Phospholipid hydroperoxide glutathione peroxidase is a selenoenzyme distinct from the classical glutathione peroxidase as evident from cDNA and amino acid sequencing

Non-coding RNA: A key regulator in the Glutathione-GPX4 pathway of ferroptosis

Ferroptosis, a form of regulated cell death, has emerged as a crucial process in diverse pathophysiological states, encompassing cancer, neurodegenerative ailments, and ischemia-reperfusion injury. The glutathione (GSH)-dependent lipid peroxidation pathway, chiefly governed by glutathione peroxidase 4 (GPX4), assumes an essential part in driving ferroptosis. GPX4, as the principal orchestrator of ferroptosis, has garnered significant attention across cancer, cardiovascular, and neuroscience domains over the past decade. Noteworthy investigations have elucidated the indispensable functions of ferroptosis in numerous diseases, including tumorigenesis, wherein robust ferroptosis within cells can impede tumor advancement. Recent research has underscored the complex regulatory role of non-coding RNAs (ncRNAs) in regulating the GSH-GPX4 network, thus influencing cellular susceptibility to ferroptosis. This exhaustive review endeavors to probe into the multifaceted processes by which ncRNAs control the GSH-GPX4 network in ferroptosis. Specifically, we delve into the functions of miRNAs, lncRNAs, and circRNAs in regulating GPX4 expression and impacting cellular susceptibility to ferroptosis. Moreover, we discuss the clinical implications of dysregulated interactions between ncRNAs and GPX4 in several conditions, underscoring their capacity as viable targets for therapeutic intervention. Additionally, the review explores emerging strategies aimed at targeting ncRNAs to modulate the GSH-GPX4 pathway and manipulate ferroptosis for therapeutic advantage. A comprehensive understanding of these intricate regulatory networks furnishes insights into innovative therapeutic avenues for diseases associated with perturbed ferroptosis, thereby laying the groundwork for therapeutic interventions targeting ncRNAs in ferroptosis-related pathological conditions.

Verteporfin induces lipid peroxidation and ferroptosis in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) has extremely poor prognosis, with a 5-year survival rate of approximately 11 %. Yes-associated protein (YAP) is a major downstream effector of the Hippo-YAP pathway and plays a pivotal role in regulation of cell proliferation and organ regeneration and tumorigenesis. Activation of YAP signaling has been associated with PDAC progression and drug resistance. Verteporfin (VP) is a photosensitizer used for photodynamic therapy and previous work showed that it can function as a YAP inhibitor. The efficacy of VP on human cancer are being tested in several trials. In this study, we examined the effect of VP on reactive oxygen species (ROS) and lipid peroxidation in pancreatic cancer cells, by using fluorescent molecular probes and by measuring the levels of malondialdehyde, a metabolic byproduct and marker of lipid peroxidation. We found that VP causes rapid increase of both overall ROS and lipid peroxide levels, independent of light activation. These effects were not dependent on YAP, as knockdown of YAP did not cause ROS or lipid peroxidation or enhance VP-induced ROS production. Temoporfin, another photodynamic drug, did not show similar activities. In addition, VP treatment led to loss of cell membrane integrity and reduction of viability. Notably, the activity of VP to induce lipid peroxidation was neutralized by ferroptosis inhibitors ferrostatin-1 or liproxstatin-1. VP treatment also reduced the levels of glutathione peroxidase 4 (GPX4), an enzyme that protects against lipid peroxidation. These results indicate that VP can induce lipid peroxidation and ferroptosis in the absence of light activation. Our findings reveal a novel mechanism by which VP inhibits tumor growth and provide insights into development of new therapeutic strategies for the treatment of pancreatic cancer.

GPX4: The hub of lipid oxidation, ferroptosis, disease and treatment

Glutathione peroxidase 4 (GPx4) moonlights as structural protein and antioxidase that powerfully inhibits lipid oxidation. In the past years, it is considered as a key regulator of ferroptosis, which takes role in the lipid and amine acid metabolism and influences the cell aging, oncogenesis, and cell death. More and more evidences show that targeting GPX4-induced ferroptosis is a promising strategy for disease therapy, especially cancer treatment. In view of these, we generalize the function of GPX4 and regulatory mechanism between GPX4 and ferroptosis, discuss its roles in the disease pathology, and focus on the recent advances of disease therapeutic potential.

Mitochondrial Peroxiredoxin 3 Is Rapidly Oxidized and Hyperoxidized by Fatty Acid Hydroperoxides

Human peroxiredoxin 3 (HsPrx3) is a thiol-based peroxidase responsible for the reduction of most hydrogen peroxide and peroxynitrite formed in mitochondria. Mitochondrial disfunction can lead to membrane lipoperoxidation, resulting in the formation of lipid-bound fatty acid hydroperoxides (_LFA-OOHs) which can be released to become free fatty acid hydroperoxides (_fFA-OOHs). Herein, we report that HsPrx3 is oxidized and hyperoxidized by _fFA-OOHs including those derived from arachidonic acid and eicosapentaenoic acid peroxidation at position 15 with remarkably high rate constants of oxidation (>3.5 × 10⁷ M^-1s^-1) and hyperoxidation (~2 × 10⁷ M^-1s^-1). The endoperoxide-hydroperoxide PGG₂, an intermediate in prostanoid synthesis, oxidized HsPrx3 with a similar rate constant, but was less effective in causing hyperoxidation. Biophysical methodologies suggest that HsPrx3 can bind hydrophobic structures. Indeed, molecular dynamic simulations allowed the identification of a hydrophobic patch near the enzyme active site that can allocate the hydroperoxide group of _fFA-OOHs in close proximity to the thiolate in the peroxidatic cysteine. Simulations performed using available and herein reported kinetic data indicate that HsPrx3 should be considered a main target for mitochondrial _fFA-OOHs. Finally, kinetic simulation analysis support that mitochondrial _fFA-OOHs formation fluxes in the range of nM/s are expected to contribute to HsPrx3 hyperoxidation, a modification that has been detected in vivo under physiological and pathological conditions.

A white paper on Phospholipid Hydroperoxide Glutathione Peroxidase (GPx4) forty years later

The purification of a protein inhibiting lipid peroxidation led to the discovery of the selenoperoxidase GPx4 forty years ago. Thus, the evidence of the enzymatic activity was reached after identifying the biological effect and unambiguously defined the relationship between the biological function and the enzymatic activity. In the syllogism where GPx4 inhibits lipid peroxidation and its inhibition is lethal, cell death is operated by lipid peroxidation. Based on this rationale, this form of cell death emerged as regulated iron-enforced oxygen toxicity and was named ferroptosis in 2012. In the last decades, we learned that reduction of lipid hydroperoxides is indispensable and, in cooperation with prooxidant systems, controls the critical steady state of lipid peroxidation. This concept defined the GPx4 reaction as both the target for possible anti-cancer therapy and if insufficient, as cause of degenerative diseases. We know the reaction mechanism, but the details of the interaction at the membrane cytosol interface are still poorly defined. We know the gene structure, but the knowledge about expression control is still limited. The same holds true for post-transcriptional modifications. Reverse genetics indicate that GPx4 has a role in inflammation, immunity, and differentiation, but the observations emerging from these studies need a more specifically addressed biochemical evidence. Finally, the role of GPx4 in spermatogenesis disclosed an area unconnected to lipid peroxidation. In its mitochondrial and nuclear form, the peroxidase catalyzes the oxidation of protein thiols in two specific aspects of sperm maturation: stabilization of the mid-piece and chromatin compaction. Thus, although available evidence converges to the notion that GPx4 activity is vital due to the inhibition of lipid peroxidation, it is reasonable to foresee other unknown aspects of the GPx4 reaction to be disclosed.

Emerging Potential Therapeutic Targets of Ferroptosis in Skeletal Diseases

Ferroptosis is a new programmed cell death characterized by the accumulation of lipid peroxidation mediated by iron and inflammation. Since the transcentury realization of ferroptosis as an iron-dependent modality of nonapoptotic cell death in 2012, there has been growing interest in the function of ferroptosis and its relationship to clinical diseases. Recent studies have shown that ferroptosis is associated with multiple diseases, including degenerative diseases, ischemia reperfusion injury, cardiovascular disease, and cancer. Cell death induced by ferroptosis has also been related to several skeletal diseases, such as inflammatory arthritis, osteoporosis, and osteoarthritis. Research on ferroptosis can clarify the pathogenesis of skeletal diseases and provide a novel therapeutic target for its treatment. In this review, we summarize current information about the molecular mechanism of ferroptosis and describe its emerging role and therapeutic potential in skeletal diseases.

Post-Translational Modification of GPX4 is a Promising Target for Treating Ferroptosis-Related Diseases

Glutathione peroxidase 4 (GPX4) is one of the most important antioxidant enzymes. As the key regulator of ferroptosis, GPX4 has attracted considerable attention in the fields of cancer, cardiovascular, and neuroscience research in the past 10 years. How to regulate GPX4 activity has become a hot topic nowadays. GPX4 protein level is regulated transcriptionally by transcription factor SP2 or Nrf2. GPX4 activity can be upregulated by supplementing intracellular selenium or glutathione, and also be inhibited by ferroptosis inducers such as ML162 and RSL3. These regulatory mechanisms of GPX4 level/activity have already shown a great potential for treating ferroptosis-related diseases in preclinical studies, especially in cancer cells. Until recently, research show that GPX4 can undergo post-translational modifications (PTMs), such as ubiquitination, succination, phosphorylation, and glycosylation. PTMs of GPX4 affect the protein level/activity of GPX4, indicating that modifying these processes can be a potential therapy for treating ferroptosis-related diseases. This article summarizes the protein characteristics, enzyme properties, and PTMs of GPX4. It also provides a hypothetical idea for treating ferroptosis-related diseases by targeting the PTMs of GPX4.

The Selenoprotein Glutathione Peroxidase 4: From Molecular Mechanisms to Novel Therapeutic Opportunities

The selenoprotein glutathione peroxidase 4 (GPX4) is one of the main antioxidant mediators in the human body. Its central function involves the reduction of complex hydroperoxides into their respective alcohols often using reduced Glutathione (GSH) as a reducing agent. GPX4 has become a hotspot therapeutic target in biomedical research following its characterization as a chief regulator of ferroptosis, and its subsequent recognition as a specific pharmacological target for the treatment of an extensive variety of human diseases including cancers and neurodegenerative disorders. Several recent studies have provided insights into how GPX4 is distinguished from the rest of the glutathione peroxidase family, the unique biochemical properties of GPX4, how GPX4 is related to lipid peroxidation and ferroptosis, and how the enzyme may be modulated as a potential therapeutic target. This current report aims to review the literature underlying all these insights and present an up-to-date perspective on the current understanding of GPX4 as a potential therapeutic target.

Editorial to Special Issue Molecular Biology of Selenium in Health and Disease

The selenium field expanded at a rapid rate for about 45 years, from the mid-1970's until about 2015 (see [...].

Redox Pioneer: Professor Regina Brigelius-Flohé

Dr. Regina Brigelius-Flohé (PhD 1978) is recognized here as redox pioneer because she has published an article on redox biology, as first author, that has been cited >1000 times, plus four articles cited >500 times, and a total of 30 articles cited >100 times. She obtained her doctorate in biochemistry at the Institute of Biochemistry of the University of Münster, Germany. She held positions in both, academia (Münster, Munich, Düsseldorf, Hannover, and Potsdam, Germany) and industry (Aachen, Germany). Dr. Brigelius-Flohé is the pioneer who, as head of the department of biochemistry of micronutrients of the German Institute of Human Nutrition (DIfE; Potsdam-Rehbrücke, Germany), worked out the metabolism of tocopherols and tocotrienols ("Key Finding 1"). She was the first to sequence glutathione peroxidase 4 (GPx4) ("Key Finding 2"), and unraveled the role of selenium, in particular of GPxs, in inflammation and carcinogenesis ("Key Finding 3"). Her contributions, thus, focused on serious biomedical problems such as nutrition, inflammation, and carcinogenesis. She has been a member of the scientific advisory board of the German Society of Biochemistry and Molecular Biology for 6 years and was president of SFRR-Europe in 2005-2006. She edited several books and serves on the editorial board of journals in the fields of nutrition, free radicals, and redox regulation. Antioxid. Redox Signal. 35, 595-601.

Opportunities for Ferroptosis in Cancer Therapy

A critical hallmark of cancer cells is their ability to evade programmed apoptotic cell death. Consequently, resistance to anti-cancer therapeutics is a hurdle often observed in the clinic. Ferroptosis, a non-apoptotic form of cell death distinguished by toxic lipid peroxidation and iron accumulation, has garnered substantial attention as an alternative therapeutic strategy to selectively destroy tumours. Although there is a plethora of research outlining the molecular mechanisms of ferroptosis, these findings are yet to be translated into clinical compounds inducing ferroptosis. In this perspective, we elaborate on how ferroptosis can be leveraged in the clinic. We discuss a therapeutic window for compounds inducing ferroptosis, the subset of tumour types that are most sensitive to ferroptosis, conventional therapeutics that induce ferroptosis, and potential strategies for lowering the threshold for ferroptosis.

The development of the concept of ferroptosis

The term ferroptosis was coined in 2012 to describe an iron-dependent regulated form of cell death caused by the accumulation of lipid-based reactive oxygen species; this type of cell death was found to have molecular characteristics distinct from other forms of regulated cell death. Features of ferroptosis have been observed periodically over the last several decades, but these molecular features were not recognized as evidence of a distinct form of cell death until recently. Here, we describe the history of observations consistent with the current definition of ferroptosis, as well as the advances that contributed to the emergence of the concept of ferroptosis. We also discuss recent implications and applications of manipulations of the ferroptotic death pathway.

Biological and physiological role of reactive oxygen species--the good, the bad and the ugly

Reactive oxygen species (ROS) are chemically reactive molecules that are naturally produced within biological systems. Research has focused extensively on revealing the multi-faceted and complex roles that ROS play in living tissues. In regard to the good side of ROS, this article explores the effects of ROS on signalling, immune response and other physiological responses. To review the potentially bad side of ROS, we explain the consequences of high concentrations of molecules that lead to the disruption of redox homeostasis, which induces oxidative stress damaging intracellular components. The ugly effects of ROS can be observed in devastating cardiac, pulmonary, neurodegenerative and other disorders. Furthermore, this article covers the regulatory enzymes that mitigate the effects of ROS. Glutathione peroxidase, superoxide dismutase and catalase are discussed in particular detail. The current understanding of ROS is incomplete, and it is imperative that future research be performed to understand the implications of ROS in various therapeutic interventions.

Mitochondrial energy metabolism and redox signaling in brain aging and neurodegeneration

SIGNIFICANCE

The mitochondrial energy-transducing capacity is essential for the maintenance of neuronal function, and the impairment of energy metabolism and redox homeostasis is a hallmark of brain aging, which is particularly accentuated in the early stages of neurodegenerative diseases.

RECENT ADVANCES

The communications between mitochondria and the rest of the cell by energy- and redox-sensitive signaling establish a master regulatory device that controls cellular energy levels and the redox environment. Impairment of this regulatory devise is critical for aging and the early stages of neurodegenerative diseases.

CRITICAL ISSUES

This review focuses on a coordinated metabolic network-cytosolic signaling, transcriptional regulation, and mitochondrial function-that controls the cellular energy levels and redox status as well as factors which impair this metabolic network during brain aging and neurodegeneration.

FUTURE DIRECTIONS

Characterization of mitochondrial function and mitochondria-cytosol communications will provide pivotal opportunities for identifying targets and developing new strategies aimed at restoring the mitochondrial energy-redox axis that is compromised in brain aging and neurodegeneration.

Genome-wide computational identification of bicistronic mRNA in humans

Mammalian bicistronic mRNA is a recently discovered mammalian gene structure. Several reported cases of mammalian bicistronic mRNA indicated that genes of this structure play roles in some important biological processes. However, a genome-wide computational identification of bicistronic mRNA in mammalian genome, such as human genome, is still lacking. Here we used a comparative genomics approach to identify the frequency of human bicistronic mRNA. We then validated the result by using a new support vector machine (SVM) model. We identified 43 human bicistronic mRNAs in 30 distinct genes. Our literature analysis shows that our method recovered 100 % (6/6) of the previously known bicistronic mRNAs which had been experimentally confirmed by other groups. Our graph theory-based analysis and GO analysis indicated that human bicistronic mRNAs are prone to produce different yet closely functionally related proteins. In addition, we also described and analyzed three different mechanisms of ORF fusion. Our method of identifying bicistronic mRNAs in human genome provides a model for the computational identification of characteristic gene structures in mammalian genomes. We anticipate that our data will facilitate further molecular characterization and functional study of human bicistronic mRNA.

Redox pioneer: Professor Leopold Flohé

Leopold Flohé is recognized here as a Redox Pioneer because has published a article on antioxidant/redox biology, as first author, that has been cited more than 1,000 times, and more than 20 articles have been cited more than 100 times. He obtained the medical doctorate at the Institute of Pharmacology and Toxicology at the University of Tübingen, Germany, in 1968. He held positions in both Academia (Tübingen, Aachen, and Braunschweig, Germany) and industry (Aachen). He is now operating the biotech company MOLISA in Magdeburg, Germany, while teaching as guest professor at the local university. Dr. Flohé is the pioneer who established the selenoprotein nature of glutathione peroxidase (GPx), the first and, for almost 10 years, the only selenoprotein known in animals. His work was pivotal to link the essential trace element selenium to metabolic processes, which led the Food and Drug Administration (FDA) to approve selenium supplementation for humans in 1980, and stimulated selenium biochemistry in general. In recent years, he embarked on investigating how pathogens protect themselves from oxidative killing. His inseminating studies on the thiol-dependent hydroperoxide metabolism of trypanosomatids and mycobacteria defined molecular drug targets, paving the way to new therapeutic strategies for neglected diseases affecting the people of developing countries.

Identification of two phospholipid hydroperoxide glutathione peroxidase (gpx4) genes in common carp

The monomeric selenoprotein, phospholipid hydroperoxide glutathione peroxidase (GPx4) is an essential member of the antioxidant defense system. This paper describes the identification of two gpx4 genes (gpx4a and gpx4b) from somatic tissues of common carp (Cyprinus carpio). The two sequences exhibited 78% and 79% identity at the DNA and the predicted protein level, respectively. The gpx4a transcript was detected in all examined tissues of unstressed animals, with the highest level in the liver. The gpx4b expression was low relative to that of gpx4a in the liver, heart, muscle and brain, and was virtually undetected in the kidney. However, in the olfactory lobe gpx4b was expressed at a fairly high level, the ratio gpx4a/gpx4b being approximately 2:1. Cold shock and Cd(2+) exposure influenced the gpx4a expression to only a slight extent, whereas gpx4b was greatly down-regulated following Cd(2+) exposure.

Analysis of selenocysteine-containing proteins

Representatives of three primary life domains--bacteria, archaea, and eukaryotes--possess specific selenium-containing proteins. The majority of naturally occurring selenoproteins contain an amino acid, selenocysteine, that is incorporated into protein in response to the code word UGA. The presence of selenium in natural selenoproteins and in proteins in which this element is introduced by chemical or biological manipulations provides additional opportunities for characterizing structure, function, and mechanism of action. This unit provides an overview of known selenocysteine-containing proteins, examples of targeted incorporation of selenium into proteins, and methods specific for selenoprotein identification and characterization.

Multitechnique mass-spectrometric approach for the detection of bovine glutathione peroxidase selenoprotein: focus on the selenopeptide

Glutathione peroxidase (isolated from bovine erythrocytes) and its behaviour during alkylation and enzymatic digestion were studied by various hyphenated techniques: gel electrophoresis-laser ablation (LA) inductively coupled plasma (ICP) mass spectrometry (MS), size-exclusion liquid chromatography-ICP MS, capillary high-performance liquid chromatography (capHPLC)-ICP MS, matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) MS, electrospray MS, and nanoHPLC-electrospray ionization (ESI) MS/MS. ESI TOF MS and MALDI TOF MS allowed the determination of the molecular mass but could not confirm the presence of selenium in the protein. The purity of the protein with respect to selenium species could be evaluated by LA ICP MS and size-exclusion chromatography (SEC)-ICP MS under denaturating and nondenaturating conditions, respectively. SEC-ICP MS and capHPLC-ICP MS turned out to be valuable techniques to study the enzymolysis efficiency, miscleavage and artefact formation during derivatization and tryptic digestion. For the first time the parallel ICP MS and ESI MS/MS data are reported for the selenocysteine-containing peptide extracted from the gel; capHPLC-ICP MS allowed the sensitive detection of the selenopeptide regardless of the matrix and nanoHPLC-electrospray made possible its identification.

Seleno-independent glutathione peroxidases

Glutathione peroxidases (GPXs, EC 1.11.1.9) were first discovered in mammals as key enzymes involved in scavenging of activated oxygen species (AOS). Their efficient antioxidant activity depends on the presence of the rare amino-acid residue selenocysteine (SeCys) at the catalytic site. Nonselenium GPX-like proteins (NS-GPXs) with a Cys residue instead of SeCys have also been found in most organisms. As SeCys is important for GPX activity, the function of the NS-GPX can be questioned. Here, we highlight the evolutionary link between NS-GPX and seleno-GPX, particularly the evolution of the SeCys incorporation system. We then discuss what is known about the enzymatic activity and physiological functions of NS-GPX. Biochemical studies have shown that NS-GPXs are not true GPXs; notably they reduce AOS using reducing substrates other than glutathione, such as thioredoxin. We provide evidence that, in addition to their inefficient scavenging action, NS-GPXs act as AOS sensors in various signal-transduction pathways.

Nuclease sensitive element binding protein 1 gene disruption results in early embryonic lethality

Nuclease sensitive element binding protein 1 (NSEP1) is a member of the EFIA/NSEP1/YB-1 family of DNA-binding proteins whose members share a cold shock domain; it has also been termed DNA-binding protein B and Y box binding protein-1 because of its recognition of transcriptional regulatory elements. In addition, NSEP1 functions in the translational regulation of renin, ferritin, and interleukin 2 transcripts, and our laboratory has reported that it plays a role in the biosynthesis of selenium-containing proteins. To test the functional importance of NSEP1 in murine embryonic development, we have utilized a clone of ES cells in which the NSEP1 gene had been disrupted by integration of a plasmid gene-trapping vector into the seventh exon. Injection of these cells into C57BL/6 blastocysts resulted in 11 high percentage chimeric mice; crosses to wild type C57BL/6 mice generated 82 F1 agouti mice, indicating germ line transmission of the ES cell clone, but genotyping showed no evidence of the disrupted allele in any of these agouti offspring even though spermatozoa from four of five tested mice contained the targeted allele. Embryos harvested after timed matings of chimeric male mice demonstrated only the wildtype allele in 27 embryos tested at E7.5, E12.5, and E18.5. These results suggest that gene targeting of NSEP1 induces a lethal phenotype in early embryos, due to either haploinsufficiency of NSEP1 or formation of a dominant negative form of the protein. In either case, these data indicate the functional importance of the NSEP1 gene in murine early embryonic development.

Molecular characterization of phospholipid hydroperoxide glutathione peroxidases from Hydra vulgaris

Apparent full-length cDNA sequences coding respectively for mitochondrial (HvGPx41) and nuclear (HvGPx42) phospholipid hydroperoxide glutathione peroxidase were isolated from Hydra vulgaris. The cDNA sequences share total identity in their 3'-end and differ in their 5'-end. The protein-coding regions of the HvGPx41 and HvGPx42 cDNA encode polypeptides of 190 and 168 amino acids, including a TGA-encoded selenocysteine, respectively. Phylogenetic analysis showed that the HvGPx41 and HvGPx42 are clustered together along with other phospholipid hydroperoxide glutathione peroxidases (PHGPx) from several organisms. A tertiary structure model generated for the H. vulgaris PHGPx displayed the thioredoxin fold. Hydrae exposed to starvation, metal and oxidative stress responded by regulating their PHGPx mRNA transcription. These results indicated that the PHGPx gene is affected by the cellular stress response and (anti)oxidative processes triggered by stressor and contaminant exposure. Hence the expression of PHGPx mRNA in hydra may have potential use as molecular biomarkers for assessing stress, toxicity and pro-oxidant quality of chemicals and aquatic environmental quality.

Nuclease sensitive element binding protein 1 associates with the selenocysteine insertion sequence and functions in mammalian selenoprotein translation

Biosynthesis of selenium-containing proteins requires insertion of the unusual amino acid selenocysteine by alternative translation of a UGA codon, which ordinarily serves as a stop codon. In eukaryotes, selenoprotein translation depends upon one or more selenocysteine insertion sequence (SECIS) elements located in the 3'-untranslated region of the mRNA, as well as several SECIS-binding proteins. Our laboratory has previously identified nuclease sensitive element binding protein 1 (NSEP1) as another SECIS-binding protein, but evidence has been presented both for and against its role in SECIS binding in vivo and in selenoprotein translation. Our current studies sought to resolve this controversy, first by investigating whether NSEP1 interacts closely with SECIS elements within intact cells. After reversible in vivo cross-linking and ribonucleoprotein immunoprecipitation, mRNAs encoding two glutathione peroxidase family members co-precipitated with NSEP1 in both human and rat cell lines. Co-immunoprecipitation of an epitope-tagged GPX1 construct depended upon an intact SECIS element in its 3'-untranslated region. To test the functional importance of this interaction on selenoprotein translation, we used small inhibitory RNAs to reduce the NSEP1 content of tissue culture cells and then examined the effect of that reduction on the activity of a SECIS-dependent luciferase reporter gene for which expression depends upon readthrough of a UGA codon. Co-transfection of small inhibitory RNAs directed against NSEP1 decreased its expression by approximately 50% and significantly reduced luciferase activity. These studies demonstrate that NSEP1 is an authentic SECIS binding protein that is structurally associated with the selenoprotein translation complex and functionally involved in the translation of selenoproteins in mammalian cells.

Marmoset glutathione peroxidases: cDNA sequences, molecular evolution, and gene expression

BACKGROUND

Dysfunction of the cellular antioxidant system and accumulation of reactive oxygen species are involved in the pathophysiology of diseases such as cardiovascular disease, neurodegenerative disorders, tumors, male infertility and aging. Two gluthathione peroxidases play key roles in the cellular protection against oxidative damage. Glutathione peroxidase (GPx-1) removes cytosolic hydroperoxides while phospholipid-hydroperoxide glutathione peroxidase (GPx-4) is a unique enzyme that reduces phospholipid peroxides in membranes.

METHODS

We cloned and sequenced the full-length cDNA for GPx-1 (GenBank: AY966403) and GPx-4 (GenBank: AY966404) from the common marmoset (Callithrix jacchus) in order to create a suitable model for studying human diseases related with oxidative stress.

RESULTS

The cDNAs encode a 202 amino acid protein for GPx-1 and a 197 amino acid protein for GPx-4. Both proteins include selenocysteine (Sec, in Gpx-1 at position 48; in GPx-4 at position 73) and showed high homology (>90%) with other mammalian GPxs. The relative levels of mRNA expression for GPx-1 and GPx-4 were determined in different marmoset tissues by quantitative real-time reverse transcriptase-polymerase chain reaction using transcription elongation factor-2 as a reference gene. GPx-1 showed increased levels of expression in the liver, heart and kidney while the highest mRNA levels for GPx-4 were detected in the testis, followed by the liver, lung, kidney and spinal cord.

CONCLUSIONS

These findings will be of value for studies designed to assess the role of glutathione peroxidases in non-human primate models for a variety of diseases in which increased oxidative stress has been implicated.

Effects of gpx4 haploid insufficiency on GPx4 activity, selenium concentration, and paraquat-induced protein oxidation in murine tissues

Selenium-dependent glutathione peroxidase-4 (GPx4) catalyzes the reduction of phospholipid hydroperoxides. Because a full gpx4 knockout is embryonic lethal, we examined the effect of deletion of one copy of gpx4 on the activities of three selenoperoxidases (GPx1, GPx3, and GPx4), selenium concentrations, and pro-oxidant-induced protein oxidation in various tissues of mice. A total of 32 gpx4 hemizygous (GPx4+/-) and wild-type (WT) mice (8- to 10-weeks old; 16 males and 16 females) were fed a selenium-adequate diet and given an intraperitoneal injection of paraquat (PQ; 24 mg/kg body wt) or phosphate-buffered saline (PBS). All mice were euthanized 4 hrs after injection to collect tissues for analyses. In PBS-treated mice, GPx4 activities in lung, liver, kidney, and testes of GPx4+/- mice were 24-39% lower (P < 0.05) than in WT mice. Among PQ-treated mice, only testis GPx4 activity in GPx4+/- mice was significantly lower (54% P < 0.05) than WT mice. Selenium concentration in testes, but not in other tissues, was reduced (34% P < 0.05) in GPx4+/- mice compared with WT mice, irrespective of treatment. Tissue GPx1 activities and plasma GPx3 and alanine aminotransferase (ALT) activities were unaffected by PQ treatment or gpx4 hemizygosity. Total protein carbonyl was elevated (73% P < 0.05) by PQ only in lung, and this effect of PQ was independent of genotypes. In conclusion, gpx4 haploid insufficiency reduced GPx4 activities and/or selenium concentrations, but had no effect on pro-oxidant-induced protein oxidation in various tissues of mice.

Phenoloxidase-like activities and the function of virus-like particles in ovaries of the parthenogenetic parasitoid Venturia canescens

The ichneumonid endoparasitoid Venturia canescens successfully develops inside the hemocoel of another insect by using maternal protein secretions, including nucleic acid-free virus-like particles (VLPs), to manipulate host physiology. These VLPs consist of four major proteins, which are produced mainly in the calyx tissue and transferred into the host insect together with the egg. One of the protein-coding genes (vlp1), with similarities to phospholipid-hydroperoxide glutathione peroxidases (PHGPx), exists in allelic forms producing two protein variants with different protein properties. Here, we summarise observations indicating that oocytes and eggs are the source of reactive electrons, which potentially damage the lining and membranes of calyx tissues. We discuss the possible role of VLP1 in counteracting the damaging effects of oxidised phospholipids on membranes surrounding VLPs in the calyx lumen.

L-PhGPx expression can be suppressed by antisense oligodeoxynucleotides

Phospholipid hydroperoxide glutathione peroxidase (PhGPx) directly reduces hydroperoxides of phospholipid and cholesterol to their corresponding alcohols. There are two forms of PhGPx: L-PhGPx localizes in mitochondria and S-PhGPx in cytosol. Antisense oligodeoxynucleotides can inhibit specific protein expression. We tested the hypothesis that antisense oligodeoxynucleotides could be designed to inhibit PhGPx expression and thereby sensitize cells to lipid peroxidation induced by singlet oxygen. We chose P4 cells, a cell line established from L-PhGPx cDNA transfected MCF-7 cells, as our cell model. Lipid peroxidation was induced by singlet oxygen generated by Photofrin and visible light. We found that the antisense oligodeoxynucleotide (5' GCCGAGGCTCATCGCGGCGG 3') was effective in suppressing L-PhGPx mRNA, PhGPx protein, and activity. This antisense oligodeoxynucleotide did not interfere with S-PhGPx. When cells were exposed to singlet oxygen, lipid hydroperoxides were produced in the cells. L-PhGPx was able to remove these hydroperoxides; this removal was inhibited by antisense treatment. The inhibition of L-PhGPx by the antisense oligodeoxynucleotides also resulted in increased membrane damage as measured by trypan blue dye exclusion. These data demonstrate that PhGPx expression can be manipulated by antisense techniques.

Pharmacokinetic model of daily selenium intake from contaminated seafood in Taiwan

Contaminated seafood has been reported as an important source of human exposure to metals in Taiwan. Seafood represents a non-negligible source of selenium in the human diet. This study was designed to determine the concentration of selenium in different types of seafood and predict the concentration of selenium in the blood of Taiwanese using a one-compartment steady-state pharmacokinetic (PK) model. Samples involved three subgroups, including fish, crustaceans and bivalve molluscs. Quantitative analysis for selenium was performed using an ICP-AES (Perkin Elmer) instrument. Selenium concentrations in seafood ranged from 0.63 to 2.01 microg/g wet wt. The highest selenium concentration found in fish was 2.01+/-0.36 microg/g wet wt in Salmo salar Linnaeus. In general, selenium concentration increased in the order of bivalve molluscs<crustacean<fish. The daily selenium intakes resulting from a high-seafood diet and an average diet were 145.2 and 60.2 microg/day, respectively. Daily selenium intake from seafood alone is higher than the US recommended daily allowance (RDA) of 55 microg/day and the World Health Organization (WHO) normative requirement of 40 microg/day. From PK model estimates, the concentrations of selenium in the blood of a typical seafood consumer and a high-seafood consumer were approximately 93 and 224 microg/l based on daily seafood intake of 60.2 and 145.2 microg/day, respectively.

Cloning and expression analysis of chicken phospholipid-hydroperoxide glutathione peroxidase

Phospholipid-hydroperoxide glutathione peroxidase (GPX4 or PHGPX) is a unique selenium dependent glutathione peroxidase that reduces phospholipid, cholesterol, and cholesteryl ester hydroperoxides. Phospholipid-hydroperoxide glutathione peroxidase has been shown to exist as both a 197 amino acid mitochondrial targeting protein and as a 170 amino acid non-mitochondrial protein. The cDNA encoding the non-mitochondrial chicken GPX4 (cGPX4) has been isolated from an immortalized DF-1 chicken embryonic fibroblast (CEF) cell line cDNA library. The nucleotide sequence of cGPX4 was 802 bp in length with an open reading frame (ORF) that encoded 170 amino acids but lacked the N-terminal domain that encoded the mitochondrial leader sequence (MLS). Chicken non-mitochondrial GPX4 was highly expressed in brain and stromal tissues. Surprisingly, it was found that ovarian stromal tissue cGPX4 expression is regulated quite differently according to the reproductive status of the bird, suggesting that GPX4 may play an important role in reproduction in response to steroid hormones, in addition to its general antioxidant functions.

Versatility of selenium catalysis in PHGPx unraveled by LC/ESI-MS/MS

Phospholipid hydroperoxide glutathione peroxidase (PHGPx; EC 1.11.1.12), a broad-spectrum thiol-dependent peroxidase, deserves renewed interest as a regulatory factor in various signaling cascades and as a structural protein in sperm cells. We present a first attempt to identify catalytic intermediates and derivatives of the selenoprotein by liquid chromatography coupled to electrospray tandem mass spectrometry (LC/ESI-MS/MS) and to explain observed specificities by molecular modeling. The ground state enzyme E proved to correspond to position 3-170 of the deduced porcine sequence with selenium being present as selenocysteine at position 46. The selenenic acid form, which is considered to be the first catalytic intermediate F formed by reaction with hydroperoxide, could not be identified. The second catalytic intermediate G was detected as Se-glutathionylated enzyme. This intermediate is generated in the reverse reaction where the active site selenol interacts with glutathione disulfide (GSSG). According to molecular models, specific binding of reduced glutathione (GSH) and of GSSG is inter alia facilitated by electrostatic attraction of Lys-48 and Lys-125. Polymerization of PHGPx is obtained under oxidizing conditions in the absence of low molecular weight thiols. Analysis of MS spectra revealed that the process is due to a selective reaction of Sec-46 with Cys-148' resulting in linear polymers representing dead-end intermediates (G'). FT Docking of PHGPx molecules allowed reactions of Sec-46 with either Cys-66', Cys-107', Cys-168' or Cys-148', the latter option being most likely as judged by the number of proposed intermediates with reasonable hydrogen bonds, interaction energies and interface areas. We conclude that the same catalytic principles, depending on the conditions, can drive the diverse actions of PHGPx, i.e. hydroperoxide reduction, GSSG reduction, S-derivatization and self-incorporation into biological structures.

Regulation of enzymatic lipid peroxidation: the interplay of peroxidizing and peroxide reducing enzymes

For a long time lipid peroxidation has only been considered a deleterious process leading to disruption of biomembranes and thus, to cellular dysfunction. However, when restricted to a certain cellular compartment and tightly regulated, lipid peroxidation may have beneficial effects. Early on during evolution of living organisms special lipid peroxidizing enzymes, called lipoxygenases, appeared and they have been conserved during phylogenesis of plants and animals. In fact, a diverse family of lipoxygenase isoforms has evolved starting from a putative ancient precursor. As with other enzymes, lipoxygenases are regulated on various levels of gene expression and there are endogenous antagonists controlling their cellular activity. Among the currently known mammalian lipoxygenase isoforms only 12/15-lipoxygenases are capable of directly oxygenating ester lipids even when they are bound to membranes and lipoproteins. Thus, these enzymes represent the pro-oxidative part in the cellular metabolism of complex hydroperoxy ester lipids. Its metabolic counterplayer, representing the antioxidative part, appears to be the phospholipid hydroperoxide glutathione peroxidase. This enzyme is unique among glutathione peroxidases because of its capability of reducing ester lipid hydroperoxides. Thus, 12/15-lipoxygenase and phospholipid hydroperoxide glutathione peroxidase constitute a pair of antagonizing enzymes in the metabolism of hydroperoxy ester lipids, and a balanced regulation of the two proteins appears to be of major cell physiological importance. This review is aimed at summarizing the recent developments in the enzymology and molecular biology of 12/15-lipoxygenase and phospholipid hydroperoxide glutathione peroxidase, with emphasis on cytokine-dependent regulation and their regulatory interplay.

The effect of aging on glutathione peroxidase-i knockout mice-resistance of the lens to oxidative stress

Populations of control, C, and glutathione peroxidase-1 (GPx-1) knockout mice, K, were studied over a period of 2 years. No significant difference was observed between the C and K populations with respect to longevity, vitality, weight, lens biochemistry or morphology based on light and electron microscopy. It was concluded that under normal animal room barrier facilities, GPx-1 is not required. Furthermore, C and K lenses placed in organ culture and observed over a 24 hr period were indistinguishable. Organ cultured C lenses degraded medium H(2)O(2)levels at only a slightly greater rate than K lenses and this did not appear to change with age. However, tertiary butyl hydroperoxide (TBHP) was degraded less effectively by K lenses and this deficiency increased with age. No indication of change in redox non-protein SH (equivalent to GSH) status was observed between C and K whole lenses or epithelial cell fractions. With H(2)O(2)stress, the drop in C and K non-protein SH was comparable and there was little change with age. Examination of the impact of photochemical stress with 1.5 microM riboflavin and 4% O(2)upon choline transport indicated considerable damage with both C and K lenses, but little difference between the two populations until 1 or 2 years of age when the K lenses appear more vulnerable. With TBHP, the detrimental effect on the K lenses is greater and is observed earlier than with photochemical stress suggesting that the K lens membrane function is more susceptible to phospholipid hydroperoxide stress than are C lenses. Light and electron microscopy of the oxidative stressed lenses indicates significant damage which was generally somewhat greater in the K lenses. TBHP was a more potent oxidant than photochemically generated oxidants particularly at the anterior pole. The overall results suggest that under normal conditions, at any age, the lens does not require the presence of GPx-1 but depending on the type of oxidative stress, the enzyme may significantly contribute to its defense and this dependency may increase with age.

Selenium in biology: facts and medical perspectives

Several decades after the discovery of selenium as an essential trace element in vertebrates approximately 20 eukaryotic and more than 15 prokaryotic selenoproteins containing the 21st proteinogenic amino acid, selenocysteine, have been identified, partially characterized or cloned from several species. Many of these proteins are involved in redox reactions with selenocysteine acting as an essential component of the catalytic cycle. Enzyme activities have been assigned to the glutathione peroxidase family, to the thioredoxin reductases, which were recently identified as selenoproteins, to the iodothyronine deiodinases, which metabolize thyroid hormones, and to the selenophosphate synthetase 2, which is involved in selenoprotein biosynthesis. Prokaryotic selenoproteins catalyze redox reactions and formation of selenoethers in (stress-induced) metabolism and energy production of E. coli, of the clostridial cluster XI and of other prokaryotes. Apart from the specific and complex biosynthesis of selenocysteine, selenium also reversibly binds to proteins, is incorporated into selenomethionine in bacteria, yeast and higher plants, or posttranslationally modifies a catalytically essential cysteine residue of CO dehydrogenase. Expression of individual eukaryotic selenoproteins exhibits high tissue specificity, depends on selenium availability, in some cases is regulated by hormones, and if impaired contributes to several pathological conditions. Disturbance of selenoprotein expression or function is associated with deficiency syndromes (Keshan and Kashin-Beck disease), might contribute to tumorigenesis and atherosclerosis, is altered in several bacterial and viral infections, and leads to infertility in male rodents.

Recognition and binding of the human selenocysteine insertion sequence by nucleolin

Prokaryotic and eukaryotic cells cotranslationally incorporate the unusual amino acid selenocysteine at a UGA codon, which conventionally serves as a termination signal. Translation of selenoprotein gene transcripts in eukaryotes depends upon a "selenocysteine insertion sequence" in the 3'-untranslated region. We have previously shown that DNA-binding protein B specifically binds this sequence element. We now report the identification of nucleolin as a partner in the selenoprotein translation complex. In RNA electromobility shift assays, nucleolin binds the selenocysteine insertion sequence from the human cellular glutathione peroxidase gene, competes with binding activity from COS cells, and shows diminished affinity for probes with mutations in functionally important, conserved sequence elements. Antibody to nucleolin interferes with the gel shift activity of COS cell extract. Antibody to DNA-binding protein B co-extracts nucleolin from HeLa cell cytosol, and the two proteins co-sediment in glycerol gradient fractions of ribosomal high salt extracts. Thus, nucleolin appears to join DNA-binding protein B and possibly other partners to form a large complex that links the selenocysteine insertion sequence in the 3'-untranslated region to other elements in the coding region and ribosome to translate the UGA "stop" codon as selenocysteine.

Tissue-specific functions of individual glutathione peroxidases

The family of glutathione peroxidases comprises four distinct mammalian selenoproteins. The classical enzyme (cGPx) is ubiquitously distributed. According to animal, cell culture and inverse genetic studies, its primary function is to counteract oxidative attack. It is dispensible in unstressed animals, and accordingly ranks low in the hierarchy of glutathione peroxidases. The gastrointestinal isoenzyme (GI-GPx) is most related to cGPx and is exclusively expressed in the gastrointestinal tract. It might provide a barrier against hydroperoxides derived from the diet or from metabolism of ingested xenobiotics. The extreme stability in selenium deficiency ranks this glutathione peroxidase highest in the hierarchy of selenoproteins and points to a more vital function than that of cGPx. Plasma GPx (pGPx) behaves similar to cGPx in selenium deficiency. It is directed to extracellular compartments and is expressed in various tissues in contact with body fluids, e.g., kidney, ciliary body, and maternal/fetal interfaces. It has to be rated as an efficient extracellular antioxidant device, though with low capacity because of the limited extracellular content of potential thiol substrates. Phospholipid hydroperoxide glutathione peroxidase (PHGPx), originally presumed to be a universal antioxidant enzyme protecting membrane lipids, appears to have adopted a variety of specific roles like silencing lipoxygenases and becoming an enzymatically inactive structural component of the mitochondrial capsule during sperm maturation. Thus, all individual isoenzymes are efficient peroxidases in principle, but beyond their mere antioxidant potential may exert cell- and tissue-specific roles in metabolic regulation, as is evident for PHGPx and may be expected for others.

Dual function of the selenoprotein PHGPx during sperm maturation

The selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) changes its physical characteristics and biological functions during sperm maturation. PHGPx exists as a soluble peroxidase in spermatids but persists in mature spermatozoa as an enzymatically inactive, oxidatively cross-linked, insoluble protein. In the midpiece of mature spermatozoa, PHGPx protein represents at least 50 percent of the capsule material that embeds the helix of mitochondria. The role of PHGPx as a structural protein may explain the mechanical instability of the mitochondrial midpiece that is observed in selenium deficiency.

Associations of antioxidant enzymes with cataract and age-related macular degeneration. The POLA Study. Pathologies Oculaires Liées à l'Age

OBJECTIVE

Oxidative mechanisms may play an important role in the etiology of cataract and age-related macular degeneration (AMD). The authors present the level of two antioxidant enzymes in relation to cataract and AMD.

DESIGN

Population-based, cross-sectional study on cataract and AMD and their risk factors.

PARTICIPANTS

This study includes 2584 participants recruited among the residents of the town of Sète (in the south of France), who were 60 years of age or older.

INTERVENTION/METHODS

Cataract was defined on the basis of slit-lamp examination, according to the Lens Opacities Classification System III, and AMD on the basis of fundus photographs according to an international classification. Biologic measurements were made centrally from blood samples for which the patient fasted.

MAIN OUTCOME MEASURES

The presence of early and late AMD and of subcapsular, cortical, nuclear, and mixed cataracts was assessed and related to the levels of plasma glutathione peroxidase and erythrocyte superoxide dismutase.

RESULTS

After multivariate adjustment, higher levels of plasma glutathione peroxidase (pIGPx) were significantly associated with a ninefold increase in late AMD prevalence, a sixfold increase in cortical cataract, and a twofold increase in nuclear and mixed cataracts. High levels of erythrocyte superoxide dismutase (SOD) activity were not associated with late AMD and early signs of AMD but were associated with a twofold increase in nuclear cataract.

CONCLUSION

The authors show here, for the first time, a strong association of high levels of pIGPx with age-related eye diseases. High levels of SOD also are associated with increased risk of nuclear cataract. More data are needed at the biochemical and epidemiologic levels for a better understanding of these findings.

Expression pattern of mitochondrial capsule selenoprotein mRNA in the hamster testis

Mitochondrial capsule selenoprotein (MCS) has been known as a structural protein of the mitochondrial sheath in spermatozoa. In the present study, to determine the expression pattern of MCS mRNA in the hamster testis, northern blot and in situ hybridization analyses using digoxigenin-labeled riboprobes for the hamster MCS were performed in the testes of 10-week-old golden hamsters. According to the northern blot analysis, hamster MCS was detected as a single transcript of about 1 kb in the testis. During spermatogenesis, the hamster MCS mRNA first appeared in step 6 spermatids, gradually increased in round spermatids during spermiogenesis, reached a peak in step 8 spermatids, and persisted a high level until step 13 spermatids. After step 14, the signal began to show a progressive decline in the spermatids and was weakly detected in the tails of step 17 spermatids. However, the signal was not observed in spermatogonia, spermatocytes, Sertoli cells, peritubular myoid cells, and interstitial cells. These findings indicate that hamster MCS is mainly related to the spermiogenesis during spermatogenesis.

UGA codon position affects the efficiency of selenocysteine incorporation into glutathione peroxidase-1

A UGA codon and a selenocysteine insertion sequence in the 3'-untranslated region are the only established mRNA elements necessary for selenocysteine (Sec or U) incorporation during translation. These two elements, however, do not universally confer efficient Sec incorporation. The objective of this study was to systematically examine the effect of UGA codon position on efficiency of Sec insertion. In a glutathione peroxidase-1 (F-GPX1) expression vector, the UGA at the native position (U47) was mutated to a cysteine codon, and codons for Ser-7, Ser-12, Ser-18, Ser-29, Ser-45, Ser-93, Cys-154, Val-172, Ser-178, and Ser-195 were individually mutated to UGA and transiently expressed in COS-7 cells. 75Se incorporation at the 11 positions was 31, 72, 54, 105, 90, 100, 146, 135, 13, 11, and 43%, respectively, of 75Se incorporation at U47, suggesting that Sec is more efficiently incorporated at UGA codons positioned in the middle of the coding region rather than close to the 5' or 3' ends. Ribonuclease protection showed that these differences were not due to differences in mRNA level. When the green fluorescence protein (GFP) coding region was placed in-frame at the 5' or 3' ends of the coding region in F-GPX1 to produce chimeric 50-51-kDa GFP/GPX1 proteins, Sec incorporation at UGA codons, formerly close to the 5' or 3' ends, was increased to levels comparable to the UGA at U47. Insertion of GFP after the UAA-stop was just as effective in increasing Sec insertion efficiency as GFP inserted before the stop. These studies used a recombinant expression model that incorporated Sec at non-native UGA codons at rates equal to those of endogenous glutathione peroxidase-1 and showed that the efficiency of Sec incorporation can be modulated by UGA position; Sec incorporation at high efficiency appears to require that the UGA be >21 nucleotides from the AUG-start and >204 nucleotides from the selenocysteine insertion sequence element.

A novel glutathione peroxidase in bovine eye. Sequence analysis, mRNA level, and translation

Bovine ciliary body contains a selenium-independent glutathione peroxidase (GPX) with a molecular mass of about 100 kDa that is composed of four identical subunits and exhibits no glutathione S-transferase activity. In this study, we isolated cDNA clones and determined the nucleotide sequence to deduce the primary structure of the enzyme. The cDNA contained 672 base pairs encoding a polypeptide with an estimated molecular mass of 25,064 Da. Translation of bovine ciliary mRNA produced a protein which was immunologically indistinguishable from GPX and showed high enzyme activity. The encoded amino acid sequence of the protein was 95% identical with that of a human keratinocyte gene product expressed in response to keratinocyte growth factor. It also showed sequence identity to bacterial alkyl hydroperoxide reductases and thiol specific antioxidant enzymes. GPX mRNA level was highest in the ciliary body, followed by the retina and iris. In various rat organs, the level of GPX mRNA was highest in the lung, followed by the muscle, liver, eye, heart, testis, thymus, kidney, and spleen. A very low level of mRNA was detected in the brain. Enzyme-linked immunosorbent assay with an antibody raised against the NH2-terminal sequence of GPX detected GPX protein in all rat tissues examined.

Cloning and expression of mitochondrial capsule selenoprotein gene in the golden hamster

Mitochondrial capsule selenoprotein (MCS) has been known as a structural protein of the mitochondrial sheath in spermatoza. In the present study, a full-length cDNA encoding the MCS was first isolated from the testes of 10-week-old golden hamsters using a RACE (rapid amplification of cDNA ends) technique and its mRNA expression pattern was investigated from the hamster tissues by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Hamster MCS cDNA was 820 bp long, including 24 bp of the 5'-untranslated region (UTR) and 243 bp of the 3'-UTR, and showed identity of 75.6% and 73.9% with mouse and rat MCS. According to the deduced amino acid (aa) sequence analysis, hamster MCS encoded a polypeptide of 184 aa, including a cysteine- and proline-rich domain which is the characteristic sequences of MCS, and contained 2 in-frame UGA codons for selenocysteine. Hamster MCS also shared aa identity of 64.4% with mouse MCS and contained an Arg-Lys-Ser-Thr-rich region in the N-terminus similar to the mitochondrial targeting signal. On the other hand, according to the RT-PCR analysis using the specific primers for hamster MCS, hamster MCS mRNA was expressed in various tissues as well as the testes. This finding indicates that MCS in hamster may have more than just a function of mitochondrial sheath formation of spermatozoa.