Interaction of hepatitis B virus with cells

Therapeutic Potential of Engineered Virus-like Particles of Parvovirus B19

Virus-like particles (VLPs) comprise one or many structural components of virions, except their genetic material. Thus, VLPs keep their structural properties of cellular recognition while being non-infectious. VLPs of Parvovirus B19 (B19V) can be produced by the heterologous expression of their structural proteins VP1 and VP2 in bacteria. These proteins are purified under denaturing conditions, refolded, and assembled into VLPs. Moreover, chimeric forms of VP2 have been constructed to harbor peptides or functional proteins on the surface of the particles without dropping their competence to form VLPs, serving as presenting nanoparticles. The in-vitro assembly approach offers exciting possibilities for the composition of VLPs, as more than one chimeric form of VP2 can be included in the assembly stage, producing multifunctional VLPs. Here, the heterologous expression and in-vitro assembly of B19V structural proteins and their chimeras are reviewed. Considerations for the engineering of the structural proteins of B19V are also discussed. Finally, the construction of multifunctional VLPs and their future potential as innovative medical tools are examined.

Nanocaged platforms: modification, drug delivery and nanotoxicity. Opening synthetic cages to release the tiger

Nanocages (NCs) have emerged as a new class of drug-carriers, with a wide range of possibilities in multi-modality medical treatments and theranostics. Nanocages can overcome such limitations as high toxicity caused by anti-cancer chemotherapy or by the nanocarrier itself, due to their unique characteristics. These properties consist of: (1) a high loading-capacity (spacious interior); (2) a porous structure (analogous to openings between the bars of the cage); (3) enabling smart release (a key to unlock the cage); and (4) a low likelihood of unfavorable immune responses (the outside of the cage is safe). In this review, we cover different classes of NC structures such as virus-like particles (VLPs), protein NCs, DNA NCs, supramolecular nanosystems, hybrid metal-organic NCs, gold NCs, carbon-based NCs and silica NCs. Moreover, NC-assisted drug delivery including modification methods, drug immobilization, active targeting, and stimulus-responsive release mechanisms are discussed, highlighting the advantages, disadvantages and challenges. Finally, translation of NCs into clinical applications, and an up-to-date assessment of the nanotoxicology considerations of NCs are presented.

Binding and Uptake into Human Hepatocellular Carcinoma Cells of Peptide-Functionalized Gold Nanoparticles

One of the most daunting challenges of nanomedicine is the finding of appropriate targeting agents to deliver suitable payloads precisely to cells affected by malignancies. Even more complex is the ability to ensure that the nanosystems enter those cells. Here, we use 2 nm (metal core) gold nanoparticles to target human hepatocellular carcinoma (HepG2) cells stably transfected with the SERPINB3 (SB3) protein. The nanoparticles were coated with a 85:15 mixture of thiols featuring, respectively, a phosphoryl choline (to ensure water solubility and biocompatibility) and a 28-mer peptide corresponding to the amino acid sequence 21-47 of the hepatitis B virus-PreS1 protein (PreS1(21-47)). Conjugation of the peptide was performed via the maleimide-thiol reaction in methanol, allowing the use of a limited amount of the targeting molecule. This is an efficient procedure also in the perspective of selecting libraries of new targeting agents. The rationale behind the selection of the peptide is that SB3, which is undetectable in normal hepatocytes, is overexpressed in hepatocellular carcinoma and in hepatoblastoma and has been proposed as a target of the hepatitis B virus (HBV). For the latter, the key recognition element is the PreS1(21-47) peptide, which is a fragment of one of the proteins composing the viral envelope. The ability of the conjugated nanoparticles to bind the target protein SB3, expressed in liver cancer cells, was investigated by surface plasmon resonance analysis and in vitro via cellular uptake analysis followed by atomic absorption analysis of digested samples. The results showed that the PreS1(21-47) peptide is a suitable targeting agent for cells overexpressing the SB3 protein. Even more important is the evidence that the gold nanoparticles are internalized by the cells. The comparison between the surface plasmon resonance analysis and the cellular uptake studies suggests that the presentation of the protein on the cell surface is critical for efficient recognition.

Hepatoepigenetic Alterations in Viral and Nonviral-Induced Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a major public health concern and one of the leading causes of tumour-related deaths worldwide. Extensive evidence endorses that HCC is a multifactorial disease characterised by hepatic cirrhosis mostly associated with chronic inflammation and hepatitis B/C viral infections. Interaction of viral products with the host cell machinery may lead to increased frequency of genetic and epigenetic aberrations that cause harmful alterations in gene transcription. This may provide a progressive selective advantage for neoplastic transformation of hepatocytes associated with phenotypic heterogeneity of intratumour HCC cells, thus posing even more challenges in HCC treatment development. Epigenetic aberrations involving DNA methylation, histone modifications, and noncoding miRNA dysregulation have been shown to be intimately linked with and play a critical role in tumour initiation, progression, and metastases. The current review focuses on the aberrant hepatoepigenetics events that play important roles in hepatocarcinogenesis and their utilities in the development of HCC therapy.

A safe and efficient hepatocyte-selective carrier system based on myristoylated preS1/21-47 domain of hepatitis B virus

A safe and efficient liver targeted PEGylated liposome (PEG-Lip) based on N-terminal myristoylated preS1/21-47 (preS1/21-47(myr)) of hepatitis B virus was successfully developed. The study aimed to elucidate the cellular uptake mechanism of preS1/21-47(myr) modified PEG-Lip (preS1/21-47(myr)-PEG-Lip) in hepatogenic cells and the distribution behavior of preS1/21-47(myr)-PEG-Lip in Vr:CD1 (ICR) mice. The cellular uptake results showed that preS1/21-47(myr)-PEG-Lip was effectively taken up by hepatogenic cells (including primary hepatocytes and liver tumor cells) through a receptor-mediated endocytosis pathway compared with non-hepatogenic cells. After systemic administration to H22 hepatoma-bearing mice, preS1/21-47(myr)-PEG-Lip showed significant liver-specific delivery and an increase in the distribution of preS1/21-47(myr)-PEG-Lip in hepatic tumor. Furthermore, the antitumor effect of preS1/21-47(myr)-PEG-Lip loaded with paclitaxel (PTX) was remarkably stronger than that of PTX injection and PTX loaded liposomes (including common liposomes and PEG-Lip). In safety evaluation, no acute systemic toxicity and immunotoxicity were observed after intravenous injection of preS1/21-47(myr)-PEG-Lip. No liver toxicity was observed despite the dramatic increase of preS1/21-47(myr)-PEG-Lip in liver. Taken together, preS1/21-47(myr)-PEG-Lip represents a promising carrier system for targeted liver disease therapy and imaging.

Liver cell specific targeting by the preS1 domain of hepatitis B virus surface antigen displayed on protein nanocages

Protein nanocages are self-organized complexes of oligomers whose three-dimensional architecture can been determined in detail. These structures possess nanoscale inner cavities into which a variety of molecules, including therapeutic or diagnostic agents, can be encapsulated. These properties yield these particles suitable for a new class of drug delivery carrier, or as a bioimaging reagent that might respond to biochemical signals in many different cellular processes. We report here the design, synthesis, and biological characterization of a hepatocyte-specific nanocage carrying small heat-shock protein. These nanoscale protein cages, with a targeting peptide composed of a preS1 derivative from the hepatitis B virus on their surfaces, were prepared by genetic engineering techniques. PreS1-carrying nanocages showed lower cytotoxicity and significantly higher specificity for human hepatocyte cell lines than other cell lines in vitro. These results suggested that small heat-shock protein-based nanocages present great potential for the development of effective targeted delivery of various agents to specific cells.

Proteomic analysis of cell lines expressing small hepatitis B surface antigen revealed decreased glucose-regulated protein 78 kDa expression in association with higher susceptibility to apoptosis

Accumulating evidence suggests a key role of hepatocyte apoptosis in the pathogenesis of viral hepatitis B. It was found in this study that stable expression of small hepatitis B surface antigen (SHBs) in HepG2 and Huh7 cells increased susceptibility to apoptosis. Proteomic analysis of SHBs expressing HepG2 cells revealed 43 down-regulated and 38 up-regulated proteins. Some have been implicated in apoptosis, including glucose-regulated protein 78 kDa (GRP78), heterogeneous nuclear ribonucleoprotein H3 (hnRNP H), Rho GDP dissociation inhibitor (GDI), cystatin B, far upstream element-binding protein (FUSEbp), and TNF receptor-associated protein 1 (TRAP1). Differential expression of GRP78 and several other proteins was confirmed by Western blot analysis. Replenishing GRP78 improved cellular resistance to apoptosis, whereas reduction of GRP78 by siRNA increased susceptibility even in the absence of SHBs. Taken together, these results suggest that HBsAg plays a pro-apoptotic role through down-regulation of GRP78.

A chemical lipid modification of recombinant preS antigen to study the mechanism of HBV attachment to the host cell

Surface antigen preS of Hepatitis B virus plays fundamental roles in mediating receptor recognition and virus internalization. Myristoylation at N-terminal Gly(2) residue of preS is essential for viral attachment and infectivity. A number of myristoylated proteins have been shown to undergo a conformational change (myristoyl switch) that alters their affinity to cell membrane. However, there is little knowledge about what effect this fatty acylation contributes in virus-host cell interaction. Here we demonstrated a new method for lipid modification of recombinant preS protein at N-terminal residue 2 with alkylating chemicals. Modified preS was able to inhibit HBV penetrating into HepG2 cells with an increased efficiency compared to unmodified form. Flow cytometric analysis indicated that lipid modification enhanced the binding affinity of preS to hepatocytes, but not resulting from hydrophobic interaction. CD analysis further revealed a conformational change of modified preS in the presence of membrane mimetics. These findings imply that the conformation transition induced by fatty acylation is important for efficient attachment of virus to cell receptors, and this method of chemical lipid modification provides a basis for designing therapeutic inhibitors to Hepatitis B virus.

Inhibition of hepatitis viral replication by siRNA

Small interfering RNA (siRNA)-mediated sequence-specific gene silencing is a powerful tool to inhibit endogenous and exogenous gene expression, and it holds great potential to prevent and eradicate viral infection, for which existing therapy is inadequate, such as HIV, hepatitis B virus (HBV) and hepatitis C virus (HCV). A number of studies have documented the effectiveness of siRNA against HBV or HCV at various regions of the viral genome in infected human hepatoma cell lines. Selected siRNA may reduce the production of viral replicons, as well as structural or non-structural proteins by > 90%. Only a few in vivo studies that demonstrated the efficacy of siRNA in the suppression of HBV replication in mice are available. Thus, reliable models of HBV and HCV infection in small animals or non-human primates are needed to evaluate the delivery and efficacy of siRNA as a therapeutic modality for viral hepatitis.

Heterogeneity analysis of the hepatitis B virus genome in intrauterine infection

There are many factors leading to intrauterine infection with hepatitis B virus (HBV). These factors include viral structure, HBV mutations, HBV DNA level, placenta barrier, immune status of the mother, and susceptibility of the fetus. The purpose of this study was to investigate the possible relationship between intrauterine infection with and HBV mutations of the genome of the virus. In this study, HBsAg-positive mothers were divided into two groups: intrauterine infection group and non-infection group according to whether the newborn infants were infected or not. The intrauterine infection group included four pairs of mother and their newborn infants infected in utero, and non-infection group included five HBsAg-positive mothers. HBV sequences from the two groups were analyzed and compared. The predominant strains in the mothers and infants from the intrauterine infection group were not completely consistent. This suggested that both HBV predominant strains and minority strains in the mothers could infect their infants through intrauterine transmission. Some HBV mutations probably related to intrauterine infection were examined and it was found that the frequencies of mutations were low in isolates of the virus of infants from the intrauterine infection group and high in the non-infection group. These results suggest that some strains of HBV from the mother may be transmitted selectively to the fetus in utero because of viral heterogeneity. The strains without screened mutations such as P21L in the pre-S1 region may infect the fetus more readily.

Autonomous activation of hepatitis B virus large surface protein

AIM: To construct the yeast expression vector of hepatitis B virus large surface protein (LHBs), and to study its autonomous activation.

METHODS: The Matchmaker GAL4 two-hybrid technique was used. The LHBs, pre-S1, pre-S2 and SHBs genes were amplified by polymerase chain reaction (PCR) with respective primers. The amplified PCR fragments were then subcloned into the EcoR I/BamH I sites (5'ands) of pGBKT7 vector to obtain the expression vectors including pGBKT7(-)-LHBs, pGBKT7(-)-preS1, pGBKT7(-)-preS2 and pGBKT7(-)-SHBs. This vectors were identifed by PCR and digestion of EcoR I/BamH I. After the constructed vectors were transformed into yeast AH109, the yeast cells were plated on synthetic dropout nutrient medium (SD/-Trp and SD/-Trp-His-Ade) containing x-a-gal for testing their autonomous activation.

RESULTS: The yeast expression vectors were constructed. The yeast cells transformed with pGBKT7-LHB and pGBKT7-preS1 vectors could grow well on both of the media. However, cells transformed with pGBKT7-preS2 and pGBKT7-SHBs vectors could only grow on the SD/-Trp medium.

CONCLUSION: The LHBs functions as a transcriptional transactivator, and serves as the functional GAL4 activation domain (AD) to activate transcription of reporter genes (ADE2, HIS3, MEL1 and LacZ). The autonomous activation of LHBs roots in its pre-S1 domain.