Plasmin-induced migration requires signaling through protease-activated receptor 1 and integrin α₉β₁

Plasmin is a major extracellular protease that elicits intracellular signals to mediate platelet aggregation, chemotaxis of peripheral blood monocytes, and release of arachidonate and leukotriene from several cell types in a G protein-dependent manner. Angiostatin, a fragment of plasmin(ogen), is a ligand and an antagonist for integrin α₉β₁. Here we report that plasmin specifically interacts with α ₉β₁ and that plasmin induces migration of cells expressing recombinant α₉β₁ (α₉-Chinese hamster ovary (CHO) cells). Migration was dependent on an interaction of the kringle domains of plasmin with α ₉β₁ as well as the catalytic activity of plasmin. Angiostatin, representing the kringle domains of plasmin, alone did not induce the migration of α₉-CHO cells, but simultaneous activation of the G protein-coupled protease-activated receptor (PAR)-1 with an agonist peptide induced the migration on angiostatin, whereas PAR-2 or PAR-4 agonist peptides were without effect. Furthermore, a small chemical inhibitor of PAR-1 (RWJ 58259) and a palmitoylated PAR-1-blocking peptide inhibited plasmin-induced migration of α₉-CHO cells. These results suggest that plasmin induces migration by kringle-mediated binding to α₉β ₁ and simultaneous proteolytic activation of PAR-1.