Clinical impact of hepatitis B and C virus envelope glycoproteins

EPHA2 Receptor as a Possible Therapeutic Target in Viral Infections

BACKGROUND

The receptor tyrosine kinase EphA2 plays a role in many diseases, like cancer, cataracts, and osteoporosis. Interestingly, it has also been linked to viral infections.

OBJECTIVE

Herein, current literature has been reviewed to clarify EphA2 functions in viral infections and explore its potential role as a target in antiviral drug discovery strategies.

METHODS

Research and review articles along with preprints connecting EphA2 to different viruses have been searched through PubMed and the web. Structures of complexes between EphA2 domains and viral proteins have been retrieved from the PDB database.

RESULTS

EphA2 assumes a key role in Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein Barr virus (EBV) infections by directly binding, through its ligand binding domain, viral glycoproteins. For human cytomegalovirus (HCMV), the role of EphA2 in maintaining virus latency state, through cooperation with specific viral proteins, has also been speculated. In certain cells, with high EphA2 expression levels, following ligand stimulation, receptor activation might contribute to severe symptoms accompanying a few viral infections, including lung injuries often related to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2).

CONCLUSION

Since EphA2 works as a host receptor for certain viruses, it might be worth more deeply investigating known compounds targeting its extracellular ligand binding domain as antiviral therapeutics. Due to EphA2's function in inflammation, its possible correlation with SARS-CoV-2 cannot be excluded, but more experimental studies are needed in this case to undoubtedly attribute the role of this receptor in viral infections.

Binding of Hepatitis B Virus Pre-S1 Domain-Derived Synthetic Myristoylated Peptide to Scavenger Receptor Class B Type 1 with Differential Properties from Sodium Taurocholate Cotransporting Polypeptide

(1) Background: The myristoylated pre-S1 peptide (Myr47) synthesized to mimic pre-S1 domain (2-48) in large (L) surface protein of hepatitis B virus (HBV) prevents HBV infection to hepatocytes by binding to sodium taurocholate cotransporting polypeptide (NTCP). We previously demonstrated that yeast-derived nanoparticles containing L protein (bio-nanocapsules: BNCs) bind scavenger receptor class B type 1 (SR-B1). In this study, we examined the binding of Mry47 to SR-B1. (2) Methods: The binding and endocytosis of fluorescence-labeled Myr47 to SR-B1 (and its mutants)-green fluorescence protein (GFP) fusion proteins expressed in HEK293T cells were analyzed using flow cytometry and laser scanning microscopy (LSM). Various ligand-binding properties were compared between SR-B1-GFP and NTCP-GFP. Furthermore, the binding of biotinylated Myr47 to SR-B1-GFP expressed on HEK293T cells was analyzed via pull-down assays using a crosslinker and streptavidin-conjugated beads. (3) Conclusions: SR-B1 bound not only Myr47 but also its myristoylated analog and BNCs, but failed to bind a peptide without myristoylation. However, NTCP only bound Myr47 among the ligands tested. Studies using SR-B1 mutants suggested that both BNCs and Myr47 bind to similar sites of SR-B1. Crosslinking studies indicated that Myr47 binds preferentially SR-B1 multimer than monomer in both HEK293T and HepG2 cells.

Binding of Nanoparticles Harboring Recombinant Large Surface Protein of Hepatitis B Virus to Scavenger Receptor Class B Type 1

(1) Background: As nanoparticles containing the hepatitis B virus (HBV) large (L) surface protein produced in yeast are expected to be useful as a carrier for targeting hepatocytes, they are also referred to as bio-nanocapsules (BNCs). However, a definitive cell membrane receptor for BNC binding has not yet been identified. (2) Methods: By utilizing fluorescence-labeled BNCs, we examined BNC binding to the scavenger receptor class B type 1 (SR-B1) expressed in HEK293T cells. (3) Results: Analyses employing SR-B1 siRNA and expression of SR-B1 fused with a green fluorescent protein (SR-B1-GFP) indicated that BNCs bind to SR-B1. As mutagenesis induced in the SR-B1 extracellular domain abrogates or attenuates BNC binding and endocytosis via SR-B1 in HEK293T cells, it was suggested that the ligand-binding site of SR-B1 is similar or close among high-density lipoprotein (HDL), silica, liposomes, and BNCs. On the other hand, L protein was suggested to attenuate an interaction between phospholipids and SR-B1. (4) Conclusions: SR-B1 can function as a receptor for binding and endocytosis of BNCs in HEK293T cells. Being expressed various types of cells, it is suggested that functions as a receptor for BNCs not only in HEK293T cells but also in other types of cells.

Hepatitis C Virus Infection and Vaccine Development

In the twenty-seven years since the discovery of hepatitis C virus (HCV) the majority of individuals exposed to HCV establish a persistent infection, which is a leading cause of chronic liver disease, cirrhosis and hepatocellular carcinoma. In developed nations, the cure rates of HCV infection could be over 90% with direct-acting antiviral (DAA) regimens, which has made the great progress in global eradication. However, the cost of these treatments is so expensive that the patients in developing nations, where the disease burden is the most severe, could not afford it, which highly restricted its access. Additionally, the largely asymptomatic nature of infection facilitates continued transmission in risk groups due to limited surveillance. Consequently a protective vaccine and likely emergence of drug-resistant viral variants call for further studies of HCV biology. In the current review, the development and the progress of preventive and therapeutic vaccines against the HCV have been reviewed in the context of peptide vaccines, recombinant protein vaccines, HCV-like particle, DNA vaccines and viral vectors expressing HCV genes.

PTD-fused p53 as a potential antiviral agent directly suppresses HBV transcription and expression

In Hepatitis B virus (HBV) infection, the virus generates numerous viral mRNAs/proteins and viral loads, which plays a major role in driving T cell tolerance, viral persistence, and hepatocellular carcinoma. However, currently available anti-HBV agents have no direct effect on viral mRNA transcription and protein expression. In this study, we designed a recombinant fusion of p53 protein with the cell-penetrating peptide PTD (protein transduction domain of trans-activator of transcription), which mediated p53 internalization into hepatocytes. PTD-p53 effectively suppressed HBV transcription and antigen expression by interaction with viral enhancers. We further provide evidence that PTD-p53 counteracts the viral transcription feedback loop and effectively suppressed HBV production of viral mRNAs, as well as HBsAg, HBeAg, and HBcAg, both in vitro and in vivo. Our results thereby provide a basis for developing a new therapeutic approach against HBV infection.

Status of hepatitis C virus vaccination: Recent update

Hepatitis C virus (HCV) infection is still a major public health problem worldwide since its first identification in 1989. At the start, HCV infection was post-transfusion viral infection, particularly in developing countries. Recently, due to iv drug abuse, HCV infection became number one health problem in well-developed countries as well. Following acute HCV infection, the innate immune response is triggered in the form of activated coordinated interaction of NK cells, dendritic cells and interferon α. The acquired immune response is then developed in the form of the antibody-mediated immune response (ABIR) and the cell-mediated immune response (CMIR). Both are responsible for clearance of HCV infection in about 15% of infected patients. However, HCV has several mechanisms to evade these antivirus immune reactions. The current review gives an overview of HCV structure, immune response and viral evasion mechanisms. It also evaluates the available preventive and therapeutic vaccines that induce innate, ABIR, CMIR. Moreover, this review highlights the progress in recent HCV vaccination studies either in preclinical or clinical phases. The unsatisfactory identification of HCV infection by the current screening system and the limitations of currently available treatments, including the ineligibility of some chronic HCV patients to such antiviral agents, mandate the development of an effective HCV vaccine.

Applications of human hepatitis B virus preS domain in bio- and nanotechnology

Human hepatitis B virus (HBV) is a member of the family Hepadnaviridae, and causes acute and chronic infections of the liver. The hepatitis B surface antigen (HBsAg) contains the large (L), middle (M), and small (S) surface proteins. The L protein consists of the S protein, preS1, and preS2. In HBsAg, the preS domain (preS1 + preS2) plays a key role in the infection of hepatocytic cells by HBV and has several immunogenic epitopes. Based on these characteristics of preS, several preS-based diagnostic and therapeutic materials and systems have been developed. PreS1-specific monoclonal antibodies (e.g., MA18/7 and KR127) can be used to inhibit HBV infection. A myristoylated preS1 peptide (amino acids 2-48) also inhibits the attachment of HBV to HepaRG cells, primary human hepatocytes, and primary tupaia hepatocytes. Antibodies and antigens related to the components of HBsAg, preS (preS1 + preS2), or preS1 can be available as diagnostic markers of acute and chronic HBV infections. Hepatocyte-targeting delivery systems for therapeutic molecules (drugs, genes, or proteins) are very important for increasing the clinical efficacy of these molecules and in reducing their adverse effects on other organs. The selective delivery of diagnostic molecules to target hepatocytic cells can also improve the efficiency of diagnosis. In addition to the full-length HBV vector, preS (preS1 + preS2), preS1, and preS1-derived fragments can be useful in hepatocyte-specific targeting. In this review, we discuss the literature concerning the applications of the HBV preS domain in bio- and nanotechnology.

Study of the putative fusion regions of the preS domain of hepatitis B virus

In a previous study, it was shown that purified preS domains of hepatitis B virus (HBV) could interact with acidic phospholipid vesicles and induce aggregation, lipid mixing and leakage of internal contents which could be indicative of their involvement in the fusion of the viral and cellular membranes (Núñez, E. et al. 2009. Interaction of preS domains of hepatitis B virus with phospholipid vesicles. Biochim. Biophys. Acta 17884:417-424). In order to locate the region responsible for the fusogenic properties of preS, five mutant proteins have been obtained from the preS1 domain of HBV, in which 40 amino acids have been deleted from the sequence, with the starting point of each deletion moving 20 residues along the sequence. These proteins have been characterized by fluorescence and circular dichroism spectroscopy, establishing that, in all cases, they retain their mostly non-ordered conformation with a high percentage of β structure typical of the full-length protein. All the mutants can insert into the lipid matrix of dimyristoylphosphatidylglycerol vesicles. Moreover, we have studied the interaction of the proteins with acidic phospholipid vesicles and each one produces, to a greater or lesser extent, the effects of destabilizing vesicles observed with the full-length preS domain. The ability of all mutants, which cover the complete sequence of preS1, to destabilize the phospholipid bilayers points to a three-dimensional structure and/or distribution of amino acids rather than to a particular amino acid sequence as being responsible for the membrane fusion process.

Specific mutations in the C-terminus domain of HBV surface antigen significantly correlate with low level of serum HBV-DNA in patients with chronic HBV infection

BACKGROUND

To define HBsAg-mutations correlated with different serum HBV-DNA levels in HBV chronically-infected drug-naive patients.

METHODS

This study included 187 patients stratified into the following ranges of serum HBV-DNA:12-2000 IU/ml, 2000-100,000 IU/ml, and >100,000 IU/ml. HBsAg-mutations were associated with HBV-DNA levels by applying a Bayesian-Partitional-Model and Fisher-exact test. Mutant and wild-type HBV genotype-D genomes were expressed in Huh7 cells and HBsAg-production was determined in cell-supernatants at 3 days-post-transfection.

RESULTS

Specific HBsAg-mutations (M197T,-S204N-Y206C/H-F220L) were significantly correlated with serum HBV-DNA <2000 IU/ml (posterior-probability>90%, P < 0.05). The presence of Y206C/H and/or F220L was also associated with lower median (IQR) HBsAg-levels and lower median (IQR) transaminases (for HBsAg:250[115-840] IU/ml for Y206C/H and/or F220L versus 4300[640-11,838] IU/ml for wild-type, P = 0.023; for ALT:28[21-40] IU/ml versus 53[34-90] IU/ml, P < 0.001). These mutations were localized in the HBsAg C-terminus, known to be involved in virion and/or HBsAg secretion. The co-occurrence of Y206C + F220L was found significant by cluster-analysis, (P = 0.02). In addition, in an in-vitro model Y206C + F220L determined a 2.8-3.3 fold-reduction of HBsAg-amount released in supernatants compared to single mutants and wt (Y206C + F220L = 5,679 IU/ml; Y206H = 16,305 IU/ml; F220L = 18,368 IU/ml; Y206C = 18,680 IU/ml; wt = 14,280 IU/ml, P < 0.05).

CONCLUSIONS

Specific HBsAg-mutations (compartmentalized in the HBsAg C-terminus) correlated with low-serum HBV-DNA and HBsAg-levels. These findings can be important to understand mechanisms underlying low HBV replicative potential including the inactive-carrier state.

Tupaia belangeri as an experimental animal model for viral infection

Tupaias, or tree shrews, are small mammals that are similar in appearance to squirrels. The morphological and behavioral characteristics of the group have been extensively characterized, and despite previously being classified as primates, recent studies have placed the group in its own family, the Tupaiidae. Genomic analysis has revealed that the genus Tupaia is closer to humans than it is to rodents. In addition, tupaias are susceptible to hepatitis B virus and hepatitis C virus. The only other experimental animal that has been demonstrated to be sensitive to both of these viruses is the chimpanzee, but restrictions on animal testing have meant that experiments using chimpanzees have become almost impossible. Consequently, the development of the tupaia for use as an animal infection model could become a powerful tool for hepatitis virus research and in preclinical studies on drug development.