RNF123 Mediates Ubiquitination and Degradation of SOCS1 To Regulate Type I Interferon Production during Duck Tembusu Virus Infection

Many RING domain E3 ubiquitin ligases play critical roles in fine-tuning the innate immune response, yet little is known about their regulatory role in flavivirus-induced innate immunity. In previous studies, we found that the suppressor of cytokine signaling 1 (SOCS1) protein mainly undergoes lysine 48 (K48)-linked ubiquitination. However, the E3 ubiquitin ligase that promotes the K48-linked ubiquitination of SOCS1 is unknown. In the present study, we found that RING finger protein 123 (RNF123) binds to the SH2 domain of SOCS1 through its RING domain and facilitates the K48-linked ubiquitination of the K114 and K137 residues of SOCS1. Further studies found that RNF123 promoted the proteasomal degradation of SOCS1 and promoted Toll-like receptor 3 (TLR3)- and interferon (IFN) regulatory factor 7 (IRF7)-mediated type I IFN production during duck Tembusu virus (DTMUV) infection through SOCS1, ultimately inhibiting DTMUV replication. Overall, these findings demonstrate a novel mechanism by which RNF123 regulates type I IFN signaling during DTMUV infection by targeting SOCS1 degradation. IMPORTANCE In recent years, posttranslational modification (PTM) has gradually become a research hot spot in the field of innate immunity regulation, and ubiquitination is one of the critical PTMs. DTMUV has seriously endangered the development of the waterfowl industry in Southeast Asian countries since its outbreak in 2009. Previous studies have shown that SOCS1 is modified by K48-linked ubiquitination during DTMUV infection, but E3 ubiquitin ligase catalyzing the ubiquitination of SOCS1 has not been reported. Here, we identify for the first time that RNF123 acts as an E3 ubiquitin ligase that regulates TLR3- and IRF7-induced type I IFN signaling during DTMUV infection by targeting the K48-linked ubiquitination of the K114 and K137 residues of SOCS1 and the proteasomal degradation of SOCS1.

SOCS-1 inhibition of type I interferon restrains Staphylococcus aureus skin host defense

The skin innate immune response to methicillin-resistant Staphylococcus aureus (MRSA) culminates in the formation of an abscess to prevent bacterial spread and tissue damage. Pathogen recognition receptors (PRRs) dictate the balance between microbial control and injury. Therefore, intracellular brakes are of fundamental importance to tune the appropriate host defense while inducing resolution. The intracellular inhibitor suppressor of cytokine signaling 1 (SOCS-1), a known JAK/STAT inhibitor, prevents the expression and actions of PRR adaptors and downstream effectors. Whether SOCS-1 is a molecular component of skin host defense remains to be determined. We hypothesized that SOCS-1 decreases type I interferon production and IFNAR-mediated antimicrobial effector functions, limiting the inflammatory response during skin infection. Our data show that MRSA skin infection enhances SOCS-1 expression, and both SOCS-1 inhibitor peptide-treated and myeloid-specific SOCS-1 deficient mice display decreased lesion size, bacterial loads, and increased abscess thickness when compared to wild-type mice treated with the scrambled peptide control. SOCS-1 deletion/inhibition increases phagocytosis and bacterial killing, dependent on nitric oxide release. SOCS-1 inhibition also increases the levels of type I and type II interferon levels in vivo. IFNAR deletion and antibody blockage abolished the beneficial effects of SOCS-1 inhibition in vivo. Notably, we unveiled that hyperglycemia triggers aberrant SOCS-1 expression that correlates with decreased overall IFN signatures in the infected skin. SOCS-1 inhibition restores skin host defense in the highly susceptible hyperglycemic mice. Overall, these data demonstrate a role for SOCS-1-mediated type I interferon actions in host defense and inflammation during MRSA skin infection.

SOCS, Intrinsic Virulence Factors, and Treatment of COVID-19

The suppressor of cytokine signaling (SOCS) family of intracellular checkpoint inhibitors has received little recognition compared to other checkpoint inhibitors. Two members of this family, SOCS1 and SOCS3, are indispensable, since SOCS1 knockout in mice results in neonatal death due to interferon gamma (IFNγ) induced inflammatory disease, and SOCS3 knockout leads to embryonic lethality. We have shown that SOCS1 and SOCS3 (SOCS1/3) function as virus induced intrinsic virulence factors for influenza A virus, EMC virus, herpes simplex virus 1 (HSV-1), and vaccinia virus infections. Other viruses such as pathogenic pig enteric coronavirus and coronavirus induced severe acute respiratory syndrome (SARS) spike protein also induce SOCS virus intrinsic virulence factors. SOCS1/3 exert their viral virulence effect via inhibition of type I and type II interferon (IFN) function. Specifically, the SOCS bind to the activation loop of receptor-associated tyrosine kinases JAK2 and TYK2 through the SOCS kinase inhibitory region (KIR), which inhibits STAT transcription factor activation by the kinases. Activated STATs are required for IFN function. We have developed a small peptide antagonist of SOCS1/3 that blocks SOCS1/3 inhibitory activity and prevents virus pathogenesis. The antagonist, pJAK2(1001-1013), is comprised of the JAK2 activation loop, phosphorylated at tyrosine 1007 with a palmitate for cell penetration. The remarkable thing about SOCS1/3 is that it serves as a broad, simple tool of perhaps most pathogenic viruses to avoid innate host IFN defense. We suggest in this Perspective that SOCS1/3 antagonist is a simple counter measure to SOCS1/3 and should be an effective mechanism as a prophylactic and/or therapeutic against the COVID-19 pandemic that is caused by coronavirus SARS-CoV2.

The evolution and function characterization of suppressor of cytokine signaling 1b (SOCS1b) in miiuy croaker

The suppressor of cytokine signaling (SOCS) was first described as inhibitors of cytokine signaling. The SOCS1, as a number of SOCS family, is an important negative regulator in the IFN signaling pathways in mammals. While data on functional characterization of SOCS1 in lower vertebrates are limited. In this study, we identified and characterized the full length SOCS1b gene of miiuy croaker (Miichthys miiuy). The sequence alignment analysis results showed that miiuy croaker SOCS1b (mmSOCS1b) have only a conserved SH2 domain that is similar to other vertebrates. To further study the functions of mmSOCS1b, we identified and determined its potential ability to perceive poly (I:C) stimulation. Stimulation experiments with poly (I:C) showed the significantly upregulated expression of mmSOCS1b in crucial immune-related tissues of spleen and kidney, indicating that mmSOCS1b might participate in the immune responses. Furthermore, the immunofluorescence assay indicated that mmSOCS1b present in the cytoplasmic of HeLa cells. In addition, mmSOCS1b could inhibit IFNα or IFNγ-induced ISRE reporter gene. In a word, we systematically and comprehensively analyzed the characterizations and functions of mmSOCS1b, which not only enriches the current knowledge of SOCS in IFN signaling regulation but also offer the basis for future research of fish SOCS family.

Inhibition of murine herpesvirus-68 replication by IFN-gamma in macrophages is counteracted by the induction of SOCS1 expression

Gamma interferon (IFN-γ) is known to negatively regulate murine gammaherpesvirus-68 (MHV-68 or γHV-68) replication. This process involves the suppression of the viral gene replication and transcription activator (RTA) promoter, as well as activation of signal transducers and activators of transcription (STAT1). Notably, this effect is gradually attenuated during MHV-68 infection of bone marrow-derived macrophages (BMMs), which raised the possibility that the virus may utilize a mechanism that counteracts the antiviral effect of IFN-γ. By identifying the cellular factors that negatively regulate JAK-STAT1 signaling, we revealed that the infection of BMMs by MHV-68 induces the expression of suppressor of cytokine signaling 1 (SOCS1) and that depletion of SOCS1 restores the inhibitory effect of IFN-γ on virus replication. Moreover, we demonstrated that the expression of SOCS1 was induced as a result of the Toll-like receptor 3 (TLR3) mediated activation of the NF-κB signaling cascade. In conclusion, we report that TLR3-TRAF-NF-κB signaling pathway play a role in the induction of SOCS1 that counteracts the antiviral effect of IFN-γ during MHV-68 infection. This process is cell type-specific: it is functional in macrophages, but not in epithelial cells or fibroblasts. Our study reveals a mechanism that balances the immune responses and the escape of a gamma-herpesvirus in some antigen-presenting cells.

While viruses have developed various mechanisms to evade immune responses, hosts also have mechanisms to negatively regulate the antiviral signaling pathways to minimize potential damage. In this study, we show that MHV-68, a gamma-herpesvirus, is able to stimulate macrophages to produce the cellular protein SOCS1, which reduces the antiviral effect initiated by IFN-γ, in a cell type specific manner. These findings provide one more example to support the concept that viruses utilize SOCS1 as an immune evasion mechanism. We also show that TLR3-NF-κB signaling is responsible for the induced production of SOCS1. Our finding that TLR3/NF-κB/SOCS1 impedes the action of IFN-γ/STAT1 on RTA might offer a reasonable explanation of how virus-host interaction achieves a balance to facilitate intra-host spreading and transmission.

Femtograms of Interferon-γ Suffice to Modulate the Behavior of Jurkat Cells: A New Light in Immunomodulation

Since interferon-γ (IFN-γ) tunes both innate and adaptive immune systems, it was expected to enter clinical practice as an immunomodulatory drug. However, the use of IFN-γ has been limited by its dose-dependent side effects. Low-dose medicine, which is emerging as a novel strategy to treat diseases, might circumvent this restriction. Several clinical studies have proved the efficacy of therapies with a low dose of cytokines subjected to kinetic activation, while no in vitro data are available. To fill this gap, we investigated whether low concentrations, in the femtogram range, of kinetically activated IFN-γ modulate the behavior of Jurkat cells, a widely used experimental model that has importantly contributed to the present knowledge about T cell signaling. In parallel, IFN-γ in the nanogram range was used and shown to activate Signal transducer and activator of transcription (STAT)-1 and then to induce suppressor of cytokine signaling-1 (SOCS-1), which inhibits downstream signaling. When added together, femtograms of IFN-γ interfere with the transduction cascade activated by nanograms of IFN-γ by prolonging the activation of STAT-1 through the downregulation of SOCS-1. We conclude that femtograms of IFN-γ exert an immunomodulatory action in Jurkat cells.