Activation of estrogen receptor-mediated gene transcription by the equine estrogen metabolite, 4-methoxyequilenin, in human breast cancer cells.
4-Methoxyequilenin (4-MeOEN) is an O-methylated metabolite in equine estrogen metabolism. O-methylation of catechol estrogens is considered as a protective mechanism; however, comparison of the properties of 4-MeOEN with estradiol (E(2)) in human breast cancer cells showed that 4-MeOEN is a proliferative, estrogenic agent that may contribute to carcinogenesis. 4-MeOEN results from O-methylation of 4-hydroxyequilenin, a major catechol metabolite of the equine estrogens present in hormone replacement therapeutics, which causes DNA damage via quinone formation, raising the possibility of synergistic hormonal and chemical carcinogenesis. 4-MeOEN induced cell proliferation with nanomolar potency and induced estrogen response element (ERE)-mediated gene transcription of an ERE-luciferase reporter and the endogenous estrogen-responsive genes pS2 and TGF-alpha. These estrogenic actions were blocked by the antiestrogen ICI 182,780. In the standard radioligand estrogen receptor (ER) binding assay, 4-MeOEN showed very weak binding. To test for alternate ligand-ER-independent mechanisms, the possibility of aryl hydrocarbon receptor (AhR) binding and ER-AhR cross talk was examined using a xenobiotic response element-luciferase reporter and using AhR small interfering RNA silencing in the ERE-luciferase reporter assay. The results negated the possibility of AhR-mediated estrogenic activity. Comparison of gene transcription time course, ER degradation, and rapid activation of MAPK/ERK in MCF-7 cells demonstrated that the actions of 4-MeOEN mirrored those of E(2) with potency for classical and nonclassical estrogenic pathways bracketing that of E(2). Methylation of 4-OHEN may not represent a detoxification pathway because 4-MeOEN is a full, potent estrogen agonist.
Chang
Minsun
M
Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, Chicago, IL 60612, USA. thatcher@uic.edu
Peng
Kuan-wei
KW
Kastrati
Irida
I
Overk
Cassia R
CR
Qin
Zhi-Hui
ZH
Yao
Ping
P
Bolton
Judy L
JL
Thatcher
Gregory R J
GR
D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004855:Equilenin / Q000031:analogs & derivatives* / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D008024:Ligands; D008156:Luciferases / Q000235:genetics; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism*; D020218:Response Elements / Q000235:genetics; D014158:Transcription, Genetic; D015533:Transcriptional Activation / Q000187:drug effects*; D015262:Xenobiotics / Q000378:metabolism
D047628:Estrogen Receptor alpha; D004967:Estrogens; D008024:Ligands; D018336:Receptors, Aryl Hydrocarbon; D011960:Receptors, Estrogen; D015262:Xenobiotics; C056919:4-methoxyequilenin; D008156:Luciferases; D048049:Extracellular Signal-Regulated MAP Kinases; D004855:Equilenin