Porcine Reproductive and Respiratory Syndrome Virus nsp11 Antagonizes Type I Interferon Signaling by Targeting IRF9

An Overview of SARS-CoV-2 Potential Targets, Inhibitors, and Computational Insights to Enrich the Promising Treatment Strategies

The rapid spread of the SARS-CoV-2 virus has emphasized the urgent need for effective therapies to combat COVID-19. Investigating the potential targets, inhibitors, and in silico approaches pertinent to COVID-19 are of utmost need to develop novel therapeutic agents and reprofiling of existing FDA-approved drugs. This article reviews the viral enzymes and their counter receptors involved in the entry of SARS-CoV-2 into host cells, replication of genomic RNA, and controlling the host cell physiology. In addition, the study provides an overview of the computational techniques such as docking simulations, molecular dynamics, QSAR modeling, and homology modeling that have been used to find the FDA-approved drugs and other inhibitors against SARS-CoV-2. Furthermore, a comprehensive overview of virus-based and host-based druggable targets from a structural point of view, together with the reported therapeutic compounds against SARS-CoV-2 have also been presented. The current study offers future perspectives for research in the field of network pharmacology investigating the large unexplored molecular libraries. Overall, the present in-depth review aims to expedite the process of identifying and repurposing drugs for researchers involved in the field of COVID-19 drug discovery.

Innate Immune Evasion of PRRSV nsp11 through Degradation of the HDAC2 by Its Endoribonuclease Activity

Porcine reproductive and respiratory syndrome virus (PRRSV), a member of the Arteriviridae family, represents a persistent menace to the global pig industry, causing reproductive failure and respiratory disease in pigs. In this study, we delved into the role of histone deacetylases (HDAC2) during PRRSV infection. Our findings revealed that HDAC2 expression is downregulated upon PRRSV infection. Notably, suppressing HDAC2 activity through specific small interfering RNA led to an increase in virus production, whereas overexpressing HDAC2 effectively inhibited PRRSV replication by boosting the expression of IFN-regulated antiviral molecules. Furthermore, we identified the virus's nonstructural protein 11 (nsp11) as a key player in reducing HDAC2 levels. Mutagenic analyses of PRRSV nsp11 revealed that its antagonistic effect on the antiviral activity of HDAC2 is dependent on its endonuclease activity. In summary, our research uncovered a novel immune evasion mechanism employed by PRRSV, providing crucial insights into the pathogenesis of this virus and guiding the development of innovative prevention strategies against PRRSV infection.

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.

Type I and II interferons, transcription factors and major histocompatibility complexes were enhanced by knocking down the PRRSV-induced transforming growth factor beta in monocytes co-cultured with peripheral blood lymphocytes

The innate and adaptive immune responses elicited by porcine reproductive and respiratory syndrome virus (PRRSV) infection are known to be poor. This study investigates the impact of PRRSV-induced transforming growth factor beta 1 (TGFβ1) on the expressions of type I and II interferons (IFNs), transcription factors, major histocompatibility complexes (MHC), anti-inflammatory and pro-inflammatory cytokines in PRRSV-infected co-cultures of monocytes and peripheral blood lymphocytes (PBL). Phosphorothioate-modified antisense oligodeoxynucleotide (AS ODN) specific to the AUG region of porcine TGFβ1 mRNA was synthesized and successfully knocked down TGFβ1 mRNA expression and protein translation. Monocytes transfected with TGFβAS1 ODN, then simultaneously co-cultured with PBL and inoculated with either classical PRRSV-2 (cPRRSV-2) or highly pathogenic PRRSV-2 (HP-PRRSV-2) showed a significant reduction in TGFβ1 mRNA expression and a significant increase in the mRNA expressions of IFNα, IFNγ, MHC-I, MHC-II, signal transducer and activator of transcription 1 (STAT1), and STAT2. Additionally, transfection of TGFβAS1 ODN in the monocyte and PBL co-culture inoculated with cPRRSV-2 significantly increased the mRNA expression of interleukin-12p40 (IL-12p40). PRRSV-2 RNA copy numbers were significantly reduced in monocytes and PBL co-culture transfected with TGFβAS1 ODN compared to the untransfected control. The yields of PRRSV-2 RNA copy numbers in PRRSV-2-inoculated monocytes and PBL co-culture were sustained and reduced by porcine TGFβ1 (rTGFβ1) and recombinant porcine IFNα (rIFNα), respectively. These findings highlight the strategy employed by PRRSV to suppress the innate immune response through the induction of TGFβ expression. The inclusion of TGFβ as a parameter for future PRRSV vaccine and vaccine adjuvant candidates is recommended.

ZNF283, a Krüppel-associated box zinc finger protein, inhibits RNA synthesis of porcine reproductive and respiratory syndrome virus by interacting with Nsp9 and Nsp10

Porcine reproductive and respiratory syndrome virus (PRRSV) is a viral pathogen with substantial economic implications for the global swine industry. The existing vaccination strategies and antiviral drugs offer limited protection. Replication of the viral RNA genome encompasses a complex series of steps, wherein a replication complex is assembled from various components derived from both viral and cellular sources, as well as from the viral genomic RNA template. In this study, we found that ZNF283, a Krüppel-associated box (KRAB) containing zinc finger protein, was upregulated in PRRSV-infected Marc-145 cells and porcine alveolar macrophages and that ZNF283 inhibited PRRSV replication and RNA synthesis. We also found that ZNF283 interacts with the viral proteins Nsp9, an RNA-dependent RNA polymerase, and Nsp10, a helicase. The main regions involved in the interaction between ZNF283 and Nsp9 were determined to be the KRAB domain of ZNF283 and amino acids 178-449 of Nsp9. The KRAB domain of ZNF283 plays a role in facilitating Nsp10 binding. In addition, ZNF283 may have an affinity for the 3' untranslated region of PRRSV. These findings suggest that ZNF283 is an antiviral factor that inhibits PRRSV infection and extend our understanding of the interactions between KRAB-containing zinc finger proteins and viruses.

Pathological observation and transcriptomic analysis of thymus injury in PRRSV-infected piglets

The thymus, the central immune organ in mammals, plays an important role in immune defense. Porcine reproductive and respiratory syndrome virus (PRRSV) infection in piglets can cause thymus injury and immunosuppression. However, the mechanisms of thymus injury remain unknown. This study was aimed at investigating the specific manifestations of thymus injury through the construction of a PRRSV-infected piglet model and histopathological observation. In this study, fourteen 40-day-old PRRSV-free piglets were randomly divided into two groups, eleven of which were intramuscularly injected with 3 mL of PRRSV WUH3 virus suspension (106 PFU /mL) in the infection group, and three of which were sham-inoculated with 3 mL of RPMI-1640 medium in the control group. Clinical necropsy and samples collection were performed on day 8 after artificial infection. With the Illumina platform, the transcriptomes of piglet thymus tissues from infected and control piglets were sequenced to explore the relationships of differentially expressed genes (DEGs) and signaling pathways with thymus injury. The immune organs of PRRSV-infected piglets were severely damaged. The histopathological findings in the thymus indicated that PRRSV infection was associated with a large decrease in lymphocytes, cell necrosis and cell apoptosis; an increase in blood vessels and macrophages; thymic corpuscle hyperplasia; and interstitial widening of the thymic lobules. The transcriptomic analysis results revealed that the Gene Ontology functions of DEGs were enriched primarily in biological processes such as angiogenesis, regulation of angiogenesis and positive regulation of cell migration. Moreover, greater numbers of blood vessels and macrophages were observed in the thymus in PRRSV-infected than control piglets. KEGG pathway enrichment analysis revealed that the DEGs were significantly enriched in the Toll-like receptor signaling pathway, chemokine signaling pathway, IL-17 signaling pathway and TNF signaling pathway. The expression of TLR8, IRF5, the chemokines CCL2, CCL3L1 and CCL5; and their receptors CCR1, CCR2 and CCR5 was significantly up-regulated in PRRSV infection, thus suggesting that these cytokines were associated with the pathological processes of thymus injury.

Seneca Valley virus 3Cpro antagonizes type I interferon response by targeting STAT1-STAT2-IRF9 and KPNA1 signals

IMPORTANCE

Type I interferon (IFN) signaling plays a principal role in host innate immune responses against invading viruses. Viruses have evolved diverse mechanisms that target the Janus kinase-signal transducer and activator of transcription (STAT) signaling pathway to modulate IFN response negatively. Seneca Valley virus (SVV), an emerging porcine picornavirus, has received great interest recently because it poses a great threat to the global pork industry. However, the molecular mechanism by which SVV evades host innate immunity remains incompletely clear. Our results revealed that SVV proteinase (3Cpro) antagonizes IFN signaling by degrading STAT1, STAT2, and IRF9, and cleaving STAT2 to escape host immunity. SVV 3Cpro also degrades karyopherin 1 to block IFN-stimulated gene factor 3 nuclear translocation. Our results reveal a novel molecular mechanism by which SVV 3Cpro antagonizes the type I IFN response pathway by targeting STAT1-STAT2-IRF9 and karyopherin α1 signals, which has important implications for our understanding of SVV-evaded host innate immune responses.

African Swine Fever Virus pF778R Attenuates Type I Interferon Response by Impeding STAT1 Nuclear Translocation

African swine fever virus (ASFV) is an extensive and intricate double-stranded DNA virus with approximately 100% lethality in domestic swine. There is no effective vaccine to combat this virus, and this has led to substantial economic losses in the swine industry. ASFV encodes various proteins that impede interferon-based immune defenses in the host by employing diverse mechanisms. However, the roles of most of these proteins remain unknown. Therefore, understanding the immune evasion mechanisms employed by ASFV may facilitate the development of effective measures against the virus. In this study, we discovered a negative regulation of the type I interferon (IFN) response by the ASFV ribonuclease reductase large subunit pF778R. This novel type Ⅰ IFN response antagonist significantly inhibits IFN-α-induced interferon-stimulated response element promoter activation, precludes the upregulation of various interferon-stimulated genes, and prevents STAT1 nuclear translocation. Mechanistically, pF778R did not affect the protein levels of crucial molecules in the JAK/STAT signaling pathway or engage in direct interactions. However, pF778R expression impedes type I IFN responses mediated by the JAK/STAT signaling pathway. Further investigations revealed that pF778R did not interfere with STAT1 phosphorylation or dimerization, but it inhibited IFN signaling by weakening the nuclear accumulation of activated STAT1. The critical role of the ASFV protein pF778R in evading IFN-I-mediated innate immunity highlights a unique mode of ASFV evasion and provides insights into the pathogenic mechanism of the virus.

African Swine Fever Virus MGF505-7R Interacts with Interferon Regulatory Factor 9 to Evade the Type I Interferon Signaling Pathway and Promote Viral Replication

African swine fever (ASF) is an acute and severe infectious disease caused by the ASF virus (ASFV). The mortality rate of ASF in pigs can reach 100%, causing huge economic losses to the pig industry. Here, we found that ASFV protein MGF505-7R inhibited the beta interferon (IFN-β)-mediated Janus-activated kinase-signal transducer and activation of transcription (JAK-STAT) signaling. Our results demonstrate that MGF505-7R inhibited interferon-stimulated gene factor 3 (ISGF3)-mediated IFN-stimulated response element (ISRE) promoter activity. Importantly, we observed that MGF505-7R inhibits ISGF3 heterotrimer formation by interacting with interferon regulatory factor 9 (IRF9) and inhibits the nuclear translocation of ISGF3. Moreover, to demonstrate the role of MGF505-7R in IFN-I signal transduction during ASFV infection, we constructed and evaluated ASFV-ΔMGF505-7R recombinant viruses. ASFV-ΔMGF505-7R restored STAT2 and STAT1 phosphorylation, alleviated the inhibition of ISGF3 nuclear translocation, and showed increased susceptibility to IFN-β, unlike the parental GZ201801 strain. In conclusion, our study shows that ASFV protein MGF505-7R plays a key role in evading IFN-I-mediated innate immunity, revealing a new mode of evasion for ASFV. IMPORTANCE ASF, caused by ASFV, is currently prevalent in Eurasia, with mortality rates reaching 100% in pigs. At present, there are no safe or effective vaccines against ASFV. In this study, we found that the ASFV protein MGF505-7R hinders IFN-β signaling by interacting with IRF9 and inhibiting the formation of ISGF3 heterotrimers. Of note, we demonstrated that MGF505-7R plays a role in the immune evasion of ASFV in infected hosts and that recombinant viruses alleviated the effect on type I IFN (IFN-I) signaling and exhibited increased susceptibility to IFN-β. This study provides a theoretical basis for developing vaccines against ASFV using strains with MGF505-7R gene deletions.

Evasion strategies of porcine reproductive and respiratory syndrome virus

During the co-evolution of viruses and their hosts, viruses have developed various strategies for overcoming host immunological defenses so that they can proliferate efficiently. Porcine reproductive and respiratory syndrome virus (PRRSV), a significant virus to the swine industry across the world, typically establishes prolonged infection via diverse and complicated mechanisms, which is one of the biggest obstacles for controlling the associated disease, porcine reproductive and respiratory syndrome (PRRS). In this review, we summarize the latest research on how PRRSV circumvents host antiviral responses from both the innate and adaptive immune systems and how this virus utilizes other evasion mechanisms, such as the manipulation of host apoptosis and microRNA. A thorough understanding of the exact mechanisms of PRRSV immune evasion will help with the development of novel antiviral strategies against PRRSV.

African swine fever virus pA104R protein acts as a suppressor of type I interferon signaling

This study evaluates the role of the late viral protein, pA104R, in African swine fever virus immunosuppression. ASFV-encoded pA104R is a putative histone-like protein that is highly conserved throughout different virulent and non-virulent isolates. Previous studies have demonstrated that pA104R plays a vital role in the ASFV replication cycle and is a potential target for antiviral therapy. Here, we demonstrated that pA104R is a potent antagonist of type I interferon signaling. IFN-stimulated response element activity and subsequent transcription of co-transfected and endogenous interferon-stimulated genes were attenuated by pA104R treatment in HEK-293 T cells. Immunoprecipitation assay and reciprocal pull-down showed that pA104R does not interact directly with STAT1, STAT2, or IRF9. However, pA104R could inhibit IFN signaling by attenuating STAT1 phosphorylation, and we identified the critical amino acid residues (R/H69,72 and K/R92,94,97) involved through the targeted mutation functional assays. Although pA104R is a histone-like protein localized to the nucleus, it did not inhibit IFN signaling through its DNA-binding capacity. In addition, activation of the ISRE promoter by IRF9-Stat2(TA), a STAT1-independent pathway, was inhibited by pA104R. Further results revealed that both the transcriptional activation and recruitment of transcriptional stimulators by interferon-stimulated gene factor 3 were not impaired. Although we failed to determine a mechanism for pA104R-mediated IFN signaling inhibition other than attenuating the phosphorylation of STAT1, these results might imply a possible involvement of epigenetic modification by ASFV pA104R. Taken together, these findings support that pA104R is an antagonist of type I interferon signaling, which may interfere with multiple signaling pathways.

The role of TRIM59 in immunity and immune-related diseases

TRIM59 is a member of the tripartite motif containing (TRIM) protein family. It functions as an E3 ubiquitin ligase through its RING domain and is expressed by multiple types of cells. Physiogically, TRIM59 is involved in development, immune response, and the invasion and metastasis of tumors. In this review, we first describe the structure, expression, and subcellular location of TRIM59. Then, we summarize emerging evidence for TRIM59 in immunological diseases including infection, vascular diseases, autoimmunity, and tumor immunity. Additionally, we discuss important molecular signaling pathways that mediate TRIM59 activity. Altogether, the accumulating evidence suggests that manipulating TRIM59 levels and activity may open an avenue for innovative therapies for immune diseases and tumors.

African Swine Fever Virus pI215L Inhibits Type I Interferon Signaling by Targeting Interferon Regulatory Factor 9 for Autophagic Degradation

African swine fever virus (ASFV) is the etiological agent of a highly lethal hemorrhagic disease in domestic pigs and wild boars that has significant economic consequences for the pig industry. The type I interferon (IFN) signaling pathway is a pivotal component of the innate antiviral response, and ASFV has evolved multiple mechanisms to antagonize this pathway and facilitate infection. Here, we reported a novel function of ASFV pI215L in inhibiting type I IFN signaling. Our results showed that ASFV pI215L inhibited IFN-stimulated response element (ISRE) promoter activity and subsequent transcription of IFN-stimulated genes (ISGs) by triggering interferon regulatory factor 9 (IRF9) degradation. Additionally, we found that catalytically inactive pI215L mutations retained the ability to block type I IFN signaling, indicating that this only known viral E2 ubiquitin-conjugating enzyme mediates IFR9 degradation in a ubiquitin-conjugating activity-independent manner. By coimmunoprecipitation, confocal immunofluorescence, and subcellular fractionation approaches, we demonstrated that pI215L interacted with IRF9 and impaired the formation and nuclear translocation of IFN-stimulated gene factor 3 (ISGF3). Moreover, further mechanism studies supported that pI215L induced IRF9 degradation through the autophagy-lysosome pathway in both pI215L-overexpressed and ASFV-infected cells. These findings reveal a new immune evasion strategy evolved by ASFV in which pI215L acts to degrade host IRF9 via the autophagic pathway, thus inhibiting the type I IFN signaling and counteracting the host innate immune response.

IMPORTANCE African swine fever virus (ASFV) causes a highly contagious and lethal disease in pigs and wild boars that is currently present in many countries, severely affecting the global pig industry. Despite extensive research, effective vaccines and antiviral strategies are still lacking, and many fundamental questions regarding the molecular mechanisms underlying host innate immunity escape remain unclear. In this study, we identified ASFV pI215L, the only known viral E2 ubiquitin-conjugating enzyme, which is involved in antagonizing the type I interferon signaling. Mechanistically, pI215L interacted with interferon regulatory factor 9 for autophagic degradation, and this degradation was independent of its ubiquitin-conjugating activity. These results increase the current knowledge regarding ASFV evasion of innate immunity, which may instruct future research on antiviral strategies and dissection of ASFV pathogenesis.

Research Progress in Porcine Reproductive and Respiratory Syndrome Virus–Host Protein Interactions

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease caused by porcine reproductive and respiratory syndrome virus (PRRSV), which has been regarded as a persistent challenge for the pig industry in many countries. PRRSV is internalized into host cells by the interaction between PRRSV proteins and cellular receptors. When the virus invades the cells, the host antiviral immune system is quickly activated to suppress the replication of the viruses. To retain fitness and host adaptation, various viruses have evolved multiple elegant strategies to manipulate the host machine and circumvent against the host antiviral responses. Therefore, identification of virus–host interactions is critical for understanding the host defense against viral infections and the pathogenesis of the viral infectious diseases. Most viruses, including PRRSV, interact with host proteins during infection. On the one hand, such interaction promotes the virus from escaping the host immune system to complete its replication. On the other hand, the interactions regulate the host cell immune response to inhibit viral infections. As common antiviral drugs become increasingly inefficient under the pressure of viral selectivity, therapeutic agents targeting the intrinsic immune factors of the host protein are more promising because the host protein has a lower probability of mutation under drug-mediated selective pressure. This review elaborates on the virus–host interactions during PRRSV infection to summarize the pathogenic mechanisms of PRRSV, and we hope this can provide insights for designing effective vaccines or drugs to prevent and control the spread of PRRS.

Porcine Epidemic Diarrhea Virus nsp7 Inhibits Interferon-Induced JAK-STAT Signaling through Sequestering the Interaction between KPNA1 and STAT1

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic enteric coronavirus that causes high mortality in piglets. Interferon (IFN) responses are the primary defense mechanism against viral infection; however, viruses always evolve elaborate strategies to antagonize the antiviral action of IFN. Previous study showed that PEDV nonstructural protein 7 (nsp7), a component of the viral replicase polyprotein, can antagonize ploy(I:C)-induced type I IFN production. Here, we found that PEDV nsp7 also antagonized IFN-α-induced JAK-STAT signaling and the production of IFN-stimulated genes. PEDV nsp7 did not affect the protein and phosphorylation levels of JAK1, Tyk2, STAT1, and STAT2 or the formation of the interferon-stimulated gene factor 3 (ISGF3) complex. However, PEDV nsp7 prevented the nuclear translocation of STAT1 and STAT2. Mechanistically, PEDV nsp7 interacted with the DNA binding domain of STAT1/STAT2, which sequestered the interaction between karyopherin α1 (KPNA1) and STAT1, thereby blocking the nuclear transport of ISGF3. Collectively, these data reveal a new mechanism developed by PEDV to inhibit type I IFN signaling pathway. IMPORTANCE In recent years, an emerging porcine epidemic diarrhea virus (PEDV) variant has gained attention because of serious outbreaks of piglet diarrhea in China and the United States. Coronavirus nonstructural protein 7 (nsp7) has been proposed to act with nsp8 as part of an RNA primase to generate RNA primers for viral RNA synthesis. However, accumulating evidence indicates that coronavirus nsp7 can also antagonize type I IFN production. Our present study extends previous findings and demonstrates that PEDV nsp7 also antagonizes IFN-α-induced IFN signaling by competing with KPNA1 for binding to STAT1, thereby enriching the immune regulation function of coronavirus nsp7.

Ribosome profiling of porcine reproductive and respiratory syndrome virus reveals novel features of viral gene expression

The arterivirus porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses to the swine industry worldwide. Here we apply ribosome profiling (RiboSeq) and parallel RNA sequencing (RNASeq) to characterise the transcriptome and translatome of both species of PRRSV and to analyse the host response to infection. We calculated programmed ribosomal frameshift (PRF) efficiency at both sites on the viral genome. This revealed the nsp2 PRF site as the second known example where temporally regulated frameshifting occurs, with increasing -2 PRF efficiency likely facilitated by accumulation of the PRF-stimulatory viral protein, nsp1β. Surprisingly, we find that PRF efficiency at the canonical ORF1ab frameshift site also increases over time, in contradiction of the common assumption that RNA structure-directed frameshift sites operate at a fixed efficiency. This has potential implications for the numerous other viruses with canonical PRF sites. Furthermore, we discovered several highly translated additional viral ORFs, the translation of which may be facilitated by multiple novel viral transcripts. For example, we found a highly expressed 125-codon ORF overlapping nsp12, which is likely translated from novel subgenomic RNA transcripts that overlap the 3' end of ORF1b. Similar transcripts were discovered for both PRRSV-1 and PRRSV-2, suggesting a potential conserved mechanism for temporally regulating expression of the 3'-proximal region of ORF1b. We also identified a highly translated, short upstream ORF in the 5' UTR, the presence of which is highly conserved amongst PRRSV-2 isolates. These findings reveal hidden complexity in the gene expression programmes of these important nidoviruses.

DEAD-Box RNA Helicase 21 (DDX21) Positively Regulates the Replication of Porcine Reproductive and Respiratory Syndrome Virus via Multiple Mechanisms

The porcine reproductive and respiratory syndrome virus (PRRSV) remains a persistent hazard in the global pig industry. DEAD (Glu-Asp-Ala-Glu) box helicase 21 (DDX21) is a member of the DDX family. In addition to its function of regulating cellular RNA metabolism, DDX21 also regulates innate immunity and is involved in the replication cycle of some viruses. However, the relationship between DDX21 and PRRSV has not yet been explored. Here, we found that a DDX21 overexpression promoted PRRSV replication, whereas knockdown of DDX21 reduced PRRSV proliferation. Mechanistically, DDX21 promoted PRRSV replication independently of its ATPase, RNA helicase, and foldase activities. Furthermore, overexpression of DDX21 stabilized the expressions of PRRSV nsp1α, nsp1β, and nucleocapsid proteins, three known antagonists of interferon β (IFN-β). Knockdown of DDX21 activated the IFN-β signaling pathway in PRRSV-infected cells, suggesting that the effect of DDX21 on PRRSV-encoded IFN-β antagonists may be a driving factor for its contribution to viral proliferation. We also found that PRRSV infection enhanced DDX21 expression and promoted its nucleus-to-cytoplasm translocation. Screening PRRSV-encoded proteins showed that nsp1β interacted with the C-terminus of DDX21 and enhanced the expression of DDX21. Taken together, these findings reveal that DDX21 plays an important role in regulating PRRSV proliferation through multiple mechanisms.

MGF360-9L Is a Major Virulence Factor Associated with the African Swine Fever Virus by Antagonizing the JAK/STAT Signaling Pathway

African swine fever (ASF)-an aggressive infectious disease caused by the African swine fever virus (ASFV)-is significantly unfavorable for swine production. ASFV has a complex structure and encodes 150-167 proteins; however, the function of most of these proteins is unknown. This study identified ASFV MGF360-9L as a negative regulator of the interferon (IFN)-β signal. Further evidence showed that MGF360-9L interacts with signal transducer and activator of transcription (STAT) 1 and STAT2 and degrades STAT1 and STAT2 through apoptosis and ubiquitin-proteasome pathways, respectively. Subsequently, the activation of IFN-β signaling was inhibited. Naturally isolated or genetically manipulated live attenuated viruses are known to protect against the virulent parental ASFV strains. Therefore, through homologous recombination, we deleted MGF360-9L from the virulent ASFV CN/GS/2018 strain to construct a recombinant strain, ASFV-Δ360-9L. Compared with the parent ASFV CN/GS/2018 strain, the replication level of ASFV-Δ360-9L decreased in primary porcine alveolar macrophage cultures at 24 h postinfection, but the difference is unlikely to be biologically relevant. Notably, ASFV-Δ360-9L was partially attenuated in pigs. To our knowledge, this study is the first to uncover the function of MGF360-9L during ASFV infection. MGF360-9L inhibits IFN-β signaling through the targeted degradation of STAT1 and STAT2. Furthermore, MGF360-9L is a key virulence gene of ASFV. Our findings reveal a new mechanism by which ASFV inhibits host antiviral response; this might facilitate the development of live attenuated ASFV vaccines. IMPORTANCE African swine fever-an acute, febrile, hemorrhagic, highly contacting, and highly lethal disease caused by African swine fever virus (ASFV)-jeopardizes the global pig industry. Understanding the mechanism ASFV employs to evade host defense during infection is essential for developing targeted drugs and vaccines against ASFV. To our knowledge, this study identifies the mechanism of innate immunity against by MGF360-9L and the effect of MGF360-9L on ASFV pathogenicity. The results showed that MGF360-9L may help ASFV escape the host immunity by degrading STAT1 and STAT2 and thus inhibiting IFN-β signaling. MGF360-9L is also an important virulence factor of ASFV. The deletion of MGF360-9L reduces ASFV virulence in pigs. This study explored a new mechanism of ASFV against innate immunity and identified a new ASFV virulence factor; these findings may guide the development of live attenuated ASFV vaccines.

A Detailed Overview of Immune Escape, Antibody Escape, Partial Vaccine Escape of SARS-CoV-2 and Their Emerging Variants With Escape Mutations

The infective SARS-CoV-2 is more prone to immune escape. Presently, the significant variants of SARS-CoV-2 are emerging in due course of time with substantial mutations, having the immune escape property. Simultaneously, the vaccination drive against this virus is in progress worldwide. However, vaccine evasion has been noted by some of the newly emerging variants. Our review provides an overview of the emerging variants' immune escape and vaccine escape ability. We have illustrated a broad view related to viral evolution, variants, and immune escape ability. Subsequently, different immune escape approaches of SARS-CoV-2 have been discussed. Different innate immune escape strategies adopted by the SARS-CoV-2 has been discussed like, IFN-I production dysregulation, cytokines related immune escape, immune escape associated with dendritic cell function and macrophages, natural killer cells and neutrophils related immune escape, PRRs associated immune evasion, and NLRP3 inflammasome associated immune evasion. Simultaneously we have discussed the significant mutations related to emerging variants and immune escape, such as mutations in the RBD region (N439K, L452R, E484K, N501Y, K444R) and other parts (D614G, P681R) of the S-glycoprotein. Mutations in other locations such as NSP1, NSP3, NSP6, ORF3, and ORF8 have also been discussed. Finally, we have illustrated the emerging variants' partial vaccine (BioNTech/Pfizer mRNA/Oxford-AstraZeneca/BBIBP-CorV/ZF2001/Moderna mRNA/Johnson & Johnson vaccine) escape ability. This review will help gain in-depth knowledge related to immune escape, antibody escape, and partial vaccine escape ability of the virus and assist in controlling the current pandemic and prepare for the next.

Induction of HOXA3 by PRRSV inhibits IFN-I response through negatively regulation of HO-1 transcription

Type I interferons (IFN-I) play a key role in the host defense against virus infection, but porcine reproductive and respiratory syndrome virus (PRRSV) infection does not effectively activate IFN-I response, and the underlying molecular mechanisms are poorly characterized. In this study, a novel transcription factor of the heme oxygenase-1 (HO-1) gene, homeobox A3 (HOXA3), was screened and identified. Here, we found that HOXA3 was significantly increased during PRRSV infection. We demonstrated that HOXA3 promotes PRRSV replication by negatively regulating the HO-1 gene transcription, which is achieved by regulating type I interferons (IFN-I) production. A detailed analysis showed that PRRSV exploits HOXA3 to suppress beta interferon (IFN-β) and IFN-stimulated gene (ISG) expression in host cells. We also provide direct evidence that the activation of IFN-I by HO-1 depends on its interaction with IRF3. Then we further proved that deficiency of HOXA3 promoted the HO-1-IRF3 interaction, and subsequently enhanced IRF3 phosphorylation and nuclear translocation in PRRSV-infected cells. These data suggest that PRRSV uses HOXA3 to negatively regulate the transcription of the HO-1 gene to suppress the IFN-I response for immune evasion. IMPORTANCE Porcine reproductive and respiratory syndrome (PRRS), caused by PRRSV, leads the pork industry worldwide to significant economic losses. HOXA3 is generally considered to be an important molecule in the process of body development and cell differentiation. Here, we found a novel transcription factor of the HO-1 gene, HOXA3, can negatively regulate the transcription of the HO-1 gene and play an important role in the suppression of IFN-I response by PRRSV. PRRSV induces the upregulation of HOXA3, which can negatively regulate HO-1 gene transcription, thereby weakening the interaction between HO-1 and IRF3 for inhibiting the type I IFN response. This study extends the function of HOXA3 to the virus field for the first time and provides new insights into PRRSV immune evasion mechanism.

Induction of UPR Promotes Interferon Response to Inhibit PRRSV Replication via PKR and NF-κB Pathway

Porcine reproductive and respiratory syndrome virus (PRRSV) was previously shown to induce a certain level of cellular stress during viral replication. Unfolded protein response (UPR) is a cellular stress response responsible for coping with stress and cellular survival. However, the pathway leading to the induction of UPR that may influence PRRSV replication is still unknown. Here, we found that PRRSV infection induced UPR prior to interferon response. Induction of UPR significantly enhanced the expression of interferon and interferon-related genes, thus leading to the suppression of PRRSV infection. Next, we explored the underlying mechanisms of UPR-induced antiviral response. We found that induction of UPR promoted the expression of protein kinase R (PKR), and PKR was highly correlated with the reduction of PRRSV replication. Furthermore, tunicamycin stimulation and PKR overexpression activated NF-κB and interferon response at the early stage of PRRSV infection, thus reinforcing the expression of type I interferons and proinflammatory cytokines and leading to inhibition of PRRSV. In addition, PRRSV nsp4 was shown to reduce the expression of PKR. These findings might have implications for our understandings of the host's immune mechanism against PRRSV and a new strategy of PRRSV to evade the host antiviral immunity.

Evasion of Antiviral Innate Immunity by Porcine Reproductive and Respiratory Syndrome Virus

Innate immunity is the front line for antiviral immune responses and bridges adaptive immunity against viral infections. However, various viruses have evolved many strategies to evade host innate immunity. A typical virus is the porcine reproductive and respiratory syndrome virus (PRRSV), one of the most globally devastating viruses threatening the swine industry worldwide. PRRSV engages several strategies to evade the porcine innate immune responses. This review focus on the underlying mechanisms employed by PRRSV to evade pattern recognition receptors signaling pathways, type I interferon (IFN-α/β) receptor (IFNAR)-JAK-STAT signaling pathway, and interferon-stimulated genes. Deciphering the antiviral immune evasion mechanisms by PRRSV will enhance our understanding of PRRSV’s pathogenesis and help us to develop more effective methods to control and eliminate PRRSV.

Human Cytomegalovirus UL23 Attenuates Signal Transducer and Activator of Transcription 1 Phosphorylation and Type I Interferon Response

Human cytomegalovirus (HCMV), the human beta-herpesvirus, can cause severe syndromes among both immunocompromised adult patients and newborns. Type I interferon (IFN-I) exerts an important effect to resist infections caused by viruses such as HCMV, while IFN evasion may serve as a key determining factor for viral dissemination and disease occurrence within hosts. In this study, UL23, a tegument protein of HCMV, was confirmed to be a key factor for negatively regulating the type I IFN immune response. A detailed analysis indicated that the viral UL23 protein increases the IFN-I antiviral resistance during HCMV infections. Furthermore, UL23 was shown to significantly reduce the levels of IFN-stimulated genes (ISGs) and promoter activity of IFN-I-stimulated response element. Mechanically, UL23 was discovered to impair the signal transducer and activator of transcription 1 (STAT1) phosphorylation, although it was not found to affect phosphorylation and expression of STAT2, Janus activated kinase 1, or tyrosine kinase 2, which are associated with IFN-I signal transduction pathway. Additionally, a significantly reduced nuclear expression of STAT1 but not of IFN regulatory factor 9 or STAT2 was observed. Findings of this study indicate that HCMV UL23 is a viral antagonist that acts against the cellular innate immunity and reveal a possible novel effect of UL23 on IFN-I signaling.

Acute Infection of Viral Pathogens and Their Innate Immune Escape

Viral infections can cause rampant disease in human beings, ranging from mild to acute, that can often be fatal unless resolved. An acute viral infection is characterized by sudden or rapid onset of disease, which can be resolved quickly by robust innate immune responses exerted by the host or, instead, may kill the host. Immediately after viral infection, elements of innate immunity, such as physical barriers, various phagocytic cells, group of cytokines, interferons (IFNs), and IFN-stimulated genes, provide the first line of defense for viral clearance. Innate immunity not only plays a critical role in rapid viral clearance but can also lead to disease progression through immune-mediated host tissue injury. Although elements of antiviral innate immunity are armed to counter the viral invasion, viruses have evolved various strategies to escape host immune surveillance to establish successful infections. Understanding complex mechanisms underlying the interaction between viruses and host’s innate immune system would help develop rational treatment strategies for acute viral infectious diseases. In this review, we discuss the pathogenesis of acute infections caused by viral pathogens and highlight broad immune escape strategies exhibited by viruses.

Porcine Reproductive and Respiratory Syndrome Virus: Immune Escape and Application of Reverse Genetics in Attenuated Live Vaccine Development

Porcine reproductive and respiratory syndrome virus (PRRSV), an RNA virus widely prevalent in pigs, results in significant economic losses worldwide. PRRSV can escape from the host immune response in several processes. Vaccines, including modified live vaccines and inactivated vaccines, are the best available countermeasures against PRRSV infection. However, challenges still exist as the vaccines are not able to induce broad protection. The reason lies in several facts, mainly the variability of PRRSV and the complexity of the interaction between PRRSV and host immune responses, and overcoming these obstacles will require more exploration. Many novel strategies have been proposed to construct more effective vaccines against this evolving and smart virus. In this review, we will describe the mechanisms of how PRRSV induces weak and delayed immune responses, the current vaccines of PRRSV, and the strategies to develop modified live vaccines using reverse genetics systems.

Amachawadi R, Dash AP, Yadav MP, Prasad KS, P S, Jain AS, Shivamallu C. COVID-19 PANDEMIC: A SYSTEMATIC REVIEW ON THE CORONAVIRUSES OF ANIMALS AND SARS-CoV-2

Coronaviruses (CoVs), classified into four genera, viz., alpha-, beta-, gamma-, and Delta- CoV, represent an important group of diverse transboundary pathogens that can infect a variety of mammalian and avian species including humans, animals, poultry, and non-poultry birds. CoVs primarily infect lung and gut epithelial cells, besides monocytes and macrophages. CoVs have high mutation rates causing changes in host specificity, tissue tropism, and mode of virus excretion and transmissions. The recent CoV zoonoses are SARS, MERS, and COVID-19 that are caused by the transmission of beta-CoVs of bats to humans. Recently, reverse zoonoses of the COVID-19 virus have been detected in dogs, tigers, and minks. Beta-CoV strains also infect bovine (BCoV) and canine species (CRCoV); both these beta-CoVs might have originated from a common ancestor. Despite the high genetic similarity between BCoV, CRCoV, and HCoV-OC43, these differ in species specificity. Alpha-CoV strains infect canine (CCoV), feline (FIPV), swine (TGEV and PEDV), and humans (HCoV229E and NL63). Six coronavirus species are known to infect and cause disease in pigs, seven in human beings, and two in dogs. The high mutation rate in CoVs is attributed to error-prone 3′-5′ exoribonuclease (NSP 14), and genetic recombination to template shift by the polymerase. The present compilation describes the important features of the CoVs and diseases caused in humans, animals, and birds that are essential in surveillance of diverse pool of CoVs circulating in nature, and monitoring interspecies transmission, zoonoses, and reverse zoonoses.

The Function of the PRRSV-Host Interactions and Their Effects on Viral Replication and Propagation in Antiviral Strategies

Porcine reproductive and respiratory syndrome virus (PRRSV) affects the global swine industry and causes disastrous economic losses each year. The genome of PRRSV is an enveloped single-stranded positive-sense RNA of approximately 15 kb. The PRRSV replicates primarily in alveolar macrophages of pig lungs and lymphatic organs and causes reproductive problems in sows and respiratory symptoms in piglets. To date, studies on how PRRSV survives in the host, the host immune response against viral infections, and pathogenesis, have been reported. PRRSV vaccines have been developed, including inactive virus, modified live virus, attenuated live vaccine, DNA vaccine, and immune adjuvant vaccines. However, there are certain problems with the durability and effectiveness of the licensed vaccines. Moreover, the high variability and fast-evolving populations of this RNA virus challenge the design of PRRSV vaccines, and thus effective vaccines against PRRSV have not been developed successfully. As is well known, viruses interact with the host to escape the host’s immune response and then replicate and propagate in the host, which is the key to virus survival. Here, we review the complex network and the mechanism of PRRSV–host interactions in the processes of virus infection. It is critical to develop novel antiviral strategies against PRRSV by studying these host–virus interactions and structures to better understand the molecular mechanisms of PRRSV immune escape.

In-silico nucleotide and protein analyses of S-gene region in selected zoonotic coronaviruses reveal conserved domains and evolutionary emergence with trajectory course of viral entry from SARS-CoV-2 genomic data

Introduction

the recent zoonotic coronavirus virus outbreak of a novel type (COVID-19) has necessitated the adequate understanding of the evolutionary pathway of zoonotic viruses which adversely affects human populations for therapeutic constructs to combat the pandemic now and in the future.

Methods

we analyzed conserved domains of the severe acute respiratory coronavirus 2 (SARS-CoV-2) for possible targets of viral entry inhibition in host cells, evolutionary relationship of human coronavirus (229E) and zoonotic coronaviruses with SARS-CoV-2 as well as evolutionary relationship between selected SARS-CoV-2 genomic data.

Results

conserved domains with antagonistic action on host innate antiviral cellular mechanisms in SARS-CoV-2 include nsp 11, nsp 13 etc. Also, multiple sequence alignments of the spike (S) gene protein of selected candidate zoonotic coronaviruses alongside the S gene protein of the SARS-CoV-2 revealed closest evolutionary relationship (95.6%) with pangolin coronaviruses (S) gene. Clades formed between Wuhan SARS-CoV-2 phylogeny data and five others suggests viral entry trajectory while revealing genomic and protein SARS-CoV-2 data from Philippines as early ancestors.

Conclusion

phylogeny of SARS-CoV-2 genomic data suggests profiling in diverse populations with and without the outbreak alongside migration history and racial background for mutation tracking and dating of viral subtype divergence which is essential for effective management of present and future zoonotic coronavirus outbreaks.

Novel Secreted Protein of Mycoplasma bovis MbovP280 Induces Macrophage Apoptosis Through CRYAB

Mycoplasma bovis causes important diseases and great losses on feedlots and dairy farms. However, there are only a few measures to control M. bovis-related diseases. As in other mycoplasma species, this is predominantly because the virulence related factors of this pathogen are largely unknown. Therefore, in this study, we aimed to identify novel virulence-related factors among the secreted proteins of M. bovis. Using bioinformatic tools to analyze its secreted proteins, we preliminarily predicted 39 secreted lipoproteins, and then selected 11 of them for confirmation based on SignalP scores >0.6 or SceP scores >0.8 and conserved domains. These 11 genes were cloned after gene modification based on the codon bias of Escherichia coli and expressed. Mouse antiserum to each recombinant protein was developed. A western blotting assay with these antisera confirmed that MbovP280 and MbovP475 are strongly expressed and secreted proteins, but only MbovP280 significantly reduced the viability of bovine macrophages (BoMac). In further experiments, MbovP280 induced the apoptosis of BoMac treated with both live M. bovis and MbovP280 protein. The conserved coiled-coil domain of MbovP280 at amino acids 210–269 is essential for its induction of apoptosis. Further, immunoprecipitation, mass spectrometry, and coimmunoprecipitation assays identified the anti-apoptosis regulator αB-crystallin (CRYAB) as an MbovP280-binding ligand. An αβ-crystallin knockout cell line BoMac-cryab⁻, Mbov0280-knockout M. bovis strain T9.297, and its complemented M. bovis strain CT9.297 were constructed and the apoptosis of BoMac-cryab⁻ induced by these strains was compared. The results confirmed that CRYAB is critical for MbovP280 function as an apoptosis inducer in BoMac. In conclusion, in this study, we identified MbovP280 as a novel secreted protein of M. bovis that induces the apoptosis of BoMac via its coiled-coil domain and cellular ligand CRYAB. These findings extend our understanding of the virulence mechanism of mycoplasmal species.

Identifying Transcriptomic Signatures and Rules for SARS-CoV-2 Infection

The world-wide Coronavirus Disease 2019 (COVID-19) pandemic was triggered by the widespread of a new strain of coronavirus named as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Multiple studies on the pathogenesis of SARS-CoV-2 have been conducted immediately after the spread of the disease. However, the molecular pathogenesis of the virus and related diseases has still not been fully revealed. In this study, we attempted to identify new transcriptomic signatures as candidate diagnostic models for clinical testing or as therapeutic targets for vaccine design. Using the recently reported transcriptomics data of upper airway tissue with acute respiratory illnesses, we integrated multiple machine learning methods to identify effective qualitative biomarkers and quantitative rules for the distinction of SARS-CoV-2 infection from other infectious diseases. The transcriptomics data was first analyzed by Boruta so that important features were selected, which were further evaluated by the minimum redundancy maximum relevance method. A feature list was produced. This list was fed into the incremental feature selection, incorporating some classification algorithms, to extract qualitative biomarker genes and construct quantitative rules. Also, an efficient classifier was built to identify patients infected with SARS-COV-2. The findings reported in this study may help in revealing the potential pathogenic mechanisms of COVID-19 and finding new targets for vaccine design.

Porcine Deltacoronavirus nsp5 Cleaves DCP1A To Decrease Its Antiviral Activity

Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus. The nonstructural protein nsp5, also called 3C-like protease, is responsible for processing viral polyprotein precursors in coronavirus (CoV) replication. Previous studies have shown that PDCoV nsp5 cleaves the NF-κB essential modulator and the signal transducer and activator of transcription 2 to disrupt interferon (IFN) production and signaling, respectively. Whether PDCoV nsp5 also cleaves IFN-stimulated genes (ISGs), IFN-induced antiviral effector molecules, remains unclear. In this study, we screened 14 classical ISGs and found that PDCoV nsp5 cleaved the porcine mRNA-decapping enzyme 1a (pDCP1A) through its protease activity. Similar cleavage of endogenous pDCP1A was also observed in PDCoV-infected cells. PDCoV nsp5 cleaved pDCP1A at glutamine 343 (Q343), and the cleaved pDCP1A fragments, pDCP1A_1-343 and pDCP1A_344-580, were unable to inhibit PDCoV infection. Mutant pDCP1A-Q343A, which resists nsp5-mediated cleavage, exhibited a stronger ability to inhibit PDCoV infection than wild-type pDCP1A. Interestingly, the Q343 cleavage site is highly conserved in DCP1A homologs from other mammalian species. Further analyses demonstrated that nsp5 encoded by seven tested CoVs that can infect human or pig also cleaved pDCP1A and human DCP1A, suggesting that DCP1A may be the common target for cleavage by nsp5 of mammalian CoVs.IMPORTANCE Interferon (IFN)-stimulated gene (ISG) induction through IFN signaling is important to create an antiviral state and usually directly inhibits virus infection. The present study first demonstrated that PDCoV nsp5 can cleave mRNA-decapping enzyme 1a (DCP1A) to attenuate its antiviral activity. Furthermore, cleaving DCP1A is a common characteristic of nsp5 proteins from different coronaviruses (CoVs), which represents a common immune evasion mechanism of CoVs. Previous evidence showed that CoV nsp5 cleaves the NF-κB essential modulator and signal transducer and activator of transcription 2. Taken together, CoV nsp5 is a potent IFN antagonist because it can simultaneously target different aspects of the host IFN system, including IFN production and signaling and effector molecules.

An ancient evolutionary connection between Ribonuclease A and EndoU families

The ribonuclease A family of proteins is well studied from the biochemical and biophysical points of view, but its evolutionary origins are obscure, as no sequences homologous to this family have been reported outside of vertebrates. Recently, the spatial structure of the ribonuclease domain from a bacterial polymorphic toxin was shown to be closely similar to the structure of vertebrate ribonuclease A. The absence of sequence similarity between the two structures prompted a speculation of convergent evolution of bacterial and vertebrate ribonuclease A-like enzymes. We show that bacterial and homologous archaeal polymorphic toxin ribonucleases with a known or predicted ribonuclease A-like fold are distant homologs of the ribonucleases from the EndoU family, found in all domains of cellular life and in viruses. We also detected a homolog of vertebrate ribonucleases A in the transcriptome assembly of the sea urchin Mesocentrotus franciscanus These observations argue for the common ancestry of prokaryotic ribonuclease A-like and ubiquitous EndoU-like ribonucleases, and suggest a better-grounded scenario for the origin of animal ribonucleases A, which could have emerged in the deuterostome lineage, either by an extensive modification of a copy of an EndoU gene, or, more likely, by a horizontal acquisition of a prokaryotic immunity-mediating ribonuclease gene.

Porcine Reproductive and Respiratory Syndrome Virus Antagonizes PCSK9's Antiviral Effect via Nsp11 Endoribonuclease Activity

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens in the swine industry worldwide. Our previous study had indicated that proprotein convertase subtilisin/kexin type 9 (PCSK9) was a responsive gene in porcine alveolar macrophages (PAMs) upon PRRSV infection. However, whether PCSK9 impacts the PRRSV replication and how the PRRSV modulates host PCSK9 remains elusive. Here, we demonstrated that PCSK9 protein suppressed the replication of both type-1 and type-2 PRRSV species. More specifically, the C-terminal domain of PCSK9 was responsible for the antiviral activity. Besides, we showed that PCSK9 inhibited PRRSV replication by targeting the virus receptor CD163 for degradation through the lysosome. In turn, PRRSV could down-regulate the expression of PCSK9 in both PAMs and MARC-145 cells. By screening the nonstructural proteins (nsps) of PRRSV, we showed that nsp11 could antagonize PCSK9’s antiviral activity. Furthermore, mutagenic analyses of PRRSV nsp11 revealed that the endoribonuclease activity of nsp11 was critical for antagonizing the antiviral effect of PCSK9. Collectively, our data provide further insights into the interaction between PRRSV and the cell host and offer a new potential target for the antiviral therapy of PRRSV.

Porcine Epidemic Diarrhea Virus nsp15 Antagonizes Interferon Signaling by RNA Degradation of TBK1 and IRF3

Porcine epidemic diarrhea virus (PEDV) causes a porcine disease associated with swine epidemic diarrhea. The type I interferon (IFN-I or IFN α/β) is a key mediator of innate antiviral response during virus infection. Different antagonistic strategies have been identified and determined as to how PEDV infection inhibits the host's IFN responses to escape the host innate immune pathway, but the pathogenic mechanisms of PEDV infection are not fully elucidated. Our preliminary results revealed that endogenous TANK-binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3), the key components in the IFN signaling pathway were downregulated in PEDV infected IPEC-J2 cells by iTRAQ analysis. In this study, we screened nsp15 as the most important viral encoded protein involved in TBK1 and IRF3 reduction. Endoribonuclease (EndoU) activity has been well determined for coronavirus nsp15. Three residues (H226, H241, and K282) of PEDV nsp15 were identified as critical amino acids for PEDV EndoU but not D265, which was not well correlated with published results of other coronaviruses, such as severe acute respiratory syndrome virus (SARS-CoV). Moreover, PEDV nsp15 can directly degrade the RNA levels of TBK1 and IRF3 dependent on its EndoU activity to suppress IFN production and constrain the induction of IFN stimulated genes (ISGs), by which PEDV antagonizes the host innate response to facilitate its replication. Collectively, these results have confirmed that PEDV nsp15 was capable of subverting the IFN response by the RNA degradation of TBK1 and IRF3.

Molecular and Cellular Mechanisms for PRRSV Pathogenesis and Host Response to Infection

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PRRSV has evolved to arm with various strategies to modify host antiviral response.

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Viral modulation of homeostatic cellular processes provides favorable conditions for PRRSV survival during infection.

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PRRSV modulation of cellular processes includes pathways for interferons, apoptosis, microRNAs, cytokines, autophagy, and viral genome recombination.

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused tremendous amounts of economic losses to the swine industry for more than three decades, but its control is still unsatisfactory. A significant amount of information is available for host cell-virus interactions during infection, and it is evident that PRRSV has evolved to equip various strategies to disrupt the host antiviral system and provide favorable conditions for survival. The current study reviews viral strategies for modulations of cellular processes including innate immunity, apoptosis, microRNAs, inflammatory cytokines, and other cellular pathways.

Porcine reproductive and respiratory syndrome virus up-regulates sialoadhesin via IFN-STAT signaling to facilitate its infection

Porcine reproductive and respiratory syndrome (PRRS) has caused huge economic losses to global swine industry. Porcine sialoadhesin (poSn) was previously reported to be a putative receptor for the causative agent, PRRS virus (PRRSV). In the current study, we first observed that PRRSV infection up-regulated expression of poSn in a dose- and time-dependent manner. Subsequently, we found that PRRSV-triggered transcription of type I interferons (IFNs) was involved in poSn up-regulation through the IFN-signal transducer and activator of transcription (STAT) signaling cascade. Interestingly, poSn up-regulation was shown to promote PRRSV infection during post-entry process. Taken together, this work deepens our understanding of PRRSV pathogenesis and provides a novel idea on its establishment of persistent infection, which will be interesting to unravel the detailed mechanisms in the future.