Serine protease that degrades elastin, fibronectin, laminin, vitronectin, and collagen types I, III, and IV (in vitro) (PubMed:3198760, PubMed:2033050, PubMed:28240246). By cleaving and activating receptor F2RL1/PAR-2, enhances endothelial cell barrier function and thus vascular integrity during neutrophil transendothelial migration (PubMed:23202369). May play a role in neutrophil transendothelial migration, probably when associated with CD177 (PubMed:22266279). Hydrolysis of proteins, including elastin, by preferential cleavage: -Ala-|-Xaa- > -Val-|-Xaa-. Inhibited by phenylmethanesulfonyl fluoride (PMSF) and diisopropyl fluorophosphate (DFP). Optimum pH is 7.4. May form dimers (PubMed:28240246). Interacts with CD177; the interaction tethers PRTN3 to the cell surface; the interaction is direct (PubMed:17244676, PubMed:28240246). Interacts with SERPINB1 (PubMed:30692621). Localizes predominantly to azurophil granules (primary secretory granules) in neutrophils (PubMed:2033050, PubMed:3198760, PubMed:7897245, PubMed:18462208). Secreted upon neutrophil stimulation by TNF-alpha, lipopolysaccharide (LPS), fMLP and CXCL8/IL8 or during neutrophil transmigration (PubMed:22266279, PubMed:28240246). Following secretion tethered to the cell membrane by CD177 (PubMed:18462208, PubMed:22266279). Expressed in polymorphonuclear leukocytes (at protein level) (PubMed:2033050, PubMed:7897245, PubMed:3198760). Expressed in neutrophils (at protein level) (PubMed:28240246, PubMed:18462208, PubMed:21193407, PubMed:22266279, PubMed:17244676). Expressed in differentiating neutrophils (PubMed:18462208). Induced during CSF3/G-CSF-mediated neutrophil differentiation. Is the major autoantigen in anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (Wegener's granulomatosis) (PubMed:2377228, PubMed:2679910). This complex, systemic disease is characterized by granulomatous inflammation with necrotizing lesions in the respiratory tract, glomerulonephritis, vasculitis, and anti-neutrophil cytoplasmatic autoantibodies detected in patient sera (PubMed:2377228, PubMed:2679910). PRTN3 causes emphysema when administered by tracheal insufflation to hamsters (PubMed:3198760). Belongs to the peptidase S1 family. Elastase subfamily. Proteinase 3 entry