Glucocorticoid receptor function regulated by coordinated action of the Hsp90 and Hsp70 chaperone cycles

Chaperone BiP controls ER stress sensor Ire1 through interactions with its oligomers

The complex multistep activation cascade of Ire1 involves changes in the Ire1 conformation and oligomeric state. Ire1 activation enhances ER folding capacity, in part by overexpressing the ER Hsp70 molecular chaperone BiP; in turn, BiP provides tight negative control of Ire1 activation. This study demonstrates that BiP regulates Ire1 activation through a direct interaction with Ire1 oligomers. Particularly, we demonstrated that the binding of Ire1 luminal domain (LD) to unfolded protein substrates not only trigger conformational changes in Ire1-LD that favour the formation of Ire1-LD oligomers but also exposes BiP binding motifs, enabling the molecular chaperone BiP to directly bind to Ire1-LD in an ATP-dependent manner. These transient interactions between BiP and two short motifs in the disordered region of Ire1-LD are reminiscent of interactions between clathrin and another Hsp70, cytoplasmic Hsc70. BiP binding to substrate-bound Ire1-LD oligomers enables unfolded protein substrates and BiP to synergistically and dynamically control Ire1-LD oligomerisation, helping to return Ire1 to its deactivated state when an ER stress response is no longer required.

Hsp90, a team player in protein quality control and the stress response in bacteria

SUMMARYHeat shock protein 90 (Hsp90) participates in proteostasis by facilitating protein folding, activation, disaggregation, prevention of aggregation, degradation, and protection against degradation of various cellular proteins. It is highly conserved from bacteria to humans. In bacteria, protein remodeling by Hsp90 involves collaboration with the Hsp70 molecular chaperone and Hsp70 cochaperones. In eukaryotes, protein folding by Hsp90 is more complex and involves collaboration with many Hsp90 cochaperones as well as Hsp70 and Hsp70 cochaperones. This review focuses primarily on bacterial Hsp90 and highlights similarities and differences between bacterial and eukaryotic Hsp90. Seminal research findings that elucidate the structure and the mechanisms of protein folding, disaggregation, and reactivation promoted by Hsp90 are discussed. Understanding the mechanisms of bacterial Hsp90 will provide fundamental insight into the more complex eukaryotic chaperone systems.

CGG repeats in the human FMR1 gene regulate mRNA localization and cellular stress in developing neurons

The human genome has many short tandem repeats, yet the normal functions of these repeats are unclear. The 5' untranslated region (UTR) of the fragile X messenger ribonucleoprotein 1 (FMR1) gene contains polymorphic CGG repeats, the length of which has differing effects on FMR1 expression and human health, including the neurodevelopmental disorder fragile X syndrome. We deleted the CGG repeats in the FMR1 gene (0CGG) in human stem cells and examined the effects on differentiated neurons. 0CGG neurons have altered subcellular localization of FMR1 mRNA and protein, and differential expression of cellular stress proteins compared with neurons with normal repeats (31CGG). In addition, 0CGG neurons have altered responses to glucocorticoid receptor (GR) activation, including FMR1 mRNA localization, GR chaperone HSP90α expression, GR localization, and cellular stress protein levels. Therefore, the CGG repeats in the FMR1 gene are important for the homeostatic responses of neurons to stress signals.

Structural basis for the dynamic chaperoning of disordered clients by Hsp90

Molecular chaperone heat shock protein 90 (Hsp90) is a ubiquitous regulator that fine-tunes and remodels diverse client proteins, exerting profound effects on normal biology and diseases. Unraveling the mechanistic details of Hsp90's function requires atomic-level insights into its client interactions throughout the adenosine triphosphate-coupled functional cycle. However, the structural details of the initial encounter complex in the chaperone cycle, wherein Hsp90 adopts an open conformation while engaging with the client, remain elusive. Here, using nuclear magnetic resonance spectroscopy, we determined the solution structure of Hsp90 in its open state, bound to a disordered client. Our findings reveal that Hsp90 uses two distinct binding sites, collaborating synergistically to capture discrete hydrophobic segments within client proteins. This bipartite interaction generates a versatile complex that facilitates rapid conformational sampling. Moreover, our investigations spanning various clients and Hsp90 orthologs demonstrate a pervasive mechanism used by Hsp90 orthologs to accommodate the vast array of client proteins. Collectively, our work contributes to establish a unified conceptual and mechanistic framework, elucidating the intricate interplay between Hsp90 and its clients.

Drug development and potential targets for Cushing's syndrome

Cushing's syndrome (CS) is a complex disorder characterized by the excessive secretion of cortisol, with Cushing's disease (CD), particularly associated with pituitary tumors, exhibiting heightened morbidity and mortality. Although transsphenoidal pituitary surgery (TSS) stands as the primary treatment for CD, there is a crucial need to optimize patient prognosis. Current medical therapy serves as an adjunctive measure due to its unsatisfactory efficacy and unpredictable side effects. In this comprehensive review, we delve into recent advances in understanding the pathogenesis of CS and explore therapeutic options by conducting a critical analysis of potential drug targets and candidates. Additionally, we provide an overview of the design strategy employed in previously reported candidates, along with a summary of structure-activity relationship (SAR) analyses and their biological efficacy. This review aims to contribute valuable insights to the evolving landscape of CS research, shedding light on potential avenues for therapeutic development.

Phosphorylation-Driven Epichaperome Assembly: A Critical Regulator of Cellular Adaptability and Proliferation

The intricate protein-chaperone network is vital for cellular function. Recent discoveries have unveiled the existence of specialized chaperone complexes called epichaperomes, protein assemblies orchestrating the reconfiguration of protein-protein interaction networks, enhancing cellular adaptability and proliferation. This study delves into the structural and regulatory aspects of epichaperomes, with a particular emphasis on the significance of post-translational modifications in shaping their formation and function. A central finding of this investigation is the identification of specific PTMs on HSP90, particularly at residues Ser226 and Ser255 situated within an intrinsically disordered region, as critical determinants in epichaperome assembly. Our data demonstrate that the phosphorylation of these serine residues enhances HSP90's interaction with other chaperones and co-chaperones, creating a microenvironment conducive to epichaperome formation. Furthermore, this study establishes a direct link between epichaperome function and cellular physiology, especially in contexts where robust proliferation and adaptive behavior are essential, such as cancer and stem cell maintenance. These findings not only provide mechanistic insights but also hold promise for the development of novel therapeutic strategies targeting chaperone complexes in diseases characterized by epichaperome dysregulation, bridging the gap between fundamental research and precision medicine.

A novel mutation in the NR3C1 gene associated with reversible glucocorticoid resistance

OBJECTIVE

Glucocorticoid resistance is a rare endocrine disease caused by variants of the NR3C1 gene encoding the glucocorticoid receptor (GR). We identified a novel heterozygous variant (GRR569Q) in a patient with uncommon reversible glucocorticoid resistance syndrome.

METHODS

We performed ex vivo functional characterization of the variant in patient fibroblasts and in vitro through transient transfection in undifferentiated HEK 293T cells to assess transcriptional activity, affinity, and nuclear translocation. We studied the impact of the variant on the tertiary structure of the ligand-binding domain through 3D modeling.

RESULTS

The patient presented initially with an adrenal adenoma with mild autonomous cortisol secretion and undetectable adrenocorticotropin hormone (ACTH) levels. Six months after surgery, biological investigations showed elevated cortisol and ACTH (urinary free cortisol 114 µg/24 h, ACTH 10.9 pmol/L) without clinical symptoms, evoking glucocorticoid resistance syndrome. Functional characterization of the GRR569Q showed decreased expression of target genes (in response to 100 nM cortisol: SGK1 control +97% vs patient +20%, P < .0001) and impaired nuclear translocation in patient fibroblasts compared to control. Similar observations were made in transiently transfected cells, but higher cortisol concentrations overcame glucocorticoid resistance. GRR569Q showed lower ligand affinity (Kd GRWT: 1.73 nM vs GRR569Q: 4.61 nM). Tertiary structure modeling suggested a loss of hydrogen bonds between H3 and the H1-H3 loop.

CONCLUSION

This is the first description of a reversible glucocorticoid resistance syndrome with effective negative feedback on corticotroph cells regarding increased plasma cortisol concentrations due to the development of mild autonomous cortisol secretion.

Structural transitions modulate the chaperone activities of Grp94

Hsp90s are ATP-dependent chaperones that collaborate with co-chaperones and Hsp70s to remodel client proteins. Grp94 is the ER Hsp90 homolog essential for folding multiple secretory and membrane proteins. Grp94 interacts with the ER Hsp70, BiP, although the collaboration of the ER chaperones in protein remodeling is not well understood. Grp94 undergoes large-scale conformational changes that are coupled to chaperone activity. Within Grp94, a region called the pre-N domain suppresses ATP hydrolysis and conformational transitions to the active chaperone conformation. In this work, we combined in vivo and in vitro functional assays and structural studies to characterize the chaperone mechanism of Grp94. We show that Grp94 directly collaborates with the BiP chaperone system to fold clients. Grp94's pre-N domain is not necessary for Grp94-client interactions. The folding of some Grp94 clients does not require direct interactions between Grp94 and BiP in vivo, suggesting that the canonical collaboration may not be a general chaperone mechanism for Grp94. The BiP co-chaperone DnaJB11 promotes the interaction between Grp94 and BiP, relieving the pre-N domain suppression of Grp94's ATP hydrolysis activity. In structural studies, we find that ATP binding by Grp94 alters the ATP lid conformation, while BiP binding stabilizes a partially closed Grp94 intermediate. Together, BiP and ATP push Grp94 into the active closed conformation for client folding. We also find that nucleotide binding reduces Grp94's affinity for clients, which is important for productive client folding. Alteration of client affinity by nucleotide binding may be a conserved chaperone mechanism for a subset of ER chaperones.

Steroid responsiveness in alcohol-associated hepatitis is linked to glucocorticoid metabolism, mitochondrial repair, and heat shock proteins

BACKGROUND

Alcohol-associated hepatitis (AH) is one of the clinical presentations of alcohol-associated liver disease. AH has poor prognosis, and corticosteroids remain the mainstay of drug therapy. However, ~40% of patients do not respond to this treatment, and the mechanisms underlying the altered response to corticosteroids are not understood. The current study aimed to identify changes in hepatic protein expression associated with responsiveness to corticosteroids and prognosis in patients with AH.

METHODS

Patients with AH were enrolled based on the National Institute on Alcohol Abuse and Alcoholism inclusion criteria for acute AH and further confirmed by a diagnostic liver biopsy. Proteomic analysis was conducted on liver samples acquired from patients with AH grouped as nonresponders (AH-NR, n = 7) and responders (AH-R, n = 14) to corticosteroids, and nonalcohol-associated liver disease controls (n = 10). The definition of responders was based on the clinical prognostic model, the Lille Score, where a score < 0.45 classified patients as AH-R and a score > 0.45 as AH-NR. Primary outcomes used to assess steroid response were Lille Score (eg, improved liver function) and survival at 24 weeks.

RESULTS

Reduced levels of the glucocorticoid receptor and its transcriptional co-activator, glucocorticoid modulatory element-binding protein 2, were observed in the hepatic proteome of AH-NR versus AH-R. The corticosteroid metabolizing enzyme, 11-beta-hydroxysteroid dehydrogenase 1, was increased in AH-NR versus AH-R along with elevated mitochondrial DNA repair enzymes, while several proteins of the heat shock pathway were reduced. Analysis of differentially expressed proteins in AH-NR who survived 24 weeks relative to AH-NR nonsurvivors revealed several protein expression changes, including increased levels of acute phase proteins, elevated coagulation factors, and reduced mast cell markers.

CONCLUSIONS

This study identified hepatic proteomic changes that may predict responsiveness to corticosteroids and mortality in patients with AH.

Insights into Hsp90 mechanism and in vivo functions learned from studies in the yeast, Saccharomyces cerevisiae

The molecular chaperone Hsp90 (Heat shock protein, 90 kDa) is an abundant and essential cytosolic protein required for the stability and/or folding of hundreds of client proteins. Hsp90, along with helper cochaperone proteins, assists client protein folding in an ATP-dependent pathway. The laboratory of Susan Lindquist, in collaboration with other researchers, was the first to establish the yeast Saccharomyces cerevisiae as a model organism to study the functional interaction between Hsp90 and clients. Important insights from studies in her lab were that Hsp90 is essential, and that Hsp90 functions and cochaperone interactions are highly conserved between yeast and mammalian cells. Here, we describe key mechanistic insights into the Hsp90 folding cycle that were obtained using the yeast system. We highlight the early contributions of the laboratory of Susan Lindquist and extend our analysis into the broader use of the yeast system to analyze the understanding of the conformational cycle of Hsp90 and the impact of altered Hsp90 function on the proteome.

TERT mediates the U-shape of glucocorticoids effects in modulation of hippocampal neural stem cells and associated brain function

BACKGROUND

Glucocorticoids (GCs) are steroidal hormones produced by the adrenal cortex. A physiological-level GCs have a crucial function in maintaining many cognitive processes, like cognition, memory, and mood, however, both insufficient and excessive GCs impair these functions. Although this phenomenon could be explained by the U-shape of GC effects, the underlying mechanisms are still not clear. Therefore, understanding the underlying mechanisms of GCs may provide insight into the treatments for cognitive and mood-related disorders.

METHODS

Consecutive administration of corticosterone (CORT, 10 mg/kg, i.g.) proceeded for 28 days to mimic excessive GCs condition. Adrenalectomy (ADX) surgery was performed to ablate endogenous GCs in mice. Microinjection of 1 μL of Ad-mTERT-GFP virus into mouse hippocampus dentate gyrus (DG) and behavioral alterations in mice were observed 4 weeks later.

RESULTS

Different concentrations of GCs were shown to affect the cell growth and development of neural stem cells (NSCs) in a U-shaped manner. The physiological level of GCs (0.01 μM) promoted NSC proliferation in vitro, while the stress level of GCs (10 μM) inhibited it. The glucocorticoid synthesis blocker metyrapone (100 mg/kg, i.p.) and ADX surgery both decreased the quantity and morphological development of doublecortin (DCX)-positive immature cells in the DG. The physiological level of GCs activated mineralocorticoid receptor and then promoted the production of telomerase reverse transcriptase (TERT); in contrast, the stress level of GCs activated glucocorticoid receptor and then reduced the expression of TERT. Overexpression of TERT by AD-mTERT-GFP reversed both chronic stresses- and ADX-induced deficiency of TERT and the proliferation and development of NSCs, chronic stresses-associated depressive symptoms, and ADX-associated learning and memory impairment.

CONCLUSION

The bidirectional regulation of TERT by different GCs concentrations is a key mechanism mediating the U-shape of GC effects in modulation of hippocampal NSCs and associated brain function. Replenishment of TERT could be a common treatment strategy for GC dysfunction-associated diseases.

Molecular mechanisms of chaperone-directed protein folding: Insights from atomistic simulations

Molecular chaperones, a family of proteins of which Hsp90 and Hsp70 are integral members, form an essential machinery to maintain healthy proteomes by controlling the folding and activation of a plethora of substrate client proteins. This is achieved through cycles in which Hsp90 and Hsp70, regulated by task-specific co-chaperones, process ATP and become part of a complex network that undergoes extensive compositional and conformational variations. Despite impressive advances in structural knowledge, the mechanisms that regulate the dynamics of functional assemblies, their response to nucleotides, and their relevance for client remodeling are still elusive. Here, we focus on the glucocorticoid receptor (GR):Hsp90:Hsp70:co-chaperone Hop client-loading and the GR:Hsp90:co-chaperone p23 client-maturation complexes, key assemblies in the folding cycle of glucocorticoid receptor (GR), a client strictly dependent upon Hsp90/Hsp70 for activity. Using a combination of molecular dynamics simulation approaches, we unveil with unprecedented detail the mechanisms that underpin function in these chaperone machineries. Specifically, we dissect the processes by which the nucleotide-encoded message is relayed to the client and how the distinct partners of the assemblies cooperate to (pre)organize partially folded GR during Loading and Maturation. We show how different ligand states determine distinct dynamic profiles for the functional interfaces defining the interactions in the complexes and modulate their overall flexibility to facilitate progress along the chaperone cycle. Finally, we also show that the GR regions engaged by the chaperone machinery display peculiar energetic signatures in the folded state, which enhance the probability of partial unfolding fluctuations. From these results, we propose a model where a dynamic cross-talk emerges between the chaperone dynamics states and remodeling of client-interacting regions. This factor, coupled to the highly dynamic nature of the assemblies and the conformational heterogeneity of their interactions, provides the basis for regulating the functions of distinct assemblies during the chaperoning cycle.

Elevated Expression of HSP72 in the Prefrontal Cortex and Hippocampus of Rats Subjected to Chronic Mild Stress and Treated with Imipramine

The HSP70 and HSP90 family members belong to molecular chaperones that exhibit protective functions during the cellular response to stressful agents. We investigated whether the exposure of rats to chronic mild stress (CMS), a validated model of depression, affects the expression of HSP70 and HSP90 in the prefrontal cortex (PFC), hippocampus (HIP) and thalamus (Thal). Male Wistar rats were exposed to CMS for 3 or 8 weeks. The antidepressant imipramine (IMI, 10 mg/kg, i.p., daily) was introduced in the last five weeks of the long-term CMS procedure. Depressive-like behavior was verified by the sucrose consumption test. The expression of mRNA and protein was quantified by real-time PCR and Western blot, respectively. In the 8-week CMS model, stress alone elevated HSP72 and HSP90B mRNA expression in the HIP. HSP72 mRNA was increased in the PFC and HIP of rats not responding to IMI treatment vs. IMI responders. The CMS exposure increased HSP72 protein expression in the cytosolic fraction of the PFC and HIP, and this effect was diminished by IMI treatment. Our results suggest that elevated levels of HSP72 may serve as an important indicator of neuronal stress reactions accompanying depression pathology and could be a potential target for antidepressant strategy.

"NO" Time in Fear Response: Possible Implication of Nitric-Oxide-Related Mechanisms in PTSD

Post-traumatic stress disorder (PTSD) is a psychiatric condition characterized by persistent fear responses and altered neurotransmitter functioning due to traumatic experiences. Stress predominantly affects glutamate, a neurotransmitter crucial for synaptic plasticity and memory formation. Activation of the N-Methyl-D-Aspartate glutamate receptors (NMDAR) can trigger the formation of a complex comprising postsynaptic density protein-95 (PSD95), the neuronal nitric oxide synthase (nNOS), and its adaptor protein (NOS1AP). This complex is pivotal in activating nNOS and nitric oxide (NO) production, which, in turn, activates downstream pathways that modulate neuronal signaling, including synaptic plasticity/transmission, inflammation, and cell death. The involvement of nNOS and NOS1AP in the susceptibility of PTSD and its comorbidities has been widely shown. Therefore, understanding the interplay between stress, fear, and NO is essential for comprehending the maintenance and progression of PTSD, since NO is involved in fear acquisition and extinction processes. Moreover, NO induces post-translational modifications (PTMs), including S-nitrosylation and nitration, which alter protein function and structure for intracellular signaling. Although evidence suggests that NO influences synaptic plasticity and memory processing, the specific role of PTMs in the pathophysiology of PTSD remains unclear. This review highlights pathways modulated by NO that could be relevant to stress and PTSD.

Stress-related cellular pathophysiology as a crosstalk risk factor for neurocognitive and psychiatric disorders

In this narrative review, we examine biological processes linking psychological stress and cognition, with a focus on how psychological stress can activate multiple neurobiological mechanisms that drive cognitive decline and behavioral change. First, we describe the general neurobiology of the stress response to define neurocognitive stress reactivity. Second, we review aspects of epigenetic regulation, synaptic transmission, sex hormones, photoperiodic plasticity, and psychoneuroimmunological processes that can contribute to cognitive decline and neuropsychiatric conditions. Third, we explain mechanistic processes linking the stress response and neuropathology. Fourth, we discuss molecular nuances such as an interplay between kinases and proteins, as well as differential role of sex hormones, that can increase vulnerability to cognitive and emotional dysregulation following stress. Finally, we explicate several testable hypotheses for stress, neurocognitive, and neuropsychiatric research. Together, this work highlights how stress processes alter neurophysiology on multiple levels to increase individuals' risk for neurocognitive and psychiatric disorders, and points toward novel therapeutic targets for mitigating these effects. The resulting models can thus advance dementia and mental health research, and translational neuroscience, with an eye toward clinical application in cognitive and behavioral neurology, and psychiatry.

Large-scale, in-cell photocrosslinking at single-residue resolution reveals the molecular basis for glucocorticoid receptor regulation by immunophilins

The Hsp90 co-chaperones FKBP51 and FKBP52 play key roles in steroid-hormone-receptor regulation, stress-related disorders, and sexual embryonic development. As a prominent target, glucocorticoid receptor (GR) signaling is repressed by FKBP51 and potentiated by FKBP52, but the underlying molecular mechanisms remain poorly understood. Here we present the architecture and functional annotation of FKBP51-, FKBP52-, and p23-containing Hsp90-apo-GR pre-activation complexes, trapped by systematic incorporation of photoreactive amino acids inside human cells. The identified crosslinking sites clustered in characteristic patterns, depended on Hsp90, and were disrupted by GR activation. GR binding to the FKBPFK1, but not the FKBPFK2, domain was modulated by FKBP ligands, explaining the lack of GR derepression by certain classes of FKBP ligands. Our findings show how FKBPs differentially interact with apo-GR, help to explain the differentiated pharmacology of FKBP51 ligands, and provide a structural basis for the development of improved FKBP ligands.

Cryo-EM reveals how Hsp90 and FKBP immunophilins co-regulate the glucocorticoid receptor

Hsp90 is an essential molecular chaperone responsible for the folding and activation of hundreds of 'client' proteins, including the glucocorticoid receptor (GR). Previously, we revealed that Hsp70 and Hsp90 remodel the conformation of GR to regulate ligand binding, aided by co-chaperones. In vivo, the co-chaperones FKBP51 and FKBP52 antagonistically regulate GR activity, but a molecular understanding is lacking. Here we present a 3.01 Å cryogenic electron microscopy structure of the human GR:Hsp90:FKBP52 complex, revealing how FKBP52 integrates into the GR chaperone cycle and directly binds to the active client, potentiating GR activity in vitro and in vivo. We also present a 3.23 Å cryogenic electron microscopy structure of the human GR:Hsp90:FKBP51 complex, revealing how FKBP51 competes with FKBP52 for GR:Hsp90 binding and demonstrating how FKBP51 can act as a potent antagonist to FKBP52. Altogether, we demonstrate how FKBP51 and FKBP52 integrate into the GR chaperone cycle to advance GR to the next stage of maturation.

Association of glucocorticoid receptor expression with key members of the insulin signaling pathway and heat shock proteins in the bovine ovary

Glucocorticoids (GCs) act through their receptor (GR) as regulators in different biological processes such as reproduction. In the absence of GCs, the GR remains inactive in the cytoplasm by associating with heat shock proteins (HSPs), which act as molecular chaperones, among which the most relevant are HSP90 and HSP70. Cytoplasmic GC-activated GR mediates non-genomic effects, interacting with members of signaling pathways such as PI3K/Akt, which participates in several metabolic processes, including the insulin signaling pathway. The aim of the present study was to evaluate possible associations between the cytoplasmic GR and the main intermediates of the insulin signaling pathway and HSP90 and HSP70 in ovaries of dairy cows. To this end, the protein expression of cytoplasmic GR, key members of the insulin signaling pathway, and HSPs was evaluated in ovarian preovulatory follicles of non-lactating Holstein cows in proestrus. Positive associations were observed between protein expression of GR and HSP90, IRS1, pIRS1, PI3K and pAkt (p < 0.05; β > 0) in granulosa cells of dominant follicles of dairy cows. Instead, in theca cells, no associations were observed between protein expression of GR and members of the insulin signaling pathway or HSPs. These data provide evidence of the possible association between the non-genomic mechanisms of action of the GR and the insulin signaling pathway in the bovine ovary.

The transportosome system as a model for the retrotransport of soluble proteins

The classic model of action of the glucocorticoid receptor (GR) sustains that its associated heat-shock protein of 90-kDa (HSP90) favours the cytoplasmic retention of the unliganded GR, whereas the binding of steroid triggers the dissociation of HSP90 allowing the passive nuclear accumulation of GR. In recent years, it was described a molecular machinery called transportosome that is responsible for the active retrograde transport of GR. The transportosome heterocomplex includes a dimer of HSP90, the stabilizer co-chaperone p23, and FKBP52 (FK506-binding protein of 52-kDa), an immunophilin that binds dynein/dynactin motor proteins. The model shows that upon steroid binding, FKBP52 is recruited to the GR allowing its active retrograde transport on cytoskeletal tracks. Then, the entire GR heterocomplex translocates through the nuclear pore complex. The HSP90-based heterocomplex is released in the nucleoplasm followed by receptor dimerization. Subsequent findings demonstrated that the transportosome is also responsible for the retrotransport of other soluble proteins. Importantly, the disruption of this molecular oligomer leads to several diseases. In this article, we discuss the relevance of this transport machinery in health and disease.

RuX: A Novel, Flexible, and Sensitive Mifepristone-Induced Transcriptional Regulation System

Inducible gene regulation methods are indispensable in diverse biological applications, yet many of them have severe limitations in their applicability. These include inducer toxicity, a limited variety of organisms the given system can be used in, and side effects of the induction method. In this study, a novel inducible system, the RuX system, was created using a mutant ligand-binding domain of the glucocorticoid receptor (CS1/CD), used together with various genetic elements such as the Gal4 DNA-binding domain or Cre recombinase. The RuX system is shown to be capable of over 1000-fold inducibility, has flexible applications, and is offered for use in cell cultures.

Single-cell transcriptomics delineates the immune cell landscape in equine lower airways and reveals upregulation of FKBP5 in horses with asthma

Equine asthma (EA) is a heterogenous, complex disease, with a significant negative impact on horse welfare and performance. EA and human asthma share fundamental similarities, making EA a useful model for studying the disease. One relevant sample type for investigating chronic lung inflammation is bronchoalveolar lavage fluid (BALF), which provides a snapshot of the immune cells present in the alveolar space. To investigate the immune cell landscape of the respiratory tract in horses with mild-to-moderate equine asthma (mEA) and healthy controls, single-cell RNA sequencing was conducted on equine BALF cells. We characterized the major immune cell populations present in equine BALF, as well as subtypes thereof. Interestingly, the most significantly upregulated gene discovered in cases of mEA was FKBP5, a chaperone protein involved in regulating the activity of the glucocorticoid receptor.

J-domain Proteins form Binary Complexes with Hsp90 and Ternary Complexes with Hsp90 and Hsp70

Hsp90 and Hsp70 are highly conserved molecular chaperones that help maintain proteostasis by participating in protein folding, unfolding, remodeling and activation of proteins. Both chaperones are also important for cellular recovery following environmental stresses. Hsp90 and Hsp70 function collaboratively for the remodeling and activation of some client proteins. Previous studies using E. coli and S. cerevisiae showed that residues in the Hsp90 middle domain directly interact with a region in the Hsp70 nucleotide binding domain, in the same region known to bind J-domain proteins. Importantly, J-domain proteins facilitate and stabilize the interaction between Hsp90 and Hsp70 both in E. coli and S. cerevisiae. To further explore the role of J-domain proteins in protein reactivation, we tested the hypothesis that J-domain proteins participate in the collaboration between Hsp90 and Hsp70 by simultaneously interacting with Hsp90 and Hsp70. Using E. coli Hsp90, Hsp70 (DnaK), and a J-domain protein (CbpA), we detected a ternary complex containing all three proteins. The interaction involved the J-domain of CbpA, the DnaK binding region of E. coli Hsp90, and the J-domain protein binding region of DnaK where Hsp90 also binds. Additionally, results show that E. coli Hsp90 interacts with E. coli J-domain proteins, DnaJ and CbpA, and that yeast Hsp90, Hsp82, interacts with a yeast J-domain protein, Ydj1. Together these results suggest that the complexes may be transient intermediates in the pathway of collaborative protein remodeling by Hsp90 and Hsp70.

The diurnal salivary glands transcriptome of Dermacentor nuttalli from the first four days of blood feeding

The ixodid tick Dermacentor nuttalli is distributed from southern Siberia to North China and is a vector of many pathogens. This species can have severe impacts on animal husbandry and human health. To date, the control of D. nuttalli is limited to the use of acaricides such as organophosphorus, synthetic pyrethroids and amidine pesticides. There are no environmentally friendly or reliable prevention and control measures, and little is known regarding key antigens involved in blood feeding. Salivary glands are major tissues involved in the blood feeding and pathogen transmission of ticks. Therefore, this study focused on salivary glands tissue to identify the dominant antigens of D. nuttalli involved in tick feeding. For this, high-throughput RNA sequencing (RNA-seq) was used for analysis. The transcriptome of female D. nuttalli ticks was assembled and characterized, and differentially expressed genes (DEGs) were identified in the salivary glands of ticks that had not fed (0 h) and of ticks after 24, 48, 72 and 96 h of feeding. There were 22,802,784, 22,275,013, 26,629,453, 24,982,389, and 22,596,230 high-quality clean reads obtained from salivary glands tissues at the five different blood feeding time points. The total number of annotated unigenes was 100,347. The differences in gene expression between different time points were compared, and functional enrichment was performed. Quantitative reverse transcription PCR (RT‒qPCR) was used to validate the RNA-seq results, the results of which showed that the differences in expressed transcripts presented similar trends. Among the identified DEGs, the most numerous were those with catalytic and binding activities and those involved in diverse metabolic pathways and cellular processes. The expression patterns of homologous and family-member proteins throughout the blood feeding period exhibited significant differences, strongly suggesting that the transcriptome composition is highly dynamic and likely subjected to important variation throughout the life cycle. Studies of gene sequences in D. nuttalli will greatly increase the information on tick protective antigens, which could potentially function as effective vaccine candidates or drug targets for the development of environmentally friendly acaricides.

Emerging Epigenetic and Posttranslational Mechanisms Controlling Resistance to Glucocorticoids in Acute Lymphoblastic Leukemia

Glucocorticoids are extensively used for the treatment of acute lymphoblastic leukemia as they pressure cancer cells to undergo apoptosis. Nevertheless, glucocorticoid partners, modifications, and mechanisms of action are hitherto poorly characterized. This hampers our understanding of therapy resistance, frequently occurring in leukemia despite the current therapeutic combinations using glucocorticoids in acute lymphoblastic leukemia. In this review, we initially cover the traditional view of glucocorticoid resistance and ways of targeting this resistance. We discuss recent progress in our understanding of chromatin and posttranslational properties of the glucocorticoid receptor that might be proven beneficial in our efforts to understand and target therapy resistance. We discuss emerging roles of pathways and proteins such as the lymphocyte-specific kinase that antagonizes glucocorticoid receptor activation and nuclear translocation. In addition, we provide an overview of ongoing therapeutic approaches that sensitize cells to glucocorticoids including small molecule inhibitors and proteolysis-targeting chimeras.

Stress, a Brief Update

Stress is fundamental for health and adaptation; it is an evolutionarily conserved response that involves several systems in the organism. The study of the stress response could be traced back to the end of the nineteenth century with George Beard's or Claude Bernard's work and, from that moment on, several studies that have allowed the elucidation of its neurobiology and the consequences of suffering from it were consolidated. In this theoretical review, we discuss the most relevant researches to our knowledge on the study of stress response, from the concept of stress, its neurobiology, the hormonal response during stress, as well as its regulation, the effects of acute and chronic stress, stress from cognition, the different stress responses during life, as well as its relationship with different psychiatric disorders. Taken together, the reviewed research updates the classic perspective on stress, increasing the factors that should be considered in research to explore the effects of stress on health.

Integrated Transcriptome and Metabolome Analysis Revealed the Causal Agent of Primary Bud Necrosis in 'Summer Black' Grape

Primary bud necrosis of grape buds is a physiological disorder that leads to decreased berry yield and has a catastrophic impact on the double cropping system in sub-tropical areas. The pathogenic mechanisms and potential solutions remain unknown. In this study, the progression and irreversibility patterns of primary bud necrosis in 'Summer Black' were examined via staining and transmission electron microscopy observation. Primary bud necrosis was initiated at 60 days after bud break and was characterized by plasmolysis, mitochondrial swelling, and severe damage to other organelles. To reveal the underlying regulatory networks, winter buds were collected during primary bud necrosis progression for integrated transcriptome and metabolome analysis. The accumulation of reactive oxygen species and subsequent signaling cascades disrupted the regulation systems for cellular protein quality. ROS cascade reactions were related to mitochondrial stress that can lead to mitochondrial dysfunction, lipid peroxidation causing damage to membrane structure, and endoplasmic reticulum stress leading to misfolded protein aggregates. All these factors ultimately resulted in primary bud necrosis. Visible tissue browning was associated with the oxidation and decreased levels of flavonoids during primary bud necrosis, while the products of polyunsaturated fatty acids and stilbenes exhibited an increasing trend, leading to a shift in carbon flow from flavonoids to stilbene. Increased ethylene may be closely related to primary bud necrosis, while auxin accelerated cell growth and alleviated necrosis by co-chaperone VvP23-regulated redistribution of auxin in meristem cells. Altogether, this study provides important clues for further study on primary bud necrosis.

The Biologist's Guide to the Glucocorticoid Receptor's Structure

The glucocorticoid receptor α (GRα) is a member of the nuclear receptor superfamily and functions as a glucocorticoid (GC)-responsive transcription factor. GR can halt inflammation and kill off cancer cells, thus explaining the widespread use of glucocorticoids in the clinic. However, side effects and therapy resistance limit GR's therapeutic potential, emphasizing the importance of resolving all of GR's context-specific action mechanisms. Fortunately, the understanding of GR structure, conformation, and stoichiometry in the different GR-controlled biological pathways is now gradually increasing. This information will be crucial to close knowledge gaps on GR function. In this review, we focus on the various domains and mechanisms of action of GR, all from a structural perspective.

Gender Differences in Cortisol and Cortisol Receptors in Depression: A Narrative Review

Stress is known to have a significant impact on mental health. While gender differences can be found in stress response and mental disorders, there are limited studies on the neuronal mechanisms of gender differences in mental health. Here, we discuss gender and cortisol in depression as presented by recent clinical studies, as well as gender differences in the role of glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs) in stress-associated mental disorders. When examining clinical studies drawn from PubMed/MEDLINE (National Library of Medicine) and EMBASE, salivary cortisol generally showed no gender correlation. However, young males were reported to show heightened cortisol reactivity compared to females of similar age in depression. Pubertal hormones, age, early life stressors, and types of bio-samples for cortisol measurement affected the recorded cortisol levels. The role of GRs and MRs in the HPA axis could be different between males and females during depression, with increased HPA activity and upregulated MR expression in male mice, while the inverse happened in female mice. The functional heterogeneity and imbalance of GRs and MRs in the brain may explain gender differences in mental disorders. This knowledge and understanding will support the development of gender-specific diagnostic markers involving GRs and MRs in depression.

Melatonin-mediated FKBP4 downregulation protects against stress-induced neuronal mitochondria dysfunctions by blocking nuclear translocation of GR

The physiological crosstalk between glucocorticoid and melatonin maintains neuronal homeostasis in regulating circadian rhythms. However, the stress-inducing level of glucocorticoid triggers mitochondrial dysfunction including defective mitophagy by increasing the activity of glucocorticoid receptors (GRs), leading to neuronal cell death. Melatonin then suppresses glucocorticoid-induced stress-responsive neurodegeneration; however, the regulatory mechanism of melatonin, i.e., associated proteins involved in GR activity, has not been elucidated. Therefore, we investigated how melatonin regulates chaperone proteins related to GR trafficking into the nucleus to suppress glucocorticoid action. In this study, the effects of glucocorticoid on suppressing NIX-mediated mitophagy, followed by mitochondrial dysfunction, neuronal cell apoptosis, and cognitive deficits were reversed by melatonin treatment by inhibiting the nuclear translocation of GRs in both SH-SY5Y cells and mouse hippocampal tissue. Moreover, melatonin selectively suppressed the expression of FKBP prolyl isomerase 4 (FKBP4), which is a co-chaperone protein that works with dynein, to reduce the nuclear translocation of GRs among the chaperone proteins and nuclear trafficking proteins. In both cells and hippocampal tissue, melatonin upregulated melatonin receptor 1 (MT1) bound to Gαq, which triggered the phosphorylation of ERK1. The activated ERK then enhanced DNA methyltransferase 1 (DNMT1)-mediated hypermethylation of FKBP52 promoter, reducing GR-mediated mitochondrial dysfunction and cell apoptosis, the effects of which were reversed by knocking down DNMT1. Taken together, melatonin has a protective effect against glucocorticoid-induced defective mitophagy and neurodegeneration by enhancing DNMT1-mediated FKBP4 downregulation that reduced the nuclear translocation of GRs.

Identification of global inhibitors of cellular glycosylation

Small molecule inhibitors of glycosylation enzymes are valuable tools for dissecting glycan functions and potential drug candidates. Screening for inhibitors of glycosyltransferases are mainly performed by in vitro enzyme assays with difficulties moving candidates to cells and animals. Here, we circumvent this by employing a cell-based screening assay using glycoengineered cells expressing tailored reporter glycoproteins. We focused on GalNAc-type O-glycosylation and selected the GalNAc-T11 isoenzyme that selectively glycosylates endocytic low-density lipoprotein receptor (LDLR)-related proteins as targets. Our screen of a limited small molecule compound library did not identify selective inhibitors of GalNAc-T11, however, we identify two compounds that broadly inhibited Golgi-localized glycosylation processes. These compounds mediate the reversible fragmentation of the Golgi system without affecting secretion. We demonstrate how these inhibitors can be used to manipulate glycosylation in cells to induce expression of truncated O-glycans and augment binding of cancer-specific Tn-glycoprotein antibodies and to inhibit expression of heparan sulfate and binding and infection of SARS-CoV-2.

HSP70 mediates a crosstalk between the estrogen and the heat shock response pathways

Cells respond to multiple signals from the environment simultaneously, which often creates crosstalk between pathways affecting the capacity to adapt to the changing environment. Chaperones are an important component in the cellular integration of multiple responses to environmental signals, often implicated in negative feedback and inactivation mechanisms. These mechanisms include the stabilization of steroid hormone nuclear receptors in the cytoplasm in the absence of their ligand. Here, we show using immunofluorescence, chromatin immunoprecipitation, and nascent transcripts production that the heat shock protein 70 (HSP70) chaperone plays a central role in a new crosstalk mechanism between the steroid and heat shock response pathways. HSP70-dependent feedback mechanisms are required to inactivate the heat shock factor 1 (HSF1) after activation. Interestingly, a steroid stimulation leads to faster accumulation of HSF1 in inactive foci following heat shock. Our results further show that in the presence of estrogen, HSP70 accumulates at HSF1-regulated noncoding regions, leading to deactivation of HSF1 and the abrogation of the heat shock transcriptional response. Using an HSP70 inhibitor, we demonstrate that the crosstalk between both pathways is dependent on the chaperone activity. These results suggest that HSP70 availability is a key determinant in the transcriptional integration of multiple external signals. Overall, these results offer a better understanding of the crosstalk between the heat shock and steroid responses, which are salient in neurodegenerative disorders and cancers.

Recent Updates on Corticosteroid-Induced Neuropsychiatric Disorders and Theranostic Advancements through Gene Editing Tools

The vast use of corticosteroids (CCSs) globally has led to an increase in CCS-induced neuropsychiatric disorders (NPDs), a very common manifestation in patients after CCS consumption. These neuropsychiatric disorders range from depression, insomnia, and bipolar disorders to panic attacks, overt psychosis, and many other cognitive changes in such subjects. Though their therapeutic importance in treating and improving many clinical symptoms overrides the complications that arise after their consumption, still, there has been an alarming rise in NPD cases in recent years, and they are seen as the greatest public health challenge globally; therefore, these potential side effects cannot be ignored. It has also been observed that many of the neuronal functional activities are regulated and controlled by genomic variants with epigenetic factors (DNA methylation, non-coding RNA, and histone modeling, etc.), and any alterations in these regulatory mechanisms affect normal cerebral development and functioning. This study explores a general overview of emerging concerns of CCS-induced NPDs, the effective molecular biology approaches that can revitalize NPD therapy in an extremely specialized, reliable, and effective manner, and the possible gene-editing-based therapeutic strategies to either prevent or cure NPDs in the future.

Cryo-EM reveals how Hsp90 and FKBP immunophilins co-regulate the Glucocorticoid Receptor

Hsp90 is an essential molecular chaperone responsible for the folding and activation of hundreds of 'client' proteins, including the glucocorticoid receptor (GR)1-3. Previously, we revealed that GR ligand binding activity is inhibited by Hsp70 and restored by Hsp90, aided by co-chaperones4. We then presented cryo-EM structures mechanistically detailing how Hsp70 and Hsp90 remodel the conformation of GR to regulate ligand binding5,6. In vivo, GR-chaperone complexes are found associated with numerous Hsp90 co-chaperones, but the most enigmatic have been the immunophilins FKBP51 and FKBP52, which further regulate the activity of GR and other steroid receptors7-9. A molecular understanding of how FKBP51 and FKBP52 integrate with the GR chaperone cycle to differentially regulate GR activation in vivo is lacking due to difficulties reconstituting these interactions. Here, we present a 3.01 Å cryo-EM structure of the GR:Hsp90:FKBP52 complex, revealing , for the first time, that FKBP52 directly binds to the folded, ligand-bound GR using three novel interfaces, each of which we demonstrate are critical for FKBP52-dependent potentiation of GR activity in vivo. In addition, we present a 3.23 Å cryo-EM structure of the GR:Hsp90:FKBP51 complex, which, surprisingly, largely mimics the GR:Hsp90:FKBP52 structure. In both structures, FKBP51 and FKBP52 directly engage the folded GR and unexpectedly facilitate release of p23 through an allosteric mechanism. We also reveal that FKBP52, but not FKBP51, potentiates GR ligand binding in vitro, in a manner dependent on FKBP52-specific interactions. Altogether, we reveal how FKBP51 and FKBP52 integrate into the GR chaperone cycle to advance GR to the next stage of maturation and how FKBP51 and FKBP52 compete for GR:Hsp90 binding, leading to functional antagonism.

CTNNAL1 enhances glucocorticoid sensitivity in HDM-induced asthma mouse model through deactivating hsp90 signaling pathway

AIMS

Adhesion molecules play vital roles in the induction of airway hyperresponsiveness (AHR) or airway inflammation. The down-regulation of catenin alpha-like 1 (CTNNAL1) in the bronchial epithelial cells of asthma patients and mice models has been noted in our previous study. In this work, we further explore the underlying mechanism of CTNNAL1 in asthma.

MAIN METHODS

We constructed a house dust mite (HDM)-induced asthma animal model on control mice and applied CTNNAL1-siRNA transfection to create CTNNAL1-deficient mice.

KEY FINDINGS

We documented much more severe airway inflammation and increased leukocyte infiltration in the lungs of the CTNNAL1-deficient mice comparing to control mice, along with elevated expression of inflammatory cytokines. Dexamethasone (DEX) treatment led to less reduced inflammation in CTNNAL1-deficient mice compared with control mice. Immunoprecipitation confirmed the interaction between heat shock protein90 (hsp90) and CTNNAL1. The expression of hsp90 was upregulated after CTNNAL1 silencing. Meanwhile, the use of hsp90 inhibitor geldanamycin significantly decreased the expression of NR3C1, ICAM-1 and the ratio of p-p65/p65 in CTNNAL1-silenced 16HBE14o- cells. Both geldanamycin and DEX could function to suppress the expression of ICAM-1 and the phosphorylation level of p65. Nevertheless, the anti-inflammatory effect of DEX proved less potent than geldanamycin in the CTNNAL1-silenced group. The combined therapy of geldanamycin and DEX significantly decreased the inflammatory responses in CTNNAL1-deficient HBE cells than DEX monotherapy.

SIGNIFICANCE

Our study corroborates that CTNNAL1 deficiency induced aggravated airway inflammation and rendered insensitivity to glucocorticoids via triggering hsp90 signaling pathway.

p23 and Aha1: Distinct Functions Promote Client Maturation

Hsp90 is a conserved molecular chaperone regulating the folding and activation of a diverse array of several hundreds of client proteins. The function of Hsp90 in client processing is fine-tuned by a cohort of co-chaperones that modulate client activation in a client-specific manner. They affect the Hsp90 ATPase activity and the recruitment of client proteins and can in addition affect chaperoning in an Hsp90-independent way. p23 and Aha1 are central Hsp90 co-chaperones that regulate Hsp90 in opposing ways. While p23 inhibits the Hsp90 ATPase and stabilizes a client-bound Hsp90 state, Aha1 accelerates ATP hydrolysis and competes with client binding to Hsp90. Even though both proteins have been intensively studied for decades, research of the last few years has revealed intriguing new aspects of these co-chaperones that expanded our perception of how they regulate client activation. Here, we review the progress in understanding p23 and Aha1 as promoters of client processing. We highlight the structures of Aha1 and p23, their interaction with Hsp90, and how their association with Hsp90 affects the conformational cycle of Hsp90 in the context of client maturation.

HSP70-HSP90 Chaperone Networking in Protein-Misfolding Disease

Molecular chaperones and their associated co-chaperones are essential in health and disease as they are key facilitators of protein-folding, quality control and function. In particular, the heat-shock protein (HSP) 70 and HSP90 molecular chaperone networks have been associated with neurodegenerative diseases caused by aberrant protein-folding. The pathogenesis of these disorders usually includes the formation of deposits of misfolded, aggregated protein. HSP70 and HSP90, plus their co-chaperones, have been recognised as potent modulators of misfolded protein toxicity, inclusion formation and cell survival in cellular and animal models of neurodegenerative disease. Moreover, these chaperone machines function not only in folding but also in proteasome-mediated degradation of neurodegenerative disease proteins. This chapter gives an overview of the HSP70 and HSP90 chaperones, and their respective regulatory co-chaperones, and explores how the HSP70 and HSP90 chaperone systems form a larger functional network and its relevance to counteracting neurodegenerative disease associated with misfolded proteins and disruption of proteostasis.

Direct observation of Hsp90-induced compaction in a protein chain

The chaperone heat shock protein 90 (Hsp90) is well known to undergo important conformational changes, which depend on nucleotide and substrate interactions. Conversely, how the conformations of its unstable and disordered substrates are affected by Hsp90 is difficult to address experimentally yet is central to its function. Here, using optical tweezers, we find that Hsp90 promotes local contractions in unfolded chains that drive their global compaction down to dimensions of folded states. This compaction has a gradual nature while showing small steps, is stimulated by ATP, and performs mechanical work against counteracting forces that expand the chain dimensions. The Hsp90 interactions suppress the formation of larger-scale folded, misfolded, and aggregated structures. The observations support a model in which Hsp90 alters client conformations directly by promoting local intra-chain interactions while suppressing distant ones. We conjecture that chain compaction may be central to how Hsp90 protects unstable clients and cooperates with Hsp70.

Ydj1 interaction at nucleotide-binding-domain of yeast Ssa1 impacts Hsp90 collaboration and client maturation

Hsp90 constitutes one of the major chaperone machinery in the cell. The Hsp70 assists Hsp90 in its client maturation though the underlying basis of the Hsp70 role remains to be explored. In the present study, using S. cerevisiae strain expressing Ssa1 as sole Ssa Hsp70, we identified novel mutations in the nucleotide-binding domain of yeast Ssa1 Hsp70 (Ssa1-T175N and Ssa1-D158N) that adversely affect the maturation of Hsp90 clients v-Src and Ste11. The identified Ssa1 amino acids critical for Hsp90 function were also found to be conserved across species such as in E.coli DnaK and the constitutive Hsp70 isoform (HspA8) in humans. These mutations are distal to the C-terminus of Hsp70, that primarily mediates Hsp90 interaction through the bridge protein Sti1, and proximal to Ydj1 (Hsp40 co-chaperone of Hsp70 family) binding region. Intriguingly, we found that the bridge protein Sti1 is critical for cellular viability in cells expressing Ssa1-T175N (A1-T175N) or Ssa1-D158N (A1-D158N) as sole Ssa Hsp70. The growth defect was specific for sti1Δ, as deletion of none of the other Hsp90 co-chaperones showed lethality in A1-T175N or A1-D158N. Mass-spectrometry based whole proteome analysis of A1-T175N cells lacking Sti1 showed an altered abundance of various kinases and transcription factors suggesting compromised Hsp90 activity. Further proteomic analysis showed that pathways involved in signaling, signal transduction, and protein phosphorylation are markedly downregulated in the A1-T175N upon repressing Sti1 expression using doxycycline regulatable promoter. In contrast to Ssa1, the homologous mutations in Ssa4 (Ssa4-T175N/D158N), the stress inducible Hsp70 isoform, supported cell growth even in the absence of Sti1. Overall, our data suggest that Ydj1 competes with Hsp90 for binding to Hsp70, and thus regulates Hsp90 interaction with the nucleotide-binding domain of Hsp70. The study thus provides new insight into the Hsp70-mediated regulation of Hsp90 and broadens our understanding of the intricate complexities of the Hsp70-Hsp90 network.

Hsp70-Hsp90 constitutes major cellular chaperone machinery in cells. The Hsp70 plays critical role in Hsp90 chaperoning pathway. We have now identified novel mutations in the nucleotide-binding domain of yeast Ssa1 Hsp70 (Ssa1-T175N and Ssa1-D158N) that adversely affect Hsp90 client maturation. As compared to wt Ssa1, the identified Ssa1 mutants bind relatively better with Ydj1, and poorly support growth in the absence of Sti1, when present as the sole source of Ssa Hsp70 in S. cerevisiae. The cells expressing Ssa1-T175N as sole Ssa Hsp70 show downregulation of pathways involved in signaling, signal transduction, and protein phosphorylation upon repressing Sti1. The study shows that Ydj1 interaction at the nucleotide-binding domain of Ssa1 Hsp70 influences Hsp90 function.

Molecular Derangements and the Diagnosis of ACTH-Dependent Cushing's Syndrome

Endogenous Cushing's syndrome (CS) is associated with morbidities (diabetes, hypertension, clotting disorders) and shortens life because of infections, pulmonary thromboembolism, and cardiovascular disease. Its clinical presentation is immensely variable, and diagnosis and treatment are often delayed. Thus, there are many opportunities for basic and clinical research leading to better tests, faster diagnosis, and optimized medical treatments. This review focuses on CS caused by excessive adrenocorticotropin (ACTH) production. It describes current concepts of the regulation of ACTH synthesis and secretion by normal corticotropes and mechanisms by which dysregulation occurs in corticotrope (termed "Cushing's disease") and noncorticotrope (so-called ectopic) ACTH-producing tumors. ACTH causes adrenal gland synthesis and pulsatile release of cortisol; the excess ACTH in these forms of CS leads to the hypercortisolism of endogenous CS. Again, the differences between healthy individuals and those with CS are highlighted. The clinical presentations and their use in the interpretation of CS screening tests are described. The tests used for screening and differential diagnosis of CS are presented, along with their relationship to cortisol dynamics, pathophysiology, and negative glucocorticoid feedback regulation in the two forms of ACTH-dependent CS. Finally, several gaps in current understanding are highlighted in the hope of stimulating additional research into this challenging disorder.

Identification of a Thyroid Hormone Binding Site in Hsp90 with Implications for Its Interaction with Thyroid Hormone Receptor Beta

While many proteins are known clients of heat shock protein 90 (Hsp90), it is unclear whether the transcription factor, thyroid hormone receptor beta (TRb), interacts with Hsp90 to control hormonal perception and signaling. Higher Hsp90 expression in mouse fibroblasts was elicited by the addition of triiodothyronine (T3). T3 bound to Hsp90 and enhanced adenosine triphosphate (ATP) binding of Hsp90 due to a specific binding site for T3, as identified by molecular docking experiments. The binding of TRb to Hsp90 was prevented by T3 or by the thyroid mimetic sobetirome. Purified recombinant TRb trapped Hsp90 from cell lysate or purified Hsp90 in pull-down experiments. The affinity of Hsp90 for TRb was 124 nM. Furthermore, T3 induced the release of bound TRb from Hsp90, which was shown by streptavidin-conjugated quantum dot (SAv-QD) masking assay. The data indicate that the T3 interaction with TRb and Hsp90 may be an amplifier of the cellular stress response by blocking Hsp90 activity.

Hsp90: From Cellular to Organismal Proteostasis

Assuring a healthy proteome is indispensable for survival and organismal health. Proteome disbalance and the loss of the proteostasis buffer are hallmarks of various diseases. The essential molecular chaperone Hsp90 is a regulator of the heat shock response via HSF1 and a stabilizer of a plethora of signaling proteins. In this review, we summarize the role of Hsp90 in the cellular and organismal regulation of proteome maintenance.

Disease-associated mutations within the yeast DNAJB6 homolog Sis1 slow conformer-specific substrate processing and can be corrected by the modulation of nucleotide exchange factors

Molecular chaperones, or heat shock proteins (HSPs), protect against the toxic misfolding and aggregation of proteins. As such, mutations or deficiencies within the chaperone network can lead to disease. Dominant mutations within DNAJB6 (Hsp40)-an Hsp70 co-chaperone-lead to a protein aggregation-linked myopathy termed Limb-Girdle Muscular Dystrophy Type D1 (LGMDD1). Here, we used the yeast prion model client in conjunction with in vitro chaperone activity assays to gain mechanistic insights into the molecular basis of LGMDD1. Here, we show how mutations analogous to those found in LGMDD1 affect Sis1 (a functional homolog of human DNAJB6) function by altering the structure of client protein aggregates, interfering with the Hsp70 ATPase cycle, dimerization and substrate processing; poisoning the function of wild-type protein. These results uncover the mechanisms through which LGMDD1-associated mutations alter chaperone activity, and provide insights relevant to potential therapeutic interventions.

Developing New Treatment Options for Castration-Resistant Prostate Cancer and Recurrent Disease

Prostate cancer (PCa) is a major diagnosed cancer among men globally, and about 20% of patients develop metastatic prostate cancer (mPCa) in the initial diagnosis. PCa is a typical androgen-dependent disease; thus, hormonal therapy is commonly used as a standard care for mPCa by inhibiting androgen receptor (AR) activities, or androgen metabolism. Inevitably, almost all PCa will acquire resistance and become castration-resistant PCa (CRPC) that is associated with AR gene mutations or amplification, the presence of AR variants, loss of AR expression toward neuroendocrine phenotype, or other hormonal receptors. Treating CRPC poses a great challenge to clinicians. Research efforts in the last decade have come up with several new anti-androgen agents to prolong overall survival of CRPC patients. In addition, many potential targeting agents have been at the stage of being able to translate many preclinical discoveries into clinical practices. At this juncture, it is important to highlight the emerging strategies including small-molecule inhibitors to AR variants, DNA repair enzymes, cell survival pathway, neuroendocrine differentiation pathway, radiotherapy, CRPC-specific theranostics and immune therapy that are underway or have recently been completed.

Grp94 works upstream of BiP in protein remodeling under heat stress

Hsp90 and Hsp70 are highly conserved molecular chaperones that promote the proper folding and activation of substrate proteins that are often referred to as clients. The two chaperones functionally collaborate to fold specific clients in an ATP-dependent manner. In eukaryotic cytosol, initial client folding is done by Hsp70 and its co-chaperones, followed by a direct transfer of client refolding intermediates to Hsp90 for final client processing. However, the mechanistic details of collaboration of organelle specific Hsp70 and Hsp90 are lacking. This work investigates the collaboration of the endoplasmic reticulum (ER) Hsp70 and Hsp90, BiP and Grp94 respectively, in protein remodeling using in vitro refolding assays. We show that under milder denaturation conditions, BiP collaborates with its co-chaperones to refold misfolded proteins in an ATP-dependent manner. Grp94 does not play a major role in this refolding reaction. However, under stronger denaturation conditions that favor aggregation, Grp94 works in an ATP-independent manner to bind and hold misfolded clients in a folding competent state for subsequent remodeling by the BiP system. We also show that the collaboration of Grp94 and BiP is not simply a reversal of the eukaryotic refolding mechanism since a direct interaction of Grp94 and BiP is not required for client transfer. Instead, ATP binding but not hydrolysis by Grp94 facilitates the release of the bound client, which is then picked up by the BiP system for subsequent refolding in a Grp94-independent manner.

Conformational Dynamics and Mechanisms of Client Protein Integration into the Hsp90 Chaperone Controlled by Allosteric Interactions of Regulatory Switches: Perturbation-Based Network Approach for Mutational Profiling of the Hsp90 Binding and Allostery

Understanding the allosteric mechanisms of the Hsp90 chaperone interactions with cochaperones and client protein clientele is fundamental to dissect activation and regulation of many proteins. In this work, atomistic simulations are combined with perturbation-based approaches and dynamic network modeling for a comparative mutational profiling of the Hsp90 binding and allosteric interaction networks in the three Hsp90 maturation complexes with FKBP51 and P23 cochaperones and the glucocorticoid receptor (GR) client. The conformational dynamics signatures of the Hsp90 complexes and dynamics fluctuation analysis revealed how the intrinsic plasticity of the Hsp90 dimer can be modulated by cochaperones and client proteins to stabilize the closed dimer state required at the maturation stage of the ATPase cycle. In silico deep mutational scanning of the protein residues characterized the hot spots of protein stability and binding affinity in the Hsp90 complexes, showing that binding hot spots may often coincide with the regulatory centers that modulate dynamic allostery in the Hsp90 dimer. We introduce a perturbation-based network approach for mutational scanning of allosteric residue potentials and characterize allosteric switch clusters that control mechanism of cochaperone-dependent client recognition and remodeling by the Hsp90 chaperone. The results revealed a conserved network of allosteric switches in the Hsp90 complexes that allow cochaperones and GR protein to become integrated into the Hsp90 system by anchoring to the conformational switch points in the functional Hsp90 regions. This study suggests that the Hsp90 binding and allostery may operate under a regulatory mechanism in which activation or repression of the Hsp90 activity can be pre-encoded in the allosterically regulated Hsp90 dimer motions. By binding directly to the conformational switch centers on the Hsp90, cochaperones and interacting proteins can efficiently modulate the allosteric interactions and long-range communications required for client remodeling and activation.

A specialized Hsp90 co-chaperone network regulates steroid hormone receptor response to ligand

Heat shock protein-90 (Hsp90) chaperone machinery is involved in the stability and activity of its client proteins. The chaperone function of Hsp90 is regulated by co-chaperones and post-translational modifications. Although structural evidence exists for Hsp90 interaction with clients, our understanding of the impact of Hsp90 chaperone function toward client activity in cells remains elusive. Here, we dissect the impact of recently identified higher eukaryotic co-chaperones, FNIP1/2 (FNIPs) and Tsc1, toward Hsp90 client activity. Our data show that Tsc1 and FNIP2 form mutually exclusive complexes with FNIP1, and that unlike Tsc1, FNIP1/2 interact with the catalytic residue of Hsp90. Functionally, these co-chaperone complexes increase the affinity of the steroid hormone receptors glucocorticoid receptor and estrogen receptor to their ligands in vivo. We provide a model for the responsiveness of the steroid hormone receptor activation upon ligand binding as a consequence of their association with specific Hsp90:co-chaperone subpopulations.

Hsp multichaperone complex buffers pathologically modified Tau

Alzheimer’s disease is a neurodegenerative disorder in which misfolding and aggregation of pathologically modified Tau is critical for neuronal dysfunction and degeneration. The two central chaperones Hsp70 and Hsp90 coordinate protein homeostasis, but the nature of the interaction of Tau with the Hsp70/Hsp90 machinery has remained enigmatic. Here we show that Tau is a high-affinity substrate of the human Hsp70/Hsp90 machinery. Complex formation involves extensive intermolecular contacts, blocks Tau aggregation and depends on Tau’s aggregation-prone repeat region. The Hsp90 co-chaperone p23 directly binds Tau and stabilizes the multichaperone/substrate complex, whereas the E3 ubiquitin-protein ligase CHIP efficiently disassembles the machinery targeting Tau to proteasomal degradation. Because phosphorylated Tau binds the Hsp70/Hsp90 machinery but is not recognized by Hsp90 alone, the data establish the Hsp70/Hsp90 multichaperone complex as a critical regulator of Tau in neurodegenerative diseases.

Alzheimer’s disease is characterized by the accumulation of aggregated tau protein. Here the authors find that Hsp chaperones, which normally protect cell homeostasis, can assemble with co-chaperones in a “multichaperone machinery” to target tau aggregation.

Non-Equilibrium Protein Folding and Activation by ATP-Driven Chaperones

Recent experimental studies suggest that ATP-driven molecular chaperones can stabilize protein substrates in their native structures out of thermal equilibrium. The mechanism of such non-equilibrium protein folding is an open question. Based on available structural and biochemical evidence, I propose here a unifying principle that underlies the conversion of chemical energy from ATP hydrolysis to the conformational free energy associated with protein folding and activation. I demonstrate that non-equilibrium folding requires the chaperones to break at least one of four symmetry conditions. The Hsp70 and Hsp90 chaperones each break a different subset of these symmetries and thus they use different mechanisms for non-equilibrium protein folding. I derive an upper bound on the non-equilibrium elevation of the native concentration, which implies that non-equilibrium folding only occurs in slow-folding proteins that adopt an unstable intermediate conformation in binding to ATP-driven chaperones. Contrary to the long-held view of Anfinsen’s hypothesis that proteins fold to their conformational free energy minima, my results predict that some proteins may fold into thermodynamically unstable native structures with the assistance of ATP-driven chaperones, and that the native structures of some chaperone-dependent proteins may be shaped by their chaperone-mediated folding pathways.