Plasmin and plasminogen activator inhibitor type 1 promote cellular motility by regulating the interaction between the urokinase receptor and vitronectin

The urokinase receptor (uPAR) coordinates plasmin-mediated cell-surface proteolysis and promotes cellular adhesion via a binding site for vitronectin on uPAR, Because vitronectin also binds plasminogen activator inhibitor type 1 (PAI-1), and plasmin cleavage of vitronectin reduces PAI-1 binding, we explored the effects of plasmin and PAI-1 on the interaction between uPAR and vitronectin. PAI-1 blocked cellular binding of and adhesion to vitronectin by over 80% (IC50 similar to 5 nM), promoted detachment of uPAR-bearing cells from vitronectin, and increased cellular migration on vitronectin, Limited cleavage of vitronectin by plasmin also abolished cellular binding and adhesion and induced cellular detachment, A series of peptides surrounding a plasmin cleavage site (arginine 361) near the carboxy-terminal end of vitronectin were synthesized. Two peptides spanning res 364-380 blocked binding of uPAR to vitronectin (IC50 similar to 8-25 mu M) identifying this region as an important site of uPAR-vitronectin interaction, These data illuminate a complex regulatory scheme for uPAR-dependent cellular adhesion to vitronectin: Active urokinase promotes adhesion and also subsequent detachment through activation of plasmin or complex formation with PAI-1, Excess PAI-1 may also promote migration by blocking cellular adhesion and/or promoting detachment, possibly accounting in part for the strong correlation between PAI-1 expression and tumor cell metastasis.