APOBEC3G directly binds Hepatitis B virus core protein in cell and cell free systems

Tribbles pseudokinase 3 promotes enterovirus A71 infection via dual mechanisms

Enterovirus A71 (EV-A71) is the main pathogen causing hand, foot and mouth disease (HFMD) in children and occasionally associated with neurological diseases such as aseptic meningitis, brainstem encephalitis (BE) and acute flaccid paralysis. We report here that cellular pseudokinase tribbles 3 (TRIB3) facilitates the infection of EV-A71 via dual mechanisms. In one hand, TRIB3 maintains the metabolic stability of scavenger receptor class B member 2 (SCARB2), the bona fide receptor of EV-A71, to enhance the infectious entry and spreading of the virus. On the other hand, TRIB3 facilitates the replication of EV-A71 RNA in a SCARB2-independent manner. The critical role of TRIB3 in EV-A71 infection and pathogenesis was further demonstrated in vivo in mice. In comparison to wild-type C57BL/6 mice, EV-A71 infection in TRIB3 knockdown mice (Trib3+/-) resulted in significantly lower viral loads in muscular tissues and reduced lethality and severity of clinical scores and tissue pathology. In addition, TRIB3 also promoted the replication of coxsackievirus B3 (CVB3) and coxsackievirus A16 (CVA16) in vitro. In conclusion, our results suggest that TRIB3 is one of key host cellular proteins required for the infection and pathogenesis of EV-A71 and some other human enteroviruses and may thus be a potential therapeutic target for combating the infection of those viruses.

Compound IMB-Z inhibits hepatitis B virus replication through increasing APOBEC3G expression and incorporation into viral nucleocapsids

OBJECTIVES

As a host restriction factor, apolipoprotein B messenger RNA-editing enzyme catalytic polypeptide-like 3G (APOBEC3G or A3G) has been shown to suppress the replication of several viruses including hepatitis B virus (HBV). Recently, we reported that IMB-Z, a N-phenylbenzamide derivative, could inhibit Enterovirus 71 replication, and A3G mediated its antiviral activity. Whether IMB-Z exhibits an inhibitory effect on HBV replication has not been investigated.

MATERIAL AND METHODS

HBV DNA, pregenomic RNA (pgRNA), core protein, and capsid levels were determined by a qPCR assay or Southern blot, Northern blot, Western blot, and particle gel assay, respectively. Mutation analysis of HBV DNAs was conducted by a differential DNA denaturation PCR assay. A3G encapsidation into HBV nucleocapsids was examined by Western blot analysis after ultracentrifugation and a co-immunoprecipitation (IP) assay between HBV core and A3G proteins.

RESULTS

In the present study, we found that IMB-Z could considerably inhibit HBV replication in HepAD38 cells. Interestingly, IMB-Z did not alter the HBV pgRNA production but could reduce the level of core protein, viral nucleocapsids, and core-associated DNA, as well as cccDNA intracellular amplification. Similar to the action of IMB-Z's inhibition of Enterovirus 71 replication, we found that IMB-Z's inhibition of HBV replication was associated with increased level of A3G. Mechanistically, we demonstrated that the inhibitory effect of IMB-Z is independent of the cytidine deaminase activity of A3G and is exerted by increasing its incorporation into viral nucleocapsids.

CONCLUSIONS

Our results indicate that IMB-Z inhibits HBV through pharmacological induction A3G expression and incorporation into HBV nucleocapsids.

Roles of APOBEC3 in hepatitis B virus (HBV) infection and hepatocarcinogenesis

APOBEC3 (A3) cytidine deaminases inhibit hepatitis B virus (HBV) infection and play vital roles in maintaining a variety of biochemical processes, including the regulation of protein expression and innate immunity. Emerging evidence indicates that the deaminated deoxycytidine biochemical activity of A3 proteins in single-stranded DNA makes them a double-edged sword. These enzymes can cause cellular genetic mutations at replication forks or within transcription bubbles, depending on the physiological state of the cell and the phase of the cell cycle. Under pathological conditions, aberrant expression of A3 genes with improper deaminase activity regulation may threaten genomic stability and eventually lead to cancer development. This review attempted to summarize the antiviral activities and underlying mechanisms of A3 editing enzymes in HBV infections. Moreover, the correlations between A3 genes and hepatocarcinogenesis were also elucidated.

The Hepatitis B Virus Interactome: A Comprehensive Overview

Despite the availability of a prophylactic vaccine, chronic hepatitis B (CHB) caused by the hepatitis B virus (HBV) is a major health problem affecting an estimated 292 million people globally. Current therapeutic goals are to achieve functional cure characterized by HBsAg seroclearance and the absence of HBV-DNA after treatment cessation. However, at present, functional cure is thought to be complicated due to the presence of covalently closed circular DNA (cccDNA) and integrated HBV-DNA. Even if the episomal cccDNA is silenced or eliminated, it remains unclear how important the high level of HBsAg that is expressed from integrated HBV DNA is for the pathology. To identify therapies that could bring about high rates of functional cure, in-depth knowledge of the virus' biology is imperative to pinpoint mechanisms for novel therapeutic targets. The viral proteins and the episomal cccDNA are considered integral for the control and maintenance of the HBV life cycle and through direct interaction with the host proteome they help create the most optimal environment for the virus whilst avoiding immune detection. New HBV-host protein interactions are continuously being identified. Unfortunately, a compendium of the most recent information is lacking and an interactome is unavailable. This article provides a comprehensive review of the virus-host relationship from viral entry to release, as well as an interactome of cccDNA, HBc, and HBx.

A3G-induced mutations show a low prevalence and exhibit plus-strand regional distribution in hepatitis B virus DNA from patients with non-hepatocellular carcinoma (HCC) and HCC

APOBEC3G (A3G) cytidine deaminase is an innate immune restriction factor that can edit and inhibit hepatitis B virus (HBV) replication. The preferred target of A3G is deamination of the third cytosine of 5'CCC to form a mutant marker 5'CC C → K. However, the distribution of A3G-induced mutations on HBV DNA during infection is not well characterized. To provide clarity, we obtained the HBV DNA sequences from HBV infected individuals with and without hepatocellular carcinoma (HCC and non-HCC, respectively), from the NCBI database, and calculated the r values of A3G-induced 5'CC C → K mutation prevalence in HBV DNA. A3G-induced mutations were weakly prevalent and mainly distributed in the plus strand of HBV DNA (r = 1.407). The mutations on the minus strand were weaker (r = .8189). There were A3G-induced mutation regions in the 1200 to 2000 nt region of the plus strand and the 1600 to 1500 nt region of the minus strand. There was no significant difference in the r values of A3G-induced mutations in HBV DNA between the HCC and non-HCC groups. However, the rvalue of the plus strand 2400 to 2800 nt regions of HCC derived HBV DNA (r = 4.2) was significantly higher than that of the same regions of non-HCC derived HBV DNA (r = 1.21). These findings clarify the weak prevalence and preferred plus-strand distribution of A3G-induced mutations on HBV DNA from HCC and non-HCC. These findings may provide valuable clues regarding the interaction mechanism between A3G and HBV DNA and inform HCC screening.

Synthesis and Bioactivity of N-(4-Chlorophenyl)-4-Methoxy-3-(Methylamino) Benzamide as a Potential Anti-HBV Agent

Introduction

Hepatitis B virus (HBV) is a global health concern that can cause acute and chronic liver diseases. Thus, there is an urgent need to research novel anti-HBV agents. Our previous reports show that N-phenylbenzamide derivatives exert broad-spectrum antiviral effects against HIV-1, HCV, and EV71 by increasing intracellular levels of APOBEC3G (A3G). As A3G is capable of inhibiting the replication of HBV, we screened the N-phenylbenzamide derivatives against HBV.

Methods

In this study, a new derivative, N-(4-chlorophenyl)-4-methoxy-3-(methylamino) benzamide (IMB-0523), was synthesized and its anti-HBV activity was evaluated in vitro and in vivo. The acute toxicity and pharmacokinetic profiles of IMB-0523 were also investigated.

Results

Our results show that IMB-0523 has higher anti-HBV activity in both wild-type HBV (IC₅₀: 1.99 µM) and drug-resistant HBV (IC₅₀: 3.30 µM) than lamivudine (3TC, IC₅₀: 7.37 µM in wild-type HBV, IC₅₀: >440 µM in drug-resistant HBV). The antiviral effect of IMB-0523 against HBV may be due to an increased level of intracellular A3G. IMB-0523 also showed low acute toxicity (LD₅₀: 448 mg/kg) in mice and promising PK properties (AUC_0-t: 7535.10±2226.73 µg·h/L) in rats. Further, IMB-0523 showed potent anti-HBV activity in DHBV-infected ducks.

Conclusion

Thus, IMB-0523 may be a potential anti-HBV agent with different mechanisms than current anti-HBV treatment options.

Correlation of APOBEC3G expression with liver function indexes of patients with chronic hepatitis B and comparison in chronic hepatitis B, liver cirrhosis and liver cancer

Correlation of APOBEC3G expression with liver function indexes of patients with chronic hepatitis B and its expression in chronic hepatitis B, liver cirrhosis and liver cancer were investigated to evaluated the significance of APOBEC3G. Fifty-eight patients with chronic hepatitis B were selected, including 20 cases of chronic hepatitis B, 19 cases of liver cirrhosis and 19 cases of liver cancer. Liver function indexes were detected and analyzed, and messenger ribonucleic acid (mRNA) and protein expression levels of APOBEC3G in liver tissues were detected via reverse transcription-polymerase chain reaction (RT-PCR), western blotting and immunohistochemistry, followed by correlation analysis. Certain liver function indexes had significant differences among the three groups of patients (P<0.05). Results of RT-PCR, Western blotting and immunohistochemistry confirmed that the content of APOBEC3G in liver tissues was the highest in patients with chronic hepatitis B, slightly lower in patients with liver cirrhosis and the lowest in patients with liver cancer. The content of APOBEC3G mRNA in liver tissues had a certain correlation with the content of alanine aminotransferase (ALT) (r² =0.34, P<0.05). Other liver function indexes had no significant correlations with APOBEC3G (P>0.05). APOBEC3G expression has a certain correlation with some liver function indexes of patients with chronic hepatitis B. There are significant differences in the expression level of APOBEC3G in patients with hepatitis, liver cirrhosis and liver cancer.

Profiling of LINE-1-Related Genes in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a prime public health concern that accounts for most of the primary liver malignancies in humans. The most common etiological factor of HCC is hepatitis B virus (HBV). Despite recent advances in treatment strategies, there has been little success in improving the survival of HCC patients. To develop a novel therapeutic approach, evaluation of a working hypothesis based on different viewpoints might be important. Long interspersed element 1 (L1) retrotransposons have been suggested to play a role in HCC. However, the molecular machineries that can modulate L1 biology in HBV-related HCC have not been well-evaluated. Here, we summarize the profiles of expression and/or activation status of L1-related genes in HBV-related HCC, and HBV- and HCC-related genes that may impact L1-mediated tumorigenesis. L1 restriction factors appear to be suppressed by HBV infection. Since some of the L1 restriction factors also limit HBV, these factors may be exhausted in HBV-infected cells, which causes de-suppression of L1. Several HBV- and HCC-related genes that interact with L1 can affect oncogenic processes. Thus, L1 may be a novel prime therapeutic target for HBV-related HCC. Studies in this area will provide insights into HCC and other types of cancers.

HBsAg blocks TYPE I IFN induced up-regulation of A3G through inhibition of STAT3

Interferon (IFN) is a regularly utilized therapeutic for the treatment of chronic hepatitis B and appears to induce superior HBeAg seroconversion comparing nucleos/tide analogs. However, the mechanisms underlying IFN inhibition of HBV replication, as well as poor responses to IFN are unclear. Apobec3G has been reported to be involved in regulating HBV replication. In this study, we investigated Apobec3G expression and regulatory pathways during HBV infection. We show that over-expression of A3G leads to inhibition of HBV replication. We also show that IFN induces a significant increase in A3G protein expression, which is associated with STAT3 activation. We further show that A3G expression in HBV patients is lower compared to non-infected controls, possibly by HBsAg which inhibits IFN induced A3G up-regulation in a dose dependent manner. This process is likely mediated through inhibition of STAT3-Ser727 phosphorylation. The results presented in this study indicate that STAT3 plays an important role in IFN-induced A3G production, and HBsAg may correlated with poor response to IFN treatment.

Associations between activation-induced cytidine deaminase/apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like cytidine deaminase expression, hepatitis B virus (HBV) replication and HBV-associated liver disease (Review)

The hepatitis B virus (HBV) infection is a major risk factor in the development of chronic hepatitis (CH) and hepa-tocellular carcinoma (HCC). The activation-induced cytidine deaminase (AID)/apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like (APOBEC) family of cytidine deaminases is significant in innate immunity, as it restricts numerous viruses, including HBV, through hypermutation-dependent and -independent mechanisms. It is important to induce covalently closed circular (ccc)DNA degradation by interferon-α without causing side effects in the infected host cell. Furthermore, organisms possess multiple mechanisms to regulate the expression of AID/APOBECs, control their enzymatic activity and restrict their access to DNA or RNA substrates. Therefore, the AID/APOBECs present promising targets for preventing and treating viral infections. In addition, gene polymorphisms of the AID/APOBEC family may alter host susceptibility to HBV acquisition and CH disease progression. Through G-to-A hypermutation, AID/APOBECs also edit HBV DNA and facilitate the mutation of HBV DNA, which may assist the virus to evolve and potentially escape from the immune responses. The AID/APOBEC family and their associated editing patterns may also exert oncogenic activity. Understanding the effects of cytidine deaminases in CH virus-induced hepatocarcinogenesis may aid with developing efficient prophylactic and therapeutic strategies against HCC.

The role of Moloney leukemia virus 10 in hepatitis B virus expression in hepatoma cells

Recent studies have shown that the Moloney leukemia virus 10 (Mov10), a putative RNA helicase, has very broad and potent antiretroviral activities. Hepatitis B virus (HBV) has a reverse transcription process, but the potential role of Mov10 in HBV replication remains unknown. In this study, Mov10 was demonstrated to affect HBV expression in HepG2 and HepG2.2.15 cell lines. The data showed that the over-expression of exogenous Mov10 resulted in an increase of the HBsAg and HBeAg levels in the culture supernatant and HBV mRNA level in transfected cells at a low dose and resulted in a decrease at a high dose, but HBV DNA in culture supernatant was not affected. The knockdown of endogenous Mov10 expression through siRNA treatment could suppress levels of HBsAg, HBeAg and HBV mRNA, but had no effect on HBV DNA. Above results indicate that an appropriate level of exogenous Mov10 is responsible for HBV replication, that any perturbation in the level of Mov10 could affect HBV replication, while the endogenous Mov10 could promote HBV replication in vitro. The precise mechanisms that underlie the action of Mov10 on HBV still need further investigation.

Differences in serum microRNA profiles in hepatitis B and C virus infection

OBJECTIVES

Patients infected with chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) are at greater risk of cirrhosis and hepatocellular carcinoma. The objective of this study was to identify virus-specific serum microRNA profiles associated with liver function and disease progression. Microarray analysis of serum microRNAs was performed using the Toray 3D array system in 22 healthy subjects, 42 HBV patients, and 30 HCV patients. Selected microRNAs were then validated by qRT-PCR in 186 HBV patients, 107 HCV patients, and 22 healthy subjects.

RESULTS

Microarray analysis showed up-regulation of a number of microRNAs in serum of both HBV and HCV patients. In qRT-PCR analysis, miR-122, miR-99a, miR-125b, miR-720, miR-22, and miR-1275 were up-regulated both in HBV patients relative to healthy subjects, and all except miR-1275 were up-regulated in HBeAg-positive patients relative to HBeAg-negative patients. Specific microRNAs were independently associated with different aspects of HBV infection. MiR-122 was independently associated with HBV DNA level, whereas miR-125b was independently associated with levels of HBV DNA, HBsAg, and HBeAg. MiR-22 and miR-1275 were independently associated with serum γ-glutamyl transpeptidase levels.

CONCLUSIONS

Serum microRNA levels reflect differences in the etiology and stage of viral hepatitis.

Altered mRNA levels of MOV10, A3G, and IFN-α in patients with chronic hepatitis B

To explore the relationship of the MOV10, A3G, and IFN-α mRNA levels with chronic hepatitis B virus (HBV) infection, Blood samples from 96 patients with chronic hepatitis B (CHB) and 21 healthy individuals as control were collected. HBV DNA load and aminotransferase in the serum were tested using real time PCR and velocity methods, respectively. The MOV10, A3G, and IFN-α mRNA levels in the peripheral blood mononuclear cells (PBMC) were examined through qRT-PCR. The MOV10, A3G, and IFN-α mRNA levels in CHB group was significantly lower than those in the control group (P<0.01, P<0.05, P<0.01, respectively). The A3G mRNA level in the high-HBV DNA load group was lower than that in the low-HBV DNA load group (P<0.05). However, no statistical difference was found in the MOV10 and IFN-α mRNA levels between the two HBV DNA load groups. Furthermore, the MOV10 mRNA level showed positive correlation with IFN-α in the control group. These results indicated that the expression of the innate immune factors MOV10, A3G, and IFN-α is affected by chronic HBV infection.

The inhibition of hepatitis B virus by APOBEC cytidine deaminases

APOBEC3 (A3) cytidine deaminases are a family of enzymes that have been shown to inhibit the replication of HIV-1 and other retroviruses as part of the innate immune responses to virus infection. They can also hyperedit HBV DNA and inhibit HBV replication. Although A3 proteins are present at low levels in normal liver, A3 gene expression is highly stimulated by both interferon-α and interferon-γ. A3 deaminases are incorporated into nascent HBV capsids where they cleave amino groups from cytidine bases converting them to uracil in newly synthesized DNA following reverse transcription of pregenomic RNA. This modified HBV DNA is susceptible to degradation, or alternatively, numerous G-to-A nucleotide mutations are incorporated into positive-strand viral DNA disrupting coding sequences. A3 proteins in which the cytidine deaminase activity has been lost can also inhibit HBV replication, suggesting that there may be more than one way in which inhibition can occur. There is also evidence that A3 proteins might play a role in the development of hepatocellular carcinoma during chronic HBV infection.

Polymorphic APOBEC3 modulates chronic hepatitis B in Moroccan population

The cytidine deaminase apolipoprotein B mRNA editing catalytic subunit-3 (APOBEC3) induces G-to-A hypermutation in hepatitis B virus (HBV) genomes and operates as part of the innate antiviral immune system. We investigated the associations between the presence of APOBEC3 variants and HBV carriage in a case-control study in the Moroccan population. A polymorphic deletion affecting the APOBEC3B gene and the H186R variant of APOBEC3G were genotyped in 179 HBV chronic carriers and 216 healthy control subjects. In addition, to assess the overall impact of APOBEC3 deaminases on circulating HBV, we looked for hyperedited forms of the viral genome using the 3DPCR technique and analysed editing context. Data analysis showed that there was no significant difference in the frequencies of deleted APOBEC3B alleles (P = 0.261) or genotypes (P = 0.333) between patients with chronic hepatitis B and control subjects. By contrast, subjects bearing deleted genotype had a faster progression of liver disease than those with the insertion genotype (adjusted OR, 3.72; 95% CI, 0.38-36.12). The analysis of the APOBEC3G H186R polymorphism revealed that R/R genotype frequencies were not significantly different in HBV infected patients and in healthy subjects. 3DPCR was positive in 26 samples (14%) among 179. Amplified viral segments displayed monomorphic G>A transitions highly reminiscent of APOBEC3G activity. Most intriguingly, hemi/homozygous carriers of the APOBEC3B deletion had significantly lower virus loads than patients with the wild type (median 539 vs. 2213 IU/mL, P = 0.0023). This result suggests that genetic variations in APOBEC3 cytidine deaminases do not predispose to chronicity but may modulate the course of persistent HBV infection.

Bridging the past and the future of virology: surface plasmon resonance as a powerful tool to investigate virus/host interactions

Despite decades of antiviral drug research and development, viruses still remain a top global healthcare problem. Compared to eukaryotic cells, viruses are composed by a limited numbers of proteins that, nevertheless, set up multiple interactions with cellular components, allowing the virus to take control of the infected cell. Each virus/host interaction can be considered as a therapeutical target for new antiviral drugs but, unfortunately, the systematic study of a so huge number of interactions is time-consuming and expensive, calling for models overcoming these drawbacks. Surface plasmon resonance (SPR) is a label-free optical technique to study biomolecular interactions in real time by detecting reflected light from a prism-gold film interface. Launched 20 years ago, SPR has become a nearly irreplaceable technology for the study of biomolecular interactions. Accordingly, SPR is increasingly used in the field of virology, spanning from the study of biological interactions to the identification of putative antiviral drugs. From the literature available, SPR emerges as an ideal link between conventional biological experimentation and system biology studies functional to the identification of highly connected viral or host proteins that act as nodal points in virus life cycle and thus considerable as therapeutical targets for the development of innovative antiviral strategies.

The potential role of APOBEC3G in limiting replication of hepatitis B virus

BACKGROUND AND STUDY AIMS

Recent findings introduced APOBEC3G (A3G) as a host factor that blocks viral replication. It induces G to A hypermutations in viral DNA at the step of reverse transcription and in response to interferon. This study aimed to investigate the expression of liver A3G protein in association with both replication of hepatitis B virus (HBV) and frequency of G to A mutations in BCP (basal core promoter)-PC (pre-core) region.

PATIENTS AND METHODS

Fifty-one liver biopsies of naïve chronic hepatitis B (CHB) patients enrolled for the expression of A3G were done by immunohistochemistry (IHC) standard method. The presence of HBV DNA and sequences of BCP-PC region at the time of liver biopsy was investigated in all patients.

RESULTS

Among 34 patients with detectable HBV DNA, 31 carried 1-5 G to A mutations in the BCP-PC region. IHC results showed that the expression level of A3G in CHB patients' liver was very low. Of all patients, A3G is expressed in three undetectable HBV DNA subjects and a patient with 2.24×10(4) copies ml(-1) of HBV DNA. G to A mutated residues were indicated at positions 1727, 1757 and 1896 of the HBV genome of this patient.

CONCLUSION

This study indicates that despite very low levels of both A3G in liver and the number of positive subjects, A3G has a potential role to restrict the in vivo replication of HBV.