C1 inhibitor-C1s complexes are internalized and degraded by the low density lipoprotein receptor-related protein.
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.
Storm
D
D
Institute of Medical Microbiology and Hygiene, Johannes Gutenberg University, 55101 Mainz, Germany.
Herz
J
J
Trinder
P
P
Loos
M
M
D000818:Animals; D002634:Chemotaxis, Leukocyte; D002851:Chromatography, High Pressure Liquid; D003174:Complement C1 Inactivator Proteins / Q000378:metabolism*; D003173:Complement C1s / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D051379:Mice; D008807:Mice, Inbred BALB C; D011956:Receptors, Cell Surface / Q000378:metabolism; D011971:Receptors, Immunologic / Q000378:metabolism*; D011973:Receptors, LDL / Q000378:metabolism*; D014018:Tissue Distribution; D000511:alpha-Macroglobulins / Q000378:metabolism*
D003174:Complement C1 Inactivator Proteins; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D011973:Receptors, LDL; D000511:alpha-Macroglobulins; C064184:serpin-enzyme complex receptor; D003173:Complement C1s