Félez J, Miles L A, Fábregas P, Jardí M, Plow E F, Lijnen R H
Institut Recerca Oncològica (IRO), Hospital Duran i Reynals, Barcelona, Spain.
Thromb Haemost. 1996 Oct;76(4):577-84.
Plasminogen and tPA bind to a common set of binding sites on nucleated cells. To assess the functional consequences of cellular binding, we have measured the kinetic changes induced by plasminogen activation by tPA on cell surfaces. These studies were carried out with U937 and THP-1 monocytoid cells, with Raji, Nalm6 and Molt4 lymphoid cells and with peripheral blood monocytes and neutrophils. The interactions of plasminogen and tPA with cells induced an increase in the rate of plasmin generation which depended upon the cell concentration. With saturating amounts of U937 monocytoid cells (1.25 x 10(5)/ml) the rate of plasmin generation was 0.39 nM.s-1 versus 0.07 and 0.09 nM.s-1 without cells or without tPA, respectively. The catalytic efficiency of Glu- or Lys-plasminogen activation by tPA increased by 7.2- and 24.2-fold, respectively. These changes were induced by a 72-242-fold reduction in the Km of these interactions which was in the range of 0.3-0.9 microM. These values are below the plasminogen concentration in plasma (1-2 microM). Moreover, we provide new data indicating that 1) only a specific subset of plasminogen binding sites, i.e. molecules exposing carboxyl terminal lysines on the cell surface, promotes plasminogen activation on cells; 2) the first four kringles of plasminogen and the finger of tPA are critical for enhanced plasmin generation on cell surfaces; 3) the simultaneous co-localization of tPA with plasminogen on cell surfaces is required for enhanced plasminogen activation; 4) modulation of plasminogen/tPA receptor expression induces concomitant modulation of the stimulatory effects of cells on plasminogen activation and 5) in a direct comparison, the mechanism by which cells and fibrin fragments accelerate plasminogen activation are similar but not identical. These data suggest that modulation of plasminogen/tPA binding sites permits local and efficient generation of plasmin on cell surfaces.
纤溶酶原和组织型纤溶酶原激活物（tPA）与有核细胞上的一组共同结合位点结合。为了评估细胞结合的功能后果，我们测量了tPA在细胞表面激活纤溶酶原所诱导的动力学变化。这些研究是用U937和THP - 1单核细胞样细胞、Raji、Nalm6和Molt4淋巴细胞以及外周血单核细胞和中性粒细胞进行的。纤溶酶原和tPA与细胞的相互作用导致纤溶酶生成速率增加，这取决于细胞浓度。在U937单核细胞样细胞饱和量（1.25×10⁵/ml）时，纤溶酶生成速率为0.39 nM·s⁻¹，而无细胞或无tPA时分别为0.07和0.09 nM·s⁻¹。tPA对谷氨酸型或赖氨酸型纤溶酶原激活的催化效率分别提高了7.2倍和24.2倍。这些变化是由这些相互作用的米氏常数（Km）降低72 - 242倍诱导的，该范围为0.3 - 0.9 microM。这些值低于血浆中纤溶酶原的浓度（1 - 2 microM）。此外，我们提供了新的数据表明：1）只有纤溶酶原结合位点的特定子集，即在细胞表面暴露羧基末端赖氨酸的分子，才能促进细胞上的纤溶酶原激活；2）纤溶酶原的前四个kringle结构域和tPA的指状结构域对于细胞表面纤溶酶生成的增强至关重要；3）tPA与纤溶酶原在细胞表面的同时共定位是增强纤溶酶原激活所必需的；4）纤溶酶原/tPA受体表达的调节会诱导细胞对纤溶酶原激活的刺激作用的相应调节；5）在直接比较中，细胞和纤维蛋白片段加速纤溶酶原激活的机制相似但不相同。这些数据表明，纤溶酶原/tPA结合位点的调节允许在细胞表面局部且有效地生成纤溶酶。
