The ratio of RUNX1-ETO oncoprotein to normal RUNX1 expression determines the balance between endothelial reprogramming and hematopoietic cell growth

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Abstract In t(8;21) acute myeloid leukemia (AML) the RUNX1 DNA binding domain is fused to the RUNX1T1 protein producing the RUNX1-ETO onco-fusion protein. We previously showed that t(8;21) leukemic stem cells aberrantly activate endothelial signalling pathways to initiate blast cell proliferation. Here, we employed a human embryonic stem cell (ESC) line expressing an inducible RUNX1-ETO transgene to determine whether RUNX1-ETO directly induces endothelial signalling pathways or whether it is dependent on AML progression. Using single cell analyses we show that RUNX1-ETO induction reprograms ESC-derived myeloid progenitors towards endothelial cells. Integrated data analysis demonstrates (i) that endothelial reprogramming is RUNX1-ETO concentration-dependent and irreversible, (ii) that when RUNX1-ETO and RUNX1 expression levels are equal, a sub-population of blood progenitors escapes reprogramming and (iii) keeps proliferating when co-cultured with endothelial cells. Our experiments provide important insights into the earliest stages of epigenetic reprogramming by oncogenic transcription factors in AML.