1
|
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.
Collapse
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.)
| |
Collapse
|
2
|
The selenocysteine tRNA STAF-binding region is essential for adequate selenocysteine tRNA status, selenoprotein expression and early age survival of mice. Biochem J 2009; 418:61-71. [PMID: 18973473 DOI: 10.1042/bj20081304] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
STAF [Sec (selenocysteine) tRNA gene transcription activating factor] is a transcription activating factor for a number of RNA Pol III- and RNA Pol II-dependent genes including the Trsp [Sec tRNA gene], which in turn controls the expression of all selenoproteins. Here, the role of STAF in regulating expression of Sec tRNA and selenoproteins was examined. We generated transgenic mice expressing the Trsp transgene lacking the STAF-binding site and made these mice dependent on the transgene for survival by removing the wild-type Trsp. The level of Sec tRNA was unaffected or slightly elevated in heart and testis, but reduced approximately 60% in liver and kidney, approximately 70% in lung and spleen and approximately 80% in brain and muscle compared with the corresponding organs in control mice. Moreover, the ratio of the two isoforms of Sec tRNA that differ by methylation at position 34 (Um34) was altered significantly, and the Um34-containing form was substantially reduced in all tissues examined. Selenoprotein expression in these animals was most affected in tissues in which the Sec tRNA levels were most severely reduced. Importantly, mice had a neurological phenotype strikingly similar to that of mice in which the selenoprotein P gene had been removed and their life span was substantially reduced. The results indicate that STAF influences selenoprotein expression by enhancing Trsp synthesis in an organ-specific manner and by controlling Sec tRNA modification in each tissue examined.
Collapse
|
3
|
Yoo MH, Xu XM, Turanov AA, Carlson BA, Gladyshev VN, Hatfield DL. A new strategy for assessing selenoprotein function: siRNA knockdown/knock-in targeting the 3'-UTR. RNA (NEW YORK, N.Y.) 2007; 13:921-9. [PMID: 17468436 PMCID: PMC1869036 DOI: 10.1261/rna.533007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Selenocysteine insertion into protein in mammalian cells requires RNA elements in the 3'-untranslated regions (3'-UTRs) of selenoprotein genes. The occurrence of these conserved sequences should make selenoproteins particularly amenable for knockdown/knock-in strategies to examine selenoprotein functions. Herein, we utilized the 3'-UTR of various selenoproteins to knock down their expression using siRNAs and then knock in expression using constructs containing mutations within the target region. Thioredoxin reductase 1 (TR1) knockdown in a mouse kidney cell line resulted in the cells growing about 10% more slowly, being more sensitive to UV radiation, and having increased apoptosis in response to UV than control cells. The knockdown cells transfected with a construct encoding the wild-type TR1 gene and having mutations in the sequences targeted by siRNA restored TR1 expression and catalytic activity, rendered the knockdown cells less sensitive to UV, and protected the cells against apoptosis. We also applied this technique to other selenoproteins, selenophosphate synthetase 2 and glutathione peroxidase 1, and found that mRNA and protein levels were restored following transfection of knockdown cells with the corresponding knock-in constructs. In addition to important new insights into the functions of key mammalian selenoproteins, the data suggest that the RNAi-based knock-in technology could distinguish phenotypes due to off-targeting and provide a new method for examining many of the subtleties of selenoprotein function not available using RNAi technology alone.
Collapse
Affiliation(s)
- Min-Hyuk Yoo
- Molecular Biology of Selenium Section, Laboratory of Cancer Prevention, Center for Cancer Research, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | | | | | | | | |
Collapse
|
4
|
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
| | | | | | | | | |
Collapse
|
5
|
Jameson RR, Diamond AM. A regulatory role for Sec tRNA[Ser]Sec in selenoprotein synthesis. RNA (NEW YORK, N.Y.) 2004; 10:1142-1152. [PMID: 15208449 PMCID: PMC1370604 DOI: 10.1261/rna.7370104] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2004] [Accepted: 04/20/2004] [Indexed: 05/24/2023]
Abstract
Selenium is biologically active through the functions of selenoproteins that contain the amino acid selenocysteine. This amino acid is translated in response to in-frame UGA codons in mRNAs that include a SECIS element in its 3' untranslated region, and this process requires a unique tRNA, referred to as tRNA([Ser]Sec). The translation of UGA as selenocysteine, rather than its use as a termination signal, is a candidate restriction point for the regulation of selenoprotein synthesis by selenium. A specialized reporter construct was used that permits the evaluation of SECIS-directed UGA translation to examine mechanisms of the regulation of selenoprotein translation. Using SECIS elements from five different selenoprotein mRNAs, UGA translation was quantified in response to selenium supplementation and alterations in tRNA([Ser]Sec) levels and isoform distributions. Although each of the evaluated SECIS elements exhibited differences in their baseline activities, each was stimulated to a similar extent by increased selenium or tRNA([Ser]Sec) levels and was inhibited by diminished levels of the methylated isoform of tRNA([Ser]Sec) achieved using a dominant-negative acting mutant tRNA([Ser]Sec). tRNA([Ser]Sec) was found to be limiting for UGA translation under conditions of high selenoprotein mRNA in both a transient reporter assay and in cells with elevated GPx-1 mRNA. This and data indicating increased amounts of the methylated isoform of tRNA([Ser]Sec) during selenoprotein translation indicate that it is this isoform that is translationally active and that selenium-induced tRNA methylation is a mechanism of regulation of the synthesis of selenoproteins.
Collapse
Affiliation(s)
- Ruth R Jameson
- Department of Human Nutrition, University of Illinois at Chicago, 1919 West Taylor Street, MC517, Chicago, IL 60612, USA
| | | |
Collapse
|
6
|
Hornberger TA, McLoughlin TJ, Leszczynski JK, Armstrong DD, Jameson RR, Bowen PE, Hwang ES, Hou H, Moustafa ME, Carlson BA, Hatfield DL, Diamond AM, Esser KA. Selenoprotein-deficient transgenic mice exhibit enhanced exercise-induced muscle growth. J Nutr 2003; 133:3091-7. [PMID: 14519790 DOI: 10.1093/jn/133.10.3091] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Dietary intake of selenium has been implicated in a wide range of health issues, including aging, heart disease and cancer. Selenium deficiency, which can reduce selenoprotein levels, has been associated with several striated muscle pathologies. To investigate the role of selenoproteins in skeletal muscle biology, we used a transgenic mouse (referred to as i6A-) that has reduced levels of selenoproteins due to the introduction and expression of a dominantly acting mutant form of selenocysteine transfer RNA (tRNA[Ser]Sec). As a consequence, each organ contains reduced levels of most selenoproteins, yet these mice are normal with regard to fertility, overall health, behavior and blood chemistries. In the present study, although skeletal muscles from i6A- mice were phenotypically indistinguishable from those of wild-type mice, plantaris muscles were approximately 50% heavier after synergist ablation, a model of exercise overload. Like muscle in wild-type mice, the enhanced growth in the i6A- mice was completely blocked by inhibition of the mammalian target of rapamycin (mTOR) pathway. Muscles of transgenic mice exhibited increased site-specific phosphorylation on both Akt and p70 ribosomal S6 kinase (p70S6k) (P < 0.05) before ablation, perhaps accounting for the enhanced response to synergist ablation. Thus, a single genetic alteration resulted in enhanced skeletal muscle adaptation after exercise, and this is likely through subtle changes in the resting phosphorylation state of growth-related kinases.
Collapse
Affiliation(s)
- Troy A Hornberger
- School of Kinesiology, University of Illinois, Chicago, IL 60608, USA
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Abstract
Selenium is an essential trace element that is incorporated into proteins as selenocysteine (Sec), the twenty-first amino acid. Sec is encoded by a UGA codon in the selenoprotein mRNA. The decoding of UGA as Sec requires the reprogramming of translation because UGA is normally read as a stop codon. The translation of selenoprotein mRNAs requires cis-acting sequences in the mRNA and novel trans-acting factors dedicated to Sec incorporation. Selenoprotein synthesis in vivo is highly selenium-dependent, and there is a hierarchy of selenoprotein expression in mammals when selenium is limiting. This review describes emerging themes from studies on the mechanism, kinetics, and efficiency of Sec insertion in prokaryotes. Recent developments that provide mechanistic insight into how the eukaryotic ribosome distinguishes between UGA/Sec and UGA/stop codons are discussed. The efficiency and regulation of mammalian selenoprotein synthesis are considered in the context of current models for Sec insertion.
Collapse
Affiliation(s)
- Donna M Driscoll
- Department of Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
| | | |
Collapse
|
8
|
Kumaraswamy E, Carlson BA, Morgan F, Miyoshi K, Robinson GW, Su D, Wang S, Southon E, Tessarollo L, Lee BJ, Gladyshev VN, Hennighausen L, Hatfield DL. Selective removal of the selenocysteine tRNA [Ser]Sec gene (Trsp) in mouse mammary epithelium. Mol Cell Biol 2003; 23:1477-88. [PMID: 12588969 PMCID: PMC151713 DOI: 10.1128/mcb.23.5.1477-1488.2003] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mice homozygous for an allele encoding the selenocysteine (Sec) tRNA [Ser]Sec gene (Trsp) flanked by loxP sites were generated. Cre recombinase-dependent removal of Trsp in these mice was lethal to embryos. To investigate the role of Trsp in mouse mammary epithelium, we deleted this gene by using transgenic mice carrying the Cre recombinase gene under control of the mouse mammary tumor virus (MMTV) long terminal repeat or the whey acidic protein promoter. While both promoters target Cre gene expression to mammary epithelium, MMTV-Cre is also expressed in spleen and skin. Sec tRNA [Ser]Sec amounts were reduced by more than 70% in mammary tissue with either transgene, while in skin and spleen, levels were reduced only with MMTV-Cre. The selenoprotein population was selectively affected with MMTV-Cre in breast and skin but not in the control tissue, kidney. Moreover, within affected tissues, expression of specific selenoproteins was regulated differently and often in a contrasting manner, with levels of Sep15 and the glutathione peroxidases GPx1 and GPx4 being substantially reduced. Expression of the tumor suppressor genes BRCA1 and p53 was also altered in a contrasting manner in MMTV-Cre mice, suggesting greater susceptibility to cancer and/or increased cell apoptosis. Thus, the conditional Trsp knockout mouse allows tissue-specific manipulation of Sec tRNA and selenoprotein expression, suggesting that this approach will provide a useful tool for studying the role of selenoproteins in health.
Collapse
MESH Headings
- Alleles
- Animals
- Blotting, Northern
- Blotting, Western
- Breast/metabolism
- Chromatography
- Crosses, Genetic
- Epithelium/metabolism
- Gene Deletion
- Genes, BRCA1
- Genes, p53/genetics
- Genetic Vectors
- Glutathione Peroxidase/metabolism
- Heterozygote
- Kidney/metabolism
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Models, Genetic
- Phenotype
- Promoter Regions, Genetic
- Proteins/metabolism
- RNA, Transfer, Amino Acyl/genetics
- RNA, Transfer, Amino Acyl/metabolism
- Recombination, Genetic
- Selenoproteins
- Tissue Distribution
- Transgenes
Collapse
Affiliation(s)
- Easwari Kumaraswamy
- Section on Molecular Biology of Selenium, Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
9
|
MESH Headings
- Animals
- Base Sequence
- Cattle
- Chromatography, Liquid
- Escherichia coli/genetics
- Escherichia coli/metabolism
- Gene Expression
- HL-60 Cells
- Humans
- In Vitro Techniques
- Liver/metabolism
- Models, Molecular
- Molecular Sequence Data
- Nucleic Acid Conformation
- Protein Biosynthesis
- Proteins/genetics
- RNA, Bacterial/chemistry
- RNA, Bacterial/genetics
- RNA, Transfer, Amino Acid-Specific/chemistry
- RNA, Transfer, Amino Acid-Specific/genetics
- RNA, Transfer, Amino Acid-Specific/isolation & purification
- Selenocysteine/genetics
- Selenocysteine/metabolism
- Selenoproteins
Collapse
Affiliation(s)
- Bradley A Carlson
- Section on Molecular Biology of Selenium, Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | |
Collapse
|
10
|
Jameson RR, Carlson BA, Butz M, Esser K, Hatfield DL, Diamond AM. Selenium influences the turnover of selenocysteine tRNA([Ser]Sec) in Chinese hamster ovary cells. J Nutr 2002; 132:1830-5. [PMID: 12097655 DOI: 10.1093/jn/132.7.1830] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Selenocysteine transfer RNA (tRNA([Ser]Sec)) is a central molecule in the production of selenium-containing proteins, and may play a role in the regulation of their biosynthesis. Selenium concentration influences both the levels of tRNA([Ser]Sec) and the relative abundance of two isoforms. To study the mechanism by which selenium affects tRNA([Ser]Sec) levels, Chinese hamster ovary (CHO) cells were treated with the transcription inhibitor, actinomycin D, and tRNA([Ser]Sec) levels were determined by Northern blotting, primer extension and reverse-phase column chromatography. Turnover of tRNA([Ser]Sec) in CHO cells was faster than the total tRNA population. Supplementation of the culture media with selenium reduced turnover of tRNA([Ser]Sec), but did not influence turnover of a randomly selected serine tRNA. Inhibition of transcription with actinomycin D resulted in a relative increase in the abundance of the isoform containing methylcarboxymethyl-5'-uridine-2'-O-methylribose in the wobble position of the anticodon. Primer extension studies, which permitted the independent evaluation of the tRNA([Ser]Sec) arising from the introduced mouse gene and that derived from the host CHO gene, indicated an accelerated decline in tRNA([Ser]Sec) derived from both the transfected and the native gene. These results provide additional insight into the levels of regulation that control the translation of selenium containing proteins in mammalian cells.
Collapse
Affiliation(s)
- Ruth R Jameson
- Department of Human Nutrition, University of Illinois at Chicago, 60612, USA
| | | | | | | | | | | |
Collapse
|
11
|
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.
| | | |
Collapse
|
12
|
Moustafa ME, Carlson BA, El-Saadani MA, Kryukov GV, Sun QA, Harney JW, Hill KE, Combs GF, Feigenbaum L, Mansur DB, Burk RF, Berry MJ, Diamond AM, Lee BJ, Gladyshev VN, Hatfield DL. Selective inhibition of selenocysteine tRNA maturation and selenoprotein synthesis in transgenic mice expressing isopentenyladenosine-deficient selenocysteine tRNA. Mol Cell Biol 2001; 21:3840-52. [PMID: 11340175 PMCID: PMC87048 DOI: 10.1128/mcb.21.11.3840-3852.2001] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Selenocysteine (Sec) tRNA (tRNA([Ser]Sec)) serves as both the site of Sec biosynthesis and the adapter molecule for donation of this amino acid to protein. The consequences on selenoprotein biosynthesis of overexpressing either the wild type or a mutant tRNA([Ser]Sec) lacking the modified base, isopentenyladenosine, in its anticodon loop were examined by introducing multiple copies of the corresponding tRNA([Ser]Sec) genes into the mouse genome. Overexpression of wild-type tRNA([Ser]Sec) did not affect selenoprotein synthesis. In contrast, the levels of numerous selenoproteins decreased in mice expressing isopentenyladenosine-deficient (i(6)A(-)) tRNA([Ser]Sec) in a protein- and tissue-specific manner. Cytosolic glutathione peroxidase and mitochondrial thioredoxin reductase 3 were the most and least affected selenoproteins, while selenoprotein expression was most and least affected in the liver and testes, respectively. The defect in selenoprotein expression occurred at translation, since selenoprotein mRNA levels were largely unaffected. Analysis of the tRNA([Ser]Sec) population showed that expression of i(6)A(-) tRNA([Ser]Sec) altered the distribution of the two major isoforms, whereby the maturation of tRNA([Ser]Sec) by methylation of the nucleoside in the wobble position was repressed. The data suggest that the levels of i(6)A(-) tRNA([Ser]Sec) and wild-type tRNA([Ser]Sec) are regulated independently and that the amount of wild-type tRNA([Ser]Sec) is determined, at least in part, by a feedback mechanism governed by the level of the tRNA([Ser]Sec) population. This study marks the first example of transgenic mice engineered to contain functional tRNA transgenes and suggests that i(6)A(-) tRNA([Ser]Sec) transgenic mice will be useful in assessing the biological roles of selenoproteins.
Collapse
Affiliation(s)
- M E Moustafa
- Section on the Molecular Biology of Selenium, Basic Research Laboratory, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Warner GJ, Berry MJ, Moustafa ME, Carlson BA, Hatfield DL, Faust JR. Inhibition of selenoprotein synthesis by selenocysteine tRNA[Ser]Sec lacking isopentenyladenosine. J Biol Chem 2000; 275:28110-9. [PMID: 10821829 DOI: 10.1074/jbc.m001280200] [Citation(s) in RCA: 133] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A common posttranscriptional modification of tRNA is the isopentenylation of adenosine at position 37, creating isopentenyladenosine (i(6)A). The role of this modified nucleoside in protein synthesis of higher eukaryotes is not well understood. Selenocysteyl (Sec) tRNA (tRNA([Ser]Sec)) decodes specific UGA codons and contains i(6)A. To address the role of the modified nucleoside in this tRNA, we constructed a site-specific mutation, which eliminates the site of isopentenylation, in the Xenopus tRNA([Ser]Sec) gene. Transfection of the mutant tRNA([Ser]Sec) gene resulted in 80% and 95% reduction in the expression of co-transfected selenoprotein genes encoding type I and II iodothyronine deiodinases, respectively. A similar decrease in type I deiodinase synthesis was observed when transfected cells were treated with lovastatin, an inhibitor of the biosynthesis of the isopentenyl moiety. Neither co-transfection with the mutant tRNA gene nor lovastatin treatment reduced type I deiodinase mRNA levels. Also, mutant tRNA expression did not alter initiation of translation or degradation of the type I deiodinase protein. Furthermore, isopentenylation of tRNA([Ser]Sec) was not required for synthesis of Sec on the tRNA. We conclude that isopentenylation of tRNA([Ser]Sec) is required for efficient translational decoding of UGA and synthesis of selenoproteins.
Collapse
Affiliation(s)
- G J Warner
- Tufts University School of Medicine, Department of Physiology, Boston, Massachusetts 02111, USA
| | | | | | | | | | | |
Collapse
|
14
|
Mansur DB, Hao H, Gladyshev VN, Korotkov KV, Hu Y, Moustafa ME, El-Saadani MA, Carlson BA, Hatfield DL, Diamond AM. Multiple levels of regulation of selenoprotein biosynthesis revealed from the analysis of human glioma cell lines. Biochem Pharmacol 2000; 60:489-97. [PMID: 10874123 DOI: 10.1016/s0006-2952(00)00366-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
To gain a better understanding of the biological consequences of the exposure of tumor cells to selenium, we evaluated the selenium-dependent responses of two selenoproteins (glutathione peroxidase and the recently characterized 15-kDa selenoprotein) in three human glioma cell lines. Protein levels, mRNA levels, and the relative distribution of the two selenocysteine tRNA isoacceptors (designated mcm(5)U and mcm(5)Um) were determined for standard as well as selenium-supplemented conditions. The human malignant glioma cell lines D54, U251, and U87 were maintained in normal or selenium-supplemented (30 nM sodium selenite) conditions. Northern blot analysis demonstrated only minor increases in steady-state GSHPx-1 mRNA in response to selenium addition. Baseline glutathione peroxidase activity was 10.7 +/- 0.7, 7.6 +/- 0.7, and 4.3 +/- 0.7 nmol NADPH oxidized/min/mg protein for D54, U251, and U87, respectively, as determined by the standard coupled spectrophotometric assay. Glutathione peroxidase activity increased in a cell line-specific manner to 19.7 +/- 1.4, 15.6 +/- 2.1, and 6. 7 +/- 0.5 nmol NADPH oxidized/min/mg protein, respectively, as did a proportional increase in cellular resistance to H(2)O(2), in response to added selenium. The 15-kDa selenoprotein mRNA levels likewise remained constant despite selenium supplementation. The selenium-dependent change in distribution between the two selenocysteine tRNA isoacceptors also occurred in a cell line-specific manner. The percentage of the methylated isoacceptor, mcm(5)Um, changed from 35.5 to 47.2 for D54, from 38.1 to 47.3 for U251, and from 49.0 to 47.6 for U87. These data represent the first time that selenium-dependent changes in selenoprotein mRNA and protein levels, as well as selenocysteine tRNA distribution, were examined in human glioma cell lines.
Collapse
Affiliation(s)
- D B Mansur
- Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60612, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Nasim MT, Jaenecke S, Belduz A, Kollmus H, Flohé L, McCarthy JE. Eukaryotic selenocysteine incorporation follows a nonprocessive mechanism that competes with translational termination. J Biol Chem 2000; 275:14846-52. [PMID: 10809727 DOI: 10.1074/jbc.275.20.14846] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The synthesis of eukaryotic selenoproteins involves the recoding of an internal UGA codon as a site for selenocysteine incorporation. This recoding event is directed by a selenocysteine insertion sequence in the 3'-untranslated region. Because UGA also functions as a signal for peptidyl-tRNA hydrolysis, we have investigated how the rates of translational termination and selenocysteine incorporation relate to cis-acting elements in the mRNA as well as to trans-acting factors in the cytoplasm. We used cis-elements from the phospholipid glutathione peroxidase gene as the basis for this work because of its relatively high efficiency of selenocysteine incorporation. The last two codons preceding the UGA were found to exert a far greater influence on selenocysteine incorporation than nucleotides downstream of it. The efficiency of selenocysteine incorporation was generally much less than 100% but could be partially enhanced by concomitant overexpression of the tRNA(Sec) gene. The combination of two or three UGA codons in one reading frame led to a dramatic reduction in the yield of full-length protein. It is therefore unlikely that multiple incorporations of selenocysteine are processive with respect to the mode of action of the ribosomal complex binding to the UGA site. These observations are discussed in terms of the mechanism of selenoprotein synthesis and its ability to compete with termination at UGA codons.
Collapse
Affiliation(s)
- M T Nasim
- Posttranscriptional Control Group, Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, United Kingdom
| | | | | | | | | | | |
Collapse
|
16
|
Xu XM, Carlson BA, Kim LK, Lee BJ, Hatfield DL, Diamond AM. Analysis of selenocysteine (Sec) tRNA([Ser]Sec) genes in Chinese hamsters. Gene 1999; 239:49-53. [PMID: 10571033 DOI: 10.1016/s0378-1119(99)00382-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Several recent observations have indicated that the primary structure of the Chinese hamster selenocysteine tRNA([Ser]sec) is different than those of other mammalian species. These reports prompted us to investigate the gene sequence for this tRNA in Chinese hamsters. Southern blotting of Chinese hamster ovary (CHO) genomic DNA derived from cultured cells with a tRNA([Ser]sec) probe indicated several hybridizing bands, and each of the corresponding genetic loci was isolated from a recombinant CHO library by molecular cloning. Sequence analysis of these regions indicated three likely pseudogenes and a single functional gene whose sequence differed from those of other mammals. Of these, only one pseudogene and the putative functional gene are actively transcribed following their microinjection into Xenopus oocytes. The possibility that the functional CHO tRNA([Ser]sec) evolved from an edited transcript is discussed.
Collapse
Affiliation(s)
- X M Xu
- Section on the Molecular Biology of Selenium, Basic Research Laboratory, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | | | | | | | | | | |
Collapse
|
17
|
Alsina B, Corominas M, Berry MJ, Baguñà J, Serras F. Disruption of selenoprotein biosynthesis affects cell proliferation in the imaginal discs and brain of Drosophila melanogaster. J Cell Sci 1999; 112 ( Pt 17):2875-84. [PMID: 10444382 DOI: 10.1242/jcs.112.17.2875] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The patufet gene encodes the Drosophila melanogaster homologue of selenophosphate synthetase, an enzyme required for selenoprotein synthesis, and appears to have a role in cell proliferation. In this paper we analyse the expression pattern of patufet during the development of imaginal discs and brain as well as the function of this gene in relation to cell proliferation. Wild-type organisms showed a highly dynamic pattern of ptuf mRNA expression during larval and pupal development. Co-localization analysis of ptuf mRNA expression and BrdU incorporation showed high levels of ptuf mRNA in dividing cells and low or undetectable levels in non-dividing cells. In addition, [(75)Se] incorporation revealed a major selenoprotein band of 42 kDa. Mutant organisms showed no selenoprotein synthesis, lower levels of cell proliferation, a higher proportion of cells arrested in G(2) as seen by cyclin B labeling and increased levels of reactive oxygen species (ROS). Because most selenoproteins identified so far are antioxidants, the role of ptuf in cell proliferation through the control of the cellular redox balance is discussed.
Collapse
Affiliation(s)
- B Alsina
- Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, Spain
| | | | | | | | | |
Collapse
|
18
|
Suppmann S, Persson BC, Böck A. Dynamics and efficiency in vivo of UGA-directed selenocysteine insertion at the ribosome. EMBO J 1999; 18:2284-93. [PMID: 10205181 PMCID: PMC1171311 DOI: 10.1093/emboj/18.8.2284] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The kinetics and efficiency of decoding of the UGA of a bacterial selenoprotein mRNA with selenocysteine has been studied in vivo. A gst-lacZ fusion, with the fdhF SECIS element ligated between the two fusion partners, gave an efficiency of read-through of 4-5%; overproduction of the selenocysteine insertion machinery increased it to 7-10%. This low efficiency is caused by termination at the UGA and not by translational barriers at the SECIS. When the selenocysteine UGA codon was replaced by UCA, and tRNASec with anticodon UGA was allowed to compete with seryl-tRNASer1 for this codon, selenocysteine was found in 7% of the protein produced. When a non-cognate SelB-tRNASec complex competed with EF-Tu for a sense codon, no effects were seen, whereas a non-cognate SelB-tRNASec competing with EF-Tu-mediated Su7-tRNA nonsense suppression of UGA interfered strongly with suppression. The induction kinetics of beta-galactosidase synthesis from fdhF'-'lacZ gene fusions in the absence or presence of SelB and/or the SECIS element, showed that there was a translational pause in the fusion containing the SECIS when SelB was present. The results show that decoding of UGA is an inefficient process and that using the third dimension of the mRNA to accommodate an additional amino acid is accompanied by considerable quantitative and kinetic costs.
Collapse
Affiliation(s)
- S Suppmann
- Lehrstuhl für Mikrobiologie der Universität München, Maria-Ward-Strasse 1a, D-80638 München, Germany
| | | | | |
Collapse
|