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.
A new computational framework for FLow cytometric Analysis of Rare Events (FLARE) has been developed specifically for fast and automatic identification of rare cell populations in very large samples ...generated by platforms like multi-parametric flow cytometry. Using a hierarchical Bayesian model and information-sharing via parallel computation, FLARE rapidly explores the high-dimensional marker-space to detect highly rare populations that are consistent across multiple samples. Further it can focus within specified regions of interest in marker-space to detect subpopulations with desired precision.
Hematopoiesis in mammalian embryos proceeds through three successive waves of hematopoietic progenitors. Since their emergence spatially and temporally overlap and phenotypic markers are often ...shared, the specifics regarding their origin, development, lineage restriction and mutual relationships have not been fully determined. The identification of wave-specific markers would aid to resolve these uncertainties. Here, we show that toll-like receptors (TLRs) are expressed during early mouse embryogenesis. We provide phenotypic and functional evidence that the expression of TLR2 on E7.5 c-kit
cells marks the emergence of precursors of erythro-myeloid progenitors (EMPs) and provides resolution for separate tracking of EMPs from primitive progenitors. Using in vivo fate mapping, we show that at E8.5 the Tlr2 locus is already active in emerging EMPs and in progenitors of adult hematopoietic stem cells (HSC). Together, this data demonstrates that the activation of the Tlr2 locus tracks the earliest events in the process of EMP and HSC specification.
Acute promyelocytic leukemia (APL) is characterized by a block in differentiation and accumulation of promyelocytes in the bone marrow and blood. The majority of APL patients harbor the t(15:17) ...translocation leading to expression of the fusion protein promyelocytic-retinoic acid receptor α. Treatment with retinoic acid leads to degradation of promyelocytic-retinoic acid receptor α protein and disappearance of leukemic cells; however, 30% of APL patients relapse after treatment. One potential mechanism for relapse is the persistence of cancer “stem” cells in hematopoietic organs after treatment. Using a novel sorting strategy we developed to isolate murine myeloid cells at distinct stages of differentiation, we identified a population of committed myeloid cells (CD34+, c-kit+, FcγRIII/II+, Gr1int) that accumulates in the spleen and bone marrow in a murine model of APL. We observed that these cells are capable of efficiently generating leukemia in recipient mice, demonstrating that this population represents the APL cancer–initiating cell. These cells down-regulate the transcription factor CCAAT/enhancer binding protein α (C/EBPα) possibly through a methylation-dependent mechanism, indicating that C/EBPα deregulation contributes to transformation of APL cancer–initiating cells. Our findings provide further understanding of the biology of APL by demonstrating that a committed transformed progenitor can initiate and propagate the disease.
Homeobox (HOX) genes are frequently dysregulated in leukemia. Previous studies have shown that aberrant HOX gene expression accompanies leukemogenesis and affects disease progression and leukemia ...patient survival. Patients with acute myeloid leukemia (AML) bearing PML-RARα fusion gene have distinct HOX gene signature in comparison to other subtypes of AML patients, although the mechanism of transcription regulation is not completely understood. We previously found an association between the mRNA levels of HOX genes and those of the histone demethylases JMJD3 and UTX in PML-RARα- positive leukemia patients. Here, we demonstrate that the release of the PML-RARα-mediated block in PML-RARα-positive myeloid leukemia cells increased both JMJD3 and HOX gene expression, while inhibition of JMJD3 using the specific inhibitor GSK-J4 reversed the effect. This effect was driven specifically through PML-RARα fusion protein since expression changes did not occur in cells with mutated RARα and was independent of differentiation. We confirmed that gene expression levels were inversely correlated with alterations in H3K27me3 histone marks localized at HOX gene promoters. Furthermore, data from chromatin immunoprecipitation followed by sequencing broaden a list of clustered HOX genes regulated by JMJD3 in PML-RARα-positive leukemic cells. Interestingly, the combination of GSK-J4 and all-trans retinoic acid (ATRA) significantly increased PML-RARα-positive cell apoptosis compared with ATRA treatment alone. This effect was also observed in ATRA-resistant NB4 clones, which may provide a new therapeutic opportunity for patients with acute promyelocytic leukemia (APL) resistant to current treatment. The results of our study reveal the mechanism of HOX gene expression regulation and contribute to our understanding of APL pathogenesis.
The transcription factor PU.1 is an important regulator of hematopoiesis; precise expression levels are critical for normal hematopoietic development and suppression of leukemia. We show here that ...noncoding antisense RNAs are important modulators of proper dosages of PU.1. Antisense and sense RNAs are regulated by shared evolutionarily conserved cis-regulatory elements, and we can show that antisense RNAs inhibit PU.1 expression by modulating mRNA translation. We propose that such antisense RNAs will likely be important in the regulation of many genes and may be the reason for the large number of overlapping complementary transcripts with so far unknown function.
The transcription factor RUNX1 is essential to establish the haematopoietic gene expression programme; however, the mechanism of how it activates transcription of haematopoietic stem cell (HSC) genes ...is still elusive. Here, we obtained novel insights into RUNX1 function by studying regulation of the human CD34 gene, which is expressed in HSCs. Using transgenic mice carrying human CD34 PAC constructs, we identified a novel downstream regulatory element (DRE), which is bound by RUNX1 and is necessary for human CD34 expression in long‐term (LT)‐HSCs. Conditional deletion of Runx1 in mice harbouring human CD34 promoter–DRE constructs abrogates human CD34 expression. We demonstrate by chromosome conformation capture assays in LT‐HSCs that the DRE physically interacts with the human CD34 promoter. Targeted mutagenesis of RUNX binding sites leads to perturbation of this interaction and decreased human CD34 expression in LT‐HSCs. Overall, our in vivo data provide novel evidence about the role of RUNX1 in mediating interactions between distal and proximal elements of the HSC gene CD34.
This study reveals molecular details of RUNX1 function in haematopoiesis. Employing various in vivo genetic models and chromatin conformation capture (3C) assays in HSCs, RUNX1 is shown to regulate CD34 expression by looping of a newly characterized distal regulatory element to the core promoter.
Mutations that activate the fms-like tyrosine kinase 3 (FLT3) receptor are among the most prevalent mutations in acute myeloid leukemias. The oncogenic role of FLT3 mutants has been attributed to the ...abnormal activation of several downstream signaling pathways, such as STAT3, STAT5, ERK1/2, and AKT. Here, we discovered that the cyclin-dependent kinase 1 (CDK1) pathway is also affected by internal tandem duplication mutations in FLT3. Moreover, we also identified C/EBPα, a granulopoiesis-promoting transcription factor, as a substrate for CDK1. We further demonstrated that CDK1 phosphorylates C/EBPα on serine 21, which inhibits its differentiation-inducing function. Importantly, we found that inhibition of CDK1 activity relieves the differentiation block in cell lines with mutated FLT3 as well as in primary patient-derived peripheral blood samples. Clinical trials with CDK1 inhibitors are currently under way for various malignancies. Our data strongly suggest that targeting the CDK1 pathway might be applied in the treatment of FLT3ITD mutant leukemias, especially those resistant to FLT3 inhibitor therapies. PUBLICATION ABSTRACT
Axon guidance relies on precise translation of extracellular signal gradients into local changes in cytoskeletal dynamics, but the molecular mechanisms regulating dose-dependent responses of growth ...cones are still poorly understood. Here, we show that during embryonic development in growing axons, a low level of Semaphorin3A stimulation is buffered by the prolyl isomerase Pin1. We demonstrate that Pin1 stabilizes CDK5-phosphorylated CRMP2A, the major isoform of CRMP2 in distal axons. Consequently, Pin1 knockdown or knockout reduces CRMP2A levels specifically in distal axons and inhibits axon growth, which can be fully rescued by Pin1 or CRMP2A expression. Moreover, Pin1 knockdown or knockout increases sensitivity to Sema3A-induced growth cone collapse in vitro and in vivo, leading to developmental abnormalities in axon guidance. These results identify an important isoform-specific function and regulation of CRMP2A in controlling axon growth and uncover Pin1-catalyzed prolyl isomerization as a regulatory mechanism in axon guidance.
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•CRMP2A, but not CRMP2B, is the dominant isoform of CRMP2 in distal axons•Pin1 specifically interacts with CDK5-phosphorylated CRMP2A in distal axons•Pin1 stabilizes CRMP2A to buffer growth cone collapse induced by low levels of Sema3A•Pin1 regulates Sema3A-driven axon guidance in embryonic development in vivo
The molecular mechanisms controlling the precise response of growing axons to gradients of extracellular guidance cues are largely unknown. Here, Balastik et al. show that the prolyl isomerase Pin1 regulates axon growth by stabilizing CDK5-phosphorylated CRMP2A in distal axons and modulates Sema3A stimulation in growing axons in vitro and in vivo.
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