Different binding of stimulatory-type and blocking-type TSH receptor antibody with guinea-pig testis membrane

Abstract

A receptor assay using [125I]bTSH-binding to guinea-pig testis membrane was developed. Unlabelled hCG and FSH inhibited [125I]bTSH binding. In patients with Graves' disease and in untreated hyperthyroid patients, almost all long-acting thyroid stimulators and thyroid-stimulating antibodies, respectively did not inhibit [125I]bTSH binding, which on the other hand was inhibited by thyroid stimulation blocking antibodies in patients with primary hypothyroidism. When the inhibitory effect on the binding of [125I]hCG and 125I-synthetic \g=a\-subunit peptide (\g=a\26-46) of hCG to testis membrane was examined, bTSH resulted in a significant inhibition. However, all three kinds of TSH receptor antibodies had no inhibitory effect. This study demonstrated 1. interaction of \g=a\-subunitof TSH and hCG with the testicular receptor; 2. binding of thyroid stimulation-blocking antibody and lack of binding of thyroid-stimulating antibody to the testicular TSH receptor in spite of binding of these TSH receptor antibodies to the thyroidal TSH receptor, and 3. lack of binding of thyroid-stimulating antibody and thyroid stimulation-blocking antibody to the testicular gonadotropin receptor.TSH receptors have been demonstrated in mem¬ branes from extrathyroid tissues (1-4). TSH, LH, FSH and hCG consist of a common ct-subunit and a hormone specific ß-subunit. Available data sug¬ gest that the ci-subunit part of pituitary glycoprotein hormones such as FSH, LH, TSH and hCG may play an important role in recognition and binding to receptor. The binding of [12oI]bovine TSH (bTSH) to its receptor was attributed to the ct-subunit (1,4-10). On the other hand, an inhibi¬ tory effect of bTSH on [125I]hCG binding to its receptor (testis or ovary) has been demonstrated (6,11,12).Long-acting thyroid stimulator (LATS) and thy¬ roid-stimulating antibody (TS-ab) have been shown to compete with TSH for binding to TSH receptor (13-16). Thyroid stimulation-blocking antibody (TSB-ab) have also a blocking action on TSH by its direct binding to the TSH receptor (17)(18)(19). How¬ ever, it has never been clear how these thyroid stimu¬ lators (TSH, LATS, TS-ab) and TSB-ab can bind to the same binding site in the receptor.In the present study binding characteristics of TSH receptor antibody (TR-ab) such as LATS, TSab, TSB-ab to the testicular TSH receptor were examined. Materials and Methods Materials and MethodsCrude bTSH (1 IU/mg protein) was obtained from Sigma Chemical Co (St. Louis, MO). Crude FSH (HMG, 75 IU/mg protein) was obtained from Nikken Co (Tokyo, Japan). The purified hCG (9000 IU/mg protein) and crude hCG preparation (1000 IU/mg protein) were ob¬ tained from UCB-Bioproducts (Brüssel, Belgium) and Mochida Co (Tokyo), respectively. Synthetic a-subunk peptide (a 26-46, Leu-Gln-CysMet-Gly-Cys-Cys-Phe-Ser-Arg-Ala-Tyr-Pro-Thr-Pro-LeuArg-Ser-Lys-Lys-Thr (NH2)) of hCG was synthesized by Curare Co Ltd (Osaka, Japan) (20,21).

Properties of Monoclonal TSH-Receptor Antibodies and Binding Proteins of Thyreotropin (TSH)

“…They are described in adipocytes, retroorbital tissue, human lymphocytes, liver, testis, adrenals and different cells, (Fig. 1) (Chang et al, 1978;Huber et al, 1992;Inui et al, 1991;Rosselli-Rehfuss et al, 1992;Rotella et al, 1986;Trokoudes et al, 1979). With exception of white and brown adipose tissue of the guinea pig, where the high affinity binding sites are encoded by expression of the TSH-R-mRNA, no mRNA is detectable by Northern analysis or in most polymerase chain reaction in guinea retroorbital tissue, human lymphocytes, testis and ovaries (Roselli-Rehfuss et al, 1992).…”