Structure of the murine Jak2 protein-tyrosine kinase and its role in interleukin 3 signal transduction

JAK/STAT in leukemia: a clinical update

Over the past three decades, considerable efforts have been expended on understanding the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway in leukemia, following the identification of the JAK2V617F mutation in myeloproliferative neoplasms (MPNs). The aim of this review is to summarize the latest progress in our understanding of the involvement of the JAK/STAT signaling pathway in the development of leukemia. We also attempt to provide insights into the current use of JAK/STAT inhibitors in leukemia therapy and explore pertinent clinical trials in this field.

2022 Cannon lecture: an ode to signal transduction: how the growth hormone pathway revealed insight into height, malignancy, and obesity

Walter Cannon was a highly regarded American neurologist and physiologist with extremely broad interests. In the tradition of Cannon and his broad interests, we discuss our laboratory's multifaceted work in signal transduction over the past 40+ years. We show how our questioning of how growth hormone (GH) in the blood communicates with cells throughout the body to promote body growth and regulate body metabolism led to insight into not only body height but also important regulators of malignancy and body weight. Highlights include finding that 1) A critical initiating step in GH signal transduction is GH activating the GH receptor-associated tyrosine kinase JAK2; 2) GH activation of JAK2 leads to activation of a number of signaling proteins, including STAT transcription factors; 3) JAK2 is autophosphorylated on multiple tyrosines that regulate the activity of JAK2 and recruit signaling proteins to GH/GH receptor/JAK2 complexes; 4) Constitutively activated STAT proteins are associated with cancer; 5) GH activation of JAK2 recruits the adapter protein SH2B1 to GH/GH receptor/JAK2 complexes where it facilitates GH regulation of the actin cytoskeleton and motility; and 6) SH2B1 is recruited to other receptors in the brain, where it enhances satiety, most likely in part by regulating leptin action and neuronal connections of appetite-regulating neurons. These findings have led to increased understanding of how GH functions, as well as therapeutic interventions for certain cancer and obese individuals, thereby reinforcing the great importance of supporting basic research since one never knows ahead of time what important insight it can provide.

Germline-somatic JAK2 interactions are associated with clonal expansion in myelofibrosis

Myelofibrosis is a rare myeloproliferative neoplasm (MPN) with high risk for progression to acute myeloid leukemia. Our integrated genomic analysis of up to 933 myelofibrosis cases identifies 6 germline susceptibility loci, 4 of which overlap with previously identified MPN loci. Virtual karyotyping identifies high frequencies of mosaic chromosomal alterations (mCAs), with enrichment at myelofibrosis GWAS susceptibility loci and recurrently somatically mutated MPN genes (e.g., JAK2). We replicate prior MPN associations showing germline variation at the 9p24.1 risk haplotype confers elevated risk of acquiring JAK2^V617F mutations, demonstrating with long-read sequencing that this relationship occurs in cis. We also describe recurrent 9p24.1 large mCAs that selectively retained JAK2^V617F mutations. Germline variation associated with longer telomeres is associated with increased myelofibrosis risk. Myelofibrosis cases with high-frequency JAK2 mCAs have marked reductions in measured telomere length – suggesting a relationship between telomere biology and myelofibrosis clonal expansion. Our results advance understanding of the germline-somatic interaction at JAK2 and implicate mCAs involving JAK2 as strong promoters of clonal expansion of those mutated clones.

Myelofibrosis is a risk factor for the development of Acute Myeloid Leukaemia. Here, the authors carry out an integrated genomic investigation of 933 myelofibrosis patients, and identified interactions between germline and somatic variation in patients who required haematopoietic cell transplantation.

Targeting Janus Kinase (JAK) for Fighting Diseases: The Research of JAK Inhibitor Drugs

Janus Kinase (JAK), a nonreceptor protein tyrosine kinase, has emerged as an excellent target through research and development since its discovery in the 1990s. As novel small-molecule targeted drugs, JAK inhibitor drugs have been successfully used in the treatment of rheumatoid arthritis (RA), myofibrosis (MF) and ulcerative colitis (UC). With the gradual development of JAK targets in the market, JAK inhibitors have also received very considerable feedback in the treatment of autoimmune diseases such as atopic dermatitis (AD), Crohn's disease (CD) and graft-versus host disease (GVHD). This article reviews the research progress of JAK inhibitor drugs: introducing the existing JAK inhibitors on the market and some JAK inhibitors in clinical trials currently. In addition, the synthesis of various types of JAK inhibitors were summarized, and the effects of different drug structures on drug inhibition and selectivity.

MARCH3 negatively regulates IL-3-triggered inflammatory response by mediating K48-linked polyubiquitination and degradation of IL-3Rα

Interleukin-3 (IL-3) is a hematopoietic growth factor and critical regulator of inflammatory response such as sepsis. IL-3 binds to IL-3 receptor α (IL-3Rα), which is then associated with IL-3Rβ to initiate signaling. How IL-3-triggered physiological and pathological effects are regulated at the receptor level is unclear. Here, we show that the plasma membrane-associated E3 ubiquitin ligase MARCH3 negatively regulates IL-3-triggered signaling. MARCH3 is associated with IL-3Rα, mediates its K48-linked polyubiquitination at K377 and promotes its proteasomal degradation. MARCH3-deficiency promotes IL-3-triggered transcription of downstream effector genes and IL-3-induced expansion of myeloid cells. In the cecal ligation and puncture (CLP) model of sepsis, MARCH3-deficiency aggravates IL-3-ampified expression of inflammatory cytokines, organ damage and inflammatory death. Our findings suggest that regulation of IL-3Rα by MARCH3 plays an important role in IL-3-triggered physiological functions and inflammatory diseases.

IL-3 in the development and function of basophils

The β common chain (βc) cytokine family includes granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3) and IL-5, all of which use βc as key signaling receptor subunit. GM-CSF, IL-3 and IL-5 have specific roles as hematopoietic growth factors. IL-3 binds with high affinity to the IL-3 receptor α (IL-3Rα/CD123) and then associates with the βc subunit. IL-3 is mainly synthesized by different subsets of T cells, but is also produced by several other immune [basophils, dendritic cells (DCs), mast cells, etc.] and non-immune cells (microglia and astrocytes). The IL-3Rα is also expressed by immune (basophils, eosinophils, mast cells, DCs, monocytes, and megacaryocytes) and non-immune cells (endothelial cells and neuronal cells). IL-3 is the most important growth and activating factor for human and mouse basophils, primary effector cells of allergic disorders. IL-3-activated basophils and mast cells are also involved in different chronic inflammatory disorders, infections, and several types of cancer. IL-3 induces the release of cytokines (i.e., IL-4, IL-13, CXCL8) from human basophils and preincubation of basophils with IL-3 potentiates the release of proinflammatory mediators and cytokines from IgE- and C5a-activated basophils. IL-3 synergistically potentiates IL-33-induced mediator release from human basophils. IL-3 plays a pathogenic role in several hematologic cancers and may contribute to autoimmune and cardiac disorders. Several IL-3Rα/CD123 targeting molecules have shown some efficacy in the treatment of hematologic malignancies.

Signaling Pathways That Regulate Normal and Aberrant Red Blood Cell Development

Blood cell development is regulated through intrinsic gene regulation and local factors including the microenvironment and cytokines. The differentiation of hematopoietic stem and progenitor cells (HSPCs) into mature erythrocytes is dependent on these cytokines binding to and stimulating their cognate receptors and the signaling cascades they initiate. Many of these pathways include kinases that can diversify signals by phosphorylating multiple substrates and amplify signals by phosphorylating multiple copies of each substrate. Indeed, synthesis of many of these cytokines is regulated by a number of signaling pathways including phosphoinositide 3-kinase (PI3K)-, extracellular signal related kinases (ERK)-, and p38 kinase-dependent pathways. Therefore, kinases act both upstream and downstream of the erythropoiesis-regulating cytokines. While many of the cytokines are well characterized, the nuanced members of the network of kinases responsible for appropriate induction of, and response to, these cytokines remains poorly defined. Here, we will examine the kinase signaling cascades required for erythropoiesis and emphasize the importance, complexity, enormous amount remaining to be characterized, and therapeutic potential that will accompany our comprehensive understanding of the erythroid kinome in both healthy and diseased states.

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.

Classical and novel GH receptor signaling pathways

In this review, I summarize historical and recent features of the classical pathways activated by growth hormone (GH) through the cell surface GH receptor (GHR). GHR is a cytokine receptor superfamily member that signals by activating the non-receptor tyrosine kinase, JAK2, and members of the Src family kinases. Activation of the GHR engages STATs, PI3K, and ERK pathways, among others, and details of these now-classical pathways are presented. Modulating elements, including the SOCS proteins, phosphatases, and regulated GHR metalloproteolysis, are discussed. In addition, a novel physical and functional interaction of GHR with IGF-1R is summarized and discussed in terms of its mechanisms, consequences, and physiological and therapeutic implications.

Targeting the alpha subunit of IL-3 receptor (CD123) in patients with acute leukemia

The IL-3 alpha chain receptor (CD123) is a cell surface protein that is widely expressed by various subtypes of acute leukemia, including acute myeloid leukemia (AML), acute lymphoblastic leukemia and blastic plasmacytoid dendritic cell neoplasm. Notably, CD123 is preferentially overexpressed in leukemia stem cells (LSC) in contrast to normal hematopoietic stem cells, and this differential expression allows for the selective eradication of LSC and leukemic blasts through therapeutic targeting of CD123, with less impact on hematopoietic cells. The level of CD123 expression in AML correlates with both treatment response and outcomes. Therefore, targeting CD123 represents a promising universal therapeutic target in advanced acute leukemias irrespective of the individual leukemia phenotype. There are currently 31 ongoing clinical trials examining the utility of CD123-based targeted therapies. Here we focus our review on current efforts to target CD123 in acute leukemia through various therapeutic constructs.

Heparanase in the Coagulation System

The hemostatic cascade is initiated by the transmembrane coagulation protein - tissue factor (TF) and eventuates in fibrin formation. Heparanase protein was demonstrated to directly enhance TF activity resulting in increased activation of the coagulation system. In addition, heparanase was found to increase hemostatic system activation via two other mechanisms: up-regulating TF expression in endothelial cells and releasing the protein tissue factor pathway inhibitor (TFPI) from the cell surface. Peptides derived from TFPI-2, a protein similar to TFPI, were shown to inhibit the TF/heparanase complex as well as attenuate sepsis and tumor growth. Increased heparanase procoagulant activity was observed in several clinical settings, including women using oral contraceptives, women at delivery, patients following orthopedic surgery and patients with diabetic foot, shift work female nurses, patients with lung cancer, retinal vein thrombosis and prosthetic heart valve thrombosis. Remarkably, the heparanase profile was significantly different across the tested groups. Inhibition of TF / heparanase interaction may represent a new target for attenuating coagulation, cancer and inflammation.

GM-CSF, IL-3, and IL-5 Family of Cytokines: Regulators of Inflammation

The β common chain cytokines GM-CSF, IL-3, and IL-5 regulate varied inflammatory responses that promote the rapid clearance of pathogens but also contribute to pathology in chronic inflammation. Therapeutic interventions manipulating these cytokines are approved for use in some cancers as well as allergic and autoimmune disease, and others show promising early clinical activity. These approaches are based on our understanding of the inflammatory roles of these cytokines; however, GM-CSF also participates in the resolution of inflammation, and IL-3 and IL-5 may also have such properties. Here, we review the functions of the β common cytokines in health and disease. We discuss preclinical and clinical data, highlighting the potential inherent in targeting these cytokine pathways, the limitations, and the important gaps in understanding of the basic biology of this cytokine family.

GWAS Analysis Indicated Importance of NF-κB Signaling Pathway in Host Resistance Against Motile Aeromonas Septicemia Disease in Catfish

Motile Aeromonas septicemia (MAS) disease caused by a bacterial pathogen, Aeromonas hydrophila, is an emerging but severe disease of catfish. Genetic enhancement of disease resistance is considered to be effective to control the disease. To provide an insight into the genomic basis of MAS disease resistance, in this study, we conducted a genome-wide association study (GWAS) to identify quantitative trait loci (QTL). A total of 1820 interspecific backcross catfish of 7 families were challenged with A. hydrophila, and 382 phenotypic extremes were selected for genotyping with the catfish 690 K SNP arrays. Three QTL on linkage group (LG) 2, 26 and 29 were identified to be significantly associated with MAS resistance. Within these regions, a total of 24 genes had known functions in immunity, 10 of which were involved in NF-κB signaling pathway, suggesting the importance of NF-κB signaling pathway in MAS resistance. In addition, three suggestively significant QTL were identified on LG 11, 17, and 20. The limited numbers of QTL involved in MAS resistance suggests that marker-assisted selection may be a viable approach for catfish breeding.

The inhibitor of interleukin-3 receptor protects against sepsis in a rat model of cecal ligation and puncture

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. There are multiple cytokines involved in the process of sepsis. As an important upstream cytokine in inflammation, Interleukin-3 (IL-3) plays a crucial role during sepsis, however, its exact role is unclear. The purpose of this study is to discuss the role of IL-3 and its receptor in cecal ligation and puncture (CLP)-induced sepsis in a rat model. The Cluster of Differentiation 123 (CD123, IL-3 receptor alpha chain, IL-3Rac) antibody (anti-CD123) was used to directly target IL-3's receptor and alleviate the effect of IL-3 in the CLP + anti-CD123 group during the early stage of sepsis. CLP was performed in the CLP and CLP + anti-CD123 groups. The time points of observation included 12 h, 24 h, and 5d after the operation. The results showed that the rats in the CLP + anti-CD123 group had lower levels of lactate, serum tumor necrosis factor-α (TNF-α), Interleukin-1β (IL-1β), and Interleukin-6 (IL-6), and also exhibited a higher core temperature, mean arterial pressure (MAP), Oxygenation Index (PO₂/FiO₂), and end-tidal carbon dioxide (ETCO₂) and serum Interleukin-10 (IL-10) levels after CLP than those in the CLP group. Additionally, administration of anti-CD123 led to a stable down-regulation of tyrosine phosphorylation of the IL-3 receptor, a decline in phosphorylation of the Janus kinase 2 (JAK2) protein, and the signal transduction and activation of transcription 5 (STAT5) proteins in lung tissues. Meanwhile, the study revealed that treatment of anti-CD123 can markedly attenuate histological damages in lung and kidney tissues, improve sublingual microcirculation, and prolong survival post sepsis. In conclusion, anti-CD123 reduces mortality and alleviates organ dysfunction by restraining the JAK2-STAT5 signaling pathway and reduces serum cytokines in the development of early sepsis in a rat model induced by CLP.

Loss of Jak2 protects cardiac allografts from chronic rejection by attenuating Th1 response along with increased regulatory T cells

Chronic rejection acts as the most formidable obstacle for organ transplantation in clinical settings. Herein we demonstrated in a cardiac transplantation model that blockade of Janus kinase 2 (Jak2) provides protection for cardiac allografts against chronic rejection. Specifically, loss of Jak2 almost completely abolished the production of IFN-γ⁺ Th1 cells, while the percentage of Foxp3⁺ regulatory T cells (Tregs) was significantly increased. As a result, loss of Jak2 significantly prolonged allograft survival (58 ± 30.6 days vs. 7 ± 0.3 days). Particularly, 4 out of 13 Jak2 deficient recipients (30%) showed long-term acceptance of allografts as manifested by the graft survival time > 100 days. Cellular studies revealed that Jak2 deficiency did not impact the intrinsic proliferative capability for CD4⁺ T cells in response to nonspecific polyclonal and allogenic stimulation. Mechanistic studies documented that the impaired Th1 development was caused by the attenuated IFN-γ/STAT1 and IL-12/STAT4 signaling along with repressed expression of Th1 transcription factors T-bet, Hlx and Runx3. However, the IL-2/STAT5 signaling remained intact, which ensured normal Treg development in Jak2^-/- naïve CD4 T cells. Together, our data support that blockade of Jak2 may have therapeutic potential for prevention and treatment of allograft rejection in clinical settings.

CD300c costimulates IgE-mediated basophil activation, and its expression is increased in patients with cow's milk allergy

BACKGROUND

Basophils express high-affinity IgE receptors (FcεRI), which play an essential role in allergic diseases. It is important to characterize new cell-surface receptors that modulate IgE-mediated basophil activation threshold to design promising immunomodulatory therapies.

OBJECTIVES

We sought to analyze the expression of CD300 receptors on human basophils and their implication in IgE-mediated basophil activation processes.

METHODS

Blood samples from healthy subjects and patients with cow's milk allergy were collected through the Basque Biobank under an institutional review board-approved protocol. PBMCs were obtained by means of density centrifugation, basophils were purified with a specific isolation kit, and phenotypic and functional studies were performed by using flow cytometry.

RESULTS

We demonstrate that basophils express the activating receptor CD300c, which is specifically upregulated in response to IL-3. CD300c works as a costimulatory molecule during IgE-mediated basophil activation, as shown by a significant increase in degranulation and cytokine production when basophils are activated in the presence of CD300c cross-linking compared with activation through the IgE/FcεRI axis alone. Coligation of FcεRI and CD300c increased intracellular calcium mobilization and phosphorylation of signaling intermediates evoked only by FcεRI ligation. We show that the natural ligands of CD300c, phosphatidylserine and phosphatidylethanolamine, modulate IgE-mediated basophil activation. Furthermore, we have observed that CD300c expression in children with cow's milk allergy is increased compared with that in healthy control subjects and that the intensity of expression correlates with the severity of the hypersensitivity symptoms.

CONCLUSION

CD300c could be considered a biomarker and therapeutic target in patients with IgE-mediated allergic diseases because it seems to be involved in the modulation of IgE-mediated basophil activation.

Role of the β Common (βc) Family of Cytokines in Health and Disease

The β common ([βc]/CD131) family of cytokines comprises granulocyte macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-3, and IL-5, all of which use βc as their key signaling receptor subunit. This is a prototypic signaling subunit-sharing cytokine family that has unveiled many biological paradigms and structural principles applicable to the IL-2, IL-4, and IL-6 receptor families, all of which also share one or more signaling subunits. Originally identified for their functions in the hematopoietic system, the βc cytokines are now known to be truly pleiotropic, impacting on multiple cell types, organs, and biological systems, and thereby controlling the balance between health and disease. This review will focus on the emerging biological roles for the βc cytokines, our progress toward understanding the mechanisms of receptor assembly and signaling, and the application of this knowledge to develop exciting new therapeutic approaches against human disease.

The Growth Hormone Receptor: Mechanism of Receptor Activation, Cell Signaling, and Physiological Aspects

The growth hormone receptor (GHR), although most well known for regulating growth, has many other important biological functions including regulating metabolism and controlling physiological processes related to the hepatobiliary, cardiovascular, renal, gastrointestinal, and reproductive systems. In addition, growth hormone signaling is an important regulator of aging and plays a significant role in cancer development. Growth hormone activates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway, and recent studies have provided a new understanding of the mechanism of JAK2 activation by growth hormone binding to its receptor. JAK2 activation is required for growth hormone-mediated activation of STAT1, STAT3, and STAT5, and the negative regulation of JAK-STAT signaling comprises an important step in the control of this signaling pathway. The GHR also activates the Src family kinase signaling pathway independent of JAK2. This review covers the molecular mechanisms of GHR activation and signal transduction as well as the physiological consequences of growth hormone signaling.

JAK-2 V617F mutation increases heparanase procoagulant activity

Patients with polycythaemia vera (PV), essential thrombocythaemia (ET) and primary myelofibrosis (PMF) are at increased risk of arterial and venous thrombosis. In patients with ET a positive correlation was observed between JAK-2 V617F mutation, that facilitates erythropoietin receptor signalling, and thrombotic events, although the mechanism involved is not clear. We previously demonstrated that heparanase protein forms a complex and enhances the activity of the blood coagulation initiator tissue factor (TF) which leads to increased factor Xa production and subsequent activation of the coagulation system. The present study was aimed to evaluate heparanase procoagulant activity in myeloproliferative neoplasms. Forty bone marrow biopsies of patients with ET, PV, PMF and chronic myelogenous leukaemia (CML) were immunostained to heparanase, TF and TF pathway inhibitor (TFPI). Erythropoietin receptor positive cell lines U87 human glioma and MCF-7 human breast carcinoma were studied. Heparanase and TFPI staining were more prominent in ET, PV and PMF compared to CML. The strongest staining was in JAK-2 positive ET biopsies. Heparanase level and procoagulant activity were higher in U87 cells transfected to over express JAK-2 V617F mutation compared to control and the effect was reversed using JAK-2 inhibitors (Ruxolitinib, VZ3) and hydroxyurea, although the latter drug did not inhibit JAK-2 phosphorylation. Erythropoietin increased while JAK-2 inhibitors decreased the heparanase level and procoagulant activity in U87 and MCF-7 parental cells. In conclusion, JAK-2 is involved in heparanase up-regulation via the erythropoietin receptor. The present findings may potentially point to a new mechanism of thrombosis in JAK-2 positive ET patients.

Interleukin-3 Prevents Cellular Death Induced by Oxidative Stress in HEK293 Cells

Interleukin-3 (IL-3) is a well-characterized growth factor in hematopoietic cells, but it is also expressed in other cell types with poorly described functions. Many studies have provided evidence that IL-3 plays an important role in cell survival. We have previously shown that IL-3 is able to increase glucose uptake in HEK293 cells, suggesting that this factor requires sustained glucose metabolism to promote cell survival. In this study, we demonstrate that IL-3 contributes to cell survival under oxidative stress, a prominent feature in the pathophysiology of cancer, diabetes, and neurodegenerative diseases, as well as in the aging process. Our results suggest a molecular mechanism that involves signaling pathways mediated by PI-3k/Akt and Erk. Altogether, these findings show an important role for IL-3 in supporting the viability of non-hematopoietic systems. J. Cell. Biochem. 118: 1330-1340, 2017. © 2016 Wiley Periodicals, Inc.

Intracellular Signaling Pathways Involved in Childhood Acute Lymphoblastic Leukemia; Molecular Targets

Acute lymphoblastic leukemia (ALL) is a malignant disease characterized by an uncontrolled proliferation of immature lymphoid cells. ALL is the most common hematologic malignancy in early childhood, and it reaches peak incidence between the ages of 2 and 3 years. The prognosis of ALL is associated with aberrant gene expression, in addition to the presence of numerical or structural chromosomal alterations, age, race, and immunophenotype. The Relapse rate with regard to pharmacological treatment rises in childhood; thus, the expression of biomarkers associated with the activation of cell signaling pathways is crucial to establish the disease prognosis. Intracellular pathways involved in ALL are diverse, including Janus kinase/Signal transducers and transcription activators (JAK-STAT), Phosphoinositide-3-kinase-protein kinase B (PI3K-AKT), Ras mitogen-activated protein kinase (Ras-MAPK), Glycogen synthase kinase-3β (GSK-3β), Nuclear factor-kappa beta (NF-κB), and Hypoxia-inducible transcription factor 1α (HIF-1α), among others. In this review, we present several therapeutic targets, intracellular pathways, and molecular markers that are being studied extensively at present.

Molecular insights into regulation of JAK2 in myeloproliferative neoplasms

The critical role of Janus kinase-2 (JAK2) in regulation of myelopoiesis was established 2 decades ago, but identification of mutations in the pseudokinase domain of JAK2 in myeloproliferative neoplasms (MPNs) and in other hematologic malignancies highlighted the role of JAK2 in human disease. These findings have revolutionized the diagnostics of MPNs and led to development of novel JAK2 therapeutics. However, the molecular mechanisms by which mutations in the pseudokinase domain lead to hyperactivation of JAK2 and clinical disease have been unclear. Here, we describe recent advances in the molecular characterization of the JAK2 pseudokinase domain and how pathogenic mutations lead to constitutive activation of JAK2.

Photoredox catalysis in a complex pharmaceutical setting: toward the preparation of JAK2 inhibitor LY2784544

We report a detailed investigation into the application of visible light-mediated photocatalysis to a challenging bond construction in a complex pharmaceutical target. The optimized reaction allowed the direct coupling of N-methylmorpholine with an unfunctionalized pyridazine in good yield and selectivity, and with high purity of the product isolated via crystallization. The reaction also facilitated the expedient synthesis of a range of analogues via the use of other commercially available N-methyl substituted tertiary amines, and therefore it represents an attractive tool for medicinal chemistry. Furthermore, a number of other interesting photoredox reactions were discovered during the course of this investigation, such as a formal methylation reaction via C-N bond cleavage, functionalization of C-H bonds alpha to amides, and a visible light-mediated iminium ion reduction.

c-Abl activates janus kinase 2 in normal hematopoietic cells

Jak2 is involved in cytokine growth factor-stimulated signal transduction, but the mechanism of its activation is largely unknown. Here, we investigated Jak2 activation in a normal hematopoietic cell line, 32D mouse myeloid cells. The bimolecular fluorescence complementation studies showed that c-Abl formed a stable complex with Jak2 in live cells. Co-immunoprecipitation results showed that c-Abl bound to the βc chain of IL-3/IL-5/GM-CSF receptors. The kinase activities of both c-Abl and Jak2 were stimulated by IL-3 in 32D cells. Decreasing c-Abl protein expression in 32D cells by inducible shRNA decreased Jak2 activity and resulted in the failure of Jak2 activation in response to IL-3. Treatment of IL-3 and serum-starved 32D cells with 1 μM imatinib mysylate inhibited IL-3 stimulated kinase activities of both c-Abl and Jak2. In addition, the kinase-deficient Bcr-Abl mutant (p210K1172R) was defective for activation of Jak2 in 32D cells and impaired IL-3 independent growth, which was rescued by overexpression of c-Abl (+Abl). IL-3 efficiently inhibited apoptosis of 32Dp210K/R+Abl cells induced by imatinib mysylate but not Jak2 kinase inhibitor TG101209. In summary, our findings provide evidence that the kinase function of c-Abl and its C-terminal CT4 region is crucial for its interaction with Jak2 and its activation. c-Abl kinase activity induced by IL-3 is required for IL-3-stimulated Jak2 and Jak1 activation. Our findings reveal a novel regulatory role of c-Abl in Jak2 activation induced by IL-3 cytokine growth factor in 32D hematopoietic cells.

IL-12 is required for mTOR regulation of memory CTLs during viral infection

The induction of functional memory CTLs is a major goal of vaccination against intracellular pathogens. IL-12 is critical for the generation of memory CTLs, and inhibition of mTOR by rapamycin can effectively enhance the memory CTL response. Yet, the role of IL-12 in mTOR’s regulation of memory CTL is unknown. Here, we hypothesized that the immunostimulatory effects of mTOR on memory CTLs requires IL-12 signaling. Our results revealed that rapamycin increased the generation of memory CTLs in vaccinia virus infection, and this enhancement was dependent upon the IL-12 signal. Furthermore, IL-12 receptor deficiency diminished the secondary expansion of rapamycin-regulated memory, and resultant secondary memory CTLs were abolished. Rapamycin enhanced IL-12 signaling by up regulating IL-12 receptor β2 expression and STAT4 phosphorylation in CTLs during early infection. In addition, rapamycin continually suppressed T-bet expression in both WT and IL-12 receptor knockout CTLs. These results indicate an essential role for IL-12 in the regulation of memory CTLs by mTOR, and highlight the importance of considering the interplay between cytokines and adjuvants during vaccine design.

Effects of Jak2 type 1 inhibitors NVP-BSK805 and NVP-BVB808 on Jak2 mutation-positive and Bcr-Abl-positive cell lines

Janus kinases are critical components of signaling pathways that regulate hematopoiesis. Mutations of the non-receptor tyrosine kinase JAK2 are found in many BCR-ABL-negative myeloproliferative neoplasms. Preclinical results support that JAK2 inhibitors could show efficacy in treating chronic myeloproliferative neoplasms. JAK2 has also been postulated to play a role in BCR-ABL signal transduction. Therefore, inhibitors of JAK2 kinases are turning into therapeutic strategies for treatment of chronic myelogenous leukemia (CML). In this study, the effects of two novel JAK2 inhibitors, NVP-BSK805 and NVP-BVB808, have been investigated in cell lines expressing either BCR-ABL or mutant JAK2. Possible synergies between NVP-BSK805/NVP-BVB808 and the kinase inhibitors imatinib and nilotinib were assessed. Proliferation and apoptosis tests with both substances showed response in the following cell lines: CHRF-288-11, SET-2 and UKE-1. All BCR-ABL-positive cell lines showed some reduction in proliferation, but with half-maximal growth-inhibitory values >1 µM. Combination of the JAK2 inhibitors with imatinib and nilotinib showed no significant additive or synergistic effects, although all BCR-ABL-positive cell lines responded well to both CML therapeutic agents. Interestingly, it seemed that the combination of imatinib with NVP-BSK805 had a protective effect on the cells. Combination treatment with nilotinib did not show this effect.

Regulation of monocyte differentiation by specific signaling modules and associated transcription factor networks

Monocyte/macrophages are important players in orchestrating the immune response as well as connecting innate and adaptive immunity. Myelopoiesis and monopoiesis are characterized by the interplay between expansion of stem/progenitor cells and progression towards further developed (myelo)monocytic phenotypes. In response to a variety of differentiation-inducing stimuli, various prominent signaling pathways are activated. Subsequently, specific transcription factors are induced, regulating cell proliferation and maturation. This review article focuses on the integration of signaling modules and transcriptional networks involved in the determination of monocytic differentiation.

Remission of food allergy by the Janus kinase inhibitor ruxolitinib in mice

To clarify the role of Janus kinase (JAK) in and the efficacy of JAK inhibitors on food allergy, we investigated the effect of the clinically available JAK inhibitor ruxolitinib on mouse food allergy and the functions of cultured mast cells in vitro. Anaphylactic symptoms including diarrhea and decreases in body temperature pursuant to oral ovalbumin (OVA) challenges in food allergy mice were attenuated by the daily oral administration of ruxolitinib. This drug inhibited increases in mouse mast cell protease-1 concentrations in the serum and mast cell numbers in the intestines of these mice as well as degranulation, IL-13 production, and the spontaneous and IL-9-dependent survival of mouse bone marrow-derived mast cells in spite of the absence of an effect of ruxolitinib on passive systemic anaphylaxis. Anti-OVA IgG2a, IgE, and IgG1 serum levels and the release of IFN-γ, IL-4, IL-9, and IL-10 from the OVA-restimulated splenocytes of food allergy mice were also decreased by the treatment. Moreover, ruxolitinib administration to mice that had already exhibited anaphylactic responses to previous challenges reduced anaphylactic responses to further oral OVA challenges, which suggested that ruxolitinib has a therapeutic potential on food allergy. Our results showed that ruxolitinib remitted food allergy in mice mainly through immunosuppression and the prevention of mast cell hyperplasia, and partially through the inhibition of mast cell activation. We consider JAK inhibition to be a promising strategy for the prevention of food allergy, and ruxolitinib along with its derivatives inhibiting JAK as good candidates for therapeutic drugs to treat food allergy.

New insights into the structure and function of the pseudokinase domain in JAK2

JAK (Janus kinase) 2 plays a critical role in signal transduction through several cytokine receptors. JAKs contain a typical tyrosine kinase domain preceded by a pseudokinase [JH2 (JAK homology 2)] domain which has been considered to be catalytically inactive. Identification of activating mutations in the JH2 domain of JAK2 as the major cause for polycythaemia vera and other MPNs (myeloproliferative neoplasms) demonstrate the critical regulatory function for this domain, but the underlying mechanisms have remained elusive. We have performed biochemical and functional analysis on the JH2 domain of JAK2. The results indicate that JH2 functions as an active protein kinase and phosphorylates two residues in JAK2 (Ser523 and Tyr570) that have been shown previously to be negative regulatory sites for JAK2 activity. The crystal structure of the JAK2 JH2 domain provides an explanation for the functional findings and shows that JH2 adopts a prototypical kinase fold, but binds MgATP through a non-canonical mode. The structure of the most prevalent pathogenic JH2 mutation V617F shows a high level of similarity to wild-type JH2. The most notable structural deviation is observed in the N-lobe αC-helix. The structural and biochemical data together with MD (molecular dynamics) simulations show that the V617F mutation rigidifies the αC-helix, which results in hyperactivation of the JH1 domain through an as yet unidentified mechanism. These results provide structural and functional insights into the normal and pathogenic function of the JH2 domain of JAK2.

Analysis of steady-state Förster resonance energy transfer data by avoiding pitfalls: interaction of JAK2 tyrosine kinase with N-methylanthraniloyl nucleotides

Förster resonance energy transfer (FRET) between the fluorescent ATP analogue 2'/3'-(N-methyl-anthraniloyl)-adenosine-5'-triphosphate (MANT-ATP) and enzymes is widely used to determine affinities for ATP-protein binding. However, in analysis of FRET fluorescence data, several important parameters are often ignored, resulting in poor accuracy of the calculated dissociation constant (Kd). In this study, we systematically analyze factors that interfere with Kd determination and describe methods for correction of primary and secondary inner filter effects that extend the use of the FRET method to higher MANT nucleotide concentrations. The interactions of the fluorescent nucleotide analogues MANT-ATP, MANT-ADP [2'/3'-O-(N-methylanthraniloyl) adenosine diphosphate], and MANT-AMP [2'/3'-O-(N-methylanthraniloyl) adenosine monophosphate] with the JAK2 tyrosine kinase domain are characterized. Taking all interfering factors into consideration, we found that JAK2 binds MANT-ATP tightly with a Kd of 15 to 25nM and excluded the presence of a second binding site. The affinity for MANT-ADP is also tight with a Kd of 50 to 80nM, whereas MANT-AMP does not bind. Titrations of JAK2 JH1 with nonhydrolyzable ATP analogue MANT-ATP-γ-S [2'/3'-O-(N-methylanthraniloyl) adenosine-5'-(thio)- triphosphate] yielded a Kd of 30 to 50nM. The methods demonstrated here are applicable to other enzyme-fluorophore combinations and are expected to help improve the analysis of steady-state FRET data in MANT nucleotide binding studies and to obtain more accurate results for the affinities of nucleotide binding proteins.

PTP1B: a simple enzyme for a complex world

Our understanding of the fundamental regulatory roles that tyrosine phosphatases play within cells has advanced significantly in the last two decades. Out-dated ideas that tyrosine phosphatases acts solely as the "off" switch counterbalancing the action of tyrosine kinases has proved to be flawed. PTP1B is the most characterized of all the tyrosine phosphatases and it acts as a critical negative and positive regulator of numerous signaling cascades. PTP1B's direct regulation of the insulin and the leptin receptors makes it an ideal therapeutic target for type II diabetes and obesity. Moreover, the last decade has also seen several reports establishing PTP1B as key player in cancer serving as both tumor suppressor and tumor promoter depending on the cellular context. Despite many key advances in these fields one largely ignored area is what role PTP1B may play in the modulation of immune signaling. The important recognition that PTP1B is a major negative regulator of Janus kinase - signal transducer and activator of transcription (JAK-STAT) signaling throughout evolution places it as a key link between metabolic diseases and inflammation, as well as a unique regulator between immune response and cancer. This review looks at the emergence of PTP1B through evolution, and then explore at the cell and systemic levels how it is controlled physiologically. The second half of the review will focus on the role(s) PTP1B can play in disease and in particular its involvement in metabolic syndromes and cancer. Finally we will briefly examine several novel directions in the development of PTP1B pharmacological inhibitors.

Acylglycerol kinase augments JAK2/STAT3 signaling in esophageal squamous cells

JAK2 activity is tightly controlled through a self-inhibitory effect via its JAK homology domain 2 (JH2), which restricts the strength and duration of JAK2/STAT3 signaling under physiological conditions. Although multiple mutations within JAK2, which abrogate the function of JH2 and sustain JAK2 activation, are widely observed in hematological malignancies, comparable mutations have not been detected in solid tumors. How solid tumor cells override the autoinhibitory effect of the JH2 domain to maintain constitutive activation of JAK2/STAT3 signaling remains puzzling. Herein, we demonstrate that AGK directly interacted with the JH2 domain to relieve inhibition of JAK2 and activate JAK2/STAT3 signaling. Overexpression of AGK sustained constitutive JAK2/STAT3 activation, consequently promoting the cancer stem cell population and augmenting the tumorigenicity of esophageal squamous cell carcinoma (ESCC) cells both in vivo and in vitro. Furthermore, AGK levels significantly correlated with increased STAT3 phosphorylation, poorer disease-free survival, and shorter overall survival in primary ESCC. More importantly, AGK expression was significantly correlated with JAK2/STAT3 hyperactivation in ESCC, as well as in lung and breast cancer. These findings uncover a mechanism for constitutive activation of JAK2/STAT3 signaling in solid tumors and may represent a prognostic biomarker and therapeutic target.

Identification of steroid-sensitive gene-1/Ccdc80 as a JAK2-binding protein

The tyrosine kinase Janus kinase 2 (JAK2) is activated by many cytokine receptors, including receptors for GH, leptin, and erythropoietin. However, very few proteins have been identified as binding partners for JAK2. Using a yeast 2-hybrid screen, we identified steroid-sensitive gene-1 (SSG1)/coiled-coil domain-containing protein 80 (Ccdc80) as a JAK2-binding partner. We demonstrate that Ccdc80 preferentially binds activated, tyrosyl-phosphorylated JAK2 but not kinase-inactive JAK2 (K882E) in both yeast and mammalian systems. Ccdc80 is tyrosyl phosphorylated in the presence of JAK2. The binding of Ccdc80 to JAK2 occurs via 1 or more of the 3 DUDES/SRPX (DRO1-URB-DRS-Equarin-SRPUL/sushi repeat containing protein, x-linked) domain 5 domains of Ccdc80. Mutagenesis of the second DUDES domain suggests that the N-terminal third of the DUDES domain is sufficient for JAK2 binding. Ccdc80 does not alter the kinase activity of JAK2. However, Ccdc80 increases GH-dependent phosphorylation of Stat (signal transducer and activator of transcription) 5b on Tyr699 and substantially enhances both basal and GH-dependent phosphorylation/activation of Stat3 on Tyr705. Furthermore, Ccdc80 belongs to the group of proteins that function both in the intracellular compartment and are secreted. Secreted Ccdc80 associates with the extracellular matrix and is also found in the medium. A substantial portion of the Ccdc80 detected in the medium is cleaved. Finally, consistent with the DUDES domain serving as a JAK2-binding domain, we also demonstrate that another protein that contains a DUDES domain, SRPX2, binds preferentially to the activated tyrosyl-phosphorylated form of JAK2.

Phosphorylation of the adaptor protein SH2B1β regulates its ability to enhance growth hormone-dependent macrophage motility

Previous studies have shown that growth hormone (GH) recruits the adapter protein SH2B1β to the GH-activated, GH receptor-associated tyrosine kinase JAK2, implicating SH2B1β in GH-dependent actin cytoskeleton remodeling, and suggesting that phosphorylation at serines 161 and 165 in SH2B1β releases SH2B1β from the plasma membrane. Here, we examined the role of SH2B1β in GH regulation of macrophage migration. We show that GH stimulates migration of cultured RAW264.7 macrophages, and primary cultures of peritoneal and bone marrow-derived macrophages. SH2B1β overexpression enhances, whereas SH2B1 knockdown inhibits, GH-dependent motility of RAW macrophages. At least two independent mechanisms regulate the SH2B1β-mediated changes in motility. In response to GH, tyrosines 439 and 494 in SH2B1β are phosphorylated. Mutating these tyrosines in SH2B1β decreases both basal and GH-stimulated macrophage migration. In addition, mutating the polybasic nuclear localization sequence (NLS) in SH2B1β or creating the phosphomimetics SH2B1β(S161E) or SH2B1β(S165E), all of which release SH2B1β from the plasma membrane, enhances macrophage motility. Conversely, SH2B1β(S161/165A) exhibits increased localization at the plasma membrane and decreased macrophage migration. Mutating the NLS or the nearby serine residues does not alter GH-dependent phosphorylation on tyrosines 439 and 494 in SH2B1β. Mutating tyrosines 439 and 494 does not affect localization of SH2B1β at the plasma membrane or movement of SH2B1β into focal adhesions. Taken together, these results suggest that SH2B1β enhances GH-stimulated macrophage motility via mechanisms involving phosphorylation of SH2B1β on tyrosines 439 and 494 and movement of SH2B1β out of the plasma membrane (e.g. as a result of phosphorylation of serines 161 and 165).

Ruxolitinib for the treatment of myelofibrosis: its clinical potential

Ruxolitinib is an orally bioavailable, selective Janus kinase (JAK) 1 and 2 inhibitor approved for the treatment of myelofibrosis (MF), a bone marrow disease in which the JAK pathway is dysregulated, leading to impaired hematopoiesis and immune function. By inhibiting JAK1 and JAK2, ruxolitinib modulates cytokine-stimulated intracellular signaling. In a phase II clinical trial in patients with MF, ruxolitinib recipients exhibited durable reductions in spleen size, reductions in circulating pro-inflammatory cytokines, improvements in physical activity, weight gain, and alleviation of symptoms (including constitutional symptoms) in patients with and without JAK2 mutation. These findings were confirmed by two phase III clinical MF studies, in which a greater proportion of ruxolitinib recipients achieved a spleen volume reduction of ≥35% from baseline at week 24, compared with placebo in one study (41.9% versus 0.7%; P < 0.0001) and with best available therapy in the other (31.9% versus 0%; P < 0.0001). Alleviation of MF symptoms and improvements in quality of life were also significantly greater in ruxolitinib recipients. Overall survival of patients treated with ruxolitinib was significantly longer than of those receiving the placebo. Owing to risks of potentially serious adverse effects, eg, myelosuppression, ruxolitinib should be used under close physician supervision. Longer follow-up of the phase III MF studies is needed to reach firm conclusions regarding ruxolitinib’s capacity to modify the natural disease course.

Prolactin-induced activation of phagocyte NADPH oxidase in the teleost fish gilthead seabream involves the phosphorylation of p47phox by protein kinase C

The pituitary hormone prolactin (PRL) is a multifunctional polypeptide which act as a key component of the neuroendocrine-immune loop and as a local regulator of the macrophage response. The involvement of PRL in regulating monocyte/macrophage functions is suggested by the presence of PRL receptors in these cells. Recently, we reported that physiological concentrations of native PRL were able to induce the expression of the pro-inflammatory cytokines IL-1β and TNFα, and the production of reactive oxygen species (ROS) in head kidney leukocytes and macrophages from the teleost fish gilthead seabream (Sparus aurata L.). In this study, we show that the NADPH oxidase subunit p47phox becomes phosphorylated in leukocytes stimulated with PRL, an effect that is blocked when neutralizing polyclonal antibodies to PRL are added. Additionally, the pharmacological inhibition of either protein kinase C (PKC) with calphostin C or the Jak/Stat signaling pathway with AG490 impaired PKC activation, p47phox phosphorylation and ROS production in seabream leukocytes activated with PRL. Taken together, our results demonstrate for the first time the need for PKC in regulating the PRL-mediated phosphorylation of p47phox, the activation of NADPH oxidase and the production of ROS by macrophages in vertebrates.

Jak/STAT pathways in cytokine signaling and myeloproliferative disorders: approaches for targeted therapies

Hematopoiesis is the cumulative result of intricately regulated signaling pathways that are mediated by cytokines and their receptors. Studies conducted over the past 10 to 15 years have revealed that hematopoietic cytokine receptor signaling is largely mediated by a family of tyrosine kinases termed Janus kinases (JAKs) and their downstream transcription factors, termed STATs (signal transducers and activators of transcription). Aberrations in these pathways, such as those caused by the recently identified JAK2(V617F) mutation and translocations of the JAK2 gene, are underlying causes of leukemias and other myeloproliferative disorders. This review discusses the role of JAK/STAT signaling in normal hematopoiesis as well as genetic abnormalities associated with myeloproliferative and myelodisplastic syndromes. This review also summarizes the status of several small molecule JAK2 inhibitors that are currently at various stages of clinical development. Several of these compounds appear to improve the quality of life of patients with myeloproliferative disorders by palliation of disease-related symptoms. However, to date, these agents do not seem to significantly affect bone marrow fibrosis, alter marrow histopathology, reverse cytopenias, reduce red cell transfusion requirements, or significantly reduce allele burden. These results suggest the possibility that additional mutational events might be associated with the development of these neoplasms, and indicate the need for combination therapies as the nature and significance of these additional molecular events is better understood.

The pseudokinase domain of JAK2 is a dual-specificity protein kinase that negatively regulates cytokine signaling

Human JAK2 tyrosine kinase mediates signaling through numerous cytokine receptors. The JAK2 JH2 domain functions as a negative regulator and is presumed to be a catalytically inactive pseudokinase, but the mechanism(s) for its inhibition of JAK2 remains unknown. Mutations in JH2 lead to increased JAK2 activity, contributing to myeloproliferative neoplasms (MPNs). Here we show that JH2 is a dual-specificity protein kinase that phosphorylates two negative regulatory sites in JAK2: Ser523 and Tyr570. Inactivation of JH2 catalytic activity increased JAK2 basal activity and downstream signaling. Notably, different MPN mutations abrogated JH2 activity in cells, and in MPN (V617F) patient cells phosphorylation of Tyr570 was reduced, suggesting that loss of JH2 activity contributes to the pathogenesis of MPNs. These results identify the catalytic activity of JH2 as a previously unrecognized mechanism to control basal activity and signaling of JAK2.

Differential biological activity of disease-associated JAK2 mutants

The JAK2V617F mutation has been identified in most patients with myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocythemia and primary myelofibrosis. Although JAK2V617F is the predominant allele associated with MPNs, other activating Janus kinase 2 (JAK2) alleles (such as K539L, T875N) also have been identified in distinct MPNs. The basis for the differences in the in vivo effects of different JAK2 alleles remains unclear. We have characterized three different classes of disease-associated JAK2 mutants (JAK2V617F, JAK2K539L and JAK2T875N) and found significant differences in biochemical, signaling and transforming properties among these different classes of JAK2 mutants.

Deficiency of SHP1 leads to sustained and increased ERK activation in mast cells, thereby inhibiting IL-3-dependent proliferation and cell death

SHP-1 plays an important role for the regulation of signaling from various hematopoietic cell receptors. In this study, we examined IL-3-induced cell proliferation and IL-3 depletion-induced apoptosis in bone marrow-derived mast cells (BMMC) established from motheaten (me) that lack SHP-1 expression, viable motheaten (me(v)) expressing phosphatase-deficient SHP-1, and wild-type (WT) mice. When BMMC were stimulated with IL-3, increased ERK activation was evident in resting state and sustained in me-BMMC relative to WT-BMMC. ERK is known to be involved in the regulation of cell proliferation and apoptosis in some cells. In accordance with sustained ERK activation, apoptosis was decreased in me- and me(v)-BMMC compared with WT-BMMC. In contrast to the predicted role of ERK as a pro-survival molecule, IL-3-induced cell proliferation was much lower in me- and me(v)-BMMC than WT-BMMC. Stimulation with lower concentration of IL-3 or addition of PD98059, a MEK inhibitor, to the culture resulted in the suppression of decreased apoptosis and cell proliferation in me- and me(v)-BMMC. Collectively, these results suggest that SHP-1 positively regulates IL-3-dependent mast cell proliferation and apoptosis by inhibiting ERK activity through its phosphatase activity. Furthermore, our results indicate that ERK would act as a negative regulator for cell proliferation and induce apoptosis when its activity is highly increased.

Both interleukin-3 and interleukin-6 are necessary for better ex vivo expansion of CD133+ cells from umbilical cord blood

Umbilical cord blood (UCB), an ideal source for transplantable hematopoietic stem cells (HSC), is readily available and is rich in progenitor cells. Identification of conditions favoring UCB-HSC ex vivo expansion and of repopulating potential remains a major challenge in hematology. CD133+ cells constitute an earlier, less-differentiated HSC group with a potentially higher engraftment capacity. The presence of SCF, Flt3-L, and TPO are essential for CD133+ and/or CD34+ cells ex vivo expansion; however, IL-3 and IL-6 influence has not yet been clearly established. We investigated this influence on CD133+ cells from UCB ex vivo expansion and the effect of these cytokines upon cell phenotype. Immediately after isolation an 85% of CD133+ cell purity was obtained, diminishing after 4 and 8 days of ex vivo expansion. CD133+ fold-increase was higher using IMDM with SCF, Flt3-L, and TPO (BM)+IL-3 or BM+IL-3+IL-6 on day 8 (13.83- and 17.47-fold increase, respectively). BM+IL-6 presented no significant difference from BM alone. We demonstrated that 5.1% of the CD133+ cells expressed IL-6 receptor (IL-6R) after isolation. After 4 and 8 days in culture, the percentage of CD133+ cells that expressed IL-6R was as follows: BM alone (9.8% and 22.02%, respectively); BM+IL-3 (8.33% and 16.74%); BM+IL-6 (9.2% and 17.67%); and BM+IL-3+IL-6 (12.5% and 61.20%). Cell cycle analysis revealed quiescent cells after isolation, 95.5% CD133+ cells in the G0/G1 phase. Regardless of culture period or cytokine incubation, CD133+ cell cycle altered to 70% of CD133+ in the G0/G1 phase. Colony-forming unit (CFU) doubled in BM+IL-3+IL-6 after 8 days of incubation compared with BM group. SOX-2 and NANOG-relative gene expression was detected on day 0 after isolation. BM+IL-6 prevented the decrease in NANOG and SOX-2 gene expression level compared to BM+IL-3 or BM+IL-3+IL-6 incubated cells. Our results indicated that UCB-isolated CD133+ cells were better ex vivo expanded in the presence of SCF, Flt3-L, TPO, IL-3+IL-6. IL-3 probably promotes higher CD133+ cell expansion and IL-6 maintains immature phenotype.

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.

IL-6: from its discovery to clinical applications

In the late 1960s, the essential role of T cells in antibody production was reported. This led to our hypothesis that T-cell-derived soluble factors would have to be involved in the activation of B cells. The factor that induced B cells to produce immunoglobulins was initially named B-cell stimulatory factor-2. In 1986, we successfully cloned the complementary DNA encoding B-cell stimulatory factor-2, now known as IL-6. At the same time, IFN-beta2 and a 26-kDa protein found in fibroblasts were independently cloned and found to be identical to IL-6. Later, a hybridoma/plasmacytoma growth factor and a hepatocyte-stimulating factor were also proven to be the same molecule as IL-6. Now, we know that IL-6 is a pleiotropic cytokine with a wide range of biological activities in immune regulation, hematopoiesis, inflammation and oncogenesis. Since the discovery of IL-6, we have further clarified its activities, the IL-6R system and the IL-6 signal transduction mechanism. On the basis of the findings, a new therapeutic approach to block the actions of IL-6 by use of a humanized anti-IL-6R antibody has been proven to be therapeutically effective for rheumatoid arthritis, systemic juvenile idiopathic arthritis and Castleman's disease. In this review, I discuss the history of IL-6 research as a paradigm of progress from basic science to clinical applications.

Tyrosines 868, 966, and 972 in the kinase domain of JAK2 are autophosphorylated and required for maximal JAK2 kinase activity

Janus kinase 2 (JAK2) is activated by a majority of cytokine family receptors including receptors for GH, leptin, and erythropoietin. To identify novel JAK2-regulatory and/or -binding sites, we set out to identify autophosphorylation sites in the kinase domain of JAK2. Two-dimensional phosphopeptide mapping of in vitro autophosphorylated JAK2 identified tyrosines 868, 966, and 972 as sites of autophosphorylation. Phosphorylated tyrosines 868 and 972 were also identified by mass spectrometry analysis of JAK2 activated by an erythropoietin-bound chimeric erythropoietin receptor/leptin receptor. Phosphospecific antibodies suggest that the phosphorylation of all three tyrosines increases in response to GH. Compared with wild-type JAK2, which is constitutively active when overexpressed, JAK2 lacking tyrosine 868, 966, or 972 has substantially reduced activity. Coexpression with GH receptor and protein tyrosine phosphatase1B allowed us to investigate GH-dependent activation of these mutated JAK2s in human embryonic kidney 293T cells. All three mutated JAK2s are activated by GH, although to a lesser extent than wild-type JAK2. The three mutated JAK2s also mediate GH activation of signal transducer and activator of transcription 3 (Stat3), signal transducer and activator of transcription 5b (Stat5b) and ERK1, but at reduced levels. Coexpression with Src-homology 2B1beta (SH2B1beta), like coexpression with GH-bound GH receptor, partially restores the activity of all three JAK2 mutants. Based on these results and the crystal structure of the JAK2 kinase domain, we hypothesize that small changes in the conformation of the regions of JAK2 surrounding tyrosines 868, 966, and 972 due to e.g. phosphorylation, binding to a ligand-bound cytokine receptor, and/or binding to Src-homology 2B1, may be essential for JAK2 to assume a maximally active conformation.

NSC114792, a novel small molecule identified through structure-based computational database screening, selectively inhibits JAK3

Background

Human or animals lacking either JAK3 or the common gamma chain (γc) expression display severe combined immunodeficiency disease, indicating the crucial role of JAK3 in T-cell development and the homeostasis of the immune system. JAK3 has also been suggested to contribute to the pathogenesis of tumorigenesis. Recent studies identified activating JAK3 mutations in patients with various hematopoietic malignancies, including acute megakaryoblastic leukemia. Importantly, functional analyses of some of those JAK3 mutations have been shown to cause lethal hematopoietic malignancies in animal models. These observations make JAK3 an ideal therapeutic target for the treatment of various human diseases. To identify novel small molecule inhibitors of JAK3, we performed structure-based virtual screen using the 3D structure of JAK3 kinase domain and the NCI diversity set of compounds.

Results

We identified NSC114792 as a lead compound. This compound directly blocked the catalytic activity of JAK3 but not that of other JAK family members in vitro. In addition, treatment of 32D/IL-2Rβ cells with the compound led to a block in IL-2-dependent activation of JAK3/STAT5 but not IL-3-dependent activation of JAK2/STAT5. Consistent with the specificity of NSC114792 for JAK3, it selectively inhibited persistently-activated JAK3, but failed to affect the activity of other JAK family members and other oncogenic kinases in various cancer cell lines. Finally, we showed that NSC114792 decreases cell viability by inducing apoptosis through down-regulating anti-apoptotic gene expression only in cancer cells harboring persistently-active JAK3.

Conclusions

NSC114792 is a lead compound that selectively inhibits JAK3 activity. Therefore, our study suggests that this small molecule inhibitor of JAK3 can be used as a starting point to develop a new class of drugs targeting JAK3 activity, and may have therapeutic potential in various diseases that are caused by aberrant JAK3 activity.