In vivo architecture of the manganese superoxide dismutase promoter

Concentration of Zinc, Copper, Selenium, Manganese, and Cu/Zn Ratio in Hair of Children and Adolescents with Myopia

The aim of this work was to determine the concentration of trace elements, zinc, copper, selenium, manganese, and Cu/Zn ratio, in scalp hair samples of children and adolescents with myopia. The study included 92 children (mean age 14.5 ± 2.5 years) with myopia and 43 healthy persons (mean age 11.8 ± 4.7 years). Each patient had a complete eye examination. Trace element concentrations in hair were determined by atomic absorption spectrometry. Cu/Zn ratio was also calculated. The zinc level in the hair of myopic patients was significantly higher (260 µg/g) in comparison to the control group (130 µg/g). There was a significantly lower Cu/Zn ratio in myopic patients (0.045) compared with controls (0.07). An insignificant difference was observed in the hair level of copper, selenium, and manganese between patients and controls. The results show that trace elements may play a significant role in the pathogenesis of myopia. Further studies should pay more attention to determine the effect of trace element on children myopia.

Serum Concentration of Zinc, Copper, Selenium, Manganese, and Cu/Zn Ratio in Children and Adolescents with Myopia

The purpose of the present study was the assessment of the serum concentration of antioxidant microelements-zinc, copper, selenium, manganese, and Cu/Zn ratio in children and adolescents with myopia. Eighty-three children were examined (mean age 14.36 ± 2.49 years) with myopia. The control group was 38 persons (mean age 12.89 ± 3.84 years). Each patient had complete eye examination. The serum concentration of zinc, copper, manganese, and selenium was determined by atomic absorption spectrometry. Cu/Zn ratio, which is the indicator of the oxidative stress, was also calculated. The average serum concentration of zinc in myopic patients was significantly lower (0.865 ± 0.221 mg L^-1) in comparison to the control group (1.054 ± 0.174 mg L^-1). There was significantly higher Cu/Zn ratio in myopic patients (1.196 ± 0.452) in comparison to that in the control group (0.992 ± 0.203). The average serum concentration of selenium in the study group was significantly lower (40.23 ± 12.07 μg L^-1) compared with that in the control group (46.00 ± 12.25 μg L^-1). There were no essential differences between serum concentration of copper and manganese in the study group and the control group. Low serum concentration of zinc and selenium in myopic children may imply an association between insufficiency of these antioxidant microelements and the development of the myopia and could be the indication for zinc and selenium supplementation in the prevention of myopia. Significantly, higher Cu/Zn ratio in the study group can suggest the relationship between myopia and oxidative stress.

Estimation of toxic elements in the samples of different cigarettes and their effect on the essential elemental status in the biological samples of Irish smoker rheumatoid arthritis consumers

Cigarette smoking interferes with the metal homeostasis of the human body, which plays a crucial role for maintaining the health. A significant flux of heavy metals, among other toxins, reaches the lungs through smoking. In the present study, the relationship between toxic element (TE) exposure via cigarette smoking and rheumatoid arthritis incidence in population living in Dublin, Ireland, is investigated. The trace {zinc (Zn), copper (Cu), manganese (Mn), and selenium (Se)} and toxic elements arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) were determined in biological (scalp hair and blood) samples of patients diagnosed with rheumatoid arthritis, who are smokers living in Dublin, Ireland. These results were compared with age- and sex-matched healthy, nonsmoker controls. The different brands of cigarette (filler tobacco, filter, and ash) consumed by the studied population were also analyzed for As, Cd, Hg, and Pb. The concentrations of trace and TEs in biological samples and different components of cigarette were measured by inductively coupled plasma mass spectrophotometer after microwave-assisted acid digestion. The validity and accuracy of the methodology were checked using certified reference materials. The recovery of all the studied elements was found to be in the range of 96.4-99.8% in certified reference materials. The filler tobacco of different branded cigarettes contains Hg, As, Cd, and Pb concentrations in the ranges of 9.55-12.4 ng, 0.432-0.727 μg, 1.70-2.12 μg, and 0.378-1.16 μg/cigarette, respectively. The results of this study showed that the mean values of As, Cd, Hg, and Pb were significantly higher in scalp hair and blood samples of rheumatoid arthritis patients as compare to healthy controls, while Zn, Cu, Mn, and Se concentrations were found to be lower in rheumatoid arthritis patients, the difference was significant in the case of smoker patients (p<0.001). The levels of four toxic elements were 2-3-folds higher in scalp hair and blood samples of nonrheumatoid arthritis smoker subjects as compared to nonsmoker controls. The high exposure of toxic metals as a result of cigarette smoking may be synergistic with risk factors associated with rheumatoid arthritis.

A TEAD1/p65 complex regulates the eutherian-conserved MnSOD intronic enhancer, eRNA transcription and the innate immune response

Manganese superoxide dismutase (MnSOD), a critical anti-oxidant enzyme, detoxifies the mitochondrial-derived reactive oxygen species, superoxide, elicited through normal respiration or the inflammatory response. Proinflammatory stimuli induce MnSOD gene expression through a eutherian-conserved, intronic enhancer element. We identified two prototypic enhancer binding proteins, TEAD1 and p65, that when co-expressed induce MnSOD expression comparable to pro-inflammatory stimuli. TEAD1 causes the nuclear sequestration of p65 leading to a novel TEAD1/p65 complex that associates with the intronic enhancer and is necessary for cytokine induction of MnSOD. Unlike typical NF-κB-responsive genes, the induction of MnSOD does not involve p50. Beyond MnSOD, the TEAD1/p65 complex regulates a subset of genes controlling the innate immune response that were previously viewed as solely NF-κB-dependent. We also identified an enhancer-derived RNA (eRNA) that is induced by either proinflammatory stimuli or the TEAD1/p65 complex, potentially linking the intronic enhancer to intra- and interchromosomal gene regulation through the inducible eRNA.

Modulation of MnSOD in Cancer:Epidemiological and Experimental Evidence

Since it was first observed in late 1970s that human cancers often had decreased manganese superoxide dismutase (MnSOD) protein expression and activity, extensive studies have been conducted to verify the association between MnSOD and cancer. Significance of MnSOD as a primary mitochondrial antioxidant enzyme is unquestionable; results from in vitro, in vivo and epidemiological studies are in harmony. On the contrary, studies regarding roles of MnSOD in cancer often report conflicting results. Although putative mechanisms have been proposed to explain how MnSOD regulates cellular proliferation, these mechanisms are not capitulated in epidemiological studies. This review discusses most recent epidemiological and experimental studies that examined the association between MnSOD and cancer, and describes emerging hypotheses of MnSOD as a mitochondrial redox regulatory enzyme and of how altered mitochondrial redox may affect physiology of normal as well as cancer cells.

A distal enhancer controls cytokine-dependent human cPLA2α gene expression

Specific control of group IVA cytosolic phospholipase A2 (cPLA2α or PLA2G4A) expression modulates arachidonic acid production, thus tightly regulating the downstream effects of pro- and anti-inflammatory eicosanoids. The significance of this pathway in human disease is apparent in a range of pathologies from inflammation to tumorigenesis. While much of the regulation of cPLA2α has focused on posttranslational phosphorylation of the protein, studies on transcriptional regulation of this gene have focused only on proximal promoter regions. We have identified a DNase I hypersensitive site encompassing a 5' distal enhancer element containing a highly conserved consensus AP-1 site involved in transcriptional activation of cPLA2α by interleukin (IL)-1β. Chromatin immunoprecipitation (ChIP), knockdown, knockout, and overexpression analyses have shown that c-Jun acts both in a negative and positive regulatory role. Transcriptional activation of cPLA2α occurs through the phosphorylation of c-Jun in conjunction with increased association of C/EBPβ with the distal novel enhancer. The association of C/EBPβ with the transcriptional activation complex does not require an obvious DNA binding site. These data provide new and important contributions to the understanding of cPLA2α regulation at the transcriptional level, with implications for eicosanoid metabolism, cellular signaling, and disease pathogenesis.

Epigenetic modification of Sod2 in the development of diabetic retinopathy and in the metabolic memory: role of histone methylation

PURPOSE

Mitochondrial superoxide levels are elevated in the retina in diabetes, and their scavenging enzyme, MnSOD, becomes subnormal. The objective of this study is to investigate the role of histone methylation of Sod2, the gene that encodes MnSOD, in the development of diabetic retinopathy and in the metabolic memory phenomenon associated with its continued progression after termination of hyperglycemia.

METHODS

Effect of high glucose on monomethyl H3K4 (H3K4me1), dimethyl H3K4 (H3K4me2), and lysine-specific demethylase-1 (LSD1) was quantified at Sod2 by chromatin immunoprecipitation in isolated retinal endothelial cells. The role of histone methylation in the metabolic memory phenomenon was investigated in the retina of rats maintained in poor glycemic control (PC, approximately 12% glycated hemoglobin [GHb]) for 3 months followed by in good glycemic control (GC, approximately 6% GHb) for 3 months.

RESULTS

Hyperglycemia reduced H3K4me1 and -me2, and increased the binding of LSD1 and Sp1 at Sod2. Regulation of LSD1 by LSD1-siRNA ameliorated glucose-induced decrease in H3K4 methylation at Sod2, and prevented decrease in Sod2 gene expression. In rats, re-institution of GC failed to reverse decrease in H3K4me1 and -me2 at Sod2, and LSD1 remained active with increased binding of LSD1 and Sp1 at Sod2. Retina from human donors with diabetic retinopathy also had decreased H3K4me2 and increased LSD1 at Sod2.

CONCLUSIONS

Histone methylation of retinal Sod2 has an important role in the development of diabetic retinopathy and in the metabolic memory phenomenon associated with its continued progression. Targeting enzymes important for histone methylation may serve as a potential therapy to halt the development of diabetic retinopathy.

Cocoa intake attenuates oxidative stress associated with rat adjuvant arthritis

Cocoa contains flavonoids with antioxidant properties. The aim of this study was to ascertain the effect of cocoa intake on oxidative stress associated with a model of chronic inflammation such as adjuvant arthritis. Female Wistar rats were fed with a 5% or 10% cocoa-enriched diet or were given p.o. a quercetin suspension every other day for 10 days. Arthritis was induced by a heat-killed Mycobacterium butyricum suspension. Reactive oxygen species (ROS) produced by macrophages, and splenic superoxide dismutase (total, cytoplasmic and mitochondrial) and catalase activities were determined. Clinically, joint swelling in arthritic rats was not reduced by antioxidants; however, the 5% cocoa diet and quercetin administration reduced ROS production. Moreover, the 5% cocoa diet normalized the activities of superoxide dismutase and catalase. In conclusion, a cocoa diet reduces the oxidative stress associated with a chronic inflammatory pathology, although it was not enough to attenuate joint swelling.

Regulation of human microsomal prostaglandin E synthase-1 by IL-1β requires a distal enhancer element with a unique role for C/EBPβ

The studies of PGE2 (prostaglandin E2) biosynthesis have focused primarily on the role of cyclo-oxygenases. Efforts have shifted towards the specific PGE2 terminal synthases, particularly mPGES-1 (microsomal PGE synthase 1), which has emerged as the crucial inducible synthase with roles in pain, cancer and inflammation. mPGES-1 is induced by pro-inflammatory cytokines with studies focusing on the proximal promoter, mediated specifically through Egr-1 (early growth-response factor 1). Numerous studies demonstrate that the mPGES-1 promoter (PTGES) alone cannot account for the level of IL-1β (interleukin 1β) induction. We identified two DNase I-hypersensitive sites within the proximal promoter near the Egr-1 element and a novel distal site near −8.6 kb. Functional analysis of the distal site revealed two elements that co-operate with basal promoter expression and a stimulus-dependent enhancer. A specific binding site for C/EBPβ (CCAAT/enhancer-binding protein β) in the enhancer was directly responsible for inducible enhancer activity. ChIP (chromatin immunoprecipitation) analysis demonstrated constitutive Egr-1 binding to the promoter and induced RNA polymerase II and C/EBPβ binding to the promoter and enhancer respectively. Knockout/knockdown studies established a functional role for C/EBPβ in mPGES-1 gene regulation and the documented interaction between Egr-1 and C/EBPβ highlights the proximal promoter co-operation with a novel distal enhancer element in regulating inducible mPGES-1 expression.

Association between essential trace and toxic elements in scalp hair samples of smokers rheumatoid arthritis subjects

The incidence of rheumatoid arthritis (RA) has been increased among people who possess habit of tobacco smoking. In the present study, zinc (Zn), copper (Cu), manganese (Mn), lead (Pb) and cadmium (Cd) were determined in scalp hair samples of smokers and nonsmokers RA patients, residents of Dublin, Ireland. For comparison purposes scalp hair samples of age and sex matched healthy smokers and nonsmokers were also analyzed. The concentrations of understudied elements were measured by inductive coupled plasma atomic emission spectrophotometer, prior to microwave assisted acid digestion. The validity and accuracy of methodology was checked using certified reference material (NCS ZC 81002b) and by the conventional wet acid digestion method on the same certified reference material and on real samples. The mean hair Zn, Cu and Mn contents were significantly lower in smokers and nonsmokers RA patients as compared to healthy individuals (p=0.01-0.001). Whereas the concentrations of Cd and Pb were significantly higher in scalp hair samples of RA patients of both group (p<0.001). The referent smokers have high level of Cd and Pb in their scalp hair samples as compared to those had not smoking tobacco (p<0.01). The ratio of Cd and Pb to Zn, Cu and Mn in scalp hair samples was also calculated. The Cd/Zn ratio was higher in smoker RA patients with related to nonsmoker RA and referents. This study is compelling evidence in support of positive associations between toxic elements, cigarette smoking, deficiency of essential trace elements and risk of arthritis.

Epigenetic changes in mitochondrial superoxide dismutase in the retina and the development of diabetic retinopathy

OBJECTIVE

To investigate the role of epigenetic regulation of the manganese superoxide dismutase gene (sod2) in the development of diabetic retinopathy and the metabolic memory phenomenon associated with its continued progression after hyperglycemia is terminated.

RESEARCH DESIGN AND METHODS

Streptozotocin-induced diabetic rats were maintained in poor glycemic control (PC, GHb ∼12%) or in good glycemic control (GC, GHb ~7.0%) for 4 months, or were allowed to maintain PC for 2 months, followed by GC for 2 additional months (PC-Rev). For experimental galactosemia, a group of normal rats were fed a 30% galactose diet for 4 months or for 2 months, followed by a normal diet for 2 additional months. Trimethyl histone H4 lysine 20 (H4K20me3), acetyl histone H3 lysine 9 (H3K9), and nuclear transcriptional factor NF-κB p65 and p50 at the retinal sod2 promoter and enhancer were examined by chromatin immunoprecipitation.

RESULTS

Hyperglycemia (diabetes or galactosemia) increased H4K20me3, acetyl H3K9, and NF-κB p65 at the promoter and enhancer of retinal sod2, upregulated protein and gene expression of SUV420h2, and increased the interactions of acetyl H3K9 and NF-κB p65 to H4K20me3. Reversal of hyperglycemia failed to prevent increases in H4K20me3, acetyl H3K9, and NF-κB p65 at sod2, and sod2 and SUV420h2 continued to be abnormal. Silencing SUV420h2 by its small interfering RNA in retinal endothelial cells prevented a glucose-induced increase in H4K20me3 at the sod2 enhancer and a decrease in sod2 transcripts.

CONCLUSIONS

Increased H4K20me3 at sod2 contributes to its downregulation and is important in the development of diabetic retinopathy and in the metabolic memory phenomenon. Targeting epigenetic changes may serve as potential therapeutic targets to retard the development and progression of diabetic retinopathy.

Some clues as to the regulation, expression, function, and distribution of fructosamine-3-kinase and fructosamine-3-kinase-related protein

Fructosamine-3-kinase (FN3K) and the more recently discovered fructosamine-3-kinase-related protein (FN3KRP) appear to protect proteins from nonenzymatic glycation. To gain a better understanding of these enzymes we performed a series of investigations including (1) in silico comparisons of their promoters; (2) real-time PCR analysis of their expression in human tissues; (3) effects of hyperglycemia, interleukin-1beta (IL-1beta), and nuclear factor kappa-B (NFkappaB) activation on their mRNA levels; (4) effects of small interfering RNA (siRNA) suppression of FN3K expression (knockdown) in cultured cells and (5) search of FN3K and FN3KRP homologs in available genomic and EST (expressed sequence tag) databases. Our results indicate that (1) both FN3K and FN3KRP promoters are TATA-less and CAAT-less and contain several homologous CpG islands and Sp1 binding sites. (2) Both genes are expressed in all human tissue examined, with FN3K showing significantly higher levels in tissues susceptible to nonenzymatic glycation and diabetic complications. (3) Treatment of fibroblasts with high glucose, IL-1beta, and activation of NFkappaB does not affect the expression of either FN3K or FN3KRP. (4) Knockdown of FN3K in cultured cells inhibits or arrests their growth. (5) FN3K-like genes are widely distributed in nature, with the notable exception of insects and yeasts. These data suggest that FN3K and FN3KRP are constitutive "housekeeping" genes and that they play an important role in cell metabolism, possibly as deglycating enzymes.

Upstream stimulatory factors, USF1 and USF2, bind to the human haem oxygenase-1 proximal promoter in vivo and regulate its transcription

The human HO-1 (haem oxygenase-1) gene encodes a microsomal enzyme responsible for the breakdown of haem, and is also cytoprotective in response to various cellular insults. HO-1 transcription is induced by a vast array of compounds including, but certainly not limited to, haem and heavy metals such as cadmium. In the present study, we show that upstream stimulatory factors, USF1 and USF2, ubiquitous proteins belonging to the basic helix-loop-helix-leucine zipper family of transcription factors, constitutively bind to the class B E-box located in the proximal promoter of the human HO-1 gene and are responsible for the enhancement of HO-1 gene transcription in human renal proximal tubular epithelial cells. Dimethylsulphate in vivo footprinting studies have identified three protected guanine residues in the E-box of the HO-1 proximal promoter. One of these guanine contact points is essential for USF binding, and when mutated mimics a deletion mutation of the entire E-box palindrome sequence encompassing all three guanine contact points. Binding of USF1 and USF2 to the HO-1 E-box was confirmed by chromatin immunoprecipitation and gel-shift assays. Furthermore, we show that overexpression of USF1 or USF2 enhances the basal expression of HO-1 and that expression of a USF dominant negative form reduces its expression. These results demonstrate for the first time that USF proteins bind to the human HO-1 promoter in vivo and are required for high-level expression of HO-1 by haem and cadmium in human renal epithelial cells.

The expression of the genes for fructosamine-3-kinase and fructosamine-3-kinase-related protein appears to be constitutive and unaffected by environmental signals

Fructosamine-3-kinase (FN3K) and the more recently discovered fructosamine-3-kinase related protein (FN3KRP) appear to protect proteins from nonenzymatic glycation. To elucidate the patterns of transcriptional regulation of these two genes, we performed in silico comparisons of their promoters along with real-time PCR assays of their expression in a variety of human tissues. Both promoters were TATA-less and CAAT-less, and contained several homologous CpG islands and Sp1 binding sites. The genes were expressed in all human tissues examined, with FN3K showing significantly higher levels in organs susceptible to nonenzymatic glycation and diabetic complications. Cultured fibroblasts treated with conditions mimicking the hormonal and biochemical profile of the diabetic state showed no changes in FN3K and FN3KRP expression relative to untreated cells. These data suggest that FN3K and FN3KRP act as protein repair enzymes and are expressed constitutively in human cells independently of some of the variables altered in the diabetic state.

Role of the intronic enhancer in tumor necrosis factor-mediated induction of manganous superoxide dismutase

Manganous superoxide dismutase (Mn-SOD), a tumor necrosis factor (TNF)-inducible gene product, plays an important role in removing superoxide anions produced inside mitochondria. Two regulatory regions, the proximal promoter region (PPR), which is upstream from the transcription initiation site, and the TNF-responsive element (TNFRE), which is inside intron 2, are responsible for Mn-SOD expression. To understand how each of these regions contributes to the transcription of Mn-SOD, quantitative reverse transcription-PCR, chromatin immunoprecipitations, and in vivo nuclease sensitivity assays were performed on the murine Mn-SOD gene. These assays demonstrate that Sp1 and nuclear factor (NF)-kappaB p65 are required for Mn-SOD induction by TNF. Sp1 bound the PPR constitutively, whereas NF-kappaB p65 and C/EBP-beta bound the TNFRE only after TNF treatment. Binding of C/EBP-beta to the TNFRE was dependent on the presence of NF-kappaB p65. The chromatin structure within the TNFRE became more accessible to nuclease digestion after TNF treatment. This accessibility required Sp1 and NF-kappaB p65. Treatment of cells with an inhibitor of histone deacetylation, or transient transfection with coactivator-expressing plasmids, enhanced the expression of Mn-SOD. NF-kappaB p65 binding was required for acetylation of histones H3 and H4 at the PPR and the TNFRE. Together, these data suggest communication between the PPR and the TNFRE which involves chromatin remodeling and histone acetylation during the induction process of Mn-SOD in response to TNF.

PIN*POINT analysis on the endogenous MnSOD promoter: specific demonstration of Sp1 binding in vivo

Manganese superoxide dismutase (MnSOD) is a critical antioxidant enzyme that protects against superoxide anion generated as a consequence of normal cellular respiration, as well as during the inflammatory response. By employing dimethyl sulfate in vivo footprinting, we have previously identified ten basal protein binding sites within the MnSOD promoter. On the basis of consensus sequence comparison and in vitro footprinting data, one would predict that Sp1 might occupy five of these binding sites. To address these findings in the context of the nucleoprotein environment, we first utilized chromatin immunoprecipitation (ChIP) to demonstrate the nuclear association of Sp1 with the MnSOD promoter region. To identify the precise location of Sp1 binding, we have modified the original protein position identification with nuclease tail (PIN*POINT) methodology, providing an approach to establish both the identity and binding occupancy of Sp1 in the context of the endogenous MnSOD promoter. These data, coupled with site-directed mutagenesis, demonstrate the functional importance of two of the Sp1 binding sites in the stimulus-specific regulation of MnSOD gene expression. We feel that the combination of ChIP and PIN*POINT analysis allows unequivocal identification and localization of protein/DNA interactions in vivo, specifically the demonstration of Sp1 with the MnSOD promoter.

Superoxide dismutase multigene family: a comparison of the CuZn-SOD (SOD1), Mn-SOD (SOD2), and EC-SOD (SOD3) gene structures, evolution, and expression

Superoxide dismutases are an ubiquitous family of enzymes that function to efficiently catalyze the dismutation of superoxide anions. Three unique and highly compartmentalized mammalian superoxide dismutases have been biochemically and molecularly characterized to date. SOD1, or CuZn-SOD (EC 1.15.1.1), was the first enzyme to be characterized and is a copper and zinc-containing homodimer that is found almost exclusively in intracellular cytoplasmic spaces. SOD2, or Mn-SOD (EC 1.15.1.1), exists as a tetramer and is initially synthesized containing a leader peptide, which targets this manganese-containing enzyme exclusively to the mitochondrial spaces. SOD3, or EC-SOD (EC 1.15.1.1), is the most recently characterized SOD, exists as a copper and zinc-containing tetramer, and is synthesized containing a signal peptide that directs this enzyme exclusively to extracellular spaces. What role(s) these SODs play in both normal and disease states is only slowly beginning to be understood. A molecular understanding of each of these genes has proven useful toward the deciphering of their biological roles. For example, a variety of single amino acid mutations in SOD1 have been linked to familial amyotrophic lateral sclerosis. Knocking out the SOD2 gene in mice results in a lethal cardiomyopathy. A single amino acid mutation in human SOD3 is associated with 10 to 30-fold increases in serum SOD3 levels. As more information is obtained, further insights will be gained.

The phytoestrogen daidzein affects the antioxidant enzyme system of rat hepatoma H4IIE cells

Phytoestrogens such as the soy isoflavonoid daidzein have potential health benefits. The antioxidant properties of phytoestrogens are considered to be responsible in part for their protective effects. The antioxidant enzyme (AOE) system plays an important role in the defense of cells against oxidative insults. To determine whether flavonoids can exert antioxidative effects not only directly but also indirectly by modulating the AOE system, we investigated the influence of the flavonoid daidzein on the expression of different AOE. Daidzein treatment of hepatoma H4IIE cells increased catalase mRNA expression two- to threefold. Expression levels of copper zinc superoxide dismutase (CuZnSOD) were not affected by exposure to daidzein. Manganese superoxide dismutase (MnSOD) mRNA expression levels decreased slightly and glutathione peroxidase (GPx) levels increased slightly after daidzein exposure. Changes in AOE mRNA expression levels were significant at 300 micromol/L daidzein. To elucidate the mechanisms underlying the strong increase in catalase mRNA, transfection experiments were performed. Transient transfection of hepatoma cells with reporter plasmids containing different parts of the upstream region of the catalase gene showed a significant one- to threefold increase in reporter gene activity after daidzein exposure. This indicates that daidzein can directly activate the rat catalase promoter region. Despite the increase in catalase mRNA, daidzein pretreatment of cells did not protect against oxidative stress resulting from H(2)O(2) exposure. On the contrary, daidzein itself exerted a mild oxidative stress. In conclusion, the changes in the AOE system provoked by daidzein affected the oxidant rather than the antioxidant properties of daidzein.

A coding region determinant of instability regulates levels of manganese superoxide dismutase mRNA

The mitochondria-localized manganese superoxide dismutase (MnSOD), serves a key cytoprotective role against reactive oxygen species arising from a variety of cellular processes and immunological stresses. Previous data from our laboratory suggest that the regulation of the rat MnSOD gene may occur not only at the transcriptional but quite possibly at the post-transcriptional level. To verify this hypothesis, we have attempted to identify regions within the rat MnSOD cDNA that may be functionally involved in regulating the stability of the mRNA. Using a c-fos-based promoter activation system, we have identified an approximately 280-nucleotide fragment within the MnSOD mRNA coding region that, when fused to a rabbit beta-globin gene, destabilizes the normally stable beta-globin mRNA. This cis-directed destabilization phenomenon confers its effects independent of position and stimulus. Most importantly, the MnSOD coding region determinant functions when placed in the 3'-untranslated region of the beta-globin transcript, demonstrating its activity in the absence of ribosome transit. We feel that these data provide a mechanistic basis for both the basal and stimulus-dependent post-transcriptional regulation of MnSOD.

TPA-activated transcription of the human MnSOD gene: role of transcription factors Sp-1 and Egr-1

Induction of manganese superoxide dismutase (MnSOD) in response to oxidative stress has been well established in animals, tissues, and cell culture. However, the role of the human MnSOD (hMnSOD) promoter in stimulus-dependent activation of transcription is unknown. The hMnSOD promoter lacks both a TATA and a CAAT box but possesses several GC motifs. In a previous study, we showed that the basal promoter contains multiple Sp1 and AP-2 binding sites and that Sp1 is essential for the constitutive expression of the hMnSOD gene. In this study, we identified an Egr-1 binding site in the basal promoter of hMnSOD. We also found that the basal promoter is responsive to 12-O-tetradecanoylphorbol-13-acetate (TPA)-activated hMnSOD transcription in the human hepatocarcinoma cell line HepG2. The contributions of these binding sites and the roles of the transcription factors Egr-1, AP-2, and Sp1 in the activation of hMnSOD transcription by TPA were investigated by site-directed mutation analysis, Western blotting, and overexpression of transcription factors. The results showed that Sp1 plays a positive role for both basal and TPA-activated hMnSOD transcription, whereas overexpression of Egr-1 has a negative role in the basal promoter activity without any effect on TPA-mediated activation of hMnSOD transcription.

Tumor necrosis factor-alpha selectively induces MnSOD expression via mitochondria-to-nucleus signaling, whereas interleukin-1beta utilizes an alternative pathway

Mitochondrial levels of the anti-oxidant enzyme, manganese superoxide dismutase (MnSOD), are dramatically elevated in response to stimulation with tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and lipopolysaccharide (LPS). However, the precise intracellular signaling pathways responsible for this inducible expression are poorly understood. MnSOD expression in pulmonary epithelial and endothelial cells, treated with inflammatory mediators and various inhibitors, was studied by Northern analysis. The mitochondrial electron transport chain inhibitors, antimycin A and myxothiazol, selectively blocked TNF-alpha-inducible expression of MnSOD but not that of IL-1beta or LPS, indicating different signaling pathways. N-Acetylcysteine could reliably decrease inducible MnSOD expression by TNF-alpha, but not IL-1, linking reactive oxygen species (ROS) to the TNF-alpha signaling pathway. Elevated levels of arachidonic acid have been demonstrated previously to generate mitochondrial ROS. A specific cytoplasmic phospholipase A(2) inhibitor reduced stimulated MnSOD expression by TNF-alpha, but not by IL-1beta, further supporting the role of ROS. Other investigators have shown that MnSOD expression may be regulated by NF-kappaB. Our results with a specific inhibitory kappa-kinase inhibitor indicate that NF-kappaB modulates IL-1beta signaling but not the TNF-alpha pathway. Thus, we have demonstrated that although inducible MnSOD transcription may appear similar at the messenger RNA level, the intracellular signaling pathways are differentially regulated.

The influence of oxidative stress on catalase and MnSOD gene transcription in astrocytes

The brain is particularly vulnerable to oxygen free radicals, which have been implicated in the pathology of several neurological disorders. The antioxidant enzyme (AOE) system of the brain may play an important role in the protection against such oxidative stress. We investigated the influence of oxidative stress on the transcription of catalase and MnSOD mRNA. Primary rat astroglial cell cultures were treated either with hydrogen peroxide (H2O2), as a direct mediator of oxidative stress, or with the redox cycling compound paraquat. Both substances led to an increase of catalase and MnSOD mRNA levels. To further elucidate the mechanisms residing behind this increase, transfection experiments were performed. Transient transfection of primary astroglial cells with a reporter plasmid containing the upstream region of the catalase gene showed a decrease in reporter gene activity after exposure of transfected cells to either H2O2 or paraquat. In contrast, transfection experiments done with reporter plasmids for the MnSOD upstream region resulted in an increase of reporter gene activity after H2O2 as well as after paraquat treatment of transfected cells. These results indicate transcriptional regulation of MnSOD and post-transcriptional regulation of catalase gene expression after oxidative stress in primary rat astrocytes.

A family of AP-2 proteins down-regulate manganese superoxide dismutase expression

Manganese superoxide dismutase (Mn-SOD) is a primary antioxidant enzyme whose expression is essential for life in oxygen. Mn-SOD has tumor suppressor activity in a wide variety of tumors and transformed cell systems. Our initial observations revealed that Mn-SOD expression was inversely correlated with expression of AP-2 transcription factors in normal human fibroblasts and their SV-40 transformed counterparts. Thus we hypothesized that AP-2 may down-regulate Mn-SOD expression. To examine the functional role of AP-2 on Mn-SOD promoter transactivation we cotransfected AP-2-deficient HepG2 cells with a human Mn-SOD promoter-reporter construct and expression vectors encoding each of the three known AP-2 family members. Our results indicated that AP-2 could significantly repress Mn-SOD promoter activity, and that this repression was both Mn-SOD promoter and AP-2-specific. The three AP-2 proteins appeared to play distinct roles in Mn-SOD gene regulation. Moreover, although all three AP-2 proteins could repress the Mn-SOD promoter, AP-2alpha and AP-2gamma were more active in this regard than AP-2beta. Transcriptional repression by AP-2 was not a general effect in this system, because another AP-2-responsive gene, c-erbB-3, was transactivated by AP-2. Repression of Mn-SOD by AP-2 was dependent on DNA binding, and expression of AP-2B, a dominant negative incapable of DNA binding, relieved the repression on Mn-SOD promoter and reactivated Mn-SOD expression in the AP-2 abundant SV40-transformed fibroblast cell line MRC-5VA. These results indicate that AP-2-mediated transcriptional repression contributes to the constitutively low expression of Mn-SOD in SV40-transformed fibroblasts and suggest a mechanism for Mn-SOD down-regulation in cancer.

Cytokine-induced changes in chromatin structure and in vivo footprints in the inducible NOS promoter

Transcription of the human inducible nitric oxide synthase (iNOS) gene is regulated by inflammatory cytokines in a tissue-specific manner. To determine whether differences in cytokine-induced mRNA levels between pulmonary epithelial cells (A549) and hepatic biliary epithelial cells (AKN-1) result from different protein or DNA regulatory mechanisms, we identified cytokine-induced changes in DNase I-hypersensitive (HS) sites in 13 kb of the iNOS 5'-flanking region. Data showed both constitutive and inducible HS sites in an overlapping yet cell type-specific pattern. Using in vivo footprinting and ligation-mediated PCR to detect potential DNA or protein interactions, we examined one promoter region near -5 kb containing both constitutive and cytokine-induced HS sites. In both cell types, three in vivo footprints were present in both control and cytokine-treated cells, and each mapped within a constitutive HS site. The remaining footprint appeared only in response to cytokine treatment and mapped to an inducible HS site. These studies, performed on chromatin in situ, identify a portion of the molecular mechanisms regulating transcription of the human iNOS gene in both lung- and liver-derived epithelial cells.

Reciprocal down-regulation of p53 and SOD2 gene expression-implication in p53 mediated apoptosis

p53 regulates the transcription of a number of genes among which are different redox-related genes. It has been proposed that these genes can induce a cellular oxidative stress leading to p53-dependent apoptosis (Polyak et al., 1997). MnSOD, the product of superoxide dismutase 2 (SOD2) gene, is one of the major cellular defences against oxidative stress. We demonstrate here that p53 is able to repress SOD2 gene expression and that this repression takes place at promoter level. We show the importance of this regulation for the p53 function, by demonstrating that an overexpression of MnSOD decreases p53-mediated induction of apoptosis. Moreover, we demonstrate that MnSOD overexpression decreases p53-gene expression at the promoter level. These findings raise the hypothesis that p53 and SOD2 genes are mutually regulated leading to the modulation of various cellular processes including apoptosis.

A NF-kappaB p65 subunit is indispensable for activating manganese superoxide: dismutase gene transcription mediated by tumor necrosis factor-alpha

Expression of the manganese superoxide dismutase (Mn-SOD) is induced by tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), and lipopolysaccharide (LPS). Recently, a TNF-responsive element (TNFRE) was identified within the second intron of the murine Mn-SOD gene. The 5' CCAAT/enhancer binding protein (C/EBP)-related region within the TNFRE was responsive to TNF, whereas the 3' NF-kappaB-related region alone was not. This report describes the minimal promoter region of the Mn-SOD gene and investigates the cis-acting elements and trans-acting factors responsible for TNF-alpha-induced Mn-SOD gene expression. Reporter plasmid transfection studies demonstrated that inducible transcription factors enhanced the transcriptional activity of the Mn-SOD gene through the intronic enhancer region. Electrophoretic mobility shift assays demonstrated that after TNF-alpha stimulation, p50 and p65 NF-kappaB subunits bound specifically to the newly identified NF-kappaB transcription factor-binding site, distinct from the previously described NF-kappaB site, within the intronic enhancer region. In addition, site-directed mutagenesis and cotransfection studies demonstrated that the NF-kappaB p65 subunit enhanced the transcriptional activity of the Mn-SOD gene through the newly identified NF-kappaB site. These results show that a NF-kappaB p65 subunit is mainly involved in the molecular mechanisms controlling TNF-alpha-mediated Mn-SOD gene transcription.

Decreased expression of manganese superoxide dismutase in transformed cells is associated with increased cytosine methylation of the SOD2 gene

Tumor cells express lower levels of manganese superoxide dismutase (MnSOD) than their normal counterparts. Enforced expression of MnSOD reverses the malignant phenotype of many transformed cells, suggesting that SOD2 is a tumor suppressor. The SOD2 gene contains a large CpG island spanning > 3.5 kb that starts near the 5' edge of the promoter and extends into intron 2. We hypothesized that the difference in SOD2 expression between tumor cells and their normal cell counterparts might be secondary to differences in their cytosine methylation patterns in this CpG island. To test this hypothesis, we analyzed the methylation status of the SOD2 gene in two cell line models that show differential MnSOD expression between normal and SV40-transformed cells: WI38 and MRC5 and their SV40-transformed variants, WI38-VA and MRC5-VA. We subdivided the SOD2 gene CpG island into 10 individual regions for analysis by bisulfite genomic sequencing. A region located in intron 2 displayed a significant increase in cytosine methylation in both transformed cell lines that expressed low levels of MnSOD mRNA compared with their normal cell counterparts. Recent studies by others have shown that SOD2 intron 2 is a potent transcriptional enhancer. The association between increased cytosine methylation of the SOD2 intron 2 region and decreased MnSOD expression in transformed cells compared with their normal counterparts suggests that an epigenetic mechanism contributes to the differential SOD2 gene expression between these normal and SV40-transformed cells.