Mediator release from mast cells (MC) is a crucial step in allergic and non-allergic inflammatory disorders. However, the final events in response to activation leading to membrane fusion and thereby facilitating degranulation have hitherto not been analyzed in human MC. Soluble N-ethyl-maleimide-sensitive factor attachment protein receptors (SNARE) represent a highly conserved family of proteins that have been shown to mediate intracellular membrane fusion events. Here, we show that mature MC isolated from human intestinal tissue express soluble N-ethylmaleide sensitive factor attachment protein (SNAP)-23, Syntaxin (STX)-1B, STX-2, STX-3, STX-4, and STX-6 but not SNAP-25. Furthermore, we found that primary human MC express substantial amounts of vesicle associated membrane protein (VAMP)-3, VAMP-7 and VAMP-8 and, in contrast to previous reports about rodent MC, only low levels of VAMP-2. Furthermore, VAMP-7 and VAMP-8 were found to translocate to the plasma membrane and interact with SNAP-23 and STX-4 upon activation. Inhibition of SNAP-23, STX-4, VAMP-7 or VAMP-8, but not VAMP-2 or VAMP-3, resulted in a markedly reduced highaffinity IgE receptor-mediated histamine release. In summary, our data show that mature human MC express a specific pattern of SNARE and that VAMP-7 and VAMP-8, but not VAMP-2, are required for rapid degranulation.Supporting Information for this article is available at http://www.wiley-vch.de/contents/jc_2040/2008/37634_s.pdf IntroductionMast cells (MC) are well known to play a key role in allergic and a number of non-allergic inflammatory conditions. They are capable of releasing a number of pre-stored or de novo synthesized proinflammatory ** The first two authors contributed equally to this work. The role of SNARE-proteins in human MC is still largely elusive. However, experiments conducted in rodent basophilic leukemia cells (RBL-2H3), a widely used MC cell line, have provided solid data, that members of the SNARE-family are indeed specifically expressed in different compartments of these cells and that they are crucially involved in mediator secretion [16][17][18][19][20]. These reports attribute a key role in exocytotic events in MC to the t-SNARE SNAP-23 [21]. SNAP-23 represents the ubiquitously expressed counterpart of its neuronal isoform and is found in tissues throughout the body [21,23,24]. Furthermore, SNAP-23 has been demonstrated to mediate exocytosis in other immune cells as well [12,25,26]. It forms a stable SNARE complex together with a syntaxin (STX), another t-SNARE. Various STX-isoforms have been identified in myeloid cells [12,27,28]. Finally, docking and fusion events at the plasma membrane require v-SNARE, namely vesicle-associated membrane proteins (VAMP). Different VAMP isoforms seem to be specifically involved in mediating the various intracellular trafficking events. VAMP-1 and VAMP-2, also called synaptobrevins, have been implicated in regulated exocytosis in neurons [29] and non-neuronal cells [30], while VAMP-3, or cellubrevin, was attributed a role in consti...

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