Newcastle disease virus induces clathrin-mediated endocytosis to establish infection through the activation of PI3K/AKT signaling pathway by VEGFR2.

The phosphatidyl-inositol 3-kinase/serine-threonine kinase (PI3K/ AKT) signaling pathway constitutes a classical phosphorylation cascade that integrates tyrosine, lipid, and serine acid-threonine phosphorylation, affecting cell function. The pathway is vulnerable to viral infection. Newcastle disease virus (NDV) poses a significant threat to the global poultry industry; however, its mechanism of early viral cell invasion and pathogenesis remain unclear. Previous in vivo and in vitro studies have shown that NDV infection activates PI3K/AKT signaling; however, it remains unclear whether NDV establishes infection through endocytosis regulated by this pathway. This study aimed to examine whether different genotypes of NDV strains could activate the PI3K/AKT signaling pathway within 2 h of in vitro infection. This activation, which relies on PI3K phosphorylation, remains unaffected by the phosphorylation-phosphatase and tensin homolog/phosphatase and tensin homolog (p-PTEN/PTEN) signaling pathway. Moreover, inhibition of PI3K activity impedes NDV replication. Additionally, interfering with the PI3K regulatory subunit p85 has no significant effect on NDV replication. Conversely, the tyrosine kinase activity upstream of PI3K can influence AKT activation and viral replication, particularly through vascular endothelial growth factor receptor 2 (VEGFR2). Additionally, NDV F protein primarily mediates PI3K and AKT phosphorylation to activate the PI3K/AKT signaling pathway. NDV F and VEGFR2 proteins, along with the PI3K p85α subunit, interact and co-localize at the cell membrane. NDV-induced PI3K/AKT signaling pathway activation impacts clathrin-mediated endocytosis, with VEGFR2 playing a pivotal role. In conclusion, this study shows that NDV infection is established early through F protein binding to VEGFR2, activating the PI3K/AKT signaling pathway and inducing clathrin-mediated endocytosis, supporting infection prevention and control measures. IMPORTANCE: Newcastle disease virus (NDV) is a threat to the global poultry industry; however, the mechanisms of NDV infection remain unclear. NDV affects the phosphatidyl-inositol 3-kinase/serine-threonine kinase (PI3K/ AKT) signaling pathway, requiring endocytosis for successful infection. Based on previous studies, we identified a close correlation between NDV infection and replication and the PI3K/AKT signaling pathway activity. This study examined the molecular mechanisms through which NDV activates the PI3K/AKT signaling pathway to regulate endocytosis and facilitate infection. This study showed that early-stage in vitro NDV infection activated the PI3K/AKT signaling pathway, enhancing clathrin-mediated endocytosis, crucial for infection onset. Notably, this process involves the interaction between NDV F protein and the vascular endothelial growth factor receptor 2 tyrosine kinase, leading to the subsequent binding and phosphorylation of the PI3K p85α regulatory subunit. This activation primes PI3K, initiating a cascade that promotes clathrin-mediated endocytosis. Our findings elucidate how NDV capitalizes on the PI3K/AKT signaling pathway to establish infection through endocytosis.

Newcastle disease virus nucleocapsid protein mediates the degradation of 14-3-3ε to antagonize the interferon response and promote viral replication.

Newcastle disease virus (NDV) is responsible for outbreaks that pose a threat to the global poultry industry. NDV triggers an interferon (IFN) response in the host upon infection. However, it also employs mechanisms that counteract this response. One important component in IFN-related signaling pathways is 14-3-3ε, which is known to interact with retinoic acid-inducible gene I (RIG-I) and mitochondrial antiviral signaling protein (MAVS). The relationship between 14 and 3-3ε and NDV infection has not been previously explored; therefore, this study aimed to investigate this relationship in vivo and in vitro using overexpressed and knockdown 14-3-3ε experiments, along with co-immunoprecipitation analysis. We found that NDV infection led to the degradation of 14-3-3ε. Furthermore, 14-3-3ε inhibited the replication of NDV, suggesting that NDV may enhance its own replication by promoting the degradation of 14-3-3ε during infection. The study revealed that 14-3-3ε is degraded by lysosomes and the viral protein nucleocapsid protein (NP) of NDV induces this degradation. It was also observed that 14-3-3ε is involved in activating the IFN pathway during NDV infection and mediates the binding of MDA5 to MAVS. Our study reveals that NDV NP mediates the entry of 14-3-3ε into lysosomes and facilitates its degradation. These findings contribute to the existing knowledge on the molecular mechanisms employed by NDV to counteract the IFN response and enhance its own replication.

NDV-induced autophagy enhances inflammation through NLRP3/Caspase-1 inflammasomes and the p38/MAPK pathway.

Newcastle disease (ND), caused by the Newcastle disease virus (NDV), is a highly virulent infectious disease of poultry. Virulent NDV can cause severe autophagy and inflammation in host cells. While studies have shown a mutual regulatory relationship between autophagy and inflammation, this relationship in NDV infection remains unclear. This study confirmed that NDV infection could trigger autophagy in DF-1 cells to promote cytopathic and viral replication. NDV-induced autophagy was positively correlated with the mRNA levels of inflammatory cytokines such as IL-1ß, IL-8, IL-18, CCL-5, and TNF-α, suggesting that NDV-induced autophagy promotes the expression of inflammatory cytokines. Further investigation demonstrated that NLRP3 protein expression, Caspase-1 activity, and p38 phosphorylation level positively correlated with autophagy, suggesting that NDV-induced autophagy could promote the expression of inflammatory cytokines through NLRP3/Caspase-1 inflammasomes and p38/MAPK pathway. In addition, NDV infection also triggered mitochondrial damage and mitophagy in DF-1 cells, but did not result in a large leakage of reactive oxygen species (ROS) and mitochondrial DNA (mtDNA), indicating that mitochondrial damage and mitophagy do not contribute to the inflammation response during NDV infection.

Newcastle disease virus activates methylation-related enzymes to reprogram m6A methylation in infected cells.

Newcastle disease virus (NDV) is a paramyxovirus with high incidence and transmissibility in birds and is currently being developed for cancer therapy. N6-methyladenosine (m6A) is a common epigenetic modification of RNA. In this study, we aimed to determine whether this modification plays an important role in NDV infection. We found that methylation-related enzymes were activated in NDV-infected cells, and the abundance of m6A notably increased in vivo and in vitro. Further functional experiments showed that m6A methylation negatively regulates NDV infection. Methylated RNA immunoprecipitation sequencing revealed that the m6A-methylated peaks on different functional components of host genes shifted, underwent reprogramming, and were primarily enriched in the coding sequence after NDV infection. The differentially modified genes were mainly enriched in cellular components, as well as autophagy and ubiquitination-mediated proteolysis signaling pathways. Association analysis of RNA sequencing results showed changes in m6A regulated mRNA transcription and revealed that YTHDC1 is a methylation-related enzyme with important catalytic and recognition roles during NDV infection. Additionally, m6A-methylated peaks were detected in the NDV genome, which may be regulated by methylation-related enzymes in the host, subsequently affecting viral replication. Comprehensive analysis of the m6A expression profile after NDV infection indicated that NDV may cause reprogramming of m6A methylation and that m6A plays important roles during infection. Overall, these findings provide insights into the epigenetic etiology and pathogenesis of NDV.

RNA sequencing reveals CircRNA expression profiles in chicken embryo fibroblasts infected with velogenic Newcastle disease virus.

Introduction: Newcastle disease virus (NDV) is an important avian pathogen prevalent worldwide; it has an extensive host range and seriously harms the poultry industry. Velogenic NDV strains exhibit high pathogenicity and mortality in chickens. Circular RNAs (circRNAs) are among the most abundant and conserved eukaryotic transcripts. They are part of the innate immunity and antiviral response. However, the relationship between circRNAs and NDV infection is unclear. Methods: In this study, we used circRNA transcriptome sequencing to analyze the differences in circRNA expression profiles post velogenic NDV infection in chicken embryo fibroblasts (CEFs). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to reveal significant enrichment of differentially expressed (DE) circRNAs. The circRNA- miRNA-mRNA interaction networks were further predicted. Moreover, circ-EZH2 was selected to determine its effect on NDV infection in CEFs. Results: NDV infection altered circRNA expression profiles in CEFs, and 86 significantly DE circRNAs were identified. GO and KEGG enrichment analyses revealed significant enrichment of DE circRNAs for metabolism-related pathways, such as lysine degradation, glutaminergic synapse, and alanine, aspartic-acid, and glutamic-acid metabolism. The circRNA- miRNA-mRNA interaction networks further demonstrated that CEFs might combat NDV infection by regulating metabolism through circRNA-targeted mRNAs and miRNAs. Furthermore, we verified that circ-EZH2 overexpression and knockdown inhibited and promoted NDV replication, respectively, indicating that circRNAs are involved in NDV replication. Conclusions: These results demonstrate that CEFs exert antiviral responses by forming circRNAs, offering new insights into the mechanisms underlying NDV-host interactions.

Phylodynamic analyses of class I Newcastle disease virus isolated in China.

Newcastle disease virus (NDV), the pathogen of Newcastle disease, has caused significant losses to the poultry industry worldwide. However, owing to its avirulence, class I NDVs have not been studied as much as class II NDVs. We aimed to epidemiologically monitor the spread of class I NDVs in China. We isolated 104 class I NDV strains from poultry in live poultry markets (LPMs) of Guangdong Province, south China, between January 2016 and December 2018. Genetic analysis revealed that all 104 isolates and most of the strains isolated from China were clustered into genotype 1.1.2 of class I NDVs. Bayesian analysis revealed that, although the United States may be the source, east and south China may be the epicentres of class I NDVs in China. In addition, in China, class I NDVs are presumably transmitted by chickens and domestic ducks as the virus is mostly prevalent in these birds. These novel findings demonstrated that class I NDVs are prevalent in south China, and it is important to perform routine surveillance and limit the numbers of different birds in different areas of LPMs to decrease the risk of intra- and interspecies transmission of NDVs.

Insights into Genomic Epidemiology, Evolution, and Transmission Dynamics of Genotype VII of Class II Newcastle Disease Virus in China.

Newcastle disease virus (NDV) is distributed worldwide and has caused significant losses to the poultry industry. Almost all virulent NDV strains belong to class II, among which genotype VII is the predominant genotype in China. However, the molecular evolution and phylodynamics of class II genotype VII NDV strains in China remained largely unknown. In this study, we identified 13 virulent NDV including 11 genotype VII strains and 2 genotype IX strains, from clinical samples during 1997 to 2019. Combined NDV sequences submitted to GenBank, we investigate evolution, and transmission dynamics of class II NDVs in China, especially genotype VII strains. Our results revealed that East and South China have the most genotypic diversity of class II NDV, and East China might be the origin of genotype VII NDVs in China. In addition, genotype VII NDVs in China are presumably transmitted by chickens, as the virus was most prevalent in chickens. Furthermore, codon usage analysis revealed that the F genes of genotype VII NDVs have stronger adaptation in chickens, and six amino acids in this gene are found under positive selection via selection model analysis. Collectively, our results revealed the genetic diversity and evolutionary dynamics of genotype VII NDVs in China, providing important insights into the epidemiology of these viruses in China.