1,721,002 research outputs found
Thyrotropin Receptor: Characterization and Purification
No full textThis paper deals with the isolation, purification and functional characterization of the TSH receptor
Thyrotropin regulation of thyroid cell functions: mechanisms and relationship to thyroid disease.
No full textA pre-Golgi membrane-bound form of thyroglobulin (TG) contains mannose phosphate and tetraiodothyronine (T4)
No full textN/
Graves’ IgG stimulation of iodide uptake in FRTL-5 rat thyroid cells: A clinical assay complementing FRTL-5 assays measuring adenylate cyclase and growth-stimulating antibodies in autoimmune thyroid disease
No full textWith optimal conditions and cells maintained in the absence of thyrotropin (TSH) for 7–10 days, IgG preparations from ∼ 90% of patients with active Graves’ disease can exhibit statistically significant stimulation of cAMP levels in rat FRTL-5 thyroid cells as compared to normal controls. FRTL-5 cells maintained in the absence of TSH for 7–10 days lose their ability to take up iodide. Iodide uptake returns upon readdition of TSH over a 60-hour period via a cAMP-mediated process; thus TSH can be replaced by dibutyryl cAMP or other agents which increase cAMP levels, for example, thyroid-stimulating autoantibodies (TSAbs) from Graves’ sera. TSAb stimulation of iodide uptake requires the continued presence of TSAb over at least the first 24 hours of a 48-hour reversal period; TSH, in contrast, can be withdrawn after 5 hours and will still achieve maximal effects at 36–48 hours. Iodide uptake, measured as a 30-minute pulse at 48 hours, appears, however, to be faster with TSAb than TSH. With optimized conditions (cells depleted of TSH > 7–10 days; 3-isobytyl-1-methyl xanthine, 0.005 mM; TSAb addition for the entire 48-hour assay period; and a 30-minute pulse of 10 μM 125I-sodium iodide at 37 C), TSAb stimulation is concentration-dependent with a half-maximal activity at ∼ 10-fold lower concentrations than in the cAMP stimulation assay. In a series of 24 patients with Graves’ disease, IgGs with positive values in the cAMP assay were positive in the iodide uptake assay. Activity coefficients expressed as percent of basal in both assays correlate extremely well (r = 0.85). Using these two assays and an FRTL-5 assay measuring growth antibodies (by their ability to increase thymidine uptake), TSAbs were found in 100% of patients with active Graves’ disease and could broadly be grouped into three categories: IgGs with high stimulatory cAMP/iodide uptake activity but low to moderate effects on thymidine uptake; IgGs with moderate effects in all assays; and IgGs with low or undetectable cAMP/iodide stimulatory activity, but high thymidine uptake activity. The value of the FRTL-5 rat thyroid cells assays system for measuring Graves’ autoantibodies appears, thus, to be superior to all current systems, including human cells and slices. © 1983, Italian Society of Endocrinology (SIE). All rights reserved
Role of phospholipids in the structure and function of the thyrotropin receptor.
No full textPhosphatidylinositol, phosphatidylserine, and phosphatidylethanolamine interact with 125I-thyrotropin and inhibit its binding to thyroid plasma membranes; phosphatidylcholine is not similarly effective. The interaction has been monitored by column chromatography on Sephadex G-100 which shows, for example, that 125I-labeled thyrotropin forms an adduct with phosphatidylinositol but not with phosphatidylcholine. Formation of the 125I-labeled thyrotropin-phosphatidylinositol adduct is dependent on the phosphatidylinositol concentration but can be reversed by both unlabeled thyrotropin and excess membranes. The efficacy of the phospholipid interaction and the phospholipid inhibition of thyrotropin binding to thyroid membranes is paralleled by changes in fluorescence and fluorescence polarization imposed on the 5-dimethylamino-1-naphthalene sulfonate (dansyl) derivative of thyrotropin. These changes are reversed by unlabeled thyrotropin but not by prolactin, placental lactogen, or growth hormone; similar changes are not observed when phospholipids are incubated with dansylated growth hormone, prolactin, and placental lactogen. Monovalent potassium, sodium, and lithium salts neither prevent nor reverse the formation of the phospholipid-dansyl-thyrotropin adduct; these results contrast with the effects of the same salts on the formation of ganglioside adducts with dansyl-thyrotropin. Despite their ability to interact witw 125I-thyrotropin in solution, neither phosphatidylinositol, phosphatidylserine, nor phosphatidylethanolamine, when incorporated in a liposome, binds the 125I-labeled ligand. These same phospholipids have no effect on ganglioside binding of 125I-labeled thyrotropin when gangliosides are incorporated in a liposome. These phospholipids do, however, modulate the expression of the glycoprotein component of the thyrotropin receptor when it is imbedded in a liposome. The phosphatidylinositol in this case serves as a negative modulator, both by decreasing the incorporation of the glycoprotein component of the receptor into the liposome and by inhibiting the binding activity of the glycoprotein component which is incorporated. Speculation is offered as to a possible role of the phospholipids in the message transmission process which would be consistent with current studies demonstrating a direct interaction of acidic phospholipids with thyrotropin. The effect of phospholipids on liposomes containing the glycoprotein component of the thyrotropin receptor raises the possibility that phospholipids and, in particular, phosphatidylinositol, may also play a role in regulating the insertion and expression of this receptor component in thyroid plasma membranes
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