title: NAADP activates two-pore channels on T cell cytolytic granules to stimulate exocytosis and killing.
abstract: A cytotoxic T lymphocyte (CTL) kills an infected or tumorigenic cell by Ca(2+)-dependent exocytosis of cytolytic granules at the immunological synapse formed between the two cells. Although inositol 1,4,5-trisphosphate (IP(3))-mediated Ca(2+) release from the endoplasmic reticulum activates the store-operated Ca(2+)-influx pathway that is necessary for exocytosis, it is not a sufficient stimulus. Here we identify the Ca(2+)-mobilizing messenger nicotinic acid adenine dinucleotide phosphate (NAADP) and its recently identified molecular target, two-pore channels (TPCs), as being important for T cell receptor signaling in CTLs. We demonstrate that cytolytic granules are not only reservoirs of cytolytic proteins but are also the acidic Ca(2+) stores mobilized by NAADP via TPC channels on the granules themselves, so that TPCs migrate to the immunological synapse upon CTL activation. Moreover, NAADP activates TPCs to drive exocytosis in a way that is not mimicked by global Ca(2+) signals induced by IP(3) or ionomycin, suggesting that critical, local Ca(2+) nanodomains around TPCs stimulate granule exocytosis. Hence, by virtue of the NAADP/TPC pathway, cytolytic granules generate Ca(2+) signals that lead to their own exocytosis and to cell killing. This study highlights a selective role for NAADP in stimulating exocytosis crucial for immune cell function and may impact on stimulus-secretion coupling in wider cellular contexts.
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK. lianne.davis@pharm.ox.ac.uk
authors.forename: Lianne C
authors.initials: LC
authors.lastname: Davis
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Morgan
authors.forename: Ji-Li
authors.initials: JL
authors.lastname: Chen
authors.forename: Charlotte M
authors.initials: CM
authors.lastname: Snead
authors.forename: Duncan
authors.initials: D
authors.lastname: Bloor-Young
authors.forename: Eugene
authors.initials: E
authors.lastname: Shenderov
authors.forename: Megan N
authors.initials: MN
authors.lastname: Stanton-Humphreys
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Conway
authors.forename: Grant C
authors.initials: GC
authors.lastname: Churchill
authors.forename: John
authors.initials: J
authors.lastname: Parrington
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Cerundolo
authors.forename: Antony
authors.initials: A
authors.lastname: Galione
mesh_terms: D000818:Animals; D003594:Cytoplasmic Granules / Q000378:metabolism; D005089:Exocytosis; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008213:Lymphocyte Activation; D009249:NADP / Q000031:analogs & derivatives* / Q000502:physiology; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
chemical_list: D009249:NADP; C024376:NAADP; D015544:Inositol 1,4,5-Trisphosphate