Tetratricopeptide repeat (TPR) motif containing co-chaperones of the chaperone Hsp90 are considered control modules that govern activity and specificity of this central folding platform. Steroid ...receptors are paradigm clients of Hsp90. The influence of some TPR proteins on selected receptors has been described, but a comprehensive analysis of the effects of TPR proteins on all steroid receptors has not been accomplished yet.
We compared the influence of the TPR proteins FK506 binding proteins 51 and 52, protein phosphatase-5, C-terminus of Hsp70 interacting protein, cyclophillin 40, hepatitis-virus-B X-associated protein-2, and tetratricopeptide repeat protein-2 on all six steroid hormone receptors in a homogeneous mammalian cell system. To be able to assess each cofactor's effect on the transcriptional activity of on each steroid receptor we employed transient transfection in a reporter gene assay. In addition, we evaluated the interactions of the TPR proteins with the receptors and components of the Hsp90 chaperone heterocomplex by coimmunoprecipitation. In the functional assays, corticosteroid and progesterone receptors displayed the most sensitive and distinct reaction to the TPR proteins. Androgen receptor's activity was moderately impaired by most cofactors, whereas the Estrogen receptors' activity was impaired by most cofactors only to a minor degree. Second, interaction studies revealed that the strongly receptor-interacting co-chaperones were all among the inhibitory proteins. Intriguingly, the TPR-proteins also differentially co-precipitated the heterochaperone complex components Hsp90, Hsp70, and p23, pointing to differences in their modes of action.
The results of this comprehensive study provide important insight into chaperoning of diverse client proteins via the combinatorial action of (co)-chaperones. The differential effects of the TPR proteins on steroid receptors bear on all physiological processes related to steroid hormone activity.
In recent years, the glutamatergic system has been implicated in the development and treatment of psychiatric disorders. Glutamate signaling is processed by different receptors, including ...metabotropic glutamate receptors (mGluRs), which in turn interact with the scaffolding protein Homer1 to modulate downstream Ca(2+) signaling. Stress is a major risk factor for the incidence of psychiatric diseases, yet acute stress episodes may have diverging effects on individuals. Cognitive impairments have often been shown to occur after episodes of stress, however the specific role of mGluR5/Homer1 signaling in the interaction of stress and cognition has not yet been elucidated. In this study we show that a single episode of social defeat stress is sufficient to specifically induce cognitive impairments in mice 8 h after the stressor without affecting the animals' locomotion or anxiety levels. We also demonstrate that Homer1b/c levels as well as mGluR5/Homer1b/c interactions in the dorsal hippocampus are reduced up to 8 h after stress. Blockade of mGluR5 during the occurrence of social stress was able to rescue the cognitive impairments. In addition, a specific overexpression of Homer1b/c in the dorsal hippocampus also reversed the behavioral phenotype, indicating that both mGluR5 and Homer1b/c play a crucial role in the mediation of the stress effects. In summary, we could demonstrate that stress induces a cognitive deficit that is likely mediated by mGluR5/Homer1 signaling in the hippocampus. These findings help to reveal the underlying effects of cognitive impairments in patients suffering from stress-related psychiatric disorders.
Cytoskeletal dynamics are pivotal to memory, learning, and stress physiology, and thus psychiatric diseases. Downregulated in renal cell carcinoma 1 (DRR1) protein was characterized as the link ...between stress, actin dynamics, neuronal function, and cognition. To elucidate the underlying molecular mechanisms, we undertook a domain analysis of DRR1 and probed the effects on actin binding, polymerization, and bundling, as well as on actin-dependent cellular processes.
DRR1 domains were cloned and expressed as recombinant proteins to perform in vitro analysis of actin dynamics (binding, bundling, polymerization, and nucleation). Cellular actin-dependent processes were analyzed in transfected HeLa cells with fluorescence recovery after photobleaching (FRAP) and confocal microscopy.
DRR1 features an actin binding site at each terminus, separated by a coiled coil domain. DRR1 enhances actin bundling, the cellular F-actin content, and serum response factor (SRF)-dependent transcription, while it diminishes actin filament elongation, cell spreading, and actin treadmilling. We also provide evidence for a nucleation effect of DRR1. Blocking of pointed end elongation by addition of profilin indicates DRR1 as a novel barbed end capping factor.
DRR1 impacts actin dynamics in several ways with implications for cytoskeletal dynamics in stress physiology and pathophysiology.
Activation of RhoA/Rho-associated kinase (ROCK) pathway and the associated changes in actin cytoskeleton induced by thrombin are crucial for activation of NF-κB and expression of its target gene ...ICAM-1 in endothelial cells. However, the events acting downstream of RhoA/ROCK to mediate these responses remain unclear. Here, we show a central role of cofilin-1, an actin-binding protein that promotes actin depolymerization, in linking RhoA/ROCK pathway to dynamic alterations in actin cytoskeleton that are necessary for activation of NF-κB and thereby expression of ICAM-1 in these cells. Stimulation of human umbilical vein endothelial cells with thrombin resulted in Ser3 phosphorylation/inactivation of cofilin and formation of actin stress fibers in a ROCK-dependent manner. RNA interference knockdown of cofilin-1 stabilized the actin filaments and inhibited thrombin- and RhoA-induced NF-κB activity. Similarly, constitutively inactive mutant of cofilin-1 (Cof1-S3D), known to stabilize the actin cytoskeleton, inhibited NF-κB activity by thrombin. Overexpression of wild type cofilin-1 or constitutively active cofilin-1 mutant (Cof1-S3A), known to destabilize the actin cytoskeleton, also impaired thrombin-induced NF-κB activity. Additionally, depletion of cofilin-1 was associated with a marked reduction in ICAM-1 expression induced by thrombin. The effect of cofilin-1 depletion on NF-κB activity and ICAM-1 expression occurred downstream of IκBα degradation and was a result of impaired RelA/p65 nuclear translocation and consequently, RelA/p65 binding to DNA. Together, these data show that cofilin-1 occupies a central position in RhoA-actin pathway mediating nuclear translocation of RelA/p65 and expression of ICAM-1 in endothelial cells.
This review portraits FK506 binding protein (FKBP) 51 as “reactivity protein” and collates recent publications to develop the concept of FKBP51 as contributor to different levels of adaptation. ...Adaptation is a fundamental process that enables unicellular and multicellular organisms to adjust their molecular circuits and structural conditions in reaction to environmental changes threatening their homeostasis. FKBP51 is known as chaperone and co‐chaperone of heat shock protein (HSP) 90, thus involved in processes ensuring correct protein folding in response to proteotoxic stress. In mammals, FKBP51 both shapes the stress response and is calibrated by the stress levels through an ultrashort molecular feedback loop. More recently, it has been linked to several intracellular pathways related to the reactivity to drug exposure and stress. Through its role in autophagy and DNA methylation in particular it influences adaptive pathways, possibly also in a transgenerational fashion.
Also see the video here.
In response to environmental change, organisms adjust certain molecular circuits to cope with the new situation. This review collates the evidence linking FK506 binding protein (FKBP) 51 to molecular pathways of adaptation. Successful adaptation depends on the reactivity of these pathways that typically are organized in molecular feedback loops.
We have previously reported the differential expression of 17 probe sets in survivors of the 9/11 attacks with current posttraumatic stress disorder (PTSD) compared to similarly exposed survivors ...with no lifetime PTSD. The current study presents an expanded analysis of these subjects, including genotype at FKBP5, a modulator of glucocorticoid receptor (GR) sensitivity. It includes data from additional subjects who developed PTSD following 9/11 but then recovered, distinguishing expression profiles associated with risk for developing PTSD, resilience, and symptom recovery. 40 Caucasians (20 with and 20 without PTSD, matched for exposure, age, and gender) were selected from a population-representative sample of persons exposed to the 9/11 attacks from which longitudinal data had been collected in four previous waves. Whole blood gene expression and cortisol levels were obtained and genome-wide gene expression was analyzed. 25 probe sets were differentially expressed in PTSD. Identified genes were generally involved in hypothalamic-pituitary-adrenal axis, signal transduction, or in brain and immune cell function. STAT5B, a direct inhibitor of GR, and nuclear factor I/A, both showed reduced expression in PTSD. Comparison of lifetime versus current PTSD identified overlapping genes with altered expression suggesting enduring markers, while some markers present only in current PTSD may reflect state measures. As a follow-up, direct comparisons of expression in current PTSD, lifetime-only PTSD, and control groups identified FKBP5 and MHC Class II as state markers, and also identified several trait markers. An analysis of indirect effects revealed that homozygosity for any of 4 PTSD risk-related polymorphisms at FKBP5 predicted FKBP5 expression, which mediated indirect effects of genotype on plasma cortisol and PTSD severity.
As the cerebellar molecular stress response is understudied, we assessed protein expression levels of hypothalamic-pituitary-adrenal (HPA) axis regulators and neurostructural markers in the ...cerebellum of a male PTSD mouse model and of unstressed vs. stressed male FK506 binding protein 51 (Fkbp5) knockout (KO) vs. wildtype mice. We explored the translatability of our findings in the Fkbp5 KO model to the situation in humans by correlating mRNA levels of candidates with those of FKBP5 in two whole transcriptome datasets of post-mortem human cerebellum and in blood of unstressed and stressed humans. Fkbp5 deletion rescued the stress-induced loss in hippocampal, prefrontal cortical, and, possibly, also cerebellar FKBP52 expression and modulated post-stress cerebellar expression levels of the glucocorticoid receptor (GR) and possibly (trend) also of glial fibrillary acidic protein (GFAP). Accordingly, expression levels of genes encoding for these three genes correlated with those of FKBP5 in human post-mortem cerebellum, while other neurostructural markers were not related to Fkbp5 either in mouse or human cerebellum. Also, gene expression levels of the two immunophilins correlated inversely in the blood of unstressed and stressed humans. We found transient changes in FKBP52 and persistent changes in GR and GFAP in the cerebellum of PTSD-like mice. Altogether, upon elucidating the cerebellar stress response we found first evidence for a novel facet of HPA axis regulation, i.e., the ability of FKBP51 to modulate the expression of its antagonist FKBP52 in the mouse and, speculatively, also in the human brain and blood and, moreover, detected long-term single stress-induced changes in expression of cerebellar HPA axis regulators and neurostructural markers of which some might contribute to the role of the cerebellum in fear extinction.
The immunophilin FK506 binding protein 51 (FKBP51) has emerged as one of the most intensely investigated proteins in stress-related mental disorders. It was originally characterized as Hsp90 ...cochaperone and part of the receptor-chaperone heterocomplex that governs the activity of steroid receptors. It turned out that the presence of FKBP51 in this heterocomplex leads to diminished activity of the corticosteroid receptors. In particular, based on its inhibitory action on the glucocorticoid receptor (GR), FKBP51 was included in a candidate gene approach to discover gene polymorphisms that might be relevant for the development and treatment of major depression. The discovery that polymorphisms in the gene coding for FKBP51 were linked to the treatment response of depressed patients intensified the research on the role of FKBP51 in stress-related diseases worldwide. It has become evident that FKBP51 is not only a regulator of GR action, but also a GR target. The function of this ultrashort intracellular feedback loop is critically important for cellular and physiological stress regulation as it does not only calibrate the function of GR, but also the levels of FKBP51. Given the pleiotropic functions of FKBP51, its levels might be equally important for mental disorders as GR function and hence for the development of potential FKBP51 drug targets.
Summary Understanding the molecular mechanisms by which stress is translated into changes in complex behavior may help to identify novel treatment strategies for stress-associated psychiatric ...disorders. The tumor suppressor gene down-regulated in renal cell carcinoma 1 (DRR1) was recently characterized as a new molecular link between stress, synaptic efficacy and behavioral performance, most likely through its ability to modulate actin dynamics. The lateral septum is one of the brain regions prominently involved in the stress response. This brain region features high DRR1 expression in adult mice, even under basal conditions. We therefore aimed to characterize and dissect the functional role of septal DRR1 in modulating complex behavior. DRR1 protein expression was shown to be expressed in both neurons and astrocytes of the lateral septum of adult mice. Septal DRR1 mRNA expression increased after acute defeat stress and glucocorticoid receptor activation. To mimic the stress-induced DRR1 increase in the lateral septum of mice, we performed adenovirus-mediated region-specific overexpression of DRR1 and characterized the behavior of these mice. Overexpression of DRR1 in the septal region increased sociability, but did not change cognitive, anxiety-like or anhedonic behavior. The observed changes in social behavior did not involve alterations of the expression of vasopressin or oxytocin receptors, the canonical social neuropeptidergic circuits of the lateral septum. In summary, our data suggest that the stress-induced increase of DRR1 expression in the lateral septum could be a protective mechanism to buffer or counterbalance negative consequences of stress exposure on social behavior.
PDF
