MEF2A suppresses replicative stress responses that trigger DDX41-dependent IFN production

ABSTRACT Interferons (IFN) are induced by sensing of self- and non-self DNA or genomic lesions by pathogen recognition receptors (PRR) that activate STING. These pathways must be kept in check by negative regulators to prevent unscheduled activation of IFN, which contributes to autoinflammation. Here we show that MEF2A as a novel negative regulator of inflammation that suppresses homeostatic induction of IFNs. Indeed, MEF2A deficiency results in the spontaneous production of type I IFN and robust downstream IFN-stimulated gene expression that coincided with a robust cellular antiviral state. Mechanistically, MEF2A depletion promoted the accumulation of R-loops that activate the DDX41/STING pathway. This pro-inflammatory pathway was dependent on ATR kinase activity, hallmark of the replicative stress response, was necessary for the activation of STING upon loss of MEF2A expression. Thus, our study connects MEF2A with protection from maladaptive type I IFN responses triggered by R-loop accumulation and links the DDX41-dependent activation of STING to the DNA damage response.