Nrf1 and Nrf2 positively and c-Fos and Fra1 negatively regulate the human antioxidant response element-mediated expression of NAD(P)H:quinone oxidoreductase1 gene

Twenty-four base pairs of the human antioxidant response element (hARE) are required for high basal transcription of the NAD(P)H:quinone oxidoreductase1 (NQO1) gene and its induction in response to xenobiotics and antioxidants. hARE is a unique cis-element that contains one perfect and one imperfect AP1 element arranged as inverse repeats separated by 3 bp, followed by a "GC" box. We report here that Jun, Fos, Fra, and Nrf nuclear transcription factors bind to the hARE. Overexpression of cDNA derived combinations of the nuclear proteins Jun and Fos or Jun and Fra1 repressed hARE-mediated chloramphenicol acetyltransferase (CAT) gene expression in transfected human hepatoblastoma (Hep-G2) cells. Further experiments suggested that this repression was due to overexpression of c-Fos and Fra1, but not due to Jun proteins. The Jun (c-Jun, Jun-B, and Jun-D) proteins in all the possible combinations were more or less ineffective in repression or upregulation of hARE-mediated gene expression. Interestingly, overexpression of Nrf1 and Nrf2 individually in Hep-G2 and monkey kidney (COS1) cells significantly increased CAT gene expression from reporter plasmid hARE-thymidine kinase-CAT in transfected cells that were inducible by beta-naphthoflavone and teri-butyl hydroquinone. These results indicated that hARE-mediated expression of the NQO1 gene and its induction by xenobiotics and antioxidants are mediated by Nrf1 and Nrf2. The hARE-mediated basal expression, however, is repressed by overexpression of c-Fos and Fra1.

Nrf2 and Nrf1 in association with Jun proteins regulate antioxidant response element-mediated expression and coordinated induction of genes encoding detoxifying enzymes

Antioxidant response element (ARE)-mediated expression and coordinated induction of genes encoding detoxifying enzymes is one mechanism of critical importance to cellular protection against oxidative stress. In the present report, we demonstrate that nuclear transcription factors Nrf2 and Nrf1 associate with Jun (c-Jun, Jun-B and Jun-D) proteins to upregulate ARE-mediated expression and coordinated induction of detoxifying enzymes in response to antioxidants and xenobiotics. Nrf-Jun association/heterodimerization and binding to the ARE required unknown cytosolic factor(s). Nrf2 containing one mutated leucine in its leucine zipper region was more efficient in upregulation of ARE-mediated gene expression, as compared to Nrf1 with two mutated leucines.

Quercetin may act as a cytotoxic prooxidant after its metabolic activation to semiquinone and quinoidal product

In the last ten years, there has been an important increase in interest in quercetin action as a unique antioxidant, but its putative role in numerous prooxidant effects is also being continually updated. The mechanism underlying this undesirable ability seems to involve its metabolic oxidoreductive activation. Based on the structural properties of quercetin, we have investigated whether its catechol moiety may be the potential tool for revealed toxicity. We demonstrated, with an ESR spin-stabilization technique coupled to conventional spectrophotometry, that o-semiquinone and o-quinone are indeed the products of enzymatically catalyzed oxidative degradation of quercetin. The former radical might serve to facilitate the formation of superoxide and depletion of GSH, which could confer a specificity of its prooxidative action in situ. The observed one-electron reduction of o-quinone may enrich the semiquinone pool, thereby magnifying its effect. The two-electron reduction of quinone can result in constant resupply of quercetin in situ, thereby also modulating another pathway of its known biological activities. We have also tried to see whether the intracellular oxidative degradation of quercetin can be confirmed under the controlled conditions of model monolayer cell cultures. The results are indicative of the intracellular metabolic activation of quercetin to o-quinone, the process which can be partially associated with the observed concentration-dependent cytotoxic effect of quercetin.

Regulation of genes encoding NAD(P)H:quinone oxidoreductases

NAD(P)H:quinone oxidoreductase (NQO1) and NRH:quinone oxidoreductase (NQO2) are flavoproteins that catalyze two-electron reduction and detoxification of quinones and its derivatives. This leads to the protection of cells against redox cycling, oxidative stress, and neoplasia. NQO1 is expressed ubiquitously in all the tissues. However, the level of expression varied among the human tissues. NQO1 gene is expressed at higher levels in several tumor tissue types, including liver and colon, as compared to normal tissues of similar origin. NQO1 gene expression is coordinately induced with other detoxifying enzyme genes in response to xenobiotics, antioxidants, oxidants, heavy metals, and radiations. Deletion mutagenesis in the NQO1 gene promoter identified several cis-elements including antioxidant response element (ARE), a basal element, and AP-2 element. ARE elements have also been found in the promoter regions of other detoxifying enzyme genes including glutathione S-transferases. ARE is essentially required for expression and coordinated induction of NQO1 and other detoxifying enzyme genes. Nuclear transcription factors Nrf2 and c-Jun bind to the ARE and activate the gene expression. The binding of Nrf2 + c-Jun to the ARE required unknown cytosolic factor(s). In addition to Nrf2 and c-Jun, other nuclear transcription factors including Nrf1, Jun-B, and Jun-D also bind to the ARE and regulate expression and induction of NQO1 gene. A hypothetical model is presented based on the available information on ARE-mediated regulation of detoxifying enzyme genes. Briefly, the Nrf2 is retained in the cytosplasm by a repressor protein Keap1 in untreated normal cells. The treatment of cells with xenobiotics and antioxidants leads to the activation of unknown cytosolic factor(s) that catalyze modification of Nrf2 and/or Keap1. The modification follows dissociation of Nrf2 and Keap1. The free Nrf2 translocates in the nucleus. Nrf2 in the nucleus heterodimerizes with c-Jun and binds to the ARE resulting in the induction of NQO1 and other ARE-regulated genes expression. The identity of cytosolic factor(s) remains unknown.

Functional characterization and role of INrf2 in antioxidant response element-mediated expression and antioxidant induction of NAD(P)H:quinone oxidoreductase1 gene

Antioxidant response element (ARE) and nuclear transcription factor Nrf2 are known to regulate expression and coordinated induction of NQO1 and other detoxifying enzyme genes in response to antioxidants and xenobiotics. A cytosolic inhibitor of Nrf2, INrf2, that retains Nrf2 in the cytoplasm, was cloned and sequenced. Treatment of cells with antioxidants and xenobiotics results in the release of Nrf2 from INrf2. Nrf2 then moves in the nucleus. This leads to the induction of ARE-mediated NQO1 and other detoxifying enzyme genes expression. INrf2 after dissociation from Nrf2 remains in the cytosol. Overexpression of INrf2 repressed ARE-mediated NQO1 gene expression. Deletion mapping of INrf2 revealed the requirement of KELCH domain (amino acid residues 361-597) and C-terminal region (amino acid residues 598-624) in retention of Nrf2 in the cytosol. Both these regions of INrf2 independently retained Nrf2 in the cytosol leading to the repression of ARE-mediated NQO1 gene expression. These results may indicate that two different regions of INrf2 interact with a single molecule of Nrf2 or two or more molecules of Nrf2 interact with a single molecule of INrf2. The transcription of Nrf2 and INrf2 did not change in response to antioxidants and xenobiotics. This indicated that INrf2 and/or Nrf2 might be post-transcriptionally modified in response to antioxidants and xenobiotics leading to the release of Nrf2 from INrf2 and induction of ARE-mediated NQO1 and other detoxifying enzyme genes expression.

NAD(P)H:quinone oxidoreductase1 (DT-diaphorase) expression in normal and tumor tissues

NAD(P)H:Quinone Oxidoreductase1 (NQO1) also known as DT-diaphorase is a flavoprotein that catalyzes the two-electron reduction of quinones, quinone imines and azo-dyes and thereby protects cells against mutagenicity and carcinogenicity resulting from free radicals and toxic oxygen metabolites generated by the one-electron reductions catalyzed by cytochromes P450 and other enzymes. High levels of NQO1 gene expression have been observed in liver, lung, colon and breast tumors as compared to normal tissues of the same origin. The transcription of the NQO1 gene is activated in response to exposure to bifunctional (e.g. beta-naphthoflavone (beta-NF), 2, 3, 7, 8 tetrachorodibenzo-p-dioxin (TCDD)) and monofunctional (phenolic antioxidants/chemoprotectors e.g. 2(3)-tert-butyl-4-hydroxy-anisole (BHA)) inducers. The high level of expression of the NQO1 gene and its induction by beta-NF and BHA require the presence of an AP1 binding site contained within the human Antioxidant Response Element (hARE) and are mediated by products of proto-oncogenes, Jun and Fos. Induction of NQO1 gene expression involves transfer of a redox signal from xenobiotics to unknown 'redox protein(s)' which in turn, modify the Jun and Fos proteins for greater affinity towards the AP1 site of the NQO1 gene and activates transcription. The expression and regulation of the NQO1 gene is complex as many additional cis-elements have been identified in the promoter region and is a subject of great future interest. In addition to established tumors, NQO1 gene expression is also increased in developing tumors, indicating a role in cellular defense during tumorigenesis. It has been proposed that low molecular weight substance(s) can diffuse from tumor cells into surrounding normal cells and activate the expression of the NQO1 gene. Purification and characterization of such substance(s) may provide important information in regard to the mechanism of activation of NQO1 gene expression and the role of increased NQO1 expression in tumor development. In view of the general consensus that NQO1 is over-expressed in tumor cells and the realization that NQO1 may either activate or detoxify xenobiotics, it is important to establish the role of NQO1 in the activation, and the detoxification of xenobiotics and drugs and in the intrinsic sensitivity of tumors to bioreductive alkylating aziridinyl benzoquinones such as diaziquone (AZQ), mitomycin C (MMC), and indoloquinone EO9, as well as to the dinitrophenyl aziridine, CB1954, and the benzotriazine-di-N-oxide, SR 4233.

Disruption of the DT diaphorase (NQO1) gene in mice leads to increased menadione toxicity

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a flavoenzyme that catalyzes two-electron reductive metabolism and detoxification of quinones and their derivatives leading to protection of cells against redox cycling and oxidative stress. To examine the in vivo role of NQO1, a NQO1-null mouse was produced using targeted gene disruption. Mice lacking NQO1 gene expression showed no detectable phenotype and were indistinguishable from wild-type mice. However, NQO1-null mice exhibited increased toxicity when administered menadione compared with wild-type mice. These results establish a role for NQO1 in protection against quinone toxicity. The NQO1-null mice are a model for NQO1 deficiency in humans and can be used to determine the role of this enzyme in sensitivity to toxicity and carcinogenesis.

Human dioxin-inducible cytochrome P1-450: complementary DNA and amino acid sequence

Induction of cytochrome P1-450 has been linked to susceptibility to certain chemically induced cancers in mouse and man. Treatment of the human cell line MCF-7 with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) results in high levels of aryl hydrocarbon (benzo[a]pyrene) hydroxylase (P1-450) activity. This cell line was used to isolate a human P1-450 full-length complementary DNA (cDNA) clone. The cDNA is 2566 nucleotides in length, encodes a polyadenylated messenger RNA (2.8 kilobases in length), and has a continuous reading frame producing a protein with 512 residues (molecular weight, 58,151). The human P1-450 cDNA and protein are 63 percent and 80 percent similar to mouse P1-450 cDNA and protein, respectively. Whereas the mouse TCDD-inducible P-450 gene subfamily has two members (P1-450 and P3-450), the human TCDD-inducible gene subfamily appears to have only one gene (P1-450).

Small maf (MafG and MafK) proteins negatively regulate antioxidant response element-mediated expression and antioxidant induction of the NAD(P)H:Quinone oxidoreductase1 gene

The antioxidant response element (ARE) is known to regulate expression and induction of NQO1, GST Ya, and other detoxifying enzyme genes in response to antioxidants and xenobiotics. The nuclear transcription factor Nrf2 and Nrf1 bind to the ARE and positively regulate expression and induction of the NQO1 and GST Ya genes. In this study, we demonstrate that overexpression of small Maf (MafG and MafK) proteins negatively regulate ARE-mediated expression and tert-butyl hydroquinone induction of the NQO1 and GST Ya genes in transfected Hep-G2 cells. In similar experiments, overexpression of small Maf proteins also repressed Nrf2-mediated up-regulation of ARE-mediated NQO1 and GST Ya genes expression in Hep-G2 cells co-transfected with Nrf2 and small Maf proteins. Band and supershift assays with the NQO1 gene ARE and nuclear proteins demonstrate that small MafG and MafK bind to the ARE as Maf-Maf homodimers and Maf-Nrf2 heterodimers. Therefore, Maf-Maf homodimers and possibly Maf-Nrf2 heterodimers play a role in negative regulation of ARE-mediated transcription and antioxidant induction of NQO1 and other detoxifying enzyme genes. In contrast to Maf-Nrf2, the Maf-Nrf1 heterodimers failed to bind with the NQO1 gene ARE and did not demonstrate the repressive effect in transfection assays.

In vivo role of NAD(P)H:quinone oxidoreductase 1 (NQO1) in the regulation of intracellular redox state and accumulation of abdominal adipose tissue

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a flavoprotein that utilizes NAD(P)H as an electron donor, catalyzing the two-electron reduction and detoxification of quinones and their derivatives. NQO1-/- mice deficient in NQO1 activity and protein were generated in our laboratory (Rajendirane, V., Joseph, P., Lee, Y. H., Kimura, S., Klein-Szanto, A. J. P., Gonzalez, F. J., and Jaiswal, A. K. (1998) J. Biol. Chem. 273, 7382-7389). Mice lacking a functional NQO1 gene (NQO1-/-) were born normal and reproduced adeptly as the wild-type NQO1+/+ mice. In the present report, we show that NQO1-/- mice exhibit significantly lower levels of abdominal adipose tissue as compared with the wild-type mice. The NQO1-/- mice showed lower blood levels of glucose, no change in insulin, and higher levels of triglycerides, beta-hydroxy butyrate, pyruvate, lactate, and glucagon as compared with wild-type mice. Insulin tolerance test demonstrated that the NQO1-/- mice are insulin resistant. The NQO1-/- mice livers also showed significantly higher levels of triglycerides, lactate, pyruvate, and glucose. The liver glycogen reserve was found decreased in NQO1-/- mice as compared with wild-type mice. The livers and kidneys from NQO1-/- mice also showed significantly lower levels of pyridine nucleotides but an increase in the reduced/oxidized NAD(P)H:NAD(P) ratio. These results suggested that loss of NQO1 activity alters the intracellular redox status by increasing the concentration of NAD(P)H. This leads to a reduction in pyridine nucleotide synthesis and reduced glucose and fatty acid metabolism. The alterations in metabolism due to redox changes result in a significant reduction in the amount of abdominal adipose tissue.

Human NAD(P)H:quinone oxidoreductase (NQO1) gene structure and induction by dioxin

The human NAD(P)H:quinone oxidoreductase (NQO1) gene, 1850 base pairs (bp) of the 5' flanking region, and 67 bp of the 3' flanking region have been sequenced. The human NQO1 gene is approximately 20 kb in length and has six exons interrupted by five introns. The start site of transcription was determined by primer extension analysis. The first exon is 118 bp in length and codes for two amino acids including the initiating methionine and one G for the first codon of the second exon. The sixth exon is the largest among the exons and is 1833 bp in length. The sequence analysis of the sixth exon revealed the presence of four potential polyadenylation signal sequences (AATAAA) and a single copy of human Alu repetitive sequence. The second intron is the smallest of all the introns (116 bp). Nuclear run-on experiments performed using nuclei isolated from 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) treated and untreated human hepatoblastoma (Hep-G2) cells demonstrated that TCDD treatment increases the rate of transcription of endogenous NQO1 gene by 3-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Nrf2 and c-Jun regulation of antioxidant response element (ARE)-mediated expression and induction of gamma-glutamylcysteine synthetase heavy subunit gene

gamma-Glutamylcysteine synthetase (gamma-GCS) is a rate-limiting enzyme in the de novo synthesis of glutathione, a known scavenger of electrophiles and reactive oxygen species (ROS). The gamma-GCS gene is expressed ubiquitously and induced coordinately with NAD(P)H:quinone oxidoreductase(1) (NQO1) and glutathione S-transferase Ya (GST Ya) in response to xenobiotics and antioxidants. The antioxidant response element (ARE) is required for expression and induction of these genes. In the current report, we demonstrated that ARE-mediated gamma-GCS gene expression and induction is regulated by similar Nrf and Jun factors as reported earlier for the NQO1 and GST Ya genes. The gamma-GCS gene ARE competed with the binding of nuclear proteins (Nrf + Jun) to the NQO1 gene ARE (hARE). In addition, the overexpression of Nrf2 and Nrf1 with c-Jun significantly up-regulated gamma-GCS ARE-mediated basal expression and beta-naphthoflavone induction of the chloramphenicol acetyltransferase gene in transfected HepG2 cells. Interestingly, Nrf2 + c-Jun was more effective than Nrf1 + c-Jun in the regulation of ARE-mediated gamma-GCS gene expression. Further experiments demonstrated that the c-Jun level within the cells is an important determinant of the level of ARE-mediated gamma-GCS gene expression. Therefore, at higher concentrations of c-Jun, gamma-GCS gene expression is repressed, presumably due to generation of a sufficient amount of c-Jun + c-Fos complex that interferes with the binding of Nrf2 + c-Jun complex to the ARE.

NAD(P)H:quinone oxidoreductase1 (DT diaphorase) specifically prevents the formation of benzo[a]pyrene quinone-DNA adducts generated by cytochrome P4501A1 and P450 reductase

Monkey kidney COS1 cells transiently transfected with plasmids pMT2-cytochrome P450 1A1 (CYP1A1), pMT2-cytochrome P450 reductase (P450 reductase), and pMT2-NAD(P)H:quinone oxidoreductase1 (NQO1 or DT diaphorase), individually or in combination, expressed significantly elevated levels of the respective enzyme(s). The transfected cells were homogenized to break cell membranes without affecting the nuclei and incubated with benzo[a]pyrene (BP) to determine the role of cDNA-encoded enzymes in metabolic activation and/or detoxification of BP. These studies were performed by measuring the capacity of the transfected cells to form DNA adducts as determined by 32P postlabeling and protein adduct detection. Cotransfection of the COS1 cells with cDNAs encoding CYP1A1 and P450 reductase resulted in eight distinct BP-DNA adducts. Inclusion of cDNA encoding NQO1 along with CYP1A1 and P450 reductase in transfection reduced the number of DNA adducts to six. The two lost DNA adducts were specifically eliminated due to the presence of cDNA-derived NQO1 activity. Subsequent experiments with BP-1,6-quinone, BP-3,6-quinone, and BP-6,12-quinone identified these two adducts as those of BP quinones. In an in vitro system, BP-3,6-quinone produced two adducts with deoxyguanosine (dG) but not with dA, dC, and dT. Furthermore, the positions of BP-3,6-quinone-dG adducts on TLC plate correspond to those that are prevented by cDNA-derived NQO1, thus identifying these adducts as BP quinones of dG. In addition, NQO1 reduced the amount of protein-BP adducts generated by CYP1A1 and P450 reductase into transfected COS1 cells. These results show that semiquinones can directly bind to DNA and demonstrate that NQO1 activity can specifically reduce the binding of quinone metabolites of BP generated by CYP1A1 and P450 reductase to DNA and protein.

High levels of expression of the NAD(P)H:quinone oxidoreductase (NQO1) gene in tumor cells compared to normal cells of the same origin

NAD(P)H:quinone oxidoreductase (NQO1) is a flavoprotein which catalyzes the two-electron reduction of quinones and azo-dyes and thus prevents the formation of free radicals and toxic oxygen metabolites that may be generated by the one-electron reductions catalyzed by cytochrome P450 reductase. Analysis of RNA indicated 20- to 50-fold higher levels of NQO1 gene expression in the liver tumors and in the tissue surrounding the tumors of patients with hepatocarcinoma than in normal individuals. An approximately 50-fold higher level of NQO1 mRNA was also observed in human hepatoblastoma (Hep-G2) cells than in normal liver. By deletion mutagenesis in the human NQO1 gene promoter and subsequent transfection into hepatic and nonhepatic cell lines, a 1.42 kb DNA segment has been identified to contain cis-acting elements responsible for high levels of expression of the NQO1 gene in tumor cells.

Antioxidant regulation of genes encoding enzymes that detoxify xenobiotics and carcinogens

Antioxidants are substances that delay or prevent the oxidation of cellular oxidizable substrates. The various antioxidants exert their effect by scavenging superoxide or by activating a battery of detoxifying/defensive proteins. In this chapter, we have focused on the mechanisms by which antioxidants induce gene expression. Many xenobiotics (e.g., beta-naphthoflavone) activate genes similar to those activated by antioxidants. The promoters of these genes contain a common cis-element, termed the antioxidant response element (ARE), which contains two TRE (TPA response element) or TRE-like elements followed by GC box. Mutational studies have identified GTGAC***GC as the core of the ARE sequence. Many transcription factors, including Nrf, Jun, Fos, Fra, Maf, YABP, ARE-BP1, Ah (aromatic hydrocarbon) receptor, and estrogen receptor bind to the ARE from the various genes. Among these factors, Nrf-Jun heterodimers positively regulate ARE-mediated expression and induction of genes in response to antioxidants and xenobiotics. This Nrf-Jun heterodimerization and binding to the ARE requires unknown cytosolic factors. The mechanism of signal transduction from antioxidants and xenobiotics includes several steps: (1) Antioxidants and xenobiotics undergo metabolism to generate superoxide and related reactive species, leading to the generation of a signal to activate expression of detoxifying/defensive genes. (2) The generation of superoxide and related reactive species is followed by activation of yet to be identified cytosolic factors by unknown mechanism(s). (3). Activated cytosolic factors catalyze modification of Nrf and/or Jun proteins, which bind to the ARE in promoters of the various detoxifying/defensive genes. (4) The transcription of genes encoding detoxifying/defensive proteins is increased. The unknown cytosolic factors are significant molecules because they represent the oxidative sensors within the cells. Identification of the cytosolic factors will be of considerable importance in the field of antioxidants and gene regulation research. Future studies will also be required to completely understand the molecular mechanism of signal transduction from antioxidants and xenobiotics to Nrf-Jun. In addition to the Nrf-Jun pathway, mammalian cells also contain other pathways that activate gene expression in response to oxidative stress. These include NF-KB-, HIF-1-, Mac-1-, and SRF-mediated pathways. It is expected that collectively these pathways increase transcription of more than four dozen genes to protect cells against oxidative stress.

miRNA-transcription factor interactions: a combinatorial regulation of gene expression

Developmental processes require a precise spatio-temporal regulation of gene expression wherein a diverse set of transcription factors control the signalling pathways. MicroRNAs (miRNAs), a class of small non-coding RNA molecules have recently drawn attention for their prominent role in development and disease. These tiny sequences are essential for regulation of processes, including cell signalling, cell development, cell death, cell proliferation, patterning and differentiation. The consequence of gene regulation by miRNAs is similar to that by transcription factors (TFs). A regulatory cascade essential for appropriate execution of several biological events is triggered through a combinatorial action of miRNAs and TFs. These two important regulators share similar regulatory logics and bring about a cooperative action in the gene regulatory network, dependent on the binding sites present on the target gene. The review addresses the biogenesis and nomenclature of miRNAs, outlines the mechanism of action and regulation of their expression, and focuses on the combinatorial action of miRNAs and TFs for the expression of genes in various regulatory cascades.

Catalytic properties of NAD(P)H:quinone oxidoreductase-2 (NQO2), a dihydronicotinamide riboside dependent oxidoreductase

Human NAD(P)H:quinone acceptor oxidoreductase-2 (NQO2) has been prepared using an Escherichia coli expression method. NQO2 is thought to be an isoform of DT-diaphorase (EC 1.6.99.2) [also referred to as NAD(P)H:quinone acceptor oxidoreductase] because there is a 49% identity between their amino acid sequences. The present investigation has revealed that like DT-diaphorase, NQO2 is a dimer enzyme with one FAD prosthetic group per subunit. Interestingly, NQO2 uses dihydronicotinamide riboside (NRH) rather than NAD(P)H as an electron donor. It catalyzes a two-electron reduction of quinones and oxidation-reduction dyes. One-electron acceptors, such as potassium ferricyanide, cannot be reduced by NQO2. This enzyme also catalyzes a four-electron reduction, using methyl red as the electron acceptor. The NRH-methyl red reductase activity of NQO2 is 11 times the NADH-methyl red reductase activity of DT-diaphorase. In addition, through a four-electron reduction reaction, NQO2 can catalyze nitroreduction of cytotoxic compound CB 1954 [5-(aziridin-1-yl)-2,4-dinitrobenzamide]. NQO2 is 3000 times more effective than DT-diaphorase in the reduction of CB 1954. Therefore, NQO2 is a NRH-dependent oxidoreductase which catalyzes two- and four-electron reduction reactions. NQO2 is resistant to typical inhibitors of DT-diaphorase, such as dicumarol, Cibacron blue, and phenindone. Flavones are inhibitors of NQO2. However, structural requirements of flavones for the inhibition of NQO2 are different from those for DT-diaphorase. The most potent flavone inhibitor tested so far is quercetin (3,5,7,3',4'-. 6pentahydroxyflavone). It has been found that quercetin is a competitive inhibitor with respect to NRH (Ki = 21 nM). NQO2 is 43 amino acids shorter than DT-diaphorase, and it has been suggested that the carboxyl terminus of DT-diaphorase plays a role in substrate binding (S. Chen et al., Protein Sci. 3, 51-57, 1994). In order to understand better the basis of catalytic differences between NQO2 and DT-diaphorase, a human NQO2 with 43 amino acids from the carboxyl terminus of human DT-diaphorase (i.e., hNQO2-hDT43) has been prepared. hNQO2-hDT43 still uses NRH as an electron donor. In addition, the chimeric enzyme is inhibited by quercetin but not dicumarol. These results suggest that additional region(s) in these enzymes is involved in differentiating NRH from NAD(P)H.

Human CYP1A2: sequence, gene structure, comparison with the mouse and rat orthologous gene, and differences in liver 1A2 mRNA expression

We have sequenced the human CYP1A2 (cytochrome P(3)450) gene, 1,906 basepairs (bp) of the 5' flanking region, and 113 bp of the 3' flanking region. The gene spans almost 7.8 kilobases, comprising seven exons and six introns. The transcriptional start site was determined by both primer extension and S1 mapping. Including the first noncoding exon of 55 bp, the entire mRNA is 3,121 bp in length, and the open reading frame, starting with nucleotide 10 of exon 2, encodes 515 amino acids (mol wt = 58,294). Between the human CYP1A2 and CYP1A1 (cytochrome P(1)450) genes, exons 2, 4, 6, and especially 5 are strikingly conserved in both nucleotide similarity and total number of bases. Alignment of the upstream sequences and exon 1 of human CYP1A2 with that of mouse or rat CYP1A2 revealed two possibly significant regions of similarity: 1) 68% in the approximately 150 bases immediately 5' from the mRNA cap site and 2) 80% identify between the human -841 to -758 segment and the mouse -1,529 to -1,439 segment. The canonical 5-bp box (CACGC), found upstream of all mammalian CYP1A1 genes to date and believed to interact with the inducer.aromatic hydrocarbon receptor complex, was not found on either strand in the 1,906 bp of the 5' flanking region of human CYP1A2. In contrast, alignment of the upstream sequences, exon 1, and intron 1 of human CYP1A1 with that of mouse or rat CYP1A1 revealed large, highly conserved regions. Conserved regions were found in intron 1 of the human, mouse, and rat CYP1A2 gene. These data suggest that the regulatory elements controlling the CYP1A2 gene might differ in location from those controlling the CYP1A1 gene. Among 12 human liver samples, striking differences (greater than 15-fold) in the 3.3-kilobase 1A2 mRNA levels were seen. This result may reflect significant genetic differences in constitutive and/or inducible CYP1A2 gene expression that could play an important role in individual risk of environmental toxicity or cancer.

ARE- and TRE-mediated regulation of gene expression. Response to xenobiotics and antioxidants

Antioxidant response elements (AREs) containing 12-O-tetradecanoylphorbol-13-acetate response element (TRE) (perfect AP1) and TRE-like (imperfect AP1) elements mediate high basal transcription of the NAD(P)H:quinone oxidoreductase1 (NQO1) and glutathione S-transferase Ya genes in tumor cells and its induction in response to xenobiotics and antioxidants. Mutations in the human NQO1 gene ARE (hARE) revealed the requirement for two TRE or TRE-like elements arranged in inverse orientation at the interval of three base pairs and a GC box for optimal expression and beta-naphthoflavone induction of the NQO1 gene. A single TRE element from the human collagenase gene failed to respond to beta-naphthoflavone. These results demonstrate that ARE (2 x TRE or TRE-like elements)-containing detoxifying enzyme genes and not genes that contain 1 x TRE are responsive to xenobiotics and antioxidants. Bandshift assays showed shifting of a complex of more or less similar mobility with hARE and TRE that could be competed by each other. Mutations in the 3'-TRE of the NQO1 gene hARE eliminated binding of nuclear proteins to the hARE and resulted in the loss of basal and induced expression, indicating that 3'-TRE is the most important element within the hARE. 5'-TRE-like element within the NQO1 gene hARE is required for xenobiotic response but may not bind to the nuclear proteins by itself. The GC box located immediately following the 3'-TRE is required for optimal expression and induction of the NQO1 gene. The comparison of AREs from several different genes indicated the requirement for specific arrangement and spacing of two TRE and TRE-like elements within the AREs.

Nucleotide and deduced amino acid sequence of a human cDNA (NQO2) corresponding to a second member of the NAD(P)H:quinone oxidoreductase gene family. Extensive polymorphism at the NQO2 gene locus on chromosome 6

NAD(P)H:quinone oxidoreductases (NQOs) are flavoproteins that catalyze the oxidation of NADH or NADPH by various quinones and oxidation-reduction dyes. We have previously described a complementary DNA that encodes a dioxin-inducible cytosolic form of human NAD(P)H:quinone oxidoreductase (NQO1). In the present report we describe the nucleotide sequence and deduced amino acid sequence for a cDNA clone that is likely to encode a second form of NAD(P)H:quinone oxidoreductase (NQO2) which was isolated by screening a human liver cDNA library by hybridization with a NQO1 cDNA probe. The NQO2 cDNA is 976 nucleotides long and encodes a protein of 231 amino acids (Mr = 25,956). The human NQO2 cDNA and protein are 54% and 49% similar to human liver cytosolic NQO1 cDNA and protein, respectively. COS1 cells transfected with NQO2 cDNA showed a 5-7-fold increase in NAD(P)H:quinone oxidoreductase activity as compared to nontransfected cells when either 2,6-dichlorophenolindophenol or menadione was used as substrate. Western blot analysis of the expressed NQO1 and NQO2 cDNA proteins showed cross-reactivity with rat NQO1 antiserum, indicating that NQO1 and NQO2 proteins are immunologically related. Northern blot analysis shows the presence of one NQO2 mRNA of 1.2 kb in control and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) treated human hepatoblastoma Hep-G2 cells and that TCDD treatment does not lead to enhanced levels of NQO2 mRNA as it does for NQO1 mRNA. Southern blot analysis of human genomic DNA suggests the presence of a single gene approximately 14-17 kb in length. The NQO2 gene locus is highly polymorphic as indicated by several restriction fragment length polymorphisms detected with five different restriction enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

NAD(P)H:quinone oxidoreductase 1 deficiency and increased susceptibility to 7,12-dimethylbenz[a]-anthracene-induced carcinogenesis in mouse skin

BACKGROUND

The phase II enzyme NAD(P)H :quinone oxidoreductase 1 (NQO1) catalyzes quinone detoxification, protecting cells from redox cycling, oxidative stress, mutagenicity, and cytotoxicity induced by quinones and its precursors. We have used NQO1(-/-) C57BL/6 mice to show that NQO1 protects them from skin cancer induced by the polycyclic aromatic hydrocarbon benzo[a]pyrene. Herein, we used NQO1(-/-) mice to investigate whether NQO1 also protects them against 7,12-dimethylbenz[a]anthracene (DMBA), where methyl substituents diminish primary quinone formation.

METHODS

Dorsal skin of NQO1(-/-) or wild-type C57BL/6 mice was shaved. When tested as a complete carcinogen, DMBA (500 or 750 microg in 100 microL of acetone) alone was applied to the shaved area. When tested as a tumor initiator, DMBA (200 or 400 nmol in 100 microL of acetone) was applied to the shaved area; 1 week later, twice-weekly applications of phorbol 12-myristate 13-acetate (PMA)-10 microg dissolved in 200 microL of acetone-to the same area began and were continued for 20 weeks. Tumor development was monitored in all mice (12-15 per group). All statistical tests were two-sided.

RESULTS

When DMBA (750 microg) was tested as a complete carcinogen, about 50% of the DMBA-treated NQO1(-/-) mice but no DMBA-treated wild-type mouse developed skin tumors. When DMBA (both concentrations) was used as a tumor initiator, NQO1(-/-) mice developed larger tumors at a greater frequency than their wild-type littermates. Twenty-three weeks after the first PMA treatment in the tumor initiator test, all 30 NQO1(-/-) mice given 400 nmol of DMBA had developed skin tumors, compared with 33% (10 of 30) of treated wild-type mice (P<.001).

CONCLUSIONS

NQO1(-/-) mice are more susceptible to DMBA-induced skin cancer than are their wild-type littermates, suggesting that NQO1 may protect cells from DMBA carcinogenesis.

SHV-7, a novel cefotaxime-hydrolyzing beta-lactamase, identified in Escherichia coli isolates from hospitalized nursing home patients

Four ceftazidime-resistant Escherichia coli strains were isolated from elderly nursing home patients in a New York hospital during 1993. Strains MCQ-2, MCQ-3, and MCQ-4 were determined to be identical by pulsed-field gel electrophoresis and plasmid profiles, whereas strain MCQ-1 was unique. Strain MCQ-1 was determined to produce a TEM-10 beta-lactamase. Strains MCQ-2, MCQ-3, and MCQ-4 were also noted to be resistant to cefotaxime. These three strains produced two beta-lactamases with pIs of 5.4 (TEM-1) and 7.6. beta-Lactamase assays revealed that the pI 7.6 enzyme hydrolyzed cefotaxime faster (at a relative hydrolysis rate of 30% compared with that of benzylpenicillin) than either ceftazidime or aztreonam (relative hydrolysis rates of 13 and 3.3%, respectively). Nucleotide sequencing of the gene encoding the pI 7.6 beta-lactamase from strain MCQ-3 revealed a blaSHV-type gene differing from the gene encoding SHV-1 at four nucleotides which resulted in amino acid substitutions: phenylalanine for isoleucine at position 8, serine for arginine at position 43, serine for glycine at position 238, and lysine for glutamate at position 240. This novel SHV-type extended-spectrum beta-lactamase is designated SHV-7.

Human P1-450 gene sequence and correlation of mRNA with genetic differences in benzo[a]pyrene metabolism

The human P1-450 gene (6,311 base pairs), as well as the 5' (1,604 bases) and 3' (113 bases) flanking regions, have been completely sequenced. Four highly homologous boxes (61, 82, 56 and 97 base pairs) between the human and mouse P1-450 genes are found in the "TATA" box promoter region, -226, -338, and -450 upstream from the cap site, respectively. Nine genomic-DNA samples were digested with each of 23 restriction endonucleases and probed with human P1-450 cDNA fragments; restriction fragment length polymorphisms are detected, although it remains to be seen whether such a recombinant DNA test will be useful in determining individuals at increased risk for cigarette smoking-induced cancer and toxicity. We show in this report, however, that human inducible P1-450 mRNA concentrations are very highly correlated (r = 0.98; N = 6) with genetic differences in benzo[a]pyrene metabolism in mitogen-activated lymphocyte cultures.

Adherence to tuberculosis treatment: lessons from the urban setting of Delhi, India

The Revised National Tuberculosis Control Programme (RNTCP), which incorporated the WHO DOTS strategy was introduced in India in the mid-1990s. An operational research project was conducted between 1996 and 1998 to assess the needs and perspectives of patients and providers in two chest clinics in Delhi, Moti Nagar and Nehru Nagar, during the introduction of the new strategy. This paper reports on the findings of the project, concentrating on information collected from 40 in-depth interviews with patient defaulters and from non-participant observations in clinics and directly observed treatment centres. In Moti Nagar chest clinic, 117 of 1786 (6.5%) patients and 195 of 1890 (10%) patients in Nehru Nagar left care before their treatment was complete. It was argued that the reasons for default stem from a poor correlation between patient and programme needs and priorities, and from particular characteristics of the disease and its treatment. Patient needs that were not met by the health system included convenient clinic timings, arrangements for the provision for treatment in the event of a family emergency and provision for complicated cases like alcoholics. The problems facing the provider were poor interpersonal communication with the health staff, lack of attention and support at the clinic, difficulty for patients to re-enter the system if they missed treatment and, in certain areas, long distances to the clinic. Problems related to diseases were inability of the staff to deal with drug side-effects, and patients' conception of equating well-being with cure. Simple, practical measures could improve the provision of tuberculosis (TB) treatment: more flexible hours, allowances for poor patients to reach the clinics and training health care staff for respectful communication and monitoring drug side-effects. The findings indicate a need to rethink the label of 'defaulter' often given to the patients. The important areas for future operational research is also highlighted.