Cytoplasmic-translocated Ku70 senses intracellular DNA and mediates interferon-lambda1 induction.

We have previously identified that human Ku70, a nuclear protein, serves as a cytosolic DNA sensor. Upon transfection with DNA or infection with DNA virus, Ku70 translocates from the nucleus into the cytoplasm and then predominately induces interferon lambda1 (IFN-λ1) rather than IFN-alpha or IFN-beta, through a STING-dependent signalling pathway. However, a detailed mechanism for Ku70 cytoplasmic translocation and its correlation with IFN-λ1 induction have not been fully elucidated. Here, we observed that cytoplasmic translocation of Ku70 only occurred in DNA-triggered IFN-λ1-inducible cells. Additionally, infection by Herpes simplex virus type-1 (HSV-1), a DNA virus, induces cytoplasmic translocation of Ku70 and IFN-λ1 induction in a strain-dependent manner: the translocation and IFN-λ1 induction were detected upon infection by HSV-1 McKrae, but not MacIntyre, strain. A kinetic analysis indicated that cytoplasmic translocation of Ku70 was initiated right after DNA transfection and was peaked at 6 hr after DNA stimulation. Furthermore, treatment with leptomycin B, a nuclear export inhibitor, inhibited both Ku70 translocation and IFN-λ1 induction, suggesting that Ku70 translocation is an essential and early event for its cytosolic DNA sensing. We further confirmed that enhancing the acetylation status of the cells promotes Ku70's cytoplasmic accumulation, and therefore increases DNA-mediated IFN-λ1 induction. These findings provide insights into the molecular mechanism by which the versatile sensor detects pathogenic DNA in a localization-dependent manner.