Epidermal growth factor (EGF) reproduces many of the effects of estrogen on the murine female reproductive tract and may partially mediate estroged-induced growth and differentiation. This study was performed to investigate the mechanism by which EGF elicits estrogen-like actions in the whole animal. EGF was ad tered to adult ovariectomized mice by slow release pellets implanted under the kidney capsule. The induction ofuterine DNA synthesis and phosphatidylinositol lipid turnover by EGF or admintation of diethylstilbestrol (5 pg/kg), a potent estrogen, was attenuated by the estrogen receptor antagonist ICI 164,384. Furthermore, EGF mimicked the effects of estrogen on enhanced nuclear localization of the estrogen receptor and the formation of a unique form of the estrogen receptor found exclusively in the nucleus. These results suggest that EGF may induce effects similar to those of estrogen in the mouse uterus by an interaction between the EGF signaling pathway and the classical estrogen receptor. The demonstration of cross-talk between polypeptide growth factors and steroid hormone receptors may be of importance to our understanding of the regulation of normal growth and differentiation as well as the mechanisms of transmission of extracellular mitogen signals to the nucleus.It has been proposed that polypeptide growth factors may act as autocrine or paracrine mediators of estrogen-induced mitogenesis (1, 2). The observations that estrogen induces mRNA and protein for both epidermal growth factor (EGF) (3,4) and its receptor (5-7) in rodent uterus are consistent with this hypothesis and implicate a role for the EGF receptor signaling pathway in steroid hormone regulation of uterine tract growth. Furthermore, exogenous EGF administration to adult ovariectomized mice mimics the effects of estrogen on proliferation and differentiation in the murine female reproductive tract (8). EGF-induced mitogenesis in this model is not affected by adrenalectomy or hypophysectomy, which indicates that adrenal or pituitary hormones do not mediate the effects of EGF. In addition, the fact that an EGF-specific antibody administered prior to estradiol partially blocks estrogen-induced uterine epithelial cell proliferation (8) suggests that production of EGF may be necessary for estrogen-induced responses.Presently, the mechanism by which the actions of estrogens and EGF converge is unknown. This study addresses the intriguing possibility that some of the physiological actions of EGF, an extracellular ligand, may be mediated through a nuclear steroid hormone receptor, namely, the estrogen receptor (ER). Two recent reports by Power et al. (9,10) support such a hypothesis. These studies demonstrated that dopamine, an extracellular ligand, was able to stimulate transcriptional enhancement by three members of the steroid receptor superfamily [the progesterone receptor (PR), ER, and COUP (chicken ovalbumin upstream promoter) transcriptional enhancer], which were transfected into CV1 monkey kidney cells. Furthermore, in MCF-7 hu...

Epidermal growth factor (EGF) elicits estrogen receptor (ER)-dependent physiological sequelae and estrogen-like biochemical effects on the ER in the mouse uterus. These in vivo observations indicate that EGF may elicit some of its actions by activation of the ER. The effect of peptide growth factors on activation of a consensus estrogen-responsive element was assessed in a strain of Ishikawa human endometrial adenocarcinoma cells with negligible levels of ERs, as determined by Western blot and [3H]estradiol binding, and in BG-1 human ovarian adenocarcinoma cells, which contain abundant ERs. EGF and transforming growth factor-alpha induced transcriptional activation of a consensus ERE in an ER-dependent manner in both cell types. Transcriptional activation by the growth factors was inhibited by ICI 164,384, an ER receptor antagonist, and neutralizing antibodies to the EGF receptor. Immunodetection of the ER in BG-1 cells demonstrated that receptor levels were not induced by transforming growth factor-alpha vs. untreated cells. ER deletion mutants containing amino acids 1-339 and 121-599 were transfected into Ishikawa cells. The 1-339 mutant was more active in inducing transcription after EGF treatment than the 121-599 mutant. Estrogen only stimulated transcription in the presence of the 121-599 mutant, while 1-339 was inactive. Interestingly, synergism between a physiological dose of estrogen and peptide growth factors was observed. The presence of cross-talk between EGF receptor and ER signaling pathways suggests that interactions between growth factors and steroid receptors may modulate hormonal activity influencing normal and aberrant function in mammalian cells.

Modulation of steroid receptor-dependent transcription by extra- cellular ligands represents a novel mechanism of steroid receptor regulation. We have assessed the effects of epidermal growth factor (EGF), transforming growth factor-alpha (TGF alpha), and insulin-like growth factor I (IGF-I) on transcription from consensus estrogen response elements (ERE) in estrogen receptor (ER)-positive BG-1 human ovarian adenocarcinoma calls. EGF, TGF alpha, IGF-I, and estradiol (E2) enhanced transcription in a dose-dependent manner using either a strong or a minimal promoter, and ICI 164,384, a specific ER antagonist, inhibited these responses. Combinations of E2 with TGF alpha or IGF-I induced synergistic activation of transcription from an ERE, whereas as additive response was observed with combinations of IGF-I and TGF alpha of EGF. Tetradecanoyl 12-phorbol 13-acetate (TPA), a protein kinase C (PKC) activator, stimulated ERE-mediated transcription, and this effect was inhibited by ICI 164,384. Bisindolylmaleimide, a relatively specific inhibitor of PKC, completely antagonized TPA-induced transcription, but did not affect the response to TGF alpha, IGF-I, or E2. The combination of TPA with E2 in transcriptional synergism was inhibited by ICI 164,384; conversely, the combination of TPA with either TGF alpha of IGF-I elicited a response only equal to the maximal TPA response. Thus, peptide growth factors elicit ER-dependent transcription independently of PFC; however, there may be a common mechanistic component, as saturation of response was observed. Finally, activation of ERE-dependent transcription in Chinese hamster ovary cells by IGF-I was observed in the presence of a mutant receptor that lacks estrogen-binding activity. The effect of both IGF-I and E2 were dependent on the ability of the ER to bind to DNA. IGF-I elicited only weak transcriptional activation in the presence of a deletion mutant that lacked the entire A/B domain; however, synergism between IGF-I and E2 was observed with this mutant. Therefore, ligand-independent activation of ER-dependent transcription by IGF-I is predominantly mediated through activation function I by a mechanism distinct from that of E2.