Nuclear translocation of metabolic enzyme PKM2 participates in high glucose-promoted HCC metastasis by strengthening immunosuppressive environment

Although some cohort studies have indicated a close association between diabetes and HCC, the underlying mechanism about the contribution of diabetes to HCC progression remains largely unknown. In the study, we applied a novel HCC model in SD rat with diabetes and a series of high glucose-stimulated cell experiments to explore the effect of a high glucose environment on HCC metastasis and its relevant mechanism. Our results uncovered a novel regulatory mechanism by which nuclear translocation of metabolic enzyme PKM2 mediated high glucose-promoted HCC metastasis. Specifically, high glucose-increased PKM2 nuclear translocation downregulates chemerin expression through the redox protein TRX1, and then strengthens immunosuppressive environment to promote HCC metastasis. To the best of our knowledge, this is the first report to elucidate the great contribution of a high glucose environment to HCC metastasis from a new perspective of enhancing the immunosuppressive microenvironment. Simultaneously, this work also highlights a previously unidentified non-metabolic role of PKM2 and opens a novel avenue for cross research and intervention for individuals with HCC and comorbid diabetes.

Trx4, a novel thioredoxin protein, is important for Toxoplasma gondii fitness

BACKGROUND

To successfully replicate within the host cell, Toxoplasma gondii employs several mechanisms to overcome the host cell defenses and mitigate the harmful effects of the free radicals resulting from its own metabolic processes using effectors such as thioredoxin proteins. In this study, we characterize the location and functions of a newly identified thioredoxin in T. gondii, which was named Trx4.

METHODS

We characterized the functional role of Trx4 in T. gondii Type I RH and Type II Pru strains by gene knockout and studied its subcellular localization by endogenous protein HA tagging using CRISPR-Cas9 gene editing. The enzyme-catalyzed proximity labeling technique, the TurboID system, was employed to identify the proteins in proximity to Trx4.

RESULTS

Trx4 was identified as a dense granule protein of T. gondii predominantly expressed in the parasitophorous vacuole (PV) and was partially co-localized with GRA1 and GRA5. Functional analysis showed that deletion of trx4 markedly influenced the parasite lytic cycle, resulting in impaired host cell invasion capacity in both RH and Pru strains. Mutation of Trx domains in Trx4 in RH strain revealed that two Trx domains were important for the parasite invasion. By utilizing the TurboID system to biotinylate proteins in proximity to Trx4, we identified a substantial number of proteins, some of which are novel, and others are previously characterized, predominantly distributed in the dense granules. In addition, we uncovered three novel proteins co-localized with Trx4. Intriguingly, deletion of trx4 did not affect the localization of these three proteins. Finally, a virulence assay demonstrated that knockout of trx4 resulted in a significant attenuation of virulence and a significant reduction in brain cyst loads in mice.

CONCLUSIONS

Trx4 plays an important role in T. gondii invasion and virulence in Type I RH strain and Type II Pru strain. Combining the TurboID system with CRISPR-Cas9 technique revealed many PV-localized proximity proteins associated with Trx4. These findings suggest a versatile role of Trx4 in mediating the processes that occur in this distinctive intracellular membrane-bound vacuolar compartment.

Specificity and dynamics of H2O2 detoxification by the cytosolic redox regulatory network as revealed by in vitro reconstitution

The thiol redox state is a decisive functional characteristic of proteins in cell biology. Plasmatic cell compartments maintain a thiol-based redox regulatory network linked to the glutathione/glutathione disulfide couple (GSH/GSSG) and the NAD(P)H system. The basic network constituents are known and in vivo cell imaging with gene-encoded probes have revealed insight into the dynamics of the [GSH]2/[GSSG] redox potential, cellular H2O2 and NAD(P)H+H+ amounts in dependence on metabolic and environmental cues. Less understood is the contribution and interaction of the network components, also because of compensatory reactions in genetic approaches. Reconstituting the cytosolic network of Arabidopsis thaliana in vitro from fifteen recombinant proteins at in vivo concentrations, namely glutathione peroxidase-like (GPXL), peroxiredoxins (PRX), glutaredoxins (GRX), thioredoxins, NADPH-dependent thioredoxin reductase A and glutathione reductase and applying Grx1-roGFP2 or roGFP2-Orp1 as dynamic sensors, allowed for monitoring the response to a single H2O2 pulse. The major change in thiol oxidation as quantified by mass spectrometry-based proteomics occurred in relevant peptides of GPXL, and to a lesser extent of PRX, while other Cys-containing peptides only showed small changes in their redox state and protection. Titration of ascorbate peroxidase (APX) into the system together with dehydroascorbate reductase lowered the oxidation of the fluorescent sensors in the network but was unable to suppress it. The results demonstrate the power of the network to detoxify H2O2, the partially independent branches of electron flow with significance for specific cell signaling and the importance of APX to modulate the signaling without suppressing it and shifting the burden to glutathione oxidation.

Unlocking the anticancer activity of gambogic acid: a shift towards ferroptosis via a GSH/Trx dual antioxidant system

Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a crucial role in ferroptosis by regulating the cellular antioxidant response and maintaining redox balance. However, compounds that induce ferroptosis through dual antioxidant pathways based on Nrf2 have not been fully explored. In our study, we investigated the impact of Gambogic acid (GA) on MCF-7 cells and HepG2 cells in vitro. The cytotoxicity, colony formation assay and cell cycle assay demonstrated potent tumor-killing ability of GA, while its effect was rescued by ferroptosis inhibitors. Furthermore, RNA sequencing revealed the enrichment of ferroptosis pathway mediated by GA. In terms of ferroptosis indicators detection, evidences for GA were provided including reactive oxygen species (ROS) accumulation, alteration in mitochondrial membrane potential (MMP), disappearance of mitochondrial cristae, lipid peroxidation induction, malondialdehyde (MDA) accumulation promotion, iron ion accumulation as well as glutathione (GSH)/thioredoxin (Trx) depletion. Notably, Ferrostatin-1 (Fer-1) and Liproxstatin-1 (Lip-1) successfully rescued GA-induced MDA accumulation. In terms of mechanism, Nrf2 was found to play a pivotal role in GA-induced ferroptosis by inducing protein alterations through the iron metabolism pathway and GSH/Trx dual antioxidant pathway. Furthermore, GA exerted good antitumor activity in vivo through GSH/Trx dual antioxidant pathway, and Fer-1 significantly attenuated its efficacy. In conclusion, our findings first provided new evidence for GA as an inducer of ferroptosis, and Nrf2-mediated GSH/Trx dual antioxidant system played an important role in GA-induced ferroptosis.

Guiding bar motif of thioredoxin reductase 1 modulates enzymatic activity and inhibitor binding by communicating with the co-factor FAD and regulating the flexible C-terminal redox motif

Thioredoxin reductase (TXNRD) is a selenoprotein that plays a crucial role in cellular antioxidant defense. Previously, a distinctive guiding bar motif was identified in TXNRD1, which influences the transfer of electrons. In this study, utilizing single amino acid substitution and Excitation-Emission Matrix (EEM) fluorescence spectrum analysis, we discovered that the guiding bar communicates with the FAD and modulates the electron flow of the enzyme. Differential Scanning Fluorimetry (DSF) analysis demonstrated that the aromatic amino acid in guiding bar is a stabilizer for TXNRD1. Kinetic analysis revealed that the guiding bar is vital for the disulfide reductase activity but hinders the selenocysteine-independent reduction activity of TXNRD1. Meanwhile, the guiding bar shields the selenocysteine residue of TXNRD1 from the attack of electrophilic reagents. We also found that the inhibition of TXNRD1 by caveolin-1 scaffolding domain (CSD) peptides and compound LCS3 did not bind to the guiding bar motif. In summary, the obtained results highlight new aspects of the guiding bar that restrict the flexibility of the C-terminal redox motif and govern the transition from antioxidant to pro-oxidant.

HyPer as a tool to determine the reductive activity in cellular compartments

A multitude of cellular metabolic and regulatory processes rely on controlled thiol reduction and oxidation mechanisms. Due to our aerobic environment, research preferentially focuses on oxidation processes, leading to limited tools tailored for investigating cellular reduction. Here, we advocate for repurposing HyPer1, initially designed as a fluorescent probe for H2O2 levels, as a tool to measure the reductive power in various cellular compartments. The response of HyPer1 depends on kinetics between thiol oxidation and reduction in its OxyR sensing domain. Here, we focused on the reduction half-reaction of HyPer1. We showed that HyPer1 primarily relies on Trx/TrxR-mediated reduction in the cytosol and nucleus, characterized by a second order rate constant of 5.8 × 102 M-1s-1. On the other hand, within the mitochondria, HyPer1 is predominantly reduced by glutathione (GSH). The GSH-mediated reduction rate constant is 1.8 M-1s-1. Using human leukemia K-562 cells after a brief oxidative exposure, we quantified the compartmentalized Trx/TrxR and GSH-dependent reductive activity using HyPer1. Notably, the recovery period for mitochondrial HyPer1 was twice as long compared to cytosolic and nuclear HyPer1. After exploring various human cells, we revealed a potent cytosolic Trx/TrxR pathway, particularly pronounced in cancer cell lines such as K-562 and HeLa. In conclusion, our study demonstrates that HyPer1 can be harnessed as a robust tool for assessing compartmentalized reduction activity in cells following oxidative stress.

Thioredoxin (Trx): A redox target and modulator of cellular senescence and aging-related diseases

Thioredoxin (Trx) is a compact redox-regulatory protein that modulates cellular redox state by reducing oxidized proteins. Trx exhibits dual functionality as an antioxidant and a cofactor for diverse enzymes and transcription factors, thereby exerting influence over their activity and function. Trx has emerged as a pivotal biomarker for various diseases, particularly those associated with oxidative stress, inflammation, and aging. Recent clinical investigations have underscored the significance of Trx in disease diagnosis, treatment, and mechanistic elucidation. Despite its paramount importance, the intricate interplay between Trx and cellular senescence-a condition characterized by irreversible growth arrest induced by multiple aging stimuli-remains inadequately understood. In this review, our objective is to present a comprehensive and up-to-date overview of the structure and function of Trx, its involvement in redox signaling pathways and cellular senescence, its association with aging and age-related diseases, as well as its potential as a therapeutic target. Our review aims to elucidate the novel and extensive role of Trx in senescence while highlighting its implications for aging and age-related diseases.

Functional diversity of YbbN/CnoX proteins: Insights from a comparative analysis of three thioredoxin-like oxidoreductases from Pseudomonas aeruginosa, Xylella fastidiosa and Escherichia coli

YbbN/CnoX are proteins that display a Thioredoxin (Trx) domain linked to a tetratricopeptide domain. YbbN from Escherichia coli (EcYbbN) displays a co-chaperone (holdase) activity that is induced by HOCl. Here, we compared EcYbbN with YbbN proteins from Xylella fastidiosa (XfYbbN) and from Pseudomonas aeruginosa (PaYbbN). EcYbbN presents a redox active Cys residue at Trx domain (Cys63), 24 residues away from SQHC motif (SQHC[N24]C) that can form mixed disulfides with target proteins. In contrast, XfYbbN and PaYbbN present two Cys residues in the CXXC (CAPC) motif, while only PaYbbN shows the Cys residue equivalent to Cys63 of EcYbbN. Our phylogenetic analysis revealed that most of the YbbN proteins are in the bacteria domain of life and that their members can be divided into four groups according to the conserved Cys residues. EcYbbN (SQHC[N24]C), XfYbbN (CAPC[N24]V) and PaYbbN (CAPC[N24]C) are representatives of three sub-families. In contrast to EcYbbN, both XfYbbN and PaYbbN: (1) reduced an artificial disulfide (DTNB) and (2) supported the peroxidase activity of Peroxiredoxin Q from X. fastidiosa, suggesting that these proteins might function similarly to the canonical Trx enzymes. Indeed, XfYbbN was reduced by XfTrx reductase with a high catalytic efficiency (kcat/Km = 1.27 x 107 M-1 s-1), similar to the canonical XfTrx (XfTsnC). Furthermore, EcYbbN and XfYbbN, but not PaYbbN displayed HOCl-induced holdase activity. Remarkably, EcYbbN gained disulfide reductase activity while lost the HOCl-activated chaperone function, when the SQHC was replaced by CQHC. In contrast, the XfYbbN CAPA mutant lost the disulfide reductase activity, while kept its HOCl-induced chaperone function. In all cases, the induction of the holdase activity was accompanied by YbbN oligomerization. Finally, we showed that deletion of ybbN gene did not render in P. aeruginosa more sensitive stressful treatments. Therefore, YbbN/CnoX proteins display distinct properties, depending on the presence of the three conserved Cys residues.

Modulation of thioredoxin by chlorogenic acid in an ischemic stroke model and glutamate-exposed neurons

Ischemic stroke increases the production of reactive oxygen species (ROS), which can eventually lead to neuronal death. Thioredoxin is a small reductase protein that acts as an eliminator of ROS and protects neurons from brain damage. Chlorogenic acid is known as a phenolic compound that has a neuroprotective effect. We investigated the change of thioredoxin expression by chlorogenic acid in a middle cerebral artery occlusion (MCAO) animal model. Adult rats were injected intraperitoneally with phosphate buffered saline or chlorogenic acid (30 mg/kg) 2 h after MCAO. MCAO damage induced neurological defects and increased ROS and lipid peroxidation levels, however, chlorogenic acid mitigated these changes. MCAO damage reduced thioredoxin expression, which was mitigated by chlorogenic acid treatment. The interaction between thioredoxin and apoptosis signal-regulating kinase 1 (ASK1) was decreased in MCAO animals, chlorogenic acid treatment prevented this decrease. In cultured neurons, chlorogenic acid dose-dependently attenuated glutamate-induced decreases in cell viability and thioredoxin expression. Glutamate toxicity downregulated bcl-2 and upregulated bax, cytochrome c, and caspase-3, however, chlorogenic acid attenuated these changes. The mitigating effect of chlorogenic acid was lower in thioredoxin siRNA-transfected cells than in non-transfected cells. These results provide evidence that chlorogenic acid exerts potent antioxidant and neuroprotective effects through regulation of thioredoxin and modulation of ASK1 and thioredoxin binding in ischemic brain injury. These findings indicate that chlorogenic acid exerts a neuroprotective effect by regulating thioredoxin expression in cerebral ischemia and glutamate exposure conditions.

Three-dimensional solution structure, dynamics and binding of thioredoxin m from Pisum sativum

Thioredoxins (TRXs) are ubiquitous small, globular proteins involved in cell redox processes. In this work, we report the solution structure of TRX m from Pisum sativum (pea), which has been determined on the basis of 1444 nuclear Overhauser effect- (NOE-) derived distance constraints. The average pairwise root-mean-square deviation (RMSD) for the 20 best structures for the backbone residues (Val7-Glu102) was 1.42 ± 0.15 Å, and 1.97 ± 0.15 Å when all heavy atoms were considered. The structure corresponds to the typical fold of TRXs, with a central five-stranded β-sheet flanked by four α-helices. Some residues had an important exchange dynamic contribution: those around the active site; at the C terminus of β-strand 3; and in the loop preceding α-helix 4. Smaller NOE values were observed at the N and C-terminal residues forming the elements of the secondary structure or, alternatively, in the residues belonging to the loops between those elements. A peptide derived from pea fructose-1,6-biphosphatase (FBPase), comprising the preceding region to the regulatory sequence of FBPase (residues Glu152 to Gln179), was bound to TRX m with an affinity in the low micromolar range, as measured by fluorescence and NMR titration experiments. Upon peptide addition, the intensities of the cross-peaks of all the residues of TRX m were affected, as shown by NMR. The value of the dissociation constant of the peptide from TRX m was larger than that of the intact FBPase, indicating that there are additional factors in other regions of the polypeptide chain of the latter protein affecting the binding to thioredoxin.

The thioredoxin h-type TdTrxh2 protein of durum wheat confers abiotic stress tolerance of the transformant Arabidopsis plants through its protective role and the regulation of redox homoeostasis

The thioredoxins (Trxs) are ubiquitous and they play a crucial role in various biological processes like growth and stress response. Although the functions of Trxs proteins are described in several previous reports, the function of the isoform Trxh2 of durum wheat (Triticum durum L.), designated as TdTrxh2, in abiotic stress response still unknown. Thus, we aimed in this study the functional characterization of TdTrxh2 through its expression in yeast cells and Arabidopsis plants. Sequence analysis revealed that TdTrxh2 protein shared the conserved redox site with the other Trxh from other plant species. Under various abiotic stresses, TdTrxh2 was up-regulated in leaves and roots of durum wheat. Interestingly, we demonstrated that TdTrxh2 exhibit protective effect on LDH activity against various treatments. Besides, the expression of TdTrxh2 in yeast cells conferred their tolerance to multiple stresses. Moreover, transgenic Arabidopsis expressing TdTrxh2 showed tolerance phenotype to several abiotic stresses. This tolerance was illustrated by high rate of proline accumulation, root proliferation, low accumulation of reactive oxygen species like H2O2 and O2·-, and high antioxidant CAT and POD enzymes activities. All these findings suggested that TdTrxh2 promotes abiotic stress tolerance through the redox homoeostasis regulation and its protective role.

Overexpression of thioredoxin-like protein ACHT2 leads to negative feedback control of photosynthesis in Arabidopsis thaliana

Thioredoxin (Trx) is a small redox mediator protein involved in the regulation of various chloroplast functions by modulating the redox state of Trx target proteins in ever-changing light environments. Using reducing equivalents produced by the photosynthetic electron transport chain, Trx reduces the disulfide bonds on target proteins and generally turns on their activities. While the details of the protein-reduction mechanism by Trx have been well investigated, the oxidation mechanism that counteracts it has long been unclear. We have recently demonstrated that Trx-like proteins such as Trx-like2 and atypical Cys His-rich Trx (ACHT) can function as protein oxidation factors in chloroplasts. Our latest study on transgenic Arabidopsis plants indicated that the ACHT isoform ACHT2 is involved in regulating the thermal dissipation of light energy. To understand the role of ACHT2 in vivo, we characterized phenotypic changes specifically caused by ACHT2 overexpression in Arabidopsis. ACHT2-overexpressing plants showed growth defects, especially under high light conditions. This growth phenotype was accompanied with the impaired reductive activation of Calvin-Benson cycle enzymes, enhanced thermal dissipation of light energy, and decreased photosystem II activity. Overall, ACHT2 overexpression promoted protein oxidation that led to the inadequate activation of Calvin-Benson cycle enzymes in light and consequently induced negative feedback control of the photosynthetic electron transport chain. This study highlights the importance of the balance between protein reduction and oxidation in chloroplasts for optimal photosynthetic performance and plant growth.

Albumin-fused thioredoxin ameliorates high-fat diet-induced non-alcoholic steatohepatitis

The pathogenesis of non-alcoholic steatohepatitis (NASH) involves the simultaneous interaction of multiple factors such as lipid accumulation, oxidative stress, and inflammatory response. Here, the effect of human serum albumin (HSA) fused to thioredoxin (Trx) on NASH was investigated. Trx is known to have anti-oxidative, anti-inflammatory, and anti-apoptotic effects. However, Trx is a low molecular weight protein and is rapidly eliminated from the blood. To overcome the low availability of Trx, HSA-Trx fusion protein was produced and evaluated the therapeutic effect on high-fat diet (HFD)-induced NASH model mice. HSA-Trx administered before the formation of NASH pathology showed it to have a preventive effect. Specifically, HSA-Trx was found to prevent the pathological progression to NASH by suppressing lipid accumulation, liver injury markers, and liver fibrosis. When HSA-Trx was administered during the early stage of NASH there was a marked reduction in lipid accumulation, inflammation, and fibrosis in the liver, indicating that HSA-Trx ameliorates NASH pathology. The findings indicate that HSA-Trx influences multiple pathological factors, such as oxidative stress, inflammation, and apoptosis, to elicit a therapeutic benefit. HSA-Trx also inhibited palmitic acid-induced lipotoxicity in HepG2 cells. Taken together, these results indicate that HSA-Trx has potential as a therapeutic agent for NASH pathology.

The effect of SP/NK1R on expression and activity of glutaredoxin and thioredoxin proteins in prostate cancer cells

Substance P (SP), an important neuropeptide, has a crucial role in the progression of several cancers, including prostate cancer, through interacting with the neurokinin-1 receptor (NK1R). Oxidative stress is also involved in the onset and progression of prostate cancer. However, no studies have been performed on the cross-talk between the SP/NK1R system and cellular redox balance in prostate cancer, and how it is involved in tumorogenesis. We aimed to investigate the effect of the SP/NK1R system and the blockage of NK1R with its specific antagonist (aprepitant) on the cellular redox status of the prostate cancer cell line (PC3 and LNCaP). We performed the resazurin assay to evaluate the toxicity of the aprepitant on the PC3 and LNCaP cell lines. The intracellular reactive oxygen species (ROS) level was measured after SP and aprepitant treatment. The alterations of expression and activity of two crucial cellular oxidoreductases, glutaredoxin, and thioredoxin were evaluated by qRT-PCR and commercial kits (ZellBio GmbH), respectively. Our results revealed that SP increased ROS production and decreased the expression and activity of glutaredoxin and thioredoxin. On the other hand, treatment of cells with aprepitant showed reverse results. In conclusion, we found that the SP/NK1R system could promote prostate cancer progression by inducing oxidative stress. In addition, the inhibition of NK1R by aprepitant modulated the effect of the SP/NK1R system on the cellular redox system. Aprepitant might therefore be introduced as a candidate for the treatment of prostate cancer; however, more studies are required to confirm the validation of this hypothesis.

The integration of TRX/GRX systems and phytohormonal signalling pathways in plant stress and development

Plant acclimation to changing environmental conditions involves the interaction of different signalling molecules, including reactive oxygen species and hormones. Redox regulation exerted by thioredoxin (TRX) and glutaredoxin (GRX), two oxidoreductases, is emerging as a specific point of control mediating signal transduction pathways associated with plant growth and stress response. Phytohormones are messengers that coordinate plant cell activities to regulate growth, defence, and productivity, although their cross-talk with components of the redox system is less known. The present review focuses on our current knowledge of the interplay that occurs between TRX and GRX systems and phytohormonal signalling pathways in connection with the control of plant development and stress responses. Here, we consider the regulation that phytohormones exert on TRX and GRX systems, as well as the involvement of these redox proteins in the control of phytohormone-mediated signalling pathways.

Astragalus polysaccharides ameliorate osteoarthritis via inhibiting apoptosis by regulating ROS-mediated ASK1/p38 MAPK signaling pathway targeting on TXN

This research aims to explore the potential of astragalus polysaccharides (APS) in treating osteoarthritis. The primary component of APS extracted in this study was glucose, and noticeably it had a relatively high content of glucuronic acids. In vitro, APS reduced ROS levels, protected chondrocytes from apoptosis, and promoted collagen II expression by regulating ASK1 (apoptosis-signal-regulating kinase1)/p38 cell apoptosis pathway. Further co-immunoprecipitation and immunofluorescence localization experiments demonstrated that the thioredoxin (TXN) antioxidant system was responsible for its bioactivity. Moreover, TXN silencing remarkably blocked the protective effects of APS, indicating that APS inhibited chondrocyte apoptosis by targeting TXN. In vivo, APS effectively mitigated cartilage loss and chondrocyte apoptosis and decreased expressions of p-ASK1 and p-p38. Collectively, this research first demonstrated that APS could ameliorate osteoarthritis by ASK1/p38 signaling pathway through regulating thioredoxin. In conclusion, APS holds promise as a nutraceutical supplement for osteoarthritis in future drug development.

Ferric reduction oxidase in Lilium pumilum affects plant saline-alkaline tolerance by regulating ROS homeostasis

Ferric reduction oxidase (FRO) plays important roles in biotic and abiotic stress. However, the function of ferric reduction oxidase from Lilium pumilum in response to NaHCO3 is unknown. Here we report the functional characterization of ferric reduction oxidase 7 in Lilium pumilum (LpFRO7) in stresses. Under NaHCO3 stress, the LpFRO7 overexpression lines exhibited lower accumulation of reactive oxygen species (ROS), higher activities in antioxidant enzyme (CAT, SOD and POD) and ferrite reductase, resulting in improved tolerance compared to the wild type (WT). In order to determine the functional network of LpFRO7, it was confirmed by EMSA assays, Yeast one-hybrid assays and Dual luciferase reporter assays that LpbHLH115 transcription factor can bind to the promoter of LpFRO7. Yeast two-hybrid assays, BiFC, and LCI assays were performed to prove that LpFRO7 can interact with LpTrx. Combining these findings, we concluded that LpFRO7 affects plant saline-alkaline tolerance by regulating ROS homeostasis.

Multiple circulating forms of neprilysin detected with novel epitope-directed monoclonal antibodies

Neprilysin (NEP) is an emerging biomarker for various diseases including heart failure (HF). However, major inter-assay inconsistency in the reported concentrations of circulating NEP and uncertainty with respect to its correlations with type and severity of disease are in part attributed to poorly characterized antibodies supplied in commercial ELISA kits. Validated antibodies with well-defined binding footprints are critical for understanding the biological and clinical context of NEP immunoassay data. To achieve this, we applied in silico epitope prediction and rational peptide selection to generate monoclonal antibodies (mAbs) against spatially distant sites on NEP. One of the selected epitopes contained published N-linked glycosylation sites at N285 and N294. The best antibody pair, mAb 17E11 and 31E1 (glycosylation-sensitive), were characterized by surface plasmon resonance, isotyping, epitope mapping, and western blotting. A validated two-site sandwich NEP ELISA with a limit of detection of 2.15 pg/ml and working range of 13.1-8000 pg/ml was developed with these mAbs. Western analysis using a validated commercial polyclonal antibody (PE pAb) and our mAbs revealed that non-HF and HF plasma NEP circulates as a heterogenous mix of moieties that possibly reflect proteolytic processing, post-translational modifications and homo-dimerization. Both our mAbs detected a ~ 33 kDa NEP fragment which was not apparent with PE pAb, as well as a common ~ 57-60 kDa moiety. These antibodies exhibit different affinities for the various NEP targets. Immunoassay results are dependent on NEP epitopes variably detected by the antibody pairs used, explaining the current discordant NEP measurements derived from different ELISA kits.

Implication of Thioredoxin 1 and Glutaredoxin 1 in H2O2-induced Phosphorylation of JNK and p38 MAP Kinases

BACKGROUND

Aerobic organisms continuously generate small amounts of Reactive Oxygen Species (ROS), which are involved in the oxidation of sensitive cysteine residues in proteins, leading to the formation of disulfide bonds. Thioredoxin (Trx1) and Glutaredoxin (Grx1) represent key antioxidant enzymes reducing disulfide bonds.

OBJECTIVE

In this work, we have focused on the possible protective effect of Trx1 and Grx1 against oxidative stress-induced DNA damage and apoptosis-signaling, by studying the phosphorylation of MAP kinases.

METHODS

Trx1 and Grx1 were overexpressed or silenced in cultured H1299 non-small cell lung cancer epithelial cells. We examined cell growth, DNA damage, and the phosphorylation status of MAP kinases following treatment with H2O2.

RESULTS

Overexpression of both Trx1 and Grx1 had a significant impact on the growth of H1299 cells and provided protection against H2O2-induced toxicity, as well as acute DNA single-strand breaks. Conversely, silencing of these proteins exacerbated DNA damage. Furthermore, overexpression of Trx1 and Grx1 inhibited the rapid phosphorylation of JNK (especially at 360 min of treatment, ****p=0.004 and **p=0.0033 respectively) and p38 MAP kinases (especially at 360 min of treatment, ****p<0.0001 and ***p=0.0008 respectively) during H2O2 exposure, while their silencing had the opposite effect (especially at 360 min of treatment, ****p<0.0001).

CONCLUSION

These results suggest that both Trx1 and Grx1 have protective roles against H2O2 induced toxicity, emphasizing their significance in mitigating oxidative stress-related cellular damage.

The role of thioredoxin and glutathione systems in arsenic-induced liver injury in rats under glutathione depletion

Antioxidant systems like thioredoxin (Trx) and glutaredoxin (Grx) maintain oxidative stress balance. These systems have cross-talk supported by some in vitro studies. We investigated the underlying mechanisms of arsenic-induced liver injury in glutathione-deficient rats and whether there was any cross-talk between the Trx and Grx systems. The rats in arsenic-treated groups were administered with sodium arsenite (10, 20 mg/kg b w/d) for four weeks. In buthionine sulfoximine (BSO, an inhibitor of GSH) and 20 mg/kg arsenic combined groups, rats were injected with 2 mmol/kg BSO intraperitoneally twice per week. BSO exacerbated arsenic-induced liver injury by increasing arsenic accumulation in urine, serum, and liver while decreasing glutathione activity and resulting in upregulated mRNA expression of the Trx system and downregulation of Grx mRNA expression. The impact of Trx lasted longer than that of the Grx. The Trx system remained highly expressed, while GSH, Grx1, and Grx2 levels were decreased. The inhibitory effect of only BSO treatment on Grx1 and Grx2 was not pronounced. However, the combined impact of arsenic and BSO upregulated Trx expression, primarily related to further reduction of GSH. As a result, the suppressed Grxs were protected by the upregulated Trxs, which serve as a backup antioxidant defense system in the liver.

TrxR/Trx inhibitor butaselen ameliorates pulmonary fibrosis by suppressing NF-κB/TGF-β1/Smads signaling

Pulmonary fibrosis is highly lethal with limited treatments. Butaselen (BS) is an inhibitor of thioredoxin reductase (TrxR)/thioredoxin (Trx) with anti-tumor activity. However, its impact on pulmonary fibrosis and the involved mechanisms remain unclear. Here, we demonstrate that BS is a potential drug for the treatment of pulmonary fibrosis. Specifically, BS can inhibit pulmonary fibrosis both in vitro and in vivo, with comparable efficacy and enhanced safety when compared with pirfenidone. BS and dexamethasone display a synergistic effect in inhibiting pulmonary fibrosis both in vitro and in vivo. Mechanistic studies reveal that BS can inhibit the TrxR activity during pulmonary fibrosis. RNA-sequencing analysis identifies that genes of ECM-related signaling pathways are notably affected by BS. BS can not only inhibit the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and reduce pulmonary fibrosis-related inflammation, but also reduce NF-κB-activated transcriptional expression of transforming growth factor-β1 (TGF-β1), which leads to the inactivation of Smad2/Smad3 and decrease of collagen formation and fibrosis. Moreover, the knockdown of Trx1 with siRNA can also inhibit NF-κB/TGF-β1/Smads signaling. In conclusion, the TrxR/Trx inhibitor butaselen can suppress pulmonary fibrosis by inhibiting NF-κB/TGF-β1/Smads signaling.

Diverse roles of low-molecular weight thiol GSH in Francisella's virulence, location sensing and GSH-stealing from host

Low-molecular weight (LMW) thiols, encompassing peptides and small proteins with active cysteine residue(s), are important to bacteria as they are involved in a wide range of redox reactions. They include the tripeptide glutathione (GSH) and the small redox proteins, thioredoxins and glutaredoxins. We review the low MW thiols and related molecules in Francisella species and what role they may play in growth and virulence. Genes for GSH biosynthesis, metabolism and thioredoxins are present in all strains of Francisella, including the fully human-virulent strains. GSH and cysteine (CSH) are the major LMW thiols in Francisella extracts. We explore the potential role of the LMW thiols to overcome the nutritional challenges of intracellular growth (high GSH conditions) as well as the nutritional challenges of planktonic growth (low GSH conditions), and their contribution to Francisella's sensing its environmental location. Francisella may also use GSH as a source of CSH, for which it is auxotrophic. "Glutathione stealing" from the host may be an important part of Francisella's success strategy as a facultative intracellular pathogen both to detect its location and obtain CSH. An understanding of GSH metabolism in Francisella provides insights into the interaction of this pathogen with its host and may reveal additional targets for therapeutic intervention for tularemia infections.

Role of thioredoxin in chronic obstructive pulmonary disease (COPD): a promising future target

INTRODUCTION

Thioredoxin (Trx) is a secretory protein that acts as an antioxidant, redox regulator, anti-allergic, and anti-inflammatory molecule. It has been used to treat dermatitis and inflammation of the digestive tract. In the lungs, Trx has a significant anti-inflammatory impact. On the other hand, Chronic Obstructive Pulmonary Disease (COPD) is one of the significant causes of death in the developed world, with a tremendous individual and socioeconomic impact. Despite new initiatives and endless treatment trials, COPD incidence and death will likely escalate in the coming decades.

AREAS COVERED

COPD is a chronic inflammatory disease impacting the airways, lung parenchyma, and pulmonary vasculature. Oxidative stress and protease-antiprotease imbalances are thought to be involved in the process. The most popular respiratory inflammatory and allergic disorders therapies are corticosteroids and β-receptor agonists. These medications are helpful but have some drawbacks, such as infection and immunosuppression; thus, addressing Trx signalling treatments may be a viable COPD treatment approach. This review shall cover the pathophysiology of COPD, the pharmacognosy of anti-COPD drugs, including the assets and liabilities of each, and the role and mechanism of Trx in COPD treatment.

EXPERT OPINION

Limited research has targeted the thioredoxin system as an anti-COPD drug. Spectating the increase in the mortality rates of COPD, this review article would be an interesting one to research.

Analysis of codon usage bias of thioredoxin in apicomplexan protozoa

BACKGROUND

Apicomplexan protozoa are a diverse group of obligate intracellular parasites causing many diseases that affect humans and animals, such as malaria, toxoplasmosis, and cryptosporidiosis. Apicomplexan protozoa possess unique thioredoxins (Trxs) that have been shown to regulate various cellular processes including metabolic redox regulation, parasite survival, and host immune evasion. However, it is still unknown how synonymous codons are used by apicomplexan protozoa Trxs.

METHODS

Codon usage bias (CUB) is the unequal usage of synonymous codons during translation which leads to the over- or underrepresentation of certain nucleotide patterns. This imbalance in CUB can impact a variety of cellular processes including protein expression levels and genetic variation. This study analyzed the CUB of 32 Trx coding sequences (CDS) from 11 apicomplexan protozoa.

RESULTS

The results showed that both codon base composition and relative synonymous codon usage (RSCU) analysis revealed that AT-ended codons were more frequently used in Cryptosporidium spp. and Plasmodium spp., while the Eimeria spp., Babesia spp., Hammondia hammondi, Neospora caninum, and Toxoplasma gondii tended to end in G/C. The average effective number of codon (ENC) value of these apicomplexan protozoa is 46.59, which is > 35, indicating a weak codon preference among apicomplexan protozoa Trxs. Furthermore, the correlation analysis among codon base composition (GC1, GC2, GC3, GCs), codon adaptation index (CAI), codon bias index (CBI), frequency of optimal codons (FOP), ENC, general average hydropathicity (GRAVY), aromaticity (AROMO), length of synonymous codons (L_sym), and length of amino acids (L_aa) indicated the influence of base composition and codon usage indices on CUB. Additionally, the neutrality plot analysis, PR2-bias plot analysis, and ENC-GC3 plot analysis further demonstrated that natural selection plays an important role in apicomplexan protozoa Trxs codon bias.

CONCLUSIONS

In conclusion, this study increased the understanding of codon usage characteristics and genetic evolution of apicomplexan protozoa Trxs, which expanded new ideas for vaccine and drug research.

Nitric oxide and thioredoxin modulate the activity of caspase 9 in HepG2 cells

The interdependent and finely tuned balance between the well-established redox-based modification, S-nitrosylation, and its counteractive mechanism of S-nitrosothiol degradation, i.e., S-denitrosylation of biological protein or non-protein thiols defines the cellular fate in the context of redox homeostasis. S-nitrosylation of cysteine residues by S-nitrosoglutathione, S-nitroso-L-cysteine-like physiological and S-nitroso-L-cysteine ethyl ester-like synthetic NO donors inactivate Caspase-3, 8, and 9, thereby hindering their apoptotic activity. However, spontaneous restoration of their activity upon S-denitrosylation of S-nitrosocaspases into their reduced, free thiol active states, aided by the members of the ubiquitous cellular redoxin (thioredoxin/ thioredoxin reductase/ NADPH) and low molecular weight dithiol (lipoic acid/ lipoamide dehydrogenase/ dihydrolipoic acid/ NADPH) systems imply a direct relevance to their proteolytic activities and further downstream signaling cascades. Additionally, our previous and current findings offer crucial insight into the concept of redundancy between thioredoxin and lipoic acid systems, and the redox-modulated control of the apoptotic and proteolytic activity of caspases, triggering their cyto- and neurotoxic effects in response to nitro-oxidative stress. Thus, this might lay the foundation for the exogenous introduction of precise and efficient NO or related donor drug delivery systems that can directly participate in catering to the S-(de)-nitrosylation-mediated functional outcomes of the cysteinyl proteases in pathophysiological settings.

TXNL1 has dual functions as a redox active thioredoxin-like protein as well as an ATP- and redox-independent chaperone

TXNL1 (also named TRP32, for thioredoxin related protein of 32 kDa) is a cytosolic thioredoxin-fold protein expressed in all cell types and conserved from yeast to mammals, but with yet poorly known function. Here, we expressed and purified human TXNL1 together with several Cys-to-Ser variants, characterizing their enzymatic properties. TXNL1 could reduce disulfides in insulin, cystine and glutathione disulfide (GSSG) in reactions coupled to thioredoxin reductase (TXNRD1, TrxR1) using NADPH, similarly to thioredoxin (TXN, Trx1), but with lower catalytic efficacy due to at least one order of magnitude higher Km of TrxR1 for TXNL1 compared to Trx1. However, in sharp contrast to Trx1, we found that TXNL1 also had efficient chaperone activity that did not require ATP. TXNL1 made non-covalent complexes with reduced insulin, thereby keeping it in solution, and TXNL1 provided chaperone function towards whole cell lysate proteins by preventing their aggregation during heating. The chaperone activities of TXNL1 did not require its redox activity or any dithiol-disulfide exchange reactions, as revealed using Cys-to-Ser substituted variants, as well as a maintained chaperone activity of TXNL1 also in the absence of TrxR1 and NADPH. These results reveal that TXNL1 has dual functions, supporting TrxR1-driven redox activities in disulfide reduction reactions, as well as being an ATP-independent chaperone that does not require involvement of its redox activity.

SBP1 promotes tumorigenesis of thyroid cancer through TXN/NIS pathway

BACKGROUND

As the tissue with the highest selenium content in the body, the occurrence and development of thyroid cancer are closely related to selenium and selenoproteins. Selenium-binding protein 1 (SBP1) has been repeatedly implicated in several cancers, but its role and molecular mechanisms in thyroid cancer remains largely undefined.

METHODS

The expression of SBP1, sodium/iodide symporter (NIS) and thioredoxin (TXN) were analyzed in clinical samples and cell lines. Cell counting kit-8 (CCK-8) and tube formation assays were used to analyze the cell viability and tube formation of cells. Immunofluorescence was used to determine the expression of the NIS. Co-immunoprecipitation (Co-IP) assay was carried out to verify the interaction of SBP1 with TXN. The mouse xenograft experiment was performed to investigate the growth of thyroid cancer cells with SBP1 knockdown in vivo.

RESULTS

SBP1 was significantly increased in human thyroid cancer tissues and cells, especially in anaplastic thyroid cancer. Overexpression of SBP1 promoted FTC-133 cell proliferation, and the culture supernatant of SBP1-overexpression FTC-133 cells promoted tube formation of human retinal microvascular endothelial cells. Knockdown of SBP1, however, inhibited cell proliferation and tube formation. Furthermore, overexpression of SBP1 inhibited cellular differentiation of differentiated thyroid cancer cell line FTC-133, as indicated by decreased expression of thyroid stimulating hormone receptors, thyroglobulin and NIS. Knockdown of SBP1, however, promoted differentiation of BHT101 cells, an anaplastic thyroid cancer cell line. Notably, TXN, a negative regulator of NIS, was found to be significantly upregulated in human thyroid cancer tissues, and it was positively regulated by SBP1. Co-IP assay implied a direct interaction of SBP1 with TXN. Additionally, TXN overexpression reversed the effect of SBP1 knockdown on BHT101 cell viability, tube formation and cell differentiation. An in vivo study found that knockdown of SBP1 promoted the expression of thyroid stimulating hormone receptors, thyroglobulin and NIS, as well as inhibited the growth and progression of thyroid cancer tumors.

CONCLUSION

SBP1 promoted tumorigenesis and dedifferentiation of thyroid cancer through positively regulating TXN.

The role of thioredoxin proteins in Mycobacterium tuberculosis probed by proteome-wide target profiling

Mycobacterium tuberculosis encounters diverse microenvironments, including oxidative assault (ROS and RNS), when it attempts to establish itself within its human host. Therefore, redox sensory and regulation processes are assumed significant importance, as these are essential processes for M. tuberculosis to survive under these hostile conditions. M. tuberculosis contains thioredoxin system to maintain redox homeostasis, which establish a balance between the thiol/dithiol couple. Still very less is known about it. In the present study, we attempted to capture the targets of all the M. tuberculosis thioredoxin proteins (viz., TrxB and TrxC) and a thioredoxin-like protein, NrdH, under aerobic and hypoxic conditions by performing thioredoxin trapping chromatography followed by mass spectrometry. We found that TrxC captured the maximum number of targets in both the physiological conditions and most of the targets of TrxB and NrdH showing overlap with targets of TrxC, indicating that TrxC acts as main thioredoxin. Further the PANTHER classification system provides involvement of targets in various metabolic processes and Gene Ontology analysis suggests that glutamine biosynthetic process and Fe-S cluster biosynthesis are the most enriched processes in the target list of TrxC and TrxB respectively. Also, we suggest that the thioredoxin system might play an important role under hypoxia by targeting those proteins which are responsible to sense and maintain hypoxic conditions. Furthermore, our studies establish a link between TrxB and iron-sulfur cluster biogenesis in M. tuberculosis. Ultimately, these findings open a new direction to target the thioredoxin system for screening new anti-mycobacterial drug targets.

A Semi-throughput Procedure for Assaying Plant NADP-malate Dehydrogenase Activity Using a Plate Reader

Chloroplast NADP-dependent malate dehydrogenase (NADP-MDH) is a redox regulated enzyme playing an important role in plant redox homeostasis. Leaf NADP-MDH activation level is considered a proxy for the chloroplast redox status. NADP-MDH enzyme activity is commonly assayed spectrophotometrically by following oxaloacetate-dependent NADPH oxidation at 340 nm. We have developed a plate-adapted protocol to monitor NADP-MDH activity allowing faster data production and lower reagent consumption compared to the classic cuvette format of a spectrophotometer. We provide a detailed procedure to assay NADP-MDH activity and measure the enzyme activation state in purified protein preparations or in leaf extracts. This protocol is provided together with a semi-automatized data analysis procedure using an R script.

Current Insights into the Redox Regulation Network in Plant Chloroplasts

Thiol/disulfide-based redox regulation is a ubiquitous post-translational protein modification. In plant chloroplasts, this regulatory mechanism is tightly associated with the light-dependent activation of photosynthetic enzymes (e.g., Calvin-Benson cycle enzymes). A thioredoxin (Trx)-mediated pathway was discovered to transmit light signals as a reducing power about half a century ago; since then, it has been accepted as the basic machinery of chloroplast redox regulation. However, during the past two decades, it has been increasingly apparent that plants have acquired multiple Trx isoforms and Trx-like proteins in chloroplasts. Furthermore, proteomics-based analyses have identified various chloroplast enzymes as potential targets of redox regulation. These facts highlight the necessity to revisit the molecular basis and physiological importance of the redox regulation system in chloroplasts. Recent studies have revealed novel aspects of this system, including unprecedented redox-regulated processes in chloroplasts and the functional diversity of Trx family proteins. Of particular significance is the identification of protein-oxidizing pathways that turn off photosynthetic metabolism during light-to-dark transitions. In this review, we summarize current insights into the redox regulation network in chloroplasts.

The contribution of glutathione peroxidases to chloroplast redox homeostasis in Arabidopsis

Oxidizing signals mediated by the thiol-dependent peroxidase activity of 2-Cys peroxiredoxins (PRXs) plays an essential role in fine-tuning chloroplast redox balance in response to changes in light intensity, a function that depends on NADPH-dependent thioredoxin reductase C (NTRC). In addition, plant chloroplasts are equipped with glutathione peroxidases (GPXs), thiol-dependent peroxidases that rely on thioredoxins (TRXs). Despite having a similar reaction mechanism than 2-Cys PRXs, the contribution of oxidizing signals mediated by GPXs to the chloroplast redox homeostasis remains poorly known. To address this issue, we have generated the Arabidopsis (Arabidopsis thaliana) double mutant gpx1gpx7, which is devoid of the two GPXs, 1 and 7, localized in the chloroplast. Furthermore, to analyze the functional relationship of chloroplast GPXs with the NTRC-2-Cys PRXs redox system, the 2cpab-gpx1gpx7 and ntrc-gpx1gpx7 mutants were generated. The gpx1gpx7 mutant displayed wild type-like phenotype indicating that chloroplast GPXs are dispensable for plant growth at least under standard conditions. However, the 2cpab-gpx1gpx7 showed more retarded growth than the 2cpab mutant. The simultaneous lack of 2-Cys PRXs and GPXs affected PSII performance and caused higher delay of enzyme oxidation in the dark. In contrast, the ntrc-gpx1gpx7 mutant combining the lack of NTRC and chloroplast GPXs behaved like the ntrc mutant indicating that the contribution of GPXs to chloroplast redox homeostasis is independent of NTRC. Further supporting this notion, in vitro assays showed that GPXs are not reduced by NTRC but by TRX y2. Based on these results, we propose a role for GPXs in the chloroplast redox hierarchy.

Protoporphyrin IX-loaded albumin nanoparticles reverse cancer chemoresistance by enhancing intracellular reactive oxygen species

Chemoresistance is the main cause of chemotherapy failure in ovarian cancer (OC). The enhanced scavenging of reactive oxygen species (ROS) by the thioredoxin system resulted in insufficient intracellular concentrations of effective ROS, leading to chemoresistance. To induce OC cell apoptosis by enhancing intracellular ROS levels, protoporphyrin IX (PpIX) and albumin-bound PTX nanoparticles (APNP) were utilized to fabricate APNP-PpIX nanoparticles. APNP-PpIX effectively generated ROS and increased the effective ROS concentration in chemoresistant cancer cells. The in vitro and in vivo experiments confirmed the effective inhibition of APNP-PpIX on chemoresistant OC cell proliferation and tumor formation. APNP-PpIX significantly improved the effectiveness of chemotherapy and photodynamic therapy, thus providing a new approach for the clinical treatment of chemoresistant OC.

Characterization of the Trr/Trx system in the fungal pathogen Candida glabrata

C. glabrata, an opportunistic fungal pathogen, can adapt and resist to different stress conditions. It is highly resistant to oxidant stress compared to other Candida spp and to the phylogenetically related but non-pathogen Saccharomyces cerevisiae. In this work, we describe the Trx/Trr system of C. glabrata composed of Trr1 and Trr2 (thioredoxin reductases) and Trx2 (thioredoxin) that are localized in the cytoplasm and Trx3 present in the mitochondrion. The transcriptional induction of TRR2 and TRX2 by oxidants depends on Yap1 and Skn7 and TRR1 and TRX3 have a low expression level. Both TRR2 and TRX2 play an important role in the oxidative stress response. The absence of TRX2 causes auxotrophy of methionine and cysteine. Trr1 and Trr2 are necessary for survival at high temperatures and for the chronological life span of C. glabrata. Furthermore, the Trx/Trr system is needed for survival in the presence of neutrophils. The role of TRR1 and TRX3 is not clear, but in the presence of neutrophils, they have non-overlapping functions with their TRR2 and TRX2 paralogues.

Hemoglobin resident in the lung epithelium is protective for smooth muscle soluble guanylate cyclase function

Hemoglobin (Hb) present in the lung epithelium is of unknown significance. However Hb being an nitric oxide (NO) scavenger can bind to NO and reduce its deleterious effects. Hence we postulated an NO scavenging role for this lung Hb. Doing transwell co-culture with bronchial epithelial cells, A549/16-HBE (apical) and human airway smooth muscle cells (HASMCs as basal), we found that Hb can protect the smooth muscle soluble guanylyl cyclase (sGC) from excess NO. Inducing the apical A549/16-HBE cells with cytokines to trigger iNOS expression and NO generation caused a time dependent increase in SNO-sGC and this was accompanied with a concomitant drop in sGC-α1β1 heterodimerization. Silencing Hbαβ in the apical cells further increased the SNO on sGC with a faster drop in the sGC heterodimer and these effects were additive along with further silencing of thioredoxin 1 (Trx1). Since heme of Hb is critical for NO scavenging we determined the Hb heme in a mouse model of allergic asthma (OVA) and found that Hb in the inflammed OVA lungs was low in heme or heme-free relative to those of naïve lungs. Further we established a direct correlation between the status of the sGC heterodimer and the Hb heme from lung samples of human asthma, iPAH, COPD and cystic fibrosis. These findings present a new mechanism of protection of lung sGC by the epithelial Hb, and suggests that this protection maybe lost in asthma or COPD where lung Hb is unable to scavenge the NO due to it being heme-deprived.

The thioredoxin expression of Cristaria plicata is regulated by Nrf2/ARE pathway under microcystin stimulation

Thioredoxin plays an important role in inhibiting apoptosis and protecting cells from oxidative stress. This study was aimed to clarify how the expression of Trx from Cristaria plicata is regulated by Nrf2/ARE pathway. The expression of CpTrx mRNA was significantly up-regulated in gill and kidney tissues under microcystin stress. The Nrf2 gene of Cristaria plicata was identified to possess an auto active domain bit. While CpNrf2 was knocked down by specific small RNA, CpTrx mRNA expression was significantly down-regulated. The promoter of CpTrx gene had high transcriptional activity, and this basic transcriptional activity persisted after ARE element mutation. The region of promoter -206 to +217 bp was a core promoter region and had forward regulatory elements. Gel shift Assay exhibited that the CpTrx promoter could bind to the purified proteins CpNrf2 and CpMafK in vitro. The binding phenomenon disappeared after the ARE element mutation in promoter region. Subcellular localization experiments displayed that fluorescence overlap between CpNrf2 and Trx promoter increased under microcystin toxin stress. These results suggested that Trx expression was regulated by Nrf2/ARE pathway under oxidative stress.

The UAS thioredoxin-like domain of UBXN7 regulates E3 ubiquitin ligase activity of RNF111/Arkadia

BACKGROUND

E3 ubiquitin ligases play critical roles in regulating cellular signaling pathways by inducing ubiquitylation of key components. RNF111/Arkadia is a RING E3 ubiquitin ligase that activates TGF-β signaling by inducing ubiquitylation and proteasomal degradation of the transcriptional repressor SKIL/SnoN. In this study, we have sought to identify novel regulators of the E3 ubiquitin ligase activity of RNF111 by searching for proteins that specifically interacts with its RING domain.

RESULTS

We found that UBXN7, a member of the UBA-UBX family, directly interacts with the RING domain of RNF111 or its related E3 RNF165/ARK2C that shares high sequence homology with RNF111. We showed that UBXN7 docks on RNF111 or RNF165 RING domain through its UAS thioredoxin-like domain. Overexpression of UBXN7 or its UAS domain increases endogenous RNF111, while an UBXN7 mutant devoid of UAS domain has no effect. Conversely, depletion of UBXN7 decreases RNF111 protein level. As a consequence, we found that UBXN7 can modulate degradation of the RNF111 substrate SKIL in response to TGF-β signaling. We further unveiled this mechanism of regulation by showing that docking of the UAS domain of UBXN7 inhibits RNF111 ubiquitylation by preventing interaction of the RING domain with the E2 conjugating enzymes. By analyzing the interactome of the UAS domain of UBXN7, we identified that it also interacts with the RING domain of the E3 TOPORS and similarly regulates its E3 ubiquitin ligase activity by impairing E2 binding.

CONCLUSIONS

Taken together, our results demonstrate that UBXN7 acts as a direct regulator for the E3 ubiquitin ligases RNF111, RNF165, and TOPORS and reveal that a thioredoxin-like domain can dock on specific RING domains to regulate their E3 ubiquitin ligase activity.

The diversity of salicylic acid biosynthesis and defense signaling in plants: Knowledge gaps and future opportunities

The phytohormone salicylic acid (SA) is known to regulate plant immunity against pathogens. Plants synthesize SA via the isochorismate synthase (ICS) pathway or the phenylalanine ammonia-lyase (PAL) pathway. The ICS pathway has been fully characterized using Arabidopsis thaliana, a model plant that exhibits pathogen-inducible SA accumulation. Many species including Populus (poplar) depend instead on the partially understood PAL pathway for constitutive as well as pathogen-stimulated SA synthesis. Diversity of SA-mediated defense is also evident in SA accumulation, redox regulation, and interplay with other hormones like jasmonic acid. This review highlights the contrast between Arabidopsis and poplar, discusses potential drivers of SA diversity in plant defenses, and offers future research directions.

TXNIP shuttling - a key molecular link in regulating inflammation and mitochondrial dysfunction in freeze tolerant wood frogs

Amphibians such as the wood frogs,Rana sylvatica, are a primary example of a freeze-tolerant vertebrate that undergoes whole body freezing. Multiple adaptations including sequestering 65-70% of total body water as extracellular/extra organ ice and producing massive amounts of glucose as a cryoprotectant support this. Interestingly, the high glucose levels induced in response to freezing can amplify oxidative stress's effects (reactive oxygen species, ROS) and induce inflammation and mitochondrial dysfunction. Since both freezing and dehydration stress (independent of freezing) can render wood frogs hyperglycemic, this study focussed on these two stresses to elucidate the role of a scaffold protein thioredoxin interacting protein (TXNIP), which localizes in multiple compartments inside the cell under hyperglycemic conditions and mediate diverse stress responses. The results from this study suggest a stress-specific response of TXNIP in inducing the cell-damaging pathway of inflammasome activation via its cytoplasmic localization during freezing. Interestingly, mitochondrial localization of TXNIP did not leads to increase in its binding to thioredoxin 2 (TRX-2) and activating the dysfunction of this organelle by releasing a mitochondrial protein cytochrome c (Cyt c) in cytoplasm under both freezing and dehydration stresses. Post-translational modifications of TXNIP hinted on changes in the regulating proteins involved in the inflammasome and mitochondrial dysfunction pathways, whereas sequential differences (cytosine residues) of amphibian TXNIP (compared to mammalian) assessed via 3D-modeling attributed to its weak binding to TRX-2. Overall, this study summarizes differential role of proteins activated under freeze and dehydration induced hyperglycemic response in freeze tolerant wood frogs.

Antioxidant activity of the thioredoxin system

The thioredoxin system is composed of thioredoxin (Trx), thioredoxin reductase (TR) and reduced nicotinamide adenine dinucleotide phosphate. Trx is an important antioxidant molecule that can resist cell death caused by various stresses and plays a prominent role in redox reactions. TR is a protein that contains selenium (selenocysteine), in three main forms, namely, TR1, TR2 and TR3. TR1, TR2 and TR3 are mainly distributed in the cytoplasm, mitochondria, and testes, respectively. TR can regulate cell growth and apoptosis. After a cell becomes cancerous, the expression of TR is increased to promote cell growth and metastasis. The Trx system is closely related to neurodegenerative diseases, parasitic infections, acquired immunodeficiency syndrome, rheumatoid arthritis, hypertension, myocarditis, and so on. In addition, the Trx system can remove the reactive oxygen species in the body and keep the inside and outside of the cell in a balanced state. In summary, the Trx system is an important target for the drug treatment of many diseases.

Bacterial production and biophysical characterization of a hard-to-fold scFv against myeloid leukemia cell surface marker, IL-1RAP

BACKGROUND

Interleukin-1 receptor accessory protein (IL-1RAP) is one of the most promising therapeutic targets proposed for myeloid leukemia. Antibodies (Abs) specific to IL-1RAP could be valuable tools for targeted therapy of this lethal malignancy. This study is about the preparation of a difficult-to-produce single-chain variable fragment (scFv) construct against the membrane-bound isoform of human IL-1RAP using Escherichia coli (E. coli).

METHODS

Different approaches were examined for refolding and characterization of the scFv. Binding activities of antibody fragments were comparatively evaluated using cell-based enzyme-linked immunosorbent assay (ELISA). Homogeneity and secondary structure of selected scFv preparation were analyzed using analytical size exclusion chromatography (SEC) and circular dichroism (CD) spectroscopy, respectively. The activity of the selected preparation was evaluated after long-term storage, repeated freeze-thaw cycles, or following incubation with normal and leukemic serum.

RESULTS

Strategies for soluble expression of the scFv failed. Even with the help of Trx, ≥ 98% of proteins were expressed as inclusion bodies (IBs). Among three different refolding methods, the highest recovery rate was obtained from the dilution method (11.2%). Trx-tag substantially enhanced the expression level (18%, considering the molecular weight (MW) differences), recovery rate (˃1.6-fold), and binding activity (˃2.6-fold increase in absorbance450nm). The produced scFv exhibited expected secondary structure as well as acceptable bio-functionality, homogeneity, and stability.

CONCLUSION

We were able to produce  21 mg/L culture functional and stable anti-IL-1RAP scFv via recovering IBs by pulse dilution procedure. The produced scFv as a useful targeting agent could be used in scheming new therapeutics or diagnostics for myeloid malignancies.

Thioredoxin-Interacting Protein Inhibited Vascular Endothelial Cell-Induced HREC Angiogenesis Treatment of Diabetic Retinopathy

Diabetic retinopathy is the most common reason for blindness among employed adults worldwide. Hyperglycemia and the overaccumulation of vascular endothelial growth factor (VEGF) lead to diabetic retinopathy, pathological angiogenesis in diabetic retinopathy, and consequent visual impairment. Expression levels of thioredoxin-interacting protein (TXNIP) substantially increase in retinal endothelial cells in diabetic circumstances. The part of TXNIP in retinal angiogenesis combined with diabetes remains unclear. This study examined the effect of reduced TXNIP expression levels and determined how it affects diabetic retinal angiogenesis. Display of human retinal vascular endothelial cells (HRECs) to moderately high glucose (MHG) encouraged tube formation and cell migration, not cell proliferation. In response to MHG conditions, in HRECs, TXNIP knockdown inhibited the production of reactive oxygen species (ROS), cell migration, tube formation, and the Akt/mTOR activation pathway. In addition, gene silencing of TXNIP decreased the VEGF-triggered angiogenic response in HRECs by preventing activation of both VEGF receptor 2 and the downstream components of the Akt/mTOR pathway signaling. Furthermore, TXNIP knockout mice reduced VEGF-induced or VEGF- and MHG-triggered ex vivo retinal angiogenesis compared to wild-type mice. Finally, our findings revealed that TXNIP knockdown suppressed VEGF- and MHG-triggered angiogenic responses in HRECs and mouse retinas, indicating that TXNIP is a promising therapeutic window against the proliferation of diabetic patients' retinopathy.

Inhibition of thioredoxin reductase activity reduces the antioxidant defense capacity of human pluripotent stem cells under conditions of mild but not severe oxidative stress

Pro-oxidative shift in redox balance, usually termed as "oxidative stress", can lead to different cell responses depending on its intensity. Excessive accumulation of reactive oxygen species ("oxidative distress") can cause DNA, lipid and protein damage. Physiological oxidative stimulus ("oxidative eustress"), in turn, can favor cell proliferation and differentiation - the processes of paramount importance primarily for stem cells. Functions of antioxidant enzymes in cells is currently a focus of intense research, however the role of different antioxidant pathways in pluripotent cell responses to oxidative distress/eustress is still under investigation. In this study, we assessed the contribution of the thioredoxin reductase (TrxR)-dependent pathways to maintaining the redox homeostasis in human induced pluripotent stem cells and their differentiated progeny cells under basal conditions and under conditions of oxidative stress of varying intensity. Employing the genetically encoded H₂O₂ biosensor cyto-HyPer and two inhibitors of thioredoxin reductase (auranofin and Tri-1), we show that the reduced activity of TrxR-dependent enzymatic systems leads to the non-cytotoxic disruption of thiol-disulfide metabolism in the cytoplasm of both pluripotent and differentiated cells under basal conditions. Quantifying the cytoplasmic concentrations of peroxide establishing in H₂O₂-stressed cells, we demonstrate that TrxR-dependent pathways contribute to the antioxidant activity in the cell cytoplasm under conditions of mild but not severe oxidative stress in both cell lines tested. The observed effects may testify about a conservative role of the TrxR-controlled enzymatic systems manifested as a response to physiological redox stimuli rather than a protection against the severe oxidative stress.

Structural Analyses of the Multicopper Site of CopG Support a Role as a Redox Enzyme

Metal ions can be both essential components of cells as well as potential toxins if present in excess. Organisms utilize a variety of protein systems to maintain the concentration of metal ions within the appropriate range for cellular function, and to avoid concentrations where cellular damage can occur. In bacteria, numerous proteins contribute to copper homeostasis, including copper transporters, chelators, and redox enzymes. The genes that encode these proteins are often found in clusters, thus providing modular components that work together to achieve homeostasis. A better understanding of how these components function and cooperate to achieve metal ion resistance is needed, given the extensive use of metal ions, including copper, as broad-spectrum biocides in a variety of clinical and environmental settings. The copG gene is a common component of such copper resistance clusters, but its contribution to copper resistance is not well understood. In this review the available information about the CopG protein encoded by this gene is summarized. Comparison of the recent structure to diverse copper-containing metallochaperones, metalloenzymes, and electron transfer proteins suggests that CopG is a redox enzyme that uses multiple copper ions as active site redox cofactors to act on additional copper ion substrates. Mechanisms for both oxidase and reductase activity are proposed, and the biological advantages that these activities can contribute in conjunction with existing systems are described.

Hydrogen peroxide detoxification through the peroxiredoxin/thioredoxin antioxidant system: A look at the pancreatic β-cell oxidant defense

Reactive oxygen species (ROS), such as hydrogen peroxide, are formed when molecular oxygen obtains additional electrons, increasing its reactivity. While low concentrations of hydrogen peroxide are necessary for regulation of normal cellular signaling events, high concentrations can be toxic. To maintain this balance between beneficial and deleterious concentrations of hydrogen peroxide, cells utilize antioxidants. Our recent work supports a primary role for peroxiredoxin, thioredoxin, and thioredoxin reductase as the oxidant defense pathway used by insulin-producing pancreatic β-cells. These three players work in an antioxidant cycle based on disulfide exchange, with oxidized targets ultimately being reduced using electrons provided by NADPH. Peroxiredoxins also participate in hydrogen peroxide-based signaling through disulfide exchange with redox-regulated target proteins. This chapter will describe the catalytic mechanisms of thioredoxin, thioredoxin reductase, and peroxiredoxin and provide an in-depth look at the roles these enzymes play in antioxidant defense pathways of insulin-secreting β-cells. Finally, we will evaluate the physiological relevance of peroxiredoxin-mediated hydrogen peroxide signaling as a regulator of β-cell function.

Molecular properties and regulation of NAD+ kinase (NADK)

Nicotinamide adenine dinucleotide (NAD⁺) kinase (NADK) phosphorylates NAD⁺, thereby producing nicotinamide adenine dinucleotide phosphate (NADP). Both NADK genes and the NADP(H)-producing mechanism are evolutionarily conserved among archaea, bacteria, plants and mammals. In mammals, NADK is activated by phosphorylation and protein-protein interaction. Recent studies conducted using genetically altered models validate the essential role of NADK in cellular redox homeostasis and metabolism in multicellular organisms. Here, we describe the evolutionary conservation, molecular properties, and signaling mechanisms and discuss the pathophysiological significance of NADK.

Computational and Experimental Evaluation of Linker Peptides and Thioredoxin Fusion Tag in CD20-rituximab Specific Interactions

Background

Overexpression of CD20 protein on the surface of B cells in lymphoma can be targeted by several anti-CD20 molecules. The development of accessible interactive epitopes is more favorable than the full-length transmembrane CD20 in the affinity assessment of anti-CD20 monoclonal antibodies (mAbs).

Methods

The sequence of these epitopes was extracted, and the effects of different linker peptides and the location of histidine (His)-tag were computationally analyzed. The impact of thioredoxin (Trx)-tag on the folding of the selected construct and its interaction with rituximab was further investigated. The two final expression cassettes were expressed in Escherichia coli after optimization of culture conditions for incubation temperature, post-induction time, optical density at the induction time, and concentration of the inducer. ELISA evaluated the binding affinity of rituximab towards the recombinant proteins.

Results

By homology modeling studies, C-terminal His-tagged structures represented more desirable folded structures. Validation of the models revealed that CD20 extracellular domain linked by the G₄S polypeptide had better stereochemical quality and structural compatibility. It was selected due to its more effective interaction with rituximab showing the highest dissociation constant of 5.8E-09M, which improved after the fusion of Trx-tag (7.1E-10M). The most influential parameters in the expression of the two selected proteins were post-induction temperature and optical density at the induction time. Homemade ELISA assays revealed a slightly higher affinity of rituximab towards the Trx-CD20 protein than the CD20/G₄S molecule.

Conclusions

Experimental in vitro studies confirmed the computationally calculated affinity of rituximab towards the two designed CD20 constructs. Also, the cell-based binding assessment of anti-CD20 mAbs could be substituted by the engineered extracellular domain of human CD20 protein.

Revealing PACMA 31 as a new chemical type TrxR inhibitor to promote cancer cell apoptosis

Thioredoxin reductase (TrxR) is a pivotal regulator of redox homeostasis, while dysregulation of redox homeostasis is a hallmark for cancer cells. Thus, there is considerable potential to inhibit the aberrantly upregulated TrxR in cancer cells to discover selective cancer therapeutic agents. Nevertheless, the structural types of TrxR inhibitors presented currently are still relatively limited. We herein report that PACMA 31, previously reported to inhibit protein disulfide isomerase (PDI), is a potent TrxR inhibitor. PACMA 31 possesses a pharmacophore scaffold that is structurally different from the announced TrxR inhibitors and exhibits effective cytotoxicity against cervical cancer cells. Our results reveal that PACMA 31 selectively inhibits TrxR over the related glutathione reductase (GR) and in the presence of reduced glutathione (GSH). Further studies with mutant enzyme and molecular docking suggest that the propynamide fragment of PACMA 31 interacts covalently with the selenocysteine residue of TrxR. Moreover, PACMA 31 effectively and selectively curbs TrxR activity in cells and further stimulates the production of reactive oxygen species (ROS) at low micromolar concentrations, which in turn triggers the accumulation of oxidized thioredoxin (Trx) and GSSG in cells. Follow-up studies demonstrate that PACMA 31 targets TrxR in cells to induce oxidative stress-mediated cancer cell apoptosis. Our results provide a new structural type of TrxR inhibitor that may serve as a useful probe for investigating the biology of TrxR-implicated pathways, and uncover a new target of PACMA 31 that contributes to it becoming a candidate for cancer treatment.

Effects of Environmental and Electric Perturbations on the pKa of Thioredoxin Cysteine 35: A Computational Study

Here we present a theoretical-computational study dealing with the evaluation of the pKa of the Cysteine residues in Thioredoxin (TRX) and in its complex with the Thioredoxin-interacting protein (TXNIP). The free energy differences between the anionic and neutral form of the Cysteine 32 and 35 have been evaluated by means of the Perturbed Matrix Method with classical perturbations due to both the environment and an exogenous electric field as provided by Molecular Dynamics (MD) simulations. The evaluation of the free energies allowed us to show that the effect of the perturbing terms is to lower the pKa of Cysteine 32 and Cysteine 35 with respect to the free amino-acid. On the other hand, in the complex TRX-TXNIP, our data show an enhanced stabilization of the neutral reduced form of Cys 35. These results suggest that external electric stimuli higher than 0.02 V/nm can modulate the Cysteine pKa, which can be connected to the tight regulation of the TRX acting as an antioxidant agent.

PUMA overexpression dissociates thioredoxin from ASK1 to activate the JNK/BCL-2/BCL-XL pathway augmenting apoptosis in ovarian cancer

ASK1-JNK signaling promotes mitochondrial dysfunction-mediated apoptosis, but the bridge between JNK and apoptosis is not fully understood. PUMA induces apoptosis through BAX/BAK. Our previous study suggests a therapeutic potential of PUMA for ovarian cancer. However, whether and how PUMA activates ASK1 remains unclear. Here, we found for the first time that PUMA activated ASK1 by dissociating thioredoxin (TRX) from ASK1, however, it neither interacted with ASK1 nor TRX. Furthermore, PUMA overexpression caused ROS release from mitochondrial. H₂O₂ significantly impaired the interaction of ASK1 with TRX, whereas ROS scavenger NAC effectively abrogated the H₂O₂ effect, partly rescued PUMA-interfered interaction of ASK1 with TRX, and also abolished ASK1 phosphorylation. Interestingly, PUMA could not impair the association of ASK1 with TRX-C32S or TRX-C35S, two TRX mutants which are no longer oxidized in response to ROS. We further showed that PUMA activated ASK1-JNK axis to phosphorylate BCL-2 and BCL-XL, further augmenting apoptosis of ovarian cancer cells. In vivo, PUMA adenovirus combined with paclitaxel significantly inhibited intrinsically cisplatin-resistant ovarian cancer growth, and caused phosphorylation of BCL-2 and BCL-XL. Our results from human ovarian cancer TMA chips also revealed a positive correlation between PUMA expression and the phosphorylation of BCL-2 and BCL-XL. More importantly, all patients had no distal metastasis, implying a possibly clinical significance. Collectively, our results reveal a new pro-apoptotic signal amplification mechanism for PUMA by which PUMA overexpression first induces ROS-mediated dissociation of TRX from ASK1, and then causes JNK activation-triggering BCL-2/BCL-XL phosphorylation, ultimately augmenting apoptosis in ovarian cancer.

Nitrative inactivation of thioredoxin-1 loses its protective effect in bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is common in the development of inflammatory lung diseases with no effective clinical drug treatment currently. As an essential redox enzyme, thioredoxin (Trx) has been reported to be involved in pulmonary fibrosis, but the mechanism is to be revealed. Therefore, in bleomycin-indued pulmonary fibrosis model in C57 mice, Trx activity and nitrated Trx were examined.,p38-MAPK apoptosis pathway was determined in lung tissues. Additionally, before BLM administration, C57/BL6 mice were treated with aminoguanidine (AG, a peroxynitrite scavenger), recombinant human Trx-1 (rhTrx-1), or SIN-1 (a peroxynitrite donor) nitrated Trx-1 (N-Trx-1). In bleomycin (BLM)-induced pulmonary fibrosis model in C57/BL6 mice, we observed that nitrated Trx increased, while its activity decreased, with the increase of alveolar epithelial cells (AECs)apoptosis by p38-MAPK pathway. We demonstrated that AG or rhTrx-1, but not N-Trx-1 significantly reduced pulmonary fibrosis. Taken together, the results above revealed that blockade of Trx-1 nitration, or supplementation of exogenous rhTrx-1, might represent novel therapies to attenuate pulmonary fibrosis in idiopathic pulmonary fibrosis patients.