Jun blockade of erythropoiesis: role for repression of GATA-1 by HERP2

CK2β Regulates Hematopoietic Stem Cell Biology and Erythropoiesis

The Ser-Thr kinase CK2 plays important roles in sustaining cell survival and resistance to stress and these functions are exploited by different types of blood tumors. Yet, the physiological involvement of CK2 in normal blood cell development is poorly known. Here, we discovered that the β regulatory subunit of CK2 is critical for normal hematopoiesis in the mouse. Fetal livers of conditional CK2β knockout embryos showed increased numbers of hematopoietic stem cells associated to a higher proliferation rate compared to control animals. Both hematopoietic stem and progenitor cells (HSPCs) displayed alterations in the expression of transcription factors involved in cell quiescence, self-renewal, and lineage commitment. HSPCs lacking CK2β were functionally impaired in supporting both in vitro and in vivo hematopoiesis as demonstrated by transplantation assays. Furthermore, KO mice developed anemia due to a reduced number of mature erythroid cells. This compartment was characterized by dysplasia, proliferative defects at early precursor stage, and apoptosis at late-stage erythroblasts. Erythroid cells exhibited a marked compromise of signaling cascades downstream of the cKit and erythropoietin receptor, with a defective activation of ERK/JNK, JAK/STAT5, and PI3K/AKT pathways and perturbations of several transcriptional programs as demonstrated by RNA-Seq analysis. Moreover, we unraveled an unforeseen molecular mechanism whereby CK2 sustains GATA1 stability and transcriptional proficiency. Thus, our work demonstrates new and crucial functions of CK2 in HSPC biology and in erythropoiesis.

ANTXR1 Regulates Erythroid Cell Proliferation and Differentiation through wnt/β-Catenin Signaling Pathway In Vitro and in Hematopoietic Stem Cell

Erythropoiesis is a highly complex and sophisticated multistage process regulated by many transcription factors, as well as noncoding RNAs. Anthrax toxin receptor 1 (ANTXR1) is a type I transmembrane protein that binds the anthrax toxin ligands and mediates the entry of its toxic part into cells. It also functions as a receptor for the Protective antigen (PA) of anthrax toxin, and mediates the entry of Edema factor (EF) and Lethal factor (LF) into the cytoplasm of target cells and exerts their toxicity. Previous research has shown that ANTXR1 inhibits the expression of γ-globin during the differentiation of erythroid cells. However, the effect on erythropoiesis from a cellular perspective has not been fully determined. This study examined the role of ANTXR1 on erythropoiesis using K562 and HUDEP-2 cell lines as well as cord blood CD34+ cells. Our study has shown that overexpression of ANTXR1 can positively regulate erythrocyte proliferation, as well as inhibit GATA1 and ALAS2 expression, differentiation, and apoptosis in K562 cells and hematopoietic stem cells. ANTXR1 knockdown inhibited proliferation, promoted GATA1 and ALAS2 expression, accelerated erythrocyte differentiation and apoptosis, and promoted erythrocyte maturation. Our study also showed that ANTXR1 may regulate the proliferation and differentiation of hematopoietic cells, though the Wnt/β-catenin pathway, which may help to establish a possible therapeutic target for the treatment of blood disorders.

Multiple pathways coordinating reprogramming of endothelial cells into osteoblasts by BMP4

Cell type transition occurs during normal development and under pathological conditions. In prostate cancer bone metastasis, prostate cancer-secreted BMP4 induces endothelial cell-to-osteoblast (EC-to-OSB) transition. Such tumor-induced stromal reprogramming supports prostate cancer progression. We delineate signaling pathways mediating EC-to-OSB transition using EC lines 2H11 and SVR. We found that BMP4-activated pSmad1-Notch-Hey1 pathway inhibits EC migration and tube formation. BMP4-activated GSK3β-βcatenin-Slug pathway stimulates Osx expression. In addition, pSmad1-regulated Dlx2 converges with the Smad1 and β-catenin pathways to stimulate osteocalcin expression. By co-expressing Osx, Dlx2, Slug and Hey1, we were able to achieve EC-to-OSB transition, leading to bone matrix mineralization in the absence of BMP4. In human prostate cancer bone metastasis specimens and MDA-PCa-118b and C4-2b-BMP4 osteogenic xenografts, immunohistochemical analysis showed that β-catenin and pSmad1 are detected in activated osteoblasts rimming the tumor-induced bone. Our results elucidated the pathways and key molecules coordinating prostate cancer-induced stromal programming and provide potential targets for therapeutic intervention.

Mesenchymal Chondrosarcoma: a Review with Emphasis on its Fusion-Driven Biology

Mesenchymal chondrosarcoma is a rare but deadly form of chondrosarcoma that typically affects adolescents and young adults. While curative intent is possible for patients with localized disease, few options exist for patients in the unresectable/metastatic setting. Thus, it is imperative to understand the fusion-driven biology of this rare malignant neoplasm so as to lead to the future development of better therapeutics for this disease. This manuscript will briefly review the clinical and pathologic features of mesenchymal chondrosarcoma followed by an appraisal of existing data linked to the fusions, HEY1-NCOA2 and IRF2BP2-CDX1, and the associated downstream pathways.

Inhibition of MEK/ERK signalling pathway promotes erythroid differentiation and reduces HSCs engraftment in ex vivo expanded haematopoietic stem cells

The MEK/ERK pathway is found to be important in regulating different biological processes such as proliferation, differentiation and survival in a wide variety of cells. However, its role in self‐renewal of haematopoietic stem cells is controversial and remains to be clarified. The aim of this study was to understand the role of MEK/ERK pathway in ex vivo expansion of mononuclear cells (MNCs) and purified CD34⁺ cells, both derived from human umbilical cord blood (hUCB). Based on our results, culturing the cells in the presence of an inhibitor of MEK/ERK pathway—PD0325901 (PD)—significantly reduces the expansion of CD34⁺ and CD34⁺ CD38⁻ cells, while there is no change in the expression of stemness‐related genes (HOXB4, BMI1). Moreover, in vivo analysis demonstrates that PD reduces engraftment capacity of ex vivo expanded CD34⁺ cells. Notably, when ERK pathway is blocked in UCB‐MNCs, spontaneous erythroid differentiation is promoted, found in concomitant with increasing number of burst‐forming unit‐erythroid colony (BFU‐E) as well as enhancement of erythroid glycophorin‐A marker. These results are in total conformity with up‐regulation of some erythroid enhancer genes (TAL1, GATA2, LMO2) and down‐regulation of some erythroid repressor genes (JUN, PU1) as well. Taken together, our results support the idea that MEK/ERK pathway has a critical role in achieving the correct balance between self‐renewal and differentiation of UCB cells. Also, we suggest that inhibition of ERK signalling could likely be a new key for erythroid induction of UCB‐haematopoietic progenitor cells.

Neonatal expression of RNA-binding protein IGF2BP3 regulates the human fetal-adult megakaryocyte transition

Hematopoietic transitions that accompany fetal development, such as erythroid globin chain switching, play important roles in normal physiology and disease development. In the megakaryocyte lineage, human fetal progenitors do not execute the adult morphogenesis program of enlargement, polyploidization, and proplatelet formation. Although these defects decline with gestational stage, they remain sufficiently severe at birth to predispose newborns to thrombocytopenia. These defects may also contribute to inferior platelet recovery after cord blood stem cell transplantation and may underlie inefficient platelet production by megakaryocytes derived from pluripotent stem cells. In this study, comparison of neonatal versus adult human progenitors has identified a blockade in the specialized positive transcription elongation factor b (P-TEFb) activation mechanism that is known to drive adult megakaryocyte morphogenesis. This blockade resulted from neonatal-specific expression of an oncofetal RNA-binding protein, IGF2BP3, which prevented the destabilization of the nuclear RNA 7SK, a process normally associated with adult megakaryocytic P-TEFb activation. Knockdown of IGF2BP3 sufficed to confer both phenotypic and molecular features of adult-type cells on neonatal megakaryocytes. Pharmacologic inhibition of IGF2BP3 expression via bromodomain and extraterminal domain (BET) inhibition also elicited adult features in neonatal megakaryocytes. These results identify IGF2BP3 as a human ontogenic master switch that restricts megakaryocyte development by modulating a lineage-specific P-TEFb activation mechanism, revealing potential strategies toward enhancing platelet production.

HEY1 functions are regulated by its phosphorylation at Ser-68

HEY1-dependent activation of the p53 tumour suppressor pathway can be inhibited through direct phosphorylation of HEY1 at Ser-68 located in the bHLH domain. STK38 and STK38L serine/threonine kinases can phosphorylate HEY1 Ser-68 and could modulate its biological function.

HEY1 (hairy/enhancer-of-split related with YRPW motif 1) is a member of the basic helix–loop–helix-orange (bHLH-O) family of transcription repressors that mediate Notch signalling. HEY1 acts as a positive regulator of the tumour suppressor p53 via still unknown mechanisms. A MALDI-TOF/TOF MS analysis has uncovered a novel HEY1 regulatory phosphorylation event at Ser-68. Strikingly, this single phosphorylation event controls HEY1 stability and function: simulation of HEY1 Ser-68 phosphorylation increases HEY1 protein stability but inhibits its ability to enhance p53 transcriptional activity. Unlike wild-type HEY1, expression of the phosphomimetic mutant HEY1-S68D failed to induce p53-dependent cell cycle arrest and it did not sensitize U2OS cells to p53-activating chemotherapeutic drugs. We have identified two related kinases, STK38 (serine/threonine kinase 38) and STK38L (serine/threonine kinase 38 like), which interact with and phosphorylate HEY1 at Ser-68. HEY1 is phosphorylated at Ser-68 during mitosis and it accumulates in the centrosomes of mitotic cells, suggesting a possible integration of HEY1-dependent signalling in centrosome function. Moreover, HEY1 interacts with a subset of p53-activating ribosomal proteins. Ribosomal stress causes HEY1 relocalization from the nucleoplasm to perinucleolar structures termed nucleolar caps. HEY1 interacts physically with at least one of the ribosomal proteins, RPL11, and both proteins cooperate in the inhibition of MDM2-mediated p53 degradation resulting in a synergistic positive effect on p53 transcriptional activity. HEY1 itself also interacts directly with MDM2 and it is subjected to MDM2-mediated degradation. Simulation of HEY1 Ser-68 phosphorylation prevents its interaction with p53, RPL11 and MDM2 and abolishes HEY1 migration to nucleolar caps upon ribosomal stress. Our findings uncover a novel mechanism for cross-talk between Notch signalling and nucleolar stress.

Notch Stimulates Both Self-Renewal and Lineage Plasticity in a Subset of Murine CD9High Committed Megakaryocytic Progenitors

This study aimed at reinvestigating the controversial contribution of Notch signaling to megakaryocytic lineage development. For that purpose, we combined colony assays and single cells progeny analyses of purified megakaryocyte-erythroid progenitors (MEP) after short-term cultures on recombinant Notch ligand rDLL1. We showed that Notch activation stimulated the SCF-dependent and preferential amplification of Kit⁺ erythroid and bipotent progenitors while favoring commitment towards the erythroid at the expense of megakaryocytic lineage. Interestingly, we also identified a CD9^High MEP subset that spontaneously generated almost exclusively megakaryocytic progeny mainly composed of single megakaryocytes. We showed that Notch activation decreased the extent of polyploidization and maturation of megakaryocytes, increased the size of megakaryocytic colonies and surprisingly restored the generation of erythroid and mixed colonies by this CD9^High MEP subset. Importantly, the size increase of megakaryocytic colonies occurred at the expense of the production of single megakaryocytes and the restoration of colonies of alternative lineages occurred at the expense of the whole megakaryocytic progeny. Altogether, these results indicate that Notch activation is able to extend the number of divisions of MK-committed CD9^High MEPs before terminal maturation while allowing a fraction of them to generate alternative lineages. This unexpected plasticity of MK-committed progenitors revealed upon Notch activation helps to better understand the functional promiscuity between megakaryocytic lineage and hematopoietic stem cells.

Notch signaling represses GATA4-induced expression of genes involved in steroid biosynthesis

Notch2 and Notch3 and genes of the Notch signaling network are dynamically expressed in developing follicles, where they are essential for granulosa cell proliferation and meiotic maturation. Notch receptors, ligands, and downstream effector genes are also expressed in testicular Leydig cells, predicting a potential role in regulating steroidogenesis. In this study, we sought to determine if Notch signaling in small follicles regulates the proliferation response of granulosa cells to FSH and represses the up-regulation steroidogenic gene expression that occurs in response to FSH as the follicle grows. Inhibition of Notch signaling in small preantral follicles led to the up-regulation of the expression of genes in the steroid biosynthetic pathway. Similarly, progesterone secretion by MA-10 Leydig cells was significantly inhibited by constitutively active Notch. Together, these data indicated that Notch signaling inhibits steroidogenesis. GATA4 has been shown to be a positive regulator of steroidogenic genes, including STAR protein, P450 aromatase, and 3B-hydroxysteroid dehydrogenase. We observed that Notch downstream effectors HEY1, HEY2, and HEYL are able to differentially regulate these GATA4-dependent promoters. These data are supported by the presence of HEY/HES binding sites in these promoters. These studies indicate that Notch signaling has a role in the complex regulation of the steroidogenic pathway.

Personalized Radioproteomics: Identification of a Protein Biomarker Signature for Preemptive Rescue by Tocopherol Succinate in CD34+ Irradiated Progenitor Cells Isolated from a Healthy Control Donor

Tocopherol succinate (TS) has been shown to protect mice against acute radiation syndrome, however, its exact mechanism of action and its possible use in humans has not yet been evaluated. Our approach has been to test the radioprotectant properties of TS on CD34-positive stem cells from healthy volunteers. We hypothesize that a radioproteomics strategy can identify a drug-dependent, personalized proteomics signature for radioprotection. To directly test the radioproteomics hypothesis, we treated human CD34-positive stem cells with 20 μM TS for 24 h, and then exposed the cells to 2 Gy of cobalt-60 gamma-radiation. We isolated protein from all cultures and used a high throughput Antibody Microarray (AbMA) platform to measure concentrations of 725 low abundance proteins. As an in vivo control, we also tested mouse CD34-positive stem cells using the same preemptive TS paradigm on progenitor colony forming units. TS pretreatment of in vitro or in vivo CD34-positive stem cells rescued radiation-induced loss of colony-forming potential of progenitors. We identified 50 of 725 proteins that could be preemptively rescued from radiation-induced reduction by pretreatment with TS. Ingenuity Pathway Analysis (IPA) reveals that the modified proteins fall into categories dominated by epigenetic regulation, DNA repair, and inflammation. Our results suggest that radioproteomics can be used to develop personalized medicine for radioprotection using protein signatures from primary CD34-positive progenitors derived from the patient or victim prior to radiation exposure. The protective effect of TS may be due to its ability to preemptively activate epigenetic mechanisms relevant to radioprotection and to preemptively activate the programs for DNA repair and inflammation leading to cell survival.

The regulatory roles of microRNA-146b-5p and its target platelet-derived growth factor receptor α (PDGFRA) in erythropoiesis and megakaryocytopoiesis

Emerging evidence has shown that microRNAs have key roles in regulating various normal physiological processes, whereas their deregulated expression is correlated with various diseases. The miR-146 family includes miR-146a and miR-146b, with a distinct expression spectrum in different hematopoietic cells. Recent work indicated that miR-146a has a close relationship with inflammation and autoimmune diseases. miR-146-deficient mice have developed some abnormal hematopoietic phenotypes, suggesting the potential functions of miR-146 in hematopoietic development. In this study, we found that miR-146b was consistently up-regulated in both K562 and CD34(+) hematopoietic stem/progenitor cells (HSPCs) undergoing either erythroid or megakaryocytic differentiation. Remarkably, erythroid and megakaryocytic maturation of K562 cells was induced by excess miR-146b but inhibited by decreased miR-146b levels. More importantly, an mRNA encoding receptor tyrosine kinase, namely platelet-derived growth factor receptor α (PDGFRA), was identified and validated as a direct target of miR-146b in hematopoietic cells. Gain-of-function and loss-of-function assays showed that PDGFRA functioned as a negative regulator in erythroid and megakaryocytic differentiation. miR-146b could ultimately affect the expression of the GATA-1 gene, which is regulated by HEY1 (Hairy/enhancer-of-split related with YRPW motif protein 1), a transcriptional repressor, via inhibition of the PDGFRA/JNK/JUN/HEY1 pathway. Lentivirus-mediated gene transfer also demonstrated that the overexpression of miR-146b promoted erythropoiesis and megakaryocytopoiesis of HSPCs via its regulation on the PDGFRA gene and effects on GATA-1 expression. Moreover, we confirmed that the binding of GATA-1 to the miR-146b promoter and induction of miR-146b during hematopoietic maturation were dependent on GATA-1. Therefore, miR-146b, PDGFRA, and GATA-1 formed a regulatory circuit to promote erythroid and megakaryocytic differentiation.

Hydroxyurea-inducible SAR1 gene acts through the Giα/JNK/Jun pathway to regulate γ-globin expression

Hydroxyurea (HU) is effectively used in the management of β-hemoglobinopathies by augmenting the production of fetal hemoglobin (HbF). However, the molecular mechanisms underlying HU-mediated HbF regulation remain unclear. We previously reported that overexpression of the HU-induced SAR1 gene closely mimics the known effects of HU on K562 and CD34(+) cells, including γ-globin induction and cell-cycle regulation. Here, we show that HU stimulated nuclear factor-κB interaction with its cognate-binding site on the SAR1 promoter to regulate transcriptional expression of SAR1 in K562 and CD34(+) cells. Silencing SAR1 expression not only significantly lowered both basal and HU-elicited HbF production in K562 and CD34(+) cells, but also significantly reduced HU-mediated S-phase cell-cycle arrest and apoptosis in K562 cells. Inhibition of c-Jun N-terminal kinase (JNK)/Jun phosphorylation and silencing of Giα expression in SAR1-transfected K562 and CD34(+) cells reduced both γ-globin expression and HbF level, indicating that activation of Giα/JNK/Jun proteins is required for SAR1-mediated HbF induction. Furthermore, reciprocal coimmunoprecipitation assays revealed an association between forcibly expressed SAR1 and Giα2 or Giα3 proteins in both K562 and nonerythroid cells. These results indicate that HU induces SAR1, which in turn activates γ-globin expression, predominantly through the Giα/JNK/Jun pathway. Our findings identify SAR1 as an alternative therapeutic target for β-globin disorders.

ZNF16 (HZF1) promotes erythropoiesis and megakaryocytopoiesis via regulation of the c-KIT gene

We previously characterized the zinc finger protein gene HZF1 [also known as ZNF16 (zinc finger protein 16)] and demonstrated its important roles in erythroid and megakaryocytic differentiation of K562 cells. In the present study, we investigated its effect on erythroid and megakaryocytic differentiation of HSPCs (haemopoietic stem/progenitor cells). We observed up-regulation of ZNF16 during erythroid and megakaryocytic differentiation of the CD34+ HSPCs, and demonstrated that ZNF16 promotes erythroid and megakaryocytic differentiation by gain-of-function and loss-of-function experiments. Using a luciferase reporter and ChIP assays ZNF16 was demonstrated to bind to the c-KIT gene promoter and inhibit its expression in K562 cells. Enforced expression and knockdown of ZNF16 down-regulated and up-regulated the expression of the c-KIT gene in K562 cells and HSPCs respectively. Significantly decreased levels of the c-Kit protein were observed following erythroid and megakaryocytic differentiation of K562 and CD34+ cells. The knockdown of c-KIT partially rescued the differentiation inhibition caused by ZNF16 knockdown. The knockdown of c-KIT also blocked the activity of the c-Raf/MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase]/ERK/c-Jun signal pathway and reduced further the level of HEY1 (hes-related family bHLH transcription factor with YRPW motif 1), a repressor of GATA1 (GATA-binding protein 1) transcription, which finally up-regulated the expression of GATA1, a central regulator of erythroid and megakaryocytic differentiation. In conclusion the results of the present study demonstrate that ZNF16 plays an important role in erythropoiesis and megakaryocytopoiesis via its regulation of the c-Kit/c-Raf/MEK/ERK/c-Jun/HEY1/GATA1 cascade.

Hey bHLH transcription factors

Hey bHLH transcription factors are direct targets of canonical Notch signaling. The three mammalian Hey proteins are closely related to Hes proteins and they primarily repress target genes by either directly binding to core promoters or by inhibiting other transcriptional activators. Individual candidate gene approaches and systematic screens identified a number of Hey target genes, which often encode other transcription factors involved in various developmental processes. Here, we review data on interaction partners and target genes and conclude with a model for Hey target gene regulation. Furthermore, we discuss how expression of Hey proteins affects processes like cell fate decisions and differentiation, e.g., in cardiovascular, skeletal, and neural development or oncogenesis and how this relates to the observed developmental defects and phenotypes observed in various knockout mice.

Interferon-γ suppresses activin A/NF-E2 induction of erythroid gene expression through the NF-κB/c-Jun pathway

Interferon (IFN)-γ is a proinflammatory cytokine that is linked to erythropoiesis inhibition and may contribute to anemia. However, the mechanism of IFN-γ-inhibited erythropoiesis is unknown. Activin A, a member of the transforming growth factor (TGF)-β superfamily, induces the erythropoiesis of hematopoietic progenitor cells. In this study, a luciferase reporter assay showed that IFN-γ suppressed activin A-induced ζ-globin promoter activation in K562 erythroblast cells in a dose-dependent manner. Activin A reversed the suppressive effect of IFN-γ on the luciferase activity of ζ-globin promoter in a dose-dependent manner. IFN-γ also suppressed the activation of activin A-induced α-globin promoter. IFN-γ reduced the mRNA expression of α-globin, ζ-globin, NF-E2p45, and GATA-1 induced by activin A. The results also showed that IFN-γ induced c-Jun expression when NF-κBp65 and c-Jun bound to two AP-1-binding sites on the c-Jun promoter. The luciferase activity of α-globin and ζ-globin promoters were enhanced by wild-type c-Jun and eliminated by dominant-negative (DN) c-Jun. The suppressive effects of IFN-γ on the mRNA expression of α-globin and ζ-globin were absent in cells expressing DN c-Jun. The ability of NF-E2 to enhance activin A-induced ζ-globin promoter activation decreased when c-Jun was present, and IFN-γ treatment further enhanced the decreasing effect of c-Jun. Chromatin immunoprecipitation revealed that NF-E2p45 bound to the upstream regulatory element (HS-40) of the α-globin gene cluster in response to activin A, whereas c-Jun eliminated this binding. These results suggest that IFN-γ modulates NF-κB/c-Jun to antagonize activin A-mediated NF-E2 transcriptional activity on globin gene expression.

Haematopoietic differentiation is inhibited when Notch activity is enhanced in FLK1(+) mesoderm progenitors

Notch signalling has been implicated during haematopoietic development in vivo and in the differentiation of haematopoietic cells from pluripotent cells in vitro. However interpretation of data from many of these studies has been complicated by the heterogeneous nature of cell populations under study and by the fact that the Notch pathway is active during embryogenesis prior to the development of the haematopoietic system. To define the role of Notch signalling in more precise cell populations during the early stages of haematopoietic development within the aorta-gonad-mesonephros (AGM) microenvironment we co-cultured differentiating ESCs on a stromal cell line derived from this region of the embryo. Our co-culture system had no effect on the production of FLK1(+) mesoderm progenitor cells but promoted their subsequent haematopoietic differentiation. We assessed the role of Notch signalling on haematopoietic differentiation of isolated FLK1(+) cells. Notch activity is dynamic and drops to basal levels as FLK1(+) cells commit to a haematopoietic fate. Further reduction of Notch activity by the inducible expression of dominant negative MAML had no functional consequences. In contrast, induction of Notch activity using an inducible NotchIC expression system had an inhibitory effect on haematopoietic differentiation. We used a Cre-mediated recombination strategy whereby NotchIC-expressing cells were marked with the hCD2 receptor and observed a reduction in the number of multi-lineage and myeloid colonies derived from NotchIC(+) compared to NotchIC(-) FLK1(+) cells isolated from the same culture. We believe that our culture system represents a good model for haematopoietic development within the AGM microenvironment and our data suggest that haematopoietic commitment of FLK1(+) cells in this setting occurs when Notch activity is below a specific threshold.

GATA-1 utilizes Ikaros and polycomb repressive complex 2 to suppress Hes1 and to promote erythropoiesis

The transcription factor Hairy Enhancer of Split 1 (HES1), a downstream effector of the Notch signaling pathway, is an important regulator of hematopoiesis. Here, we demonstrate that in primary erythroid cells, Hes1 gene expression is transiently repressed around proerythroblast stage of differentiation. Using mouse erythroleukemia cells, we found that the RNA interference (RNAi)-mediated depletion of HES1 enhances erythroid cell differentiation, suggesting that this protein opposes terminal erythroid differentiation. This is also supported by the decreased primary erythroid cell differentiation upon HES1 upregulation in Ikaros-deficient mice. A comprehensive analysis led us to determine that Ikaros favors Hes1 repression in erythroid cells by facilitating recruitment of the master regulator of erythropoiesis GATA-1 alongside FOG-1, which mediates Hes1 repression. GATA-1 is then necessary for the chromatin binding of the NuRD remodeling complex ATPase MI-2, the transcription factor GFI1B, and the histone H3K27 methyltransferase EZH2 along with Polycomb repressive complex 2. We show that EZH2 is required for the transient repression of Hes1 in erythroid cells. In aggregate, our results describe a mechanism whereby GATA-1 utilizes Ikaros and Polycomb repressive complex 2 to promote Hes1 repression as an important step in erythroid cell differentiation.

Cyclic AMP signaling inhibits megakaryocytic differentiation by targeting transcription factor 3 (E2A) cyclin-dependent kinase inhibitor 1A (CDKN1A) transcriptional axis

Signaling via the intracellular second messenger cyclic AMP (cAMP) has long been implicated in the repression of megakaryocytic differentiation. However, the mechanisms by which cAMP signaling impairs megakaryopoiesis have never been elucidated. In a human CD34(+) cell culture model, we show that the adenylyl cyclase agonist forskolin inhibits megakaryocytic differentiation in a protein kinase A-dependent manner. Using this system to screen for downstream effectors, we identified the transcription factor E2A as a key target in a novel repressive signaling pathway. Specifically, forskolin acting through protein kinase A-induced E2A down-regulation and enforced expression of E2A overrode the inhibitory effects of forskolin on megakaryopoiesis. The dependence of megakaryopoiesis on critical thresholds of E2A expression was confirmed in vivo in haploinsufficient mice and ex vivo using shRNA knockdown in human progenitors. Using a variety of approaches, we further identified p21 (encoded by CDKN1A) as a functionally important megakaryopoietic regulator residing downstream of E2A. These results thus implicate the E2A-CDKN1A transcriptional axis in the control of megakaryopoiesis and reveal the lineage-selective inhibition of this axis as a likely mechanistic basis for the inhibitory effects of cAMP signaling.

The leukemia associated nuclear corepressor ETO homologue genes MTG16 and MTGR1 are regulated differently in hematopoietic cells

Background

MTG16, MTGR1 and ETO are nuclear transcriptional corepressors of the human ETO protein family. MTG16 is implicated in hematopoietic development and in controlling erythropoiesis/megakaryopoiesis. Furthermore, ETO homologue genes are 3'participants in leukemia fusions generated by chromosomal translocations responsible of hematopoietic dysregulation. We tried to identify structural and functional promoter elements of MTG16 and MTGR1 genes in order to find associations between their regulation and hematopoiesis.

Results

5' deletion examinations and luciferase reporter gene studies indicated that a 492 bp sequence upstream of the transcription start site is essential for transcriptional activity by the MTG16 promoter. The TATA- and CCAAT-less promoter with a GC box close to the start site showed strong reporter activity when examined in erythroid/megakaryocytic cells. Mutation of an evolutionary conserved GATA -301 consensus binding site repressed promoter function. Furthermore, results from in vitro antibody-enhanced electrophoretic mobility shift assay and in vivo chromatin immunoprecipitation indicated binding of GATA-1 to the GATA -301 site. A role of GATA-1 was also supported by transfection of small interfering RNA, which diminished MTG16 expression. Furthermore, expression of the transcription factor HERP2, which represses GATA-1, produced strong inhibition of the MTG16 promoter reporter consistent with a role of GATA-1 in transcriptional activation. The TATA-less and CCAAT-less MTGR1 promoter retained most of the transcriptional activity within a -308 to -207 bp region with a GC-box-rich sequence containing multiple SP1 binding sites reminiscent of a housekeeping gene with constitutive expression. However, mutations of individual SP1 binding sites did not repress promoter function; multiple active SP1 binding sites may be required to safeguard constitutive MTGR1 transcriptional activity. The observed repression of MTG16/MTGR1 promoters by the leukemia associated AML1-ETO fusion gene may have a role in hematopoietic dysfunction of leukemia.

Conclusions

An evolutionary conserved GATA binding site is critical in transcriptional regulation of the MTG16 promoter. In contrast, the MTGR1 gene depends on a GC-box-rich sequence for transcriptional regulation and possible ubiquitous expression. Our results demonstrate that the ETO homologue promoters are regulated differently consistent with hematopoietic cell-type- specific expression and function.

Aconitase regulation of erythropoiesis correlates with a novel licensing function in erythropoietin-induced ERK signaling

BACKGROUND

Erythroid development requires the action of erythropoietin (EPO) on committed progenitors to match red cell output to demand. In this process, iron acts as a critical cofactor, with iron deficiency blunting EPO-responsiveness of erythroid progenitors. Aconitase enzymes have recently been identified as possible signal integration elements that couple erythropoiesis with iron availability. In the current study, a regulatory role for aconitase during erythropoiesis was ascertained using a direct inhibitory strategy.

METHODOLOGY/PRINCIPAL FINDINGS

In C57BL/6 mice, infusion of an aconitase active-site inhibitor caused a hypoplastic anemia and suppressed responsiveness to hemolytic challenge. In a murine model of polycythemia vera, aconitase inhibition rapidly normalized red cell counts, but did not perturb other lineages. In primary erythroid progenitor cultures, aconitase inhibition impaired proliferation and maturation but had no effect on viability or ATP levels. This inhibition correlated with a blockade in EPO signal transmission specifically via ERK, with preservation of JAK2-STAT5 and Akt activation. Correspondingly, a physical interaction between ERK and mitochondrial aconitase was identified and found to be sensitive to aconitase inhibition.

CONCLUSIONS/SIGNIFICANCE

Direct aconitase inhibition interferes with erythropoiesis in vivo and in vitro, confirming a lineage-selective regulatory role involving its enzymatic activity. This inhibition spares metabolic function but impedes EPO-induced ERK signaling and disturbs a newly identified ERK-aconitase physical interaction. We propose a model in which aconitase functions as a licensing factor in ERK-dependent proliferation and differentiation, thereby providing a regulatory input for iron in EPO-dependent erythropoiesis. Directly targeting aconitase may provide an alternative to phlebotomy in the treatment of polycythemia vera.

c-Jun binding site identification in K562 cells

Determining the binding sites of the transcription factor is important for understanding of transcriptional regulation. Transcription factor c-Jun plays an important role in cell growth, differentiation and development, but the binding sites and the target genes are not clearly defined in the whole human genome. In this study, we performed a ChIP-Seq experiment to identify c-Jun binding site in the human genome. Forty-eight binding sites were selected to process further evaluation by dsDNA microarray assay. We identified 283 c-Jun binding sites in K562 cells. Data analysis showed that 48.8% binding sites located within 100 kb of the upstream of the annotated genes, 28.6% binding sites comprised consensus TRE/CRE motif (5'-TGAC/GTCA-3', 5'-TGACGTCA-3') and variant sequences. Forty-two out of the selected 48 binding sites were found to bind the c-Jun homodimer in dsDNA microarray analysis. Data analysis also showed that 1569 genes are located in the neighborhood of the 283 binding sites and 191 genes in the neighborhood of the 42 binding sites validated by dsDNA microarray. We consulted 38 c-Jun target genes in previous studies and 16 among these 38 genes were also detected in this study. The identification of c-Jun binding sites and potential target genes in the genome scale may improve our fundamental understanding in the molecular mechanisms underlying the transcription regulation related to c-Jun.

P. falciparum modulates erythroblast cell gene expression in signaling and erythrocyte production pathways

Global, genomic responses of erythrocytes to infectious agents have been difficult to measure because these cells are e-nucleated. We have previously demonstrated that in vitro matured, nucleated erythroblast cells at the orthochromatic stage can be efficiently infected by the human malaria parasite Plasmodium falciparum. We now show that infection of orthochromatic cells induces change in 609 host genes. 592 of these transcripts are up-regulated and associated with metabolic and chaperone pathways unique to P. falciparum infection, as well as a wide range of signaling pathways that are also induced in related apicomplexan infections of mouse hepatocytes or human fibroblast cells. Our data additionally show that polychromatophilic cells, which precede the orthochromatic stage and are not infected when co-cultured with P. falciparum, up-regulate a small set of genes, at least two of which are associated with pathways of hematopoiesis and/or erythroid cell development. These data support the idea that P. falciparum affects erythropoiesis at multiple stages during erythroblast differentiation. Further P. falciparum may modulate gene expression in bystander erythroblasts and thus influence pathways of erythrocyte development. This study provides a benchmark of the host erythroblast cell response to infection by P. falciparum.

Garlic accelerates red blood cell turnover and splenic erythropoietic gene expression in mice: evidence for erythropoietin-independent erythropoiesis

Garlic (Allium sativum) has been valued in many cultures both for its health effects and as a culinary flavor enhancer. Garlic's chemical complexity is widely thought to be the source of its many health benefits, which include, but are not limited to, anti-platelet, procirculatory, anti-inflammatory, anti-apoptotic, neuro-protective, and anti-cancer effects. While a growing body of scientific evidence strongly upholds the herb's broad and potent capacity to influence health, the common mechanisms underlying these diverse effects remain disjointed and relatively poorly understood. We adopted a phenotype-driven approach to investigate the effects of garlic in a mouse model. We examined RBC indices and morphologies, spleen histochemistry, RBC half-lives and gene expression profiles, followed up by qPCR and immunoblot validation. The RBCs of garlic-fed mice register shorter half-lives than the control. But they have normal blood chemistry and RBC indices. Their spleens manifest increased heme oxygenase 1, higher levels of iron and bilirubin, and presumably higher CO, a pleiotropic gasotransmitter. Heat shock genes and those critical for erythropoiesis are elevated in spleens but not in bone marrow. The garlic-fed mice have lower plasma erythropoietin than the controls, however. Chronic exposure to CO of mice on garlic-free diet was sufficient to cause increased RBC indices but again with a lower plasma erythropoietin level than air-treated controls. Furthermore, dietary garlic supplementation and CO treatment showed additive effects on reducing plasma erythropoietin levels in mice. Thus, garlic consumption not only causes increased energy demand from the faster RBC turnover but also increases the production of CO, which in turn stimulates splenic erythropoiesis by an erythropoietin-independent mechanism, thus completing the sequence of feedback regulation for RBC metabolism. Being a pleiotropic gasotransmitter, CO may be a second messenger for garlic's other physiological effects.

Parenteral administration of recombinant human neuregulin-1 to patients with stable chronic heart failure produces favourable acute and chronic haemodynamic responses

AIMS

Neuregulin-1 (NRG-1) plays a critical role in the adaptation of the heart to injury, inhibiting apoptosis and inducing cardiomyocyte proliferation. We have shown previously that rhNRG-1 improves cardiac function and survival in animal models of cardiomyopathy. Here we report the first human study aimed at exploring the acute and chronic haemodynamic responses to recombinant human NRG-1 (beta(2a) isoform; rhNRG-1) in patients with stable chronic heart failure (CHF).

METHODS AND RESULTS

Fifteen patients (age, 60 ± 2; NYHA II:III, 9:6; left ventricular ejection fraction (LVEF) <40%) on optimal medical therapy for CHF, received a rhNRG-1 infusion daily for 11 days. Acute and chronic haemodynamic, structural and biochemical effects were determined by serial right heart catheterization, cardiac magnetic resonance (CMR), echocardiography and measurement of neurohumoral indices. Acutely, cardiac output increased by 30% during a 6 h rhNRG-1 infusion (P < 0.01). Pulmonary artery wedge pressure and systemic vascular resistance decreased 30 and 20%, respectively, at 2 h (P < 0.01). A 47% reduction in serum noradrenaline, a 55% reduction in serum aldosterone and a 3.6-fold increase in N-terminal prohormone brain natriuretic peptide levels were concurrently observed (P < 0.001). These acute haemodynamic effects were sustained, as demonstrated by the 12% increase in LVEF from 32.2 ± 2.0% (baseline) to 36.1 ± 2.3% (mean ± SE, P < 0.001) at 12 weeks. The therapy was well tolerated.

CONCLUSION

rhNRG-1 appears to produce favourable acute and chronic haemodynamic effects in patients with stable CHF on optimal medical therapy. Randomized controlled trials of rhNRG-1 in cardiac disease are thus warranted. Clinical Trial Registration Information The trial was registered with the Australian New Zealand Clinical Trials Registry, anzctr.org.au Identifier: ACTRN12607000330448.

Iron control of erythroid development by a novel aconitase-associated regulatory pathway

Human red cell differentiation requires the action of erythropoietin on committed progenitor cells. In iron deficiency, committed erythroid progenitors lose responsiveness to erythropoietin, resulting in hypoplastic anemia. To address the basis for iron regulation of erythropoiesis, we established primary hematopoietic cultures with transferrin saturation levels that restricted erythropoiesis but permitted granulopoiesis and megakaryopoiesis. Experiments in this system identified as a critical regulatory element the aconitases, multifunctional iron-sulfur cluster proteins that metabolize citrate to isocitrate. Iron restriction suppressed mitochondrial and cytosolic aconitase activity in erythroid but not granulocytic or megakaryocytic progenitors. An active site aconitase inhibitor, fluorocitrate, blocked erythroid differentiation in a manner similar to iron deprivation. Exogenous isocitrate abrogated the erythroid iron restriction response in vitro and reversed anemia progression in iron-deprived mice. The mechanism for aconitase regulation of erythropoiesis most probably involves both production of metabolic intermediates and modulation of erythropoietin signaling. One relevant signaling pathway appeared to involve protein kinase Calpha/beta, or possibly protein kinase Cdelta, whose activities were regulated by iron, isocitrate, and erythropoietin.

Effects of the NUP98-DDX10 oncogene on primary human CD34+ cells: role of a conserved helicase motif

NUP98 gene rearrangements occur in acute myeloid leukemia and result in the expression of fusion proteins. One of the most frequent is NUP98-DDX10 that fuses a portion of NUP98 to a portion of DDX10, a putative DEAD-box RNA helicase. Here we show that NUP98-DDX10 dramatically increases proliferation and self-renewal of primary human CD34+ cells, and disrupts their erythroid and myeloid differentiation. It localizes to their nuclei and extensively deregulates gene expression. Comparison to another leukemogenic NUP98 fusion, NUP98-HOXA9, reveals a number of genes deregulated by both oncoproteins, including HOX genes, COX-2, MYCN, ANGPT1, REN, HEY1, SOX4, and others. These genes may account for the similar leukemogenic properties of NUP98 fusion oncogenes. The YIHRAGRTAR sequence in the DDX10 portion of NUP98-DDX10 represents a major motif shared by DEAD-box RNA helicases that is required for ATP binding, RNA-binding, and helicase functions. Mutating this motif diminished the in vitro transforming ability of NUP98-DDX10, indicating that it plays a role in leukemogenesis. These data demonstrate for the first time the in vitro transforming ability of NUP98-DDX10 and show that it is partially dependent on one of the consensus helicase motifs of DDX10. They also point to common pathways that may underlie leukemogenesis by different NUP98 fusions.

The Notch effector Hey1 associates with myogenic target genes to repress myogenesis

Members of the Hey family of transcriptional repressors are basic helix-loop-helix proteins that are thought to act downstream of Notch in diverse tissues. Although forced expression of Hey1, a target of Notch in myoblasts, is sufficient to recapitulate inhibitory effects of the pathway on differentiation, how Hey1 interferes with myogenic transcription has not been fully elucidated. We provide multiple lines of evidence that Hey1 does not target the intrinsic transcriptional activity of the skeletal muscle master regulator MyoD. Our results indicate instead that Hey1 is recruited to the promoter regions of myogenin and Mef2C, two genes whose induction is critical for myogenesis. Expression of Hey1 in C2C12 myoblasts correlates with reduced recruitment of MyoD to these promoters, arguing that Hey1 inhibits myogenesis by associating with and repressing expression of key myogenic targets.

Dissection of the transformation of primary human hematopoietic cells by the oncogene NUP98-HOXA9

NUP98-HOXA9 is the prototype of a group of oncoproteins associated with acute myeloid leukemia. It consists of an N-terminal portion of NUP98 fused to the homeodomain of HOXA9 and is believed to act as an aberrant transcription factor that binds DNA through the homeodomain. Here we show that NUP98-HOXA9 can regulate transcription without binding to DNA. In order to determine the relative contributions of the NUP98 and HOXA9 portions to the transforming ability of NUP98-HOXA9, the effects of NUP98-HOXA9 on primary human CD34+ cells were dissected and compared to those of wild-type HOXA9. In contrast to previous findings in mouse cells, HOXA9 had only mild effects on the differentiation and proliferation of primary human hematopoietic cells. The ability of NUP98-HOXA9 to disrupt the differentiation of primary human CD34+ cells was found to depend primarily on the NUP98 portion, whereas induction of long-term proliferation required both the NUP98 moiety and an intact homeodomain. Using oligonucleotide microarrays in primary human CD34+ cells, a group of genes was identified whose dysregulation by NUP98-HOXA9 is attributable primarily to the NUP98 portion. These include RAP1A, HEY1, and PTGS2 (COX-2). Their functions may reflect the contribution of the NUP98 moiety of NUP98-HOXA9 to leukemic transformation. Taken together, these results suggest that the effects of NUP98-HOXA9 on gene transcription and cell transformation are mediated by at least two distinct mechanisms: one that involves promoter binding through the homeodomain with direct transcriptional activation, and another that depends predominantly on the NUP98 moiety and does not involve direct DNA binding.

p73 plays a role in erythroid differentiation through GATA1 induction

The TP73 gene gives rise to transactivation domain-p73 isoforms (TAp73) as well as DeltaNp73 variants with a truncated N terminus. Although TAp73alpha and -beta proteins are capable of inducing cell cycle arrest, apoptosis, and differentiation, DeltaNp73 acts in many cell types as a dominant-negative repressor of p53 and TAp73. It has been proposed that p73 is involved in myeloid differentiation, and its altered expression is involved in leukemic degeneration. However, there is little evidence as to which p73 variants (TA or DeltaN) are expressed during differentiation and whether specific p73 isoforms have the capacity to induce, or hinder, this differentiation in leukemia cells. In this study we identify GATA1 as a direct transcriptional target of TAp73alpha. Furthermore, TAp73alpha induces GATA1 activity, and it is required for erythroid differentiation. Additionally, we describe a functional cooperation between TAp73 and DeltaNp73 in the context of erythroid differentiation in human myeloid cells, K562 and UT-7. Moreover, the impaired expression of GATA1 and other erythroid genes in the liver of p73KO embryos, together with the moderated anemia observed in p73KO young mice, suggests a physiological role for TP73 in erythropoiesis.

Notch signaling regulates the differentiation of bone marrow-derived cells into smooth muscle-like cells during arterial lesion formation

Bone marrow- (BM-) derived cells can differentiate into smooth muscle-like cells (SMLC), resulting in vascular pathogenesis. However, the molecular mechanism of the differentiation remains unknown. We have recently reported that Notch signaling promotes while a Notch target HERP1 inhibit the differentiation of mesenchymal cells to SMC. During the differentiation of BM-derived mononuclear cells into smooth muscle alpha-actin (SMA)-positive cells, expression of Jagged1 and SMC-specific Notch3 was increased. Blocking Notch with gamma-secretase inhibitor prevented the induction of SMA. Wire-mediated vascular injury was produced in femoral arteries in mice transplanted with green fluorescent protein (GFP)-positive cells. Many double-positive cells for GFP/Jagged1 or GFP/Notch3 were detected in the thickened neointima. In contrast, only a few SMA-positive cells were positive for GFP in neointima where HERP1, a suppressor for Notch, were abundantly expressed. In conclusion, Notch-HERP1 pathway plays an important role in differentiation of BM-derived mononuclear cells into SMLC.

c-Jun blocks cell differentiation but not growth inhibition or apoptosis of chronic myelogenous leukemia cells induced by STI571 and by histone deacetylase inhibitors

The constitutively active Bcr-Abl tyrosine kinase plays a crucial role in chronic myelogenous leukemia (CML) pathogenesis. The Bcr-Abl protein induces the upregulation of proto-oncogene c-Jun, which is involved in Bcr-Abl transforming activity in Bcr-Abl positive cells. Recent studies reported that c-Jun inhibited hemoglobin synthesis in human CML cell line K562. However, c-Jun also plays a critical role in cell proliferation and apoptosis. In this study, we investigated the physiological roles of c-Jun in cell proliferation, apoptosis and erythroid differentiation of K562 cells. Firstly, we generated K562 cell lines stably overexpressing c-Jun. These clones have the same proliferation rate as the parental cell line in general culture medium. Endogenous c-Jun expression was analyzed to determine the effective concentration of STI571 for inhibiting Bcr-Abl signaling. Western blots show that STI571 inhibited c-Jun expression in a dose-dependent manner, reaching a maximum inhibition at 1 microM. STI571 could inhibit c-Jun expression in K562 cells, but not in c-Jun-overexpression cells. c-Jun did not alter growth inhibition and apoptotic induction by STI571 treatment, but inhibited STI571-induced erythroid differentiation. Moreover, c-Jun did not alter growth inhibition and apoptotic induction by histone deacetylase (HDAC) inhibitors (apicidin, sodium butyrate, and MS275) treatment, but inhibited HDAC inhibitors-induced erythroid differentiation. These results suggest that c-Jun may modulate anticancer drugs-induced cell differentiation but not growth inhibition and apoptosis in CML cells.

Role of NF-kappaB in hematopoietic niche function of osteoblasts after radiation injury

OBJECTIVE

Hematopoietic tissue is very sensitive to ionizing radiation (IR). In adult mammalian bone marrow, hematopoietic stem and progenitor cells (HSPC) reside next to the endosteal bone surface, which is lined primarily by osteoblastic cells. In the present study, we proposed to investigate the mechanisms by which osteoblasts in the hematopoietic niche regulate survival, proliferation, and differentiation of HSPC after radiation injury.

MATERIALS AND METHODS

Human primary CD34+ HSPC were cultured with human fetal osteoblast (hFOB) cell line cells or conditioned medium (CM) from hFOB cells with or without irradiation. Survival, apoptosis, and cell cycle were analyzed using clonogenic and flow cytometric assays. Cytokine and chemokine expression were measured by cytokine array and enzyme-linked immunosorbent assay. Their regulatory activities were assessed by quantitative real-time polymerase chain reaction, small interfering (si)RNA transfection, immunoblotting, and transbinding assays.

RESULTS

Survival of gamma-irradiated CD34+ HSPC was significantly enhanced by coculture with hFOB cells or by CM from hFOB cells. There were six factors in hFOB cell lysates and five factors released into hFOB CM enhanced by IR. IR induced phosphorylation of p53, c-Jun, and p38 and downstream p21 expression, as well as cell cycle arrest and apoptosis in hFOB cells. However, IR also induced phosphorylation of nuclear factor (NF)-kappaBp65 (ser536) and NF-kappaB activation in hFOB cells. Inhibition of NF-kappaB expression with siRNA upregulated p21, inhibited release of cytokines and chemokines, and induced hFOB and CD34+ cell apoptosis.

CONCLUSIONS

NF-kappaB is a radiation-induced prosurvival factor in human osteoblastic cells. NF-kappaB gene knockdown abrogated the hematopoietic niche function of hFOB cells in supporting survival of CD34+ cells after IR.

Cross-talk of GATA-1 and P-TEFb in megakaryocyte differentiation

The transcription factor GATA-1 participates in programming the differentiation of multiple hematopoietic lineages. In megakaryopoiesis, loss of GATA-1 function produces complex developmental abnormalities and underlies the pathogenesis of megakaryocytic leukemia in Down syndrome. Its distinct functions in megakaryocyte and erythroid maturation remain incompletely understood. In this study, we identified functional and physical interaction of GATA-1 with components of the positive transcriptional elongation factor P-TEFb, a complex containing cyclin T1 and the cyclin-dependent kinase 9 (Cdk9). Megakaryocytic induction was associated with dynamic changes in endogenous P-TEFb composition, including recruitment of GATA-1 and dissociation of HEXIM1, a Cdk9 inhibitor. shRNA knockdowns and pharmacologic inhibition both confirmed contribution of Cdk9 activity to megakaryocytic differentiation. In mice with megakaryocytic GATA-1 deficiency, Cdk9 inhibition produced a fulminant but reversible megakaryoblastic disorder reminiscent of the transient myeloproliferative disorder of Down syndrome. P-TEFb has previously been implicated in promoting elongation of paused RNA polymerase II and in programming hypertrophic differentiation of cardiomyocytes. Our results offer evidence for P-TEFb cross-talk with GATA-1 in megakaryocytic differentiation, a program with parallels to cardiomyocyte hypertrophy.

Characterization of megakaryocyte GATA1-interacting proteins: the corepressor ETO2 and GATA1 interact to regulate terminal megakaryocyte maturation

The transcription factor GATA1 coordinates timely activation and repression of megakaryocyte gene expression. Loss of GATA1 function results in excessive megakaryocyte proliferation and disordered terminal platelet maturation, leading to thrombocytopenia and leukemia in patients. The mechanisms by which GATA1 does this are unclear. We have used in vivo biotinylated GATA1 to isolate megakaryocyte GATA1-partner proteins. Here, several independent approaches show that GATA1 interacts with several proteins in the megakaryocyte cell line L8057 and in primary megakaryocytes. They include FOG1, the NURD complex, the pentameric complex containing SCL/TAL-1, the zinc-finger regulators GFI1B and ZFP143, and the corepressor ETO2. Knockdown of ETO2 expression promotes megakaryocyte differentiation and enhances expression of select genes expressed in terminal megakaryocyte maturation, eg, platelet factor 4 (Pf4). ETO2-dependent direct repression of the Pf4 proximal promoter is mediated by GATA-binding sites and an E-Box motif. Consistent with this, endogenous ETO2, GATA1, and the SCL pentameric complex all specifically bind the promoter in vivo. Finally, as ETO2 expression is restricted to immature megakaryocytes, these data suggest that ETO2 directly represses inappropriate early expression of a subset of terminally expressed megakaryocyte genes by binding to GATA1 and SCL.

The MADS transcription factor Mef2c is a pivotal modulator of myeloid cell fate

Mef2c is a MADS (MCM1-agamous–deficient serum response factor) transcription factor best known for its role in muscle and cardiovascular development. A causal role of up-regulated MEF2C expression in myelomonocytic acute myeloid leukemia (AML) has recently been demonstrated. Due to the pronounced monocytic component observed in Mef2c-induced AML, this study was designed to assess the importance of Mef2c in normal myeloid differentiation. Analysis of bone marrow (BM) cells manipulated to constitutively express Mef2c demonstrated increased monopoiesis at the expense of granulopoiesis, whereas BM isolated from Mef2cΔ/− mice showed reduced levels of monocytic differentiation in response to cytokines. Mechanistic studies showed that loss of Mef2c expression correlated with reduced levels of transcripts encoding c-Jun, but not PU.1, C/EBPα, or JunB transcription factors. Inhibiting Jun expression by short-interfering RNA impaired Mef2c-mediated inhibition of granulocyte development. Moreover, retroviral expression of c-Jun in BM cells promoted monocytic differentiation. The ability of Mef2c to modulate cell-fate decisions between monocyte and granulocyte differentiation, coupled with its functional sensitivity to extracellular stimuli, demonstrate an important role in immunity—and, consistent with findings of other myeloid transcription factors, a target of oncogenic lesions in AML.

Distinct effects of the soluble versus membrane-bound forms of the notch ligand delta-4 on human CD34+CD38low cell expansion and differentiation

Although Notch ligands are considered to activate signaling through direct cell-cell contact, the existence of soluble forms has been demonstrated. However, their roles remain controversial: soluble forms have been reported to mimic the biological activity of membrane-bound form, whereas other studies rather suggested an antagonistic activity toward their full-length counterparts. We previously observed that membrane-bound Delta4-expressing S17 stroma (mbD4/S17) reduced human CD34+CD38(low) cell proliferation and favored self-renewal. Here, we assessed the effects of a soluble form of Delta4 (solD4) by exposing CD34+CD38(low) cells to S17 feeders engineered to express solD4 (solD4/S17). In contrast to mbD4/S17, (a) solD4/S17 increased 10-fold cell production after 2 weeks, through enhanced cell proliferation, and (b) it did not preserve colony-forming cell and long-term culture-initiating cell potential of output CD34+ cells. mbD4 and solD4 appeared to also differ in their signaling. Indeed, mbD4, but not solD4, strongly activated both CSL (the nuclear mediator of Notch signaling) in Hela cells overexpressing Notch1 and transcription of some classic Notch target genes in CD34+CD38(low) cells. Furthermore, both biological effects and CSL activation elicited by mbD4 were strictly dependent upon the gamma-secretase complex, whereas solD4 enhanced cell expansion in a partially gamma-secretase-independent manner. Altogether, these results suggest that part of solD4 activity did not rely upon canonical Notch pathway.

Low-calcium serum-free defined medium selects for growth of normal prostatic epithelial stem cells

Stage-specific differentiation markers were used to evaluate the cellular composition and the origin of nonimmortalized (PrEC) and immortalized (PZ-HPV7, CA-HPV10, RWPE-1, and 957E/hTERT) human prostate cell lines. These studies documented that immortalized and nonimmortalized prostate epithelial cells established and maintained in low (i.e., <300 micromol/L) Ca(2+) serum-free defined (SFD) medium were all derived from normal nonmalignant prostate tissues and contain CD133(+)/ABCG2(+)/alpha(2)beta(1)(Hi)/p63(-)/PSCA(-)/AR(-)/PSA(-) prostate stem cells. In these cultures, prostate stem cells are able to self-renew and generate two distinct cell lineages: the minor proliferatively quiescent neuroendocrine lineage and the major transit-amplifying cell lineage. Subsequently, CD133(-)/ABCG2(-)/alpha(2)beta(1)(Hi)/p63(+)/PSCA(-)/AR(-)/PSA(-) transit-amplifying cells proliferate frequently and eventually mature into proliferatively quiescent CD133(-)/ABCG2(-)/alpha(2)beta(1)(Lo)/p63(-)/PSCA(+)/AR(-)/PSA(-) intermediate cells. Such proliferatively quiescent intermediate cells, however, do not complete their full maturation into CD133(-)/ABCG2(-)/alpha(2)beta(1)(Lo)/p63(-)/PSCA(-)/AR(+)/PSA(+) luminal-secretory cells in low Ca(2+) SFD medium. Addition of universal type I IFN and synthetic androgen (R1881) to culture medium resulted in up-regulation of androgen receptor protein expression. However, it failed to induce full differentiation of intermediate cells into AR(+)/PSA(+) luminal-secretory cells. Our results indicate that such inability of prostate epithelial cells to complete their differentiation is due to continuous expression of Notch-1 receptor and its downstream effector, Hey-1 protein, which actively suppresses differentiation via its ability to transcriptionally repress a series of genes, including the GATA family of transcription factors.

Delta-Notch--and then? Protein interactions and proposed modes of repression by Hes and Hey bHLH factors

Hes and Hey genes are the mammalian counterparts of the Hairy and Enhancer-of-split type of genes in Drosophila and they represent the primary targets of the Delta–Notch signaling pathway. Hairy-related factors control multiple steps of embryonic development and misregulation is associated with various defects. Hes and Hey genes (also called Hesr, Chf, Hrt, Herp or gridlock) encode transcriptional regulators of the basic helix-loop-helix class that mainly act as repressors. The molecular details of how Hes and Hey proteins control transcription are still poorly understood, however.

Proposed modes of action include direct binding to N- or E-box DNA sequences of target promoters as well as indirect binding through other sequence-specific transcription factors or sequestration of transcriptional activators. Repression may rely on recruitment of corepressors and induction of histone modifications, or even interference with the general transcriptional machinery. All of these models require extensive protein–protein interactions. Here we review data published on protein–protein and protein–DNA interactions of Hairy-related factors and discuss their implications for transcriptional regulation. In addition, we summarize recent progress on the identification of potential target genes and the analysis of mouse models.

5-Androstenediol Promotes Survival of γ-Irradiated Human Hematopoietic Progenitors through Induction of Nuclear Factor-κB Activation and Granulocyte Colony-Stimulating Factor Expression

5-Androstenediol (5-AED) stimulates hematopoiesis and enhances survival in animals exposed to ionizing radiation (IR), suggesting that this steroid may act on hematopoietic progenitor cells. We used gamma-irradiated primary human CD34(+) hematopoietic progenitor cells to show that 5-AED protects hematopoietic cells from IR damage, as shown by enhanced cell survival, clonogenicity, proliferation, and differentiation. Unlike in tumor cells, IR did not induce nuclear factor-kappaB (NFkappaB) activation in primary progenitors. However, IR stimulated IkappaB(beta) release from NFkappaB/IkappaB complexes and caused NFkappaB1 (p50) degradation. 5-AED stabilized NFkappaB1 in irradiated cells and induced NFkappaB gene expression and NFkappaB activation (DNA binding). 5-AED stimulated interleukin-6 and granulocyte colony-stimulating factor (G-CSF) secretion. The survival-enhancing effects of 5-AED on clonogenic cells were abrogated by small interfering RNA inhibition of NFkappaB gene expression and by neutralization of G-CSF with antibody. The effects of 5-AED on survival and G-CSF secretion were blocked by the NFkappaB inhibitor N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132). 5-AED had no effect on accumulation of the proapoptotic factor p53 after IR, as determined by Western blot. The results indicate that NFkappaB1 degradation after IR may be responsible for the radiation sensitivity of CD34+ cells compared with tumor cells. 5-AED exerts survival-enhancing effects on irradiated human hematopoietic progenitor cells via induction, stabilization, and activation of NFkappaB, which results in increased secretion of hematopoietic growth factor G-CSF.

EGO, a novel, noncoding RNA gene, regulates eosinophil granule protein transcript expression

Gene expression profiling of early eosinophil development shows increased transcript levels of proinflammatory cytokines, chemokines, transcription factors, and a novel gene, EGO (eosinophil granule ontogeny). EGO is nested within an intron of the inositol triphosphate receptor type 1 (ITPR1) gene and is conserved at the nucleotide level; however, the largest open reading frame (ORF) is 86 amino acids. Sucrose density gradients show that EGO is not associated with ribosomes and therefore is a noncoding RNA (ncRNA). EGO transcript levels rapidly increase following interleukin-5 (IL-5) stimulation of CD34(+) hematopoietic progenitors. EGO RNA also is highly expressed in human bone marrow and in mature eosinophils. RNA silencing of EGO results in decreased major basic protein (MBP) and eosinophil derived neurotoxin (EDN) mRNA expression in developing CD34(+) hematopoietic progenitors in vitro and in a CD34(+) cell line model. Therefore, EGO is a novel ncRNA gene expressed during eosinophil development and is necessary for normal MBP and EDN transcript expression.

Transcription factor CHF1/Hey2 regulates the global transcriptional response to platelet-derived growth factor in vascular smooth muscle cells

The cardiovascular restricted transcription factor CHF1/Hey2 has been previously shown to regulate the smooth muscle response to growth factors. To determine how CHF1/Hey2 affects the smooth muscle response to growth factors, we performed a genomic screen for transcripts that are differentially expressed in wild-type and knockout smooth muscle cells after stimulation with platelet-derived growth factor. We screened 45,101 probes representing >39,000 transcripts derived from at least 34,000 genes, at eight different time points. We analyzed the expression data utilizing an algorithm based on Bayesian statistics to derive the best polynomial clustering model to fit the expression data. We found that in a total of 9,827 transcripts the normalized ratio of knockout to wild-type expression diverged more than threefold from baseline in at least one time point, and these transcripts separated into 17 distinct clusters. Further analysis of each cluster revealed distinct alterations in gene expression patterns for immediate early genes, transcription factors, matrix metalloproteinases, signaling molecules, and other molecules important in vascular biology. Our findings demonstrate that CHF1/Hey2 profoundly affects vascular smooth muscle phenotype by altering both the absolute expression level of a variety of genes and the kinetics of growth factor-induced gene expression.

CD34+ hematopoietic stem-progenitor cell microRNA expression and function: a circuit diagram of differentiation control

MicroRNAs (miRNAs) are a recently identified class of epigenetic elements consisting of small noncoding RNAs that bind to the 3' untranslated region of mRNAs and down-regulate their translation to protein. miRNAs play critical roles in many different cellular processes including metabolism, apoptosis, differentiation, and development. We found 33 miRNAs expressed in CD34+ hematopoietic stem-progenitor cells (HSPCs) from normal human bone marrow and mobilized human peripheral blood stem cell harvests. We then combined these data with human HSPC mRNA expression data and with miRNA-mRNA target predictions, into a previously undescribed miRNA:mRNA interaction database called the Transcriptome Interaction Database. The in silico predictions from the Transcriptome Interaction Database pointed to miRNA control of hematopoietic differentiation through translational control of mRNAs critical to hematopoiesis. From these predictions, we formulated a model for miRNA control of stages of hematopoiesis in which many of the genes specifying hematopoietic differentiation are expressed by HSPCs, but are held in check by miRNAs until differentiation occurs. We validated miRNA control of several of these target mRNAs by demonstrating that their translation in fact is decreased by miRNAs. Finally, we chose miRNA-155 for functional characterization in hematopoiesis, because we predicted that it would control both myelopoiesis and erythropoiesis. As predicted, miRNA-155 transduction greatly reduced both myeloid and erythroid colony formation of normal human HSPCs.

Tumor necrosis factor alpha inhibits aclacinomycin A-induced erythroid differentiation of K562 cells via GATA-1

Up-regulation of tumor necrosis factor alpha (TNFalpha) is linked to solid tumors as well as to hematologic disorders including different forms of anemia and multiple myeloma. This cytokine was shown to contribute to inhibition of erythroid maturation mechanisms which are characterized by the expression of specific genes regulated by GATA-1 and NF-E2 transcription factors. Here, we assessed the inhibiting effect of TNFalpha on erythroid differentiation using K562 cells which can be chemically induced to differentiate towards the erythroid pathway by aclacinomycin A, an anthracyclin. Results show that induced hemoglobinization of K562 cells as well as gamma-globin and erythropoietin receptor gene expression are decreased by TNFalpha via the inhibition of GATA-1 at its mRNA and protein expression level. Additionally, both constitutive and induced binding activity of GATA-1 is abolished and induced activation of a GATA-1 driven luciferase reporter construct is inhibited. Altogether, our results provide insight into the molecular mechanisms of inflammation-induced inhibition of erythroid differentiation.

Jagged1-selective notch signaling induces smooth muscle differentiation via a RBP-Jkappa-dependent pathway

The Notch signaling pathway plays a crucial role in specifying cellular fates by interaction between cellular neighbors; however, the molecular mechanism underlying smooth muscle cell (SMC) differentiation by Notch signaling has not been well characterized. Here we demonstrate that Jagged1-Notch signaling promotes SMC differentiation from mesenchymal cells. Overexpression of the Notch intracellular domain, an activated form of Notch, up-regulates the expression of multiple SMC marker genes including SMC-myosin heavy chain (Sm-mhc) in mesenchymal 10T1/2 cells, but not in non-mesenchymal cells. Physiological Notch stimulation by its ligand Jagged1, but not Dll4, directly induces Sm-mhc expression in 10T1/2 cells without de novo protein synthesis, indicative of a ligand-selective effect. Jagged1-induced expression of SM-MHC was blocked bygamma-secretase inhibitor, N-(N-(3,5-difluorophenyl)-l-alanyl)-S-phenylglycine t-butyl ester, which impedes Notch signaling. Using Rbp-jkappa-deficient cells and site-specific mutagenesis of the SM-MHC gene, we show that such an induction is independent of the myocardin-serum response factor-CArG complex, but absolutely dependent on RBP-Jkappa, a major mediator of Notch signaling, and its cognate binding sequence. Of importance, Notch signaling and myocardin synergistically activate SM-MHC gene expression. Taken together, these data suggest that the Jagged1-Notch pathway constitutes an instructive signal for SMC differentiation through an RBP-Jkappa-dependent mechanism and augments gene expression mediated by the myocardin-SRF-CArG complex. Given that Notch pathway components are expressed in vascular SMC during normal development and disease, Notch signaling is likely to play a pivotal role in such situations to modulate the vascular smooth muscle cell phenotype.

Persistent expression of Notch2 delays gonadotrope differentiation

Normal pituitary gland development requires coordination between maintenance of progenitor cell pools and selection of progenitors for differentiation. The spatial and temporal expression of Notch2 during pituitary development suggested that it could control progenitor cell differentiation in the pituitary. Consistent with this idea, Notch2 is not expressed in Prop1 mutants, and anterior pituitary progenitors in Prop1 mutants appear to be unable to transition from proliferation to differentiation properly, resulting in anterior lobe failed cell specification and evolving hypoplasia. To test the function of Notch2 directly, we used the alphaGSU subunit promoter to express activated NOTCH2 persistently in pre-gonadotropes and pre-thyrotropes of transgenic mice. At birth, there is a small reduction in the population of fully differentiated thyrotropes and almost no fully differentiated gonadotropes. The temporal and spatial expression of Hey1 suggests that it could be a mediator of this effect. Gonadotropes complete their differentiation program eventually, although expression of LH and FSH is mutually exclusive with NOTCH2 transgene expression. This demonstrates that activated Notch2 is sufficient to delay gonadotrope differentiation, and it supports the hypothesis that Notch2 regulates progenitor cell differentiation in the pituitary gland.

Transcriptional regulation of guanylyl cyclase/natriuretic peptide receptor-A gene

Activation of natriuretic peptide receptor-A (NPRA) produces the second messenger cGMP, which plays a pivotal role in maintaining blood pressure and cardiovascular homeostasis. In the present study, we have examined the role of trans-acting factor Ets-1 in transcriptional regulation of Npr1 gene (coding for NPRA). Using deletional analysis of the Npr1 promoter, we have defined a 400 base pair (bp) region as the core promoter, which contains consensus binding sites for transcription factors including: Ets-1, Lyf-1, and GATA-1/2. Overexpression of Ets-1 in mouse mesangial cells (MMCs) enhanced Npr1 gene transcription by 12-fold. However, overexpression of GATA-1 or Lyf-1 repressed Npr1 basal promoter activity by 50% and 80%, respectively. The constructs having a mutant Ets-1 binding site or lacking this site failed to respond to Ets-1 activation of Npr1 gene transcription. Collectively, the present results demonstrate that Ets-1 greatly stimulates Npr1 gene promoter activity, implicating its critical role in the regulation and function of NPRA at the molecular level.

Transcription factor CHF1/Hey2 suppresses cardiac hypertrophy through an inhibitory interaction with GATA4

Pathological cardiac hypertrophy is considered a precursor to clinical heart failure. Understanding the transcriptional regulators that suppress the hypertrophic response may have profound implications for the treatment of heart disease. We report the generation of transgenic mice that overexpress the transcription factor CHF1/Hey2 in the myocardium. In response to the alpha-adrenergic agonist phenylephrine, they show marked attenuation in the hypertrophic response compared with wild-type controls, even though blood pressure is similar in both groups. Isolated myocytes from transgenic mice demonstrate a similar resistance to phenylephrine-induced hypertrophy in vitro, providing further evidence that the protective effect of CHF1/Hey2 is mediated at the myocyte level. Induction of the hypertrophy marker genes ANF, BNP, and beta-MHC in the transgenic cells is concurrently suppressed in vivo and in vitro, demonstrating that the induction of hypertrophy-associated genes is repressed by CHF1/Hey2. Transfection of CHF1/Hey2 into neonatal cardiomyocytes suppresses activation of an ANF reporter plasmid by the transcription factor GATA4, which has previously been shown to activate a hypertrophic transcriptional program. Furthermore, CHF1/Hey2 binds GATA4 directly in coimmunoprecipitation assays and inhibits the binding of GATA4 to its recognition sequence within the ANF promoter. Our findings demonstrate that CHF1/Hey2 functions as an antihypertrophic gene, possibly through inhibition of a GATA4-dependent hypertrophic program.

Erythroid inhibition by the leukemic fusion AML1-ETO is associated with impaired acetylation of the major erythroid transcription factor GATA-1

Human acute myeloid leukemias with the t(8;21) translocation express the AML1-ETO fusion protein in the hematopoietic stem cell compartment and show impairment in erythroid differentiation. This clinical finding is reproduced in multiple murine and cell culture model systems in which AML1-ETO specifically interferes with erythroid maturation. Using purified normal human early hematopoietic progenitor cells, we find that AML1-ETO impedes the earliest discernable steps of erythroid lineage commitment. Correspondingly, GATA-1, a central transcriptional regulator of erythroid differentiation, undergoes repression by AML1-ETO in a nonconventional histone deacetylase-independent manner. In particular, GATA-1 acetylation by its transcriptional coactivator, p300/CBP, a critical regulatory step in programming erythroid development, is efficiently blocked by AML1-ETO. Fusion of a heterologous E1A coactivator recruitment module to GATA-1 overrides the inhibitory effects of AML1-ETO on GATA-1 acetylation and transactivation. Furthermore, the E1A-GATA-1 fusion, but not wild-type GATA-1, rescues erythroid lineage commitment in primary human progenitors expressing AML1-ETO. These results ascribe a novel repressive mechanism to AML1-ETO, blockade of GATA-1 acetylation, which correlates with its inhibitory effects on primary erythroid lineage commitment.

KSHV RTA induces a transcriptional repressor, HEY1 that represses rta promoter

Kaposi's sarcoma-associated herpesvirus (KSHV) is a gamma-herpesvirus that is frequently associated with the formation of tumors like Kaposi's sarcoma and primary effusion lymphomas. KSHV RTA is required for lytic replication/reactivation in KSHV-infected cells. We developed an inducible RTA expression cell line to search for RTA-inducible genes. Using DNA chip technology, we showed that hey1, a basic helix-loop-helix-containing transcription factor, increased three- to fourfold in this line. In a luciferase reporter system, RTA activated the hey1 promoter in several cell lines; conversely, HEY1 repressed the rta promoter. Chromatin immunoprecipitation assays indicated that HEY did not bind the rta promoter directly, although it may repress rta expression as part of a complex. Thus, hey1 may help to downregulate RTA after its burst of expression during lytic replication/reactivation. Similar repression mechanisms may downregulate immediate-early gene expression in other herpesviruses, although different transcription factors are probably involved.