Multiple human progesterone receptor messenger ribonucleic acids and their autoregulation by progestin agonists and antagonists in breast cancer cells

CCM signaling complex (CSC) couples both classic and non-classic Progesterone receptor signaling

BACKGROUND

Breast cancer, the most diagnosed cancer, remains the second leading cause of cancer death in the United States, and excessive Progesterone (PRG) or Mifepristone (MIF) exposure may be at an increased risk for developing breast cancer. PRG exerts its cellular responses through signaling cascades involving classic, non-classic, or combined responses by binding to either classic nuclear PRG receptors (nPRs) or non-classic membrane PRG receptors (mPRs). Currently, the intricate balance and switch mechanisms between these two signaling cascades remain elusive. Three genes, CCM1-3, form the CCM signaling complex (CSC) which mediates multiple signaling cascades.

METHODS

Utilizing molecular, cellular, Omics, and systems biology approaches, we analyzed the relationship among the CSC, PRG, and nPRs/mPRs during breast cancer tumorigenesis.

RESULTS

We discovered that the CSC plays an essential role in coupling both classic and non-classic PRG signaling pathways by mediating crosstalk between them, forming the CmPn (CSC-mPRs-PRG-nPRs) signaling network. We found that mPR-specific PRG actions (PRG + MIF) play an essential role in this CmPn network during breast cancer tumorigenesis. Additionally, we have identified 4 categories of candidate biomarkers (9 intrinsic, 2 PRG-inducible, 1 PRG-repressive, 1 mPR-specific PRG-repressive, and 2 mPR-responsive) for Luminal-A breast cancers during tumorigenesis and have confirmed the prognostic application of RPL13 and RPL38 as intrinsic biomarkers using a dual validation method.

CONCLUSIONS

We have discovered that the CSC plays an essential role in the CmPn signaling network for Luminal-A breast cancers with identification of two intrinsic biomarkers. Video Abstract.

Progesterone receptors in normal breast development and breast cancer

Progesterone receptors (PR) play a pivotal role in many female reproductive tissues such as the uterus, the ovary, and the mammary gland (MG). Moreover, PR play a key role in breast cancer growth and progression. This has led to the development and study of different progestins and antiprogestins, many of which are currently being tested in clinical trials for cancer treatment. Recent reviews have addressed the role of PR in MG development, carcinogenesis, and breast cancer growth. Thus, in this review, in addition to making an overview on PR action in normal and tumor breast, the focus has been put on highlighting the still unresolved topics on hormone treatment involving PR isoforms and breast cancer prognosis.

Evaluation of Expression and Phosphorylation of Progesterone Receptor in Endometrial Stromal Cells of Patients with Recurrent Implantation Failure Compared to Healthy Fertile Women

Recurrent implantation failure (RIF) is the repeated failure of good-quality embryos in implantation process following several assisted reproduction cycles. Disruption of the endometrial receptivity is one of the main causes of RIF. Progesterone plays a pivotal role in the endometrial receptivity through the regulation of gene expression pattern by binding to its receptors in the endometrial cells. The aim of this study was to evaluate the expression level of progesterone receptor (PR) and its phosphorylated form in the endometrial stromal cells (eSC) of RIF patients and compare it to the eSC of healthy fertile women as control group. After isolation of the eSC from biopsy samples of RIF patients and healthy fertile women and their characterization, expression levels of PR mRNA, PR protein, and phospho-Ser294 PR protein were evaluated by quantitative real-time PCR and immunofluorescence staining, respectively. The results demonstrated a significant reduction in PR mRNA expression (P < 0.01.) and phospho-Ser294 PR protein (P < 0.05) level in RIF patients compared to the control group. These data for the first time suggest that the expression of PR and its phosphorylated form are impaired in RIF patients. Therefore, designing therapeutic methods for improving PR expression status and its regulation in the endometrium of RIF patients may help in improving the final reproductive outcomes of these cases.

Survey of nuclear progesterone receptor expression in the uterus of the cyclic and pregnant camel (Camelus dromedarius)

Progesterone receptors (PR) are necessary to mediate the biological effects of progesterone and are integral to the regulation of a number of different aspects of reproduction in mammals including ovulation of the oocyte, implantation of the conceptus and maintenance of pregnancy. This study investigated the expression and localization of progesterone receptors in the uterine wall of both pregnant and cyclic (nonpregnant) camels. Uterine tissue samples were collected from healthy animals and processed for routine histological and immunohistochemical staining techniques to reveal nuclear PR. Demonstration of PR was performed by indirect immunohistochemical techniques using monoclonal antibodies raised against human PR. Immunolocalization of PR was more intense in all four endometrial zones (I-IV) as well as the myometrium of non pregnant (cyclic) animals (animals with newly formed corpus luteum). In contrast, PR immunostaining in both the endometrium and the myometrium was greatly reduced in pregnancy, particularly in the latest stage examined (approximately 366 days of gestation). In conclusion, a better understanding of the expression of steroid hormones and their receptors, including progesterone and the PR is critical to improving the reproductive health and pregnancy in the domesticated dromedary camel.

Progestin and Nuclear Progestin Receptor Are Essential for Upregulation of Metalloproteinase in Zebrafish Preovulatory Follicles

Ovulation requires proteinases to promote the rupture of ovarian follicles. However, the identity of these proteinases remains unclear. In our previous studies using RNA-seq analysis of differential expressed genes, we found significant down-regulation of five metalloproteinases: adam8b (a disintegrin and metalloproteinase domain 8b), adamts8a (a disintegrin and metalloproteinase with thrombospondin motif 8a), adamts9, mmp2 (matrix metalloproteinase 2), and mmp9 in the nuclear progestin receptor knockout (pgr ^-/-) zebrafish that have failed to ovulate. We hypothesize that these metalloproteinases are responsible for ovulation and are regulated by progestin and Pgr. In this study, we first determined the expression of these five metalloproteinases and adamts1 in preovulatory follicles at different times within the spawning cycle in pgr ^-/- and wildtype (wt) zebrafish and under varying hormonal treatments. We found that transcripts of adam8b, adamts1, adamts9, and mmp9 increased drastically in the preovulatory follicular cells of wt female zebrafish, while changes of adamts8a and mmp2 were not significant. This increase of adam8b, adamts9, and mmp9 was significantly reduced in pgr ^-/-, whereas expression of adamts1 was not affected in pgr ^-/- zebrafish. Among upregulated metalloproteinases, adamts9 mRNA was found to be expressed specifically in follicular cells. Strong immunostaining of Adamts9 protein was observed in the follicular cells of wt fish, and this expression was reduced drastically in pgr ^-/-. Interestingly, about an hour prior to the increase of metalloproteinases in wt fish, both Pgr transcript and protein increased transiently in preovulatory follicular cells. The results from in vitro experiments showed that adamts9 expression markedly increased in a dose, time and Pgr-dependent manner when preovulatory follicles were exposed to a progestin, 17α,20β-dihydroxy-4-pregnen-3-one (DHP). Taken together, our results provide the first evidence that upregulation of adamts9 occurs specifically in preovulatory follicular cells of zebrafish prior to ovulation. Progestin and its receptor (Pgr) are essential for the upregulation of metalloproteinases.

Estrogenic activity of osthole and imperatorin in MCF-7 cells and their osteoblastic effects in Saos-2 cells

There is an increasing interest in phytoestrogens due to their potential medical usage in hormone replacement therapy (HRT). The present study was designed to investigate the in vitro effects of estrogen-like activities of two widespread coumarins, osthole and imperatorin, using the MCF-7 cell proliferation assay and their alkaline phosphatase (ALP) activities in osteoblasts Saos-2 cells. The two compounds were found to strongly stimulate the proliferation of MCF-7 cells. The estrogen receptor-regulated ERα, progesterone receptor (PR) and PS2 mRNA levels were increased by treatment with osthole and imperatorin. All these effects were significantly inhibited by the specific estrogen receptor antagonist ICI182, 780. Cell cycle analysis revealed that their proliferation stimulatory effect was associated with a marked increase in the number of MCF-7 cells in S phase, which was similar to that observed with estradiol. It was also observed that they significantly increased ALP activity, which was reversed by ICI182,780. These results suggested that osthole and imperatorin could stimulate osteoblastic activity by displaying estrogenic properties or through the ER pathway. In conclusion, osthole and imperatorin may represent new pharmacological tools for the treatment of osteoporosis.

Active FOXO1 Is a Key Determinant of Isoform-Specific Progesterone Receptor Transactivation and Senescence Programming

Progesterone promotes differentiation coupled to proliferation and prosurvival in the breast, but inhibits estrogen-driven growth in the reproductive tract and ovaries. Herein, it is demonstrated, using progesterone receptor (PR) isoform-specific ovarian cancer model systems, that PR-A and PR-B promote distinct gene expression profiles that differ from PR-driven genes in breast cancer cells. In ovarian cancer models, PR-A primarily regulates genes independently of progestin, while PR-B is the dominant ligand-dependent isoform. Notably, FOXO1 and the PR/FOXO1 target gene p21 (CDKN1A) are repressed by PR-A, but induced by PR-B. In the presence of progestin, PR-B, but not PR-A, robustly induced cellular senescence via FOXO1-dependent induction of p21 and p15 (CDKN2B). Chromatin immunoprecipitation (ChIP) assays performed on PR isoform-specific cells demonstrated that while each isoform is recruited to the same PRE-containing region of the p21 promoter in response to progestin, only PR-B elicits active chromatin marks. Overexpression of constitutively active FOXO1 in PR-A-expressing cells conferred robust ligand-dependent upregulation of the PR-B target genes GZMA, IGFBP1, and p21, and induced cellular senescence. In the presence of endogenous active FOXO1, PR-A was phosphorylated on Ser294 and transactivated PR-B at PR-B target genes; these events were blocked by the FOXO1 inhibitor (AS1842856). PR isoform-specific regulation of the FOXO1/p21 axis recapitulated in human primary ovarian tumor explants treated with progestin; loss of progestin sensitivity correlated with high AKT activity.

IMPLICATIONS

This study indicates FOXO1 as a critical component for progesterone signaling to promote cellular senescence and reveals a novel mechanism for transcription factor control of hormone sensitivity.

Effects of estradiol and progestogens on human breast cells: regulation of sex steroid receptors

OBJECTIVES

To examine the effects of 17β-estradiol (E2) and progestogens, used in hormone therapy, on estrogen receptors (ER), progesterone receptors (PR), and human breast tumor cell growth.

MATERIALS AND METHODS

MCF-7 cells were incubated in pure E2 (1 nM and 10 nM) as well as in E2 in conjunction with 10 nM progestogens, including progesterone (P4), medroxyprogesterone acetate (MPA), norethisterone acetate (NET), and cyproterone acetate (CPA). Cell proliferation, apoptosis, expression of caspase-3, and both ER and PR isoforms were evaluated.

RESULTS

Caspase-3 was significantly diminished in cultures with only E2, whereas ERα significantly increased. A significant increase of caspase-3 in addition to the entire abolishment of E2-induced augmentation of ERα was observed in 1 nM E2 plus MPA and 10 nM E2 plus NET, whereas PR isoform B (PRB) was significantly increased. The ratios of apoptosis: proliferation significantly increased in 1 nM E2 plus progestogens (except P4) and 10 nM E2 plus NET. The changes of the PRA/PRB ratio were inversely related to the changes of the apoptosis to proliferation ratio. Significant increase of ERβ and PRB was noted in the E2 plus MPA or NET, in addition to a significant increase of ERα and decrease of PRA in the E2 plus CPA, as well as an increase of ERα and decrease of PRA and PRB in the E2 plus P4.

CONCLUSIONS

The combination of E2 and various progestogens resulted in diverging effects on ERs and PRs expressions, which induced different effects on MCF-7 cell growth. Compared with P4, aberrant hormone and biological activity of synthetic progestin, by way of altered receptor expression, may be an important factor in affecting breast cell growth.

Post-translational modifications of the progesterone receptors

Progesterone plays a key role in the development, differentiation and maintenance of female reproductive tissues and has multiple non-reproductive neural functions. Depending on the cell and tissue, the hormonal environment, growth conditions and the developmental stage, progesterone can either stimulate cell growth or inhibit it while promoting differentiation. Progesterone receptors (PRs) belong to the steroid hormone receptor superfamily of ligand-dependent transcription factors. PR proteins are subject to extensive post-translational modifications that include phosphorylation, acetylation, ubiquitination and SUMOylation. The interplay among these modifications is complex with alteration of the receptors by one factor influencing the impact of another. Control over these modifications is species-, tissue- and cell-specific. They in turn regulate multiple functions including PR stability, their subcellular localization, protein-protein interactions and transcriptional activity. These complexities may explain how tissue- and gene-specific differences in regulation are achieved in the same organism, by the same receptor protein and hormone. Here we review current knowledge of PR post-translational modifications and discuss how these may influence receptor function focusing on human breast cancer cells. There is much left to be learned. However, our understanding of this may help to identify therapeutic agents that target PR activity in tissue-specific, even gene-specific ways.

Steroid sulphatase and oestrogen sulphotransferase in human non-small-cell lung carcinoma

Background:

Steroid sulphatase (STS) is one of the steroid-metabolising enzymes involved in desulphating inactive steroid sulphates and oestrogen sulphotransferase (EST) sulphates active oestrogen. The roles of both STS and EST have not been examined in oestrogen-dependent non-small-cell lung cancer (NSCLC).

Methods:

We evaluated the immunoreactivity of STS and EST in NSCLC cases using immunohistochemistry. The function of STS and EST was further demonstrated using NSCLC cell lines.

Results:

The immunoreactivity of STS and EST was detected in 49.5% and 27.8% of NSCLC cases, respectively. The immunoreactivity of STS was significantly higher in female adenocarcinoma cases. The STS-positive NSCLCs were also significantly correlated in an inversed manner with tumour size and cell proliferation and tended to be associated with better clinical outcome. However, the immunoreactivity of EST was significantly correlated with intracellular oestradiol concentration. Results of in vitro analysis demonstrated that oestrone sulphate (E1-S) induced and pregnenolone sulphate (Preg-S) inhibited the proliferation in STS-expressing cell lines. The inhibition by Preg-S was reversed by a specific progesterone receptor blocker. Simultaneous addition of E1-S and Preg-S significantly suppressed the proliferation.

Conclusion:

In NSCLC patients, STS is considered a good prognostic factor. Results of our present study also indicated the benefits of potential progesterone therapy for NSCLC patients.

A truncated progesterone receptor (PR-M) localizes to the mitochondrion and controls cellular respiration

The cDNA for a novel truncated progesterone receptor (PR-M) was previously cloned from human adipose and aortic cDNA libraries. The predicted protein sequence contains 16 unique N-terminal amino acids, encoded by a sequence in the distal third intron of the progesterone receptor PR gene, followed by the same amino acid sequence encoded by exons 4 through 8 of the nuclear PR. Thus, PR-M lacks the N terminus A/B domains and the C domain for DNA binding, whereas containing the hinge and hormone-binding domains. In this report, we have localized PR-M to mitochondria using immunofluorescent localization of a PR-M-green fluorescent protein (GFP) fusion protein and in Western blot analyses of purified human heart mitochondrial protein. Removal of the putative N-terminal mitochondrial localization signal obviated association of PR-M with mitochondria, whereas addition of the mitochondrial localization signal to green fluorescent protein resulted in mitochondrial localization. Immunoelectron microscopy and Western blot analysis after mitochondrial fractionation identified PR-M in the outer mitochondrial membrane. Antibody specificity was shown by mass spectrometry identification of a PR peptide in a mitochondrial membrane protein isolation. Cell models of overexpression and gene silencing of PR-M demonstrated a progestin-induced increase in mitochondrial membrane potential and an increase in oxygen consumption consistent with an increase in cellular respiration. This is the first example of a truncated steroid receptor, lacking a DNA-binding domain that localizes to the mitochondrion and initiates direct non-nuclear progesterone action. We hypothesize that progesterone may directly affect cellular energy production to meet the increased metabolic demands of pregnancy.

Progesterone receptors, their isoforms and progesterone regulated transcription

This review discusses mechanisms by which progesterone receptors (PR) regulate transcription. We examine available data in different species and tissues regarding: (1) regulation of PR levels; and (2) expression profiling of progestin-regulated genes by total PRs, or their PRA and PRB isoforms. (3) We address current views about the composition of progesterone response elements, and postulate that PR monomers acting through "half-site" elements are common, entailing cooperativity with neighboring DNA-bound transcription factors. (4) We summarize transcription data for multiple progestin-regulated promoters as directed by total PR, or PRA vs. PRB. We conclude that current models and methods used to study PR function are problematical, and recommend that future work employ cells and receptors appropriate to the species, focusing on analyses of the effects of endogenous receptors targeting endogenous genes in native chromatin.

Role of estrogen receptor-β in endometriosis

Endometriosis is an estrogen-dependent disease. The biologically active estrogen, estradiol, aggravates the pathological processes (e.g., inflammation and growth) and the symptoms (e.g., pain) associated with endometriosis. Abundant quantities of estradiol are available for endometriotic tissue via several mechanisms including local aromatase expression. The question remains, then, what mediates estradiol action. Because estrogen receptor (ER)β levels in endometriosis are >100 times higher than those in endometrial tissue, this review focuses on this nuclear receptor. Deficient methylation of the ERβ promoter results in pathological overexpression of ERβ in endometriotic stromal cells. High levels of ERβ suppress ERα expression. A severely high ERβ-to-ERα ratio in endometriotic stromal cells is associated with suppressed progesterone receptor and increased cyclo-oxygenase-2 levels contributing to progesterone resistance and inflammation. ERβ-selective estradiol antagonists may serve as novel therapeutics of endometriosis in the future.

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.

Estrogen receptor-beta, estrogen receptor-alpha, and progesterone resistance in endometriosis

Loss of progesterone signaling in the endometrium may be a causal factor in the development of endometriosis, and progesterone resistance is commonly observed in women with this disease. In endometriotic stromal cells, the levels of progesterone receptor (PR), particularly the PR-B isoform, are significantly decreased, leading to a loss of paracrine signaling. PR deficiency likely underlies the development of progesterone resistance in women with endometriosis who no longer respond to progestin therapy. Here we review the complex epigenetic and transcriptional mechanisms leading to PR deficiency. The initial event may involve deficient methylation of the estrogen receptor (ER)beta promoter resulting in pathologic overexpression of ERbeta in endometriotic stromal cells. We speculate that alterations in the relative levels of ERbeta and ERalpha in endometrial tissue dictate E2-regulated PR expression, such that a decreased ERalpha-tauomicron-ERbeta ratio may result in suppression of PR. In this review, we propose a molecular model that may be responsible for changes in ERbeta and ERalpha leading to PR loss and progesterone resistance in endometriosis.

PROGESTERONE AND THE CONTROL OF HUMAN PREGNANCY AND PARTURITION

Almost 80 years ago George Corner and colleagues provided the first evidence that progesterone maintains pregnancy and that it does so, at least in part, by promoting myometrial relaxation. In the 1950s, Arpad Csapo proposed the “progesterone block hypothesis”, which posits that progesterone maintains pregnancy by promoting myometrial relaxation and that its withdrawal initiates a cascade of hormonal interactions that transforms the myometrium to a highly contractile state leading to the onset of labour. Csapo later proposed that contractility of the pregnant myometrium is determined by the balance between relaxation induced by progesterone and contraction induced by a cohort of signals including oestrogens, uterine distention and stimulatory uterotonins such as prostaglandins (PGs) and oxytocin (OT). According to this “seesaw” hypothesis, progesterone promotes myometrial relaxation by directly inducing relaxation and/or by inhibiting the production of, or myometrial responsiveness to, stimulatory uterotonins. These landmark concepts, though derived from studies of experimental animals, form the foundation for current understanding of progesterone's role in the physiology of human pregnancy. Remarkable progress has been made over the last 20–30 years in understanding the signal transduction pathways through which steroid hormones affect target cells. This knowledge has broadened the scope of Csapo's original paradigms and we are now beginning to unravel the specific signaling pathways and molecular interactions by which progesterone affects human myometrium and how its actions are controlled at the functional level. This is important for the development of progestin-based therapeutics for the prevention or suppression of preterm labour and preterm birth. Here we review recent progress in understanding the mechanisms by which progesterone sustains pregnancy and in particular how it promotes myometrial relaxation, how its relaxatory actions are nullified at parturition, and the hormonal interactions that induce progesterone withdrawal to determine the timing of human birth.

The cytoplasmic 60 kDa progesterone receptor isoform predominates in the human amniochorion and placenta at term

BACKGROUND

The mechanism that initiates human parturition has been proposed to be 'functional progesterone withdrawal' whereby the 116 kDa B-isoform of the progesterone receptor (PR-B) switches in favour of the 94 kDa A-isoform (PR-A) in reproductive tissues. Recently, other PR isoforms, PR-S, PR-C and PR-M generated from the same gene have been identified and partially characterised.

METHODS AND RESULTS

Using immunohistochemical, western blotting and RT-PCR techniques, evidence is provided that indicates the major PR isoform present in human term fetal membranes (amnion and chorion) and syncytiotrophoblast of the placenta is neither of the classical nuclear PR-B or PR-A isoforms but is the N-terminally truncated 60 kDa PR-C isoform. Evidence is also provided that this 60 kDa isoform resides in the cytoplasm of the expressing cell types. Data are also presented to show that PR-B, PR-A and PR-S isoforms are essentially absent from the amnion and chorion, whereas PR isoforms A, B, C and S are all present in the decidua, with PR-A being the major isoform. The syncytiotrophoblast of the placenta contains the cytoplasmic 60 kDa isoform, but not isoforms PR-A, PR-B or PR-S.

CONCLUSION

The major PR isoform in the amnion, chorion and placenta is a 60 kDa protein that could be PR-C, suggesting that the cytoplasmic isoform has a specific role in extra-embryonic tissues and may be involved in the regulation of human parturition.

Progesterone modulation of alpha5 nAChR subunits influences anxiety-related behavior during estrus cycle

Smokers often report an anxiolytic effect of cigarettes. In addition, stress-related disorders such as anxiety, post-traumatic stress syndrome and depression are often associated with chronic nicotine use. To study the role of the alpha5 nicotinic acetylcholine receptor subunit in anxiety-related responses, control and alpha5 subunit null mice (alpha5(-/-)) were subjected to the open field activity (OFA), light-dark box (LDB) and elevated plus maze (EPM) tests. In the OFA and LDB, alpha5(-/-) behaved like wild-type controls. In the EPM, female alpha5(-/-) mice displayed an anxiolytic-like phenotype, while male alpha5(-/-) mice were undistinguishable from littermate controls. We studied the hypothalamus-pituitary-adrenal axis by measuring plasma corticosterone and hypothalamic corticotropin-releasing factor. Consistent with an anxiolytic-like phenotype, female alpha5(-/-) mice displayed lower basal corticosterone levels. To test whether gonadal steroids regulate the expression of alpha5, we treated cultured NTera 2 cells with progesterone and found that alpha5 protein levels were upregulated. In addition, brain levels of alpha5 mRNA increased upon progesterone injection into ovariectomized wild-type females. Finally, we tested anxiety levels in the EPM during the estrous cycle. The estrus phase (when progesterone levels are low) is anxiolytic-like in wild-type mice, but no cycle-dependent fluctuations in anxiety levels were found in alpha5(-/-) females. Thus, alpha5-containing neuronal nicotinic acetylcholine receptors may be mediators of anxiogenic responses, and progesterone-dependent modulation of alpha5 expression may contribute to fluctuations in anxiety levels during the ovarian cycle.

Use of different postmenopausal hormone therapies and risk of histology- and hormone receptor-defined invasive breast cancer

PURPOSE

We previously found that the risk of invasive breast cancer varied according to the progestagen component of combined postmenopausal hormone therapy (CHT): progesterone, dydrogesterone, or other progestagens. We conducted the present study to assess how these CHTs were associated with histology- and hormone receptor-defined breast cancer.

PATIENTS AND METHODS

We used data from the French E3N cohort study, with 80,391 postmenopausal women followed for a mean duration of 8.1 years; 2,265 histologically confirmed invasive breast cancers were identified through biennial self-administered questionnaires completed from 1990 to 2002. The relative risks (RRs) were estimated using Cox proportional hazards models.

RESULTS

Compared with postmenopausal hormone therapy (HT) never-use, ever-use of estrogen+progesterone was not significantly associated with the risk of any breast cancer subtype, but increasing duration of estrogen+progesterone was associated with increasing risks of lobular (P = .06) and estrogen receptor-positive/progesterone receptor-negative (ER+/PR-; P = .02). Estrogen+dydrogesterone was associated with a significant increase in risk of lobular carcinoma (RR, 1.7; 95% CI, 1.1 to 2.6). Estrogen+other progestagens was associated with significant increases in risk of ductal and lobular carcinomas (RR, 1.6; 95% CI, 1.3 to 1.8; and 2.0; 95% CI, 1.5 to 2.7, respectively), of ER+/PR+ and ER+/PR- carcinomas (RR, 1.8; 95% CI, 1.5 to 2.1; and 2.6; 95% CI, 1.9 to 3.5, respectively), but not of ER-/PR+ or ER-/PR- carcinomas (RR, 1.0; 95% CI, 0.5 to 2.1; and 1.4; 95% CI, 0.9 to 2.0, respectively).

CONCLUSION

The increase in risk of breast cancer observed with the use of CHTs other than estrogen+progesterone and estrogen+dydrogesterone seems to apply preferentially to ER+ carcinomas, especially those ER+/PR-, and to affect both ductal and lobular carcinomas.

Progesterone induces the expression of vascular endothelial growth factor (VEGF) 120 and Flk-1, its receptor, in bovine granulosa cells

Vascular endothelial growth factor (VEGF) isoforms (VEGF 120 and VEGF 164) secreted by granulosa cells are involved in thecal angiogenesis during follicular development in the bovine ovary. The follicular fluid in the developing follicle includes a slight amount of the progesterone. However, the progesterone (P4) effects on VEGF120 and VEGF164 isoforms have not been well characterized in the bovine granulosa cells. We investigated the effects of progesterone on the gene expression of hypoxia-inducible factor 1alpha (HIF-1alpha, transcription factor), VEGF120, VEGF164 and Flk-1, its receptors, in cultured bovine granulosa cells. Messenger RNA expression for HIF-1alpha, VEGF120, VEGF164 and Flk-1 was quantified using real-time PCR methods. The levels of VEGF120, HIF-1alpha and Flk-1 mRNAs were increased significantly by P4 at a concentration of 10 ng/ml. In contrast, the expression of VEGF 164 gene is inhibited by P4. The level of VEGF120 and Flk-1 mRNAs in the granulosa cells treated with 10 ng/ml progesterone plus 1 ng/ml estradiol significantly decreased compared with progesterone alone. In contrast, the addition of 1 ng/ml estradiol to the culture medium increased the expression of VEGF164 gene. In conclusion, our data demonstrated that progesterone might stimulate the expression of the VEGF120 via HIF-1alpha, transcription factor, in bovine granulosa cells. These results suggest the hormone-dependent expression pattern of VEGF isoforms during follicular development. Thus, our study suggested the expression of VEGF isoforms in granulosa cells might be controlled by a different pathway during follicle development in cow.

Regulation of estrogen receptor (ER) levels in MCF-7 cells by progesterone metabolites

Estradiol-17beta (E2) may participate in carcinoma of mammary cells containing estradiol receptors (ER) at sufficient levels. Hence, the regulation of ER levels may be important for the progression of estrogen-dependent mammary carcinomas. Our previous findings that the progesterone metabolite, 5alpha-pregnane-3,20-dione (5alphaP), exhibits marked mitogenic and metastatic properties, whereas the progesterone metabolites, 4-pregnen-3alpha-ol-20-one (3alphaHP) and 4-pregnen-20alpha-ol-3-one (20alphaHP), oppose these actions, prompted examination of the possible effects of these progesterone metabolites on ER concentration in MCF-7 breast cancer cells. Cells were exposed for 24h to 0 (control) or 10(-10) to 10(-6)M E2, 5alphaP, 3alphaHP, 20alphaHP or combinations of these steroids, and ER concentrations were determined for intracellular estrogen receptors by specific binding of [(3)H]E2. The total ER number (nuclear plus cytosolic) in control samples was 2551+/-164 per cell. E2 and 5alphaP resulted in significant dose-dependent increases in total ER numbers ( approximately 1.6-fold and approximately 2.2-fold at 10(-6)M, respectively). In combination, E2+5alphaP resulted in additive increases in ER numbers. Individually, 3alphaHP and 20alphaHP each resulted in dose-dependent decreases (43% and 54% at 10(-6)M, respectively) in total ER numbers and inhibited the E2- or 5alphaP-induced increases in ER levels. In combination, 3alphaHP+20alphaHP resulted in dose-dependent additive suppression of ER levels. Treatment with cycloheximide or actinomycin D indicated that both transcription and translation are involved in 5alphaP and 3alphaHP action on ER numbers. Real time RT-PCR showed increases in expression of ERalpha transcripts due to 5alphaP and increases in expression of ERbeta due to 3alphaHP; expression levels of either ERalpha or ERbeta were not significantly altered when cells were treated with 5alphaP+3alphaHP. The results are the first to show that the pro- and anti-cancer progesterone metabolites also have marked selective (up or down) regulatory effects on ER levels in MCF-7 breast cancer cells.

Focal subnuclear distribution of progesterone receptor is ligand dependent and associated with transcriptional activity

The progesterone receptor (PR) is a critical mediator of progesterone action in the female reproductive system. Expressed in the human as two proteins, PRA and PRB, the receptor is a ligand-activated nuclear transcription factor that regulates transcription by interaction with protein cofactors and binding to specific response elements in target genes. We previously reported that PR was located in discrete subnuclear foci in human endometrium. In this study, we investigated the role of ligand in the formation of PR foci and their association with transcriptional activity. PR foci were detected in mouse uterus and normal human breast tissues and were more abundant when circulating progesterone was high. In human malignant tissues, PR foci were aberrant: foci were larger in endometrial cancers than in normal endometrium, and in breast cancers hormone-dependence was decreased. Chromatin disruption also increased foci size and decreased ligand dependence, suggesting that altered nuclear architecture may contribute to the aberrant PR foci observed in endometrial and breast cancers. In breast cancer cells, movement of PR into foci required exposure to ligand and was blocked by transcriptional inhibitors and by prolonged inhibition of proteasomal degradation. Foci contained PR dimers, and fluorescence resonance energy transfer demonstrated that PR foci contained the highest concentration of receptor dimers in the nucleus. PR in foci colocalized with transcription factors and nascent RNA transcripts only in the presence of ligand, and inhibition of coactivator recruitment inhibited PR foci formation. The demonstration that focal distribution of PR within the nucleus is associated with transcription suggests a link between the subnuclear distribution of PR and its transcriptional activity that is likely to be important for normal cellular function of PR.

The progesterone receptor in human term amniochorion and placenta is isoform C

The mechanism that initiates human parturition has been proposed to be functional progesterone withdrawal whereby the 116-kDa B isoform of the progesterone receptor (PR-B) switches in favor of the 94-kDa A isoform (PR-A) in reproductive tissues. Recently other PR isoforms, PR-S, PR-C, and PR-M generated from the same gene have been identified and partially characterized. Using immunohistochemical, Western blotting, and RT-PCR techniques, evidence is provided that the major PR isoform present in human term fetal membranes (amnion and chorion) and syncytiotrophoblast of the placenta is neither of the classical nuclear PR-B or PR-A isoforms but is the N terminally truncated 60-kDa PR-C isoform. Evidence is also provided that the PR-C isoform resides in the cytoplasm of the expressing cell types. Data are also presented to show that PR-B, PR-A, and PR-S isoforms are essentially absent from the amnion and chorion, whereas PR isoforms A, B, C, and S are all present in the decidua, with PR-A being the major isoform. The syncytiotrophoblast of the placenta contains the cytoplasmic PR-C isoform but not PR-A, PR-B, or PR-S. The major PR isoform in the amnion, chorion, and placenta is PR-C, suggesting that the cytoplasmic PR-C isoform has a specific role in extraembryonic tissues and may be involved in the regulation of human parturition.

MED220/thyroid receptor-associated protein 220 functions as a transcriptional coactivator with Pit-1 and GATA-2 on the thyrotropin-beta promoter in thyrotropes

Mediator (MED) 220/thyroid receptor-associated protein (TRAP) 220 is a transcriptional mediator that interacts with liganded thyroid/steroid hormone receptors. MED220 haploinsufficient heterozygotes exhibited hypothyroidism and reduced TSHbeta transcripts, suggesting a specific function for TSHbeta transcription. We previously demonstrated that Pit-1 and GATA-2 can bind to a composite element within the proximal TSHbeta promoter and synergistically activate transcription. We detected MED220 expression in TtT-97 thyrotropes by Northern and Western blot analysis. Cotransfections in CV-1 cells showed that Pit-1, GATA-2, or MED220 alone did not markedly stimulate the TSHbeta promoter. However, Pit-1 plus GATA-2 resulted in an 10-fold activation, demonstrating synergistic cooperativity. Titration of MED220 resulted in a further dose-dependent stimulation up to 25-fold that was promoter specific. Glutathione-S-transferase interaction studies showed that MED220 or GATA-2 each bound the homeodomain of Pit-1, whereas MED220 interacted independently with each zinc finger of GATA-2 but not with either terminus. MED220 interacted with GATA-2 and Pit-1 over a broad region of its N terminus. These regions of interaction were also important for maximal function. Coimmunoprecipitation confirmed that all three factors can interact in thyrotropes and chromatin immunoprecipitation demonstrated in vivo occupancy on the proximal TSHbeta promoter. Thus, the TSHbeta gene is maximally activated by a combination of three thyrotrope transcription factors that act via both protein-DNA and protein-protein interactions.

Increased expression of fatty acid synthase and progesterone receptor in early steps of human mammary carcinogenesis

Progestins increase the risk of breast cancer in the hormone therapy of menopause, and progesterone receptor-induced fatty acid synthase (FAS) is a potential therapeutical target of breast cancer. In a first attempt to specify in which lesions at risk of breast cancer progestins might be acting, we have compared the progesterone receptor (PR) and FAS expression in preinvasive breast lesions and in adjacent "normal" mammary glands. We used archive paraffin-embedded tissues from 116 patients, with 164 lesions of increasing histological risk from nonproliferative "benign" breast disease (BBD) to in situ breast carcinomas. Immunostaining using our FAS antibody and a PR antibody from Dako was quantified as continuous variables by computer-assisted image analysis. FAS level increased (p < 10(-3) by the Kruskall-Wallis test) in all lesions, starting from nonproliferative BBD, and was maximal in in situ carcinoma. The % of PR-positive cells increased from nonproliferative BBD and was higher in proliferative atypia (p < 10(-3)). It was very low in high-grade DCIS corresponding to a likely different carcinogenesis pathway. There was a trend for a positive correlation between FAS and PR in normal glands. However, the 2 markers increased independently in BBD and were negatively correlated in in situ carcinomas. FAS and PR were positively correlated with Ki67 in BBD. The increased PR level in premalignant steps of mammary carcinogenesis suggests an early increased responsiveness to progestins. The increased FAS expression, in lesions parallel to their increased breast cancer risk, suggests further studies to develop new markers of high-risk lesions and to prevent breast cancer.

17Beta-estradiol suppresses TLR3-induced cytokine and chemokine production in endometrial epithelial cells

BACKGROUND

The human endometrium is an important site for contact between the host and pathogens ascending the reproductive tract, and thus plays an important role in female reproductive tract immunity. Previous work in our laboratory has suggested that Toll-like receptors (TLRs) are involved in endometrial epithelial recognition of pathogens and that ligation of endometrial TLRs results in the production of cytokines and chemokines important for both immune and reproductive functions of the endometrium. We have also demonstrated cyclic regulation of TLR3 mRNA and protein expression in human endometrium, suggesting that steroid hormones might play a role in the expression and function of TLR3. In this study, the effects of 17beta-estradiol (E2) and progesterone (P) on TLR3 expression and function in endometrial cell lines were investigated.

METHODS

Endometrial epithelial cell lines were cultured and examined for the presence of TLR3 and hormone receptors by endpoint RT-PCR. For hormonal studies, cells were pre-treated with ethanol vehicle, 10(-8) M E2, and/or 10(-7) M P. For antagonist assays, cells were treated with the ER antagonist, ICI 182, 780, or the PR antagonist, RU486, for two hours prior to treatment with hormones. Following hormone or hormone/antagonist pre-treatment, cells were stimulated with vehicle, the synthetic TLR3 ligand, polyinosinic-polycytidylic acid (Poly I:C), a negative dsDNA control, or a positive control. Cytokine and chemokine production post-stimulation was measured by ELISA. The effects of E2 and P on TLR3 mRNA and protein expression were measured using Real Time RT-PCR and FACS analysis, respectively.

RESULTS

Stimulation of TLR3-expressing cells with the synthetic TLR3 ligand, Poly I:C, resulted in the production of cytokines and chemokines important for endometrial function and regulation. Suppression of Poly I:C-induced cytokine and chemokine production by cells treated with 10(-8) M E2, but not cells treated with 10(-7) M P, was observed in endometrial epithelial cell lines expressing TLR3 and estrogen receptor alpha (ERalpha). The effects of E2 were not observed on cells which did not express ERalpha or in cells pre-treated with the ER antagonist, ICI 182, 780. Treatment with E2 did not affect TLR3 mRNA or protein expression. However, treatment with E2 did suppress cytokine and chemokine production resulting from TLR3 stimulation with Poly I:C, suggesting that E2 modulates TLR3 function.

CONCLUSION

The data presented in this study are the first indication that E2 can markedly alter the innate immune response to dsRNA, providing a previously unreported process by which E2 can alter immune responses.

Inhibitory effect of all-trans retinoic acid on androgen-induced growth of mouse seminal vesicles in vivo and its mechanism

We examined the effect of all-trans retinoic acid (ATRA) on the androgen-induced growth of mouse seminal vesicles (SVs) in vivo and its mechanisms. Testosterone propionate (TP) alone or with ATRA was injected daily into adult castrated BALB/c mice. Injections of ATRA significantly inhibited the TP-induced growth of SVs in terms of wet weight and DNA synthesis by a pair of SVs evaluated by [3H]thymidine uptake. The bromodeoxyuridine labelling index showed that ATRA inhibited the proliferation of both epithelial and stromal cells. Immunoreactivity for retinoic acid receptor-alpha was found in the basal epithelial cells. Injections of ATRA affected neither 5alpha-reductase activity nor the expression of mRNAs for TGF-beta1, 2 and 3 and TGF-beta receptor 1 and 2 in the SVs. However, androgen receptor (AR) binding assays and Western blotting revealed a decrease in AR without a change in ligand-binding affinity. The present study showed that retinoid inhibited the androgen-induced growth of mouse SVs in vivo, and suggests that a decrease in AR is one of its mechanisms.

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.

Cell- and Ligand-specific Regulation of Promoters Containing Activator Protein-1 and Sp1 Sites by Estrogen Receptors α and β

Estrogen plays a critical role in development and maintenance of female reproductive and mammary tissues, but is also involved in maintenance of cardiovascular, skeletal, and neural function. Although it is widely accepted that the estrogen-occupied receptor mediates its effects by interacting with estrogen response elements (EREs) residing in target genes, a number of estrogen-responsive genes contain no identifiable ERE. To understand how estrogen-responsive genes lacking EREs but containing activator protein 1 (AP-1) and Sp1 sites respond to hormone treatment, we have identified four discrete regions of the human progesterone receptor gene that contain AP-1 or Sp1 sites and examined their abilities to modulate transcription in the presence of 17 beta-estradiol, ICI 182,780, tamoxifen, raloxifene, genistein, or daidzein. Transient cotransfection assays demonstrated that ER alpha was a more potent activator of transcription than ER beta in bone, uterine, and mammary cells. The Sp1-containing promoters were substantially more potent transcriptional enhancers than the AP-1-containing promoters, but a 1.5-kb region of the human progesterone receptor gene containing both AP-1 and Sp1 sites was the most hormone-responsive promoter tested. The ability of ligands to modulate transcription of AP-1- or Sp1-containing promoters was dependent on cell context, but the expression of AP-1 or Sp1 proteins was not necessarily related to transcriptional response. Taken together, these studies have helped to delineate the roles of ER alpha and ER beta in modulating transcription of genes containing AP-1 and Sp1 sites and define the effects of widely used, pharmacologic agents in target cells with distinct cellular environments.

Differential action of polycyclic aromatic hydrocarbons on endogenous estrogen-responsive genes and on a transfected estrogen-responsive reporter in MCF-7 cells

Polycyclic aromatic hydrocarbons (PAHs) are common environmental pollutants that have been extensively studied for multiple toxicological endpoints in both laboratory animals and humans. The purpose of this study was to investigate the estrogenicity of PAHs in the human breast cancer cell line MCF-7. We investigated 14 PAHs for their ability to bind either the estrogen receptor (ER) or the aryl hydrocarbon receptor (AhR) and to activate target gene expression. PAHs were tested in a human recombinant estrogen receptor (hrER) competitive binding assay, and in both an estrogen response element (ERE)- and xenobiotic response element (XRE)-mediated reporter gene assay. We used quantitative RT-PCR to examine selected PAHs that showed activity in the ERE reporter gene assay for their ability to upregulate estrogen-responsive genes HEM45, progesterone receptor, and pS2, and the aryl hydrocarbon-responsive CYP1A1 gene. None of the 14 PAHs bound the hrER, but five of the PAHs (anthracene, B[a]A, chrysene, B[b]F, and B[a]P) induced ER-reporter activity. This activity was dependent on the metabolism of PAHs in MCF-7 cells via the AhR pathway, which resulted in the formation of metabolites that bound the ER. None of the five PAHs that induced the ER-reporter were found to upregulate estrogen-responsive genes, yet four of the five PAHs induced AhR-dependent CYP1A1 gene expression. In contrast, a metabolite of B[a]P, 3'OH-B[a]P, and a PCB metabolite, 4'OH-2,4,6-BP, did weakly upregulate all three estrogen-responsive genes. Data from these studies indicate that induction of ER-reporter activity alone does not necessarily parallel endogenous gene transcription, and that the reporter gene assay may detect interactions that are not functional in vivo.

Differential regulation of the human progesterone receptor gene through an estrogen response element half site and Sp1 sites

The progesterone receptor (PR) gene is regulated by estrogen in normal reproductive tissues and in MCF-7 human breast cancer cells. Although it is generally thought that estrogen responsiveness is mediated by interaction of the ligand-occupied estrogen receptor (ER) with estrogen response elements (EREs) in target genes, the human progesterone receptor (PR) gene lacks a palindromic ERE. Promoter A of the PR gene does, however, contain an ERE half site upstream of two adjacent Sp1 sites from +571 to +595, the +571 ERE/Sp1 site. We have examined the individual contributions of the ERE half site and the two Sp1 sites in regulating estrogen responsiveness. Transient transfection assays demonstrated that both Sp1 sites were critical for estrogen-mediated activation of the PR gene. Interestingly, rather than decreasing transcription, mutations in the ERE half site increased transcription substantially suggesting that this site plays a role in limiting transcription. Chromatin immunoprecipitation assays demonstrated that Sp1 was associated with the +571 ERE/Sp1 site in the endogenous PR gene in the absence and in the presence of estrogen, but that ERalpha was only associated with this region of the PR gene after MCF-7 cells had been treated with estrogen. Our studies provide evidence that effective regulation of transcription through the +571 ERE/Sp1 site requires the binding of ERalpha and Sp1 to their respective cis elements and the appropriate interaction of ERalpha and Sp1 with other coregulatory proteins and transcription factors.

Fos and Jun inhibit estrogen-induced transcription of the human progesterone receptor gene through an activator protein-1 site

The progesterone receptor (PR) gene is activated by estrogen in normal reproductive tissues and in MCF-7 human breast cancer cells. Although it is typically thought that estrogen responsiveness is mediated through estrogen response elements (EREs), the human PR gene lacks a palindromic ERE sequence. We have identified an activating protein-1 (AP-1) site at +745 in the human PR gene that bound purified Fos and Jun and formed a complex with Fos/Jun heterodimers present in MCF-7 nuclear extracts. Surprisingly, mutating the +745 AP-1 site in the context of a 1.5-kb region of the PR gene significantly enhanced estrogen receptor (ER) alpha-mediated transactivation, suggesting that the wild-type +745 AP-1 site plays a role in inhibiting PR gene expression in the presence of hormone. In support of this idea, transient transfection assays demonstrated that increasing levels of Fos and Jun repressed transcription of a reporter plasmid containing the +745 AP-1 site. Fos levels were transiently increased, ERalpha levels were decreased, and Jun was dephosphorylated after MCF-7 cells were treated with estrogen. Chromatin immunoprecipitation assays demonstrated that Jun was associated with the +745 AP-1 site in the endogenous PR gene in the presence and in the absence of estrogen, but that ERalpha and Fos were only associated with the +745 AP-1 site after estrogen treatment of MCF-7 cells. Our studies suggest that the human PR gene is regulated by multiple transcription factors and that the differential binding of these dynamically regulated trans-acting factors influences gene expression.

Estrogen receptor alpha and Sp1 regulate progesterone receptor gene expression

The progesterone receptor (PR) gene is induced by estrogen in reproductive and mammary tissues and in MCF-7 human breast cancer cells even though the human PR gene lacks an estrogen response element. We have identified a region from -80 to -34 in the PR gene that contains two Sp1 sites and confers estrogen responsiveness to a heterologous promoter in an estrogen and estrogen receptoralpha (ERalpha)-dependent manner. Sp1 present in MCF-7 nuclear extracts and purified Sp1 bind to and protect both Sp1 sites from DNase I cleavage, but the proximal Sp1 site is preferentially protected. Mutation of either Sp1 site decreases Sp1-DNA complex formation and ERalpha-mediated transactivation. ERalpha enhances Sp1 binding, but does not interact directly with the -80/-34 region. Our studies suggest that ERalpha confers estrogen responsiveness to the PR gene by enhancing Sp1 interaction with the Sp1 site in the -80/-34 region of the human PR gene.

Heregulin induces transcriptional activation of the progesterone receptor by a mechanism that requires functional ErbB-2 and mitogen-activated protein kinase activation in breast cancer cells

The present study addresses the capacity of heregulin (HRG), a ligand of type I receptor tyrosine kinases, to transactivate the progesterone receptor (PR). For this purpose, we studied, on the one hand, an experimental model of hormonal carcinogenesis in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in female BALB/c mice and, on the other hand, the human breast cancer cell line T47D. HRG was able to exquisitely regulate biochemical attributes of PR in a way that mimicked PR activation by progestins. Thus, HRG treatment of primary cultures of epithelial cells of the progestin-dependent C4HD murine mammary tumor line and of T47D cells induced a decrease of protein levels of PRA and -B isoforms and the downregulation of progesterone-binding sites. HRG also promoted a significant increase in the percentage of PR localized in the nucleus in both cell types. DNA mobility shift assay revealed that HRG was able to induce PR binding to a progesterone response element (PRE) in C4HD and T47D cells. Transient transfections of C4HD and T47D cells with a plasmid containing a PRE upstream of a chloramphenicol acetyltransferase (CAT) gene demonstrated that HRG promoted a significant increase in CAT activity. In order to assess the molecular mechanisms underlying PR transactivation by HRG, we blocked ErbB-2 expression in C4HD and T47D cells by using antisense oligodeoxynucleotides to ErbB-2 mRNA, which resulted in the abolishment of HRG's capacity to induce PR binding to a PRE, as well as CAT activity in the transient-transfection assays. Although the inhibition of HRG binding to ErbB-3 by an anti-ErbB-3 monoclonal antibody suppressed HRG-induced PR activation, the abolishment of HRG binding to ErbB-4 had no effect on HRG activation of PR. To investigate the role of mitogen-activated protein kinases (MAPKs), we used the selective MEK1/MAPK inhibitor PD98059. Blockage of MAPK activation resulted in complete abrogation of HRG's capacity to induce PR binding to a PRE, as well as CAT activity. Finally, we demonstrate here for the first time that HRG-activated MAPK can phosphorylate both human and mouse PR in vitro.

Messenger RNA for progesterone receptor isoforms in the late-gestation rat uterus

The progesterone receptor (PR) has three isoforms, PR-A, PR-B, and PR-C, which have different physiological effects. PR-A may inhibit PR-B-mediated transcription. Parturition requires withdrawal of progesterone (P4). This could occur through decreased P4 concentrations and/or a change in PR isoforms to diminish the effect of P4. We measured mRNA for PR isoforms in rat uterine tissues through late gestation and investigated the effects of antagonists to estrogen (tamoxifen) and P4 (RU-486). Two specific probes were used for ribonuclease protection assays; one (PR-total) measured PR-A, PR-B, and PR-C, and the other recognized only PR-B. PR-total mRNA increased significantly through late gestation, whereas PR-B was unchanged. The ratio of PR-total to PR-B peaked on the day before parturition. Tamoxifen delayed parturition and inhibited the increase in PR-total without affecting PR-B mRNA. RU-486 caused early parturition associated with increased PR-total mRNA, with no change in PR-B. We conclude that there are significant changes in PR isoforms in late-gestation rat uterus. These changes may be regulated by estrogen and P4 and may influence the timing of parturition.

Seasonal changes in hepatic progesterone receptor mRNA, estrogen receptor mRNA, and vitellogenin mRNA in the painted turtle, Chrysemys picta

Previous studies using the fresh water turtle Chrysemys picta have demonstrated that progesterone (P) inhibits estradiol (E)-induced vitellogenin (vtg) secretion in this species. Further, there is evidence for the differential expression of the two P receptor isoforms (PRA and PRB) in the liver during the turtle seasonal cycle, correlating with hepatic vitellogenesis. In this study we report changes in the hepatic PR mPNA, ER mRNA, and vitellogenin (vtg) mRNA transcripts during the reproductive cycle of the turtle. Fragments of the turtle hepatic PR and ER cDNAs were cloned and sequenced and a previously cloned turtle vtg cDNA were used as probes in Northern blotting. No 3.7-kb PR mRNA, corresponding to the smaller PR transcript, PRA of other species was found, although, a smaller 1.8-kb transcript (putative PRC mRNA) was present. These observations suggest that the turtle as in the chicken and human, the 4.5-kb PR mRNA transcript encodes both PRA and PRB proteins. Only the larger PR mRNA transcript (4.5-kb), was found to vary significantly during the annual cycle, being highest when vitellogenesis was inhibited in winter and summer. Vtg mRNA could not be detected during the summer or winter, was highest during vitellogenesis in the spring, and reappeared during the fall period of vitellogenesis and ovarian recrudescence. ER mRNA followed a similar pattern, being highest during spring and early fall, when vtg synthesis is high. The data suggest that P/PR, as well as E/ER, may be involved in the seasonal regulation of hepatic vitellogenesis in this species.

Glucocorticoid receptors in hippocampal neurons that do not engage proteasomes escape from hormone-dependent down-regulation but maintain transactivation activity

The glucocorticoid receptor (GR) protein is subjected to hormone-dependent down-regulation in most cells and tissues. This reduction in receptor levels that accompanies chronic hormone exposure serves to limit hormone responsiveness and operates at transcriptional, posttranscriptional, and posttranslational levels. The ability of glucocorticoid hormones to trigger GR down-regulation may be not universal, particularly in mature and developing neurons in which conflicting results regarding hormone control of GR protein have been reported. We find that endogenous GR is not down-regulated in the HT22 mouse hippocampal cell line and in primary hippocampal neurons derived from embryonic rats. Because GR has the capacity to be ubiquitylated in HT22 cells, receptor down-regulation must be limited by defects in either targeting of polyubiquitylated receptor to the proteasome or processing of the targeted receptor by the proteasome. Despite the lack of GR down-regulation in the HT22 cells, glucocorticoid-induced transcription from transiently transfected templates is attenuated upon prolonged hormone treatment. This termination of GR transactivation is not due to inefficient nuclear import or nuclear retention of the receptor. Furthermore, GR efficiently exports from HT22 cell nuclei in hormone-withdrawn cells, indicating that the receptor has access to both nuclear and cytoplasmic degradation pathways. Our results suggest that appropriate maturation of proteasomal degradative or targeting activities may be required, particularly in hippocampal neurons, for hormone-dependent down-regulation of GR.

Coactivation of an endogenous progesterone receptor by TIF2 in COS-7 cells

Transfection experiments, a powerful tool to study the function of steroid hormone receptors and their coregulators, are often performed in COS-7 cells, because of high transfection efficiencies and expression levels. Here we report on the presence in COS-7 cells of an endogenous steroid hormone receptor, which is highly responsive to progesterone and the synthetic steroids R1881 and ORG2058, but not to 5 alpha-DHT. A 10-fold excess of the progesterone antagonist RU486 abolishes the stimulation by progesterone, while cotransfection with the coactivator TIF2 increases its activity 6- to 7-fold. A comparison of the ligand specificity with transfected androgen or progesterone receptors indicates that the endogenous receptor is a progesterone receptor. Its presence is confirmed by steroid-binding experiments, RT-PCR and Northern blot analysis. Consequently, progesterone receptor function may be studied conveniently in COS-7 cells without cotransfection of receptor, but the endogenous receptor may interfere in studies of ligand specificity and coactivation of cotransfected receptors.

Estrogen receptor isoform-specific induction of progesterone receptors in human osteoblasts

Estrogen induction of progesterone receptor (PR) expression may be important to bone physiology because progesterone has been implicated in the control of bone formation and resorption. Although PR gene expression can be induced in osteoblasts by estrogen signaling through the estrogen receptor (ER) a isoform, it is unknown whether the ER-beta isoform is involved in this regulation. The effect of estrogen on PR expression was examined in human fetal osteoblast (hFOB) cell lines stably transfected with either ER-alpha or ER-beta. Estrogen treatment of hFOB/ER-a cells induced PR messenger RNA (mRNA) steady-state levels after 24 h and protein levels after 48 h, as established by competitive reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting. Interestingly, no induction of PR expression was observed in the hFOB/ER-beta cells during this period. However, PR mRNA was induced progressively after 48 h of treatment with estrogen with maximum levels achieved at 12 days posttreatment. ER protein also was increased after 12 days of treatment. Both A and B isoforms of PR (PRA and PRB) were induced by estrogen in the hFOB/ER-a cells as well as much later in hFOB/ER-beta cells. The pure antiestrogen ICI 182,780 prevented PR induction by estrogen in both cell lines. An ER-beta-selective antagonist R, R-tetrahydrochrysene (THC) abolished the induction of PR mRNA in hFOB/ER-beta but not in hFOB/ER-a cells, verifying that the response in the former cell line was ER-beta-mediated. Transient cotransfection of hFOB cells with ER-a or ER-beta together with either a human PRA or PRB promoter linked to a reporter plasmid revealed that although the PRB promoter was stimulated equally by estrogen activation of either ER isoform, PRA was activated preferentially by ER-alpha. Together, these results show that although estrogen can up-regulate endogenous PR gene expression in osteoblasts via both ER isoforms, ER-alpha is the predominant inducer.

Early gene expression changes preceding thyroid hormone-induced involution of a thyrotrope tumor

Treatment with thyroid hormone (TH) results in shrinkage of a thyrotropic tumor grown in a hypothyroid host. We used microarray and Northern analysis to assess the changes in gene expression that preceded tumor involution. Of the 1,176 genes on the microarray, 7 were up-regulated, whereas 40 were decreased by TH. Many of these were neuroendocrine in nature and related to growth or apoptosis. When we examined transcripts for cell cycle regulators only cyclin-dependent kinase 2, cyclin A and p57 were down-regulated, whereas p15 was induced by TH. Retinoblastoma protein, c-myc, and mdm2 were unchanged, but E2F1 was down-regulated. TH also decreased expression of brain-derived neurotrophic factor, its receptor trkB, and the receptor for TRH. These, in addition to two other genes, neuronatin and PB cadherin, which were up- and down-regulated, respectively, showed a more rapid response to TH than the cell cycle regulators and may represent direct targets of TH. Finally, p19ARF was dramatically induced by TH, and although this protein can stabilize p53 by sequestering mdm2, we found no increase in p53 protein up to 48 h of treatment. In summary, we have described early changes in the expression of genes that may play a role in TH-induced growth arrest of a thyrotropic tumor. These include repression of specific growth factor and receptors and cell cycle genes as well as induction of other factors associated with growth arrest and apoptosis.

Hormonal regulation of tumor suppressor proteins in breast cancer cells

This laboratory is studying hormonal regulation of tumor suppressor proteins, p53 and retinoblastoma (pRB). Estrogen receptor and progesterone receptor positive human breast cancer cell lines, T47D and MCF-7, were utilized for determining influence of hormonal and antihormonal agents on the level of expression of p53, state of phosphorylation of pRB, and rate of cell proliferation. The expression of p53 in T47D cells grown for 4-5 days in culture medium containing charcoal-treated (stripped) fetal bovine serum declined gradually to 10% of the level seen in control (whole serum, non charcoal-treated) groups. Supplementation of culture medium containing stripped serum with 0.1-1 nM estradiol (E(2)) restored p53 to its level seen in the control within 6-24 h. Under above conditions, treatment of cells with R5020 or RU486 reduced (15-30%) the level of p53. Incubation of cells in E(2)-containing growth medium caused cell proliferation and hyperphosphorylation of pRB; the latter effect was seen maximally between 24-72 h. The E(2)-induced hyperphosphorylation of pRB and increase in the level of p53 were sensitive to the presence of ICI and 4-hydroxy tamoxifen (OHT). T47D and MCF-7 cells were also transiently transfected with a P1CAT reporter plasmid containing c-Myc responsive element and the levels of chloramphenicol acetyltransferase (CAT) activity were observed in response to various treatments. E(2) and OHT caused P1CAT induction as seen by increased CAT activity: E(2) caused an endogenous increase in the expression of an ICI-sensitive c-Myc form. These data suggest that estrogen upregulates p53 expression while progesterone downregulates this process. Further, E(2) regulates p53 level and pRB activity in a coordinated manner.

The effect of thyroid hormone and a long-acting somatostatin analogue on TtT-97 murine thyrotropic tumors

Thyroid hormone inhibits thyrotropin (TSH) production and thyrotrope growth. Somatostatin has been implicated as a synergistic factor in the inhibition of thyrotrope function. We have previously shown that pharmacological doses of thyroid hormone (levothyroxine [LT4]) inhibit growth of murine TtT-97 thyrotropic tumors in association with upregulation of somatostatin receptor type 5 (sst5) mRNA and somatostatin receptor binding. In the current study, we examined the effect of physiological thyroid hormone replacement alone or in combination with the long-acting somatostatin analogue, Sandostatin LAR, on thyrotropic tumor growth, thyrotropin growth factor-beta (TSH-beta), and sst5 mRNA expression, as well as somatostatin receptor binding sites. Physiological LT4 replacement therapy resulted in tumor shrinkage in association with increased sst5 mRNA levels, reduced TSH-beta mRNA levels and enhanced somatostatin receptor binding. Sandostatin LAR alone had no effect on any parameter measured. However, Sandostatin LAR combined with LT4 synergistically inhibited TSH-beta mRNA production and reduced final tumor weights to a greater degree. In this paradigm, Sandostatin LAR required a euthyroid status to alter thyrotrope parameters. These data suggest an important interaction between the somatostatinergic system and thyroid hormone in the regulation of thyrotrope cell structure and function.

Phosphorylation of human progesterone receptors at serine-294 by mitogen-activated protein kinase signals their degradation by the 26S proteasome

Ligand-dependent down-regulation that leads to rapid and extensive loss of protein is characteristic of several nuclear steroid receptors, including human progesterone receptors (PRs). In breast cancer cells, >95% of PRs are degraded 6 h after the start of progestin treatment. The mechanism for down-regulation is unknown. We examined the role of PR phosphorylation by mitogen-activated protein kinases (MAPKs) in this process. Lactacystin and calpain inhibitor I, specific inhibitors of the 26S proteasome, blocked progestin-induced down-regulation, and ubiquitinated conjugates of PR accumulated in cells. Ligand-dependent PR degradation was also blocked by specific inhibition of p42 and p44 MAPKs. To define the targets of phosphorylation by this kinase, two serine/proline MAPK consensus sites on PR were mutated. We demonstrate that mutation of PR serine-294 to alanine (S294A) specifically and completely prevents ligand-dependent receptor down-regulation. We also find that rapid, ligand-independent degradation of immature PR intermediates occurs by a proteasome-mediated pathway. These results demonstrate that PR destruction, by either of two alternate routes, is mediated by the 26S proteasome. Specifically, down-regulation of mature PRs occurs by a mechanism in which ligand binding activates PR phosphorylation by MAPKs at a unique serine residue, which then targets the receptors for degradation.

Progesterone receptor A and B messenger ribonucleic acid levels in the anterior pituitary of rats are regulated by estrogen

In target tissues of most mammalian and avian species, progesterone receptors (PR) are expressed as structurally related, but functionally distinct, isoforms A and B, and they are regulated by estrogen (E) as well as by their cognate ligand, progesterone (P(4)). The objectives of the present work were to identify mRNA expression for the A and B isoforms of PR in the anterior pituitary of the rat, to examine its regulation by gonadal steroids, and to compare this regulation with that in the primary target organ, the uterus. Messenger RNAs for the PR isoforms, determined by two separate reverse transcription-polymerase chain reaction protocols, one that detects PR A and PR B equally and the other specific for PR B, were identified in anterior pituitary of female and male rats. In anterior pituitary of cycling female rats, steady-state mRNA levels for both PR A+B and PR B were highest at 0900 h on proestrus, declined rapidly to nadir values at 0900 h on metestrus (PR A+B) or 0900 h on estrus (PR B), and remained below proestrous values through 2100 h on diestrus. Administration of E to intact proestrous female rats caused significant increases in mRNA for both PR A+B and PR B on estrus and metestrus. Blockade of P(4) action by administration of the antiprogestins RU-486 and ZK-98299 on proestrus had no effect on PR mRNA levels on the morning of estrus. Ovariectomy two and ten days after surgery markedly reduced mRNA levels for both PR A+B and PR B. Whereas treatment of 10-day-ovariectomized rats with E led to marked induction of mRNA for PR A+B and PR B two days later, treatment with P(4) one day after treatment had no effect on basal or E-stimulated PR mRNA. Regulation of PR mRNA expression in the pituitary differed from that in the uterus, in which P(4) treatment of ovariectomized rats antagonized the E-induced rise in mRNA for PR B, and antiprogestins increased mRNA for both isoforms. In addition to induction of PR mRNA in the pituitary of female rats by E in vivo, we also demonstrated induction by E in primary culture of anterior pituitary cells in vitro. We conclude that in the anterior pituitary of female rats, both the A and B isoforms of PR are expressed and regulated by E.

Homologous androgen receptor up-regulation in osteoblastic cells may be associated with enhanced functional androgen responsiveness

Although androgens have myriad effects on the skeleton, the regulation of androgen action in bone is not well understood. Androgen receptors (ARs) are known to play an important role in mediating androgen action. We have examined the effects of androgens and other sex steroids on AR levels in osteoblastic cells in vitro using two clonal human cell lines, SaOS-2 and U-2 OS. AR protein levels were quantitated both by specific androgen binding studies and Western analyses, and AR messenger RNA was measured with RNase protection assays. Potential changes in AR functionality was assessed by reporter assays. Treatment of osteoblastic cells with the nonaromatizable androgen 5alpha-dihydrotestosterone (DHT) increased specific androgen binding 2-to 4-fold. Similar increases in AR protein levels were documented by Western analysis in both cell lines. The androgen-mediated increase in receptor levels was time and dose dependent as well as androgen specific. Steady-state AR messenger RNA levels were also increased by DHT. When AR concentrations in osteoblastic cells were elevated with exogenous receptor, there was an enhancement of DHT responsiveness, measured by increased trans-activation of an androgen-responsive promoter. Thus, androgen exposure increased androgen receptor protein levels and specific androgen binding in osteoblastic cells. Androgen action as measured by androgen-mediated transcriptional activation is enhanced in the presence of elevated AR levels. Consequently, these studies have revealed an additional means by which androgens may modulate skeletal metabolism.

Steroid regulation of progesterone receptor expression in cultured rat gonadotropes

During the preovulatory period, the pituitary action of progesterone is biphasic, moving from a severalfold augmentation of the gonadotropin release action of GnRH to a suppression of GnRH efficacy, which occurs in rats over a period of about 12 h, but the extent to which these biphasic effects are dependent on alterations in progesterone receptor (PR) expression is not known. To address this, as well as the localization of PR in cultured rat pituitary cells, we used cells from ovariectomized rats cultured +/- 0.2 nM E2 with acute progesterone treatment on day 3. Northern blot of poly(A+) RNA extracts showed multiple PR messenger RNA (mRNA) transcripts between 4.8-10.2 kb; E2 treatment led to a 5- to 6-fold increase in the predominant PR mRNA transcripts (5.1 and 10.1 kb). In the presence of E2, 200 nM progesterone resulted in a decrease in steady-state PR mRNA levels by 3 h of exposure, with the greatest decrease around 6 h (50% of E2 control) and recovery by 12 h. Similarly treated pituitary cultures were subjected to dual immunofluorescence staining for LH and PR. In the absence of E2, PR was undetectable. In the presence of E2, essentially all LH-positive cells were positive for PR and only 1-2% of PR-immunopositive cells were negative for LH, possibly reflecting FSH-exclusive gonadotropes. PR staining was predominantly nuclear, but 20 nM progesterone led to a gradual increase in cytoplasmic staining, with the nuclear-to-cytoplasmic ratio decreasing to near unity by 9-12 h of exposure. In summary, we show for the first time, that PR colocalizes with LH in cultured female rat pituitary cells and that E2 induces expression of PR mRNA, as well as PR protein, in rat gonadotropes. In the presence of E2, progesterone causes a rapid but transient down-regulation of PR message; recovery of PR mRNA is accompanied by an increase in cytoplasmic PR, suggestive of an increase in synthesis. These dynamic changes implicate the gonadotrope PR as having a significant role within the temporal context of the rat preovulatory period.

Convergence of progesterone with growth factor and cytokine signaling in breast cancer. Progesterone receptors regulate signal transducers and activators of transcription expression and activity

STATS (signal transducers and activators of transcription) are latent transcription factors activated in the cytoplasm by diverse cell surface signaling molecules. Like progesterone receptors (PR), Stat5a and 5b are required for normal mammary gland growth and differentiation. These two proteins are up-regulated during pregnancy, a period dominated by high levels of progesterone. We now show that progestin treatment of breast cancer cells regulates Stat5a and 5b, Stat3, and Stat1 protein levels in a PR-dependent manner. In addition, progestin treatment induces translocation of Stat5 into the nucleus, possibly mediated by the association of PR and Stat5. Last, progesterone pretreatment enhances the phosphorylation of Stat5 on tyrosine 694 induced by epidermal growth factor. Functional data show that progestin pretreatment of breast cancer cells enhances the ability of prolactin to stimulate the transcriptional activity of Stat5 on a beta-casein promoter. Progesterone and epidermal growth factor synergize to control transcription from p21(WAF1) and c-fos promoters. These data demonstrate the convergence of progesterone and growth factor/cytokine signaling pathways at multiple levels, and suggest a mechanism for coordination of PR and Stat5-mediated proliferative and differentiative events in the mammary gland.