Methylation and silencing of miRNA-124 by EVI1 and self-renewal exhaustion of hematopoietic stem cells in murine myelodysplastic syndrome

Abstract

By expressing EVI1 in murine bone marrow (BM), we previously described a myelodysplastic syndrome (MDS) model characterized by pancytopenia, dysmegakaryopoiesis, dyserythropoiesis, and BM failure. The mice invariably died 11-14 months after BM transplantation (BMT). Here, we show that a double point mutant EVI1-(1+6Mut), unable to bind Gata1, abrogates the onset of MDS in the mouse and re-establishes normal megakaryopoiesis, erythropoiesis, BM function, and peripheral blood profiles. These normal features were maintained in the reconstituted mice until the study was ended at 21 months after BMT. We also report that EVI1 deregulates several genes that control cell division and cell selfrenewal. In striking contrast, these genes are normalized in the presence of the EVI1 mutant. Moreover, EVI1, but not the EVI1 mutant, seemingly deregulates these cellular processes by altering miRNA expression. In particular, the silencing of miRNA-124 by DNA methylation is associated with EVI1 expression, but not that of the EVI1 mutant, and appears to play a key role in the upregulation of cell division in murine BM cells and in the hematopoietic cell line 32Dcl3. The results presented here demonstrate that EVI1 induces MDS in the mouse through two major pathways, both of which require the interaction of EVI1 with other factors: one, results from EVI1-Gata1 interaction, which deregulates erythropoiesis and leads to fatal anemia, whereas the other occurs by interaction of EVI1 with unidentified factors causing perturbation of the cell cycle and self-renewal, as a consequence of silencing miRNA-124 by EVI1 and, ultimately, ensues in BM failure.T he inappropriate activation of EVI1 in 10-15% of myelodysplastic syndrome (MDS) patients is associated with megakaryocytic and erythroid dysplasia, refractory anemia unresponsive to erythropoietin (EPO) administration and bone marrow (BM) failure (1). By expressing EVI1 in murine BM cells, we generated a mouse model of MDS. The reconstituted mice showed dysplastic erythropoiesis and megakaryopoiesis, progressive pancytopenia, severe anemia, and BM failure leading to their death at 11-14 months after BM transplantation (BMT), confirming the association between EVI1 and MDS in the mouse (2). However, in contrast to the majority of EVI1-positive MDS patients, the disease in the mice never progressed to acute myeloid leukemia (AML). We proposed that the primary causes of death in the EVI1-positive mice were severe anemia, associated with loss of response to Epo, and BM failure. Using in vitro assays, we later determined that the transcription factor Gata1, required for activation of EpoR and c-Mpl (3), was functionally impaired by inappropriate interaction with EVI1, but not by EVI1-(1+6Mut), a point mutant of EVI1 that does not recognize Gata1 (4). The study reported here had two major objectives. First, we set out to determine whether the disruption in vivo of the EVI1-Gata1 interaction alleviates MDS in the mouse. We compared two groups of EVI1-and EVI1-(1+6Mut)-positive mice and showed tha...

Expression and prognostic significance of microRNAs in Korean patients with myelodysplastic syndrome

“…58 In support of this finding, methylation and silencing of miR-124 by ecotropic virus integration site 1 contributes to HSC defects and MDS-like disease in mice. 59 …”

Engineering mouse models with myelodysplastic syndrome human candidate genes; how relevant are they?

“…This epigenetic event results in perturbation of cell division and self-renewal in this mouse model. 80 The TET2 gene (Ten-Eleven Translocation-2) was originally identified from an MDS patient with a rearrangement of 4q24 24 and numerous groups have identified somatic inactivating mutations (frameshifts or misense) in MDS, MPD and CMML patients. [23][24][25] As one of the most frequent mutations found in myeloid malignancies, TET2 has been proposed to be a tumor suppressor as loss of function tends to lead to disruption of progenitor myeloid differentiation leading to disease progression.…”

Epigenetic regulation of miRNA-124 and multiple downstream targets is associated with treatment response in myeloid malignancies

“…miRNA-124, a potential tumor suppressor gene with a hypothesized epigenetic role in the development of MDS and AML, has previously been shown to respond to EGT and may have a role in the therapeutic response to EGT in MDS/AML, with potential to act as a biomarker of early treatment response (1,(6)(7)(8).…”

“…Epigenetic regulation of miRNA expression has recently been implicated in the pathogenesis of MDS. Demonstration of epigenetic silencing of the miRNA-124 promoter in murine MDS studies (6) together with significant inhibition of miRNA-124 expression and excessive miRNA-124 promoter methylation in MDS patients (7) suggests miRNA-124 may not only be implicated in the pathogenesis of MDS, but also potentially in the molecular mechanisms (8).…”