The nuclear receptor superfamily: the second decade

Activation of steroid hormone receptors by metabolism-disrupting chemicals

Exposure to metabolism-disrupting chemicals (MDCs), compounds largely belonging to the group of endocrine-disrupting chemicals (EDCs), is associated with metabolic dysfunctions such as dyslipidemia, insulin resistance and hepatic steatosis. Steroid hormone receptors (SHRs) are known targets for MDCs but their regulatory environment in the presence of environmental chemicals remains elusive. Here, we studied the activation and molecular interactions of SHRs exposed to 17 suspected MDCs including pesticides, plasticizers, pharmaceuticals, flame retardants, industrial chemicals and their metabolites by combining in vitro and in silico approaches. We first established and pre-validated reporter gene assays in HepG2 hepatoma cells to assess the activation of estrogen (ER), androgen (AR), glucocorticoid (GR) and progesterone (PR) receptors. Next, using RNA-seq and publicly available protein interaction data, we identified relevant SHR-interacting coregulators expressed in hepatic cells and measured their MDC-dependent interactions with SHRs using the Microarray Assay for Real-time Coregulator-Nuclear receptor Interaction (MARCoNI) technology. Finally, we examined MDC binding to ER and GR using molecular dynamics simulations. These combined approaches lead to identification of MDCs capable of SHR activation at picomolar-to-low micromolar concentrations and paralleled with their ability to induce recruitment of multiple coregulators. MDCs induced distinct SHR-coregulator binding patterns involving multiple coactivators, corepressors and other modulatory proteins. Our results have broadened the test battery to detect MDCs and indicate that the activation of SHRs by MDCs is driven by diverse molecular interactions.

Comparative Evaluation and Profiling of Chemical Tools for the Nuclear Hormone Receptor Family 2

Nuclear receptors regulate transcription in response to ligand signals and enable the pharmacological control of gene expression. However, many nuclear receptors are still poorly explored and are not accessible to ligand-based target identification studies. In particular, most members of the NR2 family are among the least studied proteins of the class, and apart from the retinoid X receptors (RXR), validated NR2 ligands are very rare. Here, we gathered the NR2 modulators reported in literature for comparative profiling in uniform test systems. Most candidate compounds displayed insufficient on-target activity or selectivity to be used as chemical tools for NR2 receptors underscoring the urgent need for further NR2 ligand development. Nevertheless, a small NR2 modulator set could be assembled for application in a chemogenomic fashion. There are 48 ligand-activated transcription factors in humans forming the superfamily of nuclear receptors (NRs, Figure 1a),1,2 which translate (endogenous) ligand signals into changes in gene expression patterns.3 The multifaceted roles of NRs span pivotal physiological processes, encompassing metabolism, inflammation, and cellular differentiation.4 Over decades, the NR1 and NR3 receptor families, including (steroid) hormone receptors and lipid sensors, have emerged as well-explored therapeutic targets of essential drugs like, for example, glucocorticoids as anti-inflammatory drugs, estrogen receptor modulators as contraceptives and anticancer agents, and PPAR agonists as oral antidiabetics.5-7 Despite this progress, a significant portion of the NR superfamily remains understudied, particularly within the NR2 family which comprises the hepatocyte nuclear factor-4 receptors (HNF4α/γ; NR2A1/2), the retinoid X receptors (RXRα/β/γ; NR2B1-3), the testicular receptors (TR2/4; NR2C1/2), the tailless-like receptors (TLX and PNR; NR2E1/3), and the COUP-TF-like receptors (COUP-TF1/2, V-erBA-related gene; NR2F1/2/6).8,9 Apart from RXR, all NR2 receptors are considered as orphan, and their ligands remain widely elusive. Therefore, chemical tools for most NR2 receptors are rare and poorly annotated posing an obstacle to target identification and validation studies. To enable chemogenomics on NR2 receptors and improve annotation, of the few available ligands, we gathered a scarce collection of NR2 modulators (agonists, antagonists, inverse agonists) for comparative evaluation and profiling. While the NR2B family (RXR) is well covered with high-quality ligands and a few early tools are available for NR2E1, we found the available ligands of the NR2A and NR2C families of insufficient quality to be used as chemical tools.

Structural basis for the asymmetric binding of coactivator SRC1 to FXR-RXRα and allosteric communication within the complex

Farnesoid X receptor (FXR) is a promising target for treatment of metabolic associated fatty liver disease (MAFLD). In this study, we employed an integrative approach to investigate the interaction between FXR-RXRα-DNA complex and the entire coactivator SRC1-NRID (nuclear receptor interaction domain). We constructed a multi-domain model of FXR-RXRα-DNA, highlighting the interface between FXR-DBD and LBD. Using HDX-MS, XL-MS, and biochemical assays, we revealed the allosteric communications in FXR-RXRα-DNA upon agonist and DNA binding. We then demonstrated that SRC1 binds only to the coactivator binding surface of FXR within the FXR-RXRα heterodimer, with the NR-box2 and NR-box3 of SRC1 as the key binding motifs. Our findings, which provide the first model of SRC1-NRID in complex with FXR-RXRα-DNA, shed light on the molecular mechanism through which the coactivator asymmetrically interacts with nuclear receptors and provide structural basis for further understanding the function of FXR and its implications in diseases.

The Role of Androgens and Estrogens in Social Interactions and Social Cognition

Gonadal hormones are becoming increasingly recognized for their effects on cognition. Estrogens, in particular, have received attention for their effects on learning and memory that rely upon the functioning of various brain regions. However, the impacts of androgens on cognition are relatively under investigated. Testosterone, as well as estrogens, have been shown to play a role in the modulation of different aspects of social cognition. This review explores the impact of testosterone and other androgens on various facets of social cognition including social recognition, social learning, social approach/avoidance, and aggression. We highlight the relevance of considering not only the actions of the most commonly studied steroids (i.e., testosterone, 17β-estradiol, and dihydrotestosterone), but also that of their metabolites and precursors, which interact with a plethora of different receptors and signalling molecules, ultimately modulating behaviour. We point out that it is also essential to investigate the effects of androgens, their precursors and metabolites in females, as prior studies have mostly focused on males. Overall, a comprehensive analysis of the impact of steroids such as androgens on behaviour is fundamental for a full understanding of the neural mechanisms underlying social cognition, including that of humans.

Estrogen enhances the proliferation, migration, and invasion of papillary thyroid carcinoma via the ERα/KRT19 signaling axis

BACKGROUND

Estrogen is thought to be the reason for the higher prevalence of papillary thyroid carcinoma (PTC) in fertile women; however, more study is required to completely comprehend how estrogen affects PTC development at the cellular level. Therefore, we combined Oxford Nanopore Technologies (ONT) sequencing to explore molecular markers of PTC and to investigate the molecular mechanisms by which estrogen promotes PTC development.

METHODS

The expression levels of ESR1 (ERα) and KRT19 in normal thyroid tissues and cancer tissues as well as in different cancer stages, races, genders, age groups, histological subtypes and nodular metastasis status of the TCGA database were analyzed online by Ualcan; the relationship between ESR1, KRT19 and the survival of THCA patients was analyzed. A PTC xenograft tumor model was established. An ERα specific inhibitor (MPP) was administered and an EDU cell proliferation assay was used to verify the effect of estrogen on PTC proliferation. KRT19 was knocked down in KTC-1 cells, and the proliferation, migration, and invasion abilities of PTC cells were determined using CCK-8, immunofluorescence labeling, Western blot for EMT-related proteins, scratch assay, and Transwell assay. The role of ERα in relation to KRT19 was investigated by Western blot and immunofluorescence. The effects of ERα/KRT19 signaling axis on the proliferation, migration and invasion ability of PTC cells were evaluated using EDU cell proliferation assay and Transwell. Using ONT sequencing, 15 pairs of PTC tissue and paracancer tissue samples were collected. A PPI network was constructed to validate the differential expression of KRT19 in combination with biosignature analysis, and the protein interaction between KRT19 and ESR1 was verified using STRING.

RESULTS

Ualcan showed that the expression of ESR1 and KRT19 was higher in THCA tissues than in normal thyroid tissues. E2 activation of ERα promoted the growth of PTC cells and tissues. si-KRT19 inhibited the proliferation, migration and invasion of PTC cells. KRT19 together with ERα formed the ERα/KRT19 signaling axis. E2 activation of the ERα/KRT19 signaling axis promoted the proliferation, migration, and invasion of PTC cells. ONT sequencing and STRING website verified that KRT19 is significantly differentially expressed in PTC and that ESR1 and KRT19 have protein interactions and are related to the estrogen signaling pathway.

CONCLUSIONS

Using public databases, RNA sequencing, and bioinformatics, we discovered that E2 stimulates the ERα/KRT19 signaling axis to stimulate PTC proliferation, migration, and invasion.

Vitamin D and its analogs in immune system regulation

Vitamin D was discovered as the cure for nutritional rickets, a disease of bone growth arising from inadequate intestinal calcium absorption, and for much of the 20th century, it was studied for its critical role in calcium homeostasis. However, we now recognize that the vitamin D receptor and vitamin D metabolic enzymes are expressed in numerous tissues unrelated to calcium homeostasis. Notably, vitamin D signaling can induce cellular differentiation and cell cycle arrest. Moreover, the vitamin D receptor and the enzyme CYP27B1, which produces the hormonal form of vitamin D, 1,25-dihydroxyvitamin D (1,25D), are expressed throughout the immune system. In addition, CYP27B1 expression in immune cells is regulated by physiological inputs independent of those controlling its expression in calcium homeostatic tissues. These observations have driven the development of 1,25D-like secosteroidal analogs and nonsecosteroidal analogs to separate the effects of vitamin D on cell differentiation and function from its calcemic activities. Notably, some of these analogs have had considerable success in the clinic in the treatment of inflammatory and immune-related disorders. In this review, we described in detail the mechanisms of vitamin D signaling and the physiological signals controlling 1,25D synthesis and catabolism, with a focus on the immune system. We also surveyed the effects of 1,25D and its analogs on the regulation of immune system function and their implications for human immune-related disorders. Finally, we described the potential of vitamin D analogs as anticancer therapeutics, in particular, their use as adjuncts to cancer immunotherapy. SIGNIFICANCE STATEMENT: Vitamin D signaling is active in both the innate and adaptive arms of the immune system. Numerous vitamin D analogs, developed primarily to minimize the dose-limiting hypercalcemia of the active form of vitamin D, have been used widely in preclinical and clinical studies of immune system regulation. This review presents a description of the mechanisms of action of vitamin D signaling, an overview of analog development, and an in-depth discussion of the immunoregulatory roles of vitamin D analogs.

Androgen receptor ubiquitination links KCTD13 to genitourinary tract defects

The potassium channel tetramerization domain containing 13 (KCTD13) protein is a substrate-specific adapter for cullin3-based E3 ubiquitin ligase. Patients with copy number variants at this locus exhibit genitourinary tract anomalies. In this study, we show that decreased androgen receptor (AR) protein level correlated with increased AR ubiquitination in the testis of Kctd13-deficient mice, suggesting that KCTD13 inhibits AR ubiquitination. KCTD13 increased CUL3-dependent AR ubiquitination but had no effect on CUL3 binding to AR, confirming the role of KCTD13 as an adaptor of CUL3 ligase. Recombinant KCTD13 directly binds to recombinant AR, and the BTB domain of KCTD13 is critical for binding both the N-terminal domain of AR and STUB1. Moreover, KCTD13 dose-dependently decreased STUB1 binding to AR resulting in decreased AR ubiquitination. KCTD13 ΔBTB was unable to bind to AR and subsequently failed to block STUB1-mediated AR ubiquitination, strongly suggesting that reduced AR ubiquitination is dependent on KCTD13 ability to dissociate AR/STUB1 complex. Furthermore, KCTD13 increased the expression of AR target gene, FOXJ1, whereas KCTD13 ΔBTB had no effect. Our data reveal a distinctive mode of action of KCTD13 on AR ubiquitination depending on the E3 ubiquitin ligase involved: (1) KCTD13 increased CUL3-dependent AR ubiquitination but had no effect on CUL3 binding to AR; and (2) KCTD13 decreased STUB1-mediated AR ubiquitination by decreasing STUB1 binding to AR thus preventing AR ubiquitination. We hypothesize that in the testes of Kctd13-deficient mice, the absence of KCTD13 results in increased binding of STUB1 to AR leading to increased AR ubiquitination and degradation.

Impact of Estrogen on Purinergic Signaling in Microvascular Disease

Microvascular ischemia, especially in the heart and kidneys, is associated with inflammation and metabolic perturbation, resulting in cellular dysfunction and end-organ failure. Heightened production of adenosine from extracellular nucleotides released in response to inflammation results in protective effects, inclusive of adaptations to hypoxia, endothelial cell nitric oxide release with the regulation of vascular tone, and inhibition of platelet aggregation. Purinergic signaling is modulated by ectonucleoside triphosphate diphosphohydrolase-1 (NTPDase1)/CD39, which is the dominant factor dictating vascular metabolism of extracellular ATP to adenosine throughout the cardiovascular tissues. Excess levels of extracellular purine metabolites, however, have been associated with metabolic and cardiovascular diseases. Physiological estrogen signaling is anti-inflammatory with vascular protective effects, but pharmacological replacement use in transgender and postmenopausal individuals is associated with thrombosis and other side effects. Crucially, the loss of this important sex hormone following menopause or with gender reassignment is associated with worsened pro-inflammatory states linked to increased oxidative stress, myocardial fibrosis, and, ultimately, diastolic dysfunction, also known as Yentl syndrome. While there is a growing body of knowledge on distinctive purinergic or estrogen signaling and endothelial health, much less is known about the relationships between the two signaling pathways. Continued studies of the interactions between these pathways will allow further insight into future therapeutic targets to improve the cardiovascular health of aging women without imparting deleterious side effects.

Simulations Reveal Unique Roles for the FXR Hinge in the FXR-RXR Nuclear Receptor Heterodimer

Nuclear receptors are multidomain transcription factors whose full-length quaternary architecture is poorly described and understood. Most nuclear receptors bind DNA as heterodimers or homodimers, which could encompass a variety of arrangements of the individual domains. Only a handful of experimental structures currently exist describing these architectures. Given that domain interactions and protein-DNA interactions within transcriptional complexes are tightly linked to function, understanding the arrangement of nuclear receptor domains on DNA is of utmost importance. Here, we employ modeling and molecular dynamics (MD) simulations to describe the structure of the full-length farnesoid X receptor (FXR) and retinoid X receptor alpha (RXR) heterodimer bound to DNA. Combining over 100 μs of atomistic MD simulations with enhanced sampling simulations, we characterize the dynamic behavior of eight FXR-RXR-DNA complexes, showing that these complexes support a range of quaternary architectures. Our simulations reveal critical roles for the hinge in the DNA-bound dimer in facilitating interdomain allostery, mediating DNA binding and driving the dynamic flexibility of the complex. These roles have been hard to appreciate previously due to experimental limitations in studying the flexible hinge. These studies provide a much-needed framework that will enable the field to obtain a complete understanding of nuclear receptor quaternary architectures.

Antioxidant-independent activities of alpha-tocopherol

Alpha-tocopherol (vitamin E) is a plant-derived dietary lipid that is essential for the health of most animals, including humans. Originally discovered as a fertility factor in rodents, the primary health-promoting properties of the vitamin in humans was shown to be protection of neuromuscular functions. Heritable vitamin E deficiency manifests in spinocerebellar ataxia that can be stabilized by timely supplementation with high-dose α-tocopherol. The molecular basis for α-tocopherol's biological activities has been attributed primarily to the vitamin's efficacy in preventing lipid peroxidation in membranes and lipoproteins, but the possibility that the vitamin possesses additional biological activities has been postulated and debated in the literature without conclusive resolution. We designed and synthesized a novel analog of α-tocopherol, 6-hydroxymethyl α-tocopherol (6-HMTC), which retains most of the vitamin's structural, physical, and biochemical properties, yet lacks measurable radical-trapping antioxidant activity. 6-HMTC bound to the tocopherol transfer protein with high (nanomolar) affinity, like that of the natural vitamin, attesting to the analog's preservation of structural integrity. Yet, 6-HMTC did not inhibit lipid peroxidation or associated ferroptotic cell death. Notably, 6-HMTC modulated the expression of some genes in a manner essentially identical to that exhibited by α-tocopherol. These findings support the notion that α-tocopherol modulates gene expression via an antioxidant-independent mechanism.

Retinoic Acid Promotes Neuronal Differentiation While Increasing Proteins and Organelles Related to Autophagy

Retinoic acid (RA) is commonly used to differentiate SH-SY5Y neuroblastoma cells. This effect is sustained by a specific modulation of gene transcription, leading to marked changes in cellular proteins. In this scenario, autophagy may be pivotal in balancing protein synthesis and degradation. The present study analyzes whether some autophagy-related proteins and organelles are modified during RA-induced differentiation of SH-SY5Y cells. RA-induced effects were compared to those induced by starvation. SH-SY5Y cells were treated with a single dose of 10 µM RA or grown in starvation, for 3 days or 7 days. After treatments, cells were analyzed at light microscopy and transmission electron microscopy to assess cell morphology and immunostaining for specific markers (nestin, βIII-tubulin, NeuN) and some autophagy-related proteins (Beclin 1, LC3). We found that both RA and starvation differentiate SH-SY5Y cells. Specifically, cell differentiation was concomitant with an increase in autophagy proteins and autophagy-related organelles. However, the effects of a single dose of 10 μM RA persist for at least 7 days, while prolonged starvation produces cell degeneration and cell loss. Remarkably, the effects of RA are modulated in the presence of autophagy inhibitors or stimulators. The present data indicate that RA-induced differentiation is concomitant with an increased autophagy.

Discovery of N-(1,2,4-Thiadiazol-5-yl)benzo[b]oxepine-4-carboxamide Derivatives as Novel Antiresistance Androgen Receptor Antagonists

The ligand-binding pocket of the androgen receptor (AR) is the targeting site of all clinically used AR antagonists. However, various drug-resistant mutations emerged in the pocket. We previously reported a new targeting site at the dimer interface of AR (dimer interface pocket) and identified a novel antagonist M17-B15 that failed in oral administration. In this study, the head part of M17-B15 was substituted with divergent structures. Potent antagonist Z10 with benzo[b]oxepine was first identified. Subsequent structural optimization on the 2-oxopropyl moiety of Z10 generated the more powerful Y5 (IC50 = 0.04 μM). Out of the ordinary, Y5 demonstrated dual mechanisms of action, antagonized AR by disrupting AR dimerization, and induced AR degradation via the ubiquitin-proteasome pathway. Furthermore, Y5 exhibited excellent activity against variant drug-resistant AR mutants comparable to recently approved darolutamide. Furthermore, Y5 effectively suppressed the tumor growth of the LNCaP xenograft via oral administration, providing a potential novel therapeutic for drug-resistant prostate cancer.

The retinoic acid family-like nuclear receptor SmRAR identified by single-cell transcriptomics of ovarian cells controls oocyte differentiation in Schistosoma mansoni

Studies on transcription regulation in platyhelminth development are scarce, especially for parasitic flatworms. Here, we employed single-cell transcriptomics to identify genes involved in reproductive development in the trematode model Schistosoma mansoni. This parasite causes schistosomiasis, a major neglected infectious disease affecting >240 million people worldwide. The pathology of schistosomiasis is closely associated with schistosome eggs deposited in host organs including the liver. Unlike other trematodes, schistosomes exhibit distinct sexes, with egg production reliant on the pairing-dependent maturation of female reproductive organs. Despite this significance, the molecular mechanisms underlying ovary development and oocyte differentiation remain largely unexplored. Utilizing an organ isolation approach for S. mansoni, we extracted ovaries of paired females followed by single-cell RNA sequencing (RNA-seq) with disassociated oocytes. A total of 1967 oocytes expressing 7872 genes passed quality control (QC) filtering. Unsupervised clustering revealed four distinct cell clusters: somatic, germ cells and progeny, intermediate and late germ cells. Among distinct marker genes for each cluster, we identified a hitherto uncharacterized transcription factor of the retinoic acid receptor family, SmRAR. Functional analyses of SmRAR and associated genes like Smmeiob (meiosis-specific, oligonucleotide/oligosaccharide binding motif (OB) domain-containing) demonstrated their pairing-dependent and ovary-preferential expression and their decisive roles in oocyte differentiation of S. mansoni.

Downstream Link of Vitamin D Pathway with Inflammation Irrespective of Plasma 25OHD3: Hints from Vitamin D-Binding Protein (DBP) and Receptor (VDR) Gene Polymorphisms

Background: Vitamin D insufficiency/deficiency is a highly prevalent condition worldwide. At the same time, chronic inflammation is a versatile pathophysiological feature and a common correlate of various disorders, including vitamin D deficiency. Methods: We investigated the possible association of inflammation with 25-hydroxyvitamin D3 (25OHD3) levels and its down-stream pathway by exploring vitamin D-binding protein (DBP) and vitamin D receptor (VDR) genes for single-nucleotide polymorphisms (SNPs), in healthy non-elderly Bahraini adults. Plasma levels of 25OHD3 were measured by chemiluminescence, and six SNPs, four in the GC gene (rs2282679AC, rs4588CA, rs7041GT, and rs2298849TC) and two in the VDR gene (rs731236TC and rs12721377AG) were genotyped by real-time PCR. The concentrations of five inflammatory biomarkers, IL6, IL8, procalcitonin (PCT), TREM1, and uPAR, were measured by ELISA. Results: The results showed no association between the 25OHD3 level and any of the inflammatory markers' levels. However, three tested SNPs were significantly associated with the concentrations of tested biomarkers except for IL6. The TT mutant genotype of rs2298849TC was associated with lower levels of IL8 and higher levels of PCT and TREM1, the AA mutant genotype of rs2282679AC was associated with decreased levels of IL8 (p ≤ 0.001) and increased levels of TREM1 (p = 0.005), and the GG wild genotype of rs12721377AG was associated with increased levels of 25OHD3 (p = 0.026). Conclusions: Although chronic inflammation is not associated with the vitamin D system in the blood, it is downstream, as revealed by DBP and VDR genotyping. Alternatively, DBP and VDR pursue other functions beyond the vitamin D pathway.

The sequence-structure-function relationship of intrinsic ERα disorder

The oestrogen receptor (ER or ERα), a nuclear hormone receptor that drives most breast cancer1, is commonly activated by phosphorylation at serine 118 within its intrinsically disordered N-terminal transactivation domain2,3. Although this modification enables oestrogen-independent ER function, its mechanism has remained unclear despite ongoing clinical trials of kinase inhibitors targeting this region4-6. By integration of small-angle X-ray scattering and nuclear magnetic resonance spectroscopy with functional studies, we show that serine 118 phosphorylation triggers an unexpected expansion of the disordered domain and disrupts specific hydrophobic clustering between two aromatic-rich regions. Mutations mimicking this disruption rescue ER transcriptional activity, target-gene expression and cell growth impaired by a phosphorylation-deficient S118A mutation. These findings, driven by hydrophobic interactions, extend beyond electrostatic models and provide mechanistic insights into intrinsically disordered proteins7, with implications for other nuclear receptors8. This fundamental sequence-structure-function relationship advances our understanding of intrinsic ER disorder, crucial for developing targeted breast cancer therapeutics.

Harnessing nuclear receptors to modulate hepatic stellate cell activation for liver fibrosis resolution

With the recent approval of Resmetirom as the first drug targeting nuclear receptors for metabolic dysfunction-associated steatohepatitis (MASH), there is promising way to treat MASH-associated liver fibrosis. However, liver fibrosis can arise from various pathogenic factors, and effective treatments for fibrosis due to other causes remain elusive. The activation of hepatic stellate cells (HSCs) represents a central link in the pathogenesis of hepatic fibrosis. Therefore, harnessing nuclear receptors to modulate HSC activation may be an effective approach to resolving the complex liver fibrosis caused by various factors. In this comprehensive review, we systematically explore the structure and physiological functions of nuclear receptors, shedding light on their multifaceted roles in HSC activation. Recent advancements in drug development targeting nuclear receptors are discussed, providing insights into their potential as rational and effective therapeutic targets for modulating HSC activation in the context of liver fibrosis. By elucidating the intricate interplay between nuclear receptors and HSC activation, this review contributes to the discovery of new nuclear receptor targets in HSCs for resolving hepatic fibrosis.

Peroxisome proliferator-activated receptor delta and liver diseases

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors involved in transcriptional regulation and play an important role in many physiological and metabolic processes. Unlike PPAR-alpha and PPAR-gamma, PPAR-delta is ubiquitously expressed, and its activity is key to maintaining proper metabolic homeostasis within the liver. PPAR-delta not only regulates physiologic processes of lipid, glucose, and bile acid metabolism but also attenuates pathologic responses to alcohol metabolism, inflammation, fibrosis, and carcinogenesis, and is considered an important therapeutic target in liver diseases. Promising results have been reported in clinical trials for PPAR-delta agonists in liver disease, and the selective agonist seladelpar was recently conditionally approved in the United States as a new treatment option for primary biliary cholangitis. This review provides an overview of PPAR-delta's function and biology in the liver, examines its kinetics and therapeutic potential across different liver diseases, and discusses the current status of clinical trials involving its agonists.

Transcription factors in the development and treatment of immune disorders

Immune function is highly controlled at the transcriptional level by the binding of transcription factors (TFs) to promoter and enhancer elements. Several TF families play major roles in immune gene expression, including NF-κB, STAT, IRF, AP-1, NRs, and NFAT, which trigger anti-pathogen responses, promote cell differentiation, and maintain immune system homeostasis. Aberrant expression, activation, or sequence of isoforms and variants of these TFs can result in autoimmune and inflammatory diseases as well as hematological and solid tumor cancers. For this reason, TFs have become attractive drug targets, even though most were previously deemed "undruggable" due to their lack of small molecule binding pockets and the presence of intrinsically disordered regions. However, several aspects of TF structure and function can be targeted for therapeutic intervention, such as ligand-binding domains, protein-protein interactions between TFs and with cofactors, TF-DNA binding, TF stability, upstream signaling pathways, and TF expression. In this review, we provide an overview of each of the important TF families, how they function in immunity, and some related diseases they are involved in. Additionally, we discuss the ways of targeting TFs with drugs along with recent research developments in these areas and their clinical applications, followed by the advantages and disadvantages of targeting TFs for the treatment of immune disorders.

Recent Insights on the Role of Nuclear Receptors in Alzheimer's Disease: Mechanisms and Therapeutic Application

Nuclear receptors (NRs) are ligand-activated transcription factors that regulate a broad array of biological processes, including inflammation, lipid metabolism, cell proliferation, and apoptosis. Among the diverse family of NRs, peroxisome proliferator-activated receptors (PPARs), estrogen receptor (ER), liver X receptor (LXR), farnesoid X receptor (FXR), retinoid X receptor (RXR), and aryl hydrocarbon receptor (AhR) have garnered significant attention for their roles in neurodegenerative diseases, particularly Alzheimer's disease (AD). NRs influence the pathophysiology of AD through mechanisms such as modulation of amyloid-beta (Aβ) deposition, regulation of inflammatory pathways, and improvement of neuronal function. However, the dual role of NRs in AD progression, where some receptors may exacerbate the disease while others offer therapeutic potential, presents a critical challenge for their application in AD treatment. This review explores the functional diversity of NRs, highlighting their involvement in AD-related processes and discussing the therapeutic prospects of NR-targeting strategies. Furthermore, the key challenges, including the necessity for the precise identification of beneficial NRs, detailed structural analysis through molecular dynamics simulations, and further investigation of NR mechanisms in AD, such as tau pathology and autophagy, are also discussed. Collectively, continued research is essential to clarify the role of NRs in AD, ultimately facilitating their potential use in the diagnosis, prevention, and treatment of AD.

Looking beyond the ER, PR, and HER2: what's new in the ARsenal for combating breast cancer?

Breast cancer (BrCa) is a complex and heterogeneous disease with diverse molecular subtypes, leading to varied clinical outcomes and posing significant treatment challenges. The increasing global burden of BrCa, particularly in low- and middle-income countries, underscores the urgent need for more effective therapeutic strategies. The androgen receptor (AR), expressed in a substantial proportion of breast cancer cases, has emerged as a potential biomarker and therapeutic target. In breast cancer, AR exhibits diverse functions across subtypes, often interacting with other hormone receptors, thereby influencing tumor progression and treatment responses. This intricate interplay is further complicated by the presence of constitutively expressed AR splice variants (AR-Vs) that drive resistance to AR-targeting therapies through structural rearrangements in the domains and activation of aberrant signaling pathways. Although AR-targeting drugs, initially developed for prostate cancer (PCa), have shown promise in AR-positive breast cancer, significant gaps remain in understanding AR's precise functions and therapeutic potential. The systemic management of breast cancer is guided primarily by theranostic biomarkers; ER, PR, HER2, and Ki67 which also dictate the breast cancer classification. The ubiquitous expression of AR in BrCa and the emergence of AR-Vs can assist the management of disease complementing the standard of care. This article provides a comprehensive overview of AR and its splice variants in the context of breast cancer, highlighting their prognostic and predictive value across different subtypes looking beyond the conventional ER, PR, and HER2 status. This review also raises the possibility of using AR splice variants in predicting tumor aggressiveness. From the settings of developing nations, this may provide useful insight by integrating recent advances in AR-targeted therapies and exploring their translational potential, emphasizing the critical need for further research to optimize AR-based therapeutic strategies for breast cancer management.

The Homeobox Transcription Factor NKX3.1 Displays an Oncogenic Role in Castration-Resistant Prostate Cancer Cells

BACKGROUND/OBJECTIVES

Prostate cancer (PCa) is the second leading cause of cancer-related death in men. The increase in incidence rates of more advanced and aggressive forms of the disease year-to-year fuels urgency to find new therapeutic interventions and bolster already established ones. PCa is a uniquely targetable disease in that it is fueled by male hormones (androgens) that drive tumorigenesis via the androgen receptor or AR. Current standard-of-care therapies directly target AR and its aberrant signaling axis but resistance to these therapies commonly arises, and the mechanisms behind the onset of therapy-resistance are still elusive. Research has shown that even with resistant disease, AR remains the main driver of growth and survival of PCa, and AR target genes and cofactors may help mediate resistance to therapy. Here, we focused on a homeobox transcription factor that exhibits a close relationship with AR-NKX3.1. Though NKX3.1 is traditionally thought of as a tumor suppressor, it has been previously reported to promote cancer cell survival by cooperating with AR. The role of NKX3.1 as a tumor suppressor perhaps in early-stage disease also contradicts its profile as a diagnostic biomarker for advanced prostate cancer.

METHODS

We investigated the physical interaction between NKX3.1 and AR, a modulated NKX3.1 expression in prostate cancer cells via overexpression and knockdown and assayed subsequent viability and downstream target gene expression.

RESULTS

We find that the expression of NKX3.1 is maintained in advanced PCa, and it is often elevated because of aberrant AR activity. Transient knockdown experiments across various PCa cell line models reveal NKX3.1 expression is necessary for survival. Similarly, stable overexpression of NKX3.1 in PCa cell lines reveals an androgen insensitive phenotype, suggesting NKX3.1 is sufficient to promote growth in the absence of an AR ligand.

CONCLUSIONS

Our work provides new insight into NKX3.1's oncogenic influence on PCa and the molecular interplay of these transcription factors in models of late-stage prostate cancer.

Mitoxantrone inhibits and downregulates ER α through binding at the DBD-LBD interface

Targeting the estrogen receptor (ER or ERα) through competitive antagonists, receptor downregulators, or estrogen synthesis inhibition remains the primary therapeutic strategy for luminal breast cancer. We have identified a novel mechanism of ER inhibition by targeting the critical interface between its DNA-binding domain (DBD) and ligand-binding domain (LBD). We demonstrate that mitoxantrone (MTO), a topoisomerase II inhibitor, binds at this previously unexplored DBD-LBD interface. Using comprehensive computational, biophysical, biochemical, and cellular analyses, we show that independent of its DNA damage response activity, MTO binding induces distinct conformational changes in ER, leading to its cytoplasmic redistribution and subsequent proteasomal degradation. Notably, MTO effectively inhibits clinically relevant ER mutations (Y537S and D538G) that confer resistance to current endocrine therapies, outperforming fulvestrant in both in vitro and in vivo assays. Our findings establish domain-domain interaction targeting as a viable therapeutic strategy for ER, with translational implications for other nuclear receptors.

NR2F6 regulates stem cell hematopoiesis and myelopoiesis in mice

Nuclear receptors regulate hematopoietic stem cells (HSCs) and peripheral immune cells in mice and humans. The nuclear orphan receptor NR2F6 (EAR-2) has been shown to control murine hematopoiesis. Still, detailed analysis of the distinct stem cell, myeloid, and lymphoid progenitors in the bone marrow in a genetic loss of function model remains pending. In this study, we found that adult germline Nr2f6-deficient mice contained increased percentages of total long-term and short-term HSCs, as well as a subpopulation within the lineage-biased multipotent progenitor (MPP3) cells. The loss of NR2F6 thus led to an increase in the percentage of LSK+ cells. Following the differentiation from the common myeloid progenitors (CMP), the granulocyte-monocyte progenitors (GMP) were decreased, while monocyte-dendritic progenitors (MDP) were increased in Nr2f6-deficient bone marrow. Within the pre-conventional dendritic progenitors (pre-cDCs), the subpopulation of pre-cDC2s was reduced in the bone marrow of Nr2f6-deficient mice. We did not observe differences in the development of common lymphoid progenitor populations. Our findings contrast previous studies but underscore the role of NR2F6 in regulating gene expression levels during mouse bone marrow hematopoiesis and myelopoiesis.

Endocrine treatment mechanisms in triple-positive breast cancer: from targeted therapies to advances in precision medicine

Triple-positive breast cancer (TPBC), defined by the co-expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), poses unique therapeutic challenges due to complex signaling interactions and resulting treatment resistance. This review summarizes key findings on the molecular mechanisms and cross-talk among ER, PR, and HER2 pathways, which drive tumor proliferation and resistance to conventional therapies. Current strategies in TPBC treatment, including endocrine and HER2-targeted therapies, are explored alongside emerging approaches such as immunotherapy and CRISPR/Cas9 gene editing. Additionally, we discuss the tumor microenvironment (TME) and its role in treatment resistance, highlighting promising avenues for intervention through combination therapies and predictive biomarkers. By addressing these interdependent pathways and optimizing therapeutic strategies, precision medicine holds significant potential for improving TPBC patient outcomes and advancing individualized cancer care.

Androgen Signaling in Prostate Cancer: When a Friend Turns Foe

Androgen (AR) signaling is the main signaling for the development of the prostate and its normal functioning. AR is highly specific for testosterone and dihydrotestosterone, significantly contributing to prostate development, physiology, and cancer. All these receptors have emerged as crucial therapeutic targets for PCa. In the year 1966, the Noble prize was awarded to Huggins and Hodge for their groundbreaking discovery of AR. As it is a pioneer transcription factor, it belongs to the steroid hormone receptor family and consists of domains, including DNA binding domain (DBD), hormone response elements (HRE), C-terminal ligand binding domain (LBD), and N-terminal regulatory domains. Structural variations in AR, such as AR gene amplification, LBD mutations, alternative splicing of exons, hypermethylation of AR, and co- regulators, are major contributors to PCa. It's signaling is crucial for the development and functioning of the prostate gland, with the AR being the key player. The specificity of AR for testosterone and dihydrotestosterone is important in prostate physiology. However, when it is dysregulated, AR contributes significantly to PCa. However, the structural variations in AR, such as gene amplification, mutations, alternative splicing, and epigenetic modifications, drive the PCa progression. Therefore, understanding AR function and dysregulation is essential for developing effective therapeutic strategies. Thus, the aim of this review was to examine how AR was initially pivotal for prostate development and how it turned out to show both positive and detrimental implications for the prostate.

The SPARC-related modular calcium binding 1 ( Smoc1 ) regulated by androgen is required for mouse gubernaculum development and testicular descent

ABSTRACT

Testicular descent occurs in two consecutive stages: the transabdominal stage and the inguinoscrotal stage. Androgens play a crucial role in the second stage by influencing the development of the gubernaculum, a structure that pulls the testis into the scrotum. However, the mechanisms of androgen actions underlying many of the processes associated with gubernaculum development have not been fully elucidated. To identify the androgen-regulated genes, we conducted large-scale gene expression analyses on the gubernaculum harvested from luteinizing hormone/choriogonadotropin receptor knockout ( Lhcgr KO) mice, an animal model of inguinoscrotal testis maldescent resulting from androgen deficiency. We found that the expression of secreted protein acidic and rich in cysteine (SPARC)-related modular calcium binding 1 ( Smoc1 ) was the most severely suppressed at both the transcript and protein levels, while its expression was the most dramatically induced by testosterone administration in the gubernacula of Lhcgr KO mice. The upregulation of Smoc1 expression by testosterone was curtailed by the addition of an androgen receptor antagonist, flutamide. In addition, in vitro studies demonstrated that SMOC1 modestly but significantly promoted the proliferation of gubernacular cells. In the cultures of myogenic differentiation medium, both testosterone and SMOC1 enhanced the expression of myogenic regulatory factors such as paired box 7 ( Pax7 ) and myogenic factor 5 ( Myf5 ). After short-interfering RNA-mediated knocking down of Smoc1 , the expression of Pax7 and Myf5 diminished, and testosterone alone did not recover, but additional SMOC1 did. These observations indicate that SMOC1 is pivotal in mediating androgen action to regulate gubernaculum development during inguinoscrotal testicular descent.

Novel FRET-Based Biosensors for Real-Time Monitoring of Estrogen Receptor Dimerization and Translocation Dynamics in Living Cells

Estrogen receptors (ERs), comprising ER α and ER β, are crucial for regulating cell growth and differentiation via homo- and hetero-dimer formation. However, accurately detecting ER dimerization with precise spatiotemporal resolution remains a significant challenge. In this study, fluorescence resonance energy transfer-based biosensors to monitor ER dynamics in real-time, are developed and optimized. This approach involves comprehensive structural analysis, linker comparison, and the selection of optimal fluorescent protein pairs, resulting in three distinct biosensors capable of detecting all ER homo- and hetero-dimerizations within the nucleus. These biosensors are utilized to reveal interactions between ER α/β and calmodulin during dimer formation. Furthermore, by leveraging the ligand-binding domain (LBD) of ER β, ER ββ LBD biosensor is designed for real-time analysis of ER ββ homodimerization in the cytoplasm, enhancing the ability to screen ER dimerization-related drugs. Additionally, we developed a novel ER ββ translocation biosensor, which enables real-time observation of ER ββ translocation to the nucleus-a capability previously unavailable, is developed. This spatiotemporal analysis demonstrates the relevance of ER translocation in response to drug binding efficacy and extracellular matrix changes. Our biosensors offer transformative tools for studying ER dynamics, providing valuable insights for drug screening and the investigation of ER-related cellular processes.

Is genotoxicity a suitable biomarker for monitoring anabolic-androgenic steroids exposure in vivo? A systematic review and meta-analysis

Steroids stand for a class of hormones (natural and synthetic) known to be helpful for a number of disorders. Despite the aforementioned beneficial effects of using these hormones, anabolic-androgenic steroids (AAS) are also widely abused in a non-therapeutic manner for muscle-building and strength-increasing properties that may lead to genotoxicity in different tissues. The present study aims to understand whether genotoxicity may be a suitable biomarker for AAS exposure in vivo in both experimental animal and human studies. All studies published in PubMed/Medline, Scopus, and Web of Science electronic databases that presented data on DNA damage caused by AAS were analyzed. A total of 15 articles were included in this study, and after thoroughly reviewing the studies, a total of 8 articles were classified as Strong, 6 were classified as Moderate, and only 1 was classified as Weak, totaling 14 studies being considered either Strong or Moderate. This classification makes it possible to consider the present findings as reliable. The meta-analysis data revealed a statistically significant difference in Wistar rat testis cells with AAS compared to control for tail length and % tail DNA (p < 0.001), so that the selected articles were considered homogeneous and the I2 of 0% indicated low heterogeneity. In summary, genotoxicity can be considered a suitable biomarker for monitoring AAS exposure as a result of DNA breakage and oxidative DNA damage.

A Combined Approach for Rapid Dereplication of Herb-Drug Interaction Causative Agents in Botanical Extracts-A Molecular Networking Strategy To Identify Potential Pregnane X Receptor (PXR) Modulators in Yohimbe

Despite promising preliminary biology, natural products isolation efforts may be confounded when the active compound is not isolated during bioassay-guided purification or classical pharmacognostic research investigations. A more rational isolation procedure connecting the polypharmacology of an herb to its individual constituents must be applied to better detect bioactive molecules before tedious analytical steps are considered. While Pausinystalia johimbe (yohimbe) has been traditionally used in herbal medicine as a general tonic, an aphrodisiac, a performance enhancer, and an integral part of various dietary supplements, the hydroethanolic extract of yohimbe was identified to possess at least 3-4-fold induction of the pregnane X receptor (PXR) at 30 μg/mL, a key nuclear receptor implicated in adverse interactions, viz., herb-drug interactions (HDIs). For rapid dereplication of potential HDI agents within yohimbe, a novel MS/MS-based molecular networking analysis was integrated with in vitro data and in silico analysis of activity at PXR. Analysis of the molecular network of biologically active fractions resulted in the dereplication of three oxindole alkaloids, 14 indole alkaloids, and eight N-oxide alkaloids as the primary causative agents for PXR induction. The findings of this study indicate that this strategy could effectively guide the rapid dereplication of bioactive causative agents within complex botanical extracts. Additionally, it serves as a proof-of-concept for using integrated MS/MS-based molecular networking analysis to assess the safety profile of botanical supplements.

Discovery of a Novel Non-invasive AR PROTAC Degrader for the Topical Treatment of Androgenetic Alopecia

Elevated expression levels and enhanced activity of androgen receptor (AR) proteins are key factors in the development of androgenetic alopecia (AGA). AR proteolysis-targeting chimera (PROTAC) degraders have shown therapeutic potential, but their poor skin permeability requires invasive delivery methods. In this study, we conducted a structure feature analysis to investigate the effects of different linkers and E3 ligands of AR PROTACs on skin retention properties and degradation potency. Among these, compound C6 was discovered with excellent skin retention properties and nanomolar level AR degradation. By degrading AR, C6 regulated the expression levels of downstream paracrine factors associated with AGA. Additionally, after non-invasive topical application, C6 demonstrated excellent skin accumulation and achieved hair regeneration in an AGA mouse model. Overall, the development of non-invasive C6 offers a promising new strategy for AGA treatment and highlights the potential for using PROTACs in treating other skin diseases.

Nuclear receptor profiling for subtype classification and as prognostic markers in 33 cancer types

Nuclear receptors, a group of 48 transcription factors that regulate a multitude of processes within our body, have long been employed as diagnostic markers or therapeutic targets in breast cancer, prostate cancer, and acute promyelocytic leukemia. Unfortunately, no comprehensive investigation has been conducted on their significance in other cancer types. The current study aimed to explore novel diagnostic markers by classifying nuclear receptors according to their expression patterns based on transcriptome data from The Cancer Genome Atlas on 10,071 tumor samples across 33 cancer types and investigating their association with genetic mutations, histological types, and prognosis. Our analysis showed that 21 cancers, including breast cancer, can be classified into distinct clusters based on their nuclear receptor expression profiles. Moreover, significant differences in overall survival were observed in 9 of the 21 cancer types. Overall, the results of this study indicate that previously overlooked nuclear receptors, such as NR0B1 in lung adenocarcinoma, may prove beneficial in the diagnosis of several cancers.

Robustness of ancestral sequence reconstruction to among-site evolutionary heterogeneity and epistasis

Ancestral sequence reconstruction (ASR) is typically performed using homogeneous evolutionary models, which assume that the same substitution propensities affect all sites and lineages. These assumptions are routinely violated: heterogeneous structural and functional constraints favor different amino acid states at different sites, and these constraints often change among lineages as epistatic substitutions accrue at other sites. To evaluate how realistic violations of the homogeneity assumption affect ASR, we developed site-specific substitution models and parameterized them using data from deep mutational scanning experiments on three protein families; we then used these models to perform ASR on the empirical alignments and on alignments simulated under heterogeneous conditions derived from the experiments. Extensive among-site and -lineage heterogeneity is present in these datasets, but the sequences reconstructed from empirical alignments are almost identical, irrespective of whether heterogeneous or homogeneous models are used for ASR. The rare differences occur primarily when phylogenetic signal is weak - at fast-evolving sites and nodes connected by long branches. When ASR is performed on simulated data, errors in the reconstructed sequences become more likely as branch lengths increase, but incorporating heterogeneity into the model does not improve accuracy. These data establish that ASR is robust to unincorporated realistic forms of evolutionary heterogeneity, because the primary determinant of ASR is phylogenetic signal, not the substitution model. The best way to improve accuracy is therefore not to develop more elaborate models but to apply ASR to densely sampled alignments that maximize phylogenetic signal at the nodes of interest.

The ENDOMIX perspective: how everyday chemical mixtures impact human health and reproduction by targeting the immune system†

Endocrine-disrupting chemicals are natural and synthetic compounds found ubiquitously in the environment that interfere with the hormonal-immune axis, potentially impacting human health and reproduction. Exposure to endocrine-disrupting chemicals has been associated with numerous health risks, such as neurodevelopmental disorders, metabolic syndrome, thyroid dysfunction, infertility, and cancers. Nevertheless, the current approach to establishing causality between these substances and disease outcomes has limitations. Epidemiological and experimental research on endocrine-disrupting chemicals faces challenges in accurately assessing chemical exposure and interpreting non-monotonic dose response curves. In addition, most studies have focused on single chemicals or simple mixtures, overlooking complex real-life exposures and mechanistic insights, in particular regarding endocrine-disrupting chemicals' impact on the immune system. The ENDOMIX project, funded by the EU's Horizon Health Program, addresses these challenges by integrating epidemiological, risk assessment, and immunotoxicology methodologies. This systemic approach comprises the triangulation of human cohort, in vitro, and in vivo data to determine the combined effects of chemical mixtures. The present review presents and discusses current literature regarding human reproduction in the context of immunotolerance and chemical disruption mode of action. It further underscores the ENDOMIX perspective to elucidate the impact of endocrine-disrupting chemicals on immune-reproductive health.

A pan-family screen of nuclear receptors in immunocytes reveals ligand-dependent inflammasome control

Ligand-dependent transcription factors of the nuclear receptor (NR) family regulate diverse aspects of metazoan biology, enabling communications between distant organs via small lipophilic molecules. Here, we examined the impact of each of 35 NRs on differentiation and homeostatic maintenance of all major immunological cell types in vivo through a "Rainbow-CRISPR" screen. Receptors for retinoic acid exerted the most frequent cell-specific roles. NR requirements varied for resident macrophages of different tissues. Deletion of either Rxra or Rarg reduced frequencies of GATA6+ large peritoneal macrophages (LPMs). Retinoid X receptor alpha (RXRα) functioned conventionally by orchestrating LPM differentiation through chromatin and transcriptional regulation, whereas retinoic acid receptor gamma (RARγ) controlled LPM survival by regulating pyroptosis via association with the inflammasome adaptor ASC. RARγ antagonists activated caspases, and RARγ agonists inhibited cell death induced by several inflammasome activators. Our findings provide a broad view of NR function in the immune system and reveal a noncanonical role for a retinoid receptor in modulating inflammasome pathways.

Impacts of Anabolic-androgenic steroid supplementation on female health and offspring: Mechanisms, side effects, and medical perspectives

The increasing prevalence of Anabolic-androgenic steroids (AAS) among women, driven by the pursuit of improved body aesthetics, characterized by higher lean mass and reduced adipose tissue, raises significant health concerns, particularly due to the limited knowledge regarding their effects on the female organism. Prolonged use and/or high doses of AAS are linked to various harmful side effects, including mood changes, psychiatric disorders, voice deepening, clitoromegaly, menstrual irregularities, and cardiovascular complications, prompting medical societies to discourage their widespread use due to insufficient evidence supporting their safety and efficacy. Studies in female rodents have shown that AAS can lead to increased aggression, inflammation, reduced neuronal density, and negative impacts on the myocardium and blood vessels. Additionally, maternal administration of androgens during pregnancy can adversely affect offspring's reproductive, neuronal, and metabolic health, resulting in long-term impairments. The complexity of the mechanisms underlying AAS effects, and their potential genotoxicity remains poorly understood. This review aims to elucidate the various ways in which AAS can impact female physiology and that of their offspring, highlight commonly used anabolic substances, and discuss the positions of medical societies regarding AAS use.

Cellular and molecular mechanisms of action of ovarian steroid hormones. I: Regulation of central nervous system function

The conventional way steroid hormones work through receptors inside cells is widely acknowledged. There are unanswered questions about what happens to the hormone in the end and why there isn't always a strong connection between how much tissue takes up and its biological effects through receptor binding. Steroid hormones can also have non-traditional effects that happen quickly but don't involve entering the cell. Several possible mechanisms for these non-traditional actions include (a) changes in membrane fluidity, (b) steroid hormones acting on receptors on the outer surface of cells, (c) steroid hormones regulating GABAA receptors on cell membranes, and (d) activation of steroid receptors by factors like EGF, IGF-1, and dopamine. Data also suggests that steroid hormones may be inserted into DNA through receptors, acting as transcription factors. These proposed new mechanisms of action should not be seen as challenging the conventional mechanism. Instead, they contribute to a more comprehensive understanding of how hormones work, allowing for rapid, short-term, and prolonged effects to meet the body's physiological needs.

Leveraging nuclear receptor mediated transcriptional signaling for drug discovery: Historical insights and current advances

Nuclear receptors (NRs) are ligand-activated transcription factors that regulate gene expression in response to physiological signals, such as hormones and other chemical messengers. These receptors either activate or repress the transcription of target genes, which in turn promotes or suppresses physiological processes governing growth, differentiation, and homeostasis. NRs bind to specific DNA sequences and, in response to ligand binding, either promote or hinder the assembly of the transcriptional machinery, thereby influencing gene expression at the transcriptional level. These receptors are involved in a wide range of pathological conditions, including cancer, metabolic disorders, chronic inflammatory diseases, and immune system-related disorders. Modulation of NR function through targeted drugs has shown therapeutic benefits in treating such conditions. NR-targeted drugs, which either completely or selectively activate or block receptor function, represent a significant class of clinically valuable therapeutics. However, the pathways of NR-mediated gene expression and the resulting physiological effects are complex, involving crosstalk between various biomolecular components. As a result, NR-targeted drug discovery is challenging. With improved understanding of how NRs regulate physiological functions and deeper insights into their molecular structure, the process of NR-targeted drug discovery has evolved. While many traditional NR-targeting drugs are associated with side effects of varying severity, new drug candidates are being designed to minimize these adverse effects. Given that NR activity varies according to the tissue in which they are expressed and the specific isoform that is activated or repressed, achieving selectivity in targeting specific tissues and isoform classes may help reduce systemic side effects. In a recent breakthrough, the isoform-selective, hepato-targeted thyroid hormone-β agonist, Resmetirom (marketed as Rezdiffra), was approved for the treatment of non-alcoholic steatohepatitis. This chapter explores the structural and mechanistic principles guiding NR-targeted drug discovery and provides insights into recent developments in this field.

Neuroendocrine contribution to sex-related variations in adverse air pollution health effects

Air pollution exposure is ranked as a leading environmental risk factor for not only cardiopulmonary diseases but also for systemic health ailments including diabetes, reproductive abnormalities, and neuropsychiatric disorders, likely mediated by central neural stress mechanisms. Current experimental evidence links many air pollution health outcomes with activation of neuroendocrine sympathetic-adrenal-medullary and hypothalamic-pituitary-adrenal (HPA) stress axes associated with resultant increases in adrenal-derived hormone levels acting as circulating mediators of multi-organ stress reactions. Epidemiological and experimental investigations also demonstrated sex-specific responses to air pollutant inhalation, which may be attributed to hormonal interactions within the stress and reproductive axes. Sex hormones (androgens and estrogens) interact with neuroendocrine functions to influence hypothalamic responses, subsequently augmenting stress-mediated metabolic and immune changes. These neurohormonal interactions may contribute to innate sex-specific responses to inhaled irritants, inducing differing individual susceptibility. The aim of this review was to: (1) examine neuroendocrine co-regulation of the HPA axis by gonadal hormones, (2) provide experimental evidence demonstrating sex-specific respiratory and systemic effects attributed to air pollutant inhalation exposure, and (3) postulate proposed mechanisms of stress and sex hormone interactions during air pollution-related stress.

Retinoic acid receptor-related orphan receptor alpha and synthetic RORα agonist against invasion and metastasis in tongue squamous cell carcinoma

Retinoic acid receptor-related orphan receptor alpha (RORα), an essential tumor suppressor in a range of human malignancies, is classified as a member of the orphan nuclear receptor family. The most prevalent form of oral cancer, tongue squamous cell carcinoma (TSCC) is characterized by its severe malignancy and unfavorable prognosis. However, the extent to which its tumorigenesis mechanisms are associated with RORα expression levels is still not fully understood. The objective of this study was to examine the molecular mechanisms by which RORα is involved in TSCC. Through the use of immunohistochemistry (IHC), it was discovered that the expression level of RORα was significantly downregulated in TSCC tissues when compared to adjacent normal tissues in this study. To further investigate the role of RORα in TSCC, we activated the expression of RORα in human TSCC cell line (SCC9 cells) by transfecting RORα cDNA and using the selective RORα agonist SR1078. The results show that RORα can significantly inhibit the invasion, migration, proliferation, and adhesion of TSCC cells and induce cell apoptosis. In addition, xenograft models confirmed the conclusion that stable activation or treatment with SR1078 to increase RORα content significantly inhibited tumor growth and development. Taken together, this study provides solid evidence for the inhibitory role of RORα in the progression of TSCC. In addition, the preliminary application results of SR1078 in TSCC show that SR1078 is expected to be a potential therapeutic medication for TSCC. These findings provide innovative perspectives on the development of potential biomarkers and agents for TSCC therapy. The objective is to introduce novel strategy and alternatives for the prevention and treatment of TSCC.

Retinoid signaling in pancreas development, islet function, and disease

All-trans retinoic acid (ATRA) signaling is essential in numerous different biological contexts. This review highlights the diverse roles of ATRA during development, function, and diseases of the pancreas. ATRA is essential to specify pancreatic progenitors from gut tube endoderm, endocrine and exocrine differentiation, and adult islet function. ATRA concentration must be carefully regulated during the derivation of islet-like cells from human pluripotent stem cells (hPSCs) to optimize the expression of key pancreatic transcription factors while mitigating adverse and unwanted cell-types in these cultures. The ATRA pathway is integral to the pancreas and here we will present selected studies from decades of research that has laid the essential groundwork for ongoing projects dedicated to unraveling the complexities of ATRA signaling in the pancreas.

Lipid sensing by PPARα: Role in controlling hepatocyte gene regulatory networks and the metabolic response to fasting

Peroxisome proliferator-activated receptors (PPARs) constitute a small family of three nuclear receptors that act as lipid sensors, and thereby regulate the transcription of genes having key roles in hepatic and whole-body energy homeostasis, and in other processes (e.g., inflammation), which have far-reaching health consequences. Peroxisome proliferator-activated receptor isotype α (PPARα) is expressed in oxidative tissues, particularly in the liver, carrying out critical functions during the adaptive fasting response. Advanced omics technologies have provided insight into the vast complexity of the regulation of PPAR expression and activity, as well as their downstream effects on the physiology of the liver and its associated metabolic organs. Here, we provide an overview of the gene regulatory networks controlled by PPARα in the liver in response to fasting. We discuss impacts on liver metabolism, the systemic repercussions and benefits of PPARα-regulated ketogenesis and production of fibroblast growth factor 21 (FGF21), a fasting- and stress-inducible metabolic hormone. We also highlight current challenges in using novel methods to further improve our knowledge of PPARα in health and disease.

Structural perspectives on the androgen receptor, the elusive shape-shifter

The androgen receptor (AR) is a type I nuclear receptor and master transcription factor responsible for development and maintenance of male secondary sex characteristics. Aberrant AR activity is associated with numerous diseases, including prostate cancer, androgen insensitivity syndrome, spinal and bulbar muscular atrophy, and androgenic alopecia. Recent studies have shown that AR adopts numerous conformations that can modulate its ability to bind and transcribe its target DNA substrates, a feature that can be hijacked in the context of cancer. Here, we summarize a series of structural observations describing how this elusive shape-shifter binds to multiple partners, including self-interactions, DNA, and steroid and non-steroidal ligands. We present evidence that AR's pervasive structural plasticity confers an ability to broadly bind and transcribe numerous ligands in the normal and disease state, and explain the structural basis for adaptive resistance mutations to antiandrogen treatment. These evolutionary features are integral to receptor function, and are commonly lost in androgen insensitivity syndrome, or reinforced in cancer.

Role of Peroxisome Proliferator-Activated Receptor α-Dependent Mitochondrial Metabolism in Ovarian Cancer Stem Cells

Peroxisome proliferator-activated receptors (PPARs), including PPAR-α, PPAR-β/δ, and PPAR-γ, are involved in various cellular responses, including metabolism and cell proliferation. Increasing evidence suggests that PPARs are closely associated with tumorigenesis and metastasis. However, the exact role of PPARs in energy metabolism and cancer stem cell (CSC) proliferation remains unclear. This study investigated the role of PPARs in energy metabolism and tumorigenesis in ovarian CSCs. The expression of PPARs and fatty acid consumption as an energy source increased in spheroids derived from A2780 ovarian cancer cells (A2780-SP) compared with their parental cells. GW6471, a PPARα inhibitor, induced apoptosis in A2780-SP. PPARα silencing mediated by small hairpin RNA reduced A2780-SP cell proliferation. Treatment with GW6471 significantly inhibited the respiratory oxygen consumption of A2780-SP cells, with reduced dependency on fatty acids, glucose, and glutamine. In a xenograft tumor transplantation mouse model, intraperitoneal injection of GW6471 inhibited in vivo tumor growth of A2780-SP cells. These results suggest that PPARα plays a vital role in regulating the proliferation and energy metabolism of CSCs by altering mitochondrial activity and that it offers a promising therapeutic target to eradicate CSCs.

Exploring the impact of estrogen-related receptor gamma on metabolism and disease

Estrogen-related receptor gamma (ERRγ) is a member of the ERR orphan nuclear receptor family which possesses three subtypes, α, β, and γ. ERRγ is reportedly predominantly expressed in metabolically active tissues and cells, which promotes positive and negative effects in different tissues. ERRγ overexpression in the liver, pancreas, and thyroid cells is related to liver cancer, oxidative stress, reactive oxygen species (ROS) regulation, and carcinoma. Reduced ERRγ expression in the brain, immune cells, tumor cells, and energy metabolism causes neurological dysfunction, gastric cancer, and obesity. ERRγ is a constitutive receptor; however, its transcriptional activity also depends on co-regulators, agonists, and antagonists, which, when after forming a complex, can play a role in targeting and treating diseases. Moreover, ERRγ has proven crucial in regulating cellular and metabolic activity. However, many functions mediated via ERRγ remain unknown and require further exploration. Hence, considering the importance of ERRγ, this review focuses on the critical findings and interactions between ERRγ and co-regulators, agonists, and antagonists alongside its relationship with downstream and upstream signaling pathways and diseases. This review highlights new findings and provides a path to understanding the current ideas and future studies on ERRγ-mediated cellular activity.

Genes Related to Motility in an Ionizing Radiation and Estrogen Breast Cancer Model

Breast cancer is a major global health concern as it is the primary cause of cancer death for women. Environmental radiation exposure and endogenous factors such as hormones increase breast cancer risk, and its development and spread depend on cell motility and migration. The expression of genes associated with cell motility, such as ADAM12, CYR61, FLRT2, SLIT2, VNN1, MYLK, MAP1B, and TUBA1A, was analyzed in an experimental breast cancer model induced by radiation and estrogen. The results showed that TUBA1A, SLIT2, MAP1B, MYLK, and ADAM12 gene expression increased in the irradiated Alpha3 cell line but not in the control or the malignant Tumor2 cell line. Bioinformatic analysis indicated that FLERT2, SLIT2, VNN1, MAP1B, MYLK, and TUBA1A gene expressions were found to be higher in normal tissue than in tumor tissue of breast cancer patients. However, ADAM12 and CYR61 expressions were found to be higher in tumors than in normal tissues, and they had a negative correlation with ESR1 gene expression. Concerning ESR2 gene expression, there was a negative correlation with CYR61, but there was a positive correlation with FLRT2, MYLK, MAP1B, and VNN1. Finally, a decreased survival rate was observed in patients exhibiting high expression levels of TUBA1A and MAP1B. These genes also showed a negative ER status, an important parameter for endocrine therapy. The genes related to motility were affected by ionizing radiation, confirming its role in the initiation process of breast carcinogenesis. In conclusion, the relationship between the patient's expression of hormone receptors and genes associated with cell motility presents a novel prospect for exploring therapeutic strategies.

Bile Acid Signaling in Metabolic and Inflammatory Diseases and Drug Development

Bile acids are the end products of cholesterol catabolism. Hepatic bile acid synthesis accounts for a major fraction of daily cholesterol turnover in humans. Biliary secretion of bile acids generates bile flow and facilitates biliary secretion of lipids, endogenous metabolites, and xenobiotics. In intestine, bile acids facilitate the digestion and absorption of dietary lipids and fat-soluble vitamins. Through activation of nuclear receptors and G protein-coupled receptors and interaction with gut microbiome, bile acids critically regulate host metabolism and innate and adaptive immunity and are involved in the pathogenesis of cholestasis, metabolic dysfunction-associated steatotic liver disease, alcohol-associated liver disease, type-2 diabetes, and inflammatory bowel diseases. Bile acids and their derivatives have been developed as potential therapeutic agents for treating chronic metabolic and inflammatory liver diseases and gastrointestinal disorders. SIGNIFICANCE STATEMENT: Bile acids facilitate biliary cholesterol solubilization and dietary lipid absorption, regulate host metabolism and immunity, and modulate gut microbiome. Targeting bile acid metabolism and signaling holds promise for treating metabolic and inflammatory diseases.

Retinoid X receptor heterodimers in hepatic function: structural insights and therapeutic potential

Nuclear receptors (NRs) are key regulators of multiple physiological functions and pathological changes in the liver in response to a variety of extracellular signaling changes. Retinoid X receptor (RXR) is a special member of the NRs, which not only responds to cellular signaling independently, but also regulates multiple signaling pathways by forming heterodimers with various other NR. Therefore, RXR is widely involved in hepatic glucose metabolism, lipid metabolism, cholesterol metabolism and bile acid homeostasis as well as hepatic fibrosis. Specific activation of particular dimers regulating physiological and pathological processes may serve as important pharmacological targets. So here we describe the basic information and structural features of the RXR protein and its heterodimers, focusing on the role of RXR heterodimers in a number of physiological processes and pathological imbalances in the liver, to provide a theoretical basis for RXR as a promising drug target.

Extra-nuclear and cytoplasmic steroid receptor signalling in hormone dependent cancers

Steroid hormone receptors are key mediators in the execution of hormone action through a combination of genomic and non-genomic action. Since their isolation and characterisation in the early 20th Century much of our understanding of the biological actions of steroid hormones are underpinned by their activated receptor activity. Over the past two decades there has been an acceleration of more omics-based research which has resulted in a major uptick in our comprehension of genomic steroid action. However, it is well understood that steroid hormones can induce very rapid signalling events in tandem with their genomic actions wherein they exert their influence through alterations in gene expression. Thus the totality of genomic and non-genomic steroid action occurs in a simultaneous and reciprocal manner and a greater appreciation of whole cell action is required to fully evaluate steroid hormone activity in vivo. In this mini-review we outline the most recent developments in non-genomic steroid action and cytoplasmic steroid hormone receptor biology in endocrine-related cancers with a focus on the 3-keto steroid receptors, in particular the androgen receptor.

Discovering novel targets of abscisic acid using computational approaches

Abscisic acid (ABA) is a crucial plant hormone that is naturally produced in various mammalian tissues and holds significant potential as a therapeutic molecule in humans. ABA is selected for this study due to its known roles in essential human metabolic processes, such as glucose homeostasis, immune responses, cardiovascular system, and inflammation regulation. Despite its known importance, the molecular mechanism underlying ABA's action remain largely unexplored. This study employed computational techniques to identify potential human ABA receptors. We screened 64 candidate molecules using online servers and performed molecular docking to assess binding affinity and interaction types with ABA. The stability and dynamics of the best complexes were investigated using molecular dynamics simulation over a 100 ns time period. Root mean square fluctuations (RMSF), root mean square deviation (RMSD), solvent-accessible surface area (SASA), radius of gyration (Rg), free energy landscape (FEL), and principal component analysis (PCA) were analyzed. Next, the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) method was employed to calculate the binding energies of the complexes based on the simulated data. Our study successfully pinpointed four key receptors responsible for ABA signaling (androgen receptor, glucocorticoid receptor, mineralocorticoid receptor, and retinoic acid receptor beta) that have a strong affinity for binding with ABA and remained structurally stable throughout the simulations. The simulations with Hydralazine as an unrelated ligand were conducted to validate the specificity of the identified receptors for ABA. The findings of this study can contribute to further experimental validation and a better understanding of how ABA functions in humans.