XBP1s activates METTL3/METTL14 for ER-phagy and paclitaxel sensitivity regulation in breast cancer.

Cancer cells employ the unfolded protein response (UPR) or induce autophagy, especially selective removal of certain ER domains via reticulophagy (termed ER-phagy), to mitigate endoplasmic reticulum (ER) stress for ER homeostasis when encountering microenvironmental stress. N6-methyladenosine (m6A) is one of the most abundant epitranscriptional modifications and plays important roles in various biological processes. However, the molecular mechanism of m6A modification in the ER stress response is poorly understood. In this study, we first found that ER stress could dramatically elevate m6A methylation levels through XBP1s-dependent transcriptional upregulation of METTL3/METTL14 in breast cancer (BC) cells. Further MeRIP sequencing and relevant validation results confirmed that ER stress caused m6A methylation enrichment on target genes for ER-phagy. Mechanistically, METTL3/METTL14 increased ER-phagy machinery formation by promoting m6A modification of the ER-phagy regulators CALCOCO1 and p62, thus enhancing their mRNA stability. Of note, we further confirmed that the chemotherapeutic drug paclitaxel (PTX) could induce ER stress and increase m6A methylation for ER-phagy. Furthermore, the combination of METTL3/METTL14 inhibitors with PTX demonstrated a significant synergistic therapeutic effect in both BC cells and xenograft mice. Thus, our data built a novel bridge on the crosstalk between ER stress, m6A methylation and ER-phagy. Most importantly, our work provides novel evidence of METTL3 and METTL14 as potential therapeutic targets for PTX sensitization in breast cancer.