title: Evidence of a role for Munc18-2 and microtubules in mast cell granule exocytosis.
abstract: Compound exocytosis of inflammatory mediators from mast cells requires SNARE and a series of accessory proteins. However, the molecular steps that regulate secretory granule movement and membrane fusion as well as the role of the cytoskeleton are still poorly understood. Here, we report on our investigation of the role of syntaxin-binding Munc18 isoforms and the microtubule network in this process. We found that mast cells express Munc18-2, which interacts with target SNAREs syntaxin 2 or 3, as well as Munc18-3, which interacts with syntaxin 4. Munc18-2 was localised to secretory granules, whereas Munc18-3 was found on the plasma membrane. Increased expression of Munc18-2 and derived peptides containing an interfering effector loop inhibited IgE-triggered exocytosis, while increased expression of Munc18-3 showed no effect. Munc18-2 localisation on granules is polarised; however, upon stimulation Munc18-2 redistributed into forming lamellipodia and persisted on granules that were aligned along microtubules, but was excluded from F-actin ruffles. Disruption of the microtubule network with nocodazole provoked Munc18-2 redistribution and affected mediator release. These findings suggest a role for Munc18-2 and the microtubule network in the regulation of secretory granule dynamics in mast cells.
authors.affiliation: Unité d'Immuno-Allergie, Institut Pasteur, Paris, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Martin-Verdeaux
authors.forename: Isabel
authors.initials: I
authors.lastname: Pombo
authors.forename: Bruno
authors.initials: B
authors.lastname: Iannascoli
authors.forename: Michèle
authors.initials: M
authors.lastname: Roa
authors.forename: Nadine
authors.initials: N
authors.lastname: Varin-Blank
authors.forename: Juan
authors.initials: J
authors.lastname: Rivera
authors.forename: Ulrich
authors.initials: U
authors.lastname: Blank
mesh_terms: D000199:Actins / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D022081:Cell Surface Extensions / Q000187:drug effects / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D007073:Immunoglobulin E / Q000378:metabolism / Q000494:pharmacology; D007249:Inflammation / Q000378:metabolism* / Q000503:physiopathology; D008407:Mast Cells / Q000378:metabolism*; D008561:Membrane Fusion / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008870:Microtubules / Q000378:metabolism*; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D011485:Protein Binding / Q000502:physiology; D020033:Protein Isoforms / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D011506:Proteins / Q000378:metabolism*; D011554:Pseudopodia / Q000187:drug effects / Q000378:metabolism; D050765:Qa-SNARE Proteins; D051381:Rats; D022142:Secretory Vesicles / Q000378:metabolism*; D033921:Vesicular Transport Proteins
chemical_list: D000199:Actins; D008565:Membrane Proteins; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D011506:Proteins; D050765:Qa-SNARE Proteins; C497941:Stxbp2 protein, mouse; C497942:Stxbp2 protein, rat; C497943:Stxbp3 protein, mouse; D033921:Vesicular Transport Proteins; D007073:Immunoglobulin E