METTL14-dependent maturation of pri-miR-17 regulates mitochondrial homeostasis and induces chemoresistance in colorectal cancer.

miR-17-5p has been found to be involved in the proliferation and metastasis of colorectal cancer (CRC), and N-methyladenosine (mA) modification is the most common RNA modification in eukaryotes. However, whether miR-17-5p contributes to chemotherapy sensitivity in CRC via mA modification is unclear. In this study, we found that overexpression of miR-17-5p led to less apoptosis and lower drug sensitivity in vitro and in vivo under the 5-fluorouracil (5-FU) treatment, which indicated miR-17-5p led to 5-FU chemotherapy resistance. Bioinformatic analysis suggested that miR-17-5p-mediated chemoresistance was associated with mitochondrial homeostasis. miR-17-5p directly bound to the 3' untranslated region of Mitofusin 2 (MFN2), leading to decreased mitochondrial fusion and enhanced mitochondrial fission and mitophagy. Meanwhile, methyltransferase-like protein 14 (METTL14) was downregulated in CRC, resulting in lower mA level. Moreover, the low level of METTL14 promoted the expression of pri-miR-17 and miR-17-5p. Further experiments suggested that mA mRNA methylation initiated by METTL14 inhibits pri-miR-17 mRNA decay via reducing the recognition of YTHDC2 to the "GGACC" binding site. The METTL14/miR-17-5p/MFN2 signaling axis may play a critical role in 5-FU chemoresistance in CRC.