Wnt/β-catenin signaling pathway inhibits porcine reproductive and respiratory syndrome virus replication by enhancing the nuclear factor-κB-dependent innate immune response

Deletion of a 7-amino-acid region in the porcine epidemic diarrhea virus envelope protein induces higher type I and III interferon responses and results in attenuation in vivo

Porcine epidemic diarrhea virus (PEDV) leads to enormous economic losses for the pork industry. However, the commercial vaccines failed to fully protect against the epidemic strains. Previously, the rCH/SX/2016-SHNXP strain with the entire E protein and the rCH/SX/2015 strain with the deletion of 7-amino-acid (7-aa) at positions 23-29 in E protein were constructed and rescued. The pathogenicity assay indicated that rCH/SX/2015 is an attenuated strain, but rCH/SX/2016-SHNXP belongs to the virulent strains. Then, the recombination PEDV (rPEDV-EΔaa23-aa29)strain with a 7-aa deletion in the E protein was generated, using the highly virulent rCH/SX/2016-SHNXP strain (rPEDV-Ewt) as the backbone. Compared with the rPEDV-Ewt strain, the release and infectivity of the rPEDV-EΔaa23-aa29 strain were significantly reduced in vitro, but stronger interferon (IFN) responses were triggered both in vitro and in vivo. The pathogenicity assay showed that the parental strain resulted in severe diarrhea (100%) and death (100%) in all piglets. Compared with the parental strain group, rPEDV-EΔaa23-aa29 caused lower mortality (33%) and diminished fecal PEDV RNA shedding. At 21 days, all surviving pigs were challenged orally with rPEDV-Ewt. No pigs died in the two groups. Compared with the mock group, significantly delayed and milder diarrhea and reduced fecal PEDV RNA shedding were detected in the rPEDV-EΔaa23-aa29 group. In conclusion, the deletion of a 7-aa fragment in the E protein (EΔaa23-aa29) attenuated PEDV but retained its immunogenicity, which can offer new ideas for the design of live attenuated vaccines and provide new insights into the attenuated mechanism of PEDV. IMPORTANCE Porcine epidemic diarrhea virus (PEDV) causes high mortality in neonatal piglets and remains a large challenge to the pork industry. Unfortunately, no safe and effective vaccines are available yet. The pathogenesis and molecular basis of the attenuation of PEDV remain unclear, which seriously hinders the development of PEDV vaccines. This study found that the rPEDV carrying EΔaa23-aa29 mutation in the E protein induced significantly higher IFN responses than the parental virus, partially attenuated, and remained immunogenic in piglets. For the first time, PEDV E was verified as an IFN antagonist in the infection context and identified as a virulence factor of PEDV. Our data also suggested that EΔaa23-aa29 mutation can be a good target for the development of live attenuated vaccines for PEDV and also provide new perspectives for the attenuated mechanism of PEDV.

Critical role for ribonucleoside-diphosphate reductase subunit M2 in ALV-J-induced activation of Wnt/β-catenin signaling via interaction with P27

Avian leukemia virus subgroup J (ALV-J) causes various diseases associated with tumor formation and decreased fertility and induced immunosuppressive disease, resulting in significant economic losses in the poultry industry globally. Virus usually exploits the host cellular machinery for their replication. Although there are increasing evidences for the cellular proteins involving viral replication, the interaction between ALV-J and host proteins leading to the pivotal steps of viral life cycle are still unclear. Here, we reported that ribonucleoside-diphosphate reductase subunit M2 (RRM2) plays a critical role during ALV-J infection by interacting with capsid protein P27 and activating Wnt/β-catenin signaling. We found that the expression of RRM2 is effectively increased during ALV-J infection, and that RRM2 facilitates ALV-J replication by interacting with viral capsid protein P27. Furthermore, ALV-J P27 activated Wnt/β-catenin signaling by promoting β-catenin entry into the nucleus, and RRM2 activated Wnt/β-catenin signaling by enhancing its phosphorylation at Ser18 during ALV-J infection. These data suggest that the upregulation of RRM2 expression by ALV-J infection favors viral replication in host cells via activating Wnt/β-catenin signaling. IMPORTANCE Our results revealed a novel mechanism by which RRM2 facilitates ALV-J growth. That is, the upregulation of RRM2 expression by ALV-J infection favors viral replication by interacting with capsid protein P27 and activating Wnt/β-catenin pathway in host cells. Furthermore, the phosphorylation of serine at position 18 of RRM2 was verified to be the important factor regulating the activation of Wnt/β-catenin signaling. This study provides insights for further studies of the molecular mechanism of ALV-J infection.

9-Butyl-Harmol Exerts Antiviral Activity against Newcastle Disease Virus through Targeting GSK-3β and HSP90β

The paramyxoviruses represent a large family of human and animal pathogens that cause significant health and economic burdens worldwide. However, there are no available drugs against the virus. β-carboline alkaloids are a family of naturally occurring and synthetic products with outstanding antiviral activities. Here, we examined the antiviral effect of a series of β-carboline derivatives against several paramyxoviruses, including Newcastle disease virus (NDV), peste des petits ruminants virus (PPRV), and canine distemper virus (CDV). Among these derivatives, 9-butyl-harmol was identified as an effective antiviral agent against these paramyxoviruses. Further, a genome-wide transcriptome analysis in combination with target validation strategies reveals a unique antiviral mechanism of 9-butyl-harmol through the targeting of GSK-3β and HSP90β. On one hand, NDV infection blocks the Wnt/β-catenin pathway to suppress the host immune response. 9-butyl-harmol targeting GSK-3β dramatically activates the Wnt/β-catenin pathway, which results in the boosting of a robust immune response. On the other hand, NDV proliferation depends on the activity of HSP90. The L protein, but not the NP protein or the P protein, is proven to be a client protein of HSP90β, rather than HSP90α. 9-butyl-harmol targeting HSP90β decreases the stability of the NDV L protein. Our findings identify 9-butyl-harmol as a potential antiviral agent, provide mechanistic insights into the antiviral mechanism of 9-butyl-harmol, and illustrate the role of β-catenin and HSP90 during NDV infection. IMPORTANCE Paramyxoviruses cause devastating impacts on health and the economy worldwide. However, there are no suitable drugs with which to counteract the viruses. We determined that 9-butyl-harmol could serve as a potential antiviral agent against paramyxoviruses. Until now, the antiviral mechanism of β-carboline derivatives against RNA viruses has rarely been studied. Here, we found that 9-butyl-harmol exerts dual mechanisms of antiviral action, with its antiviral activities being mediated by two targets: GSK-3β and HSP90β. Correspondingly, the interaction between NDV infection and the Wnt/β-catenin pathway or HSP90 is demonstrated in this study. Taken together, our findings shed light on the development of antiviral agents against paramyxoviruses, based on the β-carboline scaffold. These results present mechanistic insights into the polypharmacology of 9-butyl-harmol. Understanding this mechanism also deepens the host-virus interaction and reveals new drug targets for anti-paramyxoviruses.

Identification of Cell Types and Transcriptome Landscapes of Porcine Epidemic Diarrhea Virus-Infected Porcine Small Intestine Using Single-Cell RNA Sequencing

Swine coronavirus-porcine epidemic diarrhea virus (PEDV) with specific susceptibility to pigs has existed for decades, and recurrent epidemics caused by mutant strains have swept the world again since 2010. In this study, single-cell RNA sequencing was used to perform for the first time, to our knowledge, a systematic analysis of pig jejunum infected with PEDV. Pig intestinal cell types were identified by representative markers and identified a new tuft cell marker, DNAH11. Excepting enterocyte cells, the goblet and tuft cells confirmed susceptibility to PEDV. Enrichment analyses showed that PEDV infection resulted in upregulation of cell apoptosis, junctions, and the MAPK signaling pathway and downregulation of oxidative phosphorylation in intestinal epithelial cell types. The T cell differentiation and IgA production were decreased in T and B cells, respectively. Cytokine gene analyses revealed that PEDV infection downregulated CXCL8, CXCL16, and IL34 in tuft cells and upregulated IL22 in Th17 cells. Further studies found that infection of goblet cells with PEDV decreased the expression of MUC2, as well as other mucin components. Moreover, the antimicrobial peptide REG3G was obviously upregulated through the IL33-STAT3 signaling pathway in enterocyte cells in the PEDV-infected group, and REG3G inhibited the PEDV replication. Finally, enterocyte cells expressed almost all coronavirus entry factors, and PEDV infection caused significant upregulation of the coronavirus receptor ACE2 in enterocyte cells. In summary, this study systematically investigated the responses of different cell types in the jejunum of piglets after PEDV infection, which deepened the understanding of viral pathogenesis.

β-catenin facilitates fowl adenovirus serotype 4 replication through enhancing virus-induced autophagy

β-catenin is a key component of the Wnt/β-catenin signal transduction cascade which is a highly conserved signaling pathway in eukaryotes. Increasing evidence suggests that the Wnt/β-catenin signaling pathway is involved in the infection of many viruses. However, its role in fowl adenovirus serotype 4 (FAdV-4) replication remains unclear. In the present study, we showed that FAdV-4 infection increased the expression of β-catenin and promoted the nuclear translocation of β-catenin. Overexpression of β-catenin and LiCl treatment stimulated the accumulation of β-catenin in the nucleus, and then facilitated FAdV-4 replication. Conversely, repression of β-catenin by inhibitors and siRNA significantly inhibited FAdV-4 replication. Furthermore, inhibition of autophagy by 3-Methyladenine (3-MA) suppressed the FAdV-4 replication, and repression of β-catenin inhibited the FAdV-4-triggered autophagy. In conclusion, the nuclear translocation of β-catenin benefits FAdV-4 replication, and suppression of β-catenin limits FAdV-4 production by inhibiting FAdV-4-induced autophagy. These findings indicated that β-catenin is an important regulator of FAdV-4 replication which can serve as a potential target for anti-FAdV-4 agents.

Identification of WNT4 alternative splicing patterns and effects on proliferation of granulosa cells in goat

Increasing ovulation numbers is one of the most important ways to promote reproduction in mammals, and follicular granulosa cells (GCs) provide the necessary nutrients and microenvironment for oocytes to ovulate. WNT4 has been shown to be a key factor in regulating the proliferation of GCs in mammalian ovarian tissues. Our previous transcriptome sequencing (RNA-seq) results have identified two alternatively spliced products of WNT4;however, little is known about the splicing mechanism and its effect on GC proliferation. In this study, two alternatively spliced products of WNT4, designated WNT4-α and WNT4-β, were identified by cloning and analyzed for their function by bioinformatics. The RT-qPCR and Western blot results showed that the expression of WNT4-α was significantly higher than that of WNT4-β in the ovary tissues and GCs of Yunshang black goats. We therefore hypothesized that WNT4-α was the main isoform affecting the proliferation of goat GCs. Subsequently, goat GC proliferation assays showed that overexpression of WNT4-α significantly promoted GC proliferation, and the opposite was true after WNT4-α inhibition. The expression of marker genes of the Wnt signaling pathway was also examined and WNT4-α was found to affect the proliferation and hormone secretion of goat GCs by regulating the Wnt signaling pathway. In addition, a series of splicing factors were involved in in the alternative splicing; in this study, SRSF6 was found to be involved as a splicing factor in the generation of WNT4 alternative splicing. In summary, WNT4 alternative splicing was mediated by the splicing factor SRSF6, and WNT4-α alternative splicing played an important role in follicle development and had a significant effect on the proliferation of goat GCs. The results of this study provide a theoretical foundation for further understanding the molecular regulatory mechanisms of the WNT4 in follicle development in goats.

Transmissible Gastroenteritis Virus Infection Promotes the Self-Renewal of Porcine Intestinal Stem Cells via Wnt/β-Catenin Pathway

Intestinal stem cells (ISCs) play an important role in tissue repair after injury. A recent report delineates the effect of transmissible gastroenteritis virus (TGEV) infection on the small intestine of recovered pigs. However, the mechanism behind the epithelium regeneration upon TGEV infection remains unclear. To address this, we established a TGEV infection model based on the porcine intestinal organoid monolayer. The results illustrated that the porcine intestinal organoid monolayer was susceptible to TGEV. In addition, the TGEV infection initiated the interferon and inflammatory responses following the loss of absorptive enterocytes and goblet cells. However, TGEV infection did not disturb epithelial integrity but induced the proliferation of ISCs. Furthermore, TGEV infection activated the Wnt/β-catenin pathway by upregulating the accumulation and nuclear translocation of β-catenin, as well as promoting the expression of Wnt target genes, such as C-myc, Cyclin D1, Mmp7, Lgr5, and Sox9, which were associated with the self-renewal of ISCs. Collectively, these data demonstrated that the TGEV infection activated the Wnt/β-catenin pathway to promote the self-renewal of ISCs and resulted in intestinal epithelium regeneration. IMPORTANCE The intestinal epithelium is a physical barrier to enteric viruses and commensal bacteria. It plays an essential role in maintaining the balance between the host and intestinal microenvironment. In addition, intestinal stem cells (ISCs) are responsible for tissue repair after injury. Therefore, prompt self-renewal of intestinal epithelium will facilitate the rebuilding of the physical barrier and maintain gut health. In the manuscript, we found that the transmissible gastroenteritis virus (TGEV) infection did not disturb epithelial integrity but induced the proliferation of ISCs and facilitated epithelium regeneration. Detailed mechanism investigations revealed that the TGEV infection activated the Wnt/β-catenin pathway to promote the self-renewal of ISCs and resulted in intestinal epithelium regeneration. These findings will contribute to understanding the mechanism of intestinal epithelial regeneration and reparation upon viral infection.

The canonical Wnt/β-catenin signaling pathway facilitates pseudorabies virus proliferation and enhances virus-induced autophagy

Pseudorabies virus (PRV) is a swine herpesvirus with a broad host range that causes significant economic losses worldwide. The Wnt/β-catenin signaling pathway is reportedly involved in multiple viruses' proliferation. In this study, we demonstrated that PRV infection significantly activated the Wnt/β-catenin signaling and promoted the nuclear translocation of β-catenin. Applying specific chemical inhibitors (FH535 and iCRT14) caused a remarkable decrease in PRV titers in various cell lines. Knockdown of β-catenin by siRNA also reduced the proliferation of PRV. On the contrary, treatment with lithium chloride (LiCl), an inhibitor of GSK3β, stimulated the Wnt/β-catenin signaling pathway and enhanced the PRV proliferation. Similarly, overexpression of β-catenin promoted PRV proliferation and reversed the antiviral effect of FH535. Moreover, LiCl promoted PRV-induced autophagy, whereas FH535 and iCRT14 showed converse effects. These findings suggest that PRV infection stimulates the canonical Wnt/β-catenin signaling pathway, facilitating PRV proliferation and regulating virus-induced autophagy. These data also provide potential targets for developing antiviral agents against PRV.

A novel amino acid site of N protein could affect the PRRSV-2 replication by regulating the viral RNA transcription

Background

Finding the key amino acid sites that could affect viral biological properties or protein functions has always been a topic of substantial interest in virology. The nucleocapsid (N) protein is one of the principal proteins of the porcine reproductive and respiratory syndrome virus (PRRSV) and plays a vital role in the virus life cycle. The N protein has only 123 or 128 amino acids, some of key amino acid sites which could affect the protein functions or impair the viral biological characteristics have been identified. In this research, our objective was to find out whether there are other novel amino acid sites of the N protein can affect N protein functions or PRRSV-2 replication.

Results

In this study, we found mutated the serine⁷⁸ and serine ⁹⁹of the nucleocapsid (N) protein can reduce the N-induced expression of IL-10 mRNA; Then, by using reverse genetics system, we constructed and rescued the mutant viruses, namely, A78 and A99.The IFA result proved that the mutations did not affect the rescue of the PRRSV-2. However, the results of the multistep growth kinetics and qPCR assays indicated that, compared with the viral replication ability, the titres and gRNA levels of A78 were significantly decreased compared with the wild-type. Further study showed that a single amino acid change from serine to alanine at position 78 of the N protein could abrogates the level of viral genomic and subgenomic RNAs. It means the mutation could significant decrease the viral replication efficiency in vitro.

Conclusions

Our results suggest that the serine⁷⁸ of N protein is a key site which could affect the N protein function and PRRSV replication ability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03274-9.

Regulation of Avian Leukosis Virus Subgroup J Replication by Wnt/β-Catenin Signaling Pathway

Wnt/β-catenin signaling is a highly conserved pathway related to a variety of biological processes in different cells. The regulation of replication of various viruses by Wnt/β-catenin signaling pathway has been reported. However, the interaction between the Wnt/β-catenin pathway and avian leukosis virus is unknown. In the present study, we investigated the effect of modulating the Wnt/β-catenin pathway during avian leukosis virus subgroup J (ALV-J) infection. The activation of the Wnt/β-catenin pathway by GSK-3 inhibitor increased ALV-J mRNA, viral protein expression, and virus production in CEF cells. This increase was suppressed by iCRT14, one of the specific inhibitors of the Wnt/β-catenin signaling pathway. Moreover, treatment with iCRT14 reduced virus titer and viral gene expression significantly in CEF and LMH cells in a dose-dependent manner. Inhibition Wnt/β-catenin signaling pathway by knockdown of β-catenin reduced virus proliferation in CEF cells also. Collectively, these results suggested that the status of Wnt/β-catenin signaling pathway modulated ALV-J replication. These studies extend our understanding of the role of Wnt/β-catenin signaling pathway in ALV-J replication and make a new contribution to understanding the virus–host interactions of avian leukosis virus.

Reappraisal of PRRS Immune Control Strategies: The Way Forward

The control of porcine reproductive and respiratory syndrome (PRRS) is still a major issue worldwide in the pig farming sector. Despite extensive research efforts and the practical experience gained so far, the syndrome still severely affects farmed pigs worldwide and challenges established beliefs in veterinary virology and immunology. The clinical and economic repercussions of PRRS are based on concomitant, additive features of the virus pathogenicity, host susceptibility, and the influence of environmental, microbial, and non-microbial stressors. This makes a case for integrated, multi-disciplinary research efforts, in which the three types of contributing factors are critically evaluated toward the development of successful disease control strategies. These efforts could be significantly eased by the definition of reliable markers of disease risk and virus pathogenicity. As for the host's susceptibility to PRRSV infection and disease onset, the roles of both the innate and adaptive immune responses are still ill-defined. In particular, the overt discrepancy between passive and active immunity and the uncertain role of adaptive immunity vis-à-vis established PRRSV infection should prompt the scientific community to develop novel research schemes, in which apparently divergent and contradictory findings could be reconciled and eventually brought into a satisfactory conceptual framework.

The significance of homeodomain transcription factor 2 in colon cancer cells

Background

Colon cancer is a serious malignant tumor. It has been reported that paired-like homeodomain transcription factor 2 (PITX2) can promote the progression of several types of cancer via regulating the Wnt/β-catenin pathway. It has also been demonstrated that high levels of long non-coding RNA (lncRNA) gastric carcinoma high expressed transcript 1 (GHET1) can also promote the development of cervical cancer via activating the Wnt/β-catenin pathway. However, whether PITX2 can affect the development of colon cancer via regulating the expression of lncRNA GHET1 remains unclear.

Results

The results demonstrated that PITX2 knockdown attenuated the proliferation, migration and invasion abilities of colon cancer cells. Additionally, PITX2 promoted the expression of lncRNA GHET1 via binding to its promoter. Overexpression of lncRNA GHET1 induced the expression of Wnt/β-catenin signaling-related proteins, cyclin D1, c-Myc and MMP-7. Furthermore, lncRNA GHET1 overexpression abrogated the PITX2 silencing-mediated decreased proliferation, migration and invasion abilities of colon cancer cells.

Conclusion

The findings of the present study suggested that PITX2 could enhance the proliferation, migration and invasion abilities of colon cancer cells via upregulating lncRNA GHET1 and activating the Wnt/β-catenin pathway.