The obligatory intracellular pathogen lacks most factors that could respond to oxidative stress (a host cell defense mechanism). We previously found that the C terminus of surface invasin, ntry-riggering rotein of (EtpE; EtpE-C) directly binds mammalian DNase X, a glycosylphosphatidylinositol-anchored cell surface receptor and that binding is required to induce bacterial entry and simultaneously to block the generation of reactive oxygen species (ROS) by host monocytes and macrophages. However, how the EtpE-C-DNase X complex mediates the ROS blockade was unknown. A mammalian transmembrane glycoprotein CD147 (basigin) binds to the EtpE-DNase X complex and is required for entry and infection of host cells. Here, we found that bone marrow-derived macrophages (BMDM) from myeloid cell lineage-selective CD147-null mice had significantly reduced -induced or EtpE-C-induced blockade of ROS generation in response to phorbol myristate acetate. In BMDM from CD147-null mice, nucleofection with CD147 partially restored the -mediated inhibition of ROS generation. Indeed, CD147-null mice as well as their BMDM were resistant to infection. Moreover, in human monocytes, anti-CD147 partially abrogated EtpE-C-induced blockade of ROS generation. Both and EtpE-C could block activation of the small GTPase Rac1 (which in turn activates phagocyte NADPH oxidase) and suppress activation of Vav1, a hematopoietic-specific Rho/Rac guanine nucleotide exchange factor by phorbol myristate acetate. Vav1 suppression by was CD147 dependent. is the first example of pathogens that block Rac1 activation to colonize macrophages. Furthermore, uses EtpE to hijack the unique host DNase X-CD147-Vav1 signaling to block Rac1 activation. is an obligatory intracellular bacterium with the capability of causing an emerging infectious disease called human monocytic ehrlichiosis. preferentially infects monocytes and macrophages, professional phagocytes, equipped with an arsenal of antimicrobial mechanisms, including rapid reactive oxygen species (ROS) generation upon encountering bacteria. As isolated from host cells are readily killed upon exposure to ROS, must have evolved a unique mechanism to safely enter phagocytes. We discovered that binding of the surface invasin to the host cell surface receptor not only triggers entry but also blocks ROS generation by the host cells by mobilizing a novel intracellular signaling pathway. Knowledge of the mechanisms by which ROS production is inhibited may lead to the development of therapeutics for ehrlichiosis as well as other ROS-related pathologies.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7175088PMC
http://dx.doi.org/10.1128/mBio.00267-20DOI Listing

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