Biomedical subjects

Anil K Jaiswal

Publications and source records attributed to Anil K Jaiswal.

At least 19 recordsLinked to original sources

PubMed2006

Low and high dose UVB regulation of transcription factor NF-E2-related factor 2.

Transcription factor NF-E2-related factor 2 (Nrf2) regulates antioxidant response element (ARE)-mediated expression and coordinated induction of chemoprotective proteins in response to chemical stress. In this report, we investigated Nrf2 response to low and high dose UVB irradiation. Low dose (7.5 J/m(2)) UVB exposure of mouse hepatoma, mouse keratinocyte, and human skin fibroblast cells led to the nuclear accumulation of Nrf2 and up-regulation of ARE-mediated gene expression. On the contrary, and intriguingly, high dose (20 J/m(2)) UVB exposure of cells led to the nuclear exclusion of Nrf2 and down-regulation of chemoprotective gene expression with possible implications in UVB carcinogenesis. We investigated the mechanism by which high dose UVB induced the nuclear exclusion of Nrf2. Prior treatment with nuclear export inhibitor, leptomycin B, abrogated the UVB-induced nuclear exclusion of Nrf2, indicating that the decrease of Nrf2 in the nucleus was due to the nuclear export of Nrf2. High dose UVB increased the phosphorylation of Nrf2Y568 which stimulated the nuclear export of Nrf2. Mutation of Nrf2Y568 to phenylalanine and src kinase inhibitor PP2 abrogated/reduced the UVB-induced phosphorylation of Nrf2Y568 and nuclear exclusion of Nrf2. Transfection with src family member Fyn small interfering RNA resulted in the nuclear accumulation of Nrf2 and an increase in the expression and UVB induction of ARE-mediated gene expression. UVB exposure also induced the nuclear localization of Fyn. These results suggest that high dose UVB induced the activation/nuclear localization of Fyn which led to increased phosphorylation of Nrf2Y568 and enhanced nuclear export of Nrf2. This resulted in nuclear exclusion of Nrf2 and down-regulation of ARE-mediated chemoprotective gene expression.

Animals↗

PubMed2006

NQO1 and NQO2 regulation of humoral immunity and autoimmunity.

NAD(P)H:quinone oxidoreductase 1 (NQO1) and NRH:quinone oxidoreductase 2 (NQO2) are cytosolic enzymes that catalyze metabolic reduction of quinones and derivatives. NQO1-null and NQO2-null mice were generated that showed decreased lymphocytes in peripheral blood, myeloid hyperplasia, and increased sensitivity to skin carcinogenesis. In this report, we investigated the in vivo role of NQO1 and NQO2 in immune response and autoimmunity. Both NQO1-null and NQO2-null mice showed decreased B-cells in blood, lower germinal center response, altered B cell homing, and impaired primary and secondary immune responses. NQO1-null and NQO2-null mice also showed susceptibility to autoimmune disease as revealed by decreased apoptosis in thymocytes and pre-disposition to collagen-induced arthritis. Further experiments showed accumulation of NADH and NRH, cofactors for NQO1 and NQO2, indicating altered intracellular redox status. The studies also demonstrated decreased expression and lack of activation of immune-related factor NF-kappaB. Microarray analysis showed altered chemokines and chemokine receptors. These results suggest that the loss of NQO1 and NQO2 leads to altered intracellular redox status, decreased expression and activation of NF-kappaB, and altered chemokines. The results led to the conclusion that NQO1 and NQO2 are endogenous factors in the regulation of immune response and autoimmunity.

Animals↗

PubMed2006

RETRACTED: Si RNA inhibition of GRP58 associated with decrease in mitomycin C-induced DNA cross-linking and cytotoxicity.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Office of Integrity of the University of Maryland due to data entered in Fig 3 of the publication that were not supported by raw data, in addition to the fact that the statistical evaluations were adultered.

Cell Line, Tumor↗

PubMed2006

Genetic deletion of NAD(P)H:quinone oxidoreductase 1 abrogates activation of nuclear factor-kappaB, IkappaBalpha kinase, c-Jun N-terminal kinase, Akt, p38, and p44/42 mitogen-activated protein kinases and potentiates apoptosis.

The NAD(P)H:quinone oxidoreductase 1 (NQO1) is a phase II enzyme that reduces and detoxifies quinones and their derivatives. Although overexpressed in tumor cells, the NQO1 has been linked with the suppression of carcinogenesis, and the effect of NQO1 on tumor necrosis factor (TNF), a cytokine that mediates tumorigenesis through proliferation, invasion, angiogenesis, and metastasis of tumors, is currently unknown. The purpose of our study was to determine the role of NQO1 in TNF cell signaling by using keratinocytes derived from wild-type and NQO1 gene-deleted mice. TNF induced nuclear factor (NF)-kappaB activation in wild-type but not in NQO1-deleted cells. The treatment of wild-type cells with dicoumarol, a known inhibitor of NQO1, also abolished TNF-induced NF-kappaB activation. NF-kappaB activation induced by lipopolysaccharide, phorbol ester, and cigarette smoke, was also abolished in NQO1-deleted cells. The suppression of NF-kappaB activation was mediated through the inhibition of IkappaBalpha kinase activation, IkappaBalpha phosphorylation, and IkappaBalpha degradation. Further, the deletion of NQO1 abolished TNF-induced c-Jun N-terminal kinase, Akt, p38, and p44/p42 mitogen-activated protein kinase activation. TNF also induced the expression of various NF-kappaB-regulated gene products involved in cell proliferation, antiapoptosis, and invasion in wild-type NQO1 keratinocytes but not in NQO1-deleted cells. The suppression of these antiapoptotic gene products increased TNF-induced apoptosis in NQO1-deleted cells. We also found that TNF activated NQO1, and NQO1-specific small interfering RNA abolished the TNF-induced NQO1 activity and NF-kappaB activation. Overall, our results indicate that NQO1 plays a pivotal role in signaling activated by TNF and other inflammatory stimuli and that its suppression is a potential therapeutic strategy to inhibit the proliferation, survival, invasion, and metastasis of tumor cells.

Animals↗

PubMed2006

NRH:quinone oxidoreductase 2 (NQO2) catalyzes metabolic activation of quinones and anti-tumor drugs.

NRH:quinone oxidoreductase 2 (NQO2) is a cytosolic flavoprotein that utilizes NRH as electron donor. The present studies investigate the role of NQO2 in metabolic detoxification/activation of quinones and quinone based anti-tumor drugs. Chinese hamster ovary (CHO) cells stably overexpressing cDNA derived mouse NQO2 and mouse keratinocytes from DMBA-induced skin tumors in wild-type and NQO2-null mice were generated. The CHO cells overexpressing NQO2 and mouse keratinocytes expressing or deficient in NQO2 were treated with varying concentrations of mitomycin C (MMC), CB1954, MMC analog BMY25067, EO9, menadione and BP-3,6-quinone, in the absence and presence of NRH. The cytotoxicity of the drugs was evaluated by colony formation. The CHO cells overexpressing higher levels of mouse NQO2 showed significantly increased cytotoxicity to menadione, BP-3,6-quinone and to the anti-tumor drugs MMC and CB1954 when compared to CHO cells expressing endogenous NQO2. The cytotoxicity increased in presence of NRH. Similar results were also observed with BMY25067 and EO9 treatments, but to a lesser extent. The results on keratinocytes deficient in NQO2 supported the data from CHO cells. The inclusion of NRH had no effect on cytotoxicity of quinones and drugs in keratinocytes deficient in NQO2. Mouse NQO2 protein was expressed in bacteria, purified and used to study the role of NQO2 in MMC-induced DNA cross-linking. Bacterially expressed and purified NQO2 efficiently catalyzed MMC activation that led to DNA cross-linking. These results concluded that NQO2 plays a significant role in the metabolic activation of both quinones and anti-tumor drugs leading to cytotoxicity and cell death.

Animals↗

PubMed2006

Phosphorylation of tyrosine 568 controls nuclear export of Nrf2.

Nuclear factor Nrf 2, under normal conditions, is retained in the cytosol by INrf 2. Antioxidants and oxidants antagonize this interaction, resulting in the release of Nrf 2. Nrf 2 translocates to the nucleus binds to ARE and activates a battery of chemopreventive genes. Once this is achieved, Nrf 2 is exported out of the nucleus, binds with INrf 2, and degrades. Nrf 2 contains well defined signals that control nuclear import and export of Nrf 2. The present studies demonstrate that phosphorylation of tyrosine 568 is required for Crm1-mediated nuclear export and degradation of Nrf 2. Mutation of tyrosine 568 to alanine and phenylalanine resulted in the loss of interaction with Crm1 and abrogation of nuclear export of Nrf 2. Nrf 2Y568A is deficient in nuclear export and displays delayed degradation compared with wild-type Nrf 2. In addition, Src inhibitor PP2 caused nuclear accumulation of Nrf 2 in normal and hydrogen peroxide-treated cells but had no effect on localization of mutant Nrf 2Y568A. Further experiments with small interfering RNA revealed that Fyn phosphorylated Nrf 2Y568 leading to nuclear export and degradation of Nrf 2.

Active Transport, Cell Nucleus↗

PubMed2006

BALT development and augmentation of hyperoxic lung injury in mice deficient in NQO1 and NQO2.

NAD(P)H/NRH:quinone oxidoreductases (NQO1 and NQO2) protect against oxidative stress and neoplasia. Cross-breeding of NQO1-/- with NQO2-/- mice generated double-knockout (DKO) mice. DKO mice were born normal yet showed myelogenous hyperplasia as observed in single-knockout mice. DKO mice also showed bronchial-associated lymphoid tissue (BALT) that increased in number and size with age. BALT was absent in wild-type and single-knockout mice. Further analysis demonstrated infiltration of neutrophils and macrophages in BALT and significant increases in the serum cytokines TNFalpha, IL-6, and IL-1beta and increased expression of iNOS and higher nitric oxide in lung macrophages. The development of BALT in DKO mice presumably led to the release of cytokines and higher lung macrophage activation, because histologically spleen, thymus, and blood cultures and urine analysis showed absence of infection. Additionally, the DKO mice upon exposure to hyperoxia demonstrated severe intra-alveolar edema and perivascular inflammation and massive infiltration with neutrophils, compared with wild-type mice. These results suggest that NQO1 and NQO2 combined protect mice against lung inflammation, BALT, and hyperoxic lung injury.

Animals↗

PubMed2005

Nuclear factor Nrf2 and antioxidant response element regulate NRH:quinone oxidoreductase 2 (NQO2) gene expression and antioxidant induction.

Human NRH:quinone oxidoreductase 2 (NQO2) is a cytosolic protein that catalyzes the metabolic reduction of quinones and provides protection against myelogenous hyperplasia and chemical carcinogenesis. NQO2 gene expression is induced in response to antioxidant tert-butylhydroquinone (tBHQ). Sequence analysis revealed six putative antioxidant response elements (ARE1 through 6) in the human NQO2 gene promoter. Deletion mutagenesis and transfection studies suggested that the ARE region between nucleotides -1433 and -1424 is essential for basal expression and antioxidant induction of NQO2 gene expression. Mutation of this ARE from 3.8 kb NQO2 gene promoter significantly repressed expression and abrogated the induction in response to antioxidant in transfected cells. Band shift, supershift, and chromatin immunoprecipitation (ChIP) assays demonstrated binding of nuclear factors Nrf2 and JunD with human NQO2 gene ARE. Coimmunoprecipitation experiments revealed an association between Nrf2 and JunD. Overexpression of Nrf2 upregulated and overexpression of Nrf2 dominant-negative mutant downregulated ARE-mediated NQO2 gene expression. The treatment of Hep-G2 cells with Nrf2-specific RNAi significantly reduced Nrf2 and NQO2 gene expression and tBHQ induction. The results combined demonstrated that Nrf2 associates with JunD, binds to ARE at nucleotide -1433, and regulates human NQO2 gene expression and induction in response to antioxidants.

Antioxidants↗

PubMed2005

Nuclear import and export signals in control of Nrf2.

Nrf2 binds to the antioxidant response element and regulates expression and antioxidant induction of a battery of chemopreventive genes. In this study, we have identified nuclear import and export signals of Nrf2 and show that the nuclear import and export of Nrf2 is regulated by antioxidants. We demonstrate that Nrf2 contains a bipartite nuclear localization signal (NLS) and a leucine-rich nuclear export signal, which regulate Nrf2 shuttling in and out of the nucleus. Immunofluorescence and immunoblot analysis revealed that Nrf2 accumulates in the nucleus within 15 min of antioxidant treatment and is exported out of nucleus by 8 h after treatment. Nrf2 mutant lacking the NLS failed to enter the nucleus and displayed diminished expression and induction of the downstream NAD(P)H:quinone oxidoreductase 1 gene. The Nrf2 NLS sequence, when fused to green fluorescence protein, resulted in the nuclear accumulation of green fluorescence protein, indicating that this signal sequence was sufficient to direct nuclear localization of Nrf2. A nuclear export signal (NES) was characterized in the C terminus of Nrf2, the deletion of which caused Nrf2 to accumulate predominantly in the nucleus. The Nrf2 NES was sensitive to leptomycin B and could function as an independent export signal when fused to a heterologous protein. Further studies demonstrate that NES-mediated nuclear export of Nrf2 is required for degradation of Nrf2 in the cytosol. These results led to the conclusion that Nrf2 localization between cytosol and nucleus is controlled by both nuclear import and export of Nrf2, and the overall distribution of Nrf2 is probably the result from a balance between these two processes. Antioxidants change this balance in favor of nuclear accumulation of Nrf2, leading to activation of chemopreventive proteins. Once this is achieved, Nrf2 exits the nucleus for binding to INrf2 and degradation.

Active Transport, Cell Nucleus↗

PubMed2005

Quinone oxidoreductases in protection against myelogenous hyperplasia and benzene toxicity.

Quinone oxidoreductases (NQO1 and NQO2) are cytosolic proteins that catalyze metabolic reduction of quinones and its derivatives to protect cells against redox cycling and oxidative stress. In humans, a high percentage of individuals with myeloid and other types of leukemia are homo- and heterozygous for a null mutant allele of NQO1. The NQO2 locus is also highly polymorphic in humans. Recently, we generated NQO1-/- and NQO2-/- mice deficient in NQO1 and NQO2 protein and activity, respectively. These mice showed no detectable developmental abnormalities and were indistinguishable from wild type mice. Interestingly, all the mice lacking expression of NQO1 and NQO2 protein demonstrated myelogenous hyperplasia of the bone marrow and increased granulocytes in the peripheral blood. Decreased apoptosis contributed to myelogenous hyperplasia. The studies on short-term exposure of NQO1-/- mice to benzene demonstrated substantially greater benzene-induced toxicity, as compared to wild type mice.

Animals↗

PubMed2005

Lower induction of p53 and decreased apoptosis in NQO1-null mice lead to increased sensitivity to chemical-induced skin carcinogenesis.

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a cytosolic protein that catalyzes metabolic detoxification of quinones and protects cells against redox cycling and oxidative stress. NQO1-null mice deficient in NQO1 protein showed increased sensitivity to 7,12-dimethylbenz(a)anthracene- and benzo(a)pyrene-induced skin carcinogenesis. In the present studies, we show that benzo(a)pyrene metabolite benzo(a)pyrene-trans-7,8-dihydrodiol-9,10-epoxide and not benzo(a)pyrene quinones contributed to increased benzo(a) pyrene-induced skin tumors in NQO1-null mice. An analysis of untreated skin revealed an altered intracellular redox state due to accumulation of NADH and reduced levels of NAD/NADH in NQO1-null mice as compared with wild-type mice. Treatment with benzo(a)pyrene failed to significantly increase p53 and apoptosis in the skin of NQO1-null mice when compared with wild-type mice. These results led to the conclusion that altered intracellular redox state along with lack of induction of p53 and decreased apoptosis plays a significant role in increased sensitivity of NQO1-null mice to benzo(a)pyrene-induced skin cancer.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed2005

Bach1 competes with Nrf2 leading to negative regulation of the antioxidant response element (ARE)-mediated NAD(P)H:quinone oxidoreductase 1 gene expression and induction in response to antioxidants.

The antioxidant response element (ARE) and Nrf2 are known to regulate the expression and coordinated induction of genes encoding detoxifying enzymes including NAD(P)H:quinone oxidoreductase1 (NQO1) in response to antioxidants. In this report, we demonstrate that overexpression of the transcription factor Bach1 in Hep-G2 cells negatively regulated NQO1 gene expression and induction in response to antioxidant t-BHQ. Bandshift and supershift assays revealed that Bach1 binds to the ARE as a heterodimer with small Maf proteins but not as a homodimer or heterodimer with Nrf2. The transfection and ChIP assays revealed that Bach1 and Nrf2 competed with each other to regulate ARE-mediated gene expression. Heme, a negative regulator of Bach1 relieved the Bach1 repression of NQO1 gene expression in transfected cells. The transcription of Bach1 and Nrf2 did not change in response to t-BHQ. Immunofluorescence assays and Western blot analysis revealed that both Bach1 and Nrf2 localized in the cytoplasm and nucleus of the untreated cells. The treatment of cells with t-BHQ resulted in the nuclear accumulation of both Bach1 and Nrf2. Interestingly, the t-BHQ-induced nuclear accumulation of Bach1 was significantly delayed over that of Nrf2. These results led to the conclusion that a balance of Nrf2 versus Bach1 inside the nucleus influences up- or down-regulation of ARE-mediated gene expression. The results further suggest that antioxidant-induced delayed accumulation of Bach1 contributes to the down-regulation of ARE-regulated genes, presumably to reduce the antioxidant enzymes to normal levels.

Antioxidants↗

PubMed2004

Effects of NQO1 deficiency on levels of cyclopurines and other oxidative DNA lesions in liver and kidney of young mice.

I-compounds are bulky indigenous DNA adducts that can be detected by (32)P-postlabeling. A subgroup, termed type II I-compounds, represents DNA lesions induced by oxidative stress. Several major type II I-compounds have been identified as dinucleotides containing 3'-terminal 8,5'-cyclo-2'-deoxyadenosine (cA). Levels of type II I-compounds depend on the pro-oxidant status of the cell. For example, enhanced formation of such oxidative DNA lesions in newborn rodents appears to be a consequence of incomplete development of neonatal antioxidant defense systems. We tested the hypothesis that young mice deficient in NAD(P)H:quinone oxidoreductase 1 (NQO1), an antioxidant enzyme catalyzing the detoxification of quinones and their derivatives, show increased formation of these oxidative DNA lesions. Type II I-compound levels were determined by (32)P-postlabeling in liver and kidney DNA of untreated male wild-type or NQO1-null C57BL/6 mice of different ages. NQO1 catalytic activities and contents were measured by spectrophotometric and Western blotting techniques, respectively. Elevated oxidative adduct levels including those containing cA were detected in NQO1-null compared to wild-type mice at 10, 30 and 90 days in liver and at 30 and 90 days in kidney DNA. Furthermore, there were statistically significant inverse relationships between type II I-compound levels and NQO1 activities in wild-type mice up to 30 days of age. Taken together, the results suggest that NQO1 plays an important role in attenuating endogenous oxidative DNA damage in vivo. Our results show also that type II I-compounds represent useful and sensitive biomarkers with utility in studies of oxidative DNA damage and its consequences.

Animals↗

PubMed2004

BRCA1 induces antioxidant gene expression and resistance to oxidative stress.

Mutations of the breast cancer susceptibility gene 1 (BRCA1), a tumor suppressor, confer an increased risk for breast, ovarian, and prostate cancers. To investigate the function of the BRCA1 gene, we performed DNA microarray and confirmatory reverse transcription-PCR analyses to identify BRCA1-regulated gene expression changes. We found that BRCA1 up-regulates the expression of multiple genes involved in the cytoprotective antioxidant response, including glutathione S-transferases, oxidoreductases, and other antioxidant genes. Consistent with these findings, BRCA1 overexpression conferred resistance while BRCA1 deficiency conferred sensitivity to several different oxidizing agents (hydrogen peroxide and paraquat). In addition, in the setting of oxidative stress (due to hydrogen peroxide), BRCA1 shifted the cellular redox balance to a higher ratio of reduced to oxidized glutathione. Finally, BRCA1 stimulated antioxidant response element-driven transcriptional activity and enhanced the activity of the antioxidant response transcription factor nuclear factor erythroid-derived 2 like 2 [also called NRF2 (NFE2L2)]. The ability of BRCA1 to stimulate antioxidant response element-dependent transcription and to protect cells against oxidative stress was attenuated by inhibition of nuclear factor erythroid-derived 2 like 2. These findings suggest a novel function for BRCA1, i.e., to protect cells against oxidative stress. This function would be consistent with the postulated role of BRCA1 as a caretaker gene in preserving genomic integrity.

Antioxidants↗

PubMed2004

Sp3 repression of polymorphic human NRH:quinone oxidoreductase 2 gene promoter.

Human NRH:quinone oxidoreductase 2 (NQO2) gene-containing 29-bp deletion/insertion polymorphic promoters were found to be associated with susceptibility to Parkinson's disease. Here, we demonstrate that the NQO2 gene is differentially expressed by the polymorphic promoters in human fibroblasts and Hep-G2 cells transfected with NQO2 gene reporter constructs. Promoter containing the 29-bp insertion polymorphism demonstrated significantly lower NQO2 gene expression. Deletion mutagenesis and DNase I footprinting analysis of the promoter without the 29-bp insertion identified three protected regions (region A, B, and C). Band- and supershift and transfection assays showed binding of transcription factor Sp1 to regions A and B, which regulated expression of the NQO2 gene. Similar studies of the NQO2 gene promoter with the 29-bp insertion polymorphism showed that regions A and C were identical and contributed similarly as in the promoter without the 29-bp insertion to NQO2 gene expression. However, region B was found to be inserted with 29-bp DNA element and bound to both Sp1 and Sp3. Binding of Sp3 led to repression of NQO2 gene transcription by the promoter containing the 29-bp insertion polymorphism. These studies also suggest that alterations in NQO2 activity might be an important factor in susceptibility to Parkinson's disease.

Alleles↗

PubMed2004

Nrf3 negatively regulates antioxidant-response element-mediated expression and antioxidant induction of NAD(P)H:quinone oxidoreductase1 gene.

Antioxidant-response element (ARE) and nuclear factor Nrf2-mediated expression and coordinated induction of genes encoding chemopreventive proteins, including NQO1, are critical mechanisms in chemoprotection. Recently, Nrf3, a new member of the Nrf family with substantial homology to Nrf2, was identified and cloned. In this report, we have investigated the role of Nrf3 in ARE-mediated gene expression and induction of NQO1 in response to antioxidants. Overexpression of Nrf3 in Hep-G2 cells led to a concentration-dependent decrease in transfected and endogenous NQO1 gene expression and induction in response to antioxidant tert-butylhydroquinone (t-BHQ). Deletion mutation analysis revealed that Nrf3 repression of NQO1 gene expression required heterodimerization and DNA binding domains but not transcriptional activation domain of Nrf3. Bandshift and supershift assays with in vitro transcribed and translated proteins and nuclear extracts from Hep-G2 cells treated with Me2SO and t-BHQ and immunoprecipitation assays demonstrated that Nrf3 associates with small Maf proteins to bind to the ARE. RNA interference specific to Nrf3 reduced intracellular Nrf3 leading to increased expression and induction of transfected and endogenous NQO1 gene expression in response to t-BHQ. These results combined suggest that Nrf3 is a negative regulator of ARE-mediated gene expression.

Antioxidants↗

PubMed2004

Deficiency of NRH:quinone oxidoreductase 2 increases susceptibility to 7,12-dimethylbenz(a)anthracene and benzo(a)pyrene-induced skin carcinogenesis.

NRH:Quinone oxidoreductase 2 (NQO2) is an enzyme that catalyzes the reductive metabolism of quinones. C57BL/6 NQO2-/- mice lacking NQO2 gene expression were generated in our laboratory. The dorsal skin of NQO2-deficient mice was exposed to 7,12-dimethylbenz(a)anthracene (DMBA) or benzo(a)pyrene alone (complete carcinogen) or with 12-O-tetradecanoylphorbol-13-acetate (TPA) (initiation/promotion model) to determine the in vivo role of NQO2 in chemical carcinogenesis. The NQO2-/- mice showed significantly increased tumor frequency with DMBA + TPA when compared with their wild-type littermates. The benzo(a)pyrene + TPA also showed increase in tumor incidence in NQO2-/- mice but to a less extent than DMBA. DMBA alone resulted in low frequency of tumor development with no difference in susceptibility between wild-type and NQO2-/- mice. Benzo(a)pyrene alone failed to induce tumors in either wild-type or NQO2-/- mice. Histologic analysis of the NQO2-/- mice tumors demonstrated proliferative activity. The treatment of NQO2-/- mice skin with benzo(a)pyrene failed to significantly increase tumor suppressor protein p53 and p53-regulated growth-related protein p21 and proapoptotic protein Bax as observed in case of wild-type mice. These results demonstrate that NQO2 protects against DMBA- and benzo(a)pyrene-induced skin carcinogenesis and suggest that NQO2 protection might be against tumor promotion. The results also suggest that lack of induction of p53, p21, and Bax proteins might contribute to increased sensitivity of NQO2-/- mice skin to benzo(a)pyrene carcinogenicity.

Animals↗

PubMed2004

Nrf2 signaling in coordinated activation of antioxidant gene expression.

Antioxidant response element (ARE)-mediated expression and coordinated induction of antioxidant enzymes is a critical mechanism of protection against chemically induced oxidative/electrophilic stress. NF-E2-related nuclear factors (Nrf1 and Nrf2) bind to ARE and regulate ARE-mediated gene expression and induction. Nrf2 is more potent than Nrf1 in activation of ARE-regulated gene expression. Nrf2 is retained in the cytoplasm by an inhibitor INrf2. Nrf2 binding to INrf2 leads to proteasomal degradation of Nrf2. An increase in oxidative/electrophilic stress, due to chemical exposure, leads to the activation of protein kinase C (PKC) and other cytosolic factors. PKC phosphorylation of Nrf2 at serine 40 results in the escape or release of Nrf2 from INrf2. Nrf2 translocates to the nucleus, forms heterodimers with its unknown partner proteins, and binds to the ARE. This leads to the coordinated activation of ARE-regulated genes. Additional nuclear factor including small Mafs (MafG and MafK), large Maf (c-Maf), c-Fos, and Fra1, also bind to ARE and negatively regulate ARE-mediated gene expression. This is presumably to keep the expression of antioxidant enzymes "in check" to maintain the cellular defenses active and/or to rapidly restore induced enzymes to normal levels. Future investigations are expected to reveal that a balance between positive and negative factors regulates ARE-mediated gene expression and induction. The future studies should also reveal a complete mechanism of signal transduction from antioxidants and xenobiotics to the transcription factors, such as Nrf2, that bind to ARE.

Animals↗