A critical role for vesicle-associated membrane protein-7 in exocytosis from human eosinophils and neutrophils

Abstract

Background: Granulocyte exocytosis is proposed to be critically dependent on the interaction of soluble N‐ethylmaleimide‐sensitive factor attachment protein (SNAP) receptors (SNAREs) located on granules/vesicles (v‐SNAREs) and plasma membrane (t‐SNAREs). Previous studies indicated that the v‐SNARE, vesicle‐associated membrane protein (VAMP)‐2, as well as t‐SNAREs (SNAP‐23, syntaxin‐4 and ‐6) are implicated in exocytosis from human granulocytes. Vesicle‐associated membrane proteins‐7 and ‐8 have been implicated in endosome/lysosome trafficking, however, their role in granulocyte exocytosis remains obscure. Objective: We sought to investigate the expression and functional role of SNARE isoforms in the secretion of different granule‐derived mediators in human eosinophils and neutrophils. Methods: The expression of SNAREs was determined by subcellular fractionation and flow cytometry. SNARE‐specific antibodies were examined for their ability to impair mediator release from permeabilized eosinophils and neutrophils. Results: Vesicle‐associated membrane proteins‐7 and ‐8 were localized to granule and membrane‐enriched fractions in eosinophils and neutrophils, whereas syntaxin‐6 was not detectable. In permeabilized cells, anti‐VAMP‐7, but not anti‐VAMP‐8, antibody impaired the secretion of all mediators examined (in eosinophils, eosinophil peroxidase and eosinophil‐derived neurotoxin; in neutrophils, myeloperoxidase, lactoferrin and matrix metalloprotease‐9) in a dose‐dependent manner. In contrast, anti‐VAMP‐2 modestly and selectively impaired secretion from small granules and vesicles. Syntaxin‐4, but not syntaxin‐6, was found to interact with SNAP‐23 and was partially involved in mediator secretion from multiple compartments. Conclusion: Our observations indicate for the first time a critical role for VAMP‐7 in both eosinophil and neutrophil mediator release.