title: Surface cytotoxic T lymphocyte-associated antigen 4 partitions within lipid rafts and relocates to the immunological synapse under conditions of inhibition of T cell activation.
abstract: T cell activation through the T cell receptor (TCR) involves partitioning of receptors into discrete membrane compartments known as lipid rafts, and the formation of an immunological synapse (IS) between the T cell and antigen-presenting cell (APC). Compartmentalization of negative regulators of T cell activation such as cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) is unknown. Recent crystal structures of B7-ligated CTLA-4 suggest that it may form lattices within the IS which could explain the mechanism of action of this molecule. Here, we show that after T cell stimulation, CTLA-4 coclusters with the TCR and the lipid raft ganglioside GM1 within the IS. Using subcellular fractionation, we show that most lipid raft-associated CTLA-4 is on the T cell surface. Such compartmentalization is dependent on the cytoplasmic tail of CTLA-4 and can be forced with a glycosylphosphatidylinositol-anchor in CTLA-4. The level of CTLA-4 within lipid rafts increases under conditions of APC-dependent TCR-CTLA-4 coligation and T cell inactivation. However, raft localization, although necessary for inhibition of T cell activation, is not sufficient for CTLA-4-mediated negative signaling. These data demonstrate that CTLA-4 within lipid rafts migrates to the IS where it can potentially form lattice structures and inhibit T cell activation.
authors.affiliation: The Biotherapeutics and Transplantation and Immunobiology Groups, The John P. Robarts Research Institute, and The Departments of Microbiology and Immunology, and Medicine, The University of Western Ontario, London, Ontario N6A 5K8, Canada.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Darlington
authors.forename: Miren L
authors.initials: ML
authors.lastname: Baroja
authors.forename: Thu A
authors.initials: TA
authors.lastname: Chau
authors.forename: Eric
authors.initials: E
authors.lastname: Siu
authors.forename: Vincent
authors.initials: V
authors.lastname: Ling
authors.forename: Beatriz M
authors.initials: BM
authors.lastname: Carreno
authors.forename: Joaquín
authors.initials: J
authors.lastname: Madrenas
mesh_terms: D000069594:Abatacept; D000938:Antigen-Presenting Cells / Q000276:immunology; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism*; D060908:CTLA-4 Antigen; D005434:Flow Cytometry; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D006801:Humans; D018796:Immunoconjugates; D007376:Interleukin-2 / Q000037:antagonists & inhibitors; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism*; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D021381:Protein Transport; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D017261:Glycosylphosphatidylinositols; D018796:Immunoconjugates; D007376:Interleukin-2; D011948:Receptors, Antigen, T-Cell; D000069594:Abatacept