Inflammatory Cytokine Responsive Enzymatic Mutagenesis Fuels Myeloproliferative Neoplasm Pre-Leukemia Stem Cell Evolution

Innate immune anti-viral adenosine to inosine (A-to-I) base editing enzymes (editases) promote hematopoietic stem cell (HSC) self-renewal and protect the human genome from retroviral integration in response to inflammatory cytokine signaling. However, hyper-editing has been linked to therapeutic resistance and cancer progression. Because myeloproliferative neoplasm (MPN) progression is typified by increased JAK2/STAT-mediated cytokine signaling, we investigated the cell type and context specific role of adenosine deaminase acting on RNA1 (ADAR1) editaseactivity in MPN pre-leukemia stem cell (pre-LSC) evolution into acute myeloid leukemia stem cells (LSCs). Here we show by whole transcriptome sequencing (RNA-seq) of 113 FACS-purified hematopoietic stem cells and progenitors from 78 individuals, including 54 MPN and AML patients and 24healthy young and aged individuals, that anti-viral signaling pathway activation and splice isoform switching from ADAR1p110 to JAK2/STAT-inducible ADAR1p150 RNA editase activation contributes to MPN progression. Pre-LSC evolution to LSC was characterized by ADAR1p150 upregulation, distinctive RNA editome patterns, STAT3 hyper-editing, increased replating as a measure of self-renewal. Moreover, LSC generation was typified by beta-catenin self-renewal pathway upregulation, which was recapitulated by lentiviral ADAR1p150 overexpression and reversed by lentiviral ADAR1p150 shRNA knockdown. Our studyunderscores the importance of inflammatory-cytokine fueled enzymatic mutagenesis in human MPN pre-LSC evolution to LSC. Thus, this study sets the stage for developing predictive RNA editome biomarkers of LSC generation to guidetherapeutic strategies aimed at preventing progression of hematopoietic malignancies. Disclosures Crews: Ionis Pharmaceuticals: Research Funding.