Soluble urokinase receptor released from human carcinoma cells: a plasma parameter for xenograft tumour studies

The urokinase plasminogen activator receptor (uPAR) plays a critical role in urokinase-mediated plasminogen activation and thereby in the process leading to invasion and metastasis. Soluble urokinase receptor (suPAR) is released from tumours, and in cancer patients the blood level of soluble receptor is increased. Using an enzyme-linked, immunosorbent assay (ELISA)-specific for the human urokinase receptor, release of soluble receptor was measured in cultures of human breast carcinoma cells, in tumour extracts and in plasma from mice with xenografted human tumours. Soluble human urokinase receptor (shuPAR) was released into culture supernatant during the growth of the human breast cancer cell line MDA-MB-231 BAG, and the level of shuPAR in conditioned medium determined by ELISA was a linear function of both viable cell number and time of incubation. Western blotting showed that the form of shuPAR measured by ELISA in conditioned medium consisted virtually exclusively of the three-domain full-length protein, while uPAR in cell lysates consisted of full-length uPAR as well as the domains (2+3) cleavage product. shuPAR was also released into the plasma of nude mice during growth of MDA-MB-231 BAG, MDA-MB-435 BAG and HCT 116 cells as subcutaneously xenografted tumours. Western blotting demonstrated that the shuPAR released from the xenografted human tumours into plasma consisted of the three-domain full-length protein, despite the finding of some cleaved uPAR in detergent extracts of tumour tissue. The levels of shuPAR determined by ELISA in the plasma of host mice during the growth of xenografted cell lines were highly correlated with tumour volume. © 1999 Cancer Research Campaig

Plasma Levels of Intact and Cleaved Urokinase Receptor Decrease in HIV-1-Infected Patients Initiating Highly Active Antiretroviral Therapy

Elevated blood levels of soluble urokinase receptor (suPAR) measured by ELISA decrease in human immunodeficiency virus-1 (HIV-1)-infected patients initiating highly active antiretroviral therapy (HAART). As the suPAR ELISA measures both three- and two-domain suPAR [suPAR(I-III), suPAR(II-III)] and suPAR(I-III)-ligand complexes, the amount by which the individual suPAR forms (suPAR(I-III), suPAR(II-III) and one-domain suPAR [suPAR(I)]) decrease in plasma in HIV-1-infected patients initiating HAART is unknown. Consequently, the objective of this study was to investigate HAART-induced changes in the individual plasma suPAR forms in HIV-1-infected patients. Plasma suPAR was measured by three time-resolved fluorescence immunoassays detecting suPAR(I-III), suPAR(I-III) + suPAR(II-III) and suPAR(I) in 29 treatment-naïve HIV-1-infected patients followed annually for 5 years after initiation of HAART and in 20 age- and gender-matched healthy individuals. In addition, plasma levels of the following inflammatory markers were also investigated: soluble tumour necrosis factor receptor (sTNFr)-II, TNF-alpha, interleukins (IL)-10, IL-6, IL-4, IL-2 and interferon (IFN)-gamma. In HIV-1-infected patients, plasma suPAR(I-III), suPAR(II-III) and suPAR(I) decreased within the first treatment year (all P &lt; 0.05) and suPAR(I-III) and suPAR(II-III) remained above normal throughout follow-up (both P &lt; 0.05). Plasma sTNFrII, IL-6, IFN-gamma and IL-10 also decreased during HAART (all P &lt; 0.05). In HIV-1-infected patients, sTNFrII correlated with all suPAR forms before (all P &lt; 0.01) and after 5 years HAART (all P &lt; 0.001), whereas sTNFrII and suPAR did not correlate in healthy individuals. Intact and cleaved plasma suPAR decreased in HIV-1-infected patients initiating HAART but remained above normal. The positive correlation with sTNFrII suggests that the individual plasma suPAR forms are linked to immune activation in HIV-1 infection.</p