Storm D, Herz J, Trinder P, Loos M
Institute of Medical Microbiology and Hygiene, Johannes Gutenberg University, 55101 Mainz, Germany.
J Biol Chem. 1997 Dec 5;272(49):31043-50. doi: 10.1074/jbc.272.49.31043.
Like other serpin-enzyme complexes (SECs), proteinase-complexed C1 inhibitor (C1-INH) is rapidly cleared from the circulation and thought to be a neutrophil chemoattractant, suggesting that complex formation causes structural rearrangements exposing a domain which is recognized by specific cell surface receptors. However, the cellular receptor(s) responsible for the catabolism and potential mediation of chemotaxis by C1-INH-protease complexes remained obscure. To determine whether the SEC receptor mediates the binding and potential chemotaxis of C1-INH.Cs, we performed binding assays with HepG2 cells, neutrophils, and monocytes, and the results show that C1-INH.Cs neither bind to these cells nor cause a chemotactic response of neutrophils and monocytes. Furthermore, C1-INH.Cs, the COOH-terminal C1 inhibitor peptide, or the tetrameric C1-INH.Cs.Cr. C1-INH complex were found to be significantly less effective in competing with the SEC receptor ligand 125I-peptide 105Y for the binding to HepG2 cells than unlabeled 105Y, indicating that the SEC receptor does not sufficiently recognize C1-INH-protease complexes. The asialoglycoprotein receptor was also ruled out to be responsible for the removal of the heavily glycosylated C1-INH.Cs complex, since asialoorosomucoid did not compete for the clearance of C1-INH. 125I-Cs and asialoglycoprotein receptor knockout mice showed no alterations in the C1-INH.125I-Cs clearance rate. We found that C1-INH.125I-Cs complexes were efficiently degraded by normal murine fibroblasts expressing the low density lipoprotein receptor-related protein (LRP) and cellular degradation was significantly reduced by chloroquine and the receptor-associated protein, which is a potent inhibitor of the binding of all known ligands to LRP. Moreover, receptor-associated protein inhibited the in vivo clearance of C1-INH.125I-Cs and murine fibroblasts genetically deficient for LRP did not degrade C1-INH.125I-Cs. Our results demonstrate that C1-INH. Cs complexes do not stimulate neutrophil or monocytic chemotaxis but are removed by LRP, further underscoring its role as a serpin-enzyme complex clearance receptor.
与其他丝氨酸蛋白酶抑制剂 - 酶复合物（SECs）一样，蛋白酶复合的C1抑制剂（C1 - INH）会迅速从循环中清除，并被认为是一种中性粒细胞趋化剂，这表明复合物的形成会导致结构重排，暴露出一个可被特定细胞表面受体识别的结构域。然而，负责C1 - INH - 蛋白酶复合物分解代谢和潜在趋化作用介导的细胞受体仍不清楚。为了确定SEC受体是否介导C1 - INH.Cs的结合和潜在趋化作用，我们用HepG2细胞、中性粒细胞和单核细胞进行了结合试验，结果表明C1 - INH.Cs既不与这些细胞结合，也不会引起中性粒细胞和单核细胞的趋化反应。此外，发现C1 - INH.Cs、C1抑制剂的COOH末端肽或四聚体C1 - INH.Cs.Cr.C1 - INH复合物在与SEC受体配体125I - 肽105Y竞争结合HepG2细胞方面，比未标记的105Y的效果要差得多，这表明SEC受体不能充分识别C1 - INH - 蛋白酶复合物。去唾液酸糖蛋白受体也被排除是负责清除高度糖基化的C1 - INH.Cs复合物的原因，因为去唾液酸血清类黏蛋白不能竞争C1 - INH.125I - Cs的清除。125I - Cs和去唾液酸糖蛋白受体基因敲除小鼠在C1 - INH.125I - Cs清除率方面没有变化。我们发现，表达低密度脂蛋白受体相关蛋白（LRP）的正常小鼠成纤维细胞能有效降解C1 - INH.125I - Cs复合物，而氯喹和受体相关蛋白可显著降低细胞降解，受体相关蛋白是所有已知配体与LRP结合的有效抑制剂。此外，受体相关蛋白抑制C1 - INH.125I - Cs在体内的清除，而LRP基因缺陷的小鼠成纤维细胞不能降解C1 - INH.125I - Cs。我们的结果表明，C1 - INH.Cs复合物不会刺激中性粒细胞或单核细胞趋化，但会被LRP清除，这进一步强调了其作为丝氨酸蛋白酶抑制剂 - 酶复合物清除受体的作用。
