RBM15-MKL1 fusion protein promotes leukemia via m6A methylation and Wnt pathway activation

ABSTRACT: The recurrent t(1;22) translocation in acute megakaryoblastic leukemia (AMKL) encodes the RBM15-MKL1 fusion protein. Dysregulation of the N6-methyladenosine (m6A) modification affects RNA fate and is linked to oncogenesis. Because RBM15 is critical for bringing the m6A writer complex to specific RNAs, we hypothesized that RM disrupts the m6A modification, thereby altering the RNA fate to drive leukemogenesis in RM-AMKL. Using a multiomics approach, we showed for the first time, to our knowledge, that RM retains the RNA-binding and m6A-modifying functions of RBM15 while also selectively regulating distinct messenger RNA targets, including Frizzled genes, in the Wnt signaling pathway. Treating murine RM-AMKL cells with the methyltransferase 3 (METTL3) inhibitor STM3675, which decreases m6A deposition, induced apoptosis in vitro and prolonged survival in transplanted mice. Frizzled genes were upregulated by RM and downregulated upon METTL3 inhibition, implicating an m6A-dependent mechanism in their dysregulation. Direct Frizzled knockdown reduced RM-AMKL growth in vitro and in vivo, highlighting Wnt signaling as a key oncogenic driver. Elevated Wnt pathway activity and Frizzled expression in multiple forms of human AMKL underscores the relevance of our findings. Together, our results establish that RM-specific m6A modifications and Wnt pathway activation are critical drivers of RM-AMKL, thereby identifying these pathways as potential therapeutic targets.