Rapid non-genomic activation of cytosolic cyclic AMP-dependent protein kinase activity and [Ca(2+)](i) by 17beta-oestradiol in female rat distal colon

Sex Differences in Colon Cancer: Genomic and Nongenomic Signalling of Oestrogen

Colon cancer (CRC) is a prevalent malignancy that exhibits distinct differences in incidence, prognosis, and treatment responses between males and females. These disparities have long been attributed to hormonal differences, particularly the influence of oestrogen signalling. This review aims to provide a comprehensive analysis of recent advances in our understanding of the molecular mechanisms underlying sex differences in colon cancer and the protective role of membrane and nuclear oestrogen signalling in CRC development, progression, and therapeutic interventions. We discuss the epidemiological and molecular evidence supporting sex differences in colon cancer, followed by an exploration of the impact of oestrogen in CRC through various genomic and nongenomic signalling pathways involving membrane and nuclear oestrogen receptors. Furthermore, we examine the interplay between oestrogen receptors and other signalling pathways, in particular the Wnt/β-catenin proliferative pathway and hypoxia in shaping biological sex differences and oestrogen protective actions in colon cancer. Lastly, we highlight the potential therapeutic implications of targeting oestrogen signalling in the management of colon cancer and propose future research directions to address the current gaps in our understanding of this complex phenomenon.

Moderate intensity continuous training reverses the detrimental effects of ovariectomy on RyR1 phosphorylation in rat skeletal muscle

High 17β-Estradiol (E2) concentrations in isolated ventricular myocytes as well as a lack of ovarian hormones in cardiac muscle of ovariectomized (OVX) rodents has been shown to lead to arrhythmogenic effects by inducing post-translational modifications, including phosphorylation of the sarcoplasmic reticulum (SR) Ca²⁺ release channel ryanodine receptor-2 (RyR2). The effects of estrogens on the phosphorylation status of the RyR1 in skeletal muscle have not been investigated before. Furthermore, while high intensity exercise has been shown to increase RyR phosphorylation, there is no data on the effects of moderate intensity continuous training (MICT). The aims of the study were to investigate the effects of a 3-day treatment with low (1 nM, moderate (5 nM) and high (10 nM, 100 nM) E2 concentrations on RyR1 mRNA and protein expression and phosphorylation status (pRyRSer²⁸⁴⁴) in cultured C2C12 myotubes and to study the effects of OVX on RyR1 expression and phosphorylation in rat skeletal muscle in combination with 3 weeks of MICT. Treatment with low, physiological E2 concentrations reduced dihydropyridine receptor (DHPR) and RyR1 mRNA content in C2C12 myotubes compared to untreated control cells, whereas RyR1 protein phosphorylation (pRyRSer²⁸⁴⁴) was significantly increased after treatment with high, non-physiological E2 concentrations (p ≤ 0.05). RyR1 protein content (p ≤ 0.05) and pRyRSer²⁸⁴⁴ (p ≤ 0.05) were significantly elevated in skeletal muscle of OVX vs. sham-operated rats. Importantly, pRyRSer²⁸⁴⁴ levels were similar to sham-operated controls in OVX rats after MICT (OVX vs. OVX + MICT, p ≤ 0.05). Our results indicate, that one of the actions of estrogens is to alter skeletal muscle Ca²⁺ homeostasis by modulating the expression and phosphorylation of the RyR1 in skeletal muscle. Notably, regular MICT was able to counteract RyR1 phosphorylation in skeletal muscle of OVX rats.

Equilin displays similar endothelium-independent vasodilator potential to 17β-estradiol regardless of lower potential to inhibit calcium entry

Conjugated equine estrogens (CEE) have been widely used by women who seek to relieve symptoms of menopause. Despite evidence describing protective effects against risk factors for cardiovascular diseases by naturally occurring estrogens, little is known about the vascular effects of equilin, one of the main components of CEE and not physiologically present in women. In this regard, the present study aims to compare the vascular effects of equilin in an experimental model of hypertension with those induced by 17β-estradiol. Resistance mesenteric arteries from female spontaneously hypertensive rats (SHR) were used for recording isometric tension in a small vessel myograph. As effectively as 17β-estradiol, equilin evoked a concentration-dependent relaxation in mesenteric arteries from female SHRs contracted with KCl, U46619, PDBu or ET-1. Equilin-induced vasodilation does not involve classical estrogen receptor activation, since the estrogen receptor antagonist (ICI 182,780) failed to inhibit relaxation in U46619-precontracted mesenteric arteries. Vasorelaxation was not affected by either endothelium removal or by inhibiting the release or action of endothelium-derived factors. Incubation with L-NAME (NOS inhibitor), ODQ (guanylyl cyclase inhibitor) or KT5823 (inhibitor of protein kinase G) did not affect equilin-induced relaxation. Similarly, indomethacin (COX inhibitor) or blockage of potassium channels with tetraethylammonium, glibenclamide, 4-aminopyridine, or ouabain did not affect equilin-induced relaxation. Inhibitors of adenylyl cyclase SQ22536 or protein kinase A (KT5720) also had no effects on equilin-induced relaxation. While 17β-estradiol inhibited calcium (Ca²⁺) -induced contractions in high-K⁺ depolarization medium in a concentration-dependent manner, equilin induced a slight rightward-shift in the contractile responses to Ca²⁺. Comparable pattern of responses were observed in the concentration-response curves to (S)-(-)-Bay K 8644, a L-type Ca²⁺ channel activator. Equilin was unable to block the transitory contraction produced by caffeine-induced Ca²⁺ release from intracellular stores. In conclusion, equilin blocks L-type Ca²⁺ channels less effectively than 17β-estradiol. Despite its lower effectiveness, equilin equally relaxes resistance mesenteric arteries by blocking Ca²⁺ entry on smooth muscle.

Rapid estrogen actions on ion channels: A survey in search for mechanisms

A survey of nearly two hundred reports shows that rapid estrogenic actions can be detected across a range of kinds of estrogens, a range of doses, on a wide range of tissue, cell and ion channel types. Striking is the fact that preparations of estrogenic agents that do not permeate the cell membrane almost always mimic the actions of the estrogenic agents that do permeate the membrane. All kinds of estrogens, ranging from natural ones, through receptor modulators, endocrine disruptors, phytoestrogens, agonists, and antagonists to novel G-1 and STX, have been reported to be effective. For actions on specific types of ion channels, the possibility of opposing actions, in different cases, is the rule, not the exception. With this variety there is no single, specific action mechanism for estrogens per se, although in some cases estrogens can act directly or via some signaling pathways to affect ion channels. We infer that estrogens can bind a large number of substrates/receptors at the membrane surface. As against the variety of subsequent routes of action, this initial step of the estrogen's binding action is the key.

Nutrient availability, the microbiome, and intestinal transport during pregnancy

Adequate adaptation of the gastrointestinal tract is important during pregnancy to ensure that the increased metabolic demands by the developing fetus are met. These include changes in surface area mediated by villus hypertrophy and enhanced functional capacity of individual nutrient receptors, including those transporting glucose, fructose, leucine, and calcium. These processes are regulated either by the enhanced nutrient demand or are facilitated by changes in the secretion of pregnancy hormones. Our review also covers recent research into the microbiome, and how pregnancy could lead to microbial adaptations, which are beneficial to the mother, yet are also similar to those seen in the metabolic syndrome. The potential role of diet in modulating the microbiome during pregnancy, as well as the potential for the intestinal microbiota to induce pregnancy complications, are examined. Gaps in the current literature are highlighted, including those where only historical evidence is available, and we suggest areas that should be a priority for further research. In summary, although a significant degree of adaptation has been described, there are both well-established processes and more recent discoveries, such as changes within the maternal microbiome, that pose new questions as to how the gastrointestinal tract effectively adapts to pregnancy, especially in conjunction with maternal obesity.

Ca2+ channel subunit α 1D promotes proliferation and migration of endometrial cancer cells mediated by 17β-estradiol via the G protein-coupled estrogen receptor

Calcium and calcium channels are closely related to the estrogen-induced nongenomic effect of endometrial carcinoma, but the specific role of calcium channels is unknown. This study aimed to explore the expression and the biologic effect of the L-type calcium channel in endometrial carcinoma cells and to clarify the molecular mechanism of the relationship between L-type calcium channels and estrogen. The immunohistochemical results showed that Ca(2+) channel subunit α 1D (Cav1.3) expression was high in atypical hyperplasia (1.90 ± 0.35) and endometrial carcinoma tissues (2.05 ± 0.82) but weak (0.80 ± 0.15) in benign endometrial tissues (P < 0.05). Treatment with 17β-estradiol rapidly increased Cav1.3 expression in a dose- and time-dependent manner, and 100 nM cell-impermeable β-estradiol-6-(O-carboxymethyl)oxime:bovine serum albumin also promoted Cav1.3 expression. Transfection with small interfering RNA against G protein-coupled estrogen receptor (GPER) suppressed estrogen-induced up-regulation of Cav1.3 compared with control cells and markedly reduced the estrogen-induced phosphorylation of ERK1/2 and CREB. Knocking down the Cav1.3 significantly suppressed estrogen-stimulated Ca(2+) influx, cell proliferation, and migration in endometrial cancer cells. Taken together, Cav1.3 was overexpressed in atypical hyperplasia and endometrial carcinoma, and the estrogen-induced phosphorylation of downstream molecular ERK1/2 and CREB is the result of activation of the GPER pathway. L-type channel Cav1.3 is required for estrogen-stimulated Ca(2+) influx and contributes broadly to the development of endometrial cancer. The Cav1.3 channel may be a new target for endometrial carcinoma treatment.

Targeting estrogen receptors for the treatment of Alzheimer's disease

The significantly higher incidence of Alzheimer's disease (AD) in women than in men has been attributed to loss of estrogen and a variety of related mechanisms at the molecular, cellular, and hormonal levels, which subsequently elucidate neuroprotective roles of estrogen against AD-related pathology. Recent studies have proposed that beneficial effects of estrogen on AD are directly linked to its ability to reduce amyloid-β peptides and tau aggregates, two hallmark lesions of AD. Despite high expectations, large clinical trials with postmenopausal women indicated that the beneficial effects of estrogen therapies were insignificant and, in fact, elicited adverse effects. Here, we review the current status of AD prevention and treatment using estrogens focusing on recent understandings of their biochemical links to AD pathophysiology. This review also discusses development of selective ligands that specifically target either estrogen receptor α (ERα) or ERβ isoforms, which are potentially promising strategies for safe and efficient treatment of AD.

Non-genomic estrogen regulation of ion transport and airway surface liquid dynamics in cystic fibrosis bronchial epithelium

Male cystic fibrosis (CF) patients survive longer than females and lung exacerbations in CF females vary during the estrous cycle. Estrogen has been reported to reduce the height of the airway surface liquid (ASL) in female CF bronchial epithelium. Here we investigated the effect of 17β-estradiol on the airway surface liquid height and ion transport in normal (NuLi-1) and CF (CuFi-1) bronchial epithelial monolayers. Live cell imaging using confocal microscopy revealed that airway surface liquid height was significantly higher in the non-CF cells compared to the CF cells. 17β-estradiol (0.1–10 nM) reduced the airway surface liquid height in non-CF and CF cells after 30 min treatment. Treatment with the nuclear-impeded Estrogen Dendrimer Conjugate mimicked the effect of free estrogen by reducing significantly the airway surface liquid height in CF and non-CF cells. Inhibition of chloride transport or basolateral potassium recycling decreased the airway surface liquid height and 17β-estradiol had no additive effect in the presence of these ion transporter inhibitors. 17β-estradiol decreased bumetanide-sensitive transepithelial short-circuit current in non-CF cells and prevented the forskolin-induced increase in ASL height. 17β-estradiol stimulated an amiloride-sensitive transepithelial current and increased ouabain-sensitive basolateral short-circuit current in CF cells. 17β-estradiol increased PKCδ activity in CF and non-CF cells. These results demonstrate that estrogen dehydrates CF and non-CF ASL, and these responses to 17β-estradiol are non-genomic rather than involving the classical nuclear estrogen receptor pathway. 17β-estradiol acts on the airway surface liquid by inhibiting cAMP-mediated chloride secretion in non-CF cells and increasing sodium absorption via the stimulation of PKCδ, ENaC and the Na⁺/K⁺ATPase in CF cells.

Estrogen regulation of epithelial ion transport: Implications in health and disease

Estrogen, 17β-estradiol (E2), has been shown to modulate the activity of ion channels in a diverse range of epithelial tissues. The channel activation or inhibition responses to E2 are often rapid, occurring in seconds to minutes, independent of protein synthesis and gene transcription ('non-genomic' response). These rapid effects of E2 require activation of specific protein kinases or changes in intracellular calcium and pH which in turn modulate the conductance, open probability or number of channels in the plasmamembrane. Estrogen has also been shown to affect the expression of ion transporters over days ('genotropic' response) causing long-term sustained changes in transepithelial ion transport. It is now accepted that so called non-genomic responses are not stand-alone events and are necessary to prime the latent genomic response and even be critical for the full latent response to occur. In a number of epithelia the non-genomic and genotropic responses to estrogen are sex-specific and variable in potency and sensitivity to E2 depending on the stage of the estrous cycle. Of increasing interest is the effect these rapid and latent actions of E2 on ion transporters have on the physiological functions of epithelia. For example, estrogen regulation of a class of voltage-gated K(+) channels (KCNQ1) can determine the rate of Cl(-) secretion in the intestine. In whole-body terms, the combined effects of estrogen on a variety of ion channels which control fluid and electrolyte transport in the kidney, intestine and lung may be necessary for endometrial expansion and implantation of the blastocyte.

Non-genomic actions of aldosterone: from receptors and signals to membrane targets

In tissues which express the mineralocorticoid receptor (MR), aldosterone modulates the expression of membrane targets such as the subunits of the epithelial Na(+) channel, in combination with important signalling intermediates such as serum and glucocorticoid-regulated kinase-1. In addition, the rapid 'non-genomic' activation of protein kinases and secondary messenger signalling cascades has also been detected in aldosterone-sensitive tissues of the nephron, distal colon and cardiovascular system. These rapid actions are variously described as being coupled to MR or to an as yet unidentified, membrane-associated aldosterone receptor. The rapidly activated signalling cascades add a level of fine-tuning to the activity of aldosterone-responsive membrane transporters and also modulate the aldosterone-induced changes in gene expression through receptor and transcription factor phosphorylation.

Estrogen inhibits chloride secretion caused by cholera and Escherichia coli enterotoxins in female rat distal colon

Excessive Cl(-) secretion is the driving force for secretory diarrhea. 17β-Estradiol has been shown to inhibit Cl(-) secretion in rat distal colon through a nongenomic pathway. We examined whether 17β-estradiol inhibits Cl(-) secretion in an animal model of secretory diarrhea and the downstream effectors involved. The effect of 17β-estradiol on cholera toxin and heat-stable enterotoxin induced Cl(-) secretion in rat colonic mucosal sheets was studied by current-voltage clamping. Selective permeabilization of apical or basolateral membranes with amphotericin B or nystatin was used to isolate basolateral K(+) channel and apical Cl(-) channel activity, respectively. 17β-Estradiol dose-dependently inhibited secretory responses to both toxins with IC(50) values of approximately 1nM. This effect was female-gender specific, with no inhibition observed in male tissues. 17β-Estradiol responses were insensitive to the pure anti-estrogen ICI 182,720. 17β-Estradiol exerted its effects downstream of enterotoxin-induced production of second messengers (cAMP and cGMP) but was dependent on PKCδ activation. In nystatin-permeabilized tissues, apical Cl(-) currents were unaffected by 17β-estradiol treatment while basolateral K(+) current was profoundly inhibited by the hormone. This current was sensitive to the specific KCNQ1 channel inhibitors chromanol 293B and HMR-1556. In conclusion, 17β-estradiol inhibits enterotoxin-induced Cl(-) secretion via a PKCδ-dependent mechanism involving inhibition of basolateral KCNQ1 channels. These data elucidate mechanisms of 17β-estradiol inhibition of Cl(-) secretion induced by enterotoxins in intestinal epithelia, which may be relevant for the treatment of diarrheal diseases.

Redox control of protein kinase C: cell- and disease-specific aspects

Hormones, growth factors, electrical stimulation, and cell-cell interactions regulate numerous cellular processes by altering the levels of second messengers, thus influencing biochemical reactions inside the cells. The Protein Kinase C family (PKCs) is a group of serine/threonine kinases that are dependent on calcium (Ca(2+)), diacylglycerol, and phospholipids. Signaling pathways that induce variations on the levels of PKC activators have been implicated in the regulation of diverse cellular functions and, in turn, PKCs are key regulators of a plethora of cellular processes, including proliferation, differentiation, and tumorigenesis. Importantly, PKCs contain regions, both in the N-terminal regulatory domain and in the C-terminal catalytic domain, that are susceptible to redox modifications. In several pathophysiological conditions when the balance between oxidants, antioxidants, and alkylants is compromised, cells undergo redox stress. PKCs are cell-signaling proteins that are particularly sensitive to redox stress because modification of their redox-sensitive regions interferes with their activity and, thus, with their biological effects. In this review, we summarize the involvement of PKCs in health and disease and the importance of redox signaling in the regulation of this family of kinases.

Advances in understanding the relationship between estrogen and colorectal cancer

Colorectal cancer is a common malignancy. Its incidence and mortality significantly increase in recent years in China. Since McMichael and Potter proposed that exogenous estrogen could reduce the incidence of colon cancer in women in 1980s, the relationship between estrogen use and the incidence of colorectal cancer has been extensively studied. This paper reviews the recent advances in understanding the relationship between estrogen and colorectal cancer.

Genomic priming of the antisecretory response to estrogen in rat distal colon throughout the estrous cycle

The secretion of Cl(-) across distal colonic crypt cells provides the driving force for the movement of fluid into the luminal space. 17beta-Estradiol (E2) produces a rapid and sustained reduction in secretion in females, which is dependent on the novel protein kinase C delta (PKC delta) isozyme and PKA isoform I targeting of KCNQ1 channels. This sexual dimorphism in the E2 response is associated with a higher expression level of PKC delta in female compared with the male tissue. The present study revealed the antisecretory response is regulated throughout the female reproductive (estrous) cycle and is primed by genomic regulation of the kinases. E2 (1-10 nm) decreased cAMP-dependent secretion in colonic epithelia during the estrus, metestrus, and diestrus stages. A weak inhibition of secretion was demonstrated in the proestrus stage. The expression levels of PKC delta and PKA fluctuated throughout the estrous cycle and correlated with the potency of the antisecretory effect of E2. The expression of PKC delta and PKA were up-regulated by estrogen at a transcriptional level via a PKC delta-MAPK-cAMP response element-binding protein-regulated pathway indicating a genomic priming of the antisecretory response. PK Cdelta was activated by the membrane-impermeant E2-BSA, and this response was inhibited by the estrogen receptor antagonist ICI 182,780. The 66-kDa estrogen receptor-alpha isoform was present at the plasma membrane of female colonic crypt cells with a lower abundance found in male colonic crypts. The study demonstrates estrogen regulation of intestinal secretion both at a rapid and transcriptional level, demonstrating an interdependent relationship between both nongenomic and genomic hormone responses.

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.

Estrogen and gastrointestinal malignancy

The concept that E2 exerts an effect on the gastrointestinal tract is not new and its actions on intestinal mucosa have been investigated for at least three decades. An attempt to consolidate results of these investigations generates more questions than answers, thus suggesting that many unexplored avenues remain and that the full capabilities of this steroid hormone are far from understood. Evidence of its role in esophageal, gastric and gallbladder cancers is confusing and often equivocal. The most compelling evidence regards the protective role conferred by estrogen (or perhaps ERbeta) against the development and proliferation of colon cancer. Not only has the effect been described but also many mechanisms of action have been explored. It is likely that, along with surgery, chemotherapy and radiotherapy, hormonal manipulation will play an integral role in colon cancer management in the very near future.

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

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

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.

Oestrogen and the colon: potential mechanisms for cancer prevention

The role of oestrogen in oncogenesis has been examined extensively, especially in the context of breast cancer, and receptor modulators are an integral part of targeted treatment in this disease. The role of oestrogen signalling in colonic carcinoma is poorly understood. Men are more susceptible than women to colon cancer. Furthermore, hormone-replacement therapy affords an additive protective effect for postmenopausal women, and when these women do develop cancer, they typically have less aggressive disease. The discovery of a second oestrogen receptor (ERbeta) and its over expression in healthy human colon coupled with reduced expression in colon cancer suggests that this receptor might be involved. The underlying mechanism, however, remains largely unknown. In this Review, we discuss the various hypotheses presented in the published literature. We examine the cellular and molecular mechanisms through which oestrogen is purported to exert its protective influence, and we review the evidence available to support these claims.

Rapid effects of 17beta-estradiol on epithelial TRPV6 Ca2+ channel in human T84 colonic cells

The control of calcium homeostasis is essential for cell survival and is of crucial importance for several physiological functions. The discovery of the epithelial calcium channel Transient Receptor Potential Vaniloid (TRPV6) in intestine has uncovered important Ca(2+) absorptive pathways involved in the regulation of whole body Ca(2+) homeostasis. The role of steroid hormone 17beta-estradiol (E(2)), in [Ca(2+)](i) regulation involving TRPV6 has been only limited at the protein expression levels in over-expressing heterologous systems. In the present study, using a combination of calcium-imaging, whole-cell patch-clamp techniques and siRNA technology to specifically knockdown TRPV6 protein expression, we were able to (i) show that TRPV6 is natively, rather than exogenously, expressed at mRNA and protein levels in human T84 colonic cells, (ii) characterize functional TRPV6 channels and (iii) demonstrate, for the first time, the rapid effects of E(2) in [Ca(2+)](i) regulation involving directly TRPV6 channels in T84 cells. Treatment with E(2) rapidly (<5 min) enhanced [Ca(2+)](i) and this increase was partially but significantly prevented when cells were pre-treated with ruthenium red and completely abolished in cells treated with siRNA specifically targeting TRPV6 protein expression. These results indicate that when cells are stimulated by E(2), Ca(2+) enters the cell through TRPV6 channels. TRPV6 channels in T84 cells contribute to the Ca(2+) entry/signalling pathway that is sensitive to 17beta-estradiol.

17beta-estradiol rapidly mobilizes intracellular calcium from ryanodine-receptor-gated stores via a PKC-PKA-Erk-dependent pathway in the human eccrine sweat gland cell line NCL-SG3

We describe a novel rapid non-genomic effect of 17beta-estradiol (E2) on intracellular Ca2+ ([Ca2+]i) signalling in the eccrine sweat gland epithelial cell line NCL-SG3. E2 had no observable effect on basal [Ca2+]i, however exposure of cells to E2 in the presence of the microsomal Ca2+ ATPase pump inhibitor, thapsigargin, produced a secondary, sustained increase in [Ca2+]i compared to thapsigargin treatment alone, where cells responded with a transient single spike-like increase in [Ca2+]i. The E2-induced increase in [Ca2+]i was not dependent on the presence of extracellular calcium and was completely abolished by ryanodine (100 microM). The estrogen receptor antagonist ICI 182,780 (1 microM) prevented the E2-induced effects suggesting a role for the estrogen receptor in the release of [Ca2+]i from ryanodine-receptor-gated stores. The E2-induced effect on [Ca2+]i could also be prevented by the protein kinase C delta (PKCdelta)-specific inhibitor rottlerin (10 microM), the protein kinase A (PKA) inhibitor Rp-adenosine 3',5'-cyclic monophosphorothioate (200 microM) and the MEK inhibitor PD98059 (10 microM). We established E2 rapidly activates the novel PKC isoform PKCepsilon, PKA and Erk 1/2 MAPK in a PKCdelta and estrogen-receptor-dependent manner. The E2-induced effect was specific to 17beta-estradiol, as other steroids had no effect on [Ca2+]i. We have demonstrated a novel mechanism by which E2 rapidly modulates [Ca2+]i release from ryanodine-receptor-gated intracellular Ca2+ stores. The signal transduction pathway involves the estrogen receptor coupled to a PKC-PKA-Erk 1/2 signalling pathway.

The role of sex steroids in controlling pubertal growth

Longitudinal growth, which is primarily due to chondrocytic activity at the level of the epiphyseal growth plate, is influenced by many hormones and growth factors in an endocrine and paracrine manner. Their influence is even more complex during the accelerated growth period of puberty that accounts for about 20% of final adult height. Although abnormalities of growth during puberty are very common, the underlying mechanisms that govern the beginning and cessation of pubertal growth at the level of the growth plate are poorly understood. Sex steroids play a crucial role in pubertal growth both at the systemic level via the GH/IGF-1 axis and at the local level of the epiphyseal growth plate. In both sexes it is now accepted that oestrogen is the critical hormone in controlling growth plate acceleration and fusion. This paper reviews the mechanisms that influence pubertal growth and the problems that are associated with disorders of gonadal function.

Direct Binding and Activation of Protein Kinase C Isoforms by Aldosterone and 17β-Estradiol

Protein kinase C (PKC) is a signal transduction protein that has been proposed to mediate rapid responses to steroid hormones. Previously, we have shown aldosterone directly activates PKCα whereas 17β-estradiol activates PKCα and PKCδ; however, neither the binding to PKCs nor the mechanism of action has been established. To determine the domains of PKCα and PKCδ involved in binding of aldosterone and 17β-estradiol, glutathione S-transferase fusion recombinant PKCα and PKCδ mutants were used to perform in vitro binding assays with [3H]aldosterone and [3H]17β-estradiol. 17β-Estradiol bound both PKCα and PKCδ but failed to bind PKC mutants lacking a C2 domain. Similarly, aldosterone bound only PKCα and mutants containing C2 domains. Thus, the C2 domain is critical for binding of these hormones. Binding affinities for aldosterone and 17β-estradiol were between 0.5–1.0 nM. Aldosterone and 17β-estradiol competed for binding to PKCα, suggesting they share the same binding site. Phorbol 12,13-dybutyrate did not compete with hormone binding; furthermore, they have an additive effect on PKC activity. EC50 for activation of PKCα and PKCδ by aldosterone and 17β-estradiol was approximately 0.5 nM. Immunoblot analysis using a phospho-PKC antibody revealed that upon binding, PKCα and PKCδ undergo autophosphorylation with an EC50 in the 0.5–1.0 nm range. 17β-Estradiol activated PKCα and PKCδ in estrogen receptor-positive and -negative breast cancer cells (MCF-7 and HCC-38, respectively), suggesting estrogen receptor expression is not required for 17β-estradiol-induced PKC activation. The present results provide first evidence for direct binding and activation of PKCα and PKCδ by steroid hormones and the molecular mechanisms involved.

Female gender-specific inhibition of KCNQ1 channels and chloride secretion by 17beta-estradiol in rat distal colonic crypts

The estrogen sex steroid 17beta-estradiol rapidly inhibits secretagogue-stimulated cAMP-dependent Cl(-) secretion in the female rat distal colonic crypt by the inhibition of basolateral K(+) channels. In Ussing chamber studies, both the anti-secretory response and inhibition of basolateral K(+) current was shown to be attenuated by pretreatment with rottlerin, a PKCdelta-specific inhibitor. In whole cell patch-clamp analysis, 17beta-estradiol inhibited a chromanol 293B-sensitive KCNQ1 channel current in isolated female rat distal colonic crypts. Estrogen had no effect on KCNQ1 channel currents in colonic crypts isolated from male rats. Female distal colonic crypts expressed a significantly higher amount of PKCdelta in comparison to male tissue. PKCdelta and PKA were activated at 5 min in response to 17beta-estradiol in female distal colonic crypts only. Both PKCdelta- and PKA-associated with the KCNQ1 channel in response to 17beta-estradiol in female distal colonic crypts, and no associations were observed in crypts from males. PKA activation, association with KCNQ1, and phosphorylation of the channel were regulated by PKCdelta as the responses were blocked by pretreatment with rottlerin. Taken together, our experiments have identified the molecular targets underlying the anti-secretory response to estrogen involving the inhibition of KCNQ1 channel activity via PKCdelta- and PKA-dependent signaling pathways. This is a novel gender-specific mechanism of regulation of an ion channel by estrogen. The anti-secretory response described in this study provides molecular insights whereby estrogen causes fluid retention effects in the female during periods of high circulating plasma estrogen levels.

Role of protein kinase C in aldosterone-induced non-genomic inhibition of basolateral potassium channels in human colonic crypts

Aldosterone produces rapid, non-genomic, inhibition of basolateral intermediate conductance K(+) (IK(Ca)) channels in human colonic crypt cells but the intracellular second messengers involved are unclear. We therefore evaluated the role of protein kinase C (PKC) in aldosterone's non-genomic inhibitory effect on basolateral IK(Ca) channels in crypt cells from normal human sigmoid colon. Patch clamp studies revealed that in cell-attached patches, IK(Ca) channel activity decreased progressively to 38+/-8% (P<0.001) of the basal value 10 min after the addition of 1 nmol/L aldosterone, and decreased further to 23+/-6% (P<0.02) of the basal value 5 min after increasing the aldosterone concentration to 10 nmol/L. Pre-incubation of crypts with 1 micromol/L chelerythrine chloride or 1 micromol/L Gö 6976 (PKC inhibitors) prevented the inhibitory effect of aldosterone. Conversely, channel activity decreased to 60+/-9% (P<0.02) of the basal value 10 min after the addition of 500 nmol/L PMA (a PKC activator), whereas 4alpha-PMA (an inactive ester) had no effect. When aldosterone (10 nmol/L) and PMA were added together, IK(Ca) channel activity was inhibited to the same extent as with aldosterone alone. These results indicate that aldosterone's non-genomic inhibitory effect on the macroscopic basolateral K(+) conductance in human colonic crypts reflects PKC-mediated inhibition of IK(Ca) channels.

Estradiol activates mast cells via a non-genomic estrogen receptor-alpha and calcium influx

BACKGROUND

Allergic airway diseases are more common in females than in males during early adulthood. A relationship between female hormones and asthma prevalence and severity has been suggested, but the cellular and molecular mechanisms are not understood.

OBJECTIVE

To elucidate the mechanism(s) by which estrogens enhance the synthesis and release of mediators of acute hypersensitivity.

METHODS

Two mast cell/basophil cell lines (RBL-2H3 and HMC-1) and primary cultures of bone marrow derived mast cells, all of which naturally express estrogen receptor-alpha, were examined. Cells were incubated with physiological concentrations of 17-beta-estradiol with and without IgE and allergens. Intracellular Ca(2+) concentrations and the release of beta-hexosaminidase and leukotriene C(4) were quantified.

RESULTS

Estradiol alone induced partial release of the preformed, granular protein beta-hexosaminidase from RBL-2H3, BMMC and HMC-1, but not from BMMC derived from estrogen receptor-alpha knock-out mice. The newly synthesized LTC(4) was also released from RBL-2H3. Estradiol also enhanced IgE-induced degranulation and potentiated LTC(4) production. Intracellular Ca(2+) concentration increased prior to and in parallel with mediator release. Estrogen receptor antagonists or Ca(2+) chelation inhibited these estrogenic effects.

CONCLUSION

Binding of physiological concentrations of estradiol to a membrane estrogen receptor-alpha initiates a rapid onset and progressive influx of extracellular Ca(2+), which supports the synthesis and release of allergic mediators. Estradiol also enhances IgE-dependent mast cell activation, resulting in a shift of the allergen dose response.

Dietary genistein stimulates anion secretion across female murine intestine

Genistein, a naturally occurring isoflavone, augments in vitro epithelial anion transport via activation of the cystic fibrosis transmembrane conductance regulator chloride channel. In this study, we examined whether chronic dietary exposure to 600 mg/kg genistein (600 G) for 1 mo would stimulate anion secretion across wild-type (Wt, normal) murine intestine. Anion secretion was assessed in freshly excised segments of murine jejuna by measuring short circuit current (I(sc)) and comparing with jejunal segments from mice fed 0 mg/kg genistein (0 G). Basal and forskolin-stimulated anion secretions were augmented (P < 0.05) in female but not in male mice fed 600 G, compared with their counterparts fed 0 G. Serum genistein concentrations were greater in both female and male mice fed 600 G (approximately 3.5-6.9 micromol/L) than those fed 0 G (approximately 100 nmol/L). Anion substitution experiments and bumetanide-sensitivity demonstrated that chloride was the major anion mediating the increased secretion. A smaller bicarbonate component was not augmented by consumption of the genistein diet. These data indicate that chronic exposure to dietary genistein stimulates a sex-dependent increase in basal and forskolin-stimulated chloride secretion across murine intestine.

Neuronal differentiation of PC12 cells abolishes the expression of membrane androgen receptors

Sex steroids affect adrenal chromaffin cell function. In the present work, we have examined the expression and functional significance of membrane androgen receptor sites in normal rat adrenal chromaffin cells and in the PC12 rat pheochromocytoma cell line which can differentiate to either a neuronal or to an epithelial phenotype and expresses membrane estrogen receptor sites. Our data are as follows: (a) no cytosolic androgen receptors were found in both normal chromaffin and PC12 cells; (b) both types of chromaffin cells expressed high affinity membrane testosterone binding sites; (c) activation of these sites increased cytosolic Ca(2+), decreased catecholamine secretion and induced apoptosis; (d) NGF-induced neuronal differentiation of PC12 cells resulted in the suppression of the number of membrane testosterone sites. In conclusion, our data provide evidence for the existence of specific membrane testosterone receptors on adrenal chromaffin cells via which androgens, (some of them originating in the cortex) modulate their function. Neuronal differentiation of chromaffin cells results in a significant attenuation of these effects, via suppression of the expression of membrane androgen receptors suggesting, that the latter are specific for epithelioid chromaffin cells.

The involvement of calcium and MAP kinase signaling pathways in the production of radiation-induced bystander effects

Much evidence now exists regarding radiation-induced bystander effects, but the mechanisms involved in the transduction of the signal are still unclear. The mitogen-activated protein kinase (MAPK) pathways have been linked to growth factor-mediated regulation of cellular events such as proliferation, senescence, differentiation and apoptosis. Activation of multiple MAPK pathways such as the ERK, JNK and p38 pathways have been shown to occur after exposure of cells to radiation and a variety of other toxic stresses. Previous studies have shown oxidative stress and calcium signaling to be important in radiation-induced bystander effects. The aim of the present study was to investigate MAPK signaling pathways in bystander cells exposed to irradiated cell conditioned medium (ICCM) and the role of oxidative metabolism and calcium signaling in the induction of bystander responses. Human keratinocytes (HPV-G cell line) were irradiated (0.005-5 Gy) using a cobalt-60 teletherapy unit. The medium was harvested 1 h postirradiation and transferred to recipient HPV-G cells. Phosphorylated forms of p38, JNK and ERK were studied by immunofluorescence 30 min-24 h after exposure to ICCM. Inhibitors of the ERK pathway (PD98059 and U0126), the JNK pathway (SP600125), and the p38 pathway (SB203580) were used to investigate whether bystander-induced cell death could be blocked. Cells were also incubated with ICCM in the presence of superoxide dismutase, catalase, EGTA, verapamil, nifedipine and thapsigargin to investigate whether bystander effects could be inhibited because of the known effects on calcium homeostasis. Activated forms of JNK and ERK proteins were observed after exposure to ICCM. Inhibition of the ERK pathway appeared to increase bystander-induced apoptosis, while inhibition of the JNK pathway appeared to decrease apoptosis. In addition, reactive oxygen species, such as superoxide and hydrogen peroxide, and calcium signaling were found to be important modulators of bystander responses. Further investigations of these signaling pathways may aid in the identification of novel therapeutic targets.

Sex-specific regulation of growth plate chondrocytes by estrogen is via multiple MAP kinase signaling pathways

Both male and female rat growth plate cartilage cells possess estrogen receptors (ERs), but 17beta-estradiol (E(2)) activates protein kinase C (PKC) and PKC-dependent biological responses to E(2) only in cells from female animals. PKC signaling can elicit genomic responses via mitogen activated protein kinase (MAPK) and E(2) has been shown to activate ERK MAPK in many cells, suggesting that MAPK may play a role in growth plate chondrocytes as well. We tested if E(2) increases MAPK activity and if so, whether the response is limited to female cells, if it is PKC-dependent, and if the mechanism involves traditional ER pathways. We also determined the contribution of MAPK to the biological response of growth plate chondrocytes and assessed the relative contributions of ERK, p38 and JNK MAPKs. Female rat costochondral cartilage cells were treated with E(2) and MAPK-specific activity determined in cell layer lysates. The mechanism of MAPK activation was determined by treating the cells with E(2) conjugated to bovine serum albumin (E(2)-BSA) to assess if membrane receptors were involved; stereospecificity was determined using 17alpha-estradiol; PKC and phospholipase C (PLC) dependence was determined using specific inhibitors; and the ER agonist diethylstilbestrol, the ER antagonist ICI 182780, and tamoxifen were used to assess the role of traditional ER pathways. E(2) regulation of ERK1/2 MAPK was assessed and the relative roles of ERK1/2, p38 and JNK MAPKs determined using specific inhibitors. E(2) caused a rapid dose-dependent activation of MAPK that was greatest in cells treated for 9 min with 10(-9) M hormone; activity remained elevated for 3 h. E(2)'s effect on MAPK was stereospecific and comparable to that of E(2)-BSA. It was insensitive to DES and ICI 182780, dependent on PKC and PLC, blocked by tamoxifen and it did not require gene transcription or translation. E(2) had no effect on ERK1 or ERK2 mRNA or protein but it caused a rapid phosphorylation of ERK1/2 at 9 min. Inhibition of ERK1/2 and p38 MAPK reduced the stimulatory effects of E(2) on alkaline phosphatase activity and [(35)S]-sulfate incorporation. These results suggest that E(2) regulates MAPK through a sex-specific membrane-mediated mechanism that does not involve cytosolic ERs in a traditional sense and that ERK1/2 and p38 mediate the downstream biological effects of the hormone.

Estrogen induces phospholipase A2 activation through ERK1/2 to mobilize intracellular calcium in MCF-7 cells

The principal secreted estrogen, 17beta-estradiol rapidly activates signaling cascades that regulate important physiological processes including ion transport across membranes, cytosolic pH and cell proliferation. These effects have been extensively studied in the MCF-7 estrogen-responsive human breast carcinoma cell line. Here, we demonstrate that a physiological concentration of 17beta-estradiol caused a rapid, synchronous and transient increase in intracellular calcium concentration in a confluent monolayer of MCF-7 cells 2-3 min after treatment. This response was abolished when cells were pre-incubated with the phospholipase A(2) (PLA(2)) inhibitor quinacrine or with the cyclooxygenase inhibitor indomethacin. The translocation of GFP-cPLA(2)alpha to perinuclear membranes occurred 1-2 min after 17beta-estradiol treatment; this translocation was concurrent with the transient phosphorylation of cPLA(2)alpha at serine residue 505. The phosphorylation and translocation of cPLA(2) were sensitive to inhibition of the extracellular signal regulated kinase (ERK) signaling cascade and occurred simultaneously with a transient activation of ERK. The phosphorylation of cPLA(2) could be stimulated by membrane impermeable 17beta-estradiol conjugated to bovine serum albumen and was blocked by an antagonist of the classical estrogen receptor. Here we show, for the first time, that PLA(2) and the eicosanoid biosynthetic pathway are involved in the 17beta-estradiol induced rapid calcium responses of breast cancer cells.

Rapid modulatory effect of estradiol on acetylcholine-induced Ca2+ signal is mediated through cyclic-GMP cascade in LHRH-releasing GT1-7 cells

Hypothalamic luteinizing hormone-releasing hormone neurons (LHRH) form the final pathway for the central control of reproduction through the release of LHRH into the pituitary-hypothalamic system. We previously found that LHRH-producing GT1-7 cells respond to acetylcholine (ACh) with an increase in intracellular calcium ([Ca2+]i) through activation of muscarinic receptors. This effect is acutely modulated by 17beta-estradiol in a manner compatible with specific membrane binding sites. Because increasing evidence suggests that second messengers are involved in the rapid action of estradiol, the aim of the present study was to identify the pathway underlying estrogen actions on ACh-induced Ca2+ signals. 8-Bromoguanosine 3',5'-cyclic monophosphate (10 microm) and C-type natriuretic peptide (10 microm) mimicked the effect of estradiol. On the contrary, neither dibutyryl cAMP (100 microm), forskolin (100 nm or 10 microm), or sodium nitroprusside (10 microm) induced any modification of [Ca2+]i in response to ACh. The effect of estradiol on calcium transients was totally blocked by two different cGMP-dependent protein kinase (PKG) inhibitors. In addition, phosphorylation of inositol 1,4,5-triphosphate (IP3) receptor was rapidly induced by estradiol but totally blocked when the cells were pretreated with a PKG inhibitor. We conclude that physiological concentrations of estradiol reduce ACh-induced Ca2+ transients via a mechanism involving a membrane-associated guanylate cyclase, which finally induces a PKG-dependent IP3 receptor phosphorylation that modifies calcium release from the endoplasmic reticulum.

Steering estrogen signals from the plasma membrane to the nucleus: Two sides of the coin

Estrogen mediate its biological effects through its association with estrogen receptors (ERs). They also regulate the expression of a variety of genes involved in distinct physiological processes, including development, metabolism, and reproduction. In addition, emerging data suggest that the estrogen-estrogen receptor complex can also function as a cytoplasmic signaling molecule and may influence processes such as cardiovascular protection, bone preservation, neuroprotection, and proliferation of various cell types. Such extranuclear or nongenomic signaling pathways are rapid and supposedly independent of transcription. A recent exciting finding was that G-coupled membrane protein receptor, GPR30, an alternative to the classical ERs, is also involved in the rapid signaling of estrogen through its direct association with estrogen. These new findings combined with the recent advances in the cytoplasmic functions of proline, glutamic acid, luecine rich protein 1 (PELP1), and metastatic tumor antigen 1 short form (MTA1s) have opened a new spectrum and raised several new concerns in the field of estrogen biology and put the attention to unveil many unknown mechanistic actions of estrogen in cellular physiology. In this review, we briefly summarize what is currently known of the cellular mechanisms and physiology of estrogen's nongenomic actions in various cellular systems used by ERs.

The negative immunoregulatory effects of fluoxetine in relation to the cAMP-dependent PKA pathway

Recently, we have shown that various types of antidepressants, including selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, have negative immunoregulatory effects. These antidepressants suppress the interferon-gamma (IFN-gamma)/interleukin-10 (IL-10) production ratio, which is of critical importance for the determination of the capacity of immunocytes to inhibit or activate monocytic/lymphocytic functions. Since cyclic adenosine monophosphate (cAMP) production is stimulated by some antidepressants, and since cAMP inhibits IFN-gamma and stimulates IL-10 production, we postulate that the negative immunoregulatory effects of antidepressants result from their effects on the cAMP-dependent protein kinase A (PKA) pathway. The aim of the present study was to determine whether the negative immunoregulatory effects of fluoxetine may be blocked by antagonists of the cAMP-dependent PKA pathway, such as, e.g., SQ 22536, an adenylate cyclase inhibitor, and Rp-8-Br-cAMPs (Rp-isomer of 8-bromo-adenosine-3',5'-monophosphorothioate), a PKA antagonist. To this end, diluted whole blood collected from 17 normal volunteers was incubated with fluoxetine (10(-6) and 10(-5) M), with or without SQ 22536 (10(-6) and 10(-4) M) and Rp-8-Br-cAMPs (10(-6) and 10(-4) M), afterwards, IFN-gamma, IL-10 and the tumor necrosis factor alpha (TNF-alpha) were determined. Fluoxetine, 10(-6) and 10(-5) M, significantly reduced the production of IFN-gamma and TNF-alpha, and significantly decreased the IFN-gamma/IL-10 production ratio. SQ 22536 and Rp-8-Br-cAMPs were unable to block the suppressant effects of fluoxetine on the IFN-gamma/IL-10 ratio. Rp-8-Br-cAMPs, 10(-4), but not 10(-6) M, normalized the fluoxetine-induced suppression of TNF-alpha production. It is concluded that the suppressant effect of fluoxetine on the IFN-gamma/IL-10 production ratio is probably not related to the induction of the cAMP-dependent PKA pathway, whereas the suppressant effect on TNF-alpha may be related to the induction of PKA. The obtained results suggest that increased activation of the PKA-dependent pathway may constitute an important molecular basis for some (suppression of TNF-alpha production), but not all (suppression of IFN-gamma production), negative immunoregulatory effects of fluoxetine.

Rapid effects of dexamethasone on intracellular pH and Na+/H+ exchanger activity in human bronchial epithelial cells

Glucocorticoids have been shown to produce rapid nongenomic responses in airway epithelia. By using an intracellular pH (pH(i)) spectrofluorescence imaging system and the NH4Cl acid-loading technique, we have shown that the synthetic glucocorticoid,dexamethasone, accelerated intracellular pH recovery after an acid load in a human bronchial epithelial cell line (16HBE14o- cells). Exposure to NH4Cl (20 mm) elicited an intracellular acidification, followed by a pH(i) recovery. Inhibition of the Na+/H+ exchanger decreased the steady-state pH(i) and antagonized the dexamethasone stimulation of pH(i) regulation. The rapid effect of dexamethasone on pH(i) was neither affected by the inhibitor of transcription, cycloheximide, nor by the classical glucocorticoid and mineralocorticoid receptors antagonists, RU486 and spironolactone, respectively. The dexamethasone effect on pH(i) regulation was reduced by inhibitors of adenylate cyclase, cAMP-dependent protein kinase and mitogenactivated protein kinase (ERK1/2). By using a PepTag assay system and Western blotting, we have shown that dexamethasone stimulated cAMP-dependent protein kinase and mitogen-activated protein kinase activities. Taken together our results provide evidence for the rapid stimulation of Na+/H+ exchange activity by glucocorticoids in bronchial epithelial cells via a nongenomic mechanism involving cAMP-dependent protein kinase and mitogen-activated protein kinase ERK1/2 pathways.

Acute impairment of contractile responses by 17beta-estradiol is cAMP and protein kinase G dependent in vascular smooth muscle cells of the porcine coronary arteries

The aim of the present study was to investigate the involvement of adenosine 3',5'-cyclic monophosphate (cAMP) cascade in the acute impairment of contraction by 17beta-estradiol in porcine coronary arteries, and to elucidate the signaling pathway leading to the activation of this cascade by the hormone. Isometric tension was recorded in isolated rings of porcine coronary arteries. The contraction to U46619 was reduced significantly following 30 min incubation with 1 nM 17beta-estradiol or 1 nM isoproterenol. There was no additive effect when 17beta-estradiol and isoproterenol were administered together. The effect of 17beta-estradiol was mimicked by both the cyclic AMP analogue 8-Br-cAMP and the guanosine 3',5'-cyclic monophosphate (cyclic GMP) analogue 8-Br-cGMP. In rings with and without endothelium, the modulatory effect of 17beta-estradiol was abolished by the adenylyl cyclase inhibitor, SQ 22536, but was unaffected by the guanylyl cyclase inhibitor, ODQ. Both the cAMP antagonist Rp-8-Br-cAMPS and the cGMP antagonist inhibitor Rp-8-Br-cGMPS inhibited the effect of 17beta-estradiol. The effect of 17beta-estradiol was unaffected by the protein kinase A inhibitor, KT5720, but was abolished by the protein kinase G (PKG) inhibitor, KT5823, which also abolished the effect of isoproterenol. These data support our earlier findings that 17beta-estradiol (1 nM) acutely impairs contractile responses of porcine coronary arteries in vitro. This acute effect of 17beta-estradiol involves cAMP in vascular smooth muscles and the activation of PKG.

Acute relaxation of mouse duodenum [correction of duodenun] by estrogens. Evidence for an estrogen receptor-independent modulation of muscle excitability

17-beta-Estradiol, the stereoisomer 17-alpha-estradiol and the synthetic estrogen diethylstilbestrol (DES), all caused a rapid (<3 min) dose-dependent reversible relaxation of mouse duodenal spontaneous activity, reduced basal tone and depressed the responses to CaCl(2) and KCl. The steroidal antiestrogen 7alpha-[9-[(4,4,5,5,5,-pentafluoropenty)sulphinyl]nonyl]-estra-1,3,5(19)-triene-3,17beta-diol (ICI182,780) failed to either mimic or prevent the effect of 17-beta-estradiol. The effect of estrogens was unrelated to activation of nitric oxide (NO), mitogen-activated protein kinase (MAPK), protein kinase A (PKA), protein kinase G (PKG) or protein kinase C (PKC). Estrogen-induced relaxation was partially reversed by 1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-pyridine-3-carboxilic acid methyl ester (BAY-K8644), depolarization, or by application of tetraethylammonium or 4-aminopyridine, but not by glibenclamide, apamin, charybdotoxin, paxilline or verruculogen. The effects of BAY-K8644 and K(+) channel blockers were synergistic, and allowed relaxed tissues to recover spontaneous activity and basal tone. We hypothesize that the rapid non-genomic spasmolytic effect of estrogens on mouse duodenal muscle might be triggered by an estrogen-receptor-independent mechanism likely involving activation of tetraethylamonium- and 4-aminopyridine-sensitive K(+) channels and inhibition of L-type Ca2(+) channels on the smooth muscle cells.

Sex-linked differences in the vasorelaxant effects of anandamide in vascular mesenteric beds: role of oestrogens

Anandamide (0.01 to 10 microM) caused greater concentration-dependent reductions of the contractile-induced responses to noradrenaline in female than in male mesenteric vascular beds isolated from adult Sprague-Dawley rats. Greater relaxant responses in females were also induced by the vanilloid TRPV1 receptor agonist capsaicin (0.01 to 10 microM), whereas no sex differences were observed for the relaxations caused by either acetylcholine or sodium nitroprusside. The effect of anandamide in either sex was reduced by the vanilloid TRPV1 receptor antagonist capsazepine but not by the cannabinoid CB1 receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide (SR141716A). In males, the anandamide-induced relaxations were potentiated by in vitro exposure during 5 min to 0.5 microM 17beta-oestradiol and unmodified by the protein synthesis inhibitor cycloheximide. The vasorelaxant effects of anandamide in female rats were decreased by ovariectomy. This decrease was prevented by in vivo treatment with 17beta-oestradiol-3-benzoate (450 microg/kg i.m., once a week during 3 weeks) and counteracted by in vitro exposure to oestrogen. In vivo treatment with 17beta-oestradiol also potentiated anandamide-induced responses in males. In conclusion, this study shows an oestrogen-dependent sensitivity to the vanilloid TRPV1 receptor-mediated vasorelaxant effects of anandamide in the mesenteric vasculature of Sprague-Dawley rats, that could be mediated by both genomic and non-genomic mechanisms.

Mechanisms of membrane estrogen receptor-alpha-mediated rapid stimulation of Ca2+ levels and prolactin release in a pituitary cell line

The role of membrane estrogen receptor-alpha (mERalpha) in rapid nongenomic responses to 17beta-estradiol (E(2)) was tested in sublines of GH3/B6 rat prolactinoma cells selected for high (GH3/B6/F10) and low (GH3/B6/D9) mERalpha expression. E(2) elicited rapid, concentration-dependent intracellular Ca(2+) concentration ([Ca(2+)](i)) increases in the F10 subline. Lack of inhibition by thapsigargin depletion of intracellular Ca(2+) pools, together with abrogation of the response in Ca(2+)-free medium, suggested an extracellular source of Ca(2+) for this response. The participation of voltage-dependent channels in the E(2)-induced [Ca(2+)](i) increase was confirmed by the specific L-type Ca(2+) channel inhibitor nifedipine. For comparison, the D9 mERalpha-depleted subline was insensitive to steroid action via this signaling mechanism. [Ca(2+)](i) elevation was correlated with prolactin (PRL) release in the F10 cell line in as little as 3 min. E(2) caused a much higher PRL release than KCl treatment (which caused maximal Ca(2+) elevation), suggesting that secretion was also controlled by additional mechanisms. Participation of mERalpha in these effects was confirmed by the ability of E(2)-peroxidase (a cell-impermeable analog of E(2)) to cause these responses, blockage of the responses with the ER antagonist ICI 182 780, and the inability of the E(2) stereoisomer 17alpha-E(2) to elicit a response. Thus rapid exocytosis of PRL is regulated in these cells by mERalpha signaling to specific Ca(2+) channels utilizing extracellular Ca(2+) sources and additional signaling mechanisms.

Estrogen receptor independent rapid non-genomic effects of environmental estrogens on [Ca2+]i in human breast cancer cells

The aim of this study was to identify and characterize an alternative pathway through which environmental estrogenic compounds may mediate their intracellular effects. Three human breast cancer cell lines were employed including MCF-7 cells, which express both ERalpha and ERbeta; MDA-MB-231 cells, which express ERbeta but not ERalpha; and SKBR-3 cells, which express neither ERalpha nor ERbeta. The effect of environmental estrogenic compounds on intracellular calcium ion concentration ([Ca(2+)](i)) was measured and compared to that of 17beta-estradiol (E2). A rapid and maintained increase in [Ca(2+)](i) was observed following the application of nanomolar concentrations of environmental estrogens and E2 regardless of the expression of ERalpha and ERbeta. Removal of extracellular Ca(2+) completely abolished the steroid-induced [Ca(2+)](i) increase. Pre-treatment of cells with the estrogen receptor (ER) antagonist ICI 182,780 had no effect on either basal [Ca(2+)](i) or the steroid-triggered [Ca(2+)](i) response. In summary, we have demonstrated ER independent rapid non-genomic effects of environmental estrogenic compounds, at nanomolar concentrations, on [Ca(2+)](i). The results of this study demonstrate an alternative pathway to explain potent intracellular effects of endocrine disrupting chemicals.

Calcium flux in neuroblastoma cells is a coupling mechanism between non-genomic and genomic modes of estrogens

Estrogens have been demonstrated to rapidly modulate calcium levels in a variety of cell types. However, the significance of estrogen-mediated calcium flux in neuronal cells is largely unknown. The relative importance of intra- and extracellular sources of calcium in estrogenic effects on neurons is also not well understood. Previously, we have demonstrated that membrane-limited estrogens, such as E-BSA given before an administration of a 2-hour pulse of 17beta-estradiol (E2), can potentiate the transcription mediated by E2 from a consensus estrogen response element (ERE)-driven reporter gene. Inhibitors to signal transduction cascades given along with E-BSA or E2 demonstrated that calcium flux is important for E-BSA-mediated potentiation of transcription in a transiently transfected neuroblastoma cell line. In this report, we have used inhibitors to different voltage-gated calcium channels (VGCCs) and to intracellular store receptors along with E-BSA in the first pulse or with E2 in the second pulse to investigate the relative importance of these channels to estrogen-mediated transcription. Neither L- nor P-type VGCCs seem to play a role in estrogen action in these cells; while N-type VGCCs are important in both the non-genomic and genomic modes of estrogen action. Specific inhibitors also showed that the ryanodine receptor and the inositol trisphosphate receptor are important to E-BSA-mediated transcriptional potentiation. This report provides evidence that while intracellular stores of calcium are required to couple non-genomic actions of estrogen initiated at the membrane to transcription in the nucleus, extracellular sources of calcium are also important in both non-genomic and genomic actions of estrogens.

Mechanisms for aldosterone and spironolactone-induced positive inotropic actions in the rat heart

Previously, we reported that aldosterone and spironolactone have inotropic effects in the isolated perfused heart. To address the mechanisms underlying these inotropic effects, we examined the effects of aldosterone and spironolactone on isolated cardiac myocyte shortening, intracellular calcium ([Ca+2]i), pHi, and calcium-dependent actinomyosin ATPase activity. Aldosterone significantly increased shortening in cardiac myocytes (8.0+/-1.0 versus 16.0+/-1.3%, P<0.01) but neither diastolic [Ca+2]i (61.0+/-1.1 versus 66.0+/-4.4 nmol/L) nor peak systolic [Ca+2]i (302+/-11 versus 304+/-17 nmol/L) was affected. Spironolactone-increased shortening was also not coupled with changes in peak systolic calcium; however, diastolic calcium was significantly increased by spironolactone. Aldosterone, but not spironolactone, increased pHi from 7.23+/-0.03 to 7.59+/-0.02 (P<0.01); this was completely blocked by coadministration of 100 micromol/L of ethyl-isopropyl amiloride (EIPA), an inhibitor of the Na+/H+ exchanger (P<0.01). Consistent with this finding, aldosterone increased cytosolic sodium concentration ([Na+]i) from 9.2+/-0.15 to 11.4+/-0.2 mmol/L and produced a leftward shift in the pCa ATPase curve (pCa=5.82+/-0.02 versus 6.35+/-0.02, P<0.01) without affecting maximal myosin ATPase activity. Conversely, spironolactone, but not aldosterone, significantly increases maximal actomyosin ATPase activity (837+/-59 versus 355+/-52 nmol inorganic phosphate (P(i)) x min(-1) x g tissue(-1)). Collectively, these data strongly suggest that the inotropic actions of aldosterone and spironolactone are caused by different mechanisms of action. Aldosterone appeared to increase inotropy primarily through increased cytosolic pH, whereas spironolactone increased myosin ATPase calcium sensitivity and diastolic calcium concentration.

Estrogen induces nitric oxide production via activation of constitutive nitric oxide synthases in human neuroblastoma cells

Although it is becoming increasingly evident that nitric oxide (NO) mediates some of estrogen's actions in the brain, the effects of estrogen on NO production through NO synthases (NOS) in neuronal cells have not yet been identified. Here we assessed changes in NO production induced by 17beta-estradiol (E2) in cells of neuronal origin using human SK-N-SH neuroblastoma cells, which we show express all three isoforms of NOS. Involvement of NOS isoforms in E2-induced NO production was examined using isoform-specific NOS inhibitors. E2 (10(-10)-10(-6) m) induced rapid increases in NO release and changes in endothelial NOS (eNOS) expression, which were blocked by ICI 182,780, an antagonist of estrogen receptors. Increased levels of NO release and NOS activity induced by E2 were blocked by N5-(1-Imino-3-butenyl)-L-ornithine, a neuronal NOS inhibitor, and N(5)-(1-Iminoethyl)-L-ornithine, an eNOS inhibitor, but not by 1400W, an inducible NOS inhibitor. These results demonstrate that E2-stimulated NO production occurs via estrogen receptor-mediated activation of the constitutive NOSs, neuronal NOS and eNOS. The E2-induced NO increase was abolished when extracellular Ca2+ was removed from the medium or after the addition of nifedipine, an L-type channel blocker, and was partially inhibited using 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, an intracellular Ca2+ chelator. However, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester itself also caused an increase in NO release that was blocked by 1400W, suggesting that inducible NOS mediates this response. Together these data reveal that constitutive NOS activities are responsible for E2-induced NO production in neuroblastoma cells and that differential activation of NOS isoforms in these cells occurs in response to different treatments.

Cross-talk between the estrogen receptor-, protein kinase A-, and mitogen-activated protein kinase-mediated signaling pathways in the regulation of lactotroph proliferation in primary culture

Using pharmacological means we investigated the functional interactions between the estrogen receptor (ER)-, protein kinase A (PKA)-, and mitogen-activating protein kinase (MAPK)-mediated pathways in the regulation of lactotroph proliferation in primary culture. Treatment of lactotrophs for 28 h with the PKA inhibitor H89 or KT5720, an effective inhibitor of forskolin-induced proliferation, inhibited both insulin- and estradiol-induced proliferation. Inhibition of the MAPK activity by PD98059 or U0126 suppressed not only insulin-induced proliferation but also forskolin- and estradiol-induced proliferation. However, treatment for 28 h with the antiestrogens 4-hydroxy tamoxifen and ICI182780 failed to antagonize estradiol-induced lactotroph proliferation but instead enhanced it. Prolonging the antiestrogen treatment time from 28 to 88 h was effective in antagonizing estradiol-induced proliferation with this long-term treatment also inhibiting insulin- and forskolin-induced proliferation. There was no decrease in these mitogen-induced proliferations following treatment with a progesterone antagonist or protein kinase C inhibitor. These results suggest that cross-talk occurs between the ER-, PKA-, and MAPK-mediated signaling pathways in the regulation of lactotroph proliferation, and that antiestrogens stimulate and inhibit estradiol-induced proliferation in a time-dependent manner.

Androgens inhibit estradiol-17beta synthesis in Atlantic croaker (Micropogonias undulatus) ovaries by a nongenomic mechanism initiated at the cell surface

The presence of androgen receptors in the ovaries of several vertebrate species, including Atlantic croaker, suggests that androgens may have important roles in ovarian function. In the current study the effects of androgens on ovarian steroidogenesis in Atlantic croaker were investigated. Addition of 17beta-hydroxy-5alpha-androstan-3-one (DHT), 11-ketotestosterone (11-KT), or Mibolerone to ovarian incubations caused dose-dependent decreases in gonadotropin-stimulated in vitro estradiol production, which was not reversed by cotreatment with the antiandrogens, cyproterone acetate or 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene. Androgen treatment also caused significant decreases in estradiol production in the presence of 17-hydroxyprogesterone, which suggests that the site of androgen action is downstream of this steroid in the steroidogenic pathway. The mechanism of androgen action on ovarian steroidogenesis was also investigated. Coincubation with actinomycin D did not reverse the inhibitory effect of the androgens, which suggests that the mechanism of androgen action is nongenomic. An androgen conjugated to bovine serum albumin (DHT-BSA), which does not enter the cell, also caused inhibition of estradiol production in vitro, indicating that the androgen is acting at the cell surface. In addition, time course experiments revealed that the androgen action is rapid; 5-min exposure to DHT was sufficient to cause a significant reduction in estradiol production. Finally, preliminary evidence was obtained for the existence of a high-affinity, low-capacity androgen binding site in croaker ovarian plasma membranes. These studies suggest that androgens can down-regulate estrogen production in croaker ovaries via a rapid, cell surface-mediated, nongenomic mechanism.

Rapid signaling of estrogen in hypothalamic neurons involves a novel G-protein-coupled estrogen receptor that activates protein kinase C

Classically, 17beta-estradiol (E2) is thought to control homeostatic functions such as reproduction, stress responses, feeding, sleep cycles, temperature regulation, and motivated behaviors through transcriptional events. Although it is increasingly evident that E2 can also rapidly activate kinase pathways to have multiple downstream actions in CNS neurons, the receptor(s) and the signal transduction pathways involved have not been identified. We discovered that E2 can alter mu-opioid and GABA neurotransmission rapidly through nontranscriptional events in hypothalamic GABA, proopiomelanocortin (POMC), and dopamine neurons. Therefore, we examined the effects of E2 in these neurons using whole-cell recording techniques in ovariectomized female guinea pigs. E2 reduced rapidly the potency of the GABAB receptor agonist baclofen to activate G-protein-coupled, inwardly rectifying K+ channels in hypothalamic neurons. These effects were mimicked by the membrane impermeant E2-BSA and selective estrogen receptor modulators, including a new diphenylacrylamide compound, STX, that does not bind to intracellular estrogen receptors alpha or beta, suggesting that E2 acts through a unique membrane receptor. We characterized the coupling of this estrogen receptor to a Galpha(q)-mediated activation of phospholipase C, leading to the upregulation of protein kinase Cdelta and protein kinase A activity in these neurons. Moreover, using single-cell reverse transcription-PCR, we identified the critical transcripts, PKCdelta and its downstream target adenylyl cyclase VII, for rapid, novel signaling of E2 in GABA, POMC, and dopamine neurons. Therefore, this unique Gq-coupled estrogen receptor may be involved in rapid signaling in hypothalamic neurons that are critical for normal homeostatic functions.

Rapid signaling of estrogen in hypothalamic neurons involves a novel G-protein-coupled estrogen receptor that activates protein kinase C

Classically, 17beta-estradiol (E2) is thought to control homeostatic functions such as reproduction, stress responses, feeding, sleep cycles, temperature regulation, and motivated behaviors through transcriptional events. Although it is increasingly evident that E2 can also rapidly activate kinase pathways to have multiple downstream actions in CNS neurons, the receptor(s) and the signal transduction pathways involved have not been identified. We discovered that E2 can alter mu-opioid and GABA neurotransmission rapidly through nontranscriptional events in hypothalamic GABA, proopiomelanocortin (POMC), and dopamine neurons. Therefore, we examined the effects of E2 in these neurons using whole-cell recording techniques in ovariectomized female guinea pigs. E2 reduced rapidly the potency of the GABAB receptor agonist baclofen to activate G-protein-coupled, inwardly rectifying K+ channels in hypothalamic neurons. These effects were mimicked by the membrane impermeant E2-BSA and selective estrogen receptor modulators, including a new diphenylacrylamide compound, STX, that does not bind to intracellular estrogen receptors alpha or beta, suggesting that E2 acts through a unique membrane receptor. We characterized the coupling of this estrogen receptor to a Galpha(q)-mediated activation of phospholipase C, leading to the upregulation of protein kinase Cdelta and protein kinase A activity in these neurons. Moreover, using single-cell reverse transcription-PCR, we identified the critical transcripts, PKCdelta and its downstream target adenylyl cyclase VII, for rapid, novel signaling of E2 in GABA, POMC, and dopamine neurons. Therefore, this unique Gq-coupled estrogen receptor may be involved in rapid signaling in hypothalamic neurons that are critical for normal homeostatic functions.