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Investigating progesterone and estrogen receptor crosstalk in breast cancer

Van der Meer, Yolandi (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Progestins are synthetic compounds designed to mimic the natural hormone progesterone (Prog), and are widely used in hormone replacement therapy (HRT) and contraception. These compounds can be divided into four generations, with newer generations increasing in progesterone receptor (PR) specificity. Although progestins have many therapeutic benefits, a number of undesirable side-effects, such as increased risk of breast cancer, have been reported. As a result, many postmenopausal women have sought alternatives for HRT, such as compounded bio-identical hormones like bio-identical Prog (bProg), claimed not to increase breast cancer risk. Progestins, Prog and bProg (collectively referred to as progestogens) elicit their biological effects primarily by binding to the PR, which exists as two predominant isoforms, PR-A and PR-B, with PR-B being the more transcriptionally active and proliferative isoform in breast cancer. Emerging evidence suggest that the PR plays an important role in breast cancer development and progression, and that there is crosstalk between the PR and estrogen receptor (ER)-α, a major etiological factor in breast cancer biology. Moreover, it has been shown that ER-α is required for PR-B-mediated effects of medroxyprogesterone acetate (MPA) on activation of gene expression and breast cancer cell proliferation. The latter raised the questions of whether ER-α is needed for PR-B-mediated effects of other progestins, and whether the ERβ subtype would also be required. Given that PR-B has both transactivation and transrepression functions, this study used transactivation and transrepression transcriptional assays to investigate the PR-B-mediated agonist efficacies and potencies of Prog, bProg and select progestins from different generations (MPA, norethisterone acetate (NET-A), levonorgestrel (LNG), gestodene (GES) and drospirenone (DRSP)), and whether these were modulated by ERα and/or ERβ. Furthermore, the effects of the progestogens on breast cancer cell proliferation were evaluated in the absence and presence of ERα- and ERβ-specific antagonists. Results showed that progestins mostly displayed similar agonist efficacies and potencies for transactivation and transrepression via PR-B. The exception was first generation MPA that was less efficacious for transactivation and least potent for transrepression, and third generation GES that was more potent for transactivation. This study is the first to show that ERα and ERβ differentially decreased PR-B-mediated agonist efficacies of progestogens for transactivation and transrepression. However, the ERα-specific antagonist had no effect on progestogen-induced expression of the endogenous PR-B regulated c-myc gene or repression of the interleukin (IL)-8 gene in the T47D breast cancer cell line, while the ERβ-specific antagonist had no effect on progestogen-induced c-myc gene expression, and appeared to abolish repression of the IL-8 gene. Additionally, we showed that all progestogens, except NET-A and DRSP, displayed similar proliferative efficacies and potencies for cell proliferation. Interestingly, while the ERα-specific antagonist had no effect on progestogen-induced cell proliferation, increased cell proliferation by LNG- and GES was enhanced by the ERβ-specific antagonist. Taken together, the results from this study, although having limitations, emphasizes the complexity of crosstalk between the PR and ER subtypes in breast cancer. Although the physiological implications of these results have to be evaluated, our findings may assist us in our understanding of crosstalk between PR-B and the ER subtypes, and how it may be contributing to progestin-induced breast cancer cell growth.

AFRIKAANSE OPSOMMING: Progestiene is sintetiese verbindings wat ontwerp is om die funksies van die natuurlike hormoon progesteroon (Prog) na te boots, en word wêreldwyd in hormoon vervagingsterapie (HVT) en voorbehoedmiddels gebruik. Hierdie verbindings kan in vier generasies verdeel word, met die nuwer generasie wat meer spesifiek is vir die progesteroon reseptor (PR). Alhoewel progestiene baie terapeutiese voordele het, is daar ook verskeie ongewenste newe-effekte, soos verhoogde risiko van borskanker, geassosieër met hul gebruik. As gevolg hiervan, het baie na-menopousale vrouens alternatiewe begin soek vir HVT, soos byvoorbeeld die saamgestelde bio-identiese hormone soos bio-identiese Prog (bProg), wat beweer word om nie die risiko van borskanker te verhoog nie. Progestiene, Prog and bProg (gesamentlik verwys daarna as progestogene) voer hul biologiese effekte uit deur hoofsaaklik te bind aan die PR, wat voorkom as twee hoof isoforme, PR-A en PR-B, met PR-B wat hoër transkripsionele aktiwiteit toon en die meer proliferatiewe isoform in borskanker is. Onlangse bewyse toon dat die PR ‘n belangrike rol in borskankerontwikkeling en -bevordering speel, en dat daar ‘n wisselwerking tussen die PR en die estrogeen reseptor (ER)-α, ‘n groot etiologiese faktor in borskankerbiologie, voorkom. Verder, is daar gevind dat ERα benodig word vir PR-B-bemiddelde effekte van medroksieprogesteroon asetaat (MPA) op die aktivering van geentranskripsie en borskanker proliferasie. Die laasgenoemde het gelei tot die vrae of ERα ook benodig word vir die PR-B-bemiddelde effekte van ander progestiene, en of die ERβ subtipe ook benodig sal word. Gegewe dat PR-B beide transaktivering en transonderdrukking funksies het, is daar in hierdie studie gebruik gemaak van transaktivering en transonderdrukking transkripsioneletoetse om die PR-B bemiddelde agonis effektiwiteit en potensie van Prog, bProg en geselekteerder progestiene van verskillende generasies (MPA, noretisteroon asetaat (NET-A), levonorgestrel (LNG), gestodeen (GES) en drospirenoon (DRSP)) te bepaal, asook om vas te stel of die effekte deur ERα en/of ERβ gemoduleer word. Verder, is die effekte van die progestogene op borskanker proliferasie in die afwesigheid en teenwordigheid van ERα- en ERβ-spesifieke antagoniste geëvalueer. Resultate het aangedui dat progestiene meestal soortgelyke agonis effektiwiteit en potensies vir transaktivering en transonderdrukking via PR-B getoon het. Die uitsonderings was die eerste generasie progestien MPA wat minder effektief vir transaktivering en minder potent vir transonderdrukking was, en die derde generasie progestien GES wat meer potent vir transaktivering was. Hierdie studie wys vir die eerste keer dat ERα en ERβ die PR-B-bemiddelde agonis effektiwiteit van die progestogene vir transaktivering en transoderdrukking differensieel verminder. Nietemin, het die ERα-spesifieke antagonis geen effek op progestogeen-geïnduseerde uitdrukking van die endogene PR-B-gereguleerde c-myc geen, of onderdrukking van die interleukin (IL)-8 geen in die T47D borskanker sellyn gehad nie, terwyl die ERβ-spesifieke antagonis geen effek op c-myc geen uidrukking gehad het nie, en wou dit voorkom asof dit die onderdrukking van die IL-8 geen verhoed. Verder het ons gewys dat alle progestogene, behalwe NET-A en DRSP, soortgelyke proliferatiewe effektiwiteit en potensies vir selproliferasie getoon het. Interessant genoeg, terwyl die ERα-spesifieke antagonis geen effek op progestogeen-geïnduseerde selproliferasie gehad het nie, is die LNG- en GES-geïnduseerde selproliferasie selfs verder verhoog deur die ERβ-spesifieke antagonis. Ten slotte, alhoewel daar sekere beperkinge is, beklemtoon die resultate van hierdie studie die kompleksiteit van die wisselwerking tussen PR-B en die ER subtipes in borskanker. Alhoewel die fisiologiese implikasies van ons resultate nog geëvalueer moet word, mag ons bevindinge bydra tot die huidige begrip van die wisselwerking tussen PR-B en die ER subtipes, en hoe dit moontlik kan bydra tot progestien-geïnduseerde groei van borskankerselle.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101432
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