The position of the alpha and beta subunits in a single chain variant of human chorionic gonadotropin affects the heterodimeric interaction of the subunits and receptor-binding epitopes

Production of Recombinant Single-Chain Eel Luteinizing Hormone and Follicle-Stimulating Hormone Analogs in Chinese Hamster Ovary Suspension Cell Culture

We produced rec-single chain eel luteinizing (rec-eel LH) and follicle-stimulating (rec- eel FSH) hormones displaying high biological activity in Chinese hamster ovary suspension (CHO-S) cells. We constructed several mutants, in which a linker, including an O-linked glycosylated carboxyl-terminal peptide (CTP) of an equine chorionic gonadotropin (eCG) β-subunit, was attached between the β- and α-subunit (LH-M and FSH-M) or in the N-terminal (C-LH and C-FSH) or C-terminal (LH-C and FSH-C) regions. The plasmids were transfected into CHO-S cells, and culture supernatants were collected. The secretion of mutants from the CHO-S cells was faster than that of eel LHβ/α-wt and FSHβ/α-wt proteins. The molecular weight of eel LHβ/α-wt and eel FSHβ/α-wt was 32-34 and 34-36 kDa, respectively, and that of LH-M and FSH-M was 40-43 and 42-45 kDa, respectively. Peptide-N-glycanase F-treatment markedly decreased the molecular weight by approximately 8-10 kDa. The EC50 value and the maximal responsiveness of the eel LH-M and eel FSH-M increased compared with the wild-type proteins. These results show that the CTP region plays a pivotal role in early secretion and signal transduction. We suggest that novel rec-eel LH and FSH proteins, exhibiting potent activity, could be produced in large quantities using a stable CHO cell system.

The Conundrum of Poor Ovarian Response: From Diagnosis to Treatment

Despite recent striking advances in assisted reproductive technology (ART), poor ovarian response (POR) diagnosis and treatment is still considered challenging. Poor responders constitute a heterogeneous cohort with the common denominator of under-responding to controlled ovarian stimulation. Inevitably, respective success rates are significantly compromised. As POR pathophysiology entails the elusive factor of compromised ovarian function, both diagnosis and management fuel an ongoing heated debate depicted in the literature. From the criteria employed for diagnosis to the plethora of strategies and adjuvant therapies proposed, the conundrum of POR still puzzles the practitioner. What is more, novel treatment approaches from stem cell therapy and platelet-rich plasma intra-ovarian infusion to mitochondrial replacement therapy have emerged, albeit not claiming clinical routine status yet. The complex and time sensitive nature of this subgroup of infertile patients indicates the demand for a consensus on a horizontally accepted definition, diagnosis and subsequent effective treating strategy. This critical review analyzes the standing criteria employed in order to diagnose and aptly categorize POR patients, while it proceeds to critically evaluate current and novel strategies regarding their management. Discrepancies in diagnosis and respective implications are discussed, while the existing diversity in management options highlights the need for individualized management.

Gonadotropins and Their Analogs: Current and Potential Clinical Applications

The gonadotropin receptors LH receptor and FSH receptor play a central role in governing reproductive competency/fertility. Gonadotropin hormone analogs have been used clinically for decades in assisted reproductive therapies and in the treatment of various infertility disorders. Though these treatments are effective, the clinical protocols demand multiple injections, and the hormone preparations can lack uniformity and stability. The past two decades have seen a drive to develop chimeric and modified peptide analogs with more desirable pharmacokinetic profiles, with some displaying clinical efficacy, such as corifollitropin alfa, which is now in clinical use. More recently, low-molecular-weight, orally active molecules with activity at gonadotropin receptors have been developed. Some have excellent characteristics in animals and in human studies but have not reached the market-largely as a result of acquisitions by large pharma. Nonetheless, such molecules have the potential to mitigate risks currently associated with gonadotropin-based fertility treatments, such as ovarian hyperstimulation syndrome and the demands of injection-based therapies. There is also scope for novel use beyond the current remit of gonadotropin analogs in fertility treatments, including application as novel contraceptives; in the treatment of polycystic ovary syndrome; in the restoration of function to inactivating mutations of gonadotropin receptors; in the treatment of ovarian and prostate cancers; and in the prevention of bone loss and weight gain in postmenopausal women. Here we review the properties and clinical application of current gonadotropin preparations and their analogs, as well as the development of novel orally active, small-molecule nonpeptide analogs.

Site specificity of eel luteinizing hormone N-linked oligosaccharides in signal transduction

Eel luteinizing hormone (eelLH) is composed of a common α-subunit and hormone specific β-subunit, both of which contain asparagine-linked carbohydrate residues, located at positions 56 and 79 on the α-subunit and position 10 on the β-subunit. The specific roles of the individual carbohydrate chains are poorly defined in eel. Thus, we characterized the biologically active single chains by fusing the α-subunit to the carboxyl terminal region of the eelLH β-subunit. Site-directed mutagenesis of the three N-linked glycosylation sites was performed to examine the function of individual glycosylation sites in secretion and signal transduction. The absence of the Asn⁷⁹N-linked sugar chain slightly reduced secretion in Chinese hamster ovary (CHO) cells. The expression of eelLHβ/α (wild-type) in CHO suspension cells was increased by approximately 2-fold higher than that of attached CHO cells. By western blotting analysis, the molecular weight of wild-type was found to be 32 kDa. Mutants (β/α△56, β/α△79, and β△10/α) of the oligosaccharide chain at a single site showed molecular weights that were reduced by approximately 10%. However, the double mutant (β/α△56.79) molecular weight was decreased by more than 20% compared to the wild-type. Enzymatic digestion of oligosaccharides using PNGaseF treatment showed that the molecular weights of all mutants, including wild-type, were reduced to 25 kDa. The results obtained in the absence of carbohydrates at Asn⁵⁶ of the α-subunit and at Asn¹⁰ of the β-subunit revealed their roles in signal transduction through the eelLH receptor. The EC₅₀ value of the cAMP response at Asn⁷⁹ of the α-subunit was increased by 5-fold, whereas the maximum response was dramatically reduced to 17.8% of wild-type levels. Specifically, removal of the carbohydrates at double mutant (β/α△56.79) is approximately 85% to wild-type levels in biopotency. These results revealed the site-specific roles of eelLH carbohydrate residues. Our data suggest that N-linked oligosaccharide chains play a pivotal role in biological activity through the eelLH receptor.

Modulation of the steroidogenic related activity according to the design of single-chain bovine FSH analogs

Single-chain (SC) gonadotropins have been genetically engineered to increase the repertoire of analogs for potential use in humans and domestic animals. The major aim of the current study was to examine the steroidogenic related activity of SC FSH analogs carrying structural differences. To address this issue, we designed and expressed three SC bovine FSH analogs in CHO cells: (i) FSHβα in which the tethered subunit domains are linked in tandem; (ii) FSHβCTPα that contains the carboxy terminal peptide (CTP) of the human choriogonadotropin (hCG) β subunit as a spacer, and (iii) FSHβboCTPα in which the linker is derived from a CTP-like sequence (boCTP) decoded from the bovine LHβ DNA. The data suggested that the secretion efficiency of these variants from the transfected cells was unaffected by the presence or absence of the CTP linker, N-glycans were attached to the analogs and the hCGβ-CTP domain in the FSHβCTPα variant was O-glycosylated. In a rat immortalized granulosa cell bioassay the potency of the three variants towards progesterone secretion varied. In immature mice, the analogs increased the ovary weight and induced StAR, Cyp11a (P450scc), Cyp17 (P450c17) and Cyp19 (P450aromatase) transcripts. However, the dose dependence and amplitude of these transcript levels differed in response to FSHβα, FSHβboCTPα and FSHβCTPα. Collectively, these data suggest that the design of the FSH analog can modulate the bioactivity in vitro and in vivo. A systematic analysis of receptor activation with ligands carrying structural differences may identify new regulatory factor/s involved in the pleiotropic FSH activity.

Cloning and sequencing of feline thyrotropin (fTSH): heterodimeric and yoked constructs

The genes encoding the mature common glycoprotein alpha (CGA) and hormone-specific beta subunits of feline thyroid stimulating hormone (fTSH) were cloned and sequenced. The feline CGA gene was cloned from RNA extracted from the feline pituitary gland by the reverse transcription polymerase chain reaction (RT-PCR). The gene fragment that encodes mature TSHbeta was cloned from feline genomic DNA after direct polymerase chain reaction (PCR). In both cases, primers were based on the consensus sequences from TSH in other species. The resulting 510 bp PCR product for the CGA-subunit included the full coding sequence for the 96 amino acid mature subunit preceded by a 24 amino acid signal peptide. The 850 bp sequence of fTSHbeta genomic DNA consisted of two coding exons, an intron of 418 bp, and a 60 bp signal sequence. The octapeptide immunoaffinity tag FLAG was added to 3' end of the alpha gene to facilitate detection and purification. Both genes were cloned independently downstream from the EF1alpha promoter of the PEAK transfer vector to facilitate co-expression studies in PEAK cells (modified human embryonic kidney (HEK) cells). A single-chain analogue of fTSH termed yoked fTSH (yfTSH) was developed by fusing the nucleotides encoding the C-terminus of the beta-subunit fused to the N-terminus of the alpha-subunit with DNA encoding the C-terminal peptide (CTP) of human chorionic gonadotropin beta-subunit as a linker peptide. The resulting single-chain analogue encoded from N-terminus to C-terminus: beta-CTP-alpha-FLAG. The resulting DNA sequence was cloned, sequenced, ligated and recloned into expression vector PEAK. This report constitutes the first cloning and sequencing of the genes encoding the subunits of feline thyrotropin.

Gonadotropin-induced adrenocortical neoplasia in NU/J nude mice

In response to prepubertal gonadectomy certain inbred mouse strains, including DBA/2J, develop sex steroid-producing adrenocortical neoplasms. This phenomenon has been attributed to a lack of gonadal hormones or a compensatory increase in gonadotropins. To assess the relative importance of these mechanisms, we created a new inbred model of adrenocortical neoplasia using female NU/J nude mice. These mice developed adrenocortical neoplasms in response to either gonadectomy or gonadotropin elevation from xenografts of human chorionic gonadotropin (hCG)-secreting Chinese hamster ovary cells. In each instance the adrenal tumors resembled the neoplasms found in gonadectomized DBA/2J mice and were composed of spindle-shaped A cells and lipid-laden B cells. Both cell populations were defined by ectopic expression of GATA-4 and an absence of the adrenocortical markers melanocortin-2-receptor and steroid 21-hydroxylase, but only B cells expressed the gonadal steroidogenic markers inhibin-alpha, LH receptor, P450c17, and P450c19. Expression of sex steroidogenic markers was attenuated in the neoplastic adrenal cortex of hCG-treated vs. gonadectomized mice. Whereas neoplastic adrenals were an obvious source of estradiol in gonadectomized mice, ovaries appeared to be the major source of this hormone in hCG-treated mice. Gonadectomy and hCG treatment elicited comparable increases in serum estradiol, but testosterone levels increased significantly only in hCG-treated mice. We conclude that chronic gonadotropin elevation, caused by either gonadectomy or hCG administration, signals a population of cells in the adrenal subcapsular region of permissive mice to undergo differentiation along a gonadal rather than an adrenal lineage. Thus, NU/J nude mice can be used as a model to study both neoplasia and adrenogonadal lineage specification.

Nude mice as a model for gonadotropin-induced adrenocortical neoplasia

Certain inbred mice (e.g., DBA/2J, CE) develop sex steroid producing adrenocortical tumors following gonadectomy. This adrenal response is thought to result from an unopposed increase in circulating gonadotropins and/or a decrease in factor(s) of gonadal origin. To differentiate between these two possibilities, we utilized the NU/J strain of nude mice, which are immunologically compromised and therefore permissive to xenografts. One group of female nude mice was gonadectomized, while another group of females received xenografts of CHO cells stably transfected with human chorionic gonadotropin (hCG). After 1-2 months, subcapsular adrenocortical neoplasms containing sex steroid-producing cells were observed in both groups. We conclude that high levels of circulating gonadotropins are sufficient to induce adrenocortical tumorigenesis, even in the presence of intact gonads.

Structural analysis of yoked chorionic gonadotropin-luteinizing hormone receptor ectodomain complexes by circular dichroic spectroscopy

Binding of the heterodimeric glycoprotein hormone, chorionic gonadotropin (CG), occurs to the heptahelical LH receptor N-terminal ectodomain (ECD), a large portion of which has been modeled as a leucine-rich repeat protein. In this study, we expressed and purified three single chain N-CG-ECD-C complexes, one comprising the full-length ECD, 1-341 (encoded by exons 1-10 and a portion of 11), and two C-terminal ECD deletion fragments, 1-294 (encoded by exons 1-10) and 1-180 (encoded by exons 1-7). The fusion proteins, including yoked CG (N-beta-alpha-C), were characterized by Western blot analysis and circular dichroism (CD). Analysis of the CD spectra obtained on the CG-ECD fusion proteins, and of the difference spectrum of each after subtracting the CG contribution, yielded secondary structures consistent with a repeating beta-strand/alpha-helix fold as predicted in the homology model. A marked decrease in helicity was observed when the C-terminal 47 amino acid residues were removed from the ECD. Removal of an additional 114 residues, i.e. the region encoded by exons 8-10, results in the loss of fewer helical residues. These results suggest that the hinge region of the ECD, predicted to contain only limited secondary structure, interacts with and stabilizes the ligand-occupied N-terminal portion. Furthermore, the results support a repeating fold, consistent with the proposed model for the LHR ECD.

Consequences of single-chain translation on the structures of two chorionic gonadotropin yoked analogs in alpha-beta and beta-alpha configurations

Human chorionic gonadotropin (hCG) is a placental-derived heterodimeric glycoprotein hormone, which, through the binding and activation of the LH receptor, rescues the corpus luteum and maintains pregnancy. The three-dimensional structure of hCG is known; however, the relevance of its fold to bioactivity is unclear. Although both subunits (alpha and beta) are required for activity, recent data with single-chain analogs have suggested a diminished role for the cystine knot and an intact heterodimeric interface in binding and receptor activation in vitro. Herein, we report the purification and structural characterization of two yoked (Y) hCG analogs, YhCG1 (beta-alpha) and YhCG3 (alpha-beta). The fusion proteins yielded higher IC50s and EC50s than those of hCG; the maximal hCG-mediated cAMP production, however, was the same. Circular dichroic spectroscopy revealed that the three proteins exhibit distinct far UV circular dichroic spectra, with YhCG1 containing somewhat more secondary structure than YhCG3 and hCG. Limited proteolysis with proteinase K indicated that heterodimeric hCG was much more resistant to cleavage than the single-chain analogs. YhCG1 was more susceptible to proteolysis than YhCG3, and the fragmentation patterns were different in the two proteins. Taken together, the data presented herein provide direct structural evidence for altered three-dimensional conformations in the two single-chain hCG analogs. Thus, the cognate G protein-coupled receptor can recognize and functionally respond to multiple ligand conformations.

Specificity of cognate ligand-receptor interactions: fusion proteins of human chorionic gonadotropin and the heptahelical receptors for human luteinizing hormone, thyroid-stimulating hormone, and follicle-stimulating hormone

The family of glycoprotein hormones and their homologous heptahelical receptors represent an excellent system for comparative structure-function studies. We have engineered single chain molecules of human chorionic gonadotropin (hCG) fused to its cognate receptor, LH receptor (LHR), and to the noncognate receptors, TSH receptor (TSHR) and FSH receptor (FSHR; N-beta-alpha-receptor-C), to create the yoked (Y) complexes YCG/LHR, YCG/TSHR, and YCG/FSHR. The expression and bioactivity of these fusion proteins were examined in transiently transfected HEK 293 cells. Western blot analysis and antibody binding assays demonstrated that each of the proteins was expressed. In the case of YCG/LHR, minimal binding of exogenous hormone was observed due to the continued occupation of receptor by the fused ligand. The presence of hCG in the YCG/TSHR and YCG/FSHR, however, did not prevent binding of exogenous cognate ligand, presumably due to the lower affinity of hCG. The basal cAMP levels in cells expressing the YCG/LHR complex was approximately 20-fold higher than that in cells expressing LHR. Increases in basal cAMP production were also observed with YCG/TSHR and YCG/FSHR, e.g. 13- and 4-fold increases, respectively. Whereas the affinity and specificity of hCG for LHR are extraordinarily high, the hormone is capable of binding to and activating both TSHR and FSHR under these conditions that mimic high ligand concentrations. These findings were confirmed by adding high concentrations of hCG to cells expressing TSHR and FSHR. Although the functional interaction of hCG and TSHR has been recognized in gestational hyperthyroidism, there are no reports linking hCG to FSHR activation. This study, however, suggests that such a functional interaction is capable of occurring under conditions of high circulating levels of hCG, e.g. the first trimester of pregnancy and in patients with hCG-secreting tumors.