Carcinogenesis Advance Access originally published online on September 10, 2008
Carcinogenesis 2008 29(12):2252-2258; doi:10.1093/carcin/bgn214
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Artemisinin selectively decreases functional levels of estrogen receptor-alpha and ablates estrogen-induced proliferation in human breast cancer cells
Department of Molecular and Cell Biology and the Cancer Research Laboratory, University of California at Berkeley, Berkeley, CA 94720, USA
* To whom correspondence should be addressed. Department of Molecular and Cell Biology, 591 LSA, University of California at Berkeley, Berkeley, CA 94720-3200, USA. Tel: +1 510 642 8319; Fax: +1 510 643 6791; Email: glfire{at}berkeley.edu
MCF7 cells are an estrogen-responsive human breast cancer cell line that expresses both estrogen receptor (ER) 
and ERβ. Treatment of MCF7 cells with artemisinin, an antimalarial phytochemical from the sweet wormwood plant, effectively blocked estrogen-stimulated cell cycle progression induced by either 17β-estradiol (E2), an agonist for both ERs, or by propyl pyrazole triol (PPT), a selective ER agonist. Artemisinin strongly downregulated ER protein and transcripts without altering expression or activity of ERβ. Transfection of MCF7 cells with ER promoter-linked luciferase reporter plasmids revealed that the artemisinin downregulation of ER promoter activity accounted for the loss of ER expression. Artemisinin treatment ablated the estrogenic induction of endogenous progesterone receptor (PR) transcripts by either E2 or PPT and inhibited the estrogenic stimulation of a luciferase reporter plasmid driven by consensus estrogen response elements (EREs). Chromatin immunoprecipitation assays revealed that artemisinin significantly downregulated the level of endogeneous ER bound to the PR promoter, whereas the level of bound endogeneous ERβ was not altered. Treatment of MCF7 cells with artemisinin and the pure antiestrogen fulvestrant resulted in a cooperative reduction of ER protein levels and enhanced G1 cell cycle arrest compared with the effects of either compound alone. Our results show that artemisinin switches proliferative human breast cancer cells from expressing a high ER:ERβ ratio to a condition in which ERβ predominates, which parallels the physiological state linked to antiproliferative events in normal mammary epithelium.
Abbreviations: ChIP, chromatin immunoprecipitation; DMSO, dimethyl sulfoxide; ER, estrogen receptor; ERE, estrogen response element; E2, 17β-estradiol; FBS, fetal bovine serum; Ful, fulvestrant; pCMV, cytomegalovirus promoter-containing plasmid; PCR, polymerase chain reaction; PPT, propyl pyrazole triol; PR, progesterone receptor; RT, reverse transcription
Received April 21, 2008; revised September 2, 2008; accepted September 6, 2008.