Constitutive Interferon Maintains GBP Expression Required for Release of Bacterial Components Upstream of Pyroptosis and Anti-DNA Responses

Abstract

SUMMARYLegionella pneumophila elicits caspase-11-driven macrophage pyroptosis through guanylate-binding proteins (GBPs) encoded on chromosome 3. It has been proposed that microbe-driven IFN upregulates GBPs to facilitate pathogen vacuole rupture and bacteriolysis preceding caspase-11 activation. We show here that macrophage death occurred independently of microbial-induced IFN signaling and that GBPs are dispensable for pathogen vacuole rupture. Instead, the host-intrinsic IFN status sustained sufficient GBP expression levels to drive caspase-1 and caspase-11 activation in response to cytosol-exposed bacteria. In addition,endogenous GBP levels were sufficient for the release of DNA from cytosol-exposed bacteria, preceding the cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/ STING) pathway for Ifnb induction. Mice deficient for chromosome 3 GBPs were unable to mount a rapid IL-1/chemokine (C-X-C motif) ligand 1 (CXCL1) response during Legionella-induced pneumonia, with defective bacterial clearance. Our results show that rapid GBP activity is controlled by host-intrinsic cytokine signaling and that GBP activities precede immune amplification responses, including IFN induction, inflammasome activation, and cell death.

Human GBP1 differentially targetsSalmonellaandToxoplasmato license recognition of microbial ligands and caspase-mediated death

“…GBP1 targeting of Tg vacuolar membranes was required for their compromise and release of Tg-DNA, which resembled bacterial lysis in the cytosol by murine GBPs (Man et al, 2015;Liu et al, 2018). In contrast, STm enters the cytosol independently of GBP1.…”

Components of the endocytic and recycling trafficking pathways interfere with the integrity of the Legionella ‐containing vacuole

“…Establishment and maintenance of LCV membrane integrity are essential for protection of L. pneumophila from innate immune cytosolic sensing (Creasey & Isberg, 2014;Liu et al, 2018). The inability of a bacterial mutant to properly form the LCV or maintain its integrity results in a severe intracellular growth defect and pathogen clearance (Creasey & Isberg, 2012;Wiater, Dunn, Maxfield, & Shuman, 1998).…”

“…In the absence of SdhA, the LCV becomes disrupted and L. pneumophila is detected in the cytoplasm of the infected macrophage (Creasey & Isberg, 2012;Laguna et al, 2006). Bacteria exposed in this fashion to the cytosol are susceptible to recruitment of the interferon-regulated guanylate-binding proteins (GBP) family of anti-microbial proteins, resulting in leakage of lipopolysaccharide (LPS) and activation of caspase-11 (Creasey & Isberg, 2012;Liu et al, 2018;Piro et al, 2017). As a consequence, gasdermin D is activated and pyroptotic cell death ensues (Aachoui et al, 2013;Pilla et al, 2014;Shi et al, 2015).…”

Dynamin-related Irgm proteins modulate LPS-induced caspase-4 activation and septic shock

“…Irgm proteins regulate the subcellular localization and function of members of a second family of IFN-inducible dynamin-like GTPase, the Gbps (Haldar, Saka et al, 2013, Traver et al, 2011. Gbps colocalize with phagocytosed bacteria expressing virulence-inducing protein secretion systems , Feeley, Pilla-Moffett et al, 2017, promote the bacteriolytic destruction of these targeted virulent bacteria, and thereby release PAMPs from lysed bacteria resulting in the activation of cytosolic pattern recognition receptors (Fisch, Bando et al, 2019, Liu, Sarhan et al, 2018, Man, Karki et al, 2015, Meunier, Wallet et al, 2015. Although Gbps fail to colocalize with avirulent E. coli, Gbps still promote caspase-4 activation in BMMs exposed to nonpathogenic bacteria through a process that is largely facilitated by the Gbp-mediated recognition and processing of bacterially secreted OMVs , Vanaja et al, 2016.…”