Heat shock transcription factor 1 as a therapeutic target in neurodegenerative diseases

Targeting Protein Quality Control Mechanisms by Natural Products to Promote Healthy Ageing

Organismal ageing is associated with increased chance of morbidity or mortality and it is driven by diverse molecular pathways that are affected by both environmental and genetic factors. The progression of ageing correlates with the gradual accumulation of stressors and damaged biomolecules due to the time-dependent decline of stress resistance and functional capacity, which eventually compromise cellular homeodynamics. As protein machines carry out the majority of cellular functions, proteome quality control is critical for cellular functionality and is carried out through the curating activity of the proteostasis network (PN). Key components of the PN are the two main degradation machineries, namely the ubiquitin-proteasome and autophagy-lysosome pathways along with several stress-responsive pathways, such as that of nuclear factor erythroid 2-related factor 2 (Nrf2), which mobilises cytoprotective genomic responses against oxidative and/or xenobiotic damage. Reportedly, genetic or dietary interventions that activate components of the PN delay ageing in evolutionarily diverse organisms. Natural products (extracts or pure compounds) represent an extraordinary inventory of highly diverse structural scaffolds that offer promising activities towards meeting the challenge of increasing healthspan and/or delaying ageing (e.g., spermidine, quercetin or sulforaphane). Herein, we review those natural compounds that have been found to activate proteostatic and/or anti-stress cellular responses and hence have the potential to delay cellular senescence and/or in vivo ageing.

Rational design and screening of peptide-based inhibitors of heat shock factor 1 (HSF1)

Heat shock factor 1 (HSF1) is a stress-responsive transcription factor that regulates expression of protein chaperones and cell survival factors. In cancer, HSF1 plays a unique role, hijacking the normal stress response to drive a cancer-specific transcriptional program. These observations suggest that HSF1 inhibitors could be promising therapeutics. However, HSF1 is activated through a complex mechanism, which involves release of a negative regulatory domain, leucine zipper 4 (LZ4), from a masked oligomerization domain (LZ1-3), and subsequent binding of the oligomer to heat shock elements (HSEs) in HSF1-responsive genes. Recent crystal structures have suggested that HSF1 oligomers are held together by extensive, buried contact surfaces, making it unclear whether there are any possible binding sites for inhibitors. Here, we have rationally designed a series of peptide-based molecules based on the LZ4 and LZ1-3 motifs. Using a plate-based, fluorescence polarization (FP) assay, we identified a minimal region of LZ4 that suppresses binding of HSF1 to the HSE. Using this information, we converted this peptide into a tracer and used it to understand how binding of LZ4 to LZ1-3 suppresses HSF1 activation. Together, these results suggest a previously unexplored avenue in the development of HSF1 inhibitors. Furthermore, the findings highlight how native interactions can inspire the design of inhibitors for even the most challenging protein-protein interactions (PPIs).

Pseudoexfoliation and Alzheimer's associated CLU risk variant, rs2279590, lies within an enhancer element and regulates CLU, EPHX2 and PTK2B gene expression

Genetic variants at PTK2B-CLU locus pose as high-risk factors for many age-related disorders. However, the role of these variants in disease progression is less characterized. In this study, we aimed to investigate the functional significance of a clusterin intronic SNP, rs2279590, that has been associated with pseudoexfoliation, Alzheimer's disease (AD) and diabetes. We have previously shown that the alleles at rs2279590 differentially regulate clusterin (CLU) gene expression in lens capsule tissues. This polymorphism resides in an active regulatory region marked by H3K27Ac and DNase I hypersensitive site and is an eQTL for CLU expression. Here, we report the presence of an enhancer element in surrounding region of rs2279590. Deletion of a 115 bp intronic region flanking the rs2279590 variant through CRISPR-Cas9 genome editing in HEK293 cells demonstrated a decreased clusterin gene expression. Electrophoretic mobility shift and chromatin immunoprecipitation assays show that rs2279590 with allele 'A' constitutes a transcription factor binding site for heat shock factor-1 (HSF1) but not with allele 'G'. By binding to allele 'A', HSF1 abrogates the enhancer effect of the locus as validated by reporter assays. Interestingly, rs2279590 locus has a widespread enhancer effect on two nearby genes, protein tyrosine kinase 2 beta (PTK2B) and epoxide hydrolase-2 (EPHX2); both of which have been previously associated with AD as risk factors. To summarize, our study unveils a mechanistic role of the common variant rs2279590 that can affect a variety of aging disorders by regulating the expression of a specific set of genes.

Proteostasis disturbance in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease affecting motoneurons in the brain and spinal cord leading to paralysis and death. Although the etiology of ALS remains poorly understood, abnormal protein aggregation and altered proteostasis are common features of sporadic and familial ALS forms. The proteostasis network is decomposed into different modules highly conserved across species and comprehends a collection of mechanisms related to protein synthesis, folding, trafficking, secretion and degradation that is distributed in different compartments inside the cell. Functional studies in various ALS models are revealing a complex scenario where distinct and even opposite effects in disease progression are observed depending on the targeted component of the proteostasis network. Importantly, alteration of the folding capacity of the endoplasmic reticulum (ER) is becoming a common pathological alteration in ALS, representing one of the earliest defects observed in disease models, contributing to denervation and motoneuron dysfunction. Strategies to target-specific components of the proteostasis network using small molecules and gene therapy are under development, and promise interesting avenues for future interventions to delay or stop ALS progression.

Azadiradione ameliorates polyglutamine expansion disease in Drosophila by potentiating DNA binding activity of heat shock factor 1

Aggregation of proteins with the expansion of polyglutamine tracts in the brain underlies progressive genetic neurodegenerative diseases (NDs) like Huntington's disease and spinocerebellar ataxias (SCA). An insensitive cellular proteotoxic stress response to non-native protein oligomers is common in such conditions. Indeed, upregulation of heat shock factor 1 (HSF1) function and its target protein chaperone expression has shown promising results in animal models of NDs. Using an HSF1 sensitive cell based reporter screening, we have isolated azadiradione (AZD) from the methanolic extract of seeds of Azadirachta indica, a plant known for its multifarious medicinal properties. We show that AZD ameliorates toxicity due to protein aggregation in cell and fly models of polyglutamine expansion diseases to a great extent. All these effects are correlated with activation of HSF1 function and expression of its target protein chaperone genes. Notably, HSF1 activation by AZD is independent of cellular HSP90 or proteasome function. Furthermore, we show that AZD directly interacts with purified human HSF1 with high specificity, and facilitates binding of HSF1 to its recognition sequence with higher affinity. These unique findings qualify AZD as an ideal lead molecule for consideration for drug development against NDs that affect millions worldwide.

Recent neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC

Niemann–Pick disease type C (NPC) is a rare autosomal recessive lysosomal storage disorder with extensive biological, molecular, and clinical heterogeneity. Recently, numerous studies have tried to shed light on the pathophysiology of the disease, highlighting possible disease pathways common to other neurodegenerative disorders, such as Alzheimer’s disease and frontotemporal dementia, and identifying possible candidate biomarkers for disease staging and response to treatment. Miglustat, which reversibly inhibits glycosphingolipid synthesis, has been licensed in the European Union and elsewhere for the treatment of NPC in both children and adults. A number of ongoing clinical trials might hold promise for the development of new treatments for NPC. The objective of the present work is to review and evaluate recent literature data in order to highlight the latest neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC pathophysiology. Furthermore, ongoing developments in disease-modifying treatments will be briefly discussed.

Bortezomib-induced heat shock response protects multiple myeloma cells and is activated by heat shock factor 1 serine 326 phosphorylation

Proteasome inhibitors such as bortezomib are highly active in multiple myeloma by affecting signaling cascades and leading to a toxic buildup of misfolded proteins. Bortezomib-treated cells activate the cytoprotective heat shock response (HSR), including upregulation of heat shock proteins (HSPs). Here we inhibited the bortezomib-induced HSR by silencing its master regulator, Heat Shock Factor 1 (HSF1). HSF1 silencing led to bortezomib sensitization. In contrast, silencing of individual and combination HSPs, except HSP40β, did not result in significant bortezomib sensitization. However, HSP40β did not entirely account for increased bortezomib sensitivity upon HSF1 silencing. To determine the mechanism of HSF1 activation, we assessed phosphorylation and observed bortezomib-inducible phosphorylation in cell lines and patient samples. We determined that this bortezomib-inducible event is phosphorylation at serine 326. Prior clinical use of HSP inhibitors in combination with bortezomib has been disappointing in multiple myeloma therapy. Our results provide a rationale for targeting HSF1 activation in combination with bortezomib to enhance multiple myeloma treatment efficacy.

Hsf1 and Hsp70 constitute a two-component feedback loop that regulates the yeast heat shock response

Models for regulation of the eukaryotic heat shock response typically invoke a negative feedback loop consisting of the transcriptional activator Hsf1 and a molecular chaperone. Previously we identified Hsp70 as the chaperone responsible for Hsf1 repression and constructed a mathematical model that recapitulated the yeast heat shock response (Zheng et al., 2016). The model was based on two assumptions: dissociation of Hsp70 activates Hsf1, and transcriptional induction of Hsp70 deactivates Hsf1. Here we validate these assumptions. First, we severed the feedback loop by uncoupling Hsp70 expression from Hsf1 regulation. As predicted by the model, Hsf1 was unable to efficiently deactivate in the absence of Hsp70 transcriptional induction. Next, we mapped a discrete Hsp70 binding site on Hsf1 to a C-terminal segment known as conserved element 2 (CE2). In vitro, CE2 binds to Hsp70 with low affinity (9 µM), in agreement with model requirements. In cells, removal of CE2 resulted in increased basal Hsf1 activity and delayed deactivation during heat shock, while tandem repeats of CE2 sped up Hsf1 deactivation. Finally, we uncovered a role for the N-terminal domain of Hsf1 in negatively regulating DNA binding. These results reveal the quantitative control mechanisms underlying the heat shock response.

A Futile Battle? Protein Quality Control and the Stress of Aging

There exists a phenomenon in aging research whereby early life stress can have positive impacts on longevity. The mechanisms underlying these observations suggest a robust, long-lasting induction of cellular defense mechanisms. These include the various unfolded protein responses of the endoplasmic reticulum (ER), cytosol, and mitochondria. Indeed, ectopic induction of these pathways, in the absence of stress, is sufficient to increase lifespan in organisms as diverse as yeast, worms, and flies. Here, we provide an overview of the protein quality control mechanisms that operate in the cytosol, mitochondria, and ER and discuss how they affect cellular health and viability during stress and aging.

Receptor-interacting protein 140 as a co-repressor of Heat Shock Factor 1 regulates neuronal stress response

Heat shock response (HSR) is a highly conserved transcriptional program that protects organisms against various stressful conditions. However, the molecular mechanisms modulating HSR, especially the suppression of HSR, is poorly understood. Here, we found that RIP140, a wide-spectrum cofactor of nuclear hormone receptors, acts as a co-repressor of heat shock factor 1 (HSF1) to suppress HSR in healthy neurons. When neurons are stressed such as by heat shock or sodium arsenite (As), cells engage specific proteosome-mediated degradation to reduce RIP140 level, thereby relieving the suppression and activating HSR. RIP140 degradation requires specific Tyr-phosphorylation by Syk that is activated in stressful conditions. Lowering RIP140 level protects hippocampal neurons from As stress, significantly it increases neuron survival and improves spine density. Reducing hippocampal RIP140 in the mouse rescues chronic As-induced spatial learning deficits. This is the first study elucidating RIP140-mediated suppression of HSF1-activated HSR in neurons and brain. Importantly, degradation of RIP140 in stressed neurons relieves this suppression, allowing neurons to efficiently and timely engage HSR programs and recover. Therefore, stimulating RIP140 degradation to activate anti-stress program provides a potential preventive or therapeutic strategy for neurodegeneration diseases.

Heat shock protein-based therapy as a potential candidate for treating the sphingolipidoses

Lysosomal storage diseases (LSDs) often manifest with severe systemic and central nervous system (CNS) symptoms. The existing treatment options are limited and have no or only modest efficacy against neurological manifestations of disease. We demonstrate that recombinant human heat shock protein 70 (HSP70) improves the binding of several sphingolipid-degrading enzymes to their essential cofactor bis(monoacyl)glycerophosphate in vitro. HSP70 treatment reversed lysosomal pathology in primary fibroblasts from 14 patients with eight different LSDs. HSP70 penetrated effectively into murine tissues including the CNS and inhibited glycosphingolipid accumulation in murine models of Fabry disease (Gla(-/-)), Sandhoff disease (Hexb(-/-)), and Niemann-Pick disease type C (Npc1(-/-)) and attenuated a wide spectrum of disease-associated neurological symptoms in Hexb(-/-) and Npc1(-/-) mice. Oral administration of arimoclomol, a small-molecule coinducer of HSPs that is currently in clinical trials for Niemann-Pick disease type C (NPC), recapitulated the effects of recombinant human HSP70, suggesting that heat shock protein-based therapies merit clinical evaluation for treating LSDs.

TDP-43 Promotes Neurodegeneration by Impairing Chromatin Remodeling

Regulation of chromatin structure is critical for brain development and function. However, the involvement of chromatin dynamics in neurodegeneration is less well understood. Here we find, launching from Drosophila models of amyotrophic lateral sclerosis and frontotemporal dementia, that TDP-43 impairs the induction of multiple key stress genes required to protect from disease by reducing the recruitment of the chromatin remodeler Chd1 to chromatin. Chd1 depletion robustly enhances TDP-43-mediated neurodegeneration and promotes the formation of stress granules. Conversely, upregulation of Chd1 restores nucleosomal dynamics, promotes normal induction of protective stress genes, and rescues stress sensitivity of TDP-43-expressing animals. TDP-43-mediated impairments are conserved in mammalian cells, and, importantly, the human ortholog CHD2 physically interacts with TDP-43 and is strikingly reduced in level in temporal cortex of human patient tissue. These findings indicate that TDP-43-mediated neurodegeneration causes impaired chromatin dynamics that prevents appropriate expression of protective genes through compromised function of the chromatin remodeler Chd1/CHD2. Enhancing chromatin dynamics may be a treatment approach to amyotrophic lateral scleorosis (ALS)/frontotemporal dementia (FTD).

The heat shock response in neurons and astroglia and its role in neurodegenerative diseases

Protein inclusions are a predominant molecular pathology found in numerous neurodegenerative diseases, including amyotrophic lateral sclerosis and Huntington's disease. Protein inclusions form in discrete areas of the brain characteristic to the type of neurodegenerative disease, and coincide with the death of neurons in that region (e.g. spinal cord motor neurons in amyotrophic lateral sclerosis). This suggests that the process of protein misfolding leading to inclusion formation is neurotoxic, and that cell-autonomous and non-cell autonomous mechanisms that maintain protein homeostasis (proteostasis) can, at times, be insufficient to prevent protein inclusion formation in the central nervous system. The heat shock response is a pro-survival pathway induced under conditions of cellular stress that acts to maintain proteostasis through the up-regulation of heat shock proteins, a superfamily of molecular chaperones, other co-chaperones and mitotic regulators. The kinetics and magnitude of the heat shock response varies in a stress- and cell-type dependent manner. It remains to be determined if and/or how the heat shock response is activated in the different cell-types that comprise the central nervous system (e.g. neurons and astroglia) in response to protein misfolding events that precede cellular dysfunctions in neurodegenerative diseases. This is particularly relevant considering emerging evidence demonstrating the non-cell autonomous nature of amyotrophic lateral sclerosis and Huntington's disease (and other neurodegenerative diseases) and the destructive role of astroglia in disease progression. This review highlights the complexity of heat shock response activation and addresses whether neurons and glia sense and respond to protein misfolding and aggregation associated with neurodegenerative diseases, in particular Huntington's disease and amyotrophic lateral sclerosis, by inducing a pro-survival heat shock response.

Rethinking HSF1 in Stress, Development, and Organismal Health

The heat shock response (HSR) was originally discovered as a transcriptional response to elevated temperature shock and led to the identification of heat shock proteins and heat shock factor 1 (HSF1). Since then HSF1 has been shown to be important for combating other forms of environmental perturbations as well as genetic variations that cause proteotoxic stress. The HSR has long been thought to be an absolute response to conditions of cell stress and the primary mechanism by which HSF1 promotes organismal health by preventing protein aggregation and subsequent proteome imbalance. Accumulating evidence now shows that HSF1, the central player in the HSR, is regulated according to specific cellular requirements through cell-autonomous and non-autonomous signals, and directs transcriptional programs distinct from the HSR during development and in carcinogenesis. We discuss here these 'non-canonical' roles of HSF1, its regulation in diverse conditions of development, reproduction, metabolism, and aging, and posit that HSF1 serves to integrate diverse biological and pathological responses.

Regulation of heat shock transcription factors and their roles in physiology and disease

The heat shock transcription factors (HSFs) were discovered over 30 years ago as direct transcriptional activators of genes regulated by thermal stress, encoding heat shock proteins. The accepted paradigm posited that HSFs exclusively activate the expression of protein chaperones in response to conditions that cause protein misfolding by recognizing a simple promoter binding site referred to as a heat shock element. However, we now realize that the mammalian family of HSFs comprises proteins that independently or in concert drive combinatorial gene regulation events that activate or repress transcription in different contexts. Advances in our understanding of HSF structure, post-translational modifications and the breadth of HSF-regulated target genes have revealed exciting new mechanisms that modulate HSFs and shed new light on their roles in physiology and pathology. For example, the ability of HSF1 to protect cells from proteotoxicity and cell death is impaired in neurodegenerative diseases but can be exploited by cancer cells to support their growth, survival and metastasis. These new insights into HSF structure, function and regulation should facilitate the development tof new disease therapeutics to manipulate this transcription factor family.

Chaperone-Based Therapies for Disease Modification in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is characterized by the presence of pathological intracellular aggregates primarily composed of misfolded α-synuclein. This pathology implicates the molecular machinery responsible for maintaining protein homeostasis (proteostasis), including molecular chaperones, in the pathobiology of the disease. There is mounting evidence from preclinical and clinical studies that various molecular chaperones are downregulated, sequestered, depleted, or dysfunctional in PD. Current therapeutic interventions for PD are inadequate as they fail to modify disease progression by ameliorating the underlying pathology. Modulating the activity of molecular chaperones, cochaperones, and their associated pathways offers a new approach for disease modifying intervention. This review will summarize the potential of chaperone-based therapies that aim to enhance the neuroprotective activity of molecular chaperones or utilize small molecule chaperones to promote proteostasis.

A CNS-permeable Hsp90 inhibitor rescues synaptic dysfunction and memory loss in APP-overexpressing Alzheimer's mouse model via an HSF1-mediated mechanism

Induction of neuroprotective heat-shock proteins via pharmacological Hsp90 inhibitors is currently being investigated as a potential treatment for neurodegenerative diseases. Two major hurdles for therapeutic use of Hsp90 inhibitors are systemic toxicity and limited central nervous system permeability. We demonstrate here that chronic treatment with a proprietary Hsp90 inhibitor compound (OS47720) not only elicits a heat-shock-like response but also offers synaptic protection in symptomatic Tg2576 mice, a model of Alzheimer's disease, without noticeable systemic toxicity. Despite a short half-life of OS47720 in mouse brain, a single intraperitoneal injection induces rapid and long-lasting (>3 days) nuclear activation of the heat-shock factor, HSF1. Mechanistic study indicates that the remedial effects of OS47720 depend upon HSF1 activation and the subsequent HSF1-mediated transcriptional events on synaptic genes. Taken together, this work reveals a novel role of HSF1 in synaptic function and memory, which likely occurs through modulation of the synaptic transcriptome.

Heterogeneous nuclear ribonucleoprotein K inhibits heat shock-induced transcriptional activity of heat shock factor 1

When cells are exposed to heat shock and various other stresses, heat shock factor 1 (HSF1) is activated, and the heat shock response (HSR) is elicited. To better understand the molecular regulation of the HSR, we used 2D-PAGE-based proteome analysis to screen for heat shock-induced post-translationally modified cellular proteins. Our analysis revealed that two protein spots typically present on 2D-PAGE gels and containing heterogeneous nuclear ribonucleoprotein K (hnRNP K) with trioxidized Cys¹³² disappeared after the heat shock treatment and reappeared during recovery, but the total amount of hnRNP K protein remained unchanged. We next tested whether hnRNP K plays a role in HSR by regulating HSF1 and found that hnRNP K inhibits HSF1 activity, resulting in reduced expression of hsp70 and hsp27 mRNAs. hnRNP K also reduced binding affinity of HSF1 to the heat shock element by directly interacting with HSF1 but did not affect HSF1 phosphorylation-dependent activation or nuclear localization. hnRNP K lost its ability to induce these effects when its Cys¹³² was substituted with Ser, Asp, or Glu. These findings suggest that hnRNP K inhibits transcriptional activity of HSF1 by inhibiting its binding to heat shock element and that the oxidation status of Cys¹³² in hnRNP K is critical for this inhibition.

Drug-Induced HSP90 Inhibition Alleviates Pain in Monoarthritic Rats and Alters the Expression of New Putative Pain Players at the DRG

Purinergic receptors (P2XRs) have been widely associated with pain states mostly due to their involvement in neuron-glia communication. Interestingly, we have previously shown that satellite glial cells (SGC), surrounding dorsal root ganglia (DRG) neurons, become activated and proliferate during monoarthritis (MA) in the rat. Here, we demonstrate that P2X7R expression increases in ipsilateral DRG after 1 week of disease, while P2X3R immunoreactivity decreases. We have also reported a significant induction of the activating transcriptional factor 3 (ATF3) in MA. In this study, we show that ATF3 knocked down in DRG cell cultures does not affect the expression of P2X7R, P2X3R, or glial fibrillary acidic protein (GFAP). We suggest that P2X7R negatively regulates P2X3R, which, however, is unlikely mediated by ATF3. Interestingly, we found that ATF3 knockdown in vitro induced significant decreases in the heat shock protein 90 (HSP90) expression. Thus, we evaluated in vivo the involvement of HSP90 in MA and demonstrated that the HSP90 messenger RNA levels increase in ipsilateral DRG of inflamed animals. We also show that HSP90 is mostly found in a cleaved form in this condition. Moreover, administration of a HSP90 inhibitor, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), attenuated MA-induced mechanical allodynia in the first hours. The drug also reversed the HSP90 upregulation and cleavage. 17-DMAG seemed to attenuate glial activation and neuronal sensitization (as inferred by downregulation of GFAP and P2X3R in ipsilateral DRG) which might correlate with the observed pain alleviation. Our data indicate a role of HSP90 in MA pathophysiology, but further investigation is necessary to clarify the underlying mechanisms.

Shaping proteostasis at the cellular, tissue, and organismal level

The proteostasis network (PN) regulates protein synthesis, folding, transport, and degradation to maintain proteome integrity and limit the accumulation of protein aggregates, a hallmark of aging and degenerative diseases. In multicellular organisms, the PN is regulated at the cellular, tissue, and systemic level to ensure organismal health and longevity. Here we review these three layers of PN regulation and examine how they collectively maintain cellular homeostasis, achieve cell type-specific proteomes, and coordinate proteostasis across tissues. A precise understanding of these layers of control has important implications for organismal health and could offer new therapeutic approaches for neurodegenerative diseases and other chronic disorders related to PN dysfunction.

Targeting chaperones, heat shock factor-1, and unfolded protein response: Promising therapeutic approaches for neurodegenerative disorders

Protein misfolding, which is known to cause several serious diseases, is an emerging field that addresses multiple therapeutic areas. Misfolding of a disease-specific protein in the central nervous system ultimately results in the formation of toxic aggregates that may accumulate in the brain, leading to neuronal cell death and dysfunction, and associated clinical manifestations. A large number of neurodegenerative diseases in humans, including Alzheimer's, Parkinson's, Huntington's, and prion diseases, are primarily caused by protein misfolding and aggregation. Notably, the cellular system is equipped with a protein quality control system encompassing chaperones, ubiquitin proteasome system, and autophagy, as a defense mechanism that monitors protein folding and eliminates inappropriately folded proteins. As the intrinsic molecular mechanisms of protein misfolding become more clearly understood, the novel therapeutic approaches in this arena are gaining considerable interest. The present review will describe the chaperones network and different approaches as the therapeutic targets for neurodegenerative diseases. Current and emerging therapeutic approaches to combat neurodegenerative diseases, addressing the roles of molecular, chemical, and pharmacological chaperones, as well as heat shock factor-1 and the unfolded protein response, are also discussed in detail.

Nuclear inclusion bodies of mutant and wild-type p53 in cancer: a hallmark of p53 inactivation and proteostasis remodelling by p53 aggregation

Although p53 protein aggregates have been observed in cancer cell lines and tumour tissue, their impact in cancer remains largely unknown. Here, we extensively screened for p53 aggregation phenotypes in tumour biopsies, and identified nuclear inclusion bodies (nIBs) of transcriptionally inactive mutant or wild-type p53 as the most frequent aggregation-like phenotype across six different cancer types. p53-positive nIBs co-stained with nuclear aggregation markers, and shared molecular hallmarks of nIBs commonly found in neurodegenerative disorders. In cell culture, tumour-associated stress was a strong inducer of p53 aggregation and nIB formation. This was most prominent for mutant p53, but could also be observed in wild-type p53 cell lines, for which nIB formation correlated with the loss of p53's transcriptional activity. Importantly, protein aggregation also fuelled the dysregulation of the proteostasis network in the tumour cell by inducing a hyperactivated, oncogenic heat-shock response, to which tumours are commonly addicted, and by overloading the proteasomal degradation system, an observation that was most pronounced for structurally destabilized mutant p53. Patients showing tumours with p53-positive nIBs suffered from a poor clinical outcome, similar to those with loss of p53 expression, and tumour biopsies showed a differential proteostatic expression profile associated with p53-positive nIBs. p53-positive nIBs therefore highlight a malignant state of the tumour that results from the interplay between (1) the functional inactivation of p53 through mutation and/or aggregation, and (2) microenvironmental stress, a combination that catalyses proteostatic dysregulation. This study highlights several unexpected clinical, biological and therapeutically unexplored parallels between cancer and neurodegeneration. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Protein misfolding in neurodegenerative diseases: implications and strategies

A hallmark of neurodegenerative proteinopathies is the formation of misfolded protein aggregates that cause cellular toxicity and contribute to cellular proteostatic collapse. Therapeutic options are currently being explored that target different steps in the production and processing of proteins implicated in neurodegenerative disease, including synthesis, chaperone-assisted folding and trafficking, and degradation via the proteasome and autophagy pathways. Other therapies, like mTOR inhibitors and activators of the heat shock response, can rebalance the entire proteostatic network. However, there are major challenges that impact the development of novel therapies, including incomplete knowledge of druggable disease targets and their mechanism of action as well as a lack of biomarkers to monitor disease progression and therapeutic response. A notable development is the creation of collaborative ecosystems that include patients, clinicians, basic and translational researchers, foundations and regulatory agencies to promote scientific rigor and clinical data to accelerate the development of therapies that prevent, reverse or delay the progression of neurodegenerative proteinopathies.

Abnormal degradation of the neuronal stress-protective transcription factor HSF1 in Huntington's disease

Huntington's Disease (HD) is a neurodegenerative disease caused by poly-glutamine expansion in the Htt protein, resulting in Htt misfolding and cell death. Expression of the cellular protein folding and pro-survival machinery by heat shock transcription factor 1 (HSF1) ameliorates biochemical and neurobiological defects caused by protein misfolding. We report that HSF1 is degraded in cells and mice expressing mutant Htt, in medium spiny neurons derived from human HD iPSCs and in brain samples from patients with HD. Mutant Htt increases CK2α' kinase and Fbxw7 E3 ligase levels, phosphorylating HSF1 and promoting its proteasomal degradation. An HD mouse model heterozygous for CK2α' shows increased HSF1 and chaperone levels, maintenance of striatal excitatory synapses, clearance of Htt aggregates and preserves body mass compared with HD mice homozygous for CK2α'. These results reveal a pathway that could be modulated to prevent neuronal dysfunction and muscle wasting caused by protein misfolding in HD.

HSF1 Relieves Amyloid-β-Induced Cardiomyocytes Apoptosis

Accumulation of amyloid-β in organs results in a series of diseases. Heat shock transcription factor 1 (HSF1) is the master regulator of genes encoding molecular chaperones and attenuates apoptosis induced by multiple factors. However, the role of HSF1 on amyloid-β-induced apoptosis is still unknown. The present study was aimed to explore the function of HSF1 in amyloid-β-induced cardiomyocytes apoptosis. TUNEL assay and flow cytometry analysis were used to detect cell apoptosis. Phalloidin staining was used to detect cytoskeleton injury. Changes in expression levels of proteins involved in apoptosis and endoplasmic reticulum stress were measured by Western blot. In our study, amyloid-β was found to promote apoptosis, impair cytoskeleton, and induce endoplasmic reticulum stress in isolated cardiomyocytes. However, these damaging effects of amyloid-β can be relieved by over-expression of HSF1, and the protective role of HSF1 might be associated with the regulation of HSPs expressions. Results of our study suggest that over-expression of HSF1 might become a promising gene therapeutic for the treatment of heart diseases associated with amyloid-β accumulation.

Dynamic control of Hsf1 during heat shock by a chaperone switch and phosphorylation

Heat shock factor (Hsf1) regulates the expression of molecular chaperones to maintain protein homeostasis. Despite its central role in stress resistance, disease and aging, the mechanisms that control Hsf1 activity remain unresolved. Here we show that in budding yeast, Hsf1 basally associates with the chaperone Hsp70 and this association is transiently disrupted by heat shock, providing the first evidence that a chaperone repressor directly regulates Hsf1 activity. We develop and experimentally validate a mathematical model of Hsf1 activation by heat shock in which unfolded proteins compete with Hsf1 for binding to Hsp70. Surprisingly, we find that Hsf1 phosphorylation, previously thought to be required for activation, in fact only positively tunes Hsf1 and does so without affecting Hsp70 binding. Our work reveals two uncoupled forms of regulation - an ON/OFF chaperone switch and a tunable phosphorylation gain - that allow Hsf1 to flexibly integrate signals from the proteostasis network and cell signaling pathways.

DOI:http://dx.doi.org/10.7554/eLife.18638.001

Proteins are strings of amino acids that carry out crucial activities inside cells, such as harvesting energy and generating the building blocks that cells need to grow. In order to carry out their specific roles inside the cell, the proteins need to “fold” into precise three-dimensional shapes.

Protein folding is critical for life, and cells don’t leave it up to chance. Cells employ “molecular chaperones” to help proteins to fold properly. However, under some conditions – such as high temperature – proteins are more difficult to fold and the chaperones can become overwhelmed. In these cases, unfolded proteins can pile up in the cell. This leads not only to the cell being unable to work properly, but also to the formation of toxic “aggregates”. These aggregates are tangles of unfolded proteins that are hallmarks of many neurodegenerative diseases such as Alzheimer’s, Parkinson’s and amyotrophic lateral sclerosis (ALS).

Protein aggregates can be triggered by high temperature in a condition termed “heat shock”. A sensor named heat shock factor 1 (Hsf1 for short) increases the amount of chaperones following heat shock. But what controls the activity of Hsf1?

To answer this question, Zheng, Krakowiak et al. combined mathematical modelling and experiments in yeast cells. The most important finding is that the ‘on/off switch’ that controls Hsf1 is based on whether Hsf1 is itself bound to a chaperone. When bound to the chaperone, Hsf1 is turned ‘off’; when the chaperone falls off, Hsf1 turns ‘on’ and makes more chaperones; when there are enough chaperones, they once again bind to Hsf1 and turn it back ‘off’. In this way, Hsf1 and the chaperones form a feedback loop that ensures that there are always enough chaperones to keep the cell’s proteins folded.

Now that we know how Hsf1 is controlled, can we harness this understanding to tune the activity of Hsf1 without disrupting how the chaperones work? If we can activate Hsf1, we can provide cells with more chaperones. This could be a therapeutic strategy to combat neurodegenerative diseases.

DOI:http://dx.doi.org/10.7554/eLife.18638.002

The myeloid heat shock transcription factor 1/β-catenin axis regulates NLR family, pyrin domain-containing 3 inflammasome activation in mouse liver ischemia/reperfusion injury

Heat shock transcription factor 1 (HSF1) has been implicated in the differential regulation of cell stress and disease states. β-catenin activation is essential for immune homeostasis. However, little is known about the role of macrophage HSF1-β-catenin signaling in the regulation of NLRP3 inflammasome activation during ischemia/reperfusion (I/R) injury (IRI) in the liver. This study investigated the functions and molecular mechanisms by which HSF1-β-catenin signaling influenced NLRP3-mediated innate immune response in vivo and in vitro. Using a mouse model of IR-induced liver inflammatory injury, we found that mice with a myeloid-specific HSF1 knockout (HSF1^M-KO ) displayed exacerbated liver damage based on their increased serum alanine aminotransferase levels, intrahepatic macrophage/neutrophil trafficking, and proinflammatory interleukin (IL)-1β levels compared to the HSF1-proficient (HSF1^FL/FL ) controls. Disruption of myeloid HSF1 markedly increased transcription factor X-box-binding protein (XBP1), NLR family, pyrin domain-containing 3 (NLRP3), and cleaved caspase-1 expression, which was accompanied by reduced β-catenin activity. Knockdown of XBP1 in HSF1-deficient livers using a XBP1 small interfering RNA ameliorated hepatocellular functions and reduced NLRP3/cleaved caspase-1 and IL-1β protein levels. In parallel in vitro studies, HSF1 overexpression increased β-catenin (Ser552) phosphorylation and decreased reactive oxygen species (ROS) production in bone-marrow-derived macrophages. However, myeloid HSF1 ablation inhibited β-catenin, but promoted XBP1. Furthermore, myeloid β-catenin deletion increased XBP1 messenger RNA splicing, whereas a CRISPR/CRISPR-associated protein 9-mediated XBP1 knockout diminished NLRP3/caspase-1.

CONCLUSION

The myeloid HSF1-β-catenin axis controlled NLRP3 activation by modulating the XBP1 signaling pathway. HSF1 activation promoted β-catenin, which, in turn, inhibited XBP1, leading to NLRP3 inactivation and reduced I/R-induced liver injury. These findings demonstrated that HSF1/β-catenin signaling is a novel regulator of innate immunity in liver inflammatory injury and implied the therapeutic potential for management of sterile liver inflammation in transplant recipients. (Hepatology 2016;64:1683-1698).

Reactive electrophilic oxylipins trigger a heat stress-like response through HSFA1 transcription factors

Abiotic and biotic stresses are often characterized by an induction of reactive electrophile species (RES) such as the jasmonate 12-oxo-phytodienoic acid (OPDA) or the structurally related phytoprostanes. Previously, RES oxylipins have been shown massively to induce heat-shock-response (HSR) genes including HSP101 chaperones. Moreover, jasmonates have been reported to play a role in basal thermotolerance. We show that representative HSR marker genes are strongly induced by RES oxylipins through the four master regulator transcription factors HSFA1a, b, d, and e essential for short-term adaptation to heat stress in Arabidopsis. When compared with Arabidopsis seedlings treated at the optimal acclimation temperature of 37 °C, the exogenous application of RES oxylipins at 20 °C induced a much weaker induction of HSP101 at both the gene and protein expression levels which, however, was not sufficient to confer short-term acquired thermotolerance. Moreover, jasmonate-deficient mutant lines displayed a wild-type-like HSR and were not compromised in acquiring thermotolerance. Hence, the OPDA- and RES oxylipin-induced HSR is not sufficient to protect seedlings from severe heat stress but may help plants to cope better with stresses associated with protein unfolding by inducing a battery of chaperones in the absence of heat.

Ste20-like kinase, SLK, activates the heat shock factor 1 - Hsp70 pathway

Expression and activation of SLK increases during renal ischemia-reperfusion injury. When highly expressed, SLK signals via c-Jun N-terminal kinase and p38 to induce apoptosis, and it exacerbates apoptosis induced by ischemia-reperfusion injury. Overexpression of SLK in glomerular epithelial cells (GECs)/podocytes in vivo induces injury and proteinuria. In response to various stresses, cells enhance expression of chaperones or heat shock proteins (e.g. Hsp70), which are involved in the folding and maturation of newly synthesized proteins, and can refold denatured or misfolded proteins. We address the interaction of SLK with the heat shock factor 1 (HSF1)-Hsp70 pathway. Increased expression of SLK in GECs (following transfection) induced HSF1 transcriptional activity. Moreover, HSF1 transcriptional activity was increased by in vitro ischemia-reperfusion injury (chemical anoxia/recovery) and heat shock, and in both instances was amplified further by SLK overexpression. HSF1 binds to promoters of target genes, such as Hsp70 and induces their transcription. By analogy to HSF1, SLK stimulated Hsp70 expression. Hsp70 was also enhanced by anoxia/recovery and was further amplified by SLK overexpression. Induction of HSF1 and Hsp70 was dependent on the kinase activity of SLK, and was mediated via polo-like kinase-1. Transfection of constitutively active HSF1 enhanced Hsp70 expression and inhibited SLK-induced apoptosis. Conversely, the proapoptotic action of SLK was augmented by HSF1 shRNA, or the Hsp70 inhibitor, pifithrin-μ. In conclusion, increased expression/activity of SLK activates the HSF1-Hsp70 pathway. Hsp70 attenuates the primary proapoptotic effect of SLK. Modulation of chaperone expression may potentially be harnessed as cytoprotective therapy in renal cell injury.

The central role of heat shock factor 1 in synaptic fidelity and memory consolidation

Networks of neuronal synapses are the fundamental basis for making and retaining memory. Reduced synapse number and quality correlates with loss of memory in dementia. Heat shock factor 1 (HSF1), the major transcription factor regulating expression of heat shock genes, plays a central role in proteostasis, in establishing and sustaining synaptic fidelity and function, and in memory consolidation. Support for this thesis is based on these observations: (1) heat shock induces improvements in synapse integrity and memory consolidation; (2) synaptic depolarization activates HSF1; (3) activation of HSF1 alone (independent of the canonical heat shock response) augments formation of essential synaptic elements-neuroligands, vesicle transport, synaptic scaffolding proteins, lipid rafts, synaptic spines, and axodendritic synapses; (4) HSF1 coalesces and activates memory receptors in the post-synaptic dendritic spine; (5) huntingtin or α-synuclein accumulation lowers HSF1 while HSF1 lowers huntingtin and α-synuclein aggregation-a potential vicious cycle; and (6) HSF1 agonists (including physical activity) can improve cognitive function in dementia models. Thus, via direct gene expression of synaptic elements, production of HSPs that assure high protein fidelity, and activation of other neuroprotective signaling pathways, HSF1 agonists could provide breakthrough therapy for dementia-associated disease.

Selective killing of cancer cells by small molecules targeting heat shock stress response

HSF1 heat shock response has emerged as a valuable non-oncogenetic intervention point in targeted cancer therapy. Current reporter based high throughput screening has led to the discovery of several compounds or chemotypes that are effective in the growth inhibition of multiple cancer cell lines and relevant animal tumor models. However, some intrinsic limitations of reporter based assays can potentially lead to biased results. Using a previously validated high content image based assay, we performed a phenotypic screen targeting HSF1 heat shock pathway with a chemically diversified library of over 100,000 compounds. Several novel functional inhibitors of HSF1 pathway were identified with different chemotypes. Western blot analysis confirmed that selective compounds inhibit phosphorylation of HSF1, followed by reduced expression of HSP proteins. Moreover, HeLa cells stably transfected with HSF1 shRNA were more resistant to the compound treatment under lethal temperature than cells containing HSF1, validating HSF1 dependent mechanism of action. These compounds demonstrate nanomolar potency toward multiple cancer cell lines with relatively low cytotoxicity to normal cells. Further SAR and target identification study will pave the way for the potential development of next generation anticancer drugs.

Holdase activity of secreted Hsp70 masks amyloid-β42 neurotoxicity in Drosophila

Alzheimer's disease (AD) is the most prevalent of a large group of related proteinopathies for which there is currently no cure. Here, we used Drosophila to explore a strategy to block Aβ42 neurotoxicity through engineering of the Heat shock protein 70 (Hsp70), a chaperone that has demonstrated neuroprotective activity against several intracellular amyloids. To target its protective activity against extracellular Aβ42, we added a signal peptide to Hsp70. This secreted form of Hsp70 (secHsp70) suppresses Aβ42 neurotoxicity in adult eyes, reduces cell death, protects the structural integrity of adult neurons, alleviates locomotor dysfunction, and extends lifespan. SecHsp70 binding to Aβ42 through its holdase domain is neuroprotective, but its ATPase activity is not required in the extracellular space. Thus, the holdase activity of secHsp70 masks Aβ42 neurotoxicity by promoting the accumulation of nontoxic aggregates. Combined with other approaches, this strategy may contribute to reduce the burden of AD and other extracellular proteinopathies.

Diverging Novobiocin Anti-Cancer Activity from Neuroprotective Activity through Modification of the Amide Tail

Novobiocin is a natural product that binds the Hsp90 C-terminus and manifests Hsp90 inhibitory activity. Structural investigations on novobiocin led to the development of both anti-cancer and neuroprotective agents. The varied pharmacological activity manifested by these novobiocin analogs prompted the investigation of structure-function studies to identify these contradictory effects, which revealed that modifications to the amide side chain produce either anti-cancer or neuroprotective activity. Compounds that exhibit neuroprotective activity contain a short alkyl or cycloalkyl amide side chain. In contrast, anti-cancer agents contain five or more carbons, disrupt interactions between Hsp90α and Aha1, and induce the degradation of Hsp90-dependent client proteins.

Targeting the Diabetic Chaperome to Improve Peripheral Neuropathy

The chaperome constitutes a broad family of molecular chaperones and co-chaperones that facilitate the folding, refolding, and degradation of the proteome. Heat shock protein 90 (Hsp90) promotes the folding of numerous oncoproteins to aid survival of malignant phenotypes, and small molecule inhibitors of the Hsp90 chaperone complex offer a viable approach to treat certain cancers. One therapeutic attribute of this approach is the selectivity of these molecules to target high affinity oncogenic Hsp90 complexes present in tumor cells, which are absent in nontransformed cells. This selectivity has given rise to the idea that disease may contribute to forming a stress chaperome that is functionally distinct in its ability to interact with small molecule Hsp90 modulators. Consistent with this premise, modulating Hsp90 improves clinically relevant endpoints of diabetic peripheral neuropathy but has little impact in nondiabetic nerve. The concept of targeting the "diabetic chaperome" to treat diabetes and its complications is discussed.

Transcription Factor Drug Targets

Transcription factors represent the point of convergence of multiple signaling pathways within eukaryotic cells. Deregulated transcription factors contribute to the pathogenesis of a plethora of human diseases, ranging from diabetes, inflammatory disorders and cardiovascular disease to many cancers, and thus these proteins hold great therapeutic potential. Direct modulation of transcription factor function by small molecules is no longer regarded a Sisyphean task, as recent work in drug discovery has revealed that transcription factors are amenable to drug inhibition. Here in we summarize, recent advances regarding the significance of transcription factors in human diseases and we discuss emerging pharmacological strategies to modulate transcription factor function. J. Cell. Biochem. 117: 2693-2696, 2016. © 2016 Wiley Periodicals, Inc.

Self-assembly and sequence length dependence on nanofibrils of polyglutamine peptides

Huntington's disease (HD) is recognized as a currently incurable, inherited neurodegenerative disorder caused by the accumulation of misfolded polyglutamine (polyQ) peptide aggregates in neuronal cells. Yet, the mechanism by which newly formed polyQ chains interact and assemble into toxic oligomeric structures remains a critical, unresolved issue. In order to shed further light on the matter, our group elected to investigate the folding of polyQ peptides - examining glutamine repeat lengths ranging from 3 to 44 residues. To characterize these aggregates we employed a diverse array of technologies, including: nuclear magnetic resonance; circular dichroism; Fourier transform infrared spectroscopy; fluorescence resonance energy transfer (FRET), and atomic force microscopy. The data we obtained suggest that an increase in the number of glutamine repeats above 14 residues results in disordered loop structures, with different repeat lengths demonstrating unique folding characteristics. This differential folding manifests in the formation of distinct nano-sized fibrils, and on this basis, we postulate the idea of 14 polyQ repeats representing a critical loop length for neurotoxicity - a property that we hope may prove amenable to future therapeutic intervention. Furthermore, FRET measurements on aged assemblages indicate an increase in the end-to-end distance of the peptide with time, most probably due to the intermixing of individual peptide strands within the nanofibril. Further insight into this apparent time-dependent reorganization of aggregated polyQ peptides may influence future disease modeling of polyQ-related proteinopathies, in addition to directing novel clinical innovations.

Heat shock proteins in the retina: Focus on HSP70 and alpha crystallins in ganglion cell survival

Heat shock proteins (HSPs) belong to a superfamily of stress proteins that are critical constituents of a complex defense mechanism that enhances cell survival under adverse environmental conditions. Cell protective roles of HSPs are related to their chaperone functions, antiapoptotic and antinecrotic effects. HSPs' anti-apoptotic and cytoprotective characteristics, their ability to protect cells from a variety of stressful stimuli, and the possibility of their pharmacological induction in cells under pathological stress make these proteins an attractive therapeutic target for various neurodegenerative diseases; these include Alzheimer's, Parkinson's, Huntington's, prion disease, and others. This review discusses the possible roles of HSPs, particularly HSP70 and small HSPs (alpha A and alpha B crystallins) in enhancing the survival of retinal ganglion cells (RGCs) in optic neuropathies such as glaucoma, which is characterized by progressive loss of vision caused by degeneration of RGCs and their axons in the optic nerve. Studies in animal models of RGC degeneration induced by ocular hypertension, optic nerve crush and axotomy show that upregulation of HSP70 expression by hyperthermia, zinc, geranyl-geranyl acetone, 17-AAG (a HSP90 inhibitor), or through transfection of retinal cells with AAV2-HSP70 effectively supports the survival of injured RGCs. RGCs survival was also stimulated by overexpression of alpha A and alpha B crystallins. These findings provide support for translating the HSP70- and alpha crystallin-based cell survival strategy into therapy to protect and rescue injured RGCs from degeneration associated with glaucomatous and other optic neuropathies.

Heat shock factor-1 knockout enhances cholesterol 7α-hydroxylase (CYP7A1) and multidrug transporter (MDR1) gene expressions to attenuate atherosclerosis

AIMS

Stress response, in terms of activation of stress factors, is known to cause obesity and coronary heart disease such as atherosclerosis in human. However, the underlying mechanism(s) of these pathways are not known. Here, we investigated the effect of heat shock factor-1 (HSF-1) on atherosclerosis.

METHODS AND RESULTS

HSF-1 and low-density lipoprotein receptor (LDLr) double knockout (HSF-1(-/-)/LDLr(-/-)) and LDLr knockout (LDLr(-/-)) mice were fed with atherogenic western diet (WD) for 12 weeks. WD-induced weight gain and atherosclerotic lesion in aortic arch and carotid regions were reduced in HSF-1(-/-)/LDLr(-/-) mice, compared with LDLr(-/-) mice. Also, repression of PPAR-γ2 and AMPKα expression in adipose tissue, low hepatic steatosis, and lessened plasma adiponectins and lipoproteins were observed. In HSF-1(-/-)/LDLr(-/-) liver, higher cholesterol 7α-hydroxylase (CYP7A1) and multidrug transporter [MDR1/P-glycoprotein (P-gp)] gene expressions were observed, consistent with higher bile acid transport and larger hepatic bile ducts. Luciferase reporter gene assays with wild-type CYP7A1 and MDR1 promoters showed lesser luminescence than with mutant promoters (HSF-1 binding site deleted), indicating that HSF-1 binding is repressive of CYP7A1 and MDR1 gene expressions.

CONCLUSION

HSF-1 ablation not only eliminates heat shock response, but it also transcriptionally up-regulates CYP7A1 and MDR1/P-gp axis in WD-diet fed HSF-1(-/-)/LDLr(-/-) mice to reduce atherosclerosis.

Mammalian Heat Shock Response and Mechanisms Underlying Its Genome-wide Transcriptional Regulation

The heat shock response (HSR) is critical for survival of all organisms. However, its scope, extent, and the molecular mechanism of regulation are poorly understood. Here we show that the genome-wide transcriptional response to heat shock in mammals is rapid and dynamic and results in induction of several hundred and repression of several thousand genes. Heat shock factor 1 (HSF1), the "master regulator" of the HSR, controls only a fraction of heat shock-induced genes and does so by increasing RNA polymerase II release from promoter-proximal pause. Notably, HSF2 does not compensate for the lack of HSF1. However, serum response factor appears to transiently induce cytoskeletal genes independently of HSF1. The pervasive repression of transcription is predominantly HSF1-independent and is mediated through reduction of RNA polymerase II pause release. Overall, mammalian cells orchestrate rapid, dynamic, and extensive changes in transcription upon heat shock that are largely modulated at pause release, and HSF1 plays a limited and specialized role.

Promoting Neuronal Tolerance of Diabetic Stress: Modulating Molecular Chaperones

The etiology of diabetic peripheral neuropathy (DPN) involves an interrelated series of metabolic and vascular insults that ultimately contribute to sensory neuron degeneration. In the quest to pharmacologically manage DPN, small-molecule inhibitors have targeted proteins and pathways regarded as "diabetes specific" as well as others whose activity are altered in numerous disease states. These efforts have not yielded any significant therapies, due in part to the complicating issue that the biochemical contribution of these targets/pathways to the progression of DPN does not occur with temporal and/or biochemical uniformity between individuals. In a complex, chronic neurodegenerative disease such as DPN, it is increasingly appreciated that effective disease management may not necessarily require targeting a pathway or protein considered to contribute to disease progression. Alternatively, it may prove sufficiently beneficial to pharmacologically enhance the activity of endogenous cytoprotective pathways to aid neuronal tolerance to and recovery from glucotoxic stress. In pursuing this paradigm shift, we have shown that modulating the activity and expression of molecular chaperones such as heat shock protein 70 (Hsp70) may provide translational potential for the effective medical management of insensate DPN. Considerable evidence supports that modulating Hsp70 has beneficial effects in improving inflammation, oxidative stress, and glucose sensitivity. Given the emerging potential of modulating Hsp70 to manage DPN, the current review discusses efforts to characterize the cytoprotective effects of this protein and the benefits and limitations that may arise in drug development efforts that exploit its cytoprotective activity.

Purification, crystallization and X-ray diffraction analysis of the DNA-binding domain of human heat-shock factor 2

Cells respond to various proteotoxic stimuli and maintain protein homeostasis through a conserved mechanism called the heat-shock response, which is characterized by the enhanced synthesis of heat-shock proteins. This response is mediated by heat-shock factors (HSFs). Four genes encoding HSF1-HSF4 exist in the genome of mammals. In this protein family, HSF1 is the orthologue of the single HSF in lower eukaryotic organisms and is the major regulator of the heat-shock response, while HSF2, which shows low sequence homology to HSF1, serves as a developmental regulator. Increasing evidence has revealed biochemical properties and functional roles that are unique to HSF2, such as its DNA-binding preference and sumoylation patterns, which are distinct from those of HSF1. The structural basis for such differences, however, is poorly understood owing to the lack of available mammalian HSF structures. The N-terminal DNA-binding domain (DBD) is the most conserved functional module and is the only crystallizable domain in HSFs. To date, only HSF1 homologue structures from yeast and fruit fly have been determined. Along with extensive studies of the HSF family, more structural information, particularly from members with a remoter phylogenic relationship to the reported structures, e.g. HSF2, is needed in order to better understand the detailed mechanisms of HSF biology. In this work, the recombinant DBD (residues 7-112) from human HSF2 was produced in Escherichia coli and crystallized. An X-ray diffraction data set was collected to 1.32 Å resolution from a crystal belonging to space group P212121 with unit cell-parameters a = 65.66, b = 67.26, c = 93.25 Å. The data-evaluation statistics revealed good quality of the collected data, thus establishing a solid basis for the determination of the first structure at atomic resolution in this protein family.

The transcriptional coactivator PGC1α protects against hyperthermic stress via cooperation with the heat shock factor HSF1

Heat shock proteins (HSPs) are required for the clearance of damaged and aggregated proteins and have important roles in protein homeostasis. It has been shown that the heat shock transcription factor, HSF1, orchestrates the transcriptional induction of these stress-regulated chaperones; however, the coregulatory factors responsible for the enhancement of HSF1 function on these target genes have not been fully elucidated. Here, we demonstrate that the cold-inducible coactivator, PGC1α, also known for its role as a regulator of mitochondrial and peroxisomal biogenesis, thermogenesis and cytoprotection from oxidative stress, regulates the expression of HSPs in vitro and in vivo and modulates heat tolerance. Mechanistically, we show that PGC1α physically interacts with HSF1 on HSP promoters and that cells and mice lacking PGC1α have decreased HSPs levels and are more sensitive to thermal challenges. Taken together, our findings suggest that PGC1α protects against hyperthermia by cooperating with HSF1 in the induction of a transcriptional program devoted to the cellular protection from thermal insults.

Structure of human heat-shock transcription factor 1 in complex with DNA

Heat-shock transcription factor 1 (HSF1) has a central role in mediating the protective response to protein conformational stresses in eukaryotes. HSF1 consists of an N-terminal DNA-binding domain (DBD), a coiled-coil oligomerization domain, a regulatory domain and a transactivation domain. Upon stress, HSF1 trimerizes via its coiled-coil domain and binds to the promoters of heat shock protein-encoding genes. Here, we present cocrystal structures of the human HSF1 DBD in complex with cognate DNA. A comparative analysis of the HSF1 paralog Skn7 from Chaetomium thermophilum showed that single amino acid changes in the DBD can switch DNA binding specificity, thus revealing the structural basis for the interaction of HSF1 with cognate DNA. We used a crystal structure of the coiled-coil domain of C. thermophilum Skn7 to develop a model of the active human HSF1 trimer in which HSF1 embraces the heat-shock-element DNA.