N6-methyladenosine (m6A) is a reversible mRNA modification that has been shown to play important roles in various biological processes. However, the roles of m6A modification in macrophages are still unknown. Here, we discover that ablation of Mettl3 in myeloid cells promotes tumour growth and metastasis in vivo. In contrast to wild-type mice, Mettl3-deficient mice show increased M1/M2-like tumour-associated macrophage and regulatory T cell infiltration into tumours. m6A sequencing reveals that loss of METTL3 impairs the YTHDF1-mediated translation of SPRED2, which enhances the activation of NF-kB and STAT3 through the ERK pathway, leading to increased tumour growth and metastasis. Furthermore, the therapeutic efficacy of PD-1 checkpoint blockade is attenuated in Mettl3-deficient mice, identifying METTL3 as a potential therapeutic target for tumour immunotherapy.

The MYC oncogene is overexpressed in hepatocellular carcinoma (HCC) and has been associated with widespread microRNA (miRNA) repression; however, the underlying mechanisms are largely unknown. Here, we report that the c-Myc oncogenic transcription factor physically interacts with enhancer of zeste homolog 2 (EZH2), a core enzymatic unit of polycomb repressive complex 2 (PRC2). Furthermore, miR-101, an important tumor-suppressive miRNA in human hepatocarcinomas, is epigenetically repressed by PRC2 complex in a c-Myc-mediated manner. miR-101, in turn, inhibits the expression of two subunits of PRC2 ( EZH2 and EED ), thus creating a double-negative feedback loop that regulates the process of hepatocarcinogenesis. Restoration of miR-101 expression suppresses multiple malignant phenotypes of HCC cells by coordinate repression of a cohort of oncogenes, including STMN1 , JUNB , and CXCR7 , and further increases expression of endogenous miR-101 by inhibition of PRC2 activation. In addition, co-overexpression of c-Myc and EZH2 in HCC samples was closely associated with lower expression of miR-101 ( P < 0.0001) and poorer prognosis of HCC patients ( P < 0.01). Conclusions : c-Myc collaborates with EZH2-containing PRC2 complex in silencing tumor-suppressive miRNAs during hepatocarcinogenesis and provides promising therapeutic candidates for human HCC. (Hepatology 2014;59:1850–1863)

Double-stranded RNA (dsRNA) is a virus-encoded signature capable of triggering intracellular Rig-like receptors (RLR) to activate antiviral signaling, but whether intercellular dsRNA structural reshaping mediated by theN⁶-methyladenosine (m⁶A) modification modulates this process remains largely unknown. Here, we show that, in response to infection by the RNA virus Vesicular Stomatitis Virus (VSV), the m⁶A methyltransferase METTL3 translocates into the cytoplasm to increase m⁶A modification on virus-derived transcripts and decrease viral dsRNA formation, thereby reducing virus-sensing efficacy by RLRs such as RIG-I and MDA5 and dampening antiviral immune signaling. Meanwhile, the genetic ablation of METTL3 in monocyte or hepatocyte causes enhanced type I IFN expression and accelerates VSV clearance. Our findings thus implicate METTL3-mediated m⁶A RNA modification on viral RNAs as a negative regulator for innate sensing pathways of dsRNA, and also hint METTL3 as a potential therapeutic target for the modulation of anti-viral immunity.