Glutaredoxin-1 regulates TRAF6 activation and the IL-1 receptor/TLR4 signalling

SLAMF7 regulates the inflammatory response in macrophages during polymicrobial sepsis

Uncontrolled inflammation occurred in sepsis results in multiple organ injuries and shock, which contributes to the death of patients with sepsis. However, the regulatory mechanisms that restrict excessive inflammation are still elusive. Here, we identified an Ig-like receptor called signaling lymphocyte activation molecular family 7 (SLAMF7) as a key suppressor of inflammation during sepsis. We found that the expression of SLAMF7 on monocytes/macrophages was significantly elevated in patients with sepsis and in septic mice. SLAMF7 attenuated TLR-dependent MAPK and NF-κB signaling activation in macrophages by cooperating with Src homology 2-containing inositol-5'‑phosphatase 1 (SHIP1). Furthermore, SLAMF7 interacted with SHIP1 and TNF receptor-associated factor 6 (TRAF6) to inhibit K63 ubiquitination of TRAF6. In addition, we found that tyrosine phosphorylation sites within the intracellular domain of SLAMF7 and the phosphatase domain of SHIP1 were indispensable for the interaction between SLAMF7, SHIP1, and TRAF6 and SLAMF7-mediated modulation of cytokine production. Finally, we demonstrated that SLAMF7 protected against lethal sepsis and endotoxemia by downregulating macrophage proinflammatory cytokines and suppressing inflammation-induced organ damage. Taken together, our findings reveal a negative regulatory role of SLAMF7 in polymicrobial sepsis, thus providing sights into the treatment of sepsis.

Identification and functional characterization of glutaredoxin 5 from the mud crab (Scylla paramamosain) in response to cadmium and bacterial challenge

Glutaredoxin (Grx) is a class molecule oxidoreductase, which plays a key role in maintaining redox homeostasis and regulating cell survival pathways. However, the expression pattern and function of Grx remain unknown in the mud crab (Scylla paramamosain). In the present study, a novel full-length of Grx 5 from the mud crab (designated as Sp-Grx 5) was cloned and characterized. The open reading frame of Sp-Grx 5 was 441 bp, which encoded a putative protein of 146 amino acids. The amino acid sequence of Sp-Grx 5 contained a typical C-G-F-S redox active motif and several GSH binding sites. Sp-Grx 5 widely existed in all tested tissues with a high-level expression in hepatopancreas. Subcellular localization showed that Sp-Grx 5 was located in the cytoplasm and nucleus. The expression of Sp-Grx 5 was significantly up-regulated after Vibrio parahaemolyticus infection and cadmium exposure, suggesting that Sp-Grx 5 was involved in innate immunity and detoxification. Furthermore, overexpression of Sp-Grx 5 could improve cells viability after H₂O₂ exposure. All these results indicated that Sp-Grx 5 played important roles in the redox homeostasis and innate immune response in crustaceans.

Redox Regulation, Oxidative Stress, and Inflammation in Group 3 Pulmonary Hypertension

Group 3 pulmonary hypertension (PH), which occurs secondary to hypoxia lung diseases, is one of the most common causes of PH worldwide and has a high unmet clinical need. A deeper understanding of the integrative pathological and adaptive molecular mechanisms within this group is required to inform the development of novel drug targets and effective treatments. The production of oxidants is increased in PH Group 3, and their pleiotropic roles include contributing to disease progression by promoting prolonged hypoxic pulmonary vasoconstriction and pathological pulmonary vascular remodeling, but also stimulating adaptation to pathological stress that limits the severity of this disease. Inflammation, which is increasingly being viewed as a key pathological feature of Group 3 PH, is subject to complex regulation by redox mechanisms and is exacerbated by, but also augments oxidative stress. In this review, we investigate aspects of this complex crosstalk between inflammation and oxidative stress in Group 3 PH, focusing on the redox-regulated transcription factor NF-κB and its upstream regulators toll-like receptor 4 and high mobility group box protein 1. Ultimately, we propose that the development of specific therapeutic interventions targeting redox-regulated signaling pathways related to inflammation could be explored as novel treatments for Group 3 PH.

Molecular characterization, redox regulation, and immune responses of monothiol and dithiol glutaredoxins from disk abalone (Haliotis discus discus)

Glutaredoxins (Grxs) are well-known oxidoreductases involved in a wide range of redox activities in organisms. In this study, two invertebrate Grxs (AbGrx1-like and AbGrx2) from disk abalone were identified and characterized in an effort to gain a deeper understanding into their immune and redox regulatory roles. Both AbGrxs share typical thioredoxin/Grx structures. AbGrx1-like and AbGrx2 were identified as monothiol and diothiol Grxs, respectively. AbGrxs were significantly expressed at the egg and 16-cell stage of early abalone development. Although the expression of both AbGrxs demonstrated similar patterns, the expression of AbGrx1-like was higher than AbGrx2 during development stages. In contrast, AbGrx2 expression was significantly higher than that of AbGrx1-like in adult tissues. Highest AbGrx1-like expression was observed in the hepatopancreas and digestive tract, while highest AbGrx2 expression was found in the gills, followed by the mantle, in healthy adult abalone tissues. The highest expression of AbGrx1-like was observed in the gills at 12 h and 6 h post injection (p.i) of Vibrio parahemolyticus and other stimulants, respectively. The highest expression of AbGrx2 in the gills were observed at 120 h, 6 h, 24 h, and 12 h post injection of V. parahaemolyticus, Listeria monocytogenes, Viral hemorrhagic septicemia virus, and Polyinosinic:polycytidylic acid, respectively. AbGrxs possessed significant 2-hydroxyethyl disulfide (HED) and dehydroascorbate (DHA) reduction activity, but AbGrx2 exhibited higher redox activity than AbGrx1-like. Altogether, our results suggest an important role of AbGrx1-like and AbGrx2 in redox homeostasis, as well as in the invertebrate immune defense system. Our findings will aid the development of new disease management strategies for this economically valuable species.

Redox Regulation via Glutaredoxin-1 and Protein S-Glutathionylation

Significance: Over the past several years, oxidative post-translational modifications of protein cysteines have been recognized for their critical roles in physiology and pathophysiology. Cells have harnessed thiol modifications involving both oxidative and reductive steps for signaling and protein processing. One of these stages requires oxidation of cysteine to sulfenic acid, followed by two reduction reactions. First, glutathione (reduced glutathione [GSH]) forms a S-glutathionylated protein, and second, enzymatic or chemical reduction removes the modification. Under physiological conditions, these steps confer redox signaling and protect cysteines from irreversible oxidation. However, oxidative stress can overwhelm protein S-glutathionylation and irreversibly modify cysteine residues, disrupting redox signaling. Critical Issues: Glutaredoxins mainly catalyze the removal of protein-bound GSH and help maintain protein thiols in a highly reduced state without exerting direct antioxidant properties. Conversely, glutathione S-transferase (GST), peroxiredoxins, and occasionally glutaredoxins can also catalyze protein S-glutathionylation, thus promoting a dynamic redox environment. Recent Advances: The latest studies of glutaredoxin-1 (Glrx) transgenic or knockout mice demonstrate important distinct roles of Glrx in a variety of pathologies. Endogenous Glrx is essential to maintain normal hepatic lipid homeostasis and prevent fatty liver disease. Further, in vivo deletion of Glrx protects lungs from inflammation and bacterial pneumonia-induced damage, attenuates angiotensin II-induced cardiovascular hypertrophy, and improves ischemic limb vascularization. Meanwhile, exogenous Glrx administration can reverse pathological lung fibrosis. Future Directions: Although S-glutathionylation modifies many proteins, these studies suggest that S-glutathionylation and Glrx regulate specific pathways in vivo, and they implicate Glrx as a potential novel therapeutic target to treat diverse disease conditions. Antioxid. Redox Signal. 32, 677-700.

Role of rockfish (Sebastes schlegelii) glutaredoxin 1 in innate immunity, and alleviation of cellular oxidative stress: Insights into localization, molecular characteristics, transcription, and function

Glutaredoxins are a group of heat stable oxidoreductases ubiquitously found in prokaryotes and eukaryotes. They are widely known for GSH (glutathione)-dependent protein disulfide reduction and cellular redox homeostasis. This study was performed to identify and characterize rockfish (Sebastes schlegelii) glutaredoxin 1 (SsGrx1) at molecular, transcriptional, and functional levels. The coding sequence of SsGrx1 was 318 bp in length and encoded a protein containing 106 amino acids. The molecular weight and theoretical isoelectric point of the putative SsGrx1 protein were 11.6 kDa and 6.71 kDa, respectively. The amino acid sequence of SsGrx1 comprised a CPYC redox active motif surrounded by several conserved GSH binding sites. The modeled protein structure was found to consist of five α-helices and four β-sheets, similar to human Grx1. SsGrx1 showed a tissue specific expression in all the tissues tested, with the highest expression in the kidney. Immune stimulation by lipopolysaccharides (LPS), polyinosinic:polycytidylic acid (polyI:C), and Streptococcus iniae (S. iniae) could significantly modulate the SsGrx1 expression pattern in the blood and gills. Analysis of its subcellular localization disclosed that SsGrx1 was prominently localized in the cytosol. Recombinant SsGrx1 (rSsGrx1) exhibited significant activity in insulin disulfide reduction assay and HED (β-Hydroxyethyl Disulfide) assay. Furthermore, transient overexpression of SsGrx1 in FHM (fathead minnow) cells significantly enhanced cell survival upon H₂O₂-induced apoptosis. Collectively, our findings strongly suggest that SsGrx1 plays a crucial role in providing rockfish immune protection against pathogens and oxidative stress.

OTUD4 alleviates hepatic ischemia-reperfusion injury by suppressing the K63-linked ubiquitination of TRAF6

Hepatic ischemia-reperfusion (IR) injury can cause serious liver damage, leading to liver dysfunction after liver surgery, which is associated with NF-κB-mediated inflammation. The K63-linked auto-polyubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6) is essential for the activation of NF-κB. Here, we found that OTU domain-containing protein 4 (OTUD4), a deubiquitinating enzyme (DUB), interacts with TRAF6 and decreases the K63 auto-polyubiquitination of TRAF6. In addition, the data showed that NF-κB activation was impaired and inflammatory factor levels were reduced after overexpressing OTUD4 in a hypoxia/reoxygenation (HR) model and a hepatic IR model. Additionally, the liver inflammatory response and tissue damage were ameliorated in mice overexpressing OTUD4.Taken together, these results show that OTUD4 can negatively regulate NF-κB activation by suppressing the K63-linked ubiquitination of TRAF6, thus alleviating hepatic ischemia-reperfusion injury.

Glutaredoxin 2 from big belly seahorse (Hippocampus abdominalis) and its potential involvement in cellular redox homeostasis and host immune responses

Glutaredoxins are oxidoreductases present in almost all living organisms. They belong to the thioredoxin superfamily and share the thioredoxin structure and catalytic motif. Glutaredoxin 2 has been identified as a mitochondrial protein in vertebrates. In this study, the sequence of Glutaredoxin 2 from Hippocampus abdominalis (HaGrx2) was analyzed by molecular, transcriptional, and functional assays. In-silico analysis revealed that HaGrx2 shows the highest homology with Hippocampus comes, while distinctly cluster with fish Grx2 orthologs. Tissue distribution analysis showed that HaGrx2 is ubiquitously expressed in all tissues tested, and the highest expression was observed in the brain and skin. Significant HaGrx2 transcript modulation was identified in blood and liver upon injecting bacterial and Pathogen Associated Molecular Patterns. The redox activity of HaGrx2 was revealed by Dehydroascorbic reduction and insulin disulfide reduction activity assays. Further, the deglutathionylation activity of 1 nM HaGrx2 was found to be equivalent to that of 0.84 nM HaGrx1. HaGrx2 exhibited antiapoptotic activity against H₂O₂-induced oxidative stress in FHM cells. Altogether, the results of this study suggest that HaGrx2 plays a role in redox homeostasis and innate immune responses in fish.

Dysregulation of the glutaredoxin/S-glutathionylation redox axis in lung diseases

Glutathione is a major redox buffer, reaching millimolar concentrations within cells and high micromolar concentrations in airways. While glutathione has been traditionally known as an antioxidant defense mechanism that protects the lung tissue from oxidative stress, glutathione more recently has become recognized for its ability to become covalently conjugated to reactive cysteines within proteins, a modification known as S-glutathionylation (or S-glutathiolation or protein mixed disulfide). S-glutathionylation has the potential to change the structure and function of the target protein, owing to its size (the addition of three amino acids) and charge (glutamic acid). S-glutathionylation also protects proteins from irreversible oxidation, allowing them to be enzymatically regenerated. Numerous enzymes have been identified to catalyze the glutathionylation/deglutathionylation reactions, including glutathione S-transferases and glutaredoxins. Although protein S-glutathionylation has been implicated in numerous biological processes, S-glutathionylated proteomes have largely remained unknown. In this paper, we focus on the pathways that regulate GSH homeostasis, S-glutathionylated proteins, and glutaredoxins, and we review methods required toward identification of glutathionylated proteomes. Finally, we present the latest findings on the role of glutathionylation/glutaredoxins in various lung diseases: idiopathic pulmonary fibrosis, asthma, and chronic obstructive pulmonary disease.

Role of Glutathionylation in Infection and Inflammation

Glutathionylation, that is, the formation of mixed disulfides between protein cysteines and glutathione (GSH) cysteines, is a reversible post-translational modification catalyzed by different cellular oxidoreductases, by which the redox state of the cell modulates protein function. So far, most studies on the identification of glutathionylated proteins have focused on cellular proteins, including proteins involved in host response to infection, but there is a growing number of reports showing that microbial proteins also undergo glutathionylation, with modification of their characteristics and functions. In the present review, we highlight the signaling role of GSH through glutathionylation, particularly focusing on microbial (viral and bacterial) glutathionylated proteins (GSSPs) and host GSSPs involved in the immune/inflammatory response to infection; moreover, we discuss the biological role of the process in microbial infections and related host responses.

Glutaredoxin 1 from big-belly seahorse (Hippocampus abdominalis): Molecular, transcriptional, and functional evidence in teleost immune responses

Glutaredoxins (Grx) are redox enzymes conserved in viruses, eukaryotes, and prokaryotes. In this study, we characterized glutaredoxin 1 (HaGrx1) from big-belly seahorse, Hippocampus abdominalis. In-silico analysis showed that HaGrx1 contained the classical glutaredoxin 1 structure with a CSYC thioredoxin active site motif. According to multiple sequence alignment and phylogenetic reconstruction, HaGrx1 presented the highest homology to the Grx1 ortholog from Hippocampus comes. Transcriptional studies demonstrated the ubiquitous distribution of HaGrx1 transcripts in all the seahorse tissues tested. Significant modulation (p < 0.05) of HaGrx1 transcripts were observed in blood upon stimulation with pathogen-associated molecular patterns and live pathogens. The β-hydroxyethyl disulfide reduction assay confirmed the antioxidant activity of recombinant HaGrx1. Further, dehydroascorbate reduction and insulin disulfide reduction assays revealed the oxidoreductase activity of HaGrx1. HaGrx1 utilized 1,4-dithiothreitol, l-cysteine, 2-mercaptoethanol, and reduced l-glutathione as reducing agent with different dehydroascorbate reduction activity levels. Altogether, our results suggested a vital role of HaGrx1 in redox homeostasis as well as the host innate immune defense system.

MicroRNA-125b protects liver from ischemia/reperfusion injury via inhibiting TRAF6 and NF-κB pathway

MicroRNA-125b (miR-125b), which was previously proved to be a potential immunomodulator in various disease, attenuated mouse hepatic ischemia/reperfusion (I/R) injury in this study. miR-125b was decreased in RAW 264.7 cells exposed to hypoxia/reoxygenation (H/R). The expression of IL-1β, IL-6 and TNF-α in both serum and supernate were reduced in miR-125b over-expression groups. The hepatic histopathological changes were reduced in miR-125b agomir groups. In the miR-125b antagomir groups, serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were significantly elevated compared with negative control (NC) groups. The protein expression of TNF receptor-associated factor 6 (TRAF6), IL-1β and the phosphorylation of p65 (p-p65) were suppressed by the up-regulation of miR-125b. Furthermore, the nuclear translocation of p-p65, measured by immunofluorescence, was enhanced by the miR-125b inhibitors. In conclusion, our study indicates that miR-125b protects liver from hepatic I/R injury via inhibiting TRAF6 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signal pathway.

IL-33 induction and signaling are controlled by glutaredoxin-1 in mouse macrophages

Interleukin (IL)-33 is an interleukin-1 like cytokine that enhances Th2 responses and mediates mucosal immunity and allergic inflammation but the mechanism regulating endogenous IL-33 production are still under investigation. In macrophages, lipopolysaccharide (LPS) administration resulted in marked induction of IL-33 mRNA that was blunted in macrophages from glutaredoxin-1 (Glrx) knockout mice and in RAW264.7 macrophages with Glrx knockdown by siRNA. Glutaredoxin-1 is a small cytosolic thioltransferase that controls a reversible protein thiol modification, S-glutationylation (protein-GSH adducts), thereby regulating redox signaling. In this study, we examined the mechanism of Glrx regulation of endogenous IL-33 induction in macrophages. Glrx knockdown resulted in impaired de-glutathionylation of TRAF6, which is required for TRAF6 activation, and inhibited downstream IKKβ and NF-κB activation. Inhibitors of NF-κB suppressed IL-33 induction and chromatin IP sequencing data analysis confirmed that IL-33 is an NF-κB-responsive gene. Since TRAF6-NF-κB activation is also essential for IL-33 signaling through its receptor, ST2L, we next tested the involvement of Glrx in exogenous IL-33 responses in RAW264.7 cells. Recombinant IL-33 (rIL-33) administration induced IL-33 mRNA expression in RAW264.7 macrophages, and this was inhibited by Glrx knockdown. Interestingly, rIL-33-induced IL-33 protein was identified as the 20 kDa cleaved form whereas LPS-induced IL-33 protein was identified as full-length IL-33, which may be less active than the cleaved form. In a clinically-relevant mouse model of asthma, intra-tracheal cockroach antigen treatment induced Glrx protein in wild type mouse lungs but Glrx induction was attenuated in IL-33 knockout mouse lungs, suggesting that IL-33 may regulate Glrx induction in vivo in response to allergen challenge. In summary, our data reveal a novel mechanism by which Glrx controls both LPS- and IL-33-mediated NF-κB activation leading to IL-33 production, and paracrine IL-33 can induce Glrx to further regulate inflammatory reactions.

Role of interleukin-23 in monocyte-derived dendritic cells of HBV-related acute-on-chronic liver failure and its correlation with the severity of liver damage

BACKGROUND

The role of interleukin-23 (IL-23) in monocyte-derived dendritic cells (MoDCs) from hepatitis B virus-related acute-on-chronic liver failure (HBV-ACLF) patients remains unclear. The aim of this study was to observe the correlation between the activation of the IL-23 signaling pathway and the prognosis of HBV-ACLF patients.

MATERIALS AND METHODS

The baseline levels of serum IL-6, IL-12, IL-17, IL-23, tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ) from immune tolerant (IT), chronic hepatitis B (CHB), HBV-ACLF patients and healthy individuals who served as healthy controls (HCs) were analyzed using the Luminex system, whereas serum IL-23 from HBV-ACLF patients was measured by ELISA before and after treatment. Purified monocytes were isolated from peripheral blood and were induced into MoDCs, IL-23, IL-23R, NF-κB and TRAF6 expression in MoDCs from 4 groups was analyzed using real-time PCR, and IL-23R and intracellular IL-23 were evaluated by flow cytometry.

RESULTS

Serum IL-6, IL-12, IL-17, IL-23 and TNF-α levels were upregulated in HBV-ACLF patients compared with IT patients, CHB patients and HCs (P<0.05 for all). Serum IL-23 was closely correlated with elevated serum IL-17 in HBV-ACLF patients (r=0.5935, P<0.0001). Moreover, IL-23 and IL-23R levels were significantly upregulated in MoDCs from patients with CHB or HBV-ACLF compared with HCs, and further upregulation of IL-23 and IL-23R was observed in HBV-ACLF patients compared to CHB patients (P<0.05 for all). IL-23 expression was markedly enhanced and was correlated with elevated NF-κB and TRAF6 in MoDCs from HBV-ACLF patients (P<0.05 for both). Linear correlation analysis demonstrated significant correlations between the expression of IL-23 and disease severity markers (MELD scoring system, international normalized ratio, prothrombin time and total bilirubin, r=0.6874, r=0.6475, r=0.6249, r=0.3771, respectively, P<0.05 for all) for individual HBV-ACLF patients, and IL-23 levels were significantly upregulated in non-survival HBV-ACLF patients compared with survival HBV-ACLF patients (P<0.05).

CONCLUSION

IL-23 in serum and MoDCs is significantly elevated in HBV-ACLF patients, TRAF6/NF-κB may play a role in IL-23 production by MoDCs in HBV-ACLF patients and high pre-treatment IL-23 levels in MoDCs are associated with mortality in HBV-ACLF patients.

Suppression of tumor cell proliferation by quinine via the inhibition of the tumor necrosis factor receptor‑associated factor 6‑AKT interaction

Protein kinase B (AKT), is a pivotal component of pathways associated with cell survival, metabolism, invasion and metastasis. AKT mediates anti‑apoptotic and proliferative signaling in response to essential cytokines. Tumor necrosis factor receptor‑associated factor (TRAF)6, an E3 ubiquitin ligase, has been shown to ubiquitylate, as well as activate AKT. The present study used computational methods to determine the relevant amino acid residues at the binding site of TRAF6 and selected small molecules, which may bind to TRAF6. An ex vivo assay was performed to determine their antitumor activities and the possible mechanism of action. Quinine, a natural alkaloid that is well‑known for its therapeutic treatment of malaria, exhibited a distinct antiproliferative and pro‑apoptotic effect in HeLa and A549 tumor cell lines via the inhibition of the antiapoptotic protein, B‑cell lymphoma (BCL)‑2, and activation of the pro‑apoptotic factor, BCL‑2‑associated X protein. Quinine inhibited the lipopolysaccharide (LPS)‑induced activation of AKT by inhibiting its phosphorylation at Thr‑308 and Ser‑473, and reversing LPS‑induced proliferation. These results suggested that the inhibition of AKT activation via targeting of TRAF6 with quinine may be a viable anticancer therapeutic approach and a successful example of the alternative use of the original therapeutic properties of this well‑known natural product.

Structure, function and disease relevance of Omega-class glutathione transferases

The Omega-class cytosolic glutathione transferases (GSTs) have distinct structural and functional attributes that allow them to perform novel roles unrelated to the functions of other GSTs. Mammalian GSTO1-1 has been found to play a previously unappreciated role in the glutathionylation cycle that is emerging as significant mechanism regulating protein function. GSTO1-1-catalyzed glutathionylation or deglutathionylation of a key signaling protein may explain the requirement for catalytically active GSTO1-1 in LPS-stimulated pro-inflammatory signaling through the TLR4 receptor. The observation that ML175 a specific GSTO1-1 inhibitor can block LPS-stimulated inflammatory signaling has opened a new avenue for the development of novel anti-inflammatory drugs that could be useful in the treatment of toxic shock and other inflammatory disorders. The role of GSTO2-2 remains unclear. As a dehydroascorbate reductase, it could contribute to the maintenance of cellular redox balance and it is interesting to note that the GSTO2 N142D polymorphism has been associated with multiple diseases including Alzheimer's disease, Parkinson's disease, familial amyotrophic lateral sclerosis, chronic obstructive pulmonary disease, age-related cataract and breast cancer.

The PP4R1 subunit of protein phosphatase PP4 targets TRAF2 and TRAF6 to mediate inhibition of NF-κB activation

TRAFs constitute a family of proteins that have been implicated in signal transduction by immunomodulatory cellular receptors and viral proteins. TRAF2 and TRAF6 have an E3-ubiquitin ligase activity, which is dependent on the integrity of their RING finger domain and it has been associated with their ability to activate the NF-κB and AP1 signaling pathways. A yeast two-hybrid screen with TRAF2 as bait, identified the regulatory subunit PP4R1 of protein phosphatase PP4 as a TRAF2-interacting protein. The interaction of TRAF2 with PP4R1 depended on the integrity of the RING finger domain of TRAF2. PP4R1 could interact also with the TRAF2-related factor TRAF6 in a RING domain-dependent manner. Exogenous expression of PP4R1 inhibited NF-κB activation by TRAF2, TRAF6, TNF and the Epstein-Barr virus oncoprotein LMP1. In addition, expression of PP4R1 downregulated IL8 induction by LMP1, whereas downregulation of PP4R1 by RNA interference enhanced the induction of IL8 by LMP1 and TNF. PP4R1 could mediate the dephosphorylation of TRAF2 Ser11, which has been previously implicated in TRAF2-mediated activation of NF-κB. Finally, PP4R1 could inhibit TRAF6 polyubiquitination, suggesting an interference with the E3 ubiquitin ligase activity of TRAF6. Taken together, our data identify a novel mechanism of NF-κB pathway inhibition which is mediated by PP4R1-dependent targeting of specific TRAF molecules.

The glutaredoxin/S-glutathionylation axis regulates interleukin-17A-induced proinflammatory responses in lung epithelial cells in association with S-glutathionylation of nuclear factor κB family proteins

Interleukin-17A (IL-17A) is a newly emerging player in the pathogenesis of chronic lung diseases that amplifies inflammatory responses and promotes tissue remodeling. Stimulation of lung epithelial cells with IL-17A leads to activation of the transcription factor nuclear factor κB (NF-κB), a key player in the orchestration of lung inflammation. We have previously demonstrated the importance of the redox-dependent posttranslational modification S-glutathionylation in limiting activation of NF-κB and downstream gene induction. Under physiological conditions, the enzyme glutaredoxin 1 (Grx1) acts to deglutathionylate NF-κB proteins, which restores functional activity. In this study, we sought to determine the impact of S-glutathionylation on IL-17A-induced NF-κB activation and expression of proinflammatory mediators. C10 mouse lung alveolar epithelial cells or primary mouse tracheal epithelial cells exposed to IL-17A show rapid activation of NF-κB and the induction of proinflammatory genes. Upon IL-17A exposure, sulfenic acid formation and S-glutathionylated proteins increased. Assessment of S-glutathionylation of NF-κB pathway components revealed S-glutathionylation of RelA (RelA-SSG) and inhibitory κB kinase α (IKKα-SSG) after stimulation with IL-17A. SiRNA-mediated ablation of Grx1 increased both RelA-SSG and IKKα-SSG and acutely increased nuclear content of RelA and tended to decrease nuclear RelB. SiRNA-mediated ablation or genetic ablation of Glrx1 decreased the expression of the NF-κB-regulated genes KC and CCL20 in response to IL-17A, but conversely increased the expression of IL-6. Last, siRNA-mediated ablation of IKKα attenuated nuclear RelA and RelB content and decreased expression of KC and CCL20 in response to IL-17A. Together, these data demonstrate a critical role for the S-glutathionylation/Grx1 redox axis in regulating IKKα and RelA S-glutathionylation and the responsiveness of epithelial cells to IL-17A.

Cellular effects of bacterial N-3-Oxo-dodecanoyl-L-Homoserine lactone on the sponge Suberites domuncula (Olivi, 1792): insights into an intimate inter-kingdom dialogue

Sponges and bacteria have lived together in complex consortia for 700 million years. As filter feeders, sponges prey on bacteria. Nevertheless, some bacteria are associated with sponges in symbiotic relationships. To enable this association, sponges and bacteria are likely to have developed molecular communication systems. These may include molecules such as N-acyl-_L-homoserine lactones, produced by Gram-negative bacteria also within sponges. In this study, we examined the role of N-3-oxododecanoyl-_L-homoserine lactone (3-oxo-C₁₂-HSL) on the expression of immune and apoptotic genes of the host sponge Suberites domuncula. This molecule seemed to inhibit the sponge innate immune system through a decrease of the expression of genes coding for proteins sensing the bacterial membrane: a Toll-Like Receptor and a Toll-like Receptor Associated Factor 6 and for an anti-bacterial perforin-like molecule. The expression of the pro-apoptotic caspase-like 3/7 gene decreased as well, whereas the level of mRNA of anti-apoptotic genes Bcl-2 Homolog Proteins did not change. Then, we demonstrated the differential expression of proteins in presence of this 3-oxo-C₁₂-HSL using 3D sponge cell cultures. Proteins involved in the first steps of the endocytosis process were highlighted using the 2D electrophoresis protein separation and the MALDI-TOF/TOF protein characterization: α and β subunits of the lysosomal ATPase, a cognin, cofilins-related proteins and cytoskeleton proteins actin, α tubulin and α actinin. The genetic expression of some of these proteins was subsequently followed. We propose that the 3-oxo-C₁₂-HSL may participate in the tolerance of the sponge apoptotic and immune systems towards the presence of bacteria. Besides, the sponge may sense the 3-oxo-C₁₂-HSL as a molecular evidence of the bacterial presence and/or density in order to regulate the populations of symbiotic bacteria in the sponge. This study is the first report of a bacterial secreted molecule acting on sponge cells and regulating the symbiotic relationship.

TRAF molecules in cell signaling and in human diseases

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of intracellular proteins were originally identified as signaling adaptors that bind directly to the cytoplasmic regions of receptors of the TNF-R superfamily. The past decade has witnessed rapid expansion of receptor families identified to employ TRAFs for signaling. These include Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), T cell receptor, IL-1 receptor family, IL-17 receptors, IFN receptors and TGFβ receptors. In addition to their role as adaptor proteins, most TRAFs also act as E3 ubiquitin ligases to activate downstream signaling events. TRAF-dependent signaling pathways typically lead to the activation of nuclear factor-κBs (NF-κBs), mitogen-activated protein kinases (MAPKs), or interferon-regulatory factors (IRFs). Compelling evidence obtained from germ-line and cell-specific TRAF-deficient mice demonstrates that each TRAF plays indispensable and non-redundant physiological roles, regulating innate and adaptive immunity, embryonic development, tissue homeostasis, stress response, and bone metabolism. Notably, mounting evidence implicates TRAFs in the pathogenesis of human diseases such as cancers and autoimmune diseases, which has sparked new appreciation and interest in TRAF research. This review presents an overview of the current knowledge of TRAFs, with an emphasis on recent findings concerning TRAF molecules in signaling and in human diseases.

Neuroprotective effect of early and short-time applying sophoridine in pMCAO rat brain: down-regulated TRAF6 and up-regulated p-ERK1/2 expression, ameliorated brain infaction and edema

BACKGROUND

Matrine has been proven to protect ischemic injury in brain and sophoridine (SOP) is an isomeride of matrine. It is unknown whether SOP has this protective effect on ischemic injury in brain. We therefore investigated the potential neuroprotective role of SOP and the underlying mechanism.

METHODS

Male, Sprague-Dawley rats were randomly assigned into five groups: Vehicle (pMCAO+saline), High dose (pMCAO+SOP 10 mg/kg), Middle dose (pMCAO+SOP 5 mg/kg), Low dose (pMCAO+SOP 2.5 mg/kg) and Sham operated group. Permanent middle cerebral artery occlusion (pMCAO) model was used and SOP was administered intraperitoneally immediately after cerebral ischemia and once daily in the following days. Neurological deficit was evaluated using a modified six point scale; brain water content and infarct volume were measured. The expression of TRAF6 and ERK1/2 were measured by immunohistochemistry, Western blotting.

RESULTS

Compared with Vehicle group, the cerebral edema was alleviated in High dose group (P<0.05), and the infarct volume was decreased in Low dose group (P<0.05). Consistent with these results, immunohistochemistry and Western blot analysis indicated that TRAF6 expression was significantly decreased in SOP administrated groups at 24 h, and the expression of phosphorylated ERK1/2 increased in Low dose at 72 h.

CONCLUSIONS

SOP protected the brain from damage caused by pMCAO, and this effect may be through down-regulation of TRAF6 expression and up-regulation of ERK1/2 phosphorylation expression.

Glutathione synthesis and its role in redox signaling

Glutathione (GSH) is the most abundant antioxidant and a major detoxification agent in cells. It is synthesized through two-enzyme reaction catalyzed by glutamate cysteine ligase and glutathione synthetase, and its level is well regulated in response to redox change. Accumulating evidence suggests that GSH may play important roles in cell signaling. This review will focus on the biosynthesis of GSH, the reaction of S-glutathionylation (the conjugation of GSH with thiol residue on proteins), GSNO, and their roles in redox signaling.

Regulation of cell physiology and pathology by protein S-glutathionylation: lessons learned from the cardiovascular system

SIGNIFICANCE

Reactive oxygen and nitrogen species contributing to homeostatic regulation and the pathogenesis of various cardiovascular diseases, including atherosclerosis, hypertension, endothelial dysfunction, and cardiac hypertrophy, is well established. The ability of oxidant species to mediate such effects is in part dependent on their ability to induce specific modifications on particular amino acids, which alter protein function leading to changes in cell signaling and function. The thiol containing amino acids, methionine and cysteine, are the only oxidized amino acids that undergo reduction by cellular enzymes and are, therefore, prime candidates in regulating physiological signaling. Various reports illustrate the significance of reversible oxidative modifications on cysteine thiols and their importance in modulating cardiovascular function and physiology.

RECENT ADVANCES

The use of mass spectrometry, novel labeling techniques, and live cell imaging illustrate the emerging importance of reversible thiol modifications in cellular redox signaling and have advanced our analytical abilities.

CRITICAL ISSUES

Distinguishing redox signaling from oxidative stress remains unclear. S-nitrosylation as a precursor of S-glutathionylation is controversial and needs further clarification. Subcellular distribution of glutathione (GSH) may play an important role in local regulation, and targeted tools need to be developed. Furthermore, cellular redundancies of thiol metabolism complicate analysis and interpretation.

FUTURE DIRECTIONS

The development of novel pharmacological analogs that specifically target subcellular compartments of GSH to promote or prevent local protein S-glutathionylation as well as the establishment of conditional gene ablation and transgenic animal models are needed.

HSV infection induces production of ROS, which potentiate signaling from pattern recognition receptors: role for S-glutathionylation of TRAF3 and 6

The innate immune response constitutes the first line of defense against infections. Pattern recognition receptors recognize pathogen structures and trigger intracellular signaling pathways leading to cytokine and chemokine expression. Reactive oxygen species (ROS) are emerging as an important regulator of some of these pathways. ROS directly interact with signaling components or induce other post-translational modifications such as S-glutathionylation, thereby altering target function. Applying live microscopy, we have demonstrated that herpes simplex virus (HSV) infection induces early production of ROS that are required for the activation of NF-κB and IRF-3 pathways and the production of type I IFNs and ISGs. All the known receptors involved in the recognition of HSV were shown to be dependent on the cellular redox levels for successful signaling. In addition, we provide biochemical evidence suggesting S-glutathionylation of TRAF family proteins to be important. In particular, by performing mutational studies we show that S-glutathionylation of a conserved cysteine residue of TRAF3 and TRAF6 is important for ROS-dependent activation of innate immune pathways. In conclusion, these findings demonstrate that ROS are essential for effective activation of signaling pathways leading to a successful innate immune response against HSV infection.

Herpes simplex virus (HSV) type 1 and 2 are important human pathogens, which can give rise to severe diseases during both primary and recurrent infections. In addition to activating “classical” innate and adaptive immune responses, many infections stimulate other cellular activities such as and production of reactive oxygen species (ROS). However, there is little knowledge on the cross-talk between ROS and the innate antiviral response. In this article we show that HSV infection leads to production of ROS, and that ROS play a critical role in activation of innate immune responses to these viruses. At the mechanistic level, we show that ROS stimulate glutathionylation (a protein modification) of the signaling molecules TRAF3 and 6, which promotes redox-sensitive signaling. Our data support the idea that the innate immune system not only detects specific HSV molecules but also senses the cellular oxidative stress level, and integrates this into the innate immune response to infections.

Protein S-glutathiolation: redox-sensitive regulation of protein function

Reversible protein S-glutathiolation has emerged as an important mechanism of post-translational modification. Under basal conditions several proteins remain adducted to glutathione, and physiological glutathiolation of proteins has been shown to regulate protein function. Enzymes that promote glutathiolation (e.g., glutathione-S-transferase-P) or those that remove glutathione from proteins (e.g., glutaredoxin) have been identified. Modification by glutathione has been shown to affect protein catalysis, ligand binding, oligomerization and protein-protein interactions. Conditions associated with oxidative or nitrosative stress, such as ischemia-reperfusion, hypertension and tachycardia increase protein glutathiolation via changes in the glutathione redox status (GSH/GSSG) or through the formation of sulfenic acid (SOH) or nitrosated (SNO) cysteine intermediates. These "activated" thiols promote reversible S-glutathiolation of key proteins involved in cell signaling, energy production, ion transport, and cell death. Hence, S-glutathiolation is ideally suited for integrating and mounting fine-tuned responses to changes in the redox state. S-glutathiolation also provides a temporary glutathione "cap" to protect protein thiols from irreversible oxidation and it could be an important mechanism of protein "encryption" to maintain proteins in a functionally silent state until they are needed during conditions of stress. Current evidence suggests that the glutathiolation-deglutathiolation cycle integrates and interacts with other post-translational mechanisms to regulate signal transduction, metabolism, inflammation, and apoptosis. This article is part of a Special Section entitled "Post-translational Modification."