Small Maf proteins in mammalian gene control: mere dimerization partners or dynamic transcriptional regulators?

BACH1, the master regulator gene: A novel candidate target for cancer therapy

BACH1 (BTB and CNC homology 1, basic leucine zipper transcription factor 1) is a transcriptional factor and a member of cap 'n' collar (CNC) and basic region leucine zipper factor family. In contrast to other bZIP family members, BACH1 appeared as a comparatively specific transcription factor. It acts as transcription regulator and is recognized as a recently hypoxia regulator and functions as an inducible repressor for the HO-1 gene in many human cell types in response to stress oxidative. In regard to studies lately, although, BACH1 has been related to the regulation of oxidative stress and heme oxidation, it has never been linked to invasion and metastasis. Recent studies have showed that BACH1 is involved in bone metastasis of breast cancer by up-regulating vital metastatic genes like CXCR4 and MMP1. This newly discovered aspect of BACH1 gene provides new insight into cancer progression study and stands on its master regulator role in metastasis process, raising the possibility of considering it as a potential target for cancer therapy.

Nuclear Factor Erythroid-2 Like 1 (NFE2L1): Structure, function and regulation

Nrf1 (also referred to as NFE2L1) is a member of the CNC-bZIP family of transcription factors that are characterized by a highly conserved CNC-domain, and a basic-leucine zipper domain required for dimerization and DNA binding. Nrf1 is ubiquitously expressed across tissue and cell types as various isoforms, and is induced by stress signals from a broad spectrum of stimuli. Evidence indicates that Nrf1 plays an important role in regulating a range of cellular functions including oxidative stress response, differentiation, inflammatory response, metabolism, and maintaining proteostasis. Thus, Nrf1 has been implicated in the pathogenesis of various disease processes including cancer development, and degenerative and metabolic disorders. This review summarizes our current understanding of Nrf1 and the molecular mechanism underlying its regulation and action in different cellular functions.

The ubiquitin ligase HERC4 mediates c-Maf ubiquitination and delays the growth of multiple myeloma xenografts in nude mice

The transcription factor c-Maf is extensively involved in the pathophysiology of multiple myeloma (MM), a fatal malignancy of plasma cells. In the present study, affinity chromatography and mass spectrometry were used to identify c-Maf ubiquitination-associated proteins, from which the E3 ligase HERC4 was found to interact with c-Maf and catalyzed its polyubiquitination and subsequent proteasome-mediated degradation. HERC4 mediated polyubiquitination at K85 and K297 in c-Maf, and this polyubiquitination could be prevented by the isopeptidase USP5. Further analysis on the NCI-60 cell line collection revealed that RPMI 8226, a MM-derived cell line, expressed the lowest level of HERC4. Primary bone marrow analysis revealed HERC4 expression was high in normal bone marrow, but was steadily decreased during myelomagenesis. These findings suggested HERC4 played an important role in MM progression. Moreover, ectopic HERC4 expression decreased MM proliferation in vitro, and delayed xenograft tumor growth in vivo. Therefore, modulation of c-Maf ubiquitination by targeting HERC4 may represent a new therapeutic modality for MM.

αKlotho deficiency in acute kidney injury contributes to lung damage

αKlotho is a circulating protein that originates predominantly from the kidney and exerts cytoprotective effects in distant sites. We previously showed in rodents that the lung is particularly vulnerable to αKlotho deficiency. Because acute lung injury is a common and serious complication of acute kidney injury (AKI), we hypothesized that αKlotho deficiency in AKI contributes to lung injury. To test the hypothesis, we created AKI by renal artery ischemia-reperfusion in rats and observed the development of alveolar interstitial edema and increased pulmonary oxidative damage to DNA, protein, and lipids. Administration of αKlotho-containing conditioned media 6 h post-AKI did not alter plasma creatinine but improved recovery of endogenous αKlotho production 3 days post-AKI, reduced lung edema and oxidative damage, and increased endogenous antioxidative capacity in the lung. Intravenously injected αKlotho rapidly exits alveolar capillaries as a macromolecule, suggesting transcytosis and direct access to the epithelium. To explore the epithelial action of αKlotho, we simulated oxidative stress in vitro by adding hydrogen peroxide to cultured A549 lung epithelial cells. Purified recombinant αKlotho directly protected cells at 20 pM with half-maximal effects at 40-50 pM, which is compatible with circulating αKlotho levels. Addition of recombinant αKlotho activated an antioxidant response element reporter and increased the levels of target proteins of the nuclear factor erythroid-derived 2 related factor system. In summary, αKlotho deficiency in AKI contributes to acute lung injury by reducing endogenous antioxidative capacity and increasing oxidative damage in the lung. αKlotho replacement partially reversed these abnormalities and mitigated pulmonary complications in AKI.

Mechanisms of activation of the transcription factor Nrf2 by redox stressors, nutrient cues, and energy status and the pathways through which it attenuates degenerative disease

Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) regulates the basal and stress-inducible expression of a battery of genes encoding key components of the glutathione-based and thioredoxin-based antioxidant systems, as well as aldo-keto reductase, glutathione S-transferase, and

NAD(P)H

quinone oxidoreductase-1 drug-metabolizing isoenzymes along with multidrug-resistance-associated efflux pumps. It therefore plays a pivotal role in both intrinsic resistance and cellular adaptation to reactive oxygen species (ROS) and xenobiotics. Activation of Nrf2 can, however, serve as a double-edged sword because some of the genes it induces may contribute to chemical carcinogenesis by promoting futile redox cycling of polycyclic aromatic hydrocarbon metabolites or confer resistance to chemotherapeutic drugs by increasing the expression of efflux pumps, suggesting its cytoprotective effects will vary in a context-specific fashion. In addition to cytoprotection, Nrf2 also controls genes involved in intermediary metabolism, positively regulating those involved in NADPH generation, purine biosynthesis, and the β-oxidation of fatty acids, while suppressing those involved in lipogenesis and gluconeogenesis. Nrf2 is subject to regulation at multiple levels. Its ability to orchestrate adaptation to oxidants and electrophiles is due principally to stress-stimulated modification of thiols within one of its repressors, the Kelch-like ECH-associated protein 1 (Keap1), which is present in the cullin-3 RING ubiquitin ligase (CRL) complex CRLKeap1. Thus modification of Cys residues in Keap1 blocks CRLKeap1 activity, allowing newly translated Nrf2 to accumulate rapidly and induce its target genes. The ability of Keap1 to repress Nrf2 can be attenuated by p62/sequestosome-1 in a mechanistic target of rapamycin complex 1 (mTORC1)-dependent manner, thereby allowing refeeding after fasting to increase Nrf2-target gene expression. In parallel with repression by Keap1, Nrf2 is also repressed by β-transducin repeat-containing protein (β-TrCP), present in the Skp1-cullin-1-F-box protein (SCF) ubiquitin ligase complex SCFβ-TrCP. The ability of SCFβ-TrCP to suppress Nrf2 activity is itself enhanced by prior phosphorylation of the transcription factor by glycogen synthase kinase-3 (GSK-3) through formation of a DSGIS-containing phosphodegron. However, formation of the phosphodegron in Nrf2 by GSK-3 is inhibited by stimuli that activate protein kinase B (PKB)/Akt. In particular, PKB/Akt activity can be increased by phosphoinositide 3-kinase and mTORC2, thereby providing an explanation of why antioxidant-responsive element-driven genes are induced by growth factors and nutrients. Thus Nrf2 activity is tightly controlled via CRLKeap1 and SCFβ-TrCP by oxidative stress and energy-based signals, allowing it to mediate adaptive responses that restore redox homeostasis and modulate intermediary metabolism. Based on the fact that Nrf2 influences multiple biochemical pathways in both positive and negative ways, it is likely its dose-response curve, in terms of susceptibility to certain degenerative disease, is U-shaped. Specifically, too little Nrf2 activity will lead to loss of cytoprotection, diminished antioxidant capacity, and lowered β-oxidation of fatty acids, while conversely also exhibiting heightened sensitivity to ROS-based signaling that involves receptor tyrosine kinases and apoptosis signal-regulating kinase-1. By contrast, too much Nrf2 activity disturbs the homeostatic balance in favor of reduction, and so may have deleterious consequences including overproduction of reduced glutathione and NADPH, the blunting of ROS-based signal transduction, epithelial cell hyperplasia, and failure of certain cell types to differentiate correctly. We discuss the basis of a putative U-shaped Nrf2 dose-response curve in terms of potentially competing processes relevant to different stages of tumorigenesis.

Multiple functions of Maf in the regulation of cellular development and differentiation

Cellular muscular aponeurotic fibrosarcoma (c-Maf) is a member of the large macrophage-activating factor family. C-Maf plays important roles in the morphogenetic processes and cellular differentiation of the lens, kidneys, liver, T cells and nervous system, and it is particularly important in pancreatic islet and erythroblastic island formation. However, the exact role of c-Maf remains to be elucidated. In this review, we summarize the research to clarify the functions of c-Maf in the cellular development and differentiation. The expression of c-Maf is higher in pancreatic duct cells than in pancreatic islet cells. Therefore, we suggest that pancreatic duct cells may be converted to the functional insulin-secreting cells by regulating c-Maf.

Mechanisms and functions of Nrf2 signaling in Drosophila

The Nrf2 transcription factor belongs to the Cap'n'collar family, named after the founding member of this group, the product of the Drosophila Cap'n'collar gene. The encoded protein, Cap'n'collar, abbreviated Cnc, offers a convenient and accessible model to study the structure, function, and biology of Nrf2 transcription factors at the organismic, tissular, cellular, and molecular levels, using the powerful genetic, genomic, and biochemical tools available in Drosophila. In this review we provide an account of the original identification of Cnc as a regulator of embryonic development. We then describe the discovery of Nrf2-like functions of Cnc and its role in acute stress signaling and aging. The establishment of Drosophila as a model organism in which the mechanisms and functions of Nrf2 signaling can be studied has led to several discoveries: the regulation of stem cell activity by an Nrf2-mediated redox mechanism, the interaction of Nrf2 with p62 and Myc in the control of tissue growth and the unfolded protein response, and more. Several of these more recent lines of investigation are highlighted. Model organisms such as the fly and the worm remain powerful experimental platforms that can help to unravel the many remaining puzzles regarding the role of Nrf2 and its relatives in controlling the physiology and maintaining the health of multicellular organisms.

High Fractional Occupancy of a Tandem Maf Recognition Element and Its Role in Long-Range β-Globin Gene Regulation

Enhancers and promoters assemble protein complexes that ultimately regulate the recruitment and activity of RNA polymerases. Previous work has shown that at least some enhancers form stable protein complexes, leading to the formation of enhanceosomes. We analyzed protein-DNA interactions in the murine β-globin gene locus using the methyltransferase accessibility protocol for individual templates (MAPit). The data show that a tandem Maf recognition element (MARE) in locus control region (LCR) hypersensitive site 2 (HS2) reveals a remarkably high degree of occupancy during differentiation of mouse erythroleukemia cells. Most of the other transcription factor binding sites in LCR HS2 or in the adult β-globin gene promoter regions exhibit low fractional occupancy, suggesting highly dynamic protein-DNA interactions. Targeting of an artificial zinc finger DNA-binding domain (ZF-DBD) to the HS2 tandem MARE caused a reduction in the association of MARE-binding proteins and transcription complexes at LCR HS2 and the adult βmajor-globin gene promoter but did not affect expression of the βminor-globin gene. The data demonstrate that a stable MARE-associated footprint in LCR HS2 is important for the recruitment of transcription complexes to the adult βmajor-globin gene promoter during erythroid cell differentiation.

Inhibition of Small Maf Function in Pancreatic β-Cells Improves Glucose Tolerance Through the Enhancement of Insulin Gene Transcription and Insulin Secretion

The large-Maf transcription factor v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA) has been found to be crucial for insulin transcription and synthesis and for pancreatic β-cell function and maturation. However, insights about the effects of small Maf factors on β-cells are limited. Our goal was to elucidate the function of small-Maf factors on β-cells using an animal model of endogenous small-Maf dysfunction. Transgenic (Tg) mice with β-cell-specific expression of dominant-negative MafK (DN-MafK) experiments, which can suppress the function of all endogenous small-Mafs, were fed a high-fat diet, and their in vivo phenotypes were evaluated. Phenotypic analysis, glucose tolerance tests, morphologic examination of β-cells, and islet experiments were performed. DN-MafK-expressed MIN6 cells were also used for in vitro analysis. The results showed that DN-MafK expression inhibited endogenous small-Maf binding to insulin promoter while increasing MafA binding. DN-MafK Tg mice under high-fat diet conditions showed improved glucose metabolism compared with control mice via incremental insulin secretion, without causing changes in insulin sensitivity or MafA expression. Moreover, up-regulation of insulin and glucokinase gene expression was observed both in vivo and in vitro under DN-MafK expression. We concluded that endogenous small-Maf factors negatively regulates β-cell function by competing for MafA binding, and thus, the inhibition of small-Maf activity can improve β-cell function.

Stringent Control of NFE2L3 (Nuclear Factor, Erythroid 2-Like 3; NRF3) Protein Degradation by FBW7 (F-box/WD Repeat-containing Protein 7) and Glycogen Synthase Kinase 3 (GSK3)

The NFE2L3 transcription factor has been implicated in various cellular processes, including carcinogenesis, stress response, differentiation, and inflammation. Previously it has been shown that NFE2L3 has a rapid turnover and is stabilized by proteasomal inhibitors. The mechanisms regulating the degradation of this protein have not been investigated. Here we report ubiquitination of NFE2L3 and demonstrate that F-box/WD repeat-containing protein 7 (FBW7 or FBWX7), a component of Skp1, Cullin 1, F-box containing complex (SCF)-type E3 ligase, is the E3 ligase mediating the degradation of NFE2L3. We showed that FBW7 interacts with NFE2L3 and that dimerization of FBW7 is required for the degradation of the transcription factor. We also demonstrate that the kinase glycogen synthase kinase 3 (GSK3) mediates the FBW7-dependent ubiquitination of NFE2L3. We show phosphorylation of NFE2L3 by GSK3 and its significance in the regulation of NFE2L3 by the tumor suppressor FBW7. FBW7 abrogated NFE2L3-mediated repression of the

NAD(P)H

quinone oxidoreductase 1 (NQO1) gene antioxidant response element (ARE). Our findings reveal FBW7 and GSK3 as novel regulators of the NFE2L3 transcription factor and a potential mechanism by which FBW7 might regulate detoxification and the cellular response to stress.

Regulation and function of the NFE2 transcription factor in hematopoietic and non-hematopoietic cells

The NFE2 transcription factor was identified over 25 years ago. The NFE2 protein forms heterodimers with small MAF proteins, and the resulting complex binds to regulatory elements in a large number of target genes. In contrast to other CNC transcription family members including NFE2L1 (NRF1), NFE2L2 (NRF2) and NFE2L3 (NRF3), which are widely expressed, earlier studies had suggested that the major sites of NFE2 expression are hematopoietic cells. Based on cell culture studies it was proposed that this protein acts as a critical regulator of globin gene expression. However, the knockout mouse model displayed only mild erythroid abnormalities, while the major phenotype was a defect in megakaryocyte biogenesis. Indeed, absence of NFE2 led to severely impaired platelet production. A series of recent data, also summarized here, shed new light on the various functional roles of NFE2 and the regulation of its activity. NFE2 is part of a complex regulatory network, including transcription factors such as GATA1 and RUNX1, controlling megakaryocytic and/or erythroid cell function. Surprisingly, it was recently found that NFE2 also has a role in non-hematopoietic tissues, such as the trophoblast, in which it is also expressed, as well as the bone, opening the door to new research areas for this transcription factor. Additional data showed that NFE2 function is controlled by a series of posttranslational modifications. Important strides have been made with respect to the clinical significance of NFE2, linking this transcription factor to hematological disorders such as polycythemias.

Transcriptional factors, Mafs and their biological roles

The Maf family of transcription factors is characterized by a typical bZip structure; these transcription factors act as important regulators of the development and differentiation of many organs and tissues, including the kidney. The Maf family consists of two subgroups that are characterized according to their structure: large Maf transcription factors and small Maf transcription factors. The large Maf subgroup consists of four proteins, designated as MAFA, MAFB, c-MAF and neural retina-specific leucine zipper. In particular, MAFA is a distinct molecule that has been attracting the attention of researchers because it acts as a strong transactivator of insulin, suggesting that Maf transcription factors are likely to be involved in systemic energy homeostasis. In this review, we focused on the regulation of glucose/energy balance by Maf transcription factors in various organs.

Dual roles of NRF2 in tumor prevention and progression: possible implications in cancer treatment

The cap'n'collar (CNC) family serves as cellular sensors of oxidative and electrophilic stresses and shares structural similarities including basic leucine zipper (bZIP) and CNC domains. They form heterodimers with small MAF proteins to regulate antioxidant and phase II enzymes through antioxidant response element (ARE)-mediated transactivation. Among the CNC family members, NRF2 is required for systemic protection against redox-mediated injury and carcinogenesis. On the other hand, NRF2 is activated by oncogenic pathways, metabolism, and hypoxia. Constitutive NRF2 activation is observed in a variety of human cancers and it is highly correlated with tumor progression and aggressiveness. In this review, we will discuss how NRF2 plays dual roles in cancer prevention and progression depending on the cellular context and environment. Therefore, a better understanding of NRF2 will be necessary to exploit this complex network of balancing antioxidant pathways to inhibit tumor progression.

Reductive potential - a savior turns stressor in protein aggregation cardiomyopathy

Redox homeostasis is essential for basal signaling of several physiological processes, but a unilateral shift towards an 'oxidative' or 'reductive' trait will alter intracellular redox milieu. Typically, such an event influences the structure and the native function of a cell or an organelle. Numerous experimental research and clinical trials over the last 6 decades have demonstrated that enhanced oxygen-derived free radicals constitute a major stimulus to trigger damage in several human diseases, including cardiovascular complications supporting the theory of oxidative stress (OS). However, until our key discovery, the dynamic interrelationship between "Reductive Stress (RS)" and cardiac health has been obscured by overwhelming OS studies (Rajasekaran et al., 2007). Notably, this seminal finding spurred considerable interest in investigations of other mechanistic insights, and thus far the results indicate a similar or stronger role for RS, as that of OS. In addition, from our own findings we strongly believe that constitutive activation of pathways that enable sustained generation of reducing equivalents of glutathione (GSH), reduced nicotinamide adenine dinucleotide phosphate (NADPH) will cause RS and impair the basal cellular signaling mechanisms operating through harmless pro-oxidative events, in turn, disrupting single and/or a combination of key cellular processes such as growth, maturation, differentiation, survival, death etc., that govern healthy cell physiology. Here, we have discussed the role of RS as a causal or contributing factor in relevant pathophysiology of a major cardiac disease of human origin.

Cytoprotection "gone astray": Nrf2 and its role in cancer

Nrf2 has gained great attention with respect to its pivotal role in cell and tissue protection. Primarily defending cells against metabolic, xenobiotic and oxidative stress, Nrf2 is essential for maintaining tissue integrity. Owing to these functions, Nrf2 is regarded as a promising drug target in the chemoprevention of diseases, including cancer. However, much evidence has accumulated that the beneficial role of Nrf2 in cancer prevention essentially depends on the tight control of its activity. In fact, the deregulation of Nrf2 is a critical determinant in oncogenesis and found in many types of cancer. Therefore, amplified Nrf2 activity has profound effects on the phenotype of tumor cells, including radio/chemoresistance, apoptosis protection, invasiveness, antisenescence, autophagy deficiency, and angiogenicity. The deregulation of Nrf2 can result from various epigenetic and genetic alterations directly affecting Nrf2 control or from the complex interplay of Nrf2 with numerous oncogenic signaling pathways. Additionally, alterations of the cellular environment, eg, during inflammation, contribute to Nrf2 deregulation and its persistent activation. Therefore, the status of Nrf2 as anti- or protumorigenic is defined by many different modalities. A better understanding of these modalities is essential for the safe use of Nrf2 as an activation target for chemoprevention on the one hand and as an inhibition target in cancer therapy on the other. The present review mainly addresses the conditions that promote the oncogenic function of Nrf2 and the resulting consequences providing the rationale for using Nrf2 as a target structure in cancer therapy.

Mutant p53 gains new function in promoting inflammatory signals by repression of the secreted interleukin-1 receptor antagonist

The TP53 tumor-suppressor gene is frequently mutated in human cancer. Missense mutations can add novel functions (gain-of-function, GOF) that promote tumor malignancy. Here we report that mutant (mut) p53 promotes tumor malignancy by suppressing the expression of a natural occurring anti-inflammatory cytokine, the secreted interleukin-1 receptor antagonist (sIL-1Ra, IL1RN). We show that mutp53 but not wild-type (wt) p53 suppresses the sIL-1Ra production in conditioned media of cancer cells. Moreover, mutp53, but not wtp53, binds physically the sIL-1Ra promoter and the protein-protein interaction with the transcriptional co-repressor MAFF (v-MAF musculoaponeurotic fibrosarcoma oncogene family, protein F) is required for mutp53-induced sIL-1Ra suppression. Remarkably, when exposed to IL-1 beta (IL-1β) inflammatory stimuli, mutp53 sustains a ready-to-be-activated in vitro and in vivo cancer cells' response through the sIL-1Ra repression. Taken together, these results identify sIL-1Ra as a novel mutp53 target gene, whose suppression might be required to generate a chronic pro-inflammatory tumor microenvironment through which mutp53 promotes tumor malignancy.

Modulation of NRF2 signaling pathway by nuclear receptors: implications for cancer

Nuclear factor-erythroid 2 p45-related factor 2 (NRF2, also known as Nfe2l2) plays a critical role in regulating cellular defense against electrophilic and oxidative stress by activating the expression of an array of antioxidant response element-dependent genes. On one hand, NRF2 activators have been used in clinical trials for cancer prevention and the treatment of diseases associated with oxidative stress; on the other hand, constitutive activation of NRF2 in many types of tumors contributes to the survival and growth of cancer cells, as well as resistance to anticancer therapy. In this review, we provide an overview of the NRF2 signaling pathway and discuss its role in carcinogenesis. We also introduce the inhibition of NRF2 by nuclear receptors. Further, we address the biological significance of regulation of the NRF2 signaling pathway by nuclear receptors in health and disease. Finally, we discuss the possible impact of NRF2 inhibition by nuclear receptors on cancer therapy.

Heme acts through the Bach1b/Nrf2a-MafK pathway to regulate exocrine peptidase precursor genes in porphyric zebrafish

Using a zebrafish model of hepatoerythropoietic porphyria (HEP), we identify a previously unknown mechanism underlying heme-mediated regulation of exocrine zymogens. Zebrafish bach1b, nrf2a and mafK are all expressed in the zebrafish exocrine pancreas. Overexpression of bach1b or knockdown of nrf2a result in the downregulation of the expression of the exocrine zymogens, whereas overexpression of nrf2a or knockdown of bach1b cause their upregulation. In vitro luciferase assays demonstrate that heme activates the zymogens in a dosage-dependent manner and that the zymogen promoter activities require the integral Maf recognition element (MARE) motif. The Bach1b-MafK heterodimer represses the zymogen promoters, whereas the Nrf2a-MafK heterodimer activates them. Furthermore, chromatin immunoprecipitation (ChIP) assays show that MafK binds to the MARE sites in the 5' regulatory regions of the zymogens. Taken together, these data indicate that heme stimulates the exchange of Bach1b for Nrf2a at MafK-occupied MARE sites and that, particularly in heme-deficient porphyria, the repressive Bach1b-MafK heterodimer dominates, which can be exchanged for the activating Nrf2a-MafK heterodimer upon treatment with hemin. These results provide novel insights into the regulation of exocrine function, as well as the pathogenesis of porphyria, and should be useful for designing new therapies for both types of disease.

Molecular mechanisms of lipopolysaccharide-mediated inhibition of glutathione synthesis in mice

Endotoxemia correlates with the degree of liver failure and may participate in worsening of liver diseases. Lipopolysaccharide (LPS; synonymous with endotoxin) treatment in mice lowered the hepatic glutathione (GSH) level, which in turn is a variable that determines susceptibility to LPS-induced injury. We previously showed that LPS treatment in mice lowered hepatic expression of the rate-limiting enzyme in GSH synthesis, glutamate-cysteine ligase (GCL). The aim of our current work was to determine the molecular mechanism(s) responsible for these changes. Studies were done using RAW cells (murine macrophages), in vivo LPS-treated mice, and mouse hepatocytes. We found that LPS treatment lowered GCL catalytic and modifier (Gclc and Gclm) subunit expression at the transcriptional level, which was unrelated to alterations in nitric oxide production or induction of NF-κB/p65 subunit. The key mechanism was a decrease in sumoylation of nuclear factor-erythroid 2-related factor 2 (Nrf2) and MafG, which is required for their heterodimerization and subsequent binding and trans-activation of the antioxidant-response element (ARE) present in the promoter region of these genes that is essential for their expression. LPS treatment lowered markedly the expression of ubiquitin-conjugating enzyme 9 (Ubc9), which is required for sumoylation. Similar findings also occurred in liver after in vivo LPS treatment and in LPS-treated mouse hepatocytes. Overexpression of Ubc9 protected against LPS-mediated inhibition of Gclc and Gclm expression in RAW cells and hepatocytes. In conclusion, LPS-mediated lowering of GCL expression in hepatocytes and macrophages is due to lowering of sumoylation of Nrf2 and MafG, leading to reduced heterodimerization, binding, and trans-activation of ARE.

Regulation of Nrf2-an update

Nrf2:INrf2 (Keap1) are cellular sensors of oxidative and electrophilic stress. Nrf2 is a nuclear factor that controls the expression and coordinated induction of a battery of genes that encode detoxifying enzymes, drug transporters, antiapoptotic proteins, and proteasomes. In the basal state, Nrf2 is constantly degraded in the cytoplasm by its inhibitor, INrf2. INrf2 functions as an adapter for Cul3/Rbx1 E3 ubiquitin ligase-mediated degradation of Nrf2. Chemicals, including antioxidants, tocopherols including α-tocopherol (vitamin E), and phytochemicals, and radiation antagonize the Nrf2:INrf2 interaction and lead to the stabilization and activation of Nrf2. The signaling events involve preinduction, induction, and postinduction responses that tightly control Nrf2 activation and repression back to the basal state. Oxidative/electrophilic signals activate unknown tyrosine kinases in a preinduction response that phosphorylates specific residues on Nrf2 negative regulators, INrf2, Fyn, and Bach1, leading to their nuclear export, ubiquitination, and degradation. This prepares nuclei for unhindered import of Nrf2. Oxidative/electrophilic modification of INrf2 cysteine 151 followed by PKC phosphorylation of Nrf2 serine 40 in the induction response results in the escape or release of Nrf2 from INrf2. Nrf2 is thus stabilized and translocates to the nucleus, resulting in a coordinated activation of gene expression. This is followed by a postinduction response that controls the "switching off" of Nrf2-activated gene expression. GSK3β, under the control of AKT and PI3K, phosphorylates Fyn, leading to Fyn nuclear localization. Fyn phosphorylates Nrf2 Y568, resulting in nuclear export and degradation of Nrf2. The activation and repression of Nrf2 provide protection against oxidative/electrophilic stress and associated diseases, including cancer. However, deregulation of INrf2 and Nrf2 due to mutations may lead to nuclear accumulation of Nrf2 that reduces apoptosis and promotes oncogenesis and drug resistance.

Jun dimerization protein 2 is a critical component of the Nrf2/MafK complex regulating the response to ROS homeostasis

Oxidative stress and reactive oxygen species (ROS) are associated with diseases such as cancer, cardiovascular complications, inflammation and neurodegeneration. Cellular defense systems must work constantly to control ROS levels and to prevent their accumulation. We report here that the Jun dimerization protein 2 (JDP2) has a critical role as a cofactor for transcription factors nuclear factor-erythroid 2-related factor 2 (Nrf2) and small Maf protein family K (MafK) in the regulation of the antioxidant-responsive element (ARE) and production of ROS. Chromatin immunoprecipitation–quantitative PCR (qPCR), electrophoresis mobility shift and ARE-driven reporter assays were carried out to examine the role of JDP2 in ROS production. JDP2 bound directly to the ARE core sequence, associated with Nrf2 and MafK (Nrf2–MafK) via basic leucine zipper domains, and increased DNA-binding activity of the Nrf2–MafK complex to the ARE and the transcription of ARE-dependent genes. In mouse embryonic fibroblasts from Jdp2-knockout (Jdp2 KO) mice, the coordinate transcriptional activation of several ARE-containing genes and the ability of Nrf2 to activate expression of target genes were impaired. Moreover, intracellular accumulation of ROS and increased thickness of the epidermis were detected in Jdp2 KO mice in response to oxidative stress-inducing reagents. These data suggest that JDP2 is required to protect against intracellular oxidation, ROS activation and DNA oxidation. qPCR demonstrated that several Nrf2 target genes such as heme oxygenase-1, glutamate–cysteine ligase catalytic and modifier subunits, the notch receptor ligand jagged 1 and NAD(P)H dehydrogenase quinone 1 are also dependent on JDP2 for full expression. Taken together, these results suggest that JDP2 is an integral component of the Nrf2–MafK complex and that it modulates antioxidant and detoxification programs by acting via the ARE.

Keap1-Nrf2 signaling pathway: mechanisms of regulation and role in protection of cells against toxicity caused by xenobiotics and electrophiles

The transcription factor Nrf2 governs the expression of a considerable group of genes involved in cell protection against oxidants, electrophiles, and genotoxic compounds. The activity of Nrf2 is sensitive to xenobiotics and endogenous electrophiles. Nrf2 is negatively regulated by specific suppressor protein Keap1, which is also a receptor of electrophiles and adapter for Cul3 ubiquitin ligase. Electrophiles react with critical thiol groups of Keap1 leading to the loss of its ability to inhibit Nrf2. The Keap1-Nrf2 signaling pathway also down-regulates NF-κB transcriptional activity and attenuates cytokine-mediated induction of proinflammatory genes. Pharmacological activation of the Keap1-Nrf2 pathway can be used for treatment and prevention of many diseases. Widely known natural Keap1-Nrf2 activators include curcumin, quercetin, resveratrol, and sulforaphane. The most effective Keap1-Nrf2 activators are synthetic oleanane triterpenoids.

Declining signal dependence of Nrf2-MafS-regulated gene expression correlates with aging phenotypes

Aging is a degenerative process characterized by declining molecular, cell and organ functions, and accompanied by the progressive accumulation of oxidatively damaged macromolecules. This increased oxidative damage may be causally related to an age-associated dysfunction of defense mechanisms, which effectively protect young individuals from oxidative insults. Consistently, older organisms are more sensitive to acute oxidative stress exposures than young ones. In studies on the Drosophila Nrf2 transcription factor CncC, we have investigated possible causes for this loss of stress resistance and its connection to the aging process. Nrf2 is a master regulator of antioxidant and stress defense gene expression with established functions in the control of longevity. Here, we show that the expression of protective Nrf2/CncC target genes in unstressed conditions does not generally decrease in older flies. However, aging flies progressively lose the ability to activate Nrf2 targets in response to acute stress exposure. We propose that the resulting inability to dynamically adjust the expression of Nrf2 target genes to the organism's internal and external conditions contributes to age-related loss of homeostasis and fitness. In support of this hypothesis, we find the Drosophila small Maf protein, MafS, an Nrf2 dimerization partner, to be critical to maintain responsiveness of the Nrf2 system: overexpression of MafS in older flies preserves Nrf2/CncC signaling competence and antagonizes age-associated functional decline. The maintenance of acute stress resistance, motor function, and heart performance in aging flies overexpressing MafS supports a critical role for signal responsiveness of Nrf2 function in promoting youthful phenotypes.

Control of Oxidative Stress and Generation of Induced Pluripotent Stem Cell-like Cells by Jun Dimerization Protein 2

We report here that the Jun dimerization protein 2 (JDP2) plays a critical role as a cofactor for the transcription factors nuclear factor-erythroid 2-related factor 2 (Nrf2) and MafK in the regulation of the antioxidants and production of reactive oxygen species (ROS). JDP2 associates with Nrf2 and MafK (Nrf2-MafK) to increase the transcription of antioxidant response element-dependent genes. Oxidative-stress-inducing reagent led to an increase in the intracellular accumulation of ROS and cell proliferation in Jdp2 knock-out mouse embryonic fibroblasts. In Jdp2-Cre mice mated with reporter mice, the expression of JDP2 was restricted to granule cells in the brain cerebellum. The induced pluripotent stem cells (iPSC)-like cells were generated from DAOY medulloblastoma cell by introduction of JDP2, and the defined factor OCT4. iPSC-like cells expressed stem cell-like characteristics including alkaline phosphatase activity and some stem cell markers. However, such iPSC-like cells also proliferated rapidly, became neoplastic, and potentiated cell malignancy at a later stage in SCID mice. This study suggests that medulloblastoma cells can be reprogrammed successfully by JDP2 and OCT4 to become iPSC-like cells. These cells will be helpful for studying the generation of cancer stem cells and ROS homeostasis.

Identification and functional studies of a new Nrf2 partner IQGAP1: a critical role in the stability and transactivation of Nrf2

AIMS

Nuclear factor-erythroid-related factor 2 (Nrf2) is a critical transcriptional factor that is used in regulating cellular defense against oxidative stress. This study is aimed at investigating new interacting protein partners of Nrf2 using One-strep tag pull-down coupled with LTQ Orbitrap LC/MS/MS, and at examining the impact on Nr2 signaling by the newly identified IQ motif containing GTPase activating protein 1 (IQGAP1).

RESULTS

Using the One-strep tag pull-down and LTQ Orbitrap LC/MS/MS, we identified IQGAP1 as a new Nrf2 interacting partner. Direct interactions between IQGAP1 and Nrf2 proteins were verified using in vitro glutathione S-transferase (GST) pull-down, transcription/translation assays, and in vivo utilizing Nrf2 overexpressing cells. Coexpression of Dsredmono-IQGAP1 and eGFP-Nrf2 increased the stability of eGFP-Nrf2 and enhanced the expression of Nrf2-target gene heme oxygenase-1 (HO-1). To confirm the functional role of IQGAP1 on Nrf2, knock-downed IQGAP1 using siIQGAP1 attenuated the expression of endogenous Nrf2, HO-1 proteins, and Nrf2-target genes GSTpi, GCLC, and

NAD(P)H

quinone oxidoreductase 1 (NQO-1). Furthermore, the stability of Nrf2 was dramatically decreased in IQGAP1-deficient mouse embryonic fibroblast (MEF) cells. Since IQGAP1 signaling could be mediated by calcium, treating the cells with calcium showed the translocation of IQGAP1/Nrf2 complex into the nucleus, suggesting that IQGAP1 may play a critical role in Nrf2 stability. Interestingly, consistent with calcium signaling for IQGAP1, treating the cells with calcium functionally enhanced Nrf2-mediated antioxidant responsive element-transcription activity and enhanced the expression of the endogenous Nrf2-target gene HO-1.

INNOVATION

In the aggregate, our current study identifies and functionally characterizes a new Nrf2 partner protein IQGAP1, which may contribute to Nrf2's regulation of antioxidant enzymes such as HO-1.

CONCLUSION

IQGAP1 may play a critical role in the stability and transactivation of Nrf2.

Pyrroloquinoline quinine protects rat brain cortex against acute glutamate-induced neurotoxicity

To investigate possible protective effects of pyrroloquinoline quinone (PQQ) on the rat cortex with glutamate injection and to understand the mechanisms linking the in vivo neuroprotection of PQQ. Adult Sprague-Dawley rats received glutamate injection into the rat cortex. Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling assay was performed to observe influences of co-treatment with PQQ (simultaneous injection with PQQ and glutamate) on neural cell apoptosis in the rat cortex. The production of reactive oxygen species (ROS) in the rat cortex was detected by flow cytometry using 2',7'-dichlorofluorescin diacetate labeling, and the activity of superoxide dismutase, glutathione and malondialdehyde was respectively determined. Real time quantitative RT-PCR and Western blot were applied to measure the mRNA and protein expressions of Nrf1, Nrf2, HO-1 and GCLC in the rat cortex. Western blot was used to detect the phosphorylation of Akt and GSK3β in the rat cortex. Co-treatment with PQQ protected neural cells in the rat cortex from glutamate-induced apoptosis. PQQ decreased the ROS production induced by glutamate injection. PQQ increased the mRNA and protein expressions of Nrf2, HO-1 and GCLC and the phosphorylation of Akt and GSK3β in the cortex of glutamate-injected rats. PQQ could produce neuroprotective effects on the rat cortex. The antioxidant properties of PQQ and PQQ-induced activation of Akt/GSK3β signal pathway might be responsible for the in vivo neuroprotection of PQQ.

Concurrent regulation of the transcription factors Nrf2 and ATF4 mediates the enhancement of glutathione levels by the flavonoid fisetin

Glutathione (GSH) and GSH-associated metabolism provide the major line of defense for the protection of cells from various forms of toxic stress. GSH also plays a key role in regulating the intracellular redox environment. Thus, maintenance of GSH levels is developing into an important therapeutic objective for the treatment of a variety of diseases. Among the transcription factors that play critical roles in GSH metabolism are NF-E2-related factor 2 (Nrf2) and activating transcription factor 4 (ATF4). Thus, compounds that can upregulate these transcription factors may be particularly useful as treatment options through their effects on GSH metabolism. We previously showed that the flavonoid fisetin not only increases basal levels of GSH but also maintains GSH levels under oxidative stress conditions. However, the mechanisms underlying these effects have remained unknown until now. Here we show that fisetin rapidly increases the levels of both Nrf2 and ATF4 as well as Nrf2- and ATF4-dependent gene transcription via distinct mechanisms. Although fisetin greatly increases the stability of both Nrf2 and ATF4, only the effect on ATF4 is dependent on protein kinase activity. Using siRNA we found that ATF4, but not Nrf2, is important for fisetin's ability to increase GSH levels under basal conditions whereas both ATF4 and Nrf2 appear to cooperate to increase GSH levels under oxidative stress conditions. Based upon these results, we hypothesize that compounds able to increase GSH levels via multiple mechanisms, such as fisetin, will be particularly effective for maintaining GSH levels under a variety of different stresses.

Interplay between chromatin state, regulator binding, and regulatory motifs in six human cell types

The regions bound by sequence-specific transcription factors can be highly variable across different cell types despite the static nature of the underlying genome sequence. This has been partly attributed to changes in chromatin accessibility, but a systematic picture has been hindered by the lack of large-scale data sets. Here, we use 456 binding experiments for 119 regulators and 84 chromatin maps generated by the ENCODE in six human cell types, and relate those to a global map of regulatory motif instances for these factors. We find specific and robust chromatin state preferences for each regulator beyond the previously reported open-chromatin association, suggesting a much richer chromatin landscape beyond simple accessibility. The preferentially bound chromatin states of regulators were enriched for sequence motifs of regulators relative to all states, suggesting that these preferences are at least partly encoded by the genomic sequence. Relative to all regions bound by a regulator, however, regulatory motifs were surprisingly depleted in the regulator's preferentially bound states, suggesting additional non-sequence-specific binding beyond the level predicted by the regulatory motifs. Such permissive binding was largely restricted to open-chromatin regions showing histone modification marks characteristic of active enhancer and promoter regions, whereas open-chromatin regions lacking such marks did not show permissive binding. Lastly, the vast majority of cobinding of regulator pairs is predicted by the chromatin state preferences of individual regulators. Overall, our results suggest a joint role of sequence motifs and specific chromatin states beyond mere accessibility in mediating regulator binding dynamics across different cell types.

Glutamate cysteine ligase (GCL) transgenic and gene-targeted mice for controlling glutathione synthesis

The tripeptide glutathione (GSH) has important antioxidant properties, scavenges free radicals, and serves as a cofactor for glutathione S-transferase conjugation of many xenobiotics. GSH is synthesized in two steps. The first and, often, rate-limiting step is the formation of γ-glutamylcysteine, which is catalyzed by the inducible heterodimeric enzyme glutamate cysteine ligase (GCL). The two subunits of GCL are the catalytic subunit (GCLC) and the modifier subunit (GCLM). In this unit, the generation and basic characterization methodologies of transgenic mouse models that have been developed to (1) conditionally over express both GCL subunits; (2) lack GCLM (Gclm null); and (3) create a hybrid between Gclm conditional over-expressing mice on a Gclm null genetic background are discussed. These models can be used to explore the fundamental role of GCLC and GCLM in GSH synthesis, as well as the toxicological role of GSH and its synthesis in xenobiotic metabolism and response to oxidative stress.

The transcription factor NF-E2-related factor 2 (Nrf2): a protooncogene?

The transcription factor Nrf2 is responsible for regulating a battery of antioxidant and cellular protective genes, primarily in response to oxidative stress. A member of the cap 'n' collar family of transcription factors, Nrf2 activation is tightly controlled by a series of signaling events. These events can be separated into the basal state, a preinduction response, gene induction, and finally a postinduction response, culminating in the restoration of redox homeostasis. However, despite the immensely intricate level of control the cellular environment imposes on Nrf2 activity, there are many opportunities for perturbations to arise in the signaling events that favor carcinogenesis and, therefore, implicate Nrf2 as both a tumor suppressor and a protooncogene. Herein, we highlight the ways in which Nrf2 is regulated, and discuss some of the Nrf2-inducible antioxidant (NQO1, NQO2, HO-1, GCLC), antiapoptotic (Bcl-2), metabolic (G6PD, TKT, PPARγ), and drug efflux transporter (ABCG2, MRP3, MRP4) genes. In addition, we focus on how Nrf2 functions as a tumor suppressor under normal conditions and how its ability to detoxify the cellular environment makes it an attractive target for other oncogenes either via stabilization or degradation of the transcription factor. Finally, we discuss some of the ways in which Nrf2 is being considered as a therapeutic target for cancer treatment.

Association between functional polymorphisms in genes involved in the MAPK signaling pathways and cutaneous melanoma risk

Genome-wide association studies (GWASs) have mainly focused on top significant single nucleotide polymorphisms (SNPs), most of which did not have clear biological functions but were just surrogates for unknown causal variants. Studying SNPs with modest association and putative functions in biologically plausible pathways has become one complementary approach to GWASs. To unravel the key roles of mitogen-activated protein kinase (MAPK) pathways in cutaneous melanoma (CM) risk, we re-evaluated the associations between 47 818 SNPs in 280 MAPK genes and CM risk using our published GWAS dataset with 1804 CM cases and 1026 controls. We initially found 105 SNPs with P ≤ 0.001, more than expected by chance, 26 of which were predicted to be putatively functional SNPs. The risk associations with 16 SNPs around DUSP14 (rs1051849) and a previous reported melanoma locus MAFF/PLA2G6 (proxy SNP rs4608623) were replicated in the GenoMEL dataset (P < 0.01) but failed in the Australian dataset. Meta-analysis showed that rs1051849 in the 3' untranslated regions of DUSP14 was associated with a reduced risk of melanoma (odds ratio = 0.89, 95% confidence interval: 0.82-0.96, P = 0.003, false discovery rate = 0.056). Further genotype-phenotype correlation analysis using the 90 HapMap lymphoblastoid cell lines from Caucasians showed significant correlations between two SNPs (rs1051849 and rs4608623) and messenger RNA expression levels of DUSP14 and MAFF (P = 0.025 and P = 0.010, respectively). Gene-based tests also revealed significant SNPs were over-represented in MAFF, PLA2G6, DUSP14 and other 16 genes. Our results suggest that functional SNPs in MAPK pathways may contribute to CM risk. Further studies are warranted to validate our findings.

Regulation of APC development, immune response, and autoimmunity by Bach1/HO-1 pathway in mice

APCs are essential for innate and adaptive immunity as well as self-immune tolerance. Here, we show that the Cap'n'collar member Bach1 regulates the generation of APCs, specifically macrophages and dendritic cells, in mice. The impaired APC development in Bach1(-/-) mice was accompanied by defects in downstream T-cell responses and partial protection from experimental autoimmune encephalomyelitis. Genomewide analyses identified a panel of Bach1 target genes and ablation of the direct Bach1 target gene HO-1 exacerbated the impaired APC development observed in Bach1(-/-) mice. This was attributed to the impaired ability of HO-1(-/-)Bach1(-/-) double mutants to produce upstream APC progenitor cells, including common myeloid progenitor (CMP)-Flk2(+). By contrast, we observed an increase in hematopoietic stem-progenitor cells (HSPCs) in these mice, suggesting a developmental block in the progression of HSPCs to CMP-Flk2(+) and subsequently APCs.

The small MAF transcription factors MAFF, MAFG and MAFK: current knowledge and perspectives

The small MAFs, MAFF, MAFG and MAFK have emerged as crucial regulators of mammalian gene expression. Previous studies have linked small MAF function, by virtue of their heterodimerization with the Cap 'n' Collar (CNC) family of transcription factors, to the stress response and detoxification pathways. Recent analyses have revealed a complex regulatory network involving small MAF transcription factors and other cellular proteins. The expression and activity of small MAFs are tightly regulated at multiple levels. With regard to their clinical importance, small MAFs have been linked to various diseases, such as diabetes, neuronal disorders, thrombocytopenia and carcinogenesis. A better understanding of the molecular mechanisms governing the activity of small MAFs will provide novel insights into the control of mammalian transcription and may lead to the development of novel therapeutic strategies to treat common human disorders.

Forkhead box A1 (FOXA1) is a key mediator of insulin-like growth factor I (IGF-I) activity

The insulin-like growth factor receptor (IGF-IR) has been implicated in a number of human tumors, including breast cancer. Data from human breast tumors has demonstrated that IGF-IR is over-expressed and hyper-phosphorylated. Additionally, microarray analysis has shown that IGF-I treatment of MCF7 cells leads to a gene signature comprised of induced and repressed genes, which correlated with luminal B tumors. FOXA1, a forkhead family transcription factor, has been shown to be crucial for mammary ductal morphogenesis, similar to IGF-IR, and expressed at high levels in luminal subtype B breast tumors. Here, we investigated the relationship between FOXA1 and IGF-I action in breast cancer cells. We show that genes regulated by IGF-I are enriched for FOXA1 binding sites, and knock down of FOXA1 blocked the ability of IGF-I to regulate gene expression. IGF-I treatment of MCF7 cells increased the half-life of FOXA1 protein and this increase in half-life appeared to be dependent on canonical IGF-I signal transduction through both MAPK and AKT pathways. Finally, knock down of FOXA1 led to a decreased ability of IGF-I to induce proliferation and protect against apoptosis. Together, these results demonstrate that IGF-I can increase the stability of FOXA1 protein expression and place it as a critical mediator of IGF-I regulation of gene expression and IGF-I-mediated biological responses.

Focused examination of the intestinal lamina propria yields greater molecular insight into mechanisms underlying SIV induced immune dysfunction

Background

The Gastrointestinal (GI) tract is critical to AIDS pathogenesis as it is the primary site for viral transmission and a major site of viral replication and CD4⁺ T cell destruction. Consequently GI disease, a major complication of HIV/SIV infection can facilitate translocation of lumenal bacterial products causing localized/systemic immune activation leading to AIDS progression.

Methodology/Principal Findings

To better understand the molecular mechanisms underlying GI disease we analyzed global gene expression profiles sequentially in the intestine of the same animals prior to and at 21 and 90d post SIV infection (PI). More importantly we maximized information gathering by examining distinct mucosal components (intraepithelial lymphocytes, lamina propria leukocytes [LPL], epithelium and fibrovascular stroma) separately. The use of sequential intestinal resections combined with focused examination of distinct mucosal compartments represents novel approaches not previously attempted. Here we report data pertaining to the LPL. A significant increase (±1.7-fold) in immune defense/inflammation, cell adhesion/migration, cell signaling, transcription and cell division/differentiation genes were observed at 21 and 90d PI. Genes associated with the JAK-STAT pathway (IL21, IL12R, STAT5A, IL10, SOCS1) and T-cell activation (NFATc1, CDK6, Gelsolin, Moesin) were notably upregulated at 21d PI. Markedly downregulated genes at 21d PI included IL17D/IL27 and IL28B/IFNγ3 (anti-HIV/viral), activation induced cytidine deaminase (B-cell function) and approximately 57 genes regulating oxidative phosphorylation, a critical metabolic shift associated with T-cell activation. The 90d transcriptome revealed further augmentation of inflammation (CXCL11, chitinase-1, JNK3), immune activation (CD38, semaphorin7A, CD109), B-cell dysfunction (CD70), intestinal microbial translocation (Lipopolysaccharide binding protein) and mitochondrial antiviral signaling (NLRX1) genes. Reduced expression of CD28, CD4, CD86, CD93, NFATc1 (T-cells), TLR8, IL8, CCL18, DECTIN1 (macrophages), HLA-DOA and GPR183 (B-cells) at 90d PI suggests further deterioration of overall immune function.

Conclusions/Significance

The reported transcriptional signatures provide significant new details on the molecular pathology of HIV/SIV induced GI disease and provide new opportunity for future investigation.

A versatile ΦC31 based reporter system for measuring AP-1 and Nrf2 signaling in Drosophila and in tissue culture

This paper describes the construction and characterization of a system of transcriptional reporter genes for monitoring the activity of signaling pathways and gene regulation mechanisms in intact Drosophila, dissected tissues or cultured cells. Transgenic integration of the reporters into the Drosophila germline was performed in a site-directed manner, using ΦC31 integrase. This strategy avoids variable position effects and assures low base level activity and high signal responsiveness. Defined integration sites furthermore enable the experimenter to compare the activity of different reporters in one organism. The reporter constructs have a modular design to facilitate the combination of promoter elements (synthetic transcription factor binding sites or natural regulatory sequences), reporter genes (eGFP, or DsRed.T4), and genomic integration sites. The system was used to analyze and compare the activity and signal response profiles of two stress inducible transcription factors, AP-1 and Nrf2. To complement the transgenic reporter fly lines, tissue culture assays were developed in which the same synthetic ARE and TRE elements control the expression of firefly luciferase.

Expedient chemical synthesis of 75mer DNA binding domain of MafA: an insight on its binding to insulin enhancer

An expedient chemical synthesis of a 75mer peptide corresponding to the DNA binding domain (DBD, 227-301) of the human MafA leucine zipper transcription factor is reported. The application of microwave-assisted solid phase peptide synthesis (MW-SPPS) with a protocol modified respect to the standard one allowed obtaining the desired 75mer peptide in a short time with high quantity and optimal purity. MW-SPPS methodology was thus demonstrated as a valuable alternative to recombinant methods to obtain protein domains. Considering that recent findings suggest an involvement of MafA in the pathogenesis of diabetes mellitus, we also performed circular dichroism studies both on DBD folding and its interaction with MafA recognition element (MARE) on insulin enhancer. From our results, it was evicted that a disorder to order transition occurs after DBD interaction with insulin MARE which is mediated by specific structural elements on the N-terminus of the DBD.

The nuclear cofactor RAC3/AIB1/SRC-3 enhances Nrf2 signaling by interacting with transactivation domains

Nuclear factor erythroid 2-related factor 2 (Nrf2, NM 006164, 605 AA) is essential for the antioxidant responsive element (ARE)-mediated expression of a group of detoxifying antioxidant genes that detoxify carcinogens and protect against oxidative stress. Several proteins have been identified as Nrf2-interacting molecules. In this study, we found that the overexpression of receptor-associated coactivator 3 (RAC3)/AIB-1/steroid receptor coactivator-3, a nuclear coregulator and oncogene frequently amplified in human breast cancers, induced heme oxygenase-1 (HO-1) through Nrf2 transactivation in HeLa cells. Next, we determined the interaction between RAC3 and Nrf2 proteins using a co-immunoprecipitation assay and fluorescence resonance energy transfer analysis. The results showed that RAC3 bound directly to the Nrf2 protein in the nucleus. Subsequently, we identified the interacting domains of Nrf2 and RAC3 using a glutathione S-transferase pull-down assay. The results showed that both the N-terminal RAC3-pasB and C-terminal RAC3-R3B3 domains were tightly bound to the Neh4 and Neh5 transactivation domains. Furthermore, chromatin immunoprecipitation showed that RAC3 bound tightly to the ARE enhancer region of the HO-1 promoter via Nrf2 binding. These data suggest that Nrf2 activation is modulated and directly controlled through interactions with the RAC3 protein in HeLa cells.

Abnormal differentiation of erythroid precursors in p45 NF-E2(-/-) mice

The transcription factor p45 nuclear factor-erythroid-derived 2 (NF-E2) plays major roles in erythroid and megakaryocytic lineages. Here, we investigated the role of p45 NF-E2 in erythroid differentiation in vivo. Absence of p45 NF-E2 in mice leads to a twofold increase in serum erythropoietin levels. In the bone marrow of these animals, we found a different distribution of precursor populations compared to wild-type mice, suggesting abnormal differentiation. Loss of p45 NF-E2 was also associated with an increase in splenic erythropoiesis, as evidenced by an accumulation of early precursors, namely, late basophilic and polychromatic erythroblasts. These observations are consistent with a stress erythropoiesis phenotype and indicate that the spleen is likely compensating for ineffective erythropoiesis in the bone marrow. Analysis of bone marrow samples revealed increased GATA1 levels, as well as an increased proportion of erythroid cells arrested at the G(1) stage of cell cycle in p45 NF-E2-deficient mice. These results suggest that p45 NF-E2 is required for the differentiation of erythroid precursors.

Dysfunction of constitutive and inducible ubiquitin-proteasome system in amyotrophic lateral sclerosis: implication for protein aggregation and immune response

The ubiquitin-proteasome system (UPS) is the major intracellular proteolytic mechanism controlling the degradation of misfolded/abnormal proteins. A common hallmark in amyotrophic lateral sclerosis (ALS) and in other neurodegenerative disorders is the accumulation of misfolded/abnormal proteins into the damaged neurons, leading to the formation of cellular inclusions that are mostly ubiquitin-positive. Although proteolysis is a complex mechanism requiring the participation of different pathways, the abundant accumulation of ubiquitinated proteins strongly suggests an important contribution of UPS to these neuropathological features. The use of cellular and animal models of ALS, particularly those expressing mutant SOD1, the gene mutation most represented in familiar ALS, has provided significant evidence for a role of UPS in protein inclusions formation and motor neuron death. This review will specifically discuss this piece of evidence and provide suggestions of potential strategies for therapeutic intervention. We will also discuss the finding that, unlike the constitutive proteasome subunits, the inducible subunits are overexpressed early during disease progression in SOD1 mice models of ALS. These subunits form the immunoproteasome and generate peptides for the major histocompatibility complex class I molecules, suggesting a role of this system in the immune responses associated with the pathological features of ALS. Since recent discoveries indicate that innate and adaptive immunity may influence the disease process, in this review we will also provide evidence of a possible connection between immune-inflammatory reactions and UPS function, in the attempt to better understand the etiopathology of ALS and to identify appropriate targets for novel treatment strategies of this devastating disease.

NFE2L3 (NRF3): the Cinderella of the Cap'n'Collar transcription factors

NFE2L3 [Nuclear factor (erythroid-derived 2)-like 3] or NRF3, a member of the Cap'n'Collar (CNC) family, is a basic-region leucine zipper (bZIP) transcription factor that was first identified over 10 years ago. Contrary to its extensively studied homolog NFE2L2 (NRF2), the regulation and function of the NFE2L3 protein have not yet attracted as much attention. Nevertheless, several recent reports have now shed light on the possible roles of NFE2L3. Structural and biochemical studies revealed a series of domains and modifications that are critical for its cellular regulation. The control of the subcellular localization of NFE2L3 appears to be essential for understanding its role in various cellular processes. Importantly, newer studies provide fascinating insights linking NFE2L3 to differentiation, inflammation, and carcinogenesis. Here, we present an overview of the current level of knowledge of NFE2L3 transcription factor biology in humans and mice. From being the Cinderella of the CNC transcription factors for many years, NFE2L3 may now rapidly come into its own.

MafA and MafB activity in pancreatic β cells

Analyses in mouse models have revealed crucial roles for MafA (musculoaponeurotic fibrosarcoma oncogene family A) and MafB in islet β cells, with MafB being required during development and MafA in adults. These two closely related transcription factors regulate many genes essential for glucose sensing and insulin secretion in a cooperative and sequential manner. Significantly, the switch from MafB to MafA expression also appears to be vital for functional maturation of β cells produced by human embryonic stem (hES) cell differentiation. This review summarizes the discovery, distribution, and function of MafA and MafB in rodent pancreatic β cells, and describes some key questions regarding their importance to β cells.

Insulin-like growth factor 1 activates methionine adenosyltransferase 2A transcription by multiple pathways in human colon cancer cells

We have previously reported that the expression of MAT2A (methionine adenosyltransferase 2A) is increased in human colon cancer and in colon cancer cells treated with IGF-1 (insulin-like growth factor-1), which was required for its mitogenic effect. The aim of the present study was to elucidate the molecular mechanisms of IGF-1-mediated MAT2A induction. Nuclear run-on analysis confirmed that the increase in MAT2A expression lies at the transcriptional level. DNase I footprinting of the MAT2A promoter region revealed a similar protein-binding pattern in colon cancer and IGF-1-treated RKO cells. IGF-1 induced MAT2A promoter activity and increased nuclear protein binding to USF (upstream stimulatory factor)/c-Myb, YY1 (Yin and Yang 1), E2F, AP-1 (activator protein 1) and NF-κB (nuclear factor κB) consensus elements. IGF-1 increased the expression of c-Jun, FosB, MafG, p65, c-Myb, E2F-1 and YY1 at the pre-translational level. Knockdown of p65, MafG, c-Myb or E2F-1 lowered basal MAT2A expression and blunted the inductive effect of IGF-1 on MAT2A, whereas knockdown of YY1 increased basal MAT2A expression and had no effect on IGF-1-mediated MAT2A induction. Consistently, mutation of AP-1, NF-κB, E2F and USF/c-Myb elements individually blunted the IGF-1-mediated increase in MAT2A promoter activity, and combined mutations completely prevented the increase. In conclusion, IGF-1 activates MAT2A transcription by both known and novel pathways. YY1 represses MAT2A expression.

NRF2 activation restores disease related metabolic deficiencies in olfactory neurosphere-derived cells from patients with sporadic Parkinson's disease

BACKGROUND

Without appropriate cellular models the etiology of idiopathic Parkinson's disease remains unknown. We recently reported a novel patient-derived cellular model generated from biopsies of the olfactory mucosa (termed olfactory neurosphere-derived (hONS) cells) which express functional and genetic differences in a disease-specific manner. Transcriptomic analysis of Patient and Control hONS cells identified the NRF2 transcription factor signalling pathway as the most differentially expressed in Parkinson's disease.

RESULTS

We tested the robustness of our initial findings by including additional cell lines and confirmed that hONS cells from Patients had 20% reductions in reduced glutathione levels and MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt] metabolism compared to cultures from healthy Control donors. We also confirmed that Patient hONS cells are in a state of oxidative stress due to higher production of H(2)O(2) than Control cultures. siRNA-mediated ablation of NRF2 in Control donor cells decreased both total glutathione content and MTS metabolism to levels detected in cells from Parkinson's Disease patients. Conversely, and more importantly, we showed that activation of the NRF2 pathway in Parkinson's disease hONS cultures restored glutathione levels and MTS metabolism to Control levels. Paradoxically, transcriptomic analysis after NRF2 pathway activation revealed an increased number of differentially expressed mRNAs within the NRF2 pathway in L-SUL treated Patient-derived hONS cells compared to L-SUL treated Controls, even though their metabolism was restored to normal. We also identified differential expression of the PI3K/AKT signalling pathway, but only post-treatment.

CONCLUSIONS

Our results confirmed NRF2 as a potential therapeutic target for Parkinson's disease and provided the first demonstration that NRF2 function was inducible in Patient-derived cells from donors with uniquely varied genetic backgrounds. However, our results also demonstrated that the response of PD patient-derived cells was not co-ordinated in the same way as in Control cells. This may be an important factor when developing new therapeutics.

Genetic activation of Nrf2 signaling is sufficient to ameliorate neurodegenerative phenotypes in a Drosophila model of Parkinson's disease

Parkinson’s disease (PD) is the most common neurodegenerative movement disorder. Oxidative stress has been associated with the etiology of both sporadic and monogenic forms of PD. The transcription factor Nrf2, a conserved global regulator of cellular antioxidant responses, has been implicated in neuroprotection against PD pathology. However, direct evidence that upregulation of the Nrf2 pathway is sufficient to confer neuroprotection in genetic models of PD is lacking. Expression of the PD-linked gene encoding α-synuclein in dopaminergic neurons of Drosophila results in decreased locomotor activity and selective neuron loss in a progressive age-dependent manner, providing a genetically accessible model of PD. Here we show that upregulation of the Nrf2 pathway by overexpressing Nrf2 or its DNA-binding dimerization partner, Maf-S, restores the locomotor activity of α-synuclein-expressing flies. Similar benefits are observed upon RNA-interference-mediated downregulation of the prime Nrf2 inhibitor, Keap1, as well as in conditions of keap1 heterozygosity. Consistently, the α-synuclein-induced dopaminergic neuron loss is suppressed by Maf-S overexpression or keap1 heterozygosity. Our data validate the sustained upregulation of the Nrf2 pathway as a neuroprotective strategy against PD. This model provides a genetically accessible in vivo system in which to evaluate the potential of additional Nrf2 pathway components and regulators as therapeutic targets.

Fine particulate matter from urban ambient and wildfire sources from California's San Joaquin Valley initiate differential inflammatory, oxidative stress, and xenobiotic responses in human bronchial epithelial cells

Environmental particulate matter (PM) exposure has been correlated with pathogenesis of acute airway inflammatory disease such as asthma and COPD. PM size and concentration have been studied extensively, but the additional effects of particulate components such as biological material, transition metals, and polycyclic aromatic hydrocarbons could also impact initial disease pathogenesis. In this study, we compared urban ambient particulate matter (APM) collected from Fresno, California with wildfire (WF) particulate matter collected from Escalon, California on early transcriptional responses in human bronchial epithelial cells (HBE). Global gene expression profiling of APM treated HBE activated genes related to xenobiotic metabolism (CYP 1B1), endogenous ROS generation and response genes (DUOX1, SOD2, PTGS2) and pro-inflammatory responses associated with asthma or COPD such as IL-1α, IL-1β, IL-8, and CCL20. WF PM treatments also induced a pro-inflammatory gene response, but elicited a more robust xenobiotic metabolism and oxidative stress response. Inhibitor studies targeting endotoxin, ROS, and trace metals, found endotoxin inhibition had modest selective inhibition of inflammation while inhibition of hydrogen peroxide and transition metals had broad effects suggesting additional interactions with xenobiotic metabolism pathways. APM induced a greater inflammatory response while WF PM had more marked metabolism and ROS related responses.

Central nervous system-specific deletion of transcription factor Nrf1 causes progressive motor neuronal dysfunction

Cap'n'Collar (CNC) proteins heterodimerize with small Maf proteins and regulate the transcription of various genes. Small Maf-deficient mice develop severe neurodegeneration, and it remains unclear whether CNC proteins are involved in this process. In this study, we examined the contribution of Nrf1, one of the CNC proteins, to neuronal homeostasis in vivo. As Nrf1 gene knockout mice are embryonic lethal, we developed a central nervous system (CNS)-specific Nrf1 knockout (CKO) mouse line using mice bearing an Nrf1(flox) allele and Nestin-Cre allele. At birth, the CKO mice appeared indistinguishable from control mice, but thereafter they showed progressive motor ataxia and severe weight loss. All Nrf1 CKO mice died within 3 weeks. These phenotypes are similar to those reported in small Maf-deficient mice, suggesting the presence of collaboration between Nrf1 and small Maf proteins. We also found aberrant accumulation of polyubiquitinated proteins in various CNS regions and apparent neuronal loss in the hippocampus of Nrf1 CKO mice. An oxidative stress marker was accumulated in the spinal cords of the mice, but the expression patterns of oxidative stress response genes regulated by Nrf2 did not change substantially. These results show that Nrf1 sustains the CNS homeostasis through regulating target genes distinct from those regulated by Nrf2.

Molecular cross-talk between the NRF2/KEAP1 signaling pathway, autophagy, and apoptosis

Oxidative stress, perturbations in the cellular thiol level and redox balance, affects many cellular functions, including signaling pathways. This, in turn, may cause the induction of autophagy or apoptosis. The NRF2/KEAP1 signaling pathway is the main pathway responsible for cell defense against oxidative stress and maintaining the cellular redox balance at physiological levels. The relation between NRF2/KEAP1 signaling and regulation of apoptosis and autophagy is not well understood. In this hypothesis article we discuss how KEAP1 protein and its direct interactants (such as PGAM5, prothymosin α, FAC1 (BPTF), and p62) provide a molecular foundation for a possible cross-talk between NRF2/KEAP1, apoptosis, and autophagy pathways. We present a hypothesis for how NRF2/KEAP1 may interfere with the cellular apoptosis-regulatory machinery through activation of the ASK1 kinase by a KEAP1 binding partner-PGAM5. Based on very recent experimental evidence, new hypotheses for a cross-talk between NF-κB and the NRF2/KEAP1 pathway in the context of autophagy-related "molecular hub" protein p62 are also presented. The roles of KEAP1 molecular binding partners in apoptosis regulation during carcinogenesis and in neurodegenerative diseases are also discussed.

Control of redox state and redox signaling by neural antioxidant systems

The glutathione/glutathione disulfide (GSH/GSSG) redox pair forms the major redox couple in cells and as such plays a critical role in regulating redox-dependent cellular functions. Not only does GSH act as an antioxidant but it can also modulate the activity of a variety of different proteins. An impairment in GSH status is thought to be the precipitating event in a wide range of neurological disorders. Therefore, understanding how to maintain GSH in the CNS could provide a valuable therapeutic approach. Intracellular GSH levels are regulated by a complex series of pathways that include substrate transport and availability, rates of synthesis and regeneration, GSH utilization, and GSH efflux. To date, the most effective approaches for maintaining GSH levels in the CNS include enhancing cyst(e)ine uptake both directly and indirectly via transcriptional upregulation of system x(c)(-), increasing GSH synthesis via transcriptional upregulation of the rate limiting enzyme in GSH biosynthesis, and decreasing GSH utilization. Among the transcription factors that play critical roles in GSH metabolism are NF-E2-related factor 2 (Nrf2) and activating transcription factor 4 (ATF4). Thus, compounds that can upregulate these transcription factors may be particularly useful in promoting the functional maintenance of the CNS through their effects on GSH metabolism.