Changes in expression of steroid receptors, their downstream target genes and their associated co-regulators during the sequential acquisition of tamoxifen resistance in vitro.

Tamoxifen resistance (TAMr) in breast cancer is a serious clinical dilemma, with no satisfactory explanation. We hypothesised that changes in the expression of steroid hormone receptors (ERalpha, ERbeta), their downstream target genes (PR, pS2) and their associated co-regulators (AIB-1, SRC-1, SRA, NCoR-1, SMRT and REA) could be related to the acquisition of TAMr. To test this hypothesis, we developed in vitro TAMr cell line models by continuous exposure of MCF-7 cells to 4-hydroxytamoxifen (4-HT) over 12 (MCF-7MMU1) and 21 (MCF-7MMU2) months, respectively and examined the expression of the above by Western blotting and immunohistochemistry. In addition, we further examined the changes in global gene expression in TAMr cells in comparison with TAM-sensitive cells by microarray analysis. We report here that acquisition of TAMr is associated with changes in the expression of PR, pS2 and several co-activators, but not ERs. In addition, genes associated with cell cycle, cell adhesion and extracellular matrix, were up-regulated while those associated with apoptosis or growth factors/hormones were down-regulated. Based on our results, it appears that increased co-activator expression, in concert with alterations in genes associated with controlling cell proliferation and survival contribute to TAMr in breast cancer.

Evaluation of seven oestrogen receptor beta antibodies for immunohistochemistry, western blotting, and flow cytometry in human breast tissue.

Two oestrogen receptors, ER alpha and ER beta, exist. While much is known about ER alpha, the role of ER beta is still undefined, especially at the protein level. The aim of this study was to determine the utility of seven ER beta antibodies (14C8, 8D5, PAI313, PPG5/10, N19, 9.88, and D7N) raised against different domains of ER beta in three commonly used laboratory applications, namely immunohistochemistry, western blot, and flow cytometry, using human breast material. For immunohistochemical analysis of frozen material, PAI313 and D7N gave stronger and more specific signals than 14C8, 8D5, and PPG5/10. In paraffin sections, 14C8, closely followed by PPG5/10, gave by far the most superior nuclear immunoreactivity, compared with the other antibodies tested. In general, flow cytometry results mirrored the immunohistochemistry data for paraffin sections, with antibodies ranked 14C8 > 8D5> or = PAI-313 > PPG5/10 >D7N. For western blotting, 8D5 and D7N yielded the strongest and most consistent bands, with weaker bands seen with the others. It is concluded that ER beta protein can be detected using specific antibodies. However, there is considerable variation between the specificity and application of these antibodies, highlighting the fact that careful optimization is required when selecting an antibody for use in a particular laboratory technique.

Coexpression of estrogen receptor alpha and beta: poor prognostic factors in human breast cancer?

The cloning of a second estrogen receptor (ER), ER beta, has prompted a reevaluation of the role of ERs in breast cancer. The aim of this study was to determine the expression of both ER isoforms in normal (n = 23) and malignant (n = 60) human breast tissue by reverse transcription-PCR and correlate this information with known prognostic factors including tumor grade and node status. In normal breast tissue, expression of ER beta predominated, with 22% of samples exclusively expressing ER beta; this was not observed in any of the breast tumor samples investigated. Most breast tumors expressed ER alpha, either alone or in combination with ER beta. Interestingly, those tumors that coexpressed ER alpha and ER beta were node positive (P = 0.02; Fisher's exact test) and tended to be of higher grade. Because antiestrogens are agonists when signaling through the AP1 element, overexpression of ER beta in tumors expressing both ER subtypes may explain the failure of antiestrogen therapy in some breast cancer patients. Thus, ER beta may be a useful prognostic factor in patients with breast cancer.