gC1q-R/p32, a C1q-binding protein, is a receptor for the InlB invasion protein of Listeria monocytogenes

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Abstract
InlB is a Listeria monocytogenes protein that promotes entry of the bacterium into mammalian cells by stimulating tyrosine phosphorylation of the adaptor proteins Gab1, Cbl and Shc, and activation of phosphatidylinositol (PI) 3‐kinase. Using affinity chromatography and enzyme‐linked immunosorbent assay, we demonstrate a direct interaction between InlB and the mammalian protein gC1q‐R, the receptor of the globular part of the complement component C1q. Soluble C1q or anti‐gC1q‐R antibodies impair InlB‐mediated entry. Transient transfection of GPC16 cells, which are non‐permissive to InlB‐mediated entry, with a plasmid‐expressing human gC1q‐R promotes entry of InlB‐coated beads. Furthermore, several experiments indicate that membrane recruitment and activation of PI 3‐kinase involve an InlB–gC1q‐R interaction and that gC1q‐R associates with Gab1 upon stimulation of Vero cells with InlB. Thus, gC1q‐R constitutes a cellular receptor involved in InlB‐mediated activation of PI 3‐kinase and tyrosine phosphorylation of the adaptor protein Gab1. After E‐cadherin, the receptor for internalin, gC1q‐R is the second identified mammalian receptor promoting entry of L.monocytogenes into mammalian cells.

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