EFFECTOR PROTEASE RECEPTOR-1 MEDIATES THE MITOGENIC ACTIVITY OF FACTOR XA FOR VASCULAR SMOOTH-MUSCLE CELLS IN-VITRO AND IN-VIVO

The binding of I-125-factor Xa to human aortic smooth muscle cell (SMC ) monolayers was studied, At 4 degrees C, (125)-factor Xa bound to a s ingle class of binding sites with a dissociation constant value of 3.6 +/- 0.7 nM and a binding site density of 11,720 +/- 1,240 sites/cell (n = 9), I-125-factor Xa binding was not affected by factor X, thrombi n, or by DX9065, a direct inhibitor of factor Xa, but was inhibited by factor Xa (IC50 = 5.4 +/- 0.2 nM; n = 9) and by antibodies specific f or the effector cell protease receptor 1 (EPR-1), a well-known recepto r of factor Xa on various cell types, A factor X peptide duplicating t he inter-EGF sequence Leu(83)-Leu(88)-(Gly) blocked the binding of I-1 25-factor Xa to these cells in a dose-dependent manner (IC50 = 110 +/- 21 nM), Factor Xa increased phosphoinositide turnover in SMCs and whe n added to SMCs in culture was a potent mitogen, These effects were in hibited by DX9065 and by antibodies directed against EPR-1 and PDGF, I ncreased expression of EPR-1 was identified immunohistochemically on S MCs growing in culture and in SMCs from the rabbit carotid artery afte r vascular injury, When applied locally to air-injured rabbit carotid arteries, antibodies directed against EPR-1 (100 mu g/artery) strongly reduced myointimal proliferation 14 d after vascular injury (65-71% i nhibition, P < 0.01), DX9065 (10 mg/kg, subcutaneous) inhibited myoint imal proliferation significantly (43% inhibition, P < 0.05), These fin dings indicate that SMCs express functional high affinity receptors fo r factor Xa related to EPR-1, which may be of importance in the regula tion of homeostasis of the vascular wall and after vascular injury.