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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To define the mechanisms by which antiestrogens inhibit breast cancer cell proliferation, the effects of the antiestrogen ICI 182780 on G1 cyclins and their cyclin-dependent kinase (CDK) partners were investigated in MCF-7 cells. Inhibition of entry into S phase became evident 9 h after treatment, with the proportion of cells in S phase reaching a minimum by 24 h. ICI 182780 increased the proportion of the hypophosphorylated, growth inhibitory form of the retinoblastoma protein (pRB). This change began at 4-6 h, preceding effects on S phase. This suggests that there are early effects on the activities of CDKs that target pRB that are not merely a consequence of changes in cell cycle progression. The kinase activity of Cdk2 decreased to low levels at 18-24 h when changes in S phase and pRB phosphorylation were well advanced. An earlier effect was seen on kinase activity associated with immunoprecipitated cyclin D1, which was reduced approximately 40% by 12 h, with further decreases at 18-24 h. Cdk2 and Cdk4 protein levels remained constant over 24 h. Cyclin D1 messenger RNA and protein were down-regulated by ICI 182780 from 2 h, with levels halved at 8 h. ICI 182780 also increased the expression of the CDK inhibitors p27KIP1 and p21WAF1/CIP1 at later times. These observations are compatible with the hypothesis that antiestrogens block entry of cells into S phase and inhibit cell proliferation as the consequence of an early decline in pRB phosphorylation contributed to by reduced cyclin D1/Cdk4 activity. At later times, increased CDK inhibitor abundance may act to repress Cdk2 and Cdk4 activities, causing additional reductions in pRB phosphorylation, thus maintaining the antiestrogen blockade of cell cycle progression.
Mol Endocrinol 1995 Dec
PMID:Antiestrogen inhibition of cell cycle progression in breast cancer cells in associated with inhibition of cyclin-dependent kinase activity and decreased retinoblastoma protein phosphorylation. 861 16

Effect of estrogens and antiestrogens (AEs) on estrogen receptor (ER) half-life was analyzed in MCF-7 cells by assessing its progressive disappearance after covalent labeling in situ with [3H]tamoxifen aziridine ([3H]TAZ). Cells were incubated for 1 h with 20 nM [3H]TAZ either in the absence or presence of a 500-fold excess of unlabeled estradiol (E2) (non-specific binding). The entire ER population was labeled by this method as established by subsequent incubation of the cells with [125I]E2. [3H]TAZ labeled cells were maintained in culture for additional 5 h in the absence (control) or presence of increasing amounts (0.1 nM - 1 microM) of either a given estrogen (E2, estrone, diethylstilbestrol, bisphenol), a pure AE (RU 58 668, ICI 164 384) or an AE with residual estrogenic activity (RU 39 411, 4-hydroxytamoxifen, keoxifene). The progressive disappearance of nuclear and cytosolic [3H]TAZ-ER complex during 5 h incubation were assessed by their immunoprecipitation with anti-ER monoclonal antibody (H 222) followed by scintillation counting or SDS-PAGE and fluorography. Fading of labeled receptors was extremely slow (approximately 10% loss after 6 h) in absence of any hormone/antihormone indicating a long half-life of the [3H]TAZ-ER complex. Addition of estrogens as well as pure AEs led to a dramatic reduction of the half-life while AEs with residual estrogenic activity were extremely less efficient in this regard providing an explanation for the ability of latter compounds to up-regulate the receptor since they do not affect ER mRNA synthesis and stability. Receptor disappearance induced by estrogens was closely related to their binding affinity for ER. Newly synthesized ER emerged during the treatment with hormones or antihormones seems to be implicated in the phenomenon since [3H]TAZ was covalently bound and could, therefore, not be displaced by these compounds. Induction of synthesis of a short half-life peptide(s) with degradative activity was demonstrated by addition of cycloheximide or puromycine (both at 50 microM) which completely blocked ER disappearance. The fact that no cleavage products of ER were detected by SDS-PAGE suggested a lysosomial hydrolysis. Hence, hormonal modulation of only a part of ERs may down-regulate their total population until it reaches the steady-state level.
J Steroid Biochem Mol Biol 1996 Feb
PMID:Estrogenic and antiestrogenic regulation of the half-life of covalently labeled estrogen receptor in MCF-7 breast cancer cells. 864 30

We examined the role of beta 1- and beta 2-adrenergic receptor (AR) density and ratio in catecholamine-stimulated cAMP responses in rat C6 glioma cells. These cells, which normally express both subtypes, were stably transfected with an isopropylthio-beta-D-galactoside-inducible vector containing either beta 1AR or beta 2AR coding sequences, and receptor expression was controlled by the time and concentration of isopropylthio-beta-D-galactoside exposure. Induction of the dominant beta 1AR subtype increased the potencies of isoproterenol (ISO) and other agonists in stimulating cAMP accumulation by 20-40-fold without changing maximal response. Induction of beta 2AR expression caused 7-13-fold increases in the potency of ISO, epinephrine, and zinterol, but not of norepinephrine, and a 20-40% loss in maximal response to all agonists. Selective antagonists showed that both subtypes contributed in a nonadditive manner in the response to ISO under different conditions. After beta 2AR induction, the effects of ISO were not blocked by the beta 1-selective antagonist CGP 20712A but were shifted 100-fold to the right by the beta 2-selective antagonist ICI 118,551. However, in the presence of ICI 118,551, CGP 20712A caused an additional 100-fold decrease in ISO potency, and Schild analysis revealed complex interactions between the two subtypes. Each antagonist alone caused smaller shifts to the right in the dose-response curve to NE and, when present simultaneously, completely abolished the NE response. We conclude that beta 1ARs and beta 2ARs have different efficiencies in activating cAMP accumulation in C6 glioma cells. Activation of coexisting subtypes results in complex and sometimes synergistic interactions between the two subtypes, which vary with agonist concentration, selectivity, subtype density, and ratio.
Mol Pharmacol 1996 Jul
PMID:Inducible expression of beta 1- and beta 2-adrenergic receptors in rat C6 glioma cells: functional interactions between closely related subtypes. 870 Jan 11

Cyclin-dependent kinases (Cdk) act to regulate G1- to S-phase transition in mammalian cells. We have studied the effects of estradiol and the steroidal antiestrogen ICI 182, 780 on induction of Cdk activity and the consequent phosphorylation of retinoblastoma protein (Rb) in estrogen-responsive MCF-7 breast cancer cells. Treatment of growth-arrested MCF-7 cells with physiological concentrations of estradiol led to a time-dependent increase in Cdk2-associated and cyclin E-dependent kinase activity, which was accompanied by hyperphosphorylation of Rb and S-phase entry. Induction of both Cdk2 activity and DNA synthesis by estradiol was dose dependent and was inhibited by coadministration of ICI 182,780. Elicitation of Cdk2 activity was found to require prolonged (> 8h) estradiol exposure. Levels of cyclins E and A were unchanged in MCF-7 cells undergoing G1- to S-transit; however, synthesis and steady state levels of cyclin D1 protein were increased by estradiol. Cdk4-associated Rb kinase activity was evident in MCF-7 cells by 6 h after estradiol exposure and was inhibited by antiestrogen. Cdk2 and Cdk4 protein levels were not altered by estrogen treatment; however, faster migrating, phosphorylated Cdk2 forms increased in estradiol-treated MCF-7 cells by 12 after release from growth arrest. Cdtk-inhibitory activities, associated with p27kip-1, were eliminated from growth-arrested MCF-7 cells after treatment with estradiol but were not eliminated from cells cotreated with estradiol and ICI 182,780. These findings suggest that estradiol regulates G1 progression in MCF-7 cells through direct effects upon Cdk activation, Rb phosphorylation, and by inducing elimination of Cdk inhibitors.
Mol Endocrinol 1996 May
PMID:Estrogen regulates activity of cyclin-dependent kinases and retinoblastoma protein phosphorylation in breast cancer cells. 873 80

Group I introns are widespread in eukaryotic organelles and nuclear-encoded ribosomal DNAs (rDNAs). The green algae are particularly rich in rDNA group I introns. To better understand the origins and phylogenetic relationships of green algal nuclear-encoded small subunit rDNA group I introns, a secondary structure-based alignment was constructed with available intron sequences and 11 new subgroup ICI and three new subgroup IB3 intron sequences determined from members of the Trebouxiophyceae (common phycobiont components of lichen) and the Ulvophyceae. Phylogenetic analyses using a weighted maximum-parsimony method showed that most group I introns form distinct lineages defined by insertion sites within the SSU rDNA. The comparison of topologies defining the phylogenetic relationships of 12 members of the 1512 group I intron insertion site lineage (position relative to the E. coli SSU rDNA coding region) with that of the host cells (i.e., SSU rDNAs) that contain these introns provided insights into the possible origin, stability, loss, and lateral transfer of ICI group I introns. The phylogenetic data were consistent with a viral origin of the 1512 group I intron in the green algae. This intron appears to have originated, minimally, within the SSU rDNA of the common ancestor of the trebouxiophytes and has subsequently been vertically inherited within this algal lineage with loss of the intron in some taxa. The phylogenetic analyses also suggested that the 1512 intron was laterally transferred among later-diverging trebouxiophytes; these algal taxa may have coexisted in a developing lichen thallus, thus facilitating cell-to-cell contact and the lateral transfer. Comparison of available group I intron sequences from the nuclear-encoded SSU rDNA of phycobiont and mycobiont components of lichens demonstrated that these sequences have independent origins and are not the result of lateral transfer from one component to the other.
Mol Biol Evol 1996 Sep
PMID:Nuclear-encoded rDNA group I introns: origin and phylogenetic relationships of insertion site lineages in the green algae. 875 6

We determined the relationship between the beta 1- and beta 2-adrenergic receptor subtypes in isolated myocytes and their physiological responsiveness in chronically instrumented conscious baboons and rats. In conscious baboons, isoproterenol (ISO) (0.02 microgram/kg) increased left ventricular (LV) dP/dt by 89 +/- 6.7% from 2898 +/- 370 mmHg/s and only by 13 +/- 3.3% from 2491 +/- 146 mmHg/s after beta 1-adrenergic receptor blockade, indicating that the predominant physiological response was mediated by beta 1-adrenergic receptors. Decreases in mean arterial pressure (-11 +/- 0.5 mmHg v -16 +/- 4.6 mmHg) and coronary vascular resistance (-3.1 +/- 0.4 v -3.6 +/- 0.4 mmHg/ml/min) induced by ISO were not different before and after beta 1-blockade, indicating that beta 2-adrenergic receptors were not blocked. In conscious rats, ISO (0.4 microgram/kg) increased LV dP/dt by 50 +/- 4.9% from 13252 +/- 2002 mmHg/s and only by 10 +/- 3.9% from 10793 +/- 1364 mmHg/s after beta 1-adrenergic receptor blockade: whereas decreases in mean arterial pressure induced by ISO were not different before and after beta 1-blockade (-19 +/- 2.4 mmHg v -16 +/- 2.2 mmHg), i.e. very consistent with the physiological responses in baboons. In vitro studies of isolated myocytes, using radioligand binding with 125I-cyanopindolol (125I-cyp) and the subtype beta 1-selective antagonist betaxolol and the beta 2-selective antagonist ICI 118551 indicated that the beta 1/beta 2 ratio of rat myocytes was 92/8: whereas baboon myocytes were more equally distributed (59/41). Thus, in both species the preponderance of effects of ISO on ventricular function was beta 1-adrenergic receptor mediated, which is consistent with the beta 1/beta 2 ratio in rat myocytes but not in baboon myocytes, where a significant fraction of beta 2-adrenergic receptors does not appear to exert an effect on conctractility in vivo.
J Mol Cell Cardiol 1996 Jun
PMID:Identification and functional role of beta-adrenergic receptor subtypes in primate and rodent: in vivo versus isolated myocytes. 878 72

Estrogens play an important role in breast cancer and the effect of estrogen on growth of breast cancer cells has been extensively studied. However, only little information is available about the response of normal breast epithelial cells to estrogen, mainly due to the difficulties in establishing estrogen receptor (ER)-positive human breast epithelial cells in culture. We have stably transfected the human estrogen receptor (hER) wt cDNA into the ER-negative, spontaneously immortalized human breast epithelial cell line, HMT-3522S1, in order to develop a model for studying the effect of estrogen on nonmalignant human breast epithelial cells. Characterization of the transfected clone F9 confirmed incorporation of the estrogen receptor gene in the genome, expression of hER mRNA and hER protein. However, proliferation of F9 cells was inhibited by both estradiol (E2) and tamoxifen, whereas the pure antiestrogen ICI 182,780 had no effect on cell proliferation. This seems paradoxical since E2 stimulated the expression of the endogenous genes, TGF-alpha, cathepsin D, and alpha1-antitrypsin. In breast cancer cell lines, high expression of these genes is correlated to estrogen-stimulated cell proliferation. The spontaneously immortalized HMT-3522S1 cells transfected with wt ER cDNA behave similarly to cell lines from nonmalignant breast tissue immortalized by carcinogens and transfected with mutated ER cDNA as described by others. The discrepancy between growth inhibition and induction of positive growth factors by E2 indicates that either ER-positive nonmalignant breast epithelial cells are growth-inhibited by E2 in contrast to malignant cells or that introduction of the ER into ER-negative cells is not sufficient for restoring "normal' estrogen responsiveness.
Mol Cell Endocrinol 1996 May 17
PMID:Characterization of a nontumorigenic human breast epithelial cell line stably transfected with the human estrogen receptor (ER) cDNA. 879 53

Rainbow trout hepatocyte primary culture was used to test the influence of some xenobiotics on the expression of two genes implicated in reproduction, those for the estrogen implicated in reproduction, those for the estrogen receptor (ER) and vitellogenin (Vg). We showed that chlordecone, nonylphenol, a polychlorobiphenol (PCB) mixture (Aroclor 1245) and lindane were able to induce ER and Vg mRNA accumulation. Antiestrogens, 4-hydroxytamoxifen and ICI 164,384, prevented the effects of the xenobiotics, indicating that the induction of gene expression is mediated by the ER. Among these four xenobiotics, only chlordecone and nonylphenol were able to displace the binding of [3H]estradiol to ER-enriched COS-1 extracts, and to activate an estrogen-dependent reporter gene (ERE-TK-CAT) cotransfected with an expression vector containing ER cDNA. The results suggest that chlordecone and nonylphenol are direct inducers of rainbow trout ER and Vg gene expression, whereas PCBs and lindane act through their hepatic metabolites. Moreover, pentachlorophenol acts as an antagonist of the induction by estradiol of rainbow trout ER and Vg gene expression.
J Mol Endocrinol 1995 Oct
PMID:Influence of xenobiotics on rainbow trout liver estrogen receptor and vitellogenin gene expression. 880 Jun 39

The 2-phenylindole system has been identified as a suitable structure for the design of non-steroidal pure estrogen antagonists [E. von Angerer et al., J. Steroid Biochem. Molec. Biol. 49 (1994) 51-62]. Derivatives with an amide function in the side chain antagonized the stimulatory effect of estrogens both in vitro and in vivo, and showed no agonistic activity when given alone. The findings of other groups who studied steroidal antiestrogens prompted us to replace the amide function by sulfide, sulfoxide, sulfone, sulfonamide and related groups. The compounds with polar sulfur functions retained the high binding affinity for the calf uterine estrogen receptor (RBA: 1-5% of estradiol; ICI 182,780; 6.2%). The estrogenic effect was quantified in a transcription assay using HeLa cells cotransfected with the expression vector HEG0 for the human estrogen receptor and a reporter plasmid that harbored a Vit. A2 ERE and the luciferase gene driven by a thymidine kinase promotor. Pentylsulfide, -sulfinyl, and -sulfonyl groups, linked to the indole nitrogen by a decamethylene spacer, were devoid of any transcriptional activity. These results were confirmed in the mouse uterine weight test. The sulfone (ZK 164,015) completely abolished the effect of a standard dose of estrone at a daily dose of 7 mg/kg. This compound strongly inhibited the growth of hormone-sensitive human MCF-7 breast cancer cells with an IC50-value close to 1 nM. Similar activity was found for the steroidal sulfoxide ICI 182,780. We were also able to demonstrate significant antineoplastic activity in vivo for some of these new 2-phenylindole derivatives.
J Steroid Biochem Mol Biol 1996 Apr
PMID:2-Phenylindoles with sulfur containing side chains. Estrogen receptor affinity, antiestrogenic potency, and antitumor activity. 880 84

The recently established, estrogen receptor positive rat endometrial adenocarcinoma cell line RUCA-I was tested for estrogen responsiveness in vivo and in vitro. In vivo, 10(6) RUCA-I cells were injected subcutaneously into intact, ovariectomized, or ovariectomized, estradiol-substituted syngenic DA/Han rats. All animals developed well differentiated endometrial adenocarcinoma, that had metastasized to peripheral lymph nodes and into the lung. Ovariectomy reduced tumor and lymph node weight, as well as number of lung metastases significantly compared to controls. In another series of experiments, treatment with the pure anti-estrogen ZK 119010 basically gave the same results as seen in ovariectomized animals, whereas tamoxifen treatment had no effect on metastasis of RUCA-I cells. These findings clearly demonstrate the estrogen dependency of growth and metastasis of RUCA-I cells in vivo. In vitro, we assessed the estrogenic and anti-estrogenic potency of various anti-estrogens, thereby investigating their effects on the expression of components of the complement C3 complex as an estradiol-induced protein and on the expression of fibronectin as an estrogen-repressed protein. Evaluating the relative anti-estrogenic potency of these anti-estrogens we found that ICI 164384 and ICI 182780 behaved as complete antagonists in vitro. Tamoxifen, like estradiol, stimulated complement C3 production and repressed fibronectin expression and has to be regarded as an agonist in this particular in vitro system. ZK 119010 if given alone had no significant influence on the biosynthesis of complement C3 and of fibronectin if compared to the unstimulated control. In addition, another estrogen dependent parameter was identified. Estrogen and anti-estrogen treatment affected glycosylation of complement C3 components. After estradiol treatment predominantly the higher glycosylated epitope of complement C3 became detectable, which could be transformed into the low molecular weight epitope by treatment with hyaluronidase. Finally, we compared the anti-proliferative effects of ICI 164384 and of tamoxifen in vitro. Both anti-estrogens slightly inhibited the growth of RUCA-I rat endometrial adenocarcinoma cells. In conclusion, RUCA-I cells represent a powerful, endometrial derived experimental model to test the agonistic and antagonistic properties of anti-estrogens on growth and metastasis in vivo and on gene expression in vitro. The effects of the tested anti-estrogens on gene expression of RUCA-I cells were found to be useful in predicting their effectiveness on tumor growth in vivo.
J Steroid Biochem Mol Biol 1996 Apr
PMID:The rat endometrial adenocarcinoma cell line RUCA-I: a novel hormone-responsive in vivo/in vitro tumor model. 880 92


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