N6-Methyladenosine Guides mRNA Alternative Translation during Integrated Stress Response

The integrated stress response (ISR) facilitates cellular adaptation to a variety of stress conditions via phosphorylation of the common target eIF2α. During ISR, the translation of certain stress-related mRNAs is upregulated in spite of global suppression of protein synthesis.The selective translation often relieson alternative mechanisms, such as leaky scanning or reinitiation, but the underlying mechanism remains incompletely understood. Here we report that,in response to amino acid starvation, the reinitiation of ATF4 is not only governed by eIF2α-controlled ternary complex availability, but is also subjected to regulation by mRNA methylation in the form of N6-methyladenosine (m6A). We demonstrate that m6A in the 5' untranslated region (5’ UTR) controls ribosome scanning and subsequent start codonselection. Global profiling of initiating ribosomes reveals widespread alternative translation events influenced by mRNA methylation. Consistently, Fto-transgenic mice manifest enhanced ATF4 expression, highlighting the critical role of 5’ UTR methylation in translational regulation of ISR at cellular and organismal levels. Ribo-seq, QTI-seq and m6A-seq in Scramble, ALKBH5 knockdown and FTO overexpression