The presence of both the amino- and carboxyl-terminal domains in the AR is essential for the completion of a transcriptionally active form with coactivators and intranuclear compartmentalization common to the steroid hormone receptors: a three-dimensional imaging study

Phasing the intranuclear organization of steroid hormone receptors

Steroid receptors (SRs) encompass a family of transcription factors that regulate the expression of thousands of genes upon binding to steroid hormones and include the glucocorticoid, androgen, progesterone, estrogen and mineralocorticoid receptors. SRs control key physiological and pathological processes, thus becoming relevant drug targets. As with many other nuclear proteins, hormone-activated SRs concentrate in multiple discrete foci within the cell nucleus. Even though these foci were first observed ∼25 years ago, their exact structure and function remained elusive. In the last years, new imaging methodologies and theoretical frameworks improved our understanding of the intranuclear organization. These studies led to a new paradigm stating that many membraneless nuclear compartments, including transcription-related foci, form through a liquid–liquid phase separation process. These exciting ideas impacted the SR field by raising the hypothesis of SR foci as liquid condensates involved in transcriptional regulation. In this work, we review the current knowledge about SR foci formation under the light of the condensate model, analyzing how these structures may impact SR function. These new ideas, combined with state-of-the-art techniques, may shed light on the biophysical mechanisms governing the formation of SR foci and the biological function of these structures in normal physiology and disease.

Effect of intranasal corticosteroid on pre-onset activation of eosinophils and mast cells in experimental Japanese cedar pollinosis

BACKGROUND

Minimal persistent inflammation (MPI) contributes to hyperreactivity in allergic rhinitis. However, little is known regarding whether pre-onset activation of eosinophils and mast cells is present or not in Japanese cedar pollinosis (JCP). Furthermore, a prophylactic effect of intranasal corticosteroids on such MPI in JCP has not been investigated.

METHODS

We designed a double-blinded, randomized, placebo-controlled, crossover trial. Twenty patients with JCP were examined outside the pollen season (UMIN000008410). Nasal provocation with paper discs containing extracts of Japanese cedar pollen was performed once a day for 3 consecutive days. Onset of nasal symptoms was monitored over 15 min after each provocation. The levels of eosinophil cationic protein (ECP) and tryptase in nasal secretions were examined. Fluticasone furoate nasal spray or placebo treatment was started one day before the first provocation.

RESULTS

In the placebo group, 25% of the patients showed onset of nasal symptoms following provocation on the first day. In addition, 75% and 68% of the patients showed symptom onset on the second and third day of provocation, respectively. After the first provocation, the levels of ECP and tryptase in nasal secretions were significantly increased. These increases were seen not only in symptomatic but also in asymptomatic subjects in response to provocation, and the levels were similar between these subjects. Prophylactic treatment with fluticasone significantly suppressed the increase in nasal ECP and tryptase associated with repeated provocations.

CONCLUSIONS

These results suggest that pre-onset activation of eosinophils and mast cells is present in experimental JCP, and that prophylactic treatment with intranasal corticosteroids has the potential to control such activation.

AZD3514: a small molecule that modulates androgen receptor signaling and function in vitro and in vivo

Continued androgen receptor (AR) expression and signaling is a key driver in castration-resistant prostate cancer (CRPC) after classical androgen ablation therapies have failed, and therefore remains a target for the treatment of progressive disease. Here, we describe the biological characterization of AZD3514, an orally bioavailable drug that inhibits androgen-dependent and -independent AR signaling. AZD3514 modulates AR signaling through two distinct mechanisms, an inhibition of ligand-driven nuclear translocation of AR and a downregulation of receptor levels, both of which were observed in vitro and in vivo. AZD3514 inhibited testosterone-driven seminal vesicle development in juvenile male rats and the growth of androgen-dependent Dunning R3327H prostate tumors in adult rats. Furthermore, this class of compound showed antitumor activity in the HID28 mouse model of CRPC in vivo. AZD3514 is currently in phase I clinical evaluation.

Ski-interacting protein (SKIP) interacts with androgen receptor in the nucleus and modulates androgen-dependent transcription

Background

The androgen receptor (AR) is a member of the nuclear receptor (NR) superfamily of ligand-inducible DNA transcription factors, and is the major mediator of male sexual development, prostate growth and the pathogenesis of prostate cancer. Cell and gene specific regulation by the AR is determined by availability of and interaction with sets of key accessory cofactors. Ski-interacting protein (SKIP; SNW1, NCOA62) is a cofactor shown to interact with several NRs and a diverse range of other transcription factors. Interestingly, SKIP as part of the spliceosome is thought to link mRNA splicing with transcription. SKIP has not been previously shown to interact with the AR.

Results

The aim of this study was to investigate whether SKIP interacts with the AR and modulates AR-dependent transcription. Here, we show by co-immunoprecipitation experiments that SKIP is in a complex with the AR. Moreover, SKIP increased 5α-dihydrotestosterone (DHT) induced N-terminal/C-terminal AR interaction from 12-fold to almost 300-fold in a two-hybrid assay, and enhanced AR ligand-independent AF-1 transactivation. SKIP augmented ligand- and AR-dependent transactivation in PC3 prostate cancer cells. Live-cell imaging revealed a fast (half-time=129 s) translocation of AR from the cytoplasm to the nucleus upon DHT-stimulation. Förster resonance energy transfer (FRET) experiments suggest a direct AR-SKIP interaction in the nucleus upon translocation.

Conclusions

Our results suggest that SKIP interacts with AR in the nucleus and enhances AR-dependent transactivation and N/C-interaction supporting a role for SKIP as an AR co-factor.

[Mechanism of action of nasal glucocorticosteroids in the treatment of allergic rhinitis. Part 2: Practical aspects of application]

Allergic rhinitis (AR) is the single most common allergic disease and one of the most common chronic diseases. It affects approximately 25-30% of the population, and can substantially worsen patients' medical conditions, reduce quality of life, and contribute to absenteeism from work or school. It is also responsible for substantial direct and indirect economic burdens on the health care system. The medical management of allergic rhinitis includes several available pharmacotherapies, such as α-sympathomimetics, anticholinergic drugs, natural saline or other nasal rinses, mast cell-stabilizing agents, topical and systemic antihistamines, topical and systemic glucocorticosteroids, leukotriene-receptor antagonists and the new monoclonal antibodies following a stepwise approach. Allergen-specific immunotherapy is the only treatment option that interferes with the natural course of the disease and, besides allergen elimination, is thought to be the only causative treatment option. Nasal glucocorticosteroids (nGCS) are thought to be the most effective treatment choice for controlling the symptoms of AR. Double-blind, randomized clinical trials have demonstrated greater efficacy of nGCSs versus placebo, antihistamines or montelukast for relief of all nasal symptoms, especially congestion. Therefore, especially in the management of AR-related nasal inflammation and congestion, nGCSs are considered the most appropriate treatment. Patients should be informed that symptom improvement can be expected after 2-4 days for intermittent rhinitis and after up to 2-3 weeks for persistent rhinitis. The medication has to be taken regularly and not as "on-demand" treatment. Adherence to treatment also affects outcomes, and this may be influenced by patient preferences for the sensory attributes of an individual drug and the awareness of possible side effects. More recently, safety studies have shown that the newer nGCS agents have improved safety profiles compared with older nGCS agents. The newer nGCS drugs have been found to have minimal adverse effects on growth and hypothalamic-pituitary-adrenal-axis function in children. This review will discuss the pathophysiology of allergic inflammation in the nasal mucosa and the mechanism of action of nGCSs; also the efficacy and safety of nGCSs will be discussed by focusing on clinical evidence.

Early interventional treatment with intranasal mometasone furoate in Japanese cedar/cypress pollinosis: a randomized placebo-controlled trial

BACKGROUND

Little is known about the safety and effectiveness of early interventional treatment (EIT) with intranasal corticosteroids for seasonal allergic rhinitis. We designed a double-blinded, randomized, placebo-controlled 12-week trial of EIT with mometasone furoate nasal spray (MFNS) for Japanese cedar/cypress pollinosis (JCCP).

METHODS

A total of 50 JCCP patients received MFNS (200μg once daily: n = 25) or placebo (n = 25) starting on February 1, 2010. Treatments continued until the end of April. The primary endpoint was the comparison of the total nasal symptom score (TNSS) between the MFNS and placebo groups. The secondary endpoints included comparisons of QOL, daytime sleepiness, nasal ECP levels, and safety.

RESULTS

Continuous dispersion of Japanese cedar pollen began on February 22. Although the placebo group showed a significant worsening of symptoms after the start of the continuous dispersion, no worsening occurred in the MFNS group. A significant difference in the TNSS between the two groups was seen starting at 4 weeks after the treatment. Similar results were seen for QOL and sleepiness. Nasal ECP levels in March were significantly lower in the MFNS group. A total of 56% of the MFNS group progressed to a persistent allergic rhinitis state in accordance with the ARIA classification, as opposed to 84% of the placebo group. MFNS was well tolerated, and the plasma cortisol concentrations were similar between the two groups.

CONCLUSIONS

EIT with MFNS for JCCP is both safe and effective. This treatment can potentially lessen symptoms and help pollinosis patients remain in the intermittent state.

ZMIZ1 preferably enhances the transcriptional activity of androgen receptor with short polyglutamine tract

The androgen receptor (AR) is a ligand-induced transcription factor and contains the polyglutamine (polyQ) tracts within its N-terminal transactivation domain. The length of polyQ tracts has been suggested to alter AR transcriptional activity in prostate cancer along with other endocrine and neurologic disorders. Here, we assessed the role of ZMIZ1, an AR co-activator, in regulating the activity of the AR with different lengths of polyQ tracts as ARQ9, ARQ24, and ARQ35 in prostate cancer cells. ZMIZ1, but not ZMIZ2 or ARA70, preferably augments ARQ9 induced androgen-dependent transcription on three different androgen-inducible promoter/reporter vectors. A strong protein-protein interaction between ZMIZ1 and ARQ9 proteins was shown by immunoprecipitation assays. In the presence of ZMIZ1, the N and C-terminal interaction of the ARQ9 was more pronounced than ARQ24 and ARQ35. Both Brg1 and BAF57, the components of SWI/SNF complexes, were shown to be involved in the enhancement of ZMIZ1 on AR activity. Using the chromatin immunoprecipitation assays (ChIP), we further demonstrated a strong recruitment of ZMIZ1 by ARQ9 on the promoter of the prostate specific antigen (PSA) gene. These results demonstrate a novel regulatory role of ZMIZ1 in modulating the polyQ tract length of AR in prostate cancer cells.

Androgen receptor and heterogeneous nuclear ribonucleoprotein K colocalize in the nucleoplasm and are modulated by bicalutamide and 4-hydroxy-tamoxifen in prostatic cancer cell lines

BACKGROUND

Bicalutamide (BIC) is widely used in prostate cancer therapy. The dose and schedule employed are well tolerated, but about 50% of patients develop gynecomastia. Several studies have shown a significant reduction of the troublesome effects when Tamoxifen is concomitantly administered with BIC. However, the results reported in the literature seem to be preliminary and possible interferences could be present. In order to clarify the molecular mechanisms of the combination of the two drugs, we have investigated whether the expression of the proteins belonging to nuclear matrix (NM), one modulator of hormone action, is altered by BIC and/or 4-hydroxy-tamoxifen (4OHT) in LNCaP cells. We focused above all on heterogeneous nuclear ribonucleoprotein K (hnRNP K) a NM protein with a key role in prostate carcinoma.

METHODS

NM proteins were analyzed by two-dimensional gel electrophoresis. Modulation and compartmentalization of the androgen receptor and the hnRNP K were studied by Western blotting, confocal microscopy, and immunoprecipitation.

RESULTS

Proteomic analysis revealed that there is a similarity in the changes of the NM proteins elicited by drugs alone but that their combination does not result in a simple additive effect. Moreover, we found that in the nucleoplasm the androgen receptor and the hnRNP K colocalize in a complex that is highly proximal to DNA and that both proteins were synchronously modulated by BIC and/or 4OHT treatment.

CONCLUSION

This study confirm the pivotal role of hnRNP K in prostate carcinoma and suggest that this role might be played by the interaction with the androgen receptor.

Effect of anabolic-androgenic steroids and glucocorticoids on the kinetics of hAR and hGR nucleocytoplasmic translocation

Although the qualitative nucleocytoplasmic transport of nuclear hormone receptors (NHRs) has been studied, there is little documentation of the cellular kinetics of this transport. Here, translocation studies using the human androgen receptor (hAR) and the human glucocorticoid receptor (hGR) were performed to aid in identifying the mechanism by which anabolic-androgenic steroids (AAS) were activating hAR and potentially interacting with hGR and how glucocorticoid ligands were interacting with the hGR and hAR. The real-time analysis of EGFP-labeled hAR and hGR ligand-induced cytoplasm-to-nucleus translocation was performed using fluorescence microscopy to better understand the action of these NHRs in a physiologically relevant cell-based model. After transient transfection, the hAR and hGR individually translocate as expected (i.e., transport is ligand-induced and dose-dependent) in this model biological system. Testosterone (TEST) had the fastest translocation rate for the hAR of 0.0525 min(-1). The other endogenous steroids, androstenedione (ANE) and dihydrotestosterone (DHT), had considerably lower hAR transport rates. The rates of hAR transport for the exogenous steroids methyltrienelone (MET), nandrolone (NAN), and oxandrolone (OXA) are lower than that of testosterone and similar to those of the endogenous steroids ANE and DHT. The hGR transport rates for cortisol (COR) and dexamethasone (DEX) are also presented. The synthetic GC, DEX, had a more rapid translocation rate (0.1599 min(-1)) at the highest dose of 100 nM compared to the endogenous GC COR (0.0431 min(-1)). The data obtained agrees with the existing qualitative data and adds an important ligand-dependent kinetic component to hAR and hGR transport. These kinetic data can aid our understanding of NHR action and interaction with other regulatory proteins, and can be useful in the development of new therapies.

A novel synthetic androgen receptor ligand, S42, works as a selective androgen receptor modulator and possesses metabolic effects with little impact on the prostate

We identified a novel synthetic steroid, S42, as a promising candidate of selective androgen receptor (AR) modulator. Results of the whole-cell binding assay using COS-7 cells exogenously expressing various steroid receptors indicated that S42 specifically binds to AR and progesterone receptor. When orchiectomized Sprague Dawley rats were administered with S42 for 3 wk, the muscle weight of the levator ani was increased as markedly as that induced by 5alpha-dihydrotestosterone (DHT), but the weight of the prostate was not elevated at any doses in contrast to DHT. The plasma concentrations of gonadotropin and adiponectin, those down-regulated by DHT, were unaffected by S42. In addition, although the plasma triglyceride level was unaffected by DHT, it was significantly reduced by S42. This effect of S42 was associated with suppression of the SRBP-1c-mediated lipogenic and insulin-desensitizing pathway in the liver and visceral fat. Taken together, S42 works as an AR agonist in muscle and as an AR antagonist in the prostate, pituitary gland, and liver, accompanying beneficial potentials on lipid metabolism.

Mechanisms and clinical implications of glucocorticosteroids in the treatment of allergic rhinitis

Allergic rhinitis is a common airway disease characterized by hypersensitivity, exudation, hypersecretion, inflammatory cell infiltration and remodelling. Intranasal glucocorticosteroids are the most effective drugs for controlling the inflammation caused by allergic rhinitis. Glucocorticosteroids exert anti-inflammatory effects through at least two pathways: the transactivation pathway and the transrepression pathway. Glucocorticosteroids also exert regulatory functions by inducing regulatory cytokines and forkhead box P3 (FoxP3(+)) regulatory T cells. Evidence suggests that intranasal glucocorticosteroids control not only nasal symptoms but also ocular symptoms. In contrast to sedating H1 receptor antagonists, intranasal glucocorticosteroids can improve impaired performance symptoms, such as daytime sleepiness, associated with allergic rhinitis. Recent studies suggest that intranasal glucocorticosteroids might also be useful for the prophylactic treatment of pollinosis; this possibility is supported by the molecular mechanism of the anti-inflammatory action of glucocorticosteroids. These findings suggest that intranasal glucocorticosteroids might be positioned as first-line drugs for the treatment of both perennial and seasonal allergic rhinitis.

Modification of androgen receptor function by IGF-1 signaling implications in the mechanism of refractory prostate carcinoma

The androgen-androgen receptor (AR) system plays important roles in a variety of biological processes, including prostate cancer (PC) development and progression. Insulin and Insulin-like growth factor-1 (IGF-1) signaling negatively regulate a member of the forkhead box-containing protein O subfamily (FoxO), Foxo-1, and associated biological functions. IGF-1 can potentiate androgen signaling through AR activation. Foxo-1, phosphorylated and inactivated by phosphatidylinositol-3-kinase (PI3K)/Akt kinase induced by IGF-1 or insulin, suppresses ligand-mediated AR transactivation. Foxo-1 reduces expression of androgen-induced AR target genes and suppresses in vitro growth of PC cells. These inhibitory effects of Foxo-1 are attenuated by IGF-1, but enhanced when it was rendered Akt-non-phosphorylatable. Foxo-1 directly interacts with the C-terminus of AR in a ligand-dependent manner, and disrupts ligand-induced AR subnuclear compartmentalization. Foxo-1 is recruited by liganded AR to the chromatin of the AR target gene promoter, while IGF-1 or insulin abolishes the Foxo-1 occupancy on the promoter. Liganded AR stimulates IGF-1 receptor expression, suggesting the presence of local positive feedback between IGF-1 and AR signaling in PC cells, presumably resulting in higher IGF-1 signaling tension and further enhancing the functions of the receptor itself. Thus, Foxo-1 is a novel corepressor for AR and IGF-1/insulin signaling may confer stimulatory effects on AR by attenuating Foxo-1 inhibition. Positive feedback between the growth factor and androgen in the local cellular environment may play important roles in AR transactivation regulation in several clinical situations including refractory PC.

Functional AR signaling is evident in an in vitro mouse follicle culture bioassay that encompasses most stages of folliculogenesis

Androgens have distinct physiological functions within the ovary. The biological action of androgens is primarily exerted through transcriptional regulation by the nuclear androgen receptor (AR), but the molecular cascades governed by AR remain largely unknown. At present, there is imminent concern that environmental man-made chemicals with antiandrogenic properties, among others, are capable of modulating hormonal responses, thereby interfering with normal physiological processes that are critical to fertility. In the present study, we aimed to further characterize a standardized and reproducible follicle culture system in terms of AR expression during in vitro folliculogenesis to be able to use it as a bioassay to study effects of antiandrogens on follicular and oocyte growth, steroid secretion profile, and oocyte meiotic maturation capacity. Immunohistochemical analysis revealed that cytoplasmic AR protein was translocated to the nucleus of granulosa and theca cells in response to endogenous androgen production in theca cells during preantral follicular development. During the antral phase in vitro, AR was differentially expressed in mural and cumulus cells, implying an oocyte-mediated regulation. Treatment of follicles with hydroxyflutamide or bicalutamide, two model antiandrogenic compounds, resulted in reduced follicular growth during the preantral phase, altered steroidogenic environment, and arrest in oocyte meiotic maturation in response to human chorionic gonadotropin. Androgen receptor expression in the culture model corresponded well to what is described in vivo, and this system revealed several ovarian functions targeted by AR antagonists that can be further investigated using more in-depth molecular techniques.

Androgen receptor functional analyses by high throughput imaging: determination of ligand, cell cycle, and mutation-specific effects

Background

Understanding how androgen receptor (AR) function is modulated by exposure to steroids, growth factors or small molecules can have important mechanistic implications for AR-related disease therapies (e.g., prostate cancer, androgen insensitivity syndrome, AIS), and in the analysis of environmental endocrine disruptors.

Methodology/Principal Findings

We report the development of a high throughput (HT) image-based assay that quantifies AR subcellular and subnuclear distribution, and transcriptional reporter gene activity on a cell-by-cell basis. Furthermore, simultaneous analysis of DNA content allowed determination of cell cycle position and permitted the analysis of cell cycle dependent changes in AR function in unsynchronized cell populations. Assay quality for EC50 coefficients of variation were 5–24%, with Z' values reaching 0.91. This was achieved by the selective analysis of cells expressing physiological levels of AR, important because minor over-expression resulted in elevated nuclear speckling and decreased transcriptional reporter gene activity. A small screen of AR-binding ligands, including known agonists, antagonists, and endocrine disruptors, demonstrated that nuclear translocation and nuclear “speckling” were linked with transcriptional output, and specific ligands were noted to differentially affect measurements for wild type versus mutant AR, suggesting differing mechanisms of action. HT imaging of patient-derived AIS mutations demonstrated a proof-of-principle personalized medicine approach to rapidly identify ligands capable of restoring multiple AR functions.

Conclusions/Significance

HT imaging-based multiplex screening will provide a rapid, systems-level analysis of compounds/RNAi that may differentially affect wild type AR or clinically relevant AR mutations.

Conformation of the c-Fos/c-Jun complex in vivo: a combined FRET, FCCS, and MD-modeling study

The activator protein-1 transcription factor is a heterodimer containing one of each of the Fos and Jun subfamilies of basic-region leucine-zipper proteins. We have previously shown by fluorescence cross-correlation spectroscopy (FCCS) that the fluorescent fusion proteins Fos-EGFP and Jun-mRFP1, cotransfected in HeLa cells, formed stable complexes in situ. Here we studied the relative position of the C-terminal domains via fluorescence resonance energy transfer (FRET) measured by flow cytometry and confocal microscopy. To get a more detailed insight into the conformation of the C-terminal domains of the complex we constructed C-terminal labeled full-length and truncated forms of Fos. We developed a novel iterative evaluation method to determine accurate FRET efficiencies regardless of relative protein expression levels, using a spectral- or intensity-based approach. The full-length C-terminal-labeled Jun and Fos proteins displayed a FRET-measured average distance of 8 +/- 1 nm. Deletion of the last 164 amino acids at the C-terminus of Fos resulted in a distance of 6.1 +/- 1 nm between the labels. FCCS shows that Jun-mRFP1 and the truncated Fos-EGFP also interact stably in the nucleus, although they bind to nuclear components with lower affinity. Thus, the C-terminal end of Fos may play a role in the stabilization of the interaction between activator protein-1 and DNA. Molecular dynamics simulations predict a dye-to-dye distance of 6.7 +/- 0.1 nm for the dimer between Jun-mRFP1 and the truncated Fos-EGFP, in good agreement with our FRET data. A wide variety of models could be developed for the full-length dimer, with possible dye-to-dye distances varying largely between 6 and 20 nm. However, from our FRET results we can conclude that more than half of the occurring dye-to-dye distances are between 6 and 10 nm.

Agonist-mediated docking of androgen receptor onto the mitotic chromatin platform discriminates intrinsic mode of action of prostate cancer drugs

This study documents the analysis of a hitherto unreported dynamic behavior of androgen receptor (AR), a member of the nuclear receptor superfamily. Employing GFP-tagged AR, we observed agonist-mediated docking of AR onto the mitotic chromatin during all the stages of mitosis. When bound to therapeutic drugs with intrinsically absolute or partial agonistic properties, AR concomitantly associated with the mitotic chromatin. Conversely, pure antagonists known to bind and subsequently translocate unliganded AR from cytoplasm to nuclear compartment did not provoke such association. The agonist-mediated docking of AR could not be competed with other transcription factors that constitutively preoccupied the chromosomal docking sites. Amongst the previously reported proteins, AR is first example of a transcription factor whose response on mitotic chromatin platform can be modulated in a ligand-specific manner. However, data from live cell imaging revealed that co-activators of agonist-activated receptor that are recruited into "nuclear foci" of interphase chromatin are dislodged from the mitotic chromatin during cell division. This implies that in absence of critical co-activators, AR transverses mitotic phase in transcriptionally silenced state. Finally, our results indicate that ligand-mediated dynamic relationship of nuclear receptors with mitotic chromatin can be effectively exploited to study, analyze and authenticate therapeutic ligands.

Mutual transactivational repression of Runx2 and the androgen receptor by an impairment of their normal compartmentalization

Steroid hormones play important roles not only in the reproductive system but also in bone metabolism. We examined the functional relationship between steroid hormone receptors and the Runx2 transcription factor that is essential for osteoblast differentiation and proliferation. A functional reporter assay using promoters carrying steroid hormone-responsive elements revealed that Runx2 suppressed ligand-dependent transcriptional activation mediated by receptors. To examine intracellular localization of these proteins, a three-dimensional imaging study was performed by laser scanning confocal microscopy of green fluorescent protein (GFP)-fused proteins. As previously reported, ligand-bound human androgen receptor (AR) was translocated from the cytoplasm to the nucleus and formed subnuclear fine foci. Coexpression of human Runx2 disrupted the AR subnuclear fine foci formation, and the intranuclear fluorescent pattern of AR became similar to that of Runx2. On the other hand, ligand-bound ARs repressed the Runx2-mediated transactivation function. Runx2 was also extracted from its original compartment by ligand-bound ARs. These results suggest that both Runx2 and ARs repress the transactivation function of the other protein by extracting it from its original compartment. The AR and Runx2 may play a mutual role in transcriptional activation in osteoblasts.

Association with Coregulators Is the Major Determinant Governing Peroxisome Proliferator-activated Receptor Mobility in Living Cells

The nucleus is an extremely dynamic compartment, and protein mobility represents a key factor in transcriptional regulation. We showed in a previous study that the diffusion of peroxisome proliferator-activated receptors (PPARs), a family of nuclear receptors regulating major cellular and metabolic functions, is modulated by ligand binding. In this study, we combine fluorescence correlation spectroscopy, dual color fluorescence cross-correlation microscopy, and fluorescence resonance energy transfer to dissect the molecular mechanisms controlling PPAR mobility and transcriptional activity in living cells. First, we bring new evidence that in vivo a high percentage of PPARs and retinoid X receptors is associated even in the absence of ligand. Second, we demonstrate that coregulator recruitment (and not DNA binding) plays a crucial role in receptor mobility, suggesting that transcriptional complexes are formed prior to promoter binding. In addition, association with coactivators in the absence of a ligand in living cells, both through the N-terminal AB domain and the AF-2 function of the ligand binding domain, provides a molecular basis to explain PPAR constitutive activity.

Insulin-like growth factor 1/insulin signaling activates androgen signaling through direct interactions of Foxo1 with androgen receptor

The androgen-androgen receptor (AR) system plays vital roles in a wide array of biological processes, including prostate cancer development and progression. Several growth factors, such as insulin-like growth factor 1 (IGF1), can induce AR activation, whereas insulin resistance and hyperinsulinemia are correlated with an elevated incidence of prostate cancer. Here we report that Foxo1, a downstream molecule that becomes phosphorylated and inactivated by phosphatidylinositol 3-kinase/Akt kinase in response to IGF1 or insulin, suppresses ligand-mediated AR transactivation. Foxo1 reduces androgen-induced AR target gene expressions and suppresses the in vitro growth of prostate cancer cells. These inhibitory effects of Foxo1 are attenuated by IGF1 but are enhanced when it is rendered Akt-nonphosphorylatable. Foxo1 interacts directly with the C terminus of AR in a ligand-dependent manner and disrupts ligand-induced AR subnuclear compartmentalization. Foxo1 is recruited by liganded AR to the chromatin of AR target gene promoters, where it interferes with AR-DNA interactions. IGF1 or insulin abolish the Foxo1 occupancy of these promoters. Of interest, a positive feedback circuit working locally in an autocrine/intracrine manner may exist, because liganded AR up-regulates IGF1 receptor expression in prostate cancer cells, presumably resulting in higher IGF1 signaling tension and further enhancing the functions of the receptor itself. Thus, Foxo1 is a novel corepressor for AR, and IGF1/insulin signaling may confer stimulatory effects on AR by attenuating Foxo1 inhibition. These results highlight the potential involvement of metabolic syndrome and hyperinsulinemia in prostate diseases and further suggest that intervention of IGF1/insulin-phosphatidylinositol 3-kinase-Akt signaling may be of clinical value for prostate diseases.

Coactivation of the N-terminal Transactivation of Mineralocorticoid Receptor by Ubc9

Molecular mechanisms underlying mineralocorticoid receptor (MR)-mediated gene expression are not fully understood. Various transcription factors are post-translationally modified by small ubiquitin-related modifier-1 (SUMO-1). We investigated the role of the SUMO-1-conjugating enzyme Ubc9 in MR transactivation. Yeast two-hybrid, GST-pulldown, and coimmunoprecipitation assays showed that Ubc9 interacted with N-terminal MR-(1-670). Endogenous Ubc9 is associated with stably expressing MR in 293-MR cells. Transient transfection assays in COS-1 cells showed that Ubc9 increased MR transactivation of reporter constructs containing MRE, ENaC, or MMTV promoter in a hormone-sensitive manner. Moreover, reduction of Ubc9 protein levels by small interfering RNA attenuated hormonal activation of a reporter construct as well as an endogenous target gene by MR. A sumoylation-inactive mutant Ubc9(C93S) similarly interacted with MR and potentiated aldosterone-dependent MR transactivation. An MR mutant in which four lysine residues within sumoylation motifs were mutated into arginine (K89R/K399R/K494R/K953R) failed to be sumoylated, but Ubc9 similarly enhanced transactivation by the mutant MR, indicating that sumoylation activity is dispensable for coactivation capacity of Ubc9. Coexpression of Ubc9 and steroid receptor coactivator-1 (SRC-1) synergistically enhanced MR-mediated transactivation in transient transfection assays. Indeed, chromatin immunoprecipitation assays demonstrated that endogenous MR, Ubc9, and SRC-1 were recruited to an endogenous ENaC gene promoter in a largely aldosterone-dependent manner. Coimmunoprecipitation assays showed a complex of MR, Ubc9, and SRC-1 in mammalian cells, and the endogenous proteins were colocalized in the nuclei of the mouse collecting duct cells. These findings support a physiological role of Ubc9 as a transcriptional MR coactivator, beyond the known SUMO E2-conjugating enzyme.

Nuclear compartmentalization of N-CoR and its interactions with steroid receptors

The repression mechanisms by the nuclear receptor corepressor (N-CoR) of steroid hormone receptor (SHR)-mediated transactivation were examined. Yellow fluorescent protein (YFP)-N-CoR was distributed as intranuclear discrete dots, while coexpression of androgen receptor (AR), glucocorticoid receptor alpha, and estrogen receptor alpha ligand-dependently triggered redistribution of YFP-N-CoR. In fluorescence recovery after photobleaching analysis, mobility of the N-CoR was reduced by 5alpha-dihydrotestosterone (DHT)-bound AR. The middle region of N-CoR mostly contributed to the interaction with agonist-bound SHRs and the suppression of their transactivation function. N-CoR impaired the DHT-induced N-C interaction of AR, and the impaired interaction was dose-dependently recovered by coexpression of SRC-1 and CBP. N-CoR also impaired the intranuclear complete (distinct) focus formation of SHRs. Coexpression of SRC-1 or CBP released YFP-N-CoR or endogenous N-CoR from incomplete foci and simultaneously recovered complete foci of AR-green fluorescent protein. These results indicate that the relative ratio of coactivators and corepressors determines the conformational equilibrium between transcriptionally active and inactive SHRs in the presence of agonists. The intranuclear foci formed by agonist-bound SHRs were completely destroyed by actinomycin D and alpha-amanitin, indicating that the focus formation does not precede the transcriptional activation. The focus formation may reflect the accumulation of SHR/coactivator complexes released from the transcriptionally active sites and thus be a mirror of transcriptionally active complex formation.

Quantifying effects of ligands on androgen receptor nuclear translocation, intranuclear dynamics, and solubility

Using manual and automated high throughput microscopy (HTM), ligand-dependent trafficking of green fluorescent protein-androgen receptor (GFP-AR) was analyzed in fixed and living cells to determine its spatial distribution, solubility, mobility, and co-activator interactions. Within minutes, addition of the agonist R1881 resulted translocation of GFP-AR from the cytoplasm to the nucleus, where it displayed a hyperspeckled pattern and extraction resistance in low expressing cells. AR antagonists (Casodex, hydroxyflutamide) also caused nuclear translocation, however, the antagonist-bound GFP-AR had a more diffuse nuclear distribution, distinct from the agonist-bound GFP-AR, and was completely soluble; overexpressed GFP-AR in treated cells was extraction resistant, independent of ligand type. To more dramatically show the different effects of ligand on AR distribution, we utilized an AR with a mutation in the DNA binding domain (ARC619Y) that forms distinct foci upon exposure to agonists but retains a diffuse nuclear distribution in the presence of antagonists. Live-cell imaging of this mutant demonstrated that cytoplasmic foci formation occurs immediately upon agonist but not antagonist addition. Fluorescence recovery after photobleaching (FRAP) revealed that agonist-bound GFP-AR exhibited reduced mobility relative to unliganded or antagonist-bound GFP-AR. Importantly, agonist-bound GFP-AR mobility was strongly affected by protein expression levels in transiently transfected cells, and displayed reduced mobility even in slightly overexpressing cells. Cyan fluorescent protein-AR (CFP-AR) and yellow fluorescent protein-CREB binding protein (YFP-CBP) in the presence of agonists and antagonists were used to demonstrate that CFP-AR specifically co-localizes with YFP-CBP in an agonist dependent manner. Dual FRAP experiments demonstrated that CBP mobility mirrored AR mobility only in the presence of agonist. HTM enabled simultaneous studies of the sub-cellular distribution of GFP-AR and ARC619Y in response to a range of concentrations of agonists and antagonists (ranging from 10(-12) to 10(-5)) in thousands of cells. These results further support the notion that ligand specific interactions rapidly affect receptor and co-factor organization, solubility, and molecular dynamics, and each can be aberrantly affected by mutation and overexpression.

Receptor-interacting protein 140 is a repressor of the androgen receptor activity

The androgen receptor (AR) is a ligand-activated transcription factor that controls growth and survival of prostate cancer cells. In the present study, we investigated the regulation of AR activity by the receptor-interacting protein 140 (RIP140). We first showed that RIP140 could be coimmunoprecipitated with the receptor when coexpressed in 293T cells. This interaction appeared physiologically relevant because chromatin immunoprecipitation assays revealed that, under R1881 treatment, RIP140 could be recruited to the prostate-specific antigen encoding gene in LNCaP cells. In vitro glutathione S-transferase pull-down assays provided evidence that the carboxy-terminal domain of AR could interact with different regions of RIP140. By means of fluorescent proteins, we demonstrated that ligand-activated AR was not only able to translocate to the nucleus but also to relocate RIP140 from very structured nuclear foci to a diffuse pattern. Overexpression of RIP140 strongly repressed AR-dependent transactivation by preferentially targeting the ligand binding domain-dependent activity. Moreover, disruption of RIP140 expression induced AR overactivation, thus revealing RIP140 as a strong AR repressor. We analyzed its mechanism of transrepression and first demonstrated that different regions of RIP140 could mediate AR-dependent repression. We then showed that the carboxy-terminal end of RIP140 could reverse transcriptional intermediary factor 2-dependent overactivation of AR. The use of mutants of RIP140 allowed us to suggest that C-terminal binding protein played no role in RIP140-dependent inhibition of AR activity, whereas histone deacetylases partly regulated that transrepression. Finally, we provided evidence for a stimulation of RIP140 mRNA expression in LNCaP cells under androgen treatment, further emphasizing the role of RIP140 in androgen signaling.

Opposite effects of alternative TZF spliced variants on androgen receptor

We previously demonstrated that testicular zinc-finger protein (TZF) was a corepressor of the androgen receptor (AR). In the present study, we further showed that TZF-L, an alternative spliced variant of TZF, enhanced transactivation function of AR. Deletion analysis of TZF-L revealed that its N-terminus, which almost corresponded to that of TZF, but not its C-terminus was able to interact with AR. Additional analysis suggested that TZF and TZF-L were able to form both homodimers and heterodimers. TZF-L inhibited the homodimer formation of TZF and the intranuclear dot formation of TZF. We propose that in the unique regulation system of AR-mediated transactivation, two spliced isoforms of TZF act as coactivator and corepressor, respectively.

Identification of the functional domains of ANT-1, a novel coactivator of the androgen receptor

Previously, we identified a transcriptional coactivator for the activation function-1 (AF-1) domain of the human androgen receptor (AR) and designated it androgen receptor N-terminal domain transactivating protein-1 (ANT-1). This coactivator, which contains multiple tetratricopeptide repeat (TPR) motifs from amino acid (aa) 294, is identical to a component of U5 small nuclear ribonucleoprotein particles and binds specifically to the AR or glucocorticoid receptor. Here, we identified four distinct functional domains. The AR-AF-1-binding domain, which bound to either aa 180-360 or 360-532 in AR-AF-1, clearly overlapped with TAU-1 and TAU-5. This domain and the subnuclear speckle formation domain in ANT-1 were assigned within the TPR motifs, while the transactivating and nuclear localization signal domains resided within the N-terminal sequence. The existence of these functional domains may further support the idea that ANT-1 can function as an AR-AF-1-specific coactivator while mediating a transcription-splicing coupling.

Impaired nuclear translocation, nuclear matrix targeting, and intranuclear mobility of mutant androgen receptors carrying amino acid substitutions in the deoxyribonucleic acid-binding domain derived from androgen insensitivity syndrome patients

CONTEXT

Recent imaging studies revealed that androgen receptor (AR) is ligand-dependently translocated from the cytoplasm into the nucleus and forms intranuclear fine foci. In this study, we examined whether intracellular dynamics of mutant ARs detected in two androgen insensitivity syndrome (AIS) patients was impaired.

OBJECTIVE

ARs with mutations in the DNA-binding domain were functionally characterized and compared with the wild-type AR.

PATIENTS

In a complete AIS patient (subject 1), cysteine residue 579 in the first zinc finger motif of AR was substituted for phenylalanine (AR-C579F). Another mutation (AR-F582Y) was found in a partial AIS patient (subject 2).

RESULTS

AR-F582Y retained less than 10% of the transactivation activity of the wild-type AR, whereas no ligand-dependent transactivation was detected for AR-C579F. Image analyses of the receptors fused to green fluorescent protein showed that the wild-type AR was ligand-dependently translocated into the nucleus in which it formed fine subnuclear foci. Surprisingly, after the addition of dihydrotestosterone, the two mutant ARs initially formed large cytoplasmic dots, many of which were found to be close to mitochondria by electron microscopy. Subsequently, a part of the ligand-bound mutant ARs gradually entered the nucleus to form a smaller number of larger dots, compared with the wild-type AR. Fluorescence recovery after photobleaching analysis revealed that the intranuclear mobility of the mutant ARs decreased, compared with that of the wild-type AR.

CONCLUSIONS

These results suggest that the abnormal translocation, localization, and mobility of the mutant ARs may be the cause of AIS in these subjects.

Modulation of Androgen Receptor Transactivation by FoxH1

Androgen signaling plays key roles in the development and progression of prostate cancer, and numerous ongoing studies focus on the regulation of androgen receptor (AR) transactivity to develop novel therapies for the treatment of androgen-independent prostate cancer. FoxH1, a member of the Forkhead-box (FOX) gene family of transcription factors, takes part in mediating transforming growth factor-beta/activin signaling through its interaction with the Smad2.Smad4 complex. Using a series of experiments, we found that FoxH1 repressed both ligand-dependent and -independent transactivation of the AR on androgen-induced promoters. This action of FoxH1 was independent of its transactivation capacity and activin A but relieved by Smad2.Smad4. In addition, the repression of the AR by FoxH1 did not require deacetylase activity. A protein-protein interaction was identified between the AR and FoxH1 independently of dihydrotestosterone. Furthermore, a confocal microscopic analysis of LNCaP cells revealed that the interaction between the AR and FoxH1 occurred in the nucleus and that FoxH1 specifically blocked the foci formation of dihydrotestosterone-activated AR, which has been shown to be correlated with the AR transactivation potential. Taken together, our results indicate that FoxH1 functions as a new corepressor of the AR. Our observations not only strengthen the role of FoxH1 in AR-mediated transactivation but also suggest that therapeutic interventions based on AR-coregulator interactions could be designed to block both androgen-dependent and -independent growth of prostate cancer.

A zinc finger protein TZF is a novel corepressor of androgen receptor

Steroid hormones control the transcriptional activity of target genes mediated by intracellular nuclear receptors, and these transcriptional activities are modulated by the combination with coactivators and corepressors. We found in this study that testicular zinc finger protein (TZF) that was a nuclear protein with a zinc finger motif of the Cys2-His2 type was a novel corepressor of androgen receptor (AR). Fusion protein with green fluorescence protein GFP formed the specific foci in nuclei and TZF-dependent foci were located close to the splicing factor compartment. In addition, TZF was recruited into AR subnuclear foci after the treatment of dihydrotestosterone. Furthermore, we revealed that TZF bound to the activation function-1 (AF-1) domain (N-terminal transactivating domain) of AR protein. Transient over-expression of TZF in COS-7 cells or LNCaP human prostatic cancer cell resulted in decreased AR activity in a ligand-dependent fashion. Moreover, a transcriptional corepressor N-CoR additively decreased the transcriptional activity of AR with TZF. These findings suggest that TZF might be a novel corepressor of AR.

Tob proteins suppress steroid hormone receptor-mediated transcriptional activation

Although sex steroid hormones have significant effects on bone metabolism, the molecular mechanisms of these actions have not been fully elucidated yet. We examined the functional relationship between steroid hormone receptors and Tob, a member of an anti-proliferative protein family and a negative regulator of osteoblast proliferation and differentiation. Luciferase assay using promoters carrying hormone-responsive elements revealed that both Tob1 and Tob2 proteins but not PC3 suppressed steroid hormone receptor-dependent transcriptional activation in MC3T3-E1 osteoblastic cells. Mutated Tob proteins carrying amino acid substitutions at an LXXLL motif also showed the same degree of inhibition of the transcriptional activation as the wild type. By observation of androgen receptor (AR)-tagged with green fluorescent protein under a confocal laser scanning microscope, we found that Tob1 inhibits the nuclear foci formation of dihydrotestosterone-bound AR. These results indicate that Tob family proteins may negatively regulate sex steroid hormone action in bone formation.

A type I DnaJ homolog, DjA1, regulates androgen receptor signaling and spermatogenesis

Two type I DnaJ homologs DjA1 (DNAJA1; dj2, HSDJ/hdj-2, rdj1) and DjA2 (DNAJA2; dj3, rdj2) work similarly as a cochaperone of Hsp70s in protein folding and mitochondrial protein import in vitro. To study the in vivo role of DjA1, we generated DjA1-mutant mice. Surprisingly, loss of DjA1 in mice led to severe defects in spermatogenesis that involve aberrant androgen signaling. Transplantation experiments with green fluorescent protein-labeled spermatogonia into DjA1(-/-) mice revealed a primary defect of Sertoli cells in maintaining spermiogenesis at steps 8 and 9. In Sertoli cells of DjA1(-/-) mice, the androgen receptor markedly accumulated with enhanced transcription of several androgen-responsive genes, including Pem and testin. Disruption of Sertoli-germ cell adherens junctions was also evident in DjA1(-/-) mice. Experiments with DjA1(-/-) fibroblasts and primary Sertoli cells indicated aberrant androgen receptor signaling. These results revealed a critical role of DjA1 in spermiogenesis and suggest that DjA1 and DjA2 are not functionally equivalent in vivo.

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.

An Alternative Splicing Variant of the Selenoprotein Thioredoxin Reductase Is a Modulator of Estrogen Signaling

The selenoprotein thioredoxin reductase (TrxR1) is an integral part of the thioredoxin system. It serves to transfer electrons from NADPH to thioredoxin leading to its reduction. Interestingly, recent work has indicated that thioredoxin reductase can regulate the activity of transcription factors such as p53, hypoxia-inducible factor, and AP-1. Here, we describe that an alternative splicing variant of thioredoxin reductase (TrxR1b) containing an LXXLL peptide motif, is implicated in direct binding to nuclear receptors. In vitro interaction studies revealed direct interaction of the TrxR1b with the estrogen receptors alpha and beta. Confocal microscopy analysis showed nuclear colocalization of the TrxR1b with both estrogen receptor alpha and beta in estradiol-17beta-treated cells. Transcriptional studies demonstrated that TrxR1b can affect estrogen-dependent gene activation differentially at classical estrogen response elements as compared with AP-1 response elements. Based on these results, we propose a model where thioredoxin reductase directly influences the estrogen receptor-coactivator complex assembly on non-classical estrogen response elements such as AP-1. In summary, our results suggest that TrxR1b is an important modulator of estrogen signaling.

The origin and functions of multiple human glucocorticoid receptor isoforms

Glucocorticoid hormones are necessary for life and are essential in all aspects of human health and disease. The actions of glucocorticoids are mediated by the glucocorticoid receptor (GR), which binds glucocorticoid hormones and regulates gene expression, cell signaling, and homeostasis. Decades of research have focused on the mechanisms of action of one isoform of GR, GRa. However, in recent years, increasing numbers of human GR (hGR) isoforms have been reported. Evidence obtained from this and other laboratories indicates that multiple hGR isoforms are generated from one single hGR gene via mutations and/or polymorphisms, transcript alternative splicing, and alternative translation initiation. Each hGR protein, in turn, is subject to a variety of posttranslational modifications, and the nature and degree of posttranslational modification affect receptor function. We summarize here the processes that generate and modify various hGR isoforms with a focus on those that impact the ability of hGR to regulate target genes. We speculate that unique receptor compositions and relative receptor proportions within a cell determine the specific response to glucocorticoids. Unchecked expression of some isoforms, for example hGRbeta, has been implicated in various diseases.

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.

Altered localization of retinoid X receptor alpha coincides with loss of retinoid responsiveness in human breast cancer MDA-MB-231 cells

To understand the mechanism of retinoid resistance, we studied the subcellular localization and function of retinoid receptors in human breast cancer cell lines. Retinoid X receptor alpha (RXR alpha) localized throughout the nucleoplasm in retinoid-sensitive normal human mammary epithelial cells and in retinoid-responsive breast cancer cell line (MCF-7), whereas it was found in the splicing factor compartment (SFC) of the retinoid-resistant MDA-MB-231 breast cancer cell line and in human breast carcinoma tissue. In MDA-MB-231 cells, RXR alpha was not associated with active transcription site in the presence of ligand. Similarly, ligand-dependent RXR homo- or heterodimer-mediated transactivation on RXR response element or RARE showed minimal response to ligand in MDA-MB-231 cells. Infecting MDA-MB-231 cells with adenoviral RXR alpha induced nucleoplasmic overexpression of RXR alpha and resulted in apoptosis upon treatment with an RXR ligand. This suggests that nucleoplasmic RXR alpha restores retinoid sensitivity. Epitope-tagged RXR alpha and a C-terminus deletion mutant failed to localize to the SFC. Moreover, RXR alpha localization to the SFC was inhibited with RXR alpha C-terminus peptide. This peptide also induced ligand-dependent transactivation on RXRE. Therefore, the RXR alpha C terminus may play a role in the intranuclear localization of RXR alpha. Our results provide evidence that altered localization of RXR alpha to the SFC may be an important factor for the loss of retinoid responsiveness in MDA-MB-231 breast cancer cells.

Transient, Ligand-Dependent Arrest of the Androgen Receptor in Subnuclear Foci Alters Phosphorylation and Coactivator Interactions

Here we report that mutations within the DNA-binding domain of AR, shown previously to inhibit nuclear export to the cytoplasm, cause an androgen-dependent defect in intranuclear trafficking of AR. Mutation of two conserved phenylalanines within the DNA recognition helix (F582, 583A) results in androgen-dependent arrest of AR in multiple subnuclear foci. A point mutation in one of the conserved phenylalanines (DeltaF582, F582Y) is known to cause androgen insensitivity syndrome (AIS). Both AIS mutants (DeltaF582, F582Y) and the export mutant (F582, 583A) displayed androgen-dependent arrest in foci, and all three mutants promoted androgen-dependent accumulation of the histone acetyl transferase CREB binding protein (CBP) in the foci. The foci correspond to a subnuclear compartment that is highly enriched for the steroid receptor coactivator glucocorticoid receptor-interacting protein (GRIP)-1. Agonist-bound wild-type AR induces the redistribution of GRIP-1 from foci to the nucleoplasm. This likely reflects a direct interaction between these proteins because mutation of a conserved residue within the major coactivator binding site on AR (K720A) inhibits AR-dependent dissociation of GRIP-1 from foci. GRIP-1 also remains foci-associated in the presence of agonist-bound F582, 583A, DeltaF582, or F582Y forms of AR. Two-dimensional phospho-peptide mapping and analysis with a phospho-specific antibody revealed that mutant forms of AR that arrest in the subnuclear foci are hypophosphorylated at Ser81, a site that normally undergoes androgen-dependent phosphorylation. Our working model is that the subnuclear foci are sites where AR undergoes ligand-dependent engagement with GRIP-1 and CBP, a recruitment step that occurs before Ser81 phosphorylation and association with promoters of target genes.

Mechanistic relationship between androgen receptor polyglutamine tract truncation and androgen-dependent transcriptional hyperactivity in prostate cancer cells

Androgen receptor (AR) signaling pathways mediate critical events in normal and neoplastic prostate growth. Shortening of the polymorphic N-terminal polyglutamine (poly(Q)) tract of the AR gene leads to transcriptional hyperactivity and has been correlated with an increased risk of prostate cancer. The underlying mechanisms for these effects are poorly understood. We show here that androgen-dependent cellular proliferation and transcription in prostate cancer cells is inversely correlated to the length of the AR poly(Q) region. We further show that AR proteins containing a shortened poly(Q) region functionally respond to lower concentrations of androgens than wild type AR. Whereas DNA binding activity is relatively unaffected by AR poly(Q) variation, we found that ligand binding affinity and the ligand-induced NH(2)- to COOH-terminal intramolecular interaction is enhanced when the poly(Q) region is shortened. Importantly, we show that AR proteins containing a shortened poly(Q) region associate in vivo with higher levels of specific p160 coactivators and components of the SWI/SNF chromatin remodeling complex as compared with the wild type AR. Collectively, our findings suggest that the AR transcriptional hyperactivity associated with shortened poly(Q) length stems from altered ligand-induced conformational changes that enhance coactivator recruitment.

Functional localization and competition between the androgen receptor and T-cell factor for nuclear beta-catenin: a means for inhibition of the Tcf signaling axis

Recent reports suggest that the beta-catenin-T-cell factor (Tcf) (BCT) signaling pathway is important in the progression of prostate cancer. Evidence suggests that the androgen receptor (AR) can repress BCT-mediated transcription both in prostate cancer and colon cancer cells (Chesire and Isaacs, 2002). In this study, we validate such findings and show that repression of BCT signaling is facilitated by competition between the AR and Tcf. Measurements of the Tcf transcriptional reporter (TOPFLASH) indicated that AR+DHT-mediated repression can inhibit BCT transcription in the presence of WT and exogenous activating beta-catenin (Delta1-130 bp). Transient transfections in SW480 cells (APC(mut/mut)) showed that this mode of repression is functionally independent of APC-mediated beta-catenin ubiquitination. Using a recently developed red flourescent protein (HcRed), we demonstrate novel observations about the nuclear distribution of Tcf. Furthermore, with the use of red (HcRed-AR and HcRed-Tcf) and green fusion proteins (beta-catenin-EGFP), we provide morphological evidence of a reciprocal balance of nuclear beta-catenin-EGFP (BC-EGFP). By cotransfecting in LNCaP prostate tumor cells and using quantitative imaging software, we demonstrated a 62.0% colocalization of HcRed-AR and BC-EGFP in the presence of DHT and 63.3% colocalization of HcRed-Tcf/BC-EGFP in the absence of DHT. Costaining for activated RNA Pol II (phosphoserine 2) and HcRed-Tcf suggested that Tcf foci contain transcriptional 'hotspots' validating that these sites have the capacity for transcriptional activity. Given this apparent androgen-dependent competition for nuclear BC-EGFP, we chose to assess our hypothesis by in vivo and in vitro binding assays. SW480 cells transiently transfected with an AR expression construct, treated with DHT and immunoprecipitated for Tcf showed less associated beta-catenin when compared to Tcf precipitates from untreated cells. Furthermore, by treating cells with DHT+Casodex, we were able to abrogate the androgen-sensitive AR/beta-catenin interaction, in addition to relieving transcriptional repression of the TOPFLASH reporter. In vitro binding assays, with increasing amounts of AR(S35), resulted in decreased Tcf(S35) association with immunoprecipitated recombinant beta-catenin-HIS. These data suggest that in steady-state conditions, AR has the ability to compete out Tcf binding for beta-catenin. Finally, using SW480 cells, we show that AR-mediated repression of the BCT pathway has implications for cell cycle progression and in vitro growth. Using FACs analysis, we observed a 26.1% increase in accumulation of cells in the G1 phase of the cell cycle, while in vitro growth assays showed a 35% reduction in viable cells transfected with AR+DHT treatment. Together, our data strongly suggest that a reciprocal balance of nuclear beta-catenin facilitates AR-mediated repression of BCT-driven transcription and cell growth.

Plant-derived 3,3'-Diindolylmethane is a strong androgen antagonist in human prostate cancer cells

3,3'-Diindolylmethane (DIM) is a major digestive product of indole-3-carbinol, a potential anticancer component of cruciferous vegetables. Our results indicate that DIM exhibits potent antiproliferative and antiandrogenic properties in androgen-dependent human prostate cancer cells. DIM suppresses cell proliferation of LNCaP cells and inhibits dihydrotestosterone (DHT) stimulation of DNA synthesis. These activities were not produced in androgen-independent PC-3 cells. Moreover, DIM inhibited endogenous PSA transcription and reduced intracellular and secreted PSA protein levels induced by DHT in LNCaP cells. Also, DIM inhibited, in a concentration-dependent manner, the DHT-induced expression of a prostate-specific antigen promoter-regulated reporter gene construct in transiently transfected LNCaP cells. Similar effects of DIM were observed in PC-3 cells only when these cells were co-transfected with a wild-type androgen receptor expression plasmid. Using fluorescence imaging with green fluorescent protein androgen receptor and Western blot analysis, we demonstrated that DIM inhibited androgen-induced androgen receptor (AR) translocation into the nucleus. Results of receptor binding assays indicated further that DIM is a strong competitive inhibitor of DHT binding to the AR. Results of structural modeling studies showed that DIM is remarkably similar in conformational geometry and surface charge distribution to an established synthetic AR antagonist, although the atomic compositions of the two substances are quite different. Taken together with our published reports of the estrogen agonist activities of DIM, the present results establish DIM as a unique bifunctional hormone disrupter. To our knowledge, DIM is the first example of a pure androgen receptor antagonist from plants.

Activation function-1 domain of androgen receptor contributes to the interaction between two distinct subnuclear compartments

The nucleus contains different sets of functional compartments often called "speckles". The splicing factor compartment (SFC) has been speculated to consist of SFs and transcription factors, which thus make transcription-splicing coupling possible at the periphery of SFC. Androgen receptor (AR), as well as glucocorticoid receptor (GR), is unique since most, if not all, of its activities are mediated via the constitutive activity of the activation function-1 (AF-1) function. Transcriptionally active AR produces 250-400 subnuclear fine speckles11 shared with GR or estrogen receptor (ER), which colocalize with chiefly activation function-2 (AF-2)-interacting p160 family- or CBP-related speckles. We herein report the isolation of ANT-1 (AR N-terminal domain (NTD) transactivating protein-1) enhancing autonomous AF-1 transactivation function of AR or GR, but not of estrogen receptor alpha (ERalpha). The ANT-1 was identical to a binding protein of human splicing factor U5 snRNP (U5 snRNP-associated protein). ANT-1 was compartmentalized into 15-20 coarse SFC speckles which were spatially distinct from but surrounded by the AR compartments. Our results suggest that ANT-1 may play a key role in the molecular interaction between two spatially distinct subnuclear compartments in a receptor-specific fashion, and thereby induce the strong autonomous transactivation functions either of AR- or GR-AF-1.

Molecular determinants of glucocorticoid receptor mobility in living cells: the importance of ligand affinity

The actions of glucocorticoids are mediated by the glucocorticoid receptor (GR), which is activated upon ligand binding, and can alter the expression of target genes either by transrepression or transactivation. We have applied FRAP (fluorescence recovery after photobleaching) to quantitatively assess the mobility of the yellow fluorescent protein (YFP)-tagged human GR alpha-isoform (hGRalpha) in the nucleus of transiently transfected COS-1 cells and to elucidate determinants of its mobility. Addition of the high-affinity agonist dexamethasone markedly decreases the mobility of the receptor in a concentration-dependent manner, whereas low-affinity ligands like corticosterone decrease the mobility to a much lesser extent. Analysis of other hGRalpha ligands differing in affinity suggests that it is the affinity of the ligand that is a major determinant of the decrease in mobility. Similar results were observed for two hGRalpha antagonists, the low-affinity antagonist ZK98299 and the high-affinity antagonist RU486. The effect of ligand affinity on mobility was confirmed with the hGRalpha mutant Q642V, which has an altered affinity for triamcinolone acetonide, dexamethasone, and corticosterone. Analysis of hGRalpha deletion mutants indicates that both the DNA-binding domain and the ligand-binding domain of the receptor are required for a maximal ligand-induced decrease in receptor mobility. Interestingly, the mobility of transfected hGRalpha differs among cell types. Finally, the proteasome inhibitor MG132 immobilizes a subpopulation of unliganded receptors, via a mechanism requiring the DNA-binding domain and the N-terminal part of the ligand-binding domain. Ligand binding makes the GR resistant to the immobilizing effect of MG132, and this effect depends on the affinity of the ligand. Our data suggest that ligand binding induces a conformational change of the receptor which is dependent on the affinity of the ligand. This altered conformation decreases the mobility of the receptor, probably by targeting the receptor to relatively immobile nuclear domains with which it transiently associates. In addition, this conformational change blocks immobilization of the receptor by MG132.

Regulation of androgen receptor activity by the nuclear receptor corepressor SMRT

Androgen receptor (AR) is a hormone-regulated transcription factor that mediates a wide array of biological processes including sexual differentiation, spermatogenesis, and prostate cancer progression. The transcriptional activity of AR and other members of the nuclear receptor superfamily are modulated by coregulatory proteins. In this study, we have investigated the regulation of AR transcriptional activity by the silencing mediator for retinoid and thyroid hormone receptors (SMRT). We found that AR possesses an intrinsic transcriptional repression activity, and AR interacts directly with SMRT. One interacting surface on AR is mapped to the ligand-binding domain, and the presence of a DNA binding/hinge region enhances this interaction. The binding surface on SMRT is mapped to the C-terminal ID2 region, and mutation in the ID2 corepressor motif inhibits the interaction. Overexpression of SMRT inhibits dihydrotestosterone-dependent transactivation by AR and further suppresses the antiandrogen flutamide-mediated inhibition of AR activity. We provide evidence to suggest that the mechanisms of SMRT-mediated inhibition of AR activity involves inhibition of AR N/C interaction and competition with the p160 coactivator. Our data establish a significant role of SMRT in modulating AR transcriptional activity.

Role of the promyelocytic leukemia body in the dynamic interaction between the androgen receptor and steroid receptor coactivator-1 in living cells

The dynamic interaction between the androgen receptor (AR) and steroid receptor coactivator-1 (SRC-1) was explored in living cells expressing chimeric forms of the receptor and the coactivator containing two spectral variants of jellyfish fluorescent protein. Laser scanning confocal imaging of transfected cells expressing fluorescently labeled SRC-1 revealed that in an unsynchronized cell population, the coactivator is distributed in approximately 40% cells as nuclear bodies of 0.2-1.0 microm in diameter. Immunostaining of cyan fluorescent protein-labeled SRC-1 (CFP-SRC1)-expressing cells with antibody to promyelocytic leukemia (PML) protein showed significant overlap of the CFP fluorescence with the antibody stain. Cotransfection of cells with a plasmid expressing the CFP conjugate of Sp100 (another marker protein for the PML nuclear body) also showed colocalization of the yellow fluorescent protein (YFP)-SRC1 containing nuclear foci with the PML bodies in living cells. Analysis of the three-dimensional structure revealed that the PML bodies are round to elliptical in shape with multiple satellite bodies on their surface. Some of these satellite bodies contain the SRC-1. Activation and nuclear import of CFP-AR by the agonistic ligand 5alpha-dihydrotestosterone, but not by the antagonist casodex, transferred YFP-SRC1 from the PML bodies to an interlacing filamentous structure. In a single living cell, agonist-activated AR caused a time-dependent movement of YFP-SRC1 from the PML bodies to this filamentous structure. Additionally, coexpression of a constitutively active mutant of AR (AR-deltaligand binding domain) also displaced YFP-SRC1 from the PML bodies to this intranuclear filamentous structure. The fluorescence recovery after photobleaching approach was used to examine changes in the kinetics of movement of YFP-SRC1 during its mobilization from the PML bodies to the intranuclear filamentous structure by the agonist-activated AR. Results of the relative half-times (t(1/2)) of replacement of YFP-SRC1 within the photobleached region of a single PML body from its surrounding nuclear space supported the conclusion that SRC-1 is actively transported from the PML bodies to the intranuclear filamentous structure by the ligand-activated AR. This observation also suggests an interaction between AR and SRC-1 before its binding to the target gene. The PML bodies have been implicated as a cross-road for multiple regulatory pathways that control cell proliferation, cellular senescence, and apoptosis. Our present results along with other recent reports expand the role of this subnuclear structure to include the regulation of steroid hormone action.

Functional analysis of hypoxia-inducible factor-1 alpha-mediated transactivation. Identification of amino acid residues critical for transcriptional activation and/or interaction with CREB-binding protein

The hypoxia-inducible factor-1 alpha (HIF-1 alpha) is a key regulator of adaptive responses to hypoxia. HIF-1 alpha has two independent transactivation domains (TADs). Whereas the N-terminal TAD (N-TAD) also constitutes a degradation box, the C-terminal TAD (C-TAD) functions in a strictly hypoxia-inducible fashion. Oxygen-dependent hydroxylation of an asparagine residue has recently been reported to regulate C-TAD function by disrupting the interaction with the CH1 domain of the p300/CBP coactivator at normoxia. Here we have performed alanine-scanning mutagenesis of a predicted alpha-helix within the C-TAD of mouse HIF-1 alpha to identify residues important for transactivation and interaction of the C-TAD with transcriptional coactivators. We observed that several hydrophobic residues, Ile(802), Leu(808), Leu(814), Leu(815), and Leu(818), were critical for transactivation and binding to the CH1 domain of CBP in hypoxic cells. Moreover, E812A/E813A and D819A mutations impaired hypoxia-dependent transactivation without disrupting binding to CH1. In the context of full-length HIF-1 alpha, mutation of the leucine residues conferred conformational changes to the protein and significantly reduced the transactivation function as well as functional interaction with the transcriptional coactivators CBP and SRC-1. These mutations also affected intranuclear redistribution of HIF-1 alpha in the presence of CBP, indicating that the integrity of the C-TAD is critical for intracellular localization of mouse HIF-1 alpha.

Activation function-1 domain of androgen receptor contributes to the interaction between subnuclear splicing factor compartment and nuclear receptor compartment. Identification of the p102 U5 small nuclear ribonucleoprotein particle-binding protein as a coactivator for the receptor

In the androgen receptor (AR), most of its transactivation activity is mediated via the activation function-1 (AF-1). By employing yeast two-hybrid assay, we isolated a cDNA sequence encoding a protein binding to AR-AF-1. This protein, named ANT-1 (AR N-terminal domain transactivating protein-1), enhanced the ligand-independent autonomous AF-1 transactivation function of AR or glucocorticoid receptor but did not enhance that of estrogen receptor alpha. In contrast, the ANT-1 did not enhance any ligand-dependent AF-2 activities. Furthermore, the ligand-independent interaction between AR-AF-1 and ANT-1 was confirmed in vivo and in vitro. The ANT-1 sequence was identical to that of a protein that binds to U5 small nuclear ribonucleoprotein particle, a human homologue of yeast splicing factor Prp6p, involved in spliceosome. ANT-1 was compartmentalized into 20-40 coarse splicing factor compartment speckles against the background of the diffuse reticular distribution. AR colocalized with ANT-1 only in the diffusely distributed area, whereas the ANT-1 speckles were spatially distinct from but surrounded by the AR compartments. The active gene transcription has been shown to couple simultaneously with pre-mRNA processing at the periphery of the splicing factor compartment. The molecular interaction between two spatially distinct subnuclear compartments mediated by ANT-1 may therefore recruit AR into the transcription-splicing-coupling machinery.

Pure antiandrogens disrupt the recruitment of coactivator GRIP1 to colocalize with androgen receptor in nuclei

We have used confocal microscopy to elucidate the effects of antiandrogens on nuclear localization of the androgen receptor (AR) with its transcriptional coactivator GRIP1. We show that the agonist-activated AR recruits GRIP1 to colocalize with the receptor in the nucleoplasm. By contrast, AR complexed to the antiandrogens hydroxyflutamide and bicalutamide fails to influence nuclear distribution of GRIP1. Likewise, the non-steroidal antiandrogens prevent the agonist-induced AR-GRIP1 colocalization from occurring. Androgen antagonists affect nuclear redistribution of AR-GRIP1 in a fashion that parallels their effects on the transcriptional activity of AR, in that the pure antagonists block GRIP1-dependent activation of AR function, whereas the mixed antagonist/agonist cyproterone acetate promotes both AR-driven redistribution of GRIP1 and activation of AR by GRIP1.