| Abstract
| - Functional in vitro and in vivo reporter gene assays haverecently been developed for the rapid determination ofexposure to (xeno)estrogens. The in vitro estrogen receptor(ER)-mediated chemically activated luciferase geneexpression (ER-CALUX) assay uses T47D human breastcancer cells stably transfected with an ER-mediated luciferasegene construct. In the in vivo assay, transgenic zebrafishare used in which the same luciferase construct hasbeen stably introduced. In both assays, luciferase reportergene activity can be easily quantified following short-term exposure to chemicals activating endogenous estrogenreceptors. The objective of this study was to compareresponses by known (xeno)estrogenic compounds in bothassays. Exposure to the (xeno)estrogens estradiol (E2),estrone, ethynylestradiol (EE2), o,p‘-DDT, nonylphenol (NP),and di(2-ethylhexyl)phthalate (DEHP) revealed that EE2was the most potent (xeno)estrogen tested and was 100times more potent than E2 in the transgenic zebrafish assay,whereas in the in vitro ER-CALUX assay, EE2 and E2were equipotent. Although the xenoestrogens o,p‘-DDTand NP were full estrogen agonists in the in vitro ER-CALUX assay, only o,p‘-DDT demonstrated weak dose-relatedestrogenic activity in vivo. To determine if differences inreporter gene activity may be explained by differential affinityof (xeno)estrogens to human and zebrafish ERs, full-length sequences of the zebrafish ER subtypes α, β, andγ were cloned, and transactivation by (xeno)estrogens wascompared to human ERα and ERβ. Using transientlytransfected recombinant ER and reporter gene constructs,EE2 also showed relatively potent activation of zebrafishERα and ERβ compared to human ERα and ERβ. ZebrafishERβ and ERγ showed higher transactivation by (xeno)estrogens relative to E2 than human ERβ.
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