Construction and Transcriptomic Study of Chicken IFNAR1-Knockout Cell Line Reveals the Essential Roles of Cell Growth- and Apoptosis-Related Pathways in Duck Tembusu Virus Infection

Duck Tembusu virus infection activates the MKK3/6-p38 MAPK signaling pathway to promote virus replication

Duck Tembusu virus (DTMUV) infection poses a serious threat to ducks, chickens, and geese, causing a range of detrimental effects, including reduced egg production, growth retardation, and even death. These consequences lead to substantial economic losses for the Chinese poultry industry. Although it is established that various viral infections can trigger activation of the p38 mitogen-activated protein kinase (MAPK) signaling pathway, the precise role and mechanisms underlying p38 MAPK activation in DTMUV infection remain poorly understood. To address this knowledge gap, we conducted a study to investigate whether the replication of DTMUV necessitates the activation of p38 MAPK. We found that DTMUV infection stimulates activation of the MKK3/6-p38 MAPK pathway, and the activation of p38 MAPK increases with viral titer. Subsequently, the use of the small molecule inhibitor SB203580 significantly reduced DTMUV replication by inhibiting p38 MAPK activity. Furthermore, downregulation of p38 MAPK protein expression by siRNA also inhibited DTMUV replication, whereas transient transfection of p38 MAPK protein promoted DTMUV replication. Interestingly, we found that the DTMUV capsid protein activates p38 MAPK, and there is interaction between DTMUV capsid and p38 MAPK. Finally, we found that DTMUV infection induces elevated mRNA expression of IFN-α, IFN-β, IFN-γ, IL-1β, IL-6, and IL-12, which is associated with p38 MAPK activity. These results indicated that virus hijacking of p38 activation is a crucial event for DTMUV replication, and that pharmacological blockade of p38 activation represents a potential anti-DTMUV strategy.

HELZ2: a new, interferon-regulated, human 3'-5' exoribonuclease of the RNB family is expressed from a non-canonical initiation codon

Proteins containing a RNB domain, originally identified in Escherichia coli RNase II, are widely present throughout the tree of life. Many RNB proteins have 3'-5' exoribonucleolytic activity but some have lost catalytic activity during evolution. Database searches identified a new RNB domain-containing protein in human: HELZ2. Analysis of genomic and expression data combined with evolutionary information suggested that the human HELZ2 protein is produced from an unforeseen non-canonical initiation codon in Hominidae. This unusual property was confirmed experimentally, extending the human protein by 247 residues. Human HELZ2 was further shown to be an active ribonuclease despite the substitution of a key residue in its catalytic center. HELZ2 RNase activity is lost in cells from some cancer patients as a result of somatic mutations. HELZ2 harbors also two RNA helicase domains and several zinc fingers and its expression is induced by interferon treatment. We demonstrate that HELZ2 is able to degrade structured RNAs through the coordinated ATP-dependent displacement of duplex RNA mediated by its RNA helicase domains and its 3'-5' ribonucleolytic action. The expression characteristics and biochemical properties of HELZ2 support a role for this factor in response to viruses and/or mobile elements.

Interferon alpha and beta receptor 1 knockout in human embryonic kidney 293 cells enhances the production efficiency of proteins or adenoviral vectors related to type I interferons

Human embryonic kidney (HEK) 293 cells are widely used in protein and viral vector production owing to their high transfection efficiency, rapid growth, and suspension growth capability. Given their antiviral, anticancer, and immune-enhancing effects, type I interferons (IFNs) have been used to prevent and treat human and animal diseases. However, the binding of type I IFNs to the IFN-α and-β receptor (IFNAR) stimulates the expression of IFN-stimulated genes (ISGs). This phenomenon induces an antiviral state and promotes apoptosis in cells, thereby impeding protein or viral vector production. In this study, we generated an IFNAR subtype 1 knockout (KO) HEK 293 suspension (IFNAR-KO) cell line by using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 nuclease (Cas9) technology. Upon treatment with human IFN-α, the IFNAR-KO cells showed a constant expression of ISGs, including 2'-5'-oligoadenylate synthetase 1 (OAS1), myxovirus resistance 1 (Mx1), protein kinase RNA-activated (PKR), and IFN-induced transmembrane protein 1 (IFITM1), when compared with the wild-type HEK 293 (WT) cells, wherein the ISGs were significantly upregulated. As a result, the titer of recombinant adenovirus expressing porcine IFN-α was significantly higher in the IFNAR-KO cells than in the WT cells. Furthermore, the IFNAR-KO cells continuously produced higher amounts of IFN-α protein than the WT cells. Thus, the CRISPR-Cas9-mediated IFNAR1 KO cell line can improve the production efficiency of proteins or viral vectors related to IFNs. The novel cell line may be used for producing vaccines and elucidating the type I IFN signaling pathway in cells.