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Faust B, Billesbølle CB, Suomivuori CM, Singh I, Zhang K, Hoppe N, Pinto AFM, Diedrich JK, Muftuoglu Y, Szkudlinski MW, Saghatelian A, Dror RO, Cheng Y, Manglik A. Autoantibody mimicry of hormone action at the thyrotropin receptor. Nature 2022; 609:846-853. [PMID: 35940205 PMCID: PMC9678024 DOI: 10.1038/s41586-022-05159-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2021] [Accepted: 07/28/2022] [Indexed: 11/08/2022]
Abstract
Thyroid hormones are vital in metabolism, growth and development1. Thyroid hormone synthesis is controlled by thyrotropin (TSH), which acts at the thyrotropin receptor (TSHR)2. In patients with Graves' disease, autoantibodies that activate the TSHR pathologically increase thyroid hormone activity3. How autoantibodies mimic thyrotropin function remains unclear. Here we determined cryo-electron microscopy structures of active and inactive TSHR. In inactive TSHR, the extracellular domain lies close to the membrane bilayer. Thyrotropin selects an upright orientation of the extracellular domain owing to steric clashes between a conserved hormone glycan and the membrane bilayer. An activating autoantibody from a patient with Graves' disease selects a similar upright orientation of the extracellular domain. Reorientation of the extracellular domain transduces a conformational change in the seven-transmembrane-segment domain via a conserved hinge domain, a tethered peptide agonist and a phospholipid that binds within the seven-transmembrane-segment domain. Rotation of the TSHR extracellular domain relative to the membrane bilayer is sufficient for receptor activation, revealing a shared mechanism for other glycoprotein hormone receptors that may also extend to other G-protein-coupled receptors with large extracellular domains.
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MESH Headings
- Cell Membrane/metabolism
- Cryoelectron Microscopy
- Graves Disease/immunology
- Graves Disease/metabolism
- Humans
- Immunoglobulins, Thyroid-Stimulating/chemistry
- Immunoglobulins, Thyroid-Stimulating/immunology
- Immunoglobulins, Thyroid-Stimulating/pharmacology
- Immunoglobulins, Thyroid-Stimulating/ultrastructure
- Phospholipids/metabolism
- Protein Domains
- Receptors, G-Protein-Coupled/agonists
- Receptors, G-Protein-Coupled/chemistry
- Receptors, G-Protein-Coupled/ultrastructure
- Receptors, Thyrotropin/agonists
- Receptors, Thyrotropin/chemistry
- Receptors, Thyrotropin/immunology
- Receptors, Thyrotropin/ultrastructure
- Rotation
- Thyrotropin/chemistry
- Thyrotropin/metabolism
- Thyrotropin/pharmacology
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Affiliation(s)
- Bryan Faust
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA, USA
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA, USA
- Biophysics Graduate Program, University of California, San Francisco, CA, USA
| | | | - Carl-Mikael Suomivuori
- Department of Computer Science, Stanford University, Stanford, CA, USA
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
- Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA, USA
| | - Isha Singh
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA, USA
| | - Kaihua Zhang
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA, USA
| | - Nicholas Hoppe
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA, USA
- Biophysics Graduate Program, University of California, San Francisco, CA, USA
| | - Antonio F M Pinto
- Mass Spectrometry Core for Proteomics and Metabolomics, Salk Institute for Biological Studies, La Jolla, CA, USA
| | - Jolene K Diedrich
- Mass Spectrometry Core for Proteomics and Metabolomics, Salk Institute for Biological Studies, La Jolla, CA, USA
| | | | | | - Alan Saghatelian
- Clayton Foundation Laboratory for Peptide Biology Lab, Salk Institute for Biological Studies, La Jolla, CA, USA
| | - Ron O Dror
- Department of Computer Science, Stanford University, Stanford, CA, USA
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
- Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA, USA
| | - Yifan Cheng
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA, USA.
- Biophysics Graduate Program, University of California, San Francisco, CA, USA.
- Howard Hughes Medical Institute, University of California, San Francisco, CA, USA.
| | - Aashish Manglik
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA, USA.
- Biophysics Graduate Program, University of California, San Francisco, CA, USA.
- Department of Anesthesia and Perioperative Care, University of California, San Francisco, CA, USA.
- Chan Zuckerberg Biohub, San Francisco, CA, USA.
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Rocco DA, Paluzzi JPV. Expression Profiling, Downstream Signaling, and Inter-subunit Interactions of GPA2/GPB5 in the Adult Mosquito Aedes aegypti. Front Endocrinol (Lausanne) 2020; 11:158. [PMID: 32296389 PMCID: PMC7137729 DOI: 10.3389/fendo.2020.00158] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Accepted: 03/06/2020] [Indexed: 12/22/2022] Open
Abstract
GPA2/GPB5 and its receptor constitute a glycoprotein hormone-signaling system native to the genomes of most vertebrate and invertebrate organisms. Unlike the well-studied gonadotropins and thyrotropin, the exact function of GPA2/GPB5 remains elusive, and whether it elicits its functions as heterodimers, homodimers or as independent monomers remains unclear. Here, the glycoprotein hormone signaling system was investigated in adult mosquitoes, where GPA2 and GPB5 subunit expression was mapped and modes of its signaling were characterized. In adult Aedes aegypti mosquitoes, GPA2 and GPB5 transcripts co-localized to bilateral pairs of neuroendocrine cells, positioned within the first five abdominal ganglia of the central nervous system. Unlike GPA2/GPB5 homologs in human and fly, GPA2/GPB5 subunits in A. aegypti lacked evidence of heterodimerization. Rather, cross-linking analysis to determine subunit interactions revealed A. aegypti GPA2 and GPB5 subunits may form homodimers, although treatments with independent subunits did not demonstrate receptor activity. Since mosquito GPA2/GPB5 heterodimers were not evident by heterologous expression, a tethered fusion construct was generated for expression of the subunits as a single polypeptide chain to mimic heterodimer formation. Our findings revealed A. aegypti LGR1 elicited constitutive activity with elevated levels of cAMP. However, upon treatment with recombinant tethered GPA2/GPB5, an inhibitory G protein (Gi/o) signaling cascade is initiated and forskolin-induced cAMP production is inhibited. These results further support the notion that heterodimerization is a requirement for glycoprotein hormone receptor activation and provide novel insight to how signaling is achieved for GPA2/GPB5, an evolutionary ancient neurohormone.
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Chen CR, McLachlan SM, Hubbard PA, McNally R, Murali R, Rapoport B. Structure of a Thyrotropin Receptor Monoclonal Antibody Variable Region Provides Insight into Potential Mechanisms for its Inverse Agonist Activity. Thyroid 2018; 28:933-940. [PMID: 29845889 PMCID: PMC6043401 DOI: 10.1089/thy.2018.0176] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
BACKGROUND The high constitutive, or ligand-independent, activity of the thyrotropin receptor (TSHR) is of clinical importance in some thyroid conditions, particularly well-differentiated thyroid carcinoma remnants following incomplete ablative therapy (surgery and radioiodine). Under these conditions, even total suppression of TSH by thyroid hormone administration does not fully reduce TSHR activity, a driver of thyrocyte growth. METHODS CS-17 is a murine monoclonal antibody that has inverse agonist activity in that it suppresses TSHR constitutive activity. This study crystallized the CS-17 Fab and determined its atomic structure at a resolution of 3.4 Å. RESULTS In silico docking of this structure to that of the TSHR extracellular domain was accomplished by targeting to TSHR residue tyrosine 195 (Y195) known to contribute to the CS-17 epitope. High affinity interaction between these two molecules, primarily by the CS-17 immunoglobulin heavy chain, was validated by energetic analysis (KD of 8.7 × 10-11 M), as well as by previously obtained data on a number of individual TSHR amino acids in three regions whose mutagenesis reduced CS-17 binding as detected by flow cytometry. CONCLUSIONS Structural insight at atomic resolution of a TSHR antibody with inverse agonist activity opens the way for the development of a molecule with therapeutic potential, particularly in thyroid carcinoma. For this purpose, CS-17 will require "humanization" by substitution of its constant region (Fc component). In addition, with its epitope defined, the CS-17 affinity can be increased further by mutagenesis of selected amino acids in its heavy- and light-chain complementarity determining regions.
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Affiliation(s)
- Chun-Rong Chen
- Thyroid Autoimmune Disease Unit, Department of Medicine, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California
| | - Sandra M. McLachlan
- Thyroid Autoimmune Disease Unit, Department of Medicine, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California
| | - Paul A. Hubbard
- Department of Biomedical Sciences, Research Division of Immunology, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California
| | - Randall McNally
- Department of Biomedical Sciences, Research Division of Immunology, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California
| | - Ramachandran Murali
- Department of Biomedical Sciences, Research Division of Immunology, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California
| | - Basil Rapoport
- Thyroid Autoimmune Disease Unit, Department of Medicine, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California
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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] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Accepted: 01/14/2016] [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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Van Hiel MB, Vandersmissen HP, Proost P, Vanden Broeck J. Cloning, constitutive activity and expression profiling of two receptors related to relaxin receptors in Drosophila melanogaster. Peptides 2015; 68:83-90. [PMID: 25064813 DOI: 10.1016/j.peptides.2014.07.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 07/04/2014] [Accepted: 07/07/2014] [Indexed: 10/25/2022]
Abstract
Leucine-rich repeat containing G protein-coupled receptors (LGRs) comprise a cluster of transmembrane proteins, characterized by the presence of a large N-terminal extracellular domain. This receptor group can be classified into three subtypes. Belonging to the subtype C LGRs are the mammalian relaxin receptors LGR7 (RXFP1) and LGR8 (RXFP2), which mediate important reproductive and other processes. We identified two related receptors in the genome of the fruit fly and cloned their open reading frames into an expression vector. Interestingly, dLGR3 demonstrated constitutive activity at very low doses of transfected plasmid, whereas dLGR4 did not show any basal activity. Both receptors exhibited a similar expression pattern during development, with relatively high transcript levels during the first larval stage. In addition, both receptors displayed higher expression in male adult flies as compared to female flies. Analysis of the tissue distribution of both receptor transcripts revealed a high expression of dLGR3 in the female fat body, while the expression of dLGR4 peaked in the midgut of both the wandering and adult stage.
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Affiliation(s)
- Matthias B Van Hiel
- Department of Animal Physiology and Neurobiology, Zoological Institute, KU Leuven, Naamsestraat 59, P.O. Box 2465, B-3000 Leuven, Belgium
| | - Hans Peter Vandersmissen
- Department of Animal Physiology and Neurobiology, Zoological Institute, KU Leuven, Naamsestraat 59, P.O. Box 2465, B-3000 Leuven, Belgium
| | - Paul Proost
- Molecular Immunology, Department of Microbiology and Immunology, KU Leuven, Minderbroedersstraat 10, P.O. Box 1030, B-3000 Leuven, Belgium
| | - Jozef Vanden Broeck
- Department of Animal Physiology and Neurobiology, Zoological Institute, KU Leuven, Naamsestraat 59, P.O. Box 2465, B-3000 Leuven, Belgium.
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McLachlan SM, Rapoport B. Thyrotropin-blocking autoantibodies and thyroid-stimulating autoantibodies: potential mechanisms involved in the pendulum swinging from hypothyroidism to hyperthyroidism or vice versa. Thyroid 2013; 23:14-24. [PMID: 23025526 PMCID: PMC3539254 DOI: 10.1089/thy.2012.0374] [Citation(s) in RCA: 127] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
BACKGROUND Thyrotropin receptor (TSHR) antibodies that stimulate the thyroid (TSAb) cause Graves' hyperthyroidism and TSHR antibodies which block thyrotropin action (TBAb) are occasionally responsible for hypothyroidism. Unusual patients switch from TSAb to TBAb (or vice versa) with concomitant thyroid function changes. We have examined case reports to obtain insight into the basis for "switching." SUMMARY TBAb to TSAb switching occurs in patients treated with levothyroxine (LT4); the reverse switch (TBAb to TSAb) occurs after anti-thyroid drug therapy; TSAb/TBAb alterations may occur during pregnancy and are well recognized in transient neonatal thyroid dysfunction. Factors that may impact the shift include: (i) LT4 treatment, usually associated with decreased thyroid autoantibodies, in unusual patients induces or enhances thyroid autoantibody levels; (ii) antithyroid drug treatment decreases thyroid autoantibody levels; (iii) hyperthyroidism can polarize antigen-presenting cells, leading to impaired development of regulatory T cells, thereby compromising control of autoimmunity; (iv) immune-suppression/hemodilution reduces thyroid autoantibodies during pregnancy and rebounds postpartum; (v) maternally transferred IgG transiently impacts thyroid function in neonates until metabolized; (vi) a Graves' disease model involving immunizing TSHR-knockout mice with mouse TSHR-adenovirus and transfer of TSHR antibody-secreting splenocytes to athymic mice demonstrates the TSAb to TBAb shift, paralleling the outcome of maternally transferred "term limited" TSHR antibodies in neonates. Finally, perhaps most important, as illustrated by dilution analyses of patients' sera in vitro, TSHR antibody concentrations and affinities play a critical role in switching TSAb and TBAb functional activities in vivo. CONCLUSIONS Switching between TBAb and TSAb (or vice versa) occurs in unusual patients after LT4 therapy for hypothyroidism or anti-thyroid drug treatment for Graves' disease. These changes involve differences in TSAb versus TBAb concentrations, affinities and/or potencies in individual patients. Thus, anti-thyroid drugs or suppression/hemodilution in pregnancy reduce initially low TSAb levels even further, leading to TBAb dominance. In contrast, TSAb emergence after LT4 administration may be sufficient to counteract TBAb inhibition. The occurrence of "switching" emphasizes the need for careful patient monitoring and management. Finally, whole genome screening of relatively rare "switch" patients and appropriate Graves' and Hashimoto's controls could provide unexpected and valuable information regarding the basis for thyroid autoimmunity.
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Affiliation(s)
- Sandra M McLachlan
- Thyroid Autoimmune Disease Unit, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California 90048, USA.
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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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Mueller S, Jaeschke H, Paschke R. Current standards, variations, and pitfalls for the determination of constitutive TSHR activity in vitro. Methods Enzymol 2010; 485:421-36. [PMID: 21050930 DOI: 10.1016/b978-0-12-381296-4.00023-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Constitutively activating mutations of the TSHR are the major cause for nonautoimmune hyperthyroidism, which is based on ligand independent, permanent receptor activation. Several reports have highlighted the difficulties to determine whether a TSHR mutation is constitutively active or not especially for borderline cases with only a slight increase of the basal cAMP activity. Current methods to precisely classify such mutants as constitutively active or not, are limited. In some cases, in vitro characterization of TSHR mutants has led to false positive conclusions regarding constitutive TSHR activity and subsequently the molecular origin of hyperthyroidism. For characterization of constitutive TSHR activity, a particular point to consider is that basal receptor activity tightly correlates with the receptor number expressed on the cell surface. Therefore, a comparison of the receptors basal activity in relation to the wild type is only possible with determination of the receptor cell surface expression. Thus, the experimental approaches to determine constitutive TSHR activity should consider the receptor's cell surface expression. We here provide a description of three methods for the determination of constitutive TSHR activity: (A) the evaluation of constitutive TSHR activity under conditions of equal receptor expression; (B) computation of the specific constitutive activity; and (C) the linear regression analysis (LRA). To date, LRA is the best experimental approach to characterize the mutant's basal activity as a function of TSHR cell surface expression. This approach utilizes a parallel measurement of basal cAMP values and receptor cell surface expression and therefore provides a more reliable decision with respect to the presence or absence of constitutive activity.
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Affiliation(s)
- Sandra Mueller
- Department for Internal Medicine, Neurology and Dermatology, Clinic for Endocrinology and Nephrology, University of Leipzig, Leipzig, Germany
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Mueller S, Gozu HI, Bircan R, Jaeschke H, Eszlinger M, Lueblinghoff J, Krohn K, Paschke R. Cases of borderline in vitro constitutive thyrotropin receptor activity: how to decide whether a thyrotropin receptor mutation is constitutively active or not? Thyroid 2009; 19:765-73. [PMID: 19583488 DOI: 10.1089/thy.2009.0006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
BACKGROUND Previous in vitro data for several constitutively activating thyrotropin receptor (TSHR) mutations reported divergent results for the constitutive activity of the same mutations. Moreover, several case reports have highlighted the difficulties in determining whether a TSHR mutation is constitutively active or not. Retrospectively, this has repeatedly been the case for mutants with only a slight increase of basal cAMP activity. We re-examined 10 previously described TSHR germline mutations with minor increases of basal cAMP activity and analyzed the influences of the cell line and vector system on the basal receptor activity. METHODS TSHR mutations were characterized by determination of cell surface expression, cAMP accumulation, and linear regression analysis of constitutive activity. RESULTS Re-examination of the previously described constitutively active TSHR germline mutations did not show constitutive activity for R310C and N670S as tested in COS-7 cells and confirmed constitutive activity for the other eight mutations. However, mutant N670S showed a slight but significant increase of basal activity measured by linear regression analysis when analyzed in HEK(GT) cells transiently transfected with pcDNA but not with the pSVL vector. This was not the case for R310C. CONCLUSIONS Our findings indicate that current methods to precisely classify mutants with only a slight increase of the basal activity as constitutively active are limited. The results concerning the level of the basal activity can be influenced by the vector and/or the cell system. A comprehensive clinical characterization of the respective patients appears as a necessary and promising adjunct for the activity classification of these borderline mutations.
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Affiliation(s)
- Sandra Mueller
- Department of Internal Medicine III, University of Leipzig, Leipzig, Germany
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Rivas M, Mellström B, Torres B, Cali G, Ferrara AM, Terracciano D, Zannini M, Morreale de Escobar G, Naranjo JR. The DREAM protein is associated with thyroid enlargement and nodular development. Mol Endocrinol 2009; 23:862-70. [PMID: 19299442 DOI: 10.1210/me.2008-0466] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are involved in the pathophysiology of a wide range of diseases and constitute an attractive therapeutic target. In the thyroid gland, TSH receptor (TSHR), a member of the GPCR family, is a major regulator of thyroid differentiation and function. Alterations in TSHR activity are often involved in the development of pathologies such as thyroid cancer and thyroid enlargement (goiter). Here we show that DREAM (downstream regulatory element antagonist modulator) modulates TSHR activity through a direct protein-protein interaction that promotes coupling between the receptor and Galphas. In transgenic mice, DREAM overexpression provokes a marked enlargement of the thyroid gland. Increased levels of DREAM protein were observed in human multinodular goiters, suggesting a novel etiopathogenic mechanism in nodular development in humans. Taken together, these findings identify a mechanism for the control of TSHR activity and provide a new approach for the study and treatment of thyroid pathologies associated with impaired TSHR function.
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Affiliation(s)
- Marcos Rivas
- Departamento Biología Molecular y Celular, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Cientificas, Madrid, Spain
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Moreno-Reyes R, Tang BNT, Seret A, Goldman S, Daumerie C, Corvilain B. Impaired iodide organification in autonomous thyroid nodules. J Clin Endocrinol Metab 2007; 92:4719-24. [PMID: 17925341 DOI: 10.1210/jc.2007-0833] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
CONTEXT The clinical evolution of autonomous thyroid nodules (ATN) is unpredictable, and thyrotoxicosis is observed at variable nodule size. In vitro data suggest that hydrogen peroxide production is decreased in ATN, indicating intranodular iodide organification impairment. OBJECTIVE We aimed to determine iodide organification efficiency in ATN and its relationship with thyroid status in patients. DESIGN Forty-six patients with a single ATN on the 123I thyroid scan were included in the study. Biological evaluation and iodine perchlorate (I-ClO4) discharge test were carried out in all subjects. SETTING The study took place at an academic hospital. RESULTS Among the 46 patients, 28 patients (61%) had a positive I-ClO4 discharge test with a mean +/- sd value of discharge of 42 +/- 13%, and 18 (39%) had a negative discharge test with mean +/- sd of 5 +/- 9%. In the group of patients with a negative discharge test but not in the group with a positive test, serum-free T3 and free T4 concentrations were significantly correlated with the 123I uptake. The severity of hyperthyroidism was not different between both groups. CONCLUSIONS Intranodular iodide organification was impaired in most patients with ATN. Whether differences in organification capability could predict the risk for evolution to overt hyperthyroidism in patients with ATN remains to be established.
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Affiliation(s)
- Rodrigo Moreno-Reyes
- Department of Nuclear Medicine, Hopital Erasme, Université Libre de Bruxelles, route de Lennik 808, 1070 Brussels, Belgium.
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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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Grasberger H, Van Sande J, Hag-Dahood Mahameed A, Tenenbaum-Rakover Y, Refetoff S. A familial thyrotropin (TSH) receptor mutation provides in vivo evidence that the inositol phosphates/Ca2+ cascade mediates TSH action on thyroid hormone synthesis. J Clin Endocrinol Metab 2007; 92:2816-20. [PMID: 17456567 DOI: 10.1210/jc.2007-0366] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT In the human thyroid gland, TSH activates both the cAMP and inositol phosphates (IP) signaling cascades via binding to the TSH receptor (TSHR). Biallelic TSHR loss-of-function mutations cause resistance to TSH, clinically characterized by hyperthyrotropinemia, and normal or reduced thyroid gland volume, thyroid hormone output, and iodine uptake. OBJECTIVE We report and study a novel familial TSHR mutation (L653V). RESULTS Homozygous individuals expressing L653V had euthyroid hyperthyrotropinemia. Paradoxically, patients had significantly higher 2-h radioiodide uptake and 2- to 24-h radioiodide uptake ratios compared with heterozygous, unaffected family members, suggesting an imbalance between iodide trapping and organification. In transfected COS-7 cells, the mutant TSHR had normal surface expression, basal activity, and TSH-binding affinity, equally (2.2-fold) increased EC50 values for TSH-induced cAMP and IP accumulation, and normal maximum cAMP generation. In contrast, the efficacy of TSH for generating IP was more than 7-fold lower with the mutant compared with wild-type TSHR. CONCLUSIONS We identified and characterized a TSHR defect, preferentially affecting the IP pathway, with a phenotype distinct from previously reported loss-of-function mutations. Results provide the first in vivo evidence for the physiological role of the TSHR/IP/Ca2+ cascade in regulating iodination. According to systematic in vitro mutagenesis studies, other TSHR mutations can result in even complete loss of IP signaling with retained cAMP induction. We hypothesize that such TSHR mutations could be the cause in unexplained partial organification defects.
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Affiliation(s)
- Helmut Grasberger
- Departments of Medicine, The University of Chicago, Chicago, Illinois 60637, USA.
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Chen CR, McLachlan SM, Rapoport B. Suppression of thyrotropin receptor constitutive activity by a monoclonal antibody with inverse agonist activity. Endocrinology 2007; 148:2375-82. [PMID: 17272389 DOI: 10.1210/en.2006-1754] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
TSH binding to the TSH receptor (TSHR) induces thyrocyte growth and proliferation primarily by activating the adenylyl cyclase signaling pathway. Relative to the other glycoprotein hormone receptors, the TSHR has considerable ligand-independent (constitutive) activity. We describe a TSHR monoclonal antibody (CS-17) with the previously unrecognized property of being an inverse agonist for TSHR constitutive activity. This property is retained, even when constitutive activity is extremely high consequent to diverse TSHR extracellular region mutations. A similar effect on an activating mutation at the base of the sixth transmembrane helix (not accessible to direct CS-17 contact) indicates that CS-17 is acting allosterically. Administered to mice in vivo, CS-17 reduces serum T(4) levels. The CS-17 epitope is conformational and a significant portion lies in the C-terminal region of the TSHR leucine-rich domain (residues 260-289). By interacting with the large TSHR extracellular domain, CS-17 is, to our knowledge, the first antibody reported to be an inverse agonist for a member of the G protein receptor superfamily. After humanization of its murine constant region, CS-17 has the potential to be an adjunctive therapeutic agent in athyreotic patients with residual well-differentiated thyroid carcinoma as well as pending definitive treatment in some selected hyperthyroidism states.
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Affiliation(s)
- Chun-Rong Chen
- Cedars-Sinai Research Institute, University of California, Los Angeles, California 90048, USA
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15
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Niepomniszcze H, Suárez H, Pitoia F, Pignatta A, Danilowicz K, Manavela M, Elsner B, Bruno OD. Follicular carcinoma presenting as autonomous functioning thyroid nodule and containing an activating mutation of the TSH receptor (T620I) and a mutation of the Ki-RAS (G12C) genes. Thyroid 2006; 16:497-503. [PMID: 16756473 DOI: 10.1089/thy.2006.16.497] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Most autonomous functioning thyroid nodules (AFTN) are benign thyroid follicular neoplasms. There are rare reports of malignant hot nodules, in which activating mutations of the TSH receptor (TSHR) were found. We report a case of follicular carcinoma presenting as an AFTN causing subclinical hyperthyroidism in a 64-year-old woman who had a 6-cm hot nodule in the left thyroid lobe. Genomic DNA was extracted from paraffin-embedded tissues from the tumor and extratumoral thyroid tissue. Sequence analyses revealed point mutations in two different genes: the normal ACC sequence at codon 620 of the TSHR gene was replaced by ATC, changing the threonine by isoleucine (T620I); and the wild-type GGT at codon 12 of Ki-RAS mutated to TGT, replacing glycine by cysteine (G12C). In transfection experiments the T620I mutant showed constitutive activity in terms of cyclic adenosine monophosphate (cAMP) production when permanently transfected in 3T3 cells. Here, we describe for the first time an activating mutation in 3codon 620 of the TSHR. In addition, the cancerous AFTN also contained a G12C Ki-RAS mutation. We hypothesize that the combination of these two mutations might have played an important role in both the hyperfunction of the tumor and the carcinogenetic process.
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Affiliation(s)
- Hugo Niepomniszcze
- Division of Endocrinology, Hospital de Clínicas, University of Buenos Aires, Buenos Aires, Argentina.
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16
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Raggo C, Ruhl R, McAllister S, Koon H, Dezube BJ, Früh K, Moses AV. Novel cellular genes essential for transformation of endothelial cells by Kaposi's sarcoma-associated herpesvirus. Cancer Res 2005; 65:5084-95. [PMID: 15958552 DOI: 10.1158/0008-5472.can-04-2822] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV) is involved in the development of lymphoproliferative diseases and Kaposi's sarcoma. The oncogenicity of this virus is reflected in vitro by its ability to transform B cells and endothelial cells. Infection of dermal microvascular endothelial cells (DMVEC) transforms the cells from a cobblestone-like monolayer to foci-forming spindle cells. This transformation is accompanied by dramatic changes in the cellular transcriptome. Known oncogenes, such as c-Kit, are among the KSHV-induced host genes. We previously showed that c-Kit is an essential cellular component of the KSHV-mediated transformation of DMVEC. Here, we test the hypothesis that the transformation process can be used to discover novel oncogenes. When expression of a panel of KSHV-induced cellular transcripts was inhibited with antisense oligomers, we observed inhibition of DMVEC proliferation and foci formation using antisense molecules to RDC1 and Neuritin. We further showed that transformation of KSHV-infected DMVEC was inhibited by small interfering RNA directed at RDC1 or Neuritin. Ectopic expression of Neuritin in NIH 3T3 cells resulted in changes in cell morphology and anchorage-independent growth, whereas RDC1 ectopic expression significantly increased cell proliferation. In addition, both RDC1- and Neuritin-expressing cells formed tumors in nude mice. RDC1 is an orphan G protein-coupled receptor, whereas Neuritin is a growth-promoting protein known to mediate neurite outgrowth. Neither gene has been previously implicated in tumorigenesis. Our data suggest that KSHV-mediated transformation involves exploitation of the hitherto unrealized oncogenic properties of RDC1 and Neuritin.
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MESH Headings
- Adaptor Proteins, Signal Transducing
- Animals
- Cell Transformation, Viral/genetics
- DNA-Binding Proteins/biosynthesis
- DNA-Binding Proteins/genetics
- Endothelial Cells/cytology
- Endothelial Cells/virology
- GPI-Linked Proteins
- Gene Expression Profiling
- Herpesvirus 8, Human/genetics
- Herpesvirus 8, Human/physiology
- Humans
- LIM Domain Proteins
- Metalloproteins/biosynthesis
- Metalloproteins/genetics
- Mice
- Mice, Nude
- NIH 3T3 Cells
- Neuropeptides/biosynthesis
- Neuropeptides/genetics
- Oligonucleotide Array Sequence Analysis
- Oligonucleotides, Antisense/genetics
- Oncogenes/physiology
- Osteopontin
- Proto-Oncogene Proteins
- RNA, Small Interfering/genetics
- Receptors, CXCR
- Receptors, Chemokine/biosynthesis
- Receptors, Chemokine/genetics
- Receptors, G-Protein-Coupled/biosynthesis
- Receptors, G-Protein-Coupled/genetics
- Sarcoma, Kaposi/genetics
- Sarcoma, Kaposi/virology
- Sialoglycoproteins/biosynthesis
- Sialoglycoproteins/genetics
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Affiliation(s)
- Camilo Raggo
- Vaccine and Gene Therapy Institute, Oregon Health and Science University, Beaverton, Oregon, USA
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17
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Abstract
A recent report of major pathophysiological significance, and opposed to present concepts, is that TSH (but not MS-1, a hamster monoclonal thyroid-stimulating antibody), cleaves the single-chain TSH receptor (TSHR) on the cell surface into its two-subunit form. We reassessed the issue using two approaches. First we wished to confirm the flow-cytometric assay previously used to quantitate TSHR cleavage. We used CHO cell lines expressing large (TSHR-10,000 cells) or conventional (TSHR-0 cells) numbers of TSHR. Cells were preincubated (16 h) in either control medium or medium supplemented with TSH (5 x 10(-8) m) or MS-1 (10 microg/ml). After stringent washing to maximize removal of residual ligand, we performed flow cytometry with two antibodies, one recognizing only the single-chain TSHR, the other recognizing all (cleaved and uncleaved) TSHRs. TSH pretreatment did not appear to increase TSHR cleavage. Instead we observed ligand occupancy of the TSHR (with MS-1) or fewer receptors on the cell surface (down-regulation), particularly with the TSHR-0 cells. Second, we covalently cross-linked [125I]TSH to monolayers of these cells, an unequivocal method to determine directly the proportion of single-chain and two-subunit TSHR forms. Pretreatment of TSHR-10,000 and TSHR-0 cells with TSH had no effect on the degree of TSHR cleavage. MS-1 slightly reduced spontaneous cleavage. In conclusion, in contrast to a recent report, we show that TSH does not alter the subunit structure of its cognate receptor, and we provide insight into the difficulties associated with the flow-cytometric assay for TSHR cleavage.
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Affiliation(s)
- Gregorio D Chazenbalk
- Autoimmune Disease Unit, Cedars-Sinai Research Institute and School of Medicine, University of California, Los Angeles, California 90048, USA
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18
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Chen CR, Chazenbalk GD, McLachlan SM, Rapoport B. Evidence that the C terminus of the A subunit suppresses thyrotropin receptor constitutive activity. Endocrinology 2003; 144:3821-7. [PMID: 12933653 DOI: 10.1210/en.2003-0430] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The TSH receptor (TSHR), unlike the LH receptor (LHR), has considerable ligand-independent adenylyl cyclase activity, a feature of pathophysiological importance. The TSHR ectodomain partially suppresses constitutive activity, an effect reversed by trypsin treatment of intact cells. Localizing the functional site of trypsin action would provide insight into how the TSHR ectodomain exerts its constraint. For this purpose, we examined the effect of trypsin on intact cells expressing a series of modified TSHR. Trypsin did not increase cAMP production by a chimeric TSH-LH receptor involving substitution of TSHR residues 261-418 (the ectodomain C terminus). In contrast, with the wild-type TSHR, trypsin enhanced constitutive activity despite mutation of the following potential tryptic cleavage sites [arginine (R) and lysine (K) residues]: 1) K565, K651, K660 in the extracellular loops of the serpentine region; 2) B subunit juxtamembrane residues K371, K401, K415; 3) A subunit residues R310, R312, K313. We previously excluded K337 and K339 from being implicated in TSHR tryptic activation. By exclusion, only one R/K cluster remains as a possible target for the functional effect of trypsin, namely K287, K290, K291, and R293. Mutation of this cluster is incompatible with TSHR cell surface expression. However, tryptic clipping at this locus would reproduce a previously demonstrated structural effect of trypsin on the TSHR, removal of about a 2-kDa polypeptide fragment extending downstream from the locus to the C terminus of the A subunit. Taken together, these data suggest that the C terminus of the A subunit functions as a suppressor of TSHR constitutive activity.
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Affiliation(s)
- Chun-Rong Chen
- Autoimmune Disease Unit, Cedars-Sinai Research Institute and School of Medicine, University of California, Los Angeles, California 90048, USA
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19
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Vandeput F, Perpete S, Coulonval K, Lamy F, Dumont JE. Role of the different mitogen-activated protein kinase subfamilies in the stimulation of dog and human thyroid epithelial cell proliferation by cyclic adenosine 5'-monophosphate and growth factors. Endocrinology 2003; 144:1341-9. [PMID: 12639917 DOI: 10.1210/en.2001-211316] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We have investigated the role of the different classes of MAPKs, i.e. ERKs, c-Jun N-terminal kinases (JNKs), and p38 MAPK in the proliferation of dog and human thyroid epithelial cells (thyrocytes) in primary cultures. In these cells, TSH, acting through cAMP, epidermal growth factor, hepatocyte growth factor (HGF), and phorbol 12-myristate 13-acetate induce DNA synthesis. With the exception of HGF, all of these factors require the presence of insulin for mitogenic effects to be expressed. We found that TSH and forskolin are without effect on the phosphorylation and activity of the different classes of MAPKs. In contrast, all the cAMP-independent growth factors, whereas without effect on the phosphorylation and activity of JNKs and p38 MAPK, stimulated the ERKs. This effect was strong and sustained in response to HGF, epidermal growth factor and 12-myristate 13-acetate but weak and transient in response to insulin. Moreover, whereas in stimulated cells DNA synthesis was inhibited by PD 098059, an inhibitor of MAPK kinase 1 and consequently of ERKs, it was not modified by SB 203580, an inhibitor of p38 MAPK. Taken together, these data 1) exclude a role of JNKs and p38 MAPK in the proliferation of dog and human thyrocytes; 2) suggest that the mitogenic action of the cAMP-independent agents requires a strong and sustained activation of both ERKs and phosphatidylinositol 3-kinase/protein kinase B as realized by HGF alone or by the other agents together with insulin; and 3) show that TSH and cAMP do not activate ERKs but that the weak activation of ERKs by insulin is nevertheless necessary for DNA synthesis to occur.
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Affiliation(s)
- Fabrice Vandeput
- Institute of Interdisciplinary Research, Université Libre de Bruxelles, Campus Erasme, B-1070 Brussels, Belgium.
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20
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Niedernberg A, Blaukat A, Schöneberg T, Kostenis E. Regulated and constitutive activation of specific signalling pathways by the human S1P5 receptor. Br J Pharmacol 2003; 138:481-93. [PMID: 12569073 PMCID: PMC1573682 DOI: 10.1038/sj.bjp.0705055] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1 We tested the hypothesis, whether G Protein-coupled receptors (GPCRs) may differentially regulate specific signalling pathways by constitutive and agonist-induced activation using the human sphingosine 1-phosphate receptor S1P(5) as a model. 2 S1P(5) receptor-expressing HEK293 cells exhibited a high degree of basal activity for both inhibition of adenylyl cyclase and extracellular signal regulated kinase (ERK) when cultured in serum, which contains high levels of sphingosine 1-phosphate (S1P). However, basal activity was independent of the presence of S1P: (i) constitutive activity remained when cells were cultured in delipidated serum, (ii) addition of S1P to delipidated serum did not increase basal S1P(5) receptor signalling. 3 Conversely, constitutive inhibition of forskolin-stimulated adenylyl cyclase was further enhanced by S1P in S1P(5)-HEK293 cells. 4 Transfection of several mammalian cell lines (CHO-K1, HEK293, NIH-3T3, RH7777) with the S1P(5) receptor induced cell rounding, which was more pronounced in the presence of S1P-containing serum. Rounded cell morphology did not correlate with apoptotic cell death, but led to detachment of cells. 5 Cell surface ELISA assays showed that a fraction of plasma membrane S1P(5) receptors were dose-dependently internalized with S1P. 6 These data reveal that intrinsic inhibition of unstimulated adenylyl cyclase or ERK activity by the S1P(5) receptor is insensitive to ligand modulation. Conversely, effects on forskolin-stimulated adenylyl cyclase, cell morphology and internalization can be further augmented with S1P. Our results suggest that different signal transduction pathways are not equally activated through constitutively active GPCRs with promiscuous signalling characteristics.
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Affiliation(s)
- Anke Niedernberg
- Disease group Cardiovascular Diseases, Aventis Pharma, Building H825, 65926 Frankfurt, Germany
| | - Andree Blaukat
- Pharmakologisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany
| | - Torsten Schöneberg
- Institut für Pharmakologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, Thielallee 69-73, 14195 Berlin, Germany
| | - Evi Kostenis
- Disease group Cardiovascular Diseases, Aventis Pharma, Building H825, 65926 Frankfurt, Germany
- Author for correspondence:
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21
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Claeysen S, Govaerts C, Lefort A, Van Sande J, Costagliola S, Pardo L, Vassart G. A conserved Asn in TM7 of the thyrotropin receptor is a common requirement for activation by both mutations and its natural agonist. FEBS Lett 2002; 517:195-200. [PMID: 12062436 DOI: 10.1016/s0014-5793(02)02620-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The wide spectrum of naturally occurring mutations able to activate the thyrotropin (TSH) receptor provides a useful tool to approach the structure of the active state(s) of the glycoprotein hormone receptors. Here we show that the side-chain of the highly conserved N7.49 (Asn 674) in TM7 is mandatory for activation of the TSH receptor, not only by TSH, but also by a panel of eight natural and two artificial activating mutations. Basal activity levels of the mutants were significantly decreased by suppression of the side-chain of N7.49 (N7.49A double mutants). In addition, comparative effects of the N7.49A substitution on the ten mutants demonstrate that basal activity and agonist- or mutation-stimulated activity might involve different structural changes.
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Affiliation(s)
- Sylvie Claeysen
- IRIBHN, Université Libre de Bruxelles, Campus Erasme, 808 route de Lennik, B-1070, Brussels, Belgium
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22
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Ford DJ, Essex A, Spalding TA, Burstein ES, Ellis J. Homologous mutations near the junction of the sixth transmembrane domain and the third extracellular loop lead to constitutive activity and enhanced agonist affinity at all muscarinic receptor subtypes. J Pharmacol Exp Ther 2002; 300:810-7. [PMID: 11861785 DOI: 10.1124/jpet.300.3.810] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previous studies have found that a mutation near the junction of the sixth transmembrane domain (TM6) and the third extracellular loop of the M5 muscarinic receptor leads to constitutive activation and enhanced agonist affinity for the mutated receptor. These results were consistent with the extended ternary complex model, which predicts a correlation between agonist affinity and constitutive activity. We have introduced the homologous mutation into all five subtypes of the highly conserved muscarinic receptor family; SerThr-->TyrPro was introduced into M1 and M5, and AsnThr-->TyrPro was introduced into M2, M3, and M4. In binding assays, these mutations produced increases in affinities toward acetylcholine and carbachol that ranged from 5-fold at the M2 receptor to 15- to 20-fold at M1, M3, and M4, to 40-fold at M5. In functional assays, all five mutant receptors exhibited constitutive activity, at levels ranging between 30 and 80% of the maximal response elicited by carbachol. In every case, the muscarinic antagonist atropine inhibited this constitutive activity with high affinity. Thus, despite differences in effector coupling and in wild-type sequence at the mutation site, all five subtypes were activated by this mutation at the top of TM6. Previous studies of the M5 subtype have indicated that TM6 is a ligand-dependent switch that sets the activation state of the receptor. Based on the results of the present study, it is possible that TM6 represents a general switch for the activation of the muscarinic receptor family.
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Affiliation(s)
- Diane J Ford
- Department of Pharmacology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA
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23
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Govaerts C, Lefort A, Costagliola S, Wodak SJ, Ballesteros JA, Van Sande J, Pardo L, Vassart G. A conserved Asn in transmembrane helix 7 is an on/off switch in the activation of the thyrotropin receptor. J Biol Chem 2001; 276:22991-9. [PMID: 11312274 DOI: 10.1074/jbc.m102244200] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The thyrotropin (TSH) receptor is an interesting model to study G protein-coupled receptor activation as many point mutations can significantly increase its basal activity. Here, we identified a molecular interaction between Asp(633) in transmembrane helix 6 (TM6) and Asn(674) in TM7 of the TSHr that is crucial to maintain the inactive state through conformational constraint of the Asn. We show that these residues are perfectly conserved in the glycohormone receptor family, except in one case, where they are exchanged, suggesting a direct interaction. Molecular modeling of the TSHr, based on the high resolution structure of rhodopsin, strongly favors this hypothesis. Our approach combining site-directed mutagenesis with molecular modeling shows that mutations disrupting this interaction, like the D633A mutation in TM6, lead to high constitutive activation. The strongly activating N674D (TM7) mutation, which in our modeling breaks the TM6-TM7 link, is reverted to wild type-like behavior by an additional D633N mutation (TM6), which would restore this link. Moreover, we show that the Asn of TM7 (conserved in most G protein-coupled receptors) is mandatory for ligand-induced cAMP accumulation, suggesting an active role of this residue in activation. In the TSHr, the conformation of this Asn residue of TM7 would be constrained, in the inactive state, by its Asp partner in TM6.
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Affiliation(s)
- C Govaerts
- Institut de Recherche Interdisciplinaire en Biologie Humaine et Nucléaire, Université Libre de Bruxelles, Campus Erasme, 808 route de Lennik, B-1070 Bruxelles, Belgium.
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24
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Ericson LE, Nilsson M. Deactivation of TSH receptor signaling in filter-cultured pig thyroid epithelial cells. Am J Physiol Endocrinol Metab 2000; 278:E611-9. [PMID: 10751193 DOI: 10.1152/ajpendo.2000.278.4.e611] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Thyrotropin [thyroid-stimulating hormone (TSH)] receptor on-off signaling was studied in polarized monolayers of pig thyrocytes cultured on permeable support. Transepithelial resistance (R) and potential difference (PD) were used as parameters to monitor the effect of altered TSH concentrations on vectorial electrolyte transport. TSH induced rapid but long-lasting changes in R (decrease) and PD (increase) that were cAMP-dependent and related to enhanced transcellular conductance of sodium and chloride. Withdrawal of TSH from cultures prestimulated with TSH (0.1 mU/ml) for 48 h resulted in restitution of R to control level within 30 min. Such deactivation was markedly accelerated by mild trypsinization, which degraded receptor-bound ligand without affecting TSH receptor responsiveness or ion transporting capacity. Small alterations in the TSH concentration (0.01-0.1 mU/ml) were followed almost instantaneously by adjustments of R. In contrast, the reversal of R after acute TSH stimulation (30 min) and subsequent TSH washout was delayed for several hours independently of cell surface trypsinization. The observations indicate that, during continuous exposure to physiological concentrations, TSH exerts a close minute-to-minute surveillance of thyroid function and the rate-limiting step of deactivation is the dissociation of ligand from the TSH receptor at the cell surface. TSH-deprived cells briefly exposed to TSH are refractory to rapid deactivation, probably because of altered metabolism downstream of TSH receptor signal transduction.
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Affiliation(s)
- L E Ericson
- Institute of Anatomy and Cell Biology, Göteborg University, SE 405 30 Goteborg, Sweden.
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25
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Park HJ, Kim JY, Park KY, Gong G, Hong SJ, Ahn IM. Expressions of human sodium iodide symporter mRNA in primary and metastatic papillary thyroid carcinomas. Thyroid 2000; 10:211-7. [PMID: 10779135 DOI: 10.1089/thy.2000.10.211] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The sodium iodide symporter (NIS) is a plasma membrane protein that is responsible for iodide transport into thyroid cells. To understand the regulation and expression of human NIS (hNIS) in papillary thyroid carcinomas, we evaluated the expression levels of hNIS mRNA in primary and lymph node metastatic papillary carcinoma tissues. The correlation of mRNA levels between hNIS and thyroid-specific genes, thyrotropin (TSH) receptor, and thyroglobulin (Tg), were also investigated. Twenty-three cases of papillary carcinoma and 7 pairs of primary and lymph node metastastic tissues were included in this study. We measured the expression levels of hNIS, TSH receptor, and Tg mRNAs by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and RNase protection assay (RPA). The levels of hNIS mRNA in lymph node metastatic tissues were evaluated by RT-PCR. By semiquantitative RT-PCR, 87% of papillary carcinoma (20/23) expressed hNIS mRNA, but the degrees of expression were variable and were lower than those of normal thyroid tissues. The decreased expression of hNIS mRNA in papillary carcinoma compared to normal thyroid tissue was also noticed by RPA. All 23 papillary carcinomas in this study showed the expression of TSH receptor and Tg mRNAs. The levels of TSH receptor mRNA were again lower in papillary thyroid carcinomas than in normal controls. The level of hNIS mRNA was correlated with the levels of TSH receptor (r = 0.449, p < 0.05), but not with Tg mRNA. In addition, significant correlation of mRNA level was observed between TSH receptor and Tg (r = 0.706, p < 0.01). Two of six lymph node metastatic tissues did not show hNIS mRNA even with significant hNIS expressions in papillary carcinoma tissues in thyroid. The levels of hNIS expression of the remaining four lymph node metastatic tissues were lower than those of corresponding primary tissues. Interestingly, one case showed no hNIS expression in primary tissue, but significant hNIS expression in lymph node metastatic tissue. No correlation was found in hNIS mRNA expression between primary and lymph node metastatic tissues. Our results suggest that the measurements of hNIS mRNA level in primary tissues may not predict the therapeutic response to radioactive iodine.
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Affiliation(s)
- H J Park
- Division of Molecular Genetics, Asan Institute for Life Sciences and Technology, Seoul, Korea
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26
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Chen G, Jayawickreme C, Way J, Armour S, Queen K, Watson C, Ignar D, Chen WJ, Kenakin T. Constitutive receptor systems for drug discovery. J Pharmacol Toxicol Methods 1999; 42:199-206. [PMID: 11033435 DOI: 10.1016/s1056-8719(00)00075-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This paper discusses the use of constitutively active G-protein-coupled receptor systems for drug discovery. Specifically, the ternary complex model is used to define the two major theoretical advantages of constitutive receptor screening-namely, the ability to detect antagonists as well as agonists directly and the fact that constitutive systems are more sensitive to agonists. In experimental studies, transient transfection of Chinese hamster ovary cyclic AMP response element (CRE) luciferase reporter cells with cDNA for human parathyroid hormone receptor, glucagon receptor, and glucagon-like peptide (GLP-1) receptor showed cDNA concentration-dependent constitutive activity with parathyroid hormone (PTH-1) and glucagon. In contrast, no constitutive activity was observed for GLP-1 receptor, yet responses to GLP-1 indicated that receptor expression had taken place. In another functional system, Xenopus laevi melanophores transfected with cDNA for human calcitonin receptor showed constitutive activity. Nine ligands for the calcitonin receptor either increased or decreased constitutive activity in this assay. The sensitivity of the system to human calcitonin increased with increasing constitutive activity. These data indicate that, for those receptors which naturally produce constitutive activity, screening in this mode could be advantageous over other methods.
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Affiliation(s)
- G Chen
- Department of Receptor Biochemistry, Glaxo Wellcome Research and Development, 5 Moore Drive, Research Triangle Park, NC 27709, USA
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27
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Abstract
The proposed mechanisms of RTH are not mutually exclusive. In fact, there is considerable experimental evidence that many if not all of these complex receptor interactions with elements of the transcriptional unit are involved in RTH. Several aspects of RTH remain unclear, in particular on a clinical level. We still do not completely understand the seeming paradox of a tight distribution of receptor mutations and wide variability in phenotypic presentation. The discovery that many of the RTH receptors have defects in corepressor interaction makes it tempting to speculate that the variability in RTH phenotype within kindreds is secondary to differences in corepressor expression. These issues may be better understood as research further proceeds into cofactors and their control of transcription. We also need better tools to determine thyroid status at a peripheral level. Basal metabolic rate, serum measurement of thyroid-responsive gene products, echocardiographic techniques, and other clinical measures have for the most part been unhelpful in determining thyroid status of specific organ systems. Consequently, therapeutic interventions for RTH are directed toward normalizing biochemical indices of thyroid homeostasis, without really knowing whether these efforts correct imbalances within crucial tissues. These studies, and the more widespread investigation of hormone receptor action in general, are moving at a breathtaking pace, and there is a keen interest in applying these principals to understanding the pathophysiologic mechanism of a variety of diseases.
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Affiliation(s)
- D L Bodenner
- Department of Internal Medicine, Division of Endocrinology and Metabolism, Little Rock, Arkansas 72205, USA
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Rapoport B, Chazenbalk GD, Jaume JC, McLachlan SM. The thyrotropin (TSH) receptor: interaction with TSH and autoantibodies. Endocr Rev 1998; 19:673-716. [PMID: 9861544 DOI: 10.1210/edrv.19.6.0352] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- B Rapoport
- Autoimmune Disease Unit, Cedars-Sinai Medical Center, Los Angeles, California 90048, USA
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29
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Levine MA, Ringel MD. Resistance to TSH in patients with normal TSH receptors--where do we turn when "Sutton's law" proves false? J Clin Endocrinol Metab 1997; 82:3930-2. [PMID: 9398690 DOI: 10.1210/jcem.82.12.4526] [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: 02/05/2023]
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Schaaf L, Leiprecht A, Saji M, Hübner U, Usadel KH, Kohn LD. Glycosylation variants of human TSH selectively activate signal transduction pathways. Mol Cell Endocrinol 1997; 132:185-94. [PMID: 9324060 DOI: 10.1016/s0303-7207(97)00136-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The oligosaccharide chains of pituitary glycoprotein hormones such as human thyroid-stimulating hormone (hTSH) have been shown to be important in biosynthesis, subunit association, secretion and bioactivity. However, the exact biological significance of these glycosylation variants (isoforms) remains controversial. The aim of this paper is to investigate the role of hTSH glycosylation variants in signal transduction. Human pituitary standard TSH (2nd International Reference Preparation 80/558; IRP-hTSH) was treated with neuraminidase, fractionated by isoelectric focusing (IEF) and affinity chromatography using the lectins concanavalin A (Con A) and lentil. To determine the in vitro bioactivity of these hTSH isoforms, simultaneous measurement of cAMP formation and inositol phosphates release was applied in two different cell systems (CHO cells stably and Cos-7 cells transiently transfected with hTSHR cDNA). Desialylated TSH variants showed a significantly increased ratio of bioactivity to immunoreactivity for cAMP production in CHO-R cells (B/I ratio desialylated variants: 3.54 +/- 0.005; B/I ratio sialylated variants: 2.84 +/- 0.01 P < 0.05). Testing the bioactivity of hTSH glycosylation variants isolated by IEF, we found basic variants to be significantly more active than acidic ones in stimulating the cAMP formation in CHO-R cells (B/I ratio basic variants: 9.92 +/- 0.64; neutral variants: 5.98 +/- 0.07; acidic variants: 2.80 +/- 0.12; P < 0.01). There were no differences in stimulation of IP-release. High-mannose TSH variants (firmly bound to Con A) showed greater potency to stimulate cAMP formation and IP-release in both CHO-R and Cos-7 cells than biantennary TSH variants (weakly bound to Con A). Both core-fucosylated (lentil-bound) and core-unfucosylated (lentil-unbound) TSH variants proved to be strong stimulators of cAMP release in CHO and Cos-7 cells. In CHO-R (Cos-7) cells, 400 microU/ml core-fucosylated TSH stimulated cAMP formation 14(2.6)-fold, core-unfucosylated TSH 7.3(2.3)-fold over control values. In contrast to our findings of cAMP activation by both core-fucosylated and core-unfucosylated TSH variants, release of IPs was stimulated only by, core-fucosylated (lentil-bound) TSH variants and not by TSH variants lacking core-fucose residues (lentil-unbound TSH). This was true for both CHO-R and Cos-7 cells. The lentil-unbound TSH therefore showed an identical differential activation of signal transduction pathways in two different cell systems: strong stimulation of the cAMP-cascade without activation of IPs release (P < 0.05). In conclusion, we showed for the first time for TSH that the two dominant intracellular signal transduction systems (cAMP formation and IPs release) are activated to different degrees by hTSH glycosylation variants.
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Affiliation(s)
- L Schaaf
- Max-Planck-Institute of Psychiatry, Clinical Institute, Department of Neuroendocrinology, Munich, Germany
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31
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Van Rampelbergh J, Poloczek P, Françoys I, Delporte C, Winand J, Robberecht P, Waelbroeck M. The pituitary adenylate cyclase activating polypeptide (PACAP I) and VIP (PACAP II VIP1) receptors stimulate inositol phosphate synthesis in transfected CHO cells through interaction with different G proteins. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1357:249-55. [PMID: 9223629 DOI: 10.1016/s0167-4889(97)00028-1] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The PACAP receptor (PACAP I receptor, selective for PACAP) and the PACAP II VIP1 receptor (recognizing PACAP and VIP with the same high affinity) were stably expressed in Chinese Hamster Ovary (CHO) cells. Cell lines expressing different receptor densities, as measured by binding saturation curves, were selected. Inositol phosphate production was stimulated dose dependently in all the cell lines by PACAP and VIP, and the order of potency of the agonists was identical to that of high affinity receptor occupancy. The stimulatory effect of a saturating peptide concentration was proportional to the total receptor density. At similar receptor densities, however, the PACAP receptor mediated stimulation was higher than the VIP receptor-mediated stimulation. Pretreatment of the cells with pertussis toxin for 8 h had no effect on receptor densities, did not alter the PACAP stimulated inositol phosphate synthesis by the cells expressing the PACAP I receptor but markedly inhibited the response of the cells expressing the PACAP II VIP1 receptor. Thus, the present results indicate that the two G(s)-coupled PACAP I and PACAP II VIP1 receptors may stimulate IP production. The maximal stimulation depended on the number of receptor expressed; the PACAP I and PACAP II VIP1 receptors probably activated the phospholipase C through G proteins of the G(q), and of the G(i)/G(o) families, respectively.
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Affiliation(s)
- J Van Rampelbergh
- Department of Biochemistry and Nutrition, School of Medicine, Université Libre de Bruxelles, Brussels, Belgium
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Allgeier A, Laugwitz KL, Van Sande J, Schultz G, Dumont JE. Multiple G-protein coupling of the dog thyrotropin receptor. Mol Cell Endocrinol 1997; 127:81-90. [PMID: 9099903 DOI: 10.1016/s0303-7207(96)03996-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We investigated, in dog thyroid membranes, the ability of the dog thyrotropin (TSH) receptor to interact with the endogenous G proteins expressed in this tissue. Activation of the receptor led to increased incorporation of the photoreactive GTP analog [alpha-(32)P]GTP azidoanilide into immunoprecipitated alpha subunits of three G protein families: G(s), G(q/11), G(i/o). This effect was not due to a general loss of receptor G protein specificity since carbamylcholine, in the same membrane preparations, only stimulated the binding of the GTP analog to the alpha subunits of G(q/11) proteins. To investigate the multiple coupling of the dog TSH receptor in intact cells, cyclic AMP accumulation, IP(3) formation and (45)Ca2+ efflux experiments were performed. When thyrocytes were pretreated with pertussis toxin (PTX), the TSH receptor-mediated accumulation of cAMP increased by approximately 45% with TSH at 1 mU/ml, suggesting that the TSH receptor coupled to both G(s) and G(i) in vivo. On the other hand, no increase in IP(3) accumulation nor Ca2+ efflux was observed in the presence of thyrotropin. These data in intact cells are thus in contradiction with those obtained in membranes, suggesting that receptor-mediated transmembrane signalling may implicate a specificity which itself may reflect a localization and organization of the different components (receptors, G proteins, ...) in the plasma membrane of intact cells. As in some cells, G(i) activates mitogenesis by hormone activated G-protein-coupled receptors, we tested its role in the stimulation by TSH of the proliferation of thyrocytes. This was not affected by PTX, suggesting that the mitogenic effect of TSH does not involve G(i)-proteins.
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Affiliation(s)
- A Allgeier
- Institute of Interdisciplinary Research, University of Brussels, Belgium
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33
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11 The cAMP in thyroid. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s1040-7952(97)80014-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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34
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Tonacchera M, Cetani F, Costagliola S, Van Sande J, Refetoff S, Vassart G. Functional characteristics of a variant thyrotropin receptor. EUROPEAN JOURNAL OF BIOCHEMISTRY 1996; 238:490-4. [PMID: 8681963 DOI: 10.1111/j.1432-1033.1996.0490z.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
A claim has been made that a variant of the human thyrotropin receptor in which Pro52 is replaced by Thr ([Thr52]thyrotropin receptor) is associated with autoimmune thyroid diseases and displays increased responsiveness to thyrotropin. We have analysed the functional characteristics of this variant receptor. Equivalent numbers of of the wild type and of the variant thyrotropin receptor, measured both by 125I-thyrotropin binding and by flow cytofluorimetry, were transiently expressed in COS-7 cells. Under these conditions, the two receptors showed the same degree of constitutive activity for the cAMP pathway, the same affinity for bovine thyrotropin, and a virtually identical responsiveness to bovine thyrotropin for activation of both the cAMP and inositol-phosphate regulatory pathways. Our results show that the [Thr52]thyrotropin receptor variant of the human thyrotropin receptor, which is present in the 12% of the population, does not affect receptor function and represents most likely a simple polymorphism.
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Affiliation(s)
- M Tonacchera
- Institut de Recherche Interdisciplinaire, Faculté de Médicine, Université Libre de Bruxelles, Belgium
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Van Sande J, Massart C, Costagliola S, Allgeier A, Cetani F, Vassart G, Dumont JE. Specific activation of the thyrotropin receptor by trypsin. Mol Cell Endocrinol 1996; 119:161-8. [PMID: 8807635 DOI: 10.1016/0303-7207(96)03804-x] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The identification of 16 different activating mutations in the TSH receptor, found in patients suffering from toxic autonomous adenomas or congenital hyperthyroidism, leads to the concept that this receptor is in a constrained conformation in its wild-type form. We used mild trypsin treatment of CHO-K1 cells or COS-7 cells, stably or transiently transfected with the human TSH receptor, respectively, and measured its consequences on the TSH receptor coupled cascades, i.e. cyclic AMP and inositol-phosphates accumulation. A 2-min, 0.01% trypsin treatment increased stably cyclic AMP but not inositol-phosphates formation. This was not observed after chymotrypsin, thrombin and endoproteinase glu C treatment. The TSH action on cyclic AMP was decreased by only 25%. The effect was also observed in cells expressing the dog TSH receptor. It was not observed in MSH receptor, LH receptor expressing or mock transfected cells (vector alone). It is therefore specific for the TSH receptor, for its action on the Gs/adenylate cyclase cascade, and for the proteolytic cleavage caused by trypsin. Using monoclonal (A. Johnstone and P. Shepherd, personal communication) and polyclonal antibodies directed against the extracellular domain of the TSH receptor, it was shown that treatment by trypsin removes or destroys a VFFEEQ epitope (residues 354-359) from the receptor. The effect mimics the action of TSH as it activates Gs alpha and enhances the action of forskolin. It is not reversible in 1 h. The results support the concept that activation of the receptor (by hormone, autoantibodies, mutations or mild proteolysis) might involve the relief of a built-in negative constrain. They suggest that the C-terminal portion of the large extracellular domain plays a role in the maintenance of this constrain.
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Affiliation(s)
- J Van Sande
- Institute of Interdisciplinary Research, School of Medicine, Free University of Brussels, Belgium
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36
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Yanagita Y, Okajima F, Sho K, Nagamachi Y, Kondo Y. An adenosine derivative cooperates with TSH and Graves' IgG to induce Ca2+ mobilization in single human thyroid cells. Mol Cell Endocrinol 1996; 118:47-56. [PMID: 8735590 DOI: 10.1016/0303-7207(96)03765-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Digital video imaging indicated that about 80% of fura-2-loaded single human thyroid cells responded to TSH, resulting in an increase in intracellular Ca2+ concentration ([Ca2+]i). Most of the TSH-sensitive cells further responded to N6-(L-2-phenylisopropyl)-adenosine (PIA) showing a transient [Ca2+]i rise in a PIA dose-dependent manner. Addition of PIA prior to TSH administration had no effect or showed only a slight [Ca2+]i increase, but in about 80% of the cells, regardless of the response to PIA, the addition of TSH after PIA resulted in a higher transient [Ca2+]i response than that in the absence of PIA. Inactivation of Gi/G(o) by pertussis toxin (PTX) treatment markedly reduced the effect of PIA on TSH action to the level induced by PIA alone. Immunoglobulin fractions obtained from two Graves' patients with high TSAb (antibody activity measured by cAMP response) activity induced [Ca2+]i increase and cooperated with PIA. Under the same conditions, TSH-dependent cAMP accumulation was inhibited by PIA. These results suggest that adenosine Ai receptor is expressed in human thyroid cells in primary culture as well as in FRTL-5 rat thyroid cells, and that in the presence of adenosine. TSH or Graves' IgG signal tends to be directed to the Ca2+ pathway in the human thyroid.
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Affiliation(s)
- Y Yanagita
- Laboratory of Signal Transduction, Gunma University, Maebashi, Japan
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37
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Cetani F, Tonacchera M, Vassart G. Differential effects of NaCl concentration on the constitutive activity of the thyrotropin and the luteinizing hormone/chorionic gonadotropin receptors. FEBS Lett 1996; 378:27-31. [PMID: 8549796 DOI: 10.1016/0014-5793(95)01384-9] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The TSH receptor (TSHR) and the LH/CG receptor (LHR) are members of the family of G protein-coupled receptors. Recently, point mutations conferring constitutive activity to the TSHR and LHR have been observed as a cause of toxic adenoma and familial/sporadic male pseudo-precocious puberty, respectively. When evaluated by transfection in COS-7 cells the wild-type (wt) TSHR displays definite constitutive activity towards Gs-dependent adenylylcyclase stimulation, while available evidence shows that the LHR does not. In order to compare the constitutive activity of both receptors, we performed functional studies in COS-7 cells using different assay conditions. Human TSHR and LHR cDNAs subcloned in the expression vector pSVL were transiently expressed in COS-7 cells and cAMP production was determined following incubation in a medium containing physiological concentration of NaCl [isotonic (NaCl)] or in the same medium without NaCl [hypotonic (NaCl-)] or where NaCl was replaced by an isoosmolar concentration of sucrose [isotonic (sucrose)]. Cells transfected with the TSHR showed higher basal cAMP levels over cells transfected with pSVL in all conditions tested. The effect was stronger when cells were incubated in isotonic (sucrose) buffer. Cells expressing LHR exhibited a minimal increase of cAMP levels over cells transfected with pSVL in isotonic (NaCl) buffer; however, a marked increase in basal cAMP levels was observed when cells were assayed in hypotonic (NaCl-) or isotonic (sucrose) buffers. Varying the pH or incubation temperature was without effect on the results obtained with both receptors. Our data show that despite extensive sequence similarity, the LH and TSH receptors differ markedly in their basal activity. The differential sensitivity of both receptors to low NaCl concentrations, suggests that the unliganded TSH receptor is less constrained than its LH homolog and may be more susceptible to activation by a wide spectrum of mutations.
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Affiliation(s)
- F Cetani
- Institute de Recherche Interdisciplinaire (IRIBHN), Faculty of Medecine, Université Libre de Bruxelles, Belgium
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