RUNX1-ETO oncoprotein levels determine the balance between endothelial reprogramming and pre-leukemic growth in a human ES cell model of AML.

In t(8;21) acute myeloid leukemia (AML), the RUNX1 DNA binding domain is fused to RUNX1T1 (ETO) producing the RUNX1-ETO fusion protein. We previously showed that t(8;21) leukemic stem cells aberrantly activate endothelial signaling pathways to initiate blast cell proliferation. Here, we employed a human embryonic stem cell (ESC) line carrying an inducible RUNX1-ETO transgene to determine whether endothelial signaling pathway activation depends on disease progression or is directly induced by RUNX1-ETO. Single-cell analyses demonstrate that RUNX1-ETO reprograms ESC-derived myeloid progenitors towards endothelial cells. We show (1) that endothelial reprogramming is RUNX1-ETO concentration-dependent and irreversible, (2) at similar RUNX1-ETO and RUNX1 expression levels, a sub-population of blood progenitors can escape reprogramming, and (3) keeps proliferating when co-cultured with endothelial cells. Our experiments highlight the role of cellular interactions in the maintenance of pre-leukemic cells and provide important insights into the earliest stages of genomic reprogramming by oncogenic transcription factors.