Analysis of the emerging physical network in young mycelia

Filamentous fungi develop intricate hyphal networks that support mycelial foraging and transport of resources. These networks have been analyzed recently using graph theory, enabling the development of models that seek to predict functional traits. However, attention has focused mainly on mature colonies. Here, we report the extraction and analysis of the graph corresponding to Trichoderma atroviride mycelia only a few hours after conidia germination. To extract the graph for a given mycelium, a mosaic conformed of multiple bright-field, optical microscopy images is digitally processed using freely available software. The resulting graphs are characterized in terms of number of nodes and edges, average edge length, total mycelium length, hyphal growth unit, maximum edge length and mycelium diameter, for colonies between 8 h and 14 h after conidium germination. Our results show that the emerging hyphal network grows first by hyphal elongation and branching, and then it transitions to a stage where hyphal-hyphal interactions become significant. As a tangled hyphal network develops with decreasing hyphal mean length, the mycelium maintains long (∼2 mm) hyphae-a behavior that suggests a combination of aggregated and dispersed architectures to support foraging. Lastly, analysis of early network development in Podospora anserina reveals striking similarity with T. atroviride, suggesting common mechanisms during initial colony formation in filamentous fungi.

Activity and stability of bifunctional perovskite/carbon-based electrodes for the removal of antipyrine by electro-Fenton process

Bifunctional perovskite/carbon-black(CB)/polytetrafluoroethylene(PTFE) electrodes for electro-generation and catalytic decomposition of hydrogen peroxide to oxidizing hydroxyl radicals have been fabricated. These electrodes were tested for electroFenton (EF) removal of antipyrine (ANT) as a model antipyretic and analgesic drug. The influence of the binder loading (20 and 40 wt % PTFE) and type of solvent (1,3-dipropanediol and water) was studied for the preparation of CB/PTFE electrodes. The electrode prepared with 20 wt % PTFE and water exhibited a low impedance and remarkable H₂O₂ electro-generation (about 1 g/L after 240 min, a production rate of ca. 6.5 mg/h·cm²). The incorporation of perovskite on CB/PTFE electrodes was also studied following two different methods: i) direct deposition on the CB/PTFE electrode surface and ii) addition in the own CB/PTFE/water paste used for the fabrication. Physicochemical and electrochemical characterization techniques were used for the electrode's characterization. The dispersion of perovskite particles in the own electrode matrix (method ii) exhibited a higher EF performance than the immobilisation onto the electrode surface (method i). EF experiments at 40 mA/cm² and pH 7 (non-acidified conditions) showed ANT and TOC removals of 30% and 17%, respectively. The increase of current intensity up to 120 mA/cm² achieved the complete removal of ANT and 92% of TOC mineralisation in 240 min. The bifunctional electrode also proved high stability and durability after 15 h of operation.

Epigenetics as a mechanism linking developmental exposures to long-term toxicity

A variety of experimental and epidemiological studies lend support to the Developmental Origin of Health and Disease (DOHaD) concept. Yet, the actual mechanisms accounting for mid- and long-term effects of early-life exposures remain unclear. Epigenetic alterations such as changes in DNA methylation, histone modifications and the expression of certain RNAs have been suggested as possible mediators of long-term health effects of environmental stressors. This report captures discussions and conclusions debated during the last Prenatal Programming and Toxicity meeting held in Japan. Its first aim is to propose a number of criteria that are critical to support the primary contribution of epigenetics in DOHaD and intergenerational transmission of environmental stressors effects. The main criteria are the full characterization of the stressors, the actual window of exposure, the target tissue and function, the specificity of the epigenetic changes and the biological plausibility of the linkage between those changes and health outcomes. The second aim is to discuss long-term effects of a number of stressors such as smoking, air pollution and endocrine disruptors in order to identify the arguments supporting the involvement of an epigenetic mechanism. Based on the developed criteria, missing evidence and suggestions for future research will be identified. The third aim is to critically analyze the evidence supporting the involvement of epigenetic mechanisms in intergenerational and transgenerational effects of environmental exposure and to particularly discuss the role of placenta and sperm. While the article is not a systematic review and is not meant to be exhaustive, it critically assesses the contribution of epigenetics in the long-term effects of environmental exposures as well as provides insight for future research.

Timeliness of care and prognosis in patients with lung cancer

BACKGROUND

Timeliness of care is an important dimension of health care quality. The determining factors of less timely care and their influence on the survival of patients with lung cancer (LC) remain uncertain.

AIMS

To analyse the delays in the diagnosis and treatment of LC in our health area, the factors associated with the timeliness of care and their possible relationship with the survival of these patients.

METHODS

A retrospective study was conducted on all patients with a cytohistologically confirmed diagnosis of LC between 1 June 2005 and 31 May 2008. The time delays for consultation (specialist delay), diagnosis (diagnosis delay), and treatment (treatment delay), were analysed, as well as the factors associated with these delays and the influence of the timeliness of care on survival.

RESULTS

A total of 307 cases were included (87 % males). The mean specialist delay was 53.6 days (median 35 days), diagnosis delay 31.5 days (median 18 days), treatment delay 23.5 days (median 14 days). The greater age of the patient and a more advanced stage were associated with a shorter specialist delay. Male sex, a more advanced stage, and poor general status were associated with a shorter treatment delay. The survival is longer in patients with a longer treatment delay.

CONCLUSIONS

The delay in the diagnosis in our population seems to be excessively long. The greater the age, a more advanced tumour stage, male sex, and poor general health status are associated with shorter delays. A longer treatment delay is associated with a longer survival.

Trends of asthma mortality in Galicia from 1993 to 2007

INTRODUCTION

In the past few years, deaths due to asthma appear to decrease at least in Western countries; but there are significant variations between populations. The aim of this study is to describe the trends in deaths due to asthma between 1993 and 2007 in our community and to analyze any factors associated with this.

METHODS

All cases, which had asthma as a cause of death, were included in the study. The mortality data were obtained from the official death certificate from the Deaths Register. Mortality relative risk, based on the calendar year, sociodemographic variables (age and gender), seasons, and days of the week, were estimated using a Poisson generalized linear model with a log-link.

RESULTS

In the 15 years of the study period, a total of 1180 people had died due to asthma, mainly in winter (34.5%), women (64.5%), and advanced age (65 years or above; 84.6%). A tendency of decreased mortality in all age groups was observed during the period of the study, which was significant in both the sexes in the 35- to 64-year-old age group, and in males above 65 years.

CONCLUSION

Death due to asthma is changing favorably in our community, with a tendency to decrease in the past few years. Advanced age, being female, and the winter period are associated with a higher mortality rate due to asthma.

[Delayed diagnosis of alpha-1 antitrypsin deficiency]

Alpha-1 antitrypsin deficiency (AAT-D) is a genetic disease, relatively common in populations of European ancestry. AAT-D remains undiagnosed in many patients, and there are often long delays between the onset of respiratory symptoms and diagnosis. AAT-D can be readily diagnosed by measurement of the serum or plasma protein level, which should be confirmed by assessing the genotype or protein phenotype when AAT levels are below the normal range. Close monitoring for the development or progression of lung disease or liver disease is required, and can improve the prognosis. We show the case of a 69 year old woman with recurrent respiratory infections and asthma symptoms. The serum levels of AAT were below the normal range, and ZZ genotype was confirmed. The delayed diagnosis of our patient seems to emphasize the need to remind the doctors about AAT-D, frequently associated with asthma or COPD symptoms.

Patient expectations are not always the same

OBJECTIVE

To validate a scale that measures patients' expectations when seeking advice for health problems of different types.

METHODS

360 patients who had consulted their general practitioner (GP) during the previous 12 months were randomly selected from the lists of 30 GPs. A questionnaire, including a 13-item expectation scale, was administered by interview in the patient's home to assess expectations in relation to five health problems, three biomedical (strong chest pain, genital discharge and the common cold) and two psychosocial (depression/sadness and serious family problem), repeating the expectation scale for each one. The frequency distribution of items was analysed, multi-level factorial analysis was performed and the reliability of the expectation scale was tested for each hypothetical clinical condition.

RESULTS

The response rate was 90%. Mean age of patients was 47.3 years (SD 16.5); 51% were women. Expectations were high but varied according to the nature and severity of the condition. The percentage of patients wanting the doctor alone to make decisions ranged from 50% for "family problem" to 68% for "chest pain". The five factorial structures differed and explained 49.3-63.9% of the variance. Similarities were observed depending on the type of problem. "Communication" and "Experience of disease" were thus separate dimensions for the biomedical diseases but mixed for the psychosocial conditions.

CONCLUSIONS

The factorial structure of expectations varied, indicating that expectations are not homogeneous in all clinical situations. The desire of the patient to participate in decision-making also differs according to the type of health problem.

Dioxin exposure is an environmental risk factor for ischemic heart disease

Epidemiologic studies have linked dioxin exposure to increased mortality caused by ischemic heart disease. To test the hypothesis that dioxin exposure may constitute an environmental risk factor for atherosclerosis, we exposed C57BL/6J mice to 5 microg/kg of dioxin daily for 3 d, and measured various molecular and physiological markers of heart disease. Dioxin treatment led to an increase in the urinary excretion of vasoactive eicosanoids and an elevation in the mean tail-cuff blood pressure. In addition, dioxin exposure led to an increase in triglycerides, but not in high-density lipoproteins, in both Apoe(+/+) mice and in hyperlipidemic Apoe(-/- mice. Dioxin exposure also led to an increase in low-density lipoproteins in Apoe(-/-) mice. After treatment, dioxin was associated with low-density lipoprotein particles, which might serve as a vehicle to deliver the compound to atherosclerotic plaques. Dioxin treatment of vascular smooth-muscle cells taken from C57Bl/6J mice resulted in the deregulation of several genes involved in cell proliferation and apoptosis. Subchronic treatment of Apoe(-/-) mice with dioxin (150 ng/kg, three times weekly) for 7 or 26 wk caused a trend toward earlier onset and greater severity of atherosclerotic lesions compared to those of vehicle treated mice. These results suggest that dioxin may increase the incidence of ischemic heart disease by exacerbating its severity.

Serologic response to hepatitis B vaccine in HIV infected and high-risk HIV uninfected adolescents in the REACH cohort. Reaching for Excellence in Adolescent Care and Health

PURPOSE

To evaluate hepatitis B (HBV) vaccine response rates in HIV infected and high-risk HIV uninfected youth and examine associations with responsiveness in the HIV infected group.

METHODS

Cohorts within the Reaching for Excellence in Adolescent Care and Health (REACH) study population were defined based on receipt of HBV vaccine both retrospectively and prospectively. Sero-responsiveness was determined by HBsAb measurements. Testing was done for HBsAg, HBsAb, and HBcAb. For HBsAb, a value of > 10 International Units per liter was considered a positive response, and the data were collected as either positive or negative from each of the reporting laboratories. Covariates of responsiveness were explored in univariate and multivariate models for each cohort.

RESULTS

Sixty-one subjects had received a three-dose vaccination course at the time of entry into REACH. HIV uninfected subjects had significantly higher rates of response by serology compared with HIV infected subjects (70% vs. 41.1%; chi(2) = .05; RR = .586, 95% CI: .36-.96). By the time of an annual visit 43 subjects had received three vaccinations with at least one occurring in the study period. The rates of response were similar for the HIV infected and uninfected groups (37.1% vs. 37.5%) in this cohort. Univariate and multivariate analysis in the prospective HIV infected group (N = 35) found an association between elevated CD8(+)/CD38(+)/HLA-DR(+) T cells and lack of HBV vaccine responsiveness (6.7% vs. 60%; chi(2) = .03; RR = .12, 95% CI: .02- .55).

CONCLUSIONS

The poor HBV vaccine response rate in the HIV uninfected high-risk adolescents was unexpected and suggests that HBV vaccination doses have not been optimized for older adolescents. This is the first report of decreased responsiveness in HIV infected subjects being associated with elevated CD8(+)/CD38(+)/HLA(-)DR(+) T cells and suggests that ongoing viral replication and concomitant immune system activation decreases the ability of the immune system in HIV infected subjects to respond to vaccination.

Regulation of transcription of the glutathione S-transferase P1 gene by methylation of the minimal promoter in human leukemia cells

To study the relationship between methylation and the transcriptional activity of the minimal promoter of the glutathione S-transferase GSTP1 gene encoding glutathione S-transferase P1-1, GSTP1 mRNA levels as well as basal promoter activity were compared in human leukemia cell lines. The K562 erythroleukemia cell line presented a strong GSTP1 promoter activity, as measured in transient transfection assays using a luciferase reporter plasmid, and correlated with a high mRNA whereas in Raji cells no mRNA was expressed. In order to establish a relationship between the expression and the methylation status, we used in vitro bisulfite sequencing which indicated that both methylated and unmethylated GSTP1 promoter alleles coexisted in K562 cells, whereas Raji lymphoma cells showed a nearly uniform hypermethylation of the promoter region. To determine the impact of methylation, we used in vitro SssI methylation of the minimal GSTP1 promoter, which led to the silencing of the promoter activity in transient transfection assays in expressing K562 as well as in non-expressing Raji cells. These data are in good agreement with previously obtained results and indicate that methylation of CpG sites of the basal promoter is an essential mechanism in the control of GSTP1 gene expression in human leukemia.

The transcriptional signature of dioxin in human hepatoma HepG2 cells

We have used a high density microarray hybridization approach to characterize the transcriptional response of human hepatoma HepG2 cells to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We find that exposure to 10 nM TCDD for 8 hr alters by at least a factor of 2.1 the expression of 310 known genes and of an equivalent number of expressed sequence tags. Treatment with TCDD in the presence of 20 microg/mL of cycloheximide blocked the effect on 202 of these genes, allowing us to distinguish between primary effects of TCDD exposure, which take place whether cycloheximide is present or not, and secondary effects, which are blocked by inhibition of protein synthesis. Of the 310 known genes affected by TCDD, 30 are up-regulated and 78 are down-regulated regardless of cycloheximide treatment, and 84 are up-regulated and 118 are down-regulated only when protein synthesis is not inhibited. Functional clustering of genes regulated by TCDD reveals many potential physiological interactions that might shed light on the multiple biological effects of this compound. Our results, however, suggest that arriving at a sound understanding of the molecular mechanisms governing the biological outcome of TCDD exposure promises to be orders of magnitude more complicated than might have been previously imagined.

Disruption of dioxin-inducible phase I and phase II gene expression patterns by cadmium, chromium, and arsenic

Recent work suggesting that cellular oxidative stress exerts an inhibitory effect on aromatic hydrocarbon receptor (AHR)-dependent gene expression led us to test the hypothesis that pro-oxidant environmental pollutants might alter the induction of detoxification genes by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an AHR ligand. We found that, in mouse hepatoma Hepa-1 cells, TCDD-inducible cytochrome P450, Cyp1a1, and nicotinamide adenine dinucleotide phosphate-quinone oxidoreductase (Nqo1) mRNA accumulation were differentially affected by cadmium (Cd(2+)), chromium (Cr(6+)), and arsenic (As(3+)). Cadmium or arsenic did not change Cyp1a1 mRNA levels but did enhance TCDD-inducible levels of Nqo1 mRNA, an effect that paralleled the ability of these metals to activate a beta-galactosidase gene reporter system regulated by an electrophile response promoter element. Chromium inhibited mRNA accumulation for both Cyp1a1 and Nqo1. Manipulation of cellular thiol status did not modify the response to combined chromium-TCDD exposure, suggesting that the response was not caused by oxidative stress. Chromium did not block DNA-binding competence of the AHR and did not have an effect on mRNA stability, but it inhibited Cyp1a1 gene transcription and the expression of an AHR-dependent luciferase reporter. These data indicate that coexposure to pro-oxidant metals and AHR ligands, which is common in the environment, can disrupt the regulation of phase I and phase II detoxification genes, leading to imbalances in gene expression that may have important consequences for the toxicity of complex mixtures.

Activation of transcription factors activator protein-1 and nuclear factor-kappaB by 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD; dioxin), the prototype agonist of the aromatic hydrocarbon (Ah) receptor, is a potent tumor promoter as well as a complete liver carcinogen that produces an oxidative stress response in rodents and in cultured cell lines. It has been proposed that TCDD promotes neoplastic transformation through oxidative signal transduction pathways, which results in activation of immediate-early response transcription factors. To set the stage for a test of this hypothesis, we evaluated the effect of TCDD treatment on the activation of several transcription factors, including those in the nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) families, which are activated by changes in the redox state of cells. In an extension of prior results, we found that TCDD treatment produced a sustained overexpression of AP-1 for at least 72 hr in wild-type mouse hepatoma Hepa-1 cells, but not in the Ah receptor-deficient derivative c35 or in cytochrome P450-1A1 (CYP1A1)-negative c37 cells. In addition, TCDD treatment caused a significant increase in the DNA binding activity of NF-kappaB, but not in the activities of the other transcription factors tested. AP-1 and NF-kappaB activation were blocked by the thiol antioxidant N-acetylcysteine and by nordihydroguaiaretic acid, an antioxidant and lipooxygenase inhibitor and an inhibitor of the epoxygenase activity of CYP1A1, and did not take place in c35, c37, or in Ah nuclear translator-deficient c4 cells. Hence, sustained activation of these two transcription factors by TCDD is likely to result from a CYP1A1-dependent and Ah receptor complex-dependent oxidative signal. Electrophoretic mobility supershift analyses with specific antibodies showed that most of the increase in NF-kappaB binding activity could be accounted for by increases in p50/p50 complexes. Since these complexes are known to repress NF-kappaB-dependent gene transcription, our results delineate a second molecular mechanism, in addition to the recently found block of tumor necrosis factor-alpha-mediated p50/p65 activation, that may be responsible for the immunosuppresive effects of TCDD.

Restoration of retinoblastoma mediated signaling to Cdk2 results in cell cycle arrest

Phosphorylation/inactivation of RB is typically required for cell cycle progression. However, we have identified a tumor cell line, C33A, which progresses through the cell cycle in the presence of an active allele of RB (PSM-RB). To determine how C33A cells evade RB-mediated arrest, we compared RB signaling to downstream effectors in this resistant cell line to that of the RB-sensitive SAOS-2 cell line. Although introduction of PSM-RB repressed E2F-mediated transcription in both C33A and SAOS-2 cells, PSM-RB failed to repress Cyclin A promoter activity in C33A. Ectopic expression of PSM-RB in SAOS-2 cells resulted in a decrease in both Cyclin A and Cdk2 protein levels without affecting Cyclin E or Cdk4. In contrast, over-expression of PSM-RB in C33A cells did not alter endogenous Cyclin A, Cyclin E, or Cdk2 protein levels or impact Cdk2 kinase activity, indicating that signaling from RB to down-stream targets is abrogated in this cell line. The importance of Cdk2 activity was demonstrated by p27Kip1, which attenuated Cdk2 activity and inhibited cell cycle progression in C33A cells. Since RB signaling to Cdk2 is disrupted in these tumor cells, we co-expressed two proteins that cooperate with RB in transcriptional repression, AHR and BRG-1, in an attempt to correct this signaling dysfunction. Co-expression of AHR/BRG-1 with PSM-RB attenuated Cyclin A and Cdk2 expression as well as Cdk2-associated kinase activity, resulting in cell cycle inhibition of C33A cells. Importantly, ectopic expression of Cyclin A was able to reverse the arrest mediated by co-expression of AHR/BRG-1 with PSM-RB. These results indicate that down-regulation of Cdk2 activity is requisite for RB-mediated cell cycle arrest. Thus, this study reveals a new mechanism through which tumor cells evade anti-proliferative signals, and provides insight into how RB-signaling is mediated.

Aromatic hydrocarbon receptor interaction with the retinoblastoma protein potentiates repression of E2F-dependent transcription and cell cycle arrest

Polyhalogenated aromatic hydrocarbons, of which 2,3,7, 8-tetrachloro-p-dioxin (TCDD) is the prototype compound, elicit a variety of toxic, teratogenic, and carcinogenic responses in exposed animals and in humans. In cultured cells, TCDD shows marked effects on the regulation of cell cycle progression, including thymocyte apoptosis, induction of keratinocyte proliferation and terminal differentiation, and inhibition of estrogen-dependent proliferation in breast cancer cells. The presence of an LXCXE domain in the dioxin aromatic hydrocarbon receptor (AHR), suggested that the effects of TCDD on cell cycle regulation might be mediated by protein-protein interactions between AHR and the retinoblastoma protein (RB). Using the yeast two-hybrid system, AHR and RB were in fact shown to bind to each other. In vitro pull-down experiments with truncated AHR peptides indicated that at least two separate AHR domains form independent complexes with hypophosphorylated RB. Coimmunoprecipitation of whole cell lysates from human breast carcinoma MCF-7 cells, which express both proteins endogenously, revealed that AHR associates with RB in vivo only after receptor transformation and nuclear translocation. However, the AHR nuclear translocator and transcriptional heterodimerization partner, is not required for (nor is it a part of) the AHR.RB complexes detected in vitro. Ectopic expression of AHR and RB in human osteosarcoma SAOS-2 cells, which lack endogenous expression of both proteins, showed that AHR synergizes with RB to repress E2F-dependent transcription and to induce cell cycle arrest. Furthermore, AHR partly blocked T-antigen-mediated reversal of RB-dependent transcriptional repression. These results uncover a potential function for the AHR in cell cycle regulation and suggest that this function may be that of serving as an environmental sensor that signals cell cycle arrest when cells are exposed to certain environmental toxicants.

Inhibition of CYP1A1 enzyme activity in mouse hepatoma cell culture by soybean isoflavones

The mechanisms by which soybean- and soybean isoflavone-enriched diets inhibit carcinogenesis are not known. We found that the isoflavones genistin and daidzin, and their respective aglucone forms daidzein and genistein, block 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin)-induced CYP1A1 enzyme activity. This inhibition is correlated with the capacity of the isoflavones to prevent CYP1A1-mediated covalent binding of benzo[a]pyrene (BaP) metabolites to DNA. We further evaluated daidzein and genistein, believed to be the active forms of the isoflavones, for the mechanism of the inhibitory process. Although daidzein and genistein appear structurally similar to known aromatic hydrocarbon receptor (AHR) agonists and antagonists, gel mobility shift assays indicated that the isoflavones do not inhibit dioxin-induced activation of the AHR or the accumulation of CYP1A1 mRNA, suggesting that the isoflavones do not act at the transcriptional level. We therefore evaluated the isoflavones for direct effects on the CYP1A1 enzyme. Daidzein and genistein non-competitive with the CYP1A1 substrate BaP for microsomal BaP hydroxylation, with apparent Ki values of 325 microM and 140 microM, respectively. The extent of CYP1A1 inhibition increases with time of preincubation at 37 degrees C, but not at 4 degrees C, in the presence of isoflavone plus NADPH; after 60 min preincubation the inhibition remains non-competitive, with apparent Ki values of 55 microM and 50 microM, respectively. Inhibition is neither prevented nor reversed by the thiol antioxidant dithiothreitol, nor by the iron chelator deferoxamine. Repeated washing of the microsomes does not reverse the inhibition. The dependency on NADPH, temperature and time for inhibition of CYP1A1 suggests that metabolism of either isoflavone or molecular oxygen to reactive species is required. Isoflavone-mediated inhibition of CYP1A1 activity may contribute to the mechanism by which these soybean isoflavones protect against carcinogenesis.

Mouse cytosolic class 3 aldehyde dehydrogenase (Aldh3a1): gene structure and regulation of constitutive and dioxin-inducible expression

The mouse cytosolic aldehyde dehydrogenase ALDH3A1 (encoded by the Aldh3a1 gene) has previously been shown in cell culture to be markedly inducible by 2,3,7,8,-tetrachlorodibenzo-p-dioxin (TCDD; dioxin), downregulated by the metabolism of functional CYP1A1/1A2 enzymes, and upregulated by a gene on Chr 7 that leads to endogenous oxidative stress. In order to study the regulation of Aldh3a1 gene expression, we isolated two overlapping genomic sequences from a B6/CBA mouse genomic library that included the entire Aldh3a1 gene, along with considerable 5' and 3' flanking sequences. The Aldh3a1 gene was shown to span approximately 10 kb and comprise 11 exons including a noncoding first exon. The sequence of 3.18 kb upstream of exon 1 reveals numerous consensus transcription factor-binding sites, some of which were shown to be important in the positive and negative control of Aldh3a1 gene expression; these include seven aromatic hydrocarbon response elements (AHREs), an electrophile response element (EPRE), and AP-1, C/EBP beta, c/EBP alpha, NF-kappaB, Sp1, and NF-1 putative binding sites. Deletion fusion constructs containing regions of the Aldh3a1 gene 5' flanking sequence, ligated to chloramphenicol experiments suggested that the 5' flanking region of the gene contains a strong promoter, at least four functional AHREs appear to act cooperatively in causing dioxin-mediated upregulation, and a putative negative regulatory element (NRE) controls basal gene expression independent of dioxin inducibility. The dioxin-mediated upregulation of Aldh3a1 expression in mouse hepatoma Hepa-1c1c7 cell cultures was shown to depend exclusively on the aromatic hydrocarbon receptor. acetyltransferase (CAT) or luciferase (LUC) reporter genes, were studied. Transient transfection experiments suggested that the 5' flanking region of the gene contains a strong promoter, at least four functional AHREs appear to act cooperatively in causing dioxin-mediated upregulation, and a putative negative regulatory element (NRE) controls basal gene expression independent of dioxin inducibility. The dioxin-mediated upregulation of Aldh3a1 expression in mouse hepatoma Hepa-1c1c7 cell cultures was shown to depend exclusively on the aromatic hydrocarbon receptor.

Regulation of gene expression by reactive oxygen

Reactive oxygen intermediates are produced in all aerobic organisms during respiration and exist in the cell in a balance with biochemical antioxidants. Excess reactive oxygen resulting from exposure to environmental oxidants, toxicants, and heavy metals perturbs cellular redox balance and disrupts normal biological functions. The resulting imbalance may be detrimental to the organism and contribute to the pathogenesis of disease and aging. To counteract the oxidant effects and to restore a state of redox balance, cells must reset critical homeostatic parameters. Changes associated with oxidative damage and with restoration of cellular homeostasis often lead to activation or silencing of genes encoding regulatory transcription factors, antioxidant defense enzymes, and structural proteins. In this review, we examine the sources and generation of free radicals and oxidative stress in biological systems and the mechanisms used by reactive oxygen to modulate signal transduction cascades and redirect gene expression.

Trout CYP1A3 Gene: Recognition of Fish DNA Motifs by Mouse Regulatory Proteins

: Transcriptional up-regulation of mammalian CYP1A1 genes by dioxin is known to require binding of dioxin to the Ah receptor (AHR), subsequent interaction of this ligand-receptor complex with the AHR nuclear translocator (ARNT), and binding of this heterodimer to aromatic hydrocarbon response elements (AHREs) located in the 5' flanking sequences. From the rainbow trout (Oncorhyncus mykiss), we have isolated and sequenced the CYP1A3 gene-spanning 4.0 kb and containing seven exons and six introns-and 1897 bp of the 5' flanking region. The transcription start site was determined by primer extension analysis. Five putative AHREs were found between -451 and -1820, with an overlap of AHRE3 and AHRE4 sharing 1 bp. The 5' flanking region of the trout CYP1A3 gene was fused to the firefly luciferase (luc) reporter gene and transiently transfected into mouse hepatoma Hepa-1c1c7 wild-type (wt) cell cultures and three benzo[a]pyrene-resistant mutant lines: c2, containing less than 10% levels of functional AHR; c4, defective in ARNT; and c37, deficient in CYP1A1 metabolism. We compared the trout CYP1A3 promoter-luc constructs with mouse and human CYP1A1 promoter-luc constructs. All of our trout CYP1A3 promoter data are consistent with dioxin-inducible luciferase activity being controlled by two or more AHREs via cooperativity with a GC-rich region (-1852)-as has previously been demonstrated for AHREs in mammalian CYP1A1 promoters. The dependence of trout CYP1A3 promoter activity on the AHR and on the ARNT, and the enhancement of CYP1A3 promoter activity in the absence of CYP1A1 metabolic capacity, are all similar to that with mammalian CYP1A promoters. These findings indicate that the DNA motifs in trout, and the mouse liver proteins that bind to these motifs, are evolutionarily conserved elements.

Dioxin causes a sustained oxidative stress response in the mouse

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) is the prototype for environmental agonists of the aromatic hydrocarbon receptor (AHR) that are known to produce multiple adverse effects in laboratory animals as well as humans. Although not directly genotoxic, dioxin is known to increase transformation and mutations in mammalian cell culture and to cause an exaggerated oxidative stress response in the female rat. In humans and mice, however, dioxin-mediated oxidative stress appears to be more subtle, causing a response that has been poorly characterized. Using the female C57BL/6J inbred mouse, we show here that intraperitoneal treatment of 5 micrograms TCDD per kilogram on 3 consecutive days produces a striking, prolonged oxidative stress response: hepatic oxidized glutathione levels increase 2-fold within 1 week, and these effects persist for at least 8 weeks despite no further dioxin treatment. Urinary levels of 8-hydroxydeoxyguanosine--a product of DNA base oxidation and subsequent excision repair--remain elevated about 20-fold at 8 weeks after dioxin treatment, consistent with chronic and potentially promutagenic DNA base damage. These results demonstrate that dioxin exposure does produce a sustained oxidative stress response in the mouse.

Regulation of mouse Ah receptor (Ahr) gene basal expression by members of the Sp family of transcription factors

The aromatic hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates the expression of several drug-metabolizing enzymes and has been implicated in immunosuppression, teratogenesis, cell-specific hyperplasia, and certain types of malignancies and toxicities. The mouse Ahr gene 5' proximal promoter region, which contains four potential Sp1 motifs, is required for efficient basal expression. Using a fragment spanning the region from nt -174 to +70 of the Ahr promoter, we found that four regions corresponding to four Sp1 sites were protected from DNase I digestion using nuclear extracts from MLE-12 (lung), F9 (embryonal carcinoma), Hepa-1 (hepatoma), and 41-5a (epidermal) cells. The Hepa-1 and F9 cell lines were shown by reverse transcriptase-polymerase chain reaction and Western blot to contain mRNA and protein for Sp1 and Sp3, but not Sp2 and Sp4. In electrophoretic mobility shift assays using oligonucleotide probes corresponding to the four Ahr Sp1 sites, nuclear extracts from Hepa-1 and F9 cells formed complexes that were determined immunologically to contain both Sp1 and Sp3 protein. The two Ahr proximal Sp1 sites (A and B) were shown to bind both Sp1 and Sp3 proteins, whereas the more distal sites (C and D) bound only Sp1. Competition gel shift experiments showed that sites A and B had 10-fold higher affinity for Sp factors than did sites C and D. To determine the transactivation potential of each of the four Ahr Sp1 sites, we fused the Ahr promoter to a luciferase (LUC) reporter gene and transfected the construct into the Drosophila cell line Schneider-2, which contains no Sp1 or Sp1-like factors. Cotransfection of this construct with expression plasmids for each of the Sp factors revealed that Sp3 was approximately 1.6-fold more efficient than Sp1 in Ahr transactivation. Mutation of the four Sp1 sites individually and in combination demonstrated that each site contributes to the overall level of expression of the reporter gene and that interactions between these sites play a minor role in regulation of the Ahr-LUC construct. These results suggest that basal Ahr expression may be regulated by the expression and distribution of Sp1-like factors.

Constitutive activation of the aromatic hydrocarbon receptor

The ligand-activated aromatic hydrocarbon receptor (AHR) dimerizes with the AHR nuclear translocator (ARNT) to form a functional complex that transactivates expression of the cytochrome P-450 CYP1A1 gene and other genes in the dioxin-inducible [Ah] gene battery. Previous work from this laboratory has shown that the activity of the CYP1A1 enzyme negatively regulates this process. To study the relationship between CYP1A1 activity and Ah receptor activation we used CYP1A1-deficient mouse hepatoma c37 cells and CYP1A1- and AHR-deficient African green monkey kidney CV-1 cells. Using gel mobility shift and luciferase reporter gene expression assays, we found that c37 cells that had not been exposed to exogenous Ah receptor ligands already contained transcriptionally active AHR-ARNT complexes, a finding that we also observed in wild-type Hepa-1 cells treated with Ellipticine, a CYP1A1 inhibitor. In CV-1 cells, transient expression of AHR and ARNT leads to high levels of AHR-ARNT-dependent luciferase gene expression even in the absence of an agonist. Using a green fluorescent protein-tagged AHR, we showed that elevated reporter gene expression correlates with constitutive nuclear localization of the AHR. Transcriptional activation of the luciferase reporter gene observed in CV-1 cells is significantly decreased by (i) expression of a functional CYP1A1 enzyme, (ii) competition with chimeric or truncated AHR proteins containing the AHR ligand-binding domain, and (iii) treatment with the AHR antagonist alpha-naphthoflavone. These results suggest that a CYP1A1 substrate, which accumulates in cells lacking CYP1A1 enzymatic activity, is an AHR ligand responsible for endogenous activation of the Ah receptor.

Sustained increase in intracellular free calcium and activation of cyclooxygenase-2 expression in mouse hepatoma cells treated with dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a non-genotoxic environmental pollutant that causes multiple adverse effects in experimental animals and in humans. We show here that TCDD treatment of mouse hepatoma cells causes a rapid mobilization of intracellular calcium both in wild type Hepa-1 cells and in its c2 variant, a cell line that has highly reduced levels of functional aromatic hydrocarbon (Ah) receptor (AHR). In wild type cells, but not in the c2 variant, TCDD treatment leads to a sustained elevation of cytosolic free calcium. TCDD also induces elevated levels of cyclooxygenase-2 (COX-2) mRNA in wild type and in c37, a CYP1A1-deficient cell line, but not in c2 cells. Induction of Cox-2 is in fact dependent on the presence of a functional Ah receptor, since it can be blocked by antisense oligonucleotides to Ah receptor mRNA. Most likely as a consequence of Cox-2 induction, we find a significant increase in the level of 12-hydroxyheptadecatrienoic acid (12-HHT) secreted from TCDD-treated Hepa-1 cells. In addition, we observe elevated levels of 6-keto prostaglandin F1alpha in c2 cells and high levels of secreted prostaglandin F2alpha in c2, c37 and c4, the variant cell line lacking aromatic hydrocarbon nuclear translocator protein. These data suggest that Cox-2 activation by TCDD leads to the release of prostaglandins, eicosanoids and other mediators which may have an important role in the biological and toxic effects of TCDD.

Lack of high affinity fiber receptor activity explains the resistance of ciliated airway epithelia to adenovirus infection

Although recombinant adenoviruses are attractive vectors for gene transfer to airway epithelia, they have proven to be relatively inefficient. To investigate the mechanisms of adenovirus-mediated gene transfer to airway epithelia, we examined the role of adenovirus fiber and penton base, the two proteins involved in attachment to and entry of virus into the cell. We used human airway epithelia grown under conditions that allow differentiation and development of a ciliated apical surface that closely resembles the in vivo condition. We found that addition of fiber protein inhibited virus binding and vector-mediated gene transfer to immature airway epithelia, as well as to primary cultures of rat hepatocytes and HeLa cells. However, fiber protein had no effect on vector binding and gene transfer to ciliated airway epithelia. We obtained similar results with addition of penton base protein: the protein inhibited gene transfer to immature epithelia, whereas there was no effect with ciliated epithelia. Moreover, infection was not attenuated with an adenovirus containing a mutation in penton base that prevents the interaction with cell surface integrins. These data suggest that the receptors required for efficient infection by adenovirus are either not present or not available on the apical surface of ciliated human airway epithelia. The results explain the reason for inefficient gene transfer and suggest approaches for improvement.

Lack of high affinity fiber receptor activity explains the resistance of ciliated airway epithelia to adenovirus infection

Although recombinant adenoviruses are attractive vectors for gene transfer to airway epithelia, they have proven to be relatively inefficient. To investigate the mechanisms of adenovirus-mediated gene transfer to airway epithelia, we examined the role of adenovirus fiber and penton base, the two proteins involved in attachment to and entry of virus into the cell. We used human airway epithelia grown under conditions that allow differentiation and development of a ciliated apical surface that closely resembles the in vivo condition. We found that addition of fiber protein inhibited virus binding and vector-mediated gene transfer to immature airway epithelia, as well as to primary cultures of rat hepatocytes and HeLa cells. However, fiber protein had no effect on vector binding and gene transfer to ciliated airway epithelia. We obtained similar results with addition of penton base protein: the protein inhibited gene transfer to immature epithelia, whereas there was no effect with ciliated epithelia. Moreover, infection was not attenuated with an adenovirus containing a mutation in penton base that prevents the interaction with cell surface integrins. These data suggest that the receptors required for efficient infection by adenovirus are either not present or not available on the apical surface of ciliated human airway epithelia. The results explain the reason for inefficient gene transfer and suggest approaches for improvement.

Human Ah receptor (AHR) gene: localization to 7p15 and suggestive correlation of polymorphism with CYP1A1 inducibility

The mammalian aromatic hydrocarbon receptor (AHR) is a ubiquitous ligand-activated transcription factor. AHR ligands include 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin), benzo[a]pyrene, and polychlorinated and polybrominated biphenyls; the endogenous ligand is not yet known. Following ligand binding, the AHR transcriptionally activates genes encoding drug-metabolizing enzymes important in both the metabolic potentiation of substrates to genotoxic reactive intermediates and ultimate carcinogens, and the detoxification of toxic or carcinogenic drugs and other environmental pollutants. AHR-mediated gene expression is also involved in many critical life processes (e.g. cell type-specific differentiation, cell division, apoptosis) by signal transduction mechanisms. Similar to mice, human populations exhibit a > 20-fold range of the CYP1A1 inducibility/AHR affinity phenotype. In the present study, we localized the human AHR gene to chromosome 7p15, using fluorescence in situ hybridization (FISH). Performing linkage analysis in a three-generation family, we show with good probability that the high CYP1A1 inducibility phenotype segregates with the 7p15 region. Sequencing 93 nt (31 amino acids) of the human AHR gene's exon 9, which is the region correlated with the mouse A375V polymorphism responsible for the major portion of high vs low CYP1A1 inducibility/AHR affinity, we found no nucleotide differences; Val-381 was present in all five individuals examined (four related and one unrelated), two of whom show "high' and three of whom show "low' CYP1A1 inducibility. These data indicate that the "high' and "low' CYP1A1 inducibility trait, in the population studied, cannot be explained by a difference among these 31 amino acids in exon 9 of the AHR gene.

Genetic polymorphisms in human drug-metabolizing enzymes: potential uses of reverse genetics to identify genes of toxicological relevance

The human mind was engaged with fundamental questions on the nature of heredity long before the study of genetics became a scientific discipline. Many traits, such as height, eye color, blood pressure, or cancer susceptibility, have been known to run in families, although the genes or combination of genes that underlie these observable characteristics remain unknown in most cases. Differences in susceptibility to environmental agents in humans are likewise determined by variations in genetic background--genetic polymorphisms. In this article, we review the current status of studies on human polymorphisms in drug-metabolizing enzymes and discuss various approaches to the analysis of genetic polymorphisms. We expect that in the near future, novel methods in genetic analysis of human populations will be likely to play a key role in the identification of genes of toxicological relevance.

Dioxin induces transcription of fos and jun genes by Ah receptor-dependent and -independent pathways

Halogenated aromatic hydrocarbons, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin), and polycyclic aromatic hydrocarbons, such as benzo[a]pyrene, are environmental contaminants that cause many apparently unrelated toxic effects. In a previous study, we have shown that treatment of mouse hepatoma cells with TCDD or B(a)P results in an increase in mRNA levels of the immediate-early protooncogenes c-fos, c-jun, junB, and junD, and the concomitant increase of the DNA-binding activity of the transcription factor AP-1, a dimer of FOS and JUN proteins. To analyze the mechanism of fos/jun activation by TCDD we have used electrophoretic mobility shift and transient expression assays of reporter gene constructs containing response elements for 12-O-tetradecanoyl-phorbol-13-acetate (TRE), serum (SRE), cAMP (CRE), and aromatic hydrocarbons (AhRE) from the fos and jun genes fused to the firefly luciferase gene under the control of the SV40 minimal promoter. In mouse hepatoma Hepa-1 cells, which have Ah receptor (AHR) and Ah receptor nuclear translocator (ARNT) proteins, inclusion of TRE, SRE, and the AhRE motifs from c-jun and junD, but not CRE or the AhREs from c-fos, fosB, and junB, causes a large TCDD-dependent increase in luciferase expression. In agreement with these results, c-jun and junD, but not c-fos, fosB, and junB AhREs, competed with a canonical Cyp1A1 AhRE for binding to the AHR ARNT heterodimeric complex. In African Green Monkey CV-1 cells, which lack AHR, expression plasmids with AhRE motifs require coexpression of AHR and ARNT for TCDD to stimulate luciferase expression. In contrast, SRE-containing expression plasmids respond equally well to TCDD whether or not AHR and ARNT are coexpressed. These results suggest that TCDD induces expression of the immediate-early response genes fos and jun by activation of possibly three separate signal transduction pathways, at least one of which does not require a functional Ah receptor complex.

Differential regulation of mouse Ah receptor gene expression in cell lines of different tissue origins

The dioxin-binding Ah receptor (AHR) is a ligand-activated transcription factor that regulates the expression of several drug-metabolizing enzymes and has been implicated in immunosuppression, teratogenesis, cell-specific hyperplasia, and certain types of malignancies and toxicities. In order to examine tissue-specific regulation of the mouse Ah receptor gene (Ahr), we studied chimeric deletion constructs, containing the Ahr 5' flanking region and the firefly luciferase reporter gene (Luc). Transient transfection assays were performed in five established mouse cell lines: Hepa-1c1c7 (derived from hepatoma), JB6-C1 41-5a (epidermis), MLE-12 (lung epithelium), F9 (embryonal carcinoma), and NIH/3T3 (fibroblasts). Treatment of the cell lines included: dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin), retinoic acid (RA), cyclic adenosine 3':5'-monophosphate (cAMP), or 12-O-tetradecanoylphorbol 13-acetate (TPA). Expression levels of Luc varied widely from one untreated cell line to another, this finding was also confirmed by measurements of AHR mRNA steady-state levels. In all cell lines except F9 cells, maximal constitutive expression was observed with constructs containing 78 bp of Ahr promoter sequences, which include several putative binding sites for the transcription factor Sp1. In contrast, in F9 cells, inclusion of sequences between -174 and -78 resulted in a fourfold stimulation of constitutive expression, suggesting that other transcription factors are important in Ahr gene expression in these cells. In MLE-12 and 41-5a cells, expression was significantly decreased by treatment with dioxin, RA, cAMP, or TPA. A similar inhibitory effect was observed in cAMP-treated MLE-12 and F9 cells; this result was confirmed by RT-PCR measurements of AHR mRNA steady-state levels. These results indicate that both up- and down-regulation of the Ahr gene occur and exhibit tissue-and cell-type specificity.

Human drug-metabolizing enzyme polymorphisms: effects on risk of toxicity and cancer

A growing number of human genetic polymorphisms in drug-metabolizing enzymes (DMEs) are being characterized. Some of these have been shown, quite convincingly, to be correlated with risk of toxicity or cancer, whereas others presently remain equivocal. There is good evidence that the correlation is stronger in populations exposed to a variety of environmental procarcinogens; perhaps 30% of DME substrates are able to be metabolically potentiated. Phase I DMEs, most of which represent cytochromes P450, metabolically activate procarcinogens to genotoxic electrophilic intermediates, and Phase II DMEs conjugate the intermediates to water-soluble derivatives, completing the detoxification cycle. It follows that genetic differences in the regulation, expression and activity of genes coding for Phase I and Phase II DMEs would be crucial factors in defining cancer susceptibility and the toxic or carcinogenic power of environmental chemicals. Not all Phase I and Phase II DMEs are implicated in detoxification; previous work from this and from other laboratories has identified candidate Phase I and Phase II genes in which certain alleles are more likely to be associated with cancer susceptibility. In some cases, the allelic frequencies vary dramatically between ethnic groups. In this review, our current knowledge about polymorphisms in the following genes are updated: the aromatic hydrocarbon receptor (AHR), the CYP1A1 structural gene (which encodes aryl hydrocarbon hydroxylase activity), the CYP1A2 structural gene (arylamine oxidations), the CYP2C19 gene (S-mephenytoin 4'-hydroxylase), the CYP2D6 gene (debrisoquine hydroxylase), the CYP2E1 gene (N,N-dimethylnitrosamine N-demethylase), the null mutant for the GSTM1 gene (glutathione transferase mu), and the NAT2 gene (arylamine N-acetyltransferase). If unequivocal biomarkers of genetic susceptibility to cancer and toxicity can be developed successfully, then identification of individuals at increased risk would be very helpful in the fields of public health and preventive medicine.

Cyp1a2(-/-) null mutant mice develop normally but show deficient drug metabolism

Cytochrome P450 1A2 (CYP1A2) is a predominantly hepatic enzyme known to be important in the metabolism of numerous foreign chemicals of pharmacologic, toxicologic, and carcinogenic significance. CYP1A2 substrates include aflatoxin B1, acetaminophen, and a variety of environmental arylamines. To define better the developmental and metabolic functions of this enzyme, we developed a CYP1A2-deficient mouse line by homologous recombination in embryonic stem cells. Mice homozygous for the targeted Cyp1a2 gene, designated Cyp1a2(-/-), are completely viable and fertile; histologic examination of 15-day embryos, newborn pups, and 3-week-old mice revealed no abnormalities. No CYP1A2 mRNA was detected by Northern blot analysis. Moreover, mRNA levels of Cyp1a1, the other gene in the same subfamily, appear unaffected by loss of the Cyp1a2 gene. Because the muscle relaxant zoxazolamine is a known substrate for CYP1A2, we studied the Cyp1a2(-/-) genotype by using the zoxazolamine paralysis test: the Cyp1a2(-/-) mice exhibited dramatically lengthened paralysis times relative to the Cyp1a2(+/+) wild-type animals, and the Cyp1a2(+/-) heterozygotes showed an intermediate effect. Availability of a viable and fertile CYP1A2-deficient mouse line will provide a valuable tool for researchers wishing to define the precise role of CYP1A2 in numerous metabolic and pharmacokinetic processes.

The Y-box motif mediates redox-dependent transcriptional activation in mouse cells

We show here that the OxyR response element (ORE) in the bacterial oxyR promoter can also function as a redox-dependent enhancer in mammalian cells. Fusion of ORE to an SV40 basal promoter driving chloramphenicol acetyltransferase (CAT) expression confers H2O2 inducibility to expression of the cat gene in mouse Hepa-1 hepatoma cells. Nuclear extracts from these cells contain DNA-binding proteins that specifically interact with ORE DNA, cannot be completed by cognate oligonucleotides to AP-1 or NF kappa B, and are constitutively expressed, since treatment with H2O2 causes no detectable changes in binding activity or DNA-protein interaction. Recombinant cDNA clones that express ORE-binding proteins were isolated from a mouse hepatoma expression library and found to be representatives of two different members of the murine Y-box family of transcription factors. Canonical Y-box and ORE oligonucleotides compete with each other for binding to Y-box proteins in gel shift assays and antibodies to FRGY2, a Xenopus Y-box protein, supershift both Y-box and ORE DNA-protein complexes. In addition, antisense oligonucleotides to mouse YB-1 mRNA abolish induction of ORE-mediated cat expression by H2O2, and luciferase reporter constructs containing ORE, or the Y-box from the human MHC class II HLA-DQ gene, exhibit identical dose-dependent H2O2 inducibilities, which can be abolished by addition of 2-mercaptoethanol to the culture medium. These results suggest that the Y-box proteins may be an integral component of a eukaryotic redox signaling pathway.

Interaction between the Ah receptor and proteins binding to the AP-1-like electrophile response element (EpRE) during murine phase II [Ah] battery gene expression

We have studied three Phase II genes in the mouse dioxin-inducible [Ah] battery: Nmo1 [encoding NAD(P)H:menadione oxidoreductase], Ahd4 (encoding the cytosolic aldehyde dehydrogenase ALDH3c), and Ugt1*06 (a UDP glucuronosyltransferase). Oxidant-induced Nmo1 gene expression in the c14CoS/c14CoS mouse appears likely to be caused by homozygous loss of the fumarylacetoacetate hydrolase (Fah) gene on Chr 7 and absence of the enzyme (FAH), which leads to increased levels of endogenous tyrosine oxidative metabolites. We show here that increases in [Ah] Phase II gene expression in the 14CoS/14CoS mouse are correlated with an AP-1-like DNA motif called the electrophile response element (EpRE), which has been found in the 5' flanking regulatory regions of all murine (Ah) Phase II genes. Aromatic hydrocarbon response element (AhREs) are responsible for dioxin-mediated upregulation of all six [Ah] battery genes, and one or more AhREs have been found in the 5' flanking regulatory regions of all of these [Ah] genes. Gel mobility shift assays, with a synthetic oligonucleotide probe corresponding to the EpRE, show that EpRE-binding proteins are more than twice as abundant in 14CoS/14CoS than in the wild-type ch/ch nuclear extracts. Competition studies of EpRE-specific binding with an excess of EpRE, mutated EpRE, AP-1, AhRE3, mutated AhRE3, and C/EBP alpha oligonucleotides suggest that several common transcriptional factors bind to the EpRE and AhRE3 motifs. Two monospecific antibodies to the Ah receptor (AHR) protein block formation of an EpRE-specific complex on gel mobility electrophoresis. These data suggest that AHR (or AHR-related protein) might be an integral part of the EpRE-binding transcriptional complex associated with the oxidative stress response. To our knowledge, this is among the first reports of the same transcription factor operating at two different response elements upstream of a single gene.

Dioxin activates HIV-1 gene expression by an oxidative stress pathway requiring a functional cytochrome P450 CYP1A1 enzyme

We have studied the effect of several environmental chemicals on the transient expression of a chloramphenicol acetyltransferase (cat) reporter gene linked to the promoter sequences in the long terminal repeat (LTR) of the human immunodeficiency virus type 1 (HIV-1). Aflatoxin B1, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) and benzo[a]pyrene cause a significant increases in CAT expression in mouse hepatoma Hepa-1 cells. The induction of CAT after TCDD treatment is abolished by administration of N-acetyl-L-cysteine or 2-mercaptoethanol and does not take place in a mutant cell line that lacks CYP1A1 enzymatic activity. Linker-scanning mutational analysis of transcription factor binding sites in the promoter revealed that both the NF kappa B and an adjacent aromatic hydrocarbon response element (AhRE) are required for TCDD-dependent CAT expression. In addition, mutation of the NFAT/AP-1 binding sites in the negative regulatory region of the promoter increases the magnitude of the TCDD effect. We conclude that induction of a functional CYP1A1 monooxygenase by TCDD stimulates a pathway that generates thiol-sensitive reactive oxygen intermediates which, in turn, are responsible for the TCDD-dependent activation of genes linked to the LTR. These data might provide an explanation for findings that TCDD increases infectious HIV-1 titers in experimental systems and for epidemiologic reports suggesting that exposure to aromatic hydrocarbons, such as found in cigarette smoke, is associated with an acceleration in AIDS progression.

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.

Interaction of the regulatory domains of the murine Cyp1a1 gene with two DNA-binding proteins in addition to the Ah receptor and the Ah receptor nuclear translocator (ARNT)

The aromatic hydrocarbon (Ah) receptor complex is a ligand-activated transcriptional activator consisting of at least two protein components. The ligand-binding component is the AhR protein, a cytosolic receptor encoded by the Ahr gene, which, upon ligand binding, translocates to the nucleus in a heterodimeric complex with the ARNT (Ah receptor nuclear translocator) component. The complex binds to several discrete DNA domains containing aromatic hydrocarbon responsive elements (AhRE) present in the regulatory region of the murine cytochrome P(1)450 Cyp1a1 gene and of the other genes in the [Ah] gene battery. As a consequence of binding, a transcriptional complex is formed that activates the expression of these genes by as yet unidentified mechanisms. We have analyzed DNA-protein interactions in four of these domains, specifically, the AhREs located between -1085 and -482 (sites A, C, E, and D) of the upstream regulatory region of the murine Cyp1a1 gene. We found that two DNA-binding proteins, present in cytosolic and nuclear extracts of mouse Hepa-1 cells, showed overlapping DNA-binding specificities to those of the Ah receptor. One of these proteins had an apparent molecular mass of 35-40 kDa, bound only to AhRE3 (site D), and has been identified tentatively as a member of the C/EBP family of transcription factors. The second protein, purified by DNA-affinity chromatography, had an apparent molecular mass of 95 kDa and bound to a larger DNA motif that included the AhRE sequence, in AhRE3 and AhRE5 (sites D and A), but not in AhRE1 or AhRE2 (sites C and E). This protein was not AhR nor was it ARNT, since it was found in receptorless (Ahr-) and in nuclear translocation-defective (Arnt-) cells, as well as in cells that had not been exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin), a potent inducer of Cyp1a1 expression. Evidence from in vivo methylation protection indicated that two G residues flanking AhRE3, one of which is required for binding of the 95-kDa protein, may be protected from methylation in uninduced cells and become exposed upon dioxin treatment, suggesting that the 95-kDa protein may be constitutively bound to AhRE3, and be displaced by binding of the Ah receptor complex. These results lend support to the concept that the transcriptional regulation of the [Ah] battery genes could be modulated by combinatorial interactions of the Ah receptor complex with other transcription factors.

Regulation of [Ah] gene battery enzymes and glutathione levels by 5,10-dihydroindeno[1,2-b]indole in mouse hepatoma cell lines

The murine aromatic hydrocarbon ([Ah]) gene battery consists of at least six genes that code for two functionalizing (Phase I) enzymes and four non-functionalizing (Phase II) enzymes. These enzymes are induced by compounds such as aromatic hydrocarbons and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) that bind to the cytosolic Ah receptor protein. Studies in rodents indicate that certain enzymes of this battery, namely cytochrome P4501A1 (CYP1A1), UDP-glucuronosyltransferase (UGT1*06) and NAD(P)H: quinone acceptor oxidoreductase (NMO1) are induced by the synthetic antioxidant 5,10-dihydroindeno[1,2-b]indole (DHII). The induction of [Ah] gene battery enzymes and the levels of reduced glutathione (GSH) were examined in mouse Hepa-1c1c7 hepatoma wild-type cells (wt), a CYP1A1 metabolism-deficient mutant (c37) and an Ah receptor nuclear translocation-defective mutant (c4). DHII and TCDD increased the activities of ethoxyresorufin O-deethylase, an indicator of CYP1A1 activity, as well as NMO1, UGT1*06, cytosolic aldehyde dehydrogenase class 3 and glutathione S-transferase form A1 in wt cells, but had little or no induction effect in c37 or c4 cells. DHII and TCDD differed in their effects on GSH levels; while DHII increased GSH levels 3-fold in wt, but not at all in c37 or c4 cells, TCDD had no effect on GSH levels in any cell type. However, GSH levels were enhanced in both wt and c4 cells by tert-butyl hydroquinone (TBHQ). L-Buthionine S,R-sulfoximine, an inhibitor of gamma-glutamylcysteine synthetase, prevented DHII-induced increases in wt cell GSH. The increase in GSH levels occurred after 8 h, while the induction of enzymes occurred within 4 h. The induction of the higher GSH levels in wt cells by DHII and TBHQ correlated with increases in intracellular levels of the GSH precursor thiol cysteine, as well as with increased activities of gamma-glutamylcysteine synthetase, the rate-limiting enzyme of GSH synthesis. However, TBHQ-mediated GSH increases in c4 cells were accompanied by increased gamma-glutamylcysteine synthetase activity with no change in intracellular cysteine concentration. The results suggest that DHII induction of [Ah] gene battery enzymes requires a functional Ah receptor, but not the functional gene product CYP1A1. Furthermore, metabolism, possibly via CYP1A1, appears to be required for DHII to enhance intracellular levels of cysteine and GCS activity that result in higher GSH levels.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is expressed in mouse skin in response to tumor-promoting agents and modulates dermal inflammation and epidermal dark cell numbers

In mouse dorsal skin multistage carcinogenesis models, tumor promotion can be mediated by chemical agents, but also by wounding or abrasion of the epidermis, suggesting that endogenous growth factors mediate this process. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is one such factor that has been reported to be produced by keratinocytes in vitro, and has been suggested both to stimulate keratinocyte proliferation, and also to be a chemoattractant for neutrophils and macrophages. In this study we examined the expression and function of GM-CSF in mouse skin following the application of tumor-promoting agents. Both single and multiple applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in accumulation of GM-CSF mRNA in the epidermis. Various phorbol and non-phorbol ester tumor promoters were found to induce increases in epidermal GM-CSF mRNA levels commensurate with their relative tumor promoting capabilities. Fluocinolone acetonide (FA) and tosyl phenylalanine chloromethyl ketone (TPCK), inhibitors of tumor promotion, inhibited tumor promoter-mediated GM-CSF accumulation, whereas all-trans-retinoic acid (RA) enhanced the TPA-induced increase. The retinoic acid analogue RO-109359 which, unlike RA, does not have tumor promoting activity per se, inhibited the TPA-induced increase in epidermal GM-CSF mRNA levels. When an antibody specific to GM-CSF was administered prior to TPA, the promoter-induced dermal inflammation and increase in epidermal dark cell number were reduced, yet promoter-induced epidermal hyperplasia was not. These findings implied that elevation of GM-CSF levels plays an important role in chemically-mediated mouse skin tumor promotion and principally via effects on promoter-induced inflammation and increased epidermal dark cell number.

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.

The 5' untranslated region of the human gamma-glutamyl transferase mRNA contains a tissue-specific active translational enhancer

We report the functional and structural analysis of the 5' untranslated region (5'UTR) of human hepatoma HepG2 gamma-glutamyltransferase (GGT) mRNA. Transient expression of a hybrid GGT-luciferase gene in HepG2, MIA-Pa-Ca-2 and MG 63 cell lines shows that this 5'UTR acts as a tissue-specific translational enhancer. Evidence for transcripts with multiple 5'UTR coding for HepG2 GGT was obtained by RNase protection. Computer analysis of this 5'UTR detected the existence of a stable stem and loop structure containing multiple steroid modulatory elements.

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.

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.