IFN-γ extends the immune functions of Guanylate Binding Proteins to inflammasome-independent antibacterial activities during Francisella novicida infection

PLoS Pathog. 2017 Oct 2;13(10):e1006630. doi: 10.1371/journal.ppat.1006630. eCollection 2017 Oct.

Abstract

Guanylate binding proteins (GBPs) are interferon-inducible proteins involved in the cell-intrinsic immunity against numerous intracellular pathogens. The molecular mechanisms underlying the potent antibacterial activity of GBPs are still unclear. GBPs have been functionally linked to the NLRP3, the AIM2 and the caspase-11 inflammasomes. Two opposing models are currently proposed to explain the GBPs-inflammasome link: i) GBPs would target intracellular bacteria or bacteria-containing vacuoles to increase cytosolic PAMPs release ii) GBPs would directly facilitate inflammasome complex assembly. Using Francisella novicida infection, we investigated the functional interactions between GBPs and the inflammasome. GBPs, induced in a type I IFN-dependent manner, are required for the F. novicida-mediated AIM2-inflammasome pathway. Here, we demonstrate that GBPs action is not restricted to the AIM2 inflammasome, but controls in a hierarchical manner the activation of different inflammasomes complexes and apoptotic caspases. IFN-γ induces a quantitative switch in GBPs levels and redirects pyroptotic and apoptotic pathways under the control of GBPs. Furthermore, upon IFN-γ priming, F. novicida-infected macrophages restrict cytosolic bacterial replication in a GBP-dependent and inflammasome-independent manner. Finally, in a mouse model of tularemia, we demonstrate that the inflammasome and the GBPs are two key immune pathways functioning largely independently to control F. novicida infection. Altogether, our results indicate that GBPs are the master effectors of IFN-γ-mediated responses against F. novicida to control antibacterial immune responses in inflammasome-dependent and independent manners.

MeSH terms

  • Animals
  • Disease Models, Animal
  • Enzyme-Linked Immunosorbent Assay
  • Female
  • Flow Cytometry
  • Fluorescent Antibody Technique
  • Francisella
  • Francisella tularensis / immunology*
  • GTP-Binding Proteins / immunology*
  • Gene Knockdown Techniques
  • Gram-Negative Bacterial Infections / immunology
  • Immunoblotting
  • Inflammasomes / immunology*
  • Interferon-gamma / immunology*
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Tularemia / immunology*

Substances

  • Inflammasomes
  • Interferon-gamma
  • GTP-Binding Proteins

Grants and funding

This work was supported by an European Research Council (ERC: https://erc.europa.eu/) starting grant 311542 to TH and the Swedish Medical Research Council (http://www.vr.se/inenglish.4.12fff4451215cbd83e4800015152.html) (K2013-8621 and 2013-4581) to AS. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.