Effect of overexpression of progesterone receptor A on endogenous progestin-sensitive endpoints in breast cancer cells

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.

High Levels of Progesterone Receptor B in MCF-7 Cells Enable Radical Anti-Tumoral and Anti-Estrogenic Effect of Progestin

The widely reported conflicting effects of progestin on breast cancer suggest that the progesterone receptor (PR) has dual functions depending on the cellular context. Cell models that enable PR to fully express anti-tumoral properties are valuable for the understanding of molecular determinant(s) of the anti-tumoral property. This study evaluated whether the expression of high levels of PR in MCF-7 cells enabled a strong anti-tumoral response to progestin. MCF-7 cells were engineered to overexpress PRB by stable transfection. A single dose of Promegestone (R5020) induced an irreversible cell growth arrest and senescence-associated secretory phenotype in MCF-7 cells with PRB overexpression (MCF-7PRB cells) but had no effect on MCF-7 cells with PRA overexpression. The growth-arresting effect was associated with downregulations of cyclin A2 and B1, CDK2, and CDK4 despite an initial upregulation of cyclin A2 and B1. R5020 also induced an evident activation of Nuclear Factor κB (NF-κB) and upregulation of interleukins IL-1α, IL-1β, and IL-8. Although R5020 caused a significant increase of CD24+CD44+ cell population, R5020-treated MCF-7PRB cells were unable to form tumorspheres and underwent massive apoptosis, which is paradoxically associated with marked downregulations of the pro-apoptotic proteins BID, BAX, PARP, and Caspases 7 and 8, as well as diminution of anti-apoptotic protein BCL-2. Importantly, R5020-activated PRB abolished the effect of estrogen. This intense anti-estrogenic effect was mediated by marked downregulation of ERα and pioneer factor FOXA1, leading to diminished chromatin-associated ERα and FOXA1 and estrogen-induced target gene expression. In conclusion, high levels of agonist-activated PRB in breast cancer cells can be strongly anti-tumoral and anti-estrogenic despite the initial unproductive cell cycle acceleration. Repression of ERα and FOXA1 expression is a major mechanism for the strong anti-estrogenic effect.

High expression of progesterone receptor may be an adverse prognostic factor in oestrogen receptor-negative/progesterone receptor-positive breast cancer: results of comprehensive re-evaluation of multi-institutional case series

Oestrogen receptor (ER)-negative (-) progesterone receptor (PgR)-positive (+) is the least common combination of steroid receptor expression observed in breast cancer. There are many controversies regarding the actual existence of ER-/PgR+ phenotype. In the current study, we aimed to perform comprehensive immunohistochemical re-evaluation of ER-/PgR+ breast cancers from multiple institutions. A total of 135 cases of ER-/PgR+ breast cancer were collected from 11 institutions from the period 2006-2020 and subsequently stained with three clinically validated anti-ER antibody clones: SP1 (Roche), 1D5 (Dako), and EP1 (Dako), and two anti-PgR antibody clones: 636 (Dako), and 1E2 (Roche). Clinicopathological characteristics of confirmed and re-categorised cases were analysed. Seventy-six cases retained the original ER-/PgR+ phenotype, including 21 HER2+ and 55 HER2- tumours. Forty-seven cases were ER+ with at least one anti-ER antibody, and 12 cases were re-categorised as double-negatives across all anti-ER and anti-PgR antibodies. No significant differences in survival were observed between groups in the HER2+ category. In the HER2- cohort, confirmed ER-/PgR+, ER+ tumours with discrepant ER staining, and triple negatives had inferior overall survival compared to concordant ER+ cases. Progesterone receptor expression in >20% of cells was identified as an adverse prognostic factor in ER-/PgR+/HER2- breast cancer in a multivariable model adjusted by stage (HR 5.0, 95% CI 1.3-19.2, p=0.019). We performed one of the largest validation studies so far on ER-/PgR+ breast cancer and confirmed the existence of this subgroup. Moreover, we identified high PgR expression as an adverse prognostic factor.

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 Signaling in the Breast Tumor Microenvironment

The tumor microenvironment (TME) is a complex infrastructure composed of stromal, epithelial, and immune cells embedded in a vasculature ECM. The microenvironment surrounding mammary epithelium plays a critical role during the development and differentiation of the mammary gland, enabling the coordination of the complex multihormones and growth factor signaling processes. Progesterone/progesterone receptor paracrine signaling interactions in the microenvironment play vital roles in stem/progenitor cell function during normal breast development. In breast cancer, the female sex hormones, estrogen and progesterone, and growth factor signals are altered in the TME. Progesterone signaling modulates not only breast tumors but also the breast TME, leading to the activation of a series of cross-communications that are implicated in the genesis of breast cancers. This chapter reviews the evidence that progesterone and PR signaling modulates not only breast epitheliums but also the breast TME. Furthermore, crosstalk between estrogen and progesterone signaling affecting different cell types within the TME is discussed. A better understanding of how PR and progesterone affect the TME of breast cancer may lead to novel drugs or a therapeutic approach for the treatment of breast cancer shortly.

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 isoform B expression in pulmonary neuroendocrine cells decreases cell proliferation

The progesterone receptor (PR) has been reported to play important roles in lung development and function, such as alveolarization, alveolar fluid clearance (AFC) and upper airway dilator muscle activity. In the lung, pulmonary neuroendocrine cells (PNECs) are important in the etiology and progression of lung neuroendocrine tumors (NETs). Women with lung NETs had significantly better survival rates than men, suggesting that sex steroids and their receptors, such as the PR, could be involved in the progression of lung NETs. The PR exists as two major isoforms, PRA and PRB. How the expression of different PR isoforms affects proliferation and the development of lung NETs is not well understood. To determine the role of the PR isoforms in PNECs, we constructed H727 lung NET cell models expressing PRB, PRA, Green Fluorescence Protein (GFP) (control). The expression of PRB significantly inhibited H727 cell proliferation better than that of PRA in the absence of progestin. The expression of the unrelated protein, GFP, had little to no effect on H727 cell proliferation. To better understand the role of the PR isoform in PNECs, we examined PR isoform expression in PNECs in lung tissues. A monoclonal antibody specific to the N-terminus of PRB (250H11 mAb) was developed to specifically recognize PRB, while a monoclonal antibody specific to a common N-terminus epitope present in both PRA and PRB (1294 mAb) was used to detect both PRA and PRB. Using these PR and PRB-specific antibodies, we demonstrated that PR (PRA&PRB) and PRB were expressed in the PNECs of the normal fetal and adult lung, with significantly higher PR expression in the fetal lung. Interestingly, PRB expression in the normal lung was associated with lower cell proliferation than PR expression, suggesting a distinct role of PRB in the PNECs. A better understanding of the molecular mechanism of PR and PR isoform signaling in lung NET cells may help in developing novel therapeutic strategies that will benefit lung NET patients in the future.

Di(2-ethylhexyl) phthalate (DEHP) increases proliferation of epithelial breast cancer cells through progesterone receptor dysregulation

The di(2-ethylhexyl) phthalate (DEHP) is a plasticizer incorporated to plastic matrices of widely used consumer products. However, it is gradually released from these products, resulting in a chronic exposure for humans. Although DEHP, similar to other members of the phthalates family, is generally considered as an endocrine disruptor, the mechanisms implicated in its toxicity are yet poorly understood. Our objective was to determine the effects of an exposure to DEHP and to one of its major metabolite, the mono(2-ethylhexyl) phthalate (MEHP) on markers involved in breast carcinogenesis. T-47D cells were exposed to environmentally relevant and higher doses of DEHP and MEHP (0.1-10 000 nM) for 4 days. Our results showed that an exposure to 10 000 nM of DEHP and 0.1 nM of MEHP significantly increased the proliferation of T-47D cells, without inducing apoptosis. In addition, a significant increase in the protein levels of the isoform A of the progesterone receptor (PR) and of nuclear levels of PR were observed in T-47D cells exposed to 10 000 nM of DEHP. Importantly, the increased proliferation and nuclear levels of PR were totally and partially inhibited, respectively, by Mifepristone, a PR antagonist. These results suggest that an exposure to DEHP or MEHP increase cell proliferation by activating PR signaling, which could potentially increase the risks to develop breast cancer. The mechanism of activation of the progesterone pathway by DEHP and the long-term consequences of this activation remained to be elucidated.

Novel RU486 (mifepristone) analogues with increased activity against Venezuelan Equine Encephalitis Virus but reduced progesterone receptor antagonistic activity

There are currently no therapeutics to treat infection with the alphavirus Venezuelan equine encephalitis virus (VEEV), which causes flu-like symptoms leading to neurological symptoms in up to 14% of cases. Large outbreaks of VEEV can result in 10,000 s of human cases and mass equine death. We previously showed that mifepristone (RU486) has anti-VEEV activity (EC50 = 20 μM) and only limited cytotoxicity (CC50 > 100 μM), but a limitation in its use is its abortifacient activity resulting from its ability to antagonize the progesterone receptor (PR). Here we generate a suite of new mifepristone analogues with enhanced antiviral properties, succeeding in achieving >11-fold improvement in anti-VEEV activity with no detectable increase in toxicity. Importantly, we were able to derive a lead compound with an EC50 of 7.2 µM and no detectable PR antagonism activity. Finally, based on our SAR analysis we propose avenues for the further development of these analogues as safe and effective anti-VEEV agents.

Molecular mechanisms underlying progesterone-induced cytoplasmic retention of p27 in breast cancer cells

It has been reported that progesterone (P4) can contribute to the aggressiveness of human breast cancers through promoting cytoplasmic localization of p27 and stimulating proliferation. However, the molecular mechanisms underlying P4-induced cytoplasmic retention of p27 are still unclear. Here, we demonstrated that P4 (12.5-100 nM) concentration-dependently increased the number of T47D and MCF-7 cells. P4 (50 nM) also time-dependently increased the levels of p27 protein. Knock-down of p27 using the small interfering RNA (siRNA) technique abolished the P4-increased cell number of T47D and MCF-7. The signaling pathway involved in the P4-promoted breast cancer cell proliferation was further investigated. Our results suggest that P4 activated the PI3K/AKT-mediated signaling, subsequently increasing phophorylation of p27 at pT198 and T157, and thereby caused cytoplasmic retention of p27 protein. In addition, P4 activated kinase-interacting stathmin (KIS), subsequently increasing phosphorylation of nuclear p27 at serine 10 (S10), and thereby caused cytoplasmic translocation of p27pS10 from the nucleus. P4 also increased the level of nuclear CDK2pT160, thereby inducing p27 phosphorylation at T187, and hence caused cytosolic translocation of p27pT187 from the nucleus. In the cytosol, both p27pS10 and p27pT187 were degraded via the ubiquitin-proteasome pathway. Taken together, our data suggest that P4 promoted breast cancer cell proliferation through cytoplasmic retention of p27pT157 and p27pT198 and nuclear export of p27pS10 and p27pT187.

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.

Estrogen and progesterone signalling in the normal breast and its implications for cancer development

The ovarian hormones estrogen and progesterone are master regulators of the development and function of a broad spectrum of human tissues, including the breast, reproductive and cardiovascular systems, brain and bone. Acting through the nuclear estrogen (ER) and progesterone receptors (PR), both play complex and essential coordinated roles in the extensive development of the lobular alveolar epithelial structures of the normal breast during puberty, the normal menstrual cycle and pregnancy. The past decade has seen major advances in understanding the mechanisms of action of estrogen and progesterone in the normal breast and in the delineation of the complex hierarchy of cell types regulated by ovarian hormones in this tissue. There is evidence for a role for both ER and PR in driving breast cancer, and both are favourable prognostic markers with respect to outcome. In this review, we summarize current knowledge of the mechanisms of action of ER and PR in the normal breast, and implications for the development and management of breast cancer.

Extranuclear signaling by sex steroid receptors and clinical implications in breast cancer

Estrogen and progesterone play essential roles in the development and progression of breast cancer. Over 70% of breast cancers express estrogen receptors (ER) and progesterone receptors (PR), emphasizing the need for better understanding of ER and PR signaling. ER and PR are traditionally viewed as transcription factors that directly bind DNA to regulate gene networks. In addition to nuclear signaling, ER and PR mediate hormone-induced, rapid extranuclear signaling at the cell membrane or in the cytoplasm which triggers downstream signaling to regulate rapid or extended cellular responses. Specialized membrane and cytoplasmic proteins may also initiate hormone-induced extranuclear signaling. Rapid extranuclear signaling converges with its nuclear counterpart to amplify ER/PR transcription and specify gene regulatory networks. This review summarizes current understanding and updates on ER and PR extranuclear signaling. Further investigation of ER/PR extranuclear signaling may lead to development of novel targeted therapeutics for breast cancer management.

Proliferation and ovarian hormone signaling are impaired in normal breast tissues from women with BRCA1 mutations: benefit of a progesterone receptor modulator treatment as a breast cancer preventive strategy in women with inherited BRCA1 mutations

Women with inherited BRCA1 mutations have an elevated risk (40-80%) for developing breast and ovarian cancers. Reproductive history has been reported to alter this risk, suggesting a relationship between ovarian hormone signaling and BRCA1-related tumor development. BRCA1 interactions with estrogen receptor (ER) and progesterone receptor (PR) signaling were previously described in human breast cancer cell lines and mouse models. However, few studies have examined the effect of ovarian hormone regulation in normal human breast tissues bearing a heterozygous BRCA1 mutation. This study compares the proliferation level (Ki67) and the expression of ER, PR, and of the PR target gene, fatty acid synthase (FASN), in histologically normal breast tissues from women with BRCA1 mutations (BRCA1+/mut, n=23) or without BRCA1 mutations (BRCA1+/+, n=28). BRCA1+/mut tissues showed an increased proliferation and impaired hormone receptor expression with a marked loss of the PR isoform, PR-B. Responses to estradiol and progesterone treatments in BRCA1+/mut and BRCA1+/+ breast tissues were studied in a mouse xenograft model, and showed that PR and FASN expression were deregulated in BRCA1+/mut breast tissues. Progesterone added to estradiol treatment increased the proliferation in a subset of BRCA1+/mut breast tissues. The PR inhibitor, ulipristal acetate (UPA), was able to reverse this aberrant progesterone-induced proliferation. This study suggests that a subset of women with BRCA1 mutations could be candidates for a UPA treatment as a preventive breast cancer strategy.

Abnormal Pathways in Endometriosis in Relation to Progesterone Resistance: A Review

Introduction

Endometriosis is an estrogen-dependent disorder, and recent studies suggest that progesterone resistance may contribute to the development and pathophysiology of the disorder. Based on this, identification of genetic and molecular perturbations in the endometrium of women with endometriosis is an important step towards understanding the pathogenesis of the disease, and the development of novel treatment and diagnostic strategies.

Methods

A systematic literature search in PubMed and Embase was performed, and 118 articles were identified for further screening. Two reviewers performed article screening independently using Covidence, and 16 studies fulfilled the inclusion criteria. The Newcastle-Ottawa Scale was used to assess the quality of these studies.

Results

This review presents data from eutopic endometrial biopsies from women with and without endometriosis. Several biomarkers related to a downregulated progesterone response were identified and discussed in detail.

Conclusions

Our review demonstrates significant results concerning the biomarkers investigated, which may substantiate the theory of progesterone resistance in women with endometriosis. However, further research is necessary to determine their specific role and relevance.

Annexin/S100A Protein Family Regulation through p14ARF-p53 Activation: A Role in Cell Survival and Predicting Treatment Outcomes in Breast Cancer

The annexin family and S100A associated proteins are important regulators of diverse calcium-dependent cellular processes including cell division, growth regulation and apoptosis. Dysfunction of individual annexin and S100A proteins is associated with cancer progression, metastasis and cancer drug resistance. This manuscript describes the novel finding of differential regulation of the annexin and S100A family of proteins by activation of p53 in breast cancer cells. Additionally, the observed differential regulation is found to be beneficial to the survival of breast cancer cells and to influence treatment efficacy. We have used unbiased, quantitative proteomics to determine the proteomic changes occurring post p14ARF-p53 activation in estrogen receptor (ER) breast cancer cells. In this report we identified differential regulation of the annexin/S100A family, through unique peptide recognition at the N-terminal regions, demonstrating p14ARF-p53 is a central orchestrator of the annexin/S100A family of calcium regulators in favor of pro-survival functions in the breast cancer cell. This regulation was found to be cell-type specific. Retrospective human breast cancer studies have demonstrated that tumors with functional wild type p53 (p53wt) respond poorly to some chemotherapy agents compared to tumors with a non-functional p53. Given that modulation of calcium signaling has been demonstrated to change sensitivity of chemotherapeutic agents to apoptotic signals, in principle, we explored the paradigm of how p53 modulation of calcium regulators in ER+ breast cancer patients impacts and influences therapeutic outcomes.

Down-regulated SOX4 expression suppresses cell proliferation, metastasis and induces apoptosis in Xuanwei female lung cancer patients

The transcription factor SOX4 has functional importance in foetal lung maturation and tumorigenesis in a number of cancers. However, its biological functions in the progression of lung tumorigenesis remain unclear. In this study, we found that the expression levels of SOX4 mRNA and protein were significantly higher in Xuanwei female lung cancer tissues than in benign lung lesions. The patients with high expression of the SOX4 protein had a higher pathological grade, lymph node (LN) metastasis, poor tumor differentiation and worse prognosis than those patients with low expression of SOX4. Knockdown of the SOX4 gene in the Xuanwei female lung cancer cell line XWLC-05 resulted in apoptotic morphological changes, decreased cell proliferation, invasion and migration. Furthermore, knockdown of the SOX4 gene resulted in obvious sub-G1 peaks and induction of apoptosis through upregulation of caspase-3 expression, while in cells treated with a caspase-3 inhibitor, apoptosis induced by silencing SOX4 expression was inhibited. In vivo analysis in nude mice further confirmed that knockdown of SOX4 suppressed tumor growth. In conclusion, SOX4 appears to be an important tumor suppressor gene in the regulation of Xuanwei female lung cancer cell proliferation, apoptosis and metastases, and it may be a potential target for effective lung cancer therapy.

Ulipristal Acetate Inhibits Progesterone Receptor Isoform A-Mediated Human Breast Cancer Proliferation and BCl2-L1 Expression

The progesterone receptor (PR) with its isoforms and ligands are involved in breast tumorigenesis and prognosis. We aimed at analyzing the respective contribution of PR isoforms, PRA and PRB, in breast cancer cell proliferation in a new estrogen-independent cell based-model, allowing independent PR isoforms analysis. We used the bi-inducible human breast cancer cell system MDA-iPRAB. We studied the effects and molecular mechanisms of action of progesterone (P4) and ulipristal acetate (UPA), a new selective progesterone receptor modulator, alone or in combination. P4 significantly stimulated MDA-iPRA expressing cells proliferation. This was associated with P4-stimulated expression of the anti-apoptotic factor BCL₂-L₁ and enhanced recruitment of PRA, SRC-1 and RNA Pol II onto the +58 kb PR binding motif of the BCL₂-L₁ gene. UPA decreased cell proliferation and repressed BCL_2-L₁ expression in the presence of PRA, correlating with PRA and SRC1 but not RNA Pol II recruitment. These results bring new information on the mechanism of action of PR ligands in controlling breast cancer cell proliferation through PRA in an estrogen independent model. Evaluation of PR isoforms ratio, as well as molecular signature studies based on PRA target genes could be proposed to facilitate personalized breast cancer therapy. In this context, UPA could be of interest in endocrine therapy. Further confirmation in the clinical setting is required.

Minireview: Progesterone Regulation of Proliferation in the Normal Human Breast and in Breast Cancer: A Tale of Two Scenarios?

Progesterone (P), which signals through the P receptor (PR), is critical in normal development of the breast, but its signaling axis is also a major driver of breast cancer risk. Here we review recent advances in the understanding of P signaling in the normal human breast, with a focus on the importance of the balance between autocrine and paracrine signaling. To date, most data (which derive largely from mouse models or human breast cancer cell line studies) have demonstrated that the vast majority of PR+ cells appear to act as "sensor" cells, which respond to P stimulation by translating these hormonal cues into paracrine signals. However, growing evidence suggests that, dependent on the cellular context, P may also signal in an autocrine manner in a subset of cells in the normal mouse mammary gland and human breast. It has been suggested that it may be dysregulation of this autocrine signaling, resulting in a "switch" from a predominance of paracrine signaling to autocrine signaling in PR+ cells, which is an early event during breast tumorigenesis. This review summarizes current evidence in the literature that demonstrates the mechanisms through which P acts in the normal human breast, as well as highlighting the important questions that remain unanswered.

Abundance and Localization of Progesterone Receptor Isoforms in Endometrium in Women With and Without Endometriosis and in Peritoneal and Ovarian Endometriotic Implants

BACKGROUND

Several studies suggest that resistance to progesterone may contribute to the pathophysiology of endometriosis. Progesterone mediates its biological activity via the 2 progesterone receptor (PR) isoforms (PR-A and PR-B). Effects of progesterone are determined by the PR-A:PR-B ratio such that a PR-B-dominant state promotes progesterone signaling, whereas a PR-A-dominant state decreases progesterone responsiveness. Our objective was to compare the abundance and cellular localization of the PR isoforms in endometrium and endometriotic lesions from women with and without peritoneal and ovarian endometriosis.

METHODS

This in vitro study was conducted in a tertiary care facility. Reproductive-age women with surgically diagnosed endometriosis (n = 18) and asymptomatic control individuals (n = 20) were prospectively recruited at the late proliferative and the early secretory phases. At laparoscopy, samples of eutopic endometrium, peritoneal and ovarian endometriosis, and disease-free peritoneum were obtained for subsequent immunohistochemical and immunoblot analysis of PR-B and total PR localization and PR-A and PR-B abundance, respectively.

RESULTS

The PR-A and PR-B were detected in eutopic endometrium and in peritoneal and ovarian endometriosis but not in disease-free peritoneum from patients with and without endometriosis. In peritoneal endometriosis, PR-A was the predominant isoform detected, whereas both receptors were detected in ovarian endometriosis and eutopic endometrium. In eutopic endometrium, levels of PR-A were significantly elevated in women with endometriosis compared with women without disease, regardless of menstrual phase. The PR-A levels were significantly elevated in ovarian endometriosis compared with peritoneal endometriosis.

CONCLUSIONS

Endometriotic lesions and eutopic endometrium from women with endometriosis are uniform in a PR-A-dominant state. The data suggest that menstrual efflux of a PR-A-dominant endometrial tissue into the peritoneal cavity may play a role in the pathophysiology of endometriosis.

Progesterone stimulates proliferation and promotes cytoplasmic localization of the cell cycle inhibitor p27 in steroid receptor positive breast cancers

Progestins are reported to increase the risk of more aggressive estrogen receptor positive, progesterone receptor positive (ER+ PR+) breast cancers in postmenopausal women. Using an in vivo rat model of ER+ PR + mammary cancer, we show that tumors arising in the presence of estrogen and progesterone exhibit increased proliferation and decreased nuclear expression of the cell cycle inhibitor p27 compared with tumors growing in the presence of estrogen alone. In human T47D breast cancer cells, progestin increased proliferation and decreased nuclear p27 expression. The decrease of nuclear p27 protein was dependent on activation of Src and PI3K by progesterone receptor isoforms PRA or PRB. Importantly, increased proliferation and decreased nuclear p27 expression were observed in invasive breast carcinoma compared with carcinoma in situ. These results suggest that progesterone specifically regulates intracellular localization of p27 protein and proliferation. Therefore, progesterone-activated pathways can provide useful therapeutic targets for treatment of more aggressive ER+ PR+ breast cancers.

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.

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.

p14ARF post-transcriptional regulation of nuclear cyclin D1 in MCF-7 breast cancer cells: discrimination between a good and bad prognosis?

As part of a cell’s inherent protection against carcinogenesis, p14ARF is upregulated in response to hyperproliferative signalling to induce cell cycle arrest. This property makes p14ARF a leading candidate for cancer therapy. This study explores the consequences of reactivating p14ARF in breast cancer and the potential of targeting p14ARF in breast cancer treatment. Our results show that activation of the p14ARF-p53-p21-Rb pathway in the estrogen sensitive MCF-7 breast cancer cells induces many hallmarks of senescence including a large flat cell morphology, multinucleation, senescence-associated-β-gal staining, and rapid G1 and G2/M phase cell cycle arrest. P14ARF also induces the expression of the proto-oncogene cyclin D1, which is most often associated with a transition from G1-S phase and is highly expressed in breast cancers with poor clinical prognosis. In this study, siRNA knockdown of cyclin D1, p21 and p53 show p21 plays a pivotal role in the maintenance of high cyclin D1 expression, cell cycle and growth arrest post-p14ARF induction. High p53 and p14ARF expression and low p21/cyclin D1 did not cause cell-cycle arrest. Knockdown of cyclin D1 stops proliferation but does not reverse senescence-associated cell growth. Furthermore, cyclin D1 accumulation in the nucleus post-p14ARF activation correlated with a rapid loss of nucleolar Ki-67 protein and inhibition of DNA synthesis. Latent effects of the p14ARF-induced cellular processes resulting from high nuclear cyclin D1 accumulation included a redistribution of Ki-67 into the nucleoli, aberrant nuclear growth (multinucleation), and cell proliferation. Lastly, downregulation of cyclin D1 through inhibition of ER abrogated latent recurrence. The mediation of these latent effects by continuous expression of p14ARF further suggests a novel mechanism whereby dysregulation of cyclin D1 could have a double-edged effect. Our results suggest that p14ARF induced-senescence is related to late-onset breast cancer in estrogen responsive breast cancers and/or the recurrence of more aggressive breast cancer post-therapy.

The biology of progesterone receptor in the normal mammary gland and in breast cancer

This paper reviews work on progesterone and the progesterone receptor (PR) in the mouse mammary gland that has been used extensively as an experimental model. Studies have led to the concept that progesterone controls proliferation and morphogenesis of the luminal epithelium in a tightly orchestrated manner at distinct stages of development by paracrine signaling pathways, including receptor activator of nuclear factor κB ligand (RANKL) as a major paracrine factor. Progesterone also drives expansion of stem cells by paracrine signals to generate progenitors required for alveologenesis. During mid-to-late pregnancy, progesterone has another role to suppress secretory activation until parturition mediated in part by crosstalk between PR and prolactin/Stat5 signaling to inhibit induction of milk protein gene expression, and by inhibiting tight junction closure. In models of hormone-dependent mouse mammary tumors, the progesterone/PR signaling axis enhances pre-neoplastic progression by a switch from a paracrine to an autocrine mode of proliferation and dysregulation of the RANKL signaling pathway. Limited experiments with normal human breast show that progesterone/PR signaling also stimulates epithelial cell proliferation by a paracrine mechanism; however, the signaling pathways and whether RANKL is a major mediator remains unknown. Work with human breast cancer cell lines, patient tumor samples and clinical studies indicates that progesterone is a risk factor for breast cancer and that alteration in progesterone/PR signaling pathways contributes to early stage human breast cancer progression. However, loss of PR expression in primary tumors is associated with a less differentiated more invasive phenotype and worse prognosis, suggesting that PR may limit later stages of tumor progression.

Progesterone receptors, their isoforms and progesterone regulated transcription

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

Apigenin induces apoptosis and blocks growth of medroxyprogesterone acetate-dependent BT-474 xenograft tumors

Recent clinical and epidemiological evidence shows that hormone replacement therapy (HRT) containing both estrogen and progestin increases the risk of primary and metastatic breast cancer in post-menopausal women while HRT containing only estrogen does not. We and others previously showed that progestins promote the growth of human breast cancer cells in vitro and in vivo. In this study, we sought to determine whether apigenin, a low molecular weight anti-carcinogenic flavonoid, inhibits the growth of aggressive Her2/neu-positive BT-474 xenograft tumors in nude mice exposed to medroxyprogesterone acetate (MPA), the most commonly used progestin in the USA. Our data clearly show that apigenin (50 mg/kg) inhibits progression and development of these xenograft tumors by inducing apoptosis, inhibiting cell proliferation, and reducing expression of Her2/neu. Moreover, apigenin reduced levels of vascular endothelial growth factor (VEGF) without altering blood vessel density, indicating that continued expression of VEGF may be required to promote tumor cell survival and maintain blood flow. While previous studies showed that MPA induces receptor activator of nuclear factor kappa-B ligand (RANKL) expression in rodent mammary gland, MPA reduced levels of RANKL in human tumor xenografts. RANKL levels remained suppressed in the presence of apigenin. Exposure of BT-474 cells to MPA in vitro also resulted in lower levels of RANKL; an effect that was independent of progesterone receptors since it occurred both in the presence and absence of the antiprogestin RU-486. In contrast to our in vivo observations, apigenin protected against MPA-dependent RANKL loss in vitro, suggesting that MPA and apigenin modulate RANKL levels differently in breast cancer cells in vivo and in vitro. These preclinical findings suggest that apigenin has potential as an agent for the treatment of progestin-dependent breast disease.

Evaluation of cell cycle arrest in estrogen responsive MCF-7 breast cancer cells: pitfalls of the MTS assay

Endocrine resistance is a major problem with anti-estrogen treatments and how to overcome resistance is a major concern in the clinic. Reliable measurement of cell viability, proliferation, growth inhibition and death is important in screening for drug treatment efficacy in vitro. This report describes and compares commonly used proliferation assays for induced estrogen-responsive MCF-7 breast cancer cell cycle arrest including: determination of cell number by direct counting of viable cells; or fluorescence SYBR®Green (SYBR) DNA labeling; determination of mitochondrial metabolic activity by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay; assessment of newly synthesized DNA using 5-ethynyl-2′-deoxyuridine (EdU) nucleoside analog binding and Alexa Fluor® azide visualization by fluorescence microscopy; cell-cycle phase measurement by flow cytometry. Treatment of MCF-7 cells with ICI 182780 (Faslodex), FTY720, serum deprivation or induction of the tumor suppressor p14ARF showed inhibition of cell proliferation determined by the Trypan Blue exclusion assay and SYBR DNA labeling assay. In contrast, the effects of treatment with ICI 182780 or p14ARF-induction were not confirmed using the MTS assay. Cell cycle inhibition by ICI 182780 and p14ARF-induction was further confirmed by flow cytometric analysis and EdU-DNA incorporation. To explore this discrepancy further, we showed that ICI 182780 and p14ARF-induction increased MCF-7 cell mitochondrial activity by MTS assay in individual cells compared to control cells thereby providing a misleading proliferation readout. Interrogation of p14ARF-induction on MCF-7 metabolic activity using TMRE assays and high content image analysis showed that increased mitochondrial activity was concomitant with increased mitochondrial biomass with no loss of mitochondrial membrane potential, or cell death. We conclude that, whilst p14ARF and ICI 182780 stop cell cycle progression, the cells are still viable and potential treatments utilizing these pathways may contribute to drug resistant cells. These experiments demonstrate how the combined measurement of metabolic activity and DNA labeling provides a more reliable interpretation of cancer cell response to treatment regimens.

Amphiregulin mediates estrogen, progesterone, and EGFR signaling in the normal rat mammary gland and in hormone-dependent rat mammary cancers

Both estrogen (E) and progesterone (P) are implicated in the etiology of human breast cancer. Defining their mechanisms of action, particularly in vivo, is relevant to the prevention and therapy of breast cancer. We investigated the molecular and cellular mechanisms of E and/or P-induced in vivo proliferation, in the normal rat mammary gland and in hormone-dependent rat mammary cancers which share many characteristics with the normal human breast and hormone-dependent breast cancers. We show that E+P treatment induced significantly greater proliferation in both the normal gland and mammary cancers compared to E alone. In both the normal gland and tumors, E+P-induced proliferation was mediated through the increased production of amphiregulin (Areg), an epidermal growth factor receptor (EGFR) ligand, and the activation of intracellular signaling pathways (Erk, Akt, JNK) downstream of EGFR that regulate proliferation. In vitro experiments using rat primary mammary organoids or T47D breast cancer cells confirmed that Areg and the synthetic progestin, R5020, synergize to promote cell proliferation through EGFR signaling. Iressa, an EGFR inhibitor, effectively blocked this proliferation. These results indicate that mediators of cross talk between E, P, and EGFR pathways may be considered as relevant molecular targets for the therapy of hormone-dependent breast cancers, especially in premenopausal women.

SOX4 overexpression regulates the p53-mediated apoptosis in hepatocellular carcinoma: clinical implication and functional analysis in vitro

BACKGROUND AND AIMS

The underlying molecular mechanisms of hepatocellular carcinoma (HCC) remain poorly understood due to its complex development process. The human T cell-specific transcription factor sex-determining region Y-related high-mobility group (HMG) box 4 (SOX4) has been linked to development and tumorigenesis. In this study, we characterized the roles of SOX4 in regulation of the p53 transcription activity and evaluated the expression patterns and prognostic value of the transcription factor SOX4 in HCC.

METHODS

The expression levels of human SOX4 were examined in HCC samples obtained from 58 patients having curative partial hepatectomy. The interaction and effects of SOX4 on the p53 pathway were assessed in HCC cell lines. Luciferase reporter assay to examine p53-mediated transcription of target genes was performed. The association of SOX4 expression level with tumor recurrence and overall survival was evaluated.

RESULTS

We showed that the HMG box domain of SOX4 interacted with p53, resulting in the inhibition of p53-mediated transcription by the Bax promoter. More importantly, SOX4 overexpression led to a significant repression of p53-induced Bax expression and subsequent repression of p53-mediated apoptosis induced by gamma-irradiation. In clinicopathological analysis, nuclear overexpression of SOX4 was observed in 37 out of 58 (63.8%) HCC samples, and this correlated with diminished risk of recurrence (P = 0.014) and improved overall survival time (P = 0.045) in HCC patients.

CONCLUSION

These results suggest that SOX4 contributes to hepatocarcinogenesis by inhibiting p53-mediated apoptosis and that its overexpression might be a useful prognostic marker for survival after surgical resection.

Estrogen and progesterone receptors: from molecular structures to clinical targets

Research involving estrogen and progesterone receptors (ER and PR) have greatly contributed to our understanding of cell signaling and transcriptional regulation. In addition to the classical ER and PR nuclear actions, new signaling pathways have recently been identified due to ER and PR association with cell membranes and signal transduction proteins. Bio-informatics has unveiled how ER and PR recognize their ligands, selective modulators and co-factors, which has helped to implement them as key targets in the treatment of benign and malignant tumors. Knowledge regarding ER and PR is vast and complex; therefore, this review will focus on their isoforms, signaling pathways, co-activators and co-repressors, which lead to target gene regulation. Moreover it will highlight ER and PR involvement in benign and malignant diseases as well as pharmacological substances influencing cell signaling and provide established and new structural insights into the mechanism of activation and inhibition of these receptors.

Progesterone receptors A and B and estrogen receptor alpha expression in normal breast tissue and fibroadenomas

Fibroadenomas are the most common benign breast tumors, occurring mainly in young women. Their responses to the hormonal environment are similar to those of normal breast tissue, which suggests that steroid receptors may play a role in tumor development. We evaluated the gene and protein expression of progesterone receptors A and B (PRA and PRB) and the protein expression of estrogen receptor alpha (ER-alpha) in fibroadenoma samples, comparing with adjacent normal breast tissue, from 11 premenopausal women. Progesterone and estradiol levels were determined. No alterations in the PRs gene and protein expression and the ER-alpha protein expression were observed between the follicular and luteal phases, in normal breast versus fibroadenomas. Protein levels of PRA and PRB were higher in fibroadenomas compared to normal breast tissue (P = 0.038 and P = 0.031), while the PRs mRNA levels were similar in both tissues (P = 0.721 and P = 0.139). There were no differences in ER-alpha protein expression between normal breast tissue and fibroadenomas (P = 0.508). The PRA:PRB ratio was similar in the tissues, and also showed a strong correlation in both (r = 0.964, P = 0.0001). Our data suggest a role of PRs in the growth and development of fibroadenomas, although without alterations of the PRA:PRB ratio in these tumors. The absence of alterations in ER-alpha protein levels could be a characteristic behavior of fibroadenomas, unlike breast cancer.

Progesterone and breast cancer

Progesterone is an ovarian steroid hormone that is essential for normal breast development during puberty and in preparation for lactation and breastfeeding. The actions of progesterone are primarily mediated by its high-affinity receptors, which include the classical progesterone receptor (PR)-A and -B isoforms, located in diverse tissues, including the brain, where progesterone controls reproductive behavior, and the breast and reproductive organs. Progestins are frequently prescribed for contraception or during postmenopausal hormone replacement therapy, in which progestins are combined with estrogen as a means to block estrogen-induced endometrial growth. The role of estrogen as a potent breast mitogen is undisputed, and inhibitors of the estrogen receptor and estrogen-producing enzymes (aromatases) are effective first-line cancer therapies. However, PR action in breast cancer is grossly understudied and remains controversial. Herein, we review existing evidence and discuss the challenges to defining a role for progesterone in breast cancer.

Challenges to defining a role for progesterone in breast cancer

Progesterone is an ovarian steroid hormone that is essential for normal breast development during puberty and in preparation for lactation. The actions of progesterone are primarily mediated by its high affinity receptors, including the classical progesterone receptor (PR) -A and -B isoforms, located in diverse tissues such as the brain where progesterone controls reproductive behavior, and the breast and reproductive organs. Progestins are frequently prescribed as contraceptives or to alleviate menopausal symptoms, wherein progestin is combined with estrogen as a means to block estrogen-induced endometrial growth. Estrogen is undisputed as a potent breast mitogen, and inhibitors of the estrogen receptor (ER) and estrogen producing enzymes (aromatases) are effective first-line cancer therapies. However, PR action in breast cancer remains controversial. Herein, we review existing evidence from in vitro and in vivo models, and discuss the challenges to defining a role for progesterone in breast cancer.

Progesterone receptor action: translating studies in breast cancer models to clinical insights

Progesterone receptors (PR) are useful prognostic indicators of breast cancers likely to respond to anti-estrogen receptor (ER) therapies. However, the role of progesterone, therapeutic progestins, or unliganded or liganded PRin breast cancer development or progression remains controversial. PR are ligand-activated transcription factors that act in concert with intracellular signaling pathways as "sensors" of multiple growth factor inputs to hormonally regulated tissues, such as the breast. The recently defined induction of rapid signaling events upon progestin-binding to PR-B provides a means to ensure that receptors and coregulators are appropriately phosphorylated as part of optimal transcription complexes. PR-activated kinase cascades may provide additional avenues for progestin-regulated gene expression independent of PR nuclear action. Herein, we present an overview ofprogesterone/PR and signaling cross-talk in breast cancer models and discuss the potential significance ofprogestin/PR action in breast cancer biology using examples from both in vitro and in vivo models, as well as limited clinical data. Kinases are emerging as key mediators of PR action. Cross-talk between PR and membrane-initiated signaling events suggests a mechanism for coordinated regulation ofgene subsets by mitogenic stimuli in hormonally responsive normal tissues. Dysregulation of this cross-talk mechanism may contribute to breast cancer biology; further studies are needed to address the potential for targeting PR in addition to ER and selected protein kinases as part of more effective breast cancer therapies.

Progestins reinitiate cell cycle progression in antiestrogen-arrested breast cancer cells through the B-isoform of progesterone receptor

Estrogen treatment of MCF-7 human breast cancer cells allows the reinitiation of synchronous cell cycle progression in antiestrogen-arrested cells. Here, we report that progestins also reinitiate cell cycle progression in this model. Using clonal cell lines derived from progesterone receptor (PR)-negative MCF-7M13 cells expressing wild-type or mutant forms of PRA and PRB, we show that this effect is mediated via PRB, not PRA. Cell cycle progression did not occur with a DNA-binding domain mutant of PRB but was unaffected by mutation in the NH(2)-terminal, SH3 domain interaction motif, which mediates rapid progestin activation of c-Src. Thus, the progestin-induced proliferative response in antiestrogen-inhibited cells is mediated primarily by the transcriptional activity of PRB. Analysis of selected cell cycle targets showed that progestin treatment induced levels of cyclin D1 expression and retinoblastoma protein (Rb) phosphorylation similar to those induced by estradiol. In contrast, progestin treatment resulted in only a 1.2-fold induction of c-Myc compared with a 10-fold induction by estradiol. These results support the conclusion that progestin, in a PRB-dependent manner, can overcome the growth-inhibitory effects of antiestrogens in estrogen receptor/PR-positive breast cancer cells by the induction of cyclin D1 expression. The mediation of this effect by PRB, but not PRA, further suggests a mechanism whereby abnormal regulation of the normal expression ratios of PR isoforms in breast cancer could lead to the attenuation of antiestrogen-mediated growth arrest.

Precursors and preinvasive lesions of the breast: the role of molecular prognostic markers in the diagnostic and therapeutic dilemma

Precursors and preinvasive lesions of the breast include atypical ductal hyperplasia (ADH), ductal carcinoma in situ (DCIS), and lobular neoplasia (LN). There is a significant debate regarding the classification, diagnosis, prognosis and management of these lesions. This review article describes the current theories regarding the pathogenesis and molecular evolution of these lesions. It reviews the implication of a variety of molecules in the continuum of breast lesions: estrogen receptors (ER-alpha and ER-beta), c-erb-B2 (Her2/neu), p53, Ki-67, bcl-2, E-cadherin, transforming growth factor-beta (TGF-beta), p27 (Kip1), p16 (INK4a), p21 (Waf1), vascular endothelial growth factor (VEGF). With respect to the aforementioned molecules, this article reviews their pathophysiological importance, and puts the stress on whether they confer additional risk for invasive breast cancer or not. This knowledge has the potential to be of importance in the therapeutic decisions presenting in the common clinical practice.

SOX4 expression in bladder carcinoma: clinical aspects and in vitro functional characterization

The human transcription factor SOX4 was 5-fold up-regulated in bladder tumors compared with normal tissue based on whole-genome expression profiling of 166 clinical bladder tumor samples and 27 normal urothelium samples. Using a SOX4-specific antibody, we found that the cancer cells expressed the SOX4 protein and, thus, did an evaluation of SOX4 protein expression in 2,360 bladder tumors using a tissue microarray with clinical annotation. We found a correlation (P < 0.05) between strong SOX4 expression and increased patient survival. When overexpressed in the bladder cell line HU609, SOX4 strongly impaired cell viability and promoted apoptosis. To characterize downstream target genes and SOX4-induced pathways, we used a time-course global expression study of the overexpressed SOX4. Analysis of the microarray data showed 130 novel SOX4-related genes, some involved in signal transduction (MAP2K5), angiogenesis (NRP2), and cell cycle arrest (PIK3R3) and others with unknown functions (CGI-62). Among the genes regulated by SOX4, 25 contained at least one SOX4-binding motif in the promoter sequence, suggesting a direct binding of SOX4. The gene set identified in vitro was analyzed in the clinical bladder material and a small subset of the genes showed a high correlation to SOX4 expression. The present data suggest a role of SOX4 in the bladder cancer disease.

Ubc9 interacts with SOX4 and represses its transcriptional activity

SOX4 is a member of SOX transcriptional factor family that is crucial for many cellular processes. In this study, a yeast two-hybrid screening of human mammary cDNA library identified human ubiquitin-conjugating enzyme 9 (hUbc9) that interacted with SOX4. This interaction was confirmed by GST pull-down in vitro and co-immunoprecipitation assays in vivo. Deletion mapping demonstrated that HMG-box domain of SOX4 is required to mediate the interaction with Ubc9 in yeast. Furthermore, confocal microscopy showed that Ubc9 co-localized with SOX4 in the nucleus. Luciferase assays found that Ubc9 specifically repressed SOX4 transcriptional activity in 293T cells. We further demonstrated that Ubc9 could functionally repress the transcriptional activity of endogenous SOX4 induced by progesterone in T47D cells. The C93S mutant of Ubc9, which abrogates SUMO-1 conjugation activity, did not abolish the ability to repress SOX4 activity. It shows that Ubc9 interacts with SOX4 and represses its transcriptional activity independent of its SUMO-1-conjugating activity.

Effect of initial subcellular localization of progesterone receptor on import kinetics and transcriptional activity

Progesterone receptors (PR) are ligand-activated transcription factors that modulate transcription by activating genes. There are two isoforms of PR, PRA and PRB. In most cell contexts, the PRA isoform is a repressor of the PRB isoform. Without hormone induction, PRA is mostly located in the nucleus whereas PRB distributes both in the nucleus and in the cytoplasm. In this paper, a new model system has been used to study the impact of initial subcellular localization, and import rate of progesterone receptor on transcriptional activity. This new model system involves using a mutant version of PRB which is found only in the cytoplasmic compartment of cells in the unliganded state, making the distribution of the receptor more homogeneous to start with compared with the previous model, wild type (wt) PRB, which has a more heterogeneous distribution (nuclear and cytoplasmic even without ligand). Import kinetics has been shown to be one of the major means by which to regulate PR transcriptional activity. Fluorescence microscopy was used to measure green fluorescent protein tagged PRB import rate into the nucleus. Luciferase reporter gene assay was used to measure transcriptional activity of PRB. In addition, a two-hybrid assay was performed to measure the interaction between PRB and importin alpha. Mutant versions of PRA and PRB with the constitutively active nuclear localization signal removed were created (PRA-NLSc mutant and PRB-NLSc mutant). These PR mutants were found to localize mainly in the cytoplasm in the absence of hormone. With addition of hormone, PR mutants translocated to the nucleus, although at a slower rate compared to wt PRB. Our results show that the activation of reporter gene transcription is proportional to the nuclear import rate of PRB-NLSc mutant, and the difference in import kinetics between wt PRB and the PRB-NLSc mutant is due to a stronger interaction of wt PRB with importin alpha. We also show that the hormone inducible NLS in PR, NLSh, is a weak nuclear localization signal even without hormone and can act as a weak hormone dependent nuclear localization signal when combined with the ligand binding domain of PR. In addition, by changing the initial subcellular localization of PRA from the nucleus to the cytoplasm, this diminished PRA's ability to act as an inhibitor of PRB.

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

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

Sox4 cooperates with Evi1 in AKXD-23 myeloid tumors via transactivation of proviral LTR

Myeloid leukemias in AKXD23 mice contain proviral insertions at Evi1, resulting in transcriptional activation. Although Evi1 is clearly involved in leukemia, gene transfer studies in mice with Evi1 fail to cause leukemia, arguing that cooperating events are necessary. We reanalyzed AKXD-23 tumors for cooperating proviral insertion and found that each tumor had a proviral insertion in Sox4, which encodes an HMG-box transcription factor. RNA analysis revealed these insertions cause increased Sox4 expression. Overexpression of Sox4 in 32Dcl3 cells markedly inhibited cytokine-induced granulocyte maturation, as documented by morphologic and mRNA analysis. Sox4-expressing cells had higher levels of transcripts associated with proliferation, including Evi1. Conversely, in leukemic cells that express Sox4 and bear provirally activated Evi1, suppression of Sox4 with short hairpin RNAs resulted in down-regulation of both Sox4 and Evi1. By cotransfection studies, Sox4 is able to transactivate the AKV long terminal repeat, which likely explains how Sox4 transcriptionally up-regulates provirally activated Evi1; however, Sox4 does not appear to regulate the native Evi1 promoter. We propose that Sox4 proviral activation is selected for in the setting of prior proviral activation of Evi1, because it transactivates the relatively weak LTR of AKV leading to higher Evi1 expression and consequent block to differentiation.

Transcriptional Profiles of Intestinal Tumors in Apc Min Mice are Unique from those of Embryonic Intestine and Identify Novel Gene Targets Dysregulated in Human Colorectal Tumors

The adenomatous polyposis coli (APC) tumor suppressor is a major regulator of the Wnt signaling pathway in normal intestinal epithelium. APC, in conjunction with AXIN and GSK-3β, forms a complex necessary for the degradation of β-catenin, thereby preventing β-catenin/T-cell factor interaction and alteration of growth-controlling genes such as c-MYC and cyclin D1. Inappropriate activation of the Wnt pathway, via Apc/APC mutation, leads to gastrointestinal tumor formation in both the mouse and human. In order to discover novel genes that may contribute to tumor progression in the gastrointestinal tract, we used cDNA microarrays to identify 114 genes with altered levels of expression in ApcMin mouse adenomas from the duodenum, jejunum, and colon. Changes in the expression of 24 of these 114 genes were not observed during mouse development at embryonic day 16.5, postnatal day 1, or postnatal day 14 (relative to normal adult intestine). These 24 genes are not previously known Wnt targets. Seven genes were validated by real-time reverse transcription-PCR analysis, whereas four genes were validated by in situ hybridization to mouse adenomas. Real-time reverse transcription-PCR analysis of human colorectal cancer cell lines and adenocarcinomas revealed that altered expression levels were also observed for six of the genes Igfbp5, Lcn2, Ly6d, N4wbp4 (PMEPA1), S100c, and Sox4.

Breast cancer patients with progesterone receptor PR-A-rich tumors have poorer disease-free survival rates

PURPOSE

No study has yet analyzed whether changes in relative expression levels of progesterone receptor (PR) isoforms A and B in human breast tumors have significance in predicting clinical outcome. Human PRs are ligand-activated nuclear transcription factors that mediate progesterone action. Their presence in breast tumors is used to predict functional estrogen receptors (ERs) and, therefore, also to predict the likelihood of response to endocrine therapies and disease prognosis. The two PR isoforms, PR-A and PR-B, possess different in vitro and in vivo activities, suggesting that in tumors, the ratio of their expression may control hormone responsiveness. In general, PR-B are strong transcriptional activators, whereas PR-A can act as dominant repressors of PR-B and ER. Thus their balance may affect tamoxifen response in breast cancers.

EXPERIMENTAL DESIGN

To determine whether differential expression of the PR isoforms is associated with clinical outcome and hormonal responsiveness, PR-A and PR-B were measured by immunoblot analysis of cell lysates from 297 axillary node-positive breast tumors.

RESULTS

Expression of the two isoforms correlated with each other, as well as with ER. Additional analyses revealed that patients with PR-positive tumors but high PR-A:PR-B ratios, which were often caused by high PR-A levels, were 2.76 times more likely to relapse than patients with lower ratios, indicating resistance to tamoxifen.

CONCLUSIONS

This study suggests that knowledge of the PR-A:PR-B ratio may identify a subgroup of ER-positive/PR-positive patients with node-positive breast cancer that benefit poorly from endocrine therapy.

Functional identification of the pro-apoptotic effector domain in human Sox4

Recent studies provide evidence that Sox4 is involved in regulating apoptosis as well as tumorigenesis of various human cancers; however, its role in the apoptotic machinery is not fully understood. Here we describe that the central domain containing glycine-rich region in Sox4, named CD, is a pivotal pro-apoptotic domain to induce apoptotic cell death. Deletion of the DNA-binding domain or trans-activation domain in Sox4 did not significantly affect pro-apoptotic activity, whereas transient transfection of the high mobility group box or the serine-rich region abrogated the apoptotic activity. Moreover, overexpression of the CD construct (aa 166-342) revealed the apoptotic activity comparable to that of wild-type Sox4, approximately 60% of cell death. Our data suggest that the apoptotic activity of Sox4 can be dissociated from its transcriptional trans-activation and is mediated through its CD.

Germ-line mutations in BRCA1 or BRCA2 in the normal breast are associated with altered expression of estrogen-responsive proteins and the predominance of progesterone receptor A

The breast cancer susceptibility genes BRCA1 and BRCA2 are responsible for a large proportion of familial breast and ovarian cancer, yet little is known of how disruptions in the functions of the proteins these genes encode increased cancer risk preferentially in hormone-dependent tissue. There is no information on whether a germ-line mutation in BRCA1 or BRCA2 causes disruptions in hormone-signaling pathways in the normal breast. In this study markers of hormone responsiveness were measured in prophylactically removed normal breast tissue (n = 31) in women bearing a germ-line pathogenic mutation in one of the BRCA genes. The estrogen receptor (ER) and proteins associated with ER action in hormone-sensitive tissues, namely, PS2 and the progesterone receptor (PR), were detected immunohistochemically. ER expression was not different in BRCA mutation carriers than in noncarriers, but there was a reduction in PS2 expression. PR expression was also reduced, and there was a striking lack of expression of the PRB isoform, which resulted in cases with PRA-only expression in BRCA1 and BRCA2 mutation carriers. The alterations in PS2 and PR expression were similar in the BRCA1 and BRCA2 carriers, demonstrating that although these proteins are structurally and functionally distinct, there is overlap in their interaction with hormone-signaling pathways. This study provides evidence for altered cell function arising from loss of function of one BRCA allele in the normal breast, leading to PS2 loss, preferential PRB loss, and expression of PRA alone. In breast cancer development, PRA overexpression becomes evident in premalignant lesions and is associated with features of poor prognosis in invasive disease and altered cell function in vitro. The results of this study suggest that heterozygosity for a germ-line mutation in BRCA1 or BRCA2 results in development of PRA predominance. This is likely to lead to changes in progesterone signaling in hormone-dependent tissues, which may be a factor in the increased risk of cancer in these tissues in women with germ-line BRCA1 or BRCA2 mutations.