Hajjar K A, Hamel N M, Harpel P C, Nachman R L
Department of Pediatrics, Cornell University Medical College, New York 10021.
J Clin Invest. 1987 Dec;80(6):1712-9. doi: 10.1172/JCI113262.
Tissue plasminogen activator (t-PA) and urokinase (u-PA), the major activators of plasminogen, are synthesized and released from endothelial cells. We previously demonstrated specific and functional binding of plasminogen to cultured human umbilical vein endothelial cells (HUVEC). In the present study we found that t-PA could bind to HUVEC. Binding of t-PA to HUVEC was specific, saturable, plasminogen-independent, and did not require lysine binding sites. The t-PA bound in a rapid and reversible manner, involving binding sites of both high (Kd, 28.7 +/- 10.8 pM; Bmax, 3,700 +/- 300) and low (Kd, 18.1 +/- 3.8 nM; Bmax 815,000 +/- 146,000) affinity. t-PA binding was 70% inhibited by a 100-fold molar excess of u-PA. When t-PA was bound to HUVEC, its apparent catalytic efficiency increased by three- or fourfold as measured by plasminogen activation. HUVEC-bound t-PA was active site-protected from its rapidly acting inhibitor: plasminogen activator inhibitor. These results demonstrate that t-PA specifically binds to HUVEC and that such binding preserves catalytic efficiency with respect to plasminogen activation. Therefore, endothelial cells can modulate hemostatic and thrombotic events at the cell surface by providing specific binding sites for activation of plasminogen.
组织型纤溶酶原激活剂（t-PA）和尿激酶（u-PA）是纤溶酶原的主要激活剂，由内皮细胞合成并释放。我们之前证明了纤溶酶原与培养的人脐静脉内皮细胞（HUVEC）存在特异性和功能性结合。在本研究中，我们发现t-PA能够与HUVEC结合。t-PA与HUVEC的结合具有特异性、饱和性、不依赖纤溶酶原，且不需要赖氨酸结合位点。t-PA以快速可逆的方式结合，涉及高亲和力（Kd，28.7±10.8 pM；Bmax，3700±300）和低亲和力（Kd，18.1±3.8 nM；Bmax 815,000±146,000）的结合位点。100倍摩尔过量的u-PA可抑制70%的t-PA结合。当t-PA与HUVEC结合时，通过纤溶酶原激活测定，其表观催化效率提高了三到四倍。与HUVEC结合的t-PA的活性位点受到其快速作用抑制剂：纤溶酶原激活剂抑制剂的保护。这些结果表明t-PA特异性结合HUVEC，并且这种结合在纤溶酶原激活方面保持了催化效率。因此，内皮细胞可以通过为纤溶酶原激活提供特异性结合位点来调节细胞表面的止血和血栓形成事件。
