DNA-dependent activator of interferon-regulatory factors inhibits hepatitis B virus replication

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.

STING, a promising target for small molecular immune modulator: A review

Stimulator of interferon genes (STING) plays a crucial role in human innate immune system, which is gradually concerned following the emerging immunotherapy. Activated STING induces the production of type I interferons (IFNs) and proinflammatory cytokines through STING-TBK1-IRF3/NF-κB pathway, which could be applied into the treatment of infection, inflammation, and tumorigenesis. Here, we provided a detailed summary of STING from its structure, function and regulation. Especially, we illustrated the canonical or noncanonical cyclic dinucleotides (CDNs) and synthetic small molecules for STING activation or inhibition and their efficacy in related diseases. Importantly, we particularly emphasized the discovery, development and modification of STING agonist or antagonist, attempting to enlighten reader's mind for enriching small molecular modulator of STING. In addition, we summarized biological evaluation methods for the assessment of small molecules activity.

Hepatitis B Virus Might Be Sensed by STING-Dependent DNA Sensors and Attenuates the Response of STING-Dependent DNA Sensing Pathway in Humans with Acute and Chronic Hepatitis B Virus Infection

DNA-dependent activator of interferon regulatory factors (DAIs), interferon gamma inducible protein 16 (IFI16), DEAD-box polypeptide 41 (DDX41), DNA-dependent protein kinase (DNA-PK), meiotic recombination 11 homolog A (MRE11), and cyclic GMP-AMP synthase (cGAS) have been identified as intracellular STING-dependent DNA sensors in recent years. Studies have shown that the DNA sensor-STING-interferon (IFN)-β pathway plays an important role in the defense against intracellular invasion of many DNA viruses. However, the intracellular recognition of hepatitis B virus (HBV) DNA by DNA sensors is still largely unclear. In this study, we aimed to determine whether the DNA sensor-STING pathway in peripheral blood mononuclear cells (PBMCs) can be activated by acute and chronic HBV infections in humans. We first evaluated the expression of these DNA sensors in PBMCs of acute and chronic HBV-infected patients by quantitative real-time polymerase chain reaction. We next compared the expression of the upregulated DNA sensor between monocytes and nonmonocytes to find its cellular source. Finally, by in vitro stimulation, we analyzed the IFN-β response of the DNA sensor-STING pathway in PBMCs and monocytes from chronic HBV-infected patients. The results showed that IFI16, DDX41, MRE11, and the adaptor STING were upregulated in chronic HBV-infected patients, whereas only IFI16 was upregulated in acute HBV-infected patients. However, IFN-β expression was not changed in PBMCs from acute and chronic HBV-infected patients. We next found IFI16 was mainly expressed in monocytes of acute and chronic hepatitis B patients. Finally, by stimulation of monocytes with VACV ds 70mer, a ligand for IFI16, we confirmed the attenuated response of the IFI16-STING pathway. Taken together, our results suggest that HBV might be sensed by DNA sensors in PBMCs of acute and chronic HBV-infected patients, and meanwhile HBV infection attenuates the response of the DNA sensor-STING pathway in PBMCs and monocytes, which may facilitate the persistence of HBV infection.

Japan Society of Hepatology Guidelines for the Management of Hepatitis B Virus Infection: 2019 update

The Drafting Committee for Hepatitis Management Guidelines established by the Japan Society of Hepatology published the first version of the Guidelines for the Management of Hepatitis B in 2013 (first English version in 2014), and has since been publishing updates to the Guidelines as new drugs become available, with the latest original Japanese version being Version 3.1. Herein, the Drafting Committee publishes the second English version that contains all the changes made since the first English version of the guidelines was published in 2014. This 2019 version covers: (i) the nucleos(t)ide analogs, tenofovir disoproxil fumarate and tenofovir alafenamide; (ii) updates to treatment recommendations and management of drug-resistant hepatitis B virus that reflect the new availability of these drugs; and (iii) new information about hepatitis B virus reactivation with each update. This latest update also contains information about treatment goals, indications for treatment and cessation of nucleos(t)ide analog therapy, most of which were covered by the first version.

SAMD4 family members suppress human hepatitis B virus by directly binding to the Smaug recognition region of viral RNA

HBV infection initiates hepatitis B and promotes liver cirrhosis and hepatocellular carcinoma. IFN-α is commonly used in hepatitis B therapy, but how it inhibits HBV is not fully understood. We screened 285 human interferon-stimulated genes (ISGs) for anti-HBV activity using a cell-based assay, which revealed several anti-HBV ISGs. Among these ISGs, SAMD4A was the strongest suppressor of HBV replication. We found the binding site of SAMD4A in HBV RNA, which was a previously unidentified Smaug recognition region (SRE) sequence conserved in HBV variants. SAMD4A binds to the SRE site in viral RNA to trigger its degradation. The SAM domain in SAMD4A is critical for RNA binding and the C-terminal domain of SAMD4A is required for SAMD4A anti-HBV function. Human SAMD4B is a homolog of human SAMD4A but is not an ISG, and the murine genome encodes SAMD4. All these SAMD4 proteins suppressed HBV replication when overexpressed in vitro and in vivo. We also showed that knocking out the Samd4 gene in hepatocytes led to a higher level of HBV replication in mice and AAV-delivered SAMD4A expression reduced the virus titer in HBV-producing transgenic mice. In addition, a database analysis revealed a negative correlation between the levels of SAMD4A/B and HBV in patients. Our data suggest that SAMD4A is an important anti-HBV ISG for use in IFN therapy of hepatitis B and that the levels of SAMD4A/B expression are related to HBV sensitivity in humans.

Tumour viruses and innate immunity

Host cells sense viral infection through pattern recognition receptors (PRRs), which detect pathogen-associated molecular patterns (PAMPs) and stimulate an innate immune response. PRRs are localized to several different cellular compartments and are stimulated by viral proteins and nucleic acids. PRR activation initiates signal transduction events that ultimately result in an inflammatory response. Human tumour viruses, which include Kaposi's sarcoma-associated herpesvirus, Epstein-Barr virus, human papillomavirus, hepatitis C virus, hepatitis B virus, human T-cell lymphotropic virus type 1 and Merkel cell polyomavirus, are detected by several different PRRs. These viruses engage in a variety of mechanisms to evade the innate immune response, including downregulating PRRs, inhibiting PRR signalling, and disrupting the activation of transcription factors critical for mediating the inflammatory response, among others. This review will describe tumour virus PAMPs and the PRRs responsible for detecting viral infection, PRR signalling pathways, and the mechanisms by which tumour viruses evade the host innate immune system.This article is part of the themed issue 'Human oncogenic viruses'.

Association between IRF1 Gene Expression and Liver Enzymes in HBV-infected Liver Transplant Recipients with and without Experience of Rejection

BACKGROUND

Liver function indices and anti-viral immune regulatory markers can both improve graft outcomes, which lead to better post-transplantation management and increase the possibility of surveillance in liver transplant recipients with chronic hepatitis B virus (HBV) infection.

OBJECTIVE

To determine the association between the interferon regulatory factor 1 (IRF1) mRNA levels and liver enzymes in HBV-infected liver transplant recipients with and without experience of rejection.

METHODS

A total of 46 chronic HBV-infected patients who had undergone liver transplant surgery was divided into 2 groups of recipients "with rejection" and "without rejection.". Blood samples were collected form each patient on days 1, 4, and 7 post-transplantation. A SYBER GREEN real-time PCR was used to evaluate the expression level of IRF1 in liver recipients. Liver enzyme activities were also measured in all patients.

RESULTS

The expression of IRF1 in the patients with rejection was up-regulated at all 3 follow-up days compared with those without rejection. The serum levels of ALT and AST were more than normal levels at 3 follow-up times in both study groups. Significant differences were found in IRF1 gene expression levels and also serum ALT levels between those with and without rejection after 7 days post-transplantation.

CONCLUSION

The IRF1 expression and serum ALT levels were increased significantly in patient with rejection compared to those without rejection. IRF1, an inflammatory factor, may also intensify induction of inflammatory pathways in engrafted liver and promote liver inflammation and injuries leading to liver enzymes elevation in patients with graft rejection.

ZBP1: Innate Sensor Regulating Cell Death and Inflammation

Z-DNA-binding protein 1 (ZBP1), initially reported as an interferon (IFN)-inducible tumor-associated protein, harbors nucleic acid-binding domains for left-handed helix (Z-form) and receptor-interacting protein homotypic interaction motif (RHIM) domains for protein homotypic interactions. Recent studies have identified ZBP1 as an innate sensor of viral infections and a target of viral evasion strategies, regulating cell death, inflammasome activation, and proinflammatory responses. ZBP1 also functions during development and can trigger perinatal lethality when its RHIM-dependent interactions are not restricted. Here we review the history and emergence of ZBP1 as a pathogen sensor and a central regulator of cell death and inflammatory responses. We also discuss the gaps in our knowledge regarding the regulation and functions of ZBP1 and highlight potential avenues for future research.

Innate immunity related pathogen recognition receptors and chronic hepatitis B infection

Innate immunity consists of several kinds of pathogen recognition receptors (PRRs), which participate in the recognition of pathogens and consequently activation of innate immune system against pathogens. Recently, several investigations reported that PRRs may also play key roles in the induction/stimulation of immune system related complications in microbial infections. Hepatitis B virus (HBV), as the main cause of viral hepatitis in human, can induce several clinical forms of hepatitis B and also might be associated with hepatic complications such as cirrhosis and hepatocellular carcinoma (HCC). Based on the important roles of PRRs in the eradication of microbial infections including viral infections and their related complications, it appears that the molecules may be a main part of immune responses against viral infections including HBV and participate in the HBV related complications. Thus, this review article has brought together information regarding the roles of PRRs in immunity against HBV and its complications.

Induction of viral interference by IPNV-carrier cells on target cells: A cell co-culture study

IPNV is a salmonid birnavirus that possesses the ability to establish asymptomatic persistent infections in a number of valuable fish species. The presence of IPNV may interfere with subsequent infection by other viruses. In the present study we show that an IPNV-carrier cell line (EPC^IPNV) can induce an antiviral state in fresh EPC by co-cultivating both cell types in three different ways: a "droplet" culture system, a plastic chamber setup, and a transmembrane (Transwell^®) system. All three cell co-culture methods were proven useful to study donor/target cell interaction. Naïve EPC cells grown in contact with EPC^IPNV cells develop resistance to VHSV superinfection. The transmembrane system seems best suited to examine gene expression in donor and target cells separately. Our findings point to the conclusion that one or more soluble factors produced by the IPNV carrier culture induce the innate immune response within the target cells. This antiviral response is associated to the up-regulation of interferon (ifn) and mx gene expression in target EPC cells. To our knowledge this is the first article describing co-culture systems to study the interplay between virus-carrier cells and naive cells in fish.

Hepatitis B virus polymerase disrupts K63-linked ubiquitination of STING to block innate cytosolic DNA-sensing pathways

The cellular innate immune system recognizing pathogen infection is essential for host defense against viruses. In parallel, viruses have developed a variety of strategies to evade the innate immunity. The hepatitis B virus (HBV), a DNA virus that causes chronic hepatitis, has been shown to inhibit RNA helicase RIG-I-mediated interferon (IFN) induction. However, it is still unknown whether HBV could affect the host DNA-sensing pathways. Here we report that in transiently HBV-transfected Huh7 cells, the stably HBV-producing cell line HepAD38, and HBV-infected HepaRG cells and primary human hepatocytes, HBV markedly interfered with IFN-β induction and antiviral immunity mediated by the stimulator of interferon genes (STING), which has been identified as a central factor in foreign DNA recognition and antiviral innate immunity. Screening analysis demonstrated that the viral polymerase (Pol), but not other HBV-encoded proteins, was able to inhibit STING-stimulated interferon regulatory factor 3 (IRF3) activation and IFN-β induction. Moreover, the reverse transcriptase (RT) and the RNase H (RH) domains of Pol were identified to be responsible for the inhibitory effects. Furthermore, Pol was shown to physically associate with STING and dramatically decrease the K63-linked polyubiquitination of STING via its RT domain without altering the expression level of STING. Taken together, these observations suggest that besides its inherent catalytic function, Pol has a role in suppression of IFN-β production by direct interaction with STING and subsequent disruption of its K63-linked ubiquitination, providing a new mechanism for HBV to counteract the innate DNA-sensing pathways.

IMPORTANCE

Although whether and how HBV infection induces the innate immune responses are still controversial, it has become increasingly clear that HBV has developed strategies to counteract the pattern recognition receptor-mediated signaling pathways. Previous studies have shown that type I IFN induction activated by the host RNA sensors could be inhibited by HBV. However, it remains unknown whether HBV as a DNA virus utilizes evasion mechanisms against foreign DNA-elicited antiviral signaling. In recent years, the cytosolic DNA sensor and key adaptor STING has been demonstrated to be essential in multiple foreign DNA-elicited innate immune signalings. Here, for the first time, we report STING as a new target of HBV to antagonize IFN induction and identify the viral polymerase responsible for the inhibitory effect, thus providing an additional molecular mechanism by which HBV evades the innate immunity; this implies that in addition to its inherent catalytic function, HBV polymerase is a multifunctional immunomodulatory protein.

Recognition of human oncogenic viruses by host pattern-recognition receptors

Human oncogenic viruses include Epstein-Barr virus, hepatitis B virus, hepatitis C virus, human papilloma virus, human T-cell lymphotropic virus, Kaposi's associated sarcoma virus, and Merkel cell polyomavirus. It would be expected that during virus-host interaction, the immune system would recognize these pathogens and eliminate them. However, through evolution, these viruses have developed a number of strategies to avoid such an outcome and successfully establish chronic infections. The persistent nature of the infection caused by these viruses is associated with their oncogenic potential. In this article, we will review the latest information on the interaction between oncogenic viruses and the innate immune system of the host. In particular, we will summarize the available knowledge on the recognition by host pattern-recognition receptors of pathogen-associated molecular patterns present in the incoming viral particle or generated during the virus' life cycle. We will also review the data on the recognition of cell-derived danger associated molecular patterns generated during the virus infection that may impact the outcome of the host-pathogen interaction and the development cancer.

STING and the innate immune response to nucleic acids in the cytosol

Cytosolic detection of pathogen-derived nucleic acids is critical for the initiation of innate immune defense against diverse bacterial, viral and eukaryotic pathogens. Conversely, inappropriate responses to cytosolic nucleic acids can produce severe autoimmune pathology. The host protein STING has been identified as a central signaling molecule in the innate immune response to cytosolic nucleic acids. STING seems to be especially critical for responses to cytosolic DNA and the unique bacterial nucleic acids called 'cyclic dinucleotides'. Here we discuss advances in the understanding of STING and highlight the many unresolved issues in the field.