Involvement of SNAP-23 and syntaxin 6 in human neutrophil exocytosis

To understand the molecular basis of exocytosis in human neutrophils, the r ole of syntaxin 6 and SNAP-23 in neutrophil degranulation was examined. Hum an syntaxin 6 was cloned and identified as a 255-amino acid protein with a carboxyterminal transmembrane region and two coiled-coil domains. Syntaxin 6 was localized mainly in the plasma membrane of human resting neutrophils, whereas SNAP-23 was located primarily in the mobilizable tertiary and spec ific granules. SNAP-23 was translocated to the cell surface, colocalizing w ith syntaxin 6, on neutrophil activation. In vitro binding studies establis hed that SNAP-23 binds to syntaxin 6, Coimmunoprecipitatlon assays indicate d that SNAP-23 interacts with syntaxin 6 in vivo, and this interaction was dramatically increased on neutrophil activation. Antibodies against SNAP-23 inhibited Ca++ and GTP-gamma-S-induced exocytosis of CD67-enriched specifi c granules, but they hardly affected exocytosis of the CD67-enriched azurop hilic granules, when introduced into electropermeabilized neutrophils. Anti -syntaxin 6 antibodies prevented exocytosis of both CD67- and CD63-enriched granules in electropermeabilized neutrophils. These data show that syntaxi n 6 and SNAP-23 are involved in human neutrophil exocytosis, demonstrating that vesicle SNAP receptor-target SNAP receptor (V-SNARE-t-SNARE) interacti ons modulate neutrophil secretion. Syntaxin 6 acts as a target for secretio n of specific and azurophilic granules, whereas SNAP-23 mediates specific g ranule secretion. (Blood. 2000;96: 2574-2583) (C) 2000 by The American Soci ety of Hematology.