miR-200a regulates Nrf2 activation by targeting Keap1 mRNA in breast cancer cells

microRNA-455 targets cullin 3 to activate Nrf2 signaling and protect human osteoblasts from hydrogen peroxide

Over-production of hydrogen peroxide (H₂O₂) will lead to human osteoblast dysfunction and apoptosis, causing progression of osteoporosis and osteonecrosis. NF-E2-related factor 2 (Nrf2) is a well-characterized anti-oxidant signaling. Cullin 3 (Cul3) ubiquitin E3 ligase dictates Nrf2 degradation. We demonstrate that microRNA-455 ("miR-455") is a putative Cul3-targeting microRNA. Forced-expression of miR-455 in both hFOB1. 19 osteoblast cell line and primary human osteoblasts induced Cul3 degradation and Nrf2 protein stabilization, which led to subsequent transcription of ARE (anti-oxidant response element)-dependent genes (NQO1, HO1 and GCLC). Cul3 silencing, by expressing miR-455 or targeted-shRNA, protected human osteoblasts from H₂O₂. Reversely, miR-455 anti-sense caused Cul3 accumulation and Nrf2 degradation, which exacerbated H₂O₂ damages in hFOB1. 19 cells. Moreover, forced over-expression of Cul3 in hFOB1. 19 cells silenced Nrf2 and sensitized H₂O₂. Together, we propose that miR-455 activated Nrf2 signaling and protected human osteoblasts from oxidative stress possibly via targeting Cul3.

microRNA-200a-3p increases 5-fluorouracil resistance by regulating dual specificity phosphatase 6 expression

Acquisition of resistance to anti-cancer drugs is a significant obstacle to effective cancer treatment. Although several efforts have been made to overcome drug resistance in cancer cells, the detailed mechanisms have not been fully elucidated. Here, we investigated whether microRNAs (miRNAs) function as pivotal regulators in the acquisition of anti-cancer drug resistance to 5-fluorouracil (5-FU). A survey using a lentivirus library containing 572 precursor miRNAs revealed that five miRNAs promoted cell survival after 5-FU treatment in human hepatocellular carcinoma Hep3B cells. Among the five different clones, the clone expressing miR-200a-3p (Hep3B-miR-200a-3p) was further characterized as a 5-FU-resistant cell line. The cell viability and growth rate of Hep3B-miR-200a-3p cells were higher than those of control cells after 5-FU treatment. Ectopic expression of a miR-200a-3p mimic increased, while inhibition of miR-200a-3p downregulated, cell viability in response to 5-FU, doxorubicin, and CDDP (cisplatin). We also showed that dual-specificity phosphatase 6 (DUSP6) is a novel target of miR-200a-3p and regulates resistance to 5-FU. Ectopic expression of DUSP6 mitigated the pro-survival effects of miR-200a-3p. Taken together, these results lead us to propose that miR-200a-3p enhances anti-cancer drug resistance by decreasing DUSP6 expression.

The KEAP1-NRF2 System in Cancer

Cancer cells first adapt to the microenvironment and then propagate. Mutations in tumor suppressor genes or oncogenes are frequently found in cancer cells. Comprehensive genomic analyses have identified somatic mutations and other alterations in the KEAP1 or NRF2 genes and in well-known tumor suppressor genes or oncogenes, such as TP53, CDKN2A, PTEN, and PIK3CA, in various types of cancer. Aberrant NRF2 activation in cancer cells occurs through somatic mutations in the KEAP1 or NRF2 gene as well as through other mechanisms that disrupt the binding of KEAP1 to NRF2. Unregulated NRF2 confers on cancer cells high-level resistance to anticancer drugs and reactive oxygen species (ROS) and directs cancer cells toward metabolic reprogramming. Therefore, NRF2 has been studied as a therapeutic target molecule in cancer. Two strategies have been used to target NRF2 via therapeutic drugs: inhibition of NRF2 and induction of NRF2. NRF2 inhibitors may be effective against NRF2-addicted cancer cells in which NRF2 is aberrantly activated. These inhibitors have not yet been established as NRF2-targeted anticancer drugs for the treatment of human cancers. Diagnosis of NRF2 activation could facilitate the use of NRF2 inhibitors for the treatment of patients with NRF2-addicted cancers. Conversely, NRF2 inducers have been used or are being developed for non-cancer diseases. In addition, NRF2 inducers may be useful for cancer chemotherapy in combination with conventional anticancer agents or even NRF2 inhibitors.

Strange Bedfellows: Nuclear Factor, Erythroid 2-Like 2 (Nrf2) and Hypoxia-Inducible Factor 1 (HIF-1) in Tumor Hypoxia

The importance of the tumor microenvironment for cancer progression and therapeutic resistance is an emerging focus of cancer biology. Hypoxia, or low oxygen, is a hallmark of solid tumors that promotes metastasis and represents a significant obstacle to successful cancer therapy. In response to hypoxia, cancer cells activate a transcriptional program that allows them to survive and thrive in this harsh microenvironment. Hypoxia-inducible factor 1 (HIF-1) is considered the main effector of the cellular response to hypoxia, stimulating the transcription of genes involved in promoting angiogenesis and altering cellular metabolism. However, growing evidence suggests that the cellular response to hypoxia is much more complex, involving coordinated signaling through stress response pathways. One key signaling molecule that is activated in response to hypoxia is nuclear factor, erythroid 2 like-2 (Nrf2). Nrf2 is a transcription factor that controls the expression of antioxidant-response genes, allowing the cell to regulate reactive oxygen species. Nrf2 is also activated in various cancer types due to genetic and epigenetic alterations, and is associated with poor survival and resistance to therapy. Emerging evidence suggests that coordinated signaling through Nrf2 and HIF-1 is critical for tumor survival and progression. In this review, we discuss the distinct and overlapping roles of HIF-1 and Nrf2 in the cellular response to hypoxia, with a focus on how targeting Nrf2 could provide novel chemotherapeutic modalities for treating solid tumors.

MicroRNA-320 inhibits invasion and induces apoptosis by targeting CRKL and inhibiting ERK and AKT signaling in gastric cancer cells

MicroRNA-320 (miR-320) downregulation has been reported in several human cancers. Until now, its expression pattern and biological roles in human cancer remain unknown. This study aims to clarify its clinical expression pattern and biological function in gastric cancers. We found miR-320 level was downregulated in gastric cancer tissues. miR-320 mimic was transfected in SGC-7901 cells with low endogenous expression. miR-320 inhibitor was used in BGC-823 cells with high endogenous expression. We found that miR-320 inhibited SGC-7901 proliferation and invasion, with decreased expression of cyclin D1 and MMP9 at both mRNA and protein levels. We also found that miR-320 mimic downregulated chemoresistance and cell survival of gastric cancer cells when treated with 5-fluorouracil. miR-320 inhibitor displayed the opposite effects in BGC-823 cell line. In addition, we discovered that miR-320 mimic could inhibit AKT and ERK activity. By using luciferase reporter assay, we found that CRKL serves as the target of miR-320. miR-320 mimic downregulated CRKL expression, whereas miR-320 inhibitor upregulated CRKL expression. miR-320 suppressed CRKL-3'-untranslated region reporter intensity in SGC-7901 cells. Furthermore, CRKL depletion abrogated the effects of miR-320. In gastric cancer tissues, we observed a negative correlation between CRKL and miR-320. In conclusion, our study demonstrated that downregulation of miR-320 was closely related with malignant progression of gastric cancer. miR-320 inhibits proliferation, invasion, and chemoresistance through ERK and AKT signaling by targeting CRKL.

Oxidative Stress-Related Mechanisms and Antioxidant Therapy in Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes and is the leading cause of blindness in young adults. Oxidative stress has been implicated as a critical cause of DR. Metabolic abnormalities induced by high-glucose levels are involved in the development of DR and appear to be influenced by oxidative stress. The imbalance between reactive oxygen species (ROS) production and the antioxidant defense system activates several oxidative stress-related mechanisms that promote the pathogenesis of DR. The damage caused by oxidative stress persists for a considerable time, even after the blood glucose concentration has returned to a normal level. Animal experiments have proved that the use of antioxidants is a beneficial therapeutic strategy for the treatment of DR, but more data are required from clinical trials. The aims of this review are to highlight the improvements to our understanding of the oxidative stress-related mechanisms underlying the development of DR and provide a summary of the main antioxidant therapy strategies used to treat the disease.

N-acetylcysteine Ameliorates Prostatitis via miR-141 Regulating Keap1/Nrf2 Signaling

Chronic prostatitis was the most common type of prostatitis and oxidative stress was reported to be highly elevated in prostatitis patients. In this study, we determined the effect of N-acetylcysteine (NAC) on prostatitis and the molecular mechanism involved in it. Male Sprague-Dawley rats were divided into three groups: control group (group A, n = 20), carrageenan-induced chronic nonbacterial prostatitis (CNP) model group (group B, n = 20), and carrageenan-induced CNP model group with NAC injection (group C, n = 20). Eye score, locomotion score, inflammatory cell count, cyclooxygenase 2 (COX2) expression, and Evans blue were compared in these three groups. The expression of miR-141 was determined by quantitative real-time PCR (qRT-PCR). Moreover, protein expressions of Kelch-like ECH-associated protein-1 (Keap1) and nuclear factor erythroid-2 related factor 2 (Nrf2) and its target genes were examined by Western blot. Luciferase reporter assay was performed in RWPE-1 cells transfected miR-141 mimic or inhibitor and the plasmid carrying 3'-UTR of Keap1. The value of eye score, locomotion score, inflammatory cell count, and Evans blue were significantly decreased in group C, as well as the expression of COX2, when comparing to that of group B. These results indicated that NAC relieved the carrageenan-induced CNP. Further, we found that NAC increased the expression of miR-141 and activated the Keap1/Nrf2 signaling. Luciferase reporter assay revealed that miR-141 mimic could suppress the activity of Keap1 and stimulate the downstream target genes of Nrf2. In addition, miR-141 inhibitor could reduce the effect of NAC on prostatitis. NAC ameliorates the carrageenan-induced prostatitis and prostate inflammation pain through miR-141 regulating Keap1/Nrf2 signaling.

Role of Nuclear Factor Erythroid 2-Related Factor 2 in Diabetic Nephropathy

Diabetic nephropathy (DN) is manifested as increased urinary protein level, decreased glomerular filtration rate, and final renal dysfunction. DN is the leading cause of end-stage renal disease worldwide and causes a huge societal healthcare burden. Since satisfied treatments are still limited, exploring new strategies for the treatment of this disease is urgently needed. Oxidative stress takes part in the initiation and development of DN. In addition, nuclear factor erythroid 2-related factor 2 (Nrf2) plays a key role in the cellular response to oxidative stress. Thus, activation of Nrf2 seems to be a new choice for the treatment of DN. In current review, we discussed and summarized the therapeutic effects of Nrf2 activation on DN from both basic and clinical studies.

Protective role of phenylalanine on the ROS-induced oxidative damage, apoptosis and tight junction damage via Nrf2, TOR and NF-κB signalling molecules in the gill of fish

This study explored the possible preventive effects of dietary phenylalanine (Phe) on antioxidant responses, apoptosis and tight junction protein transcription in the gills of young grass carp (Ctenopharyngodon idella). Fish were fed six different experimental diets containing graded levels of Phe (3.4-16.8 g kg^-1) for 8 weeks. The results showed that Phe deficiency induced protein oxidation and lipid peroxidation by decreasing the glutathione content and the activities and mRNA levels of Cu/Zn superoxide dismutase (SOD1), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST) in fish gill (P < 0.05). These results may be ascribed to the downregulation of NF-E2-related factor 2 (Nrf2), target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1), and the upregulation of Kelch-like-ECH-associated protein 1 a (Keap1a) expression in grass carp gills (P < 0.05). Additionally, Phe deficiency induced DNA fragmentation via the up-regulation of Caspase 3, Caspase 8 and Caspase 9 mRNA expression (P < 0.05). These results may be ascribed to the improvement in reactive oxygen species (ROS) levels in the fish gills (P < 0.05). Furthermore, the results indicated that Phe deficiency decreased Claudin b, Claudin 3, Occludin and ZO-1 transcription and increased Claudin 15 expression in the fish gills (P < 0.05). These effects were partly due to the downregulation of interleukin 10 (IL-10), transforming growth factor β (TGF-β) and inhibitor factor κBα (iκBα) and the upregulation of relative mRNA expression of interleukin 1β (IL-1β), interleukin 8 (IL-8), tumour necrosis factor-α (TNF-α) and nuclear transcription factor-κB p65 (NF-κB p65) (P < 0.05). Taken together, the results showed that Phe deficiency impaired the structural integrity of fish gills by regulating the expression of tight junction proteins, cytokines, antioxidant enzymes, NF-κB p65, iκBα, TOR, Nrf2, Keap1 and apoptosis-related genes in the fish gills.

Dietary Phytochemicals and Cancer Chemoprevention: A Perspective on Oxidative Stress, Inflammation, and Epigenetics

Oxidative stress occurs when cellular reactive oxygen species levels exceed the self-antioxidant capacity of the body. Oxidative stress induces many pathological changes, including inflammation and cancer. Chronic inflammation is believed to be strongly associated with the major stages of carcinogenesis. The nuclear factor erythroid 2-related factor 2 (Nrf2) pathway plays a crucial role in regulating oxidative stress and inflammation by manipulating key antioxidant and detoxification enzyme genes via the antioxidant response element. Many dietary phytochemicals with cancer chemopreventive properties, such as polyphenols, isothiocyanates, and triterpenoids, exert antioxidant and anti-inflammatory functions by activating the Nrf2 pathway. Furthermore, epigenetic changes, including DNA methylation, histone post-translational modifications, and miRNA-mediated post-transcriptional alterations, also lead to various carcinogenesis processes by suppressing cancer repressor gene transcription. Using epigenetic research tools, including next-generation sequencing technologies, many dietary phytochemicals are shown to modify and reverse aberrant epigenetic/epigenome changes, potentially leading to cancer prevention/treatment. Thus, the beneficial effects of dietary phytochemicals on cancer development warrant further investigation to provide additional impetus for clinical translational studies.

Regulation of Keap1-Nrf2 signaling: The role of epigenetics

Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (NFE2L2/Nrf2) signaling pathway is a pivotal player in the antioxidant response to oxidative and electrophilic stress and can play a role in many human diseases. Activation or inhibition of Nrf2 has been an approach to treating many diseases such as cancer and regulation of this pathway has been thoroughly studied. Recently, epigenetics has emerged as another layer for regulating Keap1-Nrf2. Epigenetics modification is defined as heritable changes to gene expression without changing DNA sequence and various modifications have been found to be involved in regulating Keap1-Nrf2. Therefore, targeting these epigenetic changes on Keap1-Nrf2 provides a potential pathway for modulating Keap1-Nrf2 to treat disease. In this review, several important and recent findings on epigenetic regulation and perspectives on Keap1-Nrf2 are discussed and shared.

Epigenetics in fibrosis

Fibrosis is a common and important disease. It is a pathological state due to excessive scar formation mediated by an increase in activated fibroblasts that express alpha smooth muscle actin and copious amounts of extracellular matrix molecules. Epigenetics is an area of research that encompasses three main mechanisms: methylation, histone modifications to the tails of histones and also non-coding RNAs including long and short non-coding RNAs. These three mechanisms all seek to regulate gene expression without a change in the underlying DNA sequence. In recent years an explosion of research, aided by deep sequencing technology becoming available, has demonstrated a role for epigenetics in fibrosis, either organ specific like lung fibrosis or more widespread as in systemic sclerosis. While the great majority of epigenetic work in fibrosis is centered on histone codes, more recently the non-coding RNAs have been examined in greater detail. It is known that one modification can affect the other and cross-talk among all three adds a new layer of complexity. This review aims to examine the role of epigenetics in fibrosis, evaluating all three mechanisms, and to suggest possible areas where epigenetics could be targeted therapeutically.

miR-200a-3p regulates TLR1 expression in bacterial challenged miiuy croaker

MicroRNAs (miRNAs) are highly conserved, small non-coding RNAs which post-transcriptionally regulate various biological processes by repressing mRNA translation or degradating mRNA. It has been demonstrated that miRNAs play crucial roles in regulating the immune system. In this study, we explored the potential roles of miR-200a-3p in regulating TLR signaling pathway in miiuy croaker. Bioinformatics analysis showed that miiuy croaker TLR1 (mmiTLR1) was a putative target of miR-200a-3p. Negative expression profiles in spleen of Vibrio anguillarum challenged miiuy croaker and in lipopolysaccharide (LPS) stimulated miiuy croaker leukocytes further validated the prediction. Luciferase reporter assays showed that the dual-luciferase reporter fused to the 3'UTR of wild type mmiTLR1 cotransfected with miR-200a-3p mimics exhibited a reduction in luciferase activity compared with the controls. All of the present data provide direct evidence that miR-200a-3p is involved in TLR1 expression modulation in miiuy croaker, which will offer a basis for better understanding of miRNA regulation in fish TLR signaling pathways.

Role of Nrf2/HO-1 system in development, oxidative stress response and diseases: an evolutionarily conserved mechanism

The multifunctional regulator nuclear factor erythroid 2-related factor (Nrf2) is considered not only as a cytoprotective factor regulating the expression of genes coding for anti-oxidant, anti-inflammatory and detoxifying proteins, but it is also a powerful modulator of species longevity. The vertebrate Nrf2 belongs to Cap 'n' Collar (Cnc) bZIP family of transcription factors and shares a high homology with SKN-1 from Caenorhabditis elegans or CncC found in Drosophila melanogaster. The major characteristics of Nrf2 are to some extent mimicked by Nrf2-dependent genes and their proteins including heme oxygenase-1 (HO-1), which besides removing toxic heme, produces biliverdin, iron ions and carbon monoxide. HO-1 and their products exert beneficial effects through the protection against oxidative injury, regulation of apoptosis, modulation of inflammation as well as contribution to angiogenesis. On the other hand, the disturbances in the proper HO-1 level are associated with the pathogenesis of some age-dependent disorders, including neurodegeneration, cancer or macular degeneration. This review summarizes our knowledge about Nrf2 and HO-1 across different phyla suggesting their conservative role as stress-protective and anti-aging factors.

Overexpression of miR-200a protects cardiomyocytes against hypoxia-induced apoptosis by modulating the kelch-like ECH-associated protein 1-nuclear factor erythroid 2-related factor 2 signaling axis

The kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2) signaling axis plays an important role in regulating oxidative stress in ischemic cardiomyocytes. Targeting Keap1 in order to promote Nrf2 activation is considered a potential method for protecting cardiomyocytes against ischemic injury. In recent years, microRNAs (miRNAs or miRs) have emerged as powerful tools for controlling gene expression. The present study aimed to determine whether Keap1-Nrf2 was regulated by specific miRNAs in cardiomyocytes under hypoxic conditions. We demonstrated that miR-200a was significantly downregulated in ischemic myocardial tissues and hypoxic cardiomyocytes. The overexpression of miR-200a was found to protect cardiomyocytes from hypoxia-induced cell damage and the excessive production of reactive oxygen species. Through bioinformatics analysis and a dual-luciferase report assay, miR-200a was found to interact with the 3'-untranslated region of Keap1, the native regulator of Nrf2. Reverse transcription-quantitative polymerase chain reaction and western blot analysis revealed that miR-200a negatively regulated the expression of Keap1. The overexpression of miR-200a significantly increased the nuclear translocation of Nrf2 as well as downstream antioxidant enzyme gene expression. The inhibition of miR-200a displayed the opposite effects. Restoring the expression of Keap1 significantly abrogated the protective effect of miR‑200a. Taken together, these findings indicate that the suppression of Keap1 by miR-200a exerted a cardioprotective effect against hypoxia-induced oxidative stress and cell apoptosis, and suggest that the activation of Nrf2 signaling by miR‑200a represents a novel and promising therapeutic strategy for the treatment of ischemic heart disease.

C66 ameliorates diabetic nephropathy in mice by both upregulating NRF2 function via increase in miR-200a and inhibiting miR-21

AIMS/HYPOTHESIS

Diabetic nephropathy is the leading cause of end-stage renal disease. Previously we reported that C66, a novel analogue of curcumin with a very high bioavailability, ameliorated diabetic nephropathy in mice, with little known about the mechanism. The present study aimed to define the mechanism by which C66 ameliorates diabetic nephropathy.

METHODS

Our aim was to discover whether C66 acts through the activation of nuclear factor (erythroid-derived 2)-like 2 (NFE2L2 or NRF2), which governs the antioxidant response. Streptozotocin-induced Nrf2 (also known as Nfe2l2)-knockout and wild-type (WT) diabetic mice were treated with C66. To determine whether the actions of C66 on NRF2 are mediated by microRNA (miR)-200a, WT diabetic mice were treated with C66 in the presence or absence of an in vivo miR-200a inhibitor (locked nucleic acid-modified anti-miR-200a [LNA-200a]) for 6 months. To determine whether miR-21 downregulation provided an NRF2-independent basis for C66 protection, Nrf2-knockout diabetic mice were treated with either C66 or an inhibitor of miR-21 (locked nucleic acid-modified anti-miR-21 [LNA-21]).

RESULTS

Deletion of Nrf2 partially abolished diabetic nephropathy protection by C66, confirming the requirement of NRF2 for this protection. Diabetic mice, but not C66-treated diabetic mice, developed significant albuminuria, renal oxidative damage and fibrosis. C66 upregulated renal miR-200a, inhibited kelch-like ECH-associated protein 1 and induced NRF2 function, effects that were prevented by LNA-200a. However, LNA-200a only partially reduced the protection afforded by C66, suggesting the existence of miR-200a/NRF2-independent mechanisms for C66 protection. C66 was also found to inhibit diabetes induction of miR-21. Both C66 and LNA-21 produced similar reductions in miR-21, albuminuria and renal fibrosis.

CONCLUSIONS/INTERPRETATION

The present study indicates that in addition to upregulating NRF2 by increasing miR-200a, C66 also protects against diabetic nephropathy by inhibiting miR-21.

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.

Cullin 3 Ubiquitin Ligases in Cancer Biology: Functions and Therapeutic Implications

Cullin-RING ubiquitin ligases are the largest E3 ligase family in eukaryotes and are multiprotein complexes. In these complexes, the Cullin protein serves as a scaffold to connect two functional modules of the ligases, the catalytic subunit and substrate-binding subunit. To date, eight members of the Cullin family proteins have been identified. In the Cul3 ubiquitin ligases, Bric-a-brac/Tramtrack/Broad complex (BTB) domain-containing proteins function as a bridge to connect Cul3 and substrates. While the BTB domain is responsible for Cul3 binding, these proteins usually contain an additional domain for substrate interaction, such as MATH, kelch, Zn finger, and PAM, Highwire, and RPM-1 (PHR domain). With the existence of a large number of BTB proteins in human, the Cul3 ubiquitin ligases ubiquitinate a wide range of substrates involving in diverse cellular functions. In this review, we will discuss recent advances on the functions of Cul3 ubiquitin ligases in cancer development, progression, and therapeutic response and the dysregulation of Cul3-mediated ubiquitination events in human malignancies. In particular, we will focus on three Cul3 substrate adaptors, kelch-like ECH-associated protein (Keap1), kelch-like family member 20 (KLHL20), and speckle type BTB/POZ protein (SPOP), with the intent to highlight novel targets in cancer therapy.

Dietary vitamin C deficiency depresses the growth, head kidney and spleen immunity and structural integrity by regulating NF-κB, TOR, Nrf2, apoptosis and MLCK signaling in young grass carp (Ctenopharyngodon idella)

This study investigated the effects of dietary vitamin C on the growth, and head kidney, spleen and skin immunity, structural integrity and related signaling molecules mRNA expression levels of young grass carp (Ctenopharyngodon idella). A total of 540 grass carp (264.37 ± 0.66 g) were fed six diets with graded levels of vitamin C (2.9, 44.2, 89.1, 133.8, 179.4 and 224.5 mg/kg diet) for 10 weeks. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila and the survival rate recorded for 14 days. The results indicated that compared with optimal vitamin C supplementation, vitamin C deficiency (2.9 mg/kg diet) decreased lysozyme (LA) and acid phosphatase (ACP) activities, and complement 3 and complement 4 (C4) contents (P < 0.05), down-regulated the mRNA levels of antimicrobial peptides [liver expressed antimicrobial peptide (LEAP) 2A, LEAP-2B, hepcidin, β-defensin] and anti-inflammatory cytokines-related factors, interleukin (IL) 4/13A, IL-4/13B (only in head kidney), IL-10, IL-11, transforming growth factor (TGF) β1, TGF-β2, inhibitor of κBα and eIF4E-binding protein 1 (P < 0.05), and up-regulated pro-inflammatory cytokines-related factors, tumor necrosis factor α, interferon γ2, IL-1β, IL-6, IL-8, IL-12 P35 (only in spleen), IL-12 P40, IL-15, IL-17D, nuclear factor κB p65, IκB kinases (IKKα, IKKβ, IKKγ), target of rapamycin and ribosomal protein S6 kinase 1 mRNA levels (P < 0.05) in the head kidney and spleen under injection fish of A. hydrophila, suggesting that vitamin C deficiency could decrease fish head kidney and spleen immunity and cause inflammation. Meanwhile, compared with optimal vitamin C supplementation, vitamin C deficiency decreased the activities and mRNA levels of copper/zinc superoxide dismutase, manganese superoxide dismutase (MnSOD), catalase, glutathione peroxidase, glutathione S-transferases and glutathione reductase (P < 0.05), and down-regulated zonula occludens (ZO) 1, ZO-2, Claudin-b, -c, -3c, -7a, -7b, B-cell lymphoma-2, inhibitor of apoptosis protein, NF-E2-related factor 2 mRNA levels (P < 0.05), increased reactive oxygen species (ROS), malondialdehyde (MDA) and protein carbonyl contents (P < 0.05), and up-regulated Claudin-12, 15a, -15b, Fas ligand, mitogen-activated protein kinase kinase 6, p38 mitogen-activated protein kinase, B-cell lymphoma protein 2 associated X protein, apoptotic protease activating factor-1, caspase-3, -7, -8, -9, Kelch-like ECH-associating protein (Keap) 1a and Keap 1b mRNA levels (P < 0.05) in the head kidney and spleen under injection fish of A. hydrophila, suggesting that vitamin C deficiency could decrease fish head kidney and spleen structural integrity through depression of antioxidative ability, induction of apoptosis and disruption of tight junctional complexes. In addition, except the activities of ACP and MnSOD, and mRNA expression levels of TGF-β1, Occludin and MnSOD, the effect of vitamin C on fish head kidney, spleen and skin immunity and structural integrity other indicators model are similar under infection of A. hydrophila. Finally, the vitamin C requirement for the growth performance (PWG) of young grass carp was estimated to be 92.8 mg/kg diet. Meanwhile, the vitamin C requirement for against skin lesion morbidity of young grass carp was estimated to be 122.9 mg/kg diet. In addition, based on the biochemical indices [immune indices (LA activity in the head kidney and C4 content in the spleen) and antioxidant indices (MDA content in the head kidney and ROS content in the spleen)] the vitamin C requirements for young grass carp were estimated to be 131.2, 137.5, 135.8 and 129.8 mg/kg diet, respectively.

Induction of methionine adenosyltransferase 2A in tamoxifen-resistant breast cancer cells

We previously showed that S-adenosylmethionine-mediated hypermethylation of the PTEN promoter was important for the growth of tamoxifen-resistant MCF-7 (TAMR-MCF-7) cancer cells. Here, we found that the basal expression level of methionine adenosyltransferase 2A (MAT2A), a critical enzyme for the biosynthesis of S-adenosylmethionine, was up-regulated in TAMR-MCF-7 cells compared with control MCF-7 cells. Moreover, the basal expression level of MAT2A in T47D cells, a TAM-resistant estrogen receptor-positive cell line was higher compared to MCF-7 cells. Immunohistochemistry confirmed that MAT2A expression in TAM-resistant human breast cancer tissues was higher than that in TAM-responsive cases. The promoter region of human MAT2A contains binding sites for nuclear factor-κB, activator protein-1 (AP-1), and NF-E2-related factor 2 (Nrf2), and the activities of these three transcription factors were enhanced in TAMR-MCF-7 cells. Both the protein expression and transcriptional activity of MAT2A in TAMR-MCF-7 cells were potently suppressed by NF-κB inhibition but not by c-Jun/AP-1 or Nrf2 knock-down. Interestingly, the expression levels of microRNA (miR)-146a and -146b were diminished in TAMR-MCF-7 cells, and miR-146b transduction decreased NF-κB-mediated MAT2A expression. miR-146b restored PTEN expression via the suppression of PTEN promoter methylation in TAMR-MCF-7 cells. Additionally, miR-146b overexpression inhibited cell proliferation and reversed chemoresistance to 4-hydroxytamoxifen in TAMR-MCF-7 cells.

Induction of methionine adenosyltransferase 2A in tamoxifen-resistant breast cancer cells

We previously showed that S-adenosylmethionine-mediated hypermethylation of the PTEN promoter was important for the growth of tamoxifen-resistant MCF-7 (TAMR-MCF-7) cancer cells. Here, we found that the basal expression level of methionine adenosyltransferase 2A (MAT2A), a critical enzyme for the biosynthesis of S-adenosylmethionine, was up-regulated in TAMR-MCF-7 cells compared with control MCF-7 cells. Moreover, the basal expression level of MAT2A in T47D cells, a TAM-resistant estrogen receptor-positive cell line was higher compared to MCF-7 cells. Immunohistochemistry confirmed that MAT2A expression in TAM-resistant human breast cancer tissues was higher than that in TAM-responsive cases. The promoter region of human MAT2A contains binding sites for nuclear factor-κB, activator protein-1 (AP-1), and NF-E2-related factor 2 (Nrf2), and the activities of these three transcription factors were enhanced in TAMR-MCF-7 cells. Both the protein expression and transcriptional activity of MAT2A in TAMR-MCF-7 cells were potently suppressed by NF-κB inhibition but not by c-Jun/AP-1 or Nrf2 knock-down. Interestingly, the expression levels of microRNA (miR)-146a and -146b were diminished in TAMR-MCF-7 cells, and miR-146b transduction decreased NF-κB-mediated MAT2A expression. miR-146b restored PTEN expression via the suppression of PTEN promoter methylation in TAMR-MCF-7 cells. Additionally, miR-146b overexpression inhibited cell proliferation and reversed chemoresistance to 4-hydroxytamoxifen in TAMR-MCF-7 cells.

MicroRNA Pharmacoepigenetics: Posttranscriptional Regulation Mechanisms behind Variable Drug Disposition and Strategy to Develop More Effective Therapy

Knowledge of drug absorption, distribution, metabolism, and excretion (ADME) or pharmacokinetics properties is essential for drug development and safe use of medicine. Varied or altered ADME may lead to a loss of efficacy or adverse drug effects. Understanding the causes of variations in drug disposition and response has proven critical for the practice of personalized or precision medicine. The rise of noncoding microRNA (miRNA) pharmacoepigenetics and pharmacoepigenomics has come with accumulating evidence supporting the role of miRNAs in the modulation of ADME gene expression and then drug disposition and response. In this article, we review the advances in miRNA pharmacoepigenetics including the mechanistic actions of miRNAs in the modulation of Phase I and II drug-metabolizing enzymes, efflux and uptake transporters, and xenobiotic receptors or transcription factors after briefly introducing the characteristics of miRNA-mediated posttranscriptional gene regulation. Consequently, miRNAs may have significant influence on drug disposition and response. Therefore, research on miRNA pharmacoepigenetics shall not only improve mechanistic understanding of variations in pharmacotherapy but also provide novel insights into developing more effective therapeutic strategies.

TrkB Promotes Breast Cancer Metastasis via Suppression of Runx3 and Keap1 Expression

In metastatic breast cancer, the acquisition of malignant traits has been associated with the increased rate of cell growth and division, mobility, resistance to chemotherapy, and invasiveness. While screening for the key regulators of cancer metastasis, we observed that neurotrophin receptor TrkB is frequently overexpressed in breast cancer patients and breast cancer cell lines. Additionally, we demonstrate that TrkB expression and clinical breast tumor pathological phenotypes show significant correlation. Moreover, TrkB expression was significantly upregulated in basal-like, claudin-low, and metaplastic breast cancers from a published microarray database and in patients with triple-negative breast cancer, which is associated with a higher risk of invasive recurrence. Interestingly, we identified a new TrkB-regulated functional network that is important for the tumorigenicity and metastasis of breast cancer. We demonstrated that TrkB plays a key role in regulation of the tumor suppressors Runx3 and Keap1. A markedly increased expression of Runx3 and Keap1 was observed upon knockdown of TrkB, treatment with a TrkB inhibitor, and in TrkB kinase dead mutants. Additionally, the inhibition of PI3K/AKT activation significantly induced Runx3 and Keap1 expression. Furthermore, we showed that TrkB enhances metastatic potential and induces proliferation. These observations suggest that TrkB plays a key role in tumorigenicity and metastasis of breast cancer cells through suppression of Runx3 or Keap1 and that it is a promising target for future intervention strategies for preventing tumor metastasis and cancer chemoprevention.

Emerging roles of Nrf2 signal in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) causes considerable mortality in the world. Owing to molecular biological progress, treatments in adenocarcinoma have evolved revolutionarily while those in squamous lung cancer remain unsatisfied. Recent studies revealed high-frequency alteration of Kelch-like ECH-associated protein 1/nuclear factor erythroid 2-like factor 2 (Keap1/Nrf2) pathway within squamous lung cancer, attracting researchers to focus on this particular pathway. In NSCLC patients, deregulated Nrf2 signal is recognized as a common feature at both DNA and protein level. Emerging associations between Nrf2 and other pathways have been elucidated. MicroRNA was also implicated in the regulation of Nrf2. Agents activating or antagonizing Nrf2 showed an effect in preclinical researches, reflecting different effects of Nrf2 during tumor initiation and progression. Prognostic evaluation demonstrated a negative impact of Nrf2 signal on NSCLC patients’ survival. Considering the importance of Nrf2 signal in NSCLC, further studies are required in the future.

p38/p53/miR-200a-3p feedback loop promotes oxidative stress-mediated liver cell death

Although our previous studies have provided evidence that oxidative stress has an essential role in total parenteral nutrition (TPN)-associated liver injury, the mechanisms involved are incompletely understood. Here, we show the existence of crosstalk between the miR-200 family of microRNAs and oxidative stress. The members of the miR-200 family are markedly enhanced in hepatic cells by hydrogen peroxide (H2O2) treatment. The upregulation of miR-200-3p in turn modulates the H2O2-mediated oxidative stress response by targeting p38α. The enhanced expression of miR-200-3p mimics p38α deficiency and promotes H2O2-induced cell death. Members of the miR-200 family that are known to inhibit the epithelial to mesenchymal transition (EMT) are induced by the tumor suppressor p53. Here, we show that p53 phosphorylation at Ser 33 contributes to H2O2-induced miR-200s transcription. In addition, we show that p38α can directly phosphorylate p53 at serine 33 upon H2O2 exposure. Thus, we suggest that in liver cells, the oxidative stress-induced, p38α-mediated phosphorylation of p53 at Ser33 is essential for the functional regulation of oxidative stress-induced miR-200 transcription by p53. Collectively, our data indicate that the p53-dependent expression of miR-200a-3p promotes cell death by inhibiting a p38/p53/miR-200 feedback loop.

Simultaneous activation of Nrf2 and elevation of antioxidant compounds for reducing oxidative stress and chronic inflammation in human Alzheimer's disease

Despite extensive research, neither the incidence nor the rate of progression of Alzheimer's disease (AD) has significantly changed. Some biochemical and genetic defects that initiate and promote AD include: (a) increased oxidative stress, (b) chronic inflammation (c) mitochondrial dysfunction, (d) Aß1-42 peptides generated from the amyloid precursor protein (APP), (e) proteasome inhibition, and (f) mutations in APP, presenilin-1 and presenilin-2 genes. Increased oxidative stress appears to precede other biochemical and genetic defects. Oxidative damage induces chronic inflammation. Therefore, reducing these defects simultaneously may reduce the development and progression of AD. Previous studies with individual antioxidants produced consistent benefits in animal models of AD; however, a similar approach produced inconsistent results in human AD. This review proposes a hypothesis that simultaneous elevation of the levels of antioxidant enzymes and antioxidant compounds is necessary for optimally reducing oxidative stress and chronic inflammation in human AD. Supplementation can enhance the levels of antioxidant compounds; but elevation of antioxidant enzymes requires activation of Nrf2. This review discusses activation and regulation of Nrf2. The need for multi- antioxidants that can affect multi-targets has been proposed without specific recommendations. This review proposes a micronutrient mixture that would simultaneously enhance the levels of antioxidant enzymes and antioxidant compounds in human AD.

The microRNA-200 family: small molecules with novel roles in cancer development, progression and therapy

MicroRNAs (miRNAs) are a large family of small non-coding RNAs that negatively regulate protein-coding gene expression post-transcriptionally via base pairing between the 5′ seed region of a miRNA and the 3′ untranslated region (3′UTR) of a messenger RNA (mRNA). Recent evidence has supported the critical role that miRNAs play in many diseases including cancer. The miR-200 family consisting of 5 members (miR-200a, -200b, -200c, -141, -429) is an emerging miRNA family that has been shown to play crucial roles in cancer initiation and metastasis, and potentially be important for the diagnosis and treatment of cancer. While miR-200s were found to be critically involved in the metastatic colonization to the lungs in mouse mammary xenograft tumor models, a large number of studies demonstrated their strong suppressive effects on cell transformation, cancer cell proliferation, migration, invasion, tumor growth and metastasis. This review aims to discuss research findings about the role of the miR-200 family in cancer initiation, each step of cancer metastatic cascade, cancer diagnosis and treatment. A comprehensive summary of currently validated miR-200 targets is also presented. It is concluded that miR-200 family may serve as novel targets for the therapy of multiple types of cancer.

Targeting heme oxygenase-1 and carbon monoxide for therapeutic modulation of inflammation

The heme oxygenase-1 (HO-1) enzyme system remains an attractive therapeutic target for the treatment of inflammatory conditions. HO-1, a cellular stress protein, serves a vital metabolic function as the rate-limiting step in the degradation of heme to generate carbon monoxide (CO), iron, and biliverdin-IXα (BV), the latter which is converted to bilirubin-IXα (BR). HO-1 may function as a pleiotropic regulator of inflammatory signaling programs through the generation of its biologically active end products, namely CO, BV and BR. CO, when applied exogenously, can affect apoptotic, proliferative, and inflammatory cellular programs. Specifically, CO can modulate the production of proinflammatory or anti-inflammatory cytokines and mediators. HO-1 and CO may also have immunomodulatory effects with respect to regulating the functions of antigen-presenting cells, dendritic cells, and regulatory T cells. Therapeutic strategies to modulate HO-1 in disease include the application of natural-inducing compounds and gene therapy approaches for the targeted genetic overexpression or knockdown of HO-1. Several compounds have been used therapeutically to inhibit HO activity, including competitive inhibitors of the metalloporphyrin series or noncompetitive isoform-selective derivatives of imidazole-dioxolanes. The end products of HO activity, CO, BV and BR may be used therapeutically as pharmacologic treatments. CO may be applied by inhalation or through the use of CO-releasing molecules. This review will discuss HO-1 as a therapeutic target in diseases involving inflammation, including lung and vascular injury, sepsis, ischemia-reperfusion injury, and transplant rejection.

MicroRNA-7 activates Nrf2 pathway by targeting Keap1 expression

Nuclear factor E2-related factor 2 (Nrf2) is a key transcription factor that regulates the expression of a number of antioxidant and detoxifying genes that provide cellular protection against various stressors including reactive oxygen species (ROS). Nrf2 activity is tightly regulated by a cytoplasmic inhibitory protein called Kelch-like ECH-associated protein 1 (Keap1). The mechanism that controls Keap1 expression, however, remains poorly understood. In the present study, we demonstrate that microRNA-7 (miR-7), which is highly expressed in the brain, represses Keap1 expression by targeting the 3'-untranslated region (UTR) of its mRNA in human neuroblastoma cells, SH-SY5Y. Subsequently, this event results in an increased Nrf2 activity, as evidenced by an increase in the expression of its transcriptional targets, heme oxygenase 1 (HO-1) and glutamate-cysteine ligase modifier subunit (GCLM), and an enhanced nuclear localization of Nrf2. In addition, miR-7 decreases the intracellular hydroperoxides level and increases the level of reduced form of glutathione, indicative of oxidative stress relief. We also demonstrate that targeted repression of Keap1 and activation of Nrf2 pathway, in part, underlies the protective effects of miR-7 against 1-methyl-4-phenylpyridinium (MPP+)-induced toxicity in SH-SY5Y and differentiated human neural progenitor cells, ReNcell VM. These findings point to a new mechanism by which miR-7 exerts cytoprotective effects by regulating the Nrf2 pathway.

Age-related loss of hepatic Nrf2 protein homeostasis: Potential role for heightened expression of miR-146a

Nrf2 regulates the expression of numerous anti-oxidant, anti-inflammatory, and metabolic genes. We observed that, paradoxically, Nrf2 protein levels decline in the livers of aged rats despite the inflammatory environment evident in that organ. To examine the cause(s) of this loss, we investigated the age-related changes in Nrf2 protein homeostasis and activation in cultured hepatocytes from young (4-6 months) and old (24-28 months) Fischer 344 rats. While no age-dependent change in Nrf2 mRNA levels was observed (p>0.05), Nrf2 protein content, and the basal and anetholetrithione (A3T)-induced expression of Nrf2-dependent genes were attenuated with age. Conversely, overexpression of Nrf2 in cells from old animals reinstated gene induction. Treatment with A3T, along with bortezomib to inhibit degradation of existing protein, caused Nrf2 to accumulate significantly in cells from young animals (p<0.05), but not old, indicating a lack of new Nrf2 synthesis. We hypothesized that the loss of Nrf2 protein synthesis with age may partly stem from an age-related increase in microRNA inhibition of Nrf2 translation. Microarray analysis revealed that six microRNAs significantly increase >2-fold with age (p<0.05). One of these, miRNA-146a, is predicted to bind Nrf2 mRNA. Transfection of hepatocytes from young rats with a miRNA-146a mimic caused a 55% attenuation of Nrf2 translation that paralleled the age-related loss of Nrf2. Overall, these results provide novel insights for the age-related decline in Nrf2 and identify new targets to maintain Nrf2-dependent detoxification with age.

Human Leukemic Cells performing Oxidative Phosphorylation (OXPHOS) Generate an Antioxidant Response Independently of Reactive Oxygen species (ROS) Production

Tumor cell metabolism is altered during leukemogenesis. Cells performing oxidative phosphorylation (OXPHOS) generate reactive oxygen species (ROS) through mitochondrial activity. To limit the deleterious effects of excess ROS, certain gene promoters contain antioxidant response elements (ARE), e.g. the genes NQO-1 and HO-1. ROS induces conformational changes in KEAP1 and releases NRF2, which activates AREs. We show in vitro and in vivo that OXPHOS induces, both in primary leukemic cells and cell lines, de novo expression of NQO-1 and HO-1 and also the MAPK ERK5 and decreases KEAP1 mRNA. ERK5 activates the transcription factor MEF2, which binds to the promoter of the miR-23a–27a–24-2 cluster. Newly generated miR-23a destabilizes KEAP1 mRNA by binding to its 3′UTR. Lower KEAP1 levels increase the basal expression of the NRF2-dependent genes NQO-1 and HO-1. Hence, leukemic cells performing OXPHOS, independently of de novo ROS production, generate an antioxidant response to protect themselves from ROS.

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Leukemic cells performing OXPHOS increase ROS and antioxidant gene expression.

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OXPHOS-mediated ERK5 activation induces miR-23 expression through MEF2.

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miR-23 blocks KEAP1 expression and increases antioxidant genes.

Cells performing oxidative phosphorylation (OXPHOS) generate reactive oxygen species (ROS) through mitochondrial activity. Excess ROS is deleterious to cells; hence they should be kept at bay. We show here that leukemic cells have a genetic program that allow them to generate an antioxidant response when performing OXPHOS and this is independent of ROS generation. Because leukemic cells need protection from ROS, this pathway is a potential target for therapeutic intervention.

Role of redoximiRs in fibrogenesis

Fibrosis can be defined as an excessive accumulation of extracellular matrix (ECM) components, ultimately leading to stiffness, scarring and devitalized tissue. MicroRNAs (miRNAs) are short, 19-25 nucleotides (nt), non-coding RNAs involved in the post-transcriptional regulation of gene expression. Recently, miRNAs have also emerged as powerful regulators of fibrotic processes and have been termed "fibromiRs". Oxidative stress represents a self-perpetuating mechanism in fibrogenesis. MiRNAs can also influence the expression of genes responsible for the generation of reactive oxygen species (ROS) and antioxidant defence and are termed "redoximiRs". Here, we review the current knowledge of mechanisms by which "redoximiRs" regulate fibrogenesis. This new set of miRNAs may be called "redoxifibromiRs".

High glucose induces renal tubular epithelial injury via Sirt1/NF-kappaB/microR-29/Keap1 signal pathway

Objective

Diabetic nephropathy (DN) is a serious complication that commonly confronted by diabetic patients. A common theory for the pathogenesis of this renal dysfunction in diabetes is cell injury, inflammation as well as oxidative stress. In this content, the detailed molecular mechanism underlying high glucose induced renal tubular epithelial injury was elaborated.

Methods

An in vivo rat model of diabetes by injecting streptozotocin (STZ) and an in vitro high glucose incubated renal tubular epithelial cell (HK-2) model were used. Expression levels of Keap1, nuclear Nrf2 and p65 were determined by western blotting. Level of microR-29 (miR-29) was assessed using quantitative RT-PCR. Combination of p65 and miR-29 promotor was assessed using chromatin immunoprecipitation. Keap1 3′-UTR activity was detected using luciferase reporter gene assay. Cell viability was determined using MTT assay.

Results

In diabetic rat, miR-29 was downregulated and its expression is negatively correlated with both of serum creatinine and creatinine clearance. In high glucose incubated HK-2 cell, deacetylases activity of Sirt1 was attenuated that leads to decreased activity of nuclear factor kappa B (NF-κB). NF-κB was demonstrated to regulate miR-29 expression by directly binding to its promotor. The data of luciferase assay showed that miR-29 directly targets to Keap1 mRNA. While high glucose induced down regulation of miR-29 contributed to enhancement of Keap1 expression that finally reduced Nrf2 content by ubiquitinating Nrf2. Additionally, overexpression of miR-29 effectively relieved high glucose-reduced cell viability.

Conclusion

High glucose induces renal tubular epithelial injury via Sirt1/NF-κB/microR-29/Keap1 signal pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0710-y) contains supplementary material, which is available to authorized users.

Oxidative stress response and Nrf2 signaling in aging

Increasing oxidative stress, a major characteristic of aging, has been implicated in a variety of age-related pathologies. In aging, oxidant production from several sources is increased, whereas antioxidant enzymes, the primary lines of defense, are decreased. Repair systems, including the proteasomal degradation of damaged proteins, also decline. Importantly, the adaptive response to oxidative stress declines with aging. Nrf2/EpRE signaling regulates the basal and inducible expression of many antioxidant enzymes and the proteasome. Nrf2/EpRE activity is regulated at several levels, including transcription, posttranslation, and interactions with other proteins. This review summarizes current studies on age-related impairment of Nrf2/EpRE function and discusses the changes in Nrf2 regulatory mechanisms with aging.

Epigenetic regulation of Keap1-Nrf2 signaling

The kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2) signaling axis serves as a "master regulator" in response to oxidative/electrophilic stresses and chemical insults through the coordinated induction of a wide array of cytoprotective genes. Therefore, activation of Nrf2 is considered to be an important approach for preventing chronic diseases triggered by stresses and toxins, including cancer. Despite extensive studies suggested that the Keap1-Nrf2 signaling pathway is subject to multiple layers of regulation at the transcriptional, translational, and post-translational levels, the potential epigenetic regulation of Nrf2 and Keap1 has begun to be recognized only in recent years. Epigenetic modifications, heritable alterations in gene expression that occur without changes in the primary DNA sequence, have been reported to be profoundly involved in oxidative stress responses. In this review, we discuss the latest findings regarding the epigenetic regulation of Keap1-Nrf2 signaling by DNA methylation, histone modification, and microRNAs. The crosstalk among these epigenetic modifications in the regulation of Keap1-Nrf2 signaling pathways is also discussed. Studies of the epigenetic modification of Nrf2 and Keap1 have not only enhanced our understanding of this complex cellular defense system but have also provided potential new therapeutic targets for the prevention of certain diseases.

Manganese deficiency or excess caused the depression of intestinal immunity, induction of inflammation and dysfunction of the intestinal physical barrier, as regulated by NF-κB, TOR and Nrf2 signalling, in grass carp (Ctenopharyngodon idella)

Intestinal mucosal immune components and mRNA levels of inflammatory cytokines, tight junction proteins, antioxidant enzymes and related signalling molecules in young grass carp (Ctenopharyngodon idellus) under dietary manganese (Mn) deficiency or excess were investigated. Fish were fed the diets containing graded levels of Mn [3.65-27.86 mg Mn kg(-1) diet] for 8 weeks. The results demonstrated that Mn deficiency significantly decreased the lysozyme and acid phosphatase (ACP) activities, up-regulated tumour necrosis factor α (TNF-α), interleukin 8 and the signalling factor nuclear factor-κB p65, and down-regulated interleukin 10 (IL-10), transforming growth factor β1, inhibitor of signalling factors κB-α and target of rapamycin mRNA levels in the proximal intestine (PI), mid intestine (MI) and distal intestine (DI). However, Mn deficiency did not change the C3 content in the PI, whereas it decreased the C3 contents in the MI and DI. Additionally, Mn depletion also resulted in significantly low mRNA levels for tight junction proteins (claudin-b, claudin-c, claudin-15, occludin and zonula occludens-1), antioxidant enzymes (MnSOD, GPx and CAT) and NF-E2-related factor-2 in the intestines of fish. Excessive Mn exhibited toxic effects similar to Mn deficiency, where optimal Mn contents reversed those indicators. In conclusion, Mn deficiency or excess causes the depression of intestinal immunity, induction of inflammation and dysfunction of the intestinal physical barrier relating to NF-κB, TOR and Nrf2 signalling in grass carp. Furthermore, quadratic regression analysis at 95% maximum response of lysozyme and acid phosphatase activities in the distal intestine of young grass carp revealed the optimum dietary Mn levels to be 8.90 and 8.99 mg kg(-1) diet, respectively.

Methylseleninic acid activates Keap1/Nrf2 pathway via up-regulating miR-200a in human oesophageal squamous cell carcinoma cells

Methylseleninic acid (MSA), as a potent second-generation selenium compound, could activate KLF4/miR-200a/Keap1/Nrf2 pathway in oesophageal squamous cell carcinoma cells.

Oesophageal squamous cell carcinoma (ESCC) occurs at a very high rates in certain regions of China. There are increasing evidences demonstrating that selenium could act as a potential anti-oesophageal cancer agent, but the precise mechanisms involved are still not completely understood. Methylseleninic acid (MSA), as a potent second-generation selenium compound, is a promising chemopreventive agent. Previous studies demonstrated that the kelch-like ECH-associated protein 1 (Keap1)/nuclear factor E2-related factor 2 (Nrf2) system plays a critical role in cancer prevention, but little is known about its association with MSA in ESCC cells. In the present study, we observed that MSA treatment significantly down-regulated Keap1, induced nuclear accumulation of Nrf2 and enhance the antioxidant response element (ARE) promoter activity in ESCC cells. MSA could also significantly induce miR-200a expression and inhibit Keap1 directly. Antagomir-200a could attenuate MSA treatment-induced Keap1 down-regulation in ESCC cells. Moreover, MSA-induced miR-200a expression was dependent on the mediation of Krüpple-like factor 4 (KLF4). These results reaffirm the potential role of MSA as a chemopreventive agent via the regulation of KLF4/miR-200a/Keap1/Nrf2 axis in ESCC cells.

Impact of Histone Deacetylase Inhibitors on microRNA Expression and Cancer Therapy: A Review

Chromatin-modifying drugs, such as histone deacetylase inhibitors (HDACi), have shown potential as cancer therapeutics, either alone or in combination with other therapies. HDACi have the ability to reverse aberrant epigenetic modifications associated with cancer, namely dysregulated histone acetylation. There are currently three FDA approved HDACi; vorinostat, romidepsin, and panobinostat. Epigenetic modifications can regulate the expression of protein coding genes, and in addition can alter expression of microRNA (miRNA) genes. Many miRNAs play key roles in cell proliferation and apoptosis, and are commonly dysregulated in cancer states. A number of in vitro and in vivo studies have demonstrated the ability of chromatin-modifying drugs to alter miRNA expression, which may provide the basis for further investigation of miRNAs as therapeutic targets or as biomarkers of drug response. This review summarises findings from studies investigating the effects of HDACi on miRNA expression, as well as key clinical trials involving HDACi. Understanding how chromatin-modifying drugs epigenetically modulate miRNA genes provides further insight into the cellular mechanisms that deliver therapeutic responses, and may assist in refining treatment strategies.

Cancer Cell Growth Is Differentially Affected by Constitutive Activation of NRF2 by KEAP1 Deletion and Pharmacological Activation of NRF2 by the Synthetic Triterpenoid, RTA 405

Synthetic triterpenoids are antioxidant inflammation modulators (AIMs) that exhibit broad anticancer activity. AIMs bind to KEAP1 and inhibit its ability to promote NRF2 degradation. As a result, NRF2 increases transcription of genes that restore redox balance and reduce inflammation. AIMs inhibit tumor growth and metastasis by increasing NRF2 activity in the tumor microenvironment and by modulating the activity of oncogenic signaling pathways, including NF-κB, in tumor cells. Accumulating evidence suggests that KEAP1 loss or mutation--which results in high levels of sustained NRF2 activity--may promote cancer growth and increase chemoresistance. Loss of KEAP1 also increases the levels of other oncogenic proteins, including IKKβ and BCL2. The apparent survival advantage provided to some tumor cells by loss of functional KEAP1 raises the question of whether pharmacological inhibition of KEAP1 could promote tumor growth. To address this issue, we characterized the basal levels of KEAP1 and NRF2 in a panel of human tumor cell lines and profiled the activity of an AIM, RTA 405. We found that in tumor cell lines with low or mutant KEAP1, and in Keap1-/- murine embryonic fibroblasts, multiple KEAP1 targets including NRF2, IKKβ, and BCL2 were elevated. Keap1-/- murine embryonic fibroblasts also had higher rates of proliferation and colony formation than their wild-type counterparts. In cells with functional KEAP1, RTA 405 increased NRF2 levels, but not IKKβ or BCL2 levels, and did not increase cell proliferation or survival. Moreover, RTA 405 inhibited growth at similar concentrations in cells with different basal NRF2 activity levels and in cells with wild-type or mutant KRAS. Finally, pre-treatment with RTA 405 did not protect tumor cells from doxorubicin- or cisplatin-mediated growth inhibition. Collectively, these data demonstrate that pharmacological activation of NRF2 by AIMs is distinct from genetic activation and does not provide a growth or survival advantage to tumor cells.

Role of growth hormone in maturation and activation of dendritic cells via miR-200a and the Keap1/Nrf2 pathway

OBJECTIVES

Dendritic cells (DCs) are antigen-presenting cells that participate in the immune response; recently, it has been reported that growth hormone (GH) promotes their maturation. The aim of this study was to investigate mechanisms by which GH acts on DC maturation and activation.

MATERIALS AND METHODS

Human peripheral blood monocytes (HPBMs) were induced to become immature DCs and treated with GH to obtain mature DCs. An osteosarcoma mouse model was established by injection of LM8 cells to investigate anti-tumour effect of GH-induced DCs in vivo.

RESULTS

After administration of GH, DCs reduced miR-200a expression and nuclear Nrf2 accumulation; miR-200a down-regulation inhibited DC maturation. Nrf2 ubiquitination level was increased by Keap1 overexpression in murine bone marrow derived dendritic cells (BMDCs), which was cancelled by miR-200a in GH exposed cells. In vivo, tumour volume was significantly reduced by GH-treated DCs and the effect was reversed by overexpression of miR-200a.

CONCLUSIONS

GH promoted maturation and activation of DCs, and regulation of miR-200a played a part in this process by modulation of the Keap1/Nrf2 pathway.

miRNA Influences in NRF2 Pathway Interactions within Cancer Models

The NRF2 transcription factor (nuclear factor-erythroid 2 p45-related factor 2) has been identified as a key molecular player in orchestrating adaptive cellular interactions following a wide spectrum of cellular stress conditions that could be either extracellular or intracellular. Dysregulation of the NRF2 system is implicated in various disease states, including inflammatory conditions. The NRF2 transcription factor is also known to permit cross talk with several other essential cellular signaling pathways. Recent literature has also elucidated the potential influences of miRNA activity over modulations of the NRF2 signalling network. Consequently, further delving into the knowledge regarding the extent of miRNA-induced epigenetic gene regulatory control on key elements of the NRF2 signalling pathway and its cross talk, particularly within the context of cancer models, can prove to be of high clinical importance. This is so since such miRNAs, once identified and validated, can be potentially exploited as novel drug targets for emerging translational medicine-based therapies.

The complexity of the Nrf2 pathway: beyond the antioxidant response

The NF-E2-related factor 2 (Nrf2)-mediated signalling pathway provides living organisms an efficient and pivotal line of defensive to counteract environmental insults and endogenous stressors. Nrf2 coordinates the basal and inducible expression of antioxidant and Phase II detoxification enzymes to adapt to different stress conditions. The stability and cellular distribution of Nrf2 is tightly controlled by its inhibitory binding protein Kelch-like ECH-associated protein 1. Nrf2 signalling is also regulated by posttranslational, transcriptional, translational and epigenetic mechanisms, as well as by other protein partners, including p62, p21 and IQ motif-containing GTPase activating protein 1. Many studies have demonstrated that Nrf2 is a promising target for preventing carcinogenesis and other chronic diseases, including cardiovascular diseases, neurodegenerative diseases and pulmonary injury. However, constitutive activation of Nrf2 in advanced cancer cells may confer drug resistance. Here, we review the molecular mechanisms of Nrf2 signalling, the diverse classes of Nrf2 activators, including bioactive nutrients and other chemicals, and the cellular functions and disease relevance of Nrf2 and discuss the dual role of Nrf2 in different contexts.

Dysregulation of the Keap1-Nrf2 pathway in cancer

Accumulating evidence suggests that dysregulation of the Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor E2-related factor 2 (Nrf2) pathway resulting in constitutively active Nrf2 and increased expression of cytoprotective Nrf2 target genes, has a pivotal role in cancer. Cancer cells are able to hijack the Keap1-Nrf2 system via multiple mechanisms leading to enhanced chemo- and radio-resistance and proliferation via metabolic reprogramming as well as inhibition of apoptosis. In this mini-review, we will describe the mechanisms leading to increased Nrf2 activity in cancer with a focus on the information achieved from large-scale multi-omics projects across various cancer types.