help button home button Endocrine Society Endocrinology
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Doisneau-Sixou, S. F.
Right arrow Articles by Favre, G.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Doisneau-Sixou, S. F.
Right arrow Articles by Favre, G.
Endocrinology Vol. 144, No. 3 989-998
Copyright © 2003 by The Endocrine Society

ARTICLE

Contrasting Effects of Prenyltransferase Inhibitors on Estrogen-Dependent Cell Cycle Progression and Estrogen Receptor-Mediated Transcriptional Activity in MCF-7 Cells

Sophie F. Doisneau-Sixou, Philippe Cestac, Sarah Chouini, Jason S. Carroll, Andrew D. Hamilton, Said M. Sebti, Marc Poirot, Patrick Balaguer, Jean-Charles Faye, Robert L. Sutherland and Gilles Favre

Département "Innovation Thérapeutique et Oncologie Moléculaire" (S.F.D.-S., P.C., S.C., M.P., J.-C.F., G.F.), Centre de Physiopathologie de Toulouse Purpan, Institut National de la Santé et de la Recherche Médicale U563, and Institut Claudius Regaud, 31052 Toulouse cedex, France; Cancer Research Program (S.F.D.-S., J.S.C., R.L.S.), Garvan Institute of Medical Research, St. Vincent’s Hospital, Darlinghurst, Sydney, New South Wales 2010, Australia; Department of Chemistry (A.D.H.), Yale University, New Haven, Connecticut 06511; Drug Discovery Program (S.M.S.), H. Lee Moffitt Cancer Center and Research Institute and Department of Biochemistry and Molecular Biology, University of South Florida, Tampa, Florida 33612; and Institut National de la Santé et de la Recherche Médicale 439 (P.B.), Pathologie Moléculaire des Récepteurs Nucléaires, 34090 Montpellier, France

Address all correspondence and requests for reprints to: Robert L. Sutherland, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, Sydney, New South Wales 2010, Australia. E-mail: r.sutherland{at}garvan.org.au.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Activation of estrogen receptors (ERs) by estrogens triggers both ER nuclear transcriptional activity and Src/Ras/Erks pathway-dependent mitogenic activity. The present study implicates prenylated proteins in both estrogenic actions. The farnesyltransferase and geranylgeranyltransferase I inhibitors (FTI-277 and GGTI-298, respectively) antagonize estradiol-stimulated cell cycle progression, progesterone receptor, cyclin D1, and c-Myc expression. In contrast, the inhibitors markedly stimulate transcription from two genes containing estrogen response elements, both in the absence and presence of estradiol. The pure antiestrogen ICI 182,780 inhibits by more than 85% these effects on transcription. We demonstrate that both FTI-277 and GGTI-298 increase the association of steroid receptor coactivator-1 with ER{alpha} and FTI-277 decreases the association of ER{alpha} with the histone deacetylase 1, a known transcriptional repressor. In addition, FTI-277 has no marked effect on the association of the two corepressors, nuclear receptor corepressor and silencing mediator of retinoid and thyroid receptor with ER{alpha}, whereas GGTI-298, similar to tamoxifen, clearly increased these associations. Together, these results demonstrate that prenylated proteins play a role in estradiol stimulation of proliferation and progesterone receptor expression. However, they antagonize the ability of ER{alpha} to stimulate estrogen response element-dependent transcriptional activity, acting presumably through coregulator complex formation.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
THE MAJOR MITOGEN for breast epithelial cells is 17ß-estradiol (E2), but it is now well accepted that peptide growth factors play important roles in controlling both mammary gland development and breast cancer progression. Most E2 actions are mediated through its nuclear receptors, estrogen receptors (ERs) {alpha} and ß, and in cancer development, growth factors have been shown to act synergistically with E2 (1, 2). For example, epidermal growth factor (EGF) is able to activate the ER and promote transcription from an estrogen response element (ERE)-containing promoter in the absence of E2. In particular, MAPK activated by growth factors, phosphorylates ER and potentiates the activation function 1 transactivation function of ER (3, 4). It has also been shown that activation of ER by E2 leads to two cascades of events that may be independent: 1) nuclear transcriptional activity of ERs and 2) activation of Src/Ras/Erk pathway that allows S-phase entry of cells (5). Phosphatidylinositol-3 kinase inhibitors as well as inhibitors of MAPK-1 have been shown to decrease the numbers of cells entering DNA synthesis after treatment with E2 (6), but this issue remains controversial because it is not clear which pathway supports the mitogenic action of E2 (7). All these data highlight evidence for cross-talk between E2 and growth factor-induced cytoplasmic signaling. Major components of these signaling pathways are low-molecular-weight GTPases such as Ras that require prenylation for function.

Ras mediates EGF phosphorylation of ER (3, 4) as well as E2 mitogenic activity in human mammary adenocarcinoma cells lines (5). Moreover, enhanced transcriptional activity of ER contributes to oncogenic K-Ras-mediated NIH-3T3 cell transformation whereas 12Val-K-Ras expression increases ER-mediated transcriptional activity (8). ER has been shown to directly interact with DNA sequences in the c-Ha-ras gene, and E2 is able to stimulate c-Ha-ras transcription. These data suggest that estrogen-mediated stimulation of c-Ha-ras transcription may play an important role in progression of breast cancer (9). Ras belongs to the Ras superfamily of low-molecular-weight proteins whose activity is controlled by a GDP/GTP cycle. Members of the Ras superfamily include Ras, Rho, and Rab subfamilies. The Ras and Rho proteins are posttranslationally modified by the isoprenoid lipids, farnesylpyrophosphate, and geranylgeranylpyrophosphate. Farnesyltransferase (FTase) and geranylgeranyltransferase I catalyze the covalent attachment of the farnesyl (C15) and the geranylgeranyl (C20) groups, respectively, to the carboxyl-terminal cysteine of prenylated proteins. Prenylation appears to be essential not only for membrane association but also for biological activity (10, 11).

Several lines of evidence suggest cross-talk between E2 action and prenylated proteins. For example, it has been reported that E2 can overcome a G1 block in MCF-7 cells, induced by 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (12), which inhibit protein prenylation by lowering the cellular pool of farnesylpyrophosphate and geranylgeranylpyrophosphate. The activated mutant forms of Rho family GTPases (RhoA, Rac1, and cdc42) inhibit ER transcriptional activation in MCF-7 and Ishikawa human uterine cancer cells (13). In breast cancers, Ras mutation has been observed in only 5% of cases (14); however, overexpression of Ras protein is common and has been associated with a more aggressive type of breast cancer (15). A marked increase of RhoB mRNA was observed in breast cancer cell lines and inversely correlated to the amount of EGF receptor (16). Furthermore, endogenous hyperactive Rac 3 was present in highly proliferative human breast cancer cells lines and tumor tissues (17). The Rho family GTPases (Rac, Cdc42, and in particular RhoA) are also overexpressed in breast cancers, compared with corresponding normal tissue (18). Finally, RhoC is overexpressed in inflammatory breast cancer (19, 20) and RhoC expression is now proposed as a potential marker for small breast carcinoma with metastatic potential (21).

In this report, we assessed the specific role of prenylated proteins in estrogenic stimulation of MCF-7 cells. Our data implicate both farnesylated and geranylgeranylated proteins in E2 action because prenylation inhibitors inhibit cell cycle progression driven by E2 and stimulate the transcriptional activity mediated by ER{alpha}. The current model of ER action suggests that ER modulates the rate of transcription through interactions with the basal transcription machinery and alterations in the recruitment of coactivators that modify chromatin organization at the promoter of target genes (22, 23, 24, 25, 26). We propose that the transcriptional stimulation of ER by the prenylation inhibitors is due to a similar shift in transcription coregulator association with ER{alpha}. Our data demonstrate that both FTase inhibitors (FTI)-277 and geranylgeranyltransferase I inhibitors and (GGTI)-298 increase the association of the coactivator SRC-1 with ER{alpha} and that FTI-277 decreases the association of histone deacetylase 1 (HDAC1), which is essential for transcriptional repression, to the ER{alpha}.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Materials
Materials for cell culture and TRIzol reagent came from Life Technology (Cergy Pontoise, France). FTI-277 and GGTI-298 were a generous gift from S. Sebti (University of South Florida, Tampa, FL) or purchased from Calbiochem (Croydon, Victoria, Australia). Tamoxifen, ribonuclease (RNase) A, Tween 20, and propidium iodide were purchased from Sigma-Aldrich (St. Quentin Fallavier, France; and Castle Hill, New South Wales, Australia). ICI 182,780 was provided by Dr. Alan Wakeling (AstraZeneca Pharmaceuticals, Macclesfield, UK), and RU38,486 was kindly provided by P. Van de Velde (Roussel Uclaf, Romainville, France).

Cell culture
The human breast adenocarcinoma cell line MCF-7 was obtained from the American Tissue Culture Collection (Manassas, VA). The development of stable transfectants of MCF-7 cells (called MELN cells) has been described previously (27). These cells were established by transfecting MCF-7 cells with the ERE-ß-globin-tk-luc-SV-Neo plasmid and thus express luciferase in an estrogen-dependent manner. MCF-7 cells were grown routinely in RPMI 1640 and MELN in DMEM growth media, supplemented with 5% fetal calf serum (FCS) (Life Technologies, Inc.). Cells were incubated at 37 C in a humidified 5% CO2 incubator.

For the experiments presented in Figs. 1–7GoGoGoGoGoGoGo, cells were grown for 5 d in phenol red-free medium, containing 5% dextran-coated charcoal-treated fetal calf serum. Medium was changed after 2 d. At d 5, cells were treated or not with FTase inhibitors and received estradiol (5 x 10-8 M) and/or inhibitors 24 h later. Both peptidomimetics FTI-277 and GGTI-298 were dissolved in a solution of 10 mM dithiothreitol (DTT) in dimethylsulfoxide (DMSO) to avoid the formation of disulfide bonds in solution, as described previously (28). Tamoxifen and ICI 182,780 were dissolved in ethanol.



View larger version (23K):
[in this window]
[in a new window]
  		Figure 1. Effects of prenyltransferase inhibitors on E2-stimulated MCF-7 cell cycle progression. A, Cells, deprived of E2 for 5 d, were treated with 50 nM E2 or ethanol with or without FTI-277 and GGTI-298 (15 µM and 10 µM, respectively, or DTT/DMSO vehicle). The percentage of cells in G0/G1 phase of the cell cycle was analyzed 48 h after E2 addition by flow cytometry, as described in Materials and Methods. Each histogram is the mean value of 104 viable cells, and results are representative of at least three independent experiments. B, Importance of inhibitor pretreatment for their effects on cell cycle progression. Cells were deprived of E2 for 6 d, and then all cells were stimulated with E2 (50 nM). Simultaneously, cells were treated or not with FTI-277 or GGTI-298 (15 µM and 10 µM, respectively, or DTT/DMSO vehicle). Fifty percent of cells were pretreated for 24 h with FTI-277 and GGTI-298 before E2 addition (same concentrations as above). The percentage of cells in G0/G1 phase of the cell cycle was analyzed 30 h after E2 addition by flow cytometry. Each histogram is the mean value of 104 viable cells.

 


View larger version (16K):
[in this window]
[in a new window]
  		Figure 2. Kinetic effect of GGTI-298 addition on E2-induced MCF-7 cell cycle progression. Cells, deprived of E2 for 5 d, were stimulated with E2 (50 nM) at time 0 and treated or not with GGTI-298 (10 µM). Addition of GGTI-298 was performed at time 0, 3, 6, 9, 12, 15, or 18 h after E2 addition. The percentage of cells in G0/G1 phase was analyzed 30 h after E2 addition by flow cytometry. Each data point is the mean value of 104 viable cells, and results are representative of three independent experiments.

 


View larger version (25K):
[in this window]
[in a new window]
  		Figure 3. Effect of prenyltransferase inhibitors on PR expression in MCF-7 cells. Cells, deprived of E2 for 5 d, were treated or not with FTI-277 (15 µM or DTT/DMSO vehicle). Twenty-four hours later, they were stimulated with E2 (50 nM) or ethanol and treated or not with FTI-277 and GGTI-298 (respectively, 15 µM and 10 µM, or DTT/DMSO vehicle). Analyses were performed 48 h after E2 addition, as described in Materials and Methods. Results are expressed as a percentage of non-E2-stimulated PR protein (A) and mRNA (B) levels. In A, 100% is equivalent to 58.2 fmol PR per milligram of protein. In B, the arrow indicates the position of the band corresponding to the PR probe for RNase mapping. Error bars indicate the mean values ± SEM from four independent experiments; they are plotted for all experimental conditions but are not visible on some histograms when too small to be distinguished from the mean.

 


View larger version (26K):
[in this window]
[in a new window]
  		Figure 4. Effect of prenyltransferase inhibitors on pS2 expression in MCF-7 cells. Cells, deprived of E2 for 5 d, were treated or not with FTI-277 (15 µM or DTT/DMSO vehicle). Twenty-four hours later, they were stimulated with E2 (50 nM) or ethanol and treated or not with FTI-277 and GGTI-298 (respectively,15 µM and 10 µM, or DTT/DMSO vehicle). Analyses were performed 48 h after E2 addition, as described in Materials and Methods. Results are expressed as a percentage of non-E2-stimulated pS2 protein level in the culture medium (A) and pS2 mRNA (B). In A, 100% is equivalent to 6.55 ng pS2 protein per milliliter of medium. In B, the arrow indicates the position of the bands corresponding to pS2 and 36B4 probes for RNase mapping. Error bars indicate the mean values ± SEM from three independent experiments; they are plotted for all conditions but are not visible on some histograms when too small to be distinguished from the mean.

 


View larger version (34K):
[in this window]
[in a new window]
  		Figure 5. Effect of prenyltransferase inhibitors on c-Myc and cyclin D1 expression in MCF-7 cells. Cells, deprived of E2 for 5 d, were treated or not with FTI-277 and GGTI-298 (respectively, 15 µM and 10 µM, or DTT/DMSO vehicle). Twenty-four hours later, they were stimulated with E2 (50 nM) or ethanol and treated or not with FTI-277 and GGTI-298 (respectively, 15 µM and 10 µM, or DTT/DMSO vehicle). Analyses were performed 3 and 6 h after E2 addition, as described in Materials and Methods. Results are expressed as a percentage of non-E2-stimulated c-Myc (A) and cyclin D1 (B) protein levels. These experiments are representative of two independent experiments.

 


View larger version (23K):
[in this window]
[in a new window]
  		Figure 6. Effect of prenyltransferase inhibitors on ER expression in MCF-7 cells. Cells, deprived of E2 for 5 d, were treated or not with FTI-277 (15 µM or DTT/DMSO vehicle). Twenty-four hours later, they were stimulated with E2 (50 nM) or ethanol and treated or not with FTI-277 and GGTI-298 (respectively, 15 µM and 10 µM, or DTT/DMSO vehicle). Analyses were performed 48 h after E2 addition, as described in Materials and Methods. Results are expressed as a percentage of non-E2-stimulated ER protein (A) and mRNA (B). In A, 100% is equivalent to 199.3 fmol of ER per milligram of protein. In B, the arrow indicates the position of the band corresponding to ER probe for RNase mapping. Error bars indicate the mean values ± SEM from three independent experiments; they are plotted for all conditions but are not visible on some histograms when too small to be distinguished from the mean.

 


View larger version (18K):
[in this window]
[in a new window]
  		Figure 7. Effect of prenyltransferase inhibitors on ERE-dependent luciferase activity in MELN cells in the presence or absence of ICI 182,780. Cells, deprived of E2 for 5 d, were treated or not with FTI-277 (15 µM or DTT/DMSO vehicle). Twenty-four hours later, they were stimulated with E2 (50 nM) or ethanol and treated or not with FTI-277 and GGTI-298 (respectively, 15 µM and 10 µM, or DTT/DMSO vehicle) and ICI 182,780 (500 nM). Luciferase activities were quantified 16 h after E2 addition, as described in Materials and Methods. Results are expressed in arbitrary units after protein normalization. Error bars indicate the mean values ± SD from triplicate experiments, and results are representative of two independent experiments.

 
Cell cycle analysis
For each condition, 3 x 105 cells were seeded per dish in two 100-mm diameter dishes and treated, as described above, in a final volume of 5 ml. Following treatment, the culture medium was aspirated and the cells were collected by trypsinization, washed twice with ice-cold PBS (100 x g, 5 min), and resuspended in 500 µl ice-cold PBS. Cells were then fixed in 1.5 ml ice-cold absolute ethanol for 30 min at 4 C, washed twice in PBS and then stained with propidium iodide (100 µg/ml RNase A in PBS, 0.25% Tween 20, and 50 µg/ml propidium iodide) for 1 h at 37 C. DNA content was determined by flow cytometry (FACScan flow cytometry system, Becton Dickinson and Co., Meglan, France), with a 488-nm laser excitation and 530-nm emission filter. The proportion of cells in G0/G1 phase of the cell cycle was calculated from the DNA histograms using the CellFit software (Becton Dickinson and Co.). Data were obtained from 104 viable cells.

Estrogen and progesterone receptor expression
For each condition, 9 x 105 cells were seeded in 140-mm diameter dishes and treated, as described above, in a final volume of 15 ml. Cells were incubated for 48 h with estradiol and/or inhibitors. Quantitation of ER{alpha} and progesterone receptor (PR) protein levels was performed on the cytosol fraction of cells. Briefly, following treatment, the culture medium was removed, the cells were washed twice with PBS and scrapped in 350 µl homogenization buffer (10 mM Tris, pH 7.4, buffer containing 20 mM molybdic acid and 12 mM monothioglycerol). Cells were lysed by three cycles of freezing/thawing (-170 C/20 C) and then centrifuged at 100,000 x g for 60 min at 4 C. We used ABBOT ER-EIA monoclonal and ABBOT PgR-EIA monoclonal kits, according to the manufacturer’s instructions (Abbott, Rungis, France). This methodology provides an accurate estimate of the total cellular ER or PR levels (29). Cytosolic protein concentrations were measured using the Bradford technique (30). For each condition, average receptor concentration was calculated from the data of two independent dishes.

pS2 expression analysis
The quantitation of pS2 protein was performed from the culture medium of cells growing in 140-mm-diameter dishes. We used ELSA-pS2 radioimmunometric assay, according to the manufacturer’s instructions (CIS Biointernational, Oris Group, Gif-sur-Yvette, France). For each condition, average pS2 concentration was calculated from the data of two independent dishes.

RNase protection assay for pS2, ER, and PR mRNA expression analysis
For each condition, 9 x 105 cells were seeded per dish in three to five 140-mm dishes and treated, as described above, in a final volume of 15 ml. Cells were incubated for 48 h with estradiol and/or inhibitors. At the end of the incubation, total RNA was isolated according to the method of Chomczynski and Sacchi (31) using TRIzol reagent. Four probes were used for the RNase protection assay experiments: PR, ER, pS2, and 36B4 (32). They were the products of an in vitro transcription in the presence of [33P]UTP (3000 Ci/mmol, ICN) of the corresponding cDNA fragments cloned in a plasmid containing the T3 and T7 (for PR, ER, and 36B4) or T7 and SP6 (for pS2) promotors, in opposite directions. For mRNA quantitation, the probe used for PR was a 460-bp fragment of the complete cDNA, for pS2 a 300-bp fragment, for ER a 379-bp fragment, and for 36B4 a 650-bp fragment, all provided by Pr. Chambon (Institut de Génétique et de Biologie Moléculaire et Cellulaire-Centre National de la Recherche Scientifique, Strasbourg, France). Fifty micrograms total RNA were incubated in the presence of pS2 and 36B4 probes (or 80 µg total RNA in the presence of PR or ER probes), and 5 x 105 to 106 cpm of each probe were used in hybridization buffer; samples were then treated according to RPA II kit instructions (Ambion, Inc., Austin, TX). Following digestion of nonhybridized material, hybridized RNA was purified, resuspended in electrophoresis sample buffer, and heated to 95 C before analysis on a denaturing polyacrylamide gel (8 M urea, 5% acrylamide). After fixation in a 10% acetic acid/10% methanol solution, the gel was dried and analyzed using a Storm 840 (Amersham Pharmacia Biotech, Orsay, France). The intensity of the band corresponding to the respective mRNA was quantified using ImageQuant software (Molecular Dynamics, Inc., Sunnyvale, CA).

Western blot analysis
At the completion of the experiments, MCF-7 cell monolayers were washed with ice-cold PBS (Sigma-Aldrich) and the cells from two 25-cm2 flasks were then scraped into 75 µl ice-cold lysis buffer: 50 mM HEPES, pH 7.5; 150 mM NaCl; 10% (vol/vol) glycerol; 1% Triton X-100; 1.5 mM MgCl2; 1 mM EGTA; 100 mM NaF; 10 mM pyrophosphate; 10 µg/ml aprotinin; 10 mg/ml leupeptin; 1 mM phenylmethylsulfonyl fluoride; 200 µM sodium orthovanadate; 1 mM DTT; and 20 µM MG132. The lysates were then placed on ice, vortexed vigorously at intervals for 10 min, centrifuged at 15,000 x g for 10 min at 4 C, and the supernatants stored at -80 C. Equal amounts of total protein (5–30 µg) were separated by SDS-PAGE and then transferred to polyvinyl difluoride membranes. Proteins were visualized using the enhanced chemiluminescence detection system (Amersham Pharmacia Biotech) after incubation (overnight at 4 C for primary and 1 h at room temperature for secondary antibodies) using the following primary antibodies: c-Myc (SC-40) and HDAC1 (SC-7872) from Santa Cruz Biotechnology, Inc. (Santa Cruz, CA); cyclin D1 (DCS-6) from Novocastra Laboratories Ltd (Newcastle-upon-Tyne, UK); SRC-1 (SRC1 Ab-1) from Neomarkers (Fremont, CA); ß-actin (AC-15) from Sigma-Aldrich, and secondary antibody antimouse horseradish peroxidase and antirabbit horseradish peroxidase from Santa Cruz Biotechnology, Inc. Nuclear receptor corepressor (N-CoR) and SMRT rabbit antisera were kindly provided by Dr. M. A. Lazar (University of Pennsylvania, Philadelphia, PA). Protein abundance was quantitated by analysis of autoradiographs. Relative band intensities were quantified by densitometric analysis (Molecular Dynamics, Inc.). Quantitation of protein levels by this method was linear over the analyzed range of protein concentrations and exposure times employed in these studies.

Luciferase assays
For each condition, 15 x 103 cells were seeded per well in 12-well plates and treated, as described above, for 16 h in a final volume of 0.5 ml. At the end of the treatment, cells were washed with PBS and lysed in 150 µl lysis buffer (Promega Corp., Charbonnières, France). Luciferase activity was measured using the luciferase assay reagent (Promega Corp.), according to the manufacturer’s instructions. Protein concentrations were measured using the Bradford technique (30) to normalize the luciferase activity data. For each condition, average luciferase activity was calculated from the data of three independent wells.

ER{alpha}-binding studies
Binding studies were performed as described earlier (33): ER was extracted from COS-7 cells transfected with pSG5-HG0 using the Lipofectamine methodology according to the manufacturer’s instructions (Life Technologies, Inc.). Briefly, transfected COS-7 cells were grown to 80% confluency in DMEM supplemented with 10% FCS, scraped, and washed twice with PBS. After centrifugation for 10 min at 120 x g, the cells were resuspended in TM buffer (20 mM Tris-HCl, pH 7.4; 20 mM sodium molybdate). Cells were broken by freeze-thaw lysis of the cell pellets in an equal volume of TM buffer. Cytosols were prepared by a 105,000 x g centrifugation at 0 C for 60 min. Glycerol was added to the cytosol to a final concentration of 10% (vol/vol), the extract frozen immediately in liquid nitrogen, and stored at -80 C until use. The cytosol was subsequently diluted to 1:10 in TM buffer and then incubated for 18 h at 4 C in a volume of 100 µl with 10 µg protein and 2 nM [3H] estradiol (91 Ci/mmol, Amersham Pharmacia Biotech), with or without 25 µM unlabeled ligand. Assays were terminated by loading 65 µl incubate on a 1.2-ml Sephadex LH-20 (Sigma-Aldrich) column equilibrated with the TM buffer. The flow-through was collected and counted for radioactivity in ready Emulsifier-safe scintillant (Packard Bioscience B.V., Gronningen, The Netherlands).

Detection of ER{alpha}-associated proteins
The 150-cm2 flasks were seeded with 1 x 106 cells. Cells were allowed to proliferate for 2 d in normal RPMI 1640 medium supplemented with 5% nontreated FCS until they reached 50% confluence, after which drugs or vehicle were added directly to the medium. Cells were treated with FTI-277, GGTI-298, tamoxifen, or vehicle. The final concentrations of ethanol and DTT/DMSO solution in the medium were 0.5% and had no effect on the rate of cell proliferation (data not shown).

After 48 h, MCF-7 cell monolayers were washed with ice-cold PBS (Sigma), and the cells from three 150-cm2 flasks were then scraped into 600 µl ice-cold lysis buffer (as described above for Western blot analysis). The lysates were then placed on ice, vortexed vigorously at intervals for 10 min, centrifuged at 15,000 x g for 10 min at 4 C, and the supernatants stored at -80 C. Lysates were obtained and stored as described above.

Coregulator complexes were immunoprecipitated from equivalent amounts of protein (500 µg) with goat polyclonal antihuman N-CoR (SC-1609) or SMRT (SC-1610) antibodies or rabbit polyclonal antihuman HDAC1 (SC-7872) or SRC-1 (SC-8995) antibodies (Santa Cruz Biotechnology, Inc.), for 1 h at 4 C. This was followed by a 1-h incubation at 4 C with protein A-Sepharose or protein G-Sepharose (Zymed Laboratories, Inc. Corp., San Francisco, CA) for conjugation to rabbit and goat antibodies, respectively. Immunoprecipitates were washed twice with ice-cold lysis buffer containing 1 M NaCl and then twice with ice-cold 50 mM HEPES, pH 7.5; 1 mM DTT. Proteins were separated from protein A- or protein G-Sepharose beads by resuspending the beads in 1x SDS sample buffer and heating at 95 C for 3 min. Proteins were then separated by SDS-PAGE and transferred to polyvinyl difluoride membrane. They were visualized using the enhanced chemiluminescence detection system (Amersham Pharmacia Biotech) after overnight incubation at 4 C using the mouse antihuman ER{alpha} antibody (M7047, DAKO Corp.). Protein abundance was visualized by densitometric analysis (Molecular Dynamics, Inc.).

Statistical analysis
Statistical analysis of the data were conducted using an unpaired two-sample t test. Significance was defined as P < 0.05.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Geranylgeranylated and farnesylated proteins are required for E2-stimulated MCF-7 cell cycle progression
We analyzed Ras and Rap1A prenylation (proteins, respectively, farnesylated and geranylgeranylated) as described previously (28) and determined the maximal concentrations of inhibitors that efficiently and specifically inhibit protein prenylation in MCF-7 cells after 48-h incubation. We found that 15 µM FTI-277 and 10 µM GGTI-298 potently and selectively inhibited H-Ras farnesylation and Rap geranylgeranylation, respectively (data not shown). To determine whether prenylated proteins are implicated in E2 stimulation of MCF-7 cells, we first assessed the effect of FTI-277 and GGTI-298 on cell cycle progression after E2 stimulation (Fig. 1AGo). After 5 d of E2 deprivation, cells were stimulated with E2 in the presence or absence of inhibitors. In the absence of inhibitors, E2 stimulated S-phase entry and hence significantly decreased the proportion of cells in G0/G1 phase of the cell cycle. In the presence of FTI-277, fewer cells entered S phase with a higher percentage of cells remaining in G0/G1 phase. In the presence of GGTI-298, the block in G0/G1 phase was almost complete. Thus, GGTI-298 and, to a lesser degree, FTI-277 prevented E2-stimulated cell cycle progression, suggesting that both farnesylation and geranylgeranylation of proteins are required for E2-stimulated cell cycle progression in MCF-7 cells.

Preincubation with FTI-277, but not GGTI-298, is necessary to inhibit E2-stimulated cell cycle progression
Most prenylated proteins have a long half-life (24 h for Ras and RhoA); however, others have half-lives as short as 2 h, i.e. RhoB (34). Prenylation is a covalent posttranslational modification of proteins and prenylation inhibitors act by inhibiting prenylation of newly synthesized proteins. We therefore determined the importance of the length of exposure to prenylation inhibitors by administering the prenyltransferase inhibitors for 24 h before E2 exposure (Fig. 1BGo). After 6 d of E2 deprivation, cells were stimulated by E2 in the presence or absence of inhibitors and cell cycle progression was analyzed 30 h later. As expected, under control conditions, E2 allowed deprived cells to enter S phase and only about 20% of cells remained in G0/G1 phase. FTI-277 had to be added 24 h before E2 to block S-phase entry with 60% of cells remaining in G0/G1. By contrast, GGTI-298 strongly inhibited S-phase entry, even without preincubation. The dramatic effect of GGTI-298 was observed as early as 16 h after E2 addition when cells began to enter S phase (data not shown).

GGTI-298 added up to 6 h after E2 inhibits E2-stimulated cell cycle progression
The observation that the simultaneous addition of E2 and GGTI-298 completely blocked S-phase entry suggested that the GGTI-298 effect occurred during early or late G1 phase. We then determined how long after E2 addition GGTI-298 efficiently inhibits cell cycle progression (Fig. 2Go). After 5 d of E2 deprivation, cells were stimulated with E2. GGTI-298 was added simultaneously or 3, 6, 9, 12, 15, or 18 h later and the percentage of cells in G0/G1 analyzed 30 h after E2 addition. In the absence of GGTI-298, E2 stimulated 50% of cells to enter S phase and 35% of cells remained in G0/G1. The addition of GGTI-298 at time 0 (time of addition of E2) induced a complete block of cells in G0/G1 (77%). The addition of GGTI-298 up to 6 h after E2 significantly impaired the E2 effect. GGTI-298 had a decreased effect if added 9 h after E2 addition and little or no effect at later times.

In subsequent experiments, a 24-h incubation with FTI-277, before E2 addition, was performed, whereas GGTI-298 was added simultaneously with E2.

Contrasting roles of prenylated proteins in E2-stimulated protein expression
We next analyzed the effect of prenyltransferase inhibitors on the expression of two well-known ER transcriptional targets, PR and pS2. We first assessed the effect of FTI-277 and GGTI-298 on PR expression after E2 stimulation (Fig. 3Go). After 5 d of E2 deprivation, cells were treated with E2 in the presence or absence of inhibitors, and PR protein concentrations (Fig. 3AGo) and mRNA levels (Fig. 3BGo) were determined 48 h later. E2 alone induced PR protein levels by 5.8-fold (Fig. 3AGo). In the presence of FTI-277 or GGTI-298, the induction was decreased to 3.6-fold and 1.9-fold, respectively. The effects of both inhibitors were statistically different from the E2-stimulated control (t test). In the absence of E2, FTI-277 had no effect on basal PR protein levels, whereas GGTI-298 decreased PR protein levels by 58%. A 6.3-fold induction of PR mRNA level was observed after E2 addition (Fig. 3BGo), and in the presence of FTI-277 or GGTI-298, induction was decreased to 4.8-fold and 4.3-fold, respectively, but this was not statistically significant. Thus, GGTI-298 and, to a lesser degree, FTI-277 significantly inhibited E2-stimulated PR expression and the same trend was observed at the mRNA level.

The pS2 expression was next analyzed under identical conditions (Fig. 4Go). Figure 4AGo shows that E2 alone increased pS2 protein levels by 6.7-fold. In the presence of FTI-277, the induction was about the same, whereas GGTI-298 allowed an 18-fold induction. Without E2, but in the presence of FTI-277, there was no change of the basal pS2 protein level, whereas in the presence of GGTI-298, a 1.9-fold induction was observed. In Fig. 4BGo, a 2.6-fold induction of pS2 mRNA level was observed after E2 addition, a nonsignificantly different 3.3-fold induction in the presence of FTI-277, and a statistically significant 6.8-fold induction in the presence of GGTI-298. Without E2 and in the presence of FTI-277, there was no change of the basal level, whereas in the presence of GGTI-298, a 1.7-fold induction was observed.

Prenylated proteins positively modulate expression of early response genes
Because both E2 and the prenyltransferases inhibitors have multiple effects after 48 h, we determined the effects of the inhibitors at earlier time points by analyzing their effect on expression of two early response genes involved in the mitogenic response to E2: c-Myc and cyclin D1. After 5 d of E2 deprivation, cells were treated with inhibitors for 24 h before E2 was added. The c-Myc (Fig. 5AGo) and cyclin D1 (Fig. 5BGo) expression was determined 3 and 6 h later. For both c-Myc and cyclin D1, E2 alone induced the protein levels by 3- and 1.5-fold, respectively, within 3 h of E2 addition. Although FTI-277 and GGTI-298 already inhibited c-Myc at 3 h, they both tended to decrease the expression at 6 h of c-Myc (by 13% and 30%, respectively) and cyclin D1 (by 30%).

Prenylated proteins positively modulate ER expression
To determine whether some of the effects of prenyltransferase inhibitors (such as the decrease of PR expression or induction of pS2 expression) can be explained by changes in ER{alpha} expression, ER{alpha} levels were quantified under the conditions previously described (Fig. 6Go). Figure 6AGo shows that in the absence of E2, FTI-277, and GGTI-298 decreased ER{alpha} protein levels by 66% and 76%, respectively. Figure 6AGo also shows that, as expected, E2 alone induced a 66% decrease in the ER{alpha} protein levels. In the presence of E2 and FTI-277 or GGTI-298, a further decrease was observed with GGTI-298 but not with FTI-277. In Fig. 6BGo, a marked decrease in the basal level of ER mRNA was observed with E2, FTI-277, or GGTI-298. Similar to the effect on protein levels, FTI-277 or GGTI-298 alone decreased the basal level of ER mRNA in the absence of E2.

FTIs and GGTI-298 markedly enhance ER-mediated transcription in MELN cells
Because we demonstrated that prenylation inhibitors are able to stimulate pS2 expression and inhibit PR expression, we next determined whether they act directly on ER transcriptional activity. For this, we analyzed their effects on an ERE-dependent luciferase reporter gene, stably expressed in MCF-7 cells (MELN cells) (27).

After 5 d of E2 deprivation, cells were treated with E2 in the presence or absence of prenyltransferase inhibitors or ICI 182,780 (Fig. 7Go), and 16 h later, luciferase activity was quantified. In vehicle-treated cells, a 10.4-fold induction of the luciferase activity by E2 was observed. This induction was inhibited by 80% in the presence of ICI 182,780. In the absence of E2, FTI-277 and GGTI-298 stimulated basal transcriptional level by 5- and 3-fold, respectively. The results shown in Fig. 7Go are representative of nine and six independent experiments, respectively, with values of 5 ± 3.3-fold for FTI-277 and 3.7 ± 1.8-fold for GGTI-298. In the presence of E2, FTI-277 and GGTI-298 enhanced the ability of E2 to stimulate transcription by an additional 2.8 ± 1.3-fold for FTI-277 and 2.9 ± 1.3-fold for GGTI-298–277 (10 and 6 experiments, respectively). In both cases, ICI 182,780 inhibited the activity by at least 80%.

We then determined the effect of the RU38,486, an antagonist of PR and the glucocorticoid receptor, and showed that it had no significant effect on luciferase activity in the absence or presence of FTI-277 and GGTI-298 (data not shown).

To determine whether the effects we observed are related to the specific structure of FTI-277 and GGTI-298 (peptidomimetics), we tested under identical conditions the effects of two other FTIs of different chemical structures and demonstrated that they all increased luciferase activity in the absence as well as presence of E2 (data not shown). In all cases, the stimulation was strongly inhibited by ICI 182,780. We also demonstrated that these inhibitors do not compete directly with E2 binding. For this, competition analysis of [3H]estradiol binding to ER{alpha} was performed in the presence of FTI-277, GGTI-298, and two other FTIs of different structures. None of these compounds exhibited any displacement of [3H]estradiol, demonstrating their lack of binding to ER{alpha} (data not shown).

FTI-277 and GGTI-298 modulate the association of coregulators with ER{alpha}
It has been shown that in mammary cells, tamoxifen promotes the binding of ERs to the nuclear receptor corepressor N-CoR and the related factor, silencing mediator of retinoid and thyroid receptors (SMRT), and that the relative expression levels of coactivators and corepressors may modulate the ability of tamoxifen to regulate ER transcriptional activity (22, 23, 24, 25). More recently cell type- and promoter-specific differences in coregulator recruitment have been shown to determine the cellular response to selective estrogen receptor modulators, such as tamoxifen (26). We therefore assessed the ability of tamoxifen, FTI-277, and GGTI-298 to regulate ER{alpha} association with various coregulators in the presence of E2 (Fig. 8AGo). As expected (26), tamoxifen increased the association of N-CoR and SMRT with ER{alpha} and dramatically enhanced HDAC1 association. FTI-277 slightly increased N-CoR association with ER{alpha} but was less potent than tamoxifen and had no effect on SMRT association with ER{alpha}. In addition, FTI-277 induced the complete dissociation of HDAC1 from ER{alpha}. Although GGTI-298 did not impair the association of HDAC1 with ER{alpha}, it unexpectedly increased ER{alpha} association with N-CoR and SMRT, even more so than tamoxifen. These effects observed in the presence of GGTI-298 are particularly marked, considering the fact that under these experimental conditions, ER{alpha} levels are about one third of those seen under the control conditions (Fig. 6Go). FTI-277 and GGTI-298 also significantly increased the association of the coactivator SRC-1 with ER{alpha} when compared with the control or tamoxifen-treated cells in which the association was considerably weaker.



View larger version (27K):
[in this window]
[in a new window]
  		Figure 8. Effect of tamoxifen, FTI-277, and GGTI-298 on various coregulators of transcription. MCF-7 cells were grown for 48 h in RPMI 1640 growth medium, supplemented with 5% FCS. Cells were then treated with tamoxifen (1 µM), FTI-277 (15 µM), GGTI-298 (10 µM), or vehicle. Whole-cell lysates were prepared at 48 h. A, Effect of the inhibitors on ER{alpha} association to the coregulators of transcription. Each of the four coregulators was immunoprecipitated from 500 µg of the same lysates. The immunoprecipitates were subjected to electrophoresis on 10% SDS-PAGE and immunoblotted with anti-ER{alpha} antibody. B, Effect of tamoxifen, FTI-277, and GGTI-298 on coregulator expression levels. Thirty micrograms total protein was separated by 6% and 10% SDS-PAGE and immunoblotted with coregulator and ß-actin antibodies or sera. Total protein levels were visualized using densitometry as described under Materials and Methods. The results are representative of two independent experiments.

 
A Western blot analysis of SMRT, N-CoR, SRC-1, and HDAC1 was performed to determine whether the inhibitors change their expression levels, potentially explaining the altered levels of association with ER{alpha}. The data shown in Fig. 8BGo indicate that the inhibitors and tamoxifen have no effect on SRC-1, whereas tamoxifen, FTI-277, and to a lesser extent GGTI-298 decrease SMRT and N-CoR levels. Regarding the HDAC1 levels, we observed a decrease in the presence of both tamoxifen and FTI-277 although the signals were very weak (data not shown). Consequently, none of these changes explain the alterations in ER{alpha} association.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The classical model of E2 action involves binding to nuclear receptors ER{alpha} and ERß, which interact with chromatin to modulate the activity of target gene promoters. Besides this genomic pathway, E2 induces nongenomic effects (often immediate and transient) via signaling pathways that may involve plasma membrane or cytoplasmic ER (1, 5, 35, 36, 37). Several mechanisms have been proposed to account for the mitogenic action of E2, including 1) hormone-regulated autocrine pathways involving polypeptide growth factors and 2) a direct mitogenic action mediated either by membrane-bound receptors (38, 39, 40) or activation of hormone-independent pathways involving tyrosine kinases or second messengers or the nuclear ER directly activating the expression of genes known to be rate limiting to cell cycle progression, e.g. c-Myc and cyclin D1 (12, 41, 42, 43). However, the exact mechanisms that mediate the mitogenic actions of E2 action are yet to be fully defined.

Because many prenylated proteins are components of signal transduction pathways stimulated by E2, we studied the effects of the prenyltransferase inhibitors, FTI-277 and GTI-298, on E2-stimulated cell cycle progression in MCF-7 cells. The inhibitors led, respectively, to partial and complete inhibition of cell cycle progression demonstrating that both farnesylated and geranylgeranylated proteins are involved in the mitogenic response to estrogen. We selected the established model of E2-deprived MCF-7 cells to specifically assess the role of prenylated proteins in E2-induced mitogenesis because it is known that FTIs such as the FTI L744,832 inhibit the growth of over 70% of human tumor cell lines, four of seven breast cancer cell lines and is unrelated to their ER status (44).

The requirement for protein prenylation for E2-stimulated proliferation is consistent with its requirement for E2-stimulated PR expression both at the protein and mRNA levels. This is in good agreement with the therapeutic behavior, where responses to endocrine therapy are increased in ER+/PR+ breast cancers. However, the PR gene does not possess any consensus EREs, and its expression is not integral to the proliferative response to estrogens because PR-/- mice develop normally at puberty and respond to repeated administration of estrogens with dramatic hyperplasia of the uterus (45). Similarly, both c-Myc and cyclin D1 expression are rapidly induced by E2 and trigger cell cycle progression, although the corresponding gene promotors contain no ERE-like sequence (46, 47). Our results show that prenylated proteins may be involved in the induction of c-Myc and/or maintain the expression level of these proteins after E2 stimulation because they do not interfere with the early induction of cyclin D1 at 3 h.

Both FTI-277 and GGTI-298 repress ER expression (at the mRNA and protein levels) mimicking an E2-like effect. GGTI-298 dramatically increases pS2 expression in the presence and absence of E2, clearly demonstrating the involvement of geranylgeranylated proteins in the negative regulation of pS2 expression, including its basal expression. The pS2 gene possesses an imperfect palindromic ERE sequence (48). In MELN cells, transcriptional activation of an ERE-dependent luciferase gene in the absence and presence of E2 is induced by FTI-277 and GGTI-298. Besides these peptidomimetic prenyltransferase inhibitors, we checked that FTIs of two different chemical structures have similar effects (data not shown). None of these four compounds exhibit binding to ER{alpha}, but their stimulatory effects on ERE-dependent transcription are prevented by ICI 182,780 in the presence as well as absence of E2. These data strongly suggest that farnesylated and geranylgeranylated proteins play a role in the negative control of the ER-mediated transcriptional activity. Although there is no definitive evidence that the effects of the inhibitors are specific to ER activity, these data are consistent with the demonstration that the prenylated Rho GTPases are important modulators of ER transcriptional activity (13). The presence of an identifiable ERE may determine the role of the prenylated proteins on ERE-mediated transcription, as suggested by our results. Nevertheless, the activity of a number of transcription factors, which may determine the overall promotor activity of ERE-containing genes, is known to be altered by prenylated proteins (e.g. SRF, nuclear factor {kappa}B) (49, 50, 51).

The ER is a ligand-activated transcriptional scaffold that, on activation, results in conformational changes in the receptor followed by recruitment of various transcription coactivators that may be general or receptor specific, such as the histone acetyltransferase (HAT), cAMP response element-binding protein/p300, and the steroid receptor coactivator (SRC)-1 (22, 23, 24, 25). They form multiprotein complexes responsible for transcription initiation by remodeling chromatin through their intrinsic HAT activity (52). The transcriptional response to specific ligands depends on the ability of the ER complex to modulate the switch between coactivator complexes with HAT activity and corepressor complexes with associated histone deacetylase activity (N-CoR and SMRT) (reviewed in Ref. 52). Histone deacetylase proteins comprise a family of proteins that act in conjunction with HAT proteins to modulate chromatin structure and transcriptional activity via changes in the acetylation status of histones. Histones H3 and H4 are the principal histone targets of HDAC enzymatic activity. The association of HDAC proteins with mSin3, N-CoR, SMRT, or other transcriptional repressors has led to the hypothesis that HDAC proteins participate in transcriptional corepressor activity (53).

We examined N-CoR, SMRT, and HDAC1 as corepressors and the general SRC-1 to assess changes in ER{alpha} association following treatment with prenyltransferase inhibitors. As expected, tamoxifen increased the binding of the two corepressors and HDAC1 to ER{alpha}, with no significant recruitment of SRC-1. In contrast, FTI-277 recruited at least SRC-1 and dissociated HDAC1 from the ER{alpha} complex, without dramatic changes in corepressor association. GGTI-298 clearly induced recruitment of SRC-1 to ER{alpha} and, surprisingly, increased the association of the two corepressors to the ER{alpha} complex. Unlike FTI-277, GGTI-298 does not influence the association of HDAC1 with ER{alpha}. It then appears that coactivator recruitment to ER complexes is an essential event that allows prenyltransferase inhibitors to increase ER-related transcriptional activity, besides their direct effects on corepressor/coactivator expression. Our results emphasize the fact that the overall balance of the relative expression levels of coactivators and corepressors and their association with ER is essential in regulating transcriptional potential following ligand-ER association.

Our work provides the first evidence of contrasting effects of FTI-277 and GGTI-298 on inhibition of E2-mediated mitogenesis and ERE-dependent transcriptional activity. This is supported by the demonstration that activation of ER by E2 may lead to these two potentially separate cascades of events (5). Many prenylated proteins are possible candidates for either of these two effects (54). A geranylgeranylated protein appears to be more potent in mediating E2-induced proliferation than a farnesylated protein. It has been suggested that RhoA, a geranylgeranylated protein, regulates cell cycle progression by modulating the protein stability of the cell cycle inhibitor p27kip1 (55) or transcription regulation of specific cell cycle regulatory genes such as c-fos (49), p21waf (56), or cyclin D1 (57). The estrogen-dependent expression of cyclin D1 is essential for estrogen-induced proliferation of MCF-7 cells (58) and is an early estrogen-mediated effect on the cell cycle machinery (41). RhoA could be eliminated from the membrane fraction during G1 progression and new RhoA synthesized for G1/S progression (59). Moreover, RhoA is overexpressed in human breast cancer cells, and its expression level is significantly higher in grade III cancers when compared with grade I cancers (18). In addition, RhoB, which can be both farnesylated and geranylgeranylated in cells, has a short half-life (2 h) and is synthesized during the S phase of the cell cycle (60). It is noteworthy that ER regulates gene transcription either by binding directly to the promoter of target genes (genes containing an ERE) or indirectly through a mechanism involving other transcription factors, such as Sp1 and activator protein-1 (AP1) (for genes containing nonclassical response sites). Because it was recently shown that AP1-mediated transcription is down-regulated by RhoB, RhoB may act on E2-mediated mitogenesis through this pathway (61).

With regard to ER transcriptional activity for ERE-containing genes, our data demonstrate that farnesylated and/or geranylgeranylated proteins inhibit basal as well as E2-dependent ER activities. A genetic screen in yeast identified Rho guanine nucleotide dissociation inhibitor as a positive regulator of ER transactivation and suggest that this effect is mediated by antagonizing Rho function (13). Moreover, it has been shown that Brx, a Dbl oncogene family member, which is a guanine nucleotide exchange factor of Rho proteins, contains a nuclear hormone receptor-binding region. Brx affects ER-mediated gene activation by a mechanism that is dependent on the Cdc42Hs signaling pathway (62). Besides, constitutively active forms of c-Raf and Rac synergistically enhance the cAMP response element-binding protein/p300-mediated increase of transcription in T-cell activation signals (63). Finally, a constitutively active form of Cdc-42 induces H4 hyperacetylation in chromatin (64).

Whether prenylated proteins have a direct action on the ERs is not known, but our data strongly suggest an action at the level of ER corepressor/coactivator equilibrium. This is in agreement with the emerging importance of the overall balance of coregulators of ER complexes in regulating ER-related transcriptional activity. The exact identity of the prenylated proteins involved in the ER coregulator complex assembly and the molecular mechanisms for transcriptional repression remains to be determined.


   Acknowledgments
 
We are grateful to Dr. N. Eche and A. Margras (Institut Claudius Regaud) for their help with the pS2 analysis, Dr. M. Gardiner-Garden for the statistical analysis, and Dr. E. A. Musgrove for her invaluable contribution to the work.


   Footnotes
 
This work was supported by Grant CA-67771 from the National Cancer Institute (to S.M.S. and A.D.H.) and grants from "Groupe de Recherche de l’Institut Claudius Regaud," Institut National de la Santé et de la Recherche Médicale, National Health and Medical Research Council of Australia, and the Cancer Council New South Wales.

Abbreviations: DMSO, Dimethylsulfoxide; DTT, dithiothreitol; E2, 17ß-estradiol; EGF, epidermal growth factor; ER, estrogen receptor; ERE, estrogen response element; FCS, fetal calf serum; FTase, farnesyl transferase; FTI, FTase inhibitor; GGTI, geranylgeranyltransferase I inhibitor; HAT, histone acetyltransferase; HDAC, histone deacetylase; N-CoR, nuclear receptor corepressor; PR, progesterone receptor; RNase, ribonuclease; SMRT, silencing mediator of retinoid and thyroid receptor; SRC, steroid receptor coactivator.

Received July 17, 2002.

Accepted for publication November 15, 2002.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Aronica SM, Katzenellenbogen BS 1993 Stimulation of estrogen receptor-mediated transcription and alteration in the phosphorylation state of the rat uterine estrogen receptor by estrogen, cyclic adenosine monophosphate, and insulin-like growth factor-I. Mol Endocrinol 7:743–752[Abstract/Free Full Text]
  2. Ignar-Trowbridge DM, Pimentel M, Parker MG, McLachlan JA, Korach KS 1996 Peptide growth factor cross-talk with the estrogen receptor requires the A/B domain and occurs independently of protein kinase C or estradiol. Endocrinology 137:1735–1744[Abstract]
  3. Kato S, Endoh H, Masuhiro Y, Kitamoto T, Uchiyama S, Sasaki H, Masushige S, Gotoh Y, Nishida Y, Kawashima H, Metzger D, Chambon P 1995 Activation of the estrogen receptor through phosphorylation by mitogen-activated-protein-kinase. Science 270:1491–1494[Abstract/Free Full Text]
  4. Bunone G, Briand PA, Miksicek RJ, Picard D 1996 Activation of the unliganded estrogen receptor by EGF involves the MAP kinase pathway and direct phosphorylation. EMBO J 15:2174–2183[Medline]
  5. Castoria G, Barone MV, Di Domenico M, Bilancio A, Ametrano D, Migliaccio A, Auricchio F 1999 Non-transcriptional action of oestradiol and progestin triggers DNA synthesis. EMBO J 18:2500–2510[CrossRef][Medline]
  6. Lobenhofer EK, Huper G, Iglehart JD, Marks JR 2000 Inhibition of mitogen-activated protein kinase and phosphatidylinositol 3-kinase activity in MCF-7 cells prevents estrogen-induced mitogenesis. Cell Growth Differ 11:99–110[Abstract/Free Full Text]
  7. Caristi S, Galera JL, Matarese F, Imai M, Caporali S, Cancemi M, Altucci L, Cicatiello L, Teti D, Bresciani F, Weisz A 2001 Estrogens do not modify MAP kinase-dependent nuclear signaling during stimulation of early G(1) progression in human breast cancer cells. Cancer Res 61:6360–6366[Abstract/Free Full Text]
  8. Kato K, Ueoka Y, Hachiya T, Nishida J, Wake N 1997 Contribution of enhanced transcriptional activation by ER to [12Val] K-Ras mediated NIH3T3 cell transformation. Oncogene 15:3037–3046[CrossRef][Medline]
  9. Pethe V, Shekhar PV 1999 Estrogen inducibility of c-Ha-ras transcription in breast cancer cells. Identification of functional estrogen-responsive transcriptional regulatory elements in exon 1/intron 1 of the c-Ha-ras gene. J Biol Chem 274:30969–30978[Abstract/Free Full Text]
  10. Marshall CJ 1993 Protein prenylation—a mediator of protein-protein interactions. Science 259:1865–1866[Free Full Text]
  11. Zhang FL, Casey PJ 1996 Protein prenylation: molecular mechanisms and functional consequences. Annu Rev Biochem 65:241–269[CrossRef][Medline]
  12. Bonapace IM, Addeo R, Altucci L, Cicatiello L, Bufulco M, Laezza C, Salzano S, Sica V, Bresciani F, Weisz A 1996 17ß-oestradiol overcomes a G1 block induced by HMG-coA reductase inhibitors and fosters cell cycle progression without inducing ERK-1 and -2 MAP kinases activation. Oncogene 12:753–763[Medline]
  13. Su LF, Knoblauch R, Garabedian MJ 2001 Rho GTPases as modulators of the estrogen receptor transcriptional response. J Biol Chem 276:3231–3237[Abstract/Free Full Text]
  14. Bos JL 1989 Ras oncogenes in human cancer: a review. Cancer Res 49:4682–4689[Abstract/Free Full Text]
  15. Smith CA, Pollice AA, Gu LP, Brown KA, Singh SG, Janocko LE, Johnson R, Julian T, Hyams D, Wolmark N, Sweeney L, Silverman JF, Shackney SE 2000 Correlations among p53, Her-2/neu, and ras overexpression and aneuploidy by multiparameter flow cytometry in human breast cancer: evidence for a common phenotypic evolutionary pattern in infiltrating ductal carcinomas. Clin Cancer Res 6:112–126[Abstract/Free Full Text]
  16. De Cremoux P, Gauville C, Closson V, Linares G, Calvo F, Tavitian A, Olofsson B 1994 EGF modulation of the ras-related rhoB gene expression in human breast-cancer cell lines. Int J Cancer 59:408–415[Medline]
  17. Mira JP, Benard V, Groffen J, Sanders LC, Knaus UG 2000 Endogenous, hyperactive rac3 controls proliferation of breast cancer cells by a p21-activated kinase-dependent pathway. Proc Natl Acad Sci USA 97:185–189[Abstract/Free Full Text]
  18. Fritz G, Just I, Kaina B 1999 Rho GTPases are over-expressed in human tumors. Int J Cancer 81:682–687[CrossRef][Medline]
  19. Van Golen KL, Wu ZF, Qiao XT, Bao LW, Merajver SD 2000 RhoC GTPase, a novel transforming oncogene for human mammary epithelial cells that partially recapitulates the inflammatory breast cancer phenotype. Cancer Res 60:5832–5838[Abstract/Free Full Text]
  20. Clark EA, Golub TR, Lander ES, Hynes RO 2000 Genomic analysis of metastasis reveals an essential role for RhoC. Nature 406:532–535[CrossRef][Medline]
  21. Kleer CG, van Golen KL, Zhang Y, Wu ZF, Rubin MA, Merajver SD 2002 Characterization of RhoC expression in benign and malignant breast disease: a potential new marker for small breast carcinomas with metastatic ability. Am J Pathol 160:579–584[Abstract/Free Full Text]
  22. Smith CL, Nawaz Z, O’Malley BW 1997 Coactivator and corepressor regulation of the agonist/antagonist activity of the mixed antiestrogen, 4-hydroxytamoxifen. Mol Endocrinol 11:657–666[Abstract/Free Full Text]
  23. Lavinsky RM, Jepsen K, Heinzel T, Torchia J, Mullen TM, Schiff R, Del-Rio AL, Ricote M, Ngo S, Gemsch J, Hilsenbeck SG, Osborne CK, Glass CK, Rosenfeld MG, Rose DW 1998 Diverse signaling pathways modulate nuclear receptor recruitment of N-CoR and SMRT complexes. Proc Natl Acad Sci USA 95:2920–2925[Abstract/Free Full Text]
  24. Graham JD, Bain DL, Richer JK, Jackson TA, Tung L, Horwitz KB 2000 Nuclear receptor conformation, coregulators, and tamoxifen-resistant breast cancer. Steroids 65:579–584[CrossRef][Medline]
  25. Shang Y, Hu X, DiRenzo J, Lazar MA, Brown M 2000 Cofactor dynamics and sufficiency in estrogen receptor-regulated transcription. Cell 103:843–852[CrossRef][Medline]
  26. Shang Y, Brown M 2002 Molecular determinants for the tissue specificity of SERMs. Science 295:2465–2468[Abstract/Free Full Text]
  27. Balaguer P, Francois F, Comunale F, Fenet H, Boussioux AM, Pons M, Nicolas JC, Casellas C 1999 Reporter cell lines to study the estrogenic effects of xenoestrogens. Sci Total Environ 233:47–56[CrossRef][Medline]
  28. Miquel K, Pradines A, Sun J, Qian Y, Hamilton AD, Sebti SA, Favre G 1997 GGTI-298 induces G0/G1 block and apoptosis whereas FTI-277 causes G2/M enrichment in A549 cells. Cancer Res 57:1846–1850[Abstract/Free Full Text]
  29. Luqmani YA, Temmim L, Memon A, Ali MA, Parkar AH 1997 Steroid receptor measurement in breast cancers: comparison between ligand binding and enzyme-immunoassay in cytosolic and nuclear extracts. Int J Cancer 71:526–538[CrossRef][Medline]
  30. Bradford MM 1976 A rapid and sensitive method for the quantitation of microgram of protein utilizing the principle of protein dye binding. Anal Biochem 72:248–254[CrossRef][Medline]
  31. Chomczyncki P, Sacchi N 1987 Single step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction. Anal. Biochem 162:156–159
  32. Laborda J 1991 36B4 cDNA used as an estradiol-independent mRNA control is the cDNA for human acidic ribosomal phosphoprotein PO. Nucleic Acids Res 19:3998[Free Full Text]
  33. Faye JC, Fargin A, Bayard F 1986 Dissimilarities between the uterine estrogen receptor in cytosol of castrated and estradiol treated rats. Endocrinology 118:2276–2283[Abstract/Free Full Text]
  34. Lebowitz PF, Davide JP, Prendergast GC 1995 Evidence that farnesyltransferase inhibitors suppress ras transformation by interfering with rho activity. Mol Cell Biol 15:6613–6622[Abstract]
  35. Migliaccio A, Di Domenico M, Castoria G, de Falco A, Bontempo P, Nola E, Auricchio F 1996 Tyrosine kinase/p21ras/MAP-kinase pathway activation by estradiol-receptor complex in MCF-7 cells. EMBO J 15:1292–1300[Medline]
  36. Razandi M, Pedram A, Levin ER 2000 Plasma membrane estrogen receptors signal to antiapoptosis in breast cancer. Mol Endocrinol 14:1434–1447[Abstract/Free Full Text]
  37. Zhang CC, Shapiro DJ 2000 Activation of the p38 mitogen-activated protein kinase pathway by estrogen or by 4-hydroxytamoxifen is coupled to estrogen receptor-induced apoptosis. J Biol Chem 275:479–486[Abstract/Free Full Text]
  38. Watters JJ, Campbell JS, Cunningham MJ, Krebs EG, Dorsa DM 1997 Rapid membrane effects of steroids in neuroblastoma cells: effects of estrogen on mitogen activated protein kinase signalling cascade and c-fos immediate early gene transcription. Endocrinology 138:4030–4033[Abstract/Free Full Text]
  39. Razandi M, Pedram A, Greene GL, Levin ER 1999 Cell membrane and nuclear estrogen receptors (ERs) originate from a single transcript: studies of ERalpha and ERbeta expressed in Chinese hamster ovary cells. Mol Endocrinol 13:307–319[Abstract/Free Full Text]
  40. Russell KS, Haynes MP, Sinha D, Clerisme E, Bender JR 2000 Human vascular endothelial cells contain membrane binding sites for estradiol, which mediate rapid intracellular signaling. Proc Natl Acad Sci USA 97:5930–5935[Abstract/Free Full Text]
  41. Prall OWJ, Sarcevic B, Musgrove EA, Watts CKW, Sutherland RL 1997 Estrogen-induced activation of Cdk4 and Cdk2 during G1-S phase progression is accompanied by increased cyclin D1 expression and decreased cyclin-dependent kinase inhibitor association with cyclin E-Cdk2. J Biol Chem 272:10882–10894[Abstract/Free Full Text]
  42. Prall OWJ, Rogan EM, Musgrove EA, Watts CKW, Sutherland RL 1998 c-Myc or cyclin D1 mimics estrogen effects on cyclin E-cdk2 activation and cell cycle reentry. Mol Cell Biol 18:4499–4508[Abstract/Free Full Text]
  43. Carroll JS, Swarbrick A, Musgrove EA, Sutherland RL 2002 Mechanisms of growth arrest by c-myc antisense oligonucleotides in MCF-7 breast cancer cells: implications for the antiproliferative effects of antiestrogens. Cancer Res 62:3126–3131[Abstract/Free Full Text]
  44. Sepp-Lorenzino L, Ma Z, Rands E, Kohl NE, Gibbs JB, Oliff A, Rosen N 1995 A peptidomimetic inhibitor of farnesyl:protein transferase blocks the anchorage-dependent and -independent growth of human tumor cell lines. Cancer Res 55:5302–5309[Abstract/Free Full Text]
  45. Lydon JP, DeMayo FJ, Funk CR, Mani SK, Hughes AR, Montgomery Jr CA, Shyamala G, Conneely OM, O’Malley BW 1995 Mice lacking progesterone receptor exhibit pleiotropic reproductive abnormalities. Genes Dev 9:2266–2278[Abstract/Free Full Text]
  46. Dubik D, Shiu RP 1992 Mechanism of estrogen activation of c-myc oncogene expression. Oncogene 7:1587–1594[Medline]
  47. Sabbah M, Courilleau D, Mester J, Redeuilh G 1999 Estrogen induction of the cyclin D1 promoter: involvement of a cAMP response-like element. Proc Natl Acad Sci USA 96:11217–11222[Abstract/Free Full Text]
  48. Berry M, Nunez AM, Chambon P 1989 Estrogen-responsive element of the human pS2 gene is an imperfectly palindromic sequence. Proc Natl Acad Sci USA 86:1218–1222[Abstract/Free Full Text]
  49. Hill CS, Wynne J, Treisman R 1995 The Rho family GTPases RhoA, rac1, and CDC42Hs regulate transcriptional activation by SRF. Cell 81:1159–1170[CrossRef][Medline]
  50. Lebowitz PF, Du W, Prendergast GC 1997 Prenylation of RhoB is required for its cell transforming function but not its ability to activate serum response element-dependent transcription. J Biol Chem 272:16093–16095[Abstract/Free Full Text]
  51. Allal C, Favre G, Couderc B, Salicio S, Sixou S, Hamilton AD, Sebti SM, Lajoie-Mazenc I, Pradines A 2000 RhoA prenylation is required for promotion of cell growth and transformation and cytoskeleton organization but not for induction of serum response element transcription. J Biol Chem 275:31001–31008[Abstract/Free Full Text]
  52. Torchia J, Glass C, Rosenfeld MG 1998 Co-activators and co-repressors in the integration of transcriptional responses. Curr Opin Cell Biol 10:373–383[CrossRef][Medline]
  53. Davie JR, Chadee DN 1998 Regulation and regulatory parameters of histone modifications. J Cell Biochem Suppl 30–31:203–213
  54. Pruitt K, Der CJ 2001 Ras and Rho regulation of the cell cycle and oncogenesis. Cancer Lett 171:1–10[CrossRef][Medline]
  55. Hu W, Bellone CJ, Baldassare JJ 1999 RhoA stimulates p27(Kip) degradation through its regulation of cyclin E/CDK2 activity. J Biol Chem 274:3396–3401[Abstract/Free Full Text]
  56. Adnane J, Bizouarn FA, Qian Y, Hamilton AD, Sebti SM 1998 p21(WAF1/CIP1) is upregulated by the geranylgeranyltransferase I inhibitor GGTI-298 through a transforming growth factor beta- and Sp1-responsive element: involvement of the small GTPase rhoA. Mol Cell Biol 18:6962–6970[Abstract/Free Full Text]
  57. Westwick JK, Lambert QT, Clark GJ, Symons M, Van Aelst L, Pestell RG, Der CJ 1997 Rac regulation of transformation, gene expression, and actin organization by multiple, PAK-independent pathways. Mol Cell Biol 17:1324–1335[Abstract]
  58. Lukas J, Bartkova J, Bartek J 1996 Convergence of mitogenic signalling cascades from diverse classes of receptors at the cyclin D-cyclin-dependent kinase-pRb-controlled G1 checkpoint. Mol Cell Biol 16:6917–6925[Abstract]
  59. Noguchi Y, Nakamura S, Yasuda T, Kitagawa M, Kohn LD, Saito Y, Hirai A 1998 Newly synthesized Rho A, not Ras, is isoprenylated and translocated to membranes coincident with progression of the G(1) to S phase of growth-stimulated rat FRTL-5 cells. J Biol Chem 273:3649–3653[Abstract/Free Full Text]
  60. Zalcman G, Closson V, Linarescruz G, Lerebours F, Honore N, Tavitian A, Olofsson B 1995 Regulation of ras-related RhoB protein expression during the cell cycle. Oncogene 10:1935–1945[Medline]
  61. Adnane J, Seijo E, Chen Z, Bizouarn F, Leal M, Sebti SM, Munoz-Antonia T 2002 RhoB, not RhoA, represses the transcription of the transforming growth factor beta type II receptor by a mechanism involving activator protein 1. J Biol Chem 277:8500–8507[Abstract/Free Full Text]
  62. Rubino D, Driggers P, Arbit D, Kemp L, Miller B, Coso O, Pagliai K, Gray K, Gutkind S, Segars J 1998 Characterization of Brx, a novel Dbl family member that modulates estrogen receptor action. Oncogene 16:2513–2526[CrossRef][Medline]
  63. Avots A, Buttmann M, Chuvpilo S, Escher C, Smola U, Bannister AJ, Rapp UR, Kouzarides T, Serfling E 1999 CBP/p300 integrates Raf/Rac-signaling pathways in the transcriptional induction of NF-ATc during T cell activation. Immunity 10:515–524[CrossRef][Medline]
  64. Alberts AS, Geneste O, Treisman R 1998 Activation of SRF-regulated chromosomal templates by Rho-family GTPases requires a signal that also induces H4 hyperacetylation. Cell 92:475–487[CrossRef][Medline]



This article has been cited by other articles:


Home page
 Molecular Cancer TherapeuticsHome page
B. Payre, P. de Medina, N. Boubekeur, L. Mhamdi, J. Bertrand-Michel, F. Terce, I. Fourquaux, D. Goudouneche, M. Record, M. Poirot, et al.
Microsomal antiestrogen-binding site ligands induce growth control and differentiation of human breast cancer cells through the modulation of cholesterol metabolism
Mol. Cancer Ther., December 1, 2008; 7(12): 3707 - 3718.
[Abstract] [Full Text] [PDF]

Home page
 Mol. Endocrinol.Home page
S. Das, M. Schapira, M. Tomic-Canic, R. Goyanka, T. Cardozo, and H. H. Samuels
Farnesyl Pyrophosphate Is a Novel Transcriptional Activator for a Subset of Nuclear Hormone Receptors
Mol. Endocrinol., November 1, 2007; 21(11): 2672 - 2686.
[Abstract] [Full Text] [PDF]

Home page
 Molecular Cancer TherapeuticsHome page
L.-A. Martin, J. E. Head, S. Pancholi, J. Salter, E. Quinn, S. Detre, S. Kaye, A. Howes, M. Dowsett, and S. R.D. Johnston
The farnesyltransferase inhibitor R115777 (tipifarnib) in combination with tamoxifen acts synergistically to inhibit MCF-7 breast cancer cell proliferation and cell cycle progression in vitro and in vivo
Mol. Cancer Ther., September 1, 2007; 6(9): 2458 - 2467.
[Abstract] [Full Text] [PDF]

Home page
 J. Pharmacol. Exp. Ther.Home page
P. de Medina, N. Boubekeur, P. Balaguer, G. Favre, S. Silvente-Poirot, and M. Poirot
The Prototypical Inhibitor of Cholesterol Esterification, Sah 58-035 [3-[Decyldimethylsilyl]-N-[2-(4-methylphenyl)-1-phenylethyl]propanamide], Is an Agonist of Estrogen Receptors
J. Pharmacol. Exp. Ther., October 1, 2006; 319(1): 139 - 149.
[Abstract] [Full Text] [PDF]

Home page
 Eur J EndocrinolHome page
J. Igarashi-Migitaka, A. Takeshita, N. Koibuchi, S. Yamada, R. Ohtani-Kaneko, and K. Hirata
Differential expression of p160 steroid receptor coactivators in the rat testis and epididymis
Eur. J. Endocrinol., October 1, 2005; 153(4): 595 - 604.
[Abstract] [Full Text] [PDF]

Home page
 Mol. Pharmacol.Home page
O. Boijoux, C. Boutonnet, C. Giamarchi, G. Favre, S. Vagner, and J. C. Faye
Chemical-Based Translational Induction of Luciferase Expression: An Efficient Tool for in Vivo Screening of Protein Farnesylation Inhibitors
Mol. Pharmacol., June 1, 2005; 67(6): 1829 - 1833.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Doisneau-Sixou, S. F.
Right arrow Articles by Favre, G.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Doisneau-Sixou, S. F.
Right arrow Articles by Favre, G.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Endocrinology Endocrine Reviews J. Clin. End. & Metab.
Molecular Endocrinology Recent Prog. Horm. Res. All Endocrine Journals