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Schorr S, Klein MC, Gamayun I, Melnyk A, Jung M, Schäuble N, Wang Q, Hemmis B, Bochen F, Greiner M, Lampel P, Urban SK, Hassdenteufel S, Dudek J, Chen XZ, Wagner R, Cavalié A, Zimmermann R. Co-chaperone Specificity in Gating of the Polypeptide Conducting Channel in the Membrane of the Human Endoplasmic Reticulum. J Biol Chem 2015; 290:18621-35. [PMID: 26085089 DOI: 10.1074/jbc.m115.636639] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Indexed: 11/06/2022] Open
Abstract
In mammalian cells, signal peptide-dependent protein transport into the endoplasmic reticulum (ER) is mediated by a dynamic polypeptide-conducting channel, the heterotrimeric Sec61 complex. Previous work has characterized the Sec61 complex as a potential ER Ca(2+) leak channel in HeLa cells and identified ER lumenal molecular chaperone immunoglobulin heavy-chain-binding protein (BiP) as limiting Ca(2+) leakage via the open Sec61 channel by facilitating channel closing. This BiP activity involves binding of BiP to the ER lumenal loop 7 of Sec61α in the vicinity of tyrosine 344. Of note, the Y344H mutation destroys the BiP binding site and causes pancreatic β-cell apoptosis and diabetes in mice. Here, we systematically depleted HeLa cells of the BiP co-chaperones by siRNA-mediated gene silencing and used live cell Ca(2+) imaging to monitor the effects on ER Ca(2+) leakage. Depletion of either one of the ER lumenal BiP co-chaperones, ERj3 and ERj6, but not the ER membrane-resident co-chaperones (such as Sec63 protein, which assists BiP in Sec61 channel opening) led to increased Ca(2+) leakage via Sec6 complex, thereby phenocopying the effect of BiP depletion. Thus, BiP facilitates Sec61 channel closure (i.e. limits ER Ca(2+) leakage) via the Sec61 channel with the help of ERj3 and ERj6. Interestingly, deletion of ERj6 causes pancreatic β-cell failure and diabetes in mice and humans. We suggest that co-chaperone-controlled gating of the Sec61 channel by BiP is particularly important for cells, which are highly active in protein secretion, and that breakdown of this regulatory mechanism can cause apoptosis and disease.
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Affiliation(s)
- Stefan Schorr
- From the Departments of Medical Biochemistry and Molecular Biology and
| | | | - Igor Gamayun
- Experimental and Clinical Pharmacology and Toxicology, Saarland University, 66421 Homburg, Germany
| | - Armin Melnyk
- From the Departments of Medical Biochemistry and Molecular Biology and
| | - Martin Jung
- From the Departments of Medical Biochemistry and Molecular Biology and
| | - Nico Schäuble
- From the Departments of Medical Biochemistry and Molecular Biology and
| | - Qian Wang
- the Department of Physiology, University of Alberta, Edmonton T6G 2H7, Canada, and
| | - Birgit Hemmis
- the Division of Biophysics, Universität Osnabrück, FB Biologie/Chemie, 49076 Osnabrück, Germany
| | - Florian Bochen
- From the Departments of Medical Biochemistry and Molecular Biology and
| | - Markus Greiner
- From the Departments of Medical Biochemistry and Molecular Biology and
| | - Pavel Lampel
- From the Departments of Medical Biochemistry and Molecular Biology and
| | | | | | - Johanna Dudek
- From the Departments of Medical Biochemistry and Molecular Biology and
| | - Xing-Zhen Chen
- the Department of Physiology, University of Alberta, Edmonton T6G 2H7, Canada, and
| | - Richard Wagner
- the Division of Biophysics, Universität Osnabrück, FB Biologie/Chemie, 49076 Osnabrück, Germany
| | - Adolfo Cavalié
- Experimental and Clinical Pharmacology and Toxicology, Saarland University, 66421 Homburg, Germany
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Fischer U, Schäuble N, Schütz S, Altvater M, Chang Y, Boulos Faza M, Panse VG. A non-canonical mechanism for Crm1-export cargo complex assembly. eLife 2015; 4:e05745. [PMID: 25895666 PMCID: PMC4402694 DOI: 10.7554/elife.05745] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Accepted: 03/26/2015] [Indexed: 01/19/2023] Open
Abstract
The transport receptor Crm1 mediates the export of diverse cargos containing leucine-rich nuclear export signals (NESs) through complex formation with RanGTP. To ensure efficient cargo release in the cytoplasm, NESs have evolved to display low affinity for Crm1. However, mechanisms that overcome low affinity to assemble Crm1-export complexes in the nucleus remain poorly understood. In this study, we reveal a new type of RanGTP-binding protein, Slx9, which facilitates Crm1 recruitment to the 40S pre-ribosome-associated NES-containing adaptor Rio2. In vitro, Slx9 binds Rio2 and RanGTP, forming a complex. This complex directly loads Crm1, unveiling a non-canonical stepwise mechanism to assemble a Crm1-export complex. A mutation in Slx9 that impairs Crm1-export complex assembly inhibits 40S pre-ribosome export. Thus, Slx9 functions as a scaffold to optimally present RanGTP and the NES to Crm1, therefore, triggering 40S pre-ribosome export. This mechanism could represent one solution to the paradox of weak binding events underlying rapid Crm1-mediated export.
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Affiliation(s)
- Ute Fischer
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Nico Schäuble
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Sabina Schütz
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
- Molecular Life Science, Graduate School, Zurich, Switzerland
| | - Martin Altvater
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
- Molecular Life Science, Graduate School, Zurich, Switzerland
| | - Yiming Chang
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Marius Boulos Faza
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
| | - Vikram Govind Panse
- Institute of Biochemistry, Department of Biology, ETH Zurich, Zurich, Switzerland
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Linxweiler M, Schorr S, Schäuble N, Jung M, Linxweiler J, Langer F, Schäfers HJ, Cavalié A, Zimmermann R, Greiner M. Targeting cell migration and the endoplasmic reticulum stress response with calmodulin antagonists: a clinically tested small molecule phenocopy of SEC62 gene silencing in human tumor cells. BMC Cancer 2013; 13:574. [PMID: 24304694 PMCID: PMC3878975 DOI: 10.1186/1471-2407-13-574] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Accepted: 11/27/2013] [Indexed: 11/16/2022] Open
Abstract
Background Tumor cells benefit from their ability to avoid apoptosis and invade other tissues. The endoplasmic reticulum (ER) membrane protein Sec62 is a key player in these processes. Sec62 is essential for cell migration and protects tumor cells against thapsigargin-induced ER stress, which are both linked to cytosolic Ca2+. SEC62 silencing leads to elevated cytosolic Ca2+ and increased ER Ca2+ leakage after thapsigargin treatment. Sec62 protein levels are significantly increased in different tumors, including prostate, lung and thyroid cancer. Methods In lung cancer, the influence of Sec62 protein levels on patient survival was analyzed using the Kaplan-Meier method and log-rank test. To elucidate the underlying pathophysiological functions of Sec62, Ca2+ imaging techniques, real-time cell analysis and cell migration assays were performed. The effects of treatment with the calmodulin antagonists, trifluoperazine (TFP) and ophiobolin A, on cellular Ca2+ homeostasis, cell growth and cell migration were compared with the effects of siRNA-mediated Sec62 depletion or the expression of a mutated SEC62 variant in vitro. Using Biacore analysis we examined the Ca2+-sensitive interaction of Sec62 with the Sec61 complex. Results Sec62 overproduction significantly correlated with reduced patient survival. Therefore, Sec62 is not only a predictive marker for this type of tumor, but also an interesting therapeutic target. The present study suggests a regulatory function for Sec62 in the major Ca2+ leakage channel in the ER, Sec61, by a direct and Ca2+-sensitive interaction. A Ca2+-binding motif in Sec62 is essential for its molecular function. Treatment of cells with calmodulin antagonists mimicked Sec62 depletion by inhibiting cell migration and rendering the cells sensitive to thapsigargin treatment. Conclusions Targeting tumors that overproduce Sec62 with calmodulin antagonists in combination with targeted thapsigargin analogues may offer novel personalized therapeutic options.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | - Markus Greiner
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Saarland, Germany.
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Schäuble N, Cavalié A, Zimmermann R, Jung M. Interaction of Pseudomonas aeruginosa Exotoxin A with the human Sec61 complex suppresses passive calcium efflux from the endoplasmic reticulum. Channels (Austin) 2013; 8:76-83. [PMID: 24088629 PMCID: PMC4048345 DOI: 10.4161/chan.26526] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Accepted: 09/18/2013] [Indexed: 11/19/2022] Open
Abstract
According to live-cell calcium-imaging experiments, the Sec61 complex is a passive calcium-leak channel in the human endoplasmic reticulum (ER) membrane that is regulated by ER luminal immunoglobulin heavy chain binding protein (BiP) and cytosolic Ca(2+)-calmodulin. In single channel measurements, the open Sec61 complex is Ca(2+) permeable. It can be closed not only by interaction with BiP or Ca(2+)-calmodulin, but also with Pseudomonas aeruginosa Exotoxin A which can enter human cells by retrograde transport. Exotoxin A has been shown to interact with the Sec61 complex and, thereby, inhibit ER export of immunogenic peptides into the cytosol. Here, we show that Exotoxin A also inhibits passive Ca(2+) leakage from the ER in human cells, and we characterized the N-terminus of the Sec61 α-subunit as the relevant binding site for Exotoxin A.
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Affiliation(s)
- Nico Schäuble
- Medical Biochemistry and Molecular Biology; Saarland University; Homburg, Germany
| | - Adolfo Cavalié
- Experimental and Clinical Pharmacology and Toxicology; Saarland University; Homburg, Germany
| | - Richard Zimmermann
- Medical Biochemistry and Molecular Biology; Saarland University; Homburg, Germany
| | - Martin Jung
- Medical Biochemistry and Molecular Biology; Saarland University; Homburg, Germany
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Schäuble N, Lang S, Jung M, Cappel S, Schorr S, Ulucan Ö, Linxweiler J, Dudek J, Blum R, Helms V, Paton AW, Paton JC, Cavalié A, Zimmermann R. BiP-mediated closing of the Sec61 channel limits Ca2+ leakage from the ER. EMBO J 2012; 31:3282-96. [PMID: 22796945 PMCID: PMC3411083 DOI: 10.1038/emboj.2012.189] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2011] [Accepted: 06/20/2012] [Indexed: 01/08/2023] Open
Abstract
In mammalian cells, signal peptide-dependent protein transport into the endoplasmic reticulum (ER) is mediated by a dynamic protein-conducting channel, the Sec61 complex. Previous work has characterized the Sec61 channel as a potential ER Ca(2+) leak channel and identified calmodulin as limiting Ca(2+) leakage in a Ca(2+)-dependent manner by binding to an IQ motif in the cytosolic aminoterminus of Sec61α. Here, we manipulated the concentration of the ER lumenal chaperone BiP in cells in different ways and used live cell Ca(2+) imaging to monitor the effects of reduced levels of BiP on ER Ca(2+) leakage. Regardless of how the BiP concentration was lowered, the absence of available BiP led to increased Ca(2+) leakage via the Sec61 complex. When we replaced wild-type Sec61α with mutant Sec61αY344H in the same model cell, however, Ca(2+) leakage from the ER increased and was no longer affected by manipulation of the BiP concentration. Thus, BiP limits ER Ca(2+) leakage through the Sec61 complex by binding to the ER lumenal loop 7 of Sec61α in the vicinity of tyrosine 344.
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Affiliation(s)
- Nico Schäuble
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Sven Lang
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Martin Jung
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Sabine Cappel
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Stefan Schorr
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Özlem Ulucan
- Department of Computational Biology, Saarland University, Saarbrücken, Germany
| | - Johannes Linxweiler
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Johanna Dudek
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
| | - Robert Blum
- Department of Clinical Neurobiology, Würzburg University, Würzburg, Germany
| | - Volkhard Helms
- Department of Computational Biology, Saarland University, Saarbrücken, Germany
| | - Adrienne W Paton
- Research Centre for Infectious Disease, School of Molecular and Biomedical Science, University of Adelaide, South Australia, Australia
| | - James C Paton
- Research Centre for Infectious Disease, School of Molecular and Biomedical Science, University of Adelaide, South Australia, Australia
| | - Adolfo Cavalié
- Department of Experimental and Clinical Pharmacology and Toxicology, Saarland University, Homburg, Germany
| | - Richard Zimmermann
- Department of Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
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Lang S, Benedix J, Fedeles SV, Schorr S, Schirra C, Schäuble N, Jalal C, Greiner M, Hassdenteufel S, Tatzelt J, Kreutzer B, Edelmann L, Krause E, Rettig J, Somlo S, Zimmermann R, Dudek J. Different effects of Sec61α, Sec62 and Sec63 depletion on transport of polypeptides into the endoplasmic reticulum of mammalian cells. J Cell Sci 2012; 125:1958-69. [PMID: 22375059 DOI: 10.1242/jcs.096727] [Citation(s) in RCA: 114] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Co-translational transport of polypeptides into the endoplasmic reticulum (ER) involves the Sec61 channel and additional components such as the ER lumenal Hsp70 BiP and its membrane-resident co-chaperone Sec63p in yeast. We investigated whether silencing the SEC61A1 gene in human cells affects co- and post-translational transport of presecretory proteins into the ER and post-translational membrane integration of tail-anchored proteins. Although silencing the SEC61A1 gene in HeLa cells inhibited co- and post-translational transport of signal-peptide-containing precursor proteins into the ER of semi-permeabilized cells, silencing the SEC61A1 gene did not affect transport of various types of tail-anchored protein. Furthermore, we demonstrated, with a similar knockdown approach, a precursor-specific involvement of mammalian Sec63 in the initial phase of co-translational protein transport into the ER. By contrast, silencing the SEC62 gene inhibited only post-translational transport of a signal-peptide-containing precursor protein.
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Affiliation(s)
- Sven Lang
- Medical Biochemistry and Molecular Biology, Saarland University, Homburg, Germany
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Lang S, Schäuble N, Cavalié A, Zimmermann R. Live cell calcium imaging combined with siRNA mediated gene silencing identifies Ca²⁺ leak channels in the ER membrane and their regulatory mechanisms. J Vis Exp 2011:e2730. [PMID: 21775954 PMCID: PMC3196168 DOI: 10.3791/2730] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
In mammalian cells, the endoplasmic reticulum (ER) plays a key role in protein biogenesis as well as in calcium signalling1. The heterotrimeric Sec61 complex in the ER membrane provides an aqueous path for newly-synthesized polypeptides into the lumen of the ER. Recent work from various laboratories suggested that this heterotrimeric complex may also form transient Ca2+ leak channels2-8. The key observation for this notion was that release of nascent polypeptides from the ribosome and Sec61 complex by puromycin leads to transient release of Ca2+ from the ER. Furthermore, it had been observed in vitro that the ER luminal protein BiP is involved in preventing ion permeability at the level of the Sec61 complex9,10. We have established an experimental system that allows us to directly address the role of the Sec61 complex as potential Ca2+ leak channel and to characterize its putative regulatory mechanisms11-13. This system combines siRNA mediated gene silencing and live cell Ca2+ imaging13. Cells are treated with siRNAs that are directed against the coding and untranslated region (UTR), respectively, of the SEC61A1 gene or a negative control siRNA. In complementation analysis, the cells are co-transfected with an IRES-GFP vector that allows the siRNA-resistant expression of the wildtype SEC61A1 gene. Then the cells are loaded with the ratiometric Ca2+-indicator FURA-2 to monitor simultaneously changes in the cytosolic Ca2+ concentration in a number of cells via a fluorescence microscope. The continuous measurement of cytosolic Ca2+ also allows the evaluation of the impact of various agents, such as puromycin, small molecule inhibitors, and thapsigargin on Ca2+ leakage. This experimental system gives us the unique opportunities to i) evaluate the contribution of different ER membrane proteins to passive Ca2+ efflux from the ER in various cell types, ii) characterize the proteins and mechanisms that limit this passive Ca2+ efflux, and iii) study the effects of disease linked mutations in the relevant components.
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Affiliation(s)
- Sven Lang
- Medical Biochemistry and Molecular Biology, Saarland University
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Erdmann F, Schäuble N, Lang S, Jung M, Honigmann A, Ahmad M, Dudek J, Benedix J, Harsman A, Kopp A, Helms V, Cavalié A, Wagner R, Zimmermann R. Interaction of calmodulin with Sec61α limits Ca2+ leakage from the endoplasmic reticulum. EMBO J 2010; 30:17-31. [PMID: 21102557 DOI: 10.1038/emboj.2010.284] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Accepted: 10/22/2010] [Indexed: 12/31/2022] Open
Abstract
In eukaryotes, protein transport into the endoplasmic reticulum (ER) is facilitated by a protein-conducting channel, the Sec61 complex. The presence of large, water-filled pores with uncontrolled ion permeability, as formed by Sec61 complexes in the ER membrane, would seriously interfere with the regulated release of calcium from the ER lumen into the cytosol, an essential mechanism for intracellular signalling. We identified a calmodulin (CaM)-binding motif in the cytosolic N-terminus of mammalian Sec61α that bound CaM but not Ca2+-free apocalmodulin with nanomolar affinity and sequence specificity. In single-channel measurements, CaM potently mediated Sec61-channel closure in Ca2+-dependent manner. At the cellular level, two different CaM antagonists stimulated calcium release from the ER through Sec61 channels. However, protein transport into microsomes was not modulated by Ca2+-CaM. Molecular modelling of the ribosome/Sec61/CaM complexes supports the view that simultaneous ribosome and CaM binding to the Sec61 complex may be possible. Overall, CaM is involved in limiting Ca2+ leakage from the ER.
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Affiliation(s)
- Frank Erdmann
- Biophysics, Osnabrück University, Osnabrück, Germany
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Abstract
Within the past decade the molecular basis of single forms of monogenic obesity has been elucidated. With the exception of functionally relevant mutations in the melanocortin-4 receptor gene, which occur in approximately 2-4% of extremely obese individuals, all other currently known monogenic forms are rare and additionally associated with distinct endocrinological abnormalities. A large number of association studies have been performed in 'normal' obesity. Whereas many associations have been reported, it is largely unclear which of these represent true positive findings. Over 20 genome scans pertaining to obesity and related phenotypes have been performed; specific chromosomal peak regions have been identified in different scans. We review the current status and discuss relevant issues related to phenotyping, association and linkage studies. We recommend that the procedure via which a consensus is reached as to what constitutes a true positive association finding requires formalization.
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Affiliation(s)
- J Hebebrand
- Clinical Research Group, Department of Child and Adolescent Psychiatry, Philipps University of Marburg, Germany.
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Schäuble N, Geller F, Siegfried W, Goldschmidt H, Remschmidt H, Hinney A, Hebebrand J. No evidence for involvement of the promoter polymorphism -866 G/A of the UCP2 gene in childhood-onset obesity in humans. Exp Clin Endocrinol Diabetes 2003; 111:73-6. [PMID: 12746756 DOI: 10.1055/s-2003-39232] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Recently, an association between obesity and the G-allele of the - 866 G/A polymorphism in the promoter region of uncoupling protein-2 gene (UCP2) was reported. Both allele frequencies and genotype distributions for this polymorphism differed between obese individuals and never-obese controls. We attempted to confirm this finding. Genotyping was performed by polymerase chain reaction with subsequent restriction fragment length polymorphism analysis (PCR-RFLP). We analysed transmission disequilibrium of the (wild type) G-allele for 200 extremely obese children and adolescents from 93 concordant sib pair families using the pedigree disequilibrium test. Additionally, using a one-sided asymptotic Pearson's chi 2-test, we tested whether the G-allele occurs more frequently in 277 extremely obese children and adolescents (including the 93 index patients of the concordant sib pairs) than in 188 never-obese controls. The one-sided asymptotic Cochran Armitage trend test was used to determine differences in genotype frequencies between extremely obese and healthy underweight individuals. The PDT analysis revealed no evidence for transmission disequilibrium in obesity. Allele and genotype frequencies did not differ between the extremely obese and never-obese subjects. In conclusion, we cannot confirm the results of ) in our young sample.
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Affiliation(s)
- N Schäuble
- Clinical Research Group, Department of Child and Adolescent Psychiatry, Philipps-University of Marburg, Marburg, Germany
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