Download or read book Molecular Mechanisms of the Non-classical Estrogen Receptor Alpha Signaling written by Monika Helena Jakacka and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In the classical signaling pathway, the estrogen receptor (ER) binds directly to estrogen response elements (EREs) to regulate gene transcription. The ER agonist, estradiol, activates ERE-mediated transcription, whereas the antagonist, ICI 182,780, induces repression. The non-classical ER signaling pathway was examined using an AP1-regulated promoter, which is controlled by the Jun/Fos family of transcription factors. In this model system, there was a reversal of ER action relative to that seen with the ERE reporter: estradiol caused suppression and ICI 182,780 stimulated transcription of the AP1 reporter. A functional interaction between Jun and ER was detected when tested in mammalian two-hybrid assays. Mutations were introduced into the DNA binding domain of mouse ERalpha to test the hypothesis that the non-classical pathway involves ER interaction with other proteins rather than direct binding to DNA. A mutation in the proximal box of the first zinc finger (E207A/G208A) eliminated ERE binding. This mutant was inactive using the ERE reporter but retained full activity on the AP1 reporter. To clarify the functional roles of these two signaling pathways in vivo we created a Non-classical Estrogen Receptor Knock-In (NERKI) mouse model by introducing the E207A/G208A mutation by targeted mutagenesis of embryonic stem cells. Unexpectedly, heterozygous NERKI females were infertile. The mice were anovulatory, and the ovaries exhibited disorganized thecal cells and lipid deposits in stromal cells. The uteri were enlarged with evidence of cystic endometrial hyperplasia. The mammary glands were underdeveloped, with decreased branching and lobuloalveolar development. Serum levels of progesterone were reduced, but levels of gonadotropins and estrogen were normal, suggesting a primary ovarian defect. Some aspects of the NERKI phenotype such as underdevelopment of mammary glands and lack of ovulation resemble the phenotype of ERalpha knock-out mice and likely reflect the dominant-negative activity of the ERE-binding-deficient ER mutant. However, the uterine features indicate excessive estrogen action, suggesting an important physiological role for the non-classical ER pathway in this tissue. Both in vitro and in vivo studies demonstrated that the ERE-binding-independent ER signaling is a part of normal actions of estrogens.