The further redefining of steroid-mediated signaling

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

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

Sex Hormones and Inflammation Role in Oral Cancer Progression: A Molecular and Biological Point of View

Oral cancers have been proven to arise from precursors lesions and to be related to risk behaviour such as alcohol consumption and smoke. However, the present paper focuses on the role of chronic inflammation, related to chronical oral infections and/or altered immune responses occurring during dysimmune and autoimmune diseases, in the oral cancerogenesis. Particularly, oral candidiasis and periodontal diseases introduce a vicious circle of nonhealing and perpetuation of the inflammatory processes, thus leading toward cancer occurrence via local and systemic inflammatory modulators and via genetic and epigenetic factors.

Extracellular Vesicles: Recent Developments in Technology and Perspectives for Cancer Liquid Biopsy

Extracellular micro- and nanoscale membrane vesicles produced by different cells progressively attract the attention of the scientific community. They function as mediators of intercellular communication and transport genetic material and signaling molecules between the cells. In the context of keeping homeostasis, the extracellular vesicles contribute to the regulation of various systemic and local processes. Vesicles released by the tumor and activated stromal cells exhibit multiple functions including support of tumor growth, preparation of the pre-metastatic niches, and immune suppression. Considerable progress has been made regarding the criteria of classification of the vesicles according to their origin, content, and function: Exosomes, microvesicles, also referred to as microparticles or ectosomes, and large oncosomes were defined as actively released vesicles. Additionally, apoptotic bodies represented by a highly heterogeneous population of particles produced during apoptosis, the programmed cell death, should be considered. Because the majority of isolation techniques do not allow the separation of different types of vesicles, a joined term "extracellular vesicles" (EVs) was recommended by the ISEV community for the definition of vesicles isolated from either the cell culture supernatants or the body fluids. Because EV content reflects the content of the cell of origin, multiple studies on EVs from body fluids in the context of cancer diagnosis, prediction, and prognosis were performed, actively supporting their high potential as a biomarker source. Here, we review the leading achievements in EV analysis from body fluids, defined as EV-based liquid biopsy, and provide an overview of the main EV constituents: EV surface proteins, intravesicular soluble proteins, EV RNA including mRNA and miRNA, and EV DNA as potential biomarkers. Furthermore, we discuss recent developments in technology for quantitative EV analysis in the clinical setting and future perspectives toward miniaturized high-precision liquid biopsy approaches.

Understanding the role of steroids in typical and atypical brain development: Advantages of using a "brain in a dish" approach

Steroids have an important role in growth, development, sexual differentiation and reproduction. All four classes of steroids, androgens, oestrogens, progestogens and glucocorticoids, have varying effects on the brain. Androgens and oestrogens are involved in the sexual differentiation of the brain, and also influence cognition. Progestogens such as progesterone and its metabolites have been shown to be involved in neuroprotection, although their protective effects are timing-dependent. Glucocorticoids are linked with stress and memory performance, also in a dose- and time-dependent manner. Importantly, dysfunction in steroid function has been implicated in the pathogenesis of disease. Moreover, regulating steroid-signalling has been suggested as potential therapeutic avenue for the treatment of a number of neurodevelopmental, psychiatric and neurodegenerative disorders. Therefore, clarifying the role of steroids in typical and atypical brain function is essential for understanding typical brain functions, as well as determining their potential use for pharmacological intervention in the atypical brain. However, the majority of studies have thus far have been conducted using animal models, with limited work using native human tissue or cells. Here, we review the effect of steroids in the typical and atypical brain, focusing on the cellular, molecular functions of these molecules determined from animal models, and the therapeutic potential as highlighted by human studies. We further discuss the promise of human-induced pluripotent stem cells, including advantages of using three-dimensional neuronal cultures (organoids) in high-throughput screens, in accelerating our understanding of the role of steroids in the typical brain, and also with respect to their therapeutic value in the understanding and treatment of the atypical brain.

Protein analysis by Mach-Zehnder interferometers with a hybrid plasmonic waveguide with nano-slots

Optical biosensing devices for the affinity analysis of molecular binding events could offer significant advantages over current analytical methods. However, most of those excited with a single optical mode are "blind" to the conformational change of bound molecules. We succeeded in designing Mach-Zehnder interferometers (MZI) with a hybrid plasmonic (HP) waveguide with nano-slots. By addressing the structure with dual polarizations, the optogeometrical properties (density and thickness) of protein layers have been determined without ambiguity. Differences in the hybrid mode dispersion between the transverse electric (TE) and transverse magnetic (TM) modes separately allow the determination of the thickness and the density at all stages during the molecular interaction. Moreover, nano-slots can be equated with an effective optical capacitance resulting in strong field confinement and low propagation loss. A proof of concept is conducted by analyzing the conformational change of HepV, a recombinant fragment of collagen V, during complicated molecular interaction. Instead of wavelength interrogation, a cost-effective method with output intensity variation at particular wavelengths due to "resonance phenomena" was employed to monitor the biological event.

Sex dimorphic regulation of osteoprogenitor progesterone in bone stromal cells

Increasing peak bone mass is a promising strategy to prevent osteoporosis. A mouse model of global progesterone receptor (PR) ablation showed increased bone mass through a sex-dependent mechanism. Cre-Lox recombination was used to generate a mouse model of osteoprogenitor-specific PR inactivation, which recapitulated the high bone mass phenotype seen in the PR global knockout mouse mode. In this work, we employed RNA sequencing analysis to evaluate sex-independent and sex-dependent differences in gene transcription of osteoprogenitors of wild-type and PR conditional knockout mice. PR deletion caused marked sex hormone-dependent changes in gene transcription in male mice as compared to wild-type controls. These transcriptional differences revealed dysregulation in pathways involving immunomodulation, osteoclasts, bone anabolism, extracellular matrix interaction and matrix interaction. These results identified many potential mechanisms that may explain our observed high bone mass phenotype with sex differences when PR was selectively deleted in the MSCs.

Sex-Dependent, Osteoblast Stage-Specific Effects of Progesterone Receptor on Bone Acquisition

The role of the progesterone receptor (PR) in the regulation of sexual dimorphism in bone has yet to be determined. Here we utilized genetic fate mapping and Western blotting to demonstrate age-dependent PR expression in the mouse femoral metaphysis and diaphysis. To define sex-dependent and osteoblast stage-specific effects of PR on bone acquisition, we selectively deleted PR at different stages of osteoblast differentiation. We found that when Prx1-Cre mice were crossed with PR floxed mice to generate a mesenchymal stem cell (MSC) conditional KO model (Prx1; PRcKO), the mutant mice developed greater trabecular bone volume with higher mineral apposition rate and bone formation. This may be explained by increased number of MSCs and greater osteogenic potential, particularly in males. Age-related trabecular bone loss was similar between the Prx1; PRcKO mice and their WT littermates in both sexes. Hormone deficiency during the period of rapid bone growth induced rapid trabecular bone loss in both the WT and the Prx1; PRcKO mice in both sexes. No differences in trabecular bone mass was observed when PR was deleted in mature osteoblasts using osteocalcin-Cre (Bglap-Cre). Also, there were no differences in cortical bone mass in all three PRcKO mice. In conclusion, PR inactivation in early osteoprogenitor cells but not in mature osteoblasts influenced trabecular bone accrual in a sex-dependent manner. PR deletion in osteoblast lineage cells did not affect cortical bone mass. © 2017 American Society for Bone and Mineral Research.

Understanding the Inguinal Sinus in Sheep (Ovis aries)-Morphology, Secretion, and Expression of Progesterone, Estrogens, and Prolactin Receptors

Post-parturient behavior of mammalian females is essential for early parent–offspring contact. After delivery, lambs need to ingest colostrum for obtaining the related immunological protection, and early interactions between the mother and the lamb are crucial. Despite visual and auditory cues, olfactory cues are decisive in lamb orientation to the mammary gland. In sheep, the inguinal sinus is located bilaterally near the mammary gland as a skin pouch (IGS) that presents a gland that secretes a strong-smelling wax. Sheep IGS gland functions have many aspects under evaluation. The objective of the present study was to evaluate sheep IGS gland functional aspects and mRNA transcription and the protein expression of several hormone receptors, such as progesterone receptor (PGR), estrogen receptor 1 (ESR1), and 2 (ESR2) and prolactin receptor (PRLR) present. In addition, another aim was to achieve information about IGS ultrastructure and chemical compounds produced in this gland. All hormone receptors evaluated show expression in IGS during the estrous cycle (follicular/luteal phases), pregnancy, and the post-partum period. IGS secretion is rich in triterpenoids that totally differ from the surrounding skin. They might be essential substances for the development of an olfactory preference of newborns to their mothers.

Mycologic Endocrinology

The interactions of fungi and chemical messenger molecules, hormones or pheromones, are addressed in this chapter. These interactions include mammalian fungal pathogens, also plant pathogens, or non-pathogenic fungi, which can result in functional responses in receptor- or non-receptor-mediated fashions. Endogenous ligands in the fungi have been demonstrated to be important for mating in a number of systems. Mammalian hormones have been demonstrated to have stimulatory or inhibitory effects on growth for organisms such as Candida albicans, Paracoccidioides brasiliensis, Saccharomyces cerevisiae, Rhizopus nigricans, Aspergillus fumigatus, Coccidioides, and dermatophytic fungi. A number of fungi have been shown to have specific binding proteins for corticosteroid, estrogen and progesterone that are stereo-specific and high affinity. In some instances, the interactions of a mammalian hormone with the organism, in vivo, affects pathogenesis. Genome expression profiles of C. albicans in the presence of estradiol or progesterone, and S. cerevisiae with progesterone, indicate major up-regulation of various drug resistance pumps, like CDR1, and CDR2, can affect antifungal susceptibility. Azole antifungal interactions occur with fungal hormone binding proteins. Azoles also can block mammalian steroidogenesis. The finding of interactions of mammalian hormones with fungi and subsequent functional responses by the fungi, suggest that hormonal interactions with fungal systems has been conserved throughout evolution and have an important role in fungal pathogenesis, as well as in the overall biology of the organisms.

Vitamin D—update for the pediatric rheumatologists

Vitamin D, upon its discovery one century ago, was classified as a vitamin. This classification still greatly affects our perception about its biological role. 1,25(OH)2D (now known as the D hormone) is a pleiotropic steroid hormone that has multiple biologic effects. It is integral to the regulation of calcium homeostasis and bone turnover as well as having anti-proliferative, pro-differentiation, anti-bacterial, immunomodulatory and anti-inflammatory properties within the body in various cells and tissues. Vitamin D (cholecalciferol) should be considered a nutritional substrate that must be ingested or synthesized in sufficient amounts for the further synthesis of the very important regulatory steroid hormone (D hormone), especially in patients with pediatric rheumatic diseases (PRD). Vitamin D insufficiency or deficiency was shown to be pandemic and associated with numerous chronic inflammatory and malignant diseases and even with increased risk of mortality. Several studies have demonstrated that a high percentage of children with pediatric rheumatic diseases (PRD-e.g., JIA, jSLE) have a vitamin D deficiency or insufficiency which might correlate with disease outcome and flares. Glucocorticoids used to treat disease may have a regulatory effect on vitamin D metabolism which can additionally aggravate bone turnover in PRD. An effort to define the optimal serum 25(OH)D concentrations for healthy children and adults was launched in 2010 but as of now there are no guidelines about supplementation in PRD. In this review we have tried to summarize the strong evidence now suggesting that as the knowledge of the optimal approach to diagnosis and treatment PRD has evolved, there is also an emerging need for vitamin D supplementation as an adjunct to regular disease treatment. So in accordance with new vitamin D recommendations, we recommend that a child with rheumatic disease, especially if treated with steroids, needs at least 2-3 time higher doses of vitamin D than the dose recommended for age (approximately 2000 UI/day). Vitamin D supplementation has become an appealing and important adjunct treatment option in PRD.

Hippocampal Pruning as a New Theory of Schizophrenia Etiopathogenesis

Pruning in neurons has been suggested to be strongly involved in Schizophrenia's (SKZ) etiopathogenesis in recent biological, imaging, and genetic studies. We investigated the impact of protein-coding genes known to be involved in pruning, collected by a systematic literature research, in shaping the risk for SKZ in a case-control sample of 9,490 subjects (Psychiatric Genomics Consortium). Moreover, their modifications through evolution (humans, chimpanzees, and rats) and subcellular localization (as indicative of their biological function) were also investigated. We also performed a biological pathways (Gene Ontology) analysis. Genetics analyses found four genes (DLG1, NOS1, THBS4, and FADS1) and 17 pathways strongly involved in pruning and SKZ in previous literature findings to be significantly associated with the sample under analysis. The analysis of the subcellular localization found that secreted genes, and so regulatory ones, are the least conserved through evolution and also the most associated with SKZ. Their cell line and regional brain expression analysis found that their areas of primary expression are neuropil and the hippocampus, respectively. At the best of our knowledge, for the first time, we were able to describe the SKZ neurodevelopmental hypothesis starting from a single biological process. We can also hypothesize how alterations in pruning fine regulation and orchestration, strongly related with the evolutionary newest (and so more sensitive) secreted proteins, may be of particular relevance in the hippocampus. This early alteration may lead to a mis-structuration of neural connectivity, resulting in the different brain alteration that characterizes SKZ patients.

Morphological aspects and expression of estrogen and progesterone receptors in the interdigital sinus in cyclic ewes

Many species that belong to Artiodactyls order show an interdigital sinus (IS), as it occurs in sheep, in all four extremities. These are considered to be scent glands responsible for sexual communication having strong attractiveness to mature males at the peak of the breeding season. The aim of this study was to evaluate, in IS in cyclic ewes, the microscopic and ultrastructure (scanning and transmission electron microscopy) anatomy, secretion composition, and mRNA and protein expression of estrogen receptors a and b and progesterone receptors. Glandular sebaceous structures occupy a superficial area of the pouch. The other glands present in the IS show a coiled tubular structure and tall and polyhedral secretory cells with irregular luminal surface resulting from the secretory process. Protein and mRNA gene transcription studies were performed to determine the presence of ER (a and b) and P4r in IS. At the follicular phase, IS cell populations analyzed using flow cytometry expressed higher levels of ERb compared with ERa (P<0.05), whereas no difference was observed between them in the luteal phase. The IS amount of secretion was the highest in the follicular phase compared with luteal phase (P<0.05) or pregnancy (P<0.001).To the best of our knowledge, for the first time, the presence of ER (a and b) within the IS was demonstrated. As estrogen action is mediated by specific receptors in target cells, the presence of these receptors in IS might be needed to trigger signaling pathways involved in conspecific chemical (sexual) communication attributed to this area.

Specificity out of clutter: a hypothetical role of G protein-coupled receptors in the non-genomic effect of steroids

The non-genomic effect has been considered to underlie the rapid action of steroids. This signaling is initiated at the plasma membrane-level and does not directly influence gene expression. Recent studies have provided detailed information on their downstream pathways, but less is known about the nature of correlated membrane-bound receptors. Here, we propose that binding of steroids to a consensus motif, namely CRAC, of G protein-coupled receptors (GPCRs) shifts the agonist-binding state of receptors and accounts for this effect to a certain extent. The interaction between steroids and GPCRs is specific, while the identities of the GPCRs involved are not restrained, which can coordinate the high heterogeneity of this signaling and reconcile multiple discrepancies in the literature.

Understanding extranuclear (nongenomic) androgen signaling: what a frog oocyte can tell us about human biology

Steroids are key factors in a myriad of mammalian biological systems, including the brain, kidney, heart, bones, and gonads. While alternative potential steroid receptors have been described, the majority of biologically relevant steroid responses appear to be mediated by classical steroid receptors that are located in all parts of the cell, from the plasma membrane to the nucleus. Interestingly, these classical steroid receptors modulate different signals depending upon their location. For example, receptors in the plasma membrane interact with membrane signaling molecules, including G proteins and kinases. In contrast, receptors in the nucleus interact with nuclear signaling molecules, including transcriptional co-regulators. These extranuclear and intranuclear signals function together in an integrated fashion to regulate important biological functions. While most studies on extranuclear steroid signaling have focused on estrogens, recent work has demonstrated that nongenomic androgen signaling is equally important and that these two steroids modulate similar signaling pathways. In fact, by taking advantage of a simple model system whereby a physiologically relevant androgen-mediated process is regulated completely independent of transcription (Xenopus laevis oocyte maturation), many novel and conserved concepts in nongenomic steroid signaling have been uncovered and characterized.

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.

Viral vector-mediated overexpression of estrogen receptor-alpha in striatum enhances the estradiol-induced motor activity in female rats and estradiol-modulated GABA release

Classical estrogen receptor-signaling mechanisms involve estradiol binding to intracellular nuclear receptors [estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta)] to promote changes in protein expression. Estradiol can also exert effects within seconds to minutes, however, a timescale incongruent with genomic signaling. In the brain, estradiol rapidly potentiates stimulated dopamine release in the striatum of female rats and enhances spontaneous rotational behavior. Furthermore, estradiol rapidly attenuates the K(+)-evoked increase of GABA in dialysate. We hypothesize that these rapid effects of estradiol in the striatum are mediated by ERalpha located on the membrane of medium spiny GABAergic neurons. This experiment examined whether overexpression of ERalpha in the striatum would enhance the effect of estradiol on rotational behavior and the K(+)-evoked increase in GABA in dialysate. Ovariectomized female rats were tested for rotational behavior or underwent microdialysis experiments after unilateral intrastriatal injections of a recombinant adeno-associated virus (AAV) containing the human ERalpha cDNA (AAV.ERalpha) into the striatum; controls received either the same vector into areas outside the striatum or an AAV containing the human alkaline phosphatase gene into the striatum (AAV.ALP). Animals that received AAV.ERalpha in the striatum exhibited significantly greater estradiol-induced contralateral rotations compared with controls and exhibited behavioral sensitization of contralateral rotations induced by a low-dose of amphetamine. ERalpha overexpression also enhanced the inhibitory effect of estradiol on K(+)-evoked GABA release suggesting that disinhibition of dopamine release from terminals in the striatum resulted in the enhanced rotational behavior.

Na⁺,K⁺-ATPase as the Target Enzyme for Organic and Inorganic Compounds

This paper gives an overview of the literature data concerning specific and non specific inhibitors of Na⁺,K⁺-ATPase receptor. The immobilization approaches developed to improve the rather low time and temperature stability of Na⁺,K⁺-ATPase, as well to preserve the enzyme properties were overviewed. The functional immobilization of Na⁺,K⁺-ATPase receptor as the target, with preservation of the full functional protein activity and access of various substances to an optimum number of binding sites under controlled conditions in the combination with high sensitive technology for the detection of enzyme activity is the basis for application of this enzyme in medical, pharmaceutical and environmental research.

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.

Aldosterone induces cardiotrophin-1 expression in HL-1 adult cardiomyocytes

Aldosterone (ALDO) may induce cardiac hypertrophy by nonhemodynamic mechanisms that are not completely defined. Cardiotrophin-1 (CT-1) is a cytokine that exerts hypertrophic actions on isolated cardiomyocytes and promotes cardiac hypertrophy in vivo. We investigated whether ALDO induces CT-1 expression in HL-1 cardiomyocytes aiming at the possibility that the cytokine is involved in ALDO-induced cardiomyocyte hypertrophy. mRNA and protein expression were quantified by RT-PCR and Western blot. Cardiomyocyte area, as an index of hypertrophy, was assayed by image analysis in phalloidin-stained HL-1 cells. ALDO addition to adult HL-1 cardiomyocytes increased (P<0.01) CT-1 mRNA and protein expression in a concentration-dependent manner. This effect was abrogated by actinomycin D, the mineralocorticoid and glucocorticoid receptor antagonists spironolactone and RU486, respectively, and the p38 MAPK blocker SB203580. CT-1 signaling pathway blockade with specific antibodies against the cytokine and its two receptor subunits avoided (P<0.01) alpha-sarcomeric actin and c-fos protein overexpression as well as cell size increase induced by ALDO in HL-1 cells. In vivo, a single ALDO injection acutely increased (P<0.01) the myocardial expression of CT-1 in C57BJ6 wild-type mice but not CT-1-null mice. The bolus of the mineralocorticoid increased (P<0.01) ANP and c-fos mRNA expression in the myocardium of wild-type mice, whereas no changes were observed in CT-1-null mice. In summary, ALDO induces CT-1 expression in adult HL-1 cardiomyocytes via genomic and nongenomic mechanisms. CT-1 up-regulation could have relevance in the direct hypertrophic effects of ALDO in cardiomyocytes.

Steroidal androgens and nonsteroidal, tissue-selective androgen receptor modulator, S-22, regulate androgen receptor function through distinct genomic and nongenomic signaling pathways

Androgen receptor (AR) ligands are important for the development and function of several tissues and organs. However, the poor oral bioavailability, pharmacokinetic properties, and receptor cross-reactivity of testosterone, coupled with side effects, place limits on its clinical use. Selective AR modulators (SARMs) elicit anabolic effects in muscle and bone, sparing reproductive organs like the prostate. However, molecular mechanisms underlying the tissue selectivity remain ambiguous. We performed a variety of in vitro studies to compare and define the molecular mechanisms of an aryl propionamide SARM, S-22, as compared with dihydrotestosterone (DHT). Studies indicated that S-22 increased levator ani muscle weight but decreased the size of prostate in rats. Analysis of the upstream intracellular signaling events indicated that S-22 and DHT mediated their actions through distinct pathways. Modulation of these pathways altered the recruitment of AR and its cofactors to the PSA enhancer in a ligand-dependent fashion. In addition, S-22 induced Xenopus laevis oocyte maturation and rapid phosphorylation of several kinases, through pathways distinct from steroids. These studies reveal novel differences in the molecular mechanisms by which S-22, a nonsteroidal SARM, and DHT mediate their pharmacological effects.

The Xenopus laevis isoform of G protein-coupled receptor 3 (GPR3) is a constitutively active cell surface receptor that participates in maintaining meiotic arrest in X. laevis oocytes

Oocytes are held in meiotic arrest in prophase I until ovulation, when gonadotropins trigger a subpopulation of oocytes to resume meiosis in a process termed "maturation." Meiotic arrest is maintained through a mechanism whereby constitutive cAMP production exceeds phosphodiesterase-mediated degradation, leading to elevated intracellular cAMP. Studies have implicated a constitutively activated Galpha(s)-coupled receptor, G protein-coupled receptor 3 (GPR3), as one of the molecules responsible for maintaining meiotic arrest in mouse oocytes. Here we characterized the signaling and functional properties of GPR3 using the more amenable model system of Xenopus laevis oocytes. We cloned the X. laevis isoform of GPR3 (XGPR3) from oocytes and showed that overexpressed XGPR3 elevated intraoocyte cAMP, in large part via Gbetagamma signaling. Overexpressed XGPR3 suppressed steroid-triggered kinase activation and maturation of isolated oocytes, as well as gonadotropin-induced maturation of follicle-enclosed oocytes. In contrast, depletion of XGPR3 using antisense oligodeoxynucleotides reduced intracellular cAMP levels and enhanced steroid- and gonadotropin-mediated oocyte maturation. Interestingly, collagenase treatment of Xenopus oocytes cleaved and inactivated cell surface XGPR3, which enhanced steroid-triggered oocyte maturation and activation of MAPK. In addition, human chorionic gonadotropin-treatment of follicle-enclosed oocytes triggered metalloproteinase-mediated cleavage of XGPR3 at the oocyte cell surface. Together, these results suggest that GPR3 moderates the oocyte response to maturation-promoting signals, and that gonadotropin-mediated activation of metalloproteinases may play a partial role in sensitizing oocytes for maturation by inactivating constitutive GPR3 signaling.

Expression profile of heptahelical putative membrane progesterone receptors in epithelial ovarian tumors

A novel class of putative progestin binding proteins has been recently identified as potential mediators of rapid nongenomic hormone actions. The proteins designated membrane progestin receptor (mPR) alpha, beta, and gamma were initially discovered in fish and shown to have a role in oocyte maturation. The predicted multiple membrane spanning domain structure of the mPRs resembles that of heptahelical G-protein-coupled receptors. Phylogenetic analysis indicated that the mPRs belong to the large progestin and adiponectin Q receptor (PAQR) gene family. Based on the reported expression of the 3 mPRs in hormone-responsive tissues of the female reproductive tract and on the role of steroid hormones in cancer, we investigated the expression of these novel progestin receptors in epithelial tumors of the ovary. The transcript levels of the 3 human mPR/PAQRs were assessed by semiquantitative reverse transcriptase polymerase chain reaction in 28 ovarian samples, including normal tissues, cystadenomas, borderline tumors, and common types of ovarian carcinomas. Two of the 3 transcripts for the mPR/PAQRs proteins appeared differentially expressed in the tumors examined. Expression of mPR alpha and beta was demonstrated in ovarian tumors at both messenger RNA and protein level, and their expression appeared to be independent of the expression of the classic nuclear progestin receptors. Expression of mPR gamma (PAQR V) was elevated in endometrioid and clear cell carcinomas, 2 related neoplastic counterparts of hormonally responsive tissues, suggesting a potential role of the mPR/PAQRs in the pathogenesis of epithelial ovarian tumors.

Extranuclear steroid receptors: nature and actions

Rapid effects of steroid hormones result from the actions of specific receptors localized most often to the plasma membrane. Fast-acting membrane-initiated steroid signaling (MISS) leads to the modification of existing proteins and cell behaviors. Rapid steroid-triggered signaling through calcium, amine release, and kinase activation also impacts the regulation of gene expression by steroids, sometimes requiring integration with nuclear steroid receptor function. In this and other ways, the integration of all steroid actions in the cell coordinates outcomes such as cell fate, proliferation, differentiation, and migration. The nature of the receptors is of intense interest, and significant data suggest that extranuclear and nuclear steroid receptor pools are the same proteins. Insights regarding the structural determinants for membrane localization and function, as well as the nature of interactions with G proteins and other signaling molecules in confined areas of the membrane, have led to a fuller understanding of how steroid receptors effect rapid actions. Increasingly, the relevance of rapid signaling for the in vivo functions of steroid hormones has been established. Examples include steroid effects on reproductive organ development and function, cardiovascular responsiveness, and cancer biology. However, although great strides have been made, much remains to be understood concerning the integration of extranuclear and nuclear receptor functions to organ biology. In this review, we highlight the significant progress that has been made in these areas.

Glucocorticoid action and the development of selective glucocorticoid receptor ligands

Glucocorticoids are important endocrine regulators of a wide range of physiological systems ranging from respiratory development, immune function to responses to stress. Glucocorticoids in cells activate the cytoplasmic glucocorticoid receptor (GR) that dimerizes, translocates to the nucleus and functions as a ligand-dependent transcriptional regulator. Synthetic glucocorticoids such as dexamethasone and prednisolone have for decades been the cornerstone for the clinical treatment of inflammatory diseases, such as rheumatoid arthritis and asthma, and in some lymphoid cancers, yet its prolonged use has undesirable side effects such as obesity, diabetes, immune suppression and osteoporosis. Detailed knowledge on the mechanism of GR action has led to the development of novel selective glucocorticoid receptor modulators (SGRMs) that show promise of being efficacious for specific treatments of disease but with fewer side effects. SGRMs promote specific recruitment of transcriptional co-regulators that elicit specific gene responses and show promise of greater efficacy and specificity in treatment of inflammatory diseases and type-2 diabetes.

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.

Steroid and G protein binding characteristics of the seatrout and human progestin membrane receptor alpha subtypes and their evolutionary origins

A novel progestin receptor (mPR) with seven-transmembrane domains was recently discovered in spotted seatrout and homologous genes were identified in other vertebrates. We show that cDNAs for the mPR alpha subtypes from spotted seatrout (st-mPRalpha) and humans (hu-mPRalpha) encode progestin receptors that display many functional characteristics of G protein-coupled receptors. Flow cytometry and immunocytochemical staining of whole MDA-MB-231 cells stably transfected with the mPRalphas using antibodies directed against their N-terminal regions show the receptors are localized on the plasma membrane and suggest the N-terminal domain is extracellular. Both recombinant st-mPRalpha and hu-mPRalpha display high affinity (Kd 4.2-7.8 nm), limited capacity (Bmax 0.03-0.32 nm), and displaceable membrane binding specific for progestins. Progestins activate a pertussis toxin-sensitive inhibitory G protein (G(i)) to down-regulate membrane-bound adenylyl cyclase activity in both st-mPRalpha- and hu-mPRalpha-transfected cells. Coimmunoprecipitation experiments demonstrate the receptors are directly coupled to the G(i) protein. Similar to G protein-coupled receptors, dissociation of the receptor/G protein complex results in a decrease in ligand binding to the mPRalphas and mutation of the C-terminal, and third intracellular loop of st-mPRalpha causes loss of ligand-dependent G protein activation. Phylogenetic analysis indicates the mPRs are members of a progesterone and adipoQ receptor (PAQR) subfamily that is only present in chordates, whereas other PAQRs also occur in invertebrates and plants. Progesterone and adipoQ receptors are related to the hemolysin3 family and have origins in the Eubacteria. Thus, mPRs arose from Eubacteria independently from members of the GPCR superfamily, which arose from Archeabacteria, suggesting convergent evolution of seven-transmembrane hormone receptors coupled to G proteins.

ClassicalXenopus laevis progesterone receptor associates to the plasma membrane through its ligand-binding domain

During the last decade, considerable evidence is accumulating that supports the view that the classic progesterone receptor (xPR-1) is mediating Xenopus laevis oocyte maturation through a non-genomic mechanism. Overexpression and depletion of oocyte xPR-1 have been shown to accelerate and to block progesterone-induced oocyte maturation, respectively. In addition, rapid inhibition of plasma membrane adenylyl cyclase (AC) by the steroid hormone, supports the idea that xPR-1 should be localized at the oocyte plasma membrane. To test this hypothesis, we transiently transfected xPR-1 cDNA into Cos-7 cells and analyzed its subcellular distribution. Through Western blot and immunofluorescence analysis, we were able to detect xPR-1 associated to the plasma membrane of transfected Cos-7 cells. Additionally, using Progesterone-BSA-FITC, we identified specific progesterone-binding sites at the cell surface of xPR-1 expressing cells. Finally, we found that the receptor ligand-binding domain displayed membrane localization, in contrast to the N-terminal domain, which expressed in similar levels, remained cytosolic. Overall, these results indicate that a fraction of xPR-1 expressed in Cos-7 cells, associates to the plasma membrane through its LBD.

Brassinosteroid signaling pathway

Plant growth is regulated by an intricate network of hormonal signaling pathways. These small-molecule hormones cause changes in gene expression that are associated with cell expansion and division and changes in development. Paradoxically, six of these hormones appear to have largely overlapping functions, yet the loss of response to any one hormone cannot be compensated by the action of another plant hormone. Among these hormones are the brassinosteroids (BRs), the polyhydroxylated steroid hormones of plants. The emerging picture of BR signal transduction diverges radically from the paradigms of animal steroid signaling, which generally involve the action of members of the nuclear receptor superfamily. BRs bind the extracellular domain of a small family of leucine-rich-repeat receptor kinases to activate intracellular signal transduction cascades that regulate the expression of hundreds of genes. The signaling pathway involves a cell surface receptor complex, a glycogen synthase kinase 3, a kelch-containing serine/threonine phosphatase, and a novel family of basic helix-loop-helix and Myc-like plant specific transcription factors. The receptor and each of the signaling components were identified in Arabidopsis thaliana, and knowledge of their sequences allowed identification of orthologs in rice, tomato, barley, and pea.

Human Homologs of the Putative G Protein-Coupled Membrane Progestin Receptors (mPRα, β, and γ) Localize to the Endoplasmic Reticulum and Are Not Activated by Progesterone

The steroid hormone progesterone exerts pleiotrophic functions in many cell types. Although progesterone controls transcriptional activation through binding to its nuclear receptors, it also initiates rapid nongenomic signaling events. Recently, three putative membrane progestin receptors (mPRα, β, and γ) with structural similarity to G protein-coupled receptors have been identified. These mPR isoforms are expressed in a tissue-specific manner and belong to the larger, highly conserved family of progestin and adiponectin receptors found in plants, eubacteria, and eukaryotes. The fish mPRα has been reported to mediate progesterone-dependent MAPK activation and inhibition of cAMP production through coupling to an inhibitory G protein. To functionally characterize the human homologs, we established human embryonic kidney 293 and MDA-MB-231 cell lines that stably express human mPRα, β, or γ. For comparison, we also established cell lines expressing the mPRα cloned from the spotted seatrout (Cynoscion nebulosus) and Japanese pufferfish (Takifugu rubripes). Surprisingly, we found no evidence that human or fish mPRs regulate cAMP production or MAPK (ERK1/2 or p38) activation upon progesterone stimulation. Furthermore, the mPRs did not couple to a highly promiscuous G protein subunit, Gαq5i, in transfection studies or provoke Ca2+ mobilization in response to progesterone. Finally, we demonstrate that transfected mPRs, as well as endogenous human mPRα, localize to the endoplasmic reticulum, and that their expression does not lead to increased progestin binding either in membrane preparations or in intact cells. Our results therefore do not support the concept that mPRs are plasma membrane receptors involved in transducing nongenomic progesterone actions.

Testosterone and progesterone rapidly attenuate plasma membrane Gbetagamma-mediated signaling in Xenopus laevis oocytes by signaling through classical steroid receptors

Many transcription-independent (nongenomic) steroid effects are regulated by G proteins. A well-established, biologically relevant example of steroid/G protein interplay is steroid-triggered oocyte maturation, or meiotic resumption, in Xenopus laevis. Oocyte maturation is proposed to occur through a release of inhibition mechanism whereby constitutive signaling by Gbetagamma and other G proteins maintains oocytes in meiotic arrest. Steroids (androgens in vivo, and androgens and progesterone in vitro) overcome this inhibition to promote meiotic resumption. To test this model, we used G protein-regulated inward rectifying potassium channels (GIRKs) as markers of Gbetagamma activity. Overexpression of GIRKs 1 and 2 in Xenopus oocytes resulted in constitutive potassium influx, corroborating the presence of basal Gbetagamma signaling in resting oocytes. Testosterone and progesterone rapidly reduced potassium influx, validating that steroids attenuate Gbetagamma activity. Interestingly, reduction of classical androgen receptor (AR) expression by RNA interference abrogated testosterone's effects on GIRK activity at low, but not high, steroid concentrations. Accordingly, androgens bound to the Xenopus progesterone receptor (PR) at high concentrations, suggesting that, in addition to the AR, the PR might mediate G protein signaling when androgens levels are elevated. In contrast, progesterone bound with high affinity to both the Xenopus PR and AR, indicating that progesterone might signal and promote maturation through both receptors, regardless of its concentration. In sum, these studies introduce a novel method for detecting nongenomic steroid effects on G proteins in live cells in real time, and demonstrate that cross talk may occur between steroids and their receptors during Xenopus oocyte maturation.

Expression and functional state of the corticosteroid receptors and 11 beta-hydroxysteroid dehydrogenase type 2 in Schwann cells

To investigate the role of steroid receptors in mediating the reported effects of steroids on Schwann cell (SC) myelination and growth, we determined mRNA contents and transcriptional activities of the corticosteroid (glucocorticosteroid and mineralocorticosteroid) receptors (GR and MR) and sex steroid (progesterone, androgen, and estrogen alpha and beta) receptors in rat SC cultured under proliferative (in the presence of insulin and forskolin, which induces a high intracellular cAMP content) and quiescent conditions. We found no or very low expression and activity of the sex steroid receptors, as shown by mRNA concentrations determined with real-time PCR and transcriptional activities using transient expression of reporter plasmids in SC. These data and binding studies in SC lines demonstrated that the levels of the sex steroid receptors were the limiting factors. GR was clearly expressed (approximately 8000 sequences/ng total RNA) and functional. No significant modification in GR mRNA levels was observed, but an increase in transcriptional efficiency was recorded in proliferating cells compared with quiescent cells. MR was also significantly expressed at the mRNA level (approximately 450 sequences/ng total RNA) under the two culture conditions. No MR transcriptional activity was observed in SC, but a low specific binding of aldosterone was detected in SC lines. 11 beta-Hydroxysteroid-dehydrogenase type 2 (HSD2), an enzyme that inactivates glucocorticoids, was strongly expressed and active in quiescent SC, although in proliferating cells, HSD2 exhibited a strong decrease in activity and mRNA concentration. These data support a physiological role for HSD2 regulation of glucocorticosteroid concentrations in nerve SC.

Inter-kingdom signaling: deciphering the language of acyl homoserine lactones

Bacteria use small secreted chemicals or peptides as auto-inducers to coordinately regulate gene expression within a population in a process called quorum sensing. Quorum sensing controls several important functions in different bacterial species, including the production of virulence factors and biofilm formation in Pseudomonas aeruginosa and bioluminescence in Vibrio fischeri. Many gram-negative bacterial species use acyl homoserine lactones as auto-inducers that function as ligands for transcriptional regulatory proteins. Several recent reports indicate that bacterial acyl homoserine lactones can also affect gene expression in host cells. Direct signaling also appears to function in the opposite direction as some eukaryotic cell types produce mimics that interact with quorum sensing systems in bacteria. Here, we will describe the evidence to support the existence of bi-directional inter-kingdom signaling via acyl homoserine lactones and eukaryotic mimics and discuss the potential molecular mechanisms that mediate these responses. The functional consequences of inter-kingdom signaling will be discussed in relation to both pathogenic and non-pathogenic bacterial-host interactions.

Oocyte maturation: the coming of age of a germ cell

Normal female fertility relies on proper development of the oocyte. This growth culminates just prior to ovulation, when oocyte maturation occurs. Oocyte maturation refers to a release of meiotic arrest that allows oocytes to advance from prophase I to metaphase II of meiosis. This precisely regulated meiotic progression is essential for normal ovulation and subsequent fertilization, and involves changes in the delicate balance between factors promoting meiotic arrest and others that are stimulating maturation. Most of the inhibitory mechanisms appear to involve the upregulation of intracellular cyclic adenosine monophosphate levels. These processes may include direct transport of the nucleotide into oocytes via gap junctions, G protein-mediated stimulation of adenylyl cyclase, and inhibition of intracellular phosphodiesterases. In contrast, potential factors that play roles in triggering oocyte maturation include gonadotropins (e.g., follicle-stimulating factor and luteinizing hormone), growth factors (e.g., amphiregulin and epiregulin), sterols (e.g., follicular fluid-derived meiosis-activating sterol), and steroids (e.g., testosterone progesterone, and estradiol). Delineating the complex interactions between these positive and negative components is critical for determining the role that oocyte maturation plays in regulating follicle development and ovulation, and may lead to novel methods that can be used to modulate these processes in women with both normal and aberrant fertility.

Human Mineralocorticoid Receptor Expression Renders Cells Responsive for Nongenotropic Aldosterone Actions

The steroid hormone aldosterone is important for salt and water homeostasis as well as for pathological tissue modifications in the cardiovascular system and the kidney. The mechanisms of action include a classical genomic pathway, but physiological relevant nongenotropic effects have also been described. Unlike for estrogens or progesterone, the mechanisms for these nongenotropic effects are not well understood, although pharmacological studies suggest a role for the mineralocorticoid receptor (MR). Here we investigated whether the MR contributes to nongenotropic effects. After transfection with human MR, aldosterone induced a rapid and dose-dependent phosphorylation of ERK1/2 and c-Jun NH2-terminal kinase (JNK) 1/2 kinases in Chinese hamster ovary or human embryonic kidney cells, which was reduced by the MR-antagonist spironolactone and involved cSrc kinase as well as the epidermal growth factor receptor. In primary human aortic endothelial cells, similar results were obtained for ERK1/2 and JNK1/2. Inhibition of MAPK kinase (MEK) kinase but not of protein kinase C prevented the rapid action of aldosterone and also reduced aldosterone-induced transactivation, most probably due to impaired nuclear-cytoplasmic shuttling of MR. Cytosolic Ca2+ was increased by aldosterone in mock- and in human MR-transfected cells to the same extend due to Ca2+ influx, whereas dexamethasone had virtually no effect. Spironolactone did not prevent the Ca2+ response. We conclude that some nongenotropic effects of aldosterone are MR dependent and others are MR independent (e.g. Ca2+), indicating a higher degree of complexity of rapid aldosterone signaling. According to this model, we have to distinguish three aldosterone signaling pathways: 1) genomic via MR, 2) nongenotropic via MR, and 3) nongenotropic MR independent.

Regulation of signal transduction pathways by estrogen and progesterone

The female sex steroid hormones 17beta-estradiol and progesterone mediate their biological effects on development, differentiation, and maintenance of reproductive tract and other target tissues through gene regulation by nuclear steroid receptors that function as ligand-dependent transcription factors. However, not all effects of 17beta-estradiol and progesterone are mediated by direct control of gene expression. These hormones also have rapid stimulatory effects on the activities of a variety of signal transduction molecules and pathways and, in many cases, these effects appear to be initiated from the plasma cell membrane. There is growing evidence that a subpopulation of the conventional nuclear steroid receptor localized at the cell membrane mediates many of the rapid signaling actions of steroid hormones; however, novel membrane receptors unrelated to conventional steroid receptors have also been implicated. This chapter reviews the nature of the receptors that mediate rapid signaling actions of estrogen and progesterone and describes the signaling molecules and pathways involved, the mechanisms by which receptors couple with components of signaling complexes and trigger responses, and the target tissues and cell functions regulated by this mode of steroid hormone action.

Pharmacokinetics and pharmacodynamics of systemically administered glucocorticoids

Glucocorticoids have pleiotropic effects that are used to treat diverse diseases such as asthma, rheumatoid arthritis, systemic lupus erythematosus and acute kidney transplant rejection. The most commonly used systemic glucocorticoids are hydrocortisone, prednisolone, methylprednisolone and dexamethasone. These glucocorticoids have good oral bioavailability and are eliminated mainly by hepatic metabolism and renal excretion of the metabolites. Plasma concentrations follow a biexponential pattern. Two-compartment models are used after intravenous administration, but one-compartment models are sufficient after oral administration.The effects of glucocorticoids are mediated by genomic and possibly nongenomic mechanisms. Genomic mechanisms include activation of the cytosolic glucocorticoid receptor that leads to activation or repression of protein synthesis, including cytokines, chemokines, inflammatory enzymes and adhesion molecules. Thus, inflammation and immune response mechanisms may be modified. Nongenomic mechanisms might play an additional role in glucocorticoid pulse therapy. Clinical efficacy depends on glucocorticoid pharmacokinetics and pharmacodynamics. Pharmacokinetic parameters such as the elimination half-life, and pharmacodynamic parameters such as the concentration producing the half-maximal effect, determine the duration and intensity of glucocorticoid effects. The special contribution of either of these can be distinguished with pharmacokinetic/pharmacodynamic analysis. We performed simulations with a pharmacokinetic/pharmacodynamic model using T helper cell counts and endogenous cortisol as biomarkers for the effects of methylprednisolone. These simulations suggest that the clinical efficacy of low-dose glucocorticoid regimens might be increased with twice-daily glucocorticoid administration.

Phenotypic anchoring of gene expression changes during estrogen-induced uterine growth

A major challenge in the emerging field of toxicogenomics is to define the relationships between chemically induced changes in gene expression and alterations in conventional toxicologic parameters such as clinical chemistry and histopathology. We have explored these relationships in detail using the rodent uterotrophic assay as a model system. Gene expression levels, uterine weights, and histologic parameters were analyzed 1, 2, 4, 8, 24, 48, and 72 hr after exposure to the reference physiologic estrogen 17 beta-estradiol (E2). A multistep analysis method, involving unsupervised hierarchical clustering followed by supervised gene ontology-driven clustering, was used to define the transcriptional program associated with E2-induced uterine growth and to identify groups of genes that may drive specific histologic changes in the uterus. This revealed that uterine growth and maturation are preceded and accompanied by a complex, multistage molecular program. The program begins with the induction of genes involved in transcriptional regulation and signal transduction and is followed, sequentially, by the regulation of genes involved in protein biosynthesis, cell proliferation, and epithelial cell differentiation. Furthermore, we have identified genes with common molecular functions that may drive fluid uptake, coordinated cell division, and remodeling of luminal epithelial cells. These data define the mechanism by which an estrogen induces organ growth and tissue maturation, and demonstrate that comparison of temporal changes in gene expression and conventional toxicology end points can facilitate the phenotypic anchoring of toxicogenomic data.

Expression of the glucocorticoid receptor from the 1A promoter correlates with T lymphocyte sensitivity to glucocorticoid-induced cell death

Glucocorticoid (GC) hormones cause pronounced T cell apoptosis, particularly in immature thymic T cells. This is possibly due to tissue-specific regulation of the glucocorticoid receptor (GR) gene. In mice the GR gene is transcribed from five separate promoters designated: 1A, 1B, 1C, 1D, and 1E. Nearly all cells express GR from promoters 1B-1E, but the activity of the 1A promoter has only been reported in the whole thymus or lymphocyte cell lines. To directly assess the role of GR promoter use in sensitivity to glucocorticoid-induced cell death, we have compared the activity of the GR 1A promoter with GC sensitivity in different mouse lymphocyte populations. We report that GR 1A promoter activity is restricted to thymocyte and peripheral lymphocyte populations and the cortex of the brain. The relative level of expression of the 1A promoter to the 1B-1E promoters within a lymphocyte population was found to directly correlate with susceptibility to GC-induced cell death, with the extremely GC-sensitive CD4+CD8+ thymocytes having the highest levels of GR 1A promoter activity, and the relatively GC-resistant alphabetaTCR+CD24(int/low) thymocytes and peripheral T cells having the lowest levels. DNA sequencing of the mouse GR 1A promoter revealed a putative glucocorticoid-response element. Furthermore, GR 1A promoter use and GR protein levels were increased by GC treatment in thymocytes, but not in splenocytes. These data suggest that tissue-specific differences in GR promoter use determine T cell sensitivity to glucocorticoid-induced cell death.

Steroids and oocyte maturation--a new look at an old story

Female fertility requires precise regulation of oocyte meiosis. Oocytes are arrested early in the meiotic cycle until just before ovulation, when ovarian factors trigger meiosis, or maturation, to continue. Although much has been learned about the late signaling events that accompany meiosis, until recently less was known about the early actions that initiate maturation. Studies using the well-characterized model of transcription-independent steroid-induced oocyte maturation in Xenopus laevis now show that steroid metabolism, classical steroid receptors, G protein-mediated signaling, and novel G protein-coupled receptors, all may play important roles in regulating meiosis. Furthermore, steroids appear to promote similar events in mammalian oocytes, implying a conserved mechanism of maturation in vertebrates. Interestingly, testosterone is a potent promoter of mammalian oocyte maturation, suggesting that androgen actions in the oocyte might be partially responsible for the polycystic ovarian phenotype and accompanying infertility associated with high androgen states such as polycystic ovarian syndrome or congenital adrenal hyperplasia. A detailed appreciation of the steroid-activated signaling pathways in frog and mammalian oocytes may therefore prove useful in understanding both normal and abnormal ovarian development in humans.

Androgens promote maturation and signaling in mouse oocytes independent of transcription: a release of inhibition model for mammalian oocyte meiosis

Normal fertility in females depends upon precise regulation of oocyte meiosis. Oocytes are arrested in prophase I of meiosis until just before ovulation, when meiosis, or maturation, is triggered to resume. Whereas sex steroids appear to promote maturation in fish and amphibians, the factors regulating mammalian oocyte maturation have remained obscure. We show here that, similar to lower vertebrates, steroids may play a role in promoting the release of meiotic inhibition in mammals. Specifically, testosterone induced maturation of mouse oocytes arrested in meiosis, as well as activation of MAPK and cyclin-dependent kinase 1 signaling. These responses appeared to be transcription independent and might involve signaling through classical androgen receptors expressed in the oocytes. Our results are the first to show that sex steroids can modulate meiosis in mammalian oocytes and suggest a model whereby dominant ovarian follicles in mammals may produce sufficient androgen and/or other steroids to overcome constitutive inhibitory signals and allow oocyte maturation and subsequent ovulation to occur.

Tamoxifen stimulates arachidonic acid release from rat liver cells by an estrogen receptor-independent, non-genomic mechanism

Background

Tamoxifen is widely prescribed for the treatment of breast cancer. Its success has been attributed to the modulation of the estrogen receptor. I have previously proposed that the release of arachidonic acid from cells may also mediate cancer prevention.

Methods

Rat liver cells were radiolabelled with arachidonic acid. The release of [³H] arachidonic acid after various times of incubation of the cells with tamoxifen was measured.

Results

Tamoxifen, at micromolar concentrations, stimulates arachidonic acid release. The stimulation is rapid and is not affected by pre-incubation of the cells with actinomycin or the estrogen antagonist ICI-182,780.

Conclusions

The stimulation of AA release by tamoxifen is not mediated by estrogen receptor occupancy and is non-genomic.

A perspective for understanding the modes of juvenile hormone action as a lipid signaling system

The juvenile hormones of insects regulate an unusually large diversity of processes during postembryonic development and adult reproduction. It is a long-standing puzzle in insect developmental biology and physiology how one hormone can have such diverse effects. The search for molecular mechanisms of juvenile hormone action has been guided by classical models for hormone-receptor interaction. Yet, despite substantial effort, the search for a juvenile hormone receptor has been frustrating and has yielded limited results. We note here that a number of lipid-soluble signaling molecules in vertebrates, invertebrates and plants show curious similarities to the properties of juvenile hormones of insects. Until now, these signaling molecules have been thought of as uniquely evolved mechanisms that perform specialized regulatory functions in the taxon where they were discovered. We show that this array of lipid signaling molecules share interesting properties and suggest that they constitute a large set of signal control and transduction mechanisms that include, but range far beyond, the classical steroid hormone signaling mechanism. Juvenile hormone is the insect representative of this widespread and diverse system of lipid signaling molecules that regulate protein activity in a variety of ways. We propose a synthetic perspective for understanding juvenile hormone action in light of other lipid signaling systems and suggest that lipid activation of proteins has evolved to modulate existing signal activation and transduction mechanisms in animals and plants. Since small lipids can be inserted into many different pathways, lipid-activated proteins have evolved to play a great diversity of roles in physiology and development.