The function of urokinase and its receptor is essential for cell migration in pathological conditions, as shown by the analysis of knockout mice phenotypes. How a protease of a fibrinolytic pathway can induce migration is not understood and no link between this protease and migration-promoting G protein-coupled receptors has been described. We now show that FPRL1͞LXA4R, a G protein-coupled receptor for a number of polypeptides and for the endogenous lipoxin A4 (LXA4), is the link between urokinase-type plasminogen activator (uPA) and migration as it directly interacts with an activated, soluble, cleaved form of uPA receptor (uPAR) (D2D3 88 -274) to induce chemotaxis. In this article we show that (i) both uPAR and FPRL1͞LXA4R are necessary for the chemotactic activity of uPA whereas FPRL1͞LXA4R is sufficient to mediate D2D388-274-induced cell migration. (ii) Inhibition or desensitization of FPRL1͞LXA4R by antibodies or specific ligands specifically prevents chemotaxis induced by D2D388-274 in THP-1 cells and human peripheral blood monocytes. (iii) Desensitization of FPRL1͞ LXA4R prevents the activation of tyrosine kinase Hck induced by D2D3 88 -274. (iv) D2D388-274 directly binds to FPRL1͞LXA4R and is competed by two specific FPRL1͞LXA4R agonists, the synthetic MMK-1 peptide and a stable analog of LXA4. Thus, a naturally produced cleaved form of uPAR is a unique endogenous chemotactic agonist for FPRL1͞LXA4R receptor and its activity can be antagonized by specific ligands. These results provide the first direct link, to our knowledge, between the fibrinolytic machinery and the inflammatory response, demonstrating that uPA-derived peptide fragments can activate a specific chemotactic receptor. U rokinase plasminogen activator (uPA) is a serine protease that activates plasminogen (Plg) to plasmin and binds to a specific high affinity cell surface receptor, uPAR (CD87) (1). The phenotype of uPA Ϫ/Ϫ and uPAR Ϫ/Ϫ mice is not caused only by the lack of Plg activation. Indeed, Plg Ϫ/Ϫ mice die early with multiple thrombosis and extensive fibrin deposits, whereas the uPA Ϫ/Ϫ and uPAR Ϫ/Ϫ mice live normally, showing rare thrombotic events and occasional fibrin deposits (2). Lack of uPA, however, causes impaired migration of lymphocytes and macrophages to tissue lesions, with impairment of the host defenses, bacterial spreading, and death (3), or resistance to the development of aneurysms in a mouse model (2). Deficient recruitment of peritoneal or lung neutrophils at inflammatory sites in Pseudomonas aeruginosa infection and deficient Mac-1 function in macrophages and neutrophils is also observed in uPARdeficient mice (4, 5).uPA binding to uPAR induces intracellular signaling affecting cell adhesion, migration, and proliferation. uPA binding to uPAR induces chemotaxis in a variety of cells, with activation of tyrosine kinases (Hck, Src), MEK, c-Raf, Tyk-3, PI-3-K, and Rac (1, 5-7).uPAR is a high affinity cell surface receptor for uPA (1), formed by three extracellular domains (D1, D2, and D3), and anchored to the plasma m...

Cyclooxygenase (COX) and lipoxygenase (LO) metabolic pathways are emerging as key regulators of cell proliferation and neo-angiogenesis. COX and LO inhibitors are being investigated as potential anticancer drugs and results from clinical trials seem to be encouraging. In this article we will review evidence of COX-2 and 5-LO involvement in cancer pathobiology, propose a model of integrated control of cell proliferation by these enzymes, and discuss the pharmacologic implications of this model.

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