SOCS3 Drives Proteasomal Degradation of TBK1 and Negatively Regulates Antiviral Innate Immunity

Merkel cell polyomavirus protein ALTO modulates TBK1 activity to support persistent infection

While Merkel cell polyomavirus (MCPyV or MCV) is an abundant virus frequently shed from healthy skin, it is one of the most lethal tumor viruses in immunocompromised individuals, highlighting the crucial role of host immunity in controlling MCPyV oncogenic potential. Despite its prevalence, very little is known about how MCPyV interfaces with the host immune response to maintain asymptomatic persistent infection and how inadequate control of MCPyV infection triggers MCC tumorigenesis. In this study, we discovered that the MCPyV protein, known as the Alternative Large Tumor Open Reading Frame (ALTO), also referred to as middle T, effectively primes and activates the STING signaling pathway. It recruits Src kinase into the complex of STING downstream kinase TBK1 to trigger its autophosphorylation, which ultimately activates the subsequent antiviral immune response. Combining single-cell analysis with both loss- and gain-of-function studies of MCPyV infection, we demonstrated that the activity of ALTO leads to a decrease in MCPyV replication. Thus, we have identified ALTO as a crucial viral factor that modulates the STING-TBK1 pathway, creating a negative feedback loop that limits viral infection and maintains a delicate balance with the host immune system. Our study reveals a novel mechanism by which a tumorigenic virus-encoded protein can link Src function in cell proliferation to the activation of innate immune signaling, thereby controlling viral spread, and sustaining persistent infection. Our previous findings suggest that STING also functions as a tumor suppressor in MCPyV-driven oncogenesis. This research provides a foundation for investigating how disruptions in the finely tuned virus-host balance, maintained by STING, could alter the fate of MCPyV infection, potentially encouraging malignancy.

The RNA-binding protein ZFP36 strengthens innate antiviral signaling by targeting RIG-I for K63-linked ubiquitination

Innate immunity is the first line of defense against infections, which functions as a significant role in resisting pathogen invasion. Rapid immune response is initiated by pattern recognition receptors (PRRs) quickly distinguishing "self" and "non-self." Upon evolutionarily conserved pathogen-associated molecular pattern (PAMP) is recognized by PRRs, innate immune response against infection is triggered via an orchestration of molecular interaction, cytokines cascades, and immune cells. RIG-I plays a critical role in type I interferon (IFN-I) production by direct recognition of cytoplasmic double-stranded viral RNA. However, the activation mechanism of RIG-I is incompletely understood. In this study, we reported RNA-binding protein ZFP36 as a positive regulator of RIG-I-mediated IFN-I production. ZFP36 is a member of Zinc finger proteins (ZFPs) characterized by the zinc finger (ZnF) motif, which broadly involved gene transcription and signal transduction. However, its role in regulating antiviral innate immune signaling is still unclear. We found that ZFP36 associates with RIG-I and potentiates the FN-β production induced by SeV. Mechanistically, ZFP36 promotes K63-linked polyubiquitination of RIG-I, mostly at K154/K164/K172, thereby facilitating the activation of RIG-I during infection. While the mutant ZFP36 (C118S/C162S) failed to increase polyubiquitination of RIG-I and SeV induced FN-β. Our findings collectively demonstrated that ZFP36 acts as a positive regulator in antiviral innate immunity by targeting RIG-I for K63-linked ubiquitination, thus improving our understanding of the activation mechanism of RIG-I.

SOCSs: important regulators of host cell susceptibility or resistance to viral infection

Suppressors of cytokine signaling (SOCSs) are implicated in viral infection and host antiviral innate immune response. Recent studies demonstrate that viruses can hijack SOCSs to inhibit Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathway, block the production and signaling of interferons (IFNs). At the same time, viruses can hijack SOCS to regulate non-IFN factors to evade antiviral response. Host cells can also regulate SOCSs to resist viral infection. The competition of the control of SOCSs may largely determine the fate of viral infection and the susceptibility or resistance of host cells, which is of significance for development of novel antiviral therapies targeting SOCSs. Accumulating evidence reveal that the regulation and function of SOCSs by viruses and host cells are very complicated, which is determined by characteristics of both viruses and host cell types. This report presents a systematic review to evaluate the roles of SOCSs in viral infection and host antiviral responses. One of messages worth attention is that all eight SOCS members should be investigated to accurately characterize their roles and relative contribution in each viral infection, which may help identify the most effective SOCS to be used in "individualized" antiviral therapy.

NLRC4 promotes the cGAS-STING signaling pathway by facilitating CBL-mediated K63-linked polyubiquitination of TBK1

TANK-binding kinase 1 (TBK1) is crucial in producing type Ⅰ interferons (IFN-Ⅰ) that play critical functions in antiviral innate immunity. The tight regulation of TBK1, especially its activation, is very important. Here we identify NLRC4 as a positive regulator of TBK1. Ectopic expression of NLRC4 facilitates the activation of the IFN-β promoter, the mRNA levels of IFN-β, ISG54, and ISG56, and the nuclear translocation of interferon regulatory factor 3 induced by cGAS and STING. Consistently, under herpes simplex virus-1 (HSV-1) infection, knockdown or knockout of NLRC4 in BJ cells and primary peritoneal macrophages from Nlrc4-deficient (Nlrc4-/- ) mice show attenuated Ifn-β, Isg54, and Isg56 mRNA transcription, TBK1 phosphorylation, and augmented viral replications. Moreover, Nlrc4-/- mice show higher mortality upon HSV-1 infection. Mechanistically, NLRC4 facilitates the interaction between TBK1 and the E3 ubiquitin ligase CBL to enhance the K63-linked polyubiquitination of TBK1. Our study elucidates a previously uncharacterized function for NLRC4 in upregulating the cGAS-STING signaling pathway and antiviral innate immunity.

Targeting Type I Interferon Induction and Signaling: How Zika Virus Escapes from Host Innate Immunity

Zika virus (ZIKV) infection causes neurological disorders and draws great attention. ZIKV infection can elicit a wide range of immune response. Type I interferons (IFNs) as well as its signaling cascade play crucial role in innate immunity against ZIKV infection and in turn ZIKV can antagonize them. ZIKV genome are mainly recognized by Toll-like receptors 3 (TLR3), TLR7/8 and RIG-I-like receptor 1 (RIG-1), which induces the expression of Type I IFNs and interferon-stimulated genes (ISGs). ISGs exert antiviral activity at different stages of the ZIKV life cycle. On the other hand, ZIKV takes multiple strategies to antagonize the Type Ⅰ IFN induction and its signaling pathway to establish a pathogenic infection, especially by using the viral nonstructural (NS) proteins. Most of the NS proteins can directly interact with the factors in the pathways to escape the innate immunity. In addition, structural proteins also participate in the innate immune evasion and activation of antibody-binding of blood dendritic cell antigen 2 (BDCA2) or inflammasome also be used to enhance ZIKV replication. In this review, we summarize the recent findings about the interaction between ZIKV infection and type I IFNs pathways and suggest potential strategies for antiviral drug development.

Kremen2 drives the progression of non-small cell lung cancer by preventing SOCS3-mediated degradation of EGFR

BACKGROUND

The transmembrane receptor Kremen2 has been reported to participate in the tumorigenesis and metastasis of gastric cancer. However, the role of Kremen2 in non-small cell lung cancer (NSCLC) and the underlying mechanism remain unclear. This study aimed to explore the biological function and regulatory mechanism of Kremen2 in NSCLC.

METHODS

The correlation between Kremen2 expression and NSCLC was assessed by analyzing the public database and clinical tissue samples. Colony formation and EdU assays were performed to examine cell proliferation. Transwell and wound healing assays were used to observe cell migration ability. Tumor-bearing nude mice and metastatic tumor models were used to detect the in vivo tumorigenic and metastatic abilities of the NSCLC cells. An immunohistochemical assay was used to detect the expression of proliferation-related proteins in tissues. Western blot, immunoprecipitation and immunofluorescence were conducted to elucidate the Kremen2 regulatory mechanisms in NSCLC.

RESULTS

Kremen2 was highly expressed in tumor tissues from NSCLC patients and was positively correlated with a poor patient prognosis. Knockout or knockdown of Kremen2 inhibited cell proliferation and migration ability of NSCLC cells. In vivo knockdown of Kremen2 inhibited the tumorigenicity and number of metastatic nodules of NSCLC cells in nude mice. Mechanistically, Kremen2 interacted with suppressor of cytokine signaling 3 (SOCS3) to maintain the epidermal growth factor receptor (EGFR) protein levels by preventing SOCS3-mediated ubiquitination and degradation of EGFR, which, in turn, promoted activation of the PI3K-AKT and JAK2-STAT3 signaling pathways.

CONCLUSIONS

Our study identified Kremen2 as a candidate oncogene in NSCLC and may provide a potential target for NSCLC treatment.

ZIKV Strains Elicit Different Inflammatory and Anti-Viral Responses in Microglia Cells

In recent years, the Zika Virus (ZIKV) has caused pandemic outbreaks associated with a high rate of congenital ZIKV syndrome (CZS). Although all strains associated with worldwide outbreaks derive from the Asian lineage, the reasons for their enhanced spread and severity are not fully understood. In this study, we conducted a comparative analysis of miRNAs (miRNA-155/146a/124) and their cellular targets (SOCS1/3, SHP1, TRAF6, IRAK1), as well as pro- and anti-inflammatory and anti-viral cytokines (IL-6, TNF-α, IFN-γ, IL-10, and IFN-β) and peroxisome proliferator-activated receptor γ (PPAR-γ) expression in BV2 microglia cells infected with ZIKV strains derived from African and Asian lineages (ZIKV_MR766 and ZIKV_PE243). BV2 cells were susceptible to both ZIKV strains, and showed discrete levels of viral replication, with delayed release of viral particles without inducing significant cytopathogenic effects. However, the ZIKV_MR766 strain showed higher infectivity and replicative capacity, inducing a higher expression of microglial activation markers than the ZIKV_PE243 strain. Moreover, infection with the ZIKV_MR766 strain promoted both a higher inflammatory response and a lower expression of anti-viral factors compared to the ZIKV_PE243 strain. Remarkably, the ZIKK_PE243 strain induced significantly higher levels of the anti-inflammatory nuclear receptor-PPAR-γ. These findings improve our understanding of ZIKV-mediated modulation of inflammatory and anti-viral innate immune responses and open a new avenue to explore underlining mechanisms involved in the pathogenesis of ZIKV-associated diseases.

Transcriptome analysis reveals the host immune response upon LMBV infection in largemouth bass (Micropterus salmoides)

Largemouth bass (Micropterus salmoides) is one of the important economical freshwater aquaculture species in China. However, the outbreak of viral diseases always caused great economic losses in the largemouth bass aquaculture industry. Largemouth bass virus (LMBV), a double-stranded DNA (dsDNA) virus belonging to genus Ranavirus, family Iridoviridae causes high mortality in cultivated largemouth bass. However, host responses, especially the molecular events involved in LMBV infection still remained largely uncertain. Here, we established an in vivo model of LMBV infection, and systematically investigated the mRNA expression profiles of host genes in liver and spleen from infected largemouth bass using RNA sequencing (RNA-seq). Histopathological analysis indicated that necrotic cells and the formed necrotic focus were present in spleen, while numerous basophilic cells, hepatocytes volume shrinkage, nucleus pyknosis, and the disappeared boundary of hepatocytes were observed in the liver of infected largemouth bass. Transcriptomic analysis showed that transcription levels of 5128 genes (2804 up-regulated genes and 2324 down-regulated) in liver and 7008 genes (2603 up-regulated and 4405 down-regulated) in spleen were altered significantly. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that numerous co-regulated differentially expressed genes (DEGs) in liver and spleen were enriched in the pathways related to cell death and immune signaling, such as apoptosis, necroptosis, cytokine-cytokine receptor interaction and JAK-STAT signaling. Moreover, the DEGs specially regulated by LMBV infection in liver were significantly enriched in the KEGG pathways related to metabolism and cell death, while those in spleen were enriched in the immune related pathways. In addition, the expression changes of several randomly selected genes, such as SOCS1, IL-6, CXCL2, CASP8, CYC and TNF from qPCR were consistent with the transcriptomic data. Taken together, our findings will provide new insights into the fundamental patterns of molecular responses induced by LMBV in vivo, but also contribute greatly to understanding the host defense mechanisms against iridoviral pathogens.

Exfoliative Cytology and Genetic Analysis for a Non-Invasive Approach to the Diagnosis of White Sponge Nevus: Case Series

BACKGROUND

White Sponge Nevus (WSN) is a rare benign disorder associated with mutations in genes coding for cytokeratin 4 (KRT4) and 13 (KRT13) characterized by dyskeratotic hyperplasia of mucous membranes. This study was aimed at examining different approaches (cytology, pathology and genetic analysis) to WSN diagnosis.

METHODS

A series of four patients with asymptomatic white diffuse oral lesions were evaluated and, before performing an incisional biopsy for pathology, an oral brush Thin Prep was collected for exfoliative liquid-based cytology (LBC). DNA for genetic analysis was also obtained from patients and both their parents, using buccal swabs.

RESULTS

Pathology and cytology showed similar results, leading to the same diagnosis of hyperkeratotic epithelium with acanthosis and spongiosis, without atypia, demonstrating the efficiency of LBC for the differential diagnosis. Sequencing analysis revealed at least 6 rare variants in the KRT4 and KRT13 genes in each patient, contributed in part by both unaffected parents.

CONCLUSIONS

Thin Prep for oral exfoliative cytology and genetic analysis are sufficient for an accurate diagnosis of WSN. The combination of cytological and genetic analyses could substitute the histologic exam, providing a non-invasive alternative for incisional biopsy.

Regulation of cGAS/STING signaling and corresponding immune escape strategies of viruses

Innate immunity is the first line of defense against invading external pathogens, and pattern recognition receptors (PRRs) are the key receptors that mediate the innate immune response. Nowadays, there are various PRRs in cells that can activate the innate immune response by recognizing pathogen-related molecular patterns (PAMPs). The DNA sensor cGAS, which belongs to the PRRs, plays a crucial role in innate immunity. cGAS detects both foreign and host DNA and generates a second-messenger cGAMP to mediate stimulator of interferon gene (STING)-dependent antiviral responses, thereby exerting an antiviral immune response. However, the process of cGAS/STING signaling is regulated by a wide range of factors. Multiple studies have shown that viruses directly target signal transduction proteins in the cGAS/STING signaling through viral surface proteins to impede innate immunity. It is noteworthy that the virus utilizes these cGAS/STING signaling regulators to evade immune surveillance. Thus, this paper mainly summarized the regulatory mechanism of the cGAS/STING signaling pathway and the immune escape mechanism of the corresponding virus, intending to provide targeted immunotherapy ideas for dealing with specific viral infections in the future.

Zika virus alters centrosome organization to suppress the innate immune response

Zika virus (ZIKV) is a flavivirus transmitted via mosquitoes and sex to cause congenital neurodevelopmental defects, including microcephaly. Inherited forms of microcephaly (MCPH) are associated with disrupted centrosome organization. Similarly, we found that ZIKV infection disrupted centrosome organization. ZIKV infection disrupted the organization of centrosomal proteins including CEP63, a MCPH-associated protein. The ZIKV nonstructural protein NS3 bound CEP63, and expression of NS3 was sufficient to alter centrosome architecture and CEP63 localization. Loss of CEP63 suppressed ZIKV-induced centrosome disorganization, indicating that ZIKV requires CEP63 to disrupt centrosome organization. ZIKV infection or CEP63 loss decreased the centrosomal localization and stability of TANK-binding kinase 1 (TBK1), a regulator of the innate immune response. ZIKV infection also increased the centrosomal accumulation of the CEP63 interactor DTX4, a ubiquitin ligase that degrades TBK1. Therefore, we propose that ZIKV disrupts CEP63 function to increase centrosomal DTX4 localization and destabilization of TBK1, thereby tempering the innate immune response.

The role of TBK1 in cancer pathogenesis and anticancer immunity

The TANK-binding kinase 1 (TBK1) is a serine/threonine kinase belonging to the non-canonical inhibitor of nuclear factor-κB (IκB) kinase (IKK) family. TBK1 can be activated by pathogen-associated molecular patterns (PAMPs), inflammatory cytokines, and oncogenic kinases, including activated K-RAS/N-RAS mutants. TBK1 primarily mediates IRF3/7 activation and NF-κB signaling to regulate inflammatory cytokine production and the activation of innate immunity. TBK1 is also involved in the regulation of several other cellular activities, including autophagy, mitochondrial metabolism, and cellular proliferation. Although TBK1 mutations have not been reported in human cancers, aberrant TBK1 activation has been implicated in the oncogenesis of several types of cancer, including leukemia and solid tumors with KRAS-activating mutations. As such, TBK1 has been proposed to be a feasible target for pharmacological treatment of these types of cancer. Studies suggest that TBK1 inhibition suppresses cancer development not only by directly suppressing the proliferation and survival of cancer cells but also by activating antitumor T-cell immunity. Several small molecule inhibitors of TBK1 have been identified and interrogated. However, to this point, only momelotinib (MMB)/CYT387 has been evaluated as a cancer therapy in clinical trials, while amlexanox (AMX) has been evaluated clinically for treatment of type II diabetes, nonalcoholic fatty liver disease, and obesity. In this review, we summarize advances in research into TBK1 signaling pathways and regulation, as well as recent studies on TBK1 in cancer pathogenesis. We also discuss the potential molecular mechanisms of targeting TBK1 for cancer treatment. We hope that our effort can help to stimulate the development of novel strategies for targeting TBK1 signaling in future approaches to cancer therapy.

The Kinase MAP4K1 Inhibits Cytosolic RNA-Induced Antiviral Signaling by Promoting Proteasomal Degradation of TBK1/IKKε

TANK-binding kinase 1 (TBK1)/IκB kinase-ε (IKKε) mediates robust production of type I interferons (IFN-I) and proinflammatory cytokines in response to acute viral infection. However, excessive or prolonged production of IFN-I is harmful and even fatal to the host by causing autoimmune disorders. In this study, we identified mitogen-activated protein kinase kinase kinase kinase 1 (MAP4K1) as a negative regulator in the RIG-I-like receptor (RLR) signaling pathway. MAP4K1, a member of Ste20-like serine/threonine kinases, was previously known as a prominent regulator in adaptive immunity by downregulating T-cell receptor (TCR) signaling and B-cell receptor (BCR) signaling. However, its role in regulating antiviral innate immune signaling is still unclear. This study reports an undiscovered role of MAP4K1, which inhibits RLR signaling by targeting TBK1/IKKε for proteasomal degradation via the ubiquitin ligase DTX4. We initially identify MAP4K1 as an interacting partner of TBK1 by yeast two-hybrid screens and subsequently investigate its function in RLR-mediated antiviral signaling pathways. Overexpression of MAP4K1 significantly inhibits RNA virus-triggered activation of IFN-β and the production of proinflammatory cytokines. Consistently, knockdown or knockout experiments show opposite effects. Furthermore, MAP4K1 promotes the degradation of TBK1/IKKε by K48-linked ubiquitination via DTX4. Knockdown of DTX4 abrogated the ubiquitination and degradation of TBK1/IKKε. Collectively, our results identify that MAP4K1 acts as a negative regulator in antiviral innate immunity by targeting TBK1/IKKε, discover a novel TBK1 inhibitor, and extend a novel functional role of MAP4K1 in immunity. IMPORTANCE TANK-binding kinase 1 (TBK1)/IκB kinase-ε (IKKε) mediates robust production of type I interferons (IFN-I) and proinflammatory cytokines to restrict the spread of invading viruses. However, excessive or prolonged production of IFN-I is harmful to the host by causing autoimmune disorders. In this study, we identified that mitogen-activated protein kinase kinase kinase kinase 1 (MAP4K1) is a negative regulator in the RLR signaling pathway. Notably, MAP4K1 promotes the degradation of TBK1/IKKε by K48-linked ubiquitination via the ubiquitin ligase DTX4, leading to the negative regulation of the IFN signaling pathway. Previous studies showed that MAP4K1 has a pivotal function in adaptive immune responses. This study identifies that MAP4K1 also plays a vital role in innate immunity and outlines a novel mechanism by which the IFN signaling pathway is tightly controlled to avoid excessive inflammation. Our study documents a novel TBK1 inhibitor, which serves as a potential therapeutic target for autoimmune diseases, and elucidated a significant function for MAP4K1 linked to innate immunity in addition to subsequent adaptive immunity.

Differential STAT gene expressions of Penaeus monodon and Macrobrachium rosenbergii in response to white spot syndrome virus (WSSV) and bacterial infections: Additional insight into genetic variations and transcriptomic highlights

Diseases have remained the major issue for shrimp aquaculture industry for decades by which different shrimp species demonstrated alternative disease resistance or tolerance. However, there had been insufficient studies on the underlying host mechanisms of such phenomenon. Hence, in this study, the main objective involves gaining a deeper understanding into the functional importance of shrimp STAT gene from the aspects of expression, sequence, structure, and associated genes. STAT gene was selected primarily because of its vital signalling roles in stress, endocrine, and immune response. The differential gene expressions of Macrobrachium rosenbergii STAT (MrST) and Penaeus monodon STAT (PmST) under White Spot Syndrome Virus (WSSV) and Vibrio parahaemolyticus/VpAHPND infections were identified through qPCR analysis. Notably, during both pathogenic infections, MrST demonstrated significant gene expression down-regulations (during either early or later post-infection time points) whereas PmST showed only significant gene expression up-regulations. Important sequence conservation or divergence was highlighted through STAT sequence comparison especially amino acid alterations at 614 aa [K (Lysine) to E (Glutamic Acid)] and 629 aa [F (Phenylalanine) to V (Valine)] from PmST (AY327491.1) to PmST (disease tolerant strain). There were significant differences observed between in silico characterized structures of MrST and PmST proteins. Important functional differentially expressed genes (DEGs) in the aspects of stress, endocrine, immune, signalling, and structural were uncovered through comparative transcriptomic analysis. The DEGs associated with STAT functioning were identified including inositol 1,4,5-trisphosphate receptor, hsp90, caspase, ATP binding cassette transmembrane transporter, C-type Lectin, HMGB, ALF1, ALF3, superoxide dismutase, glutathione peroxidase, catalase, and TBK1. The main findings of this study are STAT differential gene expression patterns, sequence divergence, structural differences, and associated functional DEGs. These findings can be further utilized for shrimp health or host response diagnostic studies. STAT gene can also be proposed as a suitable candidate for future studies of shrimp innate immune enhancement.

Stimulus-specific responses in innate immunity: Multilayered regulatory circuits

Immune sentinel cells initiate immune responses to pathogens and tissue injury and are capable of producing highly stimulus-specific responses. Insight into the mechanisms underlying such specificity has come from the identification of regulatory factors and biochemical pathways, as well as the definition of signaling circuits that enable combinatorial and temporal coding of information. Here, we review the multi-layered molecular mechanisms that underlie stimulus-specific gene expression in macrophages. We categorize components of inflammatory and anti-pathogenic signaling pathways into five layers of regulatory control and discuss unifying mechanisms determining signaling characteristics at each layer. In this context, we review mechanisms that enable combinatorial and temporal encoding of information, identify recurring regulatory motifs and principles, and present strategies for integrating experimental and computational approaches toward the understanding of signaling specificity in innate immunity.

Negative Regulation of the Innate Immune Response through Proteasomal Degradation and Deubiquitination

The rapid and dynamic activation of the innate immune system is achieved through complex signaling networks regulated by post-translational modifications modulating the subcellular localization, activity, and abundance of signaling molecules. Many constitutively expressed signaling molecules are present in the cell in inactive forms, and become functionally activated once they are modified with ubiquitin, and, in turn, inactivated by removal of the same post-translational mark. Moreover, upon infection resolution a rapid remodeling of the proteome needs to occur, ensuring the removal of induced response proteins to prevent hyperactivation. This review discusses the current knowledge on the negative regulation of innate immune signaling pathways by deubiquitinating enzymes, and through degradative ubiquitination. It focusses on spatiotemporal regulation of deubiquitinase and E3 ligase activities, mechanisms for re-establishing proteostasis, and degradation through immune-specific feedback mechanisms vs. general protein quality control pathways.

Accelerator or Brake: Immune Regulators in Malaria

Malaria is a life-threatening infectious disease, affecting over 250 million individuals worldwide each year, eradicating malaria has been one of the greatest challenges to public health for a century. Growing resistance to anti-parasitic therapies and lack of effective vaccines are major contributing factors in controlling this disease. However, the incomplete understanding of parasite interactions with host anti-malaria immunity hinders vaccine development efforts to date. Recent studies have been unveiling the complexity of immune responses and regulators against Plasmodium infection. Here, we summarize our current understanding of host immune responses against Plasmodium-derived components infection and mainly focus on the various regulatory mechanisms mediated by recent identified immune regulators orchestrating anti-malaria immunity.

SOCS3-deficient lung epithelial cells uptaking neutrophil-derived SOCS3 worsens lung influenza infection

Suppressor of cytokine signaling 3 (SOCS3) is a negative regulator of TBK1 and interferon pathway and the expression of SOCS3 is closely correlated with symptoms of influenza patients. However, whether deletion of Socs3 in the lung epithelial cells would affect influenza lung replication and inflammation in vivo is unknown. To test this, we approached the influenza infected Socs3^f/f and SpcCre.Socs3^f/f mice. We first found that knockdown of Socs3 in lung epithelial cells reduced influenza replication. However, in the in vivo study, there was a reduction of SOCS3 in the influenza-infected neutrophils coincided with an increase of SOCS3 in the CD45^-CD326⁺ lung epithelial cells in PR8-infected SpcCre.Socs3^f/f mice. SOCS3-deficient neutrophils expressed higher levels of IL-17 that enhanced chemokine expression in the lung epithelial cells. Lung SOCS3-dificient epithelial cells increased expression of GM-CSF and PGE₂ which promoted SpcCre.Socs3^f/f neutrophils to yield SOCS3. SpcCre.Socs3^f/f lung epithelial cells internalized SOCS3 released from GM-CSF + PGE₂-stimulated SpcCre.Socs3^f/f neutrophils, which could boost influenza replication in the lung epithelial cells. Thus, in the in vivo study, deletion of SOCS3 from lung epithelium could be nullified by the uptake from SOCS3 from infiltrated neutrophils. In addition, deletion of Socs3 from myeloid cells reduced lung influenza infection, but increased lung inflammation. Taken together, deletion of SOCS3 could suppress influenza replication, but intracellular SOCS3 communication between neutrophils and lung epithelial cells confounds this effect.

The E3 ubiquitin ligase MARCH1 regulates antimalaria immunity through interferon signaling and T cell activation

Malaria infection induces complex and diverse immune responses. To elucidate the mechanisms underlying host-parasite interaction, we performed a genetic screen during early (24 h) Plasmodium yoelii infection in mice and identified a large number of interacting host and parasite genes/loci after transspecies expression quantitative trait locus (Ts-eQTL) analysis. We next investigated a host E3 ubiquitin ligase gene (March1) that was clustered with interferon (IFN)-stimulated genes (ISGs) based on the similarity of the genome-wide pattern of logarithm of the odds (LOD) scores (GPLS). March1 inhibits MAVS/STING/TRIF-induced type I IFN (IFN-I) signaling in vitro and in vivo. However, in malaria-infected hosts, deficiency of March1 reduces IFN-I production by activating inhibitors such as SOCS1, USP18, and TRIM24 and by altering immune cell populations. March1 deficiency increases CD86⁺DC (dendritic cell) populations and levels of IFN-γ and interleukin 10 (IL-10) at day 4 post infection, leading to improved host survival. T cell depletion reduces IFN-γ level and reverse the protective effects of March1 deficiency, which can also be achieved by antibody neutralization of IFN-γ. This study reveals functions of MARCH1 (membrane-associated ring-CH-type finger 1) in innate immune responses and provides potential avenues for activating antimalaria immunity and enhancing vaccine efficacy.

Leukemia Inhibitory Factor Inhibits Plasmacytoid Dendritic Cell Function and Development

Plasmacytoid dendritic cells (pDCs) produce abundant type I IFNs (IFN-I) in response to viral nucleic acids. Generation of pDCs from bone marrow dendritic cell (DC) progenitors and their maintenance is driven by the transcription factor E2-2 and inhibited by its repressor Id2. In this study, we find that mouse pDCs selectively express the receptor for LIF that signals through STAT3. Stimulation of pDCs with LIF inhibited IFN-I, TNF, and IL-6 responses to CpG and induced expression of the STAT3 targets SOCS3 and Bcl3, which inhibit IFN-I and NF-κB signaling. Moreover, although STAT3 has been also reported to induce E2-2, LIF paradoxically induced its repressor Id2. A late-stage bone marrow DC progenitor expressed low amounts of LIFR and developed into pDCs less efficiently after being exposed to LIF, consistent with the induction of Id2. Conversely, pDC development and serum IFN-I responses to lymphocytic choriomeningitis virus infection were augmented in newly generated mice lacking LIFR in either CD11c⁺ or hematopoietic cells. Thus, an LIF-driven STAT3 pathway induces SOCS3, Bcl3, and Id2, which render pDCs and late DC progenitors refractory to physiological stimuli controlling pDC functions and development. This pathway can be potentially exploited to prevent inappropriate secretion of IFN-I in autoimmune diseases or promote IFN-I secretion during viral infections.

Zika Virus-Induction of the Suppressor of Cytokine Signaling 1/3 Contributes to the Modulation of Viral Replication

Zika virus (ZIKV) is a mosquito-borne flavivirus that has emerged and caused global outbreaks since 2007. Although ZIKV proteins have been shown to suppress early anti-viral innate immune responses, little is known about the exact mechanisms. This study demonstrates that infection with either the African or Asian lineage of ZIKV leads to a modulated expression of suppressor of cytokine signaling (SOCS) genes encoding SOCS1 and SOCS3 in the following cell models: A549 human lung adenocarcinoma cells; JAr human choriocarcinoma cells; human neural progenitor cells. Studies of viral gene expression in response to SOCS1 or SOCS3 demonstrated that the knockdown of these SOCS proteins inhibited viral NS5 or ZIKV RNA expression, whereas overexpression resulted in an increased expression. Moreover, the overexpression of SOCS1 or SOCS3 inhibited the retinoic acid-inducible gene-I-like receptor-mediated activation of both type I and III interferon pathways. These results imply that SOCS upregulation following ZIKV infection modulates viral replication, possibly via the regulation of anti-viral innate immune responses.

Estrogen induces indoleamine 2,3-dioxygenase expression via suppressors of cytokine signaling 3 in the chorionic villi and decidua of women in early pregnancy

PROBLEM

Indoleamine 2,3-dioxygenase (IDO) is a key protein that participates in the protection of embryos against the mother's immune system during pregnancy. How the expression of this protein is regulated at the maternal-fetal interface remains largely unknown.

METHOD OF STUDY

The chorionic villi and decidua of women in early pregnancy were collected. Tissue explants of the chorionic villi and decidua were cultured in media containing varying concentrations of 17β-estradiol and estriol with or without fulvestrant. Western blot analysis and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) were used to detect the expression of IDO and the suppressors of cytokine signaling 3 (SOCS3) in the cultured tissues from chorionic villi and decidua.

RESULTS

Both IDO and SOCS3 were expressed in chorionic villi and decidua. The expression of IDO was increased in tissue explants from chorionic villi and decidua cultured in medium containing different concentrations of 17β-estradiol or estriol, and this increase was reversed when fulvestrant was added to the medium. The expression of IDO was upregulated, and SOCS3 expression was downregulated the most in tissue explants from chorionic villi and decidua that were cultured in medium containing 17β-estradiol at a concentration of 10 ng/mL or estriol at a concentration of 1 µg/mL. This increase in IDO and decrease in SOCS3 were reversed when fulvestrant was added to the medium at a concentration of 10 µg/mL.

CONCLUSION

At a concentration similar to that present during pregnancy, estrogen may upregulate the expression of IDO via downregulating SOCS3, which implies that estrogen may contribute to the prevention of allogeneic fetal rejection, and further studies may strengthen the possibility of using estrogen as an immune modulator.

The hepatitis C virus (HCV) protein, p7, suppresses inflammatory responses to tumor necrosis factor (TNF)-α via signal transducer and activator of transcription (STAT)3 and extracellular signal-regulated kinase (ERK)-mediated induction of suppressor of cytokine signaling (SOCS)3

Viruses use a spectrum of immune evasion strategies that enable infection and replication. The acute phase of hepatitis C virus (HCV) infection is characterized by nonspecific and often mild clinical symptoms, suggesting an immunosuppressive mechanism that, unless symptomatic liver disease presents, allows the virus to remain largely undetected. We previously reported that HCV induced the regulatory protein suppressor of cytokine signaling (SOCS)3, which inhibited TNF-α-mediated inflammatory responses. However, the mechanism by which HCV up-regulates SOCS3 remains unknown. Here we show that the HCV protein, p7, enhances both SOCS3 mRNA and protein expression. A p7 inhibitor reduced SOCS3 induction, indicating that p7's ion channel activity was required for optimal up-regulation of SOCS3. Short hairpin RNA and chemical inhibition revealed that both the Janus kinase-signal transducer and activator of transcription (JAK-STAT) and MAPK pathways were required for p7-mediated induction of SOCS3. HCV-p7 expression suppressed TNF-α-mediated IκB-α degradation and subsequent NF-κB promoter activity, revealing a new and functional, anti-inflammatory effect of p7. Together, these findings identify a molecular mechanism by which HCV-p7 induces SOCS3 through STAT3 and ERK activation and demonstrate that p7 suppresses proinflammatory responses to TNF-α, possibly explaining the lack of inflammatory symptoms observed during early HCV infection.-Convery, O., Gargan, S., Kickham, M., Schroder, M., O'Farrelly, C., Stevenson, N. J. The hepatitis C virus (HCV) protein, p7, suppresses inflammatory responses to tumor necrosis factor (TNF)-α via signal transducer and activator of transcription (STAT)3 and extracellular signal-regulated kinase (ERK)-mediated induction of suppressor of cytokine signaling (SOCS)3.

THO Complex Subunit 7 Homolog Negatively Regulates Cellular Antiviral Response against RNA Viruses by Targeting TBK1

RNA virus invasion induces a cytosolic RIG-I-like receptor (RLR) signaling pathway by promoting assembly of the Mitochondrial antiviral-signaling protein (MAVS) signalosome and triggers the rapid production of type I interferons (IFNs) and proinflammatory cytokines. During this process, the pivotal kinase TANK binding kinase 1 (TBK1) is recruited to the MAVS signalosome to transduce a robust innate antiviral immune response by phosphorylating transcription factors interferon regulatory factor 3 (IRF3) and nuclear factor (NF)-κB and promoting their nuclear translocation. However, the molecular mechanisms underlying the negative regulation of TBK1 are largely unknown. In the present study, we found that THO complex subunit 7 homolog (THOC7) negatively regulated the cellular antiviral response by promoting the proteasomal degradation of TBK1. THOC7 overexpression potently inhibited Sendai virus- or polyI:C-induced IRF3 dimerization and phosphorylation and IFN-β production. In contrast, THOC7 knockdown had the opposite effects. Moreover, we simulated a node-activated pathway to show that THOC7 regulated the RIG-I-like receptors (RLR)-/MAVS-dependent signaling cascade at the TBK1 level. Furthermore, THOC7 was involved in the MAVS signalosome and promoted TBK1 degradation by increasing its K48 ubiquitin-associated polyubiquitination. Together, these findings suggest that THOC7 negatively regulates type I IFN production by promoting TBK1 proteasomal degradation, thus improving our understanding of innate antiviral immune responses.

Cullin5 deficiency promotes small-cell lung cancer metastasis by stabilizing integrin β1

Metastasis is the dominant cause of patient death in small-cell lung cancer (SCLC), and a better understanding of the molecular mechanisms underlying SCLC metastasis may potentially improve clinical treatment. Through genome-scale screening for key regulators of mouse Rb1-/- Trp53-/- SCLC metastasis using the pooled CRISPR/Cas9 library, we identified Cullin5 (CUL5) and suppressor of cytokine signaling 3 (SOCS3), two components of the Cullin-RING E3 ubiquitin ligase complex, as top candidates. Mechanistically, the deficiency of CUL5 or SOCS3 disrupted the functional formation of the E3 ligase complex and prevented the degradation of integrin β1, which stabilized integrin β1 and activated downstream focal adhesion kinase/SRC (FAK/SRC) signaling and eventually drove SCLC metastasis. Low expression levels of CUL5 and SOCS3 were significantly associated with high integrin β1 levels and poor prognosis in a large cohort of 128 clinical patients with SCLC. Moreover, the CUL5-deficient SCLCs were vulnerable to the treatment of the FDA-approved SRC inhibitor dasatinib. Collectively, this work identifies the essential role of CUL5- and SOCS3-mediated integrin β1 turnover in controlling SCLC metastasis, which might have therapeutic implications.

USP7-TRIM27 axis negatively modulates antiviral type I IFN signaling

Ubiquitination and deubiquitination are important post-translational regulatory mechanisms responsible for fine tuning the antiviral signaling. In this study, we identified a deubiquitinase, the ubiquitin-specific peptidase 7/herpes virus associated ubiquitin-specific protease (USP7/HAUSP) as an important negative modulator of virus-induced signaling. Overexpression of USP7 suppressed Sendai virus and polyinosinic-polycytidylic acid and poly(deoxyadenylic-deoxythymidylic)-induced ISRE and IFN-β activation, and enhanced virus replication. Knockdown or knockout of endogenous USP7 expression had the opposite effect. Coimmunoprecipitation assays showed that USP7 physically interacted with tripartite motif (TRIM)27. This interaction was enhanced after SeV infection. In addition, TNF receptor-associated factor family member-associated NF-kappa-B-binding kinase (TBK)-1 was pulled down in the TRIM27-USP7 complex. Overexpression of USP7 promoted the ubiquitination and degradation of TBK1 through promoting the stability of TRIM27. Knockout of endogenous USP7 led to enhanced TRIM27 degradation and reduced TBK1 ubiquitination and degradation, resulting in enhanced type I IFN signaling. Our findings suggest that USP7 acts as a negative regulator in antiviral signaling by stabilizing TRIM27 and promoting the degradation of TBK1.-Cai, J., Chen, H.-Y., Peng, S.-J., Meng, J.-L., Wang, Y., Zhou, Y., Qian, X.-P., Sun, X.-Y., Pang, X.-W., Zhang, Y., Zhang, J. USP7-TRIM27 axis negatively modulates antiviral type I IFN signaling.

Negative regulation of type I IFN signaling

Type I IFNs (α, β, and others) are a family of cytokines that are produced in physiological conditions as well as in response to the activation of pattern recognition receptors. They are critically important in controlling the host innate and adaptive immune response to viral and some bacterial infections, cancer, and other inflammatory stimuli. However, dysregulation of type I IFN production or response can contribute to immune pathologies termed "interferonopathies", pointing to the importance of balanced activating signals with tightly regulated mechanisms of tuning this signaling. Here, we summarize the recent advances of how type I IFN production and response are controlled at multiple levels of the type I IFN signaling cascade.

Productive replication of avian influenza viruses in chicken endothelial cells is determined by hemagglutinin cleavability and is related to innate immune escape

Endotheliotropism is a hallmark of gallinaceous poultry infections with highly pathogenic avian influenza (HPAI) viruses and a feature that distinguishes HPAI from low pathogenic avian influenza (LPAI) viruses. Here, we used chicken aortic endothelial cells (chAEC) as a novel in vitro infection model to assess the susceptibility, permissiveness, and host response of chicken endothelial cells (EC) to infections with avian influenza (AI) viruses. Our data show that productive replication of AI viruses in chAEC is critically determined by hemagglutinin cleavability, and is thus an exclusive trait of HPAI viruses. However, we provide evidence for a link between limited (i.e. trypsin-dependent) replication of certain LPAI viruses, and the viruses' ability to dampen the antiviral innate immune response in infected chAEC. Strikingly, this cell response pattern was also detected in HPAI virus-infected chAEC, suggesting that viral innate immune escape might be a prerequisite for robust AI virus replication in chicken EC.

The nucleolar protein GLTSCR2 is required for efficient viral replication

Glioma tumor suppressor candidate region gene 2 protein (GLTSCR2) is a nucleolar protein. In the investigation of the role of GLTSCR2 that played in the cellular innate immune response to viral infection, we found GLTSCR2 supported viral replication of rhabdovirus, paramyxovirus, and coronavirus in cells. Viral infection induced translocation of GLTSCR2 from nucleus to cytoplasm that enabled GLTSCR2 to attenuate type I interferon IFN-β and support viral replication. Cytoplasmic GLTSCR2 was able to interact with retinoic acid-inducible gene I (RIG-I) and the ubiquitin-specific protease 15 (USP15), and the triple interaction induced USP15 activity to remove K63-linked ubiquitination of RIG-I, leading to attenuation of RIG-I and IFN-β. Blocking cytoplasmic translocation of GLTSCR2, by deletion of its nuclear export sequence (NES), abrogated its ability to attenuate IFN-β and support viral replication. GLTSCR2-mediated attenuation of RIG-I and IFN-β led to alleviation of host cell innate immune response to viral infection. Our findings suggested that GLTSCR2 contributed to efficient viral replication, and GLTSCR2 should be considered as a potential target for therapeutic control of viral infection.

TBK1-like transcript negatively regulates the production of IFN and IFN-stimulated genes through RLRs-MAVS-TBK1 pathway

TANK-binding kinase 1 (TBK1) is an essential serine/threonine-protein kinase required for Toll-like receptor (TLR)- and retinoic acid-inducible gene I (RIG-I) -mediated induction of type I IFN and host antiviral defense. In the present study, TBK1-like transcript, namely TBK1L, was cloned from zebrafish. Compared with TBK1, TBK1L contains an incomplete S_TKc domain, and lacks UBL_TBK1_like domain. Realtime PCR showed that TBK1L was constitutively produced in embryos, early larvae and ZF4 cells, and unchanged in ZF4 cells following SVCV infection. Overexpression of TBK1 but not TBK1L resulted in significant activation of zebrafish IFN1 and IFN3 promoters. Similarly, TBK1L had little impact on the antiviral state of the cells. However, the overexpression of TBK1L negatively regulated the induction of zebrafish IFN1 and/or IFN3 promoters mediated by the retinoic acid-inducible gene I-like receptors (RLRs), MAVS and TBK1. In addition, the overexpression of TBK1L in zebrafish embryos led to the decreased production of many IFN-stimulated genes induced by TBK1. Collectively, these data support that zebrafish TBK1L negatively regulates RLRs-MAVS-TBK1 pathway.

Ubiquitin signaling in immune responses

Ubiquitination has emerged as a crucial mechanism that regulates signal transduction in diverse biological processes, including different aspects of immune functions. Ubiquitination regulates pattern-recognition receptor signaling that mediates both innate immune responses and dendritic cell maturation required for initiation of adaptive immune responses. Ubiquitination also regulates the development, activation, and differentiation of T cells, thereby maintaining efficient adaptive immune responses to pathogens and immunological tolerance to self-tissues. Like phosphorylation, ubiquitination is a reversible reaction tightly controlled by the opposing actions of ubiquitin ligases and deubiquitinases. Deregulated ubiquitination events are associated with immunological disorders, including autoimmune and inflammatory diseases.