SOCS1-negative feedback of STAT1 activation is a key pathway in the dsRNA-induced innate immune response of human keratinocytes

Multi-omics reveals the switch role of abnormal methylation in the regulation of decidual macrophages function in recurrent spontaneous abortion

RSA, recurrent spontaneous abortion, often causes serious physical damage and psychological pressure in reproductive women with unclarified pathogenesis. Abnormal function of decidual cells and aberrant DNA methylation have been reported to cause RSA, but their association remains unclear. Here, we integrated transcriptome, DNA methylome, and scRNA-seq to clarify the regulatory relationship between DNA methylation and decidual cells in RSA. We found that DNA methylation mainly influenced the function of decidual macrophages (DMs), of which four hub genes, HLA-A, HLA-F, SQSTM1/P62, and Interferon regulatory factor 7 (IRF7), related to 22 hypomethylated CpG sites, regulated 16 hub pathways to participate in RSA pathogenesis. In particular, using transcription factor analysis, it is suggested that the upregulation of IRF7 transcription was associated with enhanced recruitment of the transcription factor STAT1 by the hypomethylated promoter region of IRF7. As the current research on DNA methylation of macrophages in the uterine microenvironment of RSA is still blank, our systematic picture of abnormal DNA methylation in regulating DM function provides new insights into the role of DNA methylation in RSA occurrence, which may aid in further prevention and treatment of RSA.

STAT3 regulates antiviral immunity by suppressing excessive interferon signaling

This study identifies interleukin-6 (IL-6)-independent phosphorylation of STAT3 Y705 at the early stage of infection with several viruses, including influenza A virus (IAV). Such activation of STAT3 is dependent on the retinoic acid-induced gene I/mitochondrial antiviral-signaling protein/spleen tyrosine kinase (RIG-I/MAVS/Syk) axis and critical for antiviral immunity. We generate STAT3Y705F/+ knockin mice that display a remarkably suppressed antiviral response to IAV infection, as evidenced by impaired expression of several antiviral genes, severe lung tissue injury, and poor survival compared with wild-type animals. Mechanistically, STAT3 Y705 phosphorylation restrains IAV pathogenesis by repressing excessive production of interferons (IFNs). Blocking phosphorylation significantly augments the expression of type I and III IFNs, potentiating the virulence of IAV in mice. Importantly, knockout of IFNAR1 or IFNLR1 in STAT3Y705F/+ mice protects the animals from lung injury and reduces viral load. The results indicate that activation of STAT3 by Y705 phosphorylation is vital for establishment of effective antiviral immunity by suppressing excessive IFN signaling induced by viral infection.

Nuclear IL-33 Plays an Important Role in EGFR-Mediated Keratinocyte Migration by Regulating the Activation of Signal Transducer and Activator of Transcription 3 and NF-κB

Nuclear IL-33 levels are high at the epidermal edges of skin wounds and facilitate wound healing. However, IL-33-mediated regulation of keratinocyte (KC) biology during wound healing remains poorly understood. During skin-wound healing, KC migration and re-epithelialization are mediated predominantly by EGFR signaling activation and depend on the function of signal transducer and activator of transcription 3 (STAT3). We found that migrating KCs at the leading edges of mouse skin wounds exhibited concomitant induction and nuclear colocalization of IL-33 and phosphorylated STAT3. In cultured human KCs, activation of EGFR signaling caused rapid elevation of nuclear IL-33, which directly interacts with phosphorylated STAT3, promoting STAT3 activation. In vitro KC migration and wound-healing assays revealed that high nuclear IL-33 levels were required for KC migration and wound closure. KC mobility associated with a lack of suprabasal epidermal keratins and extracellular matrix degradation mediated by matrix metalloproteinases (MMPs) control cell migration at the intracellular and extracellular levels, respectively. In EGFR-activated KCs, nuclear IL-33 mediated keratin 1 and 10 downregulation and MMP9 upregulation by promoting STAT3 activation and limited MMP1, MMP3, and MMP10 induction by suppressing NF-κB transactivation. Thus, epidermal nuclear IL-33 is involved in KC migration and wound closure by regulating the STAT3 and NF-κB pathways.

Urolithin A Inactivation of TLR3/TRIF Signaling to Block the NF-κB/STAT1 Axis Reduces Inflammation and Enhances Antioxidant Defense in Poly(I:C)-Induced RAW264.7 Cells

Urolithin A is an active compound of gut-microbiota-derived metabolites of polyphenol ellagic acid that has anti-aging, antioxidative, and anti-inflammatory effects. However, the effects of urolithin A on polyinosinic acid-polycytidylic acid (poly(I:C))-induced inflammation remain unclear. Poly(I:C) is a double-stranded RNA (dsRNA) similar to a virus and is recognized by Toll-like receptor-3 (TLR3), inducing an inflammatory response in immune cells, such as macrophages. Inflammation is a natural defense process of the innate immune system. Therefore, we used poly(I:C)-induced RAW264.7 cells and attenuated the inflammation induced by urolithin A. First, our data suggested that 1–30 μM urolithin A does not reduce RAW264.7 cell viability, whereas 1 μM urolithin A is sufficient for antioxidation and the decreased production of tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), and C-C chemokine ligand 5. The inflammation-related proteins cyclooxygenase-2 and inducible nitric oxide synthase were also downregulated by urolithin A. Next, 1 μM urolithin A inhibited the levels of interferon (INF)-α and INF-β. Urolithin A was applied to investigate the blockade of the TLR3 signaling pathway in poly(I:C)-induced RAW264.7 cells. Moreover, the TLR3 signaling pathway, subsequent inflammatory-related pathways, and antioxidation pathways showed changes in nuclear factor-κB (NF-κB) signaling and blocked ERK/mitogen-activated protein kinase (MAPK) signaling. Urolithin A enhanced catalase (CAT) and superoxide dismutase (SOD) activities, but decreased malondialdehyde (MDA) levels in poly(I:C)-induced RAW264.7 cells. Thus, our results suggest that urolithin A inhibits TLR3-activated inflammatory and oxidative-associated pathways in macrophages, and that this inhibition is induced by poly(I:C). Therefore, urolithin A may have antiviral effects and could be used to treat viral-infection-related diseases.

Nuclear IL-33 Plays an Important Role in IL-31‒Mediated Downregulation of FLG, Keratin 1, and Keratin 10 by Regulating Signal Transducer and Activator of Transcription 3 Activation in Human Keratinocytes

IL-33, a chromatin-associated multifunctional cytokine, is implicated in the pathogenesis of atopic dermatitis (AD), an inflammatory skin disorder characterized by skin barrier dysfunction. IL-33 accumulates in the nuclei of epidermal keratinocytes (KCs) in AD lesions. However, it is unclear whether nuclear IL-33 directly contributes to the pathogenesis of AD. IL-31, a pruritogenic cytokine primarily produced by T helper type 2 cells, is elevated in AD lesions and promotes AD development by suppressing KC differentiation and inducing itching. In this study, we investigated the involvement of nuclear IL-33 in IL-31‒mediated suppression of KC differentiation. In monolayer cultures and living skin equivalent, IL-31 increased the expression of full-length IL-33 and the phosphorylation of signal transducer and activator of transcription 3 (STAT3) in the nuclei of human KCs, which in turn downregulated the expression of differentiation markers. We found that IL-31 and IL-4/IL-13 use very similar mechanisms to inhibit KC differentiation: nuclear IL-33 combines with phosphorylated STAT3 and functions as a STAT3 transcription cofactor, promoting phosphorylated STAT3 binding to the FLG promoter to inhibit its transcription; moreover, the nuclear IL-33/phosphorylated STAT3 complex drives the downregulation of keratin 1 and keratin 10 by reducing the availability of the transcription factor RunX1. Therefore, nuclear IL-33 plays an important role in IL-31‒mediated differentiation suppression by regulating STAT3 activation in human KCs.

Association of interleukin-18 genotypes (-607C > A) and (-137 G > C) with the hepatitis B virus disease progression to hepatocellular carcinoma

Chronic infection with HBV has been reported to be associated with the development of HCC. The inflammation mounted by cytokine-mediated immune system plays an important role in the pathogenesis of HBV-associated HCC. IL-18 is a pro-inflammatory cytokine whose role in the development of HBV-associated chronic to malignant disease state has not been much studied. The present study was conceived to determine the role of genetic polymorphisms in IL-18, serum levels of IL-18, and expression level of its signal transducers in the HBV disease progression. A total of 403 subjects were enrolled for this study including 102 healthy subjects and 301 patients with HBV infection in different diseased categories. Polymorphism was determined using PCR-RFLP. Genotypic distributions between the groups were compared using odd's ratio and 95% CI were calculated to express the relative risk. Circulating IL-18 levels were determined by ELISA. Expression levels of pSTAT-1 and pNFƙB was determined by western blotting. In case of IL-18(- 607C > A), the heterozygous genotype (CA) was found to be a protective factor while in case of IL-18(- 137G > C) the heterozygous genotype (GC) acted as a risk factor for disease progression from HBV to HCC. Moreover, serum IL-18 levels were significantly increased during HBV disease progression to HCC as compared to controls. Also the levels of activated signal transducers (pSTAT-1 and pNF-κB) of IL-18 in stimulated PBMCs were significantly increased during HBV to HCC disease progression. These findings suggest that IL-18 has the potential to act as a biomarker of HBV-related disease progression to HCC.

Nuclear IL-33 Plays an Important Role in the Suppression of FLG, LOR, Keratin 1, and Keratin 10 by IL-4 and IL-13 in Human Keratinocytes

IL-33 is a chromatin-associated multifunctional cytokine implicated in the pathogenesis of atopic dermatitis (AD), an inflammatory skin disorder characterized by skin barrier dysfunction. The previous reports show that IL-33 is highly detected in the nucleus of epidermal keratinocytes in AD lesions compared with that in unaffected or normal skin. However, it is unclear whether intracellular IL-33 directly contributes to the pathogenesis of AD. T helper type 2 cytokines IL-4 and IL-13 that are elevated in AD lesions suppress keratinocyte differentiation to impair skin barrier function. We investigated whether intracellular IL-33 is involved in IL-4 and IL-13 function. In monolayer culture and living skin equivalent analyses, IL-4 and IL-13 increased the expression of full-length IL-33 in the nucleus of keratinocytes by activating the MAPK/extracellular signal‒regulated kinase kinase/extracellular signal‒regulated kinase signaling pathway, which is necessary for the inhibition of differentiation markers FLG, LOR, keratin 1, and keratin 10. The nuclear IL-33 functions as a transcription cofactor of signal transducer and activator of transcription 3, increasing the binding of phosphorylated signal transducer and activator of transcription 3 to FLG promoter, thereby inhibiting its transcription, and it inhibits the expression of transcription factor RUNX1 by signal transducer and activator of transcription 3 and signal transducer and activator of transcription 6, thereby downregulating LOR, keratin 1, and keratin 10. Thus, the elevated nuclear IL-33 in the epidermis of AD lesions may be involved in the pathogenesis of AD by inhibiting keratinocyte differentiation and skin barrier function.

Alantolactone Enhances the Phagocytic Properties of Human Macrophages and Modulates Their Proinflammatory Functions

Aim of the Study

Phagocytosis is a crucial element of innate immune defense involved in bacterial killing. The aim of our study was to evaluate the influence of alantolactone on phagocytosis and cytokines release by THP1-derived macrophages. We assessed whether antimicrobial compound alantolactone (a sesquiterpene lactone present in Inula helenium L.) is able to stimulate immune functions of macrophages by increase of S. aureus uptake, phagosome acidification and further stimulation of phago-lysosomes formation. Simultaneously, we tested influence of alantolactone on cytokines/chemokines production and p65 NF-κB concentration. The activity of alantolactone was compared with clarithromycin at concentration 20 µM.

Methods

The cytotoxicity of alantolactone as well as S. aureus uptake, pH of phagosomes and phago-lysosomes fusion were analysed with flow cytometry. Reactive oxygen species and superoxide production were evaluated spectrophotometrically. The efficiency of phagocytosis was evaluated via quantifying viable bacteria (CFU). The effect on p65 protein concentration and cytokine production by macrophages were measured by enzyme-linked immunosorbent assay (ELISA).

Results

Alantolactone enhanced phagocytosis via increase of S. aureus uptake, acidification of phagosomes, and later stimulation of phago-lysosomes fusion. Alantolactone treatment resulted in ROS and superoxide production decrease. Furthermore, alantolactone inhibited production of pro-inflammatory cytokines TNF-α, IL-1β, IL-6, and IL-8 as well as decreased p65 concentration, the subunit responsible for NF-κB activation and cytokine production and simultaneously stimulated release of anti-inflammatory mediators (IL-10 and TGF-β).

Conclusion

Results of our study indicate that alantolactone enhances clearance of S. aureus, and simultaneously modulates immune response, preventing collateral damage of the surrounding tissues. Considering the importance of phagocytosis in the pathogen killing, alantolactone may have a great potential as the supportive treatment of S. aureus infections. Further in vivo studies are warranted to confirm this hypothesis.

Repeat exposure to polyinosinic:polycytidylic acid induces TLR3 expression via JAK-STAT signaling and synergistically potentiates NFκB-RelA signaling in ARPE-19 cells

Dry age-related macular degeneration (AMD), accounting for approximately 90% of AMD cases, is characterized by photoreceptor death, retinal pigment epithelium (RPE) dysfunction and, ultimately, geographic atrophy - the localized death of RPE leading to loss of the center of the visual field. The pathological etiology of AMD is multifactorial, but innate immune signaling and inflammation are involved in early stages of the disease. Although numerous single-nucleotide polymorphisms in innate immune genes are associated with dry AMD, no single gene appears to cause dry AMD. Here, we hypothesized that activation of TLR3 potentiates expression of TLR3 itself and the NFκB-p65 (RelA) subunit as part of pro-inflammatory RPE signaling. Furthermore, we hypothesized that TLR3 activation can 'prime' cells to future RelA stimulation, leading to enhanced, persistent RelA expression and signaling following a second TLR3 activation. We used the human RPE-derived cell line ARPE-19 as a model system for RPE signaling and measured NFκB expression and activity in response to TLR3 stimulation with its ligand, polyinosinic:polycytidylic acid (pI:C). Activation of TLR3 with pI:C led to increased TLR3 and RelA expression that was sustained for at least 24 h. Cells exposed for a second time to pI:C after an initial pI:C exposure displayed elevated RelA expression and RelA nuclear translocation above the level generated by individual primary or secondary exposures alone. Such an elevated response could also not be generated by a single application of higher concentrations of the agonist pI:C. Additionally, we determined the mechanism for TLR3 mediated TLR3 and RelA expression by using inhibitors of canonical TLR3-TBK1-IKKε and JAK-STAT signaling pathways. These data suggest that initial exposure of ARPE-19 cells to pI:C upregulates TLR3 and RelA signaling, leading to potentiated and persistent RelA signaling potentially generated by a positive feedback loop that may cause exacerbated inflammation in AMD. Furthermore, inhibition of JAK-STAT signaling may be a possible therapeutic treatment to prevent induction of TLR3 expression subsequent to pI:C exposure. Our results identify possible therapeutic targets to reduce the TLR3 positive feedback loop and subsequent overproduction of pro-inflammatory cytokines in RPE cells.

Differential Inflammatory-Response Kinetics of Human Keratinocytes upon Cytosolic RNA- and DNA-Fragment Induction

Keratinocytes are non-professional immune cells contributing actively to innate immune responses partially by reacting to a wide range of molecular patterns by activating pattern recognition receptors. Cytosolic nucleotide fragments as pathogen- or self-derived trigger factors are activating inflammasomes and inducing anti-viral signal transduction pathways as well as inducing expression of inflammatory cytokines. We aimed to compare the induced inflammatory reactions in three keratinocyte cell types—normal human epidermal keratinocytes, the HaCaT cell line and the HPV-KER cell line—upon exposure to the synthetic RNA and DNA analogues poly(I:C) and poly(dA:dT) to reveal the underlying signaling events. Both agents induced the expression of interleukin-6 and tumor necrosis factor α in all cell types; however, notable kinetic and expression level differences were found. Western blot analysis revealed rapid activation of the nuclear factor κB (NF-κB), mitogen activated protein kinase and signal transducers of activator of transcription (STAT) signal transduction pathways in keratinocytes upon poly(I:C) treatment, while poly(dA:dT) induced slower activation. Inhibition of NF-κB, p38, STAT-1 and STAT-3 signaling resulted in decreased cytokine expression, whereas inhibition of mitogen-activated protein kinase kinase 1/2 (MEK1/2) signaling showed a negative feedback role in both poly(I:C)- and poly(dA:dT)-induced cytokine expression. Based on our in vitro results nucleotide fragments are able to induce inflammatory reactions in keratinocytes, but with different rate and kinetics of cytokine expression, explained by faster activation of signaling routes by poly(I:C) than poly(dA:dT).

gga-miR-155 Enhances Type I Interferon Expression and Suppresses Infectious Burse Disease Virus Replication via Targeting SOCS1 and TANK

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by IBD virus (IBDV). MicroRNAs (miRNAs) are involved in host-pathogen interactions and innate immune response to viral infection. However, the role of miRNAs in host response to IBDV infection is not clear. We report here that gga-miR-155 acts as an anti-virus host factor inhibiting IBDV replication. We found that transfection of DF-1 cells with gga-miR-155 suppressed IBDV replication, while blockage of the endogenous gga-miR-155 by inhibitors enhanced IBDV replication. Furthermore, our data showed that gga-miR-155 enhanced the expression of type I interferon in DF-1 cells post IBDV infection. Importantly, we found that gga-miR-155 enhanced type I interferon expression via targeting SOCS1 and TANK, two negative regulators of type I IFN signaling. These results indicate that gga-miR-155 plays a critical role in cell response to IBDV infection.

Epicutaneous administration of the pattern recognition receptor agonist polyinosinic-polycytidylic acid activates the MDA5/MAVS pathway in Langerhans cells

Together with keratinocytes (KCs) and the dense network of Langerhans cells (LCs), the epidermis is an ideal portal for vaccine delivery. Pattern recognition receptor agonists, in particular polyinosinic–polycytidylic acid [p(I:C)], are promising adjuvant candidates for therapeutic vaccination to generate protective T-cell immunity. Here we established an ex vivo skin explant model to study the expression and activation of double-stranded RNA (dsRNA)-sensing pattern recognition receptors in LCs and KCs in human skin. Whereas KCs expressed all known dsRNA sensing receptors at a constitutive and inducible level, LCs exclusively expressed melanoma differentiation–associated protein 5 (MDA5) in untreated skin and freshly isolated cells. Comparative assessments of downstream signaling pathways induced by p(I:C) revealed distinct mitochondrial antiviral-signaling protein, IFN-regulatory factor 3, and NF-κB activation in LCs and KCs. Consequently, p(I:C) treatment of LCs significantly induced IFN-α and IFN-β mRNA expression, while in KCs an up-regulation of IFN-β and TNF-α mRNA was detectable. Stimulation of LCs with specific ligands revealed that not the TLR3- but only the MDA5-specific ligand induced IFN-α2, IFN-β, and TNF-α cytokines, but no IL-6 and -8. In KCs, both ligands induced production of high IL-6 and IL-8 levels, and low IFN-α2 and IFN-β levels, indicating that different dsRNA-sensing receptors and/or downstream signaling pathways are activated in both cell types. Our data suggest that MDA5 may be an attractive adjuvant target for epicutaneous delivery of therapeutic vaccines with the goal to target LCs.—Tajpara, P., Schuster, C., Schön, E., Kienzl, P., Vierhapper, M., Mildner, M., Elbe-Bürger, A. Epicutaneous administration of the pattern recognition receptor agonist polyinosinic–polycytidylic acid activates the MDA5/MAVS pathway in Langerhans cells.

Reduced-HMGB1 suppresses poly(I:C)-induced inflammation in keratinocytes

BACKGROUND

High mobility group box 1 (HMGB1) is a nuclear protein that stabilizes DNA and facilitates gene transcription. Additionally, cell stress or death induces the release of HMGB1 outside the cell membrane, where HMGB1 functions as an alarmin, causing an inflammatory response in combination with other cytokines, damage-associated molecular patterns (DAMPs), and pathogen-associated molecular patterns (PAMPs).

OBJECTIVE

To evaluate the effect of reduced-HMGB1 (previously termed chemoattractive-HMGB1) on polyinosine-polycytidylic acid [poly(I:C)]-induced inflammation in normal human keratinocytes (NHKs).

METHODS

We focused on downstream components of the poly(I:C)-Toll-like receptor 3 (TLR3), retinoic acid-inducible gene-I (RIG-I), and melanoma differentiation-associated protein 5 (MDA5) pathways, including IκBα, nuclear factor (NF)-κB p65, mitogen-activated protein kinase (MAPK), and interferon regulatory factor 3 (IRF3), and assessed whether these pathways are involved in the suppression of poly(I:C)-induced inflammation in NHKs by HMGB1. An immunoprecipitation was performed to know whether HMGB1 could bind to poly(I:C), and immunofluorescence staining and flow cytometric analysis were performed to check whether reduced-HMGB interferes with cellular uptake of poly(I:C) translocation (possibly by endocytosis).

RESULTS

Application of exogenous HMGB1 before, but not after, exerted a suppressive effect on poly(I:C)-induced inflammation in NHKs. In addition, reduced-HMGB1, but not disulfide-HMGB1, exerted a suppressive effect on poly(I:C)-induced inflammation in NHKs, suggesting the importance of the redox status of exogenous HMGB1. Pre-treatment with reduced-HMGB1 inhibited the phosphorylation of IκBα, NF-κB p65, and IRF3 induced by poly(I:C) stimulation in NHKs; however, phosphorylation of p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) was unaffected. Disulfide-HMGB1 formed a complex with poly(I:C), as did reduced- and oxidized-HMGB1, albeit to a lesser extent. Immunofluorescence staining and flow cytometric analysis indicated that reduced-HMGB interferes with cellular uptake of poly(I:C) translocation (possibly by endocytosis).

CONCLUSION

These findings suggest that pre-treatment with reduced-HMGB1 ameliorates poly(I:C)-mediated inflammation in NHKs.

Bcl-3 induced by IL-22 via STAT3 activation acts as a potentiator of psoriasis-related gene expression in epidermal keratinocytes

IL-22 induces STAT3 phosphorylation and mediates psoriasis-related gene expression. However, the signaling mechanism leading from pSTAT3 to the expression of these genes remains unclear. We focused on Bcl-3, which is induced by STAT3 activation and mediates gene expression. In cultured human epidermal keratinocytes, IL-22 increased Bcl-3, which was translocated to the nucleus with p50 via STAT3 activation. The increases in CXCL8, S100As and human β-defensin 2 mRNA expression caused by IL-22 were abolished by siRNA against Bcl-3. Although CCL20 expression was also augmented by IL-22, the knockdown of Bcl-3 increased its level. Moreover, the combination of IL-22 and IL-17A enhanced Bcl-3 production, IL-22-induced gene expression, and the expression of other psoriasis-related genes, including those encoding IL-17C, IL-19, and IL-36γ. The expression of these genes (except for CCL20) was also suppressed by the knockdown of Bcl-3. Bcl-3 overexpression induced CXCL8 and HBD2 expression but not S100As expression. We also compared Bcl-3 expression between psoriatic skin lesions and normal skin. Immunostaining revealed strong signals for Bcl-3 and p50 in the nucleus of epidermal keratinocytes from psoriatic skin. The IL-22-STAT3-Bcl-3 pathway may be important in the pathogenesis of psoriasis.

Characterization and role of suppressor of cytokine signaling 1a (SOCS1a) in a teleost fish, Miichthys miiuy

The suppressor of cytokine signaling 1 (SOCS1) is a crucial regulator in the immune systems of mammals, which functions classically as a negatively regulator in the IFN signaling pathways. However, data on functional characterization of SOCS1 in lower vertebrates is limited. In this study, we identified and characterized the full-length SOCS1a gene of miiuy croaker (Miichthys miiuy). The sequence analysis results showed that miiuy croaker SOCS1a (mmSOCS1a) shared some conserved motifs with other vertebrates. To further study the function of fish SOCS1, we identified mmSOCS1a and determined its potential ability to perceive poly(I:C) stimulation. Induction experiments with poly(I:C) indicated the significant expression levels of mmSOCS1a in liver and kidney. In addition, mmSOCS1a could inhibit poly(I:C)-induced or IFNs-induced ISRE reporter gene activation. In a word, we systematically and comprehensively analyzed evolution and function of mmSOCS1a, which will provide the basis for future research on fish SOCS family.

STAT1β enhances STAT1 function by protecting STAT1α from degradation in esophageal squamous cell carcinoma

STAT1, which carries tumor suppressor functions in several models, consists of two isoforms, namely STAT1α and STAT1β. The biological function and significance of STAT1β has never been examined in human cancer. We examined STAT1β function in esophageal squamous cell carcinoma (ESCC) by transfecting a STAT1β gene into various ESCC cell lines. The interaction between STAT1α and STAT1β was examined by using co-immunoprecipitation and confocal microscopy. The prognostic significance of STAT1β expression, detectable by immunohistochemistry and western blot, was evaluated in a large cohort of ESCC patients. Enforced expression of STAT1β induced and prolonged the expression and phosphorylation of STAT1α in ESCC cells, and these effects were amplified by gamma-interferon (IFN-γ). We also found that STAT1β interacts with STAT1α and decreases STAT1α degradation by the proteasome. Moreover, STAT1β substantially increased the DNA binding and transcription activity of STAT1. STAT1β also sensitized ESCC cells to chemotherapeutic agents, including cisplatin and 5-flurouracil. Using western blot and immunohistochemistry, we found that STAT1β was frequently decreased in esophageal cancer, as compared to their adjacent benign esophageal epithelial tissue. Loss of STAT1β significantly correlated with lymph node metastasis, invasion and shorter overall survival in ESCC patients. Therefore, STAT1β plays a key role in enhancing the tumor suppressor function of STAT1α, in ESCC, in a manner that can be amplified by IFN-γ.

Epidermal keratinocytes sense dsRNA via the NLRP3 inflammasome, mediating interleukin (IL)-1β and IL-18 release

Skin epidermis, in addition to its barrier function, is able to actively sense harmful pathogens using pattern recognition receptors. In immune cells, the nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing 3 (NLRP3) inflammasome can mediate innate immunity against viral infection via a mechanism involving viral dsRNA recognition. Epidermal keratinocytes express NLRP3 inflammasome, which can sense contact sensitizers and mite allergens, leading to pro-interleukin (IL)-1β and pro-IL-18 cleavage into their active forms. Skin often faces viral infection. However, it is unknown whether viral dsRNA can be detected by the keratinocyte NLRP3 inflammasome. We transfected polyinosinic:polycytidylic acid (poly I:C), a synthetic viral dsRNA analogue, into cultured primary human keratinocytes at the aid of Lipofectamine 2000, and found that transfected poly I:C activated caspase-1 and induced caspase-1-dependent release of IL-1β and IL-18, which were suppressed on transfection with NLRP3 siRNA. The activation of keratinocyte NLRP3 inflammasome by transfected poly I:C was dependent on dsRNA-induced protein kinase (PKR) activation, and priming with type I interferons upregulated NLRP3 inflammasome activation through promoting PKR activation in poly I:C-transfected keratinocytes. In conclusion, the NLRP3 inflammasome can act as a sensor of dsRNA in epidermal keratinocytes, which may be important in both skin innate immune defense against viral infection and skin inflammation.

Zinc Oxide Nanoparticle-Poly I:C RNA Complexes: Implication as Therapeutics against Experimental Melanoma

There is current interest in harnessing the combined anticancer and immunological effect of nanoparticles (NPs) and RNA. Here, we evaluate the bioactivity of poly I:C (pIC) RNA, bound to anticancer zinc oxide NP (ZnO-NP) against melanoma. Direct RNA association to unfunctionalized ZnO-NP is shown by observing change in size, zeta potential, and absorption/fluorescence spectra upon complexation. RNA corona was visualized by transmission electron microscopy (TEM) for the first time. Binding constant (K_b = 1.6-2.8 g^-1 L) was determined by modified Stern-Volmer, absorption, and biological surface activity index analysis. The pIC-ZnO-NP complex increased cell death for both human (A375) and mouse (B16F10) cell lines and suppressed tumor cell growth in BALB/C-B16F10 mouse melanoma model. Ex vivo tumor analysis indicated significant molecular activity such as changes in the level of phosphoproteins JNK, Akt, and inflammation markers IL-6 and IFN-γ. High throughput proteomics analysis revealed zinc oxide and poly I:C-specific and combinational patterns that suggested possible utility as an anticancer and immunotherapeutic strategy against melanoma.

TLR8 Couples SOCS-1 and Restrains TLR7-Mediated Antiviral Immunity, Exacerbating West Nile Virus Infection in Mice

West Nile virus (WNV) is a neurotropic ssRNA flavivirus that can cause encephalitis, meningitis, and death in humans and mice. Human TLR7 and TLR8 and mouse TLR7 recognize viral ssRNA motifs and induce antiviral immunity. However, the role of mouse TLR8 in antiviral immunity is poorly understood. In this article, we report that TLR8-deficient (Tlr8^-/-) mice were resistant to WNV infection compared with wild-type controls. Efficient WNV clearance and moderate susceptibility to WNV-mediated neuronal death in Tlr8^-/- mice were attributed to overexpression of Tlr7 and IFN-stimulated gene-56 expression, whereas reduced expression of the proapoptotic gene coding Bcl2-associated X protein was observed. Interestingly, suppressor of cytokine signaling (SOCS)-1 directly associated with TLR8, but not with TLR7, indicating a novel role for TLR8 regulation of SOCS-1 function, whereas selective small interfering RNA knockdown of Socs-1 resulted in induced IFN-stimulated gene-56 and Tlr7 expression following WNV infection. Collectively, we report that TLR8 coupling with SOCS-1 inhibits TLR7-mediated antiviral immunity during WNV infection in mice.

The toll-like receptor 3 pathway in homeostasis, responses to injury and wound repair

In addition to their established roles in host defence, Toll-like Receptors (TLRs) have emerging roles in control of homeostasis, injury and wound repair. The dsRNA-sensing receptor, TLR3, has been particularly implicated in such processes in several different tissues including the skin, intestine and liver, as well as in the control of reparative mechanisms in the brain, heart and kidneys, following ischemia reperfusion injury. In this review, we provide an overview of TLR3 signalling and functions in inflammation, tissue damage and repair processes, as well as therapeutic opportunities that may arise in the future from knowledge of such pathways.

Pedilanthus tithymaloides Inhibits HSV Infection by Modulating NF-κB Signaling

Pedilanthus tithymaloides (PT), a widely used ethnomedicinal plant, has been employed to treat a number of skin conditions. To extend its utility and to fully exploit its medicinal potential, we have evaluated the in vitro antiviral activity of a methanolic extract of PT leaves and its isolated compounds against Herpes Simplex Virus type 2 (HSV-2). Bioactivity-guided studies revealed that the extract and one of its constituents, luteolin, had potent antiviral activity against wild-type and clinical isolates of HSV-2 (EC₅₀ 48.5–52.6 and 22.4–27.5 μg/ml, respectively), with nearly complete inhibition at 86.5–101.8 and 40.2–49.6 μg/ml, respectively. The inhibitory effect was significant (p<0.001) when the drug was added 2 h prior to infection, and was effective up to 4 h post-infection. As viral replication requires NF-κB activation, we examined whether the observed extract-induced inhibition of HSV-2 was related to NF-κB inhibition. Interestingly, we observed that treatment of HSV-2-infected cells with extract or luteolin suppressed NF-κB activation. Although NF-κB, JNK and MAPK activation was compromised during HSV replication, neither the extract nor luteolin affected HSV-2-induced JNK1/2 and MAPK activation. Moreover, the PT leaf extract and luteolin potently down-regulated the expression of tumor necrosis factor (TNF)-α, Interleukin (IL)-1β, IL-6, NO and iNOS and the production of gamma interferon (IFN-γ), which are directly involved in controlling the NF-κB signaling pathway. Thus, our results indicate that both PT leaf extract and luteolin modulate the NF-κB signaling pathway, resulting in the inhibition of HSV-2 replication.

Interferon-λ and interleukin 22 act synergistically for the induction of interferon-stimulated genes and control of rotavirus infection

The epithelium is the main entry point for many viruses, but the processes that protect barrier surfaces against viral infections are incompletely understood. Here we identified interleukin 22 (IL-22) produced by innate lymphoid cell group 3 (ILC3) as an amplifier of signaling via interferon-λ (IFN-λ), a synergism needed to curtail the replication of rotavirus, the leading cause of childhood gastroenteritis. Cooperation between the receptor for IL-22 and the receptor for IFN-λ, both of which were 'preferentially' expressed by intestinal epithelial cells (IECs), was required for optimal activation of the transcription factor STAT1 and expression of interferon-stimulated genes (ISGs). These data suggested that epithelial cells are protected against viral replication by co-option of two evolutionarily related cytokine networks. These data may inform the design of novel immunotherapy for viral infections that are sensitive to interferons.

Alantolactone from Saussurea lappa Exerts Antiinflammatory Effects by Inhibiting Chemokine Production and STAT1 Phosphorylation in TNF-α and IFN-γ-induced in HaCaT cells

Skin inflammation is the most common condition seen in dermatology practice and can be caused by various allergic reactions and certain toxins or chemicals. In the present study, we investigated the antiinflammatory effects of Saussurea lappa, a medicinal herb, and its marker compounds alantolactone, caryophyllene, costic acid, costunolide, and dehydrocostuslactone in the HaCaT human keratinocyte cell line. HaCaT cells were stimulated with tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ), and treated with S. lappa or each of five marker compounds. Chemokine production and expression were analyzed by enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction, respectively. Phosphorylation of signal transducer and activator of transcription (STAT) 1 was determined by immunoblotting. Stimulation with TNF-α and IFN-γ significantly increased the production of the following chemokines: thymus-regulated and activation-regulated chemokine (TARC): regulated on activation, normal T-cell expressed and secreted (RANTES): macrophage-derived chemokine (MDC): and interleukin-8 (IL-8). By contrast, S. lappa and the five marker compounds significantly reduced the production of these chemokines by TNF-α and IFN-γ-treated cells. S. lappa and alantolactone suppressed the TNF-α and IFN-γ-stimulated increase in the phosphorylation of STAT1. Our results demonstrate that alantolactone from S. lappa suppresses TNF-α and IFN-γ-induced production of RANTES and IL-8 by blocking STAT1 phosphorylation in HaCaT cells.

Interferon-Gamma Enhances TLR3 Expression and Anti-Viral Activity in Keratinocytes

Toll-like receptors (TLRs) recognize specific microbial products in the innate immune response. TLR3, a double-stranded RNA sensor, is thought to have an important role in viral infections, but the regulation of TLR3 expression and its function in keratinocytes are not fully understood. Here we show the Th1 cytokine IFN-γ increased the TLR3 expression via STAT1 in cultured normal human epidermal keratinocytes (NHEKs). Co-stimulation with IFN-γ and the TLR3 ligand poly (I:C) synergistically increased the expression of IFN-β, IL-6, IL-8, and human β-defensin-2 in NHEKs compared with poly (I:C) or IFN-γ alone. These synergistic inductions were significantly inhibited by an endosomal acidification inhibitor, chloroquine, and by TLR3 siRNA. Co-stimulation with IFN-γ and poly (I:C) also significantly enhanced the anti-viral activity against herpes simplex virus type-1 in NHEKs compared with poly (I:C) or IFN-γ alone. In addition to the in vitro findings, an immunohistochemical analysis revealed IFN-γ-positive cells surrounding herpetic vesicles. These findings indicate that IFN-γ might contribute to the innate immune response to cutaneous viral infections by enhancing TLR3 expression and function in keratinocytes.

Antiviral effects of Jinxin oral liquid against respiratory syncytial virus infection in the BALB/c mice model

ETHNOPHARMACOLOGICAL RELEVANCE

Jinxin oral liquid (JOL) is used in traditional Chinese medicine (TCM) to treat influenza, cough, asthma, and viral pneumonia, on the basis of Ma Xing Shi Gan Tang (MXSGT) and the clinical experience of Professor Wang Shouchuan, one of the most prestigious pediatricians in China.

AIM OF STUDY

To investigate the anti-inflammatory and antiviral activities of JOL in mice infected with respiratory syncytial virus (RSV).

MATERIALS AND METHODS

Mice were orally administered JOL at doses of 27.6 g kg(-1) d(-1) and 55.2 g kg(-1) d(-1) for 1, 3, or 6d after RSV challenge. The viral loads in the lung tissue were measured by real-time RT-PCR. The levels of IFN-β in bronchoalveolar lavage fluid (BLAF) and lung tissue were detected by ELISA and real-time RT-PCR, respectively. The mRNA and protein expression of TLR3, IRF3, and SOCS1 were detected by real-time RT-PCR and western blot, respectively. The protein expression of phoshorylated-IRF3 (p-IRF3) was detected by western blot.

RESULTS

JOL significantly ameliorated lung inflammation in RSV-infected mice, and significantly reduced the viral load in the lung tissues. On days 2 and 4 after infection, the mRNA and protein expression of IFN-β, TLR3, IRF3 (p-IRF3), and SOCS1 were significantly downregulated in RSV-infected mice treated with JOL. However, 7d after infection, JOL significantly upregulated the RSV-induced decrease in IFN-β, TLR3, and IRF3 (p-IRF3), but reduced SOCS1 expression.

CONCLUSIONS

JOL ameliorated lung inflammation and inhibited virus replication significantly in RSV-infected mice. During early stage infection, the effect of JOL was improved through inhibition of the TLR3-IRF3-IFN-β signaling pathway and the expression of SOCS1, whereas during the later stage of infection, JOL upregulated the expression of key signaling molecules in the TLR3 signaling pathway and downregulated the expression of SOCS1.

Collaborative action of Toll-like and NOD-like receptors as modulators of the inflammatory response to pathogenic bacteria

Early sensing of pathogenic bacteria by the host immune system is important to develop effective mechanisms to kill the invader. Microbial recognition, activation of signaling pathways, and effector mechanisms are sequential events that must be highly controlled to successfully eliminate the pathogen. Host recognizes pathogens through pattern-recognition receptors (PRRs) that sense pathogen-associated molecular patterns (PAMPs). Some of these PRRs include Toll-like receptors (TLRs), nucleotide-binding oligomerization domain-like receptors (NLRs), retinoic acid-inducible gene-I- (RIG-I-) like receptors (RLRs), and C-type lectin receptors (CLRs). TLRs and NLRs are PRRs that play a key role in recognition of extracellular and intracellular bacteria and control the inflammatory response. The activation of TLRs and NLRs by their respective ligands activates downstream signaling pathways that converge on activation of transcription factors, such as nuclear factor-kappaB (NF-κB), activator protein-1 (AP-1) or interferon regulatory factors (IRFs), leading to expression of inflammatory cytokines and antimicrobial molecules. The goal of this review is to discuss how the TLRs and NRLs signaling pathways collaborate in a cooperative or synergistic manner to counteract the infectious agents. A deep knowledge of the biochemical events initiated by each of these receptors will undoubtedly have a high impact in the design of more effective strategies to control inflammation.

Cathelicidin antimicrobial peptide LL-37 augments interferon-β expression and antiviral activity induced by double-stranded RNA in keratinocytes

BACKGROUND

Cathelicidin antimicrobial peptide LL-37 has the capacity to kill a wide range of microbes and to modify host immunity. Recently, our group observed that the activation of keratinocytes by LL-37 and DNA greatly increases interferon (IFN)-β through Toll-like receptor (TLR)9. However, the effect of LL-37 on the induction of IFN-β through TLR3, a sensor of double-stranded (ds) RNA, in keratinocytes is not well known.

OBJECTIVES

To investigate whether LL-37 could affect TLR3 signalling and antiviral activity in normal human epidermal keratinocytes (NHEKs).

METHODS

We investigated the production of IFN-β in NHEKs stimulated with a TLR3 ligand, poly (I:C), in the presence of LL-37. To examine the effect of LL-37 and poly (I:C) on antiviral activity, a virus plaque assay using herpes simplex (HS) virus type-1 was carried out. The uptake of poly (I:C) conjugated with fluorescein isothiocyanate (FITC) into the keratinocytes was observed in the presence of LL-37. Immunostaining for TLR3 and LL-37 was performed using skin samples from HS.

RESULTS

LL-37 and poly (I:C) synergistically induced the expression of IFN-β in NHEKs. Furthermore, co-stimulation with LL-37 and poly (I:C) significantly decreased the viral plaque numbers compared with poly (I:C) or LL-37 alone. LL-37 enhanced the uptake of FITC-conjugated poly (I:C) into cells. Immunohistochemical analysis demonstrated that the expression of TLR3 and LL-37 is upregulated in HS lesions.

CONCLUSIONS

Our findings suggest that LL-37 augments the antiviral activity induced by dsRNA in keratinocytes, which may contribute to the innate immune response to cutaneous viral infections such as HS.

SOCS1 regulates the immune modulatory properties of mesenchymal stem cells by inhibiting nitric oxide production

Mesenchymal stem cells (MSCs) have been shown to be highly immunosuppressive and have been employed to treat various immune disorders. However, the mechanisms underlying the immunosuppressive capacity of MSCs are not fully understood. We found the suppressor of cytokine signaling 1 (SOCS1) was induced in MSCs treated with inflammatory cytokines. Knockdown of SOCS1 did not bring much difference on the proliferation and differentiation properties of MSCs. However, MSCs with SOCS1 knockdown exhibited enhanced immunosuppressive capacity, showing as inhibiting T cell proliferation at extremely low ratio (MSC to T) in vitro, significantly promoting tumor growth and inhibiting delayed-type hypersensitivity response in vivo. We further demonstrated that SOCS1 inhibited the immunosuppressive capacity of MSCs by reducing inducible nitric oxide synthase (iNOS) expression. Additionally, we found the significantly lower SOCS1 expression and higher nitric oxide (NO) production in MSCs isolated from synovial fluid of rheumatoid arthritis patients. Collectively, our data revealed a novel role of SOCS1 in regulating the immune modulatory activities of MSCs.

Conserved inhibitory role of teleost SOCS-1s in IFN signaling pathways

The suppressor of cytokine signaling 1 (SOCS-1) protein is a critical regulator in the immune systems of humans and mammals, which functions classically as an inhibitor of the IFN signaling pathways. However, data on functional characterisation of SOCS-1 in ancient vertebrates are limited. In this study, we report the function of teleost SOCS-1s in IFN signaling in fish models (zebrafish and Tetraodon) and human cells. Structurally, teleost SOCS-1s share conserved functional domains with their mammalian counterparts. Functionally, teleost SOCS-1s could be significantly induced upon stimulation with IFN stimulants and zebrafish IFNφ1. Overexpression of teleost SOCS-1s could dramatically suppress IFNφ1-induced Mx, Viperin and PKZ activation in zebrafish, and IFN-induced ISG15 activation in HeLa cells. Furthermore, a SOCS-1 variant that lacks the KIR domain was also characterised. This study demonstrates the conserved negative regulatory role of teleost SOCS-1s in IFN signaling pathways, providing perspective into the functional conservation of SOCS-1 proteins during evolution.

Suppression of interferon lambda signaling by SOCS-1 results in their excessive production during influenza virus infection

Innate cytokine response provides the first line of defense against influenza virus infection. However, excessive production of cytokines appears to be critical in the pathogenesis of influenza virus. Interferon lambdas (IFN-λ) have been shown to be overproduced during influenza virus infection, but the precise pathogenic processes of IFN-λ production have yet to be characterized. In this report, we observed that influenza virus induced robust expression of IFN-λ in alveolar epithelial cells (A549) mainly through a RIG-I-dependent pathway, but IFN-λ-induced phosphorylation of the signal transducer and activator of transcription protein 1 (STAT1) was dramatically inhibited in the infected cells. Remarkably, influenza virus infection induced robust expression of suppressor of cytokine signaling-1 (SOCS-1), leading to inhibition of STAT1 activation. Interestingly, the virus-induced SOCS-1 expression was cytokine-independent at early stage of infection both in vitro and in vivo. Using transgenic mouse model and distinct approaches altering the expression of SOCS-1 or activation of STAT signaling, we demonstrated that disruption of the SOCS-1 expression or expression of constitutively active STAT1 significantly reduced the production of IFN-λ during influenza virus infection. Furthermore, we revealed that disruption of IFN-λ signaling pathway by increased SOCS-1 protein resulted in the activation of NF-κB and thereby enhanced the IFN-λ expression. Together, these data imply that suppression of IFN-λ signaling by virus-induced SOCS-1 causes an adaptive increase in IFN-λ expression by host to protect cells against the viral infection, as a consequence, leading to excessive production of IFN-λ with impaired antiviral response.

Influenza virus infection triggers innate immune responses. However, aberrant host immune responses such as excessive production of cytokines contribute to the pathogenesis of influenza virus. Type III interferons (IFN-λ) constitute the major innate immune response to influenza virus infection, but the precise pathogenic processes of IFN-λ production and mechanistic underpinnings are not well understood. In this study, we report that influenza virus induces robust IFN-λ expression mainly through a RIG-I-dependent pathway, but signaling activated by IFN-λ was dramatically inhibited by virus-induced SOCS-1. Importantly, we found that disruption of the SOCS-1 expression or forced activation of STAT1 significantly reduced the expression of IFN-λ in vitro and in vivo, suggesting that suppression of IFN-λ signaling by SOCS-1 results in their excessive production during influenza virus infection. Furthermore, our experiments revealed that disruption of IFN-λ signaling pathway resulted in the activation of NF-κB that governs the IFN-λ expression. Together these findings, we propose that impaired antiviral response of IFN-λ due to the inhibitory effect of SOCS-1 causes an adaptive increase in IFN-λ expression by host to protect cells against the viral infection. This is a novel mechanism that may be critical in the pathogenesis of the influenza virus strains that induce hypercytokinemia.

Sodium methyldithiocarbamate exerts broad inhibition of cellular signaling and expression of effector molecules of inflammation

Sodium methyldithiocarbamate (SMD) is one of the most abundantly used conventional pesticides in the United States. At dosages relevant to occupational exposure, it causes major effects on the immune system in mice, including a decreased resistance to sepsis. This lab has identified some of the mechanisms of action of this compound and some of the immunological parameters affected, but the global effects have not previously been assessed. The purpose of the present study was to conduct transcriptomic analysis of the effects of SMD on lipopolysaccharide-induced expression of mediators important in innate immunity and inflammation. The results revealed broad effects on expression of transcription factors in both branches of Toll-like receptor 4 (TLR4) signaling (MyD88 and TRIF). However, TLR3 and interferon signaling pathways were decreased to a greater extent, and assessment of the effects of SMD on polyinosinic polycytidylic acid-induced cytokine and chemokine production revealed that these responses mediated by TLR3 were indeed sensitive to the effects of SMD, with inhibition occurring at lower dosages than required to inhibit responses to other immunological stimuli tested in our previous studies. In the downstream signaling pathways of these TLRs, functional analysis also revealed that NF-κB activation was inhibited by SMD, as indicated by gene expression analysis and a reporter construct in mice. A previously unreported effect on luteinizing hormone and follicle-stimulating hormone pathways was also observed.

Eccrine sweat contains IL-1α, IL-1β and IL-31 and activates epidermal keratinocytes as a danger signal

Eccrine sweat is secreted onto the skin's surface and is not harmful to normal skin, but can exacerbate eczematous lesions in atopic dermatitis. Although eccrine sweat contains a number of minerals, proteins, and proteolytic enzymes, how it causes skin inflammation is not clear. We hypothesized that it stimulates keratinocytes directly, as a danger signal. Eccrine sweat was collected from the arms of healthy volunteers after exercise, and levels of proinflammatory cytokines in the sweat were quantified by ELISA. We detected the presence of IL-1α, IL-1β, and high levels of IL-31 in sweat samples. To investigate whether sweat activates keratinocytes, normal human keratinocytes were stimulated with concentrated sweat. Western blot analysis demonstrated the activation of NF-κB, ERK, and JNK signaling in sweat-stimulated keratinocytes. Real-time PCR using total RNA and ELISA analysis of supernatants showed the upregulation of IL-8 and IL-1β by sweat. Furthermore, pretreatment with IL-1R antagonist blocked sweat-stimulated cytokine production and signal activation, indicating that bioactive IL-1 is a major factor in the activation of keratinocytes by sweat. Moreover, IL-31 seems to be another sweat stimulator that activates keratinocytes to produce inflammatory cytokine, CCL2. Sweat is secreted onto the skin's surface and does not come into contact with keratinocytes in normal skin. However, in skin with a defective cutaneous barrier, such as atopic dermatitis-affected skin, sweat cytokines can directly act on epidermal keratinocytes, resulting in their activation. In conclusion, eccrine sweat contains proinflammatory cytokines, IL-1 and IL-31, and activates epidermal keratinocytes as a danger signal.

Suppressor of cytokine signalling protein SOCS1 and UBP43 regulate the expression of type I interferon-stimulated genes in human microvascular endothelial cells infected with Rickettsia conorii

Rickettsia conorii, the causative agent of Mediterranean spotted fever, preferentially infects human microvascular endothelium and activates pro-inflammatory innate immune responses as evidenced by enhanced expression and secretion of cytokines and chemokines. Our recent studies reveal that human microvascular endothelial cells (HMECs) infected with R. conorii also launch 'antiviral' host defence mechanisms typically governed by type I interferons. To summarize, infected HMECs secrete IFN-β to activate STAT1 in an autocrine/paracrine manner and display increased expression of IFN-stimulated genes, for example ISG15, which in turn activate innate responses to interfere with intracellular replication of rickettsiae. We now present evidence that UBP43 and SOCS1, known negative regulators of JAK/STAT signalling, are also induced in R. conorii-infected HMECs, of which UBP43 but not SOCS1 functions to negatively regulate STAT1 activation. Interestingly, UBP43 induction is almost completely abolished in the presence of IFN-β-neutralizing antibody, implicating an important role for UBP43 as a feedback inhibitor for IFN-β-mediated STAT1 activation. In contrast, SOCS1 expression is only partially affected by IFN-β neutralization, implicating potential involvement of as-yet-unidentified IFN-independent mechanism(s) in SOCS1 induction during R. conorii infection. A number of IFN-stimulated genes, including ISG15, OAS1, MX1, IRF1, IRF9 and TAP1 are also induced in an IFN-β-dependent manner, whereas GBP1 remains unaffected by IFN-β neutralization. Increased STAT1 phosphorylation in HMECs subjected to UBP43 knockdown led to transcriptional activation of OAS1, MX1 and GBP1, confirming the negative regulatory role of UBP43. Although IRF1, IRF9 and TAP1 were induced by IFN-β, siRNA-mediated silencing of UBP43 or SOCS1 did not significantly affect their transcriptional activation. Expression of ISG15 was, however, increased in HMECs transfected with siRNA for UBP43 and SOCS1. Thus, unique regulatory patterns of induced expression of UBP43, SOCS1 and IFN-stimulated genes represent pathogen-specific responses underlying IFN-β-mediated host endothelial signalling during the pathogenesis of spotted fever group rickettsiosis.

Toll-like receptor 3 (TLR3) protects retinal pigmented epithelium (RPE) cells from oxidative stress through a STAT3-dependent mechanism

Toll-like receptors (TLRs) are essential receptors of the innate immune system and are first responders for protection against bacterial and viral pathogens. Recently, several TLRs have also been implicated in regulating cell death and survival in non-pathogen injuries such as stroke and oxidative stress. Investigating the role of TLRs during central nervous system damage is an important focus of research that may reveal new mechanisms underlying the cellular response to injury and survival. Retinal pigmented epithelium (RPE) cells form an epithelial layer underneath the neural retina that maintains the function of photoreceptors and are the primary cell type affected in the retinal disease age-related macular degeneration (AMD). Predicted loss of function polymorphisms in the TLR3 gene are associated with protection from AMD but the role of TLR3 in regulating RPE survival during AMD-like injury, such as high oxidative stress, is not known. Therefore the purpose of this study is to evaluate the effect of TLR3 signaling on RPE viability during oxidative stress. We demonstrated that TLR3 activation in the presence of oxidative stress injury significantly increased RPE cell viability, in contrast to TLR3 reducing cell viability in the absence of cellular injury. Furthermore, we show signal transducer and activator of transcription 3 (STAT3) signaling as an essential mediator of TLR3-regulated protection of RPE cells. STAT3 signaling was increased by TLR3 activation and knockdown of STAT3 transcripts using siRNA abolished the protective effect of TLR3 during oxidative stress. Together, these results demonstrate a novel pro-survival role for TLR3 signaling within the RPE during injury. These findings support the concept that dysregulation of TLR3 activity may contribute to the development of AMD, suggesting that precise regulation of the TLR3 pathway during AMD-associated injury could be of therapeutic interest.

Toll-like receptor 3 and suppressor of cytokine signaling proteins regulate CXCR4 and CXCR7 expression in bone marrow-derived human multipotent stromal cells

Background

The use of bone marrow-derived human multipotent stromal cells (hMSC) in cell-based therapies has dramatically increased in recent years, as researchers have exploited the ability of these cells to migrate to sites of tissue injury, inflammation, and tumors. Our group established that hMSC respond to “danger” signals – by-products of damaged, infected or inflamed tissues – via activation of Toll-like receptors (TLRs). However, little is known regarding downstream signaling mediated by TLRs in hMSC.

Methodology/Principal Findings

We demonstrate that TLR3 stimulation activates a Janus kinase (JAK) 2/signal transducer and activator of transcription (STAT) 1 pathway, and increases expression of suppressor of cytokine signaling (SOCS) 1 and SOCS3 in hMSC. Our studies suggest that each of these SOCS plays a distinct role in negatively regulating TLR3 and JAK/STAT signaling. TLR3-mediated interferon regulatory factor 1 (IRF1) expression was inhibited by SOCS3 overexpression in hMSC while SOCS1 overexpression reduced STAT1 activation. Furthermore, our study is the first to demonstrate that when TLR3 is activated in hMSC, expression of CXCR4 and CXCR7 is downregulated. SOCS3 overexpression inhibited internalization of both CXCR4 and CXCR7 following TLR3 stimulation. In contrast, SOCS1 overexpression only inhibited CXCR7 internalization.

Conclusion/Significance

These results demonstrate that SOCS1 and SOCS3 each play a functionally distinct role in modulating TLR3, JAK/STAT, and CXCR4/CXCR7 signaling in hMSC and shed further light on the way hMSC respond to danger signals.

Role of SOCS1 in tumor progression and therapeutic application

SOCS1, a prototype molecule of the SOCS family, was initially defined as a suppressor of cytokine signaling. The molecular mechanisms of SOCS1-mediated functions have been subsequently identified by studies using gene knockout mice and gene silencing technology. As part of a negative feedback regulation, SOCS1 downregulates cytokine signaling through direct inhibition of the JAK tyrosine kinase and the signaling cascade of activated cytokine receptors, thereby attenuating cytokine-initiated signal transduction. Moreover, other studies have demonstrated that SOCS1 also downregulates TLR signaling through direct and indirect mechanisms. Both cytokine receptor and TLR signaling pathways mediate important functions in survival, maturation and differentiation of various types of cells and in the regulation of immune function. Abnormal expression of SOCS1 in tumor cells has been detected in various human cancers, where it is associated with dysregulation of cytokine receptor and TLR signaling to promote cell transformation. Recent studies on the function of SOCS1 in tumor cells have revealed its novel role in carcinogenesis. In this review, we will focus on the mechanism of action of SOCS1 in both tumor cells and antigen-presenting cells in the tumor microenvironment. The potential of using SOCS1 as a diagnostic marker and therapeutic target in tumor diagnosis, prognosis and treatment is discussed.

Leptin as an immunomodulator

Leptin is an adipocyte-derived hormone/cytokine that links nutritional status with neuroendocrine and immune functions. In humans, leptin influences energy homeostasis and regulates neuroendocrine function primarily in states of energy deficiency. Initially described as an antiobesity hormone, leptin has subsequently been shown also to influence basal metabolism, hematopoiesis, thermogenesis, reproduction, and angiogenesis. As a cytokine, leptin can affect thymic homeostasis and the secretion of acute-phase reactants such as interleukin-1 (IL-1) and tumor-necrosis factor-alpha (TNF-α). Leptin links nutritional status and proinflammatory T helper 1 (Th1) immune responses and the decrease in leptin plasma concentration during food deprivation leads to impaired immune function. Similar to other pro-inflammatory cytokines, leptin promotes Th1-cell differentiation and can modulate the onset and progression of autoimmune responses in several animal models of disease. Here, we review the advances and controversy for a role of leptin in the pathophysiology of immune responses and discuss novel possible therapeutic implications for leptin modulators.

Cyclophosphamide induces bone marrow to yield higher numbers of precursor dendritic cells in vitro capable of functional antigen presentation to T cells in vivo

We have shown recently that cyclophosphamide (CTX) treatment induced a marked increase in the numbers of immature dendritic cells (DCs) in blood, coinciding with enhanced antigen-specific responses of the adoptively transferred CD8(+) T cells. Because this DC expansion was preceded by DC proliferation in bone marrow (BM), we tested whether BM post CTX treatment can generate higher numbers of functional DCs. BM was harvested three days after treatment of C57BL/6 mice with PBS or CTX and cultured with GM-CSF/IL-4 in vitro. Compared with control, BM from CTX-treated mice showed faster generation and yielded higher numbers of DCs with superior activation in response to toll-like receptor (TLR) agonists. Vaccination with peptide-pulsed DCs generated from BM from CTX-treated mice induced comparable adjuvant effects to those induced by control DCs. Taken together, post CTX BM harbors higher numbers of DC precursors capable of differentiating into functional DCs, which be targeted to create host microenvironment riches in activated DCs upon treatment with TLR agonists.

Primed innate immunity leads to autoinflammatory disease in PSTPIP2-deficient cmo mice

The mouse Lupo (I282N) mutation in proline-serine-threonine phosphatase-interacting protein 2 (PSTPIP2) leads to reduced expression of PSTPIP2 that is associated with a macrophage-mediated autoinflammatory disease. Another mutation in PSTPIP2, L98P, termed chronic multifocal osteomyelits (cmo), leads to a disease in mice that resembles chronic recurrent multifocal osteomyelits in humans. The cellular basis of cmo disease was investigated. cmo disease develops independently of lymphocytes and is cured by bone marrow transplantation. Macrophages, mast cells, and osteoclasts from cmo mice fail to express detectable PSTPIP2 protein. Asymptomatic Pstpip2(cmo/cmo) mice have increased circulating levels of macrophage inflammatory protein 1-alpha and interleukin-6, and their macrophages exhibit increased production of these inflammatory mediators, which is normalized by retroviral expression of wild-type PSTPIP2. Spleens of asymptomatic cmo mice contain increased numbers of macrophage precursors, and cmo mice mobilize more macrophage precursors in response to a sterile inflammatory stimulus. Signal transducer and activator of transcription 1 is elevated in cmo splenic macrophages, which also exhibit increased colony-stimulating factor-1-stimulated proliferation and increased extracellular signal-regulated kinase 1/2 phosphorylation. PSTPIP2 overexpression in macrophages leads to the opposite phenotype. Thus, PSTPIP2 deficiency causes both an expansion of macrophage progenitors and increased responsiveness of mature macrophages to activating stimuli, which together prime the organism for exaggerated and sustained responses leading to autoinflammatory disease.

Endosomal Toll-like receptors in autoimmunity: mechanisms for clinical diversity

The endosomal Toll-like receptors (TLR3, TLR7 and TLR9) have been implicated in the pathogenesis of autoimmune diseases. Their signaling pathways show remarkable similarities and yet the outcomes following activation of each of these TLRs lead to clinically distinct autoimmune disease phenotypes. This review discusses how differences may arise at a molecular and cellular level to account for this diversity of responses. Understanding the roles of individual TLR pathways and the relationships between them and non-TLR innate immune pathways in the pathogenesis of diseases such as systemic lupus erythematosis highlights potential treatment targets for this spectrum of autoimmune diseases.

SOCS1 regulates the IFN but not NFkappaB pathway in TLR-stimulated human monocytes and macrophages

SOCS1 can regulate TLR-mediated signal transduction, yet mechanistic studies in murine macrophages have been confusing and contradictory. This study has used an adenoviral transfection system to determine the role of SOCS1 in the regulation of TNF-alpha production by activated human monocytes. Monocytes were infected with AdV-SOCS1 or with an empty vector control, AdV-GFP, for 24 h before activation with the TLR4 ligand, LPS. SOCS1 did not regulate TNF-alpha mRNA or protein production within the first two hours of TLR4 activation. However, SOCS1 suppressed the sustained production of TNF-alpha by primary human monocytes and synovial fluid macrophages ex vivo. In addition, SOCS1 regulated the production of IL-6, but not IL-10, by monocytes. Analysis of the early signaling pathway downstream of TLR4 demonstrated that SOCS1 had no regulatory effect on the activation or on the DNA binding capacity of NFkappaB. The late effects of LPS are mediated in part through the MyD88-independent pathway activating IRF3 and initiating the production of IFN-beta. In response to adenoviral infection and before LPS exposure, monocytes expressed enhanced levels of IFN-beta and Myxovirus A mRNA, an anti-viral molecule characterizing IFN-beta activity. These two genes were reduced in AdV-SOCS1-infected cells. Further, SOCS1 regulated IFN-dependent pathways in LPS-activated cells as evidenced by reduced IFN-beta production and STAT1 phosphorylation. Using AdV-infection to dissect SOCS1 control of IFN-dependent pathways, this study suggests that SOCS1-regulation of the IFN-dependent component of the LPS-induced TLR4 signaling pathway may contribute to the down-regulation of inflammatory cytokine production by AdV-SOCS1-infected human monocytes.

Epstein-Barr virus BGLF4 kinase suppresses the interferon regulatory factor 3 signaling pathway

The BGLF4 protein kinase of Epstein-Barr virus (EBV) is a member of the conserved family of herpesvirus protein kinases which, to some extent, have a function similar to that of the cellular cyclin-dependent kinase in regulating multiple cellular and viral substrates. In a yeast two-hybrid screening assay, a splicing variant of interferon (IFN) regulatory factor 3 (IRF3) was found to interact with the BGLF4 protein. This interaction was defined further by coimmunoprecipitation in transfected cells and glutathione S-transferase (GST) pull-down in vitro. Using reporter assays, we show that BGLF4 effectively suppresses the activities of the poly(I:C)-stimulated IFN-beta promoter and IRF3-responsive element. Moreover, BGLF4 represses the poly(I:C)-stimulated expression of endogenous IFN-beta mRNA and the phosphorylation of STAT1 at Tyr701. In searching for a possible mechanism, BGLF4 was shown not to affect the dimerization, nuclear translocation, or CBP recruitment of IRF3 upon poly(I:C) treatment. Notably, BGLF4 reduces the amount of active IRF3 recruited to the IRF3-responsive element containing the IFN-beta promoter region in a chromatin immunoprecipitation assay. BGLF4 phosphorylates GST-IRF3 in vitro, but Ser339-Pro340 phosphorylation-dependent, Pin1-mediated downregulation is not responsible for the repression. Most importantly, we found that three proline-dependent phosphorylation sites at Ser123, Ser173, and Thr180, which cluster in a region between the DNA binding and IRF association domains of IRF3, contribute additively to the BGLF4-mediated repression of IRF3(5D) transactivation activity. IRF3 signaling is activated in reactivated EBV-positive NA cells, and the knockdown of BGLF4 further stimulates IRF3-responsive reporter activity. The data presented here thus suggest a novel mechanism by which herpesviral protein kinases suppress host innate immune responses and facilitate virus replication.

Double-stranded RNA induces an antiviral defense status in epidermal keratinocytes through TLR3-, PKR-, and MDA5/RIG-I-mediated differential signaling

Emerging evidence suggests an important role for human epidermal keratinocytes in innate immune mechanisms against bacterial and viral skin infections. The proinflammatory effect of viral infections can be mimicked by double-stranded RNA (dsRNA). Herein, we demonstrate that keratinocytes express all known dsRNA sensing receptors at a constitutive and inducible level, and that they use several downstream signaling pathways leading to a broad pattern of gene expression, not only proinflammatory and immune response genes under the control of NF-kappaB, but also genes under transcriptional control of IRF3. As a consequence, dsRNA, a stimulus for TLR3, protein kinase R (PKR), and the RNA helicases retinoic acid-inducible gene I (RIG-I) and MDA5, induces a status of antiviral defense in keratinocytes. Using inhibitors for the various dsRNA signaling pathways and specific small interfering RNA for TLR3, RIG-I, and MDA5, we demonstrated that in human keratinocytes, TLR3 seems to be necessary for NF-kappaB but not for IRF3 activation, whereas RIG-I and MDA5 are crucial for IRF3 activation. PKR is essential for the dsRNA response in both signaling pathways and thus represents the central antiviral receptor for dsRNA stimulation. Moreover, human keratinocytes up-regulate TLR7, the receptor for single-stranded RNA, in response to stimulation with dsRNA, which renders keratinocytes functionally responsive to the TLR7 agonist gardiquimod, a member of the imidazoquinoline antiviral immune response modifier family. Thus, in addition to building a physical barrier against infectious pathogens, keratinocytes are specially equipped with a full antiviral defense program that enables them to efficiently target viral infections of the skin.

Vaccinia virus subverts a mitochondrial antiviral signaling protein-dependent innate immune response in keratinocytes through its double-stranded RNA binding protein, E3

Skin keratinocytes provide a first line of defense against invading microorganisms in two ways: (i) by acting as a physical barrier to pathogen entry and (ii) by initiating a vigorous innate immune response upon sensing danger signals. How keratinocytes detect virus infections and generate antiviral immune responses is not well understood. Orthopoxviruses are dermatotropic DNA viruses that cause lethal disease in humans. Virulence in animal models depends on the virus-encoded bifunctional Z-DNA/double-stranded RNA (dsRNA)-binding protein E3. Here, we report that infection of mouse primary keratinocytes with a vaccinia DeltaE3L mutant virus triggers the production of beta interferon (IFN-beta), interleukin-6 (IL-6), CCL4, and CCL5. None of these immune mediators is produced by keratinocytes infected with wild-type vaccinia virus. The dsRNA-binding domain of E3 suffices to prevent activation of the innate immune response. DeltaE3L induction of IFN-beta, IL-6, CCL4, and CCL5 secretion requires mitochondrial antiviral signaling protein (MAVS; an adaptor for the cytoplasmic viral RNA sensors RIG-I and MDA5) and the transcription factor IRF3. IRF3 phosphorylation is induced in keratinocytes infected with DeltaE3L, an event that depends on MAVS. The response of keratinocytes to DeltaE3L is unaffected by genetic ablation of Toll-like receptor 3 (TLR3), TRIF, TLR9, and MyD88.