Regulation of estrogen target genes and growth by selective estrogen-receptor modulators in endometrial cancer cells

Turning scientific serendipity into discoveries in breast cancer research and treatment: a tale of PhD students and a 50-year roaming tamoxifen team

PURPOSE

This retrospective, about a single "mobile" laboratory in six locations on two continents, is intended as a case study in discovery for trainees and junior faculty in the medical sciences. Your knowledge of your topic is necessary to expect the unexpected.

HISTORICAL METHOD

In 1972, there was no tamoxifen, only ICI 46, 474, a non-steroidal anti-estrogen with little chance of clinical development. No one would ever be foolish enough to predict that the medicine, 20 years later, would achieve legendary status as the first targeted treatment for breast cancer, and millions of women would benefit from long-term adjuvant tamoxifen therapy. The secret of tamoxifen's success was a translational research strategy proposed in the mid 1970's. This strategy was to treat only patients with estrogen receptor (ER)-positive breast cancer and deploy 5 or more years of adjuvant tamoxifen therapy to prevent recurrence. Additionally, tamoxifen prevented mammary cancer in animals. Could the medicine prevent breast cancer in women?

RESULTS

Tamoxifen and the failed breast cancer drug raloxifene became the first selective estrogen receptor modulators (SERMs): a new drug group, discovered at the University of Wisconsin, Comprehensive Cancer Center. Serendipity can play a fundamental role in discovery, but there must be a rigorous preparation for the investigator to appreciate the possibility of a pending discovery. This article follows the unanticipated discoveries when PhD students "get the wrong answer." The secret of success of my six Tamoxifen Teams was their technical excellence to create models, to decipher mechanisms, that drove the development of new medicines. Discoveries are listed that either changed women's health or allowed an understanding of originally opaque mechanisms of action of potential therapies. These advances in women's health were supported entirely by government-sponsored peer-reviewed funding and major philanthropy from the Lynn Sage Breast Cancer Foundation, the Avon Foundation, and the Susan G. Komen Breast Cancer Foundation. The resulting lives saved or extended, families aided in a time of crisis and the injection of billions of dollars into national economies by drug development, is proof of the value of Federal or philanthropic investment into unencumbered research aimed at saving millions of lives.

SUMO-1 Promotes Ishikawa Cell Proliferation and Apoptosis in Endometrial Cancer by Increasing Sumoylation of Histone H4

OBJECTIVES

To investigate the functional role of SUMO-1 on cell proliferation and apoptosis in endometrial cancer cells (Ishikawa line) and to explore the underlying regulatory mechanisms.

METHODS

Different concentrations of estradiol (E2) and small interfering RNA (siRNA) targeting the SUMO-1 (siCo) were treated in Ishikawa cells, and then quantitative polymerase chain reaction was used to examine the expression of progesterone receptor (PR) expression in Ishikawa cells. Western blots were applied to validate histone H4 sumoylation. CCK8 assay and flow cytometry were performed to investigate cell proliferation and apoptosis in Ishikawa cells.

RESULTS

Estradiol up-regulated the expression of PR messenger RNA, most obviously at 100 nM. SUMO-1 siRNA decreased the PR expression. Estradiol up-regulated H4 sumoylation and caused the increase of Ishikawa cell proliferation, whereas SUMO-1 siRNA down-regulated H4 sumoylation, inhibited the cell proliferation, and induced apoptosis. Furthermore, SUMO-1 siRNA-transfected cells were arrested in the S and G2/M phases and E2 increased the S and G2/M phases of Ishikawa cells.

CONCLUSION

SUMO-1 regulates the Ishikawa cell proliferation and apoptosis by the sumoylation of histone H4.

Activation of the MKL1/actin signaling pathway induces hormonal escape in estrogen-responsive breast cancer cell lines

Estrogen receptor alpha (ERα) is generally considered to be a good prognostic marker because almost 70% of ERα-positive tumors respond to anti-hormone therapies. Unfortunately, during cancer progression, mammary tumors can escape from estrogen control, resulting in resistance to treatment. In this study, we demonstrate that activation of the actin/megakaryoblastic leukemia 1 (MKL1) signaling pathway promotes the hormonal escape of estrogen-sensitive breast cancer cell lines. The actin/MKL1 signaling pathway is silenced in differentiated ERα-positive breast cancer MCF-7 and T47D cell lines and active in ERα-negative HMT-3522 T4-2 and MDA-MB-231 breast cancer cells, which have undergone epithelial-mesenchymal transition. We showed that MKL1 activation in MCF-7 cells, either by modulating actin dynamics or using MKL1 mutants, down-regulates ERα expression and abolishes E2-dependent cell growth. Interestingly, the constitutively active form of MKL1 represses PR and HER2 expression in these cells and increases the expression of HB-EGF, TGFβ, and amphiregulin growth factors in an E2-independent manner. The resulting expression profile (ER-, PR-, HER2-) typically corresponds to the triple-negative breast cancer expression profile.

Growth of poorly differentiated endometrial carcinoma is inhibited by combined action of medroxyprogesterone acetate and the Ras inhibitor Salirasib

Type 2 endometrial carcinoma (EC) is a poorly differentiated EC. Unlike type 1 EC, which responds to hormonal treatment (progestins), type 2 EC is refractory to hormonal treatment because of its low expression of active estrogen and progesterone receptors (ER, PR). The aim of this study was to develop a novel drug combination designed to treat these aggressive type 2 EC tumors without surgery and with fertility potential preserved. We examined the effects of combined treatment with the progestin medroxyprogesterone acetate (MPA) and the Ras inhibitor S-farnesylthiosalicylic acid (FTS; Salirasib). Because FTS can induce cell differentiation in tumor cells, we examined whether FTS could induce re-differentiation of type 2 EC cells, thereby sensitizing them to MPA. We found that FTS reduced Ras-GTP, phospho-Akt, and phospho-ERK, and that these reductions all correlated with a decrease in ERα phosphorylation. Combined treatment with FTS and MPA induced stronger reduction in USPC1 type 2 EC cell numbers than the reduction induced by either drug alone. MPA caused ERα degradation. Death of the cells was caused by MPA but not by FTS. The phosphorylated ERα induces gene transcription manifested by enhanced cell proliferation and survival. The combination of FTS and MPA, by reducing the mRNA expression of ERα-mediated genes (i.e. PR, c-fos and ps2/TFF1), inhibited tumor growth and enhanced the death of type 2 EC cells. These promising results might herald a novel treatment for the highly aggressive, incurable type 2 endometrial carcinoma.

The use of a whole animal biophotonic model as a screen for the angiogenic potential of estrogenic compounds

BACKGROUND

Vascular endothelial growth factor (VEGF) is essential for normal vascular growth and development during wound repair. VEGF is estrogen responsive and capable of regulating its own receptor, vascular endothelial growth factor receptor-2 (VEGFR-2). Several agricultural pesticides (e.g., methoxychlor) have estrogenic potential that can initiate inappropriate physiological responses in estrogenic-sensitive tissues following exposure in vivo. Thus, the current study was designed to determine whether the VEGFR-2-Luciferase (Luc) reporter transgenic mouse is a useful model for evaluating estrogenic tendencies of methoxychlor by monitoring wound healing via VEGFR-2-mediated gene expression using bioluminescence and real-time imaging technology.

RESULTS

VEGFR-2-Luc gene activity peaked by d 7 (P<0.001) in all groups but was not different (P>0.05) between control and estrogen/methoxychlor exposed mice.

CONCLUSIONS

Changes in VEGFR-2-Luc gene activity associated with the dermal wound healing process were able to be measured via photonic emission. The increase in vasculature recruitment and formation is paralleled by the increase of VEGFR-2-Luc activity with a peak on day 7. However, estrogen/methoxychlor did not significantly alter wound healing mediated VEGFR-2-Luc gene expression patterns compared to controls. This suggests that the VEGFR-2-Luc transgenic mouse wound model tested in this study may not be optimal for use as a screen for the angiogenic potential of estrogenic compounds.

Protein Kinase C α Modulates Estrogen-Receptor-Dependent Transcription and Proliferation in Endometrial Cancer Cells

Endometrial cancer is the most common invasive gynecologic malignancy in developed countries. The most prevalent endometrioid tumors are linked to excessive estrogen exposure and hyperplasia. However, molecular mechanisms and signaling pathways underlying their etiology and pathophysiology remain poorly understood. We have shown that protein kinase C α (PKC α ) is aberrantly expressed in endometrioid tumors and is an important mediator of endometrial cancer cell survival, proliferation, and invasion. In this study, we demonstrate that expression of active, myristoylated PKC α conferred ligand-independent activation of estrogen-receptor- (ER-) dependent promoters and enhanced responses to estrogen. Conversely, knockdown of PKC α reduced ER-dependent gene expression and inhibited estrogen-induced proliferation of endometrial cancer cells. The ability of PKC α to potentiate estrogen activation of ER-dependent transcription was attenuated by inhibitors of phosphoinositide 3-kinase (PI3K) and Akt. Evidence suggests that PKC α and estrogen signal transduction pathways functionally interact, to modulate ER-dependent growth and transcription. Thus, PKC α signaling, via PI3K/Akt, may be a critical element of the hyperestrogenic environment and activation of ER that is thought to underlie the development of estrogen-dependent endometrial hyperplasia and malignancy. PKC α -dependent pathways may provide much needed prognostic markers of aggressive disease and novel therapeutic targets in ER positive tumors.

Retinoic acid inhibits endometrial cancer cell growth via multiple genomic mechanisms

Previous studies have indicated that retinoic acid (RA) may be therapeutic for endometrial cancer. However, the downstream target genes and pathways triggered by ligand-activated RA receptor α (RARα) in endometrial cancer cells are largely unknown. In this study, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, flow cytometry, and immunoblotting assays were used to assess the roles of RA and the RA agonist (AM580) in the growth of endometrial cancer cells. Illumina-based microarray expression profiling of endometrial Ishikawa cells incubated with and without AM580 for 1, 3, and 6 h was performed. We found that both RA and AM580 markedly inhibited endometrial cancer cell proliferation, while knockdown of RARα could block AM580 inhibition. Knockdown of RARα significantly increased proliferating cell nuclear antigen and BCL2 protein levels. Incubation of Ishikawa cells with or without AM580 followed by microarray expression profiling showed that 12 768 genes out of 47 296 gene probes were differentially expressed with significant P values. We found that 90 genes were the most regulated genes with the most significant P value (P<0.0001) using F-test. We selected four highly regulated genes with diverse functions, namely G0S2, TNFAIP2, SMAD3, and NRIP1. Real-time PCR verified that AM580 highly regulated these genes, whereas chromatin immunoprecipitation-PCR assay demonstrated that ligand-activated RARα interacted with the promoter of these genes in intact endometrial cancer cells. AM580 also significantly altered 18 pathways including those related to cell growth, differentiation, and apoptosis. In conclusion, AM580 treatment of Ishikawa cells causes the differential expression of a number of RARα target genes and activation of signaling pathways. These pathways could, therefore, mediate the carcinogenesis of human endometrial cancer.

Altered gene expression profile in vaginal polypoid endometriosis resembles peritoneal endometriosis and is consistent with increased local estrogen production

BACKGROUND

In a university hospital setting, a 25-year-old woman presented with large vaginal and cervical polyps. Past medical history was significant for stage IV endometriosis. Polypectomy was performed and the polyps were histologically consistent with endometriosis. Gene expression was compared with control vaginal tissue to assess if the altered gene expression profile was similar to peritoneal endometriosis.

METHODS AND RESULTS

Using quantitative reverse transcription, real-time PCR, estrogen receptor-β expression was found to be upregulated 10-fold while estrogen receptor-α expression was downregulated 5-fold in the vaginal polyp relative to control vaginal tissue. The estrogen-synthesizing enzyme aromatase was upregulated 8-fold and 3β-hydroxysteroid dehydrogenase was upregulated 400-fold in the polyp. Immunohistochemical staining revealed altered cell type localization for progesterone receptor in the polyp and increased cell proliferation in polyp stromal cells relative to control.

CONCLUSIONS

Increased proliferation in the vaginal polypoid endometriotic tissue may be due to increased local estrogen production. The altered gene expression profile was very similar to the altered gene expression profile seen in peritoneal endometriosis.

Raloxifene-stimulated experimental breast cancer with the paradoxical actions of estrogen to promote or prevent tumor growth: a unifying concept in anti-hormone resistance

We have previously demonstrated that prolonged treatments with raloxifene (RAL) in vitro will result in phase II RAL resistance and RAL-induced tumor growth. Clinical interest prompted us to re-examine RAL resistance in vivo, particularly the effects of long-term treatments (a decade or more) on the evolution of RAL resistance. In this study, we have addressed the question of this being a reproducible phenomenon in wild-type estrogen receptor (ER)-positive human breast cell line MCF-7. MCF-7 cells cultured under estrogen-deprived conditions in the presence of 1 microM RAL for more than a year develop RAL resistance resulting in an independent cell line, MCF7-RAL. The MCF7-RAL cells grow in response to both estradiol E2 and RAL. Fulvestrant (FUL) blocks RAL and E2-mediated growth. Transplantation of MCF7-RAL cells into athymic ovariectomized mice and treatment with physiologic doses of E2 causes early E2-stimulated tumor growth. In contrast, continuous treatment of implanted animals with daily oral RAL (1.5 mg daily) causes growth of small tumors within 15 weeks. Continuous re-transplantation of the tumors growing in RAL-treated mice indicated that RAL stimulated tumor growth. Tumors in the untreated mice did not grow. Bi-transplantation of MCF7-E2 and MCF7-RAL tumors into the opposing mammary fat pads of the same ovariectomized animal demonstrated that MCF7-E2 grew with E2 stimulation and not with RAL. Conversely, MCF7-RAL tumors grew with RAL and not E2, a characteristic of phase II resistance. Established phase II resistance of MCF7-RAL tumors was confirmed following up to 7 years of serial transplantation in RAL-treated athymic mice. The ERalpha was retained in these tumors. The cyclical nature of RAL resistance was confirmed and extended during a 2-year evolution of the resistant phases of the MCF7-RAL tumors. The MCF7-RAL tumors that initially were inhibited by E2 grew in the presence of E2 and subsequently grew with either RAL or E2. RAL remained the major grow stimulus and RAL enhanced E2-stimulated growth. Subsequent transplantation of E2 stimulated tumors and evaluations of the actions of RAL, demonstrated robust E2-stimulated growth that was blocked by RAL. These are the characteristics of the anti-estrogenic actions of RAL on E2-stimulated breast cancer growth with a minor component of phase I RAL resistance. Continuous transplantation of the phase I RAL-stimulated tumors for >8 months causes reversion to phase II resistance. These data and literature reports of the cyclical nature of anti-androgen/androgen responsiveness of prostate cancer growth, illustrate the generality of the evolution of anti-hormonal resistance in sex steroid-sensitive target tissues.

C-28/I2 and T/C-28a2 chondrocytes as well as human primary articular chondrocytes express sex hormone and insulin receptors--Useful cells in study of cartilage metabolism

Sex hormones and insulin have been implicated in articular cartilage metabolism. To supplement previous findings on the regulation of matrix synthesis with 17β-estradiol and insulin and to find a possible model to study cartilage metabolism in vitro, we evaluated the expression of estrogen receptors α and β (ERα, ERβ), androgen receptor (AR) and insulin receptor (IR), in immortalized C-28/I2 and T/C-28a2 chondrocytes and in human primary articular cartilage cells. Chondrocytes were treated with increasing concentrations of 17β-estradiol, dihydrotestosterone or insulin and analyzed by means of RT-PCR and Western blotting. Both cell lines as well as human articular chondrocytes expressed ER α and β, AR and IR at mRNA and protein levels. In immortalized C-28/I2 chondrocytes, we showed that increasing concentrations of 17β-estradiol diminished the 95kDa band of IR. Since 17β-estradiol suppresses insulin-induced proline incorporation and type II collagen synthesis, as we have previously demonstrated, our findings give the first clue that 17β-estradiol may have negative effects on cartilage anabolism triggered by insulin during hormonal imbalance. Compared to chondrocytes cultured without hormones, immunostaining for ERα/β, AR and IR was decreased in both cell lines after incubation of cells with the receptor-specific hormones. It can be assumed that C-28/I2 and T/C-28a2 chondrocytes interact with the respective hormones. Our findings provide a reproducible model for investigating sex hormone and insulin receptors, which are present in low concentrations in articular chondrocytes, in the tissue-specific context of cartilage metabolism.

Estrogen and selective estrogen receptor modulators regulate vascular endothelial growth factor and soluble vascular endothelial growth factor receptor 1 in human endometrial stromal cells

OBJECTIVE

To determine whether 17beta-estradiol (E(2)) and selective estrogen receptor modulators can regulate vascular endothelial growth factor (VEGF) and soluble VEGF receptor 1 (sVEGFR-1) as a VEGF antagonist in human endometrial stromal cells (ESCs).

DESIGN

In vitro experiment.

SETTING

Research laboratory at Kansai Medical University.

PATIENT(S)

Sixteen patients undergoing hysterectomy for benign reasons.

INTERVENTION(S)

The ESCs were cultured with E(2), 4-hydroxytamoxifen (OHT), and raloxifene.

MAIN OUTCOME MEASURE(S)

The VEGF and sVEGFR-1 messenger RNA (mRNA) levels in ESCs were determined using quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Free (unbound) VEGF and sVEGFR-1 protein levels from ESCs were measured using ELISA kits.

RESULT(S)

The E(2) significantly induced VEGF mRNA levels, whereas E2 caused a significant decrease in sVEGFR-1 messenger RNA (mRNA) levels. The E(2) or OHT significantly increased the VEGF production levels and attenuated the sVEGFR-1 production compared with control, but raloxifene had no significant effect. The decrease in levels of free VEGF was proportional to the increase in sVEGFR-1 levels in the culture media of ESCs.

CONCLUSION(S)

The E(2) or OHT stimulates VEGF production and concurrently attenuates sVEGFR-1 production in ESCs. This consequential increase in VEGF:sVEGFR-1 ratio might enhance the biological effects of VEGF on the angiogenic environment in human endometrium.

Comparative effects of estradiol, methyl-piperidino-pyrazole, raloxifene, and ICI 182 780 on gene expression in the murine uterus

Selective estrogen receptor modulators (SERMs) are potentially useful in treating various endometrial disorders, including endometrial cancer, as they block some of the detrimental effects of estrogen. It remains unclear whether each SERM regulates a unique subset of genes and, if so, whether the combination of a SERM and 17beta-estradiol has an additive or synergistic effect on gene expression. We performed microarray analysis with Affymetrix Mouse Genome 430 2.0 short oligomer arrays to determine gene expression changes in uteri of ovariectomized mice treated with estradiol (low and high dose), methyl-piperidino-pyrazole (MPP), ICI 182 780, raloxifene, and combinations of high dose of estradiol with one of the SERM and dimethyl sulfoxide (DMSO) vehicle control. The nine treatments clustered into two groups, with MPP, raloxifene, and high dose of estradiol in one, and low dose of estradiol, ICI + estradiol, ICI, MPP + estradiol, and raloxifene + estradiol in the second group. Surprisingly, combining a high dose of estradiol with a SERM markedly increased (P<0.02) the number of regulated genes compared with each individual treatment. Analysis of expression for selected genes in uteri of estradiol and SERM-treated mice by quantitative (Q)RT-PCR generally supported the microarray results. For some cancer-associated genes, including Klk1, Ihh, Cdc45l, and Cdca8, administration of MPP or raloxifene with estradiol resulted in greater expression than estradiol alone (P<0.05). By contrast, ICI 182 780 suppressed more genes governing DNA replication compared with MPP and raloxifene treatments. Therefore, ICI 182 780 might be superior to MPP and raloxifene to treat estrogen-induced endometrial cancer in women.

Effects of tamoxifen and raloxifene on normal human endometrial cells in an organotypic in vitro model

The selective estrogen receptor modulator tamoxifen is widely used in breast cancer therapy though its use is associated with an elevated risk of endometrial carcinoma. An organotypic culture model was employed here to examine the effects of tamoxifen and raloxifene, a related compound with no known adverse uterine effects, on epithelial cells of the premenopausal human endometrium. Changes in the expression levels of the proliferation marker Ki67, and estrogen and progesterone receptors were evaluated. No change in the Ki67 index compared to untreated controls was detected in cultures exposed to tamoxifen or tamoxifen+estradiol. In response to tamoxifen, the level of progesterone receptor-expressing organoids was shown to vary markedly between individual samples, whereas no change in estrogen receptor expression could be demonstrated. A significant decrease in Ki67 expression was observed in raloxifene-exposed cultures. Raloxifene or raloxifene+estradiol had no effect on progesterone receptor expression. The expression of estrogen receptor was markedly inhibited in response to raloxifene or raloxifene+estradiol in all but two samples displaying an intense estrogen receptor labelling. The present observations add to current clinical data on the respective estrogen receptor agonist and antagonist activities of tamoxifen and raloxifene on the human uterus by providing novel insights into the interindividual variation in cellular responses. Our organotypic model may have uses as an alternative to animal experimentation in preclinical screening of the endometrial effects of selective estrogen receptor modulators and may serve as a tool in personalized medicine by identifying patients with an increased risk of developing endometrial pathologies.

Retinoic acid (RA) regulates 17beta-hydroxysteroid dehydrogenase type 2 expression in endometrium: interaction of RA receptors with specificity protein (SP) 1/SP3 for estradiol metabolism

CONTEXT

The enzyme 17beta-hydroxysteroid dehydrogenase type 2 (HSD17B2) exerts a local antiestrogenic effect by metabolizing biologically active estradiol to inactive estrone in endometrial epithelial cells. Retinoic acid (RA) induces HSD17B2 expression, but the underlying mechanism is not known.

OBJECTIVE

Our objective was to elucidate the molecular mechanisms responsible for HSD17B2 expression in human endometrial cells.

METHOD

Human endometrial Ishikawa and RL95-2 cell lines were cultured in the presence or absence of RA to analyze endogenous HSD17B2 expression, transcription factor complex formation, and promoter activity.

RESULTS

RA induced HSD17B2 mRNA levels in a dose- and time-dependent manner in endometrial cells. The RA antagonist ANG11273 abolished RA-induced HSD17B2 expression. Small interfering RNA ablation of RA receptor (RAR)alpha or retinoid X receptor (RXR)alpha completely blocked RA-induced HSD17B2 gene expression. Analysis of serial deletion and site-directed mutants of the HSD17B2 promoter fused to a reporter gene indicated that RA induction requires a cis-regulatory sequence that binds the specificity protein (SP) class of transcription factors. Chromatin-immunoprecipitation-PCR and gel-shift assays showed that RARalpha/RXRalpha and SP1/SP3 interact with this HSD17B2 promoter sequence. Small interfering RNA ablation of SP1 and SP3 expression markedly decreased HSD17B2 basal expression and blocked RA-induced expression. Finally, immunoprecipitationimmunoblotting demonstrated RA-induced interactions between RARalpha/RXRalpha and SP1/SP3 in intact endometrial cells.

CONCLUSIONS

In endometrial epithelial cells, RA stimulates formation of a multimeric complex comprised of RARalpha/RXRalpha tethered to transcription factors SP1 and SP3 on the HSD17B2 promoter. Assembly of this transcriptional complex is necessary for RA induction of HSD17B2 expression and may be an important mechanism for local estradiol inactivation in the endometrium.

Non-nuclear actions of estrogen: new targets for prevention and treatment of cardiovascular disease

Gender-based differences in the incidence of hypertensive and coronary artery disease, the development of atherosclerosis, and myocardial remodeling after infarction are attributable to the indirect effect of estrogen on risk factor profiles, such as cholesterol levels, glucose metabolism, and insulin levels. More recent evidence, however, suggests that activated estrogen receptor (ER) mediates signaling cascades that culminate in direct protective effects such as vasodilation, inhibition of response to vessel injury, limiting myocardial injury after infarction, and attenuating cardiac hypertrophy. Although the ER is usually thought of as a ligand-dependent transcription factor, it can also rapidly mobilize signals at the plasma membrane and in the cytoplasm. Thus, a greater understanding of ER function and regulation may lead to the development of highly specific therapeutics that mediate the prevention and treatment of cardiovascular diseases.

SP1 and SP3 mediate progesterone-dependent induction of the 17beta hydroxysteroid dehydrogenase type 2 gene in human endometrium

The opposing actions of estrogen and progesterone during the menstrual cycle regulate the cyclical and predictable endometrial proliferation and differentiation that is required for implantation. Progesterone indirectly stimulates the expression of 17beta hydroxysteroid dehydrogenase type 2 (HSD17B2), which catalyzes the conversion of biologically potent estradiol to weakly estrogenic estrone in the endometrial epithelium. We previously demonstrated upregulation of the HSD17B2 gene in human endometrial epithelial cells by factors secreted from endometrial stromal cells in response to progesterone. We investigated the underlying mechanism by which these stroma-derived, progesterone-induced paracrine factors stimulate HSD17B2 expression. Here, we show that transcription factors SP1 and SP3 interact with specific motifs in HSD17B2 promoter to upregulate enzyme expression in human endometrial epithelial cell lines. Conditioned medium (CM) from progestin-treated stromal cells increased levels of SP1 and SP3 in endometrial epithelial cells and induced HSD17B2 mRNA expression. Mithramycin A, an inhibitor of SP1-DNA interaction, reduced epithelial HSD17B2 promoter activity in a dose-dependent manner. Serial deletion and site-directed mutants of the HSD17B2 promoter demonstrated that two overlapping SP1 motifs (nt -82/-65) are essential for induction of promoter activity by CM or overexpression of SP1/SP3. CM markedly enhanced, whereas anti-SP1/SP3 antibodies inhibited, binding of nuclear proteins to this region of the HSD17B2 promoter. In vivo, we demonstrated a significant spatiotemporal association between epithelial SP1/SP3 and HSD17B2 levels in human endometrial biopsies. Taken together, these data suggest that HSD17B2 expression in endometrial epithelial cells, and, therefore, estrogen inactivation, is regulated by SP1 and SP3, which are downstream targets of progesterone-dependent paracrine signals originating from endometrial stromal cells.

Growth regulation and transcriptional activities of estrogen and progesterone in human endometrial cancer cells

Estrogen-stimulated growth of the malignant human endometrium can be balanced by the differentiating properties of progesterone. To study the molecular basis behind this, gene expression profiling was performed using complementary DNA microarray analysis. In this study, the human endometrial cancer cell lines ECC-1 and PRAB-36 were used as models. The ECC-1 cell line, which expresses high levels of estrogen receptor alpha and is stimulated in growth by estrogens, was used to study estrogen regulation of gene expression. The Ishikawa sub-cell line PRAB-36, expressing both PRA and PRB, progesterone receptor isoforms, and inhibited in growth by progestagens, was used to study progesterone regulation of gene expression. Using these two well-differentiated human endometrial cancer cell lines, 148 estrogen- and 148 progesterone-regulated genes were identified. After functional classification, the estrogen- and progesterone-regulated genes could be categorized in different biologically relevant groups. Within the group of "cell growth and/or maintenance," 81 genes were clustered, from which a number of genes could be involved in arranging the cross talk that exists between estrogen and progesterone signaling. On the basis of analysis of the current findings, it is hypothesized that cross talk between estrogen and progestagen signaling does not occur by counterregulation of single genes, but rather at the level of differential regulation of different genes within the same functional families.

Molecular mechanisms of oestrogen and SERMs in endometrial carcinogenesis

Endometrial cancer is the most common gynaecological cancer, and is associated with endometrial hyperplasia, unopposed oestrogen exposure and adjuvant therapy for breast cancer using selective oestrogen-receptor modulators (SERMs), particularly tamoxifen. Oestrogen and SERMs are thought to be involved in endometrial carcinogenesis through their effects on transcriptional regulation. Ultimately, oestrogen and SERMs affect the transduction of cellular signalling pathways that govern cell growth and proliferation, through downstream effectors such as PAX2 (paired box 2).

Analysis of estrogen agonism and antagonism of tamoxifen, raloxifene, and ICI182780 in endometrial cancer cells: a putative role for the epidermal growth factor receptor ligand amphiregulin

OBJECTIVES

In different tissues, estrogens, selective estrogen receptor modulators (SERMs), and anti-estrogens exert different biologic activities. For the endometrium, estradiol and tamoxifen induce proliferation, and because of this, tamoxifen treatment of breast cancer patients results in a two- to sevenfold increased risk for development of endometrial cancer. Use of raloxifene, or the anti-estrogen ICI182780, does not result in such an increased risk. The objective of the current study was to generate and analyze gene expression profiles that reflect the transcriptional response of the human endometrium to estradiol, SERMs like tamoxifen and raloxifene, and anti-estrogens like ICI182780.

METHODS

Transient transfections were performed to analyze the transcriptional response of ECC-1 cells to estradiol, tamoxifen, raloxifene, and ICI182780. Subsequently, to reveal the molecular mechanism of action, gene expression profiles were generated and some of the observed regulated genes were confirmed by Northern blotting. Biostatistical methods were employed to analyze the expression profile results further, and amphiregulin effects on ECC-1 cell signaling were investigated using Northern and Western blotting, and 3H-thymidine incorporation.

RESULTS

Analysis of the profiles revealed that estradiol, tamoxifen, raloxifene, and ICI182780 influence the same biologic processes, but they do so via regulation of different sets of genes. Upon construction of a genetic network it was observed that the largest possible network centered on epidermal growth factor (EGF) receptor signaling. Furthermore, the EGF receptor ligand amphiregulin was differentially regulated by all four ligands. Next it was shown that amphiregulin indeed could stimulate EGF receptor signaling in ECC-1 cells. Based on these results, it was hypothesized that EGF receptor signaling could differentially be affected by estrogen, tamoxifen, raloxifene, and ICI182780 because these four compounds differentially regulate the EGF receptor ligand amphiregulin.

CONCLUSIONS

Regulation of amphiregulin coincides with the described in vivo effect of the four ligands on the endometrium. Therefore, it is possible that modulation of EGF receptor signaling is a significant player in estrogen-agonistic growth of the endometrium and needs to be investigated further.

Dioxin exerts anti-estrogenic actions in a novel dioxin-responsive telomerase-immortalized epithelial cell line of the porcine oviduct (TERT-OPEC)

Oviduct epithelial cells are important for the nourishment and survival of ovulated oocytes and early embryos, and they respond to the steroid hormones estrogen and progesterone. Endocrine-disrupting polyhalogenated aromatic hydrocarbons (PHAH) are environmental toxins that act in part through the ligand-activated transcription factor arylhydrocarbon receptor (AhR; dioxin receptor), and exposure to PHAH has been shown to decrease fertility. To investigate effects of PHAHs on the oviduct epithelium as a potential target tissue of dioxin-type endocrine disruptors, we have established a novel telomerase-immortalized oviduct porcine epithelial cell line (TERT-OPEC). TERT-OPEC exhibited active telomerase and the immunoreactive epithelial marker cytokeratin but lacked the stromal marker vimentin. TERT-OPEC contained functional estrogen receptor (ER)-alpha and AhR, as determined by the detection of ER-alpha- and AhR-specific target molecules. Treatment of TERT-OPEC with the AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in a significant increase in the production of the cytochrome P-450 microsomal enzyme CYP1A1. Activated AhR caused a downregulation of ER nuclear protein fraction and significantly decreased ER-signaling in TERT-OPEC as determined by ERE-luciferase transient transfection assays. In summary, the TCDD-induced and AhR-mediated anti-estrogenic responses by TERT-OPEC suggest that PHAH affect the predominantly estrogen-dependent differentiation of the oviduct epithelium within the fallopian tube. This action then alters the local endocrine milieu, potentially resulting in a largely unexplored cause of impaired embryonic development and female infertility.

Hypomethylation-linked activation of PAX2 mediates tamoxifen-stimulated endometrial carcinogenesis

Tamoxifen, a selective oestrogen receptor modulator, has been used in the treatment of all stages of hormone-responsive breast cancer. However, tamoxifen shows partial oestrogenic activity in the uterus and its use has been associated with an increased incidence of endometrial cancer. The molecular explanation for these observations is not known. Here we show that tamoxifen and oestrogen have distinct but overlapping target gene profiles. Among the overlapping target genes, we identify a paired-box gene, PAX2, that is crucially involved in cell proliferation and carcinogenesis in the endometrium. Our experiments show that PAX2 is activated by oestrogen and tamoxifen in endometrial carcinomas but not in normal endometrium, and that this activation is associated with cancer-linked hypomethylation of the PAX2 promoter.

The effects of the selective estrogen receptor modulators, methyl-piperidino-pyrazole (MPP), and raloxifene in normal and cancerous endometrial cell lines and in the murine uterus

Since estrogens have vital functions in the uterus but might also contribute to endometrial cancer, we sought to determine the in vitro effects of methyl-piperidino-pyrazole (MPP), raloxifene, and beta-estradiol on Ishikawa and RL-95 endometrial cancer, and ovine luminal endometrial (oLE) cell lines and the in vivo effects of these compounds in the rodent uterus. MPP and raloxifene (1 nM) induced significant apoptosis in the endometrial cancer and oLE cell lines compared to beta-estradiol treated and control cells (P <or= 0.0001-0.001). To determine the in vivo uterine effects of these compounds, ovariectomized wild-type (WT) and estrogen receptor-beta knockout (ERbetaKO) mice were treated with 25, 50, 100, or 150 microg of each compound. Although raloxifene caused no significant increase in uterine weight, the presumptive ERalpha antagonist, MPP (25-150 microg) increased uterine weight, and cell proliferation significantly relative to vehicle control in WT and ERbetaKO mice (P <or= 0.001). However, MPP did not increase uterine wet weight as effectively as beta-estradiol (P <or= 0.0001), and administration of either 50 microg of MPP or raloxifene effectively reversed the positive effects of 50 and 100 microg beta-estradiol. Unexpectedly, in view of the in vitro studies, MPP and raloxifene treatment of ovariectomized mice did not induce apoptosis of the luminal epithelial cells but rather these compounds induced apoptosis of the underlying uterine stromal cells. These results demonstrate that MPP and raloxifene can exert apparently contrasting in vitro versus in vivo effects, and that they have mixed agonist/antagonist action on murine uterine ERalpha in vivo.

IL-1β-Mediated Proinflammatory Responses Are Inhibited by Estradiol via Down-Regulation of IL-1 Receptor Type I in Uterine Epithelial Cells

The objective of this study was to examine the effects of sex hormones on IL-1beta-mediated responses by uterine epithelial cells. The mRNA expression and secretion of human beta-defensin-2 and CXCL8 by uterine epithelial cells was examined following stimulation with IL-1beta in the presence of estradiol or progesterone. Estradiol inhibited the IL-1beta-mediated mRNA expression and secretion of human beta-defensin-2 and CXCL8 by uterine epithelial cells while progesterone had no effect. Inhibition of the IL-1beta-mediated response by estradiol was dose dependent, with maximal inhibition observed using 10(-7) to 10(-10) M, and was shown to be mediated through the estrogen receptor because addition of a pure estrogen receptor antagonist abrogated this effect. The mechanism by which estradiol inhibits IL-1beta-mediated responses by uterine epithelial cells appears to be the down-modulation of the IL-1R type I, thereby reducing the uterine epithelial cell's ability to respond to IL-1beta. These results suggest that the inhibitory effect of estradiol on IL-1beta-mediated inflammatory responses by uterine epithelial cells indicates a link between the endocrine and immune systems and may be crucial for dampening proinflammatory responses during the time of ovulation or pregnancy.

The G protein-coupled receptor GPR30 mediates the proliferative effects induced by 17beta-estradiol and hydroxytamoxifen in endometrial cancer cells

The growth of both normal and transformed epithelial cells of the female reproductive system is stimulated by estrogens, mainly through the activation of estrogen receptor alpha (ERalpha), which is a ligand-regulated transcription factor. The selective ER modulator tamoxifen (TAM) has been widely used as an ER antagonist in breast tumor; however, long-term treatment is associated with an increased risk of endometrial cancer. To provide new insights into the potential mechanisms involved in the agonistic activity exerted by TAM in the uterus, we evaluated the potential of 4-hydroxytamoxifen (OHT), the active metabolite of TAM, to transactivate wild-type ERalpha and its splice variant expressed in Ishikawa and HEC1A endometrial tumor cells, respectively. OHT was able to antagonize only the activation of ERalpha by 17beta-estradiol (E2) in Ishikawa cells, whereas it up-regulated c-fos expression in a rapid manner similar to E2 and independently of ERalpha in both cell lines. This stimulation occurred through the G protein-coupled receptor named GPR30 and required Src-related and epidermal growth factor receptor tyrosine kinase activities, along with the activation of both ERK1/2 and phosphatidylinositol 3-kinase/AKT pathways. Most importantly, OHT, like E2, stimulated the proliferation of Ishikawa as well as HEC1A cells. Transfecting a GPR30 antisense expression vector in both endometrial cancer cell lines, OHT was no longer able to induce growth effects, whereas the proliferative response to E2 was completely abrogated only in HEC1A cells. Furthermore, in the presence of the inhibitors of MAPK and phosphatidylinositol 3-kinase pathways, PD 98059 and wortmannin, respectively, E2 and OHT did not elicit growth stimulation. Our data demonstrate a new mode of action of E2 and OHT in endometrial cancer cells, contributing to a better understanding of the molecular mechanisms involved in their uterine agonistic activity.

The consequences of exhaustive antiestrogen therapy in breast cancer: estrogen-induced tumor cell death

Forty years ago, the endocrine treatment for breast cancer was a last resort at palliation before the disease overwhelmed the patient (1). Ovarian ablation was the treatment of choice for the premenopausal patient, whereas either adrenalectomy or, paradoxically, high-dose synthetic estrogen therapy were used for treatment in postmenopausal patients. A reduction or an excess of estrogen provoked objective responses in one out of three women. Unfortunately, there was no way of predicting who would respond to endocrine ablation, and because so few patients responded there was no enthusiasm for developing new endocrine agents. All hopes for a cure for breast cancer turned to appropriate combinations of cytotoxic chemotherapy. Today tamoxifen, a nonsteroidal antiestrogen (2), has proven to be effective in all stages of premenopausal and postmenopausal breast cancer, and several new endocrine strategies, including aromatase inhibitors, luteinizing-hormone releasing hormone (LHRH) superagonists, and a pure antiestrogen (fulvestrant), are now available for breast cancer treatment. Additionally, tamoxifen and raloxifene, a related compound, are used to reduce the risk of breast cancer and osteoporosis, respectively, in high-risk groups (3). Hormonal modulation and strategies to prevent the actions of estrogen in the breast are ubiquitous. However, with successful changes in treatment strategies comes the consequence of change. This minireview will describe the current strategies for the treatment and prevention of breast cancer and present emerging new concepts about the consequences of exhaustive antiestrogen treatment on therapeutic resistance.

Raloxifene therapy in postmenopausal women is associated with a significant reduction in the concentration of serum vascular endothelial growth factor

OBJECTIVE

To determine whether raloxifene has an effect on serum vascular endothelial growth factor (VEGF) concentration in postmenopausal women.

DESIGN

A randomized, placebo-controlled trial.

SETTING

University-based obstetrics and gynecology unit.

PATIENT(S)

Fifty postmenopausal women who did not receive any hormone therapy in the 6 months preceding the study.

INTERVENTION(S)

The participants were randomly assigned on a one-to-one basis to receive either raloxifene (60 mg daily) or placebo for 36 weeks.

MAIN OUTCOME MEASURE(S)

Serum VEGF concentrations at baseline and at 12 weeks and 36 weeks after the commencement of intervention.

RESULT(S)

The serum VEGF concentrations in the raloxifene group were significantly reduced from 247 +/- 16 pg/mL at baseline to 195 +/- 11 pg/mL at 36 weeks after starting raloxifene. The placebo group showed no significant change in the serum VEGF concentrations throughout the intervention period.

CONCLUSION(S)

Raloxifene therapy in postmenopausal women is associated with a significant reduction in serum VEGF concentration.

Changing role of the oestrogen receptor in the life and death of breast cancer cells

The oestrogen receptor (ER) has proven to be an extraordinarily successful target for breast cancer treatment and prevention. The clinical use of tamoxifen, a nonsteroidal antioestrogen, demonstrated (1) that the strategic use of adjuvant tamoxifen in ER-positive patients could save lives and (2) that a selective ER modulator (SERM) could reduce the incidence of breast cancer in high-risk women. The ER is now the target for new and safer therapies such as the aromatase inhibitors and the pure antioestrogens that either block oestrogen synthesis or destroy the ER. However, the use of raloxifene, a SERM to prevent osteoporosis with the potential to prevent breast cancer has introduced a new dimension into preventive oncology. The widespread use of endocrine modulators (SERMs, aromatase inhibitors, and pure antioestrogens) raised the question of drug resistance. It is now clear that endocrine resistance can evolve through stages. Once a breast tumour becomes resistant to SERMs, the growth is stimulated by either the SERM or oestrogen. This is why an aromatase inhibitor is effective following SERM resistance and withdrawal. However, the extended use of repeated endocrine therapies now supersensitized the cells to oestrogen that causes apoptosis through the ER. We suggest that future clinical treatment strategies incorporate an 'oestrogen purge' to both enhance the actions of chemotherapy or completely reverse endocrine resistance and restore endocrine sensitivity. These new data build on the idea that breast cancer can be controlled as a chronic disease and will permit patients to live long and productive lives during targeted maintenance treatment.

Raloxifene analog LY117018 enhances the regeneration of sciatic nerve in ovariectomized female mice

The aim of this study was to examine the effects of LY117018, a selective estrogen receptor modulator, on peripheral nerve regeneration, using a model of sciatic nerve crush injury in mice. Sciatic functional index, an index of functional recovery, was significantly higher in LY117018 treated mice throughout regeneration. Analysis of semi-thin sections revealed a significant increase in both the total number of regenerating nerve fibers at day 7, and the mean axonal area of myelinated fibers at 7, 14, and 21 days after injury, in LY117018 treated mice. Analysis of axonal transport through retrograde labeling of motor neurons showed that LY117018 increased transport, and ICI 182,780 blocked the effects of LY117018, delineating estrogen receptors as its target. Our study suggests that LY117018 may markedly accelerate peripheral nerve regeneration and functional recovery through activation of estrogen receptors.

A well-defined in vitro three-dimensional culture of human endometrium and its applicability to endometrial cancer invasion

A three-dimensional (3-D) endometrium culture was established, in which human endometrial stromal cells embedded in a mixture of collagen I, a major component of extracellular matrix, and matrigel, a basement membrane material, supports the epithelial cells seeded on top of the collagen/matrigel matrix. The biological growth and differentiation of the epithelial cells were studied microscopically and immunohistochemically. Transmission electron microscopy showed a polarized columnar epithelium in monolayer with basally positioned nuclei. Scanning electron microscopy revealed a confluent epithelium with an abundance of microvilli and cilia as well as pinopodes on the apical surface. An immunohistochemical staining showed that integrin alpha1, alpha4, and beta3 were co-localized with cytokeratin, confirming the epithelial origin of the cells. In contrast, immunoreactivity against cyclooxygenase-1 or -2 was positive in both epithelial and stromal cells. When epithelial cells were replaced by KLE cells, an endometrial cancer cell of epithelial origin, invasion of KLE cells into the stromal fraction was observed. The invasion was closely correlated to expression of matrix metalloproteinases and their tissue inhibitors of metalloproteinases in a manner consistent with paracrine fashion. The present 3-D culture imitates the normal endometrium physiologically as well as morphologically, thus provides an excellent in vitro tissue suitable for reproducing in vivo physiological processes, including endometrial cancer invasion.

Effect of raloxifene, 17beta-estradiol, and progesterone on mRNA for vascular endothelial growth factor isoforms 121 and 165 and thrombospondin-1 in Ishikawa cells

OBJECTIVE

To compare the mRNA expression of vascular endothelial growth factor (VEGF) 121 and 165 isoforms and thrombospondin-1 (TSP-1) after raloxifene, 17beta-E(2), and P administration in cultured Ishikawa cells.

DESIGN

Prospective basic research study.

SETTING

Jones Institute for Reproductive Medicine, Eastern Virginia Medical School, Norfolk, Virginia.

PATIENT(S)

None.

INTERVENTION(S)

Ishikawa cells were cultured in vitro. Raloxifene, 17beta-E(2), and P at concentrations of 0.01, 0.1, and 1.0 microM were added to confluent cells.

MAIN OUTCOME MEASURES

The VEGF 121 and 165 isoforms and TSP-1 mRNA expression from treated Ishikawa cells were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULT(S)

17beta-Estradiol increased both VEGF 121 and 165 mRNA compared to control. Raloxifene did not increase either VEGF 121 or 165 mRNA above control values. Progesterone at all concentrations did not increase VEGF 121 isoform mRNA, whereas VEGF 165 isoform was minimally increased by P at the lowest concentration. Progesterone and raloxifene increased TSP-1 mRNA expression. 17beta-Estradiol did not stimulate TSP-1 mRNA expression at any concentration.

CONCLUSION(S)

Raloxifene did not stimulate VEGF 121 and 165, whereas it increased TSP-1 mRNA synthesis in Ishikawa cells. Our hypothesis is that raloxifene's lack of endometrial stimulation may be partly mediated by an antiangiogenic effect.

The effects of estradiol and selective estrogen receptor modulators on gene expression and messenger RNA stability in immortalized sheep endometrial stromal cells and human endometrial adenocarcinoma cells

The purpose of this study was to identify an endometrial cell line that maintained the E2 up-regulation of estrogen receptor (ER) mRNA by enhanced message stability and to assess its dependence on ER protein. Estradiol (E2) effects on gene expression were measured in three cell lines: one immortalized from sheep endometrial stroma (ST) and two from human endometrial adenocarcinomas (Ishikawa and ECC-1). E2 up-regulated ER mRNA levels in ST and Ishikawa cells, but down-regulated ER mRNA levels in ECC-1 cells. E2 up-regulated progesterone receptor (PR), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and transforming growth factor-alpha (TGF-alpha) in both Ishikawa and ECC-1 cells. The selective estrogen receptor modulator ICI 182,780 antagonized the E2-induced up-regulation of ER and/or PR mRNA levels in all three cells, while another, GW 5638, antagonized the up-regulation of PR mRNA in Ishikawa and ECC-1 cells. In mechanistic studies, E2 had no effect on ER mRNA stability in ST cells and it destabilized ER mRNA in ECC-1 cells. Thus, Ishikawa cells appear to be the most physiologically relevant cell line in which to study the up-regulation of ER mRNA levels by enhanced mRNA stability. Its antagonism by ICI 182,780 reveals that ER protein is involved in this E2 response.

Nonnuclear actions of estrogen

Estrogen has long been observed to endow cardiovascular protective effects, as evidenced by sex-specific differences in the incidence of hypertensive and coronary artery disease, the development of atherosclerosis, and myocardial remodeling after infarction. To exert its tissue-specific effects, the classic estrogen receptor (ER) functions as a ligand-dependent transcription factor. However, there is growing evidence that in response to 17beta-estradiol and heterologous signals, the ER can also mediate signaling cascades at the membrane and in the cytoplasm via various second messengers, such as receptor-mediated protein kinases. This review summarizes the current understanding of nonnuclear ER signaling and discusses the relevance to eliciting the beneficial cardiovascular effects of estrogen. These include vasodilation, inhibition of response to vessel injury, limiting myocardial injury after infarction, and attenuating cardiac hypertrophy. Defining the full repertoire of ER function promises to expose novel, highly specific targets for pharmacological interventions and may ultimately lead to the primary and secondary prevention of cardiovascular diseases.