title: Cellular FLIP (long form) regulates CD8+ T cell activation through caspase-8-dependent NF-kappa B activation.
abstract: Cellular FLIP long form (c-FLIP(L)) was originally identified as an inhibitor of Fas (CD95/Apo-1). Subsequently, additional functions of c-FLIP(L) were identified through its association with receptor-interacting protein (RIP)1 and TNFR-associated factor 2 to activate NF-kappaB, as well as by its association with and activation of caspase-8. T cells from c-FLIP(L)-transgenic (Tg) mice manifest hyperproliferation upon activation, although it was not clear which of the various functions of c-FLIP(L) was involved. We have further explored the effect of c-FLIP(L) on CD8(+) effector T cell function and its mechanism of action. c-FLIP(L)-Tg CD8(+) T cells have increased proliferation and IL-2 responsiveness to cognate Ags as well as to low-affinity Ag variants, due to increased CD25 expression. They also have a T cytotoxic 2 cytokine phenotype. c-FLIP(L)-Tg CD8(+) T cells manifest greater caspase activity and NF-kappaB activity upon activation. Both augmented proliferation and CD25 expression are blocked by caspase inhibition. c-FLIP(L) itself is a substrate of the caspase activity in effector T cells, being cleaved to a p43(FLIP) form. p43(FLIP) more efficiently recruits RIP1 than full-length c-FLIP(L) to activate NF-kappaB. c-FLIP(L) and RIP1 also coimmunoprecipitate with active caspase-8 in effector CD8(+) T cells. Thus, one mechanism by which c-FLIP(L) influences effector T cell function is through its activation of caspase-8, which in turn cleaves c-FLIP(L) to allow RIP1 recruitment and NF-kappaB activation. This provides a partial explanation of why caspase activity is required to initiate proliferation of resting T cells.
authors.affiliation: Immunobiology Program, Department of Medicine, University of Vermont College of Medicine, Burlington, VT 05405, USA.
authors.forename: Austin
authors.initials: A
authors.lastname: Dohrman
authors.forename: Takao
authors.initials: T
authors.lastname: Kataoka
authors.forename: Solange
authors.initials: S
authors.lastname: Cuenin
authors.forename: Jennifer Q
authors.initials: JQ
authors.lastname: Russell
authors.forename: Jurg
authors.initials: J
authors.lastname: Tschopp
authors.forename: Ralph C
authors.initials: RC
authors.lastname: Budd
mesh_terms: D000818:Animals; D000941:Antigens / Q000378:metabolism / Q000494:pharmacology; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D018106:CD28 Antigens / Q000502:physiology; D018414:CD8-Positive T-Lymphocytes / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D053181:Caspase 8; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D002478:Cells, Cultured; D004306:Dose-Response Relationship, Immunologic; D004527:Egg Proteins / Q000378:metabolism / Q000494:pharmacology; D005260:Female; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology*; D008213:Lymphocyte Activation / Q000235:genetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D016328:NF-kappa B / Q000378:metabolism*; D010047:Ovalbumin / Q000378:metabolism / Q000494:pharmacology; D010446:Peptide Fragments; D011506:Proteins / Q000378:metabolism; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D015375:Receptors, Interleukin-2 / Q000096:biosynthesis; D015854:Up-Regulation / Q000235:genetics / Q000276:immunology; D019014:fas Receptor / Q000502:physiology
chemical_list: D000941:Antigens; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D018106:CD28 Antigens; C506386:CFLAR protein, human; D061945:Caspase Inhibitors; C506387:Cflar protein, mouse; D004527:Egg Proteins; D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B; C110366:OVA-8; D010446:Peptide Fragments; D011506:Proteins; D015375:Receptors, Interleukin-2; D019014:fas Receptor; D010047:Ovalbumin; C506249:RIPK1 protein, human; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; C506251:Ripk1 protein, mouse; C505530:CASP8 protein, human; C505526:Casp8 protein, mouse; D053181:Caspase 8; D020169:Caspases