Function and signal transduction mediated by the interleukin 3 receptor system in hematopoiesis

Monoallelic KRAS (G13C) mutation triggers dysregulated expansion in induced pluripotent stem cell-derived hematopoietic progenitor cells

BACKGROUND

Although oncogenic RAS mutants are thought to exert mutagenic effects upon blood cells, it remains uncertain how a single oncogenic RAS impacts non-transformed multipotent hematopoietic stem or progenitor cells (HPCs). Such potential pre-malignant status may characterize HPCs in patients with RAS-associated autoimmune lymphoproliferative syndrome-like disease (RALD). This study sought to elucidate the biological and molecular alterations in human HPCs carrying monoallelic mutant KRAS (G13C) with no other oncogene mutations.

METHODS

We utilized induced pluripotent stem cells (iPSCs) derived from two unrelated RALD patients. Isogenic HPC pairs harboring either wild-type KRAS or monoallelic KRAS (G13C) alone obtained following differentiation enabled reliable comparative analyses. The compound screening was conducted with an established platform using KRAS (G13C) iPSCs and differentiated HPCs.

RESULTS

Cell culture assays revealed that monoallelic KRAS (G13C) impacted both myeloid differentiation and expansion characteristics of iPSC-derived HPCs. Comprehensive RNA-sequencing analysis depicted close clustering of HPC samples within the isogenic group, warranting that comparative studies should be performed within the same genetic background. When compared with no stimulation, iPSC-derived KRAS (G13C)-HPCs showed marked similarity with the wild-type isogenic control in transcriptomic profiles. After stimulation with cytokines, however, KRAS (G13C)-HPCs exhibited obvious aberrant cell-cycle and apoptosis responses, compatible with "dysregulated expansion," demonstrated by molecular and biological assessment. Increased BCL-xL expression was identified amongst other molecular changes unique to mutant HPCs. With screening platforms established for therapeutic intervention, we observed selective activity against KRAS (G13C)-HPC expansion in several candidate compounds, most notably in a MEK- and a BCL-2/BCL-xL-inhibitor. These two compounds demonstrated selective inhibitory effects on KRAS (G13C)-HPCs even with primary patient samples when combined.

CONCLUSIONS

Our findings indicate that a monoallelic oncogenic KRAS can confer dysregulated expansion characteristics to non-transformed HPCs, which may constitute a pathological condition in RALD hematopoiesis. The use of iPSC-based screening platforms will lead to discovering treatments that enable selective inhibition of RAS-mutated HPC clones.

Management of eosinophil-associated inflammatory diseases: the importance of a multidisciplinary approach

Elevated eosinophil counts in blood and tissue are a feature of many pathological processes. Eosinophils can migrate and accumulate in a wide variety of tissues and, by infiltrating a target organ, can mediate the development of several inflammatory diseases. The normalization of eosinophilia is a common biomarker of a treatable trait and can also be used as a prognostic and predictive biomarker since it implies a reduction in type 2 inflammation that contributes to disease pathogenesis. Biological therapies targeting this cell type and its proinflammatory mediators have been shown to be effective in the management of a number of eosinophilic diseases, and for this reason they constitute a potential common strategy in the treatment of patients with various multimorbidities that present with type 2 inflammation. Various biological options are available that could be used to simultaneously treat multiple target organs with a single drug, bearing in mind the need to offer personalized treatments under the umbrella of precision medicine in all patients with eosinophil-associated diseases (EADs). In addition to reviewing these issues, we also discuss a series of perspectives addressing the management of EAD patients from a multidisciplinary approach, with the collaboration of health professionals from different specialties who manage the different multimorbidities that frequently occur in these patients. We examine the basic principles of care that this multidisciplinary approach must cover and present a multidisciplinary expert opinion regarding the ideal management of patients with EADs, from diagnosis to therapeutic approach and follow-up.

The emerging roles of eosinophils: Implications for the targeted treatment of eosinophilic-associated inflammatory conditions

Eosinophils have multiple relevant biological functions, including the maintenance of homeostasis, host defense against infectious agents, innate immunity activities, immune regulation through Th1/Th2 balance, anti-inflammatory, and anti-tumorigenic effects. Eosinophils also have a main role in tissue damage through eosinophil-derived cytotoxic mediators that are involved in eosinophilic inflammation, as documented in Th2-high asthma and other eosinophilic-associated inflammatory conditions.

Recent evidence shows that these multiple and apparently conflicting functions may be attributed to the existence of different eosinophil subtypes (i.e.: tissue resident and inducible eosinophils). Therapeutic intervention with biological agents that totally deplete tissues and circulating eosinophils or, vice versa, maintain a minimal proportion of eosinophils, particularly the tissue-resident ones, could therefore have a very different impact on patients, especially when considering the administration of these therapies for prolonged time. In addition, the characterization of the predominant pathway underlying eosinophilic inflammation by surrogate biomarkers (circulating eosinophils, organ-specific eosinophils levels such as eosinophil count in sputum, bronchoalveolar lavage, tissue biopsy; total circulating IgE levels, or the use of FeNO) in the single patient with an eosinophilic-associated inflammatory condition could help in choosing the treatment.

These observations are crucial in light of the increasing therapeutic armamentarium effective in modulating eosinophilic inflammation through the inhibition in different, yet complementary ways of eosinophil pathways, such as the interleukin-5 one (with mepolizumab, benralizumab, reslizumab) or the interleukin-4/13 one (with dupilumab and lebrikizumab), in severe T2-high asthma as well as in other systemic eosinophilic associated diseases, such as eosinophilic granulomatosis with polyangiitis and hypereosinophilic syndrome.

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Recent evidence pointed out the existence of different eosinophil subtypes, i.e. tissue resident and inducible eosinophils, with different and apparently conflicting functions.

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Biological therapies with different mechanisms can deplete completely tissues and circulating eosinophils or maintain a minimal proportion of eosinophils, particularly the tissue-resident ones, and this could therefore have a different impact on patients, especially when considering the administration of these therapies for prolonged time.

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The identification of the predominant pathway underlying eosinophilic inflammation by surrogate biomarkers (circulating eosinophils, organ-specific eosinophils levels such as eosinophil count in sputum, bronchoalveolar lavage, tissue biopsy; total circulating IgE levels, or the use of FeNO) should be sought in the single patient with an eosinophilic-associated inflammatory condition.

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These considerations may help in choosing the best anti-eosinophilic treatment, considering the increasing therapeutic armamentarium effective in modulating eosinophilic inflammation through the inhibition of the interleukin-5 one (with mepolizumab, benralizumab, reslizumab) or the interleukin-4/13 one (with dupilumab and lebrikizumab)

Targeting CD123 in hematologic malignancies: identifying suitable patients for targeted therapy

Following the observation of interleukin 3 receptor α chain (IL-3Rα; CD123) upregulation on leukemia stem cells (LSCs) almost two decades ago, targeted treatment via CD123-diptheria toxin conjugates has now been tested in patients with diverse myeloid malignancies. Targeted eradication of LSCs could result in effective treatments for many challenging diseases initiated by these cells. Consequently, considerable effort has been directed toward targeting CD123 as a potential strategy for treating patients with hematologic malignancies in which CD123 is overexpressed. However, these therapies have had limited success so far, highlighting the need for suitable criteria to identify patients who could benefit from them. Given the diversity in CD123 expression across different hematologic malignancies, understanding CD123 expression patterns and the functional pathogenetic significance is crucial. Here, we review the methodologies available for CD123 assessment and discuss the biological and clinical characteristics of patients for whom CD123-targeting therapies may have a clinical impact.

Janus Kinases in Leukemia

Janus kinases (JAKs) transduce signals from dozens of extracellular cytokines and function as critical regulators of cell growth, differentiation, gene expression, and immune responses. Deregulation of JAK/STAT signaling is a central component in several human diseases including various types of leukemia and other malignancies and autoimmune diseases. Different types of leukemia harbor genomic aberrations in all four JAKs (JAK1, JAK2, JAK3, and TYK2), most of which are activating somatic mutations and less frequently translocations resulting in constitutively active JAK fusion proteins. JAKs have become important therapeutic targets and currently, six JAK inhibitors have been approved by the FDA for the treatment of both autoimmune diseases and hematological malignancies. However, the efficacy of the current drugs is not optimal and the full potential of JAK modulators in leukemia is yet to be harnessed. This review discusses the deregulation of JAK-STAT signaling that underlie the pathogenesis of leukemia, i.e., mutations and other mechanisms causing hyperactive cytokine signaling, as well as JAK inhibitors used in clinic and under clinical development.

The Emerging Role of Eosinophils as Multifunctional Leukocytes in Health and Disease

Eosinophils are terminally differentiated cytotoxic effector cells that have a role in parasitic infections and allergy by releasing their granule-derived cytotoxic proteins. However, an increasing number of recent observations indicate that eosinophils are not only associated with the pathogenesis of a wide range of diseases, but also contribute to the maintenance of homeostatic responses in previously underappreciated diverse tissues, such as the gastrointestinal (GI) tract and adipose tissue. In this review, we describe biological characteristics of eosinophils, as their developmental properties, permissive proliferation and survival, degranulation activity, and migration properties enable them to distribute to both homeostatic and inflamed tissues. We describe pathologic aspects of eosinophils with a role in asthma and in various GI diseases, including eosinophilic GI disorders, inflammatory bowel disease, and radiation-induced enteropathy. Finally, we discuss the beneficial role of eosinophils, which contribute to the resolution of pathogenic conditions and to the modulation of homeostatic biologic responses.

CD28/4-1BB CD123 CAR T cells in blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is associated with a remarkably poor prognosis and with no treatment consensus. The identification of relevant therapeutic targets is challenging. Here, we investigated the immune functions, antileukemia efficacy and safety of CD28/4-1BB CAR T cells targeting CD123 the interleukin (IL)-3 receptor alpha chain which is overexpressed on BPDCN. We demonstrated that both retroviral and lentiviral engineering CD28/4-1BB CD123 CAR T cells exhibit effector functions against BPDCN cells through CD123 antigen recognition and that they efficiently kill BPDCN cell lines and BPDCN-derived PDX cells. In vivo, CD28/4-1BB CD123 CAR T-cell therapy displayed strong efficacy by promoting a decrease of BPDCN blast burden. Furthermore we showed that T cells from BPDCN patient transduced with CD28/4-1BB CD123 CAR successfully eliminate autologous BPDCN blasts in vitro. Finally, we demonstrated in humanized mouse models that these effector CAR T cells exert low or no cytotoxicity against various subsets of normal cells with low CD123 expression, indicating a potentially low on-target/off-tumor toxicity effect. Collectively, our data support the further evaluation for clinical assessment of CD28/4-1BB CD123 CAR T cells in BPDCN neoplasm.

Interleukin-3 plays a vital role in hyperoxic acute lung injury in mice via mediating inflammation

Background

Interleukin (IL)-3 amplifies inflammation. However, the effect of IL-3 in acute lung injury (ALI), an acute inflammatory disease, is unclear. The aim of this study was to test the hypothesis that IL-3 plays an important role in hyperoxia-induced ALI.

Methods

Hyperoxic ALI was induced in wild-type (WT) and IL-3 gene disrupted (IL-3^−/−) mice by exposure to 100% O₂ for 72 h.

Results

Hyperoxia increased IL-3 levels in plasma and lung tissues in WT mice. Pulmonary inflammation and edema were detected by histological assay in WT mice exposed to 100% O₂ for 72 h. However, the hyperoxia-induced lung histological changes were improved in IL-3^−/− mice. The hyperoxia-induced elevation of neutrophils in bronchoalveolar lavage fluids and circulation were reduced in IL-3^−/− mice. Meanwhile, the levels of tumor necrosis factor-α and IL-6 were suppressed in IL-3^−/− mice compared with WT mice. Moreover, the hyperoxia-induced the activation of IκBα kinase (IKK) β, IκBα phosphorylation, and nuclear factor-κB translocation were inhibited in IL-3^−/− mice compared with WT mice.

Conclusions

Our results suggest IL-3 is a potential therapeutic target for hyperoxia-induced ALI.

Electronic supplementary material

The online version of this article (10.1186/s12890-018-0725-2) contains supplementary material, which is available to authorized users.

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.

Influence of IL-3 functional fragment on cord blood stem cell ex vivo expansion and differentiation

BACKGROUND

Recombinant human interleukin-3 (rhIL-3) is a multiple hematopoietic growth factor, which enhances stem cell expansion and hematopoiesis regeneration in vitro and in vivo, when administrated in combination with other cytokines. However, the structure-function study of rhIL-3 remains rarely studied, so far. The purpose of this study was to recognize the short peptide with similar function as rhIL-3, and assess the hematopoietic efficacy in umbilical cord blood (UCB) stem cell culture as well.

METHODS

Two novel monoclonal antibodies (mAb) (C1 and E1) were generated against rhIL-3 using hybridoma technique. Eleven short peptides were depicted and synthesized to overlap covering the full length sequence of rhIL-3. ELISA was employed to distinguish the antibody-binding peptide from the negative peptides. In addition, the multi-potential hematopoiesis capabilities of the positive peptides were evaluated by adding 25 ng/mL of each peptide to the culture medium of hematopoietic stem cells (HSCs) derived from UCB. Total nucleated cell number and the CD34(+) cell number from each individual treatment group were calculated on day 7. Correlated antibodies at 0.5 or 2 molar fold to each peptide were also tested in the stem cell expansion experiment, to further confirm the bioactivity of the peptides.

RESULTS

Two peptides were recognized by the novel generated antibodies, using ELISA. Peptide 3 and 8 exhibited comparable hematopoiesis potentials, with 25.01±0.14 fold, and 19.89±0.12 fold increase of total nucleated cell number on day 7, respectively, compared with the basal medium control (4.93±0.55 fold). These biological effects were neutralized by adding the corresponding mAb at a dose dependent manner.

CONCLUSIONS

Our results identified two specific regions of rhIL-3 responsible for HSC proliferation and differentiation, which were located from 28 to 49 amino acids (P3), and 107 to 127 amino acids (P8), respectively. The short peptide 3 and 8 might act synergistically, which could serve as an economic substitute to rhIL-3 in research laboratory.

Targeting of acute myeloid leukaemia by cytokine-induced killer cells redirected with a novel CD123-specific chimeric antigen receptor

Current therapeutic regimens for acute myeloid leukaemia (AML) are still associated with high rates of relapse. Immunotherapy with T-cells genetically modified to express chimeric antigen receptors (CARs) represents an innovative approach. Here we investigated the targeting of the interleukin three receptor alpha (IL3RA; CD123) molecule, which is overexpressed on AML bulk population, CD34(+) leukaemia progenitors, and leukaemia stem cells (LSC) compared to normal haematopoietic stem/progenitor cells (HSPCs), and whose overexpression is associated with poor prognosis. Cytokine-induced killer (CIK) cells were transduced with SFG-retroviral-vector encoding an anti-CD123 CAR. Transduced cells were able to strongly kill CD123(+) cell lines, as well as primary AML blasts. Interestingly, secondary colony experiments demonstrated that anti-CD123.CAR preserved in vitro HSPCs, in contrast to a previously generated anti-CD33.CAR, while keeping an identical cytotoxicity profile towards AML. Furthermore, limited killing of normal monocytes and CD123-low-expressing endothelial cells was noted, thus indicating a low toxicity profile of the anti-CD123.CAR. Taken together, our results indicate that CD123-specific CARs strongly enhance anti-AML CIK functions, while sparing HSPCs and normal low-expressing antigen cells, paving the way to develop novel immunotherapy approaches for AML treatment.

Differences in signaling through the B-cell leukemia oncoprotein CRLF2 in response to TSLP and through mutant JAK2

Approximately 10% of B-cell acute lymphoblastic leukemias (B-ALLs) overexpress the cytokine receptor subunit CRLF2, which may confer a poor prognosis. CRLF2 binds its ligand thymic stromal lymphopoietin (TSLP) as a heterodimer with IL7R. Subsets of CRLF2-overexpressing B-ALLs also have a gain-of-function CRLF2 F232C mutation or activating mutations in JAK2. Whether these mutant alleles confer differences in signaling has not been addressed. Through a domain mutation analysis, we demonstrate a distinct dependence on the CRLF2 intracellular tyrosine Y368 in signaling by CRLF2 F232C, but not signaling induced by TSLP or through CRLF2/mutant JAK2. In contrast, CRLF2 signaling in each context is strictly dependent on both the CRLF2 box1 domain and the intracellular tryptophan W286. Using a global quantitative analysis of tyrosine phosphorylation induced by TSLP, we previously identified TSLP-induced phosphorylation of multiple kinases implicated in B-cell receptor signaling, including Lyn, Btk, Hck, Syk, MAPK8, MAPK9, and MAPK10. We now demonstrate that cells dependent on CRLF2/mutant JAK2 have reduced phosphorylation at these targets, suggesting that the kinases promote TSLP-mediated proliferation but serve as negative regulators of CRLF2/mutant JAK2 signaling. Thus, targetable nodes downstream of CRLF2 differ based on the presence or absence of additional mutations in CRLF2 signaling components.

Mitochondrial dysfunction and biogenesis: do ICU patients die from mitochondrial failure?

Mitochondrial functions include production of energy, activation of programmed cell death, and a number of cell specific tasks, e.g., cell signaling, control of Ca²⁺ metabolism, and synthesis of a number of important biomolecules. As proper mitochondrial function is critical for normal performance and survival of cells, mitochondrial dysfunction often leads to pathological conditions resulting in various human diseases. Recently mitochondrial dysfunction has been linked to multiple organ failure (MOF) often leading to the death of critical care patients. However, there are two main reasons why this insight did not generate an adequate resonance in clinical settings. First, most data regarding mitochondrial dysfunction in organs susceptible to failure in critical care diseases (liver, kidney, heart, lung, intestine, brain) were collected using animal models. Second, there is no clear therapeutic strategy how acquired mitochondrial dysfunction can be improved. Only the benefit of such therapies will confirm the critical role of mitochondrial dysfunction in clinical settings. Here we summarized data on mitochondrial dysfunction obtained in diverse experimental systems, which are related to conditions seen in intensive care unit (ICU) patients. Particular attention is given to mechanisms that cause cell death and organ dysfunction and to prospective therapeutic strategies, directed to recover mitochondrial function. Collectively the data discussed in this review suggest that appropriate diagnosis and specific treatment of mitochondrial dysfunction in ICU patients may significantly improve the clinical outcome.

Role of Ras/Raf/MEK/ERK signaling in physiological hematopoiesis and leukemia development

Recent research on hematological malignancies has shown that malignant cells often co-opt physiological pathways to promote their growth and development. Bone marrow homeostasis requires a fine balance between cellular differentiation and self-renewal; cell survival and apoptosis; and cellular proliferation and senescence. The Ras/Raf/MEK/ERK pathway has been shown to be important in regulating these biological functions. Moreover, the Ras/Raf/MEK/ERK pathway has been estimated to be mutated in 30% of all cancers, thus making it the focus of many scientific studies which have lead to a deeper understanding of cancer development and help to elucidate potential weaknesses that can be targeted by pharmacological agents [1]. In this review, we specifically focus on the role of this pathway in physiological hematopoiesis and how augmentation of the pathway may lead to hematopoietic malignancies. We also discuss the challenges and success of targeting this pathway.

Flow cytometric analysis of CD123 is useful for immunophenotyping classical Hodgkin lymphoma

Although the diagnosis of classical Hodgkin lymphoma (CHL) is traditionally made morphologically in tissue sections, it is now possible to diagnose CHL by flow cytometry (FC). In an effort to identify additional antigens on Hodgkin and Reed-Sternberg (HRS) cells that might be useful for immunophenotyping this lymphoma by FC, we examined the expression of CD123 (α chain of the IL-3R) on HRS cells and compared this with the expression of CD123 in other lymph node samples (372 tissue specimens, including 98 reactive and 274 neoplastic cases), using a nine-color FC reagent combination including anti-CD123. CD123 was found to be expressed on the majority of HRS cell populations (59% of 59 CHL lymph nodes examined), rarely on B-cell non-Hodgkin lymphomas (NHLs) (3 of 3 hairy cell leukemia cases, 3 of 29 chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) cases, 1 of 55 large B-cell lymphoma cases, but not on 95 other B-cell NHL examined), and in none of the 16 T-cell NHL cases examined. In reactive lymph nodes, CD123 expression was largely limited to plasmacytoid dendritic cells and rare histiocyte populations that can readily be distinguished from HRS populations. As the expression of this antigen is shown to be relatively limited in B- and T-NHL and in reactive lymph node populations, assessment of CD123 expression is useful for supporting the FC diagnosis of CHL.

The role of the GPR91 ligand succinate in hematopoiesis

Regulation of cellular metabolism by the citric acid cycle occurs in the mitochondria. However, the citric acid cycle intermediate succinate was shown recently to be a ligand for the G-protein-coupled receptor GPR91. Here, we describe a role for succinate and its receptor in the stimulation of hematopoietic progenitor cell (HPC) growth. GPR91 mRNA and protein expression were detected in human bone marrow CD34+ progenitor cells, as well as in erythroid and megakaryocyte cultures and the erythroleukemic cell line TF-1. Treatment of these cell cultures with succinate resulted in increased proliferation rates. The proliferation response of TF-1 cells was pertussis toxin (PTX)-sensitive, suggesting a role for Gi signaling. Proliferation was also blocked when TF-1 cells were transfected with small interfering RNA specific for GPR91. Succinate stimulated activation of the Erk MAPK pathway and inositol phosphate accumulation in a PTX-sensitive manner. Pretreatment of TF-1 cells with the Erk1/2 kinase (MEK) inhibitor PD98059 blocked the proliferation response. Succinate treatment additionally protected TF-1 cells from cell death induced by serum deprivation. Finally, in vivo administration of succinate was found to elevate the levels of hemoglobin, platelets, and neutrophils in a mouse model of chemotherapy-induced myelosuppression. These results suggest that succinate-GPR91 signaling is capable of promoting HPC development.

Acute myeloid leukemia-targeted toxin activates both apoptotic and necroptotic death mechanisms

Background

Acute myelogenous leukemia (AML) is the second most common leukemia with approximately 13,410 new cases and 8,990 deaths annually in the United States. A novel fusion toxin treatment, diphtheria toxin GM-CSF (DT-GMCSF) has been shown to selectively eliminate leukemic repopulating cells that are critical for the formation of AML. We previously showed that DT-GMCSF treatment of U937 cells, an AML cell line, causes activation of caspases and the induction of apoptosis.

Methods and Findings

In this study we further investigate the mechanisms of cell death induced by DT-GMCSF and show that, in addition to the activation of caspase-dependent apoptosis, DT-GMCSF also kills AML cells by simultaneously activating caspase-independent necroptosis. These mechanisms depend on the ability of the targeted toxin to inhibit protein synthesis, and are not affected by the receptor that is targeted or the mechanism through which protein synthesis is blocked.

Conclusions

We conclude that fusion toxin proteins may be effective for treating AML cells whether or not they are defective in apoptosis.

Abnormal surface markers expression on bone marrow CD34+ cells and correlation with disease activity in patients with systemic lupus erythematosus

Defects of hematopoietic stem cells (HSCs) have been suggested to contribute to the development of systemic lupus erythematosus (SLE). The aim of this study was to investigate the phenotypic characteristics of bone marrow (BM) CD34(+) cells in patients with SLE and its relationship with SLE disease activity. Ten SLE patients and 10 healthy subjects were recruited and their BM CD34(+) cells were analyzed by flow cytometric analysis with CD45/SSC gating for the expression of CD90, CD95, CD117, CD123, CD164, CD166, FAS-L, and HLA-DR. The percentage of BM CD34(+) cells was significantly decreased in active SLE patients (1.48 +/- 0.41%, n = 7) compared to the healthy controls (2.31 +/- 0.75%, n = 10, p < 0.01), but no significant difference was found between the inactive patients (2.04 +/- 0.44%, n = 3) and the controls. The expression of CD95, CD123, and CD166 on BM CD34(+) cells were significantly increased in SLE patients (48.31 +/- 10.59%, 44.9 +/- 21.5%, 30.9 +/- 19.54%, respectively, n = 10) when compared with the control subjects (24.33 +/- 11.1%, 19.5 +/- 4.4%, 10.7 +/- 5.5%, respectively, n = 10, p < 0.05). The increased CD123 expression was negatively correlated with the number of peripheral white blood cells (r = -0.700, p < 0.05, n = 10). The percentage of CD166 expression was found significantly correlated with the index of SLE disease activity (r = 0.472, p < 0.05, n = 10) and 24 h proteinuria (r = 0.558, p < 0.05, n = 10), but negatively correlated with serum C3 level (r = -0.712, p < 0.01, n = 10). Our study found that the surface marker expression of CD95, CD123, and CD166 on BM CD34(+) cells were significantly increased in patients. This supports the hypothesis that there are abnormalities of the HSC in SLE. Since CD166 and CD123 correlated with the overall lupus activity, their role as a biomarker of inflammatory disease activity also requires further study.

Cytokines in the differentiation therapy of leukemia: from laboratory investigations to clinical applications

Differentiation therapy of leukemia is the treatment of leukemia cells with biological or chemical agents that induce the terminal differentiation of the cancer cells. It is regarded as a novel and targeted approach to leukemia treatment, based on our better understanding of the hematopoietic process and the mechanisms of its deregulation during leukemogenesis. Clinically, differentiation therapy has been most successful in acute promyelocytic leukemia using all-trans-retinoic acid as the inducer, either alone or in combination with chemotherapy. This review presents evidence that a number of hematopoietic cytokines play important roles in both normal and aberrant hematopoietic processes. In vitro laboratory investigations in the past two decades using well-characterized myeloid leukemic cell lines and primary blast cells from leukemia patients have revealed that many hematopoietic cytokines can trigger lineage-specific differentiation of leukemia cells, which may have important implications in the clinical setting. Moreover, our current understanding of cytokine interactions and the molecular mechanisms of cytokine-induced leukemic cell differentiation will be discussed in the light of recent findings. Finally, ways in which laboratory research on cytokines in the differentiation therapy of leukemia can lead to the improved design of protocols for future clinical applications to leukemia therapy will also be addressed.

Prospective isolation and global gene expression analysis of the erythrocyte colony-forming unit (CFU-E)

The erythrocyte colony-forming unit (CFU-E) is a rare bone marrow (BM) progenitor that generates erythrocyte colonies in 48 hours. The existence of CFU-Es is based on these colonies, but CFU-Es have not been purified prospectively by phenotype. We have separated the "nonstem," "nonlymphoid" compartment (lineage marker [lin]-c-Kit+Sca-1-IL-7Ralpha-) into interleukin 3 receptor alpha negative (IL-3Ralpha-) and IL-3Ralpha+ subsets. Within IL-3Ralpha- but not IL-3Ralpha+ cells we have identified TER119-CD41-CD71+ erythrocyte-committed progenitors (EPs). EPs generate CFU-E colonies at about 70% efficiency and generate reticulocytes in vivo. Depletion of EPs from BM strongly reduces CFU-E frequencies. EPs lack potential for erythrocyte burst-forming unit, megakaryocyte, granulocyte (G), and monocyte (M) colonies, and for spleen colony-forming units. Chronically suppressed erythropoiesis in interferon consensus sequence-binding protein (ICSBP)-deficient BM is associated with reduced frequencies of both the EP population and CFU-E colonies. During phenylhydrazine-induced acute anemia, numbers of both the EP population and CFU-E colonies increase. Collectively, EPs (lin-c-Kit+Sca-1-IL-7Ralpha-IL-3Ralpha-CD41-CD71+) account for most, if not all, CFU-E activity in BM. As a first molecular characterization, we have compared global gene expression in EPs and nonerythroid GM progenitors. These analyses define an erythroid progenitor-specific gene expression pattern. The prospective isolation of EPs is an important step to analyze physiologic and pathologic erythropoiesis.

Signaling through JAK2-STAT5 pathway is essential for IL-3-induced activation of microglia

Microglia, the resident macrophage of the brain, mediates immune and inflammatory responses in the central nervous system (CNS). Activation of microglia and secretion of inflammatory cytokines associate with the pathogenesis of CNS diseases, including multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease, prion disease, and AIDS dementia. Microbial pathogens, cytokines, chemokines, and costimulatory molecules are potent inducers of microglial activation in the CNS. Signaling through its receptor, IL-3 induces the activation of JAK-STAT and MAP kinase pathways in microglial cells. In this study, we found that in vitro treatment of EOC-20 microglial cells with tyrphostin AG490 blocked IL-3-induced tyrosine phosphorylation of JAK2, STAT5A, and STAT5B signaling proteins. Stable transfection of EOC-20 cells with a dominant negative JAK2 mutant also blocked IL-3-induced tyrosine phosphorylation of JAK2, STAT5A, and STAT5B in microglia. The blockade of JAK2-STAT5 pathway resulted in a decrease in IL-3-induced proliferation and expression of CD40 and major histocompatibility complex class II molecules in microglia. These findings highlight the fact that JAK2-STAT5 signaling pathway plays a critical role in mediating IL-3-induced activation of microglia.

Granulocyte-macrophage colony-stimulating factor and interleukin-3 induce cell cycle progression through the synthesis of c-Myc protein by internal ribosome entry site-mediated translation via phosphatidylinositol 3-kinase pathway in human factor-dependent leukemic cells

To investigate the roles of c-myc during hematopoietic proliferation induced by growth factors, we used factor-dependent human leukemic cell lines (MO7e and F36P) in which proliferation, cell cycle progression, and c-Myc expression were strictly regulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3). In these cell lines, both c-myc mRNA and c-Myc protein stability were not affected by GM-CSF and IL-3, suggesting a regulation of c-Myc protein at the translational level. However, rapamycin, an inhibitor of cap-dependent translation, did not block c-myc induction by GM-CSF and IL-3. Thus, we studied the cap-independent translation, the internal ribosome entry site (IRES), during c-Myc protein synthesis using dicistronic reporter gene plasmids and found that GM-CSF and IL-3 activated c-myc IRES to initiate translation. c-myc IRES activation, c-Myc protein expression, and cell cycle progression were all blocked by a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002. In another factor-dependent cell line, UT7, we observed the cell cycle progression and up-regulation of c-Myc protein, c-myc mRNA, and c-myc IRES simultaneously, which were all inhibited by LY294002. Results indicate that hematopoietic growth factors induce cell cycle progression via IRES-mediated translation of c-myc though the PI3K pathway in human factor-dependent leukemic cells.

IL-3 acts directly on osteoclast precursors and irreversibly inhibits receptor activator of NF-kappa B ligand-induced osteoclast differentiation by diverting the cells to macrophage lineage

Osteoclasts, the multinucleated cells that resorb bone, differentiate from hemopoietic precursors of the monocyte/macrophage lineage in the presence of M-CSF and receptor activator of NF-kappaB ligand (RANKL). In this study we investigated the role of IL-3 in osteoclast differentiation. We show here that IL-3, a cytokine secreted by activated T lymphocytes, inhibits RANKL-induced osteoclast differentiation by a direct action on early osteoclast precursors. Anti-IL-3 Ab neutralized the inhibitory effect of IL-3 on osteoclast differentiation. In addition, IL-3 inhibits TNF-alpha-induced osteoclast differentiation in bone marrow-derived macrophages. However, IL-3 has no inhibitory effect on mature osteoclasts. In osteoclast precursors, IL-3 prevents RANKL-induced nuclear translocation of NF-kappaB by inhibiting the phosphorylation and degradation of IkappaB. RT-PCR analysis revealed that IL-3 down-regulated c-Fos transcription. Interestingly, the osteoclast precursors in the presence of IL-3 showed strong expression of macrophage markers such as Mac-1, MOMA-2, and F4/80. Furthermore, the inhibitory effect of IL-3 on osteoclast differentiation was irreversible, and the osteoclast precursors preincubated in IL-3 were resistant to RANKL action. Thus, our results reveal for the first time that IL-3 acts directly on early osteoclast precursors and irreversibly blocks RANKL-induced osteoclast differentiation by diverting the cells to macrophage lineage.

Inhibition of the transforming activity of FLT3 internal tandem duplication mutants from AML patients by a tyrosine kinase inhibitor

FLT3 is a receptor tyrosine kinase that may play a role in a significant proportion of leukemias. In addition to being aberrantly expressed in acute leukemias, activating mutations of the FLT3 gene have been found in patients with AML, myelodysplastic syndrome (MDS) and more rarely, ALL. Internal tandem duplications (ITDs) of the FLT3 gene have been detected in 17-34% of patients with AML and portend a poor prognosis for these patients. FLT3 receptors containing ITD mutations (FLT3/ITDs) are constitutively activated in the absence of FLT3 ligand (FL) stimulation leading to the activation of downstream signaling proteins, including ERK and STAT 5. FLT3 activity, therefore, is a logical target for therapeutic intervention. AG1296 is a tyrosine kinase inhibitor of the tyrphostin class that shows inhibitory activity for wild-type FLT3, in addition to the PDGF and c-KIT receptors. We examined the inhibitory effects of AG1296 on FLT3/ITDs isolated from AML patients in the IL-3-dependent cell line, Ba/F3, as well as in primary leukemia samples from AML patients. Immunoprecipitation and immunoblotting analyses demonstrated that FLT3/ITDs were constitutively phosphorylated in the absence of FL. The auto-phosphorylation of FLT3/ITDs was inhibited by AG1296 with an IC(50) of approximately 1 microM. FLT3/ITDs were associated with constitutive phosphorylation of ERK, STAT 5A, STAT 5B, CBL, VAV and SHP2 in Ba/F3 cells. The phosphorylation of these downstream signaling molecules was suppressed in a dose-responsive fashion by AG1296. AG1296 inhibited IL-3 independent growth and induced apoptosis in Ba/F3 cells transformed by FLT3/ITDs. AG1296 also inhibited FLT3 auto-phosphorylation, and induced a cytotoxic effect, in primary AML cells. These findings suggest that inhibiting the activity of FLT3 may have a therapeutic value in some leukemias expressing FLT3/ITDs.

Zidovudine (AZT) treatment suppresses granulocyte-monocyte colony stimulating factor receptor type alpha (GM-CSFR alpha) gene expression in murine bone marrow cells

In vitro exposure of murine bone marrow cells to increasing concentrations of zidovudine (AZT, 0.1-50 microM) had a concentration dependent suppressive effect on the growth of granulocyte-monocyte colony forming unit (CFU-GM) derived colonies. In our previous published study, the mechanism of AZT-induced suppression of erythroid colony forming unit (CFU-E) derived colonies was linked to a decrease in erythropoitin receptor (Epo-R) gene expression. In this study, we have observed that AZT exposure also induced a concentration dependent suppressive effect (35-90%) on GM-CSF receptor type alpha (GM-CSFR alpha) gene expression. The suppression of GM-CSFR alpha mRNA expression was specific, since AZT caused a much lower decrease (15-22%) on the IL-3 receptor type alpha (IL-3R alpha) message level, and had an insignificant effect on glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and c-myc message levels. Erythropoietin (Epo) therapy has been used for reversal of AZT induced erythroid toxicity. Exposure to increasing concentrations (10-500 U/ml) of GM-CSF was unable to override the suppressive effect of AZT on CFU-GM derived colonies, however, treatment in combination with IL-3 (10-250 U/ml) ameliorated the suppressive effects of AZT on CFU-GM and on GM-CSFR alpha and IL-3R alpha gene expression. These findings suggest a mechanism via which AZT may suppress granulocyte-monocyte specific differentiation in murine bone marrow cells. These data also suggest that a combination of GM-CSF and IL-3 may be a superior therapeutic intervention for AZT-induced neutropenia.

Role of Bax in apoptosis of IL-3-dependent cells

IL-3 removal was reported to induce membrane association of the apoptotic effector Bax. This report demonstrates that IL-3-dependent cells from Bax-null mice failed to activate caspases after IL-3 removal and survived in an 10-fold lower concentration of IL-3. As IL-3 removal also down-regulates expression of Bcl-X, we examined the relationship between Bcl-X decrease and Bax membrane association. IL-3 removal from BAF-3 cells, followed by sorting caspase-active and caspase-inactive populations, showed that both expressed similar levels of Bcl-X. Inhibition of IL-3 signalling via PI-3 kinase and MEK1/2 resulted in cells with minimal Bcl-X, which remained viable with soluble Bax. However BAF-3-derived cells, which maintained Bcl-X expression without IL-3, also remained viable with soluble Bax on IL-3 removal. Therefore a decrease in Bcl-X is necessary, though not sufficient, for Bax membrane association on IL-3 removal. In contrast, treatment of BAF-3 cells with hydroxyurea induced apoptosis in the absence of a Bcl-X decrease. Furthermore, IL-3-dependent cells from Bax-null mice activated caspases after hydroxyurea treatment and show the same sensitivity to a variety of cytotoxic drugs. Thus, apoptosis after IL-3 removal requires a decrease in Bcl-X and Bax membrane association, whereas that induced by cytotoxic drugs does not.

Inhibition of FLT3-mediated transformation by use of a tyrosine kinase inhibitor

FLT3 is a member of the type III receptor tyrosine kinase (RTK) family. These receptors all contain an intrinsic tyrosine kinase domain that is critical to signaling. Aberrant expression of the FLT3 gene has been documented in both adult and childhood leukemias including AML, ALL and CML. In addition, 17-27% of pediatric and adult patients with AML have small internal tandem duplication mutations in FLT3. Patients expressing the mutant form of the receptor have been shown to have a decreased chance for cure. Our previous study, using a constitutively activated FLT3, demonstrated transformation of Ba/F3 cells and leukemic development in an animal model. Thus, there is accumulating evidence for a role for FLT3 in human leukemias. This has prompted us to search for inhibitors of FLT3 as a possible therapeutic approach in these patients. AG1296 is a compound of the tyrphostin class that is known to selectively inhibit the tyrosine kinase activity of the PDGF and KIT receptors. Since FLT3 is a close relative of KIT, we wanted to test the possible inhibitory activity of AG1296 on FLT3. In transfected Ba/F3 cells, AG1296 selectively and potently inhibited autophosphorylation of FL-stimulated wild-type and constitutively activated FLT3. Treatment by AG1296 abolished IL-3-independent proliferation of Ba/F3 cells expressing the constitutively activated FLT3 and thus, reversed the transformation mediated by activated FLT3. Inhibition of FLT3 activity by AG1296 in cells transformed by activated FLT3 resulted in apoptotic cell death, with no deleterious effect on their parental counterparts. Addition of IL-3 rescued the growth of cells expressing activated FLT3 in the presence of AG1296. This demonstrates that the inhibition is specific to the FLT3 pathway in that it leaves the kinases of the IL-3 pathway and other kinases further downstream involved in proliferation intact. Several proteins phosphorylated by the activated FLT3 signaling pathway, including STAT 5A, STAT 5B and CBL, were no longer phosphorylated when these cells were treated with AG1296. The activity against FLT3 suggests a potential therapeutic application for AG1296 or similar drugs in the treatment of leukemias involving deregulated FLT3 tyrosine kinase activity and as a tool for studying the biology of FLT3.

Neutralizing monoclonal antibodies can potentiate IL-5 signaling

IL-5 is a major determinant in the survival, differentiation and effector-functions of eosinophils. It mediates its effect upon binding and activation of a membrane bound receptor (R), composed of a ligand-specific alpha-chain and a beta-chain, shared with the receptors for IL-3 and granulocyte-macrophage colony-stimulating factor. We have generated and mapped the epitopes of three monoclonal antibodies (mAb) directed against this cytokine: the strong neutralizing mAb 5A5 and 1E1, and the very weak neutralizing mAb H30. We found that H30 as well as 5A5 can increase proliferation above the level induced by human (h)IL-5 alone, in a JAK-2-dependent manner, and at every sub-optimal hIL-5 concentration analyzed. This effect is dependent on mAb-mediated cross-linking of IL-5R complexes, and is only observed on cell lines expressing a hybrid human/mouse IL-5Ralpha-chain. We discuss these findings in view of the stoichiometric and topological requirements for an activated IL-5R. Since humanized anti-IL-5 mAb are currently in clinical testing, our findings imply that such mAb should be carefully evaluated for their potentiating effects.

PAL31, a nuclear protein required for progression to the S phase

PAL31 is a nuclear protein expressed by various cell types. In the present study, the expression and function of PAL31 were examined in the cytokine-regulated growth of T and B cell lines. Treatment of the cells with mitogens [ovine PRL, recombinant rat placental lactogen-I (PL-I) and human IL-3] caused a dose-dependent increase in the expression of PAL31 mRNA in the PRL-dependent cell line Nb2, and IL-3 dependent cell line BaF3. A time-course study on synchronized Nb2 cells revealed that the expression of PAL31 is specific to the late G1 and S phases. Immunocytological studies revealed that PAL31 accumulates in the nuclei at the S phase. Furthermore, the antisense oligonucleotide for PAL31 severely inhibited the proliferation of Nb2 cells by inhibiting cells progressing to the S phase. Thus, PAL31 is a nuclear protein associated with cell cycle progression.

Constitutive activation of FLT3 stimulates multiple intracellular signal transducers and results in transformation

Aberrant expression of FLT3 has been found in most cases of B-lineage ALL and AML, and subsets of T cell ALL, CML in blast crisis and CLL. In 20% of patients with AML the receptor has small internal tandem duplications of the juxtamembrane region which appear to contitutively activate the receptor. To investigate whether FLT3 activation could play a role in leukemia, we generated a constitutively activated FLT3 by fusing its cytoplasmic domain to the helix-loop-helix domain of TEL in analogy to the fusion that occurs with TEL-PDGFR in CMML. In vitro translation assays demonstrated oligomerization and intrinsic tyrosine kinase activity of the TEL-FLT3 chimeric receptor. Constitutively activated TEL-FLT3 conferred IL-3 independence and long-term proliferation to transfected Ba/F3 cells. Immunoblot analyses showed that JAK 2, STAT 3, STAT 5a, STAT 5b and CBL were tyrosine-phosphorylated in TEL-FLT3 expressing Ba/F3 cells in the absence of IL-3. These data suggest a possible role for the JAK/STAT pathway in FLT3 signaling. Transplantation of TEL-FLT3 expressing Ba/F3 cells into syngeneic mice caused mortality in all mice by 3 weeks after injection. Histopathologic analysis demonstrated a massive infiltration of mononuclear cells in the liver, spleen and bone marrow. The mimicking of naturally occurring TEL fusions provides an approach to assess aspects of the biology of activated FLT3, or other receptor-type tyrosine kinases (RTKs) in leukemic transformation.

The interleukin-3 receptor alpha chain is a unique marker for human acute myelogenous leukemia stem cells

Recent studies suggest that the population of malignant cells found in human acute myelogenous leukemia (AML) arises from a rare population of leukemic stem cells (LSCs). LSCs have been documented for nearly all AML subtypes and have been phenotypically described as CD34+/CD38- or CD34+/HLA-DR-. Given the potentially critical role of these primitive cells in perpetuating leukemic disease, we sought to further investigate their molecular and cellular characteristics. Flow cytometric studies using primary AML tissue showed that the interleukin-3 receptor alpha chain (IL-3Ralpha or CD123) was strongly expressed in CD34+/CD38- cells (98 +/- 2% positive) from 16 of 18 primary specimens. Conversely, normal bone marrow derived CD34+/CD38- cells showed virtually no detectable expression of the CD123 antigen. To assess the functional role of IL-3Ralpha positive cells, purified CD34+/CD123+ leukemia cells were transplanted into immune deficient NOD/SCID mice. These experiments showed that CD123+ cells were competent to establish and maintain leukemic populations in vivo. To begin to elucidate a biological role for CD123 in leukemia, primary AML samples were analyzed with respect to signal transduction activity in the MAPK, Akt, and Stat5 pathways. Phosphorylation was not detected in response to IL-3 stimulation, thereby suggesting CD123 is not active in conventional IL-3-mediated signaling. Collectively, these data indicate that CD123 represents a unique marker for primitive leukemic stem cells. Given the strong expression of this receptor on LSCs, we propose that targeting of CD123 may be a promising strategy for the preferential ablation of AML cells.

Interleukin-3 and stress

The importance of cytokines as mediators in numerous physiologic and pathologic processes became apparent in the early seventies. In a relatively short period of time the number of characterized and functionally defined interleukins increased rapidly. Concomitantly, the understanding of their role in various important reactions in different systems of the organism in general, and in the interaction between the immune, central nervous and neuroendocrine systems in particular increased. IL-3 is one of the cytokines of great significance for hematopoiesis. In addition, it was shown that interleukin-3 (IL-3) participates in the response of the organism to various types of stress. Surprisingly enough, the reports on its production and activation during or following stress are rather scarce. Therefore, the purpose of this review is to try and compile the information on IL-3 and its role in different types of stress, and also to contribute our own modest experience on the subject.

The differential time-course of extracellular-regulated kinase activity correlates with the macrophage response toward proliferation or activation

Bone marrow-derived macrophages proliferate in response to specific growth factors, including macrophage colony-stimulating factor (M-CSF). When stimulated with activating factors, such as lipopolysaccharide (LPS), macrophages stop proliferating and produce proinflammatory cytokines. Although triggering opposed responses, both M-CSF and LPS induce the activation of extracellular-regulated kinases (ERKs) 1 and 2. However, the time-course of ERK activation is different; maximal activation by M-CSF and LPS occurred after 5 and 15 min of stimulation, respectively. Granulocyte/macrophage colony-stimulating factor, interleukin 3, and TPA, all of which induced macrophage proliferation, also induced ERK activity, which was maximal at 5 min poststimulation. The use of PD98059, which specifically blocks ERK 1 and 2 activation, demonstrated that ERK activity was necessary for macrophage proliferation in response to these factors. The treatment with phosphatidylcholine-specific phospholipase C (PC-PLC) inhibited macrophage proliferation, induced the expression of cytokines, and triggered a pattern of ERK activation equivalent to that induced by LPS. Moreover, PD98059 inhibited the expression of cytokines induced by LPS or PC-PLC, thus suggesting that ERK activity is also required for macrophage activation by these two agents. Activation of the JNK pathway did not discriminate between proliferative and activating stimuli. In conclusion, our results allow to correlate the differences in the time-course of ERK activity with the macrophagic response toward proliferation or activation.

Opposing effects of engagement of integrins and stimulation of cytokine receptors on cell cycle progression of normal human hematopoietic progenitors

We evaluated the effect of β1-integrin receptor engagement on the expression and activity of cell cycle regulatory proteins in CD34+ cells under conditions that mimic the steady-state marrow microenvironment and in the presence of supraphysiological concentrations of interleukin-3 (IL3) and stem cell factor (SCF). Adhesion of CD34+ progenitors to fibronectin (FN) was similar whether IL3 or SCF was present or absent. Engagement of β1-integrins blocked S-phase entry of CD34+ cells in the absence of IL3 or SCF, whereas addition of 10 ng/mL IL3 or SCF prevented such a block in S-phase entry. In the absence of IL3 or SCF, cyclin-E levels were significantly lower and p27KIP1 levels significantly higher in FN-adherent than in FN-nonadherent cells, or than in poly-L-lysine (PLL)–adherent or (PLL)–nonadherent cells. Cyclin-dependent-kinase (cdk)-2 activity was decreased and levels of cyclin-E–cdk2 complexes were lower in FN-adherent than in PLL-adherent cells. In contrast, cyclin-E and p27KIP1 protein levels and cdk2 activity in cells adherent to FN in the presence of IL3 or SCF were similar to those in PLL-adherent and FN-nonadherent or PLL-nonadherent cells. In conclusion, under physiological cytokine conditions, integrin engagement prevents S-phase entrance of CD34+ cells, which is associated with elevated levels of the contact-dependent cyclin kinase inhibitor p27KIP1. Supraphysiological concentrations of IL3 or SCF prevent p27KIP1 elevation and override the integrin-mediated inhibition of entry into S phase.

Interferon-gamma has dual potentials in inhibiting or promoting cell proliferation

Many cytokines have dual functions of promoting or inhibiting cell proliferation; however, the molecular mechanism of the dual functions of cytokines is not well understood. Under normal conditions, interleukin (IL)-3 is required for Ba/F3 cell proliferation, whereas interferon (IFN)-gamma inhibits Ba/F3 cell proliferation. It is known that Stat1 play a major role in inhibition of cell growth in response to IFN-gamma. We have examined the possibility of whether IFN-gamma can act as a growth-promoting cytokine if the Stat1 function is selectively blocked. We have established variant Ba/F3 cell lines in which Stat1 function is inhibited by a dominant-negative Stat1 mutant. Intriguingly, once Stat1 function is inhibited, IFN-gamma can replace IL-3 acting as an essential growth factor for cell proliferation. To understand the molecular mechanism of regulation of cell proliferation by the cytokines, the signaling pathways and gene induction by IL-3 and IFN-gamma are further studied. Although IL-3 activates mitogenic-activated protein kinase and Akt kinase, IFN-gamma does not. Interestingly, both IL-3 and IFN-gamma induce expression of the c-Myc gene that is not dependent on the Stat1 activity. Expression of a dominant-negative mutant Myc can block IFN-gamma-mediated Ba/F3 cell proliferation, suggesting that c-Myc gene induction is required for IFN-gamma-mediated cell proliferation. These findings suggest that IFN-gamma intrinsically and simultaneously induces specific and conflicting signaling pathways and transcriptional programs that contribute to the potential dual effects of IFN-gamma in promoting or inhibiting cell proliferation.

A Composite C/EBP Binding Site Is Essential for the Activity of the Promoter of the IL-3/IL-5/Granulocyte-Macrophage Colony-Stimulating Factor Receptor βc Gene

The common β-chain (βc) is the main signaling component of the heterodimeric receptors for IL-3, IL-5, and GM-CSF and is primarily expressed on myeloid cells. The proximal βc promoter is regulated by GGAA binding proteins, including PU.1, a hemopoietic specific member of the Ets family. However, it is not likely that PU.1 alone accounts for the myeloid-restricted expression of the βc subunit. Here we describe the identification of a C/EBP binding enhancer that is located 2 kb upstream of the transcription start site. The enhancer contains two elements that bind C/EBPα and -β in U937 cells, while C/EBPε is also bound in extracts of HL-60 cells. Importantly, deletion of the enhancer or mutation of either of one of the C/EBP sites results in a complete loss of promoter activity in cell lines as well as in primary cells, showing the importance of C/EBP members in βc gene activation. We further show that PU.1 has to cooperate with C/EBP proteins to induce βc transcription. Since the βc is already expressed on CD34+ cells, these results demonstrate that both C/EBP and PU.1 are not only important for the myeloid-specific gene regulation at later stages of myeloid differentiation.

Tyrphostin B42 Inhibits IL-12-Induced Tyrosine Phosphorylation and Activation of Janus Kinase-2 and Prevents Experimental Allergic Encephalomyelitis

IL-12 is a macrophage-derived cytokine that induces proliferation, cytokine production, and cytotoxic activity of T and NK cells. Signaling through its receptor, IL-12 induces these cellular responses by tyrosine phosphorylation and activation of Janus kinase-2 (Jak-2), Tyk-2, Stat3, and Stat4. We have used tyrphostin B42 (AG490), a Jak-2 inhibitor, to determine the role of Jak-2 kinase in IL-12 signaling and IL-12-induced T cell functions. Treatment of activated T cells with tyrphostin B42 inhibited the IL-12-induced tyrosine phosphorylation and activation of Jak-2 without affecting Tyk-2 kinase. In contrast, treatment with tyrphostin A1 inhibited the tyrosine phosphorylation of Tyk-2 but not that of Jak-2 kinase. Inhibition of either Jak-2 or Tyk-2 leads to a decrease in the IL-12-induced tyrosine phosphorylation of Stat3, but not of Stat4, protein. While inhibition of Jak-2 lead to programmed cell death, the inhibition of Jak-2 or Tyk-2 resulted a decrease in IFN-γ production. We have further tested the in vivo effects of tyrphostin B42 in experimental allergic encephalomyelitis, a Th1 cell-mediated autoimmune disease. In vivo treatment with tyrphostin B42 decreased the proliferation and IFN-γ production of neural Ag-specific T cells. Treatment of mice with tyrphostin B42 also reduced the incidence and severity of active and passive EAE. These results suggest that tyrphostin B42 prevents EAE by inhibiting IL-12 signaling and IL-12-mediated Th1 differentiation in vivo.

Signal transducer and activator of transcription (STAT)5 activation by BCR/ABL is dependent on intact Src homology (SH)3 and SH2 domains of BCR/ABL and is required for leukemogenesis

Signal transducer and activator of transcription (STAT)5 is constitutively activated in BCR/ ABL-expressing cells, but the mechanisms and functional consequences of such activation are unknown. We show here that BCR/ABL induces phosphorylation and activation of STAT5 by a mechanism that requires the BCR/ABL Src homology (SH)2 domain and the proline-rich binding site of the SH3 domain. Upon expression in 32Dcl3 growth factor-dependent myeloid precursor cells, STAT5 activation-deficient BCR/ABL SH3+SH2 domain mutants functioned as tyrosine kinase and activated Ras, but failed to protect from apoptosis induced by withdrawal of interleukin 3 and/or serum and did not induce leukemia in severe combined immunodeficiency mice. In complementation assays, expression of a dominant-active STAT5B mutant (STAT5B-DAM), but not wild-type STAT5B (STAT5B-WT), in 32Dcl3 cells transfected with STAT5 activation-deficient BCR/ABL SH3+SH2 mutants restored protection from apoptosis, stimulated growth factor-independent cell cycle progression, and rescued the leukemogenic potential in mice. Moreover, expression of a dominant-negative STAT5B mutant (STAT5B-DNM) in 32Dcl3 cells transfected with wild-type BCR/ABL inhibited apoptosis resistance, growth factor-independent proliferation, and the leukemogenic potential of these cells. In retrovirally infected mouse bone marrow cells, expression of STAT5B-DNM inhibited BCR/ABL-dependent transformation. Moreover, STAT5B-DAM, but not STAT5B-WT, markedly enhanced the ability of STAT5 activation-defective BCR/ABL SH3+SH2 mutants to induce growth factor-independent colony formation of primary mouse bone marrow progenitor cells. However, STAT5B-DAM did not rescue the growth factor-independent colony formation of kinase-deficient K1172R BCR/ABL or the triple mutant Y177F+R522L+ Y793F BCR/ABL, both of which also fail to activate STAT5. Together, these data demonstrate that STAT5 activation by BCR/ABL is dependent on signaling from more than one domain and document the important role of STAT5-regulated pathways in BCR/ABL leukemogenesis.

IL-3 and IL-4 Activate Cyclic Nucleotide Phosphodiesterases 3 (PDE3) and 4 (PDE4) by Different Mechanisms in FDCP2 Myeloid Cells

In FDCP2 myeloid cells, IL-4 activated cyclic nucleotide phosphodiesterases PDE3 and PDE4, whereas IL-3, granulocyte-macrophage CSF (GM-CSF), and phorbol ester (PMA) selectively activated PDE4. IL-4 (not IL-3 or GM-CSF) induced tyrosine phosphorylation of insulin-receptor substrate-2 (IRS-2) and its association with phosphatidylinositol 3-kinase (PI3-K). TNF-α, AG-490 (Janus kinase inhibitor), and wortmannin (PI3-K inhibitor) inhibited activation of PDE3 and PDE4 by IL-4. TNF-α also blocked IL-4-induced tyrosine phosphorylation of IRS-2, but not of STAT6. AG-490 and wortmannin, not TNF-α, inhibited activation of PDE4 by IL-3. These results suggested that IL-4-induced activation of PDE3 and PDE4 was downstream of IRS-2/PI3-K, not STAT6, and that inhibition of tyrosine phosphorylation of IRS molecules might be one mechnism whereby TNF-α could selectively regulate activities of cytokines that utilized IRS proteins as signal transducers. RO31-7549 (protein kinase C (PKC) inhibitor) inhibited activation of PDE4 by PMA. IL-4, IL-3, and GM-CSF activated mitogen-activated protein (MAP) kinase and protein kinase B via PI3-K signals; PMA activated only MAP kinase via PKC signals. The MAP kinase kinase (MEK-1) inhibitor PD98059 inhibited IL-4-, IL-3-, and PMA-induced activation of MAP kinase and PDE4, but not IL-4-induced activation of PDE3. In FDCP2 cells transfected with constitutively activated MEK, MAP kinase and PDE4, not PDE3, were activated. Thus, in FDCP2 cells, PDE4 can be activated by overlapping MAP kinase-dependent pathways involving PI3-K (IL-4, IL-3, GM-CSF) or PKC (PMA), but selective activation of PDE3 by IL-4 is MAP kinase independent (but perhaps IRS-2/PI3-K dependent).

A phosphatidylinositol 3-kinase-dependent pathway that differentially regulates c-Raf and A-Raf

Cytokines trigger the rapid assembly of multimolecular signaling complexes that direct the activation of downstream protein kinase cascades. Two protein kinases that have been linked to growth factor-regulated proliferation and survival are mitogen-activated protein/ERK kinase (MEK) and its downstream target Erk, a member of the mitogen-activated protein kinase family. Using complementary pharmacological and genetic approaches, we demonstrate that MEK and Erk activation requires a phosphatidylinositol 3-kinase (PI3-K)-generated signal in an interleukin (IL)-3-dependent myeloid progenitor cell line. Analysis of the upstream pathway leading to MEK activation revealed that inhibition of PI3-K did not block c-Raf activation, whereas MEK activation was effectively blocked under these conditions. Furthermore, agents that elevated cAMP suppressed IL-3-induced c-Raf activation but did not inhibit MEK activation. Because c-Raf activation and MEK activation were inversely affected by PI3-K- and cAMP-dependent pathways, we examined whether IL-3 activated the alternative Raf isoforms A-Raf and B-Raf. Although IL-3 did not activate B-Raf, A-Raf was activated by the cytokine. Moreover, A-Raf activation, like MEK activation, was blocked by inhibition of PI3-K but was insensitive to cAMP. Experiments with dominant negative mutants of the Raf isoforms showed that overexpression of dominant negative c-Raf did not prevent MEK activation. However, dominant negative A-Raf effectively blocked MEK activation, suggesting that activation of the MEK-Erk signaling cascade is mediated through A-Raf. Taken together, these results suggest that IL-3 receptors engage and activate both c-Raf and A-Raf in hemopoietic cells. However, these intermediates are differentially regulated by upstream signaling cascades and selectively coupled to downstream signaling pathways.

H-Ras Is Involved in the Inside-out Signaling Pathway of Interleukin-3–Induced Integrin Activation

The proto-oncogene product, p21ras, has been implicated in the cellular mechanism of adhesion, although its precise role has been controversial. Numerous cytokines and growth-factors activate Ras, which is an important component of their growth-promoting signaling pathways. On the other hand, the role of Ras in cytokine-induced adhesion has not been elucidated. We therefore investigated the function of H-Ras in the inside-out signaling pathway of interleukin-3 (IL-3)–induced integrin activation in the murine Baf3 cell line after transfection of cells with either constitutively active, dominant-negative, or wild-type H-Ras cDNAs. Adhesion of Baf3 cells to fibronectin was induced by IL-3 in a dose-dependent manner via very late antigen-4 (VLA-4; 4β1 integrins) and VLA-5 (5β1 integrins) activation. On the other hand, IL-4 did not induce the adhesion of Baf3 cells to fibronectin, although IL-4 did stimulate the cell proliferation of Baf3 cells. Constitutively active H-Ras–transfected Baf3 cells adhered to fibronectin without IL-3 stimulation through VLA-4 and VLA-5, whereas dominant-negative H-Ras–transfected Baf3 cells showed significantly less adhesion induced by IL-3 compared with wild-type and constitutively active H-Ras–transfected Baf3 cells. Anti-β1 integrin antibody (clone; 9EG7), which is known to change integrin conformation and activate integrins, induced the adhesion of dominant-negative H-Ras–transfected Baf3 cells as much as the other types of H-Ras–transfected Baf3 cells. 8-Br-cAMP, Dibutyryl-cAMP, Ras-Raf-1 pathway inhibitors, and PD98059, a MAPK kinase inhibitor, suppressed proliferation and phosphorylation of MAPK detected by Western blotting with anti–phospho-MAPK antibody, but not adhesion of any type of H-Ras–transfected Baf3 cells, whereas U-73122, a phospholipase C (PLC) inhibitor, suppressed adhesion of these cells completely. These data indicate that H-Ras and PLC, but not Raf-1, MAPK kinase, or the MAPK pathway, are involved in the inside-out signaling pathway of IL-3–induced VLA-4 and VLA-5 activation in Baf3 cells.

H-Ras Is Involved in the Inside-out Signaling Pathway of Interleukin-3–Induced Integrin Activation

The proto-oncogene product, p21ras, has been implicated in the cellular mechanism of adhesion, although its precise role has been controversial. Numerous cytokines and growth-factors activate Ras, which is an important component of their growth-promoting signaling pathways. On the other hand, the role of Ras in cytokine-induced adhesion has not been elucidated. We therefore investigated the function of H-Ras in the inside-out signaling pathway of interleukin-3 (IL-3)–induced integrin activation in the murine Baf3 cell line after transfection of cells with either constitutively active, dominant-negative, or wild-type H-Ras cDNAs. Adhesion of Baf3 cells to fibronectin was induced by IL-3 in a dose-dependent manner via very late antigen-4 (VLA-4; 4β1 integrins) and VLA-5 (5β1 integrins) activation. On the other hand, IL-4 did not induce the adhesion of Baf3 cells to fibronectin, although IL-4 did stimulate the cell proliferation of Baf3 cells. Constitutively active H-Ras–transfected Baf3 cells adhered to fibronectin without IL-3 stimulation through VLA-4 and VLA-5, whereas dominant-negative H-Ras–transfected Baf3 cells showed significantly less adhesion induced by IL-3 compared with wild-type and constitutively active H-Ras–transfected Baf3 cells. Anti-β1 integrin antibody (clone; 9EG7), which is known to change integrin conformation and activate integrins, induced the adhesion of dominant-negative H-Ras–transfected Baf3 cells as much as the other types of H-Ras–transfected Baf3 cells. 8-Br-cAMP, Dibutyryl-cAMP, Ras-Raf-1 pathway inhibitors, and PD98059, a MAPK kinase inhibitor, suppressed proliferation and phosphorylation of MAPK detected by Western blotting with anti–phospho-MAPK antibody, but not adhesion of any type of H-Ras–transfected Baf3 cells, whereas U-73122, a phospholipase C (PLC) inhibitor, suppressed adhesion of these cells completely. These data indicate that H-Ras and PLC, but not Raf-1, MAPK kinase, or the MAPK pathway, are involved in the inside-out signaling pathway of IL-3–induced VLA-4 and VLA-5 activation in Baf3 cells.