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

A new approach for the treatment of breast cancer could be the use of progesterone antagonists. These compounds were originally developed for the inhibition of progesterone-dependent processes and have been shown to be effective in inhibition of nidation and interruption of pregnancy. Although the roles of progesterone and the progesterone receptor in control of cell growth remain unclear, it was found in progesterone receptor positive mammary carcinoma cell lines that the antiprogestin, Mifepristone, had an inhibitory effect on cell growth and a growth-inhibiting action on the DMBA-induced mammary carcinoma of the rat. We have shown that the progesterone antagonists, Onapristone and ZK 112993, which possess a reduced antiglucocorticoid activity compared to Mifepristone, exert a strong tumor-inhibiting effect in a panel of hormone-dependent mammary tumor models. The effects of these compounds were in some systems superior to those of tamoxifen or high dose progestins and comparable to ovariectomy. Although prerequisites for their antiproliferative potency are an affinity to the progesterone receptor as well as a sufficient number of available receptors in the tumors, the strong tumor inhibiting potential of the antiprogestins cannot be explained by a classical anti-hormonal mechanism. Surprisingly, the antitumor activity is evident in spite of elevated serum levels of ovarian and pituitary hormones. It was established by morphometric procedures that treatment with Onapristone triggers differentiation of the mitotically active polygonal tumor epithelial cell towards secretory active glandular structures and acini. All our quantitative light and electron microscopic data indicate that the antitumor action of antiprogestins is accompanied by the initiation of terminal differentiation leading to (apoptotic) cell death. Finally, our flow cytometry studies revealed an accumulation of the tumor cells in the G0G1 phase of the cell cycle, which may result from induction of differentiation since a differentiation-specific G1 arrest has already been proposed for other stem cell systems. It can be concluded from these data that the progesterone receptor antagonists differ in their mode of action from compounds used in established endocrine treatment strategies for mammary carcinoma. The ability of progesterone antagonists like Onapristone to reduce the number of cells in S-phase may offer a significant clinical advantage, since it is established that the S-phase fraction is a highly significant predictor of disease-free survival among axillary node-negative patients with diploid mammary tumors.
J Steroid Biochem Mol Biol 1992 Mar
PMID:Progesterone antagonists: tumor-inhibiting potential and mechanism of action. 156 10

Shionogi Carcinoma 115 (SC 115) is an androgen-dependent mouse tumor. Chiba Subline 2 (CS 2) is an androgen-independent subline derived from SC 115. CS 2 contains androgen receptors (AR), but is refractory to androgen and does not exhibit androgen-related responses which are observed in SC 115. In the present study the structure and function of AR in SC 115 and CS 2 are examined using cloned cells. There were no gross rearrangements or deletions in the AR genes of these cell lines when compared by Southern blot analysis with the AR gene in the mouse seminal vesicle. SC 115 and CS 2 expressed AR mRNA of normal size. When the cDNA containing DNA- and androgen-binding domains of the AR genes of both cell lines were amplified by polymerase chain reaction, no mutations were found in these regions. SC 115 and CS 2 were transfected with a plasmid containing a long terminal repeat of mouse mammary tumor virus linked to the chloramphenicol acetyltransferase (CAT) gene. Androgen stimulation of these transfectants resulted in equal elevation of CAT activity. These results indicated that the androgen-independent CS 2 contained functionally normal AR which were identical to those in the androgen-dependent parent tumor.
J Steroid Biochem Mol Biol 1992 Jul
PMID:Loss of androgen dependency with preservation of functional androgen receptors in androgen-dependent mouse tumor (Shionogi Carcinoma 115). 163 20

We have expressed fusion proteins encoding defined segments of the coding segment of the human androgen receptor (hAR) in Escherichia coli using the pGEX-2T expression vector. Large quantities of fusion proteins containing glutathione-S-transferase (GST) linked to the amino or carboxy terminal region of the receptor and a fusion protein containing the complete amino acid sequence of the androgen receptor were produced in soluble form. The GST hAR fusion proteins containing the hormone-binding domain of the androgen receptor exhibit high affinity specific binding for a variety of natural and synthetic androgens. Analysis of the binding properties of the complete and truncated androgen receptor fusion proteins revealed that the amino terminus affects the Kd of the fusion proteins for mibolerone (0.89 vs. 3.43 nM for the truncated and complete fusion proteins, respectively). Despite these differences, both the truncated and complete hAR fusion proteins exhibit a higher affinity for dihydrotestosterone than for testosterone, implying that the preferential affinity for dihydrotestosterone observed in androgen receptor prepared from native sources is a measure of the inherent structure of the hormone-binding domain. Furthermore, the ligand-receptor complex is stable, as the ligand is not easily displaced with unlabelled competitor and is stable to mild heat denaturation. Fusion proteins containing the DNA-binding domain demonstrate specific DNA binding, as evidenced by studies using segments of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) and synthetic glucocorticoid response elements. These studies establish that GST hAR fusion proteins exhibit physical properties similar to those of native androgen receptor. Affinity purification using a glutathione affinity resin and cleavage of the fusion proteins at a thrombin cleavage site permits a marked enrichment using a two-step purification. The use of such methods will facilitate the study of the normal and mutant receptor proteins.
Mol Cell Endocrinol 1992 Mar
PMID:Expression and characterization of full-length and partial human androgen receptor fusion proteins. Implications for the production and applications of soluble steroid receptors in Escherichia coli. 163 14

The assay systems for steroid receptor functions in steroid-sensitive cells (SC-3 cells) were developed in which hormone-responsive element linked to a reporter gene [chloramphenicol acetyl transferase (CAT) gene] was transfected by the electroporation technique. Stimulation with androgen of SC-3 cells transfected with mouse mammary tumor virus promoter-CAT gene (MMTV-CAT) resulted in clear enhancement of CAT activity, whereas glucocorticoid required abnormally high concentrations to obtain significant stimulation. The simultaneous addition of glucocorticoid surprisingly inhibited androgen-induced CAT activity in SC-3 cells, whereas glucocorticoid and androgen acted together synergistically to activate CAT activity in T 47D cells. When SC-3 cells were cotransfected with the expression vector of human glucocorticoid receptor (GR) gene, inhibition with glucocorticoid of androgen-enhanced CAT activity was abolished. These results would suggest that SC-3 cells contain functionally abnormal GR.
J Steroid Biochem Mol Biol 1991 May
PMID:Functional abnormality of glucocorticoid receptor in Shionogi carcinoma 115 cells as evidenced by gene transfer experiments. 164 88

The brain tissues of the rat and mouse express two types of corticosteroid binding proteins, the glucocorticoid (GR) and aldosterone (MR) receptors. Unlike the type II (GR) receptor, type I receptor has a high affinity for aldosterone (ALDO) and corticosterone and is structurally similar to the kidney mineralocorticoid receptor (MR). The results reported in this study provide direct evidence for the interaction of dexamethasone (DEX), triamcinolone acetonide (TA), dexamethasone-21-mesylate (DXM) and 11-deoxycorticosterone (DOC) with human MR expressed in cells by transient co-transfection of a hMR expression vector. The interactions of hMR with DEX, TA, DXM, DOC, promegestone (R5020) and methyltrienelone (R1881) were measured by trans-activation of mouse mammary tumor virus long terminal repeat fused to bacterial chloramphenicol acetyltransferase (MMTV-tk-CAT) in gene co-transfection experiments and by cell free hormone binding assay. The incubation of various steroid hormones in the presence of [3H]ALDO in a competition assay with extracts prepared from HeLa cells co-transfected with hMR expression vector, showed that hMR expressed under these conditions has a high relative affinity for DEX which is similar to ALDO, TA and DOC. Incubation with DXM under these conditions showed very little competition, as was observed with R1881 and R5020. Incubation of the co-transfected cells with DEX, ALDO, DOC, R5020, TA, R1881 and DXM demonstrated that the level of trans-activation did not reflect the previously observed order of binding affinity for the hMR. The level of transactivation was always higher with DEX and TA compared to ALDO and DOC. Analysis of the binding of labeled glucocorticoid regulatory element (GRE) and hMR incubated with DEX, ALDO and DXM by gel shift analysis demonstrated that the trans-activation of MMTV-tk-CAT by hMR is a result of the interaction of hMR with GRE in the MMTV-LTR.
J Steroid Biochem Mol Biol 1991 Jul
PMID:Differential regulation of mouse mammary tumor virus-bacterial chloramphenicol acetyltransferase chimeric gene by human mineralocorticoid hormone-receptor complexes. 164 51

Glucocorticoids regulate the trafficking of cell surface mouse mammary tumor virus (MMTV) glycoproteins in the virus-infected rat hepatoma cell line M1.54. The CR4 rat hepatoma sorting variant, which is derived from M1.54 cells by immunoselection, is uniquely defective in the glucocorticoid-regulated transport of MMTV glycoproteins. Indirect immunofluorescence of fixed permeabilized cells and subcellular fractionation of isolated microsomes revealed that variant CR4 cells retain the MMTV glycoproteins in Golgi-like membranes after glucocorticoid treatment. The variant CR4 phenotype can be complemented by interspecies cell fusions with human HepG2 hepatoma cells and by DNA rescue with genomic fragments isolated from either human or rat hepatoma cells. Transfected wild-type genomic fragments rescue the sorting defect in CR4 at a frequency consistant with a single genetic locus, whereas homologous transfection with CR4 genomic DNA has no effect. Thus, complementation of a rat hepatoma cell-sorting variant supports the existence of a novel protein-trafficking activity encoded by the human or rat genomes that acts in trans in the Golgi to selectively mediate the sorting of cell surface MMTV glycoproteins in glucocorticoid-treated cells.
Mol Endocrinol 1991 Mar
PMID:Evidence for a protein-trafficking gene that rescues the defective glucocorticoid-regulated transport and Golgi retention of mouse mammary tumor virus glycoproteins in a rat hepatoma cell-sorting variant. 165 90

The mouse mammary tumor virus (MMTV) promoter is positively regulated by glucocorticoid hormone via binding of glucocorticoid receptor to a specific response element. Upon addition of hormone, a nucleosome containing the glucocorticoid response element is removed or structurally altered, suggesting that the nucleosome interferes with transcription. Accordingly, inhibition of chromatin assembly should relieve the repression and result in an increased constitutive activity. We have tested this hypothesis by injecting nonspecific competitor DNA into Xenopus laevis oocytes to titrate endogenous histones. The coinjection of competitor DNA altered chromatin structure: nucleosomal ladders produced by micrococcal nuclease were disrupted, and the unique helical setting of the MMTV promoter in a nucleosome was lost, as shown by in situ DNase I footprinting. Basal MMTV transcription was drastically increased by competitor DNA, whereas a coinjected, constitutively active adenovirus 2 major late promoter was not stimulated. These results show that the uninduced MMTV promoter is under negative control and provide direct support for the theory that the nucleosomal organization maintains the repression of this promoter in its uninduced state.
Mol Cell Biol 1991 Oct
PMID:Inhibition of chromatin assembly in Xenopus oocytes correlates with derepression of the mouse mammary tumor virus promoter. 165 27

We have documented previously that glucocorticoid hormones modulate the posttranslational localization of cell surface mouse mammary tumor virus (MMTV) glycoproteins in the viral-infected M1.54 rat HTC hepatoma cell line. To determine whether glucocorticoids affect the trafficking of individually synthesized MMTV glycoproteins, HTC cells were transfected with a constitutively expressed MMTV glycoprotein gene lacking the viral phosphoprotein and polymerase genes. This construct also allows equivalent levels of MMTV glycoproteins to be compared in the presence or absence of glucocorticoids. Indirect immunofluorescence and immunoprecipitation of radiolabeled cells revealed that in transfected cells the transmembrane MMTV glycoproteins are efficiently expressed, transported to the cell surface, and proteolytically cleaved in the presence or in the absence of the synthetic glucocorticoid dexamethasone. Cell surface immunoprecipitation of [35S]methionine-labeled cells showed that the level of plasma membrane gp78 appeared to be stimulated 2-fold after dexamethasone treatment, even though fluorescence-activated cell sorting revealed no discernible change in the total concentration of cell surface MMTV glycoproteins. Analysis of oligosaccharide side chain maturation through a pulse-chase radiolabeling revealed that the rate of rough endoplasmic reticulum-Golgi transport was essentially identical in dexamethasone-treated and untreated transfected cells and was similar to that observed in dexamethasone-treated M1.54 cells. Thus, in contrast to viral-infected hepatoma cells, mostly constitutive cellular machinery mediates the trafficking and maturation of cell surface MMTV glycoproteins expressed outside of the proviral context. Taken together, our results suggest that the glucocorticoid-stimulated synthesis of nonglycosylated viral components may contribute to or be responsible for the regulated trafficking of MMTV glycoproteins observed in viral-infected rat hepatoma cells.
Mol Endocrinol 1991 Nov
PMID:Altered effects of glucocorticoids on the trafficking and processing of mouse mammary tumor virus glycoproteins constitutively expressed in rat hepatoma cells in the absence of nonglycosylated viral components. 166 47

The mouse mammary tumor virus (MMTV) initiates infection when the envelope protein, gp52, binds to a cell surface protein and triggers internalization. The hormonal regulation of this protein was studied both in vitro and in vivo. In mammary gland explant culture, levels of the MMTV binding protein were maintained only when prolactin was present in the medium. The further addition of progesterone induced levels to 164% of controls, while estradiol was without effect. These results were reproduced in ovariectomized mice which, in addition, demonstrated a need for estradiol in the maintenance of basal levels. Two growth-promoting agents were also tested in vitro: dibutyryl cAMP decreased levels to 31% of controls, while epidermal growth factor had no effect. Scatchard analyses revealed that all of these changes reflected alterations in binding protein concentration and not affinity. These results suggest that the expression of MMTV from mammary epithelium and the elevation of its binding protein are coordinated.
Mol Cell Endocrinol 1991 Dec
PMID:Regulation of the mouse mammary tumor virus (MMTV) binding site in cultured mammary tissue. 166 50

Synergistic action of multiple steroid hormone response elements (HREs) has been proposed to be due to cooperative binding of receptors. We have studied the cooperativity of steroid hormone receptor binding to synergistic HREs in two natural genes. In the mouse mammary tumor virus long terminal repeat that contains four progesterone receptor binding sites, no cooperativity in receptor binding was observed between the single distal and the three proximal sites whereas a low level of cooperativity in receptor binding (about 2-fold) was found between the three proximal sites. This contrasted with the very strong synergism of these four HREs in stimulation of transcription. In the chicken vitellogenin II gene upstream sequences, an estrogen and a progestin response elements act synergistically. In this case again, no cooperativity of binding of the estrogen and progesterone receptors to their respective binding sites was observed. We therefore conclude that cooperative receptor binding may not always be required for synergistic action of multiple HREs.
Mol Cell Endocrinol 1991 Dec
PMID:In two genes, synergism of steroid hormone action is not mediated by cooperative binding of receptors to adjacent sites. 166 57


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