A LIGAND-FREE, SOLUBLE UROKINASE RECEPTOR IS PRESENT IN THE ASCITIC FLUID FROM PATIENTS WITH OVARIAN-CANCER

We have identified a soluble form of the human urokinase plasminogen a ctivator (uPA) receptor (uPAR) in the ascitic fluids from patients wit h ovarian cancer. After purification of uPAR from the ascitic fluids b y ligand-affinity chromatography (pro-uPA Sepharose), the uPAR was ini tially identified by cross-linking to a radiolabeled amino-terminal fr agment of human uPA. The uPAR purified from the ascitic fluid has no b ound ligand (uPA), as similar amounts can be purified by ligand-affini ty chromatography as by immuno-affinity chromatography. uPAR from asci tic fluids partitions in the water phase after a temperature-dependent phase separation of a detergent extract. It therefore lacks at least the lipid moiety of the glycophospholipid anchor present in cellular-b ound uPARs. It is highly glycosylated and the deglycosylated form has the same ejectrophoretic mobility as previously characterized cellular uPAR from other sources. The immunoreactivity of the purified uPAR fr om the ascitic fluid is indistinguishable from that of characterized u PAR, demonstrated by Western blotting with three different anti-uPAR m onoclonal antibodies. The uPAR was found in 11 of 11 ascitic fluids fr om patients with ovarian cancer and in elevated amounts in the plasma from 2 of 3 patients. The concentration of soluble uPAR in the ascitic fluid was estimated to range between 1 and 10 ng/ml. Human soluble uP AR, derived from the tumor cells, was also found in the ascitic fluid and serum from nude mice xenografted intraperitoneally with three diff erent human ovarian carcinomas.