Comparative activation of estrogen receptor alpha (er alpha) by endocrine disruptors
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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).
Wu, Fei (2007). Comparative activation of estrogen receptor alpha (er alpha) by endocrine disruptors. Doctoral dissertation, Texas A&M University. Available electronically from