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, 5 (5), 1425-35

A Peroxiredoxin Promotes H2O2 Signaling and Oxidative Stress Resistance by Oxidizing a Thioredoxin Family Protein

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A Peroxiredoxin Promotes H2O2 Signaling and Oxidative Stress Resistance by Oxidizing a Thioredoxin Family Protein

Jonathon D Brown et al. Cell Rep.

Abstract

H2O2 can cause oxidative damage associated with age-related diseases such as diabetes and cancer but is also used to initiate diverse responses, including increased antioxidant gene expression. Despite significant interest, H2O2-signaling mechanisms remain poorly understood. Here, we present a mechanism for the propagation of an H2O2 signal that is vital for the adaptation of the model yeast, Schizosaccharomyces pombe, to oxidative stress. Peroxiredoxins are abundant peroxidases with conserved antiaging and anticancer activities. Remarkably, we find that the only essential function for the thioredoxin peroxidase activity of the Prx Tpx1(hPrx1/2) in resistance to H2O2 is to inhibit a conserved thioredoxin family protein Txl1(hTxnl1/TRP32). Thioredoxins regulate many enzymes and signaling proteins. Thus, our discovery that a Prx amplifies an H2O2 signal by driving the oxidation of a thioredoxin-like protein has important implications, both for Prx function in oxidative stress resistance and for responses to H2O2.

Figures

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Figure 1
Figure 1
Loss of the Thioredoxin Reductase, Trr1, but Not Trx1, Bypasses the Requirement for Tpx1 in the Oxidation and Nuclear Localization of Pap1 (A) The catalytic cycle of the Prx, Tpx1, involves reduction of Tpx1 disulfides by the thioredoxin, Trx1. Oxidized Trx1 is reduced by thioredoxin reductase using NADPH. In cells treated with H2O2, Trr1 levels are limiting such that Trx1 becomes completely oxidized unless Tpx1 becomes hyperoxidized (Day et al., 2012). The question marks (“?”) indicate that the role of Trx1 and Tpx1 in oxidation of Pap1 is unclear; it is possible that (i) Tpx1 disulfides competitively inhibit the reduction of oxidized, active Pap1 by Trx1, and/or (ii) Tpx1 has another role in Pap1 oxidation. (B–D) Tpx1 is required for the oxidation of Pap1 in Δtrx1 but not Δtrr1 mutant cells as revealed by western blot analysis, using Pap1 antibodies, of IAA-treated proteins isolated from wild-type (WT; AD82), Δtpx1 (VXOO), Δtrx1 (JB30), Δtrr1 (AD81), Δtpx1Δtrx1 (AD100), and Δtpx1Δtrr1 (AD138) cells treated with 0.2 mM H2O2 for the indicated times. Oxidized (Pap1ox) and reduced (Pap1red) Pap1 were separated on the basis of the slower mobility of Pap1 following modification of reduced cysteines with IAA. Results in (B) and (C) are representative of at least three independent experiments. (D) The proportion of oxidized Pap1 was determined by densitometric analysis (ImageJ) quantification of oxidized and total Pap1 in at least three independent experiments. The mean percentage of oxidized Pap1 is shown, and the error bars indicate the SEM. (E) Immunostaining with Pap1 antibodies revealed the localization of Pap1 in wild-type (AD82), Δtpx1 (VXOO), Δtrx1 (JB30), Δtrr1 (AD81), Δtpx1Δtrx1 (AD100), and Δtpx1Δtrr1 (AD138) cells before and following treatment with 0.2 mM H2O2 for the indicated times. Each image was captured under identical conditions and exposure time. See also Figure S1.
Figure 2
Figure 2
The Thioredoxin-like Protein Txl1 Is Present in the Nucleus and Cytoplasm and Is Regulated by H2O2 in a Tpx1- and Trr1-Dependent Manner (A) Immunolocalization with Flag antibodies of Flag epitope-tagged Txl1 (Flag-Txl1; JB95) and Trx1 (Flag-Trx1; JB35) expressed from their normal chromosomal loci, respectively, revealed that Flag-Txl1 is distributed throughout the cell, whereas Flag-Trx1 is excluded from the nucleus both before and following treatment with 0.2 mM H2O2. Nuclei were detected by DAPI staining. (B) Txl1 is oxidized by H2O2 and reduced by Trr1. The redox state of Flag-Txl1 expressed from the normal chromosomal locus was analyzed by western blot using extracts prepared by acid lysis and AMS treatment from trr1+ (JB95) and Δtrr1 (JB116) cells treated with 0.2 mM H2O2 for the indicated times. Oxidized (Txl1ox) and reduced (Txl1red) Flag-Txl1 were separated on the basis of the slower mobility of Txl1 following AMS modification of reduced cysteines. (C) Western blot analysis of the oxidation state of Tpx1 in wild-type (AD82), Δtrx1 (JB30), Δtxl1 (EV75), and Δtrx1Δtxl1 (AD140) cells before and following treatment with 0.2 mM H2O2 for the indicated times revealed that Trx1 and Txl1 are both required for reduction of Tpx1-Tpx1 disulfides. AMS modification of reduced cysteines was used to separate Tpx1-Tpx1 single disulfides () from Tpx1-Tpx1 disulfides containing two disulfide bonds (#) in which all cysteines are oxidized. (D–F) The redox state of Flag-Txl1 was determined by western blot analysis of AMS-modified proteins prepared from (D) tpx1+ (JB95) and Δtpx1 (JB113), (E) tpx1+ (JB95) and tpx1C169S (JB107), and (F) tpx1+ (JB95) cells expressing Flag-Txl1 from the normal chromosomal locus before and following treatment with 0.2 or 6 mM H2O2 as indicated. In (B) and (D)–(F), ns bands that are detected with Flag antibodies in cells expressing wild-type Txl1 (CHP429) are indicated, including a band with a similar mobility to oxidized Flag-Txl1 that is detected in cells before H2O2 treatment. (B and D–F) Oxidized (Txl1ox) and reduced (Txl1red) Flag-Txl1 were detected using Flag antibodies, and reduced Tpx1 (Tpxlred) and Tpx1 disulfides were detected using Tpx1 antibodies.
Figure 3
Figure 3
Txl1 and Trx1 Have Overlapping Functions as Inhibitors of the H2O2-Induced Activation of Pap1 Txl1 and Trx1 have overlapping functions as inhibitors of Pap1 activation as revealed by (A and C) western blot analysis using Pap1 antibodies of IAA-treated protein extracts prepared from wild-type (AD82), Δtxl1 (EV75), Δtrx1 (JB30), Δtrr1 (AD81), and Δtrx1Δtxl1 (AD140) cells treated with 0.2 mM H2O2 for the indicated times. Oxidized (Pap1ox) and reduced (Pap1red) Pap1 were separated on the basis of their different electrophoretic mobility following IAA modification of reduced cysteines. (B) The localization of Pap1 in midlog phase-growing wild-type (AD82), Δtxl1 (EV75), Δtrx1 (JB30), Δtrr1 (AD81), and Δtrx1Δtxl1 (AD140) cells treated with 0.2 mM H2O2 for the indicated times was examined by indirect immunofluorescence using Pap1 antibodies. Each image was captured under identical conditions and exposure time. See also Table S2.
Figure 4
Figure 4
Trx1 and Txl1 Inhibit pap1+ and Pap1-Dependent Gene Expression Northern blot analyses of RNA extracted from midlog phase-growing wild-type (AD82), Δtxl1 (EV75), Δtrx1 (JB30), Δtrr1 (AD81), and Δtrx1Δtxl1 (AD140) cells treated with 0.2 mM H2O2 for the indicated times. Gene-specific probes were used to detect RNA from the indicated genes. A gene-specific probe for leu1+ was used as a loading control (see also Table S1). (A) A representative blot of the indicated Pap1-dependent genes and the graphs show the quantitative analyses of three independent experiments plotted as the mean fold induction of each mRNA relative to wild-type. Error bars represent the SEM. (B) A representative blot is shown from three independent experiments illustrating the increased pap1+ mRNA levels detected in Δtrx1Δtxl1 cells. For quantified experimental data from each experiment. See Table S3.
Figure 5
Figure 5
Trx1 and Txl1 Are Important for Maintaining Pap1 in a Soluble Form that Can Be Oxidized in Response to H2O2 (A) Western blot analysis of the oxidation state of Pap1 in wild-type (AD82), Δtrx1(JB30), Δtrr1(AD81), Δtrx1Δtxl1(AD140), and Δtrx1Δtxl1Δtrr1 (JB120) cells before and following treatment with 0.2 mM H2O2 for 10 min reveals that in the absence of Txl1 and Trx1, there is a pool of reduced Pap1 that is not oxidized following exposure to H2O2. (B) Western blot analysis of Pap1 in extracts prepared under native (soluble) and denaturing (whole-cell lysate) conditions from the indicated strains and Δpap1 (TP108-3C), Δtrx1 (JB30), Δtrr1(AD81), Δtrx1Δtxl1(AD140), and Δtxl1(EV75) reveals that, although total Pap1 levels are similar in each strain, Pap1 is undetectable in extracts from Δtrx1Δtxl1 cells prepared under nondenaturing conditions. It should be noted that although, as indicated, oxidized and reduced Pap1 forms can be detected by both extraction methods, the absence of any precautions to prevent in vitro thiol exchange means that the relative levels of reduced and oxidized Pap1 in the soluble protein extracts are not a reliable indicator of the in vivo oxidation state of Pap1. See also Figure S2.
Figure 6
Figure 6
Txl1 Forms Disulfide Complexes with Pap1 and Inhibits Normal H2O2-Induced Oxidation of Pap1 in Cells Expressing the Thioredoxin Peroxidase-Defective Tpx1C169S Western blot analysis, using Pap1 antibodies, of the redox status of Pap1 in (A) cells expressing Tpx1C169S and coexpressing either txl1+ (−; JR42) or Flag-Txl1 (+; JB107) from their normal chromosomal loci before and following treatment with 0.2 mM H2O2 for the indicated times. Bands with a mobility that is consistent with Txl1-Pap1 () and Flag-Txl1-Pap1 (#) disulfides are indicated on the blot and in a selected area (white rectangle) magnified on the right-hand side of the panel. HMW Pap1 disulfides in cells expressing Flag-Txl1 whose slight reduction in mobility is consistent with the presence of the Flag epitope are also indicated (arrowheads). (B) Western blot analysis of wild-type (AD82) cells, and either txl1+ (JR42) or Δtxl1 (JB92) cells coexpressing Tpx1C169S from the normal chromosomal locus, before and following treatment with 0.2 mM H2O2 for 1 min revealed that loss of Txl1 restores normal wild-type oxidation of Pap1, and inhibits formation of HMW Pap1 disulfide complexes, in cells expressing Tpx1C169S. (C) Loss of Txl1 function restores the H2O2 resistance of cells expressing Tpx1C169S. The 10-fold serial dilutions of exponentially growing wild-type (JR68), Δtxl1 (JB99), tpx1C169Stxl1+ (JR42), and tpx1C169SΔtxl1 (JB92) cells were spotted onto media containing the indicated concentration of H2O2. Plates were incubated at 30°C for 2–3 days. See also Figure S3.
Figure 7
Figure 7
Model Illustrating How the Thioredoxin Peroxidase Activity of Prxs Can Promote H2O2 Signaling by Regulating Thioredoxin Family Proteins Thioredoxin family proteins are cofactors for multiple enzymes as well as important inhibitors of various H2O2-signaling pathways. By promoting the oxidation of thioredoxin, the peroxidase activity of Prxs provides a means for the H2O2-dependent regulation of all these pathways/enzymes, particularly when thioredoxin reductase (Trr) activity is limiting. For example, in S. pombe, the thioredoxin peroxidase activity of Tpx1 propagates H2O2 signal transduction and increases oxidative stress resistance by driving the oxidation of the thioredoxin family protein Txl1 that directly inhibits (reduces) Pap1. Thioredoxin reductase (Trr) activity counterbalances this Prx-mediated H2O2 signaling. See also Figures S4 and S5.

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