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Kiledjian NT, Shah R, Vetick MB, Copeland PR. The expression of essential selenoproteins during development requires SECIS-binding protein 2-like. Life Sci Alliance 2022; 5:e202101291. [PMID: 35210313 PMCID: PMC8881744 DOI: 10.26508/lsa.202101291] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 01/20/2022] [Accepted: 01/21/2022] [Indexed: 11/24/2022] Open
Abstract
The dietary requirement for selenium is based on its incorporation into selenoproteins, which contain the amino acid selenocysteine (Sec). The Sec insertion sequence (SECIS) is an RNA structure found in the 3' UTR of all selenoprotein mRNAs, and it is required to convert in-frame UGA codons from termination to Sec-incorporating codons. SECIS-binding protein 2 (Sbp2) is required for Sec incorporation, but its paralogue, SECIS-binding protein 2-like (Secisbp2l), while conserved, has no known function. Here we determined the relative roles of Sbp2 and Secisbp2l by introducing CRISPR mutations in both genes in zebrafish. By monitoring selenoprotein synthesis with 75Se labeling during embryogenesis, we found that sbp2 -/- embryos still make a select subset of selenoproteins but secisbp2l -/- embryos retain the full complement. Abrogation of both genes completely prevents selenoprotein synthesis and juveniles die at 14 days post fertilization. Embryos lacking Sbp2 are sensitive to oxidative stress and express the stress marker Vtg1. We propose a model where Secisbp2l is required to promote essential selenoprotein synthesis when Sbp2 activity is compromised.
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Affiliation(s)
| | - Rushvi Shah
- Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ, USA
| | | | - Paul R Copeland
- Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ, USA
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2
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Cao L, Pechan T, Lee S, Cheng WH. Identification of Selenoprotein H Isoforms and Impact of Selenoprotein H Overexpression on Protein But Not mRNA Levels of 2 Other Selenoproteins in 293T Cells. J Nutr 2021; 151:3329-3338. [PMID: 34510207 PMCID: PMC9034323 DOI: 10.1093/jn/nxab290] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Revised: 06/16/2021] [Accepted: 08/06/2021] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND Selenoprotein H (SELONOH), a member of the thioredoxin-like family proteins, is prioritized to degradation in selenium (Se) insufficiency. Recent studies implicate protective roles of SELENOH in oxidative stress, cellular senescence, and intestinal tumorigenesis. Although the nonselenoprotein H0YE28 is suggested as shortened SELENOH according to genomic and proteomic data repositories, this variant has not been verified biochemically. OBJECTIVES We sought to identify SELENOH isoforms and explore the impact of Se flux on selenoprotein expression in SELENOH-overexpressing cells. METHODS A vector expressing a FLAG (the DYKDDDDK sequence) tag on the N-terminal end of wild-type SELENOH was constructed and transiently transfected into 293T cells incubated with graded concentrations of Na2SeO3 (0-200 nM). Cells were subjected to immunoprecipitation, LC-MS/MS protein analysis, immunoblotting, qRT-PCR, and senescence assays. Data were analyzed by 1-way or 2-way ANOVA. RESULTS Results of anti-FLAG immunoblotting showed that FLAG-SELENOH transfection increased (3.7-fold; P < 0.05) protein levels of the long, but not the short, SELENOH variants in the presence of Na2SeO3 (100 nM). By contrast, SELENOH mRNA levels were increased by 53-fold upon FLAG-SELENOH transfection but were comparable with or without supplemental Se (100 nM). LC-MS/MS analyses of anti-FLAG immunoprecipitates designated both anti-FLAG bands as SELENOH and co-identified three 60S ribosomal and 9 other proteins. Overexpression of FLAG-SELENOH 1) reduced glutathione peroxidase 1 and thioredoxin reductase 1 expression at the protein rather than the mRNA level in the absence but not presence of supplemental Se (100 nM; P < 0.05); 2) increased mRNA levels of 3 heat shock proteins (HSP27, HSP70-1A, and HSP70-1B; P < 0.05); and 3) reduced senescence induced by H2O2 (20 μM, 4 hours; P < 0.05). CONCLUSIONS These cellular studies demonstrate a Se-independent, shortened SELENOH variant and suggest competition of overexpressed FLAG-SELENOH with 2 other selenoproteins for the expression at the protein but not the mRNA level in Se insufficiency.
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Affiliation(s)
- Lei Cao
- Departments of Food Science, Nutrition, and Health Promotion, Mississippi
State University, Mississippi State, MS, USA,Institute of Marine Life Science, Pukyong National
University, Busan, Republic
of Korea
| | - Tibor Pechan
- Institute for Genomics, Biocomputing and Biotechnology, Mississippi State
University, Mississippi State, MS, USA
| | - Sanggil Lee
- Department of Food Science and Nutrition, Pukyong National
University, Busan, Republic
of Korea
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3
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Sunde RA. Selenium regulation of selenoprotein enzyme activity and transcripts in a pilot study with Founder strains from the Collaborative Cross. PLoS One 2018; 13:e0191449. [PMID: 29338053 PMCID: PMC5770059 DOI: 10.1371/journal.pone.0191449] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 01/04/2018] [Indexed: 12/02/2022] Open
Abstract
Rodents and humans have 24–25 selenoproteins, and these proteins contain the 21st amino acid, selenocysteine, incorporated co-translationally into the peptide backbone in a series of reactions dependent on at least 6 unique gene products. In selenium (Se) deficiency, there is differential regulation of selenoprotein expression, whereby levels of some selenoproteins and their transcripts decrease dramatically in Se deficiency, but other selenoprotein transcripts are spared this decrease; the underlying mechanism, however, is not fully understood. To begin explore the genetic basis for this variation in regulation by Se status in a pilot study, we fed Se-deficient or Se-adequate diets (0.005 or 0.2 μg Se/g, respectively) for eight weeks to the eight Founder strains of the Collaborative Cross. We found rather uniform expression of selenoenzyme activity for glutathione peroxidase (Gpx) 3 in plasma, Gpx1 in red blood cells, and Gpx1, Gpx4, and thioredoxin reductase in liver. In Founder mice, Se deficiency decreased each of these activities to a similar extent. Regulation of selenoprotein transcript expression by Se status was also globally retained intact, with dramatic down-regulation of Gpx1, Selenow, and Selenoh transcripts in all 8 strains of Founder mice. These results indicate that differential regulation of selenoprotein expression by Se status is an essential aspect of Se metabolism and selenoprotein function. A few lone differences in Se regulation were observed for individual selenoproteins in this pilot study, but these differences did not single-out one strain or one selenoprotein that consistently had unique Se regulation of selenoprotein expression. These differences should be affirmed in larger studies; use of the Diversity Outbred and Collaborative Cross strains may help to better define the functions of these selenoproteins.
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Affiliation(s)
- Roger A. Sunde
- Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin, United States of America
- * E-mail:
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4
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Fradejas-Villar N, Seeher S, Anderson CB, Doengi M, Carlson BA, Hatfield DL, Schweizer U, Howard MT. The RNA-binding protein Secisbp2 differentially modulates UGA codon reassignment and RNA decay. Nucleic Acids Res 2017; 45:4094-4107. [PMID: 27956496 PMCID: PMC5397149 DOI: 10.1093/nar/gkw1255] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Accepted: 12/01/2016] [Indexed: 11/13/2022] Open
Abstract
Dual-assignment of codons as termination and elongation codons is used to expand the genetic code. In mammals, UGA can be reassigned to selenocysteine during translation of selenoproteins by a mechanism involving a 3΄ untranslated region (UTR) selenocysteine insertion sequence (SECIS) and the SECIS-binding protein Secisbp2. Here, we present data from ribosome profiling, RNA-Seq and mRNA half-life measurements that support distinct roles for Secisbp2 in UGA-redefinition and mRNA stability. Conditional deletions of the Secisbp2 and Trsp (tRNASec) genes in mouse liver were compared to determine if the effects of Secisbp2 loss on selenoprotein synthesis could be attributed entirely to the inability to incorporate Sec. As expected, tRNASec depletion resulted in loss of ribosome density downstream of all UGA-Sec codons. In contrast, the absence of Secisbp2 resulted in variable effects on ribosome density downstream of UGA-Sec codons that demonstrate gene-specific differences in Sec incorporation. For several selenoproteins in which loss of Secisbp2 resulted in greatly diminished mRNA levels, translational activity and Sec incorporation efficiency were shown to be unaffected on the remaining RNA. Collectively, these results demonstrate that Secisbp2 is not strictly required for Sec incorporation and has a distinct role in stabilizing mRNAs that can be separated from its effects on UGA-redefinition.
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Affiliation(s)
- Noelia Fradejas-Villar
- Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
| | - Sandra Seeher
- Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
| | | | - Michael Doengi
- Institut für Physiologie II, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
| | - Bradley A Carlson
- Molecular Biology of Selenium Section, Mouse Cancer Genetics Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Dolph L Hatfield
- Molecular Biology of Selenium Section, Mouse Cancer Genetics Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Ulrich Schweizer
- Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
| | - Michael T Howard
- Department of Human Genetics, University of Utah, Salt Lake City, UT 84112, USA
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5
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Zupanic A, Meplan C, Huguenin GVB, Hesketh JE, Shanley DP. Modeling and gene knockdown to assess the contribution of nonsense-mediated decay, premature termination, and selenocysteine insertion to the selenoprotein hierarchy. RNA (NEW YORK, N.Y.) 2016; 22:1076-1084. [PMID: 27208313 PMCID: PMC4911915 DOI: 10.1261/rna.055749.115] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 04/25/2016] [Indexed: 06/05/2023]
Abstract
The expression of selenoproteins, a specific group of proteins that incorporates selenocysteine, is hierarchically regulated by the availability of Se, with some, but not all selenoprotein mRNA transcripts decreasing in abundance with decreasing Se. Selenocysteine insertion into the peptide chain occurs during translation following recoding of an internal UGA stop codon. There is increasing evidence that this UGA recoding competes with premature translation termination, which is followed by nonsense-mediated decay (NMD) of the transcript. In this study, we tested the hypothesis that the susceptibility of different selenoprotein mRNAs to premature termination during translation and differential sensitivity of selenoprotein transcripts to NMD are major factors in the selenoprotein hierarchy. Selenoprotein transcript abundance was measured in Caco-2 cells using real-time PCR under different Se conditions and the data obtained fitted to mathematical models of selenoprotein translation. A calibrated model that included a combination of differential sensitivity of selenoprotein transcripts to NMD and different frequency of non-NMD related premature translation termination was able to fit all the measurements. The model predictions were tested using SiRNA to knock down expression of the crucial NMD factor UPF1 (up-frameshift protein 1) and selenoprotein mRNA expression. The calibrated model was able to predict the effect of UPF1 knockdown on gene expression for all tested selenoproteins, except SPS2 (selenophosphate synthetase), which itself is essential for selenoprotein synthesis. These results indicate an important role for NMD in the hierarchical regulation of selenoprotein mRNAs, with the exception of SPS2 whose expression is likely regulated by a different mechanism.
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Affiliation(s)
- Anze Zupanic
- Centre for Integrated Systems Biology of Ageing and Nutrition, Newcastle University, Newcastle-upon-Tyne NE4 5PL, United Kingdom Eawag, Institute for Aquatic Science and Technology, 8600 Dübendorf, Switzerland
| | - Catherine Meplan
- Centre for Integrated Systems Biology of Ageing and Nutrition, Newcastle University, Newcastle-upon-Tyne NE4 5PL, United Kingdom Institute for Cell and Molecular Biosciences and Human Nutrition Research Centre, Newcastle University, Newcastle-upon-Tyne NE2 4HH, United Kingdom
| | - Grazielle V B Huguenin
- Institute for Cell and Molecular Biosciences and Human Nutrition Research Centre, Newcastle University, Newcastle-upon-Tyne NE2 4HH, United Kingdom Faculty of Medicine, Federal University of Rio de Janeiro, Rio de Janeiro, CEP: 21941-902, Brazil
| | - John E Hesketh
- Centre for Integrated Systems Biology of Ageing and Nutrition, Newcastle University, Newcastle-upon-Tyne NE4 5PL, United Kingdom Institute for Cell and Molecular Biosciences and Human Nutrition Research Centre, Newcastle University, Newcastle-upon-Tyne NE2 4HH, United Kingdom
| | - Daryl P Shanley
- Centre for Integrated Systems Biology of Ageing and Nutrition, Newcastle University, Newcastle-upon-Tyne NE4 5PL, United Kingdom Institute for Cell and Molecular Biosciences and Human Nutrition Research Centre, Newcastle University, Newcastle-upon-Tyne NE2 4HH, United Kingdom
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Martínez-Montiel N, Morales-Lara L, Hernández-Pérez JM, Martínez-Contreras RD. In Silico Analysis of the Structural and Biochemical Features of the NMD Factor UPF1 in Ustilago maydis. PLoS One 2016; 11:e0148191. [PMID: 26863136 PMCID: PMC4749658 DOI: 10.1371/journal.pone.0148191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Accepted: 01/14/2016] [Indexed: 11/23/2022] Open
Abstract
The molecular mechanisms regulating the accuracy of gene expression are still not fully understood. Among these mechanisms, Nonsense-mediated Decay (NMD) is a quality control process that detects post-transcriptionally abnormal transcripts and leads them to degradation. The UPF1 protein lays at the heart of NMD as shown by several structural and functional features reported for this factor mainly for Homo sapiens and Saccharomyces cerevisiae. This process is highly conserved in eukaryotes but functional diversity can be observed in various species. Ustilago maydis is a basidiomycete and the best-known smut, which has become a model to study molecular and cellular eukaryotic mechanisms. In this study, we performed in silico analysis to investigate the structural and biochemical properties of the putative UPF1 homolog in Ustilago maydis. The putative homolog for UPF1 was recognized in the annotated genome for the basidiomycete, exhibiting 66% identity with its human counterpart at the protein level. The known structural and functional domains characteristic of UPF1 homologs were also found. Based on the crystal structures available for UPF1, we constructed different three-dimensional models for umUPF1 in order to analyze the secondary and tertiary structural features of this factor. Using these models, we studied the spatial arrangement of umUPF1 and its capability to interact with UPF2. Moreover, we identified the critical amino acids that mediate the interaction of umUPF1 with UPF2, ATP, RNA and with UPF1 itself. Mutating these amino acids in silico showed an important effect over the native structure. Finally, we performed molecular dynamic simulations for UPF1 proteins from H. sapiens and U. maydis and the results obtained show a similar behavior and physicochemical properties for the protein in both organisms. Overall, our results indicate that the putative UPF1 identified in U. maydis shows a very similar sequence, structural organization, mechanical stability, physicochemical properties and spatial organization in comparison to the NMD factor depicted for Homo sapiens. These observations strongly support the notion that human and fungal UPF1 could perform equivalent biological activities.
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Affiliation(s)
- Nancy Martínez-Montiel
- Laboratorio de Ecología Molecular Microbiana, Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, México
| | - Laura Morales-Lara
- Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla, Puebla, México
| | | | - Rebeca D. Martínez-Contreras
- Laboratorio de Ecología Molecular Microbiana, Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, México
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Abstract
SIGNIFICANCE Selenium is an essential trace element that is incorporated in the small but vital family of proteins, namely the selenoproteins, as the selenocysteine amino acid residue. In humans, 25 selenoprotein genes have been characterized. The most remarkable trait of selenoprotein biosynthesis is the cotranslational insertion of selenocysteine by the recoding of a UGA codon, normally decoded as a stop signal. RECENT ADVANCES In eukaryotes, a set of dedicated cis- and trans-acting factors have been identified as well as a variety of regulatory mechanisms, factors, or elements that control the selenoprotein expression at the level of the UGA-selenocysteine recoding process, offering a fascinating playground in the field of translational control. It appeared that the central players are two RNA molecules: the selenocysteine insertion sequence (SECIS) element within selenoprotein mRNA and the selenocysteine-tRNA([Ser]Sec); and their interacting partners. CRITICAL ISSUES After a couple of decades, despite many advances in the field and the discovery of many essential and regulatory components, the precise mechanism of UGA-selenocysteine recoding remains elusive and more complex than anticipated, with many layers of control. This review offers an update of selenoproteome biosynthesis and regulation in eukaryotes. FUTURE DIRECTIONS The regulation of selenoproteins in response to a variety of pathophysiological conditions and cellular stressors, including selenium levels, oxidative stress, replicative senescence, or cancer, awaits further detailed investigation. Clearly, the efficiency of UGA-selenocysteine recoding is the limiting stage of selenoprotein synthesis. The sequence of events leading Sec-tRNA([Ser]Sec) delivery to ribosomal A site awaits further analysis, notably at the level of a three-dimensional structure.
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Affiliation(s)
- Anne-Laure Bulteau
- Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, IPREM , CNRS/UPPA, UMR5254, Pau, France
| | - Laurent Chavatte
- Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, IPREM , CNRS/UPPA, UMR5254, Pau, France
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8
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Lin HC, Ho SC, Chen YY, Khoo KH, Hsu PH, Yen HCS. SELENOPROTEINS. CRL2 aids elimination of truncated selenoproteins produced by failed UGA/Sec decoding. Science 2015; 349:91-5. [PMID: 26138980 DOI: 10.1126/science.aab0515] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Selenocysteine (Sec) is translated from the codon UGA, typically a termination signal. Codon duality extends the genetic code; however, the coexistence of two competing UGA-decoding mechanisms immediately compromises proteome fidelity. Selenium availability tunes the reassignment of UGA to Sec. We report a CRL2 ubiquitin ligase-mediated protein quality-control system that specifically eliminates truncated proteins that result from reassignment failures. Exposing the peptide immediately N-terminal to Sec, a CRL2 recognition degron, promotes protein degradation. Sec incorporation destroys the degron, protecting read-through proteins from detection by CRL2. Our findings reveal a coupling between directed translation termination and proteolysis-assisted protein quality control, as well as a cellular strategy to cope with fluctuations in organismal selenium intake.
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Affiliation(s)
- Hsiu-Chuan Lin
- Institute of Molecular Biology, Academia Sinica, Taiwan. Genome and Systems Biology Degree Program, National Taiwan University, Taiwan
| | - Szu-Chi Ho
- Institute of Molecular Biology, Academia Sinica, Taiwan
| | - Yi-Yun Chen
- Institute of Biological Chemistry, Academia Sinica, Taiwan
| | - Kay-Hooi Khoo
- Genome and Systems Biology Degree Program, National Taiwan University, Taiwan. Institute of Biological Chemistry, Academia Sinica, Taiwan
| | - Pang-Hung Hsu
- Department of Life Science, Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Taiwan
| | - Hsueh-Chi S Yen
- Institute of Molecular Biology, Academia Sinica, Taiwan. Genome and Systems Biology Degree Program, National Taiwan University, Taiwan
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9
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Seyedali A, Berry MJ. Nonsense-mediated decay factors are involved in the regulation of selenoprotein mRNA levels during selenium deficiency. RNA (NEW YORK, N.Y.) 2014; 20:1248-1256. [PMID: 24947499 PMCID: PMC4105750 DOI: 10.1261/rna.043463.113] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 05/08/2014] [Indexed: 06/03/2023]
Abstract
Selenoproteins contain the unique amino acid selenocysteine (Sec), which is encoded by the triplet UGA. Since UGA also serves as a stop codon, it has been postulated that selenoprotein mRNAs are targeted for degradation by the nonsense-mediated mRNA decay pathway (NMD). Several reports have observed a hierarchy of selenoprotein mRNA expression when selenium (Se) is limiting, whereby the abundance of certain transcripts decline while others do not. We sought to investigate the role of NMD in this hierarchical response that selenoprotein mRNAs exhibit to environmental Se status. Selenoprotein mRNAs were categorized as being predicted sensitive or resistant to NMD based on the requirements held by the current model. About half of the selenoprotein transcriptome was predicted to be sensitive to NMD and showed significant changes in mRNA abundance in response to cellular Se status. The other half that was predicted to be resistant to NMD did not respond to Se status. RNA immunoprecipitation with essential NMD factor UPF1 revealed that the mRNAs that were the most sensitive to Se status were also the most enriched on UPF1 during Se deficiency. Furthermore, depletion of SMG1, the kinase responsible for UPF1 phosphorylation and NMD activation, abrogated the decline in transcript abundance of Se-responsive transcripts. Lastly, mRNA decay rates of Se-responsive transcripts were altered upon the addition of Se to resemble the slower decay rates of nonresponsive transcripts. Taken together, these results present novel evidence in support of a crucial role for the NMD pathway in regulating selenoprotein mRNA levels when Se is limiting.
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Affiliation(s)
- Ali Seyedali
- Department of Cell and Molecular Biology, John A. Burn School of Medicine, University of Hawaii at Manoa, Honolulu, Hawaii 96813, USA
| | - Marla J Berry
- Department of Cell and Molecular Biology, John A. Burn School of Medicine, University of Hawaii at Manoa, Honolulu, Hawaii 96813, USA
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Wurth L, Gribling-Burrer AS, Verheggen C, Leichter M, Takeuchi A, Baudrey S, Martin F, Krol A, Bertrand E, Allmang C. Hypermethylated-capped selenoprotein mRNAs in mammals. Nucleic Acids Res 2014; 42:8663-77. [PMID: 25013170 PMCID: PMC4117793 DOI: 10.1093/nar/gku580] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mammalian mRNAs are generated by complex and coordinated biogenesis pathways and acquire 5′-end m7G caps that play fundamental roles in processing and translation. Here we show that several selenoprotein mRNAs are not recognized efficiently by translation initiation factor eIF4E because they bear a hypermethylated cap. This cap modification is acquired via a 5′-end maturation pathway similar to that of the small nucle(ol)ar RNAs (sn- and snoRNAs). Our findings also establish that the trimethylguanosine synthase 1 (Tgs1) interacts with selenoprotein mRNAs for cap hypermethylation and that assembly chaperones and core proteins devoted to sn- and snoRNP maturation contribute to recruiting Tgs1 to selenoprotein mRNPs. We further demonstrate that the hypermethylated-capped selenoprotein mRNAs localize to the cytoplasm, are associated with polysomes and thus translated. Moreover, we found that the activity of Tgs1, but not of eIF4E, is required for the synthesis of the GPx1 selenoprotein in vivo.
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Affiliation(s)
- Laurence Wurth
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 67084 Strasbourg, France
| | - Anne-Sophie Gribling-Burrer
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 67084 Strasbourg, France
| | - Céline Verheggen
- Equipe labélisée Ligue contre le cancer, Institut de Génétique Moléculaire, Centre National de la Recherche Scientifique, UMR 5535, 34293 Montpellier, France
| | - Michael Leichter
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 67084 Strasbourg, France
| | - Akiko Takeuchi
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 67084 Strasbourg, France
| | - Stéphanie Baudrey
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 67084 Strasbourg, France
| | - Franck Martin
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 67084 Strasbourg, France
| | - Alain Krol
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 67084 Strasbourg, France
| | - Edouard Bertrand
- Equipe labélisée Ligue contre le cancer, Institut de Génétique Moléculaire, Centre National de la Recherche Scientifique, UMR 5535, 34293 Montpellier, France
| | - Christine Allmang
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 67084 Strasbourg, France
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11
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Touat-Hamici Z, Legrain Y, Bulteau AL, Chavatte L. Selective up-regulation of human selenoproteins in response to oxidative stress. J Biol Chem 2014; 289:14750-61. [PMID: 24706762 DOI: 10.1074/jbc.m114.551994] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Selenocysteine is inserted into selenoproteins via the translational recoding of a UGA codon, normally used as a stop signal. This process depends on the nature of the selenocysteine insertion sequence element located in the 3' UTR of selenoprotein mRNAs, selenium bioavailability, and, possibly, exogenous stimuli. To further understand the function and regulation of selenoproteins in antioxidant defense and redox homeostasis, we investigated how oxidative stress influences selenoprotein expression as a function of different selenium concentrations. We found that selenium supplementation of the culture media, which resulted in a hierarchical up-regulation of selenoproteins, protected HEK293 cells from reactive oxygen species formation. Furthermore, in response to oxidative stress, we identified a selective up-regulation of several selenoproteins involved in antioxidant defense (Gpx1, Gpx4, TR1, SelS, SelK, and Sps2). Interestingly, the response was more efficient when selenium was limiting. Although a modest change in mRNA levels was noted, we identified a novel translational control mechanism stimulated by oxidative stress that is characterized by up-regulation of UGA-selenocysteine recoding efficiency and relocalization of SBP2, selenocysteine-specific elongation factor, and L30 recoding factors from the cytoplasm to the nucleus.
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Affiliation(s)
- Zahia Touat-Hamici
- From the Centre de Génétique Moléculaire, CNRS, UPR3404, 91198 Gif-sur-Yvette, France
| | - Yona Legrain
- From the Centre de Génétique Moléculaire, CNRS, UPR3404, 91198 Gif-sur-Yvette, France
| | - Anne-Laure Bulteau
- the Centre de Recherche Institut Cochin, INSERM U567, CNRS UMR 8104, 75005 Paris, France, and the Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, CNRS/UPPA, UMR5254, 64000 Pau, France
| | - Laurent Chavatte
- From the Centre de Génétique Moléculaire, CNRS, UPR3404, 91198 Gif-sur-Yvette, France, the Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, CNRS/UPPA, UMR5254, 64000 Pau, France
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12
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Reinke EN, Ekoue DN, Bera S, Mahmud N, Diamond AM. Translational regulation of GPx-1 and GPx-4 by the mTOR pathway. PLoS One 2014; 9:e93472. [PMID: 24691473 PMCID: PMC3972146 DOI: 10.1371/journal.pone.0093472] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Accepted: 03/05/2014] [Indexed: 02/02/2023] Open
Abstract
Glutathione peroxidase activity was previously determined to be elevated in lymphocytes obtained from patients treated with the Bcr-Abl kinase inhibitor imatinib mesylate. In order to expand upon this observation, the established chronic myelogenous leukemia cell lines KU812 and MEG-01 were treated with imatinib and the effect on several anti-oxidant proteins was determined. The levels of GPx-1 were significantly increased following treatment with imatinib. This increase was not due to altered steady-state mRNA levels, and appeared to be dependent on the expression of Bcr-Abl, as no increases were observed following imatinib treatment of cells that did not express the fusion protein. The nutrient-sensing signaling protein, mammalian target of rapamycin (mTOR), can be activated by Bcr-Abl and its activity regulates the translation of many different proteins. Treatment of those same cells used in the imatinib studies with rapamycin, an inhibitor of mTOR, resulted in elevated GPx-1 and GPx-4 protein levels independent of Bcr-Abl expression. These proteins all belong to the selenoprotein family of peptides that contain the UGA-encoded amino acid selenocysteine. Collectively, these data provide evidence of a novel means of regulating anti-oxidants of the selenoprotein family via the mTOR pathway.
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Affiliation(s)
- Emily N. Reinke
- Department of Pathology, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Dede N. Ekoue
- Department of Pathology, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Soumen Bera
- Department of Pathology, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Nadim Mahmud
- Department of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Alan M. Diamond
- Department of Pathology, University of Illinois at Chicago, Chicago, Illinois, United States of America
- * E-mail:
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13
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Latrèche L, Duhieu S, Touat-Hamici Z, Jean-Jean O, Chavatte L. The differential expression of glutathione peroxidase 1 and 4 depends on the nature of the SECIS element. RNA Biol 2012; 9:681-90. [PMID: 22614831 DOI: 10.4161/rna.20147] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Selenocysteine insertion into selenoproteins involves the translational recoding of UGA stop codons. In mammals, selenoprotein expression further depends on selenium availability, which has been particularly described for glutathione peroxidase 1 and 4 (Gpx1 and Gpx4). The SECIS element located in the 3'UTR of the selenoprotein mRNAs is a modulator of UGA recoding efficiency in adequate selenium conditions. One of the current models for the UGA recoding mechanism proposes that the SECIS binds SECIS-binding protein 2 (SBP2), which then recruits a selenocysteine-specific elongation factor (EFsec) and tRNA (Sec) to the ribosome, where L30 acts as an anchor. The involvement of the SECIS in modulation of UGA recoding activity was investigated, together with SBP2 and EFsec, in Hek293 cells cultured with various selenium levels. Luciferase reporter constructs, in transiently or stably expressing cell lines, were used to analyze the differential expression of Gpx1 and Gpx4. We showed that, upon selenium fluctuation, the modulation of UGA recoding efficiency depends on the nature of the SECIS, with Gpx1 being more sensitive than Gpx4. Attenuation of SBP2 and EFsec levels by shRNAs confirmed that both factors are essential for efficient selenocysteine insertion. Strikingly, in a context of either EFsec or SBP2 attenuation, the decrease in UGA recoding efficiency is dependent on the nature of the SECIS, GPx1 being more sensitive. Finally, the profusion of selenium of the culture medium exacerbates the lack of factors involved in selenocysteine insertion.
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14
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Banerjee S, Yang S, Foster CB. A luciferase reporter assay to investigate the differential selenium-dependent stability of selenoprotein mRNAs. J Nutr Biochem 2011; 23:1294-301. [PMID: 22209284 DOI: 10.1016/j.jnutbio.2011.07.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2011] [Revised: 07/01/2011] [Accepted: 07/22/2011] [Indexed: 11/29/2022]
Abstract
The mechanisms regulating the differential selenium (Se)-dependent stability of selenoprotein mRNAs are partially characterized. To further study the Se-dependent regulation of selenoproteins, we developed a novel chemiluminescent reporter to monitor the steady-state mRNA level of an artificial selenoprotein. Our reporter is a fusion of the Renilla luciferase gene and of the β-globin gene, but contains features required for incorporation of selenocysteine (SEC), namely, a UGA-SEC codon and a 3' untranslated region RNA stem loop called a SEC incorporation sequence (SECIS). At various levels of Se, the activity of reporters containing GPX1 or GPX4 SECIS elements is proportional to the steady-state mRNA level of the reporter construct and reflects the level of the corresponding endogenous mRNA. In a reporter containing a UGA codon and a functional GPX1 SECIS, Se-dependent nonsense-mediated decay (NMD) occurred in the cytoplasm, as opposed to the more typical nuclear location. To validate the reporter system, we used genetic and pharmacologic approaches to inhibit or promote NMD. Modulation of UPF1 by siRNA, overexpression, or by inhibition of SMG1 altered NMD in this system. Our reporter is derived from a Renilla luciferase reporter gene fused to an intron containing B-globin gene and is subject to degradation by NMD when a stop codon is inserted before the second intron.
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Affiliation(s)
- Shuvojit Banerjee
- Department of Cancer Biology, Lerner Research Institute, The Cleveland Clinic, Cleveland, OH 44195, USA
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15
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Lubos E, Loscalzo J, Handy DE. Glutathione peroxidase-1 in health and disease: from molecular mechanisms to therapeutic opportunities. Antioxid Redox Signal 2011; 15:1957-97. [PMID: 21087145 PMCID: PMC3159114 DOI: 10.1089/ars.2010.3586] [Citation(s) in RCA: 766] [Impact Index Per Article: 58.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Reactive oxygen species, such as superoxide and hydrogen peroxide, are generated in all cells by mitochondrial and enzymatic sources. Left unchecked, these reactive species can cause oxidative damage to DNA, proteins, and membrane lipids. Glutathione peroxidase-1 (GPx-1) is an intracellular antioxidant enzyme that enzymatically reduces hydrogen peroxide to water to limit its harmful effects. Certain reactive oxygen species, such as hydrogen peroxide, are also essential for growth factor-mediated signal transduction, mitochondrial function, and maintenance of normal thiol redox-balance. Thus, by limiting hydrogen peroxide accumulation, GPx-1 also modulates these processes. This review explores the molecular mechanisms involved in regulating the expression and function of GPx-1, with an emphasis on the role of GPx-1 in modulating cellular oxidant stress and redox-mediated responses. As a selenocysteine-containing enzyme, GPx-1 expression is subject to unique forms of regulation involving the trace mineral selenium and selenocysteine incorporation during translation. In addition, GPx-1 has been implicated in the development and prevention of many common and complex diseases, including cancer and cardiovascular disease. This review discusses the role of GPx-1 in these diseases and speculates on potential future therapies to harness the beneficial effects of this ubiquitous antioxidant enzyme.
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Affiliation(s)
- Edith Lubos
- Department of Medicine II, University Medical Center, Johannes Gutenberg-University, Mainz, Germany
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16
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Sunde RA, Raines AM. Selenium regulation of the selenoprotein and nonselenoprotein transcriptomes in rodents. Adv Nutr 2011; 2:138-50. [PMID: 22332043 PMCID: PMC3065762 DOI: 10.3945/an.110.000240] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
This review discusses progress in understanding the hierarchy of selenoprotein expression at the transcriptome level from selenium (Se) deficiency to Se toxicity. Microarray studies of the full selenoproteome have found that 5 of 24 rodent selenoprotein mRNA decrease to <40% of Se adequate levels in Se deficient liver but that the majority of selenoprotein mRNA are not regulated by Se deficiency. These differences match with the hierarchy of selenoprotein expression, helping to explain these differences and also showing that selenoprotein transcripts can be used as molecular biomarkers for assessing Se status. The similarity of the response curves for regulated selenoproteins suggests one underlying mechanism is responsible for the downregulation of selenoprotein mRNA in Se deficiency, but the heterogeneity of the UGA position in regulated and nonregulated selenoprotein transcripts now indicates that current nonsense mediated decay models cannot explain which transcripts are susceptible to mRNA decay. Microarray studies on the full liver transcriptome in rats found only <10 transcripts/treatment were significantly down- or upregulated by Se deficiency or by supernutritional Se up to 2.0 μg Se/g diet (20× requirement), suggesting that cancer prevention associated with supernutritional Se may not be mediated by transcriptional changes. Toxic dietary Se at 50× requirement (5 μg Se/g diet), however, significantly altered ∼4% of the transcriptome, suggesting number of transcriptional changes itself as a biomarker of Se toxicity. Finally, panels of Se regulated selenoprotein plus nonselenoprotein transcripts predict Se status from deficient to toxic better than conventional biomarkers, illustrating potential roles for molecular biomarkers in nutrition.
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17
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't Hoen PAC, Hirsch M, de Meijer EJ, de Menezes RX, van Ommen GJ, den Dunnen JT. mRNA degradation controls differentiation state-dependent differences in transcript and splice variant abundance. Nucleic Acids Res 2010; 39:556-66. [PMID: 20852259 PMCID: PMC3025562 DOI: 10.1093/nar/gkq790] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Expression profiling experiments usually provide a static snapshot of messenger RNA (mRNA) levels. Improved understanding of the dynamics of mRNA synthesis and degradation will aid the development of sound bioinformatic models for control of gene expression. We studied mRNA stability in proliferating and differentiated myogenic cells using whole-genome exon arrays and reported the decay rates (half life) for ∼7000 mRNAs. We showed that the stability of many mRNAs strongly depends on the differentiation status and contributes to differences in abundance of these mRNAs. In addition, alternative splicing turns out to be coupled to mRNA degradation. Although different splice forms may be produced at comparable levels, their relative abundance is partly determined by their different stabilities in proliferating and differentiated cells. Where the 3'-untranslated region (3'-UTR) was previously thought to contain most RNA stabilizing and destabilizing elements, we showed that this also holds for transcript isoforms sharing the same 3'-UTR. There are two splice variants in Itga7, of which the isoform with an extra internal exon is highly stable in differentiated cells but preferentially degraded in the cytoplasm of proliferating cells. In conclusion, control of stability and degradation emerge as important determinants for differential expression of mRNA transcripts and splice variants.
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Affiliation(s)
- Peter A C 't Hoen
- Center for Human and Clinical Genetics, Leiden University Medical Center, Leiden, The Netherlands.
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18
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Ufer C, Wang CC, Borchert A, Heydeck D, Kuhn H. Redox control in mammalian embryo development. Antioxid Redox Signal 2010; 13:833-75. [PMID: 20367257 DOI: 10.1089/ars.2009.3044] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The development of an embryo constitutes a complex choreography of regulatory events that underlies precise temporal and spatial control. Throughout this process the embryo encounters ever changing environments, which challenge its metabolism. Oxygen is required for embryogenesis but it also poses a potential hazard via formation of reactive oxygen and reactive nitrogen species (ROS/RNS). These metabolites are capable of modifying macromolecules (lipids, proteins, nucleic acids) and altering their biological functions. On one hand, such modifications may have deleterious consequences and must be counteracted by antioxidant defense systems. On the other hand, ROS/RNS function as essential signal transducers regulating the cellular phenotype. In this context the combined maternal/embryonic redox homeostasis is of major importance and dysregulations in the equilibrium of pro- and antioxidative processes retard embryo development, leading to organ malformation and embryo lethality. Silencing the in vivo expression of pro- and antioxidative enzymes provided deeper insights into the role of the embryonic redox equilibrium. Moreover, novel mechanisms linking the cellular redox homeostasis to gene expression regulation have recently been discovered (oxygen sensing DNA demethylases and protein phosphatases, redox-sensitive microRNAs and transcription factors, moonlighting enzymes of the cellular redox homeostasis) and their contribution to embryo development is critically reviewed.
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Affiliation(s)
- Christoph Ufer
- Institute of Biochemistry, University Medicine Berlin-Charité, Berlin, FR Germany
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19
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Nicholson P, Yepiskoposyan H, Metze S, Zamudio Orozco R, Kleinschmidt N, Mühlemann O. Nonsense-mediated mRNA decay in human cells: mechanistic insights, functions beyond quality control and the double-life of NMD factors. Cell Mol Life Sci 2010; 67:677-700. [PMID: 19859661 PMCID: PMC11115722 DOI: 10.1007/s00018-009-0177-1] [Citation(s) in RCA: 254] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2009] [Revised: 09/16/2009] [Accepted: 10/06/2009] [Indexed: 12/16/2022]
Abstract
Nonsense-mediated decay is well known by the lucid definition of being a RNA surveillance mechanism that ensures the speedy degradation of mRNAs containing premature translation termination codons. However, as we review here, NMD is far from being a simple quality control mechanism; it also regulates the stability of many wild-type transcripts. We summarise the abundance of research that has characterised each of the NMD factors and present a unified model for the recognition of NMD substrates. The contentious issue of how and where NMD occurs is also discussed, particularly with regard to P-bodies and SMG6-driven endonucleolytic degradation. In recent years, the discovery of additional functions played by several of the NMD factors has further complicated the picture. Therefore, we also review the reported roles of UPF1, SMG1 and SMG6 in other cellular processes.
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Affiliation(s)
- Pamela Nicholson
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland
| | - Hasmik Yepiskoposyan
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland
| | - Stefanie Metze
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland
| | - Rodolfo Zamudio Orozco
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland
| | - Nicole Kleinschmidt
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland
| | - Oliver Mühlemann
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland
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20
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Carlson BA, Yoo MH, Tsuji PA, Gladyshev VN, Hatfield DL. Mouse models targeting selenocysteine tRNA expression for elucidating the role of selenoproteins in health and development. Molecules 2009; 14:3509-27. [PMID: 19783940 PMCID: PMC3459062 DOI: 10.3390/molecules14093509] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2009] [Revised: 09/03/2009] [Accepted: 09/07/2009] [Indexed: 01/31/2023] Open
Abstract
Selenium (Se) deficiency has been known for many years to be associated with disease, impaired growth and a variety of other metabolic disorders in mammals. Only recently has the major role that Se-containing proteins, designated selenoproteins, play in many aspects of health and development begun to emerge. Se is incorporated into protein by way of the Se-containing amino acid, selenocysteine (Sec). The synthesis of selenoproteins is dependent on Sec tRNA for insertion of Sec, the 21st amino acid in the genetic code, into protein. We have taken advantage of this dependency to modulate the expression of Sec tRNA that in turn modulates the expression of selenoproteins by generating transgenic, conditional knockout, transgenic/standard knockout and transgenic/conditional knockout mouse models, all of which involve the Sec tRNA gene, to elucidate the intracellular roles of this protein class.
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Affiliation(s)
- Bradley A. Carlson
- Molecular Biology of Selenium Section, Laboratory of Cancer Prevention, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA;E-mails: (M-H.Y.); (P.A.T.); (D.L.H.)
- Author to whom correspondence should be addressed; E-Mail:
| | - Min-Hyuk Yoo
- Molecular Biology of Selenium Section, Laboratory of Cancer Prevention, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA;E-mails: (M-H.Y.); (P.A.T.); (D.L.H.)
| | - Petra A. Tsuji
- Molecular Biology of Selenium Section, Laboratory of Cancer Prevention, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA;E-mails: (M-H.Y.); (P.A.T.); (D.L.H.)
- Cancer Prevention Fellowship Program, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Nutritional Science Research Group, Division of Cancer Prevention, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Vadim N. Gladyshev
- Department of Biochemistry and Redox Biology Center, University of Nebraska, Lincoln, NE 68588, USA; E-mail: (V.N.G.)
| | - Dolph L. Hatfield
- Molecular Biology of Selenium Section, Laboratory of Cancer Prevention, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA;E-mails: (M-H.Y.); (P.A.T.); (D.L.H.)
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21
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Selenium status highly regulates selenoprotein mRNA levels for only a subset of the selenoproteins in the selenoproteome. Biosci Rep 2009; 29:329-38. [PMID: 19076066 DOI: 10.1042/bsr20080146] [Citation(s) in RCA: 153] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Gpx (glutathione peroxidase)-1 enzyme activity and mRNA levels decrease dramatically in Se (selenium) deficiency, whereas other selenoproteins are less affected by Se deficiency. This hierarchy of Se regulation is not understood, but the position of the UGA selenocysteine codon is thought to play a major role in making selenoprotein mRNAs susceptible to nonsense-mediated decay. Thus in the present paper we studied the complete selenoproteome in the mouse to uncover additional selenoprotein mRNAs that are highly regulated by Se status. Mice were fed on Se-deficient, Se-marginal and Se-adequate diets (0, 0.05 and 0.2 microg of Se/g respectively) for 35 days, and selenoprotein mRNA levels in liver and kidney were determined using microarray analysis and quantitative real-time PCR analysis. Se-deficient mice had liver Se concentrations and liver Gpx1 and thioredoxin reductase activities that were 4, 3 and 3% respectively of the levels in Se-adequate mice, indicating that the mice were Se deficient. mRNAs for Selh (selenoprotein H) and Sepw1 (selenoprotein W) as well as Gpx1 were decreased by Se deficiency to <40% of Se-adequate levels. Five and two additional mRNAs were moderately down-regulated in Sedeficient liver and kidney respectively. Importantly, nine selenoprotein mRNAs in liver and fifteen selenoprotein mRNAs in the kidney were not significantly regulated by Se deficiency, clearly demonstrating that Se regulation of selenoprotein mRNAs is not a general phenomenon. The similarity of the response to Se deficiency suggests that there is one underlying mechanism responsible. Importantly, the position of the UGA codon did not predict susceptibility to Se regulation, clearly indicating that additional features are involved in causing selenoprotein mRNAs to be sensitive to Se status.
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22
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Ufer C, Wang CC, Fähling M, Schiebel H, Thiele BJ, Billett EE, Kuhn H, Borchert A. Translational regulation of glutathione peroxidase 4 expression through guanine-rich sequence-binding factor 1 is essential for embryonic brain development. Genes Dev 2008; 22:1838-50. [PMID: 18593884 DOI: 10.1101/gad.466308] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Phospholipid hydroperoxide glutathione peroxidase (GPx4) is a moonlighting selenoprotein, which has been implicated in basic cell functions such as anti-oxidative defense, apoptosis, and gene expression regulation. GPx4-null mice die in utero at midgestation, and developmental retardation of the brain appears to play a major role. We investigated post-transcriptional mechanisms of GPx4 expression regulation and found that the guanine-rich sequence-binding factor 1 (Grsf1) up-regulates GPx4 expression. Grsf1 binds to a defined target sequence in the 5'-untranslated region (UTR) of the mitochondrial GPx4 (m-GPx4) mRNA, up-regulates UTR-dependent reporter gene expression, recruits m-GPx4 mRNA to translationally active polysome fractions, and coimmunoprecipitates with GPx4 mRNA. During embryonic brain development, Grsf1 and m-GPx4 are coexpressed, and functional knockdown (siRNA) of Grsf1 prevents embryonic GPx4 expression. When compared with mock controls, Grsf1 knockdown embryos showed significant signs of developmental retardations that are paralleled by apoptotic alterations (TUNEL staining) and massive lipid peroxidation (isoprostane formation). Overexpression of m-GPx4 prevented the apoptotic alterations in Grsf1-deficient embryos and rescued them from developmental retardation. These data indicate that Grsf1 up-regulates translation of GPx4 mRNA and implicate the two proteins in embryonic brain development.
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Affiliation(s)
- Christoph Ufer
- Institute of Biochemistry, University Medicine Berlin-Charité, D-10117 Berlin, F.R. Germany
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23
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Neu-Yilik G, Kulozik AE. NMD: multitasking between mRNA surveillance and modulation of gene expression. ADVANCES IN GENETICS 2008; 62:185-243. [PMID: 19010255 DOI: 10.1016/s0065-2660(08)00604-4] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Gene expression is a highly specific and regulated multilayer process with a plethora of interconnections as well as safeguard and feedback mechanisms. Messenger RNA, long neglected as a mere subcarrier of genetic information, is more recently recognized as a linchpin of regulation and control of gene expression. Moreover, the awareness of not only proteins but also mRNA as a modulator of genetic disorders has vastly increased in recent years. Nonsense-mediated mRNA decay (NMD) is a posttranscriptional surveillance mechanism that uses an intricate network of nuclear and cytoplasmic processes to eliminate mRNAs, containing premature termination codons. It thus helps limit the synthesis of potentially harmful truncated proteins. However, recent results suggest functions of NMD that go far beyond this role and affect the expression of wild-type genes and the modulation of whole pathways. In both respects--the elimination of faulty transcripts and the regulation of error-free mRNAs--NMD has many medical implications. Therefore, it has earned increasing interest from researchers of all fields of the life sciences. In the following text, we (1) present current knowledge about the NMD mechanism and its targets, (2) define its relevance in the regulation of important biochemical pathways, (3) explore its medical significance and the prospects of therapeutic interventions, and (4) discuss additional functions of NMD effectors, some of which may be networked to NMD. The main focus of this chapter lies on mammalian NMD and resorts to the features and factors of NMD in other organisms if these help to complete or illuminate the picture.
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Affiliation(s)
- Gabriele Neu-Yilik
- Department for Pediatric Oncology, Hematology and Immunology, University Hospital Heidelberg and Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Im Neuenheimer Feld 156, 69120 Heidelberg, Germany
| | - Andreas E Kulozik
- Department for Pediatric Oncology, Hematology and Immunology, University Hospital Heidelberg and Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Im Neuenheimer Feld 156, 69120 Heidelberg, Germany
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Isken O, Maquat LE. Quality control of eukaryotic mRNA: safeguarding cells from abnormal mRNA function. Genes Dev 2007; 21:1833-56. [PMID: 17671086 DOI: 10.1101/gad.1566807] [Citation(s) in RCA: 433] [Impact Index Per Article: 25.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Cells routinely make mistakes. Some mistakes are encoded by the genome and may manifest as inherited or acquired diseases. Other mistakes occur because metabolic processes can be intrinsically inefficient or inaccurate. Consequently, cells have developed mechanisms to minimize the damage that would result if mistakes went unchecked. Here, we provide an overview of three quality control mechanisms--nonsense-mediated mRNA decay, nonstop mRNA decay, and no-go mRNA decay. Each surveys mRNAs during translation and degrades those mRNAs that direct aberrant protein synthesis. Along with other types of quality control that occur during the complex processes of mRNA biogenesis, these mRNA surveillance mechanisms help to ensure the integrity of protein-encoding gene expression.
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Affiliation(s)
- Olaf Isken
- Department of Biochemistry and Biophysics, School of Medicine and Dentistry, University of Rochester, Rochester, New York 14642, USA
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25
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Hoffmann PR, Höge SC, Li PA, Hoffmann FW, Hashimoto AC, Berry MJ. The selenoproteome exhibits widely varying, tissue-specific dependence on selenoprotein P for selenium supply. Nucleic Acids Res 2007; 35:3963-73. [PMID: 17553827 PMCID: PMC1919489 DOI: 10.1093/nar/gkm355] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Selenoprotein P (Sel P) is a selenium-rich glycoprotein believed to play a key role in selenium (Se) transport throughout the body. Development of a Sel P knockout mouse model has supported this notion and initial studies have indicated that selenium supply to various tissues is differentially affected by genetic deletion of Sel P. Se in the form of the amino acid, selenocysteine, is incorporated into selenoproteins at UGA codons. Thus, Se availability affects not only selenoprotein levels, but also the turnover of selenoprotein mRNAs via the nonsense-mediated decay pathway. We investigated how genetic deletion of Sel P in mice affected levels of the mRNAs encoding all known members of the murine selenoprotein family, as well as three non-selenoprotein factors involved in their synthesis, selenophosphate synthetase 1 (SPS1), SECIS-binding protein 2 (SBP2) and SECp43. Our findings present a comprehensive description of selenoprotein mRNA expression in the following murine tissues: brain, heart, intestine, kidney, liver, lung, spleen and testes. We also describe how abundance of selenoproteins and selenoprotein-synthesis factors are affected by genetic deletion of Sel P in some of these tissues, providing insight into how the presence of this selenoprotein influences selenoprotein mRNA levels, and thus, the selenoproteome.
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Affiliation(s)
- Peter R Hoffmann
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 96813, USA.
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26
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Abstract
Nonsense-mediated mRNA decay (NMD) is a process of mRNA surveillance that degrades transcripts harboring a premature termination codon (PTC). Mammalian NMD was mostly studied in cultured cells so far and there was no direct evidence yet that NMD could operate in the brain. We introduced, by homologous recombination in mouse, a PTC in the mu opioid receptor gene (mor). mor transcript was severely downregulated in the brain of these knock-in mice. A systemic cycloheximide treatment significantly increased the level of the mutant mRNA, suggesting NMD involvement. To further corroborate this hypothesis, we generated a second knock-in mouse line where the PTC was placed at 10 instead of 96 nucleotides from the downstream splice junction. As predicted by the "termination codon position rule" established in vitro, mor transcript brain expression was rescued to wild-type level. These knock-in mouse lines will be valuable models to better understand and manipulate NMD in vivo.
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27
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Rebsch CM, Penna FJ, Copeland PR. Selenoprotein expression is regulated at multiple levels in prostate cells. Cell Res 2006; 16:940-8. [PMID: 17160069 DOI: 10.1038/sj.cr.7310117] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Selenium supplementation in a population with low basal blood selenium levels has been reported to decrease the incidence of several cancers including prostate cancer. Based on the clinical findings, it is likely that the antioxidant function of one or more selenoproteins is responsible for the chemopreventive effect, although low molecular weight seleno-compounds have also been posited to selectively induce apoptosis in transformed cells. To address the effects of selenium supplementation on selenoprotein expression in prostate cells, we have undertaken an analysis of antioxidant selenoprotein expression as well as selenium toxicity in non-tumorigenic prostate epithelial cells (RWPE-1) and prostate cancer cells (LNCaP and PC-3). Our results show that two of the glutathione peroxidase family members (GPX1 and GPX4) are highly induced by supplemental selenium in prostate cancer cells but only slightly induced in RWPE-1 cells. In addition, GPX1 levels are dramatically lower in PC-3 cells as compared to RWPE-1 or LNCaP cells. GPX2 protein and mRNA, however, are only detectable in RWPE-1 cells. Of the three selenium compounds tested (sodium selenite, sodium selenate and selenomethionine), only sodium selenite shows toxicity in a physiological range of selenium concentrations. Notably and in contrast to previous studies, RWPE-1 cells were significantly more sensitive to selenite than either of the prostate cancer cell lines. These results demonstrate that selenoproteins and selenium metabolism are regulated at multiple levels in prostate cells.
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Affiliation(s)
- Cheryl M Rebsch
- Department of Molecular Genetics, Microbiology and Immunology, UMDNJ--Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA
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28
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Rehwinkel J, Raes J, Izaurralde E. Nonsense-mediated mRNA decay: Target genes and functional diversification of effectors. Trends Biochem Sci 2006; 31:639-46. [PMID: 17010613 DOI: 10.1016/j.tibs.2006.09.005] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2006] [Revised: 08/14/2006] [Accepted: 09/18/2006] [Indexed: 01/08/2023]
Abstract
Recent genome-wide identification of nonsense-mediated mRNA decay (NMD) targets in yeast, fruitfly and human cells has provided insight into the biological functions and evolution of this mRNA quality control mechanism, revealing that NMD post-transcriptionally regulates an important fraction of the transcriptome. NMD targets are associated with a broad range of biological processes, but most of these targets are not encoded by orthologous genes across different species. Yeast and fruitfly NMD effectors regulate common targets in concert, but parallel pathways have evolved in humans, whereby NMD effectors have acquired additional functions. Thus, the phenotypic differences observed across species after inhibition of NMD are driven not only by the functional diversification of NMD effectors but also by changes in the repertoire of regulated genes.
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Affiliation(s)
- Jan Rehwinkel
- EMBL, Meyerhofstrasse 1, D-69117 Heidelberg, Germany
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29
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de Jesus LA, Hoffmann PR, Michaud T, Forry EP, Small-Howard A, Stillwell RJ, Morozova N, Harney JW, Berry MJ. Nuclear assembly of UGA decoding complexes on selenoprotein mRNAs: a mechanism for eluding nonsense-mediated decay? Mol Cell Biol 2006; 26:1795-805. [PMID: 16478999 PMCID: PMC1430236 DOI: 10.1128/mcb.26.5.1795-1805.2006] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recoding of UGA from a stop codon to selenocysteine poses a dilemma for the protein translation machinery. In eukaryotes, two factors that are crucial to this recoding process are the mRNA binding protein of the Sec insertion sequence, SBP2, and the specialized elongation factor, EFsec. We sought to determine the subcellular localization of these selenoprotein synthesis factors in mammalian cells and thus gain insight into how selenoprotein mRNAs might circumvent nonsense-mediated decay. Intriguingly, both EFsec and SBP2 localization differed depending on the cell line but significant colocalization of the two proteins was observed in cells where SBP2 levels were detectable. We identify functional nuclear localization and export signals in both proteins, demonstrate that SBP2 undergoes nucleocytoplasmic shuttling, and provide evidence that SBP2 levels and localization may influence EFsec localization. Our results suggest a mechanism for the nuclear assembly of the selenocysteine incorporation machinery that could allow selenoprotein mRNAs to circumvent nonsense-mediated decay, thus providing new insights into the mechanism of selenoprotein translation.
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Affiliation(s)
- Lucia A de Jesus
- Department of Cell and Molecular Biology, University of Hawaii at Manoa, Honolulu, HI 96822, USA
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30
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Hatfield DL, Carlson BA, Xu XM, Mix H, Gladyshev VN. Selenocysteine Incorporation Machinery and the Role of Selenoproteins in Development and Health. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2006; 81:97-142. [PMID: 16891170 DOI: 10.1016/s0079-6603(06)81003-2] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Dolph L Hatfield
- Molecular Biology of Selenium Section, Laboratory of Cancer Prevention, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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31
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Unique features of selenocysteine incorporation function within the context of general eukaryotic translational processes. Biochem Soc Trans 2005; 33:1493-7. [PMID: 16246153 DOI: 10.1042/bst0331493] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Unlike other essential dietary trace elements, selenium exerts its biological actions through its direct incorporation into selenoproteins, as a part of the 21st amino acid, selenocysteine. Fundamental studies have elucidated the unique structures and putative functions of multiple co-translational factors required for the incorporation of selenocysteine into selenoproteins. The current challenge is to understand how these selenocysteine incorporation factors function within the framework of translation. In eukaryotes, co-ordinating nuclear transcription with cytoplasmic translation of genes is a challenge involving complex spatial and temporal regulation. Selenoproteins utilize the common cellular machinery required for synthesis of non-selenoproteins. This machinery includes the elements involved in transcription, mRNA splicing and transport, and translational processes. Many investigators have emphasized the differences between the expression of selenoproteins and other eukaryotic proteins, whereas this review will attempt to highlight common themes and point out where additional interactions may be discovered.
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32
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Kelly VP, Suzuki T, Nakajima O, Arai T, Tamai Y, Takahashi S, Nishimura S, Yamamoto M. The distal sequence element of the selenocysteine tRNA gene is a tissue-dependent enhancer essential for mouse embryogenesis. Mol Cell Biol 2005; 25:3658-69. [PMID: 15831471 PMCID: PMC1084291 DOI: 10.1128/mcb.25.9.3658-3669.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Appropriate expression of the selenocysteine tRNA (tRNA(Sec)) gene is necessary for the production of an entire family of selenoprotein enzymes. This study investigates the consequence of disrupting an upstream enhancer region of the mouse tRNA(Sec) gene (Trsp) known as the distal sequence element (DSE) by use of a conditional repair gene targeting strategy, in which a 3.2-kb insertion was introduced into the promoter of the gene. In the absence of DSE activity, homozygous mice failed to develop in utero beyond embryonic day 7.5 and had severely decreased levels of selenoprotein transcript. Cre-mediated removal of the selection cassette recovered DSE regulation of Trsp, restoring wild-type levels of tRNA(Sec) expression and allowing the generation of viable rescued mice. Further analysis of targeted heterozygous adult mice revealed that the enhancer activity of the DSE is tissue dependent since, in contrast to liver, heart does not require the DSE for normal expression of Trsp. Similarly, in mouse cell lines we showed that the DSE functions as a cell-line-specific inducible element of tRNA(Sec). Together, our data demonstrate that the DSE is a tissue-dependent regulatory element of tRNA(Sec) expression and that its activity is vital for sufficient tRNA(Sec) production during mouse embryogenesis.
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MESH Headings
- Animals
- Antioxidants/metabolism
- Base Sequence
- Embryo, Mammalian/cytology
- Embryo, Mammalian/enzymology
- Embryonic Development/genetics
- Embryonic Development/physiology
- Enhancer Elements, Genetic/genetics
- Enhancer Elements, Genetic/physiology
- Gene Expression Regulation, Developmental
- Gene Targeting
- Genes, Lethal/genetics
- Glutathione Peroxidase/genetics
- Glutathione Peroxidase/metabolism
- Heme Oxygenase (Decyclizing)/genetics
- Heme Oxygenase (Decyclizing)/metabolism
- Heme Oxygenase-1
- Liver/metabolism
- Membrane Proteins
- Mice/embryology
- Mice/genetics
- Molecular Sequence Data
- Myocardium/metabolism
- Proteins/genetics
- Proteins/metabolism
- RNA, Transfer, Amino Acid-Specific/analysis
- RNA, Transfer, Amino Acid-Specific/genetics
- Selenoproteins
- Tissue Distribution
- Up-Regulation
- Glutathione Peroxidase GPX1
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Affiliation(s)
- Vincent P Kelly
- Center for TARA, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba 305-8577, Japan.
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33
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Holbrook JA, Neu-Yilik G, Hentze MW, Kulozik AE. Nonsense-mediated decay approaches the clinic. Nat Genet 2004; 36:801-8. [PMID: 15284851 DOI: 10.1038/ng1403] [Citation(s) in RCA: 460] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2004] [Accepted: 06/16/2004] [Indexed: 11/09/2022]
Abstract
Nonsense-mediated decay (NMD) eliminates mRNAs containing premature termination codons and thus helps limit the synthesis of abnormal proteins. New results uncover a broader role of NMD as a pathway that also affects the expression of wild-type genes and alternative-splice products. Because the mechanisms by which NMD operates have received much attention, we discuss here the emerging awareness of the impact of NMD on the manifestation of human genetic diseases. We explore how an understanding of NMD accounts for phenotypic differences in diseases caused by premature termination codons. Specifically, we consider how the protective function of NMD sometimes benefits heterozygous carriers and, in contrast, sometimes contributes to a clinical picture of protein deficiency by inhibiting expression of partially functional proteins. Potential 'NMD therapeutics' will therefore need to strike a balance between the general physiological benefits of NMD and its detrimental effects in cases of specific genetic mutations.
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Affiliation(s)
- Jill A Holbrook
- Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, D-69120 Heidelberg, Germany
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34
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Mehta A, Rebsch CM, Kinzy SA, Fletcher JE, Copeland PR. Efficiency of mammalian selenocysteine incorporation. J Biol Chem 2004; 279:37852-9. [PMID: 15229221 PMCID: PMC2820281 DOI: 10.1074/jbc.m404639200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Five components have thus far been identified that are necessary for the incorporation of selenocysteine (Sec) into approximately 25 mammalian proteins. Two of these are cis sequences, a SECIS element in the 3'-untranslated region and a Sec codon (UGA) in the coding region. The three known trans-acting factors are a Sec-specific translation elongation factor (eEFSec), the Sec-tRNA(Sec), and a SECIS-binding protein, SBP2. Here we describe a system in which the efficiency of Sec incorporation was determined quantitatively both in vitro and in transfected cells, and in which the contribution of each of the known factors is examined. The efficiency of Sec incorporation into a luciferase reporter system in vitro is maximally 5-8%, which is 6-10 times higher than that in transfected rat hepatoma cells, McArdle 7777. In contrast, the efficiency of Sec incorporation into selenoprotein P in vitro is approximately 40%, suggesting that as yet unidentified cis-elements may regulate differential selenoprotein expression. In addition, we have found that SBP2 is the only limiting factor in rabbit reticulocyte lysate but not in transfected rat hepatoma cells where SBP2 is found to be mostly if not entirely cytoplasmic despite having a strong putative nuclear localization signal. The significance of these findings with regard to the function of known Sec incorporation factors is discussed.
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Affiliation(s)
- Anupama Mehta
- Department of Molecular Genetics, Microbiology and Immunology, University of Medicine and Dentistry of New Jersey Robert Wood Johnson Medical School, Piscataway, New Jersey 08854
| | - Cheryl M. Rebsch
- Department of Molecular Genetics, Microbiology and Immunology, University of Medicine and Dentistry of New Jersey Robert Wood Johnson Medical School, Piscataway, New Jersey 08854
| | - Scott A. Kinzy
- Department of Molecular Genetics, Microbiology and Immunology, University of Medicine and Dentistry of New Jersey Robert Wood Johnson Medical School, Piscataway, New Jersey 08854
| | - Julia E. Fletcher
- Department of Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195
| | - Paul R. Copeland
- Department of Molecular Genetics, Microbiology and Immunology, University of Medicine and Dentistry of New Jersey Robert Wood Johnson Medical School, Piscataway, New Jersey 08854
- To whom correspondence should be addressed: Dept. of Molecular Genetics, Microbiology and Immunology, UMDNJ Robert Wood Johnson Medical School, 675 Hoes Lane, Rm. 728, Piscataway, NJ 08854. Tel.: 732-235-4670; Fax: 732-235-5223;
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35
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Abstract
Studies of nonsense-mediated mRNA decay in mammalian cells have proffered unforeseen insights into changes in mRNA-protein interactions throughout the lifetime of an mRNA. Remarkably, mRNA acquires a complex of proteins at each exon-exon junction during pre-mRNA splicing that influences the subsequent steps of mRNA translation and nonsense-mediated mRNA decay. Complex-loaded mRNA is thought to undergo a pioneer round of translation when still bound by cap-binding proteins CBP80 and CBP20 and poly(A)-binding protein 2. The acquisition and loss of mRNA-associated proteins accompanies the transition from the pioneer round to subsequent rounds of translation, and from translational competence to substrate for nonsense-mediated mRNA decay.
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Affiliation(s)
- Lynne E Maquat
- Department of Biochemistry and Biophysics, School of Medicine and Dentistry, 601 Elmwood Avenue, Box 712, University of Rochester, Rochester, New York 14642, USA.
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36
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Fackenthal JD, Cartegni L, Krainer AR, Olopade OI. BRCA2 T2722R is a deleterious allele that causes exon skipping. Am J Hum Genet 2002; 71:625-31. [PMID: 12145750 PMCID: PMC379197 DOI: 10.1086/342192] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2002] [Accepted: 06/03/2002] [Indexed: 01/30/2023] Open
Abstract
Patients with a strong family history of breast cancer are often counseled to receive genetic screening for BRCA1 and BRCA2 mutations, the strongest known predictors of breast cancer. A major limitation of genetic testing is the number of inconclusive results due to unclassified BRCA1 and BRCA2 sequence variants. Many known deleterious BRCA1 and BRCA2 mutations affect splicing, and these typically lie near intron/exon boundaries. However, there are also potential internal exonic mutations that disrupt functional exonic splicing enhancer (ESE) sequences, resulting in exon skipping. Using previously established sequence matrices for the scoring of putative ESE motifs, we have systematically examined several BRCA2 mutations for potential ESE disruption mutations. These predictions revealed that BRCA2 T2722R (8393C-->G), which segregates with affected individuals in a family with breast cancer, disrupts three potential ESE sites. Reverse-transcriptase polymerase chain reaction analysis confirms that this mutation causes exon skipping, leading to an out-of-frame fusion of BRCA2 exons 17 and 19. This represents the first BRCA2 missense mutation shown to be a predicted deleterious protein-truncating mutation and suggests a potentially useful method for determining the clinical significance of a subset of the many unclassified variants in BRCA1 and BRCA2.
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Affiliation(s)
- James D. Fackenthal
- Center for Clinical Cancer Genetics, Department of Medicine, University of Chicago Medical Center, Chicago; and Cold Spring Harbor Laboratory, Cold Spring Harbor, NY
| | - Luca Cartegni
- Center for Clinical Cancer Genetics, Department of Medicine, University of Chicago Medical Center, Chicago; and Cold Spring Harbor Laboratory, Cold Spring Harbor, NY
| | - Adrian R. Krainer
- Center for Clinical Cancer Genetics, Department of Medicine, University of Chicago Medical Center, Chicago; and Cold Spring Harbor Laboratory, Cold Spring Harbor, NY
| | - Olufunmilayo I. Olopade
- Center for Clinical Cancer Genetics, Department of Medicine, University of Chicago Medical Center, Chicago; and Cold Spring Harbor Laboratory, Cold Spring Harbor, NY
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37
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Abstract
If the abundance of a particular selenoprotein mRNA is reduced during selenium deprivation, then the mRNA is likely to be a natural substrate for NMD. One assay for NMD involves changing the TGA Sec codon(s) to either a TGC cysteine codon or a TAA nonsense codon. If selenium deprivation elicits NMD and has no other effect on selenoprotein gene expression, then, regardless of selenium concentration, the level of UGC-containing mRNA should be most abundant, the level of UGA-containing mRNA should be intermediate in abundance, and the level of UAA-containing mRNA should be least abundant. Furthermore, the level of UGA-containing mRNA should be decreased by a decrease in selenium concentration, while the levels of UGC- and UAA-containing mRNAs should be unaffected by selenium concentration. A different assay for NMD involves coexpression of the particular selenoprotein gene and a vector expressing a dominant-negative version of hUpf1p. This assay is simpler and more versatile than the first assay because it can be used to assay any cellular gene in situ provided the cells can be stably transfected with the hUpf1p expression vector.
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Affiliation(s)
- Xiaolei Sun
- Department of Biochemistry and Biophysics, School of Medicine and Dentistry, University of Rochester, Rochester, New York 14642, USA
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38
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Affiliation(s)
- Dolph L Hatfield
- Molecular Biology of Selenium Section, Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
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39
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Abstract
The RNA polymerase of giardiavirus (GLV) is synthesized as a fusion protein through a -1 ribosomal frameshift in a region where gag and pol open reading frames (ORFs) overlap. A heptamer, CCCUUUA, and a potential pseudoknot found in the overlap were predicted to be required for the frameshift. A 68-nucleotide (nt) cDNA fragment containing these elements was inserted between the GLV 5' 631-nt cDNA and the out-of-frame luciferase gene that required a -1 frameshift within the 68-nt fragment for expression. Giardia lamblia trophozoites transfected with the transcript of this construct showed a frameshift frequency at 1.7%, coinciding with the polymerase-to-capsid protein ratio in GLV. The heptamer is required for the frameshift but can be replaced with other sequences of the same motif. Mutations placing stop codons in the 0 or -1 frame, located directly before or after the heptamer, implicated the latter as the site for the -1 frameshift. Shortening or destroying the putative stem decreased the frameshift efficiency threefold; the efficiency was fully recovered by mutations to restore the stem. Deleting 18 nt from the 3' end of the 68-nt fragment, which formed the second stem in the putative pseudoknot, had no effect on the frequency of the frameshift. Chemical probing of the RNA secondary structure in the frameshift region showed that bases resistant to chemical modification were clustered in the putative stem structures, thus confirming the presence of the postulated stem-loop, while all the bases in the loop were chemically modified, thus ruling out their capability of forming a pseudoknot. These results confirmed the conclusion based on data from the mutation study that there is but a simple stem-loop downstream from the heptamer. Together, they constitute the structural elements for a -1 ribosomal frameshift in the GLV transcript.
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Affiliation(s)
- L Li
- Department of Pharmaceutical Chemistry, School of Pharmacy, University of California San Francisco, 94143-0446, USA
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