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Abstract
In humans, the thyroid hormones T3 and T4 are synthesized in the thyroid gland in a process that crucially involves the iodoglycoprotein thyroglobulin. The overall structure of thyroglobulin is conserved in all vertebrates. Upon thyroglobulin delivery from thyrocytes to the follicular lumen of the thyroid gland via the secretory pathway, multiple tyrosine residues can become iodinated to form mono-iodotyrosine (MIT) and/or di-iodotyrosine (DIT); however, selective tyrosine residues lead to preferential formation of T4 and T3 at distinct sites. T4 formation involves oxidative coupling between two DIT side chains, and de novo T3 formation involves coupling between an MIT donor and a DIT acceptor. Thyroid hormone synthesis is stimulated by TSH activating its receptor (TSHR), which upregulates the activity of many thyroid gene products involved in hormonogenesis. Additionally, TSH regulates post-translational changes in thyroglobulin that selectively enhance its capacity for T3 formation - this process is important in iodide deficiency and in Graves disease. 167 different mutations, many of which are newly discovered, are now known to exist in TG (encoding human thyroglobulin) that can lead to defective thyroid hormone synthesis, resulting in congenital hypothyroidism.
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Affiliation(s)
- Cintia E Citterio
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Microbiología, Inmunología y Biotecnología/Cátedra de Genética, Buenos Aires, Argentina
- CONICET-Universidad de Buenos Aires, Instituto de Inmunología, Genética y Metabolismo (INIGEM), Buenos Aires, Argentina
| | - Héctor M Targovnik
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Microbiología, Inmunología y Biotecnología/Cátedra de Genética, Buenos Aires, Argentina
- CONICET-Universidad de Buenos Aires, Instituto de Inmunología, Genética y Metabolismo (INIGEM), Buenos Aires, Argentina
| | - Peter Arvan
- Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical School, Ann Arbor, MI, USA.
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Citterio CE, Veluswamy B, Morgan SJ, Galton VA, Banga JP, Atkins S, Morishita Y, Neumann S, Latif R, Gershengorn MC, Smith TJ, Arvan P. De novo triiodothyronine formation from thyrocytes activated by thyroid-stimulating hormone. J Biol Chem 2017; 292:15434-15444. [PMID: 28743746 DOI: 10.1074/jbc.m117.784447] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Revised: 07/24/2017] [Indexed: 01/01/2023] Open
Abstract
The thyroid gland secretes primarily tetraiodothyronine (T4), and some triiodothyronine (T3). Under normal physiological circumstances, only one-fifth of circulating T3 is directly released by the thyroid, but in states of hyperactivation of thyroid-stimulating hormone receptors (TSHRs), patients develop a syndrome of relative T3 toxicosis. Thyroidal T4 production results from iodination of thyroglobulin (TG) at residues Tyr5 and Tyr130, whereas thyroidal T3 production may originate in several different ways. In this study, the data demonstrate that within the carboxyl-terminal portion of mouse TG, T3 is formed de novo independently of deiodination from T4 We found that upon iodination in vitro, de novo T3 formation in TG was decreased in mice lacking TSHRs. Conversely, de novo T3 that can be formed upon iodination of TG secreted from PCCL3 (rat thyrocyte) cells was augmented from cells previously exposed to increased TSH, a TSHR agonist, a cAMP analog, or a TSHR-stimulating antibody. We present data suggesting that TSH-stimulated TG phosphorylation contributes to enhanced de novo T3 formation. These effects were reversed within a few days after removal of the hyperstimulating conditions. Indeed, direct exposure of PCCL3 cells to human serum from two patients with Graves' disease, but not control sera, led to secretion of TG with an increased intrinsic ability to form T3 upon in vitro iodination. Furthermore, TG secreted from human thyrocyte cultures hyperstimulated with TSH also showed an increased intrinsic ability to form T3 Our data support the hypothesis that TG processing in the secretory pathway of TSHR-hyperstimulated thyrocytes alters the structure of the iodination substrate in a way that enhances de novo T3 formation, contributing to the relative T3 toxicosis of Graves' disease.
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Affiliation(s)
- Cintia E Citterio
- From the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105.,the Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Microbiología, Inmunología y Biotecnología/Cátedra de Genética, C1113AAD Buenos Aires, Argentina.,the CONICET-Universidad de Buenos Aires, Instituto de Inmunología, Genética y Metabolismo (INIGEM), C1120AAR Buenos Aires, Argentina
| | - Balaji Veluswamy
- From the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105
| | - Sarah J Morgan
- the National Institutes of Health, NIDDK, Laboratory of Endocrinology and Receptor Biology (LERB), Bethesda, Maryland 20892
| | - Valerie A Galton
- the Department of Physiology and Neurobiology, The Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire 03756
| | - J Paul Banga
- the Department of Molecular Ophthalmology, University of Duisburg-Essen, 45147 Essen, Germany
| | - Stephen Atkins
- the Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105, and
| | - Yoshiaki Morishita
- From the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105
| | - Susanne Neumann
- the National Institutes of Health, NIDDK, Laboratory of Endocrinology and Receptor Biology (LERB), Bethesda, Maryland 20892
| | - Rauf Latif
- the Thyroid Research Unit, James J. Peters Veterans Affairs Medical Center, The Icahn School of Medicine at Mount Sinai, New York, New York 10468
| | - Marvin C Gershengorn
- the National Institutes of Health, NIDDK, Laboratory of Endocrinology and Receptor Biology (LERB), Bethesda, Maryland 20892
| | - Terry J Smith
- From the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105.,the Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105, and
| | - Peter Arvan
- From the Division of Metabolism, Endocrinology and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105,
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Yoshioka Y, Sasaki J, Yamamoto M, Saitoh K, Nakaya S, Kubokawa M. Quantitation by (1)H-NMR of dolichol, cholesterol and choline-containing lipids in extracts of normal and phathological thyroid tissue. NMR IN BIOMEDICINE 2000; 13:377-383. [PMID: 11114060 DOI: 10.1002/1099-1492(200011)13:7<377::aid-nbm658>3.0.co;2-e] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Proton magnetic resonance spectroscopy at 1.9 T was used to quantify dolichols, cholesterols, choline-containing phospholipids and double bonds in unsaturated acyl chains in lipid extracts of four types of thyroid tissue [normal (n = 27), papillary cancer (n = 15), adenoma (n = 13) and Basedow disease (n = 6)]. In normal thyroid the mean concentrations of dolichol, cholesterol and phospholipids were 1.2, 3.6 and 2.1 micromol/g wet weight, respectively. The concentrations of these lipids exhibited positive mutual correlations and positive correlations with patient age. The increase in dolichol in elderly human thyroid may be due to the accumulation of lysosomes and may help to compensate for the decrease in the activity of lysosomal enzymes and in thyroid hormone production and release. Dolichol concentrations were significantly lower in papillary cancer (0.4 micromol/g) and Basedow disease (0.3 micromol/g) compared to normal thyroid (p < 0.01 and p < 0.05, respectively), while cholesterol was enhanced only in cancer tissue (10.7 micromol/g). Benign adenoma exhibited normal levels of both dolichol and cholesterol. These results suggest that the synthesis and accumulation of isoprenoids are normal in adenoma but not in cancer.
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Affiliation(s)
- Y Yoshioka
- Department of Physiology II, School of Medicine, Iwate Medical University, Morioka 020-8505, Japan.
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Penel C, Gruffat D, Alquier C, Benoliel AM, Chabaud O. Thyrotropin chronically regulates the pool of thyroperoxidase and its intracellular distribution: a quantitative confocal microscopic study. J Cell Physiol 1998; 174:160-9. [PMID: 9428802 DOI: 10.1002/(sici)1097-4652(199802)174:2<160::aid-jcp3>3.0.co;2-m] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The regulation of thyroperoxidase (TPO) expression and of its intracellular distribution was studied in porcine thyroid cells cultured on porous bottom filters. Cells were cultured for 18 days in the absence or in the presence of thyrotropin (TSH) and with or without iodide. Microsomes were purified and analyzed by electrophoresis. TPO was detected by immunoblotting with polyclonal anti-porcine TPO antibodies and quantified by scanning the bands. The amount of TPO was increased 2-fold by TSH. High concentrations of iodide (1-50 microM, added daily) decreased the level of TPO. Confocal microscopy served to determine the intracellular localization of TPO and its quantitative distribution. Intracellular and surface-located TPO was detected by fluorescein-labeled antibodies on saponin-treated cells. Quantitative confocal microscopy showed that TSH increased the total amount of TPO 2-fold as for immunoblotting. The highest amount of TPO was found in the perinuclear area and between the nucleus and the Golgi apparatus. Only 4% of TPO was present on the apical surface and about 1% on the basolateral membrane; the remainder (about 95%) was inside the cells. TSH did not change these relative contents. TSH modified the intracellular distribution of the enzyme, increasing the TPO pool from the perinuclear area to apical membrane. This domain could be a site of storage of TPO. Adding a physiological concentration of iodide (0.5 microM, daily) did not influence the intracellular distribution of TPO. We concluded that chronic TSH stimulation 1) increased 2-fold the pool of TPO but did not change the relative proportion of TPO inside the cells and on the apical surface, and 2) modified the intracellular distribution of vesicular TPO, the major part of which was accumulated in the perinuclear and cytoplasmic area under the subapical domain of the polarized cells.
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Affiliation(s)
- C Penel
- INSERM CJF 93-11-IFR. J. Roche, Faculté de Médecine Nord, Université de la Méditerranée, Marseille, France
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