Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.11.1.8 (thyroid peroxidase)
 3,116 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The expression of the genes coding for thyroglobulin (TG), and thyroperoxidase (TPO), are regulated by TSH. These effects are mediated by cAMP as they are reproduced by forskolin. In vitro run-on transcription assays performed on nuclei isolated from dog thyrocytes in culture or from dog thyroid slices, indicate that the forskolin-induced transcriptional stimulation of TG and TPO genes are very different. For the TG gene, the kinetics of transcriptional activation vary according to the experimental model: it is rapid (1 h) in thyroid slices and slow (8 h) in primary cultures. In contrast, TPO induction is rapid in both cases. In primary cultures, insulin is responsible for the basal level and for a part of forskolin-induced TG transcription, whereas TPO transcription is not affected by insulin. The forskolin-induced increase of TG transcription requires ongoing protein synthesis, as it is blocked by cycloheximide. TPO gene transcription is unaffected by cycloheximide. Taken together with previous data on the two genes, our results suggest that while TPO regulation corresponds to the classical model of genes in which the promoter is regulated directly via cAMP regulatory elements, TG gene regulation involves the synthesis of an intermediary, rapid turnover trans-acting protein.
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PMID:Control of thyroperoxidase and thyroglobulin transcription by cAMP: evidence for distinct regulatory mechanisms. 256 Aug 10

The nature of the immunosuppressive effect of antithyroid drugs has been a subject of controversy. It has been claimed that these agents exert a direct effect on the immune system, although we and others have suggested that the drugs affect the thyroid cells primarily with consequent reduced thyrocyte-immunocyte signalling. This may occur from reduced thyroid hormone production and/or reduced antigen presentation by the thyrocytes to local T lymphocytes. Using a cytotoxicity assay system, with chromium-51 labelling, monoclonal antibodies against thyroperoxidase (TPO) and HLA-DR, and complement, we have measured the expression of TPO and HLA-DR on cultured normal human thyroid cells; we have also measured thyroglobulin (Tg) release by radioimmunoassay into the medium of the cultured cells. The thyroid cells were stimulated with TSH or thyrotropin binding inhibitory immunoglobulin (TBII) for 48 hours before measuring for TPO induction, and with interferon gamma (IFN-gamma) (with or without TSH or TBII) for thyrocyte HLA-DR expression. A dosage of 1.6 milliunits per ml of TSH resulted in a significant increase in TPO expression on thyrocytes when compared with control unstimulated thyroid cells (p less than 0.001). The concentrations of Tg released into the medium with TSH or TBII were also significantly higher than those of the control thyrocytes. IFN-gamma at 200 units per ml induced HLA-DR expression, but did not induce thyrocyte TPO expression, or Tg release. Addition of the antithyroid drug, methimazole (MMI), at different concentrations, in addition to the other stimulators, IFN-gamma, TSH, or TBII, did not result in any inhibition of TPO, Tg release, or HLA-DR expression on the thyroid cells. It would thus appear that the pathways for stimulation for the expression of TPO and HLA-DR appear to be different. Finally, MMI does not cause its immunosuppressive effect by any reduction of thyroid antigen expression or release.
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PMID:Lack of effect of methimazole on thyrocyte cell-surface antigen expression. 257 90

The ultrastructural appearance of colloid vacuoles, considered to be a typical sign of hyperactivity in the human thyroid gland, was studied in human thyroid tissue transplanted to nude mice and in human thyroid tissue fixed directly after surgical removal in patients with thyrotoxicosis. Transplanted normal thyroid tissue and toxic diffuse goiter (TDG) tissue was fixed by vascular perfusion with glutaraldehyde 5 or 12 weeks after transplantation. Light microscopic quantification showed that daily injections for 2 weeks of a gamma globulin fraction of patient sera containing thyroid-stimulating immunoglobulins (TSI) greatly increased the number of colloid vacuoles in both types of transplants. The vacuoles were mainly located in the periphery of the follicle lumen, giving the colloid a scalloped appearance. Electron microscopy of TSI-exposed tissue revealed, in addition to colloid vacuoles, the presence of large amounts of membrane material in the follicle lumen. Only sparse amounts of intraluminal membrane material were present in controls. The colloid vacuoles were almost invariably associated with such membrane material, which lined the border between the vacuole and the surrounding colloid. The intraluminal material consisted of spherical and elongated formations, each structure limited by a triple-layered membrane and often containing a dense interior. The elongated structures were often of the same dimensions as microvilli. The apical surface of follicle cells in TSI-exposed tissue expressed numerous microvilli, of which many showed a similar dense interior as the intraluminal membrane structures. The intraluminal membranes frequently showed, like the apical plasma membrane of the follicle cells, a positive reaction for peroxidase. Organelles, such as mitochondria, lysosomes or rough endoplasmic reticulum, were not encountered among the intraluminal membrane structures. These observations indicate that the intraluminal membrane material is derived from the apical plasma membrane of the follicle cells, presumably by shedding of microvilli. A similar association between colloid vacuoles and membrane material was also found in thyroid tissue from patients with thyrotoxicosis fixed directly at operation. It is suggested that the presence of membrane material in the follicle lumen precipitates the formation of colloid vacuoles in hyperactive thyroid tissue. The possible involvement of intraluminal membrane material in the development of microsomal autoantibodies in Graves' disease, i.e. exposure and presentation of thyroid microsomal antigen (identical to thyroperoxidase) to the immune system, is discussed.
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PMID:Plasma membrane shedding and colloid vacuoles in hyperactive human thyroid tissue. 290 7

This radioimmunoassay was developed for specific and large-scale routine measurement of autoantibodies to thyroperoxidase (TPO), an enzyme recently identified as the thyroid microsomal antigen. Because of the scarcity of purified thyroperoxidase, we did not base the assay on the antigen-coated method but rather on autoantibody inhibition of the binding of labeled TPO to a solid-phase-bound monoclonal antibody to TPO. This assay design ensured highly specific measurements without interference from irrelevant thyroid antigens and autoantibodies. When we used affinity-purified autoantibodies to TPO as standards, the range of the curve extended over 10(3)-fold differences in the autoantibodies' concentrations, which allowed us to assay most sera without dilution. Within- and between-assay coefficients of variation (CVs) ranged from 6.1% to 11.5% and from 6.6% to 12.0%, respectively. The correlation between anti-TPO and antimicrosomal autoantibodies, as assessed by hemagglutination test, was highly significant (r = 0.90, P less than 0.0001). This assay is sensitive, easy to perform, and requires only trace amounts of purified TPO.
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PMID:Novel routine assay of thyroperoxidase autoantibodies. 318 Apr 14

A lambda gt11 cDNA library was constructed from a normal human thyroid and screened with a rabbit anti-porcine thyroperoxidase antibody. A series of thyroperoxidase (TPO) clones were obtained which allowed determination of the complete primary structure of the protein. The library was also screened with serum from a patient with Hashimoto's thyroiditis, an autoimmune disease characterized by the presence in the serum of high titers of autoantibodies directed against the 'microsomal antigen' (McAg). Comparison of the cDNA sequences from TPO clones and McAg clones provides definite proof that the McAg is TPO. A short segment of TPO was characterized as bearing a major epitope involved in autoimmunity. The primary structure of TPO was 42% homologous to myeloperoxidase (MPO). It contains, in addition, a C-terminal extension with a membrane anchor region contiguous to two domains encoded by modules belonging to the EGF and C4b gene families. The existence in TPO of still another domain presenting a significant homology with a putative heme-binding region of cytochrome C oxidase polypeptide I raises the possibility that a mitochondrial gene module has contributed a piece to the evolution of a typical nuclear mosaic gene.
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PMID:Thyroperoxidase, an auto-antigen with a mosaic structure made of nuclear and mitochondrial gene modules. 344 5

The kinetics of free and hormone bound blood iodine after stimulation with endogenous thyroid stimulating hormone (TSH) are not satisfactorily characterized. We studied these kinetics in mice injected with 125I and thyroxine. In control mice, the injected 125I is organified within the thyroid and incorporated into thyroid hormones, whereas in mice treated with the thyreostatic drug propylthiouracil (PTU), most 125I remains inorganic, since the thyroperoxidase activity is inhibited by PTU. We found that during blockade of TSH secretion by means of thyroxine, blood 125I activity was significantly higher in PTU-treated animals than in controls, indicating that PTU impaired thyroidal uptake of 125I. On the fourth day after the thyroxine load, the blockade of TSH secretion vanished. This caused the blood 125I activity to increase markedly. The increase of blood 125I was as high in PTU-treated animals as in controls. After the peak, blood 125I was cleared according to first order kinetics, with a half-time of 0.72 days (= 17.3 hours) in PTU-treated animals and of 6.3 days in controls (P less than 0.001). It is suggested (1) that PTU impairs thyroidal uptake of iodide, (2) that endogenous TSH stimulates release from the thyroid of inorganic iodide as well as of thyroid hormones, and (3) that inorganic iodide released by the thyroid has a much shorter biological half-life than hormone-bound iodine.
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PMID:Kinetics of radioiodine released from prelabelled thyroid gland in vivo: influence of propylthiouracil. 362 85

The cell surface location of the thyroid microsomal antigen was studied by immunoelectron microscopy. Isolated, open human thyroid follicles were incubated with patient sera containing high titers of microsomal autoantibodies. Cell surface-bound antibodies were detected by the immunogold technique using IgG-coated colloidal gold particles (10 or 15 nm). Immunocytochemical incubations were performed at 4 degrees C. Gold particles were concentrated at the apical cell surface of the follicle cells, while the basolateral cell surface was almost completely unlabelled. Quantitative evaluation of four experiments with follicle cells prepared from different patients showed that about 90% of the gold particles at the apical cell surface was associated with microvilli and that the concentration of gold particles at the microvillus membrane was, although with great intercellular variation, several times higher than that at smooth portions of the apical plasma membrane. This suggests that the microsomal antigen is organized in microdomains in the apical plasma membrane. In follicles labelled immunocytochemically at 4 degrees C and then incubated at 37 degrees C, gold particles were slowly internalized. The particles appeared in smooth and coated pits of the apical plasma membrane as well as in vesicles, vacuoles and lysosomes in the apical part of the cytoplasm. Membranes of TSH-induced pseudopods were always unlabelled. Our observations indicate that thyroid microsomal antigen immunoreactivity is present in the apical but not in the basolateral plasma membrane. The antigen with bound antibodies is internalized by micropinocytosis but not by macropinocytosis. The selective location of bound microsomal antibodies at the apical plasma membrane and their absence from the membrane of TSH-induced pseudopods are compatible with the idea that the microsomal antigen and thyroperoxidase are identical.
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PMID:Immunoelectron microscopic studies on the cell surface location of the thyroid microsomal antigen. 366 97

The intraluminal distribution of newly synthesized (injection of [3H]leucine) and newly iodinated (injection of Na125I) proteins in thyroids of rats given T4 for 2 days was studied with quantitative electron microscopic autoradiography. Three, 4.5, and 6 h after [3H]leucine about 90%, 85%, and 65%, respectively, of the luminal label was confined to the microvillus region. This distribution differed from that of newly iodinated protein; already 2 min after injection only about 30% of the grains was located over the microvillus region. The remaining 70% of the grains located outside the microvillus region formed a gradient towards the center of the lumen. The grain distributions 30 min and 2 h after Na125I were similar to that present after 2 min. The distribution of grains after pulse labeling with Na125I (injected 2 min before propylthiouracil and 2 h before fixation) was also similar to that found in rats injected with Na125I alone, indicating that diffusion of labeled proteins in the lumen was very slow in T4-treated rats. A slow diffusion was also suggested by the presence of an unlabeled peripheral ring in follicle lumens of T4-treated rats injected with Na125I 48 h before fixation. In normal rats given [3H]leucine 3 h before fixation or Na125I 1 h or 48 h before fixation the grains were homogeneously distributed in most follicle lumens. Together our findings indicate that (1) administration of T4 has effects on the diffusion properties of the colloid; (2) iodine is incorporated not only into newly synthesized thyroglobulin recently delivered to the follicle lumen but also into molecules already stored in the lumen; (3) a portion of the iodine incorporated into proteins is bound to molecules which are not in direct contact with thyroperoxidase in the apical plasma membrane.
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PMID:Intraluminal iodination of thyroglobulin. 669 65

Previous experiments led us to speculate that thyrocytes contain a recycling system for GlcNAc-bearing immature thyroglobulin molecules which prevents these molecules from lysosomal degradation (Miquelis, R., C. Alquier, and M. Monsigny. 1987. J. Biol. Chem. 262:15291-15298). To confirm this hypothesis, the fate of GlcNAc-bearing proteins after internalization by thyrocytes was monitored and compared to that of fluid phase markers. Kinetic internalization studies were performed using 125I-GlcNAc-BSA and 131I-Man-BSA. We observed that the apparent intake rate as well as the amount of hydrolyzed GlcNAc-BSA are smaller than the corresponding values for Man-BSA. These differences were reduced by GlcNAc competitors (thyroglobulin and ovomucoid) or a weak base (chloroquine). Part of the internalized GlcNAc-BSA was released into the extracellular milieu at a higher rate and shorter half life (t1/2 = approximately 30 min) than the Man-BSA (t1/2 = approximately 8 h). Subcellular homing was first studied by cell fractionation after internalization using 125I-ovomucoid and 131I-BSA. During Percoll density gradient fractionation, endogenous thyroperoxidase was used to separate subsets of organelles involved in the biosynthetic exocytotic pathway. Incubation of the cell homogenate in the presence of DAB and H2O2 before cell fractionation give rise to a shift in the density of organelles containing 3.5 times more ovomucoid than BSA. Discontinuous sucrose gradient showed that: (a) thyroperoxidase was colocalized with galactosyltransferase-contraining organelles in Golgi-rich subfractions; and (b) that at every time studied from 10 to 100 min, the ovomucoid/BSA ratio was higher in these organelles than in other subfractions. Finally we also observed that: (a) ovomucoid sequestered in the Golgi-rich subfraction incorporated [3H]galactose; and (b) that part of internalized ovomucoid was localized on the Golgi stacks as well as elements of the trans-Golgi, as revealed by immunogold labeling on ultrathin cryosections. These data prove that in thyrocytes GlcNAc accessible sugar moieties on soluble internalized molecules are sufficient to trigger their recycling via the Golgi apparatus.
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PMID:Intracellular routing of GLcNAc-bearing molecules in thyrocytes: selective recycling through the Golgi apparatus. 750 65

1. Hereditary goiter and the various degrees of thyroid hypofunction are the result of structural changes in the thyroglobulin (Tg) or thyroperoxidase (TPO) proteins, the inability to couple iodotyrosines or defective iodination, impairing or substantially altering the synthesis of T4 and T3. 2. The first mutations in the Tg and TPO genes responsible for human cases of dyshormonogenesis have been described. The mutation in two siblings with hereditary goiter and marked impairment of Tg synthesis was a cytosine to thymine transition creating a stop codon at position 1510. The point mutation is removed by the preferential accumulation of a 171-nt deleted Tg mRNA. In another subject, molecular studies revealed that exon 4 was missing from the major Tg transcript due to a cytosine to guanine transversion at position minus 3 in the acceptor splice site of intron 3. 3. Genomic DNA studies identified a duplication of a 4-base sequence in the eighth exon of the TPO gene. Interestingly, besides abolishing the enzymatic activity by disrupting the reading frame of the messenger RNA and introducing stop codons, the GGCC duplication also unmasks a cryptic acceptor splice site in exon 9. 4. In conclusion, the identification of different molecular defects provided evidence that hereditary goiter associated with abnormal Tg or TPO synthesis is caused by heterogeneous genetic alterations.
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PMID:Molecular genetics of hereditary thyroid diseases due to a defect in the thyroglobulin or thyroperoxidase synthesis. 754 98


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