Integration of the non-genomic and genomic actions of estrogen. Membrane-initiated signaling by steroid to transcription and cell biology

Role of progesterone on the regulation of vascular muscle cells proliferation, migration and apoptosis

The purpose of this study was to investigate the effect of progesterone (Pg) on cellular growth, migration, apoptosis, and the molecular mechanism of action displayed by the steroid. To that end, rat aortic vascular smooth muscle cell (VSMC) cultures were employed. Pg (10nM) significantly increased [(3)H]thymidine incorporation after 24h of treatment. The enhancement in DNA synthesis was blunted in the presence of an antagonist of Pg receptor (RU486 compound). The mitogenic action of the steroid was suppressed by the presence of the compounds PD98059 (MEK inhibitor), chelerythrine (PKC inhibitor), and indomethacin (cyclooxygenase antagonist) suggesting that the stimulation of DNA synthesis involves MAPK, PKC, and cyclooxygenase transduction pathways. The proliferative effect of the hormone depends on the presence of endothelial cells (EC). When muscle cells were incubated with conditioned media obtained of EC treated with Pg, the mitogenic action of the steroid declined. Wounding assays shows that 10nM Pg enhances VSMC migration and motility. The role of the steroid on programmed cell death was measured using DNA fragmentation technique. Four hours of treatment with 10nM Pg enhanced DNA laddering in a similarly extent to the apoptotic effect induced by the apoptogen hydrogen peroxide (H(2)O(2)). In summary the results presented provide evidence that Pg enhances cell proliferation, migration, and apoptosis of VSMC. The modulation of cell growth elicited by the steroid involves integration between genomic and signal transduction pathways activation.

Relevance of serum estradiol and estrogen receptor beta expression from a high-incidence area for esophageal squamous cell carcinoma in China

The striking 3-4:1 male predominance of esophageal squamous cell carcinoma (ESCC) has not yet been well explained. Our hypothesis is that the changes in level of estrogen and/or subtype of estrogen receptor (ER) may exert a protective factor in esophageal carcinogenesis and prognosis of ESCC. Radioimmunoassay (RIA) was used to determine the serum level of estradiol in healthy cohort from high-incidence area (HIA) and low-incidence area (LIA) for esophageal cancer as well as patients with ESCC from HIA in Henan, northern China. The ERβ expression profiling during the multi-stage progression of ESCC pathogenesis was evaluated by immunohistochemistry (IHC). Both males and females from HIA had significant decreases of serum estradiol in high-risk subjects predisposing for ESCC compared to healthy counterparts from LIA (P < 0.01). Furthermore, patients with ESCC from HIA developed the lowest level of estradiol (P < 0.01). ERβ expressed in precursor lesions of ESCC and changed quantitatively and qualitatively with disease progression during the multi-stages process of esophageal carcinogenesis. High frequency of ERβ expression was correlated with less aggressive potential of clinical behavior (P = 0.012, 0.015 for lymph node metastasis and tumor stage, respectively). This study indicates that lower serum level of estradiol may represent higher predisposition for development of ESCC, and ERβ expression and/or nuclear location may predict better outcome for patients with ESCC. The present results provide clues to explain the striking gender difference for ESCC, which warrants further investigations on potential applications of estrogen or analogs in prevention of ESCC.

Differential regulation of Akt phosphorylation in endometriosis

Protein kinase B (PKB/Akt), a serine/threonine kinase, regulates the function of many cellular proteins involved in apoptosis and proliferation. It was postulated that there is a higher Akt activity in endometriosis compared with normal endometrium, and that oestrogen may be one of the factors responsible for the high Akt activation in endometriotic cells. Phospho-Akt (pAkt) concentrations in normal, eutopic and ectopic endometrial tissues were compared by immunohistochemistry, and a higher pAkt immunoreactivity was revealed in eutopic and ectopic endometrium compared with normal endometrium, in vivo. Higher Akt phosphorylation in stromal cells from eutopic endometrium was observed, when compared with normal, in vitro (P < 0.05). Akt phosphorylation was rapidly (2-10 min) stimulated when endometrial stromal cells from normal and endometriosis patients were treated with 17 beta-oestradiol. In endometrial stromal cells from the endometriosis group, ICI 182,780 (ICI, a specific oestrogen receptor antagonist) failed to antagonize the effect of oestradiol when combined with oestradiol, and revealed a stimulatory effect on Akt phosphorylation when given alone (P < 0.05). In conclusion, since Akt affects cell survival, it is suggested that increased Akt phosphorylation may be related to the altered apoptosis/proliferation harmony in endometriosis, and therefore Akt may play a critical role in the pathogenesis of endometriosis.

Oestrogen receptor-alpha activation augments post-exercise myoblast proliferation

AIM

Our laboratory has shown that oestrogen acts to augment myoblast (satellite cell) activation, proliferation and total number and that this may occur through an oestrogen receptor (OR)-mediated mechanism. The purpose of this study was to further investigate the mechanism of oestrogen influence on augmentation of post-exercise myoblast numbers through use of a specific OR-alpha agonist, propyl pyrazole triol (PPT).

METHODS

Ovariectomized rats were used (n = 64) and separated into four groups: sham, oestrogen supplemented, agonist supplemented, and a combined oestrogen and agonist supplemented group. These groups were further subdivided into control (unexercised) and exercise groups. Surgical removal of white vastus and soleus muscles was performed 72 h post-exercise. Muscle samples were immunostained for the myoblast markers Pax7 and MyoD.

RESULTS

A significant increase in total (Pax7-positive) and activated (MyoD-positive) myoblasts was found in all groups post-exercise. A further significant augmentation of total and activated myoblasts occurred in oestrogen supplemented, agonist supplemented and the combined oestrogen and agonist supplemented groups post-exercise in white vastus and soleus muscles relative to unsupplemented animals.

CONCLUSION

These results demonstrate that both oestrogen and the specific OR-alpha receptor agonist, PPT, can significantly and to similar degrees augment myoblast number and activation following exercise-induced muscle damage. This suggests that oestrogen acts through an OR-mediated mechanism to stimulate myoblast proliferation following exercise, with OR-alpha playing a primary role.

Membrane-initiated actions of estrogen on the endothelium

Estrogen-induced rapid, membrane-initiated activation of numerous signal transduction cascades has been shown in animal, cellular and molecular vascular studies, which support the favorable effects of estrogen on vascular structure and function. These effects are mediated by distinct forms of estrogen receptor (ER) alpha. This includes estrogen-stimulated, rapid activation of endothelial nitric oxide synthase (eNOS), resulting in elaboration of the athero-protective, angiogenesis-promoting product nitric oxide (NO). An N-terminus truncated short isoform of ERalpha, ER46, plays a critical role in membrane-initiated, rapid responses to 17beta-estradiol (E2) in human endothelial cells (ECs). We have proposed a ER46-centered, eNOS-activating molecular complex in human EC caveolar membranes, containing c-Src, phosphatidylinositol 3-kinase (PI3K), Akt and eNOS. In this review, we describe estrogen-induced, rapid, non-genomic actions in the endothelium.

Profile of estrogen-responsive genes in an estrogen-specific mammary gland outgrowth model

Both ovarian and pituitary hormones are required for the pubertal development of the mouse mammary gland. Estradiol directs ductal elongation and branching, while progesterone leads to tertiary branching and alveolar development. The purpose of this investigation was to identify estrogen-responsive genes associated with pubertal ductal growth in the mouse mammary gland in the absence of other ovarian hormones and at different stages of development. We hypothesized that the estrogen-induced genes and their associated functions at early stages of ductal elongation would be distinct from those induced after significant ductal elongation had occurred. Therefore, ovariectomized prepubertal mice were exposed to 17beta-estradiol from two to 28 days, and mammary gland global gene expression analyzed by microarray analysis at various times during this period. We found that: (a) gene expression changes in our estrogen-only model mimic those changes that occur in normal pubertal development in intact mice, (b) both distinct and overlapping gene profiles were observed at varying extents of ductal elongation, and (c) cell proliferation, the immune response, and metabolism/catabolism were the most common functional categories associated with mammary ductal growth. Particularly striking was the novel observation that genes active during carbohydrate metabolism were rapidly and robustly decreased in response to estradiol. Lastly, we identified mammary estradiol-responsive genes that are also co-expressed with estrogen receptor alpha in human breast cancer. In conclusion, our genomic data support the physiological observation that estradiol is one of the primary hormonal signals driving ductal elongation during pubertal mammary development.

Novel female sex-dependent actions of oestrogen in the intestine

The intestine is an oestrogen responsive organ and circulatory oestrogens suppress Cl(-) secretion across the epithelium of the colon to promote fluid retention at the luteal stage of the menstrual cycle. Ion transporters in the colon which are involved in Cl(-) secretion show differential expression between males and females as do the signalling protein kinase intermediates involved in acutely regulating these transporters. Work from our laboratory has identified the KCNQ1/KCNE3 channel as one of the principal targets for oestrogen-induced signalling cascades in the distal colon. Through inhibition of the KCNQ1 channel, basolateral K(+) recycling is decreased so reducing the favourable electrochemical gradient for Cl(-) extrusion at the apical membrane. The actions of oestrogen on non-reproductive tissues such as the colon, kidney, lung and sweat gland will affect whole body electrolyte and fluid homeostasis and also have consequences for reproductive potential.

Inhibition of cyclooxygenase-2 down-regulates aromatase activity and decreases proliferation of Leydig tumor cells

Our recent studies have revealed that estrogens stimulate an autocrine mechanism determining Leydig tumor cell proliferation. Estrogen overproduction is due to an elevated steroidogenic factor-1 (SF-1) expression and cAMP-response element-binding protein (CREB) phosphorylation, both inducing aromatase overexpression. Although we have shown that increased SF-1 expression depends mainly on higher local insulin-like growth factor I production, the mechanisms and factors determining increased CREB activation in Leydig tumor cells are not completely understood. In this study, we investigated the role of cyclooxygenase-2 (COX-2) in CREB dependent-aromatase expression in Leydig tumor cells. We found that COX-2 is expressed in rat and human Leydigiomas as well as in the rat Leydig tumor cell line R2C, but not in normal testis. Our data indicate that in R2C cells the COX-2-derived prostaglandin E2 (PGE2) binds the PGE2 receptor EP4 and activates protein kinase A (PKA) and ultimately CREB. Inhibitors for COX-2 (NS398), EP4 (AH23848), and PKA (H89) decreased aromatase expression and activity as a consequence of a decreased phosphorylated CREB recruitment to the PII promoter of the aromatase gene. The COX-2/PGE2/PKA pathway also seems to be involved in aromatase post-translational activation, an observation that requires further studies. The reduction in aromatase activity was responsible for a drop in estrogen production and subsequent reduction in cyclin E expression resulting in a decrease in tumor Leydig cell proliferation. Furthermore, COX-2 silencing caused a significant decrease in CREB phosphorylation, aromatase expression, and R2C cell proliferation. These novel findings clarify the mechanisms involved in the growth of Leydig cell tumors and should be taken into account in determining new therapeutic approaches.

Ovariectomy increases the formation of prostanoids and modulates their role in acetylcholine-induced relaxation and nitric oxide release in the rat aorta

AIMS

This study examines the effect of ovarian function on thromboxane A(2) (TXA(2)), prostaglandin (PG) I(2), PGF(2alpha), and PGE(2) release as well as the role of these substances in nitric oxide (NO) release and acetylcholine (ACh)-mediated relaxation.

METHODS AND RESULTS

Aortic segments from ovariectomized and control female Sprague-Dawley rats were used. Cyclooxygenase (COX-1 and COX-2) expression was studied. ACh-induced relaxation was analysed in the absence and presence of the COX-2 inhibitor NS-398, the TXA(2) synthesis inhibitor furegrelate, the PGI(2) synthesis inhibitor tranylcypromine (TCP), or the thromboxane-prostanoid receptor antagonist SQ-29548. TXA(2), PGI(2), PGF(2alpha), and PGE(2) release was measured, and the vasomotor effect of exogenous TXA(2), PGI(2,) PGF(2alpha), and PGE(2) was assessed. Basal and ACh-induced NO release in the absence and presence of NS-398, furegrelate, TCP, or TCP plus furegrelate was studied. Ovariectomy did not alter or increased COX-1 or COX-2 expression, respectively. NS-398 decreased, and furegrelate did not change, the ACh-induced relaxation in arteries from both groups. SQ29,548 decreased the ACh-induced relaxation only in aortas from ovariectomized rats. TCP decreased the ACh-induced relaxation in both groups, and furegrelate or SQ29,548 totally restored that response only in aortas from control rats. Ovariectomy increased the ACh-induced TXA(2), PGI(2), and PGE(2) release and the contractile responses induced by exogenous TXA(2), PGF(2alpha), or PGE(2), while it decreased the PGI(2)-induced vasodilator response. In aortas from control rats, NS-398 did not alter the ACh-induced NO release, and furegrelate, TCP, or TCP plus furegrelate increased that release. In arteries from ovariectomized rats, NS-398, furegrelate, TCP, or TCP plus furegrelate decreased the ACh-induced NO release.

CONCLUSION

Despite the prevalence of vasoconstrictor prostanoids derived from COX-2 in aortas from ovariectomized rats, the ACh-induced relaxation is maintained, probably as consequence of the positive regulation that prostanoids exert on eNOS activity.

Cross-talk between rapid and long term effects of progesterone on vascular tissue

We tested the hypothesis whether; the non-genomic action of progesterone (Pg) on vascular tissue would be associated with hormonal long term effect on the modulation of cell growth. Using rat aortic strips, we showed that the stimulatory effect of Pg on nitric oxide synthesis involved both kinase and phosphatase pathways. The increase in the vasoactive production was prevented by the MAPK inhibitor (PD98059). In addition, preincubation with a phosphatase antagonist potentiated the hormonal effect. Pg increased PKC activity, but the inhibition of PKC did not alter the stimulatory action of the hormone on nitric oxide generation. In endothelial cell cultures (EC), 24h treatment with Pg significantly diminished cell proliferation. This antiproliferative effect was suppressed by the PKC inhibitor chelerythrine (chel) and l-NAME (nitric oxide synthase inhibitor). We also observed that Pg stimulates EC migration. In summary, the present findings provide evidence of an integration of genomic and non-genomic effects in the mechanism of action displayed by Pg in vascular tissue. The fast effects elicited by the hormone implies signal transduction activation required for the regulation of vasoactive production, but also necessary for the modulation of endothelial cells growth.

Human uterine smooth muscle and leiomyoma cells differ in their rapid 17beta-estradiol signaling: implications for proliferation

Uterine leiomyomas, benign uterine smooth muscle tumors that affect 30% of reproductive-aged women, are a significant health concern. The initiation event for these tumors is unclear, but 17beta-estradiol (E2) is an established promoter of leiomyoma growth. E2 not only alters transcription of E2-regulated genes but also can rapidly activate signaling pathways. The aim of our study is to investigate the role of rapid E2-activated cytoplasmic signaling events in the promotion of leiomyomas. Western blot analysis revealed that E2 rapidly increases levels of phosphorylated protein kinase C alpha (PKC alpha) in both immortalized uterine smooth muscle (UtSM) and leiomyoma (UtLM) cell lines, but increases levels of phosphorylated ERK1/2 only in UtLM cells. Our studies demonstrate a paradoxical effect of molecular and pharmacological inhibition of PKC alpha on ERK1/2 activation and cellular proliferation in UtLM and UtSM cells. PKC alpha inhibition decreases levels of phosphorylated ERK1/2 and proliferation in UtLM cells but raises these levels in UtSM cells. cAMP-PKA signaling is rapidly activated only in UtSM cells with E2 and inhibits ERK1/2 activation and proliferation. We therefore propose a model whereby E2's rapid activation of PKC alpha and cAMP-PKA signaling plays a central role in the maintenance of a low proliferative index in normal uterine smooth muscle via its inhibition of the MAPK cascade and these pathways are altered in leiomyomas to promote MAPK activation and proliferation. These studies demonstrate that rapid E2-signaling pathways contribute to the promotion of leiomyomas.

Sexual differentiation of motivation: a novel mechanism?

Sex differences in motivation are apparent for the motivation to engage in sexual behavior, the motivation to take drugs of abuse, and the motivation to engage in parental behavior. In both males and females there is an increase in NAcc DA associated with motivated behaviors. Here it proposed that sex differences in the regulation of DA activity in the ascending mesolimbic projections may underlie sex differences in motivation. In particular, sex differences in the neuroendocrine regulation of this brain system play a role in the expression of sex differences in motivated behaviors. Here it is proposed that sexual differentiation of motivation is mediated, at least in part, by a novel mechanism in which ovarian hormones secreted at puberty in the female actively feminize the DA system.

Autocrine regulation of cell proliferation by estrogen receptor-alpha in estrogen receptor-alpha-positive breast cancer cell lines

BACKGROUND

Estrogen receptor-alpha (ERalpha) is essential for mammary gland development and is a major oncogene in breast cancer. Since ERalpha is not colocalized with the cell proliferation marker Ki-67 in the normal mammary glands and the majority of primary breast tumors, it is generally believed that paracrine regulation is involved in ERalpha mediated cell proliferation. In the paracrine model, ERalpha-positive cells don't proliferate but will release some paracrine growth factors to stimulate the neighboring cells to proliferate. In a subpopulation of cancer cells in some primary breast tumors, however, ERalpha does colocalize with the cell proliferation marker Ki-67, suggesting an autocrine regulation by ERalpha in some primary breast tumors.

METHODS

Colocalization of ERalpha with Ki-67 in ERalpha-positive breast cancer cell lines (MCF-7, T47D, and ZR75-1) was evaluated by immunofluorescent staining. Cell cycle phase dependent expression of ERalpha was determined by co-immunofluorescent staining of ERalpha and the major cyclins (D, E, A, B), and by flow cytometry analysis of ERalphahigh cells. To further confirm the autocrine action of ERalpha, MCF-7 cells were growth arrested by ICI182780 treatment, followed by treatment with EGFR inhibitor, before estrogen stimulation and analyses for colocalization of Ki-67 and ERalpha and cell cycle progression.

RESULTS

Colocalization of ERalpha with Ki-67 was present in all three ERalpha-positive breast cancer cell lines. Unlike that in the normal mammary glands and the majority of primary breast tumors, ERalpha is highly expressed throughout the cell cycle in MCF-7 cells. Without E2 stimulation, MCF-7 cells released from ICI182780 treatment remain at G1 phase. E2 stimulation of ICI182780 treated cells, however, promotes the expression and colocalization of ERalpha and Ki-67 as well as the cell cycle progressing through the S and G2/M phases. Inhibition of EGFR signaling does not inhibit the autocrine action of ERalpha.

CONCLUSION

Our data indicate that ERalpha can mediate estrogen-induced cell proliferation in an autocrine mode in ERalpha-positive breast cancer cell lines. All of the three ERalpha-positive cell lines used in our study showed colocalization of ERalpha and Ki-67, indicating that these cell lines might be originated from primary tumor cells with autocrine regulation.

Do Estrogen Receptor beta Polymorphisms Play A Role in the Pharmacogenetics of Estrogen Signaling?

Estrogen hormones play critical roles in the regulation of many tissue functions. The effects of estrogens are primarily mediated by the estrogen receptors (ER) alpha and beta. ERs are ligand-activated transcription factors that regulate a complex array of genomic events that orchestrate cellular growth, differentiation and death. Although many factors contribute to their etiology, estrogens are thought to be the primary agents for the development and/or progression of target tissue malignancies. Many of the current modalities for the treatment of estrogen target tissue malignancies are based on agents with diverse pharmacology that alter or prevent ER functions by acting as estrogen competitors. Although these compounds have been successfully used in clinical settings, the efficacy of treatment shows variability. An increasing body of evidence implicates ERalpha polymorphisms as one of the contributory factors for differential responses to estrogen competitors. This review aims to highlight the recent findings on polymorphisms of the lately identified ERbeta in order to provide a functional perspective with potential pharmacogenomic implications.

Extra-nuclear signaling of estrogen receptors

Estrogen controls multiple biological functions through binding to estrogen receptors (ERs). Traditionally, ERs have been regarded as transcription factors regulating the expression of target genes. However, growing evidence of rapid estrogen's actions in a number of tissues has been accumulating and alternative mechanisms of signal transduction have been proposed. These so called "extra-nuclear actions" do not require gene expression or protein synthesis and are independent of the nuclear localization of ERs. Indeed, some of these actions are elicited by ERs residing at or near the plasma membrane. Membrane-associated molecules such as ion channels, G proteins, the tyrosine kinase c-Src as well as growth factor receptors are modulated by liganded ERs within the membrane, leading to the activation of downstream cascades such as mitogen-activated protein kinase, phosphatidylinositol 3-OH kinase, protein kinase A, and protein kinase C. These cascades mediate some important rapid actions of estrogen, such as the activation of nitric oxide synthesis or the remodeling of actin cytoskeleton. In addition, these pathways are critical for the regulation of the expression of a number of target proteins implicated in cell proliferation, apoptosis, differentiation, movement, and homeostasis. In this manner, the extra-nuclear pathways are tightly integrated with the genomic pathways to orchestrate the full spectrum of estrogen's biological functions. The recent advancements in the characterization of the molecular basis of the extra-nuclear signaling of estrogen helps to understand the role of estrogen on human cells, and may in future turn out to be of relevance for clinical purposes.

Rapid signaling by steroid receptors

Steroid receptors transcribe genes that lead to important biological processes, including normal organ development and function, tissue differentiation, and promotion of oncogenic transformation. These actions mainly result from nuclear steroid receptor action. However, for 50 years, it has been known that rapid effects of steroid hormones occur and could result from rapid signal transduction. Examples of these effects include stress responses to secreted glucocorticoids, rapid actions of thyroid hormones in the heart, and acute uterine/vaginal responses to injected estrogen. These types of responses have increasingly been attributed to rapid signaling by steroid hormones, upon engaging binding proteins most often at the cell surface of target organs. It is clear that rapid signal transduction serves an integrated role to modify existing proteins, altering their structure and activity, and to modulate gene transcription, often through collaboration with the nuclear pool of steroid receptors. The biological outcomes of steroid hormone actions thus reflect input from various cellular pools, cocoordinating the necessary events that are restrained in temporal and kinetic fashion. Here I describe the current understanding of rapid steroid signaling that is now appreciated to extend to virtually all members of this family of hormones and their receptors.

New insights into the classical and non-classical actions of estrogen: evidence from estrogen receptor knock-out and knock-in mice

Estrogen receptor alpha (ERalpha) mediates estrogen (E2) actions in the brain and is critical for normal reproductive function and behavior. In the classical pathway, ERalpha binds to estrogen response elements (EREs) to regulate gene transcription. ERalpha can also participate in several non-classical pathways, including ERE-independent gene transcription via protein-protein interactions with transcription factors and rapid, non-genotropic pathways. To distinguish between ERE-dependent and ERE-independent mechanisms of E2 action in vivo, we have created ERalpha null mice that possess an ER knock-in mutation (E207A/G208A; "AA"), in which the mutant ERalpha cannot bind to DNA but retains activity in ERE-independent pathways (ERalpha(-/AA) mice). Understanding the molecular mechanisms of ERalpha action will be helpful in developing pharmacological therapies that differentiate between ERE-dependent and ERE-independent processes. This review focuses on how the ERalpha(-/AA) model has contributed to our knowledge of ERalpha signaling mechanisms in estrogen regulation of the reproductive axis and sexual behavior.

Caveolin proteins and estrogen signaling in the brain

Best described outside the nervous system, caveolins are structural proteins that form caveolae, functional microdomains at the plasma membrane that cluster related signaling molecules. Caveolin-associated proteins include G protein-coupled receptors and G proteins, receptor tyrosine kinases, as well as protein kinases, ion channels and various other signaling enzymes. Not surprisingly, a wide array of biological disorders are thought to be rooted in caveolin dysfunction. In addition, caveolins traffic and cluster estrogen receptors to caveolae. Interactions between the estrogen receptors ERalpha and ERbeta with caveolins appear critical in many non-neuronal cell types, e.g., disruption of normal function may underlie many forms of breast cancer. Recent findings suggest caveolins may also play an essential role in membrane estrogen receptor function in the nervous system. Not only are they expressed in neurons and glia, but different caveolin isoforms also appear necessary to generate distinct functional signaling complexes. With membrane estrogen receptors responsible for the efficient activation of a multitude of intracellular signaling pathways, which in turn influence a wide variety of nervous system functions, caveolin proteins are poised to act as the central coordinators of these processes.

Differing transcriptional responses to pulsed or continuous estradiol exposure in human umbilical vein endothelial cells

This study used human umbilical vein endothelial cells (HUVECs) that were treated with 17beta-estradiol for 5 days as 1h pulse or 24h continuous treatment at concentrations such that the 24h exposure (concentration x time) was identical in both conditions. Cell proliferation was studied and gene expression profiling was carried out using the Affymetrix GeneChip microarray analysis. Changes in morphology and apoptosis in HUVECs were examined with electron microscopy. Time-course studies of expression of genes vascular endothelial growth factor (VEGF), inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) were performed by quantitative PCR. We observed that cell proliferation was significantly decreased over days 3-5 with pulsed estradiol treatment relative to constant exposure. Microarray results showed that after 5 days, 801 genes differed (P<0.05) between continuous versus pulsed estradiol treatment. Functional analysis showed a significant number of genes to be associated with apoptosis and cell cycle pathways. We did not find any evidence of apoptosis from flow cytometry or electron microscopy examination. Our study highlights a large number of significantly different molecular responses to estradiol depending upon the mode of administration of estradiol. Significant changes were observed in genes involved in apoptosis and proliferation including VEGF, IGF receptors, and tumor protein p53.

Estrogen inhibits cardiac hypertrophy: role of estrogen receptor-beta to inhibit calcineurin

Estrogen has been reported to prevent development of cardiac hypertrophy in female rodent models and in humans. However, the mechanisms of sex steroid action are incompletely understood. We determined the cellular effects by which 17beta-estradiol (E2) inhibits angiotensin II (AngII)-induced cardiac hypertrophy in vivo. Two weeks of angiotensin infusion in female mice resulted in marked hypertrophy of the left ventricle, exacerbated by the loss of ovarian steroid hormones from oophorectomy. Hypertrophy was 51% reversed by the administration of E2 (insertion of 0.1 mg/21-d-release tablets). The effects of E2 were mainly mediated by the estrogen receptor (ER) beta-isoform, because E2 had little effect in ERbeta-null mice but comparably inhibited AngII-induced hypertrophy in wild-type or ERalpha-null mice. AngII induced a switch of myosin heavy chain production from alpha to beta, but this was inhibited by E2 via ERbeta. AngII-induced ERK activation was also inhibited by E2 through the beta-receptor. E2 stimulated brain natriuretic peptide protein expression and substantially prevented ventricular interstitial cardiac fibrosis (collagen deposition) as induced by AngII. Importantly, E2 inhibited calcineurin activity that was stimulated by AngII, related to E2 stimulating the modulatory calcineurin-interacting protein (MCIP) 1 gene and protein expression. E2 acting mainly through ERbeta mitigates the important signaling by AngII that produces cardiac hypertrophy and fibrosis in female mice.

Non-genomic actions of progesterone and estrogens in regulating reproductive events in domestic animals

It has been established that nuclear receptors mediate the action of estrogens and progestins in regulating gene expression in the hypothalamic-hypophyseal-gonadal axis of domestic animals during various reproductive states. Results of recent in vitro studies suggest that estradiol-17beta and progesterone can act non-genomically to affect signal transduction responses in target cells by binding to receptors in the plasma membrane. The genomic action of steroids is generally detectable in hours to days whereas non-genomic responses of cells occur in seconds to minutes. The nature of the plasma membrane receptors for estrogens and progesterone has been explored but has not been conclusively established for all cell types studied. In the ewe, estradiol-17beta or estradiol-bovine serum albumin conjugate has been shown by in vitro and in vivo approaches to act non-genomically to suppress luteinizing hormone secretion by gonadotropes and stimulate production of nitric oxide by uterine arterial endothelial cells. Progesterone has been shown to inhibit oxytocin (OT) binding to its receptor in isolated ovine endometrial plasma membranes. This non-genomic action of progesterone blocks OT activation of the phosphoinositide cascade and production of prostaglandin F(2alpha) by ovine and bovine endometrium. The acrosome reaction of caprine and porcine spermatozoa is activated by the non-genomic action of progesterone. Further research is required to define the biological significances of the non-genomic actions of estrogens and progestins.

Knockdown of TFIIS by RNA silencing inhibits cancer cell proliferation and induces apoptosis

Background

A common element among cancer cells is the presence of improperly controlled transcription. In these cells, the degree of specific activation of some genes is abnormal, and altering the aberrant transcription may therefore directly target cancer. TFIIS is a transcription elongation factor, which directly binds the transcription motor, RNA Polymerase II and allows it to read through various transcription arrest sites. We report on RNA interference of TFIIS, a transcription elongation factor, and its affect on proliferation of cancer cells in culture.

Methods

RNA interference was performed by transfecting siRNA to specifically knock down TFIIS expression in MCF7, MCF10A, PL45 and A549 cells. Levels of TFIIS expression were determined by the Quantigene method, and relative protein levels of TFIIS, c-myc and p53 were determined by C-ELISA. Induction of apoptosis was determined by an enzymatic Caspase 3/7 assay, as well as a non-enzymatic assay detecting cytoplasmic mono- and oligonucleosomes. A gene array analysis was conducted for effects of TFIIS siRNA on MCF7 and MCF10A cell lines.

Results

Knockdown of TFIIS reduced cancer cell proliferation in breast, lung and pancreatic cancer cell lines. More specifically, TFIIS knockdown in the MCF7 breast cancer cell line induced cancer cell death and increased c-myc and p53 expression whereas TFIIS knockdown in the non-cancerous breast cell line MCF10A was less affected. Differential effects of TFIIS knockdown in MCF7 and MCF10A cells included the estrogenic, c-myc and p53 pathways, as observed by C-ELISA and gene array, and were likely involved in MCF7 cell-death.

Conclusion

Although transcription is a fundamental process, targeting select core transcription factors may provide for a new and potent avenue for cancer therapeutics. In the present study, knockdown of TFIIS inhibited cancer cell proliferation, suggesting that TFIIS could be studied as a potential cancer target within the transcription machinery.

Raloxifene analogue LY117018 suppresses oxidative stress-induced endothelial cell apoptosis through activation of ERK1/2 signaling pathway

A selective estrogen receptor modulator, raloxifene, has been shown to reduce cardiovascular events in relatively high-risk postmenopausal women with osteoporosis. However, the mechanisms by which raloxifene exerts a pharmacological effect on cardiovascular organs have not been fully elucidated. The present study was designed to examine whether the raloxifene analogue, 6-hydroxy-2-(p-hydroxyphenyl)-benzo(b) thien-3-yl-p-(2-(pyrrolidinyl)ethoxy phenyl ketone (LY117018), could inhibit apoptosis and to clarify the signaling pathway in vascular endothelial cells. LY117018 significantly inhibited hydrogen peroxide-induced apoptosis in bovine carotid artery endothelial cells. The anti-apoptotic effect of LY117018 was abolished by an estrogen receptor antagonist, 7alpha,7beta-(9[(4,4,5,5,5-Pentafluoropentyl)sulfinyl]nonyl) estra-1,3,5(10)-triene-3,17-diol (ICI 182,780). Mitogen-activated protein kinases (MAPK), including p38, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated protein kinase1/2 (ERK1/2), and Akt, have been shown to act as apoptotic or anti-apoptotic signals. Phosphorylation of p38, JNK, ERK1/2 and Akt was examined. LY117018 increased ERK1/2 phosphorylation but did not enhance the phosphorylation of p38, JNK, or Akt. The anti-apoptotic effect of LY117018 was prevented by treatment with 2-[2'-amino-3'-methoxyphenyl]-oxanaphthalen-4-one (PD98059), an upstream inhibitor of ERK1/2. LY117018 stimulated an increase in ERK1/2 phosphorylation, which was diminished by ICI 182,780. The activation of ERK/1/2 by LY117018 was not inhibited by the transcription inhibitor, actinomycin D. These results suggest that estrogen receptors and the ERK1/2 signaling pathway are involved in the anti-apoptotic action of LY117018 in vascular endothelial cells.

Non-genomic actions of estrogens and their interaction with genomic actions in the brain

Ligands for the nuclear receptor superfamily have at least two mechanisms of action: (a) classical transcriptional regulation of target genes (genomic mechanisms); and (b) non-genomic actions, which are initiated at the cell membrane, which could also impact transcription. Though transcriptional mechanisms are increasingly well understood, membrane-initiated actions of these ligands are incompletely understood. This has led to considerable debate over the physiological relevance of membrane-initiated actions of hormones versus genomic actions of hormones, with genomic actions predominating in the endocrine field. There is good evidence that the membrane-limited actions of hormones, particularly estrogens, involve the rapid activation of kinases and the release of calcium and that these are linked to physiologically relevant scenarios in the brain. We show evidence in this review, that membrane actions of estrogens, which activate these rapid signaling cascades, can also potentiate nuclear transcription in both the central nervous system and in non-neuronal cell lines. We present a theoretical scenario which can be used to understand this phenomenon. These signaling cascades may occur in parallel or in series but subsequently, converge at the modification of transcriptionally relevant molecules such as nuclear receptors and/or coactivators. In addition, other non-cognate hormones or neurotransmitters may also activate cascades to crosstalk with estrogen receptor-mediated transcription, though the relevance of this is less clear. The idea that coupling between membrane-initiated and genomic actions of hormones is a novel idea in neuroendocrinology and provides us with a unified view of hormone action in the central nervous system.

Minireview: nuclear receptors and breast cancer

Until recently, the study of nuclear receptor (NR) function in breast cancer biology has been largely limited to estrogen and progesterone receptors. The development of reliable gene expression arrays, real-time quantitative RT-PCR, and immunohistochemical techniques for studying NR superfamily members in primary human breast cancers has now revealed the presence and potential importance of several additional NRs in the biology of breast cancer. These include receptors for steroid hormones (including androgens and corticosteroids), fat-soluble vitamins A and D, fatty acids, and xenobiotic lipids derived from diet. It is now clear that after NR activation, both genomic and nongenomic NR pathways can coordinately activate growth factor signaling pathways. Advances in our understanding of both NR functional networks and epithelial cell growth factor signaling pathways have revealed a frequent interplay between NR and epithelial cell growth factor family signaling that is clinically relevant to breast cancer. Understanding how growth factor receptors and their downstream kinases are activated by NRs (and vice-versa) is a central goal for maximizing treatment opportunities in breast cancer. In addition to the estrogen receptor, it is predicted that modulating the activity of other NRs will soon provide novel prevention and treatment approaches for breast cancer patients.

Crosstalk between the estrogen receptor and the HER tyrosine kinase receptor family: molecular mechanism and clinical implications for endocrine therapy resistance

Breast cancer evolution and tumor progression are governed by the complex interactions between steroid receptor [estrogen receptor (ER) and progesterone receptor] and growth factor receptor signaling. In recent years, the field of cancer therapy has witnessed the emergence of multiple strategies targeting these specific cancer pathways and key molecules (ER and growth factor receptors) to arrest tumor growth and achieve tumor eradication; treatment success, however, has varied and both de novo (up front) and acquired resistance have proven a challenge. Recent studies of ER biology have revealed new insights into ER action in breast cancer and have highlighted the role of an intimate crosstalk between the ER and HER family signaling pathways as a fundamental contributor to the development of resistance to endocrine therapies against the ER pathway. The aim of this review article is to summarize the current knowledge on mechanisms of resistance of breast cancer cells to endocrine therapies due to the crosstalk between the ER and the HER growth factor receptor signaling pathways and to explore new available therapeutic strategies that could prolong duration of response and circumvent endocrine resistant tumor growth.

The proliferative effect of estradiol on human prostate stromal cells is mediated through activation of ERK

BACKGROUND

Estrogen is involved in the development and progression of benign prostatic hyperplasia (BPH). It can stimulate proliferation of prostate stromal cells (PrSCs). However, the exact mechanism remains unclear.

METHODS

We used the primary cultured human PrSCs and a prostate stromal cell line, WPMY-1, to examine the signaling pathways involved in estrogen-mediated proliferation of PrSCs. Cells were treated with 17beta-estradiol (E(2)) or BSA-E(2). Cell proliferation was assessed by the MTT assay and by cell counting. Western blot analysis was used to determine the status of activation of ERK1/2.

RESULTS

Results indicated that both E(2) and BSA-E(2) stimulated proliferation of primary PrSCs and WPMY-1 cells. ERK was rapidly activated by E(2) and BSA-E(2). PD98059, which is a selective ERK inhibitor, significantly inhibited estrogen-induced cell proliferation. PrSCs expressed estrogen receptor alpha (ERalpha) and GPR30 but not ERbeta. Small hairpin RNA (shRNA) to ERalpha, but not to GPR30, blocked estrogen-mediated ERK activation and cell proliferation.

CONCLUSIONS

The results indicated that estrogen could activate ERK pathway through the non-genomic ERalpha pathway, leading to proliferation of PrSCs.

The estrogen and c-Myc target gene HSPC111 is over-expressed in breast cancer and associated with poor patient outcome

INTRODUCTION

Estrogens play a pivotal role in the initiation and progression of breast cancer. The genes that mediate these processes are not fully defined, but potentially include the known mammary oncogene MYC. Characterization of estrogen-target genes may help to elucidate further the mechanisms of estrogen-induced mitogenesis and endocrine resistance.

METHODS

We used a transcript profiling approach to identify targets of estrogen and c-Myc in breast cancer cells. One previously uncharacterized gene, namely HBV pre-S2 trans-regulated protein 3 (HSPC111), was acutely upregulated after estrogen treatment or inducible expression of c-Myc, and was selected for further functional analysis using over-expression and knock-down strategies. HSPC111 expression was also analyzed in relation to MYC expression and outcome in primary breast carcinomas and published gene expression datasets.

RESULTS

Pretreatment of cells with c-Myc small interfering RNA abrogated estrogen induction of HSPC111, identifying HSPC111 as a potential c-Myc target gene. This was confirmed by the demonstration of two functional E-box motifs upstream of the transcription start site. HSPC111 mRNA and protein were over-expressed in breast cancer cell lines and primary breast carcinomas, and this was positively correlated with MYC mRNA levels. HSPC111 is present in a large, RNA-dependent nucleolar complex, suggesting a possible role in ribosomal biosynthesis. Neither over-expression or small interfering RNA knock-down of HSPC111 affected cell proliferation rates or sensitivity to estrogen/antiestrogen treatment. However, high expression of HSPC111 mRNA was associated with adverse patient outcome in published gene expression datasets.

CONCLUSION

These data identify HSPC111 as an estrogen and c-Myc target gene that is over-expressed in breast cancer and is associated with an adverse patient outcome.

Estrogen potentiates constrictor prostanoid function in female rat aorta by upregulation of cyclooxygenase-2 and thromboxane pathway expression

Estrogen potentiates vascular reactivity to vasopressin (VP) by enhancing constrictor prostanoid function. To determine the cellular and molecular mechanisms, the effects of estrogen on arachidonic acid metabolism and on the expression of constrictor prostanoid pathway enzymes and endoperoxide/thromboxane receptor (TP) were determined in the female rat aorta. The release of thromboxane A2 (TxA2) and prostacyclin (PGI2) was measured in male (M), intact-female (Int-F), ovariectomized-female (OvX-F), and OvX + 17beta-estradiol-replaced female (OvX + ER-F) rats. The expression of mRNA for cyclooxygenase (COX)-1, COX-2, thromboxane synthase (TxS), and TP by aortic endothelium (Endo) and vascular smooth muscle (VSM) of these four experimental groups was measured by RT-PCR. The expression of COX-1, COX-2, and TxS proteins by Endo and VSM was also estimated by immunohistochemistry (IHC). Basal release of TxA2 and PGI2 was similar in M (18.8 +/- 1.9 and 1,723 +/- 153 pg/mg ring wt/45 min, respectively) and Int-F (20.2 +/- 4.2 and 1,488 +/- 123 pg, respectively) rat aortas. VP stimulated the dose-dependent release of TxA2 and PGI2 from both male and female rat aorta. OvX markedly attenuated and ER therapy restored VP-stimulated release of TxA2 and PGI2 in female rats. No differences in COX-1 mRNA levels were detected in either Endo or VSM of the four experimental groups (P > 0.1). The expression of both COX-2 and TxS mRNA were significantly higher (P < 0.05) in both Endo and VSM of Int-F and OvX + ER-F, compared with M or OvX-F. Expression of TP mRNA was significantly higher in VSM of Int-F and OvX + ER-F compared with M or OvX-F. IHC revealed the uniform staining of COX-1 in VSM of the four experimental groups, whereas staining of COX-2 and TxS was greater in Endo and VSM of Int-F and OvX + ER-F than in OvX-F or M rats. These data reveal that estrogen enhances constrictor prostanoid function in female rat aorta by upregulating the expression of COX-2 and TxS in both Endo and VSM and by upregulating the expression of TP in VSM.

APRIN is a unique Pds5 paralog with features of a chromatin regulator in hormonal differentiation

Activation of steroid receptors results in global changes of gene expression patterns. Recent studies showed that steroid receptors control only a portion of their target genes directly, by promoter binding. The majority of the changes are indirect, through chromatin rearrangements. The mediators that relay the hormonal signals to large-scale chromatin changes are, however, unknown. We report here that APRIN, a novel hormone-induced nuclear phosphoprotein has the characteristics of a chromatin regulator and may link endocrine pathways to chromatin. We showed earlier that APRIN is involved in the hormonal regulation of proliferative arrest in cancer cells. To investigate its function we cloned and characterized APRIN orthologs and performed homology and expression studies. APRIN is a paralog of the cohesin-associated Pds5 gene lineage and arose by gene-duplication in early vertebrates. The conservation and domain differences we found suggest, however, that APRIN acquired novel chromatin-related functions (e.g. the HMG-like domains in APRIN, the hallmarks of chromatin regulators, are absent in the Pds5 family). Our results suggest that in interphase nuclei APRIN localizes in the euchromatin/heterochromatin interface and we also identified its DNA-binding and nuclear import signal domains. The results indicate that APRIN, in addition to its Pds5 similarity, has the features and localization of a hormone-induced chromatin regulator.

The characteristics of aromatase deficient hairless mice indicate important roles of extragonadal estrogen in the skin

The roles of extragonadal estrogen in the skin are poorly understood, due to the lack of proper animal models. We examined the skin phenotypes of aromatase-knockout hairless (ArKO) mice and wild-type hairless (WT) mice, both of which were obtained through crossbreeding of Ar+/- mice and hairless mice. Differences in the skins of ArKO and WT mice were compared with those of ovariectomized (OVX) and control (Sham) mice. A difference was observed in the skin tone of ArKO mice, which is pale white and differs from the pinkish tone of all other mice. However, both ArKO and OVX mice similarly exhibited deteriorations of skin properties as compared to their respective controls. Furthermore, all the deteriorations were similarly amplified by chronic UVB irradiation in both ArKO and OVX mice as compared to their respective controls. The unique skin phenotype of ArKO mice was observed in sunburn reactions. Specifically, skins of ArKO mice showed no reaction after an acute UVB irradiation at dose intensities caused sunburn in others. However, follow-up observation found delayed reactions associated with brownish skin color and swelling only in ArKO mice, thereby suggesting that the role of extragonadal estrogen may be connected with the protective reactions of skin.

Extranuclear steroid receptors: nature and actions

Rapid effects of steroid hormones result from the actions of specific receptors localized most often to the plasma membrane. Fast-acting membrane-initiated steroid signaling (MISS) leads to the modification of existing proteins and cell behaviors. Rapid steroid-triggered signaling through calcium, amine release, and kinase activation also impacts the regulation of gene expression by steroids, sometimes requiring integration with nuclear steroid receptor function. In this and other ways, the integration of all steroid actions in the cell coordinates outcomes such as cell fate, proliferation, differentiation, and migration. The nature of the receptors is of intense interest, and significant data suggest that extranuclear and nuclear steroid receptor pools are the same proteins. Insights regarding the structural determinants for membrane localization and function, as well as the nature of interactions with G proteins and other signaling molecules in confined areas of the membrane, have led to a fuller understanding of how steroid receptors effect rapid actions. Increasingly, the relevance of rapid signaling for the in vivo functions of steroid hormones has been established. Examples include steroid effects on reproductive organ development and function, cardiovascular responsiveness, and cancer biology. However, although great strides have been made, much remains to be understood concerning the integration of extranuclear and nuclear receptor functions to organ biology. In this review, we highlight the significant progress that has been made in these areas.

Estrogen-induced activation of mammalian target of rapamycin is mediated via tuberin and the small GTPase Ras homologue enriched in brain

Inhibitors of the mammalian target of rapamycin (mTOR) are currently in clinical trials for the treatment of breast cancer. The mechanisms through which mTOR are activated in breast cancer and the relationship of mTOR activation to steroid hormones, such as estrogen, that are known to influence breast cancer pathogenesis, are not yet understood. Using MCF-7 cells as a model, we found that 17-beta estradiol (E(2)) rapidly increased the phosphorylation of downstream targets of mTOR: p70 ribosomal protein S6 kinase, ribosomal protein S6, and eukaryotic initiation factor 4E-binding protein 1. The phosphoinositide-3-kinase inhibitor, wortmannin, and the mTOR inhibitor, rapamycin, blocked E(2)-induced activation of p70 ribosomal protein S6 kinase. We hypothesized that tuberin and the small GTPase Ras homologue enriched in brain (Rheb), regulators of the mTOR pathway, mediate E(2)-induced activation of mTOR. Consistent with this hypothesis, E(2) rapidly (within 5 minutes) stimulated tuberin phosphorylation at T1462, a site at which Akt phosphorylates and inactivates tuberin. E(2) also rapidly decreased the inactive, GDP-bound form of Rheb. Finally, we found that small interfering RNA down-regulation of endogenous Rheb blocked the E(2)-stimulated proliferation of MCF-7 cells, demonstrating that Rheb is a key determinant of E(2)-dependent cell growth. Taken together, these data reveal that the TSC/Rheb/mTOR pathway plays a critical role in the regulation of E(2)-induced proliferation, and highlight Rheb as a novel molecular target for breast cancer therapy.

Mechanisms of primary and secondary estrogen target gene regulation in breast cancer cells

Estrogen receptors (ERs), which mediate the proliferative action of estrogens in breast cancer cells, are ligand-dependent transcription factors that regulate expression of their primary target genes through several mechanisms. In addition to direct binding to cognate DNA sequences, ERs can be recruited to DNA through other transcription factors (tethering), or affect gene transcription through modulation of signaling cascades by non-genomic mechanisms of action. To better characterize the mechanisms of gene regulation by estrogens, we have identified more than 700 putative primary and about 1300 putative secondary target genes of estradiol in MCF-7 cells through microarray analysis performed in the presence or absence of the translation inhibitor cycloheximide. Although siRNA-mediated inhibition of ERalpha expression antagonized the effects of estradiol on up- and down-regulated primary target genes, estrogen response elements (EREs) were enriched only in the vicinity of up-regulated genes. Binding sites for several other transcription factors, including proteins known to tether ERalpha, were enriched in up- and/or down-regulated primary targets. Secondary estrogen targets were particularly enriched in sites for E2F family members, several of which were transcriptionally regulated by estradiol, consistent with a major role of these factors in mediating the effects of estrogens on gene expression and cellular growth.

Estradiol upregulates activating transcription factor 3, a candidate gene in the etiology of hypospadias

Hypospadias is a penile developmental abnormality that may partly result from in utero exposure to estrogenic compounds. Expression of activating transcription factor 3 (ATF3) is elevated in human foreskin tissue from hypospadic patients, and in utero exposure to ethinyl estradiol (17-EE) causes ATF3 upregulation in a hypospadias mouse model. We investigated the effects of in vitro exposure to EE on ATF3 expression and promoter activity in human foreskin fibroblasts using immunocytochemistry, quantitative polymerase chain reaction (PCR), western blot, and the luciferase activity assay. Immunocytochemistry showed peak positive staining at 2 hours after 0.5 to 3 hours of EE treatment (0.1 microM). Western blot showed significantly increased ATF3 protein expression (P = 0.006) after EE exposure. ATF3 mRNA, as evaluated using reverse transcriptase PCR and TaqMan real-time PCR, also increased (P = 0.146). In addition, the luciferase activity assay showed that ATF3 promoter activity was significantly enhanced after 1 hour of EE exposure (P < 0.0001). Thus, EE upregulates ATF3 expression in fibroblasts in vitro, consistent with our previous results with human tissue and in vivo mouse models. ATF3 is involved in the TGF-beta epithelial-mesenchymal signaling pathway, and its involvement in hypospadias suggests that ATF3 plays a role in development of this anomaly as a result of exposure to estrogenic compounds. Its potential involvement in other manifestations of developmental endocrine disruption is worth investigating.

Cellular localization of androgen and estrogen receptors in mouse-derived motoneuron hybrid cells and mouse facial motoneurons

The ability of gonadal steroid hormones to augment axonal regeneration after peripheral nerve injury has been well established in rat and hamster motoneuron systems, and provides a foundation for the use of these agents as neurotherapeutics. With the advent of mouse genetics and the availability of transgenic and knockout mice, the use of mice in studies of neuroprotection is growing. It has recently been demonstrated that both androgens and estrogens rescue motoneurons (MN) from injury in mouse-derived motoneuron hybrid cells in vitro and mouse facial motoneurons (FMN) in vivo (Tetzlaff et al. [2006] J Mol Neurosci 28:53-64). To elucidate the molecular mechanisms of these effects, the present study examined the cellular localization of androgen and estrogen receptors in mouse MN in vitro and in vivo. Immunoblotting and immunocytochemistry studies established the presence of androgen receptor (AR) and estrogen receptor alpha/beta in immortalized mouse motoneuron hybrid cells and AR and estrogen receptor alpha in mouse FMN.

Influence of mycotoxins on spontaneous contraction in myometrial strips of prepubertal lamb

The effects of mycotoxin zearalenone and their major metabolites alpha- and beta-zearalenol on spontaneous contractions in isolated lamb uterine smooth muscle were examined. The study was carried out on 20 female prepubertal lambs aged between 45 and 50 days. Myometrial strips were set up in two isolated organ baths (10ml) at 37 degrees C and were exposed to increasing concentrations (10(-11)M-10(-6)M) of these mycoestrogens and results were compared with the effect, at the same concentrations, of natural estrogen 17beta-estradiol. Our findings suggest that mycotoxins and 17beta-estradiol, at nanomolar concentrations, rapidly enhance phasic spontaneous smooth muscle contraction. In particular, zearalenone increases the uterine activity similarly to 17beta-estradiol. On the contrary, its metabolite alpha-zearalenol significantly inhibits myometrial contractility.

CEREBROVASCULAR EFFECTS OF OESTROGEN: MULTIPLICITY OF ACTION

1. Cerebral vessels express oestrogen receptors (ER) in both the smooth muscle and endothelial cell layers of cerebral blood vessels. Levels of ERalpha are higher in female rats chronically exposed to oestrogen, either endogenous or exogenous. 2. Chronic exposure to oestrogen, either endogenous (normally cycling females) or exogenous (ovariectomized with oestrogen replacement), results in cerebral arteries that are more dilated than arteries from ovariectomized counterparts when studied in vitro. This effect is primarily mediated by an increase in the production of vasodilator factors, including nitric oxide (NO) and prostacylin. In contrast, oestrogen appears to suppress the production of endothelial-derived hyperpolarizing factor. Oestrogen treatment increases cerebrovascular levels of endothelial nitric oxide synthase (eNOS), cyclo-oxygenase (COX)-1 and prostacyclin synthase. In addition, via activation of the phosphatidylinositol 3-kinase/Akt pathway, both acute and chronic oestrogen exposure increases eNOS phosphorylation, increasing NO production. 3. Oestrogen receptors have also been localized to cerebrovascular mitochondria and exposure to oestrogen increases the efficiency of energy production while simultaneously reducing mitochondrial production of reactive oxygen species. Oestrogen increases the production of mitochondrial proteins encoded by both mitochondrial and nuclear DNA, including cytochrome c, subunits I and IV of complex IV and Mn-superoxide dismutase. Oestrogen treatment increases the activity of citrate synthase and complex IV and decreases mitochondrial production of H(2)O(2). 4. Oestrogen also has potent anti-inflammatory effects in the cerebral circulation that may have important implications for the incidence and severity of cerebrovascular disease. Administration of lipopolysaccharide or interleukin-1beta to ovariectomized female rats induces cerebrovascular COX-2 and inducible nitric oxide synthase (iNOS) protein expression and increases prostaglandin E(2) expression. Levels of COX-2 and iNOS expression vary with the stage of the oestrous cycle, and the cerebrovascular inflammatory response is suppressed in ovariectomized animals treated with oestrogen. Interleukin-1beta induction of COX-2 protein is prevented by treatment with a nuclear factor (NF)-kappaB inhibitor, and oestrogen treatment reduces cerebrovascular NF-kappaB activity. 5. Cerebrovascular dysfunction and pathology contribute to the pathogenesis of stroke, brain trauma, oedema and dementias, such as Alzheimer's disease. A better understanding of the action of oestrogen on cerebrovascular function holds promise for the development of new therapeutic entities that could be useful in preventing or treating a wide variety of cerebrovascular diseases.

Estrogen receptors outside the nucleus in breast cancer

The estrogen receptor (ER) is the single most powerful predictor of breast cancer prognosis as well as an important contributor to the biology of carcinogenesis. In addition, endocrine therapy targeting ER directly (SERMS) or indirectly (aromatase inhibitors) forms the mainstay of adjuant therapy. Traditionally, human tumors are scored for the amount and presence of ER. However, this has centered on the population of ER found in the transformed epithelial cell nucleus. Over the last 40 years, it has been appreciated that additional cellular ER pools exist, in cytoplasm and at the plasma membrane. In this review, we discuss the important functions of extra-nuclear ER in breast cancer, including integration of function with nuclear ER.

Unraveling the mechanisms of endocrine resistance in breast cancer: new therapeutic opportunities

Two thirds of breast cancers express the estrogen receptor (ER), which contributes to tumor development and progression. ER-targeted therapy is therefore widely used in breast cancer to inhibit signaling through ER and disrupt breast cancer growth. This therapeutic strategy, particularly using the antiestrogen tamoxifen, is proven to increase the cure rates in early breast cancer, improve patient outcomes in advanced disease, and reduce breast cancer incidence in the prevention setting. Despite the recent integration of more powerful endocrine agents into breast cancer care, resistance to all forms of endocrine therapy remains a major problem. New insight into ER biology and progress in understanding resistance mechanisms, mediated by molecular crosstalk between ER and various growth factor signaling pathways, are generating tremendous promise for new therapeutic opportunities to target resistance and improve breast cancer disease outcomes.

A conserved mechanism for steroid receptor translocation to the plasma membrane

Multiple steroid receptors (SR) have been proposed to localize to the plasma membrane. Some structural elements for membrane translocation of the estrogen receptor alpha (ER alpha) have been described, but the mechanisms relevant to other steroid receptors are entirely unknown. Here, we identify a highly conserved 9 amino acid motif in the ligand binding domains (E domains) of human/mouse ER alpha and ER beta, progesterone receptors A and B, and the androgen receptor. Mutation of the phenylalanine or tyrosine at position-2, cysteine at position 0, and hydrophobic isoleucine/leucine or leucine/leucine combinations at positions +5/6, relative to cysteine, significantly reduced membrane localization, MAP and PI 3-kinase activation, thymidine incorporation into DNA, and cell viability, stimulated by specific SR ligands. The localization sequence mediated palmitoylation of each SR, which facilitated caveolin-1 association, subsequent membrane localization, and steroid signaling. Palmitoylation within the E domain is therefore a crucial modification for membrane translocation and function of classical sex steroid receptors.

Up-Regulation of Estrogen Responsive Genes in Hypospadias: Microarray Analysis

PURPOSE

An unexplained increase in the incidence of hypospadias has been reported, and yet to our knowledge the molecular events and their regulation leading to hypospadias remain unknown, although environmental compounds capable of endocrine activity are suspected. We screened on a global scale abnormalities in gene expression in human hypospadiac tissue compared to those in nonhypospadiac tissue. Additionally, microarray analysis of tissue from a pair of fraternal twins, including 1 with and 1 without hypospadias, served as a control for genetic variability. We hypothesized that gene expression would differ between hypospadiac vs nonhypospadiac tissue and fraternal twin data would show patterns similar to those of group data on hypospadiac and nonhypospadiac tissue.

MATERIALS AND METHODS

Microarray analysis was performed on tissue from patients with and without hypospadias, and from a pair of fraternal twins, including 1 with and 1 without hypospadias. Analysis incorporated the expression of 22,000 genes.

RESULTS

We found significant differences in gene expression, specifically with a group of genes, including CYR61, CTGF, ATF3 and GADD45beta, known to be responsive to estrogen or to interact with estrogen receptor.

CONCLUSIONS

Our findings provide support for the hypothesis that endocrine active environmental compounds may contribute to the development of hypospadias. Additionally, regulation of these genes may have a role in formation of the urethra.

Candidate genes and their response to environmental agents in the etiology of hypospadias

The molecular events that lead to isolated hypospadias remain largely unknown, and the etiology of this common congenital anomaly seems to be multifactorial. We have explored the response of several candidate genes to environmental agents that cause hypospadias in a mouse model. Here, we provide an overview of current findings in relation to candidate genes and their response to environmental agents, including the results of genomic analyses of both mouse and human tissues. In addition to steroid-hormone receptors, one gene of specific interest is activating transcription factor 3 (ATF3). We hypothesize a potential mechanism of action for ATF3 and other identified genes, including TGF-B.