Long-term estrogen exposure promotes carcinogen bioactivation, induces persistent changes in gene expression, and enhances the tumorigenicity of MCF-7 human breast cancer cells.
The cumulative exposure to estrogens is an important determinant in the risk of breast cancer, yet the full range of mechanisms involving estrogens in the genesis and progression of breast cancer remains a subject of debate. Interactions of estrogens and environmental toxicants have received attention as putative factors contributing to carcinogenesis. Mechanistic studies have demonstrated interactions between estrogen receptor alpha (ERalpha) and the aryl hydrocarbon receptor (AhR), with consequences on the genes that they regulate. Many studies of ERalpha and AhR-mediated effects and crosstalk between them have focused on the initial molecular events. In this study, we investigated ERalpha- and AhR-mediated effects in long-term estrogen exposed (LTEE) MCF-7 human breast cancer cells, which were obtained by continuous culturing for at least 12 weeks in medium supplemented with 1 nM of 17beta-estradiol (E(2)). With these LTEE cells and with parallel control cells cultured without E(2) supplementation, we performed an extensive study of cytochrome P450 (CYP) induction, carcinogen bioactivation, global gene expression, and tumorigenicity in immunocompromised mice. We found that LTEE cells, in comparison with control cells, had higher levels of AhR mRNA and protein, greater responsiveness for AhR-regulated CYP1A1 and CYP1B1 induction, a 6-fold higher initial level of benzo(a)pyrene-DNA adducts as determined by liquid chromatography tandem mass spectrometry, marked differences in the expression of numerous genes, and a higher rate of E(2)-dependent tumor growth as xenografts. These studies indicate that LTEE causes adaptive responses in MCF-7 cells, which may reflect processes that contribute to the overall carcinogenic effect of E(2).
Spink
Barbara C
BC
Laboratory of Molecular Toxicology, Wadsworth Center, New York State Department of Health, Albany, NY 12201-0509, USA. spink@wadsworth.org
Bennett
James A
JA
Pentecost
Brian T
BT
Lostritto
Nicole
N
Englert
Neal A
NA
Benn
Geoffrey K
GK
Goodenough
Angela K
AK
Turesky
Robert J
RJ
Spink
David C
DC
D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics; D001483:Base Sequence; D001711:Biotransformation; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002273:Carcinogens / Q000493:pharmacokinetics*; D045744:Cell Line, Tumor; D002853:Chromatography, Liquid; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D065633:Cytochrome P-450 CYP1B1; D018736:DNA Adducts; D017931:DNA Primers; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D004967:Estrogens / Q000008:administration & dosage* / Q000494:pharmacology; D005260:Female; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D011401:Promoter Regions, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry
D002273:Carcinogens; D018736:DNA Adducts; D017931:DNA Primers; D020847:Estrogen Receptor Modulators; D004967:Estrogens; D000077267:Fulvestrant; D004958:Estradiol; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; C585498:Cyp1b1 protein, mouse; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1