Molecular chaperone TRiC governs avian reovirus replication by protecting outer-capsid protein σC and inner core protein σA and non-structural protein σNS from ubiquitin- proteasome degradation

The Oncolytic Avian Reovirus p17 Protein Inhibits Invadopodia Formation in Murine Melanoma Cancer Cells by Suppressing the FAK/Src Pathway and the Formation of theTKs5/NCK1 Complex

To explore whether the p17 protein of oncolytic avian reovirus (ARV) mediates cell migration and invadopodia formation, we applied several molecular biological approaches for studying the involved cellular factors and signal pathways. We found that ARV p17 activates the p53/phosphatase and tensin homolog (PTEN) pathway to suppress the focal adhesion kinase (FAK)/Src signaling and downstream signal molecules, thus inhibiting cell migration and the formation of invadopodia in murine melanoma cancer cell line (B16-F10). Importantly, p17-induced formation of invadopodia could be reversed in cells transfected with the mutant PTENC124A. p17 protein was found to significantly reduce the expression levels of tyrosine kinase substrate 5 (TKs5), Rab40b, non-catalytic region of tyrosine kinase adaptor protein 1 (NCK1), and matrix metalloproteinases (MMP9), suggesting that TKs5 and Rab40b were transcriptionally downregulated by p17. Furthermore, we found that p17 suppresses the formation of the TKs5/NCK1 complex. Coexpression of TKs5 and Rab40b in B16-F10 cancer cells reversed p17-modulated suppression of the formation of invadopodia. This work provides new insights into p17-modulated suppression of invadopodia formation by activating the p53/PTEN pathway, suppressing the FAK/Src pathway, and inhibiting the formation of the TKs5/NCK1 complex.

Chaperonin TRiC/CCT subunit CCT7 is involved in the replication of canine parvovirus in F81 cells

Canine parvovirus (CPV) is one of the most common lethal viruses in canines. The virus disease is prevalent throughout the year, with high morbidity and mortality rate, causing serious harm to dogs and the dog industry. Previously, yeast two hybrid method was used to screen the protein chaperonin containing TCP-1 (CCT7) that interacts with VP2. However, the mechanism of interactions between CCT7 and VP2 on CPV replication remains unclear. In this study, we first verified the interaction between CCT7 and viral VP2 proteins using yeast one-to-one experiment and co-immunoprecipitation (CoIP) experiment. Laser confocal microscopy observation showed that CCT7 and VP2 were able to co-localize and were mostly localized in the cytoplasm. In addition, the study of VP2 truncated mutant found that the interaction region of VP2 with CCT7 was located between amino acids 231 and 320. Cycloheximide (CHX) chase experiments showed that CCT7 can improve the stability of VP2 protein. After further regulation of CCT7 expression in F81 cells, it was found that the expression level of VP2 protein was significantly reduced after knocking down CCT7 expression by RNA interference (RNAi) or HSF1A inhibitor, and increased after overexpressing host CCT7. The study reveals the role of VP2 interacting protein CCT7 in the replication process of CPV, which could provide a potential target for the prevention and control of CPV.

Cell Entry of Avian Reovirus Modulated by Cell-Surface Annexin A2 and Adhesion G Protein-Coupled Receptor Latrophilin-2 Triggers Src and p38 MAPK Signaling Enhancing Caveolin-1- and Dynamin 2-Dependent Endocytosis

The specifics of cell receptor-modulated avian reovirus (ARV) entry remain unknown. By using a viral overlay protein-binding assay (VOPBA) and an in-gel digestion coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS), we determined that cell-surface annexin A2 (AnxA2) and adhesion G protein-coupled receptor Latrophilin-2 (ADGRL2) modulate ARV entry. Direct interaction between the ARV σC protein and AnxA2 and ADGRL2 in Vero and DF-1 cells was demonstrated in situ by proximity ligation assays. By using short hairpin RNAs (shRNAs) to silence the endogenous AnxA2 and ADGRL2 genes, ARV entry could be efficiently blocked. A significant decrease in virus yields and the intracellular specific signal for σC protein was observed in Vero cells preincubated with the specific AnxA2 and ADGRL2 monoclonal antibodies, indicating that AnxA2 and ADGRL2 are involved in modulating ARV entry. Furthermore, we found that cells pretreated with the AnxA2/S100A10 heterotetramer (A2t) inhibitor A2ti-1 suppressed ARV-mediated activation of Src and p38 mitogen-activated protein kinase (MAPK), demonstrating that Src and p38 MAPK serve as downstream molecules of cell-surface AnxA2 signaling. Our results reveal that suppression of cell-surface AnxA2 with the A2ti-1 inhibitor increased Csk-Cbp interaction, suggesting that ARV entry suppresses Cbp-mediated relocation of Csk to the membrane, thereby activating Src. Furthermore, reciprocal coimmunoprecipitation assays revealed that σC can interact with signaling molecules, lipid raft, and vimentin. The current study provides novel insights into cell-surface AnxA2- and ADGRL2-modulated cell entry of ARV which triggers Src and p38 MAPK signaling to enhance caveolin-1-, dynamin 2-, and lipid raft-dependent endocytosis. IMPORTANCE By analyzing results from VOPBA and LC-MS/MS, we have determined that cell-surface AnxA2 and ADGRL2 modulate ARV entry. After ARV binding to receptors, Src and p38 MAPK signaling were triggered and, in turn, increased the phosphorylation of caveolin-1 (Tyr14) and upregulated dynamin 2 expression to facilitate caveolin-1-mediated and dynamin 2-dependent endocytosis. In this work, we demonstrated that ARV triggers Src activation by impeding Cbp-mediated relocation of Csk to the membrane in the early stages of the life cycle. This work provides better insight into cell-surface AnxA2 and ADGRL2, which upregulate Src and p38MAPK signaling pathways to enhance ARV entry and productive infection.

Oncolytic viruses-modulated immunogenic cell death, apoptosis and autophagy linking to virotherapy and cancer immune response

Recent reports have revealed that oncolytic viruses (OVs) play a significant role in cancer therapy. The infection of OVs such as oncolytic vaccinia virus (OVV), vesicular stomatitis virus (VSV), parvovirus, mammalian reovirus (MRV), human adenovirus, Newcastle disease virus (NDV), herpes simplex virus (HSV), avian reovirus (ARV), Orf virus (ORFV), inactivated Sendai virus (ISV), enterovirus, and coxsackievirus offer unique opportunities in immunotherapy through diverse and dynamic pathways. This mini-review focuses on the mechanisms of OVs-mediated virotherapy and their effects on immunogenic cell death (ICD), apoptosis, autophagy and regulation of the immune system.

Oncolytic Avian Reovirus p17-Modulated Inhibition of mTORC1 by Enhancement of Endogenous mTORC1 Inhibitors Binding to mTORC1 To Disrupt Its Assembly and Accumulation on Lysosomes

The mechanism by which avian reovirus (ARV)-modulated suppression of mTORC1 triggers autophagy remains largely unknown. In this work, we determined that p17 functions as a negative regulator of mTORC1. This study suggest novel mechanisms whereby p17-modulated inhibition of mTORC1 occurs via upregulation of p53, inactivation of Akt, and enhancement of binding of the endogenous mTORC1 inhibitors (PRAS40, FKBP38, and FKPP12) to mTORC1 to disrupt its assembly and accumulation on lysosomes. p17-modulated inhibition of Akt leads to activation of the downstream targets PRAS40 and TSC2, which results in mTORC1 inhibition, thereby triggering autophagy and translation shutoff, which is favorable for virus replication. p17 impairs the interaction of mTORC1 with its activator Rheb, which promotes FKBP38 interaction with mTORC1. It is worth noting that p17 activates ULK1 and Beclin1 and increases the formation of the Beclin 1/class III PI3K complex. These effects could be reversed in the presence of insulin or depletion of p53. Furthermore, we found that p17 induces autophagy in cancer cell lines by upregulating the p53/PTEN pathway, which inactivates Akt and mTORC1. This study highlights p17-modulated inhibition of Akt and mTORC1, which triggers autophagy and translation shutoff by positively modulating the tumor suppressors p53 and TSC2 and endogenous mTORC1 inhibitors. IMPORTANCE The mechanisms by which p17-modulated inhibition of mTORC1 induces autophagy and translation shutoff is elucidated. In this work, we determined that p17 serves as a negative regulator of mTORC1. This study provides several lines of conclusive evidence demonstrating that p17-modulated inhibition of mTORC1 occurs via upregulation of the p53/PTEN pathway, downregulation of the Akt/Rheb/mTORC1 pathway, enhancement of binding of the endogenous mTORC1 inhibitors to mTORC1 to disrupt its assembly, and suppression of mTORC1 accumulation on lysosomes. This work provides valuable information for better insights into p17-modulated inhibition of mTORC1, which induces autophagy and translation shutoff to benefit virus replication.

Oncolytic avian reovirus σA-modulated fatty acid metabolism through the PSMB6/Akt/SREBP1/acetyl-CoA carboxylase pathway to increase energy production for virus replication

We have demonstrated previously that the σA protein of avian reovirus (ARV) functions as an activator of cellular energy, which upregulates glycolysis and the TCA cycle for virus replication. To date, there is no report with respect to σA-modulated regulation of cellular fatty acid metabolism. This study reveals that the σA protein of ARV inhibits fatty acids synthesis and enhance fatty acid oxidation by upregulating PSMB6, which suppresses Akt, sterol regulatory element-binding protein 1 (SREBP1), acetyl-coA carboxylase α (ACC1), and acetyl-coA carboxylase β (ACC2). SREBP1 is a transcription factor involved in fatty acid and cholesterol biosynthesis. Overexpression of SREBP1 reversed σA-modulated suppression of ACC1 and ACC2. In this work, a fluorescence resonance energy transfer-based genetically encoded indicator, Ateams, was used to study σA-modulated inhibition of fatty acids synthesis which enhances cellular ATP levels in Vero cells and human cancer cell lines (A549 and HeLa). By using Ateams, we demonstrated that σA-modulated inhibition of Akt, SREBP1, ACC1, and ACC2 leads to increased levels of ATP in mammalian and human cancer cells. Furthermore, knockdown of PSMB6 or overexpression of SREBP1 reversed σA-modulated increased levels of ATP in cells, indicating that PSMB6 and SREBP1 play important roles in ARV σA-modulated cellular fatty acid metabolism. Furthermore, we found that σA _R155/273A mutant protein loses its ability to enter the nucleolus, which impairs its ability to regulate fatty acid metabolism and does not increase ATP formation, suggesting that nucleolus entry of σA is critical for regulating cellular fatty acid metabolism to generate more energy for virus replication. Collectively, this study provides novel insights into σA-modulated inhibition of fatty acid synthesis and enhancement of fatty acid oxidation to produce more energy for virus replication through the PSMB6/Akt/SREBP1/ACC pathway.

p17-Modulated Hsp90/Cdc37 Complex Governs Oncolytic Avian Reovirus Replication by Chaperoning p17, Which Promotes Viral Protein Synthesis and Accumulation of Viral Proteins σC and σA in Viral Factories

In this work we have determined that heat shock protein 90 (Hsp90) is essential for avian reovirus (ARV) replication by chaperoning the ARV p17 protein. p17 modulates the formation of the Hsp90/Cdc37 complex by phosphorylation of Cdc37, and this chaperone machinery protects p17 from ubiquitin-proteasome degradation. Inhibition of the Hsp90/Cdc37 complex by inhibitors (17-N-allylamino-17-demethoxygeldanamycin 17-AGG, and celastrol) or short hairpin RNAs (shRNAs) significantly reduced expression levels of viral proteins and virus yield, suggesting that the Hsp90/Cdc37 chaperone complex functions in virus replication. The expression levels of p17 were decreased at the examined time points (2 to 7 h and 7 to 16 h) in 17-AAG-treated cells in a dose-dependent manner while the expression levels of viral proteins σA, σC, and σNS were decreased at the examined time point (7 to 16 h). Interestingly, the expression levels of σC, σA, and σNS proteins increased along with coexpression of p17 protein. p17 together with the Hsp90/Cdc37 complex does not increase viral genome replication but enhances viral protein stability, maturation, and virus production. Virus factories of ARV are composed of nonstructural proteins σNS and μNS. We found that the Hsp90/Cdc37 chaperone complex plays an important role in accumulation of the outer-capsid protein σC, inner core protein σA, and nonstructural protein σNS of ARV in viral factories. Depletion of Hsp90 inhibited σA, σC, and p17 proteins colocalized with σNS in viral factories. This study provides novel insights into p17-modulated formation of the Hsp90/Cdc37 chaperone complex governing virus replication via stabilization and maturation of viral proteins and accumulation of viral proteins in viral factories for virus assembly. IMPORTANCE Molecular mechanisms that control stabilization of ARV proteins and the intermolecular interactions among inclusion components remain largely unknown. Here, we show that the ARV p17 is an Hsp90 client protein. The Hsp90/Cdc37 chaperone complex is essential for ARV replication by protecting p17 chaperone from ubiquitin-proteasome degradation. p17 modulates the formation of Hsp90/Cdc37 complex by phosphorylation of Cdc37, and this chaperone machinery protects p17 from ubiquitin-proteasome degradation, suggesting a feedback loop between p17 and the Hsp90/Cdc37 chaperone complex. p17 together with the Hsp90/Cdc37 complex does not increase viral genome replication but enhances viral protein stability and virus production. Depletion of Hsp90 prevented viral proteins σA, σC, and p17 from colocalizing with σNS in viral factories. Our findings elucidate that the Hsp90/Cdc37 complex chaperones p17, which, in turn, promotes the synthesis of viral proteins σA, σC, and σNS and facilitates accumulation of the outer-capsid protein σC and inner core protein σA in viral factories for virus assembly.