Domain 1 of the urokinase receptor (uPAR) is required for uPAR-mediated cell binding to vitronectin

In the present paper we have analyzed uPAR-mediated cellular binding to vit ronectin using the murine erythroid progenitor cell line 32D, We show that expression of uPAR in 32D cells promotes cellular binding to vitronectin, b ut fails to support cell spreading, The strength of binding is correlated t o the expression level of uPAR and is strongly stimulated by the presence o f uPAR ligands, Using a truncated variant of uPAR lacking domain 1 and by a ntibody inhibition experiments, we demonstrate that domain 1 plays a crucia l role in uPAR-mediated cellular binding. The failure of the mutant uPAR to promote cellular binding is paralleled by a strong reduction in the affini ty for vitronectin in vitro. (C) 2000 Federation of European Biochemical So cieties.