Medroxyprogesterone acetate induces cell proliferation through up-regulation of cyclin D1 expression via phosphatidylinositol 3-kinase/Akt/nuclear factor-kappaB cascade in human breast cancer cells

SHP2 is essential for the progesterone-promoted proliferation and migration in breast cancer cell lines

Introduction

We previously demonstrated that progesterone (P4) can promote breast cancer cell proliferation and migration through activating the P4 receptor (PR)/cSrc-mediated signaling pathway. It has been suggested that high level of Src homology region 2 domain-containing phosphatase-2 (SHP2) might be involved in breast oncogenesis. This study aimed to investigate whether SHP2 is involved in the P4-mediated cSrc activation in breast cancer cells.

Methods

T47D, MCF-7 and BT-483 breast cancer cell lines were used in this study. Cell proliferation and migration were examined using MTT technique and wound healing assay, respectively. Immunoprecipitation assay and Western blot analysis were performed to evaluate protein-protein interaction and protein expression, respectively. Small interfering RNA (siRNA) technique was used to knock down protein expression.

Results

Knockdown of SHP2 expression abolished the P4-promoted cell proliferation and migration in T47D, MCF and BT-483 cell lines, suggesting that presence of SHP2 is essential for the P4-increased proliferation and migration of breast cancer cell lines. P4 (50 nM) treatment increased the complex formations of PR-cSrc-SHP2-caveolin-1, SHP2-p140Cap, and SHP2-Csk, and the level of p-cSrcY416 (activated form of cSrc). However, knockdown of SHP2 expression increased the complex formations of PR-cSrc-caveolin-1-Csk-p140Cap and the levels of p-caveolin-1, p-Csk and p-cSrcY527 (inactivated form of cSrc).

Discussion

Our data suggest that SHP2 can bind to cSrc-negative regulatory proteins (p140Cap and Csk), hence preventing the interaction between cSrc and cSrc-negative regulatory proteins, leading to decreased phosphorylation of cSrc Y527 and prolonged cSrc activation. These findings highlight the role of SHP2 in the P4-promoted breast cancer cell proliferation and migration.

Identification of Novel Progesterone Receptor (PR) Inhibitors (Homo sapiens) from Metabolites of Biotransformation Fungal: A Bioinformatics Approach

Background/Objectives: Steroids have demonstrated selective cytotoxic properties against tumor cells. The pro-gesterone receptor (PR) plays a vital role in the proliferation, cell differentiation, and maintenance of female reproductive tissue, and its malfunction can lead to breast cancer. The use of the biocatalytic method by filamentous fungi has sparked interest in the obtained of steroids due to the advantages of the process. Methods: Pharmacokinetic and toxicological properties (rat and mouse), molecular docking simulation studies, and prediction of the spectrum of biological activity were performed to select molecules with the potential for PR inhibition, from 155 biotransformed products of the progesterone. Subsequently, the chemical structures were subjected to an evaluation of their pharmacokinetic and toxicological properties and, with the application of ADMET filters. Results: Androstenedione, 17α-hydroxyprogesterone, and dihydrotestosterone, obtained by the process of biotransformation of PR by different filamentous fungi, showed good pharmacokinetic profiles and low toxicity compared to the control groups. The in-silico data associated with molecular docking studies revealed the best binding affinity and similarity in the interactions of these molecules against the human progesterone receptor target. Thus, the results of biological activity spectrum prediction highlight the great potential to investigate the role of molecular descriptors in the attribution of anti-cancer activities. Conclusions: The biocatalytic process, by filamentous fungi, can provide important molecules as a product of progesterone biotransformation, such as androstenedione, 17α-hydroxyprogesterone, and dihydrotestosterone. In this study we showed that these molecules have good pharmacokinetic profiles and low toxicity for antineoplastic activity (breast cancer).

Progestins and breast cancer hallmarks: The role of the ERK1/2 and JNK pathways in estrogen receptor positive breast cancer cells

Progestins used in hormonal contraceptives and menopausal hormone therapy (MHT) have been linked to increased breast cancer risk. Whether the association holds for all progestins is unclear and the underlying mechanisms remain poorly understood. We directly compared the effects of four progestins (medroxyprogesterone acetate (MPA), norethisterone acetate (NET-A), levonorgestrel (LNG) and drospirenone (DRSP)) to each other and the natural progestogen progesterone (P4) on selected cancer hallmarks. To provide mechanistic insight into these effects, we assessed the role of the progesterone receptor (PR), and the extracellular signal-related kinase (ERK1/2) and c-Jun N terminal (JNK) signaling pathways. We showed that the increased proliferation of the luminal T47D breast cancer cell line by P4 and all progestins, albeit to different extents, was inhibited by PR knockdown and inhibition of both the ERK1/2 and JNK pathways. While knockdown of the PR also blocked the upregulation of MKI67 and CCND1 mRNA expression by selected progestogens, only a role for the ERK1/2 pathway could be established in these effects. Similarly, only a role for the ERK1/2 pathway could be confirmed for progestogen-induced colony formation, whereas both the ERK1/2 and JNK pathways were required for cell migration in response to the three older progestins implicated in the etiology of breast cancer, MPA, NET-A and LNG. Together our results show that all the progestins elicit their effects on cell proliferation via a mechanism requiring the PR, ERK1/2 and JNK pathways. While the ERK1/2 and JNK pathways are also required for increased cell migration by the older progestins, only a role for the ERK1/2 pathway could be established in their effects on colony formation. Notably, the cytoplasmic PR was not needed for activation of the ERK1/2 pathway by the progestogens. Given that DRSP showed significantly lower proliferation than MPA and NET-A, and that it had no effect on breast cancer cell migration and colony formation, hormonal formulations containing the newer generation progestin DRSP may provide a better benefit/risk profile towards breast cancer than those containing the older generation progestins.

Altered hormone expression induced genetic changes leads to breast cancer

PURPOSE OF REVIEW

Breast cancer ranks first among gynecological cancer in India. It is associated with urbanization, changes in lifestyle and obesity. Hormones also play a crucial role in the development of breast cancer. Steroid hormones play critical role in development of breast cancer.

RECENT FINDING

Breast cancer is caused due to alteration in different hormone expressions leading to genetic instability. Loss or gains of functions due to genetic instability were associated with the alterations in housekeeping genes. Up-regulation in c-myc, signal transducer and activator of transcription (STAT), CREB-regulated transcription coactivator (CRTC), and eukaryotic translation initiation factor 4E (eIF4E) may cause the development of breast cancer. Peptide hormones are commonly following the phosphoinositide 3-kinases (PI3K) pathway for activation of cell cycle causing uncontrolled proliferation. Although steroid hormones are following the Ras/Raf/mitogen-activated protein kinase (MEK) pathway, their hyper-activation of these pathways causes extracellular-signal-regulated kinase (ERK) and MAPK activation, leading to carcinogenesis.

SUMMARY

Alteration in cell cycle proteins, oncogenes, tumor suppressor genes, transcription and translation factors lead to breast cancer. Apoptosis plays a vital role in the elimination of abnormal cells but failure in any of these apoptotic pathways may cause tumorigenesis. Hence, a complex interplay of hormonal and genetic factors is required to maintain homeostasis in breast cells. Imbalance in homeostasis of these hormone and genes may lead to breast cancer.

The role of progesterone and the progesterone receptor in cancer: progress in the last 5 years

INTRODUCTION

Patients with various advanced cancers devoid of nuclear progesterone receptors (nPR) have demonstrated increased quality and length of life when treated with the PR modulator mifepristone, which likely works by interacting with membrane PRs (mPR).

AREAS COVERED

Two immunomodulatory proteins are discussed that seem to play a role in cancers that proliferate whether the malignant tumor is positive or negative for the nPR. These two proteins are the progesterone receptor membrane component-1 (PGRMC-1) and the progesterone-induced blocking factor (PIBF). Both PGRMC-1 and the parent form of PIBF foster increased tumor aggressiveness, whereas splice variants of the 90 kDa form of PIBF inhibit immune response against cancer cells.

EXPERT OPINION

The marked clinical improvement following 200-300 mg of mifepristone is likely related to blocking PIBF. In the low dosage used, mifepristone likely acts as an agonist for PGRMC-1 protein. Mifepristone may be less effective for cancers positive for the nPR because the nPR may be protective and blocking it may have detrimental effects. Based on this hypothetical model, the development of other potential treatment options to provide even greater efficacy for treating cancer are discussed.

Progesterone: A Steroid with Wide Range of Effects in Physiology as Well as Human Medicine

Progesterone is a steroid hormone traditionally linked with female fertility and pregnancy. In current reproductive medicine, progesterone and its analogues play crucial roles. While the discovery of its effects has a long history, over recent decades, various novel actions of this interesting steroid have been documented, of which its neuro- and immunoprotective activities are the most widely discussed. Discoveries of the novel biological activities of progesterone have also driven research and development in the field of progesterone analogues used in human medicine. Progestogen treatment has traditionally and predominately been used in maintaining pregnancy, the prevention of preterm labor, various gynecological pathologies, and in lowering the negative effects of menopause. However, there are also various other medical fields where progesterone and its analogues could find application in the future. The aim of this work is to show the mechanisms of action of progesterone and its metabolites, the physiological and pharmacological actions of progesterone and its synthetic analogues in human medicine, as well as the impacts of its production and use on the environment.

Ginkgolic acid induces apoptosis and autophagy of endometrial carcinoma cells via inhibiting PI3K/Akt/mTOR pathway in vivo and in vitro

Endometrial cancer (EC) is the fourth most common malignancy in women in developed countries. The prognosis of EC is extremely poor, and it is an important factor that contributes to the death of patients. Therefore, studying EC pathogenesis and therapeutic targets, and exploring effective drugs are the primary tasks to improve the prognosis of EC. In the present study, we aimed to explore the function of ginkgolic acid (GA) in EC cell apoptosis and autophagy through PI3K/Akt/mTOR signal pathway in vitro and in vivo. Firstly, MTT assay and clone formation assay were employed to analyze the Ishikawa and HEC-1-B cell viabilities and proliferation after treatment with GA. The results showed that GA inhibited endometrial cancer cell survival. Flow cytometry assay and western blot assay were applied to examine the apoptosis and apoptosis related protein Bcl-2, Bax, Cleaved caspase-3 expression levels of Ishikawa and HEC-1-B cells after treatment with GA. Next, we applied western blot assay to analyze the autophagy associated proteins LC3I, LC3II, p62 and Beclin-1 in GA treated Ishikawa and HEC-1-B cells. We found that GA promoted apoptosis and induced autophagy of endometrial cancer cells. Meanwhile, western blot assay was also used to determine the expression levels of the PI3K/Akt/mTOR signal pathway related protein and the results revealed that GA inhibited the activity of PI3K/Akt/mTOR pathway. Finally, we found that GA inhibited tumor growth in vivo through immunohistochemistry assay. In conclusion, GA induces apoptosis and autophagy of EC cells via inhibiting PI3K/Akt/mTOR pathway in vivo and vitro.

Non-genomic signaling of steroid receptors in cancer

Steroid receptors (SRs) are members of the nuclear receptor family, which are ligand-activated transcription factors. SRs regulate many physiological functions including development and reproduction, though they can also be involved in several pathologies, especially cancer. Highly controlled cellular responses to steroids involve transcriptional regulation (genomic activity) combined with direct activation of signaling cascades (non-genomic activity). Non-genomic signaling has been extensively studied in cancer, mainly in breast cancer for ER and PR, and prostate cancer for AR. Even though most of the studies have been conducted in cells, some of them have been confirmed in vivo, highlighting the relevance of this pathway in cancer. This review provides an overview of the current and emerging knowledge on non-genomic signaling with a focus on breast and prostate cancers and its clinical relevance. A thorough understanding of ER, PR, AR and GR non-genomic pathways may open new perspectives for the development of therapeutic strategies.

Selective Progesterone Receptor Modulators-Mechanisms and Therapeutic Utility

Selective progesterone receptor modulators (SPRMs) are a new class of compounds developed to target the progesterone receptor (PR) with a mix of agonist and antagonist properties. These compounds have been introduced for the treatment of several gynecological conditions based on the critical role of progesterone in reproduction and reproductive tissues. In patients with uterine fibroids, mifepristone and ulipristal acetate have consistently demonstrated efficacy, and vilaprisan is currently under investigation, while studies of asoprisnil and telapristone were halted for safety concerns. Mifepristone demonstrated utility for the management of endometriosis, while data are limited regarding the efficacy of asoprisnil, ulipristal acetate, telapristone, and vilaprisan for this condition. Currently, none of the SPRMs have shown therapeutic success in treating endometrial cancer. Multiple SPRMs have been assessed for efficacy in treating PR-positive recurrent breast cancer, with in vivo studies suggesting a benefit of mifepristone, and multiple in vitro models suggesting the efficacy of ulipristal acetate and telapristone. Mifepristone, ulipristal acetate, vilaprisan, and asoprisnil effectively treated heavy menstrual bleeding (HBM) in patients with uterine fibroids, but limited data exist regarding the efficacy of SPRMs for HMB outside this context. A notable class effect of SPRMs are benign, PR modulator-associated endometrial changes (PAECs) due to the actions of the compounds on the endometrium. Both mifepristone and ulipristal acetate are effective for emergency contraception, and mifepristone was approved by the US Food and Drug Administration (FDA) in 2012 for the treatment of Cushing's syndrome due to its additional antiglucocorticoid effect. Based on current evidence, SPRMs show considerable promise for treatment of several gynecologic conditions.

Progesterone receptor membrane component 1 is required for mammary gland development†

The physiological functions of progesterone (P4) in female reproductive organs including the mammary glands are mediated via the progesterone receptor (PR), but not all P4 functions can be explained by PR-mediated signaling. Progesterone receptor membrane component 1 (PGRMC1), a potential mediator of P4 actions, plays an important role in the ovary and uterus in maintaining female fertility and pregnancy, but its function in mammary glands has not been elucidated. This study investigated the role of PGRMC1 in mouse mammary gland development. Unlike in the uterus, exogenous estrogen (E2) and/or P4 did not alter PGRMC1 expression in the mammary gland, and Pgrmc1-knockout (KO) mice displayed reduced ductal elongation and side branching in response to hormone treatment. During pregnancy, PGRMC1 was expressed within both the luminal and basal epithelium and gradually increased with gestation and decreased rapidly after parturition. Moreover, although lactogenic capacity was normal after parturition, Pgrmc1 KO resulted in defective mammary gland development from puberty until midpregnancy, while the expression of PR and its target genes was not significantly different between wild-type and Pgrmc1-KO mammary gland. These data suggest that PGRMC1 is essential for mammary gland development during puberty and pregnancy in a PR-independent manner.

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

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

Folic acid prevents the progesterone-promoted proliferation and migration in breast cancer cell lines

PURPOSE

We previously demonstrated that progesterone (P4) interacted with folic acid (FA) and abolished the FA-reduced endothelial cell proliferation and migration. These findings led us to investigate whether FA can interfere with the P4-promoted breast cancer cell proliferation and migration.

METHODS

We conducted MTT and wound healing assay to evaluate cell proliferation and migration, respectively. Western blot analysis and immunoprecipitation were performed to examine the protein expression and protein-protein interaction, respectively.

RESULTS

We demonstrated that P4 promoted proliferation and migration of breast cancer cell lines (T47D, MCF-7, BT474, and BT483). However, co-treatment with P4 and FA together abolished these promotion effects. Treatment with P4 alone increased the formation of PR-cSrc complex and the phosphorylation of cSrc at tyrosine 416 (Tyr416). However, co-treatment with P4 and FA together increased the formations of cSrc-p140Cap, cSrc-Csk, and cSrc-p-Csk complex, and the phosphorylation of cSrc at tyrosine 527 (Tyr527). Co-treatment with P4 and FA together also abolished the activation of cSrc-mediated signaling pathways involved in the P4-promoted breast cancer cell proliferation and migration.

CONCLUSIONS

Co-treatment with FA and P4 together abolished the P4-promoted breast cancer cell proliferation and migration through decreasing the formation of PR-cSrc complex and increasing the formations of cSrc-p140Cap and cSrc-Csk complex, subsequently activating Csk, which in turn suppressed the phosphorylation of cSrc at Tyr416 and increased the phosphorylation of cSrc at Tyr527, hence inactivating the cSrc-mediated signaling pathways. The findings from this study might provide a new strategy for preventing the P4-promoted breast cancer progress.

Activation of membrane progesterone receptor-alpha increases proliferation, migration, and invasion of human glioblastoma cells

BACKGROUND AND AIMS

Glioblastoma is the most frequent and aggressive brain tumor due to its high capacity to migrate and invade normal brain tissue. The steroid hormone progesterone (P4) contributes to the progression of glioblastoma by promoting proliferation, migration, and cellular invasion through the activation of its intracellular receptor (PR). However, the use of PR antagonist RU486 partially blocks the effects of P4, suggesting the participation of signaling pathways such as those mediated by membrane receptors to P4 (mPRs). Therefore, this study aimed to investigate the effects of mPRα subtype activation on proliferation, migration, and invasion of human glioblastoma cells.

METHODS

We treated human glioblastoma cell lines U87 and U251 with the specific mPRα agonist Org OD 02-0, and evaluated its effects on cell number, proliferation, migration, and invasion. Additionally, we measured the phosphorylation of the kinases Src and Akt in both cell lines upon Org OD 02-0 treatment.

RESULTS

Org OD 02-0 (100 nM) augmented the number of U87 and U251 cells by increasing cell proliferation. The treatment with this agonist also increased U87 and U251 cell migration and invasion. Both proliferation and cell invasion decreased when mPRα expression was silenced. Finally, we observed that Org OD 02-0 increased the content of p-Src and p-Akt in both cell lines.

CONCLUSION

Our data suggest that P4 produces its effects in human glioblastoma progression not only by PR interaction but also through cell signaling pathways activated by mPRα.

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.

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.

PI3K/AKT/mTOR pathway promotes progestin resistance in endometrial cancer cells by inhibition of autophagy

Endometrial cancer (EC) is now one of the most common malignant tumors in young women. In all, 90% of young patients with EC have a high expression of progesterone recep tor, can be treated with progestin, and have very good prognosis. However, some of the young EC patients are resistant to progestin, the mechanism of which is unclear. To illuminate the mechanism by which endometrial cells acquire progestin resistance, we treated Ishikawa cells by slowly increasing dosage of progestin and established a progestin-resistant cell subline. We show here that progesterone resistant cells acquire increased proliferation rate and interestingly decreased autophagy. To uncover the mechanism by which cells increase proliferation and bypass autophagy, we found higher activation of phosphatidylinositol 3-kinase/AKT/mTOR signaling pathway was necessary to this malignant acquirement by RNAi technique. Further, we elucidated that activation of mTOR was sufficient and necessary for progestin resistance. RAD001, an inhibitor of mTOR, decreased phosphorylation of mTOR and inhibited proliferation of progestin-resistant cancer cells by promoting autophagy. Thus, our results indicated that mTOR can be a target to treat the progestin-resistant EC.

Molecular mechanisms underlying progesterone-enhanced breast cancer cell migration

Progesterone (P4) was demonstrated to inhibit migration in vascular smooth muscle cells (VSMCs), but to enhance migration in T47D breast cancer cells. To investigate the mechanism responsible for this switch in P4 action, we examined the signaling pathway responsible for the P4-induced migration enhancement in breast cancer cell lines, T47D and MCF-7. Here, we demonstrated that P4 activated the cSrc/AKT signaling pathway, subsequently inducing RSK1 activation, which in turn increased phosphorylation of p27 at T198 and formation of the p27pT198-RhoA complex in the cytosol, thereby preventing RhoA degradation, and eventually enhanced migration in T47D cells. These findings were confirmed in the P4-treated MCF-7. Comparing the P4-induced molecular events in between breast cancer cells and VSMCs, we found that P4 increased p27 phosphorylation at T198 in breast cancer cells through RSK1 activation, while P4 increased p27 phosphorlation at Ser10 in VSMCs through KIS activation. P27pT198 formed the complex with RhoA and prevented RhoA degradation in T47D cells, whereas p-p27Ser10 formed the complex with RhoA and caused RhoA degradation in VSMCs. The results of this study highlight the molecular mechanism underlying P4-enhanced breast cancer cell migration, and suggest that RSK1 activation is responsible for the P4-induced migration enhancement in breast cancer cells.

Progestin-mediated activation of MAPK and AKT in nuclear progesterone receptor negative breast epithelial cells: The role of membrane progesterone receptors

Progesterone (P4), a steroid produced during estrous cycles and gestation for maintenance of pregnancy, also plays key roles in breast development to allow lactation post-parturition. Progestins (P4 and related steroids) are also implicated in breast cancer etiology. Hormone replacement therapy containing both estrogen and progestins increases breast cancer incidence while estrogen hormone therapy lowers breast cancer risk. P4 signaling via nuclear P4 receptors (PRs) has been extensively studied in breast cancer, however, progestin signaling via non-classical membrane bound progestin receptors (MPRs and PGRMC1) remains unclear. Moreover, P4 metabolites and synthetic progestins may bind membrane progestin receptors. We hypothesized that PR-negative breast epithelial cells express non-classical progestin receptors, which activate intracellular signaling pathways differently depending on nature of progestin. Therefore, our objectives for the current study were to determine expression of MPRs and PGRMC1 in two PR-negative non-tumorigenic breast epithelial cell lines, assess progestin-mediated signaling and biological functions. We determined five MPR isoforms and PGRMC1 were present in MCF10A cells and all progestin receptors but MPRβ in MCF12A cells. MCF10A and MCF12A cells were treated with P4, select P4 metabolites (5αP and 3αHP), medroxyprogesterone acetate (MPA), or a specific MPR-Agonist (MPR-Ag) and phosphorylation of ERK, p38, JNK, and AKT was characterized following treatment. To our knowledge this is the first report of ERK and JNK activation in MCF10A and MCF12A cells with P4, P4 metabolites, MPA, and MPR-Ag. Activation of ERK and JNK in cells treated with MPR-Ag implicates MPRs may serve as the receptors responsible for their activation. In contrast, p38 activation varied with cell type and with progestin treatment. P4 and MPA promoted AKT phosphorylation in the MCF12A cell line only whereas no activation was observed in MCF10A cells. Interestingly, cellular proliferation increased in MCF10A cells treated with MPA or 5αP, while MPR-Ag tended to slightly decrease proliferation. Collectively, our data highlights the importance of investigating the effects of synthetic progestins in breast cancer biology. Our results add to the understanding that various progestins have on breast epithelial cells and underscores the importance of considering both membrane bound receptors and progestin type in breast cancer development.

Induction of methionine adenosyltransferase 2A in tamoxifen-resistant breast cancer cells

We previously showed that S-adenosylmethionine-mediated hypermethylation of the PTEN promoter was important for the growth of tamoxifen-resistant MCF-7 (TAMR-MCF-7) cancer cells. Here, we found that the basal expression level of methionine adenosyltransferase 2A (MAT2A), a critical enzyme for the biosynthesis of S-adenosylmethionine, was up-regulated in TAMR-MCF-7 cells compared with control MCF-7 cells. Moreover, the basal expression level of MAT2A in T47D cells, a TAM-resistant estrogen receptor-positive cell line was higher compared to MCF-7 cells. Immunohistochemistry confirmed that MAT2A expression in TAM-resistant human breast cancer tissues was higher than that in TAM-responsive cases. The promoter region of human MAT2A contains binding sites for nuclear factor-κB, activator protein-1 (AP-1), and NF-E2-related factor 2 (Nrf2), and the activities of these three transcription factors were enhanced in TAMR-MCF-7 cells. Both the protein expression and transcriptional activity of MAT2A in TAMR-MCF-7 cells were potently suppressed by NF-κB inhibition but not by c-Jun/AP-1 or Nrf2 knock-down. Interestingly, the expression levels of microRNA (miR)-146a and -146b were diminished in TAMR-MCF-7 cells, and miR-146b transduction decreased NF-κB-mediated MAT2A expression. miR-146b restored PTEN expression via the suppression of PTEN promoter methylation in TAMR-MCF-7 cells. Additionally, miR-146b overexpression inhibited cell proliferation and reversed chemoresistance to 4-hydroxytamoxifen in TAMR-MCF-7 cells.

Induction of methionine adenosyltransferase 2A in tamoxifen-resistant breast cancer cells

We previously showed that S-adenosylmethionine-mediated hypermethylation of the PTEN promoter was important for the growth of tamoxifen-resistant MCF-7 (TAMR-MCF-7) cancer cells. Here, we found that the basal expression level of methionine adenosyltransferase 2A (MAT2A), a critical enzyme for the biosynthesis of S-adenosylmethionine, was up-regulated in TAMR-MCF-7 cells compared with control MCF-7 cells. Moreover, the basal expression level of MAT2A in T47D cells, a TAM-resistant estrogen receptor-positive cell line was higher compared to MCF-7 cells. Immunohistochemistry confirmed that MAT2A expression in TAM-resistant human breast cancer tissues was higher than that in TAM-responsive cases. The promoter region of human MAT2A contains binding sites for nuclear factor-κB, activator protein-1 (AP-1), and NF-E2-related factor 2 (Nrf2), and the activities of these three transcription factors were enhanced in TAMR-MCF-7 cells. Both the protein expression and transcriptional activity of MAT2A in TAMR-MCF-7 cells were potently suppressed by NF-κB inhibition but not by c-Jun/AP-1 or Nrf2 knock-down. Interestingly, the expression levels of microRNA (miR)-146a and -146b were diminished in TAMR-MCF-7 cells, and miR-146b transduction decreased NF-κB-mediated MAT2A expression. miR-146b restored PTEN expression via the suppression of PTEN promoter methylation in TAMR-MCF-7 cells. Additionally, miR-146b overexpression inhibited cell proliferation and reversed chemoresistance to 4-hydroxytamoxifen in TAMR-MCF-7 cells.

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

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

IMPLICATIONS

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

Expression of WTH3 in breast cancer tissue and the effects on the biological behavior of breast cancer cells

The aim of the present study was to investigate the expression of WTH3 in tumor and normal breast tissue. The mRNA and protein expression levels of WTH3 were detected using reverse transcription quantitative polymerase chain reaction and western blot analysis, respectively. In addition, matrix metalloproteinase (MMP)-2 protein expression was measured. The effect of WTH3 expression on the proliferation activity of breast cancer cells was detected using a Cell Counting Kit-8 assay. Furthermore, the effects of WTH3 on the invasion and migration ability of the breast cancer cells was investigated. The results revealed that WTH3 was able to significantly inhibit the proliferation of the MCF-7 and MDA-MB-231 breast cancer cell lines. In addition, the invasion and migration assay demonstrated that WTH3 was able to inhibit the invasion and migration of breast cancer cells. Western blot analysis revealed that increased expression of WTH3 resulted in decreased expression levels of MMP-2, which has an important function in the metastasis of cancer cells. In conclusion, WTH3 expression differed between the tumor and normal breast tissues. WTH3 was able to inhibit the proliferation of breast cancer cells and decrease their invasion ability. Thus, WTH3 may be a promising target for breast cancer therapy in the future.

Differential regulation of endothelium behavior by progesterone and medroxyprogesterone acetate

Medroxyprogesterone acetate (MPA) is a synthetic progestin commonly used in hormone replacement therapy (HRT). The aim of this research was to study and compare the effect of progesterone (Pg) and MPA on the regulation of cellular events associated with vascular homeostasis and disease. Platelet adhesion to endothelial cells (ECs), nitric oxide (NO) production, and cell migration were studied using murine ECs in vitro exposed to the progestins. After 7 min of treatment, MPA significantly inhibited NO synthesis with respect to control values; meanwhile, Pg markedly increased vasoactive production. In senile ECs, the stimulatory action of Pg decreases; meanwhile, MPA maintained its ability to inhibit NO synthesis. The presence of RU486 antagonized the action of each steroid. When ECs were preincubated with PD98059 (MAPK inhibitor) or chelerythrine (protein kinase C (PKC) inhibitor) before Pg or MPA treatment, the former totally suppressed the steroid action, but the PKC antagonist did not affect NO production. In the presence of a PI3K inhibitor (LY294002), a partial reduction in Pg effect and a reversal of MPA action were detected. Using indomethacin, the contribution of the cyclooxygenase (COX) pathway was also detected. On platelet adhesion assays, Pg inhibited and MPA stimulated platelet adhesion to ECs. Under inflammatory conditions, Pg prevented platelet adhesion induced by lipopolysaccharide (LPS); meanwhile, MPA potentiated the stimulatory action of LPS. Finally, although both steroids enhanced migration of ECs, MPA exhibited a greater effect. In conclusion, the data presented in this research provide evidence of a differential regulation of vascular function by Pg and MPA.

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.

Non-genomic mechanisms of progesterone action in the brain

Progesterone is a gonadal steroid hormone whose physiological effects extend well beyond the strict confines of reproductive function. In fact, progesterone can have important effects on a variety of tissues, including the bone, the heart and the brain. Mechanistically, progesterone has been thought to exert its effects through the progesterone receptor (PR), a member of the nuclear steroid hormone superfamily, and as such, acts through specific progesterone response elements (PRE) within the promoter region of target genes to regulate transcription of such genes. This has been often described as the “genomic” mechanism of progesterone action. However, just as progesterone has a diverse range of tissue targets, the mechanisms through which progesterone elicits its effects are equally diverse. For example, progesterone can activate alternative receptors, such as membrane-associated PRs (distinct from the classical PR), to elicit the activation of several signaling pathways that in turn, can influence cell function. Here, we review various non-nuclear (i.e., non-genomic) signaling mechanisms that progesterone can recruit to elicit its effects, focusing our discussion primarily on those signaling mechanisms by which progesterone influences cell viability in the brain.

AMP-Activated Protein Kinase α 2 Isoform Suppression in Primary Breast Cancer Alters AMPK Growth Control and Apoptotic Signaling

Adenosine monophosphate-activated protein kinase (AMPK) is a metabolic regulator that promotes energy conservation and restoration when cells are exposed to nutrient stress. Given the high metabolic requirement of cancer cells, AMPK activation has been suggested as a potential preventative and therapeutic target. However, previous findings have shown that AMPK activity is diminished in some cancers. Expression of the 2 catalytic isoforms, AMPKα1 and AMPKα2, was evaluated in primary breast cancer and matched nontumor-adjacent tissue samples using immunohistochemistry. AMPK-dependent growth signaling events were examined in primary human mammary epithelial cells (HMECs) using RNAi to understand the importance of AMPKα2 in normal growth regulation. To test whether AMPKα2 would reinstate growth control and apoptotic mechanisms in breast cancer cells, metabolic stress assays and tumor xenografts were performed in MCF-7 cells, expressing low levels of AMPKα2, with stable transfection of either green fluorescent protein (GFP) or AMPKα2 expression constructs. AMPKα2 was found to be significantly suppressed in breast cancer tissue samples, whereas AMPKα1 was not. In normal HMECs, low glucose stress resulted in AMPK-driven growth inhibition. Interestingly, this response was ablated when AMPKα2 was silenced. Metabolic stress assays in MCF-7 cells indicated that AMPKα2 expression reduced both mTOR signaling and cyclin D1 expression, contributing to G1-phase cell cycle arrest. Cells expressing AMPKα2 underwent apoptosis more readily than GFP control cells. Xenograft studies demonstrated that MCF-7 tumors expressing AMPKα2 display reduced proliferation and increased apoptotic events. Furthermore, AMPKα2 xenografts exhibited diminished cyclin D1 levels along with an increased amount of nuclear p53, thereby implicating the AMPKα2-p53 signaling axis as a mediator of cell apoptosis. Together, these results highlight the significance of reduced AMPK activity contributing to human carcinogenesis and, specifically, the role of AMPKα2 with respect to its control of normal mammary epithelial cell growth and its reduced expression in breast cancer.

Radiation-induced cellular senescence results from a slippage of long-term G2 arrested cells into G1 phase

Diploid cells undergoing senescence and mitotic slippage have been reported in the literature. However, the mechanisms triggering senescence in long-term G2-arrested cells are currently unclear. Previously, we reported that the cell cycle of the human uveal melanoma cell line, 92-1, is suspended for up to 6 d upon exposure to 10 Gy ionizing radiation (IR), followed by senescence. In the current study, we initially distinguished senescence in long-term blocked 92-1 cells from mitotic slippage by confirming the blockage of cells in the G2 phase. We subsequently showed that the genes essential for G2-M transition are prematurely downregulated at both the transcriptional and translational levels. Furthermore, levels of the G1-specific markers, Cyclin D1 and Caveolin-1, were distinctly increased, while S/G2-specific markers, Cyclin B1 and Aurora A, were significantly downregulated. These findings collectively imply that long-term G2-arrested cells undergo senescence via G2 slippage. To our knowledge, this is the first study to report that the cellular process of G2 slippage is the mechanism responsible for senescence of cells under long-term G2 arrest.

Progestogens used in postmenopausal hormone therapy: differences in their pharmacological properties, intracellular actions, and clinical effects

The safety of progestogens as a class has come under increased scrutiny after the publication of data from the Women's Health Initiative trial, particularly with respect to breast cancer and cardiovascular disease risk, despite the fact that only one progestogen, medroxyprogesterone acetate, was used in this study. Inconsistency in nomenclature has also caused confusion between synthetic progestogens, defined here by the term progestin, and natural progesterone. Although all progestogens by definition have progestational activity, they also have a divergent range of other properties that can translate to very different clinical effects. Endometrial protection is the primary reason for prescribing a progestogen concomitantly with postmenopausal estrogen therapy in women with a uterus, but several progestogens are known to have a range of other potentially beneficial effects, for example on the nervous and cardiovascular systems. Because women remain suspicious of the progestogen component of postmenopausal hormone therapy in the light of the Women's Health Initiative trial, practitioners should not ignore the potential benefits to their patients of some progestogens by considering them to be a single pharmacological class. There is a lack of understanding of the differences between progestins and progesterone and between individual progestins differing in their effects on the cardiovascular and nervous systems, the breast, and bone. This review elucidates the differences between the substantial number of individual progestogens employed in postmenopausal hormone therapy, including both progestins and progesterone. We conclude that these differences in chemical structure, metabolism, pharmacokinetics, affinity, potency, and efficacy via steroid receptors, intracellular action, and biological and clinical effects confirm the absence of a class effect of progestogens.

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.

Hormone replacement therapy in the geriatric patient: current state of the evidence and questions for the future. Estrogen, progesterone, testosterone, and thyroid hormone augmentation in geriatric clinical practice: part 1

This article presents an up-to-date review of the literature on hormone augmentation in the elderly to help primary care physicians better evaluate and utilize hormone replacement and optimization strategies to benefit their patients. The scientific literature suggests that hormone supplementation with estrogen, progesterone, testosterone, growth hormone, and thyroid hormone has the potential to improve quality of life and to prevent, or reverse, the many symptoms and conditions associated with aging, including fatigue, depression, weight gain,frailty, osteoporosis, loss of libido, and heart disease. Possible long-term side effects are also considered.

Structural and functional analysis of domains of the progesterone receptor

Steroid hormone receptors are multi-domain proteins composed of conserved well-structured regions, such as ligand (LBD) and DNA binding domains (DBD), plus other naturally unstructured regions including the amino-terminal domain (NTD) and the hinge region between the LBD and DBD. The hinge is more than just a flexible region between the DBD and LBD and is capable of binding co-regulatory proteins and the minor groove of DNA flanking hormone response elements. Because the hinge can directly participate in DNA binding it has also been termed the carboxyl terminal extension (CTE) of the DNA binding domain. The CTE and NTD are dynamic regions of the receptor that can adopt multiple conformations depending on the environment of interacting proteins and DNA. Both regions have important regulatory roles for multiple receptor functions that are related to the ability of the CTE and NTD to form multiple active conformations. This review focuses on studies of the CTE and NTD of progesterone receptor (PR), as well as related work with other steroid/nuclear receptors.

Differential nuclear localisation and promoter occupancy play a role in glucocorticoid receptor ligand-specific transcriptional responses

The glucocorticoid receptor (GR) is a ligand-activated transcription factor for which a number of endogenous and synthetic ligands exist. A key question in steroid receptor biology is how different ligands elicit different maximal transcriptional responses via the same receptor and on the same promoter. This question was addressed quantitatively for the GR, using a panel of agonists, partial agonists and antagonists, on the endogenous GILZ gene in two different human cell lines. It was found that the extent of GR nuclear localization correlated with the efficacy for GILZ transactivation by the GR in U2OS cells. However, in A549 cells there was no significant correlation, with all ligands resulting in similar levels of GR nuclear localization, despite different levels of transcriptional activation of the GILZ gene. Chromatin immunoprecipitation analysis on the other hand, revealed ligand-specific differences in GILZ promoter occupancy in the A549 cells, which correlated with the transcriptional efficacy of the subset of ligands investigated. This suggests that ligand-specific differences in promoter occupancy by activated GR play a major role in discrimination between agonist, partial agonist and antagonist responses on the endogenous GILZ gene in A549 cells, while differences in nuclear localisation of liganded GR play a role in determining the transcriptional outcome in U2OS cells. These cell line-specific differences were not dependent on the amount of GR present, since transient overexpression of GR in U2OS did not alter the relative ligand-selective nuclear localisation. Our results show that there is a relationship between ligand-specific transactivation efficacy, extent of nuclear translocation and recruitment of GR to the promoter. However, the relative contribution of nuclear translocation and GR promoter recruitment to ligand-specific transactivation efficacy is cell-specific.

Molecular mechanisms of steroid receptor-mediated actions by synthetic progestins used in HRT and contraception

Synthetic progestins are used by millions of women as contraceptives and in hormone replacement therapy (HRT), although their molecular mechanisms of action are not well understood. The importance of investigating these mechanisms, as compared to those of progesterone, has been highlighted by clinical evidence showing that medroxyprogesterone acetate (MPA), a first generation progestin, increases the risk of breast cancer and coronary heart disease in HRT users. A diverse range of later generation progestins with varying structures and pharmacological properties is available for therapeutic use and it is becoming clear that different progestins elicit beneficial and adverse effects to different extents. These differences in biological activity are likely to be due to many factors including variations in dose, metabolism, pharmacokinetics, bioavailability, and regulation of, and/or binding, to serum-binding proteins and steroidogenic enzymes. Since the intracellular effects on gene expression and cell signaling of steroids are mediated via intracellular steroid receptors, differential actions via the progesterone and other steroid receptors and their isoforms, are likely to be the major cause of differential intracellular actions of progestins. Since many progestins bind not only to the progesterone receptor, but also to the glucocorticoid, androgen, mineralocorticoid, and possibly the estrogen receptors, it is plausible that synthetic progestins exert therapeutic actions as well as side-effects via some of these receptors. Here we review the molecular mechanisms of intracellular actions of old (MPA, norethisterone, levonorgestrel, gestodene) vs. new (drospirenone, dienogest, trimegestone) generation progestins, via steroid receptors.

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.

Inhibiting the PI3K/Akt pathway reversed progestin resistance in endometrial cancer

Progestin resistance is the main obstacle to successful conservative therapy in young endometrial cancer patients. To investigate the molecular events that lead to progestin resistance and to find a possible way to reverse progestin resistance in endometrial cancer, we established a progestin-resistant Ishikawa cell line by long-term progestin treatment to downregulate progesterone receptor (PR) expression. Both medoxyprogesterone acetate (MPA) and LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, were assayed for their effects on the proliferation of progestin-sensitive and progestin-resistant cancer cells, respectively. The MPA inhibited the PI3K/Akt pathway and suppressed cell proliferation in progestin-sensitive Ishikawa cells, but activated the PI3K/Akt pathway and had no effect on cell proliferation in progestin-resistant Ishikawa cells or HEC-1A cells. Inhibiting the PI3K/Akt pathway by LY294002 upregulated PR expression and diminished cell growth, especially in progestin-resistant endometrial cancer cells. In vivo endometrial cancer xenograft studies in nude mice also showed that inhibiting the PI3K/Akt pathway reversed progestin resistance in endometrial cancer. Our results indicate that activation of the PI3K/Akt pathway by progestin without PR mediation plays an important role in progestin resistance to endometrial cancer cells. In addition, inhibiting the PI3K/Akt pathway might reverse progestin resistance in endometrial cancer.

Steroid signaling activation and intracellular localization of sex steroid receptors

In addition to stimulating gene transcription, sex steroids trigger rapid, non-genomic responses in the extra-nuclear compartment of target cells. These events take place within seconds or minutes after hormone administration and do not require transcriptional activity of sex steroid receptors. Depending on cell systems, activation of extra-nuclear signaling pathways by sex steroids fosters cell cycle progression, prevents apoptosis, leads to epigenetic modifications and increases cell migration through cytoskeleton changes. These findings have raised the question of intracellular localization of sex steroid receptors mediating these responses. During the past years, increasing evidence has shown that classical sex steroid receptors localized in the extra-nuclear compartment or close to membranes of target cells induce these events. The emerging picture is that a process of bidirectional control between signaling activation and sex steroid receptor localization regulates the outcome of hormonal responses in target cells. This mechanism ensures cell cycle progression in estradiol-treated breast cancer cells, and its derangement might occur in progression of human proliferative diseases. These findings will be reviewed here together with unexpected examples of the relationship between sex steroid receptor localization, signaling activation and biological responses in target cells. We apologize to scientists whose reports are not mentioned or extensively discussed owing to space limitations.

Progesterone receptor induces ErbB-2 nuclear translocation to promote breast cancer growth via a novel transcriptional effect: ErbB-2 function as a coactivator of Stat3

Progesterone receptor (PR) and ErbB-2 bidirectional cross talk participates in breast cancer development. Here, we identified a new mechanism of the PR and ErbB-2 interaction involving the PR induction of ErbB-2 nuclear translocation and the assembly of a transcriptional complex in which ErbB-2 acts as a coactivator of Stat3. We also highlighted that the function of ErbB-2 as a Stat3 coactivator drives progestin-induced cyclin D1 promoter activation. Notably, PR is also recruited together with Stat3 and ErbB-2 to the cyclin D1 promoter, unraveling a new and unexpected nonclassical PR genomic mechanism. The assembly of the nuclear Stat3/ErbB-2 transcriptional complex plays a key role in the proliferation of breast tumors with functional PR and ErbB-2. Our findings reveal a novel therapeutic intervention for PR- and ErbB-2-positive breast tumors via the specific blockage of ErbB-2 nuclear translocation.

Enhanced LH action in transgenic female mice expressing hCGbeta-subunit induces pituitary prolactinomas; the role of high progesterone levels

The etiology of pituitary adenomas remains largely unknown, with the exception of involvement of estrogens in the formation of prolactinomas. We have examined the molecular pathogenesis of prolactin-producing pituitary adenomas in transgenic female mice expressing the human choriongonadotropin (hCG) beta-subunit. The LH/CG bioactivity is elevated in the mice, with consequent highly stimulated ovarian progesterone (P(4)) production, in the face of normal estrogen secretion. Curiously, despite normal estrogen levels, large prolactinomas developed in these mice, and we provide here several lines of evidence that the elevated P(4) levels are involved in the growth of these estrogen-dependent tumors. The antiprogestin mifepristone inhibited tumor growth, and combined postgonadectomy estradiol/P(4) treatment was more effective than estrogen alone in inducing tumor growth. Evidence for direct growth-promoting effect of P(4) was obtained from cultures of primary mouse pituitary cells and rat somatomammotroph GH3 cells. The mouse tumors and cultured cells revealed stimulation of the cyclin D1/cyclin-dependent kinase 4/retinoblastoma protein/transcription factor E2F1 pathway in the growth response to P(4). If extrapolated to humans, and given the importance of endogenous P(4) and synthetic progestins in female reproductive functions and their pharmacotherapy, it is relevant to revisit the potential role of these hormones in the origin and growth of prolactinomas.

Leptin upregulates VEGF in breast cancer via canonic and non-canonical signalling pathways and NFkappaB/HIF-1alpha activation

High levels of VEGF and leptin are strongly linked to worse prognosis of breast cancer. Leptin signalling upregulates VEGF in human and mouse mammary tumor cells (MT), but the specific molecular mechanisms are largely unknown. Pharmacologic and genetic approaches were used to dissect the mechanism of leptin regulation of VEGF protein and mRNA in MT (4T1, EMT6 and MMT). A series of VEGF-promoter Luc-reporters (full-length and transcription factor-binding deletions) were transfected into MT to analyze leptin regulation of VEGF transcription. Deletion analysis of VEGF promoter and RNA knockdown shows that HIF-1alpha and NFkappaB are essentials for leptin regulation of VEGF. Leptin activation of HIF-1alpha was mainly linked to canonic (MAPK, PI-3K) and non-canonic (PKC, JNK and p38 MAP) signalling pathways. Leptin non-canonic signalling pathways (JNK, p38 MAP and to less extent PKC) were linked to NFkappaB activation. SP1 was involved in leptin regulation of VEGF in 4T1 cells. AP1 was not involved and AP2 repressed leptin-induced increase of VEGF. Overall, these data suggest that leptin signalling regulates VEGF mainly through HIF-1alpha and NFkappaB. These results delineate a comprehensive mechanism for leptin regulation of VEGF in MT. Disruption of leptin signalling could be used as a novel way to treat breast cancer.

Just when you thought it was safe to go into the membrane: the growing complexities of extra-nuclear progesterone signaling

The diversity of membrane-initiated progesterone actions has made characterization and establishment of its biological importance a complicated endeavor. A new study by Zuo and colleagues shows that progesterone via endogenous membrane progesterone receptor-α acts as a negative regulator of proliferation and epithelial to mesenchymal transition in a breast cancer cell line. These progesterone-mediated actions appear to be regulated through epidermal growth factor receptor and phosphatidylinositol 3-kinase signaling localized in caveolae. Moreover, the study shows expression of membrane progesterone receptor-α in benign and malignant breast cancer tissues. These data bring forth novel concepts with regard to progesterone actions in the breast; however, further work is warranted to fully characterize the physiologic actions of extra-nuclear progesterone signaling in the breast.

An additive interaction between the NFkappaB and estrogen receptor signalling pathways in human endometrial epithelial cells

BACKGROUND

Human embryo implantation is regulated by estradiol (E2), progesterone and locally produced mediators including interleukin-1beta (IL-1beta). Interactions between the estrogen receptor (ER) and NF kappa B (NFkappaB) signalling pathways have been reported in other systems but have not been detailed in human endometrium.

METHODS AND RESULTS

Real-time PCR showed that mRNA for the p65 and p105 NFkappaB subunits is maximally expressed in endometrium from the putative implantation window. Both subunits are localized in the endometrial epithelium throughout the menstrual cycle. Reporter assays for estrogen response element (ERE) activity were used to examine functional interactions between ER and NFkappaB in telomerase immortalized endometrial epithelial cells (TERT-EEC). E2 and IL-1beta treatment of TERT-EECs enhances ERE activity by a NFkappaB and ER dependent mechanism; this effect could be mediated by ERalpha or ERbeta. E2 and IL-1beta also positively interact to increase endogenous gene expression of prostaglandin E synthase and c-myc. This is a gene-dependent action as there is no additive effect on cyclin D1 or progesterone receptor expression.

CONCLUSION

In summary, we have established that NFkappaB signalling proteins are expressed in normal endometrium and report that IL-1beta can enhance the actions of E2 in a cell line derived from healthy endometrium. This mechanism may allow IL-1beta, possibly from the developing embryo, to modulate the function of the endometrial epithelium to promote successful implantation, for example by regulating prostaglandin production. Aberrations in the interaction between the ER and NFkappaB signalling pathways may have a negative impact on implantation contributing to pathologies such as early pregnancy loss and infertility.

Multimodal regulation of E2F1 gene expression by progestins

An analysis of mRNA expression in T47D breast cancer cells treated with the synthetic progestin R5020 revealed a subset of progesterone receptor (PR) target genes that are enriched for E2F binding sites. Following up on this observation, we determined that PR-B acts in both direct and indirect manners to positively upregulate E2F1 expression in T47D cells. The direct effects of PR on E2F1 expression were confirmed by chromatin immunoprecipitation (ChIP) analysis, which indicated that the agonist-bound receptor was recruited to several enhancer elements proximal to the E2F1 transcript. However, we also noted that cycloheximide partially inhibits R5020 induction of E2F1 expression, indicating that the ligand-dependent actions of PR on this gene may involve additional indirect regulatory pathways. In support of this hypothesis, we demonstrated that treatment with R5020 significantly increases both hyperphosphorylation of Rb and recruitment of E2F1 to its own promoter, thus activating a positive feedback loop that further amplifies its transcription. Furthermore, we established that PR-mediated induction of Krüppel-like factor 15 (KLF15), which can bind to GC-rich DNA within the E2F1 promoter, is required for maximal induction of E2F1 expression by progestins. Taken together, these results suggest a new paradigm for multimodal regulation of target gene expression by PR.

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.

Mutational analysis of progesterone receptor functional domains in stable cell lines delineates sets of genes regulated by different mechanisms

Steroid hormone receptors act directly in the nucleus on the chromatin organization and transcriptional activity of several promoters. Furthermore, they have an indirect effect on cytoplasmic signal transduction pathways, including MAPK, impacting ultimately on gene expression. We are interested in distinguishing between the two modes of action of progesterone receptor (PR) on the control of gene expression and cell proliferation. For this, we have stably expressed, in PR-negative breast cancer cells, tagged forms of the PR isoform B mutated at regions involved either in DNA binding (DNA-binding domain) or in its ability to interact with the estrogen receptor and to activate the c-Src/MAPK/Erk/Msk cascade (estrogen receptor-interacting domain). Both mutants impair PR-mediated activation of a well-understood model promoter in response to progestin, as well as hormone-induced cell proliferation. Additional mutants affecting transactivation activity of PR (activation function 2) or a zinc-finger implicated in dimerization (D-box) have also been tested. Microarrays and gene expression experiments on these cell lines define the subsets of hormone-responsive genes regulated by different modes of action of PR isoform B, as well as genes in which the nuclear and nongenomic pathways cooperate. Correlation between CCND1 expression in the different cell lines and their ability to support cell proliferation confirms CCND1 as a key controller gene.