METTL3 Mediates Epithelial–Mesenchymal Transition by Modulating FOXO1 mRNA N6-Methyladenosine-Dependent YTHDF2 Binding: A Novel Mechanism of Radiation-Induced Lung Injury

Abstract

The biological roles of epithelial–mesenchymal transition (EMT) in the pathogenesis of radiation-induced lung injury (RILI) have been widely demonstrated, but the mechanisms involved have been incompletely elucidated. N6-methyladenosine (m6A) modification, the most abundant reversible methylation modification in eukaryotic mRNAs, plays vital roles in multiple biological processes. Whether and how m6A modification participates in ionizing radiation (IR)-induced EMT and RILI remain unclear. Here, significantly increased m6A levels upon IR-induced EMT are detected both in vivo and in vitro. Furthermore, upregulated methyltransferase-like 3 (METTL3) expression and downregulated α-ketoglutarate-dependent dioxygenase AlkB homolog 5 (ALKBH5) expression are detected. In addition, blocking METTL3-mediated m6A modification suppresses IR-induced EMT both in vivo and in vitro. Mechanistically, forkhead box O1 (FOXO1) is identified as a key target of METTL3 by a methylated RNA immunoprecipitation (MeRIP) assay. FOXO1 expression is downregulated by METTL3-mediated mRNA m6A modification in a YTH-domain family 2 (YTHDF2)-dependent manner, which subsequently activates the AKT and ERK signaling pathways. Overall, the present study shows that IR-responsive METTL3 is involved in IR-induced EMT, probably by activating the AKT and ERK signaling pathways via YTHDF2-dependent FOXO1 m6A modification, which may be a novel mechanism involved in the occurrence and development of RILI.