Myelodysplastic syndrome (MDS) comprises a group of disorders with overlapping features. The majority of recurring chromosomal abnormalities associated with MDS are large deletions. There are two genes, RUNX1 and EVI1, whose deregulation is also known to be associated with MDS. RUNX1 is a master regulator of hematopoiesis that specifically binds to the DNA and regulates the expression of hematopoietic genes. Lately it has become clear that RUNX1 is frequently mutated in patients with MDS. Surprisingly, the mutations are limited to one allele, suggesting that a partial loss of function is sufficient to contribute to the disease. The second gene, EVI1, encodes a large nuclear protein characterized by two domains of zinc fingers. While the precise role of EVI1 is not known, this protein is not expressed in normal bone marrow and is inappropriately activated in very aggressive MDS by chromosomal translocations. Because alterations of both genes are not usually observed together, we have recently investigated whether there could be a potential link between the pathways regulated by RUNX1 and EVI1. Here, we report that in vivo and in vitro EVI1 physically interacts with RUNX1. We mapped the interaction domains to the eighth zinc finger motif of EVI1 and to the DNA-binding Runt domain of RUNX1. We found that this interaction alters the ability of RUNX1 to bind to its DNA consensus and represses the ability of RUNX1 to activate a reporter gene, suggesting that the interaction between EVI1 and RUNX1 could impair the hematopoietic programs regulated by RUNX1. These data suggest that inappropriate expression of EVI1 could contribute to hematopoietic transformation in part by a new mechanism that involves EVI1 association with key hematopoietic regulators leading to their functional impairment. Our results also indicate that the interaction region between RUNX1 and EVI1 could represent a novel target for therapeutic drugs for EVI1-associated leukemia.

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