Cognate Nuclear Receptors Research Articles

Rapid Nongenomic Glucocorticoid Actions in Male Mouse Hypothalamic Neuroendocrine Cells Are Dependent on the Nuclear Glucocorticoid Receptor.

Corticosteroids act classically via cognate nuclear receptors to regulate gene transcription; however, increasing evidence supports rapid, nontranscriptional corticosteroid actions via activation of membrane receptors. Using whole-cell patch clamp recordings in hypothalamic slices from male mouse genetic models, we tested for nongenomic glucocorticoid actions at glutamate and gamma aminobutyric acid (GABA) synapses in hypothalamic neuroendocrine cells, and for their dependence on the nuclear glucocorticoid receptor (GR). In enhanced green fluorescent protein-expressing CRH neurons of the paraventricular nucleus (PVN) and in magnocellular neurons of the PVN and supraoptic nucleus (SON), dexamethasone activated postsynaptic membrane-associated receptors and G protein signaling to elicit a rapid suppression of excitatory postsynaptic inputs, which was blocked by genetic deletion of type I cannabinoid receptors and a type I cannabinoid receptor antagonist. In magnocellular neurons, dexamethasone also elicited a rapid nitric oxide-dependent increase in inhibitory postsynaptic inputs. These data indicate a rapid, synapse-specific glucocorticoid-induced retrograde endocannabinoid signaling at glutamate synapses and nitric oxide signaling at GABA synapses. Unexpectedly, the rapid glucocorticoid effects on both excitatory and inhibitory synaptic transmission were lost with conditional deletion of GR in the PVN and SON in slices from a single minded-1-cre-directed conditional GR knockout mouse. Thus, the nongenomic glucocorticoid actions at glutamate and GABA synapses on PVN and SON neuroendocrine cells are dependent on the nuclear GR. The nuclear GR, therefore, is responsible for transducing the rapid steroid response at the membrane, or is either a critical component in the signaling cascade or regulates a critical component of the signaling cascade of a distinct membrane GR.

Localization and regulation of reproductive steroid receptors in the raphe serotonin system of male macaques

We previously showed that tryptophan hydroxylase 2 (TPH2) and serotonin reuptake transporter (SERT) mRNAs are increased by the androgens, testosterone (T) and dihydrotestosterone (DHT) in serotonin neurons of male macaques. In addition, we observed that serotonin in axons of a terminal region were markedly decreased by aromatase inhibition and lack of estradiol (E) from metabolism of T. These observations implicated androgen receptors (AR) and estrogen receptors (ER) in the transduction of steroid hormone actions in serotonin neurons. Due to the longer treatment period employed, the expression of the cognate nuclear receptors was sought. We used single and double immunohistochemistry to quantitate and phenotypically localize AR, ERα and ERβ in the dorsal raphe of male macaques. Male Japanese macaques (Macaca fuscata) were castrated for 5–7 months and then treated for 3 months with [1] placebo, [2] T, [3] DHT (non-aromatizable androgen) plus ATD (steroidal aromatase inhibitor), or [4] Flutamide (FLUT; androgen antagonist) plus ATD (n=5/group). After single labeling of each receptor, quantitative image analysis was applied and receptor positive neurons were counted. Double-label of raphe neurons for each receptor plus TPH2 determined whether the receptors were localized in serotonin neurons. There were significantly more AR-positive neurons in T- and DHT+ATD-treated groups (p=0.0014) compared to placebo or FLUT+ATD-treated groups. There was no difference in the number of positive-neurons stained for ERα or ERβ⋅ Double-immunohistochemistry revealed that serotonin neurons did not contain AR. Rather, AR-positive nuclei were found in neighboring cells that are likely neurons. However, approximately 40% of dorsal raphe serotonin neurons contained ERα or ERβ⋅ In conclusion, the stimulatory effect of androgens on TPH2 and SERT mRNA expression is mediated indirectly by neighboring neurons contain AR. The stimulatory effect of E, derived from T metabolism, on serotonin transport is partially mediated directly via nuclear ERs.

The effects of 3,5-diiodothyronine on energy balance.

Thyroid hormones (THs) have been known to affect energy metabolism (calorigenic effect) for over a century (Magnus-Levy, 1895; Thompson et al., 1929). In 1985 Magnus-Levy observed that patients with mixedema exhibited an abnormal low oxygen consumption when compared to normal individuals and that unusually higher amount of oxygen was consumed by hyperthyroid patients. 3,3′,5-triiodo-L-thyronine (T3) is the active form of THs and it is a major regulator of growth and development and of cellular and tissue metabolism (both intermediate and energy metabolism) throughout the body. Metabolic actions include regulation of: basal metabolic rate in homeotherms, synthesis of mitochondrial respiratory enzymes and membranes, oxidative phosphorylation and energy transduction, movement of water and Na+ ions across cell membranes; calcium and phosphorus metabolism, lipids synthesis and storage, catabolism of fatty acids, cholesterol, carbohydrate; and nitrogen (urea, creatine) metabolism; growth and developmental actions include actions on: rate of postnatal growth of many mammalian and avian tissue, maturation of fetal brain and bone, amphibian larval metamorphosis, and molting in birds. It is now recognized that T3 affects gene expression in target tissues/cells by binding to its cognate nuclear receptors (TR) which are ligand-inducible transcription factors. Two TR genes α and β encode four T3-binding receptor isoforms (α1, β1, β2, and β3). The transcriptional activity of TRs is regulated at multiple levels. Besides being regulated by T3, transcriptional activity is also regulated: (i) by the type of thyroid hormone response elements located on the promoters of T3 target genes, (ii) by the developmental- and tissue-dependent expression of TR isoforms, and (iii) by a host of nuclear coregulatory proteins (corepressors and coactivators). These nuclear proteins modulate the transcription activity of TRs in a T3-dependent manner. In the absence of T3, corepressors act to repress the basal transcriptional activity, whereas in the presence of T3, coactivators act to activate transcription. The activities regulated via the previous described mechanisms are described as “genomic actions.” However, between the mid-1980's and the beginning of the 1990's it became evident that some TH effects are non-genomic in origin. Indeed, high-affinity binding sites for thyroid hormones have for many years been recognized on the plasma membrane and other cellular sites such as mitochondria and cytoplasm (for review see Cheng et al., 2010). Recently, a structural protein of the plasma membrane, integrin αvβ3, has been shown to contain a binding domain for iodothyronines that is an initiation site for hormone-directed complex cellular events, such as cell division and angiogenesis (Bergh et al., 2005) and this qualifies the binding site for characterization as a receptor. Examples of non-genomic action of thyroid hormones are activation of: membrane Ca2-ATPase activity, 2-Deoxyglucose transport, Na, K-ATPase activity, Na+ current in myocardiocytes, Na+ current in sensory neuron, Na+/H+ exchanger, cancer cell proliferation, angiogenesis (for review see Cheng et al., 2010). In addition to this, it is now recognized that other iodothyronines or THs analogs/derivatives are able to exert relevant biological actions (for recent review, see Moreno et al., 2008; Senese et al., 2014; Zucchi et al., 2014). This article is particularly intended to describe the effects of the 3,5 diiodo-L-thyronine (T2) on energy balance (Moreno et al., 1997; Goglia, 2005).

A Novel Role for Ecdysone in Drosophila Conditioned Behavior: Linking GPCR-Mediated Non-canonical Steroid Action to cAMP Signaling in the Adult Brain

The biological actions of steroid hormones are mediated primarily by their cognate nuclear receptors, which serve as steroid-dependent transcription factors. However, steroids can also execute their functions by modulating intracellular signaling cascades rapidly and independently of transcriptional regulation. Despite the potential significance of such “non-genomic” steroid actions, their biological roles and the underlying molecular mechanisms are not well understood, particularly with regard to their effects on behavioral regulation. The major steroid hormone in the fruit fly Drosophila is 20-hydroxy-ecdysone (20E), which plays a variety of pivotal roles during development via the nuclear ecdysone receptors. Here we report that DopEcR, a G-protein coupled receptor for ecdysteroids, is involved in activity- and experience-dependent plasticity of the adult central nervous system. Remarkably, a courtship memory defect in rutabaga (Ca2+/calmodulin-responsive adenylate cyclase) mutants was rescued by DopEcR overexpression or acute 20E feeding, whereas a memory defect in dunce (cAMP-specific phosphodiestrase) mutants was counteracted when a loss-of-function DopEcR mutation was introduced. A memory defect caused by suppressing dopamine synthesis was also restored through enhanced DopEcR-mediated ecdysone signaling, and rescue and phenocopy experiments revealed that the mushroom body (MB)—a brain region central to learning and memory in Drosophila—is critical for the DopEcR-dependent processing of courtship memory. Consistent with this finding, acute 20E feeding induced a rapid, DopEcR-dependent increase in cAMP levels in the MB. Our multidisciplinary approach demonstrates that DopEcR mediates the non-canonical actions of 20E and rapidly modulates adult conditioned behavior through cAMP signaling, which is universally important for neural plasticity. This study provides novel insights into non-genomic actions of steroids, and opens a new avenue for genetic investigation into an underappreciated mechanism critical to behavioral control by steroids.

Vitamin E: the enigmatic one!

Vitamin E was first identified more than 90 years ago by Evans and Bishop as an essential dietary factor that is required by rats to maintain normal reproduction (1). Unlike the other three fat-soluble vitamins that have very specific molecular targets and actions, vitamin E lacks specific pathways or specific molecular targets that account for its requirement from the diet. Considerable research had been focused on identifying specific molecular targets and actions for vitamin E (2). For instance, as it became clear that vitamins A and D act through cognate nuclear hormone receptors to regulate vitamin-responsive gene expression, investigators sought, without success, to identify similar activities for vitamin E. These investigations simply led back to the same understanding of vitamin E obtained from studies carried out between the 1930s and the 1980s, that vitamin E acts as a fat-soluble antioxidant. Vitamin E serves as a peroxyl radical scavenger that protects polyunsaturated fatty acids in membranes and lipoproteins from oxidative damage (3). Given that many dietary substances, as well as many substances synthesized within the body, have potent antioxidant properties, what selective pressures drove evolution to require humans and other higher animals to acquire vitamin E from the diet? Is this simply due to the physical properties and/or redox chemistry of vitamin E or is there something about vitamin E that we still do not understand? This issue of the Journal of Lipid Research contains the second installment of the JLR's Thematic Review Series on fat-soluble vitamins. The biology of vitamin E and its role in human cardiovascular disease will be considered in the two reviews that comprise this edition of the Thematic Review Series on fat-soluble vitamins.

The Hepatic Orosomucoid/α1-Acid Glycoprotein Gene Cluster Is Regulated by the Nuclear Bile Acid Receptor FXR

The α-1-acid glycoprotein/orosomucoids (ORMs) are members of the lipocalin protein family. Encoded by 3 polymorphic genes in mouse (2 in man, 1 in rat), ORMs are expressed in hepatocytes and function as acute-phase proteins secreted in plasma under stressful conditions. In addition to their role of nanocarrier, ORMs are involved in several pathophysiological processes such as immunosuppression, cardioprotection, and inflammatory bowel disease. The nuclear bile acid receptor farnesoid X receptor (FXR) regulates bile acid homeostasis and lipid and glucose metabolism and is an important modulator of enterohepatic functions. Here we report that hepatic FXR deletion in mice affects the expression of several members of the lipocalin family, among which ORMs are identified as direct FXR target genes. Indeed, a FXR response element upstream of the mouse Orm1 promoter was identified to which hepatic, but not ileal, FXR can bind and activate ORM expression in vitro and in vivo. However, ORMs are regulated in a species-specific manner because the ORM cluster is regulated by FXR neither in human nor rat cell lines. Consistent with these data, chromatin immunoprecipitation sequencing analysis of the FXR genomic binding sites did not detect any FXR response element in the vicinity of the human or rat ORM gene cluster. Thus, bile acids and their cognate nuclear receptor, FXR, are regulators of ORM expression, with potential implications for the species-specific metabolic and inflammation control by FXR because the expression of the proinflammatory genes in epididymal white adipose tissue was dependent on liver FXR activation.

Effects of retinoic acid isomers on proteomic pattern in human breast cancer MCF-7 cell line

Retinoids, acting through their cognate nuclear receptors, are crucial transcriptional regulators of many cellular processes such as differentiation, development, apoptosis, carbohydrate and lipid metabolism, homeostasis, etc. The aim of this study was the exploration of molecular mechanisms in relation to therapy of human breast cancer. One of the efficient strategies is identification of biomarkers as important tools in early cancer diagnosis and advisable treatment. Retinoids have been regarded as important therapeutic agents for many types of cancers, including human breast cancer. The effects of all-trans retinoic acid and 9-cis retinoic acid or their combination on proteomic pattern in human MCF-7 breast cancer line were investigated. The total cell proteins were extracted utilizing a commercially Radio-Immunoprecipitation Assay (RIPA) buffer and separated on 1D sodium dodecyl sulfate polyacrylamide gel electrophoresis (1D SDS-PAGE). The proteins were subsequently digested in-gel by trypsin and identified by matrix assisted laser desorption ionization technique with time of flight mass analyzer (MALDI-TOF/TOF). Our data offer novel information on the proteomic pattern of proteins evaluated after treatment of MCF-7 cells with retinoic acid isomers.

Regulation of nutrient metabolism by nuclear receptor/FGF signaling pathways

The regulation of metabolism in fed and fasted states is governed by hormonal and nutrient-derived signals that are mediated in part by nuclear receptors. Just as insulin and glucagon help the body store and mobilize energy through their membrane receptors, nutrient-derived lipids activate their cognate nuclear receptors (e.g., FXR and PPARs) to govern transcriptional programs involved in energy storage and utilization during times of nutrient excess and privation. Recent work has revealed that many of the actions of these nuclear receptors are mediated by two atypical fibroblast growth factors (FGF19 and FGF21) that function as endocrine-like hormones. The characterization of these pathways in normal and metabolic disease animal models has led to an understanding of their physiologic and pharmacologic mechanism of action.

Neurosteroid Biosynthesis and Action During Cerebellar Development

The formation of the mammalian cerebellar cortex becomes complete in the neonate through the processes of migration of external granule cells, neuronal and glial growth, and synaptogenesis. In the middle 1990s, we identified the Purkinje cell, a principal cerebellar neuron, as a major site for neurosteroid formation in mammals. This discovery has provided the opportunity to understand neuronal neurosteroidogenesis and neurosteroid actions on neuronal growth and synaptic formation in the cerebellum. Based on extensive studies on mammals over the past decade, we now know that the Purkinje cell actively synthesizes progesterone and estradiol de novo from cholesterol during neonatal life, when cerebellar neuronal circuit formation occurs. Both progesterone and estradiol promote dendritic growth, spinogenesis, and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell. Such neurosteroid actions that may be mediated by neurotrophic factors contribute to the formation of cerebellar neuronal circuit during neonatal life. Allopregnanolone, a progesterone metabolite, is also synthesized in the cerebellum and acts on Purkinje cell survival in the neonate. This paper highlights the biosynthesis and biological actions of neurosteroids in the Purkinje cell during cerebellar development.

1α,25(OH)2-Vitamin D and a Nongenomic Vitamin D Analogue Inhibit Ultraviolet Radiation–Induced Skin Carcinogenesis

Exposure to ultraviolet radiation (UVR) can lead to a range of deleterious responses in the skin. An important form of damage is the DNA photolesion cyclobutane pyrimidine dimer (CPD). CPDs can be highly mutagenic if not repaired prior to cell division and can lead to UV-induced immunosuppression, making them potentially carcinogenic. UVR exposure also produces vitamin D, a prehormone. Different shapes of the steroid hormone 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] can produce biological responses through binding either to its cognate nuclear receptor (VDR) to regulate gene transcription or to the VDR associated with plasma membrane caveolae to produce, via signal transduction, nongenomic physiologic responses. Here, we show that both 1,25(OH)₂D₃ and 1α,25(OH)₂-lumisterol (JN), a conformationally restricted analogue that can generate only nongenomic responses, are effective inhibitors of UV damage in an immunocompetent mouse (Skh:hr1) model susceptible to UV-induced tumors. Both 1,25(OH)₂D₃ and JN significantly reduced UVR-induced CPD, apoptotic sunburn cells, and immunosuppression. Furthermore, these compounds inhibited skin tumor development, both papillomas and squamous cell carcinomas, in these mice. The observed reduction of these UV-induced effects by 1,25(OH)₂D₃ and JN suggests a role for these compounds in prevention against skin carcinogenesis. To the best of our knowledge, this is the first comprehensive report of an in vivo long-term biological response generated by chronic dosing with a nongenomic-selective vitamin D steroid.

Acquisition of Sexual Receptivity: Roles of Chromatin Acetylation, Estrogen Receptor-α, and Ovarian Hormones

Sexually naïve, hormone-primed, C57BL/6J female mice are not receptive to mating attempts by conspecific males. Repeated experience with sexually active males and concurrent treatment with estradiol and progesterone gradually increases female receptivity over the course of five trials to maximal levels. Ovarian hormones activate their cognate nuclear steroid receptors estrogen receptor-α and progesterone receptor to induce female sexual receptivity. Nuclear receptors recruit coactivators of transcription that include histone acetyltransferases to hormone responsive genes. In this set of studies, we found that the histone deacetylase inhibitor sodium butyrate enhances the experiential acquisition of receptivity. Evidence is provided that the actions of sodium butyrate on receptivity require activated estrogen receptor-α and progesterone.

Effects of 1α,25 dihydroxyvitamin D3 and testosterone on miRNA and mRNA expression in LNCaP cells

BackgroundThere is evidence from epidemiological and in vitro studies that the biological effects of testosterone (T) on cell cycle and survival are modulated by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in prostate cancer. To investigate the cross talk between androgen- and vitamin D-mediated intracellular signaling pathways, the individual and combined effects of T and 1,25(OH)2D3 on global gene expression in LNCaP prostate cancer cells were assessed.ResultsStringent statistical analysis identifies a cohort of genes that lack one or both androgen response elements (AREs) or vitamin D response elements (VDREs) in their promoters, which are nevertheless differentially regulated by both steroids (either additively or synergistically). This suggests that mechanisms in addition to VDR- and AR-mediated transcription are responsible for the modulation of gene expression. Microarray analysis shows that fifteen miRNAs are also differentially regulated by 1,25(OH)2D3 and T. Among these miR-22, miR-29ab, miR-134, miR-1207-5p and miR-371-5p are up regulated, while miR-17 and miR-20a, members of the miR-17/92 cluster are down regulated. A number of genes implicated in cell cycle progression, lipid synthesis and accumulation and calcium homeostasis are among the mRNA targets of these miRNAs. Thus, in addition to their well characterized effects on transcription, mediated by either or both cognate nuclear receptors, 1,25(OH)2D3 and T regulate the steady state mRNA levels by modulating miRNA-mediated mRNA degradation, generating attenuation feedback loops that result in global changes in mRNA and protein levels. Changes in genes involved in calcium homeostasis may have specific clinical importance since the second messenger Ca2+ is known to modulate various cellular processes, including cell proliferation, cell death and cell motility, which affects prostate cancer tumor progression and responsiveness to therapy.ConclusionsThese data indicate that these two hormones combine to drive a differentiated phenotype, and reinforce the idea that the age dependent decline in both hormones results in the de-differentiation of prostate tumor cells, which results in increased proliferation, motility and invasion common to aggressive tumors. These studies also reinforce the potential importance of miRNAs in prostate cancer progression and therapeutic outcomes.

RETRACTED ARTICLE: Transcriptional Controls by Nuclear Fat-Soluble Vitamin Receptors through Chromatin Reorganization

Fat-soluble ligands like vitamin A/D and steroid hormones activate their cognate nuclear receptors for ligand-dependent transcriptional regulation. Nuclear receptors constitute a gene superfamily with 48 members in higher mammals, and act as ligand-dependent transcription factors to bind stably to specific DNA elements in ligand/NR target gene promoters. Hence, most of biological actions of fat-soluble ligands are generally thought to mediate NR-mediated gene regulation. Starting in early 1990, transcriptional co-regulators supporting ligand-dependent transcriptional controls by NRs have been characterized. Initially, the transcriptional co-regulators were believed to couple with histone acethylation/deacethylation, and thereby histone acethyltransferases (HATs) and histone deacethylases (HDACs) were characterized as NR co-activators and co-repressor, respectively. However, recent progress in chromatin biology and epigenome have revealed that other histone modifying enzymes and chromatin remodelers are potential co-regulators for NRs. In this review, these cuttingedge aspects are discussed together with our recent findings on NR co-regulators.

Biosynthesis, Mode of Action, and Functional Significance of Neurosteroids in the Purkinje Cell

The brain has traditionally been considered to be a target site of peripheral steroid hormones. In addition to this classical concept, we now know that the brain has the capacity to synthesize steroids de novo from cholesterol, the so-called “neurosteroids.” In the middle 1990s, the Purkinje cell, an important cerebellar neuron, was identified as a major site for neurosteroid formation in the brain of mammals and other vertebrates. This discovery has provided the opportunity to understand neuronal neurosteroidogenesis in the brain. In addition, biological actions of neurosteroids are becoming clear by the studies using the Purkinje cell, an excellent cellular model, which is known to play an important role in memory and learning processes. Based on the studies on mammals over the past decade, it is considered that the Purkinje cell actively synthesizes progesterone and estradiol from cholesterol during neonatal life, when cerebellar neuronal circuit formation occurs. Both progesterone and estradiol promote dendritic growth, spinogenesis, and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell. Such neurosteroid actions mediated by neurotrophic factors may contribute to the formation of cerebellar neuronal circuit during neonatal life. 3α,5α-Tetrahydroprogesterone (allopregnanolone), a progesterone metabolite, is also synthesized in the cerebellum and considered to act as a survival factor of Purkinje cells in the neonate. This review summarizes the current knowledge regarding the biosynthesis, mode of action, and functional significance of neurosteroids in the Purkinje cell during development in terms of synaptic formation of cerebellar neuronal networks.

Retinoic acid protects human breast cancer cells against etoposide-induced apoptosis by NF-kappaB-dependent but cIAP2-independent mechanisms

BackgroundRetinoids, through their cognate nuclear receptors, exert potent effects on cell growth, differentiation and apoptosis, and have significant promise for cancer therapy and chemoprevention. These ligands can determine the ultimate fate of target cells by stimulating or repressing gene expression directly, or indirectly through crosstalking with other signal transducers.ResultsUsing different breast cancer cell models, we show here that depending on the cellular context retinoids can signal either towards cell death or cell survival. Indeed, retinoids can induce the expression of pro-apoptotic (i.e. TRAIL, TNF-Related Apoptosis-Inducing Ligand, Apo2L/TNFSF10) and anti-apoptotic (i.e. cIAP2, inhibitor of apoptosis protein-2) genes. Promoter mapping, gel retardation and chromatin immunoprecipitation assays revealed that retinoids induce the expression of this gene mainly through crosstalk with NF-kappaB. Supporting this crosstalk, the activation of NF-kappaB by retinoids in T47D cells antagonizes the apoptosis triggered by the chemotherapeutic drugs etoposide, camptothecin or doxorubicin. Notably apoptosis induced by death ligands (i.e. TRAIL or antiFAS) is not antagonized by retinoids. That knockdown of cIAP2 expression by small interfering RNA does not alter the inhibition of etoposide-induced apoptosis by retinoids in T47D cells reveals that stimulation of cIAP2 expression is not the cause of their anti-apoptotic action. However, ectopic overexpression of a NF-kappaB repressor increases apoptosis by retinoids moderately and abrogates almost completely the retinoid-dependent inhibition of etoposide-induced apoptosis. Our data exclude cIAP2 and suggest that retinoids target other regulator(s) of the NF-kappaB signaling pathway to induce resistance to etoposide on certain breast cancer cells.ConclusionsThis study shows an important role for the NF-kappaB pathway in retinoic acid signaling and retinoic acid-mediated resistance to cancer therapy-mediated apoptosis in breast cancer cells, independently of cIAP2. Our data support the use of NF-kappaB pathway activation as a marker for screening that will help to develop novel retinoids, or retinoid-based combination therapies with improved efficacy.

In Pursuit of Leucine-Rich Repeat-Containing G Protein-Coupled Receptor-5 Regulation and Function in the Uterus

Leucine-rich repeat-containing G protein-coupled receptor (LGR)-5 is a recently identified marker of stem cells in adult intestinal epithelium and hair follicles. Because of this characteristic, we studied the status of Lgr5 expression in the mouse uterus under various conditions. Lgr5 is highly expressed in the uterine epithelium of immature mice and is dramatically down-regulated after the mice resume estrous cycles. Surprisingly, whereas its expression is up-regulated in uteri of ovariectomized mice, the expression is down-regulated by estrogen and progesterone via their cognate nuclear receptors, estrogen receptor-alpha and progesterone receptor, respectively. Using a mouse endometrial cancer model, we also found that Lgr5 is highly expressed in the epithelium during the initial stages of tumorigenesis but is remarkably down-regulated in fully developed tumors. Lgr5 is a downstream target of Wnt signaling in the intestine. Genetic evidence shows that either excessive or absence of Wnt signaling dampens Lgr5 expression in the uterus. Collectively, our results show that Lgr5 expression in the mouse uterine epithelium is unique and dynamically regulated under various physiological and pathological states of the uterus, suggesting that this orphan receptor has important functions in uterine biology. However, identifying definitive uterine function of LGR5 will require further investigation using conditional deletion of uterine Lgr5 because systemic deletion of this gene is neonatally lethal.

RETRACTED: Maturation of MicroRNA Is Hormonally Regulated by a Nuclear Receptor

Steroid hormones and their cognate nuclear receptors exert a wide spectrum of biological actions through regulation of transcriptional and posttranscriptional processes. However, the underlying molecular mechanism by which steroid hormones control posttranscriptional processes is largely unknown. We now report that estrogen receptor alpha (ERalpha) inhibits the maturation of a particular microRNA (miRNA) and thereby stabilizes the mRNA of an ERalpha target gene through the 3'UTR. Estrogen-bound ERalpha downregulated expression of a set of miRNAs in both animals and cultured cells. Activated ERalpha attenuated the processing of primary miRNAs into pre-miRNAs through estrogen-dependent association with the Drosha complex, resulting in stabilization of the transcript of an ERalpha target gene through its 3'UTR. Thus, a steroid hormone achieves posttranscriptional control by regulating the maturation of miRNA.

Neurosteroid Biosynthesis and Action in the Purkinje Cell

It is now clearly established that steroids can be synthesized de novo by the vertebrate brain. Such steroids are called neurosteroids. To understand neurosteroid action in the brain, data on the regio- and temporal-specific synthesis of neurosteroids are needed. In the middle 1990s, the Purkinje cell, an important cerebellar neuron, was identified as a major site for neurosteroid formation in vertebrates. This discovery has allowed deeper insights into neuronal neurosteroidogenesis and biological actions of neurosteroids have become clear by the studies using the Purkinje cell as an excellent cellular model, which is known to play an important role in memory and learning processes. From the past 10 years of research on mammals, we now know that the Purkinje cell actively synthesizes progesterone and estradiol de novo from cholesterol during neonatal life, when cerebellar neuronal circuit formation occurs. Both progesterone and estradiol promote dendritic growth, spinogenesis, and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell. Such neurosteroid actions that may be mediated by neurotrophic factors contribute to the formation of cerebellar neuronal circuit during neonatal life. Allopregnanolone, a progesterone metabolite, is also synthesized in the cerebellum and acts on Purkinje cell survival in the neonate. The aim of this review is to summarize the current knowledge regarding the biosynthesis and biological actions of neurosteroids in the Purkinje cell during development.

Neurosteroids in the Purkinje Cell: Biosynthesis, Mode of Action and Functional Significance

Neurosteroids are synthesized de novo from cholesterol in the brain. To understand neurosteroid action in the brain, data on the regio- and temporal-specific synthesis of neurosteroids are needed. Recently the Purkinje cell, an important cerebellar neuron, has been identified as a major site for neurosteroid formation in vertebrates. This is the first demonstration of de novo neuronal neurosteroidogenesis in the brain. Since this discovery, organizing actions of neurosteroids are becoming clear by the studies using the Purkinje cell as an excellent cellular model. In mammals, the Purkinje cell actively synthesizes progesterone and estradiol de novo from cholesterol during neonatal life. Both progesterone and estradiol promote dendritic growth, spinogenesis, and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell. Such organizing actions that may be mediated by neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), contribute to the formation of cerebellar neuronal circuit during neonatal life. Allopregnanolone, a progesterone metabolite, is also synthesized in the cerebellum and acts on Purkinje cell survival in the neonate. This review summarizes the advances made in our understanding of the biosynthesis, mode of action and functional significance of neurosteroids in the Purkinje cell.

Triiodothyronine modulates cell proliferation of human prostatic carcinoma cells by downregulation of the B‐Cell translocation gene 2

Studies suggest that triiodothyronine (T3) and cognate nuclear receptors (hTR) are involved in regulation of prostatic cell growth and differentiation. To probe mechanisms for T3 effects, we studied prostate carcinoma cells, investigating the effect of T3 on expression of the B-cell translocation gene 2 (BTG2), which regulates the G1/S transition of the cell cycle. Effects of T3 on cell proliferation were determined by (3)H-thymidine incorporation. T3 modulation of BTG2 expression was investigated using immunoblots, Northern blots, and transient gene expression assays. The putative T3 response element was determined by electrophoretic mobility shift assay. T3 (0.1-1,000 nM) enhanced threefold the proliferation of prostate carcinoma cells and human androgen-dependent prostate carcinoma cells (LNCaP), but not PC-3 cells. T3 also inhibited BTG2 gene expression in LNCaP cells. Reporter assays showed that T3 downregulates by 50% promoter activity of the BTG2 gene in LNCaP cells but not PC-3 cells or thyroid-hormone receptor (TRbeta1)-overexpression PC-3 cells. Deleting the putative thyroid hormone response element (TRE; AGCGATGACCTCAGCG) blocked the inhibitory effect of T3 on BTG2 promoter activity. Electrophoretic mobility shift assays with purified TRbeta1 from in vitro translation, or with nuclear extracts from LNCaP cells and PC-3 cells, demonstrated the presence of T3 receptor binding sites in the TRE region. These results suggested that the T3 upregulates proliferation of LNCaP cells by downregulating BTG2 gene expression through the consensus TRE pathway.