Kuiper J, Otter M, Voorschuur A H, van Zonneveld A J, Rijken D C, van Berkel T J
Division of Biopharmaceutics, Leiden Amsterdam Center for Drug Research, University of Leiden, The Netherlands.
Thromb Haemost. 1995 Nov;74(5):1298-304.
The present study was undertaken in order to determine the recognition site for tissue-type plasminogen activator-plasminogen activator inhibitor type 1 [t-PA-PAI-1] complexes in rat liver in vivo and in vitro. After intravenous injection into rats t-PA-PAI-1 complexes were rapidly removed from the plasma and the liver took up 80% of the injected dose. Within the liver parenchymal and endothelial liver cells contributed mainly to the uptake of t-PA-PAI-1, and were responsible for 62% and 24% of the liver uptake, respectively. The interaction of t-PA-PAI-1 with isolated rat parenchymal liver cells was of high affinity (Kd 17 nM). A well-known antagonist of the alpha 2-macroglobulin receptor (alpha 2MR/low-density lipoprotein receptor-related protein (LRP), GST-39kDa protein (GST-39kDaP) efficiently inhibited the binding (IC50 0.7 nM) of t-PA-PAI-1 to rat parenchymal liver cells. The interaction of t-PA-PAI-1 with LRP on rat parenchymal liver cells was not Ca2(+)-dependent and is most probably mediated by a specific determinant on PAI-1, since an anti-PAI-1 monoclonal antibody inhibited the binding of t-PA-PAI-1, where as free t-PA did not. The binding of t-PA-PAI-1 to rat hepatocytes could not be inhibited by a complex of plasmin and alpha 2-antiplasmin nor by various other ligands of LRP like beta-VLDL and lactoferrin. Binding of t-PA-PAI-1 to rat parenchymal liver cells was followed by internalization and subsequent degradation in the lysosomal compartment. It is concluded that parenchymal and endothelial liver cells mediate the removal of t-PA-PAI-1 complexes from the circulation. LRP on rat parenchymal liver cells is responsible for the uptake and degradation of t-PA-PAI-1 and may therefore be important for the regulation of the t-PA levels in the circulation.
本研究旨在确定组织型纤溶酶原激活剂 - 纤溶酶原激活剂抑制剂1[t-PA-PAI-1]复合物在大鼠肝脏体内和体外的识别位点。将t-PA-PAI-1复合物静脉注射到大鼠体内后，其迅速从血浆中清除，肝脏摄取了80%的注射剂量。在肝脏内，实质细胞和内皮细胞对t-PA-PAI-1的摄取起主要作用，分别占肝脏摄取量的62%和24%。t-PA-PAI-1与分离的大鼠肝脏实质细胞的相互作用具有高亲和力（解离常数Kd为17 nM）。α2-巨球蛋白受体（α2MR/低密度脂蛋白受体相关蛋白（LRP））的一种著名拮抗剂，谷胱甘肽S-转移酶39 kDa蛋白（GST-39kDaP）能有效抑制t-PA-PAI-1与大鼠肝脏实质细胞的结合（半数抑制浓度IC50为0.7 nM）。t-PA-PAI-1与大鼠肝脏实质细胞上LRP的相互作用不依赖Ca2+，很可能是由PAI-1上的一个特定决定簇介导的，因为抗PAI-1单克隆抗体能抑制t-PA-PAI-1的结合，而游离的t-PA则不能。纤溶酶与α2-抗纤溶酶的复合物以及LRP的其他各种配体如β-VLDL和乳铁蛋白均不能抑制t-PA-PAI-1与大鼠肝细胞的结合。t-PA-PAI-1与大鼠肝脏实质细胞结合后会发生内化，并随后在溶酶体区室中降解。结论是肝脏实质细胞和内皮细胞介导了t-PA-PAI-1复合物从循环中的清除。大鼠肝脏实质细胞上的LRP负责t-PA-PAI-1的摄取和降解，因此可能对循环中t-PA水平的调节很重要。
