Pooled CRISPR screening identifies mA as a positive regulator of macrophage activation.

mA RNA modification is implicated in multiple cellular responses. However, its function in the innate immune cells is poorly understood. Here, we identified major mA "writers" as the top candidate genes regulating macrophage activation by LPS in an RNA binding protein focused CRISPR screening. We have confirmed that deficient macrophages exhibited reduced TNF-α production upon LPS stimulation in vitro. Consistently, ;Cre mice displayed increased susceptibility to bacterial infection and showed faster tumor growth. Mechanistically, the transcripts of the gene encoding a negative regulator of TLR4 signaling were highly decorated by mA modification. METTL3 deficiency led to the loss of mA modification on 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 mA modification in innate immune responses and implicate the mA machinery as a potential cancer immunotherapy target.