STAT3 is a serine kinase target in T lymphocytes. Interleukin 2 and T cell antigen receptor signals converge upon serine 727

JNK mediates serine phosphorylation of STAT3 in response to fatty acids released by lipolysis

Adipocytes play an essential role in energy balance and metabolic health. Excess nutrients are stored within the white adipose tissue (WAT) as triglycerides. Energetic demand is communicated to the adipocyte by the sympathetic nervous system. Catecholamines released by nerve terminals in the adipose tissue promote lipolysis, a process in which triglycerides are broken down into fatty acids and glycerol. Lipolytic activation of white adipocytes is associated with an increase in the rate of oxygen consumption. This lipolysis induced respiration requires phosphorylation of signal transducer and activator of transcription 3 (STAT3) at Ser727. This study identifies c-Jun N-terminal kinase 1 (JNK1) as the kinase responsible for this critical phosphorylation event, and thus a key regulator of lipolysis-driven oxidative metabolism. We demonstrate that JNK1 is activated in response to intracellular fatty acids released during lipolysis and phosphorylates lipid droplet-associated STAT3, leading to inhibition of glycerol-3-phosphate acyltransferase 3 (GPAT3) and suppression of fatty acid re-esterification. This mechanism promotes uncoupled mitochondrial respiration, increasing energy expenditure. Inhibition of JNK1 attenuated oxidative metabolism without affecting the rate of lipolysis. The MAP kinase cascade upstream of JNK1 in lipolytic adipocytes remains unclear. Neither apoptosis signal-regulating kinase 1 (ASK1) nor mitogen-activated protein kinase kinases 4/7 (MKK4/7) appear to be required. Our findings suggest that JNK1 functions as a metabolic sensor in adipocytes, activating oxidative metabolism through STAT3 phosphorylation in response to fatty acids, with implications for energy balance and obesity-related metabolic regulation.

Revival of recombinant IL-2 therapy - approaches from the past until today

Interleukin-2 (IL-2) was one of the first cytokines discovered and its central role in T cell function soon led to the notion that the cytokine could specifically activate immune cells to combat cancer cells. Recombinant human IL-2 (recIL-2) belonged to the first anti-cancer immunotherapeutics that received marketing authorization and while it mediated anti-tumor effects in some cancer entities, treatment was associated with severe and systemic side effects. RecIL-2 holds an exceptional therapeutic potential, which can either lead to stimulation of the immune system - favorable during cancer treatment - or immunosuppression - used for treatment of inflammatory diseases such as autoimmunity. Due to these pleiotropic immune effects, recIL-2 therapy is still a hot topic in research and modified recIL-2 drug candidates show ameliorated efficacy and safety in pre-clinical and clinical studies. The Immune Safety Avatar (imSAVAR) consortium aims to systemically assess mechanisms leading to adverse events provoked by recIL-2 immunotherapy as a use case in order to aid safety evaluation of future recIL-2-based therapies. Here, we summarize the historical use of recIL-2 therapy, associated side effects, and describe the molecular basis of the dual role of IL-2. Finally, an overview of new recIL-2 compounds and delivery systems, which are currently being developed, will be given, highlighting a possible comeback of recIL-2 therapy.

Lymphostatin, a virulence factor of attaching and effacing Escherichia coli, inhibits proliferation and cytokine responses of human T cells in a manner associated with cell cycle arrest but not apoptosis or necrosis

Lymphostatin is a virulence factor of enteropathogenic E. coli (EPEC) and non-O157 serogroup enterohaemorrhagic E. coli. Previous studies using whole-cell lysates of EPEC showed that lymphostatin inhibits the mitogen-activated proliferation of bulk human peripheral blood mononuclear cells (PBMCs) and the production of cytokines IL-2, IL-4, IL-5, and IFN-γ. Here, we used highly purified lymphostatin and PBMC-derived T cells to show that lymphostatin inhibits anti-CD3/anti-CD28-activated proliferation of human CD4⁺ and CD8⁺ T cells and blocks the synthesis of IL-2, IL-4, IL-10 and IFN-γ without affecting cell viability and in a manner dependent on an N-terminal DTD glycosyltransferase motif. Such inhibition was not observed with T cells activated by phorbol 12-myristate 13-acetate and ionomycin, implying that lymphostatin targets T cell receptor signaling. Analysis of the expression of CD69 indicated that lymphostatin suppresses T cell activation at an early stage and no impacts on apoptosis or necrosis were observed. Flow cytometric analysis of the DNA content of lymphostatin-treated CD4⁺ and CD8⁺ T cells showed a concentration- and DTD-dependent accumulation of the cells in the G0/G1 phase of the cell cycle, and corresponding reduction of the percentage of cells in S phase. Consistent with this, we found a marked reduction in the abundance of cyclins D3, E and A and loss of phosphorylated Rb over time in activated T cells from 8 donors treated with lymphostatin. Moreover, the cyclin-dependent kinase (cdk) inhibitor p27^kip1, which inhibits progression of the cell cycle at G1 by acting on cyclin E-cdk2 or cyclin D-cdk4 complexes, was found to be accumulated in lymphostatin-treated T cells. Analysis of the abundance of phosphorylated kinases involved in signal transduction found that 30 of 39 were reduced in abundance following lymphostatin treatment of T cells from 5 donors, albeit not significantly so. Our data provide novel insights into the mode of action of lymphostatin on human T lymphocytes.

IL-6 Responsiveness of CD4+ and CD8+ T Cells after Allogeneic Stem Cell Transplantation Differs between Patients and Is Associated with Previous Acute Graft versus Host Disease and Pretransplant Antithymocyte Globulin Therapy

Graft-versus-host disease (GVHD), one of the most common and serious complications after allogeneic stem cell transplantation, is mediated by allocative T cells. IL-6 mediates both pro- and anti-inflammatory effects and modulates T cell response through classical signaling and trans-signaling. We investigated the effects on the mTOR and JAK/STAT pathways after various types of IL-6 signaling for circulating T cells were derived from 31 allotransplant recipients 90 days post-transplant. Cells were stimulated with IL-6 alone, hyper-IL-6 (trans-signaling), IL-6+IL-6 receptor (IL-6R; classical + trans-signaling) and IL-6+IL-6R+soluble gp130-Fc (classical signaling), and flow cytometry was used to investigate the effects on phosphorylation of AKT (Thr308), mTOR (Ser2442), STAT3 (Ser727) and STAT3 (Tyr705). CD3⁺CD4⁺ and CD3⁺C8⁺ T cells responded to classical and trans IL-6 stimulation with increased STAT3 (Tyr705) phosphorylation; these responses were generally stronger for CD3⁺CD4⁺ cells. STAT3 (Tyr705) responses were stronger for patients with previous acute GVHD; CD3⁺CD4⁺ cells from GVHD patients showed an additional STAT3 (Ser727) response, whereas patients without acute GVHD showed additional mTOR (Ser2448) responses. Furthermore, treatment with antithymocyte globulin as a part of GVHD prophylaxis was associated with generally weaker STAT3 (Tyr705) responses and altered STAT3 (Ser727) responsiveness of CD3⁺CD4⁺ cells together with increased mTOR (Ser2448) responses for the CD3⁺CD8⁺ cells. Thus, early post-transplant CD3⁺CD4⁺ and CD3⁺ CD8⁺ T cell subsets differ in their IL-6 responsiveness; this responsiveness is modulated by antithymocyte globulin and differs between patients with and without previous acute GVHD. These observations suggest that allotransplant recipients will be heterogeneous with regard to the effects of post-transplant IL-6 targeting.

Facile discovery of surrogate cytokine agonists

Cytokines are powerful immune modulators that initiate signaling through receptor dimerization, but natural cytokines have structural limitations as therapeutics. We present a strategy to discover cytokine surrogate agonists by using modular ligands that exploit induced proximity and receptor dimer geometry as pharmacological metrics amenable to high-throughput screening. Using VHH and scFv to human interleukin-2/15, type-I interferon, and interleukin-10 receptors, we generated combinatorial matrices of single-chain bispecific ligands that exhibited diverse spectrums of functional activities, including potent inhibition of SARS-CoV-2 by surrogate interferons. Crystal structures of IL-2R:VHH complexes revealed that variation in receptor dimer geometries resulted in functionally diverse signaling outputs. This modular platform enabled engineering of surrogate ligands that compelled assembly of an IL-2R/IL-10R heterodimer, which does not naturally exist, that signaled through pSTAT5 on T and natural killer (NK) cells. This "cytokine med-chem" approach, rooted in principles of induced proximity, is generalizable for discovery of diversified agonists for many ligand-receptor systems.

Emerging roles of protein O-GlcNAcylation in cardiovascular diseases: Insights and novel therapeutic targets

Cardiovascular diseases (CVDs) are the leading cause of death globally. While the major focus of pharmacological and non-pharmacological interventions has been on targeting disease pathophysiology and limiting predisposing factors, our understanding of the cellular and molecular mechanisms underlying the pathogenesis of CVDs remains incomplete. One mechanism that has recently emerged is protein O-GlcNAcylation. This is a dynamic, site-specific reversible post-translational modification of serine and threonine residues on target proteins and is controlled by two enzymes: O-linked β-N-acetylglucosamine transferase (OGT) and O-linked β-N-acetylglucosaminidase (OGA). Protein O-GlcNAcylation alters the cellular functions of these target proteins which play vital roles in pathways that modulate vascular homeostasis and cardiac function. Through this review, we aim to give insights on the role of protein O-GlcNAcylation in cardiovascular diseases and identify potential therapeutic targets in this pathway for development of more effective medicines to improve patient outcomes.

Catecholamines suppress fatty acid re-esterification and increase oxidation in white adipocytes via STAT3

Catecholamines stimulate the mobilization of stored triglycerides in adipocytes to provide fatty acids (FAs) for other tissues. However, a large proportion is taken back up and either oxidized or re-esterified. What controls the disposition of these FAs in adipocytes remains unknown. Here, we report that catecholamines redirect FAs for oxidation through the phosphorylation of signal transducer and activator of transcription 3 (STAT3). Adipocyte STAT3 is phosphorylated upon activation of β-adrenergic receptors, and in turn suppresses FA re-esterification to promote FA oxidation. Adipocyte-specific Stat3 KO mice exhibit normal rates of lipolysis, but exhibit defective lipolysis-driven oxidative metabolism, resulting in reduced energy expenditure and increased adiposity when they are on a high-fat diet. This previously unappreciated, non-genomic role of STAT3 explains how sympathetic activation can increase both lipolysis and FA oxidation in adipocytes, revealing a new regulatory axis in metabolism.

Signaling and Function of Interleukin-2 in T Lymphocytes

The discovery of interleukin-2 (IL-2) changed the molecular understanding of how the immune system is controlled. IL-2 is a pleiotropic cytokine, and dissecting the signaling pathways that allow IL-2 to control the differentiation and homeostasis of both pro- and anti-inflammatory T cells is fundamental to determining the molecular details of immune regulation. The IL-2 receptor couples to JAK tyrosine kinases and activates the STAT5 transcription factors. However, IL-2 does much more than control transcriptional programs; it is a key regulator of T cell metabolic programs. The development of global phosphoproteomic approaches has expanded the understanding of IL-2 signaling further, revealing the diversity of phosphoproteins that may be influenced by IL-2 in T cells. However, it is increasingly clear that within each T cell subset, IL-2 will signal within a framework of other signal transduction networks that together will shape the transcriptional and metabolic programs that determine T cell fate.

O-Glycosylation with O-linked β-N-acetylglucosamine increases vascular contraction: Possible modulatory role on Interleukin-10 signaling pathway

AIMS

The interleukin-10 (IL-10) is an immuno-regulatory cytokine that plays a protective effect in the vasculature. IL-10 binding to its receptor, activating the IL-10/JAK1/STAT3 cascade to exert its effects. Therefore, STAT3 phosphorylation is essential for IL-10 actions. O-Glycosylation with linked β-N-acetylglucosamine (O-GlcNAc) is a post-translational modification able to regulate many proteins by interfering with protein on a phosphorylation level. Our aim was to determine whether O-GlcNAc promotes the inhibition of IL-10-pathway (JAK1/STAT3/IL-10), inactivationg its action in the vasculature.

MAIN METHODS

Mice (C57BL/6) aortic segments were incubated with vehicle or Thiamet G (0.1 mM, for 24 h) to increase global O-GlcNAc levels. Aortas from knockout mice for IL-10 were also used. Vascular reactivity and western blot tests were performed to evaluate protein expression.

KEY FINDINGS

High levels of O-GlcNAc, induced by Thiamet G incubation, increased vascular expression of JAK1, but decreased expression and activity of STAT3. In addition, IL-10 levels were diminished in arteries treated with Thiamet G. Absence of IL-10, as well as augmented O-GlcNAcylation, increased vascular reactivity to constrictor stimuli, an effect that was abolished by ERK 1/2 inhibitor. High levels of O-GlcNAc and the absence of IL-10 also leads to increased vascular expression of ERK1/2.

SIGNIFICANCE

Our data suggest that O-GlcNAc modification seems to (dys)regulate IL-10 signaling pathway and consequently, compromise the protective effect of this cytokine in vasculature. It is possible that there is a promising relationship in pathophysiological conditions where changes in O-GlcNAcylation and IL-10 levels are observed, such as hypertension and diabetes.

Source of dietary sucrose influences development of leptin resistance in male and female rats

Male rats offered 30% sucrose solution in addition to chow develop leptin resistance without an increase in energy intake or body fat. This study tested whether the leptin resistance was dependent on the physical form of the sucrose. Sprague-Dawley rats were offered a sucrose-free (NS) diet, a 66.6% of energy as sucrose (HS) diet, or the NS diet + 30% sucrose solution (LS). Sucrose intake of LS rats equaled that of HS rats, but total carbohydrate intake exceeded that of HS rats. After 33 days, male and female LS rats were resistant to the inhibitory effect of peripherally administered leptin on food intake. LS rats drank small, frequent meals of sucrose during light and dark periods, whereas HS rats consumed more meals during the dark than the light period and remained responsive to leptin. Diet did not affect daily energy intake or insulin sensitivity. There was a small increase in body fat in the female rats. Leptin sensitivity was restored within 5 days of withdrawal from sucrose in male LS rats. This rapid reversal suggested that leptin resistance was associated with the metabolic impact of drinking sucrose. An experiment was carried out to test whether activity of the hexosamine biosynthetic pathway and glycation of leptin signaling proteins were increased in LS rats, but the results were equivocal. A final experiment determined that female LS rats were leptin-resistant within 18 days of access to sucrose solution and that the small, but significant, increase in body fat was associated with increased adipocyte glucose utilization and insulin responsiveness, which may have been secondary to adipocyte leptin resistance.

Responses to Cytokines and Interferons that Depend upon JAKs and STATs

Many cytokines and all interferons activate members of a small family of kinases (the Janus kinases [JAKs]) and a slightly larger family of transcription factors (the signal transducers and activators of transcription [STATs]), which are essential components of pathways that induce the expression of specific sets of genes in susceptible cells. JAK-STAT pathways are required for many innate and acquired immune responses, and the activities of these pathways must be finely regulated to avoid major immune dysfunctions. Regulation is achieved through mechanisms that include the activation or induction of potent negative regulatory proteins, posttranslational modification of the STATs, and other modulatory effects that are cell-type specific. Mutations of JAKs and STATs can result in gains or losses of function and can predispose affected individuals to autoimmune disease, susceptibility to a variety of infections, or cancer. Here we review recent developments in the biochemistry, genetics, and biology of JAKs and STATs.

The kinase TBK1 functions in dendritic cells to regulate T cell homeostasis, autoimmunity, and antitumor immunity

Dendritic cells (DCs) are crucial for mediating immune responses but, when deregulated, also contribute to immunological disorders, such as autoimmunity. The molecular mechanism underlying the function of DCs is incompletely understood. In this study, we have identified TANK-binding kinase 1 (TBK1), a master innate immune kinase, as an important regulator of DC function. DC-specific deletion of Tbk1 causes T cell activation and autoimmune symptoms and also enhances antitumor immunity in animal models of cancer immunotherapy. The TBK1-deficient DCs have up-regulated expression of co-stimulatory molecules and increased T cell-priming activity. We further demonstrate that TBK1 negatively regulates the induction of a subset of genes by type I interferon receptor (IFNAR). Deletion of IFNAR1 could largely prevent aberrant T cell activation and autoimmunity in DC-conditional Tbk1 knockout mice. These findings identify a DC-specific function of TBK1 in the maintenance of immune homeostasis and tolerance.

Constitutive Phosphorylation of STAT3 by the CK2-BLNK-CD5 Complex

In chronic lymphocytic leukemia (CLL), STAT3 is constitutively phosphorylated on serine 727 and plays a role in the pathobiology of CLL. However, what induces constitutive phosphorylation of STAT3 is currently unknown. Mass spectrometry was used to identify casein kinase 2 (CK2), a serine/threonine kinase that coimmunoprecipitated with serine phosphorylated STAT3 (pSTAT3). Furthermore, activated CK2 incubated with recombinant STAT3 induced phosphorylation of STAT3 on serine 727. Although STAT3 and CK2 are present in normal B- and T cells, STAT3 is not constitutively phosphorylated in these cells. Further study found that CD5 and BLNK coexpressed in CLL, but not in normal B- or T cells, are required for STAT3 phosphorylation. To elucidate the relationship of CD5 and BLNK to CK2 and STAT3, STAT3 was immunoprecipitated from CLL cells, and CK2, CD5, and BLNK were detected in the immunoprecipitate. Conversely, STAT3, CD5, and BLNK were in the immunoprecipitate of CLL cells immunoprecipitated with CK2 antibodies. Furthermore, siRNA knockdown of CD5 or BLNK, or treatment with CD5-neutralizing antibodies significantly reduced the levels of serine pSTAT3 in CLL cells. Finally, confocal microscopy determined that CD5 is cell membrane bound, and fractionation studies revealed that the CK2/CD5/BLNK/STAT3 complex remains in the cytoplasm, whereas serine pSTAT3 is shuttled to the nucleus.Implications: These data show that the cellular proteins CK2, CD5, and BLNK are required for constitutive phosphorylation of STAT3 in CLL. Whether this protein complex phosphorylates other proteins or inhibiting its activity would have clinical benefit in patients has yet to be determined. Mol Cancer Res; 15(5); 610-8. ©2017 AACR.

Quantitative phosphoproteomics of cytotoxic T cells to reveal protein kinase d 2 regulated networks

The focus of the present study was to characterize the phosphoproteome of cytotoxic T cells and to explore the role of the serine threonine kinase PKD2 (Protein Kinase D2) in the phosphorylation networks of this key lymphocyte population. We used Stable Isotope Labeling of Amino acids in Culture (SILAC) combined with phosphopeptide enrichment and quantitative mass-spectrometry to determine the impact of PKD2 loss on the cytotoxic T cells phosphoproteome. We identified 15,871 phosphorylations on 3505 proteins in cytotoxic T cells. 450 phosphosites on 281 proteins were down-regulated and 300 phosphosites on 196 proteins were up-regulated in PKD2 null cytotoxic T cells. These data give valuable new insights about the protein phosphorylation networks operational in effector T cells and reveal that PKD2 regulates directly and indirectly about 5% of the cytotoxic T-cell phosphoproteome. PKD2 candidate substrates identified in this study include proteins involved in two distinct biological functions: regulation of protein sorting and intracellular vesicle trafficking, and control of chromatin structure, transcription, and translation. In other cell types, PKD substrates include class II histone deacetylases such as HDAC7 and actin regulatory proteins such as Slingshot. The current data show these are not PKD substrates in primary T cells revealing that the functional role of PKD isoforms is different in different cell lineages.

A CD4+ T cell antagonist epitope down-regulates activating signaling proteins, up-regulates inhibitory signaling proteins and abrogates HIV-specific T cell function

Background

CD4⁺ T cells are critically important in HIV infection, being both the primary cells infected by HIV and likely playing a direct or indirect role in helping control virus replication. Key areas of interest in HIV vaccine research are mechanisms of viral escape from the immune response. Interestingly, in HIV infection it has been shown that peptide sequence variation can reduce CD4⁺ T cell responses to the virus, and small changes to peptide sequences can transform agonist peptides into antagonist peptides.

Results

We describe, at a molecular level, the consequences of antagonism of HIV p24-specific CD4⁺ T cells. Antagonist peptide exposure in the presence of agonist peptide caused a global suppression of agonist-induced gene expression and signaling molecule phosphorylation. In addition to down-regulation of factors associated with T cell activation, a smaller subset of genes associated with negative regulation of cell activation was up-regulated, including KFL-2, SOCS-1, and SPDEY9P. Finally, antagonist peptide in the absence of agonist peptide also delivered a negative signal to T cells.

Conclusions

Small changes in p24-specific peptides can result in T cell antagonism and reductions of both T cell receptor signaling and activation. These changes are at least in part mediated by a dominant negative signal delivered by antagonist peptide, as evidenced by up-regulation of negative regulatory genes in the presence of agonist plus antagonist stimulation. Antagonism can have dramatic effects on CD4⁺ T cell function and presents a potential obstacle to HIV vaccine development.

Evaluation of the prognostic role of pSTAT3 expression in temporal bone squamous cell carcinoma

OBJECTIVE

Temporal bone squamous cell carcinoma (SCC) accounts for less than 0.2% of all head and neck tumors. Although some progress has been made in treating this aggressive tumor, the prognosis in advanced cases remains poor. More effective therapeutic strategies need to be considered, including receptor-mediated carcinoma-targeted therapy. Phosphorylated STAT3 (pSTAT3) regulates many genes that are necessarily expressed in cancer initiation, development, and progression, being involved in proliferation, anti-apoptosis, invasion, angiogenesis, and immune surveillance evasion. The aim of the present study was to preliminarily investigate the potential prognostic role of pSTAT3 expression in temporal bone SCC.

STUDY DESIGN

Retrospective clinicopathologic investigation.

SETTING

Tertiary referral centers.

PATIENTS

Twenty-five consecutively operated patients with primary temporal bone SCC.

INTERVENTION

pSTAT3 immunohistochemical expression in primary temporal bone SCCs was assessed with the aid of computer-based image analysis.

MAIN OUTCOME MEASURES

Conventional clinicopathologic parameters and pSTAT3 expression were correlated with SCC prognosis.

RESULTS

pT, stage, and surgical margin status were significantly related with recurrence rate (p = 0.002, p = 0.01, and p = 0.047, respectively) and disease-free survival (DFS) (p = 0.0049, p = 0.031, and p = 0.035, respectively). pT classification was also related with disease-specific survival (DSS) (p = 0.035). The SCC recurrence rate did not correlate with pSTAT3 expression. Statistical analyses ruled out any significant difference in DFS or DSS when patients were stratified by pSTAT3 expression (>80.0% or ≤80.0%).

CONCLUSION

Despite our preliminary results, the role of pSTAT3 in temporal bone SCC warrants further investigation in larger series because there is increasing evidence in preclinical models to indicate that inhibiting STAT3 phosphorylation can be a useful addition to different anticancer strategies.

The STAT3-Ser/Hes3 signaling axis: an emerging regulator of endogenous regeneration and cancer growth

Stem cells, by definition, are able to both self-renew (give rise to more cells of their own kind) and demonstrate multipotential (the ability to differentiate into multiple cell types). To accommodate this unique dual ability, stem cells interpret signal transduction pathways in specialized ways. Notable examples include canonical and non-canonical branches of the Notch signaling pathway, with each controlling different downstream targets (e.g., Hes1 vs. Hes3) and promoting either differentiation or self-renewal. Similarly, stem cells utilize STAT3 signaling uniquely. Most mature cells studied thus far rely on tyrosine phosphorylation (STAT3-Tyr) to promote survival and growth; in contrast, STAT3-Tyr induces the differentiation of neural stem cells (NSCs). NSCs use an alternative phosphorylation site, STAT3-Ser, to regulate survival and growth, a site that is largely redundant for this function in most other cell types. STAT3-Ser regulates Hes3, and together they form a convergence point for several signals, including Notch, Tie2, and insulin receptor activation. Disregulation and manipulation of the STAT3-Ser/Hes3 signaling pathway is important in both tumorigenesis and regenerative medicine, and worthy of extensive study.

CDK8 as the STAT1 serine 727 kinase?

Whereas cytokine-induced tyrosine phosphorylation of STAT (signal transducer and activator of transcription) proteins by JAK kinases has been well studied, much less is known about STAT-specific serine kinases and their signal-dependent regulation. The paper by Joanna Bancerek and colleagues published recently in Immunity reports that upon interferon-γ (IFNγ) stimulation of cells the chromatin-associated cyclin-dependent kinase 8 (CDK8) phosphorylates the regulatory serine residue 727 in the transactivation domain of STAT1. The authors state that the CDK8 module of the Mediator complex is a key component in the STAT1 signal pathway, linking serine phosphorylation to gene-specific transcriptional events.

Pharmacological activation of AMPK suppresses inflammatory response evoked by IL-6 signalling in mouse liver and in human hepatocytes

Interleukin-6 (IL-6) induces inflammatory signalling in liver, leading to impaired insulin action in hepatocytes. In this study, we demonstrate that pharmacological activation of AMP-activated protein kinase (AMPK) represses IL-6-stimulated expression of proinflammatory markers serum amyloid A (Saa) as well as suppressor of cytokine signalling 3 (Socs3) in mouse liver. Further studies using the human hepatocellular carcinoma cell line HepG2 suggest that AMPK inhibits IL-6 signalling by repressing IL-6-stimulated phosphorylation of several downstream components of the pathway such as Janus kinase 1 (JAK1), SH2-domain containing protein tyrosine phosphatase 2 (SHP2) and signal transducer and activator of transcription 3 (STAT3). In summary, inhibition of IL-6 signalling cascade in liver by the metabolic master switch of the body, AMPK, supports the role of this kinase as a crucial point of convergence of metabolic and inflammatory pathways in hepatocytes.

LIF-STAT signaling and trophoblast biology

Leukemia inhibitory factor (LIF) is a pleiotropic growth factor that regulates several biological functions. This review focuses on the LIF-dependent STAT activation and its impact on modulation of trophoblast functions during embryo implantation. LIF is mainly produced by the maternal endometrium at the time of implantation while its receptors are present both on the endometrium and trophoblasts. It might influence blastocyst attachment through STAT3 activation and expression of integrins. After attachment of the blastocyst, trophoblasts undergo proliferation and differentiation into invasive EVTs and non-invasive STBs. Under in vitro conditions, LIF regulates all these processes through activation of STAT- and MAPK-dependent signaling pathways. The observations that LIF and STAT3 knockout mice are infertile further strengthen the notion about the critical involvement of LIF-mediated signaling during embryo implantation. Hence, a better understanding of LIF-STAT signaling would help in improving fertility as use of LIF in in vitro blastocyst culture improves the implanting ability of blastocyst after IVF.

Nicotine/cigarette smoke promotes metastasis of pancreatic cancer through α7nAChR-mediated MUC4 upregulation

Despite evidence that long-term smoking is the leading risk factor for pancreatic malignancies, the underlying mechanism(s) for cigarette-smoke (CS)-induced pancreatic cancer (PC) pathogenesis has not been well-established. Our previous studies revealed an aberrant expression of the MUC4 mucin in PC as compared to the normal pancreas and its association with cancer progression and metastasis. Interestingly, here we explore a potential link between MUC4 expression and smoking-mediated PC pathogenesis and report that both cigarette-smoke-extract (CSE) and nicotine, which is the major component of CS, significantly up-regulates MUC4 in PC cells. This nicotine-mediated MUC4 overexpression was via α7 subunit of nicotinic acetylcholine receptor (nAChR) stimulation and subsequent activation of the JAK2/STAT3 downstream signaling cascade in cooperation with the MEK/ERK1/2 pathway; this effect was blocked by the α7nAChR antagonists, α-bungarotoxin and mecamylamine, and by specific siRNA-mediated STAT3 inhibition. Additionally, we demonstrated that nicotine-mediated MUC4 up-regulation promotes the PC cell migration through the activation of the downstream effectors such as HER2, c-Src and FAK; this effect was attenuated by shRNA-mediated MUC4 abrogation, further implying that these nicotine-mediated pathological effects on PC cells are MUC4 dependent. Furthermore, the in-vivo studies demonstrated a dramatic increase in the mean pancreatic tumor weight [low-dose (100 mg/m³ TSP), p=0.014; high-dose (247 mg/m³ TSP), p=0.02] and significant tumor metastasis to various distant organs in the CS-exposed-mice, orthotopically implanted with luciferase-transfected PC cells, as compared to the sham-controls. Moreover, the CS-exposed mice had elevated levels of serum cotinine [low-dose, 155.88±35.96 ng/ml; high-dose, 216.25±29.95 ng/ml] and increased MUC4, α7nAChR and pSTAT3 expression in the pancreatic tumor tissues. Altogether, our findings revealed for the first time that CS up-regulates the MUC4 mucin in PC via α7nAChR/JAK2/STAT3 downstream signaling cascade, thereby promoting metastasis of pancreatic cancer.

ERKs induce expression of the transcriptional repressor Blimp-1 and subsequent plasma cell differentiation

In immune cells, the positive role of the extracellular signal-regulated kinase (ERK) signaling pathway in cell cycle progression and survival is well established; however, it is unclear whether ERK signaling plays a role in cell differentiation. Here, we report that ERKs are essential for the differentiation of B cells into antibody-producing plasma cells and that ERKs induce the expression of Prdm1, which encodes Blimp-1, a transcriptional repressor and "master regulator" of plasma cell differentiation. Transgenic mice with conditional deletion of both ERK1 and ERK2 in germinal center (GC) B cells lacked plasma cells differentiated after GC formation, and memory B cells from these mice failed to differentiate into plasma cells. In addition, ERK1- and ERK2-deficient B cells exhibited impaired Prdm1 expression upon stimulation with antibody against CD40 in the presence of interleukin-4; conversely, enforced expression of Prdm1 in ERK1- and ERK2-deficient B cells restored the generation of plasma cells. Thus, our study suggests that cytokines stimulate ERKs to induce the production of Blimp-1 and that ERKs thereby contribute to the process of cellular differentiation.

Ultraviolet radiation and 12-O-tetradecanoylphorbol-13-acetate-induced interaction of mouse epidermal protein kinase Cε with Stat3 involve integration with ERK1/2

We have reported that protein kinase C epsilon (PKCε) expression level in epidermis dictates the susceptibility of mice to the development of squamous cell carcinomas (SCC) elicited either by repeated exposure to ultraviolet radiation (UVR) or by the DMBA-TPA tumor promotion protocol. To find clues about the mechanism by which PKCε mediates susceptibility to UVR-induced development of SCC, we found that PKCε-over-expressing transgenic mice, as compared to their wild-type littermates, when exposed to UVR, elicit enhanced phosphorylation of Stat3 at Ser727 residues. Stat3 is constitutively activated in SCC and UVR fails to induce SCC in Stat3 mutant mice. Stat3Ser727 phosphorylation is essential for Stat3 transcriptional activity (Cancer Res. 67: 1385, 2007). We now present several novel findings including that PKCε integrates with its downstream partner ERK1/2 to phosphorylate Stat3Ser727. In these experiments, mice were either exposed to UVR (2 kJ/m(2)/dose) emitted by Kodacel-filtered FS-40 sun lamps or treated with TPA (5 nmol). Both UVR and TPA treatment stimulated PKCε-Stat3 interaction, Stat3Ser727 phosphorylation and Stat3-regulated gene COX-2 expression. PKCε-Stat3 interaction and Stat3Ser727 phosphorylation was also observed in SCC elicited by repeated UVR exposures of mice. PKCε-Stat3 interaction was PKCε specific. UVR or TPA-stimulated Stat3Ser727 phosphorylation accompanied interaction of PKCε with ERK1/2 in intact mouse skin in vivo. Deletion of PKCε in wild-type mice attenuated both TPA and UVR-induced expression of phosphoforms of ERK1/2 and Stat3Ser727. These results indicate that PKCε integrates with ERK1/2 to mediate both TPA and UVR-induced epidermal Stat3Ser727 phosphorylation. PKCε and Stat3 may be potential molecular targets for SCC prevention.

Signal transducers and activators of transcription-from cytokine signalling to cancer biology

Signal transducers and activators of transcription (STATs) are, as the name indicates, both signal transducers and transcription factors. STATs are activated by cytokines and some growth factors and thus control important biological processes. These include cell growth, cell differentiation, apoptosis and immune responses. Dysregulation of STATs, either due to constitutive activation or function impairment, can have, therefore, deleterious biological consequences. This review places particular emphasis on their structural organization, biological activities and regulatory mechanisms most commonly utilized by cells to control STAT-mediated signalling. STATs also play important roles in cancer and immune deficiencies and are thus being exploited as therapeutic targets.

Ha-ras oncogene-induced Stat3 phosphorylation enhances oncogenicity of the cell

The ras oncogene needs a second factor to induce transformation and tumorigenicity of the cell. In this study, we show that mouse fibroblast 7-4-Stat3C cells overexpressing both Ha-ras(val12) oncogene and active-form Stat3 (Stat3C) showed higher colony formation in soft agar and xenograft tumor growth in BALB/c mice. Further studies show that both serine-727 and tyrosine-705 of Stat3 were phosphorylated while Ha-ras was overexpressed. Interleukin-6 (IL-6)-induced phosphorylation of tyrosine-705 and serine-727, as well as DNA-binding and transcriptional activity of Stat3 were further enhanced by Ha-ras overexpression. In addition, overexpression of Stat3C in 7-4-Stat3C cells prevented the cells from morphological change and apoptosis triggered by the Ha-ras oncogene under serum-depleted conditions. We demonstrate that Ha-ras and Stat3 acting together synergistically induce Stat3 phosphorylation at serine-727 phosphorylation and cyclin D1 expression and further enhance transformation and tumorigenicity of the cell. Ha-ras-induced Stat3 phosphorylation at serine-727 plays a pivotal role in transcriptional activation of cyclin D1 and suppression of cell apoptosis. The effect of Ha-ras on Stat3 phosphorylation at serine-727 was also detected in human bladder (T24) and lung (H460) cancer cells. Stat3 phosphorylation at serine-727 is important in Ras-related tumorigenesis.

Involvement of the IL-22/REG Ialpha axis in ulcerative colitis

The Regenerating gene (REG) Ialpha protein, a trophic and/or anti-apoptotic factor, is important in the pathophysiology of gastrointestinal inflammation. Interleukin (IL)-22 is a recently identified cytokine that is suggested to have pivotal roles in inflammatory bowel diseases. We therefore investigated the involvement of the IL-22/REG Ialpha axis and examined the mechanism of regulation of REG Ialpha expression by IL-22 stimulation in ulcerative colitis (UC) mucosa. Expression of IL-22, IL-22 receptor 1 (IL-22R1), and REG Ialpha in UC mucosa was analyzed by real-time RT-PCR and immunohistochemistry. The effects of IL-22 on REG Ialpha protein expression were examined using a small-interfering RNA for STAT3, an MAPK inhibitor or a PI3K inhibitor. The element responsible for IL-22-induced REG Ialpha promoter activation was determined by a promoter deletion and electrophoretic mobility shift assay. The expression of IL-22 was enhanced in infiltrating inflammatory cells, and that of IL-22R1 and REG Ialpha was concurrently enhanced in the inflamed epithelium in UC mucosa. The levels of REG Ialpha and IL-22 mRNA expression were strongly correlated, and the distributions of REG Ialpha- and IL-22R1-positive epithelial cells were very similar. IL-22 simulation enhanced the expression of REG Ialpha protein through STAT3 tyrosine phosphorylation in colon cancer cells. The IL-22-responsive element was located between -142 and -134 in the REG Ialpha promoter region. REG Ialpha protein may have a pathophysiological role as a biological mediator for immune cell-derived IL-22 in the UC mucosa.

STAT3 is constitutively phosphorylated on serine 727 residues, binds DNA, and activates transcription in CLL cells

Chronic lymphocytic leukemia (CLL) is the most common leukemia in the Western hemisphere, but its pathogenesis is still poorly understood. Constitutive tyrosine phosphorylation (p) of signal transducer and activator of transcription (STAT) 3 occurs in several solid tumors and hematologic malignancies. In CLL, however, STAT3 is constitutively phosphorylated on serine 727, not tyrosine 705, residues. Because the biologic significance of serine pSTAT3 in CLL is not known, we studied peripheral blood cells of 106 patients with CLL and found that, although tyrosine pSTAT3 was inducible, serine pSTAT3 was constitutive in all patients studied, regardless of blood count, disease stage, or treatment status. In addition, we demonstrated that constitutive serine pSTAT3 translocates to the nucleus by the karyopherin-beta nucleocytoplasmic system and binds DNA. Dephosphorylation of inducible tyrosine pSTAT3 did not affect STAT3-DNA binding, suggesting that constitutive serine pSTAT3 binds DNA. Furthermore, infection of CLL cells with lentiviral STAT3-small hairpin RNA reduced the expression of several STAT3-regulated survival and proliferation genes and induced apoptosis, suggesting that constitutive serine pSTAT3 initiates transcription in CLL cells. Taken together, our data suggest that constitutive phosphorylation of STAT3 on serine 727 residues is a hallmark of CLL and that STAT3 be considered a therapeutic target in this disease.

Histamine induces human beta-defensin-3 production in human keratinocytes

BACKGROUND

The antimicrobial peptide human beta-defensin-3 (hBD-3) is produced by epidermal keratinocytes, and promotes cutaneous antimicrobial defense, inflammation, and wound repair. hBD-3 induces histamine release from mast cells. We previously showed that histamine enhanced transcriptional activity of activator protein-1 (AP-1) in human keratinocytes by inducing the expression of AP-1 component c-Fos via the activation of extracellular signal-regulated kinase (ERK) through H1 receptors.

OBJECTIVE

To examine in vitro effects of histamine on hBD-3 production in normal human keratinocytes.

METHODS

The hBD-3 production was examined by enzyme-linked immunosorbent assays and reverse transcription-polymerase chain reaction. The transcriptional activities were analyzed by dual luciferase assays. The phosphorylation of proteins was examined by Western blotting.

RESULTS

Histamine enhanced hBD-3 secretion and mRNA expression in keratinocytes. The histamine-induced hBD-3 production was suppressed by H1 antagonist pyrilamine and antisense oligonucleotides against signal transducer and activator of transcription 3 (STAT3) and AP-1 components c-Jun and c-Fos. Histamine enhanced STAT3 transcriptional activity and induced tyrosine and serine phosphorylation of STAT3. The former was suppressed by Janus kinase 2 (JAK2) inhibitor AG490, while the latter was suppressed by mitogen-activated protein kinase kinase (MEK) inhibitor PD98059; both were suppressed by pyrilamine. AG490 and PD98059 suppressed histamine-induced hBD-3 production and STAT3 activity. Histamine induced tyrosine phosphorylation of JAK2, and pyrilamine suppressed the phosphorylation.

CONCLUSION

It is suggested that histamine induces hBD-3 production in human keratinocytes through H1 receptors by activating STAT3 and AP-1 via JAK2 and MEK/ERK. Histamine may promote cutaneous antimicrobial defense, inflammation, and wound repair through hBD-3.

Liver X receptors interfere with cytokine-induced proliferation and cell survival in normal and leukemic lymphocytes

Liver X receptors (LXRs) are nuclear receptors regulating lipid and cholesterol metabolism. Recent data indicate an additional role of LXR in immunity by controlling dendritic cell and T-cell function and in breast and prostate cancer cells. Here, we show that LXR activation interferes with IL-2 and IL-7-induced proliferation and cell cycle progression of human T-cell blasts mainly through inhibited phosphorylation of the retinoblastoma protein and decreased expression of the cell cycle protein cyclin B. Comparable results were obtained with IL-2-dependent chronic lymphoblastic leukemia (CLL) T cells. Furthermore, we show for B-CLL cells that LXR are functionally active and inhibit expression of survival genes bcl-2 and MMP-9, and significantly reduce cell viability, suggesting an interference of LXR with cytokine-dependent CLL cell survival. In conclusion, our data reveal LXR as a potent modulator of cytokine-dependent proliferation and survival of normal and malignant T and B lymphocytes. This novel LXR action could find clinical application in immunosuppressive and antileukemic therapies.

STAT3 is involved in phosphatidic acid-induced Bcl-2 expression in HeLa cells

Phosphatidic acid (PA), the product of a PLD-mediated reaction, is a lipid second messenger that participates in various intracellular signaling events and is known to regulate a growing list of signaling proteins. We found that Bcl-2 was upregulated by PA treatment in HeLa cells. However, how PA upregulates Bcl-2 expression has not yet been studied. In this study, we tried to discover the mechanisms of Bcl-2 up-regulation by PA treatment in HeLa cells. Treatment with PA resulted in significantly increased expression of Bcl-2 in HeLa cells. Moreover, PA-induced Bcl-2 expression was blocked by mepacrine, an inhibitor of PLA2, but not by propranolol, an inhibitor of PA phospholyhydrolase (PAP). Treatment of 1,2-dipalmitoryl-sn-glycero-3- phosphate (DPPA) also increased Bcl-2 expression. These results indicate that Bcl-2 expression is mediated by lysophosphatidic acid (LPA), not by arachidonic acid (AA). Thereafter, we used MEK1/2 inhibitor, PD98059 to investigate the relationship between ERK1/2 MAPK and PA-induced Bcl-2 expression. PA-induced Bcl-2 expression was decreased when ERK1/2 was inhibited by PD98059. The transcription factor such as STAT3 which is controlled by ERK1/2 MAPK was increased along with Bcl-2 expression when the cells were treated with PA. Furthermore, STAT3 siRNA treatments inhibited PA-induced Bcl-2 expression, suggesting that STAT3 (Ser727) is involved in PA-induced Bcl-2 expression. Taken together, these findings indicate that PA acts as an important mediator for increasing Bcl-2 expression through STAT3 (Ser727) activation via the ERK1/2 MAPK pathway.

Modulation of PKCdelta signaling alters the shear stress-mediated increases in endothelial nitric oxide synthase transcription: role of STAT3

We have previously shown that the regulation of endothelial nitric oxide synthase (eNOS) in endothelial cells isolated from fetal lamb under static conditions is positively regulated by PKCdelta. In this study, we explore the role of PKCdelta in regulating shear-induced upregulation of eNOS. We found that shear caused a decrease in PKCdelta activation. Modulation of PKCdelta before shear with a dominant negative mutant of PKCdelta (DN PKCdelta) or bryostatin (a known PKCdelta activator) demonstrated that PKCdelta inhibition potentiates the shear-mediated increases in eNOS expression and activity, while PKCdelta activation inhibited these events. To gain insight into the mechanism by which PKCdelta inhibits shear-induced eNOS expression, we examined activation of STAT3, a known target for PKCdelta phosphorylation. We found that shear decreased the phosphorylation of STAT3. Further the transfection of cells with DN PKCdelta reduced, while PKCdelta activation enhanced, STAT3 phosphorylation in the presence of shear. Transfection of cells with a dominant negative mutant of STAT3 enhanced eNOS promoter activity and nitric oxide production in response to shear. Finally, we found that mutating the STAT3 binding site sequence within the eNOS promoter increased promoter activity in response to shear and that this was no longer inhibited by bryostatin. In conclusion, shear decreases PKCdelta activity and, subsequently, reduces STAT3 binding to the eNOS promoter. This signaling pathway plays a previously unidentified role in the regulation of eNOS expression by shear stress.

STAT-3 and ERK 1/2 phosphorylation are critical for T-cell alloactivation and graft-versus-host disease

Graft-versus-host disease (GVHD) is a serious complication of allogeneic bone marrow transplantation, and donor T cells are indispensable for GVHD. Current therapies have limited efficacy, selectivity, and high toxicities. We used a novel flow cytometry technique for the analysis of intracellular phosphorylation events in single cells in murine BMT models to identify and validate novel GVHD drug targets.(1-7) This method circumvents the requirement for large numbers of purified cells, unlike western blots. We defined a signaling profile for alloactivated T cells in vivo and identified the phosphorylation of ERK1/2 and STAT-3 as important events during T-cell (allo)activation in GVHD. We establish that interference with STAT-3 phosphorylation can inhibit T-cell activation and proliferation in vitro and GVHD in vivo. This suggests that phospho-specific flow cytometry is useful for the identification of promising drug targets, and ERK1/2 and STAT-3 phosphorylation in alloactivated T cells may be important for GVHD.

STAT3: an important regulator of multiple cytokine functions

Maintaining T cell homeostasis is critical for normal immune response. Three sequential signals activate T cells, with signal 3 delivered by multiple cytokines that regulate cell proliferation, differentiation, and survival/death. Cytokines binding to their receptors engages two key molecular families, namely, Janus tyrosine kinases (Jaks) and signal transducers and activators of transcription (Stats). Among Stats, Stat3 is involved in the generation of T helper 17 (Th17) cells, regulation of dendritic cells, and acute inflammatory response. These aspects of Stat3 function are important for transplantation. We discuss Stat3's role in innate and adaptive immunity as well as its potential for therapeutic intervention.

T lymphocytes are targets for platelet- and trophoblast-derived microvesicles during pregnancy

Microvesicles (MVs) can derive from several cell types and their membranes contain cell surface elements. Their role is increasingly recognized in cell-to-cell communication, as they act as both paracrine and remote messengers, occurring in circulating form as well as in plasma. Successful pregnancy requires a series of interactions between the maternal immune system and the implanted fetus, such that the semi-allograft will not be rejected. These interactions occur at the materno-placental interface and/or at a systemic level. In the present study we identified for the first time the in vivo plasma pattern of the MVs of third-trimester, healthy pregnant women, their cellular origin, and their target cells using flow cytometry and confocal laser microscopy. We searched for the cellular target molecules of thrombocyte-derived MVs with the help of neutralizing antibodies. We examined the in vitro effects of MVs on STAT3 phosphorylation of primary lymphocytes and Jurkat cells. We found that both placental trophoblast-derived and maternal thrombocyte-derived MVs bind to circulating peripheral T lymphocytes, but not to B lymphocytes or NK cells. We were able to show that the P-selectin (CD62P)-PSGL-1 (CD162) interaction is one mechanism binding platelet-derived MVs to T cells. We were also able to demonstrate that MV-lymphocyte interactions induce STAT3 phosphorylation in T cells. Our findings indicate that both thrombocyte- and trophoblast-derived MVs may play an important role in the immunomodulation of pregnancy. We suggest that the transfer of different signals via MVs represents a novel form of communication between the placenta and the maternal immune system, and that MVs contribute to the establishment of stable immune tolerance to the semi-allograft fetus.

Activation of insulin and IGF-1 signaling pathways by melatonin through MT1 receptor in isolated rat pancreatic islets

Melatonin diminishes insulin release through the activation of MT1 receptors and a reduction in cAMP production in isolated pancreatic islets of neonate and adult rats and in INS-1 cells (an insulin-secreting cell line). The pancreas of pinealectomized rats exhibits degenerative pathological changes with low islet density, indicating that melatonin plays a role to ensure the functioning of pancreatic beta cells. By using immunoprecipitation and immunoblotting analysis we demonstrated, in isolated rat pancreatic islets, that melatonin induces insulin growth factor receptor (IGF-R) and insulin receptor (IR) tyrosine phosphorylation and mediates the activities of the PI3K/AKT and MEK/ERKs pathways, which are involved in cell survival and growth, respectively. Thus, the effects of melatonin on pancreatic islets do not involve a reduction in cAMP levels only. This indoleamine may regulate growth and differentiation of pancreatic islets by activating IGF-I and insulin receptor signaling pathways.

Herpes simplex virus remodels T-cell receptor signaling, resulting in p38-dependent selective synthesis of interleukin-10

Herpes simplex virus (HSV)-specific T cells are essential for viral clearance. However, T cells do not prevent HSV latent infection or reactivation, suggesting that HSV has the potential to modulate T-cell function. T-cell receptor (TCR) stimulation is a potent and specific means of activating T cells. To investigate how HSV affects T-cell function, we have analyzed how HSV affects TCR-stimulated intracellular signaling and cytokine synthesis in mock-infected and HSV-infected T cells. Mock-infected T cells stimulated through the TCR synthesized a broad range of cytokines that included the proinflammatory cytokines tumor necrosis factor alpha, gamma interferon, and interleukin-2. In contrast, HSV-infected T cells stimulated through the TCR selectively synthesized interleukin-10, a cytokine that suppresses cellular immunity and favors viral replication. To achieve selective interleukin-10 synthesis, HSV differentially affected TCR signaling pathways. HSV inhibited TCR-stimulated formation of the linker for activation of the T-cell signaling complex, and HSV inhibited TCR-stimulated NF-kappaB activation. At the same time, HSV activated the p38 and JNK mitogen-activated protein kinases as well as the downstream transcription factors ATF-2 and c-Jun. HSV did not inhibit TCR-stimulated activation of STAT3, a transcription factor involved in interleukin-10 synthesis. The activation of p38 was required for interleukin-10 synthesis in HSV-infected T cells. The ability of HSV to differentially target intracellular signaling pathways and transform an activating stimulus into an immunosuppressive response represents a novel strategy for pathogen-mediated immune modulation. Selective, TCR-stimulated interleukin-10 synthesis may play an important role in HSV pathogenesis.

Hepatitis C Virus non-structural 5A abrogates signal transducer and activator of transcription-1 nucleartranslocation induced by IFN-α through dephosphorylation

AIM: To study the effect of Hepatitis C virus non-structural 5A (HCV NS5A) on IFNα induced signal transducer and activator of transcription-1 (STAT1) phosphorylation and nuclear translocation.

METHODS: Expression of STAT1 Tyr701 phosphorylation at different time points was confirmed by Western blot, and the time point when p-STAT1 expressed most, was taken as the IFN induction time for further studies. Immunocytochemistry was used to confirm the successful transient transfection of NS5A expression plasmid. Immunofluorescene was performed to observe if there was any difference in IFNα-induced STAT1 phosphorylation and nuclear translocation between HCV NS5A-expressed and non-HCV NS5A-expressed cells. Western blot was used to compare the phosphorylated STAT1 protein of the cells.

RESULTS: Expression of HCV NS5A was found in the cytoplasm of P^{CNS5A-transfected} Huh7 cells, but not in the PRC/CMV transfected or non-transfected cells. STAT1 Tyr701 phosphorylation was found strongest in 30 min of IFN induction. STAT1 phosphorylation and nuclear import were much less in the presence of HCV NS5A protein in contrast to P^{RC/CMV-transfected} and non-transfected cells under fluorescent microscopy, which was further confirmed by Western blot.

CONCLUSION: HCV NS5A expression plasmid is successfully transfected into Huh7 cells and HCV NS5A protein is expressed in the cytoplasm of the cells. IFN-α is able to induce STAT1 phosphrylation and nuclear translocation, and this effect is inhibited by HCV NS5A protein, which might be another possible resistance mechanism to interferon alpha therapy.

Inhibition of normal lymphocyte proliferation by Indirubin-3'-monoxime: a multifactorial process

Indirubin-3'-monoxime (IO) is a derivative of Indirubin, compound of a Chinese medicinal recipe used to treat various diseases including leukemia. In this study, we investigated to what extent IO inhibits the growth of normal human lymphocytes. We defined various experimental conditions of peripheral blood lymphocyte treatment: IO introduced (i) on unstimulated lymphocytes, (ii) or on stimulated lymphocytes at the time of phytohemagglutinin stimulation (L1 protocol), (iii) 48 h after the beginning of stimulation (L2 protocol), and (iv) after nocodazole synchronization of stimulated lymphocytes. IO induces a concentration dependent cytotoxic effect yielding a characteristic sub-G1 peak in normal stimulated lymphocytes. Cell death was partly due to necrosis and apoptosis. Normal unstimulated lymphocytes remained insensitive to the cytotoxic effect of 10 microM IO treatment. A cell cycle inhibition was observed after IO treatment, stronger for the L1 than for the L2 protocol, without induction of polyploidy after Nocodazole synchronization. These cellular consequences were associated with a decrease in CDK activity, and with CDK and cyclin gene expression modifications. The inhibition of lymphocyte proliferation by IO indicates that indirubin derivatives may be potent immunosuppressive agents.

Insulin Antagonizes Interleukin-6 Signaling and Is Anti-inflammatory in 3T3-L1 Adipocytes

Adipose tissue secretes different adipokines, including interleukin-6 (IL-6), that have been implicated in the insulin resistance and inflammatory state characterizing obesity. We examined the putative cross-talk between insulin and IL-6 in adipose cells and found that insulin exerts an inhibitory effect on the IL-6 signaling pathway by altering the post-translational modifications of the signal transducer and activator of transcription 3 (STAT3). Insulin reduces the tyrosine phosphorylation and increases the serine phosphorylation of STAT3, thereby reducing its nuclear localization and transcriptional activity. Signaling through the MEK/MAPK pathway plays an important role as treatment with the MEK inhibitor PD98059 reduces the effects of insulin on IL-6 signaling. We also show that the protein tyrosine phosphatase SHP2 is activated upon insulin signaling and is required for the dephosphorylation of STAT3 and that insulin exerts a synergistic effect with IL-6 on suppressor of cytokine signaling 3 expression. As a consequence, the IL-6-induced expression of the inflammatory markers serum amyloid A 3 and haptoglobin are significantly decreased in cells incubated with both IL-6 and insulin. Thus, insulin exerts an important anti-inflammatory effect in adipose cells by impairing the IL-6 signal at several levels.

Arsenic trioxide affects signal transducer and activator of transcription proteins through alteration of protein tyrosine kinase phosphorylation

PURPOSE

Arsenic trioxide decreases proliferation of acute myeloid leukemia (AML) cells, but its precise mechanism of action is unknown.

EXPERIMENTAL DESIGN

We studied the effect of arsenic trioxide on patient samples and the AML cell line HEL, which, like leukemic blasts from 50% of AML cases, has constitutively activated signal transducer and activator of transcription (STAT) proteins.

RESULTS

Arsenic trioxide induced mitotic arrest starting at 24 hours and significant cell death at 48 hours. These events were preceded by an arsenic trioxide dose-dependent down-regulation of activated STAT proteins starting at 6 hours. We hypothesized that arsenic trioxide inhibits protein tyrosine kinases (PTK), which, among others, phosphorylate and activate STATs. We therefore studied arsenic trioxide effects on Janus kinases and on three oncogenic PTKs that are known to activate STATs [FLT3, ZNF198/fibroblast growth factor receptor 1 (FGFR1), and BCR/ABL]. Arsenic trioxide reduced STAT3 activation by Janus kinases, altered phosphorylation and electrophoretic mobility of ZNF198/fibroblast growth factor receptor 1, reduced kinase protein level, and decreased STAT3 protein phosphorylation. Arsenic trioxide also reduced the phosphorylation of BCR/ABL and FLT3 with corresponding decreased STAT5 phosphorylation.

CONCLUSIONS

These results suggest a selective activity of arsenic trioxide on PTKs and will assist in developing clinical trials in AML.

ERK Signaling Is a Molecular Switch Integrating Opposing Inputs from B Cell Receptor and T Cell Cytokines to Control TLR4-Driven Plasma Cell Differentiation

Differentiation of B cells into plasma cells represents a critical immunoregulatory checkpoint where neutralizing Abs against infectious agents must be selected whereas self-reactive Abs are suppressed. Bacterial LPS is a uniquely potent bacterial immunogen that can bypass self-tolerance within the T cell repertoire. We show here that during LPS-induced plasma cell differentiation, the ERK intracellular signaling pathway serves as a pivotal switch integrating opposing inputs from Ag via BCR and from the two best characterized B cell differentiation factors made by T cells, IL-2 and IL-5. Continuous Ag receptor signaling through the RAS/MEK/ERK pathway, as occurs in self-reactive B cells, inhibits LPS induction of Blimp-1 and the plasma cell differentiation program. Differentiation resumes after a transient pulse of Ag-ERK signaling, or upon inactivation of ERK by IL-2 and IL-5 through induction of dual-specificity phosphatase 5 (Dusp5). The architecture of this molecular switch provides a framework for understanding the specificity of antibacterial Ab responses and resistance to bacterially induced autoimmune diseases such as Guillain-Barré syndrome.

Janus tyrosine kinases and signal transducers and activators of transcription regulate critical functions of T cells in allograft rejection and transplantation tolerance

Full activation of T cells requires three sequential signals. Engagement by antigen presenting cells (APC) delivers signals 1/2, whereas signal 3 is delivered by multiple cytokines to regulate the immune homeostasis by influencing proliferation, differentiation, and survival/death. Signaling by cytokines acting through their receptors is delivered by two major molecular families, namely Janus tyrosine kinases (Jaks) and signal transducers and activators of transcription (Stats). Findings obtained from mice genetically deficient in Jaks and Stats suggest that these molecules may serve as therapeutic targets to prevent allograft rejection, induce transplantation tolerance, and inhibit autoimmune disease and lymphoid-derived tumors. This review describes the role of Jak tyrosine kinases and Stat transcription factors and their putative function in regulating T and B cell activity.

P2 purinergic receptors signal to STAT3 in astrocytes: Difference in STAT3 responses to P2Y and P2X receptor activation

Extracellular ATP, released upon tissue damage to the CNS, can evoke reactive astrogliosis. The released ATP activates P2 purinergic receptors associated with the proliferation of normally quiescent astrocytes, although the underlying mechanisms remain to be fully elucidated. Signal transducer and activator of transcription 3 (STAT3) has been implicated in reactive astrogliosis and plays an important role in cell cycle regulation. Therefore, we investigated whether extracellular ATP and purinergic receptors regulate STAT3 signaling. Using immunoblot analysis, we found that addition of ATP to primary cultures of rat cortical astrocytes increased Ser-727 phosphorylation of STAT3 in a time-sensitive and concentration-dependent manner. ATP-stimulated Ser-727 STAT3 phosphorylation was mediated through P2 receptor activation since suramin, an antagonist of P2 receptors, diminished this response, whereas 8-(para-sulfo-phenyl)-theophylline (8PSTP), an antagonist of P1 receptors, did not. We found that UTP, an agonist of P2Y(2/4/6) receptors, stimulated rapid and robust phosphorylation of Ser727-STAT3, whereas BzATP, an agonist for P2X receptors, exhibited a delayed and weaker response. In contrast, both P2Y and P2X agonists stimulated phosphorylation of Tyr705-STAT3 to a similar extent. P2 receptors can couple to extracellular signal-regulated protein kinases (ERK) and we found that inhibition of ERK signaling blocked phosphorylation of Ser727-STAT3. Further characterization of the Ser727-STAT3 phosphorylation response to P2Y receptor activation supported a role for P2Y2 and P2Y4, but not P2Y6, receptors as well as a partial role for P2Y1 receptors. Because phosphorylation of Ser727-STAT3 can promote DNA transcriptional activity of cell cycle regulatory genes, the differences in phosphorylation of Ser727-STAT3 may contribute to the mechanism by which P2Y receptors promote, whereas P2X receptors inhibit, astrocyte proliferation. In support of this hypothesis, inhibition of STAT3 activation by cucurbitacin I prevented ATP-stimulated mitogenesis. We conclude that P2 receptors stimulate STAT3 activation and suggest that P2 receptor/STAT3 signaling may play an important role in astrocyte proliferation and reactive astrogliosis.

Arginine-Vasopressin Activates the JAK-STAT Pathway in Vascular Smooth Muscle Cells

JAK (Janus-activated kinase)-STAT (signal transducers and activators of transcription) signaling is a major signal transduction pathway in mammalian cells. Different growth factors and cytokines were reported as activators of the JAK-STAT pathway in various cell types. Interestingly, arginine-vasopressin (AVP) was never reported as an inducer of the JAK-STAT pathway. In the present study, we show for the first time that AVP stimulation of vascular smooth muscle cells (VSMCs) induces STAT3 tyrosine and serine phosphorylation, followed by nuclear translocation of the phosphorylated STAT3. In addition, we found that AVP induced JAK2 tyrosine phosphorylation. Taken together, these results demonstrate that AVP activates the JAK-STAT pathway in VSMCs. Furthermore, our results indicate that AVP-induced STAT3 tyrosine phosphorylation requires both JAK2 and c-Src tyrosine kinases. The present study also implicates that extracellular signal-regulated kinase (ERK1/2), which are serine/threonine kinases, are the mediators of STAT3 serine phosphorylation upon AVP stimulation. We further suggest that AVP-induced STAT3 serine phosphorylation negatively modulates AVP-induced STAT3 tyrosine phosphorylation. Finally, our results implicate a novel role for the JAK-STAT pathway, mediating AVP-induced VSMC hypertrophy.

STAT3 ser727 phosphorylation and its association with negative estrogen receptor status in breast infiltrating ductal carcinoma

Although it is known that STAT3 transcriptional activity is modulated by phosphorylation at serine residue 727, the role of STAT3 serine phosphorylation in breast cancer remains mostly unexplored. In this study, we examined the expression patterns of serine residue 727-phosphorylated STAT3 (p-ser727-STAT3) in breast infiltrating ductal carcinoma tissues and nearby noncancer tissues by using immunoblotting techniques, and correlated the expression profiles with clinicopathological characteristics. A significantly elevated p-ser727-STAT3 expression was observed in 61.8% (42/68) of breast cancer tissues as compared to corresponding noncancer tissues (p < 0.001). Further, immunohistochemical analysis also showed an increased nuclear p-ser727-STAT3 staining in cancer lesions. The increased p-ser727-STAT3 expression in breast infiltrating ductal carcinoma tissues correlated significantly with negative estrogen receptor (ER) status, increased stage of cancer and increased tumor size (p = 0.001, 0.024 and 0.014, individually). Intriguingly, we noticed that the expression levels of p-ser727-STAT3 in ER-negative breast cancer cell lines were higher than those in ER-positive breast cancer cell lines. In ER-positive MCF7 cells, treatment with ERalpha-specific siRNA increased, whereas treatment with anticancer drug tamoxifen decreased the expression of p-ser727-STAT3, phenomena not observed in ER-negative MDA-MB-231 cells. In conclusion, our results suggest that p-ser727-STAT3 may be involved in the pathogenesis of breast cancer in an ER-dependent manner.

Heparin synergistically enhances interleukin-11 signaling through up-regulation of the MAPK pathway

Using an animal model of heparin-induced osteoporosis we previously demonstrated that heparin causes bone loss, in part, by increasing osteoclast number and activity. Furthermore, we found that, although heparin alone has no effect, it is able to synergistically enhance Interleukin-11 (IL-11)-induced signal transducer and activator of transcription 3 (STAT3) activation and thus increase osteoclast formation in vitro. In the present study, we examine the effect of various serine kinase inhibitors on the ability of heparin to act synergistically with IL-11. Inhibition of the c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), or the phosphatidylinositol 3-kinase pathways had no effect on the ability of heparin to promote either IL-11-induced STAT3.DNA complex formation or osteoclast formation in vitro. In contrast, PD098059, a MAPK kinase inhibitor, completely abolished the synergy between heparin and IL-11. In an attempt to resolve the mechanism by which this was occurring, we examined the effect of heparin on STAT3 Ser-727 phosphorylation and extracellular signal-regulated kinases 1 and 2 (Erk1/2) activation, either in the presence or absence of IL-11. Heparin alone was found to have no effect on Ser-727 phosphorylation, nor did heparin alter the phosphorylation status of Ser-727 in the presence of IL-11. Heparin was, however, found to increase Erk1/2 activation in both a time- and dose-dependent manner. When taken together, these findings suggest that heparin enhances IL-11-induced STAT3 activation and thus osteoclast formation, by a mechanism that is independent of STAT3 Ser-727 phosphorylation but that involves up-regulation of the MAPK pathway.

The role of p-STAT3 (ser727) revealed by its association with Ki-67 in cervical intraepithelial neoplasia

OBJECTIVES

Constitutive activation of signal transducer and activator of transcription 3 (STAT3) has been described in many types of cancers. However, the role of phospho-STAT3 (p-STAT3) at serine residue 727 is in large part undetermined. Our purposes of this study were to evaluate the expression patterns of p-STAT3 (ser727) in cervical intraepithelial neoplasia (CIN) and to explore its possible role in the progression of cervical cancer.

METHODS

Paraffin-embedded sections from 56 patients including 20 CIN 1, 10 CIN 2, and 26 CIN 3 were collected in this study. Immunohistochemical analysis was performed, and the expression patterns of p-STAT3 (ser727) were categorized by semiquantitative method and further correlated with the CIN histopathologic grade using the chi(2) test with Bonferroni adjustment for multiple comparisons and with the proliferation marker Ki-67 expression using Fisher's Exact Test.

RESULTS

The categorized high p-STAT3 (ser727) expression group in nuclei of dysplastic cells was significantly higher in CIN 3 (76.92%), in comparison with CIN 1/2 (13.33%, P < 0.001). Moreover, both the nuclear and cytoplasmic p-STAT3 (ser727) expressions were correlated with Ki-67 nuclear staining (P < 0.001 and < 0.001, respectively).

CONCLUSIONS

Our result revealed that aberrant expression levels of p-STAT3 (ser727) were significantly correlated with CIN lesion grade and cell proliferation. Evaluation of p-STAT3 (ser727) expression may provide additional prognostic information for the clinical course of the disease and therefore to be developed as a prognostic indicator for cervical cancer.