title: Genetic deletion of faim reveals its role in modulating c-FLIP expression during CD95-mediated apoptosis of lymphocytes and hepatocytes.
abstract: Fas-apoptosis inhibitory molecule (FAIM) is inducibly expressed in B lymphocytes and had been shown to antagonize Fas-mediated killing of B-cell lines in vitro. However, its mechanism and role in vivo are unknown. We have generated faim(-/-) mice and found these mutants to be viable. In contrast to fas(-/-) mice, faim(-/-) mice have normal B- and T-cell populations. However, faim(-/-) B cells and thymocytes show increased sensitivity to Fas-triggered apoptosis in vitro, and faim(-/-) mice suffer greater mortality and exhibit exacerbated liver damage in response to Fas (CD95) engagement in vivo. The lack of FAIM results in greater activation of caspase-8 and -3 in Fas-stimulated thymocytes. Detailed biochemical analyses further reveal the decreased expression of c-FLIP(L) and c-FLIP(R) in faim(-/-) thymocytes and increased association of caspase-8 with Fas in Fas-activated mutant cells. Decreased levels of c-FLIP(L) and c-FLIP(R) are also evident in faim(-/-) liver. Thus, FAIM plays a novel role in modulating Fas-mediated apoptosis and acts through influencing the expression of c-FLIP and regulating the physical binding of caspase-8 to Fas.
authors.affiliation: Laboratory of Immunology, Bioprocessing Technology Institute, Agency for Science, Technology and Research (A*STAR), Singapore.
authors.forename: J
authors.initials: J
authors.lastname: Huo
authors.forename: S
authors.initials: S
authors.lastname: Xu
authors.forename: K
authors.initials: K
authors.lastname: Guo
authors.forename: Q
authors.initials: Q
authors.lastname: Zeng
authors.forename: K-P
authors.initials: KP
authors.lastname: Lam
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000096:biosynthesis* / Q000235:genetics; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D053222:Fas Ligand Protein / Q000494:pharmacology; D017353:Gene Deletion; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D007155:Immunologic Factors / Q000494:pharmacology; D008099:Liver / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D019014:fas Receptor / Q000378:metabolism
chemical_list: D000893:Anti-Inflammatory Agents; D000911:Antibodies, Monoclonal; D051017:Apoptosis Regulatory Proteins; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506387:Cflar protein, mouse; C498892:Faim protein, mouse; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D007155:Immunologic Factors; D014409:Tumor Necrosis Factor-alpha; D019014:fas Receptor; D003907:Dexamethasone; C505526:Casp8 protein, mouse; D053148:Caspase 3; D053181:Caspase 8