Induction of SOCS Expression by EV71 Infection Promotes EV71 Replication

Recent Progress in Innate Immune Responses to Enterovirus A71 and Viral Evasion Strategies

Enterovirus A71 (EV-A71) is a major pathogen causing hand, foot, and mouth disease (HFMD) in children worldwide. It can lead to severe gastrointestinal, pulmonary, and neurological complications. The innate immune system, which rapidly detects pathogens via pathogen-associated molecular patterns or pathogen-encoded effectors, serves as the first defensive line against EV-A71 infection. Concurrently, the virus has developed various sophisticated strategies to evade host antiviral responses and establish productive infection. Thus, the virus-host interactions and conflicts, as well as the ability to govern biological events at this first line of defense, contribute significantly to the pathogenesis and outcomes of EV-A71 infection. In this review, we update recent progress on host innate immune responses to EV-A71 infection. In addition, we discuss the underlying strategies employed by EV-A71 to escape host innate immune responses. A better understanding of the interplay between EV-A71 and host innate immunity may unravel potential antiviral targets, as well as strategies that can improve patient outcomes.

Role of protein Post-translational modifications in enterovirus infection

Enteroviruses (EVs) are the main cause of a number of neurological diseases. Growing evidence has revealed that successful infection with enteroviruses is highly dependent on the host machinery, therefore, host proteins play a pivotal role in viral infections. Both host and viral proteins can undergo post-translational modification (PTM) which can regulate protein activity, stability, solubility and interactions with other proteins; thereby influencing various biological processes, including cell metabolism, metabolic, signaling pathways, cell death, and cancer development. During viral infection, both host and viral proteins regulate the viral life cycle through various PTMs and different mechanisms, including the regulation of host cell entry, viral protein synthesis, genome replication, and the antiviral immune response. Therefore, protein PTMs play important roles in EV infections. Here, we review the role of various host- and virus-associated PTMs during enterovirus infection.

Double-edged sword of JAK/STAT signaling pathway in viral infections: novel insights into virotherapy

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) is an intricate signaling cascade composed of various cytokines, interferons (IFN, growth factors, and other molecules. This pathway provides a delicate mechanism through which extracellular factors adjust gene expression, thereby acting as a substantial basis for environmental signals to influence cell growth and differentiation. The interactions between the JAK/STAT cascade and antiviral IFNs are critical to the host's immune response against viral microorganisms. Recently, with the emergence of therapeutic classes that target JAKs, the significance of this  cascade has been recognized in an unprecedented way. Despite the functions of the JAK/STAT pathway in adjusting immune responses against viral pathogens, a vast body of evidence proposes the role of this cascade in the replication and pathogenesis of viral pathogens. In this article, we review the structure of the JAK/STAT signaling cascade and its role in immuno-inflammatory responses. We also highlight the paradoxical effects of this pathway in the pathogenesis of viral infections. Video Abstract.

Obesity and Leptin Resistance in the Regulation of the Type I Interferon Early Response and the Increased Risk for Severe COVID-19

Obesity, and obesity-associated conditions such as hypertension, chronic kidney disease, type 2 diabetes, and cardiovascular disease, are important risk factors for severe Coronavirus disease-2019 (COVID-19). The common denominator is metaflammation, a portmanteau of metabolism and inflammation, which is characterized by chronically elevated levels of leptin and pro-inflammatory cytokines. These induce the “Suppressor Of Cytokine Signaling 1 and 3” (SOCS1/3), which deactivates the leptin receptor and also other SOCS1/3 sensitive cytokine receptors in immune cells, impairing the type I and III interferon early responses. By also upregulating SOCS1/3, Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2 adds a significant boost to this. The ensuing consequence is a delayed but over-reactive immune response, characterized by high-grade inflammation (e.g., cytokine storm), endothelial damage, and hypercoagulation, thus leading to severe COVID-19. Superimposing an acute disturbance, such as a SARS-CoV-2 infection, on metaflammation severely tests resilience. In the long run, metaflammation causes the “typical western” conditions associated with metabolic syndrome. Severe COVID-19 and other serious infectious diseases can be added to the list of its short-term consequences. Therefore, preventive measures should include not only vaccination and the well-established actions intended to avoid infection, but also dietary and lifestyle interventions aimed at improving body composition and preventing or reversing metaflammation.

Total astragalosides decrease apoptosis and pyroptosis by inhibiting enterovirus 71 replication in gastric epithelial cells

Enterovirus 71 (EV71) is one of the primary pathogens involved in severe hand, foot and mouth disease in children. EV71 infection causes various types of programmed cell death. However, there are currently no clinically approved specific antiviral drugs for control of EV71 infection. Astragalus membranaceus (AM), a Traditional Chinese medicine, has been used in antiviral therapy in China. The aim of the present study was to determine whether total astragalosides (ASTs), bioactive components of AM, protect against EV. DAPI nuclear staining was used to observe morphological changes of the nucleus and the protective effect of ASTs, which revealed that the nucleus shrank following EV71 infection, while ASTs reversed it. Cell Counting Kit-8 assay found that human normal gastric epithelial cell (GES-1 cell) viability decreased following EV71 infection, while lactate dehydrogenase (LDH) assay showed that EV71 infection induced GES-1 cell damage. Western blotting was used to measure the expression levels of apoptosis and pyroptosis marker protein to determine whether EV71 infection induced apoptosis and pyroptosis in GES-1 cells. Reverse transcription-quantitative PCR was used to determine the anti-EV71 effect of ASTs. The results showed that ASTs protected GES-1 cells from EV71-induced cell apoptosis and pyroptosis. Furthermore, the present data demonstrated that the protective effect of ASTs was exerted by suppressing EV71 replication and release. These findings suggested that ASTs may represent a potential antiviral agent for the treatment of EV71 infection.

Mycoplasma gallisepticum escapes the host immune response via gga-miR-365-3p/SOCS5/STATs axis

A disruption in the expression of gga-miR-365-3p was confirmed in the Mycoplasma gallisepticum (MG)-infected Chicken primary alveolar type II epithelial (CP-II) cells based on previous sequencing results, but the role it plays in the infection was unclear. In the present study, we demonstrate that MG evaded cellular host immunity via a gga-miR-365-3p/SOCS5-JAK/STATs negative feedback loop. Specifically, we found that at the initial stage of MG infection in cells, gga-miR-365-3p was rapidly increased and activated the JAK/STAT signaling pathway by inhibiting SOCS5, which induced the secretion of inflammatory factors and triggered immune response against MG infection. Over time, though, the infection progressed, MG gradually destroyed the immune defences of CP-II cells. In late stages of infection, MG escaped host immunity by reducing intracellular gga-miR-365-3p and inhibiting the JAK/STAT pathway to suppress the secretion of inflammatory factors and promote MG adhesion or invasion. These results revealed the game between MG and host cell interactions, providing a new perspective to gain insight into the pathogenic mechanisms of MG or other pathogens. Meanwhile, they also contributed to novel thoughts on the prevention and control of MG and other pathogenic infections, shedding light on the immune modulating response triggered by pathogen invasion and their molecular targeting.

TDRD3 is an antiviral restriction factor that promotes IFN signaling with G3BP1

Stress granules (SGs) are highly dynamic cytoplasmic foci that form in response to activation of the integrated stress response (ISR) that results in eIF2α phosphorylation and global translation shutdown. Stress granules, which are largely nucleated by G3BP1, serve as hubs for mRNA triage, but there is mounting evidence that they also perform cell signaling functions that are vital to cell survival, particularly during viral infection. We previously showed that SG formation leads to NFκB activation and JNK signaling and that this association may be due in part to G3BP1-dependent recruitment of PKR to SGs. Others have reported close associations between G3BP1 and various innate immune PRRs of the type 1 interferon signaling system, including RIG-I. We also reported SG assembly dynamics is dependent on the arginine-methylation status of G3BP1. Another protein that rapidly localizes to SGs, TDRD3, is a methyl reader protein that performs transcriptional activation and adaptor functions within the nucleus, but neither the mechanism nor its function in SGs is clear. Here, we present evidence that TDRD3 localizes to SGs partly based upon methylation potential of G3BP1. We also characterize granules that TDRD3 forms during overexpression and show that these granules can form in the absence of G3BP but also contain translation components found in canonical SGs. We also show for the first time that SGs recruit additional interferon effectors IRF3, IRF7, TBK1, and Sting, and provide evidence that TDRD3 may play a role in recruitment of these factors. We also present evidence that TDRD3 is a novel antiviral protein that is cleaved by enteroviral 2A proteinase. G3BP1 and TDRD3 knockdown in cells results in altered transcriptional regulation of numerous IFN effectors in complex modulatory patterns that are distinctive for G3BP1 and TDRD3. Overall, we describe a novel role of TDRD3 in innate immunity in which G3BP1 and TDRD3 may coordinate to play important roles in regulation of innate antiviral defenses.

When cells are exposed to environmental stresses, such as oxidative stress and viral infection, it induces a cellular response leading to the formation of Stress Granules (SGs) composed of stalled translation initiation complexes (RNA-binding proteins and mRNA) and many other cellular proteins. SGs are also considered to be antiviral structures when they form during viral infection, but viruses can block SG formation to facilitate their survival, often by targeting the essential SG protein G3BP1. Here, we show that a methyl reader protein, TDRD3, localizes to SGs partly based on the methylation potential of G3BP1, and may play a role in the recruitment of innate immune factors to SGs. Further, when overexpressed, TDRD3 can also form SG-like structures independently of G3BP1. We also present evidence that TDRD3 is a novel antiviral protein. Virus replication is enhanced in the absence of both TDRD3 and G3BP1, and virus infection leads to cleavage of TDRD3 by the enterovirus proteinase 2A. Finally, we also show that depletion of TDRD3 and G3BP1 together in cells leads to restriction of transcriptional activation of numerous IFN effectors in response to dsRNA. The patterns of transcriptional activation are distinctive for G3BP1 and TDRD3. We conclude that TDRD3 may play a novel and important role in the regulation of the host antiviral response.

SOCS3 Promotes ALV-J Virus Replication via Inhibiting JAK2/STAT3 Phosphorylation During Infection

Avian leukosis virus subgroup J (ALV-J) is an oncogenic retrovirus that causes immunosuppression and neoplastic diseases in poultry. Cytokine signal-transduction inhibitor molecule 3 (SOCS3) is an important negative regulator of the JAK2/STAT3 signaling pathway and plays certain roles in ALV-J infection. It is of significance to confirm the roles of SOCS3 in ALV-J infection and study how this gene affects ALV-J infection. In this study, we assessed the expression of the SOCS3 gene in vivo and in vitro, and investigated the roles of SOCS3 in ALV-J infection using overexpressed or interfered assays with the SOCS3 in DF-1 cells. The results showed that the SOCS3 expression of ALV-J infected chickens was different from uninfected chickens in the spleen, thymus and cecal tonsil. Further, SOCS3 is mainly expressed in the nucleus as determined by immunofluorescence assay. Overexpression of SOCS3 in DF-1 cells promoted the replication of ALV-J virus, and the expression of interferons (IFNα and INFβ), inflammatory factors (IL-6 and TNFα) along with interferon-stimulating genes (CH25H, MX1, OASL, and ZAP). Conversely, interference of SOCS3 showed the opposite results. We also observed that SOCS3 promoted ALV-J virus replication by inhibiting JAK2/STAT3 phosphorylation. In conclusion, SOCS3 promotes ALV-J replication via inhibiting the phosphorylation of the JAK2/STAT3 signaling pathway. These results would advance further understanding of the persistent infection and the viral immune evasion of the ALV-J virus.

MiR-103/miR-107 inhibits enterovirus 71 replication and facilitates type I interferon response by regulating SOCS3/STAT3 pathway

BACKGROUND

Enterovirus71 (EV71), the major cause of hand, foot, and-mouth disease (HFMD), has increasingly become a public health challenge. Type I interferons (IFNs) can regulate innate and adaptive immune responses to pathogens. MicroRNAs (miRNAs) play regulatory roles in host innate immune responses to viral infections. However, the roles of miR-103 and miR-107 in EV71 infection remain unclear.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was employed to determine the expression of miR-103, miR-107, suppressor of cytokine signaling 3 (SOCS3), VP1, IFN-α, and IFN-β. Virus titers were measured by 50% tissue culture infectious dose (TCID₅₀) assay. Western blot assay was conducted to detect the protein levels of VP1, IFN-α, IFN-β, SOCS3, signal transducer and activator of transcription 3 (STAT3), and phospho-STAT3 (p-STAT3). Immunofluorescence assay was used to detect the protein level of VP1. The concentrations of IFN-α and IFN-β were examined by Enzyme-linked immunosorbent assay (ELISA). The interaction between SOCS3 and miR-103/miR-107 was predicted by starBase and verified by dual-luciferase reporter assay and RNA pull-down assay.

RESULTS

MiR-103 and miR-107 were downregulated and SOCS3 was upregulated in serum from patients with EV71 and EV71-infected cells. Overexpression of miR-103 and miR-107 repressed EV71 replication by inhibiting EV71 titers and VP1 expression. Moreover, upregulation of miR-103 and miR-107 enhanced EV71-triggered the production of type I IFNs. In addition, miR-103 and miR-107 directly targeted SOCS3, and SOCS3 upregulation reversed the effects of miR-103 and miR-107 on EV71 replication and type I IFN response. Importantly, miR-103 and miR-107 increased STAT3 phosphorylation by targeting SOCS3 after EV71 infection.

CONCLUSION

MiR-103 and miR-107 suppressed EV71 replication and increased the production of type I IFNs by regulating SOCS3/STAT3 pathway, which might provide a novel strategy for developing effective antiviral therapy.

Yellow Fever Virus Down-Regulates mRNA Expression of SOCS1 in the Initial Phase of Infection in Human Cell Lines

Flaviviruses are constantly evolving diverse immune evasion strategies, and the exploitation of the functions of suppressors of cytokine signalling (SOCS) and protein inhibitors of activated STATs (PIAS) to favour virus replication has been described for Dengue and Japanese encephalitis viruses but not for yellow fever virus (YFV), which is still of global importance despite the existence of an effective vaccine. Some mechanisms that YFV employs to evade host immune defence has been reported, but the expression patterns of SOCS and PIAS in infected cells is yet to be determined. Here, we show that SOCS1 is down-regulated early in YFV-infected HeLa and HEK 293T cells, while SOCS3 and SOCS5 are not significantly altered, and PIAS mRNA expression appears to follow a rise-dip pattern akin to circadian-controlled genes. We also demonstrate that YFV evades interferon-β application to produce comparable viral titres. This report provides initial insight into the in vitro expression dynamics of SOCS and PIAS upon YFV infection and a basis for further investigation into SOCS/PIAS expression and how these modulate the immune response in animal models.