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¹ Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, Manitoba, Canada
² Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Mannitoba, Canada
³ Department of Physiology, University of Manitoba, Winnipeg, Manitoba, Canada

(Requests for offprints should be addressed to L C Murphy, Manitoba Institute of Cell Biology, University of Manitoba, 675 McDermot Ave., Winnipeg, Manitoba R3E 0 V9, Canada; Email: lcmurph{at}cc.umanitoba.ca)

To investigate the effect of altered oestrogen receptor (ER) and ERß expression on oestrogen and anti-oestrogen action in breast cancer, we have stably expressed an inducible ERß1 in MCF7 breast cancer cells. Stably expressing clones were isolated and over-expression of ERß1 correlated with increased levels of specific radiolabelled oestradiol (E2) binding. Increased ERß1 did not affect endogenous levels of ER but increased progesterone receptor (PR) levels. Over-expression of ERß1 reduced growth responses to E2 in contrast to little if any effect of over-expression of ER. In oestrogen-replete conditions, over-expression of ERß1 but not ER reduced proliferation. Over-expression of ERß1 did not result in anti-oestrogen resistance but was associated with increased sensitivity to 4-hydroxytamoxifen. Our results suggested that over-expression of ERß1 in the presence of an endogenously expressed ER was associated with tamoxifen sensitivity but may negatively modulate ER-mediated growth. However, not all ER activities were inhibited since endogenous PR expression was increased by both ER and ERß1 over-expression. These data paralleled those seen in some in vivo studies showing a relationship between PR and ERß expression as well as ERß expression and tamoxifen sensitivity of ER-positive breast cancer patients. These models are relevant and will be useful for dissecting the role of ERß1 expression in ER-positive breast cancer.

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				A. M. Shaaban, A. R. Green, S. Karthik, Y. Alizadeh, T. A. Hughes, L. Harkins, I. O. Ellis, J. F. Robertson, E. C. Paish, P. T.K. Saunders, et al. Nuclear and Cytoplasmic Expression of ER{beta}1, ER{beta}2, and ER{beta}5 Identifies Distinct Prognostic Outcome for Breast Cancer Patients Clin. Cancer Res., August 15, 2008; 14(16): 5228 - 5235. [Abstract] [Full Text] [PDF]

				L. C Murphy and P. H Watson Is oestrogen receptor- {beta} a predictor of endocrine therapy responsiveness in human breast cancer? Endocr. Relat. Cancer, June 1, 2006; 13(2): 327 - 334. [Abstract] [Full Text] [PDF]