In this study, the structure and function of gonadotropin-releasing hormone (GnRH) in different vertebrate species, in the classes Aves, Reptilia and Pisces was investigated. Acetic acid extracts were subjected to gel filtration chromatography and semipreparative high performance liquid chromatography (HPLC) to partially purify the GnRHs. The GnRH immunoreactivity was then characterized by analytical HPLC, and by assaying HPLC fractions by radioimmunoassay with region-specific antisera generated against mammalian GnRH, Gln⁸-GnRH and Trp⁷,Leu⁸-GnRH and assessing luteinizing hormone (LH)-releasing activity of fractions in a chicken dispersed anterior pituitary cell bioassay. Five GnRH molecular forms have thusfar been structurally characterized in vertebrate brain. In mammals a GnRH with the structure pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH₂ has been demonstrated in the hypothalamus (Matsuo et al., 1971; Burgus et al., 1972). Gln⁸-GnRH and His⁵,Trp⁷,Tyr⁸-GnRH were present in chicken hypothalamus (King and Millar, 1982a, 1982c; Miyamoto et al., 1983, 1984), Trp⁷,Leu⁸-GnRH in salmon brain (Sherwood et al., 1983) and Tyr³,Leu⁵,Glu⁶,Trp⁷,Lys⁸-GnRH in lamprey brain (Sherwood et al., 1986). In ostrich (Struthio camelus) hypothalamus two GnRHs with identical properties to Gln⁸-GnRH and His⁵,Trp⁷,Tyr⁸-GnRH have been demonstrated, as well as four other LR-releasing factors with different chromatographic and immunological properties to any of the known naturally-occurring GnRHs. Since Gln⁸-GnRH and His⁵,Trp⁷,Tyr⁸-GnRH were also present in chicken hypothalamus it appears likely that these two GnRHs occur in all birds. In alligator (Alligator mississippiensis) brain only two GnRHs were detected. These forms co-eluted with Gln⁸-GnRH and His⁵,Trp⁷,Tyr⁸-GnRH in two HPLC systems. They cross-reacted similarly to the two synthetic peptides with antisera directed against mammalian GnRH and Gln⁸-GnRH and released LH from chicken dispersed anterior pituitary cells in a similar manner to the synthetic peptides. The Archosaurs (alligators and crocodiles) are believed to be closely related to birds and therefore it seems likely that they should have identical GnRHs. In skink (Calcides ocellatus tiligugu) brain one GnRH, which co-eluted with His⁵,Trp⁷,Tyr⁸-GnRH, was demonstrated. Two other lizards (Cordylis nigra and Pordarcis s. sicula) have been studied (Powell et al., 1985; R.C. Powell, G. Ciarcia, V. Lance, R.P. Millar and J.A. King, submitted). In c. nigra four immunoreactive GnRHs were detected, two of which co-eluted released chicken LH similarly to, Trp⁷,Leu⁸-GnRH and with, and His⁵,Trp⁷,Tyr⁸-GnRH. In P. s. sicula a GnRH molecular form similar to Trp⁷,Leu⁸-GnRH occurred as well as two novel GnRHs. It thus appears that Gln⁸-GnRH does not occur in lower reptiles, but His⁵,Trp⁷,Tyr⁸-GnRH and/or Trp⁷,Leu⁸-GnRH do. His⁵,Trp⁷,Tyr⁸-GnRH appears to he a widespread GnRH, occurring in vertebrates as diverse as birds and elasmobranch fish. In dogfish (Poroderma africanum) brain seven factors, which stimulated release of LH from chicken dispersed anterior pituitary cells, were separated on analytical HPLC. Two of these factors were partially characterized as Trp⁷,Leu⁸-GnRH and His⁵,Trp⁷,Tyr⁸-GnRH. Three of the other forms cross-reacted with GnRH antisera, but appear to be novel GnRHs. In teleost (Coris julis) brain two GnRHs similar to Trp⁷,Leu⁸-GnRH and His⁵,Trp⁷,Tyr⁸-GnRH were present. These two GnRHs therefore appear to occur in both fish species studied. Trp⁷,Leu⁸-GnRH is widespread amongst teleost fish (Jackson and Pan, 1983; Sherwood et al., 1983; Breton et al., 1984; Sherwood et al., 1984; King and Millar, 1985). From these data it seems evident that the mammalian GnRH molecular form occurs only in mammals and amphibians, Gln⁸-GnRH in birds and higher reptiles, and Trp⁷,Leu⁸-GnRH in gnathostomes. His⁵,Trp⁷, Tyr⁸-GnRH appears to he present in numerous different vertebrates. Tyr³,Leu⁵,Glu⁶,Trp⁷,Lys⁸-GnRH has thus far only been detected in lamprey brain. A number of novel GnRHs, whose structures have not been elucidated are present.

In a HEK 293 cell line stably expressing seabream GHS-R1a (sbGHS-R1a), we found that a synthetic growth hormone secretagogue (GHS) increased [ 3H]-inositol phosphate production, clearly indicating coupling of this receptor to Gq/11-proteins. Using Western blotting, we found that GHS could also stimulate extracellular signal-regulated kinases 1 and 2 (ERK1/2), and that this response was inhibited by the MEK inhibitor U0126. For both the [3H]-inositol phosphate and ERK1/2 assays, the presence of the GHS-R antagonist D-Lys(3)-GHRP-6 significantly inhibited the GHS-stimulated activities, and in addition inhibited basal activities by 50% and 40%, respectively. These results showed that sbGHS-R1a is a constitutively active receptor and the antagonist D-Lys(3)-GHRP-6 is an inverse agonist. We also proposed that the expression of sbGHS-Rs was involved in the regulation of cell apoptosis. / Oligomerization of the human GHS-Rs (hGHS-Rs) was explored by transient transfection of the hGHS-Rs in HEK 293 cells followed by co-immunoprecipitation of differentially epitope-tagged forms of the receptors and bioluminescence resonance energy transfer 2 (BRET2) studies. (Abstract shortened by UMI.) / The concept that G protein-coupled receptors (GPCRs) exist and potentially function as dimers and/or higher oligomers has progressed from hypothesis to being widely accepted recently. Oligomerization of GPCRs has been increasingly noted in the regulation of the biological activity of the receptors. The growth hormone secretagogue receptor 1a (GHS-R1a) is a GPCR which principally regulates the pulsatile release of growth hormone from the pituitary gland. The GHS-R exists in two forms: GHS-R1a being a constitutively-active GPCR with 7 transmembrane (TM) domains, and GHS-R1b being a truncated version of type 1a but having only 5 TM domains. The endogenous agonist for GHS-R1a is ghrelin which exerts a wide range of physiological actions, but the function of GHS-R1b is still unclear. Since the tissue distribution patterns of the two isoforms of GHS-R are different, the objective of the present study is to explore the mechanisms of cell signalling of GHS-R1a and to determine the extent and importance of interactions between these two receptor isoforms. / Leung Po Ki. / "July 2005." / Adviser: Helen Wise. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3728. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 189-210). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / School code: 1307.

Thesis (MSc (Biochemistry))--Stellenbosch University, 2008. / Gonadotropin-releasing hormone (GnRH) acting through the cognate GnRH receptor (GnRH-R) plays an important role in the regulation of mammalian reproductive function by regulating the synthesis and release of follicle stimulating hormone (FSH) and luteinizing hormone (LH). The sensitivity of pituitary gonadotropes to GnRH depends on the number of GnRH receptors present on the gonadotrope cell surface. GnRH-R is regulated at a transcriptional, post-transcriptional and post-translational level. Hormones such as GnRH and glucocorticoids (GCs) regulate GnRH-Rs in a time- and dose-dependent manner. Previous studies have shown that the GnRH-R promoter confers glucocorticoid-dependent activation via the activating protein 1 (AP-1) site in the nongonadotrope GGH3 cell line. The mechanism by which GCs regulate the GnRH-R promoter is not precisely known as the literature is contradictory. Therefore this study investigates the mechanism of transcriptional regulation of the mouse GnRH-R promoter in the mouse gonadotrope cell line LβT2, treated with the synthetic GC dexamethasone (dex). Assays used include promoter-reporter studies, Western blotting, endogenous mRNA expression studies, electrophoretic mobility shift assay (EMSA) as well as the in vivo chromatin immunoprecipitation (ChIP) assay. A transfected promoter-reporter plasmid containing 600 bp of the mouse GnRH-R promoter was used to investigate the effect of dex on transcriptional regulation. Previously it was determined in our laboratory that the GnRH-R promoter is activated via an AP-1 binding site in the LβT2 cell line, and is regulated in a time- and dose-dependent manner by dex. In the present study in the LβT2 cell line a small induction was indeed seen upon dex treatment. Cotransfecting a expression vector for rat GR succeeded in inducing a 2 fold positive dex response. Western blot analysis revealed that GR levels remain consistent even after 8 hours dex induction. The effect of dex on the endogenous GnRH-R gene was investigated by means of real-time RT-PCR. Dex did indeed upregulate the gene in a time-dependant manner. Maximal induction (7.4 fold) was obtained after at least 12 hours of dex treatment. Untreated LβT2 nuclear extracts were investigated using EMSA, for protein binding to the mouse GnRH-R promoter AP-1 binding site, and these proteins were identified as c- Fos and GR. This suggests that the GR interacts with the AP-1 transcription factor via a tethering mechanism to mediate the positive dex response. The results of an in vivo ChIP assay were consistent with this hypothesis, showing that the GR interacted with a genomic fragment containingthe AP-1 site, in response to dex. The transactivation of the GnRH-R promoter by means of the GR tethering to AP-1 has not been shown before in the LβT2 cell line.

Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The regulation of gonadotropin releasing hormone (GnRH) receptor numbers in the pituitary is a crucial control point in reproduction. Pituitary sensitivity to GnRH can be directly correlated with GnRH receptor levels, which can be regulated at transcriptional and post-transcriptional level. The proximal promoter of the mouse GnRH receptor gene contains two cis elements bearing the consensus sequence for a Steroidogenic Factor-l (SF -1) binding site. The distal site has previously been shown to be involved in basal and tissue-specific transcriptional regulation, whereas the function of the proximal site was not established. SF-I, a member of the nuclear receptor superfamily of transcription factors, is involved in the transcriptional regulation of a large number of genes involved in steroidogenesis and reproduction. The consensus SF-I binding site can serve as a binding site for several members of the nuclear receptor superfamily. The aim of this study was to investigate the binding of SF-I protein from the aT3-1 gonadotrope cell line to the two putative SF-I binding sites in the mouse GnRH receptor promoter in vitro, in order to provide supporting evidence for their functional roles in GnRH receptor gene regulation. It was shown by Western blotting that SF-I and Nur77, another nuclear receptor transcription factor, are both expressed in aT3-1 cells, in a manner that is influenced by cell culture conditions. Gel mobility shift assays using specific antibodies showed that both SF-I and Nur77 protein in aT3-1 nuclear extracts bind to both sites in a mutually exclusive fashion. As shown by competition assays using mutated versions of the two sites, Nur77 protein had different base pair requirements than that of SF-I protein for binding to the sites. Additionally, SF-I mRNA was shown by Northern blotting to be increased in aT3-1 cells in response to stimulation of the Protein Kinase A (PKA) pathway by forskolin. These results highlight unexpected degeneracy in so-called "consensus" nuclear receptor binding sites. Furthermore, since Nur77 protein is involved in the stress response of the hypothalamic-pituitary-adrenal (HPA) axis, the unexpected presence of Nur77 protein in a gonadotrope cell line has potentially important implications for cross-talk between the HPA and hypothalamic-pituitary-gonadal (HPG) axes. / AFRIKAANSE OPSOMMING: Daar bestaan 'n direkte verband tussen pituïtêre sensitiwiteit vir gonadotropien-vrystellingshormoon (GnRH) en GnRH-reseptorvlakke Die regulering van GnRH-reseptorvlakke op transkripsionele en post-transkripsionele vlak in die pituïtêre klier is belangrik by die beheer van voortplantingsfunksies. Die proksimale promotor van die GnRH-reseptorgeen in die muis bevat twee cis elemente met die konsensus volgorde vir 'n Steroidogenic Factor-l (SF-I) bindingsetel. Die distale element is betrokke by basale en weefsel-spesifieke transkripsionele regulering, maar die funksie van die proksimale element is nog nie vasgestel nie. SF-1 is 'n lid van die superfamilie van selkernreseptore en is betrokke by die transkripsionele regulering van gene verantwoordelik vir steroïedogenese en voortplanting. Die konsensus SF-I bindingsvolgorde kan dien as bindingsetel vir verskeie selkernreseptore. Ten einde 'n beter insig ten opsigte van die regulering van die GnRH reseptorgeen te verkry, is ondersoek ingestel na die binding van SF-I-proteïen, afkomstig van die aT3-1 pituïtêre gonadotroopsellyn, aan die twee moontlike SF-l bindingsetels in die GnRH-reseptor promotor, in vitro. Die Western-klad metode het getoon dat beide SF-l en Nur77, 'n ander selkernreseptor-transkripsiefaktor, in die aT3-1 sellyn uitgedruk word. Die uitdrukking is afhanklik van selkultuurtoestande. Elektroforetiese mobiliteitsessais met spesifieke antiliggame het getoon dat SF-l en Nur77 proteïene in aT3-1 selkernproteïenekstraksies eksklusief aan beide bindingsetels bind. Nur77 proteïen benodig ander basispare as SF-l proteïen om aan die bindingsetels te bind. Hierdie resultate dui op onverwagse degenerasie in sogenaamde "konsensus" selkernreseptor-bindingsvolgordes. Die Northern-kladmetode het ook getoon dat SF-l mRNA vlakke in aT3-1 selle styg wanneer die proteïenkinase A (PKA) pad gestimuleer word met forskolin. Aangesien Nur77 proteïen betrokke is by die stres-respons van die hipotalamus-pituïtêre klier-adrenale (HP A) aksis, hou die onverwagse teenwoordigheid van Nur77 proteïen in 'n gonadotroop-sellyn potensieel belangrike inplikasies in vir kommunikasie tussen die HPA-aksis en die hipotalamus-pituïtêre klier-gonadale (HPG) aksis.

Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The GnRH receptor is a G-protein-coupled receptor in pituitary gonadotrope cells. Binding of its ligand, GnRH, results in synthesis and release of gonadotropin hormones luteinizing hormone (LH) and follicle stimulating hormone (FSH). Steroidogenic factor 1 (SF-1), a transcription factor, binds to specific sites in the promoter region of gonadotropin genes, and thus regulates transcription of these genes. The promoter region of the GnRHreceptor gene contains two SF-1-like binding sites, one at -14 to -8 (site 1) and another at -247 to -239 (site 2), relative to the methionine start codon. The role played by these two SF-1-like sites in basal transcription of the mouse GnRH receptor (mGnRH-R) gene in a pituitary precursor gonadotrope cell line, aT3 cells, was the first area of investigation during this study. Luciferase reporter constructs containing 580 bp of mGnRH-R gene promoter were prepared, where SF-1-like sites were either wildtype or mutated. Four such constructs were made, i.e. wildtype (LG), site 1 mutant (LGM1), site 2 mutant (LGM2) and mutated site 1 plus site 2 (LGM1/2). These constructs were transfected into aT3 cells to determine the effect of mutations of sites 1 and/or 2 on the basal expression of the mGnRH-R gene. Mutation of either site 1 or site 2 had no effect on basal expression of the mGnRH-R gene. It was found that only upon simultaneous mutation of both sites 1 and 2, a 50% reduction in basal transcription took place. The implications of this is that SF-1 protein seems to only require one intact DNA-binding site, to mediate basal transcription of the mGnRH-R gene, suggesting that these two sites lie in close proximity during basal transcription. The effect of the protein kinase A (PKA) pathway on the endogenous mGnRH-R gene was also investigated by incubating non- , transfected aT3 cells with the PKA activators, forskolin and 8-Br-cAMP. Similar incubations were also performed on the wild type and mutated site 1 constructs transfected into pituitary gonadotrope aT3 cells. It was found that forskolin and 8-Br-cAMP were able to increase endogenous mGnRH-R mRNA levels in a concentration-dependent fashion, showing that endogenous GnRH receptor gene expression is stimulated via a protein kinase A pathway. Similar results were obtained with the wildtype promoter construct, showing that the protein kinase A pathway stimulates transcription of the promoter. This effect was only seen with wild type and not with the mutated site 1. These results are consistent with a role for a SF-1-like transcription factor in mediating the protein kinase A effect via binding to the site 1 at position -14 in the GnRH receptor gene. A separate investigation was performed to determine whether 25-hydroxycholesterol (25-0HC) is a ligand for SF-1, by incubating aT3 cells transfected with the various constructs with 25-0HC. Results show a dose-dependant response, with an increase in gene expression at 1 μM and a decrease at higher concentrations, for both mutant and wild type constructs. This suggests that, if SF-1 is indeed the protein binding to sites 1 and 2, then 25-0HC is not a ligand for SF-1 protein in aT3 cells and that the effect of 25-0HC on the mGnRH-R gene is not mediated via site 1. The results indicate that these decreases of expression at the higher concentrations may be due to cytotoxic effects. Towards the end of the study the laboratory obtained a luminoskan instrument with automatic dispensing features. Optimisation studies on the luciferase and β-Gal assays were performed on the luminoskan in a bid to decrease experimental error. It was found that automation of these assays resulted in a decrease in experimental error, showing that future researchers could benefit substantially from these optimisation studies. / AFRIKAANSE OPSOMMING: Die GnRH reseptor is 'n G proteïen-gekoppelde reseptor in pituitêre gonadotroopselle. Binding van die ligand, GnRH, lei tot die sintese en vrystelling van die gonadotropien hormone, luteïniserende hormoon (LH) en follikel stimulerende hormoon (FSH). Steroidogeniese faktor-t (SF-1) is 'n transkripsie faktor wat aan spesifieke areas in die promotergebied van die gonadotropien hormone bind, en dus transkripsie van hierdie gene reguleer. Die promotergebied van die GnRH reseptor geen bevat twee SF-1 bindings areas, een by -14 to -8 (area 1) asook by -247 to -239 (area 2), relatief to die metionien beginkodon. Die rol wat hierdie twee SF-1 areas speel in basale transkripsie van die muis GnRH reseptor (mGnRH-R) geen in 'n pituïtêre voorloper gonadotroop sellyn, aT3 selle, was die eerste gebied van ondersoek gedurende hierdie studie. Plasmiede bestaande uit die 580 basispaar mGnRH-R promoter verbind aan 'n lusiferase geen is vervaardig, waar SF-1-soortige areas enersyds onveranderd gelaat is, of gemuteer is. Vier sulke plasmiede is vervaardig, nl. onveranderd (LG), area 1 mutant (LGM1), area 2 mutant (LGM2) en gemuteerde area 1 plus area 2 (LGM1/2). Hierdie plasmiede is gebruik om aT3 selle te transfekteer om die effek van mutasies van areas 1 en/of 2 op die basale ekspressie van die mGnRH-R geen te ondersoek. Daar is gevind dat mutasies van areas 1 of 2 geen effek op basale ekspressie op die bogenoemde geen gehad het nie. Slegs tydens gelyktydige mutasie van areas 1 en 2 het 'n 50% vermindering in basale transkripsie plaasgevind. Die implikasies hiervan is dat die SF-1 proteïen blykbaar slegs een volledige DNA-bindingsarea benodig om basale transkripsie van die mGnRH-R geen te reguleer. Dit wil dus voorkom of hierdie twee areas baie na aan mekaar geposisioneer is tydens basale transkripsie. Die effek van die proteïen kinase A (PKA) roete op die natuurlike mGnRH-R geen is ook ondersoek tydens inkubasie van nie-getransfekteerde aT3 selle met die PKA akiveerders, forskolin en 8-Br-cAMP. Soortgelyke inkubasie is ook gedoen op die onveranderde en gemuteerde area 1 plasmiede wat in aT3 selle getransfekteer is. Daar is gevind dat forskolin en 8-Br-cAMP daarin geslaag het om die natuurlike mGnRH-R geen mRNA vlakke op 'n konsentrasie-afhanklike wyse te vermeerder. Hierdie resultaat dui daarop aan dat die natuurlike mGnRH-R geen se ekspressie gestimuleer kan word via 'n proteïen kinase A roete. Soortgelyke resultate is verkry met die onveranderde promoter plasmied en dit wys ook daarop dat proteïen kinase A transkripsie deur die promoter kan stimuleer. Hierdie effek was slegs aanwesig met die onveranderde en nie met die gemuteerde area 1 plasmied nie. Die resultate stem ooreen met 'n rol vir SF-1 transkripsie faktor in die regulering van proteren kinase A effek deur middel van binding aan die area 1 by posisie -14 in die GnRH-R geen. 'n Afsonderlike ondersoek is gedoen om vas te stel of 25-hidroksiecholesterol (25-0HC) 'n ligand vir SF-1 is deur getransfekteerde aT3 selle met 25-0HC te inkubeer. Resultate toon 'n dosis-afhanklike respons met 'n verhoging in geen ekspressie by 1 μM en 'n verlaging met hoër konsentrasies vir beide onveranderde en gemuteerde plasmiede. Dit impliseer dat, indien SF-1 wel die faktor is wat aan areas 1 en 2 bind, 25-0HC nie die ligand vir SF-1 proteren in aT3 selle is nie en dat die effek van 25-0HC op die mGnRH-R geen nie gereguleer word via area 1 nie. Die verlaging in ekspressie gevind by die hoër konsentrasies is dalk die gevolg van sitotoksiese effekte. Teen die einde van die studie het die laboratorium luminoskan toerusting met outomatiese pipettering verkry. Optimiseringstudies van die lusifirase en β-Galtoetse is met die luminoskan gedoen in 'n poging om eksperimentele foute te minimaliseer. Daar is gevind dat outomatisering van hierdie toetse wel gelei het tot 'n verlaging in eksperimentele foute. Toekomstige navorsers kan dus grootliks voordeel trek uit hierdie optimiseringstudies.

Thesis (PhD (Biochemistry))--University of Stellenbosch, 2006. / Gonadotropin-releasing hormone (GnRH), acting via its cognate receptor (GnRHR) is the primary regulator of mammalian reproductive function. Pituitary sensitivity to GnRH can be directly correlated with GnRHR levels on the surface of the pituitary gonadotrope cells, which can be regulated at transcriptional, post-transcriptional and post-translational levels. This study investigated mechanisms of transcriptional regulation of mouse GnRHR expression in two mouse gonadotrope cell lines, αT3-1 and LβT2, using a combination of endogenous mRNA expression studies, promoter-reporter studies, a two-hybrid protein-protein interaction assay, Western blotting, and in vitro protein-DNA binding studies. In the first part of the study, the role of two GnRHR promoter nuclear receptor binding sites (NRSs) and their cognate transcription factors in basal and Protein Kinase A (PKA)-stimulated regulation of GnRHR promoter activity was investigated in αT3-1 cells. The distal NRS was found to be crucial for basal promoter activity in these cells. While the NRSs were not required for the PKA response in these cells, results indicate a modulatory role for the transcription factors Steroidogenic Factor-1 (SF-1) and Nur77 via these promoter elements. The second part of the study focused on elucidating the mechanism of homologous regulation of GnRHR transcription in LβT2 cells, with a view to defining the respective roles of PKA and Protein Kinase C (PKC) in the transcriptional response to GnRH. In addition, the respective roles of the NRSs, the cyclic AMP response element (CRE) and the Activator Protein-1 (AP-1) promoter cis elements, together with their cognate transcription factors, in basal and GnRH-stimulated GnRHR promoter activity, were investigated. Homologous upregulation of transcription of the endogenous gene was confirmed, and was quantified by means of real-time RTPCR. The GnRH response of the endogenous gene and of the transfected promoter-reporter construct required PKA and PKC activity, and the GnRH response of the promoter-reporter construct was found to be dependent on a functional AP-1 site. Furthermore, GnRH treatment resulted in increased binding of phosphorylated cAMP-response element binding protein (phospho-CREB) and decreased expression and binding of SF-1 to their cognate cis elements in vitro, and stimulated a direct interaction between SF-1 and CREB, suggesting that these events are also required for the full transcriptional response to GnRH. This study is the first providing detail regarding the mechanism of transcriptional regulation of GnRHR expression in LβT2 cells by GnRH. Based on results from this study, a model has been proposed which outlines for the first time the kinase pathways, the promoter cis elements and the cognate transcription factors involved in homologous regulation of GnRHR transcription in the LβT2 cell line. As certain aspects of this model have been confirmed for the endogenous GnRHR gene, the model is likely to be physiologically relevant, and provides new ideas and hypotheses to be tested in future studies.

Dissertation (PhD)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: Gonadotropin-releasing hormone (GnRH) is well known as the central regulator of the reproductive system through its stimulation of gonadotropin synthesis and release from the pituitary via binding to its specific receptor, known as the gonadotropin-releasing hormone receptor type I (GnRHR-I). The gonadotropins, luteinising hormone (LH) and follicle-stimulating hormone (FSH), bind to receptors in the gonads, leading to effects on steroidogenesis and gametogenesis. The recent finding of a second form of the GnRH receptor, known as the type II GnRHR or GnRHR-II, in non-mammalian vertebrates triggered the interest into the possible existence and function of a GnRHR-II in humans. The current study addressed this issue by investigating the presence of transcripts for a GnRHR-II in various human tissues and cells. While it was demonstrated that antisense transcripts for this receptor, containing sequence of only two of the three coding exons, are ubiquitously and abundantly expressed in all tissues examined, potentially full-length (containing all three exons), sense transcripts for a GnRHR-II were detected only in human ejaculate. Further analysis revealed that the subset of cells in the ejaculate expressing these transcripts is mature sperm. These findings, together with the reported role for GnRH in spermatogenesis and reproduction led to the further analysis of the presence of a local GnRH/GnRHR network in human and vervet monkey ejaculate or sperm. Indeed, such a network seems to be present in humans since transcripts for both forms of GnRH present in mammals, as well as transcripts for the GnRHR-I, are expressed in human ejaculate. Furthermore, transcripts for the GnRHR-II are expressed in both human and vervet monkey ejaculate. Thus, it would appear that locally produced GnRH-1 and/or GnRH-2 in the human male reproductive tract might mediate their effects on fertility via a local GnRHR-I, and possibly via GnRHR-II. Remarkably, in the pituitary, LH and FSH are present in the same gonadotropes, yet they are differentially regulated by GnRH under various physiological conditions. While it is well established that post-transcriptional regulatory mechanisms occur, the contribution of transcriptional regulation to the differential expression of the LHβ- and FSHβ-subunit genes is unclear. In this study, the role of GnRH-1 and GnRH-2 via the GnRHR-I and the GnRHR-II in transcriptional regulation of mammalian LHβ- and FSHβ genes was determined in the LβT2 mouse pituitary gonadotrope cell-line. It is demonstrated for the first time that GnRH-1 may affect gonadotropin subunit gene expression via GnRHR-II in addition to GnRHR-I, and that GnRH-2 also has the ability to regulate gonadotropin subunit gene expression via both receptors. Similar to other reports, it is shown that the transcriptional response to GnRH-1 of LHβ and FSHβ is low (about 1.4-fold for bLHβLuc and 1.2-fold for oFSHβLuc). In addition, evidence is supplied for the first time that GnRH-2 transcriptional regulation of the gonadotropin β subunits is also low (about 1.5-fold for bLHβLuc and 1.1-fold for oFSHβLuc). It is demonstrated that GnRH-1 is a more potent stimulator of bLHβ promoter activity as compared to GnRH-2 via the GnRHR-I, yet both hormones result in a similar maximum induction of bLHβ. However, GnRH-2 is a more efficacious stimulator of bLHβ transcription via the GnRHR-II than GnRH-1. No discriminatory effect of GnRH-1 vs. GnRH-2 was observed for oFSHβ promoter activity via GnRHR-I or GnRHR-II. By comparison of the ratio of expression of transfected oFSHβ- and bLHβ promoterreporters via GnRH-1 with that of GnRH-2, it is shown that GnRH-2 is a selective regulator of FSHβ gene transcription. This discriminatory effect of GnRH-2 is specific for GnRHR-I, as it is not observed for GnRHR-II, where GnRH-1 results in a greater oFSHβ- to-bLHβ ratio. These opposite selectivities for GnRHR-I and GnRHR-II on the ratios of oFSHβ:bLHβ promoter activity for GnRH-1 vs. GnRH-2 suggest a mechanism for fine control of gonadotropin regulation in the pituitary by variation of relative GnRHR-I vs. GnRHR-II levels. In addition, a concentration-dependent modulatory role for PACAP on GnRH-1- and GnRH-2-mediated regulation of bLHβ promoter activity, via both GnRHR-I and GnRHR-II, and of oFSHβ promoter activity, via GnRHR-I, is indicated. The concentration-dependent effects suggest the involvement of two different signalling pathways for the PACAP response. Together these findings suggest that transcription of the gonadotropin genes in vivo is under extensive hormonal control that can be finetuned in response to varying physiological conditions, which include changing levels of GnRH-1, GnRH-2, GnRHR-I and GnRHR-II as well as PACAP. / AFRIKAANSE OPSOMMING: Gonadotropien-vrystellingshormoon (GnRH) is bekend as die sentrale reguleerder van die voorplantingsisteem deur die stimulasie van gonadotropiensintese en - vrystelling vanaf die pituïtêre klier via binding aan ‘n spesifieke reseptor, die sogenaamde tipe I gonadotropien-vrystellingshormoonreseptor (GnRHR-I). Die gonadotropiene, lutineringshormoon (LH) en follikel-stimuleringshormoon (FSH), bind aan reseptore in die gonades waar dit steroïedogenese en gametogenese beïnvloed. Die onlangse ontdekking van ‘n tweede vorm van die GnRH-reseptor, bekend as die tipe II GnRHR of GnRHR-II, in nie-soogdier vertebrate het belangstelling in die moontlike bestaan en funksie van ‘n GnRHR-II in die mens gewek. Hierdie kwessie is aangeraak deur die teenwoordigheid van transkripte vir ‘n GnRHR-II in verskeie weefsel- en seltipes van die mens te ondersoek. Daar is aangetoon dat nie-sin transkripte vir hierdie reseptor, wat die DNA-opeenvolgings van slegs twee van die drie koderende eksons bevat het, oormatig uitgedruk word in al die weefseltipes wat ondersoek is. Daarteenoor is potensieel vollengte (bevattende al drie eksons) sin transkripte vir ‘n GnRHR-II in die mens slegs in semen gevind. Verdere analise het getoon dat dit volwasse sperma binne die semen is wat laasgenoemde transkripte uitdruk. Hierdie bevindinge, tesame met die aangetoonde rol vir GnRH in spermatogenese en reproduksie het gelei tot die verdere analise van die teenwoordigheid van ‘n lokale GnRH/GnRHR-netwerk in mens- en blouaapsemen of -sperm. So ‘n netwerk blyk om teenwoordig te wees in die mens, aangesien transkripte vir beide vorme van GnRH wat in soogdiere gevind word, asook transkripte vir die GnRHR-I, in menssemen uitgedruk word. Daarbenewens word transkripte vir die GnRHR-II uitgedruk in beide mens- en blouaapsemen. Dit wil dus voorkom asof lokaalgeproduseerde GnRH-1 en/of GnRH-2 in die manlike voortplantingstelsel van die mens hul effek op vrugbaarheid bemiddel via ‘n lokale GnRHR-I, en moontlik ook via GnRHR-II. Dit is opmerklik dat LH en FSH teenwoordig is in dieselfde gonadotroopselle van die pituïtêre klier en tog verskillend gereguleer word deur GnRH tydens verskeie fisiologiese kondisies. Terwyl dit bekend is dat post-transkripsionele reguleringsmeganismes teenwoordig is, is die bydrae van transkripsionele regulering tot die differensiële uitdrukking van die LHβ- en FSHβ-subeenheidgene minder duidelik. In hierdie studie is die rol van GnRH-1 en GnRH-2 via die GnRHR-I en die GnRHR-II in transkripsionele regulering van soogdier-LHβ- en -FSHβ-gene in die LβT2 muis pituïtêre gonadotroopsellyn bepaal. Dit is vir die eerste keer aangetoon dat GnRH-1 ‘n effek mag hê op gonadotropiensubeenheid-geenuitdrukking via GnRHR-II bykomend tot GnRHR-I, en dat GnRH-2 ook die vermoë besit om gonadotropiensubeenheid-geenuitdrukking via beide reseptore te reguleer. Soos deur ander studies aangetoon is die transkripsionele respons van LHβ en FSHβ tot GnRH-1 klein (ongeveer 1.4-voudig vir bLHβLuc en 1.2- voudig vir oFSHβLuc). Verder is daar vir die eerste keer bewys gelewer dat transkripsionele regulering van die gonadotropien β-subeenhede deur GnRH-2 ook gering is (ongeveer 1.5-voudig vir bLHβLuc en 1.1-voudig vir oFSHβLuc). Daar is aangetoon dat GnRH-1 ‘n sterker stimuleerder van bLHβ-promotoraktiwiteit is in vergelyking met GnRH-2 via die GnRHR-I, hoewel beide hormone tot ‘n soortgelyke maksimum induksie van bLHβ lei. GnRH-2 is egter ‘n meer effektiewe stimuleerder van bLHβ-transkripsie as GnRH-1 via die GnRHR-II. Geen verskille is gevind tussen die effekte van GnRH-1 en GnRH-2 op oFSHβ-promotoraktiwiteit via GnRHR-I of GnRHR-II nie. Wanneer die verhouding van uitdrukking van getransfekteerde oFSHβ- en bLHβ- promotor-verslaggewers via GnRH-1 met dié van GnRH-2 vergelyk is, is aangetoon dat GnRH-2 ‘n selektiewe reguleerder van FSHβ-geentranskripsie is. Hierdie diskriminasieeffek van GnRH-2 is spesifiek vir GnRHR-I aangesien dit nie vir GnRHR-II waargeneem word nie. GnRH-1 lei tot ‘n groter oFSHβ tot bLHβ-verhouding via GnRHR-II. Hierdie teenoorgestelde selektiwiteite van GnRHR-I en GnRHR-II op die verhoudings van oFSHβ tot bLHβ-promotoraktiwiteit vir GnRH-1 teenoor GnRH-2 suggereer dat daar ‘n meganisme bestaan vir die fyn regulering van gonadotropiene in die pituïtêre klier, deurdat die relatiewe vlakke van GnRHR-I teenoor GnRHR-II gevarieer word. Daarbenewens is ‘n konsentrasie-afhanklike moduleringsrol vir PACAP op GnRH-1- en GnRH-2-bemiddelde regulering van bLHβ-promotoraktiwiteit aangetoon, via beide GnRHR-I en GnRHR-II, asook op oFSHβ-promotoraktiwiteit via GnRHR-I. Hierdie konsentrasie-afhanklike effekte dui op die betrokkenheid van twee verskillende seinpadweë vir die PACAP-respons. Tesame suggereer hierdie bevindinge dat transkripsie van die gonadotropiengene in vivo onder ekstensiewe hormonale kontrole is wat verfyn kan word in respons to veranderlike fisiologiese kondisies. Laasgenoemde sluit veranderende vlakke van GnRH-1, GnRH-2, GnRHR-I en GnRHR-II asook PACAP in.

Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The gonadotropin-releasing hormone (GnRH) receptor is a G-protein-coupled receptor in the pituitary gonadotropes and is an important control point for reproduction. GnRH binds to the GnRH receptor (GnRHR) resulting in the synthesis and release of follicle stimulating hormone (FSH) and luteinizing hormone (LH). The sensitivity of the pituitary to GnRH can be directly correlated with GnRHR levels. The mouse GnRHR promoter contains three cis elements containing binding sites for steroidogenic factor-1 (SF-1), namely site 1 (-15/-7), site 2 (-244/- 236) and site 3 (-304/-296) as well as an activator protein-1 (AP-1)-like consensus sequence (TGAGTCA) at position –336/-330. While sites 1 and 2 and the AP-1 site have been previously shown to be involved in regulation of transcription of the mouse GnRHR (mGnRHR) promoter in some cell lines, the role of site 3 has not been previously investigated. This study investigated whether transcription of the mGnRHR gene is regulated by GnRH and glucocorticoids in the LβT2 gonadotrope pituitary cell line, and the role therein of site 3 and the AP-1 site and their cognate proteins, using a combination of in vitro protein- DNA binding studies and promoter-reporter assays. The role played by site 3 and the AP-1 site in basal transcription of the mGnRHR gene in LβT2 cells was the first area of investigation during this study. Luciferase reporter plasmids containing 600 bp of the mGnRHR promoter were used where the site 3 and AP-1 sites were either wild-type or mutated. Two constructs were prepared from the wild-type construct, i.e. wild type (LG), site 3 mutant (m3) and AP-1 mutant (mAP-1). Transfection of LG, m3 and mAP-1 plasmids into LβT2 cells was carried out to determine the effect of these mutations on the basal expression of the mGnRHR gene. Mutation of site 3 resulted in a 1.5 fold increase in the transcriptional activity of the mGnRHR promoter. This suggests that site 3 plays a role in the inhibition of basal transcriptional levels of the mGnRHR promoter in LβT2 cells. Mutation of the AP-1 site resulted in a 50% decrease in basal transcriptional levels of the mGnRHR promoter in LβT2 cells. This suggests that the AP-1 site is involved in positively mediating the basal transcriptional response of the GnRHR promoter in LβT2 cells. Experiments towards the understanding of the mechanism of the cis elements (site 3 and AP-1 site) on the mGnRHR promoter were carried out along with the role of protein kinase A (PKA) pathways, proteins involved and the effect of varying doses for varying times of GnRH, as well as the overexpression of PKA and the SF-1 protein. It was found that site 3 and the AP-1 site are not involved in the GnRH response. Results suggest that site 3 is partially involved in the PKA response in LβT2 cells. Site 3 can bind SF-1 protein as shown via competitive electrophoretic mobility shift assays (EMSA). When EMSA’s were performed on the AP-1 site the findings were that the c-Fos protein was not involved in the activation of the AP-1 site. A factor was found to bind to the AP-1 site, which did not require the intact AP-1 site, suggesting that it could be the c-Jun protein that binds to the AP-1 site under basal conditions. Another area that was investigated was whether the mGnRHR promoter can be regulated by dexamethasone (dex) either via the AP-1 site or site 3. A dose and time-dependent increase in promoter activity was observed with dex. This effect appears to require site 3 and the AP-1 site, as shown by the complete loss of response when these sites were individually mutated, consistent with a functional interaction between site 3 and the AP-1 site in LβT2 cells. / AFRIKAANSE OPSOMMING: Die gonadotropienvrystellings hormoon (GnRH) reseptor is ‘n G-proteïen-gekoppelde reseptor in die pituitêre gonadotrope en is ’n belangrike beheerpunt vir reproduksie. GnRH bind aan die GnRH reseptor (GnRHR) met die gevolg dat follikel stimulerende hormoon (FSH) en luteïeniserende (LH) gesintetiseer en vrygestel word. Die sensitiwiteit van die pituitêre klier vir GnRH kan direk met GnRHR vlakke gekorreleer word. Die muis GnRHR promotor bevat drie cis elemente met bindingssetels vir steroïedogeniese faktor 1 (SF1), naamlik setel 1 (-15/-7), setel 2 (-244/-236) en setel 3 (-304/-296) sowel as ’n aktiveerder proteïen 1 (AP-1) tipe konsensus sekwens (TGAGTCA) in posisie -336/-330. Terwyl setels 1 en 2 en die AP-1 setel voorheen getoon is om by die regulering van transkripsie van die muis GnRHR (mGnRHR) promotor in party sellyne betrokke te wees, is die rol van setel 3 nog nie vantevore bestudeer nie. In hierdie studie is ondersoek of die transkripsie van die mGnRHR geen deur GnRH en glukokortikoïede in die LβT2 gonadotroop pituitêre sellyn gereguleer word, en die rol van setel 3 en die AP-1 setel en hulle binders, deur gebruik te maak van in vitro proteïen-DNA bindings studies en promotor-verslaggewer essais. Die rol wat setel 3 en die AP-1 setel in basale transkripsie van die mGnRHR gene in LβT2 selle gespeel het, was die eerste onderwerp wat in hierdie studie bestudeer is. Lusiferase verslaggewer plasmiede wat die eerste 600 bp van die mGnRHR promotor bevat het en waarin setel 3 en die AP-1 setels óf wilde tipe óf gemuteer was, is gebruik. Two konstrukte is vanaf die wilde tipe konstruk berei, naamlik wilde tipe (LG), ’n setel 3 mutant (m3) en ’n AP-1 mutant (mAP-1). Transfeksie van LG, m3 en mAP-1 plasmiede in LβT2 selle is deurgevoer om te bepaal wat die effek van hierdie mutasies op die basale ekspressie van die mGnRHR gene was. Mutasie van setel 3 het ’n 1.5-voudige toename in die transkripsionele aktiwiteit van die mGnRHR promotor tot gevolg gehad. Dit suggereer dat setel 3 ’n rol in die inhibisie van die basale transkripsievlakke van die mGnRHR promotor in LβT2 selle speel. Mutasie van die AP-1 setel het tot ‘n 50% verlaging in basale transkripsievlakke van die mGnRHR promotor in LβT2 selle gelei. Dit suggereer dat die AP-1 setel betrokke is in die positiewe bemiddeling van die basale transkriptionele respons van die GnRHR promotor in LβT2 selle. Eksperimente wat gemik was om die meganisme van die cis-elemente (setel 3 en die AP-1 setel) op die mGnRHR promotor te verklaar, asook om die rol van proteïen kinase A (PKA) paaie, proteïene daarby betrokke en die effek van varieende dosisse vir verskillende tye van GnRH, sowel as die oorekspressie van PKA en die SF-1 proteïen, is deurgevoer. Dit is gevind dat setel 3 en die AP-1 setel nie betrokke by die GnRH respons is nie. Die resultate suggereer dat setel 3 gedeeltelik betrokke is by die PKA respons van LβT2 selle. Setel 3 kan SF-1 proteïen bind soos getoon deur kompeterence elektroforetiese mobiliteits verskuiwings essais (EMSA). As EMSA’s deurgevoer is op die AP-1 setel is bevind dat die c-Fos proteïen nie betrokke is in die aktivering van die AP-1 setel nie. ’n Faktor is gevind om aan die AP-1 setel te bind wat nie ’n intakte AP-1 setel vereis het nie, wat gesuggereer het dat dit die c-Jun proteïen kan wees wat aan die AP-1 setel onder basale omstandighede bind. ’n Ander area wat ondersoek is, is of die GnRHR promotor gereguleer kan word deur deksametasoon (dex) óf via die AP-1 setel óf via setel 3. ’n Dosis en tyds-afhanklike toename in promotor aktiwiteit is waargeneem met dex. ’n Vereiste vir hierdie effek blyk om die teenwoordigheid van setel 3 en die AP-1 setel te wees, soos aangetoon deur die totale verlies aan response as hierdie twee setels individueel gemuteer is, en wat weereens in ooreenstemming met die funksionele interaksie tussen setel 3 en die AP-1 setel in LβT2 selle is.

published_or_final_version / abstract / Zoology / Master / Master of Philosophy

published_or_final_version / abstract / Biological Sciences / Doctoral / Doctor of Philosophy