Plays a role in formation of mast cell secretory granules and mediates storage of various compounds in secretory vesicles. Required for storage of some proteases in both connective tissue and mucosal mast cells and for storage of granzyme B in T-lymphocytes. Plays a role in localizing neutrophil elastase in azurophil granules of neutrophils. Mediates processing of MMP2. Plays a role in cytotoxic cell granule-mediated apoptosis by forming a complex with granzyme B which is delivered to cells by perforin to induce apoptosis. Regulates the secretion of TNF-alpha and may also regulate protease secretion. Inhibits bone mineralization (By similarity). Binds to activated CD44 and to GZMB. Found in mast cell granules and in cytoplasmic granules of cytolytic T-lymphocytes from where it is secreted upon cell activation. Secreted constitutively by endothelial cells and macrophages. Located to Golgi apparatus during neutrophil differentiation (By similarity). O-glycosylated; contains chondroitin sulfate and heparan sulfate. Belongs to the serglycin family.