title: A novel antiestrogenic mechanism in progesterone receptor-transfected breast cancer cells.
abstract: The expression of progesterone receptor (PR) is normally estrogen-dependent, and progesterone is only active in target cells following estrogen exposure. This study revealed that the effect of estrogen was markedly disrupted by estrogen-independent expression of PR. Transfection of PR in estrogen receptor (ER)-positive MCF-7 cells abolished the estradiol-17beta growth stimulatory effect that was observed in the parental cells and the vector-transfected controls in a ligand-independent manner. The antiestrogenic effect was also observed at the level of gene transcription. Estradiol-17beta (E2)-induced gene expression of pS2 and GREB1 was impaired by 50-75% after 24-72 h of E2 treatment in PR-transfected cells. Promoter interference assay revealed that PR transfection drastically inhibited E2-mediated ER binding to estrogen response elements (ERE). The antiestrogenic effects of transfected PR are associated with enhanced metabolism of E2. HPLC analysis of [3H]E2 in the samples indicated that the percentage of [3H]E2 metabolized by PR-transfected cells in 6 h is similar to that by vector-transfected control cells in 24 h (77 and 80%, respectively). The increased metabolism of E2 may, in turn, be caused by increased cellular uptake of E2, as demonstrated by whole cell binding of [3H]E2. The findings open up a new window for a hitherto unknown functional relationship between the PR and ER. The antiestrogenic effect of transfected PR also provides a potential therapeutic strategy for estrogen-dependent breast cancer.
authors.affiliation: School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, USA.
authors.forename: Ze-Yi
authors.initials: ZY
authors.lastname: Zheng
authors.forename: Boon-Huat
authors.initials: BH
authors.lastname: Bay
authors.forename: Swee-Eng
authors.initials: SE
authors.lastname: Aw
authors.forename: Valerie C-L
authors.initials: VC
authors.lastname: Lin
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002851:Chromatography, High Pressure Liquid; D004958:Estradiol / Q000378:metabolism; D020847:Estrogen Receptor Modulators / Q000378:metabolism*; D047628:Estrogen Receptor alpha / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D011401:Promoter Regions, Genetic; D011980:Receptors, Progesterone / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D004967:Estrogens; D011980:Receptors, Progesterone; D004958:Estradiol