N6-methyladenosine demethylase FTO enhances chemo-resistance in colorectal cancer through SIVA1-mediated apoptosis

N6-methyladenosine (m 6 A) is the most pervasive RNA modification and is recognized as a novel epigenetic regulation in RNA metabolism. Although the m 6 A modification involves various physiological processes, its roles in drug resistance in colorectal cancer (CRC) still remain unknown. We analyzed the RNA expression profile of m 6 A/A (%) with MRM mass spectrometry in human 5-fluorouracil (5-FU)-resistant CRC tissues, and used the m 6 A RNA immunoprecipitation assay to validate the m 6 A-regulated target. Our results have shown that the m 6 A demethylase FTO was up-regulated in human primary and 5-FU-resistant CRC. Depletion of FTO decreased cell growth, colony formation and metastasis in 5-FU-resistant CRC cells in vitro and in vivo . Mechanistically, we identified SIVA1, a critical apoptotic gene, as a key downstream target of the FTO-mediated m 6 A demethylation. The m 6 A demethylation of SIVA1 at the CDS region induced its mRNA degradation via a YTHDF2-dependent mechanism. The SIVA1 levels were negatively correlated with the FTO levels in clinical CRC tissues. Notably, inhibition of FTO significantly reduced the tolerance of 5-FU in 5-FU-resistant CRC cells via the FTO-SIVA1 axis, whereas SIVA1-depletion could restore the m 6 A-dependent 5-FU sensitivity in CRC cells. In summary, our findings demonstrate a critical role of FTO as an m 6 A demethylase enhancing chemo-resistance in CRC cells, and suggest that FTO inhibition may restore the sensitivity of chemo-resistant CRC cells to 5-FU.