Guanylate-binding proteins convert cytosolic bacteria into caspase-4 signaling platforms

Abstract

Bacterial lipopolysaccharide triggers human caspase-4 (murine caspase-11) to cleave gasdermin-D and induce pyroptotic cell death. How lipopolysaccharide sequestered in membranes of cytosol-invading bacteria activates caspases remains unknown. Here we show that in interferon-γ stimulated cells guanylate binding proteins (GBPs) assemble on the surface of Gram-negative bacteria into polyvalent signaling platforms required for activation of caspase-4. Caspase-4 activation is hierarchically controlled by GBPs; GBP1 initiates platform assembly, GBP2 and GBP4 control caspase-4 recruitment, whereas GBP3 governs caspase-4 activation. In response to cytosol-invading bacteria, activation of caspase-4 through the GBP platform is essential to induce gasdermin-D dependent pyroptosis and processing of interleukin-18, thereby destroying the replicative niche for intracellular bacteria and alerting neighboring cells, respectively. Caspase-11 and GBPs epistatically protect mice against lethal bacterial challenge. Multiple antagonists of the pathway encoded by Shigella flexneri , a cytosol-adapted bacterium, provide compelling evolutionary evidence for the importance of the GBP-Caspase-4 pathway in anti-bacterial defense.

Human GBP1 Differentially Targets Salmonella and Toxoplasma to License Recognition of Microbial Ligands and Caspase-Mediated Death

“…IFNγ-inducible GBPs have emerged as important proteins in host defense against a range of pathogens ( Kutsch et al., 2020 ; Man et al., 2017 ; Meunier and Broz, 2016 ; Pilla-Moffett et al., 2016 ; Saeij and Frickel, 2017 ; Santos et al., 2020 ; Tretina et al., 2019 ; Wandel et al., 2020 ; Xavier et al., 2020 ). In this study, we have established that human GBP1 is essential for the breakdown of PVMs and Tg parasites through the use of two single-cell assays, combined with the artificial intelligence-driven image analysis pipeline HRMAn, that are adaptable for other pathogens ( Fisch et al., 2019b ).…”

Shigella hijacks the exocyst to cluster macropinosomes for efficient vacuolar escape

“…We reason that the exocyst-assisted docking of IAMs on S. flexneri BCV may enhance the exchange of proteins or lipids between the BCV and the IAMs, promoting the efficient disassembly of S. flexneri BCV. Cytosolic S. flexneri may thus take advantages of the exocyst-assisted vacuolar destabilization to escape of targeting by guanylate-binding proteins (GBPs) [41][42][43][44], concomitant with evasion of the LC3-dependent autophagic signaling that is initiated by the damaged vacuole [45].…”

Caspase-11 Non-canonical Inflammasomes in the Lung

“…Nonetheless, most studies suggest that GBPs are either recruited to the pathogen-containing vacuoles (PCVs), which might promote lysis of PCVs and consequent exposure of vacuolar LPS to caspase-11, or alternatively, GBPs are recruited to spontaneously ruptured bacteria-containing vacuoles or directly to cytosolic bacteria, where they act to extract or expose lipid A buried in bacterial membranes for recognition by caspase-11 (61,62,75,76). In support of this latter hypothesis, human guanylate binding protein-1 (hGBP1) associates with the surface of intracellular Gram-negative bacterial pathogens after vacuolar escape (77,78). Then, GBP1 polymerizes to coat the bacteria and initiate the recruitment of GBP2-4 to assemble a platform for caspase-4 activation (77-79).…”

“…Then, GBP1 polymerizes to coat the bacteria and initiate the recruitment of GBP2-4 to assemble a platform for caspase-4 activation (77-79). hGBP1 binds directly to LPS (77)(78)(79) and exerts a detergent-like effect of clustering LPS, which disrupts bacterial surfaces (79), thereby exposing the membraneembedded lipid A for caspase-4 detection. In mice, GBPs can serve as a docking platform to recruit another interferoninducible protein, IRGB10 that can co-localize to the intracellular bacteria to disrupt the bacterial cell membrane and to liberate bacterial ligands, including LPS and DNA, for innate immune recognition (80).…”