Porcine Mx1 Protein Inhibits Classical Swine Fever Virus Replication by Targeting Nonstructural Protein NS5B

GTPase activity of porcine Mx1 plays a dominant role in inhibiting the N-Nsp9 interaction and thus inhibiting PRRSV replication

Porcine Mx1 is a type of interferon-induced GTPase that inhibits the replication of certain RNA viruses. However, the antiviral effects and the underlying mechanism of porcine Mx1 for porcine reproductive and respiratory syndrome virus (PRRSV) remain unknown. In this study, we demonstrated that porcine Mx1 could significantly inhibit PRRSV replication in MARC-145 cells. By Mx1 segment analysis, it was indicated that the GTPase domain (68-341aa) was the functional area to inhibit PRRSV replication and that Mx1 interacted with the PRRSV-N protein through the GTPase domain (68-341aa) in the cytoplasm. Amino acid residues K295 and K299 in the G domain of Mx1 were the key sites for Mx1-N interaction while mutant proteins Mx1(K295A) and Mx1(K299A) still partially inhibited PRRSV replication. Furthermore, we found that the GTPase activity of Mx1 was dominant for Mx1 to inhibit PRRSV replication but was not essential for Mx1-N interaction. Finally, mechanistic studies demonstrated that the GTPase activity of Mx1 played a dominant role in inhibiting the N-Nsp9 interaction and that the interaction between Mx1 and N partially inhibited the N-Nsp9 interaction. We propose that the complete anti-PRRSV mechanism of porcine Mx1 contains a two-step process: Mx1 binds to the PRRSV-N protein and subsequently disrupts the N-Nsp9 interaction by a process requiring the GTPase activity of Mx1. Taken together, the results of our experiments describe for the first time a novel mechanism by which porcine Mx1 evolves to inhibit PRRSV replication.

IMPORTANCE

Mx1 protein is a key mediator of the interferon-induced antiviral response against a wide range of viruses. How porcine Mx1 affects the replication of porcine reproductive and respiratory syndrome virus (PRRSV) and its biological function has not been studied. Here, we show that Mx1 protein inhibits PRRSV replication by interfering with N-Nsp9 interaction. Furthermore, the GTPase activity of porcine Mx1 plays a dominant role and the Mx1-N interaction plays an assistant role in this interference process. This study uncovers a novel mechanism evolved by porcine Mx1 to exert anti-PRRSV activities.

Anti-Schmallenberg Virus Activities of Type I/III Interferons-Induced Mx1 GTPases from Different Mammalian Species

Mx proteins are key factors of the innate intracellular defense mechanisms that act against viruses induced by type I/III interferons. The family Peribunyaviridae includes many viruses of veterinary importance, either because infection results in clinical disease or because animals serve as reservoirs for arthropod vectors. According to the evolutionary arms race hypothesis, evolutionary pressures should have led to the selection of the most appropriate Mx1 antiviral isoforms to resist these infections. Although human, mouse, bat, rat, and cotton rat Mx isoforms have been shown to inhibit different members of the Peribunyaviridae, the possible antiviral function of the Mx isoforms from domestic animals against bunyaviral infections has, to our knowledge, never been studied. Herein, we investigated the anti-Schmallenberg virus activity of bovine, canine, equine, and porcine Mx1 proteins. We concluded that Mx1 has a strong, dose-dependent anti-Schmallenberg activity in these four mammalian species.

Dietary Supplementation with Mono-Lactate Glyceride Enhances Intestinal Function of Weaned Piglets

Mono-lactate glyceride (LG) is a short-chain fatty acid ester. It has been shown that short-chain fatty acid esters play an important role in maintaining intestinal structure and function. The aim of this study is to investigate the effects of mono-lactate glyceride on growth performance and intestinal morphology and function in weaned piglets. Sixteen 21-day-old weaned piglets of similar weight were distributed arbitrarily to two treatments: The control group (basal diet) and the LG group (basal diet + 0.6% mono-lactate glyceride). The experiment lasted for 21 days. On day 21 of the trial, piglets were weighed, and blood and intestinal samples were collected for further analysis. Results showed that dietary supplementation with 0.6% mono-lactate glyceride decreased (p < 0.05) the diarrhea rate and the contents of malondialdehyde and hydrogen peroxide in the ileum and jejunum and increased (p < 0.05) the expression of intestinal tight junction protein (Occludin) and the activities of superoxide dismutase and catalase in the ileum and colon. In addition, mono-lactate glyceride supplementation could enhance intestinal mucosal growth by increasing (p < 0.05) the mRNA levels of extracellular regulated protein kinases, promote intestinal mucosal water and nutrient transport and lipid metabolism by increasing (p < 0.05) the mRNA levels of b^0,+ amino acid transporter, aquaporin 3, aquaporin 10, gap junction protein alpha 1, intestinal fatty acid-binding protein, and lipoprotein lipase, enhance antiviral and immune function by increasing (p < 0.05) the mRNA levels of nuclear factor kappa-B, interferon-β, mucovirus resistance protein II, 2'-5'-oligoadenylate synthetase-like, interferon-γ, C-C motif chemokine ligand 2, and toll-like receptor 4, and enhance antioxidant capacity by increasing (p < 0.05) the mRNA levels of NF-E2-related factor 2 and glutathione S-transferase omega 2 and decreasing (p < 0.05) the mRNA level of NADPH oxidase 2. These results suggested that dietary supplementation with mono-lactate glyceride could decrease the diarrhea rate by improving intestinal antioxidant capacity, intestinal mucosal barrier, intestinal immune defense function, and intestinal mucosal water and nutrient transport. Collectively, dietary supplementation with 0.6% mono-lactate glyceride improved the intestinal function of weaned piglets.

Kinesin-1 Regulates Endocytic Trafficking of Classical Swine Fever Virus along Acetylated Microtubules

Classical swine fever (CSF), caused by classical swine fever virus (CSFV), is an important and highly infectious pig disease worldwide. Kinesin-1, a molecular motor responsible for transporting cargo along the microtubule, has been demonstrated to be involved in the infections of diverse viruses. However, the role of kinesin-1 in the CSFV life cycle remains unknown. Here, we first found that Kif5B played a positive role in CSFV entry by knockdown or overexpression of Kif5B. Subsequently, we showed that Kif5B was associated with the endosomal and lysosomal trafficking of CSFV in the early stage of CSFV infection, which was reflected by the colocalization of Kif5B and Rab7, Rab11, or Lamp1. Interestingly, trichostatin A (TSA) treatment promoted CSFV proliferation, suggesting that microtubule acetylation facilitated CSFV endocytosis. The results of chemical inhibitors and RNA interference showed that Rac1 and Cdc42 induced microtubule acetylation after CSFV infection. Furthermore, confocal microscopy revealed that cooperation between Kif5B and dynein help CSFV particles move in both directions along microtubules. Collectively, our study shed light on the role of kinesin motor Kif5B in CSFV endocytic trafficking, indicating the dynein/kinesin-mediated bidirectional CSFV movement. The elucidation of this study provides the foundation for developing CSFV antiviral drugs. IMPORTANCE The minus end-directed cytoplasmic dynein and the plus end-directed kinesin-1 are the molecular motors that transport cargo on microtubules in intracellular trafficking, which plays a notable role in the life cycles of diverse viruses. Our previous studies have reported that the CSFV entry host cell is dependent on the microtubule-based motor dynein. However, little is known about the involvement of kinesin-1 in CSFV infection. Here, we revealed the critical role of kinesin-1 that regulated the viral endocytosis along acetylated microtubules induced by Cdc42 and Rac1 after CSFV entry. Mechanistically, once CSFV transported by dynein met an obstacle, it recruited kinesin-1 to move in reverse to the anchor position. This study extends the theoretical basis of intracellular transport of CSFV and provides a potential target for the control and treatment of CSFV infection.

Pestiviruses infection: Interferon-virus mutual regulation

Pestiviruses are a class of viruses that in some cases can cause persistent infection of the host, thus posing a threat to the livestock industry. Interferons (IFNs) are a group of secreted proteins that play a crucial role in antiviral defense. In this review, on the one hand, we elaborate on how pestiviruses are recognized by the host retinoic acid-inducible gene-I (RIG-I), melanoma-differentiation-associated protein 5 (MDA5), and Toll-like receptor 3 (TLR3) proteins to induce the synthesis of IFNs. On the other hand, we focus on reviewing how pestiviruses antagonize the production of IFNs utilizing various strategies mediated by self-encoded proteins, such as the structural envelope protein (E^rns) and non-structural protein (N^pro). Hence, the IFN signal transduction pathway induced by pestiviruses infection and the process of pestiviruses blockade on the production of IFNs intertwines into an intricate regulatory network. By reviewing the interaction between IFN and pestiviruses (based on studies on BVDV and CSFV), we expect to provide a theoretical basis and reference for a better understanding of the mechanisms of induction and evasion of the innate immune response during infection with these viruses.

Transcriptome analysis of PK-15 cells expressing CSFV NS4A

BACKGROUND

Classical swine fever (CSF) is a severe disease of pigs that results in huge economic losses worldwide and is caused by classical swine fever virus (CSFV). CSFV nonstructural protein 4 A (NS4A) plays a crucial role in infectious CSFV particle formation. However, the function of NS4A during CSFV infection is not well understood.  RESULTS: In this study, we used RNA-seq to investigate the functional role of CSFV NS4A in PK-15 cells. A total of 3893 differentially expressed genes (DEGs) were identified in PK-15 cells expressing NS4A compared to cells expressing the empty vector (NC). Twelve DEGs were selected and further verified by RT‒qPCR. GO and KEGG enrichment analyses revealed that these DEGs were associated with multiple biological functions, including cell adhesion, apoptosis, host defence response, the inflammatory response, the immune response, and autophagy. Interestingly, some genes associated with host immune defence and inflammatory response were downregulated, and some genes associated with host apoptosis and autophagy were upregulated.

CONCLUSION

CSFV NS4A inhibits the innate immune response, and suppresses the expression of important genes associated with defence response to viruses and inflammatory response, and regulates cell adhesion, apoptosis and autophagy.

HSP90AA1 interacts with CSFV NS5A protein and regulates CSFV replication via the JAK/STAT and NF-κB signaling pathway

Classical swine fever (CSF), caused by the classical swine fever virus (CSFV), is a highly contagious and fatal viral disease, posing a significant threat to the swine industry. Heat shock protein 90 kDa alpha class A member 1 (HSP90AA1) is a very conservative chaperone protein that plays an important role in signal transduction and viral proliferation. However, the role of HSP90AA1 in CSFV infection is unknown. In this study, we found that expression of HSP90AA1 could be promoted in PK-15 and 3D4/2 cells infected by CSFV. Over-expression of HSP90AA1 could inhibit CSFV replication and functional silencing of HSP90AA1 gene promotes CSFV replication. Further exploration revealed that HSP90AA1 interacted with CSFV NS5A protein and reduced the protein levels of NS5A. Since NS5A has an important role in CSFV replication and is closely related to type I IFN and NF-κB response, we further analyzed whether HSP90AA1 affects CSFV replication by regulating type I IFN and NF-κB pathway responses. Our research found HSP90AA1 positively regulated type I IFN response by promoting STAT1 phosphorylation and nuclear translocation processes and promoted the nuclear translocation processes of p-P65. However, CSFV infection antagonizes the activation of HSP90AA1 on JAK/STAT and NF-κB pathway. In conclusion, our study found that HSP90AA1 overexpression significantly inhibited CSFV replication and may inhibit CSFV replication by interacting with NS5A and activating JAK/STAT and NF-κB signaling pathways. These results provide new insights into the mechanism of action of HSP90AA1 in CSFV infection, which abundant the candidate library of anti-CSFV.

Porcine epidemic diarrhea virus strain FJzz1 infection induces type I/III IFNs production through RLRs and TLRs-mediated signaling

Interferons (IFNs) including type I/III IFNs are the major components of the host innate immune response against porcine epidemic diarrhea virus (PEDV) infection, and several viral proteins have been identified to antagonize type I/III IFNs productions through diverse strategies. However, the modulation of PEDV infection upon the activation of the host’s innate immune response has not been fully characterized. In this study, we observed that various IFN-stimulated genes (ISGs) were upregulated significantly in a time- and dose-dependent manner in LLC-PK1 cells infected with the PEDV G2 strain FJzz1. The transcriptions of IRF9 and STAT1 were increased markedly in the late stage of FJzz1 infection and the promotion of the phosphorylation and nuclear translocation of STAT1, implicating the activation of the JAK-STAT signaling pathway during FJzz1 infection. In addition, abundant type I/III IFNs were produced after FJzz1 infection. However, type I/III IFNs and ISGs decreased greatly in FJzz1-infected LLC-PK1 cells following the silencing of the RIG-I-like receptors (RLRs), including RIG-I and MDA5, and the Toll-like receptors (TLRs) adaptors, MyD88 and TRIF. Altogether, FJzz1 infection induces the production of type-I/III IFNs in LLC-PK1 cells, in which RLRs and TLRs signaling pathways are involved, followed by the activation of the JAK-STAT signaling cascade, triggering the production of numerous ISGs to exert antiviral effects of innate immunity.

Genome-wide transcriptome profiling of CSF virus challenged monocyte-derived macrophages provides distinct insights into immune response of Landrace and indigenous Ghurrah pigs

The present study was undertaken to characterize the distinct immune response in indigenous Ghurrah and exotic Landrace pigs by challenging monocyte-derived macrophages (MDMs) with CSF virus under in-vitro conditions and assessing the variations in the transcriptome profile at 48 h post-infection (hpi). RNA-sequencing was carried out in infected and non-infected MDMs of Ghurrah (n = 3) and Landrace (n = 3) piglets prior- as well as post-stimulation. MDMs of Ghurrah showed greater immune regulation in response to CSF infection with 518 significantly differentially expressed genes (DEG) in infected versus non-infected MDMs, as compared to only 31 DEGs in Landrace MDMs. In Landrace, the principal regulators of inflammation (IL1α, IL1β and TNF) were upregulated in infected cells while in Ghurrah, these were downregulated. Overall, macrophages from indigenous Ghurrah showed more immunological dysregulation in response to virulent CSF virus infection as compared to the exotic Landrace pigs.

Warthog Genomes Resolve an Evolutionary Conundrum and Reveal Introgression of Disease Resistance Genes

African wild pigs have a contentious evolutionary and biogeographic history. Until recently, desert warthog (Phacochoerus aethiopicus) and common warthog (P. africanus) were considered a single species. Molecular evidence surprisingly suggested they diverged at least 4.4 million years ago, and possibly outside of Africa. We sequenced the first whole-genomes of four desert warthogs and 35 common warthogs from throughout their range. We show that these two species diverged much later than previously estimated, 400,000–1,700,000 years ago depending on assumptions of gene flow. This brings it into agreement with the paleontological record. We found that the common warthog originated in western Africa and subsequently colonized eastern and southern Africa. During this range expansion, the common warthog interbred with the desert warthog, presumably in eastern Africa, underlining this region’s importance in African biogeography. We found that immune system–related genes may have adaptively introgressed into common warthogs, indicating that resistance to novel diseases was one of the most potent drivers of evolution as common warthogs expanded their range. Hence, we solve some of the key controversies surrounding warthog evolution and reveal a complex evolutionary history involving range expansion, introgression, and adaptation to new diseases.

Identification of candidate genes associated with bacterial and viral infections in wild boars hunted in Tuscany (Italy)

Wild boar (Sus scrofa L.) is one of the large mammals most spread worldwide, highly adaptable, and its population rapidly increased in many areas in Europe, including Italy, where Tuscany is considered particularly suitable for wild boar. Wild boars are potential hosts for different etiological agents, such as Brucella spp., Leptospira spp. and Pseudorabies virus and they can contribute to maintain and/or to disseminate some bacterial or viral pathogens to humans and domestic animals, above all-in free-range farms. In order to identify hypothetical genomic regions associated with these infection diseases, 96 samples of wild boars hunted in Tuscany during the 2018-2019 and 2019-2020 hunting seasons were considered. Diagnosis was achieved by serological tests and 42 Pseudorabies, 31 Leptospira and 15 Brucella positive animals were identified. All animals were genotyped with Geneseek Genomic Profiler Porcine HD (70 k) and a genome-wide scan was then performed. Significant markers were highlighted for Pseudorabies (two SNPs), Brucella (seven SNPs), and Leptospira (four SNPs) and they were located within, or nearby, 29 annotated genes on chromosome 6, 9, 12, 13, 14 and 18. Eight genes are implicated in viral (SEC14L1, JMJD6, SRSF2, TMPRSS2, MX1, MX2) or bacterial (COL8A1, SPIRE1) infections, seven genes (MFSD11, METTL23, CTTNBP2, BACE2, IMPA2, MPPE1 and GNAL) are involved in mental disorders and one gene (MGAT5B) is related to the Golgi complex. Results presented here provide interesting starting points for future research, validation studies and fine mapping of candidate genes involved in bacterial and viral infections in wild boar.

Comparative Proteomic Analysis Reveals Mx1 Inhibits Senecavirus A Replication in PK-15 Cells by Interacting with the Capsid Proteins VP1, VP2 and VP3

As an emergent picornavirus pathogenic to pigs, Senecavirus A (SVA) can replicate in pig kidneys and proliferates well in porcine kidney epithelial PK-15 cells. Here, tandem mass tags (TMT) labeling coupled with liquid chromatography–tandem mass spectrometry (LC-MS/MS) was used to analyze the proteome dynamic changes in PK-15 cells during SVA infection. In total, 314, 697 and 426 upregulated differentially expressed proteins (DEPs) and 131, 263 and 342 downregulated DEPs were identified at 12, 24 and 36 hpi, respectively. After ensuring reliability of the proteomic data by quantitative PCR and Western blot testing of five randomly selected DEPs, Mx1, eIF4E, G6PD, TOP1 and PGAM1, all the DEPs were subjected to multiple bioinformatics analyses, including GO, COG, KEGG and STRING. The results reveal that the DEPs were mainly involved in host innate and adaptive immune responses in the early and middle stages of SVA infection, while the DEPs mainly participated in various metabolic processes in the late stage of infection. Finally, we demonstrated that Mx1 protein exerts antiviral activity against SVA by interacting with VP1 and VP2 proteins dependent on its GTPase, oligomerization and interaction activities, while Mx1 interacts with VP3 only depending on its oligomerization activity. Collectively, our study provides valuable clues for further investigation of SVA pathogenesis.

Anti-Classical Swine Fever Virus Strategies

Classical swine fever (CSF), caused by CSF virus (CSFV), is a highly contagious swine disease with high morbidity and mortality, which has caused significant economic losses to the pig industry worldwide. Biosecurity measures and vaccination are the main methods for prevention and control of CSF since no specific drug is available for the effective treatment of CSF. Although a series of biosecurity and vaccination strategies have been developed to curb the outbreak events, it is still difficult to eliminate CSF in CSF-endemic and re-emerging areas. Thus, in addition to implementing enhanced biosecurity measures and exploring more effective CSF vaccines, other strategies are also needed for effectively controlling CSF. Currently, more and more research about anti-CSFV strategies was carried out by scientists, because of the great prospects and value of anti-CSFV strategies in the prevention and control of CSF. Additionally, studies on anti-CSFV strategies could be used as a reference for other viruses in the Flaviviridae family, such as hepatitis C virus, dengue virus, and Zika virus. In this review, we aim to summarize the research on anti-CSFV strategies. In detail, host proteins affecting CSFV replication, drug candidates with anti-CSFV effects, and RNA interference (RNAi) targeting CSFV viral genes were mentioned and the possible mechanisms related to anti-CSFV effects were also summarized.

The ESCRT-I Subunit Tsg101 Plays Novel Dual Roles in Entry and Replication of Classical Swine Fever Virus

Classical swine fever (CSF), caused by classical swine fever virus (CSFV), is a highly contagious disease of swine with high morbidity and mortality that negatively affects the pig industry worldwide, in particular in China. Soon after the endocytosis of CSFV, the virus makes full use of the components of host cells to complete its life cycle. The endocytosis sorting complex required for transport (ESCRT) system is a central molecular machine for membrane protein sorting and scission in eukaryotic cells that plays an essential role in many physiological metabolic processes, including invasion and egress of envelope viruses. However, the molecular mechanism that ESCRT uses to regulate the replication of CSFV is unknown. In this study, we demonstrated that the ESCRT-I complex Tsg101 protein participates in clathrin-mediated endocytosis of CSFV and is also involved in CSFV trafficking. Tsg101 assists the virus in entering the host cell through the late endosome (Rab7 and Rab9) and finally reaching the lysosome (Lamp-1). Interestingly, Tsg101 is also involved in the viral replication process by interacting with nonstructural proteins 4B and 5B of CSFV. Finally, confocal microscopy showed that the replication complex of Tsg101 and double-stranded RNA (dsRNA) or NS4B and NS5B protein was close to the endoplasmic reticulum (ER), not the Golgi, in the cytoplasm. Collectively, our finding highlights that Tsg101 regulates the process of CSFV entry and replication, indicating that the ESCRT plays an important role in the life cycle of CSFV. Thus, ESCRT molecules could serve as therapeutic targets to combat CSFV infection.IMPORTANCE CSF, caused by CSFV, is a World Organization for Animal Health (OIE) notifiable disease and causes significant financial losses to the pig industry globally. The ESCRT machinery plays an important regulatory role in several members of the genera Flavivirus and Hepacivirus within the family Flaviviridae, such as hepatitis C virus, Japanese encephalitis virus, and dengue virus. Previous reports have shown that assembling and budding of these viruses require ESCRT. However, the role of ESCRT in Pestivirus infection remains to be elucidated. We determined the molecular mechanisms of the regulation of CSFV infection by the major subunit Tsg101 of ESCRT-I. Interestingly, Tsg101 plays an essential regulatory role in both clathrin-mediated endocytosis and genome replication of CSFV. Overall, the results of this study provide further insights into the molecular function of ESCRT-I complex protein Tsg101 during CSFV infection, which may serve as a molecular target for pestivirus inhibitors.

Classical swine fever virus: the past, present and future

Classical swine fever (CSF) is among the most relevant viral epizootic diseases of swine. Due to its severe economic impact, CSF is notifiable to the world organisation for animal health. Strict control policies, including systematic stamping out of infected herds with and without vaccination, have permitted regional virus eradication. Nevertheless, CSF virus (CSFV) persists in certain areas of the world and has re-emerged regularly. This review summarizes the basic established knowledge in the field and provides a comprehensive and updated overview of the recent advances in fundamental CSFV research, diagnostics and vaccine development. It covers the latest discoveries on the genetic diversity of pestiviruses, with implications for taxonomy, the progress in understanding disease pathogenesis, immunity against acute and persistent infections, and the recent findings in virus-host interactions and virulence determinants. We also review the progress and pitfalls in the improvement of diagnostic tools and the challenges in the development of modern and efficacious marker vaccines compatible with serological tests for disease surveillance. Finally, we highlight the gaps that require research efforts in the future.

Porcine enteric alphacoronavirus Inhibits IFN-α, IFN-β, OAS, Mx1, and PKR mRNA Expression in Infected Peyer's Patches in vivo

Porcine enteric alphacoronavirus (PEAV) is a newly identified swine enteropathogenic coronavirus that causes watery diarrhea in neonatal piglets. The pathogenesis and host immune responses of PEAV infection are not fully characterized. The reason lies in the stomach environment, which would degrade cell-cultured live viruses via oral infection, making it difficult to establish an effective infection model to study the pathogenesis and host immune responses in pigs with a mature immune system. To solve this problem, in this study, coated PEAV-loaded microspheres were developed by centrifugal granulation-fluidized bed coating and demonstrated as an effective oral delivery system/animal infection model to protect PEAV virion against the complex gastrointestinal environment in vitro and to cause infection in weaned piglets in vivo. Weaned piglets orally inoculated with coated PEAV-loaded microspheres developed diarrhea and virus RNA was detected in rectal swabs from one to seven days post inoculation. In addition, microscopic lesions in the small intestine were observed, and viral antigens were also detected in the small intestines with PEAV immunohistochemical staining. Importantly, PEAV significantly inhibited mRNA expression of IFN-α, IFN-β, OAS, Mx1, and PKR, the genes involved in modulation of the host immune responses, in infected Peyer's patches, indicating that PEAV can overcome the antiviral response to cause damage when infection occurs. Collectively, our research successfully established a PEAV animal infection model in weaned piglets and suggested that the observed gene expression profile might help explain immunological changes associated with PEAV infection.

MG132 Attenuates the Replication of Classical Swine Fever Virus in vitro

The 26S proteasome, in charge of intracellular protein degradation, plays significant roles in the modulation of various cellular activities as well as in the interplay between virus and host. However, studies about the relationship between 26S proteasome and classical swine fever virus (CSFV) is limited up to now. MG132 is a proteasome inhibitor and has been extensively used in studies about replication of many viruses. Herein, we investigated the role of MG132 in CSFV replication and results showed that MG132 significantly decreased virus titers and viral RNA copies in CSFV-infected PK-15 cells. Further studies demonstrated that MG132 upregulated the expression of several interferon-stimulated genes (ISGs), in CSFV-infected cells. Since the activation of ISGs is controlled by the JAK-STAT signal pathway, we next examined the effect of MG132 on the expression and localization of key molecular STAT1 in the infected cells using Western blot and confocal laser scanning microscopy, respectively. Results showed that CSFV infection and viral NS4A protein decreased the protein level of STAT1, and MG132 promoted the accumulation of STAT1 in the nucleus of cells adjacent to the CSFV-infected cells. Besides, MG132 did not affect the expressions of IFN-α, STAT1, Mx1, OAS1, and PKR genes in cells without CSFV. In conclusion, we identify that MG132 significantly inhibits CSFV replication in vitro, in which the activation of the JAK-STAT pathway and the subsequent upregulation of expressions of ISGs might play significant roles, providing a potential preventive method for CSF.

Chichen type III interferon produced by silkworm bioreactor induces ISG expression and restricts ALV-J infection in vitro

Type III interferon (IFN-λ) has recently been shown to exert a significant antiviral impact against viruses in vertebrates. Avian leukosis virus subgroup J (ALV-J), which causes tumor disease and immunosuppression in infected chicken, is a retrovirus that is difficult to prevent and control because of a lack of vaccines and drugs. Here, we obtained chicken IFN-λ (chIFN-λ) using a silkworm bioreactor and demonstrated that chIFN-λ has antiviral activity against ALV-J infection of both chicken embryo fibroblast cell line (DF1) and epithelial cell line (LMH). We found that chIFN-λ triggered higher levels of particular type III interferon-stimulated genes (type III ISGs) including myxovirus resistance protein (Mx), viperin (RSAD2), and interferon-inducible transmembrane protein 3 (IFITM3) in DF1 and LMH cells. Furthermore, over-expression of Mx, viperin, and IFITM3 could inhibit ALV-J infection in DF1 and LMH cells. Therefore, these results suggested that the anti-ALV-J function of chIFN-λ was specifically implemented by induction of expression of type III ISGs. Our data identified chIFN-λ as a critical antiviral agent of ALV-J infection and provides a potentially and attractive platform for the production of commercial chIFN-λ.

Classical Swine Fever in China-An Update Minireview

Classical swine fever (CSF) remains one of the most economically important viral diseases of domestic pigs and wild boar worldwide. The causative agent is CSF virus, it is highly contagious, with high morbidity and mortality rates; as such, it is an OIE-listed disease. Owing to a nationwide policy of vaccinations of pigs, CSF is well-controlled in China, with large-scale outbreaks rarely seen. Sporadic outbreaks are however still reported every year. In order to cope with future crises and to eradicate CSF, China should strengthen and support biosecurity measures such as the timely reporting of suspected disease, technologies for reliable diagnoses, culling infected herds, and tracing possible contacts, as well as continued vaccination and support of research into drug and genetic therapies. This mini-review summarizes the epidemiology of and control strategies for CSF in China.

Porcine deltacoronavirus induces TLR3, IL-12, IFN-α, IFN-β and PKR mRNA expression in infected Peyer's patches in vivo

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PDCoV infection caused severe diarrhea, virus shedding and intestinal lesion in weaned piglets.

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PDCoV could induce TLR3 mRNA expression in infected Peyer's patches from weaned piglets.

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PDCoV obviously induced IL-12, IFN-α, IFN-β, and PKR mRNA expression in infected Peyer's patches from weaned piglets.

Porcine deltacoronavirus (PDCoV) is a newly identified swine enteropathogenic coronavirus that causes watery diarrhea in piglets and results in significant economic losses to the pig industry. Currently there are no effective treatments or vaccines for PDCoV. In particular, the pathogenesis of PDCoV infection is still largely unknown. In this study, we reported that inoculating conventional weaned piglets with 1 × 10⁹ TCID₅₀ of the PDCoV CHN-GD-2016 strain by oral feeding could cause severe diarrhea. Virus RNA was detected in rectal swabs from 1 to 7 days post inoculation. In addition, microscopic lesions in small intestine were observed, and viral antigen also detected in the small intestines with PDCoV immunohistochemical staining. Importantly, PDCoV significantly induced mRNA expression of TLR3, IL-12, IFN-α, IFN-β, and PKR, the genes involved in modulation of the host immune responses, in infected Peyer's patches at 3 d.p.i., indicating that Peyer's patches play an important role in PDCoV immune responses in vivo. Collectively, our findings suggest that the observed gene expression profile might help explain immunological and pathological changes associated with PDCoV infection.

Rab5, Rab7, and Rab11 Are Required for Caveola-Dependent Endocytosis of Classical Swine Fever Virus in Porcine Alveolar Macrophages

The members of Flaviviridae utilize several endocytic pathways to enter a variety of host cells. Our previous work showed that classical swine fever virus (CSFV) enters porcine kidney (PK-15) cells through a clathrin-dependent pathway that requires Rab5 and Rab7. The entry mechanism for CSFV into other cell lines remains unclear, for instance, porcine alveolar macrophages (3D4/21 cells). More importantly, the trafficking of CSFV within endosomes controlled by Rab GTPases is unknown in 3D4/21 cells. In this study, entry and postinternalization of CSFV were analyzed using chemical inhibitors, RNA interference, and dominant-negative (DN) mutants. Our data demonstrated that CSFV entry into 3D4/21 cells depends on caveolae, dynamin, and cholesterol but not clathrin or macropinocytosis. The effects of DN mutants and knockdown of four Rab proteins that regulate endosomal trafficking were examined on CSFV infection, respectively. The results showed that Rab5, Rab7, and Rab11, but not Rab9, regulate CSFV endocytosis. Confocal microscopy showed that virus particles colocalize with Rab5, Rab7, or Rab11 within 30 min after virus entry and further with lysosomes, suggesting that after internalization CSFV moves to early, late, and recycling endosomes and then into lysosomes before the release of the viral genome. Our findings provide insights into the life cycle of pestiviruses in macrophages.IMPORTANCE Classical swine fever, is caused by classical swine fever virus (CSFV). The disease is notifiable to World Organisation for Animal Health (OIE) in most countries and causes significant financial losses to the pig industry globally. Understanding the processes of CSFV endocytosis and postinternalization will advance our knowledge of the disease and provide potential novel drug targets against CSFV. With this objective, we used systematic approaches to dissect these processes in CSFV-infected 3D4/21 cells. The data presented here demonstrate for the first time to our knowledge that CSFV is able to enter cells via caveola-mediated endocytosis that requires Rab5, Rab7 and Rab11, in addition to the previously described classical clathrin-dependent pathway that requires Rab5 and Rab7. The characterization of CSFV entry will further promote our current understanding of Pestivirus cellular entry pathways and provide novel targets for antiviral drug development.