Biological Actions of the Hsp90-binding Immunophilins FKBP51 and FKBP52

NFAT activation by FKBP52 promotes cancer cell proliferation by suppressing p53

FK506-binding protein 52 (FKBP52) is a member of the FKBP family of proline isomerases. FKBP52 is up-regulated in various cancers and functions as a positive regulator of steroid hormone receptors. Depletion of FKBP52 is known to inhibit cell proliferation; however, the detailed mechanism remains poorly understood. In this study, we found that FKBP52 depletion decreased MDM2 transcription, leading to stabilization of p53, and suppressed cell proliferation. We identified NFATc1 and NFATc3 as transcription factors that regulate MDM2 We also found that FKBP52 associated with NFATc3 and facilitated its nuclear translocation. In addition, calcineurin, a well-known Ca2+ phosphatase essential for activation of NFAT, plays a role in MDM2 transcription. Supporting this notion, MDM2 expression was found to be regulated by intracellular Ca2+ Taken together, these findings reveal a new role of FKBP52 in promoting cell proliferation via the NFAT-MDM2-p53 axis, and indicate that inhibition of FKBP52 could be a new therapeutic tool to activate p53 and inhibit cell proliferation.

Identification of anther thermotolerance genes by the integration of linkage and association analysis in maize

Maize is one of the world's most important staple crops, yet its production is increasingly threatened by the rising frequency of high-temperature stress (HTS). To investigate the genetic basis of anther thermotolerance under field conditions, we performed linkage and association analysis to identify HTS response quantitative trait loci (QTL) using three recombinant inbred line (RIL) populations and an association panel containing 375 diverse maize inbred lines. These analyses resulted in the identification of 16 co-located large QTL intervals. Among the 37 candidate genes identified in these QTL intervals, five have rice or Arabidopsis homologs known to influence pollen and filament development. Notably, one of the candidate genes, ZmDUP707, has been subject to selection pressure during breeding. Its expression is suppressed by HTS, leading to pollen abortion and barren seeds. We also identified several additional candidate genes potentially underly QTL previously reported by other researchers. Taken together, our results provide a pool of valuable candidate genes that could be employed by future breeding programs aiming at enhancing maize HTS tolerance.

The Role of HSP90 Molecular Chaperones in Depression: Potential Mechanisms

Major depressive disorder (MDD) is characterized by high rates of disability and death and has become a public health problem that threatens human life and health worldwide. HPA axis disorder and neuroinflammation are two common biological abnormalities in MDD patients. Hsp90 is an important molecular chaperone that is widely distributed in the organism. Hsp90 binds to the co-chaperone and goes through a molecular chaperone cycle to complete its regulation of the client protein. Numerous studies have demonstrated that Hsp90 regulates how the HPA axis reacts to stress and how GR, the HPA axis' responsive substrate, matures. In addition, Hsp90 exhibits pro-inflammatory effects that are closely related to neuroinflammation in MDD. Currently, Hsp90 inhibitors have made some progress in the treatment of a variety of human diseases, but they still need to be improved. Further insight into the role of Hsp90 in MDD provides new ideas for the development of new antidepressant drugs targeting Hsp90.

The Role of FKBPs in Complex Disorders: Neuropsychiatric Diseases, Cancer, and Type 2 Diabetes Mellitus

Stress is a common denominator of complex disorders and the FK-506 binding protein (FKBP)51 plays a central role in stress. Hence, it is not surprising that multiple studies imply the involvement of the FKBP51 protein and/or its coding gene, FKBP5, in complex disorders. This review summarizes such reports concentrating on three disorder clusters-neuropsychiatric, cancer, and type 2 diabetes mellitus (T2DM). We also attempt to point to potential mechanisms suggested to mediate the effect of FKBP5/FKBP51 on these disorders. Neuropsychiatric diseases considered in this paper include (i) Huntington's disease for which increased autophagic cellular clearance mechanisms related to decreased FKBP51 protein levels or activity is discussed, Alzheimer's disease for which increased FKBP51 activity has been shown to induce Tau phosphorylation and aggregation, and Parkinson's disease in the context of which FKBP12 is mentioned; and (ii) mental disorders, for which significant association with the single nucleotide polymorphism (SNP) rs1360780 of FKBP5 intron 7 along with decreased DNA methylation were revealed. Since cancer is a large group of diseases that can start in almost any organ or tissue of the body, FKBP51's role depends on the tissue type and differences among pathways expressed in those tumors. The FKBP51-heat-shock protein-(Hsp)90-p23 super-chaperone complex might function as an oncogene or as a tumor suppressor by downregulating the serine/threonine protein kinase (AKt) pathway. In T2DM, two potential pathways for the involvement of FKBP51 are highlighted as affecting the pathogenesis of the disease-the peroxisome proliferator-activated receptor-γ (PPARγ) and AKt.

FKBP4 correlates with CD8+ T cells and lymphatic metastases in oral squamous cell carcinoma

OBJECTIVES

To identify the engagement of CD8+ T cells in the lymph node metastasis (LNM) of oral squamous cell carcinoma (OSCC) and significant CD8+ T cell-related genes regulating the LNM.

SUBJECTS AND METHODS

Tumor samples of primary OSCC patients were obtained (n = 71). CD8 expression in LNM- and LNM+ tumors were identified using tissue microarray (TMA)-based immunohistochemistry (IHC) and compared using the Mann-Whitney U test. The LNM status, as well as the metagene expression of CD8+ T cells of OSCC patients, were obtained from The Cancer Genome Atlas (TCGA) database. Metagenes related to LNM were screened using logistic regression analyses and further identified using TMA-based IHC.

RESULTS

CD8 was significantly positively associated with LNM (p < 0.05). Furthermore, tumors with higher expression of FKBP4 had significantly higher LNM rate (HR: 1.63; 95% CI: 1.08 ~ 2.53; p < 0.05), which was also proven using TMA-based IHC analysis.

CONCLUSION

CD8+ T cells might engage in the lymphatic metastases of OSCC. Among CD8+ T cell-related genes, FKBP4 could be a promising biomarker to predict the risk of LNM of OSCC.

Early Life Stress and Major Depressive Disorder-An Update on Molecular Mechanisms and Synaptic Impairments

Early life stress (ELS), characterized as abuse, neglect, and abandonment, can cause several adverse consequences in the lives of affected individuals. ELS experiences can affect an individual's development in variable ways, persisting in the long term and promoting lasting impacts, considering that early exposure to stressors can be biologically incorporated, as prolonged stimulation of stress response systems affects the development of the brain structure and other body systems, increasing the risk of diseases associated with stress and cognitive impairment. This type of stress increases the risk of developing major depressive disorder (MDD) in a severe form that does not respond adequately to traditional antidepressant treatments. Several alterations are studied as mechanisms that relate ELS with MDD, such as epigenetic alterations, neurotransmitters, and neuronal signaling. This review discusses research that brings evidence about the ELS mechanisms involved in synaptic impairments and MDD. The processes involved in epigenetic changes and the HPA axis are highlighted, as well as changes in neurotransmitters and neuronal signaling mechanisms.

Glucocorticoids, their uses, sexual dimorphisms, and diseases: new concepts, mechanisms, and discoveries

The normal stress response in humans is governed by the hypothalamic-pituitary-adrenal (HPA) axis through heightened mechanisms during stress, raising blood levels of the glucocorticoid hormone cortisol. Glucocorticoids are quintessential compounds that balance the proper functioning of numerous systems in the mammalian body. They are also generated synthetically and are the preeminent therapy for inflammatory diseases. They act by binding to the nuclear receptor transcription factor glucocorticoid receptor (GR), which has two main isoforms (GRα and GRβ). Our classical understanding of glucocorticoid signaling is from the GRα isoform, which binds the hormone, whereas GRβ has no known ligands. With glucocorticoids being involved in many physiological and cellular processes, even small disruptions in their release via the HPA axis, or changes in GR isoform expression, can have dire ramifications on health. Long-term chronic glucocorticoid therapy can lead to a glucocorticoid-resistant state, and we deliberate how this impacts disease treatment. Chronic glucocorticoid treatment can lead to noticeable side effects such as weight gain, adiposity, diabetes, and others that we discuss in detail. There are sexually dimorphic responses to glucocorticoids, and women tend to have a more hyperresponsive HPA axis than men. This review summarizes our understanding of glucocorticoids and critically analyzes the GR isoforms and their beneficial and deleterious mechanisms and the sexual differences that cause a dichotomy in responses. We also discuss the future of glucocorticoid therapy and propose a new concept of dual GR isoform agonist and postulate why activating both isoforms may prevent glucocorticoid resistance.

DnaJs are enriched in tau regulators

The aberrant accumulation of tau protein is implicated as a pathogenic factor in many neurodegenerative diseases. Tau seeding may underlie its predictable spread in these diseases. Molecular chaperones can modulate tau pathology, but their effects have mainly been studied in isolation. This study employed a semi-high throughput assay to identify molecular chaperones influencing tau seeding using Tau RD P301S FRET Biosensor cells, which express a portion of tau containing the frontotemporal dementia-related P301S tau mutation fused to a FRET biosensor. Approximately fifty chaperones from five major families were screened using live cell imaging to monitor FRET-positive tau seeding. Among the tested chaperones, five exhibited significant effects on tau in the primary screen. Notably, three of these were from the DnaJ family. In subsequent studies, overexpression of DnaJA2, DnaJB1, and DnaJB6b resulted in significant reductions in tau levels. Knockdown experiments by shRNA revealed an inverse correlation between DnaJB1 and DnaJB6b with tau levels. DnaJB6b overexpression, specifically, reduced total tau levels in a cellular model with a pre-existing pool of tau, partially through enhanced proteasomal degradation. Further, DnaJB6b interacted with tau complexes. These findings highlight the potent chaperone activity within the DnaJ family, particularly DnaJB6b, towards tau.

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.

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.

FKBP25 regulates myoblast viability and migration and is differentially expressed in in vivo models of muscle adaptation

FKBP25 (FKBP3 gene) is a dual-domain PPIase protein that consists of a C-terminal PPIase domain and an N-terminal basic tilted helix bundle (BTHB). The PPIase domain of FKBP25 has been shown to bind to microtubules, which has impacts upon microtubule polymerisation and cell cycle progression. Using quantitative proteomics, it was recently found that FKBP25 was expressed in the top 10% of the mouse skeletal muscle proteome. However, to date there have been few studies investigating the role of FKBP25 in non-transformed systems. As such, this study aimed to investigate potential roles for FKBP25 in myoblast viability, migration and differentiation and in adaptation of mature skeletal muscle. Doxycycline-inducible FKBP25 knockdown in C2C12 myoblasts revealed an increase in cell accumulation/viability and migration in vitro that was independent of alterations in tubulin dynamics; however, FKBP25 knockdown had no discernible impact on myoblast differentiation into myotubes. Finally, a series of in vivo models of muscle adaptation were assessed, where it was observed that FKBP25 protein expression was increased in hypertrophy and regeneration conditions (chronic mechanical overload and the mdx model of Duchenne muscular dystrophy) but decreased in an atrophy model (denervation). Overall, the findings of this study establish FKBP25 as a regulator of myoblast viability and migration, with possible implications for satellite cell proliferation and migration and muscle regeneration, and as a potential regulator of in vivo skeletal muscle adaptation.

Comparing MitoQ10 and heat therapy: Evaluating mechanisms and therapeutic potential for polycystic ovary syndrome induced by circadian rhythm disruption

Environmental factors, such as sleep restriction, contribute to polycystic ovary syndrome (PCOS) by causing hyperinsulinemia, hyperandrogenism, insulin resistance, and oligo- or anovulation. This study aimed to evaluate the effects of circadian rhythm disruption on reproductive and metabolic functions and investigate the potential therapeutic benefits of MitoQ10 and hot tub therapy (HTT). Sixty female rats were divided into six groups: control, MitoQ10, HTT, and three groups with PCOS induced by continuous light exposure(L/L). The reproductive, endocrine, and structural manifestations ofL/L-induced PCOS were confirmed by serum biochemical measurements, ultrasound evaluation of ovarian size, and vaginal smear examination at week 14. Subsequently, the rats were divided into the L/L (untreated), L/L+MitoQ10-treated, andL/L+HTT-treated groups. At the end of week 22, all rats were sacrificed. Treatmentwith MitoQ10 or HTT partially reversed the reproductive, endocrine, and structural features of PCOS, leading to a decreased amplitude of isolated uterine contractions, ovarian cystic changes and size, and endometrial thickness. Furthermore, both interventions improved the elevated serum levels of anti-Mullerian hormone (AMH), kisspeptin, Fibulin-1, A disintegrin and metalloproteinase with thrombospondin motifs 19 (ADAMTS-19), lipid profile, homeostatic model assessment for insulin resistance (HOMA-IR), oxidative stress markers, androgen receptors (AR) and their transcription target genes, FKBP52 immunostaining in ovarian tissues, and uterine estrogen receptor alpha (ER-α) and PRimmunostaining. In conclusion, MitoQ10 supplementation and HTT demonstrated the potential for ameliorating metabolic, reproductive, and structural perturbations associated with PCOS induced by circadian rhythm disruption. These findings suggest a potential therapeutic role for these interventions in managing PCOS in women.

Corticosterone mediates FKBP51 signaling and inflammation response in the trigeminal ganglion in chronic stress-induced corneal hyperalgesia mice

Stress-induced hyperalgesia is a health-threatening condition that lacks effective therapeutic intervention, impairing the quality of life. Interestingly, a high prevalence of corneal pain symptoms was also found in patients experienced severe stressors. Excessive secretion corticosterone in rodents has been shown to contribute to the development of visceral and mechanical hyperalgesia under stressful conditions. The co-chaperone protein FK506-binding protein 5 (FKBP5) was reported to modulate steroid sensitivity and inhibition of FKBP51 possessed anxiolytic and anti-hyperalgesic in the stressed-mice model. However, whether corticosterone and FKBP5 play a role in chronic stress-induced corneal hyperalgesia remains unknown. The aim of this study was to evaluate the corneal sensitivity after exposure to chronic restraint stress (CRS) and investigate the potential role of corticosterone and FKBP5 mediated proinflammatory cytokines release in trigeminal ganglion (TG) in corneal hyperalgesia under chronic stressful situations. Firstly, mice displayed increased corneal sensitivity without changes in tear production and corneal injury after CRS for 4 hours/day for 14 days. Meanwhile, corticosterone deficiency via adrenalectomy could prevent CRS-induced corneal hyperalgesia, whereas chronic corticosterone feeding increased the corneal sensitivity accompanied by increasing proinflammatory cytokines levels of phospho-NF-κB (p-NF-κB), tumor necrosis factor (TNF)-α and interleukin (IL)-1β in the TG on d14. Notably, we found that FKBP51 was significantly upregulated in the TG in the stressed-mice. Intraperitoneal injection of FKBP51 inhibitor significantly alleviated CRS-induced corneal hyperalgesia, and reversed calcitonin gene related peptide (CGRP) increase and proinflammatory cytokines production in the TG. Moreover, FKBP51 inhibitor could also exert its anti-hyperalgesic effect on corneal pain through intra-TG injection. Our study proves that CRS can induce corneal hyperalgesia in mice and uncovers the role of corticosterone and FKBP51 in modulating corneal sensitivity, providing a novel treatment strategy for stress-induced corneal hyperalgesia. AVAILABILITY OF DATA AND MATERIALS: All data and additional file are available upon request from the corresponding author.

Role of FKBP5 and its genetic mutations in stress-induced psychiatric disorders: an opportunity for drug discovery

Stress-induced mental health disorders are affecting many people around the world. However, effective drug therapy for curing psychiatric diseases does not occur sufficiently. Many neurotransmitters, hormones, and mechanisms are essential in regulating the body's stress response. One of the most critical components of the stress response system is the hypothalamus-pituitary-adrenal (HPA) axis. The FKBP prolyl isomerase 51 (FKBP51) protein is one of the main negative regulators of the HPA axis. FKBP51 negatively regulates the cortisol effects (the end product of the HPA axis) by inhibiting the interaction between glucocorticoid receptors (GRs) and cortisol, causing reduced transcription of downstream cortisol molecules. By regulating cortisol effects, the FKBP51 protein can indirectly regulate the sensitivity of the HPA axis to stressors. Previous studies have indicated the influence of FKBP5 gene mutations and epigenetic changes in different psychiatric diseases and drug responses and recommended the FKBP51 protein as a drug target and a biomarker for psychological disorders. In this review, we attempted to discuss the effects of the FKBP5 gene, its mutations on different psychiatric diseases, and drugs affecting the FKBP5 gene.

FKBP5, a Modulator of Stress Responses Involved in Malignant Mesothelioma: The Link between Stress and Cancer

Malignant pleural mesothelioma (MPM) is a rare tumour characterized by a long latency period after asbestos exposure and poor survival [...].

Structure and function of the TPR-domain immunophilins FKBP51 and FKBP52 in normal physiology and disease

Coordinated cochaperone interactions with Hsp90 and associated client proteins are crucial for a multitude of signaling pathways in normal physiology, as well as in disease settings. Research on the molecular mechanisms regulated by the Hsp90 multiprotein complexes has demonstrated increasingly diverse roles for cochaperones throughout Hsp90-regulated signaling pathways. Thus, the Hsp90-associated cochaperones have emerged as attractive therapeutic targets in a wide variety of disease settings. The tetratricopeptide repeat (TPR)-domain immunophilins FKBP51 and FKBP52 are of special interest among the Hsp90-associated cochaperones given their Hsp90 client protein specificity, ubiquitous expression across tissues, and their increasingly important roles in neuronal signaling, intracellular calcium release, peptide bond isomerization, viral replication, steroid hormone receptor function, and cell proliferation to name a few. This review summarizes the current knowledge of the structure and molecular functions of TPR-domain immunophilins FKBP51 and FKBP52, recent findings implicating these immunophilins in disease, and the therapeutic potential of targeting FKBP51 and FKBP52 for the treatment of disease.

Cerebral iron deficiency may induce depression through downregulation of the hippocampal glucocorticoid-glucocorticoid receptor signaling pathway

BACKGROUND

Iron is a trace essential element to sustain the normal neurological function of human. Many researches had reported the involvement of iron deficiency (ID) in neural development and cognitive functions. However, the role of ID in pathogenesis of depression and its underlying mechanism are still unclear.

METHODS

In this study, we first used chronic unpredicted mild stress (CUMS) and iron deprivation mouse models to clarify the pathogenesis role of cerebral ID in depression. Then the role of hippocampal glucocorticoid (GC)-glucocorticoid receptor (GR) pathway in cerebral ID induced depression were elucidated in iron deprivation mice and iron deficiency anemia patients.

RESULTS

Our results revealed that both CUMS and iron deprivation could induce cerebral ID in mice, and combination of iron deprivation and CUMS could accelerate the onset and aggravate the symptoms of depression in mice. In hippocampus, ID led to neuronal injury and neurogenesis decrease, which might be related to downregulation of GC-GR signaling pathway caused GR dysfunction, thereby inhibiting the negative feedback regulation function of hippocampus on hypothalamic-pituitary-adrenal (HPA) axis. Moreover, the overactivity of HPA axis in iron deprivation mice and iron deficiency anemia patients also confirmed GR dysfunction.

LIMITATIONS

Iron deprivation led to food and water intake decrease of mice, which may affect the behavioral test. In addition, we mainly evaluated the role of hippocampal ID in depression, and the number of iron deficiency anemia patients was limited.

CONCLUSIONS

Our results identified that cerebral iron homeostasis was a key factor for maintaining mental stability.

Analysis of the Selective Antagonist SAFit2 as a Chemical Probe for the FK506-Binding Protein 51

The FK506-binding protein 51 (FKBP51) has emerged as an important regulator of the mammalian stress response and is involved in persistent pain states and metabolic pathways. The FK506 analog SAFit2 (short for selective antagonist of FKBP51 by induced fit) was the first potent and selective FKBP51 ligand with an acceptable pharmacokinetic profile. At present, SAFit2 represents the gold standard for FKBP51 pharmacology and has been extensively used in numerous biological studies. Here we review the current knowledge on SAFit2 as well as guidelines for its use.

Mitochondrial-nuclear communication by FKBP51 shuttling

The HSP90-binding immunophilin FKBP51 is a soluble protein that shows high homology and structural similarity with FKBP52. Both immunophilins are functionally divergent and often show antagonistic actions. They were first described in steroid receptor complexes, their exchange in the complex being the earliest known event in steroid receptor activation upon ligand binding. In addition to steroid-related events, several pleiotropic actions of FKBP51 have emerged during the last years, ranging from cell differentiation and apoptosis to metabolic and psychiatric disorders. On the other hand, mitochondria play vital cellular roles in maintaining energy homeostasis, responding to stress conditions, and affecting cell cycle regulation, calcium signaling, redox homeostasis, and so forth. This is achieved by proteins that are encoded in both the nuclear genome and mitochondrial genes. This implies active nuclear-mitochondrial communication to maintain cell homeostasis. Such communication involves factors that regulate nuclear and mitochondrial gene expression affecting the synthesis and recruitment of mitochondrial and nonmitochondrial proteins, and/or changes in the functional state of the mitochondria itself, which enable mitochondria to recover from stress. FKBP51 has emerged as a serious candidate to participate in these regulatory roles since it has been unexpectedly found in mitochondria showing antiapoptotic effects. Such localization involves the tetratricopeptide repeats domains of the immunophilin and not its intrinsic enzymatic activity of peptidylprolyl-isomerase. Importantly, FKBP51 abandons the mitochondria and accumulates in the nucleus upon cell differentiation or during the onset of stress. Nuclear FKBP51 enhances the enzymatic activity of telomerase. The mitochondrial-nuclear trafficking is reversible, and certain situations such as viral infections promote the opposite trafficking, that is, FKBP51 abandons the nucleus and accumulates in mitochondria. In this article, we review the latest findings related to the mitochondrial-nuclear communication mediated by FKBP51 and speculate about the possible implications of this phenomenon.

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.

A protein engineering approach toward understanding FKBP51 conformational dynamics and mechanisms of ligand binding

Most proteins are flexible molecules that coexist in an ensemble of several conformations. Point mutations in the amino acid sequence of a protein can trigger structural changes that drive the protein population to a conformation distinct from the native state. Here, we report a protein engineering approach to better understand protein dynamics and ligand binding of the FK506-binding protein 51 (FKBP51), a prospective target for stress-related diseases, metabolic disorders, some types of cancers and chronic pain. By randomizing selected regions of its ligand-binding domain and sorting yeast display libraries expressing these variants, mutants with high affinity to conformation-specific FKBP51 selective ligands were identified. These improved mutants are valuable tools for the discovery of novel selective ligands that preferentially and specifically bind the FKBP51 active site in its open conformation state. Moreover, they will help us understand the conformational dynamics and ligand binding mechanics of the FKBP51 binding pocket.

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.

Impact of Co-chaperones and Posttranslational Modifications Toward Hsp90 Drug Sensitivity

Posttranslational modifications (PTMs) regulate myriad cellular processes by modulating protein function and protein-protein interaction. Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone whose activity is responsible for the stabilization and maturation of more than 300 client proteins. Hsp90 is a substrate for numerous PTMs, which have diverse effects on Hsp90 function. Interestingly, many Hsp90 clients are enzymes that catalyze PTM, demonstrating one of the several modes of regulation of Hsp90 activity. Approximately 25 co-chaperone regulatory proteins of Hsp90 impact structural rearrangements, ATP hydrolysis, and client interaction, representing a second layer of influence on Hsp90 activity. A growing body of literature has also established that PTM of these co-chaperones fine-tune their activity toward Hsp90; however, many of the identified PTMs remain uncharacterized. Given the critical role of Hsp90 in supporting signaling in cancer, clinical evaluation of Hsp90 inhibitors is an area of great interest. Interestingly, differential PTM and co-chaperone interaction have been shown to impact Hsp90 binding to its inhibitors. Therefore, understanding these layers of Hsp90 regulation will provide a more complete understanding of the chaperone code, facilitating the development of new biomarkers and combination therapies.

FK506 binding protein 51: Its role in the adipose organ and beyond

There is a great body of evidence that the adipose organ plays a central role in the control not only of energy balance, but importantly, in the maintenance of metabolic homeostasis. Interest in the study of different aspects of its physiology grew in the last decades due to the pandemic of obesity and the consequences of metabolic syndrome. It was not until recently that the first evidence for the role of the high molecular weight immunophilin FK506 binding protein (FKBP) 51 in the process of adipocyte differentiation have been described. Since then, many new facets have been discovered of this stress-responsive FKBP51 as a central node for precise coordination of many cell functions, as shown for nuclear steroid receptors, autophagy, signaling pathways as Akt, p38 MAPK, and GSK3, as well as for insulin signaling and the control of glucose homeostasis. Thus, the aim of this review is to integrate and discuss the recent advances in the understanding of the many roles of FKBP51 in the adipose organ.

The Scaffold Immunophilin FKBP51 Is a Phosphoprotein That Undergoes Dynamic Mitochondrial-Nuclear Shuttling

The immunophilin FKBP51 forms heterocomplexes with molecular chaperones, protein-kinases, protein-phosphatases, autophagy-related factors, and transcription factors. Like most scaffold proteins, FKBP51 can use a simple tethering mechanism to favor the efficiency of interactions with partner molecules, but it can also exert more complex allosteric controls over client factors, the immunophilin itself being a putative regulation target. One of the simplest strategies for regulating pathways and subcellular localization of proteins is phosphorylation. In this study, it is shown that scaffold immunophilin FKBP51 is resolved by resolutive electrophoresis in various phosphorylated isoforms. This was evidenced by their reactivity with specific anti-phosphoamino acid antibodies and their fade-out by treatment with alkaline phosphatase. Interestingly, stress situations such as exposure to oxidants or in vivo fasting favors FKBP51 translocation from mitochondria to the nucleus. While fasting involves phosphothreonine residues, oxidative stress involves tyrosine residues. Molecular modeling predicts the existence of potential targets located at the FK1 domain of the immunophilin. Thus, oxidative stress favors FKBP51 dephosphorylation and protein degradation by the proteasome, whereas FK506 binding protects the persistence of the post-translational modification in tyrosine, leading to FKBP51 stability under oxidative conditions. Therefore, FKBP51 is revealed as a phosphoprotein that undergoes differential phosphorylations according to the stimulus.

The emerging importance of immunophilins in fibrosis development

Immunophilins are a family of proteins encompassing FK506-binding proteins (FKBPs) and cyclophilins (Cyps). FKBPs and Cyps exert peptidyl-prolyl cis-trans isomerase (PPIase) activity, which facilitates diverse protein folding assembly, or disassembly. In addition, they bind to immunosuppressant medications where FKBPs bind to tacrolimus (FK506) and rapamycin, whereas cyclophilins bind to cyclosporin. Some large immunophilins have domains other than PPIase referred to as tetratricopeptide (TPR) domain, which is involved in heat shock protein 90 (Hsp90) and heat shock protein 70 (Hsp 70) chaperone interaction. The TPR domain confers immunophilins’ pleotropic actions to mediate various physiological and biochemical processes. So far, immunophilins have been implicated to play an important role in pathophysiology of inflammation, cancer and neurodegenerative disorders. However, their importance in the development of fibrosis has not yet been elucidated. In this review we focus on the pivotal functional and mechanistic roles of different immunophilins in fibrosis establishment affecting various organs. The vast majority of the studies reported that cyclophilin A, FKBP12 and FKBP10 likely induce organ fibrosis through the calcineurin or TGF-β pathways. FKBP51 demonstrated a role in myelofibrosis development through calcineurin-dependant pathway, STAT5 or NF-κB pathways. Inhibition of these specific immunophilins has been shown to decrease the extent of fibrosis suggesting that immunophilins could be a novel promising therapeutic target to prevent or reverse fibrosis.

Progesterone as an Anti-Inflammatory Drug and Immunomodulator: New Aspects in Hormonal Regulation of the Inflammation

The specific regulation of inflammatory processes by steroid hormones has been actively studied in recent years, especially by progesterone (P₄) and progestins. The mechanisms of the anti-inflammatory and immunomodulatory P₄ action are not fully clear. The anti-inflammatory effects of P₄ can be defined as nonspecific, associated with the inhibition of NF-κB and COX, as well as the inhibition of prostaglandin synthesis, or as specific, associated with the regulation of T-cell activation, the regulation of the production of pro- and anti-inflammatory cytokines, and the phenomenon of immune tolerance. The specific anti-inflammatory effects of P₄ and its derivatives (progestins) can also include the inhibition of proliferative signaling pathways and the antagonistic action against estrogen receptor beta-mediated signaling as a proinflammatory and mitogenic factor. The anti-inflammatory action of P₄ is accomplished through the participation of progesterone receptor (PR) chaperones HSP90, as well as immunophilins FKBP51 and FKBP52, which are the validated targets of clinically approved immunosuppressive drugs. The immunomodulatory and anti-inflammatory effects of HSP90 inhibitors, tacrolimus and cyclosporine, are manifested, among other factors, due to their participation in the formation of an active ligand–receptor complex of P₄ and their interaction with its constituent immunophilins. Pharmacological agents such as HSP90 inhibitors can restore the lost anti-inflammatory effect of glucocorticoids and P₄ in chronic inflammatory and autoimmune diseases. By regulating the activity of FKBP51 and FKBP52, it is possible to increase or decrease hormonal signaling, as well as restore it during the development of hormone resistance. The combined action of immunophilin suppressors with steroid hormones may be a promising strategy in the treatment of chronic inflammatory and autoimmune diseases, including endometriosis, stress-related disorders, rheumatoid arthritis, and miscarriages. Presumably, the hormone receptor- and immunophilin-targeted drugs may act synergistically, allowing for a lower dose of each.

GP, Gopalakrishnan AV. Role of Immune Cells and Receptors in Cancer Treatment: An Immunotherapeutic Approach

Cancer immunotherapy moderates the immune system’s ability to fight cancer. Due to its extreme complexity, scientists are working to put together all the puzzle pieces to get a clearer picture of the immune system. Shreds of available evidence show the connection between cancer and the immune system. Immune responses to tumors and lymphoid malignancies are influenced by B cells, γδT cells, NK cells, and dendritic cells (DCs). Cancer immunotherapy, which encompasses adoptive cancer therapy, monoclonal antibodies (mAbs), immune checkpoint therapy, and CART cells, has revolutionized contemporary cancer treatment. This article reviews recent developments in immune cell regulation and cancer immunotherapy. Various options are available to treat many diseases, particularly cancer, due to the progress in various immunotherapies, such as monoclonal antibodies, recombinant proteins, vaccinations (both preventative and curative), cellular immunotherapies, and cytokines.

FKBP51, AmotL2 and IQGAP1 Involvement in Cilastatin Prevention of Cisplatin-Induced Tubular Nephrotoxicity in Rats

The immunophilin FKBP51, the angiomotin AmotL2, and the scaffoldin IQGAP1 are overexpressed in many types of cancer, with the highest increase in leucocytes from patients undergoing oxaliplatin chemotherapy. Inflammation is involved in the pathogenesis of nephrotoxicity induced by platinum analogs. Cilastatin prevents renal damage caused by cisplatin. This functional and confocal microscopy study shows the renal focal-segmental expression of TNFα after cisplatin administration in rats, predominantly of tubular localization and mostly prevented by co-administration of cilastatin. FKBP51, AmotL2 and IQGAP1 protein expression increases slightly with cilastatin administration and to a much higher extent with cisplatin, in a cellular- and subcellular-specific manner. Kidney tubule cells expressing FKBP51 show either very low or no expression of TNFα, while cells expressing TNFα have low levels of FKBP51. AmotL2 and TNFα seem to colocalize and their expression is increased in tubular cells. IQGAP1 fluorescence increases with cilastatin, cisplatin and joint cilastatin-cisplatin treatment, and does not correlate with TNFα expression or localization. These data suggest a role for FKBP51, AmotL2 and IQGAP1 in cisplatin toxicity in kidney tubules and in the protective effect of cilastatin through inhibition of dehydropeptidase-I.

Differential expression of genes regulated by the glucocorticoid receptor pathway in patients with pulmonary tuberculosis

AIMS

Previous studies in TB patients showed an immuno-endocrine imbalance characterized by a disease-severity associated increase in plasma levels of proinflammatory cytokines and glucocorticoids (GCs). To analyze the potential immunomodulatory effect of circulating GCs over peripheral blood mononuclear cells (PBMC) from TB patients, we investigated the expression of positively (anti-inflammatory-related genes ANXA1; FKBP51; GILZ, NFKBIA, and NFKBIB) and negatively (inflammatory genes: IL-6, IL-1β, and IFN-γ) Glucocorticoids Receptors (GR)-regulated genes. Plasma concentrations of cytokines and hormones, together with specific lymphoproliferation were also assessed.

MATERIALS AND METHODS

Gene expression was quantified by RT-qPCR, specific lymphoproliferation by ³H-thymidine incorporation, whereas plasma cytokines and hormones levels by ELISA.

KEY FINDINGS

Transcripts of ANXA1, GILZ, NFKBIB, and NFKBIA appeared significantly increased in patients, whereas FKBP51, IL-6, IL-1β, and NF-κB remained unchanged. Upon analyzing according to disease severity, mRNA levels for ANXA1 and NFKBIB were even higher in moderate and severe patients. GILZ was increased in moderate cases, with NFKBIA and IL-1 β being higher in severe ones, who also displayed increased GRβ transcripts. TB patients had reduced plasma DHEA concentrations together with increased pro and anti-inflammatory cytokines (IFN-γ, IL-6, and IL-10) cortisol and cortisol/DHEA ratio, more evident in progressive cases, in whom their PBMC also showed a decreased mycobacterial-driven proliferation. The cortisol/DHEA ratio and GRα expression were positively correlated with GR-regulated genes mainly in moderate patients.

SIGNIFICANCE

The increased expression of cortisol-regulated anti-inflammatory genes in TB patients-PBMC, predominantly in progressive disease, seems compatible with a relatively insufficient attempt to downregulate the accompanying inflammation.

Advances towards Understanding the Mechanism of Action of the Hsp90 Complex

Hsp90 (Heat Shock Protein 90) is an ATP (Adenosine triphosphate) molecular chaperone responsible for the activation and maturation of client proteins. The mechanism by which Hsp90 achieves such activation, involving structurally diverse client proteins, has remained enigmatic. However, recent advances using structural techniques, together with advances in biochemical studies, have not only defined the chaperone cycle but have shed light on its mechanism of action. Hsp90 hydrolysis of ATP by each protomer may not be simultaneous and may be dependent on the specific client protein and co-chaperone complex involved. Surprisingly, Hsp90 appears to remodel client proteins, acting as a means by which the structure of the client protein is modified to allow its subsequent refolding to an active state, in the case of kinases, or by making the client protein competent for hormone binding, as in the case of the GR (glucocorticoid receptor). This review looks at selected examples of client proteins, such as CDK4 (cyclin-dependent kinase 4) and GR, which are activated according to the so-called ‘remodelling hypothesis’ for their activation. A detailed description of these activation mechanisms is paramount to understanding how Hsp90-associated diseases develop.

FKBP52 in Neuronal Signaling and Neurodegenerative Diseases: A Microtubule Story

The FK506-binding protein 52 (FKBP52) belongs to a large family of ubiquitously expressed and highly conserved proteins (FKBPs) that share an FKBP domain and possess Peptidyl-Prolyl Isomerase (PPIase) activity. PPIase activity catalyzes the isomerization of Peptidyl-Prolyl bonds and therefore influences target protein folding and function. FKBP52 is particularly abundant in the nervous system and is partially associated with the microtubule network in different cell types suggesting its implication in microtubule function. Various studies have focused on FKBP52, highlighting its importance in several neuronal microtubule-dependent signaling pathways and its possible implication in neurodegenerative diseases such as tauopathies (i.e., Alzheimer disease) and alpha-synucleinopathies (i.e., Parkinson disease). This review summarizes our current understanding of FKBP52 actions in the microtubule environment, its implication in neuronal signaling and function, its interactions with other members of the FKBPs family and its involvement in neurodegenerative disease.

Heat Shock Proteins in Benign Prostatic Hyperplasia and Prostate Cancer

Two out of three diseases of the prostate gland affect aging men worldwide. Benign prostatic hyperplasia (BPH) is a noncancerous enlargement affecting millions of men. Prostate cancer (PCa) in turn is the second leading cause of cancer death. The factors influencing the occurrence of BPH and PCa are different; however, in the course of these two diseases, the overexpression of heat shock proteins is observed. Heat shock proteins (HSPs), chaperone proteins, are known to be one of the main proteins playing a role in maintaining cell homeostasis. HSPs take part in the process of the proper folding of newly formed proteins, and participate in the renaturation of damaged proteins. In addition, they are involved in the transport of specific proteins to the appropriate cell organelles and directing damaged proteins to proteasomes or lysosomes. Their function is to protect the proteins against degradation factors that are produced during cellular stress. HSPs are also involved in modulating the immune response and the process of apoptosis. One well-known factor affecting HSPs is the androgen receptor (AR)—a main player involved in the development of BPH and the progression of prostate cancer. HSPs play a cytoprotective role and determine the survival of cancer cells. These chaperones are often upregulated in malignancies and play an indispensable role in tumor progression. Therefore, HSPs are considered as one of the therapeutic targets in anti-cancer therapies. In this review article, we discuss the role of different HSPs in prostate diseases, and their potential as therapeutic targets.

Modulating FKBP5/FKBP51 and autophagy lowers HTT (huntingtin) levels

Current disease-modifying therapies for Huntington disease (HD) focus on lowering mutant HTT (huntingtin; mHTT) levels, and the immunosuppressant drug rapamycin is an intriguing therapeutic for aging and neurological disorders. Rapamycin interacts with FKBP1A/FKBP12 and FKBP5/FKBP51, inhibiting the MTORC1 complex and increasing cellular clearance mechanisms. Whether the levels of FKBP (FK506 binding protein) family members are altered in HD models and if these proteins are potential therapeutic targets for HD have not been investigated. Here, we found levels of FKBP5 are significantly reduced in HD R6/2 and zQ175 mouse models and human HD isogenic neural stem cells and medium spiny neurons derived from induced pluripotent stem cells. Moreover, FKBP5 interacts and colocalizes with HTT in the striatum and cortex of zQ175 mice and controls. Importantly, when we decreased FKBP5 levels or activity by genetic or pharmacological approaches, we observed reduced levels of mHTT in our isogenic human HD stem cell model. Decreasing FKBP5 levels by siRNA or pharmacological inhibition increased LC3-II levels and macroautophagic/autophagic flux, suggesting autophagic cellular clearance mechanisms are responsible for mHTT lowering. Unlike rapamycin, the effect of pharmacological inhibition with SAFit2, an inhibitor of FKBP5, is MTOR independent. Further, in vivo treatment for 2 weeks with SAFit2, results in reduced HTT levels in both HD R6/2 and zQ175 mouse models. Our studies establish FKBP5 as a protein involved in the pathogenesis of HD and identify FKBP5 as a potential therapeutic target for HD.Abbreviations : ACTB/β-actin: actin beta; AD: Alzheimer disease; BafA1: bafilomycin A1; BCA: bicinchoninic acid; BBB: blood brain barrier; BSA: bovine serum albumin; CoIP: co-immunoprecipitation; DMSO: dimethyl sulfoxide; DTT: dithiothreitol; FKBPs: FK506 binding proteins; HD: Huntington disease; HTT: huntingtin; iPSC: induced pluripotent stem cells; MAP1LC3/LC3:microtubule associated protein 1 light chain 3; MAPT/tau: microtubule associated protein tau; MES: 2-ethanesulfonic acid; MOPS: 3-(N-morphorlino)propanesulfonic acid); MSN: medium spiny neurons; mHTT: mutant huntingtin; MTOR: mechanistic target of rapamycin kinase; NSC: neural stem cells; ON: overnight; PD: Parkinson disease; PPIase: peptidyl-prolyl cis/trans-isomerases; polyQ: polyglutamine; PPP1R1B/DARPP-32: protein phosphatase 1 regulatory inhibitor subunit 1B; PTSD: post-traumatic stress disorder; RT: room temperature; SQSTM1/p62: sequestosome 1; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TBST:Tris-buffered saline, 0.1% Tween 20; TUBA: tubulin; ULK1: unc-51 like autophagy activating kinase 1; VCL: vinculin; WT: littermate controls.

Vitamin D Supplementation Improves Uterine Receptivity in a Rat Model of Vitamin D Deficiency: A Possible Role of HOXA-10/FKBP52 Axis

Synchronized uterine receptivity with the time of implantation is crucial for pregnancy continuity. Vitamin D (VD) deficiency has been linked to the failure of implantation. Therefore, we tested the link between the Homeobox transcription factor-10/immunophilin FK506-binding protein 52 (HOXA-10/FKBP52) axis and the uterine receptivity in VD-deficient rats. The effect of VD supplementation at different doses was also investigated. Forty-eight pregnant rats were divided into six groups (eight/group); normal control rats fed with standard chow (control), control rats supplemented with VD (equivalent dose of 400 IU/day) (control-D400). VD-deficient group (DEF) and the three VD deficiency groups with VD supplementation were equivalent to 400, 4,000, and 10,000 IU/day (DEF-D400, DEF-D4000, and DEF-D10000, respectively). The expression levels of HOXA-10/FKBP52, progesterone level, and histological evaluation of decidualization using osteopontin (OSN) and progesterone receptor (PGR) were estimated. An assessment of the uterine contractility was conducted for all rats. This study showed the downregulation of HOXA-10/FKBP52 together with increased amplitude and frequency of the uterine contractility in the DEF group compared to control. VD dose-dependent supplementation restored progesterone/receptor competency, upregulated the expressional response of HOXA-10 and its downstream FKBP52, and improved uterine receptivity and endometrial decidualization at the time of implantation that was documented by increased area% of OSN and the number of implantation beads.

Human FKBP5 negatively regulates transcription through inhibition of P-TEFb complex formation

Although large number of recent studies indicate strong association of FKBP5 (aka FKBP51) functions with various stress-related psychiatric disorder, the overall mechanisms are poorly understood. Beyond a few studies indicating its functions in regulating glucocorticoid receptor-, and AKT-signalling pathways, other functional roles (if any) are unclear. In this study, we report an anti-proliferative role of human FKBP5 through negative regulation of expression of proliferation-related genes. Mechanistically, we show that, owing to same region of interaction on CDK9, human FKBP5 directly competes with CyclinT1 for functional P-TEFb complex formation. In vitro biochemical coupled with cell-based assays, showed strong negative effect of FKBP5 on P-TEFb-mediated phosphorylation of diverse substrates. Consistently, FKBP5 knockdown showed enhanced P-TEFb complex formation leading to increased global RNA polymerase II CTD phosphorylation and expression of proliferation-related genes and subsequent proliferation. Thus, our results show an important role of FKBP5 in negative regulation of P-TEFb functions within mammalian cells.

With or without You: Co-Chaperones Mediate Health and Disease by Modifying Chaperone Function and Protein Triage

Heat shock proteins (HSPs) are a family of molecular chaperones that regulate essential protein refolding and triage decisions to maintain protein homeostasis. Numerous co-chaperone proteins directly interact and modify the function of HSPs, and these interactions impact the outcome of protein triage, impacting everything from structural proteins to cell signaling mediators. The chaperone/co-chaperone machinery protects against various stressors to ensure cellular function in the face of stress. However, coding mutations, expression changes, and post-translational modifications of the chaperone/co-chaperone machinery can alter the cellular stress response. Importantly, these dysfunctions appear to contribute to numerous human diseases. Therapeutic targeting of chaperones is an attractive but challenging approach due to the vast functions of HSPs, likely contributing to the off-target effects of these therapies. Current efforts focus on targeting co-chaperones to develop precise treatments for numerous diseases caused by defects in protein quality control. This review focuses on the recent developments regarding selected HSP70/HSP90 co-chaperones, with a concentration on cardioprotection, neuroprotection, cancer, and autoimmune diseases. We also discuss therapeutic approaches that highlight both the utility and challenges of targeting co-chaperones.

FKBP51 and the molecular chaperoning of metabolism

The molecular chaperone FK506-binding protein 51 (FKBP51) is gaining attention as a meaningful biomarker of metabolic dysfunction. This review examines the emerging contributions of FKBP51 in adipogenesis and lipid metabolism, myogenesis and protein catabolism, and glucocorticoid-induced skin hypoplasia and dermal adipocytes. The FKBP51 signaling mechanisms that may explain these metabolic consequences are discussed. These mechanisms are diverse, with FKBP51 independently and directly regulating phosphorylation cascades and nuclear receptors. We provide a discussion of the newly developed compounds that antagonize FKBP51, which may offer therapeutic advantages for adiposity. These observations suggest we are only beginning to uncover the complex nature of FKBP51 and its molecular chaperoning of metabolism.

Corticosteroid receptors as a model for the Hsp90•immunophilin-based transport machinery

Steroid receptors form soluble heterocomplexes with the 90-kDa heat-shock protein (Hsp90) and other chaperones and co-chaperones. The assembly and composition of the oligomer is influenced by the presence and nature of the bound steroid. Although these receptors shuttle dynamically in and out of the nucleus, their primary localization in the absence of steroid can be mainly cytoplasmic, mainly nuclear, or partitioned into both cellular compartments. Upon steroid binding, receptors become localized to the nucleus via the transportosome, a retrotransport molecular machinery that comprises Hsp90, a high-molecular-weight immunophilin, and dynein motors. This molecular machinery, first evidenced in steroid receptors, can also be used by other soluble proteins. In this review, we dissect the complete model of this transport machinery system.

The structure of an Hsp90-immunophilin complex reveals cochaperone recognition of the client maturation state

The Hsp90 chaperone promotes folding and activation of hundreds of client proteins in the cell through an ATP-dependent conformational cycle guided by distinct cochaperone regulators. The FKBP51 immunophilin binds Hsp90 with its tetratricopeptide repeat (TPR) domain and catalyzes peptidyl-prolyl isomerase (PPIase) activity during folding of kinases, nuclear receptors, and tau. Here we determined the cryoelectron microscopy (cryo-EM) structure of the human Hsp90:FKBP51:p23 complex to 3.3 Å, which, together with mutagenesis and crosslinking analyses, reveals the basis for cochaperone binding to Hsp90 during client maturation. A helix extension in the TPR functions as a key recognition element, interacting across the Hsp90 C-terminal dimer interface presented in the closed, ATP conformation. The PPIase domain is positioned along the middle domain, adjacent to Hsp90 client binding sites, whereas a single p23 makes stabilizing interactions with the N-terminal dimer. With this architecture, FKBP51 is positioned to act on specific client residues presented during Hsp90-catalyzed remodeling.

The Neurotrophic Effects and Mechanism of Action for FK1706 in Neurorrhaphy Rat Models and SH-SY5Y Cells

FK1706 is a novel non-immunosuppressive immunophilin ligand with neurotrophic activity and exerts its neurotrophic effect through NGF. The present study aimed to elaborate on the neurotrophic activity and the mechanism of action of FK1706 in end-to-side neurorrhaphy rats and SH-SY5Y cells. In the regenerating nerves of neurorrhaphy rats, FK1706 increased the thickness of myelin sheath and the level of nerve regeneration-related proteins. The mechanism of action of FK1706 on neurite regrowth was elucidated in vitro by incubating SH-SY5Y cells in different conditions (Control, NGF, FK1706, NGF + FK1706, NGF + FK1706 + geldanamycin). Under the conditions where NGF was used, the phosphorylation level of major proteins (Raf-1 and ERK) in the Ras/Raf/MAPK/ERK signaling pathway related to SH-SY5Y cell proliferation was significantly enhanced following the application of FK1706. The number of viable cells, cell viability and neurite length of SH-SY5Y cells was maximal when NGF and FK1706 were used simultaneously. The binding level of HSP90 and Raf-1 in FK1706 group was the highest. These results indicated that FK1706 could significantly promote nerve regeneration after neurorrhaphy. The putative mechanism of action stated that FK1706 could promote the binding of HSP90 and Raf-1, make Raf-1 continue to be activated, thereby affecting key proteins in the Ras/Raf/MAPK/ERK signaling pathway related to the neurotrophic effects of NGF to promote the proliferation and neurite regrowth of nerve cells.

FKBP4 integrates FKBP4/Hsp90/IKK with FKBP4/Hsp70/RelA complex to promote lung adenocarcinoma progression via IKK/NF-κB signaling

FKBP4 belongs to the family of immunophilins, which serve as a regulator for steroid receptor activity. Thus, FKBP4 has been recognized to play a critical role in several hormone-dependent cancers, including breast and prostate cancer. However, there is still no research to address the role of FKBP4 on lung adenocarcinoma (LUAD) progression. We found that FKBP4 expression was elevated in LUAD samples and predicted significantly shorter overall survival based on TCGA and our cohort of LUAD patients. Furthermore, FKBP4 robustly increased the proliferation, metastasis, and invasion of LUAD in vitro and vivo. Mechanistic studies revealed the interaction between FKBP4 and IKK kinase complex. We found that FKBP4 potentiated IKK kinase activity by interacting with Hsp90 and IKK subunits and promoting Hsp90/IKK association. Also, FKBP4 promotes the binding of IKKγ to IKKβ, which supported the facilitation role in IKK complex assembly. We further identified that FKBP4 TPR domains are essential for FKBP4/IKK interaction since its association with Hsp90 is required. In addition, FKBP4 PPIase domains are involved in FKBP4/IKKγ interaction. Interestingly, the association between FKBP4 and Hsp70/RelA favors the transport of RelA toward the nucleus. Collectively, FKBP4 integrates FKBP4/Hsp90/IKK with FKBP4/Hsp70/RelA complex to potentiate the transcriptional activity and nuclear translocation of NF-κB, thereby promoting LUAD progression. Our findings suggest that FKBP4 may function as a prognostic biomarker of LUAD and provide a newly mechanistic insight into modulating IKK/NF-κB signaling.

FKBP51 and FKBP52 regulate androgen receptor dimerization and proliferation in prostate cancer cells

The growth of prostate cancer is dependent on the androgen receptor (AR), which serves as a ligand-specific transcription factor. Although two immunophilins, FKBP51 and FKBP52, are known to regulate AR activity, the precise mechanism remains unclear. We found that depletion of either FKBP51 or FKBP52 reduced AR dimer formation, chromatin binding, and phosphorylation, suggesting defective AR signaling. Furthermore, the peptidyl-prolyl cis/trans isomerase activity of FKBP51 was found to be required for AR dimer formation and cancer cell growth. Treatment of prostate cancer cells with FK506, which binds to the FK1 domain of FKBPs, or with MJC13, an inhibitor of FKBP52-AR signaling, also inhibited AR dimer formation. Finally, elevated expression of FKBP52 was associated with a higher rate of prostate-specific antigen recurrence in patients with prostate cancer. Collectively, these results suggest that FKBP51 and FKBP52 might be promising targets for prostate cancer treatment through the inhibition of AR dimer formation.

The functions and regulation of heat shock proteins; key orchestrators of proteostasis and the heat shock response

Cells respond to protein-damaging (proteotoxic) stress by activation of the Heat Shock Response (HSR). The HSR provides cells with an enhanced ability to endure proteotoxic insults and plays a crucial role in determining subsequent cell death or survival. The HSR is, therefore, a critical factor that influences the toxicity of protein stress. While named for its vital role in the cellular response to heat stress, various components of the HSR system and the molecular chaperone network execute essential physiological functions as well as responses to other diverse toxic insults. The effector molecules of the HSR, the Heat Shock Factors (HSFs) and Heat Shock Proteins (HSPs), are also important regulatory targets in the progression of neurodegenerative diseases and cancers. Modulation of the HSR and/or its extended network have, therefore, become attractive treatment strategies for these diseases. Development of effective therapies will, however, require a detailed understanding of the HSR, important features of which continue to be uncovered and are yet to be completely understood. We review recently described and hallmark mechanistic principles of the HSR, the regulation and functions of HSPs, and contexts in which the HSR is activated and influences cell fate in response to various toxic conditions.

Transcriptome Based Estrogen Related Genes Biomarkers for Diagnosis and Prognosis in Non-small Cell Lung Cancer

Background

Lung cancer is the tumor with the highest morbidity and mortality, and has become a global public health problem. The incidence of lung cancer in men has declined in some countries and regions, while the incidence of lung cancer in women has been slowly increasing. Therefore, the aim is to explore whether estrogen-related genes are associated with the incidence and prognosis of lung cancer.

Methods

We obtained all estrogen receptor genes and estrogen signaling pathway genes in The Cancer Genome Atlas (TCGA), and then compared the expression of each gene in tumor tissues and adjacent normal tissues for lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) separately. Survival analysis was performed of the differentially expressed genes in LUAD and LUSC patients separately. The diagnostic and prognostic values of the candidate genes were validated in the Gene Expression Omnibus (GEO) datasets.

Results

We found 5 estrogen receptor genes and 66 estrogen pathway genes in TCGA. A total of 50 genes were differently expressed between tumor tissues and adjacent normal tissues and 6 of the 50 genes were related to the prognosis of LUAD in TCGA. 56 genes were differently expressed between tumor tissues and adjacent normal tissues and none of the 56 genes was related to the prognosis of LUSC in TCGA. GEO datasets validated that the 6 genes (SHC1, FKBP4, NRAS, PRKCD, KRAS, ADCY9) had different expression between tumor tissues and adjacent normal tissues in LUAD, and 3 genes (FKBP4, KRAS, ADCY9) were related to the prognosis of LUAD.

Conclusions

The expressions of FKBP4 and ADCY9 are related to the pathogenesis and prognosis of LUAD. FKBP4 and ADCY9 may serve as biomarkers in LUAD screening and prognosis prediction in clinical settings.

The Influence Mechanism of Abnormal Immunophilin FKBP52 on the Expression Levels of PR-A and PR-B in Endometriosis Based on Endometrial Stromal Cell Model in Vitro

As a chaperone protein of progesterone receptor (PR), FK-506 Binding Protein 52 (FKBP52) can enhance the activity of PR, but the mechanism of FKBP52 affecting PR expression levels is difficult to clarify. Here, we report a novel in vitro model of ectopic endometrial stromal cells (ESCM) established through the primary culture method of endometrial stromal cells, which is used to study the details of relationship between FKBP52 abnormality and PR expression level in endometriosis (Ems). At the same time, the clinical study of the relationship between FKBP52 and PR expression levels in endometriosis patients was used to verify our conclusions. The results showed that the expression levels of PR-A mRNA and protein in endometriosis are positively correlated with FKBP52 and the abnormality of FKBP52 leads to the decrease of PR-B mRNA and protein expression. When FKBP52 was deleted or reduced, the expression levels of m RNA and protein of PR-A and PR-B have decreased leading to the proliferation of ectopic endometrium cells (ESC) and the occurrence of endometriosis, which is consistent with the expression levels of clinical endometriosis patients and fully confirms our conclusions and reliability of the model, and has great guiding significance for the research of Ems disease occurrence mechanism and clinical treatment.

Differential regulation of the glucocorticoid receptor nucleocytoplasmic shuttling by TPR-domain proteins

A dimer of the heat-shock protein of 90-kDa (Hsp90) represents the critical core of the chaperone complex associated to the glucocorticoid receptor (GR) oligomer. The C-terminal end of the Hsp90 dimer shapes a functional acceptor site for co-chaperones carrying tetratricopeptide repeat (TPR) domains, where they bind in a mutually exclusive and competitive manner. They impact on the biological properties of the GR•Hsp90 complex and are major players of the GR transport machinery. Recently, we showed that the overexpression of a chimeric TPR peptide influences the subcellular distribution of GR. In this study, the functional role of endogenous proteins carrying TPR or TPR-like sequences on GR subcellular distribution was characterized. It is demonstrated that, contrarily to the positive influence of FKBP52 on GR nuclear accumulation, FKBP51 and 14-3-3 impaired this property. While SGT1α showed no significant effect, the overexpression of the Ser/Thr phosphatase PP5 resulted in a nearly equal nuclear-cytoplasmic redistribution of GR rather than its typical cytoplasmic localization in the absence of steroid. This observation led to analyse the influence of the phosphorylation status of GR, which resulted not linked to its nucleo-cytoplasmic shuttling mechanism. Nonetheless, it was evidenced that both PP5 and FKBP52 are related to the anchorage of the GR to nucleoskeleton structures. The influence of these TPR domain proteins on the steroid-dependent transcriptional activity of GR was also characterized. It is postulated that the pleiotropic actions of the GR in different cell types may be the consequence of the relative abundance of different TPR-domain interacting co-chaperones.

Cyclophilin A is a mitochondrial factor that forms complexes with p23 - correlative evidence for an anti-apoptotic action

Cyclophilin A (CyPA, also known as PPIA) is an abundant and ubiquitously expressed protein belonging to the immunophilin family, which has intrinsic peptidyl-prolyl-(cis/trans)-isomerase enzymatic activity. CyPA mediates immunosuppressive action of the cyclic undecapeptide cyclosporine A and is also involved in multiple cellular processes, such as protein folding, intracellular trafficking, signal transduction and transcriptional regulation. CyPA is abundantly expressed in cancer cells, and, owing to its chaperone nature, its expression is induced upon the onset of stress. In this study, we demonstrated that a significant pool of this immunophilin is primarily an intramitochondrial factor that migrates to the nucleus when cells are stimulated with stressors. CyPA shows anti-apoptotic action per se and the capability of forming ternary complexes with cytochrome c and the small acidic co-chaperone p23, the latter interaction being independent of the usual association of p23 with the heat-shock protein of 90 kDa, Hsp90. These CyPA•p23 complexes enhance the anti-apoptotic response of the cell, suggesting that both proteins form a functional unit, the high level of expression of which plays a significant role in cell survival.

Identification of Salmonella Typhimurium Peptidyl-prolyl cis-trans Isomerase B (PPIase B) and Assessment of their Role in the Protein Folding

BACKGROUND

Peptidyl-prolyl cis-trans isomerase (PPIases) enzyme plays a vital role in protein folding. It catalyses the cis-trans isomerisation of peptide bonds, an essential step for newly synthesized protein to acquire its correct functional conformation in both prokaryotes and eukaryotes.

OBJECTIVE

The present study showed the biochemical and molecular characterisation of cyclophilins (PpiB), a type of peptidyl-prolyl isomerases proteins from the pathogenic bacteria Salmonella Typhimurium.

METHODS

Salmonella Typhimurium is one of the leading serovars responsible for human and animal salmonellosis globally, with the majority of human cases originating through the food chain. Here successful expression and purification of PpiB protein have been demonstrated and LC-MS based analyses showed high protein score and similarity with other PPi protein. Further the enzymatic activity of the purified recombinant PpiB was determined using Succinyl-Ala-Phe-Pro- Phe-p nitroanilide as substrate and enzyme-catalysed reaction.

RESULT

Km and Vmax were calculated and found to be Vm = 1.023 ± .06400 min/μg, Km = 0.6219 ± 0.1701 μM, respectively. We have reported for the first time the presence of Salmonella PPIase-B (PpiB) protein isoforms in salmonella genome having PPi activity.

CONCLUSION

Taken together, our data clearly showed that Salmonella Cyclophilin B (PpiB) protein is active and involved in diverse biological processes and highly similar to the different domain of Cyclophilin proteins.