The Janus kinase family of protein tyrosine kinases and their role in signaling

Topical application of aerial portion of Acalypha indica Linn ameliorates psoriasis in rodents: Evidences from in vivo and in silico studies

ETHANOPHARMACOLOGICAL RELEVANCE

Acalypha indica Linn. is a weed, used traditionally for different skin diseases such as eczema and dermatitis in various parts of India. There are no previous in vivo studies reported on the antipsoriatic potential of this medicinal plant.

AIM

The aim of this study was to investigate antipsoriatic activity of coconut oil dispersion of aerial portion of Acalypha indica Linn. Few lipid-soluble phytoconstituents of this plantwere subjected to molecular docking studies on different targets to determine phytoconstituent responsible for antipsoriatic activity.

METHODS

Virgin coconut oil dispersion of aerial portion of the plant was prepared by mixing three parts of coconut oil and one part of powdered aerial portion. The acute dermal toxicity was determined according to OECD guidelines. Mouse tail model was used to evaluate the antipsoriatic activity. Molecular docking of phytoconstituents was carried out using Biovia Discovery Studio.

RESULTS

In acute dermal toxicity study,the coconut oil dispersion was found to be safe up to the dose of 20000 mg/kg. The dispersion exhibited significant antipsoriatic activity (p < 0.01) at the dose of 250 mg/kg; at 500 mg/kg dose, the activity was similar that of 250 mg/kg dose. In the docking study of the phytoconstituents, 2-methyl anthraquinone was found to be responsible for antipsoriatic activity.

CONCLUSION

This study provides new evidence of Acalypha indica Linn as antipsoriatic plant and justifies its traditional use. Computational studies also endorse the results obtained via acute dermal toxicity study and mouse tail model for evaluation of antipsoriatic potential.

Interferon Gamma Inhibits Equine Herpesvirus 1 Replication in a Cell Line-Dependent Manner

The sole equine herpesvirus 1 (EHV-1) immediate-early protein (IEP) is essential for viral replication by transactivating viral immediate-early (IE), early (E), and late (L) genes. Here, we report that treatment of mouse MH-S, equine NBL6, and human MRC-5 cells with 20 ng/mL of IFN-γ reduced EHV-1 yield by 1122-, 631-, and 10,000-fold, respectively. However, IFN-γ reduced virus yield by only 2–4-fold in mouse MLE12, mouse L-M, and human MeWo cells compared to those of untreated cells. In luciferase assays with the promoter of the EHV-1 early regulatory EICP0 gene, IFN-γ abrogated trans-activation activity of the IEP by 96% in MH-S cells, but only by 21% in L-M cells. Similar results were obtained in assays with the early regulatory UL5 and IR4 promoter reporter plasmids. IFN-γ treatment reduced IEP protein expression by greater than 99% in MH-S cells, but only by 43% in L-M cells. The expression of IEP and UL5P suppressed by IFN-γ was restored by JAK inhibitor treatment, indicating that the inhibition of EHV-1 replication is mediated by JAK/STAT1 signaling. These results suggest that IFN-γ blocks EHV-1 replication by inhibiting the production of the IEP in a cell line-dependent manner. Affymetrix microarray analyses of IFN-γ-treated MH-S and L-M cells revealed that five antiviral ISGs (MX1, SAMHD1, IFIT2, NAMPT, TREX1, and DDX60) were upregulated 3.2–18.1-fold only in MH-S cells.

Nifuroxazide as JAK2 inhibitor: A binding mode proposal and Hel cell proliferation assay

Nifuroxazide has been employed as an anti-diarrheic agent since 1966, but in the last decade has brought to the research spotlight again due to its recently described antitumoral activity through the JAK2 inhibitory potential. Since 2008, more than 70 papers have been published about the issue and more are expected to the following years. Herein we discuss the findings of molecular modelling studies which were performed to elucidate the potential binding mode of this drug into the JAK2 ATP recognition site and also into the allosteric region near the catalytic site. Molecular modelling followed by dynamics simulations indicated the NFZ could bind at both sites, such as a Type II kinase inhibitor since residues from both ATP and modulatory site would exhibit contacts with the drug when in a stable complex. Synthesis of NFZ and its sulfur bioisosteric analogue GPQF-63 were performed and experimental assays against HEL cells indicate the potential of NFZ and, mainly of its analogue GPQF-63 in acting as inhibitors of cell growth. HEL-cells present the JAK2 V617F mutation which leads to an enhanced JAK/STAT pathway and they have never been tested by the NFZ activity before. A mechanistic approach was also performed and revealed that both compounds induce cell apoptosis.Taken together, both the theoretical and experimental approaches point out the N-acylhydrazones as good starting points in the search for JAK2 modulatory small molecules which could then, be studied as promising leads toward new alternatives to control the JAK-STAT pathway related pathologies. This is the first study, as far as we have known, to propose a potential binding mode for NFZ as well as reporting the activity of this drug against HEL cells, which are a usual cellular model to human erythroleukemia and other myeloproliferative diseases.

Inhalation of Essential Oil from Mentha piperita Ameliorates PM10-Exposed Asthma by Targeting IL-6/JAK2/STAT3 Pathway Based on a Network Pharmacological Analysis

Fine particulate matter (PM) exposure exhibits a crucial risk factor to exacerbate airway epithelial remodeling, fibrosis, and pulmonary destruction in asthma. Based on the use of essential oils from aromatic plants on pain relief and anti-inflammatory properties, we investigated the inhibitory effects of essential oil derived from the Mentha species (MEO) against asthma exposed to PM10. The MEO (0.1 v/v %) was aerosolized by a nebulizer to ovalbumin and PM10-induced asthmatic mice. Histological changes were confirmed in the lung tissues. To define the mode of action of the MEO on asthma, a protein–protein interaction network was constructed using menthol and menthone as the major components of the MEO. Cytokine expression and the JAK2/STAT3 signaling pathway were analyzed in lung epithelial A549 cells co-treated with MEO and PM10. Inhalation of MEO by nebulization inhibited respiratory epithelium hyperplasia, collagen deposition, and goblet cell activation in asthmatic mice. Through a network pharmacological analysis, cytokine–cytokine receptor interaction and JAK/STAT was expected to be underlying mechanisms of MEO on asthma. Treatment with MEO significantly reduced the IL-6 levels with a decrease in pro-inflammatory and T helper 2-specific cytokines. PM10-induced phosphorylation of JAK2 and STAT3 was significantly decreased by MEO. Collectively, MEO may have an inhibitory effect on asthma under the condition of PM10 exposure through the IL-6/JAK2/STAT3 signaling pathway.

Relation of Neutrophil Gelatinase-Associated Lipocalin Overexpression to the Resistance to Apoptosis of Tumor B Cells in Chronic Lymphocytic Leukemia

The resistance to apoptosis of chronic lymphocytic leukemia (CLL) cells partly results from the deregulated production of survival signals from leukemic cells. Despite the development of new therapies in CLL, drug resistance and disease relapse still occur. Recently, neutrophil gelatinase-associated lipocalin (NGAL), a secreted glycoprotein, has been suggested to have a critical role in the biology of tumors. Thus, we investigated the relevance of NGAL in CLL pathogenesis, analyzed the expression of its cellular receptor (NGAL-R) on malignant B cells and tested whether CLL cells are resistant to apoptosis through an autocrine process involving NGAL and NGAL-R. We observed that NGAL concentrations were elevated in the serum of CLL patients at diagnosis. After treatment (and regardless of the therapeutic regimen), serum NGAL levels normalized in CLL patients in remission but not in relapsed patients. In parallel, NGAL and NGAL-R were upregulated in leukemic cells from untreated CLL patients when compared to normal peripheral blood mononuclear cells (PBMCs), and returned to basal levels in PBMCs from patients in remission. Cultured CLL cells released endogenous NGAL. Anti-NGAL-R antibodies enhanced NGAL-R⁺ leukemia cell death. Conversely, recombinant NGAL protected NGAL-R⁺ CLL cells against apoptosis by activating a STAT3/Mcl-1 signaling pathway. Our results suggest that NGAL and NGAL-R, overexpressed in untreated CLL, participate in the deregulation of the apoptotic machinery in CLL cells, and may be potential therapeutic clues for CLL treatment.

Targeting the JAK/STAT Signaling Pathway Using Phytocompounds for Cancer Prevention and Therapy

Cancer is a prevalent cause of mortality around the world. Aberrated activation of Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway promotes tumorigenesis. Natural agents, including phytochemicals, exhibit potent anticancer activities via various mechanisms. However, the therapeutic potency of phytoconstituents as inhibitors of JAK/STAT signaling against cancer has only come into focus in recent days. The current review highlights phytochemicals that can suppress the JAK/STAT pathway in order to impede cancer cell growth. Various databases, such as PubMed, ScienceDirect, Web of Science, SpringerLink, Scopus, and Google Scholar, were searched using relevant keywords. Once the authors were in agreement regarding the suitability of a study, a full-length form of the relevant article was obtained, and the information was gathered and cited. All the complete articles that were incorporated after the literature collection rejection criteria were applied were perused in-depth and material was extracted based on the importance, relevance, and advancement of the apprehending of the JAK/STAT pathway and their relation to phytochemicals. Based on the critical and comprehensive analysis of literature presented in this review, phytochemicals from diverse plant origins exert therapeutic and cancer preventive effects, at least in part, through regulation of the JAK/STAT pathway. Nevertheless, more preclinical and clinical research is necessary to completely comprehend the capability of modulating JAK/STAT signaling to achieve efficient cancer control and treatment.

3-Deoxy-2β,16-dihydroxynagilactone E, a natural compound from Podocarpus nagi, preferentially inhibits JAK2/STAT3 signaling by allosterically interacting with the regulatory domain of JAK2 and induces apoptosis of cancer cells

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathways, especially the JAK2/STAT3 pathway, play vital roles in the development of many malignancies. Overactivation of STAT3 promotes cancer cell survival and proliferation. Therefore, the JAK2/STAT3-signaling pathway has been considered a promising target for cancer therapy. In this study, we identified a natural compound 3-deoxy-2β,16-dihydroxynagilactone E (B6) from the traditional Chinese medicinal plant Podocarpus nagi as a potent inhibitor of STAT3 signaling. B6 preferentially inhibited the phosphorylation of STAT3 by interacting with and inactivating JAK2, the main upstream kinase of STAT3. B6 dose-dependently inhibited IL-6-induced STAT3 signaling with an IC₅₀ of 0.2 μM. In contrast to other JAK2 inhibitors, B6 did not interact with the catalytic domain but instead with the FERM-SH2 domain of JAK2. This interaction was JAK-specific since B6 had little effect on other tyrosine kinases. Furthermore, B6 potently inhibited the growth and induced apoptosis of MDA-MB-231 and MDA-MB-468 breast cancer cells with overactivated STAT3. Taken together, our study uncovers a novel compound and a novel mechanism for the regulation of JAK2 and offers a new therapeutic approach for the treatment of cancers with overactivated JAK2/STAT3.

JAKs to STATs: A tantalizing therapeutic target in acute myeloid leukemia

The Janus Associated Kinase-Signal Transducers and Activators of Transcription (JAK-STAT) signaling pathway plays a pivotal role in hematopoietic growth factor signaling. Hyperactive JAK-STAT signaling is implicated in the pathogenesis of myeloid malignancies, including acute myeloid leukemia (AML). The significant headway in understanding the biology of AML has led to an explosion of novel therapeutics with mechanistic rationale for the treatment of newly diagnosed and relapsed/refractory (R/R) AML. Most importantly, selective targeting of the JAK-STAT pathway has proven to be an effective therapeutic strategy in myeloproliferative neoplasms and is also being evaluated in related myeloid malignancies, including AML. This comprehensive review will focus on the apparent and evolving potential of JAK-STAT pathway inhibition in AML with emphasis on JAK inhibitors, highlighting both success and failure with this experimental approach in the clinic, and identifying rationally based combinatorial approaches.

Akt1 and Jak1 siRNA based silencing effects on the proliferation and apoptosis in head and neck squamous cell carcinoma

Based on Akt1 and Jak1 key roles in apoptosis and proliferation of many cancers, the aim of this study was to find a new gene therapy strategy by silencing of these main anti-apoptotic genes for HNSCC treatment. Cancerous HN5 and normal HUVEC cell lines were treated with Akt1 and Jak1 siRNAs alone or with each other combined with/without cisplatin. The MTS, flow cytometry, 4',6-diamidino-2-phenylindole staining, real-time PCR and ELISA methods were utilized in this study. The highest percentage of apoptosis was observed in the treatment of Jak1 siRNA/cisplatin group in cancerous HN5 cells (96.5%) where this treatment showed 12.84% apoptosis in normal HUVEC cell line. Cell viability reduced significantly to 64.57% after treatment with Akt1 siRNA in HN5 treated group. Knocking down Akt1 and Jak1 genes using siRNAs could increase levels of apoptosis and reduce proliferation rate in HNSCC indicating the powerful effects of these genes siRNAs with or without chemotherapeutic agents in HNSCC treatment. In conclusion, the combination of siRNA-mediated gene-silencing strategy can be considered as a valuable and safe approach for sensitizing cancer cells to chemotherapeutic agents thus proposed further studies regarding this issue to approve some siRNA based therapeutics for using in clinic.

Understanding the structural features of JAK2 inhibitors: a combined 3D-QSAR, DFT and molecular dynamics study

JAK2 plays a critical role in JAK/STAT signaling pathway and in patho-mechanism of myeloproliferative disorders and autoimmune diseases. Thus, effective JAK2 inhibitors provide a promising opportunity for the pharmaceutical intervention of many diseases. In this work, 3D-QSAR study was performed on a series of 1-amino-5H-pyrido-indole-4-carboxamide derivatives as JAK2 inhibitors to obtain reliable comparative molecular field analysis (CoMFA) and comparative molecular similarity analysis (CoMSIA) models with three different alignment methods. Among the different alignment methods, ligand-based (CoMFA: q² = 0.676, r² = 0.979; CoMSIA: q² = 0.700, r² = 0.953) and pharmacophore-based alignment (CoMFA: q² = 0.710, r² = 0.982; CoMSIA: q² = 0.686, r² = 0.960) has produced better statistical results when compared to receptor-based alignment (CoMFA: q² = 0.507, r² = 0.979; CoMSIA: q² = 0.544, r² = 0.917). Statistical parameters indicated that data are well fitted and have high predictive ability. The presence of electrostatic and hydrophobic field is highly desirable for potent inhibitory activity, and the steric field plays a minor role in modulating the activity. The contour analysis indicates ARG980, ASN981, ASP939 and LEU937 have more possibility of interacting with bulky, hydrophobic groups in pyrido and positive and negative groups in pyrazole ring. Based on our findings, we have designed sixteen molecules and predicted its activity and drug-like properties. Subsequently, molecular docking, molecular dynamics and DFT calculations were performed to evaluate its potency.

An indel polymorphism in the 3' untranslated region of JAK1 confers risk for hepatocellular carcinoma possibly by regulating JAK1 transcriptional activity in a Chinese population

The purpose of the present study was to assess whether the rs112395617 polymorphism located in the Janus kinase 1 (JAK1) 3' untranslated region (3' UTR) was associated with the risk of hepatocellular carcinoma (HCC), and to explore the potential mechanism of action. Genomic DNA was extracted from peripheral blood of 290 patients with HCC and 320 controls. A polymerase chain reaction-polyacrylamide gel electrophoresis assay was used to genotype the rs112395617 polymorphism. Quantitative (q)PCR was used to detect the genotype-phenotype association between HCC tissues and different genotypes. Vectors containing the insertion (ins)/ins or deletion (del)/del genotype of the rs112395617 polymorphism were constructed, and the luciferase assay was used to detect the JAK1 transcriptional activity affected by the rs112395617 polymorphism. It was identified that, when compared with the ins/ins genotype, the del/del and del/ins genotypes of rs112395617 were significantly associated with a decreased risk of HCC. The qPCR results demonstrated that the JAK1 mRNA expression level with ins/ins and ins/del genotypes was increased by 3.36 and 1.75-fold compared with the del/del genotype in human HCC tissue samples. In addition, the 'AATT' insertion allele of rs112395617 disrupted the binding site for microRNA (miR)-431-5p, thereby increasing JAK1 transcription in vitro. These data suggest that the rs112395617 polymorphism may contribute to HCC susceptibility, in full or at least partially through an effect on JAK1 transcriptional activity by disrupting its binding with miR-431-5p.

TYK2-induced phosphorylation of Y640 suppresses STAT3 transcriptional activity

STAT3 is a pleiotropic transcription factor involved in homeostatic and host defense processes in the human body. It is activated by numerous cytokines and growth factors and generates a series of cellular effects. Of the STAT-mediated signal transduction pathways, STAT3 transcriptional control is best understood. Jak kinase dependent activation of STAT3 relies on Y705 phosphorylation triggering a conformational switch that is stabilized by intermolecular interactions between SH2 domains and the pY705 motif. We here show that a second tyrosine phosphorylation within the SH2 domain at position Y640, induced by Tyk2, negatively controls STAT3 activity. The Y640F mutation leads to stabilization of activated STAT3 homodimers, accelerated nuclear translocation and superior transcriptional activity following IL-6 and LIF stimulation. Moreover, it unlocks type I IFN-dependent STAT3 signalling in cells that are normally refractory to STAT3 transcriptional activation.

Defective Suppressor of Cytokine Signaling 1 Signaling Contributes to the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease involving injuries in multiple organs and systems. Exaggerated inflammatory responses are characterized as end-organ damage in patients with SLE. Although the explicit pathogenesis of SLE remains unclear, increasing evidence suggests that dysregulation of cytokine signals contributes to the progression of SLE through the Janus kinase/signal transducer and activator of transcription (STAT) signaling pathway. Activated STAT proteins translocate to the cell nucleus and induce transcription of target genes, which regulate downstream cytokine production and inflammatory cell infiltration. The suppressor of cytokine signaling 1 (SOCS1) is considered as a classical inhibitor of cytokine signaling. Recent studies have demonstrated that SOCS1 expression is decreased in patients with SLE and in murine lupus models, and this negatively correlates with the magnitude of inflammation. Dysregulation of SOCS1 signals participates in various pathological processes of SLE such as hematologic abnormalities and autoantibody generation. Lupus nephritis is one of the most serious complications of SLE, and it correlates with suppressed SOCS1 signals in renal tissues. Moreover, SOCS1 insufficiency affects the function of several other organs, including skin, central nervous system, liver, and lungs. Therefore, SOCS1 aberrancy contributes to the development of both systemic and local inflammation in SLE patients. In this review, we discuss recent studies regarding the roles of SOCS1 in the pathogenesis of SLE and its therapeutic implications.

Unphosphorylated STAT1 represses apoptosis in macrophages during Mycobacteriumtuberculosis infection

In murine macrophages infected with Mycobacterium tuberculosis (Mtb), the level of phosphorylated STAT1 (P-STAT1), which drives the expression of many pro-apoptosis genes, increases quickly but then declines over a period of hours. By contrast, infection induces a continued increase in the level of unphosphorylated STAT1 that persists for several days. Here, we found that the level of unphosphorylated STAT1 correlated with the intracellular bacterial burden during the later stages of infection. To investigate the significance of a high level of unphosphorylated STAT1, we increased its concentration exogenously, and found that the apoptosis rate induced by Mtb was sufficiently decreased. Further experiments confirmed that unphosphorylated STAT1 affects the expression of several immune-associated genes and lessens the sensitivity of macrophages to CD95 (FAS)-mediated apoptosis during Mtb infection. Furthermore, we characterized 149 proteins that interacted with unphosphorylated STAT1 and the interactome network. The cooperation between unphosphorylated STAT1 and STAT3 results in downregulation of CD95 expression. Additionally, we verified that unphosphorylated STAT1 and IFIT1 competed for binding to eEF1A. Taken together, our data show that the role of unphosphorylated STAT1 differs from that of P-STAT1, and represses apoptosis in macrophages to promote immune evasion during Mtb infection.

JAK family members: Molecular cloning, expression profiles and their roles in leptin influencing lipid metabolism in Synechogobius hasta

Janus kinase (JAK) is a family of non-receptor tyrosine kinases that participate in transducing cytokine signals from the external environment to the nucleus in various biological processes. Currently, information about their genes structure and evolutionary history has been extensively studied in mammals as well as in several fish species. By contrast, limited reports have addressed potential role of diverse JAK in signaling responses to leptin in fish. In this study, we identified and characterized five JAK members of Synechogobius hasta. Compared to mammals, more members of the JAK family were found in S. hasta, which provided evidence that the JAK family members had arisen by the whole genome duplications during vertebrate evolution. For protein structure, all of these members possessed similar domains compared with those of mammals. Their mRNAs were expressed in a wide range of tissues, but at the different levels. Incubation in vitro of freshly isolated hepatocytes of S. hasta with different concentrations of recombinant human leptin decreased the intracellular triglyceride content and lipogenic genes expression, and increased mRNA expression of several JAK and lipolytic genes. AG490, a specific inhibitor of JAK, reversed leptin-induced effects on TG content and JAK2a, JAK2b, hormone-sensitive lipase (HSL2) and acetyl-CoA carboxylase (ACCa), indicating that the JAK2a/b may have mediated the actions of leptin on lipid metabolism at transcriptional level.

Isolation and Expression Analysis of STAT Members from Synechogobius hasta and Their Roles in Leptin Affecting Lipid Metabolism

Signal transducers and activators of transcription proteins (STATs) act as important mediators in multiple biological processes induced by a large number of cytokines. In the present study, full-length cDNA sequences of seven STAT members, including some splicing variants different from those in mammals, were obtained from Synechogobius hasta. The phylogenetic analysis revealed that the seven STAT members were derived from paralogous genes that might have arisen by whole genome duplication (WGD) events during vertebrate evolution. All of these members share similar domain structure compared with those of mammals, and were widely expressed across the tested tissues (brain, gill, heart, intestine, liver, muscle and spleen), but at variable levels. Incubation in vitro of recombinant human leptin changed the intracellular triglyceride (TG) content and mRNA levels of several STATs members, as well as expressions and activities of genes involved in lipid metabolism. Furthermore, Tyrphostin B42 (AG490), a specific inhibitor of the Janus Kinase 2(JAK2)-STAT pathway, partially reversed leptin-induced change on STAT3 and its two spliced isoforms expression, as well as expressions and activities of genes involved in lipid metabolism. As a consequence, the decrease of TG content was also reversed. Thus, our study suggests that STAT3 is the requisite for the leptin signal and the activation of the STAT3 member may account for the leptin-induced changes in lipid metabolism in S. hasta.

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.

Signal Transducers and Activators of Transcription (STAT) Regulatory Networks in Marine Organisms: From Physiological Observations towards Marine Drug Discovery

Part of our ocean's richness comes from its extensive history of supporting life, resulting in a highly diverse ecological system. To date, over 250,000 species of marine organisms have been identified, but it is speculated that the actual number of marine species exceeds one million, including several hundreds of millions of species of marine microorganisms. Past studies suggest that approximately 70% of all deep-sea microorganisms, gorgonians, and sea sponges produce secondary metabolites with anti-cancer activities. Recently, novel FDA-approved drugs derived from marine sponges have been shown to reduce metastatic breast cancer, malignant lymphoma, and Hodgkin's disease. Despite the fact that many marine natural products have been shown to possess a good inhibition potential against most of the cancer-related cell signaling pathways, only a few marine natural products have been shown to target JAK/STAT signaling. In the present paper, we describe the JAK/STAT signaling pathways found in marine organisms, before elaborating on the recent advances in the field of STAT inhibition by marine natural products and the potential application in anti-cancer drug discovery.

Functional analysis of the uropathogenic Escherichia coli R049 gene

The objective of this study was to determine the function of the novel uropathogenic Escherichia coli (UPEC) gene R049 during host infection. We infected the urinary tracts of mice with E. coli UPEC132 or the R049 deletion mutant UPEC132ΔR049.The mouse kidneys were harvested at 4 and 8h post-infection and screened for differentially expressed genes by microarray analysis. We identified 379 and 515 differentially expressed genes at 4 and 8 h post-infection, respectively. Thirty-four of these genes were associated with inflammatory and immune signaling pathways, including those related to mitogen-activated protein kinase signaling, leukocyte transendothelial migration, cytokine-cytokine receptor interaction, Toll-like receptor signaling, and apoptosis. Protein binding (GO 0005515) was the most prevalent molecular function in the Gene Ontology terms related to differentially expressed genes. In conclusion, R049 expression in UPEC132 is related to the early innate immune and inflammatory responses in UPEC-infected hosts. This work lays the foundation for further research on anti-infective immunity against UPEC.

Down-regulation of the epithelial Na⁺ channel ENaC by Janus kinase 2

Janus kinase-2 (JAK2), a signaling molecule mediating effects of various hormones including leptin and growth hormone, has previously been shown to modify the activity of several channels and carriers. Leptin is known to inhibit and growth hormone to stimulate epithelial Na(+) transport, effects at least partially involving regulation of the epithelial Na(+) channel ENaC. However, no published evidence is available regarding an influence of JAK2 on the activity of the epithelial Na(+) channel ENaC. In order to test whether JAK2 participates in the regulation of ENaC, cRNA encoding ENaC was injected into Xenopus oocytes with or without additional injection of cRNA encoding wild type JAK2, gain-of-function (V617F)JAK2 or inactive (K882E)JAK2. Moreover, ENaC was expressed with or without the ENaC regulating ubiquitin ligase Nedd4-2 with or without JAK2, (V617F)JAK2 or (K882E)JAK2. ENaC was determined from amiloride (50 μM)-sensitive current (I(amil)) in dual electrode voltage clamp. Moreover, I(amil) was determined in colonic tissue utilizing Ussing chambers. As a result, the I(amil) in ENaC-expressing oocytes was significantly decreased following coexpression of JAK2 or (V617F)JAK2, but not by coexpression of (K882E)JAK2. Coexpression of JAK2 and Nedd4-2 decreased I(amil) in ENaC-expressing oocytes to a larger extent than coexpression of Nedd4-2 alone. Exposure of ENaC- and JAK2-expressing oocytes to JAK2 inhibitor AG490 (40 μM) significantly increased I(amil). In colonic epithelium, I(amil) was significantly enhanced by AG490 pretreatment (40 μM, 1 h). In conclusion, JAK2 is a powerful inhibitor of ENaC.

Genetic manipulation of the ApoF/Stat2 locus supports an important role for type I interferon signaling in atherosclerosis

Apolipoprotein F (ApoF) is a sialoglycoprotein that is a component of the HDL and LDL fractions of human serum. We sought to test the hypothesis that ApoF plays an important role in atherosclerosis in mice by modulating lipoprotein function. Atherosclerosis was assessed in male low density lipoprotein receptor knockout (Ldlr KO) and ApoF/Ldlr double knockout (DKO) mice fed a Western diet for 16 weeks. ApoF/Ldlr DKO mice showed a 39% reduction in lesional area by en face analysis of aortas (p < 0.05), despite no significant differences in plasma lipid parameters. ApoF KO mice had reduced expression of Interferon alpha (IFNα) responsive genes in liver and spleen, as well as impaired macrophage activation. Interferon alpha induced gene 27 like 2a (Ifi27l2a), Oligoadenylate synthetases 2 and 3 (Oas2 and Oas3) were significantly reduced in the ApoF KO mice relative to wild type controls. These effects were attributable to hypomorphic expression of Stat2 in the ApoF KO mice, a critical gene in the Type I IFN pathway that is situated just 425 base pairs downstream of ApoF. These studies implicate STAT2 as a potentially important player in atherosclerosis, and support the growing evidence that the Type I IFN pathway may contribute to this complex disease.

Induction of pluripotency

The molecular and phenotypic irreversibility of mammalian cell differentiation was a fundamental principle of developmental biology at least until the 1980s, despite numerous reports dating back to the 1950s of the induction of pluripotency in amphibian cells by nuclear transfer (NT). Landmark reports in the 1980s and 1990s in sheep progressively challenged this dogmatic assumption; firstly, embryonic development of reconstructed embryos comprising whole (donor) blastomeres fused to enucleated oocytes, and famously, the cloning of Dolly from a terminally differentiated cell. Thus, the intrinsic ability of oocyte-derived factors to reverse the differentiated phenotype was confirmed. The concomitant elucidation of methods for human embryonic stem cell isolation and cultivation presented opportunities for therapeutic cell replacement strategies, particularly through NT of patient nuclei to enucleated oocytes for subsequent isolation of patient-specific (autologous), pluripotent cells from the resulting blastocysts. Associated logistical limitations of working with human oocytes, in addition to ethical and moral objections prompted exploration of alternative approaches to generate autologous stem cells for therapy, utilizing the full repertoire of factors characteristic of pluripotency, primarily through cell fusion and use of pluripotent cell extracts. Stunningly, in 2006, Japanese scientists described somatic cell reprogramming through delivery of four key factors (identified through a deductive approach from 24 candidate genes). Although less efficient than previous approaches, much of current stem cell research adopts this focused approach to cell reprogramming and (autologous) cell therapy. This chapter is a quasi-historical commentary of the various aforementioned approaches for the induction of pluripotency in lineage-committed cells, and introduces transcriptional and epigenetic changes occurring during reprogramming.

Non-catalytic tyrosine-phosphorylated receptors

Leukocytes play a critical role in recognizing and responding to infection and cancer. Central to this function is an array of cell-surface receptors that lack sequence homology. Many of these receptors have in common the fact that their signaling involves phosphorylation of cytoplasmic domains by extrinsic tyrosine kinases. These non-catalytic tyrosine-phosphorylated receptors (NTRs) share a number of other features, including small size and optimal stimulation by surface-associated ligands. We argue here that NTRs are also likely to share the same kinetic-segregation triggering mechanism, which involves segregation of the engaged NTR from receptor tyrosine phosphatases with large ectodomains such as CD45 and CD148. NTRs signal through tyrosine-containing cytoplasmic motifs, which recruit distinct cytoplasmic signaling proteins when phosphorylated, transducing activatory or inhibitory signals. They have two features that make them uniquely well suited to their role in immune recognition of infection and cancer. Their modular structure enables the coupling of many rapidly evolving receptors with diverse ligand specificities to the same conserved signaling machinery. Their similarity in size and shared signaling machinery enables them to colocalize at cell-cell interfaces when they engage ligands, facilitating the integration of activatory and inhibitory signals from multiple receptors at the cell surface.

A novel viral SOCS from infectious spleen and kidney necrosis virus: interacts with Jak1 and inhibits IFN-α induced Stat1/3 activation

Interferon (IFN)-induced Janus kinase (Jak)/signal transducer and activator of transcription (Stat) pathway is important in controlling immune responses and is negatively response-regulated by the suppressor of cytokine signaling (SOCS) proteins. However, several viruses have developed various strategies to inhibit this pathway to circumvent the anti-viral immunity of the host. The infectious spleen and kidney necrosis virus (ISKNV) is the type species of the genus Megalocytivirus in the family Iridoviridae and a causative agent of epizootics in fish. ISKNV ORF103R encodes a predicted viral SOCS (vSOCS) with high homology to the vertebrate SOCS1, but lacks a SOCS-box domain. Interestingly, vSOCS only exists in the genus Megalocytivirus. ISKNV-vSOCS can block the IFN-α-induced Jak/Stat pathway in HepG2 cells. Over-expression of ISKNV-vSOCS inhibited the activities of IFN-stimulated response element (ISRE) promoter; however, the inhibitions by ISKNV-vSOCS were dose-dependent. ISKNV-vSOCS interacted with Jak1 protein and inhibited its tyrosine kinase activity in vitro. ISKNV-vSOCS also impaired the phosphorylation of Stat1 and Stat3 proteins and suppressed their activations. The point mutations (F18D, S66A, S85A, and R64K) of ISKNV-vSOCS significantly impaired the inhibition of IFN-α-induced ISRE-promoter activation. In conclusion, vSOCS inhibits IFN-α-induced Stat1/Stat3 signaling, suggesting that Megalocytivirus has developed a novel strategy to evade IFN anti-viral immunity via vSOCS protein.

Negative regulation of human astrocytes by interferon (IFN) α in relation to growth inhibition and impaired glucose utilization

The present study assessed the direct effects of IFNs on human astrocytes. Human astrocytes were exposed to human recombinant IFNs, and the proliferation of cells was measured. Type I IFN receptor mRNA and protein expression, the phosphoprotein levels of signaling molecules including JNK, ERK1/2, IκB, p38MAPK, Stat3, and the expression of cytokines were determined respectively. In addition, cellular glucose consumption was measured as well as Glut-1 protein and activation of GSK-3β/mTOR signal were determined. The expression of Type I IFN receptor was detected in cultured human astrocytes. 2 IU/ml IFNα2a and IFNα2b significantly decreased the proliferation of human astrocytes respectively, compared to control. IFNβ had no significant effect on the proliferation of the cells. The phosphorylation of JNK stimulated by all IFNs detected was more pronounced and sustained than ERK1/2 and IκB. No effects were observed on the activation of p38MAPK and Stat3. Moreover, Treatment with IFNα, especially with IFNα2b, decreased glucose consumption and stimulated phosphorylation of GSK-3β and mTOR, but decreased the expression of Glut-1. In contrast, IFNβ had no significant effect on either glucose consumption or activation of GSK-3β/mTOR signals. INFα2b significantly decreased the levels of IL-8 whereas the levels of GM-CSF were increased. The present study demonstrates direct inhibitory effects of IFNα on cell proliferation, cell signaling and glucose utilization in human astrocytes.

Hepatitis B virus X protein inhibits extracellular IFN-α-mediated signal transduction by downregulation of type I IFN receptor

We have previously shown that hepatitis B virus (HBV) protein X (HBX), a regulatory protein of HBV, activates Stat1, leading to type I interferon (IFN) production. Type I IFN secreted from HBX-expressing hepatic cells enforces antiviral signals through its binding to the cognate type I IFN receptor. We therefore investigated how cells handle this detrimental situation. Interestingly, compared to Chang cells stably expressing an empty vector (Chang-Vec), Chang cells stably expressing HBX (Chang-HBX) showed lower levels of IFN-α receptor 1 (IFNAR1) protein, a subunit of type I IFN receptor. The levels of IFNAR1 transcripts detected in Chang-HBX cells were lower than the levels in Chang-Vec cells, indicating that HBX regulates IFNAR1 at the transcriptional level. Moreover, we observed that HBX induced the translocation of IFNAR1 to the cytoplasm. Consistent with these observations, HBX also downregulated Tyk2, which is required for the stable expression of IFNAR1 on the cell surface. Eventually, Chang-HBX cells consistently maintained a lower level of IFNAR1 expression and displayed no proper response to IFN-α, while Chang-Vec cells exhibited a proper response to IFN-α treatment. Taken together, we propose that HBX downregulates IFNAR1, leading to the avoidance of extracellular IFN-α signal transduction.

The two faces of interferon-γ in cancer

Interferon-γ is a cytokine whose biological activity is conventionally associated with cytostatic/cytotoxic and antitumor mechanisms during cell-mediated adaptive immune response. It has been used clinically to treat a variety of malignancies, albeit with mixed results and side effects that can be severe. Despite ample evidence implicating a role for IFN-γ in tumor immune surveillance, a steady flow of reports has suggested that it may also have protumorigenic effects under certain circumstances. We propose that, in fact, IFN-γ treatment is a double-edged sword whose anti- and protumorigenic activities are dependent on the cellular, microenvironmental, and/or molecular context. As such, inhibition of the IFN-γ/IFN-γ receptor pathway may prove to be a viable new therapeutic target for a subset of malignancies.

Characterization of kinase inhibitors using reverse phase protein arrays

Using the reverse protein array platform in combination with planar waveguide technology, which allows detection of proteins in spotted cell lysates with high sensitivity in a 96-well microtiter-plate format for growing, treating, and lysing cells was shown to be suitable for this approach and indicates the usefulness of the technology as a screening tool for characterization of large numbers of kinase inhibitors. In this study, we have used reverse protein arrays to profile kinase inhibitors in various cellular pathways in order to unravel their MoA. Multiplexing and simultaneous analysis of several phospho-proteins within the same lysate allows (1) the estimation of inhibitor concentrations needed to shut down an entire pathway, (2) the estimation of inhibitor selectivity, and (3) the comparison of inhibitors of different kinases within one assay. For example, parallel analysis of p-InsR, p-PKB, p-GSK-3, p-MEK, p-ERK, and p-S6rp in insulin treated A14 cells allows profiling for inhibitors of the InsR, PI3K, PKB, mTor, RAF, and MEK. Selective kinase inhibitors revealed different specific inhibitory pattern of the analyzed phospho-read outs. Altogether, multiplexed analysis of reverse (phase) protein arrays is a powerful tool to characterize kinase inhibitors in a semi-automated low to medium throughput assay format.

Gprc5a deletion enhances the transformed phenotype in normal and malignant lung epithelial cells by eliciting persistent Stat3 signaling induced by autocrine leukemia inhibitory factor

Signal transducers and activators of transcription 3 (Stat3) is activated by cytokines and growth factors in lung cancers and regulates expression of genes implicated in cell growth, survival, and transformation. Previously, we found that mice with a deletion of the G protein-coupled receptor, family C, group 5, member a (Gprc5a) gene develop lung tumors, indicating that Gprc5a is a tumor suppressor. Herein, we show that epithelial cells from Gprc5a knockout mouse lung (Gprc5a(-/-) cells) survive better in vitro in medium deprived of exogenous growth factors and form more colonies in semisolid medium than their counterparts from wild-type mice (Gprc5a(+/+) cells). Stat3 tyrosine 705 phosphorylation and expression of several Stat3-regulated antiapoptotic genes were higher in Gprc5a(-/-) than in Gprc5a(+/+) cells. Both cell types secreted leukemia inhibitory factor (Lif); however, whereas Stat3 activation was persistent in Gprc5a(-/-) cells, it was transient in Gprc5a(+/+) cells. Lung adenocarcinoma cells isolated from Gprc5a(-/-) mice also exhibited autocrine Lif-mediated Stat3 activation. The level of Socs3, the endogenous Stat3 inhibitory protein, was higher in Gprc5a(+/+) than in Gprc5a(-/-) cells, and expression of the tumor suppressor stabilized Socs3. Inhibition of Stat3 signaling in Gprc5a(-/-) normal and cancer cells by the Janus-activated kinase 2 inhibitor AG490 or by a dominant negative Stat3(Y705F) increased starvation-induced apoptosis and inhibited colony formation. These results show that persistent Stat3 activation is important for the survival and transformation of Gprc5a(-/-) lung cells and suggest that the tumor suppressive effects of Gprc5a are mediated, at least in part, by inhibition of Stat3 signaling through Socs3 stabilization.

A psychoneuroimmunological review on cytokines involved in antidepressant treatment response

OBJECTIVES

The literature exploring the role that cytokine functioning plays in the pathogenesis and treatment of depressive illness is reviewed. The review focuses on the influence of antidepressants on cytokines, and on how treatment response might be affected by genetic variants of cytokines.

METHOD

The authors systematically reviewed the scientific literature on the subject over the last 20 years, searching PubMed, PsychInfo, and Cochrane databases.

RESULTS

Antidepressants modulate cytokine functioning, and these mechanisms appear to directly influence treatment outcome in depression. Antidepressants appear to normalize serum levels of major inflammatory cytokines, including interleukin (IL)-1beta, IL-6, tumor necrosis factor alpha (TNF-alpha), and interferon gamma (IFN-gamma). Antidepressants are postulated to modulate cytokine functioning through their effects on intracellular cyclic adenosyl monophosphate (cAMP), serotonin metabolism, the hypothalamo-pituitary-adrenocortical (HPA) axis or through a direct action on neurogenesis. Preliminary research shows that cytokine genotypes and functioning may be able to help predict antidepressant treatment response.

CONCLUSIONS

Current literature demonstrates an association between antidepressant action and cytokine functioning in major depression. Improved understanding of the specific pharmacologic and pharmacogenetic mechanisms is needed. Such knowledge may serve to enhance our understanding of depression, leading to promising new directions in the pathology, nosology, and treatment of depression.

Perspectives for the use of structural information and chemical genetics to develop inhibitors of Janus kinases

Gain-of-function mutations in the genes encoding Janus kinases have been discovered in various haematologic diseases. Jaks are composed of a FERM domain, an SH2 domain, a pseudokinase domain and a kinase domain, and a complex interplay of the Jak domains is involved in regulation of catalytic activity and association to cytokine receptors. Most activating mutations are found in the pseudokinase domain. Here we present recently discovered mutations in the context of our structural models of the respective domains. We describe two structural hotspots in the pseudokinase domain of Jak2 that seem to be associated either to myeloproliferation or to lymphoblastic leukaemia, pointing at the involvement of distinct signalling complexes in these disease settings. The different domains of Jaks are discussed as potential drug targets. We present currently available inhibitors targeting Jaks and indicate structural differences in the kinase domains of the different Jaks that may be exploited in the development of specific inhibitors. Moreover, we discuss recent chemical genetic approaches which can be applied to Jaks to better understand the role of these kinases in their biological settings and as drug targets.

Gene modulation and immunoregulatory roles of interferon gamma

Interferon-gamma (IFNgamma) is a central regulator of the immune response and signals via the Janus Activated Kinase (JAK)-Signal Transducer and Activator of Transcription (STAT) pathway. Phosphorylated STAT1 homodimers translocate to the nucleus, bind to Gamma Activating Sequence (GAS) and recruit additional factors to modulate gene expression. A bioinformatics analysis revealed that greater number of putative promoters of immune related genes and also those not directly involved in immunity contain GAS compared to response elements (RE) for Interferon Regulatory Factor (IRF)1, Nuclear factor kappa B (NFkappaB) and Activator Protein (AP)1. GAS is present in putative promoters of well known IFNgamma-induced genes, IRF1, GBP1, CXCL10, and other genes identified were TLR3, VCAM1, CASP4, etc. Analysis of three microarray studies revealed that the expression of a subset of only GAS containing immune genes were modulated by IFNgamma. As a significant correlation exists between GAS containing immune genes and IFNgamma-regulated gene expression, this strategy may identify novel IFNgamma-responsive immune genes. This analysis is integrated with the literature on the roles of IFNgamma in mediating a plethora of functions: anti-microbial responses, antigen processing, inflammation, growth suppression, cell death, tumor immunity and autoimmunity. Overall, this review summarizes our present knowledge on IFNgamma mediated signaling and functions.

The JAK and STAT family members of the mandarin fish Siniperca chuatsi: molecular cloning, tissues distribution and immunobiological activity

The JAK/STAT signal transduction pathway plays a critical role in host defence against viral and bacterial infections. In the present study, we report cDNA cloning and characterization of the JAK family (mJAK1-3 and mTYK2) and STAT family members (mSTAT1, mSTAT3-6) from the mandarin fish Siniperca chuatsi. To our knowledge, JAK2, TYK2 and STAT6 genes were cloned from fish for the first time. The mJAK family proteins consist of 1112-1177 residues with a FERM domain, an SH2 domain, a pseudokinase domain, and a tyrosine kinase domain. The mSTAT family members contain 716-786 residues with similar architecture, including an N-terminal domain, a coiled coil domain, a DNA binding domain, a linker domain, an SH2 domain, and a transcription activation domain. Multiple sequence alignments of mJAKs/mSTATs and phylogenetic analysis showed that mJAK1 was closed to mTYK2, and mJAK2 was closed to mJAK3. Quantitative real-time PCR results revealed that mJAK/mSTAT family members were expressed in most tissues examined except muscle. In mandarin fish fry cells, the expressions of IRF-1, Mx, SOCS1 and SOCS3 genes were significantly induced by poly(I:C) stimulation, indicating that the mJAK/mSTAT signal pathway is activated by poly(I:C). Furthermore, expressions of all four mJAKs and four mSTATs were all up-regulated after poly(I:C) stimulation, but expression of mSTAT5 was inhibited by poly(I:C). These results suggest that mandarin fish has the JAK/STAT signal transduction pathways similar to those in mammals, and these signalling pathways may play an important role in regulation of antiviral responses in fish.

Enhancement of TRAIL cytotoxicity by AG-490 in human ALL cells is characterized by downregulation of cIAP-1 and cIAP-2 through inhibition of Jak2/Stat3

The ability of death-inducing tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to selectively kill a variety of cancer cells has been largely described, but one of the major concerns with the treatment is the occurrence of drug resistance and possible toxic side effects. Here, we report that TRAIL induces apoptosis in Jurkat and SUPT1 T cell lines and in human T-ALL blasts but not in healthy subject-derived peripheral blood mononuclear cells. In parallel, the treatment with TRAIL and Tyrphostin (AG-490), a selective Janus kinase 2 inhibitor, produces an evident enhancement of cytotoxicity, characterized by a significant inhibition of Stat3 phosphorylation compared to controls or to TRAIL alone-treated samples, and associated with a dramatic decrease of both cIAP-1 and cIAP-2 mRNA levels. Downregulation of cIAP-1 and cIAP-2 by specific small interference RNAs significantly amplifies TRAIL-reduced cytotoxicity. All together, these findings strongly indicate that cIAP-1 and cIAP-2 downregulation is a fundamental step in the signaling pathways mediating the combinatorial effect of TRAIL and AG-490 on T cell leukemia. These findings may help to open new routes for the development of less toxic pharmacological strategies in the treatment of patients affected by TRAIL-sensitive leukemias.

Receptor density is key to the alpha2/beta interferon differential activities

Multiple type I interferons (IFN-alpha/beta) elicit Jak/Stat activation, rapid gene induction, and pleiotropic effects, such as differentiation, antiviral protection, and blocks in proliferation, which are dependent on the IFN subtype and the cellular context. To date, ligand- and receptor-specific molecular determinants underlying IFN-alpha/beta differential activities or potencies have been well characterized. To analyze cellular determinants that impact subtype-specific potency, human fibrosarcoma U5A-derived clones, exhibiting a gradient of IFN sensitivity by virtue of increasing receptor levels, were monitored for Jak/Stat signaling, gene induction, cell cycle lengthening, and apoptosis. In cells with scarce receptors, IFN-beta was more potent than IFN-alpha2 in antiproliferative activity, while the two subtypes were equipotent in all other readouts. Conversely, in cells with abundant receptors, IFN-alpha2 matched or even surpassed IFN-beta in all readouts tested. Our results suggest that the differential activities of the IFN subtypes are dictated not only by the intrinsic ligand/receptor binding kinetics but also by the density of cell surface receptor components.

Molecular cloning and expression analysis of the STAT1 gene from olive flounder, Paralichthys olivaceus

Background

Signal transducer and activator of transcription 1 (STAT1) is a critical component of interferon (IFN)-alpha/beta and IFN-gamma signaling. Although seven isoforms of STAT proteins have been reported from mammals, limited information is available for the STAT genes in fish. We isolated complementary DNA with high similarity to mammalian STAT1 from the olive flounder, Paralichthys olivaceus.

Results

A DNA fragment containing the conserved SH2 domain was amplified by RT-PCR using degenerate primers designed based on the highly conserved sequences in the SH2 domains of the zebrafish and mammalian STAT1. The complete cDNA sequence was obtained by 5' and 3' RACE. The flounder STAT1 transcript consisted of 2,909 bp that encoded a polypeptide of 749 amino acids. The overall similarity between flounder STAT1 and other STATs was very high, with the highest amino acid sequence identity to snakehead (89%). Phylogenetic analyses reveal that flounder STAT1 is in the same monophyletic group with snakehead STAT1. Quantitative real time RT-PCR and in situ hybridization revealed that STAT1 was expressed in almost all examined organs and tissues, with high expression in gill, spleen, kidney, and heart. The accumulation of STAT1 mRNA in different developmental stages, as determined by real time RT-PCR, increased with development.

Conclusion

Recent cloning of various cytokine genes and the STAT1 gene of olive flounder here suggest that fish also use the highly specialized JAK-STAT pathway for cytokine signaling. Identification of other STAT genes will elucidate in detail the signal transduction system in this fish.

The Stat3-activating Tyk2 V678F mutant does not up-regulate signaling through the type I interferon receptor but confers ligand hypersensitivity to a homodimeric receptor

Tyk2 is a Jak family member involved in cytokine signaling through heterodimeric-type receptors. Here, we analyzed the impact of the Val(678)-to-Phe substitution on Tyk2 functioning. This mutation is homologous to the Jak2 Val(617)-to-Phe mutation, implicated in myeloproliferative disorders. We studied ligand-independent and ligand-dependent Jak/Stat signaling in cells expressing Tyk2 V678F. Moreover, the effect of Tyk2 V678F was monitored in the context of the native heterodimeric interferon alpha receptor and in the context of a homodimeric receptor chimera, EpoR/R1, containing the ectodomain of the erythropoietin receptor. We show that Tyk2 V678F has increased catalytic potential in vivo and in vitro and more so when it is anchored to the homodimeric receptor. Tyk2 V678F leads to constitutive Stat3 phosphorylation but has no notable effect on the canonical interferon alpha-induced signaling. However, if anchored to the homodimeric EpoR/R1, the mutant confers to the cell increased sensitivity to erythropoietin. Thus, despite the catalytic gain of function of Tyk2 V678F, the effect on ligand-induced signaling is manifest only when two mutant enzymes are juxtaposed via the homodimeric receptor.

Comparable potency of IFNalpha2 and IFNbeta on immediate JAK/STAT activation but differential down-regulation of IFNAR2

Type I IFNs (interferons) (IFNalpha/beta) form a family of related cytokines that control a variety of cellular functions through binding to a receptor composed of IFNAR (IFNalpha receptor subunit) 1 and 2. Among type I IFNs, the alpha2 and beta subtypes exhibit a large difference in their binding affinities to IFNAR1, and it was suggested that high concentrations of IFNAR1 may compensate for its low intrinsic binding affinity for IFNalpha2. We tested whether receptor-proximal signalling events are sensitive to IFNAR1 surface concentration by investigating the relationship between relative IFNAR1/IFNAR2 surface levels and IFNalpha2 and IFNbeta signalling potencies in several cell lines. For this, we monitored the activation profile of JAK (Janus kinase)/STAT (signal transducer and activator of transcription) proteins, measured basal and ligand-induced surface decay of each receptor subunit and tested the effect of variable IFNAR1 levels on IFNalpha2 signalling potency. Our data show that the cell-surface IFNAR1 level is indeed a limiting factor for assembly of the functional complex, but an increased concentration of it does not translate into an IFNalpha/beta differential JAK/STAT signalling nor does it change the dynamics of the engaged receptor. Importantly, however, our data highlight a differential effect upon routing of IFNAR2. Following binding of IFNalpha2, IFNAR2 is internalized, but, instead of being routed towards degradation as it is when complexed to IFNbeta, it recycles back to the cell surface. These observations suggest strongly that the stability and the intracellular lifetime of the ternary complex account for the differential control of IFNAR2. Moreover, the present study opens up the attractive possibility that endosomal-initiated signalling may contribute to IFNalpha/beta differential bioactivities.

Identification and expression analysis of novel Jakmip1 transcripts

Janus kinase and microtubule interacting protein 1, (Jakmip1) conserved in vertebrates and predominantly expressed in neural tissues, was identified for its ability to bind Tyk2, a member of the Janus kinase (Jak) family of non-receptor tyrosine kinases. Recently Jakmip1 was also identified as an interacting partner of GABA(B)R1 and as a regulatory protein of GABA(B)R2 mRNA. We have confirmed that this gene is highly expressed in brain and retina tissues and it is also present at lower levels in other tissues. We have identified four new transcripts of 2975 bp, 1743 bp, 2189 bp and 2420 bp respectively, named Jakmip1B, Jakmip1C, Jakmip1D and Jakmip1E. The involvement of the Janus kinase pathway in the development of mouse retina and in the control of survival and proliferation of human retinal ganglion cells, together with the restricted Jakmip1 gene expression pattern, may suggest this gene is a putative candidate for neuro-degenerative and retinal diseases. For this reason, a mutation analysis of the Jakmip1 gene in a panel of 50 unrelated patients with retinitis pigmentosa has been performed, revealing no pathogenic mutations.

A cost effective non-commercial ECL-solution for Western blot detections yielding strong signals and low background

We compared several alternative ECL solutions for Western blot detection of endogenous proteins in whole cell lysates using inexpensive, commercially available reagents. Starting from an existing protocol based on p-coumaric acid (pCA) as enhancer, we found that the ECL solution containing 4-iodophenylboronic acid (4IPBA) generated strong specific signals and low background chemiluminescence. We optimised the luminol, 4IPBA and hydrogenperoxide concentrations of this 4IPBA-ECL solution. The optimised 4IPBA-ECL solution (100 mM Tris/HCl pH 8.8, 1.25 mM luminol, 2 mM 4IPBA, 5.3 mM hydrogenperoxide) shows a greatly increased signal intensity compared to the initial pCA-ECL protocol and to some commercially available ECL solutions. In addition, the optimised 4IPBA-ECL solution also generates much lower background chemiluminescence than other non-commercial ECL solutions using p-coumaric acid or 4-iodophenol as enhancers. The 4IPBA-ECL solution was stable when stored but had the lowest background when prepared freshly from stock solutions. Thus, we present an optimised protocol for a well-performing inexpensive ECL solution which is an alternative to expensive commercial ECL solutions and which achieves a better signal and lower background than the commercial solutions tested.