Nuclear receptor modifications and endocrine cell proliferation

Epimutational effects of electronic cigarettes

Electronic cigarettes (e-cigarettes), since they do not require tobacco combustion, have traditionally been considered less harmful than conventional cigarettes (c-cigarettes). In recent years, however, researchers have found many toxic compounds in the aerosols of e-cigarettes, and numerous studies have shown that e-cigarettes can adversely affect the human epigenome. In this review, we provide an update on recent findings regarding epigenetic outcomes of e-cigarette aerosols. Moreover, we discussed the effects of several typical e-cigarette ingredients (nicotine, tobacco-specific nitrosamines, volatile organic compounds, carbonyl compounds, and toxic metals) on DNA methylation, histone modifications, and noncoding RNA expression. These epigenetic effects could explain some of the diseases caused by e-cigarettes. It also reminds the public that like c-cigarettes, inhaling e-cigarette aerosols could also be accompanied with potential epigenotoxicity on the human body.

Estrogen Receptors and Estrogen-Induced Uterine Vasodilation in Pregnancy

Normal pregnancy is associated with dramatic increases in uterine blood flow to facilitate the bidirectional maternal–fetal exchanges of respiratory gases and to provide sole nutrient support for fetal growth and survival. The mechanism(s) underlying pregnancy-associated uterine vasodilation remain incompletely understood, but this is associated with elevated estrogens, which stimulate specific estrogen receptor (ER)-dependent vasodilator production in the uterine artery (UA). The classical ERs (ERα and ERβ) and the plasma-bound G protein-coupled ER (GPR30/GPER) are expressed in UA endothelial cells and smooth muscle cells, mediating the vasodilatory effects of estrogens through genomic and/or nongenomic pathways that are likely epigenetically modified. The activation of these three ERs by estrogens enhances the endothelial production of nitric oxide (NO), which has been shown to play a key role in uterine vasodilation during pregnancy. However, the local blockade of NO biosynthesis only partially attenuates estrogen-induced and pregnancy-associated uterine vasodilation, suggesting that mechanisms other than NO exist to mediate uterine vasodilation. In this review, we summarize the literature on the role of NO in ER-mediated mechanisms controlling estrogen-induced and pregnancy-associated uterine vasodilation and our recent work on a “new” UA vasodilator hydrogen sulfide (H₂S) that has dramatically changed our view of how estrogens regulate uterine vasodilation in pregnancy.

Regulation of post-translational modification in breast cancer treatment

The small ubiquitin-related modification molecule (SUMO), one of the post-translational modification molecules, is involved in a variety of cellular functions where it regulates protein activity and stability, transcription, and cell cycling. Modulation of protein SUMOylation or deSUMOylation modification has been associated with regulation of carcinogenesis in breast cancer. In the dynamic processes of SUMOylation and deSUMOylation in a variety of cancers, SUMO proteases (SENPs), reverse SUMOylation by isopeptidase activity and SENPs are mostly elevated, and are related to poor patient prognosis. Although underlying mechanisms have been suggested for how SENPs participate in breast cancer tumorigenesis, such as through regulation of target protein transactivation, cancer cell survival, cell cycle, or other post-translational modification-related machinery recruitment, the effect of SENP isoform-specific inhibitors on the progression of breast cancer have not been well evaluated. This review will introduce the functions of SENP1 and SENP2 and the underlying signaling pathways in breast cancer for use in discovery of new biomarkers for diagnosis or therapeutic targets for treatment. [BMB Reports 2019; 52(2): 113-118].

Coordinated regulation of nuclear receptor CAR by CCRP/DNAJC7, HSP70 and the ubiquitin-proteasome system

The constitutive active/androstane receptor (CAR) plays an important role as a coordinate transcription factor in the regulation of various hepatic metabolic pathways for chemicals such as drugs, glucose, fatty acids, bilirubin, and bile acids. Currently, it is known that in its inactive state, CAR is retained in the cytoplasm in a protein complex with HSP90 and the tetratricopeptide repeat protein cytosoplasmic CAR retention protein (CCRP). Upon activation by phenobarbital (PB) or the PB-like inducer 1,4-bis[2-(3,5-dichloropyridyloxy)]-benzene (TCPOBOP), CAR translocates into the nucleus. We have identified two new components to the cytoplasmic regulation of CAR: ubiquitin-dependent degradation of CCRP and protein-protein interaction with HSP70. Treatment with the proteasome inhibitor MG132 (5 µM) causes CAR to accumulate in the cytoplasm of transfected HepG2 cells. In the presence of MG132, TCPOBOP increases CCRP ubiquitination in HepG2 cells co-expressing CAR, while CAR ubiquitination was not detected. MG132 treatment of HepG2 also attenuated of TCPOBOP-induced CAR transcriptional activation on reporter constructs which contain CAR-binding DNA elements derived from the human CYP2B6 gene. The elevation of cytoplasmic CAR protein with MG132 correlated with an increase of HSP70, and to a lesser extent HSP60. Both CCRP and CAR were found to interact with endogenous HSP70 in HepG2 cells by immunoprecipitation analysis. Induction of HSP70 levels by heat shock also increased cytoplasmic CAR levels, similar to the effect of MG132. Lastly, heat shock attenuated TCPOBOP-induced CAR transcriptional activation, also similar to the effect of MG132. Collectively, these data suggest that ubiquitin-proteasomal regulation of CCRP and HSP70 are important contributors to the regulation of cytoplasmic CAR levels, and hence the ability of CAR to respond to PB or PB-like inducers.

Aromatase inhibition: a potential target for the management of recurrent or metastatic endometrial cancer by letrozole: more questions than answers?

INTRODUCTION

Endometrial cancer generally presents as early and resectable disease, but about 20% of patients present with either incurable or recurrent/metastatic disease. Patients with good performance status will be treated with hormonal agents, including progestins and tamoxifen, followed by cytotoxic chemotherapy. The options are restricted to hormonal agents for those with multiple comorbidities and older age. Therefore, there is a need to identify novel hormonal agents and other targeted therapeutics with improved therapeutic window in this setting.

AREA COVERED

Clinical trials of letrozole in localized and metastatic settings are reviewed. In the localized setting, limited by the small sample size, preliminary and conflicting clinical activities were observed. Despite the selection of Type I endometrial cancer, which is more estrogen-dependent for its growth, modest clinical activity was observed in the metastatic setting. Thus far, no biomarkers for efficacy have been identified.

EXPERT OPINION

Further understanding of the relevance of aromatase and estrogen receptor and their interplay with other growth pathways will be necessary to guide further development of letrozole. It is premature to declare letrozole a therapeutic option in recurrent/metastatic endometrial cancer.

Phytoestrogens in postmenopausal indications: A theoretical perspective

This review discusses plant-derived compounds with estrogenic activity. The authors rightly emphasize the need for the intake of foods containing phytoestrogens in view of their positive effects on postmenopausal indications. This is particularly significant in the light of the current wave of enthusiasm for vegetarian food, in general, and phytoestrogens, in particular. Phytoestrogens are plant-derived hormone-like diphenolic compounds of dietary origin. These compounds are weakly estrogenic and could play a role in the prevention of other estrogen-related conditions, namely, cardiovascular diseases, menopausal symptoms, postmenopausal osteoporosis, neuroprotective effects, and hormone-dependent cancers (breast and endometrium cancer).

Androgen receptor signalling in prostate cancer: the functional consequences of acetylation

The androgen receptor (AR) is a ligand activated transcription factor and member of the steroid hormone receptor (SHR) subfamily of nuclear receptors. In the early stages of prostate carcinogenesis, tumour growth is dependent on androgens, and AR directly mediates these effects by modulating gene expression. During transcriptional regulation, the AR recruits numerous cofactors with acetylation-modifying enzymatic activity, the best studied include p300/CBP and the p160/SRC family of coactivators. It is known that recruitment of histone acetyltransferases (HATs) and histone deacetylases (HDACs) is key in fine-tuning responses to androgens and is thus likely to play a role in prostate cancer progression. Further, these proteins can also modify the AR itself. The functional consequences of AR acetylation, the role of modifying enzymes in relation to AR transcriptional response, and prostate cancer will be discussed.

Estrogen receptor mutations and changes in downstream gene expression and signaling

Estrogens play a crucial role in regulating the growth and differentiation of breast cancers, with approximately two thirds of all breast tumors expressing the estrogen receptor alpha (ERalpha). Therefore, therapeutic strategies directed at inhibiting the action of ERalpha by using anti-estrogens such as tamoxifen, or reducing estrogens levels by using aromatase inhibitors, such as letrozole, anastrozole, or exemestane, are the standard treatments offered to women with ERalpha-positive cancer. However, not all patients respond to endocrine therapies (termed de novo resistance), and a large number of patients who do respond will eventually develop disease progression or recurrence while on therapy (acquired resistance). Recently, variant forms of the receptor have been identified owing to alternative splicing or gene mutation. This article reviews these variant receptors and their clinical relevance in resistance to endocrine therapy, by addressing their molecular cross-talk with growth factor receptors and signaling components. Understanding the complexity of receptor-mediated signaling has promise for new combined therapeutic options that focus on more efficient blockade of receptor cross-talk.

Therapeutic targets for new therapy for corticosteroid refractory asthma

BACKGROUND

Corticosteroids are the most potent anti-inflammatory agents for the treatment of mild to moderate asthma. However, a small percentage of the asthma population (< 10%) do not respond well, or at all, to corticosteroid therapy, and this severe corticosteroid-refractory asthma contributes to more than 50% of health care expenditure for all asthma because these is no appropriate pharmacological therapy.

METHODS

If the molecular mechanism of corticosteroid insensitivity is uncovered, it may in turn provide insights into the key mechanism of corticosteroid action and rational implementation of treatment regimens that restore corticosteroid sensitivity or replace corticosteroid therapy. This review focuses on why severe asthma patients are corticosteroid-insensitive, and discusses present and future therapeutic and preventative strategies for corticosteroid-refractory asthma.

CONCLUSIONS

Corticosteroid-refractory asthma is a heterogeneous disease and can be controlled by add-on treatment of corticosteroid-sparing agents or effective new drugs based on individual abnormalities. The elucidation of the cause of the relative lack of corticosteroid response in this subgroup of asthmatic individuals may have important implications for other diseases.

The cell fate determination factor dachshund inhibits androgen receptor signaling and prostate cancer cellular growth

Initially isolated as the dominant suppressor of the mutant epidermal growth factor receptor (ellipse), the Dachshund gene plays a key role in metazoan development regulating the Retinal Determination Gene Network. Herein, the DACH1 gene was expressed in normal prostate epithelial cells with reduced expression in human prostate cancer. DACH1 inhibited prostate cancer cellular DNA synthesis, growth in colony forming assays, and blocked contact-independent growth in soft agar assays. DACH1 inhibited androgen receptor (AR) activity, requiring a conserved DS Domain (Dachshund domain conserved with Ski/Sno) that bound NCoR/HDAC and was recruited to an androgen-responsive gene promoter. DACH1 inhibited ligand-dependent activity of AR mutations identified in patients with androgen-insensitive prostate cancer. The DS domain was sufficient for repression of the AR wild-type but failed to repress an AR acetylation site point mutant. These studies show a role for the Retinal Determination Gene Network in regulating cellular growth and signaling in prostate cancer.

Do Estrogen Receptor beta Polymorphisms Play A Role in the Pharmacogenetics of Estrogen Signaling?

Estrogen hormones play critical roles in the regulation of many tissue functions. The effects of estrogens are primarily mediated by the estrogen receptors (ER) alpha and beta. ERs are ligand-activated transcription factors that regulate a complex array of genomic events that orchestrate cellular growth, differentiation and death. Although many factors contribute to their etiology, estrogens are thought to be the primary agents for the development and/or progression of target tissue malignancies. Many of the current modalities for the treatment of estrogen target tissue malignancies are based on agents with diverse pharmacology that alter or prevent ER functions by acting as estrogen competitors. Although these compounds have been successfully used in clinical settings, the efficacy of treatment shows variability. An increasing body of evidence implicates ERalpha polymorphisms as one of the contributory factors for differential responses to estrogen competitors. This review aims to highlight the recent findings on polymorphisms of the lately identified ERbeta in order to provide a functional perspective with potential pharmacogenomic implications.

Regulation of estrogen receptor alpha by the SET7 lysine methyltransferase

Estrogen receptor alpha (ER) is a ligand-dependent transcription factor. Upon binding estrogen, ER recruits coactivator complexes with histone acetyltransferase or methyltransferase activities to activate downstream target genes. In addition to histones, coactivators can modify ER itself and other proteins in the transactivation complex. Here, we show that ER is directly methylated at lysine 302 (K302) by the SET7 methyltransferase. SET7-mediated methylation stabilizes ER and is necessary for the efficient recruitment of ER to its target genes and for their transactivation. The SET7-ER complex structure reveals the molecular basis for ER peptide recognition and predicts that modifications or mutations of nearby residues would affect K302 methylation. Indeed, a breast cancer-associated mutation at K303 (K303R) alters methylation at K302 in vitro and in vivo. These findings raise the possibility that generation, recognition, and removal of modifications within the ER hinge region generate "ER modification cassettes" that yield distinct patterns for signaling downstream events.

Screening of estrogenic and antiestrogenic activities from medicinal plants

The medicinal plant extracts commercially used in Asia were screened for their estrogenic and antiestrogenic activities in a recombinant yeast system featuring both a human estrogen receptor (ER) expression plasmid and a reporter plasmid. Pueraria lobata (flower) had the highest estrogenic relative potency (RP, 7.75×10(-3); RP of 17β-estradiol=1), followed by Amomum xanthioides (1.25×10(-3)). Next potent were a group consisting of Glycyrrhiza uralensis, Zingiber officinale, Rheum undulatum, Curcuma aromatica, Eriobotrya japonica, Sophora flavescens, Anemarrhena asphodeloides, Polygonum multiflorum, and Pueraria lobata (root) (ranging from 9.5×10(-4) to 1.0×10(-4)). Least potent were Prunus persica, Lycoppus lucidus, and Adenophora stricta (ranging from 9.0×10(-5) to 8.0×10(-5)). The extracts exerting antiestrogenic effects, Cinnamomum cassia and Prunus persica, had relative potencies of 1.14×10(-3) and 7.4×10(-4), respectively (RP of tamoxifen=1). The solvent fractions from selected estrogenic or antiestrogenic herbs had higher estrogenic relative potencies, with their RP ranging from 9.3×10(-1) to 2.7×10(-4) and from 8.2×10(-1) to 9.1×10(-3), respectively. These results support previous reports on the efficacy of Oriental medicinal plants used or not used as phytoestrogens for hormone replacement therapy.

Impact of protein acetylation in inflammatory lung diseases

Chronic inflammatory lung diseases are characterized by increased expression of multiple inflammatory genes following activation by proinflammatory transcription factors, such as nuclear factor kappaB (NF-kappaB) and AP-1. Gene expression is, at least in part, regulated by acetylation of core histones through the action of coactivators, such as CREB-binding protein (CBP), which have intrinsic histone acetyltransferase (HAT) activity. Conversely gene repression is mediated via a combination of histone deacetylases (HDAC) and other corepressors. In asthma, the level of HAT activity is elevated in bronchial biopsies, whereas HDAC activity levels are only partially reduced and inhaled corticosteroids are able to reduce the increased HAT activity back to those seen in normal subjects. In contrast, in chronic obstructive pulmonary disease (COPD), there is a greater reduction in HDAC activity and HDAC2 expression but no difference in HAT activity. HAT and HDAC are also reported to modify a large and expanding number of nonhistone proteins, including nuclear import proteins, chaperones, cytoskeletal proteins, and other transcriptional factors, such as NF-kappaB and signal transducer and activation of transcription (STAT). Acetylation regulates several aspects of protein function and stability leading to differing effects on inflammatory gene expression and cell recruitment involved in the pathogenesis of inflammatory diseases. This review will examine the impact of acetylation on the function of key proteins involved in airway inflammatory disease and the effects of current therapies on acetylation status of key proteins. Further appreciation of the role of these changes may lead to the development of novel therapeutic approaches to inflammatory lung diseases that are currently difficult to treat.

Function of nuclear steroid receptors in apoptosis: role of ursodeoxycholic acid

Nuclear steroid receptors such as the glucocorticoid and the mineralocorticoid receptors modulate apoptosis in different cell types through transactivation-dependent and -independent mechanisms. They are involved in both the induction and prevention of apoptosis depending on cell type. However, it is unclear how nuclear steroid receptors can affect expression of the same gene in opposing ways for different cells. In addition to their function as modulators of gene expression, nuclear steroid receptors often act as nuclear transporters of other regulatory molecules, thus indirectly regulating several apoptosis-related genes. Curiously, nuclear steroid receptors are thought to cooperate with the antiapoptotic endogenous bile acid, ursodeoxycholic acid, to prevent programmed cell death. The next decade will almost certainly unveil the remarkable role of nuclear steroid receptors in modulating the life and death struggle of cells and organ systems in human development and function.

The small heterodimer partner is a gonadal gatekeeper of sexual maturation in male mice

The small heterodimer partner (SHP) is an atypical nuclear receptor known mainly for its role in bile acid homeostasis in the enterohepatic tract. We explore here the role of SHP in the testis. SHP is expressed in the interstitial compartment of the adult testes, which contain the Leydig cells. SHP there inhibits the expression of steroidogenic genes, on the one hand by inhibiting the expression of the nuclear receptors steroidogenic factor-1 and liver receptor homolog-1 (lrh-1), and on the other hand by directly repressing the transcriptional activity of LRH-1. Consequently, in SHP knockout mice, testicular testosterone synthesis is increased independently of the hypothalamus-pituitary axis. Independent of its action on androgen synthesis, SHP also determines the timing of germ cell differentiation by controlling testicular retinoic acid metabolism. Through the inhibition of the transcriptional activity of retinoic acid receptors, SHP controls the expression of stimulated by retinoic acid gene 8 (stra8) - a gene that is indispensable for germ cell meiosis and differentiation. Together, our data demonstrate new roles for SHP in testicular androgen and retinoic acid metabolism, making SHP a testicular gatekeeper of the timing of male sexual maturation.

The micro-ribonucleic acid (miRNA) miR-206 targets the human estrogen receptor-alpha (ERalpha) and represses ERalpha messenger RNA and protein expression in breast cancer cell lines

Micro-RNAs are small noncoding RNAs, which diminish the stability and/or translation of mRNAs. This study examined whether miR-206, previously shown to be elevated in estrogen receptor (ER)alpha-negative breast cancer, regulates the expression of ERalpha. Two putative miR-206 sites, (hERalpha1 and hERalpha2), were found in silico within the 3'-untranslated region of human ERalpha mRNA. Transfection of MCF-7 cells with pre-miR-206 or 2'-O-methyl antagomiR-206 specifically decreased or increased, respectively, ERalpha mRNA levels. Overexpression of pre-miR-206 reduced ERalpha and beta-actin protein levels, with no effect on ERbeta, E-cadherin, or glyceraldehyde-3-phosphate dehydrogenase. Reporter constructs containing the hERalpha1 or hERalpha2 binding sites inserted into the 3'-untranslated region of the luciferase mRNA conferred a 1.6- and 2.2-fold repression of luciferase activity, respectively, in HeLa cells. Both miR-206 sites responded accordingly to exogenous hsa-pre-miR-206 and 2'-O-methyl antagomiR-206, and both sites were rendered inactive by mutations that disrupted hybridization to the 5'-seed of miR-206. A C-->T single nucleotide polymorphism in the hERalpha1 site increased repression of luciferase activity to approximately 3.3-fold in HeLa cells. MiR-206 levels were higher in ERalpha-negative MB-MDA-231 cells than ERalpha-positive MCF-7 cells, but only the ERalpha1 site mediated significantly more repression in reporter constructs. MiR-206 expression was strongly inhibited by ERalpha agonists, but not by an ERbeta agonist or progesterone, indicating a mutually inhibitory feedback loop. These findings provide the first evidence for the posttranscriptional regulation of ERalpha by a micro-RNA in the context of breast cancer.

Epigenetics and the Estrogen Receptor

The position effect variegation in Drosophila and Schizosaccharomyces pombe, and higher-order chromatin structure regulation in yeast, is orchestrated by modifier genes of the Su(var) group, (e.g., histone deacetylases ([HDACs]), protein phosphatases) and enhancer E(Var) group (e.g., ATP [adenosine 5'-triphosphate]-dependent nucleosome remodeling proteins). Higher-order chromatin structure is regulated in part by covalent modification of the N-terminal histone tails of chromatin, and histone tails in turn serve as platforms for recruitment of signaling modules that include nonhistone proteins such as heterochromatin protein (HP1) and NuRD. Because the enzymes governing chromatin structure through covalent modifications of histones (acetylation, methylation, phosphorylation, ubiquitination) can also target nonhistone substrates, a mechanism is in place by which epigenetic regulatory processes can affect the function of these alternate substrates. The posttranslational modification of histones, through phosphorylation and acetylation at specific residues, alters chromatin structure in an orchestrated manner in response to specific signals and is considered the basis of a "histone code." In an analogous manner, specific residues within transcription factors form a signaling module within the transcription factor to determine genetic target specificity and cellular fate. The architecture of these signaling cascades in transcription factors (SCITs) are poorly understood. The regulation of estrogen receptor (ERalpha) by enzymes that convey epigenetic signals is carefully orchestrated and is reviewed here.

Post-translational modifications of steroid receptors

The multiple physiological functions of steroid hormones have been known for many years. The cloning of the steroid receptors in the mid-1980s led to the concept of ligand-activated transcription factors and to the identification of specific DNA response elements in the regulatory regions of target genes. The next main development was the identification of cofactors with activating or repressing functions, of which several act by modifying histones and locally affecting the chromatin structure. Work from several groups shows that the steroid receptors themselves can also be modified at various positions. Besides the long-known phosphorylation at tyrosines and serine/threonine residues, other covalent additions such as acetylation, ubiquitylation and sumoylation have been evidenced for steroid receptors in recent years. These modifications affect receptor stability and activity, and provide potential mechanisms for cell- or gene-specific regulation. A better understanding of the impact of these post-translational modifications (PTMs) on steroid receptor function should help in the identification of novel ligands with improved clinical profiles.

Epigenetic regulation of nuclear steroid receptors

Histone modifier proteins have come to the forefront in the study of gene regulation. It is now known that histone methyltransferases, acetytransferases, kinases, ubiquitinases, deacetylases and demethylases orchestrate expression of target genes by modifying both histone and non-histone proteins. The nuclear receptor (NR) superfamily govern such diverse biological processes as development, physiology and disease, including human cancer. The involvement of NR in complexes with coactivators and corepressors is necessary for regulation of target genes. This review focuses on the newly recognized interactions between the NR and histone modifying enzymes. In addition to regulating histones, the histone modifying proteins directly modify and thereby regulate NR activity. In the same manner that signaling platforms exist within the histone tails that are post-translationally processed by histone modifying proteins, cascades of post-translational modification have been identified within the NR that coordinate their activity. This review focuses on the regulation of the NR estrogen receptor (ERalpha), androgen receptor (AR) and peroxisome proliferator activated receptor-gamma (PPARgamma), given their role in tumor onset and progression.

Molecular mechanisms of oestrogen and SERMs in endometrial carcinogenesis

Endometrial cancer is the most common gynaecological cancer, and is associated with endometrial hyperplasia, unopposed oestrogen exposure and adjuvant therapy for breast cancer using selective oestrogen-receptor modulators (SERMs), particularly tamoxifen. Oestrogen and SERMs are thought to be involved in endometrial carcinogenesis through their effects on transcriptional regulation. Ultimately, oestrogen and SERMs affect the transduction of cellular signalling pathways that govern cell growth and proliferation, through downstream effectors such as PAX2 (paired box 2).

Ligand-independent orphan receptor TR2 activation by phosphorylation at the DNA-binding domain

In a previous report we demonstrated protein kinase C (PKC)-mediated phosphorylation of the ligand-binding domain (LBD) of orphan nuclear receptor TR2. In this report, we provide the evidence of PKC-mediated phosphorylation of the DNA-binding domain (DBD) of TR2. Two PKC target sites were predicted within the DBD, at Ser-170 and Ser-185, but only Ser-185 was confirmed by MS. Phosphorylation of DBD facilitated DNA binding of the TR2 receptor and its recruiting of coactivator p300/CBP-associated factor (P/CAF). Ser-185 was required for DNA binding, whereas both Ser-170 and Ser-185 were necessary for receptor interaction with P/CAF. The P/CAF-interacting domain of TR2 was located in its DBD. A double mutant (Ser-170 and Ser-185) of TR2 significantly lowered the activation of its target gene RARbeta2. This study provides the first evidence for ligand-independent activation of TR2 orphan receptor through PTM at the DBD, which enhanced its DNA-binding ability and interaction with coactivator P/CAF.

PTEN and GSK3beta: key regulators of progression to androgen-independent prostate cancer

Prostate cancer (PrCa) is characterized by progression from an androgen-dependent phenotype to one that is inevitably androgen independent (AI) and lethal. Recent evidence strongly suggests that the phosphatidylinositol-3-kinase/Akt (PI3K/Akt) and androgen receptor (AR) signalling pathways provide prostatic epithelium with the necessary signalling events to escape the apoptotic response associated with androgen withdrawal therapy. Silencing of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and glycogen synthase kinase beta (GSK3beta) are frequently associated with advanced PrCa systems and likely serve critical roles in promoting AR and PI3K/Akt gain-of-function. That PTEN negatively regulates AR and is sufficient to promote metastatic PrCa in murine models strongly implies its role as a gatekeeper of progressive PrCa. In human PrCa, PTEN loss is correlated with substantial increases in Akt(Ser473) and integrin-linked kinase expression, both of which promote Ser(9) phospho-inhibition of GSK3beta and inactivation of apoptotic factors. Sufficient evidence also suggests that GSK3beta is not only a critical regulator of proproliferative signalling but also a promiscuous one as PI3K/Akt pools of GSK3beta are, at least in part, functionally interchangeable with those of the Wnt/beta-catenin pathway. Thus, GSK3beta may serve not only as a mediator of PI3K/Akt activation but may also regulate the potent transactivation and proproliferative effects that Wnt3a and beta-catenin confer upon AR. These data suggest that prostate-specific activation of GSK3beta may serve as a viable pharmacological option. Thus, in this review, we emphasize that temporal changes in GSK3beta and PTEN expression during progression to AI PrCa are important factors when considering the potential for therapies targeting the oncogenic contributions of PI3K/Akt and AR signalling pathways.

Histone deacetylase 2-mediated deacetylation of the glucocorticoid receptor enables NF-kappaB suppression

Glucocorticoids are the most effective antiinflammatory agents for the treatment of chronic inflammatory diseases even though some diseases, such as chronic obstructive pulmonary disease (COPD), are relatively glucocorticoid insensitive. However, the molecular mechanism of this glucocorticoid insensitivity remains uncertain. We show that a defect of glucocorticoid receptor (GR) deacetylation caused by impaired histone deacetylase (HDAC) 2 induces glucocorticoid insensitivity toward nuclear factor (NF)-κB–mediated gene expression. Specific knockdown of HDAC2 by RNA interference resulted in reduced sensitivity to dexamethasone suppression of interleukin 1β–induced granulocyte/macrophage colony-stimulating factor production. Loss of HDAC2 did not reduce GR nuclear translocation, GR binding to glucocorticoid response element (GRE) on DNA, or GR-induced DNA or gene induction but inhibited the association between GR and NF-κB. GR becomes acetylated after ligand binding, and HDAC2-mediated GR deacetylation enables GR binding to the NF-κB complex. Site-directed mutagenesis of K494 and K495 reduced GR acetylation, and the ability to repress NF-κB–dependent gene expression becomes insensitive to histone deacetylase inhibition. In conclusion, we show that overexpression of HDAC2 in glucocorticoid-insensitive alveolar macrophages from patients with COPD is able to restore glucocorticoid sensitivity. Thus, reduction of HDAC2 plays a critical role in glucocorticoid insensitivity in repressing NF-κB–mediated, but not GRE-mediated, gene expression.

DNA methylation of estrogen receptor alpha gene by phthalates

The phthalates are ubiquitous industrial plasticizers and include agents such as di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), and butyl benzyl phthalate (BBP), which are classified as endocrine disruptors because of their anti-androgenic or pro-estrogenic effects. A recent study suggested that DBP produced the hypomethylation of c-myc protooncogene in mouse liver to activate c-myc. In the present study, DNA hypomethylation at the promoter region of the estrogen receptor alpha (ERalpha) gene was investigated by methylation-specific polymerase chain reaction (MSP) in a human breast cancer (MCF7) and in a normal (MCF10A) cell line after DBP treatment. Yeast-based estrogen receptor transcription assays showed that hERalpha gene expression was induced by BBP but not DBP. Moreover, MCF7 cells treated with BBP or DBP at 10(-5)M led to the demethylation of ERalpha promoter-associated CpG islands. These data suggest that an altered ER mRNA expression by BBP might be related to aberrant DNA methylation in the promoter region of ERalpha.

Effect of estrogen receptor (ER) on benzo[a]pyrene-DNA adduct formation in human breast cancer cells

To investigate the role of estrogen and estrogen receptor (ER) during benzo[a]pyrene (BaP) carcinogenesis, BaP-DNA adduct formation, and DNA synthesis were examined in ER-positive, MCF-7, and ER-negative, MDA-MB-231, human breast cancer cell lines. In MCF-7, the ER-positive human breast cancer cell line, treated with BaP, the formation of BaP-DNA adducts and DNA synthesis were inhibited in a concentration-responsive manner, but there was no change in MDA-MB-231, the ER-negative cell line. In the [3H]BaP-DNA binding assay, an increase of BaP-DNA adduct formation was observed with 17beta-estradiol (E2)-induced ERalpha. Treatments of [3H]BaP in conjunction with the E2 induced a 2.1-fold increase in BaP-DNA adduct over BaP alone in the ER-positive MCF-7 cell line. In addition, the antiestrogen tamoxifen (TAM) blocked this effect by 82%, while E2 produced no change in the ER-negative MDA-MB-231 cell line. These observations suggest that the increased formation of BaP-DNA adducts may be mediated through the ERalpha expressed by E2.

ATP-dependent chromatin remodeling complexes and their role in nuclear receptor-dependent transcription in vivo

Nuclear receptors (NRs) are ligand-dependent transcription factors that mediate transcription of target genes in chromatin. Modulation of chromatin structure plays an important part in the NR-mediated transcription process. ATP-dependent chromatin remodeling complexes have been shown to be intimately involved in NR-mediated transcription. In this review, we examine the role of chromatin remodeling complexes in facilitating the recruitment of coregulators and basal transcription factors. In addition, the role of subunit specificity within the chromatin remodeling complexes, the complexes' influence on remodeling activity, and complexes' recruitment to the NR-responsive promoters are discussed.

Acetylation of nuclear receptors in cellular growth and apoptosis

Post-translational modification of chromatin histones governs a key mechanism of transcriptional regulation. Histone acetylation, together with methylation, phosphorylation, ubiquitylation, sumoylation, glycosylation, and ADP ribosylation, modulate the activity of many genes by modifying both core histones and non-histone transcription factors. Epigenetic protein modification plays an important role in multiple cellular processes including DNA repair, protein stability, nuclear translocation, protein-protein interactions, and in regulation of cellular proliferation, differentiation and apoptosis. Histone acetyltransferases modify histones, coactivators, nuclear transport proteins, structural proteins, cell cycle components and transcription factors including p53 and nuclear receptors. The estrogen, PPARgamma and androgen receptor are members of the nuclear receptor (NR) superfamily. The androgen receptor (AR) and estrogen receptor alpha (ERalpha) are directly acetylated by histone acetyltransferases at a motif that is conserved between species and other NR. Point mutations at the lysine residue within the acetylation motif of the AR and ERalpha have been identified in prostate cancer as well as in breast cancer tissue. Acetylation of the NR governs ligand sensitivity and hormone antagonist responses. The AR is acetylated by p300, P/CAF and TIP60 and acetylation of the AR regulates co-regulator recruitment and growth properties of the receptors in cultured cells and in vivo. AR acetylation mimic mutants convey reduced apoptosis and enhanced growth properties correlating with altered promoter specificity for cell-cycle target genes. Cell-cycle control proteins, including cyclins, in turn alter the access of transcription factors and nuclear receptors to the promoters of target genes.

Steroid receptor action

The ovarian hormones oestradiol and progesterone exert their actions on target cells predominantly through the binding and activation of the oestrogen receptor (ER) and progesterone receptor (PR), respectively. These receptors are members of the steroid/thyroid hormone superfamily of ligand-dependent transcription factors and bind to the control regions (promoters) of specific genes, where they recruit co-activators or co-repressors and the transcriptional machinery necessary to elicit gene expression. The ability of a nuclear receptor to modulate gene transcription is further dependent on its interaction with other transcription factors, which in turn can be regulated by either distinct or multiple cytoplasmic signalling pathways. This chapter summarises the extraordinary diversity of factors involved in determining the cellular response to a hormonal signal and emphasises the role of ER and PR in regulating ovarian and uterine functions.