The classical progesterone receptor associates with p42 MAPK and is involved in phosphatidylinositol 3-kinase signaling in Xenopus oocytes

Role of progesterone on dexamethasone-induced alterations in placental vascularization and progesterone receptors in rats†

BACKGROUND

Intrauterine growth restriction (IUGR) is manifested by lower maternal progesterone levels, smaller placental size, and decreased placental vascularity indicated by lower expression of vascular endothelial growth factor (VEGF). Studies showed that progesterone increases angiogenesis and induces VEGF expression in different tissues. Therefore, the aim of the present study is to evaluate the effect of progesterone on placental vascular bed and VEGF expression and the modulation of nuclear and membranous progesterone receptors (PR) in dexamethasone-induced rat IUGR model.

METHODS

Pregnant Sprague-Dawley rats were allocated into four groups and given intraperitoneal injections of either saline, dexamethasone, dexamethasone, and progesterone or progesterone. Injections started on gestation day (DG) 15 and lasted until the days of euthanization (19 and 21 DG). Enzyme-linked immunosorbent assay was used to evaluate plasma progesterone levels. Real-time PCR and western blotting were used to evaluate gene and protein expressions of VEGF, and PR in labyrinth and basal placental zones. Immunohistochemistry was used to locate VEGF and different PRs in placental cells. Immunofluorescence was used to monitor the expression of blood vessel marker (αSMA).

RESULTS

Dexamethasone decreased the vascular bed fraction and the expression of VEGF in both placental zones. Progesterone co-treatment with dexamethasone prevented this reduction. Nuclear and membrane PRs showed tissue-specific expression in different placental zones and responded differently to both dexamethasone and progesterone.

CONCLUSIONS

Progesterone treatment improves the outcomes in IUGR pregnancy. Progesterone alleviated DEX-induced IUGR probably by promoting placental VEGF and angiogenesis.

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.

Y It Matters—Sex Differences in Fetal Lung Development

Within this review, sex-specific differences in alveolar epithelial functions are discussed with special focus on preterm infants and the respiratory disorders associated with premature birth. First, a short overview about fetal lung development, the challenges the lung faces during perinatal lung transition to air breathing and respiratory distress in preterm infants is given. Next, clinical observations concerning sex-specific differences in pulmonary morbidity of human preterm infants are noted. The second part discusses potential sex-specific causes of pulmonary complications, including pulmonary steroid receptors and local lung steroid metabolism. With regard to pulmonary steroid metabolism, it is important to highlight which steroidogenic enzymes are expressed at which stage during fetal lung development. Thereafter, we review the knowledge concerning sex-specific aspects of lung growth and maturation. Special focus is given to alveolar epithelial Na+ transport as a driver of perinatal lung transition and the sex differences that were noted in this process.

Mifepristone Directly Disrupts Mouse Embryonic Development in Terms of Cellular Proliferation and Maturation In Vitro

Mifepristone (RU-486), a synthetic steroid with potent antiprogestogen and anti-glucocorticoid properties, has been widely used in clinical practice. Its effect on the endometrium, ovary, and fallopian tube has been well reported in many human and animal studies. However, its direct impact on post-implantation embryos remains underexplored. Additionally, some women choose to keep their pregnancy after mifepristone treatment fails. Thus, the potential risk remains controversial. Hence, this study investigated the direct effects of mifepristone on the development of mice blastocysts in vitro in terms of implantation and post-implantation. We detected the level of progesterone (P4) associated with ovulation in vivo. The presence of progesterone receptors (PRs) in blastocysts and post-implantation embryos was also evaluated. Cultured embryos were treated directly with mifepristone. We further examined embryonic implantation and post-implantation of blastocysts in vitro to evaluate the direct effects of mifepristone on embryos by the assessment of embryonic outgrowth and differential cell staining. In the oviduct lumen, the P4 level dramatically increased at 48 h and slightly decreased at 72 and 96 h following ovulation. PR was expressed in blastocysts not only in the preimplantation stage but also in the early post-implantation period. In the evaluation of developmental stages, mifepristone significantly reduced the successful ratio of developing into the late egg cylinder and the early somite stage. In addition, it further decreased the cell number of the embryos' inner cell mass and trophectoderm. We herein provide evidence that mifepristone affects blastocyst viability directly and inhibits post-implantation embryo development in vitro. Furthermore, our data reveal a potential risk of fetus fatality and developmental problems when pregnancies are continued after mifepristone treatment fails.

Genome-Wide Network of lncRNA-mRNA During Ovine Oocyte Development From Germinal Vesicle to Metaphase II in vitro

Long non-coding RNA (lncRNA) is involved in many biological processes, and it has been closely investigated. However, research into the role of lncRNA in ovine ovarian development is scant and poorly understood, particularly in relation to the molecular mechanisms of ovine oocyte maturation. In the current study, RNA sequencing was performed with germinal vesicle (GV) and in vitro matured metaphase II (MII) stage oocytes, isolated from ewes. Through the use of bioinformatic analysis, abundant candidate lncRNAs in stage-specific ovine oocytes were identified, and their trans- and cis-regulatory effects were deeply dissected using computational prediction software. Functional enrichment analysis of these lncRNAs revealed that they were involved in the regulation of many key signaling pathways during ovine oocyte development, which was reflected by their targeted genes. From this study, multiple lncRNA-mRNA networks were presumed to be involved in key signaling pathways regarding ovine oocyte maturation and meiotic resumption. In particular, one novel lncRNA (MSTRG.17927) appeared to mediate the regulation of phosphatidylinositol 3-kinase signaling (PI3K) signaling during ovine oocyte maturation. Therefore, this research offers novel insights into the molecular mechanisms underlying ovine oocyte meiotic maturation regulated by lncRNA-mRNA networks from a genome-wide perspective.

Managing the Oocyte Meiotic Arrest-Lessons from Frogs and Jellyfish

During oocyte development, meiosis arrests in prophase of the first division for a remarkably prolonged period firstly during oocyte growth, and then when awaiting the appropriate hormonal signals for egg release. This prophase arrest is finally unlocked when locally produced maturation initiation hormones (MIHs) trigger entry into M-phase. Here, we assess the current knowledge of the successive cellular and molecular mechanisms responsible for keeping meiotic progression on hold. We focus on two model organisms, the amphibian Xenopus laevis, and the hydrozoan jellyfish Clytia hemisphaerica. Conserved mechanisms govern the initial meiotic programme of the oocyte prior to oocyte growth and also, much later, the onset of mitotic divisions, via activation of two key kinase systems: Cdk1-Cyclin B/Gwl (MPF) for M-phase activation and Mos-MAPkinase to orchestrate polar body formation and cytostatic (CSF) arrest. In contrast, maintenance of the prophase state of the fully-grown oocyte is assured by highly specific mechanisms, reflecting enormous variation between species in MIHs, MIH receptors and their immediate downstream signalling response. Convergence of multiple signalling pathway components to promote MPF activation in some oocytes, including Xenopus, is likely a heritage of the complex evolutionary history of spawning regulation, but also helps ensure a robust and reliable mechanism for gamete production.

Seasonal variation in equine follicular fluid proteome

BACKGROUND

Proteomic studies of follicular fluid (FF) exist for several species, including the horse; however, the seasonal influence on FF proteome has not been explored in livestock. The application of high-throughput proteomics of FF in horse has the potential to identify seasonal variations of proteins involved in follicle and oocyte growth.

METHODS

This study (i) profiles the proteomes of equine FF collected from dominant growing follicles during the spring anovulatory season (SAN), and spring (SOV), summer (SUM), and fall (FOV) ovulatory seasons; and (ii) identifies season-dependent regulatory networks and associated key proteins.

RESULTS

Regardless of season, a total of 90 proteins were identified in FF, corresponding to 63, 72, 69, and 78 proteins detected in the SAN, SOV, SUM, and FOV seasons, respectively. Fifty-two proteins were common to all seasons, a total of 13 were unique to either season, and 25 were shared between two seasons or more. Protein-to-protein interaction (PPI) analysis indicated the likely critical roles of plasminogen in the SAN season, the prothrombin/plasminogen combination in SUM, and plasminogen/complement C3 in both SOV and FOV seasons. The apolipoprotein A1 appeared crucial in all seasons. The present findings show that FF proteome of SUM differs from other seasons, with FF having high fluidity (low viscosity).

CONCLUSIONS

The balance between the FF contents in prothrombin, plasminogen, and coagulation factor XII proteins favoring FF fluidity may be crucial at the peak of the ovulatory season (SUM) and may explain the reported lower incidence of hemorrhagic anovulatory follicles during the SUM season.

The curious case of premature luteinization

PURPOSE

Premature luteinization (PL) affects 12.3-46.7% of fresh in vitro fertilization cycles, and there is accumulating evidence confirming its negative effect on success rates. However, despite its clinical significance, PL is poorly understood and defined. This narrative review aims to provide a fresh look at the phenomenon of PL by summarizing the existing evidence and re-evaluating fundamental issues.

METHODS

A thorough electronic search was conducted covering the period from 1978 until January 2018 in PubMed, Embase, and Medline databases, and references of relevant studies were cross-checked. Meeting proceedings of the European Society of Human Reproduction and Embryology and the American Society for Reproductive Medicine were also hand searched.

RESULTS

In the curious case of PL, one should go back to the beginning and re-consider every step of the way. The pathogenesis, definition, measurement methods, clinical implications, and management strategies are discussed in detail, highlighting controversies and offering "food for thought" for future directions.

CONCLUSIONS

Authors need to speak the same language when studying PL in order to facilitate comparisons. The terminology, progesterone cut-off, measurement methods and days of measurement should be standardized and globally accepted; otherwise, there can be no scientific dialog. Future research should focus on specific patient profiles that may require a tailored approach. Progesterone measurements throughout the follicular phase possibly depict the progesterone exposure better than an isolated measurement on the day of hCG. Adequately powered randomized controlled trials should confirm which the best prevention and management plan of PL is, before introducing any strategy into clinical practice.

Progesterone treatment shows greater protection in brain vs. retina in a rat model of middle cerebral artery occlusion: Progesterone receptor levels may play an important role

BACKGROUND/OBJECTIVE

To determine whether inflammation increases in retina as it does in brain following middle cerebral artery occlusion (MCAO), and whether the neurosteroid progesterone, shown to have protective effects in both retina and brain after MCAO, reduces inflammation in retina as well as brain.

METHODS

MCAO rats treated systemically with progesterone or vehicle were compared with shams. Protein levels of cytosolic NF-κB, nuclear NF-κB, phosphorylated NF-κB, IL-6, TNF-α, CD11b, progesterone receptor A and B, and pregnane X receptor were assessed in retinas and brains at 24 and 48 h using western blots.

RESULTS

Following MCAO, significant increases were observed in the following inflammatory markers: pNF-κB and CD11b at 24 h in both brain and retina, nuclear NF-κB at 24 h in brain and 48 h in retina, and TNF-α at 24 h in brain.Progesterone treatment in MCAO animals significantly attenuated levels of the following markers in brain: pNF-κB, nuclear NF-κB, IL-6, TNF-α, and CD11b, with significantly increased levels of cytosolic NF-κB. Retinas from progesterone-treated animals showed significantly reduced levels of nuclear NF-κB and IL-6 and increased levels of cytosolic NF-κB, with a trend for reduction in other markers. Post-MCAO, progesterone receptors A and B were upregulated in brain and downregulated in retina.

CONCLUSION

Inflammatory markers increased in both brain and retina after MCAO, with greater increases observed in brain. Progesterone treatment reduced inflammation, with more dramatic reductions observed in brain than retina. This differential effect may be due to differences in the response of progesterone receptors in brain and retina after injury.

Progestin and Nuclear Progestin Receptor Are Essential for Upregulation of Metalloproteinase in Zebrafish Preovulatory Follicles

Ovulation requires proteinases to promote the rupture of ovarian follicles. However, the identity of these proteinases remains unclear. In our previous studies using RNA-seq analysis of differential expressed genes, we found significant down-regulation of five metalloproteinases: adam8b (a disintegrin and metalloproteinase domain 8b), adamts8a (a disintegrin and metalloproteinase with thrombospondin motif 8a), adamts9, mmp2 (matrix metalloproteinase 2), and mmp9 in the nuclear progestin receptor knockout (pgr ^-/-) zebrafish that have failed to ovulate. We hypothesize that these metalloproteinases are responsible for ovulation and are regulated by progestin and Pgr. In this study, we first determined the expression of these five metalloproteinases and adamts1 in preovulatory follicles at different times within the spawning cycle in pgr ^-/- and wildtype (wt) zebrafish and under varying hormonal treatments. We found that transcripts of adam8b, adamts1, adamts9, and mmp9 increased drastically in the preovulatory follicular cells of wt female zebrafish, while changes of adamts8a and mmp2 were not significant. This increase of adam8b, adamts9, and mmp9 was significantly reduced in pgr ^-/-, whereas expression of adamts1 was not affected in pgr ^-/- zebrafish. Among upregulated metalloproteinases, adamts9 mRNA was found to be expressed specifically in follicular cells. Strong immunostaining of Adamts9 protein was observed in the follicular cells of wt fish, and this expression was reduced drastically in pgr ^-/-. Interestingly, about an hour prior to the increase of metalloproteinases in wt fish, both Pgr transcript and protein increased transiently in preovulatory follicular cells. The results from in vitro experiments showed that adamts9 expression markedly increased in a dose, time and Pgr-dependent manner when preovulatory follicles were exposed to a progestin, 17α,20β-dihydroxy-4-pregnen-3-one (DHP). Taken together, our results provide the first evidence that upregulation of adamts9 occurs specifically in preovulatory follicular cells of zebrafish prior to ovulation. Progestin and its receptor (Pgr) are essential for the upregulation of metalloproteinases.

Relative importance of phosphatidylinositol-3 kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK3/1) signaling during maturational steroid-induced meiotic G2-M1 transition in zebrafish oocytes

Participation and relative importance of phosphatidylinositol-3 kinase (PI3K) and mitogen-activated protein kinase (MAPK) signalling, either alone or in combination, have been investigated during 17α,20β-dihydroxy-4-pregnen-3-one (DHP)-induced meiotic G2-M1 transition in denuded zebrafish oocyte. Results demonstrate that concomitant with rapid phosphorylation (activation) of Akt (Ser473) and MAPK (ERK1/2) at as early as 15 min of incubation, DHP stimulation promotes enhanced an GVBD response and histone H1 kinase activation between 1 and 5 h in full-grown oocytes in vitro. While p-Akt reaches its peak at 60 to 90 min and undergoes downregulation to the basal level by 240 min, ERK1/2 phosphorylation (activation) increases gradually until 120 min and remains high thereafter. Although, priming with MEK1/2 inhibitor U0126 is without effect, PI3K inhibitors, wortmannin or LY294002, delay the GVBD response significantly (P < 0.001) until 3 h but not at 5 h of incubation. Interestingly, blocking PI3K and MEK function together could abrogate steroid-induced oocyte maturation at all time points tested. While DHP stimulation promotes phospho-PKA catalytic (p-PKAc) dephosphorylation (inactivation) between 30-120 min of incubation, simultaneous inhibition of PI3K and MEK1/2 kinases abrogates DHP action. Conversely, elevated intra-oocyte cAMP, through priming with either adenylyl cyclase (AC) activator forskolin (FK) or dibutyryl cAMP (db-cAMP), abrogates steroid-induced Akt and ERK1/2 phosphorylation. Taken together, these results suggest that DHP-induced Akt and ERK activation precedes the onset of meiosis (GVBD response) in a cAMP-sensitive manner and PI3K/Akt and MEK/MAPK pathways together have a pivotal influence in the downregulation of PKA and resumption of meiotic maturation in zebrafish oocytes in vitro.

Progesterone-Mediated Non-Classical Signaling

Progesterone is essential for pregnancy maintenance and menstrual cycle regulation. Hormone action has been primarily ascribed to the well-characterized classical signaling pathway involving ligand binding, activation of nuclear progesterone receptors (PRs), and subsequent activation of genes containing progesterone response elements (PREs). Recent studies have revealed progesterone actions via non-classical signaling pathways, often mediated by non-genomic signaling. Progesterone signaling, in conjunction with growth factor signaling, impacts on the function of growth factors and regulates important physiological actions such as cell growth and remodeling, as well as apoptosis. This review focuses on non-classical progesterone signaling pathways, both including and excluding PR, and highlights how research in this area will provide a better understanding of progesterone actions and may inform novel therapeutic strategies.

Conserved insulin signaling in the regulation of oocyte growth, development, and maturation

Insulin signaling regulates various aspects of physiology, such as glucose homeostasis and aging, and is a key determinant of female reproduction in metazoans. That insulin signaling is crucial for female reproductive health is clear from clinical data linking hyperinsulinemic and hypoinsulinemic condition with certain types of ovarian dysfunction, such as altered steroidogenesis, polycystic ovary syndrome, and infertility. Thus, understanding the signaling mechanisms that underlie the control of insulin-mediated ovarian development is important for the accurate diagnosis of and intervention for female infertility. Studies of invertebrate and vertebrate model systems have revealed the molecular determinants that transduce insulin signaling as well as which biological processes are regulated by the insulin-signaling pathway. The molecular determinants of the insulin-signaling pathway, from the insulin receptor to its downstream signaling components, are structurally and functionally conserved across evolution, from worms to mammals-yet, physiological differences in signaling still exist. Insulin signaling acts cooperatively with gonadotropins in mammals and lower vertebrates to mediate various aspects of ovarian development, mainly owing to evolution of the endocrine system in vertebrates. In contrast, insulin signaling in Drosophila and Caenorhabditis elegans directly regulates oocyte growth and maturation. In this review, we compare and contrast insulin-mediated regulation of ovarian functions in mammals, lower vertebrates, C. elegans, and Drosophila, and highlight conserved signaling pathways and regulatory mechanisms in general while illustrating insulin's unique role in specific reproductive processes.

Physiology, production and action of progesterone

INTRODUCTION

The aim of this article is to review the physiology of progesterone and focus on its physiological actions on tissues such as endometrium, uterus, mammary gland, cardiovascular system, central nervous system and bones. In the last decades, the interest of researchers has focused on the role of progesterone in genomic and non-genomic receptor mechanisms.

MATERIALS AND METHODS

We searched PubMed up to December 2014 for publications on progesterone/steroidogenesis.

RESULTS AND CONCLUSIONS

A better understanding of the biological genomic and non-genomic receptor mechanisms could enable us in the near future to obtain a more comprehensive knowledge of the safety and efficacy of this agent during hormone replacement therapy (natural progesterone), in vitro fertilization (water-soluble subcutaneous progesterone), in traumatic brain injury, Alzheimer's disease and diabetic neuropathy, even though further clinical studies are needed to prove its usefulness.

Releasing prophase arrest in zebrafish oocyte: synergism between maturational steroid and Igf1

Binding of 17β-estradiol (E2) to novel G-protein coupled receptor, Gper1, promotes intra-oocyte adenylyl cyclase activity and transactivates epidermal growth factor receptor to ensure prophase-I arrest. Although involvement of either membrane progestin receptor (mPR) or Igf system has been implicated in regulation of meiosis resumption, possibility of concurrent activation and potential synergism between 17α,20β-dihydroxy-4-pregnen-3-one (DHP)- and Igf-mediated signalling cascades in alleviating E2 inhibition of oocyte maturation (OM) has not been investigated. Here using zebrafish (Danio rerio) defolliculated oocytes, we examined the effect of DHP and Igf1, either alone or in combination, in presence or absence of E2, on OM in vitro. While priming of denuded oocytes with E2 blocked spontaneous maturation, co-treatment with DHP (3 nM) and Igf1 (10 nM), but not alone, reversed E2 inhibition and promoted a robust increase in germinal vesicle breakdown (GVBD). Although stimulation with either Igf1 or DHP promoted Akt phosphorylation, pharmacological inhibition of PI3K/Akt signalling prevented Igf1-induced GVBD but delayed DHP action till 4-5 h of incubation. Moreover, high intra-oocyte cAMP attenuates both DHP and Igf1-mediated OM and co-stimulation with DHP and Igf1 could effectively reverse E2 action on PKA phosphorylation. Interestingly, data from in vivo studies reveal that heightened expression of igf1, igf3 transcripts in intact follicles corresponded well with elevated phosphorylation of Igf1r and Akt, mPRa immunoreactivity, PKA inhibition and accelerated GVBD response just prior to ovulation. This indicates potential synergism between maturational steroid and Igf1 which might have physiological relevance in overcoming E2 inhibition of meiosis resumption in zebrafish oocytes.

New insight on a possible mechanism of progestogens in terms of breast cancer risk

OBJECTIVES

Progestogens influence mammary gland development and probably breast cancer tumorigenesis by regulating a broad spectrum of physiological processes. We investigated receptor membrane-initiated actions of progestogens in MCF-7 breast cancer cells overexpressing progesterone receptor membrane component 1 (PGRMC1).

DESIGN

MCF-7 cells were stably transfected with PGRMC1 expression plasmid (MCF-7/PGRMC1-3HA) and overexpression of PGRMC1 was verified by immune fluorescent analysis and Western blot. To test the effects of progestogens on cell proliferation, MCF-7 and MCF-7/PGRMC1-3HA cells were stimulated with a membrane-impermeable progesterone: BSA-fluorescein-isothiocyanate conjugate (P4-BSA-FITC), unconjugated progesterone (P4), medroxyprogesterone acetate (MPA), norethisterone (NET) and drospirenone (DRSP). Furthermore, reverse phase protein technology was applied to identify modified downstream signaling.

RESULTS

Progesterone did not elicit any proliferative effect on MCF-7/PGRMC1-3HA cells. By contrast, P4-BSA-FITC, DRSP, MPA and NET significantly triggered proliferation of MCF-7/PGRMC1-3HA cells, the effect being more pronounced for NET. Almost no effect of progestogens on proliferation was observed in MCF-7 cells. In MCF-7/PGRMC1-3HA cells, expression of Erk1/2 was significantly reduced by 40% compared to MCF-7 cells.

CONCLUSIONS

Our data indicate that PGRMC1 mediates a progestogen-dependent proliferative signal in MCF-7 cells. Of significant interest is that progesterone and synthetic progestins that are used for hormone therapy are different in their proliferative effects on MCF-7 and MCF-7/PGRMC1-3HA cells. Progesterone appears to act neutrally, whereas MPA, NET and DRSP trigger proliferation and thus might increase breast cancer risk. The data presented are very important in terms of the positive results of progestogens and breast cancer risk in clinical studies so far.

Genomic and non-genomic actions of progestogens in the breast

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

Heterocyclic aminoparthenolide derivatives modulate G(2)-M cell cycle progression during Xenopus oocyte maturation

Aminoparthenolide derivatives have been prepared by reaction of parthenolide with various heterocyclic amines to afford corresponding Michael addition products. These novel compounds were evaluated for their modulatory effects on Xenopus oocyte maturation. Two compounds, 6e and 6f, were identified that promote G2-M cell cycle progression.

A computational analysis of non-genomic plasma membrane progestin binding proteins: signaling through ion channel-linked cell surface receptors

A number of plasma membrane progestin receptors linked to non-genomic events have been identified. These include: (1) α1-subunit of the Na(+)/K(+)-ATPase (ATP1A1), (2) progestin binding PAQR proteins, (3) membrane progestin receptor alpha (mPRα), (4) progesterone receptor MAPR proteins and (5) the association of nuclear receptor (PRB) with the plasma membrane. This study compares: the pore-lining regions (ion channels), transmembrane (TM) helices, caveolin binding (CB) motifs and leucine-rich repeats (LRRs) of putative progesterone receptors. ATP1A1 contains 10 TM helices (TM-2, 4, 5, 6 and 8 are pores) and 4 CB motifs; whereas PAQR5, PAQR6, PAQR7, PAQRB8 and fish mPRα each contain 8 TM helices (TM-3 is a pore) and 2-4 CB motifs. MAPR proteins contain a single TM helix but lack pore-lining regions and CB motifs. PRB contains one or more TM helices in the steroid binding region, one of which is a pore. ATP1A1, PAQR5/7/8, mPRα, and MAPR-1 contain highly conserved leucine-rich repeats (LRR, common to plant membrane proteins) that are ligand binding sites for ouabain-like steroids associated with LRR kinases. LRR domains are within or overlap TM helices predicted to be ion channels (pore-lining regions), with the variable LRR sequence either at the C-terminus (PAQR and MAPR-1) or within an external loop (ATP1A1). Since ouabain-like steroids are produced by animal cells, our findings suggest that ATP1A1, PAQR5/7/8 and mPRα represent ion channel-linked receptors that respond physiologically to ouabain-like steroids (not progestin) similar to those known to regulate developmental and defense-related processes in plants.

Revisiting the roles of progesterone and allopregnanolone in the nervous system: resurgence of the progesterone receptors

Progesterone is commonly considered as a female reproductive hormone and is well-known for its role in pregnancy. It is less well appreciated that progesterone and its metabolite allopregnanolone are also male hormones, as they are produced in both sexes by the adrenal glands. In addition, they are synthesized within the nervous system. Progesterone and allopregnanolone are associated with adaptation to stress, and increased production of progesterone within the brain may be part of the response of neural cells to injury. Progesterone receptors (PR) are widely distributed throughout the brain, but their study has been mainly limited to the hypothalamus and reproductive functions, and the extra-hypothalamic receptors have been neglected. This lack of information about brain functions of PR is unexpected, as the protective and trophic effects of progesterone are much investigated, and as the therapeutic potential of progesterone as a neuroprotective and promyelinating agent is currently being assessed in clinical trials. The little attention devoted to the brain functions of PR may relate to the widely accepted assumption that non-reproductive actions of progesterone may be mainly mediated by allopregnanolone, which does not bind to PR, but acts as a potent positive modulator of γ-aminobutyric acid type A (GABA(A) receptors. The aim of this review is to critically discuss effects of progesterone on the nervous system via PR, and of allopregnanolone via its modulation of GABA(A) receptors, with main focus on the brain.

Naturally occurring steroids in Xenopus oocyte during meiotic maturation. Unexpected presence and role of steroid sulfates

In the ovary, oocytes are surrounded by follicle cells and arrested in prophase of meiosis I. Although steroidogenic activity of follicle cells is involved in oogenesis regulation, clear qualitative and quantitative data about the steroid content of follicles are missing. We measured steroid levels of Xenopus oocytes and follicles by gas chromatography-mass spectrometry. We show that dehydroepiandrosterone sulfate is the main steroid present in oocytes. Lower levels of free steroids are also detected, e.g., androgens, whereas progesterone is almost undetectable. We propose that sulfatation is a protective mechanism against local variations of active steroids that could be deleterious for follicle-enclosed oocytes. Steroid levels were measured after LH stimulation, responsible for the release by follicle cells of a steroid signal triggering oocyte meiosis resumption. Oocyte levels of androgens rise slowly during meiosis re-entry whereas progesterone increases abruptly to micromolar concentration, therefore representing the main physiological mediator of meiosis resumption in Xenopus oocyte.

Nongenomic actions of aldosterone and progesterone revisited

After almost 30 years of research, the existence of nongenomic steroid actions is no longer disputed. Yet, there is still a debate on the nature of receptors involved, and answers to the inherent questions are important for translational activities. In the case of aldosterone, the existence of receptors different from the classic mineralocorticoid receptors (MR) had been postulated 25 years ago as the pharmacology of about 50% of rapid actions of aldosterone reported so far is incompatible with MR involvement (insensitivity to classic MR antagonists). Candidates proposed as alternatives to MR were protein kinase C, sodium-potassium ATPase or aberrant forms of MR, none of which supported convincing evidence to represent 'the aldosterone membrane receptor'. Early in 2011, data on GPR30 showed its involvement in rapid aldosterone action, and major pharmacological aspects of this action are compatible with the landmark deviations from MR pharmacology mentioned above. GPR30, therefore, may be a receptor candidate for nongenomic aldosterone action. Similarly, a variety of promising candidates mediating rapid progesterone action has been described, including progesterone receptor membrane component 1 (PGRMC1) which seems to be associated with tumor proliferation, and membrane progesterone receptor (mPR) originally identified in fish with potential linkage to reproductive processes. So far, no candidate was unanimously convincing. In 2010, two independent groups reported that CatSper, a calcium channel, is a strong receptor candidate for the rapid action of progesterone on sperm fertilization. With these novel receptors cloned, translational activities ultimately leading to new drugs for cardiovascular protection (in the case of aldosterone) or fertilization benefits (for progesterone) are much more promising.

Role of phosphorylation in progesterone receptor signaling and specificity

Progesterone receptors (PR), in concert with peptide growth factor-initiated signaling pathways, initiate massive expansion of the epithelial cell compartment associated with the process of alveologenesis in the developing mammary gland. PR-dependent signaling events also contribute to inappropriate proliferation observed in breast cancer. Notably, PR-B isoform-specific cross talk with growth factor-driven pathways is required for the proliferative actions of progesterone. Indeed, PRs act as heavily phosphorylated transcription factor "sensors" for mitogenic protein kinases that are often elevated and/or constitutively activated in invasive breast cancers. In addition, phospho-PR-target genes frequently include the components of mitogenic signaling pathways, revealing a mechanism for feed-forward signaling that confers increased responsiveness of, PR +mammary epithelial cells to these same mitogenic stimuli. Understanding the mechanisms and isoform selectivity of PR/kinase interactions may yield further insight into targeting altered signaling networks in breast and other hormonally responsive cancers (i.e. lung, uterine and ovarian) in the clinic. This review focuses on PR phosphorylation by mitogenic protein kinases and mechanisms of PR-target gene selection that lead to increased cell proliferation.

ck2-dependent phosphorylation of progesterone receptors (PR) on Ser81 regulates PR-B isoform-specific target gene expression in breast cancer cells

Progesterone receptors (PR) are critical mediators of mammary gland development and contribute to breast cancer progression. Progestin-induced rapid activation of cytoplasmic protein kinases leads to selective regulation of growth-promoting genes by phospho-PR species. Herein, we show that phosphorylation of PR Ser81 is ck2 dependent and progestin regulated in intact cells but also occurs in the absence of PR ligands when cells enter the G(1)/S phase of the cell cycle. T47D breast cancer cells stably expressing a PR-B mutant receptor that cannot be phosphorylated at Ser79/81 (S79/81A) formed fewer soft agar colonies. Regulation of selected genes by PR-B, but not PR-A, also required Ser79/81 phosphorylation for basal and/or progestin-regulated (BIRC3, HSD11β2, and HbEGF) expression. Additionally, wild-type (wt) PR-B, but not S79/81A mutant PR, was robustly recruited to a progesterone response element (PRE)-containing transcriptional enhancer region of BIRC3; abundant ck2 also associated with this region in cells expressing wt but not S79/81A PR. We conclude that phospho-Ser81 PR provides a platform for ck2 recruitment and regulation of selected PR-B target genes. Understanding how ligand-independent PRs function in the context of high levels of kinase activities characteristic of breast cancer is critical to understanding the basis of tumor-specific changes in gene expression and will speed the development of highly selective treatments.

Minireview: role of kinases and chromatin remodeling in progesterone signaling to chromatin

Steroid hormones regulate gene expression by interaction of their receptors with hormone-responsive elements on DNA or with other transcription factors, but they can also activate cytoplasmic signaling cascades. Rapid activation of Erk by progestins via an interaction of the progesterone receptor (PR) with the estrogen receptor is critical for transcriptional activation of the mouse mammary tumor virus (MMTV) promoter and other progesterone target genes. Erk activation leads to the phosphorylation of PR, activation of mitogen- and stress-activated protein kinase 1, and the recruitment of a complex of the three activated proteins and of P300/CBP-associated factor (PCAF) to a single nucleosome, resulting in the phosphoacetylation of histone H3 and the displacement of heterochromatin protein 1γ. Hormone-dependent gene expression requires ATP-dependent chromatin remodeling complexes. Two switch/sucrose nonfermentable-like complexes, Brahma-related gene 1-associated factor (BAF) and polybromo-BAF are present in breast cancer cells, but only BAF is recruited to the MMTV promoter and cooperates with PCAF during activation of hormone-responsive promoters. PCAF acetylates histone H3 at K14, an epigenetic mark recognized by BAF subunits, thus anchoring the complex to chromatin. BAF catalyzes localized displacement of histones H2A and H2B, facilitating access of nuclear factor 1 and additional PR complexes to the hidden hormone-responsive elements on the MMTV promoter. The linker histone H1 is a structural component of chromatin generally regarded as a general repressor of transcription. However, it contributes to a better regulation of the MMTV promoter by favoring a more homogeneous nucleosome positioning, thus reducing basal transcription and actually enhancing hormone induced transcription. During transcriptional activation, H1 is phosphorylated and displaced from the promoter. The kinase cyclin-dependent kinase 2 is activated after progesterone treatment and could catalyze progesterone-induced phosphorylation of histone H1 by chromatin remodeling complexes. The initial steps of gene induction by progestins involve changes in the chromatin organization of target promoters that require the activation of several kinase signaling pathways initiated by membrane anchored PR. Because these pathways also respond to other external signals, they serve to integrate the hormonal response in the global context of the cellular environment.

Simple, realistic models of complex biological processes: positive feedback and bistability in a cell fate switch and a cell cycle oscillator

Here we review some of our work over the last decade on Xenopus oocyte maturation, a cell fate switch, and the Xenopus embryonic cell cycle, a highly dynamical process. Our approach has been to start with wiring diagrams for the regulatory networks that underpin the processes; carry out quantitative experiments to describe the response functions for individual legs of the networks; and then construct simple analytical models based on chemical kinetic theory and the graphical rate-balance formalism. These studies support the view that the all-or-none, irreversible nature of oocyte maturation arises from a saddle-node bifurcation in the regulatory system that drives the process, and that the clock-like oscillations of the embryo are built upon a hysteretic switch with two saddle-node bifurcations. We believe that this type of reductionistic systems biology holds great promise for understanding complicated biochemical processes in simpler terms.

Estrogen and progesterone receptors: from molecular structures to clinical targets

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

Nongenomic steroid-triggered oocyte maturation: of mice and frogs

Luteinizing hormone (LH) mediates many important processes in ovarian follicles, including cumulus cell expansion, changes in gap junction expression and activity, sterol and steroid production, and the release of paracrine signaling molecules. All of these functions work together to trigger oocyte maturation (meiotic progression) and subsequent ovulation. Many laboratories are interested in better understanding both the extra-oocyte follicular processes that trigger oocyte maturation, as well as the intra-oocyte molecules and signals that regulate meiosis. Multiple model systems have been used to study LH-effects in the ovary, including fish, frogs, mice, rats, pigs, and primates. Here we provide a brief summary of oocyte maturation, focusing primarily on steroid-triggered meiotic progression in frogs and mice. Furthermore, we present new studies that implicate classical steroid receptors rather than alternative non-classical membrane steroid receptors as the primary regulators of steroid-mediated oocyte maturation in both of these model systems.

Epiregulin can effectively mature isolated cumulus-oocyte complexes, but fails as a substitute for the hCG/epidermal growth factor stimulus on cultured follicles

Epiregulin mediates LH ovulatory effects in vitro. This study evaluated the use of epiregulin as an alternative to hCG/epidermal growth factor (EGF) stimulus upon cultured ovarian follicles in contrast to isolated cumulus-oocyte complexes (COCs). Pre-antral mouse ovarian follicles were cultured for 12 days and final maturation was induced by administration of 0.65 nM EGF or 100 nM epiregulin without or with 1.2 IU/ml hCG. Results showed that both EGF or epiregulin as sole stimulators are poor inducers of mucification/expansion of cumulus cells and oocyte meiotic reinitiation in follicle-enclosed COCs (25+/-17 and 22+/-16% GVBD respectively; versus 97+/-4 and 90+/-15% GVBD by control hCG/EGF and hCG/epiregulin respectively; mean+/-S.D). Furthermore, EGF or epiregulin did not induce follicle luteinisation: progesterone production was marginally increased and oestradiol was incompletely shut down. Supposing that the sub-normal progesterone secretion was a potential cause for incomplete meiosis in this model, effectiveness of progesterone supplementation and addition of a progesterone receptor inhibitor (RU486) were evaluated on meiotic resumption. Progesterone was not found to be a major regulator of meiosis in this mouse model. Epiregulin induced meiosis more effectively in COCs isolated from cultured preovulatory follicles in a secondary culture well. In conclusion, epiregulin has similar effects as EGF upon fully grown follicles. Used as a sole stimulator of periovulatory events in intact cultured follicles, both are poor inducers of follicle luteinisation and oocyte maturation. By contrast, epiregulin is as efficient as hCG/EGF, when used as meiotic stimulator for COCs isolated from the follicular environment (mural granulosa and theca cells; and conditioned medium).

Progesterone potentiates calcium release through IP3 receptors by an Akt-mediated mechanism in hippocampal neurons

Progesterone (P4) is a steroid hormone that plays multiple roles in the central nervous system (CNS) including promoting neuroprotection. However, the precise mechanisms involved in its neuroprotective effects are still unknown. Given that the regulation of the intracellular calcium (Ca(2+)) concentration is critical for cell survival, we determined if inositol 1, 4, 5-trisphosphate receptors (IP(3)Rs) are relevant targets of P4. Using primary hippocampal neurons, we tested the hypothesis that P4 controls the gain of IP3R-mediated intracellular Ca(2+) signaling in neurons and characterized the subcellular distribution and phosphorylation of potential signaling intermediates involved in P4s actions. Our results reveal that P4 treatment altered the intensity and distribution of IP3R immunoreactivity and induced the nuclear translocation of phosphorylated Akt. Further, P4 potentiated IP(3)R-mediated intracellular Ca(2+) responses. These results suggest a potential involvement of P4 in particular and of steroid hormone signaling pathways in general in the control of intracellular Ca(2+) signaling and its related functions.

Possible involvement of phosphatidylinositol 3-kinase, but not protein kinase B or glycogen synthase kinase 3beta, in progesterone-induced oocyte maturation in the Japanese brown frog, Rana japonica

It is known that amphibian oocytes undergo maturation through the formation and activation of maturation-promoting factor (MPF) in response to stimulation by the maturation-inducing hormone progesterone; however, the signal transduction pathway that links the hormonal stimulation on the oocyte surface to the activation of MPF in the oocyte cytoplasm remains a mystery. The aim of this study was to investigate whether the signal transduction mediated by phosphatidylinositol 3-kinase (PI3K), protein kinase B (PKB), and glycogen synthase kinase 3beta (GSK3beta) is involved in progesterone-induced oocyte maturation in the Japanese brown frog, Rana japonica. Inhibitors of PI3K, wortmannin and LY294002, inhibited progesterone-stimulated germinal vesicle breakdown (GVBD) only when the oocytes were treated at the initial phase of maturation, suggesting that PI3K is involved in the progesterone-induced maturation of Rana oocytes. However, we also obtained results suggesting that PKB and GSK3beta are not involved in Rana oocyte maturation. A constitutively active PKB expressed in the oocytes failed to induce GVBD in the absence of progesterone despite its high level of kinase activity. A Myc-tagged PKB expressed in the oocytes (used to monitor endogenous PKB activity) was not activated in the process of progesterone-induced oocyte maturation. Overexpression of GSK3beta, which is reported to retard the progress of Xenopus oocyte maturation, had no effect on Rana oocyte maturation. On the basis of these results, we propose that PI3K is involved in the initiation of Rana oocyte maturation, but that neither PKB nor GSK3beta is a component of the PI3K signal transduction pathway.

Candidates for membrane progestin receptors--past approaches and future challenges

Progestins have a broad range of functions in reproductive biology. Many rapid nongenomic actions of progestins have been identified, including induction of oocyte maturation, modulation of reproductive signaling in the brain, rapid activation of breast cancer cell signaling, induction of the acrosomal reaction and hypermotility in mammalian sperm. Currently, there are three receptor candidates for mediating rapid progestin actions: (1) membrane progestin receptors (mPRs); (2) progestin receptor membrane components (PGRMCs); and (3) nuclear progestin receptors (nPRs). The recently-described mPR family of proteins has seven integral transmembrane domains and mediates signaling via G-protein coupled pathways. The PGRMCs have a single transmembrane with putative Src homology domains for potential activation of second messengers. The classical nPRs, in addition to having well defined transcriptional activity, can also mediate rapid activation of intracellular signaling pathways. However, details of the mechanisms by which these three classes of progestin receptors mediate rapid intracellular signaling and their subcellular localization remain unclear. In addition, mPRs, nPRs and PGRMCs exhibit overlapping expression and functions in multiple tissues, implying potential interactions during oocyte maturation, parturition, and breast cancer signaling in individual cells. However, the overwhelming majority of studies to date have focused on the functions of one of these groups of receptors in isolation. This review will summarize recent findings on the three major progestin receptor candidates, emphasizing the different approaches used, some experimental pitfalls, and current controversies. We will also review evidence for the involvement of mPRs and nPRs in one of the most well-characterized nongenomic steroid actions in basal vertebrates, oocyte maturation, and conclude by suggesting some future areas of research. Clarification of the controversies surrounding the identities and localization of membrane progestin receptors may help direct future research that could advance our understanding of rapid actions of steroids.

Non-genomic progesterone actions in female reproduction

BACKGROUND

The steroid hormone progesterone is indispensable for mammalian procreation by controlling key female reproductive events that range from ovulation to implantation, maintenance of pregnancy and breast development. In addition to activating the progesterone receptors (PRs)-B and -A, members of the superfamily of ligand-dependent transcription factors, progesterone also elicits a variety of rapid signalling events independently of transcriptional or genomic regulation. This review covers our current knowledge on the mechanisms and relevance of non-genomic progesterone signalling in female reproduction.

METHODS

PubMed was searched up to August 2008 for papers on progesterone actions in ovary/breast/endometrium/myometrium/brain, focusing primarily on non-genomic signalling mechanisms.

RESULTS

Convergence and intertwining of rapid non-genomic events and the slower transcriptional actions critically determine the functional response to progesterone in the female reproductive system in a cell-type- and environment-specific manner. Several putative progesterone-binding moieties have been implicated in rapid signalling events, including the 'classical' PR and its variants, progesterone receptor membrane component 1, and the novel family of membrane progestin receptors. Progesterone and its metabolites have also been implicated in the allosteric regulation of several unrelated receptors, such as gamma-aminobutyric acid type A, oxytocin and sigma(1) receptors.

CONCLUSIONS

Identification of the mechanisms and receptors that relay rapid progesterone signalling is an area of research fraught with difficulties and controversy. More in-depth characterization of the putative receptors is required before the non-genomic progesterone pathway in normal and pathological reproductive function can be targeted for pharmacological intervention.

Heterologous expression of human mPRalpha, mPRbeta and mPRgamma in yeast confirms their ability to function as membrane progesterone receptors

The nuclear progesterone receptor (nPR) mediates many of the physiological effects of progesterone by regulating the expression of genes, however, progesterone also exerts non-transcriptional (non-genomic) effects that have been proposed to rely on a receptor that is distinct from nPR. Several members of the progestin and AdipoQ-Receptor (PAQR) family were recently identified as potential mediators of these non-genomic effects. Membranes from cells expressing these proteins, called mPRalpha, mPRbeta and mPRgamma, were shown to specifically bind progesterone and have G-protein coupled receptor (GPCR) characteristics, although other studies dispute these findings. To clarify the role of these mPRs in non-genomic progesterone signaling, we established an assay for PAQR functional evaluation using heterologous expression in Saccharomyces cerevisiae. Using this assay, we demonstrate unequivocally that mPRalpha, mPRbeta and mPRgamma can sense and respond to progesterone with EC(50) values that are physiologically relevant. Agonist profiles also show that mPRalpha, mPRbeta and mPRgamma are activated by ligands, such as 17alpha-hydroxyprogesterone, that are known to activate non-genomic pathways but not nPR. These results strongly suggest that these receptors may indeed function as the long-sought-after membrane progesterone receptors. Additionally, we show that two uncharacterized PAQRs, PAQR6 and PAQR9, are also capable of responding to progesterone. These mPR-like PAQRs have been renamed as mPRdelta (PAQR6) and mPRvarepsilon (PAQR9). Additional characterization of mPRgamma and mPRalpha indicates that their progesterone-dependent signaling in yeast does not require heterotrimeric G-proteins, thus calling into question the characterization of the mPRs as a novel class of G-protein coupled receptor.

Dexamethasone-induced expression of endothelial mitogen-activated protein kinase phosphatase-1 involves activation of the transcription factors activator protein-1 and 3',5'-cyclic adenosine 5'-monophosphate response element-binding protein and the generation of reactive oxygen species

We have recently identified the MAPK phosphatase (MKP)-1 as a novel mediator of the antiinflammatory properties of glucocorticoids (dexamethasone) in the human endothelium. However, nothing is as yet known about the signaling pathways responsible for the up-regulation of MKP-1 by dexamethasone in endothelial cells. Knowledge of the molecular basis of this new alternative way of glucocorticoid action could facilitate the identification of new antiinflammatory drug targets. Thus, the aim of our study was to elucidate the underlying molecular mechanisms. Using Western blot analysis, we found that dexamethasone rapidly activates ERK, c-jun N-terminal kinase (JNK), and p38 MAPK in human umbilical vein endothelial cells. By applying the kinase inhibitors PD98059 (MAPK kinase-1) and SP600125 (JNK), ERK and JNK were shown to be crucial for the induction of MKP-1. Using EMSA and a decoy oligonucleotide approach, the transcription factors activator protein-1 (activated by ERK and JNK) and cAMP response element-binding protein (activated by ERK) were found to be involved in the up-regulation of MKP-1 by dexamethasone. Interestingly, dexamethasone induces the generation of reactive oxygen species (measured by dihydrofluorescein assay), which participate in the signaling process by triggering JNK activation. Our work elucidates a novel alternative mechanism for transducing antiinflammatory effects of glucocorticoids in the human endothelium. Thus, our study adds valuable information to the efforts made to find new antiinflammatory principles utilized by glucocorticoids. This might help to gain new therapeutic options to limit glucocorticoid side effects and to overcome resistance.

PI3-kinase and mitogen-activated protein kinase in cumulus cells mediate EGF-induced meiotic resumption of porcine oocyte

Previous studies have shown that epidermal growth factor (EGF) has the ability to promote in vitro cultured porcine oocyte maturation. However, little is known about the detailed downstream events in EGF-induced meiotic resumption. We designed this study to determine the relationship of EGF, EGFR, phosphatidylinositol 3-kinase (PI3-kinase), MAPK, and germinal vesicle breakdown (GVBD) during oocyte maturation. Our results showed that GVBD in cumulus-enclosed oocytes (CEOs) but not in denuded oocytes (DOs) was induced by EGF in a dose-dependent manner, which indicated that cumulus cells but not oocyte itself were the main target for EGF-induced meiotic resumption. Furthermore, we found that MAPK in cumulus cells rather than in oocyte was activated immediately after EGF administration. To explore whether EGF exerts its functions through MAPK pathway, the activities of EGF receptor (EGFR) and MAPK were inhibited by employing AG1478 and U0126, respectively. Inhibition of MAPK blocked EGF-induced GVBD, whereas inhibition of EGFR prevented MAPK activation. Both AG1478 and U0126 could lead to the failure of EGF-induced GVBD singly. Notably, we found that LY294002, a specific inhibitor of PI3-kinase, effectively inhibited EGF-induced MAPK activation as well as subsequent oocyte meiotic resumption and this inhibition could not be reversed by adding additional EGF. Thus, PI3-kinase-induced MAPK activation in cumulus cells mediated EGF-induced meiotic resumption in porcine CEOs. Together, this study provides evidences demonstrating a linear relationship of EGF/EGFR, PI3-kinase, MAPK and GVBD and presents a relatively definitive mechanism of EGF-induced meiotic resumption of porcine oocyte.

Classical androgen receptors in non-classical sites in the brain

Androgen receptors are expressed in many different neuronal populations in the central nervous system where they often act as transcription factors in the cell nucleus. However, recent studies have detected androgen receptor immunoreactivity in neuronal and glial processes of the adult rat neocortex, hippocampal formation, and amygdala as well as in the telencephalon of eastern fence and green anole lizards. This review discusses previously published findings on extranuclear androgen receptors, as well as new experimental results that begin to establish a possible functional role for androgen receptors in axons within cortical regions. Electron microscopic studies have revealed that androgen receptor immunoreactive processes in the rat brain correspond to axons, dendrites and glial processes. New results show that lesions of the dorsal CA1 region by local administration of ibotenic acid reduce the density of androgen receptor immunoreactive axons in the cerebral cortex and the amygdala, suggesting that these axons may originate in the hippocampus. Androgen receptor immunoreactivity in axons is also decreased by the intracerebroventricular administration of colchicine, suggesting that androgen receptor protein is transported from the perikaryon to the axons by fast axonal transport. Androgen receptors in axons located in the cerebral cortex and amygdala and originating in the hippocampus may play an important role in the rapid behavioral effects of androgens.

A role for GPRx, a novel GPR3/6/12-related G-protein coupled receptor, in the maintenance of meiotic arrest in Xenopus laevis oocytes

Progesterone-induced Xenopus laevis oocyte maturation is mediated via a plasma membrane-bound receptor and does not require gene transcription. Evidence from several species suggests that the relevant progesterone receptor is a G-protein coupled receptor (GPCR) and that a second receptor-GPR3 and/or GPR12 in mammals-tonically opposes the progesterone receptor. We have cloned a novel X. laevis GPCR, GPRx, which may play a similar role to GPR3/GPR12 in amphibians and fishes. GPRx is related to but distinct from GPR3, GPR6, and GPR12; GPRx orthologs are present in Xenopus tropicalis and Danio rerio, but apparently not in birds or mammals. X. laevis GPRx is mainly expressed in brain, ovary, and testis. The GPRx mRNA increases during oogenesis, persists during oocyte maturation and early embryogenesis, and then falls after the midblastula transition. Microinjection of GPRx mRNA increases the concentration of cAMP in oocytes and causes the oocytes to fail to respond to progesterone, and this block is reversed by co-injecting GPRx with morpholino oligonucleotides. Morpholino injections did not cause spontaneous maturation of oocytes, but did accelerate progesterone-induced maturation. Thus, GPRx contributes to the maintenance of G2-arrest in immature X. laevis oocytes.

A beta-catenin-independent dorsalization pathway activated by Axin/JNK signaling and antagonized by aida

Axin is a scaffold protein that controls multiple important pathways, including the canonical Wnt pathway and JNK signaling. Here we have identified an Axin-interacting protein, Aida, which blocks Axin-mediated JNK activation by disrupting Axin homodimerization. During investigation of in vivo functions of Axin/JNK signaling and aida in development, it was found that Axin, besides ventralizing activity by facilitating beta-catenin degradation, possesses a dorsalizing activity that is mediated by Axin-induced JNK activation. This dorsalizing activity is repressed when aida is overexpressed in zebrafish embryos. Whereas Aida-MO injection leads to dorsalized embryos, JNK-MO and MKK4-MO can ventralize embryos. The anti-dorsalization activity of aida is conferred by its ability to block Axin-mediated JNK activity. We further demonstrate that dorsoventral patterning regulated by Axin/JNK signaling is independent of maternal or zygotic Wnt signaling. We have thus identified a dorsalization pathway that is exerted by Axin/JNK signaling and its inhibitor Aida during vertebrate embryogenesis.

Mechanisms Regulating Oocyte Meiotic Resumption: Roles of Mitogen-Activated Protein Kinase

Oocyte meiotic maturation is one of the important physiological requirements for species survival. However, little is known about the detailed events occurring during this process. A number of studies have demonstrated that MAPK plays a pivotal role in the regulation of meiotic cell cycle progression in oocytes, but controversial findings have been reported in both lower vertebrates and mammals. In this review, we summarized the roles of MAPK cascade and related signal pathways in oocyte meiotic reinitiation in both lower vertebrates and mammals. We also tried to reconcile the paradoxical results and highlight the new findings concerning the function of MAPK in both oocytes and the surrounding follicular somatic cells. The unresolved questions and future research directions regarding the role of MAPK in meiotic resumption are addressed.

Membrane-initiated effects of progesterone on calcium dependent signaling and activation of VEGF gene expression in retinal glial cells

Neurosteroids, such as progesterone, influence central nervous system development and function by regulating a broad spectrum of physiological processes. Here, we investigated membrane-initiated actions of progesterone in the retina and identified the membrane-associated progesterone receptor component 1 (PGRMC1). We found PGRMC1 expressed mainly in retinal Muller glia (RMG) and retinal pigment epithelium, and localized uniquely to microsomal and plasma membrane fractions. In RMG, membrane-impermeable progesterone conjugate induced calcium influx and subsequent phosphatidylinositol 3-kinase-mediated phosphorylation of PKC and ERK-1/2. Induction by progesterone also led to PKC-dependent activation of VEGF gene expression and protein synthesis, suggesting a contribution of membrane-initiated hormone effects to VEGF induced neovascularization within retina.

Relationship of estrogen and progesterone receptors to clinical outcome in metastatic endometrial carcinoma: A Gynecologic Oncology Group Study

INTRODUCTION

The goal of this study was to explore the relationship between the expression of hormone receptors in metastatic endometrial tumors and clinical response to daily tamoxifen citrate and intermittent weekly medroxyprogesterone acetate.

STUDY DESIGN

Patients with measurable recurrent or advanced endometrial cancer were enrolled on a clinical trial, Gynecologic Oncology Group Study 119. A pretreatment tumor biopsy was obtained and subjected to immunohistochemical analyses. Estrogen receptor-alpha (ER-alpha) and progesterone receptor (PR) were assessed on frozen tissues, and PR isoforms A and B were detected on fixed tissues. The receptors were scored using a semi-quantitative HSCORE, with a cut off greater than 75 considered positive.

RESULTS

Of the 60 eligible patients, 45 had evaluable tissues for all receptors. For ER, 40% of the cases were positive; for PR, 45% were positive. The sub-cellular distribution of PRA was exclusively nuclear, and 16% of the tumors demonstrated positive staining. PRB was nuclear and cytoplasmic, with 22% of the tumors staining for nuclear PRB and 36% of the tumors staining for cytoplasmic PRB. ER and PR from frozen tissues and PRA and cytoplasmic PRB from fixed tissues significantly decreased with increasing tumor grade. The co-expression of ER-alpha with PR from the frozen tissues (r=0.68, p<0.001) and PRA (r=0.58, p<0.001) from the fixed tissues was statistically significant. The ER HSCORE was related to both response and overall survival; there was no statistically significant correlation of PR with clinical response in this small number of patients.

CONCLUSION

ER-alpha measured in metastatic endometrial carcinoma tissue prior to hormonal therapy was statistically significantly related to clinical response to daily tamoxifen and intermittent medroxyprogesterone acetate.

Plasma membrane destination of the classical Xenopus laevis progesterone receptor accelerates progesterone-induced oocyte maturation

Xenopus laevis oocyte maturation is induced by the steroid hormone progesterone through a non-genomic mechanism initiated at the cell membrane. Recently, two Xenopus oocyte progesterone receptors have been cloned; one is the classical progesterone receptor (xPR-1) involved in genomic actions and the other a putative seven-transmembrane-G-protein-couple receptor. Both receptors are postulated to be mediating the steroid-induced maturation process in the frog oocyte. In this study, we tested the hypothesis that the classical progesterone receptor, associated to the oocyte plasma membrane, is participating in the reinitiation of the cell cycle. Addition of a myristoilation and palmytoilation signal at the amino terminus of xPR-1 (mp xPR-1), increased the amount of receptor associated to the oocyte plasma membrane and most importantly, significantly potentiated progesterone-induced oocyte maturation sensitivity. These findings suggest that the classical xPR-1, located at the plasma membrane, is mediating through a non-genomic mechanism, the reinitiation of the meiotic cell cycle in the X. laevis oocyte.

Novel perspectives for progesterone in hormone replacement therapy, with special reference to the nervous system

The utility and safety of postmenopausal hormone replacement therapy has recently been put into question by large clinical trials. Their outcome has been extensively commented upon, but discussions have mainly been limited to the effects of estrogens. In fact, progestagens are generally only considered with respect to their usefulness in preventing estrogen stimulation of uterine hyperplasia and malignancy. In addition, various risks have been attributed to progestagens and their omission from hormone replacement therapy has been considered, but this may underestimate their potential benefits and therapeutic promises. A major reason for the controversial reputation of progestagens is that they are generally considered as a single class. Moreover, the term progesterone is often used as a generic one for the different types of both natural and synthetic progestagens. This is not appropriate because natural progesterone has properties very distinct from the synthetic progestins. Within the nervous system, the neuroprotective and promyelinating effects of progesterone are promising, not only for preventing but also for reversing age-dependent changes and dysfunctions. There is indeed strong evidence that the aging nervous system remains at least to some extent sensitive to these beneficial effects of progesterone. The actions of progesterone in peripheral target tissues including breast, blood vessels, and bones are less well understood, but there is evidence for the beneficial effects of progesterone. The variety of signaling mechanisms of progesterone offers exciting possibilities for the development of more selective, efficient, and safe progestagens. The recognition that progesterone is synthesized by neurons and glial cells requires a reevaluation of hormonal aging.