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Summary Inflammasome-activated caspase-1 cleaves gasdermin D to unmask its pore-forming activity, the predominant consequence of which is pyroptosis. Here, we report an additional biological role for gasdermin D in limiting cytosolic DNA surveillance. Cytosolic DNA is sensed by Aim2 and cyclic GMP-AMP synthase (cGAS) leading to inflammasome and type I interferon responses, respectively. We found that gasdermin D activated by the Aim2 inflammasome suppressed cGAS-driven type I interferon response to cytosolic DNA and Francisella novicida in macrophages. Similarly, interferon-β (IFN-β) response to F. novicida infection was elevated in gasdermin D-deficient mice. Gasdermin D-mediated negative regulation of IFN-β occurred in a pyroptosis-, interleukin-1 (IL-1)-, and IL-18-independent manner. Mechanistically, gasdermin D depleted intracellular potassium (K+) via membrane pores, and this K+ efflux was necessary and sufficient to inhibit cGAS-dependent IFN-β response. Thus, our findings have uncovered an additional interferon regulatory module involving gasdermin D and K+ efflux. Graphical Abstract Highlights • Inflammasome-activated gasdermin D limits type I interferon responses to cytosolic DNA • Gasdermin D targets cGAS activation to inhibit IFN-β response to cytosolic DNA • Depletion of intracellular K+ by gasdermin D is responsible for limiting cGAS signaling • K+ efflux is sufficient to inhibit cGAS-dependent type I interferon responses Gasdermin D is a pore-forming protein, which upon activation by inflammasome complexes mediates pyroptotic cell death and IL-1 release. Banerjee et al. demonstrate a previously unknown regulatory role for gasdermin D-driven K+ efflux in reining in cGAS-dependent type I interferon response to cytosolic DNA. [ABSTRACT FROM AUTHOR]

Summary Sensing of lipopolysaccharide (LPS) in the cytosol triggers caspase-11 activation and is central to host defense against Gram-negative bacterial infections and to the pathogenesis of sepsis. Most Gram-negative bacteria that activate caspase-11, however, are not cytosolic, and the mechanism by which LPS from these bacteria gains access to caspase-11 in the cytosol remains elusive. Here, we identify outer membrane vesicles (OMVs) produced by Gram-negative bacteria as a vehicle that delivers LPS into the cytosol triggering caspase-11-dependent effector responses in vitro and in vivo. OMVs are internalized via endocytosis, and LPS is released into the cytosol from early endosomes. The use of hypovesiculating bacterial mutants, compromised in their ability to generate OMVs, reveals the importance of OMVs in mediating the cytosolic localization of LPS. Collectively, these findings demonstrate a critical role for OMVs in enabling the cytosolic entry of LPS and, consequently, caspase-11 activation during Gram-negative bacterial infections. [ABSTRACT FROM AUTHOR]

Summary Interferon-inducible human oligoadenylate synthetase-like (OASL) and its mouse ortholog, Oasl2 , enhance RNA-sensor RIG-I-mediated type I interferon (IFN) induction and inhibit RNA virus replication. Here, we show that OASL and Oasl2 have the opposite effect in the context of DNA virus infection. In Oasl2 −/− mice and OASL -deficient human cells, DNA viruses such as vaccinia, herpes simplex, and adenovirus induced increased IFN production, which resulted in reduced virus replication and pathology. Correspondingly, ectopic expression of OASL in human cells inhibited IFN induction through the cGAS-STING DNA-sensing pathway. cGAS was necessary for the reduced DNA virus replication observed in OASL -deficient cells. OASL directly and specifically bound to cGAS independently of double-stranded DNA, resulting in a non-competitive inhibition of the second messenger cyclic GMP-AMP production. Our findings define distinct mechanisms by which OASL differentially regulates host IFN responses during RNA and DNA virus infection and identify OASL as a negative-feedback regulator of cGAS. Graphical Abstract Highlights • Loss of human OASL and mouse Oasl2 inhibits DNA virus infection • OASL and Oasl2 inhibit cGAS-mediated IFN induction • OASL specifically binds to cGAS to inhibit cGAS enzyme activity • OASL binds to cGAS independently of double-stranded DNA The interferon (IFN)-stimulated gene OASL enhances RNA-sensor RIG-I-mediated IFN induction to inhibit RNA virus replication. In contrast, Ghosh et al. show that during DNA virus infection, OASL binds to the DNA sensor cGAS to inhibit IFN induction and enhance DNA virus replication. These findings highlight the distinct regulation of IFN induction by OASL during RNA and DNA virus infection. [ABSTRACT FROM AUTHOR]