Endocrine Abstracts

Introduction: Thyrotropin (TSH) and the gonadotropins (FSH, LH, hCG) are a family of heterodimeric glycoprotein hormones composed of two noncovalently linked subunits, α and β. hTSH, heterodimer was converted to a biologically active single-peptide chain, by fusing the common α subunit to the carboxyl-terminal end of hTSHβ subunit in the absence (hTSHβα) or presence of a ~30 aminoacid carboxyl-terminal peptide from hCGβ (CTP) as a linker (hTSHβCTPα). Ligation of CTP to the carboxyl-end of hFSH, hCGα subunit and to hTSH resulted in increasing the biological activity and longivity in vivo.

Objectives: Investigation the role of the N-linked oligosaccharides of α and β subunits on secretion and function of hTSH using the single chain variant, hTSHβCTPα.

Methods: Two deglycosylated variants were prepared using site-directed mutagenesis and gene transfer; one lacks both N-linked oligosaccharide chains on α subunit (hTSHβCTPα₁₊₂), and the other lacks also the N-linked oligosaccharide chain on β subunit of the single chain (hTSHβCTPα (deg). The single-peptide chain variants were expressed in CHO cells.

Results: Absence of N-linked oligosaccharides on α or β subunits does not affect the secretion of the variants. These results indicate that the signal for the secretion exists in the single peptide chain is independent of the oligosaccharides. hTSH variants lack of the oligosaccharide chains is less potent than hTSHβCTPα on cAMP accumulation and T₃ secretion in human cultured thyroid follicles. Moreover, both deglycosylated variants compete with normal hTSH and hTSI in a dose dependent manner in vitro and in vivo.

Conclusions: The N-linked oligosaccharides are not important for receptor binding, but they are critical for bioactivity of TSH in vitro and in vivo. This variant, behaves as potential antagonist, who may offer a novel therapeutic strategy in the treatment of Grave’s disease, the most common form of hyperthyroidism.