3138 – A TWO-STEP IN VIVO CRISPR SCREEN UNVEILS PERVASIVE RNA-BINDING PROTEIN DEPENDENCIES FOR LEUKEMIC STEM CELLS AND IDENTIFIES ELAVL1 AS A THERAPEUTIC TARGET

Acute myeloid leukemia (AML) initiation, progression and relapse is driven by a rare, subpopulation of self-renewing leukemic stem cells (LSCs) that share key characteristics with hematopoietic stem cells (HSCs). As such, LSCs must be eradicated to achieve stable remission, but similarities to their healthy counterpart cells present a challenge for LSC-targeted therapies. Interestingly, RNA-binding proteins (RBPs), which are core effectors of post-transcriptional regulation, are often dysregulated in cancers and contribute to disease progression, chemoresistance and relapse but have not been systematically explored for their role in LSC biology. Here, using an in vivo CRISPR-mediated drop out screen of RBPs enriched in human AML LSCs but expressed at uniquely low levels in long-term HSCs, we reveal 32 RBPs essential for LSC propagation and self-renewal and identify ELAVL1 as the top hit RBP. We show that depletion of Elavl1 significantly compromises LSCs across genetically distinct leukemias while sparing healthy HSCs. In human AML, we demonstrate that targeting ELAVL1 via shRNA-mediated knockdown or small molecule approaches significantly impairs LSC-driven in vivo leukemic reconstitution and selectively depletes AML versus normal progenitors. Integrative RNA-seq, proteomic and eCLIP-seq profiling revealed hematopoietic differentiation, RNA splicing and mitochondrial metabolism as key features defining the leukemic ELAVL1-mRNA interactome. Altogether, this work demonstrates that RBPs, and specifically ELAVL1, represent important regulators of LSC-survival and highlights their potential therapeutic relevance in AML.