mTOR Signaling Promotes Rapid m6A mRNA Methylation to Regulate NK-Cell Activation and Effector Functions

NK cells can be rapidly activated in response to cytokines during host defense against malignant cells or viral infection. However, it remains unclear what mechanisms precisely and rapidly regulate the expression of a large number of genes involved in activating NK cells. In this study, we discovered that NK-cell N6-methyladenosine (m6A) methylation levels were rapidly upregulated upon short-term NK-cell activation and were repressed in the tumor microenvironment (TME). Deficiency of methyltransferase-like 3 (METTL3) or METTL14 moderately influenced NK-cell homeostasis, while double-knockout of METTL3/14 more significantly impacted NK-cell homeostasis, maturation, and antitumor immunity. This suggests a cooperative role of METTL3 and METTL14 in regulating NK-cell development and effector functions. Using methylated RNA immunoprecipitation sequencing, we demonstrated that genes involved in NK-cell effector functions, such as Prf1 and Gzmb, were directly modified by m6A methylation. Furthermore, inhibiting mTOR complex 1 activation prevented m6A methylation levels from increasing when NK cells were activated, and this could be restored by S-adenosylmethionine supplementation. Collectively, we have unraveled crucial roles for rapid m6A mRNA methylation downstream of the mTOR complex 1-S-adenosylmethionine signal axis in regulating NK-cell activation and effector functions.