Mir-223 Is Dispensable for the Onset of Acute Myeloid Leukemia
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AbstractAbstract 501The functional roles of microRNAs in the development of acute myeloid leukemia (AML) are not yet clear. Due to its myeloid-specific expression, miR-223 has been one of the most-investigated miRNAs in normal and malignant hematopoiesis. However, the role of miR-223 in myeloid differentiation is not completely understood, as contradicting data exists. Genetic depletion of miR-223 led to a significant increase of myeloid progenitor cells as well as circulating hyperreactive neutrophils. Here, we investigate the role of miR-223 in the development of AML in vivo, using retroviral overexpression models of Hoxa9 with Meis1 or MN1 as two potent models of leukemic transformation in a miR-223+/+ or miR-223−/− background. In contrast to the observed high level expression of miR-223 in human CD34- bulk AML cells (p=0.0106), we could show that miR-223 was dispensable for the development of AML and did not impact on either the leukemic stem cell frequency nor the AML cell phenotype in Hoxa9-Meis1 AML cells. While these findings reveal that miR-223 is not necessary for leukemic transformation in highly aggressive AML models, we became interested if miR-223 functions rather as modulator of disease progression, especially at the early development of AML. Therefore, we investigated the role of miR-223 with regards to differentiation and self-renewal in two preleukemic model systems by retrovirally infecting miR-223−/− and miR-223+/+ BM cells with AML1-ETO and Hoxa9 respectively. Characterization of these models demonstrated that miR-223 expression is a determinant of differentiation, as miR-223−/− preleukemic cells exhibit a significant lower Mac-1 expression (p=0.0003). However, in contrast to normal miR-223−/− BM cells, which show a significantly higher colony forming capacity in methylcellulose compared to miR-233+/+ BM cells, the colony forming capacity of miR-223−/− or miR-223+/+ preleukemic cells did not significantly change.These findings demonstrate that miRNA miR-223 is hierarchically expressed in AML cells, and functionally link miR-223 to impaired differentiation rather than increased self-renewal in the initiation of AML. This indicates that miR-223 is more likely a fine tuner of leukemic development than a potent tumor suppressor or oncogenes as suggested in the literature. However, it still remains to be shown if the presence of miR-223 influences the susceptibility of preleukemic cells to convert into leukemia initiating cells.Disclosures:No relevant conflicts of interest to declare.
