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

Role of steroid receptor-associated and regulated protein in tumor progression and progesterone receptor signaling in endometrial cancer

BACKGROUND

Steroid receptor-associated and regulated protein (SRARP) suppresses tumor progression and modulates steroid receptor signaling by interacting with estrogen receptors and androgen receptors in breast cancer. In endometrial cancer (EC), progesterone receptor (PR) signaling is crucial for responsiveness to progestin therapy. The aim of this study was to investigate the role of SRARP in tumor progression and PR signaling in EC.

METHODS

Ribonucleic acid sequencing data from the Cancer Genome Atlas, Clinical Proteomic Tumor Analysis Consortium, and Gene Expression Omnibus were used to analyze the clinical significance of SRARP and its correlation with PR expression in EC. The correlation between SRARP and PR expression was validated in EC samples obtained from Peking University People's Hospital. SRARP function was investigated by lentivirus-mediated overexpression in Ishikawa and HEC-50B cells. Cell Counting Kit-8 assays, cell cycle analyses, wound healing assays, and Transwell assays were used to evaluate cell proliferation, migration, and invasion. Western blotting and quantitative real-time polymerase chain reaction were used to evaluate gene expression. The effects of SRARP on the regulation of PR signaling were determined by co-immunoprecipitation, PR response element (PRE) luciferase reporter assay, and PR downstream gene detection.

RESULTS

Higher SRARP expression was significantly associated with better overall survival and disease-free survival and less aggressive EC types. SRARP overexpression suppressed growth, migration, and invasion in EC cells, increased E-cadherin expression, and decreased N-cadherin and Wnt family member 7A ( WNT7A ) expression. SRARP expression was positively correlated with PR expression in EC tissues. In SRARP -overexpressing cells, PR isoform B (PRB) was upregulated and SRARP bound to PRB. Significant increases in PRE-based luciferase activity and expression levels of PR target genes were observed in response to medroxyprogesterone acetate.

CONCLUSIONS

This study illustrates that SRARP exerts a tumor-suppressive effect by inhibiting the epithelial-mesenchymal transition via Wnt signaling in EC. In addition, SRARP positively modulates PR expression and interacts with PR to regulate PR downstream target genes.

Profile for mRNA transcript abundances in the pig endometrium where inflammation was induced by Escherichia coli

Uterine inflammation is a common reproductive disorder in domestic animals, leading to disturbances in many reproductive processes and economic losses. More information on inflammatory pathways, however, is needed to understand mechanisms of uterine inflammation. The aim of the study was to investigate transcriptomic profiles of the pig endometrium affected by inflammation. On day 3 of the estrous cycle (day 0 = initial day of study), saline or Escherichia coli suspension were injected into uterine horns. In endometrial tissues collected 8 days later, microarray analysis results indicated there were 189 differentially abundant mRNA transcripts (DEGs, 95 in relatively greater and 94 in lesser abundance) after saline injections compared with samples where there was severe acute inflammation. Relative abundance of mRNA transcripts for proteins assigned to inflammatory response, movement of phagocytes, quantity of phagocytes, leukocyte migration and adhesion of immune cells and many other functions related to inflammation were different in the Escherichia coli-treated endometrium than in samples from gilts treated with saline. Among others, S100A9, SLC11A1, CCL15, CCL3L3, CCR1, CD48, CD163, THBS1, KIT, ITGB3, JAK3 and NFKB2 mRNA transcripts were in relatively greater abundance and there were those in relatively lesser abundance including IL24, FGG, SST, CXCL16 and CREB. In this study, for the first time, there was detection of alterations in the transcriptome of the inflamed pig endometrium which may be an important finding for maintaining uterine homeostasis and functions. Results form the basis for future studies focusing on regulation of uterine inflammation in animals and women.

Irilone from Red Clover ( Trifolium pratense) Potentiates Progesterone Signaling

The use of botanical dietary supplements is becoming increasingly popular for the alleviation of hormonal-based conditions such as hot flashes, premenstrual syndrome, and fertility. Estrogen and progesterone receptors (ER and PR) play an essential role in these processes. However, despite the fact that many therapies used to alleviate gynecological conditions act through PR-mediated mechanisms, few studies have investigated or identified any herbal natural product components that act on this receptor. In the current study, we used a progesterone response element (PRE)-luciferase (Luc) reporter assay to identify four phytoprogestins present in a standardized red clover ( Trifolium pratense) extract. We found that the component irilone (1) potentiated the effect of progesterone in both endometrial and ovarian cancer cell lines. In these cancers, progesterone action is generally associated with positive outcomes; thus the potentiating effect of 1 may provide entirely new strategies for enhancing progesterone signaling as a means of mitigating conditions such as fibroids and endometriosis. Formononetin (3) and biochanin A (4) exhibited mixed agonist activity, while prunetin (2) acted only as an antagonist. Collectively, these results suggest that the effects of red clover extract repeatedly observed in cultured cells and the inverse correlation between risk of various cancers and flavonoid intake may be due, in part, to altered progesterone signaling.

Restoration of uterine redox-balance by methanolic extract of Camellia sinensis in arsenicated rats

Arsenic, an environmental and industrial pollutant causes female reproductive disturbances and female infertility. Several researchers found that the use of Camellia sinensis (CS) (green tea) is effective as an alternative therapeutic strategy in the management of several health ailments. This study explores the role of CS extract against arsenic-induced rat uterine tissue damage. Methanolic extract of CS (10 mg/kg BW) was tested concomitantly in arsenic-treated (10 mg/kg BW) rats for a duration of two-oestrous cycle length (8 days). CS effectively attenuated arsenic-induced antioxidantdepletion and necrosis in uterine tissue. Rats treated with sodium arsenite showed significantlyreduced activities of enzymatic antioxidants like superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in uterine tissue as evidenced by the results of spectrophotometric and electrozymographic analysis. Co-administration of CS significantly reversed the above oxidative stress markers in uterine tissue along with the histopathological changes in ovarian and uterine tissue. Moreover, an increase in the level of transcription factor NF-κB in the uterine tissue in association with reduced serum levels of vitamin B12 and folic acid were mitigated in arsenic fed rats following CS co-administration.

Decreased epithelial progesterone receptor A at the window of receptivity is required for preparation of the endometrium for embryo attachment

The precise timing of progesterone signaling through its cognate receptor, the progesterone receptor (PGR), is critical for the establishment and maintenance of pregnancy. Loss of PGR expression in the murine uterine epithelium during the preimplantation period is a marker for uterine receptivity and embryo attachment. We hypothesized that the decrease in progesterone receptor A (PGRA) expression is necessary for successful embryo implantation. To test this hypothesis, a mouse model constitutively expressing PGRA (mPgrALsL/+) was generated. Expression of PGRA in all uterine compartments (Pgrcre) or uterine epithelium (Wnt7acre) resulted in infertility with defects in embryo attachment and stromal decidualization. Expression of critical PGRA target genes, indian hedgehog, and amphiregulin (Areg), was maintained through the window of receptivity while the estrogen receptor target gene, the leukemia inhibitory factor (Lif), a key regulator of embryo receptivity, was decreased. Transcriptomic and cistromic analyses of the mouse uterus at day 4.5 of pregnancy identified an altered group of genes regulating molecular transport in the control of fluid and ion levels within the uterine interstitial space. Additionally, LIF and its cognate receptor, the leukemia inhibitory factor receptor (LIFR), exhibited PGR-binding events in regions upstream of the transcriptional start sites, suggesting PGRA is inhibiting transcription at these loci. Therefore, downregulation of the PGRA isoform at the window of receptivity is necessary for the attenuation of hedgehog signaling, transcriptional activation of LIF signaling, and modulation of solutes and fluid, producing a receptive environment for the attaching embryo.

The Flavonoid Apigenin Is a Progesterone Receptor Modulator with In Vivo Activity in the Uterus

Apigenin is a flavonoid with well-documented anti-cancer properties; however, its mechanisms of action are still unclear. We previously identified apigenin as a potential phytoprogestin, a natural product with a chemical scaffold that interacts with the progesterone receptor (PR). Our objective was to characterize the ability of apigenin to interact with PR through molecular docking studies, in vitro activity assays, and the ability of apigenin to elicit progestin-like effects in vivo. Molecular docking confirmed that apigenin could interact with PR, though with lower affinity than progesterone due to fewer van der Waals interactions. In Ishikawa cells stably expressing PR-B, apigenin significantly increased progesterone response element/luciferase (PRE/Luc) activity at 5 and 10 μM, but not in the parental Ishikawa cells that lack PR expression. In the presence of 100 nM of progesterone, 10 μM apigenin reduced PRE/Luc activity, indicative of mixed agonist activity. Apigenin also triggered degradation of PR in Ishikawa PR-B cells as measured by western blot. Apigenin reduced proliferation of Ishikawa cells, but through a PR-independent mechanism. In contrast, apigenin and progesterone both stimulated proliferation of T47D cells, an effect blocked by RU486. Apigenin activated other nuclear receptors evidenced by increased luciferase activity in MDA-MB-231 cells, which are PR negative. In vivo, apigenin blocked the genistein-stimulated increase in uterine epithelial cell height; stimulated endometrial expression of Hand2, a transcription factor stimulated by PR, and significantly reduced genistein-induced proliferation. In summary, apigenin is a phytoprogestin, with mixed agonist activity that demonstrates activity in vivo by hindering estrogen receptor-mediated uterine proliferation.

An insight into the complex roles of metallothioneins in malignant diseases with emphasis on (sub)isoforms/isoforms and epigenetics phenomena

Metallothioneins (MTs) belong to a group of small cysteine-rich proteins that are ubiquitous throughout all kingdoms. The main function of MTs is scavenging of free radicals and detoxification and homeostating of heavy metals. In humans, 16 genes localized on chromosome 16 have been identified to encode four MT isoforms labelled by numbers (MT-1-MT-4). MT-2, MT-3 and MT-4 proteins are encoded by a single gene. MT-1 comprises many (sub)isoforms. The known active MT-1 genes are MT-1A, -1B, -1E, -1F, -1G, -1H, -1M and -1X. The rest of the MT-1 genes (MT-1C, -1D, -1I, -1J and -1L) are pseudogenes. The expression and localization of individual MT (sub)isoforms and pseudogenes vary at intra-cellular level and in individual tissues. Changes in MT expression are associated with the process of carcinogenesis of various types of human malignancies, or with a more aggressive phenotype and therapeutic resistance. Hence, MT (sub)isoform profiling status could be utilized for diagnostics and therapy of tumour diseases. This review aims on a comprehensive summary of methods for analysis of MTs at (sub)isoforms levels, their expression in single tumour diseases and strategies how this knowledge can be utilized in anticancer therapy.

Progesterone receptor isoforms A and B: new insights into the mechanism of progesterone resistance for the treatment of endometrial carcinoma

Progesterone therapy is an effective treatment for atypical endometrial hyperplasia and early endometrial carcinoma (EC). However, progesterone resistance is the main obstacle to the success of conservative treatment in women with type I EC and remains a major clinical challenge. Studies indicate that progesterone and progesterone receptors (PRs) play a significant role in both normal and neoplastic endometria. Most EC arises in the epithelial cells of the endometrial glands, and a large body of in vitro evidence suggests that the absence or reduced expression of PR isoform B might result in the failure of progesterone treatment and lead to aberrant PRB-mediated signalling in EC cells. A recently developed in vivo knockout mouse model suggests that enhanced DNA methylation decreases the level of stromal PR isoform A and that this is also a main contributor to progesterone resistance in EC cells. The endometrial stroma within the EC might create a microenvironment that determines how epithelial-derived cancer cells respond to progesterone. This novel study opened a new avenue for research seeking to clarify the mechanisms that regulate the specific PR isoforms that are associated with the stromal cell responses to progesterone and has led to new understanding of both endometrial cell-specific and mechanical contributions of the stroma to EC development.

Response-specific progestin resistance in a newly characterized Ishikawa human endometrial cancer subcell line resulting from long-term exposure to medroxyprogesterone acetate

Progestins, particularly medroxyprogesterone acetate (MPA), have for a long time been used as conservative treatment for young patients with clinical stage I, grade I endometrial carcinoma. However, more than 30% of patients with endometrial adenocarcinoma display resistance to endocrine therapies at the time of presentation and most cancer patients that initially respond to progestin treatment will at some point develop resistance, resulting in tumor progression. The cellular mechanisms underlying acquired resistance to progestin are poorly understood. In order to investigate the molecular mechanisms whereby human endometrial adenocarcinoma develops resistance to progestin therapy, we have undertaken to develop human endometrial adenocarcinoma cell lines that are resistant to the growth-inhibitory effects of progestins in vitro. A progestin-resistant subcell line of Ishikawa cells was developed from Ishikawa human endometrial adenocarcinoma cells by stepwise selection in increasing concentrations of the synthetic progestin, MPA, over ten months. The doubling time of the progestin-resistant cells (34.18±3.15 h) grown routinely in the medium containing 10 μM MPA was not significantly different from the doubling time of the parent Ishikawa cells (35.14±2.68 h) grown in the absence of MPA (t=-0.331, P=0.762). Moreover, the effect of treatment with MPA shifted from suppression of growth and invasiveness, as observed in the parent Ishikawa cells, to stimulation of growth and invasiveness in the progestin-resistant Ishikawa cells. The positive rates of estrogen receptor a (ERα) and progesterone receptor B (PRB) of the progestin-resistant Ishikawa cells were significantly reduced, whilst the positive rate of ERβ was significantly enhanced compared to the parent Ishikawa cells. These differences were statistically significant (P<0.05). Our results indicate that long-term treatment with MPA in Ishikawa cells may give rise to a resistance effect to MPA. When the resistant subtype is acquired, treatment with MPA enhances cancer cell proliferation and invasiveness. The imbalance of ER and PR subtypes may contribute to the mechanisms involved in progestin resistance. Determination of the subtypes of ER and PR may provide important additional information on the hormone sensitivity of endometrial carcinoma.

Differential regulation of breast cancer-associated genes by progesterone receptor isoforms PRA and PRB in a new bi-inducible breast cancer cell line

Progesterone receptor isoforms (PRA and PRB) are expressed at equal levels in normal mammary cells. However, alteration in PRA/PRB expression is often observed in aggressive breast cancer suggesting differential contribution of PR isoforms in carcinogenesis. The mechanisms underlying such processes remain to be established mainly due to paucity of appropriate cellular models. To investigate the role of PR isoforms and the impact of imbalanced PRA/PRB ratio in transcriptional regulation, we have generated an original human breast cancer cell line conditionally expressing PRA and/or PRB in dose-dependence of non-steroid inducers. We first focused on PR-dependent transcriptional regulation of the paracrine growth factor gene amphiregulin (AREG) playing important role in cancer. Interestingly, unliganded PRA increases AREG expression, independently of estrogen receptor, yet inhibitable by antiprogestins. We show that functional outcome of epidermal growth factor (EGF) on such regulation is highly dependent on PRA/PRB ratio. Using this valuable model, genome-wide transcriptomic studies allowed us to determine the differential effects of PRA and PRB as a function of hormonal status. We identified a large number of novel PR-regulated genes notably implicated in breast cancer and metastasis and demonstrated that imbalanced PRA/PRB ratio strongly impact their expression predicting poor outcome in breast cancer. In sum, our unique cell-based system strongly suggests that PRA/PRB ratio is a critical determinant of PR target gene selectivity and responses to hormonal/growth factor stimuli. These findings provide molecular support for the aggressive phenotype of breast cancers with impaired expression of PRA or PRB.

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.

Progesterone inhibits epithelial-to-mesenchymal transition in endometrial cancer

BACKGROUND

Every year approximately 74,000 women die of endometrial cancer, mainly due to recurrent or metastatic disease. The presence of tumor infiltrating lymphocytes (TILs) as well as progesterone receptor (PR) positivity has been correlated with improved prognosis. This study describes two mechanisms by which progesterone inhibits metastatic spread of endometrial cancer: by stimulating T-cell infiltration and by inhibiting epithelial-to-mesenchymal cell transition (EMT).

METHODOLOGY AND PRINCIPAL FINDINGS

Paraffin sections from patients with (n = 9) or without (n = 9) progressive endometrial cancer (recurrent or metastatic disease) were assessed for the presence of CD4+ (helper), CD8+ (cytotoxic) and Foxp3+ (regulatory) T-lymphocytes and PR expression. Progressive disease was observed to be associated with significant loss of TILs and loss of PR expression. Frozen tumor samples, used for genome-wide expression analysis, showed significant regulation of pathways involved in immunesurveillance, EMT and metastasis. For a number of genes, such as CXCL14, DKK1, DKK4, PEG10 and WIF1, quantitive RT-PCR was performed to verify up- or downregulation in progressive disease. To corroborate the role of progesterone in regulating invasion, Ishikawa (IK) endometrial cancer cell lines stably transfected with PRA (IKPRA), PRB (IKPRB) and PRA+PRB (IKPRAB) were cultured in presence/absence of progesterone (MPA) and used for genome-wide expression analysis, Boyden- and wound healing migration assays, and IHC for known EMT markers. IKPRB and IKPRAB cell lines showed MPA induced inhibition of migration and loss of the mesenchymal marker vimentin at the invasive front of the wound healing assay. Furthermore, pathway analysis of significantly MPA regulated genes showed significant down regulation of important pathways involved in EMT, immunesuppression and metastasis: such as IL6-, TGF-β and Wnt/β-catenin signaling.

CONCLUSION

Intact progesterone signaling in non-progressive endometrial cancer seems to be an important factor stimulating immunosurveilance and inhibiting transition from an epithelial to a more mesenchymal, more invasive phenotype.

Genomic instability influences the transcriptome and proteome in endometrial cancer subtypes

BACKGROUND

In addition to clinical characteristics, DNA aneuploidy has been identified as a prognostic factor in epithelial malignancies in general and in endometrial cancers in particular. We mapped ploidy-associated chromosomal aberrations and identified corresponding gene and protein expression changes in endometrial cancers of different prognostic subgroups.

METHODS

DNA image cytometry classified 25 endometrioid cancers to be either diploid (n = 16) or aneuploid (n = 9), and all uterine papillary serous cancers (UPSC) to be aneuploid (n = 8). All samples were subjected to comparative genomic hybridization and gene expression profiling. Identified genes were subjected to Ingenuity pathway analysis (IPA) and were correlated to protein expression changes.

RESULTS

Comparative genomic hybridization revealed ploidy-associated specific, recurrent genomic imbalances. Gene expression analysis identified 54 genes between diploid and aneuploid endometrioid carcinomas, 39 genes between aneuploid endometrioid cancer and UPSC, and 76 genes between diploid endometrioid and aneuploid UPSC to be differentially expressed. Protein profiling identified AKR7A2 and ANXA2 to show translational alterations consistent with the transcriptional changes. The majority of differentially expressed genes and proteins belonged to identical molecular functions, foremost Cancer, Cell Death, and Cellular Assembly and Organization.

CONCLUSIONS

We conclude that the grade of genomic instability rather than the histopathological subtype correlates with specific gene and protein expression changes. The identified genes and proteins might be useful as molecular targets for improved diagnostic and therapeutic intervention and merit prospective validation.

Progesterone inhibits growth and induces apoptosis in cancer cells through modulation of reactive oxygen species

OBJECTIVE

Progesterone (P4) has been implicated as a protective factor for ovarian and endometrial cancers, yet little is known about its mechanism of action. We have shown apoptosis in ovarian and endometrial cancer cells with high doses of P4. Increased generation of reactive oxygen species (ROS) and an altered redox status have long been observed in cancer cells. The goal of this study was to assess the effect of P4 on cell growth, ROS generation, oxidative stress markers, and the expression of antioxidant proteins.

METHODS

All experiments were performed in vitro using cancer cell lines. Cell proliferation was determined using MTS proliferation assay. Production of ROS in cells was measured with the ROS indicator dye, aminophenyl fluorescein. Alterations in expression of antioxidant and apoptotic proteins were assessed by Western blotting.

RESULTS

The exposure of ovarian and endometrial cancer cell cultures to various doses of P4 caused a dose-dependent decrease in cell viability and the activation of caspase-3. Levels of ROS, markers of oxidative stress, and antioxidant proteins were elevated in cancer cells compared to normal cells and a marked decrease in their expression was seen following P4 treatment. In cancer cells, ROS was elevated while p-53 expression was low. P4 exposure of cells resulted in increased p-53 and BAX and decreased BCL-2 expression.

CONCLUSIONS

The data indicates that P4 has antioxidant effects. It alleviates ROS stress and causes apoptosis by upregulating proapoptotic (p-53 and BAX) and decreasing antiapoptotic (BCL-2) gene expression in cancer cells. These findings could have potential therapeutic implications.

Metformin reverses progestin resistance in endometrial cancer cells by downregulating GloI expression

INTRODUCTION

A long-term treatment with progestin commonly results in progestin resistance in endometrial cancer. So, the aim of this study was to investigate the role of glyoxalase I (GloI), a mediator of chemotherapy resistance, in metformin reversal of progestin resistance in endometrial carcinoma.

METHODS

The proliferation variety of endometrial cancer cells was determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-Diphenyltetrazolium (MTT) assay after exposure to medroxyprogesterone acetate, metformin, or both reagents; apoptosis rates were assessed by flow cytometry. Real-time polymerase chain reaction was used to evaluate the effect of small interfering RNA sequence on target gene expression. Western immunoblotting was performed to determine the expression of GloI and the molecules of the mammalian target of rapamycin (mTOR) pathway.

RESULT

Knocking down GloI sensitized progestin-resistant Ishikawa cells to progestin. Metformin downregulated GloI expression, reversed progestin resistance, enhanced progestin-induced cell proliferation inhibition, and induced apoptosis in progestin-resistant Ishikawa cells. In addition, medroxyprogesterone acetate-induced mTOR phosphorylation was blocked by metformin. Metformin abolishes mTOR phosphorylation and inhibits GloI expression, attenuating proliferation and inducing apoptosis in progestin-resistant Ishikawa cells.

CONCLUSIONS

Dysregulation of GloI expression in endometrial cancer may be part of the molecular mechanisms for progestin resistance.

Inhibiting the PI3K/Akt pathway reversed progestin resistance in endometrial cancer

Progestin resistance is the main obstacle to successful conservative therapy in young endometrial cancer patients. To investigate the molecular events that lead to progestin resistance and to find a possible way to reverse progestin resistance in endometrial cancer, we established a progestin-resistant Ishikawa cell line by long-term progestin treatment to downregulate progesterone receptor (PR) expression. Both medoxyprogesterone acetate (MPA) and LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, were assayed for their effects on the proliferation of progestin-sensitive and progestin-resistant cancer cells, respectively. The MPA inhibited the PI3K/Akt pathway and suppressed cell proliferation in progestin-sensitive Ishikawa cells, but activated the PI3K/Akt pathway and had no effect on cell proliferation in progestin-resistant Ishikawa cells or HEC-1A cells. Inhibiting the PI3K/Akt pathway by LY294002 upregulated PR expression and diminished cell growth, especially in progestin-resistant endometrial cancer cells. In vivo endometrial cancer xenograft studies in nude mice also showed that inhibiting the PI3K/Akt pathway reversed progestin resistance in endometrial cancer. Our results indicate that activation of the PI3K/Akt pathway by progestin without PR mediation plays an important role in progestin resistance to endometrial cancer cells. In addition, inhibiting the PI3K/Akt pathway might reverse progestin resistance in endometrial cancer.

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.

Progesterone inhibition of Wnt/beta-catenin signaling in normal endometrium and endometrial cancer

PURPOSE

Wnt signaling regulates the fine balance between stemness and differentiation. Here, the role of Wnt signaling to maintain the balance between estrogen-induced proliferation and progesterone-induced differentiation during the menstrual cycle, as well as during the induction of hyperplasia and carcinogenesis of the endometrium, was investigated.

EXPERIMENTAL DESIGN

Endometrial gene expression profiles from estradiol (E(2)) and E(2) + medroxyprogesterone acetate-treated postmenopausal patients were combined with profiles obtained during the menstrual cycle (PubMed; GEO DataSets). Ishikawa cells were transfected with progesterone receptors and Wnt inhibitors dickkopf homologue 1 (DKK1) and forkhead box O1 (FOXO1), measuring Wnt activation. Expression of DKK1 and FOXO1 was inhibited by use of sequence-specific short hairpins. Furthermore, patient samples (hormone-treated endometria, hyperplasia, and endometrial cancer) were stained for Wnt activation using nuclear beta-catenin and CD44.

RESULTS

In vivo, targets and components of the Wnt signaling pathway (among them DKK1 and FOXO1) are regulated by E(2) and progesterone. In Wnt-activated Ishikawa cells, progesterone inhibits Wnt signaling by induction of DKK1 and FOXO1. Furthermore, using siRNA-mediated knockdown of both DKK1 and FOXO1, progesterone inhibition of Wnt signaling was partly circumvented. Subsequently, immunohistochemical analysis of the Wnt target gene CD44 showed that progesterone acted as an inhibitor of Wnt signaling in hyperplasia and in well-differentiated endometrial cancer.

CONCLUSION

Progesterone induction of DKK1 and FOXO1 results in inhibition of Wnt signaling in the human endometrium. This Wnt inhibitory effect of progesterone is likely to play a rate-limiting role in the maintenance of endometrial homeostasis and, on its loss, in tumor onset and progression toward malignancy.

Association of the progesterone receptor gene with endometrial cancer risk in a Chinese population

BACKGROUND

Single nucleotide polymorphisms (SNPs) in the progesterone receptor (PGR) gene have been associated with the risk of endometrial cancer. However, to the authors' knowledge, no study to date has systematically evaluated the role of the PGR gene in endometrial carcinogenesis.

METHODS

Exposure information and DNA samples collected in the Shanghai Endometrial Cancer Study, a population-based case-control study of 1,204 incident cases and 1,212 age- and frequency-matched population controls, were used in this study. Seven tag SNPs were identified for the PGR gene plus the 5-kilobase (kb) flanking regions using the Han Chinese data from the HapMap project with a pairwise correlation coefficient (r(2)) >or= 0.90. These 7 SNPs captured 92% of SNPs in the region with a pairwise r(2) >or= 0.90 or 100% of SNPs with a pairwise r(2) >or= 0.80. Genotyping of polymorphisms was performed by using the Affymetrix MegAllele Targeted Genotyping System. A logistic regression model was used to compute adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs).

RESULTS

Of 7 tag SNPs that were assessed, 2 polymorphisms in the 3' flanking region of the PGR gene, reference SNP identification number (rs) 11224561 (rs11224561) and rs471767, were associated with the risk of endometrial cancer. The cytosine/cytosine (CC) genotype of SNP rs11224561 was associated with decreased risk (OR, 0.68; 95% CI, 0.50-0.92) compared with the thymine/thymine (TT) genotype. Carrying the guanine (G) allele of the rs471767 SNP also was associated with decreased risk, although the association was not statistically significant (OR, 0.78, 95%CI, 0.59-1.04 and OR, 0.32, 95%CI, 0.03-3.05 for the adenine [A]G and GG genotypes, respectively, compared with the homozygote AA).

CONCLUSIONS

The current findings suggested that polymorphisms in the 3' flanking region of the PGR gene may be associated with the risk of endometrial cancer.

Progesterone-mediated regulation of catechol-O-methyl transferase expression in endometrial cancer cells

The effects of estrogen and progesterone on the expression of estrogen-metabolizing enzymes such as catechol-O-methyl transferase (COMT) are not known. COMT converts genotoxic catecholestrogens to anticarcinogenic methoxyestrogens in the endometrium. The aim of this study is to investigate the effect of progesterone on COMT expression in well-differentiated endometrial cancer cells. The wild-type Ishikawa cell line as well as progesterone receptor A- or progesterone receptor B-transfected Ishikawa cells were used for in vitro studies. The regulation of COMT expression by progesterone was studied using Western blots, Hoechst dye DNA proliferation studies, and wild-type and/or site-directed mutagenesis of COMT promoter 1-luciferase reporter gene. Progesterone upregulated COMT protein expression in Ishikawa cells through progesterone receptor A isoform. COMT promoter activity was differentially regulated by the 3 half-site progesterone response elements in the COMT promoter. High doses of 2-ME2 inhibited Ishikawa cell proliferation. These data suggest that COMT expression is hormonally regulated in well-differentiated human endometrial cancer cells. COMT regulation and 2-ME2 production in the endometrium may affect endometrial carcinogenesis.

Progesterone receptor modulators and the endometrium: changes and consequences

Progesterone receptor modulators (PRMs) have been used for contraceptive research, as well as for treatment of fibroids, endometriosis and heavy or irregular menstrual bleeding. Long-term treatment with these compounds results in changes to the endometrium resulting in potential confusion in trying to characterize endometrial biopsies. A meeting was held to discuss the properties of PRMs, the effects of perturbed hormonal control of the endometrium and the need for further understanding of the biology of progesterone receptor action to facilitate the development of new PRMs. A panel of pathologists was convened to evaluate endometrial changes associated with a minimum of three months of chronic treatment with PRMs. Four different agents were used in the treatment regimens but the pathologists were blinded to treatment regimen or agent. The panel agreed that the endometrial biopsies did not fit into a classification of either proliferative or secretory endometrium but exhibited an unusual architecture that could be characterized as glandular dilatation. There was little evidence of mitosis, consistent with a proposed anti-proliferative effect of PRMs. The panel concluded that the biopsies did not reveal evidence of safety concern and that pathologists and investigators familiar with endometrial effects of chronic PRM exposure should consider working with pharmaceutical companies and regulatory agencies to develop standard descriptions of PRM-associated endometrial changes as well as the types of histologic changes that would signal a need for intervention.

Epidermal growth factor receptor signaling enhanced by long-term medroxyprogesterone acetate treatment in endometrial carcinoma

OBJECTIVE

Progestin is an effective endocrine treatment for patients with atypical hyperplasia or with endometrial carcinoma that is estrogen receptor (ER) positive and progesterone receptor (PR) positive. However, long-term progestin treatment may lead to resistance. We have studied the progestin resistance phenotype that frequently develops in endometrial carcinoma.

METHODS

Ishikawa endometrial carcinoma cells were cultured for a long period (10 months) in the presence of the synthetic progestin medroxyprogesterone acetate (MPA), thereby generating a subline refractory to the growth-suppressive effects of MPA.

RESULTS

The MPA-resistant subline showed growth stimulation rather than inhibition after MPA treatment. Immunocytochemical analysis showed reduced ER alpha and PR-B expression and increased ER beta expression in this subline compared with parental Ishikawa cells. Progestin-resistant Ishikawa cells also showed increased expression of transforming growth factor alpha (TGFalpha), the epidermal growth factor receptor (EGFR), and EGFR tyrosine kinase (EGFR-TK); MPA treatment further stimulated the expression of TGFalpha in these cells. Additionally, progestin-resistant Ishikawa cells were highly sensitive to growth stimulation by TGFalpha and to growth inhibition by the EGFR-TK-specific inhibitor AG1478, and they showed increased dependence on TGFalpha-EGFR signaling.

CONCLUSIONS

Our results suggest that prolonged treatment of endometrial carcinoma cells with MPA induces resistance to the growth-suppressive effects of MPA and enhances cancer cell proliferation. The downregulation of ER alpha and PR-B, the upregulation of ER beta, and highly activated TGF-EGFR signaling are thus likely to contribute to progestin resistance in endometrial carcinoma. Therefore, an EGFR-TK-specific inhibitor might be useful in the treatment of progestin-resistant endometrial carcinoma.

The granulin-epithelin precursor is a steroid-regulated growth factor in endometrial cancer

OBJECTIVES

The majority of endometrial cancers arise as a result of estrogen stimulation, the molecular targets of which remain incompletely defined. We hypothesize that the granulin-epithelin precursor (GEP) may be one such target. In this study, we examined the frequency of GEP and estrogen receptor (ER) co-expression in human endometrial cancers. Once we established the co-expression of GEP with the estrogen receptor we examined the potential estrogen regulation of GEP expression, as well as the functional significance of GEP expression in vitro.

METHODS

Double immunofluorescence and confocal microscopy were used to compare GEP and ER expression among 41 endometrial cancers. The effects of estradiol and tamoxifen treatment on GEP expression in two endometrial cancer cell lines, KLE and HEC-1-A, were assessed through reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis. The antiproliferative effect of GEP silencing by short hairpin (sh)RNA, was evaluated in HEC-1-A cells using an MTT assay.

RESULTS

GEP co-expression with ER was observed in 63% of the cancers examined. A two- to fivefold increase in GEP expression with estradiol and/or tamoxifen treatment was observed in KLE cells. Silencing of GEP in HEC-1-A cells using shRNA resulted in a decrease in proliferation among transfected cells.

CONCLUSIONS

Co-expression of GEP and ER in endometrial cancer cells, and the regulation of GEP by estrogen, suggests a role for GEP in steroid-mediated endometrial cancer cell growth. Further characterization of GEP as a steroid-mediated growth factor in these cells may broaden our understanding of endometrial cancer biology and also provide guidance in the development of novel therapeutic targets.

Ligand-controlled interaction of histone acetyltransferase binding to ORC-1 (HBO1) with the N-terminal transactivating domain of progesterone receptor induces steroid receptor coactivator 1-dependent coactivation of transcription

Modulators of cofactor recruitment by nuclear receptors are expected to play an important role in the coordination of hormone-induced transactivation processes. To identify such factors interacting with the N-terminal domain (NTD) of the progesterone receptor (PR), we used this domain as bait in the yeast Sos-Ras two-hybrid system. cDNAs encoding the C-terminal MYST (MOZ-Ybf2/Sas3-Sas2-Tip60 acetyltransferases) domain of HBO1 [histone acetyltransferase binding to the origin recognition complex (ORC) 1 subunit], a member of the MYST acetylase family, were thus selected from a human testis cDNA library. In transiently transfected CV1 cells, the wild-type HBO1 [611 amino acids (aa)] enhanced transcription mediated by steroid receptors, notably PR, mineralocorticoid receptor, and glucocorticoid receptor, and strongly induced PR and estrogen receptor coactivation by steroid receptor coactivator 1a (SRC-1a). As assessed by two-hybrid and glutathione-S-transferase pull-down assays, the HBO1 MYST acetylase domain (aa 340-611) interacts mainly with the NTD, and also contacts the DNA-binding domain and the hinge domains of hormone-bound PR. The HBO1 N-terminal region (aa 1-340) associates additionally with PR ligand-binding domain (LBD). HBO1 was found also to interact through its NTD with SRC-1a in the absence of steroid receptor. The latter coassociation enhanced specifically activation function 2 activation function encompassed in the LBD. Conversely, the MYST acetylase domain specifically enhanced SRC-1 coupling with PR NTD, through a hormone-dependent mechanism. In human embryonic kidney 293 cells expressing human PRA or PRB, HBO1 raised selectively an SRC-1-dependent response of PRB but failed to regulate PRA activity. We show that HBO1 acts through modification of an LBD-controlled structure present in the N terminus of PRB leading to the modulation of SRC-1 functional coupling with activation function 3-mediated transcription. Importantly, real-time RT-PCR analysis also revealed that HBO1 enhanced SRC-1 coactivation of PR-dependent transcription of human endogenous genes such as alpha-6 integrin and 11beta-hydroxydehydrogenase 2 but not that of amphiregulin. Immunofluorescence and confocal microscopy of human embryonic kidney-PRB cells demonstrated that the hormone induces the colocalization of HBO1 with PR-SRC-1 complex into nuclear speckles characteristic of PR-mediated chromatin remodeling. Our results suggest that HBO1 might play an important physiological role in human PR signaling.