Eight-amino-acid sequence at the N-terminus of SARS-CoV-2 nsp1 is involved in stabilizing viral genome replication

Coronavirus disease 19 is caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) enveloped virus with a single-stranded positive-sense ribonucleic acid (RNA) genome. The CoV non-structural protein (nsp) 1 is a multifunctional protein that undergoes translation shutoff, messenger RNA (mRNA) cleavage, and RNA binding. The C-terminal region is involved in translational shutoff and RNA cleavage. The N-terminal region of SARS-CoV-2 nsp1 is highly conserved among isolated SARS-CoV-2 variants. However, the I-004 variant, isolated during the early SARS-CoV-2 pandemic, lost eight amino acids in the nsp1 region. In this study, we showed that the eight amino acids are important for viral replication in infected interferon-incompetent cells and that the recombinant virus that lost these amino acids had low pathogenicity in the lungs of hamster models. The loss of eight amino acids-induced mutations occurred in the 5' untranslated region (UTR), suggesting that nsp1 contributes to the stability of the viral genome during replication.

Establishment of a new reverse genetics system for respiratory syncytial virus under the control of RNA polymerase II

A reverse genetics system for the respiratory syncytial virus (RSV), which causes acute respiratory illness, is an effective tool for understanding the pathogenicity of RSV. To date, a method dependent on T7 RNA polymerase is commonly used for RSV. Although this method is well established and recombinant RSV is well rescued from transfected cells, the requirement for artificial supply of T7 RNA polymerase limits its application. To overcome this, we established a reverse genetics system dependent on RNA polymerase II, which is more convenient for the recovery of recombinant viruses from various cell lines. First, we identified human cell lines with high transfection efficiency in which RSV can replicate effectively. Two human cell lines, Huh-7 and 293T, permitted the propagation of recombinant green fluorescent protein-expressing RSV. Our minigenome system revealed that efficient transcription and replication of RSV occurred in both Huh-7 and 293T cells. We then confirmed that recombinant green fluorescent protein-expressing RSV was rescued in both Huh-7 and 293T cells. Furthermore, the growth capability of viruses rescued from Huh-7 and 293T cells was similar to that of recombinant RSV rescued using the conventional method. Thus, we succeeded in establishing a new reverse genetics system for RSV that is dependent on RNA polymerase II.

Single Amino Acid Substitution in the Receptor Binding Domain of Spike Protein Is Sufficient To Convert the Neutralization Profile between Ethiopian and Middle Eastern Isolates of Middle East Respiratory Coronavirus

Middle East respiratory syndrome coronavirus (MERS-CoV) is a zoonotic virus that causes MERS, which is endemic in the Middle East. The absence of human cases in Africa despite the presence of MERS-CoV suggests virological differences between MERS-CoVs in Africa and the Middle East. In fact, in the laboratory, recombinant MERS-CoV carrying the spike (S) protein of Ethiopian isolates exhibits attenuated properties, being more easily neutralized and replicating slower than viruses carrying the S protein of Middle Eastern isolate, EMC. In this study, to identify the amino acids that define the different virological features between Ethiopian and Middle Eastern MERS-CoVs, neutralization titers and viral replication were evaluated using recombinant MERS-CoVs carrying amino acid substitution(s) in the S protein. A single amino acid difference introduced into the receptor binding domain was sufficient to reverse the difference in the neutralizing properties of the S protein between Ethiopian and Middle Eastern MERS-CoVs. Furthermore, amino acid mutations in the S1 and S2 regions of S protein were collectively involved in slow viral replication. Since even a single amino acid difference in S protein can reverse the viral properties of MERS-CoV, it should be noted that multiple mutations may induce a significant change. Careful monitoring of genetic alterations in MERS-CoVs in Africa is therefore required to detect the emergence of virulent strains generated by a few genetic differences. IMPORTANCE There have been no reported cases of human Middle East respiratory syndrome (MERS) in Africa, despite the presence of MERS coronavirus (MERS-CoV). Previous studies have shown that recombinant MERS-CoV carrying the S protein of an Ethiopian isolate replicated slower and was more easily neutralized relative to MERS-CoV carrying the S protein of a Middle Eastern isolate. In this study, we investigated the amino acid(s) in S protein associated with the different viral characteristics between Ethiopian and Middle Eastern MERS-CoVs. The results revealed that a single amino acid difference in the receptor binding domain was sufficient to reverse the neutralization profile. This implies that slight genetic changes can alter the predominant population of MERS-CoV, similar to the transition of variants of severe acute respiratory syndrome coronavirus-2. Careful genetic monitoring of isolates is important to detect the spread of possible virulent MERS-CoVs generated by mutation(s).

Human antibody recognition and neutralization mode on the NTD and RBD domains of SARS-CoV-2 spike protein

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19). Variants of concern (VOCs) such as Delta and Omicron have developed, which continue to spread the pandemic. It has been reported that these VOCs reduce vaccine efficacy and evade many neutralizing monoclonal antibodies (mAbs) that target the receptor binding domain (RBD) of the glycosylated spike (S) protein, which consists of the S1 and S2 subunits. Therefore, identification of optimal target regions is required to obtain neutralizing antibodies that can counter VOCs. Such regions have not been identified to date. We obtained 2 mAbs, NIBIC-71 and 7G7, using peripheral blood mononuclear cells derived from volunteers who recovered from COVID-19. Both mAbs had neutralizing activity against wild-type SARS-CoV-2 and Delta, but not Omicron. NIBIC-71 binds to the RBD, whereas 7G7 recognizes the N-terminal domain of the S1. In particular, 7G7 inhibited S1/S2 cleavage but not the interaction between the S protein and angiotensin-converting enzyme 2; it suppressed viral entry. Thus, the efficacy of a neutralizing mAb targeting inhibition of S1/2 cleavage was demonstrated. These results suggest that neutralizing mAbs targeting blockade of S1/S2 cleavage are likely to be cross-reactive against various VOCs.

Versatile live-attenuated SARS-CoV-2 vaccine platform applicable to variants induces protective immunity

Live-attenuated vaccines are generally highly effective. Here, we aimed to develop one against SARS-CoV-2, based on the identification of three types of temperature-sensitive (TS) strains with mutations in nonstructural proteins (nsp), impaired proliferation at 37-39ºC, and the capacity to induce protective immunity in Syrian hamsters. To develop a live-attenuated vaccine, we generated a virus that combined all these TS-associated mutations (rTS-all), which showed a robust TS phenotype in vitro and high attenuation in vivo. The vaccine induced an effective cross-reactive immune response and protected hamsters against homologous or heterologous viral challenges. Importantly, rTS-all rarely reverted to the wild-type phenotype. By combining these mutations with an Omicron spike protein to construct a recombinant virus, protection against the Omicron strain was obtained. We show that immediate and effective live-attenuated vaccine candidates against SARS-CoV-2 variants may be developed using rTS-all as a backbone to incorporate the spike protein of the variants.

A Macroporous Magnesium Oxide-Templated Carbon Adsorbs Shiga Toxins and Type III Secretory Proteins in Enterohemorrhagic Escherichia coli, Which Attenuates Virulence

Enterohemorrhagic Escherichia coli (EHEC) is one of the most common foodborne pathogens. However, no drug that prevents the severe complications caused by this bacterium has been approved yet. This study showed that a macroporous magnesium oxide (MgO)-templated carbon material (MgOC₁₅₀) adsorbs Shiga toxins, and Type III secretory EspA/EspB proteins responsible for EHEC pathogenesis, and decreases the extracellular levels of these proteins. On the other hand, this material did not affect the growth of EHEC. Citrobacter rodentium traditionally used to estimate Type III secretion system-associated virulence in mice is highly virulent. The survival period of infected mice was prolonged when MgOC₁₅₀ was administered. This adsorbent disturbed neither mammalian cells nor normal intestinal bacteria, such as Enterococcus hirae, Lactobacillus acidophilus, and Lactobacillus casei. In contrast, MgOC₁₅₀ adsorbed antimicrobial agents, including β-lactams, quinolones, tetracyclines, and trimethoprim/sulfamethoxazole. However, fosfomycin and amikacin were not adsorbed. Thus, MgOC₁₅₀ can be used with fosfomycin and amikacin to treat infections. MgOC₁₅₀ is used for industrial purposes, such as an electrode catalyst, a bioelectrode, and enzyme immobilization. The study proposed another potential application of MgOC₁₅₀, assisting anti-EHEC chemotherapy.

3CL Protease Inhibitors with an Electrophilic Arylketone Moiety as Anti-SARS-CoV-2 Agents

The novel coronavirus, SARS-CoV-2, has been identified as the causative agent for the current coronavirus disease (COVID-19) pandemic. 3CL protease (3CLpro) plays a pivotal role in the processing of viral polyproteins. We report peptidomimetic compounds with a unique benzothiazolyl ketone as a warhead group, which display potent activity against SARS-CoV-2 3CLpro. The most potent inhibitor YH-53 can strongly block the SARS-CoV-2 replication. X-ray structural analysis revealed that YH-53 establishes multiple hydrogen bond interactions with backbone amino acids and a covalent bond with the active site of 3CLpro. Further results from computational and experimental studies, including an in vitro absorption, distribution, metabolism, and excretion profile, in vivo pharmacokinetics, and metabolic analysis of YH-53 suggest that it has a high potential as a lead candidate to compete with COVID-19.

ACE2-like carboxypeptidase B38-CAP protects from SARS-CoV-2-induced lung injury

Angiotensin-converting enzyme 2 (ACE2) is a receptor for cell entry of SARS-CoV-2, and recombinant soluble ACE2 protein inhibits SARS-CoV-2 infection as a decoy. ACE2 is a carboxypeptidase that degrades angiotensin II, thereby improving the pathologies of cardiovascular disease or acute lung injury. Here we show that B38-CAP, an ACE2-like enzyme, is protective against SARS-CoV-2-induced lung injury. Endogenous ACE2 expression is downregulated in the lungs of SARS-CoV-2-infected hamsters, leading to elevation of angiotensin II levels. Recombinant Spike also downregulates ACE2 expression and worsens the symptoms of acid-induced lung injury. B38-CAP does not neutralize cell entry of SARS-CoV-2. However, B38-CAP treatment improves the pathologies of Spike-augmented acid-induced lung injury. In SARS-CoV-2-infected hamsters or human ACE2 transgenic mice, B38-CAP significantly improves lung edema and pathologies of lung injury. These results provide the first in vivo evidence that increasing ACE2-like enzymatic activity is a potential therapeutic strategy to alleviate lung pathologies in COVID-19 patients.

Endogenous ACE2 is a receptor for SARS-CoV-2 and a recombinant soluble ACE2 protein can inhibit SARS-CoV-2 infection acting as a decoy. Here the authors show that B38-CAP, an ACE2-like enzyme but not a decoy for the virus, is protective against SARS-CoV-2-induced lung injury in animal models.

Combining machine learning and nanopore construction creates an artificial intelligence nanopore for coronavirus detection

High-throughput, high-accuracy detection of emerging viruses allows for the control of disease outbreaks. Currently, reverse transcription-polymerase chain reaction (RT-PCR) is currently the most-widely used technology to diagnose the presence of SARS-CoV-2. However, RT-PCR requires the extraction of viral RNA from clinical specimens to obtain high sensitivity. Here, we report a method for detecting novel coronaviruses with high sensitivity by using nanopores together with artificial intelligence, a relatively simple procedure that does not require RNA extraction. Our final platform, which we call the artificially intelligent nanopore, consists of machine learning software on a server, a portable high-speed and high-precision current measuring instrument, and scalable, cost-effective semiconducting nanopore modules. We show that artificially intelligent nanopores are successful in accurately identifying four types of coronaviruses similar in size, HCoV-229E, SARS-CoV, MERS-CoV, and SARS-CoV-2. Detection of SARS-CoV-2 in saliva specimen is achieved with a sensitivity of 90% and specificity of 96% with a 5-minute measurement.

Establishment of a reverse genetics system for SARS-CoV-2 using circular polymerase extension reaction

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been identified as the causative agent of coronavirus disease 2019 (COVID-19). Although multiple mutations have been observed in SARS-CoV-2, functional analysis of each mutation of SARS-CoV-2 has been limited by the lack of convenient mutagenesis methods. In this study, we establish a PCR-based, bacterium-free method to generate SARS-CoV-2 infectious clones. Recombinant SARS-CoV-2 could be rescued at high titer with high accuracy after assembling 10 SARS-CoV-2 cDNA fragments by circular polymerase extension reaction (CPER) and transfection of the resulting circular genome into susceptible cells. The construction of infectious clones for reporter viruses and mutant viruses could be completed in two simple steps: introduction of reporter genes or mutations into the desirable DNA fragments (∼5,000 base pairs) by PCR and assembly of the DNA fragments by CPER. This reverse genetics system may potentially advance further understanding of SARS-CoV-2.

Long-term acrylamide exposure exacerbates brain and lung pathology in a mouse malaria model

The consumption of dietary acrylamide (ACR), a carcinogen, results in the dysfunction of various organs and the immune system. However, the impact of ACR exposure on the progression of infectious diseases is unknown. This study investigated the effect of ACR on the progression of malaria infection using a mouse model of malaria. C57BL/6 mice were continuously treated with ACR at a dose of 20 mg/kg bodyweight/day for six weeks (long-term exposure) or phosphate-buffered saline (PBS). Next, the mice were infected with the rodent malaria parasite, Plasmodium berghei NK65 (PbNK). Parasitemia and survival rate were analyzed in the different treatment groups. Magnetic resonance imaging (MRI) and histopathological analyses were performed to evaluate the effect of ACR exposure on the morphology of various organs. Long-term ACR exposure exacerbated PbNK-induced multiorgan dysfunction. MRI and histopathological analysis revealed signs of encephalomeningitis and acute respiratory distress syndrome in the PbNK-infected long-term ACR exposure mice, which decreased the survival rate of mice, but not in the PbNK-infected long-term PBS exposure group. These findings enhance our understanding of the impact of ACR on the progression of infectious diseases, such as malaria.

The long-quarantined case of COVID-19 with prolonged viral shedding and intermittent fever for more than 70 days

A 79-year old Japanese woman was diagnosed with coronavirus disease (COVID-19), caused by SARS coronavirus 2 (SARS-CoV-2), based on a positive reverse transcription-PCR (RT-PCR) test result. Chest computed tomography revealed mild interstitial pneumonia. She had intermittent persistent inflammatory reactions with fever. Laboratory findings and RT-PCR test results showed SARS-CoV-2 positivity for more than 70 days. To the best of our knowledge, this relatively mild case has the longest duration of viral shedding recorded, as confirmed by RT-PCR analysis. This case demonstrates that the viral shedding in COVID-19 can be prolonged, even in mild disease, and highlights the difficulties in distinguishing viral shedding from SARS-CoV-2 infectivity.

Characterization of Localization and Export Signals of Bovine Torovirus Nucleocapsid Protein Responsible for Extensive Nuclear and Nucleolar Accumulation and Their Importance for Virus Growth

Torovirus (ToV) has recently been classified into the new family Tobaniviridae, although historically, it belonged to the Coronavirus (CoV) family. The nucleocapsid (N) proteins of CoVs are predominantly localized in the cytoplasm, where the viruses replicate, but in some cases the proteins are partially located in the nucleolus. Many studies have investigated the subcellular localization and nucleocytoplasmic trafficking signals of the CoV N proteins, but little is known about ToV N proteins. Here, we studied the subcellular localization of the bovine ToV (BToV) N protein (BToN) and characterized its nucleocytoplasmic trafficking signals. Unlike other CoVs, BToN in infected cells was transported mainly to the nucleolus during early infection but was distributed predominantly in the nucleoplasm rather than in the nucleolus during late infection. Interestingly, a small quantity of BToN was detected in the cytoplasm during infection. Examination of a comprehensive set of substitution or deletion mutants of BToN fused with enhanced green fluorescent protein (EGFP) revealed that clusters of arginine (R) residues comprise nuclear/nucleolar localization signals (NLS/NoLS), and the C-terminal region served as a chromosomal maintenance 1 (CRM1)-independent nuclear export signal (NES). Moreover, recombinant viruses with mutations in the NLS/NoLS, but retaining nuclear accumulation, were successfully rescued and showed slightly reduced growth ability, while the virus that lost the NLS/NoLS-mediated nuclear accumulation of BToN was not rescued. These results indicate that BToN uniquely accumulates mainly in nuclear compartments during infection, regulated by an R-rich NLS/NoLS and a CRM1-independent NES, and that the BToN accumulation in the nuclear compartment driven by NLS/NoLS is important for virus growth.IMPORTANCE ToVs are diarrhea-causing pathogens detected in many species, including humans. BToV has spread worldwide, leading to economic loss, and there is currently no treatment or vaccine available. Positive-stranded RNA viruses, including ToVs, replicate in the cytoplasm, and their structural proteins generally accumulate in the cytoplasm. Interestingly, BToN accumulated predominantly in the nucleus/nucleolus during all infectious processes, with only a small fraction accumulating in the cytoplasm despite being a major structural protein. Furthermore, we identified unique nucleocytoplasmic trafficking signals and demonstrated the importance of NLS/NoLS for virus growth. This study is the first to undertake an in-depth investigation of the subcellular localization and intracellular trafficking signals of BToN. Our findings additionally suggest that the NLS/NoLS-mediated nuclear accumulation of BToN is important for virus replication. An understanding of the unique features of BToV may provide novel insights into the assembly mechanisms of not only ToVs but also other positive-stranded RNA viruses.

The Inhaled Steroid Ciclesonide Blocks SARS-CoV-2 RNA Replication by Targeting the Viral Replication-Transcription Complex in Cultured Cells

Here, we screened steroid compounds to obtain a drug expected to block host inflammatory responses and Middle East respiratory syndrome coronavirus (MERS-CoV) replication. Ciclesonide, an inhaled corticosteroid, suppressed the replication of MERS-CoV and other coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 2019 (COVID-19), in cultured cells. The 90% effective concentration (EC90) of ciclesonide for SARS-CoV-2 in differentiated human bronchial tracheal epithelial cells was 0.55 μM. Eight consecutive passages of 43 SARS-CoV-2 isolates in the presence of ciclesonide generated 15 resistant mutants harboring single amino acid substitutions in nonstructural protein 3 (nsp3) or nsp4. Of note, ciclesonide suppressed the replication of all these mutants by 90% or more, suggesting that these mutants cannot completely overcome ciclesonide blockade. Under a microscope, the viral RNA replication-transcription complex in cells, which is thought to be detectable using antibodies specific for nsp3 and double-stranded RNA, was observed to fall in the presence of ciclesonide in a concentration-dependent manner. These observations indicate that the suppressive effect of ciclesonide on viral replication is specific to coronaviruses, highlighting it as a candidate drug for the treatment of COVID-19 patients.IMPORTANCE The outbreak of SARS-CoV-2, the cause of COVID-19, is ongoing. New and effective antiviral agents that combat the disease are needed urgently. Here, we found that an inhaled corticosteroid, ciclesonide, suppresses the replication of coronaviruses, including betacoronaviruses (murine hepatitis virus type 2 [MHV-2], MERS-CoV, SARS-CoV, and SARS-CoV-2) and an alphacoronavirus (human coronavirus 229E [HCoV-229E]), in cultured cells. Ciclesonide is safe; indeed, it can be administered to infants at high concentrations. Thus, ciclesonide is expected to be a broad-spectrum antiviral drug that is effective against many members of the coronavirus family. It could be prescribed for the treatment of MERS and COVID-19.

Neutralizing and binding activities against SARS-CoV-1/2, MERS-CoV, and human coronaviruses 229E and OC43 by normal human intravenous immunoglobulin derived from healthy donors in Japan

BACKGROUND

There are several types of coronaviruses that infect humans and cause disease. The latest is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is an emerging global threat with no current effective treatment. Normal intravenous immunoglobulin (N-IVIG) has been administered to coronavirus disease 2019 (COVID-19) patients to control severe inflammation and the cellular immune response. However, the neutralizing activity of N-IVIG against SARS-CoV-2 has not yet been fully evaluated. The aim of this study was to determine whether N-IVIG manufactured before the start of the COVID-19 pandemic contained IgG antibodies against the circulating human coronaviruses (HCoVs) that cross-react with the highly pathogenic coronaviruses SARS-CoV-1, Middle East respiratory syndrome coronavirus (MERS-CoV), and SARS-CoV-2. No cases of SARS-CoV-1 or MERS-CoV have been reported in Japan.

STUDY DESIGN AND METHODS

The neutralizing and binding activities of N-IVIG against SARS-CoV-1, MERS-CoV, SARS-CoV-2, HCoV 229E, and HCoV OC43 were evaluated. Nine N-IVIG lots manufactured between 2000 and 2018, derived from donors in Japan, were tested. Binding activity was evaluated by indirect immunofluorescence assay.

RESULTS

None of the N-IVIG lots tested displayed neutralizing or binding activity against SARS-CoV-1, MERS-CoV, or SARS-CoV-2. However, they displayed substantial neutralizing and binding activity against HCoV OC43 and weak neutralizing and substantial binding activity against HCoV 229E.

CONCLUSION

N-IVIG derived from healthy donors in Japan before the start of the COVID-19 pandemic had no direct effect against SARS-CoV-2. Further studies are warranted to determine the effects of N-IVIG manufactured after the start of the COVID-19 pandemic against SARS-CoV-2.

Blood-cerebrospinal fluid barrier: another site disrupted during experimental cerebral malaria caused by Plasmodium berghei ANKA

Cerebral malaria is one of the most severe pathologies of malaria; it induces neuro-cognitive sequelae and has a high mortality rate. Although many factors involved in the development of cerebral malaria have been discovered, its pathogenic mechanisms are still not completely understood. Most studies on cerebral malaria have focused on the blood-brain barrier, despite the importance of the blood-cerebrospinal fluid barrier, which protects the brain from peripheral inflammation. Consequently, the pathological role of the blood-cerebrospinal fluid barrier in cerebral malaria is currently unknown. To examine the status of the blood-cerebrospinal fluid barrier in cerebral malaria and malaria without this pathology (non-cerebral malaria), we developed a new method for evaluating the permeabilization of the blood-cerebrospinal fluid barrier during cerebral malaria in mice, using Evans blue dye and a software-assisted image analysis. Using C57BL/6J (B6) mice infected with Plasmodium berghei ANKA strain as an experimental cerebral malaria model and B6 mice infected with P. berghei NK65 strain or Plasmodium yoelii as non-cerebral malaria models, we revealed that the permeability of the blood-cerebrospinal fluid barrier increased during experimental cerebral malaria but not during non-cerebral malaria. We observed haemorrhaging in the cerebral ventricles and hemozoin-like structures in the choroid plexus, which is a key component of the blood-cerebrospinal fluid barrier, in cerebral malaria mice. Taken together, this evidence indicates that the blood-cerebrospinal fluid barrier is disrupted in experimental cerebral malaria, whereas it remains intact in non-cerebral malaria. We also found that P. berghei ANKA parasites and CD8⁺ T cells are involved in the blood-cerebrospinal fluid barrier disruption in experimental cerebral malaria. An understanding of the mechanisms underlying cerebral malaria might help in the development of effective strategies to prevent and manage cerebral malaria in humans.

Middle East Respiratory Syndrome Coronavirus in Dromedaries in Ethiopia Is Antigenically Different From the Middle East Isolate EMC

Middle East respiratory syndrome (MERS) is an emerging respiratory disease caused by the MERS coronavirus (MERS-CoV). MERS has been endemic to Saudi Arabia since 2012. The reservoir of MERS-CoV is the dromedary camel, suggesting that MERS is primarily a zoonotic disease. MERS-CoV is common in dromedaries throughout the Middle East, North Africa, and East Africa as evidenced by neutralizing antibodies against MERS-CoV; however, human cases have remained limited to the Middle East. To better understand the cause of this difference, the virological properties of African camel MERS-CoV were analyzed based on the spike (S) protein in Ethiopia. Nasal swabs were collected from 258 young dromedaries (≤ 2 years old) in the Afar region of Ethiopia, of which 39 were positive for MERS-CoV, as confirmed by genetic tests. All positive tests were exclusive to the Amibara woreda region. Using next-generation sequencing, two full-length genomes of Amibara isolates were successfully decoded; both isolates belonged to the C2 clade based on phylogenetic analysis of full-length and S protein sequences. Recombinant EMC isolates of MERS-CoV, in which the S protein is replaced with those of Amibara isolates, were then generated to test the roles of these proteins in viral properties. Amibara S recombinants replicated more slowly in cultured cells than in EMC S recombinants. In neutralizing assays, Amibara S recombinants were neutralized by lower concentrations of sera from both Ethiopian dromedaries and EMC isolate (wild-type)-immunized mouse sera, relative to the EMC S recombinants, indicating that viruses coated in the Amibara S protein were easier to neutralize than the EMC S protein. Neutralization experiments performed using S1/S2 chimeric recombinants of the EMC and Amibara S proteins showed that the neutralization profile was dependent on the S1 region of the S protein. These results suggest that the slower viral replication and the ease of neutralization seen in the Ethiopian MERS-CoV are due to strain-specific differences in the S protein and may account for the absence of human MERS-CoV cases in Ethiopia.

Development of fluorescent reverse transcription loop-mediated isothermal amplification (RT-LAMP) using quenching probes for the detection of the Middle East respiratory syndrome coronavirus

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Fluorescent RT-LAMP assays using quenching probes for MERS-CoV were developed.

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Quenching probe (QProbe) can solve the problem in turbidity monitoring mechanism.

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Only primer-derived signal can be monitored specifically by QProbes.

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Two primer sets were developed to enable to confirm MERS case by RT-LAMP only.

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Both sets were highly specific and sensitive in comparison with real-time RT-PCR.

Clinical detection of Middle East respiratory syndrome (MERS) coronavirus (MERS-CoV) in patients is achieved using genetic diagnostic methods, such as real-time RT-PCR assay. Previously, we developed a reverse transcription-loop-mediated isothermal amplification (RT-LAMP) assay for the detection of MERS-CoV [Virol J. 2014. 11:139]. Generally, amplification of RT-LAMP is monitored by the turbidity induced by precipitation of magnesium pyrophosphate with newly synthesized DNA. However, this mechanism cannot completely exclude the possibility of unexpected reactions. Therefore, in this study, fluorescent RT-LAMP assays using quenching probes (QProbes) were developed specifically to monitor only primer-derived signals. Two primer sets (targeting nucleocapsid and ORF1a sequences) were constructed to confirm MERS cases by RT-LAMP assay only. Our data indicate that both primer sets were capable of detecting MERS-CoV RNA to the same level as existing genetic diagnostic methods, and that both were highly specific with no cross-reactivity observed with other respiratory viruses. These primer sets were highly efficient in amplifying target sequences derived from different MERS-CoV strains, including camel MERS-CoV. In addition, the detection efficacy of QProbe RT-LAMP was comparable to that of real-time RT-PCR assay using clinical specimens from patients in Saudi Arabia. Altogether, these results indicate that QProbe RT-LAMP assays described here can be used as powerful diagnostic tools for rapid detection and surveillance of MERS-CoV infections.

Construction of a high-yield dengue virus by replacing nonstructural proteins 3-4B without increasing virulence

Producing virus at high yield is critically important for development of whole virion inactivated vaccines or live attenuated vaccines. Most dengue virus (DENV) clinical isolates, however, replicate at low levels in cultured cells, which limits their use for vaccine development. The present study examined differences between low-replicating DENV clinical isolates and high-replicating laboratory strains with the aim of engineering high-yield DENV clinical isolates. Construction of a series of recombinant chimeric viruses derived from a high-replicating laboratory DENV type 4 (DENV-4) H241 strain and a clinical isolate revealed that the NS3-NS4B region of H241 conferred a replication advantage in cultured cells. Furthermore, northern blot analysis revealed that this advantage was due to more efficient synthesis of viral RNA. Importantly, replacement of the NS3-NS4B region of H241 did not increase virulence in mice, suggesting that viral production can be increased safely. This study provided information that will facilitate engineering of safe and high-yield viruses that can be used for vaccine development.

MERS coronavirus nsp1 participates in an efficient propagation through a specific interaction with viral RNA

MERS-CoV is the only lethal human CoV still endemic in the Arabian Peninsula and neither vaccine nor therapeutics against MERS-CoV infection is available. The nsp1 of CoV is thought to be a major virulence factor because it suppresses protein synthesis through the degradation of host mRNA. In contrast, viral RNA circumvents the nsp1-mediated translational shutoff for an efficient propagation. In this study, we identified amino acid residue in MERS-CoV nsp1 that differ from those of SARS-CoV nsp1, and that appear to be crucial for circumventing the translational shutoff. In addition, reverse genetics analysis suggested the presence of a cis-acting element at the 5'-terminus of the nsp1-coding region, which contributes to the specific recognition of viral RNA that is required for an efficient viral replication. Our results suggest the CoVs share a common mechanism for circumventing the nsp1-mediated translational shutoff.

Dual functions of Rift Valley fever virus NSs protein: inhibition of host mRNA transcription and post-transcriptional downregulation of protein kinase PKR

Rift Valley fever virus (RVFV), which belongs to the genus Phlebovirus, family Bunyaviridae, is a negative-stranded RNA virus carrying a single-stranded, tripartite RNA genome. RVFV is an important zoonotic pathogen transmitted by mosquitoes and causes large outbreaks among ruminants and humans in Africa and the Arabian Peninsula. Human patients develop an acute febrile illness, followed by a fatal hemorrhagic fever, encephalitis, or ocular diseases. A viral nonstructural protein, NSs, is a major viral virulence factor. Past studies showed that NSs suppresses the transcription of host mRNAs, including interferon-beta mRNAs. Here we demonstrated that the NSs protein induced post-transcriptional downregulation of dsRNA-dependent protein kinase (PKR), to prevent phosphorylation of eIF2alpha and promoted viral translation in infected cells. These two biological activities of the NSs most probably have a synergistic effect in suppressing host innate immune functions and facilitate efficient viral replication in infected mammalian hosts.

A two-pronged strategy to suppress host protein synthesis by SARS coronavirus Nsp1 protein

The SARS coronavirus protein nsp1 can suppress host gene expression at a post-transcriptional level, with previous work showing a reduction in mRNA abundance. Now a direct effect on protein synthesis is revealed, as nsp1 modifies transcripts and also inactivates the 40S ribosomal subunit.

Severe acute respiratory syndrome coronavirus nsp1 protein suppresses host gene expression, including type I interferon production, by promoting host mRNA degradation and inhibiting host translation, in infected cells. We present evidence that nsp1 uses a novel, two-pronged strategy to inhibit host translation and gene expression. Nsp1 bound to the 40S ribosomal subunit and inactivated the translational activity of the 40S subunits. Furthermore, the nsp1–40S ribosome complex induced the modification of the 5′ region of capped mRNA template and rendered the template RNA translationally incompetent. Nsp1 also induced RNA cleavage in templates carrying the internal ribosome entry site (IRES) from encephalomyocarditis virus, but not in those carrying IRES elements from hepatitis C or cricket paralysis viruses, demonstrating that the nsp1-induced RNA modification was template-dependent. We speculate that the mRNAs that underwent the nsp1-mediated modification are marked for rapid turnover by the host RNA degradation machinery.

Rift Valley fever virus NSs protein promotes post-transcriptional downregulation of protein kinase PKR and inhibits eIF2alpha phosphorylation

Rift Valley fever virus (RVFV) (genus Phlebovirus, family Bunyaviridae) is a negative-stranded RNA virus with a tripartite genome. RVFV is transmitted by mosquitoes and causes fever and severe hemorrhagic illness among humans, and fever and high rates of abortions in livestock. A nonstructural RVFV NSs protein inhibits the transcription of host mRNAs, including interferon-β mRNA, and is a major virulence factor. The present study explored a novel function of the RVFV NSs protein by testing the replication of RVFV lacking the NSs gene in the presence of actinomycin D (ActD) or α-amanitin, both of which served as a surrogate of the host mRNA synthesis suppression function of the NSs. In the presence of the host-transcriptional inhibitors, the replication of RVFV lacking the NSs protein, but not that carrying NSs, induced double-stranded RNA-dependent protein kinase (PKR)–mediated eukaryotic initiation factor (eIF)2α phosphorylation, leading to the suppression of host and viral protein translation. RVFV NSs promoted post-transcriptional downregulation of PKR early in the course of the infection and suppressed the phosphorylated eIF2α accumulation. These data suggested that a combination of RVFV replication and NSs-induced host transcriptional suppression induces PKR-mediated eIF2α phosphorylation, while the NSs facilitates efficient viral translation by downregulating PKR and inhibiting PKR-mediated eIF2α phosphorylation. Thus, the two distinct functions of the NSs, i.e., the suppression of host transcription, including that of type I interferon mRNAs, and the downregulation of PKR, work together to prevent host innate antiviral functions, allowing efficient replication and survival of RVFV in infected mammalian hosts.

The mosquito-borne bunyavirus Rift Valley fever virus (RVFV) devastates both humans and domestic animals; it causes abortions in ruminants and complications such as hemorrhage, encephalitis, or retinal vasculitis in humans. A major RVFV virulence factor, NSs, disables host cell mRNA synthesis. Here we describe our new evidence that showed NSs working in a second way; in addition to inhibiting host cell transcription, NSs kept translation active in infected cells. It is well-established that activated protein kinase PKR phosphorylates a translation factor, eIF2α, and then this phosphorylated eIF2α suppresses translation. We found that NSs decreased PKR abundance and prevented eIF2α phosphorylation in infected cells, allowing efficient viral translation and replication. In contrast, when cells were infected with an RVFV mutant lacking NSs in the presence of transcriptional inhibitors that mimic the transcription inhibition function of NSs, the PKR reduction did not occur and phoshorylated eIF2α was accumulated, resulting in the inhibition of virus gene expression and replication. Thus, NSs functions in two ways to help RVFV replicate in mammalian hosts: its newly identified PKR downregulation function secures efficient viral translation, and its host transcription inhibition function suppresses the expression of host innate antiviral functions.

Downregulation of an astrocyte-derived inflammatory protein, S100B, reduces vascular inflammatory responses in brains persistently infected with Borna disease virus

Borna disease virus (BDV) is a neurotropic virus that causes a persistent infection in the central nervous system (CNS) of many vertebrate species. Although a severe reactive gliosis is observed in experimentally BDV-infected rat brains, little is known about the glial reactions contributing to the viral persistence and immune modulation in the CNS. In this regard, we examined the expression of an astrocyte-derived factor, S100B, in the brains of Lewis rats persistently infected with BDV. S100B is a Ca(2+)-binding protein produced mainly by astrocytes. A prominent role of this protein appears to be the promotion of vascular inflammatory responses through interaction with the receptor for advanced glycation end products (RAGE). Here we show that the expression of S100B is significantly reduced in BDV-infected brains despite severe astrocytosis with increased glial fibrillary acidic protein immunoreactivity. Interestingly, no upregulation of the expression of S100B, or RAGE, was observed in the persistently infected brains even when incited with several inflammatory stimuli, including lipopolysaccharide. In addition, expression of the vascular cell adhesion molecule 1 (VCAM-1), as well as the infiltration of encephalitogenic T cells, was significantly reduced in persistently infected brains in which an experimental autoimmune encephalomyelitis was induced by immunization with myelin-basic protein. Furthermore, we demonstrated that the continuous activation of S100B in the brain may be necessary for the progression of vascular immune responses in neonatally infected rat brains. Our results suggested that BDV infection may impair astrocyte functions via a downregulation of S100B expression, leading to the maintenance of a persistent infection.

Characterization of a Borna disease virus field isolate which shows efficient viral propagation and transmissibility

To investigate the biological characteristics of field isolates of Borna disease virus (BDV), as well as to understand BDV infections outside endemic countries, we isolated the virus from brain samples of a heifer with Borna disease in Japan. We demonstrate that the brain lysate contained replication products of BDV and induced viral propagation in rat glioma cells, suggesting that a replication-competent BDV existed in the bovine brain. This field strain of BDV, named Bo/04w, showed efficient viral release and transmissibility and also displayed a distinct pattern of expression of viral phosphoprotein (P) during infection, as compared with laboratory-adapted BDV strains. Interestingly, we found the level of P to be significantly low in cells infected with Bo/04w, and the transcription of this isolate to be more efficient than that of laboratory strain of BDV. These results indicated that the field isolate may regulate the expression of P at an optimal level in infected cells. We also confirmed that Bo/04w maintains biological significance in neonatal gerbil brain. Sequencing revealed that despite the biological differences, the field isolate is closely related genetically to the laboratory strains of BDV. We discuss here the sequence similarities between BDV isolates from endemic and nonendemic countries.

Severe acute respiratory syndrome coronavirus nsp1 protein suppresses host gene expression by promoting host mRNA degradation

Severe acute respiratory syndrome (SARS) coronavirus (SCoV) causes a recently emerged human disease associated with pneumonia. The 5' end two-thirds of the single-stranded positive-sense viral genomic RNA, gene 1, encodes 16 mature proteins. Expression of nsp1, the most N-terminal gene 1 protein, prevented Sendai virus-induced endogenous IFN-beta mRNA accumulation without inhibiting dimerization of IFN regulatory factor 3, a protein that is essential for activation of the IFN-beta promoter. Furthermore, nsp1 expression promoted degradation of expressed RNA transcripts and host endogenous mRNAs, leading to a strong host protein synthesis inhibition. SCoV replication also promoted degradation of expressed RNA transcripts and host mRNAs, suggesting that nsp1 exerted its mRNA destabilization function in infected cells. In contrast to nsp1-induced mRNA destablization, no degradation of the 28S and 18S rRNAs occurred in either nsp1-expressing cells or SCoV-infected cells. These data suggested that, in infected cells, nsp1 promotes host mRNA degradation and thereby suppresses host gene expression, including proteins involved in host innate immune functions. SCoV nsp1-mediated promotion of host mRNA degradation may play an important role in SCoV pathogenesis.

Persistent borna disease virus infection confers instability of HSP70 mRNA in glial cells during heat stress

Borna disease virus (BDV) is a highly neurotropic RNA virus that causes neurological disorders in many vertebrate species. Although BDV readily establishes lasting persistence, persistently infected cells maintain an apparently normal cell phenotype in terms of morphology, viability, and proliferation. In this study, to understand the regulation of stress responses in BDV infection, we investigated the expression of heat shock proteins (HSPs) in glial cells persistently infected with BDV. Interestingly, we found that BDV persistence did not upregulate HSP70 expression even in cells treated with heat stress. Furthermore, BDV-infected glial cells exhibited rapid rounding and detachment from the culture plate under various stressful conditions. Immunofluorescence analysis demonstrated that heat stress rapidly disrupts the cell cytoskeleton only in persistently infected cells, suggesting a lack of thermotolerance. Intriguingly, we found that although persistently infected glial cells expressed HSP70 mRNA after heat stress, its expression rapidly disappeared during the recovery period. These observations indicated that persistent BDV infection may affect the stability of HSP70 mRNA. Finally, we found that the double-stranded RNA-dependent protein kinase (PKR) is expressed at a constant level in persistently infected cells with or without heat shock. Considering the interrelationship between HSP70 and PKR production, our data suggest that BDV infection disturbs the cellular stress responses to abolish antiviral activities and maintain persistence.

Borna disease virus phosphoprotein represses p53-mediated transcriptional activity by interference with HMGB1

Borna disease virus (BDV) is a noncytolytic, neurotropic RNA virus that has a broad host range in warm-blooded animals, probably including humans. Recently, it was demonstrated that a 24-kDa phosphoprotein (P) of BDV directly binds to a multifunctional protein, amphoterin-HMGB1, and inhibits its function in cultured neural cells (W. Kamitani, Y. Shoya, T. Kobayashi, M. Watanabe, B. J. Lee, G. Zhang, K. Tomonaga, and K. Ikuta, J. Virol. 75:8742-8751, 2001). This observation suggested that expression of BDV P may cause deleterious effects in cellular functions by interference with HMGB1. In this study, we further investigated the significance of the binding between P and HMGB1. We demonstrated that P directly binds to the A-box domain on HMGB1, which is also responsible for interaction with a tumor suppression factor, p53. Recent works have demonstrated that binding between HMGB1 and p53 enhances p53-mediated transcriptional activity. Thus, we examined whether BDV P affects the transcriptional activity of p53 by interference with HMGB1. Mammalian two-hybrid analysis revealed that p53 and P competitively interfere with the binding of each protein to HMGB1 in a p53-deficient cell line, NCI-H1299. In addition, P was able to significantly decrease p53-mediated transcriptional activation of the cyclin G promoter. Furthermore, we showed that activation of p21(waf1) expression was repressed in cyclosporine-treated BDV-infected cells, as well as p53-transduced NCI-H1299 cells. These results suggested that BDV P may be a unique inhibitor of p53 activity via binding to HMGB1.

Age- and host-dependent control of Borna disease virus spread in the developing brains of gerbils and rats

Borna disease virus (BDV) is a non-cytolytic, neurotropic RNA virus that has a broad host range in warm-blooded animals, probably including humans. Recently, we have demonstrated that the neonatal gerbil is a unique model for analyzing BDV-induced acute neurological disease. In this report, to understand the effects of the brain development of gerbils in BDV-induced neuropathogenesis, as well as to investigate the host-dependent differences in BDV propagation and pathogenesis in the brains, we performed experimental infection of BDV using two different infant rodent models, gerbils and rats. We demonstrated here that most of the gerbils infected with BDV on postnatal days (PD) 14, but not on PD1 and PD7, could survive neurological disorders during the observation period of PD85. Interestingly, the levels of BDV RNA and antigen in surviving PD14 inoculated gerbil brains were extremely low, whereas diseased gerbils and both PD7 and PD14 inoculated rats contained significant amounts of BDV antigen in the central nervous system, suggesting that PD14 gerbils successfully controlled BDV spread in the brain. Furthermore, the viral distribution, as well as the expression levels of cytokine and CD8 mRNAs, in the brains was markedly different between the rodent models and between diseased and non-diseased statuses of the gerbils. These results demonstrated that developmentally regulated and host-specific factors could contribute to the prevention of BDV spread in developing animal brains. Studies using different animal systems would provide novel insights into the mechanisms of host defense responses to neurotropic virus infections.

Experimental vertical transmission of Borna disease virus in the mouse

We demonstrated the experimental vertical transmission of Borna disease virus (BDV) in pregnant BALB/c mice. Giessen strain He/80 of BDV was used in the present study. Six six-week-old mice were inoculated intraperitoneally with 10(5) 50% tissue culture infective doses (TCID50), and were bred immediately. Four pregnant mice were sacrificed under anaesthesia on the 10th and 14th days after vaginal plug formation. Nine newborns from two maternal mice were sacrificed under anaesthesia on the 7th day after birth. Positive signals with RT-nested PCR techniques for BDV p24-RNAs were seen in the fetuses, placentas and brains of all newborn mice. No immunopositivities for BDV p40 were found in the fetuses or placentas at 10 days' gestation. BDV p40 immunopositivities were found in neurons of the fetal brains and in decidual cells of the placentas at 14 days' gestation. They were also found in neurons of the brains of newborn mice. At 10 days' gestation, no positive signals for BDV p40 sense or antisense riboprobes were seen in the fetal brains or placentas. Positive signals were found in neurons of the fetal brains and decidual cells of the placentas at 14 days' gestation. Positive signals for BDV p40 sense and antisense riboprobes were found in almost all neurons throughout the brains of nine newborn mice. These results suggest that persistent infection with BDV in newborn mice may be induced by vertical transmission during gestation.

Glial expression of Borna disease virus phosphoprotein induces behavioral and neurological abnormalities in transgenic mice

One hypothesis for the etiology of behavioral disorders is that infection by a virus induces neuronal cell dysfunctions resulting in a wide range of behavioral abnormalities. However, a direct linkage between viral infections and neurobehavioral disturbances associated with human psychiatric disorders has not been identified. Here, we show that transgenic mice expressing the phosphoprotein (P) of Borna disease virus (BDV) in glial cells develop behavioral abnormalities, such as enhanced intermale aggressiveness, hyperactivity, and spatial reference memory deficit. We demonstrate that the transgenic brains exhibit a significant reduction in brain-derived neurotrophic factor and serotonin receptor expression, as well as a marked decrease in synaptic density. These results demonstrate that glial expression of BDV P leads to behavioral and neurobiological disturbances resembling those in BDV-infected animals. Furthermore, the lack of reactive astrocytosis and neuronal degeneration in the brains indicates that P can directly induce glial cell dysfunction and also suggests that the transgenic mice may exhibit neuropathological and neurophysiological abnormalities resembling those of psychiatric patients. Our results provide a new insight to explore the relationship between viral infections and neurobehavioral disorders.

Modulation of Borna disease virus phosphoprotein nuclear localization by the viral protein X encoded in the overlapping open reading frame

Borna disease virus (BDV) is a nonsegmented, negative-strand RNA virus that belongs to the Mononegavirales order. Unlike other animal viruses in this order, BDV replicates and transcribes in the nucleus of infected cells. Therefore, regulation of the intracellular movement of virus components must be critical for accomplishing the BDV life cycle in mammalian cells. Previous studies have demonstrated that BDV proteins are prone to accumulate in the nucleus of cells transiently transfected with each expression plasmid of the viral proteins. In BDV infection, however, cytoplasmic distribution of the viral proteins is frequently found in cultured cells and animal brains. In this study, to understand the modulation of subcellular localization of BDV proteins, we investigated the intracellular localization of the viral phosphoprotein (P). Transient-transfection analysis with a cDNA clone corresponding to a bicistronic transcript that expresses both viral X and P revealed that P efficiently localizes in the cytoplasm only when BDV X is expressed in the cells. Furthermore, our analysis revealed that the direct binding between X and P is necessary for the cytoplasmic localization of the P. Interestingly, we showed that X is not detectably expressed in the BDV-infected cells in which P is predominantly found in the nucleus, with little or no signal in the cytoplasm. These observations suggested that BDV P can modulate their subcellular localization through binding to X and that BDV may regulate the expression ratio of each viral product in infected cells to control the intracellular movement of the viral protein complexes. The results presented here provide a new insight into the regulation of the intracellular movement of viral proteins of a unique, nonsegmented, negative-strand RNA virus.

Borna disease virus induces acute fatal neurological disorders in neonatal gerbils without virus- and immune-mediated cell destructions

Borna disease virus (BDV) is a noncytolytic, neurotropic RNA virus that is known to cause neurological disturbances in various animal species. Our previous experiment demonstrated that neonate gerbils develop an acute fatal neurological disease following infection with BDV, Virology 282, 65-76). The study suggested that BDV directly causes functional damage of neuronal cells resulting in the lethal disorder in neonatal gerbils. To extend this finding, we examined whether BDV can induce neurological diseases in the absence of virus- and immune-mediated cell destruction, by using cyclosporine A (CsA)-treated neonatal gerbils. Although CsA completely suppressed specific antibody production and brain inflammation in the infected gerbil brains, the fatal neurological disorder was not inhibited by the treatment. Furthermore, we demonstrated that CsA treatment significantly decreased brain levels of cytokines, except interleukin (IL)-1 beta, in the infected gerbils. These results suggested that BDV replication, as well as brain cytokines, at least IL-1 beta, rapidly induces fatal disturbances in gerbil brain. We demonstrate here that BDV exhibits a unique neuropathogenesis in neonatal gerbil that may be pathologically and immunologically different from those in two other established rodent models, rats and mice. With this novel rodent model of virus infection it should be possible not only to examine acute neurological disturbances without severe neuroanatomical and immunopathological alterations but also to analyze molecular and cellular damage by virus replication in the central nervous system.

Borna disease in a dog in Japan

Borna disease (BD) was diagnosed in a 3-year-old male Welsh corgi suffering from a severe and acute progressive disorder of the central nervous system. Histopathologically, neuronal lesions were characterized by a non-suppurative encephalomyelitis dominated by large perivascular cuffs consisting of lymphocytes, macrophages and plasma cells; also present were inflammatory cell infiltrates in the neural parenchyma, neuronophagia and focal gliosis. Strong immunolabelling with BD virus (BDV) p40 antibody was diffusely distributed in the cytoplasm of small and large neurons in areas of the brain with and without inflammatory changes, and also in the spinal cord. Positive hybridization signals with BDV p40 sense and antisense riboprobes were seen in the nucleus and cytoplasm of the neurons throughout the whole brain and spinal cord. BDV p24 RNA in formalin-fixed brain tissue was detected by reverse transcriptase (RT)-nested polymerase chain reaction (PCR). BDV p24 RNA-positive signals were detected in the temporal lobe. This is the first report of spontaneous canine BD in Japan.

Varied persistent life cycles of Borna disease virus in a human oligodendroglioma cell line

Borna disease virus (BDV) establishes a persistent infection in the central nervous system of vertebrate animal species as well as in tissue cultures. In an attempt to characterize the life cycle of BDV in persistently infected cultured cells, we developed 30 clones by single-cell cloning from a human oligodendroglioma (OL) cell line after infection with BDV. According to the percentage of cells expressing the BDV major proteins, p40 (nucleoprotein) and p24 (phosphoprotein), the clones were classified into two types: type I (>20%) and type II (<20%). mRNAs corresponding to both proteins were detected by in situ hybridization (ISH) in a percentage of cells consistent with that for the protein expression in the two types. Surprisingly, ISH for the detection of the genomic RNA, mainly in type II, revealed a significantly larger cell population harboring the genomic RNA than that with the protein as well as the mRNA expression. By recloning from type II primary cell clones, the same phenotype was confirmed in the secondary cell clones obtained: i.e., low percentage of protein-positive cells and higher percentage of cells harboring the genomic RNA. After nerve growth factor treatment, the two types of clones showed increases in the percentage of cells expressing BDV-specific proteins that reached 80% in type II clones, in addition to increased expression levels per cell. Such enhancement might have been mediated by the activation of the mitogen-activated protein kinase in the clones as revealed by the detection of activated ERK1/2. Thus, our findings show that BDV may have established a persistent infection at low levels of viral expression in OL cells with the possibility of a latent infection.

Nosological study of Borna disease virus infection in race horses

To investigate the prevalence of diseases in the Borna disease virus (BDV) antibody positive race horses, we undertook seroepidemiological studies of BDV infection on 125 culled race horses in Hokkaido, Japan. The serological study disclosed the presence of antibodies only to BDV-p40 or -p24 in 19.2% (24/125) and 3.2% (4/125) of culled horses, respectively. Antibodies to both BDV-p40 and -p24 were found in 24.0% (30/125) of these horses. Of particular note was the finding that locomotorium disorders were detectable at a significantly higher rate in BDV antibody positive horses than that in the seronegative horses. These results imply that BDV infection may possibly contribute to an increase in the incidence rate of locomotorium disorders in race horses.

Borna disease virus phosphoprotein binds a neurite outgrowth factor, amphoterin/HMG-1

The Borna disease virus (BDV) p24 phosphoprotein is an abundant protein in BDV-infected cultured cells and animal brains. Therefore, there is a possibility that binding of the p24 protein to cellular factor(s) induces functional alterations of infected neural cells in the brain. To identify a cellular protein(s) that interacts with BDV p24 protein, we performed far-Western blotting with extracts from various cell lines. Using recombinant p24 protein as a probe, we detected a 30-kDa protein in all cell lines examined. Binding between the 30-kDa and BDV p24 proteins was also demonstrated using BDV p24 affinity and ion-exchange chromatography columns. Microsequence analysis of the purified 30-kDa protein revealed that its N terminus showed complete homology with rat amphoterin protein, which is a neurite outgrowth factor abundant in the brain during development. Mammalian two-hybrid and immunoprecipitation analyses also confirmed that amphoterin is a specific target for the p24 protein in vivo. Furthermore, we showed that infection by BDV, as well as purified p24 protein in the medium, significantly decreased cell process outgrowth of cells grown on laminin, indicating the functional inhibition of amphoterin by interaction with the p24 protein. Immunohistochemical analysis revealed decreased levels of amphoterin protein at the leading edges of BDV-infected cells. Moreover, the expression of the receptor for advanced glycation end products, of which the extracellular moiety is a receptor for amphoterin, was not significantly activated in BDV-infected cells during the process of extension, suggesting that the secretion of amphoterin from the cell surface is inhibited by the binding of the p24 protein. These results suggested that BDV infection may cause direct damage in the developing brain by inhibiting the function of amphoterin due to binding by the p24 phosphoprotein.

Borna disease virus nucleoprotein requires both nuclear localization and export activities for viral nucleocytoplasmic shuttling

Nuclear transport of viral nucleic acids is crucial to the life cycle of many viruses. Borna disease virus (BDV) belongs to the order Mononegavirales and replicates its RNA genome in the nucleus. Previous studies have suggested that BDV nucleoprotein (N) and phosphoprotein (P) have important functions in the nuclear import of the viral ribonucleoprotein (RNP) complexes via their nuclear targeting activity. Here, we showed that BDV N has cytoplasmic localization activity, which is mediated by a nuclear export signal (NES) within the sequence. Our analysis using deletion and substitution mutants of N revealed that NES of BDV N consists of a canonical leucine-rich motif and that the nuclear export activity of the protein is mediated through the chromosome region maintenance protein-dependent pathway. Interspecies heterokaryon assay indicated that BDV N shuttles between the nucleus and cytoplasm as a nucleocytoplasmic shuttling protein. Furthermore, interestingly, the NES region overlaps a binding site to the BDV P protein, and nuclear export of a 38-kDa form of BDV N is prevented by coexpression of P. These results suggested that BDV N has two contrary activities, nuclear localization and export activity, and plays a critical role in the nucleocytoplasmic transport of BDV RNP by interaction with other viral proteins.

Neurological diseases and viral dynamics in the brains of neonatally borna disease virus-infected gerbils

Borna disease virus (BDV) is a noncytolytic, neurotropic RNA virus that causes a chronic neurological disease in a wide variety of animal species. To develop a better understanding of the correlation between neurological disorders caused by BDV infection and virus distribution in the brain, we investigated viral dynamics in the central nervous system (CNS) of neonatally BDV-infected gerbils during the late stage of infection. Despite the severe symptoms and aggressive proliferation of BDV in the infected gerbils, no apparent neuroanatomical abnormalities or neuronal cell loss was observed in the infected gerbil brain. Furthermore, no or only minimal infiltration was observed in the infected gerbil brain. By in situ hybridization and real-time PCR analyses, we demonstrated that the predominant area of expression of BDV mRNA, as well as the protein, was shifted in the brain in association with progression of disease. In nondiseased gerbils, the virus replication was predominantly detected in the cerebral cortex and hippocampus of the CNS. On the other hand, diseased animals showed a high level of expression in the lower brain stem and cerebellum, especially in Purkinje cell neurons. These observations suggested that significant replication of the virus in specific areas of the CNS is critical for development of the neurological disorders in BDV-infected neonatal gerbils.

Molecular ratio between borna disease viral-p40 and -p24 proteins in infected cells determined by quantitative antigen capture ELISA

We developed the antigen capture enzyme-linked immunosorbent assay (ELISA) systems for quantification of Borna disease virus (BDV) major antigens, p40 and p24. Using these ELISAs, we quantified the two proteins in various BDV-infected materials, including the cell lysates and culture supernatants as well as the homogenates of experimental animal brains. The ELISAs were also applied to measure the infectious titer of BDV in persistently infected cell lines. Quantitative analysis with these ELISAs allowed us to measure the molecular ratio between the p40 and p24 in infected samples. Interestingly, the ratio of p24 to p40 in persistently infected cells was much higher than that observed in acutely infected cells although the ratios in the supernatants from both cell lines were quite similar. BDV-inoculated gerbil brain cells showed a relatively high ratio of p24 to p40 as compared with acutely infected cells. These observations suggested that the molecular ratio between the proteins strongly depended on the infectious status of BDV in the host cells. The ELISA system developed here could be a convenient method for the quantification of BDV infection and may also be beneficial for understanding viral replication and infectious status in the host cells.

Translation initiation of a bicistronic mRNA of Borna disease virus: a 16-kDa phosphoprotein is initiated at an internal start codon

We examined translational initiation of a bicistronic 0.8-kb mRNA of Borna disease virus (BDV) using a cDNA clone of the mRNA. Upon transfection with the clone, COS-7 cells produced a 16-kDa protein (P'), in addition to the previously identified products of BDV, 24- (P) and 14.5-kDa proteins. The 16-kDa product was detected by anti-P monoclonal antibody and was shown to exist in BDV-infected cell lines as well as in infected animal brain cells. Transient expression analysis of mutated cDNA clones encoding the BDV 0.8-kb mRNA revealed that the 16-kDa protein was initiated at the second AUG codon on the same open reading frame of the P protein. The mutational analysis also demonstrated that the first AUG within the 0.8-kb mRNA is not optimal, although the signal contains a better Kozak's motif. These results demonstrated the presence of three functional AUG codons in the smallest mRNA of BDV and also suggested that a leaky scanning mechanism is involved in translational initiation at AUG codons downstream of the bicistronic mRNA of BDV. Furthermore, the 16-kDa protein was located in the BDV-specific nuclear foci and was found to associate with the other viral proteins in BDV-infected cells, demonstrating an important role of the novel identified BDV protein in viral replication.

Identification of alternative splicing and negative splicing activity of a nonsegmented negative-strand RNA virus, Borna disease virus

Borna disease virus (BDV) is a nonsegmented negative-strand RNA virus that belongs to the Mononegavirales. Unlike other animal viruses of this order, BDV replicates and transcribes in the nucleus of infected cells. Previous studies have shown that BDV uses RNA splicing machinery for its mRNA expression. In the present study, we identified spliced RNAs that use an alternative 3' splice site, SA3, in BDV-infected cell lines as well as infected animal brain cells. Transient transfection analysis of cDNA clones of BDV RNA revealed that although SA3 is a favorable splice site in mammalian cells, utilization of SA3 is negatively regulated in infected cells. This negative splicing activity of the SA3 site is regulated by a putative cis-acting region, the exon splicing suppressor (ESS), within the polymerase exon of BDV. The BDV ESS contains similar motifs to other known ESSs present in viral and cellular genes. Furthermore, our results indicated that a functional polyadenylation signal just upstream of the BDV ESS is also involved in the regulation of alternative splicing of BDV. These observations represent the first documentation of complex RNA splicing in animal RNA viruses and also provide new insight into the mechanism of regulation of alternative splicing in animal viruses.

Detection of Borna disease virus in a pregnant mare and her fetus

A pregnant mare showing pyrexia, reduced appetite, ataxia and paresis was euthanized and examined for the presence of Borna disease virus (BDV). Her brain, showing multiple neuronal degeneration and necrosis with hemorrhage, and the histologically normal brain of the fetus were both positive for BDV RNA. The BDV nucleotide sequences were identical in the mare and fetus in the second open reading frame (ORF). This is the first report of the possible vertical transmission of BDV in a horse.

High prevalence of Borna disease virus in domestic cats with neurological disorders in Japan

A total of 15 (T-1-T-15) domestic cats with neurological disorders in Tokyo area were examined for association with Borna disease virus (BDV). None had detectable antibodies to feline immunodeficiency virus (FIV), feline leukemia virus, feline infectious peritonitis virus and Toxoplasma gondii, and only cat T-8 had detectable antibody to FIV. Serological and molecular epidemiological studies revealed a significantly high prevalence of BDV infection in these cats: antibodies against BDV p24 and/or p40 proteins in 10/15 (66.7%) and p24 and/or p40 RNA in peripheral blood mononuclear cells in 8/15 (53.3%). Further, in situ hybridization and immunohistochemistry analyses of the autopsied brain samples derived from one of the cats (T-15) revealed BDV RNA predominantly in neuronal cells in restricted regions, such as olfactory bulb and medulla of cerebrum. Thus, BDV is present in Japanese domestic cats with neurological disorders at a high prevalence.