Seneca Valley Virus 3Cpro Mediates Cleavage and Redistribution of Nucleolin To Facilitate Viral Replication

Seneca Valley virus (SVV) is a recently discovered pathogen that poses a significant threat to the global pig industry. It has been shown that many viruses are reliant on nucleocytoplasmic trafficking of nucleolin (NCL) for their own replication. Here, we demonstrate that NCL, a critical protein component of the nucleolus, is cleaved and translocated out of the nucleoli following SVV infection. Furthermore, our data suggest that SVV 3C protease (3Cpro) is responsible for this cleavage and subsequent delocalization from the nucleoli, and that inactivation of this protease activity abolished this cleavage and translocation. SVV 3Cpro cleaved NCL at residue Q545, and the cleavage fragment (aa 1 to 545) facilitated viral replication, which was similar to the activities described for full-length NCL. Small interfering RNA-mediated knockdown indicated that NCL is required for efficient viral replication and viral protein expression. In contrast, lentivirus-mediated overexpression of NCL significantly enhanced viral replication. Taken together, these results indicate that SVV 3Cpro targets NCL for its cleavage and redistribution, which contributes to efficient viral replication, thereby emphasizing the potential target of antiviral strategies for the control of SVV infection. IMPORTANCE The nucleolus is a subnuclear cellular compartment, and nucleolin (NCL) resides predominantly in the nucleolus. NCL participates in viral replication, translation, internalization, and also serves as a receptor for virus entry. The interaction between NCL and SVV is still unknown. Here, we demonstrate that SVV 3Cpro targets NCL for its cleavage and nucleocytoplasmic transportation, which contributes to efficient viral replication. Our results reveal novel function of SVV 3Cpro and provide further insight into the mechanisms by which SVV utilizes nucleoli for efficient replication.

Andrographolide and Deoxyandrographolide Inhibit Protease and IFN-Antagonist Activities of Foot-and-Mouth Disease Virus 3Cpro

Foot-and mouth-disease (FMD) caused by the FMD virus (FMDV) is highly contagious and negatively affects livestock worldwide. The control of the disease requires a combination of measures, including vaccination; however, there is no specific treatment available. Several studies have shown that plant-derived products with antiviral properties were effective on viral diseases. Herein, antiviral activities of andrographolide (AGL), deoxyandrographolide (DAG), and neoandrographolide (NEO) against FMDV serotype A were investigated using an in vitro cell-based assay. The results showed that AGL and DAG inhibited FMDV in BHK-21 cells. The inhibitory effects of AGL and DAG were evaluated by RT-qPCR and exhibited EC50 values of 52.18 ± 0.01 µM (SI = 2.23) and 36.47 ± 0.07 µM (SI = 9.22), respectively. The intracellular protease assay revealed that AGL and DAG inhibited FMDV 3Cpro with IC50 of 67.43 ± 0.81 and 25.58 ± 1.41 µM, respectively. Additionally, AGL and DAG significantly interfered with interferon (IFN) antagonist activity of the 3Cpro by derepressing interferon-stimulating gene (ISGs) expression. The molecular docking confirmed that the andrographolides preferentially interacted with the 3Cpro active site. However, NEO had no antiviral effect in any of the assays. Conclusively, AGL and DAG inhibited FMDV serotype A by interacting with the 3Cpro and hindered its protease and IFN antagonist activities.

Seneca Valley virus 3Cpro antagonizes type I interferon response by targeting STAT1-STAT2-IRF9 and KPNA1 signals

IMPORTANCE

Type I interferon (IFN) signaling plays a principal role in host innate immune responses against invading viruses. Viruses have evolved diverse mechanisms that target the Janus kinase-signal transducer and activator of transcription (STAT) signaling pathway to modulate IFN response negatively. Seneca Valley virus (SVV), an emerging porcine picornavirus, has received great interest recently because it poses a great threat to the global pork industry. However, the molecular mechanism by which SVV evades host innate immunity remains incompletely clear. Our results revealed that SVV proteinase (3Cpro) antagonizes IFN signaling by degrading STAT1, STAT2, and IRF9, and cleaving STAT2 to escape host immunity. SVV 3Cpro also degrades karyopherin 1 to block IFN-stimulated gene factor 3 nuclear translocation. Our results reveal a novel molecular mechanism by which SVV 3Cpro antagonizes the type I IFN response pathway by targeting STAT1-STAT2-IRF9 and karyopherin α1 signals, which has important implications for our understanding of SVV-evaded host innate immune responses.

Foot-and-mouth disease virus (FMDV) negatively regulates ZFP36 protein expression to alleviate its antiviral activity

Zinc finger protein 36 (ZFP36) is a key regulator of inflammatory and cytokine production. However, the interplay between swine zinc-finger protein 36 (sZFP36) and foot-and-mouth disease virus (FMDV) has not yet been reported. Here, we demonstrate that overexpression of sZFP36 restricted FMDV replication, while the knockdown of sZFP36 facilitated FMDV replication. To subvert the antagonism of sZFP36, FMDV decreased sZFP36 protein expression through its non-structural protein 3C protease (3Cpro). Our results also suggested that 3Cpro-mediated sZFP36 degradation was dependent on its protease activity. Further investigation revealed that both N-terminal and C-terminal-sZFP36 could be degraded by FMDV and FMDV 3Cpro. In addition, both N-terminal and C-terminal-sZFP36 decreased FMDV replication. Moreover, sZFP36 promotes the degradation of FMDV structural proteins VP3 and VP4 via the CCCH-type zinc finger and NES domains of sZFP36. Together, our results confirm that sZFP36 is a host restriction factor that negatively regulates FMDV replication.IMPORTANCEFoot-and-mouth disease (FMD) is an infectious disease of animals caused by the pathogen foot-and-mouth disease virus (FMDV). FMD is difficult to prevent and control because there is no cross-protection between its serotypes. Thus, we designed this study to investigate virus-host interactions. We first demonstrate that swine zinc-finger protein 36 (sZFP36) impaired FMDV structural proteins VP3 and VP4 to suppress viral replication. To subvert the antagonism of sZFP36, FMDV and FMDV 3Cpro downregulate sZFP36 expression to facilitate FMDV replication. Taken together, the present study reveals a previously unrecognized antiviral mechanism for ZFP36 and elucidates the role of FMDV in counteracting host antiviral activity.