title: Cell cycle-dependent regulation of FLIP levels and susceptibility to Fas-mediated apoptosis.
abstract: Activation-induced cell death of peripheral T cells results from the interaction between Fas and Fas ligand. Resting peripheral T cells are resistant to Fas-induced apoptosis and become susceptible only after their activation. We have investigated the molecular mechanism mediating the sensitization of resting peripheral T cells to Fas-mediated apoptosis following TCR stimulation. TCR activation decreases the steady state protein levels of FLIP (FLICE-like inhibitory protein), an inhibitor of the Fas signaling pathway. Reconstitution of intracellular FLIP levels by the addition of a soluble HIV transactivator protein-FLIP chimera completely restores resistance to Fas-mediated apoptosis in TCR primary T cells. Inhibition of IL-2 production by cyclosporin A, or inhibition of IL-2 signaling by rapamycin or anti-IL-2 neutralizing Abs prevents the decrease in FLIP levels and confers resistance to Fas-mediated apoptosis following T cell activation. Using cell cycle-blocking agents, we demonstrate that activated T cells arrested in G1 phase contain high levels of FLIP protein, whereas activated T cells arrested in S phase have decreased FLIP protein levels. These findings link regulation of FLIP protein levels with cell cycle progression and provide an explanation for the increase in TCR-induced apoptosis observed during the S phase of the cell cycle.
authors.affiliation: Department of Immunology, Division of Infectious Diseases, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: A
authors.initials: A
authors.lastname: Algeciras-Schimnich
authors.forename: T S
authors.initials: TS
authors.lastname: Griffith
authors.forename: D H
authors.initials: DH
authors.lastname: Lynch
authors.forename: C V
authors.initials: CV
authors.lastname: Paya
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002453:Cell Cycle / Q000276:immunology*; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects / Q000276:immunology; D006801:Humans; D007106:Immune Sera / Q000494:pharmacology; D007113:Immunity, Innate; D007376:Interleukin-2 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000276:immunology; D047908:Intracellular Signaling Peptides and Proteins; D008213:Lymphocyte Activation / Q000187:drug effects; D008969:Molecular Sequence Data; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D020123:Sirolimus / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D019014:fas Receptor / Q000502:physiology*
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; D007106:Immune Sera; D007376:Interleukin-2; D047908:Intracellular Signaling Peptides and Proteins; D011948:Receptors, Antigen, T-Cell; D019014:fas Receptor; D016572:Cyclosporine; D020123:Sirolimus