Investigating the mechanism of action of hormones used in hormone replacement therapy via estrogen receptor subtypes and the influence of the progesterone receptor

Perkins, Meghan Samantha (2018-03)

Thesis (PhD)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Estrogens and progestins used in conventional menopausal hormone therapy (HT) are associated with increased breast cancer risk. A diverse range of estrogens and progestins are available that mediate their effects primarily by binding to the estrogen receptor (ER) and progesterone receptor (PR), respectively. Although the link to breast cancer risk has not been shown for all estrogens and progestins, many women have turned to custom-compounded bioidentical hormone therapy (bHT) as it is claimed to not increase breast cancer risk. However, scientific evidence to support this claim is lacking. Estrogens and ERα are considered the main etiological factors driving breast cancer, while both ERα and the PR are required for progestin (medroxyprogesterone acetate (MPA)) effects on breast cancer cell proliferation. In this thesis, we investigated the activities of estrogens and progestins used in menopausal hormone therapies via the individual ER subtypes, and the role of ERα/PR crosstalk in mediating progestin-induced effects on gene expression, breast cancer cell proliferation and anchorage-independent growth. In the first part of the study, competitive whole cell bindings assays showed that bioidentical estradiol (bE2) and estriol (bE3) displayed similar binding affinities to the commercially available (natural) estradiol (E2) and estriol (E3) standards, while synthetic ethinylestradiol (EE) had a higher affinity for ERα, and natural E1 a lower affinity for ERβ. Furthermore, the bioidentical estrogens mimicked their respective natural estrogens and synthetic EE on transactivation and transrepression of gene expression, proliferation and anchorage-independent growth of the estrogen-sensitive MCF-7 BUS human breast cancer cell line. These assays showed that E3 and estrone (E1) are efficacious estrogens that do not antagonize E2. In the second part of this study, the estrogenic activities of selected progestins from different generations, MPA, norethisterone acetate (NET-A), levonorgestrel (LNG), gestodene (GES), nestorone (NES), nomegestrol acetate (NoMAC) and drospirenone (DRSP), were characterized relative to each other and natural progesterone (P4). Competitive binding assays revealed that only NET-A, LNG and GES could bind to ERα, while no progestin bound ERβ. Both transactivation and transrepression transcriptional assays showed that NETA, LNG and GES display estrogenic activity. In the third part of the study, the role of PR/ERα crosstalk in mediating the effects of MPA, NET and DRSP, relative to P4, on breast cancer cell proliferation, anchorage-independent growth and the expression of the ER-regulated trefoil factor 1 (pS2) and cathepsin D (CTSD) genes was investigated. All progestins could promote proliferation and anchorage-independent growth of MCF-7 BUS breast cancer cells to the same extent as P4 and E2 via a mechanism requiring both the PR and ERα, but DRSP was the least, and MPA the most potent for proliferation. Quantitative real-time RT-PCR (qPCR), chromatin immunoprecipitation (ChIP) and re-ChIP assays showed that only MPA and NET increased the expression of the pS2 and/or CTSD genes via a mechanism requiring co-recruitment of the PR and ERα to the promoter regions of these genes. In contrast, P4, MPA, NET and DRSP all caused recruitment of the PR/ERα complex to the PR-regulated oncogenes cyclin D1 and MYC. Taken together, the findings of this study suggest that there is no advantage in choosing bHT above conventional HT, and that while it is unlikely that the progestins used in this study will exert biological effects via ERα or ERβ in vivo, some progestins may increase breast cancer risk via a mechanism involving interplay between the PR and ERα.

AFRIKAANSE OPSOMMING: Die gebruik van estrogene en progestiene in konvensionele menopousale hormoonterapie (HT) word geassosieër met ‘n toename in die risiko van borskanker. ‘n Verskeidenheid van estrogene en progestiene, wat hul effekte hoofsaaklik uitvoer deur die estrogeenreseptor (ER) en progesteroonreseptor (PR) onderskeidelik, is beskikbaar. Alhoewel die toenemende risiko van borskanker nog nie vir al die estrogene en progestiene getoon is nie, maak baie vrouens eerder gebruik van persoonlike saamgestelde bioidentiese hormoonterapie (bHT) aangesien daar beweer word dat dit nie borskanker risiko verhoog nie. Wetenskaplike bewyse om hierdie bewering te ondersteun is egter nie beskikbaar nie. Estrogene en ERα word beskou as die hoof etiologiese faktore wat borskanker dryf, terwyl beide ERα en die PR vir die effekte van progestien (medroksieprogesteroonasetaat (MPA)) op borskankerselproliferasie benodig word. In hierdie tesis, het ons die aktiwiteite van estrogene en progestiene, gebruik in menopousale hormoonterapies, deur die individuele ER subtipes ondersoek, asook die rol van ERα/PR wisselwerking in progestien-geïnduseerde geenuitdrukking, borskankerselproliferasie en geankerde-onafhanklike groei. In die eerste deel van die studie het kompeterende heelsel bindingstoetse getoon dat bioidentiese estradiool (bE2) en estriool (bE3) dieselfde bindingsaffiniteite het as die komersieël beskikbare (natuurlike) estradiool (E2) en estriool (E3) standaarde, terwyl sintetiese etinielestradiool (EE) ‘n hoër affiniteit vir ERα, en natuurlike estroon (E1) ‘n laer affiniteit vir ERβ het. Verder, boots die bioidentiese estrogene hul onderskeidelike natuurlike estrogene en sintetiese EE na in terme van transaktivering en transonderdrukking van geenuitdrukking, proliferasie en geankerde-onafhanklike groei van die estrogeen-sensitiewe MCF- 7 BUS menslike borskankersellyn. Hierdie toetse het getoon dat E3 and estroon (E1) doeltreffende estrogene is wat nie E2 antagoniseer nie. In die tweede deel van die studie was die estrogeniese aktiwiteite van geselekteerde progestiene van verskillende generasies, MPA, noretisteroonasetaat (NET-A), levonorgestrel (LNG), gestodeen (GES), nestoroon (NES), nomegestroolasetaat (NoMAC) en drospirenoon (DRSP), relatief tot mekaar en natuurlike progesteroon (P4), gekarakteriseer. Kompeterende bindingstoetse het aan die lig gebring dat slegs NET-A, LNG en GES aan ERα kon bind, terwyl geen van die progestiene ERβ bind nie. Beide transaktiverings- en transonderdrukkingstoetse het gewys dat NET-A, LNG en GES estrogeniese aktiwiteite toon. In die derde deel van die studie was die rol wat PR/ERα wisselwerking speel in die uitvoering van MPA, NET en DRSP, relatief tot P4, op borskankerselproliferasie, geankerde-onafhanklike groei en die uitdrukking van die ER-gereguleerde trefoiël faktor 1 (pS2) en katepsien D (CTSD) gene ondersoek. Al die progestiene kon proliferasie en geankerde-onafhanklike groei van die MCF-7 BUS borskankerselle tot dieselfde mate as P4 en E2 bevorder deur ‘n meganisme wat beide die PR en ERα benodig, maar DRSP was die minste, en MPA die meeste potent vir proliferasie. Kwantitatiewe intydse RT-PKR, kromatienimmunopresipitasie (ChIP) en her-ChIP toetse het getoon dat slegs MPA en NET die uitdrukking van die pS2 en/of CTSD gene verhoog deur ‘n meganisme wat die mede-werwing van die PR en ERα tot die promotor areas van hierdie gene vereis. In teendeel, P4, MPA, NET en DRSP het almal die werwing van die PR/ERα kompleks tot die PR-gereguleerde onkogene siklien D1 (CCND1) en MYC veroorsaak. In samevatting, die bevindinge van hierdie studie stel voor dat daar geen voordeel is om bHT te kies bo konvensionele HT nie, en alhoewel dit onwaarskynlik is dat die progestiene wat gebruik is in hierdie studie biologiese effekte deur ERα of ERβ sal uitvoer in vivo, mag sommige progestiene wel borskanker risiko verhoog deur ‘n meganisme wat wisselwerking tussen die PR en ERα behels.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103836
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