MacDonald T J, DeClerck Y A, Laug W E
Department of Pediatrics, Childrens Hospital Los Angeles University of Southern California School of Medicine, 90027, USA.
J Neurooncol. 1998 Dec;40(3):215-26. doi: 10.1023/a:1006150506789.
The plasminogen activation (PA) system plays an important role in tumor invasion by initiating pericellular proteolysis of the extracellular matrix (ECM) and inducing cell migration. Malignant brain tumors overexpress PA members and characteristically invade by migrating on ECM-producing white matter tracts and blood vessel walls. To determine whether urokinase-type plasminogen activator (uPA) and its receptor (uPAR) directly modulate the migration of brain tumor cells, we examined six human brain tumor cell lines, 2 astrocytomas (SW1088, SW1783), 2 medullobastomas (Daoy, D341Med), and 2 glioblastomas (U87MG, U118MG), for their surface uPAR expression, endogenous PA activity, and functional proteolytic activity by an ECM-degradation assay. Migration on Transwell membranes and invasion of Matrigel was then tested by pre-incubating the cells with increasing concentrations of either uPA, the proteolytically inactive amino-terminal fragment (ATF) of uPA, or the uPAR cleaving enzyme, phosphatidylinositol-specific phospholipase C (PI-PLC). All of the cell lines, except D341Med, express surface uPAR protein and uPA activity. High levels of uPAR and uPA activity correlated with cellular degradation of ECM, cell migration, and Matrigel invasion. Cell migration and invasion were enhanced by uPA or ATF in a dose dependent manner, while PI-PLC treatment abolished the uPA effect and inhibited migration and invasion. We conclude that ligation of uPAR by uPA directly induces brain tumor cell migration, independent of uPA-mediated proteolysis; and in concert with ECM degradation, markedly enhances invasion. Conversely, removing membrane bound uPAR from the surface of the cells studied inhibited their ability to migrate and invade even in the presence of proteolytically active uPA.
纤溶酶原激活（PA）系统通过启动细胞外基质（ECM）的细胞周围蛋白水解和诱导细胞迁移，在肿瘤侵袭中发挥重要作用。恶性脑肿瘤过度表达PA成员，其特征是通过在产生ECM的白质束和血管壁上迁移来侵袭。为了确定尿激酶型纤溶酶原激活剂（uPA）及其受体（uPAR）是否直接调节脑肿瘤细胞的迁移，我们检测了六种人脑肿瘤细胞系，2种星形细胞瘤（SW1088、SW1783）、2种髓母细胞瘤（Daoy、D341Med）和2种胶质母细胞瘤（U87MG、U118MG）的表面uPAR表达、内源性PA活性以及通过ECM降解试验检测的功能性蛋白水解活性。然后通过用浓度递增的uPA、uPA的蛋白水解无活性的氨基末端片段（ATF）或uPAR切割酶磷脂酰肌醇特异性磷脂酶C（PI-PLC）预孵育细胞，来检测细胞在Transwell膜上的迁移和对基质胶的侵袭。除D341Med外，所有细胞系均表达表面uPAR蛋白和uPA活性。高水平的uPAR和uPA活性与ECM的细胞降解、细胞迁移和基质胶侵袭相关。uPA或ATF以剂量依赖性方式增强细胞迁移和侵袭，而PI-PLC处理消除了uPA的作用并抑制了迁移和侵袭。我们得出结论，uPA与uPAR的结合直接诱导脑肿瘤细胞迁移，独立于uPA介导的蛋白水解；并且与ECM降解协同作用，显著增强侵袭。相反，在所研究的细胞表面去除膜结合的uPAR，即使在存在蛋白水解活性uPA的情况下，也会抑制它们迁移和侵袭的能力。
