Inhibition of porcine reproductive and respiratory syndrome virus by specific siRNA targeting Nsp9 gene

NSP4 promotes replication of porcine reproductive and respiratory syndrome virus-2

Porcine reproductive and respiratory syndrome (PRRS) is one of the most detrimental contagious swine ailments worldwide. Currently, no effective drugs are available for its treatment. Targeting the structural and non-structural proteins (NSP) of the type 2 PRRS virus (PRRSV-2) with small interfering RNA (siRNA) is an effective approach to inhibit PRRSV replication. NSP4, which is highly conserved and possesses 3 C-like serine protease activity (3CLSP), can cleave PRRSV self-proteins, thereby contributing to viral replication. To investigate the mechanism by which NSP4 regulates PRRSV-2 replication and screen for effective siRNA inhibitors of PRRSV-2 replication, the recombinant plasmid pEGFP-C1-NSP4 was constructed, and a control siRNA pair and two siRNA pairs targeting the PRRSV-2 NSP4 gene (shRNA-ctr, shRNA-150, and shRNA-536) were synthesized and cloned into the pSilencer4.1-CMV vector. After 24 h of incubation, Marc-145 cells were transfected with recombinant plasmids, and subsequently infected with different PRRSV-2 (XH-GD, ZQ-GD, GDr180, and JXA1-R). Subsequently, the effects of NSP4 overexpression, shRNA on PRRSV-2 replication were evaluated by assessing cytopathic effects (CPE), TCID50, quantitative real-time PCR (qPCR), immunofluorescence assays (IFA), and Western blotting. The data from these CPE, TCID50, qPCR, and IFA experiments revealed that NSP4 overexpression significantly enhanced PRRSV-2 replication and shRNA targeting NSP4 can inhibit PRRSV-2 replication in Marc-145 cells, indicating that shRNA could serve as candidate molecules for fundamental research on PRRSV-2.

Role of microRNAs in host defense against porcine reproductive and respiratory syndrome virus infection: a hidden front line

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most globally devastating viruses threatening the swine industry worldwide. Substantial advancements have been achieved in recent years towards comprehending the pathogenesis of PRRSV infection and the host response, involving both innate and adaptive immune responses. Not only a multitude of host proteins actively participate in intricate interactions with viral proteins, but microRNAs (miRNAs) also play a pivotal role in the host response to PRRSV infection. If a PRRSV-host interaction at the protein level is conceptualized as the front line of the battle between pathogens and host cells, then their fight at the RNA level resembles the hidden front line. miRNAs are endogenous small non-coding RNAs of approximately 20-25 nucleotides (nt) that primarily regulate the degradation or translation inhibition of target genes by binding to the 3'-untranslated regions (UTRs). Insights into the roles played by viral proteins and miRNAs in the host response can enhance our comprehensive understanding of the pathogenesis of PRRSV infection. The intricate interplay between viral proteins and cellular targets during PRRSV infection has been extensively explored. This review predominantly centers on the contemporary understanding of the host response to PRRSV infection at the RNA level, in particular, focusing on the twenty-six miRNAs that affect viral replication and the innate immune response.

Research Progress on the NSP9 Protein of Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome (PRRS) is a contagious disease caused by the porcine reproductive and respiratory syndrome virus (PRRSV). PRRS is also called “blue ear disease” because of the characteristic blue ear in infected sows and piglets. Its main clinical features are reproductive disorders of sows, breathing difficulties in piglets, and fattening in pigs, which cause considerable losses to the swine industry. NSP9, a non-structural protein of PRRSV, plays a vital role in PRRSV replication and virulence because of its RNA-dependent RNA polymerase (RdRp) structure. The NSP9 sequence is highly conserved and contains T cell epitopes, which are beneficial for the development of future vaccines. NSP9 acts as the protein interaction hub between virus and host during PRRSV infection, especially in RNA replication and transcription. Herein, we comprehensively review the application of NSP9 in terms of genetic evolution analysis, interaction with host proteins that affect virus replication, interaction with other viral proteins, pathogenicity, regulation of cellular immune response, antiviral drugs, vaccines, and detection methods. This review can therefore provide innovative ideas and strategies for PRRSV prevention and control.

Structural Characterization of Non-structural Protein 9 Complexed With Specific Nanobody Pinpoints Two Important Residues Involved in Porcine Reproductive and Respiratory Syndrome Virus Replication

Porcine reproductive and respiratory syndrome (PRRS), caused by PRRS virus (PRRSV), is a widespread viral disease that has led to huge economic losses for the global swine industry. Non-structural protein 9 (Nsp9) of PRRSV possesses essential RNA-dependent RNA polymerase (RdRp) activity for viral RNA replication. Our previous report showed that Nsp9-specific nanobody, Nb6, was able to inhibit PRRSV replication. In this study, recombinant Nsp9 and Nsp9-Nb6 complex were prepared then characterized using bio-layer interferometry (BLI) and dynamic light scattering (DLS) analyses that demonstrated high-affinity binding of Nb6 to Nsp9 to form a homogeneous complex. Small-angle X-ray scattering (SAXS) characterization analyses revealed that spatial interactions differed between Nsp9 and Nsp9-Nb6 complex molecular envelopes. Enzyme-linked immunosorbent assays (ELISAs) revealed key involvement of Nsp9 residues Ile588, Asp590, and Leu643 and Nb6 residues Tyr62, Trp105, and Pro107 in the Nsp9-Nb6 interaction. After reverse genetics-based techniques were employed to generate recombinant Nsp9 mutant viruses, virus replication efficiencies were assessed in MARC-145 cells. The results revealed impaired viral replication of recombinant viruses bearing I588A and L643A mutations as compared with replication of wild type virus, as evidenced by reduced negative-strand genomic RNA [(−) gRNA] synthesis and attenuated viral infection. Moreover, the isoleucine at position 588 of Nsp9 was conserved across PRRSV genotypes. In conclusion, structural analysis of the Nsp9-Nb6 complex revealed novel amino acid interactions involved in viral RNA replication that will be useful for guiding development of structure-based anti-PRRSV agents.

Antiviral Strategies of Chinese Herbal Medicine Against PRRSV Infection

Bioactive compounds from Traditional Chinese Medicines (TCMs) are gradually becoming an effective alternative in the control of porcine reproductive and respiratory syndrome virus (PRRSV) because most of the commercially available PRRSV vaccines cannot provide full protection against the genetically diverse strains isolated from farms. Besides, the incomplete attenuation procedure involved in the production of modified live vaccines (MLV) may cause them to revert to the more virulence forms. TCMs have shown some promising potentials in bridging this gap. Several investigations have revealed that herbal extracts from TCMs contain molecules with significant antiviral activities against the various stages of the life cycle of PRRSV, and they do this through different mechanisms. They either block PRRSV attachment and entry into cells or inhibits the replication of viral RNA or viral particles assembly and release or act as immunomodulators and pathogenic pathway inhibitors through cytokines regulations. Here, we summarized the various antiviral strategies employed by some TCMs against the different stages of the life cycle of PRRSV under two major classes, including direct-acting antivirals (DAAs) and indirect-acting antivirals (IAAs). We highlighted their mechanisms of action. In conclusion, we recommended that in making plans for the use of TCMs to control PRRSV, the pathway forward must be built on a real understanding of the mechanisms by which bioactive compounds exert their effects. This will provide a template that will guide the focus of collaborative studies among researchers in the areas of bioinformatics, chemistry, and proteomics. Furthermore, available data and procedures to support the efficacy, safety, and quality control levels of TCMs should be well documented without any breach of data integrity and good manufacturing practices.

Glycyrrhizic-Acid-Based Carbon Dots with High Antiviral Activity by Multisite Inhibition Mechanisms

With the gradual usage of carbon dots (CDs) in the area of antiviral research, attempts have been stepped up to develop new antiviral CDs with high biocompatibility and antiviral effects. In this study, a kind of highly biocompatible CDs (Gly-CDs) is synthesized from active ingredient (glycyrrhizic acid) of Chinese herbal medicine by a hydrothermal method. Using the porcine reproductive and respiratory syndrome virus (PRRSV) as a model, it is found that the Gly-CDs inhibit PRRSV proliferation by up to 5 orders of viral titers. Detailed investigations reveal that Gly-CDs can inhibit PRRSV invasion and replication, stimulate antiviral innate immune responses, and inhibit the accumulation of intracellular reactive oxygen species (ROS) caused by PRRSV infection. Proteomics analysis demonstrates that Gly-CDs can stimulate cells to regulate the expression of some host restriction factors, including DDX53 and NOS3, which are directly related to PRRSV proliferation. Moreover, it is found that Gly-CDs also remarkably suppress the propagation of other viruses, such as pseudorabies virus (PRV) and porcine epidemic diarrhea virus (PEDV), suggesting the broad antiviral activity of Gly-CDs. The integrated results demonstrate that Gly-CDs possess extraordinary antiviral activity with multisite inhibition mechanisms, providing a promising candidate for alternative therapy for PRRSV infection.

Therapeutic effect of Xanthohumol against highly pathogenic porcine reproductive and respiratory syndrome viruses

The infection by porcine reproductive and respiratory syndrome virus (PRRSV) has a severe impact on the world swine industry. However, commercially available vaccines provide only incomplete protection against this disease. Thus, novel approaches to control PRRSV infection are essential for the robust and sustainable swine industry. In our previous study, Xanthohumol (Xn), a prenylated flavonoid extracted for hops (Humulus lupulus L), was screened from 386 natural products to inhibit PRRSV proliferation and alleviate oxidative stress induced by PRRSV via the Nrf2-HMOX1 axis in Marc-145 cells. In this study, we furtherly found that Xn could inhibit PRRSV different sub-genotype strains infection with a low IC₅₀ value in porcine primary alveolar macrophages (PAMs). In addition, it caused decreased expression of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor-α in PAMs infected with PRRSV or treated with lipopolysaccharide. Animal challenge experiments showed that Xn effectively alleviated clinical signs, lung pathology, and inflammatory responses in lung tissues of pigs induced by highly pathogenic PRRSV infection. The results demonstrate that Xn is a promising therapeutic agent to combat PRRSV infections.

Xanthohumol inhibits PRRSV proliferation and alleviates oxidative stress induced by PRRSV via the Nrf2-HMOX1 axis

Porcine reproductive and respiratory syndrome virus (PRRSV) is a prevalent and endemic swine pathogen that causes significant economic losses in the global swine industry. Commercial vaccines provide limited protection against this virus, and no highly effective therapeutic drugs are yet available. In this study, we first screened a library of 386 natural products and found that xanthohumol (Xn), a prenylated flavonoid found in hops, displayed high anti-PRRSV activity by inhibiting PRRSV adsorption onto and internalization into cells. Transcriptome sequencing revealed that Xn treatment stimulates genes associated with the antioxidant response in the nuclear factor-erythroid 2-related factor 2 (Nrf2) signalling pathway. Xn causes increased expression of Nrf2, HMOX1, GCLC, GCLM, and NQO1 in Marc-145 cells. The action of Xn against PRRSV proliferation depends on Nrf2 in Marc-145 cells and porcine alveolar macrophages (PAMs). This finding suggests that Xn significantly inhibits PRRSV proliferation and decreases viral-induced oxidative stress by activating the Nrf2–HMOX1 pathway. This information should be helpful for developing a novel prophylactic and therapeutic strategy against PRRSV infection.

Nucleotide-binding oligomerization domain-like receptor X1 restricts porcine reproductive and respiratory syndrome virus-2 replication by interacting with viral Nsp9

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PRRSV infection up-regulates NLRX1 expression.

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NLRX1 impairs PRRSV replication.

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NLRX1 suppresses the synthesis of viral subgenomic RNAs.

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NLRX1 interacts and colocalizes with the Nsp9 of PRRSV.

Porcine reproductive and respiratory syndrome virus (PRRSV) causes one of the most economically important diseases of swine worldwide. Current antiviral strategies provide only limited protection. Nucleotide-binding oligomerization domain-like receptor (NLR) X1 is unique among NLR proteins in its functions as a pro-viral or antiviral factor to different viral infections. To date, the impact of NLRX1 on PRRSV infection remains unclear. In this study, we found that PRRSV infection promoted the expression of NLRX1 gene. In turn, ectopic expression of NLRX1 inhibited PRRSV replication in Marc-145 cells, whereas knockdown of NLRX1 enhanced PRRSV propagation in porcine alveolar macrophages (PAMs). Mechanistically, NLRX1 was revealed to impair intracellular viral subgenomic RNAs accumulation. Finally, Mutagenic analyses indicated that the LRR (leucine-rich repeats) domain of NLRX1 interacted with PRRSV Nonstructural Protein 9 (Nsp9) RdRp (RNA-dependent RNA Polymerase) domain and was necessary for antiviral activity. Thus, our study establishes the role of NLRX1 as a new host restriction factor in PRRSV infection.

The phosphorylation of the N protein could affect PRRSV virulence in vivo

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We confirmed that phosphorylation modification of the N protein could impair PRRSV growth efficiency in PAMs.

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This study is the first to report that phosphorylation modification of the N protein could regulate PRRSV pathogenicity in piglets.

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Mutation of PTM sites could be a novel way to attenuate the virus. This strategy will be beneficial to distinguish the vaccine from a wild-type virus.

The porcine respiratory and reproductive syndrome virus (PRRSV) nucleocapsid (N) protein is a multiphosphorylated protein.It has been proved that the phosphorylation of N protein could regulate the growth ability of PRRSV in Marc-145 cells. However, further investigation is needed to determine whether phosphorylation of the N protein could affect PRRSV virulence in piglets. In this study, we confirmed that the mutations could impair PRRSV replication ability in porcine primary macrophages (PAMs) as they did in Marc-145 cells. The animal experiments suggested that the pathogenicity of the mutated virus (A105-120) was significantly reduced compared with parent strain (XH-GD). Our results suggested that the phosphorylation of the N protein contributes to virus replication and virulence. This study is the first to identify a specific modification involved in PRRSV pathogenicity. Mutation of PTMs sites is also a novel way to attenuate PRRSV virulence. The mutations could be a marker in a vaccine. In conclusion, our study will improve our understanding of the molecular mechanisms of PRRSV pathogenicity.

A Nanobody Targeting Viral Nonstructural Protein 9 Inhibits Porcine Reproductive and Respiratory Syndrome Virus Replication

Porcine reproductive and respiratory syndrome (PRRS) is of great concern to the swine industry due to pandemic outbreaks of the disease, current ineffective vaccinations, and a lack of efficient antiviral strategies. In our previous study, a PRRSV Nsp9-specific nanobody, Nb6, was successfully isolated, and the intracellularly expressed Nb6 could dramatically inhibit PRRSV replication in MARC-145 cells. However, despite its small size, the application of Nb6 protein in infected cells is greatly limited, as the protein itself cannot enter the cells physically. In this study, a trans-activating transduction (TAT) peptide was fused with Nb6 to promote protein entry into cells. TAT-Nb6 was expressed as an inclusion body in Escherichia coli, and indirect enzyme-linked immunosorbent assays and pulldown assays showed that E. coli-expressed TAT-Nb6 maintained the binding ability to E. coli-expressed or PRRSV-encoded Nsp9. We demonstrated that TAT delivered Nb6 into MARC-145 cells and porcine alveolar macrophages (PAMs) in a dose- and time-dependent manner, and TAT-Nb6 efficiently inhibited the replication of several PRRSV genotype 2 strains as well as a genotype 1 strain. Using a yeast two-hybrid assay, Nb6 recognition sites were identified in the C-terminal part of Nsp9 and spanned two discontinuous regions (Nsp9_aa454-551 and Nsp9_aa599-646). Taken together, these results suggest that TAT-Nb6 can be developed as an antiviral drug for the inhibition of PRRSV replication and controlling PRRS disease.IMPORTANCE The pandemic outbreak of PRRS, which is caused by PRRSV, has greatly affected the swine industry. We still lack an efficient vaccine, and it is an immense challenge to control its infection. An intracellularly expressed Nsp9-specific nanobody, Nb6, has been shown to be able to inhibit PRRSV replication in MARC-145 cells. However, its application is limited, because Nb6 cannot physically enter cells. Here, we demonstrated that the cell-penetrating peptide TAT could deliver Nb6 into cultured cells. In addition, TAT-Nb6 fusion protein could suppress the replication of various PRRSV strains in MARC-145 cells and PAMs. These findings may provide a new approach for drug development to control PRRS.

DDX5 RNA Helicases: Emerging Roles in Viral Infection

Asp-Glu-Ala-Asp (DEAD)-box polypeptide 5 (DDX5), also called p68, is a prototypical member of the large ATP-dependent RNA helicases family and is known to participate in all aspects of RNA metabolism ranging from transcription to translation, RNA decay, and miRNA processing. The roles of DDX5 in cell cycle regulation, tumorigenesis, apoptosis, cancer development, adipogenesis, Wnt-β-catenin signaling, and viral infection have been established. Several RNA viruses have been reported to hijack DDX5 to facilitate various steps of their replication cycles. Furthermore, DDX5 can be bounded by the viral proteins of some viruses with unknown functions. Interestingly, an antiviral function of DDX5 has been reported during hepatitis B virus and myxoma virus infection. Thus, the precise roles of this apparently multifaceted protein remain largely obscure. Here, we provide a rapid and critical overview of the structure and functions of DDX5 with a particular emphasis on its role during virus infection.

Serine 105 and 120 are important phosphorylation sites for porcine reproductive and respiratory syndrome virus N protein function

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We identified one novel phophorylation site of the PRRSV N protein.

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We firstly found that the mutated the residue 105 and 120 could down-regulate the N-induced IL-10.

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We firstly found that mutating the residue 105 could impair the virus growth ability.

The nucleocapsid (N) protein is the most abundant protein of porcine reproductive and respiratory syndrome virus (PRRSV). It has been shown to be multiphosphorylated. However, the phosphorylation sites are still unknown. In this study, we used liquid chromatography tandem mass spectrometry (LC–MS/MS) to analyze the phosphorylation sites of N protein expressed in Sf9 cells. The results showed that N protein contains two phosphorylation sites. Since N protein can regulate IL-10, which may facilitate PRRSV replication, we constructed four plasmids (pCA-XH-GD, pCA-A105, pCA-A120 and pCA-A105-120) and transfected them into Pig alveolar macrophages (PAMs,3D4/2). The qPCR results showed that mutations at residues 105 and 120 were associated with down-regulation of the IL-10 mRNA level, potentially decreasing the viral growth ability. Then, we mutated the phosphorylation sites (S105A and S120A) and rescued three mutated viruses, namely, A105, A120 and A105-120. Compared with wild-type virus titers, the titers of the mutated viruses at 48 hpi were significantly decreased. The Nsp(non-structural protein) 9 qPCR results were consistent with the multistep growth kinetics results. The infected PAMs (primary PAMs) results were similar with Marc-145.The findings indicated that the mutations impaired the viral replication ability. The confocal microscopy results suggested that mutations to residues 105 and 120 did not affect N protein distribution. Whether the mutations affected other functions of N protein and what the underlying mechanisms are need further investigation. In conclusion, our results show that residues 105 and 120 are phosphorylation sites and are important for N protein function and for viral replication ability.

Multi-resistance strategy for viral diseases and in vitro short hairpin RNA verification method in pigs

Objective

Foot and mouth disease (FMD) and porcine reproductive and respiratory syndrome (PRRS) are major diseases that interrupt porcine production. Because they are viral diseases, vaccinations are of only limited effectiveness in preventing outbreaks. To establish an alternative multi-resistant strategy against FMD virus (FMDV) and PRRS virus (PRRSV), the present study introduced two genetic modification techniques to porcine cells.

Methods

First, cluster of differentiation 163 (CD163), the PRRSV viral receptor, was edited with the clustered regularly interspaced short palindromic repeats-CRISPR-associated protein 9 technique. The CD163 gene sequences of edited cells and control cells differed. Second, short hairpin RNA (shRNAs) were integrated into the cells. The shRNAs, targeting the 3D gene of FMDV and the open reading frame 7 (ORF7) gene of PRRSV, were transferred into fibroblasts. We also developed an in vitro shRNA verification method with a target gene expression vector.

Results

shRNA activity was confirmed in vitro with vectors that expressed the 3D and ORF7 genes in the cells. Cells containing shRNAs showed lower transcript levels than cells with only the expression vectors. The shRNAs were integrated into CD163-edited cells to combine the two techniques, and the viral genes were suppressed in these cells.

Conclusion

We established a multi-resistant strategy against viral diseases and an in vitro shRNA verification method.

Porcine Reproductive and Respiratory Syndrome Virus Nucleocapsid Protein Interacts with Nsp9 and Cellular DHX9 To Regulate Viral RNA Synthesis

Porcine reproductive and respiratory syndrome virus (PRRSV) nucleocapsid (N) protein is the main component of the viral capsid to encapsulate viral RNA, and it is also a multifunctional protein involved in the regulation of host cell processes. Nonstructural protein 9 (Nsp9) is the RNA-dependent RNA polymerase that plays a critical role in viral RNA transcription and replication. In this study, we demonstrate that PRRSV N protein is bound to Nsp9 by protein-protein interaction and that the contacting surface on Nsp9 is located in the two predicted α-helixes formed by 48 residues at the C-terminal end of the protein. Mutagenesis analyses identified E646, E608, and E611 on Nsp9 and Q85 on the N protein as the pivotal residues participating in the N-Nsp9 interaction. By overexpressing the N protein binding fragment of Nsp9 in infected Marc-145 cells, the synthesis of viral RNAs, as well as the production of infectious progeny viruses, was dramatically inhibited, suggesting that Nsp9-N protein association is involved in the process of viral RNA production. In addition, we show that PRRSV N interacts with cellular RNA helicase DHX9 and redistributes the protein into the cytoplasm. Knockdown of DHX9 increased the ratio of short subgenomic mRNAs (sgmRNAs); in contrast, DHX9 overexpression benefited the synthesis of longer sgmRNAs and the viral genomic RNA (gRNA). These results imply that DHX9 is recruited by the N protein in PRRSV infection to regulate viral RNA synthesis. We postulate that N and DHX9 may act as antiattenuation factors for the continuous elongation of nascent transcript during negative-strand RNA synthesis.

IMPORTANCE

It is unclear whether the N protein of PRRSV is involved in regulation of the viral RNA production process. In this report, we demonstrate that the N protein of the arterivirus PRRSV participates in viral RNA replication and transcription through interacting with Nsp9 and its RdRp and recruiting cellular RNA helicase to promote the production of longer viral sgmRNAs and gRNA. Our data here provide some new insights into the discontinuous to continuous extension of PRRSV RNA synthesis and also offer a new potential anti-PRRSV strategy targeting the N-Nsp9 and/or N-DHX9 interaction.

Quantitative interactome reveals that porcine reproductive and respiratory syndrome virus nonstructural protein 2 forms a complex with viral nucleocapsid protein and cellular vimentin

Porcine reproductive and respiratory syndrome virus (PRRSV) is an Arterivirus that has heavily impacted the global swine industry. The PRRSV nonstructural protein 2 (nsp2) plays crucial roles in viral replication and host immune regulation, most likely by interacting with viral or cellular proteins that have not yet been identified. In this study, a quantitative interactome approach based on immunoprecipitation and stable isotope labeling with amino acids in cell culture (SILAC) was performed to identify nsp2-interacting proteins in PRRSV-infected cells with an nsp2-specific monoclonal antibody. Nine viral proteins and 62 cellular proteins were identified as potential nsp2-interacting partners. Our data demonstrate that the PRRSV nsp1α, nsp1β, and nucleocapsid proteins all interact directly with nsp2. Nsp2-interacting cellular proteins were classified into different functional groups and an interactome network of nsp2 was generated. Interestingly, cellular vimentin, a known receptor for PRRSV, forms a complex with nsp2 by using viral nucleocapsid protein as an intermediate. Taken together, the nsp2 interactome under the condition of virus infection clarifies a role of nsp2 in PRRSV replication and immune evasion.

BIOLOGICAL SIGNIFICANCE

Viral proteins must interact with other virus-encoded proteins and/or host cellular proteins to function, and interactome analysis is an ideal approach for identifying such interacting proteins. In this study, we used the quantitative interactome methodology to identify the viral and cellular proteins that potentially interact with the nonstructural protein 2 (nsp2) of porcine reproductive and respiratory syndrome virus (PRRSV) under virus infection conditions, thus providing a rich source of potential viral and cellular interaction partners for PRRSV nsp2. Based on the interactome data, we further demonstrated that PRRSV nsp2 and nucleocapsid protein together with cellular vimentin, form a complex that may be essential for viral attachment and replication, which partly explains the role of nsp2 in PRRSV replication and immune evasion.

Use of single chain antibody derivatives for targeted drug delivery

Single chain antibodies (scFvs), which contain only the variable domains of full-length antibodies, are relatively small molecules that can be used for selective drug delivery. In this review, we display how scFv antibodies help improve the specificity and efficiency of drugs. Small interfering RNA (siRNA) delivery using scFv-drug fusion peptides, siRNA delivery using scFv-conjugated nanoparticles, targeted delivery using scFv-viral peptide- fusion proteins, use of scFv in fusion with cell penetrating peptides for effective targeted drug delivery, scFv-mediated targeted delivery of inorganic nanoparticles, scFv-mediated increase of tumor killing activity of granulocytes, use of scFv for tumor imaging, site-directed conjugation of scFv molecules to drug carrier systems, use of scFv to relieve pain, use of scFv for increasing drug loading efficiency are among the topics that are discussed here.

Genetic variation, pathogenicity, and immunogenicity of highly pathogenic porcine reproductive and respiratory syndrome virus strain XH-GD at different passage levels

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important infectious diseases of swine worldwide. Immunization with an attenuated vaccine is considered an effective method for reducing the economic losses resulting from porcine reproductive and respiratory syndrome virus (PRRSV) infection. Several studies have shown that PRRSV can be attenuated by passage in Marc-145 cells, but it is still not clear whether this attenuation influences the immunogenicity of PRRSV and what the mechanism of attenuation is. In order to study the mechanism of attenuation and immunogenicity of highly pathogenic (HP) PRRSV, the HP-PRRSV strain XH-GD was serially 122 times passaged in Marc-145 cells. Genomic sequence comparisons were made at selected passages. To explore the differences in pathogenicity and immunogenicity at different passages, three passages (P5, P62 and P122) were selected for an animal challenge experiment, which showed that passage in Marc-145 cells resulted in attenuation of the virus. After 122 passages, 35 amino acid changes were observed in the structural proteins and non-structural proteins. The animal challenge experiment showed that pathogenicity decreased with increasing passage number. The N antibody level and specific neutralizing (SN) antibody titers also decreased with increasing passage number in the late stage of the animal experiment. This study indicated that the virulence of XH-GD was decreased by passage in Marc-145 cells and that overattenuation might influence the immunogenicity of virus. These results might contribute to our understanding of the mechanism of attenuation.