The detection of intracellular microbial DNA is critical to an appropriate innate immune response, however current knowledge on how such DNA is sensed is limited. Here we identify IFI16, a PYHIN protein, as an intracellular DNA sensor mediating interferon-β (IFNβ)-induction. IFI16 directly associated with IFNβ-inducing viral DNA motifs. STING, a critical mediator of IFNβ responses to DNA, was recruited to IFI16 after DNA stimulation. Reduction of expression of IFI16, or its murine ortholog p204, by RNA interference inhibited DNA- and herpes simplex virus (HSV)-1-induced gene induction and IRF3 and NFκB activation. IFI16/p204 is the first PYHIN protein shown to be involved in IFNβ induction, and thus together with AIM2, a PYHIN protein that senses DNA for caspase 1 activation, is part of a new family of innate DNA sensors which we term AIM2-like receptors (ALRs).

Inflammasomes regulate the activity of capase-1 and maturation of interleukin-1β and interleukin-18. Recently, AIM2 was shown to bind DNA and engage ASC to form a caspase-1 activating inflammasome. Using Aim2-deficient mice, we reveal a central role for AIM2 in regulating caspase-1-dependent maturation of IL-1β and IL-18, as well as pyroptosis in response to synthetic dsDNA. AIM2 is essential for inflammasome activation in response to Fransicella tularensis, vaccinia virus, mouse cytomegalovirus and plays a partial role in sensing Listeria monocytogenes. Moreover, production of IL-18 and NK cell-dependent IFN-γ production, events critical in early control of virus replication were dependent on AIM2 during mCMV infection in vivo. Collectively, these observations reveal the importance of AIM2 in sensing both bacterial and viral pathogens and triggering innate immunity.

SUMMARY Although Toll-like receptor 9 (TLR9) has been implicated in regulating cytokine and type I interferon (IFN) production during malaria in humans and mice, the high AT content of the Plasmodium falciparum genome prompted us to examine the possibility that malarial DNA triggered TLR9-independent DNA sensing pathways. Over 6000 ATTTTTAC (“AT-rich”) motifs are present in the genome of P. falciparum, which we show here potently induce type I IFNs. Parasite DNA, parasitized erythrocytes and oligonucleotides containing the AT-r motif induce type I IFNs via a pathway that did not involve previously described sensors including TLR9, DAI, RNA polymerase-III or IFI16/p204. Rather, AT-rich DNA sensing involved an unknown receptor that coupled to STING, TBK1 and IRF3-IRF7 signaling pathway. Mice lacking both IRF3 and IRF7, the kinase TBK1 or the type I IFN receptor were resistant to otherwise lethal cerebral malaria. Collectively, these observations implicate AT-rich DNA sensing via STING, TBK1 and IRF3-IRF7 in P. falciparum malaria.

Vascular disrupting agents (VDAs) such as DMXAA (5,6-dimethylxanthenone-4-acetic acid) represent a novel approach for cancer treatment. DMXAA has potent anti-tumor activity in mice and, despite significant pre-clinical promise, failed human clinical trials. The anti-tumor activity of DMXAA has been linked to its ability to induce type I interferons in macrophages although the molecular mechanisms involved are poorly understood. Here we identify STING as a direct receptor for DMXAA leading to TBK1 and IRF3 signaling. Remarkably, the ability to sense DMXAA was restricted to murine STING. Human STING failed to bind to or signal in response to DMXAA. Human STING also failed to signal in response to cyclic-dinucleotides, conserved bacterial second messengers known to bind and activate murine STING signaling. Collectively, these findings detail an unexpected species-specific role for STING as a receptor for an anti-cancer drug and uncover important insights that may explain the failure of DMXAA in clinical trials for human cancer.

Background: 5,6-Dimethylxanthenone-4-acetic acid (DMXAA) activates intracellular signaling through uncharacterized pathways similar to those engaged by bacterial pathogens. Results: Mitochondrial targeting agents and absence of STING impair the response to DMXAA in mouse macrophages. Conclusion: Mitochondrial membrane potential is required for optimal response to DMXAA. Significance: This study illustrates that mitochondrial physiology is pivotal in the host response to DMXAA and possibly bacterial pathogens.