Porcine RACK1 negatively regulates the infection of classical swine fever virus and the NF-κB activation in PK-15 cells

RACK1 promotes porcine reproductive and respiratory syndrome virus infection in Marc-145 cells through ERK1/2 activation

Porcine reproductive and respiratory syndrome (PRRS) is an acute infectious disease that spreads rapidly among pigs and seriously threatens the pig industry. Activation of ERK1/2 is a hallmark of most viral infections. RACK1 interacts with a variety of kinases and membrane receptors that closely associated with viral infections and the development and progression of cancer. However, no studies have clearly defined whether RACK1 can regulate PRRSV infection through ERK1/2 activation. In our study, using RT-qPCR, immunoblotting, indirect fluorescent staining, siRNA knockdown and protein overexpression techniques, we found that downregulation of cellular RACK1 inhibited ERK1/2 activation and subsequently suppressed PRRSV infection, while overexpression of RACK1 enhanced ERK1/2 activation and PRRSV infection. Bioinformatic and Co-immunoprecipitation experimental analysis revealed that cellular RACK1 could interact with viral N protein to exert its function. We elaborated that RACK1 promoted PRRSV replication in Marc-145 cells through ERK1/2 activation. Our study provides new insights into regulating the innate antiviral immune responses during PRRSV infection and contributes to further understanding of the molecular mechanisms underlying PRRSV replication.

Long non-coding RNA LOC103222771 promotes infection of porcine reproductive and respiratory syndrome virus in Marc-145 cells by downregulating Claudin-4

Porcine reproductive and respiratory syndrome (PRRS) is an important swine disease caused by infection of porcine reproductive and respiratory syndrome virus (PRRSV), which leads to huge loss in swine industry. How to effectively control PRRS is challenging. Long non-coding RNA (lncRNA) are key regulator of viral infections and anti-virus immunological responses, therefore, further understanding of lncRNAs will aid to identification of novel regulators of viral infections and better design of prevention and control strategies to viral infection related diseases and immune disorders. We demonstrated that PRRSV infection upregulated the expression of lncRNA LOC103222771 in Marc-145 cells and porcine alveolar macrophage cells (PAMs) and that LOC103222771 is mainly located in cytoplasm. Knockdown of LOC103222771 could inhibit the PRRSV infection in Marc-145 cells. RNA-seq analysis and subsequent validation revealed increased expression of Claudin-4 (CLDN4) in Marc-145 when LOC103222771 was specifically downregulated，suggesting that LOC103222771 might be an upstream regulator of CLDN4, an important component of tight junctions for establishment of the paracellular barrier that controls the flow of molecules in the intercellular space between epithelial cells. We and others showed that Downregulation of CLDN4 could boost the infection of PRRSV. Collectively, LOC103222771/CLDN4 signal axis might be a novel mechanism of PRRSV pathogenesis, implying a potential therapeutic target against PRRSV infection.

RACK1 mediates NLRP3 inflammasome activation during Pasteurella multocida infection

Pasteurella multocida is a gram-negative bacterium that causes serious diseases in a wide range of animal species. Inflammasomes are intracellular multimolecular protein complexes that play a critical role in host defence against microbial infection. Our previous study showed that bovine P. multocida type A (PmCQ2) infection induces NLRP3 inflammasome activation. However, the exact mechanism underlying PmCQ2-induced NLRP3 inflammasome activation is not clear. Here, we show that NLRP3 inflammasome activation is positively regulated by a scaffold protein called receptor for activated C kinase 1 (RACK1). This study shows that RACK1 expression was downregulated by PmCQ2 infection in primary mouse peritoneal macrophages and mouse tissues, and overexpression of RACK1 prevented PmCQ2-induced cell death and reduced the numbers of adherent and invasive PmCQ2, indicating a modulatory role of RACK1 in the cell death that is induced by P. multocida infection. Next, RACK1 knockdown by siRNA significantly attenuated PmCQ2-induced NLRP3 inflammasome activation, which was accompanied by a reduction in the protein expression of interleukin (IL)-1β, pro-IL-1β, caspase-1 and NLRP3 as well as the formation of ASC specks, while RACK1 overexpression by pcDNA3.1-RACK1 plasmid transfection significantly promoted PmCQ2-induced NLRP3 inflammasome activation; these results showed that RACK1 is essential for NLRP3 inflammasome activation. Furthermore, RACK1 knockdown decreased PmCQ2-induced NF-κB activation, but RACK1 overexpression had the opposite effect. In addition, the immunofluorescence staining and immunoprecipitation results showed that RACK1 colocalized with NLRP3 and that NEK7 and interacted with these proteins. However, inhibition of potassium efflux significantly attenuated the RACK1-NLRP3-NEK7 interaction. Our study demonstrated that RACK1 plays an important role in promoting NLRP3 inflammasome activation by regulating NF-κB and promoting NLRP3 inflammasome assembly.

Interaction of SERINC5 and IFITM1/2/3 regulates the autophagy-apoptosis-immune network under CSFV infection

The host restriction factor serine incorporator 5 (SERINC5) plays a key role in inhibiting viral activity and has been shown to inhibit classical swine fever virus (CSFV) infection. However, the action of SERINC5 in the interaction between host cells and CSFV remains poorly understood. This study found that SERINC5 represses CSFV-induced autophagy through MAPK1/3-mTOR and AKT-mTOR signalling pathways. Further research showed that SERINC5 promotes apoptosis by repressing autophagy. Likewise, it was demonstrated that SERINC5 interacting proteins IFITM1/2/3 inhibit CSFV replication and regulate autophagy in a lysosomal-associated membrane protein LAMP1-dependent manner. In addition, IFITM1/2/3 interference promotes the NF-κB signalling pathway for potential immunoregulation by inhibiting autophagy. Finally, the functional silencing of IFITM1/2/3 genes was demonstrated to enhance the inhibitory effect of SERINC5 on autophagy. Taken together, These data uncover a novel mechanism through SERINC5 and its interacting proteins IFITM1/2/3, which mediates CSFV replication, and provides new avenues for controlling CSFV.

Role of the receptor for activated C kinase 1 during viral infection

Viruses can survive only in living cells, where they depend on the host's enzymatic system for survival and reproduction. Virus-host interactions are complex. On the one hand, hosts express host-restricted factors to protect the host cells from viral infections. On the other hand, viruses recruit certain host factors to facilitate their survival and transmission. The identification of host factors critical to viral infection is essential for comprehending the pathogenesis of contagion and developing novel antiviral therapies that specifically target the host. Receptor for activated C kinase 1 (RACK1), an evolutionarily conserved host factor that exists in various eukaryotic organisms, is a promising target for antiviral therapy. This review primarily summarizes the roles of RACK1 in regulating different viral life stages, particularly entry, replication, translation, and release.

Current Status of Genetically Modified Pigs That Are Resistant to Virus Infection

Pigs play an important role in agriculture and biomedicine. The globally developing swine industry must address the challenges presented by swine-origin viruses, including ASFV (African swine fever virus), PRRSV (porcine reproductive and respiratory syndrome virus), PEDV (porcine epidemic diarrhea virus), PRV (pseudorabies virus), CSFV (classical swine fever virus), TGEV (transmissible gastroenteritis virus), et al. Despite sustained efforts by many government authorities, these viruses are still widespread. Currently, gene-editing technology has been successfully used to generate antiviral pigs, which offers the possibility for increasing animal disease tolerance and improving animal economic traits in the future. Here, we summarized the current advance in knowledge regarding the host factors in virus infection and the current status of genetically modified pigs that are resistant to virus infection in the world. There has not been any report on PEDV-resistant pigs, ASFV-resistant pigs, and PRV-resistant pigs owing to the poor understanding of the key host factors in virus infection. Furthermore, we summarized the remaining problems in producing virus-resistant pigs, and proposed several potential methods to solve them. Using genome-wide CRISPR/Cas9 library screening to explore the key host receptors in virus infection may be a feasible method. At the same time, exploring the key amino acids of host factors in virus infection with library screening based on ABEs and CBEs (Bes) may provide creative insight into producing antiviral pigs in the future.

Classical swine fever virus infection suppresses claudin-1 expression to facilitate its replication in PK-15 cells

Classical swine fever (CSF) is one of the most epidemic viral diseases in swine industry. The causative pathogen is CSF virus (CSFV), a small enveloped RNA virus of Flaviviridae family. Claudin-1 was reported to be involved in the infections of a number of viruses, including many from Flaviviridae family, but no studies have investigated the role of porcine claudin-1 during CSFV infection in PK-15 cells. In this study, on the one hand, we demonstrated that CSFV infection reduced the claudin-1 expression at both mRNA and protein levels; on the other hand, CSFV infection was enhanced after claudin-1 knockdown, but inhibited by claudin-1 overexpression in a dose-dependent manner. Furthermore, negative correlation was demonstrated between the claudin-1 expression and CSFV titer. In conclusion, claudin-1 might be a barrier for CSFV infection in PK-15 cells, while CSFV bypasses the barrier through lysosome mediated degradation of claudin-1, which could be repressed by bafilomycin A1. Although the elaborate mechanisms how claudin-1 plays its roles in CSFV infection require further investigations, this study may advance our understanding of the molecular host-pathogen interaction mechanisms underlying CSFV infection and suggests enhancement of porcine claudin-1 as a potential preventive or therapeutic strategy for CSF control.