Transcriptional regulator of oxidative stress-inducible genes: direct activation by oxidation

Characterization of an ethylene-regulated flower senescence-related gene from carnation

The programmed senescence of carnation (Dianthus caryophyllus L.) petals requires active gene expression and is associated with the expression of several senescence-related mRNAs. Expression of the mRNA represented by the cDNA clone pSR12 has previously been shown to be transcriptionally activated by ethylene specifically in senescing flowers. We report in this paper the structural analysis of this cDNA and its corresponding gene. One cloned genomic DNA fragment, SR12-B, contained the entire transcription unit in 17 exons, interrupted by 16 introns. A second gene, SR12-A, was highly homologous to SR12-B with several nucleotide substitutions and a 489 bp deletion in the 5' flanking DNA sequence. The SR12 transcript has an open reading frame of 2193 bp sufficient to encode a protein of 82.8 kDa. No significant homology at the DNA or protein levels was found with other known genes. We have identified a DNA-binding factor which specifically interacts with two upstream fragments (-149 to -337 and -688 to -1055) of SR12-B. Both fragments apparently compete for the same binding factor. The DNA-binding activity was present in nuclear extracts from both presenescent and senescing carnation petals. The upstream DNA fragments that bind this factor have sequence homology with promoter sequences of other ethylene-regulated genes.

Purification and mutant analysis of Citrobacter freundii AmpR, the regulator for chromosomal AmpC beta-lactamase

AmpR, the transcriptional regulator for the Citrobacter freundii ampC beta-lactamase gene, was purified. The purified AmpR had DNA-binding activity, the same molecular mass (32 kDa) on sodium dodecyl sulphate/polyacrylamide gel electrophoresis as previously described, and N-terminal sequencing of the first 15 amino acids was in agreement with that predicted from the nucleotide sequence. Two mutants were isolated that abolish DNA-binding and beta-lactamase induction and which map in the amino- and carboxyl-terminal ends of AmpR, respectively. The mutation in the amino terminus (S35F) was located in a helix-turn-helix region showing high homology to other members of the LysR regulator family. Therefore this mutation may directly abolish the contact between AmpR and its operator sequence. It is suggested that the C-terminal mutation (Y264N) affects subunit interactions in AmpR. One constitutive mutant was isolated which mapped in the centre of the ampR gene. This G102E mutant leads to constitutive beta-lactamase expression in the absence of both beta-lactam inducer and ampG, a gene essential for induction in wild-type enterobacteria. Another mutant protein, D135Y, showed wild-type properties in an ampG+ and an ampG::kan background, but could, unlike wild-type AmpR, activate the ampC gene in an ampG1 mutant background. It is thought that ampG1 is a missense mutant. These two types of ampR mutants suggest that activation of ampC transcription is dependent on the conversion of AmpR into a transcriptional activator and that this activation may normally involve interactions with AmpG.

d-alpha-tocopherol inhibits collagen alpha 1(I) gene expression in cultured human fibroblasts. Modulation of constitutive collagen gene expression by lipid peroxidation

Ascorbic acid stimulates collagen gene transcription in cultured fibroblasts, and this effect is mediated through the induction of lipid peroxidation by ascorbic acid. Quiescent cultured fibroblasts in the absence of ascorbic acid have a high constitutive level of collagen production, but the mechanisms of collagen gene regulation in this unstimulated state are not known. Because lipid peroxidation also occurs in normal cells, we wondered if lipid peroxidation plays a role in the regulation of basal collagen gene expression. Inhibition of lipid peroxidation in cultured human fibroblasts with d-alpha-tocopherol or methylene blue decreased the synthesis of collagen, the steady-state levels of procollagen alpha 1(I) mRNA and the transcription of the procollagen alpha 1(I) gene. This effect on collagen gene expression was selective and not associated with cellular toxicity. Thus, these experiments suggest a role for lipid peroxidation in the modulation of constitutive collagen gene expression.

Characterization of the FNR protein of Escherichia coli, an iron-binding transcriptional regulator

FNR is a transcriptional regulator mediating the activation or repression of a variety of Escherichia coli genes in response to anoxia. The FNR protein resembles CRP (the cyclic-AMP receptor protein) except for the presence of a cysteine-rich N-terminal segment which may form part of an iron-binding redoxsensing domain. The FNR protein was purified by a new procedure. It was monomeric (Mr = 30,000) and contained as much as 1.1 mol of iron per monomer when purified in the presence of added iron. This iron was associated with cysteine residues, because there was an inverse relation between iron content and titratable sulphydryl groups. Other physical and chemical properties are reported including evidence for a potential disulphide group or analogous modification. The interaction between FNR protein and target DNA appeared weak and non-specific in gel-retardation assays, but specific binding to the proposed DNA-binding site was shown for the first time in footprinting studies. A role for iron in FNR-mediated gene expression was confirmed by using cultures in which FNR was inactivated by growth in the presence of the specific chelator, ferrozine, but protected by ferrous iron.

Modulation of transcription factor NF-kappa B binding activity by oxidation-reduction in vitro

NF-kappa B is a widely used regulator of inducible and tissue-specific gene control. In the cytosol, when complexed to an inhibitory molecule, I kappa B, NF-kappa B is in an inactive form and cannot bind DNA. Activation of cells with appropriate stimuli results in the dissociation of NF-kappa B from I kappa B and its translocation to the nucleus as an active binding protein. We now demonstrate that NF-kappa B binding in vitro can be inhibited by agents that modify free sulfhydryls. Binding is eliminated after treatment with N-ethylmaleimide, an alkylating agent, and diamide, an oxidizing agent. The diamide effect can be reversed by 2-mercaptoethanol. Further, 2-mercaptoethanol acts synergistically with deoxycholate plus Nonidet P-40 in converting inactive cytosolic NF-kappa B to an active DNA-binding form. It is therefore possible that modulation of the redox state of NF-kappa B could represent a post-translational control mechanism for this factor.

Molecular and biochemical aspects of Bloom's syndrome

Bloom's syndrome (BS) is an autosomal recessive disorder, characterized by a high incidence of cancer at a young age. Cytogenetically, BS cells exhibit a high frequency of chromosomal damage and sister chromatid exchanges. Thus, BS provides one of the best correlations of a human genetic disorder exhibiting both chromosomal instability and a high incidence of cancer. It is increasingly evident that a spontaneous mutagenic event may be responsible for the inherent chromosomal instability. Oxidative stress is now shown to occur in BS cells and may be responsible for the observed chromosomal instability. Furthermore, treatment with antioxidants decreases the level of sister chromatid exchanges. The combination of a mutagenic event and an elevated rate of recombination could potentially lead to homozygosity of tumor suppressor gene function. Hypomethylation and expression of an activated c-myc gene are now demonstrated in BS lymphoblastoid cells. Identifying the mechanism(s) of the ongoing cellular and DNA damage is important in understanding the etiology of this complex disorder. This article reviews the recent biochemical and molecular advances in the study of BS.

Negative autoregulation of cysB in Salmonella typhimurium: in vitro interactions of CysB protein with the cysB promoter

CysB protein positively regulates genes of the Salmonella typhimurium cysteine regulon and negatively autoregulates cysB. The cysB promoter was characterized by primer extension of cellular RNA, which gave products identifying a major in vivo transcription start site located 95 bp upstream of the cysB start codon and two minor sites located 9 and 10 bp downstream of the major site. Gel shift binding studies and DNase I footprinting experiments showed that CysB protein binds to the cysB promoter from position -10 to +36 relative to the major transcription start site. We have designated this binding site CBS-B. CysB protein inhibited transcription initiation at the cysB promoter in an in vitro runoff assay, indicating that cysB is negatively autoregulated by the binding of CysB protein to the cysB promoter, where it acts as a repressor. N-Acetyl-L-serine, an inducer of the cysteine regulon, inhibited the binding of CysB protein to the cysB promoter and partially reversed the ability of CysB protein to inhibit transcription initiation. These effects are in contrast to those observed in studies of positively regulated cys promoters, in which N-acetyl-L-serine stimulates binding and causes CysB protein to activate transcription initiation.

Mutational analysis of a bacteriophage P4 late promoter

Transcription from the late Psid promoter of satellite bacteriophage P4 is dependent on the bacterial RNA polymerase carrying the sigma 70 subunit and is positively regulated by the product of the P4 delta gene or the ogr gene of helper bacteriophage P2. Through deletion and mutational analyses of the Psid promoter, we identified mutations in the -10 region and in a region of hyphenated dyad symmetry centered around position -55 that inactivate Psid. Most of these mutations alter base pairs that are highly conserved in the five other delta-activated P4 and P2 late promoters. We propose that the P4 delta and P2 ogr gene products bind the -55 region of the P4 and P2 late promoters.

HSP70 and other possible heat shock or oxidative stress proteins are induced in skeletal muscle, heart, and liver during exercise

Exercise causes heat shock (muscle temperatures of up to 45 degrees C, core temperatures of up to 44 degrees C) and oxidative stress (generation of O2- and H2O2), and exercise training promotes mitochondrial biogenesis (2-3-fold increases in muscle mitochondria). The concentrations of at least 15 possible heat shock or oxidative stress proteins (including one with a molecular weight of 70 kDa) were increased, in skeletal muscle, heart, and liver, by exercise. Soleus, plantaris, and extensor digitorum longus (EDL) muscles exhibited differential protein synthetic responses ([3H]leucine incorporation) to heat shock and oxidative stress in vitro but five proteins (particularly a 70 kDa protein and a 106 kDa protein) were common to both stresses. HSP70 mRNA levels were next analyzed by Northern transfer, using a [32P]-labeled HSP70 cDNA probe. HSP70 mRNA levels were increased, in skeletal and cardiac muscle, by exercise and by both heat shock and oxidative stress. Skeletal muscle HSP70 mRNA levels peaked 30-60 min following exercise, and appeared to decline slowly towards control levels by 6 h postexercise. Two distinct HSP70 mRNA species were observed in cardiac muscle; a 2.3 kb mRNA which returned to control levels within 2-3 h postexercise, and a 3.5 kb mRNA species which remained at elevated concentrations for some 6 h postexercise. The induction of HSP70 appears to be a physiological response to the heat shock and oxidative stress of exercise. Exercise hyperthermia may actually cause oxidative stress since we also found that muscle mitochondria undergo progressive uncoupling and increased O2- generation with increasing temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of transcription of katE and katF in Escherichia coli

Fusion plasmids with lacZ under the control of the katE (encoding catalase or hydroperoxidase HPII) and katF (encoding a sigma factor-like protein required for katE expression) promoters were constructed. Expression from both katE and katF promoters was low in rich medium but elevated in poor medium during log-phase growth. Furthermore, the slowdown in growth as cells entered the stationary phase in rich medium, a result of carbon source depletion, was associated with an increase in katE and katF expression. A simple reduction in the carbon source level as the cells entered the stationary phase was not responsible for the increase in expression, because transferring the culture to a medium with no glucose did not induce expression from either promoter. Spent rich medium from stationary-phase cells was capable of inducing expression, as were simple aromatic acids such as benzoate, o-hydroxybenzoate, and p-aminobenzoate added to new medium. Anaerobiosis did not cause an increase in expression, nor did it significantly change the pattern of expression. Regardless of the medium, katF expression was always turned on before or coincidently with katE expression; in the presence of benzoate katF was fully induced, whereas katE was only partially induced, suggesting that a factor in addition to KatF protein was involved in katE expression. During prolonged aerobic incubation, cells lacking katF died off more rapidly than did cells lacking either katE or katG.

Bacterial defenses against oxidative stress

Bacteria treated with low doses of oxidants such as hydrogen peroxide adapt to subsequent high doses of these oxidants by inducing the expression of numerous genes. The study of these genes and the roles they play in defending bacteria against oxidative damage has given general insights into what oxidants are hazardous to cells, what cell constituents are damaged by oxidants, and how cells sense and respond to oxidative stress.

Regulation of bacterial gene expression by metal-protein complexes

Metal ions are essential cofactors in several transacting bacterial gene regulators. Upon binding of the metal, the receptor proteins act either as repressors of gene expression or, in other systems, as transcriptional activators. Other metal-dependent regulatory proteins may function, directly or indirectly, as sensors of the cellular oxygen status, and may even be mediators in light-responsive gene regulation.

The OxyR regulon

Treatment of Salmonella typhimurium and Escherichia coli cells with low doses of hydrogen peroxide results in the induction of thirty proteins and resistance to killing by higher doses of hydrogen peroxide. The expression of nine of the hydrogen peroxide-inducible proteins, including catalase, glutathione reductase and a novel alkyl hydroperoxide reductase is controlled by the positive regulator oxyR. OxyR is homologous to the LysR-NodD family of bacterial regulatory proteins and binds to the promoters of oxyR-regulated genes. The oxidized but not reduced form of the OxyR protein activates transcription of oxyR-regulated genes in vitro suggesting that oxidation of the OxyR protein brings about a conformational change by which OxyR both senses and transduces an oxidative stress signal to RNA polymerase.

Catalase HPI influences membrane permeability in Escherichia coli following near-UV stress

The katG gene in Escherichia coli encodes catalase HPI, which is involved in membrane transport and protects the cell during oxidative stress. Hydrogen peroxide (H2O2) induces synthesis of HPI. We examined the role of HPI in membrane permeability (proline uptake) following exposure to near-ultraviolet radiation (NUV). We found that NUV resulted in the same type of induction as H2O2. KatG::Tn10 cells experienced a large drop in uptake after NUV exposure, and levels remained low following incubation. A strain carrying a katG+ plasmid, however, showed considerably less decrease in uptake after NUV, and uptake quickly resumed upon incubation. Further, in an srd mutant which lacks 4-thiouracil, NUV resulted in only a small drop in proline uptake, which was immediately resumed.

Redox regulation of fos and jun DNA-binding activity in vitro

The proto-oncogenes c-fos and c-jun function cooperatively as inducible transcription factors in signal transduction processes. Their protein products, Fos and Jun, form a heterodimeric complex that interacts with the DNA regulatory element known as the activator protein-1 (AP-1) binding site. Dimerization occurs via interaction between leucine zipper domains and serves to bring into proper juxtaposition a region in each protein that is rich in basic amino acids and that forms a DNA-binding domain. DNA binding of the Fos-Jun heterodimer was modulated by reduction-oxidation (redox) of a single conserved cysteine residue in the DNA-binding domains of the two proteins. Furthermore, a nuclear protein was identified that reduced Fos and Jun and stimulated DNA-binding activity in vitro. These results suggest that transcriptional activity mediated by AP-1 binding factors may be regulated by a redox mechanism.

Activation of the heat shock transcription factor by hypoxia in mammalian cells

Members of the stress protein family such as HSP70 are induced in ischemic tissues and may contribute to the ability of cells to survive episodes of transient circulatory insufficiency. However, the biochemical events that lead to this induction, and their degree of similarity with pathways triggered by heat stress, have not been defined. In this study, we demonstrate that transient exposure of cultured C2C12 mouse myogenic cells to a hypoxic atmosphere stimulates DNA binding activity of the heat shock transcription factor through mechanisms that are independent of new protein synthesis. Activation of heat shock transcription factor in hypoxic cells is temporally associated with induction of endogenous HSP70 gene transcription and with induction of a heterologous reporter gene controlled by the human HSP70 promoter. Furthermore, induction of the human HSP70 promoter by hypoxia requires an intact heat shock element, indicating that other cis-acting transcriptional control elements contained within this complex promoter are not sufficient to transduce signals generated within hypoxic cells. These findings provide strong evidence that hypoxia and heat shock induce expression of the HSP70 gene by similar, if not identical, mechanisms.