Transcription factor Nrf2 coordinately regulates a group of oxidative stress-inducible genes in macrophages

Vitamin C inhibits diethylmaleate-induced L-cystine transport in human vascular smooth muscle cells

Adaptive increases in intracellular glutathione (GSH) in response to oxidative stress are mediated by induction of L-cystine uptake via the anionic amino acid transport system x(c)(-). The recently cloned transporter xCT forms a heteromultimeric complex with the heavy chain of 4F2 cell surface antigen (4F2hc/CD98). Depletion of GSH by the electrophile diethylmaleate (DEM) induces the activity and expression of xCT in peritoneal macrophages. We here examine the effects of vitamin C on induction of xCT by DEM in human umbilical artery smooth muscle cells. DEM caused time- (3-24 h) and concentration- (25-100 microM) dependent increases in L-cystine transport, with GSH depleted by 50% after 6 h and restored to basal values after 24 h. xCT mRNA levels increased after 4 h DEM treatment with negligible changes detected for 4F2hc mRNA. DEM caused a rapid (5-30 min) phosphorylation of p38(MAPK). Inhibition of p38(MAPK) by SB203580 (10 microM) enhanced DEM-induced increases in L-cystine transport and GSH, whereas inhibition of p42/p44(MAPK) (PD98059, 10 microM) had no effect. Pretreatment of cells with vitamin C (100 microM, 24 h) attenuated DEM-induced adaptive increases in L-cystine transport and GSH levels. Inhibition of p38(MAPK), but not p42/p44(MAPK), reduced the cytoprotective action of vitamin C. Our findings suggest that DEM induces activation of xCT via intracellular signaling pathways involving p38(MAPK), and that vitamin C, in addition to its antioxidant properties, may modulate this signaling pathway to protect smooth muscle cells from injury.

Electrophile response element-mediated induction of the cystine/glutamate exchange transporter gene expression

In mammalian cultured cells, the cystine/glutamate exchange transport mediated by system x(c)- is important to maintain intracellular GSH levels. System x(c)- consists of two protein components, xCT and the heavy chain of 4F2 antigen. The activity of system x(c)- is induced by various stimuli, including electrophilic agents like diethyl maleate. In the present study, we have investigated the mechanism of the transcriptional regulation of xCT mRNA by diethyl maleate. The xCT gene consisted of twelve exons and sequence analysis identified four electrophile response element (EpRE)-like sequences between -230 and -1 in the 5'-flanking region, designated EpRE-1 to EpRE-4. To identify sequences mediating the constitutive and induced expression of xCT, a series of 5'-deletion mutants created from the 5'-flanking region were cloned into a luciferase reproter vector and transfected into BHK21 cells. The 5'-deletion analysis revealed that the sequence between -116 and -82 is essential for the basal expression and the sequence between -226 and -116 containing EpRE-1 is essential in response to diethyl maleate. Mutational analysis demonstrated that EpRE-1 is critically involved in the response to diethyl maleate. Other stress agents like arsenite, cadmium, and hydroquinone seemed to induce system x(c)- activity via the same sequence. Furthermore, the experiments using the mouse embryonic fibroblasts derived from the Nrf2-deficient mice revealed that the induction of xCT gene by electrophilic agents is mediated by Nrf2. EpRE occurs in a broad spectrum of genes for the proteins that are involved in the defense against xenobiotics and regulates their expression. The present results have demonstrated that xCT is a novel member of this protein family.

The transcriptional activation of the human copper/zinc superoxide dismutase gene by 2,3,7,8-tetrachlorodibenzo-p-dioxin through two different regulator sites, the antioxidant responsive element and xenobiotic responsive element

Cu/Zn superoxide dismutase (SOD1) catalyzes the dismutation of superoxide radicals produced during biological oxidations and environmental stress. The most toxic dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), induces SOD1 in human liver cells. Deletion analyses showed that the promoter region between -400 and -239 was responsible for the induction, in which two different characteristic regulatory elements, the antioxidant responsive element (ARE) and xenobiotic responsive element (XRE), are located. When the cells transfected with the plasmid containing those two cis-elements, the transactivation of SOD1 promoter was about 4-fold by TCDD, whereas mutation either on the ARE or XRE elevated the promoter activity by about 2-fold. Functional analyses of these two elements by deletion, mutation in the natural context, heterologous promoter assay, and gel mobility shift assay supported the notion that the activation of the SOD1 promoter was induced by TCDD through these two regulatory elements ARE and XRE. These results alongside our previous data indicate that the induction of SOD1 in response to TCDD is mediated by either Nrf2 protein or Ah receptor protein through ARE and XRE, respectively. These results also imply that the SOD1 can be induced by dioxin either in combination with or independently of these two regulatory elements to effectively defend cells from oxidative stress.

Phosphorylation of eukaryotic initiation factor 2 by heme-regulated inhibitor kinase-related protein kinases in Schizosaccharomyces pombe is important for fesistance to environmental stresses

Protein synthesis is regulated by the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) in response to different environmental stresses. One member of the eIF2alpha kinase family, heme-regulated inhibitor kinase (HRI), is activated under heme-deficient conditions and blocks protein synthesis, principally globin, in mammalian erythroid cells. We identified two HRI-related kinases from Schizosaccharomyces pombe which have full-length homology with mammalian HRI. The two HRI-related kinases, named Hri1p and Hri2p, exhibit autokinase and kinase activity specific for Ser-51 of eIF2alpha, and both activities were inhibited in vitro by hemin, as previously described for mammalian HRI. Overexpression of Hri1p, Hri2p, or the human eIF2alpha kinase, double-stranded-RNA-dependent protein kinase (PKR), impeded growth of S. pombe due to elevated phosphorylation of eIF2alpha. Cells from strains with deletions of the hri1(+) and hri2(+) genes, individually or in combination, exhibited a reduced growth rate when exposed to heat shock or to arsenic compounds. Measurements of in vivo phosphorylation of eIF2alpha suggest that Hri1p and Hri2p differentially phosphorylate eIF2alpha in response to these stress conditions. These results demonstrate that HRI-related enzymes are not unique to vertebrates and suggest that these eIF2alpha kinases are important participants in diverse stress response pathways in some lower eukaryotes.

Hemoprotein Bach1 regulates enhancer availability of heme oxygenase-1 gene

Heme oxygenase-1 (HO-1) protects cells from various insults including oxidative stress. Transcriptional activators, including the Nrf2/Maf heterodimer, have been the focus of studies on the inducible expression of ho-1. Here we show that a heme-binding factor, Bach1, is a critical physiological repressor of ho-1. Bach1 bound to the multiple Maf recognition elements (MAREs) of ho-1 enhancers with MafK in vitro and repressed their activity in vivo, while heme abrogated this repressor function of Bach1 by inhibiting its binding to the ho-1 enhancers. Gene targeting experiments in mice revealed that, in the absence of Bach1, ho-1 became expressed constitutively at high levels in various tissues under normal physiological conditions. By analyzing bach1/nrf2 compound-deficient mice, we documented antagonistic activities of Bach1 and Nrf2 in several tissues. Chromatin immunoprecipitation revealed that small Maf proteins participate in both repression and activation of ho-1. Thus, regulation of ho-1 involves a direct sensing of heme levels by Bach1 (by analogy to lac repressor sensitivity to lactose), generating a simple feedback loop whereby the substrate effects repressor-activator antagonism.

Multiple basic-leucine zipper proteins regulate induction of the mouse heme oxygenase-1 gene by arsenite

The mechanism of heme oxygenase-1 (ho-1) gene activation by arsenite was examined. Arsenite-stimulated expression of a ho-1 promoter/luciferase chimera in a dose-dependent manner in mouse hepatoma (Hepa) cells. Mutation analyses identified the arsenite-responsive sequence as the stress-response element (StRE), which resembles the binding sites for the AP-1 superfamily of basic-leucine zipper factors. In electrophoretic mobility shift assays, up to seven specific StRE-protein complexes were routinely detected using extracts from untreated Hepa cells whereas a single complex was typically observed after treatment with arsenite. Antibody "supershift" experiments identified Nrf2, JunD, and ATF3 in control complexes and the amount of these factors increased significantly in the arsenite-induced complex. MafG, ATF2, FosB, and JunB were also detected in the arsenite complex. Activation of a StRE-dependent luciferase gene by arsenite was inhibited to varying degrees by dominant-negative mutants of Nrf2, MafK, c-Fos, and CREB but most strongly with the latter. Together, these results implicate multiple basic-leucine zipper transcription factors in ho-1 gene activation by arsenite.

Identification of the interactive interface and phylogenic conservation of the Nrf2-Keap1 system

BACKGROUND

The transcription factor Nrf2 and its negative regulator Keap1 play important roles in transcriptional induction of a set of detoxifying and anti-oxidant enzymes. To gain an insight into our present enigma as to how cells receive oxidative and electrophilic signals and transduce them to Nrf2, we have developed a zebrafish model system for molecular toxicological studies.

RESULTS

We systematically cloned zebrafish cytoprotective enzyme cDNAs and found their expression to be efficiently induced by electrophilic agents. We consequently identified the presence of Nrf2 and Keap1 in zebrafish. Both loss- and gain-of-function analyses demonstrated that Nrf2 is the primary regulator of a subset of cytoprotective enzyme genes, while Keap1 suppresses Nrf2 activity in zebrafish. An ETGE motif, critical for the Nrf2-Keap1 interaction, was identified in the Neh2 domain of Nrf2 by reverse two-hybrid screening and found to be indispensable for the regulation of Nrf2 activity in zebrafish.

CONCLUSION

Taken together, these results indicate that the Nrf2-Keap1 system is highly conserved among vertebrates and that the interface between Nrf2 and Keap1 forms an important molecular basis of this regulatory system.

Nrf2 transcription factor, a novel target of keratinocyte growth factor action which regulates gene expression and inflammation in the healing skin wound

Keratinocyte growth factor (KGF) is a potent mitogen for epithelial cells, and it promotes survival of these cells under stress conditions. In a search for KGF-regulated genes in keratinocytes, we identified the gene encoding the transcription factor NF-E2-related factor 2 (Nrf2). Nrf2 is a key player in the cellular stress response. This might be of particular importance during wound healing, where large amounts of reactive oxygen species are produced as a defense against invading bacteria. Therefore, we studied the wound repair process in Nrf2 knockout mice. Interestingly, the expression of various key players involved in wound healing was significantly reduced in early wounds of the Nrf2 knockout animals, and the late phase of repair was characterized by prolonged inflammation. However, these differences in gene expression were not reflected by obvious histological abnormalities. The normal healing rate appears to be at least partially due to an up-regulation of the related transcription factor Nrf3, which was also identified as a target of KGF and which was coexpressed with Nrf2 in the healing skin wound. Taken together, our results reveal novel roles of the KGF-regulated transcription factors Nrf2 and possibly Nrf3 in the control of gene expression and inflammation during cutaneous wound repair.

Loss of the Nrf2 transcription factor causes a marked reduction in constitutive and inducible expression of the glutathione S-transferase Gsta1, Gsta2, Gstm1, Gstm2, Gstm3 and Gstm4 genes in the livers of male and female mice

Mice that lack the Nrf2 basic-region leucine-zipper transcription factor are more sensitive than wild-type (WT) animals to the cytotoxic and genotoxic effects of foreign chemicals and oxidants. To determine the basis for the decrease in tolerance of the Nrf2 homozygous null mice to xenobiotics, enzyme assay, Western blotting and gene-specific real-time PCR (TaqMan) have been used to examine the extent to which hepatic expression of GSH-dependent enzymes is influenced by the transcription factor. The amounts of protein and mRNA for class Alpha, Mu and Pi glutathione S-transferases were compared between WT and Nrf2 knockout (KO) mice of both sexes under both constitutive and inducible conditions. Among the class Alpha and class Mu transferases, constitutive expression of Gsta1, Gsta2, Gstm1, Gstm2, Gstm3, Gstm4 and Gstm6 subunits was reduced in the livers of Nrf2 mutant mice to between 3% and 60% of that observed in WT mice. Induction of these subunits by butylated hydroxyanisole (BHA) was more marked in WT female mice than in WT male mice. TaqMan analyses showed the increase in transferase mRNA caused by BHA was attenuated in Nrf2(-/-) mice, with the effect being most apparent in the case of Gsta1, Gstm1 and Gstm3. Amongst class Pi transferase subunits, the constitutive hepatic level of mRNA for Gstp1 and Gstp2 was not substantially affected in the KO mice, but their induction by BHA was dependent on Nrf2; this was more obvious in female mutant mice than in male mice. Nrf2 KO mice exhibited reduced constitutive expression of the glutamate cysteine ligase catalytic subunit, and, to a lesser extent, the expression of glutamate cysteine ligase modifier subunit. Little variation was observed in the levels of glutathione synthase in the different mouse lines. Thus the increased sensitivity of Nrf2(-/-) mice to xenobiotics can be partly attributed to a loss in constitutive expression of multiple GSH-dependent enzymes, which causes a reduction in intrinsic detoxification capacity in the KO animal. These data also indicate that attenuated induction of GSH-dependent enzymes in Nrf2(-/-) mice probably accounts for their failure to adapt to chronic exposure to chemical and oxidative stress.

Integration and diversity of the regulatory network composed of Maf and CNC families of transcription factors

Recent progress in the analysis of transcriptional regulation has revealed the presence of an exquisite functional network comprising the Maf and Cap 'n' collar (CNC) families of regulatory proteins, many of which have been isolated. Among Maf factors, large Maf proteins are important in the regulation of embryonic development and cell differentiation, whereas small Maf proteins serve as obligatory heterodimeric partner molecules for members of the CNC family. Both Maf homodimers and CNC-small Maf heterodimers bind to the Maf recognition element (MARE). Since the MARE contains a consensus TRE sequence recognized by AP-1, Jun and Fos family members may act to compete or interfere with the function of CNC-small Maf heterodimers. Overall then, the quantitative balance of transcription factors interacting with the MARE determines its transcriptional activity. Many putative MARE-dependent target genes such as those induced by antioxidants and oxidative stress are under concerted regulation by the CNC family member Nrf2, as clearly proven by mouse germline mutagenesis. Since these genes represent a vital aspect of the cellular defense mechanism against oxidative stress, Nrf2-null mutant mice are highly sensitive to xenobiotic and oxidative insults. Deciphering the molecular basis of the regulatory network composed of Maf and CNC families of transcription factors will undoubtedly lead to a new paradigm for the cooperative function of transcription factors.

Regulatory heme and trichloroethylene intoxication: A possible explanation of the case of "A Civil Action"

In 1998, a amovie entitled "A Civil Action" was released. The movie described the Woburn case, begun in 1982 and concluded in 1990, one of the most famous cases of trichloroethylene pollution. In a small town near Boston, twelve children died of leukemia, which seemed attributable to trichloroethylene contamination of the drinking water. The victims, however, could not win the case, since evidence that the identified chemicals could cause leukemia and other human illnesses was rather sketchy. There have been many cases of trichloroethylene pollution in industrial nations including Japan, therefore, we reconsidered the missing link. Our conclusion is that the disease occurred not by a direct effect of the chemical hazard on biological macromolecules but by an indirect effect through the physiological system such as signal transduction and transcriptional regulation. In 1984, we reported a marked reduction in the regulatory heme pool by trichloroethylene exposure, however, the biological significance was not well understood. Recently, we found that the DNA binding activity of Bach1, a negative regulator of genes, is controlled by heme, the regulation of which seems to explain how leukemia develops. The heterodimer of Bach1 with MafK recognizes Maf recognition elements (MAREs) competing with the erythroid type positive regulator, a complex of NF-E2 with MafK. Bach1/MafK occupies MAREs under lower heme conditions, whereas MAREs are open to NF-E2/MafK along with increasing heme concentration. Since the NF-E2/MafK function is closely related to normal erythroid differentiation, of which disorders such as sideroblastic anemia are often related to neoplasia; i.e., a clonal disorder that can progress to leukemia. Thus, a marked decline in regulatory heme by trichloroethylene intoxication could be one of the pathways to leukemia.

Correlation of simultaneous differential gene expression in the blood and heart with known mechanisms of adriamycin-induced cardiomyopathy in the rat

As the genomes of mammalian species become sequenced and gene functions are ascribed, the use of differential gene expression (DGE) to evaluate organ function will become common in the experimental evaluation of new drug therapies. The ability to translate this technology into useful information for human exposures depends on tissue sampling that is impractical or generally not possible in man. The possibility that the DGE of nucleated cells, reticulocytes, or platelets in blood may present the necessary link with target organ toxicity provides an opportunity to correlate preclinical with clinical outcomes. Adriamycin is highly effective alone and more frequently in combination with other chemotherapeutic agents in the treatment of a variety of susceptible malignancies. Adriamycin-induced cardiomyopathy was examined as an endpoint to measure the utility of DOE on whole blood as a predictor of cardiac toxicity. Statistically significant gene changes were observed between relevant blood and cardiac gene profiles that corroborated the accepted mechanisms of toxicity (oxidative stress, effects on carnitine transport, DNA intercalation). There were, however, clear indications that other target organs (bone marrow and intestinal tract) were affected. The divergent expression of some genes between the blood and the heart on day 7 may also indicate the timing and mechanism of development of the cardiomyopathy and confirm current therapeutic approaches for its prevention. The data demonstrate that whole blood gene expression particularly in relation to oxidative stress, in conjunction with standard hematology and clinical chemistry, may be useful in monitoring and predicting cardiac damage secondary to adriamycin administration. Appendices A & B, referenced in this paper, are not printed in this issue of Toxicologic Pathology. They are available as downloadable text files at http://taylorandfrancis.metapress.com/openurl.asp?genre=journal&issn=0192-6233. To access them, click on the issue link for 30(4), then select this article. A download option appears at the bottom of this abstract. In order to access the full article online, you must either have an individual subscription or a member subscription accessed through www.toxpath.org.

Activation of Maf/AP-1 repressor Bach2 by oxidative stress promotes apoptosis and its interaction with promyelocytic leukemia nuclear bodies

The oxidative stress response operates by inducing the expression of genes that counteract the stress. We show here that the oxidative stress-responsive transcription factor Bach2 is a generic inhibitor of gene expression directed by the 12-O-tetradecanoylphorbol-13-acetate response element, the Maf recognition element, and the antioxidant-responsive element. The Bach2-enhanced green fluorescent protein bicistronic retrovirus was used to monitor the fate of Bach2-expressing cells at the single cell level. Bach2 exerted an inhibitory effect on NIH3T3 cell proliferation and caused massive apoptosis upon mild oxidative stress in both NIH3T3 and Raji B-lymphoid cells. Interestingly, Bach1, a highly homologous protein, could not induce cell death, demonstrating the specificity for the apoptosis induction. Although both oxidative stress and leptomycin B, an inhibitor of nuclear export, induce nuclear accumulation of Bach2, the leptomycin B-induced nuclear accumulation of Bach2 was not sufficient to elicit apoptosis. Upon oxidative stress, Bach2 formed nuclear foci that associated with promyelocytic leukemia nuclear bodies. Our results suggest that Bach2 constitutes a cell lineage-specific system that couples oxidative stress and cell death and that inhibition of 12-O-tetradecanoylphorbol-13-acetate response element, the Maf recognition element, and the antioxidant-responsive element upon oxidative stress may be critical determinants for apoptosis.

Bleomycin upregulates expression of gamma-glutamylcysteine synthetase in pulmonary artery endothelial cells

The chemotherapeutic agent bleomycin induces pulmonary fibrosis through the generation of reactive oxygen species (ROS), which are thought to contribute to cellular damage and pulmonary injury. We hypothesized that bleomycin activates oxidative stress response pathways and regulates cellular glutathione (GSH). Bovine pulmonary artery endothelial cells exposed to bleomycin exhibit growth arrest and increased cellular GSH content. gamma-Glutamylcysteine synthetase (gamma-GCS) controls the key regulatory step in GSH synthesis, and Northern blots indicate that the gamma-GCS catalytic subunit [gamma-GCS heavy chain (gamma-GCS(h))] is upregulated by bleomycin within 3 h. The promoter for human gamma-GCS(h) contains consensus sites for nuclear factor-kappaB (NF-kappaB) and the antioxidant response element (ARE), both of which are activated in response to oxidative stress. Electrophoretic mobility shift assays show that bleomycin activates the transcription factor NF-kappaB as well as the ARE-binding factors Nrf-1 and -2. Nrf-1 and -2 activation by bleomycin is inhibited by the ROS quenching agent N-acetylcysteine (NAC), but not by U-0126, a MEK1/2 inhibitor that blocks bleomycin-induced MAPK activation. In contrast, NF-kappaB activation by bleomycin is inhibited by U-0126, but not by NAC. NAC and U-0126 both inhibit bleomycin-induced upregulation of gamma-GCS expression. These data suggest that bleomycin can activate oxidative stress response pathways and upregulate cellular GSH.

Oncogenic H-Ras enhances DNA repair through the Ras/phosphatidylinositol 3-kinase/Rac1 pathway in NIH3T3 cells. Evidence for association with reactive oxygen species

This study investigated the role of oncogenic H-Ras in DNA repair capacity in NIH3T3 cells. Expression of dominant-positive H-Ras (V12-H-Ras) enhanced the host cell reactivation of luciferase activity from UV-irradiated and cisplatin-treated plasmids and also increased the unscheduled DNA synthesis following cisplatin or UV treatment of cells. This observed enhancement of DNA repair capacity was inhibited by transient transfection with dominant-negative H-Ras (N17-H-Ras) or Rac1 (N17-Rac1) plasmids. Moreover, stable transfection of dominant-positive Rac1 (V12-Rac1) further enhanced DNA repair capacity. Because reactive oxygen species (ROS) are known to be a downstream effector of oncogenic Ras, we examined the role of ROS in DNA repair capacity. We found that ROS production by V12-H-Ras expression was mediated by the Ras/phosphatidylinositol 3-kinase (PI3K)/Rac1/NADPH oxidase-dependent pathway and that pretreatment of V12-H-Ras-transformed cells with an antioxidant (N-acetylcysteine) and an NADPH oxidase inhibitor (diphenyleneiodonium) decreased DNA repair capacity. Similarly, treatment with PI3K inhibitors (wortmannin and LY294002) inhibited the ability of oncogenic H-Ras to enhance DNA repair capacity. Furthermore, inhibition of the Ras/PI3K/Rac1/NADPH oxidase pathway resulted in increased sensitivity to cisplatin and UV in V12-H-Ras-expressing NIH3T3 cells. Taken together, these results provide evidence that oncogenic H-Ras activates DNA repair capacity through the Ras/PI3K/Rac1/NADPH oxidase-dependent pathway and that increased ROS production via this signaling pathway is required for enhancement of the DNA repair capacity induced by oncogenic H-Ras.

Upregulation and activation of the Nrf-1 transcription factor in the lesioned hippocampus

The Nrf-1 and Nrf-2 transcription factors play a pivotal role in the cellular defence against the toxic effects of reactive oxygen species (ROS). Although ROS are key effectors of neuronal death after ischaemic and traumatic brain injury, it is not known whether Nrf-1 and Nrf-2 are involved in neuroprotective signalling. Here, we analysed the temporal and spatial expression pattern of Nrf-1 and Nrf-2 after unilateral excitotoxic lesion of mouse hippocampus. In marked contrast to previous in vitro studies, where upregulation of these transcription factors on the mRNA level was never detected, we found a strong induction of Nrf-1 mRNA and protein expression in neurons of the lesioned hippocampus, accompanied by a weak elevation of Nrf-2 mRNA levels. Nrf-1 predominantly localized to the nucleus in the injured hippocampus. Furthermore, expression of the cytoprotective enzyme, heme oxygenase-1, a major target of Nrf-1 and Nrf-2 action, was coregulated with Nrf-1 in the same hippocampal neurons, suggesting that Nrf-1 is functionally active. Because Nrf-1 and Nrf-2 are potent inducers of various cytoprotective proteins, our data suggest a role of Nrf-1 and Nrf-2 in neuronal survival after acute brain injury.

Glutamate-cysteine ligase modifier subunit: mouse Gclm gene structure and regulation by agents that cause oxidative stress

Glutamate-cysteine ligase is a heterodimer comprising a modifier (GCLM) and a catalytic (GCLC) subunit. In mouse Hepa-1c1c7 hepatoma cell cultures, we found that tert-butylhydroquinone (tBHQ; 50 microM) induces the GCLM and GCLC mRNAs approximately 10- and approximately 2-fold, respectively, and that these increases primarily reflect de novo transcription. We determined that the mouse Gclm gene has seven exons, spanning 22.3 kb; all exons, intron-exon junctions, and 4.7 kb of 5'-flanking region were sequenced. By RNase protection analysis, we identified two major and several minor transcription start-site clusters over a 300-bp region. The Gclm 5'-flanking region is GC-rich and lacks a canonical TATA box. Transient and stable transfection studies, using luciferase reporter constructs containing incremental Gclm 5'-flanking deletions (4.7-0.5 kb), showed high basal activity but only modest ( approximately 2-fold) inducibility by tBHQ. The only candidate motif for oxidative stress regulation (in the 4.7-kb region we sequenced) is a putative inverted electrophile response element (EPRE) 9 bp upstream from the 5'-most transcription start-site. Site-directed mutagenesis of this -9 EPRE demonstrated minimal (30-40%) decreases in tBHQ induction and no effect on basal activity-suggesting that this EPRE might be necessary but not sufficient. The nuclear erythroid factor-2 (NEF2)-related factor-2 (NRF2) is known to transactivate via EPRE motifs. In the presence of co-transfected NRF cDNA expression vector, however, no increase in Gclm promoter activity was observed. Thus, the endogenous Gclm gene shows robust transcriptional activation by tBHQ in the intact Hepa-1 cell, but reporter constructs containing up to 4.7 kb of promoter (having only the one EPRE at -9) demonstrate a disappointing response, indicating that the major tBHQ-responsive regulatory element of the mouse Gclm gene must exist either further 5'- or 3'-ward of the 4.7-kb region studied.

Identification of albumin precursor protein, Phi AP3, and alpha-smooth muscle actin as novel components of redox sensing machinery in vascular smooth muscle cells

Aerobic organisms are continually subjected to environmental stressors that compromise redox homeostasis and induce cellular injury. In vascular smooth muscle cells (vSMCs), the activation/repression of redox-regulated genes after environmental stress often involves protein binding to cis-acting antioxidant response elements (AREs). The present study was conducted to identify proteins that participate in redox-regulated protein binding to human c-Ha-ras and mouse glutathione S-transferase A1 AREs in vSMCs after oxidant injury. Challenge of vSMCs with 0.3 or 3 microM hydrogen peroxide, 3-methylcholanthrene, benzo[a]pyrene-7,8-diol, 3-hydroxy benzo[a]pyrene, and benzo[a]pyrene-3,6-quinone induced concentration-related increases in ARE protein binding. The profiles of ARE complex assembly were comparable, but exhibited chemical specificity. Pretreatment with 0.5 mM N-acetylcysteine inhibited activation of ARE protein binding in hydrogen peroxide-treated cells. Preparative electrophoretic mobility shift assays coupled to Western analysis identified NF-E2-related proteins 1 and 2 and JunD in complexes assembled on AREs. Polyethylenimine affinity and sequence-specific serial immobilized DNA affinity chromatography followed by N-terminal sequencing identified albumin precursor protein, phi AP3, and alpha-smooth muscle actin as members of the ARE signaling pathway. Sequence analysis of albumin protein revealed homology to the redox-regulated transcription factors Bach1 and 2, as well as cytoskeletal and molecular motor proteins. These results implicate albumin precursor protein, phi AP3, and alpha-smooth muscle actin as participants in redox sensing in vSMCs, and suggest that protein complex assembly involves interactions between leucine zipper and zinc finger transcription factors with cytoskeletal proteins.

Enhanced expression of the transcription factor Nrf2 by cancer chemopreventive agents: role of antioxidant response element-like sequences in the nrf2 promoter

Induction of phase 2 enzymes, which neutralize reactive electrophiles and act as indirect antioxidants, is an important mechanism for protection against carcinogenesis. The transcription factor Nrf2, which binds to the antioxidant response element (ARE) found in the upstream regulatory region of many phase 2 genes, is essential for the induction of these enzymes. We have investigated the effect of the potent enzyme inducer and anticarcinogen 3H-1,2-dithiole-3-thione (D3T) on the fate of Nrf2 in murine keratinocytes. Both total and nuclear Nrf2 levels increased rapidly and persistently after treatment with D3T but could be blocked by cotreatment with cycloheximide. Nrf2 mRNA levels increased approximately 2-fold 6 h after D3T treatment. To examine the transcriptional activation of Nrf2 by D3T, the proximal region (1 kb) of the nrf2 promoter was isolated. Deletion and mutagenesis analyses demonstrated that nrf2 promoter-luciferase reporter activity was enhanced by treatment with D3T and that ARE-like sequences were required for this activation. Gel shift assays with nuclear extracts from PE cells indicated that common factors bind to typical AREs and the ARE-like sequences of the nrf2 promoter. Direct binding of Nrf2 to its own promoter was demonstrated by chromatin immunoprecipitation assay. Overexpression of Nrf2 increased the activity of the nrf2 promoter-luciferase reporter, while expression of mutant Nrf2 protein repressed activity. Thus, Nrf2 appears to autoregulate its own expression through an ARE-like element located in the proximal region of its promoter, leading to persistent nuclear accumulation of Nrf2 and protracted induction of phase 2 genes in response to chemopreventive agents.

Pathways of induction of peroxiredoxin I expression in osteoblasts: roles of p38 mitogen-activated protein kinase and protein kinase C

Peroxiredoxin I (Prx I) is an oxidative stress-inducible antioxidant protein with thioredoxin peroxidase activity. Here we report that the levels of Prx I mRNA and protein are dramatically increased in a murine osteoblast cell line, MC3T3-E1, by treatment with sodium arsenate. We further studied the signaling pathways that control the induction of Prx I expression. The treatment of osteoblasts with arsenate activated ERK1/2, JNK, and p38 MAPK. Pre-treating cells with inhibitors of p38 MAPK abolished the induction of Prx I protein but had minimal effect on the induction of Prx I mRNA, suggesting that p38 MAPK activity was required for post-transcriptional regulation. The inhibition of ERK1 and ERK2 had no effect on the induction of Prx I expression. Furthermore, rottlerin, an inhibitor of protein kinase Cdelta (PKCdelta) and calmodulin kinase III, abrogated the up-regulation at both protein and mRNA levels. Staurosporine and Go6983, inhibitors for PKC, also inhibited the induction of Prx I, suggesting that protein kinase Cdelta is required for the induction by arsenate. PKCdelta was activated by arsenate treatment by in vitro kinase assays. The inhibition of PKCdelta by rottlerin did not affect the activation of p38 MAPK by arsenate. These results suggest that there are two separate signaling pathways involved in the up-regulation of Prx I protein in response to arsenate, PKCdelta required for transcriptional activation and p38 MAPK required for post-transcriptional regulation.

Gene expression profile in fibroblast growth factor 2-transformed endothelial cells

Fibroblast growth factor-2 (FGF2) exerts paracrine and autocrine functions on endothelial cells. FGF2-overexpressing murine aortic endothelial cells (FGF2-T-MAE cells) induce opportunistic hemangioendothelioma-like tumors when inoculated in immunodeficient mice. To evaluate the impact of FGF2-mediated activation on gene expression profile in transformed endothelial cells, we performed subtractive suppression hybridization analysis between FGF2-T-MAE cells and parental MAE cells. The two cell populations were compared for differential gene expression also by gene macroarray hybridization with 32P-labeled cDNAs. The two approaches allowed the identification of 27 transcripts whose expression was upregulated by FGF2 in endothelial cells. With the exception of one unknown gene, the differentially expressed transcripts encoded for proteins involved in the modulation of cell cycle, differentiation, and cell adhesion. Among them, the stress-inducible genes A170, GADD45 and GADD153 are upregulated by FGF2 transfection or recombinant growth factor treatment. Their expression was also induced in vascular tumors originated by parental or FGF2-transfected MAE cells in nude mice. This study extends the number of genes involved in tumor angiogenesis and/or endothelial cell transformation, a finding with possible implications for the discovery of novel targets for angiostatic therapy.

Induction of heme-binding protein 23/peroxiredoxin I gene expression by okadaic acid in cultured rat hepatocytes

Heme-binding protein 23 (HBP23), also termed peroxiredoxin I (Prx I), is an antioxidant protein that is induced by various oxidative stress stimuli. HBP23/Prx I has thioredoxin-dependent peroxidase activity and noncovalently binds the prooxidant heme with high affinity. To investigate the regulatory role of cellular phosphorylation and dephosphorylation events on hepatic HBP23/Prx I gene expression, primary cultures of rat hepatocytes were treated with okadaic acid (OA) which is a specific inhibitor of the serine threonine protein phosphatases 1 and 2A. In hepatocyte cultures HBP23/Prx I was highly expressed for up to 5 days and, both protein and mRNA levels of HBP23/Prx I were induced by OA. The time kinetics of OA-dependent HBP23/Prx I mRNA upregulation were coordinate to that of heme oxygenase (HO)-1, which is the inducible isoform of the rate-limiting enzyme of heme-degradation. In contrast to HO-1, however, induction of HBP23/Prx I mRNA by OA was downregulated by dibutyryl-cAMP, and was enhanced by the specific protein kinase A inhibitors KT5720 and H-89. HBP23/Prx I induction by OA occurred on the transcriptional level as determined by studies with actinomycin D and nuclear run-off assays.

In silico approaches to mechanistic and predictive toxicology: an introduction to bioinformatics for toxicologists

Bioinformatics, or in silico biology, is a rapidly growing field that encompasses the theory and application of computational approaches to model, predict, and explain biological function at the molecular level. This information rich field requires new skills and new understanding of genome-scale studies in order to take advantage of the rapidly increasing amount of sequence, expression, and structure information in public and private databases. Toxicologists are poised to take advantage of the large public databases in an effort to decipher the molecular basis of toxicity. With the advent of high-throughput sequencing and computational methodologies, expressed sequences can be rapidly detected and quantitated in target tissues by database searching. Novel genes can also be isolated in silico, while their function can be predicted and characterized by virtue of sequence homology to other known proteins. Genomic DNA sequence data can be exploited to predict target genes and their modes of regulation, as well as identify susceptible genotypes based on single nucleotide polymorphism data. In addition, highly parallel gene expression profiling technologies will allow toxicologists to mine large databases of gene expression data to discover molecular biomarkers and other diagnostic and prognostic genes or expression profiles. This review serves to introduce to toxicologists the concepts of in silico biology most relevant to mechanistic and predictive toxicology, while highlighting the applicability of in silico methods using select examples.

Fundamental role of heme oxygenase in the protection against ischemic acute renal failure

Oxidative stress conditions such as oxidant stimuli, inflammation, exposure to xenobiotics and ionizing irradiation provoke cellular responses, principally involving transcriptional activation of genes encoding proteins that participate in the defense against oxidative tissue injuries. Excess of free heme, which is released from hemeproteins under these conditions, may constitute a major threat because it catalyzes the formation of reactive oxygen species. Exposure of mammalian cells to oxidative stimuli induces heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme degradation, as well as the 32-kDa heat shock protein. In various tissue injury systems, HO-1 induction has been shown to confer protection, while its abrogation has been shown to accelerate cellular injuries. In this review, recent findings concerning the role of HO-1 as a protective response against oxidative stress conditions are summarized, with a particular emphasis on its protective role in ischemic acute renal failure.

Role of NRF2 in protection against hyperoxic lung injury in mice

NRF2 is a transcription factor important in the protection against carcinogenesis and oxidative stress through antioxidant response element (ARE)-mediated transcriptional activation of several phase 2 detoxifying and antioxidant enzymes. This study was designed to determine the role of NRF2 in the pathogenesis of hyperoxic lung injury by comparing pulmonary responses to 95-98% oxygen between mice with site-directed mutation of the gene for NRF2 (Nrf2-/-) and wild-type mice (Nrf2+/+). Pulmonary hyperpermeability, macrophage inflammation, and epithelial injury in Nrf2-/- mice were 7.6-fold, 47%, and 43% greater, respectively, compared with Nrf2+/+ mice after 72 h hyperoxia exposure. Hyperoxia markedly elevated the expression of NRF2 mRNA and DNA-binding activity of NRF2 in the lungs of Nrf2+/+ mice. mRNA expression for ARE- responsive lung antioxidant and phase 2 enzymes was evaluated in both genotypes of mice to identify potential downstream molecular mechanisms of NRF2 in hyperoxic lung responses. Hyperoxia-induced mRNA levels of NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione-S-transferase (GST)-Ya and -Yc subunits, UDP glycosyl transferase (UGT), glutathione peroxidase-2 (GPx2), and heme oxygenase-1 (HO-1) were significantly lower in Nrf2-/- mice compared with Nrf2+/+ mice. Consistent with differential mRNA expression, NQO1 and total GST activities were significantly lower in Nrf2-/- mice compared with Nrf2+/+ mice after hyperoxia. Results demonstrated that NRF2 has a significant protective role against pulmonary hyperoxic injury in mice, possibly through transcriptional activation of lung antioxidant defense enzymes.

A sulforaphane analogue that potently activates the Nrf2-dependent detoxification pathway

Exposure of cells to a wide variety of chemoprotective compounds confers resistance to a broad set of carcinogens. For a subset of the chemoprotective compounds, protection is generated by an increase in the abundance of the protective phase II detoxification enzymes, such as glutathione S-transferase (GST). We have recently developed a cell culture system, using rat liver epithelial RL 34 cells, that potently responds to the phenolic antioxidants resulting in the induction of GST activity (Kawamoto, Y., Nakamura, Y., Naito, Y., Torii, Y., Kumagai, T., Osawa, T., Ohigashi, H., Satoh, K., Imagawa, M., and Uchida, K. (2000) J. Biol. Chem. 275, 11291-11299.) In the present study, we investigated the phase II-inducing potency of an isothiocyanate compound in vitro and in vivo and examined a possible induction mechanism. Based on an extensive screening of vegetable extracts for GST inducer activity in RL34 cells, we found Japanese horseradish, wasabi (Wasabia japonica, syn. Eutrema wasabi), as the richest source and identified 6-methylsulfinylhexyl isothiocyanate (6-HITC), an analogue of sulforaphane (4-methylsulfinylbutyl isothiocyanate) isolated from broccoli, as the major GST inducer in wasabi. 6-HITC potently induced both class alpha GSTA1 and class pi GSTP1 isozymes in RL34 cells. In animal experiments, we found that 6-MSHI was rapidly absorbed into the body and induced hepatic phase II detoxification enzymes more potently than sulforaphane. The observations that (i) 6-HITC activated the antioxidant response element (ARE), (ii) 6-HITC induced nuclear localization of the transcription factor Nrf2 that binds to ARE, and (iii) the induction of phase II enzyme genes by 6-HITC was completely abrogated in the nrf2-deficient mice, suggest that 6-HITC is a potential activator of the Nrf2/ARE-dependent detoxification pathway.

Lead, chemical porphyria, and heme as a biological mediator

One of the most well-characterized symptoms of lead poisoning is porphyria. The biochemical signs of lead intoxication related to porphyria are delta-aminolevulinic aciduria, coproporphyrinuria, and accumulation of free and zinc protoporphyrin in erythrocytes. From the 1970s to the early 80s, almost all of the enzymes in the heme pathway had been purified and characterized, and it was demonstrated that delta-aminolevulinic aciduria is due to inhibition of delta-aminolevulinate dehydratase by lead. Lead also inhibits purified ferrochelatase; however, the magnitude of inhibition was essentially nil even under pathological conditions. Further study proved the disturbance of iron-reducing activity by moderate lead exposure. Far different from these two enzymes, lead failed to inhibit purified coproporphyrinogen oxidase, i.e., the mechanism of coproporphyrinuria has not yet been understood. During the 80s to the 90s, the effects of environmental hazards including lead were elucidated through stress proteins, indicating the induction of some heme pathway enzymes as stress proteins. At that time, gene environment interaction was another focus of toxicology, since gene carriers of porphyrias are considered to be a high-risk group to chemical pollutants. Toxicological studies from the 70s to the 90s focused on the direct effect of hazards on biological molecules, such as the heme pathway enzymes, and many environmental pollutants were proved to affect cytosolic heme. Recently, we demonstrated the mechanism of the heme-controlled transcription system, which suggests that the indirect effects of environmental hazards are also important for elucidating toxicity, i.e., the hazards can affect cell functions through such biological mediators as regulatory heme. It is, therefore, probable that toxicology in the future will focus on biological systems such as gene regulation and signal transduction systems.

Rapid oxidation of dichlorodihydrofluorescin with heme and hemoproteins: formation of the fluorescein is independent of the generation of reactive oxygen species

Oxidative stress and the generation of reactive oxygen species (ROS) have been implicated in the pathogenesis of cellular damage. These events have usually been reported in terms of oxidation of a reporter molecule such as 2',7'-dichlorodihydrofluorescin diacetate (DCFH-DA). Treatment of HeLa cells with hemin or metalloporphyrins resulted in a rapid oxidation of DCFH in a time- and dose-dependent manner. This oxidation was inhibited by treatment of the cells with a large amount of superoxide dismutase and catalase, which is different from observations that these enzymes had no effect on the induction of heme oxygenase-1, a stress-induced protein, in hemin-treated cells. To examine the possibility that the oxidation of DCFH is independent of the generation of ROS, the oxidation was measured using hemoglobin-synthesizing erythroleukemia K562 cells. When K562 cells were treated with delta-aminolevulinic acid, a precursor of heme, oxidation of DCFH increased depending on the heme content in cells. Then DCFH-DA was oxidized directly with heme, hemoglobin, myoglobin and cytochrome c. These results suggest that oxidation of DCFH is not always related to the generation of ROS but may be related to heme content in cells.

Chemoprotection by phenolic antioxidants. Inhibition of tumor necrosis factor alpha induction in macrophages

Phenolic antioxidants exhibit anti-inflammatory activity in protection against chemical toxicity and cancer. To investigate the molecular mechanism of anti-inflammation, we analyzed the regulation of tumor necrosis factor alpha (TNF-alpha) expression in macrophages, a key step in inflammation, by the antioxidants. Whereas lipopolysaccharide (LPS), an inflammatory inducer, stimulates rapid synthesis of TNF-alpha protein, phenolic antioxidants, exemplified by tert-butyl hydroquinone and 1,4-dihydroquinone, block LPS-induced production of TNF-alpha protein in a time- and dose-dependent manner. Inhibition of TNF-alpha induction correlates with the capacity of the antioxidants to undergo oxidation-reduction cycling, implicating oxidative signaling in the inhibition. The antioxidants blocked LPS-induced increase of the steady-state mRNA of TNF-alpha but did not affect the half-life of the mRNA. Electrophoretic mobility shift assay reveals a total inhibition of LPS-induced formation of nuclear factor kappaB.DNA binding complexes by phenolic antioxidants. Finally, 1,4-dihydroquinone blocks the induction of TNF-alpha target genes interleukin 1beta and interleukin 6 at both mRNA and protein levels. Our findings demonstrate that phenolic antioxidants potently inhibit signal-induced TNF-alpha transcription and suggest a mechanism of anti-inflammation by the antioxidants through control of cytokine induction during inflammation.

Differential induction of mafF, mafG and mafK expression by electrophile-response-element activators

The three small Maf proteins, MafF, MafG and MafK, have been implicated in a number of physiological processes, including development, differentiation, haematopoiesis and stress response. Here we report the constitutive expression of mafF, mafG and mafK in six human cell lines derived from various tissues (HepG2, IMR-32, K-562, HEK-293, RD and A549). The expression patterns of mafF, mafG and mafK varied widely among cell lines. Because small Maf proteins have been implicated in electrophile response element (EpRE)-mediated stress response, the ability of three EpRE activators [pyrrolidinedithiocarbamate (PDTC), phenylethyl isothiocyanate (PEITC) and t-butylhydroquinone (tBHQ)] to induce small Maf expression was examined in detail in HepG2 cells. Both PDTC and PEITC induced mafF, mafG and mafK expression, whereas tBHQ failed to markedly induce any of the three small Mafs. Where a response was observed, mafF was induced to the greatest extent compared with mafG and mafK, and this response was transcriptionally mediated. PDTC also induced small Maf expression in the other cell lines examined, with patterns of induction varying among cell lines. The differences in expression among the cell lines examined, coupled with the induction patterns observed, indicate that the three small maf genes are stress-responsive, but may be regulated via differing mechanisms. Furthermore, the fact that tBHQ, PDTC and PEITC induce EpRE activity, but that tBHQ fails to markedly induce any of the small Mafs, suggests that up-regulation of small Mafs is not an absolute requirement for EpRE-mediated gene expression.

DNA microarray analyses of genes elicited by ultrasound in human U937 cells

The gene expression of human histiocytic lymphoma cell line U937 at 6 h after 1 MHz ultrasound treatment in the presence of Ar or N(2)O gas was examined by DNA microarrays. Of the 9,182 genes analyzed, only the keratin gene was identified as down-regulated in the cells exposed to ultrasound in the presence of N(2)O where no internal cavitation was observed. In contrast, five up-regulated and two down-regulated genes were identified in the cells exposed to ultrasound in the presence of Ar where internal cavitation was apparently observed. Six changes of the gene expression were confirmed by the semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Gene expression of heme oxygenase was augmented by a factor of 6.6 in microarray and by 4.0 by RT-PCR. These results indicate that internal cavitation increased the expression of genes responsive to oxidative stress in sonicated cells but non-inertial cavitation had minimal effects on gene expression.

Linkage analysis of susceptibility to hyperoxia. Nrf2 is a candidate gene

A strong role for reactive oxygen species (ROS) has been proposed in the pathogenesis of a number of lung diseases. Hyperoxia (> 95% oxygen) generates ROS and extensive lung damage, and has been used as a model of oxidant injury. However, the precise mechanisms of hyperoxia-induced toxicity have not been completely clarified. This study was designed to identify hyperoxia susceptibility genes in C57BL/6J (susceptible) and C3H/HeJ (resistant) mice. The quantitative phenotypes used for this analysis were pulmonary inflammatory cell influx, epithelial cell sloughing, and hyperpermeability. Genome-wide linkage analyses of intercross (F2) and recombinant inbred cohorts identified significant and suggestive quantitative trait loci on chromosomes 2 (hyperoxia susceptibility locus 1 [Hsl1]) and 3 (Hsl2), respectively. Comparative mapping of Hsl1 identified a strong candidate gene, Nfe2l2 (nuclear factor, erythroid derived 2, like 2 or Nrf2) that encodes a transcription factor NRF2 which regulates antioxidant and phase 2 gene expression. Strain-specific variation in lung Nrf2 messenger RNA expression and a T --> C substitution in the B6 Nrf2 promoter that cosegregated with susceptibility phenotypes in F2 animals supported Nrf2 as a candidate gene. Results from this study have important implications for understanding the mechanisms through which oxidants mediate the pathogenesis of lung disease.

Heteromeric amino acid transporters: biochemistry, genetics, and physiology

The heteromeric amino acid transporters (HATs) are composed of two polypeptides: a heavy subunit (HSHAT) and a light subunit (LSHAT) linked by a disulfide bridge. HSHATs are N-glycosylated type II membrane glycoproteins, whereas LSHATs are nonglycosylated polytopic membrane proteins. The HSHATs have been known since 1992, and the LSHATs have been described in the last three years. HATs represent several of the classic mammalian amino acid transport systems (e.g., L isoforms, y(+)L isoforms, asc, x(c)(-), and b(0,+)). Members of the HAT family are the molecular bases of inherited primary aminoacidurias cystinuria and lysinuric protein intolerance. In addition to the role in amino acid transport, one HSHAT [the heavy subunit of the cell-surface antigen 4F2 (also named CD98)] is involved in other cell functions that might be related to integrin activation. This review covers the biochemistry, human genetics, and cell physiology of HATs, including the multifunctional character of CD98.

Cloning and characterization of the mouse polyamine-modulated factor-1 (mPMF-1) gene: an alternatively spliced homologue of the human transcription factor

The natural polyamines and their analogues have been implicated in transcriptional regulation of specific genes. Human polyamine-modulated factor-1 (hPMF-1) was the first polyamine-responsive transcription factor identified. Here the mouse homologue of the hPMF-1 gene is described. Interestingly, the mouse gene (mPMF-1) codes for two alternatively spliced mRNAs. Both of the mouse splice variants, mPMF-1S and mPMF-1L, possess C-terminal coiled-coil domains nearly identical to that found in hPMF-1 and are highly homologous with the human protein. The C-terminal coiled-coil structure is necessary for transcriptional activation. However, the shorter protein, mPMF-1S, does not contain an N-terminal coiled-coil region as do both hPMF-1 and the longer mPMF-1L. mPMF-1L mRNA codes for a protein of 202 amino acids, 37 amino acids longer than the human protein. By contrast, mPMF-1S codes for only 133 amino acids, as a result of two exons being omitted compared with mPMF-1L. Both mouse transcription factors can interact with Nrf-2 (nuclear factor-E2-related factor 2), the normal partner of hPMF-1, substantiating the importance of the C-terminal coiled-coil region responsible for this interaction. Finally, the expression of mPMF-1 is induced when mouse M1 myeloid leukaemia cells are exposed to polyamine analogues, suggesting control similar to that observed for the hPMF-1.

Nrf2-deficient female mice develop lupus-like autoimmune nephritis

BACKGROUND

NF-E2-related factor 2 (Nrf2) is a basic leucine zipper transcriptional activator essential for the coordinate transcriptional induction of antioxidant enzymes and phase II drug metabolizing enzymes through the antioxidant response element/electrophile response element. The Nrf2-deficient mice were found to develop normally under standard laboratory conditions. However, upon closer examination, we found that aged female Nrf2-deficient mice displayed a shortened lifespan and developed severe glomerulonephritis. The present study investigated the glomerulonephritis findings in Nrf2-deficient mice.

METHODS

To evaluate glomerular lesions of Nrf2-deficient mice, histological and functional analyses were performed. The amounts of serum immunoglobulins, anti-double-stranded (ds) DNA antibody, and lipid peroxidation using thiobarbituric acid reactive substances (TBARS) also were measured.

RESULTS

Nrf2-deficient female mice over 60 weeks of age developed severe nephritis characterized by cellular proliferation, lobular formation, crescent formation, and subepithelial electron-dense deposits. In immunofluorescent assays, Nrf2-deficient female mice showed mesangial deposits and massive granular deposits of IgG, IgM, and C3 along the capillary walls. Higher serum levels of IgG, anti-dsDNA antibody, lower creatinine clearance, and slight splenomegaly also were found in Nrf2-deficient female mice. A higher concentration of TBARS also was found in Nrf2-deficient female mice.

CONCLUSIONS

These data indicate that the aged Nrf2-deficient female mice develop lupus-like autoimmune nephritis and suggest that nrf2 is one of the genes determining susceptibility to autoimmune disease. Analysis of nephritis in the Nrf2-deficient female mouse may clarify the mechanisms leading to the development of lupus disease.

The impaired glutathione system and its up-regulation by sulforaphane in vascular smooth muscle cells from spontaneously hypertensive rats

The glutathione (GSH) system plays an important role in reducing oxidative stress, the increase of which has been linked to the pathogenesis of hypertension. The aims of this study were to investigate: (1) whether the GSH system was impaired in aortic smooth muscle cells (SMCs) from spontaneously hypertensive rats (SHR), and (2) whether this system could be up-regulated by the phase-2 enzyme inducers, sulforaphane and t-butylhydroquinone (t-BHQ). Basal levels of cellular GSH, GSH-reductase and GSH-peroxidase were significantly lower in SMCs from SHR than from normotensive Wistar-Kyoto (WKY) rats. Heme oxygenase-1 (HO-1) was significantly higher in SHR SMCs, which correlated with the higher oxidative stress experienced by these cells. No differences were observed in the basal activity of GSH-S-transferase nor in the ability to synthesize GSH between SMCs from these two strains. Sulforaphane (0.05-1 micromol/l) and t-BHQ (10-100 micromol/l) induced significant and concentration-dependent increases in cellular GSH levels, HO-1 protein content and activities of GSH-reductase and GSH-peroxidase in SMCs from both rat strains. Upregulation of phase 2 enzymes correlated with a decrease in oxidative stress experienced by the SMCs, particularly with SHR. We conclude that SHR SMCs experience greater oxidative stress than WKY SMCs and that malfunction of the GSH system contributes to the enhanced oxidative stress in SHR SMCs.

Two domains of Nrf2 cooperatively bind CBP, a CREB binding protein, and synergistically activate transcription

BACKGROUND

Nrf2 belongs to the Cap-N-Collar (CNC) transcription factor family and is essential for the antioxidant responsive element (ARE)-mediated expression of a group of detoxifying and antioxidant genes. The forced expression of Nrf2 in mammalian cells activates the expression of target genes through the ARE, with Nrf2 showing the highest transactivation activity among the CNC family of transcription factors. To elucidate the molecular mechanisms generating this potent transactivation activity, we examined the functions of the domains within Nrf2.

RESULT

We found that Nrf2 contains two transcription activation domains, Neh4 and Neh5, which act synergistically to attain maximum a activation of reporter gene expression. Neh4 and Neh5 both individually and cooperatively bind to CBP (CREB (cAMP Responsive Element Binding protein) Binding Protein). In fact, the specific inhibitor of CBP, adenovirus E1A protein, significantly reduced Nrf2 activity. Importantly, the CBP-binding activity of Nrf2 deletion mutants positively correlated with their transactivation activity. Neh5 contains a motif which is commonly conserved among the CNC factors, whereas Neh4 contains the novel CBP-interacting motif recently identified in p53 and E2F.

CONCLUSIONS

Our results indicate that Nrf2 exploits the cooperative binding of two independent transactivation domains to CBP in the acquisition of a potent transactivation activity.

Defense mechanisms of the peritoneal cavity

The peritoneal cavity contains resident and migratory cell populations, which play crucial roles in the local defensive response against bacterial invasion. Although mononuclear phagocytes predominate in the peritoneal cavity of healthy subjects, recent attention has been focused on mesothelial and dendritic cells. Kinetic analysis of inflammatory mediators has derived from experimental models of peritonitis, but advances in the understanding of the roles of molecules such as lipocortins, PAF, leukotriene B4, PPAR gamma agonists, and chemokines has also been made. Little is known about the peritoneal response to physical trauma in the context of the abdominal compartment syndrome. Studies on the cellular and molecular pathology of intra-abdominal abscesses, peritoneal sclerosis, and other less frequent clinical entities (e.g., tertiary peritonitis) are needed. Biological therapy may contribute to improved clinical management of such diseases.

Induction of cellular antioxidative stress genes through heterodimeric transcription factor Nrf2/small Maf by antirheumatic gold(I) compounds

Gold(I)-containing compounds have long been used in the treatment of rheumatoid arthritis (RA), but the molecular mechanism of their action has remained largely unknown. In this paper we have demonstrated that gold(I) drugs selectively activate the DNA binding of a heterodimer consisting of the basic-leucine zipper transcription factors Nrf2 and small Maf. Once bound to its recognition DNA sequence termed antioxidant-responsive element or Maf-recognition element, Nrf2/small Maf induces a set of antioxidative stress genes, including heme oxygenase-1 and gamma-glutamylcysteine synthetase, whose products have been demonstrated to contribute to the scavenging of reactive oxygen species and to exhibit anti-inflammatory effects. Our findings suggest that stimulation of antioxidative stress response through activation of Nrf2/small Maf may be a pharmacologically important part of the actions of gold(I) drugs for the treatment of rheumatoid arthritis. Alternatively, activation of Nrf2/small Maf may be a protective response of cells against toxic effects of the drugs.

Versatile cytoprotective activity of lipoic acid may reflect its ability to activate signalling intermediates that trigger the heat-shock and phase II responses

Although lipoic acid (LA) and its reduced derivative (DHLA) have broad antioxidant activity, it seems unlikely that this can adequately explain the remarkable neuroprotective effects of LA observed in rodents and in diabetic patients. It is proposed that this protection is mediated, in large measure, by induction of various protective proteins. More specifically, there is some reason to suspect that LA can trigger both heat-shock and phase II responses, and that LA may achieve this by catalyzing the formation of intramolecular disulfides in certain signalling proteins that function as detectors of oxidants and/or electrophiles. This hypothesis is readily testable, and, if true, would suggest that LA may have general utility for preventing or treating neurodegenerative disorders, and possibly also may retard the adverse impact of aging on brain function. This model also predicts that LA should have anticarcinogenic activity.

Oxygen tension modulates the expression of cytokine receptors, transcription factors, and lineage-specific markers in cultured human megakaryocytes

OBJECTIVE

We have recently reported that 20% O2 significantly enhances total megakaryocyte (Mk) number, polyploidy, and proplatelet formation compared to 5% O2 in culture. In order to further elucidate the regulatory role of pO2 on megakaryocytopoiesis, we conducted a kinetic study of the expression of surface markers CD41a and CD42a; receptors for thrombopoietin (TPO), interleukin-3 (IL-3), and Flt3-ligand; the glutamate receptor of the N-methyl-D-aspartate subtype 1 (NMDAR1); and transcription factors GATA-1, NF-E2, and E2F-1.

MATERIALS AND METHODS

Mks were generated from mobilized peripheral blood (PB) CD34+ cells from normal donors in serum-free medium with TPO, IL-3, and Flt3-ligand at 20% and 5% O2. Quantitative assessment of Mk surface receptors and nuclear transcription factors was performed using multiparameter flow cytometry. mRNA levels of the nuclear transcription factors GATA-1 and NF-E2 were evaluated using RT-PCR.

RESULTS

The proportions of cells expressing the early Mk marker CD41a and the late Mk marker CD42a at day 15 were 4 and 5 times higher, respectively, at 20% O2. CD41a and CD42a protein levels per cell were also higher at 20% O2. After day 5, c-Mpl (TPO receptor) generally followed similar kinetics as CD41a. The proportion of IL-3 receptor (IL-3R)++ Mks at day 5 was 1.5 times higher at 5% O2. The NMDAR1 protein previously known to be expressed by neuronal cells has recently been identified in Mks. NMDAR1 and the transcription factors were studied on days 6, 9, and 11. NMDAR1 was expressed at a 1.5- to 1.8-fold higher level at 5% O2. Twenty percent O2 supported higher expression of the Mk-early and -late-maturation-specific transcription factors GATA-1 (1.2- to 2.2-fold higher) and NF-E2 (1.1- to 2.8-fold higher). This was consistent with RT-PCR data indicating the presence of higher levels of GATA-1 and NF-E2 mRNA at 20% O2. E2F-1, a ubiquitously expressed cell cycle transcription factor, was expressed at a 1.5-fold higher level at 20% O2 on day 6, but this difference did not persist by day 9.

CONCLUSION

These findings demonstrate that cytokine receptors c-Mpl and IL-3R, and Mk differentiation-specific surface receptors CD41a, CD42a, and NMDAR1, are significantly modulated by pO2, and suggest that one of the mechanisms of enhanced maturation at 20% O2 may involve regulation of transcription factors GATA-1 and NF-E2.

Accelerated DNA adduct formation in the lung of the Nrf2 knockout mouse exposed to diesel exhaust

Diesel exhaust (DE) has been recognized as a noxious mutagen and/or carcinogen, because its components can form DNA adducts. Mechanisms governing the susceptibility to DE and the efficiency of such DNA adduct formation require clarification. The transcription factor Nrf2 is essential for inducible and/or constitutive expression of a group of detoxification and antioxidant enzymes, and we hypothesized that the nrf2 gene knockout mouse might serve as an excellent model system for analyzing DE toxicity. To address this hypothesis, lungs from nrf2(-/-) and nrf2(+/-) mice were examined for the production of xenobiotic-DNA adducts after exposure to DE (3 mg/m(3) suspended particulate matter) for 4 weeks. Whereas the relative adduct levels (RAL) were significantly increased in the lungs of both nrf2(+/-) and nrf2(-/-) mice upon exposure to DE, the increase of RAL in the lungs from nrf2(-/-) mice exposed to DE were approximately 2.3-fold higher than that of nrf2(+/-) mice exposed to DE. In contrast, cytochrome P4501A1 mRNA levels in the nrf2(-/-) mouse lungs were similar to those in the nrf2(+/-) mouse lungs even after exposure to DE, suggesting that suppressed activity of phase II drug-metabolizing enzymes is important in giving rise to the increased level of DNA adducts in the Nrf2-null mutant mouse subjected to DE. Importantly, severe hyperplasia and accumulation of the oxidative DNA adduct 8-hydroxydeoxyguanosine were observed in the bronchial epidermis of nrf2(-/-) mice following DE exposure. These results demonstrate the increased susceptibility of the nrf2 germ line mutant mouse to DE exposure and indicate the nrf2 gene knockout mouse may represent a valuable model for the assessment of respiratory DE toxicity.

Identification of activating transcription factor 4 (ATF4) as an Nrf2-interacting protein. Implication for heme oxygenase-1 gene regulation

Nrf2 regulates expression of genes encoding enzymes with antioxidant (e.g. heme oxygenase-1 (HO-1)) or xenobiotic detoxification (e.g. NAD(P)H:quinone oxidoreductase, glutathione S-transferase) functions via the stress- or antioxidant-response elements (StRE/ARE). Nrf2 heterodimerizes with small Maf proteins, but the role of such dimers in gene induction is controversial, and other partners may exist. By using the yeast two-hybrid assay, we identified activating transcription factor (ATF) 4 as a potential Nrf2-interacting protein. Association between Nrf2 and ATF4 in mammalian cells was confirmed by co-immunoprecipitation and mammalian two-hybrid assays. Furthermore, Nrf2.ATF4 dimers bound to an StRE sequence from the ho-1 gene. CdCl(2), a potent inducer of HO-1, increased expression of ATF4 in mouse hepatoma cells, and detectable induction of ATF4 protein preceded that of HO-1 (30 min versus 2 h). A dominant-negative mutant of ATF4 inhibited basal and CdCl(2)-stimulated expression of a StRE-dependent/luciferase fusion construct (pE1-luc) in hepatoma cells but only basal expression in mammary epithelial MCF-7 cells. A dominant mutant of Nrf2 was equally inhibitory in both cell types in the presence or absence of CdCl(2). These results indicate that ATF4 regulates basal and CdCl(2)-induced expression of the ho-1 gene in a cell-specific manner and possibly in a complex with Nrf2.

Phosphatidylinositol 3-kinase, not extracellular signal-regulated kinase, regulates activation of the antioxidant-responsive element in IMR-32 human neuroblastoma cells

The antioxidant-responsive element (ARE) plays an important role in the induction of phase II detoxifying enzymes including NADPH:quinone oxidoreductase (NQO1). We report herein that activation of the human NQO1-ARE (hNQO1-ARE) by tert-butylhydroquinone (tBHQ) is mediated by phosphatidylinositol 3-kinase (PI3-kinase), not extracellular signal-regulated kinase (Erk1/2), in IMR-32 human neuroblastoma cells. Treatment with tBHQ significantly increased NQO1 protein without activation of Erk1/2. In addition, PD 98059 (a selective mitogen-activated kinase/Erk kinase inhibitor) did not inhibit hNQO1-ARE-luciferase expression or NQO1 protein induction by tBHQ. Pretreatment with LY 294002 (a selective PI3-kinase inhibitor), however, inhibited both hNQO1-ARE-luciferase expression and endogenous NQO1 protein induction. In support of a role for PI3-kinase in ARE activation we show that: 1) transfection of IMR-32 cells with constitutively active PI3-kinase selectively activated the ARE in a dose-dependent manner that was completely inhibited by treatment with LY 294002; 2) pretreatment of cells with the PI3-kinase inhibitors, LY 294002 and wortmannin, significantly decreased NF-E2-related factor 2 (Nrf2) nuclear translocation induced by tBHQ; and 3) ARE activation by constitutively active PI3-kinase was blocked completely by dominant negative Nrf2. Taken together, these data clearly show that ARE activation by tBHQ depends on PI3-kinase, which lies upstream of Nrf2.

Heme mediates derepression of Maf recognition element through direct binding to transcription repressor Bach1

Heme controls expression of genes involved in the synthesis of globins and heme. The mammalian transcription factor Bach1 functions as a repressor of the Maf recognition element (MARE) by forming antagonizing hetero-oligomers with the small Maf family proteins. We show here that heme binds specifically to Bach1 and regulates its DNA-binding activity. Deletion studies demonstrated that a heme-binding region of Bach1 is confined within its C-terminal region that possesses four dipeptide cysteine-proline (CP) motifs. Mutations in all of the CP motifs of Bach1 abolished its interaction with heme. The DNA-binding activity of Bach1 as a MafK hetero-oligomer was markedly inhibited by heme in gel mobility shift assays. The repressor activity of Bach1 was lost upon addition of hemin in transfected cells. These results suggest that increased levels of heme inactivate the repressor Bach1, resulting in induction of a host of genes with MARES: