Zinc-finger antiviral protein-mediated inhibition of porcine epidemic diarrhea virus growth is antagonized by the coronaviral nucleocapsid protein

Versatility of the Zinc-Finger Antiviral Protein (ZAP) As a Modulator of Viral Infections

The zinc-finger antiviral protein (ZAP) is a restriction factor that proficiently impedes the replication of a variety of RNA and DNA viruses. In recent years, the affinity of ZAP's zinc-fingers for single-stranded RNA (ssRNA) rich in CpG dinucleotides was uncovered. High frequencies of CpGs in RNA may suggest a non-self origin, which underscores the importance of ZAP as a potential cellular sensor of (viral) RNA. Upon binding viral RNA, ZAP recruits cellular cofactors to orchestrate a finely tuned antiviral response that limits virus replication via distinct mechanisms. These include promoting degradation of viral RNA, inhibiting RNA translation, and synergizing with other immune pathways. Depending on the viral species and experimental set-up, different isoforms and cellular cofactors have been reported to be dominant in shaping the ZAP-mediated antiviral response. Here we review how ZAP differentially affects viral replication depending on distinct interactions with RNA, cellular cofactors, and viral proteins to discuss how these interactions shape the antiviral mechanisms that have thus far been reported for ZAP. Importantly, we zoom in on the unknown aspects of ZAP's antiviral system and its therapeutic potential to be employed in vaccine design.

Developing Next-Generation Live Attenuated Vaccines for Porcine Epidemic Diarrhea Using Reverse Genetic Techniques

Porcine epidemic diarrhea virus (PEDV) is the etiology of porcine epidemic diarrhea (PED), a highly contagious digestive disease in pigs and especially in neonatal piglets, in which a mortality rate of up to 100% will be induced. Immunizing pregnant sows remains the most promising and effective strategy for protecting their neonatal offspring from PEDV. Although half a century has passed since its first report in Europe and several prophylactic vaccines (inactivated or live attenuated) have been developed, PED still poses a significant economic concern to the swine industry worldwide. Hence, there is an urgent need for novel vaccines in clinical practice, especially live attenuated vaccines (LAVs) that can induce a strong protective lactogenic immune response in pregnant sows. Reverse genetic techniques provide a robust tool for virological research from the function of viral proteins to the generation of rationally designed vaccines. In this review, after systematically summarizing the research progress on virulence-related viral proteins, we reviewed reverse genetics techniques for PEDV and their application in the development of PED LAVs. Then, we probed into the potential methods for generating safe, effective, and genetically stable PED LAV candidates, aiming to provide new ideas for the rational design of PED LAVs.

PEDV nucleocapsid antagonizes zinc-finger antiviral protein by disrupting the interaction with its obligate co-factor, TRIM25

The genomes of many pathogens contain high-CpG content, which is less common in most vertebrate host genomes. Such a distinct di-nucleotide composition in a non-self invader constitutes a special feature recognized by its host's immune system. The zinc-finger antiviral protein (ZAP) is part of the pattern recognition receptors (PRRs) that recognize CpG-rich viral RNA and subsequently initiate RNA degradation as an antiviral defense measure. To counteract such ZAP-mediated restriction, some viruses evolve to either suppress the CpG content in their genome or produce an antagonistic factor to evade ZAP sensing. We have previously shown that a coronavirus, Porcine epidermic diarrhea virus (PEDV), employs its nucleocapsid protein (PEDV-N) to suppress the ZAP-dependent antiviral activity. Here, we propose a mechanism by which PEDV-N suppresses ZAP function by interfering with the interaction between ZAP and its essential cofactor, Tripartite motif-containing protein 25 (TRIM25). PEDV-N was found to interact with ZAP through its N-terminal domain and with TRIM25 through its C-terminal domain. We showed that PEDV-N and ZAP compete for binding to the SPla and the RYanodine Receptor (SPRY) domain of TRIM25, resulting in PEDV-N preventing TRIM25 from interacting with and promoting ZAP. Our result also showed that the presence of PEDV-N in the complex reduces the E3 ligase activity of TRIM25 on ZAP, which is required for the antiviral activity of ZAP. The host-pathogen interaction mechanism presented herein provides an insight into the new function of this abundant and versatile viral protein from a coronavirus which could be a key target for development of antiviral interventions.

Pemetrexed alleviates piglet diarrhea by blocking the interaction between porcine epidemic diarrhea virus nucleocapsid protein and Ezrin

Porcine epidemic diarrhea virus (PEDV) is an enteric coronavirus that causes high mortality in piglets, thus posing a serious threat to the world pig industry. Porcine epidemic diarrhea (PED) is related to the imbalance of sodium absorption by small intestinal epithelial cells; however, the etiology of sodium imbalanced diarrhea caused by PEDV remains unclear. Herein, we first proved that PEDV can cause a significant decrease in Na+/H+ exchanger 3 (NHE3) expression on the cell membrane, in a viral dose-dependent manner. Further study showed that the PEDV nucleocapsid (N) protein participates in the regulation of NHE3 activity through interacting with Ezrin. Flame atomic absorption spectroscopy results indicated a serious imbalance in Na+ concentration inside and outside cells following overexpression of PEDV N. Meanwhile, molecular docking technology identified that the small molecule drug Pemetrexed acts on the PEDV N-Ezrin interaction region. It was confirmed that Pemetrexed can alleviate the imbalanced Na+ concentration in IPEC-J2 cells and the diarrhea symptoms of Rongchang pigs caused by PEDV infection. Overall, our data suggest that the interaction between PEDV N and Ezrin reduces the level of phosphorylated Ezrin, resulting in a decrease in the amount of NHE3 protein on the cell membrane. This leads to an imbalance of intracellular and extracellular Na+, which causes diarrhea symptoms in piglets. Pemetrexed is effective in relieving diarrhea caused by PEDV. Our results provide a reference to screen for anti-PEDV targets and to develop drugs to prevent PED.IMPORTANCEPorcine epidemic diarrhea (PED) has caused significant economic losses to the pig industry since its initial outbreak, and the pathogenic mechanism of porcine epidemic diarrhea virus (PEDV) is still under investigation. Herein, we found that the PEDV nucleocapsid protein interacts with Ezrin to regulate Na+/H+ exchanger 3 activity. In addition, we screened out Pemetrexed, a small molecule drug, which can effectively alleviate pig diarrhea caused by PEDV. These results provide support for further exploration of the pathogenesis of PEDV and the development of drugs to prevent PED.