Plow E F, Freaney D E, Plescia J, Miles L A
J Cell Biol. 1986 Dec;103(6 Pt 1):2411-20. doi: 10.1083/jcb.103.6.2411.
The capacity of cells to interact with the plasminogen activator, urokinase, and the zymogen, plasminogen, was assessed using the promyeloid leukemic U937 cell line and the diploid fetal lung GM1380 fibroblast cell line. Urokinase bound to both cell lines in a time-dependent, specific, and saturable manner (Kd = 0.8-2.0 nM). An active catalytic site was not required for urokinase binding to the cells, and 55,000-mol-wt urokinase was selectively recognized. Plasminogen also bound to the two cell lines in a specific and saturable manner. This interaction occurred with a Kd of 0.8-0.9 microM and was of very high capacity (1.6-3.1 X 10(7) molecules bound/cell). The interaction of plasminogen with both cell types was partially sensitive to trypsinization of the cells and required an unoccupied high affinity lysine-binding site in the ligand. When plasminogen was added to the GM1380 cells, a line with high intrinsic plasminogen activator activity, the bound ligand was comprised of both plasminogen and plasmin. Urokinase, in catalytically active or inactive form, enhanced plasminogen binding to the two cell lines by 1.4-3.3-fold. Plasmin was the predominant form of the bound ligand when active urokinase was added, and preformed plasmin can also bind directly to the cells. Plasmin on the cell surface was also protected from its primary inhibitor, alpha 2-antiplasmin. These results indicate that the two cell lines possess specific binding sites for plasminogen and urokinase, and a family of widely distributed cellular receptors for these components may be considered. Endogenous or exogenous plasminogen activators can generate plasmin on cell surfaces, and such activation may provide a mechanism for arming cell surfaces with the broad proteolytic activity of this enzyme.
利用早幼粒细胞白血病U937细胞系和二倍体胎儿肺GM1380成纤维细胞系评估了细胞与纤溶酶原激活剂尿激酶以及酶原纤溶酶原相互作用的能力。尿激酶以时间依赖性、特异性和可饱和的方式（解离常数Kd = 0.8 - 2.0 nM）与这两种细胞系结合。尿激酶与细胞结合不需要活性催化位点，并且能选择性识别55,000道尔顿分子量的尿激酶。纤溶酶原也以特异性和可饱和的方式与这两种细胞系结合。这种相互作用的解离常数Kd为0.8 - 0.9微摩尔，结合能力非常高（每细胞结合1.6 - 3.1×10⁷个分子）。纤溶酶原与这两种细胞类型的相互作用对细胞胰蛋白酶消化部分敏感，并且配体中需要一个未被占据的高亲和力赖氨酸结合位点。当将纤溶酶原添加到具有高内在纤溶酶原激活剂活性的GM1380细胞中时，结合的配体包括纤溶酶原和纤溶酶。有催化活性或无活性形式的尿激酶使纤溶酶原与这两种细胞系的结合增强了1.4 - 3.3倍。当添加活性尿激酶时，纤溶酶是结合配体的主要形式，并且预先形成的纤溶酶也能直接与细胞结合。细胞表面的纤溶酶也受到其主要抑制剂α₂ - 抗纤溶酶的保护。这些结果表明这两种细胞系具有纤溶酶原和尿激酶的特异性结合位点，可能存在一类广泛分布的这些成分的细胞受体。内源性或外源性纤溶酶原激活剂可在细胞表面产生纤溶酶，这种激活可能为用该酶的广泛蛋白水解活性武装细胞表面提供一种机制。
