Schlechte J W, Boyd D D
Bristol-Baylor Laboratory, Pharmacology Department, Baylor College of Medicine, Houston, TX 77030.
Cancer Commun. 1990;2(8):261-9. doi: 10.3727/095535490820874245.
This laboratory recently reported that laminin degradation by cultured colon cancer was plasminogen dependent and reflected the presence of urokinase bound to cell surface receptors. (Schlecte, W.; Murano, G.; Boyd D. Cancer Res., 49:6064-6069; 1989). The present study was undertaken to determine the sensitivity of urokinase receptor directed proteolysis to the type I plasminogen activator inhibitor (PAI-1). Colon cancer cell types, that were highly effective in degrading laminin in vitro, elaborated into their conditioned medium an inhibitor which was indistinguishable from PAI-1 on the basis of its performance in reverse zymography, western blotting, and immunoprecipitation assays. A fraction of this PAI-1 was active, as evidenced by complex formation with the active site of radioactive urokinase. Laminin degradation by the colon cancer cells, however, did not appear to be affected by the endogenous inhibitor, since an antibody to the inhibitor, which blocked urokinase-PAI-1 interactions, had little effect on laminin turnover. Further, addition of exogenous PAI-1, activated by guanidine hydrochloride pretreatment, to the colon cancer cells did not perturb laminin degradation. Because laminin degradation by colonic cells was a function of receptor bound urokinase, presumably immobilized plasminogen activator escaped the neutralizing effect of the inhibitor. These data suggest either a shielding effect of the receptor on the plasminogen activator or a physical separation of activator and inhibitor. Either way, for cultured colon cancer at least, laminin degradation directed by urokinase receptor bound plasminogen activator appeared unaffected by the presence of this inhibitor.
本实验室最近报道，培养的结肠癌细胞对层粘连蛋白的降解依赖于纤溶酶原，并反映了与细胞表面受体结合的尿激酶的存在。（施莱克特，W.；穆拉诺，G.；博伊德，D.《癌症研究》，49:6064 - 6069；1989年）。本研究旨在确定尿激酶受体介导的蛋白水解对I型纤溶酶原激活物抑制剂（PAI - 1）的敏感性。在体外能高效降解层粘连蛋白的结肠癌细胞类型，会将一种抑制剂分泌到其条件培养基中，根据其在反向酶谱分析、蛋白质免疫印迹和免疫沉淀分析中的表现，该抑制剂与PAI - 1无法区分。该PAI - 1的一部分具有活性，与放射性尿激酶的活性位点形成复合物即可证明。然而，结肠癌细胞对层粘连蛋白的降解似乎不受内源性抑制剂的影响，因为一种能阻断尿激酶 - PAI - 1相互作用的抑制剂抗体，对层粘连蛋白的周转几乎没有影响。此外，向结肠癌细胞中添加经盐酸胍预处理激活的外源性PAI - 1，并不会干扰层粘连蛋白的降解。由于结肠细胞对层粘连蛋白的降解是受体结合的尿激酶的功能，推测固定化的纤溶酶原激活物逃脱了抑制剂的中和作用。这些数据表明，要么是受体对纤溶酶原激活物有屏蔽作用，要么是激活物与抑制剂在物理上是分离的。无论哪种方式，至少对于培养的结肠癌细胞来说，尿激酶受体结合的纤溶酶原激活物介导的层粘连蛋白降解似乎不受这种抑制剂存在的影响。
