LOW-DENSITY-LIPOPROTEIN RECEPTOR-RELATED PROTEIN ALPHA-2-MACROGLOBULIN RECEPTOR IS AN HEPATIC RECEPTOR FOR TISSUE-TYPE PLASMINOGEN-ACTIVATOR
LOW-DENSITY-LIPOPROTEIN RECEPTOR-RELATED PROTEIN ALPHA-2-MACROGLOBULIN RECEPTOR IS AN HEPATIC RECEPTOR FOR TISSUE-TYPE PLASMINOGEN-ACTIVATOR
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DOI：
10.1073/pnas.89.16.7427
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发表时间：
1992-08-15
影响因子：
11.1
通讯作者：
SCHWARTZ, AL
中科院分区：
文献类型：
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作者：
BU, GJ;WILLIAMS, S;SCHWARTZ, AL
组织型纤溶酶原激活物（t-PA）是一种丝氨酸蛋白酶，催化纤溶酶级联反应的初始和限速步骤，在体内可被肝脏迅速清除。利用化学交联，我们最近在大鼠肝癌MH1C1细胞上发现了一种纤溶酶原激活物抑制剂1型（PAI-1）独立的t-PA清除受体，其相对分子质量几乎等于500 kDa。另一种最近发现的膜受体，低密度脂蛋白受体相关蛋白/ α -2巨球蛋白受体（LRP/ α - 2mr），也通过抗LRP/ α - 2mr抗体免疫沉淀在MH1C1肝癌细胞上检测到。通过SDS/PAGE分析，我们发现在MH1C1细胞上鉴定的t-PA受体与LRP/ α - 2mr的大亚基同源。将特异性结合的i- 125标记的t-PA与其受体化学交联后，用抗lrp / α - 2mr抗体免疫沉淀t-PA受体。通过化学交联研究，我们发现t-PA和甲胺激活的α -2巨球蛋白可以同时与LRP/ α - 2mr结合而不相互竞争，这表明这两种配体结合在LRP/ α - 2mr分子上的两个独立位点上。此外，一种调节配体与LRP/ α - 2mr结合的39 kda蛋白也被发现抑制t-PA与其受体的结合。这些数据表明，在mhc1肝癌细胞上鉴定的t-PA清除受体是LRP/ α - 2mr。
Tissue-type plasminogen activator (t-PA), a serine protease that catalyzes the initial and rate-limiting step in the fibrinolytic cascade, is cleared rapidly in vivo by the liver. Using chemical crosslinking, we have recently identified a plasminogen-activator inhibitor type 1 (PAI-1)-independent t-PA clearance receptor on rat hepatoma MH1C1 cells with a relative molecular mass of almost-equal-to 500 kDa. Another recently identified membrane receptor, low density lipoprotein receptor-related protein/alpha-2-macroglobulin receptor (LRP/alpha-2MR), was also detected on MH1C1 hepatoma cells by using immunoprecipitation with anti-LRP/alpha-2MR antibody. When analyzed by SDS/PAGE, we found the t-PA receptor identified on MH1C1 cells comigrated with the large subunit of LRP/alpha-2MR. The t-PA receptor was immunoprecipitated by an anti-LRP/alpha-2MR antibody after chemical crosslinking of specifically bound I-125-labeled t-PA to its receptor. Through chemical crosslinking studies, we found that t-PA and methylamine-activated alpha-2-macroglobulin could bind to LRP/alpha-2MR simultaneously without competing with one another for binding, suggesting that the two ligands bound to two independent sites on the LRP/alpha-2MR molecule. Furthermore, a 39-kDa protein, which modulates ligand binding to LRP/alpha-2MR, was also found to inhibit t-PA binding to its receptor. These data thus show that the t-PA clearance receptor identified on MH1C1 hepatoma cells is LRP/alpha-2MR.