Faculty of Chemistry, Lomonosov Moscow State University, Moscow, 119991, Russia.
Biochemistry (Mosc). 2009 Oct;74(10):1104-13. doi: 10.1134/s000629790910006x.
Angiostatins, kringle-containing fragments of plasminogen, are potent inhibitors of angiogenesis. Effects of three angiostatin forms, K1-3, K1-4, and K1-4.5 (0-2 microM), on the rate of native Glu-plasminogen activation by its physiological activators in the absence or presence of soluble fibrin were investigated in vitro. Angiostatins did not affect the intrinsic amidolytic activities of plasmin and plasminogen activators of tissue type (tPA) and urokinase type (single-chain scuPA and two-chain tcuPA), but inhibited conversion of plasminogen to plasmin in a dose-dependent manner. All three angiostatins suppressed Glu-plasminogen activation by tcuPA independently of the presence of fibrin, and the inhibitory effect increased in the order: K1-3 < K1-4 < K1-4.5. The inhibitory effects of angiostatins on the scuPA activator activity were lower and further decreased in the presence of fibrin. Angiostatin K1-3 (up to 2 microM) had no effect, while 2 microM angiostatins K1-4 and K1-4.5 inhibited the fibrin-stimulated Glu-plasminogen activation by tPA by 50 and 100%, respectively. The difference in effects of the three angiostatins on the Glu-plasminogen activation by scuPA, tcuPA, and tPA in the absence or presence of fibrin is due to the differences in angiostatin structures, mechanisms of action, and fibrin-specificity of plasminogen activators, as well as due to the influence of fibrin on the Glu-plasminogen conformation. Angiostatins in vivo, which mimic plasminogen-binding activity, can inhibit plasminogen activation stimulated by various proteins (including fibrin) of extracellular matrix, thereby blocking cell migration and angiogenesis. The data of this work indicate that the inhibition of Glu-plasminogen activation under the action of physiological plasminogen activators by angiostatins can be implicated in the complex mechanism of their antiangiogenic and antitumor action.
抑血管生成素是纤溶酶原含kringle 的片段，是血管生成的有效抑制剂。研究了三种抑血管生成素形式 K1-3、K1-4 和 K1-4.5（0-2 μM）在不存在或存在可溶性纤维蛋白的情况下对天然 Glu-纤溶酶原被其生理激活剂激活的速率的影响。抑血管生成素不影响组织型（tPA）和尿激酶型（单链 scuPA 和双链 tcuPA）纤溶酶和纤溶酶原激活剂的内在酰胺酶活性，但以剂量依赖方式抑制纤溶酶原向纤溶酶的转化。三种抑血管生成素均独立于纤维蛋白的存在抑制 Glu-纤溶酶原被 tcuPA 激活，抑制作用的顺序为：K1-3<K1-4<K1-4.5。抑血管生成素对 scuPA 激活剂活性的抑制作用较低，并且在存在纤维蛋白时进一步降低。高达 2 μM 的抑血管生成素 K1-3 没有影响，而 2 μM 的抑血管生成素 K1-4 和 K1-4.5 分别抑制纤维蛋白刺激的 tPA 对 Glu-纤溶酶原的激活作用 50%和 100%。三种抑血管生成素在不存在或存在纤维蛋白的情况下对 scuPA、tcuPA 和 tPA 激活 Glu-纤溶酶原的作用不同，这是由于抑血管生成素结构、作用机制和纤溶酶原激活剂的纤维蛋白特异性的差异，以及纤维蛋白对 Glu-纤溶酶原构象的影响。体内模拟纤溶酶原结合活性的抑血管生成素可以抑制细胞外基质各种蛋白质（包括纤维蛋白）刺激的纤溶酶原激活，从而阻断细胞迁移和血管生成。本工作的数据表明，抑血管生成素在生理纤溶酶原激活剂作用下对 Glu-纤溶酶原激活的抑制作用可能参与了其抗血管生成和抗肿瘤作用的复杂机制。
