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Hu M, Kim I, Morán I, Peng W, Sun O, Bonnefond A, Khamis A, Bonàs-Guarch S, Froguel P, Rutter GA. Multiple genetic variants at the SLC30A8 locus affect local super-enhancer activity and influence pancreatic β-cell survival and function. FASEB J 2024; 38:e23610. [PMID: 38661000 PMCID: PMC11108099 DOI: 10.1096/fj.202301700rr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 03/22/2024] [Accepted: 04/01/2024] [Indexed: 04/26/2024]
Abstract
Variants at the SLC30A8 locus are associated with type 2 diabetes (T2D) risk. The lead variant, rs13266634, encodes an amino acid change, Arg325Trp (R325W), at the C-terminus of the secretory granule-enriched zinc transporter, ZnT8. Although this protein-coding variant was previously thought to be the sole driver of T2D risk at this locus, recent studies have provided evidence for lowered expression of SLC30A8 mRNA in protective allele carriers. In the present study, we examined multiple variants that influence SLC30A8 allele-specific expression. Epigenomic mapping has previously identified an islet-selective enhancer cluster at the SLC30A8 locus, hosting multiple T2D risk and cASE associations, which is spatially associated with the SLC30A8 promoter and additional neighboring genes. Here, we show that deletion of variant-bearing enhancer regions using CRISPR-Cas9 in human-derived EndoC-βH3 cells lowers the expression of SLC30A8 and several neighboring genes and improves glucose-stimulated insulin secretion. While downregulation of SLC30A8 had no effect on beta cell survival, loss of UTP23, RAD21, or MED30 markedly reduced cell viability. Although eQTL or cASE analyses in human islets did not support the association between these additional genes and diabetes risk, the transcriptional regulator JQ1 lowered the expression of multiple genes at the SLC30A8 locus and enhanced stimulated insulin secretion.
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Affiliation(s)
- Ming Hu
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
| | - Innah Kim
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
| | - Ignasi Morán
- Life Sciences Department, Barcelona Supercomputing Center (BSC-CNS), 08034 Barcelona, Spain
| | - Weicong Peng
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
| | - Orien Sun
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
| | - Amélie Bonnefond
- Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK
- Inserm U1283, CNRS UMR 8199, EGID, Institut Pasteur de Lille, F-59000, France
- University of Lille, Lille University Hospital, Lille, F-59000, France.France
| | - Amna Khamis
- Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK
- Inserm U1283, CNRS UMR 8199, EGID, Institut Pasteur de Lille, F-59000, France
- University of Lille, Lille University Hospital, Lille, F-59000, France.France
| | - Sílvia Bonàs-Guarch
- Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK
- Center for Genomic Regulation (CRG), C/ Dr. Aiguader, 88, PRBB Building, 08003 Barcelona, Spain
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Philippe Froguel
- Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK
- Inserm U1283, CNRS UMR 8199, EGID, Institut Pasteur de Lille, F-59000, France
- University of Lille, Lille University Hospital, Lille, F-59000, France.France
| | - Guy A. Rutter
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
- Centre de Recherche du CHUM, Faculté de Médicine, Université de Montréal, Montréal, QC, Canada
- Lee Kong Chian Imperial Medical School, Nanyang Technological University, Singapore
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Hu M, Kim I, Morán I, Peng W, Sun O, Bonnefond A, Khamis A, Bonas-Guarch S, Froguel P, Rutter GA. Multiple genetic variants at the SLC30A8 locus affect local super-enhancer activity and influence pancreatic β-cell survival and function. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.13.548906. [PMID: 37502937 PMCID: PMC10369998 DOI: 10.1101/2023.07.13.548906] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Variants at the SLC30A8 locus are associated with type 2 diabetes (T2D) risk. The lead variant, rs13266634, encodes an amino acid change, Arg325Trp (R325W), at the C-terminus of the secretory granule-enriched zinc transporter, ZnT8. Although this protein-coding variant was previously thought to be the sole driver of T2D risk at this locus, recent studies have provided evidence for lowered expression of SLC30A8 mRNA in protective allele carriers. In the present study, combined allele-specific expression (cASE) analysis in human islets revealed multiple variants that influence SLC30A8 expression. Epigenomic mapping identified an islet-selective enhancer cluster at the SLC30A8 locus, hosting multiple T2D risk and cASE associations, which is spatially associated with the SLC30A8 promoter and additional neighbouring genes. Deletions of variant-bearing enhancer regions using CRISPR-Cas9 in human-derived EndoC-βH3 cells lowered the expression of SLC30A8 and several neighbouring genes, and improved insulin secretion. Whilst down-regulation of SLC30A8 had no effect on beta cell survival, loss of UTP23, RAD21 or MED30 markedly reduced cell viability. Although eQTL or cASE analyses in human islets did not support the association between these additional genes and diabetes risk, the transcriptional regulator JQ1 lowered the expression of multiple genes at the SLC30A8 locus and enhanced stimulated insulin secretion.
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Affiliation(s)
- Ming Hu
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
| | - Innah Kim
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
| | - Ignasi Morán
- Life Sciences Department, Barcelona Supercomputing Center (BSC-CNS), 08034 Barcelona, Spain
| | - Weicong Peng
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
| | - Orien Sun
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
| | - Amélie Bonnefond
- Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK
- Inserm U1283, CNRS UMR 8199, EGID, Institut Pasteur de Lille, F-59000, France
- University of Lille, Lille University Hospital, Lille, F-59000, France.France
| | - Amna Khamis
- Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK
- Inserm U1283, CNRS UMR 8199, EGID, Institut Pasteur de Lille, F-59000, France
- University of Lille, Lille University Hospital, Lille, F-59000, France.France
| | - Silvia Bonas-Guarch
- Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK
- Center for Genomic Regulation (CRG), C/ Dr. Aiguader, 88, PRBB Building, 08003 Barcelona, Spain
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Philippe Froguel
- Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK
- Inserm U1283, CNRS UMR 8199, EGID, Institut Pasteur de Lille, F-59000, France
- University of Lille, Lille University Hospital, Lille, F-59000, France.France
| | - Guy A. Rutter
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, Du Cane Road, London W12 0NN, UK
- Centre de Recherche du CHUM, Faculté de Médicine, Université de Montréal, Montréal, QC, Canada
- Lee Kong Chian Imperial Medical School, Nanyang Technological University, Singapore
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Styrpejko DJ, Cuajungco MP. Transmembrane 163 (TMEM163) Protein: A New Member of the Zinc Efflux Transporter Family. Biomedicines 2021; 9:biomedicines9020220. [PMID: 33670071 PMCID: PMC7926707 DOI: 10.3390/biomedicines9020220] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2020] [Revised: 02/17/2021] [Accepted: 02/17/2021] [Indexed: 12/27/2022] Open
Abstract
A growing body of evidence continues to demonstrate the vital roles that zinc and its transporters play on human health. The mammalian solute carrier 30 (SLC30) family, with ten current members, controls zinc efflux transport in cells. TMEM163, a recently reported zinc transporter, has similar characteristics in both predicted transmembrane domain structure and function to the cation diffusion facilitator (CDF) protein superfamily. This review discusses past and present data indicating that TMEM163 is a zinc binding protein that transports zinc in cells. We provide a brief background on TMEM163’s discovery, transport feature, protein interactome, and similarities, as well as differences, with known SLC30 (ZnT) protein family. We also examine recent reports that implicate TMEM163 directly or indirectly in various human diseases such as Parkinson’s disease, Mucolipidosis type IV and diabetes. Overall, the role of TMEM163 protein in zinc metabolism is beginning to be realized, and based on current evidence, we propose that it is likely a new CDF member belonging to mammalian SLC30 (ZnT) zinc efflux transporter proteins.
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Affiliation(s)
- Daniel J. Styrpejko
- Department of Biological Science, California State University Fullerton, Fullerton, CA 92831, USA;
| | - Math P. Cuajungco
- Department of Biological Science, California State University Fullerton, Fullerton, CA 92831, USA;
- Center for Applied Biotechnology Studies, California State University Fullerton, Fullerton, CA 92831, USA
- Correspondence:
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Sargazi S, Heidari Nia M, Sargazi FM, Sheervalilou R, Saravani R, Mirinejad S. SNPs in the 3'-untranslated region of SLC30A8 confer risk of type 2 diabetes mellitus in a south-east Iranian population: Evidences from case-control and bioinformatics studies. J Diabetes Metab Disord 2020; 19:979-988. [PMID: 33553018 PMCID: PMC7843856 DOI: 10.1007/s40200-020-00590-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Revised: 06/26/2020] [Accepted: 07/15/2020] [Indexed: 12/18/2022]
Abstract
BACKGROUND Type 2 diabetes mellitus (T2DM) is a heterogenic disease with increasing incidence. The SLC30A8 gene encodes an islet zinc transporter (ZnT8), and its variants have been associated with glucose and pro-insulin levels. This study was aimed to examine the effects of a missense variant (rs13266634 C/T), and two 3'UTR variants (rs2466294 C/G and rs2466293 T/C) in SLC30A8 gene on T2DM risk in a south-east Iranian population. METHODS In this experiment, 450 patients diagnosed with T2DM and 453 healthy subjects from the same geographic area were enrolled. Genotypes were amplified using the ARMS-PCR method. In silico analyses were performed to determine the effects of the variants on the local structure of mRNA, splicing patterns, and potential miRNA-gene interactions as well. RESULTS Significant differences were noticed between cases and controls regarding the genotypic and allelic distribution of the studied variants. As regards rs2466293 and rs2466294 variants, enhanced risk of T2DM was found under allelic, dominant, recessive, and codominant models (OR > 1). Besides, different genetic models of rs13266634 were associated with decreased risk of T2DM (OR < 1). Bioinformatics analyses indicated that the rs2466293 variant might influence the binding of some miRNAs, while the G-allele of rs2466294 decreased the stability of SLC30A8-mRNA. CONCLUSIONS In our population, both SNPs in the 3'-untranslated region of SLC30A8 increased the risk of T2DM, while the rs13266634 variant showed a protective association against T2DM susceptibility. Investigating the effects of other variants in this gene or other ZnTs can further indicate such associations in subjects from the same ethnicity.
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Affiliation(s)
- Saman Sargazi
- Cellular and Molecular Research Center, Resistant Tuberculosis Institute, Zahedan University of Medical Sciences, Zahedan, Iran
| | - Milad Heidari Nia
- Cellular and Molecular Research Center, Resistant Tuberculosis Institute, Zahedan University of Medical Sciences, Zahedan, Iran
| | - Fariba Mirani Sargazi
- Cellular and Molecular Research Center, Resistant Tuberculosis Institute, Zahedan University of Medical Sciences, Zahedan, Iran
| | - Roghayeh Sheervalilou
- Cellular and Molecular Research Center, Resistant Tuberculosis Institute, Zahedan University of Medical Sciences, Zahedan, Iran
| | - Ramin Saravani
- Cellular and Molecular Research Center, Resistant Tuberculosis Institute, Zahedan University of Medical Sciences, Zahedan, Iran
- Department of Clinical Biochemistry, School of Medicine, Zahedan University of Medical Sciences, Zahedan, Iran
| | - Shekoufeh Mirinejad
- Cellular and Molecular Research Center, Resistant Tuberculosis Institute, Zahedan University of Medical Sciences, Zahedan, Iran
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Daniels MJ, Jagielnicki M, Yeager M. Structure/Function Analysis of human ZnT8 (SLC30A8): A Diabetes Risk Factor and Zinc Transporter. Curr Res Struct Biol 2020; 2:144-155. [PMID: 34235474 PMCID: PMC8244513 DOI: 10.1016/j.crstbi.2020.06.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2020] [Revised: 06/15/2020] [Accepted: 06/22/2020] [Indexed: 12/17/2022] Open
Abstract
The human zinc transporter ZnT8 (SLC30A8) is expressed primarily in pancreatic β-cells and plays a key function in maintaining the concentration of blood glucose through its role in insulin storage, maturation and secretion. ZnT8 is an autoantigen for Type 1 diabetes (T1D) and is associated with Type 2 diabetes (T2D) through its risk allele that encodes a major non-synonymous single nucleotide polymorphism (SNP) at Arg325. Loss of function mutations improve insulin secretion and are protective against diabetes. Despite its role in diabetes and concomitant potential as a drug target, little is known about the structure or mechanism of ZnT8. To this end, we expressed ZnT8 in Pichia pastoris yeast and Sf9 insect cells. Guided by a rational screen of 96 detergents, we developed a method to solubilize and purify recombinant ZnT8. An in vivo transport assay in Pichia and a liposome-based uptake assay for insect-cell derived ZnT8 showed that the protein is functionally active in both systems. No significant difference in activity was observed between full-length ZnT8 (ZnT8A) and the amino-terminally truncated ZnT8B isoform. A fluorescence-based in vitro transport assay using proteoliposomes indicated that human ZnT8 functions as a Zn2+/H+ antiporter. We also purified E. coli-expressed amino- and carboxy-terminal cytoplasmic domains of ZnT8A. Circular dichroism spectrometry suggested that the amino-terminal domain contains predominantly α-helical structure, and indicated that the carboxy-terminal domain has a mixed α/β structure. Negative-stain electron microscopy and single-particle image analysis yielded a density map of ZnT8B at 20 Å resolution, which revealed that ZnT8 forms a dimer in detergent micelles. Two prominent lobes are ascribed to the transmembrane domains, and the molecular envelope recapitulates that of the bacterial zinc transporter YiiP. These results provide a foundation for higher resolution structural studies and screening experiments to identify compounds that modulate ZnT8 activity.
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Affiliation(s)
- Mark J. Daniels
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, 22908, USA
| | - Maciej Jagielnicki
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, 22908, USA
- Department of Biochemistry, University of Toronto, Toronto, ON, M5G 1M1, Canada
| | - Mark Yeager
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, 22908, USA
- Department of Medicine, Division of Cardiovascular Medicine, University of Virginia Health System, Charlottesville, VA, 22908, USA
- Center for Membrane and Cell Physiology, University of Virginia School of Medicine, Charlottesville, VA, 22908, USA
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6
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Ullah R, Shehzad A, Shah MA, March MD, Ismat F, Iqbal M, Onesti S, Rahman M, McPherson MJ. C-Terminal Domain of the Human Zinc Transporter hZnT8 Is Structurally Indistinguishable from Its Disease Risk Variant (R325W). Int J Mol Sci 2020; 21:ijms21030926. [PMID: 32023808 PMCID: PMC7037036 DOI: 10.3390/ijms21030926] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 01/17/2020] [Accepted: 01/19/2020] [Indexed: 02/07/2023] Open
Abstract
The human zinc transporter 8 (hZnT8) plays important roles in the storage of insulin in the secretory vesicles of pancreatic β cells. hZnT8 consists of a transmembrane domain, with its N- and C-termini protruding into the cytoplasm. Interestingly, the exchange of arginine to tryptophan at position 325 in the C-terminal domain (CTD) increases the risk of developing type 2 diabetes mellitus (T2D). In the present study, the CTDs of hZnT8 (the wild-type (WT) and its disease risk variant (R325W)) were expressed, purified, and characterized in their native forms by biophysical techniques. The data reveal that the CTDs form tetramers which are stabilized by zinc binding, and exhibit negligible differences in their secondary structure content and zinc-binding affinities in solution. These findings provide the basis for conducting further structural studies aimed at unravelling the molecular mechanism underlying the increased susceptibility to develop T2D, which is modulated by the disease risk variant.
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Affiliation(s)
- Raheem Ullah
- Drug Discovery and Structural Biology group, Health Biotechnology Division, National Institute for Biotechnology and Genetic Engineering (NIBGE), Faisalabad 44000, Pakistan; (R.U.); (A.S.); (M.A.S.); (F.I.); (M.I.)
- Structural Biology Laboratory, Elettra-Sincrotrone Trieste, 34149 Trieste, Italy; (M.D.M.); (S.O.)
| | - Aamir Shehzad
- Drug Discovery and Structural Biology group, Health Biotechnology Division, National Institute for Biotechnology and Genetic Engineering (NIBGE), Faisalabad 44000, Pakistan; (R.U.); (A.S.); (M.A.S.); (F.I.); (M.I.)
| | - Majid Ali Shah
- Drug Discovery and Structural Biology group, Health Biotechnology Division, National Institute for Biotechnology and Genetic Engineering (NIBGE), Faisalabad 44000, Pakistan; (R.U.); (A.S.); (M.A.S.); (F.I.); (M.I.)
| | - Matteo De March
- Structural Biology Laboratory, Elettra-Sincrotrone Trieste, 34149 Trieste, Italy; (M.D.M.); (S.O.)
| | - Fouzia Ismat
- Drug Discovery and Structural Biology group, Health Biotechnology Division, National Institute for Biotechnology and Genetic Engineering (NIBGE), Faisalabad 44000, Pakistan; (R.U.); (A.S.); (M.A.S.); (F.I.); (M.I.)
| | - Mazhar Iqbal
- Drug Discovery and Structural Biology group, Health Biotechnology Division, National Institute for Biotechnology and Genetic Engineering (NIBGE), Faisalabad 44000, Pakistan; (R.U.); (A.S.); (M.A.S.); (F.I.); (M.I.)
| | - Silvia Onesti
- Structural Biology Laboratory, Elettra-Sincrotrone Trieste, 34149 Trieste, Italy; (M.D.M.); (S.O.)
| | - Moazur Rahman
- Drug Discovery and Structural Biology group, Health Biotechnology Division, National Institute for Biotechnology and Genetic Engineering (NIBGE), Faisalabad 44000, Pakistan; (R.U.); (A.S.); (M.A.S.); (F.I.); (M.I.)
- Correspondence: (M.R.); (M.J.M.); Tel.: +92-41-920-1407 (M.R.); +44-113-343-2595 (M.J.M.)
| | - Michael J. McPherson
- Astbury Centre for Structural Molecular Biology and School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK
- Correspondence: (M.R.); (M.J.M.); Tel.: +92-41-920-1407 (M.R.); +44-113-343-2595 (M.J.M.)
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Cotrim CA, Jarrott RJ, Martin JL, Drew D. A structural overview of the zinc transporters in the cation diffusion facilitator family. Acta Crystallogr D Struct Biol 2019; 75:357-367. [PMID: 30988253 PMCID: PMC6465983 DOI: 10.1107/s2059798319003814] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2018] [Accepted: 03/19/2019] [Indexed: 01/07/2023] Open
Abstract
The cation diffusion facilitators (CDFs) are a family of membrane-bound proteins that maintain cellular homeostasis of essential metal ions. In humans, the zinc-transporter CDF family members (ZnTs) play important roles in zinc homeostasis. They do this by facilitating zinc efflux from the cytoplasm to the extracellular space across the plasma membrane or into intracellular organelles. Several ZnTs have been implicated in human health owing to their association with type 2 diabetes and neurodegenerative diseases. Although the structure determination of CDF family members is not trivial, recent advances in membrane-protein structural biology have resulted in two structures of bacterial YiiPs and several structures of their soluble C-terminal domains. These data reveal new insights into the molecular mechanism of ZnT proteins, suggesting a unique rocking-bundle mechanism that provides alternating access to the metal-binding site.
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Affiliation(s)
- Camila A. Cotrim
- Griffith Institute for Drug Discovery, Griffith University, Nathan, QLD 4111, Australia
| | - Russell J. Jarrott
- Griffith Institute for Drug Discovery, Griffith University, Nathan, QLD 4111, Australia
| | - Jennifer L. Martin
- Griffith Institute for Drug Discovery, Griffith University, Nathan, QLD 4111, Australia
| | - David Drew
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
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8
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Zhao T, Huang Q, Su Y, Sun W, Huang Q, Wei W. Zinc and its regulators in pancreas. Inflammopharmacology 2019; 27:453-464. [PMID: 30756223 DOI: 10.1007/s10787-019-00573-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 02/02/2019] [Indexed: 12/12/2022]
Abstract
Studies have demonstrated that susceptibility to type 2 diabetes (T2D) is influenced by common polymorphism in the zinc transporter 8 gene SLC30A8, providing novel insight into the role of zinc in diabetes. Intriguingly, zinc participates in every step of the process, including insulin synthesis, crystallization, storage, secretion and signaling. Zinc deficiency or overload is associated with various disorders, such as diabetes, cardiovascular disease and obesity. Zinc supplementation is considered as an effective means of treating or preventing T2D in people with certain SLC30A8 genotypes. Three important protein families-zinc transporters (ZnTs), zinc importers (ZiPs) and metallothionein (MT)-participate in maintaining zinc homeostasis. Here, we review research on the physiological characteristics of zinc and its role in the pancreas and homeostasis regulation mechanisms, along with the latest research on the structure and function of ZnT/ZiP and MT. In addition, we summarize the advancements in research on SLC30A8 gene polymorphism in search of a mechanism to explain the relationship between the R risk allele and zinc transporter activity.
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Affiliation(s)
- Tianjiao Zhao
- Key Laboratory of Anti-inflammatory and Immune Medicine, Institute of Clinical Pharmacology, Anhui Collaborative Innovation Center of Anti-inflammatory and Immune Medicine, Anhui Medical University, Ministry of Education, Hefei, 230032, China
| | - Qiongfang Huang
- Key Laboratory of Anti-inflammatory and Immune Medicine, Institute of Clinical Pharmacology, Anhui Collaborative Innovation Center of Anti-inflammatory and Immune Medicine, Anhui Medical University, Ministry of Education, Hefei, 230032, China
| | - Yangni Su
- Key Laboratory of Anti-inflammatory and Immune Medicine, Institute of Clinical Pharmacology, Anhui Collaborative Innovation Center of Anti-inflammatory and Immune Medicine, Anhui Medical University, Ministry of Education, Hefei, 230032, China
| | - Wuyi Sun
- Key Laboratory of Anti-inflammatory and Immune Medicine, Institute of Clinical Pharmacology, Anhui Collaborative Innovation Center of Anti-inflammatory and Immune Medicine, Anhui Medical University, Ministry of Education, Hefei, 230032, China
| | - Qiong Huang
- Key Laboratory of Anti-inflammatory and Immune Medicine, Institute of Clinical Pharmacology, Anhui Collaborative Innovation Center of Anti-inflammatory and Immune Medicine, Anhui Medical University, Ministry of Education, Hefei, 230032, China.
| | - Wei Wei
- Key Laboratory of Anti-inflammatory and Immune Medicine, Institute of Clinical Pharmacology, Anhui Collaborative Innovation Center of Anti-inflammatory and Immune Medicine, Anhui Medical University, Ministry of Education, Hefei, 230032, China.
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9
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Waberer L, Henrich E, Peetz O, Morgner N, Dötsch V, Bernhard F, Volknandt W. The synaptic vesicle protein SV31 assembles into a dimer and transports Zn 2. J Neurochem 2016; 140:280-293. [PMID: 27917477 DOI: 10.1111/jnc.13886] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 10/25/2016] [Accepted: 10/29/2016] [Indexed: 01/20/2023]
Abstract
The integral synaptic vesicle protein SV31 has been shown to bind divalent cations. Here, we demonstrate that SV31 protein synthesized within a cell-free system binds Zn2+ and to a lower extent Ni2+ and Cu2+ ions. Expression with Zn2+ stabilized the protein and increased solubility. SV31 was preferentially monomeric in detergent and revealed specific binding of Zn2+ . When co-translationally inserted into defined nanodisc bilayers, SV31 assembled into dimeric complexes, resulting in increased binding of Zn2+ . Putative Zn2+ -binding motifs within SV31 comprise aspartic acid and histidine residues. Site-directed mutagenesis of two conserved aspartic acid residues leads to a potent decrease in Zn2+ binding but did not affect dimerization. Chemical modification of histidine residues abolished some of the Zn2+ -binding capacity. We demonstrate proton-dependent transport of Zn2+ as by accumulation of fluorescent FluoZin-1 inside of SV31-containing proteoliposomes. Transport activity has a Km value of 44.3 μM and required external Zn2+ and internal acidic pH. Our results demonstrate that the synaptic vesicle-integral protein SV31 functions as a proton-dependent Zn2+ transporter. SV31 may attribute specific and yet undiscovered functions to subsets of synapses.
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Affiliation(s)
- Lisa Waberer
- Institute of Cell Biology and Neuroscience, Goethe-University, Frankfurt am Main, Germany
| | - Erik Henrich
- Institute of Biophysical Chemistry, Centre for Biomolecular Magnetic Resonance, Goethe-University, Frankfurt am Main, Germany
| | - Oliver Peetz
- Institute of Physical and Theoretical Chemistry, Goethe-University, Frankfurt am Main, Germany
| | - Nina Morgner
- Institute of Physical and Theoretical Chemistry, Goethe-University, Frankfurt am Main, Germany
| | - Volker Dötsch
- Institute of Biophysical Chemistry, Centre for Biomolecular Magnetic Resonance, Goethe-University, Frankfurt am Main, Germany
| | - Frank Bernhard
- Institute of Biophysical Chemistry, Centre for Biomolecular Magnetic Resonance, Goethe-University, Frankfurt am Main, Germany
| | - Walter Volknandt
- Institute of Cell Biology and Neuroscience, Goethe-University, Frankfurt am Main, Germany
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10
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Chabosseau P, Rutter GA. Zinc and diabetes. Arch Biochem Biophys 2016; 611:79-85. [DOI: 10.1016/j.abb.2016.05.022] [Citation(s) in RCA: 105] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 05/09/2016] [Accepted: 05/31/2016] [Indexed: 01/09/2023]
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11
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Wu Q, Wang X, Gu Y, Zhang X, Qin Y, Chen H, Xu X, Yang T, Zhang M. Screening and identification of human ZnT8-specific single-chain variable fragment (scFv) from type 1 diabetes phage display library. SCIENCE CHINA-LIFE SCIENCES 2016; 59:686-93. [PMID: 27270580 DOI: 10.1007/s11427-016-5077-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2016] [Accepted: 05/12/2016] [Indexed: 01/10/2023]
Abstract
Zinc transporter 8 (ZnT8) is a major autoantigen and a predictive marker in type 1 diabetes (T1D). To investigate ZnT8-specific antibodies, a phage display library from T1D was constructed and single-chain antibodies against ZnT8 were screened and identified. Human T1D single-chain variable fragment (scFv) phage display library consists of approximately 1×10(8) clones. After four rounds of bio-panning, seven unique clones were positive by phage ELISA. Among them, C27 and C22, which demonstrated the highest affinity to ZnT8, were expressed in Escherichia coli Top10F' and then purified by affinity chromatography. C27 and C22 specifically bound ZnT8 N/C fusion protein and ZnT8 C terminal dimer with one Arg325Trp mutation. The specificity to human islet cells of these scFvs were further confirmed by immunohistochemistry. In conclusion, we have successfully constructed a T1D phage display antibody library and identified two ZnT8-specific scFv clones, C27 and C22. These ZnT8-specific scFvs are potential agents in immunodiagnostic and immunotherapy of T1D.
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Affiliation(s)
- Qian Wu
- Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Xiaodong Wang
- Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Yong Gu
- Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Xiao Zhang
- Key Laboratory of Antibody Technique, Ministry of Health, Nanjing Medical University, Nanjing, 210029, China
| | - Yao Qin
- Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Heng Chen
- Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Xinyu Xu
- Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Tao Yang
- Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Mei Zhang
- Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China.
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12
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Abstract
Zinc is an important micronutrient, essential in the diet to avoid a variety of conditions associated with malnutrition such as diarrhoea and alopecia. Lowered circulating levels of zinc are also found in diabetes mellitus, a condition which affects one in twelve of the adult population and whose treatments consume approximately 10 % of healthcare budgets. Zn2+ ions are essential for a huge range of cellular functions and, in the specialised pancreatic β-cell, for the storage of insulin within the secretory granule. Correspondingly, genetic variants in the SLC30A8 gene, which encodes the diabetes-associated granule-resident Zn2+ transporter ZnT8, are associated with an altered risk of type 2 diabetes. Here, we focus on (i) recent advances in measuring free zinc concentrations dynamically in subcellular compartments, and (ii) studies dissecting the role of intracellular zinc in the control of glucose homeostasis in vitro and in vivo. We discuss the effects on insulin secretion and action of deleting or over-expressing Slc30a8 highly selectively in the pancreatic β-cell, and the role of zinc in insulin signalling. While modulated by genetic variability, healthy levels of dietary zinc, and hence normal cellular zinc homeostasis, are likely to play an important role in the proper release and action of insulin to maintain glucose homeostasis and lower diabetes risk.
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13
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Golan Y, Berman B, Assaraf YG. Heterodimerization, altered subcellular localization, and function of multiple zinc transporters in viable cells using bimolecular fluorescence complementation. J Biol Chem 2015; 290:9050-63. [PMID: 25657003 DOI: 10.1074/jbc.m114.617332] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Indexed: 01/19/2023] Open
Abstract
Zinc plays a crucial role in numerous key physiological functions. Zinc transporters (ZnTs) mediate zinc efflux and compartmentalization in intracellular organelles; thus, ZnTs play a central role in zinc homeostasis. We have recently shown the in situ dimerization and function of multiple normal and mutant ZnTs using bimolecular fluorescence complementation (BiFC). Prompted by these findings, we here uncovered the heterodimerization, altered subcellular localization, and function of multiple ZnTs in live cells using this sensitive BiFC technique. We show that ZnT1, -2, -3, and -4 form stable heterodimers at distinct intracellular compartments, some of which are completely different from their homodimer localization. Specifically, unlike the plasma membrane (PM) localization of ZnT1 homodimers, ZnT1-ZnT3 heterodimers localized at intracellular vesicles. Furthermore, upon heterodimerization with ZnT1, the zinc transporters ZnT2 and ZnT4 surprisingly localized at the PM, as opposed to their vesicular homodimer localization. We further demonstrate the deleterious effect that the G87R-ZnT2 mutation, associated with transient neonatal zinc deficiency, has on ZnT1, ZnT3, and ZnT4 upon heterodimerization. The functionality of the various ZnTs was assessed by the dual BiFC-Zinquin assay. We also undertook a novel transfection competition assay with ZnT cDNAs to confirm that the driving force for heterodimer formation is the core structure of ZnTs and not the BiFC tags. These findings uncover a novel network of homo- and heterodimers of ZnTs with distinct subcellular localizations and function, hence highlighting their possible role in zinc homeostasis under physiological and pathological conditions.
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Affiliation(s)
- Yarden Golan
- From the Fred Wyszkowski Cancer Research Laboratory, Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Bluma Berman
- From the Fred Wyszkowski Cancer Research Laboratory, Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Yehuda G Assaraf
- From the Fred Wyszkowski Cancer Research Laboratory, Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
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14
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Maruthur NM, Clark JM, Fu M, Linda Kao WH, Shuldiner AR. Effect of zinc supplementation on insulin secretion: interaction between zinc and SLC30A8 genotype in Old Order Amish. Diabetologia 2015; 58:295-303. [PMID: 25348609 PMCID: PMC4505931 DOI: 10.1007/s00125-014-3419-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Accepted: 09/29/2014] [Indexed: 01/29/2023]
Abstract
AIMS/HYPOTHESIS SLC30A8 encodes a zinc transporter in the beta cell; individuals with a common missense variant (rs13266634; R325W) in SLC30A8 demonstrate a lower early insulin response to glucose and an increased risk of type 2 diabetes. We hypothesised that zinc supplementation may improve insulin secretion in a genotype-dependent manner. METHODS We evaluated the early insulin response to glucose (using frequently sampled intravenous glucose tolerance testing) by R325W genotype before and after 14 days of supplementation with oral zinc acetate (50 mg elemental zinc) twice daily in healthy non-diabetic Amish individuals (N = 55). RESULTS Individuals with RW/WW genotypes (n = 32) had the lowest insulin response to glucose at 5 and 10 min at baseline (vs RR homozygotes [n = 23]). After zinc supplementation, the RW/WW group experienced 15% and 14% increases in the insulin response to glucose at 5 and 10 min, respectively (p ≤ 0.04), and, compared with RR homozygotes, experienced a 26% (p = 0.04) increase in insulin at 5 min. We observed reciprocal decreases in proinsulin:insulin in the RW/WW (p = 0.002) vs RR group (p = 0.048), suggesting a genotype-specific improvement in insulin processing. CONCLUSIONS/INTERPRETATION Zinc supplementation appears to affect the early insulin response to glucose differentially by rs13266634 genotype and could be beneficial for diabetes prevention and/or treatment for some individuals based on SLC30A8 variation. TRIAL REGISTRATION ClinicalTrials.gov NCT00981448.
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Affiliation(s)
- Nisa M Maruthur
- Division of General Internal Medicine, Johns Hopkins University School of Medicine, 2024 E. Monument Street, Suite 2-600, Baltimore, MD, 21287, USA,
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15
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Abstract
SLC30A8 encodes the secretory granule-resident and largely endocrine pancreas-restricted zinc transporter ZnT8. Interest in this gene product was sparked amongst diabetologists in 2007 when the first genome-wide association study for type 2 diabetes identified polymorphisms in SLC30A8 as affecting disease risk. Thus, the common polymorphism rs13266634 was associated with lowered beta cell function and a 14% increase in diabetes abundance per risk (C) allele. This non-synonymous variant encodes a tryptophan-to-arginine switch at position 325 in the protein's intracellular carboxy-terminal domain, resulting in reduced zinc transport activity and, consequently, decreased intragranular zinc levels. Whereas insulin secretion from isolated islets is most often increased in mice inactivated for Slc30a8, null animals usually show impaired glucose tolerance and lowered circulating insulin. Since Slc30a8 null animals display little, if any, zinc secretion from islets, the lower plasma insulin levels could be explained by increased hepatic clearance as a result of lowered local zinc levels, or less efficient insulin action on target tissues. Despite the emerging consensus on the role of ZnT8 in glucose homeostasis, a recent genetic study in humans has unexpectedly identified loss-of-function SLC30A8 mutants that are associated with protection from diabetes. Here, we attempt to reconcile these apparently contradictory findings, implicating (1) differing degrees of inhibition of ZnT8 activity in carriers of common variants vs rare loss-of-function forms, (2) effects dependent on age or hypoxic beta cell stress. We propose that these variables conspire to affect both the size and the direction of the effect of SLC30A8 risk alleles in man.
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Affiliation(s)
- Guy A Rutter
- Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Imperial Centre for Translational and Experimental Medicine, Hammersmith Hospital, Imperial College London, Du Cane Road, London, W12 ONN, UK,
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16
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Davidson HW, Wenzlau JM, O'Brien RM. Zinc transporter 8 (ZnT8) and β cell function. Trends Endocrinol Metab 2014; 25:415-24. [PMID: 24751356 PMCID: PMC4112161 DOI: 10.1016/j.tem.2014.03.008] [Citation(s) in RCA: 107] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Revised: 03/17/2014] [Accepted: 03/19/2014] [Indexed: 02/07/2023]
Abstract
Human pancreatic β cells have exceptionally high zinc content. In β cells the highest zinc concentration is in insulin secretory granules, from which it is cosecreted with the hormone. Uptake of zinc into secretory granules is mainly mediated by zinc transporter 8 (ZnT8), the product of the SLC30A8 [solute carrier family 30 (zinc transporter), member 8] gene. The minor alleles of several single-nucleotide polymorphisms (SNPs) in SLC30A8 are associated with decreased risk of type 2 diabetes (T2D), but the precise mechanisms underlying the protective effects remain uncertain. In this article we review current knowledge of the role of ZnT8 in maintaining zinc homeostasis in β cells, its role in glucose metabolism based on knockout mouse studies, and current theories regarding the link between ZnT8 function and T2D.
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Affiliation(s)
- Howard W Davidson
- Barbara Davis Center for Diabetes, University of Colorado Denver Anschutz Medical Campus, Aurora, CO 80045, USA; Integrated Department of Immunology, University of Colorado Denver Anschutz Medical Campus, Aurora, CO 80045, USA.
| | - Janet M Wenzlau
- Barbara Davis Center for Diabetes, University of Colorado Denver Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Richard M O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
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17
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Weijers RNM. Comment on Sprouse et al. SLC30A8 nonsynonymous variant is associated with recovery following exercise and skeletal muscle size and strength. Diabetes 2014;63:363-368. Diabetes 2014; 63:e8. [PMID: 24757209 DOI: 10.2337/db14-0030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Affiliation(s)
- Rob N M Weijers
- Teaching Hospital, Onze Lieve Vrouwe Gasthuis, Amsterdam, the Netherlands
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18
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Faghih H, Khatami SR, Azarpira N, Foroughmand AM. SLC30A8 gene polymorphism (rs13266634 C/T) and type 2 diabetes mellitus in south Iranian population. Mol Biol Rep 2014; 41:2709-15. [DOI: 10.1007/s11033-014-3158-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Accepted: 01/13/2014] [Indexed: 10/25/2022]
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19
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Lasry I, Golan Y, Berman B, Amram N, Glaser F, Assaraf YG. In situ dimerization of multiple wild type and mutant zinc transporters in live cells using bimolecular fluorescence complementation. J Biol Chem 2014; 289:7275-92. [PMID: 24451381 DOI: 10.1074/jbc.m113.533786] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Zinc transporters (ZnTs) facilitate zinc efflux and zinc compartmentalization, thereby playing a key role in multiple physiological processes and pathological disorders, presumed to be modulated by transporter dimerization. We recently proposed that ZnT2 homodimerization is the underlying basis for the dominant negative effect of a novel heterozygous G87R mutation identified in women producing zinc-deficient milk. To provide direct visual evidence for the in situ dimerization and function of multiple normal and mutant ZnTs, we applied here the bimolecular fluorescence complementation (BiFC) technique, which enables direct visualization of specific protein-protein interactions. BiFC is based upon reconstitution of an intact fluorescent protein including YFP when its two complementary, non-fluorescent N- and C-terminal fragments (termed YN and YC) are brought together by a pair of specifically interacting proteins. Homodimerization of ZnT1, -2, -3, -4, and -7 was revealed by high subcellular fluorescence observed upon co-transfection of non-fluorescent ZnT-YC and ZnT-YN; this homodimer fluorescence localized in the characteristic compartments of each ZnT. The validity of the BiFC assay in ZnT dimerization was further corroborated when high fluorescence was obtained upon co-transfection of ZnT5-YC and ZnT6-YN, which are known to form heterodimers. We further show that BiFC recapitulated the pathogenic role that ZnT mutations play in transient neonatal zinc deficiency. Zinquin, a fluorescent zinc probe applied along with BiFC, revealed the in situ functionality of ZnT dimers. Hence, the current BiFC-Zinquin technique provides the first in situ evidence for the dimerization and function of wild type and mutant ZnTs in live cells.
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Affiliation(s)
- Inbal Lasry
- From the Fred Wyszkowski Cancer Research Laboratory, Department of Biology, and
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20
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Lasry I, Seo YA, Ityel H, Shalva N, Pode-Shakked B, Glaser F, Berman B, Berezovsky I, Goncearenco A, Klar A, Levy J, Anikster Y, Kelleher SL, Assaraf YG. A dominant negative heterozygous G87R mutation in the zinc transporter, ZnT-2 (SLC30A2), results in transient neonatal zinc deficiency. J Biol Chem 2012; 287:29348-61. [PMID: 22733820 DOI: 10.1074/jbc.m112.368159] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Zinc is an essential mineral, and infants are particularly vulnerable to zinc deficiency as they require large amounts of zinc for their normal growth and development. We have recently described the first loss-of-function mutation (H54R) in the zinc transporter ZnT-2 (SLC30A2) in mothers with infants harboring transient neonatal zinc deficiency (TNZD). Here we identified and characterized a novel heterozygous G87R ZnT-2 mutation in two unrelated Ashkenazi Jewish mothers with infants displaying TNZD. Transient transfection of G87R ZnT-2 resulted in endoplasmic reticulum-Golgi retention, whereas the WT transporter properly localized to intracellular secretory vesicles in HC11 and MCF-7 cells. Consequently, G87R ZnT-2 showed decreased stability compared with WT ZnT-2 as revealed by Western blot analysis. Three-dimensional homology modeling based on the crystal structure of YiiP, a close zinc transporter homologue from Escherichia coli, revealed that the basic arginine residue of the mutant G87R points toward the membrane lipid core, suggesting misfolding and possible loss-of-function. Indeed, functional assays including vesicular zinc accumulation, zinc secretion, and cytoplasmic zinc pool assessment revealed markedly impaired zinc transport in G87R ZnT-2 transfectants. Moreover, co-transfection experiments with both mutant and WT transporters revealed a dominant negative effect of G87R ZnT-2 over the WT ZnT-2; this was associated with mislocalization, decreased stability, and loss of zinc transport activity of the WT ZnT-2 due to homodimerization observed upon immunoprecipitation experiments. These findings establish that inactivating ZnT-2 mutations are an underlying basis of TNZD and provide the first evidence for the dominant inheritance of heterozygous ZnT-2 mutations via negative dominance due to homodimer formation.
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Affiliation(s)
- Inbal Lasry
- The Fred Wyszkowski Cancer Research Laboratory, Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
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22
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Abstract
BACKGROUND Identification of the major humoral epitopes in zinc transporter 8 (ZnT8) will expand the range of biomarkers for human type 1 diabetes and may provide clues to the mechanisms governing disease progression. Our initial studies suggested that most ZnT8-reactive sera recognize conformational epitopes in the final 100aa region of the molecule. Subsequently we identified residue 325 as a major determinant in two epitopes linked to a genetic polymorphism with high minor allele frequency (rs13266634). The goal of the current study was to extend this analysis to identify non-polymorphic epitopes in ZnT8. METHODS Although the carboxy-terminal domains of human and mouse ZnT8 are ∼80% identical, the mouse probe is not precipitated by the majority of human type 1 diabetes sera. Thus to identify key residues we systematically 'humanized' the mouse probe at each position that differs and evaluated the probes in radio-immunoassays. RESULTS As previously reported, only the alteration of Q>R325 by itself showed any restoration of binding to human sera. However, when clusters of structurally adjacent variant residues were also changed an additional region of antigenicity was revealed that depended on residues R332, E333, K336, and K340. Using a panel of 112 sera from recent onset subjects tested with the hC325Q and m-R325R332E333K336K340 probes, 39.3% of the subjects were ZnT8(Q)A+ , of which 38.6% (17/44) also recognized the mouse probe. CONCLUSIONS We conclude that the mR-REKK probe identifies a third major epitope in ZnT8 that may add to the diagnostic utility of measuring autoantibodies to this molecule.
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Affiliation(s)
| | | | | | - Howard W. Davidson
- Corresponding author: Howard W. Davidson, PhD, Barbara Davis Center for Childhood Diabetes, Mailstop B140, 1775 Aurora Court, Aurora, CO, 80045, Tel: 303-724-6852, Fax: 303-724-6816,
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Majithia AR, Jablonski KA, McAteer JB, Mather KJ, Goldberg RB, Kahn SE, Florez JC. Association of the SLC30A8 missense polymorphism R325W with proinsulin levels at baseline and after lifestyle, metformin or troglitazone intervention in the Diabetes Prevention Program. Diabetologia 2011; 54:2570-4. [PMID: 21779873 PMCID: PMC3444290 DOI: 10.1007/s00125-011-2234-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2011] [Accepted: 06/08/2011] [Indexed: 10/18/2022]
Abstract
AIMS/HYPOTHESIS Individuals with impaired glucose tolerance have increased proinsulin levels, despite normal glucose or C-peptide levels. In the Diabetes Prevention Program (DPP), increased proinsulin levels predicted type 2 diabetes and proinsulin levels were significantly reduced following treatment with metformin, lifestyle modification or troglitazone compared with placebo. Genetic and physiological studies suggest a role for the zinc transporter gene SLC30A8 in diabetes risk, possibly through effects on insulin-processing in beta cells. We hypothesised that the risk allele at the type 2 diabetes-associated missense polymorphism rs13266634 (R325W) in SLC30A8 would predict proinsulin levels in individuals at risk of type 2 diabetes and may modulate response to preventive interventions. METHODS We genotyped rs13266634 in 3,007 DPP participants and examined its association with fasting proinsulin and fasting insulin at baseline and at 1 year post-intervention. RESULTS We found that increasing dosage of the C risk allele at SLC30A8 rs13266634 was significantly associated with higher proinsulin levels at baseline (p = 0.002) after adjustment for baseline insulin. This supports the hypothesis that risk alleles at SLC30A8 mark individuals with insulin-processing defects. At the 1 year analysis, proinsulin levels decreased significantly in all groups receiving active intervention and were no longer associated with SLC30A8 genotype (p = 0.86) after adjustment for insulin at baseline and 1 year. We found no genotype × treatment interactions at 1 year. CONCLUSIONS/INTERPRETATION In prediabetic individuals, genotype at SLC30A8 predicts baseline proinsulin levels independently of insulin levels, but does not predict proinsulin levels after amelioration of insulin sensitivity at 1 year.
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Affiliation(s)
- A R Majithia
- Center for Human Genetic Research and Diabetes Research Center (Diabetes Unit), Massachusetts General Hospital, Boston, MA, USA
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24
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Bosco MD, Mohanasundaram DM, Drogemuller CJ, Lang CJ, Zalewski PD, Coates PT. Zinc and zinc transporter regulation in pancreatic islets and the potential role of zinc in islet transplantation. Rev Diabet Stud 2011; 7:263-74. [PMID: 21713314 DOI: 10.1900/rds.2010.7.263] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The critical trace element zinc is essential for normal insulin production, and plays a central role in cellular protection against apoptosis and oxidative stress. The regulation of zinc within the pancreas and β-cells is controlled by the zinc transporter families ZnT and ZIP. Pancreatic islets display wide variability in the occurrence of these molecules. The zinc transporter, ZnT8 is an important target for autoimmunity in type 1 diabetes. Gene polymorphisms of this transporter confer sensitivity for immunosuppressive drugs used in islet transplantation. Understanding the biology of zinc transport within pancreatic islets will provide insight into the mechanisms of β-cell death, and may well reveal new pathways for improvement of diabetes therapy, including islet transplantation. This review discusses the possible roles of zinc in β-cell physiology with a special focus on islet transplantation.
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Affiliation(s)
- Mariea D Bosco
- Central Northern Adelaide Renal and Transplantation Service, Renal and Transplantation Immunology Lab, Royal Adelaide Hospital, South Australia
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