Submitted February 21, 2008
Accepted August 7, 2008
A newly identified isoform of Slp2a associates with Rab27a in cytotoxic T cells and participates to cytotoxic granule secretion
Gael Menasche, Mickael M. Menager, Juliette M. Lefebvre, Einat Deutsch, Rafika Athman, Nathalie Lambert, Nizar Mahlaoui, Magali Court, Jerome Garin, Alain Fischer, and Genevieve de Saint Basile*
Institut National de la Sante et de la Recherche Medicale, Unite U768, Laboratoire du Developpement Normal et Pathologique de Systeme Immunitaire, Paris, France
Universite Paris Descartes, Faculte de Medecine Rene Descartes, Institut Federatif de Recherche Necker Enfants-Malades (IFR95), Paris, France
Assistance Publique-Hopitaux de Paris, Hopital Necker Enfants-Malades, Unite d'Immunologie-Hematologie Pediatrique, Paris, France
Institut National de la Sante et de la Recherche Medicale, Unite U880, Grenoble, France
Universite Joseph Fourier, Grenoble, France
* Corresponding author; email: sbasile{at}necker.fr.
Cytotoxic T lymphocytes (CTLs) and natural killer cells help control infections and tumours via a killing activity which is mediated by the release of cytotoxic granules. Granule secretion at the synapse formed between the CTL and the target cell leads to apoptosis of the latter. This process involves polarization of the CTL's secretory machinery and cytotoxic granules. The small GTPase Rab27a and the hMunc13-4 protein have been shown to be required for both granule maturation and granule docking and priming at the immunological synapse. By using a tandem affinity purification technique, we identified a previously unknown hematopoietic form of Slp2a (Slp2a-hem) and determined that it is a specific effector of the active form of Rab27a. This interaction occurs in vivo in primary CTLs. We have shown that (i) Rab27a recruits Slp2a-hem on vesicular structures in peripheral CTLs and (ii) following CTL-target cell conjugate formation, the Slp2a-hem/Rab27a complex colocalizes with perforin-containing granules at the immunological synapse, where it binds to the plasma membrane through its C2 domains. The overexpression of a dominant-negative form of Slp2a-hem markedly impaired exocytosis of cytotoxic granules - indicating that Slp2a is required for cytotoxic granule docking at the immunological synapse.
