Interferon stimulatory DNA activates the DNA damage signaling through ATM and DNA-PK sensing.

In eukaryotic cells, DNA is normally confined in the nucleus and mitochondria and the presence of DNA in the cytoplasm is a danger signal that activates innate immune responses. Upon detection of cytoplasmic dsDNA in mammalian cells, the cGAS-STING pathway induces type I-Interferon and inflammatory responses, a key step in innate immune activation. Since its discovery, Interferon Stimulatory DNA (ISD), a linear double-stranded DNA, has been largely used to study the cGAS-STING pathway and its regulation. Here, we show that ISD also stimulates DNA damage signaling. We show that ISD activates both ataxia telangiectasia mutated and DNA-dependent protein kinase, the sensor kinases of the DNA damage response, independently of cGAS-STING signaling. Our results demonstrate that the DNA damage response, which is usually considered a response to genomic DNA lesions, can be promoted by foreign DNA. Our data further suggest that ISDs coordinate two central protective functions of cells, the innate immunity and DNA damage checkpoints.