In recent years, the importance of microRNAs in controlling hematopoiesis has been discussed 1. Since their discovery in 1993 2, microRNAs have been intensively studied in multidisciplinary research ...fields and have even attracted the attention of the pharmaceutical industry as potential therapeutic targets in various diseases. ...Shen et al. clearly demonstrated the importance of miR-22 for monocytic differentiation and its tumor-suppressor potential in myeloid cells.
Transcription factor C/EBPα is a master regulator of myelopoiesis and its inactivation is associated with acute myeloid leukemia. Deregulation of C/EBPα by microRNAs during granulopoiesis or acute ...myeloid leukemia development has not been studied. Here we show that oncogenic miR-182 is a strong regulator of C/EBPα. Moreover, we identify a regulatory loop between C/EBPα and miR-182. While C/EBPα blocks miR-182 expression by direct promoter binding during myeloid differentiation, enforced expression of miR-182 reduces C/EBPα protein level and impairs granulopoiesis in vitro and in vivo. In addition, miR-182 expression is highly elevated particularly in acute myeloid leukemia patients with C-terminal CEBPA mutations, thereby depicting a mechanism by which C/EBPα blocks miR-182 expression. Furthermore, we present miR-182 expression as a prognostic marker in cytogenetically high-risk acute myeloid leukemia patients. Our data demonstrate the importance of a controlled balance between C/EBPα and miR-182 for the maintenance of healthy granulopoiesis.C/EBPα is a critical transcription factor involved in myelopoiesis and its inactivation is associated with acute myeloid leukemia (AML). Here the authors show a negative feedback loop between C/EBPα and miR-182 and identify this miRNA as a marker of high-risk AML.
In acute promyelocytic leukemia (APL), all-trans retinoic acid (ATRA) treatment induces granulocytic maturation and complete remission of leukemia. microRNAs are known to be critical players in the ...formation of the leukemic phenotype. In this study, we report downregulation of the miR-181a/b gene cluster in APL blasts and NB4 leukemia cells upon ATRA treatment as a key event in the drug response. We found that miR-181a/b expression was activated by the PML/RARα oncogene in cells and transgenic knock-in mice, an observation confirmed and extended by evidence of enhanced expression of miR-181a/b in APL patient specimens. RNA interference (RNAi)-mediated attenuation of miR-181a/b expression in NB4 cells was sufficient to reduce colony-forming capacity, proliferation, and survival. Mechanistic investigations revealed that miR-181a/b targets the ATRA-regulated tumor suppressor gene RASSF1A by direct binding to its 3'-untranslated region. Enforced expression of miR-181a/b or RNAi-mediated attenuation of RASSF1A inhibited ATRA-induced granulocytic differentiation via regulation of the cell-cycle regulator cyclin D1. Conversely, RASSF1A overexpression enhanced apoptosis. Finally, RASSF1A levels were reduced in PML/RARα knock-in mice and APL patient samples. Taken together, our results define miR-181a and miR-181b as oncomiRs in PML/RARα-associated APL, and they reveal RASSF1A as a pivotal element in the granulocytic differentiation program induced by ATRA in APL.
Acute myeloid leukemia (AML) is a fatal malignant hematologic disorder. Although many patients with AML initially respond to standard chemotherapy and achieve complete remission (CR), the majority of ...patients relapse due to the development and clonal expansion of chemoresistant subclones. Albeit being a heterogenous disease, individual mutations are still scarcely considered in the current treatment regimen.
Approximately 30% of AML patients exhibit gain-of-function mutations in the FMS-like tyrosine kinase 3 receptor (FLT3-receptor) gene. Here, an internal tandem duplication (ITD) in the juxtamembrane region of the receptor is among the most frequently observed mutations. This usually entails a constitutive activation of FLT3 receptor downstream signaling pathways, leading to differential gene expression patterns and aberrant cell growth. Clinically, FLT3-ITD mutations confer adverse prognosis. Thus, many promising FLT3 signaling inhibitor-based therapies are currently utilized to improve patient survival. However, the phenomenon of treatment resistant subclones persists and constantly calls for new angles of treatment.
MicroRNAs, a group of small non-coding RNAs, regulate gene expression on a posttranscriptional level by a complementary binding to 3'UTRs of protein-coding mRNAs. They have been shown to influence healthy and malignant hematopoiesis and to predict treatment response in cancer. In addition, several candidates have been connected to treatment resistance or sensitivity in AML.
Within this study, we hypothesized that microRNAs are biological important players in the adverse treatment response and the development of chemoresistance in FLT3-ITD associated AML.
Initially, we were interested in the microRNA expression pattern in FLT3-ITD associated AML. Therefore, we performed a next generation sequencing screen in bone marrow mononuclear cells from healthy donors, AML patients with FLT3-wildtype and AML patients with FLT3-ITD mutation. Here, we identified miR-451 to be significantly lower expressed in AML compared to healthy individuals. Furthermore, it was nearly absent in FLT3-ITD associated AML. In addition, we compared our results to the AML patient cohort of “The Cancer Genome Atlas” (TCGA) and found a similar miR-451 expression distribution. In agreement with this, miR-451 expression increased during differentiation of primary human and mouse hematopoietic cells. Moreover, transduction of U937 as well as 32D cells with FLT3-ITD led to a decrease in miR-451 expression.
Downregulation of miR-451 has been shown for various cancerous diseases to correlate with an increased cancer persistence as well as recurrence, as one established target of miR-451 is multi drug resistance protein 1 (MDR1). MDR1 is an ATP dependent efflux pump that mediates chemoresistance by transporting drugs out of the cell. Today, only limited data are available on the miR-451-MDR1 axis in FLT3-ITD associated AML. Thus, we hypothesized that low miR-451 expression and high MDR1 activity is associated with treatment resistance.
Therefore, we showed an inverse correlation of miR-451 expression and MDR1 protein levels in various leukemic cells lines. Furthermore, we observed that a repression of FLT3-ITD signaling by both Quizartinib and Gilteritinib causes a miR-451 expression increment and a subsequent reduction of MDR1 protein levels. By luciferase activity assay, we could demonstrate a direct binding of miR-451 to the 3'UTR of MDR1. In order to investigate whether miR-451 alone is able to abrogate treatment resistance, we overexpressed miR-451 in both normal MV4;11 and treatment resistant MV4;11 cells (MV4;11-R). Subsequently, MDR1 protein levels were decreased and cells exhibited an enhanced sensitivity towards both FLT3-ITD inhibitor and chemotherapeutic agent-based treatment. Moreover, exogenous miR-451 was able to restore drug sensitivity in MV4;11-R cells comparable to that of normal MV4;11 cells. As proof of principle, MDR1 inhibitor Tariquidar mimicked miR-451-mediated effects and sensitized MV4;11-R cells to FLT3-ITD inhibitor Quizartinib.
In conclusion, we identified a novel mechanism by which FLT3-ITD is able to alter treatment response and confer a poor prognosis. Hence, not only inhibiting FLT3-ITD but mimicking the effects of negatively regulated downstream targets such as miR-451 presents as promising new avenue for FLT3-ITD AML treatment.
Thiede:Bayer: Consultancy, Speakers Bureau; Roche: Consultancy; Novartis: Consultancy, Speakers Bureau; Agendix: Employment.
The transcription factor CCAAT enhancer binding protein α (C/EBPα) is a master regulator in granulopoiesis and is frequently disrupted in acute myeloid leukemia (AML). We have previously shown that ...C/EBPα exerts its effects by regulating microRNAs (miRs) such as miR-223 and miR-34a. Here, we confirm miR-30c as a novel important target of C/EBPα during granulopoiesis. Thus, wild-type C/EBPα-p42 directly upregulates miR-30c expression, whereas C/EBPα-p30, found in AML, does not. miR-30c is downregulated in AML, especially in normal karyotype AML patients with CEBPA mutations. An induced C/EBPα knockout in mice leads to a significant downregulation of miR-30c expression in bone marrow cells. We identified NOTCH1 as a direct target of miR-30c. Finally, a block of miR-30c prevents C/EBPα-induced downregulation of Notch1 protein and leads to a reduced CD11b expression in myeloid differentiation. Our study presents the first evidence that C/EBPα, miR-30c, and Notch1 together play a critical role in granulocytic differentiation and AML, and particularly in AML with CEBPA mutations. These data reveal the importance of deregulated miRNA expression in leukemia and may provide novel biomarkers and therapeutic targets in AML.
•miR-30c is a direct target of C/EBPα and upregulated by C/EBPα-p42.•NOTCH1 is a direct target of miR-30c and regulated by C/EBPα and miR-30c.
Acute myeloid leukemia (AML) is a very heterogeneous disease of the hematopoietic system which is characterized by a fast progress with poor survival options. Despite intensive research standard ...treatment strategies rely since decades on the same chemotherapeutics, and the overall survival options still remain poor.
In recent years, there is an emerging role of microRNAs (miRNAs) in the regulation of cancer development and resistance to cancer therapies. Mechanistically, miRNAs regulate gene expression through modulation of multiple target mRNAs by mRNA degradation or block of translation. It is shown that miRNAs can act as tumor suppressors and oncogenes dependent on the type of cancer. The miRNA-143/145 cluster is shown to be down-regulated in most cancers and is able to modulate tumorigenesis by targeting tumor associated genes. Several miR-143/145 targets are well described oncogenes, such as ERK5, DNMT3A or Bcl2. Interestingly, recent studies showed that the miR-143/145 cluster can regulate multidrug resistance proteins (MDR) in various cancer types and that enforced expression of miR-143/145 leads to increased sensitivity to various drugs. Besides its well-studied function mainly in solid tumors the role of the miR-143/145 cluster or miR-143 alone especially in the hematopoietic system remains largely unknown.
In this study, we report a previously unrecognized function of miR-143 in granulopoiesis. Based on our observation that hematopoietic cells undergoing granulocytic differentiation exhibit increased miR-143 expression, we show that the absence of miR-143 in mice results in a reduced number of mature granulocytes but not monocytes in blood and bone marrow. Additionally, we show that overexpression or ablation of miR-143 resulted in accelerated granulocytic differentiation or block of differentiation in several in vitro systems, including leukemic cell lines and G-CSF treated CD34+ HSPCs, respectively.
To identify the mRNA targets affected by miR-143 in hematopoietic cells we performed Argonaut2-RNA-Immunoprecipitation coupled with next generation sequencing. Here we could demonstrate a strong enrichment of members of the MAPK- and mTOR-pathways in cells overexpressing miR-143. Besides several potential targets of miR-143 we found ERK5 as particularly interesting since ERK5 was found to be a central mediator of cell survival, proliferation, motility, differentiation and apoptotic regulation of normal cells. To test whether miR-143 overexpression would also affect ERK5 protein abundance we performed western blot analysis of ERK5 and activated ERK5 in hematopoietic cells infected with miR-143 O/E constructs. Here we could show that miR-143 leads to reduced ERK5 protein levels in these cells. Since deregulation of both factors miR-143 as well as ERK5 have been implicated in the response to chemotherapeutic agents we analyzed the impact of miR-143 expression on treatment response. Here we show that AML patients receiving 5-azacytidine (Vidaza) and respond to the therapy had significant higher miR-143 levels than patients which did not respond. To test whether miR-143 expression would affect the response to chemotherapeutics, we overexpressed miR-143 in leukemic cells followed by Vidaza and AC220 treatment. Our results show a significant increase of apoptosis in cells overexpressing miR-143. Finally, we observed an association of high miR-143 expression levels with a higher probability of survival in two different cohorts of patients with acute myeloid leukemia. Taken together, we identified miR-143 as a relevant factor in granulocytic differentiation, which expression may be useful as prognostic factor and as new target for therapeutic strategies in AML.
Schwind:Novartis: Consultancy.
Active
related (
) gene deactivates ras-related C3 botulinum toxin substrate 1 (RAC1), which plays an essential role in regulating normal hematopoiesis and in leukemia.
gene, closely related to ABR, ...acts as a tumor suppressor in chronic myeloid leukemia and has overlapping functions with
. Evidence for a putative tumor suppressor role of
has been shown in several solid tumors, in which deletion of ABR is present. Our results show downregulation of
in AML. A block of ABR prevents myeloid differentiation and leads to repression of the myeloid transcription factor C/EBPα, a major regulator of myeloid differentiation and functionally impaired in leukemia. Conversely, stable overexpression of ABR enhances myeloid differentiation. Inactivation of the known ABR target RAC1 by treatment with the RAC1 inhibitor NSC23766 resulted in an increased expression of C/EBPα in primary AML samples and in AML cell lines U937 and MV4;11. Finally, AML patients with high
expression at diagnosis showed a significant longer overall survival and patients who respond to azacitidine therapy showed a significant higher ABR expression. This is the first report showing that
expression plays a critical role in both myelopoiesis and AML. Our data indicate the tumor suppressor potential of
and underline its potential role in leukemia therapeutic strategies.
Acute myeloid leukemia (AML) is a heterogeneous clonal disorder of defective hematopoiesis of white blood cells and often characterized by limited treatment options and a poor prognosis. MicroRNAs, a ...class of small non-coding RNAs, have been reported over the last years to play an important role in the regulation of “normal” and pathological processes. By binding to the 3'UTR of their target mRNAs, microRNAs lead to the translational repression of their target gene. Deregulation of a certain microRNA thereby may lead to disrupted signal pathways, such as MAPK-signaling, and to tumorigenesis. However, the role of microRNAs in hematopoietic differentiation and blood cancer development remains largely unknown. In AML only few miRNAs are functionally characterized, and the clinical relevance of these miRNAs still remains to be determined. In this study we identified microRNA-143 (miR-143) to be highly upregulated in G-CSF stimulated CD34+ cells. We could also show the granulopoietic association of miR-143 in several hematopoietic cell line models. In addition, we show that miR-143 is upregulated in APL patients after ATRA treatment. QPCR analysis of pri-miR-143 expression in RIC (reduced intensity conditioning) transplanted AML patients reveal that high expression of miR-143 is associated with high event-free and overall survival. In functional studies, stable overexpression of miR-143 in K562-C/EBPα-p42 cells enhances the C/EBPalpha induced granulocytic differentiation significantly. In contrast, stable knock down of miR-143 reduced the ability of K562-C/EBPα-p42 cells to undergo granulocytic differentiation upon β-estradiol treatment. Moreover, chromatinimmunoprecipitation (ChIP) analysis show the direct binding of C/EBPα to the promoter region of miR-143. By in silico prediction, we found MAPK protein family members (MAPK1, MAPK3 and MAPK7) as predicted targets of miR-143. Western blot analysis of AML patient samples and G-CSF stimulated CD34+ cells clearly show an inverse correlation of miR-143 and MAPK7 (ERK5) protein expression. By transient overexpression of miR-143 we could show a strong downregulation of MAPK protein family member expression in NB4 cells. These studies suggest miR-143 as an essential factor in granulocytic differentiation driven by G-CSF. Deregulation of miR-143 may play an important role in the development of AML. Furthermore, we propose miR-143 as prognostic marker for AML patients undergoing RIC transplantation therapy.
No relevant conflicts of interest to declare.
Almost one tenth of acute myeloid leukemias (AML) are related to t(15;17) translocation. This aberration leads to the PML-RARα fusion protein, which causes a transcriptional block of differentiation ...and could be resolved by all-trans-retinoic acid (ATRA). MicroRNAs (miRs) are small noncoding RNAs which are ascribed to be important regulators of cell proliferation, development, differentiation and apoptosis. MiR-126 is regarded as tumor suppressor in diverse tissues, but relatively little is known about its functional role in normal and malignant hematopoiesis. In this report, we reveal that oncogenic PML-RARα fusion protein is a repressor of miR-126 expression. Thus, we could demonstrate a significant downregulation of miR-126 expression in presence of the PML-RARα fusion protein in APL versus other AML patient samples and in a PML-RARα Knock in mouse model. We further show that ATRA induced differentiation of APL cell line NB4 comes along with an increase of miR-126 expression. The transient overexpression of miR-126 enhances ATRA stimulated differentiation of myeloid cells, whereas the opposite effect was noticed when endogenous expression of miR-126 was knocked down. Most interestingly, we observed a significant upregulation of miR-126 expression in APL blasts during ATRA treatment of APL patients. C-Myb proto-oncogene was found to be a putative target of miR-126 by analysing the 3’UTR. We could show a reduced c-Myb protein level after enforced expression of miR-126. Further, we reveal that miR-126 leads to a posttransciptional downregulation of c-Myb expression by directly targeting its 3‘UTR. Our data suggest miR-126 as an important regulator of differentiation in acute promyelocytic leukemia, targeting the proto-oncogene c-Myb and recommend microRNAs to be potential therapeutic agents.
No relevant conflicts of interest to declare.
The transcription factor CCAAT enhancer binding protein alpha (C/EBPα) is a master regulator of granulopoiesis and is silenced in approximately 50% of all acute myeloid leukemia (AML) cases. There ...are several mechanisms known how C/EBPα is inactivated in AML, including promoter hypermethylation, posttranslational modifications and mutations in the ORF of the CEBPA gene. MicroRNAs, a class of small non-coding RNAs, were identified as important regulators of normal hematopoiesis and leukemia development. We have already shown that microRNAs, such as miR-223, miR-34a and miR-30c, are essential elements in C/EBPα triggered granulocytic differentiation. But to our knowledge nothing is known about inactivation of C/EBPα by microRNAs in acute myeloid leukemia.
In this study, we identified a novel network between C/EBPα and miR-182. In a next generation sequencing approach based on inducible K562-C/EBPα-ER cell line, we found miR-182 strongly downregulated by wildtype C/EBPα. We could further demonstrate an inverse correlation between C/EBPα protein amount and miR-182 expression level in several in vitro systems, including leukemic cell lines and G-CSF treated primary human CD34+progenitor cells. Additionally, C/EBPα and miR-182 showed reciprocal expression in sorted murine bone marrow subpopulations in vivo. To discover the mechanism how miR-182 is blocked by C/EBPα, we analyzed the minimal promoter region of miR-182 and performed chromatin immunoprecipitation (ChIP). Here, we could demonstrate a strong binding of C/EBPα to the miR-182 promoter, particularly to a conserved E2F binding site. Because E2F is a well known inhibitor of C/EBPα function, we tested whether E2F also effects miR-182 expression. An overexpression of E2F1 in U937 cells leads to an elevated miR-182 expression level. In addition, we measured the expression of miR-182 in bone marrow from AML patients regarding to their CEBPA mutation status. We could show that only patients with mutations in the C-terminal region of C/EBPα showed elevated miR-182 expression, while patients with N-terminal CEBPA mutations revealed no abnormal miR-182 expression compared to healthy donors or AML patients with no CEBPA mutation. The C-terminal domain of C/EBPα is necessary for E2F inhibition. These findings illustrate the importance of C/EBPα-E2F interaction during miR-182 regulation. Next, we found a highly conserved binding site of miR-182 in the 3’UTR of CEBPA itself, suggesting a possible negative feedback loop. To test this, we performed overexpression of miR-182 in U937 cells, umbilical cord blood mononuclear cells (UCB-MNCs) and primary blasts from AML patients. Here, we observed a strong reduction of C/EBPα protein after miR-182 overexpression in all cell types. Furthermore, we could demonstrate a direct binding of miR-182 to the 3’UTR of CEBPA via luciferase activity assay. Finally, we were interested in the functional impact of miR-182 in myeloid differentiation and leukemia development. We showed that enforced expression of miR-182 in U937 cells reduced the percentage of Mac-1 positive myeloid cells after treatment with all-trans retinoid acid (ATRA). Additionally, lentiviral overexpression of miR-182 induces a block of differentiation and hyperproliferation in G-CSF treated 32D cells and an enhanced replating capacity of primary mouse bone marrow mononuclear cells.
Taken together, we identified miR-182 as novel oncogenic microRNA that directly blocks C/EBPα during myeloid differentiation and leukemia development. Thus, our data display a potential new strategy for therapeutics in C/EBPα dysregulated AML.
No relevant conflicts of interest to declare.
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