IFI16 is required for DNA sensing in human macrophages by promoting production and function of cGAMP

Innate immune activation by macrophages is an essential part of the host defence against pathogen infections. Cytosolic recognition of microbial DNA in macrophages leads to induction of type I interferons (IFNs) and numerous cytokines through activation of cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING). Other host factors, including interferon-gamma inducible factor 16 (IFI16), have also been proposed to contribute to immune activation by DNA. However, their relation to the cGAS-STING pathway has not been elucidated. Here, we report that IFI16 acts in the cGAS-STING pathway at two distinct levels. Depletion of IFI16 in human macrophages impairs cGAMP production upon DNA stimulation, whereas overexpression of IFI16 amplifies the function of cGAS. Furthermore, IFI16 is found to be vital for the downstream signalling stimulated by cGAMP, facilitating recruitment and activation of TANK-binding kinase 1 (TBK1) in the STING complex. Collectively, our results suggest that IFI16 is essential for efficient sensing and signalling upon DNA challenge to drive expression of IFNs and establish an antiviral state.