Uncoating ATPase is a member of the 70 kilodalton family of stress proteins

Heat Shock Protein Network: the Mode of Action, the Role in Protein Folding and Human Pathologies

Protein folding is an extremely complicated process, which has been extensively tackled during the last decades. In vivo, a certain molecular machinery is responsible for assisting the correct folding of proteins and maintaining protein homeostasis: the members of this machinery are the heat shock proteins (HSPs), which belong among molecular chaperones. Mutations in HSPs are associated with several inherited diseases, and members of this group were also proved to be involved in neurodegenerative pathologies (e.g., Alzheimer and Parkinson diseases), cancer, viral infections, and antibiotic resistance of bacteria. Therefore, it is critical to understand the principles of HSP functioning and their exact role in human physiology and pathology. This review attempts to briefly describe the main chaperone families and the interplay between individual chaperones, as well as their general and specific functions in the context of cell physiology and human diseases.

GDP-bound Rab27a regulates clathrin disassembly through HSPA8 after insulin secretion

Clathrin-dependent endocytosis is a key process for secretory cells, in which molecules on the plasma membrane are both degraded and recycled in a stimulus-dependent manner. There are many reports showing that disruption of endocytosis is involved in the onset of various diseases. Recently, it has been reported that such disruption in pancreatic β-cells causes impaired insulin secretion and might be associated with the pathology of diabetes mellitus. Compared with exocytosis, there are few reports on the molecular mechanism of endocytosis in pancreatic β-cells. We previously reported that GDP-bound Rab27a regulates endocytosis through its GDP-dependent effectors after insulin secretion. In this study, we identified heat shock protein family A member 8 (HSPA8) as a novel interacting protein for GDP-bound Rab27a. HSPA8 directly bound GDP-bound Rab27a via the β2 region of its substrate binding domain (SBD). The β2 fragment was capable of inhibiting the interaction between HSPA8 and GDP-bound Rab27a, and suppressed glucose-induced clathrin-dependent endocytosis in pancreatic β-cells. The region also affected clathrin dynamics on purified clathrin-coated vesicles (CCVs). These results suggest that the interaction between GDP-bound Rab27a and HSPA8 regulates clathrin disassembly from CCVs and subsequent vesicle transport. The regulatory stages in endocytosis by HSPA8 differ from those for other GDP-bound Rab27a effectors. This study shows that GDP-bound Rab27a dominantly regulates each stage in glucose-induced endocytosis through its specific effectors in pancreatic β-cells.

Effect of HSPA8 gene on the proliferation, apoptosis and immune function of HD11 cells

HSPA8 (Heat shock 70 kDa protein 8) is a molecular chaperone involved in a variety of cellular processes. This gene may affect the proliferation, apoptosis and immune function of chicken macrophages, but the specific mechanism remains unclear. The purpose of this study was to explore the effect of the HSPA8 gene on the proliferation, apoptosis and immune function of chicken macrophages. In this study, a chicken HSPA8 overexpression plasmid, interference fragment and corresponding controls were transfected into HD11 cells, and then the expression of the HSPA8 gene, cell proliferation, cell cycle, apoptosis rate and immune function of each group were detected. The results showed that transfection of the HSPA8 overexpression plasmid significantly upregulated the level of HSPA8 expression in HD11 cells compared with the control; significantly promoted the proliferation of HD11 cells and the expression of PCNA, CCND1 and CCNB3; decreased the number of cells in the G1 phase and increased the number of cells in the S phase; decreased the rate of apoptosis and upregulated the expression of Bcl-2; and promoted the expression of the LPS-induced cytokines IL-1β, IL-6 and TNF-α. Transfection of the HSPA8 interference fragment significantly downregulated the level of HSPA8 expression in HD11 cells; significantly inhibited the proliferation of HD11 cells and the expression of PCNA, CCND1 and CDK1; increased the number of cells in the G1 phase and decreased the number of cells in the S phase; increased the rate of apoptosis, downregulated the expression of Bcl-2 and upregulated the expression levels of Fas and FasL; and inhibited the expression of the LPS-induced cytokines IL-1β and NF-κB. The results suggested that HSPA8 promotes the proliferation of and inhibits the apoptosis of HD11 cells and has a proinflammatory effect.

Neuronal SH2B1 attenuates apoptosis in an MPTP mouse model of Parkinson's disease via promoting PLIN4 degradation

The incidence of Parkinson's disease (PD) has increased tremendously, especially in the aged population and people with metabolic dysfunction; however, its underlying molecular mechanisms remain unclear. SH2B1, an intracellular adaptor protein, contributes to the signal transduction of several receptor tyrosine kinases and exerts beneficial metabolic effects for body weight regulation; however, whether SH2B1 plays a major role in pathological neurodegeneration in PD has not yet been investigated. This study aimed to investigate the effects of SH2B1 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)–induced PD mice with Sh2b1 deficiency or neuron-specific Sh2b1 overexpression. Cellular and molecular mechanisms were elucidated using human dopaminergic neuron SH-SY5Y cells analysed. We found that SH2B1 expression was confirmed to be downregulated in the blood samples of PD patients and in the brains of mice with MPTP-induced chronic PD. Sh2b1 deficiency caused marked exacerbation of behavioural defects and increased neuronal apoptosis in MPTP-treated mice, whereas restoration of neuron-specific Sh2b1 expression significantly reversed these effects. Similar results were observed in MPP ⁺ -treated SH-SY5Y cells. Mechanistically, upon binding to heat shock cognate 70 (HSC70), SH2B1 promotes HSC70-related recognition and PLIN4 lysosomal translocation and degradation, thus suppressing lipid peroxidation stress in the brains of PD mice. Adeno-associated virus-mediated rescue of neuronal HSC70 expression functionally alleviated the neuropathology of PD in wild-type but not in Sh2b1-deficient mice. This is the first study to examine the molecular underpinnings of SH2B1 against MPTP-induced neurodegeneration through cell autonomous promotion of neuronal survival in an in vivo PD model. Our findings reveal that SH2B1 antagonizes neurodegenerative pathology in PD via the SH2B1–HSC70–PLIN4 axis.

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Brain tissues, especially in TH⁺ neurons, of PD mice showed low SH2B1 expression.

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SH2B1 suppressed MPTP-induced neurodegeneration by inhibiting neuronal apoptosis.

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SH2B1 overexpression protected against MPP ⁺ -induced cell death via HSC70.

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SH2B1 interacts with HSC70 to form a complex that regulates PLIN4 degradation.

WITHDRAWN: Effect of HSPA8 on the proliferation, apoptosis and immune function of chicken macrophages

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Influence of formic acid treatment on the proteome of the ectoparasite Varroa destructor

The ectoparasite Varroa destructor Anderson and Trueman is the most important parasites of the western honey bee, Apis mellifera L. The most widely currently used treatment uses formic acid (FA), but the understanding of its effects on V. destructor is limited. In order to understand the mechanism of action of FA, its effect on Varroa mites was investigated using proteomic analysis by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). V. destructor was collected from honey bee colonies with natural mite infestation before and 24 h after the initiation of FA treatment and subjected to proteome analysis. A total of 2637 proteins were identified. Quantitative analysis of differentially expressed candidate proteins (fold change ≥ 1.5; p ≤ 0.05) revealed 205 differentially expressed proteins: 91 were induced and 114 repressed in the FA-treated group compared to the untreated control group. Impaired protein synthesis accompanied by increased protein and amino acid degradation suggest an imbalance in proteostasis. Signs of oxidative stress included significant dysregulation of candidate proteins of mitochondrial cellular respiration, increased endocytosis, and induction of heat shock proteins. Furthermore, an increased concentration of several candidate proteins associated with detoxification was observed. These results suggest dysregulated cellular respiration triggered by FA treatment as well as an increase in cellular defense mechanisms, including induced heat shock proteins and detoxification enzymes.

Identification of genes related to stress affecting thymus immune function in a chicken stress model using transcriptome analysis

With the rapid development of the poultry breeding industry and highly intensive production management, the losses caused by stress responses are becoming increasingly serious. To screen candidate genes related to chicken stress and provide a basis for future research on the molecular mechanisms governing the effects of stress on chicken immune function, we successfully constructed a chicken stress model by exogenously introducing corticosterone (CORT). RNA-seq technology was used to identify and analyze the mRNA and enrichment pathways of the thymus in the stress model group and the control group. The results showed that there were 101 significantly differentially expressed genes (SDEGs) (Padj < 0.05, |log2fold changes| ≥ 1 and FPKM >1), of which 44 were upregulated genes, while 57 were downregulated genes. Gene Ontology (GO) enrichment analysis found that the terms related to immunity or stress mainly included antigen processing and presentation, positive regulation of T cell-mediated immunity, and immune effector process. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the main pathways related to immunity or stress were the PPAR signaling pathway, NOD-like receptor signaling pathway, and intestinal immune network for IgA production. Among the SDEGs, XCL1, HSPA8, DMB1 and BAG3 are strongly related to immunity or stress and may be important genes involved in regulating stress affecting the immune function of chickens. The above results provide a theoretical reference for subsequent research on the molecular regulatory mechanisms by which stress affects the immune function of poultry.

Differential transcriptional and functional properties of regulatory T cells in HIV-infected individuals on antiretroviral therapy and long-term non-progressors

OBJECTIVES

Regulatory T cells (Tregs) are widely recognised as a subset of CD4+CD25+FOXP3+ T cells that have a key role in maintaining immune homeostasis. The impact of HIV-1 infection on immunological properties and effector functions of Tregs has remained the topic of debate and controversy. In the present study, we investigated transcriptional profile and functional properties of Tregs in HIV-1-infected individuals either receiving antiretroviral therapy (ART, n = 50) or long-term non-progressors (LTNPs, n = 24) compared to healthy controls (HCs, n = 38).

METHODS

RNA sequencing (RNAseq), flow cytometry-based immunophenotyping and functional assays were performed to study Tregs in different HIV cohorts.

RESULTS

Our RNAseq analysis revealed that Tregs exhibit different transcriptional profiles in HIV-infected individuals. While Tregs from patients on ART upregulate pathways associated with a more suppressive (activated) phenotype, Tregs in LTNPs exhibit upregulation of pathways associated with impaired suppressive properties. These observations may explain a higher propensity for autoimmune diseases in LTNPs. Also, we found substantial upregulation of HLA-F mRNA and HLA-F protein in Tregs from HIV-infected subjects compared to healthy individuals. These observations highlight a potential role for this non-classical HLA in Tregs in the context of HIV infection, which should be investigated further in other chronic viral infections and cancer.

CONCLUSION

Our study has provided a novel insight into Tregs at the transcriptional and functional levels in different HIV-infected groups.

The Heat Shock Protein 70 Family of Chaperones Regulates All Phases of the Enterovirus A71 Life Cycle

Enterovirus A71 (EV-A71) is one of the major etiologic agents causing hand, foot, and mouth disease (HFMD) in children and occasionally causes severe neurological diseases or even death. EV-A71 replicates rapidly in host cells. For a successful infection, viruses produce large quantities of viral proteins in a short period, which requires cellular chaperone proteins for viral protein folding and viral particle assembly. In this study, we explored the roles of the heat shock protein 70 (HSP70) chaperone subnetwork in the EV-A71 life cycle. Our results revealed that EV-A71 exploits multiple HSP70s at each step of the viral life cycle, i.e., viral entry, translation, replication, assembly and release, and that each HSP70 typically functions in several stages of the life cycle. For example, the HSP70 isoforms HSPA1, HSPA8, and HSPA9 are required for viral entry and the translational steps of the infection. HSPA8 and HSPA9 may facilitate folding and stabilize viral proteins 3D and 2C, respectively, thus contributing to the formation of a replication complex. HSPA8 and HSPA9 also promote viral particle assembly, whereas HSPA1 and HSPA8 are involved in viral particle release. Because of the importance of various HSP70s at distinct steps of the viral life cycle, an allosteric inhibitor, JG40, which targets all HSP70s, significantly blocks EV-A71 infection. JG40 also blocks the replication of several other enteroviruses, such as coxsackievirus (CV) A16, CVB1, CVB3, and echovirus 11. Thus, targeting HSP70s may be a means of providing broad-spectrum antiviral therapy.

Chaperonin-assisted protein folding: a chronologue

This chronologue seeks to document the discovery and development of an understanding of oligomeric ring protein assemblies known as chaperonins that assist protein folding in the cell. It provides detail regarding genetic, physiologic, biochemical, and biophysical studies of these ATP-utilizing machines from both in vivo and in vitro observations. The chronologue is organized into various topics of physiology and mechanism, for each of which a chronologic order is generally followed. The text is liberally illustrated to provide firsthand inspection of the key pieces of experimental data that propelled this field. Because of the length and depth of this piece, the use of the outline as a guide for selected reading is encouraged, but it should also be of help in pursuing the text in direct order.

Analysis of testis metabolome and transcriptome from the oriental river prawn (Macrobrachium nipponense) in response to different temperatures and illumination times

A better understanding of the mechanisms underlying the male sexual differentiation of Macrobrachium nipponense is urgently needed in order to maintain sustainable development of the M. nipponense industry. Environmental factors, especially temperature and illumination, have dramatic effects on gonadal development. The aim of the present study was to identify key genes and metabolites involved in the male sexual differentiation and development of M. nipponense through integrated metabolomics and transcriptome analyses of the testis in response to different temperatures and illumination times. A total of 268 differentially abundant metabolites and 11,832 differentially expressed genes (DEGs) were identified. According to integrated metabolomics and transcriptome analyses, glycerophospholipid and sphingolipid metabolism was predicted to have dramatic effects on the male sexual differentiation and development of M. nipponense. According to the KEGG enrichment analysis of DEGs, oxidative phosphorylation, glycolysis/gluconeogenesis, the HIF-1 signaling pathway, the citrate cycle, steroid hormone synthesis, and the spliceosome complex were predicted to promote male differentiation and development by providing adenosine triphosphate, promoting the synthesis of steroid hormones, and providing correct gene products. Quantitative polymerase chain reaction analysis and in situ hybridization showed that the SDHB, PDE1, HSDL1, CYP81F2, SRSF, and SNRNP40 genes were differentially expressed, suggesting roles in the male sexual differentiation and development of M. nipponense. Strong candidate sex-related metabolic pathways and genes in M. nipponense were identified by integrated metabolomics and transcriptome analyses of the testis in response to different temperatures and illumination times, as confirmed by PCR analysis and in situ hybridization.

Heat shock cognate protein 70 promotes the differentiation of C2C12 myoblast and targets Yin Yang 1

Background

Heat shock cognate protein 70 (HSC70) is a constitutively expressed molecular chaperone protein which can maintain the structure and function of the protein. HSC70 is engaged in a variety of physiological processes, yet its role during skeletal muscle differentiation is still unclear.

Methods

C2C12 cells were obtained and cultured. During differentiation, the expression of HSC70 was evaluated by RT-PCR. To determine the function of HSC70 during C2C12 myoblast differentiation, myotube transfection of siR-HSC70 was performed with Lipofectamine 2000 Reagent. Western blot was used to measure the expression of Yin Yang 1 (YY1) after down-regulating HSC70. To further assess if YY1 mediates the pro-differentiation effect of HSC70, a plasmid of YY1 overexpression was used to increase the expression of YY1 in the presence of siR-HSC70-2. The formation of myotubes was visualized by immunofluorescent staining, while the expression levels of MyoD and MyoG were evaluated by RT-PCR.

Results

In this study, we found that HSC70 was up-regulated during C2C12 myoblast differentiation. Knockdown of HSC70 not only inhibited the C2C12 myoblast differentiation but also reduced the expression of MyoD and MyoG. When YY1 protein was over-expressed, it could restore the differentiation in cells with HSC70 knockdown or inhibition.

Conclusions

Collectively, this study demonstrates that HSC70 is involved in the regulation of C2C12 myoblast differentiation via YY1 and may serve as a potential target for a therapeutic strategy to prevent muscle atrophy.

Phosphorylation of human AQP2 and its role in trafficking

Human Aquaporin 2 (AQP2) is a membrane-bound water channel found in the kidney collecting duct whose regulation by trafficking plays a key role in regulating urine volume. AQP2 trafficking is tightly controlled by the pituitary hormone arginine vasopressin (AVP), which stimulates translocation of AQP2 residing in storage vesicles to the apical membrane. The AVP-dependent translocation of AQP2 to and from the apical membrane is controlled by multiple phosphorylation sites in the AQP2 C-terminus, the phosphorylation of which alters its affinity to proteins within the cellular membrane protein trafficking machinery. The aim of this chapter is to provide a summary of what is currently known about AVP-mediated AQP2 trafficking, dissecting the roles of individual phosphorylation sites, kinases and phosphatases and interacting proteins. From this, the picture of an immensely complex process emerges, of which many structural and molecular details remains to be elucidated.

Molecular identification of HSPA8 as an accessory protein of a hyperpolarization-activated chloride channel from rat pulmonary vein cardiomyocytes

Pulmonary veins (PVs) are the major origin of atrial fibrillation. Recently, we recorded hyperpolarization-activated Cl^- current (I _{Cl, h}) in rat PV cardiomyocytes. Unlike the well-known chloride channel protein 2 (CLCN2) current, the activation curve of I _{Cl, h} was hyperpolarized as the Cl^- ion concentration ([Cl^-] _i ) increased. This current could account for spontaneous activity in PV cardiomyocytes linked to atrial fibrillation. In this study, we aimed to identify the channel underlying I _{Cl, h} Using RT-PCR amplification specific for Clcn2 or its homologs, a chloride channel was cloned from rat PV and detected in rat PV cardiomyocytes using immunocytochemistry. The gene sequence and electrophysiological functions of the protein were identical to those previously reported for Clcn2, with protein activity observed as a hyperpolarization-activated current by the patch-clamp method. However, the [Cl^-] _i dependence of activation was entirely different from the observed I _{Cl, h} of PV cardiomyocytes; the activation curve of the Clcn2-transfected cells shifted toward positive potential with increased [Cl^-] _i , whereas the I _{Cl, h} of PV and left ventricular cardiomyocytes showed a leftward shift. Therefore, we used MS to explore the possibility of additional proteins interacting with CLCN2 and identified an individual 71-kDa protein, HSPA8, that was strongly expressed in rat PV cardiomyocytes. With co-expression of HSPA8 in HEK293 and PC12 cells, the CLCN2 current showed voltage-dependent activation and shifted to negative potential with increasing [Cl^-] _i Molecular docking simulations further support an interaction between CLCN2 and HSPA8. These findings suggest that CLCN2 in rat heart contains HSPA8 as a unique accessory protein.

Oligomerization of Hsp70: Current Perspectives on Regulation and Function

The Hsp70 molecular chaperone in conjunction with Hsp90 and a suite of helper co-chaperones are required for the folding and subsequent refolding of a large proportion of the proteome. These proteins are critical for cell viability and play major roles in diseases of proteostasis which include neurodegenerative diseases and cancer. As a consequence, a large scientific effort has gone into understanding how chaperones such as Hsp70 function at the in vitro and in vivo level. Although many chaperones require constitutive self-interaction (dimerization and oligomerization) to function, Hsp70 has been thought to exist as a monomer, especially in eukaryotic cells. Recent studies have demonstrated that both bacterial and mammalian Hsp70 can exist as a dynamic pool of monomers, dimer, and oligomers. In this mini-review, we discuss the mechanisms and roles of Hsp70 oligomerization in Hsp70 function, as well as thoughts on how this integrates into well-established ideas of Hsp70 regulation.

Hsc70 is a Component of Bacterially Generated Actin-Rich Structures: An Immunolocalization Study

Enteropathogenic Escherichia coli (EPEC), Salmonella typhimurium, and Listeria monocytogenes usurp the actin cytoskeleton for their attachment, internalization and transport within and amongst infected cells. To try to gain a greater understanding of the molecular components utilized by these microbes during their infections we previously concentrated actin-rich structures generated during EPEC infections (called pedestals) and identified the heat shock cognate 70 protein (Hsc70) as a potential candidate. This multifunctional protein classically acts as a chaperone for the proper folding of a variety of proteins and is involved in uncoating clathrin from coated pits. Here we demonstrated that Hsc70 is recruited to actin structures generated during EPEC, Listeria and Salmonella infections, but not to the same location as clathrin. Anat Rec, 301:2095-2102, 2018. © 2018 Wiley Periodicals, Inc.

NECAPs are negative regulators of the AP2 clathrin adaptor complex

Eukaryotic cells internalize transmembrane receptors via clathrin-mediated endocytosis, but it remains unclear how the machinery underpinning this process is regulated. We recently discovered that membrane-associated muniscin proteins such as FCHo and SGIP initiate endocytosis by converting the AP2 clathrin adaptor complex to an open, active conformation that is then phosphorylated (Hollopeter et al., 2014). Here we report that loss of ncap-1, the sole C. elegans gene encoding an adaptiN Ear-binding Coat-Associated Protein (NECAP), bypasses the requirement for FCHO-1. Biochemical analyses reveal AP2 accumulates in an open, phosphorylated state in ncap-1 mutant worms, suggesting NECAPs promote the closed, inactive conformation of AP2. Consistent with this model, NECAPs preferentially bind open and phosphorylated forms of AP2 in vitro and localize with constitutively open AP2 mutants in vivo. NECAPs do not associate with phosphorylation-defective AP2 mutants, implying that phosphorylation precedes NECAP recruitment. We propose NECAPs function late in endocytosis to inactivate AP2.

DnaJ/Hsc70 chaperone complexes control the extracellular release of neurodegenerative-associated proteins

It is now known that proteins associated with neurodegenerative disease can spread throughout the brain in a prionlike manner. However, the mechanisms regulating the trans-synaptic spread propagation, including the neuronal release of these proteins, remain unknown. The interaction of neurodegenerative disease-associated proteins with the molecular chaperone Hsc70 is well known, and we hypothesized that much like disaggregation, refolding, degradation, and even normal function, Hsc70 may dictate the extracellular fate of these proteins. Here, we show that several proteins, including TDP-43, α-synuclein, and the microtubule-associated protein tau, can be driven out of the cell by an Hsc70 co-chaperone, DnaJC5. In fact, DnaJC5 overexpression induced tau release in cells, neurons, and brain tissue, but only when activity of the chaperone Hsc70 was intact and when tau was able to associate with this chaperone. Moreover, release of tau from neurons was reduced in mice lacking the DnaJC5 gene and when the complement of DnaJs in the cell was altered. These results demonstrate that the dynamics of DnaJ/Hsc70 complexes are critically involved in the release of neurodegenerative disease proteins.

Probing the effect of an inhibitor of an ATPase domain of Hsc70 on clathrin-mediated endocytosis

Hsc70 is known to be involved in clathrin-mediated endocytosis (CME) by which cells take up various extracellular materials. More specifically, this protein promotes the disassembly of clathrin-coated vesicles (CCVs) by directly binding to clathrin during CME. As the ATPase activity of Hsc70 is required for its association with clathrin, we have investigated the effect of an inhibitor (apoptozole, Az) of an ATPase domain of Hsc70 on CME. The results of biochemical studies show that Az binds to Hsc70 and Hsp70 without binding to other types of heat shock proteins. Structure-activity relationship studies provide information on the structural features responsible for the inhibition of the ATPase activity of Hsc70. The results obtained from cell experiments reveal that Az disrupts the interaction of Hsc70 with clathrin in cells, thereby leading to the accumulation of transferrin in CCVs and suppression of release of free Fe(3+) from CCVs during transferrin receptor-mediated endocytosis.

Pollen proteomics: from stress physiology to developmental priming

Pollen development and stress. In angiosperms, pollen or pollen grain (male gametophyte) is a highly reduced two- or three-cell structure which plays a decisive role in plant reproduction. Male gametophyte development takes place in anther locules where diploid sporophytic cells undergo meiotic division followed by two consecutive mitotic processes. A desiccated and metabolically quiescent form of mature pollen is released from the anther which lands on the stigma. Pollen tube growth takes place followed by double fertilization. Apart from its importance in sexual reproduction, pollen is also an interesting model system which integrates fundamental cellular processes like cell division, differentiation, fate determination, polar establishment, cell to cell recognition and communication. Recently, pollen functionality has been studied by multidisciplinary approaches which also include OMICS analyses like transcriptomics, proteomics and metabolomics. Here, we review recent advances in proteomics of pollen development and propose the process of developmental priming playing a key role to guard highly sensitive developmental processes.

The HSP70 co-chaperone DNAJC14 targets misfolded pendrin for unconventional protein secretion

Mutations in SLC26A4, which encodes pendrin, are responsible for hearing loss with an enlarged vestibular aqueduct and Pendred syndrome. The most prevalent mutation in East Asia is p.H723R (His723Arg), which leads to defects in protein folding and cell-surface expression. Here we show that H723R-pendrin can be rescued to the cell surface by an HSP70 co-chaperone DNAJC14-dependent unconventional trafficking pathway. Blockade of ER-to-Golgi transport or activation of ER stress signals induced Golgi-independent cell-surface expression of H723R-pendrin and restored its cell-surface Cl⁻/HCO₃⁻ exchange activity. Proteomic and short interfering RNA screenings with subsequent molecular analyses showed that Hsc70 and DNAJC14 are required for the unconventional trafficking of H723R-pendrin. Moreover, DNAJC14 upregulation was able to induce the unconventional cell-surface expression of H723R-pendrin. These results indicate that Hsc70 and DNAJC14 play central roles in ER stress-associated unconventional protein secretion and are potential therapeutic targets for diseases such as Pendred syndrome, which arise from transport defects of misfolded proteins.

Mutations in pendrin, a plasma membrane transporter, lead to Pendred syndrome, which is associated with hearing loss. Here, Jung et al. show that cell-surface expression of a mutated form of pendrin can be restored by blocking ER-to-Golgi traffic and triggering a DNAJC14 dependent unconventional secretion pathway.

Coupling of Ribostasis and Proteostasis: Hsp70 Proteins in mRNA Metabolism

A key aspect of the control of gene expression is the differential rates of mRNA translation and degradation, including alterations due to extracellular inputs. Surprisingly, multiple examples now argue that Hsp70 protein chaperones and their associated Hsp40 partners modulate both mRNA degradation and translation. Hsp70 proteins affect mRNA metabolism by various mechanisms including regulating nascent polypeptide chain folding, activating signal transduction pathways, promoting clearance of stress granules, and controlling mRNA degradation in an mRNA-specific manner. Taken together, these observations highlight the general principle that mRNA metabolism is coupled to the proteostatic state of the cell, often as assessed by the presence of unfolded or misfolded proteins.

The clathrin-binding and J-domains of GAK support the uncoating and chaperoning of clathrin by Hsc70 in the brain

Cyclin-G-associated kinase (GAK), the ubiquitously expressed J-domain protein, is essential for the chaperoning and uncoating of clathrin that is mediated by Hsc70 (also known as HSPA8). Adjacent to the C-terminal J-domain that binds to Hsc70, GAK has a clathrin-binding domain that is linked to an N-terminal kinase domain through a PTEN-like domain. Knocking out GAK in fibroblasts caused inhibition of clathrin-dependent trafficking, which was rescued by expressing a 62-kDa fragment of GAK, comprising just the clathrin-binding and J-domains. Expressing this fragment as a transgene in mice rescued the lethality and the histological defects caused by knocking out GAK in the liver or in the brain. Furthermore, when both GAK and auxilin (also known as DNAJC6), the neuronal-specific homolog of GAK, were knocked out in the brain, mice expressing the 62-kDa GAK fragment were viable, lived a normal life-span and had no major behavior abnormalities. However, these mice were about half the size of wild-type mice. Therefore, the PTEN-like domains of GAK and auxilin are not essential for Hsc70-dependent chaperoning and uncoating of clathrin, but depending on the tissue, these domains appear to increase the efficiency of these co-chaperones.

Isoform-selective Genetic Inhibition of Constitutive Cytosolic Hsp70 Activity Promotes Client Tau Degradation Using an Altered Co-chaperone Complement

The constitutively expressed heat shock protein 70 kDa (Hsc70) is a major chaperone protein responsible for maintaining proteostasis, yet how its structure translates into functional decisions regarding client fate is still unclear. We previously showed that Hsc70 preserved aberrant Tau, but it remained unknown if selective inhibition of the activity of this Hsp70 isoform could facilitate Tau clearance. Using single point mutations in the nucleotide binding domain, we assessed the effect of several mutations on the functions of human Hsc70. Biochemical characterization revealed that one mutation abolished both Hsc70 ATPase and refolding activities. This variant resembled the ADP-bound conformer at all times yet remained able to interact with cofactors, nucleotides, and substrates appropriately, resembling a dominant negative Hsc70 (DN-Hsc70). We then assessed the effects of this DN-Hsc70 on its client Tau. DN-Hsc70 potently facilitated Tau clearance via the proteasome in cells and brain tissue, in contrast to wild type Hsc70 that stabilized Tau. Thus, DN-Hsc70 mimics the action of small molecule pan Hsp70 inhibitors with regard to Tau metabolism. This shift in Hsc70 function by a single point mutation was the result of a change in the chaperome associated with Hsc70 such that DN-Hsc70 associated more with Hsp90 and DnaJ proteins, whereas wild type Hsc70 was more associated with other Hsp70 isoforms. Thus, isoform-selective targeting of Hsc70 could be a viable therapeutic strategy for tauopathies and possibly lead to new insights in chaperone complex biology.

Positive or negative involvement of heat shock proteins in multiple sclerosis pathogenesis: an overview

Multiple sclerosis (MS) is the most diffuse chronic inflammatory disease of the central nervous system. Both immune-mediated and neurodegenerative processes apparently play roles in the pathogenesis of this disease. Heat shock proteins (HSPs) are a family of highly evolutionarily conserved proteins; their expression in the nervous system is induced in a variety of pathologic states, including cerebral ischemia, neurodegenerative diseases, epilepsy, and trauma. To date, investigators have observed protective effects of HSPs in a variety of brain disease models (e.g. of Alzheimer disease and Parkinson disease). In contrast, unequivocal data have been obtained for their roles in MS that depend on the HSP family and particularly on their localization (i.e. intracellular or extracellular). This article reviews our current understanding of the involvement of the principal HSP families in MS.

Endocytic accessory factors and regulation of clathrin-mediated endocytosis

Up to 60 different proteins are recruited to the site of clathrin-mediated endocytosis in an ordered sequence. These accessory proteins have roles during all the different stages of clathrin-mediated endocytosis. First, they participate in the initiation of the endocytic event, thereby determining when and where endocytic vesicles are made; later they are involved in the maturation of the clathrin coat, recruitment of specific cargo molecules, bending of the membrane, and finally in scission and uncoating of the nascent vesicle. In addition, many of the accessory components are involved in regulating and coupling the actin cytoskeleton to the endocytic membrane. We will discuss the different accessory components and their various roles. Most of the data comes from studies performed with cultured mammalian cells or yeast cells. The process of endocytosis is well conserved between these different organisms, but there are also many interesting differences that may shed light on the mechanistic principles of endocytosis.

Overproduction and biophysical characterization of human HSP70 proteins

Heat shock proteins (HSP) perform vital cellular functions and modulate cell response pathways to physical and chemical stressors. A key feature of HSP function is the ability to interact with a broad array of protein binding partners as a means to potentiate downstream response pathways or facilitate protein folding. These binding interactions are driven by ATP-dependent conformational rearrangements in HSP proteins. The HSP70 family is evolutionarily conserved and is associated with diabetes and cancer progression and the etiopathogenesis of hepatic, cardiovascular, and neurological disorders in humans. However, functional characterization of human HSP70s has been stymied by difficulties in obtaining large quantities of purified protein. Studies of purified human HSP70 proteins are essential for downstream investigations of protein-protein interactions and in the rational design of novel family-specific therapeutics. Within this work, we present optimized protocols for the heterologous overexpression and purification of either the nucleotide binding domain (NBD) or the nucleotide and substrate binding domains of human HSPA9, HSPA8, and HSPA5 in either Escherichia coli or Saccharomyces cerevisiae. We also include initial biophysical characterization of HSPA9 and HSPA8. This work provides the basis for future biochemical studies of human HSP70 protein function and structure.

Trehalose reverses cell malfunction in fibroblasts from normal and Huntington's disease patients caused by proteosome inhibition

Huntington's disease (HD) is a neurodegenerative disorder characterized by progressive motor, cognitive and psychiatric deficits, associated with predominant loss of striatal neurons and is caused by polyglutamine expansion in the huntingtin protein. Mutant huntingtin protein and its fragments are resistant to protein degradation and produce a blockade of the ubiquitin proteasome system (UPS). In HD models, the proteasome inhibitor epoxomicin aggravates protein accumulation and the inductor of autophagy, trehalose, diminishes it. We have investigated the effects of epoxomicin and trehalose in skin fibroblasts of control and HD patients. Untreated HD fibroblasts have increased the levels of ubiquitinized proteins and higher levels of reactive oxygen species (ROS), huntingtin and the autophagy marker LAMP2A. Baseline replication rates were higher in HD than in controls fibroblasts but that was reverted after 12 passages. Epoxomicin increases the activated caspase-3, HSP70, huntingtin, ubiquitinated proteins and ROS levels in both HD and controls. Treatment with trehalose counteracts the increase in ROS, ubiquitinated proteins, huntingtin and activated caspase-3 levels induced by epoxomicin, and also increases the LC3 levels more in HD fibroblast than controls. These results suggest that trehalose could revert protein processing abnormalities in patients with Huntington's Disease.

Cloning, molecular characterization and expression analysis of heat shock cognate 70 (Hsc70) cDNA from turbot (Scophthalmus maximus)

As an essential member of the HSP70 family, heat shock cognate 70 (Hsc70) is a constitutively expressed molecular chaperone involved in protein metabolism. In this paper, turbot Hsc70 was cloned and the expression profile was also analyzed. The full-length cDNA of the turbot Hsc70 was 2,292 bp in length, including a 113-bp 5' UTR, a 223-bp 3' UTR and a 1,956-bp open reading frame coding a protein with 651 amino acid residues. Comparison of amino acid sequence revealed the existence of three classical HSP70 family signature motifs, a signature nonapeptide and one repeat of tetrapeptide in turbot Hsc70. The turbot Hsc70-deduced amino acids sequence exhibited 75.4-96.8 % homology with Hsp70s/Hsc70s of 24 other known sequences. In particular, the strongest homology was found with the cognate members of Hsc70 subfamily and the highest identity was found with Japanese flounder Hsc70. Semi-quantitative RT-PCR revealed that turbot Hsc70 transcripts were stably expressed in all tested tissues under normal physiological condition, while the expression levels also increased (~1.5-fold to ~threefold) after heat shock and bacterial infection. In addition, Hsc70 transcripts were detected throughout embryonic development and in turbot embryonic cell line (TEC) in the absence of any stress. Meanwhile, it was also heat inducible, but not cold inducible in TEC. These results suggest that Hsc70 gene may be involved in embryogenesis and cellular protection events under normal and stress condition.

HSPA8/HSC70 chaperone protein: structure, function, and chemical targeting

HSPA8/HSC70 protein is a fascinating chaperone protein. It represents a constitutively expressed, cognate protein of the HSP70 family, which is central in many cellular processes. In particular, its regulatory role in autophagy is decisive. We focused this review on HSC70 structure-function considerations and based on this, we put a particular emphasis on HSC70 targeting by small molecules and peptides in order to develop intervention strategies that deviate some of HSC70 properties for therapeutic purposes. Generating active biomolecules regulating autophagy via its effect on HSC70 can effectively be designed only if we understand the fine relationships between HSC70 structure and functions.

Hsp70 architecture: the formation of novel polymeric structures of Hsp70.1 and Hsc70 after proteotoxic stress

Heat induces Hsp70.1 (HSPA1) and Hsc70 (HSPA8) to form complex detergent insoluble cytoplasmic and nuclear structures that are distinct from the cytoskeleton and internal cell membranes. These novel structures have not been observed by earlier immunofluorescence studies as they are obscured by the abundance of soluble Hsp70.1/Hsc70 present in cells. While resistant to detergents, these Hsp70 structures display complex intracellular dynamics and are efficiently disaggregated by ATP, indicating that this pool of Hsp70.1/Hsc70 retains native function and regulation. Hsp70.1 promotes the repair of proteotoxic damage and cell survival after stress. In heated fibroblasts expressing Hsp70.1, Hsp70.1 and Hsc70 complexes are efficiently disaggregated before the cells undergo-heat induced apoptosis. In the absence of Hsp70.1, fibroblasts have increased rates of heat-induced apoptosis and maintain stable insoluble Hsc70 structures. The differences in the intracellular distribution of Hsp70.1 and Hsc70, combined with the ability of Hsp70.1, but not Hsc70, to promote the disaggregation of insoluble Hsp70.1/Hsc70 complexes, indicate that these two closely related proteins perform distinctly different cellular functions in heated cells.

Comprehensive review on the HSC70 functions, interactions with related molecules and involvement in clinical diseases and therapeutic potential

Heat shock cognate protein 70 (HSC70) is a constitutively expressed molecular chaperone which belongs to the heat shock protein 70 (HSP70) family. HSC70 shares some of the structural and functional similarity with HSP70. HSC70 also has different properties compared with HSP70 and other heat shock family members. HSC70 performs its full functions by the cooperation of co-chaperones. It interacts with many other molecules as well and regulates various cellular functions. It is also involved in various diseases and may become a biomarker for diagnosis and potential therapeutic targets for design, discovery, and development of novel drugs to treat various diseases. In this article, we provide a comprehensive review on HSC70 from the literatures including the basic general information such as classification, structure and cellular location, genetics and function, as well as its protein association and interaction with other proteins. In addition, we also discussed the relationship of HSC70 and related clinical diseases such as cancer, cardiovascular, neurological, hepatic and many other diseases and possible therapeutic potential and highlight the progress and prospects of research in this field. Understanding the functions of HSC70 and its interaction with other molecules will help us to reveal other novel properties of this protein. Scientists may be able to utilize this protein as a biomarker and therapeutic target to make significant advancement in scientific research and clinical setting in the future.

Proteomic analysis of purified Newcastle disease virus particles

Background

Newcastle disease virus (NDV) is an enveloped RNA virus, bearing severe economic losses to the poultry industry worldwide. Previous virion proteomic studies have shown that enveloped viruses carry multiple host cellular proteins both internally and externally during their life cycle. To address whether it also occurred during NDV infection, we performed a comprehensive proteomic analysis of highly purified NDV La Sota strain particles.

Results

In addition to five viral structural proteins, we detected thirty cellular proteins associated with purified NDV La Sota particles. The identified cellular proteins comprised several functional categories, including cytoskeleton proteins, annexins, molecular chaperones, chromatin modifying proteins, enzymes-binding proteins, calcium-binding proteins and signal transduction-associated proteins. Among these, three host proteins have not been previously reported in virions of other virus families, including two signal transduction-associated proteins (syntenin and Ras small GTPase) and one tumor-associated protein (tumor protein D52). The presence of five selected cellular proteins (i.e., β-actin, tubulin, annexin A2, heat shock protein Hsp90 and ezrin) associated with the purified NDV particles was validated by Western blot or immunogold labeling assays.

Conclusions

The current study presented the first standard proteomic profile of NDV. The results demonstrated the incorporation of cellular proteins in NDV particles, which provides valuable information for elucidating viral infection and pathogenesis.

The DSL1 complex: the smallest but not the least CATCHR

The DSL1 complex is a conserved tethering complex at the endoplasmic reticulum that recognizes Golgi-derived COPI vesicles and hands them over to the fusion machinery. The DSL1 complex is the simplest tethering complex of the complexes associated with tethering containing helical rods (CATCHR) family. CATCHR tethering complexes play a role at compartments along the exocytic and endocytic pathways. In this review, different functions of the DSL1 complex are discussed, some open questions with the seemingly straightforward picture are pointed out and alternative functions of the DSL1 complex members are mentioned.

MiR-3120 is a mirror microRNA that targets heat shock cognate protein 70 and auxilin messenger RNAs and regulates clathrin vesicle uncoating

We show that a single gene locus gives rise to two fully processed and functional miRNAs, i.e. that due to imperfect base pairing, two distinct microRNAs (miRNAs) can be produced from the fully complementary DNA strands. The antisense strand encodes miR-214, which is transcribed by its own promoter, whereas a novel miRNA, miR-3120, is co-expressed with its host gene mRNA. We also found that miR-3120 regulates important aspects of cellular function that are similar to that of its host gene, dynamin-3. miR-3120 was found to be located in neuronal cell bodies and to target Hsc70 and auxilin, and its lentivirus-mediated expression inhibited the uncoating of clathrin-coated vesicles. Finally, mirror miRNAs are likely to represent a new group of miRNAs with complex roles in coordinating gene expression.

Phosphorylation by Dyrk1A of clathrin coated vesicle-associated proteins: identification of the substrate proteins and the effects of phosphorylation

Dyrk1A phosphorylated multiple proteins in the clathrin-coated vesicle (CCV) preparations obtained from rat brains. Mass spectrometric analysis identified MAP1A, MAP2, AP180, and α- and β-adaptins as the phosphorylated proteins in the CCVs. Each protein was subsequently confirmed by [(32)P]-labeling and immunological methods. The Dyrk1A-mediated phosphorylation released the majority of MAP1A and MAP2 and enhanced the release of AP180 and adaptin subunits from the CCVs. Furthermore, Dyrk1A displaced adaptor proteins physically from CCVs in a kinase-concentration dependent manner. The clathrin heavy chain release rate, in contrast, was not affected by Dyrk1A. Surprisingly, the Dyrk1A-mediated phosphorylation of α- and β-adaptins led to dissociation of the AP2 complex, and released only β-adaptin from the CCVs. AP180 was phosphorylated by Dyrk1A also in the membrane-free fractions, but α- and β-adaptins were not. Dyrk1A was detected in the isolated CCVs and was co-localized with clathrin in neurons from mouse brain sections and from primary cultured rat hippocampus. Previously, we proposed that Dyrk1A inhibits the onset of clathrin-mediated endocytosis in neurons by phosphorylating dynamin 1, amphiphysin 1, and synaptojanin 1. Current results suggest that besides the inhibition, Dyrk1A promotes the uncoating process of endocytosed CCVs.

Human heat shock protein 105/110 kDa (Hsp105/110) regulates biogenesis and quality control of misfolded cystic fibrosis transmembrane conductance regulator at multiple levels

Heat shock protein 105/110-kDa (Hsp105/110), a member of the Hsp70 super family of molecular chaperones, serves as a nucleotide exchange factor for Hsc70, independently prevents the aggregation of misfolded proteins, and functionally relates to Hsp90. We investigated the roles of human Hsp105α, the constitutively expressed isoform, in the biogenesis and quality control of the cystic fibrosis transmembrane conductance regulator (CFTR). In the endoplasmic reticulum (ER), Hsp105 facilitates CFTR quality control at an early stage in its biosynthesis but promotes CFTR post-translational folding. Deletion of Phe-508 (ΔF508), the most prevalent mutation causing cystic fibrosis, interferes with de novo folding of CFTR, impairing its export from the ER and accelerating its clearance in the ER and post-Golgi compartments. We show that Hsp105 preferentially associates with and stabilizes ΔF508 CFTR at both levels. Introduction of the Hsp105 substrate binding domain potently increases the steady state level of ΔF508 CFTR by reducing its early-stage degradation. This in turn dramatically enhances ΔF508 CFTR cell surface functional expression in cystic fibrosis airway epithelial cells. Although other Hsc70 nucleotide exchange factors such as HspBP1 and BAG-2 inhibit CFTR post-translational degradation in the ER through cochaperone CHIP, Hsp105 has a primary role promoting CFTR quality control at an earlier stage. The Hsp105-mediated multilevel regulation of ΔF508 CFTR folding and quality control provides new opportunities to understand how chaperone machinery regulates the homeostasis and functional expression of misfolded proteins in the cell. Future studies in this direction will inform therapeutics development for cystic fibrosis and other protein misfolding diseases.

Expression pattern of heat-shock cognate 70 gene of humphead snapper, Lutjanus sanguineus (Cuvier), infected by Vibrio harveyi

The heat-shock cognate 70 (HSC70) gene of humphead snapper, Lutjanus sanguineus, designated as ByHSC70, was cloned by rapid amplification of cDNA ends (RACE) with the primers designed from the known expressed sequence tag (EST) identified from the subtracted cDNA library of the head kidney of humphead snapper. The full-length cDNA of ByHSC70 is 2313 bp, containing a 5' terminal untranslated region (UTR) of 96 bp, a 3' terminal UTR of 267 bp, and an open reading frame (ORF) of 1950 bp encoding a polypeptide of 650 amino acids with a theoretical molecular weight of 71.21 kDa and an estimated isoelectric point (pI) of 5.08. ByHSC70 contained three classical HSP70 family signatures. BLAST analysis showed that the amino acid sequence of ByHSC70 had the highest similarity of 99% when compared with other HSC70s. Fluorescent real-time quantitative RT-PCR was used to examine the expression of ByHSC70 gene in eight kinds of tissues/organs of humphead snapper after challenge with Vibrio harveyi. There was a clear time-dependent expression pattern of ByHSC70 in head kidney, spleen and thymus after bacterial challenge, and the expression of mRNA reached a maximum level at 9, 6 and 24 h post-infection and then returned to control levels after 15, 24 and 36 h, respectively. Our results suggest that HSC70 is an important component in the immune system of humphead snapper, its their rapid transcriptional upregulation in response to V. harveyi infection might be important for survival of humphead snapper.

Molecular mechanism of protein folding in the cell

F.-Ulrich Hartl and Arthur Horwich will share this year's Lasker Basic Medical Science Award for the discovery of the cell's protein-folding machinery, exemplified by cage-like structures that convert newly synthesized proteins into their biologically active forms. Their fundamental findings reveal mechanisms that operate in normal physiologic processes and help to explain the problems that arise in diseases of protein folding.

Characterization of human Sec16B: indications of specialized, non-redundant functions

The endoplasmic reticulum (ER) represents the entry point into the secretory pathway and from here newly synthesized proteins and lipids are delivered to the Golgi. The selective cargo export from the ER is mediated by COPII-assembly at specific sites of the ER, the so-called transitional ER (tER). The peripheral membrane protein Sec16, first identified in yeast, localizes to transitional ER and plays a key role in organization of these sites. Sec16 defines the tER and is thought to act as a scaffold for the COPII coat assembly. In humans two isoforms of Sec16 are present, the larger Sec16A and the smaller Sec16B. Nevertheless, the functional differences between the two isoforms are ill-defined. Here we describe characterization of the localization and dynamics of Sec16B relative to Sec16A, provide evidence that Sec16B is likely a minor or perhaps specialized form of Sec16, and that it is not functionally redundant with Sec16A.

Multiple hsp70 isoforms in the eukaryotic cytosol: mere redundancy or functional specificity?

Hsp70 molecular chaperones play a variety of functions in every organism, cell type and organelle, and their activities have been implicated in a number of human pathologies, ranging from cancer to neurodegenerative diseases. The functions, regulations and structure of Hsp70s were intensively studied for about three decades, yet much still remains to be learned about these essential folding enzymes. Genome sequencing efforts revealed that most genomes contain multiple members of the Hsp70 family, some of which co-exist in the same cellular compartment. For example, the human cytosol and nucleus contain six highly homologous Hsp70 proteins while the yeast Saccharomyces cerevisiae contains four canonical Hsp70s and three fungal-specific ribosome-associated and specialized Hsp70s. The reasons and significance of the requirement for multiple Hsp70s is still a subject of debate. It has been postulated for a long time that these Hsp70 isoforms are functionally redundant and differ only by their spatio-temporal expression patterns. However, several studies in yeast and higher eukaryotic organisms challenged this widely accepted idea by demonstrating functional specificity among Hsp70 isoforms. Another element of complexity is brought about by specific cofactors, such as Hsp40s or nucleotide exchange factors that modulate the activity of Hsp70s and their binding to client proteins. Hence, a dynamic network of chaperone/co-chaperone interactions has evolved in each organism to efficiently take advantage of the multiple cellular roles Hsp70s can play. We summarize here our current knowledge of the functions and regulations of these molecular chaperones, and shed light on the known functional specificities among isoforms.

Potential role of heat shock proteins in neural differentiation of murine embryonal carcinoma stem cells (P19)

HSPs (heat shock proteins) have been recognized to maintain cellular homoeostasis during changes in microenvironment. The present study aimed to investigate the HSPs expression pattern in hierarchical neural differentiation stages from mouse embryonal carcinoma stem cells (P19) and its role in heat stressed exposed cells. For induction of HSPs, cells were heated at 42°C for 30 min and recovered at 37°C in different time points. For neural differentiation, EBs (embryoid bodies) were formed by plating P19 cells in bacterial dishes in the presence of 1 mM RA (retinoic acid) and 5% FBS (fetal bovine serum). Then, on the sixth day, EBs were trypsinized and plated in differentiation medium containing neurobasal medium, B27, N2 and 5% FBS and for an extra 4 days. The expression of HSPs and neural cell markers were evaluated by Western blot, flow cytometry and immunocytochemistry in different stages. Our results indicate that HSC (heat shock constant)70 and HSP60 expressions decreased following RA treatment, EB formation and in mature neural cells derived from heat-stressed single cells and not heat-treated EBs. While the level of HSP90 increased six times following maturation process, HSP25 was expressed constantly during neural differentiation; however, its level was enhanced with heat stress. Accordingly, heat shock 12 h before the initiation of differentiation did not affect the expression of neuroectodermal and neural markers, nestin and β-tubulin III, respectively. However, both markers increased when heat shock was induced after treatment and when EBs were formed. In conclusion, our results raise the possibility that HSPs could regulate cell differentiation and proliferation under both physiological and pathological conditions.

Hsp70 and its molecular role in nervous system diseases

Heat shock proteins (HSPs) are induced in response to many injuries including stroke, neurodegenerative disease, epilepsy, and trauma. The overexpression of one HSP in particular, Hsp70, serves a protective role in several different models of nervous system injury, but has also been linked to a deleterious role in some diseases. Hsp70 functions as a chaperone and protects neurons from protein aggregation and toxicity (Parkinson disease, Alzheimer disease, polyglutamine diseases, and amyotrophic lateral sclerosis), protects cells from apoptosis (Parkinson disease), is a stress marker (temporal lobe epilepsy), protects cells from inflammation (cerebral ischemic injury), has an adjuvant role in antigen presentation and is involved in the immune response in autoimmune disease (multiple sclerosis). The worldwide incidence of neurodegenerative diseases is high. As neurodegenerative diseases disproportionately affect older individuals, disease-related morbidity has increased along with the general increase in longevity. An understanding of the underlying mechanisms that lead to neurodegeneration is key to identifying methods of prevention and treatment. Investigators have observed protective effects of HSPs induced by preconditioning, overexpression, or drugs in a variety of models of brain disease. Experimental data suggest that manipulation of the cellular stress response may offer strategies to protect the brain during progression of neurodegenerative disease.

Heat shock cognate protein 70 regulates gephyrin clustering

Formation and stabilization of postsynaptic glycine receptor (GlyR) clusters result from their association with the polymerized scaffold protein gephyrin. At the cell surface, lateral diffusion and local trapping of GlyR by synaptic gephyrin clusters is one of the main factors controlling their number. However, the mechanisms regulating gephyrin/GlyR cluster sizes are not fully understood. To identify molecular binding partners able to control gephyrin cluster stability, we performed pull-down assays with full-length or truncated gephyrin forms incubated in a rat spinal cord extract, combined with mass spectrometric analysis. We found that heat shock cognate protein 70 (Hsc70), a constitutive member of the heat shock protein 70 (Hsp70) family, selectively binds to the gephyrin G-domain. Immunoelectron microscopy of mouse spinal cord sections showed that Hsc70 could be colocalized with gephyrin at inhibitory synapses. Furthermore, ternary Hsc70-gephyrin-GlyR coclusters were formed following transfection of COS-7 cells. Upon overexpression of Hsc70 in mouse spinal cord neurons, synaptic accumulation of gephyrin was significantly decreased, but GlyR amounts were unaffected. In the same way, Hsc70 inhibition increased gephyrin accumulation at inhibitory synapses without modifying GlyR clustering. Single particle tracking experiments revealed that the increase of gephyrin molecules reduced GlyR diffusion rates without altering GlyR residency at synapses. Our findings demonstrate that Hsc70 regulates gephyrin polymerization independently of its interaction with GlyR. Therefore, gephyrin polymerization and synaptic clustering of GlyR are uncoupled events.