Hepatitis C virus NS4B induces the degradation of TRIF to inhibit TLR3-mediated interferon signaling pathway

Toll-Like Receptor 3 mRNA Expression of Peripheral Blood Mononuclear Cells Identifies Kidney Recipients with Potential for Improved Graft Performance

BACKGROUND Toll-like receptor 3 expression is detected both on the cell membrane and in endosomes of peripheral blood mononuclear cells (PBMC). Our goal in this study was to determine to what extent a single, baseline measurement of non-stimulated PBMC TLR3-mRNA can be related to baseline GFR (b-GFR) and post-follow-up-GFR (F-up-GFR) of a kidney transplant (KT) and baseline immunosuppression. MATERIAL AND METHODS In non-stimulated PBMC we investigated averaged mRNA expression of Toll-like receptor 3. A total of 133 patients were enrolled; the median of months after KT surgery was 11.4, with median F-up at 21.3 months. A favorable course (FCF) was determined if F-up-eGFR improved. An unfavorable course (UCF) was determined if F-up-eGFR was lower at the end of the observation. RESULTS The highest TLR3-mRNA expression was at b-GFR grade 3b; it was moderately higher at b-GFR grade 3a, and marginally higher at b-GFR grades 1+2. Most of the FCF group had b-GFR grade 3b, less frequent obesity, more effective immunosuppression, and much higher TLR3-mRNA (59% of cases were in the high-TLR3 area). Both delayed graft function (DGF) and TLR3-mRNA range below the median for the entire KT cohort (low-TLR3 area) had a negative association with b-GFR. The UCF group had more frequent DGFs and obesity, less effective immunosuppression, and lower TLR3-mRNA. CONCLUSIONS In patients with GFR grade 3, high levels of TLR3-mRNA are associated with improved graft efficacy. In patients with impaired graft function, low TLR3- mRNA expression reduces the likelihood of improved renal graft function.

Oncoviruses: How do they hijack their host and current treatment regimes

Viruses have the ability to modulate the cellular machinery of their host to ensure their survival. While humans encounter numerous viruses daily, only a select few can lead to disease progression. Some of these viruses can amplify cancer-related traits, particularly when coupled with factors like immunosuppression and co-carcinogens. The global burden of cancer development resulting from viral infections is approximately 12%, and it arises as an unfortunate consequence of persistent infections that cause chronic inflammation, genomic instability from viral genome integration, and dysregulation of tumor suppressor genes and host oncogenes involved in normal cell growth. This review provides an in-depth discussion of oncoviruses and their strategies for hijacking the host's cellular machinery to induce cancer. It delves into how viral oncogenes drive tumorigenesis by targeting key cell signaling pathways. Additionally, the review discusses current therapeutic approaches that have been approved or are undergoing clinical trials to combat malignancies induced by oncoviruses. Understanding the intricate interactions between viruses and host cells can lead to the development of more effective treatments for virus-induced cancers.

Modulation of cellular machineries by Zika virus-encoded proteins

The strain of Zika virus (ZIKV) that circulated during the 2015 epidemic in Brazil has been associated with more than 2000 cases of microcephaly from September 2015 through November 2016. The viral genome determines the biology and pathogenesis of a virus and the virus employs its own gene products to evade host immune surveillance, manipulate cellular machineries, and establish efficient replication. Therefore, understanding the functions of virus-encoded protein not only aids the knowledge of ZIKV biology but also guides the development of anti-ZIKV drugs. In this review, we focus on 10 proteins encoded by ZIKV and summarize their functions in ZIKV replication and pathogenesis according to studies published in the past 6 years.

Flaviviridae Nonstructural Proteins: The Role in Molecular Mechanisms of Triggering Inflammation

Members of the Flaviviridae family are posing a significant threat to human health worldwide. Many flaviviruses are capable of inducing severe inflammation in humans. Flaviviridae nonstructural proteins, apart from their canonical roles in viral replication, have noncanonical functions strongly affecting antiviral innate immunity. Among these functions, antagonism of type I IFN is the most investigated; meanwhile, more data are accumulated on their role in the other pathways of innate response. This review systematizes the last known data on the role of Flaviviridae nonstructural proteins in molecular mechanisms of triggering inflammation, with an emphasis on their interactions with TLRs and RLRs, interference with NF-κB and cGAS-STING signaling, and activation of inflammasomes.

Relationship between hepatitis C and kidney stone in US females: Results from the National Health and Nutrition Examination Survey in 2007–2018

Background

The main objective of this study is to explore the effects of hepatitis C (HCV) on the prevalence rate of kidney stones in US women.

Method

Dates for HCV infection and kidney stones were collected from National Health and Nutrition Examination Survey (NHANES) database, a cross-sectional study. The analysis samples included adults aged ≥20 years and women from six consecutive cycles of the NHANES 2007–2018. The association between HCV infection and kidney stones was performed by using logistic regression models. Subgroup analyses were conducted to find sensitive crowds.

Results

A total of 13,262 participants were enrolled, including 201 infected with HCV. After adjustment for potential confounders, we revealed a positive relationship between HCV and kidney stones (OR = 1.70, 95%CI:1.13–2.56). The crowds' statistically significant difference was characterized by other races (OR = 8.17, 95%CI:1.62–41.22) and BMI within 25–29.9 kg/m2 (OR = 2.45, 95%CI:1.24–4.83).

Conclusions

HCV infection may affect the prevalence of urolithiasis in US women, even the causal relationship remains unclear, the relation deserves special attention. We considered such a study an ideal way to begin exploring the effects of HCV on kidney stones.

Immunogenic cell stress and death

Dying mammalian cells emit numerous signals that interact with the host to dictate the immunological correlates of cellular stress and death. In the absence of reactive antigenic determinants (which is generally the case for healthy cells), such signals may drive inflammation but cannot engage adaptive immunity. Conversely, when cells exhibit sufficient antigenicity, as in the case of infected or malignant cells, their death can culminate with adaptive immune responses that are executed by cytotoxic T lymphocytes and elicit immunological memory. Suggesting a key role for immunogenic cell death (ICD) in immunosurveillance, both pathogens and cancer cells evolved strategies to prevent the recognition of cell death as immunogenic. Intriguingly, normal cells succumbing to conditions that promote the formation of post-translational neoantigens (for example, oxidative stress) can also drive at least some degree of antigen-specific immunity, pointing to a novel implication of ICD in the etiology of non-infectious, non-malignant disorders linked to autoreactivity.

Host Innate Immunity Against Hepatitis Viruses and Viral Immune Evasion

Hepatitis viruses are primary causative agents of hepatitis and represent a major source of public health problems in the world. The host innate immune system forms the first line of defense against hepatitis viruses. Hepatitis viruses are sensed by specific pathogen recognition receptors (PRRs) that subsequently trigger the innate immune response and interferon (IFN) production. However, hepatitis viruses evade host immune surveillance via multiple strategies, which help compromise the innate immune response and create a favorable environment for viral replication. Therefore, this article reviews published findings regarding host innate immune sensing and response against hepatitis viruses. Furthermore, we also focus on how hepatitis viruses abrogate the antiviral effects of the host innate immune system.

How to get away with liver innate immunity? A viruses' tale

In their never-ending quest towards persistence within their host, hepatitis viruses have developed numerous ways to counteract the liver innate immunity. This review highlights the different and common mechanisms employed by these viruses to (i) establish in the liver (passive entry or active evasion from immune recognition) and (ii) actively inhibit the innate immune response (ie modulation of pattern recognition receptor expression and/or signalling pathways, modulation of interferon response and modulation of immune cells count or phenotype).

A Tale of Two Viruses: Immunological Insights Into HCV/HIV Coinfection

Nearly 2.3 million individuals worldwide are coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV). Odds of HCV infection are six times higher in people living with HIV (PLWH) compared to their HIV-negative counterparts, with the highest prevalence among people who inject drugs (PWID) and men who have sex with men (MSM). HIV coinfection has a detrimental impact on the natural history of HCV, including higher rates of HCV persistence following acute infection, higher viral loads, and accelerated progression of liver fibrosis and development of end-stage liver disease compared to HCV monoinfection. Similarly, it has been reported that HCV coinfection impacts HIV disease progression in PLWH receiving anti-retroviral therapies (ART) where HCV coinfection negatively affects the homeostasis of CD4⁺ T cell counts and facilitates HIV replication and viral reservoir persistence. While ART does not cure HIV, direct acting antivirals (DAA) can now achieve HCV cure in nearly 95% of coinfected individuals. However, little is known about how HCV cure and the subsequent resolution of liver inflammation influence systemic immune activation, immune reconstitution and the latent HIV reservoir. In this review, we will summarize the current knowledge regarding the pathogenesis of HIV/HCV coinfection, the effects of HCV coinfection on HIV disease progression in the context of ART, the impact of HIV on HCV-associated liver morbidity, and the consequences of DAA-mediated HCV cure on immune reconstitution and HIV reservoir persistence in coinfected patients.

Is there a relationship between psoriasis and hepatitis C? A meta-analysis and bioinformatics investigation

Background

The relationship between psoriasis and hepatitis C was previously controversial, so our purpose is to investigate this connection.

Methods

We conducted a systematic review of the case–control, cross-sectional and cohort studies examining the association between psoriasis and hepatitis C in PubMed, EMBASE and Cochrane library databases and investigated the overlapping genes between psoriasis targets and hepatitis C targets using bioinformatics analysis. Based on overlapping genes and hub nodes, we also constructed the protein–protein interaction (PPI) network and module respectively, followed by the pathway enrichment analysis.

Results

We included 11 publications that reported a total of 11 studies (8 cross-sectional and 3 case–control). The case–control and cross-sectional studies included 25,047 psoriasis patients and 4,091,631 controls in total. Psoriasis was associated with a significant increase of prevalent hepatitis C (OR 1.72; 95% confidence interval [CI] (1.17–2.52)). A total of 389 significant genes were common to both hepatitis C and psoriasis, which mainly involved IL6, TNF, IL10, ALB, STAT3 and CXCL8. The module and pathway enrichment analyses showed that the common genes had the potential to influence varieties of biological pathways, including the inflammatory response, cytokine activity, cytokine–cytokine receptor interaction, Toll-like receptor signaling pathway, which play an important role in the pathogenesis of hepatitis C and psoriasis.

Conclusion

Patients with psoriasis display increased prevalence of hepatitis C and the basic related mechanisms between hepatitis C and psoriasis had been preliminarily clarified.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01606-z.

Research progress on Toll-like receptor signal transduction and its roles in antimicrobial immune responses

When microorganisms invade a host, the innate immune system first recognizes the pathogen-associated molecular patterns of these microorganisms through pattern recognition receptors (PRRs). Toll-like receptors (TLRs) are known transmembrane PRRs existing in both invertebrates and vertebrates. Upon ligand recognition, TLRs initiate a cascade of signaling events; promote the pro-inflammatory cytokine, type I interferon, and chemokine expression; and play an essential role in the modulation of the host's innate and adaptive immunity. Therefore, it is of great significance to improve our understanding of antimicrobial immune responses by studying the role of TLRs and their signal molecules in the host's defense against invading microbes. This paper aims to summarize the specificity of TLRs in recognition of conserved microbial components, such as lipoprotein, lipopolysaccharide, flagella, endosomal nucleic acids, and other bioactive metabolites derived from microbes. This set of interactions helps to elucidate the immunomodulatory effect of TLRs and the signal transduction changes involved in the infectious process and provide a novel therapeutic strategy to combat microbial infections.

A correlation analysis of the serum hepcidin concentrations and viral loads in HCV-infected patients

OBJECTIVE

To investigate the correlation between the serum hepcidin levels and the viral loads in hepatitis C virus (HCV) infected patients.

METHODS

Sixty HCV-infected patients (the study group) and 50 healthy controls (the control group) were recruited as the study cohort. The liver function and inflammation-related parameters were compared, and the 60 HCV patients were divided into mild (G1-G2), moderate (G3), and severe (G4) groups according to each patient's inflammatory activity grade (G). The serum iron (SI), ferritin (SF), and transferrin (TRF), hepcidin levels were compared. The relationships between the HCV-RNA, HCV Ag, HCV Ab, albumin (ALB), total bilirubin (TBIL), aminotransferase (ALT), and aspartate aminotransferase (AST) levels and the hepcidin levels was analyzed. The SI, SF, IL-6, ALT, AST, and TBIL levels were significantly higher, and the hepcidin, TRF, and ALB levels were significantly lower in the study group than they were in the control group (P<0.05). The G4 patients' SI and SF levels were significantly higher than they were in the G3 and the G1-G2 groups (P<0.05). The TRF and hepcidin levels in the G1-G2 group were significantly higher than they were in the G3 and G4 groups (P<0.05). The HCV-RNA, HCV Ag, and HCV Ab levels were negatively correlated with the hepcidin levels (r=-0.7679, r=-0.9062, r=-0.6095, P<0.05), positively correlated with the serum ALB, TBIL, and ALT levels (r=0.9792, r=0.9759, r=0.8236, P<0.05), and not significantly correlated with the AST levels (r=-0.2803, P>0.05).

CONCLUSION

The HCV patients' serum hepcidin levels showed an abnormal decrease, suggesting that HCV patients may have an iron metabolism disorder, which indicates that there is a possibility of evaluating the HCV patients' conditions by measuring the hepcidin levels and of improving HCV patients' prognoses by regulating the iron metabolism.

Decreased Expression of the Host Long-Noncoding RNA-GM Facilitates Viral Escape by Inhibiting the Kinase activity TBK1 via S-glutathionylation

Viruses have evolved multiple strategies to evade elimination by the immune system. Here we examined the contribution of host long noncoding RNAs (lncRNAs) in viral immune evasion. By functional screening of lncRNAs whose expression decreased upon viral infection of macrophages, we identified a lncRNA (lncRNA-GM, Gene Symbol: AK189470.1) that promoted type I interferon (IFN-I) production and inhibited viral replication. Deficiency of lncRNA-GM in mice increased susceptibility to viral infection and impaired IFN-I production. Mechanistically, lncRNA-GM bound to glutathione S-transferase M1 (GSTM1) and blocked GSTM1 interaction with the kinase TBK1, reducing GSTM1-mediated S-glutathionylation of TBK1. Decreased S-glutathionylation enhanced TBK1 activity and downstream production of antiviral mediators. Viral infection reprogrammed intracellular glutathione metabolism and furthermore, an oxidized glutathione mimetic could inhibit TBK1 activity and promote viral replication. Our findings reveal regulation of TBK1 by S-glutathionylation and provide insight into the viral mediated metabolic changes that impact innate immunity and viral evasion.

Amelioration of Beta Interferon Inhibition by NS4B Contributes to Attenuating Tembusu Virus Virulence in Ducks

Our previous studies reported that duck Tembusu virus nonstructural protein 2A (NS2A) is a major inhibitor of the IFNβ signaling pathway through competitively binding to STING with TBK1, leading to a reduction in TBK1 phosphorylation. Duck TMUV NS2B3 could cleave and bind STING to subvert the IFNβ signaling pathway. Here, we found that overexpression of duck TMUV NS4B could compete with TBK1 in binding to STING, reducing TBK1 phosphorylation and inhibiting the IFNβ signaling pathway by using the Dual-Glo^® Luciferase Assay System and the NanoBiT protein-protein interaction (PPI) assay. We further identified the E2, M3, G4, W5, K10 and D34 residues in NS4B that were important for its interaction with STING and its inhibition of IFNβ induction, which were subsequently introduced into a duck TMUV replicon and an infectious cDNA clone. We found that the NS4B M3A mutant enhanced RNA replication and exhibited significantly higher titer levels than WT at 48-72 hpi but significantly decreased mortality (80%) in duck embryos compared to WT (100%); the NS4B G4A and R36A mutants slightly reduced RNA replication but exhibited the same titer levels as WT. However, the NS4B R36A mutant did not attenuate the virulence in duck embryos, whereas the G4A mutant significantly decreased the mortality (70%) of duck embryos. In addition, the NS4B W5A mutant did not affect viral replication, whereas the D34A mutant slightly reduced RNA replication, and both mutants exhibited significantly lower titer levels than the WT and significantly decreased mortality (90% and 70%, respectively) in duck embryos. Hence, our findings provide new insight into the development of attenuated flaviviruses by targeting the disabling viral strategies used to evade the innate defense mechanisms.

UNC93B1 curbs cytosolic DNA signaling by promoting STING degradation

UNC93B1 is a trafficking chaperone of endosomal Toll-like receptors (TLRs) and plays an essential role in the TLR-mediated innate signaling. However, whether it is also involved in other innate immune sensing or cellular pathways remains largely unexplored. Here we investigated the role of UNC93B1 in cytosolic DNA-triggered cGAS-STING signaling in mouse and human cell lines. We showed that while UNC93B1 deficiency blunts the signal transduction by TLR3, it augments innate immune responses to cytosolic DNA stimulation and DNA virus infection. Mechanistic study reveals a distinct action of UNC93B1 upon STING, but not other parts along the cGAS-STING-TBK1 axis, through regulating the protein level of STING at both resting and cytosolic DNA-stimulated conditions. UNC93B1 can directly interact and traffic along with STING, and the disruption of this interaction causes accumulation of STING that subsequently leads to augmented signaling responses upon its activation. These findings reveal a new function of UNC93B1 in negatively regulating STING-mediated signaling responses.

Differential expression of viral pathogen-associated molecular pattern receptors mRNA in Egyptian chronic hepatitis C virus patients

Background

One possible mechanism utilized by hepatitis C virus (HCV) to escape from the host’s innate immune surveillance is modification of its pathogen-associated molecular patterns (PAMPs) by altering or hiding its RNA which interfering with toll-like receptors (TLRs) signaling and ultimately hindering the production of proinflammatory cytokines, chemokines, and interferons (IFNs). This study aimed to examine the expression levels of TLR3, TLR7, and IFN-α to investigate the correlated expression pattern among them in chronic HCV patients. Patients included in this study were categorized into two different groups, non-treated chronic HCV patients and treated chronic HCV patients, in addition to healthy volunteers as a control group. The blood samples were assessed for HCVAb, HCVRNA, HCV genotypes, and different biochemical analyses. The mRNA levels of TLR3, TLR7, and IFN-α in peripheral blood of chronic HCV patients were quantitatively measured in comparison to healthy controls.

Results

The expression levels of TLR3, TLR7, and IFN-α were significantly downregulated in non-treated chronic HCV patients compared to both treated HCV patients and control subjects. On the other hand, treated HCV patients showed non-significant downregulation of the same three sensing receptors (TLR3, TLR7, and IFN-α) compared to control group. Obviously, the expression levels of IFN-α were positively correlated with the levels of both TLR3 and TLR7.

Conclusion

The exhausted innate immunity against HCV may correlate to HCV downregulation of TLR3 and TLR7 expression on innate immune cells with a subsequent decrease in INF-α production and the possibility of targeting these receptors to enhance the immune response and clear the infection needs further studies.

[Hepatitis C virus (Flaviviridae: Hepacivirus: Hepacivirus C): regulation of signaling reactions of innate immunity]

Studying the regulation of signaling reactions of innate immunity by the hepatitis C virus (HCV) will help to reveal the causes of the transition of the acute form of the disease to a chronic course. The molecular mechanisms of activation by HCV RNA of innate immunity receptors TLR and RLR and signal transduction processes leading to the synthesis of IFN and inflammatory cytokines are considered. The inhibitory effects of non-structural and structural HCV proteins on immune signaling reactions are analyzed in detail. The information presented is the result of an analysis of literature data published in international databases mainly over the past 5 years. In conclusion, signaling receptors are proposed as targets for the development of new antiviral drugs with immunotherapeutic activity.

TRIM26 is a critical host factor for HCV replication and contributes to host tropism

Hepatitis C virus (HCV) remains a major human pathogen that requires better understanding of virus-host interactions. In this study, we performed a genome-wide CRISPR-Cas9 screening and identified TRIM26, an E3 ligase, as a critical HCV host factor. Deficiency of TRIM26 specifically impairs HCV genome replication. Mechanistic studies showed that TRIM26 interacts with HCV-encoded NS5B protein and mediates its K27-linked ubiquitination at residue K51, and thus promotes the NS5B-NS5A interaction. Moreover, mouse TRIM26 does not support HCV replication because of its unique six-amino acid insert that prevents its interaction with NS5B. Ectopic expression of human TRIM26 in a mouse hepatoma cell line that has been reconstituted with other essential HCV host factors promotes HCV infection. In conclusion, we identified TRIM26 as a host factor for HCV replication and a new determinant of host tropism. These results shed light on HCV-host interactions and may facilitate the development of an HCV animal model.

The bZIP Proteins of Oncogenic Viruses

Basic leucine zipper (bZIP) transcription factors (TFs) govern diverse cellular processes and cell fate decisions. The hallmark of the leucine zipper domain is the heptad repeat, with leucine residues at every seventh position in the domain. These leucine residues enable homo- and heterodimerization between ZIP domain α-helices, generating coiled-coil structures that stabilize interactions between adjacent DNA-binding domains and target DNA substrates. Several cancer-causing viruses encode viral bZIP TFs, including human T-cell leukemia virus (HTLV), hepatitis C virus (HCV) and the herpesviruses Marek’s disease virus (MDV), Epstein–Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV). Here, we provide a comprehensive review of these viral bZIP TFs and their impact on viral replication, host cell responses and cell fate.

Interferon Response in Hepatitis C Virus-Infected Hepatocytes: Issues to Consider in the Era of Direct-Acting Antivirals

When interferons (IFNs) bind to their receptors, they upregulate numerous IFN-stimulated genes (ISGs) with antiviral and immune regulatory activities. Hepatitis C virus (HCV) is a single-stranded, positive-sense RNA virus that affects over 71 million people in the global population. Hepatocytes infected with HCV produce types I and III IFNs. These endogenous IFNs upregulate a set of ISGs that negatively impact the outcome of pegylated IFN-α and ribavirin treatments, which were previously used to treat HCV. In addition, the IFNL4 genotype was the primary polymorphism responsible for a suboptimal treatment response to pegylated IFN-α and ribavirin. However, recently developed direct-acting antivirals have demonstrated a high rate of sustained virological response without pegylated IFN-α. Herein, we review recent studies on types I and III IFN responses to in HCV-infected hepatocytes. In particular, we focused on open issues related to IFN responses in the direct-acting antiviral era.

Hepatitis C Virus: Evading the Intracellular Innate Immunity

Hepatitis C virus (HCV) infections constitute a major public health problem and are the main cause of chronic hepatitis and liver disease worldwide. The existing drugs, while effective, are expensive and associated with undesirable secondary effects. There is, hence, an urgent need to develop novel therapeutics, as well as an effective vaccine to prevent HCV infection. Understanding the interplay between HCV and the host cells will certainly contribute to better comprehend disease progression and may unravel possible new cellular targets for the development of novel antiviral therapeutics. Here, we review and discuss the interplay between HCV and the host cell innate immunity. We focus on the different cellular pathways that respond to, and counteract, HCV infection and highlight the evasion strategies developed by the virus to escape this intracellular response.

Viroporins and inflammasomes: A key to understand virus-induced inflammation

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The article provides a summary on cellular receptors involved in virus immunity.

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It summarizes key findings on viroporins, a novel class of viral proteins and their role in the virus life cycle and host cell interactions.

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It presents an overview of the current understanding of inflammasomes complex activation, with special focus on NLRP3.

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It discusses the correlation between viroporins and inflammasomes activation and aggravated inflammatory cytokines production.

Viroporins are virus encoded proteins that alter membrane permeability and can trigger subsequent cellular signals. Oligomerization of viroporin subunits results in formation of a hydrophilic pore which facilitates ion transport across host cell membranes. These viral channel proteins may be involved in different stages of the virus infection cycle. Inflammasomes are large multimolecular complexes best recognized for their ability to control activation of caspase-1, which in turn regulates the maturation of interleukin-1 β (IL-1β) and interleukin 18 (IL-18). IL-1β was originally identified as a pro-inflammatory cytokine able to induce both local and systemic inflammation and a febrile reaction in response to infection or injury. Excessive production of IL-1β is associated with autoimmune and inflammatory diseases. Microbial derivatives, bacterial pore-forming toxins, extracellular ATP and other pathogen-associated molecular patterns trigger activation of NLRP3 inflammasomes. Recent studies have reported that viroporin activity is capable of inducing inflammasome activity and production of IL-1β, where NLRP3 is shown to be regulated by fluxes of K⁺, H⁺ and Ca²⁺ in addition to reactive oxygen species, autophagy and endoplasmic reticulum stress. The aim of this review is to present an overview of the key findings on viroporin activity with special emphasis on their role in virus immunity and as possible activators of inflammasomes.

Signalling, sorting and scaffolding adaptors for Toll-like receptors

Toll-like receptors (TLRs) are danger-sensing receptors that typically propagate self-limiting inflammatory responses, but can unleash uncontrolled inflammation in non-homeostatic or disease settings. Activation of TLRs by pathogen- and/or host-derived stimuli triggers a range of signalling and transcriptional pathways to programme inflammatory and anti-microbial responses, including the production of a suite of inflammatory cytokines and other mediators. Multiple sorting and signalling adaptors are recruited to receptor complexes on the plasma membrane or endosomes where they act as scaffolds for downstream signalling kinases and effectors at these sites. So far, seven proximal TLR adaptors have been identified: MyD88, MAL, TRIF (also known as TICAM1), TRAM (TICAM2), SARM (SARM1), BCAP (PIK3AP1) and SCIMP. Most adaptors tether directly to TLRs through homotypic Toll/interleukin-1 receptor domain (TIR)-TIR interactions, whereas SCIMP binds to TLRs through an atypical TIR-non-TIR interaction. In this Review, we highlight the key roles for these adaptors in TLR signalling, scaffolding and receptor sorting and discuss how the adaptors thereby direct the differential outcomes of TLR-mediated responses. We further summarise TLR adaptor regulation and function, and make note of human diseases that might be associated with mutations in these adaptors.

Porcine RING Finger Protein 114 Inhibits Classical Swine Fever Virus Replication via K27-Linked Polyubiquitination of Viral NS4B

Porcine RING finger protein 114 (pRNF114) is a member of the RING domain E3 ligases. In this study, it was shown that pRNF114 is a potential anti-CSFV factor and the anti-CSFV effect of pRNF114 depends on its E3 ligase activity. Notably, pRNF114 targets and catalyzes the K27-linked polyubiquitination of the NS4B protein and then promotes proteasome-dependent degradation of NS4B, inhibiting the replication of CSFV. To our knowledge, pRNF114 is the first E3 ligase to be identified as being involved in anti-CSFV activity, and targeting NS4B could be a crucial route for antiviral development.

In the host, many RING domain E3 ligases have been reported to inhibit viral replication through various mechanisms. In a previous screen, we found that porcine RING finger protein 114 (pRNF114), a RING domain E3 ubiquitin ligase, inhibits classical swine fever virus (CSFV) replication. This study aimed to clarify the underlying antiviral mechanism of pRNF114 against CSFV. Upon CSFV infection, pRNF114 mRNA was upregulated both in vitro and in vivo. CSFV replication was significantly suppressed in PK-pRNF114 cells stably expressing pRNF114 by the lentivirus-delivered system, whereas CSFV growth was enhanced in PK-15 cells with RNF114 knockout by the CRISPR/Cas9 system. The RING domain of pRNF114, which has E3 ubiquitin ligase activity, is crucial for its antiviral activity. Mechanistically, pRNF114 interacted with the CSFV NS4B protein through their C-terminal domains, which led to the K27-linked polyubiquitination and degradation of NS4B through a proteasome-dependent pathway. Collectively, these findings indicate that pRNF114 as a critical regulator of CSFV replication and uncover a mechanism by which pRNF114 employs its E3 ubiquitin ligase activity to inhibit CSFV replication.

IMPORTANCE Porcine RING finger protein 114 (pRNF114) is a member of the RING domain E3 ligases. In this study, it was shown that pRNF114 is a potential anti-CSFV factor and the anti-CSFV effect of pRNF114 depends on its E3 ligase activity. Notably, pRNF114 targets and catalyzes the K27-linked polyubiquitination of the NS4B protein and then promotes proteasome-dependent degradation of NS4B, inhibiting the replication of CSFV. To our knowledge, pRNF114 is the first E3 ligase to be identified as being involved in anti-CSFV activity, and targeting NS4B could be a crucial route for antiviral development.

Expression of human ficolin-2 in hepatocytes confers resistance to infection by diverse hepatotropic viruses

The liver-expressed pattern recognition receptors mannose-binding lectin (MBL), ficolin-2 and ficolin-3 contribute to the innate immune response by activating complement. Binding of soluble ficolin-2 to viral pathogens can directly neutralize virus entry. We observed that the human hepatoma cell line HuH7.5, which is routinely used for the study of hepatotropic viruses, is deficient in expression of MBL, ficolin-2 and ficolin-3. We generated a cell line that expressed and secreted ficolin-2. This cell line (HuH7.5 [FCN2]) was more resistant to infection with hepatitis C virus (HCV), ebolavirus and vesicular stomatitis virus, but surprisingly was more susceptible to infection with rabies virus. Cell-to-cell spread of HCV was also inhibited in ficolin-2 expressing cells. This illustrates that ficolin-2 expression in hepatocytes contributes to innate resistance to virus infection, but some viruses might utilize ficolin-2 to facilitate entry.

Classical swine fever virus non-structural proteins modulate Toll-like receptor signaling pathways in porcine monocyte-derived macrophages

Toll-like receptors (TLRs) are crucial activators of the innate immune response that play various roles in viral infection. Studies have confirmed that classical swine fever virus (CSFV) infection has significant effects on the expression of immune effectors participating in TLR signaling pathways; however, the involvement of CSFV-encoded proteins in TLR signaling pathways remains unclear. In this study, lentiviral individually expressing CSFV non-structural proteins (NSPs) were constructed to identify the "key proteins" that affect TLR gene expression and to analyze the impacts of these proteins on factors downstream of the TLR signaling pathways. The results indicated that N^pro, NS2, NS3, NS3/4A, NS4B and NS5A all failed to induce the activation of NF-κB p65. Furthermore, NS4B was found to inhibit poly (I:C) stimulation-mediated activation of the TLR3 signaling pathway in porcine monocyte-derived macrophages (pMDMs), thereby suppressing the TRIF mRNA transcription, the IRF3 protein translation and the NF-κB p65 phosphorylation, and ultimately affecting the secretion of IL-6 and IFN-β; CSFV NS5A protein could significantly increase the activation of MyD88 and IRF7 as well as the consequent synthesis of IFN-α in pMDMs. The results suggest that CSFV NSPs affect TLR-mediated innate immune responses in pMDMs.