Rbm5 is required for sustaining leukemia stem cells by modulating a leukemic transcriptional program in concert with the Myc network [ChIP-Seq]

Acute myeloid leukemia (AML) represents a type of malignant hematological disease that is caused by the dysregulated developmental program of leukemia stem cells (LSCs). Compared to other hematological malignancies, AML often predicts poor prognosis and unfavorable treatment outcomes in the clinic, urging the need for complex mechanism studies. Rbm5 was recently reported as a key regulator in maintaining the survival of human AML cell lines via non-canonical transcriptional activation of Hoxa9. However, its function in LSCs and the broad genome-wide transcriptional targets remain elusive. Here, using genetic mouse models, ex vivo AML culture, and patient-derived xenografts, we report that Rbm5 is required for murine leukemogenesis and maintains self-renewal of LSCs in vivo but is dispensable for normal hematopoiesis. Rbm5 is highly expressed in LSCs, and its deficiency results in specifically defective LSC function, along with the inhibition of self-renewal gene expression and the induction of a myeloid differentiation program. Multi-disciplinary mechanistic investigations targeting gene expression at both the single-cell level and in bulk populations, together with an acute RBM5 degradation system, further identified the direct transcriptional targets of Rbm5 in primary leukemia cells, including stemness genes, such as Hoxa9 and Myc. Moreover, RBM5 not only interacts with MYC but also maintains its protein levels, thereby sustaining the Myc downstream transcriptional network through its proper genome-wide occupancy. Forced expression of Myc sufficiently rescued the Rbm5-depleted defects both in vitro and in vivo. Thus, our study demonstrates that Rbm5 regulates the AML LSC program through non-canonical transcriptional mechanisms, providing a strong rationale for therapeutically targeting Rbm5 in the treatment of myeloid leukemia.