QUANTITATION OF THE RECEPTOR FOR UROKINASE PLASMINOGEN-ACTIVATOR BY ENZYME-LINKED-IMMUNOSORBENT-ASSAY

Binding of the urokinase plasminogen activator (uPA) to a specific cel l surface receptor (uPAR) plays a crucial role in proteolysis during t issue remodelling and cancer invasion. An immunosorbent assay for the quantitation of uPAR has now been developed. This assay is based on tw o monoclonal antibodies recognizing the non-ligand binding part of thi s receptor, and it detects both free and occupied uPAR, in contrast to ligand-binding assays used previously. In a variant of the assay, the occupied fraction of uPAR is selectively detected with a uPA antibody . To be used as a standard, a soluble variant of uPAR, suPAR, has been constructed by recombinant technique and the protein content of a pur ified suPAR standard preparation was determined by amino acid composit ion analysis. The sensitivity of the assay (0.6 ng uPAR/ml) is strong enough to measure uPAR in extracts of cultured cells and cancer tissue . Recent studies have shown that a high uPA level in tumor extracts is in some cancers associated with poor prognosis. The present assay wil l now allow similar prognostic studies of uPAR levels.