C1 inhibitor-C1s complexes are internalized and degraded by the low density lipoprotein receptor-related protein

Detlef Storm, Joachim Herz, Peter Trinder, Michael Loos

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


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 end potential chemotaxis of C1-INH-C1s, we performed binding assays with HepG2 cells, neutrophils, and monocytes, end the results show that C1-INH- C1s neither bind to these cells nor cause a chemotactic response of neutrophils and monocytes. Furthermore, C1-INH-C1s, the COOH-terminal C1 inhibitor peptide, or the tetrameric C1-INH-C1s-C1r-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 then 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-C1s complex, since asialoorosomucold did not compete for the clearance of C1-INH-125I- C1s and asialoglycoprotein receptor knockout mice showed no alterations in the C1-INH·125I-C1s clearance rate. We found that C1-INH·125-C1s 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·125-C1s and murine fibroblasts genetically deficient for LRP did not degrade C1-INH·125I-C1s. Our results demonstrate that C1- INH·C1s complexes do not stimulate neutrophil or monocytic chemotaxis but are removed by LRP, further underscoring its role as a serpin-enzyme complex clearance receptor.

Original languageEnglish (US)
Pages (from-to)31043-31050
Number of pages8
JournalJournal of Biological Chemistry
Issue number49
StatePublished - Dec 5 1997

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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