RBM15/IGF2BP3 promotes immune escape in bladder cancer by enhancing m6A modification of PFKFB4

The role of N6-methyladenosine (m6A) in shaping the tumor microenvironment remains incompletely understood. Here, we investigated the function of the m6A writer RBM15 in bladder cancer (BC). Single-cell sequencing and spatial transcriptomics demonstrated that RBM15 is predominantly expressed in malignant epithelial cells and exerts oncogenic effects. Integrated m6A-seq and lactylation proteomics analyses indicated that RBM15 could regulate both glycolysis and immunity through m6A modification and lactylation. Mechanistically, RIP-qPCR, MeRIP-qPCR, proteomic profiling, luciferase reporter assays, RNA stability tests, and rescue experiments revealed that RBM15 increased m6A modification and stability of PFKFB4 mRNA. We also revealed that RBM15-mediated PFKFB4 mRNA activation relied on the IGF2BP3-dependent pathway. Downregulation of RBM15 and IGF2BP3 suppressed glycolysis while enhancing the anti-tumor potential of CD8⁺ T cells, whereas PFKFB4 overexpression reversed these effects, and vice versa. In vivo, silencing RBM15 with lipid nanoparticle (LNP)-delivered siRNA enhanced the efficacy of anti-PD1 therapy and increased CD8⁺ T cell infiltration. Collectively, our findings demonstrate that RBM15 stabilizes PFKFB4 expression in BC through an m6A-IGF2BP3-dependent mechanism and thus promotes the glycolysis and inhibits CD8⁺ T cell function. Targeting RBM15 sensitizes tumors to PD1 blockade and provides a promising therapeutic strategy for BC.