Estrogen receptor beta and estrogen response in breast cancer cell lines (2008)

Ced Stewart: Estrogen receptor beta and estrogen response in breast cancer cell lines Breast cancer affects 1 in 9 women in Britain and its development and treatment are greatly influenced by hormonal status, such as exposure to endogenous estrogen and expression of estrogen receptors (ERs). ERa is an established prognostic marker in breast cancer, but the role of ERp is less certain. The ERs act to regulate gene transcription via a highly complex variety of mechanisms in response to stimuli such as estrogen, tamoxifen or fulvestrant. In order to further define the role of ERp isoforms in breast cancer, their role in the estrogen response must be characterised. This thesis has used a set of four breast cancer cell lines, as well as an MCF7 cell line engineered to over-express ERpl mRNA (MCF7PIx), to investigate the role of ERp in estrogen response. Cells were - treated with a variety of stimuli (estrogen, tamoxifen, fulvestrant, epidermal growth factor and fibroblast growth factor-2) and expression of a panel of ER isoforms, estrogen responsive genes and housekeeping genes was measured using real-time, quantitative PCR. Estrogen response is cell line specific, both in terms of the genes affected and the level of response. These responses can be partly, but not fully, related to the levels of ERa expressed by the cell lines. Expression of individual ER isoforms varies in response to treatment in a time, stimulus and cell line specific manner. Different cell lines vary expression of different subsets of ER isoforms and MCF7pIx, which constitutively over-expresses ERpl mRNA, shows down-regulation of ERpl mRNA expression in response to estrogen. Together these data suggest that regulation may occur at the level of splicing and mRNA stability, as well as at the transcription level. MCF7 and MCF7P Ix showed.remarkably similar responses to treatments. In both cell lines, similar sets of genes were both up- and down-regulated by estrogenic and growth factor treatments. Most -genes showed a similar pattern of transcriptional activation at 0 to 8 h as at 24 h, except for ERpl and ERp2, indicating the importance of control of ERp expression. It was not possible to measure the levels of ERpl protein in the cells, therefore the similarity in responses in MCF7 and MCF7pIx may indicate that, despite the higher levels of ERpl rnRNA, MCF7pIx cells do not overexpress ERPI protein. Measurement of endogenous expression of a set of estrogen responsive genes in a panel of breast cancer cell lines in response to various stimuli has afforded new insights into the levelS and variation in the response achieved in this system. Expression of ERp mRNA was shown to be controlled in a cell line and treatment specific manner, as has previously been shown for ERa. Additionally, it was shown that this regulation was isofonn specific and was maintained when the ERp was overexpressed under the control of an exogenous promoter. This is particularly interesting, as it suggests various levels of regulation, indicating the important role of ERp in downstream estrogen responses. - Supplied by The British Library - 'The world's knowledge'