Despite its prominent role as a C-type lectin (CTL) pattern recognition receptor, mannose receptor (MR, CD206)-specific signaling molecules and pathways are unknown. The MR is highly expressed on human macrophages, regulating endocytosis, phagocytosis, and immune responses and mediating Mycobacterium tuberculosis (M.tb) phagocytosis by human macrophages, thereby limiting phagosome-lysosome (P-L) fusion. We identified human MR-associated proteins using phosphorylated and non-phosphorylated MR cytoplasmic tail peptides. We found that MR binds FcRγ-chain, which is required for MR plasma membrane localization and M.tb cell association. Additionally, we discovered that MR-mediated M.tb association triggers immediate MR tyrosine residue phosphorylation and Grb2 recruitment, activating the Rac/Pak/Cdc-42 signaling cascade important for M.tb uptake. MR activation subsequently recruits SHP-1 to the M.tb-containing phagosome, where its activity limits PI(3)P generation at the phagosome and M.tb P-L fusion and promotes M.tb growth. In sum, we identify human MR signaling pathways that temporally regulate phagocytosis and P-L fusion during M.tb infection. The human mannose receptor (MR) mediates macrophage phagocytosis and immune regulation. MR-specific signaling remains a major gap in the field. Rajaram et al. identify the importance of FcRγ-chain and Grb2 during MR-mediated phagocytosis and subsequent MR-dependent recruitment of SHP-1 to the M.tb phagosome, thereby limiting PI(3)P generation and phagosome-lysosome fusion.
Rajaram, M. V. S., Arnett, E., Azad, A. K., Guirado, E., Ni, B., Gerberick, A. D., … Schlesinger, L. S. (2017). M. tuberculosis-Initiated Human Mannose Receptor Signaling Regulates Macrophage Recognition and Vesicle Trafficking by FcRγ-Chain, Grb2, and SHP-1. Cell Reports, 21(1), 126–140. https://doi.org/10.1016/j.celrep.2017.09.034