From ligand to response: generating diversity in nuclear receptor coregulator function

Cardiovascular and Renal Benefit of Novel Non-steroidal Mineralocorticoid Antagonists in Patients with Diabetes

PURPOSE OF REVIEW

Novel non-steroidal mineralocorticoid receptor (MR) antagonists (MRAs) are a new class of drugs blocking adverse MR-mediated effects with an improved benefit-risk profile compared to steroidal MRAs. This review will provide information on the preclinical and clinical pharmacology of this new drug class and will discuss their future clinical applications in patients with cardiorenal disease.

RECENT FINDINGS

Non-steroidal MRAs such as esaxerenone, AZD9977, apararenone, ocedurenone (KBP-5074), and finerenone are newly approved or in clinical development for patients with cardiorenal disease including type 2 diabetes (T2D) and chronic kidney disease (CKD), hypertension -/+ CKD or heart failure. Unlike steroidal MRAs, non-steroidal MRAs do not induce sex hormone-related side effects and appear to mediate a lower risk of hyperkalemia while maintaining compelling clinical efficacy. Recently, new data from several clinical trials with non-steroidal MRAs have been published (e.g., FIDELIO-DKD, FIGARO-DKD, ESAX-DN, and BLOCK-CKD), and additional studies are currently underway (e.g., FINEARTS-HF and CLARION-CKD). These data and the clinical scientific basis for the ongoing studies will be discussed. Non-steroidal MRAs have been extensively explored in diabetic kidney disease. Selected candidates of this drug class reduced UACR in patients with varying degrees of CKD and T2D and have shown convincing cardiorenal protection, in particular finerenone. Furthermore, finerenone is currently tested in patients with heart failure with preserved ejection fraction.

Association of polymorphic variants in GEMIN genes with the risk of depression in a Polish population

Background

The role of miRNA in depression is widely described by many researchers. miRNA is a final product of many genes involved in its formation (maturation). One of the final steps in the formation of miRNAs is the formation of the RISC complex, called the RNA-induced silencing complex, which includes, among others, GEMIN proteins. Single-nucleotide polymorphisms (SNPs) may lead to disturbance of miRNA biogenesis and function. The objective of our research was to assess the relationship between the appearance of depression and single nucleotide polymorphisms in the GEMIN3 (rs197388) and GEMIN4 (rs7813; rs3744741) genes. Our research provides new knowledge on the genetic factors that influence the risk of depression. They can be used as an element of diagnostics helpful in identifying people at increased risk, as well as indicating people not at risk of depression.

Methods

A total of 218 participants were examined, including individuals with depressive disorders (n = 102; study group) and healthy people (n = 116, control group). All the patients in the study group and the people in the control group were non-related native Caucasian Poles from central Poland. Blood was collected from study and control groups in order to assess the SNPs of GEMIN genes.

Results

An analysis of the results obtained showed that in patient population, the risk of depression is almost doubled by polymorphic variants of the genes: rs197388/GEMIN3 genotype A/A in the recessive model and rs3744741/GEMIN4 genotype T/T, codominant and recessive model. The dual role of rs7813/GEMIN4 is noteworthy, where the G/A genotype in the codominant and over dominant model protects against depression.

Membrane-initiated actions of sex steroids and reproductive behavior: A historical account

It was assumed for a long time that sex steroids are activating reproductive behaviors by the same mechanisms that produce their morphological and physiological effects in the periphery. However during the last few decades an increasing number of examples were identified where behavioral effects of steroids were just too fast to be mediated via changes in DNA transcription. This progressively forced behavioral neuroendocrinologists to recognize that part of the effects of steroids on behavior are mediated by membrane-initiated events. In this review we present a selection of these early data that changed the conceptual landscape and we provide a summary the different types of membrane-associated receptors (estrogens, androgens and progestagens receptors) that are playing the most important role in the control of reproductive behaviors. Then we finally describe in more detail three separate behavioral systems in which membrane-initiated events have clearly been established to contribute to behavior control.

Exogenous Thyroid Hormone Is Associated with Shortened Survival and Upregulation of High-Risk Gene Expression Profiles in Steroid Receptor-Positive Breast Cancers

PURPOSE

Thyroid disease is a frequent comorbidity in women with breast cancer, and many require thyroid hormone replacement therapy (THRT). We postulated that THRT has a deleterious clinical effect mechanistically through hormonal interactions, nuclear receptor cross-talk, and upregulation of high-risk breast cancer genes.

EXPERIMENTAL DESIGN

Observational studies of patients with lymph node-negative (LN-) breast cancer (n = 820 and n = 160) were performed to test interactions between THRT and clinical, histologic, outcome, and treatment variables. Differences between the two cohorts include but are not limited to patient numbers, decades of treatment, duration of follow-up/treatment, tumor sizes, incidence, and type and dose/regimen of antihormonal and/or chemotherapeutic agents. In vivo and vitro models, in silico databases, and molecular methods were used to study interactions and define mechanisms underlying THRT effects.

RESULTS

THRT significantly and independently reduced disease-free and breast cancer-specific overall survival of only the steroid receptor (SR)-positive (as compared with SR-negative) node-negative patients in both long-term observational studies. Patients with SR+ LN- breast cancer who received THRT and tamoxifen experienced the shortest survival of all treatment groups. A less potent interaction between THRT and aromatase inhibitors was noted in the second patient cohort. Using in vivo and in vitro models, TH administration enhanced estrogen and TH-associated gene expression and proliferation, nuclear colocalization of estrogen receptor and thyroid hormone receptor, and activation of genes used clinically to predict tumor aggression in SR+ breast cancer, including the IGF-IR, WNT, and TGFβ pathways.

CONCLUSIONS

We show clinically significant adverse interactions between THRT, estrogenic, and oncogenic signaling in patients with SR+ LN- breast cancer.

New concepts in the study of the sexual differentiation and activation of reproductive behavior, a personal view

Since the beginning of this century, research methods in neuroendocrinology enjoyed extensive refinements and innovation. These advances allowed collection of huge amounts of new data and the development of new ideas but have not led to this point, with a few exceptions, to the development of new conceptual advances. Conceptual advances that took place largely resulted from the ingenious insights of several investigators. I summarize here some of these new ideas as they relate to the sexual differentiation and activation by sex steroids of reproductive behaviors and I discuss how our research contributed to the general picture. This selective review clearly demonstrates the importance of conceptual changes that have taken place in this field since beginning of the 21st century. The recent technological advances suggest that our understanding of hormones, brain and behavior relationships will continue to improve in a very fundamental manner over the coming years.

GEMIN4 functions as a coregulator of the mineralocorticoid receptor

The mineralocorticoid receptor (MR) is a member of the nuclear receptor superfamily. Pathological activation of the MR causes cardiac fibrosis and heart failure, but clinical use of MR antagonists is limited by the renal side effect of hyperkalemia. Coregulator proteins are known to be critical for nuclear receptor-mediated gene expression. Identification of coregulators, which mediate MR activity in a tissue-specific manner, may allow for the development of novel tissue-selective MR modulators that confer cardiac protection without adverse renal effects. Our earlier studies identified a consensus motif among MR-interacting peptides, MPxLxxLL. Gem (nuclear organelle)-associated protein 4 (GEMIN4) is one of the proteins that contain this motif. Transient transfection experiments in HEK293 and H9c2 cells demonstrated that GEMIN4 repressed agonist-induced MR transactivation in a cell-specific manner. Furthermore, overexpression of GEMIN4 significantly decreased, while knockdown of GEMIN4 increased, the mRNA expression of specific endogenous MR target genes. A physical interaction between GEMIN4 and MR is suggested by their nuclear co-localization upon agonist treatment. These findings indicate that GEMIN4 functions as a novel coregulator of the MR.

Use of phage display to identify novel mineralocorticoid receptor-interacting proteins

The mineralocorticoid receptor (MR) plays a central role in salt and water homeostasis via the kidney; however, inappropriate activation of the MR in the heart can lead to heart failure. A selective MR modulator that antagonizes MR signaling in the heart but not the kidney would provide the cardiovascular protection of current MR antagonists but allow for normal electrolyte balance. The development of such a pharmaceutical requires an understanding of coregulators and their tissue-selective interactions with the MR, which is currently limited by the small repertoire of MR coregulators described in the literature. To identify potential novel MR coregulators, we used T7 phage display to screen tissue-selective cDNA libraries for MR-interacting proteins. Thirty MR binding peptides were identified, from which three were chosen for further characterization based on their nuclear localization and their interaction with other MR-interacting proteins or, in the case of x-ray repair cross-complementing protein 6, its known status as an androgen receptor coregulator. Eukaryotic elongation factor 1A1, structure-specific recognition protein 1, and x-ray repair cross-complementing protein 6 modulated MR-mediated transcription in a ligand-, cell- and/or promoter-specific manner and colocalized with the MR upon agonist treatment when imaged using immunofluorescence microscopy. These results highlight the utility of phage display for rapid and sensitive screening of MR binding proteins and suggest that eukaryotic elongation factor 1A1, structure-specific recognition protein 1, and x-ray repair cross-complementing protein 6 may be potential MR coactivators whose activity is dependent on the ligand, cellular context, and target gene promoter.

Progesterone receptor in the vascular endothelium triggers physiological uterine permeability preimplantation

Vascular permeability is frequently associated with inflammation and is triggered by a cohort of secreted permeability factors such as vascular endothelial growth factor (VEGF). Here, we show that the physiological vascular permeability that precedes implantation is directly controlled by progesterone receptor (PR) and is independent of VEGF. Global or endothelial-specific deletion of PR blocks physiological vascular permeability in the uterus, whereas misexpression of PR in the endothelium of other organs results in ectopic vascular leakage. Integration of an endothelial genome-wide transcriptional profile with chromatin immunoprecipitation sequencing revealed that PR induces an NR4A1 (Nur77/TR3)-dependent transcriptional program that broadly regulates vascular permeability in response to progesterone. Silencing of NR4A1 blocks PR-mediated permeability responses, indicating a direct link between PR and NR4A1. This program triggers concurrent suppression of several junctional proteins and leads to an effective, timely, and venous-specific regulation of vascular barrier function that is critical for embryo implantation.

Role of mineralocorticoid receptors on the hypothalamus-pituitary-adrenal axis in humans

This clinical review will summarize the available data regarding the role of mineralocorticoid receptors (MRs) on the hypothalamus-pituitary-adrenal (HPA) axis control in physiological and pathological conditions and in the memory processes involved in the control and appraisal of a stress event. MRs are predominantly expressed in the limbic structures, with the hippocampus being the main localization, although MRs are also found at the hypothalamic level. It is known that hyppocampal MRs control the proactive feedback involved in the maintenance of the basal HPA activity, mainly at the nadir of the circadian rhythm. In physiological conditions, the administration of pharmacological doses of both MR antagonists and agonists is able to interact with the HPA activity, modifying the quiescent phase-nadir of the circadian rhythm, although some data in the literature do not support these observations. Also, in a physiological condition such as aging, an enhanced HPA axis activity is found in the time window, when MRs are predominantly occupied by cortisol circulating levels, possibly reflecting an MR impairment in this period of life. In pathology, major depression has been correlated to MR qualitative-quantitative alterations which could reflect differences on psychological and physiological responses, possibly predicting psychopathologies. Most of the remarks reported in this review seem to indicate, in agreement with animal data, a role played by MRs in the delicate control of the HPA axis in humans and the possible predisposition to the development of pathologies in case of their alterations.

Fatty acid synthase is a potential therapeutic target in estrogen receptor-/progesterone receptor-positive endometrioid endometrial cancer

OBJECTIVE

In the current study we investigated the clinicopathological significance of fatty acid synthase (FASN) expression and its relationship with estrogen receptor (ER) and progesterone receptor (PR) in endometrioid endometrial cancer.

METHODS

FASN expression in endometrioid endometrial cancer was assessed by immunohistochemistry using 108 paraffin-embedded tissue specimens and clinical data collected from a retrospective chart review. The specific FASN inhibitor C75 was used to analyze the relationship between FASN expression and cell growth as well as ER/PR expression in endometrioid endometrial cancer cell lines.

RESULTS

Positive FASN immunostaining was observed in 77.8% (84/108) of the tumors analyzed. Deep myometrial invasion was significantly and inversely correlated with positive FASN expression (p = 0.024). Positive ER (p = 0.018) and PR status (p = 0.012) was significantly correlated with positive FASN expression. Patients with positive FASN expression in endometrioid endometrial cancer tissues tended to have a favorable progression-free/overall survival (p = 0.127 and p = 0.087, respectively). Ishikawa cells with high FASN expression also showed high expression of ER/PR, while HEC1B cells had low expression levels of both FASN and ER/PR. FASN inhibition by C75 (10 µM) significantly reduced ER/PR expression compared with control dimethyl sulfoxide treatment of Ishikawa cells. The growth of Ishikawa cells having positive FASN and ER/PR expression was significantly inhibited in the presence of C75 or FASN small-interfering RNA compared to HEC1B cells that lacked FASN and ER/PR expression.

CONCLUSION

The current findings suggest that there may be cross talk between the ER/PR and FASN signaling pathways that modulate ER/PR activation and could play a role in endometrioid endometrial cancer pathogenesis.

Synthesis and evaluation of 11β-(4-substituted phenyl) estradiol analogs: transition from estrogen receptor agonists to antagonists

INTRODUCTION

As part of our program to develop estrogen receptor (ER) targeted imaging and therapeutic agents we chose to evaluate 11β-substituted estradiol analogs as a representative scaffold. Previous synthetic studies provided an entry into this class of compounds and other work indicated that 11β-(substituted aryl) estradiol analogs were potent antagonists of the ER. Little information existed about the specific structural features involved in the transition from agonism to antagonism for the 11β-aryl estradiol analogs or their potential as scaffolds for drug conjugation.

METHODS

We prepared and characterized a series of 11β-(4-Substituted phenyl) estradiol analogs using modifications of existing synthetic methods. The new compounds, as well as standard steroidal agonists and antagonists, were evaluated as competitive ligands for the ERβ-LBD. Functional assays used the induction of alkaline phosphatase in Ishikawa cells to determine potency of the compounds as ER agonists or antagonists.

RESULTS

The synthetic strategy successfully generated a series of compounds in which the 4-substituent was sequentially modified from hydroxyl to methoxy to azidoethoxy/N,N-dimethylaminoethoxy and eventually to a prototypical 1,4-naphthoquinone-containing moiety. The new compounds all retained high relative binding affinity (RBA) for the ERα-LBD, ranging from 13-83% that of estradiol. No subtype selectivity was observed. More importantly, the transition from agonist to antagonist activity occurs at the 4-methoxy stage where the compound is a mixed antagonist. More notably, antagonism appeared to be more dependent upon the size of the 11β-substituent than upon the nature of the terminal group

CONCLUSIONS

We have developed a synthetic strategy that provides facile access to potent 11β-(4-substituted phenyl) estradiol analogs. The resultant compounds retain high affinity for the ERα-LBD and, more importantly, demonstrate potent antagonist activity in cells. Large functionalities distal to the 11β-phenyl ring had little additional effect on either affinity or efficacy, suggesting the incorporation of diverse imaging or biologically active groups can be attached without significantly compromising the ER-binding capacity. Future studies are in progress to exploit the 11β-aryl estradiol analogs as potential drug delivery systems and imaging agents.

Synthesis and evaluation of 17α-E-20-(heteroaryl)norpregn-1,3,5(10),20 tetraene-3,17β-diols [17α-(heteroaryl)vinyl estradiols] as ligands for the estrogen receptor-α ligand binding domain (ERα-LBD)

A series of 17α-(heteroaryl)vinyl estradiols was prepared to evaluate the influence of heteroatom on the affinity and efficacy of estrogenic ligands for the estrogen receptor-alpha ligand binding domain (ERα-LBD). The products demonstrated reduced binding affinity compared to the parent 17α-E-phenyl vinyl estradiol, but the binding was relatively independent of the heteroatom. The greatest influence of the heteroatom was evident in the efficacy of the compounds as the thienyl derivatives 2f,g were more potent than either the pyridyl 2b-d or pyrimidinyl 2e analogs. The results suggest that a subtle interplay of interactions between the ligands and the receptor influences the biological response.

Corepressor effect on androgen receptor activity varies with the length of the CAG encoded polyglutamine repeat and is dependent on receptor/corepressor ratio in prostate cancer cells

The response of prostate cells to androgens reflects a combination of androgen receptor (AR) transactivation and transrepression, but how these two processes differ mechanistically and influence prostate cancer risk and disease outcome remain elusive. Given recent interest in targeting AR transrepressive processes, a better understanding of AR/corepressor interaction and responses is warranted. Here, we used transactivation and interaction assays with wild-type and mutant ARs, and deletion AR fragments, to dissect the relationship between AR and the corepressor, silencing mediator for retinoic acid and thyroid hormone receptors (SMRT). We additionally tested how these processes are influenced by AR agonist and antagonist ligands, as well as by variation in the polyglutamine tract in the AR amino terminal domain (NTD), which is encoded by a polymorphic CAG repeat in the gene. SMRT was recruited to the AR ligand binding domain by agonist ligand, and as determined by the effect of strategic mutations in activation function 2 (AF-2), requires a precise conformation of that domain. A distinct region of SMRT also mediated interaction with the AR-NTD via the transactivation unit 5 (TAU5; residues 315-538) region. The degree to which SMRT was able to repress AR increased from 17% to 56% as the AR polyglutamine repeat length was increased from 9 to 42 residues, but critically this effect could be abolished by increasing the SMRT:AR molar ratio. These data suggest that the extent to which the CAG encoded polyglutamine repeat influences AR activity represents a balance between corepressor and coactivator occupancy of the same ligand-dependent and independent AR interaction surfaces. Changes in the homeostatic relationship of AR to these molecules, including SMRT, may explain the variable penetrance of the CAG repeat and the loss of AR signaling flexibility in prostate cancer progression.

Nuclear Receptor Cofactors in PPARgamma-Mediated Adipogenesis and Adipocyte Energy Metabolism

Transcriptional cofactors are integral to the proper function and regulation of nuclear receptors. Members of the peroxisome proliferator-activated receptor (PPAR) family of nuclear receptors are involved in the regulation of lipid and carbohydrate metabolism. They modulate gene transcription in response to a wide variety of ligands, a process that is mediated by transcriptional coactivators and corepressors. The mechanisms by which these cofactors mediate transcriptional regulation of nuclear receptor function are still being elucidated. The rapidly increasing array of cofactors has brought into focus the need for a clear understanding of how these cofactors interact in ligand- and cell-specific manners. This review highlights the differential effects of the assorted cofactors regulating the transcriptional action of PPARγ and summarizes the recent advances in understanding the physiological functions of corepressors and coactivators.

Histone H3K4 trimethylation by MLL3 as part of ASCOM complex is critical for NR activation of bile acid transporter genes and is downregulated in cholestasis

The nuclear receptor Farnesoid x receptor (FXR) is a critical regulator of multiple genes involved in bile acid homeostasis. The coactivators attracted to promoters of FXR target genes and epigenetic modifications that occur after ligand binding to FXR have not been completely defined, and it is unknown whether these processes are disrupted during cholestasis. Using a microarray, we identified decreased expression of mixed lineage leukemia 3 (MLL3), a histone H3 lysine 4 (H3K4) lysine methyl transferase at 1 and 3 days of post-common bile duct ligation (CBDL) in mice. Chromatin immunoprecipitation analysis (ChIP) analysis revealed that H3K4me3 of transporter promoters by MLL3 as part of activating signal cointegrator-2 -containing complex (ASCOM) is essential for activation of bile salt export pump (BSEP), multidrug resistance associated protein 2 (MRP2), and sodium taurocholate cotransporting polypeptide (NTCP) genes by FXR and glucocorticoid receptor (GR). Knockdown of nuclear receptor coactivator 6 (NCOA6) or MLL3/MLL4 mRNAs by small interfering RNA treatment led to a decrease in BSEP and NTCP mRNA levels in hepatoma cells. Human BSEP promoter transactivation by FXR/RXR was enhanced in a dose-dependent fashion by NCOA6 cDNA coexpression and decreased by AdsiNCOA6 infection in HepG2 cells. GST-pull down assays showed that domain 3 and 5 of NCOA6 (LXXLL motifs) interacted with FXR and that the interaction with domain 5 was enhanced by chenodeoxycholic acid. In vivo ChIP assays in HepG2 cells revealed ligand-dependent recruitment of ASCOM complex to FXR element in BSEP and GR element in NTCP promoters, respectively. ChIP analysis demonstrated significantly diminished recruitment of ASCOM complex components and H3K4me3 to Bsep and Mrp2 promoter FXR elements in mouse livers after CBDL. Taken together, these data show that the "H3K4me3" epigenetic mark is essential to activation of BSEP, NTCP, and MRP2 genes by nuclear receptors and is downregulated in cholestasis.

Characterization of two functional glucocorticoid receptors in the marine medaka Oryzias dancena

The cDNAs that encode the glucocorticoid receptors odGR1 and odGR2 were cloned from a euryhaline teleost, the marine medaka (Oryzias dancena). The open reading frames of odGR1 and odGR2 encode 790 and 783 amino acids, respectively, and show a sequence identity of 46% with each other. When inter- and intra-species comparisons of the GR domains were made, the N-terminal AF-1 (A/B) and hinge (D) domains showed relatively low identities, whereas the DNA-binding (C) domain (DBD) and ligand-binding (E) domain showed relatively high identities. Through phylogenetic analysis, we revealed that odGR1 and odGR2 belong to the teleost GR1 and GR2 groups, respectively. Transfection of odGR1 or odGR2 expression vectors into COS-7 cells along with a reporter vector demonstrated that cortisol and dexamethasone dose-dependently induce transcriptional activity in both GRs. As described in other teleostean fish, the transactivity of odGR2 was more sensitive at far lower concentrations of ligands than the transactivity of odGR1. When treated with aldosterone, the reporter gene was activated in COS-7 cells transfected with odGR2 but not in cells transfected with odGR1. RU486 inhibited transactivation by both GRs, but odGR2 was less sensitive to the inhibitor. Interestingly, alterations in coregulators, GRIP-1 and SMILE, mediated transactivation that was more drastic for odGR2 than odGR1. A nine-amino acid insertion (WRARQNTDG) in the DBD of odGR1 had a weak but significant influence on the transactivity of odGR2 with respect to responsiveness to agonists or coregulators. Taken together, these results indicate that the two odGRs possess distinct features not only for ligand sensitivity but also for preferential coregulator recruitment.

Aldosterone and the cardiovascular system: a dangerous association

Initial studies have focussed on the actions of aldosterone in renal electrolyte handling and, as a consequence, blood pressure control. More recently, attention has primarily been focussed on its actions on the heart and vascular system, where it is locally produced. Aldosterone by binding mineralocorticoid receptors causes oxidative stress, fibrosis and triggers an inflammatory response in the cardiovascular system. All these effects could be underlying the role of aldo-sterone on cardiac and vascular remodelling associated with different pathological situations. At the vascular level, aldo-sterone affects endothelial function because administration of aldosterone to rats impaired endothelium-dependent relaxations. In addition, the administration of mineralocorticoid receptor antagonists ameliorates endothelium-dependent relaxation in models of both hypertension and atherosclerosis, and in patients with heart failure. Several mechanisms can participate in this effect, including production of vasoconstrictor factors and a reduction in nitric oxide levels. This reduction can involve both a decrease in its production as well as an increase in its degradation by reactive oxygen species. Aldosterone can produce oxidative stress by the activation of transcription factors such as the NF-κB system, which can also trigger an inflammatory process through the production of different cytokines. At cardiac level, high levels of aldosterone can also adversely impact heart function by producing cardiac hypertrophy, diastolic dysfunction and electrical remodelling through changes in ionic channels. All these effects can explain the beneficial effect of mineralocorticoid blockade in the cardiovascular system.

Expression of a BTB/POZ protein, NAC1, is essential for the proliferation of normal cyclic endometrial glandular cells and is up-regulated by estrogen

PURPOSE

The purpose of this study was to investigate the expression and localization of NAC1, a member of the BTB/POZ gene family in the human cyclic endometrium.

EXPERIMENTAL DESIGN

NAC1 expression in normal cyclic endometrium was assessed by immunohistochemistry, and data on clinical variables were collected by retrospective chart review. To elucidate the molecular mechanisms of NAC1 expression in the normal endometrium endometrial carcinoma cell lines (Ishikawa, HHUA; ER+, PR+) and primary cultured normal endometria were tested in a sex steroid induction assay and a NAC1 knockdown assay using siRNA.

RESULTS

Expression of NAC1 in glandular cells was significantly higher in the early and mid proliferative phases than in the other menstrual phases. Both NAC1 RNA and protein expression were up-regulated by treatment with 10 nmol/L 17beta-Estradiol (E2) in Ishikawa, HHUA and primary cultured normal endometrial cells. The estrogen receptor antagonist ICI 182,780 significantly attenuated E2-induced NAC1 expression. NAC1 gene knockdown inhibited cell growth and induced apoptosis in Ishikawa, HHUA, and normal endometria, all of which expressed NAC1. Furthermore, NAC1 siRNA significantly abrogated estrogen-driven cellular proliferation in Ishikawa, HHUA, and primary cultured normal endometrial cells, whereas the control siRNA had no effect on cell growth in any of these cells.

CONCLUSIONS

These findings suggest that NAC1 is functionally involved in E2-induced cell growth of the normal endometrial glandular cells. Because NAC1 is thought to have oncogenic potential, the current findings may provide new insight into the mechanism of estrogen induced endometrial carcinogenesis.

Molecular imaging, an innovative methodology for whole-body profiling of endocrine disrupter action

Endocrine disrupters (EDs) are environment and food contaminants known to alter metabolic functions of mammals by interfering with specific endocrine pathways. Many EDs act on steroid hormone target cells by interacting with intracellular receptors (IRs) like estrogen receptors, androgen receptors, and thyroid hormone receptors; other receptors may be engaged. IRs are ligand-operated transcription factors acting in concert with general or cell-specific coregulators. The newly acquired awareness on the panoply of IR functions has increased the concern on potential, unsought, harmful effects of EDs on human health and has questioned the capability of currently available methodologies to identify and study EDs in the environment and in the food chain. Indeed, current in vivo and in vitro methodologies restrict the analysis to very specific organs or cell systems, with obvious limitations in predicting the systemic metabolic consequences of ED exposure. The emphasis recently laid by Regulatory Authorities, including European Center for the Validation of Alternative Methods, on the generation of in vitro model systems for toxicological analyses discouraged the development of models suitable to envision the whole spectrum of ED body actions required when studying compounds acting through IRs. Molecular imaging now provides the opportunity to quantify ED effects in living organisms enabling, for the first time, to acquire a full comprehension of the systemic effects of acute and prolonged exposure to EDs, solving the issue of the potential harm due to repeated low-dose exposure. The systems here reviewed are of unquestionable toxicological relevance and need to be taken into consideration to improve the methodology currently available and in use.

Individual variation and the endocrine regulation of behaviour and physiology in birds: a cellular/molecular perspective

Investigations of the cellular and molecular mechanisms of physiology and behaviour have generally avoided attempts to explain individual differences. The goal has rather been to discover general processes. However, understanding the causes of individual variation in many phenomena of interest to avian eco-physiologists will require a consideration of such mechanisms. For example, in birds, changes in plasma concentrations of steroid hormones are important in the activation of social behaviours related to reproduction and aggression. Attempts to explain individual variation in these behaviours as a function of variation in plasma hormone concentrations have generally failed. Cellular variables related to the effectiveness of steroid hormone have been useful in some cases. Steroid hormone target sensitivity can be affected by variables such as metabolizing enzyme activity, hormone receptor expression as well as receptor cofactor expression. At present, no general theory has emerged that might provide a clear guidance when trying to explain individual variability in birds or in any other group of vertebrates. One strategy is to learn from studies of large units of intraspecific variation such as population or sex differences to provide ideas about variables that might be important in explaining individual variation. This approach along with the use of newly developed molecular genetic tools represents a promising avenue for avian eco-physiologists to pursue.

Novel identification of UDP-glucuronosyltransferase 1A10 as an estrogen-regulated target gene

Recently, we have shown that UGT1A10 is actively involved in the inactivation of E(1), E(2), and their 2- and 4-hydroxylated derivatives. In the present study, we show for the first time that treatment of the MCF-7 ER-positive breast cancer cell line with E(2) produces a dose-dependent up-regulation of UGT1A10 mRNA levels, followed by a steady down-regulation. In contrast, E(2) did not stimulate mRNA expression in the MDA-MB-231 (ER)-negative breast cancer cell line. Expression of UGT1A10 mRNA was blocked by the antiestrogen, ICI 182,780, but not by the transcriptional inhibitor, actinomycin-d. These findings suggest that regulation of UGT1A10 mRNA might be a primary transcriptional response mediated through the ER. Expression of UGT1A10 mRNA was also stimulated by other estrogenic compounds including propylpyrazoletriol (PPT) and genistein (Gen). Exposure of MCF-7 cells to 0.1nM E(2) up-regulated, and then down-regulated, UGT1A protein and enzymatic activity toward E(2) at 10nM E(2) as determined by Western blot and glucuronidation activity assays. Collectively, these results suggest that induction of UGT1A10 mRNA expression by E(2) might be mediated through ER, and that this isoform is a novel, estrogen-regulated target gene in MCF-7, ER-positive human breast cancer cells. The finding of E(2)-induced expression of UGT1A10 mRNA, followed by the down-regulation of UGT1A10 at pharmacological concentrations of E(2), might have a significant moderating effect on E(2) availability for ER and estrogen clearance, thereby promoting the signaling of E(2) in breast cancer cells.

Immunodetection of thyroid hormone receptor (alpha1/alpha2) in the rat uterus and oviduct

The aim of this study was to investigate the immunolocalization and the existence of thyroid hormone receptors (THR) (alpha1/alpha2) in rat uterus and oviduct. For this purpose 6 female Wistar albino rats found in estrous period were used. Tissue samples fixed in 10% neutral formalin were examined immunohistochemically. Sections were incubated with primary mouse-monoclonal THR (alpha1/alpha2) antibody. In uterus, THR (alpha1/alpha2) immunoreacted strongly with uterine luminal epithelium, endometrial gland epithelium and endometrial stromal cells and, moderately with myometrial smooth muscle. In oviduct, they were observed moderately in the epithelium of the tube and the smooth muscle cells of the muscular layer.

In conclusion, the presence of THR in uterus and oviduct suggests that these organs are an active site of thyroid hormones.

Synthesis and Evaluation of Isomeric (17α,20E)-11β-Methoxy-21-(trifluoromethylphenyl)-19-norpregna-1,3,5(10),20-tetraene-3,17β-diols as ERα-Hormone Binding Domain Ligands: Effect of the Methoxy Group on Receptor Binding and Uterotrophic Growth

In this study we have introduced the 11beta-methoxy group, a substituent known to increase in vivo potency in other steroidal estrogens, into the (17alpha,20E)-21-(trifluoromethylphenyl)-19-norpregna-1,3,5(10),20-tetraene-3,17beta-diols: (trifluoromethylphenyl)vinyl estradiols. Receptor binding, using the ERalpha-HBD, indicated that the 11beta-methoxy group had little effect on the relative binding affinity of the target compounds compared to the corresponding 11beta-unsubstituted analogs, however, the 11beta-methoxy derivatives were significantly more potent in stimulating uterotrophic growth in immature female rats. Molecular modeling studies suggest that while the 11beta-methoxy group does not contribute significantly to the overall binding energy of the ligand-ERalpha-HBD complex, it stabilizes residues associated with the coregulator protein binding site. Such effects would influence the dynamics of subsequent events, such as transcription and biological responses.

Ligand-Selective Interdomain Conformations of Estrogen Receptor-α

Selective estrogen receptor modulators (SERMs) inhibit estrogen activation of the estrogen receptor (ER) in some tissues but activate ER in other tissues. These tissue-selective actions suggest that SERMs may be identified with tissue specificities that would improve the safety of breast cancer and hormone replacement therapies. The identification of an improved SERM would be aided by understanding the effects of each SERM on the structure and interactions of ER. To date, the inability to obtain structures of the full-length ER has limited our structural characterization of SERM action to their antiestrogenic effects on the isolated ER ligand binding domain. We studied the effects of estradiol and the clinically useful SERMs 4-hydroxytamoxifen and fulvestrant on the conformation of the full-length ERα dimer complex by comparing, in living human breast cancer cells, the amounts of energy transfer between fluorophores attached to different domains of ERα. Estradiol, 4-hydroxytamoxifen, and fulvestrant all promoted the rapid formation of ERα dimers with equivalent interaction kinetics. The amino- and carboxyl-terminal ERα domains both contain activation functions differentially affected by these ligands, but the positions of only the carboxyl termini differed upon binding with estradiol, 4-hydroxytamoxifen, or fulvestrant. The association of a specific ERα dimer conformation with the binding of ligands of different clinical effect will assist the identification of a SERM with optimal tissue-selective estrogenic and antiestrogenic activities. These studies also provide a roadmap for dissecting important structural and kinetic details for any protein complex from the quantitative analysis of energy transfer.

Changes in the Secondary Structure of Highly Polymeric DNA and CC(GCC)n-Type Oligonucleotides under the Action of Steroid Hormones and Their Complexes with Apolipoprotein A I

A small-angle X-ray scattering study showed that the action of tetrahydrocortisol (THC) in complex with apolipoprotein A I (ApoA-I) on DNA leads to local melting of DNA. The most probable site of interaction between this complex and DNA is the (GCC)n-type sequence. Oligonucleotides (duplexes) of this type have been synthesized. It was demonstrated that the interaction of this oligonucleotide with the THC-ApoA-I complex leads to dissociation into complementary oligonucleotides. The latter ones also interact with the THC-ApoA-I complex. The kinetics of this multistep process is presented. The mechanism of interaction between hormones or their ApoA-I complexes and duplex CC(GCC)5.GG(CGG)5Li2 was studied using IR spectroscopy. It was shown that the interaction with THC or the THC-ApoA-I complex leads to the formation of hydrogen bonds between the OH group of the hormone A-ring and the C=O group of cytosine or guanine. Interaction with cortisol or the cortisol-ApoA-I complex leads to the formation of a hydrogen bond with the NH group of cytosine; in addition, THC and cortisol form hydrogen bonds with the PO2 group of the duplex and with the OH group of the monosaccharide. The interaction of ApoA-I with the duplex is accompanied by the formation of hydrogen bonds between the protein NH2 group and the C=O group of cytosine and the P=O group. The order-to-order structural transition takes place in the duplex under the action of THC or cortisol, with THC causing a higher ordering as compared to cortisol. The order-to-disorder structural transition occurs in the duplex under the action of the THC-ApoA-I, cortisol-ApoA-I, or ApoA-I complexes. Shifting the pH of the medium from 7.2 to 6.0 also leads to an order-to-disorder-type structural transition.

TAF4b, a TBP associated factor, is required for oocyte development and function

Development of a fertilizable oocyte is a complex process that relies on the precise temporal and spatial expression of specific genes in germ cells and in surrounding somatic cells. Since female mice null for Taf4b, a TBP associated factor, are sterile, we sought to determine when during follicular development this phenotype was first observed. At postnatal day 3, ovaries of Taf4b null females contained fewer (P < 0.01) oocytes than ovaries of wild type and heterozygous Taf4b mice. However, expression of only one somatic cell marker Foxl2 was reduced in ovaries at day 15. Despite the reduced number of follicles, many proceed to the antral stage, multiple genes associated with granulosa cell differentiation and oocyte maturation were expressed in a normal pattern, and immature Taf4b null females could be hormonally primed to ovulate and mate. However, the ovulated cumulus oocyte complexes from the Taf4b null mice had fewer (P < 0.01) cumulus cells, and the oocytes were functionally abnormal. GVBD and polar body extrusion were reduced significantly (P < 0.01). The few oocytes that were fertilized failed to progress beyond the two-cell stage of development. Thus, infertility in Taf4b null female mice is associated with defects in early follicle formation, oocyte maturation, and zygotic cleavage following ovulation and fertilization.

Synthesis and Evaluation of (17α,20Z)-21-(4-Substituted-phenyl)-19-norpregna-1,3,5(10),20-tetraene-3,17β-diols as Ligands for the Estrogen Receptor-α Hormone Binding Domain: Comparison with 20E-Isomers

As part of our ongoing program to develop probes for the hormone binding domain of the estrogen receptor-alpha (ERalpha), we prepared and evaluated a series of 17alpha,Z-(4-substituted-phenyl)vinyl estradiol derivatives. The results indicated that the relative binding affinities (RBAs) at 25 degrees C for the new compounds were significant (RBA = 9-57) although less than that of estradiol (RBA = 100) or of the parent unsubstituted phenylvinyl estradiol (RBA = 66). All of the Z-compounds were full agonists in the uterotrophic assay, indicating that the ligands formed estrogen-like complexes with the estrogen receptor-alpha hormone binding domain (ERalpha-HBD). Comparison of corresponding Z- and E-4-substituted phenylvinyl ligands complexed with the ERalpha-HBD indicated small but significant differences in binding modes that may account for the differing trends seen in the structure-activity relationships for the two series.

From an Enhanceosome to a Repressosome: Molecular Antagonism between Glucocorticoids and EGF Leads to Inhibition of Wound Healing

Wound healing in its complexity depends on the concerted activity of many signaling pathways. Here, we analyzed how the simultaneous presence of glucocorticoids (GC), retinoic acid (RA) and epidermal growth factor (EGF) affect wound healing at the molecular, cellular and tissue levels. We found that GC inhibit wound healing by inhibiting keratinocyte migration, whereas RA does not. Furthermore, GC block EGF-mediated migration, whereas RA does not. On the molecular level, these compounds target expression of one of the earliest markers of wound healing, cytoskeletal components, keratins K6 and K16. Both GC and RA repress their transcription, whereas EGF induces it. Interestingly, the GC inhibition is mediated by a repressosome complex consisting of four monomers of the GC receptor, beta-catenin and coactivator-associated-arginine-methyltransferase-1. GC are dominant, EGF cannot rescue GC-mediated inhibition. Pre-treatment of keratinocytes with GC shifts the balance towards the repressosome, allowing for dominant inhibition of K6 even in the presence of EGF or c-fos/c-jun. Although RA receptor gamma and glucocorticoid receptor bind to the same response element repressing transcription of keratins K6/K16, RA receptor interacts with the components of the EGF-enhanceosome (co-activators: glucocorticoid-receptor-interactive protein-1(GRIP-1)/steroid-receptors coactivator-1 (SRC-1)) without breaking it. Consequently, RA has a co-dominant effect with EGF: when present simultaneously, their effects balance each other. When keratinocytes are pre-treated with mitogen-activated protein kinase (MAPK) inhibitor, thus blocking EGF, the balance is shifted towards the RA repression. Similar to clinical findings, pre-treatment of keratinocytes with RA blocks GC-mediated inhibition. In summary, our results identify complex molecular mechanisms through which RA alleviates GC-mediated inhibition of wound healing.

Regulation of androgen receptor and histone deacetylase 1 by Mdm2-mediated ubiquitylation

The androgen receptor (AR) is a member of the nuclear hormone receptor family of transcription factors and plays a critical role in regulating the expression of genes involved in androgen-dependent and -independent tumour formation. Regulation of the AR is achieved by alternate binding of either histone acetyltransferase (HAT)-containing co-activator proteins, or histone deacetylase 1 (HDAC1). Factors that control AR stability may also constitute an important regulatory mechanism, a notion that has been confirmed with the finding that the AR is a direct target for Mdm2-mediated ubiquitylation and proteolysis. Using chromatin immunoprecipitation (ChIP) and re-ChIP analyses, we show that Mdm2 associates with AR and HDAC1 at the active androgen-responsive PSA promoter in LNCaP prostate cancer cells. Furthermore, we demonstrate that Mdm2-mediated modification of AR and HDAC1 catalyses protein destabilization and attenuates AR sactivity, suggesting that ubiquitylation of the AR and HDAC1 may constitute an additional mechanism for regulating AR function. We also show that HDAC1 and Mdm2 function co-operatively to reduce AR-mediated transcription that is attenuated by the HAT activity of the AR co-activator Tip60, suggesting interplay between acetylation status and receptor ubiquitylation in AR regulation. In all, our data indicates a novel role for Mdm2 in regulating components of the AR transcriptosome.

cAMP-dependent protein kinase regulates ubiquitin-proteasome-mediated degradation and subcellular localization of the nuclear receptor coactivator GRIP1

Nuclear receptors and their coactivators are key regulators of numerous physiological functions. GRIP1 (glucocorticoid receptor-interacting protein) is a member of the steroid receptor coactivator family. Here, we show that GRIP1 is regulated by cAMP-dependent protein kinase (PKA) that induces its degradation through the ubiquitin-proteasome pathway. GRIP1 was down-regulated in transiently transfected COS-1 cells after treatment with 8-para-chlorophenylthio-cAMP or forskolin and 3-isobutyl-1-methylxanthine and in adrenocortical Y1 cells after incubation with adrenocorticotropic hormone. Pulse-chase experiments with transiently transfected COS-1 cells demonstrated that the half-life of GRIP1 was markedly reduced in cells overexpressing the PKA catalytic subunit, suggesting that activation of PKA increases the turnover of GRIP1 protein. The proteasome inhibitors MG132 and lactacystin abolished the PKA-mediated degradation of GRIP1. Using ts20 cells, a temperature-sensitive cell line that contains a thermolabile ubiquitin-activating E1 enzyme, it was confirmed that PKA-mediated degradation of GRIP1 is dependent upon the ubiquitin-proteasome pathway. Coimmunoprecipitation studies of COS-1 cells transfected with expression vectors encoding GRIP1 and ubiquitin using anti-GRIP1 and anti-ubiquitin antibodies showed that the ubiquitination of GRIP1 was increased by overexpression of PKA. Finally, we show that PKA regulates the intracellular distribution pattern of green fluorescent protein-GRIP1 and stimulates recruitment of GRIP1 to subnuclear foci that are colocalized with the proteasome. Taken together, these data demonstrate that GRIP1 is ubiquitinated and degraded through activation of the PKA pathway. This may represent a novel regulatory mechanism whereby hormones down-regulate a nuclear receptor coactivator.

Nuclear structure-associated TIF2 recruits glucocorticoid receptor and its target DNA

Assembly of multi-protein complexes on promoter and enhancer elements is a prerequisite for onset of gene transcription. At the beginning of this process, transcription factors are thought to act as nucleating centers for complex formation through the binding of their target DNA sequences, and thereafter recruit coactivators. Here, we investigated this process of assembly by determining the distribution of the glucocorticoid receptor (GR) and its coactivator, TIF2. Both endogenously and ectopically expressed TIF2 were shown to form foci in the nucleus, and GR could be recruited to the TIF2 foci upon GR agonist but not antagonist treatment. Moreover, we show that the coactivators, p300 and PCAF, are also recruited to the TIF2 foci. The TIF2 foci could recruit GR carrying a microinjected GR responsive element. We propose that TIF2 provides a nuclear compartment that allows the assembly of multi-protein complexes required for GR-mediated gene activation.

Mitogenic activity of estrogens in human breast cancer cells does not rely on direct induction of mitogen-activated protein kinase/extracellularly regulated kinase or phosphatidylinositol 3-kinase

We have addressed the question of rapid, nongenomic mechanisms that may be involved in the mitogenic action of estrogens in hormone-dependent breast cancer cells. In quiescent, estrogen-deprived MCF-7 cells, estradiol did not induce a rapid activation of either the MAPK/ERK or phosphatidylinositol-3 kinase (PI-3K)/Akt pathway, whereas the entry into the cell cycle was documented by the successive inductions of cyclin D1 expression, hyperphosphorylation of the retinoblastoma protein (Rb), activity of the promoter of the cyclin A gene, and DNA synthesis. However, pharmacological inhibitors of the src family kinases, 4-amino-5-(4-methylphenyl)-7-(t-butyl) pyrazolo[3,4-d] pyrimidine (PP1) or of the PI-3K (LY294002) did prevent the entry of the cells into the cell cycle and inhibited the late G1 phase progression, whereas the inhibitor of MAPK/ERK activation (U0126) had only a partial inhibitory effect in the early G1 phase. In agreement with these results, small interfering RNA targeting Akt strongly inhibited the estradiolinduced cell cycle progression monitored by the activation of the promoter of the cyclin A gene. The expression of small interfering RNA targeting MAPK 1 and 2 also had a clear inhibitory effect on the estradiol-induced activation of the cyclin A promoter and also antagonized the estradiol-induced transcription directed by the estrogen response element. Finally, transfection of the estrogen receptor into NIH3T3 fibroblasts did not confer to the cells sensitivity to a mitogenic action of estradiol. We conclude that the induction of the cell cycle by estradiol does not require a direct activation of MAPK/ERK or PI-3K signaling protein kinase cascades, but that these kinases appear to have a permissive role in the cell cycle progression.

Aberrant expression of CARM1, a transcriptional coactivator of androgen receptor, in the development of prostate carcinoma and androgen-independent status

BACKGROUND

Coactivator-associated arginine methyltransferase 1 (CARM1) is a transcriptional coactivator of the androgen receptor (AR). It is involved in the regulation of the biologic functions of the AR. It remains to be determined whether CARM1 is involved in prostatic carcinogenesis.

METHODS

The expression of CARM1 in normal prostate epithelium, high-grade prostatic intraepithelial neoplasia (PIN), and prostate carcinoma tissue was examined in 66 previously untreated patients with prostate carcinomas, as well as 12 patients with hormone-independent prostate carcinoma, using immunohistochemical methods.

RESULTS

Cell staining was observed in the cytoplasm and the nucleus. In 66 patients without previous hormonal treatment, the percentage of cells that stained positively for CARM1 in benign prostate tissue specimens (mean values: cytoplasm, 23%; nucleus, 16%) was statistically significantly less than the percentage of positively stained cells in PIN (mean values: cytoplasm, 56%; nucleus, 30%; P < 0.001) and in prostatic adenocarcinoma specimens (mean values: cytoplasm, 79%; nucleus, 53%; P < 0.001). The difference between adenocarcinoma and PIN also was statistically significant (P < 0.001). The staining intensity for CARM1 was significantly lower in benign prostate tissue specimens compared with PIN and prostatic adenocarcinoma specimens (P < 0.001). In the 12 patients with androgen-independent prostatic adenocarcinoma, the expression of CARM1 was significantly increased when compared with patients without previous hormonal treatment. Expression of CARM1 was not correlated with age, Gleason score sum, pathologic stage, lymph node metastasis, extraprostatic extension, surgical margin status, vascular invasion, or perineural invasion.

CONCLUSIONS

The authors found that overexpression of CARM1 was involved in the development of prostate carcinoma as well as androgen-independent prostate carcinoma. Since CARM1 is functionally different from most other transcriptional coactivators of the AR, it may serve as a new target for the treatment of hormone-independent prostate carcinoma.

Role of the Low‐Affinity Glucocorticoid Receptor in the Regulation of Behavior and Energy Metabolism in the Migratory Red KnotCalidris canutus islandica

Plasma corticosterone increases in association with migratory flight in the red knot Calidris canutus islandica, suggesting that corticosterone may promote migratory activity and/or energy mobilization in this species. This hypothesis is supported by general effects of glucocorticoids, which include stimulation of locomotion and the mobilization of energy depots. We experimentally examined the role of elevated corticosterone levels in the migratory red knot by comparing foraging behavior, flight frequency, and plasma metabolites between vehicle-injected controls and birds treated with RU486, an antagonist to the genomic low-affinity glucocorticoid receptor (GR). We predicted that RU486 treatment would interfere with energy mobilization. However, we expected no effects on flight activity because recent studies suggest that glucocorticoids affect locomotion through a nongenomic receptor. Finally, because glucocorticoids exert permissive effects on food intake, we postulated that RU486 treatment in the red knot would interfere with feeding. Results were consistent with the latter prediction, suggesting that the GR participates in the promotion of hyperphagia, the intense feeding state that is characteristic of the migratory condition. RU486 treatment did not affect flight frequency, suggesting that corticosterone may support migratory activity through a receptor other than the GR. Energy metabolism (as determined through plasma metabolites) was also unaffected by RU486, possibly because energetic demands experienced by captive birds were low.

Selective estrogen receptor modulator regulated proteins in endometrial cancer cells

Tamoxifen is the primary hormonal therapy for breast cancer and is also used as a breast cancer chemopreventative agent. A major problem with tamoxifen therapy is undesirable endometrial proliferation. To identify proteins associated with the growth stimulatory effects of tamoxifen in an ER-positive model, the present study profiled total cellular and secreted proteins regulated by estradiol and selective estrogen receptor modifiers (SERMs) in the Ishikawa endometrial adenocarcinoma cell line using two-dimensional gel electrophoresis. Following 24 h incubation with 10(-8) M estradiol, 10(-7) M 4-hydroxytamoxifen, or 10(-7) M EM-652 (Acolbifene), nine proteins exhibited significant increase in expression. The proteins identified were heat shock protein 90-alpha, and -beta, heterogeneous nuclear ribonucleoprotein F, RNA polymerase II-mediating protein, cytoskeletal keratin 8, cytoskeletal keratin 18, ubiquitin-conjugating enzyme E2-18 kDa and nucleoside diphosphate kinase B. These protein profiles may serve as novel indices of SERM response and may also provide insight into novel mechanisms of SERM-mediated growth.

Towards selectively modulating mineralocorticoid receptor function: lessons from other systems

Although there is clinical utility in blocking mineralocorticoid receptor (MR) action, the usefulness of available MR antagonists is limited because of cross-reactivity with the androgen and progesterone receptors (spironolactone) or possibly by low affinity for MR (eplerenone). MR binds aldosterone and physiologic glucocorticoids, such as cortisol, which both can act as MR agonists in epithelial tissues. However, in preliminary studies aldosterone and cortisol appear to induce different conformations in non-epithelial tissues; in the cardiomyocyte, cortisol usually acts as an MR antagonist, whereas in vascular smooth muscle cortisol mimics aldosterone actions if it can access MR, just as it does in the kidney. Thus, there are needs for improved MR antagonists with higher selectivity and potency and, if possible, for compounds that lock MR into specific desirable conformations. Efforts are underway to modulate selectively the action of many nuclear receptors, and insights from one nuclear receptor may be applicable to others given the similarities in structure and function. We have used traditional approaches aided by X-ray crystallography to obtain several classes of selective ligands that modulate thyroid receptor (TR) action. We describe the properties of these selective TR modulators here, and discuss the possibility that similar approaches to ligand design may yield MR interacting compounds with improved specificity and, possibly, tissue specificity.

Equol, a natural estrogenic metabolite from soy isoflavones: convenient preparation and resolution of R- and S-equols and their differing binding and biological activity through estrogen receptors alpha and beta

Equol is a metabolite produced in vivo from the soy phytoestrogen daidzein by the action of gut microflora. It is known to be estrogenic, so human exposure to equol could have significant biological effects. Equol is a chiral molecule that can exist as the enantiomers R-equol and S-equol. To study the biological activity of racemic (+/-)-equol, as well as that of its pure enantiomers, we developed an efficient and convenient method to prepare (+/-)-equol from available isoflavanoid precursors. Furthermore, we optimized a method to separate the enantiomers of equol by chiral HPLC, and we studied for the first time, the activities of the enantiomers on the two estrogen receptors, ERalpha and ERbeta. In binding assays, S-equol has a high binding affinity, preferential for ERbeta (K(i)[ERbeta]=16 nM; beta/alpha=13 fold), that is comparable to that of genistein (K(i)[ERbeta]=6.7 nM; beta/alpha=16), whereas R-equol binds more weakly and with a preference for ERalpha (K(i)[ERalpha]=50 nM; beta/alpha=0.29). All equol isomers have higher affinity for both ERs than does the biosynthetic precursor daidzein. The availability and the in vitro characterization of the equol enantiomers should enable their biological effects to be studied in detail.

The low-affinity glucocorticoid receptor regulates feeding and lipid breakdown in the migratory Gambel's white-crowned sparrow Zonotrichia leucophrys gambelii

Plasma corticosterone increases during spring migration in a variety of bird species, including the Gambel's white-crowned sparrow Zonotrichia leucophrys gambelii. Corticosterone is elevated specifically in association with migratory flight, suggesting that corticosterone may promote processes such as energy mobilization and/or migratory activity. General effects of glucocorticoids support such a prediction. Because glucocorticoids exert permissive effects on food intake, corticosterone may also participate in the regulation of migratory hyperphagia. To examine the role of corticosterone during migration, we induced Gambel's white-crowned sparrows to enter the migratory condition and compared food intake and locomotor activity between controls and birds injected with RU486--an antagonist to the low-affinity glucocorticoid receptor (GR). In addition, we investigated effects of RU486 in birds that were subjected to a short-term fast. Results indicate that RU486 did not affect locomotor activity. However, consistent with its effects in mammals, RU486 suppressed food intake. Thus, hyperphagia and migratory restlessness, the two behaviors that characterize migration, may be regulated by different mechanisms. Lastly, RU486 antagonized fasting-induced lipid mobilization, as evidenced by decreased plasma free fatty acids. Thus, data on spring migrants suggest that endogenous corticosterone levels act through the GR to support hyperphagia and that the GR promotes availability of lipid fuel substrates in association with periods of energetic demand, e.g. during migratory flight.

Mixed lineage kinase 2 enhances trans-repression of Alien and nuclear receptors

Alien was previously identified as a corepressor for the thyroid hormone receptor (TR) and DAX-1 which belong both to the superfamily of nuclear receptors. Here, we isolated the mixed lineage kinase 2 (MLK2) as an interacting partner for the corepressor Alien using a yeast two hybrid screen. MLK2 is an upstream activator of JNKs and activation of MLK2-mediated signaling cascades play roles in neurodegenerative and apoptotic mechanisms in the central nervous system. MLK2 has been shown to be localized both in the cytoplasm and cell nucleus. We confirmed the Alien-MLK2 interaction using GST pull-down experiments and also show that MLK2 is able to phosphorylate Alien in immune-kinase assays. Functional analyses revealed that Alien, DAX-1 and thyroid hormone receptor mediated transcriptional silencing is strongly enhanced in the presence of active MLK2. Since MAP kinase signaling pathways are important mediators of cellular responses to a wide variety of stimuli, our data suggest that signaling pathways not only regulate transactivation but also enhancement of transcriptional silencing. This novel cross-talk may represent a link between MLK2-mediated signaling and transcriptional repression of target genes during neuronal differentiation processes.

Expression of steroid receptor coactivators and corepressors in human endometrial hyperplasia and carcinoma with relevance to steroid receptors and Ki-67 expression

BACKGROUND

To examine the steroid hormone dependent growth mechanism of human endometrial hyperplasia and carcinoma, expression levels of steroid receptor cofactors, such as coactivators (steroid receptor coactivator 1 [SRC-1] and p300/cyclic AMP-response element-binding protein (p300/CBP]) and corepressors (nuclear receptor corepressor [NCoR] and silencing mediator for retinoid and thyroid-hormone receptors [SMRT]), were investigated.

METHODS

The expression levels of cofactors were examined immunohistochemically using 20 samples of normal endometria, 36 samples of hyperplastic endometria, and 58 of malignant endometria and were compared with the expression levels of estrogen receptor (ER), progesterone receptor (PR), and a proliferation marker, Ki-67.

RESULTS

In samples of normal endometria, the expression of coactivators was observed diffusely in glandular cells in the proliferative phase, with a mean positivity index (PI) of 81.8 for SRC-1 and 91.3 for p300/CBP, whereas expression levels decreased in endometrial hyperplasia (PI: SRC-1, 58.9; p300/CBP, 83.8) and endometrial carcinoma (PI: SRC-1, 45.0; p300/CBP, 55.4). In endometrial hyperplasia, there was a significant correlation between the expression of ER and SRC-1 or p300/CBP. In contrast, there were no significant statistical or topologic correlations between the expression of coactivators and the expression of ER/PR in endometrial carcinoma. The expression of corepressors generally was limited, except for elevated expression of NCoR in endometrial hyperplasia (PI, 23.8).

CONCLUSIONS

The current study showed that expression levels of the steroid receptor coactivators SRC-1 and p300/CBP were reduced in endometrial carcinoma compared with normal and hyperplastic endometrium. In addition, topologic coexpression of both coactivators and ER/PR was lost in endometrial carcinoma. Accordingly, limited response to sex steroids in patients with endometrial carcinoma may be ascribed to the dissociation of cofactors and ER/PR.

Nuclear receptor coactivator function in reproductive physiology and behavior

Gonadal steroid hormones act throughout the body to elicit changes in gene expression that result in profound effects on reproductive physiology and behavior. Steroid hormones exert many of these effects by binding to their respective intracellular receptors, which are members of a nuclear receptor superfamily of transcriptional activators. A variety of in vitro studies indicate that nuclear receptor coactivators are required for efficient transcriptional activity of steroid receptors. Many of these coactivators are found in a variety of steroid hormone-responsive reproductive tissues, including the reproductive tract, mammary gland, and brain. While many nuclear receptor coactivators have been investigated in vitro, we are only now beginning to understand their function in reproductive physiology and behavior. In this review, we discuss the general mechanisms of action of nuclear receptor coactivators in steroid-dependent gene transcription. We then review some recent and exciting findings on the function of nuclear receptor coactivators in steroid-dependent brain development and reproductive physiology and behavior.

A neuronal-specific differentiation protein that directly modulates retinoid receptor transcriptional activation

Background

The specificity of a nuclear receptor's ability to modulate gene expression resides in its ability to bind a specific lipophilic ligand, associate with specific dimerization partners and bind specific DNA sequences in the promoter regions of genes. This sequence of events appears to be the basis for targeting an additional regulatory complex composed of a variety of protein and RNA components that deliver signals for facilitation or inhibition of the RNA polymerase complex. Characterization of the tissue and cell-specific components of these coregulatory complexes appear to be integral to our understanding of nuclear receptor regulation of transcription.

Results

A novel yeast screen sensitive to retinoid-X receptor (RXR) transcriptional activation resulted in the isolation of the rat homologue of the mouse NPDC-1 gene. NPDC-1 has been shown to be involved in the control of neural cell proliferation and differentiation, possibly through interactions with the cell cycle promoting transcription factor E2F-1. Although the amino acid sequence of NPDC-1 is highly conserved between mouse, rat and human homologues, their tissue specific expression was seen to vary. A potential for direct protein:protein interaction between NPDC-1, RXR and retinoic acid receptor beta (RARβ) was observed in vitro and NPDC-1 facilitated RXR homodimer and RAR-RXR heterodimer DNA binding in vitro. Expression of NPDC-1 was also observed to repress transcription mediated by retinoid receptors as well as by several other nuclear receptor family members, although not in a universal manner.

Conclusions

These results suggest that NPDC-1, through direct interaction with retinoid receptors, functions to enhance the transcription complex formation and DNA binding function of retinoid receptors, but ultimately repress retinoid receptor-mediated gene expression. As with NPDC-1, retinoids and their receptors have been implicated in brain development and these data provide a point of convergence for NPDC-1 and retinoid mediation of neuronal differentiation.

The interplay between the glucocorticoid receptor and nuclear factor-kappaB or activator protein-1: molecular mechanisms for gene repression

The inflammatory response is a highly regulated physiological process that is critically important for homeostasis. A precise physiological control of inflammation allows a timely reaction to invading pathogens or to other insults without causing overreaction liable to damage the host. The cellular signaling pathways identified as important regulators of inflammation are the signal transduction cascades mediated by the nuclear factor-kappaB and the activator protein-1, which can both be modulated by glucocorticoids. Their use in the clinic includes treatment of rheumatoid arthritis, asthma, allograft rejection, and allergic skin diseases. Although glucocorticoids have been widely used since the late 1940s, the molecular mechanisms responsible for their antiinflammatory activity are still under investigation. The various molecular pathways proposed so far are discussed in more detail.

The neuroendocrinology of reproductive behavior in Japanese quail

Sex steroid hormones such as testosterone have widespread effects on brain physiology and function but one of their best characterized effects arguably involves the activation of male sexual behavior. During the past 20 years we have investigated the testosterone control of male sexual behavior in an avian species, the Japanese quail (Coturnix japonica). We briefly review here the main features and advantages of this species relating to the investigation of fundamental questions in the field of behavioral neuroendocrinology, a field that studies inter-relationship among hormones, brain and behavior. Special attention is given to the intracellular metabolism of testosterone, in particular its aromatization into an estrogen, which plays a critical limiting role in the mediation of the behavioral effects of testosterone. Brain aromatase activity is controlled by steroids which increase the transcription of the enzyme, but afferent inputs that affect the intraneuronal concentrations of calcium also appear to have a pronounced effect on the enzyme activity through rapid changes in its phosphorylation status. The physiological significance of these slow genomic and rapid, presumably non-genomic, changes in brain aromatase activity are also briefly discussed.

Activating signal cointegrator 2 required for liver lipid metabolism mediated by liver X receptors in mice

Activating signal cointegrator 2 (ASC-2), a cancer-amplified transcriptional coactivator of nuclear receptors and many other transcription factors, contains two LXXLL-type nuclear receptor interaction domains. Interestingly, the second LXXLL motif is highly specific to the liver X receptors (LXRs). In cotransfection, DN2, an ASC-2 fragment encompassing this motif, exerts a potent dominant-negative effect on transactivation by LXRs, which is rescued by ectopic coexpression of the full-length ASC-2 but not by other LXXLL-type coactivators, such as SRC-1 and TRAP220. In contrast, DN2/m, in which the LXXLL motif is mutated to LXXAA to abolish the interactions with LXRs, is without any effect. Accordingly, expression of DN2, but not DN2/m, in transgenic mice results in phenotypes that are highly homologous to those previously observed with LXRalpha(-/-) mice, including a rapid accumulation of large amounts of cholesterol and down-regulation of the known lipid-metabolizing target genes of LXRalpha in the liver upon being fed a high-cholesterol diet. These results identify ASC-2 as a physiologically important transcriptional coactivator of LXRs and demonstrate its pivotal role in the liver lipid metabolism.

Distinct properties and advantages of a novel peroxisome proliferator-activated protein [gamma] selective modulator

Antidiabetic thiazolidinediones (TZDs) and non-TZD compounds have been shown to serve as agonists of the peroxisome proliferator-activated receptor gamma (PPARgamma). Here, we report the identification and characterization of a novel non-TZD selective PPARgamma modulator (nTZDpa). nTZDpa bound potently to PPARgamma with high selectivity vs. PPARalpha or PPARdelta. In cell-based assays for transcriptional activation, nTZDpa served as a selective, potent PPARgamma partial agonist and was able to antagonize the activity of PPARgamma full agonists. nTZDpa also displayed partial agonist effects when its ability to promote adipogenesis in 3T3-L1 cells was evaluated. Assessment of protein conformation using protease protection or solution nuclear magnetic resonance spectroscopy methods showed that nTZDpa produced altered PPARgamma conformational stability vs. full agonists, thereby establishing a physical basis for its observed partial agonism. DNA microarray analysis of RNA from 3T3-L1 adipocytes treated with nTZDpa or several structurally diverse PPARgamma full agonists demonstrated qualitative differences in the affected gene expression profile for nTZDpa. Chronic treatment of fat-fed, C57BL/6J mice with nTZDpa or a TZD full agonist ameliorated hyperglycemia and hyperinsulinemia. However, unlike the TZD, nTZDpa caused reductions in weight gain and adipose depot size. Feed efficiency was also substantially diminished. Unlike TZDs, nTZDpa did not cause cardiac hypertrophy in mice. When a panel of PPARgamma target genes was examined in white adipose tissue, nTZDpa produced a different in vivo expression pattern vs. the full agonist. These findings establish that novel selective PPARgamma modulators can produce altered receptor conformational stability leading to distinctive gene expression profiles, reduced adipogenic cellular effects, and potentially improved in vivo biological responses. Such compounds may lead to preferred therapies for diabetes, obesity, or metabolic syndrome.

Dynamic inhibition of nuclear receptor activation by corepressor binding

Nuclear receptors adopt dramatically different conformations in the presence or absence of ligand, and such liganded (holo) and unliganded (apo) receptors are specifically recognized by transcriptional coactivators and corepressors, respectively. These two states likely exist in dynamic equilibrium, contrary to the conventional model of static off and on conformations. First, corepressor SMRT [for silencing mediator of thyroid hormone receptor (TR) and retinoic acid receptor (RAR)] inhibits the interaction of coactivator steroid receptor coactivator-1 with liganded TR/RAR. Second, SMRT enables receptors to adopt apo-form even in the presence of ligand, as demonstrated with limited proteolyses and decreased binding of radiolabeled retinoid to RAR. Finally, chromatin immunoprecipitation results indicate that SMRT and steroid receptor coactivator-1 dynamically compete for receptor bindings in vivo in the presence of ligand. These results suggest that corepressor binding can drive receptors to adopt the apo-state, even in the presence of ligand, and inhibit activated liganded (holo) nuclear receptors in vivo.