Oxidation state governs structural transitions in peroxiredoxin II that correlate with cell cycle arrest and recovery

Bronchoalveolar lavage fluid proteome in bronchiolitis obliterans syndrome: possible role for surfactant protein A in disease onset

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) affects long-term survival of lung transplant (Tx) recipients (LTRs), with no consistently effective treatment strategy. Identifying early markers of BOS is of paramount importance for improving graft survival.

METHODS

We used 2-dimensional gel electrophoresis and protein identification by mass spectrometry to compare the protein profile of bronchoalveolar lavage fluid (BALf) in two groups of LTRs: one composed of patients with BOS and the other composed of patients with good graft function at >5 years post-surgery (stable LTRs). Based on the hypothesis that only proteins of lung origin could represent reliable BOS markers, we also evaluated paired plasma samples. Proteins of interest were also assessed in the BALf of control subjects and results confirmed by dot- blot analysis.

RESULTS

Among 11 differentially expressed proteins, we identified 2 locally produced factors: peroxiredoxin II (PRXII), exclusively expressed in BOS; and surfactant protein A (SP-A), expressed consistently less in BOS patients than in stable LTRs. PRXII expression was never observed in BALf from control subjects, whereas SP-A was present in higher amounts compared with stable LTRs and BOS patients. Finally, the time course of SP-A was studied in 5 LTRs who subsequently developed BOS. A reduction in BALf SP-A content was detectable early after Tx, preceding BOS onset in 4 of 5 patients.

CONCLUSIONS

Our results suggest that testing SP-A levels in BALf could predict LTR patients who are at higher risk of BOS development.

Structure of the sulphiredoxin-peroxiredoxin complex reveals an essential repair embrace

Typical 2-Cys peroxiredoxins (Prxs) have an important role in regulating hydrogen peroxide-mediated cell signalling. In this process, Prxs can become inactivated through the hyperoxidation of an active site Cys residue to Cys sulphinic acid. The unique repair of this moiety by sulphiredoxin (Srx) restores peroxidase activity and terminates the signal. The hyperoxidized form of Prx exists as a stable decameric structure with each active site buried. Therefore, it is unclear how Srx can access the sulphinic acid moiety. Here we present the 2.6 A crystal structure of the human Srx-PrxI complex. This complex reveals the complete unfolding of the carboxy terminus of Prx, and its unexpected packing onto the backside of Srx away from the Srx active site. Binding studies and activity analyses of site-directed mutants at this interface show that the interaction is required for repair to occur. Moreover, rearrangements in the Prx active site lead to a juxtaposition of the Prx Gly-Gly-Leu-Gly and Srx ATP-binding motifs, providing a structural basis for the first step of the catalytic mechanism. The results also suggest that the observed interactions may represent a common mode for other proteins to bind to Prxs.

Discovering mechanisms of signaling-mediated cysteine oxidation

Accumulating evidence reveals hydrogen peroxide as a key player both as a damaging agent and, from emerging evidence over the past decade, as a second messenger in intracellular signaling. This rather mild oxidant acts upon downstream targets within signaling cascades to modulate the activity of a host of enzymes (e.g. phosphatases and kinases) and transcriptional regulators through chemoselective oxidation of cysteine residues. With the recent development of specific detection reagents for hydrogen peroxide and new chemical tools to detect the generation of the initial oxidation product, sulfenic acid, on reactive cysteines within target proteins, the scene is set to gain a better understanding of the mechanisms through which hydrogen peroxide acts as a second messenger in cell signaling.

S-nitrosylation of peroxiredoxin 2 promotes oxidative stress-induced neuronal cell death in Parkinson's disease

Peroxiredoxins (Prx), a family of peroxidases that reduce intracellular peroxides with the thioredoxin system as the electron donor, are highly expressed in various cellular compartments. Among the antioxidant Prx enzymes, Prx2 is the most abundant in mammalian neurons, making it a prime candidate to defend against oxidative stress. Here we report that Prx2 is S-nitrosylated (forming SNO-Prx2) by reaction with nitric oxide at two critical cysteine residues (C51 and C172), preventing its reaction with peroxides. We observed increased SNO-Prx2 in human Parkinson's disease (PD) brains, and S-nitrosylation of Prx2 inhibited both its enzymatic activity and protective function from oxidative stress. Dopaminergic neurons, which are lost in PD, become particularly vulnerable. Thus, our data provide a direct link between nitrosative/oxidative stress and neurodegenerative disorders such as PD.

Regulation of peroxiredoxins by nitric oxide in immunostimulated macrophages

Reactive oxygen species and nitric oxide (NO) are capable of both mediating redox-sensitive signal transduction and eliciting cell injury. The interplay between these messengers is quite complex, and intersection of their signaling pathways as well as regulation of their fluxes requires tight control. In this regard, peroxiredoxins (Prxs), a recently identified family of six thiol peroxidases, are central because they reduce H2O2, organic peroxides, and peroxynitrite. Here we provide evidence that endogenously produced NO participates in protection of murine primary macrophages against oxidative and nitrosative stress by inducing Prx I and VI expression at mRNA and protein levels. We also show that NO prevented the sulfinylation-dependent inactivation of 2-Cys Prxs, a reversible overoxidation that controls H2O2 signaling. In addition, studies using macrophages from sulfiredoxin (Srx)-deficient mice indicated that regeneration of 2-Cys Prxs to the active form was dependent on Srx. Last, we show that NO increased Srx expression and hastened Srx-dependent recovery of 2-Cys Prxs. We therefore propose that modulation by NO of Prx expression and redox state, as well as up-regulation of Srx expression, constitutes a novel pathway that contributes to antioxidant response and control of H2O2-mediated signal transduction in mammals.

Oxidation of 2-Cys-peroxiredoxins by arachidonic acid peroxide metabolites of lipoxygenases and cyclooxygenase-2

Human peroxiredoxins serve dual roles as anti-oxidants and regulators of H(2)O(2)-mediated cell signaling. The functional versatility of peroxiredoxins depends on progressive oxidation of key cysteine residues. The sulfinic or sulfonic forms of peroxiredoxin lose their peroxidase activity, which allows cells to accumulate H(2)O(2) for signaling or pathogenesis in inflammation, cancer, and other disorders. We report that arachidonic acid lipid hydroperoxide metabolites of 5-, 12-, 15-lipoxygenase-1, and cyclooxygenase-2 oxidize the 2-Cys-peroxiredoxins 1, 2, and 3 to their sulfinic and sulfonic forms. When added exogenously to cells, 5-, 12- and 15-hydroperoxy-eicosatetraenoic acids also over-oxidized peroxiredoxins. Our results suggest that lipoxygenases and cyclooxygenases may affect 2-Cys peroxiredoxin signaling, analogous to NADPH oxidases in the "floodgate" model (Wood, Z. A., Poole, L. B, and Karplus P. A. (2003) Science 300, 600-653). Peroxiredoxin-dependent mechanisms may modulate the receptor-dependent actions of autocoids derived from cellular lipoxygenase and cyclooxygenase catalysis.

Are peroxiredoxins tumor suppressors?

It has been known for many years that free radicals, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS), promote diseases such as cancer. Peroxiredoxins (Prdxs) are small H(2)O(2) scavenging proteins that appear to have tumor preventive functions since loss of Prdx1 in mice leads to premature death from cancer. However, as Prdxs are antioxidants they also scavenge the H(2)O(2) in cancer cells that way supporting survival and tumor maintenance. This suggests that Prdxs function as tumor 'preventers' rather than as tumor suppressors since they do not induce cell death when re-expressed in cancer cells, as it occurs with the tumor suppressor p53. Therefore, the knowledge of Prdx function and regulation may help provide a fuller understanding of the role of ROS in tumorigenesis.

Hydrogen peroxide sensing and signaling

It is well established that oxidative stress is an important cause of cell damage associated with the initiation and progression of many diseases. Consequently, all air-living organisms contain antioxidant enzymes that limit oxidative stress by detoxifying reactive oxygen species, including hydrogen peroxide. However, in eukaryotes, hydrogen peroxide also has important roles as a signaling molecule in the regulation of a variety of biological processes. Here, we will discuss the molecular mechanisms by which hydrogen peroxide is sensed and the increasing evidence that antioxidant enzymes play multiple, key roles as sensors and regulators of signal transduction in response to hydrogen peroxide.

Molecular cloning, characterization and regulation of a peroxiredoxin gene from Schizosaccharomyces pombe

A gene encoding a putative peroxiredoxin (Prx) of the fission yeast Schizosaccharomyces pombe was characterized and its regulation was studied. The full length of the prx gene was introduced into the shuttle vector pRS316 after PCR amplification, resulting in the recombinant plasmid pPrx10. The determined DNA sequence carries 1,327 bp encoding a putative Prx with a molecular mass of 19,510 Da. Prx activity was significantly increased in the S. pombe cells harboring pPrx10. The accelerated growth was observed in the S. pombe/pPrx10 cells, implying the involvement of the cloned gene in the yeast growth. To study transcriptional regulation of the prx gene, the prx-lacZ fusion gene was constructed using the yeast-E. coli shuttle vector YEp367R, and named pPrxup10. The synthesis of beta-galactosidase from the fusion gene was enhanced under carbon source-limited conditions and nitrogen starvation. Under the same growth conditions, the prx mRNA levels of the wild-type yeast cells were increased. The prx mRNA level was markedly decreased in the Pap1-negative mutant, compared with that in the wild-type yeast, suggesting that the basal expression of the prx gene is mediated by a transcription factor, Pap1. The reactive oxygen species (ROS) level was diminished in the S. pombe/pPrx10 cells than in the control cells. The extra copies of the prx gene were able to resist elevation of ROS level under limited carbon source condition and menadione treatment. In brief, the S. pombe Prx is linked with the yeast growth and up-regulated by metabolic oxidative stress on a transcriptional level. The Prx protein is partly responsible for maintaining low ROS level under normal and stressful growth conditions in the fission yeast.

Cysteine reactivity and thiol-disulfide interchange pathways in AhpF and AhpC of the bacterial alkyl hydroperoxide reductase system

AhpC and AhpF from Salmonella typhimurium undergo a series of electron transfers to catalyze the pyridine nucleotide-dependent reduction of hydroperoxide substrates. AhpC, the peroxide-reducing (peroxiredoxin) component of this alkyl hydroperoxidase system, is an important scavenger of endogenous hydrogen peroxide in bacteria and acts through a reactive, peroxidatic cysteine, Cys46, and a second cysteine, Cys165, that forms an active site disulfide bond. AhpF, a separate disulfide reductase protein, regenerates AhpC every catalytic cycle via electrons from NADH which are transferred to AhpC through a tightly bound flavin and two disulfide centers, Cys345-Cys348 and Cys129-Cys132, through putative large domain movements. In order to assess cysteine reactivity and interdomain interactions in both proteins, a comprehensive set of single and double cysteine mutants (replacing cysteine with serine) of both proteins were prepared. Based on 5,5-dithiobis(2-nitrobenzoic acid) (DTNB) and AhpC reactivity with multiple mutants of AhpF, the thiolate of Cys129 in the N-terminal domain of AhpF initiates attack on Cys165 of the intersubunit disulfide bond within AhpC for electron transfer between proteins. Cys348 of AhpF has also been identified as the nucleophile attacking the Cys129 sulfur of the N-terminal disulfide bond to initiate electron transfer between these two redox centers. These findings support the modular architecture of AhpF and its need for domain rotations for function, and emphasize the importance of Cys165 in the reductive reactivation of AhpC. In addition, two new constructs have been generated, an AhpF-AhpC complex and a "twisted" form of AhpF, in which redox centers are locked together by stable disulfide bonds which mimic catalytic intermediates.

The Lipoxin A4 receptor is coupled to SHP-2 activation: implications for regulation of receptor tyrosine kinases

Mesangial cell proliferation is pivotal to the pathology of glomerular injury in inflammation. We have previously reported that lipoxins, endogenously produced eicosanoids with anti-inflammatory and pro-resolution bioactions, can inhibit mesangial cell proliferation in response to several agents. This process is associated with elaborate receptor cross-talk involving modification receptor tyrosine kinase phosphorylation (McMahon, B., Mitchell, D., Shattock, R., Martin, F., Brady, H. R., and Godson, C. (2002) FASEB J. 16, 1817-1819). Here we demonstrate that the lipoxin A(4) (LXA(4)) receptor is coupled to activation and recruitment of the SHP-2 (SH2 domain-containing tyrosine phosphatase-2) within a lipid raft microdomain. Using site-directed mutagenesis of the cytosolic domain of the platelet-derived growth factor receptor beta (PDGFRbeta), we report that mutation of the sites for phosphatidylinositol 3-kinase (Tyr(740) and Tyr(751)) and SHP-2 (Tyr(763) and Tyr(1009)) recruitment specifically inhibit the effect of LXA(4) on the PDGFRbeta signaling; furthermore inhibition of SHP-2 expression with short interfering RNA constructs blocked the effect of LXA(4) on PDGFRbeta phosphorylation. We demonstrate that association of the PDGFRbeta with lipid raft microdomains renders it susceptible to LXA(4)-mediated dephosphorylation by possible reactivation of oxidatively inactivated SHP-2. These data further elaborate on the potential mechanisms underlying the anti-inflammatory, proresolution, and anti-fibrotic bioactions of lipoxins.