Masters Degrees (Biochemistry)

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Browsing Masters Degrees (Biochemistry) by Author "Brink, Danielle"

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    Investigating progestin-mediated crosstalk between the androgen receptor and estrogen receptor subtypes in breast cancer cell lines
    (Stellenbosch : Stellenbosch University, 2019-02) Brink, Danielle; Africander, Donita; Stellenbosch University. Faculty of Science. Dept. of Biochemistry.
    ENGLISH ABSTRACT: Estrogen and the estrogen receptor alpha (ERα) are traditionally considered as the main etiological factors in breast cancer. However, other members of the steroid receptor family, including ERβ and the androgen receptor (AR) have also been shown to play a role. It is known that ERα drives breast cancer cell proliferation, while ERβ antagonizes ERα-mediated effects. Moreover, the AR, which is expressed in the majority of ER-positive breast cancer tumours, has been shown to inhibit the transcriptional activity of ERα and increase ERβ expression when activated by the potent natural androgen, 5α-dihydrotestosterone (DHT). Together, this suggests that the AR is associated with a good prognosis in ER-positive breast cancer. The question that arises is whether all agonists binding to the AR would elicit similar effects. This is particularly relevant to progestins used by millions of women in contraception and menopausal hormone therapy (HT), as a number of progestins are known to bind to the AR, with some displaying androgenic properties similar to DHT and others displaying anti-androgenic properties. For example, progestins like medroxyprogesterone acetate (MPA), norethisterone acetate (NET-A), and levonorgestrel (LNG) have been shown to be as potent and efficacious as the natural androgen DHT, while others like nestorone (NES) and nomegesterol acetate (NOMAC) display anti-androgenic properties similar to the natural progestogen, progesterone (P4). It is noteworthy that MPA, NET-A and LNG have all been associated with an increased risk of breast cancer. However, the underlying mechanisms whereby these progestins contribute to increased breast cancer risk has not been established. In this study, our main aim was to investigate whether androgenic progestins, unlike anti-androgenic progestins, would elicit similar effects as DHT and the synthetic androgen, mibolerone (Mib), on ERβ and ERα expression in human breast cancer cell lines. First however, we used mammalian two-hybrid assays to investigate the ability of the progestins to induce the ligand-dependent interaction between the NH2- and COOH-terminal domains (N/C interaction) of the AR, and showed that progestins elicit different conformations in the receptor. Western blot analysis showed that unlike the androgens that increased AR protein levels, the progestins did not influence AR protein levels in the MCF-7 BUS or MDA-MB-453 breast cancer cells. Quantitative real-time PCR (qPCR) showed that like the androgens, MPA, NET-A and LNG all increased ERβ mRNA expression in the MDA-MB-453 cell line, while P4, NES and NOMAC did not. Moreover, by using the AR antagonist, hydroxyflutamide, we showed that these effects were mediated by the AR. Although these results suggest another mechanism by which the AR may inhibit breast cancer cell growth, the results should be interpreted with caution as we show that the ARmediated effects of the androgens and androgenic progestins, in fact, increased proliferation of the MCF-7 BUS and T47D breast cancer cell lines. Unlike, Mib and DHT, which decreased ERα mRNA expression via the AR, MPA, NET-A and LNG had no effect on ERα expression. Although the precise physiological implications of these preliminary results remain to be determined, our findings highlight the fact that the role of progestins in breast cancer is not straightforward. Moreover, these findings contribute to our understanding of crosstalk between the AR and ER subtypes in breast cancer.