Nongenomic stimulation of nitric oxide release by estrogen is mediated by estrogen receptor alpha localized in caveolae

Estrogens promote human testicular germ cell cancer through a membrane-mediated activation of extracellular regulated kinase and protein kinase A

Clinical and experimental studies have suggested that estrogens, the archetype of female hormones, participate in the control of male germ cell proliferation and that fetal exposure to environmental estrogens may contribute to hypofertility and/or to testicular germ cell cancer. However, the underlying mechanisms remain to be elucidated. 17beta-Estradiol (E2) conjugated to BSA was able to stimulate human testicular seminoma cell proliferation by triggering a rapid, nongenomic, membrane-mediated activation of ERK1/2 and cAMP-dependent protein kinase A (PKA). Both ERK1/2 and PKA participated in this promoting effect. This activation was associated with phosphorylation of the transcription factor cAMP response element-binding protein and the nuclear factor retinoblastoma protein. Enhanced proliferation together with ERK activation could be reversed by pertussis toxin, a G protein inhibitor. Estrogen receptors (ERs) in JKT-1 were characterized by immunofluorescence, subcellular fractioning, and Western blot. JKT-1 cells did not express ERalpha but ERbeta, which localized to the mitochondria and the nucleus but not to the membrane. Moreover, neither ICI-182,780, a classical ER antagonist, nor tamoxifen, a selective ER modulator, could reverse the 17beta-estradiol-BSA-induced promoting effect. Estrogens contribute to human testicular germ cell cancer proliferation by rapid activation of ERK1/2 and PKA through a membrane nonclassical ER. This nongenomic effect represents a new basis for understanding the estrogenic control of spermatogenesis and evaluating the role of fetal exposure to xenoestrogens during malignant transformation of testicular germ stem cells.

Extranuclear steroid receptors: nature and actions

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

Effects of estrogens and selective estrogen receptor modulators on vascular reactivity in the perfused mesenteric vascular bed

Estrogens and selective estrogen receptor modulators (SERMs), such as raloxifene (RAL) and tamoxifen (TAM), acutely relax arteries, but the long-term effects of estrogens and SERMs on vascular reactivity in the mesenteric vasculature have not been well defined. In this study, we used an isolated, perfused mesenteric vascular bed technique to investigate the effect of chronic treatment of estrogens and SERMs on vascular reactivity of the mesenteric bed. Ovariectomized female Sprague-Dawley rats were treated by gavage with vehicle (control, 2-hydroxypropyl-β-cyclodextrin), ethinyl estradiol, estradiol benzoate, equilin (EQ), TAM, or RAL for 3 wk. EQ and TAM increased vasoconstriction in response to all three vasoconstrictors tested (KCl, norepinephrine, and 5-HT). Ethinyl estradiol increased vasoconstriction in response to KCl and 5-HT, whereas responses to estradiol benzoate and RAL were less consistent. Only EQ (134 ± 4 mmHg) and TAM (104 ± 4 mmHg) changed mean arterial blood pressure compared with control (117 ± 4 mmHg). These data demonstrate that 3-wk gavage treatment with estrogens and SERMs affects vascular reactivity in the mesenteric vascular bed. However, the three formulations of estrogen did not produce equivalent effects, and the effects of the SERMs were different from those of the estrogens.

Risk for premenstrual dysphoric disorder is associated with genetic variation in ESR1, the estrogen receptor alpha gene

BACKGROUND

Premenstrual dysphoric disorder (PMDD) is a heritable mood disorder that is triggered by gonadal steroids during the luteal phase in susceptible women.

METHODS

We performed haplotype analyses of estrogen receptors alpha and beta (ESR1 and ESR2) in 91 women with prospectively confirmed PMDD and 56 control subjects to investigate possible sources of the genetic susceptibility to affective dysregulation induced by normal levels of gonadal steroids. We also examined associations with the valine (Val)158methionine (Met) single nucleotide polymorphism (SNP) of the gene for catechol-O-methyltransferase (COMT), an enzyme involved in estrogen metabolism and prefrontal cortical activation.

RESULTS

Four SNPs in intron 4 of ESR1 showed significantly different genotype and allele distributions between patients and control subjects. Significant case-control differences were seen in sliding-window analyses of two-, three-, and four-marker haplotypes but only in those haplotypes containing SNPs in intron 4 that were positive in the single-locus analysis. No significant associations were observed with ESR2 or with the COMT Val158Met polymorphism, although the significant associations with ESR1 were observed only in those with the Val/Val genotype.

CONCLUSIONS

These are the first positive (albeit preliminary) genetic findings in this reproductive endocrine-related mood disorder and involve the receptor for a hormone that is pathogenically relevant.

Caveolin proteins are essential for distinct effects of membrane estrogen receptors in neurons

It has become widely accepted that along with its ability to directly regulate gene expression, estradiol also influences cell signaling and brain function via rapid membrane-initiated events. Many of these novel signaling processes are dependent on estrogen receptors (ERs) localized to the neuronal membrane. However, the mechanism(s) by which ERs are able to trigger cell signaling when targeted to the neuronal membrane surface has yet to be determined. In hippocampal neurons, we find that caveolin proteins are essential for the regulation of CREB (cAMP response element-binding protein) phosphorylation after estradiol activation of metabotropic glutamate receptor (mGluR) signaling. Furthermore, caveolin-1 (CAV1) and CAV3 differentially regulate the ability of estradiol to activate two discrete signaling pathways. ER alpha activation of mGluR1a is dependent on CAV1, whereas CAV3 is necessary for ER alpha and ER beta activation of mGluR2/3. These results are consistent with previous reports in non-neuronal cells, implicating the importance of caveolin proteins in rapid estrogen signaling. In addition, the functional isolation of distinct estrogen-sensitive signaling pathways by different caveolin proteins suggests novel mechanisms through which the membrane-initiated effects of estradiol are orchestrated.

Dehydroepiandrosterone protects vascular endothelial cells against apoptosis through a Galphai protein-dependent activation of phosphatidylinositol 3-kinase/Akt and regulation of antiapoptotic Bcl-2 expression

The adrenal steroid dehydroepiandrosterone (DHEA) may improve vascular function, but the mechanism is unclear. In the present study, we show that DHEA significantly increased cell viability, reduced caspase-3 activity, and protected both bovine and human vascular endothelial cells against serum deprivation-induced apoptosis. This effect was dose dependent and maximal at physiological concentrations (0.1-10 nM). DHEA stimulation of bovine aortic endothelial cells resulted in rapid and dose-dependent phosphorylation of Akt, which was blocked by LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), the upstream kinase of Akt. Accordingly, inhibition of PI3K or transfection of the cells with dominant-negative Akt ablated the antiapoptotic effect of DHEA. The induced Akt phosphorylation and subsequent cytoprotective effect of DHEA were dependent on activation of Galphai proteins, but were estrogen receptor independent, because these effects were blocked by pertussis toxin but not by the estrogen receptor inhibitor ICI182,780 or the aromatase inhibitor aminoglutethimide. Finally, DHEA enhanced antiapoptotic Bcl-2 protein expression, its promoter activity, and gene transcription attributable to the activation of the PI3K/Akt pathway. Neutralization of Bcl-2 by antibody transfection significantly decreased the antiapoptotic effect of DHEA. These findings provide the first evidence that DHEA acts as a survival factor for endothelial cells by triggering the Galphai-PI3K/Akt-Bcl-2 pathway to protect cells against apoptosis. This may represent an important mechanism underlying the vascular protective effect of DHEA.

Estrogen receptors outside the nucleus in breast cancer

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

A conserved mechanism for steroid receptor translocation to the plasma membrane

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

MS-KIF18A, a kinesin, is associated with estrogen receptor

The study of MS-KIF18A kinesin protein is focused on its cellular distribution and association with a cargo protein. Indirect immunofluorescence (IF) analyzed the intracellular distribution of endogenous MS-KIF18A and the transfected enhanced green fluorescence protein (eGFP)-MS-KIF18A in osteogenic cells. In both cases, the proteins were localized at the plasma membrane, cytosol, and nucleus. Bioinformatics analysis suggested interactions between MS-KIF18A and estrogen receptor (ERalpha) which were further elucidated by immunoprecipitation (IP). We identified interaction between endogenous MS-KIF18A with 66 and 46 kDa isoforms of ERalpha in MBA-15 cells. Moreover, MS-KIF18A and 66 kDa ERalpha complex has been demonstrated between ectopically expressed proteins in COS-7 cells. We have shown that anti-MS-KIF18A antibody immunoprecipitated the ERalpha and pERK in cells challenged with 17beta-estrogen (17beta-E2). The hormone activation induced mitogen-activated protein kinases (MAPK) pathway and increased p-ERK. The activation was interfered when cells were pre-treated with either ICI-182,780 or MAPK inhibitor PD98059 prior the challenge with 17beta-E2 that resulted in a decrease in association between MS-KIF18A and p-ERK1/2. The obtained results suggest a role for the proteins in a non-genomic response of MBA-15 cells challenged with 17beta-E2. This study presents a novel interaction between MS-KIF18A and ER that may have important physiological and pharmacological implications for estrogen action in various cells.

Acute pretreatment with estradiol protects against CA1 cell loss and spatial learning impairments resulting from transient global ischemia

Estradiol can act to protect against hippocampal damage resulting from transient global ischemia, but little is known about the functional consequences of such neuroprotection. The present study examines whether acute estradiol administered prior to the induction of transient global ischemia protects against hippocampal cell death and deficits in performance on a spatial learning task. Ovariectomized female rats were primed with estradiol benzoate or oil vehicle 48 and 24 h prior to experiencing one of three durations of 4-vessel occlusion (0, 5, or 10 min). Performance on the cued and hidden platform versions of the Morris water maze was assessed 1 week following ischemia. On the cued platform task, neither hormone treatment nor ischemia significantly influenced acquisition. When tested on the hidden platform task, however, oil-treated rats exhibited impairments in spatial learning after either 5 or 10 min of ischemia while estradiol-treated rats showed no impairments after 5 min of ischemia and only mild impairments after 10 min of ischemia. Immediately following behavioral testing, rats were perfused and survival of CA1 pyramidal cells was assessed. Ischemia was associated with the loss of CA1 pyramidal cells but rats that received estradiol prior to ischemia showed less severe damage. Furthermore, the extent of cell loss was correlated with degree of spatial bias expressed on a probe trial following hidden platform training. These findings indicate that acute exposure to estradiol prior to ischemia is both neuroprotective and functionally protective.

Transit of hormonal and EGF receptor-dependent signals through cholesterol-rich membranes

The functional consequences of changes in membrane lipid composition that coincide with malignant growth are poorly understood. Sufficient data have been acquired from studies of lipid binding proteins, post-translational modifications of signaling proteins, and biochemical inhibition of lipidogenic pathways to indicate that growth and survival pathways might be substantially re-directed by alterations in the lipid content of membranes. Cholesterol and glycosphingolipids segregate into membrane patches that exhibit a liquid-ordered state in comparison to membrane domains containing relatively lower amounts of these classes of lipids. These "lipid raft" structures, which may vary in size and stability in different cell types, both accumulate and exclude signaling proteins and have been implicated in signal transduction through a number of cancer-relevant pathways. In prostate cancer cells, signaling from epidermal growth factor receptor (EGFR) to the serine-threonine kinase Akt1, as well as from IL-6 to STAT3, have been demonstrated to be influenced by experimental interventions that target cholesterol homeostasis. The recent finding that classical steroid hormone receptors also reside in these microdomains, and thus may function within these structures in a signaling capacity independent of their role as nuclear factors, suggests a novel means of cross-talk between receptor tyrosine kinase-derived and steroidogenic signals. Potential points of intersection between components of the EGFR family of receptor tyrosine kinases and androgen receptor signaling pathways, which may be sensitive to disruptions in cholesterol metabolism, are discussed. Understanding the manner in which these pathways converge within cholesterol-rich membranes may present new avenues for therapeutic intervention in hormone-dependent cancers.

Sex differences in inflammatory cytokine production in hepatic ischemia-reperfusion

BACKGROUND

The inflammatory response to hepatic ischemia-reperfusion (I/R) is associated with an increase in cytokine production. Studies have documented that sex hormones modulate both the innate and adaptive immune responses, and that females are more robust than males. The aim of this study was to determine whether a sex difference in cytokine response to hepatic I/R exists under normal pathophysiologic condition without hormone intervention.

METHODS

Adult C57BL/6 mice underwent 90 min of hepatic ischemia followed by various reperfusion periods (0, 1.5, 3, 6 hr). Plasma cytokine TNF-alpha, IL-6, MIP-2, and KC were measured. Liver injury was assessed by plasma alanine transaminase (ALT) levels and liver histopathology.

RESULTS

A reperfusion time-dependent increase in hepatocellular injury was observed in both males and females, as indicated by increasing levels of plasma ALT and liver histopathology. The plasma cytokines were significantly increased in both female and male I/R groups compared to their respective sham counterparts. However, there was a significant difference in cytokine kinetics between the female and male I/R groups. Female mice initially had a higher level of IL-6, KC, and MIP-2 in response to I/R, which began to decline after 3 hr of reperfusion and were significantly lower than the male I/R counterparts by 6 hr of reperfusion. In contrast, the hepatocellular injury and TNF production were only moderately lower in female IR than male IR.

CONCLUSION

The study underscores role of the gender in differential inflammatory cytokine expression in response to hepatic I/R, which may reflect the host response outcome.

Phorbol ester treatment of human myometrial cells suppresses expression of oxytocin receptor through a mechanism that does not involve activator protein-1

Oxytocin (OT) is a potent uterine agonist. Its receptor (OTR) is a G protein-coupled receptor that is downregulated by prolonged exposure to OT. We hypothesized that activation of PKC mediated this OT-induced decrease in OTR expression. Diminished PKC activity in late pregnancy could underlie the increased expression of uterine OTR preceding labor onset. Using cell cultures of transformed human uterine myocytes, we determined the effects of PKC agonists and antagonists on the expression of OTR. We also explored the effects of overexpression of activator protein-1 (AP-1, a mediator of many PKC- and phorbol ester-induced effects) using adenoviral expression vectors for the AP-1 subunits c-Jun and c-Fos. Stimulation of PKC using the phorbol ester 12-O-tetradecanoylphorbol 13-acetate caused a rapid, significant (P < or = 0.05) increase in c-Jun and c-Fos concentrations but a significant decrease in mRNA for OTR within 6 h followed by a significant decrease in OT binding by 24 h. Adenoviral infection of the cells with expression vectors for c-Jun and c-Fos increased the AP-1 subunits but had no effect on OTR expression. Furthermore, there were no changes in c-Fos or c-Jun levels in human intrauterine tissues around the time of labor onset, as measured by Western analyses. We conclude that phorbol ester treatment decreases OTR expression, likely through a mechanism that does not involve AP-1.

The Isoflavone Equol Mediates Rapid Vascular Relaxation

We recently reported that soy isoflavones increase gene expression of endothelial nitric-oxide synthase (eNOS) and antioxidant defense enzymes, resulting in improved endothelial function and lower blood pressure in vivo. In this study, we establish that equol (1-100 nM) causes acute endothelium- and nitric oxide (NO)-dependent relaxation of aortic rings and rapidly (2 min) activates eNOS in human aortic and umbilical vein endothelial cells. Intracellular Ca2+ and cyclic AMP levels were unaffected by treatment (100 nM, 2 min) with equol, daidzein, or genistein. Rapid phosphorylation of ERK1/2, protein kinase B/Akt, and eNOS serine 1177 by equol was paralleled by association of eNOS with heat shock protein 90 (Hsp90) and NO synthesis in human umbilical vein endothelial cells, expressing estrogen receptors (ER)alpha and ERbeta. Inhibition of phosphatidylinositol 3-kinase and ERK1/2 inhibited eNOS activity, whereas pertussis toxin and the ER antagonists ICI 182,750 and tamoxifen had negligible effects. Our findings provide the first evidence that nutritionally relevant plasma concentrations of equol (and other soy protein isoflavones) rapidly stimulate phosphorylation of ERK1/2 and phosphatidylinositol 3-kinase/Akt, leading to the activation of NOS and increased NO production at resting cytosolic Ca2+ levels. Identification of the nongenomic mechanisms by which equol mediates vascular relaxation provides a basis for evaluating potential benefits of equol in the treatment of postmenopausal women and patients at risk of cardiovascular disease.

Raloxifene elicits combined rapid vasorelaxation and long-term anti-inflammatory actions in rat aorta

Previous studies reported the ability of raloxifene to acutely relax arterial and venous vessels, but the underlying mechanisms are controversial. Anti-inflammatory effects of the drug have been reported in nonvascular tissues. Therefore, the aim of this study was to investigate the nature of short- and long-term effects of raloxifene on selected aspects of vascular function in rat aorta. Isometric tension changes in response to raloxifene were recorded in aortic rings from ovariectomized female rats that underwent estrogen replacement, whereas long-term experiments were performed in isolated aortic smooth muscle cells (SMCs). Raloxifene (0.1 pM-0.1 microM) induced acute vasorelaxation through endothelium- and nitric oxide (NO)-dependent, prostanoid-independent mechanisms. The relaxant response to raloxifene was significantly weaker than that to 17beta-estradiol and was sensitive to neither the nonselective estrogen receptor antagonist ICI 182,780 [7,17-[9[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol] nor a selective estrogen receptor (ER) alpha antagonist. This rapid vasorelaxant effect was retained in aortic rings from rats treated with 0.1 mg/kg, but not 1 mg/kg, lipopolysaccharide, 4 h before sacrifice. In cultured aortic SMCs, raloxifene treatment (1 nM-1 microM) for 24 h reduced inducible NO synthase activation in response to cytokines. This effect was prevented by the selective ERalpha antagonist and was associated with up-regulation of ERalpha protein levels, which dropped markedly upon cytokine stimulation. These findings illustrate the relevance of classic ER-dependent pathways to the vascular anti-inflammatory effects rather than to the nongenomic vasorelaxation induced by raloxifene and may assist in the design of novel ER isoform-selective estrogen-receptor modulators targeted to the vascular system.

Troglitazone acutely inhibits protein synthesis in endothelial cells via a novel mechanism involving protein phosphatase 2A-dependent p70 S6 kinase inhibition

Thiazolidinediones (TZDs), synthetic peroxisome proliferator-activated receptor gamma (PPARgamma) ligands, have been implicated in the inhibition of protein synthesis in a variety of cells, but the underlying mechanisms remain obscure. We report that troglitazone, the first TZD drug, acutely inhibited protein synthesis by decreasing p70 S6 kinase (p70S6K) activity in bovine aortic endothelial cells (BAEC). This inhibition was not accompanied by decreased phosphorylation status or in vitro kinase activity of mammalian target of rapamycin (mTOR). Furthermore, cotreatment with rapamycin, a specific mTOR inhibitor, and troglitazone additively inhibited both p70S6K activity and protein synthesis, suggesting that the inhibitory effects of troglitazone are not mediated by mTOR. Overexpression of the wild-type p70S6K gene significantly reversed the troglitazone-induced inhibition of protein synthesis, indicating an important role of p70S6K. Okadaic acid, a protein phosphatase 2A (PP2A) inhibitor, partially reversed the troglitazone-induced inhibition of p70S6K activity and protein synthesis. Although troglitazone did not alter total cellular PP2A activity, it increased the physical association between p70S6K and PP2A, suggesting an underlying molecular mechanism. GW9662, a PPARgamma antagonist, did not alter any of the observed inhibitory effects. Finally, we also found that the mTOR-independent inhibitory mechanism of troglitazone holds for the TZDs ciglitazone, pioglitazone, and rosiglitazone, in BAEC and other types of endothelial cells tested. In conclusion, our data demonstrate for the first time that troglitazone (and perhaps other TZDs) acutely decreases p70S6K activity through a PP2A-dependent mechanism that is independent of mTOR and PPARgamma, leading to the inhibition of protein synthesis in endothelial cells.

Protective Effects of Grape Seed Proanthocyanidins Against Oxidative Stress Induced by Lipopolysaccharides of Periodontopathogens

BACKGROUND

During phagocytosis or stimulation with bacterial components, macrophages activate various cell processes, including the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are critical for successful defense against invading organisms. Increased levels of ROS/RNS create oxidative stress that results in tissue and bone destruction. Grape seed proanthocyanidins have been reported to possess a wide range of biologic properties against oxidative stress. In the present study, we investigated the effects of a grape seed proanthocyanidin extract (GSE) and commercial polyphenols on the production of ROS and RNS and on the protein expression of inducible nitric oxide synthase (iNOS) by murine macrophages stimulated with lipopolysaccharides (LPS) of periodontopathogens.

METHODS

Macrophages (RAW 264.7) were treated with non-toxic concentrations of either GSE or commercial polyphenols (gallic acid [GA] and [-]-epigallocatechin-3-gallate [EGCG]) and stimulated with LPS of Actinobacillus actinomycetemcomitans or Fusobacterium nucleatum, and iNOS expression was evaluated by immunoblotting. Nitric oxide (NO) production was quantified using the colorimetric Griess assay, whereas ROS production was measured with the fluorescent 123-dihydrorhodamine dye.

RESULTS

GSE strongly decreased NO and ROS production and iNOS expression by LPS-stimulated macrophages. GA also revealed a strong inhibitory effect on NO production without affecting iNOS expression but slightly increasing ROS production. EGCG showed an inhibitory effect on NO and ROS production and on iNOS expression by macrophages.

CONCLUSION

Our findings demonstrate that proanthocyanidins have potent antioxidant properties and should be considered a potential agent in the prevention of periodontal diseases.

Nongenomic oestrogen signalling in oestrogen receptor negative breast cancer cells: a role for the angiotensin II receptor AT1

INTRODUCTION

Oestrogens can mediate some of their cell survival properties through a nongenomic mechanism that involves the mitogen-activated protein kinase (MAPK) pathway. The mechanism of this rapid signalling and its dependence on a membrane bound oestrogen receptor (ER), however, remains controversial. The role of G-protein-coupled receptor and epidermal growth factor (EGF) receptor in an ER-independent signalling pathway modulated by oestrogen was investigated.

METHODS

ER-positive and ER-negative breast cancer cell lines (MCF-7 and SKBR3) and primary breast cancer cell cultures were used in this study. Cell proliferation was assessed using standard MTT assays. Protein and cAMP levels were detected by Western blotting and ELISA, respectively. Antigen localization was performed by immunocytochemistry, immunohistochemistry and immunofluorescence. Protein knockdown was achieved using small interfering RNA technologies.

RESULTS

EGF and oestrogen, alone and in combination, induced cell proliferation and phosphorylation of MAPK proteins Raf and ERK (extracellular signal regulated kinase)1/2 in both ER-negative SKBR3 and ER-positive MCF-7 human breast cancer cell lines. Increased Raf phosphorylation was also observed in primary human breast cultures derived from ER-positive and ER-negative breast tumours. Oestrogen induced an increase in intracellular cAMP in ER-negative SKBR3 human breast cancer cells. Oestrogen-mediated cell growth and phosphorylation of MAPK was modified by the EGF receptor antagonist AG1478, the G-protein antagonist pertussis toxin, and the angiotensin II receptor antagonist saralasin. Knockdown of angiotensin II type 1 receptor (AT1) protein expression with small interfering RNA attenuated oestrogen-induced Raf phosphorylation in ER-negative cells. AT1 receptor was found to be expressed in the cell membrane of breast tumour epithelial cells.

CONCLUSION

These findings provide evidence that, in breast cancer cells, oestrogen can signal through AT1 to activate early cell survival mechanisms in an ER-independent manner.

Nitric oxide and hormones in breast cancer: allies or enemies?

Unlike other types of cancer, tumors of the breast are greatly influenced by steroid hormones. The effect of estrogen and progesterone depends on the presence of their specific receptors and these constitute important parameters in determining the aggressiveness of the tumor, the feasibility of certain therapies and the prediction of relapse. The molecular mechanisms of steroid hormone action have not been fully elucidated but recent findings implicate the nitric oxide (NO) pathway in some of these effects. Both hormones can regulate the nitric oxide synthases (NOS) and, in turn, the NO produced has profound consequences on tumor cell homeostasis. On one hand, estrogen increases the activity of endothelial NOS (eNOS or NOSIII), while progesterone activates inducible NOS (iNOS or NOSII) expression. The data presented suggest that the low levels of NO produced by NOSIII mediate the proliferative effect of estrogen. On the other hand, the increase in apoptosis in response to progesterone could implicate the high levels of NO produced by induction of NOSII expression. Understanding of the mechanisms and interactions of steroid hormones with the NO pathway could lead to the development of new approaches and strategies for the effective treatment of breast cancer.

Hypoxia-induced endothelial NO synthase gene transcriptional activation is mediated through the tax-responsive element in endothelial cells

Although hypoxia is known to induce upregulation of endothelial NO synthase (eNOS) gene expression, the underlying mechanism is largely unclear. In this study, we show that hypoxia increases eNOS gene expression through the binding of phosphorylated cAMP-responsive element binding (CREB) protein (pCREB) to the eNOS gene promoter. Hypoxia (1% O2) increased both eNOS expression and NO production, peaking at 24 hours, in bovine aortic endothelial cells, and these increases were accompanied by increases in pCREB. Treatment with the protein kinase A inhibitor H-89 or transfection with dominant-negative inhibitor of CREB reversed the hypoxia-induced increases in eNOS expression and NO production, with concomitant inhibition of the phosphorylation of CREB induced by hypoxia, suggesting an involvement of protein kinase A/pCREB-mediated pathway. To map the regulatory elements of the eNOS gene responsible for pCREB binding under hypoxia, we constructed an eNOS gene promoter (-1600 to +22 nucleotides) fused with a luciferase reporter gene [pGL2-eNOS(-1600)]. Hypoxia (for 24-hour incubation) increased the promoter activity by 2.36+/-0.18-fold in the bovine aortic endothelial cells transfected with pGL2-eNOS(-1600). However, progressive 5'-deletion from -1600 to -873 completely attenuated the hypoxia-induced increase in promoter activity. Electrophoretic mobility shift, anti-pCREB antibody supershift, and site-specific mutation analyses showed that pCREB is bound to the Tax-responsive element (TRE) site, a cAMP-responsive element-like site, located at -924 to -921 of the eNOS promoter. Our data demonstrate that the interaction between pCREB and the Tax-responsive element site within the eNOS promoter may represent a novel mechanism for the mediation of hypoxia-stimulated eNOS gene expression.

Nature of functional estrogen receptors at the plasma membrane

Although rapid signaling by estrogen at the plasma membrane is established, it is controversial as to the nature of the receptor protein. Estrogen may bind membrane proteins comparable to classical nuclear estrogen receptors (ERs), but some studies identify nonclassical receptors, such as G protein-coupled receptor (GPR)30. We took several approaches to define membrane-localized estrogen-binding proteins. In endothelial cells (ECs) from ERalpha/ERbeta combined-deleted mice, estradiol (E2) failed to specifically bind, and did not activate cAMP, ERK, or phosphatidyinositol 3-kinase or stimulate DNA synthesis. This is in contrast to wild-type ECs, indicating the lack of any functional estrogen-binding proteins in ERalpha/ERbeta combined-deleted ECs. To directly determine the identity of membrane and nuclear-localized ER, we isolated subcellular receptor pools from MCF7 cells. Putative ER proteins were trypsin digested and subjected to tandem array mass spectrometry. The output analysis identified membrane and nuclear E2-binding proteins as classical human ERalpha. We also determined whether GPR30 plays any role in E2 rapid actions. MCF7 (ER and GPR30 positive) and SKBR-3 (ER negative, GPR30 positive) cells were incubated with E2. Only MCF7 responded with significantly increased signaling. In MCF7, the response to E2 was not different in cells transfected with small interfering RNA to green fluorescent protein or GPR30. In contrast, interfering RNA to ERalpha or ER inhibition prevented rapid signaling and resulting biology in MCF7. In breast cancer and ECs, nuclear and membrane ERs are the same proteins. Furthermore, classical ERs mediate rapid signals induced by E2 in these cells.

CO as a cellular signaling molecule

Many biological functions of heme oxygenase (HO), such as cytoprotection against oxidative stress, vasodilation, neurotransmission in the central or peripheral nervous systems, and anti-inflammatory, anti-apoptotic, or anti-proliferative potential, have been attributed to its enzymatic byproduct carbon monoxide (CO), although roles for biliverdin/bilirubin and iron have also been proposed. In addition to these well-characterized effects, recent findings reveal that HO-derived CO may act as an oxygen sensor and circadian modulator of heme biosynthesis. In lymphocytes, CO may participate in regulatory T cell function. A number of the known signaling effects of CO depend on stimulation of soluble guanylate cyclase and/or activation of mitogen-activated protein kinases (MAPK). Furthermore, modulation of caveolin-1 status may serve as an essential component of certain aspects of CO action, such as growth control. In this review, we summarize recent findings of the beneficial or detrimental effects of endogenous CO with an emphasis on the signaling pathways and downstream targets that trigger the action of this gas.

Estrogen Dendrimer Conjugates that Preferentially Activate Extranuclear, Nongenomic Versus Genomic Pathways of Estrogen Action

Estrogenic hormones are classically thought to exert their effects by binding to nuclear estrogen receptors and altering target gene transcription, but estrogens can also have nongenomic effects through rapid activation of membrane-initiated kinase cascades. The development of ligands that selectively activate only the nongenomic pathways would provide useful tools to investigate the significance of these pathways. We have prepared large, abiotic, nondegradable poly(amido)amine dendrimer macromolecules that are conjugated to multiple estrogen molecules through chemically robust linkages. Because of their charge and size, these estrogen-dendrimer conjugates (EDCs) remain outside the nucleus. They stimulate ERK, Shc, and Src phosphorylation in MCF-7 breast cancer cells at low concentrations, yet they are very ineffective in stimulating transcription of endogenous estrogen target genes, being approximately 10,000-fold less potent than estradiol in genomic actions. In contrast to estradiol, EDC was not effective in stimulating breast cancer cell proliferation. Because these EDC ligands activate nongenomic activity at concentrations at which they do not alter the transcription of estrogen target genes, they should be useful in studying extranuclear initiated pathways of estrogen action in a variety of target cells.

Membrane estrogen receptors: genomic actions and post transcriptional regulation

The primary cellular location of the nuclear estrogen receptor II (nER II) is the plasma membrane. A number of reports that have appeared in the recent past indicate that plasma membrane localized estrogen receptor alpha (ERalpha) also exists. Whether the membrane localized ERalpha represents the receptor that binds to the estrogen responsive element (ERE) remains to be known. The mechanisms that underlie the internalization of nER II (non-activated estrogen receptor, deglycosylated) have been identified to a certain extent. The question remains: is the primary location of the ERalpha also the plasma membrane? If that is the case, it will be a challenging task to identify the molecular events that underlie the plasma membrane-to-nucleus movement of ERalpha. The internalization mechanisms for the two 66kDa plasma membrane ERs, following hormone binding, appear to be distinct and without any overlaps. Interestingly, while the major gene regulatory role for ERalpha appears to be at the level of transcription, the nER II has its major functional role in post transcriptional mechanisms. The endoplasmic reticulum associated anchor protein-55 (ap55) that was recently reported from the author's laboratory needs a closer look. It is a high affinity estrogen binding protein that anchors the estrogen receptor activation factor (E-RAF) in an estrogen-mediated event. It will be interesting to examine whether ap55 bears any structural similarity with either ERalpha or ERbeta.

Oestrogen-mediated tyrosine phosphorylation of caveolin-1 and its effect on the oestrogen receptor localisation: an in vivo study

Recently, it has been shown that 17beta estradiol (E2) induces a rapid and transient activation of the Src ERK phosphorylation cascade: a clear indication that the alpha oestrogen receptor (ERalpha) is able to associate with the plasma membrane. Increasing evidence suggests that caveolae, which are caveolin-1 containing, highly hydrophobic membrane domains, play an important role in E2 induced signal transduction. Caveolae can accumulate signalling molecules preferentially; thus, they may have a regulatory role in signalling processes. Results from previous experiments have shown that E2 treatment decreased the number of surface connected caveolae significantly in uterine smooth muscle cells and also downregulated the expression of caveolin-1. In addition to providing further evidence that ERalpha interacts with caveolin/caveolae in uterine smooth muscle cells, this study also shows that the interaction between caveolin-1 and ERalpha is actually facilitated by E2. One of the signal transduction components found to accumulate in caveolae is Src kinase in an amount that increases simultaneously with increases in the amount of ERalpha. Upon E2 treatment, Src kinase is tyrosine phosphorylated, which, in turn, stimulates Src kinase to phosphorylate caveolin-1. Phosphorylation of caveolin-1 can drive caveolae to pinch off from the plasma membrane, thereby decreasing the amount of plasma membrane-associated caveolin-1. This loss of caveolin/caveolae activates the signal cascade that triggers cell proliferation.

Heat shock protein-70 mediates the cytoprotective effect of carbon monoxide: involvement of p38 beta MAPK and heat shock factor-1

Carbon monoxide (CO), a product of heme oxygenase activity, exerts antiapoptotic and anti-inflammatory effects in vitro and in vivo. The anti-inflammatory effects of CO involve the inhibition of TNF-alpha expression and the enhancement of IL-10 production, resulting in reduced mortality after endotoxin challenge. In this study we demonstrate for the first time that the protective effects of CO involve the increased expression of the 70-kDa inducible heat shock protein (Hsp70) in murine lung endothelial cells and fibroblasts. The p38beta MAPK mediated the effects of CO on cytoprotection and Hsp70 regulation. Suppression of Hsp70 expression and/or genetic deletion of heat shock factor-1, the principle transcriptional regulator of Hsp70, attenuated the cytoprotective and immunomodulatory effects of CO in mouse lung cells and in vivo. These data provide a novel mechanism for the protective effects of CO and underscore a potential application of this gaseous molecule in anti-inflammatory therapies.

TSC-36/FRP inhibits vascular smooth muscle cell proliferation and migration

OBJECTIVE

In-stent restenosis is a vascular proliferation/migration disorder characterized by hyperplasia of vascular smooth muscle cells (VSMCs). Because mounting evidence suggests that the therapeutic potential of anti-proliferation and anti-migration therapy, we investigated possible inhibitory effects of the matricellular protein TGF-beta-stimulated clone 36 (TSC-36) on vascular smooth muscle cell proliferation and migration in vitro and in vivo.

METHODS

Human umbilical artery smooth muscle cells (SMCs) were treated with inducting agents daidzein or estradiol. TSC-36 expression was detected by nested competitive PCR and in situ hybridization. TSC-36 was expressed in Origami (DE3) cells. The recombinant protein was used to immunize rabbits to produce polyclonal antibodies. VSMCs were treated with various concentrations of recombinant TSC-36 (rTSC-36) protein and daidzein. The MTT assay was used to analyze for cell proliferation. A transwell system was used to detect cell migration. Flow cytometry was used to detect cell phase. A rat carotid artery balloon injury model was duplicated. The rats were treated with daidzein or solvent control. Animals were sacrificed 5 weeks later, and injured arteries were taken for pathology and histology.

RESULTS

TSC-36 mRNA and protein expression was induced in SMCs. Cell proliferation and migration were inhibited by rTSC-36. rTSC-36 caused accumulation of SMCs in G2 phase. The inducting agent daidzein decreased neo-intima proliferation. TSC-36 mRNA and protein expression was induced and expressed in the neo-intima.

CONCLUSION

TSC-36 can be induced in VSMCs and inhibits VSMCs proliferation in vitro and in vivo.

From clinical evidence to molecular mechanisms underlying neuroprotection afforded by estrogens

Recent studies have highlighted that female sex hormones represent potential neuroprotective agents against damage produced by acute and chronic injuries in the adult brain. Clinical reports have documented the effectiveness of estrogens to attenuate symptoms associated with Parkinson's disease, and to reduce the risk of Alzheimer's disease and cerebrovascular stroke. This evidence is corroborated by numerous experimental studies documenting the protective role of female sex hormones both in vitro and in vivo. Accordingly, estrogens have been shown to promote survival and differentiation of several neuronal populations maintained in culture, and to reduce cell death associated with excitotoxicity, oxidative stress, serum deprivation or exposure to beta-amyloid. The neuroprotective effects of estrogens have been widely documented in animal models of neurological disorders, such as Alzheimer's and Parkinson's diseases, as well as cerebral ischemia. Although estrogens are known to exert several direct effects on neurones, the cellular and molecular mechanisms implicated in their protective actions on the brain are not completely understood. Thus, on the basis of clinical and experimental evidence, in this review, we discuss recent findings concerning the neuronal effects of estrogens that may contribute to their neuroprotective actions. Both estrogen receptor-dependent and -independent mechanisms will be described. These include modulation of cell death regulators, such as Bcl-2, Akt and calpain, as well as interaction with growth factors, such as BDNF, NGF, IGF-I and their receptors. The anti-inflammatory effects of estrogens will also be described, namely their ability to reduce brain levels of inflammatory mediators, cytokines and chemokines. Finally, a brief overview about receptor-independent mechanisms of neuroprotection will aim at describing the antioxidant effects of estrogens, as well as their ability to modulate neurotransmission.

Oestradiol rapidly inhibits Ca2+ signals in ciliary neurons through classical oestrogen receptors in cytoplasm

Oestrogen plays a key role in a great variety of actions in the nervous system, either through classical or alternative pathways. The classical pathways are initiated after oestrogen binding to the oestrogen receptors ERalpha or ERbeta, which translocate from the cytoplasm to the nucleus and act there as transcription factors. Alternative pathways are initiated at the plasma membrane and cytoplasm, via binding to classical or non-classical ERs. Using isolated ciliary ganglion neurons from the chick embryo and Ca2+ imaging, we demonstrated that a 10-min exposure to 17beta-oestradiol reduces Ca2+ influx through the plasma membrane. This effect was not reproduced by oestradiol conjugated to bovine serum albumin, which does not cross the plasma membrane, indicating that 17beta-oestradiol was acting intracellularly. ERalpha was detected in the cytoplasm by immunostaining and its involvement in the regulation of Ca2+ influx by ICI182,780 inhibition. The phosphatidylinositol-3 kinase (Pi3-kinase) inhibitor wortmannin and the nitric oxide synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) both blocked the oestradiol effect. The oestradiol effect was reproduced by 8Br-cGMP and abolished in the presence of the cGMP-dependent protein kinase (PKG) inhibitor KT5823. Our study indicates that 17beta-oestradiol can regulate Ca2+ influx via PI3-kinase, NOS and PKG after activation of cytoplasmic ER.

Two types of detergent-insoluble, glycosphingolipid/cholesterol-rich membrane domains from isolated myelin

Two different types of low-density detergent-insoluble glycosphingolipid-enriched membrane domain (DIG) fractions were isolated from myelin by extraction with Triton X-100 (TX-100) in 50 mM sodium phosphate buffer at room temperature (20 degrees C) (procedure 1), in contrast to a single low-density fraction obtained by extraction with TX-100 in Tris buffer containing 150 mM NaCl and 5 mM EDTA at 4 degrees C (procedure 2). Procedure 1 has been used in the past by others for myelin extraction to preserve the cytoskeleton and/or radial component of oligodendrocytes and myelin, whereas procedure 2 is now more commonly used to isolate myelin DIG fractions. The two DIG fractions obtained by procedure 1 gave opaque bands, B1 and B2, at somewhat lower and higher sucrose density respectively than myelin itself. The single DIG fraction obtained by procedure 2 gave a single opaque band at a similar sucrose density to B1. Both B1 and B2 had characteristics of lipid rafts, i.e. high galactosylceramide and cholesterol content and enrichment in GPI-linked 120-kDa neural cell adhesion molecule (NCAM)120, as found by others for the single low-density DIG fraction obtained by procedure 2. However, B2 had most of the myelin GM1 and more of the sulfatide than B1, and they differed significantly in their protein composition. B2 contained 41% of the actin, 100% of the tubulin, and most of the flotillin-1 and caveolin in myelin, whereas B1 contained more NCAM120 and other proteins than B2. The single low-density DIG fraction obtained by procedure 2 contained only low amounts of actin and tubulin. B1 and B2 also had size-isoform selectivity for some proteins, suggesting specific interactions and different functions of the two membrane domains. We propose that B1 may come from non-caveolar raft domains whereas B2 may derive from caveolin-containing raft domains associated with cytoskeletal proteins. Some kinases present were active on myelin basic protein suggesting that the DIGs may come from signaling domains.

A Nongenomic Action of 17β-Estradiol as the Mechanism Underlying the Acute Suppression of Secretion of Luteinizing Hormone1

The objective of the present study was to determine the ability of 17beta-estradiol (E(2)) and conjugated forms of E(2) (E(2) conjugated to BSA [E(2)-BSA] and a novel conjugate, E(2) conjugated to a small peptide [E(2)-PEP]) to prevent the GnRH-induced secretion of LH and to determine the role of estradiol receptors (ERs) and ER subtypes (ERalpha, also known as ESR1, and ERbeta, also known as ESR2) in the mediation of the acute action of E(2) in primary cultures of ovine pituitary cells. Preincubation of cells for 15 min with E(2), E(2)-BSA, or E(2)-PEP prevented the GnRH-induced secretion of LH (P < 0.01). Treatment of cells with nonestrogenic steroid hormones did not affect secretion of LH when given alone, nor did these steroids impair the E(2)-induced inhibition of LH secretion (P > 0.1). Likewise, treatment of cells with the ER-antagonists tamoxifen, hydroxytamoxifen, or ICI 182 780 did not affect (P > 0.1) secretion of LH when given alone but did prevent (P < 0.01) the inhibition by E(2) and the E(2)-conjugates on GnRH-induced secretion of LH. When cells were treated with subtype-selective ER agonists, the ERalpha agonist (propylpyrazole-triol), but not the ERbeta agonist (diarylpropionitrile), decreased (P < 0.01) the GnRH-induced secretion of LH. In conclusion, the rapidity by which E(2) prevented GnRH-induced release of LH in ovine pituitary cells suggests that this inhibition is mediated via a nongenomic action of E(2). The inhibition of GnRH-induced secretion of LH proved to be steroid specific and mediated by ERs. It may occur specifically through ERalpha. The fact that E(2)-BSA or E(2)-PEP mimicked the action of E(2) suggests that this effect was mediated by an ER associated with the plasma membrane.

Estrogen receptor-alpha is associated with the plasma membrane of astrocytes and coupled to the MAP/Src-kinase pathway

Estrogens influence CNS development and a broad spectrum of neural functions. Several lines of evidence also suggest a neuroprotective role for estrogen. Different modes of estrogen action have been described at the cellular level involving classical nuclear estrogen receptor (ER)-dependent and nonclassical membrane ER-mediated rapid signaling. We have previously shown that nonclassical estrogen signaling is implicated in the control of dopamine cell function and protection. Since nonclassical interactions between estrogens and glia may contribute to these effects, our aim was to demonstrate the presence of membrane-associated ERs and their putative coupling to intracellular signaling pathways in astrocytes. Confocal image analysis and fluorescence-activated cell sorting (FACS) studies indicated the attachment of ER-alpha but not ER-beta to the plasma membrane of astrocytes. ERs were located in the cell soma region and glial processes. FACS analysis revealed that only a subpopulation of midbrain astrocytes possesses membrane ER-alpha. In FACS studies on ER-alpha knockout astrocytes, only a few membrane ER-positive cells were detected. The activation of membrane ERs appears to be coupled to the MAP-kinase/Src signaling pathway as shown by Western blotting. In conclusion, our data provide good evidence that nonclassical estrogen action in astrocytes is mediated by membrane ER-alpha. The physiological consequence of this phenomenon is not yet understood, but it might have a pivotal role in estrogen-mediated protective effects on midbrain dopamine neurons.

Regulation of signal transduction pathways by estrogen and progesterone

The female sex steroid hormones 17beta-estradiol and progesterone mediate their biological effects on development, differentiation, and maintenance of reproductive tract and other target tissues through gene regulation by nuclear steroid receptors that function as ligand-dependent transcription factors. However, not all effects of 17beta-estradiol and progesterone are mediated by direct control of gene expression. These hormones also have rapid stimulatory effects on the activities of a variety of signal transduction molecules and pathways and, in many cases, these effects appear to be initiated from the plasma cell membrane. There is growing evidence that a subpopulation of the conventional nuclear steroid receptor localized at the cell membrane mediates many of the rapid signaling actions of steroid hormones; however, novel membrane receptors unrelated to conventional steroid receptors have also been implicated. This chapter reviews the nature of the receptors that mediate rapid signaling actions of estrogen and progesterone and describes the signaling molecules and pathways involved, the mechanisms by which receptors couple with components of signaling complexes and trigger responses, and the target tissues and cell functions regulated by this mode of steroid hormone action.

Increased cholesterol decreases uterine activity: functional effects of cholesterol alteration in pregnant rat myometrium

Uterine quiescence is essential for successful pregnancy. Cholesterol and triglycerides are markedly increased in pregnancy. Cholesterol is enriched in microdomains of the plasma membrane known as rafts and caveolae. Both lipid rafts and caveolae have been implicated in cellular signaling cascades. The purpose of this work was to investigate whether manipulation of cholesterol content alters uterine contractility. Late pregnancy (19–21 days) rats were humanely euthanized and strips of longitudinal myometrium were then dissected. Force and Ca2+ measurements were simultaneously recorded and cholesterol increased by the addition of 5 mg/ml cholesterol or 0.25 mg/ml low-density lipoproteins (LDLs) or reduced by 2% methyl-β-cyclodextrin (MCD) or 2 U/ml cholesterol oxidase addition to the perfusate. Both LDLs and cholesterol profoundly inhibited spontaneous uterine force production and associated Ca2+ transients; frequency, amplitude, and duration of contraction were all significantly reduced compared with preceding control contractions. Force and Ca2+ were also reduced by cholesterol when 1 nM oxytocin was used to stimulate the myometrium. Uterine activity was significantly increased by cholesterol extraction with MCD or cholesterol oxidase treatment. Electron microscopy confirmed the lipid raft disrupting effect of MCD, as formerly electron microscopy-visible caveolae in the myometrial cell membrane all but disappeared after MCD treatment. These data show that uterine smooth muscle cell cholesterol content is critically important for functional activity. A novel finding of our study is that cholesterol is inhibitory for force generation. It may be one of the mechanisms operating to maintain uterine quiescence throughout gestation and may also contribute to difficulties in labor suffered by obese women.

The Acute Estrogenic Dilation of Rat Aorta Is Mediated Solely by Selective Estrogen Receptor-α Agonists and Is Abolished by Estrogen Deprivation

Estrogen is known to induce rapid vasodilatory response in isolated arteries. Because estrogen is a nonselective receptor agonist, the involvement of estrogen receptor (ER) subtypes in acute estrogenic responses has remained elusive. Acute administration of the selective ERalpha agonist 4,4',4''-(4-propyl-[(1)H]pyrazole-1,3,5-triyl) tris-phenol (PPT) to precontracted aortic rings from intact female rats dose-dependently induced an ER-dependent vascular relaxation fully overlapping to that induced by 17beta-estradiol. By contrast, the selective ERbeta agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) had no acute effect on vasomotion. This short-term vasorelaxant action of PPT was abolished by the NO synthase inhibitor N(omega)-nitro-l-arginine methyl ester and by endothelium removal. In aortic tissues from ovariectomized (OVX) rats, however, neither 17beta-estradiol nor PPT induced acute vascular relaxation. The effect of PPT was restored in preparations from estrogen-replaced OVX rats, whereas DPN remained ineffective even after estrogen replacement. PPT acted through an ER-dependent mechanism, as shown by impaired response in the presence of the anti-estrogen ICI 182,780 (7alpha,17beta-[9[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol). Accordingly, isolated rat aortic endothelial cells expressed both ERalpha and ERbeta. These data show that selective ERalpha but not ERbeta agonists reproduced the acute vasodilation of estrogen via a receptor-mediated pathway in the aorta from intact as well as 17beta-estradiol-replaced OVX rats. This beneficial effect was undetectable in tissues from OVX rats. Selective pharmacological targeting of ER subtypes may thus represent a novel and promising approach in the treatment of vascular disease.

Integration of the extranuclear and nuclear actions of estrogen

Estrogen receptors (ERs) are localized to many sites within the cell, potentially contributing to overall estrogen action. In the nucleus, estrogen mainly modulates gene transcription, and the resulting protein products determine the cell biological actions of the sex steroid. In addition, a small pool of ERs localize to the plasma membrane and signal mainly though coupling, directly or indirectly, to G proteins. In response to steroid, signal transduction modulates both nontranscriptional and transcriptional events and impacts both the rapid and more prolonged actions of estrogen. Cross-talk from membrane-localized ERs to nuclear ERs can be mediated through growth factor receptor tyrosine kinases, such as epidermal growth factor receptor and IGF-I receptor. Growth factor receptors enact signal transduction to kinases such as ERK and phosphatidylinositol 3-kinase that phosphorylate and activate nuclear ERs, and this can also occur in the absence of sex steroid. A complex relationship between the membrane and nuclear effects of estrogen also involves membrane-initiated phosphorylation of coactivators, recruiting these proteins to the nuclear transcriptosome. Finally, large pools of cytoplasmic ERs exist, and some are localized to mitochondria. The integration of sex steroid effects at distinct cellular locations of its receptor leads to important cellular physiological outcomes and are manifest in both reproductive and nonreproductive organs.

Mechanisms of estrogen receptor signaling: convergence of genomic and nongenomic actions on target genes

Estrogen receptors (ERs) act by regulating transcriptional processes. The classical mechanism of ER action involves estrogen binding to receptors in the nucleus, after which the receptors dimerize and bind to specific response elements known as estrogen response elements (EREs) located in the promoters of target genes. However, ERs can also regulate gene expression without directly binding to DNA. This occurs through protein-protein interactions with other DNA-binding transcription factors in the nucleus. In addition, membrane-associated ERs mediate nongenomic actions of estrogens, which can lead both to altered functions of proteins in the cytoplasm and to regulation of gene expression. The latter two mechanisms of ER action enable a broader range of genes to be regulated than the range that can be regulated by the classical mechanism of ER action alone. This review surveys our knowledge about the molecular mechanism by which ERs regulate the expression of genes that do not contain EREs, and it gives examples of the ways in which the genomic and nongenomic actions of ERs on target genes converge. Genomic and nongenomic actions of ERs that do not depend on EREs influence the physiology of many target tissues, and thus, increasing our understanding of the molecular mechanisms behind these actions is highly relevant for the development of novel drugs that target specific receptor actions.

Estrogens and Neuropeptides in Raynaud's Phenomenon

Raynaud's phenomenon (RP) is characterized by ischemia and reperfusion of the extremities. Vasomotor instability is due to a microcirculatory disturbance that may be linked to different events involving the endothelium or peripheral nerve terminals. Endothelium and nerve endings "sense" the modifications of the microenvironment and both of them release factors that contribute to find a balance between vasolidation and vasoconstriction. Moreover, estrogens may contribute to control vascular tone regulating finger skin circulation. A loss of neuropeptides has been shown in secondary RP where supplementation with factors derived from nerve endings has been demonstrated to induce a potent vasolidation. Estrogen administration improved endothelial dysfunction in secondary RP. Neuropeptides and estrogens thus share the endothelial-dependent pathway, usually mediated by nitric oxide, in inducing vasolidation. The network directed by the endothelium is in reality controlled by a neuro-hormonal axis composed by neuropeptides and estrogens. This delicate balance keeps the vascular tone, and its dysfunction may lead to a dysregulation of vascular tone, manifest in clinics as a primary or secondary RP.

Caveolae compartmentalization of heme oxygenase-1 in endothelial cells

The heme oxygenase (HO) and nitric oxide synthase (NOS) enzymes generate the gaseous signaling molecules carbon monoxide (CO) and nitric oxide, respectively. Constitutive NOSs localize to caveolae, and their activities are modulated by caveolin-1. Nothing is known of the localization of the inducible heme oxygenase-1 (HO-1) in plasma membrane caveolae. Thus, we examined the distribution and subcellular localization of HO-1, biliverdin reductase (BVR), and NADPH:cytochrome P450 reductase (NPR) in pulmonary artery endothelial cells. Each of these proteins localized in part to plasma membrane caveolae in endothelial cells. Inducers of HO-1 or overexpression of HO-1 increased the content of this protein in a detergent-resistant fraction containing caveolin-1. Inducible HO activity appeared in plasma membrane, cytosol, and isolated caveolae. In addition, caveolae contained endogenous BVR activity, supporting the same compartmentalization of both enzymes. Caveolin-1 physically interacted with HO-1, as shown by coimmunoprecipitation studies. HO activity dramatically increased in cells expressing caveolin-1 antisense transcripts, suggesting a negative regulatory role for caveolin-1. Conversely, caveolin-1 expression attenuated LPS-inducible HO activity. Since their initial characterization in 1969, HO enzymes have been described as endoplasmic reticulum-associated proteins. We demonstrate for the first time the localization of heme degradation enzymes to plasma membrane caveolae, and present novel evidence that caveolin-1 interacts with and modulates HO activity.

Antiestrogens, aromatase inhibitors, and apoptosis in breast cancer

Antiestrogens have been the therapeutic agents of choice for breast cancer patients whose tumors express estrogen receptors, regardless of menopausal status. Unfortunately, many patients will eventually develop resistance to these drugs. Antiestrogens primarily act by preventing endogenous estrogen from activating estrogen receptors and promoting cell growth, which can ultimately lead to tumor cell death. Understanding the mechanisms by which antiestrogens cause cell death or apoptosis is critical to our efforts to develop ways to circumvent resistance. This article focuses on antiestrogen-induced apoptosis both in vitro and in vivo. We review the clinical utility of both antiestrogens and aromatase inhibitors and their apoptogenic mechanisms in cell culture models. Among the key signaling components discussed are the roles of Bcl-2 family members, several cytokines, and their receptors, p53, nuclear factor kappa B (NFkappaB), IRF-1, phosphatidylinositol 3-kinase (PI3K)/Akt, and specific caspases. Finally, we discuss the evidence supporting a role for apoptotic defects in acquired and de novo antiestrogen resistance.

Estrogen receptor activation of phosphoinositide-3 kinase, akt, and nitric oxide signaling in cerebral blood vessels: rapid and long-term effects

Estrogen receptor regulation of nitric oxide production by vascular endothelium may involve rapid, membrane-initiated signaling pathways in addition to classic genomic mechanisms. In this study, we demonstrate using intact cerebral blood vessels that 17beta-estradiol rapidly activates endothelial nitric-oxide synthase (eNOS) via a phosphoinositide-3 (PI-3) kinase-dependent pathway. The effect is mediated by estrogen receptors (ERs), consistent with colocalization of ERalpha and caveolin-1 immunoreactivity at the plasma membrane of endothelial cells lining cerebral arteries. Treatment with 10 nM 17beta-estradiol for 30 min increased NO production, as measured by total nitrite assay, in cerebral vessels isolated from ovariectomized rats. This effect was significantly decreased by membrane cholesterol depletion with beta-methyl-cyclodextrin, the ER antagonist ICI 182,780 [fulvestrant (Faslodex)], and two inhibitors of PI-3 kinase: wortmannin and LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride]. In parallel with NO production, 17beta-estradiol treatment rapidly increased phosphorylation of both eNOS (p-eNOS) and Akt (p-Akt). PI-3 kinase inhibitors also blocked the latter effects; together, these data are consistent with ER activation of the PI-3 kinase-p-Akt-p-eNOS pathway. ERalpha protein (66 and 50 kDa) coimmunoprecipitated with eNOS as well as with the p85alpha regulatory subunit of PI-3 kinase, further implicating ERalpha in kinase activation of eNOS. Little is known regarding the effects of estrogen on cellular kinase pathways in vivo; therefore, we compared cerebral blood vessels isolated from ovariectomized rats that were either untreated or given estrogen replacement for 4 weeks. Long-term estrogen exposure increased levels of cerebrovascular p-Akt and p-eNOS as well as basal NO production. Thus, in addition to the rapid activation of PI-3 kinase, p-Akt, and p-eNOS, estrogen signaling via nontranscriptional, kinase mechanisms has long-term consequences for vascular function.

Expression of estrogen receptors-alpha and -beta in the pregnant ovine uterine artery endothelial cells in vivo and in vitro

Estrogen is recognized to be one of the driving forces in increases in uterine blood flow through both rapid and delayed actions via binding to its receptors, ER alpha and ER beta at the uterine artery (UA) wall, and especially in UA endothelium (UAE). However, information regarding estrogen receptor (ER) expression in UAE is limited. This study was designed to test whether ERs are expressed in UAE in vivo, and if they are, whether these receptors are maintained in cultured UA endothelial cells (UAECs) in vitro. By using immunohistochemical and Western blot analyses, we clearly demonstrated ER alpha and ER beta protein expression in pregnant (Days 120-130) sheep UA and UAE in vivo and as well as cultured UAECs in vitro. Reverse transcription-polymerase chain reaction (RT-PCR) amplified both ER alpha and ER beta mRNAs in UA, UAE, and UAECs. Of interest, a truncated ER beta (ER beta2) variant due to a splicing deletion of exon 5 of the ER beta gene was detected in these cells. Quantitative RT-PCR analysis revealed that ER alpha mRNA levels are approximately 8-fold (P < 0.01) higher than that of ER beta in UAECs, indicating that ER alpha may play a more important role than ER beta in the UAEC responses to estrogen. Fluorescence immunolabeling analysis showed that ER alpha is present in both nuclei and plasma membranes in UAECs, and the latter is also colocalized with caveolin-1. The membrane and nuclear ER alpha presumably participate in rapid and delayed responses, respectively, to estrogen on UAE. Taken together, our data demonstrated that UAE is a direct target of estrogen actions and that the UAEC culture model we established is suitable for dissecting estrogen actions on UAE.

Disentangling the molecular mechanisms of action of endogenous and environmental estrogens

The gonadal hormone 17beta-estradiol is involved in numerous cellular processes. In many cases, 17beta-estradiol actions are imitated by synthetic and natural chemicals in the environment. Their actions differ depending on the target tissue, the receptors involved and the molecular pathways activated. The plethora of estrogenic actions is triggered by different receptors and other specific structures that activate different signalling pathways. This amount of information may lead to a maze of effects triggered by endogenous and environmental estrogens that we intend to clarify in this review. Understanding the variety of estrogen receptors, their different locations and the signalling pathways activated by estrogenic ligands is fundamental for understanding the diversity of actions that estrogens have in different tissues and cells.

Effects of low-dose continuous combined HRT on vascular function in women with type 2 diabetes

BACKGROUND

Improvement in vascular endothelial function is widley cited as a beneficial effect of hormone replacement therapy (HRT). Women with type 2 diabetes (T2DM) are at increased cardiovascular risk and have impaired endothelial function. Any benefits of HRT on endothelial function in this group are of particular interest.

OBJECTIVES

We assessed effects on vascular function of oral 17beta oestradiol (1 mg) and norethisterone (0.5 mg) in postmenopausal women with T2DM.

DESIGN

Double-blind, randomised, placebo-controlled trial.

ASSESSMENTS

Twenty-eight women had pulse wave velocity (PWV) and adhesion molecules VCAM-1 and ICAM-1 assessed before and after three months' treatment. Twenty-four women also had gluteal fat biopsy for assessment of resistance vessel function (using wire myography).

RESULTS

HRT did not affect PWV, VCAM-1, ICAM-1 or carbachol response. Effects of L-NAME and indomethacin on carbachol sensitivity were similar in both groups.

CONCLUSIONS

This HRT preparation had no detectable effect on these measures of endothelial function in women with T2DM.

Membrane associated estrogen receptors and related proteins: localization at the plasma membrane and the endoplasmic reticulum

The female sex steroid, estradiol 17beta, mediates its effect through its association with estrogen receptor present in the target cell. So far the major emphasis has been given to the genomic actions of the hormone mediated by the nuclear estrogen receptors. Recent years have seen a shift in the ideas revealing the existence of estradiol binding entities both in the plasma membrane and the endoplasmic reticulum. Though the true identity of this membrane associated receptors is far from being known, a functional role for the same have been implicated both at the genomic as well as the non-genomic level. The major focus of the review is to highlight the existence of membrane associated estrogen receptors and receptor-related proteins and the functional roles played by some of them. The signalling events exerted by this class of membrane associated estrogen receptor could partly explain the physiological significance of estrogen in cardiovascular disease, osteoporosis and breast cancer as well as the molecular mechanism associated with xenoestrogen action.

Estrogen exerts neuroprotective effects via membrane estrogen receptors and rapid Akt/NOS activation

The neuroprotective role of estrogen (E2) is supported by a multitude of experimental and epidemiological data, although its mode of action is not fully understood. The present work was conducted to study the underlying mechanisms of its neuroprotective action, using the rat cell line PC12, an established model for neuronal cell apoptosis and survival. Our results show that E2 (but not androgens or progestins) prevent growth inhibition and apoptosis of PC12 cells, induced by serum deprivation. Several mechanisms of action were investigated: 1) intracellular estrogen receptors (ERs) have been identified but do not appear to mediate the protective effect of E2. 2) The antioxidant properties of E2 cannot explain their protective actions at the concentrations used (10(-12)-10(-6) M). 3) Finally, membrane sites for E2 have been identified, and the underlying initial signaling cascade (2-30 min after E2) has been tested, showing Ca(2+) mobilization-->PI3K activation-->Akt phosporylation-->NOS activation. Inhibition of PI3K or NOS completely reversed the anti-apoptotic effect of E2. These results suggest a new mechanism of neuroprotective action of estrogen.