A role of the Ca2+ binding site of DC-SIGN in the phagocytosis of E. coli

HEK293 cells stably expressing DC-SIGN (293/DC-SIGN) were examined for phagocytosis of Escherichia coli. 293/DC-SIGN stable transfectants were able to mediate phagocytosis of E. coli. The phagocytosis was inhibited by EDTA or several inhibitors specific for Syk kinase, Raf kinase and the transcription factor NF-κB. DC-SIGN consists of characteristic domains and motifs such as CRD, neck, incomplete ITAM, dileucine and tri-acidic cluster. HEK293 cells expressing mutants of DC-SIGN were also examined for the phagocytosis. It was found that Ca2+ binding sites in the CRD of DC-SIGN were involved in phagocytosis of bacteria as well as multimerization of DC-SIGN, and the neck region played a role in efficiency of binding to microbes as well as multimerization of the protein.