Mettl3-mediated mRNA m6A methylation promotes dendritic cell activation.

N6-methyladenosine (m6A) modification plays important roles in various cellular responses by regulating mRNA biology. However, how m6A modification is involved in innate immunity via affecting the translation of immune transcripts remains to be further investigated. Here we report that RNA methyltransferase Mettl3-mediated mRNA m6A methylation promotes dendritic cell (DC) activation and function. Specific depletion of Mettl3 in DC resulted in impaired phenotypic and functional maturation of DC, with decreased expression of co-stimulatory molecules CD40, CD80 and cytokine IL-12, and reduced ability to stimulate T cell responses both in vitro and in vivo. Mechanistically, Mettl3-mediated m6A of CD40, CD80 and TLR4 signaling adaptor Tirap transcripts enhanced their translation in DC for stimulating T cell activation, and strengthening TLR4/NF-κB signaling-induced cytokine production. Our findings identify a new role for Mettl3-mediated m6A modification in increasing translation of certain immune transcripts for physiological promotion of DC activation and DC-based T cell response.