m6A methylation potentiates cytosolic dsDNA recognition in a sequence-specific manner
Nucleic acid sensing through pattern recognition receptors is critical for immune recognition of microbial infections. Microbial DNA is frequently methylated at the N6 position of adenines (m6A), a modification that is rare in mammalian host DNA. We show that m6A-methylation of 5-GATC-3 motifs augments the immunogenicity of double stranded (ds)DNA in macrophages and dendritic cells. Transfection with m6A-methylated DNA increased the expression of the activation markers CD69 and CD86, and of Ifn{beta}, iNos and Cxcl10 mRNA. Recognition of m6A DNA occurs independently of TLR and RIG-I signaling but requires STING, a key mediator of cytosolic DNA sensing. Intriguingly, the response to m6A DNA is sequence-specific. m6A is immunostimulatory in some motifs, but immunosuppressive in others, a feature that is conserved between mouse and human. In conclusion, epigenetic alterations of bacterial DNA are differentially perceived by innate cells, a feature that could potentially be used for the design of immune-modulating therapeutics.