Slp1 and Slp2-a localize to the plasma membrane of CTL and contribute to secretion from the immunological synapse

Traffic. 2008 Apr;9(4):446-57. doi: 10.1111/j.1600-0854.2008.00714.x. Epub 2008 Feb 11.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Proteins / genetics
  • Blood Proteins / immunology*
  • Calpain / genetics
  • Calpain / metabolism
  • Cell Membrane / metabolism*
  • Humans
  • Membrane Proteins / genetics
  • Membrane Proteins / immunology*
  • Mice
  • Mice, Knockout
  • Nerve Tissue Proteins
  • Peptide Hydrolases / genetics
  • Peptide Hydrolases / metabolism
  • Protein Isoforms / genetics
  • Protein Isoforms / immunology
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • T-Lymphocytes, Cytotoxic / immunology*
  • Vesicular Transport Proteins
  • rab GTP-Binding Proteins / genetics
  • rab GTP-Binding Proteins / immunology
  • rab27 GTP-Binding Proteins

Substances

  • Blood Proteins
  • Membrane Proteins
  • Nerve Tissue Proteins
  • Protein Isoforms
  • Recombinant Fusion Proteins
  • STOML1 protein, human
  • STOML2 protein, human
  • SYTL2 protein, human
  • Sytl1 protein, mouse
  • Sytl2 protein, mouse
  • Vesicular Transport Proteins
  • rab27 GTP-Binding Proteins
  • Peptide Hydrolases
  • Calpain
  • Rab27a protein, mouse
  • rab GTP-Binding Proteins