Human hepatitis B virus surface and e antigens inhibit major vault protein signaling in interferon induction pathways

Major vault protein directly enhances adaptive immunity induced by Influenza A virus or indirectly through innate immunity

As we previously revealed, major vault protein (MVP) is a virus-induced host factor, and its expression is crucial for innate immune responses. Nevertheless, the function of MVP in adaptive immunity is poorly known. Here, we demonstrate that Mvp knockout mice had attenuated antibody responses and reduced survival after rechallenge with homologous influenza A virus (IAV) relative to wild-type mice. Analysis of B cell populations showed that MVP promoted germinal center (GC) responses to develop optimal antiviral humoral immunity. Although MVP-deficient T cells and dendritic cells (DCs) were not intrinsically damaged, MVP promoted activating effector T cells and T follicular helper responses and regulated specific DC subsets. These findings suggest that MVP directs an effective adaptive immune response against IAV by directly engaging in GC reactions or indirectly augmenting cellular immunity via innate immune pathways.

MVP enhances FGF21-induced ferroptosis in hepatocellular carcinoma by increasing lipid peroxidation through regulation of NOX4

Ferroptosis is a novel, iron-dependent regulatory cell death mainly caused by an imbalance between the production and degradation of intracellular reactive oxygen species (ROS). Recently, ferroptosis induction has been considered a potential therapeutic approach for hepatocellular carcinoma (HCC). Fibroblast growth factor 21 (FGF21) is a new modulator of ferroptosis; however, the regulatory role of FGF21 in HCC ferroptosis has not been investigated. In this study, we explored the role of FGF21 and its underlying molecular mechanism in the ferroptotic death of HCC cells. We identified Major vault protein (MVP) as a target of FGF21 and revealed that knockdown of MVP inhibited the lipid peroxidation levels of HCC cells by decreasing NADPH oxidase 4 (NOX4, a major source of ROS) transcription, thereby attenuating the effect of FGF21-mediated ferroptosis. On the other hand, MVP overexpression showed the opposite results. Mechanistically, MVP binds to IRF1 and thus interferes with the interaction between IRF1 and the YAP1 promoter, leading to an increase in NOX4 transcription. Importantly, forced expression of IRF1 or downregulation of YAP1 partially reversed the effect of MVP overexpression on HCC ferroptosis. Furthermore, the results in xenograft tumor models suggested that overexpression of MVP can efficiently increase the level of lipid peroxidation in vivo. Taken together, these results provide new insights into the regulatory mechanism of ferroptosis in HCC.

Structural Insights into the Roles of PARP4 and NAD + in the Human Vault Cage

Vault is a massive ribonucleoprotein complex found across Eukaryota. The major vault protein (MVP) oligomerizes into an ovular cage, which contains several minor vault components (MVCs) and is thought to transport transiently bound "cargo" molecules. Vertebrate vaults house a poly (ADP-ribose) polymerase (known as PARP4 in humans), which is the only MVC with known enzymatic activity. Despite being discovered decades ago, the molecular basis for PARP4's interaction with MVP remains unclear. In this study, we determined the structure of the human vault cage in complex with PARP4 and its enzymatic substrate NAD + . The structures reveal atomic-level details of the protein-binding interface, as well as unexpected NAD + -binding pockets within the interior of the vault cage. In addition, proteomics data show that human vaults purified from wild-type and PARP4-depleted cells interact with distinct subsets of proteins. Our results thereby support a model in which PARP4's specific incorporation into the vault cage helps to regulate vault's selection of cargo and its subcellular localization. Further, PARP4's proximity to MVP's NAD + -binding sites could support its enzymatic function within the vault.

Advances in the understanding of circRNAs that influence viral replication in host cells

Circular RNAs (circRNAs) are non-coding RNAs discovered in recent years, which are produced by back-splicing involving the 3' and 5' ends of RNA molecules. There is increasing evidence that circRNAs have important roles in cancer, neurological diseases, cardiovascular and cerebrovascular diseases, and other diseases. In addition, host circRNAs and virus-encoded circRNAs participate in the body's immune response, with antiviral roles. This review summarizes the mechanisms by which host and viral circRNAs interact during the host immune response. Comprehensive investigations have revealed that host circRNAs function as miRNA sponges in a particular manner, primarily by inhibiting viral replication. Viral circRNAs have more diverse functions, which generally involve promoting viral replication. In addition, in contrast to circRNAs from RNA viruses, circRNAs from DNA viruses can influence host cell migration, proliferation, and apoptosis, along with their effects on viral replication. In summary, circRNAs have potential as diagnostic and therapeutic targets, offering a foundation for the diagnosis and treatment of viral diseases.

Expression and purification of Hepatitis B virus core antigen using Escherichia coli and its utilization for the diagnosis of Hepatitis B virus infections

Hepatitis B virus (HBV) is responsible for most of the viral hepatitis worldwide. HBV is a partially double stranded DNA virus that is composed of four main open reading frames (ORFs) encoding its important antigens, namely hepatitis B surface antigen (HBsAg), hepatitis B core antigen (HBcAg), HBV polymerase and hepatitis B X antigen (HBxAg). In this study, we report a successful method for the cloning and expression of HBcAg. The ORF of HBcAg was successfully amplified using polymerase chain reaction (PCR), cloned into the expression vector pRSET-B and transformed to Escherichia coli (E. coli) BL-21 (DE3) pLysS strain for protein expression. Successful expression of HBcAg was accomplished, in which an induced protein with a molecular weight of 24 kDa was obtained and confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. The produced HBcAg was successfully used for the diagnosis of HBV infected patient through detection of antibodies against HBcAg (anti-HBcAg) in the serum of the patient utilizing Western blotting. Overall, this study provides a simple, convenient and efficient protocol for the production of HBcAg that can be used as an important candidate to study the diagnosis and prognosis of HBV disease, as well as for understanding the epidemiological prevalence of HBV cases and production of anti-HBcAg.

Protein Structure Predictions, Atomic Model Building, and Validation Using a Cryo-EM Density Map from Hepatitis B Virus Spherical Subviral Particle

Hepatitis B virus (HBV) infection is a global public health concern. During chronic infection, the HBV small-surface antigen is expressed in large excess as non-infectious spherical subviral particles (SVPs), which possess strong immunogenicity. To date, attempts at understanding the structure of HBV spherical SVP have been restricted to 12-30 Å with contradictory conclusions regarding its architecture. We have used cryo-electron microscopy (cryo-EM) and 3D image reconstruction to solve the HBV spherical SVP to 6.3 Å. Here, we present an extended protocol on combining AlphaFold2 prediction with a moderate-resolution cryo-EM density map to build a reliable 3D model. This protocol utilizes multiple software packages that are routinely used in the cryo-EM community. The workflow includes 3D model prediction, model evaluation, rigid-body fitting, flexible fitting, real-space refinement, model validation, and model adjustment. Finally, the described protocol can also be applied to high-resolution cryo-EM datasets (2-4 Å).

The HBV web: An insight into molecular interactomes between the hepatitis B virus and its host en route to hepatocellular carcinoma

Hepatitis B virus (HBV) is a major aetiology associated with the development and progression of hepatocellular carcinoma (HCC), the most common primary liver malignancy. Over the past few decades, direct and indirect mechanisms have been identified in the pathogenesis of HBV-associated HCC which include altered signaling pathways, genome integration, mutation-induced genomic instability, chromosomal deletions and rearrangements. Intertwining of the HBV counterparts with the host cellular factors, though well established, needs to be systemized to understand the dynamics of host-HBV crosstalk and its consequences on HCC progression. Existence of a vast array of protein-protein and protein-nucleic acid interaction databases has led to the uncoiling of the compendia of genes/gene products associated with these interactions. This review covers the existing knowledge about the HBV-host interplay and brings it down under one canopy emphasizing on the HBV-host interactomics; and thereby highlights new strategies for therapeutic advancements against HBV-induced HCC.

Innate Immunity, Inflammation, and Intervention in HBV Infection

Hepatitis B virus (HBV) infection is still one of the most dangerous viral illnesses. HBV infects around 257 million individuals worldwide. Hepatitis B in many individuals ultimately develops hepatocellular carcinoma (HCC), which is the sixth most common cancer and the third leading cause of cancer-related deaths worldwide. The innate immunity acts as the first line of defense against HBV infection through activating antiviral genes. Along with the immune responses, pro-inflammatory cytokines are triggered to enhance the antiviral responses, but this may result in acute or chronic liver inflammation, especially when the clearance of virus is unsuccessful. To a degree, the host innate immune and inflammatory responses dominate the HBV infection and liver pathogenesis. Thus, it is crucial to figure out the signaling pathways involved in the activation of antiviral factors and inflammatory cytokines. Here, we review the interplay between HBV and the signal pathways that mediates innate immune responses and inflammation. In addition, we summarize current therapeutic strategies for HBV infection via modulating innate immunity or inflammation. Characterizing the mechanisms that underlie these HBV-host interplays might provide new approaches for the cure of chronic HBV infection.

Clinical impact and mechanisms of hepatitis B virus infection concurrent with non-alcoholic fatty liver disease

ABSTRACT

Chronic hepatitis B (CHB) virus infection is an important threat to global health despite the administration of vaccines and the use of antiviral treatments. In recent years, as the prevalence of obesity and metabolic syndrome has increased, non-alcoholic fatty liver disease (NAFLD) in patients with CHB has become more common. Both diseases can lead to liver fibrosis and even hepatocellular carcinoma, but the risk of dual etiology, outcome, and CHB combined with NAFLD is not fully elucidated. In this review, we assess the overlapping prevalence of NAFLD and CHB, summarize recent studies of clinical and basic research related to potential interactions, and evaluate the progressive changes of treatments for CHB patients with NAFLD. This review increases the understanding of the relationship and mechanisms of interaction between steatosis and hepatitis B virus infection, and it provides new strategies for the future clinical management and treatment of CHB combined with NAFLD.

miR-146a Maintains Immune Tolerance of Kupffer Cells and Facilitates Hepatitis B Virus Persistence in Mice

Kupffer cells (KCs), the largest tissue-resident macrophage population in the body, play a central role in maintaining a delicate balance between immune tolerance and immunity in the liver. However, the underlying molecular mechanism remains elusive. In this study, we show that KCs express high levels of miR-146a, which is under control of the PU.1 transcription factor. miR-146a deficiency promoted KCs differentiation toward a proinflammatory phenotype; conversely, miR-146a overexpression suppressed this phenotypic differentiation. We found that hepatitis B virus (HBV) persistence or HBV surface Ag treatment significantly upregulated miR-146a expression and thereby impaired polarization of KCs toward a proinflammatory phenotype. Furthermore, in an HBV carrier mouse model, KCs depletion by clodronate liposomes dramatically promoted HBV clearance and enhanced an HBV-specific hepatic CD8⁺ T cell and CD4⁺ T cell response. Consistent with this finding, miR-146a knockout mice cleared HBV faster and elicited a stronger adaptive antiviral immunity than wild-type mice. In vivo IL-12 blockade promoted HBV persistence and tempered the HBV-specific CTL response in the liver of miR-146a knockout mice. Taken together, our results identified miR-146a as a critical intrinsic regulator of an immunosuppressive phenotype in KCs under inflammatory stimuli, which may be beneficial in maintenance of liver homeostasis under physiological condition. Meanwhile, during HBV infection, miR-146a contributed to viral persistence by inhibiting KCs proinflammatory polarization, highlighting its potential as a therapeutic target in HBV infection.

Regulation of Pattern-Recognition Receptor Signaling by HBX During Hepatitis B Virus Infection

As a small DNA virus, hepatitis B virus (HBV) plays a pivotal role in the development of various liver diseases, including hepatitis, cirrhosis, and liver cancer. Among the molecules encoded by this virus, the HBV X protein (HBX) is a viral transactivator that plays a vital role in HBV replication and virus-associated diseases. Accumulating evidence so far indicates that pattern recognition receptors (PRRs) are at the front-line of the host defense responses to restrict the virus by inducing the expression of interferons and various inflammatory factors. However, depending on HBX, the virus can control PRR signaling by modulating the expression and activity of essential molecules involved in the toll-like receptor (TLR), retinoic acid inducible gene I (RIG-I)-like receptor (RLR), and NOD-like receptor (NLR) signaling pathways, to not only facilitate HBV replication, but also promote the development of viral diseases. In this review, we provide an overview of the mechanisms that are linked to the regulation of PRR signaling mediated by HBX to inhibit innate immunity, regulation of viral propagation, virus-induced inflammation, and hepatocarcinogenesis. Given the importance of PRRs in the control of HBV replication, we propose that a comprehensive understanding of the modulation of cellular factors involved in PRR signaling induced by the viral protein may open new avenues for the treatment of HBV infection.

IFITM3 Interacts with the HBV/HDV Receptor NTCP and Modulates Virus Entry and Infection

The Na+/taurocholate co-transporting polypeptide (NTCP, gene symbol SLC10A1) is both a physiological bile acid transporter and the high-affinity hepatic receptor for the hepatitis B and D viruses (HBV/HDV). Virus entry via endocytosis of the virus/NTCP complex involves co-factors, but this process is not fully understood. As part of the innate immunity, interferon-induced transmembrane proteins (IFITM) 1–3 have been characterized as virus entry-restricting factors for many viruses. The present study identified IFITM3 as a novel protein–protein interaction (PPI) partner of NTCP based on membrane yeast-two hybrid and co-immunoprecipitation experiments. Surprisingly, IFITM3 knockdown significantly reduced in vitro HBV infection rates of NTCP-expressing HuH7 cells and primary human hepatocytes (PHHs). In addition, HuH7-NTCP cells showed significantly lower HDV infection rates, whereas infection with influenza A virus was increased. HBV-derived myr-preS1 peptide binding to HuH7-NTCP cells was intact even under IFITM3 knockdown, suggesting that IFITM3-mediated HBV/HDV infection enhancement occurs in a step subsequent to the viral attachment to NTCP. In conclusion, IFITM3 was identified as a novel NTCP co-factor that significantly affects in vitro infection with HBV and HDV in NTCP-expressing hepatoma cells and PHHs. While there is clear evidence for a direct PPI between IFITM3 and NTCP, the specific mechanism by which this PPI facilitates the infection process remains to be identified in future studies.

Major Vault Protein Inhibits Porcine Reproductive and Respiratory Syndrome Virus Infection in CRL2843CD163 Cell Lines and Primary Porcine Alveolar Macrophages

Porcine reproductive and respiratory syndrome (PRRS), a significant viral infectious disease that commonly occurs among farmed pigs, leads to considerable economic losses to the swine industry worldwide. Major vault protein (MVP) is a host factor that induces type Ⅰ interferon (IFN) production. In this study, we evaluated the effect of MVP on PRRSV infection in CRL2843^CD163 cell lines and porcine alveolar macrophages (PAMs). Our results showed that MVP expression was downregulated by PRRSV infection. Adenoviral overexpression of MVP inhibited PRRSV replication, whereas the siRNA knockdown of MVP promoted PRRSV replication. In addition, MVP knockdown has an adverse effect on the inhibitive role of MVP overexpression on PRRSV replication. Moreover, MVP could induce the expression of type Ⅰ IFNs and IFN-stimulated gene 15 (ISG15) in PRRSV-infected PAMs. Based on these results, MVP may be a potential molecular target of drugs for the effective prevention and treatment of PRRSV infection.

Virus-Induced Tumorigenesis and IFN System

Oncogenic viruses favor the development of tumors in mammals by persistent infection and specific cellular pathways modifications by deregulating cell proliferation and inhibiting apoptosis. They counteract the cellular antiviral defense through viral proteins as well as specific cellular effectors involved in virus-induced tumorigenesis. Type I interferons (IFNs) are a family of cytokines critical not only for viral interference but also for their broad range of properties that go beyond the antiviral action. In fact, they can inhibit cell proliferation and modulate differentiation, apoptosis, and migration. However, their principal role is to regulate the development and activity of most effector cells of the innate and adaptive immune responses. Various are the mechanisms by which IFNs exert their effects on immune cells. They can act directly, through IFN receptor triggering, or indirectly by the induction of chemokines, the secretion of further cytokines, or by the stimulation of cells useful for the activation of particular immune cells. All the properties of IFNs are crucial in the host defense against viruses and bacteria, as well as in the immune surveillance against tumors. IFNs may be affected by and, in turn, affect signaling pathways to mediate anti-proliferative and antiviral responses in virus-induced tumorigenic context. New data on cellular and viral microRNAs (miRNAs) machinery, as well as cellular communication and microenvironment modification via classical secretion mechanisms and extracellular vesicles-mediated delivery are reported. Recent research is reviewed on the tumorigenesis induced by specific viruses with RNA or DNA genome, belonging to different families (i.e., HPV, HTLV-1, MCPyV, JCPyV, Herpesviruses, HBV, HCV) and the IFN system involvement.

The Functions of Hepatitis B Virus Encoding Proteins: Viral Persistence and Liver Pathogenesis

About 250 million people worldwide are chronically infected with Hepatitis B virus (HBV), contributing to a large burden on public health. Despite the existence of vaccines and antiviral drugs to prevent infection and suppress viral replication respectively, chronic hepatitis B (CHB) cure remains a remote treatment goal. The viral persistence caused by HBV is account for the chronic infection which increases the risk for developing liver cirrhosis and hepatocellular carcinoma (HCC). HBV virion utilizes various strategies to escape surveillance of host immune system therefore enhancing its replication, while the precise mechanisms involved remain elusive. Accumulating evidence suggests that the proteins encoded by HBV (hepatitis B surface antigen, hepatitis B core antigen, hepatitis B envelope antigen, HBx and polymerase) play an important role in viral persistence and liver pathogenesis. This review summarizes the major findings in functions of HBV encoding proteins, illustrating how these proteins affect hepatocytes and the immune system, which may open new venues for CHB therapies.

Role of IL-6-IL-27 Complex in Host Antiviral Immune Response

The IL family of cytokines participates in immune response and regulation. We previously found that soluble IL-6 receptor plays an important role in the host antiviral response. In this study, we detected the IL-6-IL-27 complex in serum and throat swab samples from patients infected with influenza A virus. A plasmid expressing the IL-6-IL-27 complex was constructed to explore its biological function. The results indicated that the IL-6-IL-27 complex has a stronger antiviral effect than the individual subunits of IL-6, IL-27A, and EBV-induced gene 3. Furthermore, the activity of the IL-6-IL-27 complex is mainly mediated by the IL-27A subunit and the IL-27 receptor α. The IL-6-IL-27 complex can positively regulate virus-triggered expression of IFN and IFN-stimulated genes by interacting with adaptor protein mitochondrial antiviral signaling protein, potentiating the ubiquitination of TNF receptor-associated factors 3 and 6 and NF-κB nuclear translocation. The secreted IL-6-IL-27 complex can induce the phosphorylation of STAT1 and STAT3 and shows antiviral activity. Our results demonstrate a previously unrecognized mechanism by which IL-6, IL-27A, and EBV-induced gene 3 form a large complex both intracellularly and extracellularly, and this complex acts in the host antiviral response.

HBsAg, Subviral Particles, and Their Clearance in Establishing a Functional Cure of Chronic Hepatitis B Virus Infection

In diverse viral infections, the production of excess viral particles containing only viral glycoproteins (subviral particles or SVP) is commonly observed and is a commonly evolved mechanism for immune evasion. In hepatitis B virus (HBV) infection, spherical particles contain the hepatitis B surface antigen, outnumber infectious virus 10 000-100 000 to 1, and have diverse inhibitory effects on the innate and adaptive immune response, playing a major role in the chronic nature of HBV infection. The current goal of therapies in development for HBV infection is a clinical outcome called functional cure, which signals a persistent and effective immune control of the infection. Although removal of spherical SVP (and the HBsAg they carry) is an important milestone in achieving functional cure, this outcome is rarely achieved with current therapies due to distinct mechanisms for assembly, secretion, and persistence of SVP, which are poorly targeted by direct acting antivirals or immunotherapies. In this Review, the current understanding of the distinct mechanisms involved in the production and persistence of spherical SVP in chronic HBV infection and their immunoinhibitory activity will be reviewed as well as current therapies in development with the goal of clearing spherical SVP and achieving functional cure.

Effect of oxidative stress and calcium deregulation on FAM26F (CALHM6) expression during hepatitis B virus infection

Background

Family with sequence similarity 26, member F (FAM26F) is an important innate immunity modulator playing a significant role in diverse immune responses, however, the association of FAM26F expression with HBV infection is not yet known. Thus, the current study aims to explore the differential expression of FAM26F in vitro in HepAD38 and HepG2 cell lines upon HBV infection, and in vivo in HBV infected individuals. The effects of antioxidant and calcium inhibitors on the regulation of FAM26F expression were also evaluated. The expression of FAM26F was simultaneously determined with well-established HBV infection markers: IRF3, and IFN-β.

Methods

The expression of FAM26F and marker genes was analyzed through Real-time qPCR and western blot.

Results

Our results indicate that the differential expression of FAM26F followed the same trend as that of IRF3 and IFN-β. The in vitro study revealed that, in both HBV infected cell lines, FAM26F expression was significantly down-regulated as compared to uninfected control cells. Treatment of cells with N-acetyl-L-cysteine (NAC), EGTA-AM, BAPTA-AM, and Ru360 significantly upregulated the expression of FAM26F in both the cell lines. Moreover, in in vivo study, FAM26F expression was significantly downregulated in all HBV infected groups as compared to controls (p = 0.0007). The expression was higher in the HBV recovered cases, probably due to the decrease in infection and increase in the immunity of these individuals.

Conclusion

Our study is the first to show the association of FAM26F with HBV infection. It is proposed that FAM26F expression could be an early predictive marker for HBV infection, and thus is worthy of further investigation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-05888-0.

Hepatitis B Surface Antigen Suppresses the Activation of Nuclear Factor Kappa B Pathway via Interaction With the TAK1-TAB2 Complex

Chronic hepatitis B is a major health problem worldwide, with more than 250 million chronic carriers. Hepatitis B virus interferes with the host innate immune system so as to evade elimination via almost all of its constituent proteins; nevertheless, the function of HBsAg with respect to immune escape remains unclear. This study aimed to determine the role HBsAg plays in assisting HBV to escape from immune responses. We found that HBsAg suppressed the activation of the nuclear factor kappa B (NF-кB) pathway, leading to downregulation of innate immune responses. HBsAg interacted with TAK1 and TAB2 specifically, inhibiting the phosphorylation and polyubiquitination of TAK1 and the K63-linked polyubiquitination of TAB2. Autophagy is a major catabolic process participating in many cellular processes, including the life cycle of HBV. We found that HBsAg promoted the autophagic degradation of TAK1 and TAB2 via the formation of complexes with TAK1 and TAB2, resulting in suppression of the NF-κB pathway. The expression of TAK1, TAB2, and the translocation of NF-κB inversely correlated with HBsAg levels in clinical liver tissues. Taken together, our findings suggest a novel mechanism by which HBsAg interacts with TAK1-TAB2 complex and suppresses the activation of NF-κB signaling pathway via reduction of the post-translational modifications and autophagic degradation.

The Vault Nanoparticle: A Gigantic Ribonucleoprotein Assembly Involved in Diverse Physiological and Pathological Phenomena and an Ideal Nanovector for Drug Delivery and Therapy

Simple Summary

In recent decades, a molecular complex referred to as vault nanoparticle has attracted much attention by the scientific community, due to its unique properties. At the molecular scale, it is a huge assembly consisting of 78 97-kDa polypeptide chains enclosing an internal cavity, wherein enzymes involved in DNA integrity maintenance and some small noncoding RNAs are accommodated. Basically, two reasons justify this interest. On the one hand, this complex represents an ideal tool for the targeted delivery of drugs, provided it is suitably engineered, either chemically or genetically; on the other hand, it has been shown to be involved in several cellular pathways and mechanisms that most often result in multidrug resistance. It is therefore expected that a better understanding of the physiological roles of this ribonucleoproteic complex may help develop new therapeutic strategies capable of coping with cancer progression. Here, we provide a comprehensive review of the current knowledge.

Abstract

The vault nanoparticle is a eukaryotic ribonucleoprotein complex consisting of 78 individual 97 kDa-“major vault protein” (MVP) molecules that form two symmetrical, cup-shaped, hollow halves. It has a huge size (72.5 × 41 × 41 nm) and an internal cavity, wherein the vault poly(ADP-ribose) polymerase (vPARP), telomerase-associated protein-1 (TEP1), and some small untranslated RNAs are accommodated. Plenty of literature reports on the biological role(s) of this nanocomplex, as well as its involvement in diseases, mostly oncological ones. Nevertheless, much has still to be understood as to how vault participates in normal and pathological mechanisms. In this comprehensive review, current understanding of its biological roles is discussed. By different mechanisms, vault’s individual components are involved in major cellular phenomena, which result in protection against cellular stresses, such as DNA-damaging agents, irradiation, hypoxia, hyperosmotic, and oxidative conditions. These diverse cellular functions are accomplished by different mechanisms, mainly gene expression reprogramming, activation of proliferative/prosurvival signaling pathways, export from the nucleus of DNA-damaging drugs, and import of specific proteins. The cellular functions of this nanocomplex may also result in the onset of pathological conditions, mainly (but not exclusively) tumor proliferation and multidrug resistance. The current understanding of its biological roles in physiological and pathological processes should also provide new hints to extend the scope of its exploitation as a nanocarrier for drug delivery.

Hepatitis B virus rigs the cellular metabolome to avoid innate immune recognition

Glucose metabolism and innate immunity evolved side-by-side. It is unclear if and how the two systems interact with each other during hepatitis B virus (HBV) infections and, if so, which mechanisms are involved. Here, we report that HBV activates glycolysis to impede retinoic acid-inducible gene I (RIG-I)-induced interferon production. We demonstrate that HBV sequesters MAVS from RIG-I by forming a ternary complex including hexokinase (HK). Using a series of pharmacological and genetic approaches, we provide in vitro and in vivo evidence indicating that HBV suppresses RLR signaling via lactate dehydrogenase-A-dependent lactate production. Lactate directly binds MAVS preventing its aggregation and mitochondrial localization during HBV infection. Therefore, we show that HK2 and glycolysis-derived lactate have important functions in the immune escape of HBV and that energy metabolism regulates innate immunity during HBV infection.

Hepatitis B surface antigen seroclearance: Immune mechanisms, clinical impact, importance for drug development

HBsAg seroclearance occurs rarely in the natural history of chronic hepatitis B (CHB) infection and is associated with improved clinical outcomes. Many factors are associated with HBsAg seroconversion, including immune and viral factors. However, the immune mechanisms associated with HBsAg seroclearance are still difficult to elucidate. HBsAg seroclearance is the ideal aim of HBV treatment. Unfortunately, this goal is rarely achieved with current treatments. Understanding the mechanisms of HBsAg loss appears to be important for the development of curative HBV treatments. While studies from animal models give insights into the potential immune mechanisms and interactions occurring between the immune system and HBsAg, they do not recapitulate all features of CHB in humans and are subject to variability due to their complexity. In this article, we review recent studies on these immune factors, focusing on their influence on CHB progression and HBsAg seroconversion. These data provide new insights for the development of therapeutic approaches to partially restore the anti-HBV immune response. Targeting HBsAg will ideally relieve the immunosuppressive effects on the immune system and help to restore anti-HBV immune responses.

Major Vault Protein Promotes Hepatocellular Carcinoma Through Targeting Interferon Regulatory Factor 2 and Decreasing p53 Activity

BACKGROUND AND AIMS

Major vault protein (MVP) is up-regulated during infections with hepatitis B virus (HBV) and hepatitis C virus (HCV). Here, we found that MVP deficiency inhibited hepatocellular carcinoma (HCC) development induced by diethylnitrosamine, hepatitis B X protein, and HCV core.

APPROACH AND RESULTS

Forced MVP expression was sufficient to induce HCC in mice. Mechanistic studies demonstrate that the ubiquitin ligase human double minute 2 (HDM2) forms mutual exclusive complexes either with interferon regulatory factor 2 (IRF2) or with p53. In the presence of MVP, HDM2 is liberated from IRF2, leading to the ubiquitination of the tumor suppressor p53. Mouse xenograft models showed that HBV and HCV promote carcinogenesis through MVP induction, resulting in a loss of p53 mediated by HDM2. Analyses of clinical samples from chronic hepatitis B, liver cirrhosis, and HCC revealed that MVP up-regulation correlates with several hallmarks of malignancy and associates with poor overall survival.

CONCLUSIONS

Taken together, through the sequestration of IRF2, MVP promotes an HDM2-dependent loss of p53 that promotes HCC development.

Major vault protein plays important roles in viral infection

Viral replication and related protein expression inside the host cells, and host antiviral immune responses can lead to the occurrence of diverse diseases. With the outbreak of viral infection, a large number of newly diagnosed and died patients infected with various viruses are still reported every year. Viral infection has already been one of the major global public health issues and lead to huge economic and social burdens. Studying of viral pathogenesis is a very important way to find methods for prevention, diagnosis, and cure of viral infection; more evidence has confirmed that major vault protein (MVP) is closely associated with viral infection and pathogenesis, and this review is intended to provide a broad relationship between viruses and MVP to stimulate the interest of related researchers.

Chronic hepatitis B and non-alcoholic fatty liver disease: Conspirators or competitors?

Despite the widespread use of vaccines and antiviral drugs, approximately 350-400 million patients with chronic hepatitis B (CHB) remain worldwide, who carry high risk of cirrhosis and liver carcinoma. Moreover, owing to improvements in global living standards and lifestyle changes, non-alcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease. Coexistence of NAFLD and CHB is commonly observed, especially in Asian CHB populations; however, little is known regarding the relationship between these two diseases as comorbidities. In this review, we summarize recent advances in clinical and basic researches related to the underlying mutual interactions, as well as potential animal models to facilitate further investigation.

TRIM30 modulates Interleukin-22-regulated papillary thyroid Cancer cell migration and invasion by targeting Sox17 for K48-linked Polyubiquitination

BACKGROUND

Interleukin-22 (IL-22) belongs to the IL-10 cytokine family and is mainly produced by activated Th1 cells. Although IL-22 expression is reported to be elevated in many cancers, and increased IL-22 expression correlates with tumor progression and poor prognosis, little is known about the role of IL-22 in papillary thyroid cancer (PTC). We previously demonstrated that IL-22 promotes PTC cell migration and invasion through the microRNA-595/Sox17 axis.

METHODS

We used qRT-PCR and western blot to determine TRIM30, Sox17 and β-catenin expression in PTC cells. Knockdown and overexpression were performed to detect the role of TRIM30/Sox17/β-catenin axis on the migration and invasion PTC cells. Co-IP were used to determine the interaction between TRIM30 and Sox17.

FINDINGS

In this study, we demonstrated that IL-22 triggered tripartite-motif protein 30 (TRIM30) association with Sox17, thereby mediating K48-linked polyubiquitination of Sox17. We then demonstrated that TRIM30 was a positive regulator of IL-22-regulated migration and invasion of PTC cells. We also found that IL-22 induced the transcriptional activity of β-catenin and translocation of β-catenin from cytosol to the nucleus. Upon investigating the mechanisms behind this event, we found that IL-22 disrupted Sox17/β-catenin interactions by inducing TRIM30/Sox17 interactions, leading to promotion of β-catenin-dependent signaling. The analysis of hundreds of clinical specimens revealed that IL-22, TRIM30 and β-catenin levels were upregulated in PTC tissues compared with normal thyroid, and that their expression levels were closely correlated. Taken together, under the influence of IL-22, by sequestration of Sox17, TRIM30 promotes β-catenin-dependent signaling that promotes PTC cell proliferation.

Type-I-IFN-Stimulated Gene TRIM5γ Inhibits HBV Replication by Promoting HBx Degradation

To understand the molecular mechanisms that mediate the anti-hepatitis B virus (HBV) effect of interferon (IFN) therapy, we conduct high-throughput bimolecular fluorescence complementation screening to identify potential physical interactions between the HBx protein and 145 IFN-stimulated genes (ISGs). Seven HBx-interacting ISGs have consistent and significant inhibitory effects on HBV replication, among which TRIM5γ suppresses HBV replication by promoting K48-linked ubiquitination and degradation of the HBx protein on the K95 ubiquitin site. The B-Box domain of TRIM5γ under overexpression conditions is sufficient to trigger HBx degradation and is responsible both for interacting with HBx and recruiting TRIM31, which is an ubiquitin ligase that triggers HBx ubiquitination. High expression levels of TRIM5γ in IFN-α-treated HBV patients might indicate a better therapeutic effect. Thus, our studies identify a crucial role for TRIM5γ and TRIM31 in promoting HBx degradation, which may facilitate the development of therapeutic agents for the treatment of patients with IFN-resistant HBV infection.

Inducible LGALS3BP/90K activates antiviral innate immune responses by targeting TRAF6 and TRAF3 complex

The galectin 3 binding protein (LGALS3BP, also known as 90K) is a ubiquitous multifunctional secreted glycoprotein originally identified in cancer progression. It remains unclear how 90K functions in innate immunity during viral infections. In this study, we found that viral infections resulted in elevated levels of 90K. Further studies demonstrated that 90K expression suppressed virus replication by inducing IFN and pro-inflammatory cytokine production. Upon investigating the mechanisms behind this event, we found that 90K functions as a scaffold/adaptor protein to interact with TRAF6, TRAF3, TAK1 and TBK1. Furthermore, 90K enhanced TRAF6 and TRAF3 ubiquitination and served as a specific ubiquitination substrate of TRAF6, leading to transcription factor NF-κB, IRF3 and IRF7 translocation from the cytoplasm to the nucleus. Conclusions: 90K is a virus-induced protein capable of binding with the TRAF6 and TRAF3 complex, leading to IFN and pro-inflammatory production.

The innate immune system detects the presence of viruses through germline-encoded pattern-recognition receptors (PRRs) and leads to the production of proinflammatory cytokines and interferons (IFNs) as the first line of defense against viral infections. Here, we identified a host protein, LGALS3BP, as a positive regulator of PRR-mediated signal transduction pathways by interacting with TRAF6-TAK1 and TRAF3-TBK1 axes, enhancing their recruitment and promoting the ubiquitination of TRAF6 and TRAF3. LGALS3BP exhibited antiviral activity toward a broad range of viral infections. LGALS3BP^-/- mice are highly susceptible to lethal influenza A virus infection with increasing pulmonary viral load, morbidity and mortality. Thus, our study highlight the importance of LGALS3BP in host antiviral innate immune responses.

Direct Inhibition of Hepatitis B e Antigen by Core Protein Allosteric Modulator

Hepatitis B e antigen (HBeAg) is an important immunomodulator for promoting host immune tolerance during chronic hepatitis B (CHB) infection. In patients with CHB, HBeAg loss and seroconversion represent partial immune control of CHB infection and are regarded as valuable endpoints. However, the current approved treatments have only a limited efficacy in achieving HBeAg seroconversion in HBeAg-positive patients. Hepatitis B virus (HBV) core protein has been recognized as an attractive antiviral target, and two classes of core protein allosteric modulator (CpAM) have been discovered: the phenylpropenamides (PPAs) and the heteroaryldihydropyrimidines (HAPs). However, their differentiation and potential therapeutic benefit beyond HBV DNA inhibition remain to be seen. Here, we show that in contrast to PPA series compound AT-130, a HAP CpAM, HAP_R01, reduced HBeAg levels in multiple in vitro and in vivo HBV experimental models. Mechanistically, we found that HAP_R01 treatment caused the misassembly of capsids formed by purified HBeAg in vitro. In addition, HAP_R01 directly reduces HBeAg levels by inducing intracellular precore protein misassembly and aggregation. Using a HAP_R01-resistant mutant, we found that HAP_R01-mediated HBeAg and core protein reductions were mediated through the same mechanism. Furthermore, HAP_R01 treatment substantially reduced serum HBeAg levels in an HBV mouse model. Conclusion: Unlike PPA series compound AT-130, HAP_R01 not only inhibits HBV DNA levels but also directly reduces HBeAg through induction of its misassembly. HAP_R01, as well as other similar CpAMs, has the potential to achieve higher anti-HBeAg seroconversion rates than currently approved therapies for patients with CHB. Our findings also provide guidance for dose selection when designing clinical trials with molecules from HAP series.

The Effect of the Hepatitis B Virus Surface Protein Truncated sC69∗ Mutation on Viral Infectivity and the Host Innate Immune Response

Viruses could rapidly diversify into variants, which has long been known to facilitate viral adaption in the host. Recent studies showed that cooperation among variants and wild-type (WT) also increased viral fitness. Here, a mutant of sC69^∗ in small hepatitis B surface protein (SHBs) that resulted in premature stop was investigated and the frequency of sC69^∗ was 4.37% (19/435), most of which coexisted with the WT (78.95%, 15/19), indicating mixed viral populations. Functional studies showed that sC69^∗ mutant was associated with lower viral spread, but could be rescued by coexisting with the WT. The sC69^∗ mutant showed to attenuate host innate immune response during infection and poly (I:C) treatment such as IL29, ISG15, and RIG-I (p < 0.05). The lower immune response was not caused by the lower replication of sC69^∗ mutant. Our data provide information that sC69^∗ coexisting with the WT might facilitate the fitness and persistence of the viral quasispecies in the host.

Major vault protein suppresses obesity and atherosclerosis through inhibiting IKK-NF-κB signaling mediated inflammation

Macrophage-orchestrated, low-grade chronic inflammation plays a pivotal role in obesity and atherogenesis. However, the underlying regulatory mechanisms remain incompletely understood. Here, we identify major vault protein (MVP), the main component of unique cellular ribonucleoprotein particles, as a suppressor for NF-κB signaling in macrophages. Both global and myeloid-specific MVP gene knockout aggravates high-fat diet induced obesity, insulin resistance, hepatic steatosis and atherosclerosis in mice. The exacerbated metabolic disorders caused by MVP deficiency are accompanied with increased macrophage infiltration and heightened inflammatory responses in the microenvironments. In vitro studies reveal that MVP interacts with TRAF6 preventing its recruitment to IRAK1 and subsequent oligomerization and ubiquitination. Overexpression of MVP and its α-helical domain inhibits the activity of TRAF6 and suppresses macrophage inflammation. Our results demonstrate that macrophage MVP constitutes a key constraint of NF-κB signaling thereby suppressing metabolic diseases.

Metabolic diseases are associated with chronic, low-grade inflammation. Here the authors show that major vault protein (MVP) suppresses NF-κB signalling in macrophages via an IRAK1–TRAF6 axis and that loss of MVP in myeloid cells exacerbates the inflammatory response in mice fed a high fat diet.

Epigenetic Modification Is Regulated by the Interaction of Influenza A Virus Nonstructural Protein 1 with the De Novo DNA Methyltransferase DNMT3B and Subsequent Transport to the Cytoplasm for K48-Linked Polyubiquitination

The influenza virus nonstructural protein 1 (NS1) is a nonstructural protein that plays a major role in antagonizing host interferon responses during infection. However, a clear role for the NS1 protein in epigenetic modification has not been established. In this study, NS1 was found to regulate the expression of some key regulators of JAK-STAT signaling by inhibiting the DNA methylation of their promoters. Furthermore, DNA methyltransferase 3B (DNMT3B) is responsible for this process. Upon investigating the mechanisms underlying this event, NS1 was found to interact with DNMT3B but not DNMT3A, leading to the dissociation of DNMT3B from the promoters of the corresponding genes. In addition, the interaction between NS1 and DNMT3B changed the localization of DNMT3B from the nucleus to the cytosol, resulting in K48-linked ubiquitination and degradation of DNMT3B in the cytosol. We conclude that NS1 interacts with DNMT3B and changes its localization to mediate K48-linked polyubiquitination, subsequently contributing to the modulation of the expression of JAK-STAT signaling suppressors.IMPORTANCE The nonstructural protein 1 (NS1) of the influenza A virus (IAV) is a multifunctional protein that counters cellular antiviral activities and is a virulence factor. However, the involvement of NS1 in DNA methylation during IAV infection has not been established. Here, we reveal that the NS1 protein binds the cellular DNMT3B DNA methyltransferase, thereby inhibiting the methylation of the promoters of genes encoding suppressors of JAK-STAT signaling. As a result, these suppressor genes are induced, and JAK-STAT signaling is inhibited. Furthermore, we demonstrate that the NS1 protein transports DNMT3B to the cytoplasm for ubiquitination and degradation. Thus, we identify the NS1 protein as a potential trigger of the epigenetic deregulation of JAK-STAT signaling suppressors and illustrate a novel mechanism underlying the regulation of host immunity during IAV infection.

Hepatitis B virus X protein-induced SH2 domain-containing 5 (SH2D5) expression promotes hepatoma cell growth via an SH2D5-transketolase interaction

Hepatitis B virus X protein (HBx) critically contributes to the development of hepatocellular carcinoma (HCC). However, the mechanisms by which HBx promotes HCC remain unclear. In the present study, using a combination of gene expression profiling and immunohistochemistry, we found higher levels of SH2 domain-containing 5 (SH2D5) in liver tissue from HBV-associated HCC (HBV-HCC) patients than in adjacent nontumor tissues. Moreover, HBV infection elevated SH2D5 levels, and we observed that HBx plays an important role in SH2D5 induction. We also found that HBx triggers SH2D5 expression through the NF-κB and c-Jun kinase pathways. Employing SH2D5 overexpression or knockdown, we further demonstrate that SH2D5 promotes HCC cell proliferation both in vitro and in vivo While investigating the mechanism of SH2D5-mediated stimulation of HCC cell proliferation, we noted that HBV induces SH2D5 binding to transketolase (TKT), a pentose phosphate pathway enzyme, thereby promoting an interaction between and signal transducer and activator of transcription 3 (STAT3). Furthermore, HBx stimulated STAT3 phosphorylation at Tyr-705 and promoted the activity and downstream signaling pathway of STAT3 via the SH2D5-TKT interaction. Taken together, our results suggest that SH2D5 is an HBV-induced protein capable of binding to TKT, leading to induction of HCC cell proliferation.

Zebrafish MVP Recruits and Degrades TBK1 To Suppress IFN Production

IFN production is crucial for hosts to defend against viral infection, yet it must be tightly controlled to maintain immune homeostasis. TANK-binding kinase 1 (TBK1) is a pivotal kinase in the IFN induction signaling pathway, but it is negatively regulated by multiple molecules to avoid the excessive expression of IFN in mammals. However, the identified TBK1 suppressors and the mechanisms are rare in fish. In this study, we show that zebrafish major vault protein (MVP) recruits and degrades TBK1 in a lysosome-dependent manner to inhibit IFN production. Through viral infection, polyinosinic:polycytidylic acid and RIG-I-like receptor factor stimulation upregulated IFN expression, but overexpression of MVP significantly subverted these inductions. On the protein level, MVP interacted with TBK1, and interestingly, MVP recruited TBK1 from a uniformly distributed state in the cytoplasm to an aggregated state. Finally, MVP mediated the lysosome-dependent degradation of TBK1 and decreased the IFN response and IFN-stimulated genes expression. Our findings reveal that zebrafish MVP is a negative regulator of IFN production by restricting the activation of TBK1, supplying evidence of the balanced mechanisms of IFN expression in lower vertebrates.

Identification of TRIM14 as a Type I IFN-Stimulated Gene Controlling Hepatitis B Virus Replication by Targeting HBx

Hepatitis B virus (HBV) remains a major cause of hepatic disease that threatens human health worldwide. Type I IFN (IFN-I) therapy is an important therapeutic option for HBV patients. The antiviral effect of IFN is mainly mediated via upregulation of the expressions of the downstream IFN-stimulated genes. However, the mechanisms by which IFN induces ISG production and inhibits HBV replication are yet to be clarified. TRIM14 was recently reported as a key molecule in the IFN-signaling pathway that regulates IFN production in response to viral infection. In this study, we sought to understand the mechanisms by which IFN restricts HBV replication. We confirmed that TRIM14 is an ISG in the hepatic cells, and that the pattern-recognition receptor ligands polyI:C and polydAdT induce TRIM14 dependent on IFN-I production. In addition, IFN-I-activated STAT1 (but not STAT3) directly bound to the TRIM14 promoter and mediated the induction of TRIM14. Interestingly, TRIM14 played an important role in IFN-I-mediated inhibition of HBV, and the TRIM14 SPRY domain interacted with the C-terminal of HBx, which might block the role of HBx in facilitating HBV replication by inhibiting the formation of the Smc-HBx–DDB1 complex. Thus, our study clearly demonstrates that TRIM14 is a STAT1-dependent ISG, and that the IFN-I–TRIM14–HBx axis shows an alternative way to understand the mechanism by which IFN-I inhibits virus replication.

When Hepatitis B Virus Meets Interferons

Chronic hepatitis B virus (HBV) infection imposes a severe burden on global public health. Currently, there are no curative therapies for millions of chronic HBV-infected patients (Lok et al., 2017). Interferon (IFN; including pegylated IFN) is an approved anti-HBV drug that not only exerts direct antiviral activity, but also augments immunity against HBV infection. Through a systematic review of the literature, here we summarize and present recent progress in research regarding the interactions between IFN and HBV as well as dissect the antiviral mechanisms of IFN. We focus on inhibition of HBV replication by IFN-stimulated genes (ISGs) as well as inhibition of IFN signaling by HBV and viral proteins. Finally, we briefly discuss current IFN-based HBV treatment strategies. This review may help to better understand the mechanisms involved in the therapeutic action of IFN as well as the crosstalk between IFN and HBV, and facilitate the development of both direct-acting and immunology-based new HBV drugs.

MicroRNA-302 Cluster Downregulates Enterovirus 71-Induced Innate Immune Response by Targeting KPNA2

Enterovirus 71 (EV71) induces significantly elevated levels of cytokines and chemokines, leading to local or systemic inflammation and severe complications. As shown in our previous study, microRNA (miR) 302c regulates influenza A virus-induced IFN expression by targeting NF-κB-inducing kinase. However, little is known about the role of the miR-302 cluster in EV71-mediated proinflammatory responses. In this study, we found that the miR-302 cluster controls EV71-induced cytokine expression. Further studies demonstrated that karyopherin α2 (KPNA2) is a direct target of the miR-302 cluster. Interestingly, we also found that EV71 infection upregulates KPNA2 expression by downregulating miR-302 cluster expression. Upon investigating the mechanisms behind this event, we found that KPNA2 intracellularly associates with JNK1/JNK2 and p38, leading to translocation of those transcription factors from the cytosol into the nucleus. In EV71-infected patients, miR-302 cluster expression was downregulated and KPNA2 expression was upregulated compared with controls, and their expression levels were closely correlated. Taken together, our work establishes a link between the miR-302/ KPNA2 axis and EV71-induced cytokine expression and represents a promising target for future antiviral therapy.

Hepatitis B Virus Does Not Interfere With Innate Immune Responses in the Human Liver

BACKGROUND & AIMS

Most viruses are detected at early stages of cell infection and induce an innate immune response mediated by production of interferons (IFNs). IFNs induce expression of hundreds of IFN-stimulated genes (ISGs). Infection of chimpanzees with hepatitis C virus, but not hepatitis B virus (HBV), induces ISG expression in the liver. HBV might not induce an innate immune response because it is not detected by pattern recognition receptors (the stealth properties of HBV) or because HBV suppresses IFN production or signaling despite detection by pattern recognition receptors. We studied innate immune signaling in liver biopsies from patients with different stages of chronic HBV infection and uninfected individuals (controls).

METHODS

We obtained liver within 10 minutes after collection from 30 patients with chronic HBV infection (hepatitis B e antigen-positive or -negative, with or without hepatitis) and 42 controls (most with fatty liver disease). The liver tissues were analyzed by histology, immunohistochemistry, quantitative reverse-transcription polymerase chain reaction, in situ hybridization, HBV RNA quantification, and HBV genotyping; some specimens were incubated with toll-like receptor (TLR) ligands (polyinosinic-polycytidylic acid) or infected with Sendai virus and then analyzed.

RESULTS

Liver specimens from patients with HBV infection were not expressing more IFN or ISGs than those from control patients, indicating that chronic HBV infection did not activate an innate immune response. However, liver specimens from patients with HBV infection did produce IFN and induce expression of ISGs following activation of TLR3 with poly(I:C) or Sendai virus infections, so the innate immune response is not suppressed in these tissues.

CONCLUSION

Liver tissues from patients with chronic HBV infection do not have induction of an innate immune response, but this response can be activated by other factors (TLR3 binding, Sendai virus infection) in HBV-infected liver tissue. These findings support the hypothesis that HBV is invisible to pattern recognition receptors.

MicroRNA-302a suppresses influenza A virus-stimulated interferon regulatory factor-5 expression and cytokine storm induction

During influenza A virus (IAV) infection, cytokine storms play a vital and critical role in clinical outcomes. We have previously reported that microRNA (miR)-302c regulates IAV-induced IFN expression by targeting the 3'-UTR of nuclear factor κB (NF-κB)-inducing kinase. In the current study, we found that miR-302a, another member of the miR-302 cluster, controls the IAV-induced cytokine storm. According to results from cell-based and knockout mouse models, IAV induces a cytokine storm via interferon regulatory factor-5 (IRF-5). We also found that IAV infection up-regulates IRF-5 expression and that IRF-5 in turn promotes IAV replication. Furthermore, we observed that IRF-5 is a direct target of miR-302a, which down-regulated IRF-5 expression by binding its 3'-UTR. Moreover, IAV increased IRF-5 expression by down-regulating miR-302a expression. Interestingly, miR-302a inhibited IAV replication. In IAV-infected patients, miR-302a expression was down-regulated, whereas IRF-5 expression was up-regulated. Taken together, our work uncovers and defines a signaling pathway implicated in an IAV-induced cytokine storm.

Immune Evasion Strategies during Chronic Hepatitis B and C Virus Infection

Both hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are a major global healthcare problem with more than 240 million and 70 million infected, respectively. Both viruses persist within the liver and result in progressive liver disease, resulting in liver fibrosis, cirrhosis and hepatocellular carcinoma. Strikingly, this pathogenesis is largely driven by immune responses, unable to clear an established infection, rather than by the viral pathogens themselves. Even though disease progression is very similar in both infections, HBV and HCV have evolved distinct mechanisms, by which they ensure persistence within the host. Whereas HCV utilizes a cloak-and-dagger approach, disguising itself as a lipid-like particle and immediately crippling essential pattern-recognition pathways, HBV has long been considered a "stealth" virus, due to the complete absence of innate immune responses during infection. Recent developments and access to improved model systems, however, revealed that even though it is among the smallest human-tropic viruses, HBV may, in addition to evading host responses, employ subtle immune evasion mechanisms directed at ensuring viral persistence in the absence of host responses. In this review, we compare the different strategies of both viruses to ensure viral persistence by actively interfering with viral recognition and innate immune responses.

The Us2 Gene Product of Herpes Simplex Virus 2 modulates NF-κB activation by targeting TAK1

HSV-2 is one of the most common sexually transmitted pathogens worldwide and HSV-2 infection triggers cytokine and chemokine production. However, little is known about which HSV-2 genes engage in the regulation of NF-κB signaling and what mechanisms are involved. In a screen of the unique short (Us) regions of HSV-2, we observed that HSV-2 Us2 activates NF-κB signaling. We additionally indicated that deficiencies of Us2 decrease HSV-2 WT mediated NF-κB activation and cytokine and chemokine production, and overexpression of Us2 showed opposite effects. Co-immunoprecipitations indicated that Us2 interacted with TGF-β activated kinase 1 (TAK1), a serine/threonine kinase essential for NF-κB activation, and Us2 has the ability to regulate the TAK1-mediated pathway and induces TAK1 downstream signaling. Further studies verified that Us2 induced the phosphorylation of TAK1, resulting in the activation of TAK1 mediated downstream signaling. The role of Us2 in HSV-2 induced NF-κB pathways was also confirmed in the Us2-deficient mutant and HSV-2 WT infected mice. Our results indicate that HSV-2 Us2 gene product binds to TAK1 to positively regulate NF-κB signaling and, for the first time, provide insights into the molecular mechanism.

New treatments to reach functional cure: Rationale and challenges for emerging immune-based therapies

The landscape for chronic HBV therapy is rapidly evolving. The latest generation of antiviral drugs provide robust virus suppression with a high barrier to resistance that facilitates long-term treatment. However, low rates of HBsAg loss demonstrate that additional strategies are needed to consistency achieve a functional cure. The immune system can clear HBV and establish long-term control over the virus. Sufficiently boosting HBV immunity in chronic patients has been very difficult due to immune exhaustion, immune dysregulation, and inhibitory pathways suppressing the immune response. Therapeutic vaccines employing new technology, vectors and new immunomodulatory drugs that can elicit direct antiviral effects and cancel inhibitory mechanism may be able to overcome exhaustion. This review will discuss the justification for immunotherapy, lessons from previous trials and new vaccines/drugs in early stage clinical trials. The challenges of correlating immune responses induced by these drugs to clinical efficacy will also be addressed.

Inducible Rubicon facilitates viral replication by antagonizing interferon production

The RUN domain Beclin-1-interacting cysteine-rich-containing (Rubicon) protein is involved in the maturation step of autophagy and the endocytic pathway as a Beclin-1-binding partner, but little is known regarding the role of Rubicon during viral infection. Here, we performed functional studies of the identified target in interferon (IFN) signaling pathways associated with Rubicon to elucidate the mechanisms of viral resistance to IFN. The Rubicon protein levels were elevated in peripheral blood mononuclear cells, sera and liver tissues from patients with hepatitis B virus (HBV) infection relative to those in healthy individuals. Assays of the overexpression and knockdown of Rubicon showed that Rubicon significantly promoted HBV replication. In addition, Rubicon knockdown resulted in the inhibition of enterovirus 71, influenza A virus and vesicular stomatitis virus. The expression o0f Rubicon led to the suppression of virus-induced type-I interferon (IFN-α and IFN-β) and type-III interferon (IFN-λ1). Translocation of activated IRF3 and IRF7 from the cytoplasm to the nucleus was involved in this process, and the NF-κB essential modulator (NEMO), a key factor in the IFN pathway, was the target with which Rubicon interacted. Our results reveal a previously unrecognized function of Rubicon as a virus-induced protein that binds to NEMO, leading to the inhibition of type-I interferon production. Rubicon thus functions as an important negative regulator of the innate immune response, enhances viral replication and may play a role in viral immune evasion.

Inducible GBP5 Mediates the Antiviral Response via Interferon-Related Pathways during Influenza A Virus Infection

Guanylate binding protein (GBP) 5 belongs to the GBP family, which is involved in important cellular processes, including signal transduction, translation, vesicle trafficking, and exocytosis. Structurally, GBPs display a high degree of homology and share highly conserved GTP-binding or hydrolysis domains. GBP5 was reported to be a critical cellular factor in inflammasome assembly. However, little is known about its role in the host antiviral innate immune response. In this study, we found that GBP5 expression was significantly elevated in influenza patients and influenza A virus-infected A549 human lung epithelial cells. The overexpression of GBP5 inhibited virus replication by enhancing the expression of virus-induced interferon (IFN) and IFN-related effectors. Knockdown of GBP5 had the opposite effect. Moreover, GBP5 enhanced endogenous IFN expression by interacting with the NF-κB-essential modulator complex and stimulating NF-κB signaling. Additionally, the expression of proinflammatory factors, such as IL-6, IL-8, tumor necrosis factor-α, cyclooxygenase-2, and inducible nitric oxide synthase, was also activated by GBP5. Taken together, our results reveal that GBP5 inhibited virus replication through the activation of IFN signaling and proinflammatory factors.

HBV inhibits LPS-induced NLRP3 inflammasome activation and IL-1β production via suppressing the NF-κB pathway and ROS production

BACKGROUND & AIMS

Hepatitis B virus (HBV) has developed strategies to evade immune responses. However, the mechanisms involved remain unclear. The NLRP3 inflammasome plays crucial roles in antiviral host defense and its downstream factor IL-1β has been shown to inhibit HBV infection in vivo. This study aims to assess whether HBV can affect the NLRP3 inflammasome signaling pathways and shed light on the underlying mechanisms HBV utilizes to evade host innate immune responses.

METHODS

HBV inhibition of the lipopolysaccharide (LPS)-induced NLRP3 inflammasome activation was evaluated by Western blot, quantitative RT-PCR, flow cytometry and immunofluorescence.

RESULTS

Kupffer cells expressed significantly more NLRP3 and IL-1β after LPS stimulation; whereas, chronic HBV infection suppressed LPS-induced NLRP3 and pro-IL-1β expression as well as IL-1β maturation. This inhibitory activity is mediated by HBeAg, and is involved in the inhibition of NF-κB signal pathway and reactive oxygen species (ROS) production. The inhibitory effect of HBeAg was confirmed in patients with chronic hepatitis B (CHB) and hepatocellular carcinoma by comparing the levels of IL-1β and NLRP3-related proteins in para-carcinoma tissues from HBeAg-positive or negative patients. Moreover, chronic HBV infection increases the susceptibility of mice to S. typhimurium infection, possibly via inhibiting the NLRP3 inflammasome activation and IL-1β production.

CONCLUSIONS

HBeAg inhibits LPS-induced NLRP3 inflammasome activation and IL-1β production via suppressing NF-κB pathway and ROS production. This finding provides a novel mechanism for HBV-mediated suppression of innate immune responses, and identifies new therapeutic targets for chronic HBV infection and related diseases.

LAY SUMMARY

HBeAg suppresses LPS-induced NLRP3 inflammasome activation and IL-1β production in two ways, one is to repress NLRP3 and pro-IL-1β expression via inhibiting NF-κB phosphorylation, and the other is to repress caspase-1 activation and IL-1β maturation via inhibiting ROS production. This effect contributes to the HBV persistence and immune tolerance.

Inducible TAP1 Negatively Regulates the Antiviral Innate Immune Response by Targeting the TAK1 Complex

The innate immune response is critical for host defense and must be tightly controlled, but the molecular mechanisms responsible for its negative regulation are not yet completely understood. In this study, we report that transporter 1, ATP-binding cassette, subfamily B (TAP1), a virus-inducible endoplasmic reticulum-associated protein, negatively regulated the virus-triggered immune response. In this study, we observed upregulated expression of TAP1 following virus infection in human lung epithelial cells (A549), THP-1 monocytes, HeLa cells, and Vero cells. The overexpression of TAP1 enhanced virus replication by inhibiting the virus-triggered activation of NF-κB signaling and the production of IFNs, IFN-stimulated genes, and proinflammatory cytokines. TAP1 depletion had the opposite effect. In response to virus infection, TAP1 interacted with the TGF-β-activated kinase (TAK)1 complex and impaired the phosphorylation of TAK1, subsequently suppressing the phosphorylation of the IκB kinase complex and NF-κB inhibitor α (IκBα) as well as NF-κB nuclear translocation. Our findings collectively suggest that TAP1 plays a novel role in the negative regulation of virus-triggered NF-κB signaling and the innate immune response by targeting the TAK1 complex.

Type I IFN augments IL-27-dependent TRIM25 expression to inhibit HBV replication

Hepatitis B virus (HBV) can cause chronic hepatitis B, which may lead to cirrhosis and liver cancer. Type I interferon (IFN) is an approved drug for the treatment of chronic hepatitis B. However, the fundamental mechanisms of antiviral action by type I IFN and the downstream signaling pathway are unclear. TRIM25 is an IFN-stimulated gene (ISG) that has an important role in RIG-I ubiquitination and activation. Whether TRIM25 is induced in liver cells by type I IFN to mediate anti-HBV function remains unclear. Here we report that interleukin-27 (IL-27) has a critical role in IFN-induced TRIM25 upregulation. TRIM25 induction requires both STAT1 and STAT3. In TRIM25 knockout HepG2 cells, type I IFN production was consistently attenuated and HBV replication was increased, whereas overexpression of TRIM25 in HepG2 cells resulted in elevated IFN production and reduced HBV replication. More interestingly, we found that TRIM25 expression was downregulated in HBV patients and the addition of serum samples from HBV patients could inhibit TRIM25 expression in HepG2 cells, suggesting that HBV might have involved a mechanism to inhibit antiviral ISG expression and induce IFN resistance. Collectively, our results demonstrate that type I IFN -induced TRIM25 is an important factor in inhibiting HBV replication, and the IFN-IL-27-TRIM25 axis may represent a new target for treating HBV infection.

Soluble IL-6 Receptor and IL-27 Subunit p28 Protein Complex Mediate the Antiviral Response through the Type III IFN Pathway

Previously, we demonstrated that the soluble IL-6R (sIL-6R) plays an important role in the host antiviral response through induction of type I IFN and sIL-6R-mediated antiviral action via the IL-27 subunit p28; however, the mechanism that underlies sIL-6R and p28 antiviral action and whether type III IFN is involved remain unknown. In this study, we constructed a sIL-6R and p28 fusion protein (sIL-6R/p28 FP) and demonstrated that the fusion protein has stronger antiviral activity than sIL-6R alone. Consequently, knockout of sIL-6R inhibited virus-triggered IFN-λ1 expression. In addition, sIL-6R/p28 FP associated with mitochondrial antiviral signaling protein and TNFR-associated factor 6, the retinoic acid-inducible gene I adapter complex, and the antiviral activity mediated by sIL-6R/p28 FP was dependent on mitochondrial antiviral signaling protein. Furthermore, significantly reduced binding of p50/p65 and IFN regulatory factor 3 to the IFN-λ1 promoter was observed in sIL-6R knockout cells compared with the control cells. Interestingly, a novel heterodimer of c-Fos and activating transcription factor 1 was identified as a crucial transcriptional activator of IFN-λ1 The sIL-6R/p28 FP upregulated IFN-λ1 expression by increasing the binding abilities of c-Fos and activating transcription factor 1 to the IFN-λ1 promoter via the p38 MAPK signaling pathway. In conclusion, these results demonstrate the important role of sIL-6R/p28 FP in mediating virus-induced type III IFN production.

The link between TLR7 signaling and hepatitis B virus infection

Toll-Like Receptors (TLRs) play crucial roles in recognition and induction of appropriate immune responses against viral infections, including hepatitis B. TLR7 detects intracellular viral single strand RNA which leads to the activation of several pro-inflammatory transcription factors via the MYD88 dependent pathway. Patients with prolonged infectious forms of hepatitis B, including active and inactive chronic forms, are unable to clear HBV from hepatocytes completely. It is believed that the differences in genetic and immunological parameters of the patients and clearance subjects, who successfully clear HBV infections, are the main factors responsible for allowing the long term infections to persist. It appears that defective expression of TLR7 may result in impaired immune responses against HBV. The aim of this review is to address the recent information regarding the crucial roles played by TLR7 in hepatitis B infection and also the main mechanisms used by HBV to escape from recognition by TLR7 in prolonged HBV infected patients. Considering that chronic hepatitis B infection is not yet curable, it could be possible to activate TLR7-related immunological pathways as a therapy directed towards persistent HBV infection. Hence, another aim of this study is to present recent developments of TLR7 agonists as a therapeutic strategy for chronic hepatitis B.