Thioredoxin-dependent regulation of AIF-mediated DNA damage

A promising future of metal-N-heterocyclic carbene complexes in medicinal chemistry: The emerging bioorganometallic antitumor agents

Metal complexes based on N-heterocyclic carbene (NHC) ligands have emerged as promising broad-spectrum antitumor agents in bioorganometallic medicinal chemistry. In recent decades, studies on cytotoxic metal-NHC complexes have yielded numerous compounds exhibiting superior cytotoxicity compared to cisplatin. Although the molecular mechanisms of these anticancer complexes are not fully understood, some potential targets and modes of action have been identified. However, a comprehensive review of their biological mechanisms is currently absent. In general, apoptosis caused by metal-NHCs is common in tumor cells. They can cause a series of changes after entering cells, such as mitochondrial membrane potential (MMP) variation, reactive oxygen species (ROS) generation, cytochrome c (cyt c) release, endoplasmic reticulum (ER) stress, lysosome damage, and caspase activation, ultimately leading to apoptosis. Therefore, a detailed understanding of the influence of metal-NHCs on cancer cell apoptosis is crucial. In this review, we provide a comprehensive summary of recent advances in metal-NHC complexes that trigger apoptotic cell death via different apoptosis-related targets or signaling pathways, including B-cell lymphoma 2 (Bcl-2 family), p53, cyt c, ER stress, lysosome damage, thioredoxin reductase (TrxR) inhibition, and so forth. We also discuss the challenges, limitations, and future directions of metal-NHC complexes to elucidate their emerging application in medicinal chemistry.

Redox dysregulation as a driver for DNA damage and its relationship to neurodegenerative diseases

Redox homeostasis refers to the balance between the production of reactive oxygen species (ROS) as well as reactive nitrogen species (RNS), and their elimination by antioxidants. It is linked to all important cellular activities and oxidative stress is a result of imbalance between pro-oxidants and antioxidant species. Oxidative stress perturbs many cellular activities, including processes that maintain the integrity of DNA. Nucleic acids are highly reactive and therefore particularly susceptible to damage. The DNA damage response detects and repairs these DNA lesions. Efficient DNA repair processes are therefore essential for maintaining cellular viability, but they decline considerably during aging. DNA damage and deficiencies in DNA repair are increasingly described in age-related neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and Huntington's disease. Furthermore, oxidative stress has long been associated with these conditions. Moreover, both redox dysregulation and DNA damage increase significantly during aging, which is the biggest risk factor for neurodegenerative diseases. However, the links between redox dysfunction and DNA damage, and their joint contributions to pathophysiology in these conditions, are only just emerging. This review will discuss these associations and address the increasing evidence for redox dysregulation as an important and major source of DNA damage in neurodegenerative disorders. Understanding these connections may facilitate a better understanding of disease mechanisms, and ultimately lead to the design of better therapeutic strategies based on preventing both redox dysregulation and DNA damage.

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.

Mitochondrial Glrx2 Knockout Augments Acetaminophen-Induced Hepatotoxicity in Mice

Acetaminophen (APAP) is one of the most widely used drugs with antipyretic and analgesic effects, and thus hepatotoxicity from the overdose of APAP becomes one of the most common forms of drug-induced liver injury. The reaction towards thiol molecules, such as GSH by APAP metabolite, N-acetyl-p-benzo-quinonimine (NAPQI), is the main cause of APAP-induced hepatotoxicity. However, the role of many other thiol-related regulators in toxicity caused by APAP is still unclear. Here we have found that knockout of the Glrx2 gene, which encodes mitochondrial glutaredoxin2 (Grx2), sensitized mice to APAP-caused hepatotoxicity. Glrx2 deletion hindered Nrf2-mediated compensatory recovery of thiol-dependent redox systems after acetaminophen challenge, resulting in a more oxidized cellular state with a further decrease in GSH level, thioredoxin reductase activity, and GSH/GSSG ratio. The weakened feedback regulation capacity of the liver led to higher levels of protein glutathionylation and thioredoxin (both Trx1 and Trx2) oxidation in Glrx2^−/− mice. Following the cellular environment oxidation, nuclear translocation of apoptosis-inducing factor (AIF) was elevated in the liver of Glrx2^−/− mice. Taken together, these results demonstrated that mitochondrial Grx2 deficiency deteriorated APAP-induced hepatotoxicity by interrupting thiol-redox compensatory response, enhancing the AIF pathway-mediated oxidative damage.

Non-invasive medical gas plasma augments bladder cancer cell toxicity in preclinical models and patient-derived tumor tissues

INTRODUCTION

Medical gas plasma therapy has been successfully applied to several types of cancer in preclinical models. First palliative tumor patients suffering from advanced head and neck cancer benefited from this novel therapeutic modality. The gas plasma-induced biological effects of reactive oxygen and nitrogen species (ROS/RNS) generated in the plasma gas phase result in oxidation-induced lethal damage to tumor cells.

OBJECTIVES

This study aimed to verify these anti-tumor effects of gas plasma exposure on urinary bladder cancer.

METHODS

2D cell culture models, 3D tumor spheroids, 3D vascularized tumors grown on the chicken chorion-allantois-membrane (CAM) in ovo, and patient-derived primary cancer tissue gas plasma-treated ex vivo were used.

RESULTS

Gas plasma treatment led to oxidation, growth retardation, motility inhibition, and cell death in 2D and 3D tumor models. A marked decline in tumor growth was also observed in the tumors grown in ovo. In addition, results of gas plasma treatment on primary urothelial carcinoma tissues ex vivo highlighted the selective tumor-toxic effects as non-malignant tissue exposed to gas plasma was less affected. Whole-transcriptome gene expression analysis revealed downregulation of tumor-promoting fibroblast growth factor receptor 3 (FGFR3) accompanied by upregulation of apoptosis-inducing factor 2 (AIFm2), which plays a central role in caspase-independent cell death signaling.

CONCLUSION

Gas plasma treatment induced cytotoxicity in patient-derived cancer tissue and slowed tumor growth in an organoid model of urinary bladder carcinoma, along with less severe effects in non-malignant tissues. Studies on the potential clinical benefits of this local and safe ROS therapy are awaited.

The Thioredoxin System of Mammalian Cells and Its Modulators

Oxidative stress involves the increased production and accumulation of free radicals, peroxides, and other metabolites that are collectively termed reactive oxygen species (ROS), which are produced as by-products of aerobic respiration. ROS play a significant role in cell homeostasis through redox signaling and are capable of eliciting damage to macromolecules. Multiple antioxidant defense systems have evolved to prevent dangerous ROS accumulation in the body, with the glutathione and thioredoxin/thioredoxin reductase (Trx/TrxR) systems being the most important. The Trx/TrxR system has been used as a target to treat cancer through the thiol–disulfide exchange reaction mechanism that results in the reduction of a wide range of target proteins and the generation of oxidized Trx. The TrxR maintains reduced Trx levels using NADPH as a co-substrate; therefore, the system efficiently maintains cell homeostasis. Being a master regulator of oxidation–reduction processes, the Trx-dependent system is associated with cell proliferation and survival. Herein, we review the structure and catalytic properties of the Trx/TrxR system, its role in cellular signaling in connection with other redox systems, and the factors that modulate the Trx system.

Thioredoxin 1 regulates the pentose phosphate pathway via ATM phosphorylation after experimental subarachnoid hemorrhage in rats

Subarachnoid hemorrhage (SAH), a type of hemorrhagic stroke, is a neurological emergency with high morbidity and mortality. Early brain injury (EBI) after SAH is the leading cause of poor prognosis in SAH patients. TRX system is a NADPH-dependent antioxidant system which is composed of thioredoxin reductase (TRXR), thioredoxin (TRX). The pentose phosphate pathway (PPP), a pathway through which glucose can be metabolized, is a major source of NADPH. Thioredoxin 1 (TRX1) is a member of thioredoxin system mainly located in cytoplasm. Serine/threonine kinases ataxia telangiectasia mutated (ATM) is an important oxidative stress receptor, and TRX1 can regulate ATM phosphorylation and then affect the activity of PPP key enzyme glucose 6-phosphate dehydrogenase (G6PD). However, whether TRX1 is involved in the regulation of PPP pathway after subarachnoid hemorrhage remains unclear. The results showed that after SAH, the level of TRX1 and phosphor-ATM decreased while the level of TRXR1 increased. G6PD protein level remained unchanged but the activity decreased, and the NADPH contents decreased. Overexpression of TRX1 by lentivirus upregulates the level of phosphor-ATM, G6PD activity and NADPH content. TRX1 overexpression improved short-term and long-term neurobehavioral outcomes and alleviated neuronal impairment in rats. Nissl staining showed that upregulation of TRX1 reduced cortical neuron injury. Our study shows that TRX1 participates in the PPP pathway by regulating phosphorylation ATM, which is accomplished by affecting G6PD activity. TRX1 may be an important target for EBI intervention after SAH.

A proximity-based in silico approach to identify redox-labile disulfide bonds: The example of FVIII

Allosteric disulfide bonds permit highly responsive, transient 'switch-like' properties that are ideal for processes like coagulation and inflammation that require rapid and localised responses to damage or injury. Haemophilia A (HA) is a rare bleeding disorder managed with exogenous coagulation factor(F) VIII products. FVIII has eight disulfide bonds and is known to be redox labile, but it is not known how reduction/oxidation affects the structure-function relationship, or its immunogenicity-a serious complication for 30% severe HA patients. Understanding how redox-mediated changes influence FVIII can inform molecular engineering strategies aimed at improving activity and stability, and reducing immunogenicity. FVIII is a challenging molecule to work with owing to its poor expression and instability so, in a proof-of-concept study, we used molecular dynamics (MD) to identify which disulfide bonds were most likely to be reduced and how this would affect structure/function; results were then experimentally verified. MD identified Cys1899-Cys1903 disulfide as the most likely to undergo reduction based on energy and proximity criteria. Further MD suggested this reduction led to a more open conformation. Here we present our findings and highlight the value of MD approaches.

The key players of parthanatos: opportunities for targeting multiple levels in the therapy of parthanatos-based pathogenesis

Parthanatos is a form of regulated cell death involved in the pathogenesis of many diseases, particularly neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis. Parthanatos is a multistep cell death pathway cascade that involves poly (ADP-ribose) polymerase 1 (PARP-1) overactivation, PAR accumulation, PAR binding to apoptosis-inducing factor (AIF), AIF release from the mitochondria, nuclear translocation of the AIF/macrophage migration inhibitory factor (MIF) complex, and MIF-mediated large-scale DNA fragmentation. All the key players in the parthanatos pathway are pleiotropic proteins with diverse functions. An in-depth understanding of the structure-based activity of the key factors, and the biochemical mechanisms of parthanatos, is crucial for the development of drugs and therapeutic strategies. In this review, we delve into the key players of the parthanatos pathway and reveal the multiple levels of therapeutic opportunities for treating parthanatos-based pathogenesis.

The apoptosis-inducing factor family: Moonlighting proteins in the crosstalk between mitochondria and nuclei

In Homo sapiens, the apoptosis-inducing factor (AIF) family is represented by three different proteins, known as AIF, AMID and AIFL, that have in common the mitochondrial localisation in healthy cells, the presence of FAD- and NADH-dependent domains involved in an -albeit yet not well understood- oxidoreductase function and their capability to induce programmed cell death. AIF is the best characterised family member, while the information about AMID and AIFL is much scarcer. Nonetheless, available data support different roles as well as mechanisms of action of their particular apoptogenic and redox domains regarding both pro-apoptotic and anti-apoptotic activities. Moreover, diverse cellular functions, to date far from fully clarified, are envisaged for the transcripts corresponding to these three proteins. Here, we review the so far available knowledge on the moonlighting human AIF family from their molecular properties to their relevance in health and disease, through the evaluation of their potential cell death and redox functions in their different subcellular locations. This picture emerging from the current knowledge of the AIF family envisages its contribution to regulate signalling and transcription machineries in the crosstalk among mitochondria, the cytoplasm and the nucleus.

Apoptosis-inducing factor plays a role in the pathogenesis of hepatic and renal injury during cholestasis

Cholestasis is a clinical complication with different etiologies. The liver is the primary organ influenced in cholestasis. Renal injury is also a severe clinical complication in cholestatic/cirrhotic patients. Several studies mentioned the importance of oxidative stress and mitochondrial impairment as two mechanistically interrelated events in cholestasis-induced organ injury. Apoptosis-inducing factor (AIF) is a flavoprotein located in the inner mitochondrial membrane. This molecule is involved in a distinct pathway of cell death. The current study aimed to evaluate the role of AIF in the pathophysiology of cholestasis-associated hepatic and renal injury. Bile duct ligation (BDL) was used as an animal model of cholestasis. Serum, urine, and tissue samples were collected at scheduled time intervals (3, 7, 14, and 28 days after BDL surgery). Tissues' AIF mRNA levels, as well as serum, urine, and tissue activity of AIF, were measured. Moreover, markers of DNA fragmentation and apoptosis were assessed in the liver and kidney of cholestatic animals. A significant increase in liver and kidney AIF mRNA levels, in addition to increased AIF activity in the liver, kidney, serum, and urine, was detected in BDL rats. DNA fragmentation and apoptosis were raised in the liver and kidney of cholestatic animals, especially at the early stage of the disease. The apoptotic mode of cell death in the liver and kidney was connected to a higher AIF level. These data mention the importance of AIF in the pathogenesis of cholestasis-induced organ injury, especially at the early stage of this disease. Mitochondrial release of apoptosis-inducing factor (AIF) seems to play a pathogenic role in cholestasis-associated hepatic and renal injury. AIF release is directly connected to oxidative stress and mitochondrial impairment in cholestatic animals.

Intracellular Sources of ROS/H2O2 in Health and Neurodegeneration: Spotlight on Endoplasmic Reticulum

Reactive oxygen species (ROS) are produced continuously throughout the cell as products of various redox reactions. Yet these products function as important signal messengers, acting through oxidation of specific target factors. Whilst excess ROS production has the potential to induce oxidative stress, physiological roles of ROS are supported by a spatiotemporal equilibrium between ROS producers and scavengers such as antioxidative enzymes. In the endoplasmic reticulum (ER), hydrogen peroxide (H2O2), a non-radical ROS, is produced through the process of oxidative folding. Utilisation and dysregulation of H2O2, in particular that generated in the ER, affects not only cellular homeostasis but also the longevity of organisms. ROS dysregulation has been implicated in various pathologies including dementia and other neurodegenerative diseases, sanctioning a field of research that strives to better understand cell-intrinsic ROS production. Here we review the organelle-specific ROS-generating and consuming pathways, providing evidence that the ER is a major contributing source of potentially pathologic ROS.

Role of apoptosis-inducing factor in perinatal hypoxic-ischemic brain injury

Perinatal complications, such as asphyxia, can cause brain injuries that are often associated with subsequent neurological deficits, such as cerebral palsy or mental retardation. The mechanisms of perinatal brain injury are not fully understood, but mitochondria play a prominent role not only due to their central function in metabolism but also because many proteins with apoptosis-related functions are located in the mitochondrion. Among these proteins, apoptosis-inducing factor has already been shown to be an important factor involved in neuronal cell death upon hypoxia-ischemia, but a better understanding of the mechanisms behind these processes is required for the development of more effective treatments during the early stages of perinatal brain injury. In this review, we focus on the molecular mechanisms of hypoxic-ischemic encephalopathy, specifically on the importance of apoptosis-inducing factor. The relevance of apoptosis-inducing factor is based not only because it participates in the caspase-independent apoptotic pathway but also because it plays a crucial role in mitochondrial energetic functionality, especially with regard to the maintenance of electron transport during oxidative phosphorylation and in oxidative stress, acting as a free radical scavenger. We also discuss all the different apoptosis-inducing factor isoforms discovered, focusing especially on apoptosis-inducing factor 2, which is only expressed in the brain and the functions of which are starting now to be clarified. Finally, we summarized the interaction of apoptosis-inducing factor with several proteins that are crucial for both apoptosis-inducing factor functions (pro-survival and pro-apoptotic) and that are highly important in order to develop promising therapeutic targets for improving outcomes after perinatal brain injury.

Oxidation of apoptosis-inducing factor (AIF) to disulfide-linked conjugates

Apoptosis-inducing factor (AIF) is a flavoprotein and essential partner of the CHCHD4 redox protein during the mitochondrial intermembrane space import machinery. Mammalian AIF has three cysteine residues, which have received little attention. Previous reports have evidenced a redox interaction between AIF and thioredoxin 1 (Trx1), particularly after oxidant conditions. Therefore, we asked whether the cysteine residues of the human AIF could be oxidized. Our data showed that endogenous AIF could be oxidized to disulfide-linked conjugates (DLC). Overexpressed WT AIF in HEK293T cells, as well as recombinant WT AIF, formed DLC. Expression of C256S, C317S or C441S AIF mutants severely inhibited DLC formation in cells exposed to oxidants. In vitro, DLC formation was completely precluded with C256S and C441S AIF mutants and partially inhibited with the C317S mutant. DLC was shown to enhance cellular susceptibility to apoptosis induced by staurosporine, likely by preventing AIF to maintain mitochondrial oxidative phosphorylation. Cells with decreased expression of Trx1 produced more AIF DLC than those with normal Trx1 levels, and in vitro, Trx1 was able to decrease the amount of AIF DLC. Finally, confocal analysis, as well as immunoblotting of mitochondrial fraction, indicated that a fraction of Trx1 is present in mitochondria. Overall, these data provide evidence that all three cysteine residues of AIF can be oxidized to DLC, which can be disrupted by mitochondrial Trx1.

Sanggenol L Induces Apoptosis and Cell Cycle Arrest via Activation of p53 and Suppression of PI3K/Akt/mTOR Signaling in Human Prostate Cancer Cells

Prostate cancer is the most common cancer in Western countries. Recently, Asian countries are being affected by Western habits, which have had an important role in the rapid increase in cancer incidence. Sanggenol L (San L) is a natural flavonoid present in the root barks of Morus alba, which induces anti-cancer activities in ovarian cancer cells. However, the molecular and cellular mechanisms of the effects of sanggenol L on human prostate cancer cells have not been elucidated. In this study, we investigated whether sanggenol L exerts anti-cancer activity in human prostate cancer cells via apoptosis and cell cycle arrest. Sanggenol L induced caspase-dependent apoptosis (up-regulation of PARP and Bax or down-regulation of procaspase-3, -8, -9, Bid, and Bcl-2), induction of caspase-independent apoptosis (up-regulation of AIF and Endo G on cytosol), suppression of cell cycle (down-regulation of CDK1/2, CDK4, CDK6, cyclin D1, cyclin E, cyclin A, and cyclin B1 or up-regulation of p53 and p21), and inhibition of PI3K/Akt/mTOR signaling (down-regulation of PI3K, p-Akt, and p-mTOR) in prostate cancer cells. These results suggest the induction of apoptosis via suppression of PI3K/Akt/mTOR signaling and cell cycle arrest via activation of p53 in response to sanggenol L in prostate cancer cells.

Lupiwighteone induces caspase-dependent and -independent apoptosis on human breast cancer cells via inhibiting PI3K/Akt/mTOR pathway

Breast cancer is one of the most common causes of mortality in women. Lupiwighteone has anticancer effects in prostate cancer cells and neuroblastoma cells. However, the molecular and cellular mechanisms of lupiwighteone effects on human breast cancer cells are not as well known. In the present study, we investigated the effects of lupiwighteone on the proliferation and apoptosis of two different human cancer cells; MCF-7, an estrogen receptor (ER)-positive human breast cancer cell, and MDA-MB-231, a triple negative human breast cancer cell. Lupiwighteone treatment decreased the viability of MCF-7 and MDA-MB-231 cells. Lupiwighteone treatment resulted in apoptotic cell death in breast cancer cells, which was characterized by DNA fragmentation, accumulation of apoptotic cells, and nuclear condensation. We also showed that treatment with lupiwighteone induced caspase-dependent apoptosis (up-regulation of caspase-3, -7, -8, -9, PARP, and Bax or down-regulation of Bid, Bcl-2), induction of caspase-independent apoptosis (up-regulation of AIF and Endo G on cytosol), and inhibition of the PI3K/Akt/mTOR signaling pathway (down-regulation of PI3K, p-Akt, and p-mTOR) in both MCF-7 and MDA-MB-231 cells. These results suggest that lupiwighteone induces caspase-dependent and -independent apoptosis in both breast cancer cell lines via inhibiting PI3K/Akt/mTOR pathway.

Effect of Bugu granules in a drug-containing serum on chondrocyte apoptosis and the Trx2 signaling pathway

Traditional Chinese medicine for invigorating the kidney and promoting blood circulation is commonly prescribed for the treatment of osteoarthritis associated with kidney deficiency and blood stasis. However, the specific mechanisms of these medicines are still unclear. The present study aimed to evaluate the protective effects of Bugu granules against sodium nitroprusside-induced chondrocyte apoptosis and elucidate the underlying molecular mechanisms. Drug-containing serum was prepared by administering rats with Bugu granules and harvesting the serum. Chondrocytes were exposed to different dilutions of serum, and apoptosis assessed by flow cytometry after staining with annexin V‑FITC/PI. Flow cytometry showed that chondrocyte apoptosis increased significantly after incubation with 2 mol/L sodium nitroprusside for 24 h (t = -48.221, P = 0.000), and the apoptotic rate of chondrocytes decreased with increasing concentrations of drug-containing serum (F = 33.965, P = 0.000). Cellular levels of Trx2, ASK1, caspase‑3, and reactive oxygen species (ROS) were detected by enzyme-linked immunosorbent assay. The cellular content of Trx2 increased gradually with increasing concentrations of drug-containing serum (F = 2610.593, P = 0.000), while that of ASK1 (F = 2473.545, P = 0.000), caspase‑3 (F = 209.921, P = 0.000), and ROS (F = 1666.435, P = 0.000) all decreased significantly. The mRNA expression levels were analyzed by RT-qPCR, which revealed that expression levels of Trx2 and caspase‑3 mRNA increased and decreased significantly, respectively, following exposure to Bugu granules in the drug-containing serum (F = 6.974, P = 0.003 and F = 3.691, P = 0.191; respectively), but the expression of ASK1 mRNA was not significantly different between treatment groups (F = 1.784, P = 0.191). Taken together, these results support the hypothesis that the Trx2 signaling pathway is activated by Bugu granules, which in turn inhibits chondrocyte apoptosis. This may play a role in preventing the development of osteoarthritis.

Redox- and Ligand Binding-Dependent Conformational Ensembles in the Human Apoptosis-Inducing Factor Regulate Its Pro-Life and Cell Death Functions

Aims: The human apoptosis-inducing factor (hAIF) supports OXPHOS biogenesis and programmed cell death, with missense mutations producing neurodegenerative phenotypes. hAIF senses the redox environment of cellular compartments, stabilizing a charge transfer complex (CTC) dimer that modulates the protein interaction network. In this context, we aimed to evaluate the subcellular pH, CTC formation, and pathogenic mutations effects on hAIF stability, and a thermal denaturation high-throughput screening (HTS) assay to discover AIF binders. Results: Apoptotic hAIF_Δ1-101 is not stable at intermembrane mitochondrial space (IMS) pH, but the 77-101 residues confer stability to the mitochondrial isoform. hAIF and its CTC populate different conformational ensembles with redox switch to the CTC producing a less stable and compact protein. The pathogenic G308E, ΔR201, and E493V mutations modulate hAIF stability; particularly, ΔR201 causes a population shift to a less stable conformation that remodels active site structure and dynamics. We have identified new molecules that modulate the hAIF reduced nicotinamide adenine dinucleotide (NADH)/oxidized nicotinamide adenine dinucleotide (NAD⁺) association/dissociation equilibrium and regulate its catalytic efficiency. Innovation: Biophysical methods allow evaluating the regulation of hAIF functional ensembles and to develop an HTS assay to discover small molecules that might modulate hAIF stability and activities. Conclusions: The mitochondrial soluble 54-77 portion stabilizes hAIF at the IMS pH. NADH-redox-linked conformation changes course with strong NAD⁺ binding and protein dimerization, but they produce a negative impact in overall hAIF stability. Loss of functionality in the R201 deletion is due to distortion of the active site architecture. We report molecules that may serve as leads in the development of hAIF bioactive compounds.

Promotion of HeLa cells apoptosis by cynaropicrin involving inhibition of thioredoxin reductase and induction of oxidative stress

Cancer is considered as one of the highly mortal diseases globally. This is largely due to the lack of efficacious medicines for tumors, and thus development of potent anticancer agents is urgently needed. The thioredoxin (Trx) system is crucial to the survival ability of cells and its expression is up-regulated in many human tumors. Recently, increasing evidence has been established that mammalian thioredoxin reductase (TrxR), a selenocysteine-containing protein and the core component of the thioredoxin system, is a promising therapeutic target. The sesquiterpene lactone compound cynaropicrin (CYN), a major component of Cynara scolymus L., has shown multiple pharmacological functions, especially the anticancer effect, in many experimental models. Most of these functions are concomitant with the production of reactive oxygen species (ROS). Nevertheless, the target of this promising natural anticancer product in redox control has rarely been explored. In this study, we showed that CYN induces apoptosis of Hela cells. Mechanistic studies demonstrated that CYN impinges on the thioredoxin system via inhibition of TrxR, which leads to Trx oxidation and ROS accumulation in HeLa cells. Particularly, the cytotoxicity of CYN is enhanced through the genetic knockdown of TrxR, supporting the pharmacological effect of CYN is relevant to its inhibition of TrxR. Together, our studies reveal an unprecedented mechanism accounting for the anticancer effect of CYN and identify a promising therapeutic agent worthy of further development for cancer therapy.

The combination of ascorbate and menadione causes cancer cell death by oxidative stress and replicative stress

The combination of ascorbate and menadione (VC:VK3 = 100:1) is an investigational treatment for cancer under clinical trials. Dehydroascorbic acid (DHA), the oxidized form of ascorbate, can be taken up by cells via glucose transporters, over-expressed in many cancer cells. It has been known that the combination of VC/VK3 kills cancer cells by inducing hydrogen peroxide (H₂O₂) via a redox cycling reaction. However, the mechanism has not been fully understood yet. Intracellularly, DHA is reduced to ascorbate by NADPH via GSH and glutaredoxin as well as by thioredoxin (Trx) and the selenoenzyme thioredoxin reductase (TrxR). These two systems are also critical as electron donors for ribonucleotide reductase (RNR), which produces deoxyribonucleotides de novo for DNA replication and DNA repair and is highly expressed in tumor cells. We found that RNR was highly sensitive to VC/VK3 in vitro with similar effects as observed with H₂O₂. In cancer cells, VC/VK3 inhibited RNR mainly by targeting its R2 subunit. More importantly, both the Trx and GSH systems were oxidized by the combination, which resulted in the loss of GSH, increased protein glutathionylation, and highly oxidized Trx1. The mechanism of cell death induced by VC/VK3 was also elucidated. We found that VC/VK3 inhibited glutathione peroxidase activity and led to an elevated level of lipid peroxidation, which triggered apoptosis-inducing factor (AIF) mediated cell death pathway. Therefore, the combination not only induced replicative stress by inhibiting RNR, but also oxidative stress by targeting anti-oxidant systems and triggered AIF-mediated cancer cell death.

Xanthatin Promotes Apoptosis via Inhibiting Thioredoxin Reductase and Eliciting Oxidative Stress

Xanthatin (XT), a naturally occurring sesquiterpene lactone presented in cocklebur ( Xanthium strumarium L.), is under development as a potential anticancer agent. Despite the promising anticancer effect of XT, the molecular mechanism underlying its cellular action has not been well elucidated. The mammalian thioredoxin reductase (TrxR) enzymes, the essential seleno-flavoproteins containing a penultimate selenocysteine (Sec) residue at the C-terminus, represent a promising target for cancer chemotherapeutic agents. In this study, XT inhibits both the purified TrxR and the enzyme in cells. The possible binding mode of XT with the TrxR protein is predicted by the covalent docking method. Mechanism studies reveal that XT targets the Sec residue of TrxR and inhibits the enzyme activity irreversibly. Simultaneously, the inhibition of TrxR by XT promotes the oxidative stress-mediated apoptosis of HeLa cells. Importantly, the knockdown of the enzyme sensitizes the cells to XT treatment. Targeting TrxR thus discloses a novel molecular mechanism in accounting for the cellular action of XT and provides insights into the development of XT as an anticancer agent.

Apoptosis-Inducing Factor (AIF) in Physiology and Disease: The Tale of a Repented Natural Born Killer

Apoptosis-inducing factor (AIF) is a mitochondrial oxidoreductase that contributes to cell death programmes and participates in the assembly of the respiratory chain. Importantly, AIF deficiency leads to severe mitochondrial dysfunction, causing muscle atrophy and neurodegeneration in model organisms as well as in humans. The purpose of this review is to describe functions of AIF and AIF-interacting proteins as regulators of cell death and mitochondrial bioenergetics. We describe how AIF deficiency induces pathogenic processes that alter metabolism and ultimately compromise cellular homeostasis. We report the currently known AIFM1 mutations identified in humans and discuss the variability of AIFM1-related disorders in terms of onset, organ involvement and symptoms. Finally, we summarize how the study of AIFM1-linked pathologies may help to further expand our understanding of rare inherited forms of mitochondrial diseases.

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AIF is a mitochondrial NADH-dependent oxidoreductase.

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Nuclear translocation of AIF occurs during cell death and has been associated with human disorders.

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Under physiological settings, AIF participates to the biogenesis of the respiratory complexes.

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AIFM1 mutations have been identified in patients with impaired mitochondrial bioenergetics.

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Inherited AIFM1 mutations lead to a variety of clinical manifestations, including severe childhood-onset mitochondrial diseases.

The down-regulated ING5 expression in lung cancer: a potential target of gene therapy

ING5 can interact with p53, thereby inhibiting cell growth and inducing apoptosis. We found that ING5 overexpression not only inhibited proliferation, migration, and invasion, but also induced G2 arrest, differentiation, autophagy, apoptosis, glycolysis and mitochondrial respiration in lung cancer cells. ING5 transfection up-regulated the expression of Cdc2, ATG13, ATG14, Beclin-1, LC-3B, AIF, cytochrome c, Akt1/2/3, ADFP, PFK-1 and PDPc, while down-regulated the expression of Bcl-2, XIAP, survivin,β-catenin and HXK1. ING5 transfection desensitized cells to the chemotherapy of MG132, paclitaxel, and SAHA, which paralleled with apoptotic alteration. ING5 overexpression suppressed the xenograft tumor growth by inhibiting proliferation and inducing apoptosis. ING5 expression level was significantly higher in normal tissue than that in lung cancer at both protein and mRNA levels. Nuclear ING5 expression was positively correlated with ki-67 expression and cytoplasmic ING5 expression. Cytoplasmic ING5 expression was positively associated with lymph node metastasis, and negatively with age, lymphatic invasion or CPP32 expression. ING5 expression was different in histological classification: squamous cell carcinoma > adenocarcinoma > large cell carcinoma > small cell carcinoma. Taken together, our data suggested that ING5 downregulation might involved in carcinogenesis, growth, and invasion of lung cancer and could be considered as a promising marker to gauge the aggressiveness of lung cancer. It might be employed as a potential target for gene therapy of lung cancer.

Structural aspects of protein kinase ASK1 regulation

Apoptosis signal-regulating kinase 1 (ASK1, also known as MAP3K5), a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, activates the p38 mitogen-activated protein kinase and the c-Jun N-terminal kinase (JNK) signaling cascades in response to various stressors. ASK1 activity is tightly regulated through phosphorylation and interaction with various binding partners. However, the mechanistic details underlying the ASK1 regulation are still not fully understood. This review focuses on recent advances in structural studies of protein kinase ASK1 and on the insights they provide into its mechanism of regulation. In addition, we also discuss protein-protein interactions between ASK1 and its binding partners thioredoxin (TRX) and 14-3-3 protein.

Thioredoxin A Is Essential for Motility and Contributes to Host Infection of Listeria monocytogenes via Redox Interactions

Microbes employ the thioredoxin system to defend against oxidative stress and ensure correct disulfide bonding to maintain protein function. Listeria monocytogenes has been shown to encode a putative thioredoxin, TrxA, but its biological roles and underlying mechanisms remain unknown. Here, we showed that expression of L. monocytogenes TrxA is significantly induced in bacteria treated with the thiol-specific oxidizing agent, diamide. Deletion of trxA markedly compromised tolerance of the pathogen to diamide, and mainly impaired early stages of infection in human intestinal epithelial Caco-2 cells. In addition, most trxA mutant bacteria were not associated with polymerized actin, and the rare bacteria that were associated with polymerized actin displayed very short tails or clouds during infection. Deletion or constitutive overexpression of TrxA, which was regulated by SigH, severely attenuated the virulence of the pathogen. Transcriptome analysis of L. monocytogenes revealed over 270 genes that were differentially transcribed in the ΔtrxA mutant compared to the wild-type, especially for the virulence-associated genes plcA, mpl, hly, actA, and plcB. Particularly, deletion of TrxA completely reduced LLO expression, and thereby led to a thoroughly impaired hemolytic activity. Expression of these virulence factors are positively regulated by the master regulator PrfA that was found here to use TrxA to maintain its reduced forms for activation. Interestingly, the trxA deletion mutant completely lacked flagella and was non-motile. We further confirmed that this deficiency is attributable to TrxA in maintaining the reduced intracellular monomer status of MogR, the key regulator for flagellar formation, to ensure correct dimerization. In summary, we demonstrated for the first time that L. monocytogenes thioredoxin A as a vital cellular reductase is essential for maintaining a highly reducing environment in the bacterial cytosol, which provides a favorable condition for protein folding and activation, and therefore contributes to bacterial virulence and motility.

Targeting the Thioredoxin System for Cancer Therapy

Thioredoxin (Trx) and thioredoxin reductase (TrxR) are essential components of the Trx system which plays pivotal roles in regulating multiple cellular redox signaling pathways. In recent years TrxR/Trx have been increasingly recognized as an important modulator of tumor development, and hence targeting TrxR/Trx is a promising strategy for cancer treatment. In this review we first discuss the structural details of TrxR, the functions of the Trx system, and the rational of targeting TrxR/Trx for cancer treatment. We also highlight small-molecule TrxR/Trx inhibitors that have potential anticancer activity and review their mechanisms of action. Finally, we examine the challenges of developing TrxR/Trx inhibitors as anticancer agents and perspectives for selectively targeting TrxR/Trx.

Melatonin rescues cardiac thioredoxin system during ischemia-reperfusion injury in acute hyperglycemic state by restoring Notch1/Hes1/Akt signaling in a membrane receptor-dependent manner

Stress hyperglycemia is commonly observed in patients suffering from ischemic heart disease. It not only worsens cardiovascular prognosis but also attenuates the efficacies of various cardioprotective agents. This study aimed to investigate the protective effect of melatonin against myocardial ischemia-reperfusion (MI/R) injury in acute hyperglycemic state with a focus on Notch1/Hes1/Akt signaling and intracellular thioredoxin (Trx) system. Sprague Dawley rats were subjected to MI/R surgery and high-glucose (HG, 500 g/L) infusion (4 mL/kg/h) to induce temporary hyperglycemia. Rats were treated with or without melatonin (10 mg/kg/d) during the operation. Furthermore, HG (33 mmol/L)-incubated H9c2 cardiomyoblasts were treated in the presence or absence of luzindole (a competitive melatonin receptor antagonist), DAPT (a γ-secretase inhibitor), LY294002 (a PI3-kinase/Akt inhibitor), or thioredoxin-interacting protein (Txnip) adenoviral vectors. We found that acute hyperglycemia aggravated MI/R injury by suppressing Notch1/Hes1/Akt signaling and intracellular Trx activity. Melatonin treatment effectively ameliorated MI/R injury by reducing infarct size, myocardial apoptosis, and oxidative stress. Moreover, melatonin also markedly enhanced Notch1/Hes1/Akt signaling and rescued intracellular Trx system by upregulating Notch1, N1ICD, Hes1, and p-Akt expressions, increasing Trx activity, and downregulating Txnip expression. However, these effects were blunted by luzindole, DAPT, or LY294002. Additionally, Txnip overexpression not only decreased Trx activity, but also attenuated the cytoprotective effect of melatonin. We conclude that impaired Notch1 signaling aggravates MI/R injury in acute hyperglycemic state. Melatonin rescues Trx system by reducing Txnip expression via Notch1/Hes1/Akt signaling in a membrane receptor-dependent manner. Its role as a prophylactic/therapeutic drug deserves further clinical study.

Thioredoxin Inhibitors Attenuate Platelet Function and Thrombus Formation

Thioredoxin (Trx) is an oxidoreductase with important physiological function. Imbalances in the NADPH/thioredoxin reductase/thioredoxin system are associated with a number of pathologies, particularly cancer, and a number of clinical trials for thioredoxin and thioredoxin reductase inhibitors have been carried out or are underway. Due to the emerging role and importance of oxidoreductases for haemostasis and the current interest in developing inhibitors for clinical use, we thought it pertinent to assess whether inhibition of the NADPH/thioredoxin reductase/thioredoxin system affects platelet function and thrombosis. We used small molecule inhibitors of Trx (PMX 464 and PX-12) to determine whether Trx activity influences platelet function, as well as an unbiased proteomics approach to identify potential Trx substrates on the surface of platelets that might contribute to platelet reactivity and function. Using LC-MS/MS we found that PMX 464 and PX-12 affected the oxidation state of thiols in a number of cell surface proteins. Key surface receptors for platelet adhesion and activation were affected, including the collagen receptor GPVI and the von Willebrand factor receptor, GPIb. To experimentally validate these findings we assessed platelet function in the presence of PMX 464, PX-12, and rutin (a selective inhibitor of the related protein disulphide isomerase). In agreement with the proteomics data, small molecule inhibitors of thioredoxin selectively inhibited GPVI-mediated platelet activation, and attenuated ristocetin-induced GPIb-vWF-mediated platelet agglutination, thus validating the findings of the proteomics study. These data reveal a novel role for thioredoxin in regulating platelet reactivity via proteins required for early platelet responses at sites of vessel injury (GPVI and GPIb). This work also highlights a potential opportunity for repurposing of PMX 464 and PX-12 as antiplatelet agents.

Targeting Thioredoxin Reductase by Parthenolide Contributes to Inducing Apoptosis of HeLa Cells

Parthenolide (PTL), a major active sesquiterpene lactone from the herbal plant Tanacetum parthenium, has been applied in traditional Chinese medicine for centuries. Although PTL demonstrates potent anticancer efficacy in numerous types of malignant cells, the cellular targets of PTL have not been well defined. We reported here that PTL interacts with both cytosolic thioredoxin reductase (TrxR1) and mitochondrial thioredoxin reductase (TrxR2), two ubiquitous selenocysteine-containing antioxidant enzymes, to elicit reactive oxygen species-mediated apoptosis in HeLa cells. PTL selectively targets the selenocysteine residue in TrxR1 to inhibit the enzyme function, and further shifts the enzyme to an NADPH oxidase to generate superoxide anions, leading to reactive oxygen species accumulation and oxidized thioredoxin. Under the conditions of inhibition of TrxRs in cells, PTL does not cause significant alteration of cellular thiol homeostasis, supporting selective target of TrxRs by PTL. Importantly, overexpression of functional TrxR1 or Trx1 confers protection, whereas knockdown of the enzymes sensitizes cells to PTL treatment. Targeting TrxRs by PTL thus discloses an unprecedented mechanism underlying the biological activity of PTL, and provides deep insights to understand the action of PTL in treatment of cancer.

Inhibition of thioredoxin reductase by alantolactone prompts oxidative stress-mediated apoptosis of HeLa cells

The mammalian thioredoxin reductase (TrxR) isoenzymes, TrxR1 in cytosol or nucleus, TrxR2 in mitochondria, and TrxR3 in testis, are essential seleno-flavoenzymes with a conserved penultimate selenocysteine (Sec) residue at the C-terminus, and have attracted increasing interests as potential targets for development of cancer chemotherapeutic agents. The sesquiterpene lactone alantolactone (ATL), an active component from the traditional folk medicine Inula helenium, has been documented possessing multiple pharmacological functions, especially the anticancer activity. However, the underlying mechanism has not been well defined. We reported that ATL inhibits both the recombinant TrxR and the enzyme in the cellular environment. The alpha-methylene-gamma-lactone moiety in ATL and the Sec residue in TrxR are critical for targeting TrxR by ATL. By employing our newly developed pull down assay, we demonstrated the remarkable elevation of the oxidized thioredoxin in HeLa cells after ATL treatment. In addition, ATL elicits accumulation of reactive oxygen species, and eventually induces apoptosis of HeLa cells. Importantly, overexpression of the functional TrxR attenuates the cytotoxicity of ATL, while knockdown of the enzyme sensitizes the cells to ATL treatment. Targeting TrxR thus discloses a novel molecular mechanism underlying the cellular action of ATL, and sheds light in considering the usage of ATL as a potential cancer chemotherapeutic agent.

Deoxypodophyllotoxin triggers parthanatos in glioma cells via induction of excessive ROS

Parthanatos is a new form of programmed cell death that is regulated by hyper-activated PARP-1, and is emerging as a new strategy to kill cancer cells. Deoxypodophyllotoxin (DPT) is a natural chemical that is found to induce cancer cell death, in which the role of parthanatos is unknown. Thus, we investigated this issue in this study by using glioma cell lines and mice model of xenograft glioma. We found that DPT induced glioma cell death in vitro and inhibited the growth of xenograft glioma in vivo, which was accompanied with parthanatos-related biochemical events including expressional upregulation of PARP-1, cytoplasmic accumulation of PAR polymer, and nuclear translocation of AIF. In vitro study revealed that genetic knockdown of PARP-1 with small interfering RNA attenuated DPT-induced elevation in the cytoplasmic PAR-polymer and the nuclear AIF, as well as protected glioma cells against the toxicity of DPT. Further, antioxidant NAC, as well as PARP-1 inhibitor 3AB, not only alleviated the overproduction of ROS caused by DPT, but also reversed the above-mentioned biochemical events, maintained mitochondrial membrane potential and rescued glioma cells death. Therefore, we demonstrated that deoxypodophyllotoxin triggered parthanatos in glioma cells via induction of excessive ROS.