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 FPRL1/LXA4R, 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 FPRL1/LXA4R are necessary for the chemotactic activity of uPA whereas FPRL1/LXA4R is sufficient to mediate D2D3 _88–274 -induced cell migration. ( ii ) Inhibition or desensitization of FPRL1/LXA4R by antibodies or specific ligands specifically prevents chemotaxis induced by D2D3 _88–274 in THP-1 cells and human peripheral blood monocytes. ( iii ) Desensitization of FPRL1/LXA4R prevents the activation of tyrosine kinase Hck induced by D2D3 _88–274 . ( iv ) D2D3 _88–274 directly binds to FPRL1/LXA4R and is competed by two specific FPRL1/LXA4R 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 FPRL1/LXA4R 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.

Eicosanoids derived from lipoxygenase (LO)-catalyzed reactions play important roles in pulmonary inflammation. Here, we examined formation of LO-derived products by human alveolar macrophages (HAM). HAM converted [1-14C]-arachidonic acid to a product carrying 14C-radiolabel that was identified as 15(S)-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid (15-HETE) by physical methods. 15-LO mRNA was demonstrated in HAM by reverse transcription-polymerase chain reaction. Incubation of HAM for 3 d with interleukin 4(IL-4) before exposure to [1-14C]arachidonic acid led to both increased mRNA for 15-LO and a 4-fold increase in 15-HETE formation. In contrast, 5(S)-hydroxy-6-trans-8,11,14-cis-eicosatetraenoic acid generation was not significantly altered by prior exposure to IL-4. Additionally, lipoxins (LXA4 and LXB4) were detected from endogenous substrate, albeit in lower levels than leukotriene B4 (LTB4), in electrochemical detection/high performance liquid chromatography profiles from HAM incubated in the presence and absence of the chemotactic peptide (FMLP) or the calcium ionophore (A23187). Exposure of HAM to leukotriene A4 (LTA4) resulted in a 2-fold increase in LXA4 and 10-fold increase in LXB4. These results demonstrate the presence of 15-LO mRNA and enzyme activity in HAM and the production of LXA4 and LXB4 by these cells. Along with 5-LO-derived products, the biosynthesis of 15-LO-derived eicosanoids by HAM may also be relevant in modulating inflammatory responses in the lung.

Background —Hypercholesterolemia is considered a major risk factor for the development of atherosclerosis. Enhanced lipid peroxidation and persistent platelet activation can be observed in vivo in hypercholesterolemic patients and may have pathophysiological implications in the occurrence of cardiovascular events. P-selectin may play an important role in the pathogenesis of multicellular events, including atherosclerosis. We studied the impact of hypercholesterolemia and oxidative stress on plasma levels of P-selectin. Methods and Results —Plasma levels of P-selectin were measured by means of an enzyme immunoassay in 20 hypercholesterolemic patients with no clinical evidence of cardiovascular disease and in 20 sex- and age-matched normocholesterolemic subjects. Hypercholesterolemic patients had higher levels of P-selectin compared with that of control subjects (98±61 versus 56±14 ng/mL; P =.001). They also displayed increased von Willebrand Factor (vWF) levels (176±22 versus 119±12%; P =.0001). A direct correlation was observed between P-selectin and LDL cholesterol levels (ρ=.453). Administration of vitamin E (600 mg/d for 2 weeks) to hypercholesterolemic patients significantly reduced plasma P-selectin (40%), and an inverse correlation was observed between vitamin E and P-selectin plasma levels (ρ=−.446). Conclusions —Hypercholesterolemia is associated with elevated plasmatic P-selectin. Altered oxidative processes leading to endothelial dysfunction and persistent platelet activation may contribute to increased soluble P-selectin levels. P-selectin may be proposed as a marker of endothelial dysfunction in hypercholesterolemic patients.