Interplay between hepatitis B virus and the innate immune responses: implications for new therapeutic strategies. Virol Sin. 2014;29:17-24. [PMID: 24452540 DOI: 10.1007/s12250-014-3412-3]

The Mechanism of APOBEC3B in Hepatitis B Virus Infection and HBV Related Hepatocellular Carcinoma Progression, Therapeutic and Prognostic Potential

Hepatocellular carcinoma (HCC) is one of the most prevalent malignant tumors globally. Prominent factors include chronic hepatitis B (CHB) and chronic hepatitis C (CHC) virus infections, exposure to aflatoxin, alcohol abuse, diabetes, and obesity. The prevalence of hepatitis B (HBV) is substantial, and the significant proportion of asymptomatic carriers heightens the challenge in diagnosing and treating hepatocellular carcinoma (HCC), necessitating further and more comprehensive research. Apolipoprotein B mRNA editing catalytic polypeptide (APOBEC) family members are single-stranded DNA cytidine deaminases that can restrict viral replication. The APOBEC-related mutation pattern constitutes a primary characteristic of somatic mutations in various cancer types such as lung, breast, bladder, head and neck, cervix, and ovary. Symptoms in the early stages of HCC are often subtle and nonspecific, posing challenges in treatment and monitoring. Furthermore, this article primarily focuses on the established specific mechanism of action of the APOBEC3B (A3B) gene in the onset and progression of HBV-related HCC (HBV-HCC) through stimulating mutations in HBV, activating Interleukin-6 (IL-6) and promoting reactive oxygen species(ROS) production, while also exploring the potential for A3B to serve as a therapeutic target and prognostic indicator in HBV-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.

Forkhead O Transcription Factor 4 Restricts HBV Covalently Closed Circular DNA Transcription and HBV Replication through Genetic Downregulation of Hepatocyte Nuclear Factor 4 Alpha and Epigenetic Suppression of Covalently Closed Circular DNA via Interacting with Promyelocytic Leukemia Protein

Nuclear located hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) remains the key obstacle to cure chronic hepatitis B (CHB). In our previous investigation, it was found that FoxO4 could inhibit HBV core promoter activity through downregulating the expression of HNF4α. However, the exact mechanisms whereby FoxO4 inhibits HBV replication, especially its effect on cccDNA, remain unclear. Here, our data further revealed that FoxO4 could effectively inhibit cccDNA mediated transcription and HBV replication without affecting cccDNA level. Mechanistic study showed that FoxO4 could cause epigenetic suppression of cccDNA. Although FoxO4-mediated downregulation of HNF4α contributed to inhibiting HBV core promoter activity, it had little effect on cccDNA epigenetic regulation. Further, it was found that FoxO4 could colocalize within promyelocytic leukemia protein (PML) nuclear bodies and interact with PML. Of note, PML was revealed to be critical for FoxO4-mediated inhibition of cccDNA epigenetic modification and of the following cccDNA transcription and HBV replication. Furthermore, FoxO4 was found to be downregulated in HBV-infected hepatocytes and human liver tissues, and it was negatively correlated with cccDNA transcriptional activity in CHB patients. Together, these findings highlight the role of FoxO4 in suppressing cccDNA transcription and HBV replication via genetic downregulation of HNF4α and epigenetic suppression of cccDNA through interacting with PML. Targeting FoxO4 may present as a new therapeutic strategy against chronic HBV infection.

IMPORTANCE HBV cccDNA is a determining factor for viral persistence and the main obstacle for a cure of chronic hepatitis B. Strategies that target cccDNA directly are therefore of great importance in controlling persistent HBV infection. In present investigation, we found that FoxO4 could efficiently suppress cccDNA transcription and HBV replication without affecting the level of cccDNA itself. Further, our data revealed that FoxO4 might inhibit cccDNA function via a two-part mechanism: one is to epigenetically suppress cccDNA transcription via interacting with PML, and the other is to inhibit HBV core promoter activity via the genetic downregulation of HNF4α. Of note, HBV might dampen the expression of FoxO4 for its own persistent infection. We propose that manipulation of FoxO4 may present as a potential therapeutic strategy against chronic HBV infection.

HBV-Pol is crucial for HBV-mediated inhibition of inflammasome activation and IL-1β production

BACKGROUND & AIMS

Hepatitis B virus (HBV) infection is the most critical factor underlying liver cirrhosis and hepatocellular carcinoma worldwide. IL-1β and IL-18, generated by activation of the inflammasome/caspase-1 signaling pathway, play important roles in the control and clearance of HBV. However, the specific relationship between the inflammasome response and IFN-α resistance or viral persistence is yet to be established.

METHODS

Blood samples of patients and supernatant fractions of HBV cell lines were collected for analysis and the effects on inflammasome activation and IL-1β production evaluated via enzyme-linked immunosorbent assay (ELISA), western blot, quantitative RT-PCR and immunofluorescence.

RESULTS

IL-1β and IL-18 levels produced in sera of IFN-α non-responders were significantly lower than those of responders and normal donors. Additionally, expression of IL-1β and inflammasome components was decreased in peripheral blood mononuclear cells (PBMC) of non-responders, compared with those of responders. In vitro experiments on HepG2, HepG2.2.15 and HepAD38 cell lines showed that HBV induces a significant decrease in IL-1β production through inhibiting activation of the NF-κB signaling and inflammasome/caspase-1 pathways. And hepatitis B virus polymerase (HBV-Pol) appeared crucial for these inhibitory effects of HBV.

CONCLUSION

IL-1β production is suppressed in HBV carriers and IFN-α non-responders. HBV induces a significant decrease in IL-1β production through inhibiting the NF-κB signaling and inflammasome pathways, for which HBV-Pol is a crucial requirement. Trial approval number: 20 173 402.

The regulatory role of protein phosphorylation in human gammaherpesvirus associated cancers

Activation of specific sets of protein kinases by intracellular signal molecules has become more and more apparent in the past decade. Phosphorylation, one of key posttranslational modification events, is activated by kinase or regulatory protein and is vital for controlling many physiological functions of eukaryotic cells such as cell proliferation, differentiation, malignant transformation, and signal transduction mediated by external stimuli. Moreovers, the reversible modification of phosphorylation and dephosphorylation can result in different features of the target substrate molecules including DNA binding, protein-protein interaction, subcellular location and enzymatic activity, and is often hijacked by viral infection. Epstein-Barr virus (EBV) and Kaposi’s sarcomaassociated herpesvirus (KSHV), two human oncogenic gamma-herpesviruses, are shown to tightly associate with many malignancies. In this review, we summarize the recent progresses on understanding of molecular properties and regulatory modes of cellular and viral proteins phosphorylation influenced by these two tumor viruses, and highlight the potential therapeutic targets and strategies against their related cancers.

IL-33-ST2 Axis in Liver Disease: Progression and Challenge

The new member of the IL-1 family, interleukin-33 (IL-33), participates in the progression of a variety of diseases through binding with its receptor ST2. Recently, much clinical evidence and experimental data have indicated that IL-33 is associated with various liver diseases. This review primarily addresses the relationship between IL-33 and several hepatic diseases. IL-33 can alleviate high-fat diet- (HFD-) induced hepatic steatosis and insulin resistance, and IL-33 acts as an alarmin, which quickly triggers the immune system to respond to virus invasion and toxic damage to the liver. However, when liver injury is chronic, IL-33 promotes Th2 reactions and hepatic stellate cell (HSC) activity, facilitating progression to liver fibrosis. The complicated functions of IL-33 should be considered before its clinical application.

Treatment of hepatitis B virus with combination therapy now and in the future

Chronic Hepatitis B continues as a significant public health problem despite the availability of safe and effective antivirals and a highly effective protective vaccine. Current therapy, however rarely leads to cure and lifelong therapy is often required, contributing to poor uptake and ongoing morbidity. New insights into the hepatitis B viral life cycle and the host immune response have expanded the potential targets for drug therapies with interesting antiviral candidates and novel immunotherapeutic approaches in early stage development. Yet, HBV persistence is multifactorial - due to an intrahepatic reservoir and ongoing HBV-mediated immune dysregulation, making "cure" unlikely to be realized through even the most efficacious monotherapy. Building on the success seen in the treatment of hepatitis C (HCV) and human immunodeficiency virus (HIV), combination therapy may be an essential strategy to improve efficacy and decrease viral breakthrough. Combinations acting on immune and viral targets are particularly attractive. However, creating synergy while balancing efficacy and safety remains a clear challenge. Various approaches to combination therapy are reviewed, highlighting strengths and challenges of each potential strategy. Overall, combination therapies are attractive as the next step towards cure and are a key strategy for achieving treatment with finite durations and durable endpoints.

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.

Relevance of serum interleukin-33 and ST2 levels and the natural course of chronic hepatitis B virus infection

BACKGROUND

Interleukin-33 (IL-33) and ST2 have been demonstrated to be associated with liver damage. However, their potential value in hepatitis B virus (HBV) infection remains unknown. This study was designed to investigate the change of serum IL-33 and ST2 levels in the natural course of chronic HBV infection.

METHODS

A total of 120 patients with chronic hepatitis B (CHB), 20 chronic hepatitis B virus carriers in immunotolerant phase and 28 healthy controls were enrolled in this study. All patients with CHB were divided into four groups according to their serum ALT levels. The serum levels of IL-33 and ST2 of all participants were determined by enzyme-linked immunosorbent assay, and compared between each two out of those six groups.

RESULTS

No significant differences were found in serum levels of IL-33 and ST2 between the group of CHB with ALT 1-2 upper limit of normal and the healthy controls (P = 0.354 for IL-33 and P = 0.815 for ST2). Other than that, there were significant differences when serum levels of IL-33 and ST2 were compared between any other two out of those six groups (P < 0.05, respectively). The overall correlation analysis indicated that changes of serum IL-33 and ST2 levels were positively associated with ALT levels in patients with chronic HBV infection (rs = 0.879, P < 0.001 for IL-33 and rs = 0.923, P < 0.001 for ST2). No significant differences were found when the serum levels of ALT, IL-33 and ST2 were compared between patients with HBeAg-positive CHB and HBeAg-negative CHB.

CONCLUSIONS

Our study revealed that the serum levels of IL-33 and ST2 varied in different courses of chronic hepatitis B virus infection. The serum levels of IL-33 and ST2 elevated as serum ALT levels increased in patients with CHB. They might indicate liver damage for patients with CHB, just like ALT.

Crosstalk between innate and adaptive immunity in hepatitis B virus infection

Hepatitis B virus (HBV) infection is a major public health problem worldwide. HBV is not directly cytotoxic to infected hepatocytes; the clinical outcome of infection results from complicated interactions between the virus and the host immune system. In acute HBV infection, initiation of a broad, vigorous immune response is responsible for viral clearance and self-limited inflammatory liver disease. Effective and coordinated innate and adaptive immune responses are critical for viral clearance and the development of long-lasting immunity. Chronic hepatitis B patients fail to mount efficient innate and adaptive immune responses to the virus. In particular, HBV-specific cytotoxic T cells, which are crucial for HBV clearance, are hyporesponsiveness to HBV infection. Accumulating experimental evidence obtained from the development of animal and cell line models has highlighted the importance of innate immunity in the early control of HBV spread. The virus has evolved immune escape strategies, with higher HBV loads and HBV protein concentrations associated with increasing impairment of immune function. Therefore, treatment of HBV infection requires inhibition of HBV replication and protein expression to restore the suppressed host immunity. Complicated interactions exist not only between innate and adaptive responses, but also among innate immune cells and different components of adaptive responses. Improved insight into these complex interactions are important in designing new therapeutic strategies for the treatment HBV infection. In this review, we summarize the current knowledge regarding the cross-talk between the innate and adaptive immune responses and among different immunocytes in HBV infection.

Hepatitis B virus spliced variants are associated with an impaired response to interferon therapy

During hepatitis B virus (HBV) replication, spliced HBV genomes and splice-generated proteins have been widely described, however, their biological and clinical significance remains to be defined. Here, an elevation of the proportion of HBV spliced variants in the sera of patients with chronic hepatitis B (CHB) is shown to correlate with an impaired respond to interferon-α (IFN-α) therapy. Transfection of the constructs encoding the three most dominant species of spliced variants into cells or ectopic expression of the two major spliced protein including HBSP and N-terminal-truncated viral polymerase protein result in strong suppression of IFN-α signaling transduction, while mutation of the major splicing-related sites of HBV attenuates the viral anti-IFN activities in both cell and mouse models. These results have associated the productions of HBV spliced variants with the failure response to IFN therapy and illuminate a novel mechanism where spliced viral products are employed to resist IFN-mediated host defense.

Genetic, metabolic and environmental factors involved in the development of liver cirrhosis in Mexico

Liver cirrhosis (LC) is a chronic illness caused by inflammatory responses and progressive fibrosis. Globally, the most common causes of chronic liver disease include persistent alcohol abuse, followed by viral hepatitis infections and nonalcoholic fatty liver disease. However, regardless of the etiological factors, the susceptibility and degree of liver damage may be influenced by genetic polymorphisms that are associated with distinct ethnic and cultural backgrounds. Consequently, metabolic genes are influenced by variable environmental lifestyle factors, such as diet, physical inactivity, and emotional stress, which are associated with regional differences among populations. This Topic Highlight will focus on the genetic and environmental factors that may influence the metabolism of alcohol and nutrients in the setting of distinct etiologies of liver disease. The interaction between genes and environment in the current-day admixed population, Mestizo and Native Mexican, will be described. Additionally, genes involved in immune regulation, insulin sensitivity, oxidative stress and extracellular matrix deposition may modulate the degree of severity. In conclusion, LC is a complex disease. The onset, progression, and clinical outcome of LC among the Mexican population are influenced by specific genetic and environmental factors. Among these are an admixed genome with a heterogenic distribution of European, Amerindian and African ancestry; a high score of alcohol consumption; viral infections; a hepatopathogenic diet; and a high prevalence of obesity. The variance in risk factors among populations suggests that intervention strategies directed towards the prevention and management of LC should be tailored according to such population-based features.

CRISPR/Cas9-based tools for targeted genome editing and replication control of HBV

Hepatitis B virus (HBV) infection remains a major global health problem because current therapies rarely eliminate HBV infections to achieve a complete cure. A different treatment paradigm to effectively clear HBV infection and eradicate latent viral reservoirs is urgently required. In recent years, the development of a new RNA-guided gene-editing tool, the CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated nuclease 9) system, has greatly facilitated site-specific mutagenesis and represents a very promising potential therapeutic tool for diseases, including for eradication of invasive pathogens such as HBV. Here, we review recent advances in the use of CRISPR/Cas9, which is designed to target HBV specific DNA sequences to inhibit HBV replication and to induce viral genome mutation, in cell lines or animal models. Advantages, limitations and possible solutions, and proposed directions for future research are discussed to highlight the opportunities and challenges of CRISPR/Cas9 as a new, potentially curative therapy for chronic hepatitis B infection.

New insights into hepatitis B virus biology and implications for novel antiviral strategies

Hepatitis B virus (HBV), a small DNA virus with a unique replication mode, can cause chronic hepatitis (CHB), which is characterized by the persistence of the viral covalently closed circular DNA that serves as the template for HBV replication and the production of large amounts of secreted HBV surface antigen (HBsAg) that is present in excess of the levels of infectious virus. Despite the success of currently approved antiviral treatments for CHB patients, including interferon and nucleotide analogs, which suppress HBV replication and reduce the risk of CHB-related liver diseases, these therapies fail to eradicate the virus in most of the patients. With the development of the cell and animal models for HBV study, a better understanding of the HBV life cycle has been achieved and a series of novel antiviral strategies that target different stages of HBV replication have been designed to overcome the viral factors that contribute to HBV persistence. Such basic HBV research advancements and therapeutic developments are the subject of this review.

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.