The m6A demethylase FTO promotes C/EBPβ-LIP translation to perform oncogenic functions in breast cancer cells

N6-methyladenosine (m6A) is a prevalent posttranscriptional mRNA modification involved in the regulation of transcript turnover, translation, and other aspects of RNA fate. The modification is mediated by multicomponent methyltransferase complexes (so-called writers) and is reversed through the action of the m6A-demethylases fat mass and obesity-associated (FTO) and alkB homolog 5 (ALKBH5) (so-called erasers). FTO promotes cell proliferation, colony formation and metastasis in models of triple-negative breast cancer (TNBC). However, little is known about genome-wide or specific downstream regulation by FTO. Here, we examined changes in the genome-wide transcriptome and translatome following FTO knockdown in TNBC cells. Unexpectedly, FTO knockdown had a limited effect on the translatome, while transcriptome analysis revealed that genes related to extracellular matrix (ECM) and epithelial-mesenchymal transition (EMT) are regulated through yet unidentified mechanisms. Differential translation of CEBPB mRNA into the C/EBP beta transcription factor isoform C/EBP beta-LIP is known to act in a pro-oncogenic manner in TNBC cells through regulation of EMT genes. Here we show that FTO is required for efficient C/EBP beta-LIP expression, suggesting that FTO has oncogenic functions through regulation of C/EBP beta-LIP.