forename: Regina
authors.initials: R
authors.lastname: Golan-Gerstl
authors.forename: Shulamit B
authors.initials: SB
authors.lastname: Wallach-Dayan
authors.forename: Philip
authors.initials: P
authors.lastname: Zisman
authors.forename: Wellington V
authors.initials: WV
authors.lastname: Cardoso
authors.forename: Ronald H
authors.initials: RH
authors.lastname: Goldstein
authors.forename: Raphael
authors.initials: R
authors.lastname: Breuer
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D001483:Base Sequence; D015153:Blotting, Western; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism / Q000502:physiology*; D020169:Caspases / Q000378:metabolism; D049109:Cell Proliferation; D017931:DNA Primers; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D051379:Mice; D008810:Mice, Inbred C57BL; D058628:Myofibroblasts / Q000473:pathology*; D016328:NF-kappa B / Q000378:metabolism; D011658:Pulmonary Fibrosis / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D019014:fas Receptor / Q000502:physiology*
chemical_list: D017304:Annexin A5; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D017931:DNA Primers; D016328:NF-kappa B; D019014:fas Receptor; D020169:Caspases