Nongenomic actions of steroid hormones in reproductive tissues

The Distribution, Expression Patterns and Functional Analysis of NR1D1 and NR4A2 in the Reproductive Axis Tissues of the Male Tianzhu White Yak

Nuclear hormone receptors NR1D1 and NR4A2 play important roles in the synthesis and metabolism of hormones that are thought to be strictly regulated by the hypothalamus-pituitary-gonad axis (HPG) tissues via gene expression. However, in the yak, the function and regulatory mechanisms of NR1D1 and NR4A2 are not clearly understood. The current study is aimed to investigate the expression patterns, distribution and functions of these two receptors in HPG tissues in male Tianzhu white yaks. Immunohistochemical staining showed NR1D1 and NR4A2 proteins were present in all yak HPG tissues with differential expression patterns and degrees of staining, particularly in Leydig cells that were strongly positive in accordance with the immunofluorescence results. qRT-PCR and Western blot results suggested that the highest expression levels of NR1D1 and NR4A2 mRNA were present in the hypothalamus, while the expression levels of NR1D1 and NR4A2 proteins were higher in the testis and epididymis than in the hypothalamus or pituitary gland. In addition, expression levels of NR1D1 and NR4A2 mRNA and protein in testicular tissues differed by age. Expression levels were significantly higher at 6 years of age. Gene ontology (GO) and pathway analysis enrichment revealed that NR1D1 may directly regulate the synthesis and metabolism of steroid hormones via interaction with different targets, while NR4A2 may indirectly regulate the synthesis and metabolism of steroid hormones. These results showed that NR1D1 and NR4A2, as important mediators, are involved in the regulation of male yak reproduction, and especially of steroid hormones and androgen metabolism. These results will be helpful for the further understanding of the regulatory mechanisms of NR1D1 and NR4A2 in yak reproduction.

Alpha/Beta Hydrolase Domain-Containing Protein 2 Regulates the Rhythm of Follicular Maturation and Estrous Stages of the Female Reproductive Cycle

Mammalian female fertility is defined by a successful and strictly periodic ovarian cycle, which is under the control of gonadotropins and steroid hormones, particularly progesterone and estrogen. The latter two are produced by the ovaries that are engaged in controlled follicular growth, maturation, and release of the eggs, i.e., ovulation. The steroid hormones regulate ovarian cycles via genomic signaling, by altering gene transcription and protein synthesis. However, despite this well-studied mechanism, steroid hormones can also signal via direct, non-genomic action, by binding to their membrane receptors. Here we show, that the recently discovered membrane progesterone receptor α/β hydrolase domain-containing protein 2 (ABHD2) is highly expressed in mammalian ovaries where the protein plays a novel regulatory role in follicle maturation and the sexual cycle of females. Ablation of Abhd2 caused a dysregulation of the estrous cycle rhythm with females showing shortened luteal stages while remaining in the estrus stage for a longer time. Interestingly, the ovaries of Abhd2 knockout (KO) females resemble polycystic ovary morphology (PCOM) with a high number of atretic antral follicles that could be rescued with injection of gonadotropins. Such a procedure also allowed Abhd2 KO females to ovulate a significantly increased number of mature and fertile eggs in comparison with their wild-type littermates. These results suggest a novel regulatory role of ABHD2 as an important factor in non-genomic steroid regulation of the female reproductive cycle.

In vivo exposure to codeine induces reproductive toxicity: role of HER2 and p53/Bcl-2 signaling pathway

Several studies have implicated codeine use in the aetiopathogenesis of male infertility. The purpose of this study was to investigate the role of HER2, Ki67, oestrogen and p53/Bcl-2 signaling pathways and the possible outcome of codeine cessation on codeine-induced reproductive toxicity. Thirty adult male Wistar rats of comparable ages and weights were randomly allocated into 5 groups. The control animals received distilled water per os (p.o), while animals in the low-dose (LDC) and high dose (HDC) codeine-treated groups received 2 and 5 mg/kg/day of codeine respectively p.o for 6 weeks. The animals in the low-dose codeine recovery (LDC-R) and high-dose codeine recovery (HDC-R) groups received treatment as LDC and HDC respectively followed by another drug-free six weeks, recovery period. Cessation of codeine exposure led to a partial reversal of codeine-induced poor sperm quality, reduced litter size and weight, increased oxidative testicular injury, testicular apoptosis, and testicular DNA damage caused by codeine administration. Codeine-induced gonado-spermotoxicity was associated with a reduction of circulatory testosterone, suppression of testicular HER2, Ki67, and Bcl-2 expression, down-regulation of oestrogen signaling, and upregulation of testicular caspase 3 activities and p53 signaling pathway. Conclusion: Upregulation of oestrogen signaling associated with enhanced testicular HER2 and Ki67 expression during the recovery period is seemingly beneficial in protecting against codeine-related testicular injury and infertility.

Testosterone synthesis in the female songbird brain

Decades of work have established the brain as a source of steroid hormones, termed 'neurosteroids'. The neurosteroid neuroestradiol is produced in discrete brain areas and influences cognition, sensory processing, reproduction, neurotransmission, and disease. A prevailing research focus on neuroestradiol has essentially ignored whether its immediate synthesis precursor - the androgen testosterone - is also dynamically regulated within the brain. Testosterone itself can rapidly influence neurophysiology and behavior, and there is indirect evidence that the female brain may synthesize significant quantities of testosterone to regulate cognition, reproduction, and behavior. In songbirds, acoustic communication is regulated by neuroestrogens. Neuroestrogens are rapidly synthetized in the caudomedial nidopallium (NCM) of the auditory cortex of zebra finches in response to song and can influence auditory processing and song discrimination. Here, we examined the in vivo dynamics of NCM levels of the neuroestrogen synthesis precursor, testosterone. Unlike estradiol, testosterone did not appear to fluctuate in the female NCM during song exposure. However, a substantial song-induced elevation of testosterone was revealed in the left hemisphere NCM of females when local aromatization (i.e., conversion to estrogens) was locally blocked. This elevation was eliminated when local androgen synthesis was concomitantly blocked. Further, no parallel elevation was observed in the circulation in response to song playback, consistent with a local, neural origin of testosterone synthesis. To our knowledge, this study provides the first direct demonstration that testosterone fluctuates rapidly in the brain in response to socially-relevant environmental stimuli. Our findings suggest therefore that locally-derived 'neuroandrogens' can dynamically influence brain function and behavior. SIGNIFICANCE STATEMENT: This study demonstrates that androgen synthesis occurs rapidly in vivo in the brain in response to social cues, in a lateralized manner. Specifically, testosterone synthesis occurs within the left secondary auditory cortex when female zebra finches hear male song. Therefore, testosterone could act as a neuromodulator to rapidly shape sensory processing. Androgens have been linked to functions such as the control of female libido, and many steroidal drugs used for contraception, anti-cancer treatments, and sexual dysfunction likely influence the brain synthesis and action of testosterone. The current findings therefore establish a clear role for androgen synthesis in the female brain with implications for understanding neural circuit function and behavior in animals, including humans.

Vitamin D and Endothelial Function

Vitamin D is known to elicit a vasoprotective effect, while vitamin D deficiency is a risk factor for endothelial dysfunction (ED). ED is characterized by reduced bioavailability of a potent endothelium-dependent vasodilator, nitric oxide (NO), and is an early event in the development of atherosclerosis. In endothelial cells, vitamin D regulates NO synthesis by mediating the activity of the endothelial NO synthase (eNOS). Under pathogenic conditions, the oxidative stress caused by excessive production of reactive oxygen species (ROS) facilitates NO degradation and suppresses NO synthesis, consequently reducing NO bioavailability. Vitamin D, however, counteracts the activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase which produces ROS, and improves antioxidant capacity by enhancing the activity of antioxidative enzymes such as superoxide dismutase. In addition to ROS, proinflammatory mediators such as TNF-α and IL-6 are risk factors for ED, restraining NO and eNOS bioactivity and upregulating the expression of various atherosclerotic factors through the NF-κB pathway. These proinflammatory activities are inhibited by vitamin D by suppressing NF-κB signaling and production of proinflammatory cytokines. In this review, we discuss the diverse activities of vitamin D in regulating NO bioavailability and endothelial function.

Changes in Energy Metabolism Trigger Pupal Diapause Transition of Bactrocera minax After 20-Hydroxyecdysone Application

Correct timing of diapause entry and exit is critical for a species' survival. While many aspects of insect diapause are well-studied, the mechanisms underlying diapause termination remain largely unknown. The Chinese citrus fly, Bactrocera minax, is a univoltine insect with an obligatory pupal diapause. The application of 20-hydroxyecdysone (20E) is known to terminate diapause in B. minax, and we used this approach, along with isobaric tags for relative and absolute quantitation technology, to determine the proteins associated with diapause termination in this fly. Among 2,258 identified proteins, 1,169 proteins significantly differed at 1, 2, and 5 days post-injection of 20E, compared with the solvent-injected control group. Functional annotation revealed that the majority of differentially expressed proteins were enriched in the core energy metabolism of amino acids, proteins, lipids, and carbohydrates as well as in signal transduction pathways including PPAR signaling, Calcium signaling, Glucagon signaling, VEGF signaling, Ras signaling, cGMP-PKG signaling, and cAMP signaling. A combined transcriptomic and proteomic analysis suggested the involvement of energy metabolism in the response of diapause transition. RNA interference experiments disclosed that a 20E injection triggers diapause termination probably through non-genomic actions, rather than nuclear receptor mediated genomic actions. Our results provide extensive proteomic resources for insect diapause transition and offer a potential for pest control by incapacitating the regulation of diapause termination either by breaking diapause prematurely or by delaying diapause termination to render diapausing individuals at a high risk of mortality.

Role of phospho-ezrin in differentiating thyroid carcinoma

Comprehensive theory explaining the relationship between estrogen (E2) and ezrin in metastasis of thyroid cancer remains non-elicited. In vitro results revealed that E2 could stimulate the expression and phosphorylation of ezrin in a time and dose dependent manner. Our data clearly showed that E2 enhanced the migration and invasion of cells, which was reversed by the transfection of cells with ezrin specific siRNA. Further, we observed that Phosphoinositide 3-kinase (PI3K) ROCK-2 are among the kinases responsible for E2 induced phosphorylation of ezrin. Clinical validation of ezrin/phospho-ezrin revealed that phospho-ezrin was intensely expressed in follicular thyroid carcinoma (FTC) and follicular variant of papillary thyroid carcinoma (FVPTC), while it was completely absent in follicular adenoma (FA) lesions in which the differentiation of the follicular neoplasms remains subtle. When histology of different carcinomas is correlated with benign FA with respect to phospho-ezrin, we observed that the marker was highly significant (p = 0.0001). 100% sensitivity, specificity and diagnostic accuracy of the above marker in the histological association of FTC, FVPTC with FA, enables us to suggest phospho-ezrin as a diagnostic marker to differentiate the follicular neoplasms. These data are the first to suggest the dynamic regulation of ezrin phosphorylation during metastasis in FTC.

Sperm-Cultured Gate Ion-Sensitive Field-Effect Transistor for Non-Optical and Live Monitoring of Sperm Capacitation

We have successfully monitored the effect of progesterone and Ca2+ on artificially induced sperm capacitation in a real-time, noninvasive and label-free manner using an ion-sensitive field-effect transistor (ISFET) sensor. The sperm activity can be electrically detected as a change in pH generated by sperm respiration based on the principle of the ISFET sensor. Upon adding mouse sperm to the gate of the ISFET sensor in the culture medium with progesterone, the pH decreases with an increasing concentration of progesterone from 1 to 40 μM. This is because progesterone induces Ca2+ influx into spermatozoa and triggers multiple Ca2+-dependent physiological responses, which subsequently activates sperm respiration. Moreover, this pH response of the ISFET sensor is not observed for a Ca2+-free medium even when progesterone is introduced, which means that Ca2+ influx is necessary for sperm activation that results in sperm capacitation. Thus, a platform based on the ISFET sensor system can provide a simple method of evaluating artificially induced sperm capacitation in the field of male infertility treatment.

Phosphorylated Nuclear Receptor CAR Forms a Homodimer To Repress Its Constitutive Activity for Ligand Activation

The nuclear receptor CAR (NR1I3) regulates hepatic drug and energy metabolism as well as cell fate. Its activation can be a critical factor in drug-induced toxicity and the development of diseases, including diabetes and tumors. CAR inactivates its constitutive activity by phosphorylation at threonine 38. Utilizing receptor for protein kinase 1 (RACK1) as the regulatory subunit, protein phosphatase 2A (PP2A) dephosphorylates threonine 38 to activate CAR. Here we demonstrate that CAR undergoes homodimer-monomer conversion to regulate this dephosphorylation. By coexpression of two differently tagged CAR proteins in Huh-7 cells, mouse primary hepatocytes, and mouse livers, coimmunoprecipitation and two-dimensional gel electrophoresis revealed that CAR can form a homodimer in a configuration in which the PP2A/RACK1 binding site is buried within its dimer interface. Epidermal growth factor (EGF) was found to stimulate CAR homodimerization, thus constraining CAR in its inactive form. The agonistic ligand CITCO binds directly to the CAR homodimer and dissociates phosphorylated CAR into its monomers, exposing the PP2A/RACK1 binding site for dephosphorylation. Phenobarbital, which is not a CAR ligand, binds the EGF receptor, reversing the EGF signal to monomerize CAR for its indirect activation. Thus, the homodimer-monomer conversion is the underlying molecular mechanism that regulates CAR activation, by placing phosphorylated threonine 38 as the common target for both direct and indirect activation of CAR.

Androgen receptor transcriptionally regulates μ-opioid receptor expression in rat trigeminal ganglia

The involvement of testosterone in pain, inflammation, and analgesia has been reported, but the role of androgen receptor (AR), a steroid receptor for testosterone, is not well understood. We have previously shown that peripheral inflammation upregulates μ-opioid receptor (MOR) in rat trigeminal ganglia (TG) in a testosterone-dependent manner. In this study, we hypothesized that testosterone regulates MOR expression via transcriptional activities of AR in TG. We first examined whether AR is co-expressed with MOR in TG neurons. Our immunohistochemical experiment revealed that AR staining is detected in neurons of all sizes in TG and that a subset of AR is expressed in MOR as well as in TRPV1-positive neurons. We identified the promoter region of the rat MOR gene contains putative AR binding sites. Using chromatin immunoprecipitation assay, we demonstrated that AR directly binds to these sites in TG extracts. We confirmed with luciferase reporter assay that AR activated the MOR promoter in response to androgens in a human neuroblastoma cell line (5H-5YSY). These data demonstrated that AR functions as a transcriptional regulator of the MOR gene activity. Finally, we showed that flutamide, a specific AR antagonist, prevents complete Freund's adjuvant (CFA)-induced upregulation of MOR mRNA in TG, and that flutamide dose-dependently blocks the efficacy of DAMGO, a specific MOR agonist, on CFA-induced mechanical hypersensitivity. Our results expand the knowledge regarding the role of androgens and their receptor in pain and analgesia and have important clinical implications, particularly for inflammatory pain patients with low or compromised plasma testosterone levels.

The importance of non-nuclear AR signaling in prostate cancer progression and therapeutic resistance

The androgen receptor (AR) remains the major oncogenic driver of prostate cancer, as evidenced by the efficacy of androgen deprivation therapy (ADT) in naïve patients, and the continued effectiveness of second generation ADTs in castration resistant disease. However, current ADTs are limited to interfering with AR ligand binding, either through suppression of androgen production or the use of competitive antagonists. Recent studies demonstrate 1) the expression of constitutively active AR splice variants that no longer depend on androgen, and 2) the ability of AR to signal in the cytoplasm independently of its transcriptional activity (non-genomic); thus highlighting the need to consider other ways to target AR. Herein, we review canonical AR signaling, but focus on AR non-genomic signaling, some of its downstream targets and how these effectors contribute to prostate cancer cell behavior. The goals of this review are to 1) re-highlight the continued importance of AR in prostate cancer as the primary driver, 2) discuss the limitations in continuing to use ligand binding as the sole targeting mechanism, 3) discuss the implications of AR non-genomic signaling in cancer progression and therapeutic resistance, and 4) address the need to consider non-genomic AR signaling mechanisms and pathways as a viable targeting strategy in combination with current therapies.

Unconventional endocannabinoid signaling governs sperm activation via the sex hormone progesterone

Steroids regulate cell proliferation, tissue development, and cell signaling via two pathways: a nuclear receptor mechanism and genome-independent signaling. Sperm activation, egg maturation, and steroid-induced anesthesia are executed via the latter pathway, the key components of which remain unknown. Here, we present characterization of the human sperm progesterone receptor that is conveyed by the orphan enzyme α/β hydrolase domain-containing protein 2 (ABHD2). We show that ABHD2 is highly expressed in spermatozoa, binds progesterone, and acts as a progesterone-dependent lipid hydrolase by depleting the endocannabinoid 2-arachidonoylglycerol (2AG) from plasma membrane. The 2AG inhibits the sperm calcium channel (CatSper), and its removal leads to calcium influx via CatSper and ensures sperm activation. This study reveals that progesterone-activated endocannabinoid depletion by ABHD2 is a general mechanism by which progesterone exerts its genome-independent action and primes sperm for fertilization.

Androgen receptor non-nuclear regulation of prostate cancer cell invasion mediated by Src and matriptase

Castration-resistant prostate cancers still depend on nuclear androgen receptor (AR) function despite their lack of dependence on exogenous androgen. Second generation anti-androgen therapies are more efficient at blocking nuclear AR; however resistant tumors still develop. Recent studies indicate Src is highly active in these resistant tumors. By manipulating AR activity in several different prostate cancer cell lines through RNAi, drug treatment, and the use of a nuclear-deficient AR mutant, we demonstrate that androgen acting on cytoplasmic AR rapidly stimulates Src tyrosine kinase via a non-genomic mechanism. Cytoplasmic AR, acting through Src enhances laminin integrin-dependent invasion. Active Matriptase, which cleaves laminin, is elevated within minutes after androgen stimulation, and is subsequently shed into the medium. Matriptase activation and shedding induced by cytoplasmic AR is dependent on Src. Concomitantly, CDCP1/gp140, a Matriptase and Src substrate that controls integrin-based migration, is activated. However, only inhibition of Matriptase, but not CDCP1, suppresses the AR/Src-dependent increase in invasion. Matriptase, present in conditioned medium from AR-stimulated cells, is sufficient to enhance invasion in the absence of androgen. Thus, invasion is stimulated by a rapid but sustained increase in Src activity, mediated non-genomically by cytoplasmic AR, leading to rapid activation and shedding of the laminin protease Matriptase.

The TRPM8 protein is a testosterone receptor: II. Functional evidence for an ionotropic effect of testosterone on TRPM8

Testosterone is a key steroid hormone in the development of male reproductive tissues and the regulation of the central nervous system. The rapid signaling mechanism induced by testosterone affects numerous behavioral traits, including sexual drive, aggressiveness, and fear conditioning. However, the currently identified testosterone receptor(s) is not believed to underlie the fast signaling, suggesting an orphan pathway. Here we report that an ion channel from the transient receptor potential family, TRPM8, commonly known as the cold and menthol receptor is the major component of testosterone-induced rapid actions. Using cultured and primary cell lines along with the purified TRPM8 protein, we demonstrate that testosterone directly activates TRPM8 channel at low picomolar range. Specifically, testosterone induced TRPM8 responses in primary human prostate cells, PC3 prostate cancer cells, dorsal root ganglion neurons, and hippocampal neurons. Picomolar concentrations of testosterone resulted in full openings of the purified TRPM8 channel in planar lipid bilayers. Furthermore, acute applications of testosterone on human skin elicited a cooling sensation. Our data conclusively demonstrate that testosterone is an endogenous and highly potent agonist of TRPM8, suggesting a role of TRPM8 channels well beyond their well established function in somatosensory neurons. This discovery may further imply TRPM8 channel function in testosterone-dependent behavioral traits.

Identification and characterization of membrane androgen receptors in the ZIP9 zinc transporter subfamily: II. Role of human ZIP9 in testosterone-induced prostate and breast cancer cell apoptosis

Recently, we discovered a cDNA in teleost ovarian follicle cells belonging to the zinc transporter ZIP9 subfamily (SLC39A9) encoding a protein with characteristics of a membrane androgen receptor (mAR). Here, we demonstrate that human ZIP9 expressed in MDA-MB-468 breast cancer cells and stably overexpressed in human prostate cancer PC-3 cells (PC-3-ZIP9) also displays the ligand binding and signaling characteristics of a specific, high-affinity mAR. Testosterone treatment of MDA-MB-468 and PC-3-ZIP9 cells caused activation of G proteins and second messenger pathways as well as increases in intracellular free zinc concentrations that were accompanied by induction of apoptosis. [1,2,6,7-(3)H]-testosterone binding and these responses were abrogated in MDA-MB-468 cells after ZIP9 small interfering RNA (siRNA) treatment and absent in PC-3 cells transfected with empty vector, confirming that ZIP9 functions as an mAR. Testosterone treatment caused up-regulation of proapoptotic genes Bax (Bcl-2-associated X protein), p53 (tumor protein p53), and JNK (c-Jun N-terminal kinases) in both cell lines and increased expression of Bax, Caspase 3, and cytochrome C proteins. Treatment with a zinc chelator or a MAPK inhibitor blocked testosterone-induced increases in Bax, p53, and JNK mRNA expression. The results suggest that both androgen signaling and zinc transporter functions of ZIP9 mediate testosterone promotion of apoptosis. ZIP9 is widely expressed in human tissues and up-regulated in malignant breast and prostate tissues, suggesting that it is a potential therapeutic target for treating breast and prostate cancers. These results provide the first evidence for a mechanism mediated by a single protein through which steroid and zinc signaling pathways interact to regulate physiological functions in mammalian cells.

Enhancement of cell surface expression and receptor functions of membrane progestin receptor α (mPRα) by progesterone receptor membrane component 1 (PGRMC1): evidence for a role of PGRMC1 as an adaptor protein for steroid receptors

A variety of functions have been proposed for progesterone receptor membrane component 1 (PGRMC1), including acting as a component of a membrane progestin receptor and as an adaptor protein. Here we show that stable overexpression of human PGRMC1 in nuclear progesterone receptor (PR)-negative breast cancer cell lines causes increased expression of PGRMC1 and membrane progesterone receptor α (mPRα) on cell membranes that is associated with increased specific [(3)H]progesterone binding. The membrane progestin binding affinity and specificity were characteristic of mPRα, with a Kd of 4.7 nM and high affinity for the mPR-specific agonist, Org OD 02-0, and low affinity for corticosteroids. Progestin treatment caused activation of G proteins, further evidence for increased expression of functional mPRs on PGRMC1-transfected cell membranes. Immunocytochemical and coimmunoprecipitation studies showed a close association of PGRMC1 with mPRα in cell membranes. Transfection of PGRMC1 into spontaneously immortalized rat granulosa cells was associated with membrane expression of PGRMC1 and mPRα as well as antiapoptotic effects of progestins that were abolished after cotransfection with small interfering RNA for mPRα. These data demonstrate that PGRMC1 can act as an adaptor protein, transporting mPRα to the cell surface, and that the progestin binding and apoptotic functions previously ascribed to PGRMC1 are dependent on cell surface expression of mPRα. Collectively, the results suggest PGRMC1 and mPRα are components of a membrane progesterone receptor protein complex. Increased expression of estrogen receptor β was also observed in the membranes of PGRMC1-transfected cells, suggesting that PGRMC1 can act as an adaptor protein for multiple classes of steroid receptors.

Toxicological mechanism of endocrine disrupting chemicals:is estrogen receptor involved?

Endocrine disrupting chemicals (EDCs) have been shown to interfere with physiological systems, i.e., adversely affecting hormone balance (endocrine system) , or disrupting normal function, in the female and male reproductive organs. Although endocrine disruption is a global concern for human health, its impact and significance and the screening strategy for detecting these synthetic or man-made chemicals are not clearly understood in female and male reproductive functions. Thus, in this review, we summarize the interference of environmental EDCs on reproductive development and function, and toxicological mechanism (s) of EDCs in in vitro and in vivo models of male and female reproductive system. In addition, this review highlights the effect of exposure to multiple EDCs on reproductive functions, and brings attention to their toxicological mechanism (s) through estrogen receptors.

SHBG is an important factor in stemness induction of cells by DHT in vitro and associated with poor clinical features of prostate carcinomas

Androgen plays a vital role in prostate cancer development. However, it is not clear whether androgens influence stem-like properties of prostate cancer, a feature important for prostate cancer progression. In this study, we show that upon DHT treatment in vitro, prostate cancer cell lines LNCaP and PC-3 were revealed with higher clonogenic potential and higher expression levels of stemness related factors CD44, CD90, Oct3/4 and Nanog. Moreover, sex hormone binding globulin (SHBG) was also simultaneously upregulated in these cells. When the SHBG gene was blocked by SHBG siRNA knock-down, the induction of Oct3/4, Nanog, CD44 and CD90 by DHT was also correspondingly blocked in these cells. Immunohistochemical evaluation of clinical samples disclosed weakly positive, and areas negative for SHBG expression in the benign prostate tissues, while most of the prostate carcinomas were strongly positive for SHBG. In addition, higher levels of SHBG expression were significantly associated with higher Gleason score, more seminal vesicle invasions and lymph node metastases. Collectively, our results show a role of SHBG in upregulating stemness of prostate cancer cells upon DHT exposure in vitro, and SHBG expression in prostate cancer samples is significantly associated with poor clinicopathological features, indicating a role of SHBG in prostate cancer progression.

Isoform-specific regulation of cytochromes P450 expression by estradiol and progesterone

Results from clinical studies suggest that pregnancy alters hepatic drug metabolism in a cytochrome P450 (P450) isoform-specific manner, and rising concentrations of female hormones are potentially responsible for the changes. The objective of this study was to comprehensively characterize the effects of estrogen and progesterone on the expression and activity of major drug-metabolizing P450s. To this end, primary human hepatocytes were treated with estradiol and progesterone, and mRNA expression and activity levels of 10 different P450 isoforms were determined. The results showed that estradiol enhances CYP2A6, CYP2B6, and CYP3A4 expression, whereas progesterone induces CYP2A6, CYP2B6, CYP2C8, CYP3A4, and CYP3A5 expression. The induction was mainly observed when the average hormone concentrations were at the levels reached during pregnancy, suggesting that these effects are likely pregnancy-specific. Estradiol also increased enzyme activities of CYP2C9 and CYP2E1 without affecting the mRNA expression levels by unknown mechanisms. Taken together, our results show differential effects of estrogen and progesterone on P450 expression, suggesting involvement of different regulatory mechanisms in female hormone-mediated P450 regulation. Our findings potentially provide a basis in mechanistic understanding for altered drug metabolism during pregnancy.

Estrogen signaling in lung cancer: an opportunity for novel therapy

Lung cancer is the leading cause of cancer death in U.S. and represents a major public health burden. Epidemiologic data have suggested that lung cancer in women may possess different biological characteristics compared to men, as evidenced by a higher proportion of never-smokers among women with lung cancer. Emerging data indicate that female hormones such as estrogen and progesterone play a significant role in lung carcinogenesis. It has been reported that estrogen and progesterone receptors are expressed in lung cancer cell lines as well as in patient-derived tumors. Hormone related risk factors such as hormone replacement therapy have been implicated in lung carcinogenesis and several preclinical studies show activity of anti-estrogen therapy in lung cancer. In this review, we summarize the emerging evidence for the role of reproductive hormones in lung cancer and implications for lung cancer therapy.

Rapid steroid hormone actions initiated at the cell surface and the receptors that mediate them with an emphasis on recent progress in fish models

In addition to the classic genomic mechanism of steroid action mediated by activation of intracellular nuclear receptors, there is now extensive evidence that steroids also activate receptors on the cell surface to initiate rapid intracellular signaling and biological responses that are often nongenomic. Recent progress in our understanding of rapid, cell surface-initiated actions of estrogens, progestins, androgens and corticosteroids and the identities of the membrane receptors that act as their intermediaries is briefly reviewed with a special emphasis on studies in teleost fish. Two recently discovered novel proteins with seven-transmembrane domains, G protein-coupled receptor 30 (GPR30), and membrane progestin receptors (mPRs) have the ligand binding and signaling characteristics of estrogen and progestin membrane receptors, respectively, but their functional significance is disputed by some researchers. GPR30 is expressed on the cell surface of fish oocytes and mediates estrogen inhibition of oocyte maturation. mPRα is also expressed on the oocyte cell surface and is the intermediary in progestin induction of oocyte maturation in fish. Recent results suggest there is cross-talk between these two hormonal pathways and that there is reciprocal down-regulation of GPR30 and mPRα expression by estrogens and progestins at different phases of oocyte development to regulate the onset of oocyte maturation. There is also evidence in fish that mPRs are involved in progestin induction of sperm hypermotility and anti-apoptotic actions in ovarian follicle cells. Nonclassical androgen and corticosteroid actions have also been described in fish models but the membrane receptors mediating these actions have not been identified.

Membrane progesterone receptors: evidence for neuroprotective, neurosteroid signaling and neuroendocrine functions in neuronal cells

Membrane progesterone receptors (mPRs) are novel G protein-coupled receptors belonging to the progestin and adipoQ receptor family (PAQR) that mediate a variety of rapid cell surface-initiated progesterone actions in the reproductive system involving activation of intracellular signaling pathways (i.e. nonclassical actions). The mPRs are highly expressed in the brain, but research on their neural functions has only been conducted in a single neuronal cell line, GT1-7 cells, which have negligible nuclear progesterone receptor (PR) expression. GT1-7 cells express mPRα and mPRβ on their plasma membranes which is associated with the presence of high-affinity, specific [(3)H]-progesterone receptor binding. The neurosteroid, allopregnanolone, is an effective ligand for recombinant mPRα with a relative binding affinity of 7.6% that of progesterone. Allopregnanolone acts as a potent mPR agonist on GT1-7 cells, mimicking the progesterone-induced decrease in cAMP accumulation and its antiapoptotic actions at low nanomolar concentrations. The decrease in cAMP levels is associated with rapid progesterone-induced downregulation of GnRH pulsatile secretion from perifused GT1-7 cells. The recent suggestion that mPRs are alkaline ceramidases and mediate sphingolipid signaling is not supported by empirical evidence that TNFα does not bind to mPRs overexpressed in human cells and that exogenous sphingomyelinase is ineffective in mimicking progestin actions through mPRs to induce meiotic maturation of fish oocytes. Taken together, these recent studies indicate that mPRs mediate neuroprotective effects of progesterone and allopregnanolone and are also the likely intermediaries in progesterone-induced inhibition of pulsatile GnRH secretion in GT1-7 cells.

Progesterone signals through membrane progesterone receptors (mPRs) in MDA-MB-468 and mPR-transfected MDA-MB-231 breast cancer cells which lack full-length and N-terminally truncated isoforms of the nuclear progesterone receptor

The functional characteristics of membrane progesterone receptors (mPRs) have been investigated using recombinant mPR proteins over-expressed in MDA-MB-231 breast cancer cells. Although these cells do not express the full-length progesterone receptor (PR), it is not known whether they express N-terminally truncated PR isoforms which could possibly account for some progesterone receptor functions attributed to mPRs. In the present study, the presence of N-terminally truncated PR isoforms was investigated in untransfected and mPR-transfected MDA-MB-231 cells, and in MDA-MB-468 breast cancer cells. PCR products were detected in PR-positive T47D Yb breast cancer cells using two sets of C-terminus PR primers, but not in untransfected and mPR-transfected MDA-MB-231 cells, nor in MDA-MB-468 cells. Western blot analysis using a C-terminal PR antibody, 2C11F1, showed the same distribution pattern for PR in these cell lines. Another C-terminal PR antibody, C-19, detected immunoreactive bands in all the cell lines, but also recognized α-actinin, indicating that the antibody is not specific for PR. High affinity progesterone receptor binding was identified on plasma membranes of MDA-MB-468 cells which was significantly decreased after treatment with siRNAs for mPRα and mPRβ. Plasma membranes of MDA-MB-468 cells showed very low binding affinity for the PR agonist, R5020, ≤1% that of progesterone, which is characteristic of mPRs. Progesterone treatment caused G protein activation and decreased production of cAMP in MDA-MB-468 cells, which is also characteristic of mPRs. The results indicate that the progestin receptor functions in these cell lines are mediated through mPRs and do not involve any N-terminally truncated PR isoforms.

17β-Estradiol enhances breast cancer cell motility and invasion via extra-nuclear activation of actin-binding protein ezrin

Estrogen promotes breast cancer metastasis. However, the detailed mechanism remains largely unknown. The actin binding protein ezrin is a key component in tumor metastasis and its over-expression is positively correlated to the poor outcome of breast cancer. In this study, we investigate the effects of 17β-estradiol (E2) on the activation of ezrin and its role in estrogen-dependent breast cancer cell movement. In T47-D breast cancer cells, E2 rapidly enhances ezrin phosphorylation at Thr⁵⁶⁷ in a time- and concentration-dependent manner. The signalling cascade implicated in this action involves estrogen receptor (ER) interaction with the non-receptor tyrosine kinase c-Src, which activates the phosphatidylinositol-3 kinase/Akt pathway and the small GTPase RhoA/Rho-associated kinase (ROCK-2) complex. E2 enhances the horizontal cell migration and invasion of T47-D breast cancer cells in three-dimensional matrices, which is reversed by transfection of cells with specific ezrin siRNAs. In conclusion, E2 promotes breast cancer cell movement and invasion by the activation of ezrin. These results provide novel insights into the effects of estrogen on breast cancer progression and highlight potential targets to treat endocrine-sensitive breast cancers.

Rediscovering sperm ion channels with the patch-clamp technique

Upon ejaculation, mammalian spermatozoa have to undergo a sequence of physiological transformations within the female reproductive tract that will allow them to reach and fertilize the egg. These include initiation of motility, hyperactivation of motility and perhaps chemotaxis toward the egg, and culminate in the acrosome reaction that permits sperm to penetrate the protective vestments of the egg. These physiological responses are triggered through the activation of sperm ion channels that cause elevations of sperm intracellular pH and Ca(2+) in response to certain cues within the female reproductive tract. Despite their key role in sperm physiology and their absolute requirement for the process of fertilization, sperm ion channels remain poorly understood due to the extreme difficulty in application of the patch-clamp technique to spermatozoa. This review covers the topic of sperm ion channels in the following order: first, we discuss how the intracellular Ca(2+) and pH signaling mediated by sperm ion channels controls sperm behavior during the process of fertilization. Then, we briefly cover the history of the methodology to study sperm ion channels, which culminated in the recent development of a reproducible whole-cell patch-clamp technique for mouse and human cells. We further discuss the main approaches used to patch-clamp mature mouse and human spermatozoa. Finally, we focus on the newly discovered sperm ion channels CatSper, KSper (Slo3) and HSper (H(v)1), identified by the sperm patch-clamp technique. We conclude that the patch-clamp technique has markedly improved and shifted our understanding of the sperm ion channels, in addition to revealing significant species-specific differences in these channels. This method is critical for identification of the molecular mechanisms that control sperm behavior within the female reproductive tract and make fertilization possible.

Progesterone activates the principal Ca2+ channel of human sperm

Steroid hormone progesterone released by cumulus cells surrounding the egg is a potent stimulator of human spermatozoa. It attracts spermatozoa towards the egg and helps them penetrate the egg's protective vestments. Progesterone induces Ca(2+) influx into spermatozoa and triggers multiple Ca(2+)-dependent physiological responses essential for successful fertilization, such as sperm hyperactivation, acrosome reaction and chemotaxis towards the egg. As an ovarian hormone, progesterone acts by regulating gene expression through a well-characterized progesterone nuclear receptor. However, the effect of progesterone upon transcriptionally silent spermatozoa remains unexplained and is believed to be mediated by a specialized, non-genomic membrane progesterone receptor. The identity of this non-genomic progesterone receptor and the mechanism by which it causes Ca(2+) entry remain fundamental unresolved questions in human reproduction. Here we elucidate the mechanism of the non-genomic action of progesterone on human spermatozoa by identifying the Ca(2+) channel activated by progesterone. By applying the patch-clamp technique to mature human spermatozoa, we found that nanomolar concentrations of progesterone dramatically potentiate CatSper, a pH-dependent Ca(2+) channel of the sperm flagellum. We demonstrate that human CatSper is synergistically activated by elevation of intracellular pH and extracellular progesterone. Interestingly, human CatSper can be further potentiated by prostaglandins, but apparently through a binding site other than that of progesterone. Because our experimental conditions did not support second messenger signalling, CatSper or a directly associated protein serves as the elusive non-genomic progesterone receptor of sperm. Given that the CatSper-associated progesterone receptor is sperm specific and structurally different from the genomic progesterone receptor, it represents a promising target for the development of a new class of non-hormonal contraceptives.

Role of G protein-coupled estrogen receptor 1, GPER, in inhibition of oocyte maturation by endogenous estrogens in zebrafish

Estrogen inhibition of oocyte maturation (OM) and the role of GPER (formerly known as GPR30) were investigated in zebrafish. Estradiol-17beta (E2) and G-1, a GPER-selective agonist, bound to zebrafish oocyte membranes suggesting the presence of GPER which was confirmed by immunocytochemistry using a specific GPER antibody. Incubation of follicle-enclosed oocytes with an aromatase inhibitor, ATD, and enzymatic and manual removal of the ovarian follicle cell layers significantly increased spontaneous OM which was partially reversed by co-treatment with either 100 nM E2 or G-1. Incubation of denuded oocytes with the GPER antibody blocked the inhibitory effects of estrogens on OM, whereas microinjection of estrogen receptor alpha (ERalpha) antisense oligonucleotides into the oocytes was ineffective. The results suggest that endogenous estrogens produced by the follicle cells inhibit or delay spontaneous maturation of zebrafish oocytes and that this estrogen action is mediated through GPER. Treatment with E2 and G-1 also attenuated the stimulatory effect of the teleost maturation-inducing steroid, 17,20beta-dihyroxy-4-pregnen-3-one (DHP), on OM. Moreover, E2 and G-1 down-regulated the expression of membrane progestin receptor alpha (mPRalpha), the intermediary in DHP induction of OM. Conversely DHP treatment caused a >50% decline in GPER mRNA levels. The results suggest that estrogens and GPER are critical components of the endocrine system controlling the onset of OM in zebrafish. A model is proposed for the dual control of the onset of oocyte maturation in teleosts by estrogens and progestins acting through GPER and mPRalpha, respectively, at different stages of oocyte development.

Aromatase, oestrogens and human male reproduction

In most mammalian species aromatase is encoded by a single gene (Cyp19), which contains 18 exons, nine of them being translated. In man, the presence of a biologically active aromatase and oestrogen receptors (ERalpha and ERbeta) has been reported in Leydig cells, and also in immature germ cells and ejaculated spermatozoa. Concerning aromatase, the amount of transcript and enzymatic activity are decreased in immotile compared with motile sperm. We have amplified aromatase mRNA by real-time polymerase chain reaction in spermatozoa from asthenospermic, teratospermic and asthenoteratospermic men and recorded, respectively, 44, 52 and 67 per cent decreases of the amount of transcripts compared with fertile donors. A high degree of correlation (r = -0.64) between the abnormal spermatozoa (especially microcephaly and acrosome malformations) and aromatase/GAPDH transcript ratio has been observed. Idiopathic infertility is a wide health problem and no treatment is currently available. In humans, even if the role of oestrogens in spermatogenesis is still a matter of debate, the observations of decreased sperm number and motility in men genetically deficient in aromatase, together with our data and those reported in the literature, may suggest a role for aromatase/oestrogens not only during the development and maintenance of spermatogenesis but also in the final maturation of spermatozoa.

Interdependence of platelet-derived growth factor and estrogen-signaling pathways in inducing neonatal rat testicular gonocytes proliferation

We previously found that platelet-derived growth factor (PDGF) and 17beta-estradiol stimulate gonocyte proliferation in a dose-dependent, nonadditive manner. In the present study, we report that gonocytes express RAF1, MAP2K1, and MAPK1/3. Inhibition of RAF1 and MAP2K1/2, but not phosphoinositide-3-kinase, blocked PDGF-induced proliferation. AG-370, an inhibitor of PDGF receptor kinase activity, suppressed not only PDGF-induced proliferation but also that induced by 17beta-estradiol. In addition, RAF1 and MAP2K1/2 inhibitors blocked 17beta-estradiol-activated proliferation. The estrogen receptor antagonist ICI 182780 inhibited both the effects of 17beta-estradiol and PDGF. PDGF lost its stimulatory effect when steroid-depleted serum or no serum was used. Similarly, 17beta-estradiol did not induce gonocyte proliferation in the absence of PDGF. The xenoestrogens genistein, bisphenol A, and DES, but not coumestrol, stimulated gonocyte proliferation in a dose-dependent and PDGF-dependent manner similarly to 17beta-estradiol. Their effects were blocked by ICI 182780, suggesting that they act via the estrogen receptor. AG-370 blocked genistein and bisphenol A effects, demonstrating their requirement of PDGF receptor activation in a manner similar to 17beta-estradiol. These results demonstrate the interdependence of PDGF and estrogen pathways in stimulating in vitro gonocyte proliferation, suggesting that this critical step in gonocyte development might be regulated in vivo by the coordinated action of PDGF and estrogen. Thus, the inappropriate exposure of gonocytes to xenoestrogens might disrupt the crosstalk between the two pathways and potentially interfere with gonocyte development.

Gene expression profiles of intracellular and membrane progesterone receptor isoforms in the mediobasal hypothalamus during pro-oestrus

Progesterone action is mediated by its binding to specific receptors. Two progesterone receptor (PR) isoforms (PRA and PRB), three membrane progesterone receptor (mPR) subtypes (mPRalpha, mPRbeta and mPRgamma) and at least one progesterone membrane-binding protein [PR membrane component 1 (PRmc1)] have been identified in reproductive tissues and brain of various species. In the present study, we examined gene expression patterns for PR isoforms, mPR subtypes and PRmc1 in the rat mediobasal hypothalamus (MBH) during pro-oestrus. The mRNA level for each receptor subtype was quantified by a real-time reverse transcriptase-polymerase chain reaction (RT-PCR) at the time points: 13.00 h on dioestrous day 2; 09.00, 13.00, 17.00 and 22.00 h on pro-oestrus; and 13.00 h on oestrus. For PR, one primer set amplified PRA+PRB, whereas a second primer set amplified PRB. As expected, PRA+PRB mRNA expression was greater than PRB in MBH tissue. PRB mRNA levels increased throughout the day on pro-oestrus, with the highest levels being observed at 17.00 h. PRB mRNA levels in the MBH were increased by 2.4- and 3.0-fold at 13.00 and 17.00 h, respectively, on pro-oestrus compared to 13.00 h on dioestrous day 2. There were differential mRNA expression levels for mPRs and PRmc1 in the MBH, with the highest expression for PRmc1 and the lowest for mPRgamma. The mPRalpha mRNA contents at 13.00 and 17.00 h on pro-oestrus were increased by 1.5-fold compared to that at 13.00 h on dioestrous day 2. The mPRbeta mRNA levels at 13.00 and 17.00 h on pro-oestrus were 2.5- and 2.4-fold higher compared to that at 13.00 h on dioestrous day 2, respectively. PRA+PRB, mPRgamma and PRmc1 mRNA levels did not vary on pro-oestrus. These findings suggest that the higher expression of PRB, mPRalpha and mPRbeta in the MBH on pro-oestrous afternoon may influence both genomic and nongenomic mechanisms of progesterone action during the critical pre-ovulatory period.

Motivations and methods for analyzing pulsatile hormone secretion

Endocrine glands communicate with remote target cells via a mixture of continuous and intermittent signal exchange. Continuous signaling allows slowly varying control, whereas intermittency permits large rapid adjustments. The control systems that mediate such homeostatic corrections operate in a species-, gender-, age-, and context-selective fashion. Significant progress has been made in understanding mechanisms of adaptive interglandular signaling in vivo. Principal goals are to understand the physiological origins, significance, and mechanisms of pulsatile hormone secretion. Key analytical issues are: 1) to quantify the number, size, shape, and uniformity of pulses, nonpulsatile (basal) secretion, and elimination kinetics; 2) to evaluate regulation of the axis as a whole; and 3) to reconstruct dose-response interactions without disrupting hormone connections. This review will focus on the motivations driving and the methodologies used for such analyses.

Vascular actions of estrogens: functional implications

The impact of estrogen exposure in preventing or treating cardiovascular disease is controversial. But it is clear that estrogen has important effects on vascular physiology and pathophysiology, with potential therapeutic implications. Therefore, the goal of this review is to summarize, using an integrated approach, current knowledge of the vascular effects of estrogen, both in humans and in experimental animals. Aspects of estrogen synthesis and receptors, as well as general mechanisms of estrogenic action are reviewed with an emphasis on issues particularly relevant to the vascular system. Recent understanding of the impact of estrogen on mitochondrial function suggests that the longer lifespan of women compared with men may depend in part on the ability of estrogen to decrease production of reactive oxygen species in mitochondria. Mechanisms by which estrogen increases endothelial vasodilator function, promotes angiogenesis, and modulates autonomic function are summarized. Key aspects of the relevant pathophysiology of inflammation, atherosclerosis, stroke, migraine, and thrombosis are reviewed concerning current knowledge of estrogenic effects. A number of emerging concepts are addressed throughout. These include the importance of estrogenic formulation and route of administration and the impact of genetic polymorphisms, either in estrogen receptors or in enzymes responsible for estrogen metabolism, on responsiveness to hormone treatment. The importance of local metabolism of estrogenic precursors and the impact of timing for initiation of treatment and its duration are also considered. Although consensus opinions are emphasized, controversial views are presented to stimulate future research.

Characteristics of membrane progestin receptor alpha (mPRalpha) and progesterone membrane receptor component 1 (PGMRC1) and their roles in mediating rapid progestin actions

Rapid, progestin actions initiated at the cell surface that are often nongenomic have been described in a variety of reproductive tissues, but until recently the identities of the membrane receptors mediating these nonclassical progestins actions remained unclear. Evidence has been obtained in the last 4-5 years for the involvement of two types of novel membrane proteins unrelated to nuclear steroid receptors, progesterone membrane receptors (mPRs) and progesterone receptor membrane component 1 (PGMRC1), in progestin signaling in several vertebrate reproductive tissues and in the brain. The mPRs, (M(W) approximately 40 kDa) initially discovered in fish ovaries, comprise at least three subtypes, alpha, beta and gamma and belong to the seven-transmembrane progesterone adiponectin Q receptor (PAQR) family. Both recombinant and wildtype mPRs display high affinity (K(d) approximately 5 nM), limited capacity, displaceable and specific progesterone binding. The mPRs are directly coupled to G proteins and typically activate pertussis-sensitive inhibitory G proteins (G(i)), to down-regulate adenylyl cyclase activity. Recent studies suggest the alpha subtype (mPRalpha) has important physiological functions in variety of reproductive tissues. The mPRalpha is an intermediary in progestin induction of oocyte maturation and stimulation of sperm hypermotility in fish. In mammals, the mPRalphas have been implicated in progesterone regulation of uterine function in humans and GnRH secretion in rodents. The single-transmembrane protein PGMRC1 (M(W) 26-28 kDa) was first purified from porcine livers and its cDNA was subsequently cloned from porcine smooth muscle cells and a variety of other tissues by different investigators. PGMRC1 and the closely-related PGMRC2 belong to the membrane-associated progesterone receptor (MAPR) family. The PGMRC1 protein displays moderately high binding affinity for progesterone which is 2- to 10-fold greater than that for testosterone and glucocorticoids, and also can bind to other molecules such as heme, cholesterol metabolites and proteins. The signal transduction pathways induced by binding of progesterone to PGMRC1 have not been described to date, although motifs for tyrosine kinase, kinase binding, SH2 and SH3 have been predicted from the amino acid sequence. Evidence has been obtained that PGMRC1 mediates the antiapoptotic affects of progesterone in rat granulosa cells. The PGMRC1 protein may also be an intermediary in the progesterone induction of the acrosome reaction in mammalian sperm. Despite these recent advances, many aspects of progestin signaling through these two families of novel membrane proteins remain unresolved. Biochemical characterization of the receptors has been hampered by rapid degradation of the partially purified proteins. A major technical challenge has been to express sufficient amounts of the recombinant receptors on the plasma membranes in eukaryotic systems to permit investigations of their progestin binding and signal transduction characteristics. Additional basic information on the molecular and cellular mechanisms by which mPRs and PGMRC1 interact with progestins, signal transductions pathways and other proteins will be required to establish a comprehensive model of nontraditional progestin actions mediated through these novel proteins.

Regulation of BCRP/ABCG2 expression by progesterone and 17beta-estradiol in human placental BeWo cells

The breast cancer resistance protein (BCRP) is abundant in the placenta and protects the fetus by limiting placental drug penetration. We hypothesize that pregnancy-specific hormones regulate BCRP expression. Hence, we examined the effects of progesterone (P4) and 17beta-estradiol (E2) on BCRP expression in the human placental BeWo cells. P4 and E2 significantly increased and decreased BCRP protein and mRNA, respectively. Likewise, treatment with P4 and E2 increased and decreased, respectively, fumitremorgin C-inhibitable mitoxantrone efflux activity of BeWo cells. Reduction in BCRP expression by E2 was abrogated by the estrogen receptor (ER) antagonist ICI-182,780. However, the progesterone receptor (PR) antagonist RU-486 had no effect on P4-mediated induction of BCRP. P4 together with E2 further increased BCRP protein and mRNA compared with P4 treatment alone. This combined effect on BCRP expression was abolished by RU-486, ICI-182,780, or both. Further analysis revealed that E2 significantly decreased ER beta mRNA and strongly induced PR(B) mRNA in a dose-dependent manner but had no effect on PR(A) and ER alpha. P4 alone had no significant effect on mRNA of ER alpha, ER beta, PR(A), and PR(B). E2 in combination with P4 increased PR(B) mRNA, but the level of induction was significantly reduced compared with E2 treatment alone. Taken together, these results indicate that E2 by itself likely downregulates BCRP expression through an ER, possibly ER beta. P4 alone upregulates BCRP expression via a mechanism other than PR. P4 in combination with E2 further increases BCRP expression, presumably via a nonclassical PR- and/or E2-mediated synthesis of PR(B).

Novel mechanisms of resistance to endocrine therapy: genomic and nongenomic considerations

Selective estrogen receptor (ER) modulators have been the most commonly used neoadjuvant therapy for hormone-dependent breast cancer. However, resistance to endocrine therapy, either inherent or acquired during treatment, presents a major challenge in disease management. The causes of resistance to hormone therapy are not well understood and are the subject of active investigation. It is increasingly clear that decreasing sensitivity of ER-positive breast cancer cells to antiestrogens is caused by several factors. Cross talk between ER and growth factor signaling has emerged as a critical factor in endocrine resistance. Here, we present evidence that receptor tyrosine kinase signaling also plays a role in resistance by controlling the subcellular localization of ER signaling components. Localization of ER in either the nuclear or cytoplasmic compartments has functional implications. Recent work suggests that dynein light chain 1, a recently identified substrate of p21-activated kinase 1, modulates ER transactivation functions through a novel ER coactivator function. Likewise, receptor tyrosine kinase signaling can also alter the expression of ER coregulators such as metastasis-associated antigen 1, leading to hormonal independence. Furthermore, proline-, glutamic acid-, leucine-rich protein 1, an ER coactivator involved in both genomic and nongenomic signaling pathways, is activated by epidermal growth factor receptor and plays a prominent role in resistance to tamoxifen. These recent advances suggest new targeted therapeutic approaches that may lead to either reversion or prevention of endocrine resistance in breast tumors.

Altered localization of a coactivator sensitizes breast cancer cells to tumor necrosis factor–induced apoptosis

Proline-, glutamic acid-, and leucine-rich protein-1 (PELP1) is a novel coregulator of the estrogen receptor that plays a role in both genomic and nongenomic actions of the estrogen receptor. Emerging studies suggest that in addition to the nuclear localization of PELP1, it is predominantly localized in the cytoplasm in human breast tumors, leading to excessive nongenomic signaling and possibly to tamoxifen resistance. The mechanisms underlying resistance to hormones in preclinical model systems remain under intense investigation. In an effort to develop a model system to treat tumor cells with cytoplasmic PELP1 expression and tamoxifen resistance, here we used the cytokine tumor necrosis factor (TNF)-alpha. We found that clones of MCF-7 human breast cancer cells overexpressing PELP1 in the cytoplasm were distinctly sensitive to TNF-alpha-induced apoptosis than were wild-type nuclear PELP1- and pcDNA vector-expressing clones as revealed by cell growth assay, cell cycle analysis, Annexin V staining, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. We also found that the clones with cytoplasmic PELP1 overexpression had significantly less antiapoptotic protein Bcl-2 and nuclear factor-kappaB DNA binding, but increased cyclin E expression, further supporting evidence that these cells are sensitive to apoptosis. The mechanism behind TNF-induced apoptosis in these cells involves caspases, as revealed by poly(ADP-ribose) polymerase cleavage and the broad-spectrum caspase inhibitor Z-VAD-inhibited apoptosis. In conclusion, our results suggest that altered localization of PELP1 promotes heightened sensitivity to TNF-alpha in MCF-7 cells, paving the way for developing new treatment strategies for tumors with cytoplasmic PELP1 expression.

Functional implications of altered subcellular localization of PELP1 in breast cancer cells

It is increasingly accepted that steroidal receptor co-regulators may also function in the cytoplasmic compartment. Proline-, glutamic acid-, and leucine-rich protein-1 (PELP1) is a novel coregulator that plays a role in both the genomic and extranuclear actions of estrogen receptors (ER) in hormonally responsive tissues. In this study using breast tumor arrays, we found that PELP1 was localized only in the cytoplasm in 58% of the PELP1-positive breast tumors. To help explain the significance of the cytoplasmic localization of PELP1 in human breast tumors, we created a mutant protein that was expressed only in the cytoplasm (PELP1-cyto) and then generated a model system wherein MCF-7 breast cancer cells were engineered to specifically express this mutant. We found that PELP1-cyto cells were hypersensitive to estrogen but resistant to tamoxifen. PELP1-cyto cells, but not parental MCF-7 cells, formed xenograft tumors in nude mice. In addition, PELP1-cyto cells exhibited increased association of PELP1 with Src, enhanced mitogen-activated protein kinase (MAPK) activation, and constitutive activation of AKT. The altered localization of PELP1 was sufficient to trigger the interaction of PELP1 with the p85 subunit of phosphatidylinositol-3-kinase (PI3K), leading to PI3K activation. In addition, PELP1 interacted with epidermal growth factor receptors and participated in growth factor-mediated ER transactivation functions. Our results suggest that the altered localization of PELP1 modulates sensitivity to antiestrogens, potentiates tumorigenicity, presumably via the stimulation of extranuclear estrogen responses, such as the activation of MAPK and AKT, and also enhance cross-regulation of ER transactivation activity by growth factors.

The role of aromatase inhibitors in ameliorating deleterious effects of ovarian stimulation on outcome of infertility treatment

Clinical utilization of ovulation stimulation to facilitate the ability of a couple to conceive has not only provided a valuable therapeutic approach, but has also yielded extensive information on the physiology of ovarian follicular recruitment, endometrial receptivity and early embryo competency. One of the consequences of the use of fertility enhancing agents for ovarian stimulation has been the creation of a hyperestrogenic state, which may influence each of these parameters. Use of aromatase inhibitors reduces hyperestrogenism inevitably attained during ovarian stimulation. In addition, the adjunct use of aromatase inhibitors during ovarian stimulation reduces amount of gonadotropins required for optimum stimulation. The unique approach of reducing hyperestrogenism, as well as lowering amount of gonadotropins without affecting the number of mature ovarian follicles is an exciting strategy that could result in improvement in the treatment outcome by ameliorating the deleterious effects of the ovarian stimulation on follicular development, endometrial receptivity, as well as oocyte and embryo quality.

Hippocampal synapses depend on hippocampal estrogen synthesis

Estrogens have been described to induce synaptogenesis in principal neurons of the hippocampus and have been shown to be synthesized and released by exactly these neurons. Here, we have focused on the significance of local estrogen synthesis on spine synapse formation and the synthesis of synaptic proteins. To this end, we reduced hippocampal estrogen synthesis in vitro with letrozole, a reversible nonsteroidal aromatase inhibitor. In hippocampal slice cultures, letrozole treatment resulted in a dose-dependent decrease of 17beta-estradiol as quantified by RIA. This was accompanied by a significant decrease in the density of spine synapses and in the number of presynaptic boutons. Quantitative immunohistochemistry revealed a downregulation of spinophilin, a marker of dendritic spines, and synaptophysin, a protein of presynaptic vesicles, in response to letrozole. Surprisingly, no increase in the density of spines, boutons, and synapses and in spinophilin expression was seen after application of estradiol to the medium of cultures that had not been treated with letrozole. However, synaptophysin expression was upregulated under these conditions. Our results point to an essential role of endogenous hippocampal estrogen synthesis in the maintenance of hippocampal spine synapses.

Role of tyrosine phosphorylation in sperm capacitation / acrosome reaction

Capacitation is an important physiological pre-requisite before the sperm cell can acrosome react and fertilize the oocyte. Recent reports from several laboratories have amply documented that the protein phosphorylation especially at tyrosine residues is one of the most important events that occur during capacitation. In this article, we have reviewed the data from our and other laboratories, and have constructed a heuristic model for the mechanisms and molecules involved in capacitation/acrosome reaction.

Brain masculinization requires androgen receptor function

Testicular testosterone produced during a critical perinatal period is thought to masculinize and defeminize the male brain from the inherent feminization program and induce male-typical behaviors in the adult. These actions of testosterone appear to be exerted not through its androgenic activity, but rather through its conversion by brain aromatase into estrogen, with the consequent activation of estrogen receptor (ER)-mediated signaling. Thus, the role of androgen receptor (AR) in perinatal brain masculinization underlying the expression of male-typical behaviors remains unclear because of the conversion of testosterone into estrogen in the brain. Here, we report a null AR mutation in mice generated by the Cre-loxP system. The AR-null mutation in males (AR(L-/Y)) resulted in the ablation of male-typical sexual and aggressive behaviors, whereas female AR-null homozygote (AR(L-/L-)) mice exhibited normal female sexual behaviors. Treatment with nonaromatizable androgen (5alpha-dihydrotestosterone, DHT) was ineffective in restoring the impaired male sexual behaviors, but it partially rescued impaired male aggressive behaviors in AR(L-/Y) mice. Impaired male-typical behaviors in ERalpha(-/-) mice were restored on DHT treatment. The role of AR function in brain masculinization at a limited perinatal stage was studied in AR(L-/L-) mice. Perinatal DHT treatment of females led to adult females sensitive to both 17beta-estradiol and DHT in the induction of male-typical behaviors. However, this female brain masculinization was abolished by AR inactivation. Our results suggested that perinatal brain masculinization requires AR function and that expression of male-typical behaviors in adults is mediated by both AR-dependent and -independent androgen signaling.

Nongenomic steroid action: controversies, questions, and answers

Steroids may exert their action in living cells by several ways: 1). the well-known genomic pathway, involving hormone binding to cytosolic (classic) receptors and subsequent modulation of gene expression followed by protein synthesis. 2). Alternatively, pathways are operating that do not act on the genome, therefore indicating nongenomic action. Although it is comparatively easy to confirm the nongenomic nature of a particular phenomenon observed, e.g., by using inhibitors of transcription or translation, considerable controversy exists about the identity of receptors that mediate these responses. Many different approaches have been employed to answer this question, including pharmacology, knock-out animals, and numerous biochemical studies. Evidence is presented for and against both the participation of classic receptors, or proteins closely related to them, as well as for the involvement of yet poorly understood, novel membrane steroid receptors. In addition, clinical implications for a wide array of nongenomic steroid actions are outlined.

Aromatase expression and role of estrogens in male gonad : a review

The ability of the testis to convert irreversibly androgens into estrogens is related to the presence of a microsomal enzymatic complex named aromatase, which is composed of a specific glycoprotein, the cytochrome P450 aromatase (P450arom) and an ubiquitous reductase. The aromatase gene is unique in humans and contained 18 exons, 9 of them being translated. In the rat testis we have immunolocalized the P450arom not only in Leydig cells but also in germ cells and especially in elongated spermatids. Related to the stage of germ cell maturation, we have shown that the level of P450arom mRNA transcripts decreases, it is much more abundant in pachytene spermatocytes and round spermatids than in mature germ cells whereas the aromatase activity is 2-4 fold greater in spermatozoa when compared to the younger germ cells. Using a highly specific quantitative competitive RT-PCR method we have evidenced that several factors direct the expression of the aromatase gene in Leydig cells, Sertoli cells, pachytene spermatocytes and round spermatids, and it is obvious that promoter PII is the main one but other promoters could be concerned. In the bank-vole testis we have observed a positive correlation between a fully developed spermatogenesis and a strong immunoreactivity for both P450arom and estrogen receptor beta not only in Sertoli cells but also in pachytene spermatocytes and round spermatids. Our recent data obtained from ejaculated human spermatozoa demonstrate the presence of aromatase both in terms of mRNA and protein, and in addition, we suggest that aromatase could be involved in the acquisition of sperm motility. Indeed in men the congenital aromatase deficiency is associated with severe bone maturation problems and sterility. Together with the widespread distribution of estrogen receptors in testicular cells these data clearly show that estrogens play a physiological role in the regulation of spermatogenesis in mammals.

Visualizing activation of opioid circuits by internalization of G protein-coupled receptors

Mu-opioid receptor (MOR) and opioid receptor-like receptor (ORL-1) circuits in the limbic hypothalamic system are important for the regulation of sexual receptivity in the female rat. Sexual receptivity is tightly regulated by the sequential release of estrogen and progesterone from the ovary suggesting ovarian steroids regulate the activity of these neuropeptide systems. Both MOR and ORL-1 distributions overlap with the distribution of estrogen and progesterone receptors in the hypothalamus and limbic system providing a morphological substrate for interaction between steroids and the opioid circuits in the brain. Both MOR and ORL-1 are receptors that respond to activation by endogenous ligands with internalization into early endosomes. This internalization is part of the mechanism of receptor desensitization or down regulation. Although receptor activation and internalization are separate events, internalization can be used as a temporal measure of circuit activation by endogenous ligands. This review focuses on the estrogen and progesterone regulation of MOR and ORL-1 circuits in the medial preoptic nucleus and ventromedial nucleus of the hypothalamus that are central to modulating sexual receptivity.

Cloning, expression, and characterization of a membrane progestin receptor and evidence it is an intermediary in meiotic maturation of fish oocytes

The structures of membrane receptors mediating rapid, nongenomic actions of steroids have not been identified. We describe the cloning of a cDNA from spotted seatrout ovaries encoding a protein that satisfies the following seven criteria for its designation as a steroid membrane receptor: plausible structure, tissue specificity, cellular distribution, steroid binding, signal transduction, hormonal regulation, and biological relevance. For plausible structure, computer modeling predicts that the protein has seven transmembrane domains, typical of G protein-coupled receptors. The mRNA (4.0 kb) is only detected in the brain and reproductive tissues on Northern blots. Antisera only detect the protein (40 kDa) in plasma membranes of reproductive tissues. The recombinant protein produced in an Escherichia coli expression system has a high affinity (K(d) = 30 nM), saturable, displaceable, single binding site specific for progestins. Progestins alter signal transduction pathways, activating mitogen-activated protein kinase and inhibiting adenylyl cyclase, in a transfected mammalian cell line. Inhibition of adenylyl cyclase is pertussis toxin sensitive, suggesting the receptor may be coupled to an inhibitory G protein. Progestins and gonadotropin up-regulate both mRNA and protein levels in seatrout ovaries. Changes in receptor abundance in response to hormones and at various stages of oocyte development, its probable coupling to an inhibitory G protein and inhibition of progestin induction of oocyte maturation upon microinjection of antisense oligonucleotides are consistent with the identity of the receptor as an intermediary in oocyte maturation. These characteristics suggest the fish protein is a membrane progestin receptor mediating a "nonclassical" action of progestins to induce oocyte maturation in fish.

Identification, classification, and partial characterization of genes in humans and other vertebrates homologous to a fish membrane progestin receptor

Recently we discovered a previously uncharacterized gene with the characteristics of a membrane progestin receptor (mPR) in a fish model, spotted seatrout. Here, we report the identification, cloning, and characteristics of other members of this hitherto unknown family of putative mPRs from several vertebrate species, including human, mouse, pig, Xenopus, zebrafish, and Fugu, with highly conserved nucleotide and deduced amino acid sequences and similar structures to the spotted seatrout mPR. The 13 vertebrate genes identified seem to belong to an unknown gene family. Phylogenetic analysis indicates these cDNAs comprise three distinct groups (named alpha, beta, and gamma) within this gene family. Structural analyses of the translated cDNAs suggest they encode membrane proteins with seven transmembrane domains. The transcript sizes of the human alpha, beta, and gamma putative mPR mRNAs varied from 2.8 to 5.8 kb and showed distinct distributions in reproductive, neural, kidney and intestinal tissues, respectively. Recombinant human alpha, gamma, and mouse beta proteins produced in an Escherichia coli expression system demonstrated high affinity (K(d) = 20-30 nM) saturable binding for progesterone. Further analysis of binding to the gamma-subtype revealed binding was specific for progestins and was displaceable, with rapid rates of association and dissociation (t(1/2) = 2-8 min). These results suggest this is a new family of steroid receptors unrelated to nuclear steroid receptors, but instead having characteristics of G protein-coupled receptors.

Estrogen receptor-interacting protein that modulates its nongenomic activity-crosstalk with Src/Erk phosphorylation cascade

Numerous studies have demonstrated that estrogens induce rapid and transient activation of the Src/Erk phosphorylation cascade. Activation of this cascade triggers vital cellular functions including cell proliferation and differentiation. However, the details of the molecular mechanism of this process remain to be elucidated. We have identified a previously uncharacterized nuclear receptor-interacting protein designated as modulator of nongenomic activity of estrogen receptor (MNAR). Here we show that MNAR modulates estrogen-receptor (ER) interaction with members of the Src family of tyrosine kinases, which leads to a stimulation of Src enzymatic activity and activation of Erk1 and Erk2 kinases. We also show that MNAR, through activation of the Src/Erk phosphorylation cascade, affects ER transcriptional activity and ultimately ER-mediated gene expression. These data reveal that MNAR mediates the crosstalk between two important classes of signal transducing molecules and suggest that ER "genomic" and "nongenomic" activities are interrelated.

Estrogen receptor, calcium mobilization and rat sperm motility

Oral treatment with 0.4 mg/kg/day of tamoxifen citrate, an antiestrogen, has been reported to reduce the fertility of adult male rat, presumably through estrogen receptors expressed throughout the male reproductive tract. During the course of these studies, tamoxifen was observed to gradually alter the pattern of sperm motility in the cauda epididymides without reducing sperm counts. Studies were carried out to understand the mechanism involved in tamoxifen induced change in the sperm motility pattern. In order to study the direct effects of tamoxifen on motility, biochemical levels/activities of sperm calcium, cAMP, phosphodiesterase and dynein ATPase, normally implicated in sperm motility were studied In view of the fact that tamoxifen is a ligand of estrogen receptor, estrogen receptor alpha protein and transcript were localized on rat sperm membrane and the effect of tamoxifen studied. The present study demonstrated presence of estrogen receptor protein and mRNA in the rat sperm by immunofluorescence, western blotting and in situ hybridization respectively. Specificity of sperm estrogen receptors was confirmed by conventional binding studies using [3H]-estradiol. There was no effect of tamoxifen treatment on estrogen receptors in rat sperms. Biochemical analysis of the sperms from tamoxifen treated cauda epididymides revealed a significant increase in the levels of calcium and cAMP. A significant reduction was also apparent in the activity of dynein ATPase. Tamoxifen treatment did not alter phosphodiesterase activity. Estrogen receptors could be identified both in the control as well as tamoxifen treated rat sperms. It was concluded that tamoxifen treatment mobilized calcium from the intra- or extra-cellular pools with a concomitant increase in cAMP and presumably activation of PKA (protein kinase A). Tamoxifen altered the pattern of sperm motility through a calcium induced block in the activity of dynein ATPase, presumably through the activation of sperm phosphatase. The putative estrogen receptor mediated signal transduction pathway appears to be directly affected in the tamoxifen treated, sub-motile rat sperm.

PI3-kinase in concert with Src promotes the S-phase entry of oestradiol-stimulated MCF-7 cells

The p85-associated phosphatidylinositol (PI) 3-kinase/Akt pathway mediates the oestradiol-induced S-phase entry and cyclin D1 promoter activity in MCF-7 cells. Experiments with Src, p85alpha and Akt dominant-negative forms indicate that in oestradiol-treated cells these signalling effectors target the cyclin D1 promoter. Oestradiol acutely increases PI3-kinase and Akt activities in MCF-7 cells. In NIH 3T3 cells expressing ERalpha, a dominant-negative p85 suppresses hormone stimulation of Akt. The Src inhibitor, PP1, prevents hormone stimulation of Akt and PI3-kinase activities in MCF-7 cells. In turn, stimulation of Src activity is abolished in ERalpha-expressing NIH 3T3 fibroblasts by co-transfection of the dominant-negative p85alpha and in MCF-7 cells by the PI3-kinase inhibitor, LY294002. These findings indicate a novel reciprocal cross-talk between PI3-kinase and Src. Hormone stimulation of MCF-7 cells rapidly triggers association of ERalpha with Src and p85. In vitro these proteins are assembled in a ternary complex with a stronger association than that of the binary complexes composed by the same partners. The ternary complex probably favours hormone activation of Src- and PI3-kinase-dependent pathways, which converge on cell cycle progression.

Insulin-like growth factor 1 and oestradiol promote cell proliferation of MCF-7 breast cancer cells: new insights into their synergistic effects

In MCF-7 breast cancer cells, the insulin-like growth factor 1 receptor (IGF-1R) and the oestrogen receptor (ER) are coexpressed and the two signalling systems are engaged in a crosstalk that results in synergistic growth. However, coupling between the signalling cascades is poorly understood. Oestradiol enhances IGF-1R signalling by inducing the expression of insulin receptor substrate 1 (IRS-1), a substrate of the IGF-1R. Oestradiol induced expression of IRS-1 results in enhanced tyrosine phosphorylation of IRS-1 after IGF-1 stimulation, followed by enhanced mitogen activated protein kinase, phosphoinositide 3' kinase, and Akt activation. Oestradiol can also potentiate the effect of IGF-1 on the expression of cyclin D1 and cyclin E, and on the phosphorylation of the retinoblastoma protein (RB). These effects are greatly diminished in SX13 cells, which exhibit a 50% reduction in IGF-1R expression but few functional IGF-1Rs at the surface. Oestradiol and IGF-1 regulate the expression of two cyclin dependent kinase inhibitors, p21 and p27, differently. Whereas IGF-1 increases p21 expression and reduces p27 expression, oestradiol has no effect on p21. In summary, in MCF-7 cells, oestrogen potentiates the effect of IGF-1 on IGF-1R signalling and its effects on certain cell cycle components.