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

Selective inhibitors of the FK506-binding protein 51 by induced fit

The FK506-binding protein 51 (FKBP51, encoded by the FKBP5 gene) is an established risk factor for stress-related psychiatric disorders such as major depression. Drug discovery for FKBP51 has been hampered by the inability to pharmacologically differentiate against the structurally similar but functional opposing homolog FKBP52, and all known FKBP ligands are unselective. Here, we report the discovery of the potent and highly selective inhibitors of FKBP51, SAFit1 and SAFit2. This new class of ligands achieves selectivity for FKBP51 by an induced-fit mechanism that is much less favorable for FKBP52. By using these ligands, we demonstrate that selective inhibition of FKBP51 enhances neurite elongation in neuronal cultures and improves neuroendocrine feedback and stress-coping behavior in mice. Our findings provide the structural and functional basis for the development of mechanistically new antidepressants.

Control of steroid receptor dynamics and function by genomic actions of the cochaperones p23 and Bag-1L

Molecular chaperones encompass a group of unrelated proteins that facilitate the correct assembly and disassembly of other macromolecular structures, which they themselves do not remain a part of. They associate with a large and diverse set of coregulators termed cochaperones that regulate their function and specificity. Amongst others, chaperones and cochaperones regulate the activity of several signaling molecules including steroid receptors, which upon ligand binding interact with discrete nucleotide sequences within the nucleus to control the expression of diverse physiological and developmental genes. Molecular chaperones and cochaperones are typically known to provide the correct conformation for ligand binding by the steroid receptors. While this contribution is widely accepted, recent studies have reported that they further modulate steroid receptor action outside ligand binding. They are thought to contribute to receptor turnover, transport of the receptor to different subcellular localizations, recycling of the receptor on chromatin and even stabilization of the DNA-binding properties of the receptor. In addition to these combined effects with molecular chaperones, cochaperones are reported to have additional functions that are independent of molecular chaperones. Some of these functions also impact on steroid receptor action. Two well-studied examples are the cochaperones p23 and Bag-1L, which have been identified as modulators of steroid receptor activity in nuclei. Understanding details of their regulatory action will provide new therapeutic opportunities of controlling steroid receptor action independent of the widespread effects of molecular chaperones.

Analysis of FK506, timcodar (VX-853) and FKBP51 and FKBP52 chaperones in control of glucocorticoid receptor activity and phosphorylation

The immunosuppressive ligand FK506 and the FK506-binding protein FKBP52 are stimulatory to glucocorticoid receptor (GR) activity. Here, we explore the underlying mechanism by comparing GR activity and phosphorylation status in response to FK506 and the novel nonimmunosuppressive ligand timcodar (VX-853) and in the presence and absence of FKBP52 and the closely related protein FKBP51. Using mouse embryonic fibroblast cells (MEFs) deficient knockout (KO) in FKBP51 or FKBP52, we show decreased GR activity at endogenous genes in 52KO cells, but increased activity in 51KO cells. In 52KO cells, elevated phosphorylation occurred at inhibitory serine 212 and decreased phosphorylation at the stimulatory S220 residue. In contrast, 51KO cells showed increased GR phosphorylation at the stimulatory residues S220 and S234. In wild-type (WT) MEF cells, timcodar, like FK506, potentiated dexamethasone-induced GR transcriptional activity at two endogenous genes. Using 52KO and 51KO MEF cells, FK506 potentiated GR activity in 51KO cells but could not do so in 52KO cells, suggesting FKBP52 as the major target of FK506 action. Like FK506, timcodar potentiated GR in 51KO cells, but it also increased GR activity in 52KO cells. Knock-down of FKBP51 in the 52KO cells showed that the latter effect of timcodar required FKBP51. Thus, timcodar appears to have a dual specificity for FKBP51 and FKBP52. This work demonstrates phosphorylation as an important mechanism in FKBP control of GR and identifies the first nonimmunosuppressive macrolide capable of targeting GR action.

FKBP5 moderates alcohol withdrawal severity: human genetic association and functional validation in knockout mice

Alcohol withdrawal is associated with hypothalamic-pituitary-adrenal (HPA) axis dysfunction. The FKBP5 gene codes for a co-chaperone, FK506-binding protein 5, that exerts negative feedback on HPA axis function. This study aimed to examine the effects of single-nucleotide polymorphisms (SNPs) of the FKBP5 gene in humans and the effect of Fkbp5 gene deletion in mice on alcohol withdrawal severity. We genotyped six FKBP5 SNPs (rs3800373, rs9296158, rs3777747, rs9380524, rs1360780, and rs9470080) in 399 alcohol-dependent inpatients with alcohol consumption 48 h before admission and recorded scores from the Clinical Institute Withdrawal Assessment-Alcohol revised (CIWA-Ar). Fkbp5 gene knockout (KO) and wild-type (WT) mice were assessed for alcohol withdrawal using handling-induced convulsions (HICs) following both acute and chronic alcohol exposure. We found the minor alleles of rs3800373 (G), rs9296158 (A), rs1360780 (T), and rs9470080 (T) were significantly associated with lower CIWA-Ar scores whereas the minor alleles of rs3777747 (G) and rs9380524 (A) were associated with higher scores. The haplotype-based analyses also showed an association with alcohol withdrawal severity. Fkbp5 KO mice showed significantly greater HICs during withdrawal from chronic alcohol exposure compared with WT controls. This study is the first to show a genetic effect of FKBP5 on the severity of alcohol withdrawal syndrome. In mice, the absence of the Fkbp5 gene enhances sensitivity to alcohol withdrawal. We suggest that FKBP5 variants may trigger different adaptive changes in HPA axis regulation during alcohol withdrawal with concomitant effects on withdrawal severity.

FKBP51 reciprocally regulates GRα and PPARγ activation via the Akt-p38 pathway

FK506-binding protein 51 (FKBP51) is a negative regulator of glucocorticoid receptor-α (GRα), although the mechanism is unknown. We show here that FKBP51 is also a chaperone to peroxisome proliferator-activated receptor-γ (PPARγ), which is essential for activity, and uncover the mechanism underlying this differential regulation. In COS-7 cells, FKBP51 overexpression reduced GRα activity at a glucocorticoid response element-luciferase reporter, while increasing PPARγ activity at a peroxisome proliferator response element reporter. Conversely, FKBP51-deficient (knockout) (51KO) mouse embryonic fibroblasts (MEFs) showed elevated GRα but reduced PPARγ activities compared with those in wild-type MEFs. Phosphorylation is known to exert a similar pattern of reciprocal modulation of GRα and PPARγ. Knockdown of FKBP51 in 3T3-L1 preadipocytes increased phosphorylation of PPARγ at serine 112, a phospho-residue that inhibits activity. In 51KO cells, elevated phosphorylation of GRα at serines 220 and 234, phospho-residues that promote activity, was observed. Because FKBP51 is an essential chaperone to the Akt-specific phosphatase PH domain leucine-rich repeat protein phosphatase, Akt signaling was investigated. Elevated Akt activation and increased activation of p38 kinase, a downstream target of Akt that phosphorylates GRα and PPARγ, were seen in 51KO MEFs, causing activation and inhibition, respectively. Inactivation of p38 with PD169316 reversed the effects of FKBP51 deficiency on GRα and PPARγ activities and reduced PPARγ phosphorylation. Last, loss of FKBP51 caused a shift of PPARγ from cytoplasm to nucleus, as previously shown for GRα. A model is proposed in which FKBP51 loss reciprocally regulates GRα and PPARγ via 2 complementary mechanisms: activation of Akt-p38-mediated phosphorylation and redistribution of the receptors to the nucleus for direct targeting by p38.

FKBP51 controls cellular adipogenesis through p38 kinase-mediated phosphorylation of GRα and PPARγ

Glucocorticoid receptor-α (GRα) and peroxisome proliferator-activated receptor-γ (PPARγ) are critical regulators of adipogenic responses. We have shown that FK506-binding protein 51 (FKBP51) represses the Akt-p38 kinase pathway to reciprocally inhibit GRα but stimulate PPARγ by targeting serine 112 (PPARγ) and serines 220 and 234 (GRα). Here, this mechanism is shown to be essential for GRα and PPARγ control of cellular adipogenesis. In 3T3-L1 cells, FKBP51 was a prominent marker of the differentiated state and knockdown of FKBP51 showed reduced lipid accumulation and expression of adipogenic genes. Compared with wild-type (WT), FKBP51 knockout (51KO) mouse embryonic fibroblasts (MEFs) showed dramatic resistance to differentiation, with almost no lipid accumulation and greatly reduced adipogenic gene expression. These features were rescued by reexpression of FKBP51 in 51KO cells. 51KO MEFs exhibited reduced fatty acid synthase activity, increased sensitivity to GRα-induced lipolysis, and reduced PPARγ activity at adipogenic genes (adiponectin, CD36, and perilipin) but elevated GRα transrepression at these same genes. A p38 kinase inhibitor increased lipid content in WT cells and also restored lipid levels in 51KO cells, showing that elevated p38 kinase activity is a major contributor to adipogenic resistance in the 51KO cells. In 51KO cells, the S112A mutant of PPARγ and the triple S212A/S220A/S234A mutant of GRα both increased lipid accumulation, identifying these residues as targets of the FKBP51/p38 axis. Our combined investigations have uncovered FKBP51 as a key regulator of adipogenesis via the Akt-p38 pathway and as a potential target in the treatment of obesity and related disorders.

Mitochondria-nucleus shuttling FK506-binding protein 51 interacts with TRAF proteins and facilitates the RIG-I-like receptor-mediated expression of type I IFN

Virus-derived double-stranded RNAs (dsRNAs) are sensed in the cytosol by retinoic acid-inducible gene (RIG)-I-like receptors (RLRs). These induce the expression of type I IFN and proinflammatory cytokines through signaling pathways mediated by the mitochondrial antiviral signaling (MAVS) protein. TNF receptor-associated factor (TRAF) family proteins are reported to facilitate the RLR-dependent expression of type I IFN by interacting with MAVS. However, the precise regulatory mechanisms remain unclear. Here, we show the role of FK506-binding protein 51 (FKBP51) in regulating the dsRNA-dependent expression of type I IFN. The binding of FKBP51 to TRAF6 was first identified by “in vitro virus” selection and was subsequently confirmed with a coimmunoprecipitation assay in HEK293T cells. The TRAF-C domain of TRAF6 is required for its interaction, although FKBP51 does not contain the consensus motif for interaction with the TRAF-C domain. Besides TRAF6, we found that FKBP51 also interacts with TRAF3. The depletion of FKBP51 reduced the expression of type I IFN induced by dsRNA transfection or Newcastle disease virus infection in murine fibroblasts. Consistent with this, the FKBP51 depletion attenuated dsRNA-mediated phosphorylations of IRF3 and JNK and nuclear translocation of RelA. Interestingly, dsRNA stimulation promoted the accumulation of FKBP51 in the mitochondria. Moreover, the overexpression of FKBP51 inhibited RLR-dependent transcriptional activation, suggesting a scaffolding function for FKBP51 in the MAVS-mediated signaling pathway. Overall, we have demonstrated that FKBP51 interacts with TRAF proteins and facilitates the expression of type I IFN induced by cytosolic dsRNA. These findings suggest a novel role for FKBP51 in the innate immune response to viral infection.

The co-chaperones Fkbp4/5 control Argonaute2 expression and facilitate RISC assembly

Argonaute2 (Ago2) protein and associated microRNAs (miRNAs) or small interfering RNAs (siRNAs) form the RNA-induced silencing complex (RISC) for target messenger RNA cleavage and post-transcriptional gene silencing. Although Ago2 is essential for RISC activity, the mechanism of RISC assembly is not well understood, and factors controlling Ago2 protein expression are largely unknown. A role for the Hsc70/Hsp90 chaperone complex in loading small RNA duplexes into the RISC has been demonstrated in cell extracts, and unloaded Ago2 is unstable and degraded by the lysosome in mammalian cells. Here we identify the co-chaperones Fkbp4 and Fkbp5 as Ago2-associated proteins in mouse embryonic stem cells. Pharmacological inhibition of this interaction using FK506 or siRNA-mediated Fkbp4/5 depletion leads to decreased Ago2 protein levels. We find FK506 treatment inhibits, whereas Fkbp4/5 overexpression promotes, miRNA-mediated stabilization of Ago2 expression. Simultaneous treatment with a lysosome inhibitor revealed the accumulation of unloaded Ago2 complexes in FK506-treated cells. We find that, consistent with unloaded miRNAs being unstable, FK506 treatment also affects miRNA abundance, particularly nascent miRNAs. Our results support a role for Fkbp4/5 in RISC assembly.

Dynamic mitochondrial-nuclear redistribution of the immunophilin FKBP51 is regulated by the PKA signaling pathway to control gene expression during adipocyte differentiation

Glucocorticoids play an important role in adipogenesis through the glucocorticoid receptor (GR) that forms a heterocomplex with Hsp90•Hsp70 and one high molecular weight immunophilin, either FKBP51 or FKBP52. When 3T3-L1 preadipocytes are induced to differentiate, FKBP51 expression progressively increases, whereas FKBP52 decreases, and Hsp90, Hsp70, p23 and Cyp40 remain unchanged. Interestingly, FKBP51 rapidly translocates from mitochondria to the nucleus where it is retained upon its interaction with chromatin and the nuclear matrix. FKBP51 nuclear localization is transient, and after 48 hours it cycles back to mitochondria. Importantly, this dynamic FKBP51 mitochondrial-nuclear shuttling depends on PKA signaling, because its inhibition by PKI or knockdown of PKA-cα by siRNA, prevented FKBP51 nuclear translocation induced by IBMX. In addition, the electrophoretic pattern of migration of FKBP51 is altered by treatment of cells with PKI or knockdown of PKA-cα, suggesting that FKBP51 is a PKA substrate. In preadipocytes, FKBP51 colocalizes with PKA-cα in mitochondria. When adipogenesis is triggered, PKA-cα also moves to the nucleus colocalizing with FKBP51 mainly in the nuclear lamina. Moreover, FKBP51 and GR interaction increases when preadipocytes are induced to differentiate. GR transcriptional capacity is reduced when cells are incubated in the presence of IBMX, forskolin or dibutyryl-cAMP, compounds that induced FKBP51 nuclear translocation, but not by a specific activator of EPAC. FKBP51 knockdown facilitates adipogenesis, whereas ectopic expression of FKBP51 blocks adipogenesis. These findings indicate that the dynamic mitochondrial-nuclear shuttling of FKBP51 regulated by PKA may be key in fine-tuning the transcriptional control of GR target genes required for the acquisition of adipocyte phenotype.

Crystal structures of the free and ligand-bound FK1-FK2 domain segment of FKBP52 reveal a flexible inter-domain hinge

The human Hsp90 co-chaperone FKBP52 belongs to the family of FK506-binding proteins, which act as peptidyl-prolyl isomerases. FKBP52 specifically enhances the signaling of steroid hormone receptors, modulates ion channels and regulates neuronal outgrowth dynamics. In turn, small-molecule ligands of FKBP52 have been suggested as potential neurotrophic or anti-prostate cancer agents. The usefulness of available ligands is however limited by a lack of selectivity. The immunophilin FKBP52 is composed of three domains, an FK506-binding domain with peptidyl-prolyl isomerase activity, an FKBP-like domain of unknown function and a TPR-clamp domain, which recognizes the C-terminal peptide of Hsp90 with high affinity. The herein reported crystal structures of FKBP52 reveal that the short linker connecting the FK506-binding domain and the FKBP-like domain acts as a flexible hinge. This enhanced flexibility and its modulation by phosphorylation might explain some of the functional antagonism between the closely related homologs FKBP51 and FKBP52. We further present two co-crystal structures of FKBP52 in complex with the prototypic ligand FK506 and a synthetic analog thereof. These structures revealed the molecular interactions in great detail, which enabled in-depth comparison with the corresponding complexes of the other cytosolic FKBPs, FKBP51 and FKBP12. The observed subtle differences provide crucial insights for the rational design of ligands with improved selectivity for FKBP52.

Knockdown of the cochaperone SGTA results in the suppression of androgen and PI3K/Akt signaling and inhibition of prostate cancer cell proliferation

Solid tumors have an increased reliance on Hsp70/Hsp90 molecular chaperones for proliferation, survival and maintenance of intracellular signaling systems. An underinvestigated component of the chaperone system is the tetratricopeptide repeat (TPR)-containing cochaperone, which coordinates Hsp70/Hsp90 involvement on client proteins as well as having diverse individual actions. A potentially important cochaperone in prostate cancer (PCa) is small glutamine-rich TPR-containing protein alpha (SGTA), which interacts with the androgen receptor (AR) and other critical cancer-related client proteins. In this study, the authors used small interfering RNA coupled with genome-wide expression profiling to investigate the biological significance of SGTA in PCa and its influence on AR signaling. Knockdown of SGTA for 72 hr in PCa C4-2B cells significantly altered expression of >1,900 genes (58% decreased) and reduced cell proliferation (p < 0.05). The regulation of 35% of 5α-dihydrotestosterone (DHT) target genes was affected by SGTA knockdown, with gene-specific effects on basal or DHT-induced expression or both. Pathway analysis revealed a role for SGTA in p53, generic PCa and phosphoinositol kinase (PI3K) signaling pathways; the latter evident by a reduction in PI3K subunit p100β levels and decreased phosphorylated Akt. Immunohistochemical analysis of 64 primary advanced PCa samples showed a significant increase in the AR:SGTA ratio in cancerous lesions compared to patient-matched benign prostatic hyperplasia tissue (p < 0.02). This study not only provides insight into the biological actions of SGTA and its effect on genome-wide AR transcriptional activity and other therapeutically targeted intracellular signaling pathways but also provides evidence for PCa-specific alterations in SGTA expression.

SGTA: a new player in the molecular co-chaperone game

Small glutamine-rich tetratricopeptide repeat-containing protein α (SGTA) is a steroid receptor molecular co-chaperone that may substantially influence hormone action and, consequently, hormone-mediated carcinogenesis. To date, published studies describe SGTA as a protein that is potentially critical in a range of biological processes, including viral infection, cell division, mitosis, and cell cycle checkpoint activation. SGTA interacts with the molecular chaperones, heat shock protein 70 (HSP70) and HSP90, and with steroid receptor complexes, including those containing the androgen receptor. Steroid receptors are critical for maintaining cell growth and differentiation in hormonally regulated tissues, such as male and female reproductive tissues, and also play a role in disease states involving these tissues. There is growing evidence that, through its interactions with chaperones and steroid receptors, SGTA may be a key player in the pathogenesis of hormonally influenced disease states, including prostate cancer and polycystic ovary syndrome. Research into the function of SGTA has been conducted in several model organisms and cell types, with these studies showing that SGTA functionality is cell-specific and tissue-specific. However, very few studies have been replicated in multiple cell types or experimental systems. Although a broad range of functions have been attributed to SGTA, there is a serious lack of mechanistic information to describe how SGTA acts. In this review, published evidence linking SGTA with hormonally regulated disease states is summarized and discussed, highlighting the need for future research to more clearly define the biological function(s) of this potentially important co-chaperone.

Androgen receptor splice variants are resistant to inhibitors of Hsp90 and FKBP52, which alter androgen receptor activity and expression

Androgen ablation therapy is the most common treatment for advanced prostate cancer (PCa), but most patients will develop castration-resistant prostate cancer (CRPC), which has no cure. CRPC is androgen-depletion resistant but androgen receptor (AR) dependent. AR is a nuclear receptor whose transcriptional activity is regulated by hormone binding to the ligand-binding domain (LBD). Constitutively active AR splice variants that lack LBDs often are expressed in CRPC. The expression of these variants indicates that methods to inhibit AR activity that do not rely on inactivating the LBD are needed. Heat shock protein 90 (Hsp90), a potential therapeutic target in PCa, is an AR chaperone crucial for proper folding, hormone binding and transcriptional activity of AR. We generated LNCaP cell lines with regulated expression of the AR-V7 variant as well as a cell line expressing artificially truncated AR (termed AR-NTD) to characterize splice variant function. Using an Hsp90 inhibitor, Geldanamycin (GA), and an AR-Hsp90-FKBP52 specific inhibitor, MJC13, we sought to determine if the AR variants also require Hsp90 and associated co-chaperone, FKBP52, for their activity. GA inhibits AR transcriptional activity but has little effect on AR-V7 activity. Moreover, GA decreases the stability of AR protein, with no effect on AR-V7 levels. Full-length AR activity is strongly inhibited by MJC13 while AR-V7 is unaffected. Thus, the variants are resistant to inhibitors of the Hsp90-AR heterocomplex. Although Hsp90 inhibitors will continue to inhibit growth promoting kinases and signaling through activated full-length AR in CRPC, AR signaling through variants will be retained.

The helix 1-3 loop in the glucocorticoid receptor LBD is a regulatory element for FKBP cochaperones

The heat-shock protein 90 (Hsp90) cochaperone FK506-binding protein 52 (FKBP52) upregulates, whereas FKBP51 inhibits, hormone binding and nuclear targeting of the glucocorticoid receptor (GR). Decreased cortisol sensitivity in the guinea pig is attributed to changes within the helix 1 to helix 3 (H1-H3) loop of the guinea pig GR (gpGR) ligand-binding domain. It has been proposed that this loop serves as a contact point for FKBP52 and/or FKBP51 with receptor. We examined the role of the H1-H3 loop in GR activation by FKBP52 using a Saccharomyces cerevisiae model. The activity of rat GR (rGR) containing the gpGR H1-H3 loop substitutions was still potentiated by FKBP52, confirming the loop is not involved in primary FKBP52 interactions. Additional assays also excluded a role for other intervening loops between ligand-binding domain helices in direct interactions with FKBP52 associated with enhanced receptor activity. Complementary studies in FKBP51-deficient mouse embryo fibroblasts and HEK293 cells demonstrated that substitution of the gpGR H1-H3 loop residues into rGR dramatically increased receptor repression by FKBP51 without enhancing receptor-FKBP51 interaction and did not alter recruitment of endogenous Hsp90 and the p23 cochaperone to receptor complexes. FKBP51 suppression of the mutated rGR did not require FKBP51 peptidylprolyl cis-trans isomerase activity and was not disrupted by mutation of the FK1 proline-rich loop thought to mediate reciprocal FKBP influences on receptor activity. We conclude that the gpGR-specific mutations within the H1-H3 loop confer global changes within the GR-Hsp90 complex that favor FKBP51 repression over FKBP52 potentiation, thus identifying the loop as an important target for GR regulation by the FKBP cochaperones.

Mini-review: Foldosome regulation of androgen receptor action in prostate cancer

Steroid hormone receptors play diverse roles in many aspects of human physiology including cell division, apoptosis and homeostasis, tissue differentiation, sexual development and response to stress. These ligand-activated transcription factors require the functional activity of numerous chaperone and chaperone-associated proteins, collectively termed the foldosome, at the crucial step of ligand recognition and binding. Since the initial isolation of foldosome components and pioneering research by Pratt, Toft and colleagues we understand much regarding cytosolic receptor function. The classical view, that the role of foldosome components is restricted to the cytosol, has been modified over recent years by research highlighting additional roles of chaperone proteins in nuclear translocation and target gene expression. Further, dysregulation of chaperone activity and expression has been implicated in various cancers, including breast and prostate cancer. Consequently, the foldosome provides an attractive therapeutic target in steroid hormone receptor-driven malignancies. This review summarises current knowledge of how the foldosome impacts upon androgen receptor signalling, which is the key therapeutic target on prostate cancer, and how foldosome components may be used as biomarkers or therapeutic targets in this disease.

Regulation of store-operated calcium entry by FK506-binding immunophilins

Calcium entry from the extracellular space into cells is an important signaling mechanism in both physiological and pathophysiological functions. In non-excitable cells, store-operated calcium (SOC) entry represents a principal mode of calcium entry. Activation of SOC entry in pulmonary artery endothelial cells leads to the formation of inter-endothelial cell gaps and subsequent endothelial barrier disruption. Regulation of endothelial SOC entry is poorly understood. In this work, we identify two large molecular weight immunophilins, FKBP51 and FKBP52, as novel regulators of SOC entry in endothelial cells. Using cell fractionation studies and immunocytochemistry we determined that a fraction of these largely cytosolic proteins localize to the plasma membrane where SOC entry channels are found. That FKBP51 and FKBP52 associate with SOC entry channel protein complexes was supported by co-precipitation of the immunophilins with TRPC4, a subunit of the calcium-selective, SOC entry channel ISOC. Dexamethasone-induced upregulation of FKBP51 expression in pulmonary artery endothelial cells reduced global SOC entry as well as ISOC. Similar results were observed when FKBP51 was over-expressed in an inducible HEK293 cell line. On the other hand, when FKBP52 was over-expressed SOC entry was enhanced. When expression of FKBP52 was inhibited, SOC entry was decreased. Collectively, our observations support regulatory roles for these large molecular weight immunophilins in which FKBP51 inhibits, whereas FKBP52 enhances, SOC entry in endothelial cells.

Fkbp52 heterozygosity alters behavioral, endocrine and neurogenetic parameters under basal and chronic stress conditions in mice

Aversive life events represent one of the main risk factors for the development of many psychiatric diseases, but the interplay between environmental factors and genetic predispositions is still poorly understood. One major finding in many depressed patients is an impaired regulation of the hypothalamic-pituitary-adrenal (HPA) axis. The negative feedback loop of the HPA axis is mediated via the glucocorticoid receptor (GR) and the mineralocorticoid receptor. The co-chaperones FK506-binding protein 51 (FKBP51) and FK506-binding protein 52 (FKBP52) are components of the heat shock protein 90-receptor-heterocomplex and are functionally divergent regulators of both receptors. Here, we characterized heterozygous Fkbp52 knockout (Fkbp52(+/-)) mice under basal or chronic social defeat stress (CSDS) conditions with regard to physiological, neuroendocrine, behavioral and mRNA expression alterations. Fkbp52(+/-) mice displayed symptoms of increased stress sensitivity in a subset of behavioral and neuroendocrine parameters. These included increased anxiety-related behavior in the elevated plus-maze and an enhanced neuroendocrine response to a forced swim test (FST), possibly mediated by reduced GR sensitivity. At the same time, Fkbp52(+/-) mice also demonstrated signs of stress resilience in other behavioral and neuroendocrine aspects, such as reduced basal corticosterone levels and more active stress-coping behavior in the FST following CSDS. These contrasting results are in line with previous reports showing that FKBP52 is not involved in all branches of GR signaling, but rather acts in a gene-specific manner to regulate GR transcriptional activation.

Subdomain structure of the co-chaperone SGTA and activity of its androgen receptor client

Ligand-dependent activity of steroid receptors is affected by tetratricopeptide repeat (TPR)-containing co-chaperones, such as small glutamine-rich tetratricopeptide repeat-containing alpha (SGTA). However, the precise mechanisms by which the predominantly cytoplasmic TPR proteins affect downstream transcriptional outcomes of steroid signaling remain unclear. In this study, we assessed how SGTA affects ligand sensitivity and action of the androgen receptor (AR) using a transactivation profiling approach. Deletion mapping coupled with structural prediction, transcriptional assays, and in vivo regulation of AR-responsive promoters were used to assess the role of SGTA domains in AR responses. At subsaturating ligand concentrations of ≤ 0.1 nM 5α-dihydrotestosterone, SGTA overexpression constricted AR activity by an average of 32% (P<0.002) across the majority of androgen-responsive loci tested, as well as on endogenous promoters in vivo. The strength of the SGTA effect was associated with the presence or absence of bioinformatically predicated transcription factor motifs at each site. Homodimerizaion of SGTA, which is thought to be necessary for chaperone complex formation, was found to be dependent on the structural integrity of amino acids 1-80, and a core evolutionary conserved peptide within this region (amino acids 21-40) necessary for an effect of SGTA on the activity of both exogenous and endogenous AR. This study provides new insights into the subdomain structure of SGTA and how SGTA acts as a regulator of AR ligand sensitivity. A change in AR:SGTA ratio will impact the cellular and molecular response of prostate cancer cells to maintain androgenic signals, which may influence tumor progression.

Molecular mechanisms of external genitalia development

External genitalia development occurs through a combination of hormone independent, hormone dependent, and endocrine pathways. Perturbation of these pathways can lead to abnormal external genitalia development. We review human and animal mechanisms of normal and abnormal external genitalia development, and we evaluate abnormal mechanisms that lead to hypospadias. We also discuss recent laboratory findings that further our understanding of animal models of hypospadias.

Environmental and genetic contributors to hypospadias: a review of the epidemiologic evidence

This review evaluates current knowledge related to trends in the prevalence of hypospadias, the association of hypospadias with endocrine-disrupting exposures, and the potential contribution of genetic susceptibility to its etiology. The review focuses on epidemiologic evidence. Increasing prevalence of hypospadias has been observed, but such increases tend to be localized to specific regions or time periods. Thus, generalized statements that hypospadias is increasing are unsupported. Owing to the limitations of study designs and inconsistent results, firm conclusions cannot be made regarding the association of endocrine-disrupting exposures with hypospadias. Studies with more rigorous study designs (e.g., larger and more detailed phenotypes) and exposure assessment that encompasses more breadth and depth (e.g., specific endocrine-related chemicals) will be critical to make better inferences about these important environmental exposures. Many candidate genes for hypospadias have been identified, but few of them have been examined to an extent that enables solid conclusions. Further study is needed that includes larger sample sizes, comparison groups that are more representative of the populations from which the cases were derived, phenotype-specific analyses, and more extensive exploration of variants. In conclusion, examining the associations of environmental and genetic factors with hypospadias remain important areas of inquiry, although our actual understanding of their contribution to hypospadias risk in humans is currently limited.

Chaperoning steroidal physiology: lessons from mouse genetic models of Hsp90 and its cochaperones

The molecular chaperone Hsp90 is abundant, ubiquitous, and catholic to biological processes in eukaryotes, controlling phosphorylation cascades, protein stability and turnover, client localization and trafficking, and ligand-receptor interactions. Not surprisingly, Hsp90 does not accomplish these activities alone. Instead, an ever-growing number of cochaperones have been identified, leading to an explosion of reports on their molecular and cellular effects on Hsp90 chaperoning of client substrates. Notable among these clients are many members of the steroid receptor family, such as glucocorticoid, androgen, estrogen and progesterone receptors. Cochaperones typically associated with the mature, hormone-competent states of these receptors include p23, the FK506-binding protein 52 (FKBP52), FKBP51, protein phosphatase 5 (PP5) and cyclophilin 40 (Cyp40). The ultimate relevance of these cochaperones to steroid receptor action depends on their physiological effects. In recent years, the first mouse genetic models of these cochaperones have been developed. This work will review the complex and intriguing phenotypes so far obtained in genetically-altered mice and compare them to the known molecular and cellular impacts of cochaperones on steroid receptors. This article is part of a Special Issue entitled: Heat Shock Protein 90 (HSP90).

FKBP51 and FKBP52 in signaling and disease

FKBP51 and FKBP52 are diverse regulators of steroid hormone receptor signaling, including receptor maturation, hormone binding and nuclear translocation. Although structurally similar, they are functionally divergent, which is largely attributed to differences in the FK1 domain and the proline-rich loop. FKBP51 and FKBP52 have emerged as likely contributors to a variety of hormone-dependent diseases, including stress-related diseases, immune function, reproductive functions and a variety of cancers. In addition, recent studies have implicated FKBP51 and FKBP52 in Alzheimer's disease and other protein aggregation disorders. This review summarizes our current understanding of FKBP51 and FKBP52 interactions within the receptor-chaperone complex, their contributions to health and disease, and their potential as therapeutic targets for the treatment of these diseases.

Association of prolactin-induced protein with preputial development of hypospadias

OBJECTIVE

To investigate the molecular aetiology of hypospadias during a critical developmental period by identifying differentially regulated genes in the tissues of individuals with hypospadias and comparing these genes with similar genes in the tissues of control individuals.

MATERIALS AND METHODS

Pregnant Sprague-Dawley rats were administered flutamide (7.5 mg) on gestational days 15-17 to produce hypospadiac pups. Dams were killed on gestational day 17, and the genital tubercles (GTs) of male pups were harvested. Gene expression of RNA isolated from the GTs was analysed using an oligonucleotide microarray containing 20,500 genes. The results of microarray analysis were confirmed using quantitative real-time PCR (qPCR). Protein expression levels were studied using Western blot analysis. The distribution of genes associated with GT development in rats was histologically examined. Prepuces harvested from patients with hypospadias and phimosis were immunohistochemically examined for gene distribution.

RESULTS

Of the 20, 500 genes, 23 annotated genes, including prolactin-induced protein (Pip), in the GTs of the hypospadiac rats were expressed at levels less than half of that of similar genes in the GTs of the control rats. Findings from qPCR and Western blot analysis revealed significantly lower Pip/PIP expression in the GTs of the hypospadiac rats than in those of the control rats. Immunohistochemical analysis revealed PIP expression in the prepuces of the GTs of the control and hypospadiac rats. PIP was expressed in the human prepuces of the patients with hypospadias and phimosis.

CONCLUSIONS

Pip/PIP, expressed at low levels in the GTs of hypospadiac rats, may be associated with preputial development. This model can be useful to elucidate the molecular mechanisms underlying penile and urethral development as well as preputial development. Further studies should provide detailed information regarding the molecular aetiology of hypospadias.

Regulation of steroid hormone receptor function by the 52-kDa FK506-binding protein (FKBP52)

The large FK506-binding protein FKBP52 has been characterized as an important positive regulator of androgen, glucocorticoid and progesterone receptor signaling pathways. FKBP52 associates with receptor-Hsp90 complexes and is proposed to have roles in both receptor hormone binding and receptor subcellular localization. Data from biochemical and cellular studies have been corroborated in whole animal models as fkbp52-deficient male and female mice display characteristics of androgen, glucocorticoid and/or progesterone insensitivity. FKBP52 receptor specificity and the specific phenotypes displayed by the fkbp52-deficient mice have firmly established FKBP52 as a promising target for the treatment of a variety of hormone-dependent diseases. Recent studies demonstrated that the FKBP52 FK1 domain and the proline-rich loop within this domain are functionally important for FKBP52 regulation of receptor function. Based on these data, efforts are currently underway to target the FKBP52 FK1 domain and the proline-rich loop with small molecule inhibitors.

Hsp90 can accommodate the simultaneous binding of the FKBP52 and HOP proteins

The regulation of steroidogenic hormone receptor-mediated activity plays an important role in the development of hormone-dependent cancers. For example, during prostate carcinogenesis, the regulatory function played by the androgen receptor is often converted from a growth suppressor to an oncogene thus promoting prostate cancer cell survival and eventual metastasis. Within the cytoplasm, steroid hormone receptor activity is regulated by the Hsp90 chaperone in conjunction with a series of co-chaperone proteins. Collectively, Hsp90 and its binding associates form a large heteromeric complex that scaffold the fully mature receptor for binding with the respective hormone. To date our understanding of the interactions between Hsp90 with the various TPR domain-containing co-chaperone proteins is limited due to a lack of available structural information. Here we present the stable formation of Hsp90₂-FKBP52₁- HOP₂ and Hsp90₂-FKBP52₁-p23₂-HOP₂ complexes as detected by immunoprecipitation, time course dynamic light scattering and electron microscopy. The simultaneous binding of FKBP52 and HOP to the Hsp90 dimer provide direct evidence of a novel chaperone sub-complex that likely plays a transient role in the regulation of the fully mature steroid hormone receptor.

Targeting the regulation of androgen receptor signaling by the heat shock protein 90 cochaperone FKBP52 in prostate cancer cells

Drugs that target novel surfaces on the androgen receptor (AR) and/or novel AR regulatory mechanisms are promising alternatives for the treatment of castrate-resistant prostate cancer. The 52 kDa FK506 binding protein (FKBP52) is an important positive regulator of AR in cellular and whole animal models and represents an attractive target for the treatment of prostate cancer. We used a modified receptor-mediated reporter assay in yeast to screen a diversified natural compound library for inhibitors of FKBP52-enhanced AR function. The lead compound, termed MJC13, inhibits AR function by preventing hormone-dependent dissociation of the Hsp90-FKBP52-AR complex, which results in less hormone-bound receptor in the nucleus. Assays in early and late stage human prostate cancer cells demonstrated that MJC13 inhibits AR-dependent gene expression and androgen-stimulated prostate cancer cell proliferation.

The emerging role of FK506-binding proteins as cancer biomarkers: a focus on FKBPL

FKBPs (FK506-binding proteins) have long been recognized as key regulators of the response to immunosuppressant drugs and as co-chaperones of steroid receptor complexes. More recently, evidence has emerged suggesting that this diverse protein family may also represent cancer biomarkers owing to their roles in cancer progression and response to treatment. FKBPL (FKBP-like) is a novel FKBP with roles in GR (glucocorticoid receptor), AR (androgen receptor) and ER (oestrogen receptor) signalling. FKBPL binds Hsp90 (heat-shock protein 90) and modulates translocation, transcriptional activation and phosphorylation of these steroid receptors. It has been proposed as a novel prognostic and predictive biomarker, where high levels predict for increased recurrence-free survival in breast cancer patients and enhanced sensitivity to endocrine therapy. Since this protein family has roles in a plethora of signalling pathways, its members represent novel prognostic markers and therapeutic targets for cancer diagnosis and treatment.

Versatile TPR domains accommodate different modes of target protein recognition and function

The tetratricopeptide repeat (TPR) motif is one of many repeat motifs that form structural domains in proteins that can act as interaction scaffolds in the formation of multi-protein complexes involved in numerous cellular processes such as transcription, the cell cycle, protein translocation, protein degradation and host defence against invading pathogens. The crystal structures of many TPR domain-containing proteins have been determined, showing TPR motifs as two anti-parallel α-helices packed in tandem arrays to form a structure with an amphipathic groove which can bind a target peptide. This is however not the only mode of target recognition by TPR domains, with short amino acid insertions and alternative TPR motif conformations also shown to contribute to protein interactions, highlighting diversity in TPR domains and the versatility of this structure in mediating biological events.

Structural characterization of the PPIase domain of FKBP51, a cochaperone of human Hsp90

Steroid hormone receptors are key components of mammalian stress and sex hormone systems. Many of them rely on the Hsp90 chaperone system for full function and are further fine-tuned by Hsp90-associated peptidyl-prolyl isomerases such as FK506-binding proteins 51 and 52. FK506-binding protein 51 (FKBP51) has been shown to reduce glucocorticoid receptor signalling and has been genetically associated with human stress resilience and with numerous psychiatric disorders. The peptidyl-prolyl isomerase domain of FKBP51 contains a high-affinity binding site for the natural products FK506 and rapamycin and has further been shown to convey most of the inhibitory activity on the glucocorticoid receptor. FKBP51 has therefore become a prime new target for the treatment of stress-related affective disorders that could be amenable to structure-based drug design. Here, a series of high-resolution structures of the peptidyl-prolyl isomerase domain of FKBP51 as well as a cocrystal structure with the prototypic ligand FK506 are described. These structures provide a detailed picture of the drug-binding domain of FKBP51 and the molecular binding mode of its ligand as a starting point for the rational design of improved inhibitors.

FKBP51-a selective modulator of glucocorticoid and androgen sensitivity

FK506-binding protein 51 (FKBP51) is gaining increased recognition for its essential roles in cell biology. Originally discovered as a component of steroid receptor complexes, it is now known to regulate a diverse set of transcription factors, enzymes and structural proteins. Its cellular properties suggest numerous possible functions for FKBP51 in physiology, and the best clue to its potential importance may be the following: FKBP51 is a glucocorticoid-induced negative regulator of the glucocorticoid receptor. Thus, FKBP51 is intricately involved in regulation of the most pleiotropic hormone known to biology. In contrast to glucocorticoid receptor, FKBP51 is a positive regulator of the androgen receptor, suggesting that it functions as a reciprocal modulator of glucocorticoid-mediated and androgen-mediated physiology. In this work, we evaluate this hypothesis by examining recent cellular and physiological evidence.

Unraveling the role of peptidyl-prolyl isomerases in neurodegeneration

Immunophilins are a family of highly conserved proteins with a peptidyl-prolyl isomerase activity that binds immunosuppressive drugs such as FK506, cyclosporin A, and rapamycin. Immunophilins can be divided into two subfamilies, the cyclophilins, and the FK506 binding proteins (FKBPs). Next to the immunophilins, a third group of peptidyl-prolyl isomerases exist, the parvulins, which do not influence the immune system. The beneficial role of immunophilin ligands in neurodegenerative disease models has been known for more than a decade but remains largely unexplained in terms of molecular mechanisms. In this review, we summarize reported effects of parvulins, immunophilins, and their ligands in the context of neurodegeneration. We focus on the role of FKBP12 in Parkinson's disease and propose it as a novel drug target for therapy of Parkinson's disease.

Steroid up-regulation of FKBP51 and its role in hormone signaling

FK506 binding protein 51 (FKBP51, FKBP5) functions as a co-chaperone for androgen, glucocorticoid, mineralocorticoid and progesterone receptors. The FKBP51 can act as an important determinant of the responses to steroids, especially to glucocorticoids in stress and mood disorders and androgens in prostate cancer, raising medical and pharmacological interests in the protein and its gene. Recent studies have revealed the molecular mechanisms by which the androgens and the glucocorticoids via their nuclear receptors elicit the robust up-regulation of the FKBP51 gene. Several polymorphisms in the FKBP51 gene have been associated with the mood disorders and differences in glucocorticoid sensitivity. The polymorphisms may contribute to the steroid up-regulation of the FKBP51 and thus influence the regulatory loops in steroid signaling.

Bending tau into shape: the emerging role of peptidyl-prolyl isomerases in tauopathies

The Hsp90-associated cis-trans peptidyl-prolyl isomerase--FK506 binding protein 51 (FKBP51)--was recently found to co-localize with the microtubule (MT)-associated protein tau in neurons and physically interact with tau in brain tissues from humans who died from Alzheimer's disease (AD). Tau pathologically aggregates in neurons, a process that is closely linked with cognitive deficits in AD. Tau typically functions to stabilize and bundle MTs. Cellular events like calcium influx destabilize MTs, disengaging tau. This excess tau should be degraded, but sometimes it is stabilized and forms higher-order aggregates, a pathogenic hallmark of tauopathies. FKBP51 was also found to increase in forebrain neurons with age, further supporting a novel role for FKBP51 in tau processing. This, combined with compelling evidence that the prolyl isomerase Pin1 regulates tau stability and phosphorylation dynamics, suggests an emerging role for isomerization in tau pathogenesis.

The molecular chaperone Hsp90α is required for meiotic progression of spermatocytes beyond pachytene in the mouse

The molecular chaperone Hsp90 has been found to be essential for viability in all tested eukaryotes, from the budding yeast to Drosophila. In mammals, two genes encode the two highly similar and functionally largely redundant isoforms Hsp90α and Hsp90β. Although they are co-expressed in most if not all cells, their relative levels vary between tissues and during development. Since mouse embryos lacking Hsp90β die at implantation, and despite the fact that Hsp90 inhibitors being tested as anti-cancer agents are relatively well tolerated, the organismic functions of Hsp90 in mammals remain largely unknown. We have generated mouse lines carrying gene trap insertions in the Hsp90α gene to investigate the global functions of this isoform. Surprisingly, mice without Hsp90α are apparently normal, with one major exception. Mutant male mice, whose Hsp90β levels are unchanged, are sterile because of a complete failure to produce sperm. While the development of the male reproductive system appears to be normal, spermatogenesis arrests specifically at the pachytene stage of meiosis I. Over time, the number of spermatocytes and the levels of the meiotic regulators and Hsp90 interactors Hsp70-2, NASP and Cdc2 are reduced. We speculate that Hsp90α may be required to maintain and to activate these regulators and/or to disassemble the synaptonemal complex that holds homologous chromosomes together. The link between fertility and Hsp90 is further supported by our finding that an Hsp90 inhibitor that can cross the blood-testis barrier can partially phenocopy the genetic defects.

The role of FKBP5 in cancer aetiology and chemoresistance

FK506 binding protein 51 (FKBP51, also called FKBP5) belongs to a family of immunophilins, FK506 binding proteins (FKBPs). Members of this family are targets for drugs such as rapamycin and cyclosporine. Although FKBP5 shares characteristics with other FKBPs, it also has unique features, especially its role in the regulation of multiple signalling pathways and in tumourigenesis and chemoresistance. In this review, we will focus on the recently discovered role of FKBP5 in cancer aetiology and response to antineoplastic therapy.

Fkbp52 regulates androgen receptor transactivation activity and male urethra morphogenesis

Hypospadias is a common birth defect in humans, yet its etiology and pattern of onset are largely unknown. Recent studies have shown that male mice with targeted ablation of FK506-binding protein-52 (Fkbp52) develop hypospadias, most likely due to actions of Fkbp52 as a molecular co-chaperone of the androgen receptor (AR). Here, we further dissect the developmental and molecular mechanisms that underlie hypospadias in Fkbp52-deficient mice. Scanning electron microscopy revealed a defect in the elevation of prepucial swelling that led to the onset of the ventral penile cleft. Interestingly, expression of Fkbp52 was highest in the ventral aspect of the developing penis that undergoes fusion of the urethral epithelium. Although in situ hybridization and immunohistochemical analyses suggested that Fkbp52 mutants had a normal urethral epithelium signaling center and epithelial differentiation, a reduced apoptotic cell index at ventral epithelial cells at the site of fusion and a defect of genital mesenchymal cell migration were observed. Supplementation of gestating females with excess testosterone partially rescued the hypospadic phenotype in Fkbp52 mutant males, showing that loss of Fkbp52 desensitizes AR to hormonal activation. Direct measurement of AR activity was performed in mouse embryonic fibroblast cells treated with dihydrotestosterone or synthetic agonist R1881. Reduced AR activity at genes controlling sexual dimorphism and cell growth was found in Fkbp52-deficient mouse embryonic fibroblast cells. However, chromatin immunoprecipitation analysis revealed normal occupancy of AR at gene promoters, suggesting that Fkbp52 exerts downstream effects on the transactivation function of AR. Taken together, our data show Fkbp52 to be an important molecular regulator in the androgen-mediated pathway of urethra morphogenesis.

Increased FKBP51 in induced sputum cells of chronic obstructive pulmonary disease patients after therapy

Objective

Immunophilin FKBP51 assists polypeptide folding, participates in glucocorticoid actions and may play a role in glucocorticoid resistance. FKBP51 is altered in patients with asthma, but its role in chronic obstructive pulmonary disease (COPD) characterized by dysregulation of several pro/antiinflammatory genes is less clear.

Methods

We assessed changes in nuclear/cytosolic FKBP51 protein using SDS-PAGE/WB and FKBP51 mRNA by qRT-PCR in cells isolated from induced sputum of stable COPD patients treated with formoterol/budesonide or formoterol/budesonide/theophylline for 4 wk.

Results

Expression of FKBP51 was higher in formoterol/budesonide/theophylline-treated patients, compared with formoterol/budesonide group in both cytosolic and nuclear fractions by about 57% and 31%, respectively (P < 0.001, P < 0.01). FKBP51 mRNA was only slightly, but not significantly, higher in patients on formoterol/budesonide/theophylline.

Conclusions

Increased FKBP51 in COPD patients treated with formoterol/budesonide/theophylline may be important in altering signaling from corticosteroid receptors.

Differential impact of tetratricopeptide repeat proteins on the steroid hormone receptors

BACKGROUND

Tetratricopeptide repeat (TPR) motif containing co-chaperones of the chaperone Hsp90 are considered control modules that govern activity and specificity of this central folding platform. Steroid receptors are paradigm clients of Hsp90. The influence of some TPR proteins on selected receptors has been described, but a comprehensive analysis of the effects of TPR proteins on all steroid receptors has not been accomplished yet.

METHODOLOGY AND PRINCIPAL FINDINGS

We compared the influence of the TPR proteins FK506 binding proteins 51 and 52, protein phosphatase-5, C-terminus of Hsp70 interacting protein, cyclophillin 40, hepatitis-virus-B X-associated protein-2, and tetratricopeptide repeat protein-2 on all six steroid hormone receptors in a homogeneous mammalian cell system. To be able to assess each cofactor's effect on the transcriptional activity of on each steroid receptor we employed transient transfection in a reporter gene assay. In addition, we evaluated the interactions of the TPR proteins with the receptors and components of the Hsp90 chaperone heterocomplex by coimmunoprecipitation. In the functional assays, corticosteroid and progesterone receptors displayed the most sensitive and distinct reaction to the TPR proteins. Androgen receptor's activity was moderately impaired by most cofactors, whereas the Estrogen receptors' activity was impaired by most cofactors only to a minor degree. Second, interaction studies revealed that the strongly receptor-interacting co-chaperones were all among the inhibitory proteins. Intriguingly, the TPR-proteins also differentially co-precipitated the heterochaperone complex components Hsp90, Hsp70, and p23, pointing to differences in their modes of action.

CONCLUSION AND SIGNIFICANCE

The results of this comprehensive study provide important insight into chaperoning of diverse client proteins via the combinatorial action of (co)-chaperones. The differential effects of the TPR proteins on steroid receptors bear on all physiological processes related to steroid hormone activity.

Susceptibility to diet-induced hepatic steatosis and glucocorticoid resistance in FK506-binding protein 52-deficient mice

Although FK506-binding protein 52 (FKBP52) is an established positive regulator of glucocorticoid receptor (GR) activity, an in vivo role for FKBP52 in glucocorticoid control of metabolism has not been reported. To address this question, FKBP52(+/-) mice were placed on a high-fat (HF) diet known to induce obesity, hepatic steatosis, and insulin resistance. Tissue profiling of wild-type mice showed high levels of FKBP52 in the liver but little to no expression in muscle or adipose tissue, predicting a restricted pattern of FKBP52 effects on metabolism. In response to HF, FKBP52(+/-) mice demonstrated a susceptibility to hyperglycemia and hyperinsulinemia that correlated with reduced insulin clearance and reduced expression of hepatic CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1), a mediator of clearance. Livers of HF-fed mutant mice had high lipid content and elevated expression of lipogenic genes (peroxisome proliferator-activated receptor gamma, fatty acid synthase, and sterol regulatory element-binding protein 1c) and inflammatory markers (TNFalpha). Interestingly, mutant mice under HF showed elevated serum corticosterone, but their steatotic livers had reduced expression of gluconeogenic genes (phosphoenolpyruvate carboxy kinase, glucose 6 phosphatase, and pyruvate dehydrogenase kinase 4), whereas muscle and adipose expressed normal to elevated levels of glucocorticoid markers. These data suggest a state of glucocorticoid resistance arising from liver-specific loss of GR activity. Consistent with this hypothesis, reduced expression of gluconeogenic genes and CEACAM1 was observed in dexamethasone-treated FKBP52-deficient mouse embryonic fibroblast cells. We propose a model in which FKBP52 loss reduces GR control of gluconeogenesis, predisposing the liver to steatosis under HF-diet conditions attributable to a shunting of metabolism from glucose production to lipogenesis.

The ubiquitin-proteasome system in prostate cancer and its transition to castration resistance

Prostate cancer is the most common carcinoma in the male population. In its initial stage, the disease is androgen-dependent and responds therapeutically to androgen deprivation treatment but it usually progresses after a few years to an androgen-independent phase that is refractory to hormonal manipulations. The proteasome is a multi-unit protease system that regulates the abundance and function of a significant number of cell proteins, and its inhibition results in cancer cell growth inhibition and apoptosis and is already exploited in the clinic with the use of proteasome inhibitor bortezomib in multiple myeloma. In order to be recognized by the proteasome, a target protein needs to be linked to a chain of the small protein ubiquitin. In this paper, we review the role of ubiquitin-proteasome system (UPS) in androgen receptor-dependent transcription as well as in the castration resistant stage of the disease, and we discuss therapeutic opportunities that UPS inhibition offers in prostate cancer.

46,XY disorders of sex development--the undermasculinised male with disorders of androgen action

Insensitivity to the action of androgens is a common cause of undermasculinisation in 46,XY individuals. These disorders are a result of the failure of major androgens to act via the intracellular androgen receptor and, thus, the genomic effects of androgen signalling are disrupted. The phenotype of affected individuals can vary considerably, depending on the dysfunction of the receptor. In childhood, the diagnosis is often complicated due to the lack of sensitive biochemical determinants, whilst during adolescence and in adults, the diagnosis can be readily made because of the striking clinical feminisation and a conclusive laboratory analysis. A variety of mutations in the androgen receptor have been analysed, providing insight into the complex pathways of intracellular processing and signal transduction via the androgen receptor. Endocrine therapy in androgen-insensitivity syndrome is controversial, because till date the special hormonal profiles in androgen insensitivity have not been acknowledged in replacement strategies.

Alterations in the steroid hormone receptor co-chaperone FKBPL are associated with male infertility: a case-control study

BACKGROUND

Male infertility is a common cause of reproductive failure in humans. In mice, targeted deletions of the genes coding for FKBP6 or FKBP52, members of the FK506 binding protein family, can result in male infertility. In the case of FKBP52, this reflects an important role in potentiating Androgen Receptor (AR) signalling in the prostate and accessory glands, but not the testis. In infertile men, no mutations of FKBP52 or FKBP6 have been found so far, but the gene for FKBP-like (FKBPL) maps to chromosome 6p21.3, an area linked to azoospermia in a group of Japanese patients.

METHODS

To determine whether mutations in FKBPL could contribute to the azoospermic phenotype, we examined expression in mouse and human tissues by RNA array blot, RT-PCR and immunohistochemistry and sequenced the complete gene from two azoospermic patient cohorts and matching control groups. FKBPL-AR interaction was assayed using reporter constructs in vitro.

RESULTS

FKBPL is strongly expressed in mouse testis, with expression upregulated at puberty. The protein is expressed in human testis in a pattern similar to FKBP52 and also enhanced AR transcriptional activity in reporter assays. We examined sixty patients from the Japanese patient group and found one inactivating mutation and one coding change, as well as a number of non-coding changes, all absent in fifty-six controls. A second, Irish patient cohort of thirty showed another two coding changes not present in thirty proven fertile controls.

CONCLUSIONS

Our results describe the first alterations in the gene for FKBPL in azoospermic patients and indicate a potential role in AR-mediated signalling in the testis.

FKBP51 promotes assembly of the Hsp90 chaperone complex and regulates androgen receptor signaling in prostate cancer cells

Prostate cancer progression to the androgen-independent (AI) state involves acquisition of pathways that allow tumor growth under low-androgen conditions. We hypothesized that expression of molecular chaperones that modulate androgen binding to AR might be altered in prostate cancer and contribute to progression to the AI state. Here, we report that the Hsp90 cochaperone FKBP51 is upregulated in LAPC-4 AI tumors grown in castrated mice and describe a molecular mechanism by which FKBP51 regulates AR activity. Using recombinant proteins, we show that FKBP51 stimulates recruitment of the cochaperone p23 to the ATP-bound form of Hsp90, forming an FKBP51-Hsp90-p23 superchaperone complex. In cells, FKBP51 expression promotes superchaperone complex association with AR and increases the number of AR molecules that undergo androgen binding. FKBP51 stimulates androgen-dependent transcription and cell growth, and FKBP51 is part of a positive feedback loop that is regulated by AR and androgen. Finally, depleting FKBP51 levels by short hairpin RNA reduces the transcript levels of genes regulated by AR and androgen. Because the superchaperone complex plays a critical role in determining the ligand-binding competence and transcription function of AR, it provides an attractive target for inhibiting AR activity in prostate cancer cells.

FKBP51 and Cyp40 are positive regulators of androgen-dependent prostate cancer cell growth and the targets of FK506 and cyclosporin A

Prostate cancer (PCa) growth is dependent on androgens and the androgen receptor (AR), which acts by modulating gene transcription. Tetratricopeptide repeat (TPR) proteins (FKBP52, FKBP51 and Cyp40) interact with AR in PCa cells, suggesting roles in AR-mediated gene transcription and cell growth. We report here that FKBP51 and Cyp40, but not FKBP52, are significantly elevated in PCa tissues and in androgen-dependent (AD) and -independent (AI) cell lines. Overexpression of FKBP51 in AD LNCaP cells increased AR transcriptional activity in the presence and absence of androgen, whereas siRNA knockdown of FKBP51 dramatically decreased AD gene transcription and proliferation. Knockdown of Cyp40 also inhibited androgen-mediated transcription and growth in LNCaP cells. However, disruption of FKBP51 and Cyp40 in the AI C4-2 cells caused only a small reduction in proliferation, indicating that Cyp40 and FKBP51 predominantly regulate AD cell proliferation. Under knock-down conditions, the inhibitory effects of TPR ligands, CsA and FK506, on AR activity were not observed, indicating that Cyp40 and FKBP51 are the targets of CsA and FK506, respectively. Our findings demonstrate that FKBP51 and Cyp40 are positive regulators of AR that can be selectively targeted by CsA and FK506 to achieve inhibition of androgen-induced cell proliferation. These proteins and their cognate ligands thus provide new strategies in the treatment of PCa

Role of immunophilins in recovery of erectile function after cavernous nerve injury

INTRODUCTION

Immunophilin ligands provide potentially new alternatives for the treatment of erectile dysfunction (ED), which occurs after injury of the cavernous nerves (CNs).

AIM

To review and update current knowledge of the neurotrophic effects and likely mechanism of action of immunophilin proteins with emphasis on the FK506-binding protein (FKBP) subfamily and the role of immunophilin ligands for the treatment of CN injury-induced ED.

METHODS

Review of available reports of studies investigating the effects and neurotrophic mechanisms of immunophilin ligands involved in erectile function recovery in rodent models of CN injury.

MAIN OUTCOME MEASURES

Erection parameters and molecular correlations associated with CN injury and functional recovery.

RESULTS

Treatment with prototype immunosuppressive immunophilin ligands FK506 (FK) and rapamycin (Rapa) improve erectile function in animal models of CN injury. Similarly, non-immunosuppressive analogs such as GPI-1046 and FK1706 are effective in recovery of erections after CN injury. Neuronal nitric oxide may influence the erection recovery effects of immunophilin ligands after CN injury. FKBPs 38 and 65 expression changes in the penis and its innervation coincide with the neurotrophic effects of immunophilin ligands. Antioxidative actions of immunophilin ligands contribute to their neurotrophic effects. Immunophilins are localized to nerves coursing in human prostate and penile tissue.

CONCLUSIONS

The findings support the hypothesis that immunophilin ligands, working through specific receptor mechanisms that are specific to injured CN, are potentially useful to sustain erectile function in men following radical prostatectomy.