Relaxed initiation pausing of ribosomes drives oncogenic translation

Using quantitative profiling of initiating ribosomes, we found that ribosomal pausing at the start codon serves as a “brake” to restrain the translational output. In response to oncogenic RAS signaling, the initiation pausing relaxes and contributes to the increased translational flux. Intriguingly, mRNA m6A modification in the vicinity of start codons influences the behavior of initiating ribosomes. Under oncogenic RAS signaling, the reduced mRNA methylation leads to relaxed initiation pausing, thereby promoting malignant transformation and tumor growth. Restored initiation pausing by inhibiting m6A demethylases suppresses RAS-mediated oncogenic translation and subsequent tumorigenesis. Our findings unveil a new paradigm of translational control that is co-opted by RAS mutant cancer cells to drive malignant phenotypes. We took advantage of a human TtH cell line stably expressing a 4-hydroxytamoxifen (4-OHT)-inducible ER:HRASG12V fusion protein. QTI-seq, Ribo-seq, RNA-seq, m6A-seq and corresponding experiments were performed on the ER:HRASG12V cells with or without 4-OHT treatment and METTL3 or FTO knockdown.