IMPORTANCE:Vesicular stomatitis virus is a zoonotic rhabdovirus that infects livestock and can cause economically important disease. Tripartite motif-containing 25 (TRIM25) is an E3 ubiquitin ligase involved in innate antiviral signaling, but its role in pigs during vesicular stomatitis virus infection is unclear. OBJECTIVE:To define the mechanism by which swine TRIM25 restricts vesicular stomatitis virus replication. METHODS:Porcine 3D4/21 cells with TRIM25 overexpression or knockdown were infected with vesicular stomatitis virus. Viral replication was quantified by immunoblotting, quantitative reverse transcription polymerase chain reaction, and 50% tissue culture infectious dose assays. Type I interferon signaling was assessed by transcript quantification, interferon-beta and interferon-stimulated response element reporter assays, and co-immunoprecipitation. Viral RNA binding was tested by RNA immunoprecipitation. RESULTS:TRIM25 overexpression reduced viral RNA and infectious titers, whereas TRIM25 knockdown increased replication (p < 0.01). TRIM25 increased interferon-beta and interferon-stimulated gene expression and enhanced interferon-beta and interferon-stimulated response element promoter activity (p < 0.01). Mechanistically, TRIM25 promoted Lys63-linked ubiquitination of RIG-I and increased phosphorylation of TANK-binding kinase 1 and interferon regulatory factor 3. TRIM25 also bound vesicular stomatitis virus genomic RNA, and binding required the C-terminal region. CONCLUSIONS AND RELEVANCE:Porcine TRIM25 restricts vesicular stomatitis virus replication by amplifying type I interferon signaling and directly binding viral RNA.

Importance: Vesicular stomatitis virus is a zoonotic rhabdovirus that infects livestock and can cause economically important disease. Tripartite motif-containing 25 (TRIM25) is an E3 ubiquitin ligase involved in innate antiviral signaling, but its role in pigs during vesicular stomatitis virus infection is unclear. Objective: To define the mechanism by which swine TRIM25 restricts vesicular stomatitis virus replication. Methods: Porcine 3D4/21 cells with TRIM25 overexpression or knockdown were infected with vesicular stomatitis virus. Viral replication was quantified by immunoblotting, quantitative reverse transcription polymerase chain reaction, and 50% tissue culture infectious dose assays. Type I interferon signaling was assessed by transcript quantification, interferon-beta and interferon-stimulated response element reporter assays, and co-immunoprecipitation. Viral RNA binding was tested by RNA immunoprecipitation. Results: TRIM25 overexpression reduced viral RNA and infectious titers, whereas TRIM25 knockdown increased replication (p < 0.05). TRIM25 increased interferon-beta and interferon-stimulated gene expression and enhanced interferon-beta and interferonstimulated response element promoter activity (p < 0.01). Mechanistically, TRIM25 promoted Lys63-linked ubiquitination of RIG-I and increased phosphorylation of TANK-binding kinase 1 and interferon regulatory factor 3. TRIM25 also bound vesicular stomatitis virus genomic RNA, and binding required the C-terminal region. Conclusions and Relevance: Porcine TRIM25 restricts vesicular stomatitis virus replication by amplifying type I interferon signaling and directly binding viral RNA.

Background Porcine reproductive and respiratory syndrome virus (PRRSV) is the pathogen of porcine reproductive and respiratory syndrome (PRRS) which is an important viral infectious disease. PRRSV is a positive-sense single-stranded RNA virus and causes serious economic losses to the pig industry worldwide. The oligoadenylate synthesis (OAS) /Ribonuclease L (RNase L) pathway plays a key role in host innate immune response to inhibit RNA virus infection. However, whether PRRSV proteins inhibit the activation of the OAS/RNase L pathway is less well understood. Results In this study, we first found that the nonstructural protein (Nsp) 11 could significantly decrease OAS1 and RNase L expression and inhibit poly (I: C)-mediated ribosomal RNA (rRNA) degradation and apoptosis by agarose gel electrophoresis and TUNEL assay, suggesting that Nsp11 decreased activation of the OAS/RNase L pathway. Western blotting showed that the PRRSV infection or Nsp11 overexpression reduced OAS1 and RNase L expressions in an endoribonuclease-dependent manner. However, the proteasome and autophagy systems did not influence protein levels of OAS1 and RNase L. These results suggest that Nsp11 does not directly regulate the protein levels of OAS1 and RNase L. Thus, we detected the mRNA levels of OAS1 and RNase L in Nsp11 overexpressed cells. The real-time PCR analysis showed that Nsp11 decreased the mRNA levels of OAS1 and RNase L in an endoribonuclease-dependent manner. Meanwhile, Baf A1 could rescue Nsp11-induced reduction of OAS1 and RNase L mRNA. It is likely that PRRSV Nsp11 inhibits activation of OAS/RNase L pathway by decreasing mRNA levels of OAS1 and RNase L. Our findings reveal that PRRSV Nsp11 decreases the protein level of OAS1 and RNase L to inhibit the activation of OAS/RNase L pathway and promote PRRSV replication, suggesting a potential mechanism for viral evasion of host innate immunity in an autophagy-dependent manner. Conclusion Taken together, the endoribonuclease activity of PRRSV Nsp11 antagonizes the activation of the OAS/RNase L pathway to promote PRRSV replication. Our results demonstrate a novel mechanism that Nsp11 inhibits the antiviral function of the OAS/RNase L pathway, which probably leads to persistent PRRSV infection.

Porcine reproductive and respiratory syndrome virus (PRRSV) has become one of the most economically important diseases to the global pig industry. RNase L is a ubiquitous cellular endoribonuclease that is activated upon the binding of a specific ligand, 2',5'-linked oligoadenylates (2-5 A), which is synthesized by oligoadenylate synthetases (OASs). However, whether Sus scrofa RNase L (sRNase L) could inhibit PRRSV replication and its mechanism have not been fully elucidated. In this study, sRNase L was cloned and characterized in homology and structure firstly. Then the antiviral activity of sRNase L against PRRSV was explored. Overexpression of sRNase L significantly inhibited the propagation of PRRSV when treated with 2-5 A or poly(I: C) or mock treated. Furthermore, sRNase L induced degradation of cellular and viral ssRNAs, enhanced the activation of IFN-β promoter and IFN-β expression, and induced apoptosis to inhibit PRRSV replication. Taken together, we have first elucidated the anti-PRRSV function and the underlying mechanism of sRNase L, which may provide a new strategy for preventing PRRSV infection.

Ribonuclease L (RNase L), which is the effector enzyme of the oligoadenylate synthesis (OAS) /RNase L pathway, exerts its antiviral immune response by cleaving both viral and cellular single-stranded RNA (ssRNA). Beyond its role in innate immunity, RNase L is critically involved in various cellular biological processes and has been linked to disease processes. The interplay between RNase L and the host cell is essential for maintaining intracellular homeostasis and displays the antiviral function. The activation of RNase L is tightly regulated by cellular components such as RNA, 2'-phosphodiesterase (2'-PDE), and RNase L inhibitor (RLI). Conversely, nonactivated or activated RNase L regulates multiple host cellular biological processes, including RNA decay, autophagy and apoptosis crosstalk, and the formation of biological condensates. During viral replication, double-stranded RNA (dsRNA) activates OAS and synthesizes 2',5' oligoadenylate (2-5 A) from ATP. RNase L is activated by binding with 2-5 A to mediate an antiviral immune response by cleavage of viral RNA, thereby suppressing viral replication and infection. Viruses have evolved multiple mechanisms to antagonize the antiviral activity of RNase L, including suppressing OAS activity, upregulating viral 2',5'-PDE expression, and inhibiting the RNA cleavage function of RNase L. In light of recent biochemical and functional findings on RNase L, this review provides a comprehensive overview of its direct or indirect function in host antiviral immune response and diverse strategies that viruses employ to antagonize RNase L activity.

Porcine reproductive and respiratory syndrome (PRRS) is the most economically significant disease caused by porcine reproductive and respiratory syndrome virus (PRRSV). Type I interferon (IFN) induces a large number of interferon-stimulated genes (ISGs) expression to inhibit PRRSV infection. To survive in the host, PRRSV has evolved multiple strategies to antagonize host innate immune response. Previous studies have reported that PRRSV N protein decreases the expression of TRIM25 and TRIM25-mediated RIG-I ubiquitination to suppress IFN-β production. However, whether other PRRSV proteins inhibit the antiviral function of TRIM25 is less well understood. In this study, we first found that PRRSV NSP1α decreased ISGylation of TRIM25. Meanwhile, NSP1α significantly suppressed TRIM25-mediated IFN-β production to promote PRRSV replication. Further studies demonstrated that PRRSV NSP1α reduced the protein level of TRIM25 in proteasome system but did not regulate the transcription level of TRIM25. In addition, the function of NSP1α in TRIM25 degradation did not rely on its papain-like cysteine protease activity. Taken together, PRRSV NSP1α antagonizes the antiviral response of TRIM25 by mediating TRIM25 degradation to promote PRRSV replication. Our data identify TRIM25 as a natural target of PRRSV NSP1α and reveal a novel mechanism that PRRSV induces TRIM25 degradation and inhibits host antiviral immune response.

TAK1-binding protein 1 (TAB1) assembles with TAK1 through its C-terminal domain, leading to the self-phosphorylation and activation of TAK1, which plays an important role in the activation of NF-κB and MAPK signaling pathway. Pseudorabies virus (PRV) is the pathogen of Pseudorabies (PR), which belongs to the Alphaherpesvirus subfamily and causes serious economic losses to the global pig industry. However, the impact of swine TAB1 (sTAB1) on PRV infection has not been reported. In this study, evidence from virus DNA copies, virus titer and western blotting confirmed that sTAB1 could inhibit PRV replication and knockout of sTAB1 by CRISPR-Cas9 gene editing system could promote PRV replication. Further mechanistic studies by real-time PCR and luciferase reporter gene assay demonstrated that sTAB1 could enhance the production of inflammatory factors and chemokines, IFN-β transcription level and IFN-β promoter activity after PRV infection. In summary, we clarify the underlying mechanism of sTAB1 in inhibiting PRV replication for the first time, which provides a new idea for preventing PRV infection and lays a foundation for PRV vaccine development.

ABSTRACT 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.

Non-POU domain-containing octamer-binding protein (NONO) is a multi-functional nuclear protein which belongs to the Drosophila behavior/human splicing (DBHS) protein family. NONO is known to regulate multiple important biological processes including host antiviral immune response. However, whether NONO can inhibit porcine reproductive and respiratory syndrome virus (PRRSV) replication is less well understood. In this study, we demonstrated that swine NONO (sNONO) inhibited PRRSV replication, via increasing expression of IFN-β, whereas NONO knockdown or knockout in PAM-KNU cells was more susceptible to PRRSV infection. As an IRF3 positive regulation factor, NONO promoted IFN-β expression by enhancing activation of IRF3. During PRRSV infection, NONO further up-regulated IRF3-mediated IFN-β expression by interacting with PRRSV N protein. Mechanistically, NONO functioned as a scaffold protein to detect PRRSV N protein and formed N-NONO-IRF3 complex in the nucleus. Interestingly, it was found that the NONO protein reversed the inhibitory effect of PRRSV N protein on type I IFN signaling pathway. Taken together, our study provides a novel mechanism for NONO to increase the IRF3-mediated IFN-β activation by interacting with the viral N protein to inhibit PRRSV infection.

Foot-and-mouth disease virus (FMDV) has developed various strategies to antagonize the host innate immunity. FMDV Lpro and 3Cpro interfere with type I IFNs through different mechanisms. The structural protein VP3 of FMDV degrades Janus kinase 1 to suppress IFN-γ signaling transduction. Whether non-structural proteins of FMDV are involved in restraining type II IFN signaling pathways is unknown. In this study, it was shown that FMDV replication was resistant to IFN-γ treatment after the infection was established and FMDV inhibited type II IFN induced expression of IFN-γ-stimulated genes (ISGs). We also showed for the first time that FMDV non-structural protein 3C antagonized IFN-γ-stimulated JAK-STAT signaling pathway by blocking STAT1 nuclear translocation. 3Cpro expression significantly reduced the ISGs transcript levels and palindromic gamma-activated sequences (GAS) promoter activity, without affecting the protein level, tyrosine phosphorylation, and homodimerization of STAT1. Finally, we provided evidence that 3C protease activity played an essential role in degrading KPNA1 and thus inhibited ISGs mRNA and GAS promoter activities. Our results reveal a novel mechanism by which an FMDV non-structural protein antagonizes host type II IFN signaling.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped positive-stranded RNA virus which causes serious economic losses to pig industry worldwide. Type I IFN induces expression of interferon-stimulated genes 15 (ISG15) to inhibit virus replication. To survive in the host, PRRSV has evolved to antagonize the antiviral response of ISGylation. Previous studies have reported that nonstructural protein 2 of PRRSV inhibits the ISGylation and antiviral function of ISG15 depending on its ovarian tumor (OTU) domain/papain-like protease domain (PLP2). However, whether there are other PRRSV proteins inhibiting ISGylation of cellular proteins is less well understood. In this study, we first found that PRRSV Nsp11 decreased ISGylation of cellular proteins. Meanwhile, the expression level of ISG15 was significantly inhibited by Nsp11. Further mechanistic studies demonstrated that the transcription of ISG15 was reduced by endoribonuclease activity of Nsp11. Finally, we found that the Nsp11-induced degradation of ISG15 was partially relied on autophagy-lysosome system. Taken together, PRRSV Nsp11 antagonizes the antiviral response of ISG15 by its endoribonuclease activity to promote PRRSV replication. Our results reveal a novel mechanism that PRRSV inhibits ISGylation of cellular proteins and impairs host innate immune response.

利用CRISPR/Cas9 基因编辑技术构建 1 株猪TRIM56 基因敲除的PAM-KNU细胞系,并探究其在增殖猪繁殖与呼吸综合征病毒(porcine reproductive and respiratory syndrome virus,PRRSV)疫苗毒株中的应用.根据猪TRIM56 基因组外显子区域设计合成2 对特定的向导RNA引物,将引物磷酸化、退火并连接至Px459M和EZ-Guide-XH载体构建敲除质粒Px459M-sTRIM56-KO;将敲除质粒转染PAM-KNU细胞,经嘌呤霉素筛选、有限稀释法筛选获得单克隆细胞并扩大培养;通过RT-PCR、测序及Western blot筛选鉴定,最终获得了敲除细胞系sTRIM56-KO-PAM-KNU;将PRRSV R98 疫苗株感染野生型细胞及敲除细胞系,利用real-time RT-PCR、半数组织培养感染量(TCID50)以及Western blot 检测PRRSV增殖情况.结果显示,TRIM56 敲除细胞系构建成功,该敲除细胞系中sTRIM56 基因编码区第 929～2120 位 1192 个碱基缺失,未检测到sTRIM56 蛋白条带;敲除细胞系中PRRSV R98 疫苗株病毒拷贝数、病毒滴度以及N蛋白表达均显著高于对照组.本研究为猪TRIM56 抗病毒机制研究及PRRSV疫苗研发奠定了基础.

The eukaryotic expression plasmids of full-length and truncated swine TRIM56 gene were constructed， and the expression and localization of fusion proteins were confirmed. According to the sequence and structural characteristics of swine TRIM56 gene， the primers of full-length and four truncations were designed. The total RNA of porcine alveolar macrophages 3D4/21 was extracted. The full-length and truncated genes were amplified by RT-PCR and cloned into pXJ41 eukaryotic expression vector to construct their full-length and truncated eukaryotic expression plasmids. The full-length and truncated eukaryotic expression plasmids of swine TRIM56 were transfected into HEK-293T cells， and the protein expression was detected by Western blotting. The plasmids were also transfected into porcine alveolar macrophages 3D4/21 and the protein localization was detected by IFA. The results of double enzyme digestion and sequencing showed that the full-length and truncated eukaryotic expression plasmids of swine TRIM56 were successfully constructed. Western blotting results showed that the protein of swine TRIM56 was about 82 kDa， and the bands of truncated TRIM56 proteins were consistent with the expected size. IFA results showed that the full-length and four truncated proteins of swine TRIM56 were mainly localized in the cytoplasm. Our research laid a foundation for further study on the antiviral effect and molecular mechanism of swine TRIM56 protein and different domains.

Purpose:Sarcopenia has been described as a new complication of type 2 diabetes mellitus (T2DM). T2DM and sarcopenia impact each other, resulting in a variety of adverse outcomes such as frailty, disability, poor quality of life and increased mortality. Sodium butyrate (NaB) is reported to play a protective role against T2DM. The present study aimed to investigate whether NaB could ameliorate T2DM-related sarcopenia and the underlying mechanisms.Materials and Methods:The male db/db mice at 7-weeks were used as T2DM-related sarcopenia animal model with C57BL/6J mice as control. Mice were grouped according to whether they received NaB orally as follows: C57BL/6J+water group, C57BL/6J+NaB group, db/db+water group, and db/db+NaB group. Then, db/db mice receiving NaB orally were administered with inhibitors of group 2 innate lymphocytes (ILC2s), anti-CD90.2 by intraperitoneal injection divided into db/db+NaB+PBS group and db/db+NaB+anti-CD90.2 group. NaB dissolved in water at 150 mM. The skeletal muscle mass was measured by dural X-ray (DXA) test. ILC2s in spleen and skeletal muscle were evaluated by flow cytometry. The expressions of IL-33, IL-13, STAT3, P-STAT3, GATA-3 and peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) were assessed by ELISA or WB. The morphology of skeletal muscle fibers was assessed by immunofluorescence staining.Results:The proportion of ILC2s and the expressions of ILC2s markers IL-13 and GATA-3 were all significantly decreased in db/db mice, and these changes were improved by NaB. NaB increased the proportion of slow-twitch fibers in gastrocnemius, thus partially reversing the reduced exercise capacity of db/db mice. The expression of slow-twitch fibers marker PGC-1α induced by NaB was increased via activation of ILC2s/IL-13/STAT3 pathway. On the other way, IL-33 was not necessary for the activation of ILC2s/IL-13/STAT3 pathway. After depletion of ILC2s by anti-CD90.2, the ameliorating effect of NaB on T2DM-related sarcopenia was partially antagonized.Conclusion:These results indicated that NaB could ameliorate type 2 diabetes-related sarcopenia by activating IL-33-independent ILC2s/IL-13/STAT3 signaling pathway.

FMD is a highly contagious and economically important disease in cloven-hoofed animals. SUMOylation, the covalent linkage of a small ubiquitin-like protein to a variety of substrate proteins, has emerged as an important posttranslational modification that plays multiple roles in diverse biological processes.

Objective:We aimed to investigate the effects of the natural product humic acids (HA) on platelet activation and development of venous thromboembolism (VTE) in mice and further explore the relevant mechanism.Methods:Eight-week C57BL/6 mice were randomly assigned to three groups: sham operation group (n = 7), VTE group (n = 8), and VTE + HA group (n = 10). Thrombi were harvested to hematoxylin-eosin staining to evaluate the thrombolysis and recanalization of the thrombus. In addition, flow cytometry was performed to detect the expression levels of protein disulfide isomerase on endothelial-derived exosomes and glycoprotein IIb/IIIa on the surface of the activated platelets surface in plasma. Furthermore, the protein expression level of glycoprotein IIb/IIIa in thrombus was determined by immunohistochemistry and immunofluorescence.Results:The length of thrombosis in the VTE + HA group was significantly shorter than that in the VTE group (P = 0.040). No significant differences were observed in thrombolysis and recanalization between the VTE + HA group and the VTE group (P > 0.05). The content of protein disulfide isomerase carried by endothelial-derived exosomes was significantly increased in the VTE group (P = 0.008) but significantly reduced by native humic acids (P = 0.012). Compared with the VTE group, the expression of glycoprotein IIb/IIIa on activated platelet surface in the VTE + HA group was significantly decreased (P = 0.002). The concentration of plasmatic P-selectin in the VTE group was significantly higher than that in the VTE + HA group (P < 0.001).Conclusion:We demonstrate that HA possess a pharmacological property that decreases venous thrombus formation in mice. The underlying mechanism is that HA could inhibit the expression of glycoprotein IIb/IIIa on the activated platelets surface by suppressing endothelial-derived exosomes carrying on protein disulfide isomerase, thereby blocking platelet activation.

Pseudorabies virus (PRV) is a member of the genus Varicellovirus, family Herpesviridae and causes Aujeszky's disease to lead to huge economic losses in the global pig industry. The Non-POU domain-containing octamer-binding protein (NONO), as a Drosophila behavior/human splicing (DBHS) protein, plays a key role in multiple biological functions in cells, including transcriptional regulation, RNA splicing, DNA repair and so on. However, whether swine NONO (sNONO) inhibits PRV infection is less understood. In this study, we showed that sNONO was a crucial host factor for antagonizing PRV infection and positive regulated transcription levels of ISGs. After PRV infection, sNONO enhanced the activation of IFN-β promoter and IFN-β expression. Furthermore, knockout of sNONO in PAM-KNU cells impaired activation of type I IFN pathway and increased PRV propagation. Taken together, we have first elucidated the anti-PRV function and mechanism of sNONO, which may provide a new strategy for preventing DNA virus infection.