How cells respond to interferons revisited: from early history to current complexity

The roles of ebolavirus glycoproteins in viral pathogenesis

Ebolaviruses are highly dangerous pathogens exhibiting extreme virulence in humans and nonhuman primates. The majority of ebolavirus species, most notably Zaire ebolavirus, can cause Ebola virus disease (EVD), formerly known as Ebola hemorrhagic fever, in humans. EVD is associated with case-fatality rates as high as 90%, and there is currently no specific treatment or licensed vaccine available against EVD. Understanding the molecular biology and pathogenesis of ebolaviruses is important for the development of antiviral therapeutics. Ebolavirus encodes several forms of glycoproteins (GPs), which have some interesting characteristics, including the transcriptional editing coding strategy and extensive O-glycosylation modification, clustered in the mucin-like domain of GP1, full-length GP (GP_1,2), and shed GP. In addition to the canonical role of the spike protein, GP_1,2, in viral entry, ebolavirus GPs appear to have multiple additional functions, likely contributing to the complex pathogenesis of the virus. Here, we review the roles of ebolavirus GPs in viral pathogenesis.

The P Protein of Spring Viremia of Carp Virus Negatively Regulates the Fish Interferon Response by Inhibiting the Kinase Activity of TANK-Binding Kinase 1

Spring viremia of carp virus (SVCV) is an efficient pathogen causing high mortality in the common carp. Fish interferon (IFN) is a powerful cytokine enabling host cells to establish an antiviral response; therefore, the strategies that SVCV uses to avoid the cellular IFN response were investigated. Here, we report that the SVCV P protein is phosphorylated by cellular TANK-binding kinase 1 (TBK1), which decreases IFN regulatory factor 3 (IRF3) phosphorylation and suppresses IFN production. First, overexpression of P protein inhibited the IFN promoter activation induced by SVCV and the IFN activity activated by the mitochondrial antiviral signaling protein (MAVS) although TBK1 activity was not blocked by P protein. Second, P protein colocalized and interacted with TBK1. Dominant negative experiments suggested that the TBK1 N-terminal kinase domain interacted with P protein and was essential for P protein and IRF3 phosphorylation. Finally, P protein overexpression reduced the IRF3 phosphorylation activated by TBK1 and reduced host cellular ifn transcription. Collectively, our data demonstrated that the SVCV P protein is a decoy substrate for the host phosphokinase TBK1, preventing IFN production and facilitating SVCV replication.

IMPORTANCE

TBK1 is a pivotal phosphokinase that activates host IFN production to defend against viral infection; thus, it is a potential target for viruses to negatively regulate IFN response and facilitate viral evasion. We report that the SVCV P protein functions as a decoy substrate for cellular TBK1, leading to the reduction of IRF3 phosphorylation and suppression of IFN expression. These findings reveal a novel immune evasion mechanism of SVCV.

Neuroimmune Response in Ischemic Preconditioning

Ischemic preconditioning (IPC) is a robust neuroprotective phenomenon in which a brief period of cerebral ischemia confers transient tolerance to subsequent ischemic challenge. Research on IPC has implicated cellular, molecular, and systemic elements of the immune response in this phenomenon. Potent molecular mediators of IPC include innate immune signaling pathways such as Toll-like receptors and type 1 interferons. Brain ischemia results in release of pro- and anti-inflammatory cytokines and chemokines that orchestrate the neuroinflammtory response, resolution of inflammation, and transition to neurological recovery and regeneration. Cellular mediators of IPC include microglia, the resident central nervous system immune cells, astrocytes, and neurons. All of these cell types engage in cross-talk with each other using a multitude of signaling pathways that modulate activation/suppression of each of the other cell types in response to ischemia. As the postischemic neuroimmune response evolves over time there is a shift in function toward provision of trophic support and neuroprotection. Peripheral immune cells infiltrate the central nervous system en masse after stroke and are largely detrimental, with a few subtypes having beneficial, protective effects, though the role of these immune cells in IPC is largely unknown. The role of neural progenitor cells in IPC-mediated neuroprotection is another active area of investigation as is the role of microglial proliferation in this setting. A mechanistic understanding of these molecular and cellular mediators of IPC may not only facilitate more effective direct application of IPC to specific clinical scenarios, but also, more broadly, reveal novel targets for therapeutic intervention in stroke.

STAT3 signaling in immunity

The transcriptional regulator STAT3 has key roles in vertebrate development and mature tissue function including control of inflammation and immunity. Mutations in human STAT3 associate with diseases such as immunodeficiency, autoimmunity and cancer. Strikingly, however, either hyperactivation or inactivation of STAT3 results in human disease, indicating tightly regulated STAT3 function is central to health. Here, we attempt to summarize information on the numerous and distinct biological actions of STAT3, and highlight recent discoveries, with a specific focus on STAT3 function in the immune and hematopoietic systems. Our goal is to spur investigation on mechanisms by which aberrant STAT3 function drives human disease and novel approaches that might be used to modulate disease outcome.

Fish IRF6 is a positive regulator of IFN expression and involved in both of the MyD88 and TBK1 pathways

Interferon (IFN) regulatory factors (IRF) are the crucial transcription factors for IFN expression, leading host cell response to viral infection. In mammals, only IRF6 is unaffected by IFN expression in the IRF family; however, in fish, a lower vertebrate, whether IRF6 is related to IFN regulation is unclear. In this study, we identified that zebrafish IRF6 was a positive regulator of IFN transcription and could be phosphorylated by both MyD88 and TBK1. First, the transcript level of cellular irf6 was upregulated by treatment with poly I:C (a mimic of viral RNAs), indicating IRF6 might be involved in the process of host cell response to viruses. Overexpression of IRF6 could upregulate IFN promoter activity significantly, meaning IRF6 is a positive regulator of IFN transcription. Subsequently, at the protein regulation level and in the interaction relationship, IRF6 was phosphorylated by and associated with both MyD88 and TBK1. In addition, overexpression of IRF6 activated the transcription of isg15, rig-i and mavs of host cells; meanwhile, the transcripts of p, m and n genes of SVCV were significantly declined in IRF6-overexpressing cells. Taken together, our data demonstrate that fish IRF6 is distinguished from the homolog of mammals by being a positive regulator of IFN transcription and phosphorylated by MyD88 and TBK1, suggesting that differences in the IRF6 regulation pattern exist between lower and higher vertebrates.

Evaluation of interferon-induced transmembrane protein-3 (IFITM3) rs7478728 and rs3888188 polymorphisms and the risk of pulmonary tuberculosis

The current study aimed to examine the possible association between the interferon-induced transmembrane protein-3 (IFITM3) gene polymorphisms and risk of pulmonary tuberculosis (PTB) in a sample population. This case-control study was conducted on 188 PTB patients and 169 healthy subjects. The rs7478728 and rs3888188 variants of IFITM3 were genotyped using polymerase chain reaction-restriction fragment length polymorphism. The findings showed no significant association between rs7478728 polymorphism and risk of PTB. Regarding rs3888188 polymorphism, the TG genotype as well as G allele significantly increased the risk of PTB [odds ratio (OR)=2.48, 95% confidence interval (CI): 1.42-4.53; P=0.002, and OR=2.26, 95% CI: 1.33-3.86; P=0.003, respectively]. In conclusion, the findings revealed that rs3888188 polymorphism increased the risk of PTB in a sample of Iranian population. Additional investigation with larger sample sizes and different ethnicities are needed to verify our findings.

Understanding Interferon Subtype Therapy for Viral Infections: Harnessing the Power of the Innate Immune System

Type I and III interferons (IFNs) of the innate immune system belong to a polygenic family, however the individual subtype mediators of the antiviral response in viral infections have been hindered by a lack of reagents. Evaluation studies using different IFN subtypes have distinguished distinct protein properties with different efficacies towards different viruses, opening promising avenues for immunotherapy. This review largely focuses on the application of IFN-α/β and IFN-λ therapies for viral infections, influenza, herpes, HIV and hepatitis. Such IFN subtype therapies may help to cure patients with virus infections where no vaccine exists. The ability of cell types to secrete a number of IFN subtypes from a multi-gene family may be an intuitive counterattack on viruses that evade IFN subtype responses. Hence, clinical use of virus-targeted IFN subtypes may restore antiviral immunity in viral infections. Accumulating evidence suggests that individual IFN subtypes have differential efficacies in selectively activating immune cell subsets to enhance antiviral immune responses leading to production of sustained B and T cell memory. Cytokine therapy can augment innate immunity leading to clearance of acute virus infections but such treatments may have limited effects on chronic virus infections that establish lifelong latency. Therefore, exploiting individual IFN subtypes to select those with the ability to sculpt protective responses as well as reinstating those targeted by viral evasion mechanisms may inform development of improved antiviral therapy.

Genetics in Sjögren Syndrome

The genes associated with Sjögren syndrome (SS) can be assigned to the NF-kB pathway, the IFN signaling pathway, lymphocyte signaling, and antigen presentation. The frequencies of risk variants show they are common with modest genetic effects. The strongest genetic association outside the human leukocyte antigen region is in IRF5, a gene relevant in the IFN signaling pathway and for B cell differentiation. Although no association has been found with the NF-kB gene itself, associations in TNFAIP3 and TNIP1 (both genome-wide significant), VCAM1 and IRAK1BP (both suggestive), point to genetic explanations for dysregulation of the NF-kB pathway in SS.

Organ system view of the hepatic innate immunity in HCV infection

An orchestration of innate and adaptive immunity determines the infection outcome and whether the host achieves clearance or allows the pathogen to establish persistent infection. The robust activation of the innate immune response plays the most critical role in both limiting viral replication and halting the spread of the pathogen immediately after infection. The magnitude of innate immune activation is coupled with the efficient mounting of the adaptive immunity. Although immunity against HCV infection is known to be inadequate as most cases transitions to chronicity, approximately 25% of acute infection cases result in spontaneous clearance. The exact immune mechanisms that govern the infection outcome remain largely unknown; recent discoveries suggest that the innate immune system facilitates this event. Both infected hepatocytes and local innate immune cells trigger the front line defense program of the liver as well as the recruitment of diverse adaptive immune cells to the site of infection. Although hepatocyte is the target of HCV infection, nearly all cell types that exist in the liver are involved in the innate defense and contribute to the pathophysiology of hepatic inflammation. The main focus of this comprehensive review is to discuss the current knowledge on how each hepatic cell type contributes to the organ system level innate immunity against HCV infection as well as interplays with the viral evasion program. Furthermore, this review article also aims to synchronize the observations from both molecular biological studies and clinical studies with the ultimate goal of improving our understanding of HCV mediated hepatitis. J. Med. Virol. 88:2025-2037, 2016. © 2016 Wiley Periodicals, Inc.

Dynamic changes in CD45RA(-)Foxp3(high) regulatory T-cells in chronic hepatitis C patients during antiviral therapy

OBJECTIVES

CD4(+)Foxp3(+) regulatory T-cells (Treg) are known to accumulate under certain pathological conditions. This study was conducted to evaluate the characteristics of and dynamic changes in Treg cells in chronic hepatitis C (CHC) patients during antiviral therapy.

METHODS

One hundred and forty-five subjects were enrolled in this study, including 105 CHC patients and 40 healthy donors. The phenotypes and functions of Treg cells were analyzed by flow cytometry.

RESULTS

A significant elevation in Treg cells was observed in the peripheral blood of CHC patients compared with healthy donors. Interestingly, compared with non-suppressive Treg (non-Treg) and resting Treg (rTreg) cells, activated Treg (aTreg) cells expressed higher levels of ectonucleotidase, CD39, and CD73. After treatment with interferon alpha (IFN-α) and ribavirin (RBV) in vitro, the frequencies of total Treg cells and aTreg cells in peripheral blood mononuclear cells (PBMC), as well as the levels of transforming growth factor beta (TGF-β) secreted by aTreg and non-Treg cells, were significantly decreased. Importantly, it was found that levels of aTreg cells in patients with a sustained virological response (SVR) were lower than in relapsed patients, suggesting that a high frequency of aTreg cells might be associated with a poor clinical outcome in HCV infection.

CONCLUSION

These results demonstrate a decreasing trend in aTreg cells, which express higher levels of CD39, CD73, and TGF-β, in SVR patients during antiviral therapy.

Free ISG15 triggers an antitumor immune response against breast cancer: a new perspective

Interferon-Stimulated Gene 15 (ISG15), an antagonist of the canonical ubiquitin pathway, is frequently overexpressed in various cancers. In cancer cells, ISG15 is detected as free (intracellular) and conjugated to cellular proteins (ISGylation). Free ISG15 is also secreted into the extracellular milieu. ISGylation has protumor functions and extracellular free ISG15 has immunomodulatory properties in vitro. Therefore, whether ISG15 is a tumor suppressor or tumor promoter in vivo remains controversial. The current study aimed to clarify the role of free ISG15 in tumorigenesis. Breast cancer cells stably expressing control, ISG15, and UbcH8 (ISG15-specific E2 ligase) shRNAs were used to assess the immunoregulatory and antitumor function of free ISG15 in cell culture (in vitro) and in nude mice (in vivo). We show that extracellular free ISG15 suppresses breast tumor growth and increases NK cell infiltration into xenografted breast tumors in nude mice, and intracellular free ISG15 enhances major histocompatibility complex (MHC) class I surface expression in breast cancer cells. We conclude that free ISG15 may have antitumor and immunoregulatory function in vivo. These findings provides the basis for developing strategies to increase systemic levels of free ISG15 to treat cancer patients overexpressing the ISG15 pathway.

No Love Lost Between Viruses and Interferons

The interferon system protects mammals against virus infections. There are several types of interferons, which are characterized by their ability to inhibit virus replication and resultant pathogenesis by triggering both innate and cell-mediated immune responses. Virus infection is sensed by a variety of cellular pattern-recognition receptors and triggers the synthesis of interferons, which are secreted by the infected cells. In uninfected cells, cell surface receptors recognize the secreted interferons and activate intracellular signaling pathways that induce the expression of interferon-stimulated genes; the proteins encoded by these genes inhibit different stages of virus replication. To avoid extinction, almost all viruses have evolved mechanisms to defend themselves against the interferon system. Consequently, a dynamic equilibrium of survival is established between the virus and its host, an equilibrium that can be shifted to the host's favor by the use of exogenous interferon as a therapeutic antiviral agent.

Hepatic apoptotic markers are not predictors for the virological response to interferon-based therapy in chronic hepatitis C patients

INTRODUCTION

Chronic hepatitis C virus (HCV) infection is a major health problem worldwide. The majority of cases involving HCV infection develop into chronic hepatitis because of a failure to develop an effective immune response. Apoptosis of the hepatocytes plays a significant role in the pathogenesis of HCV infection: the interaction between the Fas antigen on hepatocytes and the Fas ligand on T cells corresponds to the main mechanism for hepatocyte damage. Interferon (IFN)-α has antiviral, immunoregulatory, and antiproliferative properties, and apoptosis seems to be a critical event in the action mechanisms of both IFNs. In this study, we aimed to detect any relationship between apoptotic markers in the liver and the response to the treatment.

MATERIALS AND METHODS

The study included 180 chronic HCV patients treated with IFN and ribavirin in four centers. Apoptotic markers (Fas, Fas ligand, Fas-associated death domain, caspases 3, 8, and 9, and in-situ apoptosis) were studied in the liver. The age, sex of the patients, response to therapy, ALT level, viral load, and genotype were recorded.

RESULTS

The results of the study showed that the histological activity index and fibrosis correlated with CD95 staining density, caspase-8 intensiveness, and portal and parenchymal Fas ligand scores. The apoptotic parameters of the responsive cases were not significantly different from those of the unresponsive cases.

CONCLUSION

The apoptotic parameters studied in liver tissue are associated with inflammation and fibrosis; however, these parameters may not predict response to treatment.

The Wnt5a-Ror2 axis promotes the signaling circuit between interleukin-12 and interferon-γ in colitis

Wnt5a, which regulates various cellular functions in Wnt signaling, is involved in inflammatory responses, however the mechanism is not well understood. We examined the role of Wnt5a signaling in intestinal immunity using conditional knockout mice for Wnt5a and its receptor Ror2. Removing Wnt5a or Ror2 in adult mice suppressed dextran sodium sulfate (DSS)-induced colitis. It also attenuated the DSS-dependent increase in inflammatory cytokine production and decreased interferon-γ (IFN-γ)-producing CD4⁺ Th₁ cell numbers in the colon. Wnt5a was highly expressed in stromal fibroblasts in ulcerative lesions in the DSS-treated mice and inflammatory bowel disease patients. Dendritic cells (DCs) isolated from the colon of Wnt5a and Ror2 deficient mice reduced the ability to differentiate naïve CD4⁺ T cells to IFN-γ-producing CD4⁺ Th₁ cells. In vitro experiments demonstrated that the Wnt5a-Ror2 signaling axis augmented the DCs priming effect of IFN-γ, leading to enhanced lipopolysaccharide (LPS)-induced interleukin (IL)-12 expression. Taken together, these results suggest that Wnt5a promotes IFN-γ signaling, leading to IL-12 expression in DCs, and thereby inducing Th₁ differentiation in colitis.

Single-cell analysis shows that paracrine signaling by first responder cells shapes the interferon-β response to viral infection

Immune responses to viral infection are stochastic processes, which initiate in a limited number of cells that then propagate the response. A key component of the response to viral infection entails the synthesis and secretion of type I interferons (IFNs), including the early induction of the gene encoding IFN-β (Ifnb1). With single-cell analysis and mathematical modeling, we investigated the mechanisms underlying how increases in the amount of Ifnb1 mRNA per cell and in the numbers of cells expressing Ifnb1 calibrate the response to viral infection. We used single-cell, single-molecule assays to quantify the early induction of Ifnb1 expression (the Ifnb1 response) in human monocyte-derived dendritic cells infected with Newcastle disease virus, thus retaining the physiological stoichiometry of transcriptional regulators to both alleles of the Ifnb1 gene. We applied computational methods to extract the stochastic features that underlie the cell-to-cell variations in gene expression over time. Integration of simulations and experiments identified the role of paracrine signaling in increasing the number of cells that express Ifnb1 over time and in calibrating the immune response to viral infection.

Disruption of type I interferon signaling by the nonstructural protein of severe fever with thrombocytopenia syndrome virus via the hijacking of STAT2 and STAT1 into inclusion bodies

The type I interferon (IFN) system, including IFN induction and signaling, is the critical component of the host defense line against viral infection, which, in turn, is also a vulnerable target for viral immune evasion. Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging bunyavirus. Previous data have shown that SFTSV can interfere with the early induction of type I IFNs through targeting host kinases TBK1/IKKε. In this study, we demonstrated that SFTSV also can suppress type I IFN-triggered signaling and interferon-stimulated gene (ISG) expression. Interestingly, we observed the significant inhibition of IFN signaling in cells transfected with the plasmids encoding the nonstructural protein (NSs) but not the nucleocapsid protein (NP), indicating the role of NSs as an antagonist of IFN signaling. Furthermore, coimmunoprecipitation (Co-IP) and pulldown assays indicated that NSs interacts with the cellular signal transducer and activator of transcription 2 (STAT2), and the DNA-binding domain of STAT2 may contribute to the NSs-STAT2 interaction. Combined with confocal microscopy analyses, we demonstrated that NSs sequesters STAT2 and STAT1 into viral inclusion bodies (IBs) and impairs IFN-induced STAT2 phosphorylation and nuclear translocation of both STATs, resulting in the inhibition of IFN signaling and ISG expression. SFTSV NSs-mediated hijacking of STATs in IBs represents a novel mechanism of viral suppression of IFN signaling, highlighting the role of viral IBs as the virus-built "jail" sequestering some crucial host factors and interfering with the corresponding cellular processes.

IMPORTANCE

SFTSV is an emerging bunyavirus which can cause a severe hemorrhagic fever-like disease with high case fatality rates in humans, posing a serious health threat. However, there are no specific antivirals available, and the pathogenesis and virus-host interactions are largely unclear. Here, we demonstrated that SFTSV can inhibit type I IFN antiviral signaling by the NSs-mediated hijacking of STAT2 and STAT1 into viral IBs, highlighting the interesting role of viral IBs in virus-host interactions as the virus-built jail. Sequestering signaling molecules into IBs represents a novel and, perhaps, also a general mechanism of viral suppression of IFN signaling, the understanding of which may benefit the study of viral pathogenesis and the development of antiviral therapies.

Caspase-3 and caspase-6 cleave STAT1 in leukemic cells

Signal Transducer and Activator of Transcription-1 (STAT1) is phosphorylated upon interferon (IFN) stimulation, which can restrict cell proliferation and survival. Nevertheless, in some cancers STAT1 can act in an anti-apoptotic manner. Moreover, certain malignancies are characterized by the overexpression and constitutive activation of STAT1. Here, we demonstrate that the treatment of transformed hematopoietic cells with epigenetic drugs belonging to the class of histone deacetylase inhibitors (HDACi) leads to the cleavage of STAT1 at multiple sites by caspase-3 and caspase-6. This process does not occur in solid tumor cells, normal hematopoietic cells, and leukemic cells that underwent granulocytic or monocytic differentiation. STAT1 cleavage was studied under cell free conditions with purified STAT1 and a set of candidate caspases as well as with mass spectrometry. These assays indicate that unmodified STAT1 is cleaved at multiple sites by caspase-3 and caspase-6. Our study shows that STAT1 is targeted by caspases in malignant undifferentiated hematopoietic cells. This observation may provide an explanation for the selective toxicity of HDACi against rapidly proliferating leukemic cells.

Fish viperin exerts a conserved antiviral function through RLR-triggered IFN signaling pathway

Mammalian viperin is a typical interferon (IFN)-induced antiviral protein. Fish have viperin homologs; however, little is known about the expression regulation of fish viperins. In this study, we report the expression regulation and antiviral function of a fish viperin from crucian carp Carassius auratus during IFN response. Crucian carp viperin is induced at mRNA and protein levels by fish IFNs and IFN stimuli such as poly(I:C). Consistently, this gene promoter contains multiple transcription factor binding sites including IFN-stimulated response elements (ISRE) and IFN gamma activation sequences (GAS), and is activated by two types of fish IFNs and also by the intracellular and extracellular poly(I:C). Activation of crucian carp viperin promoter by the intracellular poly(I:C) is mediated by retinoic acid-inducing gene I (RIG-I)-like receptors (RLR)-triggered IFN signaling pathway, which is further verified by the findings that each signaling molecule of RLR pathway is able to induce the expression of crucian carp viperin at mRNA and protein levels. Finally, overexpression of crucian carp viperin in cultured fish cells confers significant protection against infection of grass carp reovirus (GCRV). These data suggest that similar to mammalian homologs, crucian carp viperin exerts a conserved function through RLR-triggered IFN signaling pathway.

Signal, transduction, and the hematopoietic stem cell

The hematopoietic stem cell (HSC) is a unique cell positioned highest in the hematopoietic hierarchical system. The HSC has the ability to stay in quiescence, to self-renew, or to differentiate and generate all lineages of blood cells. The path to be actualized is influenced by signals that derive from the cell's microenvironment, which activate molecular pathways inside the cell. Signaling pathways are commonly organized through inducible protein-protein interactions, mediated by adaptor proteins that link activated receptors to cytoplasmic effectors. This review will focus on the signaling molecules and how they work in concert to determine the HSC's fate.

STAT1 signaling is essential for protection against Cryptococcus neoformans infection in mice

Nonprotective immune responses to highly virulent Cryptococcus neoformans strains, such as H99, are associated with Th2-type cytokine production, alternatively activated macrophages, and inability of the host to clear the fungus. In contrast, experimental studies show that protective immune responses against cryptococcosis are associated with Th1-type cytokine production and classical macrophage activation. The protective response induced during C. neoformans strain H99γ (C. neoformans strain H99 engineered to produce murine IFN-γ) infection correlates with enhanced phosphorylation of the transcription factor STAT1 in macrophages; however, the role of STAT1 in protective immunity to C. neoformans is unknown. The current studies examined the effect of STAT1 deletion in murine models of protective immunity to C. neoformans. Survival and fungal burden were evaluated in wild-type and STAT1 knockout (KO) mice infected with either strain H99γ or C. neoformans strain 52D (unmodified clinical isolate). Both strains H99γ and 52D were rapidly cleared from the lungs, did not disseminate to the CNS, or cause mortality in the wild-type mice. Conversely, STAT1 KO mice infected with H99γ or 52D had significantly increased pulmonary fungal burden, CNS dissemination, and 90-100% mortality. STAT1 deletion resulted in a shift from Th1 to Th2 cytokine bias, pronounced lung inflammation, and defective classical macrophage activation. Pulmonary macrophages from STAT1 KO mice exhibited defects in NO production correlating with inefficient inhibition of fungal proliferation. These studies demonstrate that STAT1 signaling is essential not only for regulation of immune polarization but also for the classical activation of macrophages that occurs during protective anticryptococcal immune responses.

Influence of interleukin-28B polymorphism on progression to hepatitis virus-induced hepatocellular carcinoma

Genetic variation of interleukin-28B (IL-28B) rs12979860 T/C polymorphism is associated with the immune response to interferon (IFN) therapy, which is applied in the treatment of chronic viral hepatitis induced by hepatitis B virus (HBV) and hepatitis C virus (HCV). These chronic liver diseases could progress to end-stage liver diseases, such as hepatocellular carcinoma (HCC). The aim of this study was to clarify whether there exists a causal association between IL-28B rs12979860 T/C polymorphism and development of HCC. In a meta-analysis of six studies with 850 cases and 811 controls, we summarized the data on the association between IL-28B rs12979860 T/C polymorphism and HCC risk and calculated ORs and 95 % CIs to estimate the association strength. We observed that IL-28B rs12979860 T/C polymorphism was positively associated with overall HCC risk (TT vs. CC: OR = 2.38; 95 %, 1.60-3.55; TT vs CT + CC: OR = 1.79; 95 %, 1.23-2.60). In the stratified analysis by ethnicity, the robust association retained in Caucasians with higher risk among TT carriers relative to the CC carriers. A similar trend was found in the studies of healthy controls when data were stratified by source of controls. The combined data suggest that IL-28B rs12979860 T/C polymorphism seems to augment the risk of developing HCC, especially in Caucasians.

Production and characterization of thirteen human type-I interferon-α subtypes

Thirteen human interferon-α (IFNα) subtypes were expressed in Escherichiacoli and purified using an N-terminal affinity tag from the prodomain of subtilisin. IFNα subtypes were expressed in soluble form and purified from cell lysates or refolded and purified from inclusion bodies. Proteins produced by either protocol exhibited biological activities equal to or greater than commercially prepared IFNα preparations. The IFNαs were used to produce an anti-IFNα16 antibody (MAb-1B12) that specifically neutralized the biological activity of IFNα16, but not the 12 other IFNαs. Using MAb-1B12, and a previously generated IFNAR1/IFNAR2-FChk heterodimer, an assay was developed to determine total type I IFN biological activity and IFNα16-derived biological activity in an unknown sample.

Sequence analysis and subcellular localization of crucian carp Carassius auratus viperin

Human viperin is known as an interferon (IFN)-inducible antiviral protein and localizes to endoplasmic reticulum (ER) via its N-terminal amphipathic α-helix. Little is known about subcellular localization of fish viperin. Herein, we characterized subcellular localization of a fish viperin from crucian carp Carassius auratus. Crucian carp viperin is nearly identical to the other viperin proteins in sequence, with the exception of the first N-terminal 70 amino acids that are defined as N-terminal variable domain including an amphipathic α-helix. In addition to N-terminal variable domain, crucian carp viperin protein harbors a conserved middle radical SAM domain and a conserved C-terminal domain. Subcellular localization analyses indicate that crucian carp viperin is a cytoplasmic protein associated with ER. Sequence analyses reveal that amino acids 1-74 forms an amphipathic α-helix domain that drives ER-localization of crucian carp viperin. In addition, Coimmunoprecipitation assays show that crucian carp viperin proteins are able to self-associate. These results together indicate that similar to mammalian homologs, fish viperins likely play important roles in IFN response.

Molecular cloning and characterization of interferon regulatory factor 9 (IRF9) in Japanese flounder, Paralichthys olivaceus

Interferon regulatory factor 9 (IRF9) in mammals is known to be involved in antiviral response. In this study, we studied the structure, mRNA tissue distribution and regulation of IRF9 from Japanese flounder, Paralichthys olivaceus. The cDNA sequence of IRF9 is 3305 bp long, containing an open reading frame (ORF) of 1308 bp that encodes a peptide of 435 amino acids. The predicted protein sequence shares 33.7-72.0% identity to other fish IRF9s. Japanese flounder IRF9 possesses a DNA-binding domain (DBD), an IRF association domain (IAD), two nuclear localization signals (NLSs) and a proline-rich domain (PRD). The IRF9 transcripts were detectable in all examined tissues of healthy Japanese flounders, with higher levels in the head kidney, kidney, liver and spleen. The IRF9 mRNA levels were up-regulated in the gills, head kidney, spleen and muscle when challenged with polyinosinic:polycytidylic acid (poly I:C) or lymphocystis disease virus (LCDV). The up-regulations were stronger and arose earlier in the case of poly I:C treatment in most tested organs in a 7-day time course, with maximum increases ranging from 1.37- to 8.59-fold and peak time points from 3 h to 3 d post injection depending on different organs, relative to those in the case of LCDV treatment which ranged from 1.32- to 3.21-fold and from 18 h to 3 d post injection, respectively. The highest and earliest inductions were detected in the spleen in both challenge cases, while the inductions by LCDV in the muscle were quite faint. These results demonstrate a role of Japanese flounder IRF9 in the host's antiviral responses.

IFN regulatory factor 10 is a negative regulator of the IFN responses in fish

IFN regulatory factor (IRF) 10 belongs to the IRF family and exists exclusively in birds and fish. Most IRFs have been identified as critical regulators in the IFN responses in both fish and mammals; however, the role of IRF10 is unclear. In this study, we identified IRF10 in zebrafish (Danio rerio) and found that it serves as a negative regulator to balance the innate antiviral immune responses. Zebrafish IRF10 (DrIRF10) was induced by intracellular polyinosinic:polycytidylic acid in ZF4 (zebrafish embryo fibroblast-like) cells. DrIRF10 inhibited the activation of zebrafish IFN1 (DrIFN1) and DrIFN3 promoters in epithelioma papulosum cyprinid cells in the presence or absence of polyinosinic:polycytidylic acid stimulation through direct interaction with the IFN promoters, and this inhibition was also shown to block IFN signaling. Overexpression of DrIRF10 was able to abolish the induction of DrIFN1 and DrIFN3 mediated by the retinoic acid-inducible gene I-like receptors. In addition, functional domain analysis of DrIRF10 showed that either the DNA binding domain or the IRF association domain is sufficient for its inhibitory activity for IFN signaling. Lastly, overexpression of DrIRF10 decreased the transcription level of several IFN-stimulated genes, resulting in the susceptibility of host cells to spring viremia of carp virus infection. Collectively, these data suggest that DrIRF10 inhibits the expression of DrIFN1 and DrIFN3 to avoid an excessive immune response, a unique regulation mechanism of the IFN responses in lower vertebrates.

STAT-1 expression is regulated by IGFBP-3 in malignant glioma cells and is a strong predictor of poor survival in patients with glioblastoma

OBJECT

Insulin-like growth factor binding proteins (IGFBPs) have been implicated in the pathogenesis of glioma. In a previous study the authors demonstrated that IGFBP-3 is a novel glioblastoma biomarker associated with poor survival. Since signal transducer and activator of transcription 1 (STAT-1) has been shown to be regulated by IGFBP-3 during chondrogenesis and is a prosurvival and radioresistant molecule in different tumors, the aim in the present study was to explore the functional significance of IGFBP-3 in malignant glioma cells, to determine if STAT-1 is indeed regulated by IGFBP-3, and to study the potential of STAT-1 as a biomarker in glioblastoma.

METHODS

The functional significance of IGFBP-3 was investigated using the short hairpin (sh)RNA gene knockdown approach on U251MG cells. STAT-1 regulation by IGFBP-3 was tested on U251MG and U87MG cells by shRNA gene knockdown and exogenous treatment with recombinant IGFBP-3 protein. Subsequently, the expression of STAT-1 was analyzed with real-time reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC) in glioblastoma and control brain tissues. Survival analyses were done on a uniformly treated prospective cohort of adults with newly diagnosed glioblastoma (136 patients) using Kaplan-Meier and Cox regression models.

RESULTS

IGFBP-3 knockdown significantly impaired proliferation, motility, migration, and invasive capacity of U251MG cells in vitro (p < 0.005). Exogenous overexpression of IGFBP-3 in U251MG and U87MG cells demonstrated STAT-1 regulation. The mean transcript levels (by real-time RT-PCR) and the mean labeling index of STAT-1 (by IHC) were significantly higher in glioblastoma than in control brain tissues (p = 0.0239 and p < 0.001, respectively). Multivariate survival analysis revealed that STAT-1 protein expression (HR 1.015, p = 0.033, 95% CI 1.001-1.029) along with patient age (HR 1.025, p = 0.005, 95% CI 1.008-1.042) were significant predictors of shorter survival in patients with glioblastoma.

CONCLUSIONS

IGFBP-3 influences tumor cell proliferation, migration, and invasion and regulates STAT-1 expression in malignant glioma cells. STAT-1 is overexpressed in human glioblastoma tissues and emerges as a novel prognostic biomarker.

Correlation between the suppressor of cytokine signaling-1 and 3 and hepatitis B virus: possible roles in the resistance to interferon treatment

BACKGROUND

The suppressor of cytokine signaling family (SOCS) is an important negative regulator in the JAK-STAT signaling pathway. This study was designed to explore the correlation between SOCS-1, 2 and 3, Hepatitis B Virus (HBV) and interferon (IFN), and the relationship between SOCS and IFN therapeutic efficacy.

METHODS

Four types of mouse models were established. Mice were administered with HBV replicative plasmid pHBV4.1 and IFN inducer Poly IC (Group A), pHBV4.1 (Group B), Poly IC (Group C) and saline (Group D), respectively. Liver tissues were harvested from the mice and SOCS expression was determined. Meanwhile, patients with chronic hepatitis B (CHB) were treated with pegylated interferon α-2b for 24-48 weeks. Liver biopsy was collected and the baseline SOCS expression was determined. Serum assay was performed for efficacy evaluation and correlation analysis.

RESULTS

In animal studies, the expression level of SOCS-1 and 3 was found in the descending order of B, A, C and D. The difference between Group B and D suggested that HBV could induce SOCS. The difference between Group A and C suggested that HBV could still induce SOCS with up-regulated endogenous IFN. The difference between Group C and D suggested that ploy IC could induce SOCS, while the difference between Group B and A suggested that Poly IC might have a stronger inhibition effect for SOCS. There was no difference in SOCS-2 expression. In clinical studies, eight of twenty-four enrolled patients achieved either complete or partial therapeutic response. The expression of both SOCS-1 and 3 was higher in CHB patients than in normal controls. The baseline HBV-DNA level was positively correlated with SOCS-1 and 3. The age, viral genotype, HBVDNA, SOCS-1 and SOCS-3 were found to be related to IFN efficacy.

CONCLUSION

HBV could induce both SOCS-1 and 3 expression regardless of endogenous IFN level. Elevated IFN could directly up-regulate SOCS-1 and 3 expression, but it could also indirectly down-regulate SOCS-1 and 3 expression by inhibiting HBV replication. HBV might play a more important role in the SOCS up-regulation than IFN, a possible reason why patients with high HBV viral load encounter poor efficacy of IFN treatment.

Induction of interferon-gamma and downstream pathways during establishment of fetal persistent infection with bovine viral diarrhea virus

Development of transplacental infection depends on the ability of the virus to cross the placenta and replicate within the fetus while counteracting maternal and fetal immune responses. Unfortunately, little is known about this complex process. Non-cytopathic (ncp) strains of bovine viral diarrhea virus (BVDV), a pestivirus in the Flaviviridae family, cause persistent infection in early gestational fetuses (<150 days; persistently infected, PI), but are cleared by immunocompetent animals and late gestational fetuses (>150 days; transiently infected, TI). Evasion of innate immune response and development of immunotolerance to ncp BVDV have been suggested as possible mechanisms for the establishment of the persistent infection. Previously we have observed a robust temporal induction of interferon (IFN) type I (innate immune response) and upregulation of IFN stimulated genes (ISGs) in BVDV TI fetuses. Modest chronic upregulation of ISGs in PI fetuses and calves reflects a stimulated innate immune response during persistent BVDV infection. We hypothesized that establishing persistent fetal BVDV infection is also accompanied by the induction of IFN-gamma (IFN-γ). The aims of the present study were to determine IFN-γ concentration in blood and amniotic fluid from control, TI and PI fetuses during BVDV infection and analyze induction of the IFN-γ downstream pathways in fetal lymphoid tissues. Two experiments with in vivo BVDV infections were completed. In Experiment 1, pregnant heifers were infected with ncp BVDV type 2 on day 75 or 175 of gestation or kept naïve to generate PI, TI and control fetuses, respectively. Fetuses were collected by Cesarean section on day 190. In Experiment 2, fetuses were collected on days 82, 89, 97, 192 and 245 following infection of pregnant heifers on day 75 of gestation. The results were consistent with the hypothesis that ncp BVDV infection induces IFN-γ secretion during acute infection in both TI and PI fetuses and that lymphoid tissues such as spleen, liver and thymus, serve both as possible sources of IFN-γ and target organs for its effects. Notably, induction of IFN-γ coincides with a decrease in BVDV RNA concentrations in PI fetal blood and tissues. This is the first report indicating the possible presence of an adaptive immune response in persistent BVDV infections, which may be contributing to the observed reduction of viremia in PI fetuses.

Critical roles for Rictor/Sin1 complexes in interferon-dependent gene transcription and generation of antiproliferative responses

We provide evidence that type I IFN-induced STAT activation is diminished in cells with targeted disruption of the Rictor gene, whose protein product is a key element of mTOR complex 2. Our studies show that transient or stable knockdown of Rictor or Sin1 results in defects in activation of elements of the STAT pathway and reduced STAT-DNA binding complexes. This leads to decreased expression of several IFN-inducible genes that mediate important biological functions. Our studies also demonstrate that Rictor and Sin1 play essential roles in the generation of the suppressive effects of IFNα on malignant erythroid precursors from patients with myeloproliferative neoplasms. Altogether, these findings provide evidence for critical functions for Rictor/Sin1 complexes in type I IFN signaling and the generation of type I IFN antineoplastic responses.

Expression regulation of zebrafish interferon regulatory factor 9 by promoter analysis

We previously showed that a fish interferon (IFN) regulatory factor 9 (IRF9) homologue, crucian carp Carassius auratus IRF9, displays constitutively nuclear localization and involvement in fish IFN-dependent JAK-STAT signaling; however, little is known about the expression regulation of fish IRF9. Here, we characterized the expression of zebrafish IRF9 by promoter analysis. Zebrafish IRF9 gene promoter contained several putative transcription factor binding sites, including one ISRE (IFN-stimulated response element), one GAS (IFN gamma activation sequence) and three GATEs (IFNγ activated transcriptional element, GATE1/2/3). Further sequence analyses revealed that GAS and GATE motifs existed in all promoters of IRF9 from mammals and fishes. Luciferase assays confirmed that zebrafish IRF9 promoter could be activated by zebrafish IFNφs and zebrafish IFNγ2, as well as transcription factors IRF3, IRF7, and combination of IRF9 and STAT2. Treatment of recombinant crucian carp IFN protein or overexpression of zebrafish IFNγ2 both led to significant increase in crucian carp IRF9 mRNA and protein in cultured fish cells. Comparison of IFN-stimulated promoter activity revealed much more significant induction of zebrafish IRF9 by zebrafish IFNγ2 than by zebrafish IFNφs. Mutation analyses showed that the putative GAS and GATE3 contributed to zebrafish IFNγ2-triggered IRF9 expression, whereas the putative ISRE and the other two GATEs were not functional for induction of zebrafish IRF9. These results together indicated that the expression property of IRF9 might be conserved from fish to mammals and that some not yet identified mechanisms could exist in IRF9 gene transcription regulation in response to IFNs.

Hepatic interferon-gamma-induced protein-10 expression is more strongly associated with liver fibrosis than interleukin-28B single nucleotide polymorphisms in hepatocellular carcinoma resected patients with chronic hepatitis C

AIM

Single nucleotide polymorphisms (SNP) around IL-28B and interferon (IFN)-stimulated gene (ISG) expression are predictors of response to standard therapy involving IFN for chronic hepatitis C virus (HCV) infection. We analyzed the association between these predictors to improve the prediction of the response to IFN therapy after liver resection for hepatocellular carcinoma (HCC).

METHODS

Data were collected from 74 patients with HCV-induced HCC. The IL-28B genotype and hepatic ISG mRNA levels were analyzed to clarify their association, focusing on the progression of liver fibrosis.

RESULTS

Fifty patients were identified as having major alleles (rs8099917 TT) and the remaining 24 patients had minor alleles (rs8099917 TG or GG). Hepatic ISG15 expression was lower in the IL-28B major group than that in the IL-28B minor group (P < 0.005). IP-10 expression was similar between the IL-28B major and minor groups (P = 0.44). IP-10 expression was elevated with advancing stages of liver fibrosis in HCV infected patients (P = 0.005). In patients with mild or no fibrosis, the IL-28B major group had lower IP-10 expression than the IL-28B minor group (P = 0.02). However, in patients with advanced fibrosis, IP-10 expression was not different between the IL-28B major and minor groups (P = 0.66).

CONCLUSION

Hepatic ISG15 expression is associated with IL-28B polymorphisms, while IP-10 is strongly affected by liver fibrosis.

Induction of TRIM22 by IFN-γ Involves JAK and PC-PLC/PKC, but Not MAPKs and pI3K/Akt/mTOR Pathways

Tripartite motif (TRIM) 22 plays an important role in interferons (IFNs)-mediated antiviral activity. We previously demonstrated that interferon regulatory factor-1 (IRF-1) played a central role in IFN-γ-induced TRIM22 expression via binding to a special cis-element named 5' extended IFN-stimulating response element (5'eISRE). In this study, we sought to identify the signaling pathways involved in TRIM22 induction by IFN-γ. By using various pharmacological inhibitors, it was found that the activity of tyrosine kinase and phosphatidylcholine-phospholipase C (PC-PLC), but not phosphatidylinositol-phospholipase C (PI-PLC) and phospholipase D (PLD), was required for IFN-γ-induced TRIM22 expression in HepG2 cells. Tyrosine kinase Janus kinase (JAK), not SRC and PYK2, played an indispensable role in TRIM22 induction. Inhibition of protein kinase C (PKC) activity also significantly attenuated IFN-γ induction of TRIM22. Although treatment with IFN-γ resulted in the stimulation of mitogen-activated protein kinases (MAPKs) (p38, ERK, and JNK) and pI3K/Akt/mTOR pathways in HepG2 cells, the inhibition of their activity did not affect IFN-γ-stimulated TRIM22 expression. Further studies showed that overexpression of JAK1 and PKCα activated TRIM22 promoter activity in a 5'eISRE-dependent manner, and inhibition of not only JAK but also PC-PLC/PKC pathways significantly attenuated IFN-γ-induced IRF-1 expression in HepG2 cells. Taken together, these data indicated that IFN-γ induced TRIM22 expression via activation of JAK and PC-PLC/PKC signaling pathways, which involved the cis-element 5'eISRE and the transactivator IRF-1.

BRD4 coordinates recruitment of pause release factor P-TEFb and the pausing complex NELF/DSIF to regulate transcription elongation of interferon-stimulated genes

RNA polymerase II (Pol II) and the pausing complex, NELF and DSIF, are detected near the transcription start site (TSS) of many active and silent genes. Active transcription starts when the pause release factor P-TEFb is recruited to initiate productive elongation. However, the mechanism of P-TEFb recruitment and regulation of NELF/DSIF during transcription is not fully understood. We investigated this question in interferon (IFN)-stimulated transcription, focusing on BRD4, a BET family protein that interacts with P-TEFb. Besides P-TEFb, BRD4 binds to acetylated histones through the bromodomain. We found that BRD4 and P-TEFb, although not present prior to IFN treatment, were robustly recruited to IFN-stimulated genes (ISGs) after stimulation. Likewise, NELF and DSIF prior to stimulation were hardly detectable on ISGs, which were strongly recruited after IFN treatment. A shRNA-based knockdown assay of NELF revealed that it negatively regulates the passage of Pol II and DSIF across the ISGs during elongation, reducing total ISG transcript output. Analyses with a BRD4 small-molecule inhibitor showed that IFN-induced recruitment of P-TEFb and NELF/DSIF was under the control of BRD4. We suggest a model where BRD4 coordinates both positive and negative regulation of ISG elongation.

Toxoplasma gondii triggers phosphorylation and nuclear translocation of dendritic cell STAT1 while simultaneously blocking IFNγ-induced STAT1 transcriptional activity

The protozoan Toxoplasma gondii actively modulates cytokine-induced JAK/STAT signaling pathways to facilitate survival within the host, including blocking IFNγ-mediated STAT1-dependent proinflammatory gene expression. We sought to further characterize inhibition of STAT1 signaling in infected murine dendritic cells (DC) because this cell type has not previously been examined, yet is known to serve as an early target of in vivo infection. Unexpectedly, we discovered that T. gondii infection alone induced sustained STAT1 phosphorylation and nuclear translocation in DC in a parasite strain-independent manner. Maintenance of STAT1 phosphorylation required active invasion but intracellular parasite replication was dispensable. The parasite rhoptry protein ROP16, recently shown to mediate STAT3 and STAT6 phosphorylation, was not required for STAT1 phosphorylation. In combination with IFNγ, T. gondii induced synergistic STAT1 phosphorylation and binding of aberrant STAT1-containing complexes to IFNγ consensus sequence oligonucleotides. Despite these findings, parasite infection blocked STAT1 binding to the native promoters of the IFNγ-inducible genes Irf-1 and Lrg47, along with subsequent gene expression. These results reinforce the importance of parasite-mediated blockade of IFNγ responses in dendritic cells, while simultaneously showing that T. gondii alone induces STAT1 phosphorylation.

A brief overview of multitalented microglia

Microglia are the resident immune cells of the central nervous system, and accumulating data demonstrates a vast array of tasks in the healthy and injured brain. Microglia participate in both innate and adaptive immune responses. These cells contribute to the brain homeostasis, including the regulation of cell death, synapse elimination, neurogenesis, and neuronal surveillance. However, microglia can also become activated and/or deregulated in the context of neurodegenerative diseases, brain injuries, and cancer and thereby contribute to disease severity. As a consequence of these developments, microglia have attracted substantial attention on themselves.

IFN-γ synergistically enhances LPS signalling in alveolar macrophages from COPD patients and controls by corticosteroid-resistant STAT1 activation

BACKGROUND AND PURPOSE

IFN-γ levels are increased in chronic obstructive airway disease (COPD) patients compared with healthy subjects and are further elevated during viral exacerbations. IFN-γ can 'prime' macrophages to enhance the response to toll-like receptor (TLR) ligands, such as LPS. The aim of this study was to examine the effect IFN-γ on corticosteroid sensitivity in alveolar macrophages (AM).

EXPERIMENTAL APPROACH

AM from non-smokers, smokers and COPD patients were stimulated with IFN-γ and/or LPS with or without dexamethasone. IL-6, TNF-α and IFN-γ-induced protein 10 kDa (IP-10) levels were measured by elisa, and Western blots were used to investigate the IFN-γ-stimulated Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signalling pathway. Real-time PCR and flow cytometry were used to investigate TLR levels following IFN-γ treatment.

KEY RESULTS

In all three subject groups, IFN-γ alone had no effect on IL-6 and TNF-α production but enhanced the effects of LPS on these cytokines. In contrast, IFN-γ alone increased the production of IP-10. IFN-γ increased TLR2 and TLR4 expression in AM. Cytokine induction and STAT1 activation by IFN-γ were insensitive to dexamethasone for all groups. The inhibition of JAK and STAT1 repressed all these IFN-γ effects.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that IFN-γ-induced STAT-1 signalling is corticosteroid resistant in AMs, and that targeting IFN-γ signalling by JAK inhibitors is a potentially novel anti-inflammatory strategy in COPD.

Adherent-invasive Escherichia coli blocks interferon-γ-induced signal transducer and activator of transcription (STAT)-1 in human intestinal epithelial cells

Adherent-invasive Escherichia coli (AIEC) is a pathogen isolated from the ileum of patients with Crohn disease. IFNγ is a key mediator of immunity, which regulates inflammatory responses to microbial infections. Previously, we showed enterohemorrhagic E. coli prevents STAT1 activation. The aim of this study was to determine whether activation of STAT1 by IFNγ was prevented by AIEC infection, and to define the mechanisms used. Human epithelial cells were infected with three different AIEC strains or other pathogenic and commensal E. coli strains. Following infection, cells were stimulated with IFNγ, and STAT1 activation was monitored by immunoblotting. Our data show that live AIEC with active protein synthesis machinery is able to prevent IFNγ-mediated STAT1 phosphorylation, and that a secreted factor may be involved. We conclude that the suppression of epithelial cell STAT1 signal transduction by AIEC strains isolated from patients with Crohn disease represents a novel mechanism by which the pathogen evades host immune responses to the infection.

Sprouty proteins are negative regulators of interferon (IFN) signaling and IFN-inducible biological responses

Interferons (IFNs) have important antiviral and antineoplastic properties, but the precise mechanisms required for generation of these responses remain to be defined. We provide evidence that during engagement of the Type I IFN receptor (IFNR), there is up-regulation of expression of Sprouty (Spry) proteins 1, 2, and 4. Our studies demonstrate that IFN-inducible up-regulation of Spry proteins is Mnk kinase-dependent and results in suppressive effects on the IFN-activated p38 MAP kinase (MAPK), the function of which is required for transcription of interferon-stimulated genes (ISGs). Our data establish that ISG15 mRNA expression and IFN-dependent antiviral responses are enhanced in Spry1,2,4 triple knock-out mouse embryonic fibroblasts, consistent with negative feedback regulatory roles for Spry proteins in IFN-mediated signaling. In other studies, we found that siRNA-mediated knockdown of Spry1, Spry2, or Spry4 promotes IFN-inducible antileukemic effects in vitro and results in enhanced suppressive effects on malignant hematopoietic progenitors from patients with polycythemia vera. Altogether, our findings demonstrate that Spry proteins are potent regulators of Type I IFN signaling and negatively control induction of Type I IFN-mediated biological responses.

G-CSF-activated STAT3 enhances production of the chemokine MIP-2 in bone marrow neutrophils

Neutrophil mobilization from the bone marrow is a critical aspect of the innate immune response, enabling a rapid deployment of phagocytes to infected or inflamed tissue. The cytokine G-CSF, which is induced rapidly during infection, elicits a swift and potent mobilizing response, yet its mechanisms of action remain poorly understood. Here, we studied the role of G-CSF and its principal signal transducer STAT3 in regulating expression of the neutrophil chemoattractant MIP-2. Our studies revealed Gr-1(hi) mature neutrophils as major sources of Cxcl2 (MIP-2) mRNA in bone marrow and G-CSF-responsive MIP-2 protein production. Induction of Cxcl2 was regulated directly by G-CSF-activated STAT3 via interaction at a STAT consensus element in the Cxcl2 promoter. G-CSF coordinately stimulated the association of STAT3, induction of the transcriptionally active H3K4me3 modification, and recruitment of RNA Pol II at the Cxcl2 proximal promoter, as well as the promoter region of Il8rb, encoding the MIP-2 receptor. These results suggest that the G-CSF-STAT3 pathway directly regulates transcriptional events that induce neutrophil mobilization.

Interferons as biomarkers and effectors: lessons learned from animal models

Interferons (IFNs) comprise type I, II and III families with multiple subtypes. Via transcription of IFN-stimulated genes (ISGs), IFNs can exert multiple biological effects on the cell. In infectious and chronic inflammatory diseases, the IFNs and their ISG sets can be potentially utilized as biomarkers of disease outcome. Animal models allow investigations into disease pathogenesis and gene knockout models have proved cause and effect relationships of molecules related to the IFN response. Sets of IFN subtypes and their ISG products provide immunological signature patterns for different viral and other diseases. In this article, we give an overview of IFNs in several virus infection models and autoimmune diseases of medical relevance. Lessons learned from animal models inform us of IFN system parameters as indicators of disease outcome and whether clinical research is warranted. Moreover, validated IFN biomarkers for prognosis enhance our understanding of therapeutic and vaccine development.

Subcellular localization and functional characterization of a fish IRF9 from crucian carp Carassius auratus

Mammalian interferon (IFN) regulatory factor 9 (IRF-9) has long been recognized as the DNA sequence recognition subunit of IFN-stimulated gene factor 3 (ISGF3) complex, which is critical for type I IFN to induce the expression of IFN-stimulated genes (ISGs) against viral infection. Recent studies have shown that fish IFN exerts antiviral effects by induction of a number of ISGs and also of itself; however, little is known about the role of fish IRF9 in IFN signaling. Here we identify a fish IRF9 orthologue (CaIRF9) from IFN-producing cell line, crucian carp Carassius auratus blastulae embryonic (CAB) cells. Analysis of subcellular distribution of CaIRF9-green fluorescent protein indicates that CaIRF9 is constitutively present in the nucleus, which is driven by two nuclear localization signals (NLS), one locating within DNA-binding domain (DBD) of CaIRF9 and the other immediately behind DBD, although human IRF9 contains only one NLS analogous to the former of CaIRF9. Overexpression of CaIRF9 together with CaSTAT2 not only activates ISRE-containing promoter but also upregulates the expression of fish ISGs. Strikingly, CaIRF9 together with CaSTAT2 also exhibits an ability to activate crucian carp IFN promoter, and blockade of cellular CaIRF9 attenuates IFN itself-induced activation of crucian carp IFN promoter. Taken together, these data suggest that crucian carp IFN induces the expression of ISGs and also of itself possibly by the JAK-STAT signaling pathway that is conserved from fish to mammals.

Histone deacetylase inhibitors block IFNγ-induced STAT1 phosphorylation

Signal transducer and activator of transcription 1 (STAT1) is important for innate and adaptive immunity. Histone deacetylase inhibitors (HDACi) antagonize unbalanced immune functions causing chronic inflammation and cancer. Phosphorylation and acetylation regulate STAT1 and different IFNs induce phosphorylated STAT1 homo-/heterodimers, e.g. IFNα activates several STATs whereas IFNγ only induces phosphorylated STAT1 homodimers. In transformed cells HDACi trigger STAT1 acetylation linked to dephosphorylation by the phosphatase TCP45. It is unclear whether acetylation differentially affects STAT1 activated by IFNα or IFNγ, and if cellular responses to both cytokines depend on a phosphatase-dependent inactivation of acetylated STAT1. Here, we report that HDACi counteract IFN-induced phosphorylation of a critical tyrosine residue in the STAT1 C-terminus in primary cells and hematopoietic cells. STAT1 mutants mimicking a functionally inactive DNA binding domain (DBD) reveal that the number of acetylation-mimicking sites in STAT1 determines whether STAT1 is recruited to response elements after stimulation with IFNγ. Furthermore, we show that IFNα-induced STAT1 heterodimers carrying STAT1 molecules mimicking acetylation bind cognate DNA and provide innate anti-viral immunity. IFNγ-induced acetylated STAT1 homodimers are though inactive, suggesting that heterodimerization and complex formation can rescue STAT1 lacking a functional DBD. Apparently, the type of cytokine determines how acetylation affects the nuclear entry and DNA binding of STAT1. Our data contribute to a better understanding of STAT1 regulation by acetylation.

The influence of treatment with pegylated interferon-alfa and ribavirin on neutrophil function and death in patients with HIV/HCV coinfection

In patients with human immunodeficiency virus (HIV) as well as in patients with hepatitis C virus (HCV) infection the impairment of neutrophil activity is observed. We decided to analyze how treatment with pegylated interferon-alfa (Peg-IFN-alfa) and ribavirin affects neutrophil function in HIV/HCV coinfected patients. The study group consisted of 18 patients with HIV/HCV coinfection, on combination antiretroviral treatment (cART), aged between 27 and 42 y (mean 33.1±4.5 y). At the beginning of treatment with Peg-IFN-alfa and ribavirin all patients had an undetectable HIV viral load, and CD4 T-cell counts higher than 350 cells/μL. At two time points, before and after 12 wk of treatment with Peg-IFN-alfa and ribavirin, we examined intracellular levels of reactive oxygen species (ROS), and expression of selected adhesion molecules on whole blood neutrophils, along with apoptosis and necrosis of these cells. These analyses were done with flow cytometry. During anti-HCV therapy undetectable HIV levels were maintained in all patients. Treatment with PEG-IFN-alfa and ribavirin resulted in increases in the expression of CD11b and CD18, and decreases of CD16 and CD62L. However, only the change in CD62L expression was statistically significant (p<0.05). Moreover, the treatment resulted in increased apoptosis of neutrophils, while necrosis remained unchanged. After 12 wk of treatment, an increase in ROS production by neutrophils stimulated with PMA was observed (p<0.01). In HIV/HCV coinfected patients on cART, PEG-IFN-alfa and ribavirin treatment caused an activation of neutrophil function, yet it did not affect the suppression of HIV replication.