Oncogenic functions of the transcription factor Nrf2

NRF2-regulated metabolic gene signature as a prognostic biomarker in non-small cell lung cancer

Mutations in Kelch-like ECH-associated protein 1 (KEAP1) cause the aberrant activation of nuclear factor erythroid-derived 2-like 2 (NRF2), which leads to oncogenesis and drug resistance in lung cancer cells. Our study was designed to identify the genes involved in lung cancer progression targeted by NRF2. A series of microarray experiments in normal and cancer cells, as well as in animal models, have revealed regulatory genes downstream of NRF2 that are involved in wide variety of pathways. Specifically, we carried out individual and combinatorial microarray analysis of KEAP1 overexpression and NRF2 siRNA-knockdown in a KEAP1 mutant-A549 non-small cell lung cancer (NSCLC) cell line. As a result, we identified a list of genes which were mainly involved in metabolic functions in NSCLC by using functional annotation analysis. In addition, we carried out in silico analysis to characterize the antioxidant responsive element sequences in the promoter regions of known and putative NRF2-regulated metabolic genes. We further identified an NRF2-regulated metabolic gene signature (NRMGS) by correlating the microarray data with lung adenocarcinoma RNA-Seq gene expression data from The Cancer Genome Atlas followed by qRT-PCR validation, and finally showed that higher expression of the signature conferred a poor prognosis in 8 independent NSCLC cohorts. Our findings provide novel prognostic biomarkers for NSCLC.

Nrf2-Keap1 pathway promotes cell proliferation and diminishes ferroptosis

Cancer cells are hallmarked by high proliferation and imbalanced redox consumption and signaling. Various oncogenic pathways such as proliferation and evading cell death converge on redox-dependent signaling processes. Nrf2 is a key regulator in these redox-dependent events and operates in cytoprotection, drug metabolism and malignant progression in cancer cells. Here, we show that patients with primary malignant brain tumors (glioblastomas, WHO °IV gliomas, GBM) have a devastating outcome and overall reduced survival when Nrf2 levels are upregulated. Nrf2 overexpression or Keap1 knockdown in glioma cells accelerate proliferation and oncogenic transformation. Further, activation of the Nrf2-Keap1 signaling upregulates xCT (aka SLC7A11 or system X_c⁻) and amplifies glutamate secretion thereby impacting on the tumor microenvironment. Moreover, both fostered Nrf2 expression and conversely Keap1 inhibition promote resistance to ferroptosis. Altogether, the Nrf2-Keap1 pathway operates as a switch for malignancy in gliomas promoting cell proliferation and resistance to cell death processes such as ferroptosis. Our data demonstrate that the Nrf2-Keap1 pathway is critical for cancer cell growth and operates on xCT. Nrf2 presents the Achilles’ heel of cancer cells and thus provides a valid therapeutic target for sensitizing cancer for chemotherapeutics.

Pan-urologic cancer genomic subtypes that transcend tissue of origin

Urologic cancers include cancers of the bladder, kidney, prostate, and testes, with common molecular features spanning different types. Here, we show that 1954 urologic cancers can be classified into nine major genomic subtypes, on the basis of multidimensional and comprehensive molecular characterization (including DNA methylation and copy number, and RNA and protein expression). Tissue dominant effects are first removed computationally in order to define these subtypes, which reveal common processes—reflecting in part tumor microenvironmental influences—driving cellular behavior across tumor lineages. Six of the subtypes feature a mixture of represented cancer types as defined by tissue or cell of origin. Differences in patient survival and in the manifestation of specific pathways—including hypoxia, metabolism, NRF2-ARE, Hippo, and immune checkpoint—can further distinguish the subtypes. Immune checkpoint markers and molecular signatures of macrophages and T cell infiltrates are relatively high within distinct subsets of each cancer type studied. The pan-urologic cancer genomic subtypes would facilitate information sharing involving therapeutic implications between tissue-oriented domains.

Urological cancers have disparate tissues and cells of origin but share many molecular features. Here, the authors use multidimensional and comprehensive molecular characterization to classify urological cancers into nine major genomic subtypes, highlighting potential therapeutic targets.

Treatment of Human Placental Choriocarcinoma Cells with Formaldehyde and Benzene Induced Growth and Epithelial Mesenchymal Transition via Induction of an Antioxidant Effect

Cigarette smoke (CS) causes about 480,000 deaths each year worldwide, and it is well-known to have harmful effects on the human body, leading to heart disease, stroke, lung cancer, and cardiovascular problems. In this study, the effects of formaldehyde (FA) and benzene (Bz), the main components of CS, on cell proliferation and epithelial mesenchymal transition (EMT) of JEG-3 human choriocarcinoma cells were examined to confirm the relationship between CS components and placenta carcinoma. Upon MTT assay, FA (10⁻⁸ M to 10⁻⁵ M) and Bz (10⁻¹¹ M to 10⁻⁸ M) increased JEG-3 cell proliferation. Western blot assay revealed that the protein expression of cyclin D1 and E1 increased, while the levels of p21 and p27 were reduced following treatment. In Scratch assay, FA (10⁻⁸ M and 10⁻⁵ M) and Bz (10⁻¹¹ M and 10⁻⁸ M) increased migration of JEG-3 cells at 24 h and 48 h compared with that at 0 h. In addition, the expression of the epithelial marker, E-cadherin, was significantly decreased, while the expression of the mesenchymal marker, N-cadherin, was significantly increased by FA (10⁻⁸ M and 10⁻⁵ M) and Bz (10⁻¹¹ M and 10⁻⁸ M). snail and slug transcriptional factors were associated with EMT, which were also up-regulated by FA and Bz, indicating that FA and Bz lead to an increase in the EMT process in JEG-3 choriocarcinoma cells. We further evaluated reactive oxygen species (ROS) and activation of antioxidant effect using dichlorofluorescin diacetate (DCFH-DA) and Western blot assay. FA and Bz increased the ROS production and an antioxidant related marker, Nrf2, in JEG-3 cells. However, eIF2α levels were reduced by FA and Bz via activation of the antioxidant reaction. Taken together, these results indicated that FA and Bz induce the growth and migration of human choriocarcinoma cells via regulation of the cell cycle and EMT and activation of ROS and antioxidant related markers.

Nrf2: a potential therapeutic target for naturally occurring anticancer drugs?

INTRODUCTION

Nuclear factor (erythroid-derived-2)-like 2 is one of the most efficient cytoprotective rheostats against exogenous or endogenous oxidative insults. At present, the modulation of the Nrf2 pathway represents an interesting and highly explored strategy in the oncological area. Area covered: In this review, we present and discuss the different modulation of the Nrf2 pathway by some natural compounds with a well demonstrated anticancer activity, and critically analyze the challenges associated with the development of an Nrf2-based anticancer strategy. Expert opinion: Many natural compounds with a well-defined anticancer activity are able to modulate this pathway. Both Nrf2 inducers and inhibitors can be useful as anticancer strategy. However, since Nrf2 modulates many networks potentially involved in the detoxification process of anticancer drugs, its activation in cancer cells could lead to chemoresistance. The switch between a beneficial or detrimental role of Nrf2 in cancer cells essentially depends on the tight control of its activity, the specific conditions of tumor microenvironment, and cell type. In line with the paucity of clear data related to the mechanisms underpinning the role of Nrf2 in cancer development and chemoresistance, discovery and development of Nrf2-based strategies is one of the most critical and challenging assignments for fighting cancers.

Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans

Oxidative stress is the result of the imbalance between reactive oxygen species (ROS) formation and enzymatic and nonenzymatic antioxidants. Biomarkers of oxidative stress are relevant in the evaluation of the disease status and of the health-enhancing effects of antioxidants. We aim to discuss the major methodological bias of methods used for the evaluation of oxidative stress in humans. There is a lack of consensus concerning the validation, standardization, and reproducibility of methods for the measurement of the following: (1) ROS in leukocytes and platelets by flow cytometry, (2) markers based on ROS-induced modifications of lipids, DNA, and proteins, (3) enzymatic players of redox status, and (4) total antioxidant capacity of human body fluids. It has been suggested that the bias of each method could be overcome by using indexes of oxidative stress that include more than one marker. However, the choice of the markers considered in the global index should be dictated by the aim of the study and its design, as well as by the clinical relevance in the selected subjects. In conclusion, the clinical significance of biomarkers of oxidative stress in humans must come from a critical analysis of the markers that should give an overall index of redox status in particular conditions.

Perspectives of the Nrf-2 signaling pathway in cancer progression and therapy

The Nuclear factor erythroid2-related factor2 (Nrf2), a master regulator of redox homoeostasis, is a key transcription factor regulating a wide array of genes for antioxidant and detoxification enzymes. It protects organs from various kinds of toxic insults. On the other hand, activation of Nrf2 is also correlated with cancer progression and chemoresistance. Downregulation of Nrf2 activity has attracted an increasing amount of attention as it may provide an alternative cancer therapy. In this review, we examine recent studies on roles of Nrf2 in several pathophysiological conditions emphasising cancer. We discuss elaborately the current knowledge on Nrf2 regulation including KEAP1-dependent and KEAP1-independent cascades. KEAP1/Nrf2 system is a master regulator of cellular response against a variety of environmental stresses. We also highlight several tightly controlled regulations of Nrf2 by numerous proteins, small molecules, toxic metals, etc. In addition, we evaluate the possible therapeutic approaches of increasing chemosensitivity via modulating Nrf2 signaling.

Succinate: An initiator in tumorigenesis and progression

As an intermediate metabolite of the tricarboxylic acid cycle in mitochondria, succinate is widely investigated for its role in metabolism. In recent years, an increasing number of studies have concentrated on the unanticipated role of succinate outside metabolism, acting as, for instance, an inflammatory signal or a carcinogenic initiator. Actually, succinate dehydrogenase gene mutations and abnormal succinate accumulation have been observed in a battery of hereditary and sporadic malignancies. In this review, we discuss the unexpected role of succinate and possible mechanisms that may contribute to its accumulation. Additionally, we describe how the high concentration of succinate in the tumor microenvironment acts as an active participant in tumorigenesis, rather than a passive bystander or innocent victim. Focusing on mechanism-based research, we summarize some targeted therapies which have been applied to the clinic or are currently under development. Furthermore, we posit that investigational drugs with different molecular targets may expand our horizon in anticancer therapy.

Nrf2 promotes progression of non-small cell lung cancer through activating autophagy

The transcription factor, NFE2-related factor 2 (Nrf2) and autophagy have been implicated in the oxidative-stress response during tumor evolution. However, few studies focus on crosstalk between Nrf2 and autophagy in cancer progression of non-small cell lung cancer (NSCLC). Herein, we evaluated the effect of Nrf2 on autophagy in NSCLC and their role in development of NSCLC. Effect of Nrf2 on overal survival (OS) of NSCLC patients were evaluated. Cell biological behaviors in response to Nrf2 were evaluated by MTT, colony formation assay and flow cytometry. Effect of 3-MA (a classical inhibitor of autophagy) on 95D-Nrf2 cells was also analyzed using flow cytometry. After up/down-regulating Nrf2 in NSCLC cell lines, expression of autophagy-related proteins were evaluated with western blot analysis. The results revealed that Nrf2 was an independent prognositc factor negtively associated with OS of NSCLC patients. Elevated Nrf2 expression promotes NSCLC progression, enhancing the escape of tumor cells from apoptosis in vivo and in vitro. Double staining with Annexin V-APC and 7-AAD showed that the proportions of apoptotic cells in 95D-Nrf2 cells were gradually increased after the addition of 3-MA. Importently, Nrf2 induced autophagosome formation and enhanced autophagic activity, which subsequently inhibits NSCLC cell apoptosis. In conclusion, our present study demonstrates that Nrf2 promotes progression of non-small cell lung cancer through activating autophagy. It provides novel insights into Nrf2-mediated of cell proliferation in NSCLC and may facilitate therapeutic development against NSCLC.

Time- and cell-resolved dynamics of redox-sensitive Nrf2, HIF and NF-κB activities in 3D spheroids enriched for cancer stem cells

Cancer cells have an altered redox status, with changes in intracellular signaling pathways. The knowledge of how such processes are regulated in 3D spheroids, being well-established tumor models, is limited. To approach this question we stably transfected HCT116 cells with a pTRAF reporter that enabled time- and cell-resolved activity monitoring of three redox-regulated transcription factors Nrf2, HIF and NF-κB in spheroids enriched for cancer stem cells. At the first day of spheroid formation, these transcription factors were activated and thereafter became repressed. After about a week, both HIF and Nrf2 were reactivated within the spheroid cores. Further amplifying HIF activation in spheroids by treatment with DMOG resulted in a dominant quiescent stem-cell-like phenotype, with high resistance to stress-inducing treatments. Auranofin, triggering oxidative stress and Nrf2 activation, had opposite effects with increased differentiation and proliferation. These novel high-resolution insights into spatiotemporal activation patterns demonstrate a striking coordination of redox regulated transcription factors within spheroids not occurring in conventional cell culture models.

Oxidative stress indicated by elevated expression of Nrf2 and 8-OHdG promotes hepatocellular carcinoma progression

Reactive oxygen species (ROS) is excessively generated in tumors creating an oxidative stress in tumor microenvironment. We investigated hepatic expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and 8-hydroxydeoxyguanosine (8-OHdG) in hepatocellular carcinoma (HCC) patients, and asked if ROS epigenetically upregulated Nrf2 and enhanced aggressiveness in HCC cells. Expression of Nrf2 (n = 100) and 8-OHdG (n = 53) was remarkably increased in HCC tissues compared with the noncancerous hepatic tissues. Elevated expression of 8-OHdG was associated with poor survival in HCC patients. H₂O₂, as ROS representative, provoked oxidative stress in HepG2 cells, indicated by increased protein carbonyl content and decreased total antioxidant capacity. Nrf2 expression and 8-OHdG formation were markedly increased in the H₂O₂-treated cells compared with the untreated control. Co-treatment with antioxidants, tocopheryl acetate (TA) and S-adenosylmethionine (SAM) effectively attenuated expression of Nrf2 and 8-OHdG in H₂O₂-treated cells. HepG2 cells treated with H₂O₂ had significantly higher migration and invasion capabilities than the untreated control cells, and this aggressiveness was significantly inhibited by TA and SAM. Bisulfite sequencing revealed that CpG dinucleotides in Nrf2 promoter were unmethylated in the H₂O₂-treated cells similar to the untreated control. In conclusion, robust histological evidence of increased antioxidative response and oxidative DNA damage in human HCC tissues was demonstrated. Elevated oxidative DNA lesion 8-OHdG was associated with shorter survival. Experimentally, ROS enhanced Nrf2 expression, 8-OHdG formation and tumor progression in HCC cells. These effects were inhibited by antioxidants. Therefore, oxidative stress-reducing regimens might be beneficial to diminish the ROS-induced HCC progression.

Dehydrobruceine B enhances the cisplatin-induced cytotoxicity through regulation of the mitochondrial apoptotic pathway in lung cancer A549 cells

Dehydrobruceine B (DHB) is a quassinoid isolated from Brucea javanica. We have shown previously that DHB induced apoptosis on two kinds of lung cancer cell lines, A549 and NCI-H292. In the present study, we investigated the interactions of DHB and cisplatin (CDDP) on apoptotic-related cancer cell death. Synergistic effects on cell proliferation and apoptosis were observed when A549 cells were treated with DHB plus CDDP. DHB combined CDDP exposure increased depolarization of mitochondrial membrane potential (MMP) and release of cytochrome c from mitochondria into the cytoplasm. The combination treatment also enhanced protein expression of Bax, reduced the protein levels of Bcl-xL and Bcl-2, and increased the cleavage of caspase-3, caspase-9 and poly (ADP-ribose) polymerase (PARP). These results indicated that DHB sensitized A549 cells to cisplatin by regulating the mitochondrial apoptotic pathway. High constitutive expression of Nrf2 was found in A549 cells, which enhance the resistance of cancer cells to chemotherapeutic agents including cisplatin. DHB reduced the protein levels of Nrf2 and its target genes, which may contribute to the increase of intracellular ROS level, consequently, induced mitochondria apoptosis. These results generated a rationale for further investigation of DHB combined with CDDP as a potential therapeutic strategy in lung cancer.

GSH depletion and consequent AKT inhibition contribute to the Nrf2 knockdown-induced decrease in proliferation in glioblastoma U251 cells

Nuclear factor erythroid 2-related factor 2 (Nrf2), a pivotal transcription regulator that controls the expression of numerous antioxidant and cytoprotective genes, was recently defined as a proto-oncogene. However, the role and mechanism of Nrf2 in glioma pathoetiology remain unclear. In the present study, we first evaluated the expression patterns of Nrf2 in normal human astrocytes and 3 glioblastoma (GBM) cell lines (U251, U87 and A172) and found that all 3 GBM cell lines overexpressed Nrf2, with the highest level observed in the U251 cells. We further assessed the biological effects of Nrf2 in U251 cells by specific knockdown of Nrf2 using lentivirus‑mediated RNA interference. We discovered that Nrf2 deficiency led to a decrease in U251 cell proliferation and caused intracellular redox imbalance [diminished glutathione (GSH) levels and increased reactive oxygen species (ROS) levels]. Both N-acetylcysteine and glutathione monoethyl ester (GMEE) supplementation completely eliminated the increased levels of ROS that were present in the Nrf2‑deficient U251 cells. However, only GMEE supplementation both reversed Nrf2 deficiency-induced cell growth arrest and restored intracellular GSH levels. Moreover, AKT and ERK1/2 signaling were both impaired in the Nrf2-knockdown U251 cells, but GMEE supplementation restored AKT signaling but not ERK1/2 signaling, and blocking AKT signaling with an AKT-specific inhibitor greatly diminished the GMEE-induced Nrf2-deficient cell proliferation. In conclusion, our findings revealed novel functions for Nrf2 in the regulation of redox status and cell proliferation, and that intracellular GSH levels and AKT signaling are required for this process, a new viewpoint by which to comprehend the role and underlying mechanism of Nrf2 in tumorigenesis.

Effect of resveratrol analogue, DMU-212, on antioxidant status and apoptosis-related genes in rat model of hepatocarcinogenesis

The aim of the study was to examine whether antioxidant properties of 3,4,4',5-tetramethoxystilbene (DMU-212) contribute to its anticarcinogenic activity and whether DMU-212 affects the expression of apoptosis-related genes. Two-stage model of hepatocarcinogenesis was used; male Wistar rats were challenged with N-nitrosodiethylamine (NDEA), 200 mg/kg body weight (b.w.), intraperitoneal, then phenobarbital (PB) in drinking water (0.05%) was administered. Simultaneously, DMU-212 was given per os at a dose 20 or 50 mg/kg b.w. two times a week for 16 weeks. DMU-212 caused a moderate decrease in hepatic thiobarbituric acid reactive substances and protein carbonyls concentration elevated in rats treated with NDEA/PB. The activity of antioxidant enzymes examined reduced by NDEA/PB treatment was not restored in rats coadministered with DMU-212. Effects of DMU-212 on messenger RNA (mRNA) expression of antioxidant enzymes in rats challenged with NDEA/PB were diversified; no changes in their protein expression were noted in any of the groups. The expression of 17,000 genes was analyzed by Affymetrix® Rat Gene 1.1 ST Array; 15 apoptosis-related genes were selected and validated by RT-q PCR. The combined treatment with NDEA/PB and DMU-212 increased the mRNA level of some genes driving mitochondria-mediated apoptosis, whereas the mRNA expression of some anti-apoptotic genes triggering receptor-mediated apoptosis was reduced. The expression of genes encoding caspases-4, -8, -9, and -12 was also increased in rats treated with DMU-212. Although antioxidant effect of DMU-212 in rats challenged with NDEA/PB was moderate, its potential anticarcinogenic properties were demonstrated as evidenced by modulation of apoptosis-related genes.

Long-Term Alteration of Reactive Oxygen Species Led to Multidrug Resistance in MCF-7 Cells

Reactive oxygen species (ROS) play an important role in multidrug resistance (MDR). This study aimed to investigate the effects of long-term ROS alteration on MDR in MCF-7 cells and to explore its underlying mechanism. Our study showed both long-term treatments of H₂O₂ and glutathione (GSH) led to MDR with suppressed iROS levels in MCF-7 cells. Moreover, the MDR cells induced by 0.1 μM H₂O₂ treatment for 20 weeks (MCF-7/ROS cells) had a higher viability and proliferative ability than the control MCF-7 cells. MCF-7/ROS cells also showed higher activity or content of intracellular antioxidants like glutathione peroxidase (GPx), GSH, superoxide dismutase (SOD), and catalase (CAT). Importantly, MCF-7/ROS cells were characterized by overexpression of MDR-related protein 1 (MRP1) and P-glycoprotein (P-gp), as well as their regulators NF-E2-related factor 2 (Nrf2), hypoxia-inducible factor 1 (HIF-1α), and the activation of PI3K/Akt pathway in upstream. Moreover, several typical MDR mediators, including glutathione S-transferase-π (GST-π) and c-Myc and Protein Kinase Cα (PKCα), were also found to be upregulated in MCF-7/ROS cells. Collectively, our results suggest that ROS may be critical in the generation of MDR, which may provide new insights into understanding of mechanisms of MDR.

The Role of the Nrf2/ARE Antioxidant System in Preventing Cardiovascular Diseases

It is widely believed that consuming foods and beverages that have high concentrations of antioxidants can prevent cardiovascular diseases and many types of cancer. As a result, many articles have been published that give the total antioxidant capacities of foods in vitro. However, many antioxidants behave quite differently in vivo. Some of them, such as resveratrol (in red wine) and epigallocatechin gallate or EGCG (in green tea) can activate the nuclear erythroid-2 like factor-2 (Nrf2) transcription factor. It is a master regulator of endogenous cellular defense mechanisms. Nrf2 controls the expression of many antioxidant and detoxification genes, by binding to antioxidant response elements (AREs) that are commonly found in the promoter region of antioxidant (and other) genes, and that control expression of those genes. The mechanisms by which Nrf2 relieves oxidative stress and limits cardiac injury as well as the progression to heart failure are described. Also, the ability of statins to induce Nrf2 in the heart, brain, lung, and liver is mentioned. However, there is a negative side of Nrf2. When over-activated, it can cause (not prevent) cardiovascular diseases and multi-drug resistance cancer.

Genetic alterations in hepatocellular carcinoma: An update

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths worldwide. Although recent advances in therapeutic approaches for treating HCC have improved the prognoses of patients with HCC, this cancer is still associated with a poor survival rate mainly due to late diagnosis. Therefore, a diagnosis must be made sufficiently early to perform curative and effective treatments. There is a need for a deeper understanding of the molecular mechanisms underlying the initiation and progression of HCC because these mechanisms are critical for making early diagnoses and developing novel therapeutic strategies. Over the past decade, much progress has been made in elucidating the molecular mechanisms underlying hepatocarcinogenesis. In particular, recent advances in next-generation sequencing technologies have revealed numerous genetic alterations, including recurrently mutated genes and dysregulated signaling pathways in HCC. A better understanding of the genetic alterations in HCC could contribute to identifying potential driver mutations and discovering novel therapeutic targets in the future. In this article, we summarize the current advances in research on the genetic alterations, including genomic instability, single-nucleotide polymorphisms, somatic mutations and deregulated signaling pathways, implicated in the initiation and progression of HCC. We also attempt to elucidate some of the genetic mechanisms that contribute to making early diagnoses of and developing molecularly targeted therapies for HCC.

Colonic Lamina Propria Inflammatory Cells from Patients with IBD Induce the Nuclear Factor-E2 Related Factor-2 Thereby Leading to Greater Proteasome Activity and Apoptosis Protection in Human Colonocytes

BACKGROUND

The antioxidant transcription factor Nrf2 confers broad cytoprotection and has a dual role in tumorigenesis. Enhancing proteasome activity is one mechanism by which Nrf2 can promote cancer development, e.g., colorectal cancer. This study investigated whether this potential oncogenic effect of Nrf2 emerges already from the epithelial adaptation to persistent oxidative stress during inflammatory bowel disease (IBD).

METHODS

Reactive oxygen species (ROS)-producing inflammatory myeloid cells (IMCs) from colon tissue of patients with IBD were cocultured with human NCM460 colonocytes. ARE-luciferase-, c-H2DCF-DA-assays, Western blotting, and quantitative polymerase chain reaction were performed for assessing Nrf2-activity, intracellular ROS-level, and Nrf2-target gene expression. Proteasome activity was quantified by Suc-LLVY-amido-4-methylcumarin-assay, and apoptosis by caspase-3/-7 assay and PARP1-Western blots. Nrf2, proteasome proteins, and IMCs were analyzed in IBD-tissues by immunohistochemistry.

RESULTS

IMC-coculture caused a temporary increase of ROS in NCM460, followed by Nrf2 activation and elevated expression of ROS-protecting enzymes (NQO1, GCLC). This was accompanied by Nrf2-dependent expression of proteasome proteins (PSMD4, PSMA5) and an enhanced proteasome activity in IMC-cocultured NCM460. Nrf2-siRNA or the ROS-scavenger Tiron blocked these alterations. Depending on Nrf2-induced proteasome activity, IMC-cocultured NCM460 or Colo320 cancer cells were less sensitive to apoptosis (TRAIL-/etoposide induced). Immunostaining of IBD-tissues confirmed Nrf2 activation in the colonic epithelium within inflamed areas, along with greater proteasome protein expression.

CONCLUSIONS

IMC/NCM460-coculture experiments and immunohistochemistry of colonic tissues from patients with IBD reveal a Nrf2-dependent adaptation of colon epithelial cells to oxidative stress caused by inflammatory cells. This involves increased proteasome activity and apoptosis resistance that protect from tissue damage due to colitis on one hand, but on the other hand, may favor carcinogenesis.

Nrf2 and Notch Signaling in Lung Cancer: Near the Crossroad

The transcription factor Nrf2 (NF-E2 related factor 2) is a master regulator of the cell antioxidant response associated with tumor growth and resistance to cytotoxic treatments. In particular, Nrf2 induces upregulation of cytoprotective genes by interacting with the closely situated AREs (Antioxidant Response Elements) in response to endogenous or exogenous stress stimuli and takes part to several oncogenic signaling pathways. Among these, the crosstalk with Notch pathway has been shown to enhance cytoprotection and maintenance of cellular homeostasis, tissue organization by modulating cell proliferation kinetics, and stem cell self-renewal in several organs. The role of Notch and Nrf2 related pathways in tumorigenesis is highly variable and when they are both abnormally activated they can synergistically cause neoplastic proliferation by promoting cell survival, differentiation, invasion, and metastases. NFE2L2, KEAP1, and NOTCH genes family appear in the list of significantly mutated genes in tumors in both combined and individual sets, supporting the crucial role that the aberrant Nrf2-Notch crosstalk might have in cancerogenesis. In this review, we summarize current knowledge about the alterations of Nrf2 and Notch pathways and their reciprocal transcriptional regulation throughout tumorigenesis and progression of lung tumors, supporting the potentiality of putative biomarkers and therapeutic targets.

An overview of chemical inhibitors of the Nrf2-ARE signaling pathway and their potential applications in cancer therapy

The Nuclear factor erythroid 2-related factor 2 (Nrf2) is a key transcription factor regulating a wide array of genes for antioxidant and detoxification enzymes in response to oxidative and xenobiotic stress. A large number of Nrf2-antioxidant response element (ARE) activators have been screened for use as chemopreventive agents in oxidative stress-related diseases and even cancer. However, constitutive activation of Nrf2 occurs in a variety of cancers. Aberrant activation of Nrf2 is correlated with cancer progression, chemoresistance, and radioresistance. In this review, we examine recent studies of Nrf2-ARE inhibitors in the context of cancer therapy. We enumerate the possible Nrf2-inhibiting mechanisms of these compounds, their effects sensitizing cancer cells to chemotherapeutic agents, and the prospect of applying them in clinical cancer therapy.

Gene regulatory effects of disease-associated variation in the NRF2 network

Reactive oxygen species (ROS), which are both a natural byproduct of oxidative metabolism and an undesirable byproduct of many environmental stressors, can damage all classes of cellular macromolecules and promote diseases from cancer to neurodegeneration. The actions of ROS are mitigated by the transcription factor NRF2, which regulates expression of antioxidant genes via its interaction with cis-regulatory antioxidant response elements (AREs). However, despite the seemingly straightforward relationship between the opposing forces of ROS and NRF2, regulatory precision in the NRF2 network is essential. Genetic variants that alter NRF2 stability or alter ARE sequences have been linked to a range of diseases. NRF2 hyperactivating mutations are associated with tumorigenesis. On the subtler end of the spectrum, single nucleotide variants (SNVs) that alter individual ARE sequences have been linked to neurodegenerative disorders including progressive supranuclear palsy and Parkinson’s disease, as well as other diseases. Although the human health implications of NRF2 dysregulation have been recognized for some time, a systems level view of this regulatory network is beginning to highlight key NRF2-targeted AREs consistently associated with disease.

Isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), fumarate hydratase (FH): three players for one phenotype in cancer?

In the early 1920s Otto Warburg observed that cancer cells have altered metabolism and from this, posited that mitochondrial dysfunction underpinned the aetiology of cancers. The more recent identification of mutations of mitochondrial metabolic enzymes in a wide range of human cancers has now provided a direct link between metabolic alterations and cancer. In this review we discuss the consequences of dysfunction of three metabolic enzymes involved in or associated with the tricarboxylic acid (TCA) cycle: succinate dehydrogenase (SDH), fumarate hydratase (FH) and isocitrate dehydrogenase (IDH) focusing on the similarity between the phenotypes of cancers harbouring these mutations.

Cancer drug resistance: redox resetting renders a way

Disruption of redox homeostasis is a crucial factor in the development of drug resistance, which is a major problem facing current cancer treatment. Compared with normal cells, tumor cells generally exhibit higher levels of reactive oxygen species (ROS), which can promote tumor progression and development. Upon drug treatment, some tumor cells can undergo a process of 'Redox Resetting' to acquire a new redox balance with higher levels of ROS accumulation and stronger antioxidant systems. Evidence has accumulated showing that the 'Redox Resetting' enables cancer cells to become resistant to anticancer drugs by multiple mechanisms, including increased rates of drug efflux, altered drug metabolism and drug targets, activated prosurvival pathways and inefficient induction of cell death. In this article, we provide insight into the role of 'Redox Resetting' on the emergence of drug resistance that may contribute to pharmacological modulation of resistance.

Brusatol Enhances the Radiosensitivity of A549 Cells by Promoting ROS Production and Enhancing DNA Damage

NF-E2-related factor 2 (Nrf2) has been identified as a master regulatory factor in the protection of cells from oxidative and electrophilic stress. However, overexpression of Nrf2 in lung cancer may cause chemoresistance, as well as radioresistance. In this study, we examined the relationship between radioresistance and Nrf2 protein levels in H1299, A549, and H460 cells, and finally chose the A549 cell line to continue with due to its strong radioresistance and high Nrf2 protein levels. We found that the Nrf2 inhibitor, brusatol, could prevent the increase and accumulation of Nrf2 after exposure to irradiation. Additionally, following treatment with 80 nM brusatol, A549 cells became sensitive to irradiation, suffering severe DNA damage. Combination treatment with brusatol and ionizing radiation (IR) can distinctly increase the level of reactive oxygen species in A549 cells, causing a 1.8-fold increase compared with the control, and a 1.4-fold increase compared with IR alone. In fact, in the treatment with both brusatol and IR, lung cancer cell proliferation is halted, gradually leading to cell death. Because Nrf2 is closely linked to DNA damage repair, inhibiting the function of Nrf2, as in brusatol treatment, may increase the DNA damage caused by radiotherapy or chemotherapy, possibly enhancing the efficacy of chemotherapeutic drugs. Our study is the first to demonstrate brusatol’s ability to enhance the responsiveness of lung cancer cells to irradiation, and its potential application as a natural sensitizer in radiotherapy.

Emerging role of NRF2 in chemoresistance by regulating drug-metabolizing enzymes and efflux transporters

Chemoresistance is a disturbing barrier in cancer therapy, which always results in limited therapeutic options and unfavorable prognosis. Nuclear factor E2-related factor 2 (NRF2) controls the expression of genes encoding cytoprotective enzymes and transporters that protect against oxidative stress and electrophilic injury to maintain intrinsic redox homeostasis. However, recent studies have demonstrated that aberrant activation of NRF2 due to genetic and/or epigenetic mutations in tumor contributes to the high expression of phase I and phase II drug-metabolizing enzymes, phase III transporters, and other cytoprotective proteins, which leads to the decreased therapeutic efficacy of anticancer drugs through biotransformation or extrusion during chemotherapy. Therefore, a better understanding of the role of NRF2 in regulation of these enzymes and transporters in tumors is necessary to find new strategies that improve chemotherapeutic efficacy. In this review, we summarized the recent findings about the chemoresistance-promoting role of NRF2, NRF2-regulated phase I and phase II drug-metabolizing enzymes, phase III drug efflux transporters, and other cytoprotective genes. Most importantly, the potential of NRF2 was proposed to counteract drug resistance in cancer treatment.

The Dual Roles of NRF2 in Cancer

NRF2 has been traditionally considered as a tumor suppressor because its cytoprotective functions are deemed to be the main cellular defense mechanism against exogenous and endogenous insults, including xenobiotics and oxidative stress. However, several recent studies demonstrate that hyperactivation of the NRF2 pathway creates an environment that favors the survival of normal as well as malignant cells, protecting them against oxidative stress, chemotherapeutic agents, and radiotherapy. In a rapidly advancing field, this review summarizes some of the known mechanisms by which NRF2 can exert its oncogenic functions, and describes the current status of NRF2 inhibitors, providing a clear rationale for the consideration of NRF2 as a powerful putative therapeutic target in cancer treatment.

Cytoplasmic localization of Nrf2 promotes colorectal cancer with more aggressive tumors via upregulation of PSMD4

Differences in subcellular localization of Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) have been associated with poor outcomes in human cancers. However, the prognostic value of subcellular localization of Nrf2 in colorectal cancer and the underlying mechanism in tumor invasion remain unknown. We enrolled tumors from colorectal patients to evaluate Nrf2, NQO1, and HO-1 expression by immunohistochemistry. NQO1 and HO-1 positive tumors showed nearly complete expression of Nrf2 in the nucleus and/or showed partial expression in the nucleus/cytoplasm (nNrf2); however, tumors negative for NQO1 and HO-1 showed almost complete expression of Nrf2 in the cytoplasm and/or partial expression in the nucleus/cytoplasm (cNrf2). Kaplan-Meier and Cox regression analysis indicated poorer overall survival in patients with cNrf2 tumors than with nNrf2 tumors. Cell models provided evidence that cNrf2, rather than nNrf2, was responsible for cell invasion and soft agar growth triggered by activation of the NF-κB/AKT/β-catenin cascade. Mechanistically, cNrf2 persistently increased PSMD4 expression by the HIF1α/β-catenin axis, whereas PSMD4 reciprocally enhanced Nrf2 nuclear export by increasing CRM1 expression through p53 degradation. The mechanistic action of the cell model was further confirmed with a nude mouse animal model in which xenograft tumors induced by cNrf2 were nearly completely suppressed by the proteasomal inhibitor carfilzomib or the β-catenin inhibitor XAV939. We therefore suggest that PSMD4 or β-catenin might be potential targets for suppressing tumor aggressiveness, and consequently, improving outcomes in patients whose tumors express cNrf2.

Mitochondrial permeabilization without caspase activation mediates the increase of basal apoptosis in cells lacking Nrf2

Nuclear factor E2-related factor-2 (Nrf2) is a cap'n'collar/basic leucine zipper (b-ZIP) transcription factor which acts as sensor of oxidative and electrophilic stress. Low levels of Nrf2 predispose cells to chemical carcinogenesis but a dark side of Nrf2 function also exists because its unrestrained activation may allow the survival of potentially dangerous damaged cells. Since Nrf2 inhibition may be of therapeutic interest in cancer, and a decrease of Nrf2 activity may be related with degenerative changes associated with aging, it is important to investigate how the lack of Nrf2 function activates molecular mechanisms mediating cell death. Murine Embryonic Fibroblasts (MEFs) bearing a Nrf2 deletion (Nrf2KO) displayed diminished cellular growth rate and shortened lifespan compared with wild-type MEFs. Basal rates of DNA fragmentation and histone H2A.X phosphorylation were higher in Nrf2KO MEFs, although steady-state levels of reactive oxygen species were not significantly increased. Enhanced rates of apoptotic DNA fragmentation were confirmed in liver and lung tissues from Nrf2KO mice. Apoptosis in Nrf2KO MEFs was associated with a decrease of Bcl-2 but not Bax levels, and with the release of the mitochondrial pro-apoptotic factors cytochrome c and AIF. Procaspase-9 and Apaf-1 were also increased in Nrf2KO MEFs but caspase-3 was not activated. Inhibition of XIAP increased death in Nrf2KO but not in wild-type MEFs. Mitochondrial ultrastructure was also altered in Nrf2KO MEFs. Our results support that Nrf2 deletion produces mitochondrial dysfunction associated with mitochondrial permeabilization, increasing basal apoptosis through a caspase-independent and AIF-dependent pathway.

The anti-oxidative transcription factor Nuclear factor E2 related factor-2 (Nrf2) counteracts TGF-β1 mediated growth inhibition of pancreatic ductal epithelial cells -Nrf2 as determinant of pro-tumorigenic functions of TGF-β1

BACKGROUND

Nuclear factor E2 related factor-2 (Nrf2) is an oxidative stress inducible transcription factor being essential in regulating cell homeostasis. Thus, acute induction of Nrf2 in epithelial cells exposed to inflammation confers protection from oxidative cell damage and mutagenesis supporting an anti-tumorigenic role for Nrf2. However, pancreatic ductal adenocarcinoma (PDAC) is characterized by persistent Nrf2 activity conferring therapy resistance which points to a pro-tumorigenic role of Nrf2. A similar dichotomous role in tumorigenesis is described for the Transforming Growth Factor-beta 1 (TGF-β1). The present study therefore aimed at elucidating whether the switch of Nrf2 function towards a tumor promoting one relates to the modulation of TGF-β1 induced cell responses and whether this might occur early in PDAC development.

METHODS

In situ analysis comprised immunohistochemical stainings of activated (phosphorylated) Nrf2 and Ki67 in pancreatic tissues containing normal ducts and pancreatic intraepithelial neoplasia (PanINs). In vitro, Nrf2 levels in benign (H6c7-pBp), premalignant (H6c7-kras) and malignant (Colo357) pancreatic ductal epithelial cells were modulated by Nrf2 specific siRNA or Nrf2 overexpression. Then, the effect of Nrf2 alone and in combination with TGF-β1 on cell growth and survival was investigated by cell counting, Ki67 staining and apoptosis assays. The underlying cell signaling was investigated by western blotting. Statistical analysis was performed by Shapiro-Wilk test for normal distribution. Parametric data were analyzed by one-way ANOVA, while non-parametric data were analyzed by Kruskal-Wallis one-way ANOVA on ranks.

RESULTS

Significantly elevated expression of activated Nrf2 and Ki67 could be detected in PanINs but not in normal pancreatic ductal epithelium. While the effect of Nrf2 on basal cell growth of H6c7-pBp, H6c7-kras and Colo357 cells was minor, it clearly attenuated the growth inhibiting effects of TGF-β1 in all cell lines. This enhanced Nrf2-mediated cell survival was predominantly based on an enhanced proliferative activity. Accordingly, expression of p21 expression along with expression of phospho-p38 and phospho-Smad3 was diminished whereas Erk-phosphorylation was enhanced under these conditions.

CONCLUSIONS

Overall, our data demonstrate that Nrf2 being elevated in early precursor lesions counteracts the growth inhibiting function of TGF-β1 already in benign and premalignant pancreatic ductal epithelial cells. This could represent one fundamental mechanism underlying the functional switch of both- TGF-β1 and Nrf2 - which may manifest already in early stages of PDAC development.

Targeting autophagy to sensitive glioma to temozolomide treatment

Temozolomide (TMZ), an alkylating agent, is widely used for treating primary and recurrent high-grade gliomas. However, the efficacy of TMZ is often limited by the development of resistance. Recently, studies have found that TMZ treatment could induce autophagy, which contributes to therapy resistance in glioma. To enhance the benefit of TMZ in the treatment of glioblastomas, effective combination strategies are needed to sensitize glioblastoma cells to TMZ. In this regard, as autophagy could promote cell survival or autophagic cell death, modulating autophagy using a pharmacological inhibitor, such as chloroquine, or an inducer, such as rapamycin, has received considerably more attention. To understand the effectiveness of regulating autophagy in glioblastoma treatment, this review summarizes reports on glioblastoma treatments with TMZ and autophagic modulators from in vitro and in vivo studies, as well as clinical trials. Additionally, we discuss the possibility of using autophagy regulatory compounds that can sensitive TMZ treatment as a chemotherapy for glioma treatment.

Glutamine at focus: versatile roles in cancer

During the past decade, a heightened understanding of metabolic pathways in cancer has significantly increased. It is recognized that many tumor cells are genetically programmed and have involved an abnormal metabolic state. Interestingly, this increased metabolic autonomy generates dependence on various nutrients such as glucose and glutamine. Both of these components participate in various facets of metabolic activity that allow for energy production, synthesis of biomass, antioxidant defense, and the regulation of cell signaling. Here, we outline the emerging data on glutamine metabolism and address the molecular mechanisms underlying glutamine-induced cell survival. We also discuss novel therapeutic strategies to exploit glutamine addiction of certain cancer cell lines.

Tumor cell survival pathways activated by photodynamic therapy: a molecular basis for pharmacological inhibition strategies

Photodynamic therapy (PDT) has emerged as a promising alternative to conventional cancer therapies such as surgery, chemotherapy, and radiotherapy. PDT comprises the administration of a photosensitizer, its accumulation in tumor tissue, and subsequent irradiation of the photosensitizer-loaded tumor, leading to the localized photoproduction of reactive oxygen species (ROS). The resulting oxidative damage ultimately culminates in tumor cell death, vascular shutdown, induction of an antitumor immune response, and the consequent destruction of the tumor. However, the ROS produced by PDT also triggers a stress response that, as part of a cell survival mechanism, helps cancer cells to cope with the PDT-induced oxidative stress and cell damage. These survival pathways are mediated by the transcription factors activator protein 1 (AP-1), nuclear factor E2-related factor 2 (NRF2), hypoxia-inducible factor 1 (HIF-1), nuclear factor κB (NF-κB), and those that mediate the proteotoxic stress response. The survival pathways are believed to render some types of cancer recalcitrant to PDT and alter the tumor microenvironment in favor of tumor survival. In this review, the molecular mechanisms are elucidated that occur post-PDT to mediate cancer cell survival, on the basis of which pharmacological interventions are proposed. Specifically, pharmaceutical inhibitors of the molecular regulators of each survival pathway are addressed. The ultimate aim is to facilitate the development of adjuvant intervention strategies to improve PDT efficacy in recalcitrant solid tumors.

The Tumorigenic Roles of the Cellular REDOX Regulatory Systems

The cellular REDOX regulatory systems play a central role in maintaining REDOX homeostasis that is crucial for cell integrity, survival, and proliferation. To date, a substantial amount of data has demonstrated that cancer cells typically undergo increasing oxidative stress as the tumor develops, upregulating these important antioxidant systems in order to survive, proliferate, and metastasize under these extreme oxidative stress conditions. Since a large number of chemotherapeutic agents currently used in the clinic rely on the induction of ROS overload or change of ROS quality to kill the tumor, the cancer cell REDOX adaptation represents a significant obstacle to conventional chemotherapy. In this review we will first examine the different factors that contribute to the enhanced oxidative stress generally observed within the tumor microenvironment. We will then make a comprehensive assessment of the current literature regarding the main antioxidant proteins and systems that have been shown to be positively associated with tumor progression and chemoresistance. Finally we will make an analysis of commonly used chemotherapeutic drugs that induce ROS. The current knowledge of cancer cell REDOX adaptation raises the issue of developing novel and more effective therapies for these tumors that are usually resistant to conventional ROS inducing chemotherapy.

Hydrogen peroxide - production, fate and role in redox signaling of tumor cells

Hydrogen peroxide (H₂O₂) is involved in various signal transduction pathways and cell fate decisions. The mechanism of the so called “redox signaling” includes the H₂O₂-mediated reversible oxidation of redox sensitive cysteine residues in enzymes and transcription factors thereby altering their activities. Depending on its intracellular concentration and localization, H₂O₂ exhibits either pro- or anti-apoptotic activities. In comparison to normal cells, cancer cells are characterized by an increased H₂O₂ production rate and an impaired redox balance thereby affecting the microenvironment as well as the anti-tumoral immune response. This article reviews the current knowledge about the intracellular production of H₂O₂ along with redox signaling pathways mediating either the growth or apoptosis of tumor cells. In addition it will be discussed how the targeting of H₂O₂-linked sources and/or signaling components involved in tumor progression and survival might lead to novel therapeutic targets.

Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates airway epithelial barrier integrity

BACKGROUND

Inhaled corticosteroids enhance airway epithelial barrier integrity. However, the mechanism by which they accomplish this is unclear. Therefore, we investigated steroid-inducible genes and signaling pathways that were involved in enhancing airway epithelial barrier integrity.

METHODS

A human bronchial epithelial cell line (16HBE cells) was cultured with 10(-6) M dexamethasone (DEX) for 3 days to enhance epithelial barrier integrity. After measuring transepithelial electrical resistance (TER) and paracellular permeability, we extracted total RNA from 16HBE cells and performed microarray and pathway analysis. After we identified candidate genes and a canonical pathway, we measured TER and immunostained for tight junction (TJ) and adherent junction (AJ) proteins in cells that had been transfected with specific small interfering RNAs (siRNAs) for these genes.

RESULTS

We identified a nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated oxidative stress response pathway which was primarily involved in the steroid-induced enhancement of airway epithelial barrier integrity. Transfecting cells with Nrf2 specific siRNA reduced the steroid-induced enhancement of airway epithelial barrier integrity and the accumulation of TJ and AJ proteins at sites of cell-cell contact. Moreover, based on pathway analysis, aldehyde oxidase 1 (AOX1) was identified as a downstream enzyme of Nrf2. Transfecting cells with AOX1-specific siRNA also reduced the steroid-induced enhancement of airway epithelial barrier integrity.

CONCLUSIONS

Our results indicated that the Nrf2/AOX1 pathway was important for enhancing airway epithelial barrier integrity. Because the airway epithelium of asthmatics is susceptible to reduced barrier integrity, this pathway might be a new therapeutic target for asthma.

SASS6 overexpression is associated with mitotic chromosomal abnormalities and a poor prognosis in patients with colorectal cancer

Spindle assembly abnormal protein 6 homolog (SASS6) plays an important role in the regulation of centriole duplication. To date, the genetic alteration of SASS6 has not been reported in human cancers. In the present study, we examined whether SASS6 expression is abnormally regulated in colorectal cancers (CRCs). Increased SASS6 mRNA and protein expression levels were observed in 49 (60.5%) of the 81 primary CRCs and 11 (57.9%) of the 19 primary CRCs, respectively. Moreover, the upregulation of SASS6 mRNA expression was statistically significant (P=0.0410). Next, using DLD-1 colon cancer cells inducibly expressing SASS6, SASS6 overexpression was shown to induce centrosome amplification, mitotic abnormalities such as chromosomal misalignment and lagging chromosome, and chromosomal numerical changes. Furthermore, SASS6 overexpression was associated with anaphase bridge formation, a type of mitotic structural abnormality, in primary CRCs (P<0.01). SASS6 upregulation in colon cancer was also revealed in the Cancer Genome Atlas (TCGA) data and was shown to be an independent predictor of poor survival (multivariate analysis: hazard ratio, 2.805; 95% confidence interval, 1.244‑7.512; P=0.0112). Finally, further analysis of the TCGA data demonstrated SASS6 upregulation in a modest manner in 8 of 11 cancer types other than colon cancer, and SASS6 upregulation was found to be associated with a poor survival outcome in patients with kidney renal cell carcinoma and lung adenocarcinoma. Our present findings revealed that the upregulation of SASS6 expression is involved in the pathogenesis of CRC and is associated with a poor prognosis among patients with colon cancer. They also suggest that SASS6 upregulation is a genetic abnormality relatively common in human cancer.

The Crosstalk between Nrf2 and TGF-β1 in the Epithelial-Mesenchymal Transition of Pancreatic Duct Epithelial Cells

Nrf2 and TGF-β1 both affect tumorigenesis in a dual fashion, either by preventing carcinogen induced carcinogenesis and suppressing tumor growth, respectively, or by conferring cytoprotection and invasiveness to tumor cells during malignant transformation. Given the involvement of Nrf2 and TGF-β1 in the adaptation of epithelial cells to persistent inflammatory stress, e.g. of the pancreatic duct epithelium during chronic pancreatitis, a crosstalk between Nrf2 and TGF-β1 can be envisaged. By using premalignant human pancreatic duct cells (HPDE) and the pancreatic ductal adenocarcinoma cell line Colo357, we could show that Nrf2 and TGF-β1 independently but additively conferred an invasive phenotype to HPDE cells, whereas acting synergistically in Colo357 cells. This was accompanied by differential regulation of EMT markers like vimentin, Slug, L1CAM and E-cadherin. Nrf2 activation suppressed E-cadherin expression through an as yet unidentified ARE related site in the E-cadherin promoter, attenuated TGF-β1 induced Smad2/3-activity and enhanced JNK-signaling. In Colo357 cells, TGF-β1 itself was capable of inducing Nrf2 whereas in HPDE cells TGF-β1 per-se did not affect Nrf2 activity, but enhanced Nrf2 induction by tBHQ. In Colo357, but not in HPDE cells, the effects of TGF-β1 on invasion were sensitive to Nrf2 knock-down. In both cell lines, E-cadherin re-expression inhibited the proinvasive effect of Nrf2. Thus, the increased invasion of both cell lines relates to the Nrf2-dependent downregulation of E-cadherin expression. In line, immunohistochemistry analysis of human pancreatic intraepithelial neoplasias in pancreatic tissues from chronic pancreatitis patients revealed strong Nrf2 activity already in premalignant epithelial duct cells, accompanied by partial loss of E-cadherin expression. Our findings indicate that Nrf2 and TGF-β1 both contribute to malignant transformation through distinct EMT related mechanisms accounting for an invasive phenotype. Provided a crosstalk between both pathways, Nrf2 and TGF-β1 mutually promote their tumorigenic potential, a condition manifesting already at an early stage during inflammation induced carcinogenesis of the pancreas.

Comparative Proteomic Characterization of 4 Human Liver-Derived Single Cell Culture Models Reveals Significant Variation in the Capacity for Drug Disposition, Bioactivation, and Detoxication

In vitro preclinical models for the assessment of drug-induced liver injury (DILI) are usually based on cryopreserved primary human hepatocytes (cPHH) or human hepatic tumor-derived cell lines; however, it is unclear how well such cell models reflect the normal function of liver cells. The physiological, pharmacological, and toxicological phenotyping of available cell-based systems is necessary in order to decide the testing purpose for which they are fit. We have therefore undertaken a global proteomic analysis of 3 human-derived hepatic cell lines (HepG2, Upcyte, and HepaRG) in comparison with cPHH with a focus on drug metabolizing enzymes and transport proteins (DMETs), as well as Nrf2-regulated proteins. In total, 4946 proteins were identified, of which 2722 proteins were common across all cell models, including 128 DMETs. Approximately 90% reduction in expression of cytochromes P450 was observed in HepG2 and Upcyte cells, and approximately 60% in HepaRG cells relative to cPHH. Drug transporter expression was also lower compared with cPHH with the exception of MRP3 and P-gp (MDR1) which appeared to be significantly expressed in HepaRG cells. In contrast, a high proportion of Nrf2-regulated proteins were more highly expressed in the cell lines compared with cPHH. The proteomic database derived here will provide a rational basis for the context-specific selection of the most appropriate ‘hepatocyte-like’ cell for the evaluation of particular cellular functions associated with DILI and, at the same time, assist in the construction of a testing paradigm which takes into account the in vivo disposition of a new drug.

Discovery of direct inhibitors of Keap1-Nrf2 protein-protein interaction as potential therapeutic and preventive agents

The Keap1–Nrf2–ARE pathway is an important antioxidant defense mechanism that protects cells from oxidative stress and the Keap1–Nrf2 protein–protein interaction (PPI) has become an important drug target to upregulate the expression of ARE-controlled cytoprotective oxidative stress response enzymes in the development of therapeutic and preventive agents for a number of diseases and conditions. However, most known Nrf2 activators/ARE inducers are indirect inhibitors of Keap1–Nrf2 PPI and they are electrophilic species that act by modifying the sulfhydryl groups of Keap1׳s cysteine residues. The electrophilicity of these indirect inhibitors may cause "off-target" side effects by reacting with cysteine residues of other important cellular proteins. Efforts have recently been focused on the development of direct inhibitors of Keap1–Nrf2 PPI. This article reviews these recent research efforts including the development of high throughput screening assays, the discovery of peptide and small molecule direct inhibitors, and the biophysical characterization of the binding of these inhibitors to the target Keap1 Kelch domain protein. These non-covalent direct inhibitors of Keap1–Nrf2 PPI could potentially be developed into effective therapeutic or preventive agents for a variety of diseases and conditions.