FKBP52

Endoplasmic reticulum stress or mutation of an EF-hand Ca(2+)-binding domain directs the FKBP65 rotamase to an ERAD-based proteolysis

FKBP65 is an endoplasmic reticulum (ER)-localized chaperone and rotamase, with cargo proteins that include tropoelastin and collagen. In humans, mutations in FKBP65 have recently been shown to cause a form of osteogenesis imperfecta (OI), a brittle bone disease resulting from deficient secretion of mature type I collagen. In this work, we describe the rapid proteolysis of FKBP65 in response to ER stress signals that activate the release of ER Ca(2+) stores. A large-scale screen for stress-induced cellular changes revealed FKBP65 proteins to decrease within 6-12 h of stress activation. Inhibiting IP(3)R-mediated ER Ca(2+) release blocked this response. No other ER-localized chaperone and folding mediators assessed in the study displayed this phenomenon, indicating that this rapid proteolysis of folding mediator is distinctive. Imaging and cellular fractionation confirmed the localization of FKBP65 (72 kDa glycoprotein) to the ER of untreated cells, a rapid decrease in protein levels following ER stress, and the corresponding appearance of a 30-kDa fragment in the cytosol. Inhibition of the proteasome during ER stress revealed an accumulation of FKBP65 in the cytosol, consistent with retrotranslocation and a proteasome-based proteolysis. To assess the role of Ca(2+)-binding EF-hand domains in FKBP65 stability, a recombinant FKBP65-GFP construct was engineered to ablate Ca(2+) binding at each of two EF-hand domains. Cells transfected with the wild-type construct displayed ER localization of the FKBP65-GFP protein and a proteasome-dependent proteolysis in response to ER stress. Recombinant FKBP65-GFP carrying a defect in the EF1 Ca(2+)-binding domain displayed diminished protein in the ER when compared to wild-type FKBP65-GFP. Proteasome inhibition restored mutant protein to levels similar to that of the wild-type FKBP65-GFP. A similar mutation in EF2 did not confer FKBP65 proteolysis. This work supports a model in which stress-induced changes in ER Ca(2+) stores induce the rapid proteolysis of FKBP65, a chaperone and folding mediator of collagen and tropoelastin. The destruction of this protein may identify a cellular strategy for replacement of protein folding machinery following ER stress. The implications for stress-induced changes in the handling of aggregate-prone proteins in the ER-Golgi secretory pathway are discussed. This work was supported by grants from the National Institutes of Health (R15GM065139) and the National Science Foundation (DBI-0452587).

Protein phosphatase 5 mediates lipid metabolism through reciprocal control of glucocorticoid receptor and peroxisome proliferator-activated receptor-γ (PPARγ)

Glucocorticoid receptor-α (GRα) and peroxisome proliferator-activated receptor-γ (PPARγ) regulate adipogenesis by controlling the balance between lipolysis and lipogenesis. Here, we show that protein phosphatase 5 (PP5), a nuclear receptor co-chaperone, reciprocally modulates the lipometabolic activities of GRα and PPARγ. Wild-type and PP5-deficient (KO) mouse embryonic fibroblast cells were used to show binding of PP5 to both GRα and PPARγ. In response to adipogenic stimuli, PP5-KO mouse embryonic fibroblast cells showed almost no lipid accumulation with reduced expression of adipogenic markers (aP2, CD36, and perilipin) and low fatty-acid synthase enzymatic activity. This was completely reversed following reintroduction of PP5. Loss of PP5 increased phosphorylation of GRα at serines 212 and 234 and elevated dexamethasone-induced activity at prolipolytic genes. In contrast, PPARγ in PP5-KO cells was hyperphosphorylated at serine 112 but had reduced rosiglitazone-induced activity at lipogenic genes. Expression of the S112A mutant rescued PPARγ transcriptional activity and lipid accumulation in PP5-KO cells pointing to Ser-112 as an important residue of PP5 action. This work identifies PP5 as a fulcrum point in nuclear receptor control of the lipolysis/lipogenesis equilibrium and as a potential target in the treatment of obesity.

Management of cytoskeleton architecture by molecular chaperones and immunophilins

Cytoskeletal structure is continually remodeled to accommodate normal cell growth and to respond to pathophysiological cues. As a consequence, several cytoskeleton-interacting proteins become involved in a variety of cellular processes such as cell growth and division, cell movement, vesicle transportation, cellular organelle location and function, localization and distribution of membrane receptors, and cell-cell communication. Molecular chaperones and immunophilins are counted among the most important proteins that interact closely with the cytoskeleton network, in particular with microtubules and microtubule-associated factors. In several situations, heat-shock proteins and immunophilins work together as a functionally active heterocomplex, although both types of proteins also show independent actions. In circumstances where homeostasis is affected by environmental stresses or due to genetic alterations, chaperone proteins help to stabilize the system. Molecular chaperones facilitate the assembly, disassembly and/or folding/refolding of cytoskeletal proteins, so they prevent aberrant protein aggregation. Nonetheless, the roles of heat-shock proteins and immunophilins are not only limited to solve abnormal situations, but they also have an active participation during the normal differentiation process of the cell and are key factors for many structural and functional rearrangements during this course of action. Cytoskeleton modifications leading to altered localization of nuclear factors may result in loss- or gain-of-function of such factors, which affects the cell cycle and cell development. Therefore, cytoskeletal components are attractive therapeutic targets, particularly microtubules, to prevent pathological situations such as rapidly dividing tumor cells or to favor the process of cell differentiation in other cases. In this review we will address some classical and novel aspects of key regulatory functions of heat-shock proteins and immunophilins as housekeeping factors of the cytoskeletal network.

Proteomics analysis of the ezrin interactome in B cells reveals a novel association with Myo18aα

The molecular regulation of recruitment and assembly of signalosomes near the B cell receptor (BCR) is poorly understood. We have previously demonstrated a role for the ERM family protein ezrin in regulating antigen-dependent lipid raft coalescence in B cells. In this study, we addressed the possibility that ezrin may collaborate with other adaptor proteins to regulate signalosome dynamics at the membrane. Using mass spectrometry-based proteomics analysis, we identified Myo18aα as a novel binding partner of ezrin. Myo18aα is an attractive candidate as it has several protein-protein interaction domains and an intrinsic motor activity. The expression of Myo18aα varied during B cell development in the bone marrow and in mature B cell subsets suggesting functional differences. Interestingly, BCR stimulation increased the association between ezrin and Myo18aα, and induced co-segregation of Myo18aα with the BCR and phosphotyrosine-containing proteins. Our data raise an intriguing possibility that the Myo18aα/ezrin complex may facilitate BCR-mediated signaling by recruiting signaling proteins that are in close proximity of the antigen receptor. Our study is not only significant with respect to understanding the molecular regulation of BCR signaling but also provides a broader basis for understanding the mechanism of action of ezrin in other cellular systems.

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.

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.

Hsp90 regulates tau pathology through co-chaperone complexes in Alzheimer's disease

Alzheimer's disease is a tauopathy which involves the deposition of microtubule-associated tau proteins into neurofibrillary tangles. Post-translational modifications, in particular site-specific phosphorylations, affect the conformation of tau protein which is an intrinsically disordered protein. These structural changes significantly increase the affinity of tau protein for certain molecular chaperones. Hsp90 is a major cellular chaperone which assembles large complexes with a variety of co-chaperones. The main function of Hsp90 complexes is to maintain protein quality control and assist in protein degradation via proteasomal and autophagic-lysosomal pathways. Tau protein is a client protein for these Hsp90 complexes. If the tau protein is in an abnormal or modified form, then it can trigger the recruitment of CHIP protein, a co-chaperone with E3 activity, to the complex which induces the ubiquitination of tau protein and activates its downstream degradation processes. Large immunophilins, FKBP51 and FKBP52 are also co-chaperones of Hsp90-tau complexes. These proteins contain peptidylprolyl cis/trans isomerase activity which catalyzes phosphorylation-dependent rotation in pSer/Thr-Pro peptide bond. The proline switch in the tau conformation triggers dephosphorylation of Ser/Thr residues phosphorylated, e.g. by two well-known tau kinases Cdk5 and GSK-3β. Binding of PP5 protein phosphatase to Hsp90 complex, can also dephosphorylate tau protein. Subsequently, dephosphorylated tau protein can be shuttled back to the microtubules. It seems that high-affinity binding of abnormal tau to Hsp90 complexes may have some counteracting effects on the aggregation process, since Hsp90 inhibitors can ameliorate the aggregation process in several neurodegenerative diseases. We will review the role of Hsp90 chaperone network in the regulation of tau biology and pathology in Alzheimer's disease.

Transgenic overexpression of HSP56 does not result in cardiac hypertrophy nor protect from ischaemia/reperfusion injury

Heat shock proteins are known to be induced during and following different forms of cardiac stress. It has previously been shown that their expression is beneficial for the heart following trauma such as ischaemia-reperfusion (I/R) injury. Heat shock protein 56 (HSP56) belongs to the family of FK506-binding immunophilin proteins and is found in steroid receptor complexes, notably the glucocorticoid receptor. We have previously shown that HSP56 and other HSPs are induced in cardiac myocytes treated with cardiotrophin-1, a cytokine with potent hypertrophic and protective properties on cardiac cells. The hypertrophic action of cardiotrophin-1 on cardiac cells is dependent on HSP56 induction and overexpression of HSP56 is sufficient for inducing hypertrophy in cardiac cells. To investigate this phenomenon in vivo, we have generated transgenic mice overexpressing HSP56 and assessed them for the development cardiac hypertrophy and resistance of their hearts to I/R-injury by Langendorff perfusion. Mice generated demonstrated stable, yet varying expression levels of HSP56. Initial characterisation identified a sex-specific phenotype where male overexpressing mice exhibited a moderate, but significant, reduced body weight compared to wild-type controls. In ex vivo stress analyses we found, unexpectedly, that significant overexpression of HSP56 does not induce myocardial hypertrophy and nor does it protect the intact heart from I/R-injury. These observations now suggest a more intricate HSP56-Sp. Cardiophenotype that requires further studies to determine if HSP56 is necessary in mediating hypertrophy induced by other myocardial stimuli.

Solid-phase synthesis and screening of N-acylated polyamine (NAPA) combinatorial libraries for protein binding

Inhibitors for protein-protein interactions are challenging to design, in part due to the unique and complex architectures of each protein's interaction domain. Most approaches to develop inhibitors for these interactions rely on rational design, which requires prior structural knowledge of the target and its ligands. In the absence of structural information, a combinatorial approach may be the best alternative to finding inhibitors of a protein-protein interaction. Current chemical libraries, however, consist mostly of molecules designed to inhibit enzymes. In this manuscript, we report the synthesis and screening of a library based on an N-acylated polyamine (NAPA) scaffold that we designed to have specific molecular features necessary to inhibit protein-protein interactions. Screens of the library identified a member with favorable binding properties to the HIV viral protein R (Vpr), a regulatory protein from HIV, that is involved in numerous interactions with other proteins critical for viral replication.

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.

Short-term recognition memory impairment is associated with decreased expression of FK506 binding protein 51 in the aged mouse brain

Evidence suggests that increased glucocorticoid receptor (GR) signaling may contribute to cognitive decline with age. We hypothesized that alterations in GR signaling pathway molecules, FK506 binding protein (FKBP) 51 and FKBP52, were associated with memory impairment in aged mice. We used the single-trial object recognition test to measure short-term memory in 18 aged mice compared to 22 young mice, and employed quantitative immunohistochemistry to assess cellular expression of those three proteins in the frontal cortex, hippocampal CA1, and dentate gyrus. Values of the discrimination ratio (DR, a measure of novelty preference) in aged mice were significantly lower than those in young mice (mean 0.54 vs. 0.67, p = 0.003, t test). Aged mice with DR below 0.54 were considered impaired (n = 9). In the three neuroanatomic regions studied, the immunoreactivity normalized to the area measured (IRn) for GR was significantly increased in aged mice regardless of their task performance compared to young mice (p < 0.005), as was the FKBP52 IRn (p < 0.007, U test). In the frontal cortex and CA1, the FKBP51 IRn was significantly lower in impaired aged mice than in unimpaired aged mice (p < 0.01 and <0.05, respectively) and in young mice (p < 0.05 and <0.01, respectively, Dunn's post hoc test). In aged mice, the frontal cortex FKBP51 IRn correlated directly with DR (r (s) = 0.68, p = 0.002, Spearman rank correlation). These observations suggest that recognition memory impairment in aged mice is associated with decreased FKBP51 expression that may promote GR-mediated glucocorticoid signaling to a greater extent than in unimpaired aged mice.

Uterine FK506-binding protein 52 (FKBP52)-peroxiredoxin-6 (PRDX6) signaling protects pregnancy from overt oxidative stress

Immunophilin FK506-binding protein 52 (FKBP52) is a cochaperone that binds to the progesterone receptor (PR) to optimize progesterone (P(4))-PR signaling. We recently showed that Fkbp52-deficient (Fkbp52(-/-)) mice have reduced uterine PR responsiveness and implantation failure which is rescued by excess P(4) supplementation in a genetic background-dependent manner. This finding led us to hypothesize that FKBP52 has functions in addition to optimizing PR activity. Using proteomics analysis, we found that uterine levels of peroxiredoxin-6 (PRDX6), a unique antioxidant, are significantly lower in Fkbp52(-/-) mice than in WT and PR-null (Pgr(-/-)) mice. We also found that Fkbp52(-/-) mice with reduced uterine PRDX6 levels are susceptible to paraquat-induced oxidative stress (OS), leading to implantation failure even with P(4) supplementation. The same dose of paraquat did not interfere with implantation in WT mice. Moreover, treatment with antioxidants alpha-tocopherol and N-acetylcysteine (NAC) attenuated paraquat-induced implantation failure in P(4)-treated Fkbp52(-/-) mice. Functional analyses using mouse embryonic fibroblasts show that Fkbp52 deficiency associated with reduced PRDX6 levels promotes H(2)O(2)-induced cell death, which is reversed by the addition of NAC or by forced expression of PRDX6, suggesting that Fkbp52 deficiency diminishes the threshold against OS by reducing PRDX6 levels. These findings provide evidence that heightened uterine OS in Fkbp52(-/-) females with reduced PRDX6 levels induces implantation failure even in the presence of excess P(4). This study shows that FKBP52-PRDX6 signaling protects pregnancy from overt OS.

Proteomic mining in the dysplastic liver of WHV/c-myc mice--insights and indicators for early hepatocarcinogenesis

Because of the asymptomatic process of carcinogenesis, the early detection of cancers such as hepatocellular carcinoma (HCC) is very challenging. Tumor-prone transgenic mouse models of oncogenesis can provide a stable and powerful tool for the analysis of cancer initiation, and are therefore promising for the discovery of early putative biomarkers of HCC. Using a label-free proteomic quantification strategy, we comprehensively investigated the protein expression profile in the livers of three 2-month-old WHV/c-myc mice at the dysplastic stage, with age-matched wt-C57 mice as controls. We identified 2781 proteins, 540 of which were differentially expressed. These proteins successfully characterized certain precancerous biological processes and alterations in transcriptional regulators before tumor onset. Two candidates, FK506-binding protein 4 (FKBP52) and ferritin heavy chain, were taken as examples for a search from the mouse model to clinical human tissues. Their levels in serum samples were determined by western blotting, and showed a noteworthy ability to distinguish between HCC and control cases. Immunohistochemical analysis with tissue microarrays confirmed the differential expression of FKBP52 between HCC and the paired controls (P < 0.001). The regulation of FKBP52 was also discovered to be relevant to HCC staging, with a dramatic decline at stage III (P < 0.05). The potentials of the candidate pool in this study were discussed in terms of delineating c-myc-induced hepatocarcinogenesis and facilitating biomarker discovery for early HCC diagnosis.

Clinical, genetic and molecular characterization of patients with familial isolated pituitary adenomas (FIPA)

Familial pituitary adenomas can occur in MEN1 and Carney complex, as well as in the recently characterized familial isolated pituitary adenoma (FIPA) syndrome. FIPA is an autosomal dominant disease with incomplete penetrance, characterized by early-onset disease, often aggressive tumor growth and a predominance of somatotroph and lactotroph adenomas. In 20% of FIPA families, heterozygous mutations have been described in the aryl hydrocarbon receptor interacting (AIP) gene, whereas in other families the causative gene(s) are unknown. It has been suggested that AIP is a tumor suppressor gene and although experimental data support this hypothesis, the exact molecular mechanism by which its disruption leads to tumorigenesis is unclear. Here we discuss the clinical, genetic and molecular features of patients with FIPA.

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 RET51/FKBP52 complex and its involvement in Parkinson disease

The tyrosine kinase receptor RET51 is expressed in distinct families of neurons where it promotes different functions. FKBP52 is an immunophilin with neuroprotective effects on different kinds of neurons. In this paper, we demonstrate that RET51 activation by both glial cell line-derived neurotrophic factor (GDNF) and NGF triggers the formation of RET51/FKBP52 complex. The substitution of the tyrosine 905 of RET51, a key residue phosphorylated by both GDNF and NGF, disrupts the RET51/FKBP52 complex. NGF and GDNF have a functional role in dopaminergic (DA) neurons where RET51 and FKBP52 are expressed with a yet undefined function. To clarify if RET51/FKBP52 complex should exert its function in DA neurons, we used an indirect approach by screening the genes encoding for RET51 and FKBP52 in a group of 30 Parkinson's disease patients. The degeneration of DA neurons is the main feature of PD, which is associated to a complex multifactorial aetiology combining environmental, age-related and genetic factors. We found a compound heterozygous carrying two mutations in RET and FKBP52 that are sufficient to disrupt the RET51/FKBP52 complex, indicating its potential role in PD.

Alternate strategies of Hsp90 modulation for the treatment of cancer and other diseases

The 90 kDa heat shock protein (Hsp90) has become a validated target for the development of anti-cancer agents. Several Hsp90 inhibitors are currently under clinical trial investigation for the treatment of cancer. All of these agents inhibit Hsp90's protein folding activity by binding to the N-terminal ATP binding site of the Hsp90 molecular chaperone. Administration of these investigational drugs elicits induction of the heat shock response, or the overexpression of several Hsps, which exhibit antiapoptotic and pro-survival effects that may complicate the application of these inhibitors. To circumvent this issue, alternate mechanisms for Hsp90 inhibition that do not elicit the heat shock response have been identified and pursued. After providing background on the structure, function, and mechanism of the Hsp90 protein folding machinery, this review describes several mechanisms of Hsp90 modulation via small molecules that do not induce the heat shock response.

Peptidyl-prolyl isomerase FKBP52 controls chemotropic guidance of neuronal growth cones via regulation of TRPC1 channel opening

Immunophilins, including FK506-binding proteins (FKBPs), are protein chaperones with peptidyl-prolyl isomerase (PPIase) activity. Initially identified as pharmacological receptors for immunosuppressants to regulate immune responses via isomerase-independent mechanisms, FKBPs are most highly expressed in the nervous system, where their physiological function as isomerases remains unknown. We demonstrate that FKBP12 and FKBP52 catalyze cis/trans isomerization of regions of TRPC1 implicated in controlling channel opening. FKBP52 mediates stimulus-dependent TRPC1 gating through isomerization, which is required for chemotropic turning of neuronal growth cones to netrin-1 and myelin-associated glycoprotein and for netrin-1/DCC-dependent midline axon guidance of commissural interneurons in the developing spinal cord. By contrast, FKBP12 mediates spontaneous opening of TRPC1 through isomerization and is not required for growth cone responses to netrin-1. Our study demonstrates a novel physiological function of proline isomerases in chemotropic nerve guidance through TRPC1 gating and may have significant implication in clinical applications of immunophilin-related therapeutic drugs.

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.

Identification of a new panel of serum autoantibodies associated with the presence of in situ carcinoma of the breast in younger women

PURPOSE

We examined the feasibility of using a panel of autoantibodies to multiple tumor-associated proteins as a method for early detection of breast cancer and, more particularly, carcinoma in situ (CIS).

EXPERIMENTAL DESIGN

PPIA, PRDX2, and FKBP52 were identified as early-stage breast cancer autoantigens by proteomic approaches. The seroreactivity of a panel of antibodies consisting of these three antigens and two previously described autoantigens, HSP60 and MUC1, was tested on 235 samples (60 from primary breast cancer patients, 82 from CIS patients, and 93 from healthy controls) with the use of specific ELISAs. FKBP52, PPIA, and PRDX2 mRNA and protein expression levels were evaluated by reverse transcription-PCR and immunohistochemistry in early-stage breast tumors.

RESULTS

Three of five autoantibodies, FKBP52, PPIA, and PRDX2, showed significantly increased reactivity in primary breast cancer and CIS compared with healthy controls. When combined, the five markers significantly discriminated primary breast cancer [receiver operating characteristic area under the curve, 0.73; 95% confidence interval (95% CI), 0.60-0.79] and CIS (receiver operating characteristic area under the curve, 0.80; 95% CI, 0.71-0.85) from healthy individuals. Importantly, the receiver operating characteristic-area under the curve value of the autoantibody panel was able to distinguish CIS, including high grades, from healthy controls in women under the age of 50 years (receiver operating characteristic area under the curve, 0.85; 95% CI, 0.61-0.92). Finally, only FKBP52 mRNA and protein levels were found to be increased in CIS and primary breast cancer compared with healthy breast tissue.

CONCLUSIONS

This autoantibody assay against a panel of five antigens allows for an accurate discrimination between early-stage breast cancer, especially CIS, and healthy individuals. These results could be of interest in detecting early breast cancer as an aid to mammography, especially in women under the age of 50 years with aggressive cancers.

Nuclear import of the glucocorticoid receptor-hsp90 complex through the nuclear pore complex is mediated by its interaction with Nup62 and importin beta

Glucocorticoid receptor (GR) is cytoplasmic in the absence of ligand and localizes to the nucleus after steroid binding. Previous evidence demonstrated that the hsp90-based heterocomplex bound to GR is required for the efficient retrotransport of the receptor to the nuclear compartment. We examined the putative association of GR and its associated chaperone heterocomplex with structures of the nuclear pore. We found that importin beta and the integral nuclear pore glycoprotein Nup62 interact with hsp90, hsp70, p23, and the TPR domain proteins FKBP52 and PP5. Nup62 and GR were able to interact in a more efficient manner when chaperoned by the hsp90-based heterocomplex. Interestingly, the binding of hsp70 and p23 to Nup62 does not require the presence of hsp90, whereas the association of FKBP52 and PP5 is hsp90 dependent, as indicated by the results of experiments where the hsp90 function was disrupted with radicicol. The ability of both FKBP52 and PP5 to interact with Nup62 was abrogated in cells overexpressing the TPR peptide. Importantly, GR cross-linked to the hsp90 heterocomplex was able to translocate to the nucleus in digitonin-permeabilized cells treated with steroid, suggesting that GR could pass through the pore in its untransformed state.

Promotion of neurite extension by protrudin requires its interaction with vesicle-associated membrane protein-associated protein

Protrudin is a protein that contains a Rab11-binding domain and a FYVE (lipid-binding) domain and that functions to promote neurite formation through interaction with the GDP-bound form of Rab11. Protrudin also contains a short sequence motif designated FFAT (two phenylalanines in an acidic tract), which in other proteins has been shown to mediate binding to vesicle-associated membrane protein-associated protein (VAP). We now show that protrudin associates and colocalizes with VAP-A, an isoform of VAP expressed in the endoplasmic reticulum. Both the interaction between protrudin and VAP-A as well as the induction of process formation by protrudin were markedly inhibited by mutation of the FFAT motif. Furthermore, depletion of VAP-A by RNA interference resulted in mislocalization of protrudin as well as in inhibition of neurite outgrowth induced by nerve growth factor in rat pheochromocytoma PC12 cells. These defects resulting from depletion of endogenous rat VAP-A in PC12 cells were corrected by forced expression of (RNA interference-resistant) human VAP-A but not by VAP-A mutants that have lost the ability to interact with protrudin. These results suggest that VAP-A is an important regulator both of the subcellular localization of protrudin and of its ability to stimulate neurite outgrowth.

The switch I region of Rheb is critical for its interaction with FKBP38

The Ras-like small GTPase Rheb is an upstream activator of the mammalian target of rapamycin (mTOR). It has recently been shown that Rheb activates mTOR by binding to its endogenous inhibitor FKBP38 and preventing it from association with mTOR. The interaction of Rheb with FKBP38 is controlled by its guanine nucleotide binding states, which are responsive to growth factor and amino acid conditions. In this study, we show that Rheb interacts with FKBP38 through a section within its switch I region that is equivalent to the effector domain of other Ras-like small GTPases. We find that the ability for Rheb to interact with FKBP38 correlates with its activity for mTOR activation. Our findings suggest that FKBP38 is a bona fide effector of Rheb and that the ability to interact with FKBP38 is important for Rheb as an activator of mTOR.

The aryl hydrocarbon receptor complex and the control of gene expression

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that controls the expression of a diverse set of genes. The toxicity of the potent AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin is almost exclusively mediated through this receptor. However, the key alterations in gene expression that mediate toxicity are poorly understood. It has been established through characterization of AhR-null mice that the AhR has a required physiological function, yet how endogenous mediators regulate this orphan receptor remains to be established. A picture as to how the AhR/ARNT heterodimer actually mediates gene transcription is starting to emerge. The AhR/ARNT complex can alter transcription both by binding to its cognate response element and through tethering to other transcription factors. In addition, many of the coregulatory proteins necessary for AhR-mediated transcription have been identified. Cross talk between the estrogen receptor and the AhR at the promoter of target genes appears to be an important mode of regulation. Inflammatory signaling pathways and the AhR also appear to be another important site of cross talk at the level of transcription. A major focus of this review is to highlight experimental efforts to characterize nonclassical mechanisms of AhR-mediated modulation of gene transcription.

Structure-based classification of 45 FK506-binding proteins

The FK506-binding proteins (FKBPs) are a unique group of chaperones found in a wide variety of organisms. They perform a number of cellular functions including protein folding, regulation of cytokines, transport of steroid receptor complexes, nucleic acid binding, histone assembly, and modulation of apoptosis. These functions are mediated by specific domains that adopt distinct tertiary conformations. Using the Threading/ASSEmbly/Refinement (TASSER) approach, tertiary structures were predicted for a total of 45 FKBPs in 23 species. These models were compared with previously characterized FKBP solution structures and the predicted structures were employed to identify groups of homologous proteins. The resulting classification may be utilized to infer functional roles of newly discovered FKBPs. The three-dimensional conformations revealed that this family may have undergone several modifications throughout evolution, including loss of N- and C-terminal regions, duplication of FKBP domains as well as insertions of entire functional motifs. Docking simulations suggest that additional sequence segments outside FKBP domains may modulate the binding affinity of FKBPs to immunosuppressive drugs. The docking models also indicate the presence of a helix-loop-helix (HLH) region within a subset of FKBPs, which may be responsible for the interaction between this group of proteins and nucleic acids.

Analysis of FK506-mediated protection in an organotypic model of spinal cord damage: heat shock protein 70 levels are modulated in microglial cells

Functional loss after spinal cord injuries is originated by primary and secondary injury phases whose underlying mechanisms include massive release of excitatory amino acids to cytotoxic levels that contribute to neural death. Attenuation of this excitotoxicity is a key point for improving the functional outcome after injury. One of the drugs with potential neuroprotective actions is FK506, a molecule widely used as an immunosuppressant. FK506 may exert neuroprotection via inhibition of calcineurin by binding the FKBP12, or by binding other immunophilins such as FKBP52, leading to modulation of heat shock proteins (Hsp) 90 and 70. In the present study, we used an in vitro model of organotypic culture of rat spinal cord slices to assess whether FK506 is able to protect them against glutamate excitotoxicity. The results showed that FK506 promoted a significant protective effect on the spinal cord tissue at concentrations of 50 and 100 nM. Hsp70 induction was restricted to microglial cells in spinal cord slices treated with either glutamate or FK506. In contrast, the combination of both agents led to a transient reduction in Hsp70 levels in parallel to a marked reduction in IL-1beta precursor production by glial cells. The use of geldanamycin, which promotes persistent induction of Hsp70 in these cells as well as in motoneurons, did not produce tissue neuroprotection. These observations suggest that FK506 might protect spinal cord tissue by targeting on microglial cells and that transient downregulation of Hsp70 on these cells after excitotoxicity is a relevant mechanism of action of FK506.

Global profiling of influence of intra-ischemic brain temperature on gene expression in rat brain

Mild to moderate differences in brain temperature are known to greatly affect the outcome of cerebral ischemia. The impact of brain temperature on ischemic disorders has been mainly evaluated through pathological analysis. However, no comprehensive analyses have been conducted at the gene expression level. Using a high-density oligonucleotide microarray, we screened 24000 genes in the hippocampus under hypothermic (32 degrees C), normothermic (37 degrees C), and hyperthermic (39 degrees C) conditions in a rat ischemia-reperfusion model. When the ischemic group at each intra-ischemic brain temperature was compared to a sham-operated control group, genes whose expression levels changed more than three-fold with statistical significance could be detected. In our screening condition, thirty-three genes (some of them novel) were obtained after screening, and extensive functional surveys and literature reviews were subsequently performed. In the hypothermic condition, many neuroprotective factor genes were obtained, whereas cell death- and cell damage-associated genes were detected as the brain temperature increased. At all intra-ischemic brain temperatures, multiple molecular chaperone genes were obtained. The finding that intra-ischemic brain temperature affects the expression level of many genes related to neuroprotection or neurotoxicity coincides with the different pathological outcomes at different brain temperatures, demonstrating the utility of the genetic approach.

Control of androgen receptor signaling in prostate cancer by the cochaperone small glutamine rich tetratricopeptide repeat containing protein alpha

Although the androgen receptor (AR) is accepted as the major determinant of prostate cancer cell survival throughout disease progression, it is currently unclear how the receptor sustains genomic signaling under conditions of systemic androgen ablation. Here, we show that the evolutionarily conserved Hsp70/Hsp90 cochaperone, small glutamine-rich tetratricopeptide repeat containing protein alpha (alphaSGT), interacts with the hinge region of the human AR in yeast and mammalian cells. Overexpression and RNA interference revealed that alphaSGT acts to (a) promote cytoplasmic compartmentalization of the AR, thereby silencing the receptors basal/ligand-independent transcriptional activity, (b) regulate the sensitivity of receptor signaling by androgens, and (c) limit the capacity of noncanonical ligands to induce AR agonist activity. Immunofluorescence, coactivator, and chromatin immunoprecipitation analyses strongly suggest that these effects of alphaSGT on AR function are mediated by interaction in the cytoplasm and are distinct from the receptors response to classic coregulators. Quantitative immunohistochemical analysis of alphaSGT and AR levels in a cohort of 32 primary and 64 metastatic human prostate cancers revealed dysregulation in the level of both proteins during disease progression. The significantly higher AR/alphaSGT ratio in metastatic samples is consistent with the sensitization of prostate tumor cells to androgen signaling with disease progression, particularly in a low-hormone environment. These findings implicate alphaSGT as a molecular rheostat of in vivo signaling competence by the AR, and provide new insight into the determinants of androgen sensitivity during prostate cancer progression.

Glucocorticoid receptor physiology

Glucocorticoid action in cells is mediated by a specific receptor protein, the glucocorticoid receptor (GR). GR is a member of a superfamily of ligand-inducible transcription factors that control a variety of physiological functions; such as, metabolism, development, and reproduction. Unliganded GR is predominantly localized within the cytoplasm but rapidly and efficiently translocates to the nucleus following hormone binding. This review will focus on the intracellular signaling pathway utilized by the GR including the mechanisms that control its intracellular trafficking, hormone binding and transcriptional regulation. Many receptor-interacting proteins are involved in distinct steps in GR signal transduction, each with a unique mechanism to regulate receptor action and providing potential drug targets for the manipulation of cellular responses to glucocorticoids.

Identification of candidate prostate cancer biomarkers in prostate needle biopsy specimens using proteomic analysis

Although serum prostate specific antigen (PSA) is a well-established diagnostic tool for prostate cancer (PCa) detection, the definitive diagnosis of PCa is based on the information contained in prostate needle biopsy (PNBX) specimens. To define the proteomic features of PNBX specimens to identify candidate biomarkers for PCa, PNBX specimens from patients with PCa or benign prostatic hyperplasia (BPH) were subjected to comparative proteomic analysis. 2-DE revealed that 52 protein spots exhibited statistically significantly changes among PCa and BPH groups. Interesting spots were identified by MALDI-TOF-MS/MS. The 2 most notable groups of proteins identified included latent androgen receptor coregulators [FLNA(7-15) and FKBP4] and enzymes involved in mitochondrial fatty acid beta-oxidation (DCI and ECHS1). An imbalance in the expression of peroxiredoxin subtypes was noted in PCa specimens. Furthermore, different post-translationally modified isoforms of HSP27 and HSP70.1 were identified. Importantly, changes in FLNA(7-15), FKBP4, and PRDX4 expression were confirmed by immunoblot analyses. Our results suggest that a proteomics-based approach is useful for developing a more complete picture of the protein profile of PNBX specimen. The proteins identified by this approach may be useful molecular targets for PCa diagnostics and therapeutics.

Tête-à-tête: the function of FKBPs in plant development

Compared with that of other eukaryotes, the nuclear genome of the model plant Arabidopsis thaliana encodes an expanded family of FK506-binding proteins (FKBPs). Whereas approximately half of the FKBPs are implicated in the regulation of photosynthetic processes, a subcluster appears to be stress responsive. Recent reports indicate that a discrete group of Arabidopsis multidomain FKBPs regulate plant hormone pathways by recruiting or modulating client proteins via direct protein-protein interactions (tête-à-tête). This suggests that multidomain FKBPs function as central elements in plant development by linking hormone responses with other signal transduction pathways. Here, we present a summary of current research demonstrating that, in addition to their role in protein folding, subsets of plant FKBPs exhibit diverse functionality.

The immunophilin ligands cyclosporin A and FK506 suppress prostate cancer cell growth by androgen receptor-dependent and -independent mechanisms

The androgen receptor (AR) contributes to growth of prostate cancer even under conditions of androgen ablation. Thus, new strategies to target AR activity are needed. The AR interacts with the immunophilin FK506-binding protein 52 (FKBP52), and studies in the FKBP52 knockout mouse have shown that this protein is essential to AR activity in the prostate. Therefore, we tested whether the immunophilin ligand FK506 affected AR activity in prostate cancer cell lines. We also tested the hypothesis that the AR interacts with another immunophilin, cyclophilin 40 (Cyp40), and is regulated by its cognate ligand cyclosporin A (CsA). We show that levels of FKBP52, FKBP51, Cyp40, and a related co-chaperone PP5 were much higher in prostate cancer cells lines [(LNCaP), PC-3, and DU145] compared with primary prostate cells, and that the AR of LNCaP cells can interact with Cyp40. In the absence of androgen, CsA caused inhibition of cell growth in the AR-positive LNCaP and AR-negative PC-3 and DU145 cell lines. Interestingly, FK506 only inhibited LNCaP cells, suggesting a dependence on the AR for this effect. Both CsA and FK506 inhibited growth without inducing apoptosis. In LNCaP cells, CsA completely blocked androgen-stimulated growth, whereas FK506 was partially effective. Further studies in LNCaP cells revealed that CsA and FK506 were able to block or attenuate several stages of AR signaling, including hormone binding, nuclear translocation, and activity at several AR-responsive reporter and endogenous genes. These findings provide the first evidence that CsA and FK506 can negatively modulate proliferation of prostate cells in vitro. Immunophilins may now serve as new targets to disrupt AR-mediated prostate cancer growth.

The glucocorticoid responses are shaped by molecular chaperones

The glucocorticoid receptor is a known regulator of a variety of physiological processes. Its mode of action is well defined: upon hormone binding, it undergoes a conformational change, translocates to the nucleus and modulates the transcription of target genes. Molecular chaperones have a widely recognized role in the folding of newly made proteins, but their participation in further maturation of folded proteins to their active states and beyond tends to be underestimated. This review presents the current knowledge on how the Hsp70 and Hsp90 chaperone machines help to shape the responses to glucocorticoids. We discuss the contributions of these molecular chaperones to folding, activation, intracellular transport, transcriptional regulation, and decay of the glucocorticoid receptor.

Characterization of immunophilins in the silkmoth Bombyx mori

The FK506-binding proteins (FKBPs) perform an extensive variety of functions in numerous organisms from archaea to humans. The FKBPs are distinguished by their peptidyl-prolyl cis-trans isomerase (PPIase) activity and ability to bind the immunosuppressive drugs FK506 and rapamycin. Here, we report the isolation and characterization of FKBP45, a novel member of the FKBP family obtained from U1 small nuclear RNA (snRNA) binding assays using Bombyx mori nuclear extracts. The protein, an apparent orthologue of FKBP46 from the armyworm, Spodoptera frugiperda, was found to associate with U1 stem-loop I RNA in vitro. The FKBP45 cDNA was isolated and the genomic sequence was characterized, including the positions of exon/intron junctions and consensus splice sites. Using bioinformatics, transcription factor consensus binding sites were identified and subsequent Western blotting from developing eggs indicate that FKBP45 is differentially expressed during embryogenesis. A database was assembled using more than 1,800 available FKBP amino acid sequences and pairwise sequence alignments revealed several putative FKBP45 orthologues in various species. Analysis of these sequences revealed the position of an RNA binding domain within this new protein. In addition, FKBP45 possesses similar characteristics to several potential orthologues, including the presence of bipartite nuclear localization signals (NLSs) and phosphorylation sites.

Anchoring of the 26S proteasome to the organellar membrane by FKBP38

FK506-binding protein 38 (FKBP38) is a member of the immunophilin family that resides in the mitochondrial outer membrane and the endoplasmic reticulum (ER) membrane. To investigate the physiological function of FKBP38, we performed a comprehensive search for proteins with which it interacts in human cells by liquid chromatographic and mass spectrometric analysis of FKBP38 immunoprecipitates. Almost all subunits of the 26S proteasome were thus found to interact with FKBP38. In vivo co-immunoprecipitation analyses confirmed that FKBP38 indeed associates with the 26S proteasome via its three tandem tetratricopeptide repeats (TPRs). Binding assays in vitro also revealed that FKBP38 directly interacts with the S4 subunit of the 19S proteasome. Immunofluorescence analysis demonstrated that the subcellular distributions of FKBP38 and the 26S proteasome partially overlapped at mitochondria. Both the abundance and activity of the proteasome in a membrane fraction were markedly reduced for mouse embryonic fibroblasts prepared from Fkbp38(-/-) mice compared with those prepared from wild-type mice. These results suggest that FKBP38 functions to anchor the 26S proteasome at the organellar membrane.

Biochemical basis of regulation of human copper-transporting ATPases

Copper is essential for cell metabolism as a cofactor of key metabolic enzymes. The biosynthetic incorporation of copper into secreted and plasma membrane-bound proteins requires activity of the copper-transporting ATPases (Cu-ATPases) ATP7A and ATP7B. The Cu-ATPases also export excess copper from the cell and thus critically contribute to the homeostatic control of copper. The trafficking of Cu-ATPases from the trans-Golgi network to endocytic vesicles in response to various signals allows for the balance between the biosynthetic and copper exporting functions of these transporters. Although significant progress has been made towards understanding the biochemical characteristics of human Cu-ATPase, the mechanisms that control their function and intracellular localization remain poorly understood. In this review, we summarize current information on structural features and functional properties of ATP7A and ATP7B. We also describe sequence motifs unique for each Cu-ATPase and speculate about their role in regulating ATP7A and ATP7B activity and trafficking.

The immunophilin FKBP52 specifically binds to tubulin and prevents microtubule formation

The FK506 binding protein FKBP52 belongs to the large family of immunophilins and is known as a steroid receptor-associated protein. Previous data suggest that FKBP52 is associated with the motor protein dynein and with the cytoskeleton during mitosis. Here we demonstrate a specific and direct interaction between FKBP52 and tubulin. The region of FKBP52 located between aa 267 and 400, which includes the tetratricopeptide repeat domain, is required for tubulin binding. We provide evidence that FKBP52 prevents tubulin polymerization and that an 84 residue sequence located in the C-terminal part of the molecule (aa 375-458) is necessary and sufficient for its microtubule depolymerization activity. In colocalization experiments in PC12 cells, FKBP52 is associated with tubulin in motile cellular compartments. Furthermore, we suggest that, by using siRNA, a decrease of FKBP52 expression in PC12 cells may lead to differentiated cell phenotype characterized by neurite extensions. Collectively, our data define an unexpected property of FKBP52 as a novel regulator of microtubule dynamics. The possible role of microtubule formation and tubulin binding of other immunophilins such as FKBP12 and FKBP51 is discussed.

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

Fkbp52 and Fkbp51 are tetratricopeptide repeat proteins found in steroid receptor complexes, and Fkbp51 is an androgen receptor (AR) target gene. Although in vitro studies suggest that Fkbp52 and Fkbp51 regulate hormone binding and/or subcellular trafficking of receptors, the roles of Fkbp52 and Fkbp51 in vivo have not been extensively investigated. Here, we evaluate their physiological roles in Fkbp52-deficient and Fkbp51-deficient mice. Fkbp52-deficient males developed defects in select reproductive organs (e.g. penile hypospadias and prostate dysgenesis but normal testis), pointing to a role for Fkbp52 in AR-mediated signaling and function. Surprisingly, ablation of Fkbp52 did not affect AR hormone binding or nuclear translocation in vivo and in vitro. Molecular studies in mouse embryonic fibroblast cells uncovered that Fkbp52 is critical to AR transcriptional activity. Interestingly, Fkbp51 expression was down-regulated in Fkbp52-deficient males but only in affected tissues, providing further evidence of tissue-specific loss of AR activity and suggesting that Fkbp51 is an AR target gene essential to penile and prostate development. However, Fkbp51-deficient mice were normal, showing no defects in AR-mediated reproductive function. Our work demonstrates that Fkbp52 but not Fkbp51 is essential to AR-mediated signaling and provides evidence for an unprecedented Fkbp52 function, direct control of steroid receptor transcriptional activity.

Molecular mechanisms involved in progesterone receptor regulation of uterine function

The ovarian steroid hormone progesterone is a major regulator of uterine function. The actions of this hormone is mediated through its cognate receptor, the progesterone receptor, Pgr. Ablation of the Pgr has shown that this receptor is critical for all female reproductive functions including the ability of the uterus to support and maintain the development of the implanting mouse embryo. High density DNA microarray analysis has identified direct and indirect targets of Pgr action. One of the targets of Pgr action is a member of the Hedgehog morphogen Indian Hedgehog, Ihh. Ihh and members of the Hh signaling cascade show a coordinate expression pattern in the mouse uterus during the preimplantation period of pregnancy. The expression of Ihh and its receptor Patched-1, Ptc1, as well as, down stream targets of Ihh-Ptch1 signaling, such as the orphan nuclear receptor COUP-TF II show that this morphogen pathway mediates communication between the uterine epithelial and stromal compartments. The members of the Ihh signaling axis may function to coordinate the proliferation, vascularization and differentiation of the uterine stroma during pregnancy. This analysis demonstrates that progesterone regulates uterine function in the mouse by coordinating the signals from the uterine epithelium to stroma in the preimplantation mouse uterus.

The Arabidopsis tetratricopeptide repeat-containing protein TTL1 is required for osmotic stress responses and abscisic acid sensitivity

Mutations in the Arabidopsis (Arabidopsis thaliana) TETRATRICOPEPTIDE-REPEAT THIOREDOXIN-LIKE 1 (TTL1) cause reduced tolerance to NaCl and osmotic stress that is characterized by reduced root elongation, disorganization of the root meristem, and impaired osmotic responses during germination and seedling development. Expression analyses of genes involved in abscisic acid (ABA) biosynthesis and catabolism suggest that TTL1 is not involved in the regulation of ABA levels but is required for ABA-regulated responses. TTL1 regulates the transcript levels of several dehydration-responsive genes, such as the transcription factor DREB2A, and genes encoding dehydration response proteins, such as ERD1 (early response to dehydration 1), ERD3, and COR15a. The TTL1 gene encodes a novel plant protein with tetratricopeptide repeats and a region with homology to thioredoxin proteins. Based on homology searches, there are four TTL members in the Arabidopsis genome with similar intron-exon structure and conserved amino acid domains. Proteins containing tetratricopeptide repeat motifs act as scaffold-forming multiprotein complexes and are emerging as essential elements for plant hormonal responses (such as gibberellin responses and ethylene biosynthesis). In this report, we identify TTL1 as a positive regulator of ABA signaling during germination and seedling development under stress.

Role of endogenous XAP2 protein on the localization and nucleocytoplasmic shuttling of the endogenous mouse Ahb-1 receptor in the presence and absence of ligand

Studies using transient expression systems have implicated the hepatitis B virus X-associated protein (XAP2) in the control of aryl hydrocarbon receptor (AHR) stability and subcellular location. Studies were performed in Hepa-1 cells to evaluate these functions of XAP2 on the mouse Ahb-1 receptor under endogenous stoichiometry. The Ahb-1 receptor is cytoplasmic, and it becomes predominantly nuclear after 30 to 60 min of ligand exposure with minimal degradation. During this time, XAP2 coprecipitates with the AHR, suggesting that it does not affect the nuclear localization of the liganded receptor. Overexpression of XAP2 in Hepa-1 cells does not result in increased association with the endogenous Ahb-1 complex or influence the receptors cytoplasmic localization. Knockdown of endogenous XAP2 by small interfering RNA results in >or=90% reduction in the amount of XAP2 associated with the endogenous Ahb-1 receptor complex. Despite the reduction in XAP2, the unliganded Ahb-1 receptor complex remains cytoplasmic, although inhibition of nuclear export results in accumulation of the receptor in the nucleus. Truncation of the C-terminal 305 amino acids of the Ahb-1 receptor (AHR500) results in proteins that exhibit a predominantly nuclear localization and remain associated with the same level of endogenous XAP2 as full-length AHRs. Together, these results support a model in which the majority of the unliganded Ahb-1 receptor complexes are associated with XAP2, and the association prevents dynamic nucleocytoplasmic shuttling in the unliganded state. After ligand binding, XAP2 remains associated with the Ahb-1 receptor complex, and it does not impair nuclear translocation but may function to limit receptor "transformation".

FKBP133: a novel mouse FK506-binding protein homolog alters growth cone morphology

FK506-binding proteins are the peptidyl prolyl cis-trans isomerases that are involved in various intracellular events. We characterized a novel mouse FK506-binding protein homolog, FKBP133/KIAA0674, in the developing nervous system. FKBP133 contains a domain similar to Wiskott-Aldrich syndrome protein homology region 1 (WH1) and a domain homologous to FK506-binding protein motif. FKBP133 was predominantly expressed in cerebral cortex, hippocampus, and peripheral ganglia at embryonic day 18.5. FKBP133 protein was distributed in the axonal shafts and was partially co-localized with F-actin in the growth cones of dorsal root ganglion neurons (DRG). The number of filopodia was increased in the DRG neurons overexpressing FKBP133. In contrast, the overexpression of a mutant deleted the WH1 domain reduced the growth cone size and the number of filopodia. Furthermore, the neurons overexpressing FKBP133 became significantly resistant to Semaphorin-3A induced collapse response. These results suggest that FKBP133 modulates growth cone behavior with the WH1 domain.

Cyclophilin A: an auxiliary but not necessary cofactor for TRIM5alpha restriction of HIV-1

Cyclophilin A (Cyp A) binds the human immunodeficiency virus type 1 (HIV-1) capsid (CA) protein and contributes to the early events in virus replication in some cells. The retroviral restriction factor TRIM5alpha can inhibit the early, post-entry phase of infection by associating with the incoming viral capsid. Cyp A has been proposed to prevent restriction factor binding in human cells, thus enhancing HIV-1 infectivity, and to potentiate restriction of HIV-1 in monkey cells. Here we show that the positive effects of Cyp A-CA binding on HIV-1 infectivity do not depend on human TRIM5alpha. Disruption of Cyp A binding to CA partially relieved the block to HIV-1 infection imposed by several TRIM5alpha variants, but Cyp A-CA binding was not absolutely required for TRIM5alpha antiviral activity. Inhibition of Cyp A function by cyclosporine significantly decreased the efficiency of TRIM5alpha-mediated restriction only when the restricted virus capsid interacted with Cyp A.

Isolating the whole complex of target proteins of FK506 using affinity resins from novel solid phases

The development of novel solid phases enabled us to create affinity resins that could be used to isolate the whole complex of target proteins responsible for the immunosuppressive effects of FK506 from rat brain lysate, whereas the affinity resins from commercially available matrices could not achieve this isolation. The results illustrate the enhanced effectiveness of the affinity resin made from this novel material at identifying the target protein of the bioactive compound compared to resins made from the well-known materials Affigel or Toyopearl. This effectiveness arises because the novel material is hydrophilic enough to reduce nonspecific binding proteins and because it has a higher density of ligands that capture the nonubiquitous target protein.

Molecular pathways that influence human tau-induced pathology in Caenorhabditis elegans

Mutations in the gene encoding tau cause frontotemporal dementia with parkinsonism--chromosome 17 type (FTDP-17). In FTDP-17, Alzheimer's disease, and other tauopathies, aggregated hyper-phosphorylated tau forms the neurofibrillary tangles characteristic of these disorders. We previously reported a Caenorhabditis elegans model for tauopathies using human normal and FTDP-17 mutant tau as transgenes. Neuronal transgene expression caused insoluble phosphorylated tau accumulation, neurodegeneration and uncoordinated (Unc) movement. Here we describe a genome-wide RNA-mediated interference (RNAi) screen for genes that modify the tau-induced Unc phenotype. We tested RNAi sequences for 16,757 genes and found 75 that enhanced the transgene-induced Unc phenotype. Forty-six of these genes have sequence similarity to known human genes and fall into a number of broad classes including kinases, chaperones, proteases and phosphatases. The remaining 29 modifiers have sequence similarity only with other nematode genes. To determine if the enhancers are specific for the tau-induced Unc behavior, we exposed several non-tau Unc mutants to tau RNAi enhancer clones. Fifteen enhancers modified phenotypes in multiple Unc mutants, whereas 60 modified only the Unc phenotype in the tau transgenic lines. We also introduced the tau transgene into the background of genetic loss-of-function mutations for a subset of the enhancer genes. Tau transgenic animals homozygous for loss of these enhancer genes exhibited increased impaired motility relative to the tau transgene line alone. This work uncovers novel candidate genes that prevent tau toxicity, as well as genes previously implicated in tau-mediated neurodegeneration.

Cochaperone immunophilin FKBP52 is critical to uterine receptivity for embryo implantation

Embryo implantation in the uterus is a critical step in mammalian reproduction, requiring preparation of the uterus receptive to blastocyst implantation. Uterine receptivity, also known as the window of implantation, lasts for a limited period, and it is during this period blastocysts normally implant. Ovarian steroid hormones estrogen and progesterone (P(4)) are the primary regulators of this process. The immunophilin FKBP52 serves as a cochaperone for steroid hormone nuclear receptors to govern appropriate hormone action in target tissues. Here we show a critical role for FKBP52 in mouse implantation. This immunophilin has unique spatiotemporal expression in the uterus during implantation, and females missing the Fkbp52 gene have complete implantation failure due to lack of attainment of uterine receptivity. The overlapping uterine expression of FKBP52 with nuclear progesterone receptor (PR) in wild-type mice together with reduced P(4) binding to PR, attenuated PR transcriptional activity and down-regulation of several P(4)-regulated genes in uteri of Fkbp52(-/-) mice, establishes this cochaperone as a critical regulator of uterine P(4) function. Interestingly, ovulation, another P(4)-mediated event, remains normal. Collectively, the present investigation provides evidence for an in vivo role for this cochaperone in regulating tissue-specific hormone action and its critical role in uterine receptivity for implantation.

Redefining the role of the endogenous XAP2 and C-terminal hsp70-interacting protein on the endogenous Ah receptors expressed in mouse and rat cell lines

Studies using transient expression systems have implicated the XAP2 protein in the control of aryl hydrocarbon receptor (AHR) stability and subcellular location. Thus, studies were performed in cell lines that expressed endogenous rat or mouse Ah(b-1) (C57BL/6) or Ah(b-2) (C3H) AHRs with similar levels of endogenous XAP2. Unliganded rat and mouse Ah(b-2) receptor complexes associated with reduced levels of XAP2 and exhibited dynamic nucleocytoplasmic shuttling in comparison with Ah(b-1) receptors. Rat and mouse Ah(b-2) receptors also exhibited a greater magnitude of ligand-induced degradation than Ah(b-1) receptors. Small interfering RNA reduction of endogenous XAP2 by >80% had minimal impact on the level of Ah(b-2) receptors but resulted in a 25-30% reduction of Ah(b-1) receptors. XAP2 reduction resulted in increased susceptibility of the Ah(b-1) receptor to ligand-induced degradation yet produced higher levels of endogenous CYP1A1 induction. Stable expression of the Ah(b-2) receptor in the C57BL/6 background resulted in a protein with reduced association with XAP2, dynamic nucleocytoplasmic shuttling, and increased levels of ligand-induced degradation. Small interfering RNA reduction of endogenous XAP2 in a C-terminal hsp70-interacting protein knockout mouse cell line, exhibited a 25-30% reduction in the level of endogenous Ah(b-1) AHR and showed high levels of ligand-induced degradation. Thus, endogenous XAP2 exerts a negative function on a small fraction of the endogenous Ah(b-1) receptor complex but appears to have a minimal impact on endogenous rat or Ah(b-2) receptors. This implies that the analysis of the AHR-mediated signaling via rat and mouse Ah(b-2) receptors may better represent the physiology of this signal transduction pathway.