Ferroptosis surveillance independent of GPX4 and differentially regulated by sex hormones.

Ferroptosis, a cell death process driven by iron-dependent phospholipid peroxidation, has been implicated in various diseases. There are two major surveillance mechanisms to suppress ferroptosis: one mediated by glutathione peroxidase 4 (GPX4) that catalyzes the reduction of phospholipid peroxides and the other mediated by enzymes, such as FSP1, that produce metabolites with free radical-trapping antioxidant activity. In this study, through a whole-genome CRISPR activation screen, followed by mechanistic investigation, we identified phospholipid-modifying enzymes MBOAT1 and MBOAT2 as ferroptosis suppressors. MBOAT1/2 inhibit ferroptosis by remodeling the cellular phospholipid profile, and strikingly, their ferroptosis surveillance function is independent of GPX4 or FSP1. MBOAT1 and MBOAT2 are transcriptionally upregulated by sex hormone receptors, i.e., estrogen receptor (ER) and androgen receptor (AR), respectively. A combination of ER or AR antagonist with ferroptosis induction significantly inhibited the growth of ER+ breast cancer and AR+ prostate cancer, even when tumors were resistant to single-agent hormonal therapies.

Therapeutic Ligands Antagonize Estrogen Receptor Function by Impairing Its Mobility.

Estrogen receptor-positive (ER+) breast cancers frequently remain dependent on ER signaling even after acquiring resistance to endocrine agents, prompting the development of optimized ER antagonists. Fulvestrant is unique among approved ER therapeutics due to its capacity for full ER antagonism, thought to be achieved through ER degradation. The clinical potential of fulvestrant is limited by poor physicochemical features, spurring attempts to generate ER degraders with improved drug-like properties. We show that optimization of ER degradation does not guarantee full ER antagonism in breast cancer cells; ER "degraders" exhibit a spectrum of transcriptional activities and anti-proliferative potential. Mechanistically, we find that fulvestrant-like antagonists suppress ER transcriptional activity not by ER elimination, but by markedly slowing the intra-nuclear mobility of ER. Increased ER turnover occurs as a consequence of ER immobilization. These findings provide proof-of-concept that small molecule perturbation of transcription factor mobility may enable therapeutic targeting of this challenging target class.

Multimodal Analysis of Cell Types in a Hypothalamic Node Controlling Social Behavior.

The ventrolateral subdivision of the ventromedial hypothalamus (VMHvl) contains ∼4,000 neurons that project to multiple targets and control innate social behaviors including aggression and mounting. However, the number of cell types in VMHvl and their relationship to connectivity and behavioral function are unknown. We performed single-cell RNA sequencing using two independent platforms-SMART-seq (∼4,500 neurons) and 10x (∼78,000 neurons)-and investigated correspondence between transcriptomic identity and axonal projections or behavioral activation, respectively. Canonical correlation analysis (CCA) identified 17 transcriptomic types (T-types), including several sexually dimorphic clusters, the majority of which were validated by seqFISH. Immediate early gene analysis identified T-types exhibiting preferential responses to intruder males versus females but only rare examples of behavior-specific activation. Unexpectedly, many VMHvl T-types comprise a mixed population of neurons with different projection target preferences. Overall our analysis revealed that, surprisingly, few VMHvl T-types exhibit a clear correspondence with behavior-specific activation and connectivity.

Multiplexed Proteome Dynamics Profiling Reveals Mechanisms Controlling Protein Homeostasis.

Protein degradation plays important roles in biological processes and is tightly regulated. Further, targeted proteolysis is an emerging research tool and therapeutic strategy. However, proteome-wide technologies to investigate the causes and consequences of protein degradation in biological systems are lacking. We developed "multiplexed proteome dynamics profiling" (mPDP), a mass-spectrometry-based approach combining dynamic-SILAC labeling with isobaric mass tagging for multiplexed analysis of protein degradation and synthesis. In three proof-of-concept studies, we uncover different responses induced by the bromodomain inhibitor JQ1 versus a JQ1 proteolysis targeting chimera; we elucidate distinct modes of action of estrogen receptor modulators; and we comprehensively classify HSP90 clients based on their requirement for HSP90 constitutively or during synthesis, demonstrating that constitutive HSP90 clients have lower thermal stability than non-clients, have higher affinity for the chaperone, vary between cell types, and change upon external stimuli. These findings highlight the potential of mPDP to identify dynamically controlled degradation mechanisms in cellular systems.

The steroid hormone ADIOL promotes learning by reducing neural kynurenic acid levels.

Reductions in brain kynurenic acid levels, a neuroinhibitory metabolite, improve cognitive function in diverse organisms. Thus, modulation of kynurenic acid levels is thought to have therapeutic potential in a range of brain disorders. Here we report that the steroid 5-androstene 3ß, 17ß-diol (ADIOL) reduces kynurenic acid levels and promotes associative learning in Caenorhabditis elegans We identify the molecular mechanisms through which ADIOL links peripheral metabolic pathways to neural mechanisms of learning capacity. Moreover, we show that in aged animals, which normally experience rapid cognitive decline, ADIOL improves learning capacity. The molecular mechanisms that underlie the biosynthesis of ADIOL as well as those through which it promotes kynurenic acid reduction are conserved in mammals. Thus, rather than a minor intermediate in the production of sex steroids, ADIOL is an endogenous hormone that potently regulates learning capacity by causing reductions in neural kynurenic acid levels.

A tamoxifen receptor within a voltage-gated sodium channel.

Voltage-gated sodium channels are targets for many analgesic and antiepileptic drugs whose therapeutic mechanisms and binding sites have been well characterized. We describe the identification of a previously unidentified receptor site within the NavMs voltage-gated sodium channel. Tamoxifen, an estrogen receptor modulator, and its primary and secondary metabolic products bind at the intracellular exit of the channel, which is a site that is distinct from other previously characterized sodium channel drug sites. These compounds inhibit NavMs and human sodium channels with similar potencies and prevent sodium conductance by delaying channel recovery from the inactivated state. This study therefore not only describes the structure and pharmacology of a site that could be leveraged for the development of new drugs for the treatment of sodium channelopathies but may also have important implications for off-target health effects of this widely used therapeutic drug.

RNA fine-tunes estrogen receptor-alpha binding on low-affinity DNA motifs for transcriptional regulation.

Transcription factors (TFs) regulate gene expression by binding with varying strengths to DNA via their DNA-binding domain. Additionally, some TFs also interact with RNA, which modulates transcription factor binding to chromatin. However, whether RNA-mediated TF binding results in differential transcriptional outcomes remains unknown. In this study, we demonstrate that estrogen receptor α (ERα), a ligand-activated TF, interacts with RNA in a ligand-dependent manner. Defects in RNA binding lead to genome-wide loss of ERα recruitment, particularly at weaker ERα-motifs. Furthermore, ERα mobility in the nucleus increases in the absence of its RNA-binding capacity. Unexpectedly, this increased mobility coincides with robust polymerase loading and transcription of ERα-regulated genes that harbor low-strength motifs. However, highly stable binding of ERα on chromatin negatively impacts ligand-dependent transcription. Collectively, our results suggest that RNA interactions spatially confine ERα on low-affinity sites to fine-tune gene transcription.

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.

A molecular switch from tumor suppressor to oncogene in ER+ve breast cancer: Role of androgen receptor, JAK-STAT, and lineage plasticity.

Cancers develop resistance to inhibitors of oncogenes mainly due to target-centric mechanisms such as mutations and splicing. While inhibitors or antagonists force targets to unnatural conformation contributing to protein instability and resistance, activating tumor suppressors may maintain the protein in an agonistic conformation to elicit sustainable growth inhibition. Due to the lack of tumor suppressor agonists, this hypothesis and the mechanisms underlying resistance are not understood. In estrogen receptor (ER)-positive breast cancer (BC), androgen receptor (AR) is a druggable tumor suppressor offering a promising avenue for this investigation. Spatial genomics suggests that the molecular portrait of AR-expressing BC cells in tumor microenvironment corresponds to better overall patient survival, clinically confirming AR's role as a tumor suppressor. Ligand activation of AR in ER-positive BC xenografts reprograms cistromes, inhibits oncogenic pathways, and promotes cellular elasticity toward a more differentiated state. Sustained AR activation results in cistrome rearrangement toward transcription factor PROP paired-like homeobox 1, transformation of AR into oncogene, and activation of the Janus kinase/signal transducer (JAK/STAT) pathway, all culminating in lineage plasticity to an aggressive resistant subtype. While the molecular profile of AR agonist-sensitive tumors corresponds to better patient survival, the profile represented in the resistant phenotype corresponds to shorter survival. Inhibition of activated oncogenes in resistant tumors reduces growth and resensitizes them to AR agonists. These findings indicate that persistent activation of a context-dependent tumor suppressor may lead to resistance through lineage plasticity-driven tumor metamorphosis. Our work provides a framework to explore the above phenomenon across multiple cancer types and underscores the importance of factoring sensitization of tumor suppressor targets while developing agonist-like drugs.

JMJD6 Licenses ERα-Dependent Enhancer and Coding Gene Activation by Modulating the Recruitment of the CARM1/MED12 Co-activator Complex.

Whereas the actions of enhancers in gene transcriptional regulation are well established, roles of JmjC-domain-containing proteins in mediating enhancer activation remain poorly understood. Here, we report that recruitment of the JmjC-domain-containing protein 6 (JMJD6) to estrogen receptor alpha (ERα)-bound active enhancers is required for RNA polymerase II recruitment and enhancer RNA production on enhancers, resulting in transcriptional pause release of cognate estrogen target genes. JMJD6 is found to interact with MED12 in the mediator complex to regulate its recruitment. Unexpectedly, JMJD6 is necessary for MED12 to interact with CARM1, which methylates MED12 at multiple arginine sites and regulates its chromatin binding. Consistent with its role in transcriptional activation, JMJD6 is required for estrogen/ERα-induced breast cancer cell growth and tumorigenesis. Our data have uncovered a critical regulator of estrogen/ERα-induced enhancer coding gene activation and breast cancer cell potency, providing a potential therapeutic target of ER-positive breast cancers.

SRC-3 Coactivator Governs Dynamic Estrogen-Induced Chromatin Looping Interactions during Transcription.

Enhancers are thought to activate transcription by physically contacting promoters via looping. However, direct assays demonstrating these contacts are required to mechanistically verify such cellular determinants of enhancer function. Here, we present versatile cell-free assays to further determine the role of enhancer-promoter contacts (EPCs). We demonstrate that EPC is linked to mutually stimulatory transcription at the enhancer and promoter in vitro. SRC-3 was identified as a critical looping determinant for the estradiol-(E2)-regulated GREB1 locus. Surprisingly, the GREB1 enhancer and promoter contact two internal gene body SRC-3 binding sites, GBS1 and GBS2, which stimulate their transcription. Utilizing time-course 3C assays, we uncovered SRC-3-dependent dynamic chromatin interactions involving the enhancer, promoter, GBS1, and GBS2. Collectively, these data suggest that the enhancer and promoter remain "poised" for transcription via their contacts with GBS1 and GBS2. Upon E2 induction, GBS1 and GBS2 disengage from the enhancer, allowing direct EPC for active transcription.

Exploring the Spatial Landscape of the Estrogen Receptor Proximal Proteome With Antibody-Based Proximity Labeling.

Estrogen receptor α (ERα) drives the transcription of genes involved in breast cancer (BC) progression, relying on coregulatory protein recruitment for its transcriptional and biological activities. Mutation of ERα as well as aberrant recruitment of its regulatory proteins contribute to tumor adaptation and drug resistance. Therefore, understanding the dynamic changes in ERα protein interaction networks is crucial for elucidating drug resistance mechanisms in BC. Despite progress in studying ERα-associated proteins, capturing subcellular transient interactions remains challenging and, as a result, significant number of important interactions remain undiscovered. In this study, we employed biotinylation by antibody recognition (BAR), an innovative antibody-based proximity labeling (PL) approach, coupled with mass spectrometry to investigate the ERα proximal proteome and its changes associated with resistance to aromatase inhibition, a key therapy used in the treatment of ERα-positive BC. We show that BAR successfully detected most of the known ERα interactors and mainly identified nuclear proteins, using either an epitope tag or endogenous antibody to target ERα. We further describe the ERα proximal proteome rewiring associated with resistance applying BAR to a panel of isogenic cell lines modeling tumor adaptation in the clinic. Interestingly, we find that ERα associates with some of the canonical cofactors in resistant cells and several proximal proteome changes are due to increased expression of ERα. Resistant models also show decreased levels of estrogen-regulated genes. Sensitive and resistant cells harboring a mutation in the ERα (Y537C) revealed a similar proximal proteome. We provide an ERα proximal protein network covering several novel ERα-proximal partners. These include proteins involved in highly dynamic processes such as sumoylation and ubiquitination difficult to detect with traditional protein interaction approaches. Overall, we present BAR as an effective approach to investigate the ERα proximal proteome in a spatial context and demonstrate its application in different experimental conditions.

17ß-estradiol promotes extracellular vesicle release and selective miRNA loading in ERα-positive breast cancer.

The causes and consequences of abnormal biogenesis of extracellular vesicles (EVs) are not yet well understood in malignancies, including in breast cancers (BCs). Given the hormonal signaling dependence of estrogen receptor-positive (ER+) BC, we hypothesized that 17ß-estradiol (estrogen) might influence EV production and microRNA (miRNA) loading. We report that physiological doses of 17ß-estradiol promote EV secretion specifically from ER+ BC cells via inhibition of miR-149-5p, hindering its regulatory activity on SP1, a transcription factor that regulates the EV biogenesis factor nSMase2. Additionally, miR-149-5p downregulation promotes hnRNPA1 expression, responsible for the loading of let-7's miRNAs into EVs. In multiple patient cohorts, we observed increased levels of let-7a-5p and let-7d-5p in EVs derived from the blood of premenopausal ER+ BC patients, and elevated EV levels in patients with high BMI, both conditions associated with higher levels of 17ß-estradiol. In brief, we identified a unique estrogen-driven mechanism by which ER+ BC cells eliminate tumor suppressor miRNAs in EVs, with effects on modulating tumor-associated macrophages in the microenvironment.

Serine starvation silences estrogen receptor signaling through histone hypoacetylation.

Loss of estrogen receptor (ER) pathway activity promotes breast cancer progression, yet how this occurs remains poorly understood. Here, we show that serine starvation, a metabolic stress often found in breast cancer, represses estrogen receptor alpha (ERα) signaling by reprogramming glucose metabolism and epigenetics. Using isotope tracing and time-resolved metabolomic analyses, we demonstrate that serine is required to maintain glucose flux through glycolysis and the TCA cycle to support acetyl-CoA generation for histone acetylation. Consequently, limiting serine depletes histone H3 lysine 27 acetylation (H3K27ac), particularly at the promoter region of ER pathway genes including the gene encoding ERα, ESR1. Mechanistically, serine starvation impairs acetyl-CoA-dependent gene expression by inhibiting the entry of glycolytic carbon into the TCA cycle and down-regulating the mitochondrial citrate exporter SLC25A1, a critical enzyme in the production of nucleocytosolic acetyl-CoA from glucose. Consistent with this model, total H3K27ac and ERα expression are suppressed by SLC25A1 inhibition and restored by acetate, an alternate source of acetyl-CoA, in serine-free conditions. We thus uncover an unexpected role for serine in sustaining ER signaling through the regulation of acetyl-CoA metabolism.

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.

Running the Female Power Grid Across Lifespan Through Brain Estrogen Signaling.

The role of central estrogen in cognitive, metabolic, and reproductive health has long fascinated the lay public and scientists alike. In the last two decades, insight into estrogen signaling in the brain and its impact on female physiology is beginning to catch up with the vast information already established for its actions on peripheral tissues. Using newer methods to manipulate estrogen signaling in hormone-sensitive brain regions, neuroscientists are now identifying the molecular pathways and neuronal subtypes required for controlling sex-dependent energy allocation. However, the immense cellular complexity of these hormone-sensitive brain regions makes it clear that more research is needed to fully appreciate how estrogen modulates neural circuits to regulate physiological and behavioral end points. Such insight is essential for understanding how natural or drug-induced hormone fluctuations across lifespan affect women's health.

Signaling pathways and steroid receptors modulating estrogen receptor α function in breast cancer.

Estrogen receptor α (ER) is the major driver of ∼75% of breast cancers, and multiple ER targeting drugs are routinely used clinically to treat patients with ER+ breast cancer. However, many patients relapse on these targeted therapies and ultimately develop metastatic and incurable disease, and understanding the mechanisms leading to drug resistance is consequently of utmost importance. It is now clear that, in addition to estrogens, ER function is modulated by other steroid receptors and multiple signaling pathways (e.g., growth factor and cytokine signaling), and many of these pathways affect drug resistance and patient outcome. Here, we review the mechanisms through which these pathways impact ER function and drug resistance as well as discuss the clinical implications.

AKT signaling modulates latent viral reservoir viability in HIV-1-infected blood-brain barrier pericytes.

Despite antiretroviral therapy (ART), chronic forms of HIV-associated neurocognitive disorders (HAND) affect an estimated 50% of individuals living with HIV, greatly impacting their quality of life. The prevailing theory of HAND progression posits that chronic inflammation arising from the activation of latent viral reservoirs leads to progressive damage in the central nervous system (CNS). Recent evidence indicates that blood-brain barrier (BBB) pericytes are capable of active HIV-1 infection; however, their latent infection has not been defined. Given their location and function, BBB pericytes are poised to be a key viral reservoir in the development of HAND. We present the first transcriptional analysis of uninfected, active, and latent human BBB pericytes, revealing distinct transcriptional phenotypes. In addition, we demonstrate that latent infection of BBB pericytes relies on AKT signaling for reservoir survival. These findings provide insight into the state of reservoir maintenance in the CNS during HIV-1 infection and provide novel targets for reservoir clearance.

G protein-coupled estrogen receptor 1 ameliorates nonalcoholic steatohepatitis through targeting AMPK-dependent signaling.

Nonalcoholic fatty liver disease (NAFLD), especially nonalcoholic steatohepatitis (NASH), has emerged as a prevalent cause of liver cirrhosis and hepatocellular carcinoma, posing severe public health challenges worldwide. The incidence of NASH is highly correlated with an increased prevalence of obesity, insulin resistance, diabetes, and other metabolic diseases. Currently, no approved drugs specifically targeted for the therapies of NASH partially due to the unclear pathophysiological mechanisms. G protein-coupled estrogen receptor 1 (GPER1) is a membrane estrogen receptor involved in the development of metabolic diseases such as obesity and diabetes. However, the function of GPER1 in NAFLD/NASH progression remains unknown. Here, we show that GPER1 exerts a beneficial role in insulin resistance, hepatic lipid accumulation, oxidative stress, or inflammation in vivo and in vitro. In particular, we observed that the lipid accumulation, inflammatory response, fibrosis, or insulin resistance in mouse NAFLD/NASH models were exacerbated by hepatocyte-specific GPER1 knockout but obviously mitigated by hepatic GPER1 activation in female and male mice. Mechanistically, hepatic GPER1 activates AMP-activated protein kinase signaling by inducing cyclic AMP release, thereby exerting its protective effect. These data suggest that GPER1 may be a promising therapeutic target for NASH.

Hexestrol, an estrogen receptor agonist, inhibits Lassa virus entry.

Lassa virus (LASV) is the causative agent of human Lassa fever which in severe cases manifests as hemorrhagic fever leading to thousands of deaths annually. However, no approved vaccines or antiviral drugs are currently available. Recently, we screened approximately 2,500 compounds using a recombinant vesicular stomatitis virus (VSV) expressing LASV glycoprotein GP (VSV-LASVGP) and identified a P-glycoprotein inhibitor as a potential LASV entry inhibitor. Here, we show that another identified candidate, hexestrol (HES), an estrogen receptor agonist, is also a LASV entry inhibitor. HES inhibited VSV-LASVGP replication with a 50% inhibitory concentration (IC50) of 0.63 µM. Importantly, HES also inhibited authentic LASV replication with IC50 values of 0.31 µM-0.61 µM. Time-of-addition and cell-based membrane fusion assays suggested that HES inhibits the membrane fusion step during virus entry. Alternative estrogen receptor agonists did not inhibit VSV-LASVGP replication, suggesting that the estrogen receptor itself is unlikely to be involved in the antiviral activity of HES. Generation of a HES-resistant mutant revealed that the phenylalanine at amino acid position 446 (F446) of LASVGP, which is located in the transmembrane region, conferred resistance to HES. Although mutation of F446 enhanced the membrane fusion activity of LASVGP, it exhibited reduced VSV-LASVGP replication, most likely due to the instability of the pre-fusion state of LASVGP. Collectively, our results demonstrated that HES is a promising anti-LASV drug that acts by inhibiting the membrane fusion step of LASV entry. This study also highlights the importance of the LASVGP transmembrane region as a target for anti-LASV drugs.IMPORTANCELassa virus (LASV), the causative agent of Lassa fever, is the most devastating mammarenavirus with respect to its impact on public health in West Africa. However, no approved antiviral drugs or vaccines are currently available. Here, we identified hexestrol (HES), an estrogen receptor agonist, as the potential antiviral candidate drug. We showed that the estrogen receptor itself is not involved in the antiviral activity. HES directly bound to LASVGP and blocked membrane fusion, thereby inhibiting LASV infection. Through the generation of a HES-resistant virus, we found that phenylalanine at position 446 (F446) within the LASVGP transmembrane region plays a crucial role in the antiviral activity of HES. The mutation at F446 caused reduced virus replication, likely due to the instability of the pre-fusion state of LASVGP. These findings highlight the potential of HES as a promising candidate for the development of antiviral compounds targeting LASV.