Impact of aging on heat shock protein expression in the substantia nigra and striatum of the female rat

Many heat shock proteins are chaperones that help refold or degrade misfolded proteins and battle apoptosis. Because of their capacity to protect against protein misfolding, they may help keep diseases of aging at bay. A few reports have examined heat shock proteins (eg. Hsp25, Hsp60, Hsp70, and heat shock cognate 70 or Hsc70) as a function of age in the striatum and nigra. In the present study, we examined the impact of aging on Hsp25, heme oxygenase 1 (HO1 or Hsp32), Hsp40, Hsp60, Hsc70, Hsc/Hsp70 interacting protein (Hip), 78 kDa glucose-regulated protein (GRP78), Hsp90, and ubiquitinated proteins in the nigra and striatum of the female rat by infrared immunoblotting. Female animals are not typically examined in aging studies, adding further to the novelty of our study. Striatal HO1 and Hsp40 were both higher in middle-aged females than in the oldest group. Hsp60 levels were also highest in middle age in the nigra, but were highest in the oldest animals in the striatum. Striatal levels of Hsc70 and the co-chaperone Hip were lower in the oldest group relative to the youngest animals. In contrast, Hsp25 rose with advancing age in both regions. Hsp25 was also colocalized with tyrosine hydroxylase in nigral neurons. Ubiquitinated proteins exhibited a trend to rise in the oldest animals in both regions, and K48 linkage-specific ubiquitin rose significantly from 4–6 to 16–19 months in the striatum. Our study reveals a complex array of age-related changes in heat shock proteins. Furthermore, the age-related rises in some proteins, such as Hsp25, may reflect endogenous adaptations to cellular stress.     

Saturation, competition, and specificity in interaction of heat shock proteins (hsp) gp96, hsp90, and hsp70 with CD11b+ cells

Heat shock proteins (hsp(s)) have been postulated to interact with APCs through specific receptors, although the receptors are yet to be identified. Specificity, saturation, and competition are the three defining attributes of a receptor-ligand interaction. We demonstrate here that the interaction of the heat shock proteins gp96 and hsp90 with CD11b+ cells is specific and saturable and that gp96 can compete with itself in gp96-macrophage interaction. Interestingly, the phylogenetically related hsp90 also competes quite effectively with gp96 for binding to macrophages, whereas the unrelated hsp70 does so relatively poorly, although it binds CD11b+ cells just as effectively. These data provide evidence that the heat shock proteins interact with APCs with specificity and for the existence of at least two distinct receptors, one for gp96 and hsp90 and the other for hsp70.     

Heat shock protein 70 and glycoprotein 96 are differentially expressed on the surface of malignant and nonmalignant breast cells

Heat shock proteins (HSPs), which are important for a number of different intracellular functions, are occasionally found on the surface of cells. The function of heat shock protein on the cell surface is not understood, although it has been shown to be greater in some tumor cells and some virally infected cells. Surface expression of both glycoprotein 96 (gp96) and Hsp70 occurs on tumor cells, and this expression correlates with natural killer cell killing of the cells. We examined the surface expression of gp96 and Hsp70 on human breast cell lines MCF7, MCF10A, AU565, and HS578, and in primary human mammary epithelial cells by immunofluorescence microscopy and flow cytometry. The nonmalignant cell lines HS578, MCF10A, and HMEC showed no surface expression of gp96, whereas malignant cell lines MCF7 and AU565 were positive for gp96 surface expression. All of the breast cell lines examined showed Hsp70 surface expression. These results also confirm previous studies, demonstrating that Hsp70 is on the plasma membrane of tumor cell lines. Given the involvement of heat shock proteins, gp96 and Hsp70, in innate and adaptive immunity, these observations may be important in the immune response to tumor cells.     

Physiological and molecular assessment of altered expression of Hsc70-1 in Arabidopsis. Evidence for pleiotropic consequences

Hsp70s function as molecular chaperones. The protective chaperone activities of hsp70 help to confer tolerance to heat, glucose deprivation, and drought. Overexpression of hsp70s in many organisms correlates with enhanced thermotolerance, altered growth, and development. To better understand the roles of hsp70 proteins in Arabidopsis, the molecular and physiological consequences of altered expression of the major heat shock cognate, Hsc70-1, were analyzed. Extensive efforts to achieve underexpression of Hsc70-1 mRNA using a full-length antisense cDNA resulted in no viable transgenic plants, suggesting that reduced expression is lethal. Constitutive overexpression of Hsc70-1 also appeared to be deleterious to viability, growth, and development because fewer transformants were recovered, and most were dwarfed with altered root systems. Despite being dwarfed, the overexpression plants progressed normally through four selected developmental stages. Heat treatment revealed that Hsc70-1 overexpression plants were more tolerant to heat shock (44 degrees C for 10 min). The elevated basal levels of HSC70-1 in transgenic plants led to delayed heat shock response of several heat shock genes. The data in this study suggest that tight regulation of Hsc70-1 expression is critical for the viability of Arabidopsis and that the functions of HSC70-1 contribute to optimum growth, development, thermotolerance, and regulation of the heat shock response.     

Identification of novel nuclear export and nuclear localization-related signals in human heat shock cognate protein 70

Heat shock cognate protein 70 (Hsc70) serves nuclear transport of several proteins as a molecular chaperone. We have recently identified a novel variant of human Hsc70, heat shock cognate protein 54 (Hsc54), that lacks amino acid residues 464-616 in the protein binding and variable domains of Hsc70. In the present study, we examined nucleocytoplasmic localization of Hsc70 and Hsc54 by using green fluorescent protein (GFP) fusions. GFP-Hsc70 is localized in both the cytoplasm and the nucleus at 37 degrees C and accumulated into the nucleolus/nucleus after heat shock, whereas GFP-Hsc54 always remained exclusively in the cytoplasm under these conditions. Mutation studies indicated that 20 amino acid residues of nuclear localization-related signals, which are missing in Hsc54 but are retained in Hsc70, are required for proper nuclear localization of Hsc70. We further found that Hsc54 contains a functional leucine-rich nuclear export signal (NES, (394)LDVTPLSL(401)) which is differently situated from the previously proposed NES in Saccharomyces cerevisiae Ssb1p. The cytoplasmic localization of Hsc54 was impaired by a mutation in NES as well as by a nuclear export inhibitor, leptomycin B, suggesting that Hsc54 is actively exported from the nucleus to the cytoplasm through a CRM1-dependent mechanism. In contrast, the nucleocytoplasmic localization of Hsc70 was not affected by the same mutation of NES or leptomycin B. These results suggest that the nuclear localization-related signal could functionally mask NES leading to prolonged retention of Hsc70 in the nucleus. An additional mechanism for unmasking the NES may regulate nucleocytoplasmic trafficking of Hsc70.     

Mapping the role of active site residues for transducing an ATP-induced conformational change in the bovine 70-kDa heat shock cognate protein.

ATP binding induces a conformational change in 70-kDa heat shock proteins (Hsp70s) that facilitates release of bound polypeptides. Using the bovine heat shock cognate protein (Hsc70) as a representative of the Hsp70 family, we have characterized the effect of mutations on the coupling between ATP binding and the nucleotide-induced conformational change. Steady-state solution small-angle X-ray scattering and kinetic fluorescence measurements on a 60-kDa fragment of Hsc70 show that point mutations K71M, E175S, D199S, and D206S in the nucleotide binding cleft impair the ability of ATP to induce a conformational change. A secondary mutation in the peptide binding domain, E543K, "rescues" the ATP-induced transition for three of these mutations (E175S/E543K, D199S/E543K, and D206S/E543K) but not for K71M/E543K. Analysis of kinetics of the ATPase cycle confirm that these effects do not result from unexpectedly rapid ATP hydrolysis or slow ATP binding. Crystallographic structures of E175S, D199S, and D206S mutant ATPase fragment proteins show that the mutations do not perturb the tertiary structure of the protein but do significantly alter the protein-ligand interactions, due in part to an apparent charge compensation effect whereby mutating a (probably) negatively charged carboxyl group to a neutral serine displaces a K+ ion from the nucleotide binding cleft in two out of three cases (E175S and D199S but not D206S).     

Quantitative evidence that both Hsc70 and Hsp70 contribute to thermal adaptation in hybrids of the livebearing fishes Poeciliopsis

The 70-kilodalton heat shock protein family is composed of both environmentally inducible (Hsp) and constitutively expressed (Hsc) family members. While the role of the constitutively expressed stress proteins in thermotolerance is largely unknown, de novo expression stress proteins in response to elevated temperatures has been associated with increased thermotolerance in many cell lines, developing embryos and adult organisms. Distinct, hemiclonal hybrids between the livebearing fish species Poeciliopsis monacha and P. lucida varied in their abilities to survive temperature stress, with survival being greatest when rates of temperature increase to 40°C were slowest and when P. monacha genomes were combined with a sympatric P. lucida genome. Quantification of Hsp70 under heat shock conditions and Hsc70 under normal physiological conditions indicated that variation in survival among hemiclones was best explained by the combined effects of these two proteins. Similar complex interactions between maternal and paternal genomes and rate of temperature increase were found to underline patterns of survival, Hsp70 accumulation and Hsc70 abundance. These data suggest that the relationship between Hsps and thermotolerance is more intricate than previously thought and that Hsps contribute to thermal adaptation in these fishes through genetic interactions specific to particular environments.     

Hsc70 protein interaction with soluble and fibrillar alpha-synuclein

The aggregation of α-synuclein (α-Syn), the primary component of Lewy bodies, into high molecular weight assemblies is strongly associated with Parkinson disease. This event is believed to result from a conformational change within native α-Syn. Molecular chaperones exert critical housekeeping functions in vivo including refolding, maintaining in a soluble state, and/or pacifying protein aggregates. The influence of the stress-induced heat shock protein 70 (Hsp70) on α-Syn aggregation has been notably investigated. The constitutively expressed chaperone Hsc70 acts as an antiaggregation barrier before cells are overwhelmed with α-Syn aggregates and Hsp70 expression induced. Here, we investigate the interaction between Hsc70 and α-Syn, the consequences of this interaction, and the role of nucleotides and co-chaperones Hdj1 and Hdj2 as modulators. We show that Hsc70 sequesters soluble α-Syn in an assembly incompetent complex in the absence of ATP. The affinity of Hsc70 for soluble α-Syn diminishes upon addition of ATP alone or together with its co-chaperones Hdj1 or Hdj2 allowing faster binding and release of client proteins thus abolishing α-Syn assembly inhibition by Hsc70. We show that Hsc70 binds α-Syn fibrils with a 5-fold tighter affinity compared with soluble α-Syn. This suggests that Hsc70 preferentially interacts with high molecular weight α-Syn assemblies in vivo. Hsc70 binding certainly has an impact on the physicochemical properties of α-Syn assemblies. We show a reduced cellular toxicity of α-Syn fibrils coated with Hsc70 compared with "naked" fibrils. Hsc70 may therefore significantly affect the cellular propagation of α-Syn aggregates and their spread throughout the central nervous system in Parkinson disease.     

<Superscript>1</Superscript>H, <Superscript>15</Superscript>N and <Superscript>13</Superscript>C resonance assignments for free and IEEVD peptide-bound forms of the tetratricopeptide repeat domain from the human E3 ubiquitin ligase CHIP

The ubiquitin ligase CHIP catalyzes covalent attachment of ubiquitin to unfolded proteins chaperoned by the heat shock proteins Hsp70/Hsc70 and Hsp90. CHIP interacts with Hsp70/Hsc70 and Hsp90 by binding of a C-terminal IEEVD motif found in Hsp70/Hsc70 and Hsp90 to the tetratricopeptide repeat (TPR) domain of CHIP. Although recruitment of heat shock proteins to CHIP via interaction with the CHIP-TPR domain is well established, alterations in structure and dynamics of CHIP upon binding are not well understood. In particular, the absence of a structure for CHIP-TPR in the free form presents a significant limitation upon studies seeking to rationally design inhibitors that may disrupt interactions between CHIP and heat shock proteins. Here we report the ¹H, ¹³C, and ¹⁵N backbone and side chain chemical shift assignments for CHIP-TPR in the free form, and backbone chemical shift assignments for CHIP-TPR in the IEEVD-bound form. The NMR resonance assignments will enable further studies examining the roles of dynamics and structure in regulating interactions between CHIP and the heat shock proteins Hsp70/Hsc70 and Hsp90.     

Heat shock proteins gp96 and hsp70 activate the release of nitric oxide by APCs

NO is a cytotoxic and immunomodulatory cytokine produced by macrophages and dendritic cells. We show that stimulation of murine and human macrophages with the heat shock proteins gp96 and hsp70 results in induction of inducible NO synthase and the production of NO. The release of NO by monocytes exposed to hsp60 has been documented previously. Immature, but not mature, dendritic cells respond in the same manner. The activity of heat shock proteins is relatively unaffected by an antagonist of LPS, and is abrogated by heat denaturation. Macrophages have been shown previously to produce NO in response to stimulation with IFN-gamma; stimulation of macrophages with mixtures of IFN-gamma and gp96 or hsp70 leads to a synergistic production of NO. The present observations extend the roles of these heat shock proteins in innate immune responses to another potent and highly conserved function of APC.     

The 70-Kilodalton Heat Shock Cognate Can Act as a Molecular Chaperone during the Membrane Translocation of a Plant Secretory Protein Precursor

When a model secretory precursor was synthesized in vitro and analyzed by rate-zonal sedimentation, it appeared to be associated with other proteins present in a wheat germ extract. At least one of the associated proteins is a member of the 70-kD family of stress proteins. It was possible to immunoprecipitate the secretory precursor with anti-heat shock cognate 70 (Hsc70) antibodies in the absence but not in the presence of ATP, suggesting that the association was specific. ATP-sensitive association is one diagnostic characteristic of molecular chaperone-type proteins. Increasing incubation temperature decreased the amount of precursor associated with Hsc70. A method was developed for the removal of Hsc70 from a wheat germ in vitro translation mixture by immunoprecipitation. Cotranslational translocation and processing of the secretory precursor by maize endosperm microsomes were inefficient in the Hsc70-depleted system but were greatly stimulated by addition of purified preparations of various heat shock 70 proteins (Hsp70s). Cytosolic Hsc70 from maize endosperm was capable of autophosphorylation in vitro. Phosphorylated Hsc70 was much less efficient in promoting membrane translocation of the secretory precursor. These results suggest that chaperone function in vivo could be regulated by phosphorylation.     

ATP and ADP modulate a cation channel formed by Hsc70 in acidic phospholipid membranes

Heat shock proteins are molecular chaperones that participate in different cellular processes, particularly the folding and translocation of polypeptides across membranes. In this regard, members of the Hsp70 family of heat shock proteins have been observed in close proximity to cellular membranes. In this study, the direct interaction between Hsc70, which is constitutively expressed in cells, and lipid membranes was investigated. Recombinant Hsc70 was incorporated into artificial lipid bilayers, and a transmembrane ion flow was detected, suggesting the incorporation of an ion pathway. This ion flow was very stable and occurred in well defined, multilevel discrete electrical current events, indicating the formation of a multiconductance ion channel. The Hsc70 channel activity is ATP-dependent and is reversibly blocked by ADP. This channel has cationic selectivity. Thus, Hsc70 can directly interact with lipid membranes to create functionally stable ATP-dependent cationic pathways.     

Heat stress-induced localization of small heat shock proteins in mouse myoblasts: intranuclear lamin A/C speckles as target for alphaB-crystallin and Hsp25

We examined the effect of heat stress on localization of two sHsps, alphaB-crystallin and Hsp25, and of Hsc70, a member of a different class of heat shock proteins (Hsps), in both undifferentiated and differentiated mouse C2C12 cells. Under normal conditions, alphaB-crystallin and Hsp25 are found in the cytoplasm; only alphaB-crystallin is also found in the nucleus, distributed in a speckled pattern. Hsc70 is found to be homogeneously distributed throughout the cell. On heat stress, all these proteins translocate almost entirely into the nucleus and upon recovery relocate to the cytoplasm. Dual staining experiments using C2C12 myoblasts show that alphaB-crystallin and Hsp25, but not Hsc70, colocalize with the intranuclear lamin A/C and the splicing factor SC-35, suggesting interactions of sHsps and intranuclear lamin A/C. Interestingly, none of these proteins are found in the myotube nuclei. Upon heat stress, only Hsc70 translocates into the myotube nuclei. This differential entry of alphaB-crystallin and Hsp25 into the nuclei of myoblasts and myotubes upon heat stress may have functional role in the development and/or in the maintenance of muscle cells. Our study therefore suggests that these sHsps may be a part of the intranuclear lamin A/C network or stabilizing this specific network.     

Tissue-specific Expression of Dominant Negative Mutant Drosophila HSC70 Causes Developmental Defects and Lethality

The Drosophila melanogaster HSC3 and HSC4 genes encode Hsc70 proteins homologous to the mammalian endoplasmic reticulum (ER) protein BiP and the cytoplasmic clathrin uncoating ATPase, respectively. These proteins possess ATP binding/hydrolysis activities that mediate their ability to aid in protein folding by coordinating the sequential binding and release of misfolded proteins. To investigate the roles of HSC3 (Hsc3p) and HSC4 (Hsc4p) proteins during development, GAL4-targeted gene expression was used to analyze the effects of producing dominant negatively acting Hsc3p (D231S, K97S) and Hsc4p (D206S, K71S) proteins, containing single amino acid substitutions in their ATP-binding domains, in specific tissues of Drosophila throughout development. We show that the production of each mutant protein results in lethality over a range of developmental stages, depending on the levels of protein produced and which tissues are targeted. We demonstrate that the functions of both Hsc3p and Hsc4p are required for proper tissue establishment and maintenance. Production of mutant Hsc4p, but not Hsc3p, results in induction of the stress-inducible Hsp70 at normal temperatures. Evidence is presented that lethality is caused by tissue-specific defects that result from a global accumulation of misfolded protein caused by lack of functional Hsc70. We show that both mutant Hsc3ps are defective in ATP-induced substrate release, although Hsc3p(D231S) does undergo an ATP-induced conformational change. We believe that the amino acid substitutions in Hsc3p interfere with the structural coupling of ATP binding to substrate release, and this defect is the basis for the mutant proteins' dominant negative effects in vivo.     

Lipid interaction differentiates the constitutive and stress-induced heat shock proteins Hsc70 and Hsp70

Heat shock proteins play a major role in the process of protein folding, and they have been termed molecular chaperones. Two members of the Hsp70 family, Hsc70 and Hsp70, have a high degree of sequence homology. But they differ in their expression pattern. Hsc70 is constitutively expressed, whereas Hsp70 is stress inducible. These 2 proteins are localized in the cytosol and the nucleus. In addition, they have also been observed in close proximity to cellular membranes. We have recently reported that Hsc70 is capable of interacting with a lipid bilayer forming ion-conductance channels. In the present study, we found that both Hsc70 and Hsp70 interact with lipids and can be differentiated by their characteristic induction of liposome aggregation. These proteins promote the aggregation of phosphatidylserine liposomes in a time- and protein concentration-dependent manner. Although both proteins are active in this process, the level and kinetics of aggregation are different between them. Calcium ions enhance Hsc70 and Hsp70 liposome aggregation, but the effect is more dramatic for Hsc70 than for Hsp70. Addition of adenosine triphosphate blocks liposome aggregation induced by both proteins. Adenosine diphosphate (ADP) also blocks Hsp70-mediated liposome aggregation. Micromolar concentrations of ADP enhance Hsc70-induced liposome aggregation, whereas at millimolar concentrations the nucleotide has an inhibitory effect. These results confirm those of previous studies indicating that the Hsp70 family can interact with lipids directly. It is possible that the interaction of Hsp70s with lipids may play a role in the folding of membrane proteins and the translocation of polypeptides across membranes.     

Tissue- and stressor-specific differential expression of two hsc70 genes in carp

Two genes expressing 70 kDa heat shock proteins were identified in Cyprinus carpio. The sequence similarities and the intron-interrupted structure of the coding regions indicate that carp Hsc70-1 and Hsc70-2 belong to the Hsp70 cognate subfamily. The expressions of the two hsc70 genes were followed by semi-quantitative RT-PCR. Both genes are expressed under unstressed conditions in a characteristic tissue-specific manner. Inducibility of the response to elevated temperature, cold shock, and Cd treatment was investigated in the liver and muscle, in whole-animal experiments. Both genes were insensitive to or only weakly induced by the stressors, with two exceptions: Cd treatment resulted in an 11-13-fold enhanced induction of hsc70-1 in the liver and cold shock enhanced induction of hsc70-2 in the muscle by 7.5-10-fold.     

BAG-1 modulates the chaperone activity of Hsp70/Hsc70.

The 70 kDa heat shock family of molecular chaperones is essential to a variety of cellular processes, yet it is unclear how these proteins are regulated in vivo. We present evidence that the protein BAG-1 is a potential modulator of the molecular chaperones, Hsp70 and Hsc70. BAG-1 binds to the ATPase domain of Hsp70 and Hsc70, without requirement for their carboxy-terminal peptide-binding domain, and can be co-immunoprecipitated with Hsp/Hsc70 from cell lysates. Purified BAG-1 and Hsp/Hsc70 efficiently form heteromeric complexes in vitro. BAG-1 inhibits Hsp/Hsc70-mediated in vitro refolding of an unfolded protein substrate, whereas BAG-1 mutants that fail to bind Hsp/Hsc70 do not affect chaperone activity. The binding of BAG-1 to one of its known cellular targets, Bcl-2, in cell lysates was found to be dependent on ATP, consistent with the possible involvement of Hsp/Hsc70 in complex formation. Overexpression of BAG-1 also protected certain cell lines from heat shock-induced cell death. The identification of Hsp/Hsc70 as a partner protein for BAG-1 may explain the diverse interactions observed between BAG-1 and several other proteins, including Raf-1, steroid hormone receptors and certain tyrosine kinase growth factor receptors. The inhibitory effects of BAG-1 on Hsp/Hsc70 chaperone activity suggest that BAG-1 represents a novel type of chaperone regulatory proteins and thus suggest a link between cell signaling, cell death and the stress response.     

Expression and localization of Drosophila melanogaster hsp70 cognate proteins.

Monoclonal antibodies have been used to identify three proteins in Drosophila melanogaster that share antigenic determinants with the major heat shock proteins hsp70 and hsp68. While two of the proteins are major proteins at all developmental stages, one heat shock cognate protein, hsc70, is especially enriched in embryos. hsc70 is shown to be the product of a previously identified gene, Hsc4. We have examined the levels of hsp70-related proteins in adult flies and larvae during heat shock and recovery. At maximal induction in vivo, hsp70 and hsp68 never reach the basal levels of the major heat shock cognate proteins. Monoclonal antibodies to hsc70 have been used to localize it to a meshwork of cytoplasmic fibers that are heavily concentrated around the nucleus.     

Heat shock protein gp96 regulates Toll-like receptor 9 proteolytic processing and conformational stability

Nucleic acid-sensing Toll-like receptors (TLRs) initiate innate immune responses to foreign RNA and DNA, yet can detect and respond to host DNA. To avoid autoimmune pathologies, nucleic acid sensing TLRs are tightly regulated. TLR9 primarily resides in the endoplasmic reticulum, traffics to endosomes, is proteolytically processed and responds to DNA. The heat shock protein gp96 is one of several accessory proteins that regulate intracellular trafficking of TLR9. In the absence of gp96, TLR9 fails to exit the endoplasmic reticulum, and therefore gp96-deficient macrophages fail to respond to CpG DNA. However, absence of gp96 precludes studies on potential chaperoning functions of gp96 for TLR9. Here we demonstrate that pharmacologic interference with gp96 function inhibits TLR9 signaling. TLR9 remains associated with gp96 during intracellular trafficking, and gp96-specific inhibitors increase TLR9 sensitivity to proteolytic degradation. We propose that gp96 is critical for both TLR9 egress from the ER, and for protein conformational stability in the endosomal compartment. These studies highlight the importance of examining gp96-specific inhibitors for modulating TLR9 activation, and the treatment autoimmune diseases.