UROKINASE PLASMINOGEN-ACTIVATOR RECEPTOR, BETA-2-INTEGRINS, AND SRC-KINASES WITHIN A SINGLE RECEPTOR COMPLEX OF HUMAN MONOCYTES

The glycosylphosphatidylinositol (GPI)-anchored membrane protein uroki nase plasminogen activator-receptor (uPA-R; CD87) is one of the key mo lecules involved in migration of leukocytes and tumor cells. uPA bound to uPA-R provides the cell proteolytic potential used for degradation of extracellular matrix. uPA-R is also involved in induction of cell adhesion and chemotaxis. Here, we provide a molecular explanation for these uPA-R-related cellular events. By size fractionation of monocyte lysate and affinity isolation on its natural ligand uPA, we demonstra te uPA-R as a component of a receptor complex of relatively large size . Reprecipitation and immunoblotting techniques allowed us to detect t he protein tyrosine kinases (PTKs) p60(fyn), p53/56(lyn), p58/64(hck), and p59(fgr) as components of this ''uPA-R complex'' Activation of mo nocytes even with enzymatically inactivated uPA resulted in induction of tyrosine phosphorylation, suggesting modulation of uPA-R-associated PTKs upon ligand binding. In spite of their presence in large complex es, we did not find the GPI-linked proteins CD14, CD58, and CD59 in th e uPA-R complex, which indicates the presence of different receptor do mains containing GPI-linked proteins in monocytes. However, we identif ied the leukocyte integrins LFA-1 and CR3 as components of the uPA-R c omplex as indicated by coisolation of these molecules, as well as by c ocapping and comodulation of uPA-R and leukocyte integrins on the mono cyte surface. The assemblage of uPA-R, PTKs and membrane spanning beta 2-integrins in one receptor complex indicates functional cooperation. In regard to the involvement of these molecules in pericellular prote olysis, signal transduction, as well as adhesion and chemotactic movem ent, we suggest uPA-R complex as a potential cellular device for cell migration.