Oxidative stress and thioredoxin-interacting protein promote intravasation of melanoma cells

Redox pathways in melanoma

Cases of melanoma are doubling every 12 years, and in stages III and IV, the disease is associated with high mortality rates concomitant with unresectable metastases and therapeutic drug resistance. Despite some advances in treatment success, there is a marked need to understand more about the pathology of the disease. The present review provides an overview of how melanoma cells use and modulate redox pathways to facilitate thiol homeostasis and melanin biosynthesis and describes plausible redox targets that may improve therapeutic approaches in managing malignant disease and metastasis. Melanotic melanoma has some unique characteristics. Making melanin requires a considerable dedication of cellular energy resources and utilizes glutathione and glutathione transferases in certain steps in the biosynthetic pathway. Melanin is an antioxidant but is also functionally important in hematopoiesis and influential in various aspects of host immune responses, giving it unique characteristics. Together with other redox traits that are specific to melanoma, a discussion of possible therapeutic approaches is also provided.

Involvement of redox signalling in tumour cell dormancy and metastasis

Decades of research on oncogene-driven carcinogenesis and gene-expression regulatory networks only started to unveil the complexity of tumour cellular and molecular biology. This knowledge has been successfully implemented in the clinical practice to treat primary tumours. In contrast, much less progress has been made in the development of new therapies against metastasis, which are the main cause of cancer-related deaths. More recently, the role of epigenetic and microenviromental factors has been shown to play a key role in tumour progression. Free radicals are known to communicate the intracellular and extracellular compartments, acting as second messengers and exerting a decisive modulatory effect on tumour cell signalling. Depending on the cellular and molecular context, as well as the intracellular concentration of free radicals and the activation status of the antioxidant system of the cell, the signalling equilibrium can be tilted either towards tumour cell survival and progression or cell death. In this regard, recent advances in tumour cell biology and metastasis indicate that redox signalling is at the base of many cell-intrinsic and microenvironmental mechanisms that control disseminated tumour cell fate and metastasis. In this manuscript, we will review the current knowledge about redox signalling along the different phases of the metastatic cascade, including tumour cell dormancy, making emphasis on metabolism and the establishment of supportive microenvironmental connections, from a redox perspective.

Redox-Related Proteins in Melanoma Progression

Melanoma is the most aggressive type of skin cancer. Despite the available therapies, the minimum residual disease is still refractory. Reactive oxygen and nitrogen species (ROS and RNS) play a dual role in melanoma, where redox imbalance is involved from initiation to metastasis and resistance. Redox proteins modulate the disease by controlling ROS/RNS levels in immune response, proliferation, invasion, and relapse. Chemotherapeutics such as BRAF and MEK inhibitors promote oxidative stress, but high ROS/RNS amounts with a robust antioxidant system allow cells to be adaptive and cooperate to non-toxic levels. These proteins could act as biomarkers and possible targets. By understanding the complex mechanisms involved in adaptation and searching for new targets to make cells more susceptible to treatment, the disease might be overcome. Therefore, exploring the role of redox-sensitive proteins and the modulation of redox homeostasis may provide clues to new therapies. This study analyzes information obtained from a public cohort of melanoma patients about the expression of redox-generating and detoxifying proteins in melanoma during the disease stages, genetic alterations, and overall patient survival status. According to our analysis, 66% of the isoforms presented differential expression on melanoma progression: NOS2, SOD1, NOX4, PRX3, PXDN and GPX1 are increased during melanoma progression, while CAT, GPX3, TXNIP, and PRX2 are decreased. Besides, the stage of the disease could influence the result as well. The levels of PRX1, PRX5 and PRX6 can be increased or decreased depending on the stage. We showed that all analyzed isoforms presented some genetic alteration on the gene, most of them (78%) for increased mRNA expression. Interestingly, 34% of all melanoma patients showed genetic alterations on TRX1, most for decreased mRNA expression. Additionally, 15% of the isoforms showed a significant reduction in overall patient survival status for an altered group (PRX3, PRX5, TR2, and GR) and the unaltered group (NOX4). Although no such specific antioxidant therapy is approved for melanoma yet, inhibitors or mimetics of these redox-sensitive proteins have achieved very promising results. We foresee that forthcoming investigations on the modulation of these proteins will bring significant advances for cancer therapy.

ROS Pleiotropy in Melanoma and Local Therapy with Physical Modalities

Metabolic energy production naturally generates unwanted products such as reactive oxygen species (ROS), causing oxidative damage. Oxidative damage has been linked to several pathologies, including diabetes, premature aging, neurodegenerative diseases, and cancer. ROS were therefore originally anticipated as an imperative evil, a product of an imperfect system. More recently, however, the role of ROS in signaling and tumor treatment is increasingly acknowledged. This review addresses the main types, sources, and pathways of ROS in melanoma by linking their pleiotropic roles in antioxidant and oxidant regulation, hypoxia, metabolism, and cell death. In addition, the implications of ROS in various physical therapy modalities targeting melanoma, such as radiotherapy, electrochemotherapy, hyperthermia, photodynamic therapy, and medical gas plasma, are also discussed. By including ROS in the main picture of melanoma skin cancer and as an integral part of cancer therapies, a greater understanding of melanoma cell biology is presented, which ultimately may elucidate additional clues on targeting therapy resistance of this most deadly form of skin cancer.

Low expression of the PPARγ-regulated gene thioredoxin-interacting protein accompanies human melanoma progression and promotes experimental lung metastases

The thioredoxin system plays key roles in regulating cancer cell malignancy. Here we identify the Thioredoxin-interacting protein (TXNIP) as a gene, which expression is regulated by PPARγ in melanoma cells. We show that high TXNIP expression levels associate with benign melanocytic lesions, with tumor regression in patients on MAP kinase targeted therapy, with decreased proliferation in patients’ melanoma biopsies, and with cell cycle arrest in human melanoma cell lines. In contrast, reduced TXNIP expression associates with advanced melanoma and with disease progression in patients. TXNIP depletion in human melanoma cells altered the expression of integrin beta-3 and the localization of the integrin alpha-v/beta-3 dimer at their surface. Moreover, TXNIP depletion affected human melanoma cell motility and improved their capacity to colonize mouse lungs in an in vivo assay. This study establishes TXNIP as a PPARγ-regulated gene in melanoma cells, thereby suggesting a link between these two proteins both involved in the regulation of cancer and of energy metabolism. It also reveals that the decrease in TXNIP expression, which is observed in advanced patient tumors, likely favors lung metastatic seeding of malignant cells.

TXNIP/TBP-2: A Master Regulator for Glucose Homeostasis

Identification of thioredoxin binding protein-2 (TBP-2), which is currently known as thioredoxin interacting protein (TXNIP), as an important binding partner for thioredoxin (TRX) revealed that an evolutionarily conserved reduction-oxidation (redox) signal complex plays an important role for pathophysiology. Due to the reducing activity of TRX, the TRX/TXNIP signal complex has been shown to be an important regulator for redox-related signal transduction in many types of cells in various species. In addition to its role in redox-dependent regulation, TXNIP has cellular functions that are performed in a redox-independent manner, which largely rely on their scaffolding function as an ancestral α-Arrestin family. Both the redox-dependent and -independent TXNIP functions serve as regulatory pathways in glucose metabolism. This review highlights the key advances in understanding TXNIP function as a master regulator for whole-body glucose homeostasis. The potential for therapeutic advantages of targeting TXNIP in diabetes and the future direction of the study are also discussed.

Sex and Gender Disparities in Melanoma

Worldwide, the total incidence of cutaneous melanoma is higher in men than in women, with some differences related to ethnicity and age and, above all, sex and gender. Differences exist in respect to the anatomic localization of melanoma, in that it is more frequent on the trunk in men and on the lower limbs in women. A debated issue is if-and to what extent-melanoma development can be attributed to gender-specific behaviors or to biologically intrinsic differences. In the search for factors responsible for the divergences, a pivotal role of sex hormones has been observed, although conflicting results indicate the involvement of other mechanisms. The presence on the X chromosome of numerous miRNAs and coding genes playing immunological roles represents another important factor, whose relevance can be even increased by the incomplete X chromosome random inactivation. Considering the known advantages of the female immune system, a different cancer immune surveillance efficacy was suggested to explain some sex disparities. Indeed, the complexity of this picture emerged when the recently developed immunotherapies unexpectedly showed better improvements in men than in women. Altogether, these data support the necessity of further studies, which consider enrolling a balanced number of men and women in clinical trials to better understand the differences and obtain actual gender-equitable healthcare.

BRAFi induced demethylation of miR-152-5p regulates phenotype switching by targeting TXNIP in cutaneous melanoma

Treatment of advanced BRAFV600-mutant melanoma using BRAF inhibitors (BRAFi) eventually leads to drug resistance and selects for highly metastatic tumor cells. We compared the most differentially dysregulated miRNA expression profiles of vemurafenib-resistant and highly-metastatic melanoma cell lines obtained from GEO DataSets. We discovered miR-152-5p was a potential regulator mediating melanoma drug resistance and metastasis. Functionally, knockdown of miR-152-5p significantly compromised the metastatic ability of BRAFi-resistant melanoma cells and overexpression of miR-152-5p promoted the formation of slow-cycling phenotype. Furthermore, we explored the cause of how and why miR-152-5p affected metastasis in depth. Mechanistically, miR-152-5p targeted TXNIP which affected metastasis and BRAFi altered the methylation status of MIR152 promoter. Our study highlights the crucial role of miR-152-5p on melanoma metastasis after BRAFi treatment and holds significant implying that discontinuous dosing strategy may improve the benefit of advanced BRAFV600-mutant melanoma patients.

Hepatic Expression of the Serine Palmitoyltransferase Subunit Sptlc2 Reduces Lipid Droplets in the Liver by Activating VLDL Secretion

Objective

Ceramide is a signaling molecule that contributes to insulin resistance and hepatosteatosis. In the present study, we activated de novo ceramide synthesis by inducing the hepatic expression of Sptlc2 to investigate the role of ceramide in glucose and lipid metabolism.

Methods

We first constructed an adenovirus containing Sptlc2 (AdSptlc2), which encodes a major catalytic subunit of serine palmitoyltransferase (SPT). We then infected hepatocytes and mice fed a regular diet with AdSptlc2 to activate de novo ceramide biosynthesis. The liver-specific effects of ceramide biosynthesis on glucose and lipid metabolism were investigated by measuring changes in insulin signaling, lipid droplet formation, and very low-density lipoprotein (VLDL) secretion.

Results

In HepG2 hepatocytes, adenoviral Sptlc2 expression inhibited insulin signaling and increased ceramide levels via activation of c-Jun N-terminal kinase and serine phosphorylation of insulin receptor substrate 1. In contrast, in mice, AdSptlc2 infection decreased plasma glucose levels by downregulating gluconeogenic genes and increased plasma triglyceride levels by increasing VLDL secretion. In mice infected with AdSptlc2, glucose intolerance and insulin sensitivity improved, while pyruvate utilization via gluconeogenesis decreased.

Conclusion

Hepatic ceramide was found to modulate hepatosteatosis and the insulin response via increased VLDL secretion and inhibition of gluconeogenesis in vivo. Although inhibition of the insulin response was observed in vitro, the compensatory mechanism of relieving ceramide-induced stress and reducing ceramide levels resulted in improvements of glucose and lipid metabolic profiles in vivo. This discrepancy between in vitro and in vivo regulation mechanisms suggests that ceramide plays a role in non-alcoholic fatty liver disease and insulin resistance.

Thioredoxin interacting protein promotes invasion in hepatocellular carcinoma

Background

Considerable evidence suggests that oxidative stress plays an essential role in the progression of hepatocellular carcinoma (HCC). While acquired resistance to oxidative stress is the main driver of aggressive cell phenotype, the underlying mechanisms remain unknown. Here, we tested the hypothesis that elevated expression of Thioredoxin-interacting protein (TXNIP) is a main regulator of the aggressive phenotype in HCC.

Materials and Methods

To test this hypothesis, we measured TXNIP expression levels in 11 HCC cell lines by qPCR and western blotting. In addition, 80 pairs of HCC tissues and matched liver tissues of 73 cases, as well as 11 normal liver tissue samples were examined by immunohistochemistry. Besides, TXNIP expression levels were analyzed by Oncomine Platform in seven independent microarray datasets. Finally, the functional role of TXNIP in HCC was investigated in vitro and in vivo by silencing and overexpression studies.

Results

Our results show that TXNIP expression is significantly increased in HCC compared to non-tumor counterparts (p < 0.0001) as well as to normal (p < 0.0001) and cirrhotic (p < 0.0001) liver tissues. Moreover, stable overexpression of TXNIP in HCC cells (i) significantly increases ROS levels, (ii) induces EMT phenotype, (iii) increases motility, invasion and 3D branching tubulogenesis, (iv) decreases apoptosis, and (v) elevates in vivo metastasis in zebrafish embryos. Finally, we identify sinusoidal/stromal and cytoplasmic TXNIP staining patterns as risk factors for intrahepatic vascular invasion (p:0.0400).

Conclusion

Our results strongly suggest that overexpression of TXNIP has a pivotal role in HCC progression by inducing cell survival, invasion, and metastasis.

Hepatitis B virus X protein promotes hepatocellular carcinoma invasion and metastasis via upregulating thioredoxin interacting protein

Hepatitis B virus X protein (HBx), a multifunctional protein encoded by the X gene of the hepatitis B virus (HBV) is involved in the metastasis of HBV-associated hepatocellular carcinoma (HCC) through various pathways, including upregulating intracellular reactive oxygen species (ROS). Thioredoxin interacting protein (TXNIP) is a key mediator of intracellular ROS, but its function in HBx-mediated metastasis of HBV-associated HCC is elusive. In the present study, HBV-associated HCC tissues with or without metastasis and HepG2 cells were used to study the function of TXNIP in HBx-mediated metastasis of HBV-associated HCC. Initially, the expression levels of TXNIP and HBx in HBV-associated HCC tissues were detected by immunohistochemistry and reverse transcription-quantitative polymerase chain reaction. The results revealed that high expression of TXNIP may be an independent risk factor for metastasis of HBV-associated HCC, and the mRNA levels of TXNIP and HBx were positively associated. Secondly, the association between HBx and TXNIP was investigated using a HBx expression stable cell line, in which HBx expression was induced and controlled by doxycycline. The results demonstrated that HBx may upregulate TXNIP expression in HepG2 cells. Thirdly, the effects of TXNIP and HBx on HepG2 cell migration and invasion were studied by scratch and Matrigel invasion assays, respectively. The results demonstrated that TXNIP overexpression enhanced HepG2 cell migration and invasion. In addition, ectopic expression of HBx promoted HepG2 cell migration and invasion, and this effect may be attenuated by knockdown of TXNIP expression, which indicated that TXNIP may be involved in the process. In summary, the present results demonstrated that TXNIP may be involved in HBx-mediated metastasis of HBV-associated HCC.

Tumour endothelial cells in high metastatic tumours promote metastasis via epigenetic dysregulation of biglycan

Tumour blood vessels are gateways for distant metastasis. Recent studies have revealed that tumour endothelial cells (TECs) demonstrate distinct phenotypes from their normal counterparts. We have demonstrated that features of TECs are different depending on tumour malignancy, suggesting that TECs communicate with surrounding tumour cells. However, the contribution of TECs to metastasis has not been elucidated. Here, we show that TECs actively promote tumour metastasis through a bidirectional interaction between tumour cells and TECs. Co-implantation of TECs isolated from highly metastatic tumours accelerated lung metastases of low metastatic tumours. Biglycan, a small leucine-rich repeat proteoglycan secreted from TECs, activated tumour cell migration via nuclear factor-κB and extracellular signal–regulated kinase 1/2. Biglycan expression was upregulated by DNA demethylation in TECs. Collectively, our results demonstrate that TECs are altered in their microenvironment and, in turn, instigate tumour cells to metastasize, which is a novel mechanism for tumour metastasis.

Expression of thioredoxin-1 (TXN) and its relation with oxidative DNA damage and treatment outcome in adult AML and ALL: A comparative study

OBJECTIVE

Thioredoxin-1 (TXN) is a key element in the elimination of reactive oxygen species as well as activation of tumor suppressor genes and DNA repair enzymes. Several studies showed that TXN was over expressed in solid tumors and this was correlated to poorer prognosis. However, TXN expression has been insufficiently studied, particularly in newly diagnosed adult acute leukemia.

METHODS

This study was designed to evaluate the gene expression of TXN in acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL) adult patients and to investigate its association with oxidative DNA damage. The expression of TXN was analyzed using quantitative reverse transcriptase-polymerase chain reaction while oxidative DNA damage was evaluated by measuring serum 8-hydroxy-2-deoxyguanosine (8-OHdG) by enzyme-linked immunosorbent assay and strand breaks by the comet assay.

RESULTS

We found that TXN was under expressed in both AML and ALL groups (P < 0.001 for both) as compared to the control group. Also TXN expression level was negatively correlated with serum 8-OHdG and tail moment in both AML (P = 0.042 and 0.047, respectively) and ALL (P < 0.001 and P = 0.02, respectively) while it showed no correlation with treatment outcome in either groups.

DISCUSSION

This study suggests that TXN expression is hindered in adult acute leukemia which augments oxidative DNA damage and hence mutagenesis.

CONCLUSION

This study provides a new insight into the pathogenesis of acute leukemia and suggests TXN as a new screening test for the risk for acute leukemia.

Tumor cell intravasation

The process of entering the bloodstream, intravasation, is a necessary step in the development of distant metastases. The focus of this review is on the pathways and molecules that have been identified as being important based on current in vitro and in vivo assays for intravasation. Properties of the vasculature which are important for intravasation include microvessel density and also diameter of the vasculature, with increased intravasation correlating with increased vessel diameter in some tumors. TGFB signaling can enhance intravasation at least in part through induction of EMT, and we discuss other TGFB target genes that are important for intravasation. In addition to TGFB signaling, a number of studies have demonstrated that activation of EGF receptor family members stimulates intravasation, with downstream signaling through PI3K, N-WASP, RhoA, and WASP to induce invadopodia. With respect to proteases, there is strong evidence for contributions by uPA/uPAR, while the roles of MMPs in intravasation may be more tumor specific. Other cells including macrophages, fibroblasts, neutrophils, and platelets can also play a role in enhancing tumor cell intravasation. The technology is now available to interrogate the expression patterns of circulating tumor cells, which will provide an important reality check for the model systems being used. With a better understanding of the mechanisms underlying intravasation, the goal is to provide new opportunities for improving prognosis as well as potentially developing new treatments.

Targeting mitosis-regulating genes in cisplatin-sensitive and -resistant melanoma cells: A live-cell RNAi screen displays differential nucleus-derived phenotypes

Chemoresistance in malignant melanoma remains an unresolved clinical issue. In the search for novel molecular targets, a live-cell high-content RNAi screen based on gene expression data was performed in cisplatin-sensitive and cisplatin-resistant MeWo melanoma cells, Mel-28 cells and a melanocyte cell line. Cells were exposed to 91 siRNAs and distinct nucleus-derived phenotypes such as cell division, cell death and migration phenotypes were detected by time-lapse microscopy over 60 h. Using this approach, cisplatin-sensitive and cisplatin-resistant melanoma cells were compared by automated image analysis and visual inspection. In cisplatin-sensitive MeWo melanoma cells, 14 genes were identified that showed distinct phenotype abnormalities after exposure to gene-specific siRNAs. In cisplatin-resistant MeWo cells, five genes were detected. Nine genes were detected whose knock-down led to differential nuclear phenotypes in cisplatin-sensitive and -resistant cells. In Mel-28 cells, nine genes were identified which induced nuclear phenotypes including all eight genes which were identified in cisplatin-resistant MeWo cells. An analogous RNAi screen on melanocytes revealed no detectable phenotype abnormalities after RNAi. Pathway analysis showed in cisplatin-sensitive MeWo cells and Mel-28 cells an enrichment of at least three genes in major mitotic pathways. We hereby show that siRNA screening may help to identify tumor-specific genes leading to phenotype abnormalities. These genes may serve as potential therapeutic targets in the treatment of melanoma.

Thioredoxin-interacting protein: a potential therapeutic target for treatment of progressive fibrosis in diabetic nephropathy

Thioredoxin-interacting protein (TXNIP) is an endogenous inhibitor of the antioxidant thioredoxin, and a critical agent in the in vivo regulation of glucose. The well-described induction of TXNIP by high glucose may represent an important pathogenic trigger of complications arising in the diabetic environment, with sustained overexpression of TXNIP triggering the increased production of reactive oxygen species and collagen, both major contributors to the development of diabetic nephropathy (DN). To examine a possible therapeutic role for targeted TXNIP inhibition in DN, transgenic (mRen-2)27 rats were rendered diabetic with streptozotocin and then treated with 20 μM TXNIP deoxyribozyme (DNAzyme) delivered continuously over 12 weeks by an implanted osmotic mini-pump. Renal injury was measured using biochemical parameters of kidney function along with histological markers of damage. Catalytic activity of TXNIP DNAzyme was determined by TXNIP gene and peptide expression in the rat kidneys. TXNIP DNAzyme localization was demonstrated with a fluorescent-labelled TXNIP DNAzyme. A panel of markers was used to assess the extent of oxidative stress and renal fibrosis including superoxide level, nitrotyrosine staining, TGF-β1, NLRP3 and collagen IV expression. Fluorescent-labelled TXNIP DNAzyme was localized to tubulo-epithelial cells, but was not identified in glomeruli or endothelial cells. Elevated renal cortical TXNIP gene and protein expression seen in kidneys of DN animals were significantly attenuated by TXNIP DNAzyme (p < 0.05). Downstream markers of TXNIP activity, particularly oxidative stress, inflammasome signalling, tubulo-interstitial fibrosis and collagen deposition, were also attenuated in the tubulo-interstitium of DN rats treated with TXNIP DNAzyme. Consistent with the identified site of action of the DNAzyme, the effects of the TXNIP inhibition were limited to the tubulo-interstitial compartment. This study supports the role of TXNIP as an important mediator of progressive tubulo-interstitial fibrosis in DN, and also supports the notion of TXNIP inhibition as a potential new therapeutic target for DN.

Disruption of GRM1-mediated signalling using riluzole results in DNA damage in melanoma cells

Gain of function of the neuronal receptor, metabotropic glutamate receptor 1 (Grm1), was sufficient to induce melanocytic transformation in vitro and spontaneous melanoma development in vivo when ectopically expressed in melanocytes. The human form of this receptor, GRM1, has been shown to be ectopically expressed in a subset of human melanomas but not benign nevi or normal melanocytes, suggesting that misregulation of GRM1 is involved in the pathogenesis of certain human melanomas. Sustained stimulation of Grm1 by the ligand, glutamate, is required for the maintenance of transformed phenotypes in vitro and tumorigenicity in vivo. In this study, we investigate the mechanism of an inhibitor of glutamate release, riluzole, on human melanoma cells that express metabotropic glutamate receptor 1 (GRM1). Various in vitro assays conducted show that inhibition of glutamate release in several human melanoma cell lines resulted in an increase of oxidative stress and DNA damage response markers.

Oxidative stress in melanocyte senescence and melanoma transformation

Melanoma is a severe type of skin cancer with a high metastasis potential and poor survival rates once metastasized. The causes of melanoma formation are multifactorial and not fully understood. Several signaling cascades such as the RAS/RAF/ERK1/2 pathway, the PI3K/AKT pathway, RAC1 and NF-κB are involved in melanoma initiation and progression. Reactive oxygen species (ROS) are induced by these signal transduction cascades, and they play a fundamental role in melanomagenic processes. Cells derived from the melanocytic lineage are particularly sensitive to an increase in ROS, and thus, melanoma cells rely on efficient antioxidant measures. This review summarizes the causes and consequences of ROS generation in melanocytes and melanoma and discusses the potential of pro-oxidant therapy in melanoma treatment.

Mouse Melanoma Cell Migration is Dependent on Production of Reactive Oxygen Species under Normoxia Condition

Cell migration plays a role in many physiological and pathological processes. Reactive oxygen species (ROS) produced in mammalian cells influence intracellular signaling processes which in turn regulate various biological activities. Here, we investigated whether melanoma cell migration could be controlled by ROS production under normoxia condition. Cell migration was measured by wound healing assay after scratching confluent monolayer of B16F10 mouse melanoma cells. Cell migration was enhanced over 12 h after scratching cells. In addition, we found that ROS production was increased by scratching cells. ERK phosphorylation was also increased by scratching cells but it was decreased by the treatment with ROS scavengers, N-acetylcysteine (NAC). Tumor cell migration was inhibited by the treatment with PD98059, ERK inhibitor, NAC or DPI, well-known ROS scavengers. Tumor cell growth as judged by succinate dehydrogenase activity was inhibited by NAC treatment. When mice were intraperitoneally administered with NAC, the intracellular ROS production was reduced in peripheral blood mononuclear cells. In addition, B16F10 tumor growth was significantly inhibited by in vivo treatment with NAC. Collectively, these findings suggest that tumor cell migration and growth could be controlled by ROS production and its downstream signaling pathways, in vitro and in vivo.

Peroxiredoxin-2 represses melanoma metastasis by increasing E-Cadherin/β-Catenin complexes in adherens junctions

In melanoma, transition to the vertical growth phase is the critical step in conversion to a deadly malignant disease. Here, we offer the first evidence that an antioxidant enzyme has a key role in this transition. We found that the antioxidant enzyme peroxiredoxin-2 (Prx2) inversely correlated with the metastatic capacity of human melanoma cells. Silencing Prx2 expression stimulated proliferation and migration, whereas ectopic expression of Prx2 produced the opposite effect. Mechanistic investigations indicated that Prx2 negatively regulated Src/ERK activation status, which in turn fortified adherens junctions function by increasing E-cadherin expression and phospho-Y654-dependent retention of β-catenin in the plasma membrane. In murine melanoma cells, Prx2 silencing enhanced lung metastasis in vivo. Interestingly, the natural compound gliotoxin, which is known to exert a Prx-like activity, inhibited proliferation and migration as well as lung metastasis of Prx2-deficient melanoma cells. Overall, our findings reveal that Prx2 is a key regulator of invasion and metastasis in melanoma, and also suggest a pharmacologic strategy to effectively decrease deadly malignant forms of this disease.

Structure of the N-terminal domain of human thioredoxin-interacting protein

Thioredoxin-interacting protein (TXNIP) is one of the six known α-arrestins and has recently received considerable attention owing to its involvement in redox signalling and metabolism. Various stress stimuli such as high glucose, heat shock, UV, H2O2 and mechanical stress among others robustly induce the expression of TXNIP, resulting in the sequestration and inactivation of thioredoxin, which in turn leads to cellular oxidative stress. While TXNIP is the only α-arrestin known to bind thioredoxin, TXNIP and two other α-arrestins, Arrdc4 and Arrdc3, have been implicated in metabolism. Furthermore, owing to its roles in the pathologies of diabetes and cardiovascular disease, TXNIP is considered to be a promising drug target. Based on their amino-acid sequences, TXNIP and the other α-arrestins are remotely related to β-arrestins. Here, the crystal structure of the N-terminal domain of TXNIP is reported. It provides the first structural information on any of the α-arrestins and reveals that although TXNIP adopts a β-arrestin fold as predicted, it is structurally more similar to Vps26 proteins than to β-arrestins, while sharing below 15% pairwise sequence identity with either.

Thioredoxin binding protein (TBP)-2/Txnip and α-arrestin proteins in cancer and diabetes mellitus

Thioredoxin binding protein -2/ thioredoxin interacting protein is an α-arrestin protein that has attracted much attention as a multifunctional regulator. Thioredoxin binding protein -2 expression is downregulated in tumor cells and the level of thioredoxin binding protein is correlated with clinical stage of cancer. Mice with mutations or knockout of the thioredoxin binding protein -2 gene are much more susceptible to carcinogenesis than wild-type mice, indicating a role for thioredoxin binding protein -2 in cancer suppression. Studies have also revealed roles for thioredoxin binding protein -2 in metabolic control. Enhancement of thioredoxin binding protein -2 expression causes impairment of insulin sensitivity and glucose-induced insulin secretion, and β-cell apoptosis. These changes are important characteristics of type 2 diabetes mellitus. Thioredoxin binding protein -2 regulates transcription of metabolic regulating genes. Thioredoxin binding protein -2-like inducible membrane protein/ arrestin domain containing 3 regulates endocytosis of receptors such as the β(2)-adrenergic receptor. The α-arrestin family possesses PPXY motifs and may function as an adaptor/scaffold for NEDD family ubiquitin ligases. Elucidation of the molecular mechanisms of α-arrestin proteins would provide a new pharmacological basis for developing approaches against cancer and type 2 diabetes mellitus.

Oxidative stress, inflammation, and cancer: how are they linked?

Extensive research during the past 2 decades has revealed the mechanism by which continued oxidative stress can lead to chronic inflammation, which in turn could mediate most chronic diseases including cancer, diabetes, and cardiovascular, neurological, and pulmonary diseases. Oxidative stress can activate a variety of transcription factors including NF-κB, AP-1, p53, HIF-1α, PPAR-γ, β-catenin/Wnt, and Nrf2. Activation of these transcription factors can lead to the expression of over 500 different genes, including those for growth factors, inflammatory cytokines, chemokines, cell cycle regulatory molecules, and anti-inflammatory molecules. How oxidative stress activates inflammatory pathways leading to transformation of a normal cell to tumor cell, tumor cell survival, proliferation, chemoresistance, radioresistance, invasion, angiogenesis, and stem cell survival is the focus of this review. Overall, observations to date suggest that oxidative stress, chronic inflammation, and cancer are closely linked.

Reactive oxygen species in cancer

Elevated rates of reactive oxygen species (ROS) have been detected in almost all cancers, where they promote many aspects of tumour development and progression. However, tumour cells also express increased levels of antioxidant proteins to detoxify from ROS, suggesting that a delicate balance of intracellular ROS levels is required for cancer cell function. Further, the radical generated, the location of its generation, as well as the local concentration is important for the cellular functions of ROS in cancer. A challenge for novel therapeutic strategies will be the fine tuning of intracellular ROS signalling to effectively deprive cells from ROS-induced tumour promoting events, towards tipping the balance to ROS-induced apoptotic signalling. Alternatively, therapeutic antioxidants may prevent early events in tumour development, where ROS are important. However, to effectively target cancer cells specific ROS-sensing signalling pathways that mediate the diverse stress-regulated cellular functions need to be identified. This review discusses the generation of ROS within tumour cells, their detoxification, their cellular effects, as well as the major signalling cascades they utilize, but also provides an outlook on their modulation in therapeutics.

Reactive oxygen species and melanoma: an explanation for gender differences in survival?

Epidemiological research consistently shows a female advantage in melanoma survival. So far, no definite candidate for the explanation of this phenomenon has emerged. We propose that gender differences in oxidative stress caused by radical oxygen species (ROS) underlie these survival differences. It is known that males express lower amounts of anti-oxidant enzymes, resulting in more oxidative stress than females. The primary melanoma environment is characterized by high ROS levels, from exogenous sources as well as ROS production within melanoma cells themselves. ROS are known to be able to promote metastasis through a wide variety of mechanisms. We hypothesize that the higher levels of ROS in men enhance selection of ROS-resistance in melanoma cells. Subsequently, ROS can stimulate the metastatic potential of melanoma cells. In addition, due to the lower anti-oxidant defenses in men, ROS produced by melanoma cells cause more damage to healthy tissues surrounding the tumor, further stimulating metastasis. Therefore, ROS may explain the observed differences between males and females in melanoma survival.

The thioredoxin system: a key target in tumour and endothelial cells

Thioredoxin is a redox-sensitive molecule that has pleiotropic cellular effects, such as the control of proliferation, redox states and apoptosis, and is often upregulated in malignancy. The system controls the activation of a number of transcription factors through sulphydryl transfer and, through its activity on hypoxia inducible factor 1alpha, it is able to regulate vascular endothelial growth factor levels and hence angiogenesis. The thioredoxin protein has been shown to be upregulated in hypoxic regions of certain tumours, suggesting that inhibitors could potentially exhibit enhanced hypoxic toxicity and/or indirect anti-angiogenic effects. Evidence of this is becoming apparent in the literature. The current report reviews the thioredoxin system as an anticancer drug target and focuses upon two recent compounds, PMX464 and PX12, which reportedly inhibit this important pathway.

Regulation of thioredoxin by ceramide in retinal pigment epithelial cells

The purpose of this study was to determine the expression, regulation and signaling of a key redoxin family member thioredoxin 1 (Trx1) in normal, oxidant-stimulated and growth factor-pretreated RPE cells. Trx1 is expressed in early passage, human RPE cell cultures. RPE cells exposed to C(2)-ceramide for 24h showed no significant change in expression of Trx1 vs. controls with and without pretreatment for 24h with hepatocyte growth factor (HGF). Neither hypoxia from 1% O(2) or from CoCl(2) exposure resulted in any alteration in Trx1 expression in RPE cells. C(2)-ceramide treatment caused translocation of Trx1 from cytosol to the nucleus, which was abolished by pre-treatment of cells with a p38 MAPK-specific inhibitor. Furthermore, the gene and protein expression of thioredoxin interacting protein (Txnip) increased with ceramide treatment and was significantly (p<0.001) elevated with HGF preincubation vs. untreated controls. Prominent protection from ceramide-induced RPE cell death by exogenous rTrx1 was demonstrated. Although Trx1 directly interacts with its inhibitor, Txnip, p38 inhibition does not appear to have a role in this interaction. We found no direct interaction between apoptosis signal regulating kinase (ASK-1) and Txnip under the same experimental conditions. In summary, our data demonstrate the expression of Trx1 and Txnip in human RPE cells. Ceramide treatment results in translocation of Trx1 to the nucleus, and upregulation of Txnip expression; exogenous rTrx1 protects from ceramide-induced cell death. These results suggest that Trx1 and Txnip play an important role in the response of RPE to ceramide toxicity.

The antitumor agent imexon activates antioxidant gene expression: evidence for an oxidative stress response

PURPOSE

The aim of this study was to identify biomarkers that may be predictive for the clinical activity of the redox-active antitumor agent imexon.

EXPERIMENTAL DESIGN

cDNA microarray and quantitative real-time PCR were used to identify global changes in gene expression in peripheral blood mononuclear cells (PBMC) collected from patients treated with imexon during a phase I trial. Electrophoretic mobility shift assays and Western blot analysis were done using the RPMI8226 myeloma cell line grown in vitro and PBMCs treated ex vivo to investigate the molecular mechanism responsible for these gene changes.

RESULTS

Both cDNA microarray and quantitative real-time PCR showed the up-regulation of many antioxidant genes, including thioredoxin reductase-1, glutaredoxin-2, and peroxiredoxin-3 in PBMCs collected from patients treated with imexon. Studies in PBMCs treated ex vivo and RPMI8226 myeloma cells showed that imexon increased binding to the activator protein-1 consensus sequence measured by electrophoretic mobility shift assay. Supershift analysis showed that the majority of the activator protein-1 DNA binding activity was c-Jun, with minor contribution of Jun-D. Nuclear translocation of the nuclear factor (erythroid-derived 1)-like 2 transcription factor and its binding to the antioxidant response element was also increased after imexon treatment, which correlated with an increase in the message levels for nuclear factor (erythroid-derived 1)-like 2/antioxidant response element-regulated antioxidant genes.

CONCLUSIONS

Together, these results show that a predominant biological effect of imexon is a change in redox state that can be detected in surrogate normal tissues as increased redox-sensitive transcription factor binding and increased antioxidant gene expression.

Thioredoxin in the cardiovascular system

The thioredoxin (TRX) system (TRX, TRX reductase, and NADPH) is a ubiquitous thiol oxidoreductase system that regulates cellular reduction/oxidation (redox) status. The impairment of cell redox state alters multiple cell pathways, which may contribute to the pathogenesis of cardiovascular disorders including hypertension, atherosclerosis, and heart failure. In this manuscript, we review the essential roles that TRX plays by limiting oxidative stress directly via antioxidant effects and indirectly by protein-protein interactions with key signaling molecules such as thioredoxin interacting protein (TXNIP). TRX and its endogenous regulators may represent important future targets to develop clinical therapies for diseases associated with oxidative stress.

Inhibition of tumour metastasis by targeted delivery of antioxidant enzymes

Metastasis is one of the most harmful aspects of malignant neoplasm. Interaction of tumour cells with normal cells such as tissue macrophages may generate reactive oxygen species, which would affect various aspects of tumour metastasis. Reactive oxygen species cause damage to both tumour and normal cells and some of them, especially hydrogen peroxide, can also act as intracellular second messengers at sublethal concentrations to increase the transcription of various genes, which can then accelerate the proliferation of tumour cells in metastatic colonies. Therefore, eliminating hydrogen peroxide is one approach to inhibiting tumour metastasis. In this article, the roles of reactive oxygen species in tumour metastasis are reviewed, and the strategies to inhibit tumour metastasis by the targeted delivery of catalase, an enzyme that detoxifies hydrogen peroxide, are discussed.

Metastasis suppressor proteins: discovery, molecular mechanisms, and clinical application

Clinically and experimentally, primary tumor formation and metastasis are distinct processes — locally growing tumors can progress without the development of metastases. This observation prompted the hypothesis that the molecular processes regulating tumorigenicity and metastasis are distinguishable and could be targeted therapeutically. During the process of transformation and subsequent progression to a malignant phenotype, both genetic and epigenetic alterations alter a cell’s ability to perceive and respond to signals that regulate normal tissue homeostasis. A minority of tumorigenic cells accrue the full complement of alterations that enables them to disseminate from the primary tumor, survive insults from the immune system and biophysical forces, and respond to growth-promoting and/or inhibitory signals from the distant tissues and thrive there. Identification of genes and proteins that specifically inhibit the ability of cells to form metastases (e.g., metastasis suppressors) is providing new insights into the molecular mechanisms that regulate this complex process. This review will highlight: (a ) the functional identification of metastasis suppressors, (b ) the signaling cascades and cellular phenotypes which are controlled or modulated by metastasis suppressors, and (c ) op portunities for translation and clinical trials that are based on mechanistic studies regarding metastasis suppressors.

Characterization of the expression of the hypoxia-induced genes neuritin, TXNIP and IGFBP3 in cancer

By triggering an adaptive response to hypoxia which is a common feature of tumor microenvironments, endothelial cells contribute to the onset of angiogenic responses involved in tumor growth. Therefore, identifying hypoxic markers represent a challenge for a better understanding of tumor angiogenesis and for the optimization of anti-angiogenic therapeutic strategy. Using representational difference analysis combined with microarray, we here report the identification of 133 hypoxia-induced transcripts in human microendothelial cells (HMEC-1). By Northern blot, we confirm hypoxia-induced expression of insulin-like growth factor binding protein 3 (igfbp3), thioredoxin-interacting protein (txnip), neuritin (nrn1). Finally, by performing in situ hybridization on several types of human tumors, we provide evidence for nrn1 and txnip as hypoxic perinecrotic markers and for igfbp3 as a tumor endothelial marker. We propose these hypoxia-induced genes could represent relevant prognostic tools and targets for therapeutic intervention in cancers.

Inhibition of metastatic tumor growth by targeted delivery of antioxidant enzymes

To develop effective anti-metastatic therapy, targeted or sustained delivery of catalase was examined in mice. We found that mouse lung with metastatic colonies of adenocarcinoma colon26 cells exhibited reduced catalase activity. The interaction of the tumor cells with macrophages or hepatocytes generated detectable amounts of ROS, and increased the activity of matrix metalloproteinases. Hepatocyte-targeted delivery of catalase was successfully achieved by galactosylation, which was highly effective in inhibiting the hepatic metastasis of colon26 cells. PEGylation, which increased the retention of catalase in the circulation, effectively inhibited the pulmonary metastasis of the cells. To examine which processes in tumor metastasis are inhibited by catalase derivatives, the tissue distribution and proliferation of tumor cells in mice was quantitatively analyzed using firefly luciferase-expressing tumor cells. An injection of PEG-catalase just before the inoculation of melanoma B16-BL6/Luc cells significantly reduced the number of the tumor cells in the lung at 24 h. Daily dosing of PEG-catalase greatly inhibited the proliferation of the tumor cells, and increased the survival rate of the tumor-bearing mice. These results indicate that targeted or sustained delivery of catalase to sites where tumor cells metastasize is a promising approach for inhibiting metastatic tumor growth.

Selective neuronal vulnerability and inadequate stress response in superoxide dismutase mutant mice

To understand the role of oxidative stress and mitochondrial defects in the development of neurodegeneration, we examined the age-related pathological changes and corresponding gene expression profiles in homozygous mutant mice deficient in the mitochondrial form of superoxide dismutase (MnSOD, SOD2). These Sod2-/- mice, generated on a B6D2F1 background, developed ataxia at Postnatal Day (P) 11 and progressively deteriorated with frequent seizures by P14. Histopathological examination revealed neurodegenerative changes consistent with the neurological signs. Vacuolar degeneration was observed in neurons and neuropil throughout the brainstem and rostral cortex. The motor trigeminal nucleus in brainstem and the deeper layers of the motor cortex were the earliest regions to degenerate, with the thalamus and hippocampus affected at later stages. Oligonucleotide microarrays were used to compare gene expression profiles in the brainstem and thalamus of Sod2+/+ and -/- mice from birth to P18. Notably, a large set of heat-shock protein genes was transcriptionally down regulated, and this was most likely due to a reduction in the heat-shock transcription factor 1 (HSF1). Other major classes of differentially expressed genes include lipid biosynthesis and ROS metabolism.