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D W Nebert

Publications and source records attributed to D W Nebert.

At least 91 records · Page 5Linked to original sources
PubMed1994

Possible role of cytochromes P450 in lupus erythematosus and related disorders.

Cytochromes P450 comprise a superfamily of enzymes pivotal in the metabolism of innumerable substrates of both endogenous and exogenous origin. The total number of distinct P450 genes, each encoding a different enzyme in humans, is estimated to be at least 60 and possibly several hundred. The cytochrome P450 (CYP) superfamily nomenclature system is based on divergent evolution of the genes. Most of the enzymes within gene families CYP1, CYP2, CYP3 and CYP4 appear to have evolved as the body's primary defense against the onslaught of chemicals confronted on a daily basis. Whereas P450 enzymes more than 3.5 billion years ago were undoubtedly designed as necessary components of signal transduction pathways, in the past billion years most P450 enzymes have become generally responsible for the detoxification of numerous foreign chemicals. During such oxidative metabolism, it has become increasingly apparent that these enzymes are also capable of functioning in an ambivalent manner, generating toxic intermediates. More than a dozen human P450 polymorphisms have been characterized. Genetic variability in P450 expression is therefore likely to have significant bearing on individual susceptibility to chemical toxicity. In this review, genetic differences in human P450 expression are outlined, and their possible relationship to autoimmune disease is examined. In addition, the speculative role of P450 polymorphisms in several 'lupus-like' disorders is discussed.

Autoimmune Diseases↗
PubMed1994

1462V mutation in the human CYP1A1 gene: lack of correlation with either the Msp I 1.9 kb (M2) allele or CYP1A1 inducibility in a three-generation family of east Mediterranean descent.

A 15-member three-generation family of Eastern Mediterranean descent was previously studied, and an association between CYP1A1 (cytochrome P1450, benzo[a]pyrene hydroxylase) inducibility and a CYP1A1 3'-polymorphism (the Msp I 1.9 kb allele) was reported (Petersen et al., Am J Hum Genet 1991:48, 720-725). Here we have re-examined the original DNA (and in some cases, newly prepared DNA from freshly drawn blood) from these same individuals, in order to assess the association between CYP1A1 inducibility and both the CYP1A1 gene Msp I RFLP polymorphism and the CYP1A1 gene A-->G polymorphism at codon 462. This latter nucleotide change results in an altered amino acid (462Ile-->Val), which is purported to increase CYP1A1 enzyme activity and mutagenicity towards benzo[a]pyrene about two-fold among Japanese. Among the 15 members of this three-generation family examined, no absolute correlation was observed between the 1462V genotype and either the Msp I 1.9 kb allele or the CYP1A1 inducibility phenotype. We also found no absolute correlation between the Msp I 1.9 kb allele and the CYP1A1 inducibility phenotype.

Alleles↗
PubMed1994

Mouse dioxin-inducible NAD(P)H: menadione oxidoreductase: NMO1 cDNA sequence and genetic differences in mRNA levels.

We have cloned and sequenced the mouse NMO1 cDNA, which encodes the NAD(P)H:menadione oxidoreductase [also called NAD(P)H:(quinone acceptor) oxidoreductase; quinone reductase; azo dye reductase; DT diaphorase; EC 1.6.99.2]. The cDNA is 1528 bp in length excluding the poly(A+) tail, and has 5' and 3' nontranslated regions of 108 bp and 595 bp, respectively. The deduced protein contains 274 amino acids, including the first methionine (M(r) = 30,959). The mouse NMO1 protein is: 94% similar to the rat NMO1 and 86.5% to the human NMO1 proteins; 49.3% identical to the human NQO2 protein; and < 20% similar to several dozen other proteins in the quinone oxidoreductase superfamily. Southern hybridization analysis of mouse DNA reveals that the Nmo1 gene is likely to span less than a total of 20 kb. The Nmo1 gene is highly inducible by 2,3,7,8,-tetrachlorodibenzo-p-dioxin (dioxin; TCDD) in mouse liver and mouse cell cultures. TCDD inducibility of NMO1 is detectable at 12 and 18 days of gestation, but markedly elevated at 1-3 weeks post partum as compared with the 6- and 12-week-old mouse. NMO1 mRNA levels are strikingly elevated in the untreated mouse hepatoma Hepa-1c1c7 mutant line c37 lacking CYP1A1 (aryl hydrocarbon hydroxylase) activity, and in the untreated 14CoS/14CoS mouse cell line having an 'oxidative stress response' caused by homozygous deletion of about 3800 kb on chromosome 7. Previous work and the data in this report show that the murine Nmo1 gene is regulated by three distinct mechanisms: CYP1A1 metabolism-dependent repression, Ah receptor-mediated induction by TCDD, and activation by the chromosome 7-mediated oxidative stress response.

3T3 Cells↗
PubMed1993

Role of the Ah receptor and the dioxin-inducible [Ah] gene battery in toxicity, cancer, and signal transduction.

1. On the basis of our current knowledge about the evolution of drug-metabolizing enzymes, it appears to be extremely likely that these enzymes play a critical role in maintaining steady-state levels of the ligands involved in ligand-modulated transcription of genes effecting growth, differentiation, homeostasis, and neuroendocrine functions. 2. The original observations about genetic differences in CYP1A1 (cytochrome P1-450) induction by TCDD or benzo[a]pyrene in the mouse have led to an appreciation for a similar polymorphism in the human and the recent cloning of the murine Ah receptor (Ahr) and human Ah receptor nuclear translocator (ARNT) genes. It is most likely that the correlation between genetic differences in human or murine CYP1A1 inducibility by polycyclic hydrocarbons or TCDD and increased risk of cancer will be explained by differences in the AHR gene, leading to enhanced tumor promotion (rather than in the CYP1A1 structural gene). Perhaps the same will be found for birth defects, immunotoxicity, and other forms of toxic damage caused by these environmental chemicals. 3. In a manner similar to that of the phorbol ester tumor promoter, TCDD induces intracellular Ca2+ changes, accumulation of FOS and JUN mRNAs, and large increases in AP-1 transcription factor activity. Interestingly, these early effects of TCDD, and also of benzo[a]pyrene, appear not to require the Ah receptor. 4. Many genes are induced by TCDD, and many others are induced by electrophilic metabolites such as quinones and H2O2; using several mouse experimental systems, we have defined a subset of six of these genes as constituting the [Ah] battery by the sole criterion that a functional CYP1A1 or CYP1A2 enzyme is able to repress the expression of genes that are members of this gene battery.

Animals↗
PubMed1993

Menadione toxicity in two mouse liver established cell lines having striking genetic differences in quinone reductase activity and glutathione concentrations.

Established cell lines derived from newborn livers of c14CoS/c14CoS and cch/cch mice were examined for differences in menadione toxicity. The 14CoS/14CoS cells exhibit 10-fold higher NAD(P)H:menadione oxidoreductase (NMO1) activity and 3-fold greater concentrations of reduced glutathione (GSH) than the ch/ch cells. In 14CoS/14CoS cells there are also 50% to 3-fold increases in glutathione transferase (GSTA1), UDP glucuronosyltransferase, and the copper, zinc-dependent superoxide dismutase activities. Catalase activity, on the other hand, is six times lower in the 14CoS/14CoS than the ch/ch line. The 14CoS/14CoS cells are two to four times more resistant to menadione killing than ch/ch cells. At concentrations of dicumarol that completely block NMO1 and GSTA1 activities, the 14CoS/14CoS cells show more than twice as much resistance to menadione toxicity than the ch/ch cells. Although superoxide formation is three times higher in untreated 14CoS/14CoS than ch/ch cells, menadione-induced superoxide formation is greater in the dying ch/ch than in the 14CoS/14CoS cells. Cellular resistance to menadione toxicity is correlated with intracellular GSH levels, rather than with the percentage of oxidized glutathione; cytotoxicity is not observed as long as GSH concentrations are sufficiently high (about 5-8 nmol/mg protein). For menadione, the results are consistent with a dominant role of GSH depletion in mediating toxicity and support a protective role for NMO1 activity. This report demonstrates the usefulness of these cell lines as a model system to study mechanisms of oxidative chemically induced toxicity, as well as to understand how intracellular levels of GSH are regulated.

Animals↗
PubMed1993

Localization of the murine Hmg1 gene, encoding an HMG-box protein, to mouse chromosome 2.

In conclusion, using concatenated AhRE sequences and the recognition site probe methodology, we have cloned the murine Hmg1 cDNA and determined an additional 141 bp of 5' noncoding sequence (GenBank Accession No. S50213; entry name MUSHMG1A). The gene product represents an HMG-box transcription factor that recognizes DNA shape- and sequence-specific elements; this is perhaps the reason that this cDNA was isolated with concatomeric oligonucleotides. We have mapped the Hmg1 gene to mouse Chr 2, between regions homologous with human Chr 2q and 11p11-q12.

Animals↗
PubMed1993

Evolutionary pharmacogenetics of CYP2D6 in Ngawbe Guaymi of Panama: allele-specific PCR detection of the CYP2D6B allele and RFLP analysis.

Gene cluster CYP2D controls the biosynthesis of enzyme CYP2D6, which is responsible for the polymorphic oxidation of sparteine, debrisoquine and related drugs. This cluster consists of the functional gene D6 and of two pseudogenes, D7 and D8. RFLP Bam HI analysis of CYP2D in 37 unrelated and eight related Ngawbe Guaymi Amerindians of Panama showed a polymorphism characterized by the presence of two alleles: 4.7 + 7.9 and 2.3 + 6.0 (frequencies: 0.63 and 0.37, respectively, n = 35 unrelated subjects). The possible genotypes for these alleles follow the Hardy-Weinberg distribution (chi 2 = 1.76; 0.10 < p < 0.25). All PMs of sparteine or debrisoquine (n = 7) were homozygotes for the second allele, but not all homozygotes (n = 10) were PMs, so there was not an exclusive association between the Bam HI genotype and the observed phenotype. A similar analysis with the endonuclease Xba I proved to be non-informative in relation to phenotype, since all subjects (n = 40) showed only the 29 kb allele. Allele-specific PCR studies of selected subjects indicated the existence of the CYP2D6B allele (freq = 0.17; C.I.95% = 0.085, 0.29; n = 30 unrelated subjects), in addition to the wild-type. The mutant CYP2D6B allele was responsible for the enzyme deficiency present in PMs. Its presence in Amerindians suggests that this allele has a far more ancient evolutionary history than previously thought. The over-all RFLP and PCR analyses point to a diminished genetic diversity for the Ngawbe subjects, consistent with their demographic history and population genetics.

Alleles↗
PubMed1993

Mouse dioxin-inducible cytosolic aldehyde dehydrogenase-3: AHD4 cDNA sequence, genetic mapping, and differences in mRNA levels.

We have cloned and sequenced the murine AHD4 cDNA encoding the 'Class 3' cytosolic aldehyde dehydrogenase (ALDH-3c). The cDNA is 1722 bp in length, excluding the poly(A+) tail, and has 5' and 3' nontranslated regions of 174 bp and 186 bp, respectively. AHD4 encodes a protein of 453 amino acids, including the first methionine (M(r) = 50,466). The murine AHD4 protein is 91% and 80% similar to the rat and human ALDH3c proteins, respectively, 64% identical to the rat microsomal ALDH3 protein, and < 28% similar to ALDH 'Class 1' and 'Class 2' proteins. Surprisingly, in contrast to the rat gene that is expressed in both cell cultures and the intact liver, the murine Ahd-4 gene is inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) or benzo[a]pyrene in cell cultures but not in liver of the intact adult or newborn mouse. Southern hybridization analysis of mouse DNA probed with the full-length cDNA reveals that the Ahd-4 gene is likely to span less than a total of 15 kb, and was mapped to chromosome (Chr) 11 between the Mgat-1 and Shbg loci by analysis of two multilocus crosses. AHD4 mRNA levels are strikingly elevated in the untreated mouse hepatoma Hepa-1c1c7 mutant line c37 lacking CYP1A1 (aryl hydrocarbon hydroxylase) activity and in the untreated 14CoS/14CoS mouse cell line having a homozygous deletion of about 1.2 cM on Chr 7. Our data suggest that the Ahd-4 gene in murine cell cultures is regulated by three distinct mechanisms: Ah receptor-mediated induction by TCDD or benzo[a]pyrene, CYP1A1 metabolism-dependent repression, and Chr 7-mediated putative derepression.

Aldehyde Dehydrogenase↗
PubMed1993

Ten nucleotide differences, five of which cause amino acid changes, are associated with the Ah receptor locus polymorphism of C57BL/6 and DBA/2 mice.

We have analysed by heteroduplex formation (HF), single stranded conformational polymorphism (SSCP), denaturing gradient gel electrophoresis (DGGE), and nucleotide sequencing the cDNAs of the Ahrb-1 and Ahrd allelic forms of the aromatic hydrocarbon receptor (AhR) present in inbred strains of mice. The Ahrb-1 allele, found in the C57BL and C57BR strains, encodes a 95 kDa receptor with an affinity for ligand 15-20 times higher than the affinity of the 104 kDa receptor encoded by the Ahrd allele, found in the DBA/2 strain. Five overlapping fragments of the AhR coding sequence were obtained from liver RNA by reverse transcriptase synthesis of a cDNA first strand, followed by polymerase chain reaction amplification of these cDNA sequences (RT-PCR). Analysis by HF and SSCP revealed the presence of sequence differences in three of the five fragments. When the complete nucleotide sequence of the coding regions was determined by PCR sequencing, we found a total of ten nucleotide differences between the two alleles, nine of which localized to the three fragments where differences were detected by HF and SSCP. Five of the differences are silent. Of the other five, one changes the opal termination codon in Ahrb-1 to the codon for Arg in Ahrd, extending translation of the mRNA by 43 amino acids and accounting for the larger size of the AhR peptide in DBA/2 mice. One of the four remaining differences causes the replacement of a leucine residue in Ahrb-1 by a proline residue in Ahrd, and breaks a potential alpha-helix near the AhR Q-rich region; it is likely that structural changes associated with this amino acid change are responsible for the differences in agonist affinity observed between the Ah receptors of these two strains of mice.

Amino Acid Sequence↗
PubMed1992

Negative regulation of the murine cytosolic aldehyde dehydrogenase-3 (Aldh-3c) gene by functional CYP1A1 and CYP1A2 proteins.

We have examined enzyme activities and mRNA levels corresponding to aldehyde dehydrogenase-3 genes encoding cytosolic (ALDH3c) and microsomal (ALDH3m) forms. In contrast to negligible activities in the intact mouse liver, both ALDH3c and ALDH3m enzyme activities are inducible by benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mouse hepatoma Hepa-1c1c7 cell cultures. Constitutive mRNA levels of ALDH3c are virtually absent, whereas those of ALDH3m are substantial; using Hepa-1 mutant lines, we show that both ALDH3c and ALDH3m are TCDD-inducible by an Ah receptor-dependent mechanism. Basal mRNA levels of ALDH3c, but not those of ALDH3m, are strikingly elevated in untreated mutant cells lacking a functional CYP1A1 enzyme; low ALDH3c basal mRNA levels can be restored by introduction of a functional murine CYP1A1 or human CYP1A2 enzyme into these mutant cells. These data suggest that the TCDD induction process is distinct from the CYP1A1/CYP1A2 metabolism-dependent repression of constitutive gene expression; we suggest that this latter property classifies the Aldh-3c gene, but not the Aldh-3m gene, as a member of the murine [Ah] battery.

Aldehyde Dehydrogenase↗
PubMed1992

"Oxidative stress" response in liver of an untreated newborn mouse having a 1.2-centimorgan deletion on chromosome 7.

The c14CoS/c14CoS mouse has a homozygous deletion of about 1.2 cM on chromosome 7 that includes the albino (c) locus. The untreated 14CoS/14CoS newborn has been reported to exhibit a marked transcriptional activation of the hepatic NAD(P)H:menadione oxidoreductase (Nmo-1; DT diaphorase; quinone reductase; azo dye reductase) gene, as well as elevated UDP glucuronosyl-transferase (UGT1*06) and glutathione transferase (GT1) activities, when compared with the cch/cch wild-type and the cch/c14CoS heterozygote. We show here that the newborn hepatic activities of seven enzymes that play a role in the oxidative stress response--NMO1, UGT1*06, GT1, copper-zinc superoxide dismutase, glutathione peroxidase, glutathione reductase, and glucose-6-phosphate dehydrogenase--are increased 1.5- to 25-fold in 14CoS/14CoS, as compared with ch/ch and ch/14CoS mice. The activities of four additional enzymes having no known association with the oxidative stress response--benzo[a]pyrene hydroxylase (CYP1A1, cytochrome P(1)450), acetanilide 4-hydroxylase (CYP1A2, cytochrome P(3)450), lactate dehydrogenase (LDH), and NADPH-cytochrome c reductase--are not significantly different among the three genotypes. These data suggest that there exists an "oxidative stress" response in the untreated 14CoS/14CoS newborn. We postulate that a chromosome 7 regulatory gene, which we have named Nmo-1n, might encode a trans-acting negative effector of the Nmo-1 gene, and genes corresponding to the other elevated enzymic activities described above. When both copies of Nmo-1n are deleted, as is the case in 14CoS/14CoS mice, a battery of genes involved in oxidative stress is released from negative control and becomes activated--despite the absence of any apparent oxidative insult by foreign chemicals.

Animals↗
PubMed1992

Transcriptional derepression of the murine Cyp1a-1 gene by mevinolin.

In mouse hepatoma Hepa-1c1c7 cultures, polycyclic aromatic compounds such as benzol[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) activate the Cyp1a-1 (cytochrome P(1)450) and Nmo-1[NAD(P)H:menadione-oxidoreductase] genes, two members of the aromatic hydrocarbon (Ah)-responsive gene battery. Mevinolin is known to inhibit 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase (EC 1.1.1.34), the rate-limiting step in cholesterol biosynthesis. We show here that in the absence of TCDD, mevinolin markedly increases Cyp1a-1 transcription, CYP1A1 mRNA and protein levels and enzyme activity, and NMO1 mRNA concentrations. Addition of mevalonate, the product of HMG-CoA reductase activity, fails to reverse the effects of mevinolin. In fact, when used at high concentrations, mevalonate activates Cyp1a-1 transcription. Mevinolin-induced Cyp1a-1 gene activation: (1) occurs independently of the lipid content of the growth medium, (2) is not suppressed by adding 25-hydroxycholesterol, which blocks MHG-CoA reductase activity, and (3) requires a functional Ah receptor and unimpaired nuclear translocation of the receptor. It is possible that an unknown metabolite (or metabolites) of mevinolin activates Cyp1a-1 expression and that high concentrations of mevalonate act via the same mechanism. Using chimaeric plasmids that contain different lengths of Cyp1a-1 5' flanking regions fused to the bacterial neomycin (neo) gene, we find that the mevinolin effect on Cyp1a-1 induction requires the 5' flanking sequences between -1647 and -824, which are also needed for TCDD induction. Mevinolin, however, is not a ligand for the Ah receptor. Gel mobility shift assays revealed that Cyp1a-1 activation caused by mevinolin does not involve the ligand-dependent formation of a functional Ah receptor-dependent DNA-binding complex, but instead appears to be correlated with release of a putative repressor from its cognate DNA site. Our results suggest that the basel level of Cyp1a-1 transcription is maintained by an unknown negative regulatory factor. We propose that Cyp1a-1 transcriptional activation can result not only from induction by polycyclic aromatic compounds but also from derepression by mevinolin, independent of HMG-CoA reductase inhibition.

Animals↗
PubMed1992

Dioxin induces expression of c-fos and c-jun proto-oncogenes and a large increase in transcription factor AP-1.

Among environmental pollutants, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) is one of the most potent tumor promoters and teratogens known. The molecular mechanisms responsible for the biological activity of TCDD, however, remain largely unknown. In this report, we show that the first observable effects of TCDD in cultured murine hepatoma cells are a rapid, transient increase in Ca2+ influx and a minor but significant elevation of activated, membrane-bound protein kinase C. These changes are then followed by induction of the immediate early proto-oncogenes c-fos, jun-B, c-jun, and jun-D, and by large increases in AP-1 transcription factor activity. Induction of these changes by TCDD is delayed compared with that by phorbol esters, although the magnitude of the effects caused by both treatments is similar, and both induction processes can be blocked by staurosporine, a protein kinase C inhibitor. In cultured cells, proto-oncogene induction by TCDD appears to be independent of the presence of a functional aryl hydrocarbon (Ah) receptor or nuclear translocation protein. These results reveal early events that may lead to the elucidation of the molecular basis of TCDD-induced tumor promotion.

Alkaloids↗
PubMed1992

Dioxin-dependent activation of murine Cyp1a-1 gene transcription requires protein kinase C-dependent phosphorylation.

Transcriptional activation of the murine Cyp1a-1 (cytochrome P(1)450) gene by inducers such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (dioxin) requires the aromatic hydrocarbon (Ah) receptor and the interaction of an inducer-receptor complex with one or more of the Ah-responsive elements (AhREs) located about 1 kb upstream from the transcriptional initiation site. We find that treatment of mouse hepatoma Hepa-1 cells with 2-aminopurine, an inhibitor of protein kinase activity, inhibits CYP1A1 mRNA induction by TCDD as well as the concomitant increase in CYP1A1 enzyme activity. Formation of DNA-protein complexes between the Ah receptor and its AhRE target is also inhibited by 2-aminopurine, as determined by gel mobility shift assays. Phosphorylation is required for the formation of Ah receptor-specific complexes, since in vitro dephosphorylation of nuclear extracts from TCDD-treated Hepa-1 cells abolishes the capacity of the Ah receptor to form specific complexes with its cognate AhRE sequences. To determine whether any one of several known protein kinases was involved in the transcriptional regulation of the Cyp1a-1 gene, we treated Hepa-1 cells with nine other protein kinase inhibitors prior to induction with TCDD; nuclear extracts from these cells were analyzed for their capacity to form specific DNA-protein complexes. Only extracts from cells treated with staurosporine, a protein kinase C inhibitor, were unable to form these complexes. In addition, staurosporine completely inhibited CYP1A1 mRNA induction by TCDD. Depletion of protein kinase C by prolonged treatment with phorbol ester led to the complete suppression of CYP1A1 mRNA induction by TCDD. We conclude that (i) phosphorylation is necessary for the formation of a transcriptional complex and for transcriptional activation of the Cyp1a-1 gene; (ii) the phosphorylation site(s) exists on at least one of the proteins constituting the transcriptional complex, possibly the Ah receptor itself; and (iii) the enzyme responsible for the phosphorylation is likely to be protein kinase C.

Alkaloids↗
PubMed1991

The human dioxin-inducible NAD(P)H: quinone oxidoreductase cDNA-encoded protein expressed in COS-1 cells is identical to diaphorase 4.

NAD(P)H: quinone oxidoreductase (NQO1) is believed to be protective against cancer and toxicity caused by exposure to quinones and their metabolic precursors. This enzyme catalyzes the two-electron reduction of compounds, compared with one-electron reduction mediated by NADPH: cytochrome-P450 oxidoreductase which produces toxic and mutagenic free radicals. Recently we cloned and sequenced the cDNA encoding human 2.3,7,8-tetrachlorodibenzo-p-dioxin (dioxin)-inducible cytosolic NQO1 [Jaiswal et al. (1988) J. Biol. Chem. 263, 13572-13578] and provided preliminary evidence that this enzyme may correspond to diaphorase 4, an enzymatic activity present in various tissues that catalyzes the reduction of a variety of quinones by both NADH and NADPH [Edwards et al. (1980) Biochem. J. 187, 429-436]. In the present report we characterize the catalytic properties of the protein encoded by the NQO1 cDNA. The enzyme was synthesized in monkey kidney COS-1 cells transfected with a pMT2-based expression plasmid containing the NQO1 cDNA. Western blot analysis of the transfected cells using an antibody against rat liver cytosolic NQO1 revealed a 31-kDa band that was not detected in nontransfected cells. This band corresponded to a polypeptide with the same electrophoretic mobility as the endogenous NQO1 protein detected in the human hepatoblastoma (Hep-G2) cells with the same antibody. The immunoreactive protein detected in human Hep-G2 cells was induced approximately fourfold by exposure of the cultures to dioxin, an increase commensurate with the increased in quinone oxidoreductase activity. These studies suggest that the protein encoded by NQO1 cDNA is indeed similar, if not identical, to the dioxin-inducible protein band detected in human Hep-G2 cells. Further characterization of the product of NQO1 cDNA, which was present at approximately 20-30-fold higher levels in transfected COS cells than the endogenous product in uninduced human Hep-G2 cells indicated that it had very high capacity (greater than 1000-fold over background) to catalyze the reduction of 2.6-dichloroindophenol and menadione. Besides these two commonly used substrates for quinone reductase, the expressed NQO1 protein also effectively metabolized 2,6-dimethylbenzoquinone, methylene blue, p-benzoquinone, 1,4-naphthoquinone, 2-methyl-1,4-benzoquinone, with the latter being the most potent electron acceptor at 50 microM concentration of the substrate.

Animals↗