Differential Interactions of Estrogenic Chemicals with Estrogen Receptors From Several Different Species. Zacharewski T.R., Matthews J.B., Celius T., Fertuck K, Huang Y-W.

This studied examined the ability of 15 natural and synthetic estrogenic chemicals to induce gene expression mediated through both ER subtypes and ERs different species. MCF-7 cells were transiently co-transfected with a Gal4-ER chimeric receptors consisting of the D, E and F domains of either the human alpha (Gal4-hERa), mouse alpha (Gal4-mERa), mouse beta (Gal4-mERb), chicken (Gal4-cER), green anole (Gal4-aER), xenopus (Gal4-xER) or rainbow trout ERs (Gal4-rtERdef), and a Gal4 regulated luciferase reporter gene. The ability of 17b-estradiol (E2) to induce reporter gene expression was similar for 6 of the 7 chimeric receptors, with EC50 values ranging from 0.05 to 0.7 nM. The ability of E2 to induce reporter gene expression mediated by Gal4-rtER was 2 orders of magnitude lower, with an EC50 value of 28 nM at 37 C. This discrepancy was primarily due to temperature since at 20 C only 9-fold difference in EC50 values was observed. Therefore the ability of the estrogenic chemicals to induce Gal4-rtER mediate gene expression was assayed at 37 C and 20 C. In general, the ability of several compounds to induced Gal4-rtER mediated gene expression was increased at 20 C. Although, the response of E2 was similar among the ERs, many differences were observed. For example, a-zearalenol induced reporter gene expression mediated by Gal4-rtER at lower concentrations than E2, which was in contrast to other Gal4-ERs. Coumestrol induced reported gene expression 280- and 14-fold greater mediated through Gal4-mERb and Gal4-aER, respectively, than through the other Gal4 chimeric receptors. These data show that certain estrogenic compounds exhibit a differentially ability to induce reporter gene activity mediated by both ER subtypes and ERs from different species, and also illustrate the importance of temperature when examining rtER mediated activity.