Sitrin R G, Gyetko M R, Kole K L, McKeever P, Varani J
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109.
Cancer Res. 1990 Aug 15;50(16):4957-61.
Expression of plasminogen activator (PA) enzyme activity is believed to be one of the mechanisms by which malignant cells cause pericellular proteolysis of stromal structures during implantation and tissue invasion. In this study, four cell lines derived from human gliomas were studied to ascertain which PA enzymes and PA inhibitors determine the level of secreted PA activity. A plasminogen-dependent esterolytic assay was used, and two lines (U251 and U373) were found to secrete high levels of PA activity, while PA activity was undetectable in the conditioned media from the remaining two lines (U138 and LM). The PA produced by U251 and U373 resolved as single bands comigrating with high molecular weight urokinase (Mr 54,000) on casein-plasminogen zymography. Northern blot analysis demonstrated high levels of mRNA for urokinase-type PA (uPA) in U251 and U373, as well as a considerably lower level of uPA message in LM. U251 and U373 also contained mRNA for tissue-type PA (tPA), although secreted tPA activity was not demonstrated by zymography. The U138 line contained essentially undetectable levels of mRNA for either uPA or tPA. U138 was also unique in secreting PA inhibitor activity and contained high levels of mRNA for PA inhibitor 2, which was not seen in any other line. All cell lines contained PA inhibitor 1 mRNA, with substantially more expression in the U138 and LM lines than in U251 and U373. None of the lines secreted measureable anti-plasmin activity. We conclude that there is considerable heterogeneity among human glioma cells in expression of PA enzymes and PA inhibitors. The coordinated regulation of these proteins likely determines secreted PA activity and the resultant role of plasminogen activation in tumor implantation and invasion.
纤溶酶原激活物（PA）酶活性的表达被认为是恶性细胞在植入和组织侵袭过程中导致基质结构细胞周围蛋白水解的机制之一。在本研究中，对源自人胶质瘤的四种细胞系进行了研究，以确定哪些PA酶和PA抑制剂决定了分泌型PA活性的水平。采用了纤溶酶原依赖性酯解测定法，发现两条细胞系（U251和U373）分泌高水平的PA活性，而在其余两条细胞系（U138和LM）的条件培养基中未检测到PA活性。在酪蛋白 - 纤溶酶原酶谱分析中，U251和U373产生的PA表现为与高分子量尿激酶（分子量54,000）共迁移的单一条带。Northern印迹分析表明，U251和U373中尿激酶型PA（uPA）的mRNA水平较高，而LM中uPA信息的水平则低得多。U251和U373也含有组织型PA（tPA）的mRNA，尽管酶谱分析未显示分泌的tPA活性。U138细胞系中uPA或tPA的mRNA水平基本检测不到。U138在分泌PA抑制剂活性方面也很独特，并且含有高水平的PA抑制剂2的mRNA，这在其他任何细胞系中都未见到。所有细胞系都含有PA抑制剂1的mRNA，U138和LM细胞系中的表达明显多于U251和U373细胞系。没有一个细胞系分泌可测量的抗纤溶酶活性。我们得出结论，人胶质瘤细胞在PA酶和PA抑制剂的表达上存在相当大的异质性。这些蛋白质的协同调节可能决定了分泌型PA活性以及纤溶酶原激活在肿瘤植入和侵袭中的最终作用。
