Autophagy induced by avian reovirus enhances viral replication in chickens at the early stage of infection.

BACKGROUND: Avian reovirus (ARV) is an important pathogen that can cause serious disease in poultry. Though several in vitro studies revealed some molecular mechanisms that are responsible for ARV-induced autophagy, it is still largely unknown how ARV manipulates autophagy to promote its own propagation. RESULTS: In this study, we demonstrated that ARV infection triggered autophagy in chicken tissues, evident from the enhancement of LC3-I/-II conversion and the appearance of abundant autophagosomes. Moreover, viral replication and the expression of IL-1ß were coupled with the process of ARV-induced autophagy in the early stage of infection. Furthermore, regulation of autophagy affected the accumulation of LC3-II, the production of ARV and the expression of IL-1ß. CONCLUSIONS: Altogether, our data suggest that ARV induces autophagy, which benefits its replication and dissemination in chicken tissues at the early infection stage.

Transcriptome analysis of avian reovirus-mediated changes in gene expression of normal chicken fibroblast DF-1 cells.

BACKGROUND: Avian reovirus (ARV) is an important poultry pathogen that can cause immunosuppression. In this study, RNA-Seq technology was applied to investigate the transcriptome-wide changes of DF-1 cells upon ARV infection at the middle stage. RESULTS: Total RNA of ARV-infected or mock-infected samples at 10 and 18 h post infection (hpi) was extracted to build RNA-Seq datasets. Analysis of the sequencing data revealed that the expressions of numerous genes were altered, and a panel of differentially expressed genes were confirmed with RT-qPCR. At 10 hpi, 104 genes were down-regulated and 64 were up-regulated, while the expressions of 47 genes were increased and only one was down-regulated, which may play a role in retinoic acid biosynthesis, at 18 hpi in the ARV-infected cells. The similar profiles of up-regulated genes between the two groups of infected cells suggest that ARV infection activated a prolonged antiviral response of host cells. Alternative splicing analysis found no significantly changed events altered by ARV infection. CONCLUSIONS: Overall, the differential expression profile presented in this study can be used to expand our understanding of the comprehensive interactions between ARV and the host cells, and may be helpful for us to reveal the pathogenic mechanism on the molecular level.

The papain-like protease of avian infectious bronchitis virus has deubiquitinating activity.

Coronavirus papain-like proteases (PLPs) can act as proteases that process virus-encoded large replicase polyproteins and also as deubiquitinating (DUB) enzymes. Like the PLPs of other coronaviruses (CoVs), the avian infectious bronchitis virus (IBV) PLP catalyzes proteolysis of Gly-Gly dipeptide bonds to release mature cleavage products. However, the other functions of the IBV PLP are not well understood. In this study, we found that IBV exhibits strong global DUB activity with significant reductions of the levels of ubiquitin (Ub)-, K48-, and K63-conjugated proteins. The DUB activity exhibited a clear time dependence, with stronger DUB activity in the early stage of viral infection. Furthermore, the IBV replicase-encoded PLP, including the downstream transmembrane (TM) domain, is a DUB enzyme and dramatically reduced the level of Ub-conjugated proteins, while processing both K48- and K63-linked polyubiquitin chains. By contrast, PLP did not cause any reduction of haemagglutinin (HA)-Ub-conjugated proteins. In addition, mutations of the catalytic residues of PLP-TM, Cys1274Ser and His1437Lys, reduced DUB activity against Ub-, K48- and K63- conjugated proteins, indicating that the DUB activity of the PLP-TM wild-type protein is not completely dependent on its catalytic activity. Overall, these results demonstrate that the IBV-encoded PLP-TM functions as a DUB enzyme and suggest that IBV may interfere with the activation of host antiviral signaling pathway by degrading polyubiquitin-associated proteins.

Avian infectious bronchitis virus disrupts the melanoma differentiation associated gene 5 (MDA5) signaling pathway by cleavage of the adaptor protein MAVS.

BACKGROUND: Melanoma differentiation associated gene 5 (MDA5) and retinoic acid-inducible gene-I (RIG-I) selectively sense cytoplasmic viral RNA to induce an antiviral immune response. Infectious bronchitis virus (IBV) is one of the most important infectious agents in chickens, and in chicken cells, it can be recognized by MDA5 to activate interferon production. RIG-I is considered to be absent in chickens. However, the absence of RIG-I in chickens raises the question of whether this protein influences the antiviral immune response against IBV infection. RESULTS: Here, we showed that chicken cells transfected with domestic goose RIG-I (dgRIG-I) exhibited increased IFN-ß activity after IBV infection. We also found that IBV can cleave MAVS, an adaptor protein downstream of RIG-I and MDA5 that acts as a platform for antiviral innate immunity at an early stage of infection. CONCLUSIONS: Although chicken MDA5 (chMDA5) is functionally active during IBV infection, the absence of RIG-I may increase the susceptibility of chickens to IBV infection, and IBV may disrupt the activation of the host antiviral response through the cleavage of MAVS.

The Distribution of 18 Enterotoxin and Enterotoxin-Like Genes in Staphylococcus aureus Strains from Different Sources in East China.

The distribution of 18 staphylococcal enterotoxin (SE) or SE-like (SEl) genes in Staphylococcus aureus strains from different sources in east China was investigated. Among all 496 S. aureus strains, 291 strains carried one or more SE genes. The more frequently occurred genes were sea, seb, seg, selk, sell, selm, selo, and seq; the less frequent occurred genes were sec, selj, and ser. The classic SE genes and the enterotoxin gene cluster (egc) (seg, sei, selm, seln, selo, and/or selu) accounted for 25.67% and 61.68% of all detected genes, respectively. There were three gene clusters (egc, sea-sek-seq, and sed-sej-ser), of which the egc cluster was the important one that could generate novel complexes, and the sea-sek-seq cluster was a close relative to the hospital-acquired methicillin-resistant S. aureus. The SE gene distributions were different among strains of different sources and formed diverse toxin gene profiles. The human- and foodborne-origin strains harbored classic and novel SE and SEl genes, whereas animal-origin strains harbored egc and other novel SE and SEl genes mainly. The foodborne- and human-origin strains were the main dangerous factors of classic staphylococcal foodborne poisoning, whereas the strains (especially from animals) that carried egc and other novel genes mainly should be new potential dangerous factors for food safety.

Generation and evaluation of a vaccine candidate of attenuated and heat-resistant genotype VIII Newcastle disease virus.

Newcastle disease, which is a highly contagious and fatal disease caused by the Newcastle disease virus (NDV), has harmed the poultry industry for decades. The administration of effective vaccines can control most outbreaks and epidemics of Newcastle disease in the world. However, vaccination failures of live attenuated vaccines becasue of storage and transportation problems have been reported. Hence, thermostable live vaccine strains, such as V4 and I-2 strains, are being used and welcomed in tropical regions such as Africa and Southeast Asia. In this study, a thermostable, attenuated vaccine candidate strain NDV/rHR09 was generated using the genotype VIII heat-resistant virulent NDV strain HR09 by the reverse genetics system. The results of the determination of the mean death time and intracerebral pathogenicity index indicated that NDV/rHR09 is lentogenic even after 15 serial passages in embryonated chicken eggs. The thermostability assessment showed that the NDV/rHR09 strain exhibited hemagglutination activity and infectivity when exposed to 56°C for 60 min. Compared with the commercially available La Sota and V4 vaccines, the NDV/rHR09 induced higher antibody titers in specific pathogen-free chickens. In addition, NDV/rHR09 conferred complete protection against virulent genotype VII NDV challenge and virus shedding from vaccinated chickens. These results suggest that NDV/rHR09 is a promising thermostable vaccine candidate strain.