FKBP ligands as novel therapeutics for neurological disorders

Given their clinical importance for the treatment of acute and chronic neurodegenerative diseases in humans including nerve injuries (e.g. Alzheimer's disease, Parkinson's disease, diabetic neuropathy) a number of different approaches were pursued to obtain selectively acting FK506-binding protein (FKBP) ligands: computational methods and target-oriented screening of natural compound and synthetic product libraries. The resulting monofunctional ligands, which inhibit the peptidyl prolyl cis/trans isomerase activity of FKBPs, highlight the role of these enzymes in neuronal signaling. The exploration of the mechanisms of neuroregenerative and neuroprotective action of some of these compounds is the main focus of ongoing neuropharmaceutical research.     

Organization and function of the FKBP52 and FKBP51 genes

Best established as components of steroid hormone receptor complexes, it is now clear that the large molecular weight immunophilins, FKBP52 and FKBP51, play important regulatory roles elsewhere in the cell. This review outlines what is known about the organization of the genes, FKBP4 and FKBP5, respectively, encoding these proteins and describes their diverse actions in the nervous system, reproduction, and cancer. The organization of FKBP4 and FKBP5 is very similar among the chordates, and gene expression is influenced by both genetic and epigenetic mechanisms. Recent studies identifying roles of FKBP52 and FKBP51 in the regulation of the microtubule-associated protein tau and microtubule assembly are discussed, as is their interaction with and influence on the transient receptor potential canonical (TRPC) subfamily of ion channel proteins.     

Exploration of pipecolate sulfonamides as binders of the FK506-binding proteins 51 and 52

FK506-binding proteins (FKBP) 51 and 52 are cochaperones that modulate the signal transduction of steroid hormone receptors. Single nucleotide polymorphisms in the gene encoding FKBP51 have been associated with a variety of psychiatric disorders. Rapamycin and FK506 are two macrocyclic natural products, which tightly bind to most FKBP family members, including FKBP51 and FKBP52. A bioisosteric replacement of the α-ketoamide moiety of rapamycin and FK506 with a sulfonamide was envisaged with the retention of the conserved hydrogen bonds. A focused solid support-based synthesis protocol was developed, which led to ligands with submicromolar affinity for FKBP51 and FKBP52. The molecular binding mode for one sulfonamide analogue was confirmed by X-ray crystallography.     

From cell death to viral replication: the diverse functions of the membrane-associated FKBP38

FKBP38 is in many ways an exceptional member of the FK506-binding proteins. The calmodulin-regulated activity of FKBP38 for instance is unique within this protein family. The activated FKBP38 participates in apoptosis signaling by inhibiting the anti-apoptotic Bcl-2. Beyond this role in programmed cell death, FKBP38 seems to be involved in very different cellular processes that do not necessarily depend on the FKBP domain. These functions involve regulation of the kinase mTOR, regulation of neural tube formation, regulation of cellular hypoxia response, but also Hepatitis C virus replication. Pharmacological targeting of FKBP38 might therefore prove a successful strategy for intervention in different FKBP38-dependent processes, including programmed cell death in cancer or neurodegenerative diseases.     

脑缺血再灌注损伤中 FK506结合蛋白51对半胱氨酸蛋白酶－3及大鼠海马 CA1区神经元坏死的影响

目的：探讨脑缺血再灌注损伤中FK506结合蛋白51（FKBP51）对半胱氨酸蛋白酶－3（Caspase－3）及大鼠海马CA1区神经元坏死的影响。方法将清洁级SD大鼠随机分成假手术组（ Sham组）、缺血再灌注组（ I／R组）、溶剂对照组（ TE组）、FKBP51反义寡核苷酸组（ FKBP51 ASODN组）和FKBP51错义寡核苷酸组（ FKBP51 MSODN组），采用四血管阻塞模型大鼠全脑缺血模型造模。应用免疫印迹法测定FKBP51蛋白表达、FKBP51 ASODN对FKBP51蛋白水平的表达和Caspase－3活性的影响；采用苏木精－伊红溶液染色法测定FKBP51 ASODN对大鼠海马CA1区神经元坏死的影响。结果（1）在Sham组和I／R组（缺血再灌注0 min、15 min、30 min、1 h、3 h、6 h、1 d、3 d）中，FKBP51蛋白均有表达，并且表达量间的差异无统计学意义（F＝0．64，P＞0．05）。（2）FKBP51 ASODN组的FKBP51蛋白表达量明显减少，与Sham组差异有统计学意义（t＝8．21，P＜0．05）。（3）Sham组活化Caspase－3的表达量明显低于其他各组，差异有统计学意义（F＝12．31，P＜0．05）；与FKBP51 MSODN组比较，FKBP51 ASODN组的表达量相对较低，差异有统计学意义（ t＝9．71，P＜0．05）。（4）Sham组海马CA1区锥体细胞数量多[（186．3±2．5）个]并且排列密集，核大且圆，核仁明显；I／R 5 d组[（15．4±2．6）个]、TE组[（18．5±2．2）个]和FKBP51 MSODN组[（17．5±1．8）个]海马CA1区锥体细胞几乎完全消失，仅残留少数细胞，大量变性锥体细胞核固缩深染，胞浆嗜伊红，胞膜破裂，胞内容物释放， Sham组与其余各组之间的差异有统计学意义（χ^2＝81．91，P＜0．05）；FKBP51 ASODN组[（92．8±2．6）个]海马CA1区锥体细胞存活数增加，与其余各组的差异有统计学意义（χ^2＝52．36，P＜0．05）。结论在脑缺血再灌注损伤中，FKBP51可以增强活化的Caspase－3的表达并抑制神经元的存?     

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.     

The emerging role of large immunophilin FK506 binding protein 51 in cancer

FK506 binding protein 51 (FKBP51) is an immunophilin physiologically expressed in lymphocytes. Very recently, aberrant expression of this protein was found in melanoma; FKBP51 expression correlates with melanoma aggressiveness and is maximal in metastatic lesions. FKBP51 promotes NF-κB activation and is involved in the resistance to genotoxic agents, including anthracyclines and ionizing radiation. FKBP51 is a cochaperone with peptidyl-prolyl isomerase activity that regulates several biological processes through protein-protein interaction. There is increasing evidence that FKBP51 hyperexpression is associated with cancer and this protein has a relevant role in sustaining cell growth, malignancy, and resistance to therapy. There is also evidence that FKBP ligands are potent anticancer agents, in addition to their immunosuppressant activity. In particular, rapamycin and its analogs have shown antitumor activity across a variety of human cancers in clinical trials. Although, classically, rapamycin actions are ascribed to inhibition of mTOR, recent studies indicate FKBP51 is also an important molecular determinant of the drug's anticancer activity. The aim of this article is to review the functions of FKBP51, especially in view of the recent findings that this protein is a potential oncogene when deregulated and a candidate target for signaling therapies against cancer.     

Gene–Stress–Epigenetic Regulation of FKBP5: Clinical and Translational Implications

Stress responses and related outcomes vary markedly across individuals. Elucidating the molecular underpinnings of this variability is of great relevance for developing individualized prevention strategies and treatments for stress-related disorders. An important modulator of stress responses is the FK506-binding protein 51 (FKBP5/FKBP51). FKBP5 acts as a co-chaperone that modulates not only glucocorticoid receptor activity in response to stressors but also a multitude of other cellular processes in both the brain and periphery. Notably, the FKBP5 gene is regulated via complex interactions among environmental stressors, FKBP5 genetic variants, and epigenetic modifications of glucocorticoid-responsive genomic sites. These interactions can result in FKBP5 disinhibition that has been shown to contribute to a number of aberrant phenotypes in both rodents and humans. Consequently, FKBP5 blockade may hold promise as treatment intervention for stress-related disorders, and recently developed selective FKBP5 blockers show encouraging results in vitro and in rodent models. Although risk for stress-related disorders is conferred by multiple environmental and genetic factors, the findings related to FKBP5 illustrate how a deeper understanding of the molecular and systemic mechanisms underlying specific gene–environment interactions may provide insights into the pathogenesis of stress-related disorders.     

FKBP51 regulation of AKT/protein kinase B phosphorylation

FK506 binding protein 51 (FKBP51, also called FKBP5) belongs to a family of immunophilins, FK506 binding proteins (FKBPs). FKBP family members are targets for drugs such as rapamycin. Although FKBP51 shares characteristics with other FKBPs, it also has unique features, especially the role in its regulation of important signaling pathways such as the AKT kinase/protein kinase B pathway. In this review, we will focus on the function of FKBP51 as a scaffolding protein in the regulation of AKT activation and, in turn, its role in tumorigenesis and response to chemotherapy.     

FK506-binding protein 12 ligands: a patent review

Introduction: FK506-binding protein 12 (FKBP12) is an endogenous protein with peptidyl-prolyl isomerase (PPIase) activity. Natural compounds FK506, rapamycin and ascomycin, are FKBP12 ligands used for treating organ transplant rejection and other diseases. Small ligands that also interact with FKBP12 are designed and synthetized based on the natural ligands. This suggests that targeting FKBP12 has potential in the treatment of multiple diseases.

Areas covered: This article describes the features of FKBP12 and the therapeutic actions of agents targeting FKBP12 reported in the published articles and patents.

Expert opinion: The multiple functions of FKBP12 cause side effects during therapy with FKBP12 ligands. The interaction between FKBP12 and other receptors should be explored to guide their use as drugs in the clinical setting. In addition, the neuroprotective mechanism of small-molecule FKBP12 ligands needs further study in order to develop them as novel drugs for treating neurological disorders.     

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.     

FKBP12 Depletion Leads to Loss of Sarcoplasmic Reticulum Ca2+ Stores in Rat Vas Deferens

The immunophilin 12-kDa FK506 binding protein (FKBP12) stabilizes intracellular Ca²⁺ release channel (CRC) activity in different tissues. In this work, the presence of FKBP12 in rat vas deferens (RVD) and its possible contribution to RVD function was investigated. Treatment under appropriate pH, temperature, and ionic conditions was used to strip FKBP12 from CRC binding sites; Western blotting revealed FKBP12 in control but not in treated homogenates. Disruption of the FKBP12-CRC complex in RVD decreased the Ca²⁺ content of sarcoplasmic reticulum (SR) by increasing Ca²⁺ leakage through the ryanodine receptor (RyR3 isoform) but not through 1,4,5-iNOSitol trisphosphate receptors (IP₃R1 and IP₃R3 isoforms). The decrease of SR Ca²⁺ content was not related to inhibition of SERCA ATPase. It seems that dissociation of FKBP12-RyR leads to conformational changes in RyR that make it difficult for ryanodine to access its binding site. Rapamycin, which is commonly used as a pharmacological tool to disrupt the FKBP12-RyR complex, decreased phenylephrine-induced contractions in RVD epididymal halves. The data suggest that FKBP12 is expressed in RVD in a labile association with RyR3. Disruption of the FKBP12-RyR3 complex may lead to modifications of RVD physiology and in consequence may compromise male fertility.     

Transgenic analysis of the role of FKBP12.6 in cardiac function and intracellular calcium release

FK506 binding protein12.6 (FKBP12.6) binds to the Ca(2+) release channel ryanodine receptor (RyR2) in cardiomyocytes and stabilizes RyR2 to prevent premature sarcoplasmic reticulum Ca(2+) release. Previously, two different mouse strains deficient in FKBP12.6 were reported to have different abnormal cardiac phenotypes. The first mutant strain displayed sex-dependent cardiac hypertrophy, while the second displayed exercise-induced cardiac arrhythmia and sudden death. In this study, we tested whether FKBP12.6-deficient mice that display hypertrophic hearts can develop exercise-induced cardiac sudden death and whether the hypertrophic heart is a direct consequence of abnormal calcium handling in mutant cardiomyocytes. Our data show that FKBP12.6-deficient mice with cardiac hypertrophy do not display exercise-induced arrhythmia and/or sudden cardiac death. To investigate the role of FKBP12.6 overexpression for cardiac function and cardiomyocyte calcium release, we generated a transgenic mouse line with cardiac specific overexpression of FKBP12.6 using α-myosin heavy chain (αMHC) promoter. MHC-FKBP12.6 mice displayed normal cardiac development and function. We demonstrated that MHC-FKBP12.6 mice are able to rescue abnormal cardiac hypertrophy and abnormal calcium release in FKBP12.6-deficient mice.     

The serpins alpha-1-antitrypsin and alpha-1-antichymotrypsin specifically interact with immunophilins

In a yeast two-hybrid screen FKBP13, a member of the FK506 Binding Protein (FKBP) family, was detected to interact with the serpin alpha-1-antichymotrypsin (ACT). The specificity of the interaction was confirmed in vitro and by the lack of interaction of ACT with FKBP25 and FKBP52. Mutational analysis of ACT revealed that the entire protein is necessary to interact with FKBP13. ACT but also different unrelated small regions of the ACT protein were able to interact with the smaller FKBP12, demonstrating a rather nonspecific interaction with this immunophilin. Naturally occuring mutants of ACT were able to interact as well. Antitrypsin (AT) closely related to ACT did only interfere with FKBP12 a protein that does presumably not reside in the same cellular compartment with AT and ACT. Both serpins interacted with the unrelated immunophilin cyclophilin A. In conclusion the serpin alpha-1-antichymotrypsin physiologically interacts with the ER-immunophilin FKBP13 and the secreted immunophilin cyclophilin A in vivo whereas alpha-1-antitrypsin might only react with cyclophilin A; both serpins may be controlled thereby in their genuine function.     

大环内酯类免疫抑制剂的研究进展

FK506结合蛋白12(FK506 binding protein12,FKBP12)是FK506结合蛋白的重要成员,目前对其参与免疫抑制剂抗器官移植后排斥反应的研究较多。他克莫司(FK506,tacrolimus)、雷帕霉素(rapamycin)和子囊霉素(ascomycin)是FKBP12的三个天然存在的大环内酯类配体,除了免疫抑制外还具有其他生理功能。这三个配体的衍生物也对FKBP12有一定的亲和力,且有些已经作为药物被应用于临床上。本文针对FKBP12的配体及其治疗作用进行综述。     

FKBP38-Bcl-2 interaction: a novel link to chemoresistance

FKBP38, a noncanonical member of the immunosuppressive drug FK506 binding protein (FKBP) family members, possesses an inducible rotamase. FKBP38 interacts with several proteins and regulates multiple signaling pathways such as cell survival, apoptosis, proliferation, and metastasis. Deregulation of apoptosis is associated with chemoresistance and tumor relapse. The antiapoptotic protein Bcl-2 is a key player for increasing the apoptotic threshold in response to various cytotoxic drugs. The molecular interaction of Bcl-2 with FKBP38 potentiates the biological function of Bcl-2 and contributes to tumorigenesis and chemoresistance. Here, we discuss recent advances in the role of FKBP38 in connection with Bcl-2 and its possible link to chemotherapeutic resistance.     

NMR studies of an FK-506 analog, [U-13C]ascomycin, bound to FK-506-binding protein.

Multidimensional, heteronuclear NMR methods were used to determine the complete 1H and 13C resonance assignments for [U-13C]ascomycin bound to recombinant FKBP, including stereospecific assignment of all 22 methylene protons. The conformation of ascomycin was then determined from an analysis of NOEs observed in a 13C-edited 3D HMQC-NOESY spectrum of the [U-13C]ascomycin/FKBP. This structure is found to be quite different from the solution structure of the two forms of uncomplexed FK-506. However, it is very similar to the X-ray crystal structure of FK-506 bound to FKBP, rms deviation = 0.56 A. The methods used for resonance assignment and structure calculation are presented in detail. Furthermore, FKBP/ascomycin NOEs are reported which help define the structure of the ascomycin binding pocket. This structural information obtained in solution was compared to the recently described X-ray crystal structure of the FKBP/FK-506 complex.     

Peptidomics of the Prolyl Peptidases

The prolyl peptidases are a family of enzymes characterized by a biochemical preference for cleaving proline-containing peptides. The members of this enzyme family include prolyl endopeptidase, prolyl endopeptidase-like, dipeptidyl peptidase 4 (DPP4), DPP7, DPP8, DPP9, and fibroblast activation protein. DPP4 is the best studied member of the family, due to its role in physiological glucose tolerance, exerted through the regulation of the insulinotropic peptide glucagon-like peptide-1. While other members of the prolyl peptidase family have also been implicated in various (patho)physiological processes, the underlying peptides and pathways regulated by these enzymes are less clear. The identification of endogenous substrates of the prolyl peptidases is an important step in elucidating the molecular mechanisms of these enzymes. Here, we highlight the utility of liquid chromatography–mass spectrometry-based peptidomics to enable the discovery of endogenous prolyl peptidase substrates directly from tissues, and demonstrate the utility of this information in understanding the biochemical and physiological functions of the prolyl peptidases.