Measles virus suppresses interferon-alpha signaling pathway: suppression of Jak1 phosphorylation and association of viral accessory proteins, C and V, with interferon-alpha receptor complex

African swine fever virus pH240R enhances viral replication via inhibition of the type I IFN signaling pathway

African swine fever (ASF) is an acute, hemorrhagic, and severe infectious disease caused by ASF virus (ASFV) infection. At present, there are still no safe and effective drugs and vaccines to prevent ASF. Mining the important proteins encoded by ASFV that affect the virulence and replication of ASFV is the key to developing effective vaccines and drugs. In this study, ASFV pH240R, a capsid protein of ASFV, was found to inhibit the type I interferon (IFN) signaling pathway. Mechanistically, pH240R interacted with IFNAR1 and IFNAR2 to disrupt the interaction of IFNAR1-TYK2 and IFNAR2-JAK1. Additionally, pH240R inhibited the phosphorylation of IFNAR1, TYK2, and JAK1 induced by IFN-α, resulting in the suppression of the nuclear import of STAT1 and STAT2 and the expression of IFN-stimulated genes (ISGs). Consistent with these results, H240R-deficient ASFV (ASFV-∆H240R) infection induced more ISGs in porcine alveolar macrophages compared with its parental ASFV HLJ/18. We also found that pH240R enhanced viral replication via inhibition of ISGs expression. Taken together, our results clarify that pH240R enhances ASFV replication by inhibiting the JAK-STAT signaling pathway, which highlights the possibility of pH240R as a potential drug target.IMPORTANCEThe innate immune response is the host's first line of defense against pathogen infection, which has been reported to affect the replication and virulence of African swine fever virus (ASFV) isolates. Identification of ASFV-encoded proteins that affect the virulence and replication of ASFV is the key step in developing more effective vaccines and drugs. In this study, we found that pH240R interacted with IFNAR1 and IFNAR2 by disrupting the interaction of IFNAR1-TYK2 and IFNAR2-JAK1, resulting in the suppression of the expression of interferon (IFN)-stimulated genes (ISGs). Consistent with these results, H240R-deficient ASFV (ASFV-∆H240R) infection induces more ISGs' expression compared with its parental ASFV HLJ/18. We also found that pH240R enhanced viral replication via inhibition of ISGs' expression. Taken together, our findings showed that pH240R enhances ASFV replication by inhibiting the IFN-JAK-STAT axis, which highlights the possibility of pH240R as a potential drug target.

Ribavirin inhibits peste des petits ruminants virus proliferation in vitro

Peste des petits ruminants virus (PPRV), a member of the family Paramyxoviridae, belongs to the genus Morbillivirus. It causes devastating viral diseases in small ruminants and has been rapidly spreading over various regions in Africa, the Middle East, and Asia. Although vaccination is thought to be an effective management strategy against PPR infections, the heat sensitivity of PPRV vaccines severely restricts their use in regions with hot climates. In this research, we studied the antiviral activities of ribavirin and aimed to understand the potential mechanisms of action of ribavirin in the African green monkey kidney cells (Vero cells). In brief, the adsorption, intrusion, replication, and release of PPRV, as well as the mRNA expression level of RNA-dependent RNA polymerase (RdRp), were significantly inhibited in the ribavirin-treated Vero cells compared to those in the PPRV-infected cells that were not treated with ribavirin. Additionally, ribavirin has potential as an antiviral drug against PPRV, and its antiviral activity is mediated by the Janus kinase signal transducer and activator of transcription (JAK/STAT) and PI3K/AKT pathways.

Analysis of transcriptome expression profiling data in oral leukoplakia and early and late‑stage oral squamous cell carcinoma

The present study screened, potential prognostic biomarkers for oral carcinogenesis. The GSE85195 dataset, which consisted of oral leukoplakia (OL) and early and late-stage oral squamous cell carcinoma (OSCC) samples, was used. The differentially expressed genes (DEGs) in early OSCC vs. OL, late OSCC vs. OL and late OSCC vs. early OSCC groups were screened using the limma package in R. The Short Time-series Expression Miner software package was used to cluster DEGs with similar expression patterns in the course of disease progression (from OL to early and then late-stage OSCC). Moreover, the Database for Annotation, Visualization and Integrated Discovery online analysis tool was used to perform Gene Ontology functional annotation and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. A protein-protein interaction (PPI) network was also constructed using the Search Tool for the Retrieval of Interacting Genes/Proteins database. Reverse transcription-quantitative PCR was performed to assess the mRNA expression levels of hub node genes in clinical samples, and receiver operating characteristic curve analysis was performed to assess the prognostic value of the hub genes. A total of 4,595, 6,042 and 2,738 DEGs were screened in the early OSCC vs. OL, late OSCC vs. OL and late OSCC vs. early OSCC groups, respectively. A total of 665 overlapping genes were identified when the screened DEGs were compared. Cluster 1 and cluster 7 were identified as the significant clusters, which contained 496 and 341 DEGs, respectively. A PPI network was constructed with 440 interaction pairs. There were five differentially expressed hub nodes identified in different stages from OL to OSCC. The results of the present study indicated that fibronectin 1, signal transducer and activator of transcription 1, collagen type II α1 chain, collagen type X α1 chain and collagen type IV α6 chain might serve as independent diagnostic factors for OL and OSCC, and as prognostic biomarkers for OL carcinogenesis.

Reprogramming viral immune evasion for a rational design of next-generation vaccines for RNA viruses

Type I interferons (IFNs-α/β) are antiviral cytokines that constitute the innate immunity of hosts to fight against viral infections. Recent studies, however, have revealed the pleiotropic functions of IFNs, in addition to their antiviral activities, for the priming of activation and maturation of adaptive immunity. In turn, many viruses have developed various strategies to counteract the IFN response and to evade the host immune system for their benefits. The inefficient innate immunity and delayed adaptive response fail to clear of invading viruses and negatively affect the efficacy of vaccines. A better understanding of evasion strategies will provide opportunities to revert the viral IFN antagonism. Furthermore, IFN antagonism-deficient viruses can be generated by reverse genetics technology. Such viruses can potentially serve as next-generation vaccines that can induce effective and broad-spectrum responses for both innate and adaptive immunities for various pathogens. This review describes the recent advances in developing IFN antagonism-deficient viruses, their immune evasion and attenuated phenotypes in natural host animal species, and future potential as veterinary vaccines.

Measles Virus-Induced Host Immunity and Mechanisms of Viral Evasion

The immune system deploys a complex network of cells and signaling pathways to protect host integrity against exogenous threats, including measles virus (MeV). However, throughout its evolutionary path, MeV developed various mechanisms to disrupt and evade immune responses. Despite an available vaccine, MeV remains an important re-emerging pathogen with a continuous increase in prevalence worldwide during the last decade. Considerable knowledge has been accumulated regarding MeV interactions with the innate immune system through two antagonistic aspects: recognition of the virus by cellular sensors and viral ability to inhibit the induction of the interferon cascade. Indeed, while the host could use several innate adaptors to sense MeV infection, the virus is adapted to unsettle defenses by obstructing host cell signaling pathways. Recent works have highlighted a novel aspect of innate immune response directed against MeV unexpectedly involving DNA-related sensing through activation of the cGAS/STING axis, even in the absence of any viral DNA intermediate. In addition, while MeV infection most often causes a mild disease and triggers a lifelong immunity, its tropism for invariant T-cells and memory T and B-cells provokes the elimination of one primary shield and the pre-existing immunity against previously encountered pathogens, known as "immune amnesia".

Updates on Measles Incidence and Eradication: Emphasis on the Immunological Aspects of Measles Infection

Measles is an RNA virus infectious disease mainly seen in children. Despite the availability of an effective vaccine against measles, it remains a health issue in children. Although it is a self-limiting disease, it becomes severe in undernourished and immune-compromised individuals. Measles infection is associated with secondary infections by opportunistic bacteria due to the immunosuppressive effects of the measles virus. Recent reports highlight that measles infection erases the already existing immune memory of various pathogens. This review covers the incidence, pathogenesis, measles variants, clinical presentations, secondary infections, elimination of measles virus on a global scale, and especially the immune responses related to measles infection.

Zika virus NS1 suppresses the innate immune responses via miR-146a in human microglial cells

Zika virus (ZIKV) is a positive-single strand RNA virus that belongs to the Flaviviridae family. ZIKV infection causes congenital ZIKV syndrome (CZS) in children and Guillain Barre Syndrome (GBS) in adults. ZIKV infected cells secrete non-structural protein 1 (sNS1), which plays an important role in viral replication and immune evasion. The microglial cells are the brain resident macrophages that mediate the immune responses in CNS. The miRNAs are small non-coding RNAs that regulate the expression of their target genes by binding to the 3'UTR region. The present study highlights the bystander effect of ZIKV-NS1 via miR-146a. The Real-Time PCR, Immunoblotting, overexpression, knockdown studies, and reactive oxygen species measurement have been done to study the immunomodulatory effects of ZIKV-NS1 in human microglial cells. ZIKV-NS1 induced the expression of miR-146a and suppressed the ROS activity in human microglial cells. The up-regulated miR-146a led to the decreased expression of TRAF6 and STAT-1. The reduced expression of TRAF6 in turn led to the suppression of pNF-κBp65 and TNF-α downstream. The miR-146a suppressed the pro-inflammatory and cellular antiviral responses in microglial cells. Our findings demonstrate the bystander role of ZIKV-NS1 in suppressing the pro-inflammatory and cellular antiviral responses through miR-146a in human microglial cells.

Differential white spot syndrome virus-binding proteins in two hemocyte subpopulations of Chinese shrimp (Fenneropenaeus chinensis)

A number of white spot syndrome virus (WSSV)-binding proteins have been identified previously in the hemocytes of Fenneropenaeus chinensis. In order to further investigate the differential WSSV-binding proteins in hemocyte subpopulations, granular hemocytes and hyalinocytes were sorted from WSSV-infected shrimp by immunomagnetic bead (IMB) method. The results of ELISA and immuno-dot blot assay showed that the WSSV-binding activity of granular hemocytes proteins was much stronger than that of hyalinocytes proteins. And the percentage of WSSV-positive granular hemocytes was significantly higher than that of hyalinocytes post WSSV infection, indicating that granular hemocytes were more susceptible to WSSV infection. Moreover, a total of 9 WSSV-binding proteins were successfully identified in granular hemocytes and hyalinocytes by two-dimensional virus overlay protein binding assay (2D-VOPBA) and MALDI-TOF MS analysis, of which 3 binding proteins (arginine kinase, protease 1 and transglutaminase) existing in both hyalinocytes and granular hemocytes and 6 proteins (F₁ATP synthase β-chain, hnRNPs, GAPDH, RACK1, β-actin and cellular retinoic acid) detected only in granular hemocytes. Among these identified WSSV-binding proteins, the transglutaminase (TG) was further recombinantly expressed, and the recombinant TG could be bound with WSSV. Subsequently, quantitative real-time PCR analysis showed that differential expression levels of WSSV-binding proteins were observed in granular hemocytes and hyalinocytes. The results of this study revealed that the WSSV-binding proteins were differentially expressed in granular hemocytes and hyalinocytes, which provided a deeper insight into the interaction between WSSV and hemocyte subpopulations.

RACK1 T50 Phosphorylation by AMPK Potentiates Its Binding with IRF3/7 and Inhibition of Type 1 IFN Production

The receptor for activated C kinase 1 (RACK1) adaptor protein has been implicated in viral infection. However, whether RACK1 promotes in vivo viral infection in mammals remains unknown. Moreover, it remains elusive how RACK1 is engaged in antiviral innate immune signaling. In this study, we report that myeloid RACK1 deficiency does not affect the development and survival of myeloid cells under resting conditions but renders mice less susceptible to viral infection. RACK1-deficient macrophages produce more IFN-α and IFN-β in response to both RNA and DNA virus infection. In line with this, RACK1 suppresses transcriptional activation of type 1 IFN gene promoters in response to virus infection. Analysis of virus-mediated signaling indicates that RACK1 inhibits the phosphorylation of IRF3/7. Indeed, RACK1 interacts with IRF3/7, which is enhanced after virus infection. Further exploration indicates that virus infection triggers AMPK activation, which in turn phosphorylates RACK1 at Thr⁵⁰ RACK1 phosphorylation at Thr⁵⁰ enhances its interaction with IRF3/7 and thereby limits IRF3/7 phosphorylation. Thus, our results confirm that myeloid RACK1 promotes in vivo viral infection and provide insight into the control of type 1 IFN production in response to virus infection.

The Measles Virus V Protein Binding Site to STAT2 Overlaps That of IRF9

Measles virus (MeV) is a highly immunotropic and contagious pathogen that can even diminish preexisting antibodies and remains a major cause of childhood morbidity and mortality worldwide despite the availability of effective vaccines. MeV is one of the most extensively studied viruses with respect to the mechanisms of JAK-STAT antagonism. Of the three proteins translated from the MeV P gene, P and V are essential for inactivation of this pathway. However, the lack of data from direct analyses of the underlying interactions means that the detailed molecular mechanism of antagonism remains unresolved. Here, we prepared recombinant MeV V protein, which is responsible for human JAK-STAT antagonism, and a panel of variants, enabling the biophysical characterization of V protein, including direct V/STAT1 and V/STAT2 interaction assays. Unambiguous direct interactions between the host and viral factors, in the absence of other factors such as Jak1 or Tyk2, were observed, and the dissociation constants were quantified for the first time. Our data indicate that interactions between the C-terminal region of V and STAT2 is 1 order of magnitude stronger than that of the N-terminal region of V and STAT1. We also clarified that these interactions are completely independent of each other. Moreover, results of size exclusion chromatography demonstrated that addition of MeV-V displaces STAT2-core, a rigid region of STAT2 lacking the N- and C-terminal domains, from preformed complexes of STAT2-core/IRF-associated domain (IRF9). These results provide a novel model whereby MeV-V can not only inhibit the STAT2/IRF9 interaction but also disrupt preassembled interferon-stimulated gene factor 3.IMPORTANCE To evade host immunity, many pathogenic viruses inactivate host Janus kinase signal transducer and activator of transcription (STAT) signaling pathways using diverse strategies. Measles virus utilizes P and V proteins to counteract this signaling pathway. Data derived largely from cell-based assays have indicated several amino acid residues of P and V proteins as important. However, biophysical properties of V protein or its direct interaction with STAT molecules using purified proteins have not been studied. We have developed novel molecular tools enabling us to identify a novel molecular mechanism for immune evasion whereby V protein disrupts critical immune complexes, providing a clear strategy by which measles virus can suppress interferon-mediated antiviral gene expression.

Immunoglobulin A Targeting on the N-Terminal Moiety of Viral Phosphoprotein Prevents Measles Virus from Evading Interferon-β Signaling

Immunoglobulin A (IgA) can inhibit intracellular viral replication during its transport across the epithelial cells. We find a monoclonal IgA antibody 7F1-IgA against the N-terminal moiety of the phosphoprotein (PNT) of measles virus (MV), which inhibits the intracellular replication of MV in Caco-2 cells but not in interferon-deficient Vero-pIgR cells. Transcytosis of 7F1-IgA across the MV-infected Caco-2 cells enhances the production of interferon-β (IFN-β) and the expression of IFN-stimulated genes, rendering Caco-2 cells with higher antiviral immunity. 7F1-IgA specifically interacts with MV phosphoprotein inside the MV-infected Caco-2 cell and prevents MV phosphoprotein from inhibiting the phosphorylation of JAK1 and STAT1. The intraepithelial interaction between 7F1-IgA and the viral phosphoprotein results in an earlier and stronger phosphorylation of JAK1 and STAT1 and, consequently, a more efficient nuclear translocation of STAT1 for the activation of the type I interferon pathway. Thus, IgA against phosphoprotein prevents a virus from evading type I IFN signaling and confers host epithelial cells efficient innate antiviral immunity, which potentiates a new antiviral target and an antiviral strategy.

Seek and hide: the manipulating interplay of measles virus with the innate immune system

The innate immune system is the first line of defense against infections with pathogens. It provides direct antiviral mechanisms to suppress the viral life cycle at multiple steps. Innate immune cells are specialized to recognize pathogen infections and activate and modulate adaptive immune responses through antigen presentation, co-stimulation and release of cytokines and chemokines. Measles virus, which causes long-lasting immunosuppression and immune-amnesia, primarily infects and replicates in innate and adaptive immune cells, such as dendritic cells, macrophages, T cells and B cells. To achieve efficient replication, measles virus has evolved multiple mechanisms to manipulate innate immune responses by both stimulation and blocking of specific signals necessary for antiviral immunity. This review will highlight our current knowledge in this and address open questions.

An oncolytic measles virus-sensitive Group 3 medulloblastoma model in immune-competent mice

Background

Oncolytic measles virus (MV) is effective in xenograft models of many tumor types in immune-compromised mice. However, no murine cell line exists that is tumorigenic, grows in immune-competent mice, and is killed by MV. The lack of such a model prevents an examination of the effect of the immune system on MV oncotherapy.

Methods

Cerebellar stem cells from human CD46-transgenic immunocompetent mice were transduced to express Sendai virus C-protein, murine C-Myc, and Gfi1b proteins. The resultant cells were injected into the brain of NSG mice, and a cell line, called CSCG, was prepared from the resulting tumor.

Results

CSCG cells are highly proliferative, and express stem cell markers. These cells are permissive for replication of MV and are killed by the virus in a dose- and time-dependent manner. CSCG cells form aggressive tumors that morphologically resemble medulloblastoma when injected into the brains of immune-competent mice. On the molecular level, CSCG tumors overexpress natriuretic peptide receptor 3 and gamma-aminobutyric acid type A receptor alpha 5, markers of Group 3 medulloblastoma. A single intratumoral injection of MV‒green fluorescent protein resulted in complete tumor regression and prolonged survival of animals compared with treatments with phosphate buffered saline (P = 0.0018) or heat-inactivated MV (P = 0.0027).

Conclusions

This immune-competent model provides the first platform to test therapeutic regimens of oncolytic MV for Group 3 medulloblastoma in the presence of anti-measles immunity. The strategy presented here can be used to make MV-sensitive murine models of any human tumor for which the driving mutations are known.

Host Cellular Receptors for the Peste des Petits Ruminant Virus

Peste des Petits Ruminant (PPR) is an important transboundary, OIE-listed contagious viral disease of primarily sheep and goats caused by the PPR virus (PPRV), which belongs to the genus Morbillivirus of the family Paramyxoviridae. The mortality rate is 90–100%, and the morbidity rate may reach up to 100%. PPR is considered economically important as it decreases the production and productivity of livestock. In many endemic poor countries, it has remained an obstacle to the development of sustainable agriculture. Hence, proper control measures have become a necessity to prevent its rapid spread across the world. For this, detailed information on the pathogenesis of the virus and the virus host interaction through cellular receptors needs to be understood clearly. Presently, two cellular receptors; signaling lymphocyte activation molecule (SLAM) and Nectin-4 are known for PPRV. However, extensive information on virus interactions with these receptors and their impact on host immune response is still required. Hence, a thorough understanding of PPRV receptors and the mechanism involved in the induction of immunosuppression is crucial for controlling PPR. In this review, we discuss PPRV cellular receptors, viral host interaction with cellular receptors, and immunosuppression induced by the virus with reference to other Morbilliviruses.

Herpes Simplex Virus 1 UL36USP Antagonizes Type I Interferon-Mediated Antiviral Innate Immunity

Type I interferons (IFNs), as major components of the innate immune system, play a vital role in host resistance to a variety of pathogens. Canonical signaling mediated by type I IFNs activates the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway through binding to the IFN-α/β receptor (IFNAR), resulting in transcription of IFN-stimulated genes (ISGs). However, viruses have evolved multiple strategies to evade this process. Here, we report that herpes simplex virus 1 (HSV-1) ubiquitin-specific protease (UL36USP) abrogates the type I IFN-mediated signaling pathway independent of its deubiquitinase (DUB) activity. In this study, ectopically expressed UL36USP inhibited IFN-β-induced activation of ISRE promoter and transcription of ISGs, and overexpression of UL36USP lacking DUB activity did not influence this effect. Furthermore, UL36USP was demonstrated to antagonize IFN-β-induced activation of JAKs and STATs via specifically binding to the IFNAR2 subunit and blocking the interaction between JAK1 and IFNAR2. More importantly, knockdown of HSV-1 UL36USP restored the formation of JAK1-IFNAR2 complex. These findings underline the roles of UL36USP-IFNAR2 interaction in counteracting the type I IFN-mediated signaling pathway and reveal a novel evasion mechanism of antiviral innate immunity by HSV-1.IMPORTANCE Type I IFNs mediate transcription of numerous antiviral genes, creating a remarkable antiviral state in the host. Viruses have evolved various mechanisms to evade this response. Our results indicated that HSV-1 encodes a ubiquitin-specific protease (UL36USP) as an antagonist to subvert type I IFN-mediated signaling. UL36USP was identified to significantly inhibit IFN-β-induced signaling independent of its deubiquitinase (DUB) activity. The underlying mechanism of UL36USP antagonizing type I IFN-mediated signaling was to specifically bind with IFNAR2 and disassociate JAK1 from IFNAR2. For the first time, we identify UL36USP as a crucial suppressor for HSV-1 to evade type I IFN-mediated signaling. Our findings also provide new insights into the innate immune evasion by HSV-1 and will facilitate our understanding of host-virus interplay.

Mycoplasma hyorhinis reduces sensitivity of human lung carcinoma cells to Nutlin-3 and promotes their malignant phenotype

PURPOSE

MDM2 inhibitors are promising anticancer agents that induce cell cycle arrest and tumor cells death via p53 reactivation. We examined the influence of Mycoplasma hyorhinis infection on sensitivity of human lung carcinoma cells NCI-H292 to MDM2 inhibitor Nutlin-3. In order to unveil possible mechanisms underlying the revealed effect, we investigated gene expression changes and signal transduction networks activated in NCI-H292 cells in response to mycoplasma infection.

METHODS

Sensitivity of NCI-Н292 cells to Nutlin-3 was estimated by resazurin-based cell viability assay. Genome-wide transcriptional profiles of NCI-H292 and NCI-Н292^Myc.h cell lines were determined using Illumina Human HT-12 v3 Expression BeadChip. Search for key transcription factors and key node molecules was performed using the geneXplain platform. Ability for anchorage-independent growth was tested by soft agar colony formation assay.

RESULTS

NCI-Н292^Myc.h cells were shown to be 1.5- and 5.2-fold more resistant to killing by Nutlin-3 at concentrations of 15 and 30 µM than uninfected NCI-Н292 cells (P < 0.05 and P < 0.001, respectively). Transcriptome analysis revealed differential expression of multiple genes involved in cancer progression and metastasis as well as epithelial-mesenchymal transition (EMT). Moreover, we have shown experimentally that NCI-Н292^Myc.h cells were more capable of growing and dividing without binding to a substrate. The most likely mechanism explaining the observed changes was found to be TLR4- and IL-1b-mediated activation of NF-κB pathway.

CONCLUSIONS

Our results provide evidence that mycoplasma infection is an important factor modulating the effect of MDM2 inhibitors on cancer cells and is able to induce EMT-related changes.

Progress in the synthesis and biological evaluation of lipid A and its derivatives

Lipid A is one of the core structures of bacterial lipopolysaccharides (LPSs), and it is mainly responsible for the strong immunostimulatory activities of LPS through interactions with the Toll-like receptors and other molecules in the human immune system. To obtain structurally homogeneous and well-defined lipid As and its derivatives in quantities meaningful for various biological studies and applications, their chemical synthesis has become a focal point. This review has provided a survey of significant progresses made in the synthesis of lipid A, and its derivatives that carry diverse saturated and unsaturated lipids, have the phosphate group at its reducing end replaced with a more stable phosphate or carboxyl group, or lack the reducing end phosphate or both phosphate groups, as well as progresses in the synthesis of LPS analogs and other lipid A conjugates. These synthetic molecules have facilitated the elucidation of the structure-activity relationships of lipid A useful for the design and development of lipid A based therapeutics, such as those utilized to treat sepsis, and other medical applications, for example the use of monophosphoryl lipid A as a carrier molecule for the study of fully synthetic self-adjuvanting conjugate vaccines. These topics are also briefly covered in the current review.

Interplay between Janus Kinase/Signal Transducer and Activator of Transcription Signaling Activated by Type I Interferons and Viral Antagonism

Interferons (IFNs), which were discovered a half century ago, are a group of secreted proteins that play key roles in innate immunity against viral infection. The major signaling pathway activated by IFNs is the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, which leads to the expression of IFN-stimulated genes (ISGs), including many antiviral effectors. Viruses have evolved various strategies with which to antagonize the JAK/STAT pathway to influence viral virulence and pathogenesis. In recent years, notable progress has been made to better understand the JAK/STAT pathway activated by IFNs and antagonized by viruses. In this review, recent progress in research of the JAK/STAT pathway activated by type I IFNs, non-canonical STAT activation, viral antagonism of the JAK/STAT pathway, removing of the JAK/STAT antagonist from viral genome for attenuation, and the potential pathogenesis roles of tyrosine phosphorylation-independent non-canonical STATs activation during virus infection are discussed in detail. We expect that this review will provide new insight into the understanding the complexity of the interplay between JAK/STAT signaling and viral antagonism.

Measles virus induces persistent infection by autoregulation of viral replication

Natural infection with measles virus (MV) establishes lifelong immunity. Persistent infection with MV is likely involved in this phenomenon, as non-replicating protein antigens never induce such long-term immunity. Although MV establishes stable persistent infection in vitro and possibly in vivo, the mechanism by which this occurs is largely unknown. Here, we demonstrate that MV changes the infection mode from lytic to non-lytic and evades the innate immune response to establish persistent infection without viral genome mutation. We found that, in the persistent phase, the viral RNA level declined with the termination of interferon production and cell death. Our analysis of viral protein dynamics shows that during the establishment of persistent infection, the nucleoprotein level was sustained while the phosphoprotein and large protein levels declined. The ectopic expression of nucleoprotein suppressed viral replication, indicating that viral replication is self-regulated by nucleoprotein accumulation during persistent infection. The persistently infected cells were able to produce interferon in response to poly I:C stimulation, suggesting that MV does not interfere with host interferon responses in persistent infection. Our results may provide mechanistic insight into the persistent infection of this cytopathic RNA virus that induces lifelong immunity.

Roles of nuclear trafficking in infection by cytoplasmic negative-strand RNA viruses: paramyxoviruses and beyond

Genome replication and virion production by most negative-sense RNA viruses (NSVs) occurs exclusively in the cytoplasm, but many NSV-expressed proteins undergo active nucleocytoplasmic trafficking via signals that exploit cellular nuclear transport pathways. Nuclear trafficking has been reported both for NSV accessory proteins (including isoforms of the rabies virus phosphoprotein, and V, W and C proteins of paramyxoviruses) and for structural proteins. Trafficking of the former is thought to enable accessory functions in viral modulation of antiviral responses including the type I IFN system, but the intranuclear roles of structural proteins such as nucleocapsid and matrix proteins, which have critical roles in extranuclear replication and viral assembly, are less clear. Nevertheless, nuclear trafficking of matrix protein has been reported to be critical for efficient production of Nipah virus and Respiratory syncytial virus, and nuclear localization of nucleocapsid protein of several morbilliviruses has been linked to mechanisms of immune evasion. Together, these data point to the nucleus as a significant host interface for viral proteins during infection by NSVs with otherwise cytoplasmic life cycles. Importantly, several lines of evidence now suggest that nuclear trafficking of these proteins may be critical to pathogenesis and thus could provide new targets for vaccine development and antiviral therapies.

Viral Inhibition of the IFN-Induced JAK/STAT Signalling Pathway: Development of Live Attenuated Vaccines by Mutation of Viral-Encoded IFN-Antagonists

The interferon (IFN) induced anti-viral response is amongst the earliest and most potent of the innate responses to fight viral infection. The induction of the Janus kinase/signal transducer and activation of transcription (JAK/STAT) signalling pathway by IFNs leads to the upregulation of hundreds of interferon stimulated genes (ISGs) for which, many have the ability to rapidly kill viruses within infected cells. During the long course of evolution, viruses have evolved an extraordinary range of strategies to counteract the host immune responses in particular by targeting the JAK/STAT signalling pathway. Understanding how the IFN system is inhibited has provided critical insights into viral virulence and pathogenesis. Moreover, identification of factors encoded by viruses that modulate the JAK/STAT pathway has opened up opportunities to create new anti-viral drugs and rationally attenuated new generation vaccines, particularly for RNA viruses, by reverse genetics.

Measles Virus Genotype D Wild Strains Suppress Interferon-Stimulated Gene Expression More Potently than Laboratory Strains in SiHa Cells

Changes in interferon (IFN)-stimulated gene (ISG) expression in cells infected with measles virus (MeV), four wild strains (belonging to different genotypes), and the laboratory strain Edmonston were examined. ISGs [MxA, 2'-5'-oligoadenylate synthetase, and interferon regulatory factor-1] were upregulated in an MeV-infection-induced manner and in an IFN-induced manner. In MeV-infected SiHa cell lines, the MeV infection-induced expression levels were in the order of A>H1>D8>D5>D3. On the other hand, all infected cell lines abolished type I and III IFN-induced ISG expression. However, partial type II IFN-mediated induction was observed in the MeV-infected cells. The wild strain of genotype D3 was the most potent inhibitor of MeV infection-induced and IFN-induced ISG expression and generated the highest titer of infectious viral particles. Edmonston triggered the highest levels of MeV infection-induced ISG expression in SiHa cells and produced the lowest titer of infectious particles. Expression of the viral C protein was associated with suppression of MeV infection-induced and type II IFN-induced ISG expression.

Actin-Modulating Protein Cofilin Is Involved in the Formation of Measles Virus Ribonucleoprotein Complex at the Perinuclear Region

In measles virus (MV)-infected cells, the ribonucleoprotein (RNP) complex, comprised of the viral genome and the nucleocapsid (N) protein, phosphoprotein (P protein), and large protein, assembles at the perinuclear region and synthesizes viral RNAs. The cellular proteins involved in the formation of the RNP complex are largely unknown. In this report, we show that cofilin, an actin-modulating host protein, interacts with the MV N protein and aids in the formation of the RNP complex. Knockdown of cofilin using the short hairpin RNA reduces the formation of the RNP complex after MV infection and that of the RNP complex-like structure after plasmid-mediated expression of MV N and P proteins. A lower level of formation of the RNP complex results in the reduction of viral RNA synthesis. Cofilin phosphorylation on the serine residue at position 3, an enzymatically inactive form, is increased after MV infection and the phosphorylated form of cofilin is preferentially included in the complex. These results indicate that cofilin plays an important role in MV replication by increasing formation of the RNP complex and viral RNA synthesis.

IMPORTANCE

Many RNA viruses induce within infected cells the structure called the ribonucleoprotein (RNP) complex in which viral RNA synthesis occurs. It is comprised of the viral genome and proteins that include the viral RNA polymerase. The cellular proteins involved in the formation of the RNP complex are largely unknown. In this report, we show that cofilin, an actin-modulating host protein, binds to the measles virus (MV) nucleocapsid protein and plays an important role in the formation of the MV RNP complex and MV RNA synthesis. The level of the phosphorylated form of cofilin, enzymatically inactive, is increased after MV infection, and the phosphorylated form is preferentially associated with the RNP complex. Our findings determined with cofilin will help us better understand the mechanism by which the RNP complex is formed in virus-infected cells and develop new antiviral drugs targeting the RNP complex.

Type I IFN family members: similarity, differences and interaction

Interferons (IFN) are key cytokines with multifaceted antiviral and cell-modulatory properties. Three distinct types of IFN are recognized (I-III) based on structural features, receptor usage, cellular source and biological activities. The action of IFNs is mediated by a complex, partially overlapping, transcriptional program initiated by the interaction with specific receptors. Genetic diversity, with polymorphisms and mutations, can modulate the extent of IFN responses and the susceptibility to infections. Almost all viruses developed mechanisms to subvert the IFN response, involving both IFN induction and effector mechanisms. Interactions between IFN types may occur, for both antiviral and cell-modulatory effects, in a complex interplay, involving both synergistic and antagonistic effects. Interferon-associated diseases, not related to virus infections may occur, some of them frequently observed in IFN-treated patients. On the whole, IFNs are pleiotropic biologic response modifiers, that, upon activation of thousands genes, induce a broad spectrum of activities, regulating cell cycle, differentiation, plasma membrane molecules, release of mediators, etc., that can be relevant for cell proliferation, innate and adaptive immunity, hematopoiesis, angiogenesis and other body functions.

Dengue Virus Control of Type I IFN Responses: A History of Manipulation and Control

The arthropod-borne diseases caused by dengue virus (DENV) are a major and emerging problem of public health worldwide. Infection with DENV causes a series of clinical manifestations ranging from mild flu syndrome to severe diseases that include hemorrhage and shock. It has been demonstrated that the innate immune response plays a key role in DENV pathogenesis. However, in recent years, it was shown that DENV evades the innate immune response by blocking type I interferon (IFN-I). It has been demonstrated that DENV can inhibit both the production and the signaling of IFN-I. The viral proteins, NS2A and NS3, inhibit IFN-I production by degrading cellular signaling molecules. In addition, the viral proteins, NS2A, NS4A, NS4B, and NS5, can inhibit IFN-I signaling by blocking the phosphorylation of the STAT1 and STAT2 molecules. Finally, NS5 mediates the degradation of STAT2 using the proteasome machinery. In this study, we briefly review the most recent insights regarding the IFN-I response to DENV infection and its implication for pathogenesis.

RACK1 Function in Cell Motility and Protein Synthesis

The receptor for activated C kinase 1 (RACK1) serves as an adaptor for a number of proteins along the MAPK, protein kinase C, and Src signaling pathways. The abundance and near ubiquitous expression of RACK1 reflect its role in coordinating signaling molecules for many critical biological processes, from mRNA translation to cell motility to cell survival and death. Complete deficiency of Rack1 is embryonic lethal, but the recent development of genetic Rack1 hypomorphic mice has highlighted the central role that RACK1 plays in cell movement and protein synthesis. This review focuses on the importance of RACK1 in these processes and places the recent work in the larger context of understanding RACK1 function.

Proteome profiling of virus-host interactions of wild type and attenuated measles virus strains

Quantitative gel-based proteomics (2D DIGE coupled to MALDI-TOF/TOF MS) has been used to investigate the effects of different measles virus (MV) strains on the host cell proteome. A549/hSLAM cells were infected either with wild type MV strains, an attenuated vaccine or a multiple passaged Vero cell adapted strain. By including interferon beta treatment as a control it was possible to distinguish between the classical antiviral response and changes induced specifically by the different strains. Of 38 differentially expressed proteins in total (p-value ≤0.05, fold change ≥2), 18 proteins were uniquely modulated following MV infection with up to 9 proteins specific per individual strain. Interestingly, wt strains displayed distinct protein patterns particularly during the late phase of infection. Proteins were grouped into cytoskeleton, metabolism, transcription/translation, immune response and mitochondrial proteins. Bioinformatics analysis revealed mostly changes in proteins regulating cell death and apoptosis. Surprisingly, wt strains affected the cytokeratin system much stronger than the vaccine strain. To our knowledge, this is the first study on the MV-host proteome addressing interstrain differences.

BIOLOGICAL SIGNIFICANCE

In the present study we investigated the host cell proteome upon measles virus (MV) infection. The novelty about this study is the side-by side comparison of different strains from the same virus, which has not been done at the proteome level for any other virus including MV. We used different virus strains including a vaccine strain, wild type isolates derived from MV-infected patients as well as a Vero cell adapted strain, which serves as an intermediate between vaccine and wild type strain. We observed differences between vaccine and wild type strains as well as common features between different wild type strains. Perhaps one of the most surprising findings was that differences did not only occur between wild type and vaccine or Vero cell adapted strains but also between different wild type strains. In fact our study suggests that besides the cytokeratin and the IFN system wild type viruses seem to differ as much among each other than from vaccine strains. Thus our results are suggestive of complex and diverse virus-host interactions which differ considerably between different wild type strains. Our data indicate that interstrain differences are prominent and have so far been neglected by proteomics studies.

Peste des petits ruminants virus infection of small ruminants: a comprehensive review

Peste des petits ruminants (PPR) is caused by a Morbillivirus that belongs to the family Paramyxoviridae. PPR is an acute, highly contagious and fatal disease primarily affecting goats and sheep, whereas cattle undergo sub-clinical infection. With morbidity and mortality rates that can be as high as 90%, PPR is classified as an OIE (Office International des Epizooties)-listed disease. Considering the importance of sheep and goats in the livelihood of the poor and marginal farmers in Africa and South Asia, PPR is an important concern for food security and poverty alleviation. PPR virus (PPRV) and rinderpest virus (RPV) are closely related Morbilliviruses. Rinderpest has been globally eradicated by mass vaccination. Though a live attenuated vaccine is available against PPR for immunoprophylaxis, due to its instability in subtropical climate (thermo-sensitivity), unavailability of required doses and insufficient coverage (herd immunity), the disease control program has not been a great success. Further, emerging evidence of poor cross neutralization between vaccine strain and PPRV strains currently circulating in the field has raised concerns about the protective efficacy of the existing PPR vaccines. This review summarizes the recent advancement in PPRV replication, its pathogenesis, immune response to vaccine and disease control. Attempts have also been made to highlight the current trends in understanding the host susceptibility and resistance to PPR.

Mechanisms underlying the inhibition of interferon signaling by viruses

A hallmark of the antiviral response is the induction of interferons. First discovered in 1957 by Issac and Lindeman, interferons are noted for their ability to interfere with viral replication. Interferons act via autocrine and paracrine pathways to induce an antiviral state in infected cells and in neighboring cells containing interferon receptors. Interferons are the frontline defenders against viral infection and their primary function is to locally restrict viral propagation. Viruses have evolved mechanisms to escape the host interferon response, thus gaining a replicative advantage in host cells. This review will discuss recent findings on the mechanisms viruses use to evade the host interferon response. This knowledge is important because the treatment of viral infections is a challenge of global proportions and a better understanding of the mechanisms viruses use to persist in the host may uncover valuable insights applicable to the discovery of novel drug targets.

An anti-interferon activity shared by paramyxovirus C proteins: inhibition of Toll-like receptor 7/9-dependent alpha interferon induction

Paramyxovirus C protein targets the host interferon (IFN) system for virus immune evasion. To identify its unknown anti-IFN activity, we examined the effect of Sendai virus C protein on activation of the IFN-α promoter via various signaling pathways. This study uncovers a novel ability of C protein to block Toll-like receptor (TLR) 7- and TLR9-dependent IFN-α induction, which is specific to plasmacytoid dendritic cells. C protein interacts with a serine/threonine kinase IKKα and inhibits phosphorylation of IRF7. This anti-IFN activity of C protein is shared across genera of the Paramyxovirinae, and thus appears to play an important role in paramyxovirus immune evasion.

The measles virus phosphoprotein interacts with the linker domain of STAT1

The measles virus (MV) phosphoprotein (P) and V proteins block the interferon (IFN) response by impeding phosphorylation of the signal transducer and activator of transcription 1 (STAT1) by the Janus kinase 1 (JAK1). We characterized how STAT1 mutants interact with P and JAK1 phosphorylation. Certain mutants of the linker, the Src-homology 2 domain (SH2), or the transactivation domain had reduced or abolished phosphorylation through JAK1 after IFN treatment. Other mutants, mainly localized in the linker, failed to interact with P as documented by the lack of interference with nuclear translocation. Thus the functional footprint of P on STAT1 localizes mainly to the linker domain; there is also some overlap with the STAT1 phosphorylation functional footprint on the SH2 domain. Based on these observations, we discuss how the MV-P might operate to inhibit the JAK/STAT pathway.

Induction of dendritic cell production of type I and type III interferons by wild-type and vaccine strains of measles virus: role of defective interfering RNAs

The innate immune response to viral infection frequently includes induction of type I interferons (IFN), but many viruses have evolved ways to block this response and increase virulence. In vitro studies of IFN production after infection of susceptible cells with measles virus (MeV) have often reported greater IFN synthesis after infection with vaccine than with wild-type strains of MeV. However, the possible presence in laboratory virus stocks of 5' copy-back defective interfering (DI) RNAs that induce IFN independent of the standard virus has frequently confounded interpretation of data from these studies. To further investigate MeV strain-dependent differences in IFN induction and the role of DI RNAs, monocyte-derived dendritic cells (moDCs) were infected with the wild-type Bilthoven strain and the vaccine Edmonston-Zagreb strain with and without DI RNAs. Production of type I IFN, type III IFN, and the interferon-stimulated genes (ISGs) Mx and ISG56 by infected cells was assessed with a flow cytometry-based IFN bioassay, quantitative reverse transcriptase PCR (RT-PCR), and immunoassays. Bilthoven infected moDCs less efficiently than Edmonston-Zagreb. Presence of DI RNAs in vaccine stocks resulted in greater maturation of moDCs, inhibition of virus replication, and induction of higher levels of IFN and ISGs. Production of type I IFN, type III IFN, and ISG mRNA and protein was determined by both the level of infection and the presence of DI RNAs. At the same levels of infection and in the absence of DI RNA, IFN induction was similar between wild-type and vaccine strains of MeV.

Morbillivirus v proteins exhibit multiple mechanisms to block type 1 and type 2 interferon signalling pathways

Morbilliviruses form a closely related group of pathogenic viruses which encode three non-structural proteins V, W and C in their P gene. Previous studies with rinderpest virus (RPV) and measles virus (MeV) have demonstrated that these non-structural proteins play a crucial role in blocking type I (IFNα/β) and type II (IFNγ) interferon action, and various mechanisms have been proposed for these effects. We have directly compared four important morbilliviruses, rinderpest (RPV), measles virus (MeV), peste des petits ruminants virus (PPRV) and canine distemper virus (CDV). These viruses and their V proteins could all block type I IFN action. However, the viruses and their V proteins had varying abilities to block type II IFN action. The ability to block type II IFN-induced gene transcription correlated with co-precipitation of STAT1 with the respective V protein, but there was no correlation between co-precipitation of either STAT1 or STAT2 and the abilities of the V proteins to block type I IFN-induced gene transcription or the creation of the antiviral state. Further study revealed that the V proteins of RPV, MeV, PPRV and CDV could all interfere with phosphorylation of the interferon-receptor-associated kinase Tyk2, and the V protein of highly virulent RPV could also block the phosphorylation of another such kinase, Jak1. Co-precipitation studies showed that morbillivirus V proteins all form a complex containing Tyk2 and Jak1. This study highlights the ability of morbillivirus V proteins to target multiple components of the IFN signalling pathways to control both type I and type II IFN action.

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

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

Synthesis and immunomodulatory activities of Helicobacter pylori lipophilic terminus of lipopolysaccharide including lipid A

Helicobacter pylori, a Gram-negative bacterium, causes gastroduodenal inflammatory diseases such as chronic gastritis and peptic ulcers, and is also a risk factor for gastric carcinogenesis. In this article, we review recent developments and findings in the chemical synthesis and immunomodulatory activities of H. pylori lipid A and 3-deoxy-D-manno-2-octulosonic acid (Kdo)-lipid A, to clarify the structural basis for the inflammatory response to H. pylori LPS. The synthetic methods include a new divergent synthetic approach with a widely applicable key intermediate for other types of lipid A structures, as well as a selective α-glycosylation reaction between Kdo and lipid A. Cytokine induction assays of the chemically synthesized lipid A structures showed selective cytokine induction depending on the patterns of acyl groups and phosphate groups. The results of cytokine induction assay suggested that H. pylori LPS can modulate the immune response during infection, and also plays a role in chronic inflammatory responses.

Adenosine deaminase acting on RNA 1 (ADAR1) suppresses the induction of interferon by measles virus

ADAR1, the interferon (IFN)-inducible adenosine deaminase acting on RNA, catalyzes the C-6 deamination of adenosine (A) to produce inosine (I) in RNA substrates with a double-stranded character. Because double-stranded RNA is a known inducer of IFN, we tested the role of ADAR1 in IFN induction following virus infection. HeLa cells made stably deficient in ADAR1 (ADAR1(kd)) were compared to vector control (CON(kd)) and protein kinase PKR-deficient (PKR(kd)) cells for IFN-β induction following infection with either parental (wild-type [WT]) recombinant Moraten vaccine strain measles virus (MV) or isogenic knockout mutants deficient for either V (V(ko)) or C (C(ko)) protein expression. We observed potent IFN-β transcript induction in ADAR1(kd) cells by all three viruses; in contrast, in ADAR1-sufficient CON(kd) cells, only the C(ko) mutant virus was an effective inducer and the IFN-β RNA induction was amplified by PKR. The enhanced IFN-β transcript-inducing capacity of the WT and V(ko) viruses seen in ADAR1-deficient cells correlated with the enhanced activation of PKR, IFN regulatory factor IRF3, and activator of transcription ATF2, reaching levels similar to those seen in C(ko) virus-infected cells. However, the level of IFN-β protein produced was not proportional to the level of IFN-β RNA but rather correlated inversely with the level of activated PKR. These results suggest that ADAR1 functions as an important suppressor of MV-mediated responses, including the activation of PKR and IRF3 and the induction of IFN-β RNA. Our findings further implicate a balanced interplay between PKR and ADAR1 in modulating IFN-β protein production following virus infection.

The nucleocapsid protein of measles virus blocks host interferon response

Measles virus (MV) belongs to the genus Morbillivirus of the family Paramyxoviridae. A number of paramyxoviruses inhibit host interferon (IFN) signaling pathways in host immune systems by various mechanisms. Inhibition mechanisms have been described for many paramyxoviruses. Although there are inconsistencies among previous reports concerning MV, it appears that P/V/C proteins interfere with the pathways. In this study, we confirmed the effects of MV P gene products of a wild MV strain on IFN pathways and examined that of other viral proteins on it. Interestingly, we found that N protein acts as an IFN-α/β and γ-antagonist as strong as P gene products. We further investigated the mechanisms of MV-N inhibition, and revealed that MV-N blocks the nuclear import of activated STAT without preventing STAT and Jak activation or STAT degradation, and that the nuclear translocation of MV-N is important for the inhibition. The inhibitory effect of the N protein was observed as a common feature of other morbilliviruses. The results presented in this report suggest that N protein of MV as well as P/V/C proteins is involved in the inhibition of host IFN signaling pathways.

Measles virus C protein interferes with Beta interferon transcription in the nucleus

Transcriptional induction of beta interferon (IFN-β) through pattern recognition receptors is a key event in the host defense against invading viruses. Infection of cells by paramyxoviruses, like measles virus (MV) (genus Morbillivirus), is sensed predominantly by the ubiquitous cytoplasmic helicase RIG-I, recognizing viral 5'-triphosphate RNAs, and to some degree by MDA5. While MDA5 activation is effectively prevented by the MV V protein, the viral mechanisms for inhibition of MDA5-independent induction of IFN-β remained obscure. Here, we identify the 186-amino-acid MV C protein, which shuttles between the nucleus and the cytoplasm, as a major viral inhibitor of IFN-β transcription in human cells. Activation of the transcription factor IRF3 by upstream kinases and nuclear import of activated IRF3 were not affected in the presence of C protein, suggesting a nuclear target. Notably, C proteins of wild-type MV isolates, which are poor IFN-β inducers, were found to comprise a canonical nuclear localization signal (NLS), whereas the NLSs of all vaccine strains, irrespective of their origins, were mutated. Site-directed mutagenesis of the C proteins from an MV wild-type isolate and from the vaccine virus strain Schwarz confirmed a correlation of nuclear localization and inhibition of IFN-β transcription. A functional NLS and efficient nuclear accumulation are therefore critical for MV C to retain its potential to downregulate IFN-β induction. We suggest that a defect in efficient nuclear import of C protein contributes to attenuation of MV vaccine strains.

Nipah and hendra virus interactions with the innate immune system

Nipah virus and Hendra virus are related, highly pathogenic paramyxoviruses with unusually broad host ranges. Henipaviruses encode several proteins that block innate immune responses, and these are likely to serve as virulence factors. Specfically, four virus-encoded proteins, the phosphoprotein (P), the V protein, the W protein, and the C protein have each been demonstrated to counteract aspects of the interferon (IFN)-α/β response, a key component of the innate immune response to virus infection. The available data indicate that V and W can inhibit the production of IFNα/β in response to various stimuli, while the P, V, and W proteins also block the ability of IFNs to signal and induce an antiviral state in cells. The C protein also inhibits the antiviral effects of IFNα/β by a poorly characterized mechanism. Reverse genetics systems, which allow the generation of recombinant viruses bearing specific mutations, have demonstrated the importance of the viral IFN-antagonists for replication. With these systems in hand, the field is now poised to define how specific viral IFN-antagonist functions influence viral pathogenesis.

Chemical synthesis of Helicobacter pylori lipopolysaccharide partial structures and their selective proinflammatory responses

Helicobacter pylori is a common cause of gastroduodenal inflammatory diseases such as chronic gastritis and peptic ulcers and also an important factor in gastric carcinogenesis. Recent reports have demonstrated that bacterial inflammatory processes, such as stimulation with H. pylori lipopolysaccharide (LPS), initiate atherosclerosis. To establish the structures responsible for the inflammatory response of H. pylori LPS, we synthesized various kinds of lipid A structures (i.e., triacylated lipid A and Kdo-lipid A compounds), with or without the ethanolamine group at the 1-phosphate moiety, by a new divergent synthetic route. Stereoselective α-glycosylation of Kdo N-phenyltrifluoroacetimidate was achieved by use of microfluidic methods. None of the lipid A and Kdo-lipid A compounds were a strong inducer of IL-1β, IL-6, or IL-8, suggesting that H. pylori LPS is unable to induce acute inflammation. In fact, the lipid A and Kdo-lipid A compounds showed antagonistic activity against cytokine induction by E. coli LPS, except for the lipid A compound with the ethanolamine group, which showed very weak agonistic activity. On the other hand, these H. pylori LPS partial structures showed potent IL-18- and IL-12-inducing activities. IL-18 has been shown to correlate with chronic inflammation, so H. pylori LPS might be implicated in the chronic inflammatory responses induced by H. pylori. These results also indicated that H. pylori LPS can modulate the immune response: NF-κB activation through hTLR4/MD-2 was suppressed, whereas production of IL-18 and IL-12 was promoted.

Measles virus V protein inhibits NLRP3 inflammasome-mediated interleukin-1β secretion

Inflammasomes are cytosolic protein complexes that stimulate the activation of caspase-1, which in turn induces the secretion of the inflammatory cytokines Interleukin-1β (IL-1β) and IL-18. Recent studies have indicated that the inflammasome known as the NOD-like-receptor-family, pyrin domain-containing 3 (NLRP3) inflammasome recognizes several RNA viruses, including the influenza and encephalomyocarditis viruses, whereas the retinoic acid-inducible gene I (RIG-I) inflammasome may detect vesicular stomatitis virus. We demonstrate that measles virus (MV) infection induces caspase-1-dependent IL-1β secretion in the human macrophage-like cell line THP-1. Gene knockdown experiments indicated that IL-1β secretion in MV-infected THP-1 cells was mediated by the NLRP3 inflammasome but not the RIG-I inflammasome. MV produces the nonstructural V protein, which has been shown to antagonize host innate immune responses. The recombinant MV lacking the V protein induced more IL-1β than the parental virus. THP-1 cells stably expressing the V protein suppressed NLRP3 inflammasome-mediated IL-1β secretion. Furthermore, coimmunoprecipitation assays revealed that the V protein interacts with NLRP3 through its carboxyl-terminal domain. NLRP3 was located in cytoplasmic granular structures in THP-1 cells stably expressing the V protein, but upon inflammasome activation, NLRP3 was redistributed to the perinuclear region, where it colocalized with the V protein. These results indicate that the V protein of MV suppresses NLRP3 inflammasome-mediated IL-1β secretion by directly or indirectly interacting with NLRP3.

Human metapneumovirus inhibits IFN-β signaling by downregulating Jak1 and Tyk2 cellular levels

Human metapneumovirus (hMPV), a leading cause of respiratory tract infections in infants, inhibits type I interferon (IFN) signaling by an unidentified mechanism. In this study, we showed that infection of airway epithelial cells with hMPV decreased cellular level of Janus tyrosine kinase (Jak1) and tyrosine kinase 2 (Tyk2), due to enhanced proteosomal degradation and reduced gene transcription. In addition, hMPV infection also reduced the surface expression of type I IFN receptor (IFNAR). These inhibitory mechanisms are different from the ones employed by respiratory syncytial virus (RSV), which does not affect Jak1, Tyk2 or IFNAR expression, but degrades downstream signal transducer and activator of transcription proteins 2 (STAT2), although both viruses are pneumoviruses belonging to the Paramyxoviridae family. Our study identifies a novel mechanism by which hMPV inhibits STAT1 and 2 activation, ultimately leading to viral evasion of host IFN responses.

Type-III interferon, not type-I, is the predominant interferon induced by respiratory viruses in nasal epithelial cells

As an innate immune response against diverse viral infections, a host induces two types of interferon (IFN), type-I (IFN-β/α) and type-III (IFN-λ). We investigated IFN inductions by respiratory viruses, including respiratory syncytial virus (RSV), measles virus and mumps virus in human nasal epithelial cells (NECs). IFN-λ, but not IFN-β/α, was induced by respiratory virus infection in primary NECs and immortalized NECs through transfection with the human telomerase reverse transcriptase gene (hTERT-NECs). In contrast, both IFN-λ and IFN-β/α were induced by RSV infection in human bronchiolar carcinoma cell line A549. Suppression of retinoic acid-inducible gene-I (RIG-I) expression using siRNA significantly reduced IFN-λ1 production in RSV-infected hTERT-NECs, while suppression of melanoma differentiation-associated gene 5 (MDA5) expression did not. Exogenous IFN-λ1 treatment suppressed RSV replication and chemokine induction in hTERT-NECs. These data indicate that IFN-λ, but not IFN-β/α, contributes to the main first line defense via RIG-I-dependent pathway against respiratory virus infection in NECs.

Measles virus C protein suppresses gamma-activated factor formation and virus-induced cell growth arrest

Measles virus (MeV) produces two accessory proteins, V and C, from the P gene. These accessory proteins have been reported to contribute to efficient virus proliferation through the modulation of host cell events. Our previous paper described that Vero cell-adapted strains of MeV led host cells to growth arrest through the upregulation of interferon regulatory factor 1 (IRF-1), and wild strains did not. In the present study, we found that C protein expression levels varied among MeV strains in infected SiHa cells. C protein levels were inversely correlated with IRF-1 expression levels and with cell growth arrest. Forced expression of C protein released cells from growth arrest. C-deficient recombinant virus efficiently upregulated IRF-1 and caused growth arrest more efficiently than the wild-type virus. C protein preferentially bound to phosphorylated STAT1 and suppressed STAT1 dimer formation. We conclude that MeV C protein suppresses IFN-γ signaling pathway via inhibition of phosphorylated STAT1 dimerization.

The Ikaros gene family: transcriptional regulators of hematopoiesis and immunity

The Ikaros family of proteins - comprising Ikaros, Aiolos, Helios, Eos and Pegasus - are zinc finger transcription factors. These proteins participate in a complex network of interactions with gene regulatory elements, other family members and a raft of other transcriptional regulators to control gene expression including via chromatin remodelling. In this way, Ikaros family members regulate important cell-fate decisions during hematopoiesis, particularly in the development of the adaptive immune system. Mutation of several family members results in hematological malignancies,especially those of a lymphoid nature. This review describes the key roles of Ikaros proteins in development and disease, their mechanisms of action and gene targets, as well as explaining their evolutionary origins and role in the emergence of adaptive immunity.

Use of attenuated paramyxoviruses for cancer therapy

Paramyxoviruses, measles virus (MV), mumps virus (MuV) and Newcastle disease virus (NDV), are well known for causing measles and mumps in humans and Newcastle disease in birds. These viruses have been tamed (attenuated) and successfully used as vaccines to immunize their hosts. Remarkably, pathogenic MuV and vaccine strains of MuV, MV and NDV efficiently infect and kill cancer cells and are consequently being investigated as novel cancer therapies (oncolytic virotherapy). Phase I/II clinical trials have shown promise but treatment efficacy needs to be enhanced. Technologies being developed to increase treatment efficacy include: virotherapy in combination with immunosuppressive drugs (cyclophosphamide); retargeting of viruses to specific tumor types or tumor vasculature; using infected cell carriers to protect and deliver the virus to tumors; and genetic manipulation of the virus to increase viral spread and/or express transgenes during viral replication. Transgenes have enabled noninvasive imaging or tracking of viral gene expression and enhancement of tumor destruction.