Estrogen receptor α (ERα) is a ligand activated transcription factor. Many widely
used synthetic compounds and natural chemicals can activate ERα. The
compounds investigated in this study include 17β-estradiol (E2), diethylstilbestrol
(DES), antiestrogens ICI 182,780, 4-hydroxytamoxifen, the phytoestrogen
resveratrol, and the xenoestrogens bisphenol A (BPA), nonylphenol (NP),
octylphenol (OP), endosulfan, kepone, 2,2-bis(p-hydroxyphenyl)-1,1,1-
trichloroethane (HPTE) and 2,3,4,5-tetrachlorobiphenylol-4-ol (HO-PCB-Cl4).
With the exception of the antiestrogens, all the compounds induced
transactivation in MCF-7 or MDA-MB-231 cells transfected with wild-type ERα
and a construct (pERE3) containing three tandem estrogen responsive elements
(EREs) linked to a luciferase gene. However, these compounds differentially
activated C-terminal deletion mutants of ERα. For example, neither E2 nor DES
induced transactivation in MCF-7 transfected with ERα(1-537) due to partial
deletion of helix 12 of ERα; however, OP, NP, resveratrol, kepone and HPTE
induced this ERα mutant, demonstrating that the estrogenic activity of these
synthetic compounds do not require activation function 2 (AF-2) of ERα.
This study also investigated the effects of xenoestrogens on activation of
reporter gene activity in MCF-7 and MDA-MB-231 cells transfected with a
construct (pSp13) containing three tandem GC-rich Sp binding sites linked to the
luciferase gene. In MCF-7 cells, antiestrogen-induced activation of ERα/Sp1 required the zinc finger motifs of ERα, whereas activation by estrogen and some
xenoestrogens activation, such as endosulfan, NP and OP required the H12 of
ERα. In contrast, xenoestrogens, such as HPTE, BPA, kepone and HO-PCBCl4,
significantly induced transactivation of all four ERα deletion mutants tested
in this study. Moreover, RNA interference assays demonstrated structuredependent
differences in activation of ERα/Sp1, ERα/Sp3 and ERα/Sp4.
The in vivo activities of E2, ICI 182,780, BPA and NP were further investigated
in a transgenic mouse model containing pSp13 transgene. All the compounds
induced luciferase activity in the mouse uterus; however activities observed in
the penis and testis of male and stomach of both male and female mice were
structure-dependent,.
These results demonstrate that various ER ligands differentially activate ERα in
breast cancer cells and transgenic mice, and their activities are dependent on
ERα variants, promoter-, cell-context and selective use of different Sp proteins,
suggesting these structurally diverse compounds are selective ER modulators
(SERMs).
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2433 |
| Date | 15 May 2009 |
| Creators | Wu, Fei |
| Contributors | Safe, Stephen |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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