The Glycoprotein α-Subunit is Critical for Secretion and Stability of the Human Thyrotropin β-Subunit

Matzuk, Martin M.; Kornmeier, C. M.; Whitfield, G. Kerr; Kourides, Ione A.; Boime, Irving

doi:10.1210/mend-2-2-95

Cited by 69 publications

(23 citation statements)

References 24 publications

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“…Free TSH ␤-subunit, similarly to free LH ␤-subunit, is degraded intracellularly, and Ͻ10% produced is secreted into the culture medium. Therefore, simultaneous coexpression of ␣-subunit prevents intracellular degradation of TSH ␤-subunit (118). The most important domains in TSH expression and bioactivity recognized thus far are depicted in Figure 3.…”

Section: B Studies Of Protein Domainsmentioning

confidence: 99%

Thyroid-Stimulating Hormone and Thyroid-Stimulating Hormone Receptor Structure-Function Relationships

Szkudlinski

Frémont²,

Ronin³

et al. 2002

Physiological Reviews

398

256

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This review focuses on recent advances in the structure-function relationships of thyroid-stimulating hormone (TSH) and its receptor. TSH is a member of the glycoprotein hormone family constituting a subset of the cystine-knot growth factor superfamily. TSH is produced by the pituitary thyrotrophs and released to the circulation in a pulsatile manner. It stimulates thyroid functions using specific membrane TSH receptor (TSHR) that belongs to the superfamily of G protein-coupled receptors (GPCRs). New insights into the structure-function relationships of TSH permitted better understanding of the role of specific protein and carbohydrate domains in the synthesis, bioactivity, and clearance of this hormone. Recent progress in studies on TSHR as well as studies on the other GPCRs provided new clues regarding the molecular mechanisms of receptor activation. Such advances are a result of extensive site-directed mutagenesis, peptide and antibody approaches, detailed sequence analyses, and molecular modeling as well as studies on naturally occurring gain- and loss-of-function mutations. This review integrates expanding information on TSH and TSHR structure-function relationships and summarizes current concepts on ligand-dependent and -independent TSHR activation. Special emphasis has been placed on TSH domains involved in receptor recognition, constitutive activity of TSHR, new insights into the evolution of TSH bioactivity, and the development of high-affinity TSH analogs. Such structural, physiological, pathophysiological, evolutionary, and therapeutic implications of TSH-TSHR structure-function studies are frequently discussed in relation to concomitant progress made in studies on gonadotropins and their receptors.

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Section: B Studies Of Protein Domainsmentioning

confidence: 99%

Thyroid-Stimulating Hormone and Thyroid-Stimulating Hormone Receptor Structure-Function Relationships

Szkudlinski

Frémont²,

Ronin³

et al. 2002

Physiological Reviews

398

256

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“…These rare aberrant transcripts would not be expected to make functional protein because the folded tertiary structure of the a-subunit protein is crucial for binding to both [~-subunit and receptor (Lapthorn et al 1994). Secretion of the [3-subunits cannot occur without heterodimerization with the a-subunit (Corless et al 1987;Matzuk et al 1988Matzuk et al , 1989Keene et al 1989). Thus, the targeted disruption created a true null mutation for functional a-subunit in addition to the hormones TSH, LH, and FSH.…”

Section: Left) Paraffin Sections Of Ovaries or Testes Were Stained Wmentioning

confidence: 99%

Targeted disruption of the pituitary glycoprotein hormone alpha-subunit produces hypogonadal and hypothyroid mice.

Kendall¹,

Samuelson²,

Saunders³

et al. 1995

Genes Dev.

246

104

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Pituitary thyrotropin (TSH) and gonadotropins (LH and FSH) are thought to be critical for thyroid and gonadal development and function. Each of these pituitary hormones is a heterodimer composed of a common a-subunit and unique ~-subunit, and heterodimerization is required for function. No mutations in the a-subunit or any of the 13-subunit genes have been reported in mice. To assess directly the functional role of TSH, LH, and FSH in thyroid and gonadal development, we created a disruption of the a-subunit gene by homologous recombination. The homozygous mutant animals were hypogonadal and exhibited profound hypothyroidism resulting in dwarfism. Thyroid development was arrested in late gestation, but GnRH neuron migration, development of secondary sex organs, and fetal and neonatal gonadal development were normal. This establishes the importance of thyrotropin in ontogeny and reveals that fetal pituitary gonadotropins are not required for sexual differentiation or genital development in male or female fetuses. The pituitary cells that produce TSH 13-subunit exhibited dramatic hypertrophy and hyperplasia as a result of the lack of thyroid function. This proliferative response occurred at the expense of somatotrope and lactotrope cells, consistent with a derivation of these three cell types from a common precursor.

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“…The pM2 vector containing the insert encoding the single chain was transfected into CHO cells by calcium phosphate as described (6,11). Stable clones were selected by using the active equivalent of G418 at 0.25 mg/ml.…”

mentioning

confidence: 99%

Biosynthesis of a biologically active single peptide chain containing the human common alpha and chorionic gonadotropin beta subunits in tandem.

Pixley

Minami

et al. 1995

Proc. Natl. Acad. Sci. U.S.A.

105

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One of the distinguishing features of the gonadotropin and thyrotropin hormone family is their heterodimeric structure, consisting of a common a subunit and a hormone-specific f8 subunit. Subunit assembly is vital to the function of these hormones: The conformation of the heterodimer is essential for controlling secretion, hormonespecific posttranslational modifications, and signal transduction. To address whether a and ,3 subunits can be synthesized as one chain and also maintain biological activity, a chimera composed of the human chorionic gonadotropin (hCG) ,3 subunit genetically fused to the a subunit was constructed. question of whether the common a subunit and a hormonespecific (3 subunit can be synthesized as a single chain to achieve the biological response. For structure-function studies, the ability to express a heterodimer as a single biologically active chain would likely avoid mutagenesis-induced defects in combination and secretion of individual subunits. In addition, since subunit dissociation will inactivate the in vivo activity of the heterodimer, single-chain analogs could have a longer biological half-life. A chimera composed of the C-terminal end of hCG(3 genetically fused to the N-terminal end of the a subunit was constructed because these regions can be modified without significant effects on the biological activity of the heterodimer (7,8). Expression of this chimeric gene in CHO cells produced a single polypeptide hCG molecule that was biologically active in vitro and in vivo. These results demonstrate that the a and hCG,B subunits encoded as single chain can fold into an appropriate conformation and that a noncovalent linkage of the a and 13 subunits is not required for biological activity. This approach can be used to further investigate structure-function relationships of hCG and related glycoprotein hormones that were previously not tractable because of the absolute dependence on subunit assembly for biological activity.

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The Glycoprotein α-Subunit is Critical for Secretion and Stability of the Human Thyrotropin β-Subunit

Cited by 69 publications

References 24 publications

Thyroid-Stimulating Hormone and Thyroid-Stimulating Hormone Receptor Structure-Function Relationships

Thyroid-Stimulating Hormone and Thyroid-Stimulating Hormone Receptor Structure-Function Relationships

Targeted disruption of the pituitary glycoprotein hormone alpha-subunit produces hypogonadal and hypothyroid mice.

Biosynthesis of a biologically active single peptide chain containing the human common alpha and chorionic gonadotropin beta subunits in tandem.

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