Estrogen Receptor Regulation of the Na+/H+ Exchanger Regulatory Factor

Abstract

To better understand the actions of estrogens and antiestrogens in estrogen target cells, we have searched for estrogen-regulated genes in human breast cancer cells, in which the number of genes known to be directly activated by estrogen is quite small. Using differential display RNA methods, we have identified the human homolog of the Na+ -H+ exchanger regulatory factor (NHE-RF), an approximately 50-kDa protein that is also an ezrin-radixin-moesin-binding phosphoprotein, as being under rapid and direct regulation by estrogen in estrogen receptor (ER)-containing breast cancer cells. Stimulation by estrogen of NHE-RF RNA is rapid, being near maximal (approximately 6-fold) by 1 h, and is not blocked by cycloheximide, indicating that it is a primary response. Stimulation is selective for estrogen ligands, with no stimulation by other classes of steroid hormones, and stimulation by estrogen is suppressed by the antiestrogens tamoxifen and ICI 182,780. Induction is shown to require an active ER through several approaches, including the use of ER-negative breast cancer cells containing a stably integrated ER. NHE-RF protein levels, monitored using antibodies specific for this protein, increase after estrogen and reach maximal levels at 24-48 h. Interestingly, NHE-RF is a PDZ domain-containing protein that is enriched in polarized epithelia, where it is known to be localized in microvilli. Among various human tissues we have examined, we found that NHE-RF is expressed at a fairly high level in mammary tissue. NHE-RF regulates protein kinase A inhibition of the Na+ -H+ exchanger and may serve as a scaffold adaptor protein that contributes to the specificity of signal transduction events. Our findings suggest that the early, known effects of estrogen on cell cytoarchitecture (e.g. increasing microvilli on breast cancer cells) and on some cell signaling pathways (e.g. those involving cAMP) may involve rapid estrogen-mediated changes in the production of NHE-RF.

Ezrin-Radixin-Moesin-Binding Phosphoprotein (EBP50), an Estrogen-Inducible Scaffold Protein, Contributes to Biliary Epithelial Cell Proliferation

“…The EBP50 gene possesses 13 half-estrogen responsive elements and is overexpressed in response to estrogens in proliferative mammary and endometrial cells. 4,7,9,10,43 Notably, 17␤-estradiol was recently shown to increase the amount of EBP50 in the nuclear fraction of human airway epithelial cells. 44 In addition, cholangiocyte proliferation is regulated by cyclic AMP, 45 which has also been shown to induce an intracellular redistribution of EBP50 in renal epithelial cells.…”

“…The liver is the tissue that displays the highest level of EBP50 expression. 3,4 We previously showed that in rat liver, EBP50 is expressed both in hepatocytes and in cholangiocytes, and that, in the latter, the interaction of cystic fibrosis transmembrane conductance regulator (CFTR) with the PDZ1 domain of EBP50 is required for cAMP-dependent chloride secretion, 5 suggesting an important role of EBP50 in bile secretory functions.…”

“…Whereas in vitro experiments have suggested anti-proliferative functions of EBP50, 14 -16 a positive correlation between EBP50 expression, estrogen receptor status, and tumor progression has been found in human breast cancer. 9,10 Of particular interest with respect to biliary pathophysiology, the major regulators of EBP50 expression are estrogens, 4,17 which are known to target the biliary tree, where they modulate the proliferative activities of cholangiocytes. 18 -20 In the present study, we examined the expression of EBP50 and binding partners in the human liver, under normal conditions and in the setting of biliary disorders, ie, in different types of human cholangiopathies and after bile duct ligation (BDL) in rats.…”

Ezrin-radixin-moesin–binding phosphoprotein 50 is expressed at the apical membrane of rat liver epithelia

“…13,22 Previous studies indicate EBP50 messenger RNA (mRNA) and protein levels are high in whole liver, but the cellular expression and distribution of EBP50 and related proteins is unknown. 17,23 Given the known protein-protein interactions of EBP50 and E3KARP, the demonstrated capacity of EBP50 and E3KARP to modulate cAMP-dependent transport in other epithelia and the known stimulatory effect of cAMP on bile formation, the present studies sought to (1) identify the cell type-specific expression and intracellular localization of EBP50 in liver epithelia, (2) compare and contrast these expression patterns with E3KARP, (3) determine the codistribution of ERM proteins with EBP50 and E3KARP, and (4) assess the potential contribution of EBP50 to the cAMP-mediated secretory responses of liver epithelia. The findings indicate that EBP50 is critically localized to play a key role in the organization and regulation of apical transport in bile secretory epithelia and is required for the cAMP-dependent Cl Ϫ secretory response in a cultured cholangiocyte cell model.…”

Regulation of Expression and Localisation of the Na+/H+ Exchanger (NHE) 3 and the NHE Regulatory Factor 2 in Baboon Placental Syncytiotrophoblast by Oestrogen

“…Estrogen has been shown to enhance NHERF1 expression in MCF-7 cells [10], whereas cortisol increased NHE3 expression in the adult rat kidney [11] and transcriptional activation of the rat NHE3 gene [12]. Moreover, we previously demonstrated that estrogen regulated the developmental increase in placental syncytiotrophoblast levels and change in the localization of the 11β-hydroxysteroid dehydrogenase-1/-2 (11β-HSD-1/2) enzymes [13,14] controlling glucocorticoid metabolism, biochemical and structural events that we proposed underpinned the increase in placental conversion of cortisol to cortisone that occurs between mid and late gestation [15,16].…”