MicroRNAs (miRNAs or miRs) regulate diverse normal and abnormal cell functions. We have identified a regulatory pathway in normal megakaryopoiesis, involving the PLZF transcription factor, miR-146a and the SDF-1 receptor CXCR4. In leukaemic cell lines PLZF overexpression downmodulated miR-146a and upregulated CXCR4 protein, whereas PLZF knockdown induced the opposite effects. In vitro assays showed that PLZF interacts with and inhibits the miR-146a promoter, and that miR-146a targets CXCR4 mRNA, impeding its translation. In megakaryopoietic cultures of CD34(+) progenitors, PLZF was upregulated, whereas miR-146a expression decreased and CXCR4 protein increased. MiR-146a overexpression and PLZF or CXCR4 silencing impaired megakaryocytic (Mk) proliferation, differentiation and maturation, as well as Mk colony formation. Mir-146a knockdown induced the opposite effects. Rescue experiments indicated that the effects of PLZF and miR-146a are mediated by miR-146a and CXCR4, respectively. Our data indicate that megakaryopoiesis is controlled by a cascade pathway, in which PLZF suppresses miR-146a transcription and thereby activates CXCR4 translation.

CXCR4 is a negative prognostic marker in acute myeloid leukemias (AMLs). Therefore, it is necessary to develop novel ways to inhibit CXCR4 expression in leukemia. AMD3100 is an inhibitor of CXCR4 currently used to mobilize cancer cells. CXCR4 is a target of microRNA (miR)-146a that may represent a new tool to inhibit CXCR4 expression. We then investigated CXCR4 regulation by miR-146a in primary AMLs and found an inverse correlation between miR-146a and CXCR4 protein expression levels in all AML subtypes. As the lowest miR-146a expression levels were observed in M5 AML, we analyzed the control of CXCR4 expression by miR-146a in normal and leukemic monocytic cells and showed that the regulatory miR-146a/CXCR4 pathway operates during monocytopoiesis, but is deregulated in AMLs. AMD3100 treatment and miR-146a overexpression were used to inhibit CXCR4 in leukemic cells. AMD3100 treatment induces the decrease of CXCR4 protein expression, associated with miR-146a increase, and increases sensitivity of leukemic blast cells to cytotoxic drugs, this effect being further enhanced by miR-146a overexpression. Altogether our data indicate that miR-146a and AMD3100, acting through different mechanism, downmodulate CXCR4 protein levels, impair leukemic cell proliferation and then may be used in combination with anti-leukemia drugs, for development of new therapeutic strategies.

CD147 is a transmembrane glycoprotein with multiple functions in human healthy tissues and diseases, in particular in cancer. Overexpression of CD147 correlates with biological functions that promote tumor progression and confers resistance to chemotherapeutic drugs. In contrast to solid tumors, the role of CD147 has not been extensively studied in leukemia. Understanding whether CD147 represents a new hematologic target and whether its inhibitor AC-73 may be used in leukemia therapy may reveal an alternative treatment strategy in patients with acute myeloid leukemia (AML). We analyzed CD147 expression and function in hematopoietic progenitor cells from normal cord blood, in several leukemic cell lines and in primary leukemic blasts obtained from patients with AML. We investigated the effects of AC-73, used alone or in combination with arabinosylcytosine (Ara-C) and arsenic trioxide (ATO), on leukemic cell proliferation. We demonstrated that CD147 overexpression promotes leukemic cell proliferation. We showed that AC-73 exhibits a potent growth inhibitory activity in leukemic cells, by inhibiting the ERK/STAT3 activation pathway and activating autophagy. We demonstrated that AC-73 exerts an anti-proliferative effect additive to chemotherapy by enhancing leukemic cell sensitivity to Ara-C-induced cytotoxicity or to ATO-induced autophagy. We also reported CD147 expression in the fraction of leukemic blasts expressing CD371, a marker of leukemic stem cells. Altogether, our study indicates CD147 as a novel potential target in the treatment of AML and AC-73 as an anti-proliferative drug and an inducer of autophagy in leukemic cells to use in combination with chemotherapeutic agents.

Metabolism in acute myeloid leukemia (AML) cells is dependent primarily on oxidative phosphorylation. However, in order to sustain their high proliferation rate and metabolic demand, leukemic blasts use a number of metabolic strategies, including glycolytic metabolism. Understanding whether monocarboxylate transporters MCT1 and MCT4, which remove the excess of lactate produced by cancer cells, represent new hematological targets, and whether their respective inhibitors, AR-C155858 and syrosingopine, can be useful in leukemia therapy, may reveal a novel treatment strategy for patients with AML. We analyzed MCT1 and MCT4 expression and function in hematopoietic progenitor cells from healthy cord blood, in several leukemic cell lines and in primary leukemic blasts from patients with AML, and investigated the effects of AR-C155858 and syrosingopine, used alone or in combination with arabinosylcytosine, on leukemic cell proliferation. We found an inverse correlation between MCT1 and MCT4 expression levels in leukemic cells, and showed that MCT4 overexpression is associated with poor prognosis in AML patients. We also found that AR-C155858 and syrosingopine inhibit leukemic cell proliferation by activating two different cell-death related pathways, i.e., necrosis for AR-C155858 treatment and autophagy for syrosingopine, and showed that AR-C155858 and syrosingopine exert an anti-proliferative effect, additive to chemotherapy, by enhancing leukemic cells sensitivity to chemotherapeutic agents. Altogether, our study shows that inhibition of MCT1 or MCT4 impairs leukemic cell proliferation, suggesting that targeting lactate metabolism may be a new therapeutic strategy for AML, and points to MCT4 as a potential therapeutic target in AML patients and to syrosingopine as a new anti-proliferative drug and inducer of autophagy to be used in combination with conventional chemotherapeutic agents in AML treatment.

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© F e r r a t a S t o r t i F o u n d a t i o ndromes for its deletion on chromosome 5 37 and in the progression of chronic myeloid leukemia. 38 We previously identified the molecular mechanism that regulates the level of CXCR4 protein expression by miR146a targeting 29 (miR-146a/CXCR4) during monocytopoiesis. 39 We also reported that in acute monocytic leukemia (AML-M5), a high CXCR4 protein level is associated with low/absent miR-146a expression. 39 We then showed that enforced miR-146a expression in leukemic cells decreases the level of CXCR4 protein and improves the sensitivity of these cells to drugs. 39CXCR4 is a target gene of HIF-1α and a post-transcriptional target of miR-146a, 9,39 in monocytic cells, known to originate from a common myeloid precursor in the bone marrow giving rise to tissue macrophages and dendritic cells 40 and subject to very different oxygen (O 2 ) levels. 41In this study, we investigated the impact of chronic hypoxia on the miR-146a/CXCR4 regulatory axis during monocytopoiesis and in monocytic leukemic cells. The levels of hypoxia studied were mild (5% O 2 ), such as that present in the sinusoidal cavity of bone marrow, and more severe (1% O 2 ), such as that in hypoxic niches in bone marrow.Altogether, our data demonstrated how the differential expression of HIF-1α and HIF-2α is mediated by O 2 level (mild or severe) and down-regulates CXCR4 expression through a post-transcriptional mechanism mediated by up-regulation of miR-146a in normal monocytic cells and in monocytic leukemia cell lines, expressing a moderate level of CXCR4. However, this mechanism is dysregulated in primary AML-M5 blast cells that fail to decrease CXCR4 expression significantly in response to hypoxia. This dysregulation helps to explain why leukemic blasts express high CXCR4 levels, even in hypoxic conditions, and how they are protected from anti-leukemic drugs through CXCR4 activation mediated by SDF-1α secreted in the hypoxic bone marrow microenvironment. MethodsAdditional information is provided in the Online Supplement. Cell culturesAfter obtaining informed consent, human cord blood was taken from healthy donors and samples of blood were taken from patients with AML. This study was approved by the local ethical committees of the Italian National Institute of Health and the University of Tor Vergata.Cord blood CD34 + hematopoietic progenitor cell purification, unilineage monocytic differentiation and morphological analyses were performed as previously described. 39 Human primary AML-M5 blasts were maintained in culture in vitro in Iscove medium supplemented with 10% fetal calf serum, granulocyte-macrophage colony-stimulating factor (10 ng/mL), stem cell factor (50 ng/mL), and interleukin-3 (10 ng/mL) (PeproTech Inc. Rocky Hill, NJ, USA). RNA and protein samples were prepared as described elsewhere. 39 Leukemic cell lines, U937 and HL-60, were grown in RPMI medium supplemented with 10% fetal calf serum (Gibco, Carlsbad, CA, USA). HypoxiaTo provide a mild or more severe hypoxic environment, acute ...

MicroRNA miR-146a and PLZF are reported as major players in the control of hematopoiesis, immune function and cancer. PLZF is described as a miR-146a repressor, whereas CXCR4 and TRAF6 were identified as miR-146a direct targets in different cell types. CXCR4 is a co-receptor of CD4 molecule that facilitates HIV-1 entry into T lymphocytes and myeloid cells, whereas TRAF6 is involved in immune response. Thus, the role of miR-146a in HIV-1 infection is currently being thoroughly investigated. In this study, we found that PLZF mediates suppression of miR-146a to control increases of CXCR4 and TRAF6 protein levels in human primary CD4(+) T lymphocytes. We show that miR-146a upregulation by AMD3100 treatment or PLZF silencing, decreases CXCR4 protein expression and prevents HIV-1 infection of leukemic monocytic cell line and CD4(+) T lymphocytes. Our findings improve the prospects of developing new therapeutic strategies to prevent HIV-1 entry via CXCR4 by using the PLZF/miR-146a axis.

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