Transcriptional hyperactivity of human progesterone receptors is coupled to their ligand-dependent down-regulation by mitogen-activated protein kinase-dependent phosphorylation of serine 294

Regulatory mechanisms of steroid hormone receptors on gene transcription through chromatin interaction and enhancer reprogramming

Regulation of steroid hormone receptors (SHRs) on transcriptional reprogramming is crucial for breast cancer progression. SHRs, including estrogen receptor (ER), androgen receptor (AR), progesterone receptor (PR), and glucocorticoid receptor (GR) play key roles in remodeling the transcriptome of breast cancer cells. However, the molecular mechanisms by which SHRs regulate chromatin landscape in enhancer regions and transcription factor interactions remain largely unknown. In this review, we summarized the regulatory effects of 3 types of SHRs (AR, PR, and GR) on gene transcription through chromatin interactions and enhancer reprogramming. Specifically, AR and PR exhibit bi-directional regulatory effects (both inhibitory and promoting) on ER-mediated gene transcription, while GR modulates the transcription of pro-proliferation genes in ER-positive breast cancer cells. In addition, we have presented four enhancer reprogramming mechanisms (transcription factor cooperation, pioneer factor binding, dynamic assisted loading, and tethering) and the multiple enhancer-promoter contact models. Based on these mechanisms and models, this review proposes that the combination of multiple therapy strategies such as agonists/antagonists of SHRs plus endocrine therapy and the adoption of the latest sequencing technologies are expected to improve the efficacy of ER positive breast cancer treatment.

Site-specific O-GlcNAcylation of progesterone receptor (PR) supports PR attenuation of interferon stimulated genes (ISGs) and tumor growth in breast cancer

Hormone receptor positive (HR+) breast cancer, defined by expression of estrogen receptor (ER) and/or progesterone receptor (PR), is the most commonly diagnosed type of breast cancer. PR alters the transcriptional landscape to support tumor growth in concert with, or independent of, ER. Understanding the mechanisms regulating PR function is critical to developing new strategies to treat HR+ breast cancer. O-linked β-N-acetylglucosamine (O-GlcNAc) is a posttranslational modification responsible for nutrient sensing that modulates protein function. Although PR is heavily posttranslationally modified, through both phosphorylation and O-GlcNAcylation, specific sites of O-GlcNAcylation on PR and how they regulate PR action have not been investigated. Using established PR-expressing breast cancer cell lines, we mapped several sites of O-GlcNAcylation on PR. RNA-sequencing after PR O-GlcNAc site mutagenesis revealed site-specific O-GlcNAcylation of PR is critical for ligand-independent suppression of interferon signaling, a regulatory function of PR in breast cancer. Furthermore, O-GlcNAcylation of PR enhances PR-driven tumor growth in vivo. Herein, we have delineated one contributing mechanism to PR function in breast cancer that impacts tumor growth and provided additional insight into the mechanism through which PR attenuates interferon signaling.

Progesterone (P4) ameliorates cigarette smoke-induced chronic obstructive pulmonary disease (COPD)

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory lung disease associated with high morbidity and mortality worldwide. Oxidative injury and mitochondrial dysfunction in the airway epithelium are major events in COPD progression.

METHODS AND RESULTS

The therapeutic effects of Progesterone (P4) were investigated in vivo and in vitro in this study. In vivo, in a cigarette smoke (CS) exposure-induced COPD mouse model, P4 treatment significantly ameliorated CS exposure-induced physiological and pathological characteristics, including inflammatory cell infiltration and oxidative injury, in a dose-dependent manner. The c-MYC/SIRT1/PGC-1α pathway is involved in the protective function of P4 against CS-induced COPD. In vitro, P4 co-treatment significantly ameliorated H2O2-induced oxidative injury and mitochondrial dysfunctions by promoting cell proliferation, increasing mitochondrial membrane potential, decreasing ROS levels and apoptosis, and increasing ATP content. Moreover, P4 co-treatment partially attenuated H2O2-caused inhibition in Nrf1, Tfam, Mfn1, PGR-B, c-MYC, SIRT1, and PGC-1α levels. In BEAS-2B and ASM cells, the c-MYC/SIRT1 axis regulated P4's protective effects against H2O2-induced oxidative injury and mitochondrial dysfunctions.

CONCLUSION

P4 activates the c-MYC/SIRT1 axis, ameliorating CS-induced COPD and protecting both airway epithelial cells and smooth muscle cells against H2O2-induced oxidative damage. PGC-1α and downstream mitochondrial signaling pathways might be involved.

Progesterone resistance in endometriosis: A pathophysiological perspective and potential treatment alternatives

Background

Endometriosis is a common gynecological disease affecting women of reproductive age. Patients with endometriosis frequently experience severe chronic pain and have higher chances to experience infertility. Progesterone resistance is a major problem that develops during the medical treatment of endometriosis, which often leads to treatment failure of hormonal therapies. Previous studies indicated that the dysregulation of progesterone receptors (PR) is the primary factor leading to progesterone resistance in endometriosis.

Methods

This review article systematically reviewed and summarized findings extracted from previously published papers available on PubMed, encompassing both experimental studies and clinical trials.

Main findings

Various determinants influencing PR expression in endometriosis have been identified, including the environmental toxins, microRNAs, cell signaling pathways, genetic mutations, and the pro-inflammatory cytokines. The selective estrogen/progesterone receptor modulators have emerged as novel therapeutic approaches for treating endometriosis, offering potential improvements in overcoming progesterone resistance.

Conclusion

Concerns and limitations persist despite the newly developed drugs. Therefore, studies on unraveling new therapeutic targets based on the molecular mechanisms of progesterone resistance is warranted for the development potential alternatives to overcome hormonal treatment failure in endometriosis.

Regulation of progesterone receptor expression in endometriosis, endometrial cancer, and breast cancer by estrogen, polymorphisms, transcription factors, epigenetic alterations, and ubiquitin-proteasome system

The uterus and breasts are hormone-responsive tissues. Progesterone and estradiol regulate gonadotropin secretion, prepare the endometrium for implantation, maintain pregnancy, and regulate the differentiation of breast tissue. Dysregulation of these hormones causes endometriosis, endometrial cancer, and breast cancer, damaging the physical and mental health of women. Emerging evidence has shown that progesterone resistance or elevated progesterone activity is the primary hormonal substrate of these diseases. Since progesterone acts through its specific nuclear receptor, the abnormal expression of the progesterone receptor (PR) dysregulates progesterone function. This review discusses the regulatory mechanisms of PR expression in patients with endometriosis, and endometrial or breast cancer, including estrogen, polymorphisms, transcription factors, epigenetics, and the ubiquitin-proteasome system. (1) Estrogen promotes the expression of PRA (a PR isoform) mRNA and protein through the interaction of estrogen receptors (ERs) and Sp1 with half-ERE/Sp1 binding sites. ERs also affect the binding of Sp1 and Sp1 sites to promote the expression of PRB (another PR isoform)(2) PR polymorphisms, mainly PROGINS and + 331 G/A polymorphism, regulate PR expression by affecting DNA methylation and transcription factor binding. (3) The influence of epigenetic alterations on PR expression occurs through DNA methylation, histone modification, and microRNA. (4) As one of the main protein degradation pathways in vivo, the ubiquitin-proteasome system (UPS) regulates PR expression by participating in protein degradation. These mechanisms may provide new molecular targets for diagnosing and treating endometriosis, endometrial, and breast cancer.

Enhancing progestin therapy via HDAC inhibitors in endometrial cancer

Uterine endometrial cancer (EC) incidence and deaths are on the rise. Hormone therapy, a traditional treatment regimen for this disease, uses progesterone and its synthetic analogue, progestin, to induce cell differentiation, apoptosis, and inhibition of invasion. This therapy is highly effective for progesterone receptor (PR) positive tumors in the short term. However, responsiveness decreases over time due to loss of PR expression; acquired resistance leads to treatment failure and poor prognosis. Primary resistance occurs in advanced, PR-negative tumors. Regardless, progestin therapy can be effective if the PR downregulation mechanism is reversed and if functional PR expression is restored. Using histone deacetylase inhibitors (HDACi), we inhibited cell proliferation in three EC cell lines and restored functional PR expression at the mRNA and protein levels. Two HDACi were tested using an endometrial xenograft tumor model: entinostat, an oral drug, and romidepsin, an IV drug. In vitro and in vivo studies support that entinostat decreased EC tumor growth, induced differentiation, and increased expression of the PR-targeted gene, PAEP. These findings supported the approval of a new NIH NCTN clinical trial, NRG-GY011, which concluded that dual treatment of MPA and entinostat, decreased expression of the proliferation marker, Ki67, but did not increase PR expression relative to single treatment with MPA in this short-term study. Therefore, a more potent HDACi, romidepsin, was investigated. Romidepsin treatment inhibited tumor growth and enhanced progestin treatment efficacy. More importantly, PR, PAEP, and KIAA1324 expressions were upregulated. Using a chromatin immunoprecipitation assay, we verified that HDACi can reverse PR downregulation mechanisms in mice models. Other potential drug efficacy markers, such as CD52, DLK1, GALNT9, and GNG2, were identified by transcriptome analysis and verified by q-PCR. Many of the upregulated drug efficacy markers predict favorable patient outcomes, while downregulated genes predict worse survival. Here, our current data suggests that romidepsin is a more potent HDACi that has the potential to achieve more robust upregulation of PR expression and may be a more promising candidate for future clinical trials.

PRMT1, a Key Modulator of Unliganded Progesterone Receptor Signaling in Breast Cancer

The progesterone receptor (PR) is a key player in major physiological and pathological responses in women, and the signaling pathways triggered following hormone binding have been extensively studied, particularly with respect to breast cancer development and progression. Interestingly, growing evidence suggests a fundamental role for PR on breast cancer cell homeostasis in hormone-depleted conditions, with hormone-free or unliganded PR (uPR) involved in the silencing of relevant genes prior to hormonal stimulation. We herein identify the protein arginine methyltransferase PRMT1 as a novel actor in uPR signaling. In unstimulated T47D breast cancer cells, PRMT1 interacts and functions alongside uPR and its partners to target endogenous progesterone-responsive promoters. PRMT1 helps to finely tune the silencing of responsive genes, likely by promoting a proper BRCA1-mediated degradation and turnover of unliganded PR. As such, PRMT1 emerges as a key transcriptional coregulator of PR for a subset of relevant progestin-dependent genes before hormonal treatment. Since women experience periods of hormonal fluctuation throughout their lifetime, understanding how steroid receptor pathways in breast cancer cells are regulated when hormones decline may help to determine how to override treatment failure to hormonal therapy and improve patient outcome.

Membrane-Initiated Estrogen, Androgen, and Progesterone Receptor Signaling in Health and Disease

Rapid effects of steroid hormones were discovered in the early 1950s, but the subject was dominated in the 1970s by discoveries of estradiol and progesterone stimulating protein synthesis. This led to the paradigm that steroid hormones regulate growth, differentiation, and metabolism via binding a receptor in the nucleus. It took 30 years to appreciate not only that some cellular functions arise solely from membrane-localized steroid receptor (SR) actions, but that rapid sex steroid signaling from membrane-localized SRs is a prerequisite for the phosphorylation, nuclear import, and potentiation of the transcriptional activity of nuclear SR counterparts. Here, we provide a review and update on the current state of knowledge of membrane-initiated estrogen (ER), androgen (AR) and progesterone (PR) receptor signaling, the mechanisms of membrane-associated SR potentiation of their nuclear SR homologues, and the importance of this membrane-nuclear SR collaboration in physiology and disease. We also highlight potential clinical implications of pathway-selective modulation of membrane-associated SR.

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.

Mechanical stiffness augments ligand-dependent progesterone receptor B activation via MEK 1/2 and Rho/ROCK-dependent signaling pathways in uterine fibroid cells

OBJECTIVE

To test whether mechanical substrate stiffness would influence progesterone receptor B (PRB) signaling in fibroid cells. Uterine fibroids feature an excessive extracellular matrix, increased stiffness, and altered mechanical signaling. Fibroid growth is stimulated by progestins and opposed by anti-progestins, but a functional interaction between progesterone action and mechanical signaling has not been evaluated.

DESIGN

Laboratory studies.

SETTING

Translational science laboratory.

PATIENT(S)/ANIMAL(S)

Human fibroid cell lines and patient-matched fibroid and myometrial cell lines.

INTERVENTION(S)

Progesterone receptor B-dependent reporter assays and messenger RNA quantitation in cells cultured on stiff polystyrene plates (3GPa) or soft silicone plates (930KPa). Pharmacologic inhibitors of extracellular signal-related protein kinase (ERK) kinase 1/2 (MEK 1/2; PD98059), p38 mitogen-activated protein kinase (SB202190), receptor tyrosine kinases (RTKs; nintedanib), RhoA (A13), and Rho-associated coiled-coil kinase (ROCK; Y27632).

MAIN OUTCOME MEASURE(S)

Progesterone-responsive reporter activation.

RESULT(S)

Fibroid cells exhibited higher PRB-dependent reporter activity with progesterone (P4) in cells cultured on stiff vs. soft plates. Mechanically induced PRB activation with P4 was decreased 62% by PD98059, 78% by nintedanib, 38% by A13, and 50% by Y27632. Overexpression of the Rho-guanine nucleotide exchange factor (Rho-GEF), AKAP13, significantly increased PRB-dependent reporter activity. Collagen 1 messenger RNA levels were higher in fibroid cells grown on stiff vs. soft plates with P4.

CONCLUSION(S)

Cells cultured on mechanically stiff substrates had enhanced PRB activation via a mechanism that required MEK 1/2 and AKAP13/RhoA/ROCK signaling pathways. These studies provide a framework to explore the mechanisms by which mechanical stiffness affects progesterone receptor activation.

Progesterone modulates neuronal excitability bidirectionally

Progesterone acts on neurons directly by activating its receptor and through metabolic conversion to neurosteroids. There is emerging evidence that progesterone exerts excitatory effects by activating its cognate receptors (progesterone receptors, PRs) through enhanced expression of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs). Progesterone metabolite 5α,3α-tetrahydro-progesterone (allopregnanolone, THP) mediates its anxiolytic and sedative actions through the potentiation of synaptic and extrasynaptic γ-aminobutyric acid type-A receptors (GABAARs). Here, we review progesterone's neuromodulatory actions exerted through PRs and THP and their opposing role in regulating seizures, catamenial epilepsy, and seizure exacerbation associated with progesterone withdrawal.

Expression of nuclear progesterone receptors (nPRs), membrane progesterone receptors (mPRs) and progesterone receptor membrane components (PGRMCs) in the human endometrium after 6 months levonorgestrel low dose intrauterine therapy

The classical steroid receptors (nuclear receptors), including those for progesterone (nPRs), are thoroughly characterized. The knowledge about so-called non-genomic effects, which are mediated by extra-nuclear initiated signals, has increased immensely the last decades. In a previous clinical study of endometrial hyperplasia, we observed that the antiproliferative progestin effect persisted after 3 months treatment with levonorgestrel (LNG) intrauterine system (IUS) even with a complete downregulation of nPRs. This raised the question of what other mechanisms than signaling through nPRs could explain such an observation. In the present study, RT-qPCR was employed to characterize mRNA expression for nPRs, membrane progesterone receptors (mPRs) and progesterone receptor membrane components (PGRMCs) in women (n = 42) with endometrial hyperplasia that received intrauterine low dose LNG for 6 months. At the end of this period endometrial tissue showed that nPRs were virtually completely downregulated (≈ 10 % of baseline) whereas the levels of remaining mPRs, subtype-α, -β and -γ were 76 %, 59 % and 73 % of baseline, respectively. PGRMC1 was downregulated to 15 % of baseline, in contrast to PGRMC2, which was upregulated to about 30 % above baseline. We used human cancer cells from uterine cervix (C-4I cells) as control. Progesterone caused a concentration-dependent antiproliferative effect but in several and separate studies, we were unable to detect nPRs (immunocytochemistry) in the C-4I cells. The use of RT-qPCR showed that nPRs were undetectable in C-4I cells, in contrast to mPRs and PGRMCs with a distinct mRNA expression. The present study suggests that mPRs and/or PGRMCs preserve the antiproliferative effect of LNG in the human endometrium and are responsible for the concentration-dependent antiproliferative effect of progesterone in C-4I cells.

90 YEARS OF PROGESTERONE: Steroid receptors as MAPK signaling sensors in breast cancer: let the fates decide

Steroid hormone receptors (SRs) are classically defined as ligand-activated transcription factors that function as master regulators of gene programs important for a wide range of processes governing adult physiology, development, and cell or tissue homeostasis. A second function of SRs includes the ability to activate cytoplasmic signaling pathways. Estrogen (ER), androgen (AR), and progesterone (PR) receptors bind directly to membrane-associated signaling molecules including mitogenic protein kinases (i.e. c-SRC and AKT), G-proteins, and ion channels to mediate context-dependent actions via rapid activation of downstream signaling pathways. In addition to making direct contact with diverse signaling molecules, SRs are further fully integrated with signaling pathways by virtue of their N-terminal phosphorylation sites that act as regulatory hot-spots capable of sensing the signaling milieu. In particular, ER, AR, PR, and closely related glucocorticoid receptors (GR) share the property of accepting (i.e. sensing) ligand-independent phosphorylation events by proline-directed kinases in the MAPK and CDK families. These signaling inputs act as a 'second ligand' that dramatically impacts cell fate. In the face of drugs that reliably target SR ligand-binding domains to block uncontrolled cancer growth, ligand-independent post-translational modifications guide changes in cell fate that confer increased survival, EMT, migration/invasion, stemness properties, and therapy resistance of non-proliferating SR+ cancer cell subpopulations. The focus of this review is on MAPK pathways in the regulation of SR+ cancer cell fate. MAPK-dependent phosphorylation of PR (Ser294) and GR (Ser134) will primarily be discussed in light of the need to target changes in breast cancer cell fate as part of modernized combination therapies.

PRMT1 Is Critical for the Transcriptional Activity and the Stability of the Progesterone Receptor

The progesterone receptor (PR) is an inducible transcription factor that plays critical roles in female reproductive processes and in several aspects of breast cancer tumorigenesis. Our report describes the type I protein arginine methyltransferase 1 (PRMT1) as a cofactor controlling progesterone pathway, through the direct methylation of PR. Mechanistic assays in breast cancer cells indicate that PRMT1 methylates PR at the arginine 637 and reduces the stability of the receptor, thereby accelerating its recycling and finally its transcriptional activity. Depletion of PRMT1 decreases the expression of a subset of progesterone-inducible genes, controlling breast cancer cells proliferation and migration. Consistently, Kaplan-Meier analysis revealed that low expression of PRMT1 predicts a longer survival among the subgroup with high PR. Our study highlights PR methylation as a molecular switch adapting the transcription requirement of breast cells during tumorigenesis.

Effect of 1,25(OH)2-vitamin D3 on expression and phosphorylation of progesterone receptor in cultured endometrial stromal cells of patients with repeated implantation failure

Repeated implantation failure (RIF) occurs in a condition when good quality embryos fail to implant in the endometrium following several in vitro fertilization (IVF) cycles. Suboptimal endometrial receptivity is one of the main underlying factors that causes this failure. Progesterone is the key regulator of endometrial receptivity which regulates gene expression through binding to its receptors in the endometrial stromal cells (eSC). The aim of this study was to evaluate the effect of 1,25(OH)2-vitamin D3 on progesterone receptor (PR) expression level and its phosphorylation on Ser294 residues in eSC of RIF patients and healthy fertile women. After isolation of the eSC from biopsy samples of RIF patients and healthy fertile women and their characterization, the cells were incubated with vitamin D3 and the expression level of PR mRNA, PR protein and phospho-Ser294 PR protein were evaluated after treatment. The results showed that vitamin D3 treatment increases PR mRNA and protein level and phospho-Ser294 PR protein level in the isolated eSC of both RIF patients and the control group. These results suggest that vitamin D3 may possibly play a key role during the embryo implantation process by affecting the expression pattern and regulatory modifications of the PR in the eSC.

Molecular mechanisms underlying progesterone receptor action in breast cancer: Insights into cell proliferation and stem cell regulation

The ovarian steroid hormone progesterone and its nuclear receptor, the Progesterone Receptor (PR), play an essential role in the regulation of cell proliferation and differentiation in the mammary gland. In addition, experimental and clinical evidence demonstrate their critical role in controlling mammary gland tumorigenesis and breast cancer development. When bound to its ligand, the main action of PR is as a transcription factor, which regulates the expression of target genes networks. PR also activates signal transduction pathways through a rapid or non-genomic mechanism in breast cancer cells, an event that is fully integrated with its genomic effects. This review summarizes the molecular mechanisms of the ligand-activated PR actions that drive epithelial cell proliferation and the regulation of the stem cell population in the normal breast and in breast cancer.

Two thalidomide analogs induce persistent estrous behavior and inhibit uterus contractility in rats: The central role of cAMP

The effects of 4NO₂PDPMe and 4APDPMe, which are thalidomide (Tha) analogs that act as selective phosphodiesterase (PDE-4) inhibitors, on estrous behavior (lordosis and proceptive behaviors) and on uterine contraction were studied in ovariectomized (OVX) estrogen-primed Sprague Dawley (SD) and in intact non-pregnant Wistar rats, respectively. We found that intracerebroventricular (ICV) infusion of either 4NO₂PDPMe or 4APDPMe (20 to 80 μg) stimulated intense lordosis and proceptive behavior in response to mounts from a sexually active male, within the first 4 h after infusion, and persisting for up to 24 h. Inhibitors of the progesterone receptor (RU486, administered subcutaneously), the estrogen receptor (tamoxifen, ICV), the adenylate cyclase (AC)/ cyclic AMP (cAMP)/protein kinase A (PKA) pathway (administered ICV), and the mitogen activated protein kinase (MAPK) pathway (administered ICV) significantly decreased lordosis and proceptive behavior induced by Tha analogs. Uterine contractility studies showed that Tha analogs inhibited both the K⁺- and the Ca²⁺-induced tonic contractions in rat uterus. Tha analogs were equally effective, but 4APDPMe was more potent than 4NO₂PDPMe. These results strongly suggest the central role of cAMP in both processes, sexual behavior, and uterine relaxation, and suggest that Tha analogs may also act as Ca²⁺-channel blockers.

FGFs/FGFRs-dependent signalling in regulation of steroid hormone receptors - implications for therapy of luminal breast cancer

Stromal stimuli mediated by growth factor receptors, leading to ligand-independent activation of steroid hormone receptors, have long been implicated in development of breast cancer resistance to endocrine therapy. Mutations in fibroblast growth factor receptor (FGFR) genes have been associated with a higher incidence and progression of breast cancer. Increasing evidence suggests that FGFR-mediated interaction between luminal invasive ductal breast carcinoma (IDC) and its microenvironment contributes to the progression to hormone-independence. Therapeutic strategies based on FGFR inhibitors hold promise for overcoming resistance to the ER-targeting treatment. A series of excellent reviews discuss a potential role of FGFR in development of IDC. Here, we provide a concise updated summary of existing literature on FGFR-mediated signalling with an emphasis on an interaction between FGFR and estrogen/progesterone receptors (ER/PR) in IDC. Focusing on the regulatory role of tumour microenvironment in the activity of steroid hormone receptors, we compile the available functional data on FGFRs-mediated signalling, as a fundamental mechanism of luminal IDC progression and failure of anti-ER treatment. We also highlight the translational value of the presented findings and summarize ongoing oncologic clinical trials investigating FGFRs inhibition in interventional studies in breast cancer.

FGF2 induces breast cancer growth through ligand-independent activation and recruitment of ERα and PRBΔ4 isoform to MYC regulatory sequences

Progression to hormone-independent growth leading to endocrine therapy resistance occurs in a high proportion of patients with estrogen receptor alpha (ERα) and progesterone receptors (PR) positive breast cancer. We and others have previously shown that estrogen- and progestin-induced tumor growth requires ERα and PR interaction at their target genes. Here, we show that fibroblast growth factor 2 (FGF2)-induces cell proliferation and tumor growth through hormone-independent ERα and PR activation and their interaction at the MYC enhancer and proximal promoter. MYC inhibitors, antiestrogens or antiprogestins reverted FGF2-induced effects. LC-MS/MS identified 700 canonical proteins recruited to MYC regulatory sequences after FGF2 stimulation, 397 of which required active ERα (ERα-dependent). We identified ERα-dependent proteins regulating transcription that, after FGF2 treatment, were recruited to the enhancer as well as proteins involved in transcription initiation that were recruited to the proximal promoter. Also, among the ERα-dependent and independent proteins detected at both sites, PR isoforms A and B as well as the novel protein product PRBΔ4 were found. PRBΔ4 lacks the hormone-binding domain and was able to induce reporter gene expression from estrogen-regulated elements and to increase cell proliferation when cells were stimulated with FGF2 but not by progestins. Analysis of the Cancer Genome Atlas data set revealed that PRBΔ4 expression is associated with worse overall survival in luminal breast cancer patients. This discovery provides a new mechanism by which growth factor signaling can engage nonclassical hormone receptor isoforms such as PRBΔ4, which interacts with growth-factor activated ERα and PR to stimulate MYC gene expression and hence progression to endocrine resistance.

Sialic Acid-Binding Lectin from Bullfrog Eggs Exhibits an Anti-Tumor Effect Against Breast Cancer Cells Including Triple-Negative Phenotype Cells

Sialic acid-binding lectin from Rana catesbeiana eggs (cSBL) is a multifunctional protein that has lectin and ribonuclease activity. In this study, the anti-tumor activities of cSBL were assessed using a panel of breast cancer cell lines. cSBL suppressed the cell growth of all cancer cell lines tested here at a concentration that is less toxic, or not toxic at all, to normal cells. The growth suppressive effect was attributed to the cancer-selective induction of apoptosis. We assessed the expressions of several key molecules associated with the breast cancer phenotype after cSBL treatment by western blotting. cSBL decreased the expression level of estrogen receptor (ER) α, while it increased the phosphorylation level of p38 mitogen-activated protein kinase (MAPK). cSBL also suppressed the expression of the progesterone receptor (PgR) and human epidermal growth factor receptor type 2 (HER2). Furthermore, it was revealed that cSBL decreases the expression of the epidermal growth factor receptor (EGFR/HER1) in triple-negative breast cancer cells. These results indicate that cSBL induces apoptosis with decreasing ErbB family proteins and may have great potential for breast cancer chemotherapy, particularly in triple-negative phenotype cells.

Transcriptional regulation of O-GlcNAc homeostasis is disrupted in pancreatic cancer

Many intracellular proteins are reversibly modified by O-linked GlcNAc (O-GlcNAc), a post-translational modification that dynamically regulates fundamental cellular processes in response to diverse environmental cues. Accumulating evidence indicates that both excess and deficiency of protein O-GlcNAcylation can have deleterious effects on the cell, suggesting that maintenance of O-GlcNAc homeostasis is essential for proper cellular function. However, the mechanisms through which O-GlcNAc homeostasis is maintained in the physiologic state and altered in the disease state have not yet been investigated. Here, we demonstrate the existence of a homeostatic mechanism involving mutual regulation of the O-GlcNAc-cycling enzymes O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) at the transcriptional level. Specifically, we found that OGA promotes Ogt transcription through cooperation with the histone acetyltransferase p300 and transcription factor CCAAT/enhancer-binding protein β (C/EBPβ). To examine the role of mutual regulation of OGT and OGA in the disease state, we analyzed gene expression data from human cancer data sets, which revealed that OGT and OGA expression levels are highly correlated in numerous human cancers, particularly in pancreatic adenocarcinoma. Using a Kras^G12D -driven primary mouse pancreatic ductal adenocarcinoma (PDAC) cell line, we found that inhibition of extracellular signal-regulated kinase (ERK) signaling decreases OGA glycosidase activity and reduces OGT mRNA and protein levels, suggesting that ERK signaling may alter O-GlcNAc homeostasis in PDAC by modulating OGA-mediated Ogt transcription. Our study elucidates a transcriptional mechanism that regulates cellular O-GlcNAc homeostasis, which may lay a foundation for exploring O-GlcNAc signaling as a therapeutic target for human disease.

Biological and clinical impact of imbalanced progesterone receptor isoform ratios in breast cancer

There is a consensus that progestins and thus their cognate receptor molecules, the progesterone receptors (PR), are essential in the development of the adult mammary gland and regulators of proliferation and lactation. However, a role for natural progestins in breast carcinogenesis remains poorly understood. A hint to that possible role came from studies in which the synthetic progestin medroxyprogesterone acetate was associated with an increased breast cancer risk in women under hormone replacement therapy. However, progestins have been also used for breast cancer treatment and to inhibit the growth of several experimental breast cancer models. More recently, PR have been shown to be regulators of estrogen receptor signaling. With all this information, the question is how can we target PR, and if so, which patients may benefit from such an approach? PR are not single unique molecules. Two main PR isoforms have been characterized, PRA and PRB, that exert different functions and the relative abundance of one isoform respect to the other determines the response of PR agonists and antagonists. Immunohistochemistry with standard antibodies against PR do not discriminate between isoforms. In this review, we summarize the current knowledge on the expression of both PR isoforms in mammary glands, in experimental models of breast cancer and in breast cancer patients, to better understand how the PRA/PRB ratio can be exploited therapeutically to design personalized therapeutic strategies.

Fibroblast growth factor signalling induces loss of progesterone receptor in breast cancer cells

We have recently demonstrated that, fibroblast growth factor 2 (FGFR2), signalling via ribosomal S6 kinase 2 (RSK2), promotes progression of breast cancer (BCa). Loss of progesterone receptor (PR), whose activity in BCa cells can be stimulated by growth factor receptors (GFRs), is associated with poor patient outcome. Here we showed that FGF7/FGFR2 triggered phosphorylation of PR at Ser294, PR ubiquitination and subsequent receptor`s degradation via the 26S proteasome pathway in BCa cells. We further demonstrated that RSK2 mediated FGF7/FGFR2-induced PR downregulation. In addition, a strong synergistic effect of FGF7 and progesterone (Pg), reflected in the enhanced anchorage-independent growth and cell migration, was observed. Analysis of clinical material demonstrated that expression of PR inversely correlated with activated RSK (RSK-P) (p = 0.016). Patients with RSK-P(+)/PR(–) tumours had 3.629-fold higher risk of recurrence (p = 0.002), when compared with the rest of the cohort. Moreover, RSK-P(+)/PR(–) phenotype was shown as an independent prognostic factor (p = 0.006). These results indicate that the FGF7/FGFR2-RSK2 axis promotes PR turnover and activity, which may sensitize BCa cells to stromal stimuli and contribute to the progression toward steroid hormone negative BCa.

Lordosis facilitated by GPER-1 receptor activation involves GnRH-1, progestin and estrogen receptors in estrogen-primed rats

The present study assessed the participation of membrane G-protein coupled estrogen receptor 1 (GPER-1) and gonadotropin releasing hormone 1 (GnRH-1) receptor in the display of lordosis induced by intracerebroventricular (icv) administration of G1, a GPER-1 agonist, and by unesterified 17β-estradiol (free E₂). In addition, we assessed the participation of both estrogen and progestin receptors in the lordosis behavior induced by G1 in ovariectomized (OVX), E₂-benzoate (EB)-primed rats. In Experiment 1, icv injection of G1 induced lordosis behavior at 120 and 240min. In Experiment 2, icv injection of the GPER-1 antagonist G15 significantly reduced lordosis behavior induced by either G1 or free E₂. In addition, Antide, a GnRH-1 receptor antagonist, significantly depressed G1 facilitation of lordosis behavior in OVX, EB-primed rats. Similarly, icv injection of Antide blocked the stimulatory effect of E₂ on lordosis behavior. In Experiment 3, systemic injection of either tamoxifen or RU486 significantly reduced lordosis behavior induced by icv administration of G1 in OVX, EB-primed rats. The results suggest that GnRH release activates both estrogen and progestin receptors and that this activation is important in the chain of events leading to the display of lordosis behavior in response to activation of GPER-1 in estrogen-primed rats.

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.

Inhibiting Nuclear Phospho-Progesterone Receptor Enhances Antitumor Activity of Onapristone in Uterine Cancer

Although progesterone receptor (PR)-targeted therapies are modestly active in patients with uterine cancer, their underlying molecular mechanisms are not well understood. The clinical use of such therapies is limited because of the lack of biomarkers that predict response to PR agonists (progestins) or PR antagonists (onapristone). Thus, understanding the underlying molecular mechanisms of action will provide an advance in developing novel combination therapies for cancer patients. Nuclear translocation of PR has been reported to be ligand-dependent or -independent. Here, we identified that onapristone, a PR antagonist, inhibited nuclear translocation of ligand-dependent or -independent (EGF) phospho-PR (S294), whereas trametinib inhibited nuclear translocation of EGF-induced phospho-PR (S294). Using orthotopic mouse models of uterine cancer, we demonstrated that the combination of onapristone and trametinib results in superior antitumor effects in uterine cancer models compared with either monotherapy. These synergistic effects are, in part, mediated through inhibiting the nuclear translocation of EGF-induced PR phosphorylation in uterine cancer cells. Targeting MAPK-dependent PR activation with onapristone and trametinib significantly inhibited tumor growth in preclinical uterine cancer models and is worthy of further clinical investigation. Mol Cancer Ther; 17(2); 464-73. ©2017 AACR.

Gene expression effects of glucocorticoid and mineralocorticoid receptor agonists and antagonists on normal human skeletal muscle

Mineralocorticoid and glucocorticoid receptors are closely related steroid hormone receptors that regulate gene expression through many of the same hormone response elements. However, their transcriptional activities and effects in skeletal muscles are largely unknown. We recently identified mineralocorticoid receptors (MR) in skeletal muscles after finding that combined treatment with the angiotensin-converting enzyme inhibitor lisinopril and MR antagonist spironolactone was therapeutic in Duchenne muscular dystrophy mouse models. The glucocorticoid receptor (GR) agonist prednisolone is the current standard-of-care treatment for Duchenne muscular dystrophy because it prolongs ambulation, likely due to its anti-inflammatory effects. However, data on whether glucocorticoids have a beneficial or detrimental direct effect on skeletal muscle are controversial. Here, we begin to define the gene expression profiles in normal differentiated human skeletal muscle myotubes treated with MR and GR agonists and antagonists. The MR agonist aldosterone and GR agonist prednisolone had highly overlapping gene expression profiles, supporting the notion that prednisolone acts as both a GR and MR agonist that may have detrimental effects on skeletal muscles. Co-incubations with aldosterone plus either nonspecific or selective MR antagonists, spironolactone or eplerenone, resulted in similar numbers of gene expression changes, suggesting that both drugs can block MR activation to a similar extent. Eplerenone treatment alone decreased a number of important muscle-specific genes. This information may be used to develop biomarkers to monitor clinical efficacy of MR antagonists or GR agonists in muscular dystrophy, develop a temporally coordinated treatment with both drugs, or identify novel therapeutics with more specific downstream targets.

Posttranslationally modified progesterone receptors direct ligand-specific expression of breast cancer stem cell-associated gene programs

Background

Estrogen and progesterone are potent breast mitogens. In addition to steroid hormones, multiple signaling pathways input to estrogen receptor (ER) and progesterone receptor (PR) actions via posttranslational events. Protein kinases commonly activated in breast cancers phosphorylate steroid hormone receptors (SRs) and profoundly impact their activities.

Methods

To better understand the role of modified PRs in breast cancer, we measured total and phospho-Ser294 PRs in 209 human breast tumors represented on 2754 individual tissue spots within a tissue microarray and assayed the regulation of this site in human tumor explants cultured ex vivo. To complement this analysis, we assayed PR target gene regulation in T47D luminal breast cancer models following treatment with progestin (promegestone; R5020) and antiprogestins (mifepristone, onapristone, or aglepristone) in conditions under which the receptor is regulated by Lys388 SUMOylation (K388 intact) or is SUMO-deficient (via K388R mutation to mimic persistent Ser294 phosphorylation). Selected phospho-PR-driven target genes were validated by qRT-PCR and following RUNX2 shRNA knockdown in breast cancer cell lines. Primary and secondary mammosphere assays were performed to implicate phospho-Ser294 PRs, epidermal growth factor signaling, and RUNX2 in breast cancer stem cell biology.

Results

Phospho-Ser294 PR species were abundant in a majority (54%) of luminal breast tumors, and PR promoter selectivity was exquisitely sensitive to posttranslational modifications. Phospho-PR expression and target gene programs were significantly associated with invasive lobular carcinoma (ILC). Consistent with our finding that activated phospho-PRs undergo rapid ligand-dependent turnover, unique phospho-PR gene signatures were most prevalent in breast tumors clinically designated as PR-low to PR-null (luminal B) and included gene sets associated with cancer stem cell biology (HER2, PAX2, AHR, AR, RUNX). Validation studies demonstrated a requirement for RUNX2 in the regulation of selected phospho-PR target genes (SLC37A2). In vitro mammosphere formation assays support a role for phospho-Ser294-PRs via growth factor (EGF) signaling as well as RUNX2 as potent drivers of breast cancer stem cell fate.

Conclusions

We conclude that PR Ser294 phosphorylation is a common event in breast cancer progression that is required to maintain breast cancer stem cell fate, in part via cooperation with growth factor-initiated signaling pathways and key phospho-PR target genes including SLC37A2 and RUNX2. Clinical measurement of phosphorylated PRs should be considered a useful marker of breast tumor stem cell potential. Alternatively, unique phospho-PR target gene sets may provide useful tools with which to identify patients likely to respond to selective PR modulators that block PR Ser294 phosphorylation as part of rational combination (i.e., with antiestrogens) endocrine therapies designed to durably block breast cancer recurrence.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0462-7) contains supplementary material, which is available to authorized users.

Progesterone induces progesterone receptor gene (PGR) expression via rapid activation of protein kinase pathways required for cooperative estrogen receptor alpha (ER) and progesterone receptor (PR) genomic action at ER/PR target genes

Progesterone Receptors (PRs) are critical effectors of estrogen receptor (ER) signaling required for mammary gland development and reproductive proficiency. In breast and reproductive tract malignancies, PR expression is a clinical prognostic marker of ER action. While estrogens primarily regulate PR expression, other factors likely contribute to a dynamic range of receptor expression across diverse tissues. In this study, we identified estrogen-independent but progestin (R5020)-dependent regulation of ER target genes including PGR in ER+/PR+ cancer cell lines. R5020 (10nM-10μM range) induced dose-dependent PR mRNA and protein expression in the absence of estrogen but required both PR and ERα. Antagonists of either PR (RU486, onapristone) or ERα (ICI 182,780) attenuated R5020 induction of TFF1, CTSD, and PGR. Chromatin immunoprecipitation (ChIP) assays performed on ER+/PR+ cells demonstrated that both ERα and PR were recruited to the same ERE/Sp1 site-containing region of the PGR proximal promoter in response to high dose progestin (10μM). Recruitment of ERα and PR to chromatin and subsequent PR mRNA induction were dependent upon rapid activation of MAPK/ERK and AKT; inhibition of these kinase pathways via U0126 or LY294002 blocked these events. Overall, we have identified a novel mechanism of ERα activation initiated by rapid PR-dependent kinase pathway activation and associated with phosphorylation of ERα Ser118 for estrogen-independent but progestin-dependent ER/PR cross talk. These studies may provide insight into mechanisms of persistent ER-target gene expression during periods of hormone (i.e. estrogen) ablation and suggest caution following prolonged treatment with aromatase or CYP17 inhibitors (i.e. contexts when progesterone levels may be abnormally elevated).

miR-196a overexpression activates the MEK/ERK signal and represses the progesterone receptor and decidualization in eutopic endometrium from women with endometriosis

STUDY QUESTION

Do microRNAs (miRNAs) contribute to aberrant progesterone receptor (PGR) expression in the eutopic endometrium of women with endometriosis? SUMMARY ANSWER: miR-196a upregulates MEK/ERK signalling, mediating a downregulation of PGR expression in the eutopic endometrium of women with minimal or mild endometriosis.

WHAT IS KNOWN ALREADY

Implantation failure is strongly suggested as an underlying cause for the observed infertility in minimal or mild endometriosis. Progesterone resistance, which is mainly caused by aberrantly expressed progesterone receptor in the eutopic endometrium, is considered as a key factor of decreased endometrial receptivity; thus far, epigenetics, but not miRNA, has been shown to affect PGR expression in the endometrium.

STUDY DESIGN SIZE, DURATION

Microarray analysis was used to analyse the eutopic endometrium. The differential expression of miR-196a was validated. Bioinformatics analysis predicted that miR-196a targets the 3'-untranslated region (UTR) of the PGR. The relationship between the miR-196a level and PGR expression was studied and the role of the MEK/ERK signal pathway was investigated.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Total RNA was extracted from eutopic endometrium samples in three infertile women with mild/minimal endometriosis and three disease-free control subjects. The miRNA and mRNA expression levels were analysed by microarray analysis. The miR-196a expression was validated by qRT-PCR [endometriosis (n = 22) and control (n = 20)], while functional analysis utilised in vitro transfection of endometrial stromal cells (ESCs), induction of decidualization of ESCs, and luciferase reporter assays in 293 T cell lines.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 66 dysregulated miRNAs and 357 dysregulated mRNAs were screened by microarray analysis. miR-196a and P-MEK/P-ERK were both found to be significantly upregulated in the eutopic endometrium in patients with mild/minimal endometriosis. PGR and PGR-B mRNA were inhibited by miR-196a overexpression and upregulated by miR-196a inhibition. Luciferase reporter failed to confirm the target regulation of miR-196a on PGR. Transfection of ESCs with a miR-196a mimic led to an increase in the P-MEK/P-ERK protein levels, decrease in the PGR protein levels, and atypical decidualization. Following miR-196a inhibition, the P-MEK/P-ERK protein was downregulated and the PGR protein was upregulated. Inhibition of P-MEK/P-ERK also increased PGR expression.

LARGE SCALE DATA

Data are presented in Supplementary Tables SI and SII.

LIMITATIONS REASONS FOR CAUTION

This study focused on the role of miR-196a, and therefore does not involve other miRNAs; hence, it is possible that other miRNAs may also be responsible for progestin resistance in endometriosis.

WIDER IMPLICATIONS OF THE FINDINGS

Our data revealed altered miRNA expression and activated MEK/ERK signalling in the eutopic endometrium in minimal or mild endometriosis. We showed that the miR-196a level is associated with reduced expression of PGR isoforms through MEK/ERK, suggesting that miR-196a and MEK/ERK are both potential biomarkers of endometriosis. These results provide a novel approach to target the mechanisms behind progesterone resistance in endometriosis.

STUDY FUNDING/COMPETING INTERESTS

This research was supported by the National Natural Science Foundation of China (No. 81370693). The authors have no conflicts of interest.

Progesterone receptor blockade in human breast cancer cells decreases cell cycle progression through G2/M by repressing G2/M genes

Background

The synthesis of specific, potent progesterone antagonists adds potential agents to the breast cancer prevention and treatment armamentarium. The identification of individuals who will benefit from these agents will be a critical factor for their clinical success.

Methods

We utilized telapristone acetate (TPA; CDB-4124) to understand the effects of progesterone receptor (PR) blockade on proliferation, apoptosis, promoter binding, cell cycle progression, and gene expression. We then identified a set of genes that overlap with human breast luteal-phase expressed genes and signify progesterone activity in both normal breast cells and breast cancer cell lines.

Results

TPA administration to T47D cells results in a 30 % decrease in cell number at 24 h, which is maintained over 72 h only in the presence of estradiol. Blockade of progesterone signaling by TPA for 24 h results in fewer cells in G2/M, attributable to decreased expression of genes that facilitate the G2/M transition. Gene expression data suggest that TPA affects several mechanisms that progesterone utilizes to control gene expression, including specific post-translational modifications, and nucleosomal organization and higher order chromatin structure, which regulate access of PR to its DNA binding sites.

Conclusions

By comparing genes induced by the progestin R5020 in T47D cells with those increased in the luteal-phase normal breast, we have identified a set of genes that predict functional progesterone signaling in tissue. These data will facilitate an understanding of the ways in which drugs such as TPA may be utilized for the prevention, and possibly the therapy, of human breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2355-5) contains supplementary material, which is available to authorized users.

Progesterone receptor antagonism inhibits progestogen-related carcinogenesis and suppresses tumor cell proliferation

PURPOSE

Blockade of the progestogen-progesterone receptor (PR) axis is a novel but untested strategy for breast cancer prevention. We report preclinical data evaluating telapristone acetate (TPA), ulipristal acetate (UPA), and mifepristone.

METHODS

Tumors were induced with medroxyprogesterone acetate (MPA) plus 7,12-dimethylbenz[a]anthracene (DMBA) in mice, and MPA or progesterone plus N-methyl-N-nitrosourea (MNU) in rats. Mammary gland histology, tumor incidence, latency, multiplicity, burden and histology were evaluated, along with immunohistochemical labeling of pHH3 (proliferation), CD34 (angiogenesis), and estrogen and progesterone receptors (ER and PR). A concentration gradient of TPA, UPA, and mifepristone was tested for growth inhibition of T47D spheroids.

RESULTS

In mouse mammary glands, no tumors formed, but TPA opposed the pro-hyperplastic effects of MPA (p = 0.002). In rats, TPA decreased tumor incidence (p = 0.037 for MPA + TPA vs. MPA, and p = 0.032 for progesterone + TPA vs. progesterone) and tumor burden (p = 0.042 for progesterone + TPA vs. progesterone), with significant decreases in pHH3 and CD34 positive cells. TPA and UPA were superior to mifepristone in growth inhibition of T47D spheroids.

CONCLUSION

TPA has consistent anti-tumorigenic effects in several models, which are accompanied by decreases in cell proliferation, angiogenesis, and hormone receptor expression.

Modifications to glucocorticoid and progesterone receptors alter cell fate in breast cancer

Steroid hormone receptors (SRs) are heavily posttranslationally modified by the reversible addition of a variety of molecular moieties, including phosphorylation, acetylation, methylation, SUMOylation, and ubiquitination. These rapid and dynamic modifications may be combinatorial and interact (i.e. may be sequential, complement, or oppose each other), creating a vast array of uniquely modified receptor subspecies that allow for diverse receptor behaviors that enable highly sensitive and context-dependent hormone action. For example, in response to hormone or growth factor membrane-initiated signaling events, posttranslational modifications (PTMs) to SRs alter protein-protein interactions that govern the complex process of promoter or gene-set selection coupled to transcriptional repression or activation. Unique phosphorylation events allow SRs to associate or disassociate with specific cofactors that may include pioneer factors and other tethering partners, which specify the resulting transcriptome and ultimately change cell fate. The impact of PTMs on SR action is particularly profound in the context of breast tumorigenesis, in which frequent alterations in growth factor-initiated signaling pathways occur early and act as drivers of breast cancer progression toward endocrine resistance. In this article, with primary focus on breast cancer relevance, we review the mechanisms by which PTMs, including reversible phosphorylation events, regulate the closely related SRs, glucocorticoid receptor and progesterone receptor, allowing for precise biological responses to ever-changing hormonal stimuli.

Regulation of steroid hormone receptors and coregulators during the cell cycle highlights potential novel function in addition to roles as transcription factors

Cell cycle progression is tightly controlled by several kinase families including Cyclin-Dependent Kinases, Polo-Like Kinases, and Aurora Kinases. A large amount of data show that steroid hormone receptors and various components of the cell cycle, including cell cycle regulated kinases, interact, and this often results in altered transcriptional activity of the receptor. Furthermore, steroid hormones, through their receptors, can also regulate the transcriptional expression of genes that are required for cell cycle regulation. However, emerging data suggest that steroid hormone receptors may have roles in cell cycle progression independent of their transcriptional activity. The following is a review of how steroid receptors and their coregulators can regulate or be regulated by the cell cycle machinery, with a particular focus on roles independent of transcription in G2/M.

Differential Regulation of Progesterone Receptor-Mediated Transcription by CDK2 and DNA-PK

Progesterone receptor (PR) function is altered by cell signaling, but the mechanisms of kinase-specific regulation are not well defined. To examine the role of cell signaling in the regulation of PR transcriptional activity, we have utilized a previously developed mammalian-based estrogen-response element promoter array cell model and automated cell imaging and analysis platform to visualize and quantify effects of specific kinases on different mechanistic steps of PR-mediated target gene activation. For these studies, we generated stable estrogen-response element array cell lines expressing inducible chimeric PR that contains a swap of the estrogen receptor-α DNA-binding domain for the DNA-binding domain of PR. We have focused on 2 kinases important for steroid receptor activity: cyclin-dependent kinase 2 and DNA-dependent protein kinase. Treatment with either a Cdk1/2 inhibitor (NU6102) or a DNA-dependent protein kinase inhibitor (NU7441) decreased hormone-mediated chromatin decondensation and transcriptional activity. Further, we observed a quantitative reduction in the hormone-mediated recruitment of select coregulator proteins with NU6102 that is not observed with NU7441. In parallel, we determined the effect of kinase inhibition on hormone-mediated induction of primary and mature transcripts of endogenous genes in T47D breast cancer cells. Treatment with NU6102 was much more effective than NU7441, in inhibiting induction of PR target genes that exhibit a rapid increase in primary transcript expression in response to hormone. Taken together, these results indicate that the 2 kinases regulate PR transcriptional activity by distinct mechanisms.

Tumor suppressor SPOP mediates the proteasomal degradation of progesterone receptors (PRs) in breast cancer cells

Progesterone induces proliferation of breast cancer cells and contributes to the development of breast cancer. The effects of progesterone are mediated by progesterone receptors (PRs). However, it is still not fully understood how the proliferative effects of PR is regulated in vivo. Increasing amount of evidence strongly suggests that dysregulation of ubiquitin-proteasome system is closely associated with cancer pathogenesis. Speckle-type POZ protein (SPOP) is an adaptor protein of the CUL3-based E3 ubiquitin ligase complexes. SPOP represents one of the highest loci for loss of heterozygosity (LOH) in breast cancer. SPOP downregulation contributes to breast cancer cell growth and invasion. In this study, we revealed PR as a bona fide substrate for SPOP. SPOP interacts with PR in vivo and targets PR for ubiquitin-dependent proteasomal degradation. Moreover, SPOP suppresses progesteroneinduced PR transactivation, S phase entry, and Erk1/2 activation. Our study revealed novel molecular mechanisms underlying the regulation of PR protein homeostasis in breast cancer cells, and provided insights in understanding the relationship between SPOP inactivation and the development of breast cancer.

Finerenone Impedes Aldosterone-dependent Nuclear Import of the Mineralocorticoid Receptor and Prevents Genomic Recruitment of Steroid Receptor Coactivator-1

Aldosterone regulates sodium homeostasis by activating the mineralocorticoid receptor (MR), a member of the nuclear receptor superfamily. Hyperaldosteronism leads todeleterious effects on the kidney, blood vessels, and heart. Although steroidal antagonists such as spironolactone and eplerenone are clinically useful for the treatment of cardiovascular diseases, they are associated with several side effects. Finerenone, a novel nonsteroidal MR antagonist, is presently being evaluated in two clinical phase IIb trials. Here, we characterized the molecular mechanisms of action of finerenone and spironolactone at several key steps of the MR signaling pathway. Molecular modeling and mutagenesis approaches allowed identification of Ser-810 and Ala-773 as key residues for the high MR selectivity of finerenone. Moreover, we showed that, in contrast to spironolactone, which activates the S810L mutant MR responsible for a severe form of early onset hypertension, finerenone displays strict antagonistic properties. Aldosterone-dependent phosphorylation and degradation of MR are inhibited by both finerenone and spironolactone. However, automated quantification of MR subcellular distribution demonstrated that finerenone delays aldosterone-induced nuclear accumulation of MR more efficiently than spironolactone. Finally, chromatin immunoprecipitation assays revealed that, as opposed to spironolactone, finerenone inhibits MR, steroid receptor coactivator-1, and RNA polymerase II binding at the regulatory sequence of the SCNN1A gene and also remarkably reduces basal MR and steroid receptor coactivator-1 recruitment, unraveling a specific and unrecognized inactivating mechanism on MR signaling. Overall, our data demonstrate that the highly potent and selective MR antagonist finerenone specifically impairs several critical steps of the MR signaling pathway and therefore represents a promising new generation MR antagonist.

PKCα and PKCδ activation regulates transcriptional activity and degradation of progesterone receptor in human astrocytoma cells

Progesterone regulates cancer cell proliferation and invasion through its receptors (PR-A and PR-B), whose phosphorylation modifies their transcriptional activity and induce their degradation. We identified by in silico analysis a putative residue (Ser400) in PR that might be phosphorylated by protein kinase C (PKC), a family of enzymes involved in the proliferation and infiltration of astrocytomas, the most frequent and aggressive brain tumors. A grade III human astrocytoma-derived cell line was used to study the role of PKC in PR phosphorylation, transcriptional activity, and degradation. Treatment with PKC activator [tetradecanoyl phorbol acetate (TPA)] increased PR phosphorylation in Ser400 after 5 minutes, which in turn induced PR transcriptional activity and its subsequent degradation by the 26S proteasome 3-5 hours after treatment. Silencing or inhibition of PKCα and PKCδ blocked PR phosphorylation and degradation induced by TPA. Both PR isoforms were associated with PKCα and reached the maximum association after 5 minutes of TPA addition. These data correlated with immunnofluorescence assays in which nuclear colocalization of PKCα with PR increased after TPA treatment. We observed a 2-fold increase in cell proliferation after PKC activation with TPA that was reduced with the PR antagonist, RU486. The PR S400A mutant revealed that this residue is essential for PKC-mediated PR phosphorylation and degradation. Our results show a key participation of PKCα and PKCδ in PR regulation and function.

Progesterone regulation of tissue factor depends on MEK1/2 activation and requires the proline-rich site on progesterone receptor

To characterize the molecular mechanism and map the response element used by progesterone (P) to upregulate tissue factor (TF) in breast cancer cells. TF expression and mRNA levels were analyzed in breast cancer ZR-75 and T47D cells, using Western blot and real-time PCR, respectively. Mapping of the TF promoter was performed using luciferase vectors. Progesterone receptor (PR) and specificity protein 1 (Sp1) binding to the TF promoter were analyzed by chromatin immuno precipitation assay. Specific or selective inhibitors were used for the MEK1/2 and the c-Src pathways (UO126 and PP2, respectively). TF mRNA increase peaks at 18 h following P treatment in ZR-75 and T47D cells. P upregulation occurs via a transcriptional mechanism that depends on PR and MEK1/2 activation, PR and Sp1 transcription factors bind to a region in the TF promoter that contains three Sp1 sites. TF mRNA upregulation requires an intact PR proline-rich site (mPRO), but it is independent from c-Src. TF upregulation by P is mediated by Sp1 sites in the TF promoter region. Transcriptional upregulation in breast cancer cells occurs via a new mechanism that requires MEK1/2 activation and the mPRO site but independent of c-Src activity. PR Phosphorylation at serine 294 and 345 is not essential.

Progesterone receptor activation downregulates GATA3 by transcriptional repression and increased protein turnover promoting breast tumor growth

Introduction

The transcription factor GATA3 is involved in mammary gland development and is crucial for the maintenance of the differentiated status of luminal epithelial cells. The role of GATA3 in breast cancer as a tumor suppressor has been established, although insights into the mechanism of GATA3 expression loss are still required.

Methods

Chromatin immunoprecipitation assays were conducted to study progestin modulation of recruitment of transcription factors to GATA3 promoter. We performed western blot and reverse RT-qPCR experiments to explore progestin regulation of GATA3 protein and mRNA expression respectively. Confocal microscopy and in vitro phosphorylation studies were conducted to examine progestin capacity to induce GATA3 serine phosphorylation in its 308 residue. GATA3 participation in progestin-induced breast cancer growth was addressed in in vitro proliferation and in vivo tumor growth experiments.

Results

In this study, we demonstrate that progestin-activated progesterone receptor (PR) reduces GATA3 expression through regulation at the transcriptional and post-translational levels in breast cancer cells. In the former mechanism, the histone methyltransferase enhancer of zeste homolog 2 is co-recruited with activated PR to a putative progesterone response element in the GATA3 proximal promoter, increasing H3K27me3 levels and inducing chromatin compaction, resulting in decreased GATA3 mRNA levels. This transcriptional regulation is coupled with increased GATA3 protein turnover through progestin-induced GATA3 phosphorylation at serine 308 followed by 26S proteasome-mediated degradation. Both molecular mechanisms converge to accomplish decreased GATA3 expression levels in breast cancer cells upon PR activation. In addition, we demonstrated that decreased GATA3 levels are required for progestin-induced upregulation of cyclin A2, which mediates the G1 to S phase transition of the cell cycle and was reported to be associated with poor prognosis in breast cancer. Finally, we showed that downregulation of GATA3 is required for progestin stimulation of both in vitro cell proliferation and in vivo tumor growth.

Conclusions

In the present study, we reveal that progestin-induced PR activation leads to loss of GATA3 expression in breast cancer cells through transcriptional and post-translational regulation. Importantly, we demonstrate that GATA3 downregulation is required for progestin-induced upregulation of cyclin A2 and for progestin-induced in vitro and in vivo breast cancer cell growth.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0491-x) contains supplementary material, which is available to authorized users.

Role of nuclear progesterone receptor isoforms in uterine pathophysiology

BACKGROUND

Progesterone is a key hormonal regulator of the female reproductive system. It plays a major role to prepare the uterus for implantation and in the establishment and maintenance of pregnancy. Actions of progesterone on the uterine tissues (endometrium, myometrium and cervix) are mediated by the combined effects of two progesterone receptor (PR) isoforms, designated PR-A and PR-B. Both receptors function primarily as ligand-activated transcription factors. Progesterone action on the uterine tissues is qualitatively and quantitatively determined by the relative levels and transcriptional activities of PR-A and PR-B. The transcriptional activity of the PR isoforms is affected by specific transcriptional coregulators and by PR post-translational modifications that affect gene promoter targeting. In this context, appropriate temporal and cell-specific expression and function of PR-A and PR-B are critical for normal uterine function.

METHODS

Relevant studies describing the role of PRs in uterine physiology and pathology (endometriosis, uterine leiomyoma, endometrial cancer, cervical cancer and recurrent pregnancy loss) were comprehensively searched using PubMed, Cochrane Library, Web of Science, and Google Scholar and critically reviewed.

RESULTS

Progesterone, acting through PR-A and PR-B, regulates the development and function of the endometrium and induces changes in cells essential for implantation and the establishment and maintenance of pregnancy. During pregnancy, progesterone via the PRs promotes myometrial relaxation and cervical closure. Withdrawal of PR-mediated progesterone signaling triggers menstruation and parturition. PR-mediated progesterone signaling is anti-mitogenic in endometrial epithelial cells, and as such, mitigates the tropic effects of estrogen on eutopic normal endometrium, and on ectopic implants in endometriosis. Similarly, ligand-activated PRs function as tumor suppressors in endometrial cancer cells through inhibition of key cellular signaling pathways required for growth. In contrast, progesterone via PR activation appears to increase leiomyoma growth. The exact role of PRs in cervical cancer is unclear. PRs regulate implantation and therefore aberrant PR function may be implicated in recurrent pregnancy loss (RPL). PRs likely regulate key immunogenic factors involved in RPL. However, the exact role of PRs in the pathophysiology of RPL and the use of progesterone for therapeutic benefit remains uncertain.

CONCLUSIONS

PRs are key mediators of progesterone action in uterine tissues and are essential for normal uterine function. Aberrant PR function (due to abnormal expression and/or function) is a major cause of uterine pathophysiology. Further investigation of the underlying mechanisms of PR isoform action in the uterus is required, as this knowledge will afford the opportunity to create progestin/PR-based therapeutics to treat various uterine pathologies.

Systematic dissection of the mechanisms underlying progesterone receptor downregulation in endometrial cancer

Progesterone, acting through its receptor, PR (progesterone receptor), is the natural inhibitor of uterine endometrial carcinogenesis by inducing differentiation. PR is downregulated in more advanced cases of endometrial cancer, thereby limiting the effectiveness of hormonal therapy. Our objective was to understand and reverse the mechanisms underlying loss of PR expression in order to improve therapeutic outcomes. Using endometrial cancer cell lines and data from The Cancer Genome Atlas, our findings demonstrate that PR expression is downregulated at four distinct levels. In well-differentiated cancers, ligand-induced receptor activation and downregulation are intact. miRNAs mediate fine tuning of PR levels. As differentiation is lost, PR silencing is primarily at the epigenetic level. Initially, recruitment of the polycomb repressor complex 2 to the PR promoter suppresses transcription. Subsequently, DNA methylation prevents PR expression. Appropriate epigenetic modulators reverse these mechanisms. These data provide a rationale for combining epigenetic modulators with progestins as a therapeutic strategy for endometrial cancer.

SIGNIFICANCE

Traditional hormonal therapy for women with endometrial cancer can be molecularly enhanced by combining progestins with epigenetic modulators, thereby increasing progesterone receptor expression and significantly improving treatment efficacy.

Tracking progesterone receptor-mediated actions in breast cancer

Ovarian steroid hormones contribute to breast cancer initiation and progression primarily through the actions of their nuclear transcription factors, the estrogen receptor alpha (ERα) and progesterone receptors (PRs). These receptors are important drivers of the luminal A and B subtypes of breast cancer, where estrogen-blocking drugs have been effective endocrine therapies for patients with these tumors. However, many patients do not respond, or become resistant to treatment. When endocrine therapies fail, the luminal subtypes of breast cancer are more difficult to treat because these subtypes are among the most heterogeneous in terms of mutation diversity and gene expression profiles. Recent evidence suggests that progestin and PR actions may be important drivers of luminal breast cancers. Clinical trial data has demonstrated that hormone replacement therapy with progestins drives invasive breast cancer and results in greater mortality. PR transcriptional activity is dependent upon cross-talk with growth factor signaling pathways that alter PR phosphorylation, acetylation, or SUMOylation as mechanisms for regulating PR target gene selection required for increased cell proliferation and survival. Site-specific PR phosphorylation is the primary driver of gene-selective PR transcriptional activity. However, PR phosphorylation and heightened transcriptional activity is coupled to rapid PR protein degradation; the range of active PR detected in tumors is likely to be dynamic. Thus, PR target gene signatures may provide a more accurate means of tracking PR's contribution to tumor progression rather than standard clinical protein-based (IHC) assays. Further development of antiprogestin therapies should be considered alongside antiestrogens and aromatase inhibitors.

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.

Progesterone receptor-cyclin D1 complexes induce cell cycle-dependent transcriptional programs in breast cancer cells

The progesterone receptor (PR) and its coactivators are direct targets of activated cyclin-dependent kinases (CDKs) in response to peptide growth factors, progesterone, and deregulation of cell cycle inhibitors. Herein, using the T47D breast cancer model, we probed mechanisms of cell cycle-dependent PR action. In the absence of exogenous progestin, the PR is specifically phosphorylated during the G2/M phase. Accordingly, numerous PR target genes are cell cycle regulated, including HSPB8, a heat-shock protein whose high expression is associated with tamoxifen resistance. Progestin-induced HSPB8 expression required cyclin D1 and was insensitive to antiestrogens but blocked by antiprogestins or inhibition of specificity factor 1 (SP1). HSPB8 expression increased with or without ligand when cells were G2/M synchronized or contained high levels of cyclin D1. Knockdown of PRs abrogated ligand-independent HSPB8 expression in synchronized cells. Notably, PRs and cyclin D1 copurified in whole-cell lysates of transiently transfected COS-1 cells and in PR-positive T47D breast cancer cells expressing endogenous cyclin D1. PRs, cyclin D1, and SP1 were recruited to the HSPB8 promoter in progestin-treated T47D breast cancer cells. Mutation of PR Ser345 to Ala (S345A) or inhibition of CDK2 activity using roscovitine disrupted PR/cyclin D1 interactions with DNA and blocked HSPB8 mRNA expression. Interaction of phosphorylated PRs with SP1 and cyclin D1 provides a mechanism for targeting transcriptionally active PRs to selected gene promoters relevant to breast cancer progression. Understanding the functional linkage between PRs and cell cycle regulatory proteins will provide keys to targeting novel PR/cyclin D1 cross talk in both hormone-responsive disease and HSPB8-high refractory disease with high HSPB8 expression.

Mammalian MYC Proteins and Cancer

The MYC family of proteins is a group of basic-helix-loop-helix-leucine zipper transcription factors that feature prominently in cancer. Overexpression of MYC is observed in the vast majority of human malignancies and promotes an extraordinary set of changes that impact cell proliferation, growth, metabolism, DNA replication, cell cycle progression, cell adhesion, differentiation, and metastasis. The purpose of this review is to introduce the reader to the mammalian family of MYC proteins, highlight important functional properties that endow them with their potent oncogenic potential, describe their mechanisms of action and of deregulation in cancer cells, and discuss efforts to target the unique properties of MYC, and of MYC-driven tumors, to treat cancer.

Links between oestrogen receptor activation and proteolysis: relevance to hormone-regulated cancer therapy

Oestrogen receptor-α (ERα) is a master transcription factor that regulates cell proliferation and homeostasis in many tissues. Despite beneficial ERα functions, sustained oestrogenic exposure increases the risk and/or the progression of various cancers, including those of the breast, endometrium and ovary. Oestrogen–ERα interaction can trigger post-translational ERα modifications through crosstalk with signalling pathways to promote transcriptional activation and ubiquitin-mediated ERα proteolysis, with co-activators that have dual roles as ubiquitin ligases. These processes are reviewed herein. The elucidation of mechanisms whereby oestrogen drives both ERα transactivation and receptor proteolysis might have important therapeutic implications not only for breast cancer but also potentially for other hormone-regulated cancers.

Phosphorylation: a fundamental regulator of steroid receptor action

Steroid hormone receptors (SHRs) are hormone-activated transcription factors involved in numerous cellular functions and in health and disease. Their activities depend on the cellular level of the receptor, the presence of coregulator proteins, and the cell signaling pathways that are active in the cell. SHRs and their coregulators are phosphorylated on multiple sites by a wide variety of kinases. Each site may contribute to multiple functions and the net effect of an individual phosphorylation depends on the activating kinase. Here we discuss functions of known SHR phosphorylation sites, kinase regulation, evidence of translational relevance, and crosstalk between SHRs and cell signaling pathways. Understanding how cell signaling pathways regulate SHRs might yield novel therapeutic targets for multiple human diseases.

ERα, SKP2 and E2F-1 form a feed forward loop driving late ERα targets and G1 cell cycle progression

Estrogen triggers transactivation coupled estrogen receptor α (ERα) proteolysis, but mechanisms thereof remain obscure. Present data link estrogen:ERα-driven transcription with cell cycle progression. Although liganded ERα induces many genes within 1-4 h, gene activation after 6 h is thought to be indirect. Here, we identify SKP2 as a late-acting coactivator that drives ERα targets to promote G1-to-S progression. Data support a model in which estrogen-activated cyclin E-CDK2 binds and phosphorylates ERαS341, to prime ERα-SCF(SKP2) binding via SKP2-L248QTLL252 in late G1. SKP2 activates ERα ubiquitylation and proteolysis. Putative late ERα targets were identified by expression profiling. SKP2 knockdown attenuated E2F-1 and BLM induction. SKP2 overexpression, but not coactivator motif mutant SKP2-L248QTAA252, enhanced estrogen-induced E2F-1 and BLM expression. SKP2 knockdown impaired estrogen-stimulated ERα, SKP2, SRC3 and RNA polymerase II recruitment to E2F-1 and BLM promoters. This work not only identifies these late-activated genes as bona fide ERα targets but describes a novel mechanism for their periodic activation. SKP2 serves as dual ERα E3 ligase/coactivator for late-activated target genes, revealing a novel mechanism whereby ERα/SCF(SKP2) transactivation of E2F-1 feeds forward to drive G1-to-S.

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

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