Mechanisms of the Hsp70 chaperone system

HSFA2 Functions in the Physiological Adaptation of Undifferentiated Plant Cells to Spaceflight

Heat Shock Factor A2 (HsfA2) is part of the Heat Shock Factor (HSF) network, and plays an essential role beyond heat shock in environmental stress responses and cellular homeostatic control. Arabidopsis thaliana cell cultures derived from wild type (WT) ecotype Col-0 and a knockout line deficient in the gene encoding HSFA2 (HSFA2 KO) were grown aboard the International Space Station (ISS) to ascertain whether the HSF network functions in the adaptation to the novel environment of spaceflight. Microarray gene expression data were analyzed using a two-part comparative approach. First, genes differentially expressed between the two environments (spaceflight to ground) were identified within the same genotype, which represented physiological adaptation to spaceflight. Second, gene expression profiles were compared between the two genotypes (HSFA2 KO to WT) within the same environment, which defined genes uniquely required by each genotype on the ground and in spaceflight-adapted states. Results showed that the endoplasmic reticulum (ER) stress and unfolded protein response (UPR) define the HSFA2 KO cells' physiological state irrespective of the environment, and likely resulted from a deficiency in the chaperone-mediated protein folding machinery in the mutant. Results further suggested that additional to its universal stress response role, HsfA2 also has specific roles in the physiological adaptation to spaceflight through cell wall remodeling, signal perception and transduction, and starch biosynthesis. Disabling HsfA2 altered the physiological state of the cells, and impacted the mechanisms induced to adapt to spaceflight, and identified HsfA2-dependent genes that are important to the adaption of wild type cells to spaceflight. Collectively these data indicate a non-thermal role for the HSF network in spaceflight adaptation.

The expanding world of plant J-domain proteins

Plants maintain cellular proteostasis during different phases of growth and development despite a barrage of biotic and abiotic stressors in an ever-changing environment. This requires a collaborative effort of a cadre of molecular chaperones. Hsp70s and their obligate co-chaperones, J-domain proteins (JDPs), are arguably the most ubiquitous and formidable components of the cellular chaperone network, facilitating numerous and diverse cellular processes and allowing survival under a plethora of stressful conditions. JDPs are also among the most versatile chaperones. Compared to Hsp70s, the number of JDP-encoding genes has proliferated, suggesting the emergence of highly complex Hsp70-JDP networks, particularly in plants. Recent studies indicate that besides the increase in the number of JDP encoding genes; regulatory differences, neo- and sub-functionalization, and inter- and intra-class combinatorial interactions, is rapidly expanding the repertoire of Hsp70-JDP systems. This results in highly robust and functionally diverse chaperone networks in plants. Here, we review the current status of plant JDP research and discuss how the paradigm shift in the field can be exploited toward a better understanding of JDP function and evolution.

Two Arabidopsis Chloroplast GrpE Homologues Exhibit Distinct Biological Activities and Can Form Homo- and Hetero-Oligomers

Flowering plants have evolved two distinct clades of chloroplast GrpE homologues (CGEs), which are the nucleotide exchange factor for Hsp70. In Arabidopsis, they are named AtCGE1 (At5g17710) and AtCGE2 (At1g36390). Characterization of their corresponding T-DNA insertion mutants revealed that there is no visible change in phenotype except a defect in protein import in an AtCGE2-knockout mutant under normal growth conditions. However, the embryo development of an AtCGE1-knockout mutant was arrested early at the globular stage. An AtCGE1-knockdown mutant, harboring a T-DNA insertion in the 5'-UTR region, exhibited growth retardation and protein import defect, and its mutant phenotypes became more severe when AtCGE2 was further knocked out. Sub-organellar distribution implied that AtCGE2 might be important for membrane biology due to its preferential association with chloroplast membranes. Biochemical studies and complementation tests showed that only AtCGE1, but not AtCGE2, can effectively rescue the heat-sensitive phenotype of Escherichia coli grpE mutant and robustly stimulate the refolding of denatured luciferase by DnaK. Interestingly, AtCGE1 and AtCGE2 are tending to form heterocomplexes, which exhibit comparable co-chaperone activity to AtCGE1 homocomplexes. Our data indicate that AtCGE1 is the principle functional homologue of GrpE. The possibility that AtCGE2 has a subsidiary or regulatory function through homo- and/or hetero-oligomerization is discussed.

Heat shock protein 70 as a supplementary receptor facilitates enterovirus 71 infections in vitro

As one of the major causative agents of hand, foot and mouth disease (HFMD), enterovirus 71 (EV71) is a small, non-enveloped positive stranded RNA virus. Children suffering EV71 infection may cause severe symptoms including neurological complications, pulmonary edema and aseptic meningitis. EV71 is a neurotropic virus and it can cause the damage of nervous cells, cytokine storm and toxic substance. Identifying the factors that mediate viral binding or entry to host cells is important to uncover the mechanisms which viruses utilize to cause diseases in human body. Heat shock protein 70 (HSP70) is induced during virus infection and facilitates proper protein folding during viral propagation. The role that HSP70 plays during EV71 infection is still unclear. In this study, siRNA interference technique and transgenic technique were used to investigate the interaction between HSP70 and EV71 virus. The result demonstrated that the cell surface HSP70 is not essential for EV71 infection but helps the initial binding of virus to host cells and that multiple receptors are involved during EV71 infection. In addition, HSP70 was upregulated in human neuroblastoma cells (SK-N-SH) infected with EV71.

Highly polluted life history and acute heat stress, a hazardous mix for blue mussels

Intertidal sessile organisms constitute through their life history unintended stress recorders. This study focuses on the impact of pollution on Mytilus edulis ability to cope with an additional stress. For this purpose, two acclimation stages to different temperatures were conducted before an acute stress exposure in mussels collected from a heavily polluted site. Gill proteomes were analyzed by 2DE and regulated proteins identified. Massive mortality was observed for organisms acclimated to colder temperatures. Despite this major difference, both groups shared a common response with a strong representation of proteoforms corresponding to "folding, sorting and degradation" processes. Nevertheless, surviving mussels exhibit a marked increase in protein degradation consistent with the observed decrease of cell defense proteins. Mussels acclimated to warmer temperature response is essentially characterized by an improved heat shock response. These results show the differential ability of mussels to face both pollution and acute heat stress, particularly for low-acclimated organisms.

Proteasome-Rich PaCS as an Oncofetal UPS Structure Handling Cytosolic Polyubiquitinated Proteins. In Vivo Occurrence, in Vitro Induction, and Biological Role

In this article, we outline and discuss available information on the cellular site and mechanism of proteasome interaction with cytosolic polyubiquitinated proteins and heat-shock molecules. The particulate cytoplasmic structure (PaCS) formed by barrel-like particles, closely reproducing in vivo the high-resolution structure of 26S proteasome as isolated in vitro, has been detected in a variety of fetal and neoplastic cells, from living tissue or cultured cell lines. Specific trophic factors and interleukins were found to induce PaCS during in vitro differentiation of dendritic, natural killer (NK), or megakaryoblastic cells, apparently through activation of the MAPK-ERK pathway. Direct interaction of CagA bacterial oncoprotein with proteasome was shown inside the PaCSs of a Helicobacter pylori-infected gastric epithelium, a finding suggesting a role for PaCS in CagA-mediated gastric carcinogenesis. PaCS dissolution and autophagy were seen after withdrawal of inducing factors. PaCS-filled cell blebs and ectosomes were found in some cells and may represent a potential intercellular discharge and transport system of polyubiquitinated antigenic proteins. PaCS differs substantially from the inclusion bodies, sequestosomes, and aggresomes reported in proteinopathies like Huntington or Parkinson diseases, which usually lack PaCS. The latter seems more linked to conditions of increased cell proliferation/differentiation, implying an increased functional demand to the ubiquitin–proteasome system.

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.

Hsc70-2 is required for Beet black scorch virus infection through interaction with replication and capsid proteins

Dissecting the complex molecular interplay between the host plant and invading virus improves our understanding of the mechanisms underlying viral pathogenesis. In this study, immunoprecipitation together with the mass spectrometry analysis revealed that the heat shock protein 70 (Hsp70) family homolog, Hsc70-2, was co-purified with beet black scorch virus (BBSV) replication protein p23 and coat protein (CP), respectively. Further experiments demonstrated that Hsc70-2 interacts directly with both p23 and CP, whereas there is no interaction between p23 and CP. Hsc70-2 expression is induced slightly during BBSV infection of Nicotiana benthamiana, and overexpression of Hsc70-2 promotes BBSV accumulation, while knockdown of Hsc70-2 in N. benthamiana leads to drastic reduction of BBSV accumulation. Infection experiments revealed that CP negatively regulates BBSV replication, which can be mitigated by overexpression of Hsc70-2. Further experiments indicate that CP impairs the interaction between Hsc70-2 and p23 in a dose-dependent manner. Altogether, we provide evidence that besides specific functions of Hsp70 family proteins in certain aspects of viral infection, they can serve as a mediator for the orchestration of virus infection by interacting with different viral components. Our results provide new insight into the role of Hsp70 family proteins in virus infection.

THE ROLE OF PROTEIN CHAPERONES IN THE SURVIVAL FROM ANTHRACYCLINE-INDUCED OXIDATIVE STRESS IN SACCHAROMYCES CEREVISIAE

Several S. cerevisiae deletion strains involving heat-shock response factors were among the most sensitive mutants identified in a previous genetic screen for doxorubicin hypersensitivity. These strains included ydj1Δ, ssz1Δ and zuo1Δ mutants. In addition, new1Δ, whose function was unknown, also displayed significant sensitivity to anthracyclines. We further investigated the basis for the sensitivity of these mutants. We determined that heat-shock could partially rescue the sensitivity of the strains to doxorubicin, including the homologous recombination mutant rad52Δ, which is sensitive to doxorubicin-mediated DNA double strand breaks (DSBs). However, none of the heat-shock response mutants were sensitive to DSBs, but were highly sensitive to reactive oxygen species (ROS) generated by quinone-ring-containing agents, such as anthracyclines and menadione. A fluorescent-based assay indicates that doxorubicin causes protein aggregation. Interestingly, the disaggregase mutant hsp104Δ is not sensitive to anthracyclines or menadione suggesting that Hsp104p does not play a role in disaggregating doxorubicin-induced protein aggregates. However New1p, which has been recently shown to be a novel disaggregase, is essential for cell viability after exposure to anthracyclines and menadione and it is not involved in thermotolerance. Our data suggest that in S. cerevisiae, doxorubicin produces protein aggregation through ROS and requires Ydj1p and New1p for resolution.

Introgression of heat shock protein (Hsp70 and sHsp) genes into the Malaysian elite chilli variety Kulai (Capsicum annuum L.) through the application of marker-assisted backcrossing (MAB)

Backcrossing together with simple sequence repeat marker strategy was adopted to improve popular Malaysian chilli Kulai (Capsicum annuum L.) for heat tolerance. The use of molecular markers in backcross breeding and selection contributes significantly to overcoming the main drawbacks such as increase linkage drag and time consumption, in the ancient manual breeding approach (conventional), and speeds up the genome recovery of the recurrent parent. The strategy was adopted to introgress heat shock protein gene(s) from AVPP0702 (C. annuum L.), which are heat-tolerant, into the genetic profile of Kulai, a popular high-yielding chilli but which is heat sensitive. The parents were grown on seed trays, and parental screening was carried out with 252 simple sequence repeat markers. The selected parents were crossed and backcrossed to generate F1 hybrids and backcross generations. Sixty-eight markers appeared to be polymorphic and were used to assess the backcross generation; BC1F1, BC2F1 and BC3F1. The average recipient allele of the selected four BC1F1 plants was 80.75% which were used to produce the BC2F1 generation. BC1-P7 was the best BC1F1 plant because it had the highest recovery at 83.40% and was positive to Hsp-linked markers (Hsp70-u2 and AGi42). After three successive generations of backcrossing, the average genome recovery of the recurrent parent in the selected plants in BC3F1 was 95.37%. Hsp gene expression analysis was carried out on BC1F1, BC2F1 and BC3F1 selected lines. The Hsp genes were found to be up-regulated when exposed to heat treatment. The pattern of Hsp expression in the backcross generations was similar to that of the donor parent. This confirms the successful introgression of a stress-responsive gene (Hsp) into a Kulai chilli pepper variety. Furthermore, the yield performance viz. plant height, number of fruits, fruit length and weight and total yield of the improved plant were similar with the recurrent parent except that the plant height was significantly lower than the Kulai (recurrent) parent.

Alfalfa-derived HSP70 administered intranasally improves insulin sensitivity in mice

Heat shock protein (HSP) 70 is an abundant cytosolic chaperone protein that is deficient in insulin-sensitive tissues in diabetes and unhealthy aging, and is considered a longevity target. It is also protective in neurological disease models. Using HSP70 purified from alfalfa and administered as an intranasal solution, we tested in whether the administration of Hsp70 to diet-induced diabetic mice would improve insulin sensitivity. Both the 10 and 40 μg given three times per week for 26 days significantly improved the response to insulin. The HSP70 was found to pass into the olfactory bulbs within 4-6 hours of a single dose. These results suggest that a relatively inexpensive, plentiful source of HSP70 administered in a simple, non-invasive manner, has therapeutic potential in diabetes.

Dynamin-Like Proteins Are Potentially Involved in Membrane Dynamics within Chloroplasts and Cyanobacteria

Dynamin-like proteins (DLPs) are a family of membrane-active proteins with low sequence identity. The proteins operate in different organelles in eukaryotic cells, where they trigger vesicle formation, membrane fusion, or organelle division. As discussed here, representatives of this protein family have also been identified in chloroplasts and DLPs are very common in cyanobacteria. Since cyanobacteria and chloroplasts, an organelle of bacterial origin, have similar internal membrane systems, we suggest that DLPs are involved in membrane dynamics in cyanobacteria and chloroplasts. Here, we discuss the features and activities of DLPs with a focus on their potential presence and activity in chloroplasts and cyanobacteria.

Expression of VEGF and Cox-2 in Patients with Esophageal Squamous Cell Carcinoma

Esophageal cancer is a highly aggressive neoplasm. In Brazil, it is the sixth most frequent among men and fifteenth among women. The most common type is squamous cell carcinoma (SCC), responsible for 96% of cases. Twenty-eight specimens of Esophael squamous cell carcinoma (ESCC) were obtained by surgery procedures.The tissues were fixed in formalin and embedded in paraffin. In each case, all available hematoxylin and eosin stained sections were examined and a representative block was selected. The ages of these patients ranged from 40 to 93 years, with a mean age of 60 years. Results: The histological grade of tumors was 4 well-differentiated, 19 moderately differentiated and 5 poorly differentiated. Expression of Cox-2 and VEGF in ESCC was demonstrated in 23 (82,14%) and 13 (44,43%) cases, respectively. Adjacent normal mucosa was positive in 11 (39,29%) samples and 9 (32,15%) samples for Cox-2 and VEGF, respectively. No relationship between the expression of Cox-2 and VEGF with the clinicopathological parameters, including gender, age, surgical margin, lymph node status and tumor differentiation. The median follow-up period was 60 months. Survival analysis of patients with ESCC showed no relationship with the expression of Cox-2 and VEGF. Conclusion: VEGF and Cox-2 are expressed in ESCC. Cox-2, VEGF, play a significant role in the origin and development of ESCC and the inhibitors of these proteins could prove to be an important therapeutic tool in the control of this disease.

Biophysical analysis of the effect of chemical modification by 4-oxononenal on the structure, stability, and function of binding immunoglobulin protein (BiP)

Binding immunoglobulin protein (BiP) is a molecular chaperone important for the folding of numerous proteins, which include millions of immunoglobulins in human body. It also plays a key role in the unfolded protein response (UPR) in the endoplasmic reticulum. Free radical generation is a common phenomenon that occurs in cells under healthy as well as under stress conditions such as ageing, inflammation, alcohol consumption, and smoking. These free radicals attack the cell membranes and generate highly reactive lipid peroxidation products such as 4-oxononenal (4-ONE). BiP is a key protein that is modified by 4-ONE. In this study, we probed how such chemical modification affects the biophysical properties of BiP. Upon modification, BiP shows significant tertiary structural changes with no changes in its secondary structure. The protein loses its thermodynamic stability, particularly, that of the nucleotide binding domain (NBD) where ATP binds. In terms of function, the modified BiP completely loses its ATPase activity with decreased ATP binding affinity. However, modified BiP retains its immunoglobulin binding function and its chaperone activity of suppressing non-specific protein aggregation. These results indicate that 4-ONE modification can significantly affect the structure-function of key proteins such as BiP involved in cellular pathways, and provide a molecular basis for how chemical modifications can result in the failure of quality control mechanisms inside the cell.

Cellular Chaperones As Therapeutic Targets in ALS to Restore Protein Homeostasis and Improve Cellular Function

Heat shock proteins (Hsps) are ubiquitously expressed chaperone proteins that enable cells to cope with environmental stresses that cause misfolding and denaturation of proteins. With aging this protein quality control machinery becomes less effective, reducing the ability of cells to cope with damaging environmental stresses and disease-causing mutations. In neurodegenerative disorders such as Amyotrophic Lateral Sclerosis (ALS), such mutations are known to result in protein misfolding, which in turn results in the formation of intracellular aggregates cellular dysfunction and eventual neuronal death. The exact cellular pathology of ALS and other neurodegenerative diseases has been elusive and thus, hindering the development of effective therapies. However, a common scheme has emerged across these "protein misfolding" disorders, in that the mechanism of disease involves one or more aspects of proteostasis; from DNA transcription, RNA translation, to protein folding, transport and degradation via proteosomal and autophagic pathways. Interestingly, members of the Hsp family are involved in each of these steps facilitating normal protein folding, regulating the rate of protein synthesis and degradation. In this short review we summarize the evidence that suggests that ALS is a disease of protein dyshomeostasis in which Hsps may play a key role. Overwhelming evidence now indicates that enabling protein homeostasis to cope with disease-causing mutations might be a successful therapeutic strategy in ALS, as well as other neurodegenerative diseases. Novel small molecule co-inducers of Hsps appear to be able to achieve this aim. Arimoclomol, a hydroxylamine derivative, has shown promising results in cellular and animal models of ALS, as well as other protein misfolding diseases such as Inclusion Body Myositis (IBM). Initial clinical investigations of Arimoclomol have shown promising results. Therefore, it is possible that the long series of unsuccessful clinical trials for ALS may soon be reversed, as optimal targeting of proteostasis in ALS may now be possible, and may deliver clinical benefit to patients.

Silver nanoparticles and dissolved silver activate contrasting immune responses and stress-induced heat shock protein expression in sea urchin

Using immune cells of sea urchin Strongylocentrotus droebachiensis in early development as a model, the cellular protective mechanisms against ionic and poly(allylamine)-coated silver nanoparticle (AgNPs; 14 ± 6 nm) treatments at 100 μg L^-1 were investigated. Oxidative stress, heat shock protein expression, and pigment production by spherulocytes were determined as well as AgNP translocation pathways and their multiple effects on circulating coelomocytes. Sea urchins showed an increasing resilience to Ag over time because ionic Ag is accumulated in a steady way, although nanoAg levels dropped between 48 h and 96 h. A clotting reaction emerged on tissues injured by dissolved Ag (present as chloro-complexes in seawater) between 12 h and 48 h. Silver contamination and nutritional state influenced the production of reactive oxygen species. After passing through coelomic sinuses and gut, AgNPs were found in coelomocytes. Inside blood vessels, apoptosis-like processes appeared in coelomocytes highly contaminated by poly(allylamine)-coated AgNPs. Increasing levels of Ag accumulated by urchins once exposed to AgNPs pointed to a Trojan-horse mechanism operating over 12-d exposure. However, under short-term treatments, physical interactions of poly(allylamine)-coated AgNPs with cell structures might be, at some point, predominant and responsible for the highest levels of stress-related proteins detected. The present study is the first report detailing nano-translocation in a marine organism and multiple mechanisms by which sea urchin cells can deal with toxic AgNPs. Environ Toxicol Chem 2017;36:1872-1886. © 2016 SETAC.

The Role of the Multifunctional BAG3 Protein in Cellular Protein Quality Control and in Disease

In neurons, but also in all other cells the complex proteostasis network is monitored and tightly regulated by the cellular protein quality control (PQC) system. Beyond folding of newly synthesized polypeptides and their refolding upon misfolding the PQC also manages the disposal of aberrant proteins either by the ubiquitin-proteasome machinery or by the autophagic-lysosomal system. Aggregated proteins are primarily degraded by a process termed selective macroautophagy (or aggrephagy). One such recently discovered selective macroautophagy pathway is mediated by the multifunctional HSP70 co-chaperone BAG3 (BCL-2-associated athanogene 3). Under acute stress and during cellular aging, BAG3 in concert with the molecular chaperones HSP70 and HSPB8 as well as the ubiquitin receptor p62/SQSTM1 specifically targets aggregation-prone proteins to autophagic degradation. Thereby, BAG3-mediated selective macroautophagy represents a pivotal adaptive safeguarding and emergency system of the PQC which is activated under pathophysiological conditions to ensure cellular proteostasis. Interestingly, BAG3-mediated selective macroautophagy is also involved in the clearance of aggregated proteins associated with age-related neurodegenerative disorders, like Alzheimer’s disease (tau-protein), Huntington’s disease (mutated huntingtin/polyQ proteins), and amyotrophic lateral sclerosis (mutated SOD1). In addition, based on its initial description BAG3 is an anti-apoptotic protein that plays a decisive role in other widespread diseases, including cancer and myopathies. Therefore, in the search for novel therapeutic intervention avenues in neurodegeneration, myopathies and cancer BAG3 is a promising candidate.

Response a chronic effects of PBDE-47: Up-regulations of HSP60 and HSP70 expression in freshwater bivalve Anodonta woodiana

Heat shock proteins (HSPs) play an important role in adaption of environmental stress by protein folding, membrane translocation, degradation of misfolded proteins and other regulatory processes. Our previous study showed oxidative stress generated from polybrominated diphenyl ether-47 (PBDE-47) could cause an acute toxicity on freshwater bivalve Anodonta Woodiana, but the effect of chronic toxicity need to be elucidated. In order to further investigate the chronic effect of PBDE-47, clams A. Woodiana were randomly divided into the PBDE-47 treated group administrated with PBDE-47 at a concentration 3.36 μg/L and control group treated with a similar volume dimethyl sulfoxide. Two complete HSP sequences were isolated from A. Woodianaa and respectively named AwHSP60 and AwHSP70. They were widely distributed in foot, gill, hepatopancreas, adductor muscle, heart, hemocytes and mantle. Administration of PBDE-47 could result in a significant up-regulation of AwHSP60 and AwHSP70 expressions in the hepatopancreas, gill and hemocytes. In the hepatopancreas, compared with that of control group, mRNA level of AwHSP60 increased more than 89.9% (P < 0.05) from day 1-15, AwHSP70 increased more 2.79 times (P < 0.01). In the gill, during experiment observed, expression of AwHSP60 increased more 2.09 times (P < 0.01) in contrasted with that of control group. Significant up-regulation of AwHSP70 expression showed a reversed U shape. In the hemocytes, AwHSP60 and AwHSP70 expressions of PBDE-47 treated group respectively increased more 2.09 times (P < 0.05) and 1.81 times (P < 0.05) compared with that of control group. These results indicated that up-regulations of AwHSP60 and AwHSP70 expression are contribute to enhancing adaption of bivalve A. Woodiana exposed to PBDE-47 treatment.

Nilotinib induces ER stress and cell death in H9c2 cells

Tyrosine kinases inhibitors (TKi) represent a relatively novel class of anticancer drugs that target cellular pathways overexpressed in certain types of malignancies, such as chronic myeloid leukaemia (CML). Nilotinib, ponatinib and imatinib exhibit cardiotoxic and vascular effects. In this study, we focused on possible cardiotoxicity of nilotinib using H9c2 cells as a suitable cell model. We studied role of endoplasmic reticulum (ER) stress and apoptosis in nilotinib toxicity using a complex approach. Nilotinib impaired mitochondrial function and induced formation of ROS under clinically relevant concentrations. In addition, ability of nilotinib to induce ER stress has been shown. These events result in apoptotic cell death. All these mechanisms contribute to cytotoxic effect of the drug. In addition, involvement of ER stress in nilotinib toxicity may be important in co-treatment with pharmaceuticals affecting ER and ER stress, e.g. beta-blockers or sartans, and should be further investigated.

Identification of calmodulin binding proteins in the entomopathogenic fungus Beauveria bassiana

Calmodulin (CaM) is a primary Ca²⁺ receptor and plays a pivotal role in a variety of cellular responses in eukaryotes. Even though a large number of CaM-binding proteins are well known in yeast, plants, and animals, little is known regarding CaM-targeted proteins in filamentous fungi. To identify CaM-binding proteins in filamentous fungi, we used a proteomics method coupled with co-immunoprecipitation (CoIP) and MALDI-TOF/TOF mass spectrometry (MS) in Beauveria bassiana. Through this method, we identified ten CaM-binding proteins in B. bassiana. One of the CaM-targeted proteins was the heat shock protein 70 (BbHSP70) in B. bassiana. Our biochemical study showed that ATP inhibits the molecular interaction between BbHSP70 and CaM, suggesting a regulatory mechanism between CaM and ATP for regulating BbHSP70.

Co-enzyme Q10 and acetyl salicylic acid enhance Hsp70 expression in primary chicken myocardial cells to protect the cells during heat stress

We investigated the effects of co-enzyme Q10 (Q10) and acetyl salicylic acid (ASA) on expression of Hsp70 in the protection of primary chicken myocardial cells during heat stress. Western blot analysis showed that Q10 and ASA accelerated the induction of Hsp70 when chicken myocardial cells were exposed to hyperthermia. In the absence of heat stress, however, neither Q10 nor ASA are able to upregulate Hsp70 expression. Analysis of enzymes that respond to cellular damage and pathological examination revealed that ectopic expression of ASA and Q10 alleviate cellular damage during heat stress. Quantification of heat shock factors (HSF) indicated that treatment of ASA increased the expression of HSF-1 and HSF-3 during heat stress. Treatment with Q10 resulted in the elevation of HSF-1 expression. Expression of HSF-2 and HSF-4 was not affected by ASA or Q10. Subcellular distribution analysis of HSF-1 and HSF-3 showed that in response to heat stress ASA promoted nuclear translocation of HSF-1 and HSF-3, while Q10 promoted only HSF-1 nuclear translocation. Chromatin immunoprecipitation (ChIP) analysis indicated that HSF-1 occupies the Hsp70 promoter in chicken primary myocardial cells during heat stress and under normal conditions, while HSF-3 occupies the Hsp70 promoter only during heat stress. Real-time PCR analysis revealed that ASA induces HSF-1 and HSF-3 binding to Hsp70 HSE, while Q10 only induces HSF1 binding to Hsp70 HSE, in agreement with the impact of HSF1 and HSF3 silencing on Hsp70 expression. These data demonstrate that ASA and Q10 both induce the expression of Hsp70 to protect chicken primary myocardial cells during heat stress, but through distinct pathways.

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

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

High-Throughput Screening to Identify Inhibitors of DEAD Box Helicase DDX41

The human DEAD (Asp-Glu-Ala-Asp) box protein DDX41, a member of the DEXDc helicase family, has nucleic acid-dependent ATPase and RNA and DNA translocase and unwinding activities. DDX41 is affected by somatic mutations in sporadic cases of myeloid neoplasms as well as in a biallelic fashion in 50% of patients with germline DDX41 mutations. The R525H mutation in DDX41 is thought to play important roles in the development of hereditary myelodysplastic syndrome and acute myelocytic leukemia. In this study, human DDX41 and its R525H mutant (R525H) were expressed in Escherichia coli and purified. The ATPase activities of the recombinant DDX41 and R525H proteins were dependent on both ATP and double-stranded DNA (dsDNA), such as poly(dG-dC) and poly(dA-dT). High-throughput screening was performed with a dsDNA-dependent ATPase assay using the human R525H proteins. After hit confirmation and counterscreening, several small-molecule inhibitors were successfully identified. These compounds show DDX41-selective inhibitory activities.

Locus coeruleus at asymptomatic early and middle Braak stages of neurofibrillary tangle pathology

AIMS

The present study analyses molecular characteristics of the locus coeruleus (LC) and projections to the amygdala and hippocampus at asymptomatic early and middle Braak stages of neurofibrillary tangle (NFT) pathology.

METHODS

Immunohistochemistry, whole-transcriptome arrays and RT-qPCR in LC and western blotting in hippocampus and amygdala in a cohort of asymptomatic individuals at stages I-IV of NFT pathology were used.

RESULTS

NFTs in the LC increased in parallel with colocalized expression of tau kinases, increased neuroketal adducts and decreased superoxide dismutase 1 in neurons with hyperphosphorylated tau and decreased voltage-dependent anion channel in neurons containing truncated tau were found. These were accompanied by increased microglia and AIF1, CD68, PTGS2, IL1β, IL6 and TNF-α gene expression. Whole-transcriptome arrays revealed upregulation of genes coding for proteins associated with heat shock protein binding and genes associated with ATP metabolism and downregulation of genes coding for DNA-binding proteins and members of the small nucleolar RNAs family, at stage IV when compared with stage I. Tyrosine hydroxylase (TH) immunoreactivity was preserved in neurons of the LC, but decreased TH and increased α_2A adrenergic receptor protein levels were found in the hippocampus and the amygdala.

CONCLUSIONS

Complex alteration of several metabolic pathways occurs in the LC accompanying NFT formation at early and middle asymptomatic stages of NFT pathology. Dopaminergic/noradrenergic denervation and increased expression of α_2A adrenergic receptor in the hippocampus and amygdala occur at first stage of NFT pathology, suggesting compensatory activation in the face of decreased adrenergic input occurring before clinical evidence of cognitive impairment and depression.

A disulfide-bonded DnaK dimer is maintained in an ATP-bound state

DnaK, a major Hsp70 molecular chaperones in Escherichia coli, is a widely used model for studying Hsp70s. We recently solved a crystal structure of DnaK in complex with ATP and showed that DnaK was packed as a dimer in the crystal structure. Our previous biochemical studies supported the formation of a specific DnaK dimer as observed in the crystal structure in solution in the presence of ATP and suggested an important role of this dimer in efficient interaction with Hsp40 co-chaperones. In this study, we dissected the biochemical properties of this DnaK dimer. To restrict DnaK in this dimer form, we mutated two residues on the dimer interface to cysteine, A303C, and H541C. Upon oxidation, this DnaK-A303C-H541C protein formed a specific dimer linked by disulfide bonds formed between A303C and H541C only in the presence of ATP, consistent with the crystal structure. Intriguingly, this disulfide-bond-linked dimer of DnaK-A303C-H541C has reduced ATPase activity and decreased affinity for peptide substrate. More interestingly, unlike wild-type DnaK, the peptide substrate-binding kinetics of this dimer is drastically accelerated even in the absence of ATP, suggesting this dimer is restricted in an ATP-bound conformation regardless of nucleotide bound, which was further supported by our analysis using tryptophan fluorescence and ATP-induced peptide release. Thus, formation of the dimer restricted DnaK in an ATP-bound state and blocked the progression through the chaperone cycle. Productive progression through the chaperone cycle requires the dissociation of this transient dimer. Surprisingly, a significantly compromised interaction with Hsp40 co-chaperone was observed for this disulfide-bond-linked dimer. Thus, dissociation of this DnaK dimer is equally crucial for efficient Hsp40 interaction. An initial interaction between Hsp70 and Hsp40 requires the formation of DnaK dimer; but a stable Hsp70-Hsp40 interaction may follow the dissociation of the dimer.

Differences in structure and changes in gene regulation of murrel molecular chaperone HSP family during epizootic ulcerative syndrome (EUS) infection

Heat shock proteins (HSPs) are immunogenic, ubiquitous class of molecular chaperones, which are induced in response to various environmental and microbial stressful conditions. It plays a vital role in maintaining cellular protein homeostasis in eukaryotic cells. In this study, we described a comprehensive comparative data by bioinformatics approach on three different full length cDNA sequences of HSP family at molecular level. The cDNA sequences of three HSPs were identified from constructed cDNA library of Channa striatus and named as CsCPN60, CsHSP60 and CsHSP70. We have conducted various physicochemical study, which showed that CsHSP70 (666 amino acid) possessed a larger polypeptides followed by CsCPN60 (575) and CsCPN60 (542). Three dimensional structural analysis of these HSPs showed maximum residues in α-helices and least in β-sheets; also CsHSP60 lacks β-sheet and formed helix-turn-helix structure. Further analysis indicated that each HSP carried distinct domains and gene specific signature motif, which showed that each HSP are structurally diverse. Homology and phylogenetic study showed that the sequences taken for analysis shared maximum identity with fish HSP family. Tissue specific mRNA expression analysis revealed that all the HSPs showed maximum expression in one of the major immune organ such as CsCPN60 in kidney, CsHSP60 in spleen and CsHSP70 in head kidney. To understand the function of HSPs in murrel immune system, the elevation in mRNA expression level was analyzed against microbial oxidative stressors such as fungal (Aphanomyces invadans) and bacterial (Aeromonas hydrophila). It is interesting to note that all the HSP showed a different expression pattern and reached maximum up-regulation at 48 h post-infection (p.i) during fungal stress, whereas in bacterial stress only CsCPN60 showed maximum up-regulation at 48 h p.i, but CsHSP60 and CsHSP70 showed maximum up-regulation at 24 h p.i. The differential expression pattern showed that each HSP is diverse in function. Overall, the elevation in expression levels showed that HSPs might have potential involvement in murrel immune protection thus, protecting the organism against various external stimuli including environmental and microbial stress.

Formal Models of Biological Systems

Recent biomedical research studies are focused in the mechanisms by which misfolded proteins lead to the generation of oxidative stress in the form of reactive oxygen species (ROS), often implicated in neurodegenerative diseases and aging. Moreover, biological experiments are designed to investigate how proteostasis depends on the balance between the folding capacity of chaperone networks and the continuous flux of potentially nonnative proteins. Nevertheless, biological experimental methods can examine the protein folding quality control mechanisms only in individual cells, but not in a multicellular level. Formal models offer a dynamic form of modelling, which allows to explore various parameter values in an integrated time-dependent system. This paper aims to present a formal approach of a mathematical descriptive model using as example a representation of a known molecular chaperone system and its relation to diseases associated to protein misfolding and neurodegeneration.

Targeting of Heat Shock Protein HSPA6 (HSP70B') to the Periphery of Nuclear Speckles is Disrupted by a Transcription Inhibitor Following Thermal Stress in Human Neuronal Cells

Heat shock proteins (Hsps) are a set of highly conserved proteins involved in cellular repair and protective mechanisms. The intracellular localization of inducible members of the HSPA (HSP70) family can be used as an index to identify stress-sensitive sites in differentiated human neuronal cells. Following thermal stress, the little studied HSPA6 (HSP70B') was targeted to the periphery of nuclear speckles (perispeckles) that are sites of transcription factories. Triptolide, a fast-acting transcription inhibitor, knocked down levels of the large subunit of RNA polymerase II, RPB1, during the time-frame when HSPA6 associated with perispeckles. Administration of triptolide to heat shocked human neuronal SH-SY5Y cells, disrupted HSPA6 localization to perispeckles, suggesting the involvement of HSPA6 in transcriptional recovery after stress. The HSPA6 gene is present in the human genome but is not found in the genomes of the mouse and rat. Hence current animal models of neurodegenerative diseases lack a member of the HSPA family that exhibits the feature of stress-induced targeting to perispeckles.

Biochemical characterization of the interaction between HspA1A and phospholipids

Seventy-kilodalton heat shock proteins (Hsp70s) are molecular chaperones essential for maintaining cellular homeostasis. Apart from their indispensable roles in protein homeostasis, specific Hsp70s localize at the plasma membrane and bind to specific lipids. The interaction of Hsp70s with lipids has direct physiological outcomes including lysosomal rescue, microautophagy, and promotion of cell apoptosis. Despite these essential functions, the Hsp70-lipid interactions remain largely uncharacterized. In this study, we characterized the interaction of HspA1A, an inducible Hsp70, with five phospholipids. We first used high concentrations of potassium and established that HspA1A embeds in membranes when bound to all anionic lipids tested. Furthermore, we found that protein insertion is enhanced by increasing the saturation level of the lipids. Next, we determined that the nucleotide-binding domain (NBD) of the protein binds to lipids quantitatively more than the substrate-binding domain (SBD). However, for all lipids tested, the full-length protein is necessary for embedding. We also used calcium and reaction buffers equilibrated at different pH values and determined that electrostatic interactions alone may not fully explain the association of HspA1A with lipids. We then determined that lipid binding is inhibited by nucleotide-binding, but it is unaffected by protein-substrate binding. These results suggest that the HspA1A lipid-association is specific, depends on the physicochemical properties of the lipid, and is mediated by multiple molecular forces. These mechanistic details of the Hsp70-lipid interactions establish a framework of possible physiological functions as they relate to chaperone regulation and localization.

Cucumber Necrosis Virus Recruits Cellular Heat Shock Protein 70 Homologs at Several Stages of Infection

RNA viruses often depend on host factors for multiplication inside cells due to the constraints of their small genome size and limited coding capacity. One such factor that has been exploited by several plant and animal viruses is heat shock protein 70 (HSP70) family homologs which have been shown to play roles for different viruses in viral RNA replication, viral assembly, disassembly, and cell-to-cell movement. Using next generation sequence analysis, we reveal that several isoforms of Hsp70 and Hsc70 transcripts are induced to very high levels during cucumber necrosis virus (CNV) infection of Nicotiana benthamiana and that HSP70 proteins are also induced by at least 10-fold. We show that HSP70 family protein homologs are co-opted by CNV at several stages of infection. We have found that overexpression of Hsp70 or Hsc70 leads to enhanced CNV genomic RNA, coat protein (CP), and virion accumulation, whereas downregulation leads to a corresponding decrease. Hsc70-2 was found to increase solubility of CNV CP in vitro and to increase accumulation of CNV CP independently of viral RNA replication during coagroinfiltration in N. benthamiana. In addition, virus particle assembly into virus-like particles in CP agroinfiltrated plants was increased in the presence of Hsc70-2. HSP70 was found to increase the targeting of CNV CP to chloroplasts during infection, reinforcing the role of HSP70 in chloroplast targeting of host proteins. Hence, our findings have led to the discovery of a highly induced host factor that has been co-opted to play multiple roles during several stages of the CNV infection cycle.

IMPORTANCE

Because of the small size of its RNA genome, CNV is dependent on interaction with host cellular components to successfully complete its multiplication cycle. We have found that CNV induces HSP70 family homologs to a high level during infection, possibly as a result of the host response to the high levels of CNV proteins that accumulate during infection. Moreover, we have found that CNV co-opts HSP70 family homologs to facilitate several aspects of the infection process such as viral RNA, coat protein and virus accumulation. Chloroplast targeting of the CNV CP is also facilitated, which may aid in CNV suppression of host defense responses. Several viruses have been shown to induce HSP70 during infection and others to utilize HSP70 for specific aspects of infection such as replication, assembly, and disassembly. We speculate that HSP70 may play multiple roles in the infection processes of many viruses.

Close and Allosteric Opening of the Polypeptide-Binding Site in a Human Hsp70 Chaperone BiP

Binding immunoglobulin protein (BiP), an essential and ubiquitous Hsp70 chaperone in the ER, plays a key role in protein folding and quality control. BiP contains two functional domains: a nucleotide-binding domain (NBD) and a substrate-binding domain (SBD). NBD binds and hydrolyzes ATP; the substrates for SBD are extended polypeptides. ATP binding allosterically accelerates polypeptide binding and release. Although crucial to the chaperone activity, the molecular mechanisms of polypeptide binding and allosteric coupling of BiP are poorly understood. Here, we present crystal structures of an intact human BiP in the ATP-bound state, the first intact eukaryotic Hsp70 structure, and isolated BiP-SBD with a peptide substrate bound representing the ADP-bound state. These structures and our biochemical analysis demonstrate that BiP has a unique NBD-SBD interface that is highly conserved only in eukaryotic Hsp70s found in the cytosol and ER to fortify its ATP-bound state and promote the opening of its polypeptide-binding pocket.

HspA1A, a 70-kDa heat shock protein, differentially interacts with anionic lipids

HspA1A, a 70-kDa heat shock protein, binds to specific lipids. This interaction allows HspA1A to associate with the plasma and other cellular membranes, where it regulates many vital functions like immunity, membrane stabilization, autophagy, and apoptosis. However, the molecular mechanism of the HspA1A-lipid interactions has yet to be fully characterized. Therefore, in this study, we characterized the interaction of HspA1A with three lipids, bis-(monoacylglycero)-phosphate, cardiolipin, and sulfatide. Our results revealed that, first, HspA1A embeds in membranes when bound to liposomes composed of cardiolipin and sulfatide. Second, the binding of HspA1A to lipids is complex and although important, electrostatic interactions alone cannot fully explain the observed binding. Third, the two HspA1A domains, the nucleotide-binding domain and the substrate-binding domain, differentially bind to lipids in a lipid-specific manner. Fourth, HspA1A lipid-binding is reduced by the presence of nucleotides, but it is unaffected by the presence of a peptide-substrate. These observations suggest that HspA1A binds to lipids via a multi-step mechanism and this interaction depends on the specific physicochemical properties of the lipid. We speculate that the association of HspA1A with lipids like the mitochondrial cardiolipin, which is an organelle marker, may facilitate the translocation and localized function of the molecular chaperone to particular sub-cellular compartments.

Molecular Chaperones of Leishmania: Central Players in Many Stress-Related and -Unrelated Physiological Processes

Molecular chaperones are key components in the maintenance of cellular homeostasis and survival, not only during stress but also under optimal growth conditions. Folding of nascent polypeptides is supported by molecular chaperones, which avoid the formation of aggregates by preventing nonspecific interactions and aid, when necessary, the translocation of proteins to their correct intracellular localization. Furthermore, when proteins are damaged, molecular chaperones may also facilitate their refolding or, in the case of irreparable proteins, their removal by the protein degradation machinery of the cell. During their digenetic lifestyle, Leishmania parasites encounter and adapt to harsh environmental conditions, such as nutrient deficiency, hypoxia, oxidative stress, changing pH, and shifts in temperature; all these factors are potential triggers of cellular stress. We summarize here our current knowledge on the main types of molecular chaperones in Leishmania and their functions. Among them, heat shock proteins play important roles in adaptation and survival of this parasite against temperature changes associated with its passage from the poikilothermic insect vector to the warm-blooded vertebrate host. The study of structural features and the function of chaperones in Leishmania biology is providing opportunities (and challenges) for drug discovery and improving of current treatments against leishmaniasis.

Mutations in the Yeast Hsp70, Ssa1, at P417 Alter ATP Cycling, Interdomain Coupling, and Specific Chaperone Functions

The major cytoplasmic Hsp70 chaperones in the yeast Saccharomyces cerevisiae are the Ssa proteins, and much of our understanding of Hsp70 biology has emerged from studying ssa mutant strains. For example, Ssa1 catalyzes multiple cellular functions, including protein transport and degradation, and to this end, the ssa1-45 mutant has proved invaluable. However, the biochemical defects associated with the corresponding Ssa1-45 protein (P417L) are unknown. Consequently, we characterized Ssa1 P417L, as well as a P417S variant, which corresponds to a mutation in the gene encoding the yeast mitochondrial Hsp70. We discovered that the P417L and P417S proteins exhibit accelerated ATPase activity that was similar to the Hsp40-stimulated rate of ATP hydrolysis of wild-type Ssa1. We also found that the mutant proteins were compromised for peptide binding. These data are consistent with defects in peptide-stimulated ATPase activity and with results from limited proteolysis experiments, which indicated that the mutants' substrate binding domains were highly vulnerable to digestion. Defects in the reactivation of heat-denatured luciferase were also evident. Correspondingly, yeast expressing P417L or P417S as the only copy of Ssa were temperature sensitive and exhibited defects in Ssa1-dependent protein translocation and misfolded protein degradation. Together, our studies suggest that the structure of the substrate binding domain is altered and that coupling between this domain and the nucleotide binding domain is disabled when the conserved P417 residue is mutated. Our data also provide new insights into the nature of the many cellular defects associated with the ssa1-45 allele.

Hsp70 forms antiparallel dimers stabilized by post-translational modifications to position clients for transfer to Hsp90

Protein folding in cells is regulated by networks of chaperones, including the heat shock protein 70 (Hsp70) system, which consists of the Hsp40 cochaperone and a nucleotide exchange factor. Hsp40 mediates complex formation between Hsp70 and client proteins prior to interaction with Hsp90. We used mass spectrometry (MS) to monitor assemblies formed between eukaryotic Hsp90/Hsp70/Hsp40, Hop, p23, and a client protein, a fragment of the glucocorticoid receptor (GR). We found that Hsp40 promotes interactions between the client and Hsp70, and facilitates dimerization of monomeric Hsp70. This dimerization is antiparallel, stabilized by post-translational modifications (PTMs), and maintained in the stable heterohexameric client-loading complex Hsp90₂Hsp70₂HopGR identified here. Addition of p23 to this client-loading complex induces transfer of GR onto Hsp90 and leads to expulsion of Hop and Hsp70. Based on these results, we propose that Hsp70 antiparallel dimerization, stabilized by PTMs, positions the client for transfer from Hsp70 to Hsp90.

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Antiparallel dimerization of Hsp70 is stabilized by PTMs

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Hsp40 catalyzes Hsp70 dimerization and client transfer to Hsp70

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Hsp70 antiparallel dimerization is maintained in the client-loading complex

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Addition of p23 induces transfer of GR onto Hsp90 and loss of Hop and Hsp70

Diversification, evolution and sub-functionalization of 70kDa heat-shock proteins in two sister species of antarctic krill: differences in thermal habitats, responses and implications under climate change

BACKGROUND

A comparative thermal tolerance study was undertaken on two sister species of Euphausiids (Antarctic krills) Euphausia superba and Euphausia crystallorophias. Both are essential components of the Southern Ocean ecosystem, but occupy distinct environmental geographical locations with slightly different temperature regimes. They therefore provide a useful model system for the investigation of adaptations to thermal tolerance.

METHODOLOGY/PRINCIPAL FINDING

Initial CTmax studies showed that E. superba was slightly more thermotolerant than E. crystallorophias. Five Hsp70 mRNAs were characterized from the RNAseq data of both species and subsequent expression kinetics studies revealed notable differences in induction of each of the 5 orthologues between the two species, with E. crystallorophias reacting more rapidly than E. superba. Furthermore, analyses conducted to estimate the evolutionary rates and selection strengths acting on each gene tended to support the hypothesis that diversifying selection has contributed to the diversification of this gene family, and led to the selective relaxation on the inducible C form with its possible loss of function in the two krill species.

CONCLUSIONS

The sensitivity of the epipelagic species E. crystallorophias to temperature variations and/or its adaptation to cold is enhanced when compared with its sister species, E. superba. These results indicate that ice krill could be the first of the two species to be impacted by the warming of coastal waters of the Austral ocean in the coming years due to climate change.

BiP and its nucleotide exchange factors Grp170 and Sil1: mechanisms of action and biological functions

BiP (immunoglobulin heavy-chain binding protein) is the endoplasmic reticulum (ER) orthologue of the Hsp70 family of molecular chaperones and is intricately involved in most functions of this organelle through its interactions with a variety of substrates and regulatory proteins. Like all Hsp70 family members, the ability of BiP to bind and release unfolded proteins is tightly regulated by a cycle of ATP binding, hydrolysis, and nucleotide exchange. As a characteristic of the Hsp70 family, multiple DnaJ-like co-factors can target substrates to BiP and stimulate its ATPase activity to stabilize the binding of BiP to substrates. However, only in the past decade have nucleotide exchange factors for BiP been identified, which has shed light not only on the mechanism of BiP-assisted folding in the ER but also on Hsp70 family members that reside throughout the cell. We will review the current understanding of the ATPase cycle of BiP in the unique environment of the ER and how it is regulated by the nucleotide exchange factors, Grp170 (glucose-regulated protein of 170kDa) and Sil1, both of which perform unanticipated roles in various biological functions and disease states.

A functional DnaK dimer is essential for the efficient interaction with Hsp40 heat shock protein

Highly conserved molecular chaperone Hsp70 heat shock proteins play a key role in maintaining protein homeostasis (proteostasis). DnaK, a major Hsp70 in Escherichia coli, has been widely used as a paradigm for studying Hsp70s. In the absence of ATP, purified DnaK forms low-ordered oligomer, whereas ATP binding shifts the equilibrium toward the monomer. Recently, we solved the crystal structure of DnaK in complex with ATP. There are two molecules of DnaK-ATP in the asymmetric unit. Interestingly, the interfaces between the two molecules of DnaK are large with good surface complementarity, suggesting functional importance of this crystallographic dimer. Biochemical analyses of DnaK protein supported the formation of dimer in solution. Furthermore, our cross-linking experiment based on the DnaK-ATP structure confirmed that DnaK forms specific dimer in an ATP-dependent manner. To understand the physiological function of the dimer, we mutated five residues on the dimer interface. Four mutations, R56A, T301A, N537A, and D540A, resulted in loss of chaperone activity and compromised the formation of dimer, indicating the functional importance of the dimer. Surprisingly, neither the intrinsic biochemical activities, the ATP-induced allosteric coupling, nor GrpE co-chaperone interaction is affected appreciably in all of the mutations except for R56A. Unexpectedly, the interaction with co-chaperone Hsp40 is significantly compromised. In summary, this study suggests that DnaK forms a transient dimer upon ATP binding, and this dimer is essential for the efficient interaction of DnaK with Hsp40.

Bringing dynamic molecular machines into focus by methyl-TROSY NMR

Large macromolecular assemblies, so-called molecular machines, are critical to ensuring proper cellular function. Understanding how proper function is achieved at the atomic level is crucial to advancing multiple avenues of biomedical research. Biophysical studies often include X-ray diffraction and cryo-electron microscopy, providing detailed structural descriptions of these machines. However, their inherent flexibility has complicated an understanding of the relation between structure and function. Solution NMR spectroscopy is well suited to the study of such dynamic complexes, and continued developments have increased size boundaries; insights into function have been obtained for complexes with masses as large as 1 MDa. We highlight methyl-TROSY (transverse relaxation optimized spectroscopy) NMR, which enables the study of such large systems, and include examples of applications to several cellular machines. We show how this emerging technique contributes to an understanding of cellular function and the role of molecular plasticity in regulating an array of biochemical activities.

The role of the cytosolic HSP70 chaperone system in diseases caused by misfolding and aberrant trafficking of ion channels

Protein-folding diseases are an ongoing medical challenge. Many diseases within this group are genetically determined, and have no known cure. Among the examples in which the underlying cellular and molecular mechanisms are well understood are diseases driven by misfolding of transmembrane proteins that normally function as cell-surface ion channels. Wild-type forms are synthesized and integrated into the endoplasmic reticulum (ER) membrane system and, upon correct folding, are trafficked by the secretory pathway to the cell surface. Misfolded mutant forms traffic poorly, if at all, and are instead degraded by the ER-associated proteasomal degradation (ERAD) system. Molecular chaperones can assist the folding of the cytosolic domains of these transmembrane proteins; however, these chaperones are also involved in selecting misfolded forms for ERAD. Given this dual role of chaperones, diseases caused by the misfolding and aberrant trafficking of ion channels (referred to here as ion-channel-misfolding diseases) can be regarded as a consequence of insufficiency of the pro-folding chaperone activity and/or overefficiency of the chaperone ERAD role. An attractive idea is that manipulation of the chaperones might allow increased folding and trafficking of the mutant proteins, and thereby partial restoration of function. This Review outlines the roles of the cytosolic HSP70 chaperone system in the best-studied paradigms of ion-channel-misfolding disease--the CFTR chloride channel in cystic fibrosis and the hERG potassium channel in cardiac long QT syndrome type 2. In addition, other ion channels implicated in ion-channel-misfolding diseases are discussed.

Escherichia coli-induced temporal and differential secretion of heat-shock protein 70 and interleukin-1β by human fetal membranes in a two-compartment culture system

INTRODUCTION

Escherichia coli is recognized as an etiological bacteria associated with chorioamnionitis and the preterm premature rupture of fetal membranes. This pathological condition induces pro-inflammatory cytokines and degradative metalloproteinases, which are considered biological markers secreted in an acute stage of infection. Heat-shock proteins (HSPs) are an important component of the innate immunity response and are found in different pathological conditions. They have not been previously measured in human fetal membranes in response to infectious conditions. We hypothesized that the choriodecidual tissue and amniotic epithelium secreted temporal and differential Hsp-60, Hsp-70, and interleukin (IL)-1β mediated by E. coli infection.

METHODS

Fetal membranes were mounted in a two-compartment culture system and infected with two passes of live E. coli at different doses (10², 10⁴, 10⁵, and 10⁶ colony-forming units (CFU)/mL) and intervals of incubation (3, 6, and 24 h). The culture medium was collected, and Hsp-60, Hsp-70, and IL-1β were assessed using the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

After 3 and 6 h of infection, E. coli induced an increase in Hsp-70 secretion in the choriodecidual tissue. However, after 24 h of incubation, Hsp-70 was downregulated and we observed an increase in IL-1β secretion. By contrast, E. coli induced a lower Hsp-60 secretion in the amnion compared to Hsp-70.

DISCUSSION

Human fetal membranes responded actively to E. coli infection, with an increase in Hsp-70 during the first hours of infection. After 24 h, there was an increase in the liberation of IL-1β.

Molecular cloning, characterization and expression analysis of HSP60, HSP70 and HSP90 in the golden apple snail, Pomacea canaliculata

The golden apple snail, Pomacea canaliculata, has strong tolerance to high temperature, facilitating its invasion in East and Southeast Asia. In the present study, three cDNAs encoding heat shock proteins (PocaHSP60, PocaHSP70, PocaHSP90) in P. canaliculata were cloned and characterized. The PocaHSP60 cDNA was 2447 bp, containing an ORF encoding a polypeptide of 574 amino acids. The PocaHSP70 cDNA was 2644 bp, containing an ORF encoding a polypeptide of 643 amino acids. The PocaHSP90 cDNA was 2546 bp, containing an ORF encoding a polypeptide of 726 amino acids. Genomic DNA analysis showed that PocaHSP60 had 11 introns in the coding region and PocaHSP90 had 7 introns but PocaHSP70 had no one. The expression changes of these three PocaHSPs in the gill, digestive gland, kidney and foot muscle of P. canaliculata exposed to high and low temperature were investigated. The results of quantitative PCR and western blotting showed that the expression level of PocaHSP90 was much higher than PocaHSP60 and PocaHSP70 at room temperature, and PocaHSP70 expression level was the lowest among them. Afterheat shock, PocaHSP70 expression increased rapidly, much more significantly than PocaHSP90 expression, and the effect of heat shock on the expression of PocaHSP70 and PocaHSP90 in the different tissues of P. canaliculata was not the same. Unlike PocaHSP70 and PocaHSP90, PocaHSP60 expression seemed not to be affected by heat shock, because its expression was moderately induced only in the foot muscle. However, cool shock had little effect on the expression change of above three PocaHSPs. These results indicated that HSPs might be related to the thermal resistance of P. canaliculata.