Epidermal growth factor receptor is essential for Toll-like receptor 3 signaling

Putative neural mechanisms underlying release-mode-specific abnormalities in dopamine neural activity in a schizophrenia-like model: The distinct roles of glutamate and serotonin in the impaired regulation of dopamine neurons

Abnormalities in dopamine function might be related to psychiatric disorders such as schizophrenia. Even at the same concentration, dopamine exerts opposite effects on information processing in the prefrontal cortex depending on independent dopamine release modes known as tonic and phasic releases. This duality of dopamine prevents a blanket interpretation of the implications of dopamine abnormalities for diseases on the basis of absolute dopamine levels. Moreover, the mechanisms underlying the mode-specific dopamine abnormalities are not clearly understood. Here, I show that the two modes of dopamine release in the prefrontal cortex of a schizophrenia-like model are disrupted by different mechanisms. In the schizophrenia-like model established by perinatal exposure to inflammatory cytokine, epidermal growth factor, tonic release was enhanced and phasic release was decreased in the prefrontal cortex. I examined the activity of dopamine neurons in the ventral tegmental area (VTA), which sends dopamine projections to the prefrontal cortex, under anaesthesia. The activation of VTA dopamine neurons during excitatory stimulation (local application of glutamate or N-methyl-d-aspartic acid [NMDA]), which is associated with phasic activity, was blunt in this model. Dopaminergic neuronal activity in the resting state related to tonic release was increased by disinhibition of the dopamine neurons due to the impairment of 5HT2 (5HT2A) receptor-regulated GABAergic inputs. Moreover, chronic administration of risperidone ameliorated this disinhibition of dopaminergic neurons. These results provide an idea about the mechanism of dopamine disturbance in schizophrenia and may be informative in explaining the effects of atypical antipsychotics as distinct from those of typical drugs.

EGF-Receptor-Dependent TLR7 Signaling in Macrophages Promotes Glomerular Injury in Crescentic Glomerulonephritis

Glomerulonephritis (GN) is a group of inflammatory diseases and an important cause of morbidity and mortality worldwide. The initiation of the inflammatory process is quite different for each type of GN; however, each GN is characterized commonly and variably by acute inflammation with neutrophils and macrophages and crescent formation, leading to glomerular death. Toll-like receptor (TLR) 7 is a sensor for self-RNA and implicated in the pathogenesis of human and murine GN. Here, we show that TLR7 exacerbates glomerular injury in nephrotoxic serum nephritis (NTN), a murine model of severe crescentic GN. TLR7-/- mice were resistant to NTN, although TLR7-/- mice manifested comparable immune-complex deposition to wild-type mice without significant defects in humoral immunity, suggesting that endogenous TLR7 ligands accelerate glomerular injury. TLR7 was expressed exclusively in macrophages in glomeruli in GN but not in glomerular resident cells or neutrophils. Furthermore, we discovered that epidermal growth factor receptor (EGFR), a receptor-type tyrosine kinase, is essential for TLR7 signaling in macrophages. Mechanistically, EGFR physically interacted with TLR7 upon TLR7 stimulation, and EGFR inhibitor completely blocked the phosphorylation of TLR7 tyrosine residue(s). EGFR inhibitor attenuated glomerular damage in wild-type mice, and no additional glomerular protective effects by EGFR inhibitor were observed in TLR7-/- mice. Finally, mice lacking EGFR in macrophages were resistant to NTN. This study clearly demonstrated that EGFR-dependent TLR7 signaling in macrophages is essential for glomerular injury in crescentic GN.

TRIM3 attenuates cytokine storm caused by Dabie bandavirus via promoting Toll-like receptor 3 degradation

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that was caused by the Dabie bandavirus (DBV), and it has become a global public health threat. Cytokine storm is considered to be an important pathogenesis of critical SFTS. Tripartite motif-containing 3 (TRIM3), as a member of the TRIM protein family, may contribute to the regulation of the immune and inflammatory responses after viral infection. However, whether TRIM3 plays a major role in the pathogenesis of SFTS has not yet been investigated.

Methods

TRIM3 mRNA levels were detected in PBMCs between 29 SFTS patients and 29 healthy controls by qRT-PCR. We established the pathogenic IFNAR^-/- SFTS mouse model successfully by inoculating subcutaneously with DBV and testing the expression levels of TRIM3 mRNA and protein by qRT-PCR and immunofluorescence in the livers, spleens, lungs, and kidneys. TRIM3^OE THP-1 cells and peritoneal macrophages extracted from TRIM3^-/- mice were infected with DBV. The effect of TRIM3 on cytokines was detected by qRT-PCR and ELISA. Then we examined Toll-like receptor 3 (TLR3) and protein phosphorylation in the MAPK pathway after DBV infection using Western blot. Flow cytometry was used to verify TLR3 expression on peripheral blood monocytes in SFTS patients. We further explored the interaction between TRIM3 and TLR3 using CO-IP and Western blot.

Results

Compared to healthy controls, TRIM3 mRNA expression in PBMCs is decreased in SFTS patients, especially in severe cases. TRIM3 mRNA and protein were synchronously reduced in the livers, spleens, lungs, and kidney tissues of the IFNAR^-/- SFTS mice model. In the DBV-infected cell model, TRIM3 overexpression can inhibit the DBV-induced release of IL-1β, IL-6, and TNF-α, the expression of TLR3, and protein phosphorylation in the MAPK pathway, which plays an anti-inflammatory role, while TRIM3 deficiency exacerbates the pro-inflammatory effects. We further found that TRIM3 can promote TLR3 degradation through K48-linked ubiquitination.

Conclusion

TRIM3 can inhibit the production of cytokines by regulating the degradation of TLR3 through K48-linked ubiquitination, which can be a therapeutic target for improving the prognosis of SFTS.

Role of TLRs in EGFR-mediated IL-8 secretion by enteroaggregative Escherichia coli-infected cultured human intestinal epithelial cells

Enteroaggregative Escherichia coli (EAEC) is an emerging enteric pathogen associated with persistent diarrhea in travelers, immunocompromised patients and children worldwide. However, the pathogenesis of this organism is yet to be established. In this study, the role of Toll-like receptors (TLRs) was evaluated in epidermal growth factor receptor (EGFR)-mediated IL-8 secretion by EAEC-infected human small intestinal and colonic epithelial cells (INT-407 and HCT-15, respectively). We observed that EAEC-induced upregulation of TLR2, TLR4 and TLR5 transcripts in both types of cells, and the maximum level of these transcripts was seen in cells infected with EAEC-T8 (an invasive clinical isolate). All these TLRs made a significant contribution to the EAEC-T8-mediated EGFR activation in these cells. Furthermore, these TLRs were found to be associated with activation of the downstream effectors (ERK-1/2, PI3 kinase and Akt) and transcription factors (NF-κB, c-Jun, c-Fos and STAT-3) of EGFR-mediated signal transduction pathways. Moreover, the involvement of these TLRs was also noted in IL-8 secretion by both EAEC-T8-infected cell types. Our findings suggest that EAEC-induced upregulation of TLR2, TLR4 and TLR5 is important for the IL-8 response via EGFR-mediated signal transduction pathways in these cells.

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.

Unexpected Need of the Epidermal Growth Factor Receptor Tyrosine Kinase Activity for Signaling by Intracellular Pattern Recognition Receptors of Nucleic Acids

Many pattern recognition receptors in mammalian cells initiate signaling processes that culminate in mounting an innate protective response mediated by induced synthesis of a large number of proteins including type I interferons and other cytokines. Many of these receptors are not located on the plasma membrane but on the membranes of intracellular organelles such as endosomes, mitochondria, and the endoplasmic reticulum; they primarily recognize microbial or cellular nucleic acids. In the course of biochemical analyses of the signaling pathways triggered by these receptors, we discovered that they require tyrosine phosphorylation by the protein kinase activity of the epidermal growth factor receptor (EGFR), which is located not only on the plasma membrane but also on the intracellular membranes. Here, we discuss how specific members of this family of receptors, such as TLR3, TLR9, or STING, interact with EGFR and other protein tyrosine kinases and what are the functional consequences of their post-translational modifications. The article highlights an unexpected functional link between a growth factor receptor and cellular innate immune response.

Schizophrenia Animal Modeling with Epidermal Growth Factor and Its Homologs: Their Connections to the Inflammatory Pathway and the Dopamine System

Epidermal growth factor (EGF) and its homologs, such as neuregulins, bind to ErbB (Her) receptor kinases and regulate glial differentiation and dopaminergic/GABAergic maturation in the brain and are therefore implicated in schizophrenia neuropathology involving these cell abnormalities. In this review, we summarize the biological activities of the EGF family and its neuropathologic association with schizophrenia, mainly overviewing our previous model studies and the related articles. Transgenic mice as well as the rat/monkey models established by perinatal challenges of EGF or its homologs consistently exhibit various behavioral endophenotypes relevant to schizophrenia. In particular, post-pubertal elevation in baseline dopaminergic activity may illustrate the abnormal behaviors relevant to positive and negative symptoms as well as to the timing of this behavioral onset. With the given molecular interaction and transactivation of ErbB receptor kinases with Toll-like receptors (TLRs), EGF/ErbB signals are recruited by viral infection and inflammatory diseases such as COVID-19-mediated pneumonia and poxvirus-mediated fibroma and implicated in the immune-inflammatory hypothesis of schizophrenia. Finally, we also discuss the interaction of clozapine with ErbB receptor kinases as well as new antipsychotic development targeting these receptors.

Antiviral response within different cell types of the CNS

The central nervous system (CNS) is a constitutive structure of various cell types conserved by anatomical barriers. Many of the major CNS cell-type populations distributed across the different brain regions are targets for several neurotropic viruses. Numerous studies have demonstrated that viral susceptibility within the CNS is not absolute and initiates a cell-type specific antiviral defence response. Neurons, astrocytes, and microglial cells are among the major resident cell populations within the CNS and are all equipped to sense viral infection and induce a relative antiviral response mostly through type I IFN production, however, not all these cell types adopt a similar antiviral strategy. Rising evidence has suggested a diversity regarding IFN production and responsiveness based on the cell type/sub type, regional distinction and cell`s developmental state which could shape distinct antiviral signatures. Among CNS resident cell types, neurons are of the highest priority to defend against the invading virus due to their poor renewable nature. Therefore, infected and uninfected glial cells tend to play more dominant antiviral roles during a viral infection and have been found to be the major CNS IFN producers. Alternatively, neuronal cells do play an active part during antiviral responses but may adopt differential strategies in addition to induction of a typical type I IFN response, to minimize the chance of cellular damage. Heterogeneity observed in neuronal IFN responsiveness may be partially explained by their altered ISGs and/or lower STATS expression levels, however, further in vivo studies are required to fully elucidate the specificity of the acquired antiviral responses by distinct CNS cell types.

Composition and regulation of the immune microenvironment of salivary gland in Sjögren’s syndrome

Primary Sjögren’s syndrome (pSS) is a systemic autoimmune disease characterized by exocrine gland dysfunction and inflammation. Patients often have dry mouth and dry eye symptoms, which seriously affect their lives. Improving dry mouth and eye symptoms has become a common demand from patients. For this reason, researchers have conducted many studies on external secretory glands. In this paper, we summarize recent studies on the salivary glands of pSS patients from the perspective of the immune microenvironment. These studies showed that hypoxia, senescence, and chronic inflammation are the essential characteristics of the salivary gland immune microenvironment. In the SG of pSS, genes related to lymphocyte chemotaxis, antigen presentation, and lymphocyte activation are upregulated. Interferon (IFN)-related genes, DNA methylation, sRNA downregulation, and mitochondrial-related differentially expressed genes are also involved in forming the immune microenvironment of pSS, while multiple signaling pathways are involved in regulation. We further elucidated the regulation of the salivary gland immune microenvironment in pSS and relevant, targeted treatments.

Toll-Like Receptor 3 in Cardiovascular Diseases

Toll-like receptor 3 (TLR3) is an important member of the innate immune response receptor toll-like receptors (TLRs) family, which plays a vital role in regulating immune response, promoting the maturation and differentiation of immune cells, and participating in the response of pro-inflammatory factors. TLR3 is activated by pathogen-associated molecular patterns and damage-associated molecular patterns, which support the pathophysiology of many diseases related to inflammation. An increasing number of studies have confirmed that TLR3, as a crucial medium of innate immunity, participates in the occurrence and development of cardiovascular diseases (CVDs) by regulating the transcription and translation of various cytokines, thus affecting the structure and physiological function of resident cells in the cardiovascular system, including vascular endothelial cells, vascular smooth muscle cells, cardiomyocytes, fibroblasts and macrophages. The dysfunction and structural damage of vascular endothelial cells and proliferation of vascular smooth muscle cells are the key factors in the occurrence of vascular diseases such as pulmonary arterial hypertension, atherosclerosis, myocardial hypertrophy, myocardial infarction, ischaemia/reperfusion injury, and heart failure. Meanwhile, cardiomyocytes, fibroblasts, and macrophages are involved in the development of CVDs. Therefore, the purpose of this review was to explore the latest research published on TLR3 in CVDs and discuss current understanding of potential mechanisms by which TLR3 contributes to CVDs. Even though TLR3 is a developing area, it has strong treatment potential as an immunomodulator and deserves further study for clinical translation.

Toll-Like Receptor 3 Overexpression Induces Invasion of Prostate Cancer Cells, whereas Its Activation Triggers Apoptosis

Toll-like receptor 3 (TLR3) is an endosomal receptor expressed in several immune and epithelial cells. Recent studies have highlighted its expression also in solid tumors, including prostate cancer (PCa), and described its role mainly in the proinflammatory response and induction of apoptosis. It has been found up-regulated in some castration-resistant prostate cancers. However, the role of TLR3 in prostate cancer progression remains largely unknown. We have experimentally demonstrated that exogenous TLR3 activation in PCa cell lines leads to the significant induction of secretion of the cytokines IL-6, IL-8, and interferon-β, depending on the model and chemoresistance status. Transcriptomic analysis of TLR3-overexpressing cells revealed a functional program that is enriched for genes involved in the regulation of cell motility, migration, and tumor invasiveness. Increased motility, migration, and invasion in TLR3-overexpressing cell line were confirmed by several in vitro assays and using an orthotopic prostate xenograft model in vivo. Furthermore, TLR3-ligand induced apoptosis via cleavage of caspase-3/7 and poly (ADP-ribose) polymerase, predominantly in TLR3-overexpressing cells. We conclude that TLR3 may be involved in prostate cancer progression and metastasis; however, it might also represent an Achilles heel of PCa, which can be exploited for targeted therapy.

Role of EGF Receptor Regulatory Networks in the Host Response to Viral Infections

In this review article, we will first provide a brief overview of EGF receptor (EGFR) structure and function, and its importance as a therapeutic target in epithelial carcinomas. We will then compare what is currently known about canonical EGFR trafficking pathways that are triggered by ligand binding, versus ligand-independent pathways activated by a variety of intrinsic and environmentally induced cellular stresses. Next, we will review the literature regarding the role of EGFR as a host factor with critical roles facilitating viral cell entry and replication. Here we will focus on pathogens exploiting virus-encoded and endogenous EGFR ligands, as well as EGFR-mediated trafficking and signaling pathways that have been co-opted by wild-type viruses and recombinant gene therapy vectors. We will also provide an overview of a recently discovered pathway regulating non-canonical EGFR trafficking and signaling that may be a common feature of viruses like human adenoviruses which signal through p38-mitogen activated protein kinase. We will conclude by discussing the emerging role of EGFR signaling in innate immunity to viral infections, and how viral evasion mechanisms are contributing to our understanding of fundamental EGFR biology.

STING-Mediated Interferon Induction by Herpes Simplex Virus 1 Requires the Protein Tyrosine Kinase Syk

The nature and the intensity of innate immune response to virus infection determine the course of pathogenesis in the host. Among the many pathogen-associated molecular pattern recognition receptors, STING, an endoplasmic reticulum (ER)-associated protein, plays a pivotal role in triggering responses to microbial or cellular cytoplasmic DNA. Herpes simplex virus 1 (HSV-1), a common human pathogen, activates STING signaling, and the resultant induction of type I interferon causes inhibition of virus replication. In this context, we have observed that phosphorylation of Tyr245 of STING by epidermal growth factor receptor kinase is necessary for interferon induction. Here, we report that phosphorylation of Tyr240 by the tyrosine kinase Syk is essential for all signaling activities of STING. Our analysis showed that upon ligand-binding, STING dimerizes and interacts with membrane-bound EGFR, which autophosphorylates and provides the platform for the recruitment of cytoplasmic Syk to the signaling complex and its activation. Activated Syk phosphorylates Tyr240 of STING, followed by phosphorylation of Tyr245 by epidermal growth factor receptor (EGFR). Pharmacological or genetic ablation of Syk activity resulted in an arrest of STING in the ER compartment and a complete block of gene induction. Consequently, in the absence of Syk, HSV-1 could not induce interferon, and it replicated more robustly. IMPORTANCE The innate immune response to virus infection leads to interferon production and inhibition of viral replication. STING, an ER-bound protein, mediates such a response to cytoplasmic cellular or microbial DNA. HSV-1, a DNA virus, activates STING, and it replicates more efficiently in the absence of STING signaling. We demonstrate that phosphorylation of Tyr240 of STING by the protein tyrosine kinase Syk is essential for STING-mediated gene induction. To signal, ligand-activated STING recruits two kinases, Syk and EGFR, which phosphorylate Tyr240 and Tyr245, respectively. The dependence of STING signaling on Syk has broad significance, because STING plays a major role in many microbial, mitochondrial, and autoimmune diseases as well as in cancer development and therapy.

DEAD/H-box helicases:Anti-viral and pro-viral roles during infections

DEAD/H-box RNA helicases make the prominent family of helicases super family-2 which take part in almost all RNA-related processes, from initiation of transcription to RNA decay pathways. In addition to these RNA-related activities, in recent years a certain number of these helicases are reported to play important roles in anti-viral immunity through various ways. Along with RLHs, endosomal TLRs, and cytosolic DNA receptors, many RNA helicases including DDX3, DHX9, DDX6, DDX41, DHX33, DDX60, DHX36 and DDX1-DDX21-DHX36 complex act as viral nucleic acid sensors or co-sensors. These helicases mostly follow RLHs-MAVS and STING mediated signaling cascades to trigger induction of type-I interferons and pro-inflammatory cytokines. Many of them also function as downstream adaptor molecules (DDX3), segments of stress and processing bodies (DDX3 and DDX6) or negative regulators (DDX19, DDX24, DDX25, DDX39A and DDX46). On the contrary, many studies indicated that several DEAD/H-box helicases such as DDX1, DDX3, DDX6, DDX24, and DHX9 could be exploited by viruses to evade innate immune responses, suggesting that these helicases seem to have a dual function as anti-viral innate immune mediators and viral replication cofactors. In this review, we summarized the current knowledge on several representative DEAD/H-box helicases, with an emphasis on their functions in innate immunity responses, involved in their anti-viral and pro-viral roles.

Mechanisms of TLR4-Mediated Autophagy and Nitroxidative Stress

Pathogenic infections have badly affected public health and the development of the breeding industry. Billions of dollars are spent every year fighting against these pathogens. The immune cells of a host produce reactive oxygen species and reactive nitrogen species which promote the clearance of these microbes. In addition, autophagy, which is considered an effective method to promote the destruction of pathogens, is involved in pathological processes. As research continues, the interplay between autophagy and nitroxidative stress has become apparent. Autophagy is always intertwined with nitroxidative stress. Autophagy regulates nitroxidative stress to maintain homeostasis within an appropriate range. Intracellular oxidation, in turn, is a strong inducer of autophagy. Toll-like receptor 4 (TLR4) is a pattern recognition receptor mainly involved in the regulation of inflammation during infectious diseases. Several studies have suggested that TLR4 is also a key regulator of autophagy and nitroxidative stress. In this review, we describe the role of TLR4 in autophagy and oxidation, and focus on its function in influencing autophagy-nitroxidative stress interactions.

Toll-like receptor 3 (TLR3) regulation mechanisms and roles in antiviral innate immune responses

Toll-like receptor 3 (TLR3) is a member of the TLR family, mediating the transcriptional induction of type I interferons (IFNs), proinflammatory cytokines, and chemokines, thereby collectively establishing an antiviral host response. Studies have shown that unlike other TLR family members, TLR3 is the only RNA sensor that is utterly dependent on the Toll-interleukin-1 receptor (TIR)‍-domain-containing adaptor-inducing IFN-‍β (TRIF). However, the details of how the TLR3-TRIF signaling pathway works in an antiviral response and how it is regulated are unclear. In this review, we focus on recent advances in understanding the antiviral mechanism of the TRIF pathway and describe the essential characteristics of TLR3 and its antiviral effects. Advancing our understanding of TLR3 may contribute to disease diagnosis and could foster the development of novel treatments for viral diseases.

ZCCHC3 modulates TLR3-mediated signaling by promoting recruitment of TRIF to TLR3

Toll-like receptor 3 (TLR3)-mediated signaling is important for host defense against RNA virus. Upon viral RNA stimulation, toll and interleukin-1 receptor domain-containing adaptor inducing IFN-β (TRIF) is recruited to TLR3 and then undergoes oligomerization, which is required for the recruitment of downstream molecules to transmit signals. Here, we identified zinc finger CCHC-type containing 3 (ZCCHC3) as a positive regulator of TLR3-mediated signaling. Overexpression of ZCCHC3 promoted transcription of downstream antiviral genes stimulated by the synthetic TLR3 ligand poly(I:C). ZCCHC3-deficiency markedly inhibited TLR3- but not TLR4-mediated induction of type I interferons (IFNs) and proinflammatory cytokines. Zcchc3^−/− mice were more resistant to poly(I:C)- but not lipopolysaccharide-induced inflammatory death. Mechanistically, ZCCHC3 promoted recruitment of TRIF to TLR3 after poly(I:C) stimulation. Our findings reveal that ZCCHC3 plays an important role in TLR3-mediated innate immune response by promoting the recruitment of TRIF to TLR3 after ligand stimulation.

Cell type-specific roles of PAR1 in Coxsackievirus B3 infection

Protease-activated receptor 1 (PAR1) is widely expressed in humans and mice, and is activated by a variety of proteases, including thrombin. Recently, we showed that PAR1 contributes to the innate immune response to viral infection. Mice with a global deficiency of PAR1 expressed lower levels of CXCL10 and had increased Coxsackievirus B3 (CVB3)-induced myocarditis compared with control mice. In this study, we determined the effect of cell type-specific deletion of PAR1 in cardiac myocytes (CMs) and cardiac fibroblasts (CFs) on CVB3-induced myocarditis. Mice lacking PAR1 in either CMs or CFs exhibited increased CVB3 genomes, inflammatory infiltrates, macrophages and inflammatory mediators in the heart and increased CVB3-induced myocarditis compared with wild-type controls. Interestingly, PAR1 enhanced poly I:C induction of CXCL10 in rat CFs but not in rat neonatal CMs. Importantly, activation of PAR1 reduced CVB3 replication in murine embryonic fibroblasts and murine embryonic cardiac myocytes. In addition, we showed that PAR1 reduced autophagy in murine embryonic fibroblasts and rat H9c2 cells, which may explain how PAR1 reduces CVB3 replication. These data suggest that PAR1 on CFs protects against CVB3-induced myocarditis by enhancing the anti-viral response whereas PAR1 on both CMs and fibroblasts inhibits viral replication.

TLR3 agonists: RGC100, ARNAX, and poly-IC: a comparative review

Toll-like receptors 3 (TLR3) have been broadly studied among all TLRs over the last few decades together with its agonists due to their contribution to cancer regression. These agonists undeniably have some shared characteristics such as mimicking dsRNA but pathways through which they exhibit antitumor properties are relatively diverse. In this review, three widely studied agonists RGC100, ARNAX, and poly-IC are discussed along with their structural and physiochemical differences including the signaling cascades through which they exert their actions. Comparison has been made to identify the finest agonist with maximum effectivity and the least side effect profile.

The distinct roles of zinc finger CCHC-type (ZCCHC) superfamily proteins in the regulation of RNA metabolism

The zinc finger CCHC-type (ZCCHC) superfamily proteins, characterized with the consensus sequence C-X₂-C-X₄-H-X₄-C, are accepted to have high-affinity binding to single-stranded nucleic acids, especially single-stranded RNAs. In human beings 25 ZCCHC proteins have been annotated in the HGNC database. Of interest is that among the family, most members are involved in the multiple steps of RNA metabolism. In this review, we focus on the diverged roles of human ZCCHC proteins on RNA transcription, biogenesis, splicing, as well as translation and degradation.

ZNRF1 Mediates Epidermal Growth Factor Receptor Ubiquitination to Control Receptor Lysosomal Trafficking and Degradation

Activation of the epidermal growth factor receptor (EGFR) is crucial for development, tissue homeostasis, and immunity. Dysregulation of EGFR signaling is associated with numerous diseases. EGFR ubiquitination and endosomal trafficking are key events that regulate the termination of EGFR signaling, but their underlying mechanisms remain obscure. Here, we reveal that ZNRF1, an E3 ubiquitin ligase, controls ligand-induced EGFR signaling via mediating receptor ubiquitination. Deletion of ZNRF1 inhibits endosome-to-lysosome sorting of EGFR, resulting in delayed receptor degradation and prolonged downstream signaling. We further demonstrate that ZNRF1 and Casitas B-lineage lymphoma (CBL), another E3 ubiquitin ligase responsible for EGFR ubiquitination, mediate ubiquitination at distinct lysine residues on EGFR. Furthermore, loss of ZNRF1 results in increased susceptibility to herpes simplex virus 1 (HSV-1) infection due to enhanced EGFR-dependent viral entry. Our findings identify ZNRF1 as a novel regulator of EGFR signaling, which together with CBL controls ligand-induced EGFR ubiquitination and lysosomal trafficking.

Toll-like receptor-mediated innate immunity against herpesviridae infection: a current perspective on viral infection signaling pathways

Background

In the past decades, researchers have demonstrated the critical role of Toll-like receptors (TLRs) in the innate immune system. They recognize viral components and trigger immune signal cascades to subsequently promote the activation of the immune system.

Main body

Herpesviridae family members trigger TLRs to elicit cytokines in the process of infection to activate antiviral innate immune responses in host cells. This review aims to clarify the role of TLRs in the innate immunity defense against herpesviridae, and systematically describes the processes of TLR actions and herpesviridae recognition as well as the signal transduction pathways involved.

Conclusions

Future studies of the interactions between TLRs and herpesviridae infections, especially the subsequent signaling pathways, will not only contribute to the planning of effective antiviral therapies but also provide new molecular targets for the development of antiviral drugs.

The role of toll-like receptor 4 (TLR4) in cancer progression: A possible therapeutic target?

The toll-like receptor (TLR) family consists of vital receptors responsible for pattern recognition in innate immunity, making them the core proteins involved in pathogen detection and eliciting immune responses. The most studied member of this family, TLR4, has been the center of attention regarding its contributory role in many inflammatory diseases including sepsis shock and asthma. Notably, mounting pieces of evidence have proved that this receptor is aberrantly expressed on the tumor cells and the tumor microenvironment in a wide range of cancer types and it is highly associated with the initiation of tumorigenesis as well as tumor progression and drug resistance. Cancer therapy using TLR4 inhibitors has recently drawn scientists' attention, and the promising results of such studies may pave the way for more investigation in the foreseeable future. This review will introduce the key proteins of the TLR4 pathway and how they interact with major growth factors in the tumor microenvironment. Moreover, we will discuss the many aspects of tumor progression affected by the activation of this receptor and provide an overview of the recent therapeutic approaches using various TLR4 antagonists.

ROLE OF TOLL-LIKE RECEPTORS IN CORONAVIRUS INFECTION AND IMMUNE RESPONSE

The emergence of a novel coronavirus referred to as SARS-CoV-2 has become a global health apprehension due to rapid transmission tendency, severity, and wide geographical spread. This emergence was started from Wuhan, China in 2019 from the zoonotic source and spread worldwide, infecting almost half of the community on this earth. Many of the receptors are involved in proceeding with this infection in the organism's body. Toll-like receptors (TLRs) play essential and protective functions from a wide range of microbial pathogens. Small setup of TLR adaptor proteins leads to activate nuclear factor kappa B (NF-kB) and interferon-regulatory factor (IRF). Consequently, various advanced inflammatory cytokines, chemokines, and interferon reaction properties can be up-regulated. Similarly, TLR flagging works on autophagy in macrophages. Autophagy is a cell response to starvation that helps to eliminate damaged cytosol organelles and persistent proteins. It is also able to prevent the replication of intracellular pathogens. Several microbes subvert the autophagy pathways to sustain their viability. This review investigates how TLRs can modulate a macrophagic system and analyze the role of natural resistance autophagy.

Intracellular PRRs Activation in Targeting the Immune Response Against Fungal Infections

The immune response against fungal infections is complex and exhibits several factors involving innate elements that participate in the interaction with the fungus. The innate immune system developed pattern recognition receptors that recognize different pathogen-associated molecular patterns present both on the surface of the fungi cell wall and on their genetic material. These receptors have the function of activating the innate immune response and regulating a subsequent adaptive immune response. Among pattern recognition receptors, the family of Toll-like receptors and C-type lectin receptors are the best described and characterized, they act directly in the recognition of pathogen-associated molecular patterns expressed on the wall of the fungus and consequently in directing the immune response. In recent years, the role of intracellular pattern recognition receptors (TLR3, TLR7, TLR8, and TLR9) has become increasingly important in the pathophysiology of some mycoses, as paracoccidioidomycosis, cryptococcosis, aspergillosis, and candidiasis. The recognition of nucleic acids performed by these receptors can be essential for the control of some fungal infections, as they can be harmful to others. Therefore, this review focuses on highlighting the role played by intracellular pattern recognition receptors both in controlling the infection and in the host's susceptibility against the main fungi of medical relevance.

EGFR-mediated tyrosine phosphorylation of STING determines its trafficking route and cellular innate immunity functions

STING (STimulator of INterferon Genes) mediates protective cellular response to microbial infection and tissue damage, but its aberrant activation can lead to autoinflammatory diseases. Upon ligand stimulation, the endoplasmic reticulum (ER) protein STING translocates to endosomes for induction of interferon production, while an alternate trafficking route delivers it directly to the autophagosomes. Here, we report that phosphorylation of a specific tyrosine residue in STING by the epidermal growth factor receptor (EGFR) is required for directing STING to endosomes, where it interacts with its downstream effector IRF3. In the absence of EGFR-mediated phosphorylation, STING rapidly transits into autophagosomes, and IRF3 activation, interferon production, and antiviral activity are compromised in cell cultures and mice, while autophagic activity is enhanced. Our observations illuminate a new connection between the tyrosine kinase activity of EGFR and innate immune functions of STING and suggest new experimental and therapeutic approaches for selective regulation of STING functions.

A genome-wide CRISPR screen identifies regulation factors of the TLR3 signalling pathway

A subset of TLRs is specialised in the detection of incoming pathogens by sampling endosomes for nucleic acid contents. Among them, TLR3 senses the abnormal presence of double-stranded RNA in the endosomes and initiates a potent innate immune response via activation of NF-κB and IRF3. Nevertheless, mechanisms governing TLR3 regulation remain poorly defined. To identify new molecular players involved in the TLR3 pathway, we performed a genome-wide screen using CRISPR/Cas9 technology. We generated TLR3⁺ reporter cells carrying a NF-κB-responsive promoter that controls GFP expression. Cells were next transduced with a single-guide RNA (sgRNA) library, subjected to sequential rounds of stimulation with poly(I:C) and sorting of the GFP-negative cells. Enrichments in sgRNA estimated by deep sequencing identified genes required for TLR3-induced activation of NF-κB. Among the hits, five genes known to be critically involved in the TLR3 pathway, including TLR3 itself and the chaperone UNC93B1, were identified by the screen, thus validating our strategy. We further studied the top 40 hits and focused on the transcription factor aryl hydrocarbon receptor (AhR). Depletion of AhR had a dual effect on the TLR3 response, abrogating IL-8 production and enhancing IP-10 release. Moreover, in primary human macrophages exposed to poly(I:C), AhR activation enhanced IL-8 and diminished IP-10 release. Overall, these results reveal AhR plays a role in the TLR3 cellular innate immune response.

RNA Signaling in Pulmonary Arterial Hypertension-A Double-Stranded Sword

Recognition of and response to pathogens and tissue injury is driven by the innate immune system via activation of pattern recognition receptors. One of the many patterns recognized is RNA and, while several receptors bind RNA, Toll-like receptor 3 (TLR3) is well placed for initial recognition of RNA molecules due to its localization within the endosome. There is a growing body of work describing a role for TLR3 in maintenance of vascular homeostasis. For example, TLR3 deficiency has been shown to play repair and remodeling roles in the systemic vasculature and in lung parenchyma. A hallmark of pulmonary arterial hypertension (PAH) is pulmonary vascular remodeling, yet drivers and triggers of this remodeling remain incompletely understood. Based on its role in the systemic vasculature, our group discovered reduced endothelial TLR3 expression in PAH and revealed a protective role for a TLR3 agonist in rodent models of pulmonary hypertension. This review will provide an overview of RNA signaling in the vasculature and how it relates to PAH pathobiology, including whether targeting double-stranded RNA signaling is a potential treatment option for PAH.

Epidermal Growth Factor Receptor Inhibitors and Other Tyrosine Kinase Inhibitors for Solid Tumors

This article analyzes the risk of infection associated with small molecule kinase inhibitors used to treat solid organ malignancies and establishes specific recommendations. Most of these drugs are orally administered and have the ability to inhibit distinct kinases, which play a major role in cancer initiation and progression. Although the true extent of adverse events is not yet known, risk of infection does not seem to be a major problem with these drugs. Because of the limited clinical experience and the constant evolution of targeted therapies, recommendations may evolve in the near future.

Human Immunodeficiency Virus-Associated Exosomes Promote Kaposi's Sarcoma-Associated Herpesvirus Infection via the Epidermal Growth Factor Receptor

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causal agent for Kaposi’s sarcoma (KS), the most common malignancy in HIV/AIDS patients. Oral transmission through saliva is considered the most common route for spreading the virus among HIV/AIDS patients. However, the role of HIV-specific components in the cotransfection of KSHV is unclear. We demonstrate that exosomes purified from the saliva of HIV-positive patients and secreted by HIV-infected T-cell lines promote KSHV infectivity in immortalized and primary oral epithelial cells. HIV-associated exosomes promote KSHV infection, which depends on HIV trans-activation response element (TAR) RNA and EGFR of oral epithelial cells, which can be targeted for reducing KSHV infection. These results reveal that HIV-associated exosomes are a risk factor for KSHV infection in the HIV-infected population.

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causal agent for Kaposi’s sarcoma (KS), the most common malignancy in people living with human immunodeficiency virus (HIV)/AIDS. The oral cavity is a major route for KSHV infection and transmission. However, how KSHV breaches the oral epithelial barrier for spreading to the body is not clear. Here, we show that exosomes purified from either the saliva of HIV-positive individuals or the culture supernatants of HIV-1-infected T-cell lines promote KSHV infectivity in immortalized and primary human oral epithelial cells. HIV-associated saliva exosomes contain the HIV trans-activation response element (TAR), Tat, and Nef RNAs but do not express Tat and Nef proteins. The TAR RNA in HIV-associated exosomes contributes to enhancing KSHV infectivity through the epidermal growth factor receptor (EGFR). An inhibitory aptamer against TAR RNA reduces KSHV infection facilitated by the synthetic TAR RNA in oral epithelial cells. Cetuximab, a monoclonal neutralizing antibody against EGFR, blocks HIV-associated exosome-enhanced KSHV infection. Our findings reveal that saliva containing HIV-associated exosomes is a risk factor for the enhancement of KSHV infection and that the inhibition of EGFR serves as a novel strategy for preventing KSHV infection and transmission in the oral cavity.

IMPORTANCE Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causal agent for Kaposi’s sarcoma (KS), the most common malignancy in HIV/AIDS patients. Oral transmission through saliva is considered the most common route for spreading the virus among HIV/AIDS patients. However, the role of HIV-specific components in the cotransfection of KSHV is unclear. We demonstrate that exosomes purified from the saliva of HIV-positive patients and secreted by HIV-infected T-cell lines promote KSHV infectivity in immortalized and primary oral epithelial cells. HIV-associated exosomes promote KSHV infection, which depends on HIV trans-activation response element (TAR) RNA and EGFR of oral epithelial cells, which can be targeted for reducing KSHV infection. These results reveal that HIV-associated exosomes are a risk factor for KSHV infection in the HIV-infected population.

Relative Contributions of the cGAS-STING and TLR3 Signaling Pathways to Attenuation of Herpes Simplex Virus 1 Replication

The innate immune response is crucial for defense against viral infections. Cells recognize virus infection through pattern recognition receptors and induce type I interferons as well as proinflammatory cytokines to orchestrate an innate immune response. Herpes simplex virus 1 (HSV-1) triggers both the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) and Toll-like receptor 3 (TLR3) pathways. It is well known that TLR3 uses the adaptor protein Toll/interleukin-1 receptor (IL-1R) domain-containing adaptor-inducing beta interferon (TRIF) for signaling, but we recently reported that STING signaling also requires TRIF. Because STING directly binds to TRIF, we identified the STING-interacting domain of TRIF and generated STING-noninteracting mutants of human and mouse TRIFs. The mutant TRIFs were unable to support STING signaling, although they were fully functional in the TLR3 pathway. These mutants were used to assess the relative contributions of the TLR3 and STING pathways to the attenuation of HSV-1 replication in mouse and human cell lines. For this purpose, the mouse L929 and NB41A3 cell lines and the human HT1080 and HeLa-M cell lines, in which both the TLR3 and the STING pathways are operational, were used. The TRIF gene was disrupted in these lines by CRISPR/Cas9, before reconstituting them with mutant and wild-type TRIF expression vectors. Infection of the reconstituted cells with HSV-1 revealed that both the cGAS-STING and the TLR3 signaling pathways are required for the attenuation of virus replication, but their relative contributions in attenuating HSV-1 replication were found to be different in mouse versus human cell lines. Thus, our study suggests that the relative contributions of the cGAS-STING and the TLR3 pathways in the attenuation of viral infection may be species specific.IMPORTANCE The magnitude of fatal infections caused by all different viruses in human and animal populations justifies a better understanding of the host innate immune response process that attenuates virus replication. In particular, the relative contributions of different signaling pathways which are responsible for the generation of the innate immune response are still largely unknown. In this study, we used STING-noninteracting TRIF mutants to decipher the relative contributions of the TLR3 and cGAS-STING signaling pathways to the attenuation of HSV-1 infection. We show that the relative contributions of the two pathways to the attenuation of viral infection are different in mouse versus human cell lines. Together, our results provide new insights into the relative contributions of two different signaling pathways in the attenuation of viral infection and may lead to the development of new antiviral strategies aimed at blocking viral infection at very early stages.

Avian Pattern Recognition Receptor Sensing and Signaling

Pattern recognition receptors (PRRs) are a class of immune sensors that play a critical role in detecting and responding to several conserved patterns of microorganisms. As such, they play a major role in the maintenance of immune homeostasis and anti-microbial defense. Fundamental knowledge pertaining to the discovery of PRR functions and their ligands continue to advance the understanding of immune system and disease resistance, which led to the rational design and/or application of various PRR ligands as vaccine adjuvants. In addition, the conserved nature of many PRRs throughout the animal kingdom has enabled the utilization of the comparative genomics approach in PRR identification and the study of evolution, structural features, and functions in many animal species including avian. In the present review, we focused on PRR sensing and signaling functions in the avian species, domestic chicken, mallard, and domestic goose. In addition to summarizing recent advances in the understanding of avian PRR functions, the present review utilized a comparative biology approach to identify additional PRRs, whose functions have been well studied in mammalians but await functional characterization in avian.

Analysis of Virus and Host Proteomes During Productive HSV-1 and VZV Infection in Human Epithelial Cells

Herpes simplex virus 1 (HSV-1) and varicella-zoster virus (VZV) are two closely related human alphaherpesviruses that persistently infect most adults worldwide and cause a variety of clinically important diseases. Herpesviruses are extremely well adapted to their hosts and interact broadly with cellular proteins to regulate virus replication and spread. However, it is incompletely understood how HSV-1 and VZV interact with the host proteome during productive infection. This study determined the temporal changes in virus and host protein expression during productive HSV-1 and VZV infection in the same cell type. Results demonstrated the temporally coordinated expression of HSV-1 and VZV proteins in infected cells. Analysis of the host proteomes showed that both viruses affected extracellular matrix composition, transcription, RNA processing and cell division. Moreover, the prominent role of epidermal growth factor receptor (EGFR) signaling during productive HSV-1 and VZV infection was identified. Stimulation and inhibition of EGFR leads to increased and decreased virus replication, respectively. Collectively, the comparative temporal analysis of viral and host proteomes in productively HSV-1 and VZV-infected cells provides a valuable resource for future studies aimed to identify target(s) for antiviral therapy development.

Genetic Modification of CD8+ T Cells to Express EGFR: Potential Application for Adoptive T Cell Therapies

Adoptive immunotherapy with ex vivo-expanded tumor-infiltrating lymphocytes (TILs) has achieved objective clinical responses in a significant number of patients with cancer. The failure of many patients to develop long-term tumor control may be, in part, due to exhaustion of transferred T cells in the presence of a hostile tumor microenvironment. In several tumor types, growth and survival of carcinoma cells appear to be sustained by a network of receptors/ligands of the ErbB family. We speculated that if transferred T cells could benefit from EGFR ligands produced by the tumor, they might proliferate better and exert their anti-tumor activities more efficiently. We found that CD8⁺ T cells transduced with a retrovirus to express EGFR responded to EGFR ligands activating the EGFR signaling pathway. These EGFR-expressing effector T cells proliferated better and produced more IFN-γ and TNF-α in the presence of EGFR ligands produced by tumor cells in vitro. EGFR-expressing CD8 T cells from OT-1 mice were more efficient killing B16-OVA cells than control OT-1 CD8 T cells. Importantly, EGFR-expressing OT-1 T cells injected into B16-OVA tumor bearing mice were recruited into the tumor, expressed lower levels of the exhaustion markers PD1, TIGIT, and LAG3, and were more efficient in delaying tumor growth. Our results suggest that genetic modification of CD8⁺ T cells to express EGFR might be considered in immunotherapeutic strategies based on adoptive transfer of anti-tumor T cells against cancers expressing EGFR ligands.

Host signaling and EGR1 transcriptional control of human cytomegalovirus replication and latency

Sustained phosphotinositide3-kinase (PI3K) signaling is critical to the maintenance of alpha and beta herpesvirus latency. We have previously shown that the beta-herpesvirus, human cytomegalovirus (CMV), regulates epidermal growth factor receptor (EGFR), upstream of PI3K, to control states of latency and reactivation. How signaling downstream of EGFR is regulated and how this impacts CMV infection and latency is not fully understood. We demonstrate that CMV downregulates EGFR early in the productive infection, which blunts the activation of EGFR and its downstream pathways in response to stimuli. However, CMV infection sustains basal levels of EGFR and downstream pathway activity in the context of latency in CD34+ hematopoietic progenitor cells (HPCs). Inhibition of MEK/ERK, STAT or PI3K/AKT pathways downstream of EGFR increases viral reactivation from latently infected CD34⁺ HPCs, defining a role for these pathways in latency. We hypothesized that CMV modulation of EGFR signaling might impact viral transcription important to latency. Indeed, EGF-stimulation increased expression of the UL138 latency gene, but not immediate early or early viral genes, suggesting that EGFR signaling promotes latent gene expression. The early growth response-1 (EGR1) transcription factor is induced downstream of EGFR signaling through the MEK/ERK pathway and is important for the maintenance of hematopoietic stemness. We demonstrate that EGR1 binds the viral genome upstream of UL138 and is sufficient to promote UL138 expression. Further, disruption of EGR1 binding upstream of UL138 prevents the establishment of latency in CD34⁺ HPCs. Our results indicate a model whereby UL138 modulation of EGFR signaling feeds back to promote UL138 gene expression and suppression of replication for latency. By this mechanism, the virus has hardwired itself into host cell biology to sense and respond to changes in homeostatic host cell signaling.

Host signaling is important for regulating states of cytomegalovirus (CMV) replication and latency. We have shown that human cytomegalovirus regulates EGFR levels and trafficking and that sustained EGFR or downstream PI3K signaling is a requirement for viral latency. Changes in host signaling have the ability to alter viral and host gene expression to impact the outcome of infection. Here we show that EGFR signaling through MEK/ERK pathway induces the host EGR1 transcription factor that is highly expressed in hematopoietic stem cells and necessary for the maintenance of hematopoietic stemness. Downregulation of EGR1 promotes stem cell mobilization and differentiation, known stimuli for CMV reactivation. We identified functional EGR1 binding sites upstream of the UL138 CMV latency gene and EGR1 stimulated UL138 expression to reinforce the latent infection. Mutant viruses where the regulation of UL138 by EGR1 is disrupted are unable to establish latency in CD34⁺ HPCs. This study advances our understanding of how host signaling impacts decisions to enter into or exit from latency. The regulation of viral gene expression by host signaling allows the virus to sense and respond to changes in host stress or differentiation.

The zinc-finger protein ZFYVE1 modulates TLR3-mediated signaling by facilitating TLR3 ligand binding

Recognition of viral dsRNA by Toll-like receptor 3 (TLR3) leads to the induction of downstream antiviral effectors and the innate antiviral immune response. Here, we identified the zinc-finger FYVE domain-containing protein ZFYVE1, a guanylate-binding protein (GBP), as a positive regulator of TLR3-mediated signaling. Overexpression of ZFYVE1 promoted the transcription of downstream antiviral genes upon stimulation with the synthetic TLR3 ligand poly(I:C). Conversely, ZFYVE1 deficiency had the opposite effect. Zfyve1^-/- mice were less susceptible than wild-type mice to inflammatory death induced by poly(I:C) but not LPS. ZFYVE1 was associated with TLR3, and the FYVE domain of ZFYVE1 and the ectodomain of TLR3 were shown to be responsible for their interaction. ZFYVE1 was bound to poly(I:C) and increased the binding affinity of TLR3 to poly(I:C). These findings suggest that ZFYVE1 plays an important role in the TLR3-mediated innate immune and inflammatory responses by promoting the ligand binding of TLR3.

Immunological implications of epidermal growth factor receptor signaling in persistent infections

Infectious diseases account for a large proportion of global health emergencies and are rising more so owing to the paucity of effective vaccination and chemotherapeutic strategies. The severity is compounded by the development of antibiotic resistance among major pathogenic strains, capable of residing in the hostile host microenvironment by hijacking its signaling mechanisms and molecular circuitry. Among such processes, studies on epidermal growth factor receptor (EGFR) have revealed specific contributions of this classical oncogenic signaling axis during distinct infection conditions. Here, we review the current status of EGFR family members in the context of host-pathogen interactions and speculate the possible dimensions of exploration and manipulation of the EGFR pathway for host-directed therapeutic purposes.

Small-molecule inhibitors and the salivary gland epithelium in Sjögren's syndrome

INTRODUCTION

The salivary gland (SG) in primary Sjögren's syndrome (pSS) is characterized by its lack of function (hyposalivation) and lymphocytic invasion. Small-molecule inhibitors (SMIs) are a new class of drugs, whose diminutive size permits diffusion into cells. SMIs targeting components of the immune system are eagerly being trialed for their potential therapeutic utility in pSS. Neglected until now, however, is a discussion of the potential effects of SMIs on the SG epithelium.

AREAS COVERED

We begin by reminding the reader of the SG epithelial compartment, its complicity in inflammatory milieu formation in pSS, and categories of SMIs which merit attention. We discuss each SMI category, including pre-clinical data concerning pSS and likely consequences of their application on the SG epithelium.

EXPERT OPINION

Recovery of saliva production in pSS requires restoring the function of the SG epithelium, not solely on inflammation resolution. Many SMIs, for example, those blocking JAK-STAT signaling, interfere with critical epithelial cell pathways, most notably EGF signaling. If the effect of SMIs on SG epithelium is ignored, recovery of SG function will be challenging. We predict that NFκB signaling blockade will impart the least SG epithelium damage whilst reducing inflammation and facilitating recovery from hyposalivation in pSS.

Roles of Toll-Like Receptors in Nitroxidative Stress in Mammals

Free radicals are important antimicrobial effectors that cause damage to DNA, membrane lipids, and proteins. Professional phagocytes produce reactive oxygen species (ROS) and reactive nitrogen species (RNS) that contribute towards the destruction of pathogens. Toll-like receptors (TLRs) play a fundamental role in the innate immune response and respond to conserved microbial products and endogenous molecules resulting from cellular damage to elicit an effective defense against invading pathogens, tissue injury, or cancer. In recent years, several studies have focused on how the TLR-mediated activation of innate immune cells leads to the production of pro-inflammatory factors upon pathogen invasion. Here, we review recent findings that indicate that TLRs trigger a signaling cascade that induces the production of reactive oxygen and nitrogen species.

Syk and Hrs Regulate TLR3-Mediated Antiviral Response in Murine Astrocytes

Toll-like receptors (TLRs) sense the presence of pathogen-associated molecular patterns. Nevertheless, the mechanisms modulating TLR-triggered innate immune responses are not yet fully understood. Complex regulatory systems exist to appropriately direct immune responses against foreign or self-nucleic acids, and a critical role of hepatocyte growth factor-regulated tyrosine kinase substrate (HRS), endosomal sorting complex required for transportation-0 (ESCRT-0) subunit, has recently been implicated in the endolysosomal transportation of TLR7 and TLR9. We investigated the involvement of Syk, Hrs, and STAM in the regulation of the TLR3 signaling pathway in a murine astrocyte cell line C8-D1A following cell stimulation with a viral dsRNA mimetic. Our data uncover a relationship between TLR3 and ESCRT-0, point out Syk as dsRNA-activated kinase, and suggest the role for Syk in mediating TLR3 signaling in murine astrocytes. We show molecular events that occur shortly after dsRNA stimulation of astrocytes and result in Syk Tyr-342 phosphorylation. Further, TLR3 undergoes proteolytic processing; the resulting TLR3 N-terminal form interacts with Hrs. The knockdown of Syk and Hrs enhances TLR3-mediated antiviral response in the form of IFN-β, IL-6, and CXCL8 secretion. Understanding the role of Syk and Hrs in TLR3 immune responses is of high importance since activation and precise execution of the TLR3 signaling pathway in the brain seem to be particularly significant in mounting an effective antiviral defense. Infection of the brain with herpes simplex type 1 virus may increase the secretion of amyloid-β by neurons and astrocytes and be a causal factor in degenerative diseases such as Alzheimer's disease. Errors in TLR3 signaling, especially related to the precise regulation of the receptor transportation and degradation, need careful observation as they may disclose foundations to identify novel or sustain known therapeutic targets.

Diverse Roles of DEAD/DEAH-Box Helicases in Innate Immunity and Diseases

DEAD/DEAH-box helicases are enzymes that belong to the DEAD/H-box family of SF2 helicase superfamily. These enzymes are essential in RNA metabolism, where they are involved in a number of processes that require manipulation of RNA structure. Recent studies have found that some DEAD/DEAH-box helicases play important roles in innate immunity, where they act as sensors of cytosolic DNA/RNA, as adaptor proteins, or as regulators of signaling and gene expression. In spite of their function in immunity, DEAD/DEAH-box helicases can also be hijacked and exploited by viruses to circumvent detection and aid in viral replication. These findings not only imply that DEAD/DEAH-box helicases have a broader function than previously thought, but also give us a much better understanding of immune mechanisms and diseases that arise due to the dysregulation or evasion thereof. In this chapter, we demonstrate the known scope of activities of human DEAD/DEAH-box helicases in innate immunity and interaction with viruses or other pathogens. Additionally, we give an outline of diseases in which they are, or may be, involved in the context of immunity.

Exosomes derived from HIV-1-infected cells promote growth and progression of cancer via HIV TAR RNA

People living with HIV/AIDS on antiretroviral therapy have increased risk of non-AIDS-defining cancers (NADCs). However, the underlying mechanism for development and progression of certain NADCs remains obscure. Here we show that exosomes released from HIV-infected T cells and those purified from blood of HIV-positive patients stimulate proliferation, migration and invasion of oral/oropharyngeal and lung cancer cells. The HIV transactivation response (TAR) element RNA in HIV-infected T-cell exosomes is responsible for promoting cancer cell proliferation and inducing expression of proto-oncogenes and Toll-like receptor 3 (TLR3)-inducible genes. These effects depend on the loop/bulge region of the molecule. HIV-infected T-cell exosomes rapidly enter recipient cells through epidermal growth factor receptor (EGFR) and stimulate ERK1/2 phosphorylation via the EGFR/TLR3 axis. Thus, our findings indicate that TAR RNA-containing exosomes from HIV-infected T cells promote growth and progression of particular NADCs through activation of the ERK cascade in an EGFR/TLR3-dependent manner.

HIV patients have an increased risk of developing non-AIDS-defining cancers but the molecular mechanisms underlying this predisposition are unclear. Here the authors show that exosomes secreted by HIV-infected T cells or isolated from the blood of HIV-positive patients, stimulate oncogenic properties of cancer cells through the activation of ERK1/2 signaling pathway.

Crosstalk of toll-like receptors signaling and Nrf2 pathway for regulation of inflammation

Inflammation as a second line of defense of innate immunity plays a crucial role in eliminating invading pathogens (bacteria, viruses, fungi as well as other parasites). The inflammatory response may also activate adaptive immune system involving lymphocytes to mount either antibody dependent or cell-mediated immune responses to clear pathogenic insult. However, if continued, the inflammatory processes may become uncontrolled culminating in cellular injury and tissue destruction, thereby manifesting itself in chronic form. The chronic inflammation has been associated with numerous human pathological conditions like allergies and autoimmune diseases, atherosclerosis, arthritis, Alzheimer's disease, cancer, obesity, type 2 diabetes, schizophrenia, neuro-degenerative diseases and numerous others. The dysregulated inflammatory process is associated with overproduction of free radicals leading to oxidative stress and activation of different cell signaling pathways. The regulation of inflammation by TLR signaling as well as Nrf2 pathways separately is widely documented. Since both these major signaling pathways modulate inflammation, they may crosstalk to bring about coordinated inflammatory responses. The linkage between TLR signaling and Nrf2-Keap1 pathway may serve as a bridge between immune regulation and oxidative stress responses through regulation of inflammation. Also, inflammation is reportedly responsible for the plethora of diseased conditions; a study of its regulation by targeting the TLR-Nrf2 cross-talks may also be beneficial for the development of therapeutic therapies or prophylactic treatments. Hence, present review focuses on the crosstalk between TLR signaling and Nrf2 pathway with respect to their role in modulation of inflammation in normal as well as pathologic conditions.

Identification of Biologically Essential Nodes via Determinative Power in Logical Models of Cellular Processes

A variety of biological networks can be modeled as logical or Boolean networks. However, a simplification of the reality to binary states of the nodes does not ease the difficulty of analyzing the dynamics of large, complex networks, such as signal transduction networks, due to the exponential dependence of the state space on the number of nodes. This paper considers a recently introduced method for finding a fairly small subnetwork, representing a collection of nodes that determine the states of most other nodes with a reasonable level of entropy. The subnetwork contains the most determinative nodes that yield the highest information gain. One of the goals of this paper is to propose an algorithm for finding a suitable subnetwork size. The information gain is quantified by the so-called determinative power of the nodes, which is obtained via the mutual information, a concept originating in information theory. We find the most determinative nodes for 36 network models available in the online database Cell Collective (http://cellcollective.org). We provide statistical information that indicates a weak correlation between the subnetwork size and other variables, such as network size, or maximum and average determinative power of nodes. We observe that the proportion represented by the subnetwork in comparison to the whole network shows a weak tendency to decrease for larger networks. The determinative power of nodes is weakly correlated to the number of outputs of a node, and it appears to be independent of other topological measures such as closeness or betweenness centrality. Once the subnetwork of the most determinative nodes is identified, we generate a biological function analysis of its nodes for some of the 36 networks. The analysis shows that a large fraction of the most determinative nodes are essential and involved in crucial biological functions. The biological pathway analysis of the most determinative nodes shows that they are involved in important disease pathways.

Molecular Determinants and the Regulation of Human Cytomegalovirus Latency and Reactivation

Human cytomegalovirus (HCMV) is a beta herpesvirus that establishes a life-long persistence in the host, like all herpesviruses, by way of a latent infection. During latency, viral genomes are maintained in a quieted state. Virus replication can be reactivated from latency in response to changes in cellular signaling caused by stress or differentiation. The past decade has brought great insights into the molecular basis of HCMV latency. Here, we review the complex persistence of HCMV with consideration of latent reservoirs, viral determinants and their host interactions, and host signaling and the control of cellular and viral gene expression that contributes to the establishment of and reactivation from latency.

Porcine Epidemic Diarrhea Virus-Induced Epidermal Growth Factor Receptor Activation Impairs the Antiviral Activity of Type I Interferon

Porcine epidemic diarrhea virus (PEDV) causes acute and devastating enteric disease in suckling piglets and results in huge economic losses in the pig industry worldwide. To establish productive infection, viruses must first circumvent the host innate immune response. In this study, we found that PEDV infection stimulated epidermal growth factor receptor (EGFR) activation, which has been linked to not only anticancer therapeutics, but also antiviral signaling. Therefore, we determined whether EGFR activation affected PEDV infection by using an activator or overexpression assay. The data showed that EGFR activation enhanced virus replication in both cases. We also found that specific inhibition of EGFR by either inhibitors or small interfering RNA (siRNA) led to a decrease in virus yields. Further analysis revealed that inhibition of EGFR produced augmentation of type I interferon genes. We next observed that the EGFR downstream cascade STAT3 was also activated upon PEDV infection. Similar to the case of EGFR, specific inhibition of STAT3 by either inhibitor or siRNA increased the antiviral activity of interferon and resulted in decreased PEDV RNA levels, and vice versa. The data on STAT3 depletion in combination with EGFR activation suggest that the attenuation of antiviral activity by EGFR activation requires activation of the STAT3 signaling pathway. Taken together, these data demonstrate that PEDV-induced EGFR activation serves as a negative regulator of the type I interferon response and provides a novel therapeutic target for virus infection.IMPORTANCE EGFR is a transmembrane tyrosine receptor that mediates various cellular events, as well as several types of human cancers. In this study, we investigated for the first time the role of EGFR in PEDV infection. We observed that PEDV infection induced EGFR activation. The role of EGFR activation is to impair the antiviral activity of type I interferon, which requires the involvement of the EGFR downstream signaling cascade STAT3. Our findings reveal a new mechanism evolved by PEDV to circumvent the host antiviral response, which might serve as a therapeutic target against virus infection.

Constitutively Bound EGFR-Mediated Tyrosine Phosphorylation of TLR9 Is Required for Its Ability To Signal

Mammalian TLRs recognize microbial infection or cell death-associated danger signals and trigger the appropriate cellular response. These responses determine the strength and the outcome of the host-microbe interaction. TLRs are transmembrane proteins located on the plasma or the endosomal membrane. Their ectodomains recognize specific microbial or endogenous ligands, and the cytoplasmic domains interact with specific proteins to activate intracellular signaling pathways. TLR9, an endosomal TLR, is activated by endocytosed DNA. Activated TLR9 recruits the cytoplasmic adapter MyD88 and other signaling proteins to induce the synthesis of inflammatory cytokines and IFN. Uncontrolled activation of TLR9 leads to the undesired overproduction of inflammatory cytokines and consequent pathogenesis. Therefore, appropriate activation and the regulation of TLR9 signaling are critical. Tyrosine (Tyr) phosphorylation of TLR9 is essential for its activation; however, the role of specific Tyr kinases is not clear. In this article, we report that epidermal growth factor receptor (EGFR), a membrane-bound protein Tyr kinase, is essential for TLR9 signaling. Genetic ablation of EGFR or pharmacological inhibition of its kinase activity attenuates TLR9-mediated induction of genes in myeloid and nonmyeloid cell types. EGFR is constitutively bound to TLR9; upon ligand stimulation, it mediates TLR9 Tyr phosphorylation, which leads to the recruitment of MyD88, activation of the signaling kinases and transcription factors, and gene induction. In mice, TLR9-mediated liver injury and death are blocked by an EGFR inhibitor or deletion of the EGFR gene from myeloid cells, which are the major producers of inflammatory cytokines.

Inhibition of epidermal growth factor receptor attenuates LPS-induced inflammation and acute lung injury in rats

Acute lung injury (ALI) and its severe form acute respiratory distress syndrome remain the leading cause of morbidity and mortality in intensive care units. Inhibition of epidermal growth factor receptor (EGFR) has been found to be able to reduce inflammatory response. However, it is still unclear whether EGFR inhibition can prevent ALI. This study aimed to validate the EGFR's role in ALI and investigated the effects of EGFR inhibition on lipopolysaccharides (LPS)-induced ALI in rats. In vitro, both pharmacological inhibitors (AG1478 and 451) and si-RNA silencing of EGFR significantly inhibited LPS-induced EGFR signaling activation and inflammatory response in human lung epithelial cells or macrophages. Mechanistically, LPS induced EGFR activation via TLR4 and c-Src signaling. In vivo, rat model with ALI induced by intratracheal instillation of LPS was treated by oral administration of AG1478 and 451. It was observed that AG1478 and 451 blocked the activation of EGFR signaling in lung tissue and reduced the LPS-induced infiltration of inflammatory cells, inflammatory gene expression, and lung injuries. This study demonstrates that TLR4/c-Src-dependent EGFR signaling plays an important role in LPS-induced ALI, and that EGFR may be a potential target in treating ALI.

Cytokines 2017 in Kanazawa: Looking beyond the horizon of integrated cytokine research from the sea of Japan

At the 5th Annual meeting of the International Cytokine and Interferon Society held in Kanazawa, Japan from Oct. 29-Nov. 2 2017, new research was presented in the broad field of cytokine and interferon research. The meeting provided an outstanding platform for investigators in basic science and clinical research to communicate, share and discuss their recent findings in this fast moving area of research.

ESCMID Study Group for Infections in Compromised Hosts (ESGICH) Consensus Document on the safety of targeted and biological therapies: an infectious diseases perspective (Cell surface receptors and associated signaling pathways)

BACKGROUND

The present review is part of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Study Group for Infections in Compromised Hosts (ESGICH) consensus document on the safety of targeted and biologic therapies.

AIMS

To review, from an infectious diseases perspective, the safety profile of therapies targeting cell surface receptors and associated signaling pathways among cancer patients and to suggest preventive recommendations.

SOURCES

Computer-based Medline searches with MeSH terms pertaining to each agent or therapeutic family.

CONTENT

Vascular endothelial growth factor (VEGF)-targeted agents (bevacizumab and aflibercept) are associated with a meaningful increase in the risk of infection, likely due to drug-induced neutropaenia, although no clear benefit is expected from the universal use of anti-infective prophylaxis. VEGF tyrosine kinase inhibitors (i.e. sorafenib or sunitinib) do not seem to significantly affect host's susceptibility to infection, and universal anti-infective prophylaxis is not recommended either. Anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (cetuximab or panitumumab) induce neutropaenia and secondary skin and soft tissue infection in cases of severe papulopustular rash. Systemic antibiotics (doxycycline or minocycline) should be administered to prevent the latter complication, whereas no recommendation can be established on the benefit from antiviral, antifungal or anti-Pneumocystis prophylaxis. A lower risk of infection is reported for anti-ErbB2/HER2 monoclonal antibodies (trastuzumab and pertuzumab) and ErbB receptor tyrosine kinase inhibitors (including dual-EGFR/ErbB2 inhibitors such as lapatinib or neratinib) compared to conventional chemotherapy, presumably as a result of the decreased occurrence of drug-induced neutropaenia.

IMPLICATIONS

With the exception of VEGF-targeted agents, the overall risk of infection associated with the reviewed therapies seems to be low.