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

N6-methyladenosine (mA) is the most pervasive RNA modification and is recognized as a novel epigenetic regulation in RNA metabolism. Although the mA modification involves various physiological processes, its roles in drug resistance in colorectal cancer (CRC) still remain unknown. We analyzed the RNA expression profile of mA/A (%) with MRM mass spectrometry in human 5-fluorouracil (5-FU)-resistant CRC tissues, and used the mA RNA immunoprecipitation assay to validate the mA-regulated target. Our results have shown that the mA 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 mA demethylation. The mA 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 mA-dependent 5-FU sensitivity in CRC cells. In summary, our findings demonstrate a critical role of FTO as an mA demethylase enhancing chemo-resistance in CRC cells, and suggest that FTO inhibition may restore the sensitivity of chemo-resistant CRC cells to 5-FU.