GROUP LEADER: Dr. Donita Africander
Position: Senior lecturer
Office: A116, JC Smuts building
PhD, University of Stellenbosch, Biochemistry, 2010
Gene regulation, Steroid receptors, Progestins, Bioidentical hormones, Immune function, Breast cancer
The research in our laboratory is focused on understanding the fundamental mechanisms of how compounds such as progestins and bio-identical hormones used in hormone replacement therapy (HRT) contribute to the development and progression of inflammation and breast cancer. Considering that these hormones mediate their effects by binding to steroid receptors and that different steroid receptors can be expressed in breast cancer tumours, with emerging evidence showing a clinically relevant interplay between some receptors, we have a specific interest in how different levels and combinations of steroid receptors may influence these mechanisms. We explore these using molecular approaches, with the aim of aiding in the development of new therapeutic strategies to effectively prevent or treat breast cancer.
Characterization of the role of progestins via progesterone receptor isoforms in breast cancer
Progestins are a class of synthetically developed compounds based on the similarity of their biological actions to that of the endogenous ovarian hormone progesterone. There are a wide range of different progestins used as contraceptives, in HRT, and in the treatment of gynaecological disorders such as endometriosis. Recent clinical evidence showing increased risk for breast cancer and cardiovascular disease in HRT users has highlighted the importance of choice of progestin. Progestins and progesterone act via binding to the progesterone receptor (PR) in target cells. The progestin-bound PR translocates to the nucleus where it activates (transactivation) or represses (transrepression) transcription of specific target genes. There are two functional isoforms of the PR, PR-A and PR-B, which are transcribed from two promoters of a single gene. The ratios of the individual isoforms vary in reproductive tissues, and they have different physiological functions. It is known that the ratio of PR-A/PR-B is a determining factor of breast carcinogenesis. For example, breast cancer patients expressing more PR-A than PR-B are more likely to relapse due to resistance to breast cancer treatment. Thus, the biological actions of a progestin may be affected by cell-specific differences in PR-A:PR-B ratios. Little is known about the mechanisms by which the progestin-bound PR isoforms participate in breast cancer growth. Our research thus focuses on PR isoform-mediated actions of progesterone versus different progestins on various target genes involved in inflammation and breast cancer biology, and how these events cause breast cancer cells to grow.
Role of steroid receptor crosstalk in breast cancer
In addition to binding to the PR, some progestins also interact with the glucocorticoid, androgen, mineralocorticoid and estrogen receptors (GR, AR, MR and ER), respectively. It is thus possible that multiple steroid receptors may play a role in progestin-induced increased risk of breast cancer, and in fact this has been shown for the progestin medroxyprogesterone acetate (MPA). For example, MPA has been implicated in PR-mediated increased breast cancer cell migration and invasion, as well as anti- AR activity to increase breast cancer cell proliferation. Moreover, recent evidence in the literature suggests that an association of both PR isoforms with ER-α is needed for MPA-induced breast cancer cell proliferation. It is unclear whether this would be similar for all progestins, or what the role of the other members of the steroid receptor family would be. Considering that these steroid receptors all share similar mechanisms of action and it is known that there is crosstalk between some of these receptors, we are interested in whether changes in steroid receptor levels and crosstalk between receptors influence the regulation of genes involved in breast cancer development and progression.
Mechanism of bioidentical hormones
HRT is commonly prescribed to alleviate menopausal symptoms experienced by women, and includes administration of either estrogen alone, or estrogen combined with a progestin. Recent clinical evidence showing increased risk for invasive breast cancer and cardiovascular disease with the use of HRT caused much confusion and alarm amongst HRT users. As a result many postmenopausal women have stopped using conventional HRT, and are seeking alternate "safer", "natural" treatments, and thus often request bioidentical hormones as therapy to manage the symptoms of menopausal transition. Bioidentical hormones are structural mimics of the hormones produced by the human body and considered to be 'natural' as they are synthesised from a weakly estrogenic plant precursor, diosgenin. These hormones are claimed to be more effective and safer than conventional HRT and do not increase breast cancer risk. Typically, bioidentical HRT includes estrogen (17β-estradiol, estrone and/or estriol), progesterone, testosterone, androstenedione and dehydroepiandrosterone. However, there have been no studies addressing the molecular mechanism of these bioidentical hormones, particularly in the breast. We are thus investigating the actions of these bioidentical hormones on various target genes such as those involved in breast cancer biology.
The techniques used in our laboratory include mammalian tissue culture, Western blotting, proliferation assays, apoptosis assays, transient transfections, promoter-reporter assays, RNA isolation, cDNA synthesis, quantitative real-time PCR, immunoprecipitations, chromatin immunoprecipitation (ChIP), re-ChIP, and basic molecular biology techniques such as plasmid DNA preparation, restriction enzyme digests, agarose-gel electrophoresis.
We collaborate extensively with the group of Prof. Janet Hapgood at the Department of Molecular and Cell Biology, University of Cape Town. We also collaborate with the groups of Dr Karl Storbeck, Prof Ann Louw and Prof Amanda Swart in the Biochemistry department at the University of Stellenbosch.
R. Louw-du Toit, J. P. Hapgood and D. Africander. (2014) Medroxyprogesterone acetate differentially regulates IL-12 and IL-10 gene expression in a human ectocervical epithelial cell line in a GR-dependent manner. J.Biol.Chem. 289, 31136 – 31149.
D. Africander, K. Storbeck and J. Hapgood. (2014) A comparative study of the androgenic properties of progesterone and the synthetic progestins, medroxyprogesterone acetate and norethisterone acetate. J Steroid Biochem Mol Biol. 143: 404-415.
Hapgood, J., Africander, D., Louw,R., Ray, R., Rohwer, J.M. (2014) Potency of progestogens used in hormonal therapy: Towards understanding differential actions. J Steroid Biochem Mol Biol. 142: 39-47.
Africander, D., Louw, R. and Hapgood, J.P. (2013) Investigating the anti-mineralocorticoid properties of synthetic progestins used in hormone replacement therapy. Biochem Biophys Res Commun. 433 (3): 305-310.
Africander, D., Louw, R., Verhoog, N., Noeth, D. and Hapgood, J.P. (2011) Differential regulation of endogenous pro-inflammatory cytokine genes by medroxyprogesterone acetate and norethisterone acetate in cell lines of the female genital tract. Contraception. 84 (4), 423-435.
Africander, D., Verhoog, N., Hapgood, J.P. (2011) Molecular mechanisms of steroid receptor-mediated actions by synthetic progestins used in HRT and contraception. Steroids. 76(7): 636-652.
Hapgood, J.P., Koubovec, D., Louw, A and Africander, D. (2004) Not all progestins are the same: Implications for usage. Trends Pharmacol Sci. 25 (11):554-7.