Acts as a receptor for urokinase plasminogen activator. Plays a role in localizing and promoting plasmin formation. Mediates the proteolysis-independent signal transduction activation effects of U-PA. It is subject to negative-feedback regulation by U-PA which cleaves it into an inactive form (By similarity). Monomer (Probable). Interacts (via the UPAR/Ly6 domains) with SRPX2. Interacts with MRC2. Interacts with FAP (seprase); the interaction occurs at the cell surface of invadopodia membrane. Interacts with SORL1 (via N-terminal ectodomain); this interaction decreases PLAUR internalization (By similarity). The ternary complex composed of PLAUR-PLAU-SERPINE1 also interacts with SORL1 (By similarity). Colocalized with FAP (seprase) preferentially at the cell surface of invadopodia membrane in a cytoskeleton-, integrin- and vitronectin-dependent manner.