Guanylate-binding proteins promote activation of the AIM2 inflammasome during infection with Francisella novicida

Abstract

The AIM2 inflammasome detects double-stranded DNA in the cytosol and induces caspase-1-dependent pyroptosis as well as release of the inflammatory cytokines IL-1β and IL-18. AIM2 is critical for host defense against DNA viruses and bacteria that replicate in the cytosol, such as Francisella novicida. AIM2 activation by F. novicida requires bacteriolysis, yet whether this process is accidental or a host-driven immune mechanism remained unclear. Using siRNA screening for nearly 500 interferon-stimulated genes, we identified guanylate-binding proteins GBP2 and GBP5 as key AIM2 activators during F. novicida infection. Their prominent role was validated in vitro and in a mouse model of tularemia. Mechanistically, these two GBPs target cytosolic F. novicida and promote bacteriolysis. Thus, besides their role in host defense against vacuolar pathogens, GBPs also facilitate the presentation of ligands by directly attacking cytosolic bacteria.

Ubiquitin systems mark pathogen-containing vacuoles as targets for host defense by guanylate binding proteins

“…GBPs exert their antimicrobial and proinflammatory activities in part by binding to and disrupting PV membranes (5,6). Additionally, GBPs can translocate to cytoplasmic bacterial pathogens, where they induce bacteriolysis (8,12). The mechanisms by which GBPs recognize either PVs or cytoplasmic bacteria are currently unknown.…”

“…For quantification of ruptured C. trachomatis inclusions, we adapted and modified a published protocol for Digitonin-mediated permeabilization of plasma membranes (8). MEFs were infected with GFP + C. trachomatis at a multiplicity of infection (MOI) of 2 followed by treatment with 100 U/mL of IFNγ at 3 hpi or left untreated.…”

“…Critical mediators of host-directed attacks on PVs are two families of IFNγ-inducible GTPases: immunityrelated GTPases (IRGs) and guanylate binding proteins (GBPs) (2). Members of both GTPase families play roles in host-mediated lysis of PVs, a process resulting in the release of microbes into the host cell cytoplasm, subsequent killing of PV-expelled microbes, and host cell death (3)(4)(5)(6)(7)(8). Additionally, GBPs help deliver cytosolic subunits of the antimicrobial NADPH oxidase NOX2 for assembly on phagosomal membranes, orchestrate the capture of PV-resident microbes inside degradative autophagolysosomes, and promote the activation of canonical and noncanonical inflammasome pathways (5,(8)(9)(10)(11)(12).…”

Cellular and molecular regulation of innate inflammatory responses

“…GBPs are encoded by Nucleus TRAF6 TRAF6 IRAK1 IRAK1 MAPKs MAPKs NF-κB IRF3 IRF3 IRF7 IRF7 TIRAP TIRAP TRAM TRAM TRIF TRIF IRAK2 IRAK2 IRAK4 IRAK4 TAB3 TAB3 TAB2 TAB2 TAK1 interferon-stimulated genes which is induced by F. novicida via the DNA sensor cGAS and its adaptor STING. 38,39 In addition, RNA viral infection also triggers inflammasome activation and IL-1β production. Recognition of RNA virus by RIG-I mediates ASC/caspase-1 inflammasome-dependent IL-1β procession in a manner independent of MAVS and NLRP3.…”

Guanylate Binding Proteins Regulate Inflammasome Activation in Response to Hyperinjected Yersinia Translocon Components

“…Gbp Chr3Ϫ/Ϫ BMDMs exhibit reduced levels of caspase-11-dependent pyroptosis in response to transfection of LPS or to infection by Gram-negative bacteria that enter the host cytoplasm (28). Gbp5 and -2 also promote canonical inflammasome activation by lysis of cytoplasmic bacteria and activation of an Aim2 inflammasome due to released bacterial DNA or by direct binding of Gbp5 to NLRP3 (63,69,70). We therefore sought to test whether GBPs were acting in one or both of these inflammasome pathways in response to hyperinjection of the Yersinia translocon.…”