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Nature Metabolism Jul 2020The micronutrient selenium is incorporated via the selenocysteine biosynthesis pathway into the rare amino acid selenocysteine, which is required in selenoproteins such...
The micronutrient selenium is incorporated via the selenocysteine biosynthesis pathway into the rare amino acid selenocysteine, which is required in selenoproteins such as glutathione peroxidases and thioredoxin reductases. Here, we show that selenophosphate synthetase 2 (SEPHS2), an enzyme in the selenocysteine biosynthesis pathway, is essential for survival of cancer, but not normal, cells. SEPHS2 is required in cancer cells to detoxify selenide, an intermediate that is formed during selenocysteine biosynthesis. Breast and other cancer cells are selenophilic, owing to a secondary function of the cystine/glutamate antiporter SLC7A11 that promotes selenium uptake and selenocysteine biosynthesis, which, by allowing production of selenoproteins such as GPX4, protects cells against ferroptosis. However, this activity also becomes a liability for cancer cells because selenide is poisonous and must be processed by SEPHS2. Accordingly, we find that SEPHS2 protein levels are elevated in samples from people with breast cancer, and that loss of SEPHS2 impairs growth of orthotopic mammary-tumour xenografts in mice. Collectively, our results identify a vulnerability of cancer cells and define the role of selenium metabolism in cancer.
Topics: Amino Acid Transport System y+; Animals; Breast Neoplasms; Cell Line, Tumor; Cell Survival; Female; Ferroptosis; Humans; Inactivation, Metabolic; Mice; Mice, Nude; Neoplasms; Phospholipid Hydroperoxide Glutathione Peroxidase; Phosphotransferases; Selenium; Selenium Compounds; Selenocysteine; Xenograft Model Antitumor Assays
PubMed: 32694795
DOI: 10.1038/s42255-020-0224-7 -
Free Radical Biology & Medicine Aug 2022Glutathione peroxidase 1 (GPx1) is an important cellular antioxidant enzyme that is found in the cytoplasm and mitochondria of mammalian cells. Like most selenoenzymes,... (Review)
Review
Glutathione peroxidase 1 (GPx1) is an important cellular antioxidant enzyme that is found in the cytoplasm and mitochondria of mammalian cells. Like most selenoenzymes, it has a single redox-sensitive selenocysteine amino acid that is important for the enzymatic reduction of hydrogen peroxide and soluble lipid hydroperoxides. Glutathione provides the source of reducing equivalents for its function. As an antioxidant enzyme, GPx1 modulates the balance between necessary and harmful levels of reactive oxygen species. In this review, we discuss how selenium availability and modifiers of selenocysteine incorporation alter GPx1 expression to promote disease states. We review the role of GPx1 in cardiovascular and metabolic health, provide examples of how GPx1 modulates stroke and provides neuroprotection, and consider how GPx1 may contribute to cancer risk. Overall, GPx1 is protective against the development and progression of many chronic diseases; however, there are some situations in which increased expression of GPx1 may promote cellular dysfunction and disease owing to its removal of essential reactive oxygen species.
Topics: Animals; Antioxidants; Glutathione Peroxidase; Mammals; Oxidative Stress; Reactive Oxygen Species; Selenium; Selenocysteine; Glutathione Peroxidase GPX1
PubMed: 35691509
DOI: 10.1016/j.freeradbiomed.2022.06.004 -
Cell Jan 2018Selenoproteins are rare proteins among all kingdoms of life containing the 21 amino acid, selenocysteine. Selenocysteine resembles cysteine, differing only by the...
Selenoproteins are rare proteins among all kingdoms of life containing the 21 amino acid, selenocysteine. Selenocysteine resembles cysteine, differing only by the substitution of selenium for sulfur. Yet the actual advantage of selenolate- versus thiolate-based catalysis has remained enigmatic, as most of the known selenoproteins also exist as cysteine-containing homologs. Here, we demonstrate that selenolate-based catalysis of the essential mammalian selenoprotein GPX4 is unexpectedly dispensable for normal embryogenesis. Yet the survival of a specific type of interneurons emerges to exclusively depend on selenocysteine-containing GPX4, thereby preventing fatal epileptic seizures. Mechanistically, selenocysteine utilization by GPX4 confers exquisite resistance to irreversible overoxidation as cells expressing a cysteine variant are highly sensitive toward peroxide-induced ferroptosis. Remarkably, concomitant deletion of all selenoproteins in Gpx4 cells revealed that selenoproteins are dispensable for cell viability provided partial GPX4 activity is retained. Conclusively, 200 years after its discovery, a specific and indispensable role for selenium is provided.
Topics: Animals; Apoptosis; Cell Survival; Cells, Cultured; Female; Glutathione Peroxidase; HEK293 Cells; Humans; Hydrogen Peroxide; Interneurons; Lipid Peroxidation; Male; Mice; Mice, Inbred C57BL; Phospholipid Hydroperoxide Glutathione Peroxidase; Seizures; Selenium
PubMed: 29290465
DOI: 10.1016/j.cell.2017.11.048 -
Proceedings of the National Academy of... Aug 2016Ferroptosis is form of regulated nonapoptotic cell death that is involved in diverse disease contexts. Small molecules that inhibit glutathione peroxidase 4 (GPX4), a...
Ferroptosis is form of regulated nonapoptotic cell death that is involved in diverse disease contexts. Small molecules that inhibit glutathione peroxidase 4 (GPX4), a phospholipid peroxidase, cause lethal accumulation of lipid peroxides and induce ferroptotic cell death. Although ferroptosis has been suggested to involve accumulation of reactive oxygen species (ROS) in lipid environments, the mediators and substrates of ROS generation and the pharmacological mechanism of GPX4 inhibition that generates ROS in lipid environments are unknown. We report here the mechanism of lipid peroxidation during ferroptosis, which involves phosphorylase kinase G2 (PHKG2) regulation of iron availability to lipoxygenase enzymes, which in turn drive ferroptosis through peroxidation of polyunsaturated fatty acids (PUFAs) at the bis-allylic position; indeed, pretreating cells with PUFAs containing the heavy hydrogen isotope deuterium at the site of peroxidation (D-PUFA) prevented PUFA oxidation and blocked ferroptosis. We further found that ferroptosis inducers inhibit GPX4 by covalently targeting the active site selenocysteine, leading to accumulation of PUFA hydroperoxides. In summary, we found that PUFA oxidation by lipoxygenases via a PHKG2-dependent iron pool is necessary for ferroptosis and that the covalent inhibition of the catalytic selenocysteine in Gpx4 prevents elimination of PUFA hydroperoxides; these findings suggest new strategies for controlling ferroptosis in diverse contexts.
Topics: Catalytic Domain; Cell Death; Cell Line, Tumor; Deuterium; Epithelial Cells; Fatty Acids, Unsaturated; Gene Expression Regulation; Glutathione Peroxidase; Green Fluorescent Proteins; Humans; Iron; Lipid Peroxidation; Lipid Peroxides; Lipoxygenases; Phospholipid Hydroperoxide Glutathione Peroxidase; Phosphorylase Kinase; Protein Transport; Recombinant Fusion Proteins; Selenocysteine; Signal Transduction
PubMed: 27506793
DOI: 10.1073/pnas.1603244113 -
Nature Chemical Biology May 2020We recently described glutathione peroxidase 4 (GPX4) as a promising target for killing therapy-resistant cancer cells via ferroptosis. The onset of therapy resistance...
We recently described glutathione peroxidase 4 (GPX4) as a promising target for killing therapy-resistant cancer cells via ferroptosis. The onset of therapy resistance by multiple types of treatment results in a stable cell state marked by high levels of polyunsaturated lipids and an acquired dependency on GPX4. Unfortunately, all existing inhibitors of GPX4 act covalently via a reactive alkyl chloride moiety that confers poor selectivity and pharmacokinetic properties. Here, we report our discovery that masked nitrile-oxide electrophiles, which have not been explored previously as covalent cellular probes, undergo remarkable chemical transformations in cells and provide an effective strategy for selective targeting of GPX4. The new GPX4-inhibiting compounds we describe exhibit unexpected proteome-wide selectivity and, in some instances, vastly improved physiochemical and pharmacokinetic properties compared to existing chloroacetamide-based GPX4 inhibitors. These features make them superior tool compounds for biological interrogation of ferroptosis and constitute starting points for development of improved inhibitors of GPX4.
Topics: Animals; Cell Line, Tumor; Enzyme Inhibitors; Ferroptosis; Humans; Lipid Peroxidation; Mice, SCID; Molecular Probes; Molecular Targeted Therapy; Nitriles; Oxides; Phospholipid Hydroperoxide Glutathione Peroxidase; Prodrugs; Rats, Wistar; Selenocysteine; Small Molecule Libraries; Structure-Activity Relationship
PubMed: 32231343
DOI: 10.1038/s41589-020-0501-5 -
BMC Genomics Oct 2020Selenium is an essential trace element, and selenocysteine (Sec, U) is its predominant form in vivo. Proteins that contain Sec are selenoproteins, whose special...
BACKGROUND
Selenium is an essential trace element, and selenocysteine (Sec, U) is its predominant form in vivo. Proteins that contain Sec are selenoproteins, whose special structural features include not only the TGA codon encoding Sec but also the SECIS element in mRNA and the conservation of the Sec-flanking region. These unique features have led to the development of a series of bioinformatics methods to predict and research selenoprotein genes. There have been some studies and reports on the evolution and distribution of selenoprotein genes in prokaryotes and multicellular eukaryotes, but the systematic analysis of single-cell eukaryotes, especially algae, has been very limited.
RESULTS
In this study, we predicted selenoprotein genes in 137 species of algae by using a program we previously developed. More than 1000 selenoprotein genes were obtained. A database website was built to record these algae selenoprotein genes ( www.selenoprotein.com ). These genes belong to 42 selenoprotein families, including three novel selenoprotein gene families.
CONCLUSIONS
This study reveals the primordial state of the eukaryotic selenoproteome. It is an important clue to explore the significance of selenium for primordial eukaryotes and to determine the complete evolutionary spectrum of selenoproteins in all life forms.
Topics: Codon, Terminator; Eukaryota; Evolution, Molecular; Proteome; Selenium; Selenocysteine; Selenoproteins
PubMed: 33028229
DOI: 10.1186/s12864-020-07101-z -
EMBO Molecular Medicine Aug 2023Ferroptosis has emerged as an attractive strategy in cancer therapy. Understanding the operational networks regulating ferroptosis may unravel vulnerabilities that could...
Ferroptosis has emerged as an attractive strategy in cancer therapy. Understanding the operational networks regulating ferroptosis may unravel vulnerabilities that could be harnessed for therapeutic benefit. Using CRISPR-activation screens in ferroptosis hypersensitive cells, we identify the selenoprotein P (SELENOP) receptor, LRP8, as a key determinant protecting MYCN-amplified neuroblastoma cells from ferroptosis. Genetic deletion of LRP8 leads to ferroptosis as a result of an insufficient supply of selenocysteine, which is required for the translation of the antiferroptotic selenoprotein GPX4. This dependency is caused by low expression of alternative selenium uptake pathways such as system Xc . The identification of LRP8 as a specific vulnerability of MYCN-amplified neuroblastoma cells was confirmed in constitutive and inducible LRP8 knockout orthotopic xenografts. These findings disclose a yet-unaccounted mechanism of selective ferroptosis induction that might be explored as a therapeutic strategy for high-risk neuroblastoma and potentially other MYCN-amplified entities.
Topics: Humans; Cell Line, Tumor; Ferroptosis; N-Myc Proto-Oncogene Protein; Neuroblastoma; Selenocysteine; Animals
PubMed: 37435859
DOI: 10.15252/emmm.202318014 -
Antioxidants & Redox Signaling Sep 2020Bioinformatics has brought important insights into the field of selenium research. The progress made in the development of computational tools in the last two decades,... (Review)
Review
Bioinformatics has brought important insights into the field of selenium research. The progress made in the development of computational tools in the last two decades, coordinated with growing genome resources, provided new opportunities to study selenoproteins. The present review discusses existing tools for selenoprotein gene finding and other bioinformatic approaches to study the biology of selenium. The availability of complete selenoproteomes allowed assessing a global distribution of the use of selenocysteine (Sec) across the tree of life, as well as studying the evolution of selenoproteins and their biosynthetic pathway. Beyond gene identification and characterization, human genetic variants in selenoprotein genes were used to examine adaptations to selenium levels in diverse human populations and to estimate selective constraints against gene loss. The synthesis of selenoproteins is essential for development in mice. In humans, several mutations in selenoprotein genes have been linked to rare congenital disorders. And yet, the mechanism of Sec insertion and the regulation of selenoprotein synthesis in mammalian cells are not completely understood. Omics technologies offer new possibilities to study selenoproteins and mechanisms of Sec incorporation in cells, tissues, and organisms.
Topics: Animals; Computational Biology; Humans; Protein Biosynthesis; Research; Selenocysteine; Selenoproteins
PubMed: 32031018
DOI: 10.1089/ars.2020.8044 -
International Journal of Molecular... Jun 2023Selenocysteine is a catalytic residue at the active site of all selenoenzymes in bacteria and mammals, and it is incorporated into the polypeptide backbone by a... (Review)
Review
Selenocysteine is a catalytic residue at the active site of all selenoenzymes in bacteria and mammals, and it is incorporated into the polypeptide backbone by a co-translational process that relies on the recoding of a UGA termination codon into a serine/selenocysteine codon. The best-characterized selenoproteins from mammalian species and bacteria are discussed with emphasis on their biological function and catalytic mechanisms. A total of 25 genes coding for selenoproteins have been identified in the genome of mammals. Unlike the selenoenzymes of anaerobic bacteria, most mammalian selenoenzymes work as antioxidants and as redox regulators of cell metabolism and functions. Selenoprotein P contains several selenocysteine residues and serves as a selenocysteine reservoir for other selenoproteins in mammals. Although extensively studied, glutathione peroxidases are incompletely understood in terms of local and time-dependent distribution, and regulatory functions. Selenoenzymes take advantage of the nucleophilic reactivity of the selenolate form of selenocysteine. It is used with peroxides and their by-products such as disulfides and sulfoxides, but also with iodine in iodinated phenolic substrates. This results in the formation of Se-X bonds (X = O, S, N, or I) from which a selenenylsulfide intermediate is invariably produced. The initial selenolate group is then recycled by thiol addition. In bacterial glycine reductase and D-proline reductase, an unusual catalytic rupture of selenium-carbon bonds is observed. The exchange of selenium for sulfur in selenoproteins, and information obtained from model reactions, suggest that a generic advantage of selenium compared with sulfur relies on faster kinetics and better reversibility of its oxidation reactions.
Topics: Animals; Selenocysteine; Selenium; Selenoproteins; Glutathione Peroxidase; Sulfur; Mammals
PubMed: 37373256
DOI: 10.3390/ijms241210109 -
Experimental Biology and Medicine... Dec 2022Selenium is a naturally found trace element, which provides multiple benefits including antioxidant, anticancer, and antiaging, as well as boosting immunity. One unique... (Review)
Review
Selenium is a naturally found trace element, which provides multiple benefits including antioxidant, anticancer, and antiaging, as well as boosting immunity. One unique feature of selenium is its incorporation as selenocysteine, a rare 21st amino acid, into selenoproteins. Twenty-five human selenoproteins have been discovered, and a majority of these serve as crucial antioxidant enzymes for redox homeostasis. Unlike other amino acids, incorporation of selenocysteine requires a distinctive UGA stop codon recoding mechanism. Although many studies correlating selenium, selenoproteins, aging, and senescence have been performed, it has not yet been explored if the upstream events regulating selenoprotein synthesis play a role in senescence-associated pathologies. The epitranscriptomic writer alkylation repair homolog 8 (ALKBH8) is critical for selenoprotein production, and its deficiency can significantly decrease levels of selenoproteins that are essential for reactive oxygen species (ROS) detoxification, and increase oxidative stress, one of the major drivers of cellular senescence. Here, we review the potential role of epitranscriptomic marks that govern selenocysteine utilization in regulating the senescence program.
Topics: Humans; Selenium; Antioxidants; Selenocysteine; Selenoproteins; Codon, Terminator; AlkB Homolog 8, tRNA Methyltransferase
PubMed: 36036467
DOI: 10.1177/15353702221116592