Research ArticleImmunology

STING is an essential mediator of the Ku70-mediated production of IFN-λ1 in response to exogenous DNA

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Sci. Signal.  18 Jul 2017:
Vol. 10, Issue 488, eaah5054
DOI: 10.1126/scisignal.aah5054

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STINGing viruses with IFN-λ1

When cells sense cytosolic DNA, such as occurs during viral infection, they produce type I interferons (IFNs) as part of the antiviral response. Various cytosolic DNA sensors and their downstream effectors stimulate activation of the transcription factor IFN regulatory factor 3 (IRF3) to induce expression of genes encoding type I IFNs. Sui et al. investigated the mechanism by which the DNA protein kinase (DNA-PK) component Ku70, a DNA repair protein, induced production of the type III IFN IFN-λ1 in human cells exposed to cytosolic DNA or infected with the DNA virus HSV-2. Ku70 translocated from the nucleus to the cytosol to interact with the adaptor protein STING, a well-characterized mediator of type I IFN production. However, in the Ku70 pathway, IRF1 and IRF7 were required in addition to IRF3, and type III IFN production was slower than that of type I IFN. Together, these data suggest a role for STING in the late phase of the antiviral IFN response to DNA viruses.

Abstract

We previously identified Ku70, a subunit of a DNA repair protein complex, as a cytosolic DNA sensor that induces the production of interferon-λ1 (IFN-λ1) by human primary cells and cell lines. IFN-λ1 is a type III IFN and has similar antiviral activity to that of the type I IFNs (IFN-α and IFN-β). We observed that human embryonic kidney (HEK) 293T cells, which are deficient in the innate immune adaptor protein STING (stimulator of IFN genes), did not produce IFN-λ1 in response to DNA unless they were reconstituted with STING. Conversely, parental HEK 293 cells produced IFN-λ1 after they were exposed to exogenous DNA; however, when STING was knocked out in the HEK 293 cells through the CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 genome editing system, they lost this response. Through confocal microscopy, we demonstrated that endogenous Ku70 was located in the nucleus and then translocated to the cytoplasm upon DNA exposure to form a complex with STING. Additionally, the DNA binding domain of Ku70 was essential for formation of the Ku70-STING complex. Knocking down STING in primary human macrophages inhibited their ability to produce IFN-λ1 in response to transfection with DNA or infection with the DNA virus HSV-2 (herpes simplex virus–2). Together, these data suggest that STING mediates the Ku70-mediated IFN-λ1 innate immune response to exogenous DNA or DNA virus infection.

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