The antiviral state induced by alpha interferon and gamma interferon requires transcriptionally active Stat1 protein

Uncovering new insights into the role of the ubiquitin ligase Smurf1 on the regulation of innate immune signaling and resistance to infection

Innate immunity is the body's first line of defense against infections. Innate immune cells express pattern recognition receptors in distinct cellular compartments that are responsible to detect either pathogens-associated molecules or cellular components derived from damaged cells, to trigger intracellular signaling pathways that lead to the activation of inflammatory responses. Inflammation is essential to coordinate immune cell recruitment, pathogen elimination and to keep normal tissue homeostasis. However, uncontrolled, misplaced or aberrant inflammatory responses could lead to tissue damage and drive chronic inflammatory diseases and autoimmunity. In this context, molecular mechanisms that tightly regulate the expression of molecules required for the signaling of innate immune receptors are crucial to prevent pathological immune responses. In this review, we discuss the ubiquitination process and its importance in the regulation of innate immune signaling and inflammation. Then, we summarize the roles of Smurf1, a protein that works on ubiquitination, on the regulation of innate immune signaling and antimicrobial mechanisms, emphasizing its substrates and highlighting its potential as a therapeutic target for infectious and inflammatory conditions.

Deactivation of the antiviral state by rabies virus through targeting and accumulation of persistently phosphorylated STAT1

Antagonism of the interferon (IFN)-mediated antiviral state is critical to infection by rabies virus (RABV) and other viruses, and involves interference in the IFN induction and signaling pathways in infected cells, as well as deactivation of the antiviral state in cells previously activated by IFN. The latter is required for viral spread in the host, but the precise mechanisms involved and roles in RABV pathogenesis are poorly defined. Here, we examined the capacity of attenuated and pathogenic strains of RABV that differ only in the IFN-antagonist P protein to overcome an established antiviral state. Importantly, P protein selectively targets IFN-activated phosphorylated STAT1 (pY-STAT1), providing a molecular tool to elucidate specific roles of pY-STAT1. We find that the extended antiviral state is dependent on a low level of pY-STAT1 that appears to persist at a steady state through ongoing phosphorylation/dephosphorylation cycles, following an initial IFN-induced peak. P protein of pathogenic RABV binds and progressively accumulates pY-STAT1 in inactive cytoplasmic complexes, enabling recovery of efficient viral replication over time. Thus, P protein-pY-STAT1 interaction contributes to ‘disarming’ of the antiviral state. P protein of the attenuated RABV is defective in this respect, such that replication remains suppressed over extended periods in cells pre-activated by IFN. These data provide new insights into the nature of the antiviral state, indicating key roles for residual pY-STAT1 signaling. They also elucidate mechanisms of viral deactivation of antiviral responses, including specialized functions of P protein in selective targeting and accumulation of pY-STAT1.

Following viral infection, the host activates multiple antiviral defenses. The ability of viruses to overcome these defenses is critical to disease. The earliest antiviral response involves the production of interferon messenger molecules. Interferons act on infected cells to inhibit viral proliferation, as well as on non-infected cells to establish an antiviral state before infection and so limit viral spread through the host organism. Many strategies used by viruses to overcome the former are well understood, but mechanisms important to the latter, and their importance to disease, are less well defined. In this study, we investigated how rabies virus overcomes a pre-established antiviral state in target cells. We found that the capacity to disable the antiviral state correlates with the ability to cause disease, and involves binding of a viral protein to cellular signaling proteins, which our data indicate are responsible for the maintenance of a prolonged antiviral state. This advances our understanding of antiviral responses, and identifies a key step in lethal infection by rabies virus that causes approximately 60,000 human deaths per year. The findings may contribute to new approaches for the development of vaccines or antivirals.

FTO Suppresses STAT3 Activation and Modulates Proinflammatory Interferon-Stimulated Gene Expression

Signaling initiated by type I interferon (IFN) results in the induction of hundreds of IFN-stimulated genes (ISGs). The type I IFN response is important for antiviral restriction, but aberrant activation of this response can lead to inflammation and autoimmunity. Regulation of this response is incompletely understood. We previously reported that the mRNA modification m⁶A and its deposition enzymes, METTL3 and METTL14 (METTL3/14), promote the type I IFN response by directly modifying the mRNA of a subset of ISGs to enhance their translation. Here, we determined the role of the RNA demethylase fat mass and obesity-associated protein (FTO) in the type I IFN response. FTO, which can remove either m⁶A or cap-adjacent m⁶Am RNA modifications, has previously been associated with obesity and body mass index, type 2 diabetes, cardiovascular disease, and inflammation. We found that FTO suppresses the transcription of a distinct set of ISGs, including many known pro-inflammatory genes, and that this regulation requires its catalytic activity but is not through the actions of FTO on m⁶Am. Interestingly, depletion of FTO led to activation of the transcription factor STAT3, whose role in the type I IFN response is not well understood. This activation of STAT3 increased the expression of a subset of ISGs. Importantly, this increased ISG induction resulting from FTO depletion was partially ablated by depletion of STAT3. Together, these results reveal that FTO negatively regulates STAT3-mediated signaling that induces proinflammatory ISGs during the IFN response, highlighting an important role for FTO in suppression of inflammatory genes.

Inhibitory effects of Lactobacillus plantarum metabolites on porcine epidemic diarrhea virus replication

Porcine epidemic diarrhea virus (PEDV) is an enteropathogenic coronavirus; it causes diarrhea in pigs and is associated with high morbidity and mortality in sucking piglets. In this study, we performed in vitro and in vivo experiments to determine the inhibitory effects of Lactobacillus plantarum metabolites (LPM) on PEDV replication. Gas chromatography-mass spectrometry revealed exopolysaccharides to be one of the main components of LPM. We then determine whether L. plantarum exopolysaccharides (LPE) have an antiviral effect and also detected the expression levels of the apoptosis-related genes Bax and Bcl-2 and of the pro-apoptotic protein caspase-3. Further, we assessed the transcription levels of an immune-related protein (STAT1) and antiviral factors (MX1, MX2, ISG15, ZAP, PKR, and OAS1). Our results showed that the most effective method was to pretreat cells with LPM and that the optimal dose of LPM that could be safely administered to Vero cells was 1/8 times of the stock solution. LPE had a strong inhibitory effect on PEDV; the most effective method of administration was to co-incubate cells with LPE and PEDV, and the optimal concentration of LPE was 1.35 mg/mL. To conclude, LPE prevented PEDV adsorption and also alleviated inflammatory responses and induced early apoptosis of injured cells, but it could not regulate the immune function of cells.

Allo-priming as a universal anti-viral vaccine: protecting elderly from current COVID-19 and any future unknown viral outbreak

BACKGROUND

We present the rationale for a novel allo-priming approach to serve the elderly as a universal anti-virus vaccine, as well serving to remodel the aging immune system in order to reverse immunosenescence and inflammaging. This approach has the potential to protect the most vulnerable from disease and provide society an incalculable economic benefit. Allo-priming healthy elderly adults is proposed to provide universal protection from progression of any type of viral infection, including protection against progression of the current outbreak of COVID-19 infection, and any future variants of the causative SARS-CoV-2 virus or the next 'Disease X'. Allo-priming is an alternative approach for the COVID-19 pandemic that provides a back-up in case vaccination strategies to elicit neutralizing antibody protection fails or fails to protect the vulnerable elderly population. The allo-priming is performed using activated, intentionally mismatched, ex vivo differentiated and expanded living Th1-like cells (AlloStim^®) derived from healthy donors currently in clinical use as an experimental cancer vaccine. Multiple intradermal injections of AlloStim^® creates a dominate titer of allo-specific Th1/CTL memory cells in circulation, replacing the dominance of exhausted memory cells of the aged immune system. Upon viral encounter, by-stander activation of the allo-specific memory cells causes an immediate release of IFN-ϒ, leading to development of an "anti-viral state", by-stander activation of innate cellular effector cells and activation of cross-reactive allo-specific CTL. In this manner, the non-specific activation of allo-specific Th1/CTL initiates a cascade of spatial and temporal immune events which act to limit the early viral titer. The release of endogenous heat shock proteins (HSP) and DAMP from lysed viral-infected cells, in the context of IFN-ϒ, creates of conditions for in situ vaccination leading to viral-specific Th1/CTL immunity. These viral-specific Th1/CTL provide sterilizing immunity and memory for protection from disease recurrence, while increasing the pool of Th1/CTL in circulation capable of responding to the next viral encounter.

CONCLUSION

Allo-priming has potential to provide universal protection from viral disease and is a strategy to reverse immunosenescence and counter-regulate chronic inflammation (inflammaging). Allo-priming can be used as an adjuvant for anti-viral vaccines and as a counter-measure for unknown biological threats and bio-economic terrorism.

Cellular Signaling Analysis shows antiviral, ribavirin-mediated ribosomal signaling modulation

As antiviral drug resistance develops and new viruses emerge there is a pressing need to develop strategies to rapidly develop antiviral therapeutics. Here we use phospho-specific flow cytometry to assess perturbations of many different cellular signaling pathways during treatment with drug combinations that are highly effective in blocking Herpes simplex virus type 1 (HSV-1) infection. We discovered two antiviral drug combinations act on distinct signaling pathways, either STAT1 or S6 phosphorylation, to block HSV-1 infection. We focused on upregulation of S6 phosphorylation by HSV-1 infection, and our subsequent finding that ribavirin antagonizes this upregulation of S6 phosphorylation. We go on to show that the S6 kinase inhibitor SL0101 blocks HSV-1 replication in vitro and in an in vivo animal model of HSV-1 infection. Overall, we have used an unbiased analysis of cellular signaling pathways during treatment by antiviral drug combinations to discover a novel antiviral drug target against HSV-1 infection. The outcomes of the approach we present highlight the importance of analyzing how antiviral drugs modulate cellular and pathogen-induced signaling as a method to discover new drug therapy targets.

Transcriptional Responses to IFN-γ Require Mediator Kinase-Dependent Pause Release and Mechanistically Distinct CDK8 and CDK19 Functions

Transcriptional responses to external stimuli remain poorly understood. Using global nuclear run-on followed by sequencing (GRO-seq) and precision nuclear run-on sequencing (PRO-seq), we show that CDK8 kinase activity promotes RNA polymerase II pause release in response to interferon-γ (IFN-γ), a universal cytokine involved in immunity and tumor surveillance. The Mediator kinase module contains CDK8 or CDK19, which are presumed to be functionally redundant. We implemented cortistatin A, chemical genetics, transcriptomics, and other methods to decouple their function while assessing enzymatic versus structural roles. Unexpectedly, CDK8 and CDK19 regulated different gene sets via distinct mechanisms. CDK8-dependent regulation required its kinase activity, whereas CDK19 governed IFN-γ responses through its scaffolding function (i.e., it was kinase independent). Accordingly, CDK8, not CDK19, phosphorylates the STAT1 transcription factor (TF) during IFN-γ stimulation, and CDK8 kinase inhibition blocked activation of JAK-STAT pathway TFs. Cytokines such as IFN-γ rapidly mobilize TFs to "reprogram" cellular transcription; our results implicate CDK8 and CDK19 as essential for this transcriptional reprogramming.

Fine-Tuning of Type I Interferon Response by STAT3

Type I interferon (IFN-I) is induced during innate immune response and is required for initiating antiviral activity, growth inhibition, and immunomodulation. STAT1, STAT2, and STAT3 are activated in response to IFN-I stimulation. STAT1, STAT2, and IRF9 form ISGF3 complex which transactivates downstream IFN-stimulated genes and mediates antiviral response. However, the role of STAT3 remains to be characterized. Here, we review the multiple actions of STAT3 on suppressing IFN-I responses, including blocking IFN-I signaling, downregulating the expression of ISGF3 components, and antagonizing the transcriptional activity of ISGF3. Finally, we discuss the evolution of the suppressive activity of STAT3 and the therapeutic potential of STAT3 inhibitors in host defense against viral infections and IFN-I-associated diseases.

Fludarabine as an Adjuvant Improves Newcastle Disease Virus-Mediated Antitumor Immunity in Hepatocellular Carcinoma

In addition to direct oncolysis, oncolytic viruses (OVs) also induce antitumor immunity, also called viro-immunotherapy. Limited viral replication and immune-negative feedback are the major hurdles to effective viro-immunotherapy. In this study, we found that use of an adjuvant of fludarabine, a chemotherapeutic drug for chronic myeloid leukemia, increased the replication of Newcastle disease virus (NDV) by targeting signal transducer and activator of transcription 1 (STAT1), which led to enhanced oncolysis of hepatocellular carcinoma (HCC) cells. Moreover, fludarabine accelerated ubiquitin-proteasomal degradation by enhancing ubiquitylation rather than proteasomal activity. This resulted in accelerated degradation of phosphorylated STAT3 and indoleamine 2, 3-dioxygenase 1 (IDO1), whose expression was induced by NDV infection. In addition, fludarabine significantly increased the NDV-induced infiltration of NK cells and decreased the number of NDV-induced myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment. The aforementioned effects of fludarabine significantly improved NDV-mediated antitumor immunity and prolonged survival in mouse model of HCC. Our findings indicate the utility of fludarabine as an adjuvant for oncolytic anticancer viro-immunotherapy.

Interferon regulated gene (IRG) expression-signature in a mouse model of chikungunya virus neurovirulence

Interferon regulated genes (IRGs) are critical in controlling virus infections. Here, we analyzed the expression profile of IRGs in the brain tissue in a mouse model of chikungunya virus (CHIKV) neurovirulence. Neurovirulence is one of the newer complications identified in disease caused by re-emerging strains of CHIKV, an alphavirus with positive-strand RNA in the Togaviridae family. In microarray analysis, we identified significant upregulation of 269 genes, out of which a predominant percentage (76%) was IRGs. The highly modulated IRGs included Ifit1, Ifi44, Ddx60, Usp18, Stat1, Rtp4, Mnda, Gbp3, Gbp4, Gbp7, Oasl2, Oas1g, Ly6a, Igtp, and Gbp10, along with many others exhibiting lesser changes in expression levels. We found that these IRG mRNA transcripts are modulated in parallel across CHIKV-infected mouse brain tissues, human neuronal cell line IMR-32 and hepatic cell line Huh-7. The genes identified to be highly modulated both in mouse brain and human neuronal cells were Ifit1, Ifi44, Ddx60, Usp18, and Mnda. In Huh-7 cells, however, only two IRGs (Gbp4 and Gbp7) showed a similar level of upregulation. Concordant modulation of IRGs in both mice and human cells indicates that they might play important roles in regulating CHIKV replication in the central nervous system (CNS). The induction of several IRGs in CNS during infection underscores the robustness of IRG-mediated innate immune response in CHIKV restriction. Further studies on these IRGs would help in evolving possibilities for their targeting in host-directed therapeutic interventions against CHIKV.

Nipah and Hendra Virus Nucleoproteins Inhibit Nuclear Accumulation of Signal Transducer and Activator of Transcription 1 (STAT1) and STAT2 by Interfering with Their Complex Formation

Henipaviruses, such as Nipah (NiV) and Hendra (HeV) viruses, are highly pathogenic zoonotic agents within the Paramyxoviridae family. The phosphoprotein (P) gene products of the paramyxoviruses have been well characterized for their interferon (IFN) antagonist activity and their contribution to viral pathogenicity. In this study, we demonstrated that the nucleoprotein (N) of henipaviruses also prevents the host IFN signaling response. Reporter assays demonstrated that the NiV and HeV N proteins (NiV-N and HeV-N, respectively) dose-dependently suppressed both type I and type II IFN responses and that the inhibitory effect was mediated by their core domains. Additionally, NiV-N prevented the nuclear transport of signal transducer and activator of transcription 1 (STAT1) and STAT2. However, NiV-N did not associate with Impα5, Impβ1, or Ran, which are members of the nuclear transport system for STATs. Although P protein is known as a binding partner of N protein and actively retains N protein in the cytoplasm, the IFN antagonist activity of N protein was not abolished by the coexpression of P protein. This suggests that the IFN inhibition by N protein occurs in the cytoplasm. Furthermore, we demonstrated that the complex formation of STATs was hampered in the N protein-expressing cells. As a result, STAT nuclear accumulation was reduced, causing a subsequent downregulation of interferon-stimulated genes (ISGs) due to low promoter occupancy by STAT complexes. This novel route for preventing host IFN responses by henipavirus N proteins provides new insight into the pathogenesis of these viruses.IMPORTANCE Paramyxoviruses are well known for suppressing interferon (IFN)-mediated innate immunity with their phosphoprotein (P) gene products, and the henipaviruses also possess P, V, W, and C proteins for evading host antiviral responses. There are numerous studies providing evidence for the relationship between viral pathogenicity and antagonistic activities against IFN responses by P gene products. Meanwhile, little attention has been paid to the influence of nucleoprotein (N) on host innate immune responses. In this study, we demonstrated that both the NiV and HeV N proteins have antagonistic activity against the JAK/STAT signaling pathway by preventing the nucleocytoplasmic trafficking of STAT1 and STAT2. This inhibitory effect is due to an impairment of the ability of STATs to form complexes. These results provide new insight into the involvement of N protein in viral pathogenicity via its IFN antagonism.

Increased incidence of cytomegalovirus coinfection in HCV-infected patients with late liver fibrosis is associated with dysregulation of JAK-STAT pathway

Herein, we examined the association between cytomegalovirus (CMV) coinfection and the progression of liver fibrosis in hepatitis C virus (HCV) infection, and investigated the effect of CMV coinfection on JAK-STAT pathway. CMV DNAemia was detected by PCR in DNA from controls (n = 120), and HCV patients with early (F0-F1, n = 131) and late (F2-F4, n = 179) liver fibrosis. By quantitative real time PCR (qRT-PCR), we examined the profile of 8 JAK-STAT transcripts in PBMCs RNA from 90 HCV patients (39 CMV positive and 51 CMV negative), 4 CMV mono-infected patients, and 15 controls. Our results demonstrated higher incidence of CMV in F2-F4 group than in control (OR 5.479, 95% CI 3.033–9.895, p < 0.0001) or F0-F1 groups (OR 2, 95% CI 1.238–3.181, p = 0.005). qRT-PCR showed downregulation of STAT2 (p = 0.006) and IRF7 (p = 0.02) in CMV positive group compared to CMV negative one. The downregulation of STAT2 and IRF7 was mainly in CMV positive patients with late fibrosis compared to CMV negative patients (p = 0.0007 for IRF7 and p = 0.01 for STAT2). Our results are the first to report that CMV coinfection is a possible risk factor for the progression of HCV-induced liver fibrosis, and thereby CMV screening and treatment are important for HCV patients.

Transcriptomic Analysis of Host Immune Response in the Skin of Chickens Infected with Marek's Disease Virus

Marek's disease virus (MDV), a highly cell-associated oncogenic α-herpesvirus, is the causative agent of T cell lymphoma and neuropathic disease called Marek's disease. The skin is the only anatomical site where infectious enveloped cell-free virions are produced and shed into the environment. Studies have demonstrated that MDV infection induces immunological responses within the skin, including the release of cytokines and the recruitment of T lymphocytes. The host immune response, however, is not sufficient to block replication and shedding of the virus particles from the skin. In this study, we examined the gene expression profiling in the skin tissues of MDV-infected chickens to identify viral-induced alterations in the host gene expression pattern. To identify these genes in an unbiased and comprehensive manner, we performed RNA-seq on skin samples of MDV-infected chickens at 10, 20, and 30 days postinfection (dpi). We identified 820, 1,333, and 1,571 upregulated genes in the skin of MDV-infected chickens at 10, 20, and 30 dpi, respectively. In addition, we identified 461, 878, and 1,751 downregulated genes corresponding to the same time points, respectively. Analysis of the upregulated genes resulted in the identification of multiple gene ontology (GO) categories, with most falling under the host immune response. Searching these immune related GO categories, we identified six genes, gga-let-7d, interleukin 22 receptor subunit alpha 2, tumor necrosis factor receptor superfamily member 21, Proline-serine-threonine phosphatase-interacting protein 2, Suppressor of cytokine signaling (SOCS)1, and SOCS3, with known immunosuppressive properties that are upregulated in the skin of MDV-infected chickens.

Preparation and characterization of latex films photo-immobilized with IFN-α

We developed a biomaterial by photo-immobilizing interferon-α (IFN-α) on the surface of latex condom films for the prevention and treatment of cervicitis, cervical cancers and diseases caused by cervical virus. The IFN-α modification by photoactive N-(4-azidobenzoyloxy) succinimide was characterized on a nano-scale by spectroscopy analysis and micro morphology. The anti-bacterial, anti-cancer, and anti-viral effects of the modified bioactive latex films were evaluated by antibacterial susceptibility testing, Gram staining, flow cytometry, immunofluorescence, and Western blotting. Our results showed that the photo-immobilized IFN-α latex films effectively inhibited the growth of both Neisseria gonorrhoeae and human cervical cancer HeLa cells. Moreover, the expression of anti-viral proteins, including P56, MxA, and 2', 5'-OAS, in the human cervical epithelial cell line NC104 was significantly increased by photo-immobilized IFN-α latex films. Taken together, these results suggest that photo-immobilized IFN-α latex films may have therapeutic effects against cervicitis, cervical cancers, and cervical virus.

Parainfluenza Virus 3 Blocks Antiviral Mediators Downstream of the Interferon Lambda Receptor by Modulating Stat1 Phosphorylation

Parainfluenza viruses are known to inhibit type I interferon (IFN) production; however, there is a lack of information regarding the type III IFN response during infection. Type III IFNs signal through a unique heterodimeric receptor, IFN-λR1/interleukin-10R2 (IL-10R2), which is primarily expressed by epithelial cells. Parainfluenza virus 3 (PIV-3) infection is highly restricted to the airway epithelium. We therefore sought to examine type III IFN signaling pathways during PIV-3 infection of epithelial cells. We used three strains of PIV-3: human PIV-3 (HPIV-3), bovine PIV-3 (BPIV-3), and dolphin PIV-1 (Tursiops truncatus PIV-1, or TtPIV-1). Here, we show that message levels of IL-29 are significantly increased during PIV-3 infection, yet downstream antiviral signaling molecules are not upregulated to levels similar to those of the positive control. Furthermore, in Vero cells infected with PIV-3, stimulation with recombinant IL-29/-28A/-28B does not cause upregulation of downstream antiviral molecules, suggesting that PIV-3 interferes with the JAK/STAT pathway downstream of the IFN-λR1/IL-10R2 receptor. We used Western blotting to examine the phosphorylation of Stat1 and Stat2 in Vero cells and the bronchial epithelial cell line BEAS-2B. In Vero cells, we observed reduced phosphorylation of the serine 727 (S727) site on Stat1, while in BEAS-2B cells Stat1 phosphorylation was decreased at the tyrosine 701 (Y701) site during PIV-3 infection. PIV-3 therefore interferes with the phosphorylation of Stat1 downstream of the type III IFN receptor. These data provide new evidence regarding strategies employed by parainfluenza viruses to effectively circumvent respiratory epithelial cell-specific antiviral immunity.

IMPORTANCE

Parainfluenza virus (PIV) in humans is associated with bronchiolitis and pneumonia and can be especially problematic in infants and the elderly. Also seen in cattle, bovine PIV-3 causes respiratory infections in young calves. In addition, PIV-3 is one of a number of pathogens that contribute to the bovine respiratory disease complex (BRDC). As their name suggests, interferons (IFNs) are produced by cells to interfere with viral replication. Paramyxoviruses have previously been shown to block production and downstream signaling of type I IFNs. For the first time, it is shown here that PIV-3 can induce protective type III IFNs in epithelial cells, the primary site of PIV-3 infection. However, we found that PIV-3 modulates signaling pathways downstream of the type III IFN receptor to block production of several specific molecules that aid in a productive antiviral response. Importantly, this work expands our understanding of how PIV-3 effectively evades host innate immunity.

Severe epistaxis due to aberrant vasculature in a patient with STAT-1 mutation

BACKGROUND

Signal transducer and activator 1 (STAT-1) mutations are rare and have been implicated in combined immunodeficiency, enhanced tumorigenesis, and vascular defects.

METHODS

A 60-year-old woman with a novel STAT-1 mutation and resulting immunodeficiency, squamous cell carcinoma, and vascular disease presented with profuse epistaxis secondary to rupture of an aberrant artery that she developed in part because of this mutation. After unsuccessful posterior packing, embolization was initiated but subsequently aborted because of a bovine origin carotid artery and a history of multiple carotid dissections.

RESULTS

After repeat posterior packing, hemostasis was achieved. No additional episodes of epistaxis occurred in the subsequent 13 months.

CONCLUSION

Vascular anomalies can present challenges in epistaxis management. In patients with conditions known to cause vascular anomalies, it is critical to obtain vascular imaging before intervention.

Genome-wide transcriptional profiling reveals that HIV-1 Vpr differentially regulates interferon-stimulated genes in human monocyte-derived dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells (APCs) that directly link the innate and adaptive immune responses. HIV-1 infection of DCs leads to a diverse array of changes in gene expression and play a major role in dissemination of the virus into T-cells. Although HIV-1 Vpr is a pleiotropic protein involved in HIV-1 replication and pathogenesis, its exact role in APCs such as DCs remains elusive. In this study, utilizing a microarray-based systemic biology approach, we found that HIV-1 Vpr differentially regulates (fold change >2.0) more than 200 genes, primarily those involved in the immune response and innate immune response including type I interferon signaling pathway. The differential expression profiles of select genes involved in innate immune responses (interferon-stimulated genes [ISGs]), including MX1, MX2, ISG15, ISG20, IFIT1, IFIT2, IFIT3, IFI27, IFI44L, and TNFSF10, were validated by real-time quantitative PCR; the results were consistent with the microarray data. Taken together, our findings are the first to demonstrate that HIV-1 Vpr induces ISGs and activates the type I IFN signaling pathway in human DCs, and provide insights into the role of Vpr in HIV-1 pathogenesis.

Polyomavirus T antigens activate an antiviral state

Ectopic expression of Simian Virus 40 (SV40) large T antigen (LT) in mouse embryonic fibroblasts (MEFs) increased levels of mRNAs encoding interferon stimulated genes (ISGs). The mechanism by which T antigen increases levels of ISGs in MEFs remains unclear. We present evidence that expression of T antigen from SV40, Human Polyomaviruses BK (BKV) or JC (JCV) upregulate production of ISGs in MEFs, and subsequently result in an antiviral state, as determined by inhibition of VSV or EMCV growth. The first 136 amino acids of LT are sufficient for these activities. Furthermore, increased ISG expression and induction of the antiviral state requires STAT1. Finally, the RB binding motif of LT is necessary for activation of STAT1. We conclude that the induction of the STAT1 mediated innate immune response in MEFs is a common feature shared by SV40, BKV and JCV.

Mendelian susceptibility to mycobacterial disease: genetic, immunological, and clinical features of inborn errors of IFN-γ immunity

Mendelian susceptibility to mycobacterial disease (MSMD) is a rare condition characterized by predisposition to clinical disease caused by weakly virulent mycobacteria, such as BCG vaccines and environmental mycobacteria, in otherwise healthy individuals with no overt abnormalities in routine hematological and immunological tests. MSMD designation does not recapitulate all the clinical features, as patients are also prone to salmonellosis, candidiasis and tuberculosis, and more rarely to infections with other intramacrophagic bacteria, fungi, or parasites, and even, perhaps, a few viruses. Since 1996, nine MSMD-causing genes, including seven autosomal (IFNGR1, IFNGR2, STAT1, IL12B, IL12RB1, ISG15, and IRF8) and two X-linked (NEMO, and CYBB) genes have been discovered. The high level of allelic heterogeneity has already led to the definition of 18 different disorders. The nine gene products are physiologically related, as all are involved in IFN-γ-dependent immunity. These disorders impair the production of (IL12B, IL12RB1, IRF8, ISG15, NEMO) or the response to (IFNGR1, IFNGR2, STAT1, IRF8, CYBB) IFN-γ. These defects account for only about half the known MSMD cases. Patients with MSMD-causing genetic defects may display other infectious diseases, or even remain asymptomatic. Most of these inborn errors do not show complete clinical penetrance for the case-definition phenotype of MSMD. We review here the genetic, immunological, and clinical features of patients with inborn errors of IFN-γ-dependent immunity.

Novel antiviral host factor, TNK1, regulates IFN signaling through serine phosphorylation of STAT1

In response to viral infection, the host induces over 300 IFN-stimulated genes (ISGs), which are the central component of intracellular antiviral innate immunity. Inefficient induction of ISGs contributes to poor control and persistence of hepatitis C virus infection. Therefore, further understanding of the hepatocytic ISG regulation machinery will guide us to an improved management strategy against hepatitis C virus infection. In this study, comprehensive genome-wide, high-throughput cDNA screening for genes regulating ISG expression identified a tyrosine kinase nonreceptor 1 (TNK1) as a unique player in the ISG induction pathway. The immune-modulatory function of TNK1 has never been studied, and this study characterizes its significance in antiviral innate immunity. TNK1 is abundantly expressed in hepatocytes and maintains basal ISG expression. More importantly, TNK1 plays a critical role in type I IFN-mediated ISG induction. We discovered that the activated IFN receptor complex recruits TNK1 from the cytoplasm. TNK1 is then phosphorylated to enhance its kinase activity. The activated TNK1 potentiates JAK-STAT signaling through dual phosphorylation of STAT1 at tyrosine 701 and serine 727 amino acid positions. Our loss-of-function approach demonstrated that TNK1 governs a cluster of ISG expression that defines the TNK1 pathway effector genes. More importantly, TNK1 abundance is inversely correlated to viral replication efficiency and is also a determinant factor for the hepatocytic response to antiviral treatment. Taken together, our studies found a critical but unidentified integrated component of the IFN-JAK-STAT signaling cascade.

Inhibition of p38 mitogen-activated protein kinase impairs influenza virus-induced primary and secondary host gene responses and protects mice from lethal H5N1 infection

Highly pathogenic avian influenza viruses (HPAIV) induce severe inflammation in poultry and men. One characteristic of HPAIV infections is the induction of a cytokine burst that strongly contributes to viral pathogenicity. This cell-intrinsic hypercytokinemia seems to involve hyperinduction of p38 mitogen-activated protein kinase. Here we investigate the role of p38 MAPK signaling in the antiviral response against HPAIV in mice as well as in human endothelial cells, the latter being a primary source of cytokines during systemic infections. Global gene expression profiling of HPAIV-infected endothelial cells in the presence of the p38-specific inhibitor SB 202190 revealed that inhibition of p38 MAPK leads to reduced expression of IFNβ and other cytokines after H5N1 and H7N7 infection. More than 90% of all virus-induced genes were either partially or fully dependent on p38 signaling. Moreover, promoter analysis confirmed a direct impact of p38 on the IFNβ promoter activity. Furthermore, upon treatment with IFN or conditioned media from HPAIV-infected cells, p38 controls interferon-stimulated gene expression by coregulating STAT1 by phosphorylation at serine 727. In vivo inhibition of p38 MAPK greatly diminishes virus-induced cytokine expression concomitant with reduced viral titers, thereby protecting mice from lethal infection. These observations show that p38 MAPK acts on two levels of the antiviral IFN response. Initially the kinase regulates IFN induction and, at a later stage, p38 controls IFN signaling and thereby expression of IFN-stimulated genes. Thus, inhibition of MAP kinase p38 may be an antiviral strategy that protects mice from lethal influenza by suppressing excessive cytokine expression.

CDK8-mediated STAT1-S727 phosphorylation restrains NK cell cytotoxicity and tumor surveillance

The transcription factor STAT1 is important in natural killer (NK) cells, which provide immediate defense against tumor and virally infected cells. We show that mutation of a single phosphorylation site (Stat1-S727A) enhances NK cell cytotoxicity against a range of tumor cells, accompanied by increased expression of perforin and granzyme B. Stat1-S727A mice display significantly delayed disease onset in NK cell-surveilled tumor models including melanoma, leukemia, and metastasizing breast cancer. Constitutive phosphorylation of S727 depends on cyclin-dependent kinase 8 (CDK8). Inhibition of CDK8-mediated STAT1-S727 phosphorylation may thus represent a therapeutic strategy for stimulating NK cell-mediated tumor surveillance.

Hepatitis C virus targets the interferon-α JAK/STAT pathway by promoting proteasomal degradation in immune cells and hepatocytes

JAK/STAT signalling is essential for anti-viral immunity, making IFN-α an obvious anti-viral therapeutic. However, many HCV+ patients fail treatment, indicating that the virus blocks successful IFN-α signalling. We found that STAT1 and STAT3 proteins, key components of the IFN-α signalling pathway were reduced in immune cells and hepatocytes from HCV infected patients, and upon HCV expression in Huh7 hepatocytes. However, STAT1 and STAT3 mRNA levels were normal. Mechanistic analysis revealed that in the presence of HCV, STAT3 protein was preferentially ubiquitinated, and degradation was blocked by the proteasomal inhibitor MG132. These findings show that HCV inhibits IFN-α responses in a broad spectrum of cells via proteasomal degradation of JAK/STAT pathway components.

IL-17A but not IL-22 suppresses the replication of hepatitis B virus mediated by over-expression of MxA and OAS mRNA in the HepG2.2.15 cell line

Interleukin-17A (IL-17A) and interleukin-22 (IL-22), mainly secreted by interleukin-17-producing T help cells (Th17), are pleiotropic cytokines that regulate the biological responses of several target cells, including hepatocytes. Th17 frequency was reported to negatively correlate with plasma hepatitis B virus (HBV) DNA load in patients with HBV infection. Several studies have indicated that cytokines, such as IL-6 and IL-4, are involved in the noncytopathic suppression of HBV replication. We therefore hypothesized that IL-17A and IL-22 might have a potent suppressive effect on HBV replication. In our present study, we analyzed the suppressive effect of IL-17A and IL-22 on HBV replication in the hepatocellular carcinoma cell line HepG2.2.15. IL-17A did not inhibit the proliferation of HepG2.2.15 cells. It decreased the levels of HBV s antigen (HBsAg) and HBV e antigen (HBeAg) in culture medium and the levels of intracellular HBV DNA. By contrast, blockage of IL-17 receptor (IL-17R) increased the levels of HBsAg and extracellular HBV DNA in culture medium and the levels of intracellular HBV DNA. The expression of antiviral proteins, including myxovirus resistance A (MxA) and oligoadenylate synthetase (OAS), was enhanced by IL-17A. IL-22 and anti-human IL-22 receptor (IL-22R) antibody did not change any indexes. We demonstrated that IL-17A effectively suppressed HBV replication in a noncytopathic manner and the over-expression of MxA and OAS mRNA was involved in the suppression of HBV replication by IL-17A.

Host factors and measles virus replication

This review takes a general approach to describing host cell factors that facilitate measles virus (MeV) infection and replication. It relates our current understanding of MeV entry receptors, with emphasis on how these host cell surface proteins contribute to pathogenesis within its host. The roles of SLAM/CD150 lymphocyte receptor and the newly discovered epithelial receptor PVRL4/nectin-4 are highlighted. Host cell factors such as HSP72, Prdx1, tubulin, casein kinase, and actin, which are known to impact viral RNA synthesis and virion assembly, are also discussed. Finally the review describes strategies used by measles virus to circumvent innate immunity and confound the effects of interferon within the host cell. Proteomic studies and genome wide RNAi screens will undoubtedly advance our knowledge in the future.

Smurf1 protein negatively regulates interferon-γ signaling through promoting STAT1 protein ubiquitination and degradation

Interferons are important cytokines that mediate antiviral, antiproliferative, antitumor, and immunoregulatory activities. However, uncontrolled IFN signaling may lead to autoimmune diseases. Here we identified Smurf1 as a negative regulator for IFN-γ signaling by targeting STAT1 for ubiquitination and proteasomal degradation. Smurf1 interacted with STAT1 through the WW domains of Smurf1 and the PY motif in STAT1 and catalyzed K48-linked polyubiquitination of STAT1. Interestingly, the Smurf1-mediated ubiquitination and degradation did not require STAT1 tyrosine and serine phosphorylation. Subsequently, overexpression of Smurf1 attenuated IFN-γ-mediated STAT1 activation and antiviral immune responses, whereas knockdown of Smurf1 enhanced IFN-γ-mediated STAT1 activation, expression of STAT1 target genes, and antiviral immune responses. Furthermore, IFN-γ stimulation led to enhanced expression of Smurf1. Therefore, our results demonstrate that Smurf1 is a negative feedback regulator for IFN-γ signaling by targeting STAT1 for ubiquitination and proteasomal degradation.

The ebola virus interferon antagonist VP24 directly binds STAT1 and has a novel, pyramidal fold

Ebolaviruses cause hemorrhagic fever with up to 90% lethality and in fatal cases, are characterized by early suppression of the host innate immune system. One of the proteins likely responsible for this effect is VP24. VP24 is known to antagonize interferon signaling by binding host karyopherin α proteins, thereby preventing them from transporting the tyrosine-phosphorylated transcription factor STAT1 to the nucleus. Here, we report that VP24 binds STAT1 directly, suggesting that VP24 can suppress at least two distinct branches of the interferon pathway. Here, we also report the first crystal structures of VP24, derived from different species of ebolavirus that are pathogenic (Sudan) and nonpathogenic to humans (Reston). These structures reveal that VP24 has a novel, pyramidal fold. A site on a particular face of the pyramid exhibits reduced solvent exchange when in complex with STAT1. This site is above two highly conserved pockets in VP24 that contain key residues previously implicated in virulence. These crystal structures and accompanying biochemical analysis map differences between pathogenic and nonpathogenic viruses, offer templates for drug design, and provide the three-dimensional framework necessary for biological dissection of the many functions of VP24 in the virus life cycle.

Knockdown of menin affects pre-mRNA processing and promoter fidelity at the interferon-gamma inducible IRF1 gene

BACKGROUND

The tumor suppressor menin (MEN1) is mutated in the inherited disease multiple endocrine neoplasia type I, and has several documented cellular roles, including the activation and repression of transcription effected by several transcription factors. As an activator, MEN1 is a component of the Set1-like mixed lineage leukemia (MLL) MLL1/MLL2 methyltransferase complex that methylates histone H3 lysine 4 (H3K4). MEN1 is localized to the signal transducer and activator of transcription 1 (STAT1)-dependent gene, interferon regulatory factor 1 (IRF1), and is further recruited when IRF1 transcription is triggered by interferon-γ signaling.

RESULTS

RNAi-mediated knockdown of MEN1 alters the H3K4 dimethylation and H3 acetylation profiles, and the localization of histone deacetylase 3, at IRF1. While MEN1 knockdown does not impact the rate of transcription, IRF1 heteronuclear transcripts become enriched in MEN1-depleted cells. The processed mRNA and translated protein product are concomitantly reduced, and the antiviral state is attenuated. Additionally, the transcription start site at the IRF1 promoter is disrupted in the MEN1-depleted cells. The H3K4 demethylase, lysine specific demethylase 1, is also associated with IRF1, and its inhibition alters H3K4 methylation and disrupts the transcription start site as well.

CONCLUSIONS

Taken together, the data indicate that MEN1 contributes to STAT1-activated gene expression in a novel manner that includes defining the transcription start site and RNA processing.

IL-29 and IFN-α regulate the expression of MxA, 2',5'-OAS and PKR genes in association with the activation of Raf-MEK-ERK and PI3K-AKT signal pathways in HepG2.2.15 cells

Interferons (IFNs) can activate the PI3K-AKT and Raf-MEK-ERK signal pathways and induce antiviral proteins (MxA, 2',5'-OAS and PKR) expression in specific cell lines. However, the relationship between those antiviral proteins expression and signal pathways remains unknown at present. Thus our experiments were designed to determine the exact relationship in HepG2.2.15 cell line. The results demonstrated that IFN-α and IL-29 were both able to activate PI3K-AKT and Raf-MEK-ERK signal pathways, and IFN-α up-regulated the expression of MxA, 2',5'-OAS and PKR whereas IL-29 increased mRNA expression of MxA and 2',5'-OAS and had no influence on PKR. Furthermore, MxA, 2',5'-OAS and PKR expression were down-regulated while PI3K-AKT signal pathway was blocked by LY294002. And MxA was up-regulated after Raf-MEK-ERK signal pathway being blocked by PD98059. These findings indicate that the expression of MxA, 2',5'-OAS and PKR are up-regulate by PI3K-AKT signal pathway, and Raf-MEK-ERK signal pathway has a negative regulatory effect on the expression of MxA and no significant effect on 2',5'-OAS and PKR.

Host responses to herpes simplex virus and herpes simplex virus vectors

Herpes simplex virus (HSV) is a well-known, ubiquitous pathogen of humans. Engineered mutants of HSV can also be exploited as vectors in gene therapy or for virotherapy of tumors. HSV has multiple abilities to evade and modulate the innate and adaptive responses of the host. The increasing knowledge on the mutual interactions of the invading HSV with the host defenses will contribute to our deeper understanding of the relationship between HSV and the host, and thereby lead to future development of more effective and specific HSV vectors for treatment of human diseases. The future advances of HSV vaccines and vaccine vectors are based on the knowlegde of the complex interplay between HSV and the host defenses.

Mast cell homeostasis and the JAK-STAT pathway

The Janus kinase/signal transducer and activator of transcription (JAK-STAT) pathway mediates important responses in immune cells. Activation of any of the four JAK family members leads to phosphorylation of one or more of seven STAT family members. Phosphorylation of STAT family members leads to their dimerization and translocation into the nucleus, in which they bind specific DNA sequences to activate gene transcription. Regulation of JAKs and STATs therefore has a significant effect on signal transduction and subsequent cellular responses. Mast cells are important mediators of allergic disease and asthma. These cells have the ability to cause profound inflammation and vasodilation upon the release of preformed mediators, as well as subsequent synthesis of new inflammatory mediators. The regulation of mast cells is therefore of intense interest for the treatment of allergic disease. An important regulator of mast cells, STAT5, is activated downstream of the receptors for immunoglobulin E, interleukin-3 and stem cell factor. STAT5 contributes to mast cell homeostasis, by mediating proliferation, survival, and mediator release. Regulators of the JAK-STAT pathway, such as the suppressors of cytokine signaling (SOCS) and protein inhibitor of activated STAT (PIAS) proteins, are required to fine tune the immune response and maintain homeostasis. A better understanding of the role and regulation of JAKs and STATs in mast cells is vital for the development of new therapeutics.

Inhibition of IFN-gamma-dependent antiviral airway epithelial defense by cigarette smoke

BACKGROUND

Although individuals exposed to cigarette smoke are more susceptible to respiratory infection, the effects of cigarette smoke on lung defense are incompletely understood. Because airway epithelial cell responses to type II interferon (IFN) are critical in regulation of defense against many respiratory viral infections, we hypothesized that cigarette smoke has inhibitory effects on IFN-gamma-dependent antiviral mechanisms in epithelial cells in the airway.

METHODS

Primary human tracheobronchial epithelial cells were first treated with cigarette smoke extract (CSE) followed by exposure to both CSE and IFN-gamma. Epithelial cell cytotoxicity and IFN-gamma-induced signaling, gene expression, and antiviral effects against respiratory syncytial virus (RSV) were tested without and with CSE exposure.

RESULTS

CSE inhibited IFN-gamma-dependent gene expression in airway epithelial cells, and these effects were not due to cell loss or cytotoxicity. CSE markedly inhibited IFN-gamma-induced Stat1 phosphorylation, indicating that CSE altered type II interferon signal transduction and providing a mechanism for CSE effects. A period of CSE exposure combined with an interval of epithelial cell exposure to both CSE and IFN-gamma was required to inhibit IFN-gamma-induced cell signaling. CSE also decreased the inhibitory effect of IFN-gamma on RSV mRNA and protein expression, confirming effects on viral infection. CSE effects on IFN-gamma-induced Stat1 activation, antiviral protein expression, and inhibition of RSV infection were decreased by glutathione augmentation of epithelial cells using N-acetylcysteine or glutathione monoethyl ester, providing one strategy to alter cigarette smoke effects.

CONCLUSIONS

The results indicate that CSE inhibits the antiviral effects of IFN-gamma, thereby presenting one explanation for increased susceptibility to respiratory viral infection in individuals exposed to cigarette smoke.

STAT1 and pathogens, not a friendly relationship

STAT1 belongs to the STAT family of transcription factors, which comprises seven factors: STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B and STAT6. STAT1 is a 91 kDa protein originally identified as the mediator of the cellular response to interferon (IFN) α, and thereafter found to be a major component of the cellular response to IFNγ. STAT1 is, in fact, involved in the response to several cytokines and to growth factors. It is activated by cytokine receptors via kinases of the JAK family. STAT1 becomes phosphorylated and forms a dimer which enters the nucleus and triggers the transcription of its targets. Although not lethal at birth, selective gene deletion of STAT1 in mice leads to rapid death from severe infections, demonstrating its major role in the response to pathogens. Similarly, in humans who do not express STAT1, there is a lack of resistance to pathogens leading to premature death. This indicates a key, non-redundant function of STAT1 in the defence against pathogens. Thus, to successfully infect organisms, bacterial, viral or parasitic pathogens must overcome the activity of STAT1, and almost all the steps of this pathway can be blocked or inhibited by proteins produced in infected cells. Interestingly, some pathogens, like the oncogenic Epstein–Barr virus, have evolved a strategy which uses STAT1 activation.

Differential effects of cytokines and corticosteroids on toll-like receptor 2 expression and activity in human airway epithelia

Background

The recognition of microbial molecular patterns via Toll-like receptors (TLRs) is critical for mucosal defenses.

Methods

Using well-differentiated primary cultures of human airway epithelia, we investigated the effects of exposure of the cells to cytokines (TNF-α and IFN-γ) and dexamethasone (dex) on responsiveness to the TLR2/TLR1 ligand Pam3CSK4. Production of IL-8, CCL20, and airway surface liquid antimicrobial activity were used as endpoints.

Results

Microarray expression profiling in human airway epithelia revealed that first response cytokines markedly induced TLR2 expression. Real-time PCR confirmed that cytokines (TNF-α and IFN-γ), dexamethasone (dex), or cytokines + dex increased TLR2 mRNA abundance. A synergistic increase was seen with cytokines + dex. To assess TLR2 function, epithelia pre-treated with cytokines ± dex were exposed to the TLR2/TLR1 ligand Pam3CSK4 for 24 hours. While cells pre-treated with cytokines alone exhibited significantly enhanced IL-8 and CCL20 secretion following Pam3CSK4, mean IL-8 and CCL20 release decreased in Pam3CSK4 stimulated cells following cytokines + dex pre-treatment. This marked increase in inflammatory gene expression seen after treatment with cytokines followed by the TLR2 ligand did not correlate well with NF-κB, Stat1, or p38 MAP kinase pathway activation. Cytokines also enhanced TLR2 agonist-induced beta-defensin 2 mRNA expression and increased the antimicrobial activity of airway surface liquid. Dex blocked these effects.

Conclusion

While dex treatment enhanced TLR2 expression, co-administration of dex with cytokines inhibited airway epithelial cell responsiveness to TLR2/TLR1 ligand over cytokines alone. Enhanced functional TLR2 expression following exposure to TNF-α and IFN-γ may serve as a dynamic means to amplify epithelial innate immune responses during infectious or inflammatory pulmonary diseases.

Long-term pegylated interferon-alpha and its potential in the treatment of melanoma

Conventional interferons including interferon-alpha (IFN-alpha) are cytokines used for years in the treatment of solid tumors and hematological malignancies. Their half-life is short. Pegylated forms of IFN-alpha present an improved pharmacokinetic profile that rendered them the preferred IFNs in hepatitis therapy. In the last decade, pegylated interferons (PegIFNs) have been investigated in melanoma patients. We review the scientific published literature on biology, pharmacokinetics, side effects and clinical applications of PegIFN-alpha in the treatment of stage III and IV melanoma. In the adjuvant setting, PegIFNalpha-2b has significant prolonged distant metastases free survival in patients with microscopic nodal involvement (stage TxN1aM0) and therefore is a promising treatment option in this patient population. In the palliative setting, monotherapy with PegIFNalpha-2alpha can induce complete remissions in a minority of stage IV melanoma patients. The combination of monochemotherapy is feasible and may result in lasting complete remissions. Ongoing research must focus on the identification of patients who mostly benefit, so that unnecessary toxicity would be avoided. Combining PegIFNs and chemotherapy or targeted agents deserves further exploration.

Enhanced induction of LPS-induced fibroblast MCP-1 by interferon-gamma: involvement of JNK and MAPK phosphatase-1

IFN-gamma has significant immunoregulatory activity and plays an important role in both innate and adaptive immunity. Additive effects of IFN-gamma and the Toll-like receptor ligand LPS has been investigated in macrophages, but in fibroblasts is incompletely understood. IFN-gamma and LPS synergistically induced MCP-1 and NO release in primary murine dermal fibroblasts. IFN-gamma enhanced LPS-induced JNK and p38 MAPK phosphorylation but had no effect on NF-kappaB activity. The induction of both MCP-1 and NO was attenuated by inhibition of JNK but not p38 MAPK. Serine 727 STAT1 phosphorylation by IFN-gamma was increased by LPS, and this was also attenuated by inhibition of JNK but not p38 MAPK. IFN-gamma inhibited the basal expression of MAPK phosphatase-1, a negative regulator of MAPK signaling pathway. These results suggest that enhancement of LPS-induced JNK activation by IFN-gamma associated with inhibition of MAPK phosphatase-1 may be one of the mechanisms of additive effects between IFN-gamma and LPS in fibroblasts.

IFNgamma signaling-does it mean JAK-STAT?

The molecular pathways involved in the cellular response to interferon (IFN)gamma have been the focus of much research effort due to their importance in host defense against infection and disease, as well as its potential as a therapeutic agent. The discovery of the JAK-STAT signaling pathway greatly enhanced our understanding of the mechanism of IFNgamma-mediated gene transcription. However, in recent years it has become apparent that other pathways, including MAP kinase, PI3-K, CaMKII and NF-kappaB, either co-operate with or act in parallel to JAK-STAT signaling to regulate the many facets of IFNgamma biology in a gene- and cell type-specific manner. The complex interactions between JAK/STAT and alternate pathways and the impact of these signaling networks on the biological responses to IFNgamma are beginning to be understood. This review summarizes and appraises current advances in our understanding of these complex interactions, their specificity and proposed biological outcomes.

Nuclear beta-arrestin1 functions as a scaffold for the dephosphorylation of STAT1 and moderates the antiviral activity of IFN-gamma

Signal transducers and activators of transcription 1 (STAT1) is activated by tyrosine phosphorylation upon interferon-gamma (IFN-gamma) stimulation. Phosphorylated STAT1 translocates into nucleus to initiate the transcription of IFN-gamma target genes that are important in mediating antiviral, antiproliferative, and immune response. The inactivation of STAT1 is mainly accomplished via tyrosine dephosphorylation by the nuclear isoform of T cell protein tyrosine phosphatase (TC45) in nucleus. Here we show that beta-arrestin1 directly interacts with STAT1 in nucleus after IFN-gamma treatment and accelerates STAT1 tyrosine dephosphorylation by recruiting TC45. Consequently, beta-arrestin1 negatively regulates STAT1 transcription activity as well as the IFN-gamma-induced gene transcription. Application of beta-arrestin1 siRNA significantly enhances IFN-gamma-induced antiviral response in vesicular stomatitis virus (VSV)-infected cells. Our results reveal that nuclear beta-arrestin1, acting as a scaffold for the dephosphorylation of STAT1, is an essential negative regulator of IFN-gamma signaling and participates in the IFN-gamma-induced cellular antiviral response.

Type I IFN induced IL1-Ra expression in hepatocytes is mediated by activating STAT6 through the formation of STAT2: STAT6 heterodimer

The biological activities of type I interferons (IFNs) are mediated by their binding to a heterodimer receptor complex (IFNAR1 and IFNAR2), resulting in the activation of the JAK (JAK1 and TYK2)-STAT (1, 2, 3, 5 isotypes) signalling pathway. Although several studies have indicated that IFN-alpha and IFN-beta can activate complexes containing STAT6, the biological role of this activation is still unknown. We found that exposure of hepatoma cells (HuH7 and Hep3B) to IFN-alpha or IFN-beta led to the activation of STAT6. Activated STAT6 in turn induced the formation of STAT2: STAT6 complexes, which led to the secretion of IL-1Ra. The activation of STAT6 by type I IFN in hepatocytes was mediated by JAK1 and Tyk2. In addition, IFN-alpha or IFN-beta significantly enhanced the stimulatory effect of IL-1beta on production of IL-1Ra. The present study suggests a novel function of IFN-alpha and IFN-beta signalling in human hepatocytes. Our results provide evidence for the mechanism how IFN-alpha and IFN-beta modulate inflammatory responses through activation of STAT6 and production of secreted IL-1Ra.

STAT2 is a primary target for measles virus V protein-mediated alpha/beta interferon signaling inhibition

Measles virus, a member of the Morbillivirus family, infects millions of people each year despite the availability of effective vaccines. The V protein of measles virus is an important virulence factor that can interfere with host innate immunity by inactivating alpha/beta interferon (IFN-alpha/beta) and IFN-gamma signaling through protein interactions with signal transducer and activator of transcription proteins STAT1 and STAT2. Here we demonstrate that although STAT1 interference results from protein interactions within a V protein N-terminal region encompassed by amino acids 110 to 130, detection of STAT1 interaction and IFN-gamma signaling inhibition requires the presence of cellular STAT2. Cell-specific variability in STAT1 interference was observed to correlate with V protein expression level. A more direct target for measles virus V protein-mediated IFN-alpha/beta evasion is STAT2. Results indicate that the widely conserved C-terminal zinc finger domain of measles virus V protein is both necessary and sufficient to bind STAT2 and disrupt IFN-alpha/beta signal transduction. Mutagenesis and molecular modeling define a contact surface for STAT2 association that includes aspartic acid residue 248 as critical for STAT2 interference and IFN antiviral immune suppression. These findings clearly define the molecular determinants for measles virus IFN evasion and validate specific targets as candidates for therapeutic intervention.

STAT1 signaling modulates HIV-1-induced inflammatory responses and leukocyte transmigration across the blood-brain barrier

The relationship among neuroinflammation, blood-brain barrier (BBB) dysfunction, and progressive HIV-1 infection as they affect the onset and development of neuroAIDS is incompletely understood. One possible link is signal transducers and activators of transcription (STATs) pathways. These respond to proinflammatory and regulatory factors and could affect neuroinflammatory responses induced from infected cells and disease-affected brain tissue. Our previous works demonstrated that HIV-1 activates pro-inflammatory and interferon-alpha-inducible genes in human brain microvascular endothelial cells (HBMECs) and that these genes are linked to the Janus kinase (JAK)/STAT pathway. We now demonstrate that HIV-1 activates STAT1, induces IL-6 expression, and diminishes expression of claudin-5, ZO-1, and ZO-2 in HBMECs. The STAT1 inhibitor, fludarabine, blocked HIV-1-induced IL-6, diminished HIV-1-induced claudin-5 and ZO-1 down-regulation, and blocked HIV-1- and IL-6-induced monocyte migration across a BBB model. Enhanced expression and activation of STAT1 and decreased claudin-5 were observed in microvessels from autopsied brains of patients with HIV-1-associated dementia. These data support the notion that STAT1 plays an integral role in HIV-1-induced BBB damage and is relevant to viral neuropathogenesis. Inhibition of STAT1 activation could provide a unique therapeutic strategy to attenuate HIV-1-induced BBB compromise and as such improve clinical outcomes.

Dual ligand stimulation of RAW 264.7 cells uncovers feedback mechanisms that regulate TLR-mediated gene expression

To characterize how signaling by TLR ligands can be modulated by non-TLR ligands, murine RAW 264.7 cells were treated with LPS, IFN-gamma, 2-methyl-thio-ATP (2MA), PGE(2), and isoproterenol (ISO). Ligands were applied individually and in combination with LPS, for 1, 2, and 4 h, and transcriptional changes were measured using customized oligo arrays. We used nonadditive transcriptional responses to dual ligands (responses that were reproducibly greater or less than the expected additive responses) as a measure of pathway interaction. Our analysis suggests that cross-talk is limited; <24% of the features with significant responses to the single ligands responded nonadditively to a dual ligand pair. PGE(2) and ISO mainly attenuated, while 2MA enhanced, LPS-induced transcriptional changes. IFN-gamma and LPS cross-regulated the transcriptional response induced by each other: while LPS preferentially enhanced IFN-gamma-induced changes in gene expression at 1 h, IFN-gamma signaling primarily attenuated LPS-induced changes at 4 h. Our data suggest specific cross-talk mechanisms: 1) LPS enhances the expression of IFN-gamma-response genes by augmenting STAT1 activity and by activating NF-kappaB, which synergizes with IFN-gamma-induced transcriptional factors; 2) IFN-gamma attenuates the late LPS transcriptional response by increasing the expression of suppressor of cytokine signaling 1 and cytokine-inducible SH2-containing protein expression; 3) 2MA modulates LPS secondary transcriptional response by increasing IFN-beta and inhibiting IL-10 gene expression; 4) PGE(2) and ISO similarly regulate the LPS transcriptional response. They increase IL-10 transcription, resulting in attenuated expression of known IL-10-suppressed genes.

H. saimiri tyrosine-kinase interacting protein inhibits Tat function: A prototypic strategy for restricting HIV-1-induced cytopathic effects in immune cells

Herpesvirus saimiri (HVS)-transformed human T cells become permissive for X4 and R5 strains of human immunodeficiency virus type 1 (HIV-1), evidence that HVS-encoded proteins associated with T cell transformation enhance HIV-1 replication. Analyzing the contribution of transformation-associated bicistronic HVS open reading frames (ORF) to HIV-1 replication revealed expression of the second ORF saimiri transformation-associated protein type C (StpC) conferred the permissive phenotype to T cells. In contrast, expression of the first HVS ORF tyrosine-kinase interacting protein (Tip) in the absence of StpC enhanced restriction of HIV-1 replication in T cell lines and peripheral blood mononuclear cells. Understanding the mechanism whereby Tip enhanced restriction of HIV-1 replication may uncover unique pathways that could be targeted therapeutically. Here we report that Tip restricts HIV-1 replication in a monocyte-derived cell line and restricts reactivation of replication of HIV-1 in a T cell line harboring provirus. In this report, we begin to unravel the molecular underpinnings of Tip-mediated restriction. Tip mediates both lymphocyte-cell-specific kinase (Lck)-dependent and -independent effects on HIV-1 replication. We also provide evidence that Tip-mediated restriction is in part due to inhibition of Tat transactivation of the HIV-1 long terminal repeat (LTR). Expression of Tip in T cells increased activation of Stat1 and Stat3, as well as activation of protein kinase RNA-dependent (PKR/p68) and interferon-gamma production. Taken together, these results provide evidence that Tip restricts HIV-1 replication and reactivation by inhibiting HIV-1 transcription while inducing an intercellular antiviral state. We propose that genetically engineered vectors driving Tip expression could provide a prototypic strategy for restricting HIV-1 replication and reactivation in diverse cell lineages.

Differentially regulated interferon response determines the outcome of Newcastle disease virus infection in normal and tumor cell lines

Newcastle disease virus (NDV) is a negative-strand RNA virus with oncolytic activity against human tumors. Its effectiveness against tumors and safety in normal tissue have been demonstrated in several clinical studies. Here we show that the spread of NDV infection is drastically different in normal cell lines than in tumor cell lines and that the two cell types respond differently to beta interferon (IFN-beta) treatment. NDV rapidly replicated and killed HT-1080 human fibrosarcoma cells but spread poorly in CCD-1122Sk human skin fibroblast cells. Pretreatment with endogenous or exogenous IFN-beta completely inhibited NDV replication in normal cells but had little or no effect in tumor cells. Thus, the outcome of NDV infection appeared to depend on the response of uninfected cells to IFN-beta. To investigate their differences in IFN responsiveness, we analyzed and compared the expression and activation of components of the IFN signal transduction pathway in these two types of cells. The levels of phosphorylated STAT1 and STAT2 and that of the ISGF3 complex were markedly reduced in IFN-beta-treated tumor cells. Moreover, cDNA microarray analysis revealed significantly fewer IFN-regulated genes in the HT-1080 cells than in the CDD-1122Sk cells. This finding suggests that tumor cells demonstrate a less-than-optimum antiviral response because of a lesion in their IFN signal transduction pathway. The rapid spread of NDV in HT-1080 cells appears to be caused by their deficient expression of anti-NDV proteins upon exposure to IFN-beta.

Stat1 and Stat2 but not Stat3 arbitrate contradictory growth signals elicited by alpha/beta interferon in T lymphocytes

Alpha/beta interferon (IFN-alpha/beta) triggers antiviral and antiproliferative responses in target cells through modulation of gene expression. The JAK-STAT pathway is the major mediator of these biological effects through the activation of the transcription factors STAT1 and STAT2, and gene ablation studies have demonstrated that both STAT1 and STAT2 are required for most antiviral responses induced by IFN-alpha/beta. However, additional signaling pathways are also activated by IFN. Here, we show that these additional pathways provoke a proliferative response in activated T lymphocytes. While activation of IFN-stimulated gene factor 3 produces a dominant inhibitory signal capable of overriding the mitogenic response, absence of either STAT1 or STAT2 leads to a proliferative response to IFN. Growth stimulation by IFN-alpha/beta is independent of other STAT proteins, particularly of STAT3, since T lymphocytes from STAT1-STAT3 double-knockout mice are growth stimulated by IFN-alpha/beta treatment. IFN-alpha/beta can cooperate with numerous T-cell mitogens, including interleukin-2 (IL-2), IL-4, IL-7, and IL-12, and can contribute to the rapid restoration of the thymus following glucocorticoid-mediated ablation. These results underscore the complexity of the cellular response to IFN and suggest that the ultimate outcome of IFN action results from a balance between growth-inhibitory and -stimulatory effects.

Role of protein kinase C-δ (PKC-δ) in the generation of the effects of IFN-α in chronic myelogenous leukemia cells

OBJECTIVE

The mechanisms by which interferon alpha (IFN-alpha) induces antileukemic responses in chronic myelogenous leukemia (CML) cells are not known. We examined whether a member of the protein kinase C (PKC) family of proteins, PKC-delta, is activated during treatment of BCR-ABL cells with IFN-alpha and participates in the induction of interferon responses.

METHODS

Immunoblots and immune complex kinase assays were performed to study the phosphorylation and activation of PKC-delta in response to IFN-alpha in CML-derived cell lines. The effects of pharmacological inhibition of PKC-delta on the suppressive effects of IFN-alpha on leukemic CFU-GM progenitors from CML patients were assessed by clonogenic assays in methylcellulose.

RESULTS

IFN-alpha treatment of the sensitive CML-derived KT-1 cell line resulted in phosphorylation of PKC-delta and activation of its kinase domain. Such phosphorylation/activation of PKC-delta was required for phosphorylation of Stat1 on serine 727, as inhibition of PKC-delta activity blocked the IFN-alpha-dependent serine phosphorylation of Stat1 and IFN-alpha-inducible gene transcription. IFN-alpha treatment strongly inhibited leukemic CFU-GM progenitor colony formation from bone marrow or peripheral blood of patients with CML, and such inhibition was reversed by concomitant treatment of the cells with the PKC-delta pharmacologic inhibitor rottlerin.

CONCLUSION

Taken altogether, our data demonstrate that PKC-delta plays a critical role in Type I IFN signaling in BCR-ABL expressing cells, acting as a serine kinase for Stat1, to regulate transcriptional activation of interferon-regulated genes and induction of antileukemic responses.

Interferon-gamma expression is an independent prognostic factor in ovarian cancer

BACKGROUND

Epithelial ovarian cancer prognosis is improved by the presence of intratumoral CD3 + T cells, which are known to produce interferon-gamma. We therefore speculated that interferon-gamma expression in ovarian cancer-infiltrating T-lymphocytes might cause better prognosis.

PATIENTS AND METHODS

Reverse transcriptase polymerase chain reaction was performed to measure the expression of interferon-gamma and other related genes in normal ovaries (n = 19) and in ovarian cancer specimens (n = 99). Median follow-up of patients was 5.8 years.

RESULTS

Interferon-gamma and CD-3 expression did not significantly differ in normal and malignant tissue. Patients with high levels of interferon-gamma expression had significantly longer progression-free and overall survival. Median time to progression was 10 and 29 months for patients with low and high interferon-gamma expression, respectively ( P = .039). Corresponding survival times were 29 and 44 months ( P < .032). Application of multivariate Cox regression analysis showed interferon-gamma expression to be an independent prognostic factor for progression-free and overall survival.

CONCLUSION

Elevated interferon-gamma expression correlates with improved clinical outcome in patients with ovarian cancer.

p38 Mitogen-activated protein kinase mediates synergistic induction of inducible nitric-oxide synthase by lipopolysaccharide and interferon-gamma through signal transducer and activator of transcription 1 Ser727 phosphorylation in murine aortic endothelial cells

Nitric oxide (NO) can be produced in large amounts by up-regulation of inducible NO synthase (iNOS). iNOS is induced in many cell types by pro-inflammatory agents, such as bacterial lipopolysaccharide (LPS) and cytokines. Overproduction by endothelial cells (EC) may contribute to vascular diseases. In contrast to macrophages, murine aortic endothelial cells (MAEC) produced no NO in response to either LPS or interferon gamma (IFNgamma), whereas combined treatment was highly synergistic. In this study, we investigated the mechanisms of synergy in MAEC. LPS activated p38 mitogen-activated protein kinase (MAPK), whereas IFNgamma activated Janus kinase and signal transducer and activator of transcription-1 (STAT1). Both pathways were required for iNOS induction because herbimycin A, a tyrosine kinase inhibitor, and 4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole. HCl (SB202190), a p38 MAPKalpha/beta inhibitor, each blocked induction. LPS increased the phosphorylation of STAT1alpha at serine 727 in IFNgamma-treated MAEC. SB202190, but not 2'-amino-3'-methoxyflavone (PD98059), an inhibitor of p44/p42 MAPK activation, abolished the phosphorylation and induction of iNOS. SB202190 did not affect tyrosine 701 phosphorylation or nuclear translocation of STAT1. However, STAT1-DNA binding activity was reduced by SB202190. Although LPS stimulated the DNA binding activity of nuclear factor kappaB and activating protein-1, combined treatment with IFNgamma did not enhance activation, and SB202190 did not inhibit it. The results indicate that p38 MAPKalpha and/or beta are required for the synergistic induction of iNOS by LPS and IFNgamma in MAEC. Furthermore, the synergistic induction is associated with phosphorylation of STAT1alpha serine 727 in MAEC. This observation may explain potentially beneficial effects of p38 MAPK inhibitors in vascular inflammatory diseases.