Porcine reproductive and respiratory syndrome virus (PRRSV) is an important globally distributed and highly contagious pathogen that has restricted cell tropism in vivo and in vitro. In the present study, we found that annexin A2 (ANXA2) is upregulated expressed in porcine alveolar macrophages infected with PRRSV. Additionally, PRRSV replication was significantly suppressed after reducing ANXA2 expression in Marc-145 cells using siRNA. Bioinformatics analysis indicated that ANXA2 may be relevant to vimentin, a cellular cytoskeleton component that is thought to be involved in the infectivity and replication of PRRSV. Co-immunoprecipitation assays and confocal analysis confirmed that ANXA2 interacts with vimentin, with further experiments indicating that the B domain (109–174 aa) of ANXA2 contributes to this interaction. Importantly, neither ANXA2 nor vimentin alone could bind to PRRSV and only in the presence of ANXA2 could vimentin interact with the N protein of PRRSV. No binding to the GP2, GP3, GP5, nor M proteins of PRRSV was observed. In conclusion, ANXA2 can interact with vimentin and enhance PRRSV growth. This contributes to the regulation of PRRSV replication in infected cells and may have implications for the future antiviral strategies.

Porcine reproductive and respiratory syndrome virus (PRRSV) is a single-stranded positive-sense RNA virus, and the current strategies for controlling PRRSV are limited. Interferon gamma-inducible protein 16 (IFI16) has been reported to have a broader role in the regulation of the type I interferons (IFNs) response to RNA and DNA viruses. However, the function of IFI16 in PRRSV infection is unclear. Here, we revealed that IFI16 acts as a novel antiviral protein against PRRSV-2. IFI16 could be induced by interferon-beta (IFN-β). Overexpression of IFI16 could significantly suppress PRRSV-2 replication, and silencing the expression of endogenous IFI16 by small interfering RNAs led to the promotion of PRRSV-2 replication in MARC-145 cells. Additionally, IFI16 could promote mitochondrial antiviral signaling protein (MAVS)-mediated production of type I interferon and interact with MAVS. More importantly, IFI16 exerted anti-PRRSV effects in a MAVS-dependent manner. In conclusion, our data demonstrated that IFI16 has an inhibitory effect on PRRSV-2, and these findings contribute to understanding the role of cellular proteins in regulating PRRSV replication and may have implications for the future antiviral strategies.

Porcine reproductive and respiratory syndrome (PRRS) is a disease caused by PRRS virus (PRRSV), which seriously harms the pig industry. Revealing the mechanism by which PRRSV inhibits immune response will help prevent and control PRRS. Here, we found that PRRSV-2 may hijack host miR-541-3p to inhibit host innate immune response. Firstly, this work showed that miR-541-3p mimics could facilitate the replication of PRRSV-2 and the results of the quantitative real time polymerase chain reaction (qRT-PCR) showed that PRRSV-2 could up-regulate the expression of miR-541-3p in MARC-145 cells. Since previous studies have shown that type I interferon could effectively inhibit the replication of PRRSV-2, the present work explored whether miR-541-3p regulated the expression of type I interferon and found that miR-541-3p could negatively regulate the transcription of type I interferon by targeting interferon regulatory factor 7 (IRF7). More importantly, PRRSV-2 infection could down-regulate the expression of IRF7 and over-expression of IRF7 could down-regulate the replication of PRRSV-2 in MARC-145 cells. In conclusion, PRRSV-2 infection up-regulated the expression of miR-541-3p to promote its replication in MARC-145 cells, since miR-541-3p can negatively regulate the transcription of type I interferon by targeting IRF7.

Porcine reproductive and respiratory syndrome virus (PRRSV), the causative pathogen of PRRS, remains one of the most important pathogens threatening the global pig industry. Due to the genetic diversity of PRRSV, the existing commercially vaccines cannot completely protect pigs from PRRSV infection. Flavonoid compounds play an important role in inhibiting viral replication. In this study, we found that calycosin, a natural active compound isolated from astragalus, could inhibit PRRSV replication regardless of whether calycosin was added pre-, co-, or post-PRRSV infection in vitro . Furthermore, coincubation of calycosin with PRRSV showed a better inhibitory effect compared to separate incubation, and calycosin mainly inhibited virus replication, assembly and release stages. Importantly, calycosin enhanced the antiviral immunity, as shown by the increased expression of IFN-β and ISG56. Subsequently, we discovered that calycosin promoted the expression of RIG-I and MAVS, and induced the phosphorylation and nuclear translocation of IRF3 during PRRSV infection. Collectively, calycosin could markedly inhibit PRRSV replication and activate the RIG-I/IRF3 signaling pathway. These data contribute to understanding the role of calycosin in PRRSV replication, and may provide valuable insights for the development of future antiviral strategies.

Porcine reproductive and respiratory syndrome virus (PRRSV) remains one of the most important pathogens, resulting in huge economic losses to the global pig industry. Ipriflavone is an isoflavone derivative involved in various biological processes, showing anti-inflammatory, anti-apoptotic, antioxidant, and neuroprotective effects. However, the role of ipriflavone in antiviral immune response to PRRSV is unknown. In this study, we discovered that ipriflavone could significantly inhibit PRRSV replication. Moreover, ipriflavone inhibited PRRSV replication regardless of whether ipriflavone was added pre-, co-, or post-PRRSV infection, and ipriflavone mainly inhibited virus replication and assembly stages. Importantly, ipriflavone had the capacity to upregulate the expression levels of IFN-β and ISG56. Additionally, ipriflavone promoted the expression of RIG-I and MAVS, and induced phosphorylation of IRF3 and STAT1, while reducing PRRSV replication. Collectively, ipriflavone could enhance the RIG-I/IRF3 signaling pathway, thereby inhibiting PRRSV replication. These findings will provide an important theoretical basis for the development of therapeutic agents against PRRSV infection.