Estrogen receptor transcription and transactivation: Structure-function relationship in DNA- and ligand-binding domains of estrogen receptors

Estrogen receptors are members of the nuclear receptor steroid family that exhibit specific structural features, ligand-binding domain sequence identity and dimeric interactions, that single them out. The crystal structures of their DNA-binding domains give some insight into how nuclear receptors discriminate between DNA response elements. The various ligand-binding domain crystal structures of the two known estrogen receptor isotypes (α and β) allow one to interpret ligand specificity and reveal the interactions responsible for stabilizing the activation helix H12 in the agonist and antagonist positions

Raloxifene: Mechanism of Action, Effects on Bone Tissue, and Applicability in Clinical Traumatology Practice

Raloxifene, a member of the class of selective estrogen receptor modulators (SERM), reproduces the beneficial effects of estrogens on the skeletal systems, without the negative effects estrogens on breast and endometrium

Estrogen receptor transcription and transactivation: Estrogen receptor alpha and estrogen receptor beta - regulation by selective estrogen receptor modulators and importance in breast cancer

Estrogens display intriguing tissue-selective action that is of great biomedical importance in the development of optimal therapeutics for the prevention and treatment of breast cancer, for menopausal hormone replacement, and for fertility regulation. Certain compounds that act through the estrogen receptor (ER), now referred to as selective estrogen receptor modulators (SERMs), can demonstrate remarkable differences in activity in the various estrogen target tissues, functioning as agonists in some tissues but as antagonists in others. Recent advances elucidating the tripartite nature of the biochemical and molecular actions of estrogens provide a good basis for understanding these tissue-selective actions. As discussed in this thematic review, the development of optimal SERMs should now be viewed in the context of two estrogen receptor subtypes, ERα and ERβ, that have differing affinities and responsiveness to various SERMs, and differing tissue distribution and effectiveness at various gene regulatory sites. Cellular, biochemical, and structural approaches have also shown that the nature of the ligand affects the conformation assumed by the ER-ligand complex, thereby regulating its state of phosphorylation and the recruitment of different coregulator proteins. Growth factors and protein kinases that control the phosphorylation state of the complex also regulate the bioactivity of the ER. These interactions and changes determine the magnitude of the transcriptional response and the potency of different SERMs. As these critical components are becoming increasingly well defined, they provide a sound basis for the development of novel SERMs with optimal profiles of tissue selectivity as medical therapeutic agents

Molecular basis of agonism and antagonism in the oestrogen receptor.

Oestrogens are involved in the growth, development and homeostasis of a number of tissues. The physiological effects of these steroids are mediated by a ligand-inducible nuclear transcription factor, the oestrogen receptor (ER). Hormone binding to the ligand-binding domain (LBD) of the ER initiates a series of molecular events culminating in the activation or repression of target genes. Transcriptional regulation arises from the direct interaction of the ER with components of the cellular transcription machinery. Here we report the crystal structures of the LBD of ER in complex with the endogenous oestrogen, 17beta-oestradiol, and the selective antagonist raloxifene, at resolutions of 3.1 and 2.6 A, respectively. The structures provide a molecular basis for the distinctive pharmacophore of the ER and its catholic binding properties. Agonist and antagonist bind at the same site within the core of the LBD but demonstrate different binding modes. In addition, each class of ligand induces a distinct conformation in the transactivation domain of the LBD, providing structural evidence of the mechanism of antagonism

Effects of raloxifene on sex steroid hormones and C-telopeptide in postmenopausal women with primary breast cancer

Within a multicentric, double-blind, placebo-controlled phase II trial, postmenopausal women with primary breast cancer were randomized to either 60 or 600 mg daily of raloxifene or placebo administered for 2 weeks prior to surgery. Circulating levels of sex-hormone binding globulin (SHBG), dehydroepiandrosterone-sulfate (DHEA-S), estrone (E1), estrone-sulfate (E1-S), estradiol (E2), and C-terminal telopeptide (CTX), were determined at baseline and the day before surgery in 37 women enrolled at the European Institute of Oncology in Milan. Raloxifene had a statistically significant different effect compared with placebo on SHBG (p<0.001) and E2 (p=0.03), without any dose-response relationship. Women on raloxifene (n=26) showed an increase from baseline of 10.7% (inter-quartile range: 5.9; 24.2) in SHBG and of 1.3% (inter-quartile range: -8.0; 24.5) in E2, whereas women on placebo (n=11) showed a decrease by 15.5% (inter-quartile range: 7.9; 18.1) and 17.3% (inter-quartile range: 6.5; 40.0), respectively. No significant differences were found on the other variables. A positive correlation was observed between DHEA-S and E1-S (p=0.001) or E2 (p<0.001), while SHBG correlated negatively with E1-S (p=0.024) and E2 (p=0.01), and positively with DHEA-S (p=0.016) and CTX (p=0.040). Our results provide evidence for an early endocrine effect of raloxifene which further suggests a favorable impact on breast cancer prevention. © Springer 2006