Serine protease that degrades elastin, fibronectin, laminin, vitronectin, and collagen types I, III, and IV (in vitro). By cleaving and activating receptor F2RL1/PAR-2, enhances endothelial cell barrier function and thus vascular integrity during neutrophil transendothelial migration. May play a role in neutrophil transendothelial migration, probably when associated with CD177. Hydrolysis of proteins, including elastin, by preferential cleavage: -Ala-|-Xaa- > -Val-|-Xaa-. May form dimers. Interacts with CD177; the interaction tethers PRTN3 to the cell surface; the interaction is direct. Interacts with SERPINB1. Localizes predominantly to azurophil granules (primary secretory granules) in neutrophils. Secreted upon neutrophil stimulation by TNF-alpha, lipopolysaccharide (LPS), fMLP and CXCL8/IL8 or during neutrophil transmigration. Following secretion tethered to the cell membrane by CD177. Belongs to the peptidase S1 family. Elastase subfamily.