Abstract 1588: NR2F6, a novel regulator of stem cell maintenance, is necessary and sufficient for initiation of acute leukemia
Authors: Ichim Christine V. , Chesney Alden , Reis Marciano , Iscove Norman N. , Wells Richard A. 
Published: February 2011

Abstract
The mechanisms that instruct hematopoietic stem cells (HSCs) to choose between self-renewal and differentiation remain elusive. These mechanisms are of particular interest with respect to acute myeloid leukemia (AML) where leukemia stem cell self-renewal is a tantalizing therapeutic target.
The orphan nuclear receptor NR2F6 has no previously identified role in hematopoiesis. In a screen of the transcription profiles of single AML cells we found that NR2F6 mRNA expression is 4.6 fold higher in clonogenic vs. non-clonogenic cells. We showed that NR2F6 is expressed highly in long-term HSCs, with expression of NR2F6 generally declining with progenitor cell differentiation. Interestingly, expression of NR2F6 was deregulated in patients with myelodysplastic syndrome (MDS), chronic myelomonocytic leukemia, and AML compared to normal bone marrow (BM).
Animals transplanted with retrovirally transduced NR2F6 marked BM were profoundly pancytopenic and rapidly developed AML (median survival of four weeks). Pre-leukemic recipients showed a &gt;10 fold increase in the proportion and absolute number of lineage− Sca1+ cKit+ (LSK) cells. There was also a striking increase (15-18 fold) in the number of CD49b− LSK and CD34− LSK cells, indicating expansion of the long-term HSC population.
NR2F6-overexpressing HSCs had increased competitive repopulation ability when transplanted into lethally irradiated hosts. Transplant chimeras reconstituted with a mixture of wild type and NR2F6-overexpressing cells develop key features of MDS including hypercellular BM, increase in blasts, abnormal localization of immature precursors, morphological dysplasia, and eventual progression to AML. In colony forming cell assays, BM from recipients of NR2F6-overexpressing HSCs showed a significant reduction in the number of primary erythroid and myeloid colonies, consistent with the notion that NR2F6 inhibits maturation of normal BM, while augmented serial replating of methylcellulose cultures indicates enhanced in vitro self-renewal ability.
Our data suggests that the modulation of NR2F6 function using an antagonistic ligand may be a novel strategy for the targeting of MDS and AML stem cells. As proof of the principle we observed that silencing of NR2F6 using shRNA in two distinct hematopoietic cell lines (U937 human myelomonocytic cells and 32D murine multipotent hematopoietic cells) resulted in spontaneous differentiation and apoptosis. Furthermore, silencing of NR2F6 in murine HSCs rapid depleted LSK cells in ex vivo culture showing that modulation of NR2F6 can force the differentiation of HSCs.
Taken together these data suggest that NR2F6 may contribute to the pathogenesis of MDS and AML by affecting HSC homeostasis and progenitor cell differentiation. These data raise the exciting possibility that natural or synthetic antagonist ligands for NR2F6 can be found that may act as anti-leukemic therapeutics.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1588.