Classical Steroid Receptors Research Articles

Nuclear receptors as potential therapeutic targets in peripheral arterial disease and related myopathy.

Peripheral arterial disease (PAD) is a prevalent cardiovascular complication of limb vascular insufficiency, causing ischemic injury, mitochondrial metabolic damage and functional impairment in the skeletal muscle, and ultimately leading to immobility and mortality. While potential therapies have been mostly focussed on revascularization, none of the currently available pharmacological treatments are fully effective in PAD, often leading to amputations, particularly in chronic metabolic diseases. One major limitation of focussed angiogenesis and revascularization as a therapeutic strategy is a limited effect on metabolic restoration and muscle regeneration in the affected limb. Therefore, additional preclinical investigations are needed to discover novel treatment options for PAD preferably targeting multiple aspects of muscle recovery. In this review, we propose nuclear receptors expressed in the skeletal muscle as potential candidates for ischemic muscle repair in PAD. We review classic steroid and orphan receptors that have been reported to be involved in the regulation of paracrine muscle angiogenesis, oxidative metabolism, mitochondrial biogenesis and muscle regeneration, and discuss how these receptors could be critical for recovery from ischemic muscle damage. Furthermore, we identify existing gaps in our understanding of nuclear receptor signalling in the skeletal muscle and propose future areas of research that could be instrumental in exploring nuclear receptors as therapeutic candidates for treating PAD.

Inhibition of ABCC5-mediated cGMP transport by progesterone, testosterone and their analogues

The biodynamics and biokinetics of sex hormones are complex. In addition to the classical steroid receptors (nuclear receptors), these hormones act through several non-genomic mechanisms. Modulation of ABC-transporters by progesterone represents a non-genomic mechanism. In the present study, we employed inside out vesicles from human erythrocytes to characterize high affinity cGMP transport by ABCC5 (member 5 of the ATP-Binding Cassette subfamily C). Progesterone and testosterone inhibited the transport with respective Ki of 1.2 ± 0.3 and 2.0 ± 0.6 μmol/L. We used virtual ligand screening (VLS) to identify analogues to progesterone and testosterone. A large number of substances were screened in silico and the 19 most promising candidates were screened in vitro. Each substance was tested for a concentration of 10 μmol/L. The range of cGMP transport reduction was 21.5% to 86.2% for progesterone analogues and 8.6% to 93.8 % for testosterone analogues. Three of the most potent test compounds (TC) of each analogue class, in addition to progesterone and testosterone, were characterized for concentrations from 1 nanomol/L to 1 mmol/L. The progesterone analogues showed following Ki-values (μmol/L): TC-08: 0.61, TC-16: 0.66 and TC-15: 9.3. The Ki-values (μmol/L) for the testosterone analogues were: TC-18: 0.10, TC-07: 0.67 andTC-05: 2.0. The present study shows that VLS may be a versatile tool in the development of membrane transport modulating agents (MTMAs).

Nuclear androgen and progestin receptors inversely affect aggression and social dominance in male zebrafish (Danio rerio)

Aggression is a fundamental behavior displayed universally among animal species, but hyper- or hypo-aggressiveness can be maladaptive with negative consequences for individuals and group members. While the social and ecological significance of aggression is well understood, the specific neurobiological and hormonal mechanisms responsible for mediating aggression have not been fully elucidated. Previous studies have shown a relationship between aggressive acts and circulating gonadal steroids, but whether classical nuclear steroid receptors regulate aggression in animals is still uncertain. We examined whether the nuclear androgen receptor (Ar) and nuclear progestin receptor (Pgr) were necessary for aggressive behaviors and maintenance of a dominance relationship in male zebrafish (Danio rerio). Dyadic social interactions of Ar knockout (ArKO), Pgr knockout (PgrKO) and wildtype (WT) controls were observed for two weeks (2-weeks). ArKO zebrafish were significantly less aggressive and had a less defined dominance relationship, whereas PgrKO dominant zebrafish were significantly and persistently more aggressive with a robust dominance relationship. Our results demonstrate the importance of nuclear steroid hormone receptors in regulating aggression of adult male zebrafish and provide new models for understanding of the mechanisms of aggression.

Expression of nuclear progesterone receptors (nPRs), membrane progesterone receptors (mPRs) and progesterone receptor membrane components (PGRMCs) in the human endometrium after 6 months levonorgestrel low dose intrauterine therapy

The classical steroid receptors (nuclear receptors), including those for progesterone (nPRs), are thoroughly characterized. The knowledge about so-called non-genomic effects, which are mediated by extra-nuclear initiated signals, has increased immensely the last decades. In a previous clinical study of endometrial hyperplasia, we observed that the antiproliferative progestin effect persisted after 3 months treatment with levonorgestrel (LNG) intrauterine system (IUS) even with a complete downregulation of nPRs. This raised the question of what other mechanisms than signaling through nPRs could explain such an observation. In the present study, RT-qPCR was employed to characterize mRNA expression for nPRs, membrane progesterone receptors (mPRs) and progesterone receptor membrane components (PGRMCs) in women (n = 42) with endometrial hyperplasia that received intrauterine low dose LNG for 6 months. At the end of this period endometrial tissue showed that nPRs were virtually completely downregulated (≈ 10 % of baseline) whereas the levels of remaining mPRs, subtype-α, -β and -γ were 76 %, 59 % and 73 % of baseline, respectively. PGRMC1 was downregulated to 15 % of baseline, in contrast to PGRMC2, which was upregulated to about 30 % above baseline. We used human cancer cells from uterine cervix (C-4I cells) as control. Progesterone caused a concentration-dependent antiproliferative effect but in several and separate studies, we were unable to detect nPRs (immunocytochemistry) in the C-4I cells. The use of RT-qPCR showed that nPRs were undetectable in C-4I cells, in contrast to mPRs and PGRMCs with a distinct mRNA expression. The present study suggests that mPRs and/or PGRMCs preserve the antiproliferative effect of LNG in the human endometrium and are responsible for the concentration-dependent antiproliferative effect of progesterone in C-4I cells.

Antiproliferative effect of mifepristone (RU486) on human neuroblastoma cells (SK-N-SH): in vitro and in vivo studies.

RU486 (mifepristone), a glucocorticoid and progesterone receptor antagonist, has been reported to exert antiproliferative effects on tumor cells. Experiments were performed to analyze the effects of RU486 on the proliferation of the human neuroblastoma, both in vitro and in vivo, using the human neuroblastoma SK-N-SH cell line. The exposure in vitro of SK-N-SH cells to RU486 revealed a dose-dependent inhibition of 3H-thymidine incorporation due to a rapid but persistent inhibition of MAPKinase activity and ERK phosphorylation. A significant decrease of SK-N-SH cell number was evident after 3, 6, and 9 days of treatment (up to 40% inhibition), without evident cell death. The inhibitory effect exerted by RU486 was not reversed by the treatment of the cells with dexamethasone or progesterone. Moreover, RU486 induced a shift in SK-N-SH cell phenotypes, with an almost complete disappearance of the neuronal-like and a prevalence of the epithelial-like cell subtypes. Finally, the treatment with RU486 of nude mice carrying a SK-N-SH cell xenograft induced a strong inhibition (up to 80%) of tumor growth. These results indicated a clear effect of RU486 on the growth of SK-N-SH neuroblastoma cells that does not seem to be mediated through the classical steroid receptors. RU486 acted mainly on the more aggressive component of the SK-N-SH cell line and its effect in vivo was achieved at a concentration already used to inhibit oocyte implantation.

Role of Sex and GPER in Renal Damage Induced by Ang II Hypertension

The protective cardiovascular effects of estrogen are mediated by both the classic steroid receptors (ERα/β) and the novel G protein‐coupled estrogen receptor (GPER). We previously showed that genetic deletion of GPER does not alter the pressor response to Ang II but exacerbates pulse pressure and resistance artery contractility. The objective of the current study was to assess whether G protein‐coupled estrogen receptor (GPER) deletion is associated with evidence of renal damage in mice with intact ERα/β signaling. Male (M) and female (F) wildtype (wt) and GPER knockout (ko) mice were infused with Ang II (700 ng/kg/min) for two weeks. Kidneys were weighed, formalin‐fixed, and paraffin‐embedded. Renal damage was assessed in 4 mm sections mounted onto slides. Renal vascular fibrosis was quantified as percent of pixels with positive Masson's Trichrome staining, and renal infiltration was scored on a scale of 1–5 in sections stained with hematoxylin & eosin. Statistical analysis was completed using two‐way ANOVA. Kidney weights in Ang II‐infused mice were significantly higher in males (P< 0.0001) but were not impacted by GPER deletion (P=0.16; Fwt: 6.3 ± 0.2, Fko 6.1 ± 0.1, Mwt 7.6 ± 0.3, Mko 7.2 ± 0.2 mg/g body weight, n=7–9/group). Renal vascular fibrosis was not significantly affected by sex (P=0.29) or genotype (P=0.93). Interstitial infiltration was observed in the medulla, but there was no effect of sex (P=0.24) or genotype (P=0.58). Our findings indicate that neither sex nor GPER deletion significantly impacted renal damage in response to two week Ang II infusion. Future studies will determine whether sex and GPER play a role in renal damage when Ang II hypertension is induced for longer than two weeks.Support or Funding InformationFunding was provided by NIH HL133619 to SHL. The STRIDE Fellowship is supported by the American Physiological Society and NIH HL115473.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Role of GPER in the anterior pituitary gland focusing on lactotroph function.

Ovarian steroids control a variety of physiological functions. They exert actions through classical nuclear steroid receptors, but rapid non-genomic actions through specific membrane steroid receptors have been also described. In this study, we demonstrate that the G-protein-coupled estrogen receptor (GPER) is expressed in the rat pituitary gland and, at a high level, in the lactotroph population. Our results revealed that ~40% of the anterior pituitary cells are GPER positive and ~35% of the lactotrophs are GPER positive. By immunocytochemical and immuno-electron-microscopy studies, we demonstrated that GPER is localized in the plasmatic membrane but is also associated to the endoplasmic reticulum in rat lactotrophs. Moreover, we found that local Gper expression is regulated negatively by 17β-estradiol (E2) and progesterone (P4) and fluctuates during the estrus cycle, being minimal in proestrus. Interestingly, lack of ovarian steroids after an ovariectomy (OVX) significantly increased pituitary GPER expression specifically in the three morphologically different subtypes of lactotrophs. We found a rapid estradiol stimulatory effect on PRL secretion mediated by GPER, both in vitro and ex vivo, using a GPER agonist G1, and this effect was prevented by the GPER antagonist G36, demonstrating a novel role for this receptor. Then, the increased pituitary GPER expression after OVX could lead to alterations in the pituitary function as all three lactotroph subtypes are target of GPER ligand and could be involved in the PRL secretion mediated by GPER. Therefore, it should be taken into consideration in the response of the gland to an eventual hormone replacement therapy.

Abstract LB-B04: Development of a first-in-class leukemia inhibitory factor (LIF)/LIFR inhibitor, EC359 for targeted therapy

Abstract Background: An IL-6 family member, leukemia inhibitory factor (LIF), is a pleotropic cytokine involved in multiple cellular signaling and pathophysiology of various malignancies including cancer. Overexpression of LIF is significantly correlated with advanced tumor stage, larger tumor size and worse relapse free survival rate. The objective of present study to develop and characterize next generation steroidal LIF/LIFR inhibitor based on our first LIF inhibitor, EC330. In this study, we optimized EC330 by synthetic modifications and generated EC359 to reduce its binding to classical steroid receptors and to improve its oral bioavailability. Material and methods: In silico docking studies were used to identify putative interaction of EC359 and LIF/LIFR receptor complex. We confirmed binding of EC359 to LIFR using surface plasmon resonance (SPR). Biophysical and biological characterization was performed by measuring cytotoxicity in various cancer cell lines and anchorage-independent colony assays. Specificity to LIF/LIFR was measured by GST pull-down assay and by SPR using commercially available recombinant proteins of LIF and LIFR. In vivo efficacy and toxicity was tested using syngeneic mice tumors and xenograft models. Results: EC359 showed cytotoxicity in various cancer cells at low nano-molar range, blocked formation of colonies in soft agar and inhibited triple negative breast cancer (TNBC) stem cells. Physical direct-interaction was confirmed by SPR which showed EC359 binding to LIFR with an affinity of 81μM. EC359 showed cytoskeletal disruption and targeting cancer-associated fibroblasts (CAFs) through inhibition of alpha-SMA but not beta-tubulin. Blockade of LIF-LIFR interaction reduced the STAT3 phosphorylation, mTOR and further downstream signaling cascades. In vivo, EC359 treatment (1 and 5mg/kg) dose dependently reduced tumor burden in both TNBC xenograft and murine syngeneic MM51 models. Pharmacologically, EC359 exhibits a high oral bioavailability and long half-life in rats with a wide therapeutic window. Conclusions: Our findings establish EC359 as a novel LIF/LIFR targeting drug with therapeutic perspectives for patients with advanced primary tumors. LIF/LIFR targeting may result in the blockade of JAK- STAT signaling pathway as well as cancer fibroblast associated pro invasive tumor microenvironment in regular as well as therapy resistant tumors. Citation Format: Hareesh B. Nair, Bindu Santhamma, Suryavathi Viswanadhapalli, Gangadhara R. Sareddy, Xinlei Pan, Vijaya Manthati, Ratna K. Vadlamudi, Murali Ramachandran, Klaus J. Nickisch. Development of a first-in-class leukemia inhibitory factor (LIF)/LIFR inhibitor, EC359 for targeted therapy [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B04.

Rare genetic variants in the sodium-dependent organic anion transporter SOAT (SLC10A6): Effects on transport function and membrane expression

Sulfo-conjugated steroid hormones, such as dehydroepiandrosterone sulfate (DHEAS), pregnenolone sulfate or estrone-3-sulfate are abundant in the body, but are biologically inactive at classical androgen and estrogen steroid receptors. However, after carrier-mediated import and de-conjugation by the steroid sulfatase, these compounds participate in the overall steroid regulation of reproductive organs. The sodium-dependent organic anion transporter SOAT, coded by the SLC10A6 gene, is specific for the transport of steroid sulfates and is highly expressed in testicular germ cells, including pachytene spermatocytes, secondary spermatocytes, and round spermatids. Therefore, SOAT is supposed to be involved in the regulation of spermatogenesis and male fertility. In the present study, the SLC10A6 gene was analyzed for rare genetic variants, which might affect transport function or membrane expression of SOAT. Among the 31 SOAT variants analyzed, L44P, Q75R, P107L, G109S, S112F, N113K, S133F, G241D, G263E, G294R, and Y308N showed no transport activity for DHEAS at all. In the case of P107L, G241D, G263E, and Y308N, this was most likely due to significantly reduced expression in the plasma membrane. Other variants are located directly at (Q75R, S112F, N113K) or close to (G109S, S133F, and G263E) the supposed SOAT Na+ binding sites and thus could disable the sodium-coupled transport cycle. If these loss-of-function SOAT variants are more frequent in men with impaired spermatogenesis or infertility needs further investigation.

Effects of Subchronic Finasteride Treatment and Withdrawal on Neuroactive Steroid Levels and Their Receptors in the Male Rat Brain

The enzymatic conversion of progesterone and testosterone by the enzyme 5alpha-reductase exerts a crucial role in the control of nervous function. The effects of finasteride in the brain, an inhibitor of this enzyme used for the treatment of human benign prostatic hyperplasia and androgenic alopecia, have been poorly explored. Therefore, the effects of a subchronic treatment with finasteride at low doses (3 mg/kg/day) and the consequences of its withdrawal on neuroactive steroid levels in plasma, cerebrospinal fluid and some brain regions as well as on the expression of classical and non-classical steroid receptors have been evaluated in male rats. After subchronic treatment (i.e., for 20 days) the following effects were detected: (i) depending on the compartment considered, alteration in the levels of neuroactive steroids, not only in 5alpha-reduced metabolites but also in its precursors and in neuroactive steroids from other steroidogenic pathways and (ii) an upregulation of the androgen receptor in the cerebral cortex and beta3 subunit of the GABA-A receptor in the cerebellum. One month after the last treatment (i.e., withdrawal period), some of these effects persisted (i.e., the upregulation of the androgen receptor in the cerebral cortex, an increase of dihydroprogesterone in the cerebellum, a decrease of dihydrotestosterone in plasma). Moreover, other changes in neuroactive steroid levels, steroid receptors (i.e., an upregulation of the estrogen receptor alpha and a downregulation of the estrogen receptor beta in the cerebral cortex) and GABA-A receptor subunits (i.e., a decrease of alpha 4 and beta 3 mRNA levels in the cerebral cortex) were detected. These findings suggest that finasteride treatment may have broad consequences for brain function.

Abstract 079: G Protein-Coupled Estrogen Receptor Deletion Exacerbates Pulse Pressure in Female but not Male Hypertensive Mice

The protective cardiovascular effects of estrogen are mediated by both the classic steroid receptors (ERα/β) and the novel G protein-coupled estrogen receptor (GPER). Our previous work demonstrates a role for GPER in the beneficial effects of estrogen on blood pressure, vascular tone, end organ damage, and aortic remodeling in hypertensive females, due to both direct vasodilatory effects and local regulation of the renin-angiotensin system. Therefore, we hypothesized that genetic deletion of GPER in female mice exacerbates Ang II-induced hypertension and associated tissue damage. Male (M) and female (F) wt and GPER ko mice were implanted with radiotelemetry probes at 11-13 weeks of age to measure baseline blood pressure before infusing Ang II (700 ng/kg/min) for two weeks. MAP (in mmHg) was similar at baseline (F-wt: 108 ± 2, n=4, F-ko: 105 ± 2, n=3, M-wt: 106 ± 4, n=3, and M-ko: 105 ± 0.5, n=3; P = 0.62), and after Ang II (F-wt: 136 ± 11, F-ko: 131 ± 3, M-wt: 148 ± 7, M-ko: 135 ± 5; P=0.51). Pulse pressure was significantly higher in response to Ang II in both sexes (*P<0.0001), and GPER deletion exacerbated this increase in females (30 ± 1 vs 43 ± 4 mmHg, *P<0.05) but not males (37 ± 3 vs. 39 ± 4, P=0.61). Further evaluation of the circadian pattern revealed that pulse pressure was particularly higher in F-ko during the day (28 ± 1 vs. 40 ± 4 mmHg, *P<0.05). Moreover, F-ko mesenteric arteries exhibited enhanced contractility to both receptor-dependent (PGF2α, *P<0.05) and receptor-independent (KCl, *P<0.05) stimulation. Our findings indicate that in females with intact ERα/β signaling, GPER deletion does not alter the initial pressor response to Ang II but exacerbates pulse pressure and resistance artery contractility during hypertension. Pulse pressure is an indirect measure of arterial stiffness and an independent risk factor for adverse cardiovascular events. While pulse pressure increases with aging in both sexes, this increase is markedly exacerbated in women. Our results indicate that loss of endogenous GPER activation due to low circulating estrogen may underlie increased pulse pressure in aging postmenopausal women.

English

For citation purposes: Laurentino S, Pinto P, Correia S, Cavaco JE, Canario AVM, Socorro S. Structural variants of sex steroid hormone receptors in the testis: from molecular biology to physiological roles. OA Biotechnology 2012 Dec 17;1(2):4. Licensee OA Publishing London 2012. Creative Commons Attribution License (CC-BY) Abstract Introduction Sex steroid hormones, androgens and oestrogens regulate diverse physiological processes by interacting with their intracellular protein receptors and modulating the expression of target genes. Classical sex steroid hormone receptors belong to the nuclear receptor superfamily, which forms the largest known family of transcription factors in eukaryotes. A common feature of sex steroid hormone receptors genes is the incidence of alternative splicing, a process that generates multiple variants from a single mRNA precursor molecule. This process facilitates the production of functionally distinct proteins and contributes to proteome diversity in higher eukaryotes. Herein we will critically review current information about the diversity of oestrogen receptors and androgen receptors variants, discussing their structural features and physiological functions. Conclusion The identification of structural variants of both ERs and ARs in healthy testis and a broad range of vertebrate species, highlights the newly revealed complexity of SSHRs signalling mechanisms in this tissue. Structural variants of sex steroid hormone receptors in the testis: from molecular biology to physiological roles

Age-related changes in neuroactive steroid levels in 3xTg-AD mice

Although neuroactive steroids exert neuroprotective actions in different experimental models of neurodegenerative diseases, including those of Alzheimer's disease (AD), their relationships with aged related physiologic and pathologic brain changes remain to be clarified. In this study the levels of pregnenolone, dehydroepiandrosterone, progesterone, dihydroprogesterone, tetrahydroprogesterone, isopregnanolone, testosterone, dihydrotestosterone, 5α-androstane-3α,17β-diol, 5α-androstane-3β,17β-diol, 17α-estradiol, and 17β-estradiol were assessed in the limbic region of young adult (7 months) and aged (24 months) male wild type and triple transgenic AD mice. Age related neuropathological changes in AD brains, such as β-amyloid accumulation and gliosis, were associated with modified levels of specific neuroactive steroids and particularly with changes in the levels of progesterone and testosterone metabolites. The altered levels of neuroactive steroids in aged AD brains might impact on the activation of neuroprotective signaling mediated by classic and nonclassic steroid receptors, like the gamma-aminobuttyric acid (GABA)-A receptor.

P4-02-09: Estrogen-Related Receptor a Mediates Insulin-Like Growth Factor-I Dependent Migration in Breast Cancer Cells.

Abstract The orphan nuclear estrogen-related receptors (ERR) have homology to steroid hormone receptors. Unlike classical steroid hormone receptors, ERRs do not have known ligands but are transcriptionally activated upon binding to nuclear receptor coregulators such as PGC1α, PGC1β, and PPRC1. ERRs regulate energy metabolism and are accordingly expressed in tissues that require high energy production. ERRs recognize their own ERRE (estrogen-related receptor response element) gene promoters, but can also activate transcription via ERE (estrogen receptor response element) promoters, representing the ability of ERRs to cross participate in ERα regulatory pathways in the absence of estrogen. Of the three family members (α,β,γ), ERRα is the most highly expressed in breast tissue. ERRα expression was found to be increased in ERα negative breast cancers and associated with poor prognoses. ERRα and its coactivators can increase the expression of a critical mediator of breast tumor angiogenesis and metastasis, VEGFA. We have previously shown that VEGFA is regulated by insulin and IGF receptor activation and hypothesized that ERRα may be a mediator of this finding. We therefore explored whether ERRα and its coactivators are necessary for IGF-I/insulin dependent regulation of VEGFA and cell migration. ERRα was expressed in breast cancer cell lines, but no correlation was observed with breast cancer subtypes. Reducing endogenous ERRα levels by shRNA reduced IGF-I dependent migration in MDA-MB-231 cells. These results were confirmed using an ERRα specific inverse agonist (XCT-790), which also inhibited MDA-MB-231 cell migration. Modulating ERRα mRNA levels via shRNA resulted in decreased VEGFA mRNA levels in MCF7L cells and increased VEGFA mRNA levels in MDA-MB-231 cells, while the inverse agonist XCT-790 caused an increase in VEGFA mRNA levels in both cell lines. Reducing ERRa levels did not affect the expression of the IGF1R, InsR, IRS-1, IRS-2, PI-3K-Akt-mTOR dependent signaling pathway. Neither ERRα protein nor mRNA levels were modulated by IGF-I or insulin. We conclude that ERRα is important for mediating IGF-I dependent migration, but have shown that ERRα is not directly regulated by the IGF signaling. We will next explore the role of ERRα's coregulators (PGC1α, PGC1β, and PPRC1) in the regulation of VEGFA by the IGF/insulin pathway given their central role in regulating ERRα's function. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-02-09.

Physiological consequences of membrane-initiated estrogen signaling in the brain

Many of the actions of 17beta-estradiol (E2) in the central nervous system (CNS) are mediated via the classical nuclear steroid receptors, ER(alpha) and ERbeta, which interact with the estrogen response element to modulate gene expression. In addition to the nuclear-initiated estrogen signaling, E2 signaling in the brain can occur rapidly within minutes prior to any sufficient effects on transcription of relevant genes. These rapid, membrane-initiated E2 signaling mechanisms have now been characterized in many brain regions, most importantly in neurons of the hypothalamus and hippocampus. Furthermore, our understanding of the physiological effects of membrane-initiated pathways is now a major field of interest in the hypothalamic control of reproduction, energy balance, thermoregulation and other homeostatic functions as well as the effects of E2 on physiological and pathophysiological functions of the hippocampus. Membrane signaling pathways impact neuronal excitability, signal transduction, cell death, neurotransmitter release and gene expression. This review will summarize recent findings on membrane-initiated E2 signaling in the hypothalamus and hippocampus and its contribution to the control of physiological and behavioral functions.

Steroid signaling activation and intracellular localization of sex steroid receptors

In addition to stimulating gene transcription, sex steroids trigger rapid, non-genomic responses in the extra-nuclear compartment of target cells. These events take place within seconds or minutes after hormone administration and do not require transcriptional activity of sex steroid receptors. Depending on cell systems, activation of extra-nuclear signaling pathways by sex steroids fosters cell cycle progression, prevents apoptosis, leads to epigenetic modifications and increases cell migration through cytoskeleton changes. These findings have raised the question of intracellular localization of sex steroid receptors mediating these responses. During the past years, increasing evidence has shown that classical sex steroid receptors localized in the extra-nuclear compartment or close to membranes of target cells induce these events. The emerging picture is that a process of bidirectional control between signaling activation and sex steroid receptor localization regulates the outcome of hormonal responses in target cells. This mechanism ensures cell cycle progression in estradiol-treated breast cancer cells, and its derangement might occur in progression of human proliferative diseases. These findings will be reviewed here together with unexpected examples of the relationship between sex steroid receptor localization, signaling activation and biological responses in target cells. We apologize to scientists whose reports are not mentioned or extensively discussed owing to space limitations.

ER-α36, a novel isoform of ER-α66, is commonly over-expressed in apocrine and adenoid cystic carcinomas of the breast

BackgroundER-α36 is a novel 36 kDa isoform of the full-length oestrogen receptor alpha (ER-α66). ER-α36 primarily localises to the cytoplasm and the plasma membrane, and responds to membrane-initiated oestrogen and...

Do Steroid Hormones Play a Role in the Etiology of Glioma?

Gliomas are the most common type of primary malignant brain tumor and have a very poor prognosis. Little is known, however, about the etiology of these tumors. Evidence from a number of sources suggests that endogenous steroid hormones may play a role in the development of gliomas. First, the descriptive epidemiology of glioma suggests a relative protection of females compared with males, particularly during the premenopausal years. Second, some gliomas and glioblastomas express estrogen receptors (ER), especially ERβ, as well as aromatase, the enzyme responsible for the conversion of testosterone to estradiol, and possibly other steroid hormone receptors. Third, experimental studies indicate that glioblastomas transplanted into animals grow at a slower rate in females compared with males. Finally, experimental studies show that estradiol, 2-methoxyestradiol, and a number of selective estrogen receptor modulators inhibit proliferation of gliomas and induce cell death. These hormonal agonists and antagonists may act either through classical steroid hormone receptors or independently of such receptors. In view of these findings, further clinical, experimental, and epidemiologic studies are needed to elucidate the role of steroid hormone agonists and antagonists in the development and proliferation of glioma. If hormonal pathways are involved in gliomagenesis, this could eventually lead to the design of preventive strategies.

Minireview: Extranuclear Steroid Receptors: Roles in Modulation of Cell Functions

Steroid receptors existing outside the nucleus are increasingly being recognized in many organs and cell types, impacting the biology of bone, the heart and blood vessels, and the central nervous system. Some controversy exists as to the nature of the receptors at the plasma membrane. However, compelling evidence has been advanced that at least some classical steroid receptors mediate steroid ligand actions originating as signaling from the cell surface. Here I review the recent findings in this evolving field emphasizing the in vivo impact of these receptor pools with a focus on estrogen receptors.

Minireview: Rapid Actions of Sex Steroids in the Endothelium

The endothelium is a dynamic interface between the blood vessel and the circulating blood that plays a pivotal role in vascular homeostasis. As such, studies on sex steroid regulation of endothelial function are critical to understanding the role of sex steroids in cardiovascular health and disease. The classical model of steroid action involves liganded steroid receptors binding to specific response elements on target genes to regulate gene transcription. In whole organisms, the time lag between steroid administration and observable effects produced by newly synthesized protein is typically in the order of hours to days. And yet, some effects of steroids, such as vasodilatation, occur within seconds to minutes of steroid administration. Studies in multiple cell types have also shown that steroids can cause the rapid initiation of multiple signaling cascades and second messenger systems, prompting investigations into alternate, transcription independent mechanisms of steroid action. Studies of the endothelium over the past two decades have revealed fundamental mechanisms in rapid sex steroid signaling. In particular, endothelium-dependent vasodilatation by estradiol-induced activation of endothelial nitric oxide synthase has proven to be an uniquely informative model to study sex steroid signaling via classical sex steroid receptors localized to the cell membrane. Despite the complexity of feedback and cross talk between rapid sex steroid signaling and other modes of steroid action, recent studies in this field are facilitating the development of steroidal drugs that selectively target the ability of sex steroids to initiate signaling cascades.