title: Involvement of Munc18 isoforms in the regulation of granule exocytosis in neutrophils.
abstract: Human neutrophil granule exocytosis mobilizes a complex set of secretory granules. This involves different combinations of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins to facilitate membrane fusion. The control mechanisms governing the late fusion steps are still poorly understood. Here, we have analyzed SNARE-interacting Sec1/Munc18 (SM) family members. We found that human neutrophils express Munc18-2 and Munc18-3 isoforms and that Munc18-2 interacts with the target-SNARE syntaxin 3. Munc18-2 was associated preferentially with primary granules but could also be found with secondary and tertiary granules, while Munc18-3 was majorily associated with secondary and tertiary granules. Ultrastructural analysis showed that both Munc18-2 and Munc18-3 were often located in close proximity to their respective SNARE-binding partners syntaxin 3 and syntaxin 4. Both isoforms were also found in plasma membrane fractions and in the cytosol, where they associate with cytoskeletal elements. Upon stimulation, Munc18-2 and Munc18-3 redistributed and became enriched on granules and in the plasma membrane. Munc18-2 primary granule exocytosis can be blocked by introduction of Munc18-2-specific antibodies indicating a crucial role in primary granule fusion. Our results suggest that Munc18-2 acts as a regulator of primary granule exocytosis, while Munc18-3 may preferentially regulate the fusion of secondary granules.
authors.affiliation: Inserm U699, Paris, F-75018, France.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Brochetta
authors.forename: Francesca
authors.initials: F
authors.lastname: Vita
authors.forename: Neeraj
authors.initials: N
authors.lastname: Tiwari
authors.forename: Lisa
authors.initials: L
authors.lastname: Scandiuzzi
authors.forename: Maria Rosa
authors.initials: MR
authors.lastname: Soranzo
authors.forename: Claudine
authors.initials: C
authors.lastname: Guérin-Marchand
authors.forename: Giuliano
authors.initials: G
authors.lastname: Zabucchi
authors.forename: Ulrich
authors.initials: U
authors.lastname: Blank
mesh_terms: D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism*; D005089:Exocytosis; D006801:Humans; D046529:Microscopy, Electron, Transmission; D051938:Munc18 Proteins / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D009504:Neutrophils / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport
chemical_list: D051938:Munc18 Proteins; D020033:Protein Isoforms