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Scope and mechanism of eIF4F-independent mRNA translation

ABSTRACT: In eukaryotic cells, protein synthesis typically begins with the binding of eIF4F to the 7-methylguanylate (m7G)cap found on the 5’ end of the majority of mRNAs. Surprisingly, overall translational output remains robust under eIF4F inhibition. The sustained protein synthesis has been largely attributed to cap-independent translation mediated by internal ribosome entry sites (IRES). However, the IRES-driven translation is substrate-specific and largely incompatible with the broad spectrum of eIF4F-resistant translatomes.Here, we report that N6-methyladenosine (m6A)-mediated translation prevails on capped mRNAs and is resistant to eIF4F inactivation.Depletion of the methyltransferase METTL3 selectively inhibits translation of mRNAs bearing 5’UTR methylation, but not mRNAs with 5’ terminal oligopyrimidine (TOP) elements. Mechanistically, we identify ABCF1 as a critical mediator of m6A-promoted translation under both stress and physiological conditions. Supporting the role of ABCF1 in m6A-mediated cap-independent translation, ABCF1-sensitive transcripts largely overlap with METTL3-responsible mRNA targets. By illustrating the scope and the mechanism of translation initiation that is neither cap- nor IRES-dependent, these findingsreshape our current perceptions of cellular translational pathways

ORGANISM(S): Mus musculus

PROVIDER: GSE101865 | GEO | 2017/07/26

SECONDARY ACCESSION(S): PRJNA395723

REPOSITORIES: GEO

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METTL3 preferentially enhances non-m6A translation of epigenetic factors and promotes tumorigenesis (eCLIP-seq)

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METTL3 preferentially enhances non-m6A translation of epigenetic factors and promotes tumorigenesis (meRIP, RIP and polysome-seq)

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.

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Transcription profiling of mRNAs that remained associated with polysomes isolated from human cells after infection with poliovirus

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