Activation of a uterine insulin-like growth factor I signaling pathway by clinical and environmental estrogens:: Requirement of estrogen receptor-α

Recent data indicate that insulin-like growth factor I (IGF-I) may have a function in mediating the mitogenic effects of 17 beta-estradiol (E-2) in the uterus and in regulating the growth of uterine neoplasms. This study was designed to determine whether synthetic and plant-derived chemicals that interact with estrogen receptor-alpha (ER alpha) and elicit estrogenic responses also mimic E-2 by activating the uterine IGF-I signaling pathway. Ovariectomized adult female mice were treated with both environmental and clinically relevant chemicals previously reported to display estrogenic and/or antiestrogenic properties, and their uteri were evaluated for an activated IGF-I signaling pathway. Diethylstilbestrol, 4-hydroxytamoxifen, the raloxifene analog LY353381, 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), bisphenol A, and genistein were shown to mimic E-2 in the uterus by increasing the level of IGF-I messenger RNA, inducing IGF-I receptor (TGF-IR) tyrosine phosphorylation, stimulating the formation of IGF-IR signaling complexes, and increasing both proliferating cell nuclear antigen expression and the number of mitotic cells in the epithelium. The dose of chemical necessary to activate IGF-I signaling varied, with the order of potency: E-2 = diethylstilbestrol > LY353381 > 1-hydroxytamoxifen > genistein > HPTE > bisphenol A. Administration of the chemicals to ER alpha knockout mice did not activate IGF-IR, indicating that ER alpha is required for activation of uterine IGF-IR by these diverse chemicals. This study demonstrates that several chemicals shown previously to display estrogenic activities also mimic E-2 by activating uterine IGF-I signaling.