Post-transcriptional adenosine-to-inosine RNA editing mediated by adenosine deaminase acting on RNA1 (ADAR1) promotes cancer progression and therapeutic resistance. However, ADAR1 editase-dependent mechanisms governing leukemia stem cell (LSC) generation have not been elucidated. In blast crisis chronic myeloid leukemia (BC CML), we show that increased JAK2 signaling and BCR-ABL1 amplification activate ADAR1. In a humanized BC CML mouse model, combined JAK2 and BCR-ABL1 inhibition prevents LSC self-renewal commensurate with ADAR1 downregulation. Lentiviral ADAR1 wild-type, but not an editing-defective ADAR1(E912A) mutant, induces self-renewal gene expression and impairs biogenesis of stem cell regulatory let-7 microRNAs. Combined RNA sequencing, qRT-PCR, CLIP-ADAR1, and pri-let-7 mutagenesis data suggest that ADAR1 promotes LSC generation via let-7 pri-microRNA editing and LIN28B upregulation. A small-molecule tool compound antagonizes ADAR1's effect on LSC self-renewal in stromal co-cultures and restores let-7 biogenesis. Thus, ADAR1 activation represents a unique therapeutic vulnerability in LSCs with active JAK2 signaling.

Adenosine deaminase associated with RNA1 (ADAR1) deregulation contributes to therapeutic resistance in many malignancies. Here we show that ADAR1-induced hyper-editing in normal human hematopoietic progenitors impairs miR-26a maturation, which represses CDKN1A expression indirectly via EZH2, thereby accelerating cell-cycle transit. However, in blast crisis chronic myeloid leukemia progenitors, loss of EZH2 expression and increased CDKN1A oppose cell-cycle transit. Moreover, A-to-I editing of both the MDM2 regulatory microRNA and its binding site within the 3' UTR region stabilizes MDM2 transcripts, thereby enhancing blast crisis progenitor propagation. These data reveal a dual mechanism governing malignant transformation of progenitors that is predicated on hyper-editing of cell-cycle-regulatory miRNAs and the 3' UTR binding site of tumor suppressor miRNAs.