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Estrogen Responses in Bovine Fetal Uterine Cells Involve Pathways Directed by Both Estrogen Response Element and Activator Protein-1¹

^a Department of Infectious Disease and Physiology, College of Veterinary Medicine, Oklahoma State University, Stillwater, Oklahoma 74078-2006

Objectives were to examine possible roles of estrogen receptor (ER) in development of the bovine uterine endometrium in the context of ER type, enhancer type, and ligand-independent activation. Expression vectors producing either ER or ERß were introduced into fetal uterine cells from Day 110 to 120 of gestation (UBF120 cells) and into rat embryo fibroblasts (Rat-1 cells), neither of which express endogenous ER. Reporter constructs containing either an estrogen response element (ERE) or activator protein-1 (AP-1) response element were cotransfected. These reporters were also transfected into fetal uterine cells from Day 180 to 200 of gestation (UBF180 cells), which express ER. In UBF120 and Rat-1 cells transfected with either ER or ERß, treatment with estradiol-17ß (E₂) resulted in increased activity of an ERE reporter construct, but not an AP-1 element reporter construct. The antiestrogen ICI 182,780 (ICI) exhibited E₂ antagonist activity with both ER and ERß. Thus, all components were present for E₂-dependent transcription from an ERE except ER; however, cells were not competent for E₂-dependent transcription mediated through AP-1. In UBF180 cells, E₂ treatment increased both ERE and AP-1 reporter activity. ICI exhibited E₂ antagonist activity. Treatment with epidermal growth factor resulted in increased ERE reporter activity that was inhibited by ICI, indicative of ligand-independent activation of ER. These data suggest that multiple pathways for ER-mediated gene regulation occur in the developing fetal uterus and that nuclear components necessary for action of both ER and ERß are present prior to expression of the receptor.

¹ This study was supported by NIH NICHHD 34260 and USDA NRICGP 94–37206–0937.

² Correspondence: FAX: 405 744 7110; malayer{at}okway.okstate.edu

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