Nucleic acids from bacteria or viruses induce potent immune responses in infected cells1–4. The detection of pathogen-derived nucleic acids is a central strategy by which the host senses infection and initiates protective immune responses5,6. Cyclic GMP-AMP synthase (cGAS) is a double-stranded DNA sensor7,8. It catalyzes the synthesis of cyclic GMP-AMP (cGAMP)9–12, which stimulates the induction of type I interferons (IFN-Is) through the STING-TBK1-IRF-3 signaling axis13–15. Stimulator of interferon genes (STING) oligomerizes upon cGAMP binding, leading to the recruitment and activation of tank-binding kinase 1 (TBK1)8,16. Interferon regulatory factor 3 (IRF-3) is then recruited to the signaling complex and activated by TBK18,17–20. Phosphorylated IRF-3 translocates to the nucleus and initiates the expression of IFN-Is21. However, the precise mechanisms governing STING activation by cGAMP and subsequent TBK1 activation by STING remained poorly understood. Here we show that a conserved PLPLRT/SD motif within the C-terminal tail of STING mediates the recruitment and activation of TBK1. Crystal structures of TBK1 bound to STING reveal that the PLPLRT/SD motif binds to the dimer interface of TBK1. Cell-based studies confirm that the direct interaction between TBK1 and STING is essential for IFN-β induction upon cGAMP stimulation. Moreover, we show that full-length STING oligomerizes upon cGAMP binding and highlight this as an essential step in the activation of STING-mediated signaling.

Pathogen-derived nucleic acids induce potent innate immune responses 1 - 6 . Cyclic GMP-AMP synthase (cGAS) is a dsDNA sensor that catalyzes the synthesis of a cyclic dinucleotide cGAMP, which mediates the induction of type I interferons through the STING-TBK1-IRF3 signaling axis 7 - 11 . It was widely accepted that cGAS is not reactive to self-DNA due to its cytosolic localization 2 , 12 , 13 . However, recent studies revealed that cGAS is mostly localized in the nucleus and tight nuclear tethering keeps cGAS inactive 14 - 18 . Here we show that cGAS binds to nucleosomes with nanomolar affinity and nucleosome binding potently inhibits the catalytic activity of cGAS. To elucidate the molecular basis of cGAS inactivation by nuclear tethering, we have determined the structure of mouse cGAS bound to human nucleosome by cryo-EM. The structure shows that cGAS binds to a negatively charged acidic patch formed by histone H2A and H2B via its second DNA binding site 19 . High affinity nucleosome binding blocks dsDNA binding and keeps cGAS in an inactive conformation. Mutations of cGAS that disrupt nucleosome binding dramatically affect cGAS mediated signaling in cells.

Background:The mechanisms of transcriptional regulation of TNFRSF10A and TNFRSF10B are not well described. Results: DDIT3 and KAT2A cooperatively up-regulated TNFRSF10A and TNFRSF10B. Conclusion: DDIT3 and KAT2A promote the transcription of TNFRSF10A and TNFRSF10B via the AP-1 and DDIT3 binding sites, respectively. Significance: Our findings offer new insights on the mechanisms of ER stress-mediated apoptosis.