Respiratory syncytial virus NS1 inhibits anti-viral Interferon-α-induced JAK/STAT signaling, by limiting the nuclear translocation of STAT1.

Human respiratory viruses are the most prevalent cause of disease in humans, with the highly infectious RSV being the leading cause of infant bronchiolitis and viral pneumonia. Responses to type I IFNs are the primary defense against viral infection. However, RSV proteins have been shown to antagonize type I IFN-mediated antiviral innate immunity, specifically dampening intracellular IFN signaling. Respiratory epithelial cells are the main target for RSV infection. In this study, we found RSV-NS1 interfered with the IFN-α JAK/STAT signaling pathway of epithelial cells. RSV-NS1 expression significantly enhanced IFN-α-mediated phosphorylation of STAT1, but not pSTAT2; and neither STAT1 nor STAT2 total protein levels were affected by RSV-NS1. However, expression of RSV-NS1 significantly reduced ISRE and GAS promoter activity and anti-viral IRG expression. Further mechanistic studies demonstrated RSV-NS1 bound STAT1, with protein modeling indicating a possible interaction site between STAT1 and RSV-NS1. Nuclear translocation of STAT1 was reduced in the presence of RSV-NS1. Additionally, STAT1's interaction with the nuclear transport adapter protein, KPNA1, was also reduced, suggesting a mechanism by which RSV blocks STAT1 nuclear translocation. Indeed, reducing STAT1's access to the nucleus may explain RSV's suppression of IFN JAK/STAT promoter activation and antiviral gene induction. Taken together these results describe a novel mechanism by which RSV controls antiviral IFN-α JAK/STAT responses, which enhances our understanding of RSV's respiratory disease progression.

Neutrophils in COVID-19: Not Innocent Bystanders.

Unusually for a viral infection, the immunological phenotype of severe COVID-19 is characterised by a depleted lymphocyte and elevated neutrophil count, with the neutrophil-to-lymphocyte ratio correlating with disease severity. Neutrophils are the most abundant immune cell in the bloodstream and comprise different subpopulations with pleiotropic actions that are vital for host immunity. Unique neutrophil subpopulations vary in their capacity to mount antimicrobial responses, including NETosis (the generation of neutrophil extracellular traps), degranulation and de novo production of cytokines and chemokines. These processes play a role in antiviral immunity, but may also contribute to the local and systemic tissue damage seen in acute SARS-CoV-2 infection. Neutrophils also contribute to complications of COVID-19 such as thrombosis, acute respiratory distress syndrome and multisystem inflammatory disease in children. In this Progress review, we discuss the anti-viral and pathological roles of neutrophils in SARS-CoV-2 infection, and potential therapeutic strategies for COVID-19 that target neutrophil-mediated inflammatory responses.

The Effect of Age, Gender and Comorbidities Upon SARS-CoV-2 Spike Antibody Induction After Two Doses of Sinopharm Vaccine and the Effect of a Pfizer/BioNtech Booster Vaccine.

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 emerged in China in 2019 and has since travelled the world infecting millions. SARS-CoV-2 causes Corona Virus Disease (COVID-19), that has to date taken over 4 million lives. The Kingdom of Bahrain's vaccine roll-out has consisted of Sinopharm's BBIBP-CorV (Sinopharm) and Pfizer/BioNtech's BNT162b2 (Pfizer/BioNtech). Testing for SARS-CoV-2 anti-Spike (S) antibodies is a useful technique in estimating an individual's immune protection against the infection. In this study we evaluated S antibody levels by electro-chemiluminescence immunoassay in 379 individuals double vaccinated with Sinopharm and 15 of whom were given a booster with the Pfizer/BioNtech vaccine. Among our double vaccinated cohort, we found a spectrum of S antibody levels. Indeed, we found that a significant proportion of individuals with low S antibody levels had clinical conditions, which were mainly immune-related disorders. Furthermore, a significant proportion of individuals with low S antibody levels were above 50 years of age. Finally, we observed a significant increase in S antibody levels after the Pfizer/BioNtech booster was administered. These findings reveal that while a large proportion of Sinopharm vaccinated individuals did not develop high levels of antibodies against the S protein, a booster dose of the Pfizer/BioNtech vaccine significantly enhances S antibody levels, revealing this "triple dose" vaccination strategy as a useful method of ensuring protective immunity against SARS-CoV-2.

Inhibition of the IFN-α JAK/STAT Pathway by MERS-CoV and SARS-CoV-1 Proteins in Human Epithelial Cells.

Coronaviruses (CoVs) have caused several global outbreaks with relatively high mortality rates, including Middle East Respiratory Syndrome coronavirus (MERS)-CoV, which emerged in 2012, and Severe Acute Respiratory Syndrome (SARS)-CoV-1, which appeared in 2002. The recent emergence of SARS-CoV-2 highlights the need for immediate and greater understanding of the immune evasion mechanisms used by CoVs. Interferon (IFN)-α is the body's natural antiviral agent, but its Janus kinase/signal transducer and activators of transcription (JAK/STAT) signalling pathway is often antagonized by viruses, thereby preventing the upregulation of essential IFN stimulated genes (ISGs). Therapeutic IFN-α has disappointingly weak clinical responses in MERS-CoV and SARS-CoV-1 infected patients, indicating that these CoVs inhibit the IFN-α JAK/STAT pathway. Here we show that in lung alveolar A549 epithelial cells expression of MERS-CoV-nsp2 and SARS-CoV-1-nsp14, but not MERS-CoV-nsp5, increased basal levels of total and phosphorylated STAT1 & STAT2 protein, but reduced IFN-α-mediated phosphorylation of STAT1-3 and induction of MxA. While MERS-CoV-nsp2 and SARS-CoV-1-nsp14 similarly increased basal levels of STAT1 and STAT2 in bronchial BEAS-2B epithelial cells, unlike in A549 cells, they did not enhance basal pSTAT1 nor pSTAT2. However, both viral proteins reduced IFN-α-mediated induction of pSTAT1-3 and ISGs (MxA, ISG15 and PKR) in BEAS-2B cells. Furthermore, even though IFN-α-mediated induction of pSTAT1-3 was not affected by MERS-CoV-nsp5 expression in BEAS-2B cells, downstream ISG induction was reduced, revealing that MERS-CoV-nsp5 may use an alternative mechanism to reduce antiviral ISG induction in this cell line. Indeed, we subsequently discovered that all three viral proteins inhibited STAT1 nuclear translocation in BEAS-2B cells, unveiling another layer of inhibition by which these viral proteins suppress responses to Type 1 IFNs. While these observations highlight cell line-specific differences in the immune evasion effects of MERS-CoV and SARS-CoV-1 proteins, they also demonstrate the broad spectrum of immune evasion strategies these deadly coronaviruses use to stunt antiviral responses to Type IFN.

Unravelling the Immunomodulatory Effects of Viral Ion Channels, towards the Treatment of Disease.

The current COVID-19 pandemic has highlighted the need for the research community to develop a better understanding of viruses, in particular their modes of infection and replicative lifecycles, to aid in the development of novel vaccines and much needed anti-viral therapeutics. Several viruses express proteins capable of forming pores in host cellular membranes, termed "Viroporins". They are a family of small hydrophobic proteins, with at least one amphipathic domain, which characteristically form oligomeric structures with central hydrophilic domains. Consequently, they can facilitate the transport of ions through the hydrophilic core. Viroporins localise to host membranes such as the endoplasmic reticulum and regulate ion homeostasis creating a favourable environment for viral infection. Viroporins also contribute to viral immune evasion via several mechanisms. Given that viroporins are often essential for virion assembly and egress, and as their structural features tend to be evolutionarily conserved, they are attractive targets for anti-viral therapeutics. This review discusses the current knowledge of several viroporins, namely Influenza A virus (IAV) M2, Human Immunodeficiency Virus (HIV)-1 Viral protein U (Vpu), Hepatitis C Virus (HCV) p7, Human Papillomavirus (HPV)-16 E5, Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) Open Reading Frame (ORF)3a and Polyomavirus agnoprotein. We highlight the intricate but broad immunomodulatory effects of these viroporins and discuss the current antiviral therapies that target them; continually highlighting the need for future investigations to focus on novel therapeutics in the treatment of existing and future emergent viruses.

Neutrophils: Need for Standardized Nomenclature.

Neutrophils are the most abundant innate immune cell with critical anti-microbial functions. Since the discovery of granulocytes at the end of the nineteenth century, the cells have been given many names including phagocytes, polymorphonuclear neutrophils (PMN), granulocytic myeloid derived suppressor cells (G-MDSC), low density neutrophils (LDN) and tumor associated neutrophils (TANS). This lack of standardized nomenclature for neutrophils suggest that biologically distinct populations of neutrophils exist, particularly in disease, when in fact these may simply be a manifestation of the plasticity of the neutrophil as opposed to unique populations. In this review, we profile the surface markers and granule expression of each stage of granulopoiesis to offer insight into how each stage of maturity may be identified. We also highlight the remarkable surface marker expression profiles between the supposed neutrophil populations.

An Overview of Current Knowledge of Deadly CoVs and Their Interface with Innate Immunity.

Coronaviruses are a large family of zoonotic RNA viruses, whose infection can lead to mild or lethal respiratory tract disease. Severe Acute Respiratory Syndrome-Coronavirus-1 (SARS-CoV-1) first emerged in Guangdong, China in 2002 and spread to 29 countries, infecting 8089 individuals and causing 774 deaths. In 2012, Middle East Respiratory Syndrome-Coronavirus (MERS-CoV) emerged in Saudi Arabia and has spread to 27 countries, with a mortality rate of ~34%. In 2019, SARS-CoV-2 emerged and has spread to 220 countries, infecting over 100,000,000 people and causing more than 2,000,000 deaths to date. These three human coronaviruses cause diseases of varying severity. Most people develop mild, common cold-like symptoms, while some develop acute respiratory distress syndrome (ARDS). The success of all viruses, including coronaviruses, relies on their evolved abilities to evade and modulate the host anti-viral and pro-inflammatory immune responses. However, we still do not fully understand the transmission, phylogeny, epidemiology, and pathogenesis of MERS-CoV and SARS-CoV-1 and -2. Despite the rapid application of a range of therapies for SARS-CoV-2, such as convalescent plasma, remdesivir, hydroxychloroquine and type I interferon, no fully effective treatment has been determined. Remarkably, COVID-19 vaccine research and development have produced several offerings that are now been administered worldwide. Here, we summarise an up-to-date understanding of epidemiology, immunomodulation and ongoing anti-viral and immunosuppressive treatment strategies. Indeed, understanding the interplay between coronaviruses and the anti-viral immune response is crucial to identifying novel targets for therapeutic intervention, which may even prove invaluable for the control of future emerging coronavirus.

The high prevalence of asymptomatic SARS-CoV-2 infection reveals the silent spread of COVID-19.

PURPOSE: The COVID-19 pandemic has led to over 92 million cases and 1.9 million deaths worldwide since its outbreak. Public health responses have focused on identifying symptomatic individuals to halt spread. However, evidence is accruing that asymptomatic individuals are infectious and contributing to this global pandemic. METHODS: Observational data of 320 index cases and their 1289 positive contacts from the National COVID-19 Database in Bahrain were used to analyze symptoms, infectivity rate and PCR Cycle threshold (Ct) values. RESULTS: No significant difference (p = 1.0) in proportions of symptomatic (n = 160; 50.0%) and asymptomatic index cases (n = 160; 50.0%) were seen; however, SARS-CoV-2 positive contact cases were predominantly asymptomatic (n = 1127, 87.4%). Individuals aged 0-19 years constituted a larger proportion of positive contact cases (20.8%) than index cases (4.7%; p < 0.001). A total of 22% of the positive contacts were infected by symptomatic male index cases aged between 30-39 years. The total numbers of exposed contacts (p = 0.33), infected contacts (p = 0.81) and hence infectivity rate (p = 0.72) were not different between symptomatic and asymptomatic index cases. PCR Ct values were higher in asymptomatic compared to symptomatic index cases (p < 0.001), and higher in asymptomatic compared to symptomatic positive contacts (p < 0.001). No differences between the infectivity rates of index cases with Ct values <30 and values ≥30 were observed (p = 0.13). CONCLUSION: These data reveal that the high asymptomatic incidence of SARS-CoV-2 infection in Bahrain and subsequent positive contacts from an index case were more likely to be asymptomatic, showing the high "silent" risk of transmission and need for comprehensive screening for each positive infection to help halt the ongoing pandemic.

Potential Role of Flavivirus NS2B-NS3 Proteases in Viral Pathogenesis and Anti-flavivirus Drug Discovery Employing Animal Cells and Models: A Review.

Flaviviruses are known to cause a variety of diseases in humans in different parts of the world. There are very limited numbers of antivirals to combat flavivirus infection, and therefore new drug targets must be explored. The flavivirus NS2B-NS3 proteases are responsible for the cleavage of the flavivirus polyprotein, which is necessary for productive viral infection and for causing clinical infections; therefore, they are a promising drug target for devising novel drugs against different flaviviruses. This review highlights the structural details of the NS2B-NS3 proteases of different flaviviruses, and also describes potential antiviral drugs that can interfere with the viral protease activity, as determined by various studies. Moreover, optimized in vitro reaction conditions for studying the NS2B-NS3 proteases of different flaviviruses may vary and have been incorporated in this review. The increasing availability of the in silico and crystallographic/structural details of flavivirus NS2B-NS3 proteases in free and drug-bound states can pave the path for the development of promising antiflavivirus drugs to be used in clinics. However, there is a paucity of information available on using animal cells and models for studying flavivirus NS2B-NS3 proteases, as well as on the testing of the antiviral drug efficacy against NS2B-NS3 proteases. Therefore, on the basis of recent studies, an effort has also been made to propose potential cellular and animal models for the study of flavivirus NS2B-NS3 proteases for the purposes of exploring flavivirus pathogenesis and for testing the efficacy of possible drugs targets, in vitro and in vivo.

The hepatitis C virus (HCV) protein, p7, suppresses inflammatory responses to tumor necrosis factor (TNF)-α via signal transducer and activator of transcription (STAT)3 and extracellular signal-regulated kinase (ERK)-mediated induction of suppressor of cytokine signaling (SOCS)3.

Viruses use a spectrum of immune evasion strategies that enable infection and replication. The acute phase of hepatitis C virus (HCV) infection is characterized by nonspecific and often mild clinical symptoms, suggesting an immunosuppressive mechanism that, unless symptomatic liver disease presents, allows the virus to remain largely undetected. We previously reported that HCV induced the regulatory protein suppressor of cytokine signaling (SOCS)3, which inhibited TNF-α-mediated inflammatory responses. However, the mechanism by which HCV up-regulates SOCS3 remains unknown. Here we show that the HCV protein, p7, enhances both SOCS3 mRNA and protein expression. A p7 inhibitor reduced SOCS3 induction, indicating that p7's ion channel activity was required for optimal up-regulation of SOCS3. Short hairpin RNA and chemical inhibition revealed that both the Janus kinase-signal transducer and activator of transcription (JAK-STAT) and MAPK pathways were required for p7-mediated induction of SOCS3. HCV-p7 expression suppressed TNF-α-mediated IκB-α degradation and subsequent NF-κB promoter activity, revealing a new and functional, anti-inflammatory effect of p7. Together, these findings identify a molecular mechanism by which HCV-p7 induces SOCS3 through STAT3 and ERK activation and demonstrate that p7 suppresses proinflammatory responses to TNF-α, possibly explaining the lack of inflammatory symptoms observed during early HCV infection.-Convery, O., Gargan, S., Kickham, M., Schroder, M., O'Farrelly, C., Stevenson, N. J. The hepatitis C virus (HCV) protein, p7, suppresses inflammatory responses to tumor necrosis factor (TNF)-α via signal transducer and activator of transcription (STAT)3 and extracellular signal-regulated kinase (ERK)-mediated induction of suppressor of cytokine signaling (SOCS)3.

HIV-1 Promotes the Degradation of Components of the Type 1 IFN JAK/STAT Pathway and Blocks Anti-viral ISG Induction.

Anti-retroviral therapy successfully suppresses HIV-1 infection, but fails to provide a cure. During infection Type 1 IFNs normally play an essential role in viral clearance, but in vivo IFN-α only has a modest impact on HIV-1 infection, suggesting its possible targeting by HIV. Here, we report that the HIV protein, Vif, inhibits effective IFN-α signalling via degradation of essential JAK/STAT pathway components. We found that STAT1 and STAT3 are specifically reduced in HEK293T cells expressing Vif and that full length, infectious HIV-1 IIIB strain promotes their degradation in a Vif-dependent manner. HIV-1 IIIB infection of myeloid ThP-1 cells also reduced the IFN-α-mediated induction of the anti-viral gene, ISG15, but not MxA, revealing a functional consequence of this HIV-1-mediated immune evasion strategy. Interestingly, while total STAT levels were not reduced upon in vitro IIIB infection of primary human PBMCs, IFN-α-mediated phosphorylation of STAT1 and STAT3 and ISG induction were starkly reduced, with removal of Vif (IIIBΔVif), partially restoring pSTATs, ISG15 and MxB induction. Similarly, pSTAT1 and pSTAT3 expression and IFN-α-induced ISG15 were reduced in PBMCs from HIV-infected patients, compared to healthy controls. Furthermore, IFN-α pre-treatment of a CEM T lymphoblast cells significantly inhibited HIV infection/replication (measured by cellular p24), only in the absence of Vif (IIIBΔVif), but was unable to suppress full length IIIB infection. When analysing the mechanism by which Vif might target the JAK/STAT pathway, we found Vif interacts with both STAT1 and STAT3, (but not STAT2), and its expression promotes ubiquitination and MG132-sensitive, proteosomal degradation of both proteins. Vif's Elongin-Cullin-SOCS-box binding motif enables the formation of an active E3 ligase complex, which we found to be required for Vif's degradation of STAT1 and STAT3. In fact, the E3 ligase scaffold proteins, Cul5 and Rbx2, were also found to be essential for Vif-mediated proteasomal degradation of STAT1 and STAT3. These results reveal a target for HIV-1-Vif and demonstrate how HIV-1 impairs the anti-viral activity of Type 1 IFNs, possibly explaining why both endogenous and therapeutic IFN-α fail to activate more effective control over HIV infection.

Control of HIV infection by IFN-α: implications for latency and a cure.

Viral infections, including HIV, trigger the production of type I interferons (IFNs), which in turn, activate a signalling cascade that ultimately culminates with the expression of anti-viral proteins. Mounting evidence suggests that type I IFNs, in particular IFN-α, play a pivotal role in limiting acute HIV infection. Highly active anti-retroviral treatment reduces viral load and increases life expectancy in HIV positive patients; however, it fails to fully eliminate latent HIV reservoirs. To revisit HIV as a curable disease, this article reviews a body of literature that highlights type I IFNs as mediators in the control of HIV infection, with particular focus on the anti-HIV restriction factors induced and/or activated by IFN-α. In addition, we discuss the relevance of type I IFN treatment in the context of HIV latency reversal, novel therapeutic intervention strategies and the potential for full HIV clearance.

Advances in anti-viral immune defence: revealing the importance of the IFN JAK/STAT pathway.

Interferon-alpha (IFN-α) is a potent anti-viral cytokine, critical to the host immune response against viruses. IFN-α is first produced upon viral detection by pathogen recognition receptors. Following its expression, IFN-α embarks upon a complex downstream signalling cascade called the JAK/STAT pathway. This signalling pathway results in the expression of hundreds of effector genes known as interferon stimulated genes (ISGs). These genes are the basis for an elaborate effector mechanism and ultimately, the clearance of viral infection. ISGs mark an elegant mechanism of anti-viral host defence that warrants renewed research focus in our global efforts to treat existing and emerging viruses. By understanding the mechanistic role of individual ISGs we anticipate the discovery of a new "treasure trove" of anti-viral mediators that may pave the way for more effective, targeted and less toxic anti-viral therapies. Therefore, with the aim of highlighting the value of the innate type 1 IFN response in our battle against viral infection, this review outlines both historic and recent advances in understanding the IFN-α JAK/STAT pathway, with a focus on new research discoveries relating to specific ISGs and their potential role in curing existing and future emergent viral infections.

A novel anti-viral role for STAT3 in IFN-α signalling responses.

The cytokine, Interferon (IFN)-α, induces a wide spectrum of anti-viral mediators, via the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. STAT1 and STAT2 are well characterised to upregulate IFN-stimulated gene (ISG) expression; but even though STAT3 is also activated by IFN-α, its role in anti-viral ISG induction is unclear. Several viruses, including Hepatitis C and Mumps, reduce cellular STAT3 protein levels, via the promotion of ubiquitin-mediated proteasomal degradation. This viral immune evasion mechanism suggests an undiscovered anti-viral role for STAT3 in IFN-α signalling. To investigate STAT3's functional involvement in this Type I IFN pathway, we first analysed its effect upon the replication of two viruses, Influenza and Vaccinia. Viral plaque assays, using Wild Type (WT) and STAT3-/- Murine Embryonic Fibroblasts (MEFs), revealed that STAT3 is required for the inhibition of Influenza and Vaccinia replication. Furthermore, STAT3 shRNA knockdown also enhanced Influenza replication and hindered induction of several, well characterised, anti-viral ISGs: PKR, OAS2, MxB and ISG15; while STAT3 expression had no effect upon induction of a separate ISG group: Viperin, IFI27, CXCL10 and CCL5. These discoveries reveal, for the first time, an anti-viral role for STAT3 in the IFN-α pathway and characterise a requirement for STAT3 in the expression of specific ISGs. These findings also identify STAT3 as a therapeutic target against viral infection and highlight it as an essential pathway component for endogenous and therapeutic IFN-α responsiveness.

MicroRNA: master controllers of intracellular signaling pathways.

Signaling pathways are essential intracellular networks that coordinate molecular outcomes to external stimuli. Tight regulation of these pathways is essential to ensure an appropriate response. MicroRNA (miRNA) is a class of small, non-coding RNA that regulates gene expression at a post-transcriptional level by binding to the complementary sequence on target mRNA, thus limiting protein translation. Intracellular pathways are controlled by protein regulators, such as suppressor of cytokine signaling and A20. Until recently, expression of these classical protein regulators was thought to be controlled solely by transcriptional induction and proteasomal degradation; however, there is a growing body of evidence describing their regulation by miRNA. This new information has transformed our understanding of cell signaling by adding a previously unknown layer of regulatory control. This review outlines the miRNA regulation of these classical protein regulators and describes their broad effects at both cellular and disease levels. We review the regulation of three important signaling pathways, including the JAK/STAT, NF-κB, and TGF-ß pathways, and summarize an extensive catalog of their regulating miRNAs. This information highlights the importance of the miRNA regulon and reveals a previously unknown regulatory landscape that must be included in the identification and development of novel therapeutic targets for clinical disorders.

Interdependent and independent roles of type I interferons and IL-6 in innate immune, neuroinflammatory and sickness behaviour responses to systemic poly I:C.

Type I interferons (IFN-I) are expressed in the brain during many inflammatory and neurodegenerative conditions and have multiple effects on CNS function. IFN-I is readily induced in the brain by systemic administration of the viral mimetic, poly I:C (synthetic double-stranded RNA). We hypothesised that IFN-I contributes to systemically administered poly I:C-induced sickness behaviour, metabolic and neuroinflammatory changes. IFN-I receptor 1 deficient mice (IFNAR1(-/-)) displayed significantly attenuated poly I:C-induced hypothermia, hypoactivity and weight loss compared to WT C57BL/6 mice. This amelioration of sickness was associated with equivalent IL-1ß and TNF-α responses but much reduced IL-6 responses in plasma, hypothalamus and hippocampus of IFNAR1(-/-) mice. IFN-ß injection induced trivial IL-6 production and limited behavioural change and the poly I:C-induced IFN-ß response did not preceed, and would not appear to mediate, IL-6 induction. Rather, IFNAR1(-/-) mice lack basal IFN-I activity, have lower STAT1 levels and show significantly lower levels of several inflammatory transcripts, including stat1. Basal IFN-I activity appears to play a facilitatory role in the full expression of the IL-6 response and activation of the tryptophan-kynurenine metabolism pathway. The deficient IL-6 response in IFNAR1(-/-) mice partially explains the observed incomplete sickness behaviour response. Reconstitution of circulating IL-6 revealed that the role of IFNAR in burrowing activity is mediated via IL-6, while IFN-I and IL-6 have additive effects on hypoactivity, but the role of IFN-I in anorexia is independent of IL-6. Hence, we have demonstrated both interdependent and independent roles for IFN-I and IL-6 in systemic inflammation-induced changes in brain function.

In vitro blood cell responsiveness to IFN-α predicts clinical response independently of IL28B in hepatitis C virus genotype 1 infected patients.

BACKGROUND: Treatment with interferon-alpha (IFN-α) and ribavirin successfully clears hepatitis C virus (HCV) infection in 50% of patients infected with genotype 1. Addition of NS3-4A protease inhibitors (PIs) increases response rates but results in additional side effects and significant economic costs. Here, we hypothesised that in vitro responsiveness of peripheral blood mononuclear cells (PBMCs) to IFN-α stimulation would identify patients who achieved sustained virological response (SVR) on dual therapy alone and thus not require addition of PIs. METHODS: PBMCs were isolated from HCV infected patients (n = 42), infected with either HCV genotype 1 or genotype 3, before commencing therapy and stimulated in vitro with IFN-α. Expression of the IFN stimulated genes (ISGs) PKR, OAS and MxA was measured and correlated with subsequent treatment response and IL28B genotype. RESULTS: Genotype 1 infected patients who achieved SVR had significantly higher pre-treatment expression of PKR (p = 0.0148), OAS (p = 0.0019) and MxA (p = 0.0019) in IFN-α stimulated PBMCs, compared to genotype 1 infected patients who did not achieve SVR or patients infected with genotype 3, whose in vitro ISG expression did not correlate with clinical responsiveness. IL28B genotype (rs12979860) did not correlate with endogenous or IFN-α stimulated ISG responsiveness. CONCLUSIONS: In vitro responsiveness of PBMCs to IFN-α from genotype 1 infected patients predicts clinical responsiveness to dual therapy, independently of IL28B genotype. These results indicate that this sub-group of HCV infected patients could be identified pre-treatment and successfully treated without PIs, thus reducing adverse side effects and emergence of PI resistant virus while making significant economic savings.

Hepatitis C virus (HCV)-induced suppressor of cytokine signaling (SOCS) 3 regulates proinflammatory TNF-α responses.

TNF-α is a proinflammatory cytokine, dramatically elevated during pathogenic infection and often responsible for inflammation-induced disease pathology. SOCS proteins are inhibitors of cytokine signaling and regulators of inflammation. In this study, we found that both SOCS1 and SOCS3 were transiently induced by TNF-α and negatively regulate its NF-κB-mediated signal transduction. We discovered that PBMCs from HCV-infected patients have elevated endogenous SOCS3 expression but less TNF-α-mediated IκB degradation and proinflammatory cytokine production than healthy controls. HCV protein expression in Huh7 hepatocytes also induced SOCS3 and directly inhibited TNF-α-mediated IL-8 production. Furthermore, we found that SOCS3 associates with TRAF2 and inhibits TRAF2-mediated NF-κB promoter activity, suggesting a mechanism by which SOCS3 inhibits TNF-α-mediated signaling. These results demonstrate a role for SOCS3 in regulating proinflammatory TNF-α signal transduction and reveal a novel immune-modulatory mechanism by which HCV suppresses inflammatory responses in primary immune cells and hepatocytes, perhaps explaining mild pathology often associated with acute HCV infection.

miR-19a: an effective regulator of SOCS3 and enhancer of JAK-STAT signalling.

Suppressors of cytokine signalling (SOCS) proteins are classic inhibitors of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. Many cytokines and pathogenic mediators induce expression of SOCS, which act in a negative feedback loop to inhibit further signal transduction. SOCS mRNA expression is regulated by DNA binding of STAT proteins, however, their post-transcriptional regulation is poorly understood. microRNAs (miRNAs) are small non-coding RNAs that bind to complementary sequences on target mRNAs, often silencing gene expression. miR-19a has been shown to regulate SOCS1 expression during mutiple myeloma and be induced by the anti-viral cytokine interferon-(IFN)-α, suggesting a role in the regulation of the JAK-STAT pathway. This study aimed to identify targets of miR-19a in the JAK-STAT pathway and elucidate the functional consequences. Bioinformatic analysis identified highly conserved 3'UTR miR-19a target sequences in several JAK-STAT associated genes, including SOCS1, SOCS3, SOCS5 and Cullin (Cul) 5. Functional studies revealed that miR-19a significantly decreased SOCS3 mRNA and protein, while a miR-19a antagomir specifically reversed its inhibitory effect. Furthermore, miR-19a-mediated reduction of SOCS3 enhanced IFN-α and interleukin (IL)-6 signal transduction through STAT3. These results reveal a novel mechanism by which miR-19a may augment JAK-STAT signal transduction via control of SOCS3 expression and are fundamental to the understanding of inflammatory regulation.

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.