Progestin Resistance and Corresponding Management of Abnormal Endometrial Hyperplasia and Endometrial Carcinoma

With a younger tendency in morbidity age, endometrial cancer (EC) incidence has grown year after year. Worse, even more commonly occurring is endometrial hyperplasia (EH), which is a precancerous endometrial proliferation. For young women with early EC and EH who want to preserve fertility, progestin therapy has been utilized as a routine fertility-preserving treatment approach. Nevertheless, progestin medication failure in some patients is mostly due to progestin resistance and side effects. In order to further analyze the potential mechanisms of progestin resistance in EH and EC, to provide theoretical support for effective therapeutic strategies, and to lay the groundwork for searching novel treatment approaches, this article reviews the current therapeutic effects of progestin in EH and EC, as well as the mechanisms and molecular biomarkers of progestin resistance, and systematically expounds on the potential therapeutic methods to overcome progestin resistance.

Irilone, a Red Clover Isoflavone, Combined with Progesterone Enhances PR Signaling through the Estrogen and Glucocorticoid Receptors

Trifolium pratense L. (red clover) is a popular botanical supplement used for women's health. Irilone isolated from red clover previously demonstrated progestogenic potentiation activity. In this study, irilone enhanced progesterone signaling was determined to not occur due to post-translational phosphorylation or by reducing progesterone receptor (PR) protein levels but instead increased PR protein levels in T47D breast cancer cells, which could be blocked by estrogen receptor (ER) antagonists, suggesting an ER dependent effect. Further, irilone increased luciferase activity from a hormone responsive element in a cell line that lacked ER and PR but expressed the glucocorticoid receptor (GR). A siRNA knockdown of GR in Ishikawa PR-B endometrial cancer cells reduced irilone's ability to enhance progesterone signaling. In an ovariectomized CD-1 mouse model, irilone did not induce uterine epithelial cell proliferation. The mechanism of action of irilone gives insight into PR crosstalk with other steroid hormone receptors, which can be important for understanding botanicals that are used for women's health.

Baicalein Is a Phytohormone that Signals Through the Progesterone and Glucocorticoid Receptors

While flavonoids have been studied extensively for estrogen receptor activity, they have not been well studied for their ability to modify progesterone receptor (PR) and glucocorticoid receptor (GR) signaling. Three flavonoid compounds, tangeretin, wogonin, and baicalein, were selected for testing for PR and GR activity based on their structural similarity to known phytoprogesterone-like compounds. Each compound was docked in the binding pocket of PR and GR. Of these compounds, baicalein was predicted to be most likely to bind to both receptors. A fluorescence polarization competitive binding assay for PR and GR confirmed that baicalein binds to both the PR and GR with IC₅₀ values of 15.30 μM and 19.26 μM, respectively. In Ishikawa PR-B and T47D cells, baicalein acted as a PR antagonist in a hormone response element (HRE) luciferase (Luc) assay. In OVCAR5 cells, which only express GR, baicalein was a GR agonist via an HRE/Luc assay and induced GR target genes, FKBP5 and GILZ. RU486, a PR and GR antagonist, abrogated baicalein's activity in OVCAR5 cells, confirming baicalein's activity is mediated through the GR. In vivo, baicalein administered intraperitoneally to female mice twice a week for 4 weeks at a dose of 25 mg/kg induced the GR target gene GILZ in the reproductive tract, which was blocked by RU486. In summary, baicalein has PR antagonist and GR agonist activity in vitro and demonstrates GR agonist activity in the uterus in vivo.

CRISPR/Cas9-Mediated Gene Knockout of ARID1A Promotes Primary Progesterone Resistance by Downregulating Progesterone Receptor B in Endometrial Cancer Cells

Medroxyprogesterone (MPA) is used for the conservative treatment of endometrial cancer. Unfortunately, progesterone resistance seriously affects its therapeutic effect. The purpose of the current study was to investigate the influence of deletion of AT-rich interactive domain 1A (ARID1A) in progesterone resistance in Ishikawa cells. Ablation of ARID1A was conducted through the CRISPR/Cas9 technology. Acquired progesterone-resistant Ishikawa (Ishikawa-PR) cells were generated by chronic exposure of Ishikawa cells to MPA. The sensitivity of the parental Ishikawa, Ishikawa-PR, and ARID1A-deficient cells to MPA and/or LY294002 was determined using the Cell Counting Kit-8 (CCK-8) assay and flow cytometry analysis. In addition, Western blot analysis and reverse transcription-polymerase chain reaction was performed to evaluate the mRNA and protein expression levels of ARID1A, progesterone receptor B (PRB), and P-AKT. Both Ishikawa-PR and ARID1A knockout cells showed insensitivity to MPA, downregulation of PRB, and hyperphosphorylation of AKT compared to the parental Ishikawa cells. Pretreatment with LY294002 significantly enhanced the ability of MPA to suppress proliferation and to induce apoptosis in the parental and Ishikawa-PR cells via the inhibition of AKT activation and upregulation of PRB transcriptional activity. However, the PRB transcriptional activity and insensitivity to MPA were irreversible by LY294002 in ARID1A-deficient cells. Ablation of ARID1A is associated with low PRB expression, which serves an important role in primary progesterone resistance. Akt inhibition cannot rescue PRB or sensitize to MPA in ARID1A knockout cells. These findings suggest that ARID1A may act as a reliable biomarker to predict the response for the combination of AKT inhibitor and MPA treatment.

Investigations on the mechanism of progesterone in inhibiting endometrial cancer cell cycle and viability via regulation of long noncoding RNA NEAT1/microRNA-146b-5p mediated Wnt/β-catenin signaling

Progesterone is often used to protect the endometrium and prevent endometrial cancer. An intensive study on its molecular mechanism in endometrial cancer would contribute to the development of more promising therapies. Relevant lncRNAs and mRNAs expression data in endometrial cancer cell line Ishikawa pretreated and post-treated with progesterone were derived from Gene Expression Omnibus (accession no. GSE29435), and then we analyzed long noncoding RNAs and mRNAs with differential expressions in two different conditions. The Cytoscape software, TargetScan, miRanda, and Human microRNA Disease Database (HMDD) websites were employed. Gene set enrichment analysis (GSEA) was used to determine related Kyoto Encyclopedia of Genes and Genomes pathways alteration in Ishikawa cells treated with progesterone. In addition to bioinformatics analysis, Reverse Transcription-Polymerase Chain Reaction (RT-PCR), Western blot, and dual-luciferase reporter assays were performed. The impact of progesterone on cell propagation and cell cycle was testified by colony formation and flow cytometry analysis. LncRNA nuclear enriched abundant transcript 1 (NEAT1) was the most significantly downregulated lncRNA in endometrial cancer cells treated with progesterone. Lymphoid enhancing factor 1 (LEF1) was positively associated with NEAT1, and eventually hsa_miR-146b-5p was validated to target both LEF1 and NEAT1. Wnt/β-catenin signaling pathway was identified to involve in endometrial cancer. NEAT1 or LEF1 was overexpressed in endometrial cancer cells while downregulated following post-treatment with progesterone. Conversely, miR-146b-5p was notably decreased in Ishikawa cells while upregulated after treatment with progesterone. Downstream gene c-myc or MMP9 regulated by upstream gene LEF1 in Wnt/β-catenin signaling pathway was remarkably increased in Ishikawa cells and positively related with NEAT1. Progesterone inhibited cell cycle and viability through regulating NEAT1/miR-146b-5p axis via Wnt/β-catenin signaling pathway. Progesterone exerted suppressive influence on endometrial cancer progression via regulation of lncRNA NEAT1/miR-146b-5p-mediated Wnt/β-catenin signaling pathway, which might reveal new strategies for developing more effective therapeutics. © 2018 IUBMB Life, 71(1):223-234, 2019.

Epigenetics in endometrial carcinogenesis - part 1: DNA methylation

Carcinogenesis is a multistep multifactorial process that involves the accumulation of genetic and epigenetic alterations. In the past two decades, there has been an exponential growth of knowledge establishing the importance of epigenetic changes in cancer. Our work focused on reviewing the main role of epigenetics in the pathogenesis of endometrial carcinoma, highlighting the reported results concerning each epigenetic mechanistic layer. The present review is the first part of this work, in which we examined the contribution of DNA methylation alterations for endometrial carcinogenesis.

Progesterone-induced miR-133a inhibits the proliferation of endometrial epithelial cells

AIM

This study aimed to understand the role of miR-133a in progesterone actions, explore the regulative mechanism of the progesterone receptor, and investigate the effects of miR-133a on the progesterone-inhibited proliferation of mouse endometrial epithelial cells.

METHODS

The expression of miR-133a induced by progesterone was detected by quantitative real-time PCR both in vivo and in vitro. Ishikawa subcell lines stably transfected with progesterone receptor subtypes were used to determine the receptor mechanism of progesterone inducing miR-133a. Specific miR-133a mimics or inhibitors were transfected into mouse uteri and primary cultured endometrial epithelial cells to overexpress or downregulate the miR-133a. The roles of miR-133a in the cell cycle and proliferation of endometrial epithelial cells were analysed by flow cytometry and Edu incorporation analysis. The protein levels of cyclinD2 in uterine tissue sections and primary cultured endometrial epithelial cells were determined by immunohistochemistry and Western blot analysis.

RESULTS

Progesterone could induce miR-133a expression in a PRB-dependent manner in endometrial epithelial cells. miR-133a inhibited endometrial epithelial cell proliferation by arresting cell cycle at the G₁ -S transition. Moreover, miR-133a acted as an inhibitor in downregulating cyclinD2 in endometrial epithelial cells.

CONCLUSION

We showed for the first time that progesterone-induced miR-133a inhibited the proliferation of endometrial epithelial cells by downregulating cyclinD2. Our research indicated an important mechanism for progesterone inhibiting the proliferation of endometrial epithelial cells by inducing special miRNAs to inhibit positive regulatory proteins in the cell cycle.

Progesterone-Induced miR-152 Inhibits the Proliferation of Endometrial Epithelial Cells by Downregulating WNT-1

Progesterone (P4) is an important ovarian hormone that inhibits estrogen-dependent proliferation of endometrial epithelial cells (EECs). miR-152 has been reported to be a cell cycle regulator. In this study, we first demonstrated that P4 induced the expression of miR-152 in ovariectomized mice and Ishikawa cell. miR-152 was detected in the human endometrial cell lines that were stably transfected with P4 receptor. Results showed that P4 induced its expression through its receptor B subtype. Then, using the specific miRNA mimic and inhibitor, we proved that miR-152 impeded G₁/S transition in the cell cycle of EECs and inhibited cellular proliferation via downregulating WNT-1 in mice and human endometrial cancer cell lines (Ishikawa, HEC-1-b, and KLE). miR-152 induced by P4 is an important inhibitor for the proliferation of EECs. miR-152 may be an important tumor suppressor microRNA in endometrial cancer.

Immunomodulatory and Transcriptional Effects of Progesterone Through Progesterone A and B Receptors in Hec50co Poorly Differentiated Endometrial Cancer Cells

OBJECTIVE

Derivatives of progesterone, progestins, are used to treat endometrial cancer; however, the pathways activated by the hormone have not been fully investigated. Progesterone acts through two receptor isoforms, progesterone receptors A and B (PRA and PRB), transcription factors that control the expression of downstream genes leading to endometrial differentiation. The purpose of this study was to perform an expression analysis to identify the mechanisms underlying progesterone's growth suppressive and immunomodulatory effects in endometrial cancer.

METHODS

To study the molecular effects of progesterone, PRs were introduced into Hec50co cells. Expression array analyses followed by confirmatory semiquantitive reverse-transcriptase polymerase chain reaction (RT-PCR) experiments were performed.

RESULTS

Expression analysis demonstrated a significant effect of progesterone after 12 hours of treatment on a number of genes, including cell signaling, DNA remodeling, apoptotic, tumor-suppressor, and transcription factors. Of particular interest was the consistent modulation of cytokines, which generally predicted for a powerful anti-inflammatory effect of progesterone through PR. Specifically, pro-inflammatory genes such as TNFalpha, IL-1beta, and MCP-1/MCAF-1 were down-regulated and anti-inflammatory genes such as TRAP1 and SMAD4 were induced.

CONCLUSION

We have discovered that progesterone has a modulatory effect on inflammation and many other important cellular functions. These effects likely underlie the inhibitory effects of progesterone on tumor growth and invasion.

Akt regulates progesterone receptor B-dependent transcription and angiogenesis in endometrial cancer cells

Progestins have long been used clinically for the treatment of endometrial cancers, however, the response rates to progestin therapy vary and the molecular mechanisms behind progestin insensitivity are poorly understood. We hypothesized that in PTEN mutated endometrial cancers, hyperactive Akt signaling downregulates Progesterone Receptor B (PRB) transcriptional activity, leading to overall impaired progestin responses. We report that inhibition of Akt with the Akt inhibitor, MK-2206 (MK), in conjunction with progestin (R5020) treatment, is sufficient to upregulate a subset of PRB target genes in Ishikawa cells stably expressing PRB (PRB-Ishikawa). Through gene ontology analysis of Akt-regulated PRB target genes, angiogenesis was found to be the principle process regulated by Akt-PRB. To further interrogate the mechanism by which Akt modulates PRB transcriptional activity, ChIP-Mass Spectrometry was performed to identify potential cofactors that differentially interact with PRB in the presence of the R5020 and MK+R5020. 14-3-3σ was identified as a protein enriched in the MK+R5020 dataset, and it was demonstrated that 14-3-3σ is required for the upregulation in PRB target gene expression following inhibition of Akt. In order to determine the ramifications of MK+R5020 treatment on angiogenesis, in vitro assays were performed and combinatorial MK+R5020 treatment significantly decreased endothelial cell invasion and tube formation more than MK or R5020 treatment alone. Furthermore, we found that combinatorial MK-2206+Progesterone treatments decreased angiogenesis and proliferation in the Pten^d/d conditional mouse model of endometrial cancer. Taken together, these findings suggest that a combinatorial therapeutic approach utilizing Akt inhibitors with progestins may improve the efficacy of progestin therapy for the treatment of endometrial cancer.

A new strategy for selective targeting of progesterone receptor with passive antagonists

Currently available progesterone (P4) receptor (PR) antagonists, such as mifepristone (RU486), lack specificity and display partial agonist properties, leading to potential drawbacks in their clinical use. Recent x-ray crystallographic studies have identified key contacts involved in the binding of agonists and antagonists with PR opening the way for a new rational strategy for inactivating PR. We report here the synthesis and characterization of a novel class of PR antagonists (APRn) designed from such studies. The lead molecule, the homosteroid APR19, displays in vivo endometrial anti-P4 activity. APR19 inhibits P4-induced PR recruitment and transactivation from synthetic and endogenous gene promoters. Importantly, it exhibits high PR selectivity with respect to other steroid hormone receptors and is devoid of any partial agonist activity on PR target gene transcription. Two-hybrid and immunostaining experiments reveal that APR19-bound PR is unable to interact with either steroid receptor coactivators 1 and 2 (SRC1 and SCR2) or nuclear receptor corepressor (NcoR) and silencing mediator of retinoid acid and thyroid hormone receptor (SMRT), in contrast to RU486-PR complexes. APR19 also inhibits agonist-induced phosphorylation of serine 294 regulating PR transcriptional activity and turnover kinetics. In silico docking studies based on the crystal structure of the PR ligand-binding domain show that, in contrast to P4, APR19 does not establish stabilizing hydrogen bonds with the ligand-binding cavity, resulting in an unstable ligand-receptor complex. Altogether, these properties highly distinguish APR19 from RU486 and likely its derivatives, suggesting that it belongs to a new class of pure antiprogestins that inactivate PR by a passive mechanism. These specific PR antagonists open new perspectives for long-term hormonal therapy.

Progesterone action in endometrial cancer, endometriosis, uterine fibroids, and breast cancer

Progesterone receptor (PR) mediates the actions of the ovarian steroid progesterone, which together with estradiol regulates gonadotropin secretion, prepares the endometrium for implantation, maintains pregnancy, and differentiates breast tissue. Separation of estrogen and progesterone actions in hormone-responsive tissues remains a challenge. Pathologies of the uterus and breast, including endometrial cancer, endometriosis, uterine fibroids, and breast cancer, are highly associated with estrogen, considered to be the mitogenic factor. Emerging evidence supports distinct roles of progesterone and its influence on the pathogenesis of these diseases. Progesterone antagonizes estrogen-driven growth in the endometrium, and insufficient progesterone action strikingly increases the risk of endometrial cancer. In endometriosis, eutopic and ectopic tissues do not respond sufficiently to progesterone and are considered to be progesterone-resistant, which contributes to proliferation and survival. In uterine fibroids, progesterone promotes growth by increasing proliferation, cellular hypertrophy, and deposition of extracellular matrix. In normal mammary tissue and breast cancer, progesterone is pro-proliferative and carcinogenic. A key difference between these tissues that could explain the diverse effects of progesterone is the paracrine interactions of PR-expressing stroma and epithelium. Normal endometrium is a mucosa containing large quantities of distinct stromal cells with abundant PR, which influences epithelial cell proliferation and differentiation and protects against carcinogenic transformation. In contrast, the primary target cells of progesterone in the breast and fibroids are the mammary epithelial cells and the leiomyoma cells, which lack specifically organized stromal components with significant PR expression. This review provides a unifying perspective for the diverse effects of progesterone across human tissues and diseases.

Primate-specific melanoma antigen-A11 regulates isoform-specific human progesterone receptor-B transactivation

Progesterone acting through the progesterone receptor (PR) and its coregulators prepares the human endometrium for receptivity to embryo implantation and maintains pregnancy. The menstrual cycle-dependent expression of melanoma antigen-A11 (MAGE-11) in the mid-secretory human endometrium suggested a novel function in human PR signaling. Here we show that MAGE-11 is an isoform-specific coregulator responsible for the greater transcriptional activity of human PR-B relative to PR-A. PR was recruited to progesterone response regions of progesterone-regulated FK506-binding protein 5 (FKBP5) immunophilin and small Ras family G protein cell growth inhibitor RASD1 genes. Expression of MAGE-11 lentivirus shRNA in human endometrial Ishikawa cells expressing PR-B showed that MAGE-11 is required for isoform-specific PR-B up-regulation of FKBP5. In contrast, MAGE-11 was not required for progesterone up-regulation of RASD1 in endometrial cells expressing the PR-A/B heterodimer. Target gene specificity of PR-B depended on the synergistic actions of MAGE-11 and p300 mediated by the unique PR-B NH(2)-terminal (110)LLXXVLXXLL(119) motif that interacts with the MAGE-11 F-box region in a phosphorylation- and ubiquitinylation-dependent manner. A progesterone-dependent mechanism is proposed in which MAGE-11 and p300 increase PR-B up-regulation of the FKBP5 gene. MAGE-11 down-regulates PR-B, similar to the effects of progesterone, and interacts with FKBP5 to stabilize a complex with PR-B. We conclude that the coregulator function of MAGE-11 extends to isoform-specific regulation of PR-B during the cyclic development of the human endometrium.

Inhibition of AKT with the orally active allosteric AKT inhibitor, MK-2206, sensitizes endometrial cancer cells to progestin

Progestin resistance is a major obstacle to treating early stage, well-differentiated endometrial cancer as well as recurrent endometrial cancer. The mechanism behind the suboptimal response to progestin is not well understood. The PTEN tumor suppressor gene is frequently mutated in type I endometrial cancers and this mutation results in hyperactivation of the PI3K/AKT pathway. We hypothesized that increased activation of AKT promotes an inadequate response to progestins in endometrial cancer cells. Ishikawa cells stably transfected with progesterone receptor B (PRB23 cells) were treated with the AKT inhibitor, MK-2206, which effectively decreased levels of p(Ser473)-AKT in a dose-dependent (10 nM to 1 uM) and time-dependent manner (0.5 h to 24 h). MK-2206 inhibited levels of p(Thr308)-AKT and a downstream target, p(Thr246)-PRAS40, but did not change levels of p(Thr202/Tyr204)ERK or p(Thr13/Tyr185)SAPK/JNK, demonstrating specificity of MK-2206 for AKT. Additionally, MK-2206 treatment of PRB23 cells resulted in a significant increase in levels of progesterone receptor B (PRB) protein. Microarray analysis of PRB23 cells identified PDK4 as the most highly upregulated gene among 70 upregulated genes in response to R5020. Inhibition of AKT further upregulated progestin-mediated expression of PDK4 but did not affect another progestin-responsive gene, SGK1. Treatment of PRB23 cells with R5020 and MK-2206 independently decreased viability of cells while the combination of R5020 and MK-2206 caused the greatest decrease in cell viability. Furthermore, mice with xenografted tumors treated with MK-2206 alone or with progesterone alone exhibited modest reductions in their tumor volume. The largest decrease in tumor size was observed in the mice treated with both MK-2206 and progesterone; these tumors exhibited the least proliferation (Ki67) and the most apoptosis (cleaved caspase-3) of all the treatment groups. In summary, inhibition of AKT stabilizes the Progesterone Receptor B and augments progesterone response in endometrial cancer cells that have hyperactivated AKT.

G protein-coupled estrogen receptor (GPER) expression in normal and abnormal endometrium

Rapid estrogen effects are mediated by membrane receptors, and evidence suggests a role for both a membrane-associated form of estrogen receptor alpha (ESR1; ERα) and G-protein coupled receptor 30 (GPER; GPR30). Considering estrogen's importance in endometrial physiology and endometriosis pathophysiology, we hypothesized that GPER could be involved in both cyclic changes in endometrial estrogen action and that aberrant expression might be seen in the eutopic endometrium of women with endometriosis. Using real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemical analysis of normal endometrium, endometrial samples demonstrated cycle-regulated expression of GPER, with maximal expression in the proliferative phase. Eutopic and ectopic endometrium from women with endometriosis overexpressed GPER as compared to eutopic endometrium of normal participants. Ishikawa cells, an adenocarcinoma cell line, expressed GPER, with increased expression upon treatment with estrogen or an ESR1 agonist, but not with a GPER-specific agonist. Decreased expression was seen in Ishikawa cells stably transfected with progesterone receptor A. Together, these data suggest that normal endometrial GPER expression is cyclic and regulated by nuclear estrogen and progesterone receptors, while expression is dysregulated in endometriosis.

The role of progesterone and its receptor on cyclin G1 expression in endometrial carcinoma cells

Cyclin G1 protein is expressed in normal endometrial epithelial cells in a progesterone-dependent manner. It is an important mediator of the inhibiting effect of progesterone on cell proliferation. Moreover, the expression of cyclin G1 is also found to be decreased in human endometrial carcinoma cells (ECCs). To study the mechanism of decrease in the expression levels of cyclin G1, 3 ECC cell lines, Ishikawa, HEC-1-B, and KLE cells were treated with progesterone (P(4)). The KLE cells, in which progesterone receptor (PR) expression was absent, were transfected with PR-expressing plasmid before treatment with P(4). The results showed that cyclin G1 expression increased in Ishikawa and HEC-1-B cells after treatment with P(4), additionally the cell proliferation was suppressed but not in KLE cells. When the PR-expressing plasmid was transfected into KLE cells, the effect of P(4) was restored. Our data suggest that the deficiency of progesterone and its receptors is an important cause of the decreased expression of cyclin G1 in endometrial carcinoma, which may account for carcinogenesis and development of endometrial carcinomas.

p38 and p42/44 MAPKs differentially regulate progesterone receptor A and B isoform stabilization

Progesterone receptor (PR) isoforms (PRA and PRB) are implicated in the progression of breast cancers frequently associated with imbalanced PRA/PRB expression ratio. Antiprogestins represent potential antitumorigenic agents for such hormone-dependent cancers. To investigate the mechanism(s) controlling PR isoforms degradation/stability in the context of agonist and antagonist ligands, we used endometrial and mammary cancer cells stably expressing PRA and/or PRB. We found that the antiprogestin RU486 inhibited the agonist-induced turnover of PR isoforms through active mechanism(s) involving distinct MAPK-dependent phosphorylations. p42/44 MAPK activity inhibited proteasome-mediated degradation of RU486-bound PRB but not PRA in both cell lines. Ligand-induced PRB turnover required neosynthesis of a mandatory down-regulating partner whose interaction/function is negatively controlled by p42/44 MAPK. Such regulation strongly influenced expression of various endogenous PRB target genes in a selective manner, supporting functional relevance of the mechanism. Interestingly, in contrast to PRB, PRA stability was specifically increased by MAPK kinase kinase 1-induced p38 MAPK activation. Selective inhibition of p42/p44 or p38 activity resulted in opposite variations of the PRA/PRB expression ratio. Moreover, MAPK-dependent PR isoforms stability was independent of PR serine-294 phosphorylation previously proposed as a major sensor of PR down-regulation. In sum, we demonstrate that MAPK-mediated cell signaling differentially controls PRA/PRB expression ratio at posttranslational level through ligand-sensitive processes. Imbalance in PRA/PRB ratio frequently associated with carcinogenesis might be a direct consequence of disorders in MAPK signaling that might switch cellular responses to hormonal stimuli and contribute towards pathogenesis.

Ligand-dependent degradation of SRC-1 is pivotal for progesterone receptor transcriptional activity

The progesterone receptor (PR), a ligand-activated transcription factor, recruits the primary coactivator steroid receptor coactivator-1 (SRC-1) gene promoters. It is known that PR transcriptional activity is paradoxically coupled to its ligand-dependent down-regulation. However, despite its importance in PR function, the regulation of SRC-1 expression level during hormonal exposure is poorly understood. Here we report that SRC-1 expression level (but not other p160 family members) is down-regulated by the agonist ligand R5020 in a PR-dependent manner. In contrast, the antagonist RU486 fails to induce down-regulation of the coactivator and impairs PR agonist-dependent degradation of SRC-1. We show that SRC-1 proteolysis is a proteasome- and ubiquitin-mediated process that, predominantly but not exclusively, occurs in the cytoplasmic compartment in which SRC-1 colocalizes with proteasome antigens as demonstrated by confocal imaging. Moreover, SRC-1 was stabilized in the presence of leptomycin B or several proteasomal inhibitors. Two degradation motifs, amino-acids 2-16 corresponding to a PEST motif and amino acids 41-136 located in the basic helix loop helix domain of the coactivator, were identified and shown to control the stability as well as the hormone-dependent down-regulation of the coactivator. SRC-1 degradation is of physiological importance because the two nondegradable mutants that still interacted with PR as demonstrated by coimmunoprecipitation failed to stimulate transcription of exogenous and endogenous target genes, suggesting that concomitant PR/SRC-1 ligand-dependent degradation is a necessary step for PR transactivation activity. Collectively our findings are consistent with the emerging role of proteasome-mediated proteolysis in the gene-regulating process and indicate that the ligand-dependent down-regulation of SRC-1 is critical for PR transcriptional activity.

Inhibition of apoptosis by progesterone in cardiomyocytes

While gender-based differences in heart disease have raised the possibility that estrogen (ES) or progesterone (PG) may have cardioprotective effects, recent controversy regarding hormone replacement therapy has questioned the cardiac effects of these steroids. Using cardiomyocytes, we tested whether ES or PG has protective effects at the cellular level. We found that PG but not ES protects cardiomyocytes from apoptotic cell death induced by doxorubicin (Dox). PG inhibited apoptosis in a dose-dependent manner, by 12 ± 4.0% at 1 μm and 60 ± 1.0% at 10 μm. The anti-apoptotic effect of PG was also time dependent, causing 18 ± 5% or 62 + 2% decrease in caspase-3 activity within 1 h or 72 h of pretreatment. While PG causes nuclear translocation of its receptor within 20 min, the cytoprotective effect of PG was canceled by mifepristone (MF), a PG receptor antagonist. Analyses using Affymetrix high-density oligonucleotide array and RT-PCR found that PG induced Bcl-xL, metallothionine, NADPH quinone oxidoreductase 1, glutathione peroxidase-3, and four isoforms of glutathione S-transferase. Western blot analyses revealed that PG indeed induced an elevation of Bcl-xL protein in a dose- and time-dependent manner. Nuclear run-on assay indicated that PG induced Bcl-xL gene transcription. Inhibiting the expression of Bcl-xL using siRNA reduced the cytoprotective effect of PG. Our data suggests that PG induces a cytoprotective effect in cardiomyocytes in association with induction of Bcl-xL gene.

The regulation and function of the forkhead transcription factor, Forkhead box O1, is dependent on the progesterone receptor in endometrial carcinoma

In many type I endometrial cancers, the PTEN gene is inactivated, which ultimately leads to constitutively active Akt and the inhibition of Forkhead box O1 (FOXO1), a member of the FOXO subfamily of Forkhead/winged helix family of transcription factors. The expression, regulation, and function of FOXO1 in endometrial cancer were investigated in this study. Immunohistochemical analysis of 49 endometrial tumor tissues revealed a decrease of FOXO1 expression in 95.9% of the cases compared with the expression in normal endometrium. In four different endometrial cancer cell lines (ECC1, Hec1B, Ishikawa, and RL95), FOXO1 mRNA was expressed at similar levels; however, protein levels were low or undetectable in Ecc1, Ishikawa, and RL95 cells. Using small interfering RNA technology, we demonstrated that the low levels of FOXO1 protein were due to the involvement of Skp2, an oncogenic subunit of the Skp1/Cul1/F-box protein ubiquitin complex, given that silencing Skp2 increased FOXO1 protein expression in Ishikawa cells. Inhibition of Akt in Ishikawa cells also increased nuclear FOXO1 protein levels. Additionally, progestins increased FOXO1 protein levels, specifically through progesterone receptor B (PRB) as determined by using stably transfected PRA-specific and PRB-specific Ishikawa cell lines. Finally, overexpression of triple mutant (Tm) FOXO1 in the PR-specific Ishikawa cell lines caused cell cycle arrest and significantly decreased proliferation in the presence and absence of the progestin, R5020. Furthermore, TmFOXO1 overexpression induced apoptosis in PRB-specific cells in the presence and absence of ligand. Taken together, these data provide insight into the phosphoinositide-3-kinase/Akt/FOXO pathway for the determination of progestin responsiveness and the development of alternate therapies for endometrial cancer.

Glycodelin blocks progression to S phase and inhibits cell growth: a possible progesterone-induced regulator for endometrial epithelial cell growth

Prolonged exposure to unopposed estrogen in the absence of progesterone gives rise to endometrial hyperplasia and carcinoma. Post-ovulatory progesterone is necessary for the proper growth and differentiation of endometrial epithelial cells (EECs). Progesterone exposure induces the endometrial production of numerous bioactive substances, one of which is the glycoprotein, glycodelin (Gd). We investigated the role of Gd in cell cycle progression and cell growth to better understand how Gd affects EEC behavior and endometrial cancer pathogenesis. Ishikawa cells, a well-differentiated human endometrial epithelial cancer cell line, were transfected with expression plasmids encoding enhanced green fluorescent protein (EGFP) or EGFP-fused Gd (EGFP-Gd). They were then subjected to a cell proliferation assay, flow cytometry cell cycle analysis and RT-PCR analysis of cyclin-dependent kinase inhibitors (CDKIs) including p21, p27 and p16. Overexpression of EGFP-Gd resulted in a reduction of cell proliferation activity, an accumulation of G1-phase cells and up-regulation of p21, p27 and p16 mRNAs. Furthermore, progesterone-induced inhibition of Ishikawa cell growth was partially attenuated by Gd knockdown using siRNA. These results indicate that Gd causes inhibition of G1/S progression together with up-regulation of CDKIs thereby reducing cell growth. Thus, progesterone-induced expression of Gd may, at least in part, contribute to the suppression of endometrial epithelial growth observed during the secretory phase.

A novel loss-of-function mutation in TP53 in an endometrial cancer cell line and uterine papillary serous carcinoma model

The etiology of carcinoma of the uterine endometrium (ECa) is poorly understood. However, loss of apoptosis is one of the major factors that allow cancer cells to survive and progress. Hec50co, a poorly differentiated human ECa cell line, is widely used in the investigation of ECa. Previously, Hec50co xenograft tumor model in nude mice developed an advanced phenotype, similar to that of uterine papillary serous carcinoma (UPSC). Importantly, loss-of-function mutation in tumor suppressor TP53 was found in 20-30% of all ECa and >90% of UPSC. Thus, understanding the status of TP53 in Hec50co is essential for using Heco50co as a model for UPSC. To obtain an accurate genotype-phenotype status of TP53 in Hec50co, we performed mutation and functional analysis of TP53 gene of Hec50co by RT-PCR, genomic-PCR, and cloning and expression of mutant and wildtype TP53 alleles. We found a novel 42-bp deletion mutation in the exon6-intron6 splice junction of TP53 (TP53.del42bp) leading to a 113-bp exon6-deleted/skipped transcript was identified in Hec50co. In addition, the other TP53 allele in Hec50co is inactivated through a large deletion. Adenovirus (AD) harboring wildtype full-length TP53 cDNA induces caspase-dependent apoptosis; while the AD-TP53.del42bp allele does not. In addition, messenger RNA of TP53.del42bp allele is stable whereas the protein product of TP53.del42bp allele is made but not stable. Taken together, we demonstrate that Hec50co is a TP53-null cell line possessing one TP53.del42bp allele and the other lost allele and therefore provides an excellent model to dissect the molecular and cellular bases of UPSC and other p53-null cancers.

Large-scale gene expression studies of the endometrium: what have we learnt?

The endometrium is a dynamic tissue that undergoes coordinated changes under the influence of steroid hormones. This results in proliferation and differentiation culminating in a receptive state, followed by menstruation and endometrial repair. These functions involve complex interactions between the epithelium, stroma and leucocytes in the endometrium. Understanding the underlying causes of endometrial disorders, such as infertility, endometriosis and heavy menstrual bleeding, therefore represents a considerable challenge. Recently developed techniques, such as differential display and DNA microarrays permit the abundance of thousands of mRNA transcripts within cells or tissues to be measured simultaneously. This provides a new approach to understanding the complex interactions that underlie both healthy and disease states. Responses of the endometrium to hormones or drugs can be studied and the response of the system as an integrated whole can be assessed. Comparisons of endometrium from healthy women and those with endometrial dysfunction have advanced our understanding of key areas of endometrial physiology, including infertility, receptivity, endometriosis and cancer. Using this approach, novel genes controlling specific endometrial functions like receptivity have been identified for functional testing. This paper will review the impact of these techniques for transcript profiling on our understanding of selected areas of endometrial biology and discuss the potential applications in future.

Differences in invasive capacity of endometrial cancer cell lines expressing different progesterone receptor isotypes: possible involvement of cadherins

OBJECTIVE

Loss of expression of progesterone receptors (PR) in endometrial cancer is related to a more invasive and metastatic phenotype. In this study we aim to investigate whether selective loss of PRA or PRB affects the invasive capacity of endometrial cancer cells.

METHODS

cDNA microarrays were performed to compare gene expression profiles of a set of endometrial cancer sub-cell lines expressing PRA and/or PRB. In vitro invasion assays were performed to assess whether differences in gene expression between the lines were reflected by their invasive behavior.

RESULTS

It was observed that cell lines that express only PRA express higher levels of cadherins, and show a lower level of invasion compared to cell lines that express PRB. When cadherin function was inhibited in exclusively PRA-expressing cell lines, an increase of in vitro invasion was observed. In support of these findings, it was observed that in higher grade and more invasive endometrial cancer, expression of E-cadherin decreased.

CONCLUSIONS

These results indicate that relative loss of PRA during progression of endometrial cancer can have a negative impact on cadherin expression, which may lead to development of a more metastatic phenotype.

Progesterone-induced inhibition of growth and differential regulation of gene expression in PRA- and/or PRB-expressing endometrial cancer cell lines

OBJECTIVE

Progesterone plays an important role in controlling proliferation and differentiation of the human endometrium. Because there are two progesterone receptor isoforms (PRA and PRB), it was important to generate tools to be able to study the role of these two progesterone receptors separately.

METHODS

Using stable transfection techniques, both human progesterone receptor isoforms (hPRA and hPRB) were reintroduced into a hPR-negative subclone of the well-differentiated endometrial cancer cell line Ishikawa. Several Ishikawa subcell lines were constructed, each expressing different levels of hPRA, hPRB, or hPRA and hPRB, respectively.

RESULTS

These Ishikawa subcell lines showed a marked progesterone-induced growth inhibition with induction of apoptosis after long-term culture in the presence of hormone. Upon measuring gene regulation, a clear difference in regulation of expression of the selected genes by progesterone treatment was observed between the PRA-, PRB-, or PRA/B-expressing cell lines. Integrin beta4 (ITGB4) was only regulated in PRA-expressing cells; amphiregulin was highly regulated in PRB-expressing cells; insulin-like growth factor binding protein 3 (IGFBP3) was only regulated in PRB- and PRA/B-expressing cells; and metallothionein 1L (MT1L) was highly regulated in PRA/B-expressing cells. Interestingly, based on literature data, these genes can be implicated in induction of apoptosis, but are modulated here in such a way that suggests induction of resistance against apoptosis.

CONCLUSION

Reintroduction of PRs into Ishikawa cells rescued progesterone responsiveness in these cells. Furthermore, using these human endometrial cancer subcell lines, clear and distinct functional differences between the PR isoforms were observed.

Estrogen-induced loss of progesterone receptor expression in normal and malignant ovarian surface epithelial cells

While estrogens are suspected risk factors for epithelial ovarian cancer (OCa), progesterone (P4) has been shown to exert protective effects. The biological actions of P4 in target cells are mediated by progesterone receptors (PRs) that exist principally as A- and B-isoforms. We observed overexpression of PR-A and PR-B protein in two lines of OCa cells when compared to two lines of nontumorigenic, normal human ovarian surface epithelial (HOSE) cells. Treatment of HOSE or OCa cells with estrone or 17beta-estradiol at 10(-8) M for a period of 72 h induced significant loss of PR-A and PR-B mRNA and protein expression, with the regulation primarily controlled at the transcriptional level. In contrast, breast cancer cells (line MCF-7) exposed to estrogens upregulated PR-A and PR-B expression. Of significance, both the inhibitory and stimulatory actions of estrogens were blocked by the specific ER-antagonist ICI 182,780 (ICI, 10(-5) M), confirming estrogen specificity. Co-treatment of estrogen-exposed HOSE, OCa, and MCF-7 cell lines with inhibitors of type 1- and type 2-17beta hydroxysteroid dehydrogenase did not affect the previously observed changes in PR expression, suggesting that the action of each estrogen is direct and not mediated via conversion to its metabolic counterpart. Green fluorescence protein (GFP)-PR-A and GFP-PR-B were localized in the cytoplasmic compartment of untreated HOSE cells and translocated to the nucleus after P4 treatment, while both chimera PRs resided in the nuclei of OCa cells in a ligand-independent manner. In OCa cell cultures, P4 (10(-6) M), but not RU486 (10(-5) M), induced apoptosis that was blocked by co-treatment with the antiprogestin but enhanced by co-treatment with ICI. In sharp contrast, P4 induced proliferation, while ICI and RU486 caused cell death in MCF-7 cells. In conclusion, this study is first to demonstrate estrogens as negative regulators of PR expression in HOSE/OCa cells and to provide a mechanistic basis upon which to explain the antagonism of estrogens on the anti-OCa action of progestins. It also raises the possibility of using progestin and ICI as a combinational therapy for OCa treatment.

Aberrations in the progesterone receptor gene and the risk of recurrent endometrial carcinoma

A case-control study was performed in order to determine whether expression of the progesterone receptor (PR) and/or aberrations of the PR gene contribute to the development of recurrent endometrial carcinoma. Primary tumours from 44 patients with recurrence of stage I endometrial carcinoma (patients) within 3 years after initial treatment were compared with tumours from 44 matched patients who were free of recurrence for a minimum of 3 years (controls). Paraffin wax-embedded primary tumours (n = 88) and recurrent tumours (n = 32) were analysed immunohistochemically for PR expression. A staining index (SI = 0-9) based on the staining intensity and the number of stained cells was calculated. DNA extracted from paraffin wax-embedded tissues was subjected to PCR-restriction fragment length polymorphism analysis (PCR-RFLP) for determination of the PROGINS DNA sequence alterations and the +331G/A-promoter polymorphism. Low PR expression (SI < 1.0) was observed in 7% of primary tumours derived from controls, 25% of primary tumours from patients with recurrence, and 38% of recurrent tumours. The expression of PR was significantly lower in primary tumours from patients with recurrence (SI = 4.0 +/- 0.5) than in the tumours in the control group (SI = 5.6 +/- 0.5) (T-test for paired analysis, p < 0.05). The PROGINS and +331G/A-promoter polymorphism were not related to age at diagnosis, tumour grade or myometrial invasion. The +331G/A-promoter polymorphism was present in 14% of primary tumours from patients without recurrence, compared with 17% of patients with recurrence. The PROGINS polymorphism was observed in 16% of primary tumours from patients without, and in 34% of patients with, recurrence (OR 2.6; 95% CI: 0.9-7.6). Most interestingly, patients who carried the PROGINS variant and in whom a PR-expressing tumour was diagnosed were at significantly enhanced risk of relapse (OR 4.7; 95% CI: 1.3-17.1). In conclusion, low PR expression tended to be associated with recurrent disease, and PR expression in tumours from patients carrying the PROGINS allele was predictive of the risk of recurrence.

Progesterone receptors in endometrial cancer invasion and metastasis: development of a mouse model

Progestagens inhibit growth of endometrial cancer cells in vivo and in vitro, and also are reported to inhibit endometrial cancer cell invasion. The progesterone receptor (PR) isotypes PRA and PRB have different transcriptional activity. There are indications that relative over expression of PRB could lead to development of a more invasive phenotype in endometrial cancer. To study the effect of progestagens and the two PR isotypes on tumor dissemination, in vitro and in vivo models should be applied. The Ishikawa endometrial cancer cell line (clone 3H12) was transfected to stably express a high level of human PRB (hPRB), which resulted in the PRB-1 sub-cell line. Ovariectomized athymic NMRI nu/nu mice were injected intraperitoneally with these PRB-1 cells. After 3, 5 and 10 weeks, the animals were sacrificed. Spread of PRB-1 cells in and outside the peritoneal cavity was studied macroscopically and microscopically, and also by PCR detection. After 10 weeks, the PRB-1 cells had formed extensive tumor mass in the peritoneal cavity. Also, cells could be detected outside the peritoneal cavity, indicating metastatic ability of these cells. The present study describes an in vivo model that can provide a valuable tool in studying the influence of progestagens and the two PR isotypes on endometrial cancer cell invasion and metastasis.

Progestogenic effects of tibolone on human endometrial cancer cells

Tibolone, a synthetic steroid acting in a tissue-specific manner and used in hormone replacement therapy, is converted into three active metabolites: a Delta(4) isomer (exerting progestogenic and androgenic effects) and two hydroxy metabolites, 3 alpha-hydroxytibolone (3 alpha-OH-tibolone) and 3beta-OH-tibolone (exerting estrogenic effects). In the present study an endometrial carcinoma cell line (Ishikawa PRAB-36) was used to investigate the progestogenic properties of tibolone and its metabolites. This cell line contains progesterone receptors A and B, but lacks estrogen and androgen receptors. When tibolone was added to the cells, complete conversion into the progestogenic/androgenic Delta(4) isomer was observed within 6 d. Furthermore, when cells were cultured with tibolone or when the Delta(4) isomer or the established progestagen medroxyprogesterone acetate was added to the medium, marked inhibition of growth was observed. Interestingly, 3 beta-OH-tibolone also induces some inhibition of growth. These growth inhibitions were not observed in progesterone receptor-negative parental Ishikawa cells, and progestagen-induced growth inhibition of PRAB-36 cells could readily be reversed using the antiprogestagen Org-31489. Upon measuring the expression of two progesterone-regulated genes (fibronectin and IGF-binding protein-3), tibolone, the Delta(4) isomer and medroxyprogesterone acetate showed similar gene expression regulation. These results indicate that tibolone, the Delta(4) metabolite, and to some extent 3 beta-OH-tibolone exert progestogenic effects. Tibolone and most likely 3 beta-OH-tibolone are converted into the Delta(4) metabolite.