Expression of RUNX1::RUNX1T1 deregulates the proteome, induces C/EBPβ suppression and blocks myeloid differentiation

Expression of RUNX1::RUNX1T1 (also known as RUNX1::ETO) is frequently observed in acute myeloid leukemia and has been shown to block myeloid development. Whilst there are several studies showing RUNX1::RUNX1T1 transcriptional deregulation, the analysis of the proteome in human hematopoietic stem progenitor cells (HSPC) is poorly characterized. Using mass spectrometry, we show that expression of RUNX1::RUNX1T1 in human HSPC was linked to differential expression of 257 proteins including CEBPβ downregulation. Consistent with this observation while CEBPB mRNA is generally overexpressed in AML, patients harboring a t(8;21) have comparatively low CEBPB expression. We show in human HSPC that ectopic expression of CEBPβ is able to promote proliferation of myeloid cells. Conversely, shRNA mediated knock down of CEBPβ inhibited the growth of normal human myeloid cells, however, it promoted the growth of cells expressing RUNX1::RUNX1T1. CEBPβ also influenced differentiation with ectopic expression promoting monocyte development while reduction in expression favored granulocyte differentiation which in turn suggests that CEBPβ expression may act as a lineage discriminator for these myeloid cell types. In summary, our data show how RUNX1::RUNX1T1 drives deregulation of the HSPC proteome and suggests a mechanism of how RUNX1::RUNX1T1 expression contributes to leukemia development including CEBPβ which itself impacts normal myeloid development.