Seneca Valley Virus 3Cpro Substrate Optimization Yields Efficient Substrates for Use in Peptide-Prodrug Therapy

The Seneca Valley virus 3C protease cleaves DCP1A to attenuate its antiviral effects

Seneca Valley virus (SVV), a new member of Picornaviridae, causes idiopathic vesicular symptoms in pregnant sows and acute death in neonatal piglets, considerably damaging the swine industry. The viral protease 3C (3Cpro) cleaves host immune-related molecules to create a favorable environment for viral replication. In this study, we found that mRNA decapping enzyme 1A (DCP1A) is a novel antiviral effector against SVV infection that targets 3D viral RNA-dependent RNA polymerase for OPTN-mediated autophagic degradation. To counteract this effect, SVV 3Cpro targets DCP1A for cleavage at glutamine 343 (Q343), resulting in the cleaved products DCP1A (1-343) and DCP1A (344-580), which lose the ability to restrict SVV replication. In contrast, the 3C cleavage-resistant DCP1A-Q343A mutant exhibited stronger antiviral effects than the wild-type DCP1A. Additionally, the degradation of the viral 3D protein targeted by DCP1A was abolished after its cleavage by SVV 3Cpro. In conclusion, our study demonstrated that SVV 3Cpro is a pivotal ISG antagonist that cleaves DCP1A. These results offer novel insight into how viruses evade host immunity.

Seneca Valley Virus Induces DHX30 Cleavage to Antagonize Its Antiviral Effects

Seneca Valley virus (SVV) is a new pathogen associated with porcine idiopathic vesicular disease (PIVD) in recent years. However, SVV-host interaction is still unclear. In this study, through LC-MS/MS analysis and coimmunoprecipitation analysis, DHX30 was identified as a 3C^pro-interacting protein. 3C^pro mediated the cleavage of DHX30 at a specific site, which depends on its protease activity. Further study showed that DHX30 was an intrinsic antiviral factor against SVV that was dependent on its helicase activity. DHX30 functioned as a viral-RNA binding protein that inhibited SVV replication at the early stage of viral infection. RIP-seq showed comparatively higher coverage depth at SVV 5'UTR, but the distribution across SVV RNA suggested that the interaction had low specificity. DHX30 expression strongly inhibited double-stranded RNA (dsRNA) production. Interestingly, DHX30 was determined to interact with 3D in an SVV RNA-dependent manner. Thus, DHX30 negatively regulated SVV propagation by blocking viral RNA synthesis, presumably by participating in the viral replication complex. IMPORTANCE DHX30, an RNA helicase, is identified as a 3C^pro-interacting protein regulating Seneca Valley virus (SVV) replication dependent on its helicase activity. DHX30 functioned as a viral-RNA binding protein that inhibited SVV replication at the early stage of virus infection. DHX30 expression strongly inhibited double-stranded RNA (dsRNA) production. In addition, 3C^pro abolished DHX30 antiviral effects by inducing DHX30 cleavage. Thus, DHX30 is an intrinsic antiviral factor that inhibits SVV replication.

2B and 3C Proteins of Senecavirus A Antagonize the Antiviral Activity of DDX21 via the Caspase-Dependent Degradation of DDX21

Senecavirus A (SVA), also known as Seneca Valley virus, is a recently discovered picornavirus that can cause swine vesicular disease, posing a great threat to the global swine industry. It can replicate efficiently in cells, but the molecular mechanism remains poorly understood. This study determined the host’s differentially expressed proteins (DEPs) during SVA infection using dimethyl labeling based on quantitative proteomics. Among the DE proteins, DDX21, a member of the DEAD (Asp-Glu-Ala-Asp)-box RNA helicase (DDX) family, was downregulated and demonstrated inhibiting SVA replication by overexpression and knockdown experiment. To antagonize this antiviral effect of DDX21, SVA infection induces the degradation of DDX21 by 2B and 3C proteins. The Co-IP results showed that 2B and 3C did not interact with DDX21, suggesting that the degradation of DDX21 did not depend on their interaction. Moreover, the 3C protein protease activity was necessary for the degradation of DDX21. Furthermore, our study revealed that the degradation of DDX21 by 2B and 3C proteins of SVA was achieved through the caspase pathway. These findings suggest that DDX21 was an effective antiviral factor for suppressing SVA infection and that SVA antagonized its antiviral effect by degrading DDX21, which will be useful to guide further studies into the mechanism of mutual regulation between SVA and the host.

Senecavirus A as an Oncolytic Virus: Prospects, Challenges and Development Directions

Oncolytic viruses have the capacity to selectively kill infected tumor cells and trigger protective immunity. As such, oncolytic virotherapy has become a promising immunotherapy strategy against cancer. A variety of viruses from different families have been proven to have oncolytic potential. Senecavirus A (SVA) was the first picornavirus to be tested in humans for its oncolytic potential and was shown to penetrate solid tumors through the vascular system. SVA displays several properties that make it a suitable model, such as its inability to integrate into human genome DNA and the absence of any viral-encoded oncogenes. In addition, genetic engineering of SVA based on the manipulation of infectious clones facilitates the development of recombinant viruses with improved therapeutic indexes to satisfy the criteria of safety and efficacy regulations. This review summarizes the current knowledge and strategies of genetic engineering for SVA, and addresses the current challenges and future directions of SVA as an oncolytic agent.

Seneca Valley Virus 3C Protease Induces Pyroptosis by Directly Cleaving Porcine Gasdermin D

Seneca Valley virus (SVV), a newly emerging virus belonging to the Picornaviridae family, has caused vesicular disease in the swine industry. However, the molecular mechanism of viral pathogenesis remains poorly understood. This study revealed that SVV infection could induce pyroptosis in SK6 cells in a caspase-dependent and -independent manner. SVV may inhibit caspase-1 activation at late infection because of 3Cpro cleavage of NLRP3, which counteracted pyroptosis activation. Further study showed that 3Cpro targeted porcine gasdermin D (pGSDMD) for cleavage through its protease activity. 3Cpro cleaved porcine GSDMD (pGSDMD) at two sites, glutamine 193 (Q193) and glutamine 277 (Q277), and Q277 was close to the caspase-1-induced pGSDMD cleavage site. pGSDMD1-277 triggered cell death, which was similar to N-terminal fragment produced by caspase-1 cleavage of pGSDMD, and other fragments exhibited no significant inhibitory effects on cellular activity. Ectopic expression of pGSDMD converted 3Cpro-induced apoptosis to pyroptosis in 293T cells. Interestingly, 3Cpro did not cleave mouse GSDMD or human GSDMD. And, both pGSDMD and pGSDMD1-277 exhibited bactericidal activities in vivo. Nevertheless, pGSDMD cannot kill bacteria in vitro. Taken together, our results reveal a novel pyroptosis activation manner produced by viral protease cleavage of pGSDMD, which may provide an important insight into the pathogenesis of SVV and cancer therapy.

Selective autophagy receptor SQSTM1/ p62 inhibits Seneca Valley virus replication by targeting viral VP1 and VP3

Macroautophagy/autophagy plays a critical role in antiviral immunity through targeting viruses and initiating host immune responses. The receptor protein, SQSTM1/p62 (sequestosome 1), plays a vital role in selective autophagy. It serves as a receptor targeting ubiquitinated proteins or pathogens to phagophores for degradation. In this study, we explored the reciprocal regulation between selective autophagy receptor SQSTM1 and Seneca Valley virus (SVV). SVV infection induced autophagy. Autophagy promoted SVV infection in pig cells but played opposite functions in human cells. Overexpression of SQSTM1 decreased viral protein production and reduced viral titers. Further study showed that SQSTM1 interacted with SVV VP1 and VP3 independent of its UBA domain. SQSTM1 targeted SVV VP1 and VP3 to phagophores for degradation to inhibit viral replication. To counteract this, SVV evolved strategies to circumvent the host autophagic machinery to promote viral replication. SVV 3C^pro targeted the receptor SQSTM1 for cleavage at glutamic acid 355, glutamine 392, and glutamine 395 and abolished its capacity to mediate selective autophagy. At the same time, the 3C^pro-mediated SQSTM1 cleavage products lost the ability to inhibit viral propagation. Collectively, our results provide evidence for selective autophagy in host against viruses and reveal potential viral strategies to evade autophagic machinery for successful pathogenesis. Abbreviations: Baf.A1: bafilomycin A₁; Co-IP: co-immunoprecipitation; hpi: h post-infection; LIR: LC3-interacting region; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MOI: multiplicity of infection; PB1: N-terminal Phox/Bem1p; Rap.: rapamycin; Seneca Valley virus: SVV; SQSTM1/p62: sequestosome 1; SQSTM1-N355: residues 1 to 355 of SQSTM1; SQSTM1-C355: residues 355 to 478 of SQSTM1; SQSTM1-N392: residues 1 to 392 of SQSTM1; SQSTM1-C392: residues 392 to 478 of SQSTM1; SQSTM1-N388: residues 1 to 388 of SQSTM1; SQSTM1-N397: residues 1 to 397 of SQSTM1; UBA: ubiquitin association; Ubi: ubiquitin.

Oncolytic Seneca Valley Virus: past perspectives and future directions

Seneca Valley Virus isolate 001 (SVV-001) is an oncolytic RNA virus of the Picornaviridae family. It is also the first picornavirus discovered of the novel genus Senecavirus. SVV-001 replicates through an RNA intermediate, bypassing a DNA phase, and is unable to integrate into the host genome. SVV-001 was originally discovered as a contaminant in the cell culture of fetal retinoblasts and has since been identified as a potent oncolytic virus against tumors of neuroendocrine origin. SVV-001 has a number of features that make it an attractive oncolytic virus, namely, its ability to target and penetrate solid tumors via intravenous administration, inability for insertional mutagenesis, and being a self-replicating RNA virus with selective tropism for cancer cells. SVV-001 has been studied in both pediatric and adult early phase studies reporting safety and some clinical efficacy, albeit primarily in adult tumors. This review summarizes the current knowledge of SVV-001 and what its future as an oncolytic virus may hold.