hsp70: nuclear concentration during environmental stress and cytoplasmic storage during recovery

The interaction between the import carrier Hikeshi and HSP70 is modulated by heat, facilitating the nuclear import of HSP70 under heat stress conditions

Heat stress strongly triggers the nuclear localization of the molecular chaperone HSP70. Hikeshi functions as a unique nuclear import carrier of HSP70. However, how the nuclear import of HSP70 is activated in response to heat stress remains unclear. Here, we investigated the effects of heat on the nuclear import of HSP70. In vitro transport assays revealed that pretreatment of the test samples with heat facilitated the nuclear import of HSP70. Furthermore, binding of Hikeshi to HSP70 increased when temperatures rose. These results indicated that heat is one of the factors that activates the nuclear import of HSP70. Previous studies showed that the F97A mutation in Hikeshi in an extended loop induced an opening in the hydrophobic pocket and facilitated the translocation of Hikeshi through the nuclear pore complex. We found that nuclear accumulation of HSP70 occurred at a lower temperature in cells expressing the Hikeshi-F97A mutant than in cells expressing wild-type Hikeshi. Collectively, our results show that the movement of the extended loop may play an important role in the interaction of Hikeshi with both FG (phenylalanine-glycine)-nucleoporins and HSP70 in a temperature-dependent manner, resulting in the activation of nuclear import of HSP70 in response to heat stress.

Effect of dexpanthenol on cyclophosphamide-induced ovarian toxicity: a histological and molecular study in rats

RESEARCH QUESTION

Does dexpanthenol work as an effective therapeutic agent against cyclophosphamide (CYC)-induced premature ovarian failure (POF) in rats?

DESIGN

A total of 28 female Wistar Albino rats were randomly divided into four groups (n = 7 per group). The POF and POF plus dexpanthenol groups were intraperitoneally administered CYC at an initial dose of 50 mg/kg, followed by 8 mg/kg for 14 days. The dexpanthenol and POF plus dexpanthenol groups were both intraperitoneally administered dexpanthenol at a dose of 500 mg/kg/day for 15 days.

RESULTS

In the group administered CYC, the following was observed: a decrease in the ovarian index; a decrease in the numbers of primordial, primary, secondary and antral follicles; an increase in the number of corpus luteum and atretic follicles; a decrease in proliferation cell nuclear antigen immunoreactivity; a significant reduction in anti-Müllerian hormone and oestradiol levels; and an increase in serum FSH levels compared with controls. Dexpanthenol, on the other hand, reversed these effects. Quantitative reverse transcription polymerase chain reaction analyses showed that dexpanthenol increased Bcl-2, Akt1, mTOR, Nrf2 and HO-1 in CYC-induced ovarian tissues, but decreased Bax, Cas3, Hsp27, Hsp70, and Hsp90. Dexpanthenol treatment has a potential for inhibiting the intrinsic apoptotic pathway and oxidative stress levels in ovarian tissues via the downregulation of the mRNA expression of heat shock proteins and the activation of Nrf2/HO-1 pathways.

CONCLUSIONS

Our findings demonstrated that dexpanthenol is an effective agent against POF caused by CYC; however, further experimental and clinical data are needed to use it effectively.

Advances in nuclear proteostasis of metazoans

The proteostasis network and associated protein quality control (PQC) mechanisms ensure proteome functionality and are essential for cell survival. A distinctive feature of eukaryotic cells is their high degree of compartmentalization, requiring specific and adapted proteostasis networks for each compartment. The nucleus, essential for maintaining the integrity of genetic information and gene transcription, is one such compartment. While PQC mechanisms have been investigated for decades in the cytoplasm and the endoplasmic reticulum, our knowledge of nuclear PQC pathways is only emerging. Recent developments in the field have underscored the importance of spatially managing aberrant proteins within the nucleus. Upon proteotoxic stress, misfolded proteins and PQC effectors accumulate in various nuclear membrane-less organelles. Beyond bringing together effectors and substrates, the biophysical properties of these organelles allow novel PQC functions. In this review, we explore the specificity of the nuclear compartment, the effectors of the nuclear proteostasis network, and the PQC roles of nuclear membrane-less organelles in metazoans.

Multi-proteomic Biomarker Risk Scores for Predicting Risk and Guiding Therapy in Patients with Coronary Artery Disease

PURPOSE OF REVIEW

Patients with established coronary artery disease (CAD) are at high residual risk for adverse events, despite guideline-based treatments. Herein, we aimed to determine whether risk scores based on multiple circulating biomarkers that represent activation of various pathophysiologically important pathways involved in atherosclerosis and myocardial dysfunction help identify those at greatest residual risk.

RECENT FINDINGS

Numerous circulating proteins, representing dysregulation of the pathways involved in the development and stability of coronary and myocardial diseases, have been identified. When aggregated together, biomarker risk scores (BRS) more accurately stratify patients with established CAD that may help target interventions in those individuals who are at elevated risk. Moreover, intensification of guideline-based therapies has been associated with parallel improvements in both BRS and outcomes, indicating that these risk scores may be employed clinically to target therapy. Multi-protein BRS are predictive of risk, independent of, and in addition to traditional risk factor assessments in patients with CAD. Those with elevated risk may benefit from optimization of therapies, and improvements in the BRS will identify those with improved outcomes.

Nuclear import carrier Hikeshi cooperates with HSP70 to promote murine oligodendrocyte differentiation and CNS myelination

Dysregulation of factors in nucleocytoplasmic transport is closely linked to neural developmental diseases. Mutation in Hikeshi, encoding a nonconventional nuclear import carrier of heat shock protein 70 family (HSP70s), leads to inherited leukodystrophy; however, the pathological mechanisms remain elusive. Here, we showed that Hikeshi is essential for central nervous system (CNS) myelination. Deficiency of Hikeshi, which is observed in inherited leukodystrophy patients, resulted in murine oligodendrocyte maturation arrest. Hikeshi is required for nuclear translocation of HSP70s upon differentiation. Nuclear-localized HSP70 promotes murine oligodendrocyte differentiation and remyelination after white matter injury. Mechanistically, HSP70s interacted with SOX10 in the nucleus and protected it from E3 ligase FBXW7-mediated ubiquitination degradation. Importantly, we discovered that Hikeshi-dependent hyperthermia therapy, which induces nuclear import of HSP70s, promoted oligodendrocyte differentiation and remyelination following in vivo demyelinating injury. Overall, these findings demonstrate that Hikeshi-mediated nuclear translocation of HSP70s is essential for myelinogenesis and provide insights into pathological mechanisms of Hikeshi-related leukodystrophy.

Genomic loss of the HSP70cA gene in the vertebrate lineage

Metazoan 70 kDa heat shock protein (HSP70) genes have been classified into four lineages: cytosolic A (HSP70cA), cytosolic B (HSP70cB), endoplasmic reticulum (HSP70er), and mitochondria (HSP70m). Because previous studies have identified no HSP70cA genes in vertebrates, we hypothesized that this gene was lost on the evolutionary path to vertebrates. To test this hypothesis, the present study conducted a comprehensive database search followed by phylogenetic and synteny analyses. HSP70cA genes were found in invertebrates and in two of the three subphyla of Chordata, Cephalochordata (lancelets) and Tunicata (tunicates). However, no HSP70cA gene was found in the genomes of Craniata (another subphylum of Chordata; lamprey, hagfish, elephant shark, and coelacanth), suggesting the loss of the HSP70cA gene in the early period of vertebrate evolution. Synteny analysis using available genomic resources indicated that the synteny around the HSP70 genes was generally conserved between tunicates but was largely different between tunicates and lamprey. These results suggest the presence of dynamic chromosomal rearrangement in early vertebrates that possibly caused the loss of the HSP70cA gene in the vertebrate lineage.

Nuclear proteostasis imbalance in laminopathy-associated premature aging diseases

Laminopathies are a group of rare genetic disorders with heterogeneous clinical phenotypes such as premature aging, cardiomyopathy, lipodystrophy, muscular dystrophy, microcephaly, epilepsy, and so on. The cellular phenomena associated with laminopathy invariably show disruption of nucleoskeleton of lamina due to deregulated expression, localization, function, and interaction of mutant lamin proteins. Impaired spatial and temporal tethering of lamin proteins to the lamina or nucleoplasmic aggregation of lamins are the primary molecular events that can trigger nuclear proteotoxicity by modulating differential protein-protein interactions, sequestering quality control proteins, and initiating a cascade of abnormal post-translational modifications. Clearly, laminopathic cells exhibit moderate to high nuclear proteotoxicity, raising the question of whether an imbalance in nuclear proteostasis is involved in laminopathic diseases, particularly in diseases of early aging such as HGPS and laminopathy-associated premature aging. Here, we review nuclear proteostasis and its deregulation in the context of lamin proteins and laminopathies.

Suboptimal Mitochondrial Activity Facilitates Nuclear Heat Shock Responses for Proteostasis and Genome Stability

Thermal stress induces dynamic changes in nuclear proteins and relevant physiology as a part of the heat shock response (HSR). However, how the nuclear HSR is fine-tuned for cellular homeostasis remains elusive. Here, we show that mitochondrial activity plays an important role in nuclear proteostasis and genome stability through two distinct HSR pathways. Mitochondrial ribosomal protein (MRP) depletion enhanced the nucleolar granule formation of HSP70 and ubiquitin during HSR while facilitating the recovery of damaged nuclear proteins and impaired nucleocytoplasmic transport. Treatment of the mitochondrial proton gradient uncoupler masked MRP-depletion effects, implicating oxidative phosphorylation in these nuclear HSRs. On the other hand, MRP depletion and a reactive oxygen species (ROS) scavenger non-additively decreased mitochondrial ROS generation during HSR, thereby protecting the nuclear genome from DNA damage. These results suggest that suboptimal mitochondrial activity sustains nuclear homeostasis under cellular stress, providing plausible evidence for optimal endosymbiotic evolution via mitochondria-to-nuclear communication.

Cytoplasmic Hsp70s promote EcR transport into the nucleus by responding to various stimuli

Metamorphosis is one of the most important physiological processes in insects, which is coordinated by juvenile hormone (JH) and 20-hydroxyecdysone (20E). Ecdysone receptor (EcR) is a steroid receptor (SR), which usually presents in cytoplasm and transfers into nucleus after binding to 20E. Heat shock proteins (Hsps) are suggested to be important members of the SR complex. However, their role in nucleocytoplasmic shuttle of the EcR remains unclear. In the present study, we found that apoptozole (Hsp70 inhibitor) suppressed the larval molting by decreasing the expression of ecdysone signaling genes. Two cytoplasmic (Cy) Hsp70s (Hsp72 and Hsp73) interacted with both EcR and ultraspiracle (USP, the heterodimer partner of EcR). By immunohistochemistry experiments, we revealed that CyHsp70 co-localized with EcR in the cytoplasm, and that both apoptozole and interfering of CyHsp70 significantly inhibited the process of EcR entering the nucleus under 20E induction, while reducing the expression of ecdysone signaling genes. Interestingly, the nuclear localization of EcR was also promoted by two other stimuli, including JH and heat stress, and this promotion was inhibited by apoptozole. This implies that various stimuli can induce EcR entry into the nucleus, and that this process is mediated by CyHsp70. Curiously, neither JH nor heat stress activated the ecdysone signaling genes; instead, they have a significant inhibitory effect on them. Taken together, it seems that Cytoplasmic Hsp70s promote EcR transport into the nucleus by responding to various stimuli, and that the biological effects of various stimuli passing through the EcR are different. Thus, our data provide a new viewpoint to understand the mechanism of nucleocytoplasmic shuttle of EcR.

Nuclear and cytoplasmic spatial protein quality control is coordinated by nuclear-vacuolar junctions and perinuclear ESCRT

Effective protein quality control (PQC), essential for cellular health, relies on spatial sequestration of misfolded proteins into defined inclusions. Here we reveal the coordination of nuclear and cytoplasmic spatial PQC. Cytoplasmic misfolded proteins concentrate in a cytoplasmic juxtanuclear quality control compartment, while nuclear misfolded proteins sequester into an intranuclear quality control compartment (INQ). Particle tracking reveals that INQ and the juxtanuclear quality control compartment converge to face each other across the nuclear envelope at a site proximal to the nuclear-vacuolar junction marked by perinuclear ESCRT-II/III protein Chm7. Strikingly, convergence at nuclear-vacuolar junction contacts facilitates VPS4-dependent vacuolar clearance of misfolded cytoplasmic and nuclear proteins, the latter entailing extrusion of nuclear INQ into the vacuole. Finding that nuclear-vacuolar contact sites are cellular hubs of spatial PQC to facilitate vacuolar clearance of nuclear and cytoplasmic inclusions highlights the role of cellular architecture in proteostasis maintenance.

Heat stress delays detoxification of phenanthrene in the springtail Folsomia candida

Climate change has intensified the occurrence of heat waves, resulting in organisms being exposed to thermal and chemical stress at the same time. The effects of mild heat shock combined with sublethal concentrations of phenanthrene (PHE) on defense mechanisms in springtails Folsomia candida were investigated. The transcription of Heat Shock Protein 70 (HSP70) was significantly upregulated by heat shock but tended to reach the control levels after 42 h of recovery. The transcription of cytochrome P450 3A13 (CYP3A13) was upregulated 3-13 fold by PHE but suppressed by heat shock. The suppression by heat shock might contribute to the reduced detoxification of PHE during high-temperature exposure. In line with this, we found that the internal PHE concentration was approximately 70% higher in heat-shocked springtails than in animals kept at control temperature. In general, the transcription of genes encoding enzymes of detoxification phase Ⅱ (glutathione S-transferase 3) and phase Ⅲ (ABC transporter 1) and the activity of antioxidant defense enzymes (superoxide dismutase and catalase) were less influenced than genes encoding phase I detoxification mechanisms (CYP3A13). These results indicate that heat shock delays the detoxification of PHE in springtails.

The hsp70 new functions as a regulator of reproduction both female and male in Ophraella communa

Heat shock proteins (Hsps) function as molecular chaperones that enable organisms to withstand stress and maintain normal life activities. In this study, we identified heat shock protein 70 (encoded by hsp70), which exhibits a higher expression in the mature male testis than in the unmature testis of Ophraella communa. Tissue expression profile revealed that Ochsp70 levels in males were highest in the testis, whereas those in females were highest in the head. Moreover, the expression of Ochsp70 was found to be significantly induced in female bursa copulatrix after mating. Double-stranded RNA dsOchsp70 was injected into males to performance RNA interference, which significantly decreased the male Ochsp70 expression levels within 20 d post-injection, whereas no effect was observed on the Ochsp70 expression level in the females after mating with dsOchsp70-injected males. However, significant downregulation of female fertility was marked simultaneously. Furthermore, knockdown of female Ochsp70 expression also led to a significant reduction in fertility. Finally, comparative transcriptomic analysis identified glucose dehydrogenase and insulin-like growth factor binding protein as putative downstream targets of Ochsp70. Overall, we deduced that Ochsp70 is an indispensable gene and a potential male mating factor in O. communa, which regulates reproduction.

Elevation of major constitutive heat shock proteins is heat shock factor independent and essential for establishment and growth of Lgl loss and Yorkie gain-mediated tumors in Drosophila

Cancer cells generally overexpress heat shock proteins (Hsps), the major components of cellular stress response, to overcome and survive the diverse stresses. However, the specific roles of Hsps in initiation and establishment of cancers remain unclear. Using loss of Lgl-mediated epithelial tumorigenesis in Drosophila, we induced tumorigenic somatic clones of different genetic backgrounds to examine the temporal and spatial expression and roles of major heat shock proteins in tumor growth. The constitutively expressed Hsp83, Hsc70 (heat shock cognate), Hsp60 and Hsp27 show elevated levels in all cells of the tumorigenic clone since early stages, which persists till their transformation. However, the stress-inducible Hsp70 is expressd only in a few cells at later stage of established tumorous clones that show high F-actin aggregation. Intriguingly, levels of heat shock factor (HSF), the master regulator of Hsps, remain unaltered in these tumorous cells and its down-regulation does not affect tumorigenic growth of lgl- clones overexpressing Yorkie, although down-regulation of Hsp83 prevents their survival and growth. Interestingly, overexpression of HSF or Hsp83 in lgl- cells makes them competitively successful in establishing tumorous clones. These results show that the major constitutively expressed Hsps, but not the stress-inducible Hsp70, are involved in early as well as late stages of epithelial tumors and their elevated expression in lgl- clones co-overexpressing Yorkie is independent of HSF.

A biosensor of protein foldedness identifies increased "holdase" activity of chaperones in the nucleus following increased cytosolic protein aggregation

Chaperones and other quality control machinery guard proteins from inappropriate aggregation, which is a hallmark of neurodegenerative diseases. However, how the systems that regulate the 'foldedness' of the proteome remain buffered under stress conditions and in different cellular compartments remains incompletely understood. In this study, we applied a FRET-based strategy to explore how well quality control machinery protects against the misfolding and aggregation of "bait" biosensor proteins, made from the prokaryotic ribonuclease barnase, in the nucleus and cytosol of HEK293T cells. We found those barnase biosensors prone to misfolding, were less engaged by quality control machinery and more prone to inappropriate aggregation in the nucleus as compared to the cytosol, and that these effects could be regulated by chaperone Hsp70-related machinery. Furthermore, aggregation of mutant huntingtin exon 1 protein (Httex1) in the cytosol appeared to outcompete and thus prevented the engagement of quality control machinery with the biosensor in the cytosol. This effect correlated with reduced levels of DNAJB1 and HSPA1A chaperones in the cell outside those sequestered to the aggregates, particularly in the nucleus. Unexpectedly, we found Httex1 aggregation also increased the apparent engagement of the barnase biosensor with quality control machinery in the nucleus suggesting an independent implementation of 'holdase' activity of chaperones other than DNAJB1 and HSPA1A. Collectively these results suggest that proteostasis stress can trigger a rebalancing of chaperone abundance in different subcellular compartments through a dynamic network involving different chaperone-client interactions.

Lack of Hikeshi activates HSF1 activity under normal conditions and disturbs the heat-shock response

Hikeshi mediates the nuclear import of the molecular chaperone HSP70 under heat-shock (acute heat stress) conditions, which is crucial for recovery from cellular damage. The cytoplasmic function of HSP70 is well studied, but its nuclear roles, particularly under nonstressed conditions, remain obscure. Here, we show that Hikeshi regulates the nucleocytoplasmic distribution of HSP70 not only under heat-shock conditions but also under nonstressed conditions. Nuclear HSP70 affects the transcriptional activity of HSF1 and nuclear proteostasis under nonstressed conditions. Depletion of Hikeshi induces a reduction in nuclear HSP70 and up-regulation of the mRNA expression of genes regulated by HSF1 under nonstressed conditions. In addition, the heat-shock response is impaired in Hikeshi-knockout cells. Our results suggest that HSF1 transcriptional activity is tightly regulated by nuclear HSP70 because nuclear-localized Hsp70 effectively suppresses transcriptional activity in a dose-dependent manner. Furthermore, the cytotoxicity of nuclear pathologic polyglutamine proteins was increased by Hikeshi depletion. Thus, proper nucleocytoplasmic distribution of HSP70, mediated by Hikeshi, is required for nuclear proteostasis and adaptive response to heat shock.

A Census of Hsp70-Mediated Proteome Solubility Changes upon Recovery from Heat Stress

Eukaryotic cells respond to heat shock through several regulatory processes including upregulation of stress responsive chaperones and reversible shutdown of cellular activities through formation of protein assemblies. However, the underlying regulatory mechanisms of the recovery of these heat-induced protein assemblies remain largely elusive. Here, we measured the proteome abundance and solubility changes during recovery from heat shock in the mouse Neuro2a cell line. We found that prefoldins and translation machinery are rapidly down-regulated as the first step in the heat shock response. Analysis of proteome solubility reveals that a rapid mobilization of protein quality control machineries, along with changes in cellular energy metabolism, translational activity, and actin cytoskeleton are fundamental to the early stress responses. In contrast, longer term adaptation to stress involves renewal of core cellular components. Inhibition of the Hsp70 family, pivotal for the heat shock response, selectively and negatively affects the ribosomal machinery and delays the solubility recovery of many nuclear proteins. ProteomeXchange: PXD030069.

Comprehensive Profiling of Paper Mulberry (Broussonetia papyrifera) Crotonylome Reveals the Significance of Lysine Crotonylation in Young Leaves

Lysine crotonylation is a newly discovered and reversible posttranslational modification involved in various biological processes, especially metabolism regulation. A total of 5159 lysine crotonylation sites in 2272 protein groups were identified. Twenty-seven motifs were found to be the preferred amino acid sequences for crotonylation sites. Functional annotation analyses revealed that most crotonylated proteins play important roles in metabolic processes and photosynthesis. Bioinformatics analysis suggested that lysine crotonylation preferentially targets a variety of important biological processes, including ribosome, glyoxylate and dicarboxylate metabolism, carbon fixation in photosynthetic organisms, proteasome and the TCA cycle, indicating lysine crotonylation is involved in the common mechanism of metabolic regulation. A protein interaction network analysis revealed that diverse interactions are modulated by protein crotonylation. These results suggest that lysine crotonylation is involved in a variety of biological processes. HSP70 is a crucial protein involved in protecting plant cells and tissues from thermal or abiotic stress responses, and HSP70 protein was found to be crotonylated in paper mulberry. This systematic analysis provides the first comprehensive analysis of lysine crotonylation in paper mulberry and provides important resources for further study on the regulatory mechanism and function of the lysine crotonylated proteome.

Microarray-Based Screening of Putative HSP90 Inhibitors Predicted and Isolated from Microorganisms

Protein microarrays are useful tools for detecting the presence of a target where different prey and bait combinations exist. Here we describe the extended application for a functional target-oriented screening assay with full length Heat shock proteins (HSPs ) for the identification of novel compounds.

The interaction of heat shock proteins with cellular membranes: a historical perspective

The interaction of heat shock proteins (HSP) with cellular membranes has been an enigmatic process, initially observed by morphological studies, inferred during the purification of HSP70s, and confirmed after the detection of these proteins on the surface of cancer cells and their insertion into artificial lipid bilayers. Today, the association of several HSP with lipid membranes is well established. However, the mechanisms for membrane insertion have been elusive. There is conclusive evidence indicating that HSP70s have a great selectivity for negatively charged phospholipids, whereas other HSP have a broader spectrum of lipid specificity. HSP70 also oligomerizes upon membrane insertion, forming ion conductance channels. The functional role of HSP70 lipid interactions appears related to membrane stabilization that may play a role during cell membrane biogenesis. They could also play a role as membrane chaperones as well as during endocytosis, microautophagy, and signal transduction. Moreover, HSP membrane association is a key component in the extracellular export of these proteins. The presence of HSP70 on the surface of cancer cells and its interaction with lysosome membranes have been envisioned as potential therapeutic targets. Thus, the biology and function of HSP membrane association are reaching a new level of excitement. This review is an attempt to preserve the recollection of the pioneering contributions of many investigators that have participated in this endeavor.

Distinct Gene Expression Patterns of Two Heat Shock Protein 70 Members During Development, Diapause, and Temperature Stress in the Freshwater Crustacean Daphnia magna

Dormancy is a lifecycle delay that allows organisms to escape suboptimal environmental conditions. As a genetically programmed type of dormancy, diapause is usually accompanied by metabolic depression and enhanced tolerance toward adverse environmental factors. However, the drivers and regulators that steer an organism’s development into a state of suspended animation to survive environmental stress have not been fully uncovered. Heat shock proteins 70 (HSP70s), which are often produced in response to various types of stress, have been suggested to play a role in diapause. Considering the diversity of the Hsp70 family, different family members may have different functions during diapause. In the present study, we demonstrate the expression of two hsp70 genes (A and B together with protein localization of B) throughout continuous and diapause interrupted development of Daphnia magna. Before and after diapause, the expression of Dmhsp70-A is low. Only shortly before diapause and during diapause, Dmhsp70-A is significantly upregulated and may therefore be involved in diapause preparation and maintenance. In contrast, Dmhsp70-B is expressed only in developing embryos but not in diapausing embryos. During continuous development, the protein of this Hsp70 family member is localized in the cytosol. When we expose both embryo types to heat stress, expression of both hsp70 genes increases only in developing embryos, and the protein of family member B is translocated to the nucleus. In this stress formation, this protein provides effective protection of nucleoplasmic DNA. As we also see this localization in diapausing embryos, it seems that Daphnia embryo types share a common subcellular strategy when facing dormancy or heat shock, i.e., they protect their DNA by HSP70B nuclear translocation. Our study underlines the distinctive roles that different Hsp70 family members play throughout continuous and diapause interrupted development.

Heat therapy: mechanistic underpinnings and applications to cardiovascular health

Cardiovascular diseases (CVD) are the leading cause of death worldwide, and novel therapies are drastically needed to prevent or delay the onset of CVD to reduce the societal and healthcare burdens associated with these chronic diseases. One such therapy is "heat therapy," or chronic, repeated use of hot baths or saunas. Although using heat exposure to improve health is not a new concept, it has received renewed attention in recent years as a growing number of studies have demonstrated robust and widespread beneficial effects of heat therapy on cardiovascular health. Here, we review the existing literature, with particular focus on the molecular mechanisms that underscore the cardiovascular benefits of this practice.

Direct exposure to mild heat stress stimulates cell viability and heat shock protein expression in primary cultured broiler fibroblasts

Fibroblasts produce collagen which is mainly essential for repairing tissue damage and maintaining the structural integrity of tissues. However, studies have given scientific evidence about harmful effect of thermal manipulation in fibroblast. Therefore, the aim of this study was to determine the mild heat stress temperature which increased broiler fibroblast viability. The experiment was divided into two groups (37 °C and 41 °C), and each group was divided into five subgroups based on different incubation times (6 h, 12 h, 24 h, 48 h, and 72 h) with three replications. In experimental group (41 °C), fibroblast viability increased significantly in 12 h but decreased in 72 h compared with control (37 °C). At 41 °C, live cell increased significantly in 24 h and then declined in 48 h as well as 72 h than control. Moreover, the S phase lengthened in shorter incubation time of experimental group compared with control. Protein and mRNA (HSP70, HSP60, and HSP47) expressions were significantly higher at 41 °C compared with 37 °C, but at the end of the experiment, HSP expression level was higher in both groups. Finally, this study recommended 41 °C as a mild heat stress temperature for increasing broiler fibroblast viability.

The Nucleolus and PARP1 in Cancer Biology

The nucleolus has been known for a long time to fulfill crucial functions in ribosome biogenesis, of which cancer cells can become addicted to in order to produce sufficient amounts of proteins for cell proliferation. Recently, the nucleolus has emerged as a central regulatory hub in many other cancer-relevant processes, including stress sensing, DNA damage response, cell cycle control, and proteostasis. This fostered the idea that nucleolar processes can be exploited in cancer therapy. Interestingly, a significant proportion of poly(ADP-ribose) polymerase 1 (PARP1) molecules are localized in the nucleolus and PARP1 also plays crucial roles in many processes that are important in cancer biology, including genome maintenance, replication, transcription, and chromatin remodeling. Furthermore, during the last years, PARP1 came into focus in oncology since it represents a promising target of pharmacological PARP inhibitors in various types of cancers. Here, we provide an overview of our current understanding on the role of PARP1 in nucleolar functions and discuss potential implications in cancer biology and therapy.

Measurements of Physiological Stress Responses in C. Elegans

Organisms are often exposed to fluctuating environments and changes in intracellular homeostasis, which can have detrimental effects on their proteome and physiology. Thus, organisms have evolved targeted and specific stress responses dedicated to repair damage and maintain homeostasis. These mechanisms include the unfolded protein response of the endoplasmic reticulum (UPR^ER), the unfolded protein response of the mitochondria (UPR^MT), the heat shock response (HSR), and the oxidative stress response (OxSR). The protocols presented here describe methods to detect and characterize the activation of these pathways and their physiological consequences in the nematode, C. elegans. First, the use of pathway-specific fluorescent transcriptional reporters is described for rapid cellular characterization, drug screening, or large-scale genetic screening (e.g., RNAi or mutant libraries). In addition, complementary, robust physiological assays are described, which can be used to directly assess sensitivity of animals to specific stressors, serving as functional validation of the transcriptional reporters. Together, these methods allow for rapid characterization of the cellular and physiological effects of internal and external proteotoxic perturbations.

Membrane-Associated Heat Shock Proteins in Oncology: From Basic Research to New Theranostic Targets

Heat shock proteins (HSPs) constitute a large family of conserved proteins acting as molecular chaperones that play a key role in intracellular protein homeostasis, regulation of apoptosis, and protection from various stress factors (including hypoxia, thermal stress, oxidative stress). Apart from their intracellular localization, members of different HSP families such as small HSPs, HSP40, HSP60, HSP70 and HSP90 have been found to be localized on the plasma membrane of malignantly transformed cells. In the current article, the role of membrane-associated molecular chaperones in normal and tumor cells is comprehensively reviewed with implications of these proteins as plausible targets for cancer therapy and diagnostics.

Expression of Heat Shock Protein 70 Is Insufficient To Extend Drosophila melanogaster Longevity

It has been known for over 20 years that Drosophila melanogaster flies with twelve additional copies of the hsp70 gene encoding the 70 kD heat shock protein lives longer after a non-lethal heat treatment. Since the heat treatment also induces the expression of additional heat shock proteins, the biological effect can be due either to HSP70 acting alone or in combination. This study used the UAS/GAL4 system to determine whether hsp70 is sufficient to affect the longevity and the resistance to thermal, oxidative or desiccation stresses of the whole organism. We observed that HSP70 expression in the nervous system or muscles has no effect on longevity or stress resistance but ubiquitous expression reduces the life span of males. We also observed that the down-regulation of hsp70 using RNAi did not affect longevity.

The Nuclear and DNA-Associated Molecular Chaperone Network

Maintenance of a healthy and functional proteome in all cellular compartments is critical to cell and organismal homeostasis. Yet, our understanding of the proteostasis process within the nucleus is limited. Here, we discuss the identified roles of the major molecular chaperones Hsp90, Hsp70, and Hsp60 with client proteins working in diverse DNA-associated pathways. The unique challenges facing proteins in the nucleus are considered as well as the conserved features of the molecular chaperone system in facilitating DNA-linked processes. As nuclear protein inclusions are a common feature of protein-aggregation diseases (e.g., neurodegeneration), a better understanding of nuclear proteostasis is warranted.

The nucleolus functions as a phase-separated protein quality control compartment

The nuclear proteome is rich in stress-sensitive proteins, which suggests that effective protein quality control mechanisms are in place to ensure conformational maintenance. We investigated the role of the nucleolus in this process. In mammalian tissue culture cells under stress conditions, misfolded proteins entered the granular component (GC) phase of the nucleolus. Transient associations with nucleolar proteins such as NPM1 conferred low mobility to misfolded proteins within the liquid-like GC phase, avoiding irreversible aggregation. Refolding and extraction of proteins from the nucleolus during recovery from stress was Hsp70-dependent. The capacity of the nucleolus to store misfolded proteins was limited, and prolonged stress led to a transition of the nucleolar matrix from liquid-like to solid, with loss of reversibility and dysfunction in quality control. Thus, we suggest that the nucleolus has chaperone-like properties and can promote nuclear protein maintenance under stress.

Expression and localization of heat-shock proteins during skeletal muscle cell proliferation and differentiation and the impact of heat stress

Skeletal myogenesis is a coordinated sequence of events associated with dramatic changes in cell morphology, motility, and metabolism, which causes cellular stress and alters proteostasis. Chaperones, such as heat-shock proteins (HSPs), play important roles in limiting cellular stresses and maintaining proteostasis, but whether HSPs are specifically involved in myogenesis is not well understood. Here, we characterized gene and protein expression and subcellular localization of various HSPs in proliferating C2C12 myoblasts and differentiating myotubes under control conditions and in response to heat stress. Hsp25, Hsp40, and Hsp60 protein expression declined by 48, 35, and 83%, respectively, during differentiation. In contrast, Hsp70 protein levels doubled during early differentiation. Hsp25 was predominantly localized to the cytoplasm of myoblasts and myotubes but formed distinct aggregates in perinuclear spaces of myoblasts after heat-shock. Hsp40 was distributed diffusely throughout the cytoplasm and nucleus and, after heat-shock, translocated to the nucleus of myoblasts but formed aggregates in myotubes. Hsp60 localized to the perinuclear space in myoblasts but was distributed more diffusely across the cytoplasm in myotubes. Hsp70 was expressed diffusely throughout the cytoplasm and nucleus and translocated to the nucleus after heat-shock in myoblasts, but not in myotubes. Hsp90 was expressed diffusely across the cytoplasm in both myoblasts and myotubes under control conditions and did not change in response to heat-shock. These findings reveal distinct and different roles for HSPs in the regulation of myogenic cell proliferation and differentiation.

Description of strongly heat-inducible heat shock protein 70 transcripts from Baikal endemic amphipods

Heat shock proteins/cognates 70 are chaperones essential for proper protein folding. This protein family comprises inducible members (Hsp70s) with expression triggered by the increased concentration of misfolded proteins due to protein-destabilizing conditions, as well as constitutively expressed cognate members (Hsc70s). Previous works on non-model amphipod species Eulimnogammarus verrucosus and Eulimnogammarus cyaneus, both endemic to Lake Baikal in Eastern Siberia, have only revealed a constitutively expressed form, expression of which was moderately further induced by protein-destabilizing conditions. Here we describe heat-inducible hsp70s in these species. Contrary to the common approach of using sequence similarity with hsp/hsc70 of a wide spectrum of organisms and some characteristic features, such as absence of introns within genes and presence of heat shock elements in their promoter areas, the present study is based on next-generation sequencing for the studied or related species followed by differential expression analysis, quantitative PCR validation and detailed investigation of the predicted polypeptide sequences. This approach allowed us to describe a novel type of hsp70 transcripts that overexpress in response to heat shock. Moreover, we propose diagnostic sequence features of this Hsp70 type for amphipods. Phylogenetic comparisons with different types of Hsp/Hsc70s allowed us to suggest that the hsp/hsc70 gene family in Amphipoda diversified into cognate and heat-inducible paralogs independently from other crustaceans. Thus, the cognate and inducible hsp70 types in distant taxa may not be recognized by sequence similarity.

Molecular basis for efficacy of Guduchi and Madhuyashti feeding on different environmental stressors in Drosophila

Stressors of different kinds adversely affect life history parameters like growth, development, and reproduction. Organisms overcome the negative impact of environmental stressors and strive to reach a tolerant state through genetic and metabolic activities. Ayurvedic formulations are reported to have life trait benefitting properties which improve capacity to withstand stress and tolerate adverse conditions. Guduchi (Tinospora cordifolia) and Madhuyashti (Glycirrhiza glabra) Ayurvedic formulations are known to have immunomodulatory, intellect promoting, and adaptogenic properties, thus favoring good health and healthy aging. Present study investigates the efficacy of Guduchi and Madhuyashti in providing tolerance to different stresses and the underlying mechanisms using the Drosophila model. Drosophila larvae/flies fed on Guduchi or Madhuyashti were better thermo-protected, which correlated with increased expression of heat shock genes even without the heat shock. Guduchi or Madhuyashti feeding also increased antimicrobial peptide expression, thus providing better tolerance to pathogenic assaults. Feeding on Guduchi- or Madhuyashti- supplemented food also enhanced starvation and desiccation tolerance. However, neither of these formulations provided beneficial effects when grown under crowded conditions or when exposed to oxidative stressors.

Characterization of three heat shock protein 70 genes from Liriomyza trifolii and expression during thermal stress and insect development

Heat shock proteins (HSPs) participate in diverse physiological processes in insects, and HSP70 is one of the most highly conserved proteins in the HSP family. In this study, full-length cDNAs of three HSP70 genes (Lthsc70, Lthsp701, and Lthsp702) were cloned and characterized from Liriomyza trifolii, an important invasive pest of vegetable crops and horticultural crops worldwide. These three HSP70s exhibited signature sequences and motifs that are typical of the HSP70 family. The expression patterns of the three Lthsp70s during temperature stress and in different insect development stages were studied by real-time quantitative PCR. Lthsp701 was strongly induced by high- and low-temperature stress, but Lthsc70 and Lthsp702 were not very sensitive to temperature changes. All three Lthsp70s were expressed during insect development stages, but the expression patterns were quite different. The expression of Lthsc70 and Lthsp702 showed significant differences in expression during leafminer development; Lthsc70 was most highly expressed in female adults, whereas Lthsp702 was abundantly expressed in larvae and prepupae. Lthsp701 expression was not significantly different among leafminer stages. These results suggest that functional differentiation within the LtHSP70 subfamily has occurred in response to thermal stress and insect development.

Quiescent Human Mesenchymal Stem Cells Are More Resistant to Heat Stress than Cycling Cells

Quiescence is the prevailing state of many cell types under homeostatic conditions. Yet, surprisingly, little is known about how quiescent cells respond to environmental challenges. The aim of the present study is to compare stress responses of cycling and quiescent mesenchymal stem cells (MSC). Human endometrial mesenchymal cells (eMSС) were employed as adult stem cells. eMSC quiescence was modeled by serum starvation. Sublethal heat shock (HS) was used as a stress factor. Both quiescent and cycling cells were heated at 45°C for 30 min and then returned to standard culture conditions for their recovery. HS response was monitored by DNA damage response, stress-induced premature senescence (SIPS), cell proliferation activity, and oxidative metabolism. It has been found that quiescent cells repair DNA more rapidly, resume proliferation, and undergo SIPS less than proliferating cells. HS-enforced ROS production in heated cycling cells was accompanied with increased expression of genes regulating redox-active proteins. Quiescent cells exposed to HS did not intensify the ROS production, and genes involved in antioxidant defense were mostly silent. Altogether, the results have shown that quiescent cells are more resistant to heat stress than cycling cells. Next-generation sequencing (NGS) demonstrates that HS-survived cells retain differentiation capacity and do not exhibit signs of spontaneous transformation.

Nuclear Accumulation of HSP70 in Mouse Skeletal Muscles in Response to Heat Stress, Aging, and Unloading With or Without Reloading

The purpose of this study was to investigate the nuclear accumulation of heat shock protein 70 (HSP70), a molecular chaperonin in mouse skeletal muscle in response to aging, heat stress, and hindlimb unloading with or without reloading. Profiles of HSP70-specific nuclear transporter Hikeshi in skeletal muscles were also evaluated. Heat stress-associated nuclear accumulation of HSP70 was observed in slow soleus (SOL) and fast plantaris (PLA) muscles of young (10-week-old) mice. Mean nuclear expression level of HSP70 in slow medial gastrocnemius (MGAS) and PLA muscles of aged (100-week-old) mice increased ~4.8 and ~1.7 times, compared to that of young (10-week-old) mice. Reloading following 2-week hindlimb unloading caused accumulation of HSP70 in myonuclei in MGAS and PLA of young mice ( p < 0.05). However, reloading-associated nuclear accumulation of HSP70 was not observed in both types of muscles of aged mice. On the other hand, 2-week hindlimb unloading had no impact on the nuclear accumulation of HSP70 in both muscles of young and aged mice. Nuclear expression level of Hikeshi in both MGAS and PLA in mice was suppressed by aging. No significant changes in the nuclear Hikeshi in both muscles were induced by unloading with or without reloading. Results of this study indicate that the nuclear accumulation of HSP70 might show a protective response against cellular stresses in skeletal muscle and that the protective response may be suppressed by aging. Protective response to aging might depend on muscle fiber types.

Influence of hyperthermal regimes on experimental teratoma development in vitro

We screened for the impact of hyperthermal regimes varying in the cumulative equivalent minutes at 43°C (CEM43°C) and media composition on tumour development using an original teratoma in vitro model. Rat embryos (three germ layers) were microsurgically isolated and cultivated at the air‐liquid interface. During a two week period, ectodermal, mesodermal and endodermal derivatives developed within trilaminar teratomas. Controls were grown at 37°C. Overall growth was measured, and teratoma survival and differentiation were histologically assessed. Cell proliferation was stereologically quantified by the volume density of Proliferating Cell Nuclear Antigen. Hyperthermia of 42°C, applied for 15 minutes after plating (CEM43°C 3.75 minutes), diminished cell proliferation (P ˂ .0001) and enhanced differentiation of both myotubes (P ˂ .01) and cylindrical epithelium (P ˂ .05). Hyperthermia of 43°C applied each day for 30 minutes during the first week (CEM43°C 210 minutes) impaired overall growth (P ˂ .01) and diminished cell proliferation (P ˂ .0001). Long‐term hyperthermia of 40.5°C applied for two weeks (CEM43°C 630 minutes) significantly impaired survival (P ˂ .005). Long‐term hyperthermia of 40.5°C applied from the second day when differentiation of tissues begins (CEM43°C 585 minutes) impaired survival (P ˂ .0001), overall growth (P ˂ .01) and cartilage differentiation (P ˂ .05). No teratomas survived extreme regimes: 43°C for 24 hours (CEM43°C 1440 minutes), hyperthermia in the scant serum‐free medium (CEM43°C 630 minutes) or treatment with an anti‐HSP70 antibody before long‐term hyperthermia 40.5°C from the second day (CEM43°C 585 minutes). This in vitro research provided novel insights into the impact of hyperthermia on the development of experimental teratomas from their undifferentiated sources and are thus of potential interest for future therapeutic strategies in corresponding in vivo models.

Hsp70 expression induced by Co-Enzyme Q10 protected chicken myocardial cells from damage and apoptosis under in vitro heat stress

The aim of this study was to investigate whether induction of Hsp70 expression by co-enzyme Q10 (Q10) treatment protects chicken primary myocardial cells (CPMCs) from damage and apoptosis in response to heat stress for 5 hours. Analysis of the expression and distribution of Hsp70 and the levels of the damage-related enzymes creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH), as well as pathological analysis showed that co-enzyme Q10 alleviated the damage caused to CPMCs during heat stress. Further, analysis of cell apoptosis and the expression of cleaved caspase-3 indicated that co-enzyme Q10 did have an anti-apoptotic role during heat stress. Western blot analysis showed that pretreatment with co-enzyme Q10 led to a significant increase in the expression of Hsp70 during heat stress. Immunostaining assays confirmed the results of western blot analysis and also showed that co-enzyme Q10 could accelerate the translocation of Hsp70 into the nucleus during heat stress, but this was not observed in the group that was treated with only co-enzyme Q10. These findings seem to indicate that co-enzyme Q10 protected CPMCs from heat stress via the induction of Hsp70. To investigate this, 200 μM quercetin, an Hsp70 inhibitor, was used to inhibit the expression of Hsp70 2 h before heat stress. Quercetin pre-treatment was observed to suppress the expression of Hsp70 as well the protective function of co-enzyme Q10 at 5 h of heat stress. This finding confirms that Q10 brought about its effects via Hsp70 expression, but the mechanism underlying this needs further investigation.

Heat stress-induced nuclear transport mediated by Hikeshi confers nuclear function of Hsp70s

The prime feature of eukaryotic cells is the separation of the intracellular space into two compartments, the nucleus and the cytoplasm. Active nuclear transport is crucial for the maintenance of this separation. In this report, we focus on a nuclear transport receptor named Hikeshi, which mediates the heat stress-induced nuclear import of 70-kDa heat shock proteins (Hsp70s), and discuss how the same protein can function differently depending on the cellular compartment in which it is localized. Hsp70 is a molecular chaperone that is predominantly localized in the cytoplasm under normal conditions but is known to accumulate in the nucleus under conditions of heat stress. Although the reported function of Hsp70 is mostly attributed to its molecular function in the cytoplasm, the functions of Hsp70 may extend beyond molecular chaperone activity in the nucleus.

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.

Mild heat induces a distinct "eustress" response in Chinese Hamster Ovary cells but does not induce heat shock protein synthesis

The current research on cellular heat stress management focuses on the roles of heat shock proteins (HSPs) and the proteostasis network under severe stress conditions. The mild, fever-type stress and the maintenance of membrane homeostasis are less well understood. Herein, we characterized the acute effect of mild, fever-range heat shock on membrane organization, and HSP synthesis and localization in two mammalian cell lines, to delineate the role of membranes in the sensing and adaptation to heat. A multidisciplinary approach combining ultrasensitive fluorescence microscopy and lipidomics revealed the molecular details of novel cellular “eustress”, when cells adapt to mild heat by maintaining membrane homeostasis, activating lipid remodeling, and redistributing chaperone proteins. Notably, this leads to acquired thermotolerance in the complete absence of the induction of HSPs. At higher temperatures, additional defense mechanisms are activated, including elevated expression of molecular chaperones, contributing to an extended stress memory and acquired thermotolerance.

Hikeshi modulates the proteotoxic stress response in human cells: Implication for the importance of the nuclear function of HSP70s

Hikeshi mediates the heat stress-induced nuclear import of heat-shock protein 70 (HSP70s: HSP70/HSC70). Dysfunction of Hikeshi causes some serious effects in humans; however, the cellular function of Hikeshi is largely unknown. Here, we investigated the effects of Hikeshi depletion on the survival of human cells after proteotoxic stress and found opposite effects in HeLa and hTERT-RPE1 (RPE) cells; depletion of Hikeshi reduced the survival of HeLa cells, but increased the survival of RPE cells in response to proteotoxic stress. Hikeshi depletion sustained heat-shock transcription factor 1 (HSF1) activation in HeLa cells after recovery from stress, but introduction of a nuclear localization signal-tagged HSC70 in Hikeshi-depleted HeLa cells down-regulated HSF1 activity. In RPE cells, the HSF1 was efficiently activated, but the activated HSF1 was not sustained after recovery from stress, as in HeLa cells. Additionally, we found that p53 and subsequent up-regulation of p21 were higher in the Hikeshi-depleted RPE cells than in the wild-type cells. Our results indicate that depletion of Hikeshi renders HeLa cells proteotoxic stress-sensitive through the abrogation of the nuclear function of HSP70s required for HSF1 regulation. Moreover, Hikeshi depletion up-regulates p21 in RPE cells, which could be a cause of its proteotoxic stress resistant.

Heat shock-induced HIKESHI protects cell viability via nuclear translocation of heat shock protein 70

Heat shock proteins (HSPs), particularly HSP70, help restore normal cellular function following damage caused by stressors. HSP expression in tumor tissues indicates cancer progression, and while the development of HSP inhibitors is progressing, these substances are not widely used to treat cancer. HIKESHI (C11orf73) does not control the intracellular movement of HSP70 at normal temperatures; however, it does regulate the function and movements of HSP70 during heat shock. In this study, we examined the intracellular movement of HSP70 during heat shock to investigate the significance of HIKESHI expression in gastric cancer (GC) and determine if HIKESHI inhibition has cytotoxic effects. We examined HIKESHI using GC cell lines and immunostaining in 207 GC tissue samples. HIKESHI expression in GC tissues was associated with the progression of lymphatic invasion. Suppressing HIKESHI using siRNA did not affect cell viability at normal temperatures. However, suppressing HIKESHI during heat shock inhibited HSP70 nuclear transport and suppressed cell viability. Our results suggest that HIKESHI is a marker of cancer progression and that the combination of HIKESHI inhibition and hyperthermia is a therapeutic tool for refractory GC.

UBQLN2 Mediates Autophagy-Independent Protein Aggregate Clearance by the Proteasome

Clearance of misfolded and aggregated proteins is central to cell survival. Here, we describe a new pathway for maintaining protein homeostasis mediated by the proteasome shuttle factor UBQLN2. The 26S proteasome degrades polyubiquitylated substrates by recognizing them through stoichiometrically bound ubiquitin receptors, but substrates are also delivered by reversibly bound shuttles. We aimed to determine why these parallel delivery mechanisms exist and found that UBQLN2 acts with the HSP70-HSP110 disaggregase machinery to clear protein aggregates via the 26S proteasome. UBQLN2 recognizes client-bound HSP70 and links it to the proteasome to allow for the degradation of aggregated and misfolded proteins. We further show that this process is active in the cell nucleus, where another system for aggregate clearance, autophagy, does not act. Finally, we found that mutations in UBQLN2, which lead to neurodegeneration in humans, are defective in chaperone binding, impair aggregate clearance, and cause cognitive deficits in mice.

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UBQLN2 clears aggregates independent of autophagy via HSP70 and the proteasome

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A disease mutation in UBQLN2 prevents its binding to HSP70

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Mutant UBQLN2 is defective in clearance of aggregates in vivo

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UBQLN2 knockin mice develop cognitive impairment and brain pathology

Expression of hsrω-RNAi transgene prior to heat shock specifically compromises accumulation of heat shock-induced Hsp70 in Drosophila melanogaster

A delayed organismic lethality was reported in Drosophila following heat shock when developmentally active and stress-inducible noncoding hsrω-n transcripts were down-regulated during heat shock through hs-GAL4-driven expression of the hsrω-RNAi transgene, despite the characteristic elevation of all heat shock proteins (Hsp), including Hsp70. Here, we show that hsrω-RNAi transgene expression prior to heat shock singularly prevents accumulation of Hsp70 in all larval tissues without affecting transcriptional induction of hsp70 genes and stability of their transcripts. Absence of the stress-induced Hsp70 accumulation was not due to higher levels of Hsc70 in hsrω-RNAi transgene-expressing tissues. Inhibition of proteasomal activity during heat shock restored high levels of the induced Hsp70, suggesting very rapid degradation of the Hsp70 even during the stress when hsrω-RNAi transgene was expressed ahead of heat shock. Unexpectedly, while complete absence of hsrω transcripts in hsrω (66) homozygotes (hsrω-null) did not prevent high accumulation of heat shock-induced Hsp70, hsrω-RNAi transgene expression in hsrω-null background blocked Hsp70 accumulation. Nonspecific RNAi transgene expression did not affect Hsp70 induction. These observations reveal that, under certain conditions, the stress-induced Hsp70 can be selectively and rapidly targeted for proteasomal degradation even during heat shock. In the present case, the selective degradation of Hsp70 does not appear to be due to down-regulation of the hsrω-n transcripts per se; rather, this may be an indirect effect of the expression of hsrω-RNAi transgene whose RNA products may titrate away some RNA-binding proteins which may also be essential for stability of the induced Hsp70.

Leukoencephalopathy and early death associated with an Ashkenazi-Jewish founder mutation in the Hikeshi gene

BACKGROUND

Leukodystrophies are genetic white matter disorders affecting the formation or maintenance of myelin. Among the recently discovered genetic defects associated with leukodystrophies, several genes converge on a common mechanism involving protein transcription/translation and ER stress response.

METHODS

The genetic basis of a novel congenital leukodystrophy, associated with early onset spastic paraparesis, acquired microcephaly and optic atrophy was studied in six patients from three unrelated Ashkenazi-Jewish families. To this end we used homozygosity mapping, exome analysis, western blot (Hikeshi, HSF1-pS326 and b-actin) in patient fibroblasts, indirect immunofluorescence (HSP70 and HSF1) in patient fibroblasts undergoing heat shock stress, nuclear injection of plasmids expressing Hikeshi or EGFP in patient fibroblasts, in situ hybridization and Immunoblot analysis of Hikeshi in newborn and adult mouse brain.

RESULTS

All the patients were homozygous for a missense mutation, p.Val54Leu, in C11ORF73 encoding HSP70 nuclear transporter protein, Hikeshi. The mutation segregated with the disease in the families and was carried by 1:200 Ashkenazi-Jewish individuals. The mutation was associated with undetectable level of Hikeshi in the patients' fibroblasts and with lack of nuclear HSP70 during heat shock stress, a phenomenon which was reversed upon the introduction of normal human Hikeshi to the patients cells. Hikeshi was found to be expressed in central white matter of mouse brain.

CONCLUSIONS

These data underscore the importance of Hikeshi for HSP70 relocation into the nucleus. It is likely that in the absence of Hikeshi, HSP70 cannot attenuate the multiple heat shock induced nuclear phenotypes, leaving the cells unprotected during heat shock stress. We speculate that the sudden death of three of the six patients following a short febrile illness and the life-threatening myo-pericarditis in the fourth are the result of excess extra-nuclear HSP70 level which initiates cytokine release or provide target for natural killer cells. Alternatively, nuclear HSP70 might play an active role in stressed cells protection.

How the nucleus copes with proteotoxic stress

The proper folding of proteins is continuously challenged by intrinsic and extrinsic stresses, and the accumulation of toxic misfolded proteins is associated with many human diseases. Eukaryotic cells have evolved a complex network of protein quality control pathways to protect the proteome, and these pathways are specialized for each subcellular compartment. While many details have been elucidated for how the cytosol and endoplasmic reticulum counteract proteotoxic stress, relatively little is known about the pathways protecting the nucleus from protein misfolding. Proper maintenance of nuclear proteostasis has important implications in preserving genomic integrity, as well as for aging and disease. Here, we offer a conceptual framework for how proteostasis is maintained in this organelle. We define the particular requirements that must be considered for the nucleus to manage proteotoxic stress, summarize the known and implicated pathways of nuclear protein quality control, and identify the unresolved questions in the field.

TCP1 complex proteins interact with phosphorothioate oligonucleotides and can co-localize in oligonucleotide-induced nuclear bodies in mammalian cells

Phosphorothioate (PS) antisense oligonucleotides (ASOs) have been successfully developed as drugs to reduce the expression of disease-causing genes. PS-ASOs can be designed to induce degradation of complementary RNAs via the RNase H pathway and much is understood about that process. However, interactions of PS-ASOs with other cellular proteins are not well characterized. Here we report that in cells transfected with PS-ASOs, the chaperonin T-complex 1 (TCP1) proteins interact with PS-ASOs and enhance antisense activity. The TCP1-β subunit co-localizes with PS-ASOs in distinct nuclear structures, termed phosphorothioate bodies or PS-bodies. Upon Ras-related nuclear protein (RAN) depletion, cytoplasmic PS-body-like structures were observed and nuclear concentrations of PS-ASOs were reduced, suggesting that TCP1-β can interact with PS-ASOs in the cytoplasm and that the nuclear import of PS-ASOs is at least partially through the RAN-mediated pathway. Upon free uptake, PS-ASOs co-localize with TCP1 proteins in cytoplasmic foci related to endosomes/lysosomes. Together, our results indicate that the TCP1 complex binds oligonucleotides with TCP1-β subunit being a nuclear PS-body component and suggest that the TCP1 complex may facilitate PS-ASO uptake and/or release from the endocytosis pathway.