Increased Receptor Binding by Bovine (b) TSH Bound to Monoclonal Antibody to bTSHβ-subunit

• Published in: Endocrine Journal Vol. 55; no. 1; pp. 105 - 111
• Main Authors: OCHI, Yukio, HAMAZU, Masanari, KAJITA, Yoshihiro, HACHIYA, Takashi, KUNIMATSU, Mitoshi, SATO, Takaaki, NAGATA, Atsuo
• Format: Journal Article
• Language: English
• Published: The Japan Endocrine Society 2008
• Subjects: cAMP; Glycoprotein hormone; Monoclonal antibody to TSH; TSH; TSH receptor assay
• ISSN: 0918-8959; 1348-4540
• DOI: 10.1507/endocrj.K07E-015

TSH receptor (R) binding and cAMP production by bovine (b) TSH-bound to a monoclonal antibody (MoAb) or polyclonal antibody (Ab) to bTSH were examined, using TSH receptor (R) coating tube and porcine thyroid cells. 125 I-bTSH bound-to MoAbs to bTSH(α) or discontinuous type MoAb showed TSHR binding (10%) similar to intact 125 I-bTSH. TSHR binding was completely decreased (<2%) when 125 I-bTSH was bound by polyclonal Abs to bTSH(α) in Graves' patient or rabbit polyclonal Abs to bTSH. When either of the two MoAb (No. 1 and 2) to bTSH(β) was bound to 125 I-bTSH, TSHR binding was 4 times higher (40%) compared to intact 125 I-bTSH. Binding of another MoAb (No. 3) caused no increased binding. TSHR binding of intact 125 I-bTSH was decreased from 10% to 2% by excess amounts of bTSH. Binding of 125 I-bTSH bound to MoAb to bTSH(β) (No. 1 and 2) decreased from 40% to 30% by excess amounts of bTSH. When 125 I-bTSH bound-Fab of MoAb was used, the binding was reduced from 30 to 10% (No. 1) and from 25 to 6% (No. 2), respectively. In contrast, cAMP production by bTSH was decreased by pre-binding of all MoAbs and polyclonal Abs. Binding of 125 I-MoAb to bTSH (β) to a synthetic peptide array of bTSH (β) sequence was examined by the radioautography. The epitope of MoAb to bTSH(β) was suggested to be LPK (β 42-44) for No. 1, KLF (β 39-41) for No. 2 and PKYA (β 43-46) for No. 3, respectively, although the existence of discontinuous epitope could not be ruled out. The increased TSHR binding and the decreased cAMP production by bTSH bound to MoAbs may be due to the conformational change of TSH molecule or TSHR by binding of both bTSH and MoAb.