Cancer mutations rewire the RNA methylation specificity of METTL3-METTL14

Chemical modification of RNAs is important for posttranscriptional gene regulation. The METTL3-METTL14 complex generates most N⁶-methyladenosine (m⁶A) modifications in messenger RNAs (mRNAs), and dysregulated methyltransferase expression has been linked to cancers. Here we show that a changed sequence context for m⁶A can promote oncogenesis. A gain-of-function missense mutation from patients with cancer, METTL14^R298P, increases malignant cell growth in culture and transgenic mice without increasing global m⁶A levels in mRNAs. The mutant methyltransferase preferentially modifies noncanonical sites containing a GGAU motif, in vitro and in vivo. The m⁶A in GGAU context is detected by the YTH family of readers similarly to the canonical sites but is demethylated less efficiently by an eraser, ALKBH5. Combining the biochemical and structural data, we provide a model for how the cognate RNA sequences are selected for methylation by METTL3-METTL14. Our work highlights that sequence-specific m⁶A deposition is important and that increased GGAU methylation can promote oncogenesis.