Signal transducer and activator of transcription 5a (STAT5a) is required for eosinophil differentiation of human cord blood-derived CD34+ cells

Targeting cancer cell plasticity by HDAC inhibition to reverse EBV-induced dedifferentiation in nasopharyngeal carcinoma

Application of differentiation therapy targeting cellular plasticity for the treatment of solid malignancies has been lagging. Nasopharyngeal carcinoma (NPC) is a distinctive cancer with poor differentiation and high prevalence of Epstein-Barr virus (EBV) infection. Here, we show that the expression of EBV latent protein LMP1 induces dedifferentiated and stem-like status with high plasticity through the transcriptional inhibition of CEBPA. Mechanistically, LMP1 upregulates STAT5A and recruits HDAC1/2 to the CEBPA locus to reduce its histone acetylation. HDAC inhibition restored CEBPA expression, reversing cellular dedifferentiation and stem-like status in mouse xenograft models. These findings provide a novel mechanistic epigenetic-based insight into virus-induced cellular plasticity and propose a promising concept of differentiation therapy in solid tumor by using HDAC inhibitors to target cellular plasticity.

Carbazole Derivatives as STAT Inhibitors: An Overview

The carbazole class is made up of heterocyclically structured compounds first isolated from coal tar. Their structural motif is preponderant in different synthetic materials and naturally occurring alkaloids extracted from the taxonomically related higher plants of the genus Murraya, Glycosmis, and Clausena from the Rutaceae family. Concerning the biological activity of these compounds, many research groups have assessed their antiproliferative action of carbazoles on different types of tumoral cells, such as breast, cervical, ovarian, hepatic, oral cavity, and small-cell lung cancer, and underlined their potential effects against psoriasis. One of the principal mechanisms likely involved in these effects is the ability of carbazoles to target the JAK/STATs pathway, considered essential for cell differentiation, proliferation, development, apoptosis, and inflammation. In this review, we report the studies carried out, over the years, useful to synthesize compounds with carbazole moiety designed to target these kinds of kinases.

Recurrent activating STAT5B N642H mutation in myeloid neoplasms with eosinophilia

Determining the underlying cause of persistent eosinophilia is important for effective clinical management but remains a diagnostic challenge in many cases. We identified STAT5B N642H, an established oncogenic mutation, in 27/1715 (1.6%) cases referred for investigation of eosinophilia. Of the 27 mutated cases, a working diagnosis of hypereosinophilic syndrome (HES; n = 7) or a myeloid neoplasm with eosinophilia (n = 20) had been made prior to the detection of STAT5B N642H. Myeloid panel analysis identified a median of 2 additional mutated genes (range 0–4) with 4 cases having STAT5B N642H as a sole abnormality. STAT5B N642H was absent in cultured T cells of 4/4 positive cases. Individuals with SF3B1 mutations (9/27; 33%) or STAT5B N642H as a sole abnormality had a markedly better overall survival compared to cases with other additional mutations (median 65 months vs. 14 months; hazard ratio = 8.1; P < 0.001). The overall survival of STAT5B-mutated HES cases was only 30 months, suggesting that these cases should be reclassified as chronic eosinophilic leukemia, not otherwise specified (CEL-NOS). The finding of STAT5B N642H as a recurrent mutation in myeloid neoplasia with eosinophilia provides a new diagnostic and prognostic marker as well as a potential target for therapy.

Protective Effect of JXT Ethanol Extract on Radiation-Induced Hematopoietic Alteration and Oxidative Stress in the Liver

This study aims at investigating the radioprotective effect of ethanol extract from Ji-Xue-Teng (JXT, Spatholobus suberectus) on radiation-induced hematopoietic alteration and oxidative stress in the liver. Mice were exposed to a single acute γ-radiation for the whole body at the dose of 6.0 Gy, then subjected to administration of amifostine (45 mg/kg) or JXT (40 g crude drug/kg) once a day for 28 consecutive days, respectively. Bone marrow cells and hemogram including white cells, red cells, platelet counts, and hemoglobin level were examined. The protein expression levels of pJAK2/JAK2, pSTAT5a/STAT5a, pSTAT5b/STAT5b, and Bcl-2 in bone marrow tissue; levels of reactive oxygen species (ROS); and the activity of superoxide dismutase (SOD), malondialdehyde (MDA), and glutathione peroxidase (GSH-Px) in serum and liver tissue were determined. At the end of the experiment, the effect of JXT on cell viability and G-CSF and G-CSFR levels in NFS-60 cells were tested by CCK-8 assay, ELISA, and flow cytometry. The results showed that the mice exposed to γ-radiation alone exhibited a typical hematopoietic syndrome. In contrast, at the end of the 28-day experiment, irradiated mice subjected to oral administration of JXT showed an obvious improvement on blood profile with reduced leucopenia, thrombocytopenia (platelet counts), RBC, and hemoglobin levels, as well as bone marrow cells. The expression of pJAK2/JAK2, pSTAT5a/STAT5a, and Bcl-2 in bone marrow tissue was increased after JXT treatment. The elevation of ROS was due to radiation-induced toxicity, but JXT significantly reduced the ROS level in serum and liver tissue, elevated endogenous SOD and GSH-PX levels, and reduced the MDA level in the liver. JXT could also increase cell viability and G-CSFR level in NFS-60 cells, which was similar to exogenous G-CSF. Our findings suggested that oral administration of JXT effectively facilitated the recovery of hematopoietic bone marrow damage and oxidative stress of the mice induced by γ-radiation.

Development of a robust reporter gene based assay for the bioactivity determination of IL-5-targeted therapeutic antibodies

Eosinophilic asthma is characterized by the eosinophilic inflammation with the allergen independent activation of Th2 lymphocytes. Since IL-5 plays an important role in the maturation, survival and migration of eosinophils, hence the pathogenesis of eosinophilic asthma, biotherapeutics targeting IL-5/IL-5Rα have been developed and/or marketed, including Mepolizumab, Reslizumab, and Benralizumab. Accurate determination of bioactivity is crucial for the safety and efficacy of therapeutic antibodies. The current mode of action (MOA) based method used in the quality control and stability tests for anti-IL-5 mAbs is anti-proliferation assay, which is tedious with long duration and high variation. We describe here the development and validation of a reporter gene assay (RGA), based on an IL-5-dependent TF-1 cell line variant we established that stably expresses the luciferase reporter under the control of STAT5 response elements. After careful optimization, we demonstrate the excellent specificity, precision, accuracy and linearity of the established RGA. Our study also proves that the assay is superior on precision, sensitivity and assay simplicity to the anti-proliferation assay. The established RGA is also applicable to another anti-IL-5Rα mAb. These results show for the first time that this novel RGA, based on the IL-5-IL-5R-STAT5 pathway, can be a valuable supplement to the anti-proliferation assay and employed in the bioactivity determination of anti-IL-5/anti-IL-5Rα biotherapeutics.

Eosinophil-specific deletion of IκBα in mice reveals a critical role of NF-κB-induced Bcl-xL for inhibition of apoptosis

Eosinophils are associated with type 2 immune responses to allergens and helminths. They release various proinflammatory mediators and toxic proteins on activation and are therefore considered proinflammatory effector cells. Eosinophilia is promoted by the cytokines interleukin (IL)-3, IL-5, and granulocyte macrophage-colony-stimulating factor (GM-CSF) and can result from enhanced de novo production or reduced apoptosis. In this study, we show that only IL-5 induces differentiation of eosinophils from bone marrow precursors, whereas IL-5, GM-CSF, and to a lesser extent IL-3 promote survival of mature eosinophils. The receptors for these cytokines use the common β chain, which serves as the main signaling unit linked to signal transducer and activator of transcription 5, p38 mitogen-activated protein kinase, and nuclear factor (NF)-κB pathways. Inhibition of NF-κB induced apoptosis of in vitro cultured eosinophils. Selective deletion of IκBα in vivo resulted in enhanced expression of Bcl-xL and reduced apoptosis during helminth infection. Retroviral overexpression of Bcl-xL promoted survival, whereas pharmacologic inhibition of Bcl-xL in murine or human eosinophils induced rapid apoptosis. These results suggest that therapeutic strategies targeting Bcl-xL in eosinophils could improve health conditions in allergic inflammatory diseases.

STAT5-mediated self-renewal of normal hematopoietic and leukemic stem cells

The level of transcription factor activity critically regulates cell fate decisions such as hematopoietic stem cell self-renewal and differentiation. The balance between hematopoietic stem cell self-renewal and differentiation needs to be tightly controlled, as a shift toward differentiation might exhaust the stem cell pool, while a shift toward self-renewal might mark the onset of leukemic transformation. A number of transcription factors have been proposed to be critically involved in governing stem cell fate and lineage commitment, such as Hox transcription factors, c-Myc, Notch1, β-catenin, C/ebpα, Pu.1 and STAT5. It is therefore no surprise that dysregulation of these transcription factors can also contribute to the development of leukemias. This review will discuss the role of STAT5 in both normal and leukemic hematopoietic stem cells as well as mechanisms by which STAT5 might contribute to the development of human leukemias.

The effects of thymic stromal lymphopoietin and IL-3 on human eosinophil-basophil lineage commitment: Relevance to atopic sensitization

An important immunopathological hallmark of allergic disease is tissue eosinophilic and basophilic inflammation, a phenomenon which originates from hemopoietic progenitors (HP). The fate of HP is determined by local inflammatory cytokines that permit “in situ hemopoiesis,” which leads to the accumulation of eosinophils and basophils (Eo/B). Given that recent evidence supports a critical immunomodulatory role for thymic stromal lymphopoietin (TSLP) in allergic inflammation, as well as TSLP effects on CD34+ progenitor cytokine and chemokine secretion, we investigated the role of TSLP in mediating eosinophilo- and basophilopoiesis, the mechanisms involved, and the association of these processes with atopic sensitisation. In the studies presented herein, we demonstrate a direct role for TSLP in Eo/B differentiation from human peripheral blood CD34+ cells. In the presence of IL-3, TSLP significantly promoted the formation of Eo/B colony forming units (CFU) (including both eosinophils and basophils) from human HP (HHP), which was dependent on TSLP–TSLPR interactions. IL-3/TSLP-stimulated HHP actively secreted an array of cytokines/chemokines, key among which was TNFα, which, together with IL-3, enhanced surface expression of TSLPR. Moreover, pre-stimulation of HHP with IL-3/TNFα further promoted TSLP-dependent Eo/B CFU formation. HHP isolated from atopic individuals were functionally and phenotypically more responsive to TSLP than those from nonatopic individuals. This is the first study to demonstrate enhanced TSLP-mediated hemopoiesis ex vivo in relation to clinical atopic status. The capacity of HHP to participate in TSLP-driven allergic inflammation points to the potential importance of “in situ hemopoiesis” in allergic inflammation initiated at the epithelial surface.

Cell signalling during human eosinophil differentiation

Eosinophil differentiation is a complex series of events regulated by cytokines at multiple levels, including proliferation, survival, and maturation. The development of an ex vivo eosinophil differentiation model, using the current knowledge on factors involved in this process, has facilitated efforts to understand the molecular mechanisms underlying human eosinophil development. Differentiation of human hematopoietic progenitor cells, isolated by density centrifugation and immunomagnetic cell separation, towards mature eosinophils, involves a 17-day culture period in the presence of a mixture of cytokines. At early stages of differentiation, these cells can be retrovirally transduced resulting in modulation of the expression of genes of interest to examine their role in eosinophil development. Eosinophil maturation can be analyzed by combining three different methods: histochemical analysis, flow cytometric analysis, and Luxol Fast Blue staining. In addition to this ex vivo differentiation model, human hematopoietic progenitors can be transplanted into immune-deficient mice resulting in the development of all human hematopoietic lineages in the mouse bone marrow, including eosinophils. Although the ex vivo differentiation model can be used separately, combining it with the transplantation model will give insight into not only regulation of human eosinophil development but also hematopoiesis in general.

Therapeutic modulators of STAT signalling for human diseases

The signal transducer and activator of transcription (STAT) proteins have important roles in biological processes. The abnormal activation of STAT signalling pathways is also implicated in many human diseases, including cancer, autoimmune diseases, rheumatoid arthritis, asthma and diabetes. Over a decade has passed since the first inhibitor of a STAT protein was reported and efforts to discover modulators of STAT signalling as therapeutics continue. This Review discusses the outcomes of the ongoing drug discovery research endeavours against STAT proteins, provides perspectives on new directions for accelerating the discovery of drug candidates, and highlights the noteworthy candidate therapeutics that have progressed to clinical trials.

Toll-like receptor-mediated eosinophil-basophil differentiation: autocrine signalling by granulocyte-macrophage colony-stimulating factor in cord blood haematopoietic progenitors

Eosinophils are multi-functional leucocytes that play a role in inflammatory processes including allergy and infection. Although bone marrow (BM) inflammatory cells are the main source of eosinophil-basophil (Eo/B) differentiation-inducing cytokines, a recent role has been demonstrated for cytokine induction through Toll-like receptor (TLR)-mediated signalling in BM progenitors. Having previously demonstrated that cord blood (CB) progenitors induce Eo/B colony-forming units (CFU) after lipopolysaccharide (LPS) stimulation, we sought to investigate the intracellular mechanisms by which LPS induces Eo/B differentiation. Freshly isolated CD34-enriched human CB cells were stimulated with LPS (and/or pharmacological inhibitors) and assessed for alterations in haematopoietic cytokine receptor expression and signalling pathways by flow cytometry, Eo/B CFU in methylcellulose cultures, and cytokine secretion using Luminex assays. The LPS stimulation resulted in a significant increase in granulocyte-macrophage colony-stimulating factor (GM-CSF)-responsive, as opposed to interleukin-5-responsive, Eo/B CFU, which also correlated with significant increases in CD34(+) cell GM-CSFRα expression. Functionally, CB CD34(+) cells secrete abundant amounts of GM-CSF following LPS stimulation, via a p38 mitogen-activated protein kinase (MAPK)-dependent mechanism; this secretion was responsible for Eo/B CFU formation ex vivo, as shown by antibody blockade. We show for the first time that LPS stimulation of CB progenitor cells results in autocrine activation of p38 MAPK-dependent GM-CSF secretion facilitating Eo/B differentiation ex vivo. This work provides evidence that early life exposure to products of bacterial agents can modulate Eo/B differentiation, representing a novel mechanism by which progenitor cells can respond to microbial stimuli and so affect immune and inflammatory responses.

Recent patents on therapeutic applications of the transcription factor decoy approach

INTRODUCTION

Transcription is considered as an important target of drugs employed in biomedicine. Therefore, novel strategies to inhibit the biological effects of transcription factors (TFs) are of interest, such as targeting promoters with triple-helix-forming oligonucleotides and antisense targeting of mRNAs coding for TFs.

AREAS COVERED

The objective of this review is to describe studies considering inhibition of TF functions with molecules mimicking TF binding sites (transcription factor decoy approach, TFD) and to summarize the patents on possible clinical applications of this approach.

EXPERT OPINION

Treatment of cells with TFD molecules leads to inhibition (or activation) of genes regulated by the target transcription factors. The studies and patents on this specific issue have taken in great consideration the delivery strategy, which is a very important parameter. The TFD strategy has been proven effective in vivo. The stability of the TFD molecules in vivo should be carefully considered, as well as the possible toxicity and/or possible effects on innate and adaptive immune response. In order to improve clinical parameters, many patents suggest the use of the TFD molecules in combination with drugs already employed in therapy. We are expecting in the near future relevant clinical trials based on the TFD strategy.

ETV6-PDGFRB and FIP1L1-PDGFRA stimulate human hematopoietic progenitor cell proliferation and differentiation into eosinophils: the role of nuclear factor-κB

BACKGROUND

ETV6-PDGFRB (also called TEL-PDGFRB) and FIP1L1-PDGFRA are receptor-tyrosine kinase fusion genes that cause chronic myeloid malignancies associated with hypereosinophilia. The aim of this work was to gain insight into the mechanisms whereby fusion genes affect human hematopoietic cells and in particular the eosinophil lineage.

DESIGN AND METHODS

We introduced ETV6-PDGFRB and FIP1L1-PDGFRA into human CD34(+) hematopoietic progenitor and stem cells isolated from umbilical cord blood.

RESULTS

Cells transduced with these oncogenes formed hematopoietic colonies even in the absence of cytokines. Both oncogenes also stimulated the proliferation of cells in liquid culture and their differentiation into eosinophils. This model thus recapitulated key features of the myeloid neoplasms induced by ETV6-PDGFRB and FIP1L1-PDGFRA. We next showed that both fusion genes activated the transcription factors STAT1, STAT3, STAT5 and nuclear factor-κB. Phosphatidylinositol-3 kinase inhibition blocked nuclear factor-κB activation in transduced progenitor cells and patients' cells. Nuclear factor-κB was also activated in the human FIP1L1-PDGFRA-positive leukemia cell line EOL1, the proliferation of which was blocked by bortezomib and the IκB kinase inhibitor BMS-345541. A mutant IκB that prevents nuclear translocation of nuclear factor-κB inhibited cell growth and the expression of eosinophil markers, such as the interleukin-5 receptor and eosinophil peroxidase, in progenitors transduced with ETV6-PDGFRB. In addition, several potential regulators of this process, including HES6, MYC and FOXO3 were identified using expression microarrays.

CONCLUSIONS

We show that human CD34(+) cells expressing PDGFR fusion oncogenes proliferate autonomously and differentiate towards the eosinophil lineage in a process that requires nuclear factor-κB. These results suggest new treatment possibilities for imatinib-resistant myeloid neoplasms associated with PDGFR mutations.

Eosinophil differentiation in the bone marrow is inhibited by T cell-derived IFN-gamma

To explore whether and how T cells can affect myelopoiesis, we investigated myeloid differentiation in a model for T cell-mediated immune activation. We found that CD70-transgenic (CD70TG) mice, which have elevated numbers of interferon-γ (IFN-γ)-producing effector T cells in the periphery and bone marrow, are almost devoid of eosinophilic granulocytes. Induction of allergic airway inflammation in these mice failed to induce eosinophilia as well as airway hyperresponsiveness. CD70TG mice also have strongly reduced numbers of eosinophil lineage-committed progenitors, whereas granulocyte/macrophage progenitors from these mice are unable to generate eosinophils in vitro. We found that granulocyte/macrophage progenitors express IFN-γR1 and that IFN-γ is sufficient to inhibit eosinophil differentiation of both murine and human progenitor cells in vitro. We demonstrate that inhibition of eosinophil development in CD70TG mice is IFN-γ-dependent and that T cell-derived IFN-γ is sufficient to inhibit eosinophil formation in vivo. Finally, we found that IFN-γ produced on anti-CD40 treatment and during viral infection can also suppress eosinophil formation in wild-type mice. These data demonstrate that IFN-γ inhibits the differentiation of myeloid progenitors to eosinophils, indicating that the adaptive immune system plays an important role in orchestrating the formation of the appropriate type of myeloid cells during immune activation.

The signaling mechanism of eosinophil activation

Eosinophils play an important role in certain aspects of asthma pathogenesis. This review focuses on the mechanism of activation of eosinophils by the growth factor interleukin-5 and the CC chemokine receptor-3. Interleukin-5 activates members of the Janus and Src family of kinases. The latter kinases are largely responsible for the generation of initial signaling events. CC chemokine receptor-3, in contrast, signals through heterotrimeric G-proteins. Subsequently, various signaling pathways are activated, which converge on four major pathways - the mitogen-activated protein kinase pathway, the phosphoinositide-3 kinase pathway, the calcium signaling pathway and the Janus-signal transducer and activator of transcription signaling pathway. The biologic consequences of many of these signaling pathways are also discussed.

STAT5 requires the N-domain for suppression of miR15/16, induction of bcl-2, and survival signaling in myeloproliferative disease

Phosphorylated signal transducer and activator of transcription 5 (STAT5) is a biomarker and potential molecular target for hematologic malignancies. We have shown previously that lethal myeloproliferative disease (MPD) in mice mediated by persistently activated STAT5 (STAT5a(S711F)) requires the N-domain, but the mechanism was not defined. We now demonstrate by retrovirally complementing STAT5ab(null/null) primary mast cells that relative to wild-type STAT5a, STAT5a lacking the N-domain (STAT5aDeltaN) ineffectively protected against cytokine withdrawal-induced cell death. Both STAT5a and STAT5aDeltaN bound to a site in the bcl-2 gene and both bound near the microRNA 15b/16 cluster. However, only STAT5a could effectively induce bcl-2 mRNA and reciprocally suppress miR15b/16 leading to maintained bcl-2 protein levels. After retroviral complementation of STAT5ab(null/null) fetal liver cells and transplantation, persistently active STAT5a(S711F) lacking the N-domain (STAT5aDeltaN(S711F)) was insufficient to protect c-Kit(+)Lin(-)Sca-1(+) (KLS) cells from apoptosis and unable to induce bcl-2 expression, whereas STAT5a(S711F) caused robust KLS cell expansion, induction of bcl-2, and lethal MPD. Severe attenuation of MPD by STAT5aDeltaN(S711F) was reversed by H2k/bcl-2 transgenic expression. Overall, these studies define N-domain-dependent survival signaling as an Achilles heel of persistent STAT5 activation and highlight the potential therapeutic importance of targeting STAT5 N-domain-mediated regulation of bcl-2 family members.

p38 MAP kinase inhibits neutrophil development through phosphorylation of C/EBPalpha on serine 21

Many extracellular stimuli regulate growth, survival, and differentiation responses through activation of the dual specificity mitogen activated protein kinase (MAPK) kinase three (MKK3) and its downstream effector p38 MAPK. Using CD34+ hematopoietic progenitor cells, here we describe a novel role for MKK3-p38MAPK in the regulation of myelopoiesis. Inhibition of p38MAPK utilizing the pharmacological inhibitor SB203580, enhanced neutrophil development ex vivo, but conversely reduced eosinophil differentiation. In contrast, constitutive activation of MKK3 dramatically inhibited neutrophil differentiation. Transplantation of beta2-microglobulin(-/-) nonobese diabetic/severe combined immune deficient (NOD/SCID) mice with CD34+ cells ectopically expressing constitutively active MKK3 resulted in reduced neutrophil differentiation in vivo, whereas eosinophil development was enhanced. Inhibitory phosphorylation of CCAAT/enhancer binding protein alpha (C/EBPalpha) on serine 21 was induced upon activation of p38MAPK. Moreover, ectopic expression of a non-phosphorylatable C/EBPalpha mutant was sufficient to abrogate MKK3-induced inhibition of neutrophil development. Furthermore, treatment of CD34+ progenitors from patients with severe congenital neutropenia with SB203580 restored neutrophil development. These results establish a novel role for MKK3-p38MAPK in the regulation of lineage choices during myelopoiesis through modulation of C/EBPalpha activity. This signaling module may thus provide an important therapeutic target in the treatment of bone marrow failure.

Ectopic expression of C/EBPalpha and ID1 is sufficient to restore defective neutrophil development in low-risk myelodysplasia

BACKGROUND

In patients with myelodysplasia, a general defect in the multipotent stem-cell compartment results in disturbed proliferation and differentiation of the erythroid, megakaryocytic and myeloid lineages. Although a number of genetic defects in myelodysplastic progenitor cells have been described, the intracellular signaling pathways underlying aberrant regulation of myelopoiesis remain relatively undefined.

DESIGN AND METHODS

Here, an ex vivo differentiation system was used to selectively screen for molecules improving defective hematopoiesis in myelodysplastic CD34(+) progenitor cells.

RESULTS

Bone marrow-derived CD34(+) cells isolated from patients with low-risk myelodysplastic syndrome showed impaired capacity to proliferate and differentiate as well as increased levels of apoptosis. In an attempt to improve the expansion and differentiation of the myelodysplastic CD34(+) progenitors, cells were treated with the p38MAPK pharmacological inhibitor SB203580, or retrovirally transduced to ectopically express active protein kinase B (PKB/c-akt), or the transcriptional regulators STAT5, C/EBPalpha or ID1. Whereas treatment of progenitors with SB203580, PKB or STAT5 did not enhance neutrophil development, ID1- and C/EBPalpha-transduced cells exhibited increased granulocyte/macrophage colony formation. Furthermore, ectopic expression of C/EBPalpha resulted in improved neutrophil maturation.

CONCLUSIONS

These data suggest that targeting the ID1 and C/EBPalpha transcriptional regulators may be of benefit in the design of novel therapies for low-risk myelodysplasia.

Regulation of myelopoiesis through syntenin-mediated modulation of IL-5 receptor output

The granulocyte-macrophage colony-stimulating factor (GM-CSF)/interleukin (IL)–3/IL-5 receptor family regulates the production and function of myeloid cells. These cytokines signal through receptor complexes that consist of unique ligand-binding α-chains and common signaling β-chains. IL-5 is distinct from IL-3 and GM-CSF in its capacity to induce eosinophil development, however, the molecular mechanisms that generate functional diversity within this receptor family are mostly unknown. Here, we characterized the selective IL-5Rα–binding adapter protein syntenin in IL-5R function. Syntenin and IL-5Rα colocalize at the plasma membrane and in early endosomal compartments. Manipulation of syntenin expression by ectopic expression or knockdown selectively modulated IL-5R but not GM-CSF receptor signaling, and severely affected IL-5–induced eosinophil differentiation from primary human CD34+ hematopoietic progenitor cells. We found syntenin up-regulated during eosinophilopoiesis but down-regulated during neutropoiesis. Syntenin forms complexes with multiple IL-5Rα chains, suggesting that syntenin-enhanced IL-5R output may result from stabilization of an IL-5–induced oligomeric receptor complex. These data demonstrate that cytokine-specific functions can be transduced by unique receptor α-chain–associating adapter proteins.

Human C/EBP-epsilon activator and repressor isoforms differentially reprogram myeloid lineage commitment and differentiation

CCAAT enhancer-binding protein-epsilon (C/EBP-epsilon) is required for the terminal differentiation of neutrophils and eosinophils. Human C/EBP-epsilon is expressed as 4 isoforms (32, 30, 27, and 14 kDa) through differential RNA splicing, and alternative promoters and translational start sites. The C/EBP-epsilon(32/30) isoforms are transcriptional activators, whereas C/EBP-epsilon(27) interacts with and represses GATA-1 transactivation of eosinophil promoters. C/EBP-epsilon(14) contains only DNA-binding and -dimerization domains and may function as a dominant-negative regulator. To define functional activities for these C/EBP-epsilon isoforms in myelopoiesis, human CD34(+) progenitors were transduced with internal ribosomal entry site-enhanced green fluorescent protein retroviral vectors encoding the 32/30, 27, and 14-kDa isoforms, purified by fluorescence-activated cell sorter, and analyzed in colony-forming assays and suspension cultures. Progenitors transduced with C/EBP-epsilon(32/30) default exclusively to eosinophil differentiation and gene expression, independent of interleukin-5, and regardless of inclusion of cytokines to induce other lineages. In contrast, the putative repressor C/EBP-epsilon(27) isoform strongly inhibits eosinophil differentiation and gene expression, including GATA-1, promoting granulocyte (neutrophil)-macrophage differen-tiation. The C/EBP-epsilon(14) repressor isoform strongly inhibits eosinophil development and gene expression, promoting erythroid differentiation, an effect enhanced by erythropoietin. Thus, C/EBP-epsilon isoforms can reprogram myeloid lineage commitment and differentiation consistent with their predicted activities based on activator and repressor domains and in vitro functional activities.

Maximal STAT5-induced proliferation and self-renewal at intermediate STAT5 activity levels

The level of transcription factor activity critically regulates cell fate decisions, such as hematopoietic stem cell (HSC) self-renewal and differentiation. We introduced STAT5A transcriptional activity into human HSCs/progenitor cells in a dose-dependent manner by overexpression of a tamoxifen-inducible STAT5A(1*6)-estrogen receptor fusion protein. Induction of STAT5A activity in CD34(+) cells resulted in impaired myelopoiesis and induction of erythropoiesis, which was most pronounced at the highest STAT5A transactivation levels. In contrast, intermediate STAT5A activity levels resulted in the most pronounced proliferative advantage of CD34(+) cells. This coincided with increased cobblestone area-forming cell and long-term-culture-initiating cell frequencies, which were predominantly elevated at intermediate STAT5A activity levels but not at high STAT5A levels. Self-renewal of progenitors was addressed by serial replating of CFU, and only progenitors containing intermediate STAT5A activity levels contained self-renewal capacity. By extensive gene expression profiling we could identify gene expression patterns of STAT5 target genes that predominantly associated with a self-renewal and long-term expansion phenotype versus those that identified a predominant differentiation phenotype.

Homeostatic intracellular-free Ca2+ is permissive for Rap1-mediated constitutive activation of alpha4 integrins on eosinophils

Although much progress has been made in understanding the molecular mechanisms underlying agonist-induced "inside-out" activation of integrins, little is known about how basal levels of integrin function are maintained. This is particularly important for nonactivated eosinophils, where intermediate activation of alpha(4)beta(1) integrin supports recruitment to endothelial cells under flow conditions. Depletion of intracellular Ca(2+) and pharmacological inhibition of phospholipase C (but not other intracellular signaling molecules, including PI3K, ERK1/2, p38 MAPK, and tyrosine kinase activity) abrogated basal alpha(4) integrin activity in nonactivated eosinophils. Basal alpha(4) integrin activation was associated with activation of the small GTPase Rap1, a known regulator of agonist-induced integrin function. Basal Rap activation was dependent upon phospholipase C, but not intracellular Ca(2+). However, depletion of intracellular Ca(2+) in CD34(+) hematopoietic progenitor cells abolished RapV12-mediated induction of alpha(4) integrin activity. Thus, residual Rap activity or constitutively active Rap activity in Ca(2+)-depleted cells is not sufficient to induce alpha(4) integrin activation. These data suggest that activation of functional alpha(4) integrin activity in resting eosinophils is mediated by Rap1 provided that the intracellular-free Ca(2+) is at a normal homeostatic concentration.

Tissue factor/FVIIa activates Bcl-2 and prevents doxorubicin-induced apoptosis in neuroblastoma cells

Background

Tissue factor (TF) is a transmembrane protein that acts as a receptor for activated coagulation factor VII (FVIIa), initiating the coagulation cascade. Recent studies demonstrate that expression of tumor-derived TF also mediates intracellular signaling relevant to tumor growth and apoptosis. Our present study investigates the possible mechanism by which the interaction between TF and FVIIa regulates chemotherapy resistance in neuroblastoma cell lines.

Methods

Gene and siRNA transfection was used to enforce TF expression in a TF-negative neuroblastoma cell line and to silence endogenous TF expression in a TF-overexpressing neuroblastoma line, respectively. The expression of TF, Bcl-2, STAT5, and Akt as well as the phosphorylation of STAT5 and Akt in gene transfected cells or cells treated with JAK inhibitor and LY294002 were determined by Western blot assay. Tumor cell growth was determined by a clonogenic assay. Cytotoxic and apoptotic effect of doxorubicin on neuroblastoma cell lines was analyzed by WST assay and annexin-V staining (by flow cytometry) respectively.

Results

Enforced expression of TF in a TF-negative neuroblastoma cell line in the presence of FVIIa induced upregulation of Bcl-2, leading to resistance to doxorubicin. Conversely, inhibition of endogenous TF expression in a TF-overexpressing neuroblastoma cell line using siRNA resulted in down-regulation of Bcl-2 and sensitization to doxorubicin-induced apoptosis. Additionally, neuroblastoma cells expressing high levels of either endogenous or transfected TF treated with FVIIa readily phosphorylated STAT5 and Akt. Using selective pharmacologic inhibitors, we demonstrated that JAK inhibitor I, but not the PI3K inhibitor LY294002, blocked the TF/FVIIa-induced upregulation of Bcl-2.

Conclusion

This study shows that in neuroblastoma cell lines overexpressed TF ligated with FVIIa produced upregulation of Bcl-2 expression through the JAK/STAT5 signaling pathway, resulting in resistance to apoptosis. We surmise that this TF-FVIIa pathway may contribute, at least in part, to chemotherapy resistance in neuroblastoma.

Protein kinase B (c-akt) regulates hematopoietic lineage choice decisions during myelopoiesis

Hematopoiesis is a highly regulated process resulting in the formation of all blood lineages. Aberrant regulation of phosphatidylinositol-3-kinase (PI3K) signaling has been observed in hematopoietic malignancies, suggesting that regulated PI3K signaling is critical for regulation of blood cell production. An ex vivo differentiation system was used to investigate the role of PI3K and its downstream effector, protein kinase B (PKB/c-akt) in myelopoiesis. PI3K activity was essential for hematopoietic progenitor survival. High PKB activity was found to promote neutrophil and monocyte development, while, conversely, reduction of PKB activity was required to induce optimal eosinophil differentiation. In addition, transplantation of β2-microglobulin (−/−) NOD/SCID mice with CD34+ cells ectopically expressing constitutively active PKB resulted in enhanced neutrophil and monocyte development, whereas ectopic expression of dominant-negative PKB induced eosinophil development in vivo. Inhibitory phosphorylation of C/EBPα on Thr222/226 was abrogated upon PKB activation in hematopoietic progenitors. Ectopic expression of a nonphosphorylatable C/EBPα mutant inhibited eosinophil differentiation ex vivo, whereas neutrophil development was induced, demonstrating the importance of PKB-mediated C/EBPα phosphorylation in regulation of granulopoiesis. These results identify an important novel role for PKB in regulation of cell fate choices during hematopoietic lineage commitment.

Molecular mechanisms underlying FIP1L1-PDGFRA-mediated myeloproliferation

An interstitial deletion on chromosome 4q12 resulting in the formation of the FIP1L1-PDGFRA fusion protein is involved in the pathogenesis of imatinib-sensitive chronic eosinophilic leukemia. The molecular mechanisms underlying the development of disease are largely undefined. Human CD34(+) hematopoietic progenitor cells were used to investigate the role of FIP1L1-PDGFRA in modulating lineage development. FIP1L1-PDGFRA induced both proliferation and differentiation of eosinophils, neutrophils, and erythrocytes in the absence of cytokines, which could be inhibited by imatinib. Whereas expression of FIP1L1-PDGFRA in hematopoietic stem cells and common myeloid progenitors induced the formation of multiple myeloid lineages, expression in granulocyte-macrophage progenitors induced only the development of eosinophils, neutrophils, and myeloblasts. Deletion of amino acids 30 to 233 in the FIP1L1 gene [FIP1L1(1-29)-PDGFRA] gave rise to an intermediate phenotype, exhibiting a dramatic reduction in the number of erythrocytes. FIP1L1-PDGFRA and FIP1L1(1-29)-PDGFRA both induced the activation of p38 and extracellular signal-regulated kinase 1/2 (ERK1/2) in myeloid progenitors, whereas signal transducers and activators of transcription 5 (STAT5) and protein kinase B/c-akt were only activated by FIP1L1-PDGFRA. Dominant-negative STAT5 partially inhibited FIP1L1-PDGFRA-induced colony formation, whereas combined inhibition of phosphatidylinositol-3-kinase and ERK1/2 significantly reversed FIP1L1-PDGFRA-induced colony formation. Taken together, these results suggest that expression of FIP1L1-PDFGRA in human hematopoietic progenitors induce a myeloproliferative phenotype via activation of multiple signaling molecules including phosphatidylinositol-3-kinase, ERK1/2, and STAT5.

Differentiation of eosinophilic leukemia EoL-1 cells into eosinophils induced by histone deacetylase inhibitors

EoL-1 cells differentiate into eosinophils in the presence of n-butyrate, but the mechanism has remained to be elucidated. Because n-butyrate can inhibit histone deacetylases, we hypothesized that the inhibition of histone deacetylases induces the differentiation of EoL-1 cells into eosinophils. In this study, using n-butyrate and two other histone deacetylase inhibitors, apicidin and trichostatin A, we have analyzed the relationship between the inhibition of histone deacetylases and the differentiation into eosinophils in EoL-1 cells. It was demonstrated that apicidin and n-butyrate induced a continuous acetylation of histones H4 and H3, inhibited the proliferation of EoL-1 cells without attenuating the level of FIP1L1-PDGFRA mRNA, and induced the expression of markers for mature eosinophils such as integrin beta7, CCR1, and CCR3 on EoL-1 cells, while trichostatin A evoked a transient acetylation of histones and induced no differentiation into eosinophils. These findings suggest that the continuous inhibition of histone deacetylases in EoL-1 cells induces the differentiation into mature eosinophils.

Expression and prognostic significance of Stat5a and E-cadherin in extramammary Paget's disease

BACKGROUND

Stat5 has been shown to regulate the proliferation and inhibition of apoptosis in cancer cells. E-cadherin plays an important role in maintaining epithelial stability and is widely regarded as a prognostic marker in many types of human cancers. The expression of Stat5 has not been investigated in extramammary Paget's disease (EMPD).

OBJECTIVES

To study the expression of Stat5a and E-cadherin protein in EMPD and to evaluate the relationships between them.

METHODS

Thirty-six tissue samples from 34 cases with primary EMPD were subjected to immunohistochemical staining for Stat5a and E-cadherin.

RESULTS

Twenty-nine of 30 in situ EMPD specimens were positive for Stat5a expression, and the staining pattern for Stat5a was mainly nuclear in the majority of Paget's cells. All four invasive specimens and two metastatic lymph node specimens were negative for Stat5a. Twenty-six of 30 in situ EMPD specimens expressed E-cadherin in more than 50% of tumor cells, and three of 30 in situ EMPD specimens expressed E-cadherin in less than 50% of tumor cells. One in situ EMPD specimen and one invasive specimen expressed E-cadherin in less than 25% of tumor cells. Three invasive specimens and two metastatic lymph node specimens were negative, with occasional membranous staining for E-cadherin. There is a significant correlation between the expression of Stat5a and E-cadherin.

CONCLUSIONS

Our results showed that these proteins were found in in situ lesions, and it is speculated that these proteins may play some role in the prognosis/invasion of EMPD.

STAT5 represses BCL6 expression by binding to a regulatory region frequently mutated in lymphomas

Deregulated expression of BCL6 is a pathogenic event in many lymphomas. BCL6 blocks cellular differentiation by repressing transcription of its target genes, and this may promote tumorigenesis. Conversely, the transcription factor signal transducers and activators of transcription (STAT)5 promotes differentiation in many systems. STAT5 upregulates a number of genes repressed by BCL6, raising the possibility that STAT5 and BCL6 have opposing roles in transcriptional regulation. Therefore, we sought to determine the effects of STAT5 activation on BCL6 expression and function. We found that activation of STAT5 downregulates BCL6 expression in B-lymphoma cells and other hematopoietic cell lines. We identified two potential STAT-binding regions in the first exon and first intron of BCL6 that fell within regions of high inter-species homology, suggesting conservation of regulatory function. STAT5 can bind inducibly and regulate transcription at one of these regions, identifying BCL6 as a STAT5 target gene. Additionally, STAT5-mediated downregulation of BCL6 results in loss of BCL6 repression of its target genes, confirming that STAT5 is a negative regulator of BCL6 function. The STAT5 responsive region of the BCL6 gene is mutated frequently in B-cell lymphomas, suggesting that loss of the repressive effects of STAT5 on BCL6 might contribute to the pathogenesis of these cancers.

The biological functions of the versatile transcription factors STAT3 and STAT5 and new strategies for their targeted inhibition

Signal transducers and activators of transcription (STATs) comprise a unique family of transcription factors, which transmit the interactions of cytokines, hormones and growth factors with their cell surface receptors into transcriptional programs. The mechanism of STAT activation has been well-established and comprises tyrosine phosphorylation, dimerization, nuclear translocation, binding to specific DNA response elements, recruitment of co-activators or co-repressors and transcriptional induction or repression of target genes. Gene deletion, microarrays, proteomics and chromatin immunoprecipitation experiments have revealed target genes with a broad range of functions regulated by STAT3 and STAT5. In the mammary gland, STAT5-induced genes contribute mainly to the prolactin dependent lobulo-alveolar development, whereas STAT3 induced genes control apoptosis during involution. Crucial effects have also been observed in other tissues. The germ line deletion of STAT3 or STAT5 causes early embryonal or perinatal lethality in mice. STAT5 is also required for proliferation of T- and B-cells and hematopoietic stem cell self-renewal. Deregulated STAT activity is often found associated with tumorigenesis and activated STATs seem to be limiting components in tumor cells. This review summarizes the functions of STAT3 and STAT5 in different cell types and the strategies that are used to counteract their action in tumor cells.

Src Family Kinase Activity Is Required for Murine Embryonic Stem Cell Growth and Differentiation

Self-renewal and differentiation of embryonic stem (ES) cells are regulated by cytokines and growth factors through tyrosine kinase-dependent signaling pathways. In murine ES cells, signals for self-renewal are generated by the leukemia inhibitory factor (LIF). LIF and other growth factors are linked to the activation of the Src family of cytoplasmic protein-tyrosine kinases (SFKs), which consists of eight members having shared structural architecture. In this article, we show that murine ES cells express seven SFKs, three of which (Hck, Src, and Fyn) exhibit constitutive activity in self-renewing ES cells. Differentiation of ES cells to embryoid bodies was associated with rapid transcriptional silencing of Hck and Lck and with the loss of the corresponding kinase proteins. The expression of other family members remained relatively constant, although some loss of Fgr and Lyn proteins was observed during differentiation. Like ES cells, embryoid bodies maintained constitutive Src and Fyn kinase activity. Partial inhibition of endogenous SFK activity with the ATP-competitive inhibitors 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine or Src kinase inhibitor-1 induced differentiation of ES cells in the presence of LIF. In contrast, suppression of all SFK activity with higher concentrations of these inhibitors, or with the more potent compound A-419259 (Bioorg Med Chem Lett 12:1683-1686, 2002) blocked differentiation in response to LIF withdrawal. It is surprising that these inhibitor-treated cells remained pluripotent despite the absence of LIF. Our results implicate individual members of the Src kinase family in distinct ES cell renewal and differentiation pathways and show that small-molecule SFK inhibitors can control ES cell fate.

Mechanism of the eosinophilic differentiation of HL-60 clone 15 cells induced by n-butyrate

n-Butyrate is one of the most powerful chemical inducers of the differentiation of human eosinophilic leukemia HL-60 clone 15 cells into mature eosinophils. We have recently reported that the mechanism by which HL-60 clone 15 cells differentiate into eosinophils by n-butyrate is that n-butyrate continuously inhibits histone deacetylase activity as a histone deacetylase inhibitor, resulting in continuous acetylation of histones. In this review, we discuss roles of histone acetyltransferase, histone deacetylase and histone deacetylase inhibitors in the differentiation of HL-60 clone 15 cells into eosinophils.

Signal transducer and activator of transcription 5 (STAT5)

Signal transducer and activator of transcription 5 (STAT5) activity is induced by a plethora of cytokines and growth factors resulting in transcriptional activation of specific target genes. STAT5 plays an important role in a variety of cellular processes, including proliferation, differentiation, and apoptosis. Aberrant regulation of STAT5 has been observed in solid tumors as well as in patients with either chronic or acute myeloid leukemia. Kinase inhibitors are currently being developed to negatively regulate STAT5 activity for clinical purposes.

Constitutive activation of STAT5A promotes human hematopoietic stem cell self-renewal and erythroid differentiation

Activation of the transcription factor signal transducer and activator of transcription (STAT)5 is involved in various aspects of hematopoiesis, affecting cell proliferation, differentiation, and cell survival. Constitutive activation of STAT5 has also been associated with leukemic transformation. We overexpressed the constitutively active mutant STAT5A(1*6) in human cord blood CD34⁺ cells and evaluated the effects on the hematopoietic potential of stem cells in a variety of in vitro and in vivo systems. The observed phenotypic changes were correlated with differential gene expression patterns induced by STAT5A(1*6). Our data indicate that a persistent activation of STAT5A in human hematopoietic stem and progenitor cells results in their enhanced self-renewal and diverts differentiation to the erythroid lineage.

Biochemical assessment of intracellular signal transduction pathways in eosinophils: implications for pharmacotherapy

Allergic asthma and allergic rhinitis are inflammatory diseases of the airway. Cytokines and chemokines produced by T helper (Th) type 2 cells (GM-CSF, IL-4, IL-5, IL-6, IL-9, IL-10 and IL-13), eotaxin, transforming growth factor-beta, and IL-11 orchestrate most pathophysiological processes of the late-phase allergic reaction, including the recruitment, activation, and delayed apoptosis of eosinophils, as well as eosinophilic degranulation to release eosinophilic cationic protein, major basic protein, and eosinophil-derived neurotoxin. These processes are regulated through an extensive network of interactive intracellular signal transduction pathways that have been intensively investigated recently. Our present review updates the cytokine and chemokine-mediated signal transduction mechanisms including the RAS-RAF-mitogen-activated protein kinases, Janus kinases (signal transducers and activators of transcription), phosphatidylinositol 3-kinase, nuclear factor-kappa B, activator protein-1, GATA, and cyclic AMP-dependent pathways, and describes the roles of different signaling pathways in the regulation of eosinophil differentiation, recruitment, degranulation, and expression of adhesion molecules. We shall also discuss different biochemical methods for the assessment of various intracellular signal transduction molecules, and various antagonists of receptors, modulators, and inhibitors of intracellular signaling molecules, many of which are potential therapeutic agents for treating allergic diseases.

The influence of antisense oligonucleotides against STAT5 on the regulation of normal haematopoiesis in a bone marrow model

Cytokines and growth factors that take part in the regulation of haematopoietic cell development activate many signalling pathways in target cells. The STAT5 (signal transducers and activators of transcription) proteins are members of a family of signal transducers and activators of transcription that can be activated after cytokine stimulation. Their binding to promoters of different genes influences cell proliferation, differentiation and survival. It is suggested that they play an important role in haematopoiesis, however, the question of the real function of STAT5 proteins requires further examination. The aim of our study was to investigate the role of STAT5 in the proliferation and apoptosis of normal haematopoietic bone marrow cells derived from heparinized cadaveric organ donors (HCOD). We applied antisense oligodeoxynucleotides (ODNs) to block STAT5A and STAT5B at the mRNA level and the reverse transcription polymerase chain reaction method to study STAT5 mRNA expression in the cells after incubation with ODNs. Moreover, we performed Western blot analysis of the STAT5A protein after exposure to antisense STAT5A. We analysed the clonogenicity of the colony-forming unit of granulocytes-macrophages and the burst-forming unit of erythrocytes in methylcellulose cultures according to the type and the dose of ODNs. We also examined apoptosis induced in bone marrow mononuclear and CD34(+) cells by employing annexin V staining and the TUNEL method using flow cytometry (FACScan). We found that the perturbation of STAT5 expression decreased the clonogenicity of bone marrow haematopoietic cells. However, we did not observe any significant increase in the percentage of apoptotic cells after incubation with antisense ODNs. It was concluded that the STAT5 proteins play a significant role in the proliferation of human bone marrow cells harvested from HCOD. These proteins might be critical in the regulation of haematopoiesis, especially under stress conditions.

Possible mechanism of action of the histone deacetylase inhibitors for the induction of differentiation of HL-60 clone 15 cells into eosinophils

1 We have examined the effect of the histone deacetylase inhibitors apicidin, trichostatin A (TSA) and n-butyrate on the histone acetylation and the differentiation of human eosinophilic leukemia HL-60 clone 15 cells into eosinophils. 2 Viability of the cells incubated with apicidin (100 nm), TSA (30 nm) or n-butyrate (500 microm) did not change significantly, but higher concentrations of apicidin (> or =300 nm) or TSA (> or =100 nm) decreased the viability when examined at day 1. 3 Apicidin (100 nm) as well as n-butyrate (500 microm) induced continuous acetylations of histone H4 and lysine14 residue on histone H3, while TSA (30 nm) induced transient acetylations. 4 After 6 days incubation, eosinophilic cells stained by Luxol-fast-blue were generated by apicidin (100 nm) and n-butyrate (500 microm) but not by TSA (30 nm). Other markers for differentiation into eosinophils such as changes in intracellular structure, and expressions of integrin beta7 and major basic protein, and the inhibition of cell proliferation were also induced by apicidin and n-butyrate but not by TSA. 5 Continuous acetylation of histone H4 achieved by repeated treatment with TSA (30 nm) at an interval of 12 h for more than three times induced such changes when examined on day 6. In addition, the induction was impaired by shortening the period of incubation with apicidin (100 nm) or n-butyrate (500 microm). 6 CCAAT/enhancer binding protein was continuously activated by apicidin (100 nm) and n-butyrate (500 microm), but was transiently activated by TSA (30 nm). 7 These findings suggest that the continuous acetylation of histones H3 and H4 is necessary for the differentiation of HL-60 clone 15 cells into eosinophils.

Characterization of the human STAT5A and STAT5B promoters: evidence of a positive and negative mechanism of transcriptional regulation

We recently published the genomic characterization of the STAT5A and STAT5B paralogous genes that are located head to head in the 17q21 chromosome and share large regions of sequence identity. We here demonstrate by transient in vitro transfection that STAT5A and STAT5B promoters are able to direct comparable levels of transcription. The expression of basal promoters is enhanced after Sp1 up-regulation in HeLa and SL2 cells while DNA methylation associated to the recruitment of MeCP2 methyl CpG binding protein down-regulates STAT5A and B promoters by interfering with Sp1-induced transcription. In addition, cross-species sequence comparison identified a bi-directional negative cis-acting regulatory element located in the STAT5 intergenic region.

FVIIa:TF induces cell survival via G12/G13-dependent Jak/STAT activation and BclXL production

Tissue factor (TF), apart from activating the extrinsic pathway of the blood coagulation, is a principal regulator of embryonic and oncogenic angiogenesis, inflammation, leukocyte reverse transmigration, and tumor progression. It has become clear that these events are mediated by intracellular signal transduction elicited by TF/factor VIIa (FVIIa) interaction, but the details of this signaling remain largely obscure. In this study, we show that FVIIa/TF-interaction produces STAT5 phosphorylation, STAT5 nuclear translocation and transactivation of a STAT5 reporter construct. FVIIa-dependent STAT5 activation was dependent on FVIIa proteolytic activity but not on generation of the downstream coagulation factors Xa and thrombin, nor on the TF cytoplasmic domain. FVIIa-induced STAT5 phosphorylation was dependent on functional G12/G13 class G proteins and Jak2 activity, but not Jak1 or Tyk2. Finally, we show that FVIIa leads to cell survival through a Jak2/STAT5-dependent production of the antiapoptotic STAT5 target Bcl(XL) as well as Jak2-dependent activation of the antiapoptotic protein PKB. In conclusion, our results show that FVIIa induces cell survival through STAT5-dependent Bcl(XL) production and Jak2-dependent activation of PKB. Finally, we demonstrated for the first time that TF/FVIIa-signal transduction is dependent on G12/G13 class G proteins.

Stat5a is tyrosine phosphorylated and nuclear localized in a high proportion of human breast cancers

Signal transducers and activators of transcription (STATs) are latent cytoplasmic transcription factors that are activated and translocated into the nucleus after phosphorylation at a conserved tyrosine residue. Mouse model studies have demonstrated that activated Stat5a acts as a critical survival factor for normal, preneoplastic and malignant mammary epithelial cells. Very limited information is available, however, on the expression, tyrosine phosphorylation status and nuclear localization of Stat5a in human breast cancers. In our study, the pattern of Stat5a cellular localization was analyzed by immunohistochemistry in a series of 83 randomly selected primary human breast adenocarcinomas. Immunoprecipitation/Western blotting and immunohistochemistry assays employing different phospho-specific antibodies verified Stat5a tyrosine phosphorylation status. Stat5a was nuclear localized and tyrosine phosphorylated in 59 of 78 (76%) breast cancers examined; 38 of 78 (49%) demonstrated Stat5a nuclear localization in more than 25% of the breast cancer cells within the adenocarcinomas. Nuclear localized Stat5a was associated positively with increased levels of histologic differentiation (p = 0.03). A statistically significant positive association with p27 nuclear localization also was identified (p = 0.05). No relationship was found between nuclear localized Stat5a and menopausal status, tumor size, ploidy, percentage of cells in S-phase, lymph node metastases, ER, ErbB2, nuclear localized p21 or nuclear localized Stat5b/Stat3. As its role in human breast cancer progression and response to therapy is defined, Stat5a could become a new molecular target for breast cancer therapy.

Acute myeloid leukemia fusion proteins deregulate genes involved in stem cell maintenance and DNA repair

Acute myelogenous leukemias (AMLs) are genetically heterogeneous and characterized by chromosomal rearrangements that produce fusion proteins with aberrant transcriptional regulatory activities. Expression of AML fusion proteins in transgenic mice increases the risk of myeloid leukemias, suggesting that they induce a preleukemic state. The underlying molecular and biological mechanisms are, however, unknown. To address this issue, we performed a systematic analysis of fusion protein transcriptional targets. We expressed AML1/ETO, PML/RAR, and PLZF/RAR in U937 hemopoietic precursor cells and measured global gene expression using oligonucleotide chips. We identified 1,555 genes regulated concordantly by at least two fusion proteins that were further validated in patient samples and finally classified according to available functional information. Strikingly, we found that AML fusion proteins induce genes involved in the maintenance of the stem cell phenotype and repress DNA repair genes, mainly of the base excision repair pathway. Functional studies confirmed that ectopic expression of fusion proteins constitutively activates pathways leading to increased stem cell renewal (e.g., the Jagged1/Notch pathway) and provokes accumulation of DNA damage. We propose that expansion of the stem cell compartment and induction of a mutator phenotype are relevant features underlying the leukemic potential of AML-associated fusion proteins.

Differential effect of dexamethasone on cell death and STAT5 activation during in vitro eosinopoiesis

Glucorticoids reduce eosinophilia through a direct effect on eosinophils or indirectly on cells producing cytokines and chemokines. Conflicting data have been previously reported concerning glucocorticoid effects on eosinopoiesis. To elucidate this point, dexamethasone was added during eosinophil differentiation of CD34+ cells. Dexamethasone enhanced proliferation and differentiation through an early effect on immature cells. Dexamethasone inhibited apoptosis during early differentiation, whereas death of mature cells was increased. Signal transducer and activator of transcription 5 (STAT5) is a transcription factor involved in the proliferation, differentiation and survival of haematopoietic cells, which interacts with glucocorticoid receptor. Activation of STAT5 by interleukin-5 was investigated during eosinophil differentiation. Long isoforms of STAT5 were activated during the entire period in the culture as well as in blood eosinophils, while short isoforms were only activated during early differentiation. Short isoforms were less activated in the presence of dexamethasone. This suggests that dexamethasone could act on proliferation, differentiation and apoptosis during eosinophil differentiation through an association of STAT5 with the glucocorticoid receptor.

Enhanced hematopoietic differentiation of embryonic stem cells conditionally expressing Stat5

The signal transducer Stat5 plays a key role in the regulation of hematopoietic differentiation and hematopoietic stem cell function. To evaluate the effects of Stat5 signaling in the earliest hematopoietic progenitors, we have generated an embryonic stem cell line in which Stat5 signaling can be induced with doxycycline. Ectopic Stat5 activation at the point of origin of the hematopoietic lineage (from day 4 to day 6 of embryoid body differentiation) significantly enhances the number of hematopoietic progenitors with colony-forming potential. It does so without significantly altering total numbers or apoptosis of hematopoietic cells, suggesting a cell-intrinsic effect of Stat5 on either the developmental potential or clonogenicity of this population. From day-6 embryoid bodies, under the influence of Stat5 signaling, a population of semiadherent cells can be expanded on OP9 stromal cells that is comprised of primitive hematopoietic blast cells with ongoing, mainly myeloid, differentiation. When these cells are injected into lethally irradiated mice, they engraft transiently in a doxycycline-dependent manner. These results demonstrate that the hematopoietic commitment of embryonic stem cells may be augmented by a Stat5-mediated signal, and highlight the utility of manipulating individual components of signaling pathways for engineering tissue-specific differentiation of stem cells.