AML-1/RUNX-1 Is Overexpressed in Patients with Myeloproliferative Neoplasms and Mediates JAK2 ^V617F-Independent Overexpression of NF-E2.

Abstract 3893

Poster Board III-829

The transcription factor nuclear factor erythroid-2 (NF-E2) plays an essential role in both erythropoiesis and megakaryopoiesis. In addition to erythroid, megakaryocytic and granulocytic progenitors, NF-E2 is expressed in hematopoietic stem cells and in mature granulocytes. We have previously shown that NF-E2 is overexpressed in the vast majority of patients with polycythemia vera (PV). Concomitantly, 90 – 95% of these patients carry the JAK2^V617F point mutation. Even though NF-E2 levels correlated with JAK2^V671F allele burden in some PV cohorts, the molecular mechanism causing aberrant NF-E2 expression in PV patients has not been described. Here we show that NF-E2 expression is also increased in patients with Essential Thrombocythemia (ET) and that this is independent of the presence of the JAK2^V617F mutation. Characterization of the NF-E2 promoter revealed multiple binding sites for Acute Myeloid Leukemia-1 (AML-1/RUNX-1), which were shown to be functional by deletion analysis and site directed mutagenesis. Chromatin Immunoprecipitation (ChIP) demonstrated AML-1 binding to the NF-E2 promoter in vivo. Moreover, AML-1 binding to the NF-E2 promoter in vivo is significantly increased in primary granulocytes from PV patients compared to healthy controls. Subsequently, we demonstrated that mRNA and protein expression of AML-1 is elevated in PV and ET patients, both in the presence and absence of JAK2^V617F. In addition, AML-1 and NF-E2 expression are highly correlated. RNAi-mediated suppression of AML-1 levels significantly decreased NF-E2 expression. In summary, our data identify NF-E2 as a novel AML-1 target gene and point to a role of aberrant AML-1 expression in mediating elevated NF-E2 expression in MPN patients.