STING is a cell-intrinsic metabolic checkpoint restricting aerobic glycolysis by targeting HK2

The presence of DNA in the cytoplasm of mammalian cells is a danger signal that triggers host immune responses such as the production of type I interferons. Cytosolic DNA induces interferons through the production of cyclic guanosine monophosphate-adenosine monophosphate (cyclic GMP-AMP, or cGAMP), which binds to and activates the adaptor protein STING. Through biochemical fractionation and quantitative mass spectrometry, we identified a cGAMP synthase (cGAS), which belongs to the nucleotidyltransferase family. Overexpression of cGAS activated the transcription factor IRF3 and induced interferon-β in a STING-dependent manner. Knockdown of cGAS inhibited IRF3 activation and interferon-β induction by DNA transfection or DNA virus infection. cGAS bound to DNA in the cytoplasm and catalyzed cGAMP synthesis. These results indicate that cGAS is a cytosolic DNA sensor that induces interferons by producing the second messenger cGAMP.

Macrophages have an important role in the maintenance of tissue homeostasis. To perform this function, macrophages must have the capacity to monitor the functional states of their 'client cells': namely, the parenchymal cells in the various tissues in which macrophages reside. Tumours exhibit many features of abnormally developed organs, including tissue architecture and cellular composition. Similarly to macrophages in normal tissues and organs, macrophages in tumours (tumour-associated macrophages) perform some key homeostatic functions that allow tumour maintenance and growth. However, the signals involved in communication between tumours and macrophages are poorly defined. Here we show that lactic acid produced by tumour cells, as a by-product of aerobic or anaerobic glycolysis, has a critical function in signalling, through inducing the expression of vascular endothelial growth factor and the M2-like polarization of tumour-associated macrophages. Furthermore, we demonstrate that this effect of lactic acid is mediated by hypoxia-inducible factor 1α (HIF1α). Finally, we show that the lactate-induced expression of arginase 1 by macrophages has an important role in tumour growth. Collectively, these findings identify a mechanism of communication between macrophages and their client cells, including tumour cells. This communication most probably evolved to promote homeostasis in normal tissues but can also be engaged in tumours to promote their growth.

We report here the identification, following expression cloning, of a molecule, STING (STimulator of INterferon Genes) that regulates innate immune signaling processes. STING, comprising 5 putative transmembrane (TM) regions, predominantly resides in the endoplasmic reticulum (ER) and is able to activate both NF-κB and IRF3 transcription pathways to induce type I IFN and exert a potent anti-viral state following expression. In contrast, loss of STING rendered murine embryonic fibroblasts (STING −/−MEFs) extremely susceptible to negative-stranded virus infection, including vesicular stomatitis virus, VSV. Further, STING ablation abrogated the ability of intracellular B-form DNA, as well as members of the herpes virus family, to induce IFNβ, but did not significantly affect the Toll-like receptor (TLR pathway). Yeast-two hybrid and co-immunprecipitation studies indicated that STING interacts with RIG-I and with Ssr2/TRAPβ, a member of the translocon-associated protein (TRAP) complex required for protein translocation across the ER membrane following translation[1, 2]. RNAi ablation of TRAPβ and translocon adaptor Sec61β was subsequently found to inhibit STING’s ability to stimulate IFNβ. Thus, aside from identifying a novel regulator of innate immune signaling, this data implicates for the first time a potential role for the translocon in innate signaling pathways activated by select viruses as well as intracellular DNA.