title: Slp1 and Slp2-a localize to the plasma membrane of CTL and contribute to secretion from the immunological synapse.
abstract: Rab27a is required for polarized secretion of lysosomes from cytotoxic T lymphocytes (CTLs) at the immunological synapse. A series of Rab27a-interacting proteins have been identified; however, only Munc13-4 has been found to be expressed in CTL. In this study, we screened for expression of the synaptotagmin-like proteins (Slps): Slp1/JFC1, Slp2-a/exophilin4, Slp3-a, Slp4/granuphilin, Slp5 and rabphilin in CTL. We found that both Slp1 and Slp2-a are expressed in CTL. Isoforms of Slp2-a in CTL showed variation of the linker region but conserved the C2A and C2B and Slp homology (SHD) domains. Both Slp1 and Slp2-a interact with Rab27a in CTL, and Slp2-a, but not Slp1, is rapidly degraded when Rab27a is absent. Slp2-a contains PEST-like sequences within its linker region, which render it susceptible to degradation. Both Slp1 and Slp2-a localize predominantly to the plasma membrane of both human and mouse CTLs, and we show that Slp2-a can focus tightly at the immunological synapse formed with a target cell. Individual knockouts of either Slp2-a or Slp1 fail to impair CTL-mediated killing of targets; however, overexpression of a dominant-negative construct consisting of the SHD of Slp2-a, which is 56% identical to that of Slp1, reduces target cell death, suggesting that both Slp1 and Slp2-a contribute to secretory lysosome exocytosis from CTL. These results suggest that both Slp1 and Slp2-a may form part of a docking complex, capturing secretory lysosomes at the immunological synapse.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, South Parks Rd, Oxford, OX1 3RE, UK.
authors.forename: Oliver
authors.initials: O
authors.lastname: Holt
authors.forename: Eiko
authors.initials: E
authors.lastname: Kanno
authors.forename: Giovanna
authors.initials: G
authors.lastname: Bossi
authors.forename: Sarah
authors.initials: S
authors.lastname: Booth
authors.forename: Tiziana
authors.initials: T
authors.lastname: Daniele
authors.forename: Alessandra
authors.initials: A
authors.lastname: Santoro
authors.forename: Maurizio
authors.initials: M
authors.lastname: Arico
authors.forename: Chika
authors.initials: C
authors.lastname: Saegusa
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Griffiths
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000235:genetics / Q000276:immunology*; D002154:Calpain / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000276:immunology; D000075745:rab27 GTP-Binding Proteins
chemical_list: D001798:Blood Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C117201:STOML1 protein, human; C406287:STOML2 protein, human; C486043:SYTL2 protein, human; C424133:Sytl1 protein, mouse; C424134:Sytl2 protein, mouse; D033921:Vesicular Transport Proteins; D000075745:rab27 GTP-Binding Proteins; D010447:Peptide Hydrolases; D002154:Calpain; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins