Structure of a biologically active estrogen receptor-coactivator complex on DNA

Transcription factors and hormone receptors: Sex‑specific targets for cancer therapy (Review)

Despite advancements in diagnostic and therapeutic technologies, cancer continues to pose a challenge to disease-free longevity in humans. Numerous factors contribute to the onset and progression of cancer, among which sex differences, as an intrinsic biological condition, warrant further attention. The present review summarizes the roles of hormone receptors estrogen receptor α (ERα), estrogen receptor β (ERβ) and androgen receptor (AR) in seven types of cancer: Breast, prostate, ovarian, lung, gastric, colon and liver cancer. Key cancer-related transcription factors known to be activated through interactions with these hormone receptors have also been discussed. To assess the impact of sex hormone receptors on different cancer types, hormone-related transcription factors were analyzed using the SignaLink 3.0 database. Further analysis focused on six key transcription factors: CCCTC-binding factor, forkhead box A1, retinoic acid receptor α, PBX homeobox 1, GATA binding protein 2 and CDK inhibitor 1A. The present review demonstrates that these transcription factors significantly influence hormone receptor activity across various types of cancer, and elucidates the complex interactions between these transcription factors and hormone receptors, offering new insights into their roles in cancer progression. The findings suggest that targeting these common transcription factors could improve the efficacy of hormone therapy and provide a unified approach to treating various types of cancer. Understanding the dual and context-dependent roles of these transcription factors deepens the current understanding of the molecular mechanisms underlying hormone-driven tumor progression and could lead to more effective targeted therapeutic strategies.

Allosteric communications between domains of nuclear receptors

Nuclear receptors (NRs) regulate gene expression in response to hormonal signals, influencing diverse physiological processes and diseases. Structural and dynamics investigations based on X-ray crystallography, cryo-electron microscopy (cryo-EM), hydrogen-deuterium exchange mass spectrometry, and molecular dynamics simulations, have significantly deepened our understanding of the conformational states, dynamics, and interdomain interactions of multi-domain NRs. Structural studies have examined heterodimeric complexes such as peroxisome proliferator-activated receptor gamma (PPAR-γ) with retinoid X receptor alpha (RXRα), liver X receptor beta (LXRβ) with RXRα, and retinoic acid receptor beta (RARβ) with RXRα, as well as homodimers like hepatic nuclear factor 4 alpha (HNF-4α), androgen receptor (AR), and glucocorticoid receptor (GR). These investigations highlight critical allosteric communication between ligand-binding domains (LBDs) and DNA-binding domains (DBDs), emphasizing the roles of flexible hinge regions and N-terminal segments in adapting to diverse DNA configurations. Both non-steroid receptor heterodimers and homodimers exhibit robust interdomain connections that mediate allosteric signaling. For instance, AR demonstrates three distinct conformational states that underscore its dynamic behavior, while GR exhibits unique ligand-dependent domain interactions shaping receptor signaling. The collective findings so far suggest a conserved mechanism of cross-domain communication across the NR family. Supported by complementary biophysical, spectroscopic, mutagenesis, and computational studies, this body of research has elucidated the nature of domain-domain interfaces and their pivotal roles in regulating the transcriptional activity of steroid and non-steroid receptors.

The role of estrogen receptors in intracellular estrogen signaling pathways, an overview

To date five members of estrogen receptors (ESRs) have been reported. They are grouped into two classes, the nuclear estrogen receptors are members of the nuclear receptor family which found at nuclear, cytoplasm and plasma membrane, and the membrane estrogen receptors, such as G protein-coupled estrogen receptor 1, ESR-X and Gq-coupled membrane estrogen receptor. The structure and function of estrogen receptors, and interaction between ESR and coregulators were reviewed. In canonical pathway ESRs can translocate to the nucleus, bind to the target gene promotor with or without estrogen responsive element and regulate transcription, mediating the genomic effects of estrogen. Coactivators and corepressors are recruited to activate or inhibit transcription by activated ESRs. Many coactivators and corepressors are recruited to activate or inhibit ESR mediated gene transcription via different mechanisms. ESRs also indirectly bind to the promoter via interaction with other transcription factors, tethering the transcription factors. ESRs can be phosphorylated by several kinases such as p38, extracellular-signal-regulated kinase, and activated protein kinase B, and which activates transcription without ligand binding. Non-genomic estrogen action can be manifested by the increases of cytoplasmic NO and Ca2+ through the activation of membrane ESRs. In female, ESRs signaling is crucial for folliculogenesis, oocyte growth, ovulation, oviduct and uterus. In male, ESRs signaling modulates libido, erectile function, leydig cell steroidogenesis, sertoli cell's function, and epididymal fluid homeostatsis, supporting spermatogenesis and sperm maturation. The abnormal ESRs signaling is believed to be closely related to reproductive diseases and cancer.

Pyrimidine-triazole-tethered tert-butyl-piperazine-carboxylate suppresses breast cancer by targeting estrogen receptor signaling and β-catenin activation

Several chemotherapeutics against breast cancer are constrained by their adverse effects and chemoresistance. The development of novel chemotherapeutics to target metastatic breast cancer can bring effective clinical outcomes. Many breast cancer patients present with tumors that are positive for estrogen receptors (ERs), highlighting the importance of targeting the ER pathway in this particular subtype. Although selective estrogen receptor modulators (SERMs) are commonly used, their side effects and resistance issues necessitate the development of new ER-targeting agents. In this study, we report that a newly synthesized compound, TTP-5, a hybrid of pyrimidine, triazole, and tert-butyl-piperazine-carboxylate, effectively binds to estrogen receptor alpha (ERα) and suppresses breast cancer cell growth. We assessed the impact of TTP-5 on cell proliferation using MTT and colony formation assays and evaluated its effect on cell motility through wound healing and invasion assays. We further explored the mechanism of action of this novel compound by detecting protein expression changes using Western blotting. Molecular docking was used to confirm the interaction of TTP-5 with ERα. The results indicated that TTP-5 significantly reduced the proliferation of MCF-7 cells by blocking the ERα signaling pathway. Conversely, although it did not influence the growth of MDA-MB-231 cells, TTP-5 hindered their motility by modulating the expression of proteins associated with epithelial-mesenchymal transition (EMT), possibly via the Wnt/β-catenin pathway.

The N-terminal activation function AF-1 domain of ERα interacts directly with the C-terminal AF-2-holding ligand-binding domain to recruit the coactivator proteins

Cryoelectron microscopy (cryo-EM) clarified the quaternary structure of the DNA complex of coactivator-bound estrogen receptor alpha (ERα), revealing the adjacency of the N-terminal domain (NTD) and C-terminal ligand-binding domain (LBD). ERα-NTD and LBD constitute activation function 1 (AF-1) and activation function 2 (AF-2), respectively. These domains are essential for transcription activation. Their spatial proximity was judged to be essential for ERα to recruit the SRC coactivator proteins. In the present study, we first evaluated untethered free ERα-NTD(AF-1) [residues 1-180] and its-truncated desNTD(AF-1)-ERα [residues 181-595] in a luciferase reporter gene assay. ERα-NTD(AF-1) was completely inactive, whereas desNTD(AF-1)-ERα exhibited 66% activity of wild-type ERα. Surprisingly, ERα-NTD(AF-1) was found to inhibit desNTD(AF-1)-ERα markedly. Therefore, assuming that ERα-NTD(AF-1) must also inhibit wild-type full-length ERα, we co-expressed ERα-NTD(AF-1) and full-length ERα. As expected, ERα-NTD(AF-1) inhibited ERα in a dose-dependent manner, but non-competitively for 17β-estradiol. When their intracellular transport was examined immunocytochemically, ERα-NTD(AF-1) showed a distinct translocation from the cytoplasm to the nucleus, despite being expressed solely in the cytoplasm without full-length ERα. This nuclear translocation was attributable to a direct interaction between ERα-NTD(AF-1) and full-length ERα consisting of the nuclear localization signal. The present results demonstrated that, in full-length ERα, the N-terminally tethered NTD(AF-1) domain collaborates with the C-terminal LBD(AF-2) for coactivator recruitment.

The Drosophila EcR-Hippo component Taiman promotes epithelial cell fitness by control of the Dally-like glypican and Wg gradient

Rapidly dividing cells can eliminate slow growing neighbors through the apoptotic process of cell competition. This process ensures that only high fitness cells populate embryonic tissues and is proposed to underlie the ability of oncogene-transformed cells to progressively replace normal cells within a tissue. Patches of cells in the Drosophila wing disc overexpressing the oncogenic Taiman (Tai) transcriptional coactivator kill normal neighbors by secreting Spz ligands that trigger pro-apoptotic Toll signaling in receiving cells. However, extracellular signaling mechanisms responsible for elimination of slow growing cells by normal neighbors remain poorly defined. Here we show that slow growing cells with reduced Tai (Tailow) are killed by normal neighbors through a mechanism involving competition for the Wingless (Wg/Wnt) ligand. Elevated Wg signaling significantly rescues elimination of Tailow cells in multiple organs, suggesting that Tai may normally promote Wg activity. Examining distribution of Wg components reveals that Tai promotes extracellular spread of the Wg ligand from source cells across the wing disc, thus ensuring patterned expression of multiple Wg-regulated target genes. Tai controls Wg spread indirectly through the extracellular glypican Dally-like protein (Dlp), which binds Wg and promotes its extracellular diffusion and capture by receptors. Data indicate that Tai likely controls Dlp at two levels: transcription of dlp mRNA and Dlp intracellular trafficking. Overall, these data indicate that the Tai acts through Dlp to enable Wg transport and signaling, and that cell competition in the Tailow model arises due to inequity in the ability of epithelial cells to sequester limiting amounts of the Wg growth factor.

Identification of an ionic mechanism for ERα-mediated rapid excitation in neurons

The major female ovarian hormone, 17β-estradiol (E2), can alter neuronal excitability within milliseconds to regulate a variety of physiological processes. Estrogen receptor-α (ERα), classically known as a nuclear receptor, exists as a membrane-bound receptor to mediate this rapid action of E2, but the ionic mechanisms remain unclear. Here, we show that a membrane channel protein, chloride intracellular channel protein-1 (Clic1), can physically interact with ERα with a preference to the membrane-bound ERα. Clic1-mediated currents can be enhanced by E2 and reduced by its depletion. In addition, Clic1 currents are required to mediate the E2-induced rapid excitations in multiple brain ERα populations. Further, genetic disruption of Clic1 in hypothalamic ERα neurons blunts the regulations of E2 on female body weight balance. In conclusion, we identified the Clic1 chloride channel as a key mediator for E2-induced rapid neuronal excitation, which may have a broad impact on multiple neurobiological processes regulated by E2.

UBE2M forms a positive feedback loop with estrogen receptor to drive breast cancer progression and drug resistance

UBE2M, a NEDD8-conjugating enzyme, is dysregulated in various human cancers and promotes tumor cell proliferation. However, its role in estrogen receptor-positive (ER+) breast cancer remains unknown. We found that UBE2M expression was significantly higher in ER+ breast cancer tissues than in ER-negative (ER-) breast cancer tissues. Higher expression of UBE2M indicated a poorer prognosis in patients with ER+ breast cancer but not in those with ER- breast cancer. Of interest, a positive feedback loop was observed between UBE2M and ERα. Specifically, ERα enhanced the HIF-1α-mediated transcription of UBE2M. In turn, UBE2M maintained ERα expression by inhibiting its ubiquitination and degradation through UBE2M-CUL3/4A-E6AP-ERα axis. Functionally, silencing of UBE2M suppressed the growth of breast cancer cells by inducing cell cycle arrest and apoptosis and improved their sensitivity to fulvestrant both in vitro and in vivo. Altogether, our findings reveal that the UBE2M-ERα feedback loop drives breast cancer progression and fulvestrant resistance, suggesting UBE2M as a viable target for endocrine therapy of ER+ breast cancer.

Asymmetric allostery in estrogen receptor-α homodimers drives responses to the ensemble of estrogens in the hormonal milieu

The estrogen receptor-α (ER) is thought to function only as a homodimer but responds to a variety of environmental, metazoan, and therapeutic estrogens at subsaturating doses, supporting binding mixtures of ligands as well as dimers that are only partially occupied. Here, we present a series of flexible ER ligands that bind to receptor dimers with individual ligand poses favoring distinct receptor conformations-receptor conformational heterodimers-mimicking the binding of two different ligands. Molecular dynamics simulations showed that the pairs of different ligand poses changed the correlated motion across the dimer interface to generate asymmetric communication between the dimer interface, the ligands, and the surface binding sites for epigenetic regulatory proteins. By examining the binding of the same ligand in crystal structures of ER in the agonist vs. antagonist conformers, we also showed that these allosteric signals are bidirectional. The receptor conformer can drive different ligand binding modes to support agonist vs. antagonist activity profiles, a revision of ligand binding theory that has focused on unidirectional signaling from the ligand to the coregulator binding site. We also observed differences in the allosteric signals between ligand and coregulator binding sites in the monomeric vs. dimeric receptor, and when bound by two different ligands, states that are physiologically relevant. Thus, ER conformational heterodimers integrate two different ligand-regulated activity profiles, representing different modes for ligand-dependent regulation of ER activity.

Asymmetric Allostery in Estrogen Receptor-α Homodimers Drives Responses to the Ensemble of Estrogens in the Hormonal Milieu

The estrogen receptor-α (ER) is thought to function only as a homodimer, but responds to a variety of environmental, metazoan, and therapeutic estrogens at sub-saturating doses, supporting binding mixtures of ligands as well as dimers that are only partially occupied. Here, we present a series of flexible ER ligands that bind to receptor dimers with individual ligand poses favoring distinct receptor conformations -receptor conformational heterodimers-mimicking the binding of two different ligands. Molecular dynamics simulations showed that the pairs of different ligand poses changed the correlated motion across the dimer interface to generate asymmetric communication between the dimer interface, the ligands, and the surface binding sites for epigenetic regulatory proteins. By examining binding of the same ligand in crystal structures of ER in the agonist versus antagonist conformers, we also showed that these allosteric signals are bidirectional. The receptor conformer can drive different ligand binding modes to support agonist versus antagonist activity profiles, a revision of ligand binding theory that has focused on unidirectional signaling from ligand to the coregulator binding site. We also observed differences in the allosteric signals between ligand and coregulator binding sites in the monomeric versus dimeric receptor, and when bound by two different ligands, states that are physiologically relevant. Thus, ER conformational heterodimers integrate two different ligand-regulated activity profiles, representing new modes for ligand-dependent regulation of ER activity.

Significance

The estrogen receptor-α (ER) regulates transcription in response to a hormonal milieu that includes low levels of estradiol, a variety of environmental estrogens, as well as ER antagonists such as breast cancer anti-hormonal therapies. While ER has been studied as a homodimer, the variety of ligand and receptor concentrations in different tissues means that the receptor can be occupied with two different ligands, with only one ligand in the dimer, or as a monomer. Here, we use X-ray crystallography and molecular dynamics simulations to reveal a new mode for ligand regulation of ER activity whereby sequence-identical homodimers can act as functional or conformational heterodimers having unique signaling characteristics, with ligand-selective allostery operating across the dimer interface integrating two different signaling outcomes.

Lead Compound Development of SRC-3 Inhibitors with Improved Pharmacokinetic Properties and Anticancer Efficacy

Steroid receptor coactivator 3 (SRC-3) is a critical mediator of many intracellular signaling pathways that are crucial for cancer proliferation and metastasis. In this study, we performed structure-activity relationship exploration and drug-like optimization of the hit compound SI-2, guided by in vitro/in vivo metabolism studies and cytotoxicity assays. Our efforts led to the discovery of two lead compounds, SI-10 and SI-12. Both compounds exhibit potent cytotoxicity against a panel of human cancer cell lines and demonstrate acceptable pharmacokinetic properties. A biotinylated estrogen response element pull-down assay demonstrated that SI-12 could disrupt the recruitment of SRC-3 and p300 in the estrogen receptor complex. Importantly, SI-10 and SI-12 significantly inhibited tumor growth and metastasis in vivo without appreciable acute toxicity. These results demonstrate the potential of SI-10 and SI-12 as drug candidates for cancer therapy, given their potent SRC-3 inhibition and promising pharmacokinetic and toxicity profiles.

Bacterial Lactonases ZenA with Noncanonical Structural Features Hydrolyze the Mycotoxin Zearalenone

Zearalenone (ZEN) is a mycoestrogenic polyketide produced by Fusarium graminearum and other phytopathogenic members of the genus Fusarium. Contamination of cereals with ZEN is frequent, and hydrolytic detoxification with fungal lactonases has been explored. Here, we report the isolation of a bacterial strain, Rhodococcus erythropolis PFA D8-1, with ZEN hydrolyzing activity, cloning of the gene encoding α/β hydrolase ZenA encoded on the linear megaplasmid pSFRL1, and biochemical characterization of nine homologues. Furthermore, we report site-directed mutagenesis as well as structural analysis of the dimeric ZenARe of R. erythropolis and the more thermostable, tetrameric ZenAScfl of Streptomyces coelicoflavus with and without bound ligands. The X-ray crystal structures not only revealed canonical features of α/β hydrolases with a cap domain including a Ser-His-Asp catalytic triad but also unusual features including an uncommon oxyanion hole motif and a peripheral, short antiparallel β-sheet involved in tetramer interactions. Presteady-state kinetic analyses for ZenARe and ZenAScfl identified balanced rate-limiting steps of the reaction cycle, which can change depending on temperature. Some new bacterial ZEN lactonases have lower KM and higher kcat than the known fungal ZEN lactonases and may lend themselves to enzyme technology development for the degradation of ZEN in feed or food.

Gene transcription regulation by ER at the single cell and allele level

In this short review we discuss the current view of how the estrogen receptor (ER), a pivotal member of the nuclear receptor superfamily of transcription factors, regulates gene transcription at the single cell and allele level, focusing on in vitro cell line models. We discuss central topics and new trends in molecular biology including phenotypic heterogeneity, single cell sequencing, nuclear phase separated condensates, single cell imaging, and image analysis methods, with particular focus on the methodologies and results that have been reported in the last few years using microscopy-based techniques. These observations augment the results from biochemical assays that lead to a much more complex and dynamic view of how ER, and arguably most transcription factors, act to regulate gene transcription.

MAF amplification licenses ERα through epigenetic remodelling to drive breast cancer metastasis

MAF amplification increases the risk of breast cancer (BCa) metastasis through mechanisms that are still poorly understood yet have important clinical implications. Oestrogen-receptor-positive (ER+) BCa requires oestrogen for both growth and metastasis, albeit by ill-known mechanisms. Here we integrate proteomics, transcriptomics, epigenomics, chromatin accessibility and functional assays from human and syngeneic mouse BCa models to show that MAF directly interacts with oestrogen receptor alpha (ERα), thereby promoting a unique chromatin landscape that favours metastatic spread. We identify metastasis-promoting genes that are de novo licensed following oestrogen exposure in a MAF-dependent manner. The histone demethylase KDM1A is key to the epigenomic remodelling that facilitates the expression of the pro-metastatic MAF/oestrogen-driven gene expression program, and loss of KDM1A activity prevents this metastasis. We have thus determined that the molecular basis underlying MAF/oestrogen-mediated metastasis requires genetic, epigenetic and hormone signals from the systemic environment, which influence the ability of BCa cells to metastasize.

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Androgen receptor in breast cancer and its clinical implication

Breast cancer is a heterogeneous group of diseases characterized by diverse subtypes. Currently, the classification of breast cancer is based on the status of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2). In addition to these receptors, the presence of the androgen receptor (AR) in breast cancer cells adds a layer of complexity to our understanding of the disease. The role of AR in breast cancer is intricate, as it can alter diverse signaling pathways in the presence of different hormone receptors (HRs). This complex interplay between signaling pathways affects patient outcomes and prognosis, and the presence of AR has a significant effect. While AR positivity is common in breast cancer, the efficacy of utilizing AR blockade as a monotherapy has been limited, demonstrating only modest results. To address this challenge, substantial efforts have been directed toward comprehending the intricacies of AR's role and pathways in breast cancer development in the hope of understanding its utility as a biomarker or drug target. Multiple ongoing clinical trials are currently investigating combination treatments involving AR inhibitors and other agents to disrupt oncogenic signaling pathways and their crosstalk. Particularly in the context of triple-negative breast cancer (TNBC), where targeted therapeutic options are lacking, extensive research efforts have been dedicated to exploring the potential of AR-related interventions. This review aims to provide an overview of the various breast cancer subtypes with AR signaling mechanisms, and ongoing clinical trials that hold the potential to reshape future clinical approaches.

Nuclear Estrogen Receptors in Prostate Cancer: From Genes to Function

Estrogens are almost ubiquitous steroid hormones that are essential for development, metabolism, and reproduction. They exert both genomic and non-genomic action through two nuclear receptors (ERα and ERβ), which are transcription factors with disregulated functions and/or expression in pathological processes. In the 1990s, the discovery of an additional membrane estrogen G-protein-coupled receptor augmented the complexity of this picture. Increasing evidence elucidating the specific molecular mechanisms of action and opposing effects of ERα and Erβ was reported in the context of prostate cancer treatment, where these issues are increasingly investigated. Although new approaches improved the efficacy of clinical therapies thanks to the development of new molecules targeting specifically estrogen receptors and used in combination with immunotherapy, more efforts are needed to overcome the main drawbacks, and resistance events will be a challenge in the coming years. This review summarizes the state-of-the-art on ERα and ERβ mechanisms of action in prostate cancer and promising future therapies.

The androgen receptor

The Androgen Receptor (AR) is a ligand (androgen) activated transcription factor and a member of the nuclear receptor (NR) superfamily. It is required for male sex hormone function. AR-FL (full-length) has the domain structure of NRs, an N-terminal domain (NTD) required for transactivation, a DNA-binding domain (DBD), a nuclear localization signal (NLS) and a ligand-binding domain (LBD). Paradoxes exist in that endogenous ligands testosterone (T) and 5α-dihydrotestosterone (DHT) have differential effects on male sexual development while binding to the same receptor and transcriptional specificity is achieved even though the androgen response elements (AREs) are identical to those seen for the progesterone, glucocorticoid and mineralocorticoid receptors. A high resolution 3-dimensional structure of AR-FL by either cryo-EM or X-ray crystallography has remained elusive largely due to the intrinsic disorder of the NTD. AR function is regulated by post-translational modification leading to a large number of proteoforms. The interaction of these proteoforms in multiprotein complexes with co-activators and co-repressors driven by interdomain coupling mediates the AR transcriptional output. The AR is a drug target for selective androgen receptor modulators (SARMS) that either have anabolic or androgenic effects. Protstate cancer is treated with androgen deprivation therapy or by the use of AR antagonists that bind to the LBD. Drug resistance occurs due to adaptive AR upregulation and the appearance of splice variants that lack the LBD and become constitutively active. Bipolar T treatment and NTD-antagonists could surmount these resistance mechanisms, respectively. These recent advances in AR signaling are described.

Full-length nuclear receptor allosteric regulation

Nuclear receptors are a superfamily of transcription factors regulated by a wide range of lipids that include phospholipids, fatty acids, heme-based metabolites, and cholesterol-based steroids. Encoded as classic two-domain modular transcription factors, nuclear receptors possess a DNA-binding domain (DBD) and a lipid ligand-binding domain (LBD) containing a transcriptional activation function. Decades of structural studies on the isolated LBDs of nuclear receptors established that lipid-ligand binding allosterically regulates the conformation of the LBD, regulating transcriptional coregulator recruitment and thus nuclear receptor function. These structural studies have aided the development of several FDA-approved drugs, highlighting the importance of understanding the structure-function relationships between lipids and nuclear receptors. However, there are few published descriptions of full-length nuclear receptor structure and even fewer descriptions of how lipids might allosterically regulate full-length structure. Here, we examine multidomain interactions based on the published full-length nuclear receptor structures, evaluating the potential of interdomain interfaces within these nuclear receptors to act as inducible sites of allosteric regulation by lipids.

New Perspectives on Sex Steroid Hormones Signaling in Cancer-Associated Fibroblasts of Non-Small Cell Lung Cancer

The importance of sex hormones, especially estrogen, in the pathogenesis of non-small-cell lung cancer (NSCLC) has attracted attention due to its high incidence among young adults and nonsmokers, especially those who are female. Cancer-associated fibroblasts (CAFs) reside in the cancer stroma and influence cancer growth, invasion, metastasis, and acquisition of drug resistance through interactions with cancer cells and other microenvironmental components. Hormone-mediated cell-cell interactions are classic cell-cell interactions and well-known phenomena in breast cancer and prostate cancer CAFs. In cancers of other organs, including NSCLC, the effects of CAFs on hormone-receptor expression and hormone production in cancer tissues have been reported; however, there are few such studies. Many more studies have been performed on breast and prostate cancers. Recent advances in technology, particularly single-cell analysis techniques, have led to significant advances in the classification and function of CAFs. However, the importance of sex hormones in cell-cell interactions of CAFs in NSCLC remains unclear. This review summarizes reports on CAFs in NSCLC and sex hormones in cancer and immune cells surrounding CAFs. Furthermore, we discuss the prospects of sex-hormone research involving CAFs in NSCLC.

Structural insights into the HNF4 biology

Hepatocyte Nuclear Factor 4 (HNF4) is a transcription factor (TF) belonging to the nuclear receptor (NR) family that is expressed in liver, kidney, intestine and pancreas. It is a master regulator of liver-specific gene expression, in particular those genes involved in lipid transport and glucose metabolism and is crucial for the cellular differentiation during development. Dysregulation of HNF4 is linked to human diseases, such as type I diabetes (MODY1) and hemophilia. Here, we review the structures of the isolated HNF4 DNA binding domain (DBD) and ligand binding domain (LBD) and that of the multidomain receptor and compare them with the structures of other NRs. We will further discuss the biology of the HNF4α receptors from a structural perspective, in particular the effect of pathological mutations and of functionally critical post-translational modifications on the structure-function of the receptor.

Pathological discrimination between luteinized thecoma associated with sclerosing peritonitis and thecoma

BACKGROUND

Similarities between luteinized thecoma associated with sclerosing peritonitis (LTSP) and thecoma, cause difficulty in clinical differential diagnoses. To improve the situation, we selected 10 specified molecular pathological markers that are frequently used in clinical pathology of ovarian sex cord-stromal tumors to determine whether they exert a discriminatory effect.

METHODS

Applying immunohistochemistry, we analyzed the expression of alpha-1,6-mannosylglycoprotein 6-beta-n-acetylglucosaminyltransferase B (MGAT5B), nuclear receptor coactivator 3 (NCOA3), proliferation marker protein Ki-67 (MKI67), estrogen receptor, progesterone receptor, Vimentin, receptor tyrosine-protein kinase erbB-2, Catenin beta-1 (β-Catenin), CD99 antigen (CD99) and Wilms tumor protein (WT1) in 102 cases of diseases containing 11 LTSP and 91 thecoma. Whole-exome sequencing and fluorescence in situ hybridization were used to examine the MGAT5B-NCOA3 fusion gene in LTSP. Statistical analysis was performed using t test, one-way analysis of variance test, and post hoc test.

RESULTS

Six significant markers were verified for the discrimination between LTSP and thecoma, containing 4 upregulating indicators MGAT5B, NCOA3, MKI67, β-Catenin, and 2 downregulating markers CD99 and WT1 in luteinized cells. In addition, the MGAT5B-NCOA3 fusion gene was identified in LTSP for the first time with significantly rich expression compared to thecoma.

CONCLUSIONS

We verified 6 significant molecular pathological markers containing MGAT5B, NCOA3, MKI67, β-Catenin, CD99, and WT1 and identified MGAT5B-NCOA3 fusion gene in LTSP; this work will help clinicians to discriminate between medical conditions and treat patients accurately.

Post-translational modifications of histones: Mechanisms, biological functions, and therapeutic targets

Histones are DNA-binding basic proteins found in chromosomes. After the histone translation, its amino tail undergoes various modifications, such as methylation, acetylation, phosphorylation, ubiquitination, malonylation, propionylation, butyrylation, crotonylation, and lactylation, which together constitute the "histone code." The relationship between their combination and biological function can be used as an important epigenetic marker. Methylation and demethylation of the same histone residue, acetylation and deacetylation, phosphorylation and dephosphorylation, and even methylation and acetylation between different histone residues cooperate or antagonize with each other, forming a complex network. Histone-modifying enzymes, which cause numerous histone codes, have become a hot topic in the research on cancer therapeutic targets. Therefore, a thorough understanding of the role of histone post-translational modifications (PTMs) in cell life activities is very important for preventing and treating human diseases. In this review, several most thoroughly studied and newly discovered histone PTMs are introduced. Furthermore, we focus on the histone-modifying enzymes with carcinogenic potential, their abnormal modification sites in various tumors, and multiple essential molecular regulation mechanism. Finally, we summarize the missing areas of the current research and point out the direction of future research. We hope to provide a comprehensive understanding and promote further research in this field.

Cryo-EM technique and its application: Structure of steroid hormone receptors

In recent years, cryo-electron microscopy (cryo-EM) has become one of the most powerful tools to solve the 3-D structure of macromolecules. Unlike X-ray crystallography, the cryo-EM method has advantage of providing an in-depth insight into the dynamic behavior of macromolecules, which is particularly useful to determine 3-D structural analyses of large protein complexes. Due to recent technical advancements, cryo-EM has become the method of choice for the determination of protein structures. Among other proteins, solving 3-D structure of steroid hormone receptors (SHRs) complexed with DNA and coactivators has been a challenge for decades. The limitations with X-ray crystallography and NMR to solve SHR protein structures prompted investigators to move towards cryo-EM technique. The cryo-EM structural analyses have been successful in revealing structural dynamics of several SHRs in recent years. Though, limited by low-resolution, the structural analyses of these SHRs may be useful in understanding many receptor functions as well as provide a platform to refine high-resolution structural analyses in future. This review article discusses the cryo-EM technique in general as well as structural information gained for SHRs using cryo-EM.

Structure and functions of the N-terminal domain of steroid hormone receptors

The steroid hormone receptors (SHRs) belong to the large superfamily of nuclear receptors that selectively modulate gene expression in response to specific hormone ligands. The SHRs are required in a broad range of normal physiological processes as well as associated with numerous pathological conditions. Over years, the understanding of the SHR biology and mechanisms of their actions on target cells have found many clinical applications and management of various endocrine-related disorders. However, the effectiveness of SHR-based therapies in endocrine-related cancers remain a clinical challenge. This, in part, is due to the lack of in-depth understanding of structural dynamics and functions of SHRs' intrinsically disordered N-terminal domain (NTD). Recent progress in delineating SHR structural information and their correlations with receptor action in a highly dynamic environment is ultimately helping to explain how diverse SHR signaling mechanisms can elicit selective biological effects. Recent developments are providing new insights of how NTD's structural flexibility plays an important role in SHRs' allosteric regulation leading to the fine tuning of target gene expression to more precisely control SHRs' cell/tissue-specific functions. In this review article, we are discussing the up-to-date knowledge about the SHR actions with a particular emphasis on the structure and functions of the NTD.

Non-Coding RNAs Modulating Estrogen Signaling and Response to Endocrine Therapy in Breast Cancer

The largest part of human DNA is transcribed into RNA that does not code for proteins. These non-coding RNAs (ncRNAs) are key regulators of protein-coding gene expression and have been shown to play important roles in health, disease and therapy response. Today, endocrine therapy of ERα-positive breast cancer (BC) is a successful treatment approach, but resistance to this therapy is a major clinical problem. Therefore, a deeper understanding of resistance mechanisms is important to overcome this resistance. An increasing amount of evidence demonstrate that ncRNAs affect the response to endocrine therapy. Thus, ncRNAs are considered versatile biomarkers to predict or monitor therapy response. In this review article, we intend to give a summary and update on the effects of microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) on estrogen signaling in BC cells, this pathway being the target of endocrine therapy, and their role in therapy resistance. For this purpose, we reviewed articles on these topics listed in the PubMed database. Finally, we provide an assessment regarding the clinical use of these ncRNA types, particularly their circulating forms, as predictive BC biomarkers and their potential role as therapy targets to overcome endocrine resistance.

Quaternary glucocorticoid receptor structure highlights allosteric interdomain communication

The glucocorticoid receptor (GR) is a ligand-activated transcription factor that binds DNA and assembles co-regulator complexes to regulate gene transcription. GR agonists are widely prescribed to people with inflammatory and autoimmune diseases. Here we present high-resolution, multidomain structures of GR in complex with ligand, DNA and co-regulator peptide. The structures reveal how the receptor forms an asymmetric dimer on the DNA and provide a detailed view of the domain interactions within and across the two monomers. Hydrogen-deuterium exchange and DNA-binding experiments demonstrate that ligand-dependent structural changes are communicated across the different domains in the full-length receptor. This study demonstrates how GR forms a distinct architecture on DNA and how signal transmission can be modulated by the ligand pharmacophore, provides a platform to build a new level of understanding of how receptor modifications can drive disease progression and offers key insight for future drug design.

The marionette mechanism of domain-domain communication in the antagonist, agonist, and coactivator responses of the estrogen receptor

The human estrogen receptor α (hERα) is involved in the regulation of growth, development, and tissue homeostasis. Agonists that bind to the receptor's ligand-binding domain (LBD) lead to recruitment of coactivators and the enhancement of gene expression. In contrast, antagonists bind to the LBD and block the binding of coactivators thus decreasing gene expressions. In this work, we carry out simulations using the AWSEM (Associative memory, Water mediated, Structure and Energy Model)-Suite force field along with the 3SPN.2C force field for DNA to predict the structure of hERα and study its dynamics when binding to DNA and coactivators. Using simulations of antagonist-bound hERα and agonist-bound hERα by themselves and also along with bound DNA and coactivators, principal component analyses and free energy landscape analyses capture the pathway of domain-domain communication for agonist-bound hERα. This communication is mediated through the hinge domains that are ordinarily intrinsically disordered. These disordered segments manipulate the hinge domains much like the strings of a marionette as they twist in different ways when antagonists or agonists are bound to the ligand-binding domain.

Cytochrome P450 1B1 Expression Regulates Intracellular Iron Levels and Oxidative Stress in the Retinal Endothelium

Cytochrome P450 (CYP) 1B1 is a heme-containing monooxygenase found mainly in extrahepatic tissues, including the retina. CYP1B1 substrates include exogenous aromatic hydrocarbons, such as dioxins, and endogenous bioactive compounds, including 17β-estradiol (E2) and arachidonic acid. The endogenous compounds and their metabolites are mediators of various cellular and physiological processes, suggesting that CYP1B1 activity is likely important in maintaining proper cellular and tissue functions. We previously demonstrated that lack of CYP1B1 expression and activity are associated with increased levels of reactive oxygen species and oxidative stress in the retinal vasculature and vascular cells, including retinal endothelial cells (ECs). However, the detailed mechanism(s) of how CYP1B1 activity modulates redox homeostasis remained unknown. We hypothesized that CYP1B1 metabolism of E2 affects bone morphogenic protein 6 (BMP6)-hepcidin-mediated iron homeostasis and lipid peroxidation impacting cellular redox state. Here, we demonstrate retinal EC prepared from Cyp1b1-deficient (Cyp1b1-/-) mice exhibits increased estrogen receptor-α (ERα) activity and expresses higher levels of BMP6. BMP6 is an inducer of the iron-regulatory hormone hepcidin in the endothelium. Increased hepcidin expression in Cyp1b1-/- retinal EC resulted in decreased levels of the iron exporter protein ferroportin and, as a result, increased intracellular iron accumulation. Removal of excess iron or antagonism of ERα in Cyp1b1-/- retinal EC was sufficient to mitigate increased lipid peroxidation and reduce oxidative stress. Suppression of lipid peroxidation and antagonism of ERα also restored ischemia-mediated retinal neovascularization in Cyp1b1-/- mice. Thus, CYP1B1 expression in retinal EC is important in the regulation of intracellular iron levels, with a significant impact on ocular redox homeostasis and oxidative stress through modulation of the ERα/BMP6/hepcidin axis.

Structure-function relationships of the aldosterone receptor

The cellular response to the adrenal steroid aldosterone is mediated by the mineralocorticoid receptor (MR), a member of the nuclear receptor superfamily of ligand-dependent transcription factors. The MR binds more than one physiological ligand with binding at the MR determined by pre-receptor metabolism of glucocorticoid ligands by 11β hydroxysteroid dehydrogenase type 2. The MR has a wide tissue distribution with multiple roles beyond the classical role in electrolyte homeostasis including cardiovascular function, immune cell signaling, neuronal fate and adipocyte differentiation. The MR has three principal functional domains, an N-terminal ligand domain, a central DNA binding domain and a C-terminal, ligand binding domain, with structures having been determined for the latter two domains but not for the whole receptor. MR signal-transduction can be best viewed as a series of interactions which are determined by the conformation conferred on the receptor by ligand binding. This conformation then determines subsequent intra- and inter-molecular interactions. These interactions include chromatin, coregulators and other transcription factors, and additional less well characterized cytoplasmic non-genomic effects via crosstalk with other signaling pathways. This chapter will provide a review of MR structure and function, and an analysis of the critical interactions involved in MR-mediated signal transduction, which contribute to ligand- and tissue-specificity. Understanding the relevant mechanisms for selective MR signaling in terms of these interactions opens the possibility of novel therapeutic approaches for the treatment of MR-mediated diseases.

Multilayered allosteric modulation of coupled folding and binding by phosphorylation, peptidyl-prolyl cis/trans isomerization, and diversity of interaction partners

Intrinsically disordered proteins (IDPs) play key roles in cellular regulation, including signal transduction, transcription, and cell-cycle control. Accordingly, IDPs can commonly interact with numerous different target proteins, and their interaction networks are expected to be highly regulated. However, many of the underlying regulatory mechanisms have remained unclear. Here, we examine the representative case of the nuclear coactivator binding domain (NCBD) of the large multidomain protein CBP, a hub in transcriptional regulation, and the interaction with several of its binding partners. Single-molecule Förster resonance energy transfer measurements show that phosphorylation of NCBD reduces its binding affinity, with effects that vary depending on the binding partner and the site and number of modifications. The complexity of the interaction is further increased by the dependence of the affinities on peptidyl-prolyl cis/trans isomerization in NCBD. Overall, our results reveal the potential for allosteric regulation on at least three levels: the different affinities of NCBD for its different binding partners, the differential modulation of these affinities by phosphorylation, and the effect of peptidyl-prolyl cis/trans isomerization on binding.

Interactions governing transcriptional activity of nuclear receptors

The key players in transcriptional regulation are transcription factors (TFs), proteins that bind specific DNA sequences. Several mechanisms exist to turn TFs ‘on’ and ‘off’, including ligand binding which induces conformational changes within TFs, subsequently influencing multiple inter- and intramolecular interactions to drive transcriptional responses. Nuclear receptors are a specific family of ligand-regulated TFs whose activity relies on interactions with DNA, coregulator proteins and other receptors. These multidomain proteins also undergo interdomain interactions on multiple levels, further modulating transcriptional outputs. Cooperation between these distinct interactions is critical for appropriate transcription and remains an intense area of investigation. In this review, we report and summarize recent findings that continue to advance our mechanistic understanding of how interactions between nuclear receptors and diverse partners influence transcription.

Steroid receptor coactivators - their role in immunity

Steroid Receptor Coactivators (SRCs) are essential regulators of transcription with a wide range of impact on human physiology and pathology. In immunology, SRCs play multiple roles; they are involved in the regulation of nuclear factor-κB (NF-κB), macrophage (MΦ) activity, lymphoid cells proliferation, development and function, to name just a few. The three SRC family members, SRC-1, SRC-2 and SRC-3, can exert their immunological function either in an independent manner or act in synergy with each other. In certain biological contexts, one SRC family member can compensate for lack of activity of another member, while in other cases one SRC can exert a biological function that competes against the function of another family counterpart. In this review we illustrate the diverse biological functionality of the SRCs with regard to their role in immunity. In the light of recent development of SRC small molecule inhibitors and stimulators, we discuss their potential relevance as modulators of the immunological activity of the SRCs for therapeutic purposes.

Spatial definition of the human progesterone receptor-B transcriptional complex

We report the quaternary structure of core transcriptional complex for the full-length human progesterone receptor-B (PR-B) homodimer with primary coactivator steroid receptor coactivator-2 (SRC-2) and the secondary coactivator p300/CREB-binding protein (CBP). The PR-B homodimer engages one SRC-2 mainly through its activation function 1 (AF1) in N-terminus. SRC-2 is positioned between PR-B and p300 leaving space for direct interaction between PR-B and p300 through PR-B's C-terminal AF2 and its unique AF3. Direct AF3/p300 interaction provides long-desired structural insights into the known functional differences between PR-B and the PR-A isoform lacking AF3. We reveal the contributions of each AF and demonstrate their structural basis in forming the PR-B dimer interface and PR-B/coactivator complex. Comparison of the PR-B/coactivator complex with other steroid receptor (estrogen receptor and androgen receptor) complexes also shows that each receptor has its unique mechanism for recruiting coactivators due to the highly variable N-termini among receptors.

Retinoic acid receptor structures: the journey from single domains to full-length complex

The retinoic acid receptors (RARα, β, and γ) are multi-domain polypeptides that heterodimerize with retinoid X receptors (RXRα, β, and γ) to form functional transcription factors. Understanding the three-dimensional molecular organization of these nuclear receptors (NRs) began with RAR and RXR DNA-binding domains (DBDs), and were followed with studies on isolated ligand-binding domains (LBDs). The more complete picture emerged in 2017 with the multi-domain crystal structure of RXRα-RARβ on its response element with retinoic acid molecules and coactivator segments on both proteins. The analysis of that structure and its complementary studies have clarified the direct communication pathways within RXR-RAR polypeptides, through which DNA binding, protein-ligand, and protein-protein interactions are integrated for overall functional responses. Understanding the molecular connections in the RXR-RAR complex has benefited from direct observations of the multi-domain structures of RXRα-PPARγ, RXRα-LXRβ, HNF-4α homodimer, and androgen receptor homodimer, each bound to its response element. These comprehensive NR structures show unique quaternary architectures, yet all have DBD-DBD, LBD-LBD, and DBD-LBD domain-domain contacts within them. These convergence zones allow signals from discrete domains of their polypeptides to be propagated and integrated across their entire complex, shaping their overall responses in an allosteric fashion.

Activation function 1 of progesterone receptor is required for progesterone antagonism of oestrogen action in the uterus

BACKGROUND

Progesterone receptor (PGR) is a master regulator of uterine function through antagonistic and synergistic interplays with oestrogen receptors. PGR action is primarily mediated by activation functions AF1 and AF2, but their physiological significance is unknown.

RESULTS

We report the first study of AF1 function in mice. The AF1 mutant mice are infertile with impaired implantation and decidualization. This is associated with a delay in the cessation of epithelial proliferation and in the initiation of stromal proliferation at preimplantation. Despite tissue selective effect on PGR target genes, AF1 mutations caused global loss of the antioestrogenic activity of progesterone in both pregnant and ovariectomized models. Importantly, the study provides evidence that PGR can exert an antioestrogenic effect by genomic inhibition of Esr1 and Greb1 expression. ChIP-Seq data mining reveals intermingled PGR and ESR1 binding on Esr1 and Greb1 gene enhancers. Chromatin conformation analysis shows reduced interactions in these genes' loci in the mutant, coinciding with their upregulations.

CONCLUSION

AF1 mediates genomic inhibition of ESR1 action globally whilst it also has tissue-selective effect on PGR target genes.

Estrogen receptor α revised: Expression, structure, function, and stability

Estrogen receptor α (ERα) is a ligand-dependent transcription factor that regulates the expression of estrogen-responsive genes. Approximately 70% of patients with breast cancer are ERα positive. Estrogen stimulates cancer cell proliferation and contributes to tumor progression. Endocrine therapies, which suppress the ERα signaling pathway, significantly improve the prognosis of patients with breast cancer. However, the development of de novo or acquired endocrine therapy resistance remains a barrier to breast cancer treatment. Therefore, understanding the regulatory mechanisms of ERα is essential to overcome the resistance to treatment. This review focuses on the regulation of ERα expression, including copy number variation, epigenetic regulation, transcriptional regulation, and stability, as well as functions from the point of view post-translational modifications.

Current strategies and progress for targeting the "undruggable" transcription factors

Transcription factors (TFs) specifically bind to DNA, recruit cofactor proteins and modulate target gene expression, rendering them essential roles in the regulation of numerous biological processes. Meanwhile, mutated or dysregulated TFs are involved in a variety of human diseases. As multiple signaling pathways ultimately converge at TFs, targeting these TFs directly may prove to be more specific and cause fewer side effects, than targeting the upfront conventional targets in these pathways. All these features together endue TFs with great potential and high selectivity as therapeutic drug targets. However, TFs have been historically considered "undruggable", mainly due to their lack of structural information, especially about the appropriate ligand-binding sites and protein-protein interactions, leading to relatively limited choices in the TF-targeting drug design. In this review, we summarize the recent progress of TF-targeting drugs and highlight certain strategies used for targeting TFs, with a number of representative drugs that have been approved or in the clinical trials as examples. Various approaches in targeting TFs directly or indirectly have been developed. Common direct strategies include aiming at defined binding pockets, proteolysis-targeting chimaera (PROTAC), and mutant protein reactivation. In contrast, the indirect ones comprise inhibition of protein-protein interactions between TF and other proteins, blockade of TF expression, targeting the post-translational modifications, and targeting the TF-DNA interactions. With more comprehensive structural information about TFs revealed by the powerful cryo-electron microscopy technology and predicted by machine-learning algorithms, plus more efficient compound screening platforms and a deeper understanding of TF-disease relationships, the development of TF-targeting drugs will certainly be accelerated in the near future.

A Novel Mechanism of Coactivator Recruitment by the Nurr1 Nuclear Receptor

Nuclear receptors constitute one of the largest families of transcription factors that regulate genes in metazoans in response to small molecule ligands. Many receptors harbor two transactivation domains, one at each end of the protein sequence. Whereas the molecular mechanisms of transactivation mediated by the ligand-binding domain at the C-terminus of the protein are generally well established, the mechanism involving the N-terminal domain called activation function 1 (AF1) has remained elusive. Previous studies implicated the AF1 domain as a significant contributor towards the overall transcriptional activity of the NR4A family of nuclear receptors and suggested that the steroid receptor coactivators (SRCs) play an important role in this process. Here we show that a short segment within the AF1 domain of the NR4A receptor Nurr1 can directly engage with the SRC1 PAS-B domain. We also show that this segment forms a helix upon binding to a largely hydrophobic groove on PAS-B, overlapping with the surface engaged by the STAT6 transcription factor, suggesting that this mode of recruitment could be shared by diverse transcription factors including other nuclear receptors.

CREBBP/EP300 acetyltransferase inhibition disrupts FOXA1-bound enhancers to inhibit the proliferation of ER+ breast cancer cells

Therapeutic targeting of the estrogen receptor (ER) is a clinically validated approach for estrogen receptor positive breast cancer (ER+ BC), but sustained response is limited by acquired resistance. Targeting the transcriptional coactivators required for estrogen receptor activity represents an alternative approach that is not subject to the same limitations as targeting estrogen receptor itself. In this report we demonstrate that the acetyltransferase activity of coactivator paralogs CREBBP/EP300 represents a promising therapeutic target in ER+ BC. Using the potent and selective inhibitor CPI-1612, we show that CREBBP/EP300 acetyltransferase inhibition potently suppresses in vitro and in vivo growth of breast cancer cell line models and acts in a manner orthogonal to directly targeting ER. CREBBP/EP300 acetyltransferase inhibition suppresses ER-dependent transcription by targeting lineage-specific enhancers defined by the pioneer transcription factor FOXA1. These results validate CREBBP/EP300 acetyltransferase activity as a viable target for clinical development in ER+ breast cancer.

Structural overview and perspectives of the nuclear receptors, a major family as the direct targets for small-molecule drugs

The nuclear receptors (NRs) are an evolutionarily related family of transcription factors, which share certain common structural characteristics and regulate the expressions of various genes by recognizing different response elements. NRs play important roles in cell differentiation, proliferation, survival and apoptosis, rendering them indispensable in many physiological activities including growth and metabolism. As a result, dysfunctions of NRs are closely related to a variety of diseases, such as diabetes, obesity, infertility, inflammation, the Alzheimer's disease, cardiovascular diseases, prostate and breast cancers. Meanwhile, small-molecule drugs directly targeting NRs have been widely used in the treatment of above diseases. Here we summarize recent progress in the structural biology studies of NR family proteins. Compared with the dozens of structures of isolated DNA-binding domains (DBDs) and the striking more than a thousand of structures of isolated ligand-binding domains (LBDs) accumulated in the Protein Data Bank (PDB) over thirty years, by now there are only a small number of multi-domain NR complex structures, which reveal the integration of different NR domains capable of the allosteric signal transduction, or the detailed interactions between NR and various coregulator proteins. On the other hand, the structural information about several orphan NRs is still totally unavailable, hindering the further understanding of their functions. The fast development of new technologies in structural biology will certainly help us gain more comprehensive information of NR structures, inspiring the discovery of novel NR-targeting drugs with a new binding site beyond the classic LBD pockets and/or a new mechanism of action.

The extra-nuclear interactome of the estrogen receptors: implications for physiological functions

Over the last decades, a great body of evidence has defined a novel view of the cellular mechanism of action of the steroid hormone 17β-estradiol (E2) through its estrogen receptors (i.e., ERα and ERβ). It is now clear that the E2-activated ERs work both as transcription factors and extra-nuclear plasma membrane-localized receptors. The activation of a plethora of signal transduction cascades follows the E2-dependent engagement of plasma membrane-localized ERs and is required for the coordination of gene expression, which ultimately controls the occurrence of the pleiotropic effects of E2. The definition of the molecular mechanisms by which the ERs locate at the cell surface (i.e., palmitoylation and protein association) determined the quest for understanding the specificity of the extra-nuclear E2 signaling. The use of mice models lacking the plasma membrane ERα localization unveiled that the extra-nuclear E2 signaling is operational in vivo but tissue-specific. However, the underlying molecular details for such ERs signaling diversity in the perspective of the E2 physiological functions in the different cellular contexts are still not understood. Therefore, to gain insights into the tissue specificity of the extra-nuclear E2 signaling to physiological functions, here we reviewed the known ERs extra-nuclear interactors and tried to extrapolate from available databases the ERα and ERβ extra-nuclear interactomes. Based on literature data, it is possible to conclude that by specifically binding to extra-nuclear localized proteins in different sub-cellular compartments, the ERs fine-tune their molecular activities. Moreover, we report that the context-dependent diversity of the ERs-mediated extra-nuclear E2 actions can be ascribed to the great flexibility of the physical structures of ERs and the spatial-temporal organization of the logistics of the cells (i.e., the endocytic compartments). Finally, we provide lists of proteins belonging to the potential ERα and ERβ extra-nuclear interactomes and propose that the systematic experimental definition of the ERs extra-nuclear interactomes in different tissues represents the next step for the research in the ERs field. Such characterization will be fundamental for the identification of novel druggable targets for the innovative treatment of ERs-related diseases.

Steroid Receptor Coregulators Can Modulate the Action of Progesterone Receptor during the Estrous Cycle in Cow Endometrium

Simple Summary

Proper functioning of the endometrium is necessary for the implantation of the embryo after fertilization and its development throughout pregnancy. The key role in this process plays appropriate action of progesterone through the nuclear receptor isoforms. The action of the receptor is regulated by the attachment of receptor modulators called coregulators which include coactivators and corepressors. Their improper expression in humans causes a malfunction of progesterone receptors and leads to disorders of pregnancy. However, in farm animals, such disorders may be one of the reasons leading up to early embryonic lethality, which in cows reaches up to 40%. Obtained results indicate the important role of the studied coregulators in regulating progesterone activity in endometrial cells, especially during the preimplantation period. Therefore, they can be helpful in better understanding the regulation and expression of the coactivators and corepressors in cow endometrium during the estrous cycle and can contribute to reducing this problem. They can also be of significant practical importance, making for the increased efficiency of breeding these animals.

Abstract

Nuclear receptor coregulators include coactivators and corepressors which associate with the progesterone receptor (PGR) during its activation. Fluctuations in the transcription levels of their respective genes and subsequent protein production as well as in related activities for histone acetyltransferase (HAT) and histone deacetylase (HDAC) can affect PGR function and thus change the action of progesterone (P4) in bovine endometrium during the estrous cycle. Endometrial tissue on days 2–5, 6–10, 11–16, and 17–20 of the estrous cycle was used for determination of the mRNA expression levels of coactivators P300, CREB, and SRC-1 along with corepressor NCOR-2 using Real-Time PCR, with protein levels by Western blot. Coregulators cellular localizations were assessed by immunohistochemistry whereas the activities of HAT and HDAC by using EIA. The highest levels of mRNA and proteins for all of the investigated coregulators, as well as the highest levels of activity for HAT and HDAC, were detected over days 2–16 of the estrous cycle. All of the tested coregulatory proteins were localized in the nuclei of endometrial cells. This research indicates the important role of coregulators of the PGR receptor in regulating P4 activity in endometrial cells, especially during the pre-implantation period.

Conformational Changes of RORγ During Response Element Recognition and Coregulator Engagement

The retinoic acid receptor-related orphan receptor γ (RORγ) is a ligand-dependent transcription factor of the nuclear receptor super family that underpins metabolic activity, immune function, and cancer progression. Despite being a valuable drug target in health and disease, our understanding of the ligand-dependent activities of RORγ is far from complete. Like most nuclear receptors, RORγ must recruit coregulatory protein to enact the RORγ target gene program. To date, a majority of structural studies have been focused exclusively on the RORγ ligand-binding domain and the ligand-dependent recruitment of small peptide segments of coregulators. Herein, we examine the ligand-dependent assembly of full length RORγ:coregulator complexes on cognate DNA response elements using structural proteomics and small angle x-ray scattering. The results from our studies suggest that RORγ becomes elongated upon DNA recognition, preventing long range interdomain crosstalk. We also determined that the DNA binding domain adopts a sequence-specific conformation, and that coregulatory protein may be able to 'sense' the ligand- and DNA-bound status of RORγ. We propose a model where ligand-dependent coregulator recruitment may be influenced by the sequence of the DNA to which RORγ is bound. Overall, the efforts described herein will illuminate important aspects of full length RORγ and monomeric orphan nuclear receptor target gene regulation through DNA-dependent conformational changes.

Structural insights into glucocorticoid receptor function

The glucocorticoid receptor (GR) is a steroid hormone-activated transcription factor that binds to various glucocorticoid response elements to up- or down- regulate the transcription of thousands of genes involved in metabolism, development, stress and inflammatory responses. GR consists of two domains enabling interaction with glucocorticoids, DNA response elements and coregulators, as well as a large intrinsically disordered region that mediates condensate formation. A growing body of structural studies during the past decade have shed new light on GR interactions, providing a new understanding of the mechanisms driving context-specific GR activity. Here, we summarize the established and emerging mechanisms of action of GR, primarily from a structural perspective. This minireview also discusses how the current state of knowledge of GR function may guide future glucocorticoid design with an improved therapeutic index for different inflammatory disorders.

Positive Regulation of Estrogen Receptor Alpha in Breast Tumorigenesis

Estrogen receptor alpha (ERα, NR3A1) contributes through its expression in different tissues to a spectrum of physiological processes, including reproductive system development and physiology, bone mass maintenance, as well as cardiovascular and central nervous system functions. It is also one of the main drivers of tumorigenesis in breast and uterine cancer and can be targeted by several types of hormonal therapies. ERα is expressed in a subset of luminal cells corresponding to less than 10% of normal mammary epithelial cells and in over 70% of breast tumors (ER+ tumors), but the basis for its selective expression in normal or cancer tissues remains incompletely understood. The mapping of alternative promoters and regulatory elements has delineated the complex genomic structure of the ESR1 gene and shed light on the mechanistic basis for the tissue-specific regulation of ESR1 expression. However, much remains to be uncovered to better understand how ESR1 expression is regulated in breast cancer. This review recapitulates the current body of knowledge on the structure of the ESR1 gene and the complex mechanisms controlling its expression in breast tumors. In particular, we discuss the impact of genetic alterations, chromatin modifications, and enhanced expression of other luminal transcription regulators on ESR1 expression in tumor cells.

Transcriptome and Proteome Analysis Revealed Key Pathways Regulating Final Stage of Oocyte Maturation of the Turkey (Meleagris gallopavo)

In birds, the zona pellucida (ZP) matrix that surrounds the ovulated oocyte—called the inner perivitelline layer—is involved in sperm–zona interaction and successful fertilization. To identify the important genes and proteins connected with the final step of egg development, next-generation sequencing and two-dimensional electrophoresis, combined with mass spectrometry, were used for the analysis of mature oocytes at the F1 developmental stage. A total of 8161 genes and 228 proteins were annotated. Six subfamilies of genes, with codes ZP, ZP1–4, ZPD, and ZPAX, were identified, with the dominant expression of ZPD. The main expression site for ZP1 was the liver; however, granulosa cells may also participate in local ZP1 secretion. A ubiquitination system was identified in mature oocytes, where ZP1 was found to be the main ubiquitinated protein. Analysis of transcripts classified in estrogen receptor (ESR) signaling indicated the presence of ESR1 and ESR2, as well as a set of estrogen-dependent genes involved in both genomic and nongenomic mechanisms for the regulation of gene expression by estrogen. Oxidative phosphorylation was found to be a possible source of adenosine triphosphate, and the nuclear factor erythroid 2-related factor 2 signaling pathway could be involved in the response against oxidative stress. Oocyte–granulosa cell communication by tight, adherens, and gap junctions seems to be essential for the final step of oocyte maturation.