Where, When, and How: Context-Dependent Functions of RNA Methylation Writers, Readers, and Erasers

Since the identification of the first RNA demethylase and the establishment of methylated RNA immunoprecipitation-sequencing methodology 6 to 7 years ago, RNA methylation has emerged as a widespread phenomenon and a critical regulator of transcript expression. This new layer of regulation is termed “epitranscriptomics.” The most prevalent RNA methylation, N6-methyladenosine (m6A), occurs in approximately 25% of transcripts at the genome-wide level and is enriched around stop codons, in 5′- and 3′-untranslated regions, and within long internal exons. RNA m6A modification regulates RNA splicing, translocation, stability, and translation into protein. m6A is catalyzed by the RNA methyltransferases METTL3, METTL14, and METTL16 (writers), is removed by the demethylases FTO and ALKBH5 (erasers), and interacts with m6A-binding proteins, such as YTHDF1 and IGF2BP1 (readers). RNA methyltransferases, demethylases, and m6A-binding proteins are frequently upregulated in human cancer tissues from a variety of organ origins, increasing onco-transcript and oncoprotein expression, cancer cell proliferation, survival, tumor initiation, progression, and metastasis. Although RNA methyltransferase inhibitors are not available yet, FTO inhibitors have shown promising anticancer effects in vitro and in animal models of cancer. Further screening for selective and potent RNA methyltransferase, demethylase, or m6A-binding protein inhibitors may lead to compounds suitable for future clinical trials in cancer patients.

https://cancerres.aacrjournals.org/content/canres/79/7/1285.full.pdf

The Critical Role of RNA m6A Methylation in Cancer

Differential m6A, m6Am, and m1A Demethylation Mediated by FTO in the Cell Nucleus and Cytoplasm

Small-Molecule Targeting of Oncogenic FTO Demethylase in Acute Myeloid Leukemia.

Epitranscriptomic m6A Regulation of Axon Regeneration in the Adult Mammalian Nervous System.

N6-methyladenosine (m6A) is a reversible modification in mRNA and has been shown to regulate processing, translation and decay of mRNA. However, the roles of m6A modification in neuronal development are still not known. Here, we found that the m6A eraser FTO is enriched in axons and can be locally translated. Axon-specific inhibition of FTO by rhein, or compartmentalized siRNA knockdown of Fto in axons led to increases of m6A levels. GAP-43 mRNA is modified by m6A and is a substrate of FTO in axons. Loss-of-function of this non-nuclear pool of FTO resulted in increased m6A modification and decreased local translation of axonal GAP-43 mRNA, which eventually repressed axon elongation. Mutation of a predicted m6A site in GAP-43 mRNA eliminated its m6A modification and exempted regulation of its local translation by axonal FTO. This work showed an example of dynamic internal m6A demethylation of non-nuclear localized mRNA by the demethylase FTO. Regulation of m6A modification of axonal mRNA by axonal FTO might be a general mechanism to control their local translation in neuronal development.

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Haijiao Huang

Papers

Dynamic m6A modification regulates local translation of mRNA in axons.