title: Recruitment of the actin-binding protein HIP-55 to the immunological synapse regulates T cell receptor signaling and endocytosis.
abstract: Actin cytoskeleton dynamics critically regulate T cell activation. We found that the cytoplasmic adaptor HIP-55, a Src/Syk-kinases substrate and member of the drebrin/Abp1 family of actin-binding proteins, localized to the T cell-antigen-presenting cell (APC) contact site in an antigen-dependent manner. Using green fluorescent protein fusion proteins, both Src homology 3 (SH3) and actin binding domains were found necessary for recruitment at the T cell-APC interface. HIP-55 was not implicated in conjugate formation and actin polymerization but regulated distal signaling events through binding and activation of hematopoietic progenitor kinase 1 (HPK1), a germinal center kinase (GCK) family kinase involved in negative signaling in T cells. Using RNA interference and overexpression experiments, the HIP-55-HPK1 complex was found to negatively regulate nuclear factor of activated T cell (NFAT) activation by the T cell antigen receptor. Moreover, we show that HIP-55, which partly co-localized with early endocytic compartments, promoted both basal and ligand-dependent T cell receptor (TCR) down-modulation, resulting in a decreased TCR expression. SH3 and actin-depolymerizing factor homology domains were required for this function. As controls, the expression of CD28 and the glycosylphosphatidylinositol-linked protein CD59 was not affected by HIP-55 overexpression. These results suggest that, in addition to binding to HPK1, HIP-55 might negatively regulate TCR signaling through down-regulation of TCR expression. Our findings show that HIP-55 is a key novel component of the immunological synapse that modulates T cell activation by connecting actin cytoskeleton and TCRs to gene activation and endocytic processes.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale Unité 576, Hôpital de l'Archet, Cedex 3, 06202 Nice, France. deckert@unice.fr
authors.forename: Séverine
authors.initials: S
authors.lastname: Le Bras
authors.forename: Isabelle
authors.initials: I
authors.lastname: Foucault
authors.forename: Arnaud
authors.initials: A
authors.lastname: Foussat
authors.forename: Chrystelle
authors.initials: C
authors.lastname: Brignone
authors.forename: Oreste
authors.initials: O
authors.lastname: Acuto
authors.forename: Marcel
authors.initials: M
authors.lastname: Deckert
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D018106:CD28 Antigens / Q000096:biosynthesis; D017252:CD3 Complex / Q000096:biosynthesis; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D018957:CD59 Antigens / Q000096:biosynthesis; D002469:Cell Separation; D003599:Cytoskeleton / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D004705:Endocytosis / Q000502:physiology*; D004789:Enzyme Activation; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins; D006801:Humans; D015151:Immunoblotting; D007376:Interleukin-2 / Q000378:metabolism; D019169:Jurkat Cells; D008024:Ligands; D008156:Luciferases / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D008213:Lymphocyte Activation; D051379:Mice; D008840:Microfilament Proteins / Q000096:biosynthesis* / Q000737:chemistry*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D010957:Plasmids / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013569:Synapses / Q000378:metabolism*; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D018909:src Homology Domains
chemical_list: D000199:Actins; D018106:CD28 Antigens; D017252:CD3 Complex; D018957:CD59 Antigens; C117063:DBNL protein, human; D004268:DNA-Binding Proteins; C485512:Dbnl protein, mouse; D007376:Interleukin-2; D008024:Ligands; D008164:Luminescent Proteins; D008840:Microfilament Proteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D011948:Receptors, Antigen, T-Cell; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D008156:Luciferases; C102102:hematopoietic progenitor kinase 1; D017346:Protein Serine-Threonine Kinases