Progesterone-independent effects of human progesterone receptors (PRs) in estrogen receptor-positive breast cancer: PR isoform-specific gene regulation and tumor biology

Insulin-like growth factor binding protein-6 modulates proliferative antagonism in response to progesterone in breast cancer

Breast cancer is one of the most diagnosed cancers worldwide. The insulin-like growth factor (IGF) system promotes proliferation and survival in breast cancer cells and is regulated by 6 insulin-like growth factor binding proteins (IGFBPs). The IGFBPs sequester IGFs to prolong their half-life and attenuate binding to insulin-like growth factor 1 receptor (IGF1R). While IGFBP-6 has been studied in some cancers it has not been studied extensively in hormone receptor positive breast cancer. Survival analysis using available databases indicated that high IGFBP-6 levels improve overall survival in progesterone receptor positive breast cancers. IGFBP-6 is transcriptionally induced by progesterone in T47D breast cancer cells resulting in increased intracellular and extracellular IGFBP-6 protein. Knockdown of IGFBP-6 resulted in reduced proliferative antagonism when estradiol stimulated T47D cells were cotreated with progesterone and protein levels of both progesterone receptor isoforms (PR-A and PR-B) were decreased following knockdown of IGFBP-6. P21(Cip1/Waf1), which is progesterone responsive, was not induced in response to progesterone following knockdown of IGFBP-6. Cyclin E2, a cell cycle regulator, is induced by progesterone only when IGFBP-6 is knocked down. Stable overexpression of IGFBP-6 in MCF-7 cells resulted in an increase in Epidermal Growth Factor Receptor (EGFR) and this expression was further enhanced when cells were cotreated with progesterone and estradiol. These results indicate that IGFBP-6 is a regulator of progesterone action, and that PR is required for the observed protective effects of IGFBP-6 in breast cancer.

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 Receptor Signaling Promotes Cancer Associated Fibroblast Mediated Tumorigenicity in ER+ Breast Cancer

Breast cancer progression involves intricate interactions between cancer cells and the tumor microenvironment (TME). This study elucidates the critical role of progesterone receptor (PR) signaling in mediating the protumorigenic effects of cancer-associated fibroblasts (CAFs) on estrogen receptor-positive (ER+) luminal breast cancer cells. We demonstrate that CAFs produce physiologically relevant levels of estrogen and progesterone, which significantly contribute to breast cancer tumorigenicity. Specifically, CAF conditioned media (CM) promoted PR-dependent anchorage-independent growth, tumorsphere formation/stem cell expansion, and CD44 upregulation. CAF cells formed co-clusters more frequently with PR+ breast cancer cells relative to PR-null models. While both PR isoforms mediated these actions, PR-A was a dominant driver of tumorsphere formation/stemness, while PR-B induced robust CD44 expression and CAF/tumor cell co-cluster formation. CD44 knockdown impaired CAF/tumor cell co-clustering. Fibroblast growth factor 2 (FGF2), also secreted by CAFs, phosphorylated PR (Ser294) in a MAPK-dependent manner and activated PR to enhance CD44 expression and breast cancer tumorigenicity. The FGF receptor (FGFR) inhibitor PD173074 diminished CAF- and FGF2-dependent PR activation, tumorsphere formation, and co-clustering. In summary, this study reveals a novel mechanism through which stromal CAFs orchestrate elevated PR signaling in ER+ luminal breast cancer via secretion of both progesterone and FGF2, a potent activator of ERK1/2. Understanding tumor cell/TME interactions provides insights into potential therapeutic strategies aimed at disrupting PR- and/or FGF2/FGFR-dependent signaling pathways to prevent early metastasis in patients with ER+ breast cancer.

Antiprogestins for breast cancer treatment: We are almost ready

The development of antiprogestins was initially a gynecological purpose. However, since mifepristone was developed, its application for breast cancer treatment was immediately proposed. Later, new compounds with lower antiglucocorticoid and antiandrogenic effects were developed to be applied to different pathologies, including breast cancer. We describe herein the studies performed in the breast cancer field with special focus on those reported in recent years, ranging from preclinical biological models to those carried out in patients. We highlight the potential use of antiprogestins in breast cancer prevention in women with BRCA1 mutations, and their use for breast cancer treatment, emphasizing the need to elucidate which patients will respond. In this sense, the PR isoform ratio has emerged as a possible tool to predict antiprogestin responsiveness. The effects of combined treatments of antiprogestins together with other drugs currently used in the clinic, such as tamoxifen, CDK4/CDK6 inhibitors or pembrolizumab in preclinical models is discussed since it is in this scenario that antiprogestins will be probably introduced. Finally, we explain how transcriptomic or proteomic studies, that were carried out in different luminal breast cancer models and in breast cancer samples that responded or were predicted to respond to the antiprogestin therapy, show a decrease in proliferative pathways. Deregulated pathways intrinsic of each model are discussed, as well as how these analyses may contribute to a better understanding of the mechanisms involved.

Progesterone receptor-Grb2 interaction is associated with better outcomes in breast cancer

In addition to mediating nuclear transcription, PR mediates extranuclear functions mainly through the PR polyproline domain (PPD) interaction with the SH3 domain of cytoplasmic signaling molecules. PR-PPD-SH3 interaction inhibits EGF-mediated signaling and decreases lung cancer cell proliferation. Grb2 is an essential adaptor molecule with an SH2 domain flanked by two SH3 domains. In this study, we examined whether PR, through interaction between PR-PPD and Grb2-SH3, can interact with Grb2 in cells and breast cancer tissues. Our previous study shows that interaction between PR-PPD and Grb2 could interfere with cytoplasmic signaling and lead to inhibition of EGF-mediated signaling. GST-pulldown analysis shows that PR-PPD specifically interacts with the SH3 domains of Grb2. Immunofluorescence staining shows colocalization of PR and Grb2 in both the nucleus and cytoplasm in BT-474 breast cancer cells. Using Bimolecular Fluorescence Complementation (BiFC) analysis, we show that PR and Grb2 interact in breast cancer cells through the Grb2-SH3 domain. Proximity Ligation Assay (PLA) analysis of 43 breast cancer specimens shows that PR-Grb2 interaction is associated with low histological stage and negatively correlates with lymph node invasion and metastasis in breast cancer. These results, together with our previous findings, suggest that PR-PPD interaction with Grb2 plays an essential role in PR-mediated growth factor signaling inhibition and could contribute significantly to better prognosis in PR- and Grb2-positive breast cancer. Our finding provides a basis for additional studies to explore a novel therapeutic strategy for cancer treatment.

Progesterone receptor isoform ratios influence the transcriptional activity of progestins via the progesterone receptor

Progestins (synthetic progestogens) are progesterone receptor (PR) ligands used globally by women in both hormonal contraception and menopausal hormone therapy. Although four generations of unique progestins have been developed, studies seldom distinguish between the activities of progestins via the two functionally distinct PR isoforms, PR-A and PR-B. Moreover, not much is known about the action of progestins in breast cancer tumors where PR-A is mostly overexpressed relative to PR-B. Understanding progestin action in breast cancer is crucial since the clinical use of some progestins has been associated with an increased risk of developing breast cancer. This study directly compared the agonist activities of selected progestins from all four generations for transactivation and transrepression via either PR-A or PR-B, and when PR-A and PR-B were co-expressed at ratios comparable to those detected in breast cancer tumors. Comparative dose-response analysis showed that earlier generation progestins mostly displayed similar efficacies for transactivation on a minimal progesterone response element via the PR isoforms, while most of the 4th generation progestins, similar to the natural progestogen, progesterone (P4), were more efficacious via PR-B. Most of the progestogens were however more potent via PR-A. We are the first to show that the efficacies of the selected progestogens via the individual PR isoforms were generally decreased when PR-A and PR-B were co-expressed, irrespective of the ratio of PR-A:PR-B. While the potencies of most progestogens via PR-B were enhanced when the ratio of PR-A relative to PR-B was increased, those via PR-A were minimally influenced. This study is also the first to report that all progestogens evaluated, except 1st generation medroxyprogesterone acetate and 4th generation drospirenone, displayed similar agonist activity for transrepression via PR-A and PR-B on a minimal nuclear factor kappa B containing promoter. Moreover, we showed that the progestogen activity for transrepression was significantly increased when PR-A and PR-B were co-expressed. Taken together, our results highlight that PR agonists (progestogens) do not always display the same activity via PR-A and PR-B, or when PR-A and PR-B are co-expressed at ratios mimicking those found in breast cancer tumors. These results suggest that biological responses are progestogen- and PR isoform-dependent and may differ in target tissues expressing varying PR-A:PR-B ratios.

Unveiling the Role of Hormonal Imbalance in Breast Cancer Development: A Comprehensive Review

Breast cancer is a complex and multifactorial disease with a significant global impact. Hormonal imbalance has emerged as a crucial factor in breast cancer development, highlighting the importance of understanding the intricate interplay between hormones and breast tissue. This comprehensive review aims to unveil the role of hormonal imbalance in breast cancer by exploring the involvement of key hormones, including estrogen and progesterone, and their receptors in tumor development. The review delves into how hormonal imbalance impacts breast tissue, emphasizing the significance of hormone receptor status in guiding treatment decisions. Furthermore, the review investigates the influence of other hormones, such as insulin and growth factors, and their cross-talk with hormone pathways in breast cancer progression. The implications of hormonal imbalance assessment in breast cancer risk assessment and the importance of hormone testing in diagnosis and treatment decisions are also discussed. Moreover, the review provides an overview of the various hormonal therapies used in breast cancer treatment, their benefits, limitations, and ongoing research efforts to optimize their efficacy and overcome resistance. Future directions in hormonal therapy research, including developing novel therapies and personalized medicine approaches, are explored. This review underscores the need for a comprehensive understanding of hormonal imbalance in breast cancer to enhance prevention, diagnosis, and treatment strategies, ultimately improving outcomes for individuals affected by this disease.

The Role of Progesterone Receptors in Breast Cancer

The progesterone receptor (PR) modulates estrogen receptors α (ERα) action in breast cancer; it is an upregulated target gene of ER, and its expression is dependent on estrogen. PR is also a valuable prognostic biomarker in breast cancer, especially in hormone-positive breast cancer. High expression of PR is more frequently observed in tumors with a better baseline prognosis (ie, luminal A) than tumors with a poor baseline prognosis (ie, luminal B). In the following review, we present the role of PR in breast cancer, including the genomic characteristics and pathways in breast cancer, PR and endocrine therapy.

Choosing the right partner in hormone-dependent gene regulation: Glucocorticoid and progesterone receptors crosstalk in breast cancer cells

Steroid hormone receptors (SHRs) belong to a large family of ligand-activated nuclear receptors that share certain characteristics and possess others that make them unique. It was thought for many years that the specificity of hormone response lay in the ligand. Although this may be true for pure agonists, the natural ligands as progesterone, corticosterone and cortisol present a broader effect by simultaneous activation of several SHRs. Moreover, SHRs share structural and functional characteristics that range from similarities between ligand-binding pockets to recognition of specific DNA sequences. These properties are clearly evident in progesterone (PR) and glucocorticoid receptors (GR); however, the biological responses triggered by each receptor in the presence of its ligand are different, and in some cases, even opposite. Thus, what confers the specificity of response to a given receptor is a long-standing topic of discussion that has not yet been unveiled. The levels of expression of each receptor, the differential interaction with coregulators, the chromatin accessibility as well as the DNA sequence of the target regions in the genome, are reliable sources of variability in hormone action that could explain the results obtained so far. Yet, to add further complexity to this scenario, it has been described that receptors can form heterocomplexes which can either compromise or potentiate the respective hormone-activated pathways with its possible impact on the pathological condition. In the present review, we summarized the state of the art of the functional cross-talk between PR and GR in breast cancer cells and we also discussed new paradigms of specificity in hormone action.

Progesterone receptor isoform ratio dictates antiprogestin/progestin effects on breast cancer growth and metastases: A role for NDRG1

Progesterone receptors (PR) ligands are being tested in luminal breast cancer. There are mainly two PR isoforms, PRA and PRB, and their ratio (PRA/PRB) may be predictive of antiprogestin response. Our aim was to investigate: the impact of the PR isoform ratio on metastatic behavior, the PR isoform ratio in paired primary tumors and lymph node metastases (LNM) and, the effect of antiprogestin/progestins on metastatic growth. Using murine and human metastatic models, we demonstrated that tumors with PRB > PRA (PRB-H) have a higher proliferation index but less metastatic ability than those with PRA > PRB (PRA-H). Antiprogestins and progestins inhibited metastatic burden in PRA-H and PRB-H models, respectively. In breast cancer samples, LNM retained the same PRA/PRB ratio as their matched primary tumors. Moreover, PRA-H LNM expressed higher total PR levels than the primary tumors. The expression of NDRG1, a metastasis suppressor protein, was higher in PRB-H compared with PRA-H tumors and was inversely regulated by antiprogestins/progestins. The binding of the corepressor SMRT at the progesterone responsive elements of the NDRG1 regulatory sequences, together with PRA, impeded its expression in PRA-H cells. Antiprogestins modulate the interplay between SMRT and AIB1 recruitment in PRA-H or PRB-H contexts regulating NDRG1 expression and thus, metastasis. In conclusion, we provide a mechanistic interpretation to explain the differential role of PR isoforms in metastatic growth and highlight the therapeutic benefit of using antiprogestins in PRA-H tumors. The therapeutic effect of progestins in PRB-H tumors is suggested. This article is protected by copyright. All rights reserved.

In Vivo Receptor Visualization and Evaluation of Receptor Occupancy with Positron Emission Tomography

Positron emission tomography (PET) is useful for noninvasive in vivo visualization of disease-related receptors, for evaluation of receptor occupancy to determine an appropriate drug dosage, and for proof-of-concept of drug candidates in translational research. For these purposes, the specificity of the PET tracer for the target receptor is critical. Here, we review work in this area, focusing on the chemical structures of reported PET tracers, their K_i/K_d values, and the physical properties relevant to target receptor selectivity. Among these physical properties, such as cLogP, cLogD, molecular weight, topological polar surface area, number of hydrogen bond donors, and pK_a, we focus especially on LogD and LogP as important physical properties that can be easily compared across a range of studies. We discuss the success of PET tracers in evaluating receptor occupancy and consider likely future developments in the field.

Triple SILAC identified progestin-independent and dependent PRA and PRB interacting partners in breast cancer

Progesterone receptor (PR) isoforms, PRA and PRB, act in a progesterone-independent and dependent manner to differentially modulate the biology of breast cancer cells. Here we show that the differences in PRA and PRB structure facilitate the binding of common and distinct protein interacting partners affecting the downstream signaling events of each PR-isoform. Tet-inducible HA-tagged PRA or HA-tagged PRB constructs were expressed in T47DC42 (PR/ER negative) breast cancer cells. Affinity purification coupled with stable isotope labeling of amino acids in cell culture (SILAC) mass spectrometry technique was performed to comprehensively study PRA and PRB interacting partners in both unliganded and liganded conditions. To validate our findings, we applied both forward and reverse SILAC conditions to effectively minimize experimental errors. These datasets will be useful in investigating PRA- and PRB-specific molecular mechanisms and as a database for subsequent experiments to identify novel PRA and PRB interacting proteins that differentially mediated different biological functions in breast cancer.

Progesterone receptor isoform-dependent cross-talk between prolactin and fatty acid synthase in breast cancer

Progesterone receptor (PR) isoforms can drive unique phenotypes in luminal breast cancer (BC). Here, we hypothesized that PR-B and PR-A isoforms differentially modify the cross-talk between prolactin and fatty acid synthase (FASN) in BC. We profiled the responsiveness of the FASN gene promoter to prolactin in T47D_co BC cells constitutively expressing PR-A and PR-B, in the PR-null variant T47D-Y cell line, and in PR-null T47D-Y cells engineered to stably re-express PR-A (T47D-YA) or PR-B (T47D-YB). The capacity of prolactin to up-regulate FASN gene promoter activity in T47D_co cells was lost in T47D-Y and TD47-YA cells. Constitutively up-regulated FASN gene expression in T47-YB cells and its further stimulation by prolactin were both suppressed by the prolactin receptor antagonist hPRL-G129R. The ability of the FASN inhibitor C75 to decrease prolactin secretion was more conspicuous in T47-YB cells. In T47D-Y cells, which secreted notably less prolactin and downregulated prolactin receptor expression relative to T47D_co cells, FASN blockade resulted in an augmented secretion of prolactin and up-regulation of prolactin receptor expression. Our data reveal unforeseen PR-B isoform-specific regulatory actions in the cross-talk between prolactin and FASN signaling in BC. These findings might provide new PR-B/FASN-centered predictive and therapeutic modalities in luminal intrinsic BC subtypes.

Classical and Non-Classical Progesterone Signaling in Breast Cancers

Much emphasis is placed on estrogen (E2) and estrogen receptor (ER) signaling as most research is focused on understanding E2 and ER’s ability to enhance proliferative signals in breast cancers. Progesterone (P4) is important for normal mammary gland development, function and menstrual control. However, P4 and its receptors (PRs) in breast cancer etiology continue to be understudied and its role in breast cancer remains controversial. The Women’s Health Initiative (WHI) clinical trial clearly demonstrated the importance of progestogens in breast cancer development. P4 has historically been associated with classical-signaling through nuclear receptors, however non-classical P4 signaling via membrane receptors has been described. Progestogens have the ability to bind to nuclear and membrane receptors and studies have demonstrated that both can promote breast cancer cell proliferation and breast tumor growth. In this review, we attempt to understand the classical and non-classical signaling role of P4 in breast cancers because both nuclear and membrane receptors could become viable therapeutic options for breast cancer patients.

Differential quantitative proteomics reveals key proteins related to phenotypic changes of breast cancer cells expressing progesterone receptor A

Progesterone receptor isoforms A and B exert different biological effects in breast cancer cells. Alteration of PRA/PRB ratio is often observed during breast cancer progression. High PRA/PRB ratios in breast cancer patients are associated with resistance to chemotherapy and poor prognosis. While it is well accepted that PRA and PRB regulate different sets of genes, how the expression of PRA and PRB alters breast cancer proteomes has not been fully investigated. To directly investigate the effects of PR isoform expression on the breast cancer proteome, both in the presence and absence of progestin, PRA and PRB were independently stably expressed in T47DC42 PR-null breast cancer cells using a doxycycline (Dox)-regulated promoter. Dox induction dose-dependently increased PRA and PRB expression. Dox-induced PRA and PRB showed normal receptor localization and were transcriptionally active. Differential quantitative proteomic analysis by stable isotope dimethyl labeling was performed to quantitatively examine how PR isoforms altered global breast cancer proteomes. Cells expressing PRA in the absence of progestin were enriched in proteins involved in the TCA cycle and enriched in proteins involved in glycolysis in the presence of progestin, whilst cells expressing PRB in the absence and presence progestin were significantly enriched in proteins involved in the cell cycle and cell apoptosis pathways. This proteomic data revealed a link between PR isoform expression and alteration in cell metabolism, cell proliferation, and apoptosis. The enrichment of proteins involved in the glycolytic pathway in breast cancer cells expressing PRA is consistent with stem cell-like properties, previously reported in PRA-rich breast cancer cells. Moreover, compared to liganded PRB, liganded PRA differentially upregulated proteins involved in chromatin remodeling, such as linker histone H1.2. Silencing H1.2 gene expression suppressed PRA-mediated cell proliferation and promoted G2/M and S phase entry of the cell cycle. Additionally, liganded PRA upregulated the expression of cathepsin D (CTSD) protease, whose expression is associated with poor prognosis in breast cancer patients. Together, our data demonstrated that the expression of PRA or PRB dramatically and differentially altered breast cancer cell proteomes. These isoform-specific changes in the breast cancer proteome will help to explain the distinct phenotypic properties of breast cancer cells expressing different levels of PRA and PRB.

Progesterone receptor-mediated actions and the treatment of central nervous system disorders: An up-date of the known and the challenge of the unknown

Progesterone has been shown to exert a wide range of remarkable protective actions in experimental models of central nervous system injury or disease. However, the intimate mechanisms involved in each of these beneficial effects are not fully depicted. In this review, we intend to give the readers a thorough revision on what is known about the participation of diverse receptors and signaling pathways in progesterone-mediated neuroprotective, pro-myelinating and anti-inflammatory outcomes, as well as point out to novel regulatory mechanisms that could open new perspectives in steroid-based therapies.

Decreased NDRG1 expression is associated with pregnancy loss in mice and attenuates the in vitro decidualization of endometrial stromal cells

Embryo implantation is an essential step for a successful pregnancy, and any defect in this process can lead to a range of pregnancy pathologies. The objective of this study was to explore the role of N-myc downregulated gene 1 (NDRG1) in embryo implantation. It was found that uterine NDRG1 expression has a dynamic pattern during the estrous cycle in nonpregnant mice and that uterine NDRG1 expression was elevated during the implantation process in pregnant mice. The distinct accumulation of NDRG1 protein signals was observed in the primary decidual zone adjacent to the implanting embryo during early pregnancy. Furthermore, uterine NDRG1 expression could be induced by activated implantation or artificial decidualization in mice. Decreased uterine NDRG1 expression was associated with pregnancy loss in mice and was associated with recurrent miscarriages in humans. The in vitro decidualization of both mouse and human endometrial stromal cells (ESCs) was accompanied by increased NDRG1 expression and downregulated NDRG1 expression in ESCs effectively inhibited decidualization. Collectively, these data suggest that NDRG1 plays an important role in decidualization during the implantation process, and the abnormal expression of NDRG1 may be involved in pregnancy loss.

Sensitivity and Isoform Specificity of 18F-Fluorofuranylnorprogesterone for Measuring Progesterone Receptor Protein Response to Estradiol Challenge in Breast Cancer

The purpose of this study was to evaluate the ability of 21-¹⁸F-fluoro-16α,17α-[(R)-(1'-α-furylmethylidene)dioxy]-19-norpregn-4-ene-3,20-dione (¹⁸F-FFNP) to measure alterations in progesterone receptor (PR) protein level and isoform expression in response to estradiol challenge. Methods: T47D human breast cancer cells and female mice-bearing T47D tumor xenografts were treated with 17β-estradiol (E2) to increase PR expression. ¹⁸F-FFNP uptake was measured using cell uptake and tissue biodistribution assays. MDA-MB-231 breast cancer clonal cell lines were generated that express the A or B isoforms of human PR. PR protein levels, transcriptional function, and subcellular localization were determined. In vitro ¹⁸F-FFNP binding was measured via saturation and competitive binding curves. In vivo ¹⁸F-FFNP uptake was measured using tumor xenografts and positron emission tomography. Statistical significance was determined using analysis of variance and t-tests. Results: After 48 and 72 h of E2, ¹⁸F-FFNP uptake in T47D cells was maximally increased compared to both vehicle and 24 h E2 treatment (p<0.0001 vs ethanol; P = 0.02 and P = 0.0002 vs 24 h for 48 and 72 h, respectively). T47D tumor xenografts in mice treated with 72 h E2 had maximal ¹⁸F-FFNP uptake compared to ethanol-treated mice (11.3±1.4 vs 5.2±0.81 %ID/g; P = 0.002). Corresponding tumor-to-muscle uptake ratios were 4.1±0.6, 3.9±0.5, and 2.3±0.4 for 48 h E2, 72 h E2, and ethanol-treated mice, respectively. There was no significant preferential ¹⁸F-FFNP binding or uptake by PR-A versus PR-B in the PR isoform-specific cell lines and tumor xenografts. Conclusion:¹⁸F-FFNP is capable of measuring estrogen-induced shifts in total PR expression in human breast cancer cells and tumor xenografts with equivalent isoform binding.

Cadmium induces progesterone receptor gene expression via activation of estrogen receptor in human ovarian cancer cells

Cadmium (Cd) as a metalloesterogen may have a role in development of ovarian cancer. One of the critical target genes of estrogens is progesterone receptors (PRs). There are controversial studies on association between Cd, PRs, and cell proliferation. This study investigates the effect of Cd on proliferation of ovarian cancer cell lines, PRA and PRB expression and their relationship. OVCAR3 and SKOV3 cells were treated with CdCl₂ (1-100 nM) and cell proliferation was assayed using bromodeoxyuridine (BrdU) method. The mechanism underlying the proliferative effect of Cd mediated by PRs was examined using cell transfection with PR- small interfering RNA (siRNA) and western blot analysis. Our results showed the involvement of PRs in Cd induced proliferation of ovarian cancer cells. Progesterone receptors are involved in proliferative effect of Cd. Moreover, Cd modified the expression of PRA and PRB and induced ovarian cancer cell proliferation through the change of PRA/PRB ratio. In conclusion, there is a mechanistic association between Cd effects on ovarian cancer cell proliferation, estrogen receptors and PRs expression.

The choice of progestogen for HRT in menopausal women: breast cancer risk is a major issue

Doctors and patients fear the risk of breast cancer when using hormone replacement therapy (HRT). This review focuses on the choice of progestogen for HRT in menopausal. The Women's Health Initiative (WHI) has been the only large double-blind placebo-controlled study testing the risk of breast cancer (BC) using HRT. No increased risk using estrogen (E)-only was seen, there was a significant decrease in mortality due to BC after the use of HRT which persisted during the recent 18-year follow-up of the WHI. In contrast in the combined arm the risk increased. In about 20 observational studies using mostly medroxyprogesterone acetate (MPA) or estradiol-norethisterone acetate (NETA) an increased BC-risk was observed comparable with the WHI. Only for natural progestogen, progesterone and for dydrogesterone (retro-isomer of progesterone) was no increased risk seen for up to 5-8 years, when compared directly with other progestogens, but for longer treatment an increased risk cannot be excluded. In contrast, the mortality due to BC after use of E-only and combined HRT decreased in about a dozen observational studies, and was very recently confirmed in a Finnish study evaluating 490,000 women using estradiol (E2) plus different progestogens. There have been already more than 70 studies evaluating the risk of BC during HRT, and still there are many open questions. Therefore, this review covers our own and other experimental research which could answer important questions. Experimental research has demonstrated that certain synthetic progestogens, but not progesterone and to some extent also not dydrogesterone, can accelerate the proliferation of breast cancer cells in vitro and in animal studies via special cell membrane components which we recently also detected in patients with BC, and we found differences comparing all available synthetic progestogens. Derived from these mechanisms future research may provide screening for patients at risk and predict the prognosis of possible BC.

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.

Gene expression profile and cancer-associated pathways linked to progesterone receptor isoform a (PRA) predominance in transgenic mouse mammary glands

Background

Progesterone receptor (PR) is expressed from a single gene as two isoforms, PRA and PRB. In normal breast human tissue, PRA and PRB are expressed in equimolar ratios, but isoform ratio is altered during malignant progression, usually leading to high PRA:PRB ratios. We took advantage of a transgenic mouse model where PRA isoform is predominant (PRA transgenics) and identified the key transcriptional events and associated pathways underlying the preneoplastic phenotype in mammary glands of PRA transgenics as compared with normal wild-type littermates.

Methods

The transcriptomic profiles of PRA transgenics and wild-type mammary glands were generated using microarray technology. We identified differentially expressed genes and analyzed clustering, gene ontology (GO), gene set enrichment analysis (GSEA), and pathway profiles. We also performed comparisons with publicly available gene expression data sets of human breast cancer.

Results

We identified a large number of differentially expressed genes which were mainly associated with metabolic pathways for the PRA transgenics phenotype while inflammation- related pathways were negatively correlated. Further, we determined a significant overlap of the pathways characterizing PRA transgenics and those in breast cancer subtypes Luminal A and Luminal B and identified novel putative biomarkers, such as PDHB and LAMB3.

Conclusion

The transcriptional targets identified in this study should facilitate the formulation or refinement of useful molecular descriptors for diagnosis, prognosis, and therapy of breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4550-z) contains supplementary material, which is available to authorized users.

Molecular Signaling of Progesterone, Growth Hormone, Wnt, and HER in Mammary Glands of Dogs, Rodents, and Humans: New Treatment Target Identification

Mammary tumors are the most common form of neoplasia in the bitch. Female dogs are protected when they are spayed before the first estrus cycle, but this effect readily disappears and is already absent when dogs are spayed after the second heat. As the ovaries are removed during spaying, ovarian steroids are assumed to play an essential role in tumor development. The sensitivity toward tumor development is already present during early life, which may be caused by early mutations in stem cells during the first estrus cycles. Later on in life, tumors arise that are mostly steroid-receptor positive, although a small subset of tumors overexpressing human epidermal growth factor 2 (HER2) and some lacking estrogen receptor, progesterone receptor (PR), and HER2 (triple negative) are present, as is the situation in humans. Progesterone (P₄), acting through PR, is the major steroid involved in outgrowth of mammary tissue. PRs are expressed in two forms, the progesterone receptor A (PRA) and progesterone receptor B (PRB) isoforms derived from splice variants from a single gene. The dog and the whole family of canids have only a functional PRA isoform, whereas the PRB isoform, if expressed at all, is devoid of intrinsic biological activity. In human breast cancer, overexpression of the PRA isoform is related to more aggressive carcinomas making the dog a unique model to study PRA-related mammary cancer. Administration of P₄ to adult dogs results in local mammary expression of growth hormone (GH) and wing less-type mouse mammary tumor virus integration site family 4 (Wnt4). Both proteins play a role in activation of mammary stem cells. In this review, we summarize what is known on P₄, GH, and Wnt signaling in canine mammary cancer, how the family of HER receptors could interact with this signaling, and what this means for comparative and translational oncological aspects of human breast cancer development.

Emerging functional roles of nuclear receptors in breast cancer

Nuclear receptors (NRs) have been targets of intensive drug development for decades due to their roles as key regulators of multiple developmental, physiological and disease processes. In breast cancer, expression of the estrogen and progesterone receptor remains clinically important in predicting prognosis and determining therapeutic strategies. More recently, there is growing evidence supporting the involvement of multiple nuclear receptors other than the estrogen and progesterone receptors, in the regulation of various processes important to the initiation and progression of breast cancer. We review new insights into the mechanisms of action of NRs made possible by recent advances in genomic technologies and focus on the emerging functional roles of NRs in breast cancer biology, including their involvement in circadian regulation, metabolic reprogramming and breast cancer migration and metastasis.

Progesterone receptor in the prostate: A potential suppressor for benign prostatic hyperplasia and prostate cancer

Advanced prostate cancer undergoing androgen receptor pathway inhibition (ARPI) eventually progresses to castrate-resistant prostate cancer (CRPC), suggesting that (i) androgen receptor (AR) blockage is incomplete, and (ii) there are other critical molecular pathways contributing to prostate cancer (PCa) progression. Although most PCa occurs in the epithelium, prostate stroma is increasingly believed to play a crucial role in promoting tumorigenesis and facilitating tumor progression. In the stroma, sex steroid hormone receptors such as AR and estrogen receptor-α are implicated to have important functions, whereas the progesterone receptor (PR) remains largely under-investigated despite the high sequence and structural similarities between PR and AR. Stromal progesterone/PR signaling may play a critical role in PCa development and progression because not only progesterone is a critical precursor for de novo androgen steroidogenesis and an activator of mutant androgen receptors, but also PR functions in a ligand-independent manner in various important pathways. In fact, recent progress in our understanding of stromal PR function suggests that this receptor may exert an inhibitory effect on benign prostatic hyperplasia (BPH), reactive stroma development, and PCa progression. These early findings of stromal PR warrant further investigations as this receptor could be a potential biomarker and therapeutic target in PCa management.

CCAAT/enhancer binding protein β negatively regulates progesterone receptor expression in human glioblastoma cells

Many progesterone (P4) actions are mediated by its intracellular receptor (PR), which has two isoforms (PR-A and PR-B) differentially transcribed from separate promoters of a single gene. In glioblastomas, the most frequent and aggressive brain tumors, PR-B is the predominant isoform. In an in silico analysis we showed putative CCAAT/Enhancer Binding Protein (C/EBP) binding sites at PR-B promoter. We evaluated the role of C/EBPβ in PR-B expression regulation in glioblastoma cell lines, which expressed different ratios of PR and C/EBPβ isoforms (LAP1, LAP2, and LIP). ChIP assays showed a significant basal binding of C/EBPβ, specific protein 1 (Sp1) and estrogen receptor alpha (ERα) to PR-B promoter. C/EBPβ knockdown increased PR-B expression and treatment with estradiol (E2) reduced C/EBPβ binding to the promoter and up-regulated PR-B expression. P4 induced genes were differently regulated when CEBP/β was silenced. These data show that C/EBPβ negatively regulates PR-B expression in glioblastoma cells.

Steroid Hormone Receptor Positive Breast Cancer Patient-Derived Xenografts

The vast majority of breast cancers are positive for estrogen receptor (ER) and depend on estrogens for growth. These tumors are treated with a variety of ER-targeted endocrine therapies, although eventual resistance remains a major clinical problem. Other steroid hormone receptors such as progesterone receptor (PR) and androgen receptor (AR) are emerging as additional prospective targets in breast cancer. The fundamental mechanism of action of these steroid receptors in gene regulation has been defined mainly by several breast cancer cell lines that were established in the late 1970s. More recently, breast cancer patient-derived xenografts (PDX) have been developed by multiple groups at institutions in several countries. These new models capture the large degree of heterogeneity between patients and within tumors and promise to advance our understanding of steroid hormone receptor positive breast cancer and endocrine resistance. Unfortunately, steroid hormone receptor positive breast cancers are much more difficult than their receptor negative counterparts to establish into sustainable PDX. Herein we discuss the derivation of steroid hormone receptor positive breast cancer PDX, several pitfalls in their genesis, and their utility in preclinical and translational steroid hormone receptor research.

Molecular evidence of functional progesterone withdrawal in human myometrium

Progesterone suppresses uterine contractility acting through its receptors (PRA/B). The mechanism by which human labour is initiated in the presence of elevated circulating progesterone has remained an enigma since Csapo first theorized of a functional withdrawal of progesterone in 1965. Here we report that in vitro progesterone-liganded nuclear PRB forms a complex including JUN/JUN homodimers and P54(nrb)/Sin3A/HDAC to repress transcription of the key labour gene, Cx43. In contrast, unliganded PRA paradoxically activates Cx43 transcription by interacting with FRA2/JUND heterodimers. Furthermore, we find that while nuclear progesterone receptor (PR) is liganded during human pregnancy, it becomes unliganded during both term and preterm labour as a result of increased expression of the progesterone-metabolizing enzyme 20α HSD and reduced nuclear progesterone levels. Our data provide a mechanism by which human labour can occur in the presence of elevated circulating progesterone and suggests non-metabolizable progestogen might represent an alternative new therapeutic approach to preterm birth prevention.

A Review of the Clinical Implications of Breast Cancer Biology

BACKGROUND

Histologically similar tumors may have different prognoses and responses to treatment. These differences are due to molecular differences. Hence, in this review, the biological interaction of breast cancer in several different areas is discussed. In addition, the performance and clinical application of the most widely-recognized biomarkers, metastasis, and recurrences from a biological perspective and current global advances in these areas are addressed.

OBJECTIVE

This review provides the performance and clinical application of the most widely-recognized biomarkers, metastasis, and recurrences from the biological perspective and current global advances in these areas.

METHODS

PubMed, Scopus, and Google Scholar were searched comprehensively with combinations of the following keywords: "breast cancer," "biological markers," and "clinical." The definition of breast cancer, diagnostic methods, biological markers, and available treatment approaches were extracted from the literature.

RESULTS

Estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor-2 (HER-2), and Ki-67 are the most well-known biological markers that have important roles in prognosis and response to therapeutic methods. Some studies showed the response of ER-positive and PR-negative tumors to anti-estrogenic treatment to be lower than ER-positive and PR-positive tumors. Patients with high expression of HER-2 and Ki-67 had a poor prognosis. In addition, recent investigations indicated the roles of new biomarkers, such as VEGF, IGF, P53 and P21, which are associated with many factors, such as age, race, and histological features.

CONCLUSION

The objective of scientists, from establishing a relationship between cancer biology infrastructures with clinical manifestations, is to find new ways of prevention and progression inhibition and then possible introduction of less dangerous and better treatments to resolve this dilemma of human society.

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.

Role of the short isoform of the progesterone receptor in breast cancer cell invasiveness at estrogen and progesterone levels in the pre- and post-menopausal ranges

Overexpression of the progesterone receptor (PR) isoform A (PR-A) is a negative prognosticator for estrogen receptor (ER)-positive breast cancer but in vitro studies have implicated PR-B in progestin-induced invasiveness. As estrogen is known to suppress invasiveness and tumor progression and as the in vitro studies were conducted in models that either lacked ER or excluded estrogen, we examined the role of PR isoforms in the context of estrogen signaling. Estrogen (< 0.01nM) strongly suppressed invasiveness in various ER+ model cell lines. At low (< 1nM) concentrations, progestins completely abrogated inhibition of invasiveness by estrogen. It was only in a higher (5 nM - 50 nM) concentration range that progestins induced invasiveness in the absence of estrogen. The ability of low dose progestins to rescue invasiveness from estrogen regulation was exclusively mediated by PR-A, whereas PR-B mediated the estrogen-independent component of progestin-induced invasiveness. Overexpression of PR-A lowered the progestin concentration needed to completely rescue invasiveness. Among estrogen-regulated genes, progestin/PR-A counter-regulated a distinctive subset, including breast tumor progression genes (e.g., HES1, PRKCH, ELF5, TM4SF1), leading to invasiveness. In this manner, at relatively low hormone concentrations (corresponding to follicular stage and post-menopausal breast tissue or plasma levels), progesterone influences breast cancer cell invasiveness by rescuing it from estrogen regulation via PR-A, whereas at higher concentrations the hormone also induces invasiveness independent of estrogen signaling, through PR-B. The findings point to a direct functional link between PR-A and progression of luminal breast cancer in the context of the entire range of pre- and post-menopausal plasma and breast tissue hormone levels.

Steroid hormones, steroid receptors, and breast cancer stem cells

The ovarian hormones progesterone and estrogen play important roles in breast cancer etiology, proliferation, and treatment. Androgens may also contribute to breast cancer risk and progression. In recent years, significant advances have been made in defining the roles of these steroid hormones in stem cell homeostasis in the breast. Stem cells are potential origins of breast cancer and may dictate tumor phenotype. At least a portion of breast cancers are proposed to be driven by cancer stem cells (CSCs), cells that mimic the self-renewing and repopulating properties of normal stem cells, and can confer drug resistance. Progesterone has been identified as the critical hormone regulating normal murine mammary stem cell (MaSC) populations and normal human breast stem cells. Synthetic progestins increase human breast cancer risk; one theory speculates that this occurs through increased stem cells. Progesterone treatment also increases breast CSCs in established breast cancer cell lines. This is mediated in part through progesterone regulation of transcription factors, signal transduction pathways, and microRNAs. There is also emerging evidence that estrogens and androgens can regulate breast CSC numbers. The evolving concept that a breast CSC phenotype is dynamic and can be influenced by cell signaling and external cues emphasizes that steroid hormones could be crucial players in controlling CSC number and function. Here we review recent studies on steroid hormone regulation of breast CSCs, and discuss mechanisms by which this occurs.

Pregnancy-associated breast cancer in Taiwanese women: potential treatment delay and impact on survival

This study investigated the clinicopathologic characteristics and survival of women diagnosed with pregnancy-associated breast cancer (PABC) in Taiwan. PABC is defined as breast cancer diagnosed during pregnancy or within 1 year after obstetric delivery. Our sample of PABC patients (N = 26) included all patients diagnosed at a major medical center in northern Taiwan from 1984 through 2009. Among these patients, 15 were diagnosed during pregnancy and 11 were diagnosed within 1 year after delivery. The comparison group included 104 patients within the same age range as the PABC patients and diagnosed with breast cancer not associated with pregnancy from 2004 through 2009 at the same hospital. Patients' initiating treatment delayed, 5-year and 10-year overall survival were delineated by stratified Kaplan-Meier estimates. Patients' characteristics were associated with initiating treatment delayed was evaluated with multivariate proportional hazards modeling. Antepartum PABC patients were younger and had longer time between diagnosis and treatment initiation than postpartum PABC patients. The predictor of treatment delayed was including birth parity, cancer stage, and pregnancy. The PABC group had larger tumors, more advanced cancer stage, and tumors with less progesterone receptor than the comparison group. The antepartum PABC patients had higher mortality than postpartum PABC and comparison groups within 5 years after diagnosis. Based on these results, we confirmed that pregnant women with breast cancer were more likely to delay treatment. Therefore, we recommend that breast cancer screening should be integrated into the prenatal and postnatal routine visits for early detection of the women's breast problems.

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.

Progesterone receptor status and Ki-67 index may predict early relapse in luminal B/HER2 negative breast cancer patients: a retrospective study

PURPOSE

Few studies has documented early relapse in luminal B/HER2-negative breast cancer. We examined prognostic factors for early relapse among these patients to improve treatment decision-making.

PATIENTS AND METHODS

A total 398 patients with luminal B/HER2-negative breast cancer were included. Kaplan-Meier curves were applied to estimate disease-free survival and Cox regression to identify prognostic factors.

RESULTS

Progesterone receptor (PR) negative expression was associated with higher tumor grade (p<.001) and higher Ki-67 index (p = .010). PR-negative patients received more chemotherapy than the PR-positive group (p = .009). After a median follow-up of 28 months, 17 patients (4.3%) had early relapses and 8 patients (2.0%) died of breast cancer. The 2-year disease-free survival was 97.7% in the PR-positive and 90.4% in the PR-negative groups (Log-rank p = .002). Also, patients with a high Ki-67 index (defined as >30%) had a reduced disease-free survival (DFS) when compared with low Ki-67 index group (≤30%) (98.0% vs 92.4%, respectively, Log-rank p = .013). In multivariate analysis, PR negativity was significantly associated with a reduced DFS (HR = 3.91, 95% CI 1.29-11.88, p = .016).

CONCLUSION

In this study, PR negativity was a prognostic factor for early relapse in luminal B/HER2-negative breast cancer, while a high Ki-67 index suggested a higher risk of early relapse.

Consideration of GREB1 as a potential therapeutic target for hormone-responsive or endocrine-resistant cancers

INTRODUCTION

Steroid hormones increase the incidence and promote the progression of many types of cancer. Exogenous estrogens increase the risk of developing breast, ovarian and endometrial cancer and many breast cancers initially respond to estrogen deprivation. Although steroid hormone signaling has been extensively studied, the mechanisms of hormone-stimulated cancer growth have not yet been fully elucidated, limiting opportunities for novel approaches to therapeutic intervention.

AREAS COVERED

This review examines growing evidence for the important role played by the steroid hormone-induced gene called GREB1, or growth regulation by estrogen in breast cancer 1. GREB1 is a critical mediator of both the estrogen-stimulated proliferation of breast cancer cells and the androgen-stimulated proliferation of prostate cancer cells.

EXPERT OPINION

Although its exact function in the cascade of hormone action remains unclear, the ability of GREB1 to modulate tumor progression in models of breast, ovarian and prostate cancer renders this gene an excellent candidate for further consideration as a potential therapeutic target. Research examining the mechanism of GREB1 action will help to elucidate its role in proliferation and its potential contribution to endocrine resistance and will determine whether GREB1 interference may have therapeutic efficacy.

Genomic and non-genomic actions of progestogens in the breast

Evidence is growing that progestogens may enhance breast cancer risk under hormone therapy in the postmenopause or hormonal contraception. However, differences may exist within the progestogen class and certain progestogens may have a higher potency in terms of breast cancer risk. The mechanism(s) by which these progestogens might influence breast cancer risk appear to be mediated via genomic and/or non-genomic effects triggered by activated progestogen receptors. In general, regulation of gene expression by progestogen receptors seems to be a multifactorial process involving both actions which often converge. In the present review, we describe the known genomic and non-genomic effects in the breast, especially focusing on the progestins. This article is part of a Special Issue entitled 'Menopause'.

Deep sequencing reveals new aspects of progesterone receptor signaling in breast cancer cells

Despite the pleiotropic effects of the progesterone receptor in breast cancer, the molecular mechanisms in play remain largely unknown. To gain a global view of the PR-orchestrated networks, we used next-generation sequencing to determine the progestin-regulated transcriptome in T47D breast cancer cells. We identify a large number of PR target genes involved in critical cellular programs, such as regulation of transcription, apoptosis, cell motion and angiogenesis. Integration of the transcriptomic data with the PR-binding profiling of hormonally treated cells identifies numerous components of the small-GTPases signaling pathways as direct PR targets. Progestin-induced deregulation of the small GTPases may contribute to the PR's role in mammary tumorigenesis. Transcript expression analysis reveals significant expression changes of specific transcript variants in response to the extracellular hormonal stimulus. Using the NET1 gene as an example, we show that the PR can dictate alternative promoter usage leading to the upregulation of an isoform that may play a role in metastatic breast cancer. Future studies should aim to characterize these selectively regulated variants and evaluate their clinical utility in prognosis and targeted therapy of hormonally responsive breast tumors.

The Molecular and Cellular Events That Take Place during Craniofacial Distraction Osteogenesis

Summary:

Gradual bone lengthening using distraction osteogenesis principles is the gold standard for the treatment of hypoplastic facial bones. However, the long treatment time is a major disadvantage of the lengthening procedures. The aim of this study is to review the current literature and summarize the cellular and molecular events occurring during membranous craniofacial distraction osteogenesis. Mechanical stimulation by distraction induces biological responses of skeletal regeneration that is accomplished by a cascade of biological processes that may include differentiation of pluripotential tissue, angiogenesis, osteogenesis, mineralization, and remodeling. There are complex interactions between bone-forming osteoblasts and other cells present within the bone microenvironment, particularly vascular endothelial cells that may be pivotal members of a complex interactive communication network in bone. Studies have implicated number of cytokines that are intimately involved in the regulation of bone synthesis and turnover. The gene regulation of numerous cytokines (transforming growth factor-β, bone morphogenetic proteins, insulin-like growth factor-1, and fibroblast growth factor-2) and extracellular matrix proteins (osteonectin, osteopontin) during distraction osteogenesis has been best characterized and discussed. Understanding the biomolecular mechanisms that mediate membranous distraction osteogenesis may guide the development of targeted strategies designed to improve distraction osteogenesis and accelerate bone regeneration that may lead to shorten the treatment duration.

Prolactin suppresses a progestin-induced CK5-positive cell population in luminal breast cancer through inhibition of progestin-driven BCL6 expression

Prolactin controls the development and function of milk-producing breast epithelia but also supports growth and differentiation of breast cancer, especially luminal subtypes. A principal signaling mediator of prolactin, Stat5, promotes cellular differentiation of breast cancer cells in vitro, and loss of active Stat5 in tumors is associated with antiestrogen therapy failure in patients. In luminal breast cancer, progesterone induces a cytokeratin-5 (CK5)-positive basal cell-like population. This population possesses characteristics of tumor stem cells including quiescence, therapy resistance and tumor-initiating capacity. Here we report that prolactin counteracts induction of the CK5-positive population by the synthetic progestin (Pg) R5020 in luminal breast cancer cells both in vitro and in vivo. CK5-positive cells were chemoresistant as determined by fourfold reduced rate of apoptosis following docetaxel exposure. Pg-induction of CK5 was preceded by marked upregulation of BCL6, an oncogene and transcriptional repressor critical for the maintenance of leukemia-initiating cells. Knockdown of BCL6 prevented induction of CK5-positive cell population by Pg. Prolactin suppressed Pg-induced BCL6 through Jak2-Stat5 but not Erk- or Akt-dependent pathways. In premenopausal but not postmenopausal patients with hormone receptor-positive breast cancer, tumor protein levels of CK5 correlated positively with BCL6, and high BCL6 or CK5 protein levels were associated with unfavorable clinical outcome. Suppression of Pg-induction of CK5-positive cells represents a novel prodifferentiation effect of prolactin in breast cancer. The present progress may have direct implications for breast cancer progression and therapy as loss of prolactin receptor-Stat5 signaling occurs frequently and BCL6 inhibitors currently being evaluated for lymphomas may have value for breast cancer.

Progesterone receptors induce FOXO1-dependent senescence in ovarian cancer cells

Loss of nuclear progesterone receptors (PR) and low circulating progesterone levels are associated with increased ovarian cancer (OC) risk. However, PR are abundantly expressed in a significant percentage of serous and endometrioid ovarian tumors; patients with PR+ tumors typically experience longer progression-free survival relative to those with PR-null tumors. The molecular mechanisms of these protective effects are poorly understood. To study PR action in OC in the absence of added estrogen (i.e., needed to induce robust PR expression), we created ES-2 OC cells stably expressing vector control or GFP-tagged PR-B (GFP-PR). Progestin (R5020) stimulation of ES-2 cells stably expressing GFP-PR induced cellular senescence characterized by altered cellular morphology, prolonged survival, senescence-associated β-galactosidase activity, G1 cell cycle arrest and upregulation of the cell cycle inhibitor, p21, as well as the Forkhead-box transcription factor, FOXO1; these results repeated in unmodified ER+/PR+ PEO4 OC cells. PR-B and FOXO1 were detected within the same PRE-containing regions of the p21 upstream promoter. Knockdown of p21 resulted in molecular compensation via FOXO1-dependent upregulation of numerous FOXO1 target genes (p15, p16, p27) and an increased rate of senescence. Inhibition of FOXO1 (with AS1842856) or stable FOXO1 knockdown inhibited progestin-induced p21 expression and blocked progestin-induced senescence. Overall, these findings support a role for PR as a tumor suppressor in OC cells, which exhibits inhibitory effects by inducing FOXO1-dependent cellular senescence. Clinical "priming" of the PR-FOXO1-p21 signaling pathway using PR agonists may provide a useful strategy to induce irreversible cell cycle arrest and thereby sensitize OC cells to existing chemotherapies as part of combination "two-step" therapies.

Progesterone receptor isoforms PRA and PRB differentially contribute to breast cancer cell migration through interaction with focal adhesion kinase complexes

Conditionally expressed progesterone receptor isoforms PRA and PRB enhance breast cancer cell migration through interaction with focal adhesion kinase (FAK) and differential regulation of FAK phosphorylation and turnover. PRB-stimulated migration is reduced by progestins, which is prevented by PR antagonists or agonist-bound PRA.

Progesterone receptor (PR) and progestins affect mammary tumorigenesis; however, the relative contributions of PR isoforms A and B (PRA and PRB, respectively) in cancer cell migration remains elusive. By using a bi-inducible MDA-MB-231 breast cancer cell line expressing PRA and/or PRB, we analyzed the effect of conditional PR isoform expression. Surprisingly, unliganded PRB but not PRA strongly enhanced cell migration as compared with PR(–) cells. 17,21-Dimethyl-19-norpregna-4,9-dien-3,20-dione (R5020) progestin limited this effect and was counteracted by the antagonist 11β-(4-dimethyl­amino)­phenyl-17β-hydroxy-17-(1-propynyl)­estra-4,9-dien-3-one (RU486). Of importance, PRA coexpression potentiated PRB-mediated migration, whereas PRA alone was ineffective. PR isoforms differentially regulated expressions of major players of cell migration, such as urokinase plasminogen activator (uPA), its inhibitor plasminogen activator inhibitor type 1, uPA receptor (uPAR), and β1-integrin, which affect focal adhesion kinase (FAK) signaling. Moreover, unliganded PRB but not PRA enhanced FAK Tyr397 phosphorylation and colocalized with activated FAK in cell protrusions. Because PRB, as well as PRA, coimmunoprecipitated with FAK, both isoforms can interact with FAK complexes, depending on their respective nucleocytoplasmic trafficking. In addition, FAK degradation was coupled to R5020-dependent turnovers of PRA and PRB. Such an effect of PRB/PRA expression on FAK signaling might thus affect adhesion/motility, underscoring the implication of PR isoforms in breast cancer invasiveness and metastatic evolution with underlying therapeutic outcomes.

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

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

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

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