Redox status of thioredoxin-1 (TRX1) determines the sensitivity of human liver carcinoma cells (HepG2) to arsenic trioxide-induced cell death

The cold-inducible RNA-binding protein-Thioredoxin 1 pathway ameliorates mitochondrial dysfunction and mitochondrial dynamin-related protein 1 level in the hippocampus of aged mice with perioperative neurocognitive dysfunction

BACKGROUND

As a multi-disease model, neuroinflammation, mitochondrial dysfunction, and oxidative stress might be involved in the pathogenic process of perioperative neurocognitive dysfunction (PND). Dynamin-related protein 1 (Drp1) could mediate mitochondrial fission and play important roles in mitochondrial dynamic homeostasis and mitochondria function. The Drp1 may be involved in PND development. The cold-inducible RNA-binding protein (Cirbp) could bind to the 3'-UTR of the thioredoxin 1 (Trx1) mRNA, control oxidative stress, and improve mitochondrial function. In this study, we hypothesized that the Cirbp-Trx1 pathway could ameliorate mitochondrial dysfunction and Drp1 levels in PND mice.

METHODS

Differentially expressed genes were screened using the Gene Expression Omnibus (GEO) database GSE95426 and validated using PCR. Eighteen-month-old C57BL/6 mice were subjected to tibial fracture surgery to generate a PND model. Cirbp was upregulated by hippocampal stereotaxic injections of over-Cirbp plasmid according to the manufacturer's instructions for the in vivo DNA transfection reagent. Cirbp expression was measured using western blot (WB) and immunofluorescence (IF). The Morris water maze (MWM) was used to assess cognitive function. After behavioral testing, the hippocampal tissue was extracted to examine changes in mitochondrial Drp1, mitochondrial function, neuroinflammation, and oxidative stress.

RESULTS

Differential gene screening showed that Cirbp expression was significantly downregulated (fold change >1.5, p = 0.003272) in the PND model. In this study, we also found that Cirbp protein levels were downregulated, accompanied by an impairment of cognition, a decrease in superoxide dismutase (SOD) activity, and an increase in malondialdehyde (MDA) content, mitochondrial Drp1 levels, neuroinflammation, and apoptosis. Cirbp overexpression increased Trx1 protein levels and reversed the damage. However, this protective effect was abolished by PX-12 treatment with a Trx1 inhibitor.

CONCLUSIONS

The Cirbp-Trx1 pathway may regulate mitochondrial dysfunction and mitochondrial Drp1 expression in the hippocampus of PND mice to ameliorate cognitive dysfunction.

Promising Strategy of mPTP Modulation in Cancer Therapy: An Emerging Progress and Future Insight

Cancer has been progressively a major global health concern. With this developing global concern, cancer determent is one of the most significant public health challenges of this era. To date, the scientific community undoubtedly highlights mitochondrial dysfunction as a hallmark of cancer cells. Permeabilization of the mitochondrial membranes has been implicated as the most considerable footprint in apoptosis-mediated cancer cell death. Under the condition of mitochondrial calcium overload, exclusively mediated by oxidative stress, an opening of a nonspecific channel with a well-defined diameter in mitochondrial membrane allows free exchange between the mitochondrial matrix and the extra mitochondrial cytosol of solutes and proteins up to 1.5 kDa. Such a channel/nonspecific pore is recognized as the mitochondrial permeability transition pore (mPTP). mPTP has been established for regulating apoptosis-mediated cancer cell death. It has been evident that mPTP is critically linked with the glycolytic enzyme hexokinase II to defend cellular death and reduce cytochrome c release. However, elevated mitochondrial Ca2+ loading, oxidative stress, and mitochondrial depolarization are critical factors leading to mPTP opening/activation. Although the exact mechanism underlying mPTP-mediated cell death remains elusive, mPTP-mediated apoptosis machinery has been considered as an important clamp and plays a critical role in the pathogenesis of several types of cancers. In this review, we focus on structure and regulation of the mPTP complex-mediated apoptosis mechanisms and follow with a comprehensive discussion addressing the development of novel mPTP-targeting drugs/molecules in cancer treatment.

Effects of Antioxidant Gene Overexpression on Stress Resistance and Malignization In Vitro and In Vivo: A Review

Reactive oxygen species (ROS) are normal products of a number of biochemical reactions and are important signaling molecules. However, at the same time, they are toxic to cells and have to be strictly regulated by their antioxidant systems. The etiology and pathogenesis of many diseases are associated with increased ROS levels, and many external stress factors directly or indirectly cause oxidative stress in cells. Within this context, the overexpression of genes encoding the proteins in antioxidant systems seems to have become a viable approach to decrease the oxidative stress caused by pathological conditions and to increase cellular stress resistance. However, such manipulations unavoidably lead to side effects, the most dangerous of which is an increased probability of healthy tissue malignization or increased tumor aggression. The aims of the present review were to collect and systematize the results of studies devoted to the effects resulting from the overexpression of antioxidant system genes on stress resistance and carcinogenesis in vitro and in vivo. In most cases, the overexpression of these genes was shown to increase cell and organism resistances to factors that induce oxidative and genotoxic stress but to also have different effects on cancer initiation and promotion. The last fact greatly limits perspectives of such manipulations in practice. The overexpression of GPX3 and SOD3 encoding secreted proteins seems to be the "safest" among the genes that can increase cell resistance to oxidative stress. High efficiency and safety potential can also be found for SOD2 overexpression in combinations with GPX1 or CAT and for similar combinations that lead to no significant changes in H₂O₂ levels. Accumulation, systematization, and the integral analysis of data on antioxidant gene overexpression effects can help to develop approaches for practical uses in biomedical and agricultural areas. Additionally, a number of factors such as genetic and functional context, cell and tissue type, differences in the function of transcripts of one and the same gene, regulatory interactions, and additional functions should be taken into account.

Arsenic inhibits citric acid accumulation via downregulating vacuolar proton pump gene expression in citrus fruits

Citric acid content is a critical quality determinant in citrus (Citrus spp.) fruits. Although arsenic (As) can effectively reduce citric acid content to improve citrus fruit quality, it can have adverse environmental effects. The discovery of nontoxic substitutes is hampered by the incomplete elucidation of the underlying mechanisms of As action in citrus fruits. Metabolic, transcriptomic, and physiological analyses were employed to investigate As action on citric acid accumulation to discover the mechanisms of As action in citrus. The enzyme activity related to citrate biosynthesis was not inhibited and the content of the involved metabolites was not reduced in As-treated fruits. However, the proton pump genes CitPH5 and CitPH1 control the vacuolar citric acid accumulation and transcription factor genes CitTT8 and CitMYB5, which regulate CitPH5 and CitPH1, were downregulated. The oxidative stress-response genes were upregulated in As-treated fruits. The reactive oxygen species (ROS) treatment also downregulated CitTT8 and CitMYB5 in juice cells. The mitochondrial ROS production rate increased in As-treated fruits. As^III was more potent in stimulating isolated mitochondria to overproduce ROS compared to As^V. Our results indicate that the As inhibition of citric acid accumulation may be primarily due to the transcriptional downregulation of CitPH5, CitPH1, CitTT8, and CitMYB5. As-induced oxidative stress signaling may operate upstream to downregulate these acid regulator genes. Mitochondrial thiol proteins may be the principal targets of As action in citrus fruits.

Unraveling Potential Candidate Targets Associated with Expression of p16INK4a or p16 Truncated Fragment by Comparative Proteomics Analysis

Background:

p16 is a tumor suppressor protein that is significantly involved in cycle regulation through the reduction of cell progression from the G1 phase to the S phase via CDK-cyclin D/p16INK4a/pRb/E2F cascade. The minimum functional domain of p16 has been uncovered that may function comparable to wild type p16.

Objective:

To expand the knowledge on molecules and mechanisms by which p16 or p1666-156 fragment suppresses human fibrosarcoma cell line growth, differential proteome profiles of fibrosarcoma cells following p16 full length or the functional domain overexpression, were analyzed.

Methods:

Following transfecting HT-1080 fibrosarcoma cells with p16 full length, p1666-156 truncated form, and pcDNA3.1 empty vector, protein extract of each sample was harvested and clarified by centrifugation, and then the protein content was determined via Bradford assay. All protein extract of each sample was analyzed by two-dimensional gel electrophoresis. Immunoblot analysis was performed as further validation of the expression status of identified proteins.

Results:

Expression of p16 or p1666-156 fragment could induce mostly the common alterations (up/- down-regulation) of proteome profile of HT-1080 cells. Mass spectrometry identification of the differentially expressed protein spots revealed several proteins that were grouped in functional clusters, including cell cycle regulation and proliferation, cell migration and structure, oxidative stress, protein metabolism, epigenetic regulation, and signal transduction.

Conclusion:

The minimum functional domain of p16 could act in the same way as p16 full length. Also, these new findings can significantly enrich the understanding of p16 growth-suppressive function at the molecular level by the introduction of potential candidate targets for new treatment strategies. Furthermore, the present study provides strong evidence on the functional efficacy of the identified fragment of p16 for further attempts toward peptidomimetic drug design or gene transfer to block cancer cell proliferation.

Thioredoxin reductase as a pharmacological target

Thioredoxin reductases (TrxRs) belong to the pyridine nucleotide disulfide oxidoreductase family enzymes that reduce thioredoxin (Trx). The couple TrxR and Trx is one of the major antioxidant systems that control the redox homeostasis in cells. The thioredoxin system, comprised of TrxR, Trx and NADPH, exerts its activities via a disulfide-dithiol exchange reaction. Inhibition of TrxR is an important clinical goal in all conditions in which the redox state is perturbed. The present review focuses on the most critical aspects of the cellular functions of TrxRs and their inhibition mechanisms by metal ions or chemicals, through direct targeting of TrxRs or their substrates or protein interactors. To update the involvement of overactivation/dysfunction of TrxRs in various pathological conditions, human diseases associated with TrxRs genes were critically summarized by publicly available genome-wide association study (GWAS) catalogs and literature. The pieces of evidence presented here justify why TrxR is recognized as one of the most critical clinical targets and the growing current interest in developing molecules capable of interfering with the functions of TrxR enzymes.

Thioredoxin 1 is required for stress granule assembly upon arsenite-induced oxidative stress

Arsenic is a major water pollutant and health hazard, leading to acute intoxication and, upon chronic exposure, several diseases including cancer development. Arsenic exerts its pronounced cellular toxicity through its trivalent oxide arsenite (ASN), which directly inhibits numerous proteins including Thioredoxin 1 (Trx1), and causes severe oxidative stress. Cells respond to arsenic by inhibition of protein synthesis and subsequent assembly of stress granules (SGs), cytoplasmic condensates of stalled mRNAs, translation factors and RNA-binding proteins. The biological role of SGs is diverse and not completely understood; they are important for regulation of cell signaling and survival under stress conditions, and for adapting de novo protein synthesis to the protein folding capacity during the recovery from stress. In this study, we identified Trx1 as a novel component of SGs. Trx1 is required for the assembly of ASN-induced SGs, but not for SGs induced by energy deprivation or heat shock. Importantly, our results show that Trx1 is essential for cell survival upon acute exposure to ASN, through a mechanism that is independent of translation inhibition.

Mild microwave ablation combined with HSP90 and TGF‑β1 inhibitors enhances the therapeutic effect on osteosarcoma

Osteosarcoma is the most common malignant bone tumour and the second leading cause of cancer-related death in children and adolescents. Microwave ablation has an excellent therapeutic effect on bone tumours by instantaneously increasing the temperature in the tumour; however, there is a risk of damaging the surrounding healthy tissues by exposure to a high temperature when the treatment power is too large. In the present study, two anti-tumour reagents, a heat shock protein 90 (HSP90) inhibitor (PF-04929113) and a transforming growth factor-β1 (TGF-β1) inhibitor (SB-525334) were employed to enhance the therapeutic effect of mild-power microwave ablation. It was revealed that microwaving to 48°C combined with HSP90 and TGF-β1 inhibitors significantly increased the apoptotic rate of VX2 cells. The same results were observed during in vivo experiments using New Zealand rabbits to model osteosarcoma. In addition, the results indicated that the expression of cytochrome c, caspase-3 and caspase-9 were upregulated in response to the treatment, which indicated that the mitochondrial apoptotic signalling pathway had been activated. These findings may provide a novel strategy for the development of microwave ablation in osteosarcoma treatment, which could effectively kill tumour cells without damaging the surrounding normal tissues.

Neuroprotective effects of notoginsenoside R1 by upregulating Trx-1 on acrylamide-induced neurotoxicity in PC12

Acrylamide (ACR) is a water-soluble chemical that is commonly used in chemical and cosmetic manufacture. Many studies have been carried out to investigate the neurotoxicity mechanisms of ACR, resulting in oxidative stress and nerve damages. One of the commonly used traditional Chinese medicines is notoginsenoside R1 (NR1). However, its mitochondrial-mediated apoptotic effect caused in ACR-induced neurotoxicity has not been reported. Our results have shown that NR1 resisted the neurotoxicity induced by ACR by upregulating the levels of thioredoxin-1 (Trx-1) in Rat adrenal chromaffin cell tumor (PC12) cells. NR1 inhibited the increase in levels of Bax, caspase-9, and caspase-3, which was instigated by ACR. Moreover, NR1 inhibited the decrease in levels of B-cell lymphoma 2 and Trx-1 induced by ACR. The downregulation of Trx-1 aggravated the mitochondrial-mediated apoptosis and increased the expression of the above molecules, which was induced by ACR. In contrast, overexpression of Trx-1 attenuated the mitochondrial-mediated apoptosis and inhibited the expression of the mentioned molecules induced by ACR. Our results suggested that NR1 protected ACR-induced mitochondrial apoptosis by upregulating Trx-1.

The role of thioredoxin system in cancer: strategy for cancer therapy

PURPOSE

Cancer, a major public health problem, exhibits significant redox alteration. Thioredoxin (Trx) system, including Trx and Trx reductase (TrxR), as well as Trx-interacting protein (TXNIP) play important roles in controlling the cellular redox balance in cancer cells. In most cancers, Trx and TrxR are usually overexpressed and TXNIP is underexpressed. In recent years, some agents targeting Trx, TrxR, and TXNIP were used to explore a therapy approach for cancer patients.

METHODS

A systematic search of PMC and the PubMed Database was conducted to summarize the potential of Trx system inhibitors for cancer treatment.

RESULTS

In this article, we first summarize the functions of Trx, TrxR, and TXNIP in cancers. We also review some small molecule inhibitors of Trx/TrxR and D-allose (TXNIP inducer) and discuss their antitumor mechanisms. We highlight the combined inhibition of Trx system and GSH system in cancer therapy. We expect that a highly specific and selective antitumor agent with no cytotoxicity on human normal cells could be developed in the future.

CONCLUSION

In conclusion, Trx system may be very promising for clinical therapy of cancer in the future.

Pharmacological levels of hydrogen sulfide inhibit oxidative cell injury through regulating the redox state of thioredoxin

Hydrogen sulfide (H₂S) is a gaseous mediator with multifaceted biological activities. It has anti-inflammatory and anti-oxidative effects. Currently, the mechanisms are not fully understood. Given that Trx/ASK1/P38 signaling pathway mediates many oxidative cell responses, we tested whether and how H₂S affected this pathway. Exposure of podocytes to Adriamycin (ADR), an antitumor drug, led to a P38-mediated oxidative cell injury, as evidenced by the increased protein carbonylation, oxidative activation of P38, and prevention of the cell death by antioxidants, NADPH oxidase inhibitor and P38 inhibitor. In the presence of H₂S donor NaHS, however, the podocyte injury was largely prevented. NaHS also significantly prevented cell death elicited by H₂O₂, menadione, and thioredoxin (Trx) inhibitors. These effects of H₂S were also associated with a potent inhibition of P38. Further analysis revealed that H₂S did not affect the protein level of TXNIP and Trx, two pivotal regulators of ASK1/P38 activation, but it promoted the dissociation of Trx from TXNIP. Moreover, it disrupted the H₂O₂-initiated polymerization of Trx and converted Trx from the oxidized to the reduced form. In HepG2 cells, inhibition of H₂S-producing enzyme cystathionine γ-lyase (CSE) increased Trx oxidation, promoted Trx binding to TXNIP and exaggerated cell injury caused by Trx inhibition. Collectively, our results indicate that H₂S exerted its antioxidative effects through the regulation of the redox state of Trx and interference with Trx/ASK1/P38 signaling pathway. Given the importance of the pathway in the mediation of multiple oxidative cell responses, our study thus provides novel mechanistic insight into the action of H₂S.

Environmental arsenic exposure: From genetic susceptibility to pathogenesis

More than 200 million people in 70 countries are exposed to arsenic through drinking water. Chronic exposure to this metalloid has been associated with the onset of many diseases, including cancer. Epidemiological evidence supports its carcinogenic potential, however, detailed molecular mechanisms remain to be elucidated. Despite the global magnitude of this problem, not all individuals face the same risk. Susceptibility to the toxic effects of arsenic is influenced by alterations in genes involved in arsenic metabolism, as well as biological factors, such as age, gender and nutrition. Moreover, chronic arsenic exposure results in several genotoxic and epigenetic alterations tightly associated with the arsenic biotransformation process, resulting in an increased cancer risk. In this review, we: 1) review the roles of inter-individual DNA-level variations influencing the susceptibility to arsenic-induced carcinogenesis; 2) discuss the contribution of arsenic biotransformation to cancer initiation; 3) provide insights into emerging research areas and the challenges in the field; and 4) compile a resource of publicly available arsenic-related DNA-level variations, transcriptome and methylation data. Understanding the molecular mechanisms of arsenic exposure and its subsequent health effects will support efforts to reduce the worldwide health burden and encourage the development of strategies for managing arsenic-related diseases in the era of personalized medicine.

EF24 induces ROS-mediated apoptosis via targeting thioredoxin reductase 1 in gastric cancer cells

Gastric cancer (GC) is one of the leading causes of cancer mortality in the world, and finding novel agents for the treatment of advanced gastric cancer is of urgent need. Diphenyl difluoroketone (EF24), a molecule having structural similarity to curcumin, exhibits potent anti-tumor activities by arresting cell cycle and inducing apoptosis. Although EF24 demonstrates potent anticancer efficacy in numerous types of human cancer cells, the cellular targets of EF24 have not been fully defined. We report here that EF24 may interact with the thioredoxin reductase 1 (TrxR1), an important selenocysteine (Sec)-containing antioxidant enzyme, to induce reactive oxygen species (ROS)-mediated apoptosis in human gastric cancer cells. By inhibiting TrxR1 activity and increasing intracellular ROS levels, EF24 induces a lethal endoplasmic reticulum stress in human gastric cancer cells. Importantly, knockdown of TrxR1 sensitizes cells to EF24 treatment. In vivo, EF24 treatment markedly reduces the TrxR1 activity and tumor cell burden, and displays synergistic lethality with 5-FU against gastric cancer cells. Targeting TrxR1 with EF24 thus discloses a previously unrecognized mechanism underlying the biological activity of EF24, and reveals that TrxR1 is a good target for gastric cancer therapy.

The Natural Diterpenoid Isoforretin A Inhibits Thioredoxin-1 and Triggers Potent ROS-Mediated Antitumor Effects

Aberrant expression of thioredoxin 1 (Trx1) plays an important role in cancer initiation and progression and has gained attention as an anticancer drug target. Here we report that the recently discovered natural diterpenoid isoforretin A (IsoA) significantly inhibits Trx1 activity and mediates anticancer effects in multiple preclinical settings. The inhibitory effect of IsoA was antagonized by free radical scavengers polyethylene glycol-catalase, polyethylene glycol superoxide dismutase, thiol-based antioxidants N-acetylcysteine and glutathione. Mass spectrometry analysis revealed that the mechanism of action was based on direct conjugation of IsoA to the Cys32/Cys35 residues of Trx1. This conjugation event attenuated reversible thiol reduction of Trx1, leading to ROS accumulation and a broader degradation of thiol redox homeostasis in cancer cells. Extending these in vitro findings, we documented that IsoA administration inhibited the growth of HepG2 tumors in a murine xenograft model of hepatocellular carcinoma. Taken together, our findings highlight IsoA as a potent bioactive inhibitor of Trx1 and a candidate anticancer natural product. Cancer Res; 77(4); 926-36. ©2016 AACR.

In Vivo and In Vitro Arsenic Exposition Induces Oxidative Stress in Anterior Pituitary Gland

Inorganic arsenic (iAs) is at the top of toxic metalloids. Inorganic arsenic-contaminated water consumption is one of the greatest environmental health threats worldwide. Human iAs exposure has been associated with cancers of several organs, neurological disorders, and reproductive problems. Nevertheless, there are no reports describing how iAs affects the anterior pituitary gland. The aim of this study was to investigate the mechanisms involved in iAs-mediated anterior pituitary toxicity both in vivo and in vitro. We showed that iAs administration (from 5 to 100 ppm) to male rats through drinking water increased messenger RNA expression of several oxidative stress-responsive genes in the anterior pituitary gland. Serum prolactin levels diminished, whereas luteinizing hormone (LH) levels were only affected at the higher dose tested. In anterior pituitary cells in culture, 25 µmol/L iAs significantly decreased prolactin release in a time-dependent fashion, whereas LH levels remained unaltered. Cell viability was significantly reduced mainly by apoptosis evidenced by morphological and phosphatidylserine externalization studies. This process is characterized by early depolarization of mitochondrial membrane potential and increased levels of reactive oxygen species. Expression of some key oxidative stress-responsive genes, such as heme oxygenase-1 and metallothionein-1, was also stimulated by iAs exposure. The antioxidant N-acetyl cysteine prevented iAs-induced effects on the expression of oxidative stress markers, prolactin release, and apoptosis. In summary, the present work demonstrates for the first time that iAs reduces prolactin release both in vivo and in vitro and induces apoptosis in anterior pituitary cells, possibly resulting from imbalanced cellular redox status.

Low-level sodium arsenite induces apoptosis through inhibiting TrxR activity in pancreatic β-cells

In our previous study, we reported that sodium arsenite induced ROS-dependent apoptosis through lysosomal-mitochondrial pathway in pancreatic β-cells. Since the thioredoxin (Trx) system is the key antioxidant factor in mammalian cells, we investigate whether the inhibition of Trx system contributes to sodium arsenite-induced apoptosis in this study. After treatment with low-level (0.25-1μM) sodium arsenite for 96h, the thioredoxin reductase (TrxR) activity was decreased significantly in pancreatic INS-1 cells. Following with the inactivation of TrxR, ASK1 was released from combining with Trx, which was evidenced by increased levels of ASK1 in sodium arsenite-treated INS-1 cells. Subsequently, activated ASK1 accelerated the expression of proapoptotic protein Bax and reduced the expression of anti-apoptic protein Bcl-2. Finally, low-level sodium arsenite induced apoptosis via caspase-3 in INS-1 cells. Knockdown of ASK1 alleviated sodium arsenite-induced apoptosis. In summary, the precise molecular mechanisms through which arsenic is related to diabetes have not been completely elucidated, inactivation of Trx system might provide insights into the underlying mechanisms at the environmental exposure levels.

Arsenic trioxide-induced cytotoxicity in small cell lung cancer via altered redox homeostasis and mitochondrial integrity

Arsenic trioxide (ATO) has demonstrated anticancer activity in different malignancies, especially acute promyelocytic leukemia, with a wide array of putative mechanisms. In this study, we aimed to elucidate the activity and mechanisms of ATO in small cell lung cancer (SCLC). A panel of SCLC cell lines (H841, DMS79, H526, H69 and H187) was employed to demonstrate the activity of ATO. Cell viability, apoptosis and mitochondrial membrane depolarization were assessed. Western blotting was performed to determine the alteration of pro-apoptotic and anti-apoptotic mediators. Reactive oxygen species (ROS) (hydrogen peroxide and superoxide) and intracellular glutathione (GSH) were measured. Antioxidants, N-acetyl-L-cysteine (NAC) and butylated hydroxyanisole (BHA), were applied to restore GSH content and reduce production of ROS. All SCLC cell lines were relatively sensitive to ATO with IC50 values below 10 µM. ATO induced cell death mainly through apoptosis in H841 cells in a dose-dependent manner. Hydrogen peroxide was the major ROS in SCLC cells induced by ATO. Along with GSH depletion and Bcl-2 downregulation, mitochondrial membrane permeabilization was enhanced, followed by release of AIF and SMAC from mitochondria to initiate different cell death pathways. NAC reversed cell death and molecular changes induced by ATO via restoring GSH and reducing ROS content. BHA inhibited hydrogen peroxide production completely and partially restored GSH content accounting for partial reversal of cell inhibition and mitochondrial dysfunction. Nonetheless, ATO reduced both reduced and oxidized form of thioredoxin 1 (Trx1) with no effect on Trx1 redox potential. ATO led to cell death in SCLC mainly through mitochondrial dysfunction, resulting from altered cellular redox homeostasis, namely, hydrogen peroxide generation, GSH depletion and Trx1 downregulation.

Reactive oxygen species, glutathione, and thioredoxin influence suberoyl bishydroxamic acid-induced apoptosis in A549 lung cancer cells

Suberoyl bishydroxamic acid (SBHA) as a histone deacetylase (HDAC) inhibitor can induce apoptosis through the formation of reactive oxygen species (ROS). However, there is no report about the regulation of ROS and antioxidant enzymes in SBHA-treated lung cancer cells. Here, we investigated the toxicological effects of SBHA on the regulations of ROS, glutathione (GSH), and antioxidant enzymes, especially thioredoxin (Trx) in A549 lung cancer cells. SBHA inhibited the growth of A549 cells in time- and dose-dependent manners, and it induced apoptosis which accompanied by the loss of mitochondrial membrane potential (MMP; ΔΨm). SBHA significantly increased ROS levels including O2 (•-) level at 72 h whereas it decreased ROS levels at the early time points (30 min to 3 h). SBHA also induced GSH depletion at 24 and 72 h. N-acetyl cysteine (NAC; a well-known antioxidant) prevented apoptotic cell death and GSH depletion via decreasing ROS in SBHA-treated A549 cells. In addition, SBHA changed the levels of antioxidant-related proteins, especially Trx1. The expression and activity of Trx1 in A549 cells were reduced by SBHA. While the downregulation of Trx1 enhanced cell death, ROS level, and GSH depletion in SBHA-treated A549 cells, the overexpression of Trx1 decreased ROS level in these cells without the prevention of cell death and GSH depletion. In conclusion, SBHA-induced A549 cell death was influenced by changes in ROS and GSH levels. The basal status of Trx1 among other antioxidant proteins was closely correlated with the survival of A549 cells.

Adiponectin induces apoptosis in hepatocellular carcinoma through differential modulation of thioredoxin proteins

Adiponectin blocks hepatocellular carcinoma (HCC) progression by inducing cell apoptosis through the modulation of C-Jun N-terminal kinase and mammalian target of rapamycin. However, the precise upstream signaling pathways or molecules remain elusive. In the present study, we analyzed the role of antioxidant protein thioredoxin (Trx) in adiponectin-induced apoptosis in HCC. Adiponectin treatment decreased the viabilities of both HepG2 and Huh7 HCC cells accompanied by increased accumulation of intracellular reactive oxygen species, as evidenced by 2',7'-dichlorodihydrofluorescein diacetate staining. Pretreatment of these cells with the deoxidant N-acetylcysteine blocked the inhibitory effect of adiponectin. Levels of Trx2 protein in both HCC cells were significantly decreased, and the level of Trx1 was significantly inhibited in Huh7 cells while unchanged in HepG2 cells. However, the redox state of Trx1 was altered from reduced to the oxidized form following adiponectin treatment in HepG2 cells. Overexpression of both Trx proteins rescued adiponectin-induced cell apoptosis, whereas mutated Trx proteins were less effective. Further analysis suggested that both ASK1 and JNK signaling are involved in this process. Trx1 and Trx2 proteins also manifested protective effects on HCC cells in response to adiponectin treatment in a xenograft tumor model. Furthermore, high levels of Trx proteins and low adiponectin expression levels were found in primary human HCC samples compared with paracancerous tissues. These results suggest that Trx proteins play important roles in mediating adiponectin-induced HCC cell apoptosis, thus providing new insights into the pathogenesis of HCC and identifying adiponectin and Trx proteins as potential combinational therapeutic targets for the treatment of HCC.

Is trichloroacetic acid an insufficient sample quencher of redox reactions?

The global protein thiol pool has been reported to play a major role in the defense against oxidative stress as a redox buffer similar to glutathione. The present study uses a novel method to visualize cellular changes of the global protein thiol pool in response to induced oxidative stress. Unexpectedly, the results showed an uneven distribution of protein thiols in resting cells with no apparent change in their level or distribution in response to diamide as has been reported previously. Further analysis revealed that thiol pool oxidation is artificially high due to insufficient activity of the widely used sample quencher trichloroacetic acid (TCA). This suggests that previously published articles based on TCA as a quencher should be interpreted with caution as TCA could have caused similar artifacts. Overall, the results presented here question the major role for the global thiol pool in the defense against oxidative stress. Instead our hypothesis is that the fraction of proteins involved in response to oxidative stress is much smaller than previously anticipated in support of a fine-tuned cell signaling by redox regulation.

Emerging roles for the pro-oncogenic anterior gradient-2 in cancer development

Clinical studies have defined the core 'genetic blueprint' of a cancer cell, but this information does not necessarily predict the cancer phenotype. Signalling hubs that mediate such phenotype have been identified largely using OMICS platforms that measure dynamic molecular changes within the cancer cell landscape. The pro-oncogenic protein anterior gradient 2 (AGR2) is a case in point; AGR2 has been shown using a range of expression platforms to be involved in asthma, inflammatory bowel disease, cell transformation, cancer drug resistance and metastatic growth. AGR2 protein is also highly overexpressed in a diverse range of human cancers and can be secreted and detected in extracellular fluids, thus representing a compelling pro-oncogenic signalling intermediate in human cancer. AGR2 belongs to the protein disulphide isomerase family with all the key features of an endoplasmic reticulum-resident protein-this gives clues into how it might function as an oncoprotein through the regulation of protein folding, maturation and secretion that can drive metastatic cell growth. In this review, we will describe the known aspects of AGR2 molecular biology, including gene structure and regulation, emerging protein interaction networks and how its subcellular localization mediates its biological functions. We will finally review the cases of AGR2 expression in human cancers, the pathophysiological consequences of AGR2 overexpression, its potential role as a tumour biomarker that predicts the response to therapy and how the AGR2 pathway might form the basis for drug discovery programmes aimed at targeting protein folding/maturation pathways that mediate secretion and metastasis.

Mitochondrial glutaminase release contributes to glutamate-mediated neurotoxicity during human immunodeficiency virus-1 infection

Human immunodeficiency virus (HIV) induces a neurological disease culminating in frank dementia referred to as HIV-associated dementia (HAD). Neurotoxins from HIV-1-infected and activated mononuclear phagocytes contribute to the neuropathogenesis of HAD. Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS) and functions through activation of multiple receptors. Excessive glutamate production by HIV-infected macrophages in HAD may contribute to neuronal injury. Our previous studies have suggested that mitochondrial glutaminase is responsible for the excessive production of glutamate. However, how HIV-1 infection regulates glutamate over-production remains unclear. In this study, we propose that HIV infection-induced oxidative stress contributes to mitochondrial glutaminase release, which results in the excessive production of glutamate and subsequent neuronal injury. We collected conditioned media from HIV-1 infected macrophages and analyzed glutamate concentration in the media by RP-HPLC, and found that the cyclosporine A (CsA), an inhibitor of HIV-1 replication and mitochondrial permeability transition pore, and N-acetylcysteine (NAC), a remover of reactive oxygen species (ROS), not only blocked the excessive glutamate production, but also decreased the glutamate-mediated neurotoxicity. In addition, HIV-infection-induced ROS generation was accompanied with the excessive glutamate production, suggesting that oxidative stress was involved in glutamate regulation. Using the isolated rat brain mitochondria as an ex vivo model and over-expressing GFP-glutaminase fusion protein in mammalian cells as a cell model, we confirm oxidative stress-mediated mitochondrial glutaminase release during HIV-1 infection contributes to glutamate over-production and the subsequent neurotoxicity. These results may provide insight into HAD pathogenesis and a therapeutic strategy for HAD treatment.

Thioredoxin-1 contributes to protection against DON-induced oxidative damage in HepG2 cells

Leucocytes are susceptible to the toxic effects of deoxynivalenol (DON), which is a trichothecene mycotoxin produced by a number of fungi including Fusarium species. One mechanism of action is mediated by reactive oxygen species (ROS). The liver is an important target for toxicity caused by foreign compounds including mycotoxins. On the other hand, little is known about the influence of the redox state on hepatocytes treated with DON. The present study investigated the effect of DON on the cytosolic redox state and antioxidative system in the human hepatoma cell line HepG2. The cell viability of human monocyte cell line THP-1 or leukemia cell line KU812 treated with 2.5 and 5 μmol/l DON were significantly reduced. However, HepG2 cells showed no toxic effects under the same conditions and did not exhibit an increased oxidative state. Further experiments showed that thioredoxin-1 (Trx-1) protein levels but not glutathione increased in the cells treated with 10 μmol/l DON. In addition, the enhancement of Trx-1 content was repressed by antioxidants. These results suggest that DON-induced accumulation of Trx-1 in HepG2 cells plays one of the key roles in protection against cytotoxicity caused by DON and that the mechanism may be mediated by the antioxidant properties of Trx-1.

Suppression of TG-interacting factor sensitizes arsenic trioxide-induced apoptosis in human hepatocellular carcinoma cells

HCC (hepatocellular carcinoma) is among the most common and lethal cancers worldwide with a poor prognosis mainly due to a high recurrence rate and chemotherapy resistance. ATO (arsenic trioxide) is a multi-target drug that has been effectively used as an anticancer drug in acute promyelocytic leukaemia. However, a Phase II trial involving patients with HCC indicates that the use of arsenic as a single agent is not effective against HCC. TGIF (TG-interacting factor) is a transcriptional co-repressor that interferes with TGF-β (transforming growth factor-β) signalling which plays a growth-inhibitory role in HCC. In the present study, we demonstrated that ATO induced hepatocellular apoptosis via TGF-β/Smad signalling and led to downstream induction of p21(WAF1/CIP1) (p21). However, ATO could also induce TGIF expression via a post-transcriptional regulation mechanism to antagonize this effect. Using a biotin-labelled RNA probe pull-down assay and in vivo RNA immunoprecipitation analysis, we identified that HuR (human antigen R) bound to the TGIF mRNA 3'-UTR (3'-untranslated region) and prevented it from degradation. ATO treatment increased the interaction between HuR and TGIF mRNA, and reduction of HuR expression inhibited ATO-induced TGIF expression. Moreover, the EGFR (epidermal growth factor receptor)/PI3K (phosphoinositide 3-kinase)/Akt pathway was shown to mediate the post-transcriptional regulation of TGIF in response to ATO. Finally, we also demonstrated that the down-regulation of TGIF could sensitize ATO-induced HepG2 cell apoptosis. Collectively, we propose that the EGFR/PI3K/Akt pathway may regulate the post-transcriptional regulation of TGIF expression to antagonize ATO-induced apoptosis in HCC. Blockage of the PI3K/Akt pathway or TGIF expression combined with ATO treatment may be a promising strategy for HCC therapy.

Anticancer activity of metal complexes: involvement of redox processes

Cells require tight regulation of the intracellular redox balance and consequently of reactive oxygen species for proper redox signaling and maintenance of metal (e.g., of iron and copper) homeostasis. In several diseases, including cancer, this balance is disturbed. Therefore, anticancer drugs targeting the redox systems, for example, glutathione and thioredoxin, have entered focus of interest. Anticancer metal complexes (platinum, gold, arsenic, ruthenium, rhodium, copper, vanadium, cobalt, manganese, gadolinium, and molybdenum) have been shown to strongly interact with or even disturb cellular redox homeostasis. In this context, especially the hypothesis of "activation by reduction" as well as the "hard and soft acids and bases" theory with respect to coordination of metal ions to cellular ligands represent important concepts to understand the molecular modes of action of anticancer metal drugs. The aim of this review is to highlight specific interactions of metal-based anticancer drugs with the cellular redox homeostasis and to explain this behavior by considering chemical properties of the respective anticancer metal complexes currently either in (pre)clinical development or in daily clinical routine in oncology.

Reprogrammed mouse astrocytes retain a "memory" of tissue origin and possess more tendencies for neuronal differentiation than reprogrammed mouse embryonic fibroblasts

Direct reprogramming of a variety of somatic cells with the transcription factors Oct4 (also called Pou5f1), Sox2 with either Klf4 and Myc or Lin28 and Nanog generates the induced pluripotent stem cells (iPSCs) with marker similarity to embryonic stem cells. However, the difference between iPSCs derived from different origins is unclear. In this study, we hypothesized that reprogrammed cells retain a "memory" of their origins and possess additional potential of related tissue differentiation. We reprogrammed primary mouse astrocytes via ectopic retroviral expression of OCT3/4, Sox2, Klf4 and Myc and found the iPSCs from mouse astrocytes expressed stem cell markers and formed teratomas in SCID mice containing derivatives of all three germ layers similar to mouse embryonic stem cells besides semblable morphologies. To test our hypothesis, we compared embryonic bodies (EBs) formation and neuronal differentiation between iPSCs from mouse embryonic fibroblasts (MEFsiPSCs) and iPSCs from mouse astrocytes (mAsiPSCs). We found that mAsiPSCs grew slower and possessed more potential for neuronal differentiation compared to MEFsiPSCs. Our results suggest that mAsiPSCs retain a "memory" of the central nervous system, which confers additional potential upon neuronal differentiation.

The NRF2-mediated oxidative stress response pathway is associated with tumor cell resistance to arsenic trioxide across the NCI-60 panel

Background

Drinking water contaminated with inorganic arsenic is associated with increased risk for different types of cancer. Paradoxically, arsenic trioxide can also be used to induce remission in patients with acute promyelocytic leukemia (APL) with a success rate of approximately 80%. A comprehensive study examining the mechanisms and potential signaling pathways contributing to the anti-tumor properties of arsenic trioxide has not been carried out.

Methods

Here we applied a systems biology approach to identify gene biomarkers that underlie tumor cell responses to arsenic-induced cytotoxicity. The baseline gene expression levels of 14,500 well characterized human genes were associated with the GI₅₀ data of the NCI-60 tumor cell line panel from the developmental therapeutics program (DTP) database. Selected biomarkers were tested in vitro for the ability to influence tumor susceptibility to arsenic trioxide.

Results

A significant association was found between the baseline expression levels of 209 human genes and the sensitivity of the tumor cell line panel upon exposure to arsenic trioxide. These genes were overlayed onto protein-protein network maps to identify transcriptional networks that modulate tumor cell responses to arsenic trioxide. The analysis revealed a significant enrichment for the oxidative stress response pathway mediated by nuclear factor erythroid 2-related factor 2 (NRF2) with high expression in arsenic resistant tumor cell lines. The role of the NRF2 pathway in protecting cells against arsenic-induced cell killing was validated in tumor cells using shRNA-mediated knock-down.

Conclusions

In this study, we show that the expression level of genes in the NRF2 pathway serve as potential gene biomarkers of tumor cell responses to arsenic trioxide. Importantly, we demonstrate that tumor cells that are deficient for NRF2 display increased sensitivity to arsenic trioxide. The results of our study will be useful in understanding the mechanism of arsenic-induced cytotoxicity in cells, as well as the increased applicability of arsenic trioxide as a chemotherapeutic agent in cancer treatment.

Japanese encephalitis virus down-regulates thioredoxin and induces ROS-mediated ASK1-ERK/p38 MAPK activation in human promonocyte cells

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, causes severe neurological disease with high mortality. Molecular mechanisms of JEV pathogenesis such as upstream apoptotic processes and pathways are not yet completely resolved or understood. In this study, JEV replication in human promonocyte cells induced time-dependent apoptosis and activated virus dose-dependent caspases 3, 8 and 9. Proteomic analysis demonstrated up- and down-regulated (more or less than 1.5-fold) proteins in JEV-infected promonocyte cells. Biological process categorization showed processes of antioxidation, free radical removal, and sulfur redox metabolism entailed many identified up- and down-regulated proteins. Down-regulation of thioredoxin, confirmed by using Western blotting, was involved in the apoptosis process of the oxidative stress response pathway. JEV infection caused increased intracellular ROS production and activation of ASK1-ERK/p38 MAPK signaling. ERK/p38 MAPK inhibitor PD98059 treatment definitely suppressed this apoptosis. Down-regulation of thioredoxin, increased intracellular ROS, and activation of ASK1-ERK/p38 MAPK signaling all were associated with JEV-induced apoptosis. These results are suggestive of an oxidative stress-pathway as a key element of JE pathogenesis.

Low 8-oxo-7,8-dihydro-2'-deoxyguanosine levels and influence of genetic background in an Andean population exposed to high levels of arsenic

BACKGROUND

Arsenic (As) causes oxidative stress through generation of reactive oxygen species. 8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a sensitive marker of oxidative DNA damage, has been associated with As exposure in some studies, but not in others, possibly due to population-specific genetic factors.

OBJECTIVES

To evaluate the association between As and 8-oxodG in urine in a population with a low urinary monomethylated As (%MMA) and high dimethylated As (%DMA), as well as the genetic impact on (a) 8-oxodG concentrations and (b) the association between As and 8-oxodG.

MATERIALS AND METHODS

Women (N=108) in the Argentinean Andes were interviewed and urine was analyzed for arsenic metabolites (ICPMS) and 8-oxodG (LC-MS/MS). Twenty-seven polymorphisms in genes related to oxidative stress and one in As(+III)methyltransferase (AS3MT) were studied.

RESULTS

Median concentration of 8-oxodG was 4.7 nmol/L (adjusted for specific weight; range 1.6-13, corresponding to 1.7 microg/g creatinine, range 0.57-4.8) and of total urinary As metabolites (U-As) 290 microg/L (range 94-720; 380 microg/g creatinine, range 140-1100). Concentrations of 8-oxodG were positively associated with %MMA (strongest association, p=0.013), and weakly associated with U-As (positively) and %DMA (negatively). These associations were strengthened when taking ethnicity into account, possibly reflecting genetic differences in As metabolism and genes regulating oxidative stress and DNA maintenance. A genetic influence on 8-oxodG concentrations was seen for polymorphisms in apurinic/apyrimidinic endonuclease 1 (APEX1), DNA-methyltransferases 1 and 3b (DNMT1, DNMT3B), thioredoxin reductase 1 (TXNRD1) and 2 (TXNRD2) and glutaredoxin (GLRX).

CONCLUSION

Despite high As exposure, the concentrations of 8-oxodG in this population were low compared with other As-exposed populations studied. The strongest association was found for %MMA, stressing that some inconsistencies between As and 8-oxodG partly depend on population variations in As metabolism. We found evidence of genetic impact on 8-oxodG concentrations.

Selenite induces redox-dependent Bax activation and apoptosis in colorectal cancer cells

Emerging evidence suggests that selenium has chemotherapeutic potential by inducing cancer cell apoptosis with minimal side effects to normal cells. However, the mechanism by which selenium induces apoptosis is not well understood. We have investigated the role of Bax, a Bcl-2 family protein and a critical regulator of the mitochondrial apoptotic pathway, in selenite-induced apoptosis in colorectal cancer cells. We found that supranutritional doses of selenite could induce typical apoptosis in colorectal cancer cells in vitro and in xenograft tumors. Selenite triggers a conformational change in Bax, as detected by the 6A7 antibody, and leads to Bax translocation into the mitochondria, where Bax forms oligomers to mediate cytochrome c release. Importantly, we show that the two conserved cysteine residues of Bax seem to be critical for sensing the intracellular ROS to initiate Bax conformational changes and subsequent apoptosis. Our results show for the first time that selenite can activate the apoptotic machinery through redox-dependent activation of Bax and further suggest that selenite could be useful in cancer therapy.

In vitro glutaminase regulation and mechanisms of glutamate generation in HIV-1-infected macrophage

Mononuclear phagocyte (MP, macrophages and microglia) dysfunction plays a significant role in the pathogenesis of HIV-1-associated dementia (HAD) through the production and release of soluble neurotoxic factors including glutamate. Glutamate production is greatly increased following HIV-1 infection of cultured MP, a process dependent upon the glutamate-generating enzyme glutaminase. Glutaminase inhibition was previously found to significantly decrease macrophage-mediated neurotoxicity. Potential mechanisms of glutaminase-mediated excitotoxicity including enzyme up-regulation, increased enzyme activity and glutaminase localization were investigated in this report. RNA and protein analysis of HIV-infected human primary macrophage revealed up-regulation of the glutaminase isoform GAC, yet identified no changes in the kidney-type glutaminase isoform over the course of infection. Glutaminase is a mitochondrial protein, but was found to be released into the cytosol and extracellular space following infection. This released enzyme is capable of rapidly converting the abundant extracellular amino acid glutamine into excitotoxic levels of glutamate in an energetically favorable process. These findings support glutaminase as a potential component of the HAD pathogenic process and identify a possible therapeutic avenue for the treatment of neuroinflammatory states such as HAD.