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The steroid receptor-associated TPR cochaperones FKBP51, FKBP52, CyP40 and PP5 have non-redundant roles in steroid receptor function that impact steroid hormone-binding affinity, nucleocyoplasmic shuttling and transcriptional activation of target genes in a tissue-specific manner. Aberrant expression of these TPR immunophilins has the potential to cause steroid-based diseases, including breast and prostate cancer, diabetes and metabolic disorders, male and female infertility and major depressive and neurodegenerative disorders. This review summaries the function of these proteins as cochaperones in steroid receptor-Hsp90 complexes and elaborates on their role in alternative, Hsp90-dependent and -independent signalling pathways not involving steroid receptors. The review also extensively covers current knowledge of the link between the steroid receptor-associated immunophilins and human disease. An improved understanding of their mechanisms of action has revealed opportunities for molecular therapies to enhance or inhibit cellular processes under their control that contribute both to human health and disease.

Immunophilins consist of a family of highly conserved proteins which possess binding abilities to immunosuppressive drugs. Cyclophilins (Cyps) and FK506-binding proteins (FKBP) are family proteins collectively referred as immunophilins. Most Cyps and FKBP family members catalyse peptidyl-prolyl cis/trans isomerase (PPIase) mediated reactions and form binary complexes with their ligands cyclosporine A and FK506. Immunophilins are also involved in key biochemical processes including protein folding, receptor signalling, protein trafficking, and transcription and exhibit versatile biological functions, when complexed with their ligands. Therapeutic implications of immunophilins and effects of their ligands in neurodegenerative disorders, cancer, and infectious diseases have been accumulating in recent years. This review focuses on molecular characteristics of the canonical and non-canonical immunophilin family members from human and Plasmodium falciparum and P. vivax, recent progress on immunophilin inhibitor development, and future perspectives of structure-based design of non-immunosuppressive immunophilin ligands with potential pharmacological activities against infectious diseases.

Unlabelled: Platelet hyperaggregability might contribute to vascular complications associated with type 2 diabetes mellitus (DM2).Experimental evidence supports a direct link between altered Ca(2+) entry and hyperaggregability in DM2 patients., Objectives: We aimed to investigate whether altered immunophilin expression and function are involved in the abnormal Ca(2+) entry observed in platelets from DM2 patients., Results: Inhibition of immunophilins by tacrolimus (FK506) and sirolimus (rapamycin) reduced Ca(2+) entry in platelets from healthy donors and DM2 patients. Similarly, immunophilin inhibitors reduced platelet degranulation in both healthy and DM2 subjects. Nevertheless, α-granule secretion reduction was greater than that observed for dense granules in platelets from DM2 patients. However, no difference was observed in the inhibition of secretion in platelets from healthy subjects. Additionally, altered expression of FK506 binding protein-52 (FKBP52) and coupling to Ca(2+) channels were found in platelets from DM2 patients compared to healthy subjects. Finally, reduction in platelet function from healthy subjects and DM2 patients in the presence of immunophilin antagonists was observed, being this dysfunction more evident in platelets from DM2 patients., Conclusions: We suggest that, among others, FKBP52 expression and function are altered in platelets from DM2 patients, contributing to the altered Ca(2+) entry and hyperaggregability in these cells.

The immunophilin family includes a large group of proteins with peptidyl prolyl-isomerase activity (PPI-ase). Immunophilins chaperone activity has been documented to be crucial for the correct folding and activation of many proteins. Thus, they have been subjected of intense investigation since they were firstly described in the last decades of the past century. Many of these studies have been focused on leukocyte constitutively expressed immunophilins, due to their relevance in the correct folding, and subsequently, sensitization and activation of the glycoprotein receptor (RGBs) of lymphocyte T CD4+ and Treg, hence regulating immunological responses against pathogen insults. Several clinical trials have been completed in the last decade reporting that administration of immunophilin-binding drugs, derived from macrolide lactones, like cyclosporine A (CsA) and tacrolimus (FK506), induced successful results in preventing organ rejection. By contrast, the expression of immunophilins and their physiological function remain poorly investigated in others cell types, such as platelets, where a reduced number of studies presenting evidences of immunophilins expression and their physiological contribution have been published, despite a number of clinical trials have noticed side effects of these drugs in thrombosis and platelet count, thus suggesting a possible regulatory function of immunophilins in human platelets, which is reviewed here.

The immunophilins are proteins which are capable of influencing the immune response in combination with an immunosuppressive drug. Their natural function, however, is mainly the cis/trans isomerization of peptidyl-prolyl bonds in other proteins. This review lists all immunophilin structure coordinates currently available in the RCSB protein data bank and highlights the key active-site factors that define their catalytic and immunological action. In addition, an overview of biologically-relevant functions is provided for various immunophilin members.

Immunophilins belong to a highly conserved family of proteins with cis-trans peptidyl-prolyl isomerase activity, generally classified by their ability to selectively bind specific immunosuppressive drugs, thereby regulating their activity. Immunophilins include Cyclophilins (CyPs), which are specific targets of the immunosuppressant drug cyclosporin A (CsA); FKBPs (FK506-binding proteins), that are sensitive to both FK506 (tacrolimus) and rapamycin (sirolimus); and FCBPs which are sensitive to CsA and FK506. Immunophilins are expressed in multiple human tissues, including brain, heart, kidney, liver and lung and regulate functions as diverse as intracellular calcium signaling, protein transport, protein folding and gene transcription. In particular, immunophilins play key functional roles in the cardiovascular system, where they can associate with proteins such as ryanodine and IP3 receptors (RyR and IP3R), calcineurin, and mitochondrial permeability transition pore (MPTP) and Heat-shock proteins-caveolin-cholesterol complex and regulate their function. The biological importance of immunophilins is further revealed by the pathophysiology, as they have been implicated in several cardiovascular diseases, including vascular stenosis, atherosclerosis, heart failure and arrhythmias. This review summarizes some of the most recent studies on immunophilins and focuses on their roles in the mechanisms underlying the cardiovascular disease.

The immunophilin ligands cyclosporin A, FK506 and rapamycin are best known for their immunosuppressive properties and their clinical use in transplantation medicine. These compounds or their analogs are also clinically used or investigated in various types of cancer, coronary angioplasty, dermatology, hepatitis C infections, and neuroprotection. Furthermore, the role of immunophilins in various pathologies is increasingly being recognized, supporting the preclinical drug development for novel immunophilin targets. Finally, immunophilin ligands are widely used as sophisticated tools in chemical biology. This review shows the progress on three major areas made in the last five years. An update of the immunosuppressive ligands and their clinical applications is discussed in the first part of the review, followed by a discussion about the emerging immunophilin targets and their respective ligands. The final section gives a detailed assessment of immunophilin ligand-based tools.

Since the first attempt to replace a dysfunctional organ, clinics and scientific had to overcome many setbacks in order to warrant the success and viability of both the organ and the receptor. Despite the improvement of surgical procedures, some grafts fail within the following days or week due to immunologic rejection. Many ongoing researches are still seeking the perfect immunossupresors. Calcineurin targeting agents have been consolidated as a worldwide immnunossupressant therapy, but due to its widely functional role in many cell types, this strategy often represents a highly risk therapy due to side effects observed with these agents. Here we summarized the latest and past knowledge regarding immunossupression therapies, including the promising and widely used Immunophilin-targeting antagonist therapies.

In case of nervous damages, like nervous system trauma or various neurodegenerative diseases such as dementia or Parkinson, several treatments are available to restore neurological function. In spite of these treatments, results are often insufficient or not satisfactory in many neurologic diseases, especially for central nervous system (CNS) lesions. To minimize neurological dysfunction, it is critical to reduce neuronal death, avoiding loss of the synaptic connections, and securing viable neurons to extend axons. Unfortunately, there are no effective strategies to fulfill these basic needs except for some cases of peripheral neural damage up to now. Rescue of damaged neurons, stimulation of neurogenesis and transplantation of nervous tissue are strategies proposed to prevent neurodegenerative disorders. A number of studies have recently reported successful axon regeneration and neurological recovery by using immunosuppressants, such as FK506. Immunosuppressants act as excellent agents for enhancing the rate and extent of axon regeneration and neurological recovery. FK506 and other neuroimmunophilin ligands (NILs) might reverse neuronal degeneration. In several animal models mimicking Parkinson's disease, dementia and surgical damage, NILs induces resprouting, by acting as neurotrophic agents and preventing nerve damage, although more studies are necessary to identify new NILs with neuroprotective action, but lacking the side immunological effects observed in the ligands analyzed to date. This review explores the new clinical role of immunosuppressants in the treatment of nerve surgery of autologous, allografts or xenografts. Results of studies regarding immunosuppressant treatment of nervous system trauma and neurodegenerative diseases, like neurogenic erectile dysfunction, will be here considered.

Spinal cord (SC) injury causes serious neurological alterations that importantly disturb the physical, emotional and economical stability of affected individuals. Damage to the neural tissue is primarily caused by the lesion itself and secondarily by a multitude of destructive mechanisms that develop afterwards. Unfortunately, the restoring capacity of the central nervous system is very limited because of reduced intrinsic growth capacity and non-permissive environment for axonal elongation. The regenerative processes are blocked by diverse factors such as growth inhibitory proteins and the glial scar formed in the site of lesion. In spite of these problems, central neurons regenerate if a permissive environment is provided. In line with this thought, some pharmacological compounds have been tested to achieve neuroregeneration. The main objective of this manuscript is to provide the state-of-art of chemotherapeutic treatments for spinal cord regeneration after injury in the field. The efficacy and usefulness of different therapeutic strategies will be reviewed, including Rho-ROCK inhibitors, cyclic AMP-enhancers, glial scar inhibitors and immunophilin ligands. Aside from this, the use of hydrogels alone or in combination with drugs, growth factors or stem cells will also be revised.

After spinal cord injury, a number of destructive events developed immediately after the primary insult increase tissue damage. Several therapeutic approaches are directed to neutralize these phenomena. The present manuscript revises diverse pharmacological treatments used to promote neuroprotection, both in clinical and experimental acute spinal cord injuries.

Non-immunosuppressive immunophilin ligands (NI-IPLs) are attracting attention as new candidate drugs for neuroprotection and/or neurorestoration, particularly since they do not have the adverse effects of immunosuppressants. However, it is not yet enough to understand that NI-IPLs are useful drugs for treating neurological disorders. In particular, the molecular mechanism of NI-IPL activity in target cells in the brain remains obscure. In this review, we focused on the molecular basis of the neuroprotective properties of IPLs. Our findings suggest that IPLs have neuroprotective effects mediated by multiple beneficial properties such as a glutathione (GSH)-activating effect, a neurotrophic factor (NTF)-activating effect, and an anti-apoptotic effect, but not by an immunosuppressive effect, both in cell cultures and in vivo. In particular, the GSH-activating effect and the NTF-activating effect of NI-IPLs may be essential to the expression of their neuroprotective properties. Thus, NI-IPLs might have a potentially beneficial effect by ameliorating neurological disorders, since they do not cause serious side effects such as immune deficiency.

There is a significant unmet need for therapeutic agents in the treatment of neurodegenerative diseases. Given their clinical importance, prototypical molecules that clearly exhibit both neuroprotective and neuroregenerative activities have been highly sought after. The journey led to the exploitation of neurotrophins, a family of proteins that had extraordinary therapeutic properties in pre-clinical models of neurodegeneration. Although experimentally promising, clinical development of neurotrophins for various neurological indications, such as Alzheimer's Disease, Amyotrophic Lateral Sclerosis, and Parkinson's Disease was met with severe obstacles and setbacks, such as the inability to deliver these large proteins to target population of neurons, instability of the proteins, and non-specific activity. Immunophilins are proteins that act as receptors for immunosuppresant drugs, i.e. FK506 (tacrolimus), cyclosporin A, and rapamycin (sirolimus, Rapamune). Studies indicate immunophilins are expressed 10-100 fold higher in CNS and PNS tissue than in immune tissue. Subsequent studies revealed potent neuroprotective and neuroregenerative properties of immunophilin ligands in both culture and animal models. In contrast to neurotrophins, most immunophilin ligands are highly stable, small molecules that can readily cross the blood-brain barrier and are orally bioavailable. Taken together, these data prompted the development of nonimmunosuppressive immunophilin ligands with potent therapeutic activities, although the potency of select compounds has come into question in more recent studies. This review will examine the experimental evidence supporting the use of immunophilin ligands for the treatment of neurodegenerative diseases and the current progression of these molecules in clinical trials.

Immunophilin ligands such as FK506 and Cyclosporin A, used in immunosuppression, are well-characterized drugs. In the past, they had been the center of attention as a putative therapeutic strategy for neuroregeneration and neuroprotection. In contrast to Cyclosporin A, FK506 readily crosses the brain-blood-barrier and, thus together with its derivatives, may represent a novel approach to the treatment of neurological disorders. FK506 exerts profound neuroprotective and neuroregenerative effects in vivo and in vitro. The mechanism underlying neuroregeneration is fairly well understood. It is independent of the inhibition of calcineurin, which is responsible for the immunosuppression, but operates via the binding of FKBP52 and the heat shock protein (Hsp) 90. In contrast, the underlying pathways of neuroprotection are far less understood. Protection is apparently independent of calcineurin, as shown by non-calcineurin inhibiting derivatives, such as V-10,367 and GPI-1046, but the intracellular actions remain to be defined. FK506 has been shown to interfere with the apoptotic pathway of neuronal cells, including inhibiting JNK activity, cytochrome c release, caspase 3 activation, and CD95 ligand expression. These effects are in part mediated by the inhibition of calcineurin and may not contribute to protection. Our recent studies suggest that the protective properties of FK506 and its non-calcineurin inhibiting derivatives are realized by a fast induction of heat shock proteins. The induction of the heat shock response by immunophilin ligands might prove to be an interesting target for neuroregeneration and neuroprotection.

Information recovered from genome sequencing projects, multiple sequence alignments, structural analyses of PPIase and published records were used in deciphering the biological diversity, functions and targets of four groups of proteins encoded by dissimilar sets of sequences whose spatial representations exhibit peptidylprolyl cis/trans isomerase activity (PPIase). In the human genome there are encoded fifteen proteins whose segments have significant homology with the sequence of 12 kDa protein which is the target of the potent immunosuppressive macrolides FK506 or rapamycin. The 12 kDa archetype of the FK506-binding protein (FKBP), known as FKBP-12a, is an abundant intracellular protein whereas other FKBPs possessing from one to four FK506-like binding domains (FKBDs) have nominal masses varying from 13 to 135 kDa. The human genome contains at least sixteen genes encoding proteins comprising one cyclosporin-A (CsA) binding domain (CLD) called cyclophilins whose nominal masses vary from 17 to 324 kDa and multiple coding segments for small cyclophilins (17-19 kDa) whose transcription levels and functions remain unknown. The third group of PPIases encoded in the genome comprises two proteins (hPin1 and hParv14) where hPin1 is an important PPIase for cell cycle. The A. thaliana, C. elegans, D. melanogaster and S. cerevisiae genomes encode a less diverse spectrum of PPIases whereas the prokaryotic genomes contain from none to three cyclophilins, from none to four genes encoding FKBPs, one distant homologue of the Pin1 protein named parvulin and the fourth group of PPIases known as trigger factors. PPIases are discretely distributed to different cellular compartments and interact with a number of targets that control a range of cellular processes. Analyses of the sequence alignments of the two groups of PPIases, namely cyclophilins and FKBPs from diverse phyla, show that in each group their sequences diverge but the amino acid residues which form the PPIase activity site and macrolide binding cavity remain well conserved in the majority of them which suggests that the spatial structures and functions of each group of PPIases remain conserved.

It is well established that the immunosuppressive effects of cyclosporin A (CsA) and FK506 (also known as tacrolimus) are mediated through binding to their cognate cellular proteins cyclophilin and FKBP (collectively termed immunophilins), respectively. Biochemical analysis had revealed that cyclophilin-CsA and FKBP-FK506 complexes bind to and inactivate Ca(2+)-dependent serine/threonine phosphatase calcineurin. Since calcineurin regulates nuclear translocation and subsequent activation of nuclear factor of activated T cells (NFAT) transcription factors that is one of essential steps for cytokine gene expression in activated T cells, it is believed that inhibition of calcineurin is a molecular basis of the immunosuppressive properties of CsA and FK506. However, recent studies indicate that both CsA and FK506 can block activation of JNK and p38 signaling pathways during T cell activation. CsA and FK506, thus, have two distinct mechanisms of action; one is the inhibition of the protein phosphatase activity of calcineurin, leading to the blockade of the nuclear translocation of NFAT transcription factors, and the other is the suppression of JNK and p38 activation pathways. It is likely that the presence of two distinct targets in T cell activation makes CsA and FK506 highly potent immunosuppressive drugs. Here we discuss the action of immunophilin-ligand complexes on JNK and p38 activation pathways. We also argue the possibility of immunotherapeutic application targeting at JNK and p38 signaling pathways.

The ryanodine receptor (RyR) is the major calcium (Ca(2+)) release channel in the sarcoplasmic reticulum (SR) of skeletal and cardiac muscle and is required for excitation-contraction (EC) coupling. The 565 kDa RyR protein forms a tetrameric channel that is part of a macromolecular signaling complex that also includes four FK506 binding proteins (FKBPs). The RyR channel complex is localized on specialized regions of the SR, such that the large RyR cytoplasmic domain is closely opposed to the transverse tubule (T-tubule) of the plasma membrane. RyR channel complexes are organized in regular arrays such that neighboring RyRs are in physical contact with each other. We have shown that physical and functional association between RyR1 or RyR2 channels results in coordinated gating behavior termed coupled gating. Coupled gating requires FKBP12 or FKBP12.6 in the RyR1 or RyR2 macromolecular complexes, respectively. FKBPs are known to stabilize single RyR channel function. Coupled gating describes an additional role for FKBPs in the functional coordination of RyR channel complexes that allows clusters of channels to function as "Ca2+ release units" (CRU). In addition, the FKBP-RyR interaction is regulated by PKA phosphorylation. In failing hearts PKA hyperphosphorylation of RyR2 causes depletion of FKBP12.6 from the channel macromolecular complex and may contribute to contractile dysfunction by impairing EC coupling. As FKBPs are potent modulators of RyR channel function, the FKBP-RyR interaction is a focus for determining molecular mechanisms of coupled gating and presents an exciting pharmacologic target for restoration of RyR complex function in diseased states.

The macrolactam natural product, FK506 (Tacrolimus), acts as a powerful and clinically useful immnosuppressant through disruption of signaling events mediated by the calcium-dependent serine/threonine protein phosphatase, calcineurin (CaN), in T lymphocytes. Its mechanism of action involves the formation of a molecular complex with the intracellular FK506-binding protein-12 (FKBP12), thereby acquiring the ability to interact with CaN and to interfere with its access to and dephosphorylation of various substrates. Among the CaN substrates whose activity is altered by FK506, the nuclear factors of activated T cells (NFAT), a family of transcription factors regulating lymphokine gene expression, have been shown to play a prominent role in FK506-induced immunosuppression. Over the past few years, additional members of the FKBP and NFAT families of proteins have been identified, providing further insights into the complexity of FK506 biological effects. Furthermore, it has become clear that, predominantly as a result of CaN inhibition, FK506 alters multiple biochemical processes in a variety of cells besides lymphocytes. This may account for the adverse side effects of the drug, including neurotoxicity and nephrotoxicity. Extensive medicinal chemistry efforts have been devoted to the generation of analogs of FK506 with the hope of identifying compounds with an improved therapeutic index, that could have broader therapeutic utility than the parent drug. These efforts yielded several compounds with unique biochemical attributes, showing evidence for a dissociation between immunosuppressive and toxic properties, which may pave the way towards designing safer FK506-related immunosuppressants.