Influence of Estrogens on Mouse Uterine Epidermal Growth Factor Precursor Protein and Messenger Ribonucleic Acid

Abstract

Estrogens stimulate the in vivo proliferation of epithelial cells of the mouse uterus. The cumulative evidence from several earlier studies suggests that the mitogenic effect of estrogens is mediated indirectly through a polypeptide growth factor. The primary focus of the present investigation was to determine whether an epidermal growth factor (EGF)-related polypeptide originates in the uterus of the immature or adult mouse under normal or altered estrogen status. Hybridization experiments revealed the presence of the 4.7-kilobase prepro-EGF mRNA in uteri of immature CD-1 mice. The level of this mRNA was augmented at least 2-fold in immature mice treated for 4 days with estrogen, but levels remained markedly low compared to those in submaxillary gland or kidney. Two preparations of pooled uterine luminal fluid from estrogen-treated immature mice contained EGF immunoreactivity (1.2 and 1.7 ng/ml) that was stable in response to acid (50 mM acetic acid) and heat. Negligible EGF (less than 20 pg/uterus) was detected in acid extracts of uteri from ovariectomized or cycling adult mice. After injection of 17 beta-estradiol (0.2 or 2.0 micrograms, ip), the levels of acid-extractable uterine EGF in ovariectomized adult mice up to 48 h after treatment were not different from those obtained with vehicle alone. Immunolocalization of EGF in the mouse uterus was demonstrated only after paraffin sections were first briefly treated with pronase. Staining was observed along the borders of luminal and glandular epithelial cells, especially at the apical region of the cells. Some staining was also observed in the myometrium; stromal cells were negative. Synthesis of the reactive material was apparently estrogen independent, since localization was retained in uteri of both ovariectomized and immature mice. Immunoblots of preparations of membranes from uterine homogenates or epithelial cells revealed a band at mol wt of about 130,000, which, along with other findings of the present study, suggests that EGF occurs predominantly as the membrane-bound precursor form in this organ, as has been previously shown for the kidney. Although the biological role of the precursor in the uterus is not known, we speculate that estrogens function in an autocrine circuit by stimulating processing of the membrane-bound EGF precursor. EGF elaborated by this mechanism might conceivably react with known complementary receptors on uterine epithelial cells to stimulate proliferation.

Uterine epithelial estrogen receptor α is dispensable for proliferation but essential for complete biological and biochemical responses

“…Based on previous studies (5,8,9,17), we evaluated whether Cebpb and Igf1 could be mediators of E 2 -induced uterine epithelial proliferation. E 2 significantly up-regulated Cebpb at 2 h (Fig.…”

“…production of growth factors such as IGF-1 and EGF, and these growth factors induce uterine DNA synthesis (8)(9)(10)16). Igf1 knockout mice exhibited impaired uterine response to estrogen, which implicated the essential role of IGF-1 on uterine growth (32).…”

“…Several studies demonstrated that a number of growth factors, such as IGF-1, EGF, or transforming growth factor α (TGFα) (8)(9)(10) and their receptors were induced and activated, respectively, in the uterus under the influence of E 2 treatment (8-12). IGF-1 was shown experimentally to be a key growth factor that stimulates growth of the nearby epithelial cells as a result of their estrogen-dependent expression in the uterus (13).…”

Role of estrogen receptor β in uterine stroma and epithelium: Insights from estrogen receptor β −/− mice

“…The role of the EGF family in estrogenic effects in the female genital tract is well documented (31). Estrogens have effects on both EGF and EGFR in the uterus (32,33). The present study revealed that EGFR is found not only in association with the cell membrane but also in the cytoplasm and in nuclei of stromal cells in ER␤ Ϫ/Ϫ mice treated with E 2 ϩ P 4 .…”

Estrogen receptor (ER) and its messenger ribonucleic acid expression in the genital tract of female mice exposed neonatally to tamoxifen and diethylstilbestrol

“…We compared the changes in expression of ER mRNA and ER protein in the uterus and vagina of mice exposed neonatally to Tx and DES and changes in expression of ER mRNA in the ovariectomized adult mice given Tx and DES injections. We also tested the hypothesis that epidermal growth factor (EGF) acts as a mediator of estrogenic compounds (DiAugustine et al, 1988) by ER induction in newborn mouse uterine epithelium. …”