Hypoxic stabilization of RIPOR3 mRNA via METTL3-mediated m6A methylation drives breast cancer progression and metastasis.

Dysregulated N⁶-methyladenosine (m⁶A) modification has been associated with breast cancer pathogenesis. Hypoxia which characterizes solid tumors is known to reprogram the m⁶A epitranscriptome, but the underlying mechanisms of how this process contributes to breast cancer progression remain poorly understood. Through integrative analyses of m⁶A-RIP sequencing and RNA sequencing databases, we reveal a cluster of mRNAs with upregulated m⁶A methylation and expression under hypoxia, that are enriched by many oncogenic pathways, including PI3K-Akt signaling. Furthermore, we identify the mRNA, RIPOR3, as a target of METTL3-mediated m⁶A methylation in response to hypoxia. We find that m⁶A methylation stabilizes RIPOR3, increasing its protein expression in a METTL3 catalytic activity-dependent manner, and consequently driving breast tumor growth and metastasis. RIPOR3 is found to be overexpressed in breast cancer cell lines and tumor tissues from breast cancer patients, in whom elevated RIPOR3 is associated with a worse prognosis. Mechanistically, we show that RIPOR3 interacts with EGFR and is essential for the PI3K-Akt pathway activation. In conclusion, we identify RIPOR3 as a hypoxia-stabilized oncogenic driver via METTL3-mediated m⁶A methylation, thus provide a potential therapeutic target for breast cancer.