Expression Of Capsid Protein Research Articles

Infectious spleen and kidney necrosis virus induces the reactive oxidative species/Nrf2-mediated oxidative stress response for the regulation of mitochondrion-mediated Bax/Bak cell death signals in GF-1 cells.

Infectious spleen and kidney necrosis virus (ISKNV) infections can trigger host cell death and are correlated with viral replication; however, they have rarely been considered in terms of the host organelle involvement. In the present study, we demonstrated that ISKNV triggered an oxidative stress signal in the Nrf2-mediated oxidative stress response and induced stress signals for Bax/Bak-mediated host cell death in fish GF-1 cells. The results showed that after ISKNV infection, the levels of reactive oxidative species (ROS) increased by 60–80% from day 3 to day 5, as assessed by an H2DCFDA assay for tracing hydrogen peroxide (H2O2), which was correlated with up to a one-fold change in the fish GF-1 cells. Furthermore, we found that ISKNV infection induced Nrf2-mediated ROS stress signals from D1 to D5, which were correlated with the upregulation of antioxidant enzymes, such as catalase, SOD1, and SOD2; these effects were blocked by the antioxidants GSH and NAC. By analyzing Nrf2-mediated ROS stress signals for cell death regulation via an apoptotic assay, we found that treatment with antioxidants reduced annexin-V-positive signals by 10% (GSH) to 15% (NAC); moreover, necrotic-positive signals were reduced by 6% (GSH) and 32% (NAC) at day 5 (D5) in GF-1 cells, as indicated by PI staining. Furthermore, we found that Nrf2-mediated ROS stress regulated mitochondrion-mediated Bax/Bak death signals at D3 and D5; this was effectively blocked by antioxidant treatment in the GF-1 cells, as demonstrated by a JC1 assay (ΔΨm) and western blot analysis. In addition, we found that downstream signals for caspase-9 and -3 activation were apparently blocked by antioxidant treatment at D3 and D5. Finally, we found that treatment with GSH and NAC reduced major capsid protein (MCP) expression and virus titer (TCID50%) by up to 15-fold at D5 in GF-1 cells. Thus, our data suggest that ISKNV can induce ROS production, which triggers Nrf2-mediated stress signals. Then, these stress signals can regulate mitochondrion-mediated Bax/Bak apoptotic signaling, which is connected to downstream caspase-9 and -3 activation. If ISKNV-induced Nrf2-mediated stress signaling is blocked, then the antioxidants GSH and NAC can also suppress apoptotic signals or reduce viral replication. These findings may provide insights into the control and treatment of double-stranded DNA viruses.

AtGSTU19 and AtGSTU24 as Moderators of the Response of Arabidopsis thaliana to Turnip mosaic virus.

Plants produce glutathione as a response to the intercellular redox state. Glutathione actively participates in the reactive oxygen species (ROS)-dependent signaling pathway, especially under biotic stress conditions. Most of the glutathione S-transferases (GSTs) are induced in cells during the defense response of plants not only through highly specific glutathione-binding abilities but also by participating in the signaling function. The tau class of GSTs has been reported to be induced as a response under stress conditions. Although several studies have focused on the role of the tau class of GSTs in plant–pathogen interactions, knowledge about their contribution to the response to virus inoculation is still inadequate. Therefore, in this study, the response of Atgstu19 and Atgstu24 knockout mutants to mechanical inoculation of Turnip mosaic virus (TuMV) was examined. The systemic infection of TuMV was more dynamically promoted in Atgstu19 mutants than in wild-type (Col-0) plants, suggesting the role of GSTU19 in TuMV resistance. However, Atgstu24 mutants displayed virus limitation and downregulation of the relative expression of TuMV capsid protein, accompanied rarely by TuMV particles only in vacuoles, and ultrastructural analyses of inoculated leaves revealed the lack of virus cytoplasmic inclusions. These findings indicated that Atgstu24 mutants displayed a resistance-like reaction to TuMV, suggesting that GSTU24 may suppress the plant resistance. In addition, these findings confirmed that GSTU1 and GSTU24 are induced and contribute to the susceptible reaction to TuMV in the Atgstu19–TuMV interaction. However, the upregulation of GSTU19 and GSTU13 highly correlated with virus limitation in the resistance-like reaction in the Atgstu24–TuMV interaction. Furthermore, the highly dynamic upregulation of GST and glutathione reductase (GR) activities resulted in significant induction (between 1 and 14 days post inoculation [dpi]) of the total glutathione pool (GSH + GSSG) in response to TuMV, which was accompanied by the distribution of active glutathione in plant cells. On the contrary, in Atgstu19, which is susceptible to TuMV interaction, upregulation of GST and GR activity only up to 7 dpi symptom development was reported, which resulted in the induction of the total glutathione pool between 1 and 3 dpi. These observations indicated that GSTU19 and GSTU24 are important factors in modulating the response to TuMV in Arabidopsis thaliana. Moreover, it was clear that glutathione is an important component of the regulatory network in resistance and susceptible response of A. thaliana to TuMV. These results help achieve a better understanding of the mechanisms regulating the Arabidopsis–TuMV pathosystem.

Grouper ATF1 plays an antiviral role in response to iridovirus and nodavirus infection

Transcription factor ATF1 is a member of the ATF/CREB family of the CREB subfamily and is involved in physiological processes such as tumorigenesis, organ development, reproduction, cell survival, and apoptosis in mammals. However, studies on ATF1 in fish have been relatively poorly reported, especially on its role in antiviral immunity in fish. In this study, ATF1 from orange-spotted grouper (named EcATF1) were cloned and characterized. Molecular characterization analysis showed that EcATF1 encodes a 307-amino-acid protein, containing PKID and bZIP_CREB1 domains. Homology analysis showed that had the highest homology with E. lanceolatus(88.93%). Tissue expression pattern showed that EcATF1 was extensively distributed in twelve selected tissues, with higher expression in the skin, gill, liver and spleen. Subcellular localization analysis showed that EcATF1 was distributed in the nucleus of GS cells. EcATF1 overexpression inhibits Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV) replication, as evidenced by a diminished degree of CPE induced by SGIV and RGNNV and a reduction in the level of viral gene transcription and viral capsid protein expression. Furthermore, EcATF1 overexpression upregulated interferon pathway-related genes and proinflammatory factors, and increased the promoter activities of IFN, IFN stimulated response element (ISRE), and nuclear factor κB(NFκB). Meanwhile, EcATF1 overexpression positive regulate the MHC-I signaling pathway, and upregulated the promoter activity of MHC-I. Collectively, these data demonstrate that EcATF1 plays an important role during the host antiviral immune response. This study provides insights into the function of ATF1 in the immune system of lower vertebrates.

Live enteroviruses, but not other viruses, detected in human pancreas at the onset of type 1 diabetes in the DiViD study

Aims/hypothesisEnterovirus (EV) infection of pancreatic islet cells is one possible factor contributing to type 1 diabetes development. We have reported the presence of EV genome by PCR and of EV proteins by immunohistochemistry in pancreatic sections. Here we explore multiple human virus species in the Diabetes Virus Detection (DiViD) study cases using innovative methods, including virus passage in cell cultures.MethodsSix recent-onset type 1 diabetes patients (age 24–35) were included in the DiViD study. Minimal pancreatic tail resection was performed under sterile conditions. Eleven live cases (age 43–83) of pancreatic carcinoma without diabetes served as control cases. In the present study, we used EV detection methods that combine virus growth in cell culture, gene amplification and detection of virus-coded proteins by immunofluorescence. Pancreas homogenates in cell culture medium were incubated with EV-susceptible cell lines for 3 days. Two to three blind passages were performed. DNA and RNA were extracted from both pancreas tissue and cell cultures. Real-time PCR was used for detecting 20 different viral agents other than EVs (six herpesviruses, human polyomavirus [BK virus and JC virus], parvovirus B19, hepatitis B virus, hepatitis C virus, hepatitis A virus, mumps, rubella, influenza A/B, parainfluenza 1–4, respiratory syncytial virus, astrovirus, norovirus, rotavirus). EV genomes were detected by endpoint PCR using five primer pairs targeting the partially conserved 5′ untranslated region genome region of the A, B, C and D species. Amplicons were sequenced. The expression of EV capsid proteins was evaluated in cultured cells using a panel of EV antibodies.ResultsSamples from six of six individuals with type 1 diabetes (cases) and two of 11 individuals without diabetes (control cases) contained EV genomes (p<0.05). In contrast, genomes of 20 human viruses other than EVs could be detected only once in an individual with diabetes (Epstein–Barr virus) and once in an individual without diabetes (parvovirus B19). EV detection was confirmed by immunofluorescence of cultured cells incubated with pancreatic extracts: viral antigens were expressed in the cytoplasm of approximately 1% of cells. Notably, infection could be transmitted from EV-positive cell cultures to uninfected cell cultures using supernatants filtered through 100 nm membranes, indicating that infectious agents of less than 100 nm were present in pancreases. Due to the slow progression of infection in EV-carrying cell cultures, cytopathic effects were not observed by standard microscopy but were recognised by measuring cell viability. Sequences of 5′ untranslated region amplicons were compatible with EVs of the B, A and C species. Compared with control cell cultures exposed to EV-negative pancreatic extracts, EV-carrying cell cultures produced significantly higher levels of IL-6, IL-8 and monocyte chemoattractant protein-1 (MCP1).Conclusions/interpretationSensitive assays confirm that the pancreases of all DiViD cases contain EVs but no other viruses. Analogous EV strains have been found in pancreases of two of 11 individuals without diabetes. The detected EV strains can be passaged in series from one cell culture to another in the form of poorly replicating live viruses encoding antigenic proteins recognised by multiple EV-specific antibodies. Thus, the early phase of type 1 diabetes is associated with a low-grade infection by EVs, but not by other viral agents. Graphical abstract

Glycosylphosphatidylinositol Mannosyltransferase Ⅰ Protects Chinese Giant Salamander, Andrias davidianus, against Iridovirus.

Glycosylphosphatidylinositol mannosyltransferase I (GPI-MT-I) is an essential glycosyltransferase of glycosylphosphatidylinositol-anchor proteins (GPI-APs) that transfers the first of the four mannoses in GPI-AP precursors, which have multiple functions, including immune response and signal transduction. In this study, the GPI-MT-I gene that regulates GPI-AP biosynthesis in Andrias davidianus (AdGPI-MT-I) was characterized for the first time. The open reading frame (ORF) of AdGPI-MT-I is 1293 bp and encodes a protein of 430 amino acids that contains a conserved PMT2 superfamily domain. AdGPI-MT-I mRNA was widely expressed in the tissues of the Chinese giant salamander. The mRNA expression level of AdGPI-MT-I in the spleen, kidney, and muscle cell line (GSM cells) was significantly upregulated post Chinese giant salamander iridovirus (GSIV) infection. The mRNA expression of the virus major capsid protein (MCP) in AdGPI-MT-I-overexpressed cells was significantly reduced. Moreover, a lower level of virus MCP synthesis and gene copying in AdGPI-MT-I-overexpressed cells was confirmed by western blot and ddPCR. These results collectively suggest that GSIV replication in GSM cells was significantly reduced by the overexpression of the AdGPI-MT-I protein, which may contribute to a better understanding of the antiviral mechanism against iridovirus infection.

Neomycin inhibits Megalocytivirus infection in fish by antagonizing the increase of intracellular reduced glutathione

Infectious spleen and kidney necrosis virus (ISKNV) is the type species of the Megalocytivirus genus that infects a number of marine and freshwater fishes, causing huge economic losses in aquaculture. The ISKNV infection leads to increase of reducing power in cells. As the antibiotic neomycin can promote the production of reactive oxygen species (ROS) in animal cells, in the current study, the potential therapeutic effect of neomycin on ISKNV infection was explored. We showed that neomycin could decrease the reducing power in cultured MFF-1 cells and inhibit ISKNV infection by antagonizing the shift of the cellular redox balance toward reduction. In vivo experiments further demonstrated that neomycin treatment significantly suppresses ISKNV infection in mandarin fish. Expression of the major capsid protein (MCP) and the proportion of infected cells in tissues were down-regulated after neomycin treatment. Furthermore, neomycin showed complex effects on expression of a set of antiviral related genes of the host. Taking together, the current study suggested that the viral-induced redox imbalance in the infected cells could be used as a target for suppressing ISKNV infection. Neomycin can be potentially utilized for therapeutic treatment of Megalocytivirus diseases by antagonizing intracellular redox changes.

Construction of recombinant adenovirus expressing capsid protein of serotype O foot-and-mouth disease virus and analysis of its immunogenicity

In order to construct a recombinant replication deficient human type 5 adenovirus (Ad5) expressing a foot-and-mouth disease virus (FMDV) capsid protein, specific primers for P12A and 3B3C genes of FMDV-OZK93 were synthesized. The P12A and 3B3C genes were then amplified and connected by fusion PCR, and a recombinant shuttle plasmid pDC316-mCMV-EGFP-P12A3B3C expressing the FMDV-OZK93 capsid protein precursor P12A and 3B3C protease were obtained by inserting the P12A3B3C gene into the pDC316-mCMV-EGFP plasmid. The recombinant adenovirus rAdv-P12A3B3C-OZK93 was subsequently packaged, characterized and amplified using AdMaxTM adenovirus packaging system, and the expression was verified by infecting human embryonic kidney cell HEK-293. The humoral and cellular immunity levels of well-expressed and purified recombinant adenovirus immunized mice were evaluated. The results showed that rAdv-P12A3B3C-OZK93 could be stably passaged and the maximum virus titer reached 1×109.1 TCID50/mL. Western blotting and indirect immunofluorescence showed that rAdv-P12A3B3C-OZK93 expressed the FMDV-specific proteins P12A and VP1 in HEK-293 cells. In addition, the PK cell infection experiment confirmed that rAdv-P12A3B3C-OZK93 could infect porcine cells, which is essential for vaccination in pigs. Comparing with the inactivated vaccine group, the recombinant adenovirus could induce higher FMDV-specific IgG antibodies, γ-IFN and IL-10. This indicates that the recombinant adenovirus has good immunity for animal, which is very important for the subsequent development of foot-and-mouth disease vaccine.

Assembly-defective Tembusu virus ectopically expressing capsid protein is an approach for live-attenuated flavivirus vaccine development

Live-attenuated vaccines (LAVs) represent a promising approach for flavivirus vaccine development. In the present study, we demonstrated a method for generating flavivirus LAVs based on breaking spatially and temporally regulated C-prM cleavage to disturb the viral assembly process, using an avian flavivirus (Tembusu virus) as the model. Using reverse genetics technology, we successfully generated two recombinant viruses (CQW1-IRES-mC and CQW1-MINI-mC) with bicistronic genomic RNA in which native capsid genes were deleted and instead expressed in the 3’UTR under the control of an internal ribosome entry site (IRES) or minimum IRES. Both viruses showed a significantly attenuated phenotype in vitro due to impaired viral assembly, and the engineered mutations were genetically stable in vitro within ten passages. Importantly, their virulence was also highly attenuated in ducklings and suckling mice and did not cause any overt clinical symptoms or mortality. In addition, a single dose of immunization with any of these mutant viruses could completely protect ducklings from a lethal challenge, and no viremia was detected after immunization and challenge, even though the viruses induced a relatively moderate immune response in terms of the T-lymphocytes proliferative response and the level of neutralization antibodies compared with that obtained with the wild-type virus. Besides, a recombinant virus ectopically expressing the prM-E protein was also generated in the present study, but this virus was too attenuated with severely decreased proliferation. Our results indicated that the use of a recombinant flavivirus that ectopically expresses structural proteins could be an effective and universal method for flavivirus LAVs development.

Keratinocyte Carcinomas in Immunocompromised Patients Are Reduced After Administration of the Nonavalent Human Papillomavirus Vaccine.

Immunosuppression, as seen in solid organ transplant recipients, is highly associated with the development of keratinocyte carcinomas (KCs). Reducing the level of immunosuppression lowers the incidence of KCs but at the cost of increased potential morbidity and mortality. Recent studies have revealed a greater prevalence of HPV DNA, especially that of &beta;-HPV, in KCs of immunocompromised patients compared to KCs of immunocompetent individuals. A prior report demonstrated that the HPV vaccine was associated with reducing KC incidence in immunocompetent patients. The nonavalent HPV vaccine was administered to two immunosuppressed individuals with histories of multiple prior KCs. Both patients are male, with Patient 1 being a liver transplant recipient who was on tacrolimus for an extended period and Patient 2 having Crohn&rsquo;s disease and currently being treated with mercaptopurine. The treatment was well tolerated without adverse events and was associated with dramatic reductions in average incidence of KCs/year in both patients. Patient 1 demonstrated an 88% reduction in new KCs/year (87% squamous cell carcinomas (SCCs); 100% basal cell carcinomas (BCCs) post-injection of the intramuscular vaccine and Patient 2 demonstrated a 63% reduction in incidence of KCs/year (30% SCCs; 100% BCCs). Evidence links the &beta;-HPV genera to the development of SCCs and actinic keratoses. The nonavalent HPV vaccine, containing antigens of the &alpha;-HPV genera, may also induce humoral immunity to &beta;-HPV due to shared expression of L1 and L2 capsid proteins. The HPV vaccine may be an effective tool in the prevention of KCs in immunosuppressed patients. J Drugs Dermatol. 2022;21(5):526-528. doi:10.36849/JDD.6536.

Low molecular weight sulfated chitosan efficiently reduces infection capacity of porcine circovirus type 2 (PCV2) in PK15 cells

BackgroundPorcine circovirus type 2 (PCV2)-associated diseases are a major problem for the swine industry worldwide. In addition to vaccines, the availability of antiviral polymers provides an efficient and safe option for reducing the impact of these diseases. By virtue of their molecular weight and repetitious structure, polymers possess properties not found in small-molecule drugs. In this perspective, we focus on chitosan, a ubiquitous biopolymer, that adjusts the molecular weight and sulfated-mediated functionality can act as an efficient antiviral polymer by mimicking PCV2-cell receptor interactions.MethodsSulfated chitosan (Chi-S) polymers of two molecular weights were synthesized and characterized by FTIR, SEM–EDS and elemental analysis. The Chi-S solutions were tested against PCV2 infection in PK15 cells in vitro and antiviral activity was evaluated by measuring the PCV2 DNA copy number, TCID50 and capsid protein expression, upon application of different molecular weights, sulfate functionalization, and concentrations of polymer. In addition, to explore the mode of action of the Chi-S against PCV2 infection, experiments were designed to elucidate whether the antiviral activity of the Chi-S would be influenced by when it was added to the cells, relative to the time and stage of viral infection.ResultsChi-S significantly reduced genomic copies, TCID50 titers and capsid protein of PCV2, showing specific antiviral effects depending on its molecular weight, concentration, and chemical functionalization. Assays designed to explore the mode of action of the low molecular weight Chi-S revealed that it exerted antiviral activity through impeding viral attachment and penetration into cells.ConclusionsThese findings help better understanding the interactions of PCV2 and porcine cells and reinforce the idea that sulfated polymers, such as Chi-S, represent a promising candidates for use in antiviral therapies against PCV2-associated diseases. Further studies in swine are warranted.

Finger printing human norovirus-like particles by capillary isoelectric focusing with whole column imaging detection

Owing to the limitation of in vitro culture of human noroviruses (HuNoVs), the development of HuNoV vaccines has to depend on the self-assembling virus-like particles (VLPs) with capsid protein expression. The heterogeneity of artificial VLPs exert an impact on the immunogenicity, and should be considered as one of the factors in vaccine evaluation. In this study, we biochemically finger print the HuNoV VLPs with different genogroups, genotypes and sub-genotypes which constitute for a candidate vaccine, by using capillary isoelectric focusing with whole column imaging detection (cIEF-WCID). The electropherograms of GI.1, GII.3, GII.4 and GII.17 VLPs in fluorescence signal were described in the monomer VP1 forms after degenerated by 8 M urea. The four HuNoV VLPs showed different properties in electropherogram finger prints. The finger prints were also reproducible within a certain concentration range (approx. 150 ∼ 20 ug/ml). This method can also tell the changes of pI finger-print patterns when the expired HoNoV VLPs were tested. In conclusion, cIEF-WCID shows great promise for evaluating the production consistency of HuNoV VLP vaccine.

Iridovirus isolated from marine giant sea perch causes infection in freshwater ornamental fish

Ornamental fish are frequently infected with iridoviruses and their transport via international trade can easily cause the spread of the viral pathogens. An iridovirus was isolated from farmed giant sea perch (Lates calcarifer) and identified as a grouper iridovirus of Taiwan (TGIV) belonging to the genus Megalocytivirus. High mortality rate in dwarf gouramis was observed when the freshwater ornamental fish dwarf gouramis (Trichogaster lalius) was challenged with spleen tissue extracts of the TGIV-infected giant sea perch. Similar results were obtained when dwarf gouramis were challenged with grouper iridovirus (GIV) isolated from marine fish. The spleen tissue extracts of dwarf gouramis infected with TGIV and GIV were also used to challenge swordtails (Xiphophorus helleri; freshwater ornamental fish); both viruses resulted in high mortality rates in swordtails, indicating that iridovirus, a marine fish pathogen, could also infect freshwater ornamental fish, resulting in high mortality rates. Furthermore, when orange-spotted groupers (Epinephelus coioides) were experimentally challenged with the tissue extracts of TGIV- and GIV-infected dwarf gouramis, both viruses caused infection in orange-spotted groupers. In contrast with the results obtained in freshwater ornamental fish, the mortality rate of the GIV-infected orange-spotted groupers was higher (with earlier deaths) than that of their TGIV-infected counterparts. The iridovirus isolated from infected freshwater ornamental fish also resulted in high mortality rates in marine fish. Finally, the tissue extracts of the TGIV- and GIV-infected dwarf gouramis were used to infect healthy dwarf gouramis, and TGIV and GIV were subsequently detected in the spleen tissues of healthy dwarf gouramis. The results showed that TGIV was more lethal than GIV in dwarf gouramis. The expression of the viral major capsid protein could be detected. GIV and TGIV infections also resulted in pronounced vacuolation and necrosis of the spleen tissue. Transmission electron microscopy revealed the accumulation of nearly icosahedral viral particles in the spleen tissues of dwarf gouramis infected with TGIV and GIV. This study demonstrated that iridoviruses can survive and be infectious in both fresh and marine water habitats.

#51: Neurotropic Astrovirus-VA1: Identifying the distinctions from classical genotypes

Abstract Background Human astroviruses (HAstV) are a leading cause of acute gastroenteritis in children, particularly those under the age of 2 or with immunosuppressive conditions. Indeed, our studies suggest that children with hematological malignancies are at high risk of infection. However, it has become increasingly clear that HAstV infections can also be associated with respiratory and even central nervous system (CNS) diseases. In the last decade, there have been at least 12 cases of astrovirus-induced CNS disease resulting in encephalitis and meningitis, including 2 St Jude patients. The CNS-associated infections are overwhelmingly fatal and are primarily caused by a novel astrovirus genotype, VA1, that is genetically more similar to animal astroviruses that also induce CNS-associated infections. The recent ability to propagate the VA1 strain in cell lines affords us the opportunity to better understand VA1 infection and how it compares to the better-studied HAstV1 strain. Methods Viral kinetics were determined by infection of human intestinal adenocarcinoma Caco-2 cells with either HAstV1 or VA1 and monitored for 24 hours post-infection (hpi). Infected cells were identified via immunofluorescent microscopy using antibodies against double-stranded RNA and viral capsid. Epithelial permeability of astrovirus-infected Caco-2 cells was measured using transepithelial electrical resistance (TER) and monitored for 24hpi. Nitazoxanide efficacy was identified by immunofluorescent analysis as described previously. Results Our findings demonstrate that HAstV1 and VA1 replicate in intestinal epithelial cells without inducing cell death or a pro-inflammatory cytokine response. However, these two strains have distinct replication kinetics. VA1 appears to have an ~8 hour lag in the expression of dsRNA and capsid protein compared to HAstV1 and does not require exogenous proteases to process the viral outer coat (capsid) protein, Additionally, we demonstrated that the increase in epithelial barrier permeability associated with HAstV1-infection is not found in VA1-infected cells, which is intriguing and may explain why HAstV1 is more likely to cause diarrhea. Of clinical importance, we have revealed a similar susceptibility of VA1 to the antiviral drug, nitazoxanide, which we have recently demonstrated its effectiveness inhibiting classical HAstV strains. Conclusion Overall, our studies highlight that VA1 pathogenesis is distinct from HAstV1, which could explain the differences in vivo. Future studies will be necessary to investigate viral replication and pathogenesis in distinct neuronal cells and in vivo.

Characterisation of the Semliki Forest Virus-host cell interactome reveals the viral capsid protein as an inhibitor of nonsense-mediated mRNA decay.

The positive-sense, single-stranded RNA alphaviruses pose a potential epidemic threat. Understanding the complex interactions between the viral and the host cell proteins is crucial for elucidating the mechanisms underlying successful virus replication strategies and for developing specific antiviral interventions. Here we present the first comprehensive protein-protein interaction map between the proteins of Semliki Forest Virus (SFV), a mosquito-borne member of the alphaviruses, and host cell proteins. Among the many identified cellular interactors of SFV proteins, the enrichment of factors involved in translation and nonsense-mediated mRNA decay (NMD) was striking, reflecting the virus' hijacking of the translation machinery and indicating viral countermeasures for escaping NMD by inhibiting NMD at later time points during the infectious cycle. In addition to observing a general inhibition of NMD about 4 hours post infection, we also demonstrate that transient expression of the SFV capsid protein is sufficient to inhibit NMD in cells, suggesting that the massive production of capsid protein during the SFV reproduction cycle is responsible for NMD inhibition.

Single-Cell Transcriptomics Reveals a Heterogeneous Cellular Response to BK Virus Infection.

BK virus (BKV) is a human polyomavirus that is generally harmless but can cause devastating disease in immunosuppressed individuals. BKV infection of renal cells is a common problem for kidney transplant patients undergoing immunosuppressive therapy. In cultured primary human renal proximal tubule epithelial (RPTE) cells, BKV undergoes a productive infection. The BKV-encoded large T antigen (LT) induces cell cycle entry, resulting in the upregulation of numerous genes associated with cell proliferation. Consistently, microarray and transcriptome sequencing (RNA-seq) experiments performed on bulk infected cell populations identified several proliferation-related pathways that are upregulated by BKV. These studies revealed few genes that are downregulated. In this study, we analyzed viral and cellular transcripts in single mock- or BKV-infected cells. We found that the levels of viral mRNAs vary widely among infected cells, resulting in different levels of LT and viral capsid protein expression. Cells expressing the highest levels of viral transcripts account for approximately 20% of the culture and have a gene expression pattern that is distinct from that of cells expressing lower levels of viral mRNAs. Surprisingly, cells expressing low levels of viral mRNA do not progress with time to high expression, suggesting that the two cellular responses are determined prior to or shortly following infection. Finally, comparison of cellular gene expression patterns of cells expressing high levels of viral mRNA with those of mock-infected cells or cells expressing low levels of viral mRNA revealed previously unidentified pathways that are downregulated by BKV. Among these are pathways associated with drug metabolism and detoxification, tumor necrosis factor (TNF) signaling, energy metabolism, and translation.IMPORTANCE The outcome of viral infection is determined by the ability of the virus to redirect cellular systems toward progeny production countered by the ability of the cell to block these viral actions. Thus, an infected culture consists of thousands of cells, each fighting its own individual battle. Bulk measurements, such as PCR or RNA-seq, measure the average of these individual responses to infection. Single-cell transcriptomics provides a window to the one-on-one battle between BKV and each cell. Our studies reveal that only a minority of infected cells are overwhelmed by the virus and produce large amounts of BKV mRNAs and proteins, while the infection appears to be restricted in the remaining cells. Correlation of viral transcript levels with cellular gene expression patterns reveals pathways manipulated by BKV that may play a role in limiting infection.

Herpes simplex virus 1 infection induces ubiquitination of UBE1a.

Herpes simplex virus 1 (HSV-1) is a human DNA virus that causes cold sores, keratitis, meningitis, and encephalitis. Ubiquitination is a post-translational protein modification essential for regulation of cellular events, such as proteasomal degradation, signal transduction, and protein trafficking. The process is also involved in events for establishing viral infection and replication. The first step in ubiquitination involves ubiquitin (Ub) binding with Ub-activating enzyme (E1, also termed UBE1) via a thioester linkage. Our results show that HSV-1 infection alters protein ubiquitination pattern in host cells, as evidenced by MS spectra and co-immunoprecipitation assays. HSV-1 induced ubiquitination of UBE1a isoform via an isopeptide bond with Lys604. Moreover, we show that ubiquitination of K604 in UBE1a enhances UBE1a activity; that is, the activity of ubiquitin-transfer to E2 enzyme. Subsequently, we investigated the functional role of UBE1a and ubiquitination of K604 in UBE1a. We found that UBE1-knockdown increased HSV-1 DNA replication and viral production. Furthermore, overexpression of UBE1a, but not a UBE1a K604A mutant, suppressed viral replication. Furthermore, we found that UBE1a and ubiquitination at K604 in UBE1a retarded expression of HSV-1 major capsid protein, ICP5. Our findings show that UBE1a functions as an antiviral factor that becomes activated upon ubiquitination at Lys604.

A model for long-term infection of bovine papillomavirus type 1 in Saccharomyces cerevisiae.

We have previously reported that bovine papillomavirus type 1 (BPV1) can replicate its genome and produces infectious virus-like particles in short-term BPV1 virion-infected Sacharomyces cerevisiae (Zhao and Frazer, 2002). Here, we report viral RNA transcription and L1 capsid protein expression in long-term BPV1 virion-infected S. cerevisiae culture. Northern blot hybridization showed that viral RNA was detected in long-term BPV1-infected S. cerevisiae cultures (82-108 days). The levels of the viral RNA transcription varied significantly over the long time period, which showed active transcription at an early stage (Day 3 to Day 16), weak transcription at a middle stage (Day 23 to Day 45) and stable transcription at the late stage of culture (Day 55 to Day 82/85/95). Three major BPV1 transcripts of 4.3, 2.6 and 1.8Kb were identified, with 4.3Kb a minor transcript and the 1.8Kb the most prominent transcript compared with the 2.6Kb species. Immunoblotting showed that L1 capsid protein was expressed, with its variable amounts corresponding to the levels of RNA transcription over the time period. 35S-methionine/cysteine labeling and immunoprecipitation proved that the detected L1 protein was newly synthesized in BPV1-infected S. cerevisiae cultures. 33.3-54.2% of the cell colonies expressed L1 protein. Thus, the S. cerevisiae system, as a promising model, may be used not only for the study of virus like particle formation of BPV1 in vitro, but also for further functional analysis of individual viral genes in BPV1 life cycle. Keywords: BPV1; viral RNA transcription; expression of L1 capsid protein; virion-infected Saccharomyces cerevisiae.

High repetitive arginine in the anterior of PCV3 capsid protein is a severe obstacle for its expression in E. coli

Porcine circovirus type 3 (PCV3) is a novel circovirus identified in sows with PDNS-like clinical signs and reproductive failure. The capsid protein (CAP) of PCV3 is expected to be an effective vaccine candidate. Here, we expressed the original capsid protein, truncated capsid protein without anterior highly repetitive arginine (ΔCAP) and their codon-optimized counterparts in E. coli. These results showed that lots of repeated arginine could severely lower the expression of PCV3 capsid protein in E. coli. At the same time, the recombined truncated PCV3 capsid protein forms typic virions. The efficient expression of capsid protein is expected to serve the development of PCV3 vaccines and other studies of PCV3 capsid protein.

Optimized Adenoviral Vector That Enhances the Assembly of FMDV O1 Virus-Like Particles in situ Increases Its Potential as Vaccine for Serotype O Viruses.

Although replication-defective human adenovirus type 5 (Ad5) vectors that express in situ the capsid-encoding region of foot-and-mouth disease virus (FMDV) have been proven to be effective as vaccines in relevant species for several viral strains, the same result was not consistently achieved for the O1/Campos/Brazil/58 strain. In the present study, an optimization of the Ad5 system was explored and was proven to enhance the expression of FMDV capsid proteins and their association into virus-like particles (VLPs). Particularly, we engineered a novel Ad5 vector (Ad5[PVP2]OP) which harbors the foreign transcription unit in a leftward orientation relative to the Ad5 genome, and drives the expression of the FMDV sequences from an optimized cytomegalovirus (CMV) enhancer-promoter as well. The Ad5[PVP2]OP vaccine candidate also contains the amino acid substitutions S93F/Y98F in the VP2 protein coding sequence, predicted to stabilize FMD virus particles. Cells infected with the optimized vector showed an ∼14-fold increase in protein expression as compared to cells infected with an unmodified Ad5 vector tested in previous works. Furthermore, amino acid substitutions in VP2 protein allowed the assembly of FMDV O1/Campos/Brazil/58 VLPs. Evaluation of several serological parameters in inoculated mice with the optimized Ad5[PVP2]OP candidate revealed an enhanced vaccine performance, characterized by significant higher titers of neutralizing antibodies, as compared to our previous unmodified Ad5 vector. Moreover, 94% of the mice vaccinated with the Ad5[PVP2]OP candidate were protected from homologous challenge. These results indicate that both the optimized protein expression and the stabilization of the in situ generated VLPs improved the performance of Ad5-vectored vaccines against the FMDV O1/Campos/Brazil/58 strain and open optimistic expectations to be tested in target animals.

Chikungunya virus antagonizes cGAS-STING mediated type-I interferon responses by degrading cGAS.

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus known to cause epidemics resulting in predominantly symptomatic infections, which in rare cases cause long term debilitating arthritis and arthralgia. Significant progress has been made in understanding the roles of canonical RNA sensing pathways in the host recognition of CHIKV; however, less is known regarding antagonism of CHIKV by cytosolic DNA sensing pathways like that of cyclic GMP-AMP synthase (cGAS) and Stimulator of Interferon Genes (STING). With the use of cGAS or STING null cells we demonstrate that the pathway restricts CHIKV replication in fibroblasts and immune cells. We show that DNA accumulates in the cytoplasm of infected cells and that CHIKV blocks DNA dependent IFN-β transcription. This antagonism of DNA sensing is via an early autophagy-mediated degradation of cGAS and expression of the CHIKV capsid protein is sufficient to induce cGAS degradation. Furthermore, we identify an interaction of CHIKV nsP1 with STING and map the interaction to 23 residues in the cytosolic loop of the adaptor protein. This interaction stabilizes the viral protein and increases the level of palmitoylated nsP1 in cells. Together, this work supports previous publications highlighting the relevance of the cGAS-STING pathway in the early detection of (+)ssRNA viruses and provides direct evidence that CHIKV interacts with and antagonizes cGAS-STING signaling.