title: Fas apoptosis inhibitory molecule regulates T cell receptor-mediated apoptosis of thymocytes by modulating Akt activation and Nur77 expression.
abstract: Fas apoptosis inhibitory molecule (FAIM) has been demonstrated to confer resistance to Fas-induced apoptosis of lymphocytes and hepatocytes in vitro and in vivo. Here, we show that FAIM is up-regulated in thymocytes upon T cell receptor (TCR) engagement and that faim(-/-) thymocytes are highly susceptible to TCR-mediated apoptosis with increased activation of caspase-8 and -9. Furthermore, injection of anti-CD3 antibodies leads to augmented depletion of CD4(+)CD8(+) T cells in the thymus of faim(-/-) mice compared with wild-type control, suggesting that FAIM plays a role in thymocyte apoptosis. Cross-linking of the TCR on faim(-/-) thymocytes leads to an elevated protein level of the orphan nuclear receptor Nur77, which plays a role in thymocyte apoptosis. Interestingly, in the absence of FAIM, there are reduced ubiquitination and degradation of the Nur77 protein. Faim(-/-) thymocytes also exhibit a defective TCR-induced activation of Akt whose activity we now show is required for Nur77 ubiquitination. Further analyses utilizing FAIM-deficient primary thymocytes and FAIM-overexpressing DO-11.10 T cells indicate that FAIM acts upstream of Akt during TCR signaling and influences the localization of Akt to lipid rafts, hence affecting its activation. Taken together, our study defined a TCR-induced FAIM/Akt/Nur77 signaling axis that is critical for modulating the apoptosis of developing thymocytes.
authors.affiliation: Immunology Group, Bioprocessing Technology Institute, Agency for Science, Technology and Research, Singapore.
authors.forename: Jianxin
authors.initials: J
authors.lastname: Huo
authors.forename: Shengli
authors.initials: S
authors.lastname: Xu
authors.forename: Kong-Peng
authors.initials: KP
authors.lastname: Lam
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000276:immunology / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism; D004789:Enzyme Activation; D066298:In Vitro Techniques; D021962:Membrane Microdomains / Q000378:metabolism; D051379:Mice; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1 / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology* / Q000276:immunology / Q000378:metabolism*; D014162:Transfection; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C494773:Bak1 protein, mouse; C494827:Bax protein, mouse; C498892:Faim protein, mouse; C539818:Nr4a1 protein, mouse; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D011948:Receptors, Antigen, T-Cell; D011994:Recombinant Proteins; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051057:Proto-Oncogene Proteins c-akt; C506434:Casp9 protein, mouse; D053453:Caspase 9