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Results for “Nrf2 pathway”

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PubMed2004

A strategy for cancer prevention: stimulation of the Nrf2-ARE signaling pathway.

Many genes, with products involved in the protection of cells against carcinogens, oxidants, and other toxic chemicals, are under the transcriptional control of a simple DNA regulatory element [i.e., the antioxidant response element (ARE)]. One or more functional AREs have been confirmed or are believed to exist in the upstream region of many anticarcinogenic/antioxidant genes and have been shown to mediate the coordinate transcriptional up-regulation of these genes by many chemical agents [i.e., the ARE-mediated inducers]. There is strong evidence that increased expression of ARE-regulated genes inhibits cancer development. The signaling system leading to ARE activation has been partly elucidated, and nuclear factor erythroid 2-related factor 2 (Nrf2) has been identified as the key transcriptional factor that serves to transmit the inducer signal to ARE. It is now known that nuclear factor erythroid 2-related factor 2, which is normally sequestered in the cytoplasm by Kelch-like ECH-associated protein 1, dissociates from Kelch-like ECH-associated protein 1 on exposure to ARE-mediated inducers, translocates to the nucleus, complexes with other nuclear factors, and binds to ARE. Rapid and simple assays have been devised to identify chemical agents that can stimulate this signaling pathway. Moreover, many ARE-mediated inducers have been identified, and several of them have shown promising cancer preventive activity.

Anticarcinogenic Agents↗

PubMedDate not supplied

Role of the Nrf2-mediated signaling pathway as a negative regulator of inflammation: implications for the impact of particulate pollutants on asthma.

Particulate matter (PM) is an environmental factor that may contribute to the exacerbation and possibly the development of asthma. PM contain redox-active chemicals and transition metals which generate reactive oxygen species (ROS). Excessive ROS can induce oxidative stress, which proceeds in hierarchical fashion to generate cellular responses. The most sensitive cellular response to mild oxidative stress is the activation of antioxidant and phase II enzymes (tier 1). If this protection fails, further increase of oxidative stress can induce inflammation (tier 2) and cell death (tier 3). Tier 1 antioxidant defenses are critical for protecting against airway inflammation and asthma. The expression of these antioxidant enzymes is regulated by the transcription factor, Nrf2. In response to oxidative stress, Nrf2 escapes from Keap1-mediated proteasomal degradation resulting in prolonged protein half-life and its nuclear accumulation. Nrf2 interacts with the antioxidant response element (ARE) in the promoters of phase II enzyme genes, leading to their transcriptional activation. Several phase II expression polymorphisms are associated with an increased risk of asthma. The indispensable role of Nrf2 in tier-1 oxidative stress response suggests that polymorphisms of Nrf2-regulated genes may be useful susceptibility markers for asthma. Moreover, chemopreventive Nrf2 inducers may be used for treating PM-exacerbated asthma.

Animals↗

PubMed2006

Insulin induces heme oxygenase-1 through the phosphatidylinositol 3-kinase/Akt pathway and the Nrf2 transcription factor in renal cells.

Heme oxygenase-1 catalyzes the breakdown of heme and is protective in models of kidney transplantation. In this study we describe the induction of heme oxygenase-1 mRNA and protein by insulin. Following treatment with insulin, a five-fold increase in heme oxygenase-1 mRNA and a four-fold increase in protein expression were observed in renal adenocarcinoma cells; insulin-induced heme oxygenase-1 expression was also demonstrated in mouse primary tubular epithelial cells. The induction of heme oxygenase-1 in renal adenocarcinoma cells was blocked by actinomycin D and cycloheximide and was abolished by the phosphatidylinositol 3-kinase inhibitor, LY294002, but not by the inactive analog LY303511. Overexpressing a dominant-negative form of Akt abrogated the heme oxygenase-1-inducing effects of insulin, whereas cells transfected with a constitutively active Akt construct demonstrated an increase in heme oxygenase-1 promoter activity and protein expression. The transcription factor NF-E2-related factor-2 was found to translocate to the nucleus following insulin treatment in a phosphatidylinositol 3-kinase-dependent manner. Pretreatment with NF-E2-related factor-2 small-interfering RNA abolished insulin-induced heme oxygenase-1 induction. Insulin was also found to activate the mitogen-activated protein kinase cascades p38 and extracellular signal-related kinase; however, inhibition of these pathways with SB202190 and PD98059 did not alter insulin-induced heme oxygenase-1 expression. Thus, insulin induces heme oxygenase-1 mRNA and protein expression in renal cells in a phosphatidylinositol 3-kinase/Akt and NF-E2-related factor-2-dependent manner.

Adenocarcinoma↗

PubMed2026

JP1 peptide modulates oxidative stress and autophagy via Keap1-Nrf2-ARE in ALS model mice.

BACKGROUND: The simultaneous modulation of oxidative stress and autophagy represents a potential therapeutic strategy for amyotrophic lateral sclerosis (ALS), yet agents capable of coordinately regulating both processes remain scarce. The Keap1‑Nrf2‑ARE pathway serves as a critical hub linking redox homeostasis and autophagic regulation, making it an attractive target for ALS intervention. JWA is a stress‑responsive protein involved in cellular protection against oxidative injury, and its neuroprotective effects have been shown to depend on activation of the MEK/ERK‑Nrf2 axis. JP1 is a functional oligopeptide derived from the JWA protein that has been engineered to cross the blood-brain barrier and specifically target integrin αVβ3. Based on the link between JWA and Nrf2 signaling, we hypothesized that JP1 activates the Keap1‑Nrf2‑ARE pathway to coordinate antioxidant defense and autophagic clearance. Here, we evaluated this hypothesis in the SOD1‑G93A mouse model, a well‑established transgenic model of familial ALS, and elucidated the underlying mechanisms. METHODS: We evaluated the efficacy of JP1 in the SOD1-G93A mice model using behavioral phenotyping and survival analysis. The coordinated mechanism was investigated in spinal cord tissues by profiling the Keap1-Nrf2-ARE pathway and oxidative stress, quantifying autophagic flux (by Western blotting and transmission electron microscopy) and neuronal apoptosis, and evaluating histology (by Nissl staining and immunofluorescence). Integrated transcriptomic and proteomic analyses further elucidated the global molecular landscape underlying the therapeutic effects of JP1. RESULTS: JP1 treatment ameliorated motor deficits and extended survival in SOD1-G93A mice without adversely affecting liver or kidney function. JP1 crossed the blood-brain barrier, targeted motor neurons expressing integrin αVβ3, and activated the ERK pathway. This promoted Keap1/Cul3 degradation and Nrf2 nuclear translocation, thereby activating the Keap1-Nrf2-ARE pathway to alleviate oxidative stress. Concurrently, JP1 restored autophagic flux, increased autophagic activity, attenuated motor neuron injury, suppressed neuronal apoptosis, and preserved neuronal structural integrity. The Nrf2 inhibitor ML385 reversed the protective effects of JP1 on survival, motor function, autophagy, oxidative stress, and neuronal apoptosis, which confirms that JP1 acts via the Nrf2 pathway. CONCLUSIONS: JP1 acts as a promising coordinator of antioxidant and autophagic processes by targeting the Keap1-Nrf2-ARE pathway, thus highlighting its therapeutic potential for ALS.

Animals↗

PubMed2002

Nrf2 degradation by the ubiquitin proteasome pathway is inhibited by KIAA0132, the human homolog to INrf2.

INrf2 tethering of the transcription factor Nrf2 in the cytosol prevents Nrf2 activation of antioxidant response element (ARE) mediated gene expression. This investigation was undertaken to determine if tethering affected Nrf2 degradation. Data is presented showing that Nrf2 is degraded by the ubiquitin-proteasome pathway. Nrf2 co-immunoprecipitated with a HA tagged ubiquitin polymer and accumulated in cells expressing inactive ubiquitin activating enzyme El. Inhibition of proteasome activity resulted in accumulation of Nrf2. The rate of Nrf2 degradation, measured under conditions where the majority of Nrf2 was not tethered, exhibited a T(1/2) of approximately 3 h. Over-expression of human INrf2, KIAA0132, blocked Nrf2 conjugation to the ubiquitin polymer and blocked Nrf2 degradation. These results suggest that association of Nrf2 with INrf2 inhibits ubiquitin-proteasome degradation of Nrf2. Maintaining the majority of Nrf2 in a tethered form, resistant to ubiquitin-proteasome dependent degradation, allows a pool of Nrf2 to be available for rapid Nrf2/ARE-dependent gene transcription following stress mediated release from INrf2. Further, the observation that free Nrf2 is degraded by the ubiquitin proteasome pathway provides a potential mechanism by which ARE-dependent gene transcription is attenuated after induction.

Animals↗

PubMed2002

Degradation of transcription factor Nrf2 via the ubiquitin-proteasome pathway and stabilization by cadmium.

Nrf2 mediates inducer-dependent activation of the heme oxygenase-1 (HO-1) gene (Alam, J., Stewart, D., Touchard, C., Boinapally, S., Choi, A. M., and Cook, J. L. (1999) J. Biol. Chem. 274, 26071-26078), but the mechanism by which HO-1 inducers regulate Nrf2 function is not known. Treatment of mouse hepatoma (Hepa) cells with 50 microm CdCl(2) increased the amount of Nrf2 protein in a time-dependent manner; induction was observed within 30 min, prior to the accumulation of HO-1 mRNA. Cadmium did not significantly affect the steady-state level of Nrf2 mRNA or the initial rate of Nrf2 protein synthesis but increased the half-life of Nrf2 from approximately 13 to 100 min. Proteasome inhibitors, but not other protease inhibitors, enhanced the expression of Nrf2, and ubiquitinylated Nrf2 was detected after proteasome inhibition. Cycloheximide inhibited cadmium-stimulated Nrf2 expression and DNA binding activity and attenuated HO-1 mRNA accumulation. Conversely, proteasome inhibitors enhanced HO-1 mRNA and protein accumulation by a Nrf2-dependent mechanism. Together, these results indicate that Nrf2 is targeted for rapid degradation by the ubiquitin-proteasome pathway and that cadmium delays the rate of Nrf2 degradation leading to ho-1 gene activation.

Animals↗

PubMed2004

Regulation of Nrf2 transactivation domain activity. The differential effects of mitogen-activated protein kinase cascades and synergistic stimulatory effect of Raf and CREB-binding protein.

Transcription factor NF-E2-related factor 2 (Nrf2) regulates the induction of Phase II detoxifying enzymes as well as anti-oxidative enzymes. In this study, we investigated the transactivation potential of different Nrf2 transactivation domain regions by using the Gal4-Nrf2 chimeras and Gal4-Luc reporter co-transfection assay system in HepG2 cells. The results indicated that chimera Gal4-Nrf2-(1-370), which contains the full transactivation domain showed very potent transactivation activity. The high transactivation activity of Gal4-Nrf2-(113-251) and the diminished transactivation activities of chimera Gal4-Nrf2-(1-126) and Gal4-Nrf2-(230-370) suggested that the Nrf2 N-terminal 113-251 amino acids region is critical in maintaining its transactivation activity. Overexpression of upstream MAPKs such as Raf, MEKK1, TAK1-DeltaN, and ASK1 up-regulated the transactivation activities of Gal4-Nrf2-(1-370) and Gal4-Nrf2-(113-251) in a dose-dependent manner. Further investigation on the effects of the three MAPK pathways on Nrf2 transactivation domain activity demonstrated that both ERK and JNK signaling pathways stimulated the Gal4-Nrf2-(1-370) transactivation activity while the p38 pathway played a negative role. Site-directed mutagenesis studies on potential MAPK phosphorylation sites of Gal4-Nrf2-(113-251) showed no significant effect on its basal transactivation activity or the fold of induction by Raf. Interestingly, the nuclear transcription coactivator CREB-binding protein (CBP), which can bind to Nrf2 transactivation domain and can be activated by ERK cascade, showed synergistic stimulation with Raf on the transactivation activities of both the chimera Gal4-Nrf2-(1-370) and the full-length Nrf2. Taken together, this study clearly demonstrated that different segments of Nrf2 transactivation domain have different transactivation potential and different MAPKs have differential effects on Nrf2 transcriptional activity. It also suggested that the up-regulation of Nrf2 transactivation domain activity by upstream MAPKs such as Raf may not be mediated by direct phosphorylation of the Nrf2 transactivation domain, but rather by regulation of the transcriptional activity of coactivator CBP.

CREB-Binding Protein↗

PubMed2006

Differential expressions of antioxidant status in aging rats: the role of transcriptional factor Nrf2 and MAPK signaling pathway.

Antioxidant enzymes (AOEs) play an important role in the protection of cells against reactive oxygen species and facilitate the prevention of oxidative stress-induced aging. In the present study, the antioxidant indices, including the content of peroxidation product and the expression of AOEs in rat livers of varying ages (2, 12 and 18-24 months old) were evaluated. Erythrocytes haemolysis induced by free radicals showed significant age-dependent increases (P < 0.05). The content of oxidation products in livers showed that increasing age was associated with serious oxidative injury. The activities of AOEs decreased with increasing age. Expression of the antioxidant and age-related gene, klotho, decreased with increasing age. Western blot assay showed that aged rats experience higher levels of oxidative stress. Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) exhibited an age-dependent decrease. Additionally, the mitogen-activated protein kinase cascade (MAPK) played a regulatory role in signaling transduction. Overall, we suggest that age-related declines of the antioxidant defense are closely involved with the expression of Nrf2 and are regulated by the MAPK family.

Aging↗

PubMed2006

Bis(2-hydroxybenzylidene)acetone, a potent inducer of the phase 2 response, causes apoptosis in mouse leukemia cells through a p53-independent, caspase-mediated pathway.

Bis(2-hydroxybenzylidene)acetone is a potent inducer of the phase 2 response through the Keap1-Nrf2-ARE pathway. This double Michael reaction acceptor reacts directly with Keap1, the sensor protein for inducers, leading to enhanced transcription of phase 2 genes and protection against oxidant and electrophile toxicities. In our efforts to identify potent chemoprotective agents, we found that in rapidly growing murine leukemia cells (L1210) low concentrations (in the submicromolar range) of bis(2-hydroxybenzylidene)acetone markedly increased the activities of NAD(P)H:quinone acceptor oxidoreductase 1 (NQO1) and glutathione reductase, and the levels of total glutathione, three markers of the phase 2 response. In contrast, at high concentrations (in the micromolar range) the same compound caused G2/M cell cycle arrest and apoptosis. Importantly, a mutant L1210 cell line (Y8), selected for resistance to deoxyadenosine and lacking expression of p53 protein, was considerably more sensitive to the apoptotic effects of bis(2-hydroxybenzylidene)acetone. When caspase activities were evaluated in cell-free extracts prepared from treated wild type or mutant L1210 cells, the activities of caspase-3, the terminal caspase in the cascade leading to apoptosis, and caspase-10 were found to be markedly elevated. The activities of other caspases measured, caspase-1, -6 and -8, were not appreciably affected. Thus, both induction of the phase 2 response and p53-independent, caspase-3-mediated apoptosis could act cooperatively in chemoprotection. The concentration-dependent differential effects on these two pathways should be carefully considered in mechanistic explanations and strategic designs.

Acetone↗

PubMed2006

Induction of detoxifying enzymes in rodent white adipose tissue by aryl hydrocarbon receptor agonists and antioxidants.

The liver is the main organ of drug metabolism, but the expression and induction by xenobiotics of drug-metabolizing enzymes is also often observed in extrahepatic tissues. Recently, we reported that lipophilic cytochrome P450 inducers, beta-naphthoflavone (BNF), phenobarbital, and dexamethasone, induced CYP1, CYP2B, and CYP3A enzymes, respectively, in rat epididymal white adipose tissue (WAT) at both mRNA and protein levels. To further confirm the xenobiotic-induced expression of drug-metabolizing enzymes in adipose tissue, we studied the induction of CYP1A1 and other detoxifying enzymes by aryl hydrocarbon receptor (AhR) agonists and antioxidants. BNF increased CYP1A1 mRNA levels in several visceral WATs (epididymal, perirenal, and mesenteric) to a greater degree than in subcutaneous WAT in rats. Using C57BL/6 and DBA/2 mice with different responsiveness to aryl hydrocarbons and detecting cytoplasmic levels of AhR proteins, we have demonstrated that AhR mediates this CYP1A1 induction by BNF in WAT. Moreover, the NF-E2-related factor 2 (Nrf2)/antioxidant responsive element pathway is also functional in WAT, since BNF, which is known to activate both AhR and Nrf2, and antioxidants including tert-butylhydroquinone, 1-chloro-2,4-dinitrobenzene, and menadione induced the expression of Nrf2-target genes (NAD-(P)H:quinone oxidoreductase, glutathione S-transferase A subunits, and heme oxygenase-1) in rats and mice. These results suggest that both AhR and Nrf2 pathways are active in WAT and that lipophilic compounds accumulated in WAT can activate these transcription factors to increase detoxification capability in the tissue.

Adipocytes↗

PubMed2005

Differential responses of the Nrf2-Keap1 system to laminar and oscillatory shear stresses in endothelial cells.

The Nrf2-Keap1 system coordinately regulates cytoprotective gene expression via the antioxidant responsive element (ARE). The expression of several ARE-regulated genes was found to be up-regulated in endothelial cells by laminar shear stress, suggesting that Nrf2 contributes to the anti-atherosclerosis response via the ARE. To gain further insight into the roles that Nrf2 plays in the development of atherosclerosis, we examined how Nrf2 regulates gene expression in response to anti-atherogenic laminar flow (L-flow) or pro-atherogenic oscillatory flow (O-flow). Exposure of human aortic endothelial cells (HAECs) to L-flow, but not to O-flow, induced the expression of cytoprotective genes, such as NAD(P)H quinone oxidoreductase 1 (NQO1) by 5-fold and heme oxygenase-1 by 8-fold. The critical contribution of Nrf2 to the expression induced by L-flow was ascertained in siRNA-mediated knock-down experiments. Two cyclooxygenase-2 (COX-2) specific inhibitors attenuated Nrf2 nuclear accumulation in the acute phase of L-flow exposure. A downstream product of COX-2, 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2), activated the Nrf2 regulatory pathway in HAECs through binding to the cysteines of Keap1. These results demonstrate that 15d-PGJ2 is essential for L-flow to activate Nrf2 and induce anti-atherosclerotic gene expression. Whereas both L-flow and O-flow induced the nuclear accumulation of Nrf2 to comparable levels, chromatin immunoprecipitation analysis revealed that Nrf2 binding to the NQO1 ARE was significantly diminished in the case of O-flow compared with that of L-flow. These results suggest that O-flow inhibits Nrf2 activity at the DNA binding step, thereby suppressing athero-protective gene expression and hence predisposing the blood vessels to the formation of atherosclerosis.

Aorta↗

PubMed2006

Induction of 26S proteasome subunit PSMB5 by the bifunctional inducer 3-methylcholanthrene through the Nrf2-ARE, but not the AhR/Arnt-XRE, pathway.

The 26S proteasome is responsible for degradation of abnormal intracellular proteins, including oxidatively damaged proteins and may play a role as a component of a cellular antioxidative system. However, little is known about regulation of proteasome expression. In the present study, regulation of proteasome expression by the bifunctional enzyme inducer and a specific signaling pathway for this regulation were investigated in murine neuroblastoma cells. Expression of catalytic core subunits including PSMB5 and peptidase activities of the proteasome were elevated following incubation with 3-methylcholanthrene (3-MC). Studies using reporter genes containing the murine Psmb5 promoter showed that transcriptional activity of this gene was enhanced by 3-MC. Overexpression of AhR/Arnt did not affect activation of the Pmsb5 promoter by 3-MC and deletion of the xenobiotic response elements (XREs) from this promoter exerted modest effects on inducibility in response to 3-MC. However, mutation of the proximal AREs of the Psmb5 promoter largely abrogated its inducibility by 3-MC. In addition, this promoter showed a blunted response toward 3-MC in the absence of nrf2; 3-MC incubation increased nuclear levels of Nrf2 only in wild-type cells. Collectively, these results indicate that expression of proteasome subunit PSMB5 is modulated by bifunctional enzyme inducers in a manner independent of the AhR/Arnt-XRE pathway but dependent upon the Nrf2-ARE pathway.

Animals↗

PubMed2026

Redox Regulation in Glioblastoma: Mechanisms, Biomarkers, and Therapeutic Implications.

Glioblastoma is the most aggressive primary tumor of the central nervous system, characterized by high invasiveness, rapid progression, and a poor prognosis despite the current treatment modalities. Molecular stratification, using biomarkers such as IDH1, TERT, and MGMT, is a crucial step in the 2021 WHO classification for improving diagnosis and prognosis. Oxidative stress, a feature of GB, has been identified as an important factor in the initiation, progression, and resistance to treatment. It occurs due to an imbalance between reactive oxygen species generated by mitochondrial metabolism, NADPH oxidases, and exogenous sources such as ionizing radiation and xenobiotics and antioxidant defense. This imbalance leads to DNA damage, genomic instability, and deregulation of signaling pathways involved in cell proliferation, apoptosis, and tumor progression. This review provides an overview of key oxidative stress biomarkers and their dual roles in tumor suppression and progression. It highlights how oxidative stress contributes to treatment responses and resistance to current GB treatments, including redox-adaptive mechanisms such as the Nrf2-Keap1 pathway, which promotes radioresistance. Finally, it discusses the potential of understanding these mechanisms to develop therapeutic strategies that target redox balance and homeostasis, aiming to overcome resistance and improve survival outcomes for glioblastoma patients.

Humans↗

PubMed2006

Butylated hydroxyanisole regulates ARE-mediated gene expression via Nrf2 coupled with ERK and JNK signaling pathway in HepG2 cells.

Many natural and synthetic cancer chemopreventive compounds are potent inducers of phase II detoxifying and antioxidant stress responsive genes. The phase II/antioxidant gene expression plays critical role in chemoprevention of carcinogenesis. The antioxidant responsive element (ARE), located on many phase II/antioxidant genes, binds with the transcription factor Nrf2, and is required for the activation of these phase II/antioxidant gene expression induced by many natural and synthetic cancer chemopreventive compounds. In this study, we investigated the potential roles of extracellular signal-regulated kinase (ERK) and c-jun N-terminal kinase (JNK) in the regulation of butylated hydroxyanisole (BHA)-induced and Nrf2-dependent ARE transcriptional activity and ARE-mediated endogenous heme oxygenase-1 (HO-1) protein expression in HepG2 cells. ARE transcriptional activity and HO-1 protein expression were increased dose dependently after treatment with BHA in HepG2 cells. Dose-response and time-course experiments showed that BHA increased the accumulation of Nrf2, and concomitantly decreased the protein level of Keap1. We next examined the phosphorylation of the MAPKs, and found that BHA significantly increased the phosphorylation levels of ERK1/2 and JNK1/2. Importantly BHA-induced ARE transcriptional activity was attenuated by the inhibition of ERK and JNK signaling using biochemical inhibitors and their dominant-negative mutants. Using confocal microscopy technique, treatment with BHA showed the release of Nrf2 sequestered by Keap1 in the cytosol, and that Nrf2 translocated into the nucleus. Importantly, cDNA transfections of ERK and JNK signaling pathways similarly released Nrf2 from Keap1 cytosolic sequestration and translocating Nrf2 into the nucleus. Taken together, these results strongly suggested that ERK and JNK signaling pathways played important and positive roles in BHA-induced and Nrf2-dependent regulation of ARE-mediated gene expression, as well as the nuclear translocation of Nrf2 in HepG2 cells.

Blotting, Western↗

PubMed2003

Mechanism of rat UDP-glucuronosyltransferase 1A6 induction by oltipraz: evidence for a contribution of the Aryl hydrocarbon receptor pathway.

The utility of oltipraz as a cancer chemopreventive agent is thought to depend on the induction of enzymes involved in phase 2 xenobiotic detoxification. Although studies of some enzymes induced by oltipraz implicate a novel transcriptional activating pathway involving Nrf2 and antioxidant-response elements (AREs), the mechanism of phenol UGT induction has remained unclear. Previous work showed that UGT1A6 is transcribed from two promoters, P1 and P2, that are both induced by oltipraz in rat liver. The effect also occurs in rat hepatocytes treated with oltipraz (concentrations >3 microM). To investigate the mechanism, luciferase reporter plasmids under the control of P1 [p(-1078/+27)1A6P1-luc] or P2 [p(-1354/+65)1A6P2-luc] were transfected into rat hepatocytes and tested for inducibility. P1, but not P2, showed responsiveness to oltipraz (2- to 5-fold increase) and 3-methylcholanthrene (10- to 30-fold increase). Because P1 contained no visible AREs, the role of a xenobiotic response element (XRE) centered between bases -134 and -129 was evaluated. Mutation of the XRE core reduced the effects of both oltipraz and 3-methylcholanthrene on the P1 reporter. The 1A6 XRE conferred oltipraz responsiveness on the simian virus 40 promoter of pGL3-Promoter. Comparative effects of oltipraz and 3-methylcholanthrene on transfected cytochrome P4501A1 reporters support the general but relatively weak XRE-stimulating activity of oltipraz. The involvement of the aryl hydrocarbon receptor (AHR) and aryl hydrocarbon nuclear translocator (ARNT) in mediating the effects of oltipraz on the XRE is supported by electrophoretic mobility supershift data and AHR/ARNT overexpression studies. These data raise questions about the contribution of AHR and other secondary induction pathways in the mechanism of oltipraz.

Animals↗

PubMed2006

Gene expression profiles induced by cancer chemopreventive isothiocyanate sulforaphane in the liver of C57BL/6J mice and C57BL/6J/Nrf2 (-/-) mice.

Sulforaphane (SFN) is a potent and promising naturally occurring dietary cancer chemopreventive compound that exerts its cancer protective effects by the induction of genes including cellular defensive genes such as phase II detoxifying and antioxidant enzymes. This gene induction primarily occurs via the transcription factor Nrf2 acting on the antioxidant response element (ARE) located at the 5'-flanking region of these genes. In the present study, transcriptional expression profiles of the livers obtained from the nrf2 wild-type mice and the nrf2 knockout (-/-) mice after treatments with vehicle or SFN at 3 and 12h were generated using the Affymetrix 39K oligonucleotide microarray. The Nrf2-dependent, SFN-inducible genes were identified which include detoxification phase I, II drug metabolizing enzymes and phase III transporters. Unexpected clusters of genes include genes for heat shock proteins (HSP), ubiquitin/26S proteasome subunits, and lipid metabolism genes. Collectively, SFN increases the expression of genes through the Nrf2 signaling pathway that directly detoxify exogenous toxins/carcinogens or endogenous reactive oxygen species, and genes involved in the recognition and repair/removal of damaged proteins, which could provide secondary protection against DNA or protein damage that enhance cell survival.

Animals↗

PubMed2004

The pathways and molecular mechanisms regulating Nrf2 activation in response to chemical stress.

The induction of many antioxidant and phase II drug-metabolizing enzymes by phenolic antioxidants and electrophilic compounds is regulated at the transcriptional level. The response to these compounds is mediated by the cis-acting antioxidant response element (ARE) found in the promoter of the encoding genes. The transcription factor NF-E2-related factor 2, or Nrf2, has emerged as the central protein that binds to the ARE to activate gene transcription. Data from many studies indicate that Nrf2 is constitutively and ubiquitously expressed in a number of tissues and cell lines and is thus responsible for the low-level expression of its target genes observed under physiological conditions. However, in cells exposed to oxidative stress, Nrf2 activity is increased, further driving the transcriptional activation of genes whose expression is essential to control cellular redox homeostasis. Recent studies suggest that the activation of Nrf2 involves a coordinated process and is regulated at multiple levels. Nrf2 activity is believed to be repressed through the binding of the cytoskeleton-associated protein Keap1, and its activation involves mechanisms that interfere with this interaction. Activation of Nrf2 has also been demonstrated to be dependent on mechanisms that mediate its stabilization. In this review, the mechanisms controlling this activation process as reported in recent studies will be examined and discussed, with particular emphasis on those affecting Nrf2 stability at the molecular level.

Animals↗

PubMed2003

Induction of phase 2 enzymes by serum oxidized polyamines through activation of Nrf2: effect of the polyamine metabolite acrolein.

The naturally occurring polycationic polyamines including putrescine, spermidine, and spermine play an important role in cell growth, differentiation, and gene expression. However, circulating polyamines are potential substrates for several oxidizing enzymes including copper-containing serum amine oxidase. These enzymes are capable of oxidizing serum polyamines to several toxic metabolites including aldehydes and H(2)O(2). In this study, we investigated the effects of polyamines as inducers of phase 2 enzymes and other genes that promote cell survival in a cell culture system in the presence of bovine serum. Spermidine and spermine (50 microM) increased NAD(P)H quinone oxidoreductase (NQO1) activity up to 3-fold in murine keratinocyte PE cells. Transcript levels for glutathione S-transferase (GST) A1, GST M1, NQO1, gamma-glutamylcysteine ligase regulatory subunit, and UDP-glucuronyltransferase 1A6 were significantly increased by spermidine and this effect was mediated through the antioxidant response element (ARE). The ARE from the mouse GST A1 promoter was activated about 9-fold by spermine and 5-fold by spermidine treatment, but could be inhibited by the amine oxidase inhibitor, aminoguanidine, suggesting that acrolein or hydrogen peroxide generated from polyamines by serum amine oxidase may be mediators for phase 2 enzyme induction. Elevations of ARE-luciferase expression and NQO1 enzyme activity by spermidine were not affected by catalase, while both were completely repressed by aldehyde dehydrogenase treatment. Direct addition of acrolein to PE cells induced multiple phase 2 genes and elevated nuclear levels of Nrf2, a transcription factor that binds to the ARE. Expression of mutant Nrf2 repressed the activation of the ARE-luciferase reporter by polyamines and acrolein. These results indicate that spermidine and spermine increase the expression of phase 2 genes in cells grown in culture through activation of the Nrf2-ARE pathway by generating the sulfhydryl reactive aldehyde, acrolein.

Acrolein↗