Project description:N6-methyladenosine (m6A) modification of mRNA catalyzed by METTL3 is enriched at a subset of stop codons. METTL3 can promote translation but the mechanism and widespread relevance remain unknown. Here we show that METTL3 enhances translation only when tethered to reporter mRNA at sites close to the stop codon supporting a mRNA looping mechanism for ribosome recycling and translational control. Electron microscopy revealed the topology of individual polyribosomes with single METTL3 foci found in close proximity to 5’ cap-binding proteins. We identify a direct physical and functional interaction between METTL3 and the eukaryotic translation initiation factor 3 subunit h (eIF3h). METTL3 promotes translation of a large subset of oncogenic mRNAs, including BRD4 that are also m6A-modified in human primary lung tumors. The METTL3-eIF3h interaction is required for enhanced translation, formation of densely packed polyribosomes, and oncogenic transformation. METTL3 depletion inhibits tumorigenicity and sensitizes lung cancer cells to BRD4 inhibition. These findings uncover a mRNA looping mechanism of translation control and identify METTL3-eIF3h as a potential cancer therapeutic target.
Project description:we find METTL3 associates with polyribosomes and promotes translation. METTL3 depletion inhibits translation, and both wild-type and catalytically inactive METTL3 promote translation when tethered to the 3' untranslated region (UTR) of a reporter mRNA. Mechanistically, METTL3 enhances mRNA translation through an interaction with the translation initiation machinery. m6A seq in A549 and H1299 cells, RNA seq in METTL3 knockdown cells
Project description:we find METTL3 associates with polyribosomes and promotes translation. METTL3 depletion inhibits translation, and both wild-type and catalytically inactive METTL3 promote translation when tethered to the 3' untranslated region (UTR) of a reporter mRNA. Mechanistically, METTL3 enhances mRNA translation through an interaction with the translation initiation machinery.
Project description:Methyltransferase-like 3 (METTL3) is the predominant catalytic enzyme which forms a stable complex with METTL14 and WTAP to promote m6A methylation in the nucleus. Recently, accumulating evidence has shown that METTL3 can express in the cytoplasm but the function of cytoplasmic METTL3 is not fully understood. Here, we demonstrated that METTL3 inhibition significantly delayed tumorigenesis in gastric cancer both in and ex vivo. Surprisingly, our data revealed that METTL3 could not only facilitate cancer progression via mRNA m6A modification, but also bind to numerous non-m6A-modified mRNAs, suggesting an unexpected role of METTL3 that was independent of m6A modification. Mechanistically, cytoplasm-anchored METTL3 interacted with poly(A) binding protein cytoplasmic 1 (PABPC1) to stabilize its association with cap-binding complex eIF4F, which preferentially promoted the translation of epigenetic factors without m6A modification. Clinical investigation using both xenograft models and patient samples showed that cytoplasmic distributed METTL3 was highly correlated with gastric cancer progression, and this finding could be expanded in prostate cancer patients. We therefore propose that cytoplasmic METTL3 enhances the translation of both m6A and non-m6A-modified epigenetic mRNAs thus serves as an oncogenic driver in cancer progression, and METTL3 subcellular distribution can assist diagnose and predict prognosis for cancer patients.
Project description:N6-methyladenosine (m6A) is an abundant internal RNA modification, in both coding and non-coding RNAs, catalyzed by the METTL3/METTL14 methyltransferase complex. We identified METTL3 as an essential gene for acute myeloid leukemia (AML) cell growth in two distinct genetic screens. Down-regulation of METTL3 results in cell cycle arrest, differentiation of leukemic cells and failure to establish leukemia in immunodeficient mice. We show that METTL3, independently of METTL14, associates with chromatin and localizes to the transcriptional start site (TSS) of 83 active genes. The vast majority of these genes have a CAATT-box motif at their TSS, are occupied by a specific set of transcription factors including NFY, WDR5, KLF9 and they harbor specific histone modifications (e.g. H3R2me2s). Promoter bound METTL3 induces m6A modification within the coding region of the associated mRNA transcript and it enhances translation due to relief of ribosome stalling. We show that genes regulated by METTL3 in this way are necessary for AML-leukemia. Together, these data define a new mechanism of gene regulation by METTL3 and identify this enzyme as a novel therapeutic target for AML.
Project description:Methyltransferase-like 3 (METTL3) is the best known m6A methyltransferase of the N6-adenosine-methyltransferase complex that functions in the reversible epi-transcriptome modulation of m6A modification. Besides acting as a m6A methyltransferase, METTL3 also regulates mRNA translation as well as other biological processes either through m6A “reader”-mediated downstream effect or directly binding to m6A sites, but the underlying mechanism and biological significance of these cytoplasmic events remain undefined. Here, we demonstrated that METTL3 inhibition significantly delayed gastric tumorigenesis in patient-derived xenograft model. Intriguingly, global METTL3-binding profiling revealed METTL3 occupied numerous oncogenic mRNAs without m6A signals, indicating a novel mechanism independent of m6A machinery. Furthermore, METTL3 was observed to translocate from nucleus to cytoplasm during gastric carcinogenesis, and its cytoplasm-to-nucleus ratio was correlated with cancer progression. In addition, the nuclear retention of METTL3 nearly abolished its tumor-promoting activity. Mechanistically, METTL3 interacted with PABPC1 to promote RNA looping, thus facilitating the translation of multiple oncogenic mRNAs. Taken together, our findings indicate an unexpected role of METTL3 as an important translational regulator independent of either m6A-“writer” or -“reader” activities and suggest METTL3 as a therapeutic target in gastric cancer.
Project description:Considering m6A modification in mRNA was reported to be intensively corelated with RNA metabolism like RNA decay and RNA translation, we wonderd whether deleting Mettl3, the main catalzing enzyme, affect the RNA translation efficiency of mouse dendritic cells.
Project description:METTL3 and METTL14 are considered to faithfully form the m6A writing complex in a 1:1 ratio, regulating the fate of mRNA by adding m6A modifications. However, recent studies have shown inconsistent expression and prognostic value of METTL3 and METTL14 in some tumors, suggesting that they may not be faithful in tumors. Pan-cancer analysis based on TCGA data reveals significant differences in expression, function, tumor burden correlation, and immune correlation between METTL3 and METTL14, especially in esophageal squamous cell carcinoma (ESCC). Knockdown of METTL3 significantly inhibits the cell proliferation in vitro and in vivo in ESCC EC109 cells, while the impact of METTL14 knockdown on proliferation is limited, and it cannot abolish the expression of METTL3 protein. mRNA-seq results indicate that METTL3 independently regulates the expression of 1615 genes, while only 776 genes are co-regulated by METTL3 and METTL14. Furthermore, through immunofluorescence co-localization, it is observed that METTL3 and METTL14 have certain inconsistencies in cellular localization. HPLC-MS results show that METTL3 independently binds to the Nop56p-associated pre-rRNA complex and mRNA splicing complex, separate from METTL14. Through bioinformatics and various omics studies, we have preliminarily discovered that METTL3 independently regulating tumor cell proliferation, and the participation in mRNA splicing may be a critical molecular mechanism. Our study provides an experimental basis and theoretical foundation for further understanding of the m6A writing complex and tumor therapy targeting METTL3.
Project description:Spermatogenesis is precisely controlled at the transcriptional, posttranscriptional, and translational levels. Here we report that N6-methyladenosine (m6A), an epitranscriptomic mark regulating gene expression, plays essential roles during spermatogenesis. We present comprehensive m6A mRNA methylomes of mouse spermatogenic cells from five developmental stages: undifferentiated spermatogonia, type A1 spermatogonia, preleptotene spermatocytes, pachytene/diplotene spermatocytes, and round spermatids. Germ cell-specific inactiva- tion of the m6A RNA methyltransferase Mettl3 or Mettl14 with Vasa-Cre causes loss of m6A and depletion of SSCs. m6A depletion dysregulates translation of transcripts that are required for SSC proliferation/differentiation. Com- bined deletion of Mettl3 and Mettl14 in advanced germ cells with Stra8-GFPCre disrupts spermiogenesis, whereas mice with single deletion of either Mettl3 or Mettl14 in advanced germ cells show normal spermatogenesis. The sper- matids from double-mutant mice exhibit impaired translation of haploid-specific genes that are essential for spermio- genesis. This study highlights crucial roles of mRNA m6A modification in germline development, potentially ensuring coordinated translation at different stages of spermatogenesis.