Nuclear thioredoxin-1 is required to suppress cisplatin-mediated apoptosis of MCF-7 cells

Reactions of Cisplatin with Thioredoxin-1 Regulate Intracellular Redox Homeostasis

Cisplatin is a widely used anticancer drug. In addition to inducing DNA damage, increased levels of reactive oxygen species (ROS) play a significant role in cisplatin-induced cell death. Thioredoxin-1 (Trx1), a redox regulatory protein that can scavenge ROS, has been found to eliminate cisplatin-induced ROS, while elevated Trx1 levels are associated with cisplatin resistance. However, it is unknown whether the effect of Trx1 on the cellular response to cisplatin is due to its direct reaction and how this reaction influences the activity of Trx1. In this work, we performed detailed studies of the reaction between Trx1 and cisplatin. Trx1 is highly reactive to cisplatin, and the catalytic motif of Trx1 (CGPC) is the primary binding site of cisplatin. Trx1 can bind up to 6 platinum moieties, resulting in the structural alteration and oligomerization of Trx1 depending on the degree of platination. Platination of Trx1 inhibits its interaction with ASK1, a Trx1-binding protein that regulates cell apoptosis. Furthermore, the reaction with cisplatin suppresses drug-induced ROS generation, which could be associated with drug resistance. This study provides more insight into the mechanism of action of cisplatin.

Thioredoxin (Trxo1) interacts with proliferating cell nuclear antigen (PCNA) and its overexpression affects the growth of tobacco cell culture

Thioredoxins (Trxs), key components of cellular redox regulation, act by controlling the redox status of many target proteins, and have been shown to play an essential role in cell survival and growth. The presence of a Trx system in the nucleus has received little attention in plants, and the nuclear targets of plant Trxs have not been conclusively identified. Thus, very little is known about the function of Trxs in this cellular compartment. Previously, we studied the intracellular localization of PsTrxo1 and confirmed its presence in mitochondria and, interestingly, in the nucleus under standard growth conditions. In investigating the nuclear function of PsTrxo1 we identified proliferating cellular nuclear antigen (PCNA) as a PsTrxo1 target by means of affinity chromatography techniques using purified nuclei from pea leaves. Such protein-protein interaction was corroborated by dot-blot and bimolecular fluorescence complementation (BiFC) assays, which showed that both proteins interact in the nucleus. Moreover, PsTrxo1 showed disulfide reductase activity on previously oxidized recombinant PCNA protein. In parallel, we studied the effects of PsTrxo1 overexpression on Tobacco Bright Yellow-2 (TBY-2) cell cultures. Microscopy and flow-cytometry analysis showed that PsTrxo1 overexpression increases the rate of cell proliferation in the transformed lines, with a higher percentage of the S phase of the cell cycle at the beginning of the cell culture (days 1 and 3) and at the G2/M phase after longer times of culture (day 9), coinciding with an upregulation of PCNA protein. Furthermore, in PsTrxo1 overexpressed cells there is a decrease in the total cellular glutathione content but maintained nuclear GSH accumulation, especially at the end of the culture, which is accompanied by a higher mitotic index, unlike non-overexpressing cells. These results suggest that Trxo1 is involved in the cell cycle progression of TBY-2 cultures, possibly through its link with cellular PCNA and glutathione.

Cross Talk between Two Antioxidant Systems, Thioredoxin and DJ-1: Consequences for Cancer

Oxidative stress, which is associated with an increased concentration of reactive oxygen species (ROS), is involved in the pathogenesis of numerous diseases including cancer. In response to increased ROS levels, cellular antioxidant molecules such as thioredoxin, peroxiredoxins, glutaredoxins, DJ-1, and superoxide dismutases are upregulated to counteract the detrimental effect of ROS. However, cancer cells take advantage of upregulated antioxidant molecules for protection against ROS-induced cell damage. This review focuses on two antioxidant systems, Thioredoxin and DJ-1, which are upregulated in many human cancer types, correlating with tumour proliferation, survival, and chemo-resistance. Thus, both of these antioxidant molecules serve as potential molecular targets to treat cancer. However, targeting one of these antioxidants alone may not be an effective anti-cancer therapy. Both of these antioxidant molecules are interlinked and act on similar downstream targets such as NF-κβ, PTEN, and Nrf2 to exert cytoprotection. Inhibiting either thioredoxin or DJ-1 alone may allow the other antioxidant to activate downstream signalling cascades leading to tumour cell survival and proliferation. Targeting both thioredoxin and DJ-1 in conjunction may completely shut down the antioxidant defence system regulated by these molecules. This review focuses on the cross-talk between thioredoxin and DJ-1 and highlights the importance and consequences of targeting thioredoxin and DJ-1 together to develop an effective anti-cancer therapeutic strategy.

Co-delivery of thioredoxin 1 shRNA and doxorubicin by folate-targeted gemini surfactant-based cationic liposomes to sensitize hepatocellular carcinoma cells

Folate-targeted gemini surfactant-based cationic liposomes are constructed to co-deliver thioredoxin 1 and doxorubicin to inhibit the cell viability and induce apoptosis in hepatocellular carcinoma cells.

Over-expression of Thioredoxin-1 mediates growth, survival, and chemoresistance and is a druggable target in diffuse large B-cell lymphoma

Diffuse Large B cell lymphomas (DLBCL) are the most prevalent of the non-Hodgkin lymphomas and are currently initially treated fairly successfully, but frequently relapse as refractory disease, resulting in poor salvage therapy options and short survival. The greatest challenge in improving survival of DLBCL patients is overcoming chemo-resistance, whose basis is poorly understood. Among the potential mediators of DLBCL chemo-resistance is the thioredxoin (Trx) family, primarily because Trx family members play critical roles in the regulation of cellular redox homeostasis, and recent studies have indicated that dysregulated redox homeostasis also plays a key role in chemoresistance. In this study, we showed that most of the DLBCL-derived cell lines and primary DLBCL cells express higher basal levels of Trx-1 than normal B cells and that Trx-1 expression level is associated with decreased patients survival. Our functional studies showed that inhibition of Trx-1 by small interfering RNA or a Trx-1 inhibitor (PX-12) inhibited DLBCL cell growth, clonogenicity, and also sensitized DLBCL cells to doxorubicin-induced cell growth inhibition in vitro. These results indicate that Trx-1 plays a key role in cell growth and survival, as well as chemoresistance, and is a potential target to overcome drug resistance in relapsed/refractory DLBCL.

IKK-β mediates chemoresistance by sequestering FOXO3; a critical factor for cell survival and death

Chemotherapeutic drugs proved only 50% successful in breast cancer because of cell type-dependent resistance mechanisms. FOXO3 is known to be involved in the regulation of several cell death-related genes; however, the extent of FOXO3 regulation in chemoresistance is still not fully understood. Here, we show that FOXO3 critically mediates cisplatin chemosensitivity of MCF-7 breast cancer cells which express higher levels of FOXO3 compared to resistant MDA-MB-231 cells. Administration of cisplatin induces apoptosis in MCF-7 cells in a FOXO3-dependent manner as indicated by RNA interference. On the other hand, IKK-β (IκB kinase) appears to inhibit FOXO3 action after cisplatin treatment and promotes chemoresistance in MDA-MB-231 cells. IKK-β directly interacts and sequesters FOXO3 in the cytosol preventing its nuclear localization. Moreover, cisplatin treatment induces autophagosome formation through LC-3 conversion while inhibiting the cleavage of caspase 9 and caspase 3 in MDA-MB-231 cells manipulated to overexpress FOXO3. In brief, our findings demonstrate that in addition to cellular level of active FOXO3, cisplatin chemoresistance is also regulated by IKK-β sequestration of FOXO3 in cytosol.

Chloroethyl urea derivatives block tumour growth and thioredoxin-1 nuclear translocation

Aryl chloroethyl ureas (CEUs) are new protein alkylating agents exhibiting anticancer activity both in vitro and in vivo. We report herein that 14C-labeled CEU derivatives, designated CEU-025 and CEU-027, covalently bind to thioredoxin-1 (TRX1). Covalent binding of these molecules slightly decreases the disulfide-reducing activity of recombinant TRX1, when compared with the effect of strong thioalkylating agents such as N-ethylmaleimide. Moreover, site-directed mutagenesis and diamide competition assays demonstrated that TRX1 cysteinyl residues are not the prime targets of CEUs. CEU-025 abrogates the nuclear translocation of TRX1 in human cancer cells. In addition, we show that CEU-025 can block TRX1 nuclear translocation induced by cisplatin. Unexpectedly, pretreatment with sublethal CEU-025 concentrations that block TRX1 nuclear translocation protected the cells against cisplatin cytotoxicity. Overexpression of TRX1 in HT1080 fibrosarcoma cells attenuated CEU-025 cytotoxicity, while its suppression using TRX1-specific siRNA increased the effects of CEU-025, suggesting that loss of function of TRX1 is involved, at least in part, in the cytotoxic activity of CEU-025. These results suggest that CEU-025 and CEU-027 exhibit anticancer activity through a novel, unique mechanism of action. The importance of TRX1 and the dependence of the cytotoxicity of CEU-025 and CEU-027 on TRX1 intracellular localization are also discussed.

Redox control systems in the nucleus: mechanisms and functions

Proteins with oxidizable thiols are essential to many functions of cell nuclei, including transcription, chromatin stability, nuclear protein import and export, and DNA replication and repair. Control of the nuclear thiol-disulfide redox states involves both the elimination of oxidants to prevent oxidation and the reduction of oxidized thiols to restore function. These processes depend on the common thiol reductants, glutathione (GSH) and thioredoxin-1 (Trx1). Recent evidence shows that these systems are controlled independent of the cytoplasmic counterparts. In addition, the GSH and Trx1 couples are not in redox equilibrium, indicating that these reductants have nonredundant functions in their support of proteins involved in transcriptional regulation, nuclear protein trafficking, and DNA repair. Specific isoforms of glutathione peroxidases, glutathione S-transferases, and peroxiredoxins are enriched in nuclei, further supporting the interpretation that functions of the thiol-dependent systems in nuclei are at least quantitatively distinct, and probably also qualitatively distinct, from similar processes in the cytoplasm. Elucidation of the distinct nuclear functions and regulation of the thiol redox pathways in nuclei can be expected to improve understanding of nuclear processes and also to provide the basis for novel approaches to treat aging and disease processes associated with oxidative stress in the nuclei.

Thioredoxin-1 phosphorylated at T100 is needed for its anti-apoptotic activity in HepG2 cancer cells

AIMS

Thioredoxin-1 (Trx) is an important protein involved in the regulation of apoptosis and in enhancing drug resistance in cancer cells. Threonine100 (T100) of Trx was reported to be phosphorylated; however, the role of this phosphorylation in regulating activity remains unresolved. We explored whether and how the phosphorylation of Trx is involved in drug resistance in cancer cells.

MAIN METHODS

The levels of phosphorylated Trx were detected by sandwich ELISA. Cell viability was investigated using Alamar Blue assay, and apoptosis was evaluated with Hoechst33258 staining. Western blotting was used to examine the changes in the expression levels of Trx, NF-kappaB p65 subunit, ASK-1 and 6His tag. Additionally, we took advantage of phorbol-12-myristate-13-acetate (PMA)to activate protein kinase C (PKC) and staurosporine to inhibit PKC.

KEY FINDINGS

Trx mutated at T100 causes lower survival rate induced by H(2)O(2), and higher apoptosis rate induced by cis-platinum and adriamycin in HepG2 cells. T100 of Trx can be phosphorylated through the PKC-dependent pathway. Furthermore, the resistance of anticancer drugs can be decreased when the phosphorylation of T100 in Trx was blocked by staurosporine. Though the Trx-ASK1 complex is not affected, the phosphorylation contributes to the nuclear location of Trx, and then up-regulates the activity of NF-kappaB.

SIGNIFICANCE

It was firstly found that the phosphorylation of Trx at T100 plays an important role in its cytoprotective activity in cancer cells. Thus, besides blocking the active site of Trx, inhibiting the phosphorylation of Trx at T100 may be a new potential cancer therapy target.

Isobaric peptide termini labeling for MS/MS-based quantitative proteomics

Since its introduction, isobaric peptide labeling has played an important role in relative quantitative comparisons of proteomes. This paper describes isobaric peptide termini labeling (IPTL), a novel approach for the identification and quantification of two differentially labeled states using MS/MS spectra. After endoproteinase Lys-C digestion, peptides were labeled at C-terminal lysine residues with either 2-methoxy-4,5-dihydro-1H-imidazole (MDHI) or with tetradeuterated MDHI-d(4). Subsequently, their N-termini were derivatized either with tetradeuterated succinic anhydride (SA-d(4)) or with SA. The mixed isotopic labeling results in isobaric masses and provided several quantification data points per peptide. The suitability of this approach is demonstrated with MS and MS/MS analyses of Lys-C digests of standard proteins. A conceptually simple quantification strategy with a dynamic range of 25 is achieved through the use of Mascot score ratios. The utility of IPTL for the analysis of proteomes was verified by comparing the well-characterized effect of the antimitotic inhibitor S-Trityl-l-Cysteine (STLC) on HeLa cells that were treated for either 24 or 48 h with the inhibitor. Many apoptosis-linked proteins were identified as being differentially regulated, confirming the suitability of IPTL for the analysis of complex proteomes.

Alterations of cellular redox state during NNK-induced malignant transformation and resistance to radiation

Cancer cells often exhibit increased reactive oxygen species generation and altered redox regulation. The current study was conducted to investigate the biochemical and molecular events associated with redox alterations during chemical-induced malignant transformation and to evaluate their potential roles in radiation sensitivity. Immortalized nonmalignant human bronchial epithelial cells were exposed to the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and a clone of cells exhibiting malignant behaviors was isolated and characterized. This clone initially exhibited an increase in cellular superoxide that eventually decreased after a long-term culture in vitro, associated with altered expression of antioxidant molecules, including an increase in thioredoxin-1 and manganese superoxide dismutase, and a decrease in glutathione peroxidase-1. These cells also showed a significant decrease in sensitivity to ionizing radiation, as demonstrated by less cell death in acute apoptosis analyses and long-term cell proliferation assays. Using biochemical redox modulation and siRNA approach, we showed that the increase in thioredoxin-1 played a significant role in conferring resistance to IR. Although there was a substantial increase in cellular glutathione, inhibition of glutathione synthesis did not increase IR sensitivity. Our study showed complex redox alterations during NNK-induced malignant transformation, and identified Trx-1 as a radiosensitivity modulator.