Dengue and Zika virus multi-epitope antigen expression in insect cells

Dengue virus and Zika virus are arthropod-borne flaviviruses that cause millions of infections worldwide. The co-circulation of both viruses makes serological diagnosis difficult as they share high amino acid similarities in viral proteins. Antigens are one of the key reagents in the differential diagnosis of these viruses through the detection of IgG antibodies in serological assays during the convalescent-phase of infections. Here, we report the expression of Dengue virus (DENV) and Zika virus (ZIKV) antigens containing non-conserved and immunodominant amino acid sequences using the baculovirus expression vector system in insect cells. We designed DENV and ZIKV antigens based on the domain III of the E protein (EDIII) after analyzing previously reported epitopes and by multiple alignment of the most important flaviviruses. The ZIKV and DENV multi-epitope genes were designed as tandem repeats or impaired repeats separated by tetra- or hexa-glycine linkers. The biochemical analyses revealed adequate expression of the antigens. Then, the obtained multi-epitope antigens were semi-purified in a sucrose gradient and tested using patients' sera collected during the convalescent-phase that were previously diagnosed positive for anti-DENV and -ZIKV IgG antibodies. The optimal serum dilution was 1:200, and the mean absorbance values in the preliminary tests show that multi-epitope antigens have been recognized by human sera. The production of both antigens using the multi-epitope strategy in the eukaryotic system and based on the EDIII regions provide a proof of concept for the use of antigens in the differentiation between DENV and ZIKV.

Chikungunya E2 Protein Produced in E. coli and HEK293-T Cells-Comparison of Their Performances in ELISA

Chikungunya virus (CHIKV) is a mosquito-borne pathogen that causes a disease characterized by the acute onset of fever accompanied by arthralgia and intense joint pain. Clinical similarities and cocirculation of this and other arboviruses in many tropical countries highlight the necessity for efficient and accessible diagnostic tools. CHIKV envelope proteins are highly conserved among alphaviruses and, particularly, the envelope 2 glycoprotein (CHIKV-E2) appears to be immunodominant and has a considerable serodiagnosis potential. Here, we investigate how glycosylation of CHIKV-E2 affects antigen/antibody interaction and how this affects the performance of CHIKV-E2-based Indirect ELISA tests. We compare two CHIKV-E2 recombinant antigens produced in different expression systems: prokaryotic-versus eukaryotic-made recombinant proteins. CHIKV-E2 antigens are expressed either in E. coli BL21(DE3)-a prokaryotic system unable to produce post-translational modifications-or in HEK-293T mammalian cells-a eukaryotic system able to add post-translational modifications, including glycosylation sites. Both prokaryotic and eukaryotic recombinant CHIKV-E2 react strongly to anti-CHIKV IgG antibodies, showing accuracy levels that are higher than 90%. However, the glycan-added viral antigen presents better sensitivity and specificity (85 and 98%) than the non-glycosylated antigen (81 and 71%, respectively) in anti-CHIKV IgM ELISA assays.

E. coli production process yields stable dengue 1 virus-sized particles (VSPs)

Dengue fever is one of the most wide-spread vector-borne diseases in the world. Although dengue-associated mortality is low, morbidity and economic impact are high. Current licensed vaccines are limited and mediate only partial protection, thus a cost-effective vaccine with improved efficacy is strongly needed. In this work, recombinant dengue serotype 1 E protein was produced in E. coli, inclusion bodies were isolated and the E protein solubilized in urea and purified using an immobilized metal chelate affinity column. The protein was refolded by dialysis in order to obtain virus-like particles (VLPs). Particle assembly was confirmed using size-exclusion chromatography, dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy and stimulated emission depletion fluorescence (STED) microscopy. Particle diameter was strongly dependent on temperature, pH, buffer salt composition, and addition of L-arginine. Particles were stable in carbonate buffer at pH 9.5 and higher at 4 °C and did not aggregate during short-term temperature increase up to 55 °C. However, on basis of the above analyses, especially the results of DLS, TEM and STED, it was concluded that the particles obtained did not have an optimal virus-like structure and were therefore designated "virus-sized particles" (VSPs) rather than VLPs. Immunization of rabbits with the particles did not induce neutralizing antibodies, despite the recognition of the native virus by rabbit antibodies. As the titers against the immunogen were much higher than against the (heat-inactivated) virus, it is assumed that the conformation of the particles at the time of immunization was not optimal. Studies are currently underway to improve the quality of the E protein virus-sized particles towards true virus-like particles in order to optimize its potential as a dengue vaccine candidate.

Overexpression of the human cytomegalovirus UL111A is correlated with favorable survival of patients with gastric cancer and changes T-cell infiltration and suppresses carcinogenesis

Purpose

We previously found that human cytomegalovirus (HCMV) infection is associated with gastric cancer (GC) development. UL111A plays a role during HCMV productive or latent infection. However, UL111A expression profiles in GC tissues and their relationship with this disease are unknown.

Methods

PCR and nested RT-PCR were performed to verify UL111A expression in 71 GC tissues and its transcripts in 16 UL111A-positive GC samples. UL111A expression levels in GC patients were evaluated by immunohistochemistry on a tissue microarray for 620 GC patients. The correlations among UL111A expression levels, clinicopathological characteristics, and prognosis were analyzed. Further, the effects of overexpression of latency-associated viral interleukin-10 (LAcmvIL-10) and cmvIL-10 on GC cell proliferation, colony formation, migration, and invasion were assessed.

Results

The UL111A detection rate in GC tissues was 32.4% (23/71) and that of its mRNA expression was 68.75% (11/16). High expression of UL111A was also related to better overall and disease-free survival in GC patients. GC patients with TNM II/III stage expressing higher UL111A levels might benefit from adjuvant chemotherapy (ACT) after surgery. Moreover, high UL111A expression was also associated with increased CD4+ , CD8+ T-lymphocyte and Foxp3+ T-cell infiltration. In vitro assays further demonstrated that LAcmvIL-10 and cmvIL-10 overexpression inhibits GC cell line proliferation, colony formation, migration, and invasion.

Conclusions

High UL111A expression changes the number of infiltrating T cells and is associated with favorable survival. Therefore, UL111A could be used as an independent prognostic biomarker and might be a potential therapeutic target for GC.

Electronic supplementary material

The online version of this article (10.1007/s00432-019-03092-x) contains supplementary material, which is available to authorized users.

Expression, Purification, and Crystallization of Full-Length HSV-1 gB for Structure Determination

HSV glycoproteins play important roles in the viral life cycle, particularly viral cell entry. Here we describe the protocol for expression, purification, and crystallization of full-length HSV-1 glycoprotein B. The protocol provides a framework for incorporating transmembrane domain-stabilizing amphipols into the crystallization setup and can be adapted to isolate other complete HSV glycoproteins.

Production of tetravalent dengue virus envelope protein domain III based antigens in lettuce chloroplasts and immunologic analysis for future oral vaccine development

Dengue fever is a mosquito (Aedes aegypti) -transmitted viral disease that is endemic in more than 125 countries around the world. There are four serotypes of the dengue virus (DENV 1-4) and a safe and effective dengue vaccine must provide protection against all four serotypes. To date, the first vaccine, Dengvaxia (CYD-TDV), is available after many decades' efforts, but only has moderate efficacy. More effective and affordable vaccines are hence required. Plants offer promising vaccine production platforms and food crops offer additional advantages for the production of edible human and animal vaccines, thus eliminating the need for expensive fermentation, purification, cold storage and sterile delivery. Oral vaccines can elicit humoural and cellular immunity via both the mucosal and humoral immune systems. Here, we report the production of tetravalent EDIII antigen (EDIII-1-4) in stably transformed lettuce chloroplasts. Transplastomic EDIII-1-4-expressing lettuce lines were obtained and homoplasmy was verified by Southern blot analysis. Expression of EDIII-1-4 antigens was demonstrated by immunoblotting, with the EDIII-1-4 antigen accumulating to 3.45% of the total protein content. Immunological assays in rabbits showed immunogenicity of EDIII-1-4. Our in vitro gastrointestinal digestion analysis revealed that EDIII-1-4 antigens are well protected when passing through the oral and gastric digestion phases but underwent degradation during the intestinal phase. Our results demonstrate that lettuce chloroplast engineering is a promising approach for future production of an affordable oral dengue vaccine.

Assembly of tomato blistering mosaic virus-like particles using a baculovirus expression vector system

The expression of several structural proteins from a wide variety of viruses in heterologous cell culture systems results in the formation of virus-like particles (VLPs). These VLPs structurally resemble the wild-type virus particles and have been used to study viral assembly process and as antigens for diagnosis and/or vaccine development. Tomato blistering mosaic virus (ToBMV) is a tymovirus that has a 6.3-kb positive-sense ssRNA genome. We have employed the baculovirus expression vector system (BEVS) for the production of tymovirus-like particles (tVLPs) in insect cells. Two recombinant baculoviruses containing the ToBMV wild-type coat protein (CP) gene or a modified short amino-terminal deletion (Δ_2-24CP) variant were constructed and used to infect insect cells. Both recombinant viruses were able to express ToBMV CP and Δ_2-24CP from infected insect cells that self-assembled into tVLPs. Therefore, the N-terminal residues (2-24) of the native ToBMV CP were shown not to be essential for self-assembly of tVLPs. We also constructed a third recombinant baculovirus containing a small sequence coding for the major epitope of the chikungunya virus (CHIKV) envelope protein 2 (E2) replacing the native CP N-terminal 2-24 amino acids. This recombinant virus also produced tVLPs. In summary, ToBMV VLPs can be produced in a baculovirus/insect cell heterologous expression system, and the N-terminal residues 2-24 of the CP are not essential for this assembly, allowing its potential use as a protein carrier that facilitates antigen purification and might be used for diagnosis.

Bardoxolone Methyl Suppresses Hepatitis B Virus Large Surface Protein Variant W4P-Related Carcinogenesis and Hepatocellular Carcinoma Cell Proliferation Via the Inhibition of Signal Transducer and Activator of Transcription 3 Signaling

Bardoxolone methyl (CDDO-me) is a synthetic triterpenoid that has been shown to suppress various cancers and inflammation. It has been implicated for the suppression of signal transducer and activator of transcription 3 (STAT3)-mediated signaling, which plays crucial roles in the development and progression of hepatocellular carcinoma (HCC). Previously, we showed that hepatitis B virus (HBV) large surface protein (LHB) variant W4P promotes carcinogenesis and tumor progression through STAT3 activation. Thus, we examined the anti-cancer activity of CDDO-me against HCC using W4P-LHB-expressing NIH3T3 cells and HepG2 and Huh7 HCC cell lines. CDDO-me exerted cytotoxic activity against W4P-LHB-expressing NIH3T3 cells, HepG2 cells, and Huh7 cells, and induced apoptotic cell death in a dose-dependent manner, demonstrating its anti-cancer activity against HCC. Sublethal concentrations of CDDO-me suppressed STAT3 activation by W4P-LHB ectopic expression and interleukin-6 treatment in W4P-LHB-NIH3T3 and Huh7 cells respectively. The suppression of STAT3 activation by CDDO-me in W4P-LHB-NIH3T3 cells was further confirmed by decreased cyclin D1 protein levels and increased p21 and p53 mRNA synthesis. In addition, CDDO-me treatment resulted in decreased cell migration and colony formation in in vitro assays using W4P-LHB-NIH3T3, HepG2, or Huh7 cell lines, supporting its anti-cancer activity through STAT3 inhibition. Furthermore, -CDDO-me administration significantly suppressed tumor growth induced by W4P-LHB-expressing NIH3T3 cells in nude mice, confirming its anti-cancer activity. Collectively, our findings demonstrated that CDDO-me is capable of suppressing STAT3 activation in HCC cells and cells transformed by the natural variant of HBV protein. The results suggest that CDDO-me can be a potential therapeutic agent against HCC, especially tumors related to HBV mutations.

VSV-G Viral Envelope Glycoprotein Prepared from Pichia pastoris Enhances Transfection of DNA into Animal Cells

Vesicular stomatitis virus G glycoprotein (VSV-G) has been widely used for pseudotyping retroviral, lentiviral, and artificial viral vectors. The objective of this study was to establish a potential approach for large-scale production of VSV-G. To this end, VSV-G was cloned with an N-terminal His-tag into Pichia pastoris expression vector pPIC3.5K. Three clones (Mut^s) containing the VSV-G expression cassette were identified by PCR. All clones proliferated normally in expansion medium, whereas the proliferation was reduced significantly under induction conditions. VSV-G protein was detected in cell lysates by western blot analysis, and the highest expression level was observed at 96 h post induction. VSV-G could also be obtained from the condition medium of yeast protoplasts. Furthermore, VSV-G could be incorporated into Ad293 cells and was able to induce cell fusion, leading to the transfer of cytoplasmic protein. Finally, VSV-G-mediated DNA transfection was assayed by flow cytometry and luciferase measurement. Incubation of VSV-G lysate with the pGL3-control DNA complex increased the luciferase activity in Ad293 and HeLa cells by about 3-fold. Likewise, incubation of VSV-G lysate with the pCMV-DsRed DNA complex improved the transfection efficiency into Ad293 by 10% and into HeLa cells by about 1-fold. In conclusion, these results demonstrate that VSV-G could be produced from P. pastoris with biofunctionalities, demonstrating that large-scale production of the viral glycoprotein is feasible.

Expression of HERV-K108 envelope interferes with HIV-1 production

The human endogenous retroviruses (HERV)-K of the HML-2 group include full-length or near full-length elements encoding functional proteins, and are classified as type-1 or type-2 (type-1 has a deletion in the 5' end of the env gene). Because proteins of different retroviruses can interact, we hypothesized that HERV-K envelope (Env) could influence HIV-1 replication. Here we describe the negative effect of envelope expression of certain type-2 HERV-Ks on HIV-1 production. All HIV-1 and SIV strains tested were susceptible to various degrees to inhibition by the HERV-K108 envelope. We identified four residues within HERV-K108 Env as being critical to inhibit HIV-1 production. No inhibition was observed on EGFP expression, indicating that HERV-K Env does not affect general protein production. These findings demonstrate that envelope proteins from some endogenous retroviruses can limit production of exogenous lentiviruses such as HIV-1. Future studies will elucidate the mechanism mediating HIV-1 inhibition by HERV Envs.

A new strategy for full-length Ebola virus glycoprotein expression in E.coli

Ebola virus (EBOV) causes severe hemorrhagic fever in humans and non-human primates with high rates of fatality. Glycoprotein (GP) is the only envelope protein of EBOV, which may play a critical role in virus attachment and entry as well as stimulating host protective immune responses. However, the lack of expression of full-length GP in Escherichia coli hinders the further study of its function in viral pathogenesis. In this study, the vp40 gene was fused to the full-length gp gene and cloned into a prokaryotic expression vector. We showed that the VP40-GP and GP-VP40 fusion proteins could be expressed in E.coli at 16 °C. In addition, it was shown that the position of vp40 in the fusion proteins affected the yields of the fusion proteins, with a higher level of production of the fusion protein when vp40 was upstream of gp compared to when it was downstream. The results provide a strategy for the expression of a large quantity of EBOV full-length GP, which is of importance for further analyzing the relationship between the structure and function of GP and developing an antibody for the treatment of EBOV infection.

WSV399, a viral tegument protein, interacts with the shrimp protein PmVRP15 to facilitate viral trafficking and assembly

Viral responsive protein 15 (PmVRP15) has been identified as a highly up-regulated gene in the hemocyte of white spot syndrome virus (WSSV)-infected shrimp Penaeus monodon. However, the function of PmVRP15 in host-viral interaction was still unclear. To elucidate PmVRP15 function, the interacting partner of PmVRP15 from WSSV was screened by yeast two-hybrid assay and then confirmed by co-immunoprecipitation (Co-IP). Only WSV399 protein was identified as a PmVRP15 binding protein; however, the function of WSV399 has not been characterized. Localization of WSV399 on the WSSV virion was revealed by immunoblotting analysis (in vitro) and immunoelectron microscopy (in vivo). The results showed that WSV399 is a structural protein of the WSSV virion and is particularly located on the tegument. Gene silencing of wsv399 in WSSV-infected shrimp reduced the percentage of cumulative mortality by 74%, although the expression level of a viral replication marker gene, vp28, was not changed suggesting that WSV399 might not involved in viral replication but viral assembly. Because it has already been known that tegument proteins function in capsid transport during viral trafficking and assembly, interaction between PmVRP15 on hemocyte nuclear membrane and the WSV399 viral tegument protein suggests that PmVRP15 might be required for trafficking and assembly of WSSV during infection.

Molecular optimization of rabies virus glycoprotein expression in Pichia pastoris

In this work, different approaches were investigated to enhance the expression rabies virus glycoprotein (RABV-G) in the yeast Pichia pastoris; this membrane protein is responsible for the synthesis of rabies neutralizing antibodies. First, the impact of synonymous codon usage bias was examined and an optimized RABV-G gene was synthesized. Nevertheless, data showed that the secretion of the optimized RABV-G gene was not tremendously increased as compared with the non-optimized one. In addition, similar levels of RABV-G were obtained when α-factor mating factor from Saccharomyces cerevisiae or the acid phosphatase PHO1 was used as a secretion signal. Therefore, sequence optimization and secretion signal were not the major bottlenecks for high-level expression of RABV-G in P. pastoris. Unfolded protein response (UPR) was induced in clones containing high copy number of RABV-G expression cassette indicating that folding was the limiting step for RABV-G secretion. To circumvent this limitation, co-overexpression of five factors involved in oxidative protein folding was investigated. Among these factors only PDI1, ERO1 and GPX1 proved their benefit to enhance the expression. The highest expression level of RABV-G reached 1230 ng ml(-1). Competitive neutralizing assay confirmed that the recombinant protein was produced in the correct conformational form in this host.

Sodium tanshinone IIA sulfonate affects Marek's disease virus replication by inhibiting gB expression

CONTEXT

Previous studies demonstrated that sodium tanshinone IIA sulfonate (STS) could inhibit MDV replication in vitro. The mechanism about how STS inhibits MDV replication is still not well understood.

OBJECTIVE

In this study, we evaluated the effect of STS on gB gene/protein of Marek's disease virus (MDV).

MATERIALS AND METHODS

The concentration of 0.25 mg/ml of STS was used in this study. Meanwhile, 0.25 mg/ml of acyclovir (ACV) was used as a positive control. About 9-11-d-old embryonated specific-pathogen-free (SPF) chicken eggs were used to prepare CEF cells. CEF cells were infected with MDV 2 h, followed by treatment with STS. Real-time PCR and western blot assay were used to measure the gB (UL27) gene/protein expression in STS treatment group at 24, 48, 72, and 96 h post-infection.

RESULTS

Compared with MDV control, the gB gene copies were significantly decreased in STS and ACV treatment groups at 72 h and 96 h (p < 0.05), both in the DNA and in the mRNA level. Furthermore, the expression of gB protein was also inhibited by STS at 24, 72, and 96 h.

DISCUSSION AND CONCLUSION

Our study demonstrated that STS could effectively inhibit the MDV replication by suppressing gB gene/protein expression in cell culture.

Characterization of two novel ADP ribosylation factors from giant freshwater prawn Macrobrachium rosenbergii and their responses to WSSV challenge

ADP-ribosylation factors (Arfs) are small GTP-binding proteins that have an essential function in intracellular trafficking and organelle structure. To date, little information is available on the Arfs in the economically important giant freshwater prawn Macrobrachium rosenbergii and their relationship to viral infection. Here we identified two Arf genes from M. rosenbergii (MrArf1 and MrArf2) for the first time. Phylogenetic analysis showed that MrArf1, together with MjArf1 from shrimp Marsupenaeus japonicus belonged to Class I Arfs. By contrast, MrArf2 didn't not match any of the Arfs classes of I/II/III, although it could be clustered with an Arf protein from M. japonicas called MjArfn, which may represent an analog of the Arf. MrArf1 was ubiquitously expressed in all the examined tissues, with the highest transcription level in the hepatopancreas, whereas MrArf2 was only highly expressed in the hepatopancreas and exhibited very low levels in the heart, stomach, gills and intestine. The expression level of MrArf1 in the gills was down-regulated post 24 h WSSV challenge, and reached the maximal level at 48 h. MrArf1 in the hepatopancreas went up from 24 to 48 h WSSV challenge. MrArf2 transcript in the gill also went down at 24 h and then was upregulated at 48 h WSSV challenge. MrArf2 increased significantly in the hepatopancreas 24 h after infection and then went down at 48 h WSSV challenge. RNAi results showed that knockdown of MrArf1 or MrArf2 could inhibit the expression of the envelope protein gene vp28 of the WSSV. So, it could be speculated that MrArf1 and MrArf2 might play important roles in the innate immune system against WSSV infection.

Pichia pastoris-expressed dengue 2 envelope forms virus-like particles without pre-membrane protein and induces high titer neutralizing antibodies

Dengue is a mosquito-borne viral disease with a global prevalence. It is caused by four closely-related dengue viruses (DENVs 1–4). A dengue vaccine that can protect against all four viruses is an unmet public health need. Live attenuated vaccine development efforts have encountered unexpected interactions between the vaccine viruses, raising safety concerns. This has emphasized the need to explore non-replicating dengue vaccine options. Virus-like particles (VLPs) which can elicit robust immunity in the absence of infection offer potential promise for the development of non-replicating dengue vaccine alternatives. We have used the methylotrophic yeast Pichia pastoris to develop DENV envelope (E) protein-based VLPs. We designed a synthetic codon-optimized gene, encoding the N-terminal 395 amino acid residues of the DENV-2 E protein. It also included 5’ pre-membrane-derived signal peptide-encoding sequences to ensure proper translational processing, and 3’ 6× His tag-encoding sequences to facilitate purification of the expressed protein. This gene was integrated into the genome of P. pastoris host and expressed under the alcohol oxidase 1 promoter by methanol induction. Recombinant DENV-2 protein, which was present in the insoluble membrane fraction, was extracted and purified using Ni²⁺-affinity chromatography under denaturing conditions. Amino terminal sequencing and detection of glycosylation indicated that DENV-2 E had undergone proper post-translational processing. Electron microscopy revealed the presence of discrete VLPs in the purified protein preparation after dialysis. The E protein present in these VLPs was recognized by two different conformation-sensitive monoclonal antibodies. Low doses of DENV-2 E VLPs formulated in alum were immunogenic in inbred and outbred mice eliciting virus neutralizing titers >1∶1200 in flow cytometry based assays and protected AG129 mice against lethal challenge (p<0.05). The formation of immunogenic DENV-2 E VLPs in the absence of pre-membrane protein highlights the potential of P. pastoris in developing non-replicating, safe, efficacious and affordable dengue vaccine.

HIV-1 Env C2-V4 diversification in a slow-progressor infant reveals a flat but rugged fitness landscape

Human immunodeficiency virus type-1 (HIV-1) fitness has been associated with virus entry, a process mediated by the envelope glycoprotein (Env). We previously described Env genetic diversification in a Zambian, subtype C infected, slow-progressor child (1157i) in parallel with an evolving neutralizing antibody response. Because of the role the Variable-3 loop (V3) plays in transmission, cell tropism, neutralization sensitivity, and fitness, longitudinally isolated 1157i C2-V4 alleles were cloned into HIV-1NL4-3-eGFP and -DsRed2 infectious molecular clones. The fluorescent reporters allowed for dual-infection competitions between all patient-derived C2-V4 chimeras to quantify the effect of V3 diversification and selection on fitness. 'Winners' and 'losers' were readily discriminated among the C2-V4 alleles. Exceptional sensitivity for detection of subtle fitness differences was revealed through analysis of two alleles differing in a single synonymous amino acid. However, when the outcomes of N = 33 competitions were averaged for each chimera, the aggregate analysis showed that despite increasing diversification and divergence with time, natural selection of C2-V4 sequences in this individual did not appear to be producing a 'survival of the fittest' evolutionary pattern. Rather, we detected a relatively flat fitness landscape consistent with mutational robustness. Fitness outcomes were then correlated with individual components of the entry process. Env incorporation into particles correlated best with fitness, suggesting a role for Env avidity, as opposed to receptor/coreceptor affinity, in defining fitness. Nevertheless, biochemical analyses did not identify any step in HIV-1 entry as a dominant determinant of fitness. Our results lead us to conclude that multiple aspects of entry contribute to maintaining adequate HIV-1 fitness, and there is no surrogate analysis for determining fitness. The capacity for subtle polymorphisms in Env to nevertheless significantly impact viral fitness suggests fitness is best defined by head-to-head competition.

Photohighlighting approaches to access membrane dynamics of the Golgi apparatus

By providing quantitative, visual data of live cells, fluorescent protein-based microscopy techniques are furnishing novel insights into the complexities of membrane trafficking pathways and organelle dynamics. In this chapter, we describe experimental protocols employing fluorescent protein-based photohighlighting techniques to quantify protein movement into and out of the Golgi apparatus, an organelle that serves as the central sorting and processing station of the secretory pathway. The methods allow kinetic characteristics of Golgi-associated protein trafficking to be deciphered, which can help clarify how the Golgi maintains itself as a steady-state structure despite a continuous flux of secretory cargo passing into and out of this organelle. The guidelines presented in this chapter can also be applied to examine the dynamics of other intracellular organelle systems, elucidating mechanisms for how proteins are maintained in specific organelles and/or circulated to other destinations within the cell.

The role of proteolytic processing and the stable signal peptide in expression of the Old World arenavirus envelope glycoprotein ectodomain

Maturation of the arenavirus GP precursor (GPC) involves proteolytic processing by cellular signal peptidase and the proprotein convertase subtilisin kexin isozyme 1 (SKI-1)/site 1 protease (S1P), yielding a tripartite complex comprised of a stable signal peptide (SSP), the receptor-binding GP1, and the fusion-active transmembrane GP2. Here we investigated the roles of SKI-1/S1P processing and SSP in the biosynthesis of the recombinant GP ectodomains of lymphocytic choriomeningitis virus (LCMV) and Lassa virus (LASV). When expressed in mammalian cells, the LCMV and LASV GP ectodomains underwent processing by SKI-1/S1P, followed by dissociation of GP1 from GP2. The GP2 ectodomain spontaneously formed trimers as revealed by chemical cross-linking. The endogenous SSP, known to be crucial for maturation and transport of full-length arenavirus GPC was dispensable for processing and secretion of the soluble GP ectodomain, suggesting a specific role of SSP in the stable prefusion conformation and transport of full-length GPC.

Marek's disease virus expresses multiple UL44 (gC) variants through mRNA splicing that are all required for efficient horizontal transmission

Marek's disease (MD) is a devastating oncogenic viral disease of chickens caused by Gallid herpesvirus 2, or MD virus (MDV). MDV glycoprotein C (gC) is encoded by the alphaherpesvirus UL44 homolog and is essential for the horizontal transmission of MDV (K. W. Jarosinski and N. Osterrieder, J. Virol. 84:7911-7916, 2010). Alphaherpesvirus gC proteins are type 1 membrane proteins and are generally anchored in cellular membranes and the virion envelope by a short transmembrane domain. However, the majority of MDV gC is secreted in vitro, although secondary-structure analyses predict a carboxy-terminal transmembrane domain. In this report, two alternative mRNA splice variants were identified by reverse transcription (RT)-PCR analyses, and the encoded proteins were predicted to specify premature stop codons that would lead to gC proteins that lack the transmembrane domain. Based on the size of the intron removed for each UL44 (gC) transcript, they were termed gC104 and gC145. Recombinant MDV viruses were generated in which only full-length viral gC (vgCfull), gC104 (vgC104), or gC145 (vgC145) was expressed. Predictably, gCfull was expressed predominantly as a membrane-associated protein, while both gC104 and gC145 were secreted, suggesting that the dominant gC variants expressed in vitro are the spliced variants. In experimentally infected chickens, the expression of each of the gC variants individually did not alter replication or disease induction. However, horizontal transmission was reduced compared to that of wild-type or revertant viruses when the expression of only a single gC was allowed, indicating that all three forms of gC are required for the efficient transmission of MDV in chickens.

Immunocompetent truncated E2 glycoprotein of bovine viral diarrhea virus (BVDV) expressed in Nicotiana tabacum plants: a candidate antigen for new generation of veterinary vaccines

The bovine viral diarrhea virus (BVDV) is the etiological agent responsible for a wide spectrum of clinical diseases in cattle. The glycoprotein E2 is the major envelope protein of this virus and the strongest inductor of the immune response. There are several available commercial vaccines against bovine viral diarrhea (BVD), which show irregular performances. Here, we report the use of tobacco plants as an alternative productive platform for the expression of the truncated version of E2 glycoprotein (tE2) from the BVDV. The tE2 sequence, lacking the transmembrane domain, was cloned into the pK7WG2 Agrobacterium binary vector. The construct also carried the 2S2 Arabidopsis thaliana signal for directing the protein into the plant secretory pathway, the Kozak sequence, an hexa-histidine tag to facilitate protein purification and the KDEL endoplasmic reticulum retention signal. The resulting plasmid (pK-2S2-tE2-His-KDEL) was introduced into Agrobacterium tumefaciens strain EHA101 by electroporation. The transformed A. tumefaciens was then used to express tE2 in leaves of Nicotiana tabacum plants. Western blot and ELISA using specific monoclonal antibodies confirmed the presence of the recombinant tE2 protein in plant extracts. An estimated amount of 20 μg of tE2 per gram of fresh leaves was regularly obtained with this plant system. Injection of guinea pigs with plant extracts containing 20 μg of rtE2 induced the production of BVDV specific antibodies at equal or higher levels than those induced by whole virus vaccines. This is the first report of the production of an immunocompetent tE2 in N. tabacum plants, having the advantage to be free of any eventual animal contaminant.

A novel system for rapid and cost-effective production of detection and diagnostic reagents of West Nile virus in plants

The threat of West Nile virus (WNV) epidemics necessitates the development of a technology platform that can produce reagents to support detection and diagnosis rapidly and inexpensively. A plant expression system is attractive for protein production due to its low-cost and high-scalability nature and its ability to make appropriate posttranslational modifications. Here, we investigated the feasibility of using plants to produce two WNV detection and diagnostic reagents to address the current cost and scalability issues. We demonstrated that WNV DIII antigen and E16 monoclonal antibody are rapidly produced at high levels in two plant species and are easily purified. Furthermore, they are effective in identifying WNV and in detecting human IgM response to WNV infection. E16 mAb does not cross-react with other flaviviruses, therefore, is valuable for improving diagnostic accuracy. This study provides a proof of principle for using plants as a robust and economical system to produce diagnostic reagents for arboviruses.

[Influence of physiological state of Escherichia coli cells on the expression of soluble protein--recombinant analog of glycoprotein G of Herpes simplex virus of type 2]

It is shown that the recombinant protein GST-HSV2gG, containing the immunodominant regions of glycoprotein G of HSV-2 is accumulated in the form of inclusion bodies or in soluble form in the Escherichia coli BL21 (DE3) cells. The ratio between protein fractions varied depending on the physiological state of cells before biosynthesis. The kinetic parameters of bacterial populations were determined by mathematical modeling of growth curves based on the Verhulst logistic function. It was established that the induction of biosynthesis in the growth acceleration phase (at OD600 = 0.3) with 0.1 mM IPTG gives the maximum yield of soluble protein (26.75 mg/l or 17.6 mg/g biomass). The target protein was purified using the immobilized metal ion affinity and affinity chromatography technologies. Antigenic activity of the soluble form of recombinant protein GST-HSV2gG, was significantly (three times) higher than that of the protein purified from inclusion bodies (p < 0.05) and was comparable with the activity of the commercial analog (p > 0.05), that allows using this product in the immunosorbent test kits for diagnosis of IgG to HSV-2.

Newcastle disease virus-vectored rabies vaccine is safe, highly immunogenic, and provides long-lasting protection in dogs and cats

Effective, safe, and affordable rabies vaccines are still being sought. Newcastle disease virus (NDV), an avian paramyxovirus, has shown promise as a vaccine vector for mammals. Here, we generated a recombinant avirulent NDV La Sota strain expressing the rabies virus glycoprotein (RVG) and evaluated its potential to serve as a vaccine against rabies. The recombinant virus, rL-RVG, retained its high-growth property in chicken eggs, with titers of up to 10⁹·⁸ 50% egg infective doses (EID₅₀)/ml of allantoic fluid. RVG expression enabled rL-RVG to spread from cell to cell in a rabies virus-like manner, and RVG was incorporated on the surface of the rL-RVG viral particle. RVG incorporation did not alter the trypsin-dependent infectivity of the NDV vector in mammalian cells. rL-RVG and La Sota NDV showed similar levels of sensitivity to a neutralization antibody against NDV and similar levels of resistance to a neutralization antibody against rabies virus. Animal studies demonstrated that rL-RVG is safe in several species, including cats and dogs, when administered as multiple high doses of recombinant vaccine. Intramuscular vaccination with rL-RVG induced a substantial rabies virus neutralization antibody response and provided complete protection from challenge with circulating rabies virus strains. Most importantly, rL-RVG induced strong and long-lasting protective neutralization antibody responses to rabies virus in dogs and cats. A low vaccine dose of 10⁸·³ EID₅₀ completely protected dogs from challenge with a circulating strain of rabies virus for more than a year. This is the first study to demonstrate that immunization with an NDV-vectored vaccine can induce long-lasting, systemic protective immunity against rabies.

[Construction and expression of the eukaryotic expression vector carrying HSV-1 gC glycoprotein gene]

AIM

To stably express herpes simplex virus type 1 (HSV-1) glycoprotein C (gC) in Chinese hamster ovary cells (CHO-K1).

METHODS

The eukaryotic expression vector pCI-mCMV-gC-1-IRES-DHFR-L22R was constructed and transfected into CHO-K1 cells by Lipofectamine 2000. The transfected cells were selected by G418 and methotrexate (MTX). The expression of HSV-1 gC was analyzed by Slot blot. HSV-1 gC proteins were purified with His-Ni Sepharose and then detected by Western blot.

RESULTS

The eukaryotic expression vector pCI-mCMV-gC-1-IRES-DHFR-L22R was constructed successfully. CHO-K1 cells stably expressing HSV-1 gC proteins were established and confirmed by Western blot.

CONCLUSION

The HSV-1 gC proteins have been expressed successfully and have good bioactivity. The results make it possible for further study and clinical use of HSV-1 gC.

[Characterization and development of recombinant vaccinia viruses expressing different segments of spike protein derived from human coronavirus NL-63]

The spike (S) glycoprotein of HCoV-NL63 is a major target in the development of diagnostic assays and vaccines, but its antigenic and immunogenic properties remain unclear. Four fragments coding spike proteins (S1, S2, RL and RS) from HCoV-NL63 were amplified and cloned into the expression vector derived from vaccinia virus (Tiantan strain), and recombinant vaccinia viruses expressing four segments of spike proteins were generated (vJSC1175-S1; vJSC1175-S2; vJSC1175-RL; vJSC1175-RS), respectively. Their expression location in cell and level were characterized using indirect immune fluorescence assay (IFA) and Western-Blot, respectively. The expressions of four segments of spike proteins in recombinant vaccinia viruses were showed at appropriate level and with posttranslational modification (glycosylation), and S1, RL and RS were mainly distributed in the cell membrane, while the S2 was mainly distributed in the cytoplasm. Our results provide a basis for further exploring diagnostic role and vaccine development of different spike segments from HCoV-NL63.

Molecular study of porcine transmissible gastroenteritis virus after serial animal passages revealed point mutations in S protein

Porcine respiratory coronavirus is related genetically to porcine transmissible gastroenteritis virus with a large deletion in S protein. The respiratory virus is a mutated form that may be a consequence of the gastroenteritis virus's evolution. Intensive passages of the virus in its natural host may enhance the appearance of mutations and therefore may contribute to any attenuated form of the virus. The objective of this study was to characterize the porcine transmissible gastroenteritis virus TMK22 strain after passages in piglets from 1992 until 2007. A typical experimental infection, molecular characterization, and serological analysis were also carried out to further characterize and to evaluate any significant difference between strains. The sequence analysis showed two amino acid deletions and loss of an N-glycosylation site in transmissible gastroenteritis virus S protein after passages in piglets. Although these deletions were positioned at the beginning of the antigenic site B of S protein, no clinical differences were observed in piglets infected experimentally either with the native virus or the mutated one. Serological tests did not show any antibody reactivity difference between the two strains. In this article, we report that the S protein deletion did not affect the virus's pathogenicity. The variety of the virus's evolutionary forms may be a result, not only of the multiple passages in natural hosts, but also of other factors, such as different pathogens co-infection, nutrition, immunity, and others. Further studies need to be carried out to characterize the mutated strain.

Recombinant West Nile virus envelope protein E and domain III expressed in insect larvae protects mice against West Nile disease

In this study, West Nile virus (WNV) envelope (rE) protein and its domain III (rDIII) were efficiently expressed in a cost-effective system based on insect larvae as non-fermentative living biofactories. Mice immunized with the partially purified rE or rDIII elicited high antibodies titers that neutralized viral infectivity in cell culture and in suckling mice. All vaccinated animals were fully protected when challenged with neurovirulent WNV NY99. Passive transfer of protective antibodies from immunized mothers to their offspring occurred both by transplacental and lactation routes. These results indicate that the insect-derived antigens tested may constitute potential vaccine candidates to be further evaluated.

Cloning and expression of envelope protein of Thai genotype I strain KE-093 of Japanese encephalitis virus

The purpose of this study was to clone and express envelope (E) gene of Japanese encephalitis virus (JEV) genotype I, Thai strain KE-093. The E gene was amplified by PCR and cloned using the expression vector, pET-15b. Analysis of the insert sequence revealed a point mutation, which was corrected by site directed mutagenesis. The envelope 53 kDa protein expression was generated by in vitro coupled transcription translation system. Heterologous expression in Escherichia coli Rosetta 2 strain, but not in E. coli BL21 (DE3) resulted in 2 immunoreactive bands (13 and 53 kDa) using anti-JEV E protein antibodies, and an additional band (35 kDa) using anti-His antibodies, suggesting that E protein antigenicity is located at the carboxy-terminal region. This is the first report of a successful cloning and heterologous expression of an E gene of JEV genotype I. This should prove useful in the application for diagnostics and vaccine development of JEV genotype I strains.

Antibody-mediated targeted gene transfer to NMDA NR1-containing neurons in rat neocortex by helper virus-free HSV-1 vector particles containing a chimeric HSV-1 glycoprotein C-staphylococcus A protein

Because of the heterogeneous cellular composition of the brain, and especially the forebrain, cell type-specific expression will benefit many potential applications of direct gene transfer. The two prevalent approaches for achieving cell type-specific expression are using a cell type-specific promoter or targeting gene transfer to a specific cell type. Targeted gene transfer with Herpes Simplex Virus (HSV-1) vectors modifies glycoprotein C (gC) to replace the heparin binding domain, which binds to many cell types, with a binding activity for a specific cell surface protein. We previously reported targeted gene transfer to nigrostriatal neurons using chimeric gC-glial cell line-derived neurotrophic factor or gC-brain-derived neurotrophic factor protein. Unfortunately, this approach is limited to cells that express the cognate receptor for either neurotrophic factor. Thus, a general strategy for targeting gene transfer to many different types of neurons is desirable. Antibody-mediated targeted gene transfer has been developed for targeting specific virus vectors to specific peripheral cell types; a specific vector particle protein is modified to contain the Staphylococcus A protein ZZ domain, which binds immunoglobulin (Ig) G. Here, we report antibody-mediated targeted gene transfer of HSV-1 vectors to a specific type of forebrain neuron. We constructed a chimeric gC-ZZ protein, and showed this protein is incorporated into vector particles and binds Ig G. Complexes of these vector particles and an antibody to the NMDA receptor NR1 subunit supported targeted gene transfer to NR1-containing neocortical neurons in the rat brain, with long-term (2 months) expression.

Exploring different strategies to express Dengue virus envelope protein in a plant system

Dengue virus envelope glycoprotein (E-protein) is the main protein associated with immunity induction. To produce a candidate for subunit vaccines and to provide an antigen for diagnostic kits, it was expressed in a novel plant system using deconstructed viral modules. A truncated version of the E-protein was designed to be expressed alone and co-expressed with Dengue virus structural proteins. As well, the critical domain III of E-protein was fused to hepatitis B core antigen (HBcore). The recombinant proteins were produced in Nicotiana benthamiana plants and were reactive with the anti-E antibody. The fusion was reactive with both anti-E and anti-HBcore antibodies.

[Eucaryotic expression and bioactivity analysis of the recombinant HSV-gD1]

Envelope proteins of herpes simplex virus (HSV) plays a vital role not only in the infection process of adsorption and invasion but also in the stimulation to the organism that gives rise to immune response. Among the envelope proteins, glycoprotein D (gD), which can induce specific immune response, are the primary targets of humoral and cellular immunity of the host. In order to analyze the antigenicity and immunogenicity of HSV-gD1, we chemically synthesized the extracellular domain fragment gene of gD1, cloned it into eucaryotic expression vector pCEP4, and transfected the HEK293 cells with the recombinant vector. Then we identified the recombinant protein by Western blotting, and detected antigenicity of the protein by ELISA. Finally, we used the purified gD1 protein to immunize Kunming mice in 1, 3, 5 weeks, and collected antiserum in 3, 5 and 7 weeks. We titrated the sera for the detection of anti gD1 using an ELISA assay. Gene sequencing analysis demonstrated that the recombinant plasmid pCEP4-gD1 was constructed successfully. Western blotting analysis indicated one major protein band, which molecular weights is approximate 46 kDa corresponding to the truncated forms of gD1 protein, was observed. ELISA assay showed that the expressed recombinant protein gD1 had good antigenicity. After the third immunization, antibody titer of the mouse anti-gD1 was at least 5 x10(3). The successful expression of the recombinant protein gD1, which can induce humoral immune response, lays a foundation for serological diagnosis and vaccine study of HSV.

[Preparation and bioactivity of anti-human red blood cell ScFv and CSFV E2 bifunctional fusion protein]

The aim of this study is to construct a bifunctional fusion protein, which can conjugate both human red blood cells and antibodies against classical swine fever virus (CSFV). We respectively amplified 2E8ScFv and mE2 genes from different recombinant vectors, in which 2E8ScFv gene is the single chain Fv gene against H antigen of human red blood cells, whereas mE2 gene is the main antigen coding region gene of CSFV E2 protein. We used overlap extension PCR to obtain an artificial fusion gene segment 2E8mE2 containing genes of Both 2E8ScFv and mE2, then ligated into the expression vector pET-DsbA and expressed in Escherichia coli BL21(DE3) PlysS host cells, after induced with IPTG the target fusion protein was successfully expressed and identified in inclusion bodies by SDS-PAGE and Western blotting. We purified the fusion protein and renatured it from inclusion bodies to obtain a native state of well biological activity. The Erythrocyte agglutination test results indicated that the fusion protein can conjugate both human red blood cells and antibodies of CSFV.

[Construction and immunogenicity of recombinant adenoviruses expressing Cap protein of PCV2 and GP5 protein of PRRSV in mice]

Porcine circovirus 2 (PCV2) has been implicated as the etiological agent of postweaning multisystemic wasting syndrome (PMWS). Co-infection of PCV2 and porcine reproductive and respiratory syndrome virus (PRRSV) can result in severe economic losses to the swine industry. In this study, we constructed the recombinant adenovirus rAd-Cap-GP5 expressing Cap of PCV2 and GP5 of PRRSV. And the expression of Cap and GP5 protein in the HEK-293 cells inoculated with rAd-Cap-GP5 were confirmed by immunoperoxidase monolayer assay (IPMA), indirect immunofluorescence assay (IFA) and Western blotting, respectively. The immunogenicity of recombinant adenoviruses rAd-Cap-GP5 was examined in mice by vaccination with the recombinant adenovirus. The results showed that the mice could produce anti-PCV2 and PRRSV antibodies detected by indirect ELISA and virus neutralization assay. It indicated that rAd-Cap-GP5 could provide humoral immunity responses in mice. The recombinant adenovirus rAd-Cap-GP5 might be an attractive candidate vaccine for preventing the disease associated with PCV2 and PRRSV infection.

[Construction of a recombinant adenovirus carrying the Hantaan virus glycoprotein G2 gene and its expression in Hela cells]

We constructed the recombinant adenovirus expressing the glycoprotein G2 of Hantaan virus. Firstly we obtained coding gene fragment of G2 by PCR, and subsequently inserted the gene of interest into the Adenoviral pShuttle vector pAd5-CMV. Then we co-transfected the recombinant pShuttle vector and adenovirus skeleton plasmid into HEK293 cells by Calcium phosphate precipitation method. After the recombinant adenovirus were packaged and amplified in HEK293 cells, we observed the expression of reporter gene eGFP by fluorescent microscopy, and we obtained the recombinant adenovirus containing Hantaan virus glycoprotein G2. The recombinant adenoviruses were used to infect Hela cells and the expressed protein was detected by Indirect Immuno-fluorescence and Western blotting. The construct was confirmed at several levels: first restriction enzyme analysis demonstrated that the recombinant adenovirus vector was constructed correctly, second RT-PCR showed that the G2 gene could transcribe correctly in Hela cells. Then Fluorescent microscopy proved the expression of eGFP in the infected Hela cells. Finally, Indirect Immune-fluorescence and Western-blot confirmed the expression of interested protein identified by anti-G2 monoclonal antibody. In conclusions, this study successfully constructed the recombinant adenovirus containing Hantaan virus envelope glycoprotein G2, meanwhile obtained the G2 protein, it may lay solid foundation for the structure study of G2 protein and the new vaccine of Hantaan virus.

[Immunogenicity and antigenicity of Japanese encephalitis virus envelope protein domain III]

To express the domain III gene of Japanese encephalitis virus (JEV) and to learn the possibility of developing the Dil protein as a subunit vaccine, we amplified the JEV DIII gene by PCR and constructed the expression plasmid pET-JE DIII by inserting JEV DIII gene into the prokaryotic expression vector pET-32a(+). The domain III protein of the attenuated strain SA14-14-2 was expressed as a thioredoxin (Trx) fusion protein, which was unique in forming a large fraction of the soluble recombinant protein. We immunized the rabbits and mice with the purified protein, tested the antigenicity and immunogenicity of JEV DIII protein by ELISA, Western blotting, plaque reduction test and observed the protective efficacy on challenged weanling mice with JEV. Rabbits immunized with the purified JEV DIII protein generated 1: 7 x 10(5) anti-JEV specific antibody titers. BALB/c mice immunized with the purified JEV E DIII protein generated 1: 8.2 x 10(4) anti-JEV specific antibody titers. And the neutralized antibody titer can reach 1:256, the survival rate of the immunized weanling mice was approximately 75%. Overall, this study highlighted that recombinant JEV E DIII protein delivered in mice and rabbits can generate high antibody titers against JEV, and protect some mice challenged with JEV. These studies can provide useful information for further developing the domain III recombinant protein as subunit vaccine against JEV.

[HERV-K-associated carcinogenesis: co-expression of viral and cellular proteins in the development of human germ-cell tumors]

To elucidate the role of some viral and cellular proteins in the occurrence and development of HERV-K-associated germ-cell tumors (GCT), reverse-transcription polymerase chain reaction using specific primers has been employed to study the transcription of the protein Rec HERV-K and the possible interaction of the protein Rec(cORF), that has transforming properties, and the cellular protein PLZF, that is a negative regulator of cell division, in human GCT tissues, in the testicular parenchyma adjacent to a tumor, and in the normal testicular tissues. It was shown that there was expression of Rec(cORF) of mRNA, rather than cellular PLZF in all malignant GCT tissues, this led to the conclusion that no interaction occured between the Rec HERV-K and PLZF proteins in the GCT cells. At the same time co-expression of Rec and PLZF protein was first revealed at the level of transcription in the testicular parenchyma adjacent to a tumor that exhibited carcinoma in situ cells. By taking into account that the protein Rec HERV-K has transforming activity and it is presumed to be Implicated in the development of GCT, the authors discuss a possible role in the Rec HERV-K/HTDV and cellular PLZF interaction in the pathogenesis of GST at the early stages of its genesis.

[Prokaryotic expression of S2 extracellular domain of SARS coronavirus spike protein and its fusion with Hela cell membrane]

OBJECTIVE

To construct the expression plasmid of S2 extracellular domain (S2ED) of SARS-coronavirus (SARS- Cov) spike protein (S protein) and enhanced green fluorescent protein (EGFP) to obtain the fusion protein expressed in prokaryotic cells.

METHODS

S2ED based on bioinformatics prediction and EGFP sequence were amplified by PCR and inserted into pET-14b plasmid. The recombinant protein His-S2ED-EGFP was expressed in E. coli by IPTG induction. After purification by Ni-NTA agarose beads, the soluble fractions of the fusion protein were collected and identified by SDS-PAGE and Western blotting. The fusion of S2ED with Hela cell membranes was observed with fluorescent microscope.

RESULTS

The pET-14b-S2ED-EGFP plasmid was correctly constructed and highly expressed in BL21 (DE3). When incubated with Hela cells, the purified protein could not internalize through membrane fusion.

CONCLUSIONS

The expression plasmid containing S2ED of SARS-Cov S protein and EGFP sequence is constructed successfully. Although the recombinant protein obtained has not shown the expected fusion effect with Hela cell membrane, this work may enrich the understanding of the process of membrane fusion mediated by S2 protein and lay the foundation for future study of targeting cell transport system based on cell-specific binding peptide.

Characterization of HCV quasispecies in the hypervariable region 1 (HVR1) by in vitro translation and mass spectrometry

HCV infection provides a classic example of the phenomenon of quasispecies. Because several lines of investigation support the contribution of quasispecies to HCV's capacity to maintain a persistent infection, adequate characterization of the quasispecies is important. The hypervariable region 1 (HVR1) of the E2 glycoprotein has been particularly well studied in this regard. We present here a rapid method for characterizing the HVR1 quasispecies, based on in vitro coupled transcription/translation of the amplicons, followed by mass spectrometry of the resulting peptide mix.

Detection of neutralizing antibodies with HCV pseudoparticles (HCVpp)

Infectious HCV pseudoparticles (HCVpp) can be assembled by display of unmodified and functional HCV glycoproteins on retroviral and lentiviral core particles. HCVpp have been shown to mimic the early infection steps of parental HCV. The presence of a marker gene packaged within these HCV pseudoparticles allows reliable and fast determination of infectivity mediated by the HCV glycoproteins. With this highly flexible system, E1E2 from a broad range of HCV strains can be investigated, including autologous HCV strains from patients' virus, and it has allowed careful investigation of the humoral response to HCV.

Production of pseudotyped retrovirus and the generation of proviral transgenic zebrafish

This chapter describes a method for generation of the high-titer pseudotyped Moloney murine leukemia virus (MLV) that efficiently infects zebrafish embryos (i.e., more than 25 retroviral copies per cell). Injection techniques are also described for production of the retrovirus-infected mosaic "founder" fish. We describe a quantitative PCR (qPCR)-based assay as a quick way to assess the infectivity after each round of viral production and injection. Most of the required equipment is commercially available and commonly present in most research laboratories.

[Generation and immunogenicity of a recombinant adenovirus expressing the E2 protein of classical swine fever virus in rabbits]

Classical swine fever (CSF), which is caused by classical swine fever virus (CSFV), causes significant losses in pig industry in many countries in Asia and Europe. The E2 glycoprotein of CSFV is the main target for neutralizing antibodies. In this study, a recombinant replication-defective human adenovirus expressing the CSFV E2 gene (rAdV-E2) was generated and evaluated for the immunogenicity in rabbits. The results showed that the rabbits immunized with rAdV-E2 developed high-level CSFV-specific antibodies. The rAdV-E2-immunized rabbits were all free of the regular fever and the viral replication in the spleen upon challenge with C-strain, which were seen in the rabbits immunized with the parent adenovirus of rAdV-E2. This indicates that the recombinant adenovirus can be an attractive candidate vaccine against CSF.

Bacterial-based systems for expression and purification of recombinant Lassa virus proteins of immunological relevance

BACKGROUND

There is a significant requirement for the development and acquisition of reagents that will facilitate effective diagnosis, treatment, and prevention of Lassa fever. In this regard, recombinant Lassa virus (LASV) proteins may serve as valuable tools in diverse antiviral applications. Bacterial-based systems were engineered for expression and purification of recombinant LASV nucleoprotein (NP), glycoprotein 1 (GP1), and glycoprotein 2 (GP2).

RESULTS

Full-length NP and the ectodomains of GP1 and GP2 were generated as maltose-binding protein (MBP) fusions in the Rosetta strains of Escherichia coli (E. coli) using pMAL-c2x vectors. Average fusion protein yields per liter of culture for MBP-NP, MBP-GP1, and MBP-GP2 were 10 mg, 9 mg, and 9 mg, respectively. Each protein was captured from cell lysates using amylose resin, cleaved with Factor Xa, and purified using size-exclusion chromatography (SEC). Fermentation cultures resulted in average yields per liter of 1.6 mg, 1.5 mg, and 0.7 mg of purified NP, GP1 and GP2, respectively. LASV-specific antibodies in human convalescent sera specifically detected each of the purified recombinant LASV proteins, highlighting their utility in diagnostic applications. In addition, mouse hyperimmune ascitic fluids (MHAF) against a panel of Old and New World arenaviruses demonstrated selective cross reactivity with LASV proteins in Western blot and enzyme-linked immunosorbent assay (ELISA).

CONCLUSION

These results demonstrate the potential for developing broadly reactive immunological assays that employ all three arenaviral proteins individually and in combination.

[Characterization of murine leukemia virus recombinants bearing PRRSV GP5 glycoproteins]

The highly virulent PRRSV isolate strain HN-1/06 was cultivated on Marc-145. To study the viral entry mechanisms, the GP5 gene of PRRSV isolate was amplified by RT-PCR and cloned into pcDNA3.0 to generate the expressing plasmid pcDNA-GP5. pcDNA-GP5 was transfected into 293T by the calcium phosphate precipitation method. Analysis of flow cytometry confirmed that the GP5 proteins were expressed in surface of the 293T cells. Then 293T cells were transfected with pcDNA-GP5, pHIT60 and pHIT111 plasmids to generate pseudotyping virus. The pseudotyping virus supernatant was harvested 48 hours post-transfection and was detected by Western blotting and infection assay. Western blotting indicated that the GP5 glycoproteins were incorporated into the retroviral pseudotyped virus. Infection assay showed that the pseudotyped virus infected 293T and Mark-145 cell. The pseudotyped virus could be used to further study infectious mechanism of PRRSV.

[Construction and biological characteristic for the recombinant modified vaccinia virus ankara co-expressing modified GP5 and M protein of porcine reproductive and respiratory syndrome virus]

Modified ORF5 (MORF5) and ORF6 gene of PRRSV were cloned into two multiple cloning sites of MVA transfer vector pLR-gpt to construct the recombinant plasmid pLR-MORF5/ORF6. Homologous recombination between pLR-MORF5/ORF6 and the wtMVA on BHK-21 cell line was mediated with liposome by infecting the cell with 0.01 MOI wtMVA two hours before transfecting the recombinant plasmid into the cell. When the cytopathic effect (CPE) was obvious, virus was collected from the cell plate and the recombinant virus was selected with drug selecting medium (2% MXHAT). After 12 cycles of selection, rMVA with a selection marker Eco gpt was obtained and named as rMVAgpt-MGP5/M. By infecting BHK-Cre expressing Cre recombinant enzyme, the Eco gpt marker in rMVAgpt-MGP5/M was deleted and this rMVA was named as rMVA-MGP5/M. The insertion of MORF5 and ORF6 into the MVA genome was confirmed with PCR analysis and the expression of MGP5 and M protein was identified with Western blot and IFA. Through biological study on the recombinant MVA, no obvious difference was observed between rMVA-MGP5/M and the wtMVA regarding to the CPE and growth curve. The recombinant MVA constructed in this study could coexpress the modified GP5 and M protein and the expressed product had good immunocompetence. Furthermore, the insertion of the MORF5 and ORF6 into MVA genome had no obvious effect on the replication and biological characteristics of this virus.

Expression of the herpes simplex virus type 2 glycoprotein D in baculovirus expression system and evaluation of its immunogenicity in guinea pigs

BACKGROUND

Herpes simplex virus type 2 (HSV-2) is highly prevalent and major cause of genital herpes in humans. The life-long nature of infection and the increasing prevalence of genital herpes imply that vaccination is the best strategy for controlling the spread of infection and limiting HSV disease. HSV glycoprotein D (gD) is one of the most important viral immunogen which has an essential role in virus infectivity and induction of immune responses.

METHODS

HSV-2 DNA was extracted and used as template in polymerase chain reactions to amplify gD2 gene. The PCR product was confirmed by restriction enzyme analysis, cloned into a cloning vector and then sequenced. The Bac-to-Bac expression system was used to express HSV-2 gD in insect cells. The expressed protein was used as subunit vaccine to immunize guinea pigs after confirmation.

RESULTS

The expressed protein was confirmed with SDS-PAGE and Western-blot analysis. In Western-blot analysis, two major protein bands, with approximate molecular weights of 52-55 and 41-43 kDa corresponding to the glycosylated and non-glycosylated forms of gD2 protein, were observed, respectively. Immunization with the recombinant gD2 could elicit humoral responses in guinea pigs as measured by neutralization test and ELISA, and offered high protection against induced HSV-2 genital disease.

CONCLUSION

The baculovirus expression of heterologous genes permits proper folding, post-translational modification and oligomerization in manners that are often identical to those that occur in mammalian cells. Expression of proteins under the control of the strong polyhedrin promoter, allowing high level protein production, can be used as subunit vaccine.

[Study of the diagnostic potential of various regions of tick-borne encephalitis virus glycoprotien E]

Bioinformation techniques were used to analyze envelope glycoprotein of tick-borne encephalitis virus in order to determine the potential diagnostically significant antigenic clusters. Five selected regions of the amino acid sequence of protein E were retranslated to nucleic sequences, by employing the optimum code for E. coli. The resultant DNA fragments were synthesized by polymerase chain reaction from synthetic oligonucleotides and expressed in E. coli cells. The recombinant antigen replicating the region from 296 to 414 aminoacids demonstrated the most significant antigenic activity. The findings lead to the conclusion that this recombinant protein may be considered as a candidate for the development of a diagnostic assay.

[Expression and study of the functional proteins of hepatitis C virus in CHO cell line]

Recently, the interactions between hepatitis C virus (HCV) genes and the host cell factors were the focus of this field. Cell factors in the different biochemical pathway were approved to be interfered when HCV infection. To make sure which HCV gene(s) was the major factor during the interaction process, ten eukaryotic expression plasmids containing different functional genes of HCV: Core, E1, E2, p7, NS2, NS3, NS4A, NS4B, NS5A and NS5B were transfected into the CHO-K1 cells respectively. Then ten stable cell lines expressing different HCV functional proteins were constructed under the selective pressure of G418. DNA and mRNA of the HCV genes were both detected by PCR and RT-PCR respectively in the corresponding stable cell lines, freezation and anabiosis would not lose the HCV genes. Besides, the El, E2 and NS5B proteins were detected by Western-blot which demonstrated that the HCV genes have formed stable expression in the host cells. The activity of UDP-glucose ceramide glucosyltransferase (UGCG) in the stable cell lines increased in different degree by TLC assay. For example, the activity of UGCG in CHO-K1-E2 and CHO-K1-p7 was doubled according to the control cells,and in CHO-K1-NS2 and CHO-K1-NS5A was about 1.6 times compared with the control cells. The establishment of the stable cell lines containing different single HCV gene will provide foundation for investigating the interactions between the virus and the host factors, and for the filtration of antiviral medicine.

Increased human immunodeficiency virus type 1 Env expression and antibody induction using an enhanced alphavirus vector

Viral vectors encoding heterologous vaccine antigens are potent inducers of cellular immune responses, but they are generally less efficient at stimulating humoral immunity. To improve the induction of antibody responses by Semliki Forest virus-based vaccines, a vector encoding a translation-enhancer element and a novel internal signal sequence for increased expression and secretion of soluble antigens was designed. Approximately tenfold more human immunodeficiency virus type 1 gp120 was secreted into culture supernatants of infected cells using the enhanced vector compared with the parental vector. This translated into a significant increase in gp120-specific antibodies in immunized mice, suggesting that antigen-expression levels from the parental vector are limiting for induction of antibody responses. These data encourage the use of the enhanced vector for elicitation of immune responses against heterologous antigens during vaccination.