Two distinct upstream regions are involved in expression of the catalase gene in Schizosaccharomyces pombe in response to oxidative stress

A Redox-Sensitive Thiol in Wis1 Modulates the Fission Yeast Mitogen-Activated Protein Kinase Response to H2O2 and Is the Target of a Small Molecule

Oxidation of a highly conserved cysteine (Cys) residue located in the kinase activation loop of mitogen-activated protein kinase kinases (MAPKK) inactivates mammalian MKK6. This residue is conserved in the fission yeast Schizosaccharomyces pombe MAPKK Wis1, which belongs to the H2O2-responsive MAPK Sty1 pathway. Here, we show that H2O2 reversibly inactivates Wis1 through this residue (C458) in vitro We found that C458 is oxidized in vivo and that serine replacement of this residue significantly enhances Wis1 activation upon addition of H2O2 The allosteric MAPKK inhibitor INR119, which binds in a pocket next to the activation loop and C458, prevented the inhibition of Wis1 by H2O2in vitro and significantly increased Wis1 activation by low levels of H2O2in vivo We propose that oxidation of C458 inhibits Wis1 and that INR119 cancels out this inhibitory effect by binding close to this residue. Kinase inhibition through the oxidation of a conserved Cys residue in MKK6 (C196) is thus conserved in the S. pombe MAPKK Wis1.

Monitoring cytosolic H2O2 fluctuations arising from altered plasma membrane gradients or from mitochondrial activity

Genetically encoded probes monitoring H₂O₂ fluctuations in living organisms are key to decipher redox signaling events. Here we use a new probe, roGFP2-Tpx1.C169S, to monitor pre-toxic fluctuations of peroxides in fission yeast, where the concentrations linked to signaling or to toxicity have been established. This probe is able to detect nanomolar fluctuations of intracellular H₂O₂ caused by extracellular peroxides; expression of human aquaporin 8 channels H₂O₂ entry into fission yeast decreasing membrane gradients. The probe also detects H₂O₂ bursts from mitochondria after addition of electron transport chain inhibitors, the extent of probe oxidation being proportional to the mitochondrial activity. The oxidation of this probe is an indicator of steady-state levels of H₂O₂ in different genetic backgrounds. Metabolic reprogramming during growth in low-glucose media causes probe reduction due to the activation of antioxidant cascades. We demonstrate how peroxiredoxin-based probes can be used to monitor physiological H₂O₂ fluctuations.

Reliable methods of measuring intracellular H₂O₂ fluctuations are necessary to advance redox biology. Here the authors design a H₂O₂ sensor based on the fission yeast peroxiredoxin Tpx1 to sense nanomolar fluctuations of intracellular H₂O₂ in response to genetic and environmental perturbations.

A genetic approach to study H2O2 scavenging in fission yeast--distinct roles of peroxiredoxin and catalase

The main peroxiredoxin in Schizosaccharomyces pombe, Tpx1, is important to sustain aerobic growth, and cells lacking this protein are only able to grow on solid plates under anaerobic conditions. We have found that deletion of the gene coding for thioredoxin reductase, trr1, is a suppressor of the sensitivity to aerobic growth of Δtpx1 cells, so that cells lacking both proteins are able to grow on solid plates in the presence of oxygen. We have investigated this suppression effect, and determined that it depends on the presence of catalase, which is constitutively expressed in Δtrr1 cells in a transcription factor Pap1-dependent manner. A complete characterization of the repertoire of hydrogen peroxide scavenging activities in fission yeast suggests that Tpx1 is the only enzyme with sufficient sensitivity for peroxides and cellular abundance as to control the low levels produced during aerobic growth, catalase being the next barrier of detoxification when the steady-state levels of peroxides are increased in Δtpx1 cells. Gpx1, the only glutathione peroxidase encoded by the S. pombe genome, only has a minor secondary role when extracellular peroxides are added. Our study proposes non-overlapping roles for the different hydrogen peroxide scavenging activities of this eukaryotic organism.

Expression of catalase and glutathione S-transferase genes in Chironomus riparius on exposure to cadmium and nonylphenol

Antioxidant enzymes play important roles in the protection against oxidative damage caused by environmental pollutants by scavenging high levels of reactive oxygen species and have been quantified as oxidative stress markers. However, combining mRNA expressions of genes coding for detoxification enzymes along with enzyme activities will be more useful biomarkers of stress. Therefore, in this study the cDNA of the catalase gene from the aquatic midge, Chironomus riparius (CrCAT) was sequenced using 454 pyrosequencing. The 2139 bp CrCAT cDNA included an open reading frame of 1503 bp encoding a putative protein of 500 amino acids with a predicted molecular mass of 56.72 kDa. There was an 18 bp 5' and a long 618 bp 3' untranslated region with a polyadenylation signal site (AATAAA). The deduced amino acid sequence of CrCAT contained several highly conserved motifs including the proximal heme-ligand signature sequence RLFSYNDTX and the proximal active site signature FXRERIPERVVHAKGXGA. A comparative analysis showed the presence of conserved amino acid residues and all of the catalytic amino acids (His(70), Asn(143), and Tyr(353)) were conserved in all species. The CrCAT contained three potential glycosylation sites and a peroxisome targeting signal of 'AKM'. The mRNA was detected using RT-PCR at all developmental stages. The time-course expression of CrCAT was measured using quantitative real-time PCR after exposure to different concentration and durations of Paraquat (PQ), cadmium chloride (Cd) and nonylphenol (NP). The expression of CrCAT was significantly up regulated on exposure to 50 and 100mg/L PQ for 12 and 24h. Among the different concentrations and durations of Cd tested, significantly highest level of expression for CrCAT mRNA and catalase enzyme activity was observed on exposure to 10mg/L for 24h. In the case of NP, the highest level of CrCAT expression was observed after exposure to 100 μg/L for 24h. The expression profiles of three selected C. riparius glutathione S-transferase genes (CrGSTs) viz. CrGSTdelta3, CrGSTsigma4 and CrGSTepsilon1 was also studied on exposure to NP and were up or down regulated at different time points and concentrations. Significantly highest level of expression for CrGSTdelta3 was observed after 48 h and for CrGSTsigma4 and CrGSTepsilon1 after 24h exposure to 100 μg/L of NP. The results show that CrGSTs and CrCAT could be used as potential biomarkers in C. riparius for aquatic ecotoxicological studies.

Atf1-Pcr1-M26 complex links stress-activated MAPK and cAMP-dependent protein kinase pathways via chromatin remodeling of cgs2+

Although co-ordinate interaction between different signal transduction pathways is essential for developmental decisions, interpathway connections are often obscured and difficult to identify due to cross-talk. Here signals from the fission yeast stress-activated MAPK Spc1 are shown to regulate Cgs2, a negative regulator of the cAMP-dependent protein kinase (protein kinase A) pathway. Pathway integration is achieved via Spc1-dependent binding of Atf1-Pcr1 heterodimer to an M26 DNA site in the cgs2+ promoter, which remodels chromatin to regulate expression of cgs2+ and targets downstream of protein kinase A. This direct interpathway connection co-ordinates signals of nitrogen and carbon source depletion to affect a G0 cell-cycle checkpoint and sexual differentiation. The Atf1-Pcr1-M26 complex-dependent chromatin remodeling provides a molecular mechanism whereby Atf1-Pcr1 heterodimer can function differentially as either a transcriptional activator, or as a transcriptional repressor, or as an inducer of meiotic recombination. We also show that the Atf1-Pcr1-M26 complex functions as both an inducer and repressor of chromatin remodeling, which provides a way for various chromatin remodeling-dependent effector functions to be regulated.

Enhancement of catalase activity by repetitive low-grade H2O2 exposures protects fibroblasts from subsequent stress-induced apoptosis

Exposure of Chinese hamster V79 fibroblasts to mild and repetitive H2O2 doses in culture for 15 weeks produced no change in lipid peroxidation status, GSH/GSSG ratio and glutathione peroxidase activity of these cells (VST cells). In contrast, in VST cells catalase levels underwent a prominent increase which could be significantly inhibited and brought down to control levels after treatment with the catalase inhibitor 3-aminotriazole (3-AT). When control (VC) cells were exposed to UV radiation (UVC 5 J/m2) or H2O2 (7.5mM, 15 min), intracellular reactive oxygen species (ROS) levels rose prominently with significant activation of caspase-3. Marked nuclear fragmentation and lower cell viability were also noted in these cells. In contrast, VST cells demonstrated a significantly lower ROS level, an absence of nuclear fragmentation and an unchanged caspase-3 activity after exposure to UVC or H2O2. Cell viability was also significantly better preserved in VST cells than VC cells after UV or H2O2 exposures. Following 3-AT treatment of VST cells, UVC radiation or H2O2 brought about significantly higher elevations in intracellular ROS, increases in caspase-3 activity, significantly lowered cell viability and marked nuclear fragmentation, indicating the involvement of high catalase levels in the cytoprotective effects of repetitive stress. Therefore, upregulation of the antioxidant defense after repetitive oxidative stress imparted a superior ability to cope with subsequent acute stress and escape apoptotic death and loss of viability.

In vitro transcription and start site selection in Schizosaccharomyces pombe

We have used the fission yeast Schizosaccharomyces pombe to establish both a biochemical and genetic system to study the roles of general transcription factors in transcription initiation. Extracts were prepared that faithfully transcribed S. pombe promoters and the results confirm that, in contrast to the budding yeast Saccharomyces cerevisiae, in vitro transcription in S. pombe initiates near to the TATA element. S. pombe transcription relies on upstream activation sequence elements and these can be replaced successfully with sites for binding Gal4-VP16 activators. Although it is mammalian-like in these respects, S. pombe initiation uses an unusual scanning mechanism. This directs initiation, preferentially using purines, within a narrow window approximately 25-40 base-pairs downstream from the edge of the TATA element. Genetic experiments showed that this scanning mechanism was associated with the properties of the TFIIB polypeptide. When human TFIIB was expressed in S. pombe, it was accepted by the endogenous transcription machinery and caused initiation to be restricted to the closer edge of this window, corresponding to the distance in humans. Preliminary experiments suggested that S. cerevisiae TFIIB was not accepted. The results enlarge the potential for using fission yeast to study the properties of general transcription factors such as TFIIB in choosing the sites at which transcription initiates.

Distinct regulatory proteins control the graded transcriptional response to increasing H(2)O(2) levels in fission yeast Schizosaccharomyces pombe

The signaling pathways that sense adverse stimuli and communicate with the nucleus to initiate appropriate changes in gene expression are central to the cellular stress response. Herein, we have characterized the role of the Sty1 (Spc1) stress-activated mitogen-activated protein kinase pathway, and the Pap1 and Atf1 transcription factors, in regulating the response to H(2)O(2) in the fission yeast Schizosaccharomyces pombe. We find that H(2)O(2) activates the Sty1 pathway in a dose-dependent manner via at least two sensing mechanisms. At relatively low levels of H(2)O(2), a two component-signaling pathway, which feeds into either of the two stress-activated mitogen-activated protein kinase kinase kinases Wak1 or Win1, regulates Sty1 phosphorylation. In contrast, at high levels of H(2)O(2), Sty1 activation is controlled predominantly by a two-component independent mechanism and requires the function of both Wak1 and Win1. Individual transcription factors were also found to function within a limited range of H(2)O(2) concentrations. Pap1 activates target genes primarily in response to low levels of H(2)O(2), whereas Atf1 primarily controls the transcriptional response to high concentrations of H(2)O(2). Our results demonstrate that S. pombe uses a combination of stress-responsive regulatory proteins to gauge and effect the appropriate transcriptional response to increasing concentrations of H(2)O(2).

Schizosaccharomyces pombe homologue of glutathione peroxidase, which does not contain selenocysteine, is induced by several stresses and works as an antioxidant

We have cloned a gene of Schizosaccharomyces pombe homologues to the glutathione peroxidase gene. The cloned gene, named gpx1(+), encoded a protein that was 158 amino acids in length and had a molecular mass of 18 kDa. The gpx1(+) gene is homologous with many glutathione peroxidase genes but the selenocysteine codon (UGA) position of mammalian genes is a cysteine codon (UGU) in S. pombe. gpx1(+) mRNA was induced by various stresses, including oxidative stress, osmostress and heat stress. These stresses activate the Wis1-Sty1/Spc1 MAP kinase cascade in S. pombe. Transcriptional factors Atf1 and Pap1 are under the control of this MAP kinase. In the disruption of the atf1(+) gene, gpx1(+) was not transcribed or induced. However, the expression of gpx1(+) was not affected by the disruption of the pap1(+) gene. These results indicated that gpx1(+) was under the control of transcription factor Atf1. Catalase can detoxicate H(2)O(2) in the same way as GPx and the disruptant of the catalase gene of S. pombe is hypersensitive to H(2)O(2). The catalase gene disruptant of S. pombe harbouring multicopy plasmid containing gpx1(+) restored the hypersensitivity to H(2)O(2) of the catalase gene disruptant. These results suggest that Gpx1 acts as a scavenger of H(2)O(2) in vivo.

Identification of the catalase gene promoter region involved in superinduction in Schizosaccharomyces pombe caused by cycloheximide and hydrogen peroxide

Superinduction of the catalase gene was observed in Schizosaccharomyces pombe cells treated with cycloheximide and hydrogen peroxide. The promoter analysis of the catalase gene revealed that element A (the region from -111 to -90, numbered with the transcription start site as +1), involved in the induction of the gene under oxidative stress, was required for superinduction by hydrogen peroxide and cycloheximide. Although Atf1 is a transcription factor responsible for the induction of the catalase gene by several stresses, a disruptant of atf1 exhibited superinduction. Moreover, in a deletion mutant that lacks element A but has an Atf1 binding site, the cells treated with hydrogen peroxide and cycloheximide expressed as much catalase mRNA as those treated with hydrogen peroxide alone. This suggests that cycloheximide does not stabilize the catalase mRNA but enhances the transcription via element A. Staurosporine, a strong inhibitor of protein phosphorylation, did not inhibit superinduction.

The role of catalase in hydrogen peroxide resistance in fission yeast Schizosaccharomyces pombe

The role of catalase in hydrogen peroxide resistance in Schizosaccharomyces pombe was investigated. A catalase gene disruptant completely lacking catalase activity is more sensitive to hydrogen peroxide than the parent strain. The mutant does not acquire hydrogen peroxide resistance by osmotic stress, a treatment that induces catalase activity in the wild-type cells. The growth rate of the disruptant is not different from that of the parent strain. Additionally, transformed cells that overexpress the catalase activity are more resistant to hydrogen peroxide than wildtype cells with normal catalase activity. These results indicate that the catalase of S. pombe plays an important role in resistance to high concentrations of hydrogen peroxide but offers little in the way of protection from the hydrogen peroxide generated in small amounts under normal growth conditions.