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

Membrane Progesterone Receptors (mPRs/PAQRs) Are Going beyond Its Initial Definitions

Progesterone (PRG) is a key cyclical reproductive hormone that has a significant impact on female organs in vertebrates. It is mainly produced by the corpus luteum of the ovaries, but can also be generated from other sources such as the adrenal cortex, Leydig cells of the testes and neuronal and glial cells. PRG has wide-ranging physiological effects, including impacts on metabolic systems, central nervous systems and reproductive systems in both genders. It was first purified as an ovarian steroid with hormonal function for pregnancy, and is known to play a role in pro-gestational proliferation during pregnancy. The main function of PRG is exerted through its binding to progesterone receptors (nPRs, mPRs/PAQRs) to evoke cellular responses through genomic or non-genomic signaling cascades. Most of the existing research on PRG focuses on classic PRG-nPR-paired actions such as nuclear transcriptional factors, but new evidence suggests that PRG also exerts a wide range of PRG actions through non-classic membrane PRG receptors, which can be divided into two sub-classes: mPRs/PAQRs and PGRMCs. The review will concentrate on recently found non-classical membrane progesterone receptors (mainly mPRs/PAQRs) and speculate their connections, utilizing the present comprehension of progesterone receptors.

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.

Whence CRIPTO: The Reemergence of an Oncofetal Factor in 'Wounds' That Fail to Heal

There exists a set of factors termed oncofetal proteins that play key roles in ontogeny before they decline or disappear as the organism's tissues achieve homeostasis, only to then re-emerge in cancer. Although the unique therapeutic potential presented by such factors has been recognized for more than a century, their clinical utility has yet to be fully realized1. This review highlights the small signaling protein CRIPTO encoded by the tumor derived growth factor 1 (TDGF1/Tdgf1) gene, an oft cited oncofetal protein whose presence in the cancer literature as a tumor promoter, diagnostic marker and viable therapeutic target continues to grow. We touch lightly on features well established and well-reviewed since its discovery more than 30 years ago, including CRIPTO's early developmental roles and modulation of SMAD2/3 activation by a selected set of transforming growth factor β (TGF-β) family ligands. We predominantly focus instead on more recent and less well understood additions to the CRIPTO signaling repertoire, on its potential upstream regulators and on new conceptual ground for understanding its mode of action in the multicellular and often stressful contexts of neoplastic transformation and progression. We ask whence it re-emerges in cancer and where it 'hides' between the time of its fetal activity and its oncogenic reemergence. In this regard, we examine CRIPTO's restriction to rare cells in the adult, its potential for paracrine crosstalk, and its emerging role in inflammation and tissue regeneration-roles it may reprise in tumorigenesis, acting on subsets of tumor cells to foster cancer initiation and progression. We also consider critical gaps in knowledge and resources that stand between the recent, exciting momentum in the CRIPTO field and highly actionable CRIPTO manipulation for cancer therapy and beyond.

Identification of steroidal saponins from Tribulus terrestris and their in silico docking studies

Tribulus terrestris is known to possess many pharmacological properties, most notably its anticancer activities, owing to its rich steroidal saponin contents. Even though many reports are available elucidating the anticancer potential of the herb, we, for the very first time have attempted to isolate and identified the active compound present in seed crude saponin extract and confers its in silico docking ability with various cellular targets proteins. High performance thin layer chromatography confirms the presence of active saponins in leaf and seed saponin extracts which were further fractionated by silica gel column chromatography. Fractions collected were assessed for cytotoxicity on human breast cancer cells. High resolution liquid chromatography and mass spectroscopy was employ to identify the active components present in fraction with highest cytotoxicity. Intriguingly, Nautigenin type of steriodal saponin was identified to present in the active fraction of seed extract (SF11) and the identified compound was further analyzed for its in silico docking interaction using PyRx AutodockVina. Docking studies revealed the high binding affinity of Nuatigenin at significant sites with apoptotic proteins Bcl-2, Bax, caspase-3, caspase-8, p53 and apoptosis inducing factor along with cell surface receptors estrogen receptor, projesterone receptor, epidermal growth factor receptor, and human epidermal growth factor receptor-2. Thus, the conclusions were drawn that saponin fraction of Tribulus terrestis possesses active compounds having anticancer property and specifically, Nuatigenin saponin can be considered as an important therapeutic drug for the breast cancer treatment.

The glucocorticoid receptor interferes with progesterone receptor-dependent genomic regulation in breast cancer cells

The glucocorticoid and progesterone receptors (GR and PR) are closely related members of the steroid receptor family. Despite sharing similar structural and functional characteristics; the cognate hormones display very distinct physiological responses. In mammary epithelial cells, PR activation is associated with the incidence and progression of breast cancer, whereas the GR is related to growth suppression and differentiation. Despite their pharmacological relevance, only a few studies have compared GR and PR activities in the same system. Using a PR⁺/GR⁺ breast cancer cell line, here we report that either glucocorticoid-free or dexamethasone (DEX)-activated GR inhibits progestin-dependent gene expression associated to epithelial-mesenchymal-transition and cell proliferation. When both receptors are activated with their cognate hormones, PR and GR can form part of the same complex according to co-immunoprecipitation, quantitative microscopy and sequential ChIP experiments. Moreover, genome-wide studies in cells treated with either DEX or R5020, revealed the presence of several regions co-bound by both receptors. Surprisingly, GR also binds novel genomic sites in cells treated with R5020 alone. This progestin-induced GR binding was enriched in REL DNA motifs and located close to genes coding for chromatin remodelers. Understanding GR behavior in the context of progestin-dependent breast cancer could provide new targets for tumor therapy.

Complex interactomes and post-translational modifications of the regulatory proteins HABP4 and SERBP1 suggest pleiotropic cellular functions

The 57 kDa antigen recognized by the Ki-1 antibody, is also known as intracellular hyaluronic acid binding protein 4 and shares 40.7% identity and 67.4% similarity with serpin mRNA binding protein 1, which is also named CGI-55, or plasminogen activator inhibitor type-1-RNA binding protein-1, indicating that they might be paralog proteins, possibly with similar or redundant functions in human cells. Through the identification of their protein interactomes, both regulatory proteins have been functionally implicated in transcriptional regulation, mRNA metabolism, specifically RNA splicing, the regulation of mRNA stability, especially, in the context of the progesterone hormone response, and the DNA damage response. Both proteins also show a complex pattern of post-translational modifications, involving Ser/Thr phosphorylation, mainly through protein kinase C, arginine methylation and SUMOylation, suggesting that their functions and locations are highly regulated. Furthermore, they show a highly dynamic cellular localization pattern with localizations in both the cytoplasm and nucleus as well as punctuated localizations in both granular cytoplasmic protein bodies, upon stress, and nuclear splicing speckles. Several reports in the literature show altered expressions of both regulatory proteins in a series of cancers as well as mutations in their genes that may contribute to tumorigenesis. This review highlights important aspects of the structure, interactome, post-translational modifications, sub-cellular localization and function of both regulatory proteins and further discusses their possible functions and their potential as tumor markers in different cancer settings.

Progesterone Receptor Isoform Ratio: A Breast Cancer Prognostic and Predictive Factor for Antiprogestin Responsiveness

Background

Compelling evidence shows that progestins regulate breast cancer growth. Using preclinical models, we demonstrated that antiprogestins are inhibitory when the level of progesterone receptor isoform A (PR-A) is higher than that of isoform B (PR-B) and that they might stimulate growth when PR-B is predominant. The aims of this study were to investigate ex vivo responses to mifepristone (MFP) in breast carcinomas with different PR isoform ratios and to examine their clinical and molecular characteristics.

Methods

We performed human breast cancer tissue culture assays (n = 36) to evaluate the effect of MFP on cell proliferation. PR isoform expression was determined by immunoblotting (n = 282). Tumors were categorized as PRA-H (PR-A/PR-B ≥ 1.2) or PRB-H (PR-A/PR-B ≤ 0.83). RNA was extracted for Ribo-Zero-Seq sequencing to evaluate differentially expressed genes. Subtypes and risk scores were predicted using the PAM50 gene set, the data analyzed using The Cancer Genome Atlas RNA-seq gene analysis and other publicly available gene expression data. Tissue microarrays were performed using paraffin-embedded tissues (PRA-H n = 53, PRB-H n = 24), and protein expression analyzed by immunohistochemistry. All statistical tests were two-sided.

Results

One hundred sixteen out of 222 (52.3%) PR+ tumors were PRA-H, and 64 (28.8%) PRB-H. Cell proliferation was inhibited by MFP in 19 of 19 tissue cultures from PRA-H tumors. A total of 139 transcripts related to proliferative pathways were differentially expressed in nine PRA-H and seven PRB-H tumors. PRB-H and PRA-H tumors were either luminal B or A phenotypes, respectively ( P = .03). PRB-H cases were associated with shorter relapse-free survival (hazard ratio [HR] = 2.70, 95% confidence interval [CI] = 1.71 to 6.20, P = .02) and distant metastasis-free survival (HR = 4.17, 95% CI = 2.18 to 7.97, P <  .001). PRB-H tumors showed increased tumor size ( P <  .001), Ki-67 levels ( P <  .001), human epidermal growth factor receptor 2 expression ( P =  .04), high grades ( P =  .03), and decreased total PR ( P =  .004) compared with PRA-H tumors. MUC-2 ( P <  .001) and KRT6A ( P =  .02) were also overexpressed in PRB-H tumors.

Conclusion

The PRA/PRB ratio is a prognostic and predictive factor for antiprogestin responsiveness in breast cancer.

Phase 1b study of orteronel in postmenopausal women with hormone-receptor positive (HR+) metastatic breast cancer

Introduction Suppressing both androgens and estrogens may circumvent hormone receptor resistance in breast cancer by reducing androgen receptor stimulation. Selective inhibition of the 17, 20-lyase enzyme by orteronel leads to decreased androgen production in men and would be anticipated to reduce estrogen and androgen production in women. Thus, we conducted a phase 1b study of orteronel in postmenopausal women with hormone-receptor positive (HR+) metastatic breast cancer. Methods The primary objective was to identify the recommended phase 2 dose (R2PD) of orteronel in women; escalation was via standard 3 + 3 design. The initial dose was 300 mg BID and escalated to 400 mg BID. Cycle length was 28 days. Enrolled patients had HR+ metastatic breast cancer and were evaluated every 8 weeks for disease progression. Results Eight heavily pre-treated women enrolled [median age: 57 yo (range 47-73)]. Four received 300 mg BID at dose level 1; 4 received 400 mg BID at dose level 2. No dose limiting toxicities (DLTs) were observed. Adverse events (AE) at least possibly related to orteronel included grade 1-2 nausea (n = 4) and bone pain (n = 3), and grade 1 hypokalemia, hot flashes, myalgia and AST elevation (n = 2). The only grade 3 AE was hypertension (n = 2) with 8 patients receiving 34 cycles of treatment. No objective responses were seen; clinical benefit was seen in 2 patients with stable disease for more than 6 months. Serum estrogens and testosterone were suppressed from baseline on both doses of orteronel. Conclusions Orteronel 400 mg BID is well tolerated in postmenopausal women, and significantly suppresses serum estrogens and testosterone. Clinical benefit was seen among heavily pretreated postmenopausal women with HR+ metastatic breast cancer.

Abiraterone acetate, exemestane or the combination in postmenopausal patients with estrogen receptor-positive metastatic breast cancer

Resistance to nonsteroidal aromatase inhibitors is a major obstacle in the management of estrogen receptor-positive postmenopausal metastatic breast cancer. The addition of abiraterone acetate to exemestane did not improve clinical outcomes compared with exemestane alone in an androgen receptor-enriched population, potentially due to induced serum progesterone as a resistance mechanism.

Background

Androgen receptor (AR) signaling and incomplete inhibition of estrogen signaling may contribute to metastatic breast cancer (MBC) resistance to a nonsteroidal aromatase inhibitor (NSAI; letrozole or anastrozole). We assessed whether combined inhibition of androgen biosynthesis with abiraterone acetate plus prednisone and estradiol synthesis with exemestane (E) may be of clinical benefit to postmenopausal patients with NSAI-pretreated estrogen receptor-positive (ER+) MBC.

Patients and methods

Patients (N = 297) were stratified by the number of prior therapies for metastatic disease (0–1 versus 2) and by prior NSAI use (adjuvant versus metastatic), and randomized (1 : 1 : 1) to receive oral once daily 1000 mg abiraterone acetate plus 5 mg prednisone (AA) versus AA with 25 mg E (AAE) versus 25 mg E alone (E). Each treatment arm was well balanced with regard to the proportion of patients with AR-positive breast cancer. The primary end point was progression-free survival (PFS). Secondary end points included overall survival, clinical benefit rate, duration of response, and overall response rate.

Results

There was no significant difference in PFS with AA versus E (3.7 versus 3.7 months; hazard ratio [HR] = 1.1; 95% confidence interval [CI] 0.82–1.60; P = 0.437) or AAE versus E (4.5 versus 3.7 months; HR = 0.96; 95% CI 0.70–1.32; P = 0.794). Increased serum progesterone concentrations were observed in both arms receiving AA, but not with E. Grade 3 or 4 treatment-emergent adverse events associated with AA, including hypokalemia and hypertension, were less common in patients in the E (2.0% and 2.9%, respectively) and AA arms (3.4% and 1.1%, respectively) than in the AAE arm (5.8% for both).

Conclusions

Adding AA to E in NSAI-pretreated ER+ MBC patients did not improve PFS compared with treatment with E. An AA-induced progesterone increase may have contributed to this lack of clinical activity.

ClinicalTrials.gov

NCT01381874.

ERrrr…where are the progenitors? Hormone receptors and mammary cell heterogeneity

The mammary epithelium is a highly heterogenous and dynamic tissue that includes a range of cell types with varying levels of proliferative capacity and differentiation potential, from stem to committed progenitor and mature cells. Generation of mature cells through expansion and specification of immature precursors is driven by hormonal and local stimuli. Intriguingly, although circulating hormones can be directly sensed only by a subset of mammary cells, they also regulate the behaviour of cells lacking their cognate receptors through paracrine mechanisms. Thus, mapping the hormonal signalling network on to the emerging mammary cell hierarchy appears to be a difficult task. Nevertheless, a first step towards a better understanding is the characterization of the hormone receptor expression pattern across individual cell types in the mammary epithelium. Here we review the most relevant findings on the cellular distribution of hormone receptors in the mammary gland, taking into account differences between mice and humans, the methods employed to assess receptor expression as well as the variety of approaches used to resolve the mammary cell heterogeneity.

Progestin and antiprogestin responsiveness in breast cancer is driven by the PRA/PRB ratio via AIB1 or SMRT recruitment to the CCND1 and MYC promoters

There is emerging interest in understanding the role of progesterone receptors (PRs) in breast cancer. The aim of this study was to investigate the proliferative effect of progestins and antiprogestins depending on the relative expression of the A (PRA) and B (PRB) isoforms of PR. In mifepristone (MFP)-resistant murine carcinomas antiprogestin responsiveness was restored by re-expressing PRA using demethylating agents and histone deacetylase inhibitors. Consistently, in two human breast cancer xenograft models, one manipulated to overexpress PRA or PRB (IBH-6 cells), and the other expressing only PRA (T47D-YA) or PRB (T47D-YB), MFP selectively inhibited the growth of PRA-overexpressing tumors and stimulated IBH-6-PRB xenograft growth. Furthermore, in cells with high or equimolar PRA/PRB ratios, which are stimulated to proliferate in vitro by progestins, and are inhibited by MFP, MPA increased the interaction between PR and the coactivator AIB1, and MFP favored the interaction between PR and the corepressor SMRT. In a PRB-dominant context in which MFP stimulates and MPA inhibits cell proliferation, the opposite interactions were observed. Chromatin immunoprecipitation assays in T47D cells in the presence of MPA or MFP confirmed the interactions between PR and the coregulators at the CCND1 and MYC promoters. SMRT downregulation by siRNA abolished the inhibitory effect of MFP on MYC expression and cell proliferation. Our results indicate that antiprogestins are therapeutic tools that selectively inhibit PRA-overexpressing tumors by increasing the SMRT/AIB1 balance at the CCND1 and MYC promoters.

Expansion of CD11b(+)Ly6G (+)Ly6C (int) cells driven by medroxyprogesterone acetate in mice bearing breast tumors restrains NK cell effector functions

The progesterone analog medroxyprogesterone acetate (MPA) is widely used as a hormone replacement therapy in postmenopausal women and as contraceptive. However, prolonged administration of MPA is associated with increased incidence of breast cancer through ill-defined mechanisms. Here, we explored whether exposure to MPA during mammary tumor growth affects myeloid-derived suppressor cells (MDSCs; CD11b(+)Gr-1(+), mostly CD11b(+)Ly6G(+)Ly6C(int) and CD11b(+)Ly6G(-)Ly6C(high) cells) and natural killer (NK) cells, potentially restraining tumor immunosurveillance. We used the highly metastatic 4T1 breast tumor (which does not express the classical progesterone receptor and expands MDSCs) to challenge BALB/c mice in the absence or in the presence of MPA. We observed that MPA promoted the accumulation of NK cells in spleens of tumor-bearing mice, but with reduced degranulation ability and in vivo cytotoxic activity. Simultaneously, MPA induced a preferential expansion of CD11b(+)Ly6G(+)Ly6C(int) cells in spleen and bone marrow of 4T1 tumor-bearing mice. In vitro, MPA promoted nuclear mobilization of the glucocorticoid receptor (GR) in 4T1 cells and endowed these cells with the ability to promote a preferential differentiation of bone marrow cells into CD11b(+)Ly6G(+)Ly6C(int) cells that displayed suppressive activity on NK cell degranulation. Sorted CD11b(+)Gr-1(+) cells from MPA-treated tumor-bearing mice exhibited higher suppressive activity on NK cell degranulation than CD11b(+)Gr-1(+) cells from vehicle-treated tumor-bearing mice. Thus, MPA, acting through the GR, endows tumor cells with an enhanced capacity to expand CD11b(+)Ly6G(+)Ly6C(int) cells that subsequently display a stronger suppression of NK cell-mediated anti-tumor immunity. Our results describe an alternative mechanism by which MPA may affect immunosurveillance and have potential implication in breast cancer incidence.

Breast cancer among nurses: is the intensity of night work related to hormone receptor status?

The aim of this study was to investigate whether night work is related to breast cancer receptor status. The effect of night work on the risk of estrogen receptor- and progesterone receptor-defined breast cancers was evaluated in 513 nurses diagnosed with breast cancer between 1996 and 2007 and in 757 frequency-matched controls, all of whom were selected from a cohort of Norwegian nurses. Odds ratios for the exposure "duration of work with a minimum of 6 consecutive night shifts" were compared for tumor subgroups with respect to the common control group through the use of polytomous logistic regression. Statistically significant associations were observed between breast cancer and work durations of ≥ 5 years with ≥ 6 consecutive night shifts, with the highest risk observed for progesterone receptor-positive tumors (odds ratio = 2.4, 95% confidence interval: 1.3, 4.3; P-trend = 0.01). When the exposure variable was dichotomized (ever/never worked ≥ 6 consecutive night shifts), a borderline statistically significant heterogeneity (P = 0.05) was seen between progesterone receptor-positive and progesterone receptor-negative tumors in postmenopausal women. The association observed between consecutive night shifts and progesterone receptor-positive cancers suggests that progesterone could play an important role in the detrimental effects of night work.

Mifepristone improves chemo-radiation response in glioblastoma xenografts

Background

We have investigated the ability of Mifepristone, an anti-progestin and anti-glucocorticoid drug, to modulate the antitumor effect of current standard clinical treatment in glioblastoma xenografts.

Methods

The effect of radiation alone or combined with Mifepristone and Temozolamide was evaluated on tumor growth in glioblastoma xenografts, both in terms of preferentially triggering tumor cell death and inhibiting angiogenesis. Tumor size was measured once a week using a caliper and tumor metabolic-activity was carried out by molecular imaging using a microPET/CT scanner. The effect of Mifepristone on the expression of angiogenic factors after concomitant radio-chemotherapy was determined using a quantitative real-time PCR analysis of VEGF gene expression.

Results

The analysis of the data shows a significant antitumoral effect by the simultaneous administration of radiation-Mifepristone-Temozolamide in comparison with radiation alone or radiation-Temozolamide.

Conclusion

Our results suggest that Mifepristone could improve the efficacy of chemo-radiotherapy in Glioblastoma. The addition of Mifepristone to standard radiation-Temozolamide therapy represents a potential approach as a chemo-radio-sensitizer in treating GBMs, which have very limited treatment options.

Overexpression of SERBP1 (Plasminogen activator inhibitor 1 RNA binding protein) in human breast cancer is correlated with favourable prognosis

Background

Plasminogen activator inhibitor 1 (PAI-1) overexpression is an important prognostic and predictive biomarker in human breast cancer. SERBP1, a protein that is supposed to regulate the stability of PAI-1 mRNA, may play a role in gynaecological cancers as well, since upregulation of SERBP1 was described in ovarian cancer recently. This is the first study to present a systematic characterisation of SERBP1 expression in human breast cancer and normal breast tissue at both the mRNA and the protein level.

Methods

Using semiquantitative realtime PCR we analysed SERBP1 expression in different normal human tissues (n = 25), and in matched pairs of normal (n = 7) and cancerous breast tissues (n = 7). SERBP1 protein expression was analysed in two independent cohorts on tissue microarrays (TMAs), an initial evaluation set, consisting of 193 breast carcinomas and 48 normal breast tissues, and a second large validation set, consisting of 605 breast carcinomas. In addition, a collection of benign (n = 2) and malignant (n = 6) mammary cell lines as well as breast carcinoma lysates (n = 16) were investigated for SERBP1 expression by Western blot analysis. Furthermore, applying non-radioisotopic in situ hybridisation a subset of normal (n = 10) and cancerous (n = 10) breast tissue specimens from the initial TMA were analysed for SERBP1 mRNA expression.

Results

SERBP1 is not differentially expressed in breast carcinoma compared to normal breast tissue, both at the RNA and protein level. However, recurrence-free survival analysis showed a significant correlation (P = 0.008) between abundant SERBP1 expression in breast carcinoma and favourable prognosis. Interestingly, overall survival analysis also displayed a tendency (P = 0.09) towards favourable prognosis when SERBP1 was overexpressed in breast cancer.

Conclusions

The RNA-binding protein SERBP1 is abundantly expressed in human breast cancer and may represent a novel breast tumour marker with prognostic significance. Its potential involvement in the plasminogen activator protease cascade warrants further investigation.

Effect of progesterone receptor status on maspin synthesis via nitric oxide production in neutrophils in human breast cancer

BACKGROUND

Although progesterone receptor (PR) status, similarly to estrogen receptor status, is of prognostic importance in breast cancer, the involvement of the PR in breast cancer remains obscure. Studies were conducted to determine the function of the PR in neutrophils in the nitric oxide-induced synthesis of maspin, an anti-breast-cancer protein produced in nonmalignant mammary cells and in neutrophils in the circulation.

METHODS

PR status was determined by immunohistochemistry. Maspin synthesis was determined by in-vitro translation of messenger RNA and quantified by enzyme-linked immunosorbent assay. Nitric oxide was determined by the methemoglobin method.

RESULTS

It was found that PR status in neutrophils was identical with that in malignant breast tissues. A Scatchard plot for progesterone binding to normal and PR-positive (PR+) neutrophils revealed that whereas normal neutrophils had 11.5 × 10(10) PR sites/cell with K d = 47.619 nM, PR+ neutrophils had 6.6 × 10(10) PR sites/cell with K d = 47.619 nM. The progesterone negative (PR-) neutrophils failed to bind to progesterone. Incubation of normal and PR+ neutrophils with 25 nM progesterone produced 1.317 μM NO and 2.329 nM maspin; the PR+ neutrophils produced 0.72 μM NO and 1.138 nM maspin. The PR- neutrophils failed to produce any NO or maspin in the presence of progesterone. Inhibition of progesterone-induced NO synthesis led to complete inhibition of maspin synthesis in all neutrophils.

CONCLUSION

These results suggest that estrogen and progesterone complement each other in NO-induced maspin synthesis, and do not necessarily antagonize in the synthesis of the anti-breast-cancer protein.

Crossing paths in Human Renal Cell Carcinoma (hRCC)

Historically, cell-signaling pathways have been studied as the compilation of isolated elements into a unique cascade that transmits extracellular stimuli to the tumor cell nucleus. Today, growing evidence supports the fact that intracellular drivers of tumor progression do not flow in a single linear pathway, but disseminate into multiple intracellular pathways. An improved understanding of the complexity of cancer depends on the elucidation of the underlying regulatory networks at the cellular and intercellular levels and in their temporal dimension. The high complexity of the intracellular cascades causes the complete inhibition of the growth of one tumor cell to be very unlikely, except in cases in which the so-called “oncogene addiction” is known to be a clear trigger for tumor catastrophe, such as in the case of gastrointestinal stromal tumors or chronic myeloid leukemia. In other words, the separation and isolation of the driver from the passengers is required to improve accuracy in cancer treatment. This review will summarize the signaling pathway crossroads that govern renal cell carcinoma proliferation and the emerging understanding of how these pathways facilitate tumor escape. We outline the available evidence supporting the putative links between different signaling pathways and how they may influence tumor proliferation, differentiation, apoptosis, angiogenesis, metabolism and invasiveness. The conclusion is that tumor cells may generate their own crossroads/crosstalk among signaling pathways, thereby reducing their dependence on stimulation of their physiologic pathways.

Antiprogestins in breast cancer treatment: are we ready?

Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death in females worldwide. It is accepted that breast cancer is not a single disease, but instead constitutes a spectrum of tumor subtypes with distinct cellular origins, somatic changes, and etiologies. Molecular gene expression studies have divided breast cancer into several categories, i.e. basal-like, ErbB2 enriched, normal breast-like (adipose tissue gene signature), luminal subtype A, luminal subtype B, and claudin-low. Chances are that as our knowledge increases, each of these types will also be subclassified. More than 66% of breast carcinomas express estrogen receptor alpha (ERα) and respond to antiestrogen therapies. Most of these ER+ tumors also express progesterone receptors (PRs), the expression of which has been considered as a reliable marker of a functional ER. In this paper we will review the evidence suggesting that PRs are valid targets for breast cancer therapy. Experimental data suggest that both PR isoforms (A and B) have different roles in breast cancer cell growth, and antiprogestins have already been clinically used in patients who have failed to other therapies. We hypothesize that antiprogestin therapy may be suitable for patients with high levels of PR-A. This paper will go over the experimental evidence of our laboratory and others supporting the use of antiprogestins in selected breast cancer patients.

Progesterone receptor action: defining a role in breast cancer

The ovarian steroid hormones, estradiol and progesterone, and their nuclear receptors (estrogen receptor [ER] and progesterone receptor [PR]), are involved in breast cancer development. As ER-positive/PR-positive tumors progress, they are likely to become steroid hormone-resistant/independent, yet often retain expression of their steroid receptors. Notably, up to 40% of women with steroid receptor-positive tumors exhibit de novo resistance or eventually fail on estrogen- or ERα-blocking therapies (acquired resistance). Indeed, most of the research on this topic has centered on mechanisms of ER 'escape' from endocrine therapy and the design of better ER-blocking strategies; signaling pathways that mediate endocrine (i.e., anti-estrogen) resistance are also excellent therapeutic targets. However, serious consideration of PR isoforms as important drivers of early breast cancer progression and ER modulators is timely and significant. Indeed, progress has been hindered by ER-centric experimental approaches. This article will focus on defining a role for PR in breast cancer with hopes of providing a refreshing PR-focused perspective.

Progesterone induces expression of the prolactin receptor gene through cooperative action of Sp1 and C/EBP

Prolactin (Prl) and progesterone (P) cooperate synergistically during mammary gland development and tumorigenesis. We hypothesized that one mechanism for these effects may be through mutual induction of receptors (R). EpH4 mouse mammary epithelial cells stably transfected with PR-A express elevated levels of PrlR mRNA and protein compared to control EpH4 cells that lack the PR. Likewise, T47D human breast cancer cells treated with P overexpress the PrlR and activate PrlR promoter III. PrlR promoter III does not contain a classical P response element but contains several binding sites for transcription proteins, including C/EBP, Sp1 and AP1, which may also interact with the PR. Using promoter deletion and site directed mutagenesis analyses as well as gel shift assays, cooperative activation of the C/EBP and adjacent Sp1A, but not the Sp1B or AP1, sites by P is shown to confer P responsiveness leading to increased PrlR transcription.

Mammographic density and hormone receptor expression in breast cancer: the Multiethnic Cohort Study

BACKGROUND

It is unclear whether mammographic breast density, a strong risk factor for breast cancer, predicts subtypes of breast cancer defined by estrogen receptor (ER) and/or progesterone receptor (PR) expression.

METHODS

In a nested case-control study, we compared the breast density of 667 controls and 607 breast cancer cases among women of Caucasian, Japanese, and Native Hawaiian ancestry in the Hawaii component of the Multiethnic Cohort Study. A reader blinded to disease status performed computer assisted density assessment on prediagnostic mammograms. Receptor status was obtained from the statewide Hawaii Tumor Registry. Tumors were classified into ER+PR+ (n=341), ER-PR- (n=50), ER+PR-/ER-PR+ (n=64), and unstaged/unknown (n=152). Mean percent density values were computed for women with more than one mammogram. Polytomous logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) while adjusting for confounders.

RESULTS

Mean percent density was significantly greater for ER+PR+ but not for ER-PR- tumors compared to controls after adjusting for age: 37.3%, 28.9% versus 29.4%, respectively. The overall OR per 10% increase in percent density were similar for ER+PR+ and ER+PR-/ER-PR+ tumors: 1.26 (95% CI 1.17-1.36) and 1.23 (95% CI 1.07-1.42), respectively. However, percent density was not found to be a predictor for ER-PR- tumors (OR 1.00, 95% CI 0.84-1.18). The results did not differ by ethnicity, nor by menopausal status, parity, or HRT use.

CONCLUSIONS

Our findings indicate that within a multiethnic population, women with higher breast density have an increased risk for ER+PR+ but not ER-PR- tumors.

Protein modifications as potential biomarkers in breast cancer

A variety of post-translational protein modifications (PTMs) are known to be altered as a result of cancer development. Thus, these PTMs are potentially useful biomarkers for breast cancer. Mass spectrometry, antibody microarrays and immunohistochemistry techniques have shown promise for identifying changes in PTMs. In this review, we summarize the current literature on PTMs identified in the plasma and tumor tissue of breast-cancer patients or in breast cell lines. We also discuss some of the analytical techniques currently being used to evaluate PTMs.

Protein kinases mediate ligand-independent derepression of sumoylated progesterone receptors in breast cancer cells

In advanced breast tumors, protein kinases are upregulated and steroid hormone receptors often function independently of ligand. Herein, we explored mechanisms of ligand-independent progesterone receptor (PR) activity. We showed previously that growth factor-induced phosphorylation of PR Ser-294 blocks PR Lys-388 sumoylation. SUMO-deficient mutant PR-B (K388R) thus provides a model receptor for the study of PR function in the context of high kinase activities. T47D cells stably expressing K388R PR-B exhibited increased ligand-independent proliferation and growth in soft agar relative to cells expressing wt PR-B or phospho-mutant (sumoylated) S294A PR-B. Expression of selected PR target genes (HB-EGF, IRS-1, and STC1) was significantly elevated in cells containing desumoylated (K388R) PR-B. Basal PR transcriptional activity occurred independently of progestins, was increased by activated CDK2, and attenuated by RU486. Notably, ChIP assays demonstrated that K388R PR-B and SRC1 were constitutively recruited to the STC1 promoter in the absence of progestin; PR Lys-388 sumoylation was required for HDAC3 recruitment. Knock-down of STC1 inhibited proliferation of cells expressing K388R PR-B. These data suggest a mechanism whereby phosphorylated, and thus desumoylated, PRs mediate increased expression of growth promoting genes. Our data explain why breast cancer models often remain insensitive to progestins, but are growth-inhibited by antiprogestins, and underscore the need to target PR-B and associated kinase activities as part of breast cancer therapy.

Advances in the Treatment of Menopausal Symptoms

Vasomotor symptoms and vaginal atrophy are both common menopausal symptoms. Hormone therapy is currently the only FDA-approved treatment for hot flashes. Current recommendations are to use the lowest dose of hormone therapy for the shortest period that will allow treatment goals to be met. Although the reanalysis of the WHI in 2007 by Roussow et al. provided evidence of coronary heart safety for users of hormone therapy under the age of 60 years and within 10 years of the onset of menopause, not all women desire or are candidates for hormone therapy. In this review we present an evidence-based discussion considering the effectiveness of hormonal and nonhormonal therapies for the relief of vasomotor symptoms and vaginal atrophy. Concern exists regarding systemic absorption of vaginal estrogen and possible adverse effects on the breast and uterus. Selective estrogen receptor modulators and estrogen agonists offer benefits through targeted estrogen agonist/antagonistic effects and are being evaluated with and without estrogen for symptomatic menopausal women. Centrally acting nonhormonal therapies that are effective for the relief of vasomotor symptoms include various antidepressants, gabapentin and clonidine. A limited number of clinical trials have been conducted with nonprescription remedies, including paced respiration, yoga, acupuncture, exercise, homeopathy and magnet therapy, and some, but not all of these, have been found to be more effective than placebo. Dietary herbal supplements, such as soy and black cohosh, have demonstrated mixed and inconclusive results in placebo-controlled trials. Potential therapies for vasomotor symptoms and vaginal atrophy require randomized, placebo-controlled trials of sufficient duration to establish efficacy and safety. Agents under investigation for vasomotor symptoms relief include neuroactive agents, such as gabapentin and desvenlafaxine; an estrogen receptor-β-targeted herbal therapy, MF-101; and the selective estrogen receptor modulator, bazedoxifene, paired with estrogen.

Transcriptome analysis of mammary epithelial subpopulations identifies novel determinants of lineage commitment and cell fate

Background

Understanding the molecular control of cell lineages and fate determination in complex tissues is key to not only understanding the developmental biology and cellular homeostasis of such tissues but also for our understanding and interpretation of the molecular pathology of diseases such as cancer. The prerequisite for such an understanding is detailed knowledge of the cell types that make up such tissues, including their comprehensive molecular characterisation. In the mammary epithelium, the bulk of the tissue is composed of three cell lineages, namely the basal/myoepithelial, luminal epithelial estrogen receptor positive and luminal epithelial estrogen receptor negative cells. However, a detailed molecular characterisation of the transcriptomic differences between these three populations has not been carried out.

Results

A whole transcriptome analysis of basal/myoepithelial cells, luminal estrogen receptor negative cells and luminal estrogen receptor positive cells isolated from the virgin mouse mammary epithelium identified 861, 326 and 488 genes as highly differentially expressed in the three cell types, respectively. Network analysis of the transcriptomic data identified a subpopulation of luminal estrogen receptor negative cells with a novel potential role as non-professional immune cells. Analysis of the data for potential paracrine interacting factors showed that the basal/myoepithelial cells, remarkably, expressed over twice as many ligands and cell surface receptors as the other two populations combined. A number of transcriptional regulators were also identified that were differentially expressed between the cell lineages. One of these, Sox6, was specifically expressed in luminal estrogen receptor negative cells and functional assays confirmed that it maintained mammary epithelial cells in a differentiated luminal cell lineage.

Conclusion

The mouse mammary epithelium is composed of three main cell types with distinct gene expression patterns. These suggest the existence of a novel functional cell type within the gland, that the basal/myoepithelial cells are key regulators of paracrine signalling and that there is a complex network of differentially expressed transcription factors controlling mammary epithelial cell fate. These data will form the basis for understanding not only cell fate determination and cellular homeostasis in the normal mammary epithelium but also the contribution of different mammary epithelial cell types to the etiology and molecular pathology of breast disease.