Differential interaction of the methoxychlor metabolite 2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane with estrogen receptors alpha and beta.
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abstract
Concern that some chemicals in our environment may affect human health by disrupting normal endocrine function has prompted research on interactions of environmental contaminants with steroid hormone receptors. We compared the activity of 2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), an estrogenic metabolite of the organochlorine pesticide methoxychlor, at estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta). Human hepatoma cells (HepG2) were transiently transfected with either human or rat ERalpha or ERbeta plus an estrogen-responsive, complement 3-luciferase construct containing a complement 3 gene promoter sequence linked to a luciferase reporter gene. After transfection, cells were treated with various concentrations of HPTE in the presence (for detecting antagonism) or absence (for detecting agonism) of 17beta-estradiol. HPTE was a potent ERalpha agonist in HepG2 cells, with EC50 values of approximately 5 x 10(-8) and 10(-8) M for human and rat ERalpha, respectively. In contrast, HPTE had minimal agonist activity with either human or rat ERbeta and almost completely abolished 17beta-estradiol-induced ERbeta-mediated activity. Moreover, HPTE behaved as an ERalpha agonist and an ERbeta antagonist with other estrogen-responsive promoters (ERE-MMTV and vtERE) in HepG2 and HeLa cells. This study demonstrates the complexity involved in determining the mechanism of action of endocrine-active chemicals that may act as agonists or antagonists through one or more hormone receptors.
