Pooled CRISPR screening identifies m(6)A as a positive regulator of macrophage activation

m(6)A RNA modification is implicated in multiple cellular responses. However, its function in the innate immune cells is poorly understood. Here, we identified major m(6)A “writers” as the top candidate genes regulating macrophage activation by LPS in an RNA binding protein focused CRISPR screening. We have confirmed that Mettl3-deficient macrophages exhibited reduced TNF-α production upon LPS stimulation in vitro. Consistently, Mettl3(flox/flox);Lyzm-Cre mice displayed increased susceptibility to bacterial infection and showed faster tumor growth. Mechanistically, the transcripts of the Irakm gene encoding a negative regulator of TLR4 signaling were highly decorated by m(6)A modification. METTL3 deficiency led to the loss of m(6)A modification on Irakm mRNA and slowed down its degradation, resulting in a higher level of IRAKM, which ultimately suppressed TLR signaling–mediated macrophage activation. Our findings demonstrate a previously unknown role for METTL3-mediated m(6)A modification in innate immune responses and implicate the m(6)A machinery as a potential cancer immunotherapy target.