Evaluation of potential implication of membrane estrogen binding sites on ERE-dependent transcriptional activity and intracellular estrogen receptor-alpha regulation in MCF-7 breast cancer cells

Dynamic regulation of BDNF gene expression by estradiol and lncRNA HOTAIR

Brain derived neurotrophic factor (BDNF) is a major neurotransmitter that controls growth and maintenance of neurons and its misregulation is linked to neurodegeneration and human diseases. Estradiol (E2) is well-known to regulate the process of differentiation and plasticity of hippocampal neurons. Here we examined the mechanisms of BDNF gene regulation under basal conditions and under stimuli such as E2. Our results demonstrated that BDNF expression is induced by E2 in vitro in HT22 cells (hippocampal neuronal cells) and in vivo (in ovariectomized mouse brain under E2-treatment). Using chromatin immunoprecipitation assay, we demonstrated that estrogen receptors (ERα, ERβ) were enriched at the BDNF promoter in presence of E2. Additionally, ER-coregulators (e.g., CBP/p300, MLL3), histone acetylation, H3K4-trimethylation, and RNA polymerase II levels were also elevated at the BDNF promoter in an E2-dependent manner. Additionally, under the basal conditions (in the absence of E2), the long noncoding RNA HOTAIR and its interacting partners PRC2 and LSD1 complexes binds to the promoter of BDNF and represses its expression. HOTAIR knockdown -relieves the repression resulting in elevation of BDNF expression. Further, levels of HOTAIR-interacting partners, EZH2 and LSD1 were reduced at the BDNF promoter upon HOTAIR-knockdown revealing that HOTAIR plays a regulatory role in BDNF gene expression by modulating promoter histone modifications. Additionally, we showed that E2 induced-BDNF expression is mediated by the displacement of silencing factors, EZH2 and LSD1 at BDNF promoter and subsequent recruitment of active transcription machinery. These results reveal the mechanisms of BDNF gene regulation under the basal condition and in presence of a positive regulator such as E2 in neuronal cells.

Pathological Maintenance and Evolution of Breast Cancer: The Convergence of Irreversible Biological Actions of ER Alpha

Estrogen receptor alpha (ERα) is a modulator of breast cancer maintenance and evolution. Hence, analysis of underlying mechanisms by which ERα operates is of importance for the improvement of the hormonal therapy of the disease. This review focuses on the irreversible character of the mechanism of action of ERα, which also concerns other members of the steroid hormones receptors family. ERα moves in permanence between targets localized especially at the chromatin level to accomplish gene transcriptions imposed by the estrogenic ligands and specific antagonists. Receptor association as at the plasma membrane, where it interacts with other recruitment sites, extends its regulatory potency to growth factors and related peptides through activation of signal transductions pathways. If the latter procedure is suitable for the transcriptions in which the receptor operates as a coregulator of another transcription factor, it is of marginal influence with regard to the direct estrogenic regulation procedure, especially in the context of the present review. Irreversibility of the successive steps of the underlying transcription cycle guarantees maintenance of homeostasis and evolution according to vital necessities. To justify this statement, reported data are essentially described in a holistic view rather than in the context of exhaustive analysis of a molecular event contributing to a specific function as well as in a complementary perspective to elaborate new therapeutic approaches with antagonistic potencies against those tumors promoting ERα properties.

Palmitoylation regulates 17β-estradiol-induced estrogen receptor-α degradation and transcriptional activity

The estrogen receptor-α (ERα) is a transcription factor that regulates gene expression through the binding to its cognate hormone 17β-estradiol (E2). ERα transcriptional activity is regulated by E2-evoked 26S proteasome-mediated ERα degradation and ERα serine (S) residue 118 phosphorylation. Furthermore, ERα mediates fast cell responses to E2 through the activation of signaling cascades such as the MAPK/ERK and phosphoinositide-3-kinase/v-akt murine thymoma viral oncogene homolog 1 pathways. These E2 rapid effects require a population of the ERα located at the cell plasma membrane through palmitoylation, a dynamic enzymatic modification mediated by palmitoyl-acyl-transferases. However, whether membrane-initiated and transcriptional ERα activities integrate in a unique picture or represent parallel pathways still remains to be firmly clarified. Hence, we evaluated here the impact of ERα palmitoylation on E2-induced ERα degradation and S118 phosphorylation. The lack of palmitoylation renders ERα more susceptible to E2-dependent degradation, blocks ERα S118 phosphorylation and prevents E2-induced ERα estrogen-responsive element-containing promoter occupancy. Consequently, ERα transcriptional activity is prevented and the receptor addressed to the nuclear matrix subnuclear compartment. These data uncover a circuitry in which receptor palmitoylation links E2-dependent ERα degradation, S118 phosphorylation, and transcriptional activity in a unique molecular mechanism. We propose that rapid E2-dependent signaling could be considered as a prerequisite for ERα transcriptional activity and suggest an integrated model of ERα intracellular signaling where E2-dependent early extranuclear effects control late receptor-dependent nuclear actions.

Capacity of type I and II ligands to confer to estrogen receptor alpha an appropriate conformation for the recruitment of coactivators containing a LxxLL motif-Relationship with the regulation of receptor level and ERE-dependent transcription in MCF-7 cells

Estrogen receptor alpha (ERalpha) belongs to the superfamily of nuclear receptors and as such acts as a ligand-modulated transcription factor. Ligands elicit in ERalpha conformational changes leading to the recruitment of coactivators required for the transactivation of target genes via cognate response elements. In many cells, activated ERalpha also undergoes downregulation by proteolysis mediated by the ubiquitin/proteasome system. Although these various molecular processes have been well characterized, little is known as to which extent they are interrelated. In the present study, we used a panel of type I (estradiol derivatives and "linear", non-steroidal ligands) and type II ("angular" ligands) estrogens, in order to identify possible relationships between ligand binding affinity, recruitment of LxxLL-containing coactivators, ERalpha downregulation in MCF-7 cells and related transactivation activity of ligand-bound ERalpha. For type I estrogens, there was a clear-cut relationship between ligand binding affinity, hydrophobicity around C-11 of estradiol and ability of ERalpha to associate with LxxLL motifs, both in cell-free condition and in vivo (MCF-7 cells). Moreover, LxxLL motif recruitment by ERalpha seemed to be a prerequisite for the downregulation of the receptor. By contrast, type II ligands, as well as estradiol derivatives bearing a bulky side chain at 11beta, had much less tendency to promote ERalpha-LxxLL interaction or even behaved as antagonists in this respect, in agreement with the well known partial estrogenicity/antiestrogenicity of some of these compounds. Interestingly, some type II ligands which antagonized LxxLL motif recruitment were nonetheless able to enhance ERalpha-mediated gene transactivation.

Membrane ERalpha-dependent activation of PKCalpha in endometrial cancer cells by estradiol

The purpose of this study was to investigate the role of the oestrogen receptor subtypes ERalpha and ERbeta in mediating the non-genomic effects of 17-beta-estradiol (E(2)) in two human endometrial cancer cell lines (RL95-2 and HEC-1A) expressing different levels of these receptor subtypes. Western blotting analysis using phosphorylation site-specific antibodies showed that physiological concentrations of E(2) rapidly (<20 min) activated PKCalpha, but not PKCdelta in the RL95-2 cell line. E(2) had no effect on PKCalpha or PKCdelta activity in the HEC-1A cell line and suppressed basal levels of PKA activity in both cell lines. PKCalpha activation coincided with its membrane translocation. ERalpha was detected in the RL95-2 cell line by Western blotting and RT-PCR but not in the HEC-1A cells, which did express ERbeta. A selective ERalpha agonist PPT had the same effect as E(2) on PKCalpha activation in the RL95-2 cells, but the selective ERbeta agonist DPN had no such effect. A 46kDa variant of ERalpha increased in abundance in the cell membrane within 20 min of E(2) treatment suggesting that ERalpha mediated the E(2) non-genomic effects on PKCalpha through the formation of a membrane associated signalling complex.

The Forkhead box M1 protein regulates the transcription of the estrogen receptor alpha in breast cancer cells

In this study, we have identified the Forkhead transcription factor FoxM1 as a physiological regulator of estrogen receptor alpha (ERalpha) expression in breast carcinoma cells. Our survey of a panel of 16 different breast cell lines showed a good correlation (13/16) between FoxM1 expression and expression of ERalpha at both protein and mRNA levels. We have also demonstrated that ectopic expression of FoxM1 in two different estrogen receptor-positive breast cancer cell lines, MCF-7 and ZR-75-30, led to up-regulation of ERalpha expression at protein and transcript levels. Furthermore, treatment of MCF-7 cells with the MEK inhibitor U0126, which blocks ERK1/2-dependent activation of FoxM1, also repressed ERalpha expression. Consistent with this, silencing of FoxM1 expression in MCF-7 cells using small interfering RNA resulted in the almost complete abrogation of ERalpha expression. We also went on to show that FoxM1 can activate the transcriptional activity of human ERalpha promoter primarily through two closely located Forkhead response elements located at the proximal region of the ERalpha promoter. Chromatin immunoprecipitation and biotinylated oligonucleotide pulldown assays have allowed us to confirm these Forkhead response elements as important for FoxM1 binding. Further co-immunoprecipitation experiments showed that FoxO3a and FoxM1 interact in vivo. Together with the chromatin immunoprecipitation and biotinylated oligonucleotide pulldown data, the co-immunoprecipitation results also suggest the possibility that FoxM1 and FoxO3a cooperate to regulate ERalpha gene transcription.

Naloxone acts as an antagonist of estrogen receptor activity in MCF-7 cells

Estrogen promotes the growth of breast cancer via estrogen receptors (ER). Earlier studies showed that the opioid receptor antagonist naloxone inhibits MCF-7 breast cancer growth in mice. We examined the cellular and molecular mechanism of naloxone antagonism of ERalpha activity in human MCF-7 cells. Naloxone (100 nmol/L) inhibited 17beta-estradiol (E2)-induced (10 nmol/L) MCF-7 cell proliferation by 65% and mitogen-activated protein kinase/extracellular signal-regulated kinase phosphorylation. Naloxone blocked the E2-induced activation of ERalpha, with 85% inhibition after 5 minutes and 100% recovery after 60 minutes. This assay is based on quantitation of E2-activated nuclear ERalpha binding to the immobilized coactivator peptide. A significant decrease in E2-induced ERalpha transactivation was observed in the presence of naloxone in the estrogen response element-luciferase reporter assay (P < 0.05, E2 versus E2 + naloxone). Naloxone also blocked E2-induced down-regulation of ERalpha mRNA at 30 minutes and 6 hours. Although naloxone inhibits ERalpha activity directly, it also induces a cross-talk between mu-opioid receptor (MOR) and ERalpha. Immunoprecipitates with anti-MOR antibody showed the presence of ERalpha in cells incubated with E2 in the presence of naloxone but not in cells incubated with E2 or naloxone alone. Higher amounts of ERalpha associated with MOR after 60 minutes compared with 10 minutes of incubation. Naloxone inhibited E2-bovine serum albumin-FITC binding to plasma membrane-associated ERalpha and also inhibited the direct binding of [3H]E2 to ERalpha. Thus, naloxone modulates ERalpha activity directly as well as indirectly via MOR. This study suggests that naloxone-like compounds can be developed as novel therapeutic molecules for breast cancer therapy.

Growth factors change nuclear distribution of estrogen receptor-alpha via mitogen-activated protein kinase or phosphatidylinositol 3-kinase cascade in a human breast cancer cell line

In the present study, to examine the dynamic changes in the localization of nuclear estrogen receptor (ER)alpha induced by growth factors, we used time-lapse confocal microscopy to directly visualized ERalpha fused with green fluorescent protein (GFP-ERalpha) in single living cells treated with epidermal growth factor (EGF) or IGF-I. We observed that 17beta-estradiol (E2) changed the normally diffuse distribution of GFP-ERalpha throughout the nucleoplasm to a hyperspeckled distribution within 10 min. Both EGF and IGF-I also changed the nuclear distribution of GFP-ERalpha, similarly to E2 treatment. However, the time courses of the nuclear redistribution of GFP-ERalpha induced by EGF or IGF-I were different from that induced by E2 treatment. In the EGF-treated cells, the GFP-ERalpha nuclear redistribution was observed at 30 min and reached a maximum at 60 min, whereas in the IGF-I-treated cells, the GFP-ERalpha nuclear redistribution was observed at 60 min and reached a maximum at 90 min. The EGF-induced redistribution of GFP-ERalpha was blocked by pretreatment with a MAPK cascade inhibitor, PD98059, whereas the IGF-I-induced redistribution of GFP-ERalpha was blocked by pretreatment with a phosphatidylinositol 3-kinase inhibitor, LY294002. Analysis using an activation function-2 domain deletion mutant of GFP-ERalpha showed that the change in the distribution of GFP-ERalpha was not induced by E2, EGF, or IGF-I treatment. These data suggest that MAPK and phosphatidylinositol 3-kinase cascades are involved in the nuclear redistribution of ERalpha by EGF and IGF-I, respectively, and that the activation function-2 domain of ERalpha may be needed for the nuclear redistribution of ERalpha.

Potentiation of genomic actions of estrogen by membrane actions in mcf-7 cells and the involvement of protein kinase C activation

It is now well established that estrogens (E) have at least two kinds of actions: genomic and nongenomic. But the relationship between these actions has hardly been explored. In this study we investigated this relationship in MCF-7 cells, a human breast cancer cell line, and explored the possible involvement of protein kinase C (PKC) signaling pathways. For this purpose a two-pulse paradigm was used: cells were treated with 17beta-estradiol (E), E conjugated with bovine serum albumin (E-BSA or fE'), or other test agents in the first pulse and with E in the second pulse following a 4-h interval. An E-BSA+E paradigm was used to show that replacement of E with the membrane-impermeable E-BSA in the first pulse could potentiate genomic actions of E, in the second pulse. To investigate involvement of signaling pathways, two PKC activators, phorbol 12,13-diacetate (PDAc) or phorbol 12-myristate 13-acetate (PMA), and inhibitors (chelerythrine chloride and H7-dihydrochloride) were used to replace E or E-BSA in the first pulse. PDAc was as effective as E or E-BSA in potentiating the genomic action of E in the second pulse, while PMA was almost without an effect. Conversely, the potentiating effects of E-BSA and PDAc were blocked by chelerythrine chloride but, interestingly, not by H7. The exact reason underlying these differences is not known. In summary, in MCF-7 cells a membrane action of E can potentiate a later genomic action and involves PKC signaling.

Characterization of estrogen-responsive epithelial cell lines and their infectivity by genital Chlamydia trachomatis

Chlamydial attachment and infectivity in vitro and ascending disease and sequelae in vivo have been reported to be enhanced/modulated by estrogen. Endometrial carcinoma cell lines Ishikawa and HEC-1B and the breast cancer lines MCF-7 and HCC-1806 were examined for Chlamydia trachomatis E infectivity. Estrogen receptor (ER) presence was confirmed by Western blot and qRT-PCR analyses. FACS analysis was used to determine the percent of plasma membrane-localized ERs (mERs), and their activity was tested by estrogen binding and competitive estrogen antagonists assays. Chlamydiae grew in all cell lines with HEC (90%) >> MCF-7 (57%)>Ishikawa (51%) >> HCC-1806 (20%). The cell line ER isoform composition was re-defined as: ERalpha + ERbeta + for MCF-7, HCC-1806 and Ishikawa; and ERbeta only for HEC-1B. HeLa cells were also tested and found to express ERbeta, but not ERalpha. A small percentage of both ERs were surface-exposed and functionally active. The endometrium-predominant ERbeta isoform was found in all cell lines, including those most representative of the common sites of C. trachomatis infection. Thus, the role of chlamydial attachment/infectivity will now be analyzed in ERbeta+and-isogenic HEC-1B cells.

Opposing effects of estradiol- and testosterone-membrane binding sites on T47D breast cancer cell apoptosis

Classical steroid mode of action involves binding to intracellular receptors, the later acting as ligand-activated nuclear transcription factors. Recently, membrane sites for different steroids have been also identified, mediating rapid, non-genomic, steroid actions. Membrane sites for estrogen and androgen have been found in a number of different cell types, bearing or not classical intracellular receptors. In the present study, with the use of radioligand binding, flow cytometry and confocal laser microscopy, we report that T47D human breast cancer cells express specific and saturable membrane receptors for both estrogen (K(D) 4.06 +/- 3.31 nM) and androgen (K(D) 7.64 +/- 3.15 nM). Upon activation with BSA-conjugated, non-permeable ligands (E(2)-BSA and testosterone-BSA), membrane estrogen receptors protect cells from serum-deprivation-induced apoptosis, while androgen receptors induce apoptosis in serum-supplemented T47D cells. In addition, co-incubation of cells with a fixed concentration of one steroid and varying concentrations of the other reversed the abovementioned effect (apoptosis for androgen, and anti-apoptosis for E(2)), suggesting that the fate of the cell depends on the relative concentration of either steroid in the culture medium. We also report the identification of membrane receptors for E(2) and androgen in biopsy slides from breast cancer patients. Both sites are expressed, with the staining for membrane E(2) being strongly present in ER-negative, less differentiated, more aggressive tumors. These findings suggest that aromatase inhibitors may exert their beneficial effects on breast cancer by also propagating the metabolism of local steroids towards androgen, inducing thus cell apoptosis through membrane androgen receptor activation.

Binding of estrogen receptor with estrogen conjugated to bovine serum albumin (BSA)

BACKGROUND: The classic model of estrogen action requires that the estrogen receptor (ER) activates gene expression by binding directly or indirectly to DNA. Recent studies, however, strongly suggest that ER can act through nongenomic signal transduction pathways and may be mediated by a membrane bound form of the ER. Estradiol covalently linked to membrane impermeable BSA (E2-BSA) has been widely used as an agent to study these novel membrane-associated ER events. However, a recent report suggests that E2-BSA does not compete for E2 binding to purified ER in vitro. To resolve this apparent discrepancy, we performed competition studies examining the binding of E2 and E2-BSA to both purified ER preparations and ER within intact cells. To eliminate potential artifacts due to contamination of commercially available E2-BSA preparations with unconjugated E2 (usually between 3-5%), the latter was carefully removed by ultrafiltration. RESULTS: As previously reported, a 10-to 1000-fold molar excess of E2-BSA was unable to compete with 3H-E2 binding to ER when added simultaneously. However, when ER was pre-incubated with the same concentrations of E2-BSA, the binding of 3H-E2 was significantly reduced. E2-BSA binding to a putative membrane-associated ER was directly visualized using fluorescein labeled E2-BSA (E2-BSA-FITC). Staining was restricted to the cell membrane when E2-BSA-FITC was incubated with stable transfectants of the murine ERalpha within ER-negative HeLa cells and with MC7 cells that endogenously produce ERalpha. This staining appeared highly specific since it was competed by pre-incubation with E2 in a dose dependent manner and with the competitor ICI-182,780. CONCLUSIONS: These results demonstrate that E2-BSA does bind to purified ER in vitro and to ER in intact cells. It seems likely that the size and structure of E2-BSA requires more energy for it to bind to the ER and consequently binds more slowly than E2. More importantly, these findings demonstrate that in intact cells that express ER, E2-BSA binding is localized to the cell membrane, strongly suggesting a membrane bound form of the ER.

Biphasic estradiol-induced AKT phosphorylation is modulated by PTEN via MAP kinase in HepG2 cells

We reported previously in HepG2 cells that estradiol induces cell cycle progression throughout the G1-S transition by the parallel stimulation of both PKC-alpha and ERK signaling molecules. The analysis of the cyclin D1 gene expression showed that only the MAP kinase pathway was involved. Here, the presence of rapid/nongenomic, estradiol-regulated, PI3K/AKT signal transduction pathway, its modulation by the levels of the tumor suppressor PTEN, its cross-talk with the ERK pathway, and its involvement in DNA synthesis and cyclin D1 gene promoter activity have all been studied in HepG2 cells. 17beta-Estradiol induced the rapid and biphasic phosphorylation of AKT. These phosphorylations were independent of each other, being the first wave of activation independent of the estrogen receptor (ER), whereas the second was dependent on ER. Both activations were dependent on PI3K activity; furthermore, the ERK pathway modulated AKT phosphorylation by acting on the PTEN levels. The results showed that the PI3K pathway, as well as ER, were strongly involved in both G1-S progression and cyclin D1 promoter activity by acting on its proximal region (-254 base pairs). These data indicate that in HepG2 cells, different rapid/nongenomic estradiol-induced signal transduction pathways modulate the multiple steps of G1-S phase transition.

The biological actions of estrogens on skin

There is still extensive disparity in our understanding of how estrogens exert their actions, particularly in non-reproductive tissues such as the skin. Although it has been recognized for some time that estrogens have significant effects on many aspects of skin physiology and pathophysiology, studies on estrogen action in skin have been limited. However, estrogens clearly have an important function in many components of human skin including the epidermis, dermis, vasculature, hair follicle and the sebaceous, eccrine and apocrine glands, having significant roles in skin aging, pigmentation, hair growth, sebum production and skin cancer. The recent discovery of a second intracellular estrogen receptor (ERbeta) with different cell-specific roles to the classic estrogen receptor (ERalpha), and the identification of cell surface estrogen receptors, has provided further challenges to understanding the mechanism of estrogen action. It is now time to readdress many of the outstanding questions regarding the role of estrogens in skin and improve our understanding of the physiology and interaction of steroid hormones and their receptors in human skin. Not only will this lead to a better understanding of estrogen action, but may also provide a basis for further interventions in pathological processes that involve dysregulation of estrogen action.