Effects of histone deacetylase inhibitors on estradiol-induced proliferation and hyperplasia formation in the mouse uterus

in Journal of Endocrinology

It is suggested that estrogen hormones recruit mechanisms controlling histone acetylation to bring about their effects in the uterus. However, it is not known how the level of histone acetylation affects estrogen-dependent processes in the uterus, especially proliferation and morphogenetic changes. Therefore, this study examined the effects of histone deacetylase blockers, trichostatin A and sodium butyrate, on proliferative and morphogenetic reactions in the uterus under long-term estrogen treatment. Ovari-ectomized mice were treated with estradiol dipropionate (4 μg per 100 g; s.c., once a week) or vehicle and trichostatin A (0.008 mg per 100 g; s.c., once a day) or sodium butyrate (1% in drinking water), or with no additional treatments for a month. In animals treated with estradiol and trichostatin A or sodium butyrate, uterine mass was increased, and abnormal uterine glands and atypical endometrial hyperplasia were found more often. Both histone deacetylase inhibitors produced an increase in the numbers of mitotic and bromodeoxyuridine-labelled cells in luminal and glandular epithelia, in stromal and myometrial cells. Levels of estrogen receptor-α and progesterone receptors in uterine epithelia, stromal and myometrial cells were decreased in mice treated with estradiol and trichostatin A or sodium butyrate. Expression of β-catenin in luminal and glandular epithelia was attenuated in mice treated with estradiol with trichostatin A or sodium butyrate. Both histone deacetylase inhibitors have similar unilateral effects; however the action of trichostatin A was more expressed than that of sodium butyrate. Thus, histone deacetylase inhibitors exert proliferative and morphogenetic effects of estradiol. The effects of trichostatin A and sodium butyrate are associated with changes in expression of estrogen receptor-α, progesterone receptors and β-catenin in the uterus.

Abstract

It is suggested that estrogen hormones recruit mechanisms controlling histone acetylation to bring about their effects in the uterus. However, it is not known how the level of histone acetylation affects estrogen-dependent processes in the uterus, especially proliferation and morphogenetic changes. Therefore, this study examined the effects of histone deacetylase blockers, trichostatin A and sodium butyrate, on proliferative and morphogenetic reactions in the uterus under long-term estrogen treatment. Ovari-ectomized mice were treated with estradiol dipropionate (4 μg per 100 g; s.c., once a week) or vehicle and trichostatin A (0.008 mg per 100 g; s.c., once a day) or sodium butyrate (1% in drinking water), or with no additional treatments for a month. In animals treated with estradiol and trichostatin A or sodium butyrate, uterine mass was increased, and abnormal uterine glands and atypical endometrial hyperplasia were found more often. Both histone deacetylase inhibitors produced an increase in the numbers of mitotic and bromodeoxyuridine-labelled cells in luminal and glandular epithelia, in stromal and myometrial cells. Levels of estrogen receptor-α and progesterone receptors in uterine epithelia, stromal and myometrial cells were decreased in mice treated with estradiol and trichostatin A or sodium butyrate. Expression of β-catenin in luminal and glandular epithelia was attenuated in mice treated with estradiol with trichostatin A or sodium butyrate. Both histone deacetylase inhibitors have similar unilateral effects; however the action of trichostatin A was more expressed than that of sodium butyrate. Thus, histone deacetylase inhibitors exert proliferative and morphogenetic effects of estradiol. The effects of trichostatin A and sodium butyrate are associated with changes in expression of estrogen receptor-α, progesterone receptors and β-catenin in the uterus.

Introduction

Estrogen hormones have a variety of effects in the uterus. Proliferation and changes in structure and architecture of uterine tissues are estrogen-dependent events (Martin et al. 1973, Bigsby 2002). Endometrial cancer is also an estrogen-dependent disease, and it can be regarded as a consequence of estrogen-induced alteration in proliferation and morphogenesis (Emons et al. 2000, Archer 2004). Endometrial hyperplasia and cancer can easily be induced in laboratory rodents by continuous estrogen exposure (Akhmedkhanov et al. 2001). Administration of estrogen hormones can lead to endometrial cancer formation in women (Deligdisch 2000). Numerous cases of endometrial cancer are registered each year in every country (Archer 2004). Therefore, regulation of estrogen action and the interactions between estrogens and target tissues must be investigated more intensively in order to achieve more effective prevention and treatment of estrogen-dependent pathology.

It is known that the action of estrogen is regulated by a variety of extracellular factors – such as hormones, growth factors and others (Couse & Korach 1999, Gunin et al. 2001). Recent data showed that estrogen also recruits intracellular regulatory systems to bring about its action (Couse & Korach 1999, Deroo et al. 2004, Gunin et al. 2004b). The scientific literature gives some direct and indirect evidence that the system that maintains the status of histone acetylation interacts with estrogen signalling (Alao et al. 2004, Kurtev et al. 2004, Margueron et al. 2004).

Several types of histone deacetylases are present in the nucleus of cells, and together with histone acetyltrans-ferases they determine the acetylation status of histone proteins (Margueron et al. 2004). Shifts in the level of histone acetylation are accompanied by changes in the activity of the transcription process (Riester et al. 2004). Histone deacetylase activity keeps chromatin in a transcriptionally inactive state (Riester et al. 2004). Data have been published showing interactions between estrogen signalling and acetylation of histones (Jang et al. 2004, Margueron et al. 2004). It has also been reported that estrogen hormones affect the level of histone acetylation in target tissues (Sun et al. 2001). There is some evidence that histone acetylation is involved in processes that are also regulated by estrogens, for example proliferation and cell differentiation (Sakai et al. 2003). It is therefore supposed that shifts in histone acetylation can affect the action of estrogen on the uterus, such as proliferation and morphogenetic alterations. However, it is not known how the histone acetylation status influences estrogen-dependent processes in the uterus, such as proliferation and changes in structure of tissues. Therefore, the aim of this research was to examine estrogen-induced processes in the uterus and their response to substances that change the level of histone acetylation.

Trichostatin A, an antifungal antibiotic, has a potent and specific inhibitory effect on histone deacetylase activity (Riester et al. 2004). Butyric acid and its salts are also well-known blockers of the activity of histone deacetylases (Riester et al. 2004). Therefore two reagents, trichostatin A and sodium butyrate, were chosen for use in our experiments to block histone deacetylases; this was followed by induction of a hyperacetylated histone state.

Material and Methods

Animals

All procedures were performed in accordance with the UFAW Handbook on the Care and Management of Laboratory Animals and with the Chuvash State University Rules for work with laboratory animals. White out-bred CFW female mice (19.1±0.3 g, mean±s.e.m.) were used. Animals were obtained from the Animal Department of Chuvash State University (Cheboksary, Russia) and were housed with free access to water and food. Mice were ovariectomized 2 weeks before the experiments were started. All surgical procedures were performed under anesthesia with ketamine and diazepam (75 and 0.12 mg/kg respectively, i.p.; Gedeon-Richter, Budapest, Hungary).

Treatments

Ovariectomized mice were divided into several groups according to the treatments, as follows. The first group (n=15) was treated with s.c. injections of estradiol dipropionate in olive oil (Minmedprom, Rostov-Don, Russia) at a dose of 4 μg per 100 g of body mass once a week and received s.c. injections of saline (0.15 M sodium chloride) at a dose of 0.1 ml per mouse once a day for 30 days. The second group (n=15) was treated with s.c. injections of estradiol once a week and received s.c. injections of trichostatin A (Sigma) at a dose 0.008 mg per 100 g once a day for 30 days. Trichostatin A was dissolved in 0.15 M sodium chloride. The third group of mice (n=15) was treated with injections with estradiol once a week and allowed to drink tap water with 1% (w/v) sodium butyrate (Sigma) for 30 days. These groups also received s.c. injections of saline (0.1 ml per mouse) once a day for 30 days.

The fourth (n=5), fifth (n=5) and sixth (n=5) groups received s.c. injections of the vehicle of estradiol (olive oil; 0.1 ml per mouse) once a week and saline or trichostatin A or sodium butyrate, respectively, once a day for 30 days.

Our previous observations clearly showed that treatment with estradiol for 30 days was quite enough to produce expressed estrogen-dependent changes in uterine morphology and to induce hyperplastic changes in the uterus (Gunin et al. 2001, 2002, 2004a,Gunin et al.b). This estradiol dose and treatment regime produced estradiol levels in the blood that were close to the normal physiologic values (Gunin et al. 2004a).

The uteri were removed 48 h after the last estradiol or vehicle injection. All animals were injected i.p. with bromodeoxyuridine (BrdU; 5 mg per 100 g of body mass; Sigma) dissolved in 0.15 M sodium chloride 2 h before the tissues were removed. Organs were removed under deep ether anesthesia. Uteri were weighed and middle segments of uterine horns were then placed in modified Bouin’s fixative (Gunin et al. 2000) for 6 h at room temperature, and were then dehydrated and embedded in paraffin. Uteri were transversely oriented and cut at 5–7 μm.

Uterine histology

Histological changes in the uterus were analyzed and diagnosed according to Scully et al.(1994). To estimate the extent of any hyperplastic or neoplastic changes in the endometrium, uterine glands were subdivided into four morphological types: (1) normal glands (simple tubular glands which can appear in section as round, oval, or elongated with a narrow lumen; this type has no branches or daughter glands); (2) cystic glands (round-shaped glands of more than average or large size); (3) glands with daughter glands (these glands have various shapes (round, elongate, tortuous) and sizes and have forming or formed daughter gland or glands inside the epithelium or inside the mother gland lumen, or on the outer surface of the mother gland); (4) conglomerate of glands (this type has a very complex architecture in which individual glands are closely disposed to each other almost without intervening stroma and have multiple interconnecting lumens – this type may develop from glands with daughter glands), as described in Gunin et al. 2001). The numbers of each type of gland were calculated in randomly selected sections. No less than three sections from each animal were examined. Results were expressed as the percentage of each type of gland. The epithelium of all glands in randomly selected sections was examined and typed as simple, pseudostratified or stratified (multilayered) epithelia. The percentage of glands with each type of epithelium was calculated.

The number of mitotic and BrdU-labelled cells

Proliferative processes were assessed from the number of mitotic and BrdU-labelled cells as described previously (Gunin et al. 2001). Mitoses were counted in sections stained with iron haematoxylin. BrdU was detected immunohistochemically. Anti-BrdU mouse monoclonal antibody conjugated with biotin (catalog number, MO 5215; Caltag Laboratories, Burlingame, CA, USA) diluted 1:50 in Tris-buffered saline (TBS) (pH 7.2–7.6) was used as the primary antibody. Streptavidin conjugated with alkaline phosphatase (catalog number, SA 1008; Caltag Laboratories) diluted 1:50 in TBS with 0.1% (v/v) Triton X-100 was then applied. Alkaline phosphatase activity was revealed through the use of naphtol AS-BI-phosphate and new fuchsin as chromogens. Control sections were stained in a similar manner, except the primary antibody was replaced with normal mouse serum. All results were expressed as the percentage of mitotic or labelled cells.

Estrogen receptor-α, progesterone receptors and β-catenin

Estrogen receptor-α, progesterone receptors and β-catenin were detected using routine indirect immunohistochemical staining. Rabbit anti-estrogen receptor-α polyclonal antibody (catalog number, sc-542; Santa Cruz Biotechnology Inc., Santa Cruz, CA, USA) diluted 1:50, rabbit anti-progesterone receptors antiserum (catalog number, sc-538; Santa Cruz Biotechnology Inc.) diluted 1:50 and rabbit anti-β-catenin antiserum (catalog number, C2206; Sigma) diluted 1:50 were used as primary antibodies. For detection of estrogen receptors, goat anti-rabbit immunoglobulin G antibody conjugated with alkaline phosphatase (catalog number 111–055–045; Jackson ImmunoResearch Laboratories Inc., West Grove, PA, USA) was used as secondary antibody, and alkaline phosphatase activity was then revealed using naphtol AS-BI-phosphate and new fuchsin as chromogens. For progesterone receptors and β-catenin, goat anti-rabbit immunoglobulin G antibody conjugated with peroxidase (catalog number 111–035–045; Jackson ImmunoResearch Laboratories Inc.) was used as the secondary antibody, peroxidase activity was then developed by the use of hydrogen peroxide and diaminobenzidine (Sigma) techniques, slides were also preincubated in 0.1% hydrogen peroxide in distilled water for 10 min to block endogenous peroxidase activity. Control sections were stained in a similar manner, except the primary antibody was replaced with normal rabbit serum. To avoid possible differences in the intensity of staining, sections from all mice were processed simultaneously for each antigen, so that all sections were incubated in exactly the same TBS, the same mixtures of primary and secondary antibodies, the same mixture for development of enzyme activity, for the same times, at the same temperature.

Intensity of immunostaining was quantified by photo-metric measurement of optical density (D) for positive-stained components of a tissue (Gunin et al. 2002, 2004a). The photometric procedure was performed using Sigma Scan Pro software (SPSS Inc., Chicago, IL, USA). Initially, uterine sections immunohistochemically stained for estrogen or progesterone receptors were photographed using an Olympus light microscope (objective magnification 40), an Olympus C3040-ADU camera adapter and an Olympus Camedia 4040z 4 megapixel digital camera. At least three randomly selected sections were photographed for each mouse, and three to five randomly selected fields were photographed from one section. Photographs were then loaded in Sigma Scan Pro software and analyzed to find the optical density. It was performed by measuring the intensity of staining of positive-stained structures (F) and structures with no staining (F0). The intensify of staining was measured from equal areas of tissue image (19 pixels). Positive staining for estrogen and progesterone receptors was detected in the nuclei of all uterine tissues (luminal epithelium, glandular epithelium, stromal cells, myometrial cells). Therefore, the intensity of nuclear staining (F; positive staining) and the intensity of staining of the internuclear space in the endometrial stroma (F0; negative staining) were measured for estrogen and progesterone receptors.

β-Catenin was detected in luminal and glandular epithelia. Therefore, the intensity of staining of cytoplasm of these epithelial cells (F; positive staining) and intensity of staining of the internuclear space in the endometrial stroma (F0; negative staining) was measured for β-catenin. Optical density (light absorption) was calculated from the formula D=l g(F0/F). The level of expression was considered as the value of optical density (Gunin et al. 2002, 2004a). At least 100 nuclei were analyzed for each structure in each mouse.

Statistics

Arithmetic means and standards errors were calculated for each data group. The significance of differences was determined by Student’s t-test (uterine mass, proliferation, estrogen and progesterone receptors, β-catenin) and by the use of the observed versus expected χ2 test (gland types, epithelium types, pathology). Values of P<0.05 were considered significant.

Results

Uterine mass

The uterine mass of ovariectomized mice receiving olive oil instead of estradiol and saline for 30 days (group 4) was 115.2±22.4 mg per 100 g body mass (mean±s.e.m.; n=5); the addition of trichostatin A (group 5; 120.6±24.1 mg per 100 g body mass; n=5) or sodium butyrate (group 6; 116.8±19.7 mg per 100 g body mass; n=5) for 30 days had no effect on uterine mass.

Treatment with estradiol and trichostatin A for 30 days (group 2) resulted in a 34% increase in uterine mass as compared with data for control mice receiving estradiol alone (group 1). Administration of estradiol and sodium butyrate (group 3) also produced a 17% increase in uterine mass (Fig. 1).

Uterine histology

All uteri of ovariectomized mice, which were not treated with estradiol and received trichostatin A (group 5) or sodium butyrate (group 6) or no additional treatments (group 4) for 30 days, were diagnosed with atrophic endometrium (Fig. 2). All endometrial glands in all these uteri had a narrow lumen, and had a round, oval, or elongated shape (a microscopical reflection of simple tubular glands), which were regarded as normal. All glands were lined with simple cuboidal epithelium.

In control mice receiving estradiol for 30 days (group 1), abnormal glands, especially glands with daughter glands and glands forming conglomerates, were observed (Figs 2 and 3). Glands lined with pseudostratified or atypical stratified epithelium were also found in these uteri (Figs 2 and 3). Atypical endometrial hyperplasia was diagnosed in 36.5% of control mice treated with estradiol for a month.

In animals treated with estradiol and trichostatin A for 30 days (group 2), glands with daughter glands, glands forming conglomerates and glands with atypical stratified columnar epithelium were observed more often (Figs 2 and 3). Atypical endometrial hyperplasia was found in 78.6% of cases, and there were no cases of simple endometrial hyperplasia. Normal proliferative endometrium was also not diagnosed in mice receiving estradiol and trichostatin A (Figs 2 and 3).

In the uteri of mice treated with estradiol and sodium butyrate for 30 days (group 3), glands with daughter glands, conglomerates of glands and glands with atypical epithelium were also found in a greater percentage of cases (Figs 2 and 3). Atypical endometrial hyperplasia was found in 64.3% of cases (Figs 2 and 3).

Proliferation

Proliferation in the uterus was estimated by two parameters: the number of mitotic cells and the number of BrdU-labelled cells. Treatment with estradiol and trichostatin A for 30 days (group 2) led to an increase in the percentage of mitotic and BrdU-labelled cells in all uterine tissues (Fig. 4). Treatment with estradiol and sodium butyrate for 30 days (group 3) also produced an increase in the number of mitotic and BrdU-labelled cells in all structures (Fig. 4). Mice that received the estradiol vehicle (olive oil) with no additional treatments (group 4) or with trichostatin A (group 5) or sodium butyrate (group 6) for 30 days had no changes in proliferative parameters in all uterine tissues (Fig. 4b and d).

Estrogen receptor-α

Using immunohistochemistry, estrogen receptor-α was found in luminal and glandular epithelia, in stromal and myometrial cells of the uterus. Treatment with estradiol and trichostatin A for 30 days (group 2) reduced the level of estrogen receptor-α in all uterine compartments, as compared with that in control animals (group 1) treated with estradiol (Figs 2 and 5). Treatment with estradiol and sodium butyrate also led to a reduction in estrogen receptor levels in all uterine tissues.

Mice that received the estradiol vehicle (olive oil) and trichostatin A or sodium butyrate, or with no additional treatments for 30 days (groups 4 to 6) had no changes in estrogen receptor expression (Fig. 5).

Progesterone receptors

Using immunohistochemistry, progesterone receptors were detected in luminal and glandular epithelia, stromal and myometrial cells of the uteri of mice in all treatments group. Treatment with estradiol and trichostatin A for 30 days (group 2) led to marked reduction in the level of progesterone receptors in all uterine compartments, as compared with that in control animals (group 1) treated with estradiol (Figs 2 and 6). Treatment with estradiol and sodium butyrate (group 3) also resulted in a marked decrease in progesterone receptor expression in all uterine tissues.

The data from mice treated with estradiol vehicle only or with trichostatin A, or with sodium butyrate for a month (groups 4 to 6) are shown in Fig. 6b. There are no differences in progesterone receptor levels among these groups.

β-Catenin

Immunohistochemical staining for β-catenin showed that this protein was clearly detected in luminal and glandular epithelia of the uteri of mice in all treatment groups. Treatment with estradiol and trichostatin A (group 2) or with sodium butyrate (group 3) for 30 days led to a reduction in the level of β-catenin in both epithelia (Figs 2 and 7). The effect of trichostatin A was more expressed.

The data from mice treated with estradiol vehicle only or with trichostatin A, or with sodium butyrate for a month (groups 4 to 6) are shown in Fig. 7b. There are no differences in β-catenin level among these groups.

Discussion

A group of parameters was employed to estimate estradiol action in the uterus. Uterine mass is a well-known indicator of estrogen action (Emons et al. 2000, Bigsby 2002). Proliferation, which was determined by the numbers of mitotic and BrdU-labelled cells, also depends on estrogen action (Martin et al. 1973, Gunin et al. 2000). In addition, morphogenetic alterations – such as shape of glands, type of glandular epithelium and pathology findings – appear in the uterus under long-term estrogen action (Martin et al. 1973, Gunin et al. 2002). Moreover, hyperplastic changes in the endometrium are often found. Some hyperplastic changes have nonfavorable prognosis, especially complex and atypical hyperplasies. Complex hyperplasia is characterized by architectural disarray in gland shape and glandular epithelium. Glands may have multiple lumens which interconnect. Glandular epithelium may be tall and columnar or pseudostratified. However, epithelial cells in general do retain their orientation to the lumen. Atypical hyperplasia has approximately the same characteristics, but hyperplastic endometrium shows cytologic atypia including large nuclei of variable size and shape that have lost polarity. Of all endometrial hyperplasies, atypical hyperplasia has the most increased risk for progression to endometrial cancer (Scully et al. 1994, Deligdisch 2000).

Results clearly showed that both histone deacetylase blockers had unilateral effects and led to an increase in uterine mass and proliferation and to more expressed morphogenetic alterations than in control mice. The effect of trichostatin A is more expressed than that of butyrate. This situation is probably associated with the fact that trichostatin A has a more specific and a stronger action in blocking histone deacetylase activity (Riester et al. 2004). For all parameters tested, the effects of histone deacetylase inhibitors were found only in estrogen-treated mice and were not documented in control animals receiving olive oil instead of estradiol. Hence, these results support the supposition that histone deacetylase inhibitors affect some steps in the mechanism of estrogen action.

In our previous experiments, treatments sometimes had an effect on proliferation but had no action on morpho-genetic changes in the uterus, and vice versa (Gunin et al. 2001, 2004a,Gunin et al.b). The present results show that histone deacetylase blockers affect both proliferation and morphogenetic alterations. It is known that proliferation and control of cell shape, differentiation, adhesion and apoptosis are regulated by different mechanisms and depend on the work of different genes (Bigsby 2002, Klotz et al. 2002). Hence, histone deacetylases are involved in the control of all these estrogen-dependent processes, and inhibition of these deacetylases intensifies proliferative and morphogenetic estrogen actions. One more well-known estrogen effect in the uterus is the induction of progesterone receptors (Couse & Korach 1999). Our current results showed that both histone deacetylase blockers led to a decrease in progesterone receptor expression in all uterine tissues. Hence, it can be concluded that histone deacetylases also manage this part of estrogen action, but their blockade attenuates the estrogen effect on progesterone receptor expression.

To define some possible mechanisms involved in the action of histone deacetylases on estrogen-induced effects, the expression of estrogen receptor-α and progesterone receptors in uterine tissues was examined. Results showed that both blockers reduced the level of estrogen receptor-α in all uterine compartments, as compared with control. Other data support our observation and also show that histone deacetylase blockers decrease estrogen receptor-α levels in ovarian, endometrial and mammary gland cancer cell lines (Alao et al. 2004, Margueron et al. 2004).

In general, the level of receptors in a tissue depends on a balance between their synthesis and degradation (Ing & Ott 1999, Nephew et al. 2000). Histone deacetylase blockers probably attenuate estrogen receptor synthesis or activate their degradation. The effect of histone deacetylase blockers on progesterone receptor levels may also be caused by a decrease in the speed of their synthesis or by acceleration of their degradation. Other researchers also reported that trichostatin A decreased the levels of progesterone receptor coactivators and impaired progesterone receptor function (Wilson et al. 2002, Condon et al. 2003).

It is interesting to note that in mice treated with histone deacetylase blockers and estradiol, the more intensive estrogen-dependent processes (increase in mass, proliferation, morphogenesis) in the uterus proceed with lower levels of estrogen and progesterone receptors. Other data also showed that more malignant and less-differentiated endometrial tumors had low levels of estrogen and progesterone receptors (Sivridis et al. 2001, Ali et al. 2004). It is possible that a diminished level of estrogen and progesterone receptors does not allow estrogens to adequately control the processes managing the morphogenesis that leads to atypical hyperplasia formation.

β-Catenin is implicated in cell adhesion and is a component of the Wnt-pathway (Cong et al. 2003). β-Catenin provides intercellular adhesion and it is possible that if its concentration is high, cell–cell connection is more stable and that this protects from the formation of precancerous changes. In the case of low β-catenin concentration, cell–cell interactions are less solid, which provides a foundation for cancer development. It has been reported that the level of β-catenin in the uterus was decreased following estrogen action and cancer formation (Fujimoto et al. 1998, Nei et al. 1999, Miyamoto et al. 2000, Gunin et al. 2004b). There is a decrease in β-catenin expression in uterine epithelia in mice treated with estradiol and histone deacetylase blockers compared with that of mice treated with estradiol alone. Our results showed that more expressed morphogenetic shifts, which were found in estradiol and trichostatin A or sodium butyrate treated mice, are accompanied by decreased levels of β-catenin. Hence, β-catenin is involved in changes in estrogen-dependent uterine morphology which are affected by histone deacetylase blockers.

β-Catenin content in a tissue is also a result of the balance between its synthesis and degradation. It has previously been shown that changes in β-catenin expression can be caused by the work of glycogen-synthase kinase-3β, an enzyme which takes part in β-catenin degradation (Gunin et al. 2003). Other data showed that estrogen hormones can attenuate β-catenin biosynthesis in the uterus (Fujimoto et al. 1996). Direct interactions between β-catenin and histone deacetylases were documented (Billin et al. 2000). It was also shown that β-catenin led to a loss of activity of histone deacetylases (Henderson et al. 2002, Baek et al. 2003). A function of β-catenin is compromised by fusion to a transcriptional repressor domain from histone deacetylase (Cong et al. 2003). However, further studies are needed to elucidate the roles of histone deacetylases in the regulation of β-catenin content in the uterus, as well as to define the role of β-catenin in uterine morphogenesis.

There are reports showing that histone deacetylase blockers – trichostatin A, sodium butyrate and others – led to a decrease in proliferation in endometrial and mammary gland cancer cell lines (Takai et al. 2004a,b). Our results showed that trichostatin A or sodium butyrate enhanced proliferation and hyperplasia formation in the murine uterus. What are the sources of these contradictions? First, most of the studies examining the effects of changes in the level of histone acetylation on proliferation and differentiation in uterine and mammary gland cell lines were performed in the absence of estrogen administration (Adhikari et al. 2000, Terao et al. 2001). Secondly, most works that showed the antiproliferative and anticancer potency of histone deacetylase blockers were performed in vitro. However, in vitro and in vivo conditions are principally different. Concentrations of reagents are constant in vitro, but in vivo, concentrations of acting substances are subjected to fluctuations depending on the activity of metabolic processes. There is a report showing a rapid increase in proliferation of human endometrial adenocarcinoma cells after removal of sodium butyrate from a medium (Saito et al. 1991). Other works demonstrated that in large intestine sodium butyrate has an antineoplastic effect when used in vitro (Deschner et al. 1990, Lupton 2004) and accelerates cancer formation in vivo (Freeman 1986, Lupton 2004). There are, however, observations documenting an increase in colon cancer formation under sodium butyrate treatment in vitro and in vivo (Deschner et al. 1990). Finally, all published data were obtained on already formed cancer cells, but not on normal cells that are transforming to cancerous cells. Our experiments were done on normal, nonmalignant, uterine tissues which were then exposed to estrogen followed by hyperplasia formation. One more interesting remark, valproic acid, which is used for treatment of epilepsy and has a mechanism of action which involves the blockade of histone deacetylases, revealed expressed teratogenic effects in humans (Phiel et al. 2001, Kultima et al. 2004). Trichostatin A also has teratogenic effects in vertebrate embryos (Phiel et al. 2001). However, further studies are needed to explain some contradictory points and to elucidate the exact mechanisms involved in the interactions between estrogen signalling and histone deacetylases.

Thus, this research provides evidence that histone deacetylase blockers, trichostatin A and sodium butyrate, enhance proliferative and morphogenetic estrogen action and support the development of estrogen-dependent endometrial hyperplasia. However, the exact mechanisms of the actions of histone deacetylase blockers on estrogen-dependent changes in uterine tissues remain unclear. It is possible that histone deacetylase inhibitors affect the activity of estrogen-regulated genes in the uterus and this is an important avenue for further research. We hope that this research will lead to a better understanding of the origin and progression of estrogen-dependent cancer of the female reproductive system.

Funding

This work was supported by grants from the Russian Foundation for Basic Research (03–04–48000) and the Ministry of Education and Science of Russia (E02–6.0–136; yp. 11.01.026). The authors declare that there is no conflict of interest that would prejudice the impartiality of this scientific work.

Figure 1

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Figure 1

The data on uterine mass (mg per 100 g body mass of ovariectomized mice treated with estradiol and saline (open bars) or with trichostatin A (grey bars) or sodium butyrate (black bars) for 30 days. Values are means±s.e.m. *P<0.05; ***P<0.001; Student’s t-test.

Citation: Journal of Endocrinology 185, 3; 10.1677/joe.1.06118

Figure 2

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Figure 2

Photomicrographs demonstrating histological findings (row a), immunohistochemical staining for estrogen receptor-α (row b), progesterone receptors (row c) and β-catenin (row d) in the uterus of mice treated with estradiol with no additional treatments (column i), estradiol and trichostatin A (column ii), estradiol and sodium butyrate (column iii) for 30 days. Multiple enlarged glands with small daughter glands and conglomerates of glands are seen in the uterus of mice receiving estradiol and trichostatin A (a-ii) or sodium butyrate (a-iii). In control mice treated with estradiol only (a-i), glands with daughter glands are also present, but in a lower percentage of cases. However, normal glands with small dimensions and lined with simple columnar or cuboidal epithelia are also seen in the uterus of control mice (a-i). There is a marked decrease in the levels of estrogen receptor-α (b-ii, b-iii), progesterone receptors (c-ii, c-iii) and β-catenin (d-ii, d-iii) in uterine tissues of mice treated with estradiol and trichostatin A (ii) or sodium butyrate (iii) for 30 days, as compared with control (b-i, c-i). Panels in column 0 represent the general histology (a-0), expression of estrogen receptor-α (b-0), progesterone receptors (c-0) and β-catenin (d-0) in the uterus of control mice treated with olive oil (the estradiol vehicle) for 30 days. le, luminal epithelium; g, endometrial glands; s, endometrial stroma. Scale bar, 100 μm.

Citation: Journal of Endocrinology 185, 3; 10.1677/joe.1.06118

Figure 3

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Figure 3

Types of endometrial glands, types of glandular epithelium, and pathology diagnosis in uteri of ovariectomized mice treated with estradiol with no additional treatments, estradiol and trichostatin A, estradiol and sodium butyrate for 30 days. PE, proliferative endometrium; SH, simple hyperplasia; CoH, complex hyperplasia; AH, atypical hyperplasia; A, normal glands; B, cystic glands; C, glands with daughter glands; D, glands forming conglomerate; 1, simple columnar epithelium; 2, pseudostratified columnar epithelium; 3, stratified columnar epithelium. Values are means+s.e.m. P<0.001; χ2 test).

Citation: Journal of Endocrinology 185, 3; 10.1677/joe.1.06118

Figure 4

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Figure 4

The numbers of mitotic (a) and BrdU-labelled cells (c) in the compartments of the uteri of ovariectomized mice treated with estradiol alone (open bars) or with trichostatin A (grey bars) or sodium butyrate (black bars) for 30 days. The numbers of mitotic (b) and BrdU-labelled cells (d) of mice treated with olive oil (vehicle of estradiol) only (thin-hatched bars, vehicle of estradiol) or with trichostatin A (thick-hatched bars) or sodium butyrate (parallel-line-filled bars) for 30 days. No mitoses were found in stromal and myometrial cells of mice treated with olive oil only or with trichostatin A or with sodium butyrate for 30 days (panels b and d). Values are means+s.e.m. *P<0.05; **P<0.01; ***P<0.001; Student’s t-test.

Citation: Journal of Endocrinology 185, 3; 10.1677/joe.1.06118

Figure 5

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Figure 5

(a) Expression of estrogen receptor-α in uterine tissues of mice treated with estradiol alone (open bars) or together with trichostatin A (grey bars) or with sodium butyrate (black bars) for 30 days. (b) Data from mice treated with olive oil (vehicle of estradiol) alone (thin-hatched bars) or with trichostatin A (thick-hatched bars), or sodium butyrate (parallel-line-filled bars) for 30 days. Quantitation of immunostaining was performed by photometric determination of optical density (light absorption) of positively stained components of a tissue. The value of optical density was used as the level of expression. Values are means+s.e.m. **P<0.01; ***P<0.001; Student’s t-test.

Citation: Journal of Endocrinology 185, 3; 10.1677/joe.1.06118

Figure 6

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Figure 6

(a) Expression of progesterone receptors in uterine tissues of mice treated with estradiol alone (open bars) or together with trichostatin A (grey bars) or with sodium butyrate (black bars) for 30 days. (b) Data from mice treated with olive oil (vehicle of estradiol) alone (thin-hatched bars) or with trichostatin A (thick-hatched bars) or sodium butyrate (parallel-line-filled bars) for 30 days. Quantitation of immunostaining was performed by photometric determination of optical density (light absorption) of positively stained components of a tissue. The value of optical density was used as the level of expression. Values are means+s.e.m. **P<0.01; ***P<0.001; Student’s t-test.

Citation: Journal of Endocrinology 185, 3; 10.1677/joe.1.06118

Figure 7

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Figure 7

(a) Expression of β-catenin in uterine tissues of mice treated with estradiol alone (open bars) or together with trichostatin A (grey bars), or with sodium butyrate (black bars) for 30 days. (b) Data from mice treated with olive oil (vehicle of estradiol) alone (thin-hatched bars) or with trichostatin A (thick-hatched bars), or sodium butyrate (parallel-line-filled bars) for 30 days. Quantitation of immunostaining was performed by photometric determination of optical density (light absorption) of positively stained components of a tissue. The value of optical density was used as the level of expression. Values are means+s.e.m. *P<0.05; **P<0.01; Student’s t-test.

Citation: Journal of Endocrinology 185, 3; 10.1677/joe.1.06118

References

  • AdhikariD2000 Pretreatment of endometrial carcinoma cell lines with butyrate results in upregulation of Bax and correlates with potentiation of radiation induced cell kill. In Vivo14603–609.

  • AkhmedkhanovA2001 Role of exogenous and endogenous hormones in endometrial cancer: review of the evidence and research perspectives. Annals of the New York Academy of Sciences943296–315.

  • AlaoJP2004 Histone deacetylase inhibitor trichostatin A represses estrogen receptor-alpha-dependent transcription and promotes proteasomal degradation of cyclin D1 in human breast carcinoma cell lines. Clinical Cancer Research108094–8104.

  • AliSH2004 Overexpression of estrogen receptor-alpha in the endometrial carcinoma cell line Ishikawa: inhibition of growth and angiogenic factors. Gynecological Oncology95637–645.

  • ArcherDF2004 Neoplasia of the female reproductive tract: effects of hormone therapy. Endocrine24259–264.

  • BaekSH2003 Regulated subset of G1 growth-control genes in response to derepression by the Wnt pathway. PNAS3245–3250.

  • BigsbyRM2002 Control of growth and differentiation of the endometrium: the role of tissue interactions. Annals of the New York Academy of Sciences955110–117.

  • BillinAN2000 Beta-catenin-histone deacetylase interactions regulate the transition of LEF1 from a transcriptional repressor to an activator. Molecular and Cellular Biology206882–6890.

  • CondonJC2003 A decline in the levels of progesterone receptor coactivators in the pregnant uterus at term may antagonize progesterone receptor function and contribute to the initiation of parturition. PNAS1009518–9523.

  • CongF2003 Requirement for a nuclear function of beta-catenin in Wnt signaling. Molecular and Cellular Biology238462–8470.

  • CouseJF & Korach KS 1999 Estrogen receptor null mice: what have we learned and where will they lead us? Endocrine Reviews20358–417.

  • DeligdischL2000 Hormonal pathology of the endometrium. Modern Pathology13285–294.

  • DerooBJ2004 Estradiol regulates the thioredoxin antioxidant system in the mouse uterus. Endocrinology1455485–5492.

  • DeschnerEE1990 Dietary butyrate (tributyrin) does not enhance AOM-induced colon tumorigenesis. Cancer Letters5279–82.

  • EmonsG2000 Hormonal interactions in endometrial cancer. Endocrine Related Cancer7227–242.

  • FreemanHJ1986Gastroenterology91596–602.

  • FujimotoJ1996Gynecological Endocrinology10187–191.

  • FujimotoJ1998 Expressions of E-cadherin and alpha- and beta-catenin mRNAs in uterine endometrial cancers. European Journal of Gynaecological Oncology1978–81.

  • GuninAG2000 Two month glucocorticoid treatment increases estradiol-induced stromal and myometrial cell proliferation in the uterus of ovariectomized rats. European Journal of Obstetrics & Gynecology and Reproductive Biology88171–179.

  • GuninAG2001Journal of Endocrinology16923–31.

  • GuninAG2002 Effect of adrenocorticotrophic hormone on the development of oestrogen-induced changes and hyperplasia formation in the mouse uterus. Reproduction123601–611.

  • GuninAG2003 Uterine response to estradiol under action of chorionic gonadotropin in mice. International Journal of Gynecological Cancer13485–496.

  • GuninA2004a Effects of peroxisome proliferator activated receptors-alpha and gamma agonists on estradiol-induced proliferation and hyperplasia formation in the mouse uterus. Journal of Endocrinology182229–239.

  • GuninA2004b Lithium treatment enhances estradiol-induced proliferation and hyperplasia formation in the uterus of mice. European Journal of Obstetrics & Gynecology and Reproductive Biology11483–91.

  • HendersonBR2002 Lymphoid enhancer factor-1 blocks adenomatous polyposis coli-mediated nuclear export and degradation of beta-catenin. Regulation by histone deacetylase 1. Journal of Biological Chemistry27724258–24264.

  • IngNH & Ott TL 1999 Estradiol up-regulates estrogen receptor-alpha messenger ribonucleic acid in sheep endometrium by increasing its stability. Biology of Reproduction60134–139.

  • JangER2004 The histone deacetylase inhibitor trichostatin A sensitizes estrogen receptor alpha-negative breast cancer cells to tamoxifen. Oncogene231724–1736.

  • KlotzDM2002 Requirement of estrogen receptor-alpha in insulin-like growth factor-1 (IGF-1)-induced uterine responses and in vivo evidence for IGF-1/estrogen receptor cross-talk. Journal of Biological Chemistry2778531–8537.

  • KultimaK2004 Valproic acid teratogenicity: a toxicogenomics approach. Environmental Health Perspectives1121225–1235.

  • KurtevV2004 Transcriptional regulation by the repressor of estrogen receptor activity via recruitment of histone deacetylases. Journal of Biological Chemistry27924834–24843.

  • LuptonJR2004 Microbial degradation products influence colon cancer risk: the butyrate controversy. Journal of Nutrition134479–482.

  • MargueronR2004 Histone deacetylase inhibition and estrogen signalling in human breast cancer cells. Biochemical Pharmacology681239–1246.

  • MartinL1973 Hypertrophy and hyperplasia in the mouse uterus after oestrogen treatment: an autoradiographic study. Journal of Endocrinology56133–144.

  • MiyamotoS2000 Changes in E-cadherin associated with cytoplasmic molecules in well and poorly differentiated endometrial cancer. British Journal of Cancer831168–1175.

  • NeiH1999 Nuclear localization of beta-catenin in normal and carcinogenic endometrium. Molecular Carcinogenesis25207–218.

  • NephewKP2000 Effect of estradiol on estrogen receptor expression in rat uterine cell types. Biology of Reproduction62168–177.

  • PhielCJ2001Journal of Biological Chemistry27636734–36741.

  • RiesterD2004 Members of the histone deacetylase superfamily differ in substrate specificity towards small synthetic substrates. Biochemical and Biophysical Research Communications3241116–1123.

  • SaitoS1991 Flow cytometric and biochemical analysis of dose-dependent effects of sodium butyrate on human endometrial adenocarcinoma cells. Cytometry12757–764.

  • SakaiN2003 Involvement of histone acetylation in ovarian steroid-induced decidualization of human endometrial stromal cells. Journal of Biological Chemistry27816675–16682.

  • ScullyRE1994 Histological typing of female genital tract tumours. In International Histological Classification of Tumours

  • SivridisE2001 Endometrial carcinoma: association of steroid hormone receptor expression with low angiogenesis and bcl-2 expression. Virchows Archiv438470–477.

  • SunJM2001 Effect of estradiol on histone acetylation dynamics in human breast cancer cells. Journal of Biological Chemistry27649435–49442.

  • TakaiN2004a Histone deacetylase inhibitors have a profound antigrowth activity in endometrial cancer cells. Clinical Cancer Research101141–1149.

  • TakaiN2004b Human ovarian carcinoma cells: histone deacetylase inhibitors exhibit antiproliferative activity and potently induce apoptosis. Cancer1012760–2770.

  • TeraoY2001 Sodium butyrate induces growth arrest and senescence-like phenotypes in gynecologic cancer cells. International Journal of Cancer94257–267.

  • WilsonMA2002 The histone deacetylase inhibitor trichostatin A blocks progesterone receptor-mediated transactivation of the mouse mammary tumor virus promoter in vivo. Journal of Biological Chemistry27715171–15181.

 

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Figures

  • View in gallery

    The data on uterine mass (mg per 100 g body mass of ovariectomized mice treated with estradiol and saline (open bars) or with trichostatin A (grey bars) or sodium butyrate (black bars) for 30 days. Values are means±s.e.m. *P<0.05; ***P<0.001; Student’s t-test.

  • View in gallery

    Photomicrographs demonstrating histological findings (row a), immunohistochemical staining for estrogen receptor-α (row b), progesterone receptors (row c) and β-catenin (row d) in the uterus of mice treated with estradiol with no additional treatments (column i), estradiol and trichostatin A (column ii), estradiol and sodium butyrate (column iii) for 30 days. Multiple enlarged glands with small daughter glands and conglomerates of glands are seen in the uterus of mice receiving estradiol and trichostatin A (a-ii) or sodium butyrate (a-iii). In control mice treated with estradiol only (a-i), glands with daughter glands are also present, but in a lower percentage of cases. However, normal glands with small dimensions and lined with simple columnar or cuboidal epithelia are also seen in the uterus of control mice (a-i). There is a marked decrease in the levels of estrogen receptor-α (b-ii, b-iii), progesterone receptors (c-ii, c-iii) and β-catenin (d-ii, d-iii) in uterine tissues of mice treated with estradiol and trichostatin A (ii) or sodium butyrate (iii) for 30 days, as compared with control (b-i, c-i). Panels in column 0 represent the general histology (a-0), expression of estrogen receptor-α (b-0), progesterone receptors (c-0) and β-catenin (d-0) in the uterus of control mice treated with olive oil (the estradiol vehicle) for 30 days. le, luminal epithelium; g, endometrial glands; s, endometrial stroma. Scale bar, 100 μm.

  • View in gallery

    Types of endometrial glands, types of glandular epithelium, and pathology diagnosis in uteri of ovariectomized mice treated with estradiol with no additional treatments, estradiol and trichostatin A, estradiol and sodium butyrate for 30 days. PE, proliferative endometrium; SH, simple hyperplasia; CoH, complex hyperplasia; AH, atypical hyperplasia; A, normal glands; B, cystic glands; C, glands with daughter glands; D, glands forming conglomerate; 1, simple columnar epithelium; 2, pseudostratified columnar epithelium; 3, stratified columnar epithelium. Values are means+s.e.m. P<0.001; χ2 test).

  • View in gallery

    The numbers of mitotic (a) and BrdU-labelled cells (c) in the compartments of the uteri of ovariectomized mice treated with estradiol alone (open bars) or with trichostatin A (grey bars) or sodium butyrate (black bars) for 30 days. The numbers of mitotic (b) and BrdU-labelled cells (d) of mice treated with olive oil (vehicle of estradiol) only (thin-hatched bars, vehicle of estradiol) or with trichostatin A (thick-hatched bars) or sodium butyrate (parallel-line-filled bars) for 30 days. No mitoses were found in stromal and myometrial cells of mice treated with olive oil only or with trichostatin A or with sodium butyrate for 30 days (panels b and d). Values are means+s.e.m. *P<0.05; **P<0.01; ***P<0.001; Student’s t-test.

  • View in gallery

    (a) Expression of estrogen receptor-α in uterine tissues of mice treated with estradiol alone (open bars) or together with trichostatin A (grey bars) or with sodium butyrate (black bars) for 30 days. (b) Data from mice treated with olive oil (vehicle of estradiol) alone (thin-hatched bars) or with trichostatin A (thick-hatched bars), or sodium butyrate (parallel-line-filled bars) for 30 days. Quantitation of immunostaining was performed by photometric determination of optical density (light absorption) of positively stained components of a tissue. The value of optical density was used as the level of expression. Values are means+s.e.m. **P<0.01; ***P<0.001; Student’s t-test.

  • View in gallery

    (a) Expression of progesterone receptors in uterine tissues of mice treated with estradiol alone (open bars) or together with trichostatin A (grey bars) or with sodium butyrate (black bars) for 30 days. (b) Data from mice treated with olive oil (vehicle of estradiol) alone (thin-hatched bars) or with trichostatin A (thick-hatched bars) or sodium butyrate (parallel-line-filled bars) for 30 days. Quantitation of immunostaining was performed by photometric determination of optical density (light absorption) of positively stained components of a tissue. The value of optical density was used as the level of expression. Values are means+s.e.m. **P<0.01; ***P<0.001; Student’s t-test.

  • View in gallery

    (a) Expression of β-catenin in uterine tissues of mice treated with estradiol alone (open bars) or together with trichostatin A (grey bars), or with sodium butyrate (black bars) for 30 days. (b) Data from mice treated with olive oil (vehicle of estradiol) alone (thin-hatched bars) or with trichostatin A (thick-hatched bars), or sodium butyrate (parallel-line-filled bars) for 30 days. Quantitation of immunostaining was performed by photometric determination of optical density (light absorption) of positively stained components of a tissue. The value of optical density was used as the level of expression. Values are means+s.e.m. *P<0.05; **P<0.01; Student’s t-test.

References

AdhikariD2000 Pretreatment of endometrial carcinoma cell lines with butyrate results in upregulation of Bax and correlates with potentiation of radiation induced cell kill. In Vivo14603–609.

AkhmedkhanovA2001 Role of exogenous and endogenous hormones in endometrial cancer: review of the evidence and research perspectives. Annals of the New York Academy of Sciences943296–315.

AlaoJP2004 Histone deacetylase inhibitor trichostatin A represses estrogen receptor-alpha-dependent transcription and promotes proteasomal degradation of cyclin D1 in human breast carcinoma cell lines. Clinical Cancer Research108094–8104.

AliSH2004 Overexpression of estrogen receptor-alpha in the endometrial carcinoma cell line Ishikawa: inhibition of growth and angiogenic factors. Gynecological Oncology95637–645.

ArcherDF2004 Neoplasia of the female reproductive tract: effects of hormone therapy. Endocrine24259–264.

BaekSH2003 Regulated subset of G1 growth-control genes in response to derepression by the Wnt pathway. PNAS3245–3250.

BigsbyRM2002 Control of growth and differentiation of the endometrium: the role of tissue interactions. Annals of the New York Academy of Sciences955110–117.

BillinAN2000 Beta-catenin-histone deacetylase interactions regulate the transition of LEF1 from a transcriptional repressor to an activator. Molecular and Cellular Biology206882–6890.

CondonJC2003 A decline in the levels of progesterone receptor coactivators in the pregnant uterus at term may antagonize progesterone receptor function and contribute to the initiation of parturition. PNAS1009518–9523.

CongF2003 Requirement for a nuclear function of beta-catenin in Wnt signaling. Molecular and Cellular Biology238462–8470.

CouseJF & Korach KS 1999 Estrogen receptor null mice: what have we learned and where will they lead us? Endocrine Reviews20358–417.

DeligdischL2000 Hormonal pathology of the endometrium. Modern Pathology13285–294.

DerooBJ2004 Estradiol regulates the thioredoxin antioxidant system in the mouse uterus. Endocrinology1455485–5492.

DeschnerEE1990 Dietary butyrate (tributyrin) does not enhance AOM-induced colon tumorigenesis. Cancer Letters5279–82.

EmonsG2000 Hormonal interactions in endometrial cancer. Endocrine Related Cancer7227–242.

FreemanHJ1986Gastroenterology91596–602.

FujimotoJ1996Gynecological Endocrinology10187–191.

FujimotoJ1998 Expressions of E-cadherin and alpha- and beta-catenin mRNAs in uterine endometrial cancers. European Journal of Gynaecological Oncology1978–81.

GuninAG2000 Two month glucocorticoid treatment increases estradiol-induced stromal and myometrial cell proliferation in the uterus of ovariectomized rats. European Journal of Obstetrics & Gynecology and Reproductive Biology88171–179.

GuninAG2001Journal of Endocrinology16923–31.

GuninAG2002 Effect of adrenocorticotrophic hormone on the development of oestrogen-induced changes and hyperplasia formation in the mouse uterus. Reproduction123601–611.

GuninAG2003 Uterine response to estradiol under action of chorionic gonadotropin in mice. International Journal of Gynecological Cancer13485–496.

GuninA2004a Effects of peroxisome proliferator activated receptors-alpha and gamma agonists on estradiol-induced proliferation and hyperplasia formation in the mouse uterus. Journal of Endocrinology182229–239.

GuninA2004b Lithium treatment enhances estradiol-induced proliferation and hyperplasia formation in the uterus of mice. European Journal of Obstetrics & Gynecology and Reproductive Biology11483–91.

HendersonBR2002 Lymphoid enhancer factor-1 blocks adenomatous polyposis coli-mediated nuclear export and degradation of beta-catenin. Regulation by histone deacetylase 1. Journal of Biological Chemistry27724258–24264.

IngNH & Ott TL 1999 Estradiol up-regulates estrogen receptor-alpha messenger ribonucleic acid in sheep endometrium by increasing its stability. Biology of Reproduction60134–139.

JangER2004 The histone deacetylase inhibitor trichostatin A sensitizes estrogen receptor alpha-negative breast cancer cells to tamoxifen. Oncogene231724–1736.

KlotzDM2002 Requirement of estrogen receptor-alpha in insulin-like growth factor-1 (IGF-1)-induced uterine responses and in vivo evidence for IGF-1/estrogen receptor cross-talk. Journal of Biological Chemistry2778531–8537.

KultimaK2004 Valproic acid teratogenicity: a toxicogenomics approach. Environmental Health Perspectives1121225–1235.

KurtevV2004 Transcriptional regulation by the repressor of estrogen receptor activity via recruitment of histone deacetylases. Journal of Biological Chemistry27924834–24843.

LuptonJR2004 Microbial degradation products influence colon cancer risk: the butyrate controversy. Journal of Nutrition134479–482.

MargueronR2004 Histone deacetylase inhibition and estrogen signalling in human breast cancer cells. Biochemical Pharmacology681239–1246.

MartinL1973 Hypertrophy and hyperplasia in the mouse uterus after oestrogen treatment: an autoradiographic study. Journal of Endocrinology56133–144.

MiyamotoS2000 Changes in E-cadherin associated with cytoplasmic molecules in well and poorly differentiated endometrial cancer. British Journal of Cancer831168–1175.

NeiH1999 Nuclear localization of beta-catenin in normal and carcinogenic endometrium. Molecular Carcinogenesis25207–218.

NephewKP2000 Effect of estradiol on estrogen receptor expression in rat uterine cell types. Biology of Reproduction62168–177.

PhielCJ2001Journal of Biological Chemistry27636734–36741.

RiesterD2004 Members of the histone deacetylase superfamily differ in substrate specificity towards small synthetic substrates. Biochemical and Biophysical Research Communications3241116–1123.

SaitoS1991 Flow cytometric and biochemical analysis of dose-dependent effects of sodium butyrate on human endometrial adenocarcinoma cells. Cytometry12757–764.

SakaiN2003 Involvement of histone acetylation in ovarian steroid-induced decidualization of human endometrial stromal cells. Journal of Biological Chemistry27816675–16682.

ScullyRE1994 Histological typing of female genital tract tumours. In International Histological Classification of Tumours

SivridisE2001 Endometrial carcinoma: association of steroid hormone receptor expression with low angiogenesis and bcl-2 expression. Virchows Archiv438470–477.

SunJM2001 Effect of estradiol on histone acetylation dynamics in human breast cancer cells. Journal of Biological Chemistry27649435–49442.

TakaiN2004a Histone deacetylase inhibitors have a profound antigrowth activity in endometrial cancer cells. Clinical Cancer Research101141–1149.

TakaiN2004b Human ovarian carcinoma cells: histone deacetylase inhibitors exhibit antiproliferative activity and potently induce apoptosis. Cancer1012760–2770.

TeraoY2001 Sodium butyrate induces growth arrest and senescence-like phenotypes in gynecologic cancer cells. International Journal of Cancer94257–267.

WilsonMA2002 The histone deacetylase inhibitor trichostatin A blocks progesterone receptor-mediated transactivation of the mouse mammary tumor virus promoter in vivo. Journal of Biological Chemistry27715171–15181.

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