Fine-mapping of the B-cell epitope domain at the N-terminus of the preS2 region of the hepatitis B surface antigen

Role of Small Envelope Protein in Sustaining the Intracellular and Extracellular Levels of Hepatitis B Virus Large and Middle Envelope Proteins

Hepatitis B virus (HBV) expresses co-terminal large (L), middle (M), and small (S) envelope proteins. S protein drives virion and subviral particle secretion, whereas L protein inhibits subviral particle secretion but coordinates virion morphogenesis. We previously found that preventing S protein expression from a subgenomic construct eliminated M protein. The present study further examined impact of S protein on L and M proteins. Mutations were introduced to subgenomic construct of genotype A or 1.1 mer replication construct of genotype A or D, and viral proteins were analyzed from transfected Huh7 cells. Mutating S gene ATG to prevent expression of full-length S protein eliminated M protein, reduced intracellular level of L protein despite its blocked secretion, and generated a truncated S protein through translation initiation from a downstream ATG. Truncated S protein was secretion deficient and could inhibit secretion of L, M, S proteins from wild-type constructs. Providing full-length S protein in trans rescued L protein secretion and increased its intracellular level from mutants of lost S gene ATG. Lost core protein expression reduced all the three envelope proteins. In conclusion, full-length S protein could sustain intracellular and extracellular L and M proteins, while truncated S protein could block subviral particle secretion.

Unusual Features of Sodium Taurocholate Cotransporting Polypeptide as a Hepatitis B Virus Receptor

Cell culture (cc)-derived hepatitis B virus (HBV) can infect differentiated HepaRG cells, but efficient infection requires addition of polyethylene glycol (PEG) during inoculation. Identification of sodium taurocholate cotransporting polypeptide (NTCP) as an HBV receptor enabled ccHBV infection of NTCP reconstituted HepG2 cells, although very little hepatitis B surface antigen (HBsAg) is produced. We found infection by patient serum-derived HBV (sHBV), which required purification of viral particles through ultracentrifugation or PEG precipitation, was PEG independent and much more efficient in HepaRG cells than in HepG2/NTCP cells. In contrast to hepatitis B e antigen (HBeAg), HBsAg was not a reliable marker of productive sHBV infection at early time points. A low HBsAg/HBeAg ratio by ccHBV-infected HepG2/NTCP cells was attributable to dimethyl sulfoxide (DMSO) in culture medium, NTCP overexpression, and HBV genotype D. HepG2/NTCP cells released more viral antigens than HepG2 cells after HBV genome delivery by adeno-associated virus, and stable expression of NTCP in a ccHBV producing cell line increased viral mRNAs, proteins, replicative DNA, and covalently closed circular DNA. NTCP protein expression in HepG2/NTCP cells, despite being driven by the cytomegalovirus promoter, was markedly increased by DMSO treatment. This at least partly explains ability of DMSO to promote ccHBV infection in such cell lines. In conclusion, NTCP appeared inefficient to mediate infection by serum-derived HBV. It could promote HBV RNA transcription while inhibiting HBsAg secretion. Efficient PEG-independent sHBV infection of HepaRG cells permits comparative studies of diverse clinical HBV isolates and will help identify additional factors on virion surface promoting attachment to hepatocytes.

IMPORTANCE

Currently in vitro infection with hepatitis B virus (HBV) depends on cell culture-derived HBV inoculated in the presence of polyethylene glycol. We found patient serum-derived HBV could efficiently infect differentiated HepaRG cells independent of polyethylene glycol, which represents a more physiological infection system. Serum-derived HBV has poor infectivity in HepG2 cells reconstituted with sodium taurocholate cotransporting polypeptide (NTCP), the currently accepted HBV receptor. Moreover, HepG2/NTCP cells secreted very little hepatitis B surface antigen after infection with cell culture-derived HBV, which was attributed to NTCP overexpression, genotype D virus, and dimethyl sulfoxide added to culture medium. NTCP could promote HBV RNA transcription, protein expression, and DNA replication in HepG2 cells stably transfected with HBV DNA, while dimethyl sulfoxide could increase NTCP protein level despite transcriptional control by a cytomegalovirus promoter. Therefore, this study revealed several unusual features of NTCP as an HBV receptor and established conditions for efficient serum virus infection in vitro.

Potato virus Y-like particles as a new carrier for the presentation of foreign protein stretches

Virus-like particle (VLP) technology represents a promising approach for the creation of efficient vaccines and materials for use in nanotechnological applications. For construction of a new carrier for foreign protein sequences, the coat protein (CP) gene from potato virus Y (PVY) was cloned and expressed in Escherichia coli cells. The PVY CP self-assembles into PVY-like particles, as demonstrated by electron microscopy analysis of purified VLP preparations. The PVY CP with an N-terminal insertion of a foreign epitope (preS1) or of a whole protein (rubredoxin) retains its ability to form filamentous particles, whereas adding a foreign sequence to the C-terminus of the PVY CP generates mostly unstructured protein aggregates. This new filamentous plant virus-derived VLP carrier accommodates a foreign protein sequence that is up to 71 amino acids in length on the VLP surface and can be produced in E. coli in preparative amounts. The PVY CP VLPs are stable in physiological conditions, but they are sensitive to EDTA, high salt, and extreme pH. The presence of the preS1 epitope decreases the stability of the chimeric PVY CP particles at elevated temperatures. Mice that are immunized with chimeric PVY CP particles carrying preS1 epitopes exhibit a strong anti-preS1 immune response, even in the absence of adjuvants.

Retrospective characterization of the S open reading frame of HBV isolated from children with membranous nephropathy treated with interferon-alpha2b

BACKGROUND

A causal relationship exists between HBV infection and membranous nephropathy. The association is especially close in Black children in sub-Saharan Africa. Interferon-alpha2b is commonly used to treat this condition, but is effective in only 30-40% of patients. The reason for the poor response is unknown. The objective of this study was to determine if mutations in the surface gene of HBV isolated from Black children with HBV-associated membranous nephropathy before, during and after interferon treatment, have any effect on treatment response and vice versa.

METHODS

HBV DNA was extracted from a responder, a reverter and a non-responder before and after initiation of 16 weeks of interferon-alpha2b treatment. The preS1/preS2/S region was amplified, cloned and sequenced.

RESULTS

The preS2 region was the most variable in the reverter and the non-responder, and the S region was the most variable in the non-responder. Phylogenetic analysis showed that the viral population dynamics between the responder and the reverter/non-responder strains differed as a result of mutations in the surface gene.

CONCLUSIONS

The presence of mutations in the S region of HBV could be used as predictive markers to differentiate interferon-alpha2b responders from non-responders provided that detailed analysis of further genomes confirms our findings.

Construction and immunological evaluation of multivalent hepatitis B virus (HBV) core virus-like particles carrying HBV and HCV epitopes

A multivalent vaccine candidate against hepatitis B virus (HBV) and hepatitis C virus (HCV) infections was constructed on the basis of HBV core (HBc) virus-like particles (VLPs) as carriers. Chimeric VLPs that carried a virus-neutralizing HBV pre-S1 epitope corresponding to amino acids (aa) 20 to 47 in the major immunodominant region (MIR) and a highly conserved N-terminal HCV core epitope corresponding to aa 1 to 60 at the C terminus of the truncated HBcDelta protein (N-terminal aa 1 to 144 of full-length HBc) were produced in Escherichia coli cells and examined for their antigenicity and immunogenicity. The presence of two different foreign epitopes within the HBc molecule did not interfere with its VLP-forming ability, with the HBV pre-S1 epitope exposed on the surface and the HCV core epitope buried within the VLPs. After immunization of BALB/c mice, specific T-cell activation by both foreign epitopes and a high-titer antibody response against the pre-S1 epitope were found, whereas an antibody response against the HBc carrier was notably suppressed. Both inserted epitopes also induced a specific cytotoxic-T-lymphocyte (CTL) response, as shown by the gamma interferon (IFN-gamma) production profile.

Expression in and purification of Hepatitis B surface antigen (S-protein) from methylotrophic yeast Pichia pastoris

The study describes expression and purification of recombinant hepatitis B small surface antigen (rHBsAg hereafter) in methylotrophic yeast Pichia pastoris strain GS115. For expression of the rHBsAg, a single copy of 678 bp cDNA was inserted at the unique EcoRI site downstream of the alcohol oxidase (AOX 1) promoter of the 8.2 kb pHIL-D2 vector. The cDNA-pHIL-D2 construct was used to transform the strain GS115, resulting in a Mut(S) (Methanol Utilizing Slow) phenotype in which the 226 amino acids containing active and full-length rHBsAg protein could be expressed intra-cellularly during slow growth and induction with methanol. The recombinant protein from the Mut(S) expressor was harvested by cell disruption, and purified first by adsorption-desorption on aerosil followed by two-step chromatographic separation i.e. anion exchange on DEAE resin followed by gel permeation on Superdex 75. Reversed passive hem-agglutination assay (RPHA) was used to test the antigenicity while SDS-PAGE was performed to check the purity of the 27 kDa rHBsAg and its aggregates. The results showed that disruption at 12 Kpsi (three cycles), or 30 Kpsi (1 cycle), desorption with 10mM carbonate buffer (pH 9-10), and storage at 4 degrees C without detergent did not adversely affect the antigenicity of the rHbsAg. However, the presence of detergents such as TritonX100 and deoxycholate in the disruption and desorption buffers, respectively resulted in reduced antigenicity during storage both at 4 and -20 degrees C in spite of higher initial yields.