IFI16 senses and protects stalled replication forks.

Replication stress is a key driver of DNA damage and genome instability. Here, we report that replication stress induces an inflammatory response in the absence of DNA damage. The DNA-sensing factor interferon-γ-inducible factor 16 (IFI16) binds nascent DNA at stalled replication forks and signals via the adaptor stimulator of interferon genes (STING) to induce activation of nuclear factor κB (NF-κB) and the production of pro-inflammatory cytokines, independently of the cytosolic DNA sensor cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS). Replication stress-induced fork remodeling generates a new DNA end that is vulnerable to degradation by nucleases and is protected by a range of factors, including the tumor suppressors BRCA1 and BRCA2. IFI16 acts directly at stalled replication forks to protect nascent DNA from degradation by the nucleases MRE11, EXO1, and DNA2. Furthermore, IFI16 is required for the interferon-mediated rescue of fork protection in BRCA-deficient cells, highlighting the critical role of IFI16 in the crosstalk between innate immunity and fork protection during replication stress.