Function of the t-SNARE SNAP-23 and secretory carrier membrane proteins (SCAMPs) in exocytosis in mast cells

Mast cells acutely respond to allergens and other stimuli by releasing accumulated internal stores of inflammatory mediators and other secretory products by "compound" exocytosis involving massive granule-to-plasma membrane and granule-to-granule fusion. Our recent findings implicate the SNAP receptor (SNARE) protein SNAP-23 and secretory carrier membrane protein 2 (SCAMP2) as regulators of this process. We summarize evidence indicating that stimulus-induced relocation of SNAP-23 from foci in the plasma membrane to putative sites of membrane fusion both at the cell surface and intracellularly between granules is an essential link in coupling stimulation to exocytosis. We also review recent findings showing that the candidate exocytotic SNAREs SNAP-23 and syntaxin 4 colocalize with SCAMPs, especially SCAMP2, and that SCAMP2 is likely to be a partner in the compound exocytotic process.