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Marques-da-Silva D, Lagoa R. Rafting on the Evidence for Lipid Raft-like Domains as Hubs Triggering Environmental Toxicants' Cellular Effects. Molecules 2023; 28:6598. [PMID: 37764374 PMCID: PMC10536579 DOI: 10.3390/molecules28186598] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 09/07/2023] [Accepted: 09/07/2023] [Indexed: 09/29/2023] Open
Abstract
The plasma membrane lipid rafts are cholesterol- and sphingolipid-enriched domains that allow regularly distributed, sub-micro-sized structures englobing proteins to compartmentalize cellular processes. These membrane domains can be highly heterogeneous and dynamic, functioning as signal transduction platforms that amplify the local concentrations and signaling of individual components. Moreover, they participate in cell signaling routes that are known to be important targets of environmental toxicants affecting cell redox status and calcium homeostasis, immune regulation, and hormonal functions. In this work, the evidence that plasma membrane raft-like domains operate as hubs for toxicants' cellular actions is discussed, and suggestions for future research are provided. Several studies address the insertion of pesticides and other organic pollutants into membranes, their accumulation in lipid rafts, or lipid rafts' disruption by polychlorinated biphenyls (PCBs), benzo[a]pyrene (B[a]P), and even metals/metalloids. In hepatocytes, macrophages, or neurons, B[a]P, airborne particulate matter, and other toxicants caused rafts' protein and lipid remodeling, oxidative changes, or amyloidogenesis. Different studies investigated the role of the invaginated lipid rafts present in endothelial cells in mediating the vascular inflammatory effects of PCBs. Furthermore, in vitro and in vivo data strongly implicate raft-localized NADPH oxidases, the aryl hydrocarbon receptor, caveolin-1, and protein kinases in the toxic mechanisms of occupational and environmental chemicals.
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Affiliation(s)
- Dorinda Marques-da-Silva
- LSRE—Laboratory of Separation and Reaction Engineering and LCM—Laboratory of Catalysis and Materials, School of Management and Technology, Polytechnic Institute of Leiria, Morro do Lena-Alto do Vieiro, 2411-901 Leiria, Portugal;
- ALiCE—Associate Laboratory in Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
- School of Technology and Management, Polytechnic Institute of Leiria, Morro do Lena-Alto do Vieiro, 2411-901 Leiria, Portugal
| | - Ricardo Lagoa
- LSRE—Laboratory of Separation and Reaction Engineering and LCM—Laboratory of Catalysis and Materials, School of Management and Technology, Polytechnic Institute of Leiria, Morro do Lena-Alto do Vieiro, 2411-901 Leiria, Portugal;
- ALiCE—Associate Laboratory in Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
- School of Technology and Management, Polytechnic Institute of Leiria, Morro do Lena-Alto do Vieiro, 2411-901 Leiria, Portugal
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Mezei M, Latif R, Davies TF. Modeling TSH Receptor Dimerization at the Transmembrane Domain. Endocrinology 2022; 163:6759649. [PMID: 36223484 PMCID: PMC9761578 DOI: 10.1210/endocr/bqac168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Indexed: 01/26/2023]
Abstract
Biophysical studies have established that the thyrotropin (TSH) receptor (TSHR) undergoes posttranslational modifications including dimerization. Following our earlier simulation of a TSHR-transmembrane domain (TMD) monomer (called TSHR-TMD-TRIO) we have now proceeded with a molecular dynamics simulation (MD) of TSHR-TMD dimerization using this improved membrane-embedded model. The starting structure was the TMD protein with all extracellular and intracellular loops and internal waters, which was placed in the relative orientation of the model originally generated with Brownian dynamics. Furthermore, this model was embedded in a DPPC lipid bilayer further solvated with water and added salt. Data from the MD simulation studies showed that the dimeric subunits stayed in the same relative orientation and distance during the 1000 ns of study. Comparison of representative conformations of the individual monomers when dimerized with the conformations from the monomer simulation showed subtle differences as represented by the backbone root mean square deviations. Differences in the conformations of the ligand-binding sites, suggesting variable affinities for these "hot spots," were also revealed by comparing the docking scores of 46 small-molecule ligands that included known TSHR agonists and antagonists as well as their derivatives. These data add further insight into the tendency of the TSHR-TMD to form dimeric and oligomeric structures and show that the differing conformations influence small-molecule binding sites within the TMD.
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Affiliation(s)
- Mihaly Mezei
- Correspondence: Mihaly Mezei, PhD, Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Pl, New York, NY 10029, USA.
| | - Rauf Latif
- Thyroid Research Unit, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, New York 10029, USA
- Department of Medicine, James J. Peters VA Medical Center, New York, New York 10468, USA
| | - Terry F Davies
- Thyroid Research Unit, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, New York 10029, USA
- Department of Medicine, James J. Peters VA Medical Center, New York, New York 10468, USA
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Characterization of Glycosphingolipids in the Human Parathyroid and Thyroid Glands. Int J Mol Sci 2021; 22:ijms22137044. [PMID: 34208903 PMCID: PMC8269270 DOI: 10.3390/ijms22137044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Revised: 06/15/2021] [Accepted: 06/23/2021] [Indexed: 11/16/2022] Open
Abstract
As part of a systematic investigation of the glycosphingolipids in human tissues, acid and non-acid glycosphingolipids from human thyroid and parathyroid glands were isolated and characterized with mass spectrometry and binding of carbohydrate-recognizing ligands, with a focus on complex compounds. The glycosphingolipid patterns of the human parathyroid and thyroid glands were very similar. The major acid glycosphingolipids were sulfatide and the gangliosides GM3, GD3, GD1a, GD1b, GT1b and Neu5Ac-neolactotetraosylceramide, and the major non-acid glycosphingolipids were globotriaosylceramide and globoside. We also found neolactotetra- and neolactohexaosylceramide, the x2 glycosphingolipid, and complex glycosphingolipids with terminal blood group O and A determinants in both tissues. A glycosphingolipid with blood group Leb determinant was identified in the thyroid gland, and the parathyroid sample had a glycosphingolipid with terminal blood group B determinant. Immunohistochemistry demonstrated the expression of blood group A antigens in both the thyroid and parathyroid glands. A weak cytoplasmatic expression of the GD1a ganglioside was present in the thyroid, while the parathyroid gland had a strong GD1a expression on the cell surface. Thus, the glycosylation of human thyroid and parathyroid glands is more complex than previously appreciated. Our findings provide a platform for further studies of alterations of cell surface glycosphingolipids in thyroid and parathyroid cancers.
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Rossi M, Taddei AR, Fasciani I, Maggio R, Giorgi F. The cell biology of the thyroid-disrupting mechanism of dichlorodiphenyltrichloroethane (DDT). J Endocrinol Invest 2018. [PMID: 28639207 DOI: 10.1007/s40618-017-0716-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
OBJECTIVE Dichlorodiphenyltrichloroethane (DDT) is an organochlorine known for its pesticide properties and for its negative effects on human health. It was banned in most countries for its toxicity to the endocrine system, but due to its persistence at clinically relevant concentrations in both soil and animal tissues, DDT is still linked to several health and social problems. METHODS We have previously shown that DDT exposure is causally related to the extracellular release of vesicular organelles such as microvesicles and/or exosomes by using immunocytochemistry with gold-tagged antibodies and various fluorescent membrane markers. RESULTS It is now well recognized that microvesicles and/or exosomes organelles are implicated in cell-to-cell communication, and that they are fundamental elements for transferring proteins, RNA, DNA, lipids and transcriptional factors among cells. In this short review, we discussed the role of extracellular vesicle formation in the thyroid-disrupting mechanism of DDT. In particular, we described how DDT, by dislodging the thyrotropin hormone (TSH) receptor from the raft containing compartments of the cells, prevents its activation and internalization. CONCLUSION Based on our earlier finding and on the large body of evidence here reviewed, we propose that DDT-induced formation of extracellular vesicles containing the TSH receptor could be directly involved in the development of autoimmune responses against the TSH receptor and that, therefore, their release could lead to the development of the Graves' disease.
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Affiliation(s)
- M Rossi
- Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, USA
| | - A R Taddei
- Section of Electron Microscopy, Great Equipment Center, University of Tuscia, Viterbo, Italy
| | - I Fasciani
- Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, L'Aquila, Italy
| | - R Maggio
- Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, L'Aquila, Italy.
| | - F Giorgi
- Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, Pisa, Italy
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Albi E, Krüger M, Hemmersbach R, Lazzarini A, Cataldi S, Codini M, Beccari T, Ambesi-Impiombato FS, Curcio F. Impact of Gravity on Thyroid Cells. Int J Mol Sci 2017; 18:E972. [PMID: 28471415 PMCID: PMC5454885 DOI: 10.3390/ijms18050972] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 04/27/2017] [Accepted: 04/28/2017] [Indexed: 12/15/2022] Open
Abstract
Physical and mental health requires a correct functioning of the thyroid gland, which controls cardiovascular, musculoskeletal, nervous, and immune systems, and affects behavior and cognitive functions. Microgravity, as occurs during space missions, induces morphological and functional changes within the thyroid gland. Here, we review relevant experiments exposing cell cultures (normal and cancer thyroid cells) to simulated and real microgravity, as well as wild-type and transgenic mice to hypergravity and spaceflight conditions. Well-known mechanisms of damage are presented and new ones, such as changes of gene expression for extracellular matrix and cytoskeleton proteins, thyrocyte phenotype, sensitivity of thyrocytes to thyrotropin due to thyrotropin receptor modification, parafollicular cells and calcitonin production, sphingomyelin metabolism, and the expression and movement of cancer molecules from thyrocytes to colloids are highlighted. The identification of new mechanisms of thyroid injury is essential for the development of countermeasures, both on the ground and in space, against thyroid cancer. We also address the question whether normal and cancer cells show a different sensitivity concerning changes of environmental conditions.
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Affiliation(s)
- Elisabetta Albi
- Department of Pharmaceutical Science, University of Perugia, San Costanzo, via Romana, 06121 Perugia, Italy.
| | - Marcus Krüger
- Clinic and Policlinic for Plastic, Aesthetic and Hand Surgery, Otto-von-Guericke-University, Leipziger Str. 44, 39120 Magdeburg, Germany.
| | - Ruth Hemmersbach
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Gravitational Biology, Linder Höhe, 51147 Cologne, Germany.
| | - Andrea Lazzarini
- Laboratory of Nuclear Lipid BioPathology, CRABiON, Perugia, via Ponchielli 4, 06073 Perugia, Italy.
| | - Samuela Cataldi
- Department of Pharmaceutical Science, University of Perugia, San Costanzo, via Romana, 06121 Perugia, Italy.
| | - Michela Codini
- Department of Pharmaceutical Science, University of Perugia, San Costanzo, via Romana, 06121 Perugia, Italy.
| | - Tommaso Beccari
- Department of Pharmaceutical Science, University of Perugia, San Costanzo, via Romana, 06121 Perugia, Italy.
| | | | - Francesco Curcio
- Dipartimento di Area Medica (DAME), University of Udine, p.le M. Kolbe 4, 33100 Udine, Italy.
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Rapoport B, McLachlan SM. TSH Receptor Cleavage Into Subunits and Shedding of the A-Subunit; A Molecular and Clinical Perspective. Endocr Rev 2016; 37:114-34. [PMID: 26799472 PMCID: PMC4823380 DOI: 10.1210/er.2015-1098] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The TSH receptor (TSHR) on the surface of thyrocytes is unique among the glycoprotein hormone receptors in comprising two subunits: an extracellular A-subunit, and a largely transmembrane and cytosolic B-subunit. Unlike its ligand TSH, whose subunits are encoded by two genes, the TSHR is expressed as a single polypeptide that subsequently undergoes intramolecular cleavage into disulfide-linked subunits. Cleavage is associated with removal of a C-peptide region, a mechanism similar in some respects to insulin cleavage into disulfide linked A- and B-subunits with loss of a C-peptide region. The potential pathophysiological importance of TSHR cleavage into A- and B-subunits is that some A-subunits are shed from the cell surface. Considerable experimental evidence supports the concept that A-subunit shedding in genetically susceptible individuals is a factor contributing to the induction and/or affinity maturation of pathogenic thyroid-stimulating autoantibodies, the direct cause of Graves' disease. The noncleaving gonadotropin receptors are not associated with autoantibodies that induce a "Graves' disease of the gonads." We also review herein current information on the location of the cleavage sites, the enzyme(s) responsible for cleavage, the mechanism by which A-subunits are shed, and the effects of cleavage on receptor signaling.
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Affiliation(s)
- Basil Rapoport
- Thyroid Autoimmune Disease Unit, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California 90048
| | - Sandra M McLachlan
- Thyroid Autoimmune Disease Unit, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California 90048
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Rapoport B, McLachlan SM. Withdrawn: TSH Receptor Cleavage Into Subunits and Shedding of the A-Subunit; A Molecular and Clinical Perspective. Endocr Rev 2016; 2016:23-42. [PMID: 27454362 PMCID: PMC6958993 DOI: 10.1210/er.2015-1098.2016.1.test] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Accepted: 01/14/2016] [Indexed: 12/29/2022]
Abstract
The TSH receptor (TSHR) on the surface of thyrocytes is unique among the glycoprotein hormone receptors in comprising two subunits: an extracellular A-subunit, and a largely transmembrane and cytosolic B-subunit. Unlike its ligand TSH, whose subunits are encoded by two genes, the TSHR is expressed as a single polypeptide that subsequently undergoes intramolecular cleavage into disulfide-linked subunits. Cleavage is associated with removal of a C-peptide region, a mechanism similar in some respects to insulin cleavage into disulfide linked A- and B-subunits with lossofaC-peptideregion. The potential pathophysiological importance of TSHR cleavage into A-and B-subunits is that some A-subunits are shed from the cell surface. Considerable experimental evidence supports the concept that A-subunit shedding in genetically susceptible individuals is a factor contributing to the induction and/or affinity maturation of pathogenic thyroid-stimulating autoantibodies, the direct cause of Graves' disease. The noncleaving gonadotropin receptors are not associated with autoantibodies that induce a "Graves' disease of the gonads." We also review herein current information on the location of the cleavage sites, the enzyme(s) responsible for cleavage, the mechanism by which A-subunits are shed, and the effects of cleavage on receptor signaling. (Endocrine Reviews 37: 114-134, 2016).
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Affiliation(s)
- Basil Rapoport
- Thyroid Autoimmune Disease Unit, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California 90048
| | - Sandra M McLachlan
- Thyroid Autoimmune Disease Unit, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California 90048
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Davies TF, Latif R. Targeting the thyroid-stimulating hormone receptor with small molecule ligands and antibodies. Expert Opin Ther Targets 2015; 19:835-47. [PMID: 25768836 DOI: 10.1517/14728222.2015.1018181] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
INTRODUCTION The thyroid-stimulating hormone receptor (TSHR) is the essential molecule for thyroid growth and thyroid hormone production. Since it is also a key autoantigen in Graves' disease and is involved in thyroid cancer pathophysiology, the targeting of the TSHR offers a logical model for disease control. AREAS COVERED We review the structure and function of the TSHR and the progress in both small molecule ligands and TSHR antibodies for their therapeutic potential. EXPERT OPINION Stabilization of a preferential conformation for the TSHR by allosteric ligands and TSHR antibodies with selective modulation of the signaling pathways is now possible. These tools may be the next generation of therapeutics for controlling the pathophysiological consequences mediated by the effects of the TSHR in the thyroid and other extrathyroidal tissues.
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Affiliation(s)
- Terry F Davies
- Icahn School of Medicine at Mount Sinai and the James J. Peters VA Medical Center, Thyroid Research Unit , 1 Gustave L Levy Place, New York, NY 10029 , USA +1 212 241 7975 ; +1 212 428 6748 ;
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Abstract
The TSH receptor (TSHR) has the propensity to form dimers and oligomers. Our data using ectodomain-truncated TSHRs indicated that the predominant interfaces for oligomerization reside in the transmembrane (TM) domain. To map the potentially interacting residues, we first performed in silico studies of the TSHR transmembrane domain using a homology model and using Brownian dynamics (BD). The cluster of dimer conformations obtained from BD analysis indicated that TM1 made contact with TM4 and two residues in TM2 made contact with TM5. To confirm the proximity of these contact residues, we then generated cysteine mutants at all six contact residues predicted by the BD analysis and performed cysteine cross-linking studies. These results showed that the predicted helices in the protomer were indeed involved in proximity interactions. Furthermore, an alternative experimental approach, receptor truncation experiments and LH receptor sequence substitution experiments, identified TM1 harboring a major region involved in TSHR oligomerization, in agreement with the conclusion from the cross-linking studies. Point mutations of the predicted interacting residues did not yield a substantial decrease in oligomerization, unlike the truncation of the TM1, so we concluded that constitutive oligomerization must involve interfaces forming domains of attraction in a cooperative manner that is not dominated by interactions between specific residues.
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Affiliation(s)
- Rauf Latif
- Thyroid Research Unit (R.L., M.R.A., T.F.D.) and Departments of Medicine (R.L., M.R.A., T.F.D.) and Structural and Chemical Biology (M.M.), Icahn School of Medicine at Mt Sinai School of Medicine, New York, New York 10029; and James J. Peters Veterans Affairs Medical Center (R.L., M.R.A., T.F.D.), New York, New York 10468
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Lu M, Yang CB, Gao L, Zhao JJ. Mechanism of subclinical hypothyroidism accelerating endothelial dysfunction (Review). Exp Ther Med 2014; 9:3-10. [PMID: 25452768 PMCID: PMC4247316 DOI: 10.3892/etm.2014.2037] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2014] [Accepted: 09/02/2014] [Indexed: 12/26/2022] Open
Abstract
The association between subclinical hypothyroidism (SH) and cardiovascular disease has received increasing attention in recent years. The predisposition of patients with SH to endothelial dysfunction, an early sign of atherosclerosis, has been observed. This predisposition may be partially explained by the factors also found in patients with SH, including changes in lipid profile, low grade chronic inflammation, oxidative stress and insulin resistance. The proportional risks of endothelial dysfunction to thyroid stimulating hormone (TSH) also indicate that the action of TSH on extra thyroidal-stimulating hormone receptor (TSHR) is a possible mechanism underlying the correlation, which has later been supported by the associated basic studies. L-thyroxine replacement therapy appears to improve the aforementioned aspects, whereas there remain certain controversies, particularly for the elderly. Thus, more study data are required to confirm the benefit of L-thyroxine treatment for patients with SH.
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Affiliation(s)
- Ming Lu
- Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, Shandong, P.R. China ; Institute of Endocrinology and Metabolic Diseases, Shandong Academy of Clinical Medicine, Jinan, Shandong, P.R. China
| | - Chong-Bo Yang
- Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, Shandong, P.R. China ; Institute of Endocrinology and Metabolic Diseases, Shandong Academy of Clinical Medicine, Jinan, Shandong, P.R. China
| | - Ling Gao
- Institute of Endocrinology and Metabolic Diseases, Shandong Academy of Clinical Medicine, Jinan, Shandong, P.R. China ; Scientific Center, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, Shandong, P.R. China
| | - Jia-Jun Zhao
- Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, Shandong, P.R. China ; Institute of Endocrinology and Metabolic Diseases, Shandong Academy of Clinical Medicine, Jinan, Shandong, P.R. China
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Key T, Duncan R. A compact, multifunctional fusion module directs cholesterol-dependent homomultimerization and syncytiogenic efficiency of reovirus p10 FAST proteins. PLoS Pathog 2014; 10:e1004023. [PMID: 24651689 PMCID: PMC3961370 DOI: 10.1371/journal.ppat.1004023] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 02/05/2014] [Indexed: 12/11/2022] Open
Abstract
The homologous p10 fusion-associated small transmembrane (FAST) proteins of the avian (ARV) and Nelson Bay (NBV) reoviruses are the smallest known viral membrane fusion proteins, and are virulence determinants of the fusogenic reoviruses. The small size of FAST proteins is incompatible with the paradigmatic membrane fusion pathway proposed for enveloped viral fusion proteins. Understanding how these diminutive viral fusogens mediate the complex process of membrane fusion is therefore of considerable interest, from both the pathogenesis and mechanism-of-action perspectives. Using chimeric ARV/NBV p10 constructs, the 36–40-residue ectodomain was identified as the major determinant of the differing fusion efficiencies of these homologous p10 proteins. Extensive mutagenic analysis determined the ectodomain comprises two distinct, essential functional motifs. Syncytiogenesis assays, thiol-specific surface biotinylation, and liposome lipid mixing assays identified an ∼25-residue, N-terminal motif that dictates formation of a cystine loop fusion peptide in both ARV and NBV p10. Surface immunofluorescence staining, FRET analysis and cholesterol depletion/repletion studies determined the cystine loop motif is connected through a two-residue linker to a 13-residue membrane-proximal ectodomain region (MPER). The MPER constitutes a second, independent motif governing reversible, cholesterol-dependent assembly of p10 multimers in the plasma membrane. Results further indicate that: (1) ARV and NBV homomultimers segregate to distinct, cholesterol-dependent microdomains in the plasma membrane; (2) p10 homomultimerization and cholesterol-dependent microdomain localization are co-dependent; and (3) the four juxtamembrane MPER residues present in the multimerization motif dictate species-specific microdomain association and homomultimerization. The p10 ectodomain therefore constitutes a remarkably compact, multifunctional fusion module that directs syncytiogenic efficiency and species-specific assembly of p10 homomultimers into cholesterol-dependent fusion platforms in the plasma membrane. Natural infections by fusogenic orthoreoviruses can result in severe afflictions ranging from neuropathogenicity to pneumonia and death. The fusogenic capacity of these viruses, attributable to a unique family of fusion-associated small transmembrane (FAST) proteins, is a correlate of virulence. The FAST proteins are the only known examples of nonenveloped virus membrane fusion proteins, and they are the smallest known viral fusogens whose structural and functional attributes are incompatible with current models of protein-mediated membrane fusion. Exploiting the sequence divergence and distinct syncytiogenic rates of representative p10 FAST proteins from avian and bat reovirus isolates, we determined the p10 ectodomain is a compact, complex fusion module comprising two independent functional motifs. One motif determines species-specific p10 fusion efficiency by governing formation of a cystine loop fusion peptide, while the other directs reversible clustering and multimerization of p10 in cholesterol-dependent membrane microdomains. Remarkably, a juxtamembrane tetra-peptide is solely responsible for co-dependent clustering and multimerization of p10 in distinct, species-specific fusion platforms. This is the first example of a viral fusogen utilizing a membrane-proximal ectodomain region (MPER) to direct cholesterol-dependent multimerization and assembly into fusion platforms.
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Affiliation(s)
- Tim Key
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Roy Duncan
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada
- * E-mail:
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Albi E, Curcio F, Spelat R, Lazzarini A, Lazzarini R, Loreti E, Ferri I, Ambesi-Impiombato FS. Observing the mouse thyroid sphingomyelin under space conditions: a case study from the MDS mission in comparison with hypergravity conditions. ASTROBIOLOGY 2012; 12:1035-1041. [PMID: 23082746 DOI: 10.1089/ast.2012.0881] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
This is a case report of apparent thyroid structural and functional alteration in a single mouse subjected to low Earth orbit spaceflight for 91 days. Histological examination of the thyroid gland revealed an increase in the average follicle size compared to that of three control animals and three animals exposed to hypergravity (2g) conditions. Immunoblotting analysis detected an increase in two thyroid gland enzymes, sphingomyelinase and sphingomyelin-synthase1. In addition, sphingomyelinase, an enzyme confined to the cell nucleus in the control animals, was found in the mouse exposed to hypogravity to be homogeneously distributed throughout the cell bodies. It represents the first animal observation of the influence of weightlessness on sphingomyelin metabolism.
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Affiliation(s)
- E Albi
- Laboratory of Nuclear Lipid BioPathology, CRABioN, 06073 Perugia, Italy. ealbi.nlbp.slc.@crabion.it
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Antibody protection reveals extended epitopes on the human TSH receptor. PLoS One 2012; 7:e44669. [PMID: 22957097 PMCID: PMC3434159 DOI: 10.1371/journal.pone.0044669] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 08/06/2012] [Indexed: 11/19/2022] Open
Abstract
Stimulating, and some blocking, antibodies to the TSH receptor (TSHR) have conformation-dependent epitopes reported to involve primarily the leucine rich repeat region of the ectodomain (LRD). However, successful crystallization of TSHR residues 22-260 has omitted important extracellular non-LRD residues including the hinge region which connects the TSHR ectodomain to the transmembrane domain and which is involved in ligand induced signal transduction. The aim of the present study, therefore, was to determine if TSHR antibodies (TSHR-Abs) have non-LRD binding sites outside the LRD. To obtain this information we employed the method of epitope protection in which we first protected TSHR residues 1-412 with intact TSHR antibodies and then enzymatically digested the unprotected residues. Those peptides remaining were subsequently delineated by mass spectrometry. Fourteen out of 23 of the reported stimulating monoclonal TSHR-Ab crystal contact residues were protected by this technique which may reflect the higher binding energies of certain residues detected in this approach. Comparing the protected epitopes of two stimulating TSHR-Abs we found both similarities and differences but both antibodies also contacted the hinge region and the amino terminus of the TSHR following the signal peptide and encompassing cysteine box 1 which has previously been shown to be important for TSH binding and activation. A monoclonal blocking TSHR antibody revealed a similar pattern of binding regions but the residues that it contacted on the LRD were again distinct. These data demonstrated that conformationally dependent TSHR-Abs had epitopes not confined to the LRDs but also incorporated epitopes not revealed in the available crystal structure. Furthermore, the data also indicated that in addition to overlapping contact regions within the LRD, there are unique epitope patterns for each of the antibodies which may contribute to their functional heterogeneity.
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Abstract
INTRODUCTION The thyrotropin receptor (TSHR) is essential for thyroid growth and for the production of thyroid hormones. It is unique among the glycoprotein hormone receptors, in that some of the TSHRs undergo cleavage and shedding of the alpha subunit. AREAS COVERED This review discusses the structure and function of the TSHR, followed by an evaluation of its role in thyroid disease. Possible limitations of the TSHR as a therapeutic target are also discussed. EXPERT OPINION The TSHR is involved in a number of hereditary and acquired disorders of the thyroid making it of potential importance as a therapeutic target in thyroid disease. Expression of the TSHR in several non-thyroidal tissues and the development of systemic manifestations of thyroid disease suggest that the TSHR is also of interest as a therapeutic target outside the thyroid.
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Affiliation(s)
- Samer El-Kaissi
- Specialized Diabetes and Endocrine Centre, King Fahad Medical City, Dabab Street, P.O. Box 59046, Riyadh 11525, Saudi Arabia.
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15
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Masini MA, Albi E, Barmo C, Bonfiglio T, Bruni L, Canesi L, Cataldi S, Curcio F, D'Amora M, Ferri I, Goto K, Kawano F, Lazzarini R, Loreti E, Nakai N, Ohira T, Ohira Y, Palmero S, Prato P, Ricci F, Scarabelli L, Shibaguchi T, Spelat R, Strollo F, Ambesi-Impiombato FS. The impact of long-term exposure to space environment on adult mammalian organisms: a study on mouse thyroid and testis. PLoS One 2012; 7:e35418. [PMID: 22558148 PMCID: PMC3338839 DOI: 10.1371/journal.pone.0035418] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2011] [Accepted: 03/15/2012] [Indexed: 12/30/2022] Open
Abstract
Hormonal changes in humans during spaceflight have been demonstrated but the underlying mechanisms are still unknown. To clarify this point thyroid and testis/epididymis, both regulated by anterior pituitary gland, have been analyzed on long-term space-exposed male C57BL/10 mice, either wild type or pleiotrophin transgenic, overexpressing osteoblast stimulating factor-1. Glands were submitted to morphological and functional analysis.In thyroids, volumetric ratios between thyrocytes and colloid were measured. cAMP production in 10(-7)M and 10(-8)M thyrotropin-treated samples was studied. Thyrotropin receptor and caveolin-1 were quantitized by immunoblotting and localized by immunofluorescence. In space-exposed animals, both basal and thyrotropin-stimulated cAMP production were always higher. Also, the structure of thyroid follicles appeared more organized, while thyrotropin receptor and caveolin-1 were overexpressed. Unlike the control samples, in the space samples thyrotropin receptor and caveolin-1 were both observed at the intracellular junctions, suggesting their interaction in specific cell membrane microdomains.In testes, immunofluorescent reaction for 3β- steroid dehydrogenase was performed and the relative expressions of hormone receptors and interleukin-1β were quantified by RT-PCR. Epididymal sperm number was counted. In space-exposed animals, the presence of 3β and 17β steroid dehydrogenase was reduced. Also, the expression of androgen and follicle stimulating hormone receptors increased while lutenizing hormone receptor levels were not affected. The interleukin 1 β expression was upregulated. The tubular architecture was altered and the sperm cell number was significantly reduced in spaceflight mouse epididymis (approx. -90% vs. laboratory and ground controls), indicating that the space environment may lead to degenerative changes in seminiferous tubules.Space-induced changes of structure and function of thyroid and testis/epididymis could be responsible for variations of hormone levels in human during space missions. More research, hopefully a reflight of MDS, would be needed to establish whether the space environment acts directly on the peripheral glands or induces changes in the hypotalamus-pituitary-glandular axis.
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Affiliation(s)
| | - Elisabetta Albi
- Department of Clinical and Experimental Medicine, University of Perugia, Perugia, Italy
| | | | | | - Lara Bruni
- DIPTERIS, University of Genoa, Genova, Italy
| | | | - Samuela Cataldi
- Department of Clinical and Experimental Medicine, University of Perugia, Perugia, Italy
| | - Francesco Curcio
- Department of Clinical and Biological Sciences, University of Udine, Udine, Italy
| | | | - Ivana Ferri
- Institute of Pathologic Anatomy and Histology, University of Perugia, Perugia, Italy
| | - Katsumasa Goto
- School of Health Sciences, Toyohashi SOZO University, Aichi, Japan
| | | | - Remo Lazzarini
- Department of Clinical and Experimental Medicine, University of Perugia, Perugia, Italy
| | - Elisabetta Loreti
- Institute of Pathologic Anatomy and Histology, University of Perugia, Perugia, Italy
| | - Naoya Nakai
- Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Takashi Ohira
- Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
| | - Yoshinobu Ohira
- Graduate School of Medicine, Osaka University, Osaka, Japan
- Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
| | | | - Paola Prato
- DIPTERIS, University of Genoa, Genova, Italy
| | | | | | | | - Renza Spelat
- Department of Clinical and Biological Sciences, University of Udine, Udine, Italy
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16
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Activation of myeloid cell-specific adhesion class G protein-coupled receptor EMR2 via ligation-induced translocation and interaction of receptor subunits in lipid raft microdomains. Mol Cell Biol 2012; 32:1408-20. [PMID: 22310662 DOI: 10.1128/mcb.06557-11] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The adhesion class G protein-coupled receptors (adhesion-GPCRs) play important roles in diverse biological processes ranging from immunoregulation to tissue polarity, angiogenesis, and brain development. These receptors are uniquely modified by self-catalytic cleavage at a highly conserved GPCR proteolysis site (GPS) dissecting the receptor into an extracellular subunit (α) and a seven-pass transmembrane subunit (β) with cellular adhesion and signaling functions, respectively. Using the myeloid cell-restricted EMR2 receptor as a paradigm, we exam the mechanistic relevance of the subunit interaction and demonstrate a critical role for GPS autoproteolysis in mediating receptor signaling and cell activation. Interestingly, two distinct receptor complexes are identified as a result of GPS proteolysis: one consisting of a noncovalent α-β heterodimer and the other comprising two completely independent receptor subunits which distribute differentially in membrane raft microdomains. Finally, we show that receptor ligation induces subunit translocation and colocalization within lipid rafts, leading to receptor signaling and inflammatory cytokine production by macrophages. Our present data resolve earlier conflicting results and provide a new mechanism of receptor signaling, as well as providing a paradigm for signal transduction within the adhesion-GPCR family.
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17
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Albi E, Curcio F, Spelat R, Lazzarini R, Loreti E, Ferri I, Ambesi-Impiombato FS. The thyroid lobes: the different twins. Arch Biochem Biophys 2011; 518:16-22. [PMID: 22178560 DOI: 10.1016/j.abb.2011.12.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2011] [Revised: 11/29/2011] [Accepted: 12/02/2011] [Indexed: 10/14/2022]
Abstract
Although differences in size of the right and left thyroid lobes are well defined, differences in morphology, follicles structure, cAMP production, thyrotropin receptor, and protein involved in cell signalling have not previously been reported. This study provides morpho-functional data of right and left thyroid lobes by biochemical, immunohistochemistry, immunoblotting and immunofluorescence analysis. We demonstrate that, in comparison with the left lobe, the right lobe has a higher activation index, is more sensitive to thyrotropin treatment, is rich in thyrotropin receptor and caveolin 1 involved in thyroid hormone synthesis as well as in epithelial thyroid cell homeostasis, is characterised by a high content of molecules involved in cell signalling such as stat3, raf1, sphingomyelinase and sphingomyelin-synthase whose activity ratio is necessary for epithelial cell activity and finally has more areas calcitonin-dependent. The relation between structure/function of right lobe and its susceptibility to the higher risk of pathological modifications with respect the left lobe is discussed.
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Affiliation(s)
- E Albi
- Department of Clinical and Experimental Medicine, Physiopathology Section, University of Perugia, Perugia, Italy.
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18
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McCaffrey G, Staatz WD, Quigley CA, Nametz N, Seelbach MJ, Campos CR, Brooks TA, Egleton RD, Davis TP. Tight junctions contain oligomeric protein assembly critical for maintaining blood-brain barrier integrity in vivo. J Neurochem 2011; 103:2540-55. [PMID: 17931362 DOI: 10.1111/j.1471-4159.2007.04943.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Tight junctions (TJs) are major components of the blood-brain barrier (BBB) that physically obstruct the interendothelial space and restrict paracellular diffusion of blood-borne substances from the peripheral circulation to the CNS. TJs are dynamic structures whose intricate arrangement of oligomeric transmembrane and accessory proteins rapidly alters in response to external stressors to produce changes in BBB permeability. In this study, we investigate the constitutive trafficking of the TJ transmembrane proteins occludin and claudin-5 that are essential for forming the TJ seal between microvascular endothelial cells that inhibits paracellular diffusion. Using a novel, detergent-free OptiPrep density-gradient method to fractionate rat cerebral microvessels, we identify a plasma membrane lipid raft domain that contains oligomeric occludin and claudin-5. Our data suggest that oligomerization of occludin involves disulfide bond formation within transmembrane regions, and that assembly of the TJ oligomeric protein complex is facilitated by an oligomeric caveolin scaffold. This is the first time that distribution of oligomeric TJ transmembrane proteins within plasma membrane lipid rafts at the BBB has been examined in vivo. The findings reported in this study are critical to understand the mechanism of assembly of the TJ multiprotein complex that is essential for maintaining BBB integrity.
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Affiliation(s)
- Gwen McCaffrey
- Department of Medical Pharmacology, University of Arizona College of Medicine, 1501 N. Campbell Ave, Tucson, Arizona, USA.
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The insecticide 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT) alters the membrane raft location of the TSH receptor stably expressed in Chinese hamster ovary cells. Toxicol Appl Pharmacol 2011; 253:121-9. [PMID: 21466821 DOI: 10.1016/j.taap.2011.03.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 03/21/2011] [Accepted: 03/25/2011] [Indexed: 12/11/2022]
Abstract
DDT is a highly lipophilic molecule known to deplete membrane rafts of their phosphoglycolipid and cholesterol contents. However, we have recently shown that DDT can also alter the thyroid homeostasis by inhibiting TSH receptor (TSHr) internalization. The present study was undertaken to verify whether DDT goitrogenic effects are due to the insecticide acting directly on TSHr or via alteration of the membrane rafts hosting the receptor itself. Our results demonstrate that, in CHO-TSHr transfected cells, TSHr is activated in the presence of TSH, while it is inhibited following DDT exposure. DDT can also reduce the endocytic vesicular traffic, alter the extension of multi-branched microvilli along their plasma membranes and induce TSHr shedding in vesicular forms. To verify whether TSHr displacement might depend on DDT altering the raft constitution of CHO-TSHr cell membranes the extent of TSHr and lipid raft co-localization was examined by confocal microscopy. Evidence shows that receptor/raft co-localization increased significantly upon exposure to TSH, while receptors and lipid rafts become dislodged on opposite cell poles in DDT-exposed CHO-TSHr cells. As a control, under similar culturing conditions, diphenylethylene, which is known to be a lipophilic substance that is structurally related to DDT, did not affect the extent of TSHr and lipid raft co-localization in CHO-TSHr cells treated with TSH. These findings corroborate and extend our view that, in CHO cells, the DDT disrupting action on TSHr is primarily due to the insecticide acting on membranes to deplete their raft cholesterol content, and that the resulting inhibition on TSHr internalization is due to receptor dislodgement from altered raft microdomains of the plasma membrane.
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20
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Albi E, Ambesi-Impiombato FS, Peverini M, Damaskopoulou E, Fontanini E, Lazzarini R, Curcio F, Perrella G. Thyrotropin receptor and membrane interactions in FRTL-5 thyroid cell strain in microgravity. ASTROBIOLOGY 2011; 11:57-64. [PMID: 21294645 DOI: 10.1089/ast.2010.0519] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The aim of this work was to analyze the possible alteration of thyrotropin (TSH) receptors in microgravity, which could explain the absence of thyroid cell proliferation in the space environment. Several forms of the TSH receptor are localized on the plasma membrane associated with caveolae and lipid rafts. The TSH regulates the fluidity of the cell membrane and the presence of its receptors in microdomains that are rich in sphingomyelin and cholesterol. TSH also stimulates cyclic adenosine monophosphate (cAMP) accumulation and cell proliferation. Reported here are the results of an experiment in which the FRTL-5 thyroid cell line was exposed to microgravity during the Texus-44 mission (launched February 7, 2008, from Kiruna, Sweden). When the parabolic flight brought the sounding rocket to an altitude of 264 km, the culture media were injected with or without TSH in the different samples, and weightlessness prevailed on board for 6 minutes and 19 seconds. Control experiments were performed, in parallel, in an onboard 1g centrifuge and on the ground in Kiruna laboratory. Cell morphology and function were analyzed. Results show that in microgravity conditions the cells do not respond to TSH treatment and present an irregular shape with condensed chromatin, a modification of the cell membrane with shedding of the TSH receptor in the culture medium, and an increase of sphingomyelin-synthase and Bax proteins. It is possible that real microgravity induces a rearrangement of specific sections of the cell membrane, which act as platforms for molecular receptors, thus influencing thyroid cell function in astronauts during space missions.
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Affiliation(s)
- E Albi
- Department of Clinical and Experimental Medicine, University School of Medicine, Perugia, Italy.
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21
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Chen CR, McLachlan SM, Rapoport B. Evidence that the thyroid-stimulating hormone (TSH) receptor transmembrane domain influences kinetics of TSH binding to the receptor ectodomain. J Biol Chem 2010; 286:6219-24. [PMID: 21190937 DOI: 10.1074/jbc.m110.211003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Thyroid-stimulating hormone (TSH)-induced reduction in ligand binding affinity (negative cooperativity) requires TSH receptor (TSHR) homodimerization, the latter involving primarily the transmembrane domain (TMD) but with the extracellular domain (ECD) also contributing to this association. To test the role of the TMD in negative cooperativity, we studied the TSHR ECD tethered to the cell surface by a glycosylphosphatidylinositol (GPI) anchor that multimerizes despite the absence of the TMD. Using the infinite ligand dilution approach, we confirmed that TSH increased the rate of dissociation (k(off)) of prebound (125)I-TSH from CHO cells expressing the TSH holoreceptor. Such negative cooperativity did not occur with TSHR ECD-GPI-expressing cells. However, even in the absence of added TSH, (125)I-TSH dissociated much more rapidly from the TSHR ECD-GPI than from the TSH holoreceptor. This phenomenon, suggesting a lower TSH affinity for the former, was surprising because both the TSHR ECD and TSH holoreceptor contain the entire TSH-binding site, and the TSH binding affinities for both receptor forms should, theoretically, be identical. In ligand competition studies, we observed that the TSH binding affinity for the TSHR ECD-GPI was significantly lower than that for the TSH holoreceptor. Further evidence for a difference in ligand binding kinetics for the TSH holoreceptor and TSHR ECD-GPI was obtained upon comparison of the TSH K(d) values for these two receptor forms at 4 °C versus room temperature. Our data provide the first evidence that the wild-type TSHR TMD influences ligand binding affinity for the ECD, possibly by altering the conformation of the closely associated hinge region that contributes to the TSH-binding site.
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Affiliation(s)
- Chun-Rong Chen
- Thyroid Autoimmune Disease Unit, Cedars-Sinai Research Institute and the David Geffen School of Medicine, UCLA, Los Angeles, California 90048, USA
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22
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Latif R, Michalek K, Morshed SA, Davies TF. A tyrosine residue on the TSH receptor stabilizes multimer formation. PLoS One 2010; 5:e9449. [PMID: 20195479 PMCID: PMC2829087 DOI: 10.1371/journal.pone.0009449] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Accepted: 02/04/2010] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The thyrotropin stimulating hormone receptor (TSHR) is a G protein coupled receptor (GPCR) with a large ectodomain. The ligand, TSH, acting via this receptor regulates thyroid growth and thyroid hormone production and secretion. The TSH receptor (TSHR) undergoes complex post-translational modifications including intramolecular cleavage and receptor multimerization. Since monomeric and multimeric receptors coexist in cells, understanding the functional role of just the TSHR multimers is difficult. Therefore, to help understand the physiological significance of receptor multimerization, it will be necessary to abrogate multimer formation, which requires identifying the ectodomain and endodomain interaction sites on the TSHR. Here, we have examined the contribution of the ectodomain to constitutive multimerization of the TSHR and determined the possible residue(s) that may be involved in this interaction. METHODOLOGY/PRINCIPAL FINDINGS We studied ectodomain multimer formation by expressing the extracellular domain of the TSHR linked to a glycophosphotidyl (GPI) anchor in both stable and transient expression systems. Using co-immunoprecipitation and FRET of tagged receptors, we established that the TSH receptor ectodomain was capable of multimerization even when totally devoid of the transmembrane domain. Further, we studied the effect of two residues that likely made critical contact points in this interaction. We showed that a conserved tyrosine residue (Y116) on the convex surface of the LRR3 was a critical residue in ectodomain multimer formation since mutation of this residue to serine totally abrogated ectodomain multimers. This abrogation was not seen with the mutation of cysteine 176 on the inner side of the LRR5, demonstrating that inter-receptor disulfide bonding was not involved in ectodomain multimer formation. Additionally, the Y116 mutation in the intact wild type receptor enhanced receptor degradation. CONCLUSIONS/SIGNIFICANCE These data establish the TSH receptor ectodomain as one site of multimerization, independent of the transmembrane region, and that this interaction was primarily via a conserved tyrosine residue in LRR3.
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Affiliation(s)
- Rauf Latif
- Thyroid Research Unit, James J. Peters VA Medical Center, Mount Sinai School of Medicine, New York, New York, United States of America.
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Latif R, Morshed SA, Zaidi M, Davies TF. The thyroid-stimulating hormone receptor: impact of thyroid-stimulating hormone and thyroid-stimulating hormone receptor antibodies on multimerization, cleavage, and signaling. Endocrinol Metab Clin North Am 2009; 38:319-41, viii. [PMID: 19328414 DOI: 10.1016/j.ecl.2009.01.006] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The thyroid-stimulating hormone receptor (TSHR) has a central role in thyrocyte function and is also one of the major autoantigens for the autoimmune thyroid diseases. We review the post-translational processing, multimerization, and intramolecular cleavage of TSHR, all of which may modulate its signal transduction. The recent characterization of monoclonal antibodies to the TSHR, including stimulating, blocking, and neutral antibodies, have also revealed unique biologic insights into receptor activation and the variety of these TSHR antibodies may help explain the multiple clinical phenotypes seen in autoimmune thyroid diseases. Knowledge of the structure/function relationship of the TSHR is beginning to provide a greater understanding of thyroid physiology and thyroid autoimmunity.
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Affiliation(s)
- Rauf Latif
- Thyroid Research Unit, Mount Sinai School of Medicine and the James J. Peters VA Medical Center, New York, NY 10468, USA.
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Sura-Trueba S, Aumas C, Carre A, Durif S, Leger J, Polak M, de Roux N. An inactivating mutation within the first extracellular loop of the thyrotropin receptor impedes normal posttranslational maturation of the extracellular domain. Endocrinology 2009; 150:1043-50. [PMID: 18927215 DOI: 10.1210/en.2008-1145] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The TSH receptor (TSHR), a member of the large family of G protein-coupled receptors, controls both function and growth of thyroid cells; hence, mutations of this receptor result in thyroid dysfunction. Here, we took advantage of the description of a new inactivating TSHR mutation (Q489H) in two brothers with hypothyroidism, to precise maturation, intracellular trafficking, exporting pathways, and activation mechanisms of this receptor. Functional characterization of the Q489H-TSHR in transiently transfected HEK293 cells showed cell surface expression, normal TSH binding affinity, and its inability to generate intracellular cAMP in response to TSH stimulation. Western blot analysis of the whole membrane proteins or proteins expressed at the cell surface showed that Q489H-TSHR expressed in HEK293 transfected cells are restricted to mannose-rich uncleaved receptor. Analysis of the export pathway toward cell surface indicated that both Q489H and wild-type receptors followed the same intracellular route to cell surface throughout endoplasmic reticulum and Golgi apparatus. This study shows that Q489H substitution impedes complete glycosylation of TSHR extracellular domain within the Golgi apparatus and that Q489H-TSHR expressed at the cell surface is unable to undergo intramolecular cleavage as well as to switch toward an active conformation under TSH stimulation. Altogether, our results show that 1) Q489H substitution within the first extracellular loop induces a misfolding of TSHR, blocking it into an inactive conformation and impeding complete glycosylation and intramolecular cleavage, and 2) a misfolded G protein-coupled receptor can bypass endoplasmic reticulum or Golgi apparatus quality control and reach the cell surface as an immature receptor.
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Affiliation(s)
- Sylvia Sura-Trueba
- Institut National de la Santé et de la Recherche Médicale (INSERM) Unité 690, Hôpital Robert-Debré, Paris, France
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Svendsen AM, Zalesko A, Kønig J, Vrecl M, Heding A, Kristensen JB, Wade JD, Bathgate RAD, De Meyts P, Nøhr J. Negative cooperativity in H2 relaxin binding to a dimeric relaxin family peptide receptor 1. Mol Cell Endocrinol 2008; 296:10-7. [PMID: 18723073 DOI: 10.1016/j.mce.2008.07.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Revised: 07/16/2008] [Accepted: 07/22/2008] [Indexed: 11/26/2022]
Abstract
H2 relaxin, a member of the insulin superfamily, binds to the G-protein-coupled receptor RXFP1 (relaxin family peptide 1), a receptor that belongs to the leucine-rich repeat (LRR)-containing subgroup (LGRs) of class A GPCRs. We recently demonstrated negative cooperativity in INSL3 binding to RXFP2 and showed that this subgroup of GPCRs functions as constitutive dimers. In this work, we investigated whether the binding of H2 relaxin to RXFP1 also shows negative cooperativity, and whether this receptor functions as a dimer using BRET(2). Both binding and dissociation were temperature dependent, and the pH optimum for binding was pH 7.0. Our results showed that RXFP1 is a constitutive dimer with negative cooperativity in ligand binding, that dimerization occurs through the 7TM domain, and that the ectodomain has a stabilizing effect on this interaction. Dimerization and negative cooperativity appear to be general properties of LGRs involved in reproduction as well as other GPCRs.
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Sandoval KE, Witt KA. Blood-brain barrier tight junction permeability and ischemic stroke. Neurobiol Dis 2008; 32:200-19. [PMID: 18790057 DOI: 10.1016/j.nbd.2008.08.005] [Citation(s) in RCA: 739] [Impact Index Per Article: 46.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Revised: 07/29/2008] [Accepted: 08/10/2008] [Indexed: 01/01/2023] Open
Abstract
The blood-brain barrier (BBB) is formed by the endothelial cells of cerebral microvessels, providing a dynamic interface between the peripheral circulation and the central nervous system. The tight junctions (TJs) between the endothelial cells serve to restrict blood-borne substances from entering the brain. Under ischemic stroke conditions decreased BBB TJ integrity results in increased paracellular permeability, directly contributing to cerebral vasogenic edema, hemorrhagic transformation, and increased mortality. This loss of TJ integrity occurs in a phasic manner, which is contingent on several interdependent mechanisms (ionic dysregulation, inflammation, oxidative and nitrosative stress, enzymatic activity, and angiogenesis). Understanding the inter-relation of these mechanisms is critical for the development of new therapies. This review focuses on those aspects of ischemic stroke impacting BBB TJ integrity and the principle regulatory pathways, respective to the phases of paracellular permeability.
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Affiliation(s)
- Karin E Sandoval
- Department of Pharmaceutical Sciences, School of Pharmacy, Southern Illinois University Edwardsville, Edwardsville, IL 62026, USA
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28
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Abstract
The application of molecular biology to the study of the thyrotropin receptor (TSHR) has led to major advances in our understanding of its structure, function, and relationship to the pathogenesis of Graves' disease. This review summarizes many of these features and also provides a personal perspective, questioning some assumptions and general concepts, as well as describing remaining challenges. Among the issues raised are the limits in our understanding of the spatial orientation of the structural domains of the TSHR, including the enigmatic hinge region. We review the phenomenon of TSHR intramolecular cleavage, the shedding of the A-subunit component of the ectodomain, and the importance of the latter in generating thyroid-stimulating antibodies. The epitopes of thyroid-stimulating and -blocking autoantibodies have been a confusing and controversial subject that requires review and evaluation of available data. Finally, we address the potential physiological or pathophysiological significance of TSHR multimerization in TSHR. Taken together, this review will, hopefully, convey the fascination and excitement that molecular biology has contributed to the study of the TSHR, especially as it relates to the pathogenesis of Graves' disease.
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Affiliation(s)
- Basil Rapoport
- Autoimmune Disease Unit, Cedars-Sinai Research Institute and UCLA School of Medicine, Los Angeles, California, USA.
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