Abstract
ABSTRACTDynamin-like guanylate binding proteins (GBPs) are gamma interferon (IFN-γ)-inducible host defense proteins that can associate with cytosol-invading bacterial pathogens. Mouse GBPs promote the lytic destruction of targeted bacteria in the host cell cytosol, but the antimicrobial function of human GBPs and the mechanism by which these proteins associate with cytosolic bacteria are poorly understood. Here, we demonstrate that human GBP1 is unique among the seven human GBP paralogs in its ability to associate with at least two cytosolic Gram-negative bacteria, Burkholderia thailandensis and Shigella flexneri. Rough lipopolysaccharide (LPS) mutants of S. flexneri colocalize with GBP1 less frequently than wild-type S. flexneri does, suggesting that host recognition of O antigen promotes GBP1 targeting to Gram-negative bacteria. The targeting of GBP1 to cytosolic bacteria, via a unique triple-arginine motif present in its C terminus, promotes the corecruitment of four additional GBP paralogs (GBP2, GBP3, GBP4, and GBP6). GBP1-decorated Shigella organisms replicate but fail to form actin tails, leading to their intracellular aggregation. Consequentially, the wild type but not the triple-arginine GBP1 mutant restricts S. flexneri cell-to-cell spread. Furthermore, human-adapted S. flexneri, through the action of one its secreted effectors, IpaH9.8, is more resistant to GBP1 targeting than the non-human-adapted bacillus B. thailandensis. These studies reveal that human GBP1 uniquely functions as an intracellular “glue trap,” inhibiting the cytosolic movement of normally actin-propelled Gram-negative bacteria. In response to this powerful human defense program, S. flexneri has evolved an effective counterdefense to restrict GBP1 recruitment.
Highlights
Dynamin-like guanylate binding proteins (GBPs) are gamma interferon (IFN-␥)-inducible host defense proteins that can associate with cytosol-invading bacterial pathogens
While we failed to detect any colocalization between human GBPs and the Gram-positive bacterium L. monocytogenes, we found that GBP1, independently of other human GBP paralogs, targeted both of the Gram-negative bacteria B. thailandensis and S. flexneri
We observed that GBP1 was the sole human GBP family member to colocalize with the cytosolic Gram-negative bacterium B. thailandensis in either naive or IFN-␥-primed A549 cells (Fig. 1B)
Summary
Dynamin-like guanylate binding proteins (GBPs) are gamma interferon (IFN-␥)-inducible host defense proteins that can associate with cytosol-invading bacterial pathogens. We systematically tested all seven members of the human GBP protein family for their ability to colocalize with the cytosolic bacterial pathogens Listeria monocytogenes, Shigella flexneri, and Burkholderia thailandensis All of these bacterial species are equipped with the ability to coopt the host actin polymerization machinery for actin-based cytosolic motility and cell-to-cell spread [20]. While we failed to detect any colocalization between human GBPs and the Gram-positive bacterium L. monocytogenes, we found that GBP1, independently of other human GBP paralogs, targeted both of the Gram-negative bacteria B. thailandensis and S. flexneri This specific interaction between GBP1 and bacteria, which is determined by a unique C-terminal triple-arginine motif, inhibits actin tail formation of GBP1-decorated bacteria, resulting in a reduction of bacterial cell-to-cell spread. This study provides a novel understanding of the role of human GBPs in immunity to bacterial pathogens and defines a virulence strategy employed by a human-adapted microbe to escape from GBP1-regulated host defense
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