Direct binding of occupied urokinase receptor (uPAR) to LDL receptor-related protein is required for endocytosis of uPAR and regulation of cell surface urokinase activity
Direct binding of occupied urokinase receptor (uPAR) to LDL receptor-related protein is required for endocytosis of uPAR and regulation of cell surface urokinase activity
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DOI：
10.1091/mbc.12.5.1467
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发表时间：
2001-05-01
影响因子：
3.3
通讯作者：
Farquhar, MG
中科院分区：
文献类型：
--
作者：
Czekay, RP;Kuemmel, TA;Farquhar, MG
低密度脂蛋白受体相关蛋白(LRP)介导尿激活酶：纤溶酶原激活物抑制物复合体(uPA：PAI-1)和尿激活酶受体(UPAR)的内化。在这里，我们研究了糖基磷脂酰肌醇锚定蛋白uPAR和跨膜受体LRP之间的直接相互作用是否需要清除uPA：PAI-1，再生未被占据的uPAR，激活纤溶酶原，以及HT1080细胞侵袭细胞外基质的能力。我们发现，在没有uPA：PAI-1的情况下，uPAR在质膜上是随机分布的，而uPA：PAI-1促进了uPAR-LRP复合体的形成，并启动了uPAR被占据的重新分配到被笼蛋白包裹的凹坑。UPAR-LRP复合体通过包被网状蛋白的小泡被内吞，并与早期内小体(EE)一起运输，因为它们可以从免疫隔离的EE中免疫共沉淀，内化被细胞内K+的耗尽所阻止。UPAR的结构域3(D3)与LRP的直接结合是清除uPA-PAI-1占据的uPAR所必需的，因为重组D3的孵育阻止了内化。此外，在D3的存在下，依赖uPA的纤溶酶的产生和HT1080细胞通过Matrigel包被的侵袭室迁移的能力也被抑制。这些结果表明，GPI锚定的uPAR是通过携带在LRP上的方式内吞的，而被占据的uPAR与LRP的直接结合对于被占据的uPAR的内化、未被占据的uPAR的再生、纤溶酶的产生以及通过细胞外基质的侵袭和迁移是必不可少的。
Low-density lipoprotein receptor-related protein (LRP) mediates internalization of urokinase: plasminogen activator inhibitor complexes (uPA:PAI-1) and the urokinase receptor (uPAR). Here we investigated whether direct interaction between uPAR, a glycosyl-phosphatidylinositol-anchored protein, and LRP, a transmembrane receptor, is required for clearance of uPA:PAI-1, regeneration of unoccupied uPAR, activation of plasminogen, and the ability of HT1080 cells to invade extracellular matrix. We found that in the absence of uPA:PAI-1, uPAR is randomly distributed along the plasma membrane, whereas uPA:PAI-1 promotes formation of uPAR-LRP complexes and initiates redistribution of occupied uPAR to clathrin-coated pits. uPAR-LRP complexes are endocytosed via clathrin-coated vesicles and traffic together to early endosomes (EE) because they can be coimmunoprecipitated from immunoisolated EE, and internalization is blocked by depletion of intracellular K+. Direct binding of domain 3 (D3) of uPAR to LRP is required for clearance of uPA-PAI-1-occupied uPAR because internalization is blocked by incubation with recombinant D3. Moreover, uPA-dependent plasmin generation and the ability of HT1080 cells to migrate through Matrigel-coated invasion chambers are also inhibited in the presence of D3. These results demonstrate that GPI-anchored uPAR is endocytosed by piggy-backing on LRP and that direct binding of occupied uPAR to LRP is essential for internalization of occupied uPAR, regeneration of unoccupied uPAR, plasmin generation, and invasion and migration through extracellular matrix.