Direct interaction between Nrf2 and p21(Cip1/WAF1) upregulates the Nrf2-mediated antioxidant response

Role of Nrf2 in cell senescence regulation

Nuclear factor-E2-related factor 2 (Nrf2) is a key transcription factor known to be involved in maintaining cell redox balance and signal transduction and plays central role in reducing intracellular oxidative stress damage, delaying cell senescence and preventing age-related diseases. However, it has been shown that the level of Nrf2 decreases with age and that the silencing of the Nrf2 gene is associated with the induction of premature senescence. Therefore, a plethora of researchers have focused on elucidating the regulatory mechanism of Nrf2 in the prevention of cell senescence. This complex regulatory mechanism of Nrf2 in the cell senescence process involves coordinated regulation of multiple signaling molecules. After summarizing the function of Nrf2 and its relationship with cell senescence pathway, this review focuses on the recent advances and progress made in elucidating the regulatory mechanism of Nrf2 in the cell senescence process. Additionally, the information collected here may provide insights for further research on Nrf2, in particular, on its regulatory mechanism in the cell senescence process.

Involvement of the p62/Nrf2/HO-1 pathway in the browning effect of irisin in 3T3-L1 adipocytes

Irisin has gained attention because of its potential applications in the treatment of metabolic diseases. Accumulating evidence indicates that irisin attenuates obesity via the browning of white adipose tissue; however, the underlying mechanisms are unclear. Here, we evaluated the effects of irisin on adipocyte browning and the underlying mechanisms. The western blotting and immunofluorescence analyses demonstrated that irisin significantly induced the up-regulation of brown fat-specific proteins (PGC1α, PRDM16, and UCP-1) and HO-1 in 3T3-L1 adipocytes. Moreover, irisin significantly increased the levels of cytosolic p62 and nuclear Nrf2. These effects of irisin in the adipocytes were attenuated by treatment with SnPP or p62 siRNA. In addition, the browning effect of irisin was observed in BAT-WT-1 cells. These findings suggest that irisin induced browning effect via the p62/Nrf2/HO-1 signalling pathway and that it may be a potential candidate for preventing or treating obesity.

Dietary Flavonoids in p53-Mediated Immune Dysfunctions Linking to Cancer Prevention

The p53 protein plays a central role in mediating immune functioning and determines the fate of the cells. Its role as a tumor suppressor, and in transcriptional regulation and cytokine activity under stress conditions, is well defined. The wild type (WT) p53 functions as a guardian for the genome, while the mutant p53 has oncogenic roles. One of the ways that p53 combats carcinogenesis is by reducing inflammation. WT p53 functions as an anti-inflammatory molecule via cross-talk activity with multiple immunological pathways, such as the major histocompatibility complex I (MHCI) associated pathway, toll-like receptors (TLRs), and immune checkpoints. Due to the multifarious roles of p53 in cancer, it is a potent target for cancer immunotherapy. Plant flavonoids have been gaining recognition over the last two decades to use as a potential therapeutic regimen in ameliorating diseases. Recent studies have shown the ability of flavonoids to suppress chronic inflammation, specifically by modulating p53 responses. Further, the anti-oxidant Keap1/Nrf2/ARE pathway could play a crucial role in mitigating oxidative stress, leading to a reduction of chronic inflammation linked to the prevention of cancer. This review aims to discuss the pharmacological properties of plant flavonoids in response to various oxidative stresses and immune dysfunctions and analyzes the cross-talk between flavonoid-rich dietary intake for potential disease prevention.

Saponin Formosanin C-induced Ferritinophagy and Ferroptosis in Human Hepatocellular Carcinoma Cells

Ferroptosis, a recently discovered form of iron-dependent cell death, requires an increased level of lipid-reactive oxygen species (ROS). Ferritinophagy, a ferritin degradation pathway, depends on a selective autophagic cargo receptor (NCOA4). By screening various types of natural compounds, formosanin C (FC) was identified as a novel ferroptosis inducer, characterized by attenuations of FC-induced viability inhibition and lipid ROS formation in the presence of ferroptosis inhibitor. FC also induced autophagic flux, evidenced by preventing autophagic marker LC3-II degradation and increasing yellow LC3 puncta in tandem fluorescent-tagged LC3 (mRFP-GFP) reporter plasmid (ptfLC3) transfected cells when combined with autophagic flux inhibitor. It is noteworthy that FC-induced ferroptosis and autophagic flux were stronger in HepG2 cells expressing higher NCOA4 and lower ferritin heavy chain 1 (FTH1) levels, agreeing with the results of gene expression analysis using CTRP and PRISM, indicating that FTH1 expression level exhibited a significant negative correlation with the sensitivity of the cells to a ferroptosis inducer. Confocal and electron microscopy confirmed the pronounced involvement of ferritinophagy in FC-induced ferroptosis in the cells with elevated NCOA4. Since ferroptosis is a non-apoptotic form of cell death, our data suggest FC has chemotherapeutic potential against apoptosis-resistant HCC with a higher NCOA4 expression via ferritinophagy.

Associations between the Nrf2/Keap1 pathway and mitochondrial functions in colorectal cancer are affected by metastasis

BACKGROUND

Both mitochondria and the Nrf2/Keap1 pathway are targets of cancer therapy. Reactive oxygen species released from mitochondria can activate Nrf2, and the Nrf2/Keap1 pathway affects glycolysis, oxidative phosphorylation, mitochondrial biogenesis and mitophagy.

OBJECTIVE

This study investigates the associations between the expressions of proteins in the Nrf2/Keap1 pathway and those related to mitochondrial function and glycolysis in colorectal cancer (CRC) with or without metastasis.

METHODS

The protein levels of HO1, Nrf2, Keap1, Bach1, p21, p62, NRF1, LC3, ATP5B, HSP60 and GAPDH in the normal and tumor tissues of 60 CRC subjects were determined by Western blot.

RESULTS

The Keap1 protein levels, the ATP5B/HSP60 ratio and the BEC index were higher in the tumor than in the normal tissues of CRC with or without metastasis. The following clusters were found in the dendrogram: Nrf2 and p21 with ATP5B and GADPH in all the tissues and with NRF1 in all except the tumor tissues with metastasis; Bach1 with ATP5B and GAPDH in the tumor tissues; Keap1 with p62 in all the tissues, with LC3 in the tumor tissues and with NRF1 and HO1 in the tumor tissues with metastasis.

CONCLUSIONS

Nrf2, Keap1, Bach1 and p21 have the association with the proteins related to mitochondrial functions different among the tissues of CRC with or without metastasis.

Autophagy is involved in the protective effect of p21 on LPS-induced cardiac dysfunction

p21 has emerged as an important protein involved in cardiovascular diseases, but its role remains controversial. Recently, p21 has been reported to mediate inflammatory responses. As inflammatory responses are a feature of sepsis, our study investigated whether p21 has a role in cardiac dysfunction induced by sepsis and analyzed the mechanisms involved. To establish a mouse sepsis model, p21 global knockout (p21KO) and C57BL/6J wild-type (WT) male mice were treated with 5 mg/kg LPS intraperitoneally for 6, 24, or 48 h. After LPS stimulation, the level of p21 had significantly increased in the WT mice and in cardiomyocytes. Cardiac dysfunction induced by LPS was markedly aggravated in p21KO mice relative to that of WT mice. Downregulation of p21 expression exacerbated the LPS-mediated inflammatory response, and it increased oxidative stress as well as mitochondrial damage in the heart and in cardiomyocytes. In contrast, overexpressing p21 attenuated the increase of TNFα and promoted the increase of SOD2. Moreover, p21 regulated the LPS-induced autophagy activation; that is, the increase in autophagy was impaired when p21 expression was decreased, whereas the increase was significant when p21 was overexpressed. The autophagy inducer rapamycin partially rescued the cardiac deterioration caused by p21 downregulation in the LPS-stimulated groups. In addition, p21 regulated the autophagy level by interacting with LC3B. These results revealed that p21 controls LPS-induced cardiac dysfunction by modulating inflammatory and oxidative stress, and it is partially dependent on regulating the autophagy level. This study is the first to show that p21 could interact with LC3B to promote autophagy for the improvement of cardiac function during sepsis.

p53 as a hub in cellular redox regulation and therapeutic target in cancer

The TP53 tumor suppressor gene encodes a DNA-binding transcription factor that regulates multiple cellular processes including cell growth and cell death. The ability of p53 to bind to DNA and activate transcription is tightly regulated by post-translational modifications and is dependent on a reducing cellular environment. Some p53 transcriptional target genes are involved in regulation of the cellular redox homeostasis, e.g. TIGAR and GLS2. A large fraction of human tumors carry TP53 mutations, most commonly missense mutations that lead to single amino acid substitutions in the core domain. Mutant p53 proteins can acquire so called gain-of-function activities and influence the cellular redox balance in various ways, for instance by binding of the Nrf2 transcription factor, a major regulator of cellular redox state. The DNA-binding core domain of p53 has 10 cysteine residues, three of which participate in holding a zinc atom that is critical for p53 structure and function. Several novel compounds that refold and reactivate missense mutant p53 bind to specific p53 cysteine residues. These compounds can also react with other thiols and target components of the cellular redox system, such as glutathione. Dual targeting of mutant p53 and redox homeostasis may allow more efficient treatment of cancer.

NRF2, a Transcription Factor for Stress Response and Beyond

Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that regulates the cellular defense against toxic and oxidative insults through the expression of genes involved in oxidative stress response and drug detoxification. NRF2 activation renders cells resistant to chemical carcinogens and inflammatory challenges. In addition to antioxidant responses, NRF2 is involved in many other cellular processes, including metabolism and inflammation, and its functions are beyond the originally envisioned. NRF2 activity is tightly regulated through a complex transcriptional and post-translational network that enables it to orchestrate the cell’s response and adaptation to various pathological stressors for the homeostasis maintenance. Elevated or decreased NRF2 activity by pharmacological and genetic manipulations of NRF2 activation is associated with many metabolism- or inflammation-related diseases. Emerging evidence shows that NRF2 lies at the center of a complex regulatory network and establishes NRF2 as a truly pleiotropic transcription factor. Here we summarize the complex regulatory network of NRF2 activity and its roles in metabolic reprogramming, unfolded protein response, proteostasis, autophagy, mitochondrial biogenesis, inflammation, and immunity.

Redox toxicology of environmental chemicals causing oxidative stress

Living organisms are surrounded with heavy metals such as methylmercury, manganese, cobalt, cadmium, arsenic, as well as pesticides such as deltamethrin and paraquat, or atmospheric pollutants such as quinone. Extensive studies have demonstrated a strong link between environmental pollutants and human health. Redox toxicity is proposed as one of the main mechanisms of chemical-induced pathology in humans. Acting as both a sensor of oxidative stress and a positive regulator of antioxidants, the nuclear factor erythroid 2-related factor 2 (NRF2) has attracted recent attention. However, the role NRF2 plays in environmental pollutant-induced toxicity has not been systematically addressed. Here, we characterize NRF2 function in response to various pollutants, such as metals, pesticides and atmospheric quinones. NRF2 related signaling pathways and epigenetic regulations are also reviewed.

A ruthenium(II)-curcumin compound modulates NRF2 expression balancing the cancer cell death/survival outcome according to p53 status

Abstract

Background

Tumor progression and tumor response to anticancer therapies may be affected by activation of oncogenic pathways such as the antioxidant one induced by NRF2 (nuclear factor erythroid 2-related factor 2) transcription factor and the pathways modified by deregulation of oncosuppressor p53. Often, oncogenic pathways may crosstalk between them increasing tumor progression and resistance to anticancer therapies. Therefore, understanding that interplay is critical to improve cancer cell response to therapies. In this study we aimed at evaluating NRF2 and p53 in several cancer cell lines carrying different endogenous p53 status, using a novel curcumin compound since curcumin has been shown to target both NRF2 and p53 and have anti-tumor activity.

Methods

We performed biochemical and molecular studies by using pharmacologic of genetic inhibition of NRF2 to evaluate the effect of curcumin compound in cancer cell lines of different tumor types bearing wild-type (wt) p53, mutant (mut) p53 or p53 null status.

Results

We found that the curcumin compound induced a certain degree of cell death in all tested cancer cell lines, independently of the p53 status. At molecular level, the curcumin compound induced NRF2 activation, mutp53 degradation and/or wtp53 activation. Pharmacologic or genetic NRF2 inhibition further increased the curcumin-induced cell death in both mutp53- and wtp53-carrying cancer cell lines while it did not increase cell death in p53 null cells, suggesting a cytoprotective role for NRF2 and a critical role for functional p53 to achieve an efficient cancer cell response to therapy.

Conclusions

These findings underline the prosurvival role of curcumin-induced NRF2 expression in cancer cells even when cells underwent mutp53 downregulation and/or wtp53 activation. Thus, NRF2 inhibition increased cell demise particularly in cancer cells carrying p53 either wild-type or mutant suggesting that p53 is crucial for efficient cancer cell death. These results may represent a paradigm for better understanding the cancer cell response to therapies in order to design more efficient combined anticancer therapies targeting both NRF2 and p53.

Nuclear factor erythroid 2 (NF-E2) p45-related factor 2 interferes with homeodomain-interacting protein kinase 2/p53 activity to impair solid tumors chemosensitivity

Resistance to chemotherapy represents a major hurdle to successful cancer treatment. A key role for efficient response to anticancer therapies is played by TP53 oncosuppressor gene that indeed is mutated in 50% of human cancers or inactivated at protein level in the remaining 50%. Homeodomain-interacting protein kinase 2 (HIPK2) is the wild-type p53 (wtp53) apoptotic activator, and its inhibition by hypoxia or hyperglycemia may contribute to tumor chemoresistance mainly by impairing p53 apoptotic activity. Another important molecule able to induce chemoresistance is nuclear factor erythroid 2 (NF-E2) p45-related factor 2 (NRF2) transcription factor, whose activation by oxidative and/or electrophilic stress regulates a transcriptional antioxidant program allowing cancer cells to adapt and survive to stresses. NRF2 may shift from cytoprotective to tumor-promoting function, according to tumor phases. NRF2 may crosstalk with both wtp53 and mutant p53 (mutp53), inhibiting the wtp53 apoptotic function and strengthening the mutp53 oncogenic function. NRF2 has also been shown to induce HIPK2 mRNA expression cooperating in inducing cytoprotection. Although HIPK2, p53, and NRF2 have been individually extensively studied, their interplay has not been clearly addressed yet. On the basis of the background and our results, we aim at hypothesizing the unexpected pro-survival activity played by the NRF2/HIPK2/p53 interplay that can be hijacked by cancer cells to bypass drugs cytotoxicity.

Sodium butyrate inhibits high cholesterol-induced neuronal amyloidogenesis by modulating NRF2 stabilization-mediated ROS levels: involvement of NOX2 and SOD1

The gut-brain axis is currently being studied as a therapeutic strategy for neurological diseases, especially Alzheimer's disease (AD). Obesity results in the gut microbiota dysbiosis, which includes butyrate-producing bacteria are reduced. Although sodium butyrate (NaB) has emerged as the potential therapeutic substance in AD, there is a lack of detailed results into what signaling pathways affect amyloidogenesis in AD induced by obesity. Thus, we investigated the regulatory role of NaB on amyloidogenesis in neuronal cells under high cholesterol. In our results, we verified that increased amyloid β peptide (Aβ) accumulation in the brain of obese mice and a reduction in butyrate-producing bacteria due to the gut microbiota dysbiosis induced by obesity. We showed that NaB decreased the expression levels of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) and Aβ accumulation induced by high cholesterol in SK-N-MC cells. We demonstrated that NaB was absorbed in cells through sodium-coupled monocarboxylate transporter 1 (SMCT1) and then inhibited high cholesterol-induced Aβ accumulation. Subsequently, we also observed that reactive oxygen species (ROS) were overproduced because of increased NADPH oxidase 2 (NOX2) expression under high cholesterol. Meanwhile, NaB decreased NOX2 levels through a reduction of NF-κB activity, which ultimately inhibited Aβ accumulation caused by high cholesterol. We demonstrated that NaB increased the expression levels of p21 under high cholesterol, contributing to p21/NRF2 (Nuclear factor erythroid 2-related factor 2) colocalization, which leads to NRF2 stabilization. NRF2 stabilization causes NF-κB inactivation, followed by NOX2 suppression and superoxide dismutase 1 (SOD1) upregulation. Thus, NaB with SOD1 silencing under high cholesterol did not eliminate excessive ROS, and eventually resulted in Aβ accumulation. In conclusion, we demonstrated that NaB prevents excessive ROS through NOX2 suppression and SOD1 upregulation by p21/NRF2 pathway, which is critical for inhibiting BACE1-dependent amyloidogenesis in neuronal cells exposed to high cholesterol environment.

NRF2 Regulation Processes as a Source of Potential Drug Targets against Neurodegenerative Diseases

NRF2 acts by controlling gene expression, being the master regulator of the Phase II antioxidant response, and also being key to the control of neuroinflammation. NRF2 activity is regulated at several levels, including protein degradation by the proteasome, transcription, and post-transcription. The purpose of this review is to offer a concise and critical overview of the main mechanisms of NRF2 regulation and their actual or potential use as targets for the treatment of neurodegenerative diseases.

RPB5-Mediating Protein Promotes Cholangiocarcinoma Tumorigenesis and Drug Resistance by Competing With NRF2 for KEAP1 Binding

BACKGROUND AND AIMS

Cancer cell survival depends on the balance between reactive oxygen species production and scavenging, which is regulated primarily by NRF2 during tumorigenesis. Here, we demonstrate that deletion of RBP5-mediating protein (RMP) in an autonomous mouse model of intrahepatic cholangiocarcinoma (ICC) delays tumor progression.

APPROACH AND RESULTS

RMP-overexpressing tumor cells exhibited enhanced tolerance to oxidative stress and apoptosis. Mechanistically, RMP competes with NRF2 for binding to the Kelch domain of KEAP1 (Kelch-like ECH-associated protein 1) through the E**E motif, leading to decreased NRF2 degradation via ubiquitination, thus increasing NRF2 nuclear translocation and downstream transactivation of antioxidant genes. This RMP-KEAP1-NRF2 axis promotes ICC tumorigenesis, metastasis, and drug resistance. Consistent with these findings, the RMP level in human ICC is positively correlated with the protein level of NRF2 and is associated with poor prognosis.

CONCLUSION

These findings reveal that RMP is involved in the oxidative stress defense program and could be exploited for targeted cancer therapies.

BCATc modulates crosstalk between the PI3K/Akt and the Ras/ERK pathway regulating proliferation in triple negative breast cancer

The cytosolic branched chain aminotransferase (BCATc) protein has been found to be highly expressed in breast cancer subtypes, including triple negative breast cancer (TNBC), compared with normal breast tissue. The catabolism of branched-chain amino acids (BCAAs) by BCATc leads to the production of glutamate and key metabolites which further drive the TCA cycle, important for cellular metabolism and growth. Upregulation of BCATc has been associated with increased cell proliferation, cell cycle progression and metastasis in several malignancies including breast, gliomas, ovarian and colorectal cancer but the underlying mechanisms are unclear. As nutrient levels of BCAAs, substrates of BCATc, regulate the PI3K/Akt pathway we hypothesized that increased expression of BCATc would contribute to tumour cell growth through upregulation of the insulin/IGF-1 signalling pathway. This pathway is known to potentiate proliferation and metastasis of malignant cells through the activation of PI3K/Akt and the RAS/ERK signalling cascades. Here we show that knockdown of BCATc significantly reduced insulin and IGF-1-mediated proliferation, migration and invasion of TNBC cells. An analysis of this pathway showed that when overexpressed BCATc regulates proliferation through the PI3K/Akt axis, whilst simultaneously attenuating the Ras/Erk pathway indicating that BCATc acts as a conduit between these two pathways. This ultimately led to an increase in FOXO3a, a key regulator of cell proliferation and Nrf2, which mediates redox homeostasis. Together this data indicates that BCATc regulates TNBC cell proliferation, migration and invasion through the IGF-1/insulin PI3K/Akt pathway, culminating in the upregulation of FOXO3a and Nrf2, pointing to a novel therapeutic target for breast cancer treatment.

Inhibition of Nrf2 might enhance the anti-tumor effect of temozolomide in glioma cells via inhibition of Ras/Raf/MEK signaling pathway

BACKGROUND

Glioblastoma (GBM) is the most common aggressive primary cancer occurring in the brain tissue. GBM accounts 16% of primary brain tumors and half of gliomas. Additionally, the incidence of GBM is increases with aging, and reaches the peak at the age of 75 to 84 years. The survival of patients with GBM remains at a low level, only less than 5% patients diagnosed with GBM survive for 5 years. Temozolomide (TMZ) is a DNA alkylating agent and is currently a first line chemotherapeutic treatment for GBM. TMZ combined with radiation therapy has been shown to prolong the overall survival (OS) to 14.6 months compared with 12.1 months for radiation therapy alone. NF-E2-related factor 2 (Nrf2) is a transcription factor that contains seven functional domains. The binding of Keap1 to Nrf2 is a central regulator of the cellular defense mechanism against environmental stresses.

METHODS

First, Nrf2 overexpression and inhibition models were constructed in U251 cells using transfection. The percentage of viable cells was detected using the MTT assay. Then, the expression of the HO-1 regulator was detected using qPCR, and the concentrations of oxidative stress related factors were detected using ELISAs. The levels of proteins related to oxidative stress and the Ras/Raf/MEK signaling pathway was detected using western blotting analysis.

RESULTS

We initially established Nrf2 inhibition and activation cell models in U251 cells and found that the inhibition of Nrf2 expression decreased the mRNA and protein levels of the anti-oxidative enzymes, as well as the secretion of these enzymes into the cellular microenvironment. These effects might be mediated by the inhibition of Ras/Raf/MEK signaling pathway, leading to the inhibition of cellular proliferation.

CONCLUSIONS

Inhibition of Nrf2 expression might enhance the effect of TMZ on the treatment of GBM and might be a new therapeutic strategy.

Flavolignans from Silymarin as Nrf2 Bioactivators and Their Therapeutic Applications

Silymarin (SM) is a mixture of flavolignans extracted from the seeds of species derived from Silybum marianum, commonly known as milk thistle or St. Mary'sthistle. These species have been widely used in the treatment of liver disorders in traditional medicine since ancient times. Several properties had been attributed to the major SM flavolignans components, identified as silybin, isosilybin, silychristin, isosilychristin, and silydianin. Previous research reported antioxidant and protective activities, which are probably related to the activation of the nuclear factor erythroid 2 (NFE2)-related factor 2 (Nrf2), known as a master regulator of the cytoprotector response. Nrf2 is a redox-sensitive nuclear transcription factor able to induce the downstream-associated genes. The disruption of Nrf2 signaling has been associated with different pathological conditions. Some identified phytochemicals from SM had shown to participate in the Nrf2 signaling pathway; in particular, they have been suggested as activators that disrupt interactions in the Keap1-Nrf2 system, but also as antioxidants or with additional actions regarding Nrf2 regulation. Thus, the study of these molecules makes them appear attractive as novel targets for the treatment or prevention of several diseases.

Molecular mechanisms and systemic targeting of NRF2 dysregulation in cancer

NF-E2-related factor 2 (NRF2) is a master regulator of redox homeostasis and provides cellular protection against oxidants and electrophiles by inducing the expression of a wide array of phase II cytoprotective genes. Until now, a number of NRF2 activators have been developed for treatment of chronic diseases and some are under evaluation in the clinical studies. On the other hand, accumulating evidence indicates that NRF2 confers chemoresistance and radioresistance, and its expression is correlated with poor prognosis in cancer patients. Studies in the last decade demonstrate that diverse mechanisms such as somatic mutations, accumulation of KEAP1 binding proteins, transcriptional dysregulation, oncogene activation, and accumulation of reactive metabolites contribute to NRF2 activation in cancer. In the present review, we illustrate the molecular mechanisms governing the function of NRF2 and explain how they are hijacked in cancer. We also provide some examples of NRF2 inhibitors together with a brief explanation of their mechanisms of action.

Sporadic activation of an oxidative stress-dependent NRF2-p53 signaling network in breast epithelial spheroids and premalignancies

Breast and mammary epithelial cells experience different local environments during tissue development and tumorigenesis. Microenvironmental heterogeneity gives rise to distinct cell regulatory states whose identity and importance are just beginning to be appreciated. Cellular states diversify when clonal three-dimensional (3D) spheroids are cultured in basement membrane, and one such state is associated with stress tolerance and poor response to anticancer therapeutics. Here, we found that this state was jointly coordinated by the NRF2 and p53 pathways, which were costabilized by spontaneous oxidative stress within 3D cultures. Inhibition of NRF2 or p53 individually disrupted some of the transcripts defining the regulatory state but did not yield a notable phenotype in nontransformed breast epithelial cells. In contrast, combined perturbation prevented 3D growth in an oxidative stress-dependent manner. By integrating systems models of NRF2 and p53 signaling in a single oxidative stress network, we recapitulated these observations and made predictions about oxidative stress profiles during 3D growth. NRF2 and p53 signaling were similarly coordinated in normal breast epithelial tissue and hormone-negative ductal carcinoma in situ lesions but were uncoupled in triple-negative breast cancer (TNBC), a subtype in which p53 is usually mutated. Using the integrated model, we correlated the extent of this uncoupling in TNBC cell lines with the importance of NRF2 in the 3D growth of these cell lines and their predicted handling of oxidative stress. Our results point to an oxidative stress tolerance network that is important for single cells during glandular development and the early stages of breast cancer.

Jdp2-deficient granule cell progenitors in the cerebellum are resistant to ROS-mediated apoptosis through xCT/Slc7a11 activation

The Jun dimerization protein 2 (Jdp2) is expressed predominantly in granule cell progenitors (GCPs) in the cerebellum, as was shown in Jdp2-promoter-Cre transgenic mice. Cerebellum of Jdp2-knockout (KO) mice contains lower number of Atoh-1 positive GCPs than WT. Primary cultures of GCPs from Jdp2-KO mice at postnatal day 5 were more resistant to apoptosis than GCPs from wild-type mice. In Jdp2-KO GCPs, the levels of both the glutamate‒cystine exchanger Sc7a11 and glutathione were increased; by contrast, the activity of reactive oxygen species (ROS) was decreased; these changes confer resistance to ROS-mediated apoptosis. In the absence of Jdp2, a complex of the cyclin-dependent kinase inhibitor 1 (p21^Cip1) and Nrf2 bound to antioxidant response elements of the Slc7a11 promoter and provide redox control to block ROS-mediated apoptosis. These findings suggest that an interplay between Jdp2, Nrf2, and p21^Cip1 regulates the GCP apoptosis, which is one of critical events for normal development of the cerebellum.

Crosstalk between the mTOR and Nrf2/ARE signaling pathways as a target in the improvement of long-term potentiation

In recent years, a significant progress was made in understanding molecular mechanisms of long-term memory. Long-term memory formation requires strengthening of neuronal connections (LTP, long-term potentiation) associated with structural rearrangement of neurons. The key role in the synthesis of proteins essential for these rearrangements belong to mTOR (mammalian target of rapamycin) complexes and signaling pathways involved in mTOR regulation. Suppression of mTOR activity may impair synaptic plasticity and long-term memory, while mTOR activation inhibits autophagy, thereby potentiating amyloidosis and development of Alzheimer's disease (AD) accompanied by irreversible memory loss. Because of this, suppression/inhibition of mTOR might have unpredictable consequences on memory. The Nrf2/ARE signaling pathway affects almost all mitochondrial processes. The activation of this pathway improves memory and exhibits therapeutic effect in AD. In this review, we discuss the crosstalk between the Nrf2/ARE signaling and mTOR in the maintenance of synaptic plasticity. Nrf2 pathway can be activated by pharmacological agents and by changes in mitochondria functioning accompanying various neuronal dysfunctions.

Transcriptomic profiling identifies a critical role of Nrf2 in regulating the inflammatory response to fly ash particles in mouse lung

Exposure to combustion-derived nanoparticles is recognized as a major health hazard, but the molecular responses are still insufficiently described. The transcription factor erythroid 2-related factor 2 (Nrf2, also known as NFE2L2) is a master regulator of the pulmonary defense system against insults by particulate matter. However, its downstream molecular processes are not fully characterized. In the current study, BALB/c wild-type (WT) and Nrf2^-/- mice were exposed by intranasal administration to fly ash particles (F3-S; 20 mg/kg BW), which were collected from a municipal waste incinerator in China, for three consecutive days. Using a comparative transcriptomics approach, the pulmonary global gene expression profiles to F3-S exposure were characterized for both genotypes. The preponderance of the differentially-expressed genes (DEGs) in WT mice induced by the fly ash particles, was related to inflammation. Functional enrichment and molecular pathway mapping of the DEGs specific to Nrf2^-/- mice exposed to the particles revealed that all of the top 10 perturbed molecular pathways were associated with the inflammatory response. Our study identified a transcriptional signature related to the initial pulmonary injury in mouse upon fly ash exposure, and suggests an anti-inflammatory role of Nrf2 in protecting the lung against such exposure.

Potential Applications of NRF2 Modulators in Cancer Therapy

The nuclear factor erythroid 2-related factor 2 (NRF2)-Kelch-like ECH-associated protein 1 (KEAP1) regulatory pathway plays an essential role in protecting cells and tissues from oxidative, electrophilic, and xenobiotic stress. By controlling the transactivation of over 500 cytoprotective genes, the NRF2 transcription factor has been implicated in the physiopathology of several human diseases, including cancer. In this respect, accumulating evidence indicates that NRF2 can act as a double-edged sword, being able to mediate tumor suppressive or pro-oncogenic functions, depending on the specific biological context of its activation. Thus, a better understanding of the mechanisms that control NRF2 functions and the most appropriate context of its activation is a prerequisite for the development of effective therapeutic strategies based on NRF2 modulation. In line of principle, the controlled activation of NRF2 might reduce the risk of cancer initiation and development in normal cells by scavenging reactive-oxygen species (ROS) and by preventing genomic instability through decreased DNA damage. In contrast however, already transformed cells with constitutive or prolonged activation of NRF2 signaling might represent a major clinical hurdle and exhibit an aggressive phenotype characterized by therapy resistance and unfavorable prognosis, requiring the use of NRF2 inhibitors. In this review, we will focus on the dual roles of the NRF2-KEAP1 pathway in cancer promotion and inhibition, describing the mechanisms of its activation and potential therapeutic strategies based on the use of context-specific modulation of NRF2.

Tsg101 positively regulates P62-Keap1-Nrf2 pathway to protect hearts against oxidative damage

Currently, most antioxidants do not show any favorable clinical outcomes in reducing myocardial ischemia-reperfusion (I/R) injury, suggesting an urgent need for exploring a new regulator of redox homeostasis in I/R hearts. Here, using heart-specific transgenic (TG) and knockdown (KD) mouse models, tumor susceptibility gene 101 (Tsg101) is defined as a novel cardiac-protector against I/R-triggered oxidative stress. RNA sequencing and bioinformatics data surprisingly reveal that most upregulated genes in Tsg101-TG hearts are transcribed by Nrf2. Accordingly, pharmacological inhibition of Nrf2 offsets Tsg101-elicited cardio-protection. Mechanistically, Tsg101 interacts with SQSTM1/p62 through its PRR domain, and promotes p62 aggregation, leading to recruitment of Keap1 for degradation by autophagosomes and release of Nrf2 to the nucleus. Furthermore, knockout of p62 abrogates Tsg101-induced cardio-protective effects during I/R. Hence, our findings uncover a previously unrecognized role of Tsg101 in the regulation of p62/Keap1/Nrf2 signaling cascades and provide a new strategy for the treatment of ischemic heart disease.

Nonlinearities in the cellular response to ionizing radiation and the role of p53 therein

Many aspects of the cellular response to agents such as ionizing radiation that cause genotoxic and/or oxidative stress exhibit a nonlinear relationship to the applied stress level. These include elements of the antioxidant response and of the damage-signaling pathways that determine cell fate decisions. The wild-type p53 protein, which is mutated in many cancers, coordinates these responses and is a key determinant of this nonlinearity. Indeed, p53 has been referred to as a 'cellular rheostat' that favors antioxidant/cytoprotective functions at low stress levels while switching to a pro-oxidant/cytotoxic role under high-stress conditions. For solid tumor-derived cell lines, moderate doses of radiation, typical of those used to generate clonogenic survival curves (i.e. ≤10 Gy), predominantly invoke a dose-dependent cytostatic response. For cancer cell lines with wild-type p53, cytostasis is primarily associated with features of senescence, whereas cancer cells with aberrant p53 primarily undergo endopolyploidization and enlargement. In line with a commentary by Meyn et al. [Int J Radiat Biol. 2009, 85:107-115] concluding that apoptosis is not the primary cause of radiation-induced loss of clonogenicity in solid tumor-derived cell lines, significant levels of apoptosis are typically seen only after higher doses (≥5 Gy) and this is almost all of the delayed (rather than primary) type. Nonlinearity of the oxidative/genotoxic stress response is already apparent in the early antioxidant events activated by transcription factors such as p53 and Nrf2 and the Ref1 transcription coactivator. These cytoprotective pathways serve to minimize damage to important cellular targets caused by reactive oxygen species (ROS) and other electrophiles. After high/supra-lethal levels of stress these inducible antioxidant pathways can be deactivated in a manner that would reinforce the establishment of the pro-oxidant state, resulting in elevated ROS levels and to cytostasis or apoptosis. Understanding the complex regulation of these damage-signaling pathways in relation to the stress levels is important for the optimal utilization of radiation therapy for cancer.

The PI3K-AKT network at the interface of oncogenic signalling and cancer metabolism

The altered metabolic programme of cancer cells facilitates their cell-autonomous proliferation and survival. In normal cells, signal transduction pathways control core cellular functions, including metabolism, to couple the signals from exogenous growth factors, cytokines or hormones to adaptive changes in cell physiology. The ubiquitous, growth factor-regulated phosphoinositide 3-kinase (PI3K)-AKT signalling network has diverse downstream effects on cellular metabolism, through either direct regulation of nutrient transporters and metabolic enzymes or the control of transcription factors that regulate the expression of key components of metabolic pathways. Aberrant activation of this signalling network is one of the most frequent events in human cancer and serves to disconnect the control of cell growth, survival and metabolism from exogenous growth stimuli. Here we discuss our current understanding of the molecular events controlling cellular metabolism downstream of PI3K and AKT and of how these events couple two major hallmarks of cancer: growth factor independence through oncogenic signalling and metabolic reprogramming to support cell survival and proliferation.

The NRF2 Signaling Network Defines Clinical Biomarkers and Therapeutic Opportunity in Friedreich's Ataxia

Friedreich’s ataxia (FA) is a trinucleotide repeats expansion neurodegenerative disorder, for which no cure or approved therapies are present. In most cases, GAA trinucleotide repetitions in the first intron of the FXN gene are the genetic trigger of FA, determining a strong reduction of frataxin, a mitochondrial protein involved in iron homeostasis. Frataxin depletion impairs iron–sulfur cluster biosynthesis and determines iron accumulation in the mitochondria. Mounting evidence suggests that these defects increase oxidative stress susceptibility and reactive oxygen species production in FA, where the pathologic picture is worsened by a defective regulation of the expression and signaling pathway modulation of the transcription factor NF-E2 p45-related factor 2 (NRF2), one of the fundamental mediators of the cellular antioxidant response. NRF2 protein downregulation and impairment of its nuclear translocation can compromise the adequate cellular response to the frataxin depletion-dependent redox imbalance. As NRF2 stability, expression, and activation can be modulated by diverse natural and synthetic compounds, efforts have been made in recent years to understand if regulating NRF2 signaling might ameliorate the pathologic defects in FA. Here we provide an analysis of the pharmaceutical interventions aimed at restoring the NRF2 signaling network in FA, elucidating specific biomarkers useful for monitoring therapeutic effectiveness, and developing new therapeutic tools.

Cullin 3 and Its Role in Tumorigenesis

Cullin 3 (Cul3) family of ubiquitin ligases comprises three components, the RING finger protein RBX1, the Cul3 scaffold, and a Bric-a-brac/Tramtrack/Broad complex (BTB) protein. The BTB protein serves as a bridge to connect Cul3 to substrate and is functionally equivalent to the combination of substrate adaptor and linker in other Cullin complexes. Human genome encodes for ~180 BTB proteins, implying a broad spectrum of ubiquitination signals and substrate repertoire. Accordingly, Cul3 ubiquitin ligases are involved in diverse cellular processes, including cell division, differentiation, cytoskeleton remodeling, stress responses, and nerve cell functions. Emerging evidence has pointed to the prominent role of Cul3 ubiquitin ligases in cancer. This chapter will describe recent advances on the roles of Cul3 E3 ligase complexes in regulating various cancer hallmarks and therapeutic responses and the mutation/dysregulation of Cul3 substrate adaptors in cancer. In particular, we will focus on several extensively studied substrate adaptors, such as Keap1, SPOP, KLHL20, and LZTR1, and will also discuss other recently identified Cul3 adaptors with oncogenic or tumor-suppressive functions. We conclude that Cul3 ubiquitin ligases represent master regulators of human malignancies and highlight the importance of developing modulating agents for oncogenic/tumor-suppressive Cul3 E3 ligase complexes to prevent or intervene tumorigenesis.

Nrf2 and the Nrf2-Interacting Network in Respiratory Inflammation and Diseases

Atmospheric pollutants and cigarette smoke influence the human respiratory system and induce airway inflammation, injury, and pathogenesis. Activation of the NF-E2-related factor 2 (Nrf2) transcription factor and downstream antioxidant response element (ARE)-mediated transcriptions play a central role in protecting respiratory cells against reactive oxidative species (ROS) that are induced by airway toxins and inflammation. Recent studies have revealed that Nrf2 can also target and activate many genes involved in developmental programs such as cell proliferation, cell differentiation, cell death, and metabolism. Nrf2 is closely regulated by the interaction with kelch-like ECH-associated protein 1 (Keap1), while also directly interacts with a number of other proteins, including inflammatory factors, transcription factors, autophagy mediators, kinases, epigenetic modifiers, etc. It is believed that the multiple target genes and the complicated interacting network of Nrf2 account for the roles of Nrf2 in physiologies and pathogeneses. This chapter summarizes the molecular functions and protein interactions of Nrf2, as well as the roles of Nrf2 and the Nrf2-interacting network in respiratory inflammation and diseases, including acute lung injury (ALI), asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (PF), cystic fibrosis (CF), viral/bacterial infections, and lung cancers. Therapeutic applications that target Nrf2 and its interacting proteins in respiratory diseases are also reviewed.

Repeated Fractions of X-Radiation to the Breast Fat Pads of Mice Augment Activation of the Autotaxin-Lysophosphatidate-Inflammatory Cycle

Breast cancer patients are usually treated with multiple fractions of radiotherapy (RT) to the whole breast after lumpectomy. We hypothesized that repeated fractions of RT would progressively activate the autotaxin–lysophosphatidate-inflammatory cycle. To test this, a normal breast fat pad and a fat pad containing a mouse 4T1 tumor were irradiated with X-rays using a small-animal “image-guided” RT platform. A single RT dose of 7.5 Gy and three daily doses of 7.5 Gy increased ATX activity and decreased plasma adiponectin concentrations. The concentrations of IL-6 and TNFα in plasma and of VEGF, G-CSF, CCL11 and CXCL10 in the irradiated fat pad were increased, but only after three fractions of RT. In 4T1 breast tumor-bearing mice, three fractions of 7.5 Gy augmented tumor-induced increases in plasma ATX activity and decreased adiponectin levels in the tumor-associated mammary fat pad. There were also increased expressions of multiple inflammatory mediators in the tumor-associated mammary fat pad and in tumors, which was accompanied by increased infiltration of CD45+ leukocytes into tumor-associated adipose tissue. This work provides novel evidence that increased ATX production is an early response to RT and that repeated fractions of RT activate the autotaxin–lysophosphatidate-inflammatory cycle. This wound healing response to RT-induced damage could decrease the efficacy of further fractions of RT.

The Regulation of NFE2L2 (NRF2) Signalling and Epithelial-to-Mesenchymal Transition in Age-Related Macular Degeneration Pathology

Age-related macular degeneration (AMD) is a mounting cause of loss of sight in the elderly in the developed countries, a trend enhanced by the continual ageing of the population. AMD is a multifactorial and only partly understood, malady. Unfortunately, there is no effective treatment for most AMD patients. It is known that oxidative stress (OS) damages the retinal pigment epithelium (RPE) and contributes to the progression of AMD. We review here the potential importance of two OS-related cellular systems in relation to AMD. First, the nuclear factor erythroid 2-related factor 2 (NFE2L2; NRF2)-mediated OS response signalling pathway is important in the prevention of oxidative damage and a failure of this system could be critical in the development of AMD. Second, epithelial-to-mesenchymal transition (EMT) represents a change in the cellular phenotype, which ultimately leads to the fibrosis encountered in RPE, a characteristic of AMD. Many of the pathways triggering EMT are promoted by OS. The possible interconnections between these two signalling routes are discussed here. From a broader perspective, the control of NFE2L2 and EMT as ways of preventing OS-derived cellular damage could be potentially valuable in the therapy of AMD.

Binding partners of NRF2: Functions and regulatory mechanisms

NRF2 is a redox-sensitive transcription factor that plays an important role in protecting organisms against diverse types of electrophiles or oxidants. The level of NRF2 is maintained low in normal cells, but highly elevated in cancer provoking chemoresistance or radioresistance. It is now recognized that NRF2 does not merely maintain the redox balance, but also plays significant roles in autophagy, apoptosis, cell cycle progression, and stem cell differentiation, all of which could be possibly attributable to the existence of multiple binding proteins. In the present manuscript, we summarize direct binding partners of NRF2 and illustrate how they bind to NRF2 and regulate its stability or activity.

The Role of Nrf2 Activity in Cancer Development and Progression

Nrf2 is a transcription factor that stimulates the expression of genes which have antioxidant response element-like sequences in their promoter. Nrf2 is a cellular protector, and this principle applies to both normal cells and malignant cells. While healthy cells are protected from DNA damage induced by reactive oxygen species, malignant cells are defended against chemo- or radiotherapy. Through our literature search, we found that Nrf2 activates several oncogenes unrelated to the antioxidant activity, such as Matrix metallopeptidase 9 (MMP-9), B-cell lymphoma 2 (BCL-2), B-cell lymphoma-extra large (BCL-xL), Tumour Necrosis Factor α (TNF-α), and Vascular endothelial growth factor A (VEGF-A). We also did a brief analysis of The Cancer Genome Atlas (TCGA) data of lung adenocarcinoma concerning the effects of radiation therapy and found that the therapy-induced Nrf2 activation is not universal. For instance, in the case of recurrent disease and radiotherapy, we observed that, for the majority of Nrf2-targeted genes, there is no change in expression level. This proves that the universal, axiomatic rationale that Nrf2 is activated as a response to chemo- and radiation therapy is wrong, and that each scenario should be carefully evaluated with the help of Nrf2-targeted genes. Moreover, there were nine genes involved in lipid peroxidation, which showed underexpression in the case of new radiation therapy: ADH1A, ALDH3A1, ALDH3A2, ADH1B, GPX2, ADH1C, ALDH6A1, AKR1C3, and NQO1. This may relate to the fact that, while some studies reported the co-activation of Nrf2 and other oncogenic signaling pathways such as Phosphoinositide 3-kinases (PI3K), mitogen-activated protein kinase (MAPK), and Notch1, other reported the inverse correlation between Nrf2 and the tumor-promoter Transcription Factor (TF), Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Lastly, Nrf2 establishes its activity through interactions at multiple levels with various microRNAs. MiR-155, miR-144, miR-28, miR-365-1, miR-93, miR-153, miR-27a, miR-142, miR-29-b1, miR-340, and miR-34a, either through direct repression of Nrf2 messenger RNA (mRNA) in a Kelch-like ECH-associated protein 1 (Keap1)-independent manner or by enhancing the Keap1 cellular level, inhibit the Nrf2 activity. Keap1–Nrf2 interaction leads to the repression of miR-181c, which is involved in the Nuclear factor kappa light chain enhancer of activated B cells (NF-κB) signaling pathway. Nrf2’s role in cancer prevention, diagnosis, prognosis, and therapy is still in its infancy, and the future strategic planning of Nrf2-based oncological approaches should also consider the complex interaction between Nrf2 and its various activators and inhibitors.

Nestin regulates cellular redox homeostasis in lung cancer through the Keap1-Nrf2 feedback loop

Abnormal cancer antioxidant capacity is considered as a potential mechanism of tumor malignancy. Modulation of oxidative stress status is emerging as an anti-cancer treatment. Our previous studies have found that Nestin-knockdown cells were more sensitive to oxidative stress in non-small cell lung cancer (NSCLC). However, the molecular mechanism by which Nestin protects cells from oxidative damage remains unclear. Here, we identify a feedback loop between Nestin and Nrf2 maintaining the redox homeostasis. Mechanistically, the ESGE motif of Nestin interacts with the Kelch domain of Keap1 and competes with Nrf2 for Keap1 binding, leading to Nrf2 escaping from Keap1-mediated degradation, subsequently promoting antioxidant enzyme generation. Interestingly, we also map that the antioxidant response elements (AREs) in the Nestin promoter are responsible for its induction via Nrf2. Taken together, our results indicate that the Nestin-Keap1-Nrf2 axis regulates cellular redox homeostasis and confers oxidative stress resistance in NSCLC.

Regulation of Nrf2 Signaling

Regulation of antioxidant gene expression is essential for controlling oxidative stress and maintaining physiological homeostasis. In this context, the nuclear factor E2-related factor 2 (Nrf2) has been identified as the chief regulator of the transcription of diverse antioxidant genes as well as many other cytoprotective genes. Nrf2 activity is subjected to the regulation at various levels including protein stability, transcription, and post-transcription. Among the various regulatory pathways, the Keap1-Cul3-Rbx1 axis is the most prominent regulator of Nrf2 activity. Being a tightly controlled transcriptional activator of antioxidant genes, Nrf2 signaling is intimately involved in health and disease. While Nrf2 is a protector against oxidative and electrophilic tissue injury, persistent activation of Nrf2 signaling may also contribute to disease pathophysiology, such as cancer progression.

Prognostic significance of 8-hydroxy-2'-deoxyguanosine in solid tumors: a meta-analysis

Background

High level of reactive oxygen species (ROS) has been detected in almost all cancers, which make it become one of the best-characterized phenotypes in cancers. Though ROS plays an important role in tumors, the degree of oxidative stress can be better evaluated by assessing stable metabolites of oxidative reactions because of its high instability. 8-hydroxy-2′-deoxyguanosine (8-OHdG), a product of oxidative damage to 2′-deoxyguanosine, is known as a useful marker for assessing oxidative DNA damage and has been a feature of carcinogenesis in several researches. But the exact prognostic value of 8-OHdG expression in patients with cancer is still unclear.

Methods

A comprehensive search was performed in PubMed, Web of Science, EMBASE. Eligible studies were included based on defined exclusion and inclusion criteria to perform a meta-analysis. STATA 14.0 was used to estimate pooled hazard ratios (HRs) with 95% confidence interval (95% CI), the heterogeneity among studies and publication bias to judge the prognostic value.

Results

A total of 2121 patients from 21 eligible studies were included in the meta-analysis. A significant association was found between elevated 8-OHdG expression and poor OS (overall survival) in cancer patients (pooled HR 1.921, 95% CI: 1.437–2.570); In the subgroup analysis, race of sample, cancer types, detection method of 8-OHdG, sample classification, detection location of 8-OHdG and paper quality (score more or less than 7) did not alter the association between 8-OHdG expression and cancer prognosis. Furthermore, 8-OHdG expression was an independent prognostic marker for overall survival in patients with cancer (pooled HR 2.110, 95% CI: 1.482–3.005) using Cox multivariate analyses.

Conclusions

This meta-analysis found that highly expressed 8-OHdG in tumor tissues may be a predictor of prognosis in most solid tumors. However, especially in breast cancer, low 8-OHdG expression is associated with poor prognosis, which is partly because of the increased antioxidant mechanisms in breast cancer tissues. This study demonstrates for the first time that 8-OHdG expression is associated with the prognosis of cancer patients. In the future, whether the expression level of 8-OHdG can be used as a biomarker for the prognosis of all human cancers requires more research.

Mechanisms and consequences of oxidant-induced renal preconditioning: an Nrf2-dependent, P21-independent, anti-senescence pathway

Background

P21, a cyclin kinase inhibitor, is upregulated by renal 'ischemic preconditioning' (IPC), and induces a 'cytoresistant' state. However, P21-induced cell cycle inhibition can also contribute to cellular senescence, a potential adverse renal event. Hence, this study assessed whether: (i) IPC-induced P21 upregulation is associated with subsequent renal senescence; and (ii) preconditioning can be established 'independent' of P21 induction and avoid a post-ischemic senescent state?

Methods

CD-1 mice were subjected to either IPC (5-15 min) or to a recently proposed 'oxidant-induced preconditioning' (OIP) strategy (tin protoporphyrin-induced heme oxygenase inhibition +/- parental iron administration). P21 induction [messenger RNA (mRNA)/protein], cell proliferation (KI-67, phosphohistone H3 nuclear staining), kidney senescence (P16ink4a; P19Arf mRNAs; senescence-associated beta-galactosidase levels) and resistance to ischemic acute kidney injury were assessed.

Results

IPC induced dramatic (10-25×) and persistent P21 activation and 'downstream' tubular senescence. Conversely, OIP did not upregulate P21, it increased, rather than decreased, cell proliferation markers, and it avoided a senescence state. OIP markedly suppressed ischemia-induced P21 up-regulation, it inhibited the development of post-ischemic senescence and it conferred near-complete protection against ischemic acute renal failure (ARF). To assess OIP's impact on a non-P21-dependent cytoprotective pathway, its ability to activate Nrf2, the so-called 'master regulator' of endogenous cell defenses, was assessed. Within 4 h, OIP activated each of three canonical Nrf2-regulated genes (NQO1, SRXN1, GCLC; 3- to 5-fold mRNA increases). Conversely, this gene activation pathway was absent in Nrf2-/- mice, confirming Nrf2 specificity. Nrf2-/- mice also did not develop significant OIP-mediated protection against ischemic ARF.

Conclusions

OIP (i) activates the cytoprotective Nrf2, but not the P21, pathway; (ii) suppresses post-ischemic P21 induction and renal senescence; and (iii) confers marked protection against ischemic ARF. In sum, these findings suggest that OIP may be a clinically feasible approach for safely activating the Nrf2 pathway, and thereby confer protection against clinical renal injury.

Keap1 Cystenine 151 as a Potential Target for Artemisitene-Induced Nrf2 Activation

Artemisitene (ATT) activates the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) by increasing its stabilization and reducing ubiquitination. The cysteine (Cys) residues of the cytosolic Nrf2 repressor Kelch-like ECH-associated protein-1 (Keap1) function as redox sensors and may be crucial in activating Nrf2. To determine whether ATT-induced Nrf2 activation is dependent on the modification of Keap1 and to elucidate the underlying mechanism, we transfected cell lines with six different Keap1 mutant constructs, each with a Cys (-77, -151, -257, -273, -288, and -297) to Ser substitution. Only the Cys151Ser mutant prevented ATT-mediated activation of Nrf2, indicating that the Cys151 residue of Keap1 likely interacts with ATT and is essential for Nrf2 stabilization and transcription of downstream genes. Our finding provides a pharmacological basis for using artemisitene against oxidative stress-related diseases.

Effect of Hepatitis Viruses on the Nrf2/Keap1-Signaling Pathway and Its Impact on Viral Replication and Pathogenesis

With respect to their genome and their structure, the human hepatitis B virus (HBV) and hepatitis C virus (HCV) are complete different viruses. However, both viruses can cause an acute and chronic infection of the liver that is associated with liver inflammation (hepatitis). For both viruses chronic infection can lead to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Reactive oxygen species (ROS) play a central role in a variety of chronic inflammatory diseases. In light of this, this review summarizes the impact of both viruses on ROS-generating and ROS-inactivating mechanisms. The focus is on the effect of both viruses on the transcription factor Nrf2 (nuclear factor erythroid 2 (NF-E2)-related factor 2). By binding to its target sequence, the antioxidant response element (ARE), Nrf2 triggers the expression of a variety of cytoprotective genes including ROS-detoxifying enzymes. The review summarizes the literature about the pathways for the modulation of Nrf2 that are deregulated by HBV and HCV and describes the impact of Nrf2 deregulation on the viral life cycle of the respective viruses and the virus-associated pathogenesis.

Dual roles and therapeutic potential of Keap1-Nrf2 pathway in pancreatic cancer: a systematic review

Pancreatic cancer (PC) is one of the most fatal diseases with a very high rate of metastasis and low rate of survival. Despite the advances in understanding this devastating disease, PC still accounts for 3% of all cancers and causes almost 7% of death of cancer patients. Recent studies have demonstrated that the transcription factor nuclear factor-erythroid 2-related factor 2 (Nrf2) and its key negative regulator Kelch-like ECH-associated protein 1 (Keap1) are dysregulated in PC and the Keap1-Nrf2 pathway is an emerging target for PC prevention and therapy. Indeed, Nrf2 plays an either tumor-suppressive or promoting function in PC, which depends on the developmental stages of the disease and the cellular context. Several natural-product Nrf2 activators have been developed to prevent pancreatic carcinogenesis, while the Nrf2 inhibitors have been examined for their efficacy in inhibiting PC growth and metastasis and reversing chemoresistance. However, further preclinical and clinical studies for determining the effectiveness and safety of targeting the Keap1-Nrf2 pathway for PC prevention and therapy are warranted. In this review, we comprehensively discuss the dual roles of the Keap1-Nrf2 signaling pathway in PC as well as the current targeting strategies and known activators and inhibitors of Nrf2. We also propose new strategies that may be used to address the current issues and develop more specific and more effective Nrf2 activator/inhibitors for PC prevention and therapy.

Curcumin protects against methylmercury-induced cytotoxicity in primary rat astrocytes by activating the Nrf2/ARE pathway independently of PKCδ

Methylmercury (MeHg) is a ubiquitous environmental toxicant that leads to long-lasting neurological deficits in animals and humans. Curcumin, a polyphenol obtained from the rhizome of turmeric, has well-known antioxidant functions. Here, we evaluated curcumin's efficacy in mitigating MeHg-induced cytotoxicity and further investigated the underlying mechanism of this neuroprotection in primary rat astrocytes. Pretreatment with curcumin (2, 5, 10 and 20 μM for 3, 6, 12 or 24 h) protected against MeHg-induced (5 μM for 6 h) cell death in a time and dose-dependent manner. Curcumin (2, 5, 10 or 20 μM) pretreatment for 12 h significantly ameliorated the MeHg-induced astrocyte injury and oxidative stress, as evidenced by morphological alterations, lactate dehydrogenase (LDH) release, reactive oxygen species (ROS) generation, and glutathione (GSH) and catalase (CAT) levels. Moreover, curcumin pretreatment increased Nrf2 nuclear translocation and downstream enzyme expression, heme oxygenase-1 (HO-1) and NADPH quinone reductase-1 (NQO1). Knockdown of Nrf2 with siRNA attenuated the protective effect of curcumin against MeHg-induced cell death. However, both the pan-protein kinase C (PKC) inhibitor, Ro 31-8220, and the selective PKCδ inhibitor, rottlerin, failed to suppress the curcumin-activated Nrf2/Antioxidant Response Element(ARE) pathway and attenuate the protection exerted by curcumin. Taken together, these findings confirm that curcumin protects against MeHg-induced neurotoxicity by activating the Nrf2/ARE pathway and this protection is independent of PKCδ activation. More studies are needed to understand the mechanisms of curcumin cytoprotection.

Fetal origin confers radioresistance on liver macrophages via p21cip1/WAF1

BACKGROUND & AIMS

Cells of hematopoietic origin, including macrophages, are generally radiation sensitive, but a subset of Kupffer cells (KCs) is relatively radioresistant. Here, we focused on the identity of the radioresistant KCs in unmanipulated mice and the mechanism of radioresistance.

METHODS

We employed Emr1- and inducible CX3Cr1-based fate-mapping strategies combined with the RiboTag reporter to identify the total KCs and the embryo-derived KCs, respectively. The KC compartment was reconstituted with adult bone-marrow-derived KCs (bm-KCs) using clodronate depletion. Mice were lethally irradiated and transplanted with donor bone marrow, and the radioresistance of bone-marrow- or embryo-derived KCs was studied. Gene expression was analyzed using in situ mRNA isolation via RiboTag reporter mice, and the translatomes were compared among subsets.

RESULTS

Here, we identified the radioresistant KCs as the long-lived subset that is derived from CX3CR1-expressing progenitor cells in fetal life, while adult bm-KCs do not resist irradiation. While both subsets upregulated the Cdkn1a gene, encoding p21-^cip1/WAF1 protein, radioresistant embryo-derived KCs showed a greater increase in response to irradiation. In the absence of this molecule, the radioresistance of KCs was compromised. Replacement KCs, derived from adult hematopoietic stem cells, differed from radioresistant KCs in their expression of genes related to immunity and phagocytosis.

CONCLUSIONS

Here, we show that, in the murine liver, a subset of KCs of embryonic origin resists lethal irradiation through Cdkn1a upregulation and is maintained for a long period, while bm-KCs do not survive lethal irradiation.

LAY SUMMARY

Kupffer cells (KCs) are the tissue-resident macrophages of the liver. KCs can be originated from fetal precursors and from monocytes during the fetal stage and post-birth, respectively. Most immune cells in mice are sensitive to lethal-irradiation-induced death, while a subset of KCs resists radiation-induced death. These radioresistant KCs continue to live in the irradiated mice. We discovered that this relatively radioresistant KC subset are the fetal-derived KCs, and they achieve this through cell-cycle arrest. Understanding the radiobiology of KCs will provide valuable insights into the mechanisms that elicit radiation-induced liver disease.

PIDD interaction with KEAP1 as a new mutation-independent mechanism to promote NRF2 stabilization and chemoresistance in NSCLC

Chemotherapy resistance is a major problem in non-small cell lung cancer (NSCLC) treatment. A major mechanism of chemoresistance involves stabilization of the NRF2 transcription factor. NRF2 levels are normally tightly regulated through interaction with KEAP1, an adaptor that targets NRF2 to the CUL3 E3 ubiquitin ligase for proteolysis. In NSCLC, aberrant NRF2 stabilization is best understood through mutations in NRF2, KEAP1, or CUL3 that disrupt their interaction. Biochemical studies, however, have revealed that NRF2 can also be stabilized through expression of KEAP1-interacting proteins that competitively sequester KEAP1 away from NRF2. Here, we have identified PIDD, as a novel KEAP1-interactor in NSCLC that regulates NRF2. We show that this interaction allows PIDD to reduce NRF2 ubiquitination and increase its stability. We also demonstrate that PIDD promotes chemoresistance in NSCLC cells both in vitro and in vivo, and that this effect is dependent on NRF2. Finally, we report that NRF2 protein expression in a NSCLC cohort exceeds the typical incidence of combined NRF2, KEAP1, and CUL3 mutations, and that NRF2 expression in this cohort is correlated with PIDD levels. Our data identify PIDD as a new NRF2 regulator, and suggest that variations in PIDD levels contribute to differential chemosensitivities among NSCLC patients.

Reduced chemotherapeutic sensitivity in high glucose condition: implication of antioxidant response

Resistance to chemotherapy represents a major obstacle to successful treatment. The generation of reactive oxygen species (ROS) has been directly linked to the cytotoxic effects of several antitumor agents, including Adriamycin (ADR), and modulation of the oxidative balance has been implicated in the development and/or regulation of resistance to chemotherapeutic drugs. We recently showed that high glucose (HG) markedly diminished the cancer cell death induced by anticancer agents such as ADR. In the present study we attempted to evaluate the mechanism that impaired the cytotoxic effect of ADR in HG. We found that, in colon cancer cells, HG attenuated ADR-induced ROS production that consequently diminished ADR-induced H2AX phosphorylation and micronuclei (MN) formation. Mechanistically, HG attenuation of ADR-induced ROS production correlated with increased antioxidant response promoted by NRF2 activity. Thus, pharmacologic inhibition of NRF2 pathway by brusatol re-established the ADR cytotoxic effect impaired by HG. Together, the data provide new insights into chemotherapeutic-resistance mechanisms in HG condition dictated by increased NRF2-induced antioxidant response and how they may be overcome in order to restore chemosensitivity and ADR-induced cell death.

Activation of KEAP1/NRF2/P62 signaling alleviates high phosphate-induced calcification of vascular smooth muscle cells by suppressing reactive oxygen species production

Vascular calcification is a complication of diseases and conditions such as chronic kidney disease, diabetes, and aging. Previous studies have demonstrated that high concentrations of inorganic phosphate (Pi) can induce oxidative stress and vascular smooth muscle cell calcification. KEAP1 (Kelch-like ECH-associated protein 1)/NF-E2-related factor 2 (NRF2) signaling has been shown to play important roles in protecting cells from oxidative stress. The current study aims to investigate the possible involvement of the KEAP1/NRF2/P62 -mediated antioxidant pathway in vascular calcification induced by high Pi levels. Exposure of vascular smooth muscle cells (VSMCs) to high Pi concentrations promoted the accumulation of reactive oxygen species (ROS) and the nuclear translocation of NRF2, along with an increase in P62 levels and a decrease in KEAP1 levels. A classic NRF2 activator, tert-butylhydroquinone (tBHQ), significantly decreased ROS levels and calcium deposition in VSMCs by promoting the nuclear translocation of NRF2 and upregulating P62 and KEAP1 expression. In contrast, silencing NRF2 and P62 with siRNAs increased the levels of ROS and calcium deposition in VSMCs. In conclusion, VSMC calcification can be alleviated by the activation of the KEAP1/NRF2/P62 antioxidative pathway, which could have a protective role when it is exogenously activated by tBHQ.