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PubMed2004

Early and midluteal phase blood estradiol levels after ovum pickup and pregnancy rates after ICSI cycles.

OBJECTIVE: To examine whether blood estradiol level tendencies during the late follicular and early luteal phases and the 11 days after embryo transfer have any association with the outcome of intracytoplasmic sperm injection-embryo transfer (ICSI-ET) cycles. STUDY DESIGN: This prospective study involved 38 assisted reproductive technology cycles in 35 infertile patients treated with assisted reproductive technologies in which blood samples taken on the 4th, 7th, 9th and 11th days following ET were tested for progesterone, estradiol and hCG levels using an enzyme-linked immunoassay. The estradiol blood levels were compared with the maximal follicular phase blood estradiol. The data were analyzed using Microsoft Excel (Redmond, Washington) and SPSS 10.0 (Chicago, Illinois). The chi2, Mann-Whitney U, Wilcoxon and Pearson tests were usedfor statistical analysis. RESULTS: Average maximum estradiol blood level, number of oocytes produced,fertilization rates and cleavage rates did not show any significant difference between pregnant and nonpregnant cycles. The lower the ratios of estradiol levels measured on posttransfer days 4, 7 and 9 to the maximumfollicular phase level, the lower the probability of pregnancy (P < .01, P < .01 and P < .01, respectively). CONCLUSION: The steeper the decline in blood estradiol levels (affecting the periimplantation period) following ovum pickup relative to the maximum follicular phase estradiol levels, the lower the chance of pregnancy in ICSI-ET cycles.

Biomarkers↗
PubMed2004

Non-genomic action of 17beta-estradiol on opening of Ca(2+)- and voltage-activated K+ channel in lacrimal acinar cells.

The effect of the sex hormone 17 beta-estradiol on the opening of Ca(2+)- and voltage-activated K+ channels (BK channels) in the basolateral plasma membrane of mouse lacrimal acinar cells was studied by patch-clamp single-channel recording and Ca(2+)-measurement using fura-2 AM. In intact cells (the cell-attached configuration) using a pipette containing a Na+ -rich solution, estradiol was added to the bath solution, which does not have direct contact with the electrically isolated areas of membrane patch from which the single-channel currents were recorded. Estradiol increased the frequency of opening of the BK channels within a few minutes after its application. The effect of estradiol on the opening of the BK channels in acinar cells in male mice was greater than that in females. In Ca(2+)-measurement using fura-2 AM, estradiol did not increase the level of intracellular Ca2+ during a 5-minute observation period. The application of estradiol with propranolol, a beta-adrenergic receptor blocker, did not increase BK channel opening. The application of estradiol with Rp-cAMPS, an inhibitor of cyclic AMP-dependent protein kinase (protein kinase A), also inhibited the increase in channel opening. The addition of a catalytic unit of protein kinase A to the inside of the excised membrane patch increased the frequency of opening of the BK channels. These results suggest that estradiol interacts with beta-adrenergic receptor on the basolateral membrane and regulates the opening of BK channels by protein phosphorylation via a cyclic AMP pathway, without a change in the Ca2+ level.

Action Potentials↗
PubMed2005

Effect of estradiol and raloxifene on MUC1 expression and adhesive properties of Ishikawa cells.

The MUC1 is a transmembrane protein with a large mucin-like extracellular domain protruding high above the cell surface. Steroid regulation of MUC1 gene expression is essential, since overexpression of MUC1 may influence the metastatic potential of cancer cells. Our earlier results demonstrated that tamoxifen, alone and combined with estradiol, inhibits MUC1 biosynthesis in endometrial adenocarcinoma cells, in contrast to estradiol. In the present study, we examine the effect of administering raloxifene or estradiol at concentrations of 1 x 10(-8)-5 x 10(-7) M, and both drugs together, on the expression of MUC1 protein, its incorporation into the cell membrane, shedding to culture medium and adhesive properties of cancer cells to the extracellular matrix (ECM). The obtained results demonstrate that raloxifene, to a lesser degree than estradiol, stimulates [3)H]Thr incorporation to the cellular, as well as the extracellular MUC1 protein. Raloxifene-treated cells show a higher cell adhesion to collagen than estradiol-treated cells, especially at lower concentrations of these drugs, probably the result of smaller amounts of sialic acid residues in the terminal glycan chains with T and Tn antigens. Sole administration of raloxifene has a lesser effect on the expression of alpha(2)beta(1) integrin than estradiol, which is in contrast to the combined action of estradiol and raloxifene. Therefore, raloxifene, which stimulates MUC1 expression in cancer cells and inhibits their adhesion to collagen to a lesser degree than estradiol, may be a clinically safe treatment for the endometrium.

Antibodies, Monoclonal↗
PubMed2006

Comparative evaluation of Estredox, a brain-targeted estradiol delivery system versus traditional estrogen replacement therapy.

Estredox is a novel brain-targeted delivery system for estradiol (E2). The mechanism of this estradiol-chemical delivery system (E2-CDS) is based on an interconvertible dihydropiridine <--> pyridinium salt carrier (targetor) attached to E2. After administration of the E2-CDS, the targetor moiety is oxidized to a quaternary pyridinium salt (E2-Q+). Here we demonstrate that a single i.v. injection with E2-CDS (3 mg/kg) resulted in sustained presence of E2-Q+ in three various brain regions. The sustained and gradual release of estradiol from E2-Q+ is reflected by the time-course of plasma estrogen level. At the end of repeated administration of E2-CDS (daily once 0.3 mg/kg i.v. for 10 consecutive days) we found a sharp decrease in the levels of plasma estradiol followed by a gradual decrease. The levels of E2-Q+ in the investigated brain regions decreased gradually from the first post-treatment day, however, a detectable amount of E2-Q+ was still present in the hypothalamus, striatum, and cortex even on the 24th post-treatment day. Strikingly different plasma estradiol levels were found in the groups of orchidectomized rats that received daily i.v. injections of estradiol benzoate (E2-BZ). The plasma estradiol levels in these animals were much higher compared to E2-CDS-treated animals throughout the treatment period but the level sharply dropped immediately after the treatments. In contrast to the E2-CDS-treated animals there was no estradiol in any of the brain regions of E2-BZ-treated rats on the 1st and 2nd post-treatment day. All of these data are in line with the long-lasting pharmacological effects of E2-CDS-treatment on estrogen-mediated functions in castrated rats and give further experimental support for brain-targeting estrogen-treatment approach as opposed to the traditional estrogen replacement therapy.

Animals↗
PubMed2006

Differential mechanisms involved in effects of genistein and 17-beta-estradiol on porcine coronary arteries.

The purpose of this work was to examine the differential mechanisms involved in relaxation induced by genistein and 17-beta-estradiol in isolated porcine coronary arteries. Similar to 17-beta-estradiol, genistein could dose-dependently relax 30 mM KCI-precontracted coronary artery rings. The pD2 values of genistein and 17-beta-estradiol were 4.91 +/- 0.13 and 4.98 +/- 0.12 respectively. Incubation with N-L-nitroarginine (L-NNA), endothelium removal or in the presence of a potent inhibitor of protein tyrosine phosphatase sodium orthovanadate did not affect the relaxation induced by genistein, but could partially reduce the vasorelaxation induced by 17-beta-estradiol. The relaxations induced by genistein and 17-beta-estradiol were unaffected by the estrogen receptor antagonist tamoxifen, the inhibitor of prostanoid synthesis indomethacin and the protein synthesis inhibitor, cycloheximide. In addition, both of genistein and 17-beta-estradiol could decrease the contractile responses of KCI, 5-HT and CaCl2, and shift their cumulative concentration-response curves rightward in a parallel manner. These findings suggest that the relaxant effects induced by genistein and 17-beta-estradiol are probably mainly due to inhibition of Ca2+ influx through voltage-dependent calcium channels (VDCCs), and are not related to sex hormone receptor and classical genomic activities. Also there is an interesting finding that the relaxing response of 17-beta-estradiol is partially endothelium-dependent, but that of genistein is not.

Animals↗
PubMed1976

17 alpha estradiol: separation of estrogen effect on collagen from other clinical and biochemical effects in man.

In rodents the effect of 17alpha estradiol upon collagen is identical to that of 17beta estradiol, but the 17alpha estradiol effect upon uterine lining is 1/1000 that of 17beta estradiol. Both steroids reverse the effect of D-penicillamine on rodent skin collagen. Five human beings with the skin collagen changes associated with D-penicillamine were treated with 17alpha estradiol for three to six weeks. 17alpha estradiol caused no detectable changes in blood pressure, breast development, menstrual periods, serum liver enzymes, serum proteins, plasma growth hormone, insulin, serum clotting factors, serum triglycerides, serum copper or serum ceruloplasma. In contrast, 17alpha estradiol increased skin prolyl hydroxylase activity, increased soluble collagen content in the skin and increased urinary hydroxyproline excretion. These studies with 17alpha estradiol, point out a specificity difference between the various sites of estrogen action in human beings.

Collagen↗
PubMed1990

Estradiol dependence of the specific mammary tissue targeting of polyoma virus oncogenicity in nude mice.

We have previously reported (Berebbi et al., 1988) that in athymic nude mice, Polyoma virus induces mammary adenocarcinomas (MAC) at high frequency and exclusively in females. In the present study we show that in nude mice: (1) Ovariectomy results in a reduced frequency of MAC and a longer latency period of induction. When testosterone is administered to ovariectomized females, tumor induction is drastically reduced. (2) When estradiol is administered continuously to ovariectomized females the incidence and kinetics of MAC induction are the same as in control females. (3) MAC are induced in castrated males administered with estradiol although only osteosarcomas are observed in control males. (4) The tumor cells are found to harbor functional estradiol and progesterone receptors. (5) MAC can be transplanted from females to males, indicating that tumor growth is estradiol independent. (6) Estradiol is required only between day 10 and day 20 following polyoma injection, whereas the first tumors are detected only around day 60. Our results indicate that MAC induction by Polyoma virus in nude mice is estradiol-dependent during a short initiation period and that tumor progression is estradiol-independent in spite of the fact tumor cells carry functional estradiol and progesterone receptors.

Animals↗
PubMed1990

A new comprehensive technique of catheterisation, blood sampling, sample preparation and sample analysis by means of high-pressure liquid chromatography for pharmacokinetic studies with estradiol-linked nitrosoureas and their metabolites.

Estradiol-linked nitrosoureas are offering new perspectives in the antineoplastic chemotherapy of estradiol-receptor positive mammary carcinomas. In such a molecule estradiol has the function of a carrier which brings about a specific accumulation of the anticancer drug in estradiol-receptor containing tumor cells. However, there is only little knowledge about the pharmacokinetic behavior of this new group of anticancer agents. For that reason a new comprehensive technique of catheterisation, blood sampling, sample preparation and sample analysis with high-pressure liquid chromatography (HPLC) for preclinical pharmacokinetic studies with estradiol-linked nitrosoureas and their metabolites has been developed. N-(2-Chloroethyl)-N-nitroso-carbamoyl-L-alanine-estradiol-17-ester (CNC-alanine-estradiol-17-ester) and N-(2-chloroethyl)-N-nitroso-carbamoyl-L-alanine (CNC-alanine) were used as test compounds. The drugs were tested in female Sprague-Dawley rats with chemically induced mammary carcinomas. The laboratory animals were supplied with two catheters prior to the pharmacokinetic experiments. The blood samples were drawn from the vena cava catheter after the drug had been applied through a vena jugularis catheter. The compounds were extracted from plasma with C18 silicagel reversed phase cartridges. The clean-up technique delivered clear samples only slightly contaminated with the biological matrix. The recovery from plasma was 75 +/- 5% for the hormone-linked CNC-alanine-estradiol-17-ester and 70 +/- 5% for the unlinked CNC-alanine. The analysis was carried out by means of HPLC.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1989

[Mechanism of the stimulating effect of estradiol on protein kinase C in plasma membranes of target cells].

Using inhibitors and activators of protein kinase C, it was demonstrated that in isolated plasma membranes of target cells estradiol-17 beta selectively stimulates protein phosphorylation by endogenous protein kinase C. In estradiol-dependent tissues, estradiol effectuates the translocation of protein kinase C from the cytosol to the membrane fraction within 10-12 minutes. Estradiol activates protein kinase C in cellular membranes of target tissues via a mechanism which is different from that of phorbol ester (TPA): 3H-estradiol, in contrast with 3H-TPA, it is not bound by protein kinase C and, in contrast with TPA, estradiol-17 beta does not activate purified protein kinase C in vitro. In this case, the specific stimulation of protein kinase C translocation to membranes and the estradiol-induced increase in the phosphorylation of plasma membrane proteins seem to be due to the estradiol-induced activation of the transmembrane system of polyphosphoinositide degradation, eventually resulting in the formation of diacylglycerol, a protein kinase C activator.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1987

Effect of estradiol and progesterone on antistaphylococcal activity of neutrophils from ovariectomized mares.

Neutrophils isolated from jugular blood of ovariectomized mares were studied for the effect of estradiol and progesterone on bactericidal activity against Staphylococcus aureus. In experiment 1, neutrophils obtained from 4 mares were tested for bactericidal activity by adding estradiol (43 pg/ml) or progesterone (6.4 ng/ml) to the bactericidal assay. In experiment 2, 3 of the 4 ovariectomized mares were given 2 mg of estradiol, IM, daily for 3 days. Eighteen days after the initial estradiol injection, mares were given 300 mg of progesterone, IM, for 6 days. Neutrophils from these mares were tested for bactericidal activity 4 days after the initial estradiol injection, 17 days after the initial estradiol injection (control), and 7 days after the first progesterone injection. Bactericidal activity was measured at 30 and 120 minutes by counting the number of colony-forming units remaining. Neutrophil antistaphylococcal activity was not altered by adding estradiol and progesterone to the assay or by supplementing ovariectomized mares with estradiol and progesterone (P greater than 0.05).

Animals↗
PubMed1985

Role of polyamines in estradiol-induced growth of human breast cancer cells.

The present study explored the possible involvement of polyamines in estradiol-stimulated proliferation of human breast cancer cells using the estrogen-responsive subline of T-47D cells (clone 11). 17 beta-Estradiol (10(-10) M) stimulated cell growth 2- to 4-fold. This estradiol-induced proliferation was associated with a peak (at 12-24 h) of activity of ornithine decarboxylase (ODC), the first and rate-limiting enzyme of polyamine biosynthesis. Estradiol-induced cell growth and ODC activity were observed only in the presence of 10% charcoal-treated fetal bovine serum, suggesting that serum factors are required for estrogen action. alpha-Difluoromethylornithine (DFMO, 0.1 mM), a specific inhibitor of ODC, blocked the estradiol-induced cell proliferation and ODC activity. Putrescine (0.1 mM) rescued the inhibitory effect of DFMO on growth of steroid-treated cells. Putrescine alone was not stimulatory to cells, and in combinations with estradiol, it did not augment the effect of estradiol. In addition, DFMO abolished the estradiol-induced growth of several other hormone-responsive cell lines but did not affect the proliferation of unresponsive cells. Hormone-responsive cells exhibited differential sensitivity to DFMO; resistant cell lines (e.g., MCF-7) were found to possess higher endogeneous levels of ODC than sensitive cell lines (e.g., T-47D and ZR-75-1). Our findings indicate that polyamines are essential, although not sufficient, in estrogen stimulation of human breast cancer cells.

Breast Neoplasms↗
PubMed1971

Estradiol- and testosterone-induced alterations in phosphatidylcholine and triglyceride synthesis in hepatic endoplasmic reticulum.

Pathways of phosphatidylcholine and triglyceride biosynthesis were studied in hepatic endoplasmic reticulum from castrated and noncastrated male rats pretreated with estradiol or testosterone. In vitro measurements of hepatic microsomal enzymes which catalyze phosphatidylcholine biosynthesis revealed a significant increase in the specific activity of the enzyme governing phosphatidylcholine biosynthesis by the sequential methylation of phosphatidylethanolamine in the estradiol-treated castrate animals. The specific activity of phosphorylcholine-glyceride transferase was decreased by estradiol treatment in both castrate and noncastrate animals. The specific activity of diglyceride acyltransferase, which catalyzes triglyceride biosynthesis, was decreased by estradiol pretreatment in both castrate and noncastrate animals and was increased by testosterone in the castrate animals. The changes in specific activity of the enzymes governing phosphatidylcholine biosynthesis may account for the previously noted increased in vivo incorporation of methyl groups of l-methionine into hepatic phosphatidylcholine in female and estradiol-treated animals; the data suggest that in female and estradiol-treated rats a greater proportion of hepatic phosphatidylcholine is synthesized by the stepwise methylation of phosphatidylethanolamine. The decrease in diglyceride acyltransferase specific activity seen after estradiol administration may account for the lipotropic-like effect of estradiol.

Acyltransferases↗
PubMed1980

Characterization of cholestasis induced by estradiol-17 beta-D-glucuronide in the rat.

Estradiol-17 beta-D-glucuronide induced an immediate, profound and reversible inhibition of bile flow after its i.v. administration in the rat. The degree of cholestasis was dose-dependent in the range of 8.5 to 21 mumol/kg i.v. A dose of 11 mumol/kg i.v. inhibited bile flow and bile acid secretory rate 65 to 70% within 15 to 30 min of its administration; bile flow and bile acid secretion had returned to near control values within 3 hr. Linear regression analysis of the relationship between bile flow and bile acid secretion indicated a substantial decrease in bile acid independent flow. In contrast, neither estradiol-17 beta, estradiol-3-glucuronide nor estradiol-3-sulfate-17 beta-D-glucuronide at an equimolar dose had any inhibitory effect on these parameters. After a dose of [3H]estradiol-17 beta-D-glucuronide, 79% of the administered radioactivity was excreted in the bile in 3 hr. Estradiol-3-sulfate-17 beta-D-glucuronide was tentatively identified as the predominant biliary metabolite with estradiol-17 beta-D-glucuronide also present in substantial amounts. These data indicate that estradiol-17 beta-D-glucuronide is toxicologically active and suggest the possibility that this estrogen metabolite may induce hepatic pathology in vivo.

Animals↗
PubMed1995

Estradiol regulation of the human retinoic acid receptor alpha gene in human breast carcinoma cells is mediated via an imperfect half-palindromic estrogen response element and Sp1 motifs.

Estrogen receptor (ER)-positive human breast carcinoma (HBC) cell lines express significantly higher levels of retinoic acid receptor alpha (RAR alpha) (isoform 1) mRNA than ER-negative HBCs. Estradiol enhances RAR alpha mRNA expression in different ER-positive HBCs by 2-3-fold, which in turn results in increased sensitivity of ER-positive HBCs to the growth inhibitory effects of retinoic acid. To investigate the regulatory mechanisms of estradiol-mediated enhancement of RAR alpha mRNA expression, the functional promoter for the human RAR alpha isoform 1 was cloned and used to assess estradiol-mediated promoter-dependent enhancement of firefly luciferase reporter gene activity in transiently transfected ER-positive (MCF-7 and T47D) and ER-negative (MDA-MB-231) HBCs. Deletional promoter constructs were obtained to further delineate the promoter region responsible for estradiol-mediated enhancement of promoter activity. Here, we present evidence that approximately 130 bp of the promoter fragment preceding the transcriptional start site are responsible for estradiol-mediated enhancement of hRAR alpha gene expression. The estradiol-mediated enhancement is dependent on ER binding. Further deletional analysis showed that a promoter sequence of 42 base pairs, located approximately 100 bases upstream of the transcriptional start site, contains elements for estradiol-mediated enhancement. Specific deletion of either the Sp1 motif or mutations in the imperfect half-palindromic estrogen response element motif of this fragment abolish its estradiol responsiveness in transient transfections.

Base Sequence↗
PubMed1995

Serum estradiol levels in normal men and men with idiopathic infertility.

Serum estradiol levels were measured in 360 men attending an infertility clinic and 68 proven fertile men to determine whether estradiol measurements are clinically useful. The normal range of estradiol levels found in fertile men was 10-82 pg/ml. Serum concentrations of estradiol in azoospermic or oligozoospermic patients were significantly lower than those in normozoospermic men (p < 0.021). Serum concentrations of testosterone were also significantly decreased in infertile patients (p < 0.025). This decrease in serum estradiol may be partly due to reduced testosterone levels in these men because estradiol is mainly formed by peripheral aromatization of testosterone in fatty and muscle tissues. However, the exact mechanism for the decrease in the serum estradiol levels remains undetermined. It is concluded that serum estradiol levels are significantly low in the men with various testicular disorders.

Adult↗
PubMed1993

Immediate and transient stimulation of protein tyrosine phosphorylation by estradiol in MCF-7 cells.

Estradiol stimulates protein phosphorylation on tyrosine in human breast cancer MCF-7 cells under conditions of estradiol-stimulated cell growth. The stimulatory effect of estradiol has been observed by 32P-labeling of cells followed by purification of proteins using antiphosphotyrosine antibody coupled to agarose and confirmed by immunoblotting analysis with antiphosphotyrosine antibody. This stimulation is immediate (maximal in 10 s) and transient. In addition, it is receptor-mediated since estradiol stimulation is prevented by two well-known antiestrogens, OH-Tamoxifen and ICI 164,384. Estradiol fails to stimulate tyrosine protein phosphorylation of Cos cells which do not express the estradiol receptor. Two substrates of the estrogen stimulated phosphorylation on tyrosine with approximate mol wt of 55 and 60 kDa interact with a polyclonal antibody raised against amino acids 527-533 of pp60c-src (anti-cst.1 antibody). Tyrosine kinase activity of immunoprecipitates made using either anti cst.1 antibody or the monoclonal 327 antibody specific for pp60c-src shows that kinase(s) strongly related to pp60c-src are immediately and transiently stimulated by estradiol treatment of cells. The present findings provide the first demonstration that a steroid hormone rapidly stimulates tyrosine phosphorylation of target cells and induces functional modifications of substrates of this phosphorylation. These modifications might initiate the estradiol action on cell growth.

Breast Neoplasms↗
PubMed1995

The role of estradiol receptor in the proliferative activity of vanadate on MCF-7 cells.

Vanadate stimulates growth of the estradiol-responsive MCF-7 cells in the absence of estrogens through a mechanism requiring tyrosine kinase activity. The proliferative effect of vanadate is mediated by estradiol receptor, and is inhibited by three antiestrogens, hydroxytamoxifen, ICI 164,384, and ICI 182,780. Estradiol abolishes the inhibitory effect of ICI 164,384 or ICI 182,780. Before stimulating cell proliferation, vanadate induces accumulation of tyrosine phosphorylation in several proteins including estradiol receptor and epidermal growth factor receptor. In addition, vanadate increases the binding activity of the estradiol receptor for its ligand. This is the first evidence of in vivo association between estradiol receptor tyrosine phosphorylation and its hormone-binding activation. Antiestrogens abolish the vanadate effect on estradiol receptor and epidermal growth factor receptor phosphorylation and reduce it on general protein tyrosine phosphorylation. These findings show that vanadate, apparently through estradiol receptor tyrosine phosphorylation, triggers activity of this receptor, which in turn stimulates protein tyrosine phosphorylation and induces cell proliferation.

Cell Division↗
PubMed1993

Estradiol induction of retinoic acid receptors in human breast cancer cells.

Retinoic acid inhibits proliferation and steroid receptor gene expression in human breast cancer cell lines. Retinoic acid receptors (RAR)alpha, -beta, and -gamma are expressed in these cells and the expression of RAR alpha is significantly greater in estrogen receptor (ER)-positive cells. This study was undertaken to determine whether the same relationship between RAR alpha and ER gene expression was present in human breast cancers and to explore the possibility that the higher level of RAR alpha in ER-positive cells was due to estrogen regulation of RAR alpha gene expression. RAR alpha and ER mRNA expression were determined by Northern blot analysis in 116 primary breast tumors; 94 (81%) tumors were ER-positive and of these 87 (93%) were also RAR alpha-positive. The coexpression of ER and RAR alpha was statistically significant (P = 0.0052 by chi 2 contingency analysis). There was also a positive correlation (by linear regression analysis) between the levels of expression of ER and RAR alpha mRNA (r2 = 0.251, P = 0.0001), which confirmed the relationship previously documented in breast cancer cell lines and suggested that RAR alpha expression may be modulated in breast cancer in vivo by estrogens acting via the ER. The ability of estradiol to regulate RAR alpha gene expression was examined in vitro using T-47D cells which had been rendered sensitive to estrogen by repeated passage in steroid-depleted medium. Estradiol increased RAR alpha gene expression, but not that of RAR beta or RAR gamma, in a concentration-dependent manner, with the effect being maximal at 10(-10) M and less marked at higher concentrations. The effect was rapid, being detectable 1 h after and maximal 6 h after treatment with 10(-10) M estradiol. Co-treatment of cells with estradiol and antiestrogens (tamoxifen or ICI 164384, 4 x 10(-7) M for 6 h) inhibited the estradiol induction of RAR alpha gene expression, demonstrating that the effect was ER mediated. The estradiol sensitivity of the effect was underscored by the demonstration that addition of untreated serum to cells growing under steroid-depleted conditions was sufficient to induce maximal RAR alpha gene expression. This effect was totally abolished by addition of ICI 164384. In summary, the demonstration that estradiol increased RAR alpha mRNA levels in breast cancer cells supports the hypothesis that the correlation between RAR alpha and ER gene expression in breast tumors and breast cancer cell lines is due to estradiol augmentation of RAR alpha gene expression.

Breast Neoplasms↗