Essential role for Co-chaperone Fkbp52 but not Fkbp51 in androgen receptor-mediated signaling and physiology

Knocking out Fkbp51 decreases CCl4-induced liver injury through enhancement of mitochondrial function and Parkin activity

BACKGROUND AND AIMS

Previously, we found that FK506 binding protein 51 (Fkbp51) knockout (KO) mice resist high fat diet-induced fatty liver and alcohol-induced liver injury. The aim of this research is to identify the mechanism of Fkbp51 in liver injury.

METHODS

Carbon tetrachloride (CCl4)-induced liver injury was compared between Fkbp51 KO and wild type (WT) mice. Step-wise and in-depth analyses were applied, including liver histology, biochemistry, RNA-Seq, mitochondrial respiration, electron microscopy, and molecular assessments. The selective FKBP51 inhibitor (SAFit2) was tested as a potential treatment to ameliorate liver injury.

RESULTS

Fkbp51 knockout mice exhibited protection against liver injury, as evidenced by liver histology, reduced fibrosis-associated markers and lower serum liver enzyme levels. RNA-seq identified differentially expressed genes and involved pathways, such as fibrogenesis, inflammation, mitochondria, and oxidative metabolism pathways and predicted the interaction of FKBP51, Parkin, and HSP90. Cellular studies supported co-localization of Parkin and FKBP51 in the mitochondrial network, and Parkin was shown to be expressed higher in the liver of KO mice at baseline and after liver injury relative to WT. Further functional analysis identified that KO mice exhibited increased ATP production and enhanced mitochondrial respiration. KO mice have increased mitochondrial size, increased autophagy/mitophagy and mitochondrial-derived vesicles (MDV), and reduced reactive oxygen species (ROS) production, which supports enhancement of mitochondrial quality control (MQC). Application of SAFit2, an FKBP51 inhibitor, reduced the effects of CCl4-induced liver injury and was associated with increased Parkin, pAKT, and ATP production.

CONCLUSIONS

Downregulation of FKBP51 represents a promising therapeutic target for liver disease treatment.

Sex-Specific Impact of Fkbp5 on Hippocampal Response to Acute Alcohol Injection: Involvement in Alterations of Metabolism-Related Pathways

High levels of alcohol intake alter brain gene expression and can produce long-lasting effects. FK506-binding protein 51 (FKBP51) encoded by Fkbp5 is a physical and cellular stress response gene and has been associated with alcohol consumption and withdrawal severity. Fkbp5 has been previously linked to neurite outgrowth and hippocampal morphology, sex differences in stress response, and epigenetic modification. Presently, primary cultured Fkbp5 KO and WT mouse neurons were examined for neurite outgrowth and mitochondrial signal with and without alcohol. We found neurite specification differences between KO and WT; particularly, mesh-like morphology was observed after alcohol treatment and confirmed higher MitoTracker signal in cultured neurons of Fkbp5 KO compared to WT at both naive and alcohol-treated conditions. Brain regions that express FKBP51 protein were identified, and hippocampus was confirmed to possess a high level of expression. RNA-seq profiling was performed using the hippocampus of naïve or alcohol-injected (2 mg EtOH/Kg) male and female Fkbp5 KO and WT mice. Differentially expressed genes (DEGs) were identified between Fkbp5 KO and WT at baseline and following alcohol treatment, with female comparisons possessing a higher number of DEGs than male comparisons. Pathway analysis suggested that genes affecting calcium signaling, lipid metabolism, and axon guidance were differentially expressed at naïve condition between KO and WT. Alcohol treatment significantly affected pathways and enzymes involved in biosynthesis (Keto, serine, and glycine) and signaling (dopamine and insulin receptor), and neuroprotective role. Functions related to cell morphology, cell-to-cell signaling, lipid metabolism, injury response, and post-translational modification were significantly altered due to alcohol. In summary, Fkbp5 plays a critical role in the response to acute alcohol treatment by altering metabolism and signaling-related genes.

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.

Genetically engineered mouse models of FK506-binding protein 5

FK506 binding protein 51 (FKBP51) is a molecular chaperone that influences stress response. In addition to having an integral role in the regulation of steroid hormone receptors, including glucocorticoid receptor, FKBP51 has been linked with several biological processes including metabolism and neuronal health. Genetic and epigenetic alterations in the gene that encodes FKBP51, FKBP5, are associated with increased susceptibility to multiple neuropsychiatric disorders, which has fueled much of the research on this protein. Because of the complexity of these processes, animal models have been important in understanding the role of FKBP51. This review examines each of the current mouse models of FKBP5, which include whole animal knockout, conditional knockout, overexpression, and humanized mouse models. The generation of each model and observational details are discussed, including behavioral phenotypes, molecular changes, and electrophysiological alterations basally and following various challenges. While much has been learned through these models, there are still many aspects of FKBP51 biology that remain opaque and future studies are needed to help illuminate these current gaps in knowledge. Overall, FKBP5 continues to be an exciting potential target for stress-related disorders.

Functions of the Hsp90-Binding FKBP Immunophilins

The Hsp90 chaperone is known to interact with a diverse array of client proteins. However, in every case examined, Hsp90 is also accompanied by a single or several co-chaperone proteins. One class of co-chaperone contains a tetratricopeptide repeat (TPR) domain that targets the co-chaperone to the C-terminal region of Hsp90. Within this class are Hsp90-binding peptidylprolyl isomerases, most of which belong to the FK506-binding protein (FKBP) family. Despite the common association of FKBP co-chaperones with Hsp90, it is abundantly clear that the client protein influences, and is often influenced by, the particular FKBP bound to Hsp90. Examples include Xap2 in aryl hydrocarbon receptor complexes and FKBP52 in steroid receptor complexes. In this chapter, we discuss the known functional roles played by FKBP co-chaperones and, where possible, relate distinctive functions to structural differences between FKBP members.

Contribution of the co-chaperone FKBP51 in the ventromedial hypothalamus to metabolic homeostasis in male and female mice

Objective

Steroidogenic factor 1 (SF1) expressing neurons in the ventromedial hypothalamus (VMH) have been directly implicated in whole-body metabolism and in the onset of obesity. The co-chaperone FKBP51 is abundantly expressed in the VMH and was recently linked to type 2 diabetes, insulin resistance, adipogenesis, browning of white adipose tissue (WAT) and bodyweight regulation.

Methods

We investigated the role of FKBP51 in the VMH by conditional deletion and virus-mediated overexpression of FKBP51 in SF1-positive neurons. Baseline and high fat diet (HFD)-induced metabolic- and stress-related phenotypes in male and female mice were obtained.

Results

In contrast to previously reported robust phenotypes of FKBP51 manipulation in the entire mediobasal hypothalamus (MBH), selective deletion or overexpression of FKBP51 in the VMH resulted in only a moderate alteration of HFD-induced bodyweight gain and body composition, independent of sex.

Conclusions

Overall, this study shows that animals lacking and overexpressing Fkbp5 in Sf1-expressing cells within the VMH display only a mild metabolic phenotype compared to an MBH-wide manipulation of this gene, suggesting that FKBP51 in SF1 neurons within this hypothalamic nucleus plays a subsidiary role in controlling whole-body metabolism.

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Loss of FKBP51 in SF1 neurons of the VMH induces a mild metabolic phenotype.

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Male and female mice develop similar metabolic responses to the loss of FKBP51.

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VMH-specific overexpression of FKBP51 induces phenotypes comparable to knockout.

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FKBP51 in the VMH mediates whole-body metabolism in a U-shaped manner.

Exposure to the organophosphate pesticide fenitrothion directly induced defects in mouse embryonic external genitalia

Many industrial chemicals have been reported as anti-androgenic substances. Exposure to these substances represents a potential risk to human health, particularly to the development of reproductive organs such as embryonic external genitalia (eExG). Currently, there is a need for more assay systems that can elucidate the toxicological actions and mechanisms of endocrine disrupting chemicals (EDCs). In this study, we show that the eExG slice culture assay is useful for the evaluation of the differing modes of action of EDCs on urethra formation. We assessed the possible endocrine disrupting activity of three chemicals with reported anti-androgenic function, diazinon (DZN), dibutyl phthalate (DBP) and fenitrothion (FNT) on eExG slices. Exposure to FNT, but not DZN and DBP, induced defects of androgen-induced urethral masculinization and reduced expression of the androgen-target gene Mafb. Live imaging analyses showed that FNT treatment inhibited androgen-dependent MAFB induction within 12 hours. Furthermore, FNT-treated tissue slices showed reduced expression of the androgen receptor (AR). These results indicate that FNT disrupts androgen signaling by reduction of AR expression during androgen-induced eExG masculinization. The current study thus highlights the importance of animal models which allow for the effective assessment of tissue-specific endocrine-disrupting activity to further reveal the etiology of chemical-induced congenital anomalies.

One Tool for Many Jobs: Divergent and Conserved Actions of Androgen Signaling in Male Internal Reproductive Tract and External Genitalia

In the 1940s, Alfred Jost demonstrated the necessity of testicular secretions, particularly androgens, for male internal and external genitalia differentiation. Since then, our knowledge of androgen impacts on differentiation of the male internal (Wolffian duct) and external genitalia (penis) has been drastically expanded upon. Between these two morphologically and functionally distinct organs, divergent signals facilitate the establishment of tissue-specific identities. Conversely, conserved actions of androgen signaling are present in both tissues and are largely responsible for the growth and expansion of the organs. In this review we synthesize the existing knowledge of the cell type-specific, organ specific, and conserved signaling mechanisms of androgens. Mechanistic studies on androgen signaling in the Wolffian duct and male external genitalia have largely been conducted in mouse model organisms. Therefore, the majority of the review is focused on mouse model studies.

FKBP52 and FKBP51 differentially regulate the stability of estrogen receptor in breast cancer

SignificanceEstrogen receptor α (ERα) is a transcription factor that induces cell proliferation and exhibits increased expression in a large subset of breast cancers. We comprehensively searched for indicators of poor prognosis in ERα-positive breast cancer through the multiple databases, including interactome, transcriptome, and survival analysis, and identified FKBP52. We found that two immunophilins, FKBP52 and FKBP51, have opposing effects on ERα stability and propose that therapeutic targeting of FKBP52 could be useful for the prevention and treatment of ERα-positive breast cancers, including endocrine therapy-resistant breast cancers.

FKBP51 modulates hippocampal size and function in post-translational regulation of Parkin

FK506-binding protein 51 (encoded by Fkpb51, also known as Fkbp5) has been associated with stress-related mental illness. To investigate its function, we studied the morphological consequences of Fkbp51 deletion. Artificial Intelligence-assisted morphological analysis revealed that male Fkbp51 knock-out (KO) mice possess more elongated dentate gyrus (DG) but shorter hippocampal height in coronal sections when compared to WT. Primary cultured Fkbp51 KO hippocampal neurons were shown to exhibit larger dendritic outgrowth than wild-type (WT) controls and pharmacological manipulation experiments suggest that this may occur through the regulation of microtubule-associated protein. Both in vitro primary culture and in vivo labeling support a role for FKBP51 in the regulation of microtubule-associated protein expression. Furthermore, Fkbp51 KO hippocampi exhibited decreases in βIII-tubulin, MAP2, and Tau protein levels, but a greater than 2.5-fold increase in Parkin protein. Overexpression and knock-down FKBP51 demonstrated that FKBP51 negatively regulates Parkin in a dose-dependent and ubiquitin-mediated manner. These results indicate a potential novel post-translational regulatory mechanism of Parkin by FKBP51 and the significance of their interaction on disease onset. KO has more flattened hippocampus using AI-assisted measurement Both pyramidal cell layer (PCL) of CA and granular cell layer (GCL) of DG distinguishable as two layers: deep cell layer and superficial layer. Distinct MAP2 expression between deep and superficial layer between KO and WT, Higher Parkin expression in KO brain Mechanism of FKBP51 inhibition resulting in Parkin, MAP2, Tau, and Tubulin expression differences between KO and WT mice, and resulting neurite outgrowth differences.

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.

The nonreceptor tyrosine kinase SRMS inhibits autophagy and promotes tumor growth by phosphorylating the scaffolding protein FKBP51

Nutrient-responsive protein kinases control the balance between anabolic growth and catabolic processes such as autophagy. Aberrant regulation of these kinases is a major cause of human disease. We report here that the vertebrate nonreceptor tyrosine kinase Src-related kinase lacking C-terminal regulatory tyrosine and N-terminal myristylation sites (SRMS) inhibits autophagy and promotes growth in a nutrient-responsive manner. Under nutrient-replete conditions, SRMS phosphorylates the PHLPP scaffold FK506-binding protein 51 (FKBP51), disrupts the FKBP51-PHLPP complex, and promotes FKBP51 degradation through the ubiquitin-proteasome pathway. This prevents PHLPP-mediated dephosphorylation of AKT, causing sustained AKT activation that promotes growth and inhibits autophagy. SRMS is amplified and overexpressed in human cancers where it drives unrestrained AKT signaling in a kinase-dependent manner. SRMS kinase inhibition activates autophagy, inhibits cancer growth, and can be accomplished using the FDA-approved tyrosine kinase inhibitor ibrutinib. This illuminates SRMS as a targetable vulnerability in human cancers and as a new target for pharmacological induction of autophagy in vertebrates.

This study describes the discovery and characterization of a nutrient-sensitive signaling pathway that drives growth and inhibits autophagy in mammalian cells. This pathway, which involves the non-receptor tyrosine kinase SRMS and the PHLPP scaffold protein FKBP51, promotes tumor growth and is amenable to pharmacological inhibition.

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 helix-loop-helix transcriptional regulator Id4 is required for terminal differentiation of luminal epithelial cells in the prostate

Inhibitor of differentiation 4 (Id4), a member of the helix-loop-helix family of transcriptional regulators has emerged as a tumor suppressor in prostate cancer. In this study we investigated the effect of loss of Id4 (Id4-/-) on mouse prostate development. Histological analysis was performed on prostates from 25 days, 3 months and 6 months old Id4-/- mice. Expression of Amacr, Ck8, Ck18, Fkbp51, Fkbp52, androgen receptor, Pten, sca-1 and Nkx3.1 was investigated by immunohistochemistry. Results were compared to the prostates from Nkx3.1-/- mice. Id4-/- mice had smaller prostates with fewer and smaller tubules. Subtle PIN like lesions were observed at 6mo. Decreased Nkx3.1 and Pten and increased stem cell marker sca-1, PIN marker Amacr and basal cell marker p63 was observed at all ages. Persistent Ck8 and Ck18 expression suggested that loss of Id4 results in epithelial commitment but not terminal differentiation in spite of active Ar. Loss of Id4 attenuates normal prostate development and promotes hyperplasia/ dysplasia with PIN like lesions. The results suggest that loss of Id4 maintains stem cell phenotype of "luminal committed basal cells", identifying a unique prostate developmental pathway regulated by Id4.

The Role of Androgen Signaling in Male Sexual Development at Puberty

Puberty is characterized by major changes in the anatomy and function of reproductive organs. Androgen activity is low before puberty, but during pubertal development, the testes resume the production of androgens. Major physiological changes occur in the testicular cell compartments in response to the increase in intratesticular testosterone concentrations and androgen receptor expression. Androgen activity also impacts on the internal and external genitalia. In target cells, androgens signal through a classical and a nonclassical pathway. This review addresses the most recent advances in the knowledge of the role of androgen signaling in postnatal male sexual development, with a special emphasis on human puberty.

Eighty Years of Targeting Androgen Receptor Activity in Prostate Cancer: The Fight Goes on

Simple Summary

Prostate cancer is the second most common cancer in men world-wide, with nearly 1.3 million new cases each year, and over the next twenty years the incidence and death rate are predicted to nearly double. For decades, this lethal disease has been more or less successfully treated using hormonal therapy, which has the ultimate aim of inhibiting androgen signalling. However, prostate tumours can evade such hormonal therapies in a number of different ways and therapy resistant disease, so-called castration-resistant prostate cancer (CRPC) is the major clinical problem. Somewhat counterintuitively, the androgen receptor remains a key therapy target in CRPC. Here, we explain why this is the case and summarise both new hormone therapy strategies and the recent advances in knowledge of androgen receptor structure and function that underpin them.

Abstract

Prostate cancer (PCa) is the most common cancer in men in the West, other than skin cancer, accounting for over a quarter of cancer diagnoses in US men. In a seminal paper from 1941, Huggins and Hodges demonstrated that prostate tumours and metastatic disease were sensitive to the presence or absence of androgenic hormones. The first hormonal therapy for PCa was thus castration. In the subsequent eighty years, targeting the androgen signalling axis, where possible using drugs rather than surgery, has been a mainstay in the treatment of advanced and metastatic disease. Androgens signal via the androgen receptor, a ligand-activated transcription factor, which is the direct target of many such drugs. In this review we discuss the role of the androgen receptor in PCa and how the combination of structural information and functional screenings is continuing to be used for the discovery of new drug to switch off the receptor or modify its function in cancer cells.

Etiology of Hypospadias: A Comparative Review of Genetic Factors and Developmental Processes Between Human and Animal Models

Hypospadias is a congenital anomaly of the penis with an occurrence of approximately 1 in 200 boys, but the etiology of the majority of hypospadias has remained unknown. Numerous genes have been reported as having variants in hypospadias patients, and many studies on genetic deletion of key genes in mouse genital development have also been published. Until now, no comparative analysis in the genes related literature has been reported. The basic knowledge of penile development and hypospadias is mainly obtained from animal model studies. Understanding of the differences and similarities between human and animal models is crucial for studies of hypospadias. In this review, mutations and polymorphisms of hypospadias-related genes have been compared between humans and mice, and differential genotype–phenotype relationships of certain genes between humans and mice have been discussed using the data available in PubMed and MGI online databases, and our analysis only revealed mutations in seven out of 43 human hypospadias related genes which have been reported to show similar phenotypes in mutant mice. The differences and similarities in the processes of penile development and hypospadias malformation among human and commonly used animal models suggest that the guinea pig may be a good model to study the mechanism of human penile development and etiology of hypospadias.

Modulation of Ago2 Loading by Cyclophilin 40 Endows a Unique Repertoire of Functional miRNAs during Sperm Maturation in Drosophila

In gene silencing, Hsp90 chaperone machinery assists Argonaute (Ago) binding and unwinding of silencing small RNA (sRNA) duplexes. This enables the formation of effector RNA-induced silencing complex (RISC) that often displays cargo preferences. Hence, in Drosophila, microRNAs (miRNAs) and small-interfering RNAs (siRNAs) are differentially sorted into Ago1-RISC and Ago2-RISC, respectively. Here, we identify fly Cyclophilin 40 (Cyp40) as a testis-specialized Hsp90 co-chaperone essential for spermatogenesis and for modulating Ago2-RISC formation. We show that testis-distinctive Ago-sorting and strand-selection mechanisms accumulate a unique set of miRNAs on Ago2. Cyp40 interacts with duplex-incorporating Ago2 through Hsp90 in vitro and selectively promotes the build-up of Ago2-bound miRNAs, but not endogenous siRNAs, in vivo. Moreover, one of Cyp40-dependent Ago2-sorted miRNAs is required for late spermatogenesis, unraveling the physiological relevance of the unconventional yet conserved Drosophila miRNA-Ago2 sorting pathway. Collectively, these results identify RISC-regulatory roles for Hsp90 machinery and, more generally, highlight the tissue-specific adaptation of sRNA pathways through chaperone diversification.

The FKBP4 Gene, Encoding a Regulator of the Androgen Receptor Signaling Pathway, Is a Novel Candidate Gene for Androgen Insensitivity Syndrome

Androgen insensitivity syndrome (AIS), manifesting incomplete virilization in 46,XY individuals, is caused mostly by androgen receptor (AR) gene mutations. Therefore, a search for AR mutations is a routine approach in AIS diagnosis. However, some AIS patients lack AR mutations, which complicates the diagnosis. Here, we describe a patient suffering from partial androgen insensitivity syndrome (PAIS) and lacking AR mutations. The whole exome sequencing of the patient and his family members identified a heterozygous FKBP4 gene mutation, c.956T>C (p.Leu319Pro), inherited from the mother. The gene encodes FKBP prolyl isomerase 4, a positive regulator of the AR signaling pathway. This is the first report describing a FKBP4 gene mutation in association with a human disorder of sexual development (DSD). Importantly, the dysfunction of a homologous gene was previously reported in mice, resulting in a phenotype corresponding to PAIS. Moreover, the Leu319Pro amino acid substitution occurred in a highly conserved position of the FKBP4 region, responsible for interaction with other proteins that are crucial for the AR functional heterocomplex formation and therefore the substitution is predicted to cause the disease. We proposed the FKBP4 gene as a candidate AIS gene and suggest screening that gene for the molecular diagnosis of AIS patients lacking AR gene mutations.

Development of Non-Immunosuppressive FK506 Derivatives as Antifungal and Neurotrophic Agents

FK506, also known as tacrolimus, is a clinically important immunosuppressant drug and has promising therapeutic potentials owing to its antifungal, neuroprotective, and neuroregenerative activities. To generate various FK506 derivatives, the structure of FK506 has been modified by chemical methods or biosynthetic pathway engineering. Herein, we describe the mode of the antifungal action of FK506 and the structure-activity relationship of FK506 derivatives in the context of immunosuppressive and antifungal activities. In addition, we discuss the neurotrophic mechanism of FK506 known to date, along with the neurotrophic FK506 derivatives with significantly reduced immunosuppressive activity. This review suggests the possibility to generate novel FK506 derivatives as antifungal as well as neuroregenerative/neuroprotective agents.

Promotion of Myoblast Differentiation by Fkbp5 via Cdk4 Isomerization

Fkbp5 is a widely expressed peptidyl prolyl isomerase that serves as a molecular chaperone through conformational changes of binding partners. Although it regulates diverse protein functions, little is known about its roles in myogenesis. We found here that Fkbp5 plays critical roles in myoblast differentiation through two mechanisms. First, it sequesters Cdk4 within the Hsp90 storage complex and prevents the formation of the cyclin D1-Cdk4 complex, which is a major inhibitor of differentiation. Second, Fkbp5 promotes cis-trans isomerization of the Thr172-Pro173 peptide bond in Cdk4 and inhibits phosphorylation of Thr172, an essential step for Cdk4 activation. Consistent with these in vitro findings, muscle regeneration is delayed in Fkbp5^−/− mice. The related protein Fkbp4 also sequesters Cdk4 within the Hsp90 complex but does not isomerize Cdk4 or induce Thr173 phosphorylation despite its highly similar sequence. This study demonstrates protein isomerization as a critical regulatory mechanism of myogenesis by targeting Cdk4.

Functional Comparison of Human and Zebra Fish FKBP52 Confirms the Importance of the Proline-Rich Loop for Regulation of Steroid Hormone Receptor Activity

Previous studies demonstrated that the 52-kDa FK506-binding protein (FKBP52) proline-rich loop is functionally relevant in the regulation of steroid hormone receptor activity. While zebra fish (Danio rerio; Dr) FKBP52 contains all of the analogous domains and residues previously identified as critical for FKBP52 potentiation of receptor activity, it fails to potentiate activity. Thus, we used a cross-species comparative approach to assess the residues that are functionally critical for FKBP52 function. Random selection of gain-of-function DrFKBP52 mutants in Saccharomyces cerevisiae identified two critical residues, alanine 111 (A111) and threonine 157 (T157), for activation of receptor potentiation by DrFKBP52. In silico homology modeling suggests that alanine to valine substitution at position 111 in DrFKBP52 induces an open conformation of the proline-rich loop surface similar to that observed on human FKBP52, which may allow for sufficient surface area and increased hydrophobicity for interactions within the receptor-chaperone complex. A second mutation in the FKBP12-like domain 2 (FK2), threonine 157 to arginine (T157R), also enhanced potentiation, and the DrFKBP52-A111V/T157R double mutant potentiated receptor activity similar to human FKBP52. Collectively, these results confirm the functional importance of the FKBP52 proline-rich loop, suggest that an open conformation on the proline-rich loop surface is a predictor of activity, and highlight the importance of an additional residue within the FK2 domain.

Biological Actions of the Hsp90-binding Immunophilins FKBP51 and FKBP52

Immunophilins are a family of proteins whose signature domain is the peptidylprolyl-isomerase domain. High molecular weight immunophilins are characterized by the additional presence of tetratricopeptide-repeats (TPR) through which they bind to the 90-kDa heat-shock protein (Hsp90), and via this chaperone, immunophilins contribute to the regulation of the biological functions of several client-proteins. Among these Hsp90-binding immunophilins, there are two highly homologous members named FKBP51 and FKBP52 (FK506-binding protein of 51-kDa and 52-kDa, respectively) that were first characterized as components of the Hsp90-based heterocomplex associated to steroid receptors. Afterwards, they emerged as likely contributors to a variety of other hormone-dependent diseases, stress-related pathologies, psychiatric disorders, cancer, and other syndromes characterized by misfolded proteins. The differential biological actions of these immunophilins have been assigned to the structurally similar, but functionally divergent enzymatic domain. Nonetheless, they also require the complementary input of the TPR domain, most likely due to their dependence with the association to Hsp90 as a functional unit. FKBP51 and FKBP52 regulate a variety of biological processes such as steroid receptor action, transcriptional activity, protein conformation, protein trafficking, cell differentiation, apoptosis, cancer progression, telomerase activity, cytoskeleton architecture, etc. In this article we discuss the biology of these events and some mechanistic aspects.

Expression of FKBP52 in the ovaries of PCOS rats

The present study aimed to examine the expression of FK-506 binding protein 52 (FKBP52) in the ovary tissues of rats with polycystic ovarian syndrome (PCOS) and its action on mediating androgen receptor (AR) through the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway. PCOS model rats were established by dehydroepiandrosterone injection. Enzyme-linked immunosorbent assay (ELISA) measured serum sex hormones. Hematoxylin and eosin (H&E) staining was used to examine histological changes of the ovarian tissues. The expression levels of FKBP52 were detected by immunohistochemical (IHC) staining, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis and western blotting (WB). In addition, RT-qPCR analysis was used to detect the mRNA expression of AR, and WB was used to detect the protein expression levels of AR, ERK1/2 and phosphorylated (p-) ERK1/2. In granulosa cell (GC) experiments, primary GCs were extracted and cultured. FKBP4 is the FKBP52-encoding gene, therefore, adenovirus vectors Ad-Oe-FKBP4-EGFP and Ad-siRNA-FKBP4-EGFP were constructed to examine the association among the above factors using the RT-qPCR and WB methods. In the animal experiment, the vaginal smear, H&E staining and ELISA results showed that the PCOS model was successfully established. The IHC staining revealed that the expression of FKBP52 in the GCs of the PCOS model group was higher than the remaining groups (P<0.01). The mRNA and expression levels of FKBP52 and AR in the PCOS model rats were significantly increased, when compared with levels in the other rats (P<0.05). The expression level of p-ERK1/2 was also higher (P<0.05). In the GC experiment, following overexpression of the FKBP4 gene, the mRNA and expression levels of FKBP52 and AR were increased (P<0.05). The expression level of p-ERK1/2 was also increased (P<0.05). Following FKBP4 gene silencing, the mRNA and expression levels of FKBP52 and AR were decreased (P<0.05). The expression level of ERK1/2 was also decreased (P<0.05). However, the expression level of p-ERK1/2 was increased (P<0.05). In conclusion, the upregulation of co-chaperone FKBP52 may mediate the activation of AR through the MAPK/ERK pathway.

Deletion of the glucocorticoid receptor chaperone FKBP51 prevents glucocorticoid-induced skin atrophy

FKBP51 (FK506-binding protein 51) is a known co-chaperone and regulator of the glucocorticoid receptor (GR), which usually attenuates its activity. FKBP51 is one of the major GR target genes in skin, but its role in clinical effects of glucocorticoids is not known. Here, we used FKBP51 knockout (KO) mice to determine FKBP51's role in the major adverse effect of topical glucocorticoids, skin atrophy. Unexpectedly, we found that all skin compartments (epidermis, dermis, dermal adipose and CD34+ stem cells) in FKBP51 KO animals were much more resistant to glucocorticoid-induced hypoplasia. Furthermore, despite the absence of inhibitory FKBP51, the basal level of expression and glucocorticoid activation of GR target genes were not increased in FKBP51 KO skin or CRISPR/Cas9-edited FKBP51 KO HaCaT human keratinocytes. FKBP51 is known to negatively regulate Akt and mTOR. We found a significant increase in AktSer473 and mTORSer2448 phosphorylation and downstream pro-growth signaling in FKBP51-deficient keratinocytes in vivo and in vitro. As Akt/mTOR-GR crosstalk is usually negative in skin, our results suggest that Akt/mTOR activation could be responsible for the lack of increased GR function and resistance of FKBP51 KO mice to the steroid-induced skin atrophy.

Delineation of human prostate cancer evolution identifies chromothripsis as a polyclonal event and FKBP4 as a potential driver of castration resistance

Understanding the evolutionary mechanisms and genomic events leading to castration-resistant (CR) prostate cancer (PC) is key to improve the outcome of this otherwise deadly disease. Here, we delineated the tumour history of seven patients progressing to castration resistance by analysing matched prostate cancer tissues before and after castration. We performed genomic profiling of DNA content-based flow-sorted populations in order to define the different evolutionary patterns. In one patient, we discovered that a catastrophic genomic event, known as chromothripsis, resulted in multiple CRPC tumour populations with distinct, potentially advantageous copy number aberrations, including an amplification of FK506 binding protein 4 (FKBP4, also known as FKBP52), a protein enhancing the transcriptional activity of androgen receptor signalling. Analysis of FKBP4 protein expression in more than 500 prostate cancer samples revealed increased expression in CRPC in comparison to hormone-naïve (HN) PC. Moreover, elevated FKBP4 expression was associated with poor survival of patients with HNPC. We propose FKBP4 amplification and overexpression as a selective advantage in the process of tumour evolution and as a potential mechanism associated with the development of CRPC. Furthermore, FKBP4 interaction with androgen receptor may provide a potential therapeutic target in PC. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Identification and characterisation of the epididymal proteins in the lizard, Eutropis carinata (Reptilia, Squamata) (Schneider, 1801)

Lizards are seasonal breeders. Cyclic reproductive nature makes lizard as a useful model for the study of the reproductively active protein secretions in the epididymis. During breeding season, the epididymides of the lizard secret proteins that mixes with the spermatozoa and create a favourable environment for sperm maturation. In this spectrum, the aim of this study is to identify and characterize proteins which are present in the lumen of the epididymis of the lizard, E. carinata during the active phase of reproduction. The identification and analysis of the proteins are done through the proteomic approaches. The epididymal luminal fluid sample was taken from the reproductively active and inactive phase and these are subjected to the size exclusion chromatography. Two major peaks (peak 1 and peak 2) were obtained in the epididymal luminal fluid sample taken during the reproductively active phase. On the other hand, the sample from the reproductively inactive phase showed one peak (peak 1) whereas, peak 2 is not present during this phase. The peak 2 belong to reproductively active phase was later subjected to the proteomic analysis. Appropriate gel electrophoresis separation and purification methods are combined with LC-MS/MS in order to identify and characterize the proteins that are presented during the reproductively active phase. Further, in this work, nine proteins are identified including three enzymes and three heat shock proteins. Among the identified proteins, bioinformatics analysis predicts that majority of them are localized in the cytoplasm. In addition to this, an observation is made in the endoplasmic reticulum where it is seen that a close protein-protein interaction network of three molecular chaperones are involved in protein processing. Overall, this paper opens up a new dimension search for epididymal markers for the first time in reptiles, particularly lizards.

Evidence for Hsp90 Co-chaperones in Regulating Hsp90 Function and Promoting Client Protein Folding

Molecular chaperones are a diverse group of highly conserved proteins that transiently interact with partially folded polypeptide chains during normal cellular processes such as protein translation, translocation, and disassembly of protein complexes. Prior to folding or after denaturation, hydrophobic residues that are normally sequestered within a folded protein are exposed to the aqueous environment and are prone to aggregation or misfolding. Multiple classes of molecular chaperones, such as Hsp70s and Hsp40s, recognize and transiently bind polypeptides with exposed hydrophobic stretches in order to prevent misfolding. Other types of chaperones, such as Hsp90, have more specialized functions in that they appear to interact with only a subset of cellular proteins. This chapter focuses on the role of Hsp90 and partner co-chaperones in promoting the folding and activation of a diverse group of proteins with critical roles in cellular signaling and function.

Imbalances in the Hsp90 Chaperone Machinery: Implications for Tauopathies

The ATP-dependent 90 kDa heat shock protein, Hsp90, is a major regulator of protein triage, from assisting in nascent protein folding to refolding or degrading aberrant proteins. Tau, a microtubule associated protein, aberrantly accumulates in Alzheimer's disease (AD) and other neurodegenerative diseases, deemed tauopathies. Hsp90 binds to and regulates tau fate in coordination with a diverse group of co-chaperones. Imbalances in chaperone levels and activity, as found in the aging brain, can contribute to disease onset and progression. For example, the levels of the Hsp90 co-chaperone, FK506-binding protein 51 kDa (FKBP51), progressively increase with age. In vitro and in vivo tau models demonstrated that FKBP51 synergizes with Hsp90 to increase neurotoxic tau oligomer production. Inversely, protein phosphatase 5 (PP5), which dephosphorylates tau to restore microtubule-binding function, is repressed with aging and activity is further repressed in AD. Similarly, levels of cyclophilin 40 (CyP40) are reduced in the aged brain and further repressed in AD. Interestingly, CyP40 was shown to breakup tau aggregates in vitro and prevent tau-induced neurotoxicity in vivo. Moreover, the only known stimulator of Hsp90 ATPase activity, Aha1, increases tau aggregation and toxicity. While the levels of Aha1 are not significantly altered with aging, increased levels have been found in AD brains. Overall, these changes in the Hsp90 heterocomplex could drive tau deposition and neurotoxicity. While the relationship of tau and Hsp90 in coordination with these co-chaperones is still under investigation, it is clear that imbalances in these proteins with aging can contribute to disease onset and progression. This review highlights the current understanding of how the Hsp90 family of molecular chaperones regulates tau or other misfolded proteins in neurodegenerative diseases with a particular emphasis on the impact of aging.

Molecular dynamics simulation, binding free energy calculation and unbinding pathway analysis on selectivity difference between FKBP51 and FKBP52: Insight into the molecular mechanism of isoform selectivity

As co-chaperones of the 90-kDa heat shock protein(HSP90), FK506 binding protein 51 (FKBP51) and FK506 binding protein 52 (FKBP52) modulate the maturation of steroid hormone receptor through their specific FK1 domains (FKBP12-like domain 1). The inhibitors targeting FK1 domains are potential therapies for endocrine-related physiological disorders. However, the structural conservation of the FK1 domains between FKBP51 and FKBP52 make it difficult to obtain satisfactory selectivity in FK506-based drug design. Fortunately, a series of iFit ligands synthesized by Hausch et al exhibited excellent selectivity for FKBP51, providing new opportunity for design selective inhibitors. We performed molecular dynamics simulation, binding free energy calculation and unbinding pathway analysis to reveal selective mechanism for the inhibitor iFit4 binding with FKBP51 and FKBP52. The conformational stability evaluation of the "Phe67-in" and "Phe67-out" states implies that FKBP51 and FKBP52 have different preferences for "Phe67-in" and "Phe67-out" states, which we suggest as the determinant factor for the selectivity for FKBP51. The binding free energy calculations demonstrate that nonpolar interaction is favorable for the inhibitors binding, while the polar interaction and entropy contribution are adverse for the inhibitors binding. According to the results from binding free energy decomposition, the electrostatic difference of residue 85 causes the most significant thermodynamics effects on the binding of iFit4 to FKBP51 and FKBP52. Furthermore, the importance of substructure units on iFit4 were further evaluated by unbinding pathway analysis and residue-residue contact analysis between iFit4 and the proteins. The results will provide new clues for the design of selective inhibitors for FKBP51.

Pathway-based expression profiling of benign prostatic hyperplasia and prostate cancer delineates an immunophilin molecule associated with cancer progression

Aberrant restoration of AR activity is linked with prostate tumor growth, therapeutic failures and development of castrate-resistant prostate cancer. Understanding the processes leading to AR-reactivation should provide the foundation for novel avenues of drug discovery. A differential gene expression study was conducted using biopsies from CaP and BPH patients to identify the components putatively responsible for reinstating AR activity in CaP. From the set of genes upregulated in CaP, FKBP52, an AR co-chaperone, was selected for further analysis. Expression of FKBP52 was positively correlated with that of c-Myc. The functional cross-talk between c-Myc and FKBP52 was established using c-Myc specific-siRNA to LNCaP cells that resulted in reduction of FKBP52. A non-canonical E-box sequence housing a putative c-Myc binding site was detected on the FKBP4 promoter using in silico search. LNCaP cells transfected with the FKBP52 promoter cloned in pGL3 basic showed increased luciferase activity which declined considerably when the promoter-construct was co-transfected with c-Myc specific-siRNA. ChIP-PCR confirmed the binding of c-Myc with the conserved E-box located in the FKBP52 promoter. c-Myc downregulation concomitantly affected expression of FGF8. Since expression of FGF8 is controlled by AR, our study unveiled a novel functional axis between c-Myc, AR and FGF8 operating through FKBP52.

Inactivation of ID4 promotes a CRPC phenotype with constitutive AR activation through FKBP52

Castration-resistant prostate cancer (CRPC) is the emergence of prostate cancer cells that have adapted to the androgen-depleted environment of the prostate. In recent years, targeting multiple chaperones and co-chaperones (e.g., Hsp27, FKBP52) that promote androgen receptor (AR) signaling and/or novel AR regulatory mechanisms have emerged as promising alternative treatments for CRPC. We have shown that inactivation of inhibitor of differentiation 4 (ID4), a dominant-negative helix loop helix protein, promotes de novo steroidogenesis and CRPC with a gene expression signature that resembles constitutive AR activity in castrated mice. In this study, we investigated the underlying mechanism through which loss of ID4 potentiates AR signaling. Proteomic analysis between prostate cancer cell line LNCaP (L+ns) and LNCaP lacking ID4 (L(-)ID4) revealed elevated levels of Hsp27 and FKBP52, suggesting a role for these AR-associated co-chaperones in promoting constitutively active AR signaling in L(-)ID4 cells. Interestingly, protein interaction studies demonstrated a direct interaction between ID4 and the 52-kDa FK506-binding protein (FKBP52) in vitro, but not with AR. An increase in FKBP52-dependent AR transcriptional activity was observed in L(-)ID4 cells. Moreover, pharmacological inhibition of FKBP52-AR signaling, by treatment with MJC13, attenuated the tumor growth, weight, and volume in L(-)ID4 xenografts. Together, our results demonstrate that ID4 selectively regulates AR activity through direct interaction with FKBP52, and its loss, promotes CRPC through FKBP52-mediated AR signaling.

Loss of FKBP5 impedes adipocyte differentiation under both normoxia and hypoxic stress

FK506-binding protein 51 (FKBP51) is one of the most important regulators in the GR-mediated stress response, and we previously demonstrated that loss of FKBP5 arrests adipogenesis and renders mice resistant to diet-induced obesity (DIO). However, the exact role of FKBP5 in the process of adipocyte differentiation under hypoxic conditions (the common microenvironment where adipocytes reside in obese individuals) is still unclear. Here, by isolating and culturing WT- and Fkbp5-knockout mouse embryonic fibroblasts (MEFs), and treat them at normal oxygen environment (21% O2, nomorxia) or low oxygen environment (5% O2, hypoxia). Enhanced adipogenesis were observed at hypoxia when compared to normal oxygen environment. The loss of FKBP5 significantly prevents the adipogenesis from KO MEFs under nomorxia condition, with subtle enhancement of adipogenesis at hypoxia condition, which is similar as observed in WT-MEFs at hypoxia condition but with obvious enhancement of adipogenesis. Importantly, the protein level of FKBP5 reduced in undifferentiated MEFs under acute hypoxic stress (24 h), but drastically increased during the mid-late stage of adipocyte (Day 6) differentiation from WT-MEFs under chronic hypoxia. Furthermore, we find under normal and hypoxic conditions that FKBP5 deletion alters the expression profile of adipogenesis-related genes, including those involved in lipogenesis, lipolysis, and energy metabolism, which partially explains the compromised adipocyte differentiation in FKBP51-KO MEFs. Taken together, our findings identify a novel role of FKBP5 in hypoxia-regulated adipogenesis, and provide a candidate for anti-obesity strategies targeting FKBP51.

Adult Gli2+/-;Gli3Δ699/+ Male and Female Mice Display a Spectrum of Genital Malformation

Disorders of sexual development (DSD) encompass a broad spectrum of urogenital malformations and are amongst the most common congenital birth defects. Although key genetic factors such as the hedgehog (Hh) family have been identified, a unifying postnatally viable model displaying the spectrum of male and female urogenital malformations has not yet been reported. Since human cases are diagnosed and treated at various stages postnatally, equivalent mouse models enabling analysis at similar stages are of significant interest. Additionally, all non-Hh based genetic models investigating DSD display normal females, leaving female urogenital development largely unknown. Here, we generated compound mutant mice, Gli2^+/–;Gli3^Δ699/+, which exhibit a spectrum of urogenital malformations in both males and females upon birth, and also carried them well into adulthood. Analysis of embryonic day (E)18.5 and adult mice revealed shortened anogenital distance (AGD), open ventral urethral groove, incomplete fusion of scrotal sac, abnormal penile size and structure, and incomplete testicular descent with hypoplasia in male mice, whereas female mutant mice displayed reduced AGD, urinary incontinence, and a number of uterine anomalies such as vaginal duplication. Male and female fertility was also investigated via breeding cages, and it was identified that male mice were infertile while females were unable to deliver despite becoming impregnated. We propose that Gli2^+/–;Gli3^Δ699/+ mice can serve as a genetic mouse model for common DSD such as cryptorchidism, hypospadias, and incomplete fusion of the scrotal sac in males, and a spectrum of uterine and vaginal abnormalities along with urinary incontinence in females, which could prove essential in revealing new insights into their equivalent diseases in humans.

FKBP51 Null Mice Are Resistant to Diet-Induced Obesity and the PPARγ Agonist Rosiglitazone

FK506-binding protein-51 (FKBP51) is a molecular cochaperone recently shown to be a positive regulator of peroxisome proliferator-activated receptor (PPAR)γ, the master regulator of adipocyte differentiation and function. In cellular models of adipogenesis, loss of FKBP51 not only reduced PPARγ activity but also reduced lipid accumulation, suggesting that FKBP51 knock-out (KO) mice might have insufficient development of adipose tissue and lipid storage ability. This model was tested by examining wild-type (WT) and FKBP51-KO mice under regular and high-fat diet conditions. Under both diets, FKBP51-KO mice were resistant to weight gain, hepatic steatosis, and had greatly reduced white adipose tissue (WAT) but higher amounts of brown adipose tissue. Under high-fat diet, KO mice were highly resistant to adiposity and exhibited reduced plasma lipids and elevated glucose and insulin tolerance. Profiling of perigonadal and sc WAT revealed elevated expression of brown adipose tissue lineage genes in KO mice that correlated increased energy expenditure and a shift of substrate oxidation to carbohydrates, as measured by indirect calorimetry. To directly test PPARγ involvement, WT and KO mice were fed rosiglitazone agonist. In WT mice, rosiglitazone induced whole-body weight gain, increased WAT mass, a shift of substrate oxidation to lipids, and elevated expression of PPARγ-regulated lipogenic genes in WAT. In contrast, KO mice had reduced rosiglitazone responses for these parameters. Our results identify FKBP51 as an important regulator of PPARγ in WAT and as a potential new target in the treatment of obesity and diabetes.

The FKBP5 Gene Affects Alcohol Drinking in Knockout Mice and Is Implicated in Alcohol Drinking in Humans

FKBP5 encodes FK506-binding protein 5, a glucocorticoid receptor (GR)-binding protein implicated in various psychiatric disorders and alcohol withdrawal severity. The purpose of this study is to characterize alcohol preference and related phenotypes in Fkbp5 knockout (KO) mice and to examine the role of FKBP5 in human alcohol consumption. The following experiments were performed to characterize Fkpb5 KO mice. (1) Fkbp5 KO and wild-type (WT) EtOH consumption was tested using a two-bottle choice paradigm; (2) The EtOH elimination rate was measured after intraperitoneal (IP) injection of 2.0 g/kg EtOH; (3) Blood alcohol concentration (BAC) was measured after 3 h limited access of alcohol; (4) Brain region expression of Fkbp5 was identified using LacZ staining; (5) Baseline corticosterone (CORT) was assessed. Additionally, two SNPs, rs1360780 (C/T) and rs3800373 (T/G), were selected to study the association of FKBP5 with alcohol consumption in humans. Participants were college students (n = 1162) from 21–26 years of age with Chinese, Korean or Caucasian ethnicity. The results, compared to WT mice, for KO mice exhibited an increase in alcohol consumption that was not due to differences in taste sensitivity or alcohol metabolism. Higher BAC was found in KO mice after 3 h of EtOH access. Fkbp5 was highly expressed in brain regions involved in the regulation of the stress response, such as the hippocampus, amygdala, dorsal raphe and locus coeruleus. Both genotypes exhibited similar basal levels of plasma corticosterone (CORT). Finally, single nucleotide polymorphisms (SNPs) in FKBP5 were found to be associated with alcohol drinking in humans. These results suggest that the association between FKBP5 and alcohol consumption is conserved in both mice and humans.

FK506 binding protein 51 integrates pathways of adaptation: FKBP51 shapes the reactivity to environmental change

This review portraits FK506 binding protein (FKBP) 51 as "reactivity protein" and collates recent publications to develop the concept of FKBP51 as contributor to different levels of adaptation. Adaptation is a fundamental process that enables unicellular and multicellular organisms to adjust their molecular circuits and structural conditions in reaction to environmental changes threatening their homeostasis. FKBP51 is known as chaperone and co-chaperone of heat shock protein (HSP) 90, thus involved in processes ensuring correct protein folding in response to proteotoxic stress. In mammals, FKBP51 both shapes the stress response and is calibrated by the stress levels through an ultrashort molecular feedback loop. More recently, it has been linked to several intracellular pathways related to the reactivity to drug exposure and stress. Through its role in autophagy and DNA methylation in particular it influences adaptive pathways, possibly also in a transgenerational fashion. Also see the video abstract here.

Small Glutamine-Rich Tetratricopeptide Repeat-Containing Protein Alpha (SGTA) Ablation Limits Offspring Viability and Growth in Mice

Small glutamine-rich tetratricopeptide repeat-containing protein α (SGTA) has been implicated as a co-chaperone and regulator of androgen and growth hormone receptor (AR, GHR) signalling. We investigated the functional consequences of partial and full Sgta ablation in vivo using Cre-lox Sgta-null mice. Sgta(+/-) breeders generated viable Sgta(-/-) offspring, but at less than Mendelian expectancy. Sgta(-/-) breeders were subfertile with small litters and higher neonatal death (P < 0.02). Body size was significantly and proportionately smaller in male and female Sgta(-/-) (vs WT, Sgta(+/-) P < 0.001) from d19. Serum IGF-1 levels were genotype- and sex-dependent. Food intake, muscle and bone mass and adiposity were unchanged in Sgta(-/-). Vital and sex organs had normal relative weight, morphology and histology, although certain androgen-sensitive measures such as penis and preputial size, and testis descent, were greater in Sgta(-/-). Expression of AR and its targets remained largely unchanged, although AR localisation was genotype- and tissue-dependent. Generally expression of other TPR-containing proteins was unchanged. In conclusion, this thorough investigation of SGTA-null mutation reports a mild phenotype of reduced body size. The model's full potential likely will be realised by genetic crosses with other models to interrogate the role of SGTA in the many diseases in which it has been implicated.

Association study of androgen signaling pathway genes in polycystic ovary syndrome

OBJECTIVE

To evaluate genes involved in androgen receptor (AR) signaling as candidate genes for polycystic ovary syndrome (PCOS).

DESIGN

Two groups of women with PCOS and control women (discovery and replication cohorts), were genotyped for single-nucleotide polymorphisms (SNPs) in eight genes for AR chaperones and co-chaperones: HSPA1A, HSPA8, ST13, STIP1, PTGES3, FKBP4, BAG1, and STUB1. Single-nucleotide polymorphisms were tested for association with PCOS status and with androgenic and metabolic parameters.

SETTING

Tertiary referral center.

PATIENT(S)

Discovery cohort: 354 women with PCOS and 161 control women. Replication cohort: 397 women with PCOS and 306 control women.

INTERVENTION(S)

Phenotypic and genotypic assessment.

MAIN OUTCOME MEASURE(S)

Single-nucleotide polymorphism genotypes, association with PCOS status, and androgenic and metabolic parameters.

RESULT(S)

In the discovery cohort, FKBP4 SNPs rs2968909 and rs4409904 were associated with lower odds of PCOS. This finding was not confirmed in the replication cohort analysis; however, when combining the two cohorts, rs4409904 was associated with lower odds of PCOS. In subjects with PCOS in the replication cohort as well as in the combined cohort, rs2968909 was associated with lower body mass index.

CONCLUSION(S)

Single-nucleotide polymorphisms in FKBP4, which codes for the AR co-chaperone FKBP52, may be associated with PCOS and body mass index in patients with PCOS. The remaining genes studied do not seem to be major contributors to the development of PCOS. These findings warrant confirmation in future studies, and genes encoding other androgen pathway components remain to be studied.

Do endocrine disruptors cause hypospadias?

Introduction

Endocrine disruptors or environmental agents, disrupt the endocrine system, leading to various adverse effects in humans and animals. Although the phenomenon has been noted historically in the cases of diethylstilbestrol (DES) and dichlorodiphenyltrichloroethane (DDT), the term “endocrine disruptor” is relatively new. Endocrine disruptors can have a variety of hormonal activities such as estrogenicity or anti-androgenicity. The focus of this review concerns on the induction of hypospadias by exogenous estrogenic endocrine disruptors. This has been a particular clinical concern secondary to reported increased incidence of hypospadias. Herein, the recent literature is reviewed as to whether endocrine disruptors cause hypospadias.

Methods

A literature search was performed for studies involving both humans and animals. Studies within the past 5 years were reviewed and categorized into basic science, clinical science, epidemiologic, or review studies.

Results

Forty-three scientific articles were identified. Relevant sentinel articles were also reviewed. Additional pertinent studies were extracted from the reference of the articles that obtained from initial search results. Each article was reviewed and results presented. Overall, there were no studies which definitely stated that endocrine disruptors caused hypospadias. However, there were multiple studies which implicated endocrine disruptors as one component of a multifactorial model for hypospadias.

Conclusions

Endocrine disruption may be one of the many critical steps in aberrant development that manifests as hypospadias.

The Genetic and Environmental Factors Underlying Hypospadias

Hypospadias results from a failure of urethral closure in the male phallus and affects 1 in 200-300 boys. It is thought to be due to a combination of genetic and environmental factors. The development of the penis progresses in 2 stages: an initial hormone-independent phase and a secondary hormone-dependent phase. Here, we review the molecular pathways that contribute to each of these stages, drawing on studies from both human and mouse models. Hypospadias can occur when normal development of the phallus is disrupted, and we provide evidence that mutations in genes underlying this developmental process are causative. Finally, we discuss the environmental factors that may contribute to hypospadias and their potential immediate and transgenerational epigenetic impacts.

Adipogenesis is under surveillance of Hsp90 and the high molecular weight Immunophilin FKBP51

Adipose tissue plays a central role in the control of energy balance as well as in the maintenance of metabolic homeostasis. It was not until recently that the first evidences of the role of heat shock protein (Hsp) 90 and high molecular weight immunophilin FKBP51 have been described in the process of adipocyte differentiation. Recent reports describe their role in the regulation of PPARγ, a key transcription factor in the control of adipogenesis and the maintenance of the adipocyte phenotype. In addition, novel roles have been uncovered for FKBP51 in the organization of the architecture of the nucleus through its participation in the reorganization of the nuclear lamina. Therefore, the aim of this review is to integrate and discuss the recent advances in the field, with special emphasis on the roles of Hsp90 and FKBP51 in the process of adipocyte differentiation.

The FKBP52 Cochaperone Acts in Synergy with β-Catenin to Potentiate Androgen Receptor Signaling

FKBP52 and β-catenin have emerged in recent years as attractive targets for prostate cancer treatment. β-catenin interacts directly with the androgen receptor (AR) and has been characterized as a co-activator of AR-mediated transcription. FKBP52 is a positive regulator of AR in cellular and whole animal models and is required for the development of androgen-dependent tissues. We previously characterized an AR inhibitor termed MJC13 that putatively targets the AR BF3 surface to specifically inhibit FKBP52-regulated AR signaling. Predictive modeling suggests that β-catenin interacts with the AR hormone binding domain on a surface that overlaps with BF3. Here we demonstrate that FKBP52 and β-catenin interact directly in vitro and act in concert to promote a synergistic up-regulation of both hormone-independent and -dependent AR signaling. Our data demonstrate that FKBP52 promotes β-catenin interaction with AR and is required for β-catenin co-activation of AR activity in prostate cancer cells. MJC13 effectively blocks β-catenin interaction with the AR LBD and the synergistic up-regulation of AR by FKBP52 and β-catenin. Our data suggest that co-regulation of AR by FKBP52 and β-catenin does not require FKBP52 PPIase catalytic activity, nor FKBP52 binding to Hsp90. However, the FKBP52 proline-rich loop that overhangs the PPIase pocket is critical for synergy.

Biological relevance of Hsp90-binding immunophilins in cancer development and treatment

Immunophilins are a family of intracellular receptors for immunosuppressive drugs. Those immunophilins that are related to immunosuppression are the smallest proteins of the family, i.e., FKBP12 and CyPA, whereas the other members of the family have higher molecular weight because the show additional domains to the drug-binding site. Among these extra domains, the TPR-domain is perhaps the most relevant because it permits the interaction of high molecular weight immunophilins with the 90-kDa heat-shock protein, Hsp90. This essential molecular chaperone regulates the biological function of several protein-kinases, oncogenes, protein phosphatases, transcription factors and cofactors . Hsp90-binding immunophilins where first characterized due to their association with steroid receptors. They regulate the cytoplasmic transport and the subcellular localization of these and other Hsp90 client proteins, as well as transcriptional activity, cell proliferation, cell differentiation and apoptosis. Hsp90-binding immunophilins are frequently overexpressed in several types of cancers and play a key role in cell survival. In this article we analyze the most important biological actions of the best characterized Hsp90-binding immunophilins in both steroid receptor function and cancer development and discuss the potential use of these immunophilins for therapeutic purposes as potential targets of specific small molecules.

Functions of the Hsp90-binding FKBP immunophilins

Hsp90 functionally interacts with a broad array of client proteins, but in every case examined Hsp90 is accompanied by one or more co-chaperones. One class of co-chaperone contains a tetratricopeptide repeat domain that targets the co-chaperone to the C-terminal region of Hsp90. Within this class are Hsp90-binding peptidylprolyl isomerases, most of which belong to the FK506-binding protein (FKBP) family. Despite the common association of FKBP co-chaperones with Hsp90, it is now clear that the client protein influences, and is influenced by, the particular FKBP bound to Hsp90. Examples include Xap2 in aryl hydrocarbon receptor complexes and FKBP52 in steroid receptor complexes. In this chapter, we discuss the known functional roles played by FKBP co-chaperones and, where possible, relate distinctive functions to structural differences between FKBP members.