Progestins and breast cancer : significance of progesterone receptor isoforms and their altered ratios
| dc.contributor.advisor | Africander, Donita | en_ZA |
| dc.contributor.advisor | Louw-du Toit, Renate | en_ZA |
| dc.contributor.author | Cartwright, Meghan Carni | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Biochemistry. | en_ZA |
| dc.date.accessioned | 2021-05-21T12:25:53Z | |
| dc.date.available | 2021-05-21T12:25:53Z | |
| dc.date.issued | 2021-03 | |
| dc.description | Thesis (PhD)--Stellenbosch University, 2021. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Progestins used in menopausal hormonal therapy have been associated with increased incidence of breast cancer. While these synthetic ligands were designed, in four consecutive generations, to mimic the activity of natural progesterone (P4) via the progesterone receptor (PR), the precise mechanism whereby some progestins and/or their metabolites may cause an increase in breast cancer incidence is still mostly unknown. Whether the PR, existing as two isoforms, PR-A and PR-B, plays a role in mediating the effects of progestins on breast cancer is unclear. As the metabolism of a progestin can ultimately influence effects via the PR, ultrahigh performance supercritical fluid chromatography-tandem mass spectrometry was used to investigate the metabolism of P4 and selected progestins in three breast cancer cell lines in the first part of this thesis. Unlike P4 that was rapidly metabolised in all three cell lines, promegestone (R5020), gestodene (GES) and nomegestrol acetate (NOMAC) were not metabolised, while only drospirenone (DRSP) was metabolised in the MDA-MB-231 and T47D cells. Additionally, we showed that P4 metabolism occurred at a similar rate in the MDAMB- 231 and T47D cells, but faster than its metabolism in the MCF-7 BUS cells. In the second part of this study, transactivation and transrepression transcriptional assays showed that the activities of a selected panel of progestins from all four generations are not all similar to each other, P4 or R5020, via PR-A and PR-B. For transactivation, most progestins were more efficacious via PR-B, but more potent via PR-A. We also showed that an increase in PR-A density and excess PR-A relative to PR-B, resulted in decreased efficacies of all progestins for transactivation. While an increase in PR-A density resulted in an increase in the activity of all progestins for transrepression, the activity of only a few progestins were influenced by excess expression of PR-A relative to PR-B. Realtime PCR showed progestin- and gene-specific regulation of endogenous genes known to play a role in breast cancer in T47D breast cancer cells. While the response of some progestins on the selected genes were PR-B mediated, some progestin effects were not mediated by either PR-A or PR-B. In the third part of this thesis, investigations into the effects of the progestins on proliferation, apoptosis, anchorageindependent growth, migration and invasion showed that these processes are differentially influenced by P4 and the selected progestins, and that the responses are also differentially mediated by PR-A or PR-B. Excess expression of PR-A resulted in both positive and/or negative ligand-independent, as well as progestin-induced, effects on these cancer hallmarks. Taken together, the findings of this thesis emphasize the fact that progestins do not always mimic the activities of P4 or each other. The results further highlight the complexity of progestin action via the PR, underscoring the importance of distinguishing progestin activities via PR-A and PR-B, and also considering the PR-A:PR-B ratio when investigating the mechanisms of progestins and the PR in breast cancer. Finally, our results suggest that a progestin such as medroxyprogesterone acetate (MPA) acting via PR-A and/or PR-B may indeed increase breast cancer risk, while others like DRSP may not. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Progestiene wat in menopausale hormoonterapie gebruik word, word geassosieer met ‘n verhoogde risiko van borskanker. Alhoewel dié sintetiese ligande, wat in vier opeenvolgende generasies ontwerp is om die aktiwiteit van natuurlike progesteroon (P4) via die progesteroonreseptor (PR) na te boots, is die presiese meganisme waardeur sommige progestiene en/of hul metaboliete 'n toename in borskanker kan veroorsaak nog meestal onbekend. Dit is egter onduidelik of die PR, wat bestaan uit twee isovorme, PR-A en PR-B, 'n rol speel in die bemiddeling van die effekte van progestiene op borskanker. Aangesien die metabolisme van ‘n progestien ook effekte via die PR kan beïnvloed, was superkritiese vloeistofchromatografie en tandem massaspektrometrie in die eerste deel van hierdie proefskrif gebruik om die metabolisme van P4 en geselekteerde progestiene in drie borskanker-sellyne te ondersoek. In teenstelling met P4 wat vinnig in al drie sellyne gemetaboliseer is, is promegestoon (R5020), gestodene (GES) en nomegestrol asetaat (NOMAC) nie gemetaboliseer nie, terwyl slegs drospirenoon (DRSP) in die MDA-MB-231- en T47D-selle gemetaboliseer is. Verder het ons getoon dat die metabolisme van P4 teen 'n soortgelyke tempo in beide MDA-MB-231- en T47D-selle plaasgevind het, maar vinniger as die metabolisme daarvan in die MCF-7 BUS-selle. In die tweede deel van hierdie studie het transkripsie-toetse vir transaktivering en transonderdrukking getoon dat die aktiwiteit van 'n geselekteerde paneel progestiene uit al vier generasies, verskillend is van mekaar, P4 en R5020, via PR-A en PR-B. Die transaktivering van meeste progestiene was meer doeltreffend via PR-B, maar meer potent via PR-A. Ons het ook getoon dat 'n toename in PR-A digtheid en 'n oormaat PR-A in verhouding tot PR-B, gelei het tot verminderde doeltreffentheid van alle progestiene vir transaktivering. Terwyl 'n toename in PR-A digtheid gelei het tot 'n toename in die aktiwiteit van alle progestiene vir transonderdrukking, is die aktiwiteit van slegs enkele progestiene beïnvloed deur oormatige uitdrukking van PR-A relatief tot PR-B. Deur gebruik te maak van intydse PKR het ons getoon dat die regulering van endogeniese gene, wat 'n rol in borskanker speel, progestien- en geenspesifiek is in die T47D-borskankerselle,. Alhoewel die reaksie van sommige progestiene op die geselekteerde gene deur PR-B bemiddel is, word sommige progestien-effekte nie deur PR-A óf PR-B bemiddel nie. In die derde deel van hierdie proefskrif het ondersoeke na die effekte van progestiene op proliferasie, apoptose, anker-onafhanklike groei, migrasie en indringing getoon dat hierdie prosesse differensieel deur P4 en die geselekteerde progestiene beïnvloed word, en dat die reaksies ook differensieel deur PR-A of PR-B bemiddel word. Oormatige uitdrukking van PR-A het gelei tot beide positiewe en/of negatiewe ligandonafhanklike, sowel as progestien-geïnduseerde, effekte op hierdie kanker kenmerke. In samevatting, die bevindings van hierdie proefskrif beklemtoon die feit dat progestiene nie altyd die aktiwiteite van P4 of van mekaar naboots nie. Die resultate dui verder daarop dat progestien-aksie via die PR kompleks is, en beklemtoon die feit dat daar van progestien-aktiwiteite via PR-A en PR-B onderskei moet word, asook dat die PR-A:PR-B verhouding in ag geneem moet word wanneer progestien meganismes en die PR in borskanker ondersoek word. Ten slotte dui ons resultate daarop dat 'n progestien soos medroksieprogesteroonasetaat (MPA) wat via PR-A en/of PR-B optree, wel die risiko van borskanker kan verhoog, maar nie ander soos DRSP nie. | af_ZA |
| dc.description.version | Doctoral | |
| dc.embargo.terms | 2022-06-30 | |
| dc.format.extent | xxii, 301 pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/110472 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Progestational hormones | en_ZA |
| dc.subject | Menopause -- Hormone therapy | en_ZA |
| dc.subject | Breast -- Cancer -- Hormone therapy | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | Progestins and breast cancer : significance of progesterone receptor isoforms and their altered ratios | en_ZA |
| dc.type | Thesis | en_ZA |