Bladder cancer (BC) presents a major clinical challenge due to high recurrence and progression rates, highlighting the need for novel therapeutic targets. While the N6-methyladenosine (m6A) writer complex is broadly implicated, the specific function and regulatory mechanism of its adaptor protein RNA binding motif protein 15 (RBM15) remain poorly defined in BC. This study reveals the oncogenic role of RBM15 in BC and its m6A-dependent regulatory axis, providing a new rationale for targeted intervention.

The clinical relevance of RBM15 was established by assessing its expression and prognostic significance in public datasets and a large clinical cohort. The biological function of RBM15 and its effect on global m6A methylation were subsequently investigated using a comprehensive suite of in vitro assays and in vivo models. We performed integrated multiomics analyses (RNA-seq, m6A-seq, and RIP-seq) and validated the underlying molecular mechanisms by performing additional targeted assays to elucidate the downstream regulatory network. Finally, the therapeutic potential of targeting this axis was validated in preclinical models using the METTL3 catalytic inhibitor STM2457.

RBM15 was significantly upregulated in BC, and its elevated expression served as an independent predictor of a poor prognosis. Functionally, RBM15 increased global m6A levels and promoted the malignant progression of BC cells both in vitro and in vivo; these oncogenic effects were reversed upon RBM15 knockdown. Mechanistically, RBM15 bound Zona Occludens 2 (ZO2) mRNA and recruited the methyltransferase 3–methyltransferase 14–Wilms’ tumor 1-associating protein (METTL3-METTL14-WTAP) methyltransferase complex to increase the level of the m6A modification on the ZO2 mRNA. This modification was recognized by YTH N(6)-methyladenosine RNA binding protein 2 (YTHDF2) to accelerate ZO2 mRNA decay. Although ZO2 expression was globally reduced, its preferential nuclear accumulation was increased, which promoted Snail expression and accelerated malignant progression. The METTL3 catalytic inhibitor STM2457 suppressed BC growth and lung metastasis by targeting the METTL3/RBM15/ZO2 axis, with no observable toxicity.

RBM15 acts as an oncogenic driver in BC by facilitating the m6A-dependent degradation of ZO2 mRNA via the recruitment of the METTL3 complex and recognition by YTHDF2. Targeting this METTL3/RBM15/ZO2 axis with STM2457 represents a promising therapeutic strategy for BC.