Physiological coupling of growth factor and steroid receptor signaling pathways: estrogen receptor knockout mice lack estrogen-like response to epidermal growth factor.

Abstract

Past studies have shown that epidermal growth factor (EGF) is able to mimic the uterotropic effects of estrogen in the rodent. These studies have suggested a "cross-talk" model in which EGF receptor (EGF-R) signaling results in activation of nuclear estrogen receptor (ER) and its target genes in an estrogen-independent manner. Furthermore, in vitro studies have indicated the requirement for ER in this mechanism. To verify the requirement for ER in an in vivo system, EGF effects were studied in the uteri of ER knockout (ERKO) mice, which lack functional ER. The EGF-R levels, autophosphorylation, and c-fos induction were observed at equivalent levels in both genotypes indicating that removal of ER did not disrupt the EGF responses. Induction of DNA synthesis and the progesterone receptor gene in the uterus were measured after EGF treatment of both ERKO and wild-type animals. Wild-type mice showed increases of 4.3-fold in DNA synthesis, as well as an increase in PR mRNA after EGF treatment. However, these responses were absent in ERKO mice, confirming that the estrogen-like effects of EGF in the mouse uterus do indeed require the ER. These data conclusively demonstrate the coupling of EGF and ER signaling pathways in the rodent reproductive tract.Estradiol, epidermal growth factor (EGF), and insulin-like growth factors are known mitogens in the rodent reproductive tract (1-3). Estrogen has been shown to increase the uterine levels of both EGF and its receptor (EGF-R) (3-10), suggesting a link between the mitogenic effects of estrogens and growth factors. Furthermore, EGF has been shown to mimic the effects of estrogen in the mouse reproductive tract in terms of increased DNA synthesis and cornification of the vaginal epithelium (11), as well as increased phosphorylation and nuclear retention of the estrogen receptor (ER) (12). When estradiol is administered in conjunction with an EGF-specific antibody, a 60-70% reduction in the hormone-induced proliferation of the epithelium is observed in the mouse uterus and vagina (11). These data indicate a possible role for EGF as a mediator of estrogen action. Further evidence of EGF/ estrogen cross-talk was provided by experiments showing that pre-treatment of mice with the pure anti-estrogen ICI 164,384 greatly diminished the uterine response to EGF (12). Because ICI 164,384 significantly reduces the level of uterine ER (13), these studies suggest the necessity for the ER in the mitogenic actions of EGF. This was supported by studies in Ishikawa cells, a human endometrial carcinoma cell line devoid of ER, in which an estrogen-responsive chloramphenicol acetyltransferase reporter gene could only be activated by EGF after cotransfection with an ER-expression plasmid (14).These studies have led to a model in which EGF plays a role in ER-mediated events in a ligand-independent manner. To gain further insight into the role of the ER in this cross-talk mechanism, EGF studies were carried out in the ER "knockout" (ERKO) mice. In the ERKO, both alleles of the ER gene have b...

Crosstalk between steroid receptors and the c-Src-receptor tyrosine kinase pathways: implications for cell proliferation

“…Similar observations have been made in the mammary gland (Ankrapp et al, 1998), and at least part of this biological cooperation may occur because E2 can induce the synthesis and secretion of EGF (Dickson et al, 1986). However, studies in ERaknockout mice demonstrated that EGF could no longer induce transcription or DNA synthesis in the uterus, even in the presence of wild-type levels of EGF and EGF-R and a functional EGF signaling system (Curtis et al, 1996). In EGF-R knockout mice, the E2 response in stromal but not epithelial cells of the uterus and vagina is severely limited (Hom et al, 1998).…”

FGF signaling activates STAT1 and p21 and inhibits the estrogen response and proliferation of MCF-7 cells

“…These growth factors are able to activate the estrogen receptor and promote transcription from an EREcontaining promoter in the absence of estrogen. In the reproductive tract EGF can mimic the physiological e ects of estrogen (Ignar-Trowbridge et al, 1992;Curtis et al, 1996). This ligand-independent activation of ER by IGF or EGF has been shown to be mediated through phosphorylation of a serine residue at position 118 in ER by activated MAP kinase (Kato et al, 1995;Bunone et al, 1996).…”

Inhibition of Cell Migration by 24-kDa Fibroblast Growth Factor-2 Is Dependent upon the Estrogen Receptor

“…The activation of the ER by a peptide growth hormone is not unusual; direct evidence for peptide growth factor activation of the ER has been obtained in multiple cell types (13)(14)(15)(16) and in ER knockout animals (42). Transforming growth factor-␣ or EGF treatment of HeLa, Ishikawa (endometrial), and BG-1 (ovarian) cells transiently transfected with ER-responsive target genes results in the dose-dependent activation of theER in an estrogen-independent manner (38).…”