Quinn K A, Grimsley P G, Dai Y P, Tapner M, Chesterman C N, Owensby D A
Center for Thrombosis and Vascular Research, University of New South Wales, Sydney 2052, Australia.
J Biol Chem. 1997 Sep 19;272(38):23946-51. doi: 10.1074/jbc.272.38.23946.
Our studies have identified a soluble molecule in normal human plasma and serum with the characteristics of the alpha-chain of the low density lipoprotein receptor-related protein (LRP). LRP is a large multifunctional receptor mediating the clearance of diverse ligands, including selected lipoproteins, various protease inhibitor complexes, and thrombospondin. A soluble molecule (sLRP) has been isolated from plasma using an affinity matrix coupled with methylamine-activated alpha2-macroglobulin, the ligand uniquely recognized by LRP, and eluted with EDTA. This eluate contains a protein that co-migrates on SDS-polyacrylamide gel electrophoresis with authentic human placental LRP alpha-chain, is recognized by anti-LRP alpha-chain monoclonal antibodies, and binds the 39-kDa receptor-associated protein (RAP) and tissue plasminogen activator-inhibitor complexes. A similar RAP-binding molecule was detected in medium conditioned for 24 h by primary cultures of rat hepatocytes, suggesting that the liver may be the in vivo source of sLRP. In contrast, immunoprecipitation experiments failed to detect the production of sLRP by cultured HepG2 hepatoma and primary human fibroblast cells. Addition of a soluble form of LRP to cultured HepG2 cells resulted in a significant inhibition of capacity of these cells to degrade tPA, a process that has been demonstrated to be mediated by cell surface LRP. Preliminary data indicate that the concentration of sLRP is altered in the plasma of patients with liver disease. Increased levels of sLRP may antagonize the clearance of ligands by cell bound LRP perturbing diverse processes including lipid metabolism, cell migration and extracellular proteinase activity.
我们的研究在正常人血浆和血清中鉴定出一种可溶性分子，其具有低密度脂蛋白受体相关蛋白（LRP）α链的特征。LRP是一种大型多功能受体，介导多种配体的清除，包括特定的脂蛋白、各种蛋白酶抑制剂复合物和血小板反应蛋白。已使用与甲胺活化的α2-巨球蛋白偶联的亲和基质从血浆中分离出一种可溶性分子（sLRP），α2-巨球蛋白是LRP唯一识别的配体，并用EDTA洗脱。该洗脱液含有一种蛋白质，在SDS-聚丙烯酰胺凝胶电泳上与 authentic human placental LRP α链共迁移，被抗LRP α链单克隆抗体识别，并结合39 kDa受体相关蛋白（RAP）和组织纤溶酶原激活物-抑制剂复合物。在大鼠肝细胞原代培养24小时的条件培养基中检测到类似的RAP结合分子，这表明肝脏可能是sLRP的体内来源。相比之下，免疫沉淀实验未能检测到培养的HepG2肝癌细胞和原代人成纤维细胞产生sLRP。向培养的HepG2细胞中添加可溶性形式的LRP会导致这些细胞降解tPA的能力显著受到抑制，这一过程已被证明是由细胞表面LRP介导的。初步数据表明，肝病患者血浆中sLRP的浓度发生了改变。sLRP水平升高可能会拮抗细胞结合的LRP对配体的清除，从而扰乱包括脂质代谢、细胞迁移和细胞外蛋白酶活性在内的多种过程。
