Porcine reproductive and respiratory syndrome virus replication is suppressed by inhibition of the extracellular signal-regulated kinase (ERK) signaling pathway

The effect of matrine and glycyrrhizic acid on porcine reproductive and respiratory syndrome virus in Vitro and in vivo

Porcine reproductive and respiratory syndrome (PRRS) is endemic worldwide, seriously affecting the development of the pig industry, but vaccines have limited protective effects against PRRSV transmission. The aim of this study was to identify potential anti-PRRSV drugs. We examined the cytotoxicity of seven compounds formulated based on the mass ratio of glycyrrhizic acid to matrine and calculated their inhibition rates against PRRSV in vitro. The results showed that the seven compounds all had direct killing and therapeutic effects on PRRSV, and the compounds inhibited PRRSV replication in a time- and dose-dependent manner. The compound with the strongest anti-PRRSV effect was selected for subsequent in vivo experiments. Pigs were divided into a control group and a medication group for the in vivo evaluation. The results showed that pigs treated with the 4:1 compound had 100% morbidity after PRRSV challenge, and the mortality rate reached 75% on the 8th day of the virus challenge. These results suggest that this compound has no practical anti-PRRSV effect in vivo and can actually accelerate the death of infected pigs. Next, we further analyzed the pigs that exhibited semiprotective effects following vaccination with the compound to determine whether the compound can synergize with the vaccine in vivo. The results indicated that pigs treated with the compound had higher mortality rates and more severe clinical reactions after PRRSV infection (p < 0.05). The levels of proinflammatory cytokines (IL-6, IL-8, IL-1β, IFN-γ, and TNF-α) were significantly greater in the compound-treated pigs than in the positive control-treated pigs (p < 0.05), and there was no synergistic enhancement with the live attenuated PRRSV vaccine (p < 0.05). The compound enhanced the inflammatory response, prompted the body to produce excessive levels of inflammatory cytokines and caused body damage, preventing a therapeutic effect. In conclusion, the present study revealed that the in vitro effectiveness of these agents does not indicate that they are effective in vivo or useful for developing anti-PRRSV drugs. Our findings also showed that, to identify effective anti-PRRSV drugs, comprehensive drug screening is needed, for compounds with solid anti-inflammatory effects both in vitro and in vivo. Our study may aid in the development of new anti-PRRSV drugs.

Porcine reproductive and respiratory syndrome virus infection induces microRNA novel-216 production to facilitate viral-replication by targeting MAVS 3´UTR

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused significant economic losses in the swine industry. In this study, the high-throughput sequencing, microRNAs (miRNAs) mimic, and lentivirus were used to screen for potential miRNAs that can promote PRRSV infection in porcine alveolar macrophages or Marc-145 cells. It was observed that novel-216, a previously unidentified miRNA, was upregulated through the p38 signaling pathway during PRRSV infection, and its overexpression significantly increased PRRSV replication. Further analysis revealed that novel-216 regulated PRRSV replication by directly targeting mitochondrial antiviral signaling protein (MAVS), an upstream molecule of type Ⅰ IFN that mediates the production and response of type Ⅰ IFN. The proviral function of novel-216 on PRRSV replication was abolished by MAVS overexpression, and this effect was reversed by the 3'UTR of MAVS, which served as the target site of novel-216. In conclusion, this study demonstrated that PRRSV-induced upregulation of novel-216 served to inhibit the production and response of typeⅠ IFN and facilitate viral replication, providing new insights into viral immune evasion and persistent infection.

Research Advances on Swine Acute Diarrhea Syndrome Coronavirus

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a virulent pathogen that causes acute diarrhea in piglets. The virus was first discovered in Guangdong Province, China, in 2017 and has since emerged in Jiangxi, Fujian, and Guangxi Provinces. The outbreak exhibited a localized and sporadic pattern, with no discernable temporal continuity. The virus can infect human progenitor cells and demonstrates considerable potential for cross-species transmission, representing a potential risk for zoonotic transmission. Therefore, continuous surveillance of and comprehensive research on SADS-CoV are imperative. This review provides an overview of the temporal and evolutionary features of SADS-CoV outbreaks, focusing on the structural characteristics of the virus, which serve as the basis for discussing its potential for interspecies transmission. Additionally, the review summarizes virus-host interactions, including the effects on host cells, as well as apoptotic and autophagic behaviors, and discusses prevention and treatment modalities for this viral infection.

Systematic Identification and Comparison of the Expressed Profiles of Exosomal MiRNAs in Pigs Infected with NADC30-like PRRSV Strain

Exosomes are biological vesicles secreted and released by cells that act as mediators of intercellular communication and play a unique role in virus infection, antigen presentation, and suppression/promotion of body immunity. Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most damaging pathogens in the pig industry and can cause reproductive disorders in sows, respiratory diseases in pigs, reduced growth performance, and other diseases leading to pig mortality. In this study, we used the PRRSV NADC30-like CHsx1401 strain to artificially infect 42-day-old pigs and isolate serum exosomes. Based on high-throughput sequencing technology, 305 miRNAs were identified in serum exosomes before and after infection, among which 33 miRNAs were significantly differentially expressed between groups (13 relatively upregulated and 20 relatively downregulated). Sequence conservation analysis of the CHsx1401 genome identified 8 conserved regions, of which a total of 16 differentially expressed (DE) miRNAs were predicted to bind to the conserved region closest to the 3' UTR of the CHsx1401 genome, including 5 DE miRNAs capable of binding to the CHsx1401 3' UTR (ssc-miR-34c, ssc-miR-375, ssc-miR-378, ssc-miR-486, ssc-miR-6529). Further analysis revealed that the target genes of differentially expressed miRNAs were widely involved in exosomal function-related and innate immunity-related signaling pathways, and 18 DE miRNAs (ssc-miR-4331-3p, ssc-miR-744, ssc-miR-320, ssc-miR-10b, ssc-miR-124a, ssc-miR-128, etc.) associated with PRRSV infection and immunity were screened as potential functional molecules involved in the regulation of PRRSV virus infection by exosomes.

Swine acute diarrhea syndrome coronavirus replication is reduced by inhibition of the extracellular signal-regulated kinase (ERK) signaling pathway

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a newly discovered enteric coronavirus. We have previously shown that the caspase-dependent FASL-mediated and mitochondrion-mediated apoptotic pathways play a central role in SADS-CoV-induced apoptosis, which facilitates viral replication. However, the roles of intracellular signaling pathways in SADS-CoV-mediated cell apoptosis and the relative advantages that such pathways confer on the host or virus remain largely unknown. In this study, we show that SADS-CoV induces the activation of ERK during infection, irrespective of viral biosynthesis. The knockdown or chemical inhibition of ERK1/2 significantly suppressed viral protein expression and viral progeny production. The inhibition of ERK activation also circumvented SADS-CoV-induced apoptosis. Taken together, these data suggest that ERK activation is important for SADS-CoV replication, and contributes to the virus-mediated changes in host cells. Our findings demonstrate the takeover of a particular host signaling mechanism by SADS-CoV and identify a potential approach to inhibiting viral spread.

Porcine reproductive and respiratory syndrome virus increases SOCS3 production via activation of p38/AP-1 signaling pathway to promote viral replication

SOCS3 belongs to the suppressor of cytokine signaling (SOCS) family, which function as negative factors in host immune responses. Prior studies have noted the importance of SOCS family proteins in immunosuppression induced by some viruses. Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important swine-borne viruses and has threatened the global swine industry with huge economic losses since it was first described in the 1980s. PRRSV is the etiological agent of PRRS, which causes reproductive failure and respiratory disorders. PRRSV causes immunosuppression thus establishing persistent infection. In this study, it was observed that SOCS3 was upregulated in PRRSV-infected primary porcine alveolar macrophages (PAMs) and Marc-145 cells with dose-dependent effects, which depends on virus replication. Deletion of AP-1 binding motif located in SOCS3 promoter inhibited promoter activities, which indicates that AP-1 is essential for PRRSV-induced SOCS3. This result was confirmed by experiments using AP-1 inhibitor, whose pretreatment suppressed SOCS3 mRNA and protein expression. Further research showed that p38 was crucial for PRRSV-induced SOCS3 production. Importantly, SOCS3 enhanced PRRSV replication during infection. Taken together, this study indicates that PRRSV infection induced SOCS3 expression through p38/AP-1 signaling pathway. These results revealed the molecular basis of SOCS3 upregulation and would advance further understanding of the strategy for viral immune evasion.

Epigallocatechin-3-Gallate, the Main Polyphenol in Green Tea, Inhibits Porcine Epidemic Diarrhea Virus In Vitro

There are currently no licensed drugs against porcine epidemic diarrhea virus (PEDV), but vaccines are available. We identified a natural molecule, epigallocatechin-3-gallate (EGCG), the main polyphenol in green tea, which is effective against infection with PEDV. We used a variety of methods to test its effects on PEDV in Vero cells. Our experiments show that EGCG can effectively inhibit PEDV infections (with HLJBY and CV777 strains) at different time points in the infection using western blot analysis. We found that EGCG inhibited PEDV infection in a dose-dependent manner 24 h after the infection commenced using western blotting, plaque formation assays, immunofluorescence assays (IFAs), and quantitative reverse-transcriptase PCR (qRT-PCR). We discovered that EGCG treatment of Vero cells decreased PEDV attachment and entry into them by the same method analysis. Western blotting also showed that PEDV replication was inhibited by EGCG treatment. Whereas EGCG treatment was found to inhibit PEDV assembly, it had no effect on PEDV release. In summary, EGCG acts against PEDV infection by inhibiting PEDV attachment, entry, replication, and assembly.

Upregulation of DUSP6 impairs infectious bronchitis virus replication by negatively regulating ERK pathway and promoting apoptosis

Elucidating virus-cell interactions is fundamental to understanding viral replication and identifying targets for therapeutic control of viral infection. The extracellular signal-regulated kinase (ERK) pathway has been shown to regulate pathogenesis during many viral infections, but its role during coronavirus infection is undetermined. Infectious bronchitis virus is the representative strain of Gammacoronavirus, which causes acute and highly contagious diseases in the poultry farm. In this study, we investigated the role of ERK1/2 signaling pathway in IBV infection. We found that IBV infection activated ERK1/2 signaling and the up-regulation of phosphatase DUSP6 formed a negative regulation loop. Pharmacological inhibition of MEK1/2-ERK1/2 signaling suppressed the expression of DUSP6, promoted cell death, and restricted virus replication. In contrast, suppression of DUSP6 by chemical inhibitor or siRNA increased the phosphorylation of ERK1/2, protected cells from apoptosis, and facilitated IBV replication. Overexpression of DUSP6 decreased the level of phospho-ERK1/2, promoted apoptosis, while dominant negative mutant DUSP6-DN lost the regulation function on ERK1/2 signaling and apoptosis. In conclusion, these data suggest that MEK-ERK1/2 signaling pathway facilitates IBV infection, probably by promoting cell survival; meanwhile, induction of DUSP6 forms a negative regulation loop to restrict ERK1/2 signaling, correlated with increased apoptosis and reduced viral load. Consequently, components of the ERK pathway, such as MEK1/2 and DUSP6, represent excellent targets for the development of antiviral drugs.

Inhibition of porcine reproductive and respiratory syndrome virus by PKC inhibitor dequalinium chloride in vitro

As a severe disease characterized by reproductive failure and respiratory distress, porcine reproductive and respiratory syndrome (PRRS) is one of the most leading threats to the swine industry worldwide. Highly evolving porcine reproductive and respiratory syndrome virus (PRRSV) strains with distinct genetic diversity make the current vaccination strategy much less cost-effective and thus urge alternative protective host directed therapeutic approaches. RACK1-PKC-NF-κB signalling axis was suggested as a potential therapeutic target for PRRS control, therefore we tested the inhibitory effect of PKC inhibitor dequalinium chloride (DECA) on the PRRSV infection in vitro. RT-qPCR, western blot, Co-IP and cytopathic effect (CPE) observations revealed that DECA suppressed PRRSV infection and protected Marc-145 cells and porcine alveolar macrophages (PAMs) from severe cytopathic effects, by repressing the PKCα expression, the interaction between RACK1 and PKCα, and subsequently the NF-κB activation. In conclusion, the data presented in this study shed more light on deeper understanding of the molecular pathogenesis upon PRRSV infection and more importantly suggested DECA as a potential promising drug candidate for PRRS control.

Porcine Reproductive and Respiratory Syndrome Virus Interferes with Swine Influenza A Virus Infection of Epithelial Cells

Respiratory infections are still a major concern in pigs. Amongst the involved viruses, the porcine reproductive and respiratory syndrome virus (PRRSV) and the swine influenza type A virus (swIAV) have a major impact. These viruses frequently encounter and dual infections are reported. We analyzed here the molecular interactions between viruses and porcine tracheal epithelial cells as well as lung tissue. PRRSV-1 species do not infect porcine respiratory epithelial cells. However, PRRSV-1, when inoculated simultaneously or shortly before swIAV, was able to inhibit swIAV H1N2 infection, modulate the interferon response and alter signaling protein phosphorylations (ERK, AKT, AMPK, and JAK2), in our conditions. SwIAV inhibition was also observed, although at a lower level, by inactivated PRRSV-1, whereas acid wash treatment inactivating non-penetrated viruses suppressed the interference effect. PRRSV-1 and swIAV may interact at several stages, before their attachment to the cells, when they attach to their receptors, and later on. In conclusion, we showed for the first time that PRRSV can alter the relation between swIAV and its main target cells, opening the doors to further studies on the interplay between viruses. Consequences of these peculiar interactions on viral infections and vaccinations using modified live vaccines require further investigations.

Porcine deltacoronavirus activates the Raf/MEK/ERK pathway to promote its replication

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PDCoV activated the ERK signaling pathway irrespective of viral replication.

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Chemical inhibition and ERK1/2 knockdown markedly impaired PDCoV biosynthesis.

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Cellular and viral cholesterols were involved to PDCoV-induced ERK activation.

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There was no crosstalk between ERK and apoptotic pathways during PDCoV infection.

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PDCoV exploits the ERK cascade to complete successful viral infection.

Porcine deltacoronavirus (PDCoV) is a newly emerged swine coronavirus that causes acute enteritis in neonatal piglets. To date, little is known about the host factors or cellular signaling mechanisms associated with PDCoV replication. Since the Raf/MEK/ERK pathway is involved in modulation of various important cellular functions, numerous DNA and RNA viruses coopt this pathway for efficient propagation. In the present study, we found that PDCoV induces the activation of ERK1/2 and its downstream substrate Elk-1 early in infection irrespective of viral biosynthesis. Chemical inhibition or knockdown of ERK1/2 significantly suppressed viral replication, whereas treatment with an ERK activator increased viral yields. Direct pharmacological inhibition of ERK activation had no effect on the viral entry process but sequentially affected the post-entry steps of the virus life cycle. In addition, pharmacological sequestration of cellular or viral cholesterol downregulated PDCoV-induced ERK signaling, highlighting the significance of the cholesterol contents in ERK activation. However, ERK inhibition had no effect on PDCoV-triggered apoptosis through activation of the cytochrome c-mediated intrinsic mitochondrial pathway, suggesting the irrelevance of ERK activation to the apoptosis pathway during PDCoV infection. Altogether, our findings indicate that the ERK signaling pathway plays a pivotal role in viral biosynthesis to facilitate the optimal replication of PDCoV.

Porcine Reproductive and Respiratory Syndrome Virus Enhances Self-Replication via AP-1-Dependent Induction of SOCS1

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused tremendous economic losses in the swine industry since its emergence in the late 1980s. PRRSV exploits various strategies to evade immune responses and establish chronic persistent infections. Suppressor of cytokine signaling (SOCS) 1, a member of the SOCS family, is a crucial intracellular negative regulator of innate immunity. In this study, it was shown that SOCS1 can be co-opted by PRRSV to evade host immune responses, facilitating viral replication. It was observed that PRRSV induced SOCS1 production in porcine alveolar macrophages, monkey-derived Marc-145 cells, and porcine-derived CRL2843-CD163 cells. SOCS1 inhibited the expression of IFN-β and IFN-stimulated genes, thereby markedly enhancing PRRSV replication. It was observed that the PRRSV N protein has the ability to upregulate SOCS1 production and that nuclear localization signal-2 (NLS-2) is essential for SOCS1 induction. Moreover, SOCS1 upregulation was dependent on p38/AP-1 and JNK/AP-1 signaling pathways rather than classical type I IFN signaling pathways. In summary, to our knowledge, the findings of this study uncovered the molecular mechanism that underlay SOCS1 induction during PRRSV infection, providing new insights into viral immune evasion and persistent infection.

Isobavachalcone inhibits post-entry stages of the porcine reproductive and respiratory syndrome virus life cycle

Porcine reproductive and respiratory syndrome virus (PRRSV) is a pathogen of great economic significance that impacts the swine industry globally. Since the first report of a porcine reproductive and respiratory syndrome (PRRS) outbreak, tremendous efforts to control this disease, including various national policies and plans incorporating the use of multiple modified live-virus vaccines, have been made. However, PRRSV is still a significant threat to the swine industry, and new variants continually emerge as a result of PRRSV evolution. Several studies have shown that pandemic PRRSV strains have enormous genetic diversity and that commercial vaccines can only provide partial protection against these strains. Therefore, effective anti-PRRSV drugs may be more suitable and reliable for PRRSV control. In this study, we observed that isobavachalcone (IBC), which was first isolated from Psoralea corylifolia, had potent anti-PRRSV activity in vitro. Although many biological activities of IBC have been reported, this is the first report describing the antiviral activity of IBC. Furthermore, after a systematic investigation, we demonstrated that IBC inhibits PRRSV replication at the post-entry stage of PRRSV infection. Thus, IBC may be a candidate for further evaluation as a therapeutic agent against PRRSV infection of swine in vivo.

Cellular cholesterol is required for porcine nidovirus infection

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine epidemic diarrhea virus (PEDV) are porcine nidoviruses that are considered emerging and re-emerging viral pathogens of pigs that pose a significant economic threat to the global pork industry. Although cholesterol is known to affect the replication of a broad range of viruses in vitro, its significance and role in porcine nidovirus infection remains to be elucidated. Therefore, the present study was conducted to determine whether cellular or/and viral cholesterol levels play a role in porcine nidovirus infection. Our results showed that depletion of cellular cholesterol by treating cells with methyl-β-cyclodextrin (MβCD) dose-dependently suppressed the replication of both nidoviruses. Conversely, cholesterol depletion from the viral envelope had no inhibitory effect on porcine nidovirus production. The addition of exogenous cholesterol to MβCD-treated cells moderately restored the infectivity of porcine nidoviruses, indicating that the presence of cholesterol in the target cell membrane is critical for viral replication. The antiviral activity of MβCD on porcine nidovirus infection was found to be predominantly exerted when used as a treatment pre-infection or prior to the viral entry process. Furthermore, pharmacological sequestration of cellular cholesterol efficiently blocked both virus attachment and internalization and, accordingly, markedly affected subsequent post-entry steps of the replication cycle, including viral RNA and protein biosynthesis and progeny virus production. Taken together, our data indicate that cell membrane cholesterol is required for porcine nidovirus entry into cells, and pharmacological drugs that hamper cholesterol-dependent virus entry may have antiviral potential against porcine nidoviruses.

Pyrithione inhibits porcine reproductive and respiratory syndrome virus replication through interfering with NF-κB and heparanase

Porcine reproductive and respiratory syndrome virus (PRRSV) is a continuous threat to the pig industry, causing high economic losses worldwide. Current vaccination strategies provide only limited protection against PRRSV infection. Consequently, there is a need to develop new antiviral strategies. Pyrithione (PT), a zinc ionophore, is used as an antibacterial and antifungal agent, and evidence has shown that PT inhibits the replication of various RNA viruses. However, there is no data regarding its effects against PRRSV infection until now. In this study, we showed that PT strongly inhibited PRRSV replication in Marc-145 cells. Similar inhibitory effects were also found in porcine alveolar macrophages, the major target cell type of PRRSV infection in pigs in vivo. PT also attenuated virus-induced apoptosis during the late phase of infection. In addition, we provided evidence that PT caused a rapid import of extracellular zinc ions into cells, and imported Zn²⁺ was responsible for its antiviral property. We investigated the molecular mechanisms of PT against PRRSV and found that PT inhibited NF-κB and heparanase, producing the increased heparan sulfate expression to block the release of virus and cytokines, thus decreasing viral replication. These findings suggest that PT has the potential to the development of prophylactic and therapeutic strategies against PRRSV infection.

Mitogen-Activated Protein Kinase Kinase 2, a Novel E2-Interacting Protein, Promotes the Growth of Classical Swine Fever Virus via Attenuation of the JAK-STAT Signaling Pathway

The mitogen-activated protein kinase kinase/extracellular regulated kinase (MEK1/2/ERK1/2) cascade is involved in the replication of several members of the Flaviviridae family, including hepatitis C virus and dengue virus. The effects of the cascade on the replication of classical swine fever virus (CSFV), a fatal pestivirus of pigs, remain unknown. In this study, MEK2 was identified as a novel binding partner of the E2 protein of CSFV using yeast two-hybrid screening. The E2-MEK2 interaction was confirmed by glutathione S-transferase pulldown, coimmunoprecipitation, and laser confocal microscopy assays. The C termini of E2 (amino acids [aa] 890 to 1053) and MEK2 (aa 266 to 400) were mapped to be crucial for the interaction. Overexpression of MEK2 significantly promoted the replication of CSFV, whereas knockdown of MEK2 by lentivirus-mediated small hairpin RNAs dramatically inhibited CSFV replication. In addition, CSFV infection induced a biphasic activation of ERK1/2, the downstream signaling molecules of MEK2. Furthermore, the replication of CSFV was markedly inhibited in PK-15 cells treated with U0126, a specific inhibitor for MEK1/2/ERK1/2, whereas MEK2 did not affect CSFV replication after blocking the interferon-induced Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway by ruxolitinib, a JAK-STAT-specific inhibitor. Taken together, our results indicate that MEK2 positively regulates the replication of CSFV through inhibiting the JAK-STAT signaling pathway.

IMPORTANCE Mitogen-activated protein kinase kinase 2 (MEK2) is a kinase that operates immediately upstream of extracellular regulated kinase 1/2 (ERK1/2) and links to Raf and ERK via phosphorylation. Currently, little is known about the role of MEK2 in the replication of classical swine fever virus (CSFV), a devastating porcine pestivirus. Here, we investigated the roles of MEK2 and the MEK2/ERK1/2 cascade in the growth of CSFV for the first time. We show that MEK2 positively regulates CSFV replication. Notably, we demonstrate that MEK2 promotes CSFV replication through inhibiting the interferon-induced JAK-STAT signaling pathway, a key antiviral pathway involved in innate immunity. Our work reveals a novel role of MEK2 in CSFV infection and sheds light on the molecular basis by which pestiviruses interact with the host cell.

Pathogenesis of highly pathogenic porcine reproductive and respiratory syndrome virus in Chinese Tibetan swine

Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) was first characterized in 2006 in China, and it causes great economic losses to the Chinese swine production industry. A China Landrace pig, the Tibetan pig, which has striking phenotypic and physiological differences from lowland pigs, is mainly distributed in the Tibetan highlands of China. The susceptibility of the Tibetan pig to HP-PRRSV has not been reported. In this study, 15 4-week-old Tibetan piglets were divided into three groups, and their susceptibility to HP-PRRSV was examined in the highland region. Five pigs in group 1 were inoculated intranasally with HP-PRRSV strain BB0907. At 2days post-inoculation, five other pigs were introduced into this group and then removed to a separated room to serve as contact group 2. Meanwhile, five pigs in group 3 were mock infected and used as controls. The results showed that the pigs in the inoculated and contact groups showed high fevers and clear clinical signs, including depression, anorexia, lethargy, sticky eye secretions, and hind limb paralysis, with high mortality. The main symptom was interstitial pneumonia. Viremia appeared on days 4 to 14 post-infection. HP-PRRSV infection resulted in inflammatory responses within the first week of infection, as evidenced by the expression of tumor necrosis factor alpha, interleukin (IL)-1β, IL-6, and IL-10. All the data indicate that the Tibetan pig is susceptible to HP-PRRSV infection. Thus, it is necessary to investigate and prevent PRRSV infections in the highland region in China.

JNK and p38 mitogen-activated protein kinase pathways contribute to porcine epidemic diarrhea virus infection

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PEDV infection activated p38 MAPK and JNK1/2 in vitro.

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UV-inactivated virus failed to induce p38 MAPK and JNK1/2 activation.

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Pharmacological inhibition of p38 MAPK or JNK activation impaired PEDV replication.

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SAPK cascades do not affect the apoptosis pathway during PEDV infection.

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PEDV exploits the p38 MAPK and JNK signaling pathways for optimal replication.

The mitogen-activated protein kinase (MAPK) pathways, which are central building blocks in the intracellular signaling network, are often manipulated by viruses of diverse families to favor their replication. Among the MAPK family, the extracellular signal-regulated kinase (ERK) pathway is known to be modulated during the infection with porcine epidemic diarrhea virus (PEDV); however, involvement of stress-activated protein kinases (SAPKs) comprising p38 MAPK and c-Jun NH₂-terminal kinase (JNK) remains to be determined. Therefore, in the present study, we investigated whether activation of p38 MAPK and JNK cascades is required for PEDV replication. Our results showed that PEDV activates p38 MAPK and JNK1/2 up to 24 h post-infection, whereas, thereafter their phosphorylation levels recede to baseline levels or even fall below them. Notably, UV-irradiated inactivated PEDV, which can enter cells but cannot replicate inside them, failed to induce phosphorylation of p38 MAPK and JNK1/2 suggesting that viral biosynthesis is essential for activation of these kinases. Treatment of cells with selective p38 or JNK inhibitors markedly impaired PEDV replication in a dose-dependent manner and these antiviral effects were found to be maximal during the early times of the infection. Furthermore, direct pharmacological inhibition of p38 MAPK or JNK1/2 activation resulted in a significant reduction of viral RNA synthesis, viral protein expression, and progeny release. However, independent treatments with either SAPK inhibitor did not inhibit PEDV-induced apoptotic cell death mediated by activation of mitochondrial apoptosis-inducing factor (AIF) suggesting that SAPKs are irrelevant to the apoptosis pathway during PEDV infection. In summary, our data demonstrated critical roles of the p38 and JNK1/2 signaling pathways in facilitating successful viral infection during the post-entry steps of the PEDV life cycle.

Autophagy postpones apoptotic cell death in PRRSV infection through Bad-Beclin1 interaction

Autophagy and apoptosis play significant roles in PRRSV infection and replication. However, the interaction between these 2 processes in PRRSV replication is still far from been completely understood. In our studies, the exposure of MARC-145 cells to PRRSV confirmed the activation of autophagy and subsequent induction of apoptosis. The inhibition of autophagy by 3-methyladenine (3-MA) caused a significant increase in PRRSV-induced apoptosis, showing a potential connection between both mechanisms. Moreover, we observed an increase in Bad expression (a pro-apoptotic protein) and Beclin1 (an autophagy regulator) in virus-infected cells up to 36h. Co-immunoprecipitation assays showed the formation of Bad and Beclin1 complex in PRRSV infected cells. Accordingly, Bad co-localized with Beclin1 in MARC-145 infected cells. Knockdown of Beclin1 significantly decreased PRRSV replication and PRRSV-induced autophagy, while Bad silencing resulted in increased autophagy and enhanced viral replication. Furthermore, PRRSV infection phosphorylated Bad (Ser112) to promote cellular survival. These results demonstrate that autophagy can favor PRRSV replication by postponing apoptosis through the formation of a Bad-Beclin1 complex.

Actinobacillus pleuropneumoniae induces SJPL cell cycle arrest in G2/M-phase and inhibits porcine reproductive and respiratory syndrome virus replication

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens in the swine industry and causes important economic losses. No effective antiviral drugs against it are commercially available. We recently reported that the culture supernatant of Actinobacillus pleuropneumoniae, the porcine pleuropneumonia causative agent, has an antiviral activity in vitro against PRRSV in SJPL cells. Objectives of this study were (i) to identify the mechanism behind the antiviral activity displayed by A. pleuropneumoniae and (ii) to characterize the active molecules present in the bacterial culture supernatant.

Methods

Antibody microarray analysis was used in order to point out cellular pathways modulated by the A. pleuropneumoniae supernatant. Subsequent, flow cytometry analysis and cell cycle inhibitors were used to confirm antibody microarray data and to link them to the antiviral activity of the A. pleuropneumoniae supernatant. Finally, A. pleuropneumoniae supernatant characterization was partially achieved using mass spectrometry.

Results

Using antibody microarray, we observed modulations in G2/M-phase cell cycle regulation pathway when SJPL cells were treated with A. pleuropneumoniae culture supernatant. These modulations were confirmed by a cell cycle arrest at the G2/M-phase when cells were treated with the A. pleuropneumoniae culture supernatant. Furthermore, two G2/M-phase cell cycle inhibitors demonstrated the ability to inhibit PRRSV infection, indicating a potential key role for PRRSV infection. Finally, mass spectrometry lead to identify two molecules (m/z 515.2 and m/z 663.6) present only in the culture supernatant.

Conclusions

We demonstrated for the first time that A. pleuropneumoniae is able to disrupt SJPL cell cycle resulting in inhibitory activity against PRRSV. Furthermore, two putative molecules were identified from the culture supernatant. This study highlighted the cell cycle importance for PRRSV and will allow the development of new prophylactic or therapeutic approaches against PRRSV.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-015-0404-3) contains supplementary material, which is available to authorized users.

Ivermectin inhibits porcine reproductive and respiratory syndrome virus in cultured porcine alveolar macrophages

Porcine reproductive and respiratory syndrome virus (PRRSV) is a devastating viral pathogen of swine that causes huge financial losses in the pig industry worldwide. Ivermectin is known to be a potent inhibitor of importin α/β-mediated nuclear transport and exhibits antiviral activity towards several RNA viruses by blocking the nuclear trafficking of viral proteins. Although PRRSV replication occurs exclusively in the cytoplasm of infected cells, the nucleocapsid (N) protein has been shown to distinctly localize in the nucleus and nucleolus throughout infection. Here, we sought to assess whether ivermectin suppresses PRRSV replication in cultured porcine alveolar macrophage (PAM) cells and to investigate the effect of ivermectin on the subcellular localization of the PRRSV N protein. Our data demonstrate that ivermectin treatment inhibits PRRSV infection in PAM-pCD163 cells in a dose-dependent manner. The antiviral activity of ivermectin on PRRSV replication was most effective when cells were treated during the early stage of infection. Treatment of PRRSV-infected cells with ivermectin significantly suppressed viral RNA synthesis, viral protein expression, and progeny virus production. However, immunofluorescence and cell fractionation assays revealed that ivermectin was incapable of disrupting the nuclear localization of the N protein, both in PRRSV-infected PAM-pCD163 cells and in PAM cells stably expressing the PRRSV N protein. This finding suggests that an alternative mechanism of action accounts for the ability of ivermectin to diminish PRRSV replication. Taken together, our results suggest that ivermectin is an invaluable therapeutic or preventative agent against PRRSV infection.

Extracellular signal-regulated kinase (ERK) activation is required for porcine epidemic diarrhea virus replication

Porcine epidemic diarrhea virus (PEDV) is a highly enteropathogenic coronavirus of swine that causes acute enteritis with high mortality in nursery piglets. To date, the cellular factors involved in PEDV replication have not been well defined. The extracellular signal-regulated kinase (ERK) that serves as a critical component of cellular signal transduction pathways to modulate a variety of cellular functions has been shown to regulate several viral infections. In the present study, we found that PEDV activates ERK1/2 early in infection independently of viral replication. The PEDV-induced ERK1/2 activation resulted in the phosphorylation of its downstream substrate Elk-1 in infected cells. Treatment with ERK inhibitors or ERK1/2 knockdown significantly suppressed viral progeny production. Inhibition of ERK activation also diminished viral protein expression and genomic and subgenomic RNA transcription. These findings indicate that the ERK signaling pathway plays an important role in the PEDV life cycle and beneficially contributes to viral infection.

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PEDV infection activates the ERK signaling pathway in vitro.

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PEDV phosphorylates the ERK downstream substrate Elk-1.

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Chemical inhibition and ERK1/2 knockdown impairs the replication of PEDV.

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ERK activation is not associated with PEDV-induced apoptotic cell death.

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The ERK signaling pathway plays a central role in PEDV replication.

Inhibition of porcine reproductive and respiratory syndrome virus by Cecropin D in vitro

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to cause substantial economic losses to the pig industry worldwide. Although vaccines are commercially available for the control of PRRSV infection, no vaccination regimen has been proved sustained success in terms of generating a protective immune response. Therefore, the development of novel antivirals is urgently needed. Antimicrobial peptides display broad-spectrum antimicrobial activities against bacteria, fungi, and viruses and play an important role in host innate immune response. Here, we tested whether Cecropin D (CD) could inhibit PRRSV infection and replication in vitro. The inhibitory effect of CD occurred during viral attachment and the early period of viral entry into Marc-145 cells. CD also attenuated virus-induced apoptosis during the late phase of PRRSV infection and suppressed virus release in Marc-145 cells, which might contribute to the inhibition of PRRSV infection. Similar inhibitory effects on PRRSV infection were also found with CD treatment in porcine alveolar macrophages, the major target cell type of PRRSV infection in pigs in vivo. These findings suggest that CD has the potential to develop a new therapeutic agent against PRRSV infection.

Sasa quelpaertensis Nakai extract suppresses porcine reproductive and respiratory syndrome virus replication and modulates virus-induced cytokine production

Although Sasa quelpaertensis Nakai, a dwarf bamboo, is known to exert a variety of beneficial effects on health, its antiviral effect remains to be elucidated. Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most devastating viral pathogens of swine and has a substantial economic impact on the global pork industry. Therefore, the present study was conducted to determine whether Sasa quelpaertensis Nakai extract (SQE) inhibits PRRSV infection in cultured porcine alveolar macrophages (PAMs). Our results demonstrated that SQE treatment suppressed the replication of PRRSV in a dose-dependent manner. The antiviral activity of SQE on PRRSV replication was found to be primarily exerted at early times postinfection. Treatment with SQE resulted in marked reduction of viral genomic and subgenomic RNA synthesis, viral protein expression, and progeny virus production. Notably, pro-inflammatory cytokine production in PAM cells infected with PRRSV was shown to be modulated in the presence of SQE. Taken together, our data indicate that SQE has potential as a therapeutic agent against PRRSV.

Proteome analysis of porcine epidemic diarrhea virus (PEDV)-infected Vero cells

Porcine epidemic diarrhea virus (PEDV) causes an acute, highly contagious, and devastating viral enteric disease with a high mortality rate in suckling pigs. A large‐scale outbreak of PED occurred in China in 2010, with PEDV emerging in the United States in 2013 and spreading rapidly, posing significant economic and public health concerns. In this study, LC–MS/MS coupled to iTRAQ labeling was used to quantitatively identify differentially expressed cellular proteins in PEDV‐infected Vero cells. We identified 49 differentially expressed cellular proteins, of which 8 were upregulated and 41 downregulated. These differentially expressed proteins were involved in apoptosis, signal transduction, and stress responses. Based on these differentially expressed proteins, we propose that PEDV might utilize apoptosis and extracellular signal regulated kinases pathways for maximum viral replication. Our study is the first attempt to analyze the protein profile of PEDV‐infected cells by quantitative proteomics, and we believe our findings provide valuable information with respect to better understanding the host response to PEDV infection.

Modulation of innate immune signaling by nonstructural protein 1 (nsp1) in the family Arteriviridae

Arteriviruses infect immune cells and may cause persistence in infected hosts. Inefficient induction of pro-inflammatory cytokines and type I IFNs are observed during infection of this group of viruses, suggesting that they may have evolved to escape the host immune surveillance for efficient survival. Recent studies have identified viral proteins regulating the innate immune signaling, and among these, nsp1 (nonstructural protein 1) is the most potent IFN antagonist. For porcine reproductive and respiratory syndrome virus (PRRSV), individual subunits (nsp1α and nsp1β) of nsp1 suppress type I IFN production. In particular, PRRSV-nsp1α degrades CREB (cyclic AMP responsive element binding)-binding protein (CBP), a key component of the IFN enhanceosome, whereas PRRSV-nsp1β degrades karyopherin-α1 which is known to mediate the nuclear import of ISGF3 (interferon-stimulated gene factor 3). All individual subunits of nsp1 of PRRSV, equine arteritis virus (EAV), lactate dehydrogenase-elevating virus (LDV), and simian hemorrhagic fever virus (SHFV) appear to contain IFN suppressive activities. As with PRRSV-nsp1α, CBP degradation is evident by LDV-nsp1α and partly by SHFV-nsp1γ. This review summarizes the biogenesis and the role of individual subunits of nsp1 of arteriviruses for innate immune modulation.

PKCδ is required for porcine reproductive and respiratory syndrome virus replication

Protein kinase C (PKC) that transduces signals to modulate a wide range of cellular functions has been shown to regulate a number of viral infections. Herein, we showed that inhibition of PKC with the PKC inhibitor GF109203X significantly impaired porcine reproductive and respiratory syndrome virus (PRRSV) replication. Inhibition of PKC led to virus yield reduction, which was associated with decreased viral RNA synthesis and lowered virus protein expression. And this inhibitory effect by PKC inhibitor was shown to occur at the early stage of PRRSV infection. Subsequently, we found that PRRSV infection activated PKCδ in PAMs and knockdown of PKCδ by small interfering RNA (siRNA) suppressed PRRSV replication, suggesting that novel PKCδ may play an important factor in PRRSV replication. Taken together, these data imply that PKC is involved in PRRSV infection and beneficial to PRRSV replication, extending our understanding of PRRSV replication.

Genomic analysis and pathogenic characteristics of Type 2 porcine reproductive and respiratory syndrome virus nsp2 deletion strains isolated in Korea

Porcine reproductive and respiratory syndrome virus (PRRSV) is a globally ubiquitous swine virus that exhibits genetic and pathogenic heterogeneity among isolates. The present study was conducted to determine the complete genome sequence and pathogenicity of two Korean type 2 PRRSV nonstructural protein 2 (nsp2) deletion mutants, CA-2 and KNU-12-KJ4. The full-length genomes of CA-2 and KNU-12-KJ4 were determined to be 15,018 and 15,019 nucleotides in length, excluding the poly(A) tail, respectively, which were 393- or 392-nucleotide shorter than that of the type 2 NA prototype strain VR-2332 due to the presence of notable large deletions within the nsp2 gene. The genomes of CA-2 and KNU-12-KJ4 consisted of a 189- or 190-nucleotide 5' untranslated region (UTR), a 14,677-nucleotide protein-coding region, and a 151-nucleotide 3' UTR. Whole genome evaluation revealed that the nucleotide sequences of CA-2 and KNU-12-KJ4 are most similar to each other (10.7% sequence divergence), and then to the Korean strain CA-1 (11.3% sequence divergence) and the US strain MN184C (13.1% sequence divergence), respectively. To evaluate the in vitro immunity of nsp2 deletion variants, we sought to explore alteration of inflammatory cytokine and chemokine expression in PAM-pCD163 cells infected with each virus strain using quantitative real-time RT-PCR. Cytokine genes including IL-8, IL-10, and TNF-α, and chemokines such as MCP-1 and RANTES were found to be significantly elevated in nsp2 deletion virus-infected PAM cells. In contrast, expression of interferons (IFN-β, γ, and λ) and antiviral genes including ISG-15, -54, and -56 were unchanged or down-regulated in PAM cells infected with the nsp2 deletion mutants. Animal studies to assess the pathogenicity of nsp2 deletion PRRSVs demonstrated that both CA-2 and KNU-12-KJ4 strains notably produce weight loss in infected pigs. Furthermore, the nsp2 deletion mutants replicated well in pigs with significantly increased and prolonged viremia kinetics. Taken together, our results indicate that, among the three isolates, the outcome of in vitro and in vivo infection by CA-2 and KNU-12-KJ4 is comparable, suggesting that the large nsp2 deletion may be one of the viral genetic determinants contributing to PRRSV pathogenicity.

Potential role of porcine reproductive and respiratory syndrome virus structural protein GP2 in apoptosis inhibition

Porcine reproductive and respiratory syndrome virus (PRRSV) is a serious threat to the pork industry, and its pathogenesis needs further investigations. To study the role of two structural proteins of PRRSV in virus-host cells interactions, two stable cell lines (MARC-2a and MARC-N) expressing GP2 and N proteins, respectively, were established. We induced apoptosis in these cells by treating them with staurosporine and found a significant reduction in the number of apoptotic cells in MARC-2a as compared to MARC-N and MARC-145 cells. In addition, we found significantly higher activities of transcriptional factors (NF- κ B and AP-1) in both cell lines as compared to MARC-145 (parent cells). Overall, our data suggest that, although both stable cell lines activate NF- κ B and AP-1, GP2 triggers the antiapoptotic process through an intermediate step that needs to be further investigated.

Highly pathogenic porcine reproductive and respiratory syndrome virus infection results in acute lung injury of the infected pigs

Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) was firstly characterized in 2006 in China. The virus has caused great economic loss to the Chinese swine production during the past years. Herein, we experimentally infected SPF pigs using two strains of PRRSV with different pathogenicity and observed the lung pathological changes looking for new sights on the possible pathogenesis associated with the virulence of HP-PRRSV. The results indicated that the HP-PRRSV-infected pigs died and exhibited severe pathological changes of lungs featuring increased neutrophils, mast cells and mononuclear macrophages, compared with the pigs inoculated with low pathogenic (LP-) PRRSV. Furthermore, the pigs infected with HP-PRRSV showed the higher levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, interleukin (IL)-8 and histamine, leukotriene B4 (LTB4), platelet activation factor (PAF) in sera than those inoculated with LP-PRRSV. Additionally, the fibrosis of lung was observed in the HP-PRRSV-infected pigs. At present, our findings suggest that the aberrant immune responses triggered by HP-PRRSV infection are closely related to acute lung injury (ALI), and especially the pathological changes in lung vascular system are of particular significance. These associated pathological changes of lung are in part responsible for the additional morbidity and mortality observed in HP-PRRSV infection.

DHEA inhibits measles virus through a mechanism independent of its ability to modulate the Raf/MEK/ERK signaling pathway

Aim: Despite the existence of an effective vaccine, measles infection is still frequent in many developing countries with reduced health infrastructure, and it is one of the major causes of child death globally. In the past decade numerous outbreaks have occurred in developed countries, giving a fresh impetus to antiviral research against measles virus. The aim of this study was to investigate the antiviral activity of the natural steroid hormone DHEA against measles virus and the role of the Raf/MEK/ERK signaling pathway in viral multiplication and DHEA’s antiviral activity. Materials & methods: The antiviral activity of DHEA and two ERK modulators, UO126 and anisomycin, was determined using a virus yield reduction assay. Furthermore, we studied DHEA’s virucidal activity and the viral multiplication step affected by the compound. The effect of virus infection on the Raf/MEK/ERK pathway and the activity of those compounds against measles virus spread and induced cytopathic effect were studied using western blot and indirect immunofluorescence. Results & conclusion: We found that DHEA and UO126 are active against measles virus and that they are able to diminish virus-induced cytopathic effects. Also, our study showed that early events in the viral multiplication cycle trigger ERK activation, suggesting that DHEA, a Raf/MEK/ERK modulator, may not exert its antiviral activity through the modulation of this pathway. Our results may provide a first step in the development of new antiviral agents against measles virus.

Ribavirin efficiently suppresses porcine nidovirus replication

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine epidemic diarrhea virus (PEDV) are porcine nidoviruses that represent emerging viral pathogens causing heavy economic impacts on the swine industry. Although ribavirin is a well-known antiviral drug against a broad range of both DNA and RNA viruses in vitro, its inhibitory effect and mechanism of action on porcine nidovirus replication remains to be elucidated. Therefore, the present study was conducted to determine whether ribavirin suppresses porcine nidovirus infection. Our results demonstrated that ribavirin treatment dose-dependently inhibited the replication of both nidoviruses. The antiviral activity of ribavirin on porcine nidovirus replication was found to be primarily exerted at early times post-infection. Treatment with ribavirin resulted in marked reduction of viral genomic and subgenomic RNA synthesis, viral protein expression, and progeny virus production in a dose-dependent manner. Investigations into the mechanism of action of ribavirin against PRRSV and PEDV revealed that the addition of guanosine to the ribavirin treatment significantly reversed the antiviral effects, suggesting that depletion of the intracellular GTP pool by inhibiting IMP dehydrogenase may be essential for ribavirin activity. Further sequencing analysis showed that the mutation frequency in ribavirin-treated cells was similar to that in untreated cells, indicating that ribavirin did not induce error-prone replication. Taken together, our data indicate that ribavirin might not only be a good therapeutic agent against porcine nidovirus, but also a potential candidate to be evaluated against other human and animal coronaviruses.

Induction of interleukin-10 is dependent on p38 mitogen-activated protein kinase pathway in macrophages infected with porcine reproductive and respiratory syndrome virus

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) causes reproductive failure and respiratory illness in pigs and usually establishes a persistent infection. Previous studies suggested that interleukin-10 (IL-10) could play a critical role in PRRSV-induced immunosuppression. However, the ability of PRRSV to induce IL-10 in infected cells is controversial. In this study, we further investigated this issue using PRRSV strain CH-1a, which is the first North American genotype strain isolated in China.

Results

PRRSV strain CH-1a could significantly up-regulate IL-10 production both at mRNA and protein levels in porcine alveolar macrophages (PAMs), bone marrow-derived macrophages (BMDMs), and monocyte-derived macrophages (MDMs). However, up-regulation of IL-10 by PRRSV was retarded by specific inhibitors of p38 mitogen-activated protein kinase (MAPK) (SB203580) and NF-κB (BAY11-7082). Additionally, p38 MAPK and NF-κB pathways but not ERK1/2 MAPK were actually activated in PRRSV-infected BMDMs as demonstrated by western blot analysis, suggesting that p38 MAPK and NF-κB pathways are involved in the induction of IL-10 by PRRSV infection. Transfection of PAMs and PAM cell line 3D4/21 (CRL-2843) with viral structural genes showed that glycoprotein5 (GP5) could significantly up-regulate IL-10 production, which was dependent on p38 MAPK and signal transducer and activator of transcription-3 (STAT3) activation. We also demonstrated that a full-length glycoprotein was essential for GP5 to induce IL-10 production.

Conclusions

PRRSV strain CH-1a could significantly up-regulate IL-10 production through p38 MAPK activation.

Porcine reproductive and respiratory syndrome virus induces autophagy to promote virus replication

An increasing number of studies demonstrate that autophagy, an intrinsic mechanism that can degrade cytoplasmic components, is involved in the infection processes of a variety of pathogens. It can be hijacked by various viruses to facilitate their replication. In this study, we found that PRRSV infection significantly increases the number of double- or single-membrane vesicles in the cytoplasm of host cells in ultrastructural analysis. Our results showed the LC3-I was converted into LC3-II after virus infection, suggesting the autophagy machinery was activated. We further used pharmacological agents and shRNAs to confirm that autophagy promoted the replication of PRRSV in host cells. Confocal microscopy analysis showed that PRRSV inhibited the fusion between autophagosomes and lysosomes, suggesting that PRRSV induced incomplete autophagy. This suppression caused the accumulation of autophagosomes which may serve as replication site to enhance PRRSV replication. It has been shown that NSP2 and NSP3 of arterivirus are two components of virus replication complex. We also found in our studies that NSP2 colocalized with LC3 in MARC-145 cells by performing confocal microscopy analysis and continuous density gradient centrifugation. Our studies presented here indicated that autophagy was activated during PRRSV infection and enhanced PRRSV replication in host cells by preventing autophagosome and lysosome fusion.

Recent progress in studies of arterivirus- and coronavirus-host interactions

Animal coronaviruses, such as infectious bronchitis virus (IBV), and arteriviruses, such as porcine reproductive and respiratory syndrome virus (PRRSV), are able to manifest highly contagious infections in their specific native hosts, thereby arising in critical economic damage to animal industries. This review discusses recent progress in studies of virus-host interactions during animal and human coronavirus and arterivirus infections, with emphasis on IBV-host cell interactions. These interactions may be directly involved in viral replication or lead to the alteration of certain signaling pathways, such as cell stress response and innate immunity, to facilitate viral replication and pathogenesis.

In vitro antiviral activity of dehydroepiandrosterone, 17 synthetic analogs and ERK modulators against herpes simplex virus type 1

In the present study the in vitro antiviral activity of dehydroepiandrosterone (DHEA) and 17 synthetic derivatives against herpes simplex type 1 (HSV-1) was determined. DHEA, epiandrosterone (EA), two synthetic DHEA analogs and three synthetic EA analogs showed a selective inhibitory effect on HSV in vitro multiplication. DHEA and E2, a synthetic derivative of EA, were not found to be virucidal to cell-free HSV-1 and did not impair virus adsorption or penetration. We determined that treatment with both compounds decreased viral protein synthesis. Moreover, inhibitory effect of DHEA and E2 on extracellular viral titer was stronger than the inhibition found on total viral infectivity, suggesting that the antiherpetic activity of these compounds may also be in part due to an inhibition in virus formation and release. Since DHEA is a known Raf/MEK/ERK signaling pathway activator, we studied the role of this pathway on HSV-1 infection. ERK1/2 phosphorylation was stimulated in HSV-1 infected cultures. UO126, a Raf/MEK/ERK signaling pathway inhibitor, impaired viral multiplication, while anisomycin, an activator of this pathway, enhanced it. Treatment with DHEA 6 h before infection enhanced HSV-1 multiplication. On the contrary, pre-treatment with E2, which does not modulate Raf/MEK/ERK signaling pathway, did not produce an increase of viral replication. Taking together these results, the antiviral activity of DHEA seems to occur via a mechanism independent of its ability to modulate ERK phosphorylation.

Highly pathogenic porcine reproductive and respiratory syndrome virus impairs LPS- and poly(I:C)-stimulated tumor necrosis factor-alpha release by inhibiting ERK signaling pathway

Atypical porcine reproductive and respiratory syndrome (PRRS) characterized by high morbidity and mortality emerged in China in 2006. The causative agent was confirmed to be a highly pathogenic PRRS virus (HP-PRRSV). However, the pathogenesis of HP-PRRSV is still uncertain. Here, the ability of the highly pathogenic strains (HV and JX) to induce tumor necrosis factor alpha (TNF-α) was studied. Our results showed that HV and JX were weaker inducers of TNF-α than the conventional strain CH-1a. Moreover, HV infection was demonstrated to suppress extracellular signal-regulated kinase (ERK) phosphorylation at the early time points. Pharmacologic inhibition or activation of ERK revealed that TNF-α production in HV-infected macrophages was associated with the activation status of ERK. Furthermore, HV- and JX-infection could potently impair lipopolysaccharide (LPS)- and poly(I:C)-stimulated TNF-α release in a dose dependent manner whereas synergistic effects were observed at mRNA level. The observation suggested the involvement of posttranslational impact of HP-PRRSV on TNF-α production, which might be attributed to the reduced ERK1/2 phosphorylation in response to toll-like receptor (TLR)-ligation. Taken together, our results indicated that HP-PRRSV infection could impair TNF-α production by inhibiting ERK signaling pathway, which might partially contribute to the pathogenesis of HP-PRRSV.

Stress-activated protein kinases are involved in porcine reproductive and respiratory syndrome virus infection and modulate virus-induced cytokine production

The present study examined the role of the p38 MAPK and JNK pathways during PRRSV infection in immortalized porcine alveolar macrophage (PAM) cells. Infection with PRRSV was found to progressively activate p38 and JNK1/2 up to 36 h postinfection and then their phosphorylation levels dramatically decreased to baseline at 48 h postinfection. In contrast, UV-inactivated PRRSV failed to trigger phosphorylation of these SAPKs, indicating that the post-entry process is responsible for their activation. Independent treatment of cells with a selective p38 or JNK inhibitor markedly impaired PRRSV infection, resulting in significant reduction in synthesis of viral genomic and subgenomic RNAs, viral protein expression, and progeny virus production. Notably, cytokine production in PAM cells infected with PRRSV was shown to be altered by inhibiting these SAPKs. Altogether, our data suggest that the p38 and JNK signaling pathways play pivotal roles in PRRSV replication and may regulate immune responses during virus infection.

Regulation of cell signaling and porcine reproductive and respiratory syndrome virus

In order to successfully survive in host and persistent infection, porcine reproductive and respiratory syndrome virus (PRRSV) utilized sophisticated mechanisms to suppress or escape from the host' innate and adaptive immune systems, and then changed host gene expression. Signaling pathways play a pivotal role in the regulation of diverse biological processes. Once signaling pathways are activated by a variety of different stimuli, immune responses will be triggered by the activation of chemokines, transcription factors, and inflammatory cytokines to adjust the aggressive replication and dissemination of viruses. PRRSV infection is able to get many signaling pathways activation that facilitates distinct cell functions to modulate immune responses. In addition, the cross-talk of cell signaling pathways also can regulate PRRSV replication and also is present in this review by recent finding.

Lipopolysaccharide down-regulates carbolesterases 1 and 2 and reduces hydrolysis activity in vitro and in vivo via p38MAPK-NF-κB pathway

Carboxylesterases constitute a class of enzymes that hydrolyze drugs containing such functional groups as carboxylic acid ester, amide, and thioester. Hydrolysis of many drugs is reduced in liver diseases such as hepatitis and cirrhosis. In this study, we have demonstrated, in vitro and in vivo, treatment with LPS decreased the expression of HCE1 and HCE2 and the capacity of hydrolytic activity. In HepG2 cells, the decreased expression by LPS occurred at both mRNA and protein levels. Both HCE1 and HCE2 promoters were significantly repressed by LPS, and the repression was comparable with the decrease in HCE1 and HCE2 mRNA, suggesting the transrepression is responsible for suppressed expression. Further study showed that both PDTC, a NF-κB inhibitor, and SB203580, a p38MAPK inhibitor, could abolish the repression of HCE1 and HCE2 mediated by LPS, but U0126, a selective ERK1/2 inhibitor, could not do so, suggesting the repression of HCE1 and HCE2 by LPS through the p38MAPK-NF-κB pathway. In addition, being pretreated with LPS, HepG2 cells altered the cellular responsiveness to ester therapeutic agents, including clopidogrel (hydrolyzed by HCE1) and irinotecan (hydrolyzed by HCE2). The altered cellular responsiveness occurred at low micromolar concentrations, suggesting that suppressed expression of carboxylesterases by LPS has profound pharmacological and toxicological consequences, particularly with those that are hydrolyzed in an isoform-specific manner. This study provides new insight into the understanding of the pharmacological and toxicological effects and the mechanisms for repressing drug metabolism enzymes in inflammation.