Disease relevance of TSHR

• These studies suggest that TSHR gene mutations are not a common cause of feline thyrotoxicosis [1].
• Detection of autoantibodies to the TSH receptor (TSH-R) in Graves' disease has found widespread use in clinical routine and is performed mostly by commercial RRAs measuring TSH binding inhibitory activity [2].
• Hashimoto's disease antibodies bind to a determinant on the TSH receptor separate from the one on which TSH and Graves' IgG bind [3].

High impact information on TSHR

• It is concluded that the binding of TSH to its receptor involves extensive contacts and that the TSHR peptides 12-30 and 324-344 contain specific binding regions for TSH that might be either independent sites or two faces (subsites) within a large binding site [4].
• Two regions of human thyrotropin (thyroid-stimulating hormone, TSH) receptor (TSHR) (residues 12-44 and 308-364) were selected on the basis that they exhibit no sequence resemblance to luteinizing hormone/chorionic gonadotropin receptor [4].
• TSH/cAMP coordinate regulation of common transcription factors may, therefore, be the basis for self-tolerance and the absence of autoimmunity in the face of TSHR-mediated increases in gene products that are important for thyroid growth and function but are able to act as autoantigens [5].
• TSHR cleavage or noncleavage after substitution of GQE367-369 with other triplets (AAA, NQE, and NQT) was consistent with a role for N-linked glycosylation at this site [6].
• TSH/cAMP decreases the binding of each factor to its respective site, thereby decreasing TSHR gene expression [7].

Biological context of TSHR

• The cDNA for the bovine TSH receptor consists of an open reading frame 2289 nucleotides in length, corresponding to a protein of 763 amino acids (estimated molecular mass of 86.4 kDa) which includes a 20 amino acid putative leading signal peptide [8].
• Thus, the N-terminus of the extracellular domain of the LH/CGR can couple TSH binding to signal transduction events even better than the N-terminus of the TSHR [9].
• The TSH-induced effect in each case is inhibited by cycloheximide; the TSH-induced decrease in SSBP/DNA complex formation requires the presence of insulin or calf serum, exactly as does TSH-induced down-regulation of TSHR RNA levels [7].
• A 1.3-kilobase variant of the TSHR messenger ribonucleic acid (mRNA) has been described in normal and Graves' thyroids; it contains exons 1-8 of the major mRNA species and a unique 3'-sequence predicted to encode further amino acids and a polyadenylated tail [10].
• We have also determined the DNA sequence of this region of the TSHR in five of the cases of sporadic feline thyrotoxicosis and the two familial thyrotoxic cats [1].

Anatomical context of TSHR

• In this study, we found TSHR RNA in infant and adult adipose tissues and isolated adipocytes with reverse transcriptase-PCR [11].
• Northern blot hybridization on RNA prepared from infant adipose tissue showed a transcript of the expected size, and the expression of TSHR seemed higher in infant than in adult adipose tissue [11].
• Transfection experiments with rat liver cells support their independent activities and show that the SSBP site contributes to TSHR gene expression in non-thyroid tissue [7].
• In a previous study we were unable to demonstrate transcripts for the complete TSHR in retroocular muscle containing also fibroblasts [10].
• Design: Chinese Hamster ovary (CHO) cells stably expressing the TSHR, LHR, and FSHR and purified M22 IgG preparations were used in the study [12].

Associations of TSHR with chemical compounds

• Results: Cyclic AMP levels increased in a dose-dependent manner after incubation of CHO-TSHR cells with TSH or M22 IgG, and on a molar basis the effects of TSH and M22 were similar [12].
• A murine monoclonal antibody was selected for binding to the native TSH-R without interfering with autoantibodies or TSH and was coated to polystyrene tubes [2].
• TSH desensitization involves decreased coupling of the TSH receptor to the adenylate cyclase regulatory protein, Gs [13].
• Hydrocortisone (10(-5)--10(-3) M) and d,l-propranolol (10(-3) M) inhibited receptor release. cAMP increased the release of TSH receptor [14].
• The characteristics of binding of bovine [125I]TSH to the released TSH receptor were almost the same as those of binding to TSH receptors solubilized by lithium 3,5-diiodosalicylate or to the original plasma membrane [14].

Physical interactions of TSHR

• These data strongly suggest that the 68,000 and 80,000 TSH-receptor complexes are the result of crosslinking to the TSH alpha-beta dimer and not to one subunit in the case of the 68,000 complex and to the TSH alpha-beta dimer in the case of the 80,000 complex, as had been hypothesized previously [15].

Analytical, diagnostic and therapeutic context of TSHR

• In contrast, a strong and highly significant correlation was found between TSHR stimulating activity (luminescence) as measured with the TBII bioassay and serum free T4 levels (R = 0.80, P < 0.001) [16].
• We have used the polymerase chain reaction (PCR) to amplify codons 480-640 of the previously uncharacterized feline thyrotropin receptor (TSHR) gene, and have determined the DNA sequence in this transmembrane domain region [1].
• Methods: CHO-TSHR, CHO-LHR, and CHO-FSHR cells were incubated with bovine TSH (0.1-25mU/mL), human recombinant chorionic gonadotropin (hCG; 0.5-10mU/mL) or human recombinant FSH (100-5000mU/mL) or with M22 IgG (0.001-5.0 microg/mL), and the extracellular cyclic AMP was measured by radioimmunoassay [12].
• Purification (800-fold) of the bovine TSH receptor was achieved by a combination of TSH and B. simplicifolia I affinity chromatographies [17].
• In the first, a particulate fraction has been prepared from COS cells, transiently expressing the human TSH-R and used in a radioreceptor assay in conjunction with bovine 125I-TSH [18].

References