Differential requirements of Hsp90 and DNA for the formation of estrogen receptor homodimers and heterodimers

The two estrogen receptor (ER) subforms, ERalpha and ERbeta, are capable of forming DNA-binding homodimers and heterodimers. Although binding to DNA is thought to stabilize ER dimers, how ERalpha/alpha, ERbeta/beta, and ERalpha/beta dimerization is regulated by DNA and the chaperone protein Hsp90 is poorly understood. Using our highly optimized bioluminescence resonance energy transfer assays in conjunction with assays for transcriptional activation of ERs, we determined that DNA binding appears to play a minor role in the stabilization of ER dimers, especially in the case of ERbeta/beta homodimers. These findings suggest that ER dimers form before they associate with chromatin and that DNA binding plays a minor role in stabilizing ER dimers. Additionally, although Hsp90 is essential for the proper dimerization of ERalpha/alpha and ERalpha/beta, it is not required for the proper dimerization of ERbeta/beta. Despite this, Hsp90 is critical for the estrogen-dependent transcriptional activity of the ERbeta/beta homodimer. Thus, Hsp90 is implicated as an important regulator of distinct aspects of ERalpha and ERbeta action.

Comparative effects of R- and S-equol and implication of transactivation functions (AF-1 and AF-2) in estrogen receptor-induced transcriptional activity

Equol, one of the main metabolites of daidzein, is a chiral compound with pleiotropic effects on cellular signaling. This property may induce activation/inhibition of the estrogen receptors (ER) a or b, and therefore, explain the beneficial/deleterious effects of equol on estrogen-dependent diseases. With its asymmetric centre at position C-3, equol can exist in two enantiomeric forms (R- and S-equol). To elucidate the yet unclear mechanisms of ER activation/inhibition by equol, we performed a comprehensive analysis of ERa and ERb transactivation by racemic equol, as well as by enantiomerically pure forms. Racemic equol was prepared by catalytic hydrogenation from daidzein and separated into enantiomers by chiral HPLC. The configuration assignment was performed by optical rotatory power measurements. The ER-induced transactivation by R- and S-equol (0.1–10 µM) and 17b-estradiol (E2, 10 nM) was studied using transient transfections of ERα and ERβ in CHO, HepG2 and HeLa cell lines. R- and S-equol induce ER transactivation in an opposite fashion according to the cellular context. R-equol and S-equol are more potent in inducing ERα in an AF-2 and AF-1 permissive cell line, respectively. Involvement of ERα transactivation functions (AF-1 and AF-2) in these effects has been examined. Both AF-1 and AF-2 are involved in racemic equol, R-equol and S-equol induced ERα transcriptional activity. These results could be of interest to find a specific ligand modulating ER transactivation and could contribute to explaining the diversity of equol actions in vivo.

FKBPL regulates estrogen receptor signaling and determines response to endocrine therapy

The HSP90 chaperone and immunophilin FKBPL is an estrogen-responsive gene that interacts with estogen receptor alpha (ERalpha) and regulates its levels. In this study, we explored the effects of FKBPL on breast cancer proliferation. Breast cancer cells stably overexpressing FKBPL became dependent on estrogen for their growth and were dramatically more sensitive to the antiestrogens tamoxifen and fulvestrant, whereas FKBPL knockdown reverses this phenotype. FKBPL knockdown also decreased the levels of the cell cycle inhibitor p21WAF1 and increased ERalpha phosphorylation on Ser(118) in response to 17beta-estradiol and tamoxifen. In support of the likelihood that these effects explained FKBPL-mediated cell growth inhibition and sensitivity to endocrine therapies, FKBPL expression was correlated with increased overall survival and distant metastasis-free survival in breast cancer patients. Our findings suggest that FKBPL may have prognostic value based on its impact on tumor proliferative capacity and sensitivity to endocrine therapies, which improve outcome.

Therapeutic potential of new 4-hydroxy-tamoxifen-loaded pH-gradient liposomes in a multiple myeloma experimental model

PURPOSE

To determine the better liposomal formulation incorporating the active metabolite of tamoxifen, 4-hydroxy-tamoxifen (4HT) and the biological impact of 4HT-pH-gradient liposomes on response to in vivo treatment.

METHODS

Several pegylated liposomes were formulated by varying the composition of lipids, increasing external pH from 7.4 to 9.0 and doubling the lipid concentration. Dipalmitoylphosphatidylcholine / cholesterol / distearoylphosphoethanolamine poly(ethylene)glycol liposomes (DL-9 liposomes) were chosen for their physico-chemical properties. Toxicity and release kinetics were assessed in breast cancer MCF-7 as well as in multiple myeloma (MM) cells. In vivo antitumor activity and bio-distribution were measured in the RPMI8226 MM model.

RESULTS

Compared to conventional non-pH-gradient liposomes, 4HT-DL-9 liposomes resulted in concentration of up to 1 mM 4HT, greater stability, relative toxicity and slow 4HT release. Intravenous injections of 4HT-DL-9 liposomes at 4 mg/kg/week blocked MM tumor growth. Ki67 and CD34 labeling decreased in treated tumors, concomitantly with increase of activated caspase-3 supporting a cell proliferation arrest, a decrease of tumor vasculature and the induction of tumor cell death.

CONCLUSION

This antitumor effect was assumed to be the result of a modified biodistribution of 4HT once trapped in DL-9 liposomes. Such 4HT-containing pH-gradient Stealth nanocarriers could be helpful for MM treatment.

Single plasmids expressing human steroid hormone receptors and a reporter gene for use in yeast signaling assays

Single plasmids designed to express the six human type I steroid hormone receptors and detect signaling activity are described in this report. These stably replicating plasmids reported ligand-induced transcriptional activation via lacZ assays in Baker's yeast (Saccharomyces cerevisiae). The ligand concentrations needed to activate signaling in yeast expressing these plasmids spanned five orders of magnitude as based on comparisons of EC(50) values. Radicicol, a direct inhibitor of heat shock protein 90 (Hsp90) and an indirect inhibitor of steroid hormone receptor signaling, was used to determine the functional utility of this yeast reporter system. The inhibitory effect of radicicol was similar on the signaling of all six steroid hormone receptors and was distinguishable from cytotoxic effects that occurred with higher concentrations. These yeast plasmids provide a high throughput system for comparative assessment of steroid hormone receptor signaling and may be useful in screening for pharmacological or xenobiotic activities.

Research into Specific Modulators of Vascular Sex Hormone Receptors in the Management of Postmenopausal Cardiovascular Disease

Cardiovascular disease (CVD) is more common in men and postmenopausal women than premenopausal women, suggesting vascular benefits of female sex hormones. Studies on the vasculature have identified estrogen receptors ERα, ERβ and a novel estrogen binding membrane protein GPR30, that mediate genomic and/or non-genomic effects. Estrogen promotes endothelium-dependent relaxation by inducing the production/activity of nitric oxide, prostacyclin, and hyperpolarizing factor, and inhibits the mechanisms of vascular smooth muscle contraction including [Ca(2+)](i), protein kinase C, Rho kinase and mitogen-activated protein kinase. Additional effects of estrogen on the cytoskeleton, matrix metalloproteinases and inflammatory factors contribute to vascular remodeling. However, the experimental evidence did not translate into vascular benefits of menopausal hormone therapy (MHT), and the HERS, HERS-II and WHI clinical trials demonstrated adverse cardiovascular events. The discrepancy has been partly related to delayed MHT and potential changes in the vascular ER amount, integrity, affinity, and downstream signaling pathways due to the subjects' age and preexisting CVD. The adverse vascular effects of MHT also highlighted the need of specific modulators of vascular sex hormone receptors. The effectiveness of MHT can be improved by delineating the differences in phramcokinetics and pharmacodynamics of natural, synthetic, and conjugated equine estrogens. Estriol, "hormone bioidenticals" and phytoestrogens are potential estradiol substitutes. The benefits of low dose MHT, and transdermal or vaginal estrogens over oral preparations are being evaluated. Specific ER modulators (SERMs) and ER agonists are being developed to maximize the effects on vascular ERs. Also, the effects of estrogen are being examined in the context of the whole body hormonal environment and the levels of progesterone and androgens. Thus, the experimental vascular benefits of estrogen can be translated to the outcome of MHT in postmenopausal CVD, as more specific modulators of sex hormone receptors become available and are used at the right dose, route of administration and timing, depending on the subject's age and preexisting cardiovascular condition.

Hexachlorobenzene induces cell proliferation and IGF-I signaling pathway in an estrogen receptor alpha-dependent manner in MCF-7 breast cancer cell line

Hexachlorobenzene (HCB) is an organochlorine pesticide widely distributed in the biosphere. ERalpha regulates the expression of genes involved in growth and development, and plays an important role in breast cancer. The present study focuses attention on the effect of HCB (0.005, 0.05, 0.5, 5 microM) on cell proliferation in estrogen receptor alpha (ERalpha)(+) MCF-7, and ERalpha(-) MDA-MB-231 breast cancer cell lines. We also studied the insulin growth factor-I (IGF-I) signaling pathway in MCF-7 cells. HCB (0.005 and 0.05 microM) stimulated cell proliferation in MCF-7, but not in MDA-MB-231 cells. The pesticide increased apoptosis in MCF-7, at HCB (0.5 and 5 microM). At these doses, HCB induced the expression of the aryl hydrocarbon receptor (AhR)-regulated gene cytochrome P4501A1. MCF-7 cells exposed to HCB (0.005 and 0.05 microM) overexpressed IGF-IR and insulin receptor (IR). IRS-1-phosphotyrosine content was increased in a dose dependent manner. ICI 182,780 prevented HCB-induced cell proliferation and IGF-I signaling in MCF-7 cells incubated in phenol-red free media. In addition, HCB (0.005 microM) increased c-Src activation, Tyr537-ERalpha phosphorylation and ERalpha down-regulation. Taken together, our data indicate that HCB stimulation of cell proliferation and IGF-I signaling is ERalpha dependent in MCF-7 cells.

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

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

Isoflavones are safe compounds for therapeutical applications - evaluation of in vitro data

Isoflavone-rich food and food supplements have gained increasing popularity also in the Western world. Their weak estrogenic effect has been considered as a potential risk, although all epidemiological studies and clinical trials show a significant cancer protection and decreased risk of cardiovascular diseases. In vitro data suggest that the concerted action of the isoflavones and their metabolites show antiproliferative behaviour, reduce angiogenesis, reduce tumor progression and exert antiinflammatory effects. For the evaluation of the biological effects, special emphasis has to be put on the concerted action between the isoflavones and their metabolites. For instance, while isolated genistein shows some growth promoting effect at low concentrations, the metabolite equol or soy extract show growth retardation as well as higher concentrations of genistein do. The isoflavones have multiple affinities to other members of the steroid hormone receptor superfamily. The beneficial effect on metabolic diseases and weight reduction by isoflavone consumption can be partly explained by its affinity for the PPAR family. In light of the in vitro experiments, together with the epidemiological observations and the clinical experience, isoflavones can be considered as safe compounds and their consumption as food and food supplements has to be promoted.

CK1delta modulates the transcriptional activity of ERalpha via AIB1 in an estrogen-dependent manner and regulates ERalpha-AIB1 interactions

Oncogenesis in breast cancer often requires the overexpression of the nuclear receptor coactivator AIB1/SRC-3 acting in conjunction with estrogen receptor-α (ERα). Phosphorylation of both ERα and AIB1 has been shown to have profound effects on their functions. In addition, proteasome-mediated degradation plays a major role by regulating their stability and activity. CK1δ, a member of the ubiquitous casein kinase-1 family, is implicated in the progression of breast cancer. In this study, we show that both ERα and AIB1 are substrates for CK1δ in vitro, and identify a novel AIB1 phosphorylation site (S601) targeted by CK1δ, significant for the co-activator function of AIB1. CK1δ is able to interact with ERα and AIB1 in vivo, while overexpression of CK1δ in breast cancer cells results in an increased association of ERα with AIB1 as confirmed by co-immunoprecipitation assays from cell lysates. Using an siRNA-based approach, luciferase reporter assays and qRT-PCR, we observe that silencing of CK1δ leads to reduced ERα transcriptional activity, despite increased ERα levels, similarly to proteasome inhibition. We provide evidence that AIB1 protein levels are reduced by CK1δ silencing, in an estradiol-dependent manner; such destabilization can be inhibited by pre-treatment with the proteasome inhibitor MG132. We propose that differing activities adopted by ERα and AIB1 as a consequence of their interactions with and phosphorylation by CK1δ, particularly AIB1 stabilization, influence the transcriptional activity of ERα, and therefore have a role in breast cancer development.

Developmental programming: prenatal androgen excess disrupts ovarian steroid receptor balance

Steroid hormones play an important role in reproduction and the receptors through which they signal change in a developmental time, follicle stage, and cell-specific manner. Disruption in steroid receptor expression affects follicle formation and differentiation. In this study, using prenatal testosterone (T) and dihydrotestosterone (DHT)-treated female sheep as model systems, we tested the hypothesis that prenatal androgen excess disrupts the developmental ontogeny of ovarian steroid receptor protein expression. Pregnant Suffolk ewes were injected twice weekly with T propionate or DHT propionate (a non-aromatizable androgen) in cottonseed oil from days 30 to 90 of gestation. Changes in ovarian estrogen receptors (ER; ESR1, ESR2), androgen receptor (AR) and progesterone receptor (PGR) proteins were determined at fetal (days 90 and 140), postpubertal (10 months), and adult (21 months; only prenatal T-treated sheep studied) ages by immunohistochemistry. Prenatal T and DHT treatment induced selective increase in AR but not ER or PGR expression in the stroma and granulosa cells of fetal days 90 and 140 ovaries. An increase in ESR1 and decrease in ESR2 immunostaining coupled with increased AR expression were evident in granulosa cells of antral follicles of 10- and 21-month-old prenatal T but not DHT-treated females (analyzed only at 10 months). These findings provide evidence that an early increase in ovarian AR is the first step in the altered ovarian developmental trajectory of prenatal T-treated females, and manifestations of postnatal ovarian dysfunction are likely facilitated via altered equilibrium of antral follicular granulosa cell ER/AR protein expression.

Resveratrol and chemoprevention

Resveratrol is a phytoalexin, highly abundant in skins of red grapes and moderately abundant in peanuts and blueberries. Originally a constituent of oriental medicines, it has lately been rediscovered for a plethora of beneficial properties such as anti-cancer, anti-aging, antiviral, cardiovascular and neuroprotective effects, thereby making it one of the most sought after phytochemicals for supplementing human diet. Studies done in various laboratories have shown its modulatory effects on multitudes of cell signaling and gene expression pathways. Although most of its effects have been observed in cultured cells, quite a few have also been validated in whole animals as well. It is thus necessary to have a comprehensive look at all those effects of resveratrol in an organismal context. The following review summarizes the effects of resveratrol in the context of chemoprevention.

Targeted magnetic iron oxide nanoparticles for tumor imaging and therapy

Magnetic iron oxide (IO) nanoparticles with a long blood retention time, biodegradability and low toxicity have emerged as one of the primary nanomaterials for biomedical applications in vitro and in vivo. IO nanoparticles have a large surface area and can be engineered to provide a large number of functional groups for cross-linking to tumor-targeting ligands such as monoclonal antibodies, peptides, or small molecules for diagnostic imaging or delivery of therapeutic agents. IO nanoparticles possess unique paramagnetic properties, which generate significant susceptibility effects resulting in strong T2 and T*2 contrast, as well as T1 effects at very low concentrations for magnetic resonance imaging (MRI), which is widely used for clinical oncology imaging. We review recent advances in the development of targeted IO nanoparticles for tumor imaging and therapy.

Estrogen and hypoxia regulate estrogen receptor alpha in a synergistic manner

Hypoxia activates and degrades estrogen receptor alpha (ERalpha) in human breast cancer cells, which may play an important role in the development and progression of breast cancer. In this study, the synergistic effects of estrogen (E(2)) and hypoxia on ERalpha-mediated transactivation and ERalpha degradation were investigated. ERalpha-mediated transcriptional activity was synergistically increased by E(2) and hypoxia, as determined by the transient expression of ERalpha and ER-responsive reporter plasmids in HEK 293 cells. Twenty hours of E(2) and hypoxia treatment synergistically induced degradation of ERalpha by 95% via a proteasome-dependent pathway in MCF-7 cells. These results provide evidence that hypoxia may stimulate yet unknown factor(s), which can further stimulate ERalpha signal transduction pathways.

Heat shock protein90 in lobular neoplasia of the breast

Background

Heat shock protein 90 (Hsp90) overexpression has been implicated in breast carcinogenesis, with putative prognostic and therapeutic implications. The purpose of this study is to evaluate the immunohistochemical expression of Hsp90 and to examine whether Hsp90 expression is associated with estrogen receptor alpha (ER-alpha) and beta (ER-beta) immunostaining in lobular neoplasia (LN) of the breast.

Methods

Tissue specimens were taken from 44 patients with LN. Immunohistochemical assessment of Hsp90, ER-alpha and ER-beta was performed both in the lesion and the adjacent normal breast ducts and lobules; the latter serving as control. As far as Hsp90 evaluation is concerned: i) the percentage of positive cells, and ii) the intensity was separately analyzed. Additionally, the Allred score was adopted and calculated. Accordingly, Allred score was separately evaluated for ER-alpha and ER-beta. The intensity was treated as an ordinal variable-score (0: negative, low: 1, moderate: 2, high: 3). Statistical analysis followed.

Results

Hsp90 immunoreactivity was mainly cytoplasmic in both the epithelial cells of normal breast (ducts and lobules) and LN. Some epithelial cells of LN also showed nuclear staining, but all the LN foci mainly disclosed a positive cytoplasmic immunoreaction for Hsp90. In addition, rare intralobular inflammatory cells showed a slight immunoreaction. The percentage of Hsp90 positive cells in the LN areas was equal to 67.1 ± 12.2%, whereas the respective percentage in the normal adjacent breast tissue was 69.1 ± 11.6%; the difference was not statistically significant. The intensity score of Hsp90 staining was 1.82 ± 0.72 in LN foci, while in the normal adjacent tissue the intensity score was 2.14 ± 0.64. This difference was statistically significant (p = 0.029, Wilcoxon matched-pairs signed-ranks test). The Hsp90 Allred score was 6.46 ± 1.14 in the LN foci, significantly lower than in the normal adjacent tissue (6.91 ± 0.92, p = 0.049, Wilcoxon matched-pairs signed-ranks test). Within the LN foci, the Hsp90 Allred score was neither associated with ER-alpha, nor with ER-beta percentage.

Conclusion

Hsp90 was lower in LN foci both at the level of intensity and Allred score, a finding contrary to what might have been expected, given that high Hsp90 expression is detected in invasive breast carcinomas. Hsp90 deregulation does not seem to be a major event in LN pathogenesis.

The UPS: a promising target for breast cancer treatment

During the past decade, progress in endocrine therapy and the use of trastuzumab has significantly contributed to the decline in breast cancer mortality for hormone receptor-positive and ERBB2 (HER2)-positive cases, respectively. As a result of these advances, a breast cancer cluster with poor prognosis that is negative for the estrogen receptor (ESR1), the progesterone receptor (PRGR) and ERBB2 (triple negative) has come to the forefront of medical therapeutic attention. DNA microarray analyses have revealed that this cluster is phenotypically most like the basal-like breast cancer that is caused by deficiencies in the BRCA1 pathways. To gain further improvements in breast cancer survival, new types of drugs might be required, and small molecules targeting the ubiquitin proteasome system have moved into the spotlight. The success of bortezomib in the treatment of multiple myeloma has sent encouraging signals that proteasome inhibitors could be used to treat other types of cancers. In addition, ubiquitin E3s involved in ESR1, ERBB2 or BRCA1 pathways could be ideal targets for therapeutic intervention. This review summarizes the ubiquitin proteasome pathways related to these proteins and discusses the possibility of new drugs for the treatment of breast cancers. PUBLICATION HISTORY : Republished from Current BioData's Targeted Proteins database (TPdb; http://www.targetedproteinsdb.com).

Structure activity relationships and differential interactions and functional activity of various equine estrogens mediated via estrogen receptors (ERs) ERalpha and ERbeta

The human estrogen receptors (ERs) alpha and beta interact with 17beta-estradiol (17beta-E2), estrone, 17alpha-estradiol, and the ring B unsaturated estrogens, equilin, 17beta-dihydroequilin, 17alpha-dihydroequilin, equilenin, 17beta-dihydroequilenin, 17alpha-dihydroequilenin, Delta8-estrone, and Delta8, 17beta-E2 with varying affinities. In comparison to 17beta-E2, the relative binding affinities of most ring B unsaturated estrogens were 2- to 8-fold lower for ERalpha and ERbeta, however, some of these unique estrogens had two to four times greater affinity for ERbeta than ERalpha. The transcriptional activity of these estrogens in HepG2 cells transfected with ERalpha or ERbeta, or both, and the secreted-alkaline phosphatase gene showed that all estrogens were functionally active. 17beta-E2 induced the activity of secreted-alkaline phosphatase by ERalpha to a level higher than any other estrogen. Activity of other estrogens was 12-17% that of 17beta-E2. In contrast, 17beta-E2 stimulated the activity of ERbeta to a 5-fold lower level than that with ERalpha, whereas the activity of other estrogens was 66-290% that of 17beta-E2, with equilenin being the most active. The presence of both ER subtypes did not alter the functional activity of 17beta-E2, although it further enhanced the activity of 17beta-dihydroequilin (200%), 17beta-dihydroequilenin (160%), and Delta8, 17beta-E2 (130%). Except for 17beta-E2, no correlation was observed between the functional activities and their binding affinities for ER. In conclusion, our results show that the effects of ring B unsaturated estrogens are mainly mediated via ERbeta and that the presence of both ER subtypes further enhances their activity. It is now possible to develop hormone replacement therapy using selective ring B unsaturated estrogens for target tissues where ERbeta is the predominant ER.

Estrogen actions on mitochondria--physiological and pathological implications

Estrogens are potent neuroprotective hormones and mitochondria are the site of cellular life-death decisions. As such, it is not surprising that we and others have shown that estrogens have remarkable effects on mitochondrial function. Herein we provide evidence for a primary effect of estrogens on mitochondrial function, achieved in part by the import of estrogen receptor beta (ERbeta) into the mitochondria where it mediates a number of estrogen actions on this vital organelle. ERbeta is imported into the mitochondria, through tethering to cytosolic chaperone protein and/or through direct interaction with mitochondrial import proteins. In the mitochondria, ERbeta can affect transcription of critical mitochondrial genes through the interaction with estrogen response elements (ERE) or through protein-protein interactions with mitochondrially imported transcription factors. The potent effects of estrogens on mitochondrial function, particularly during mitochondrial stress, argues for a role of estrogens in the treatment of mitochondrial defects in chronic neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD) and more acute conditions of mitochondrial compromise, like cerebral ischemia and traumatic brain injury.

Protein interaction with a Pluronic-modified poly(lactic acid) Langmuir monolayer

Interaction of bovine serum albumin (BSA) with poly(lactic acid) (PLA) layers mixed with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers (Pluronic) at air/solution interfaces was studied by the Langmuir balance technique. Wettability of the mixed PLA-Pluronic system was characterized in the form of a transferred one-layer Langmuir-Blodgett film, and considerable hydrophilization was obtained for all of the Pluronics (6400, 6800, 10500, and 12700) applied here. The density of PEO chains in the monolayer and hence the coverage of PLA was controlled by the composition and the compression of the mixed monolayers. Tensiometric investigations revealed that a significant reduction of BSA adsorption/penetration was achieved by applying the Pluronic 6800 and 12700 with long PEO blocks for hydrophilization of PLA. Interaction of BSA with the modified PLA monolayer depended on the density and length of the PEO chains. The surface morphological characteristics of the films determined by atomic force microscopy were in good correlation with the results of BSA interaction. The average roughness of the polymer LB layer was high due to BSA penetration into the PLA film, while smooth surfaces with small roughness were obtained when the PLA layer was modified by Pluronic 6800.

Liposomal delivery improves the growth-inhibitory and apoptotic activity of low doses of gemcitabine in multiple myeloma cancer cells

Gemcitabine-loaded pegylated unilamellar liposomes (200 nm) were proposed for the treatment of multiple myeloma cancer disease. Physicochemical and technological parameters of liposomes were evaluated by using laser light scattering and gel permeation chromatography. The growth-inhibitory activity of gemcitabine-loaded liposomes compared to the free drug was assayed in vitro on U266 (autocrine, interleukin-6-independent) and INA-6 (IL-6-dependent) multiple myeloma cell lines. Liposomes noticeably improved the growth-inhibitory activity of gemcitabine in terms of both dose-dependent and incubation-time effects. Liposomal delivery of gemcitabine consistently and significantly increased induction of apoptosis and caused a complete inhibition of proliferation. Liposomes were able to interact with multiple myeloma cells as demonstrated by confocal laser scanning microscopy and hence to improve the intracellular gemcitabine delivery. Gemcitabine-loaded liposomes were much more effective in vitro than the free drug. This formulation may offer even more in vivo advantages both in terms of drug pharmacokinetic and biodistribution.

Estrogen receptor-alpha hinge-region lysines 302 and 303 regulate receptor degradation by the proteasome

Cellular levels of estrogen receptor-alpha (ERalpha) protein are regulated primarily by the ubiquitin-proteasome pathway. Dynamic interactions between ERalpha and the protein degradation machinery facilitate the down-regulation process by targeting receptor lysine residues for polyubiquitination. To date, the lysines that control receptor degradation have not been identified. Two receptor lysines, K302 and K303, located in the hinge-region of ERalpha, serve multiple regulatory functions, and we examined whether these might also regulate receptor polyubiquitination, turnover, and receptor-protein interactions. We used ERalpha-negative breast cancer C4-12 cells to generate cells stably expressing wild-type (wt)ERalpha or ERalpha with lysine-to-alanine substitutions at K302 and K303 (ERalpha-AA). In the unliganded state, ERalpha-AA displayed rapid polyubiquitination and enhanced basal turnover, as compared with wtERalpha, due to its elevated association with the ubiquitin ligase carboxy terminus of Hsc70-interacting protein (CHIP) and the proteasome-associated cochaperone Bag1. Treatment of C4-12 cells with either 17beta-estradiol (E2) or the pure antiestrogen ICI 182,780 (ICI) induced rapid degradation of wtERalpha via the ubiquitin-proteasome pathway; however, in the presence of these ligands, ERalpha-AA was less efficiently degraded. Furthermore, ERalpha-AA was resistant to ICI-induced polyubiquitination, suggesting that these lysines are polyubiquitinated in response to the antiestrogen and demonstrate a novel role for these two lysines in the mechanism of action of ICI-induced receptor down-regulation. The reduced stability of ERalpha-AA in the unliganded state and the increased stability of ERalpha-AA in the liganded state were concordant with reporter gene assays demonstrating that ERalpha-AA has lower basal activity but higher E2 inducibility than wtERalpha. These data provide the first evidence that K302/303 protect ERalpha from basal degradation and are necessary for efficient E2- and ICI-induced turnover in breast cancer cells.

Trophic effect in MCF-7 cells of ERalpha17p, a peptide corresponding to a platform regulatory motif of the estrogen receptor alpha--underlying mechanisms

As yet, estrogen receptor alpha (ERalpha) inhibitors used in clinical practice target a unique site, i.e. the hormone-binding pocket. With the aim of discovering other potential therapeutic targets in the receptor, we studied its AF-2a domain, a site that proves to be critical for ligand-independent ERalpha activity. Previous studies from our laboratory highlighted an auto-inhibitory action associated with a site included in this domain, i.e. the P295-T311 sequence. Accordingly, a deletion of this sequence produces a constitutively activated receptor mutant. More interestingly, a synthetic peptide with the P295-T311 sequence (ERalpha17p) elicits in breast cancer cell lines estrogenic responses that may be ascribed to a competitive mechanism towards the P295-T311-associated auto-inhibition of ERalpha. In the present study, we show that ERalpha17p sustains MCF-7 cell growth in estrogen-depleted culture medium by inducing molecular events promoting G1/S phase transition. We demonstrate, moreover, that this proliferative activity is associated with receptor down regulation (acceleration of ERalpha degradation and repression of ESR1 gene transcription), similar to that induced by estrogen agonists. Complementary studies suggest that our observations may be, at least in part, relevant to a competitive inhibition affecting ERalpha-Hsp70 association. Hence, the design of drugs able to stabilize ERalpha-Hsp70 complexes - where the receptor is in an inactive conformation - may be of therapeutic value.

The role of estrogens and estrogen receptors in normal prostate growth and disease

Estrogens have significant direct and indirect effects on prostate gland development and homeostasis and have been long suspected in playing a role in the etiology of prostatic diseases. Direct effects are mediated through prostatic estrogen receptors alpha (ERalpha) and beta (ERbeta) with expression levels changing over time and with disease progression. The present review examines the evidence for a role of estrogens and specific estrogen receptors in prostate growth, differentiation and disease states including prostatitis, benign prostatic hyperplasia (BPH) and cancer and discusses potential therapeutic strategies for growth regulation via these pathways.

Effects of thyroid hormones on human breast cancer cell proliferation

The involvement of estrogens in breast cancer development and growth has been well established. However, the effects of thyroid hormones and their combined effects with estrogens are not well studied. We investigated the response of human breast cancer cells to thyroid hormone, particularly the role of T3 in mediating cell proliferation and gene expression. We demonstrated that 17beta-estradiol (E2) or triiodothyronine (T3) promoted cell proliferation in a dose-dependent manner in both MCF-7 and T47-D cell lines. The E2- or T3-dependent cell proliferation was suppressed by co-administration of the ER antagonist ICI. We also demonstrated that T3 could enhance the effect of E2 on cell proliferation in T47-D cells. Using an estrogen response element (ERE)-mediated luciferase assay, we determined that T3 was able to induce the activation of ERE-mediated gene expression in MCF-7 cells, although the effects were much weaker than that induced by E2. These results suggest that T3 can promote breast cancer cell proliferation and increase the effect of E2 on cell proliferation in some breast cancer cell lines and thus that T3 may play a role in breast cancer development and progression.

Estrogen replacement regimen and brain infusion of lipopolysaccharide differentially alter steroid receptor expression in the uterus and hypothalamus

The regimen of estrogen replacement can alter the consequences of estrogen therapy and stressors. To determine the long-term effects and interaction of these systems on the brain and periphery, adult female rats were infused with lipopolysaccharide (LPS) into the fourth ventricle of the brain for 4 weeks, and ovariectomized rats were administered either constant or pulsed regimens of estrogen replacement (17beta-estradiol) until sacrifice at 8 weeks. Constant, but not pulsed, estrogen replacement reduced ERalpha and increased HSP90, HSP70, and PR(B) uterine protein levels. Both estrogen regimens increased ERbeta, HSP27, and PR(A) uterine proteins. Both regimens reduced hypothalamic levels of ERalpha, but not ERbeta, HSP, or PR. No changes were observed in the hippocampus. Long-term brain infusion of LPS activated microglia and reduced body weight, but did not alter corticosterone or nitrotyrosine levels. LPS infusion into intact rats suppressed uterine weight, increased ERalpha and decreased HSP90 in the uterus. LPS did not alter uterine weight in ovariectomized rats treated with constant or pulsed estrogen. Together, these data suggest the timing of estrogen replacement and neuroinflammatory stressors can profoundly affect uterine and hypothalamic steroid receptor expression and may be important parameters to consider in the post-menopausal intervention with estrogen.

New novobiocin analogues as antiproliferative agents in breast cancer cells and potential inhibitors of heat shock protein 90

Selective hsp90 inhibitors simultaneously destabilize and deplete key signaling proteins involved in cell proliferation and survival, angiogenesis, and metastasis. Investigation of novobiocin analogues lacking the noviose moiety as novel inhibitors of hsp90 was carried out. A novel series of 3-aminocoumarin analogues has been produced and screened in cell proliferation, and the molecular signature of hsp90 inhibition was assessed by depletion of estrogen receptor, HER2, Raf-1, and cdk4 in human breast cancer cells. This structure-activity relationship study highlights the crucial role of the C-4 and/or C-7 positions of coumarin which appeared to be essential for degradation of hsp90 client proteins. Removal of the noviose moiety in novobiocin together with introduction of a tosyl substituent at C-4 or C-7 coumarins provides 6e and 6f as lead structures which compared favorably with novobiocin as demonstrated by enhanced rates of cell death. The processing and activation of caspases 7 and 8 and the subsequent cleavage of PARP by 6e suggest stimulation of the extrinsic apoptosis pathway.

Synthesis and characterization of bioactive tamoxifen-conjugated polymers

Macromolecular conjugates of tamoxifen could perhaps be used to circumvent some of the limitations of the extensively used breast cancer drug. To test the feasibility of these conjugates, a 4-hydroxytamoxifen analogue was conjugated to a diaminoalkyl linker and then conjugated to activated esters of a poly(methacrylic acid) polymer synthesized by atom transfer radical polymerization. A polymer conjugated to the 4-hydroxytamoxifen analogue with a six-carbon linker showed high affinity for both estrogen receptor alpha and estrogen receptor beta and potent antagonism of the estrogen receptor in cell-based transcriptional reporter assays. These results suggest that the conjugation of 4-hydroxytamoxifen to a polymer results in a macromolecular conjugate that can display ligand in a manner that can be recognized by estrogen receptor and still act as a potent antiestrogen in cells.

Phosphorylation of activation function-1 regulates proteasome-dependent nuclear mobility and E6-associated protein ubiquitin ligase recruitment to the estrogen receptor beta

The ubiquitin-proteasome pathway has been recognized as an important regulator in the hormonal response by estrogen receptor (ER) alpha, but its impact on ERbeta function is poorly characterized. In the current study, we investigated the role of the ubiquitin-proteasome pathway in regulating ERbeta activity and identified regulatory sites within the activation function (AF)-1 domain that modulate ERbeta ubiquitination and nuclear dynamics in a hormone-independent manner. Although both ERalpha and ERbeta were dependent on proteasome function for their maximal response to estrogen, they were regulated differently by proteasome inhibition in the absence of hormone, an effect shown to be dependent on their respective AF-1 domain. Given the role of AF-1 phosphorylation to regulate ER activity, we found that sequential substitutions of specific serine residues contained in MAPK consensus sites conferred transcriptional activation of ERbeta in a proteasome-dependent manner through reduced ubiquitination and enhanced accumulation of mutant receptors. Specifically, serines 94 and 106 within ERbeta AF-1 domain were found to modulate subnuclear mobility of the receptor to transit between inactive clusters and a more mobile state in a proteasome-dependent manner. In addition, cellular levels of ERbeta were regulated through these sites by facilitating the recruitment of the ubiquitin ligase E6-associated protein in a phosphorylation-dependent manner. These findings suggest a role for ERbeta AF-1 in contributing to the activation-degradation cycling of the receptor through a functional clustering of phosphorylated serine residues that cooperate in generating signals to the ubiquitin-proteasome pathway.

Hydroxamic acid analogue histone deacetylase inhibitors attenuate estrogen receptor-alpha levels and transcriptional activity: a result of hyperacetylation and inhibition of chaperone function of heat shock protein 90

PURPOSE

The molecular chaperone heat shock protein (hsp)-90 maintains estrogen receptor (ER)-alpha in an active conformation, allowing it to bind 17beta-estradiol (E2) and transactivate genes, including progesterone receptor (PR)-beta and the class IIB histone deacetylase HDAC6. By inhibiting HDAC6, the hydroxamic acid analogue pan-HDAC inhibitors (HA-HDI; e.g., LAQ824, LBH589, and vorinostat) induce hyperacetylation of the HDAC6 substrates alpha-tubulin and hsp90. Hyperacetylation of hsp90 inhibits its chaperone function, thereby depleting hsp90 client proteins. Here, we determined the effect of HA-HDIs on the levels and activity of ERalpha, as well as on the survival of ERalpha-expressing, estrogen-responsive human breast cancer MCF-7 and BT-474 cells.

EXPERIMENTAL DESIGN

Following exposure to HA-HDIs, hsp90 binding, polyubiquitylation levels, and transcriptional activity of ERalpha, as well as apoptosis and loss of survival, were determined in MCF-7 and BT-474 cells.

RESULTS

Treatment with HA-HDI induced hsp90 hyperacetylation, decreased its binding to ERalpha, and increased polyubiquitylation and depletion of ERalpha levels. HA-HDI treatment abrogated E2-induced estrogen response element-luciferase expression and attenuated PRbeta and HDAC6 levels. Exposure to HA-HDI also depleted p-Akt, Akt, c-Raf, and phospho-extracellular signal-regulated kinase-1/2 levels, inhibited growth, and sensitized ERalpha-positive breast cancer cells to tamoxifen.

CONCLUSIONS

These findings show that treatment with HA-HDI abrogates ERalpha levels and activity and could sensitize ERalpha-positive breast cancers to E2 depletion or ERalpha antagonists.

Estrogenic or antiestrogenic therapies for multiple myeloma?

Multiple myeloma (MM) is a common hematological malignancy which remains incurable due to both intrinsic and acquired resistance to conventional or more novel drugs. Estrogenic and antiestrogenic compounds are very promising drugs for the treatment of MM. Indeed, they inhibit cell proliferation in vitro. They block cell cycle and/or induce apoptosis even in drug-resistant MM cells but not normal B cells. They interfere with survival pathways often deregulated in myelomas. They co-operate with conventional drugs to enhance apoptosis or to overcome resistance. In vivo, they act also on tumoral angiogenesis in xenograft models. As a whole, they possess all the criteria which render them attractive for a new therapeutic strategy. Importantly, they are well-tolerated at the doses tested in vitro or in vivo, encouraging the rapid onset of critical trials.

Estrogen receptors: how do they signal and what are their targets

During the past decade there has been a substantial advance in our understanding of estrogen signaling both from a clinical as well as a preclinical perspective. Estrogen signaling is a balance between two opposing forces in the form of two distinct receptors (ER alpha and ER beta) and their splice variants. The prospect that these two pathways can be selectively stimulated or inhibited with subtype-selective drugs constitutes new and promising therapeutic opportunities in clinical areas as diverse as hormone replacement, autoimmune diseases, prostate and breast cancer, and depression. Molecular biological, biochemical, and structural studies have generated information which is invaluable for the development of more selective and effective ER ligands. We have also become aware that ERs do not function by themselves but require a number of coregulatory proteins whose cell-specific expression explains some of the distinct cellular actions of estrogen. Estrogen is an important morphogen, and many of its proliferative effects on the epithelial compartment of glands are mediated by growth factors secreted from the stromal compartment. Thus understanding the cross-talk between growth factor and estrogen signaling is essential for understanding both normal and malignant growth. In this review we focus on several of the interesting recent discoveries concerning estrogen receptors, on estrogen as a morphogen, and on the molecular mechanisms of anti-estrogen signaling.

Biomedical nanotechnology for cancer

Nanotechnology may hold the key to controlling many devastating diseases. In the fight against the pain, suffering, and death due to cancer, nanotechnology will allow earlier diagnosis and even prevention of malignancy at premalignant stages, in addition to providing multimodality treatment not possible with current conventional techniques. This review discusses nanotechnology already used in diagnostic and therapeutic applications for cancer. Also addressed are theoretic and evolving uses of nanotechnology, including multifunctional nanoparticles for imaging and therapy, nanochannel implants for controlled release of drugs, nanoscale devices for evaluation of proteomics and genomics, and diagnostic techniques that take advantage of physical changes in diseased tissue.

A genome-wide study of the repressive effects of estrogen receptor beta on estrogen receptor alpha signaling in breast cancer cells

Transcriptional effects of estrogen result from its activation of two estrogen receptor (ER) isoforms; ERalpha that drives proliferation and ERbeta that is antiproliferative. Expression of ERbeta in xenograft tumors from the T47D breast cancer cell line reduces tumor growth and angiogenesis. If ERbeta can halt tumor growth, its introduction into cancers may be a novel therapeutic approach to the treatment of estrogen-responsive cancers. To assess the complete impact of ERbeta on transcription, we have made a full transcriptome analysis of ERalpha- and ERbeta-mediated gene regulation in T47D cell line with Tet-Off regulated ERbeta expression. Of the 35 000 genes and transcripts analysed, 4.1% (1434) were altered by ERalpha activation. Tet withdrawal and subsequent ERbeta expression inhibited the ERalpha regulation of 998 genes and, in addition, altered expression of 152 non-ERalpha-regulated genes. ERalpha-induced and ERbeta-repressed genes were involved in proliferation, steroid/xenobiotic metabolism and ion transport. The ERbeta repressive effect was further confirmed by proliferation assays, where ERbeta was shown to completely oppose the ERalpha-E2 induced proliferation. Additional analysis of ERbeta with a mutated DNA-binding domain revealed that this mutant, at least for a quantity of genes, antagonizes ERalpha even more strongly than ERbeta wt. From an examination of the genes regulated by ERalpha and ERbeta, we suggest that introduction of ERbeta may be an alternative therapeutic approach to the treatment of certain cancers.

Tamoxifen-induced rapid death of MCF-7 breast cancer cells is mediated via extracellularly signal-regulated kinase signaling and can be abrogated by estrogen

Tamoxifen (Tam) is widely used in chemotherapy of breast cancer. It inhibits proliferation and induces apoptosis of breast cancer cells by estrogen receptor (ER)-dependent modulation of gene expression. In addition, recent reports have shown that Tam also has nongenomic effects. We previously reported induction of a rapid mitochondrial death program in breast cancer cells at pharmacological concentrations of Tam. Here we studied the upstream signaling events leading to mitochondrial disruption by Tam. We observed that 5 mum Tam rapidly induced sustained activation of ERK1/2 in ER-positive breast cancer cell lines (MCF-7 and T47D) and that PD98059 (inhibitor of ERK activation) was able to protect MCF-7 cells against Tam-induced death. These data suggest that activation of ERK has a primary role in the acute death response of the cells. In addition, inhibition of epidermal growth factor receptor (EGFR) opposed both Tam-induced ERK1/2 phosphorylation and cell death, which suggests that EGFR-associated mechanisms are involved in Tam-induced death. ERK1/2 phosphorylation was associated with a prolonged nuclear localization of ERK1/2 as determined by fluorescence microscopy with ERK2-green fluorescent protein construct. 17beta-Estradiol was shown to exert a different kind of temporal pattern of ERK nuclear localization in comparison with Tam. Moreover, 17beta-estradiol was found to oppose the rapid effects of Tam in MCF-7 and T47D cells but not in MDA-MB-231 cells, which implies a role for estrogen receptors in the protective effect of estrogen. The pure antiestrogen ICI182780 could not, however, prevent Tam-induced ERK1/2 phosphorylation, suggesting that the Tam-induced rapid cell death is primarily ER-independent or mediated by ICI182780 insensitive nongenomic mechanisms.

Differential Regulation of Estrogen Receptor α Turnover and Transactivation by Mdm2 and Stress-Inducing Agents

In mammalian cells, the level of estrogen receptor alpha (ERalpha) is rapidly decreased upon estrogen treatment, and this regulation involves proteasome degradation. Using different approaches, we showed that the Mdm2 oncogenic ubiquitin-ligase directly interacts with ERalpha in a ternary complex with p53 and is involved in the regulation of ERalpha turnover (both in the absence or presence of estrogens). Several lines of evidence indicated that this effect of Mdm2 required its ubiquitin-ligase activity and involved the ubiquitin/proteasome pathway. Moreover, in MCF-7 human breast cancer cells, various p53-inducing agents (such as UV irradiation) or treatment with RITA (which inhibits the interaction of p53 with Mdm2) stabilized ERalpha and abolished its 17beta-estradiol-dependent turnover. Interestingly, our data indicated that ligand-dependent receptor turnover was not required for efficient transactivation. Altogether, our results indicate that the Mdm2 oncoprotein and stress-inducing agents complexly and differentially regulate ERalpha stability and transcriptional activity in human cancer cells.

The interaction of PP1 with BRCA1 and analysis of their expression in breast tumors

Background

The breast cancer susceptibility gene, BRCA1, is implicated in multiple cellular processes including DNA repair, the transactivation of genes, and the ubiquitination of proteins; however its precise functions remain to be fully understood. Identification and characterization of BRCA1 protein interactions may help to further elucidate the function and regulation of BRCA1. Additionally, detection of changes in the expression levels of BRCA1 and its interacting proteins in primary human breast tumors may further illuminate their role in the development of breast cancer.

Methods

We performed a yeast two-hybrid study to identify proteins that interact with exon11 of BRCA1 and identified Protein Phosphatase 1β (PP1β), an isoform of the serine threonine phosphatase, PP1. GST-pull down and co-immunoprecipitation assays were performed to further characterize this interaction. Additionally, Real-Time PCR was utilized to determine the expression of BRCA1, PP1α, β and γ in primary human breast tumors and normal breast tissue to identify alterations in the expression of these genes in breast cancer.

Results

PP1 and BRCA1 co-immunoprecipitate and the region within BRCA1 as well as the specific PP1 interacting domain mediating this interaction were identified. Following mRNA expression analysis, we identified low levels of BRCA1 and variable levels of PP1α and β in primary sporadic human breast tumors. Furthermore, BRCA1, PP1β and PP1γ were significantly higher in normal tissue specimens (BRCA1 p = 0.01, PP1β: p = 0.03, PP1γ, p = 1.9 × 10^-6) compared to sporadic breast tumor samples. Interestingly, we also identified that ER negative tumors are associated with low levels of PP1α expression.

Conclusion

The identification and characterization of the interaction of BRCA1 with PP1 and detection of changes in the expression of PP1 and genes encoding other BRCA1 associated proteins identifies important genetic pathways that may be significant to breast tumorigenesis. Alterations in the expression of genes, particularly phosphatases that operate in association with BRCA1, could negatively affect the function of BRCA1 or BRCA1 associated proteins, contributing to the development of breast cancer.

Distinct temporal and spatial activities of RU486 on progesterone receptor function in reproductive organs of ovariectomized mice

RU486 is an incomplete progesterone receptor (PR) antagonist due to its partial agonist activity. To investigate the tissue-specific effects of RU486 on PR function in an ovariectomized mouse model, we used the progesterone receptor activity indicator mouse and evaluated the key determinants of progesterone-dependent gene activity: PR, coregulators, and kinases. As might be expected, acute RU486 treatment (6 h after injection) reduced PR transcriptional activity in the uterus, compared with vehicle or progesterone (P4) treatments. Chronic RU486 treatment (3 d) had a distinctly different effect on PR-mediated transcription, elevating PR activity in both the uterus and mammary gland, whereas chronic P4 treatment reduced PR activity in both tissues. This elevated uterine PR activity was associated with increased modified forms of PR and total protein levels of steroid receptor coactivator (SRC)-1 without affecting SRC-2 or SRC-3 protein levels. In addition to increased levels of coactivators, chronic RU486 treatment activated the ERK-1/2 and c-Jun N-terminal kinase signaling pathways in the uterus in a manner comparable with P4 treatment. In contrast to our observations in the uterus, chronic RU486 treatment increased modified forms of PR and the SRC-3 protein levels (but not SRC-1 and SRC-2 levels) in luminal epithelial cells of the mammary gland. Chronic RU486 also activated the c-Jun N-terminal kinase, but not ERK-1/2, signaling pathways in mammary luminal epithelial cells. This report suggests that in comparison with chronic natural hormone (P4), a mixed antagonist/agonist (RU486) induces a distinct temporal and spatial pattern of cellular genetic regulators that accompany ligand-specific gene expression.

Oestrogen receptors pathways to oestrogen responsive elements: the transactivation function-1 acts as the keystone of oestrogen receptor (ER)beta-mediated transcriptional repression of ERalpha

Oestrogen receptors (ER)alpha and beta modify the expression of genes involved in cell growth, proliferation and differentiation through binding to oestrogen response elements (EREs) located in a number of gene promoters. Transient transfection of different luciferase reporter vectors 3xEREs-Vit, 2xEREs-tk and ERE-C3 showed that the transactivation capacity of both ER subtypes was influenced by 1) the nature of the inducer (oestradiol (E2), phyto- and anti-oestrogen (AE)), 2) the structure of the promoter (nucleotidic sequence, number of ERE, length of the promoter sequence) and 3) the cell line (containing endogenous ER (MCF-7) or in which ER was stably expressed (MDA-MB-231-HE-5 (ERalpha+) or MDA-MB-231-HERB (ERbeta+)). ER subtype did not display the same efficacy on the different constructions in the presence of E2 and of AE according to the cell (e.g. in MCF-7 cells: tk>>Vit>>C3 approximately 0 while in MDA-MB-231 cells: Vit>>tk approximately C3). E2 response was higher in MCF-7 cells, probably due to higher ER expression level (maximal at 10(-10)M instead of 10(-8)M for E2 in HE-5 cells). Finally, the same ligand could exert opposite activities on the same promoter according to the ER isoform expressed: in the MDA-MB-231 cells, AE acted as inducers of the C3 promoter via ERbeta whereas ERalpha/AE complexes down-regulated this promoter. Approximately 70% of breast tumours express ER and most tumour cells coexpress both ER isotypes. Thus, different types of ER dimers can be formed in such tumours (ERbeta or ERalpha homodimers or ERalpha/ERbeta heterodimers). We therefore studied the influence of the coexistence of the two ERs on the ligand-induced transcriptional process following transient transfection of ERalpha in ERbeta+ cells, and inversely ERbeta in ERalpha+ cells. ERbeta-transfection inhibited the E2- and genistein-induced ERalpha-dependent transcription on all promoters in all cell lines except C3 in MCF-7; this inhibitory effect was lost following transfection of ERbeta deleted of its AF-1 (ERbeta-AF-2). These results suggest that the dominant negative properties of ERbeta are mainly due to its AF-1 function. Interestingly, transfection of an ERbeta-AF-2 construct into MCF-7 cells potentiated the transcription inhibitory capacity of 4-OH-tamoxifen (OHT) on the Vit and tk promoters. Thus, (1) OHT exerts an agonistic activity through the AF-1 function of ER and (2) expression of ERbeta in breast cancer cells seems to favour the AE treatment. Contrary to ERbeta, ERalpha-transfection had little effect on ERbeta transactivation capacity in HERB cells. Finally, the ratio ERalpha/ERbeta constitutes one decisive parameters to orientate the transcriptional mechanism of a target gene in the presence of agonist as well as of antagonist ligands.

Raloxifene and ICI182,780 increase estrogen receptor-alpha association with a nuclear compartment via overlapping sets of hydrophobic amino acids in activation function 2 helix 12

The basis for the differential repressive effects of antiestrogens on transactivation by estrogen receptor-alpha (ERalpha) remains incompletely understood. Here, we show that the full antiestrogen ICI182,780 and, to a lesser extent, the selective ER modulator raloxifene (Ral), induce accumulation of exogenous ERalpha in a poorly soluble fraction in transiently transfected HepG2 or stably transfected MDA-MB231 cells and of endogenous receptor in MCF7 cells. ERalpha remained nuclear in HepG2 cells treated with either compound. Replacement of selected hydrophobic residues of ERalpha ligand-binding domain helix 12 (H12) enhanced receptor solubility in the presence of ICI182,780 or Ral. These mutations also increased transcriptional activity with Ral or ICI182,780 on reporter genes or on the endogenous estrogen target gene TFF1 in a manner requiring the integrity of the N-terminal AF-1 domain. The antiestrogen-specific effects of single mutations suggest that they affect receptor function by mechanisms other than a simple decrease in hydrophobicity of H12, possibly due to relief from local steric hindrance between these residues and the antiestrogen side chains. Fluorescence anisotropy experiments indicated an enhanced regional stabilization of mutant ligand-binding domains in the presence of antiestrogens. H12 mutations also prevent the increase in bioluminescence resonance energy transfer between ERalpha monomers induced by Ral or ICI182,780 and increase intranuclear receptor mobility in correlation with transcriptional activity in the presence of these antiestrogens. Our data indicate that ICI182,780 and Ral locally alter the ERalpha ligand binding structure via specific hydrophobic residues of H12 and decrease its transcriptional activity through tighter association with an insoluble nuclear structure.

A novel dual-target steroid sulfatase inhibitor and antiestrogen: SR 16157, a promising agent for the therapy of breast cancer

Endocrine therapy is the ideal treatment choice for estrogen receptor alpha (ERalpha)-positive breast cancer patients. Principal used therapies target either the ERalpha e.g. by selective ERalpha modulators (SERMs) such as tamoxifen or target estrogen biosynthesis with aromatase inhibitors. Steroid sulfatase (STS) plays a crucial role in formation of compounds with estrogenic properties, converting inactive sulfate-conjugated steroids to active non-conjugated forms. Steroid sulfates are considered as a reservoir for active steroids due to their prolonged half-life and increased concentration in plasma. STS is present in several tissues including the breast, and the STS the mRNA level and enzyme activity is significantly increased in ERalpha-positive breast tumors. Inhibition of STS is therefore a new approach for decreasing estrogenic steroids that stimulate breast cancer. The novel dual-acting compound SR 16157 is designed as a sulfamate-containing STS inhibitor that releases a tissue-selective SERM SR 16137. Use of a dual-target STS inhibitor and SERM represents a new strategy in the treatment of hormone-dependent breast cancer. In this study, we tested the potential of SR 16157 and SR 16137 on STS activity, cell growth and ERalpha function in MCF-7 breast cancer cells. We confirmed that the dual-target compound SR 16157 exerts STS inhibition and antiestrogenic effects. SR 16157 was a highly effective growth inhibitor, being 10 times more potent than the antiestrogens SR 16137 and tamoxifen. Relative to tamoxifen, SR 16137 displays profoundly improved ERalpha binding affinity and antiestrogenic effects on expression of estrogen-regulated genes. Thus, the dual-target SR 16157 is possibly a promising new treatment alternative, superior to tamoxifen.

Improved anti-tumoral capacity of mixed and pure anti-oestrogens in breast cancer cell xenografts after their administration by entrapment in colloidal nanosystems

Anti-oestrogens (AEs) are currently used for treating hormone-dependent breast cancers. They specifically bind to oestrogen receptors (ERs) and inhibit their transactivation capacity. However, ERs are present in various other tissues in which AEs may have either a beneficial or detrimental action. AE administration via systems targeting breast tumours may be an important therapeutic improvement. Thus, several biodegradable drug delivery systems containing either "mixed" (4-hydroxytamoxifen - 4-HT) or "pure" (RU 58668 - RU) AEs were prepared. Liposomes and nanospheres (NS, composed of non-toxic and biodegradable lipids and poly(d,l-lactic acid) incorporated up to 1 and 0.5 mM AE, respectively. Nanocapsules (NCs) in which an oily core solubilises the AE incorporated no more than 0.02 mM of the drug. PEG-functionalised nanoparticles survived longer in plasma and had better controlled release of the drug. The small size of the vectors (100-250 nm) was compatible with their extravasation through the discontinuous endothelium of tumour vasculature, allowing their accumulation in MCF-7 cell xenografts and leading to a prolonged exposure of the tumour to AEs. In these tumours and in MCF-7/ras xenografts, RU-NS and RU-NC (6.5mg/kg/week and 0.27 mg/kg/week, respectively, doses at which free RU had a very weak effect), both inhibited tumour growth. Entrapped RU significantly induced involution of tumours and strongly induced apoptosis in tumour cells, concomitantly with inhibiting tumour angiogenesis. 4-HT-nanoparticles also arrest oestradiol-induced tumour growth, inducing apoptosis and inhibiting angiogenesis. However, unlike RU-nanoparticles, they did not promote ERalpha subtype loss in tumour cells. Subcutaneous administration of both RU- and 4-HT-NS in MCF-7 xenografts strongly arrested tumour growth for prolonged periods and RUNS decreased the number of tumour epithelial cells. Analysis of the proteins involved in cell cycle proliferation and apoptosis confirmed that RU-nanoparticles were more efficient than 4-HT-nanoparticles. Their lack of toxicity and high anti-tumour potency that affects only tumour cells in the xenograft models mean these AE-loaded colloidal systems are a breakthrough in hormone-dependent breast cancer treatment.

Quantitative profiling of drug-associated proteomic alterations by combined 2-nitrobenzenesulfenyl chloride (NBS) isotope labeling and 2DE/MS identification

The identification of drug-responsive biomarkers in complex protein mixtures is an important goal of quantitative proteomics. Here, we describe a novel approach for identifying such drug-induced protein alterations, which combines 2-nitrobenzenesulfenyl chloride (NBS) tryptophan labeling with two-dimensional gel electrophoresis (2DE)/mass spectrometry (MS). Lysates from drug-treated and control samples are labeled with light or heavy NBS moiety and separated on a common 2DE gel, and protein alterations are identified by MS through the differential intensity of paired NBS peptide peaks. Using NBS/2DE/MS, we profiled the proteomic alterations induced by tamoxifen (TAM) in the estrogen receptor (ER) positive MCF-7 breast cancer cell line. Of 88 protein spots that significantly changed upon TAM treatment, 44 spots representing 23 distinct protein species were successfully identified with NBS-paired peptides. Of these 23 TAM-altered proteins, 16 (70%) have not been previously associated with TAM or ER activity. We found the NBS labeling procedure to be both technically and biologically reproducible, and the NBS/2DE/MS alterations exhibited good concordance with conventional 2DE differential protein quantitation, with discrepancies largely due to the comigration of distinct proteins in the regular 2DE gels. To validate the NBS/2DE/MS results, we used immunoblotting to confirm GRP78, CK19, and PA2G4 as bona fide TAM-regulated proteins. Furthermore, we demonstrate that PA2G4 expression can serve as a novel prognostic factor for disease-free survival in two independent breast cancer patient cohorts. To our knowledge, this is the first report describing the proteomic changes in breast cancer cells induced by TAM, the most commonly used selective estrogen receptor modulator (SERM). Our results indicate that NBS/2DE/MS may represent a more reliable approach for cellular protein quantitation than conventional 2DE approaches.

Identification of novel proteins induced by estradiol, 4-hydroxytamoxifen and acolbifene in T47D breast cancer cells

Tamoxifen is currently used as adjuvant therapy for estrogen receptor (ER) positive breast cancer patients and as a chemopreventative agent. Although ER is a predictive marker for tamoxifen response, ER status fails to predict tamoxifen response in a significant number of patients highlighting the need to identify new pathways for tamoxifen sensitivity/resistance. To identify novel proteins induced by tamoxifen in breast cancer cells sensitive to tamoxifen growth inhibition, two-dimensional (2D) gel electrophoresis was used to profile proteins in T47D breast cancer cells. Six proteins were identified that were differentially regulated by 17beta-estradiol, 4-hydroxytamoxifen and the pure antagonist acolbifene (EM-652); calreticulin, synapse associated protein 1 (SYAP1), CD2 antigen binding protein 2 (CD2BP2), nucleosome assembly protein 1 like 1 (NAP1L1), d-3-phosphoglycerate dehydrogenase (3-PHGDH) and pyridoxine 5' phosphate oxidase (PNPO). At the mRNA level, these ligands differentially regulated expression of mRNAs encoding the identified proteins in T47D and MCF7 cells but had no effect on mRNA in ERalpha-negative MDA-MB-231 breast cancer cells. These novel SERM-regulated proteins may participate in new or existing pathways for sensitivity or resistance to SERMs.

Targeting the ubiquitin-proteasome pathway in breast cancer therapy

The ubiquitin-proteasome pathway (UPP) is the major eukaryotic mechanism for regulated intracellular proteolysis. Targeting this pathway with proteasome inhibitors has been validated as a rational strategy against hematologic malignancies, but for most solid tumor populations, including breast cancer, such agents have not shown encouraging activity. However, there is an increasing body of evidence showing that UPP dysregulation plays an important role in mammary tumorigenesis. Moreover, modulation of ubiquitin-proteasome function is emerging as a rational strategy to enhance chemosensitivity and overcome chemoresistance. Taken together, these facts suggest that we are only beginning to appreciate the relevance of this pathway for the current and future therapy of patients with breast cancer. This review provides an overview of the biology of the UPP, its role in the malignant process, the current state of knowledge regarding clinical heat shock protein and proteasome inhibition, and some likely future directions that may enhance our ability to exploit this pathway therapeutically.