Convergence of the adhesive and fibrinolytic systems: recognition of urokinase by integrin αMβ2 as well as by the urokinase receptor regulates cell adhesion and migration

Abstract

Previous studies demonstrated that integrin ␣ M ␤ 2 (CD11b/18, Mac-1) forms a physical complex with the urokinase-type plasminogen activator receptor (uPAR/ CD87) on leukocytes. In this study, we used human peripheral blood neutrophils and transfected cells expressing ␣ M ␤ 2 , uPAR, or both receptors to show that the integrin can directly interact with urokinase (uPA). We demonstrate that ␣ M ␤ 2 supported adhesion and migration of these cells to uPA, and, in each case, blockade of ␣ M ␤ 2 suppressed the response. Within uPA, both the kringle and proteolytic domains are recognized by ␣ M ␤ 2 , which are distinct from the growth factor domain that binds to uPAR. Within the ␣ M subunit of the integrin, the I domain interacts with uPA, which is distinct from the region that interacts with uPAR.

Species-specific urokinase receptor ligands reduce glioma growth and increase survival primarily by an antiangiogenesis mechanism

“…46 More importantly, the kringle domain of uPA has been shown to directly interact with the I-domain of aMb2, to create trimolecular interactions between uPA, uPAR, and the integrin, with uPA as the bridging ligand. 47 Our observations that the uPA1-48 peptides block ATF-stimulated migration for endothelial and tumor cells suggest that these phenomena are more widespread. The possibility that the uPA kringle domain may also interact with I-like domains of other integrins known to be important for glioma and endothelial cell proliferation should not be discounted, in the light of the recent elucidation of the structure of the avb3 integrin.…”

“…11 The increasing recognition of the role of the uPA kringle domain in integrin-mediated processes and the antagonism of these effects by the uPA1-48 peptides is likely to play a significant part in the effects seen. 47 Finally, inhibition of uPAR recycling by prevention of uPA:PAI-1 complex clearance via LRP and related receptors may play a role. 55 Further dissection of these effects will be enabled by the availability of the immunodeficient uPA-knock-out mice, 14 for example, by determining whether tumor growth is affected in these mice, and also whether treatment with PEGhm1-48 or related molecules still has an effect in the absence of host uPA.…”

Distinct Roles for the α and β Subunits in the Functions of Integrin αMβ2

“…The cell lines obtained were maintained in Dulbecco's modified Eagle's medium/nutrient mixture F-12 supplemented with 10% fetal bovine serum, 100 units/ml penicillin, 100 g/ml streptomycin, 2 M L-glutamine, and 2 mg/ml neomycin (all from Invitrogen) (33). For selected experiments, a HEK cell line expressing both ␣ M ␤ 2 and the urokinase-type plasminogen activator receptor was used; these cells have been described previously (46).…”

Conformational Regulation of Urokinase Receptor Function

“…The molecular basis underlying this dependence is, however, still controversial, and several models, including uPAR dimerization (9,19,26), direct interactions with integrins (27)(28)(29), or other adaptor proteins (30,31) have been advocated. In the present study, we have revisited this molecular interplay guided by the structural data obtained recently on this ternary complex (17,18), and we now present independent functional data pointing to a crucial role of the molecular flexibility in uPAR.…”