Evidence for a lipochaperonin: association of active protein-folding GroESL oligomers with lipids can stabilize membranes under heat shock conditions

Key role of lipids in heat stress management

Heat stress is a common and, therefore, an important environmental impact on cells and organisms. While much attention has been paid to severe heat stress, moderate temperature elevations are also important. Here we discuss temperature sensing and how responses to heat stress are not necessarily dependent on denatured proteins. Indeed, it is clear that membrane lipids have a pivotal function. Details of membrane lipid changes and the associated production of signalling metabolites are described and suggestions made as to how the interconnected signalling network could be modified for helpful intervention in disease.

Ras GTPase activating (RasGAP) activity of the dual specificity GAP protein Rasal requires colocalization and C2 domain binding to lipid membranes

Rasal, belonging to the GAP1 subfamily of Ras GTPase-activating proteins (RasGAPs) with dual RasGAP/RapGAP specificity, is epigenetically silenced in several tumor types. Surprisingly, the isolated protein has GAP activity on Rap but not on Ras. Its membrane recruitment is regulated by interaction with calcium and lipids, which simultaneously induces its RasGAP activity through a yet unknown mechanism. Here we show that the interaction of Rasal with membranes induces Rasal RasGAP activity by spatial and conformational regulation, although it does not have any effect on its RapGAP activity. Not only is colocalization of Rasal and Ras in the membrane essential for RasGAP activation, but direct and Ca-dependent interaction between the tandem C2 domains of Rasal and lipids of the membrane is also required. Whereas the C2A domain binds specifically phosphatidylserine, the C2B domain interacts with several phosphoinositol lipids. Finally we show, that similar to the C2 domains of synaptotagmins, the Rasal tandem C2 domains are able to sense and induce membrane curvature by the insertion of hydrophobic loops into the membrane.

The oligomer plasticity of the small heat-shock protein Lo18 from Oenococcus oeni influences its role in both membrane stabilization and protein protection

The ability of the small Hsp (heat-shock protein) Lo18 from Oenococcus oeni to modulate the membrane fluidity of liposomes or to reduce the thermal aggregation of proteins was studied as a function of the pH in the range 5-9. We have determined by size-exclusion chromatography and analytical ultracentrifugation that Lo18 assembles essentially as a 16-mer at acidic pH. Its quaternary structure evolves to a mixture of lower molecular mass oligomers probably in dynamic equilibrium when the pH increases. The best Lo18 activities are observed at pH 7 when the particle distribution contains a major proportion of dodecamers. At basic pH, particles corresponding to a dimer prevail and are thought to be the building blocks leading to oligomerization of Lo18. At acidic pH, the dimers are organized in a double-ring of stacked octamers to form the 16-mer as shown by the low-resolution structure determined by electron microscopy. Experiments performed with a modified protein (A123S) shown to preferentially form dimers confirm these results. The α-crystallin domain of Methanococcus jannaschii Hsp16.5, taken as a model of the Lo18 counterpart, fits with the electron microscopy envelope of Lo18.

Biotechnical applications of small heat shock proteins from bacteria

The stress responses of most bacteria are thought to involve the upregulation of small heat shock proteins. We describe here some of the most pertinent aspects of small heat shock proteins, to highlight their potential for use in various applications. Bacterial species have between one and 13 genes encoding small heat shock proteins, the precise number depending on the species considered. Major efforts have recently been made to characterize the protein protection and membrane stabilization mechanisms involving small heat shock proteins in bacteria. These proteins seem to be involved in the acquisition of cellular heat tolerance. They could therefore potentially be used to maintain cell viability under unfavorable conditions, such as heat shock or chemical treatments. This review highlights the potential roles of applications of small heat shock proteins in stabilizing overproduced heterologous proteins in Escherichia coli, purified bacterial small heat shock proteins in protein biochip technology, proteomic analysis and food technology and the potential impact of these proteins on some diseases. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Heat shock response in photosynthetic organisms: membrane and lipid connections

The ability of photosynthetic organisms to adapt to increases in environmental temperatures is becoming more important with climate change. Heat stress is known to induce heat-shock proteins (HSPs) many of which act as chaperones. Traditionally, it has been thought that protein denaturation acts as a trigger for HSP induction. However, increasing evidence has shown that many stress events cause HSP induction without commensurate protein denaturation. This has led to the membrane sensor hypothesis where the membrane's physical and structural properties play an initiating role in the heat shock response. In this review, we discuss heat-induced modulation of the membrane's physical state and changes to these properties which can be brought about by interaction with HSPs. Heat stress also leads to changes in lipid-based signaling cascades and alterations in calcium transport and availability. Such observations emphasize the importance of membranes and their lipids in the heat shock response and provide a new perspective for guiding further studies into the mechanisms that mediate cellular and organismal responses to heat stress.

Legionella pneumophila requires polyamines for optimal intracellular growth

The Gram-negative intracellular pathogen Legionella pneumophila replicates in a membrane-bound compartment known as the Legionella-containing vacuole (LCV), into which it abundantly releases its chaperonin, HtpB. To determine whether HtpB remains within the LCV or reaches the host cell cytoplasm, we infected U937 human macrophages and CHO cells with L. pneumophila expressing a translocation reporter consisting of the Bordetella pertussisa denylate cyclase fused to HtpB. These infections led to increased cyclic AMP levels, suggesting that HtpB reaches the host cell cytoplasm. To identify potential functions of cytoplasmic HtpB, we expressed it in the yeast Saccharomyces cerevisiae, where HtpB induced pseudohyphal growth. A yeast-two-hybrid screen showed that HtpB interacted with S-adenosylmethionine decarboxylase (SAMDC), an essential yeast enzyme (encoded by SPE2) that is required for polyamine biosynthesis. Increasing the copy number of SPE2 induced pseudohyphal growth in S. cerevisiae; thus, we speculated that (i) HtpB induces pseudohyphal growth by activating polyamine synthesis and (ii) L. pneumophila may require exogenous polyamines for growth. A pharmacological inhibitor of SAMDC significantly reduced L. pneumophila replication in L929 mouse cells and U937 macrophages, whereas exogenously added polyamines moderately favored intracellular growth, confirming that polyamines and host SAMDC activity promote L. pneumophila proliferation. Bioinformatic analysis revealed that most known enzymes required for polyamine biosynthesis in bacteria (including SAMDC) are absent in L. pneumophila, further suggesting a need for exogenous polyamines. We hypothesize that HtpB may function to ensure a supply of polyamines in host cells, which are required for the optimal intracellular growth of L. pneumophila.

Heat stress causes spatially-distinct membrane re-modelling in K562 leukemia cells

Cellular membranes respond rapidly to various environmental perturbations. Previously we showed that modulations in membrane fluidity achieved by heat stress (HS) resulted in pronounced membrane organization alterations which could be intimately linked to the expression and cellular distribution of heat shock proteins. Here we examine heat-induced membrane changes using several visualisation methods. With Laurdan two-photon microscopy we demonstrate that, in contrast to the enhanced formation of ordered domains in surface membranes, the molecular disorder is significantly elevated within the internal membranes of cells preexposed to mild HS. These results were compared with those obtained by anisotropy, fluorescence lifetime and electron paramagnetic resonance measurements. All probes detected membrane changes upon HS. However, the structurally different probes revealed substantially distinct alterations in membrane heterogeneity. These data call attention to the careful interpretation of results obtained with only a single label. Subtle changes in membrane microstructure in the decision-making of thermal cell killing could have potential application in cancer therapy.

The Legionella pneumophila Chaperonin - An Unusual Multifunctional Protein in Unusual Locations

The Legionella pneumophila chaperonin, high temperature protein B (HtpB), was discovered as a highly immunogenic antigen, only a few years after the identification of L. pneumophila as the causative agent of Legionnaires’ disease. As its counterparts in other bacterial pathogens, HtpB did not initially receive further attention, particularly because research was focused on a few model chaperonins that were used to demonstrate that chaperonins are essential stress proteins, present in all cellular forms of life and involved in helping other proteins to fold. However, chaperonins have recently attracted increasing interest, particularly after several reports confirmed their multifunctional nature and the presence of multiple chaperonin genes in numerous bacterial species. It is now accepted that bacterial chaperonins are capable of playing a variety of protein folding-independent roles. HtpB is clearly a multifunctional chaperonin that according to its location in the bacterial cell, or in the L. pneumophila-infected cell, plays different roles. HtpB exposed on the bacterial cell surface can act as an invasion factor for non-phagocytic cells, whereas the HtpB released in the host cell can act as an effector capable of altering organelle trafficking, the organization of actin microfilaments and cell signaling pathways. The road to discover the multifunctional nature of HtpB has been exciting and here we provide a historical perspective of the key findings linked to such discovery, as well as a summary of the experimental work (old and new) performed in our laboratory. Our current understanding has led us to propose that HtpB is an ancient protein that L. pneumophila uses as a key molecular tool important to the intracellular establishment of this fascinating pathogen.

Analysis of the bacterial heat shock response to photodynamic therapy-mediated oxidative stress

Antimicrobial photodynamic therapy (PDT) has recently emerged as an effective modality for the selective destruction of bacteria and other pathogenic microorganisms. We investigated whether PDT induced protective responses such as heat shock proteins (HSPs) in bacteria. Using the photosensitizer Toluidine Blue O (TBO) at sublethal PDT conditions, a seven-fold increase in bacterial HSP GroEL and a three-fold increase in HSP DnaK were observed in Escherichia coli post PDT. Pretreatment with 50°C heat for 30 min reduced PDT killing in both E. coli and in Enterococcus faecalis, with the most pronounced inhibition occurring at 50 μm TBO with 5 J cm(-2) 635 nm light, where E. coli killing was reduced by 2 log(10) and E. faecalis killing was reduced by 4 log(10). Finally, inhibition of the highly conserved chaperone DnaK using a small molecule benzylidene lactam HSP inhibitor potentiated (but not significantly) the effect of PDT at a TBO concentration of 2.5 μm in E. faecalis; however, this effect was not observed in E. coli presumably because inhibitor could not gain access due to Gram-negative permeability barrier. Induction of HSPs may be a mechanism whereby bacteria could become resistant to PDT and warrants the need for further study in the application of dual PDT-HSP-inhibition therapies.

Heat-shock protein 60 translocates to the surface of apoptotic cells and differentiated megakaryocytes and stimulates phagocytosis

Heat-shock protein 60 (Hsp60) is a highly conserved stress protein which has chaperone functions in prokaryotes and mammalian cells. Hsp60 is associated with the mitochondria and the plasma membrane through phosphorylation by protein kinase A, and is incorporated into lipid membranes as a protein-folding chaperone. Its diverse intracellular chaperone functions include the secretion of proteins where it maintains the conformation of precursors and facilitates their translocation through the plasma membrane. We report here that Hsp60 is concentrated in apoptotic membrane blebs and translocates to the surface of cells undergoing apoptosis. Hsp60 is also enriched in platelets derived from terminally differentiated megakaryocytes and expressed at the surface of senescent platelets. Furthermore, the exposure of monocytic U937 cells to Hsp60 enhanced their phagocytic activity. Our results suggests that externalized Hsp60 in apoptotic cells and senescent platelets influences events subsequent to apoptosis, such as the clearance of apoptotic cells by phagocytes.

Environmental factors affecting indole production in Escherichia coli

A variety of both Gram-positive and Gram-negative bacteria produce large quantities of indole as an intercellular signal in microbial communities. Biosynthesis of indole is well-studied, and while carbon sources and amino acids are important environmental cues for indole production in Escherichia coli, other environmental factors affecting indole production for this strain are less clear. This study demonstrates that the environmental cue pH is an important factor for indole production that further controls biofilm formation of E. coli. Moreover, E. coli produced a higher level of extracellular indole in the presence of the antibiotics ampicillin and kanamycin, and the increased indole enhanced cell survival during antibiotic stress. Additionally, we found here that temperature is another important factor for indole production; E. coli produces and accumulates a large amount of indole at 50 °C, even at low cell densities. Overall, our results suggest that indole is a stable biological compound, and E. coli may utilize indole to protect itself against other microorganisms.

Neuroprotective effect of small heat shock protein, Hsp27, after acute and chronic alcohol administration

Alcohol induces degeneration of neurons and inhibits neurogenesis in the brain. Small heat shock proteins are able to protect neurons in cerebral ischemia and oxidative stress. In this study, we investigated the neuroprotective effect of small heat shock protein, Hsp27, after acute and chronic ethanol administrations using transgenic mice overexpressing the human Hsp27 protein. Transgenic mice and wild-type littermates were injected with 2 g/kg ethanol intraperitoneally, and then motor coordination and muscle strength were analyzed using different behavioral tests, such as footprint analysis, balance beam, and inverted screen tests. Ethanol-injected transgenic mice showed similar footprints to control saline-injected mice, did not fall of the beam, and were able to climb to the top of the inverted screen, while wild-type mice showed ataxia and incoordination after ethanol injection. The effect of Hsp27 on chronic ethanol consumption was also investigated. Drinking water of mice was replaced by a 20% ethanol solution for 5 weeks, and then brain sections were stained with Fluoro Jade C staining. We found significantly lesser amount of degenerating neurons in the brain of ethanol-drinking transgenic mice compared to wild-type mice. We conclude that Hsp27 can protect neurons against the acute and chronic toxic effects of ethanol.

Comparative transcriptional and translational analysis of leptospiral outer membrane protein expression in response to temperature

Background

Leptospirosis is a global zoonosis affecting millions of people annually. Transcriptional changes in response to temperature were previously investigated using microarrays to identify genes potentially expressed upon host entry. Past studies found that various leptospiral outer membrane proteins are differentially expressed at different temperatures. However, our microarray studies highlighted a divergence between protein abundance and transcript levels for some proteins. Given the abundance of post-transcriptional expression control mechanisms, this finding highlighted the importance of global protein analysis systems.

Methodology/Principal Findings

To complement our previous transcription study, we evaluated differences in the proteins of the leptospiral outer membrane fraction in response to temperature upshift. Outer membrane protein-enriched fractions from Leptospira interrogans grown at 30°C or overnight upshift to 37°C were isolated and the relative abundance of each protein was determined by iTRAQ analysis coupled with two-dimensional liquid chromatography and tandem mass spectrometry (2-DLC/MS-MS). We identified 1026 proteins with 99% confidence; 27 and 66 were present at elevated and reduced abundance respectively. Protein abundance changes were compared with transcriptional differences determined from the microarray studies. While there was some correlation between the microarray and iTRAQ data, a subset of genes that showed no differential expression by microarray was found to encode temperature-regulated proteins. This set of genes is of particular interest as it is likely that regulation of their expression occurs post-transcriptionally, providing an opportunity to develop hypotheses about the molecular dynamics of the outer membrane of Leptospira in response to changing environments.

Conclusions/Significance

This is the first study to compare transcriptional and translational responses to temperature shift in L. interrogans. The results thus provide an insight into the mechanisms used by L. interrogans to adapt to conditions encountered in the host and to cause disease. Our results suggest down-regulation of protein expression in response to temperature, and decreased expression of outer membrane proteins may facilitate minimal interaction with host immune mechanisms.

Leptospirosis, caused by Leptospira spp., is a disease of worldwide significance affecting millions of people annually. Bacteria of this species are spread by various carrier animals, including rodents and domestic livestock, which shed the leptospires via their urine into the environment. Humans become infected through direct contact with carrier animals or indirectly via contaminated water or soil. Temperature is a key trigger used by many bacteria to sense changes in environmental conditions, including entry from the environment into the host. This study was the first comprehensive research into changes occurring in the outer membrane of Leptospira in response to temperature and how these changes correlate with gene expression changes. An understanding of the regulation and function of these proteins is important as they may provide an adaptation and survival advantage for the microorganism which may enhance its ability to infect hosts and cause disease. Our data suggest regulation of proteins in the outer membrane which may possibly be a mechanism to minimise interactions with the host immune response.

Regulation of HSP70 on activating macrophages using PDT-induced apoptotic cells

Although anti-tumor immunological responses have been mainly associated with necrosis, apoptosis-associated immune responses have been recently suggested as well. In this study, we investigated anti-tumor immune responses and regulatory mechanisms of HSP70 using apoptotic cells induced by photodynamic therapy (PDT). The relationships between HSP70 release, HSP70 translocation and macrophage responses were studied using confocal fluorescence microscopy, FACS and ELISA. Macrophages incubated with apoptotic cells as well as necrotic tumor cells showed a high level of TNFalpha secretion. Apoptotic cells but not the apoptotic cell supernatants induced TNFalpha secretion. During both necrosis and apoptosis processes, the TNFalpha production was diminished drastically when HSP70 or TLR-2 was inhibited. After the PDT treatment, cytoplasmic HSP70 was released from the necrotic cells, while HSP70 rapidly translocated to the surface of the apoptotic cells. Furthermore, the TNFalpha secretion and the tumor cytotoxicity of splenocytes from mice immunized with apoptotic cells appeared similar to that of splenocytes immunized with necrotic cells. Our in vitro and in vivo results show that apoptosis can potentially have higher impact in inducing immunological responses, hence clarifying the immunological regulatory mechanisms of HSP70 under cell apoptosis and necrosis induced by PDT treatment. These findings could lead to an optimal PDT treatment based on immunological responses.

The purified and recombinant Legionella pneumophila chaperonin alters mitochondrial trafficking and microfilament organization

A portion of the total cellular pool of the Legionella pneumophila chaperonin, HtpB, is found on the bacterial cell surface, where it can mediate invasion of nonphagocytic cells. HtpB continues to be abundantly produced and released by internalized L. pneumophila and may thus have postinvasion functions. We used here two functional models (protein-coated beads and expression of recombinant proteins in CHO cells) to investigate the competence of HtpB in mimicking early intracellular trafficking events of L. pneumophila, including the recruitment of mitochondria, cytoskeletal alterations, the inhibition of phagosome-lysosome fusion, and association with the endoplasmic reticulum. Microscopy and flow cytometry studies indicated that HtpB-coated beads recruited mitochondria in CHO cells and U937-derived macrophages and induced transient changes in the organization of actin microfilaments in CHO cells. Ectopic expression of HtpB in the cytoplasm of transfected CHO cells also led to modifications in actin microfilaments similar to those produced by HtpB-coated beads but did not change the distribution of mitochondria. Association of phagosomes containing HtpB-coated beads with the endoplasmic reticulum was not consistently detected by either fluorescence or electron microscopy studies, and only a modest delay in the fusion of TrOv-labeled lysosomes with phagosomes containing HtpB-coated beads was observed. HtpB is the first Legionella protein and the first chaperonin shown to, by means of our functional models, induce mitochondrial recruitment and microfilament rearrangements, two postinternalization events that typify the early trafficking of virulent L. pneumophila.

Overexpression of the groESL operon enhances the heat and salinity stress tolerance of the nitrogen-fixing cyanobacterium Anabaena sp. strain PCC7120

The bicistronic groESL operon, encoding the Hsp60 and Hsp10 chaperonins, was cloned into an integrative expression vector, pFPN, and incorporated at an innocuous site in the Anabaena sp. strain PCC7120 genome. In the recombinant Anabaena strain, the additional groESL operon was expressed from a strong cyanobacterial P(psbA1) promoter without hampering the stress-responsive expression of the native groESL operon. The net expression of the two groESL operons promoted better growth, supported the vital activities of nitrogen fixation and photosynthesis at ambient conditions, and enhanced the tolerance of the recombinant Anabaena strain to heat and salinity stresses.

Mycobacterium tuberculosis Cpn60.2 and DnaK are located on the bacterial surface, where Cpn60.2 facilitates efficient bacterial association with macrophages

Mycobacterium tuberculosis, the causative agent of tuberculosis, initially contacts host cells with elements of its outer cell wall, or capsule. We have shown that capsular material from the surface of M. tuberculosis competitively inhibits the nonopsonic binding of whole M. tuberculosis bacilli to macrophages in a dose-dependent manner that is not acting through a global inhibition of macrophage binding. We have further demonstrated that isolated M. tuberculosis capsular proteins mediate a major part of this inhibition. Two-dimensional polyacrylamide gel electrophoresis analysis of the capsular proteins showed the presence of a wide variety of protein species, including proportionately high levels of the Cpn60.2 (Hsp65, GroEL2) and DnaK (Hsp70) molecular chaperones. Both of these proteins were subsequently detected on the bacterial surface. To determine whether these molecular chaperones play a role in bacterial binding, recombinant Cpn60.2 and DnaK were tested for their ability to inhibit the association of M. tuberculosis bacilli with macrophages. We found that recombinant Cpn60.2 can inhibit approximately 57% of bacterial association with macrophages, while DnaK was not inhibitory at comparable concentrations. Additionally, when polyclonal F(ab')(2) fragments of anti-Cpn60.2 and anti-DnaK were used to mask the surface presentation of these molecular chaperones, a binding reduction of approximately 34% was seen for anti-Cpn60.2 F(ab')(2), while anti-DnaK F(ab')(2) did not significantly reduce bacterial association with macrophages. Thus, our findings suggest that while M. tuberculosis displays both surface-associated Cpn60.2 and DnaK, only Cpn60.2 demonstrates adhesin functionality with regard to macrophage interaction.

Multiple chaperonins in bacteria--why so many?

A significant proportion of bacteria express two or more chaperonin genes. Chaperonins are a group of molecular chaperones, defined by sequence similarity, required for the folding of some cellular proteins. Chaperonin monomers have a mass of c. 60 kDa, and are typically found as large protein complexes containing 14 subunits arranged in two rings. The mechanism of action of the Escherichia coli GroEL protein has been studied in great detail. It acts by binding to unfolded proteins and enabling them to fold in a protected environment where they do not interact with any other proteins. GroEL can assist the folding of many proteins of different sizes, sequences, and structures, and homologues from many different bacteria can functionally replace GroEL in E. coli. What then are the functions of multiple chaperonins? Do they provide a mechanism for cells to increase their general chaperoning ability, or have they become specialized to take on specific novel cellular roles? Here I will review the genetic, biochemical, and phylogenetic evidence that has a bearing on this question, and show that there is good evidence for at least some specificity of function in multiple chaperonin genes.

Hypertonic saline increases gammadeltaT cell-mediated killing of activated neutrophils

OBJECTIVE

Hypertonic saline fluids used to resuscitate trauma patients can prevent neutrophil-mediated lung tissue damage, making them attractive alternatives to conventional resuscitation fluids. We have previously shown that gammadeltaT cells, a small T lymphocyte subset, reduce acute inflammatory lung damage by eliminating activated neutrophils that express heat shock protein 72 on the cell surface. Here, we studied whether these protective effects of hypertonic saline are related to improved gammadeltaT cell-mediated neutrophil killing.

DESIGN

Laboratory investigation.

SETTING

University research laboratory.

SUBJECTS

Human peripheral blood from healthy subjects--isolated gammadeltaT lymphocytes and neutrophils.

INTERVENTIONS

Isolated blood cells were treated with different concentrations of hypertonic saline and endotoxin of Escherichia coli O111:B4 (lipopolysaccharide). In some experiments, gammadeltaT cells were activated by CD3 cross-linking or by phorbol-myristate acetate and ionomycin, or by phytohemagglutinin.

MEASUREMENTS AND MAIN RESULTS

Clinically relevant concentrations of hypertonic saline (20 mM) significantly augmented CD69 expression of gammadeltaT cells that were stimulated with 100 ng/mL lipopolysaccharide. Additionally, lipopolysaccharide induced a three- to five-fold increase in tumor necrosis factor-alpha and interleukin-10 expression by gammadeltaT cells. This response was completely abrogated by hypertonic saline. These data indicate that hypertonic saline can modulate gammadeltaT cell functions. Stimulation of neutrophils with 1-1,000 ng/mL lipopolysaccharide caused a greater than 3-fold increase in heat shock protein-72 expression on the cell surface, which was significantly augmented by hypertonic saline. In cocultures of gammadeltaT cells with autologous neutrophils, 15.6 +/- 3.4% of all neutrophils were killed within 120 min. In the presence of lipopolysaccharide (1 microg/mL), this percentage increased to 23.7 +/- 2.1%, and it was further increased to 31.8 +/- 3.1% when 20 mM hypertonic saline was added with lipopolysaccharide.

CONCLUSIONS

Our findings suggest that hypertonic saline enhances the elimination of inflammatory neutrophils by gammadeltaT cells by augmenting heat shock protein-72 expression on the cell surface of neutrophils. Hypertonic saline resuscitation may therefore protect host tissues by enhancing neutrophil clearance from the lungs.

A mutant small heat shock protein with increased thylakoid association provides an elevated resistance against UV-B damage in synechocystis 6803

Besides acting as molecular chaperones, the amphitropic small heat shock proteins (sHsps) are suggested to play an additional role in membrane quality control. We investigated sHsp membrane function in the model cyanobacterium Synechocystis sp. PPC 6803 using mutants of the single sHsp from this organism, Hsp17. We examined mutants in the N-terminal arm, L9P and Q16R, for altered interaction with thylakoid and lipid membranes and examined the effects of these mutations on thylakoid functions. These mutants are unusual in that they retain their oligomeric state and chaperone activity in vitro but fail to confer thermotolerance in vivo. We found that both mutant proteins had dramatically altered membrane/lipid interaction properties. Whereas L9P showed strongly reduced binding to thylakoid and model membranes, Q16R was almost exclusively membrane-associated, properties that may be the cause of reduced heat tolerance of cells carrying these mutations. Among the lipid classes tested, Q16R displayed the highest interaction with negatively charged SQDG. In Q16R cells a specific alteration of the thylakoid-embedded Photosystem II (PSII) complex was observed. Namely, the binding of plastoquinone and quinone analogue acceptors to the Q(B) site was modified. In addition, the presence of Q16R dramatically reduced UV-B damage of PSII activity because of enhanced PSII repair. We suggest these effects occur at least partly because of increased interaction of Q16R with SQDG in the PSII complex. Our findings further support the model that membrane association is a functional property of sHsps and suggest sHsps as a possible biotechnological tool to enhance UV protection of photosynthetic organisms.

Roles of heat shock proteins and gamma delta T cells in inflammation

Elimination of activated inflammatory cells that infiltrate and damage host organs can reduce morbidity and mortality. A better understanding of the mechanisms by which these processes occur may lead to new approaches to prevent tissue damage. The lungs, gastrointestinal tract, and skin are particularly prone to infection and collateral damage by inflammatory cells. Specialized lymphocytes protect these organs from collateral tissue damage by eliminating neutrophils and macrophages from inflamed tissues. These lymphocytes recognize signals produced by inflammatory cells. One such signal is heat shock protein (Hsp) expressed on the cell surface of inflamed phagocytes. Mammalian Hsp molecules closely resemble their microbial equivalents, and therefore phagocytes decorated with these molecules are recognized as target cells. T lymphocytes bearing the gammadelta T cell receptor (TCR) elicit cytotoxic activity toward macrophages and neutrophils that express Hsp60 and Hsp70, respectively, protecting host organs from collateral tissue damage by phagocytes.

Chaperone activity of ERD10 and ERD14, two disordered stress-related plant proteins

ERD10 and ERD14 (for early response to dehydration) proteins are members of the dehydrin family that accumulate in response to abiotic environmental stresses, such as high salinity, drought, and low temperature, in Arabidopsis (Arabidopsis thaliana). Whereas these proteins protect cells against the consequences of dehydration, the exact mode(s) of their action remains poorly understood. Here, detailed evidence is provided that ERD10 and ERD14 belong to the family of intrinsically disordered proteins, and it is shown in various assays that they act as chaperones in vitro. ERD10 and ERD14 are able to prevent the heat-induced aggregation and/or inactivation of various substrates, such as lysozyme, alcohol dehydrogenase, firefly luciferase, and citrate synthase. It is also demonstrated that ERD10 and ERD14 bind to acidic phospholipid vesicles without significantly affecting membrane fluidity. Membrane binding is strongly influenced by ionic strength. Our results show that these intrinsically disordered proteins have chaperone activity of rather wide substrate specificity and that they interact with phospholipid vesicles through electrostatic forces. We suggest that these findings provide the rationale for the mechanism of how these proteins avert the adverse effects of dehydration stresses.

Membrane-associated stress proteins: more than simply chaperones

The protein- and/or lipid-mediated association of chaperone proteins to membranes is a widespread phenomenon and implicated in a number of physiological and pathological events that were earlier partially or completely overlooked. A temporary association of certain HSPs with membranes can re-establish the fluidity and bilayer stability and thereby restore the membrane functionality during stress conditions. The fluidity and microdomain organization of membranes are decisive factors in the perception and transduction of stresses into signals that trigger the activation of specific HS genes. Conversely, the membrane association of HSPs may result in the inactivation of membrane-perturbing signals, thereby switch off the heat shock response. Interactions between certain HSPs and specific lipid microdomains ("rafts") might be a previously unrecognized means for the compartmentalization of HSPs to specific signaling platforms, where key signaling proteins are known to be concentrated. Any modulations of the membranes, especially the raft-lipid composition of the cells can alter the extracellular release and thus the immuno-stimulatory activity of certain HSPs. Reliable techniques, allowing mapping of the composition and dynamics of lipid microdomains and simultaneously the spatio-temporal localization of HSPs in and near the plasma membrane can provide suitable means with which to address fundamental questions, such as how HSPs are transported to and translocated through the plasma membrane. The possession of such information is critical if we are to target the membrane association principles of HSPs for successful drug development in most various diseases.

Dynamics and mechanism of HSP70 translocation induced by photodynamic therapy treatment

Heat shock protein 70 (HSP70) is involved in nearly all intracellular compartments. It has been recently shown to be expressed on the outer cellular membrane under photodynamic therapy (PDT) treatment. However, the mechanism and function of HSP70 translocation to the cell surface during PDT treatment are not well understood. In this study, the dynamics and mechanism of HSP70 translocation onto the cell surface and its relationship with several key intracellular events after PDT treatment were investigated using confocal microscopy. HeLa and ASTC-a-1 tumor cells were treated by PDT using different doses. In the case of PDT-induced apoptosis, cytoplasmic HSP70 rapidly translocated to the cell surface after treatment, but it was not released into the medium. Such translocation was found to be dependent on the PDT dose. Moreover, during apoptosis, the translocation of HSP70 was closely related to the changes of mitochondrial transmembrane potential (DeltaPsim). Under non-lethal PDT induced surface stress, HSP70 also translocated to the cell surface, but with a slower rate and a lower final surface concentration. These findings reaffirm the HSP70 translocation onto the cell surface under PDT treatment in living cells. Our results also indicate that the function of the surface expression of HSP70, either initiated by mitochondrial disruption or direct surface stress, is to stabilize the plasma membrane integrity, although such function failed to prevent apoptosis induced by lethal PDT treatment, as evidenced in our study.

Membranes: a meeting point for lipids, proteins and therapies

Membranes constitute a meeting point for lipids and proteins. Not only do they define the entity of cells and cytosolic organelles but they also display a wide variety of important functions previously ascribed to the activity of proteins alone. Indeed, lipids have commonly been considered a mere support for the transient or permanent association of membrane proteins, while acting as a selective cell/organelle barrier. However, mounting evidence demonstrates that lipids themselves regulate the location and activity of many membrane proteins, as well as defining membrane microdomains that serve as spatio-temporal platforms for interacting signalling proteins. Membrane lipids are crucial in the fission and fusion of lipid bilayers and they also act as sensors to control environmental or physiological conditions. Lipids and lipid structures participate directly as messengers or regulators of signal transduction. Moreover, their alteration has been associated with the development of numerous diseases. Proteins can interact with membranes through lipid co-/post-translational modifications, and electrostatic and hydrophobic interactions, van der Waals forces and hydrogen bonding are all involved in the associations among membrane proteins and lipids. The present study reviews these interactions from the molecular and biomedical point of view, and the effects of their modulation on the physiological activity of cells, the aetiology of human diseases and the design of clinical drugs. In fact, the influence of lipids on protein function is reflected in the possibility to use these molecular species as targets for therapies against cancer, obesity, neurodegenerative disorders, cardiovascular pathologies and other diseases, using a new approach called membrane-lipid therapy.

Trehalose As a “Chemical Chaperone”

Trehalose is a disaccharide of glucose that is found at high concentrations in a wide variety of organisms that naturally survive drying in nature. Many years ago we reported that this molecule has the remarkable ability to stabilize membranes and proteins in the dry state. A mechanism for the stabilization rapidly emerged, and it was sufficiently attractive that a myth grew up about trehalose as a universal protectant and chemical chaperone. Many of the claims in this regard can be explained by what is now known about the physical properties of this interesting sugar. It is emerging that these properties may make it unusually useful in stabilizing intact cells in the dry state.

Membrane-regulated stress response: a theoretical and practical approach

Anumber of observations have lent support to a model in which thermal stress is transduced into a signal at the level of the cellular membranes. Our alternative, but not exclusive, approach is based on the concept that the initial stress-sensing events are associated with the physical state and lipid composition of cellular membranes, i.e., the subtle alteration(s) of membrane fluidity, phase state, and/or microheterogeneity may operate as a cellular thermometer. In fact, various pathological states and aging are associated with typical "membrane defects" and simultaneous dysregulation of heat shock protein synthesis. The discovery of nonproteotoxic membrane-lipid interacting compounds, capable of modulating membrane microdomains engaged in primary stress sensing may be of paramount importance for the design of new drugs with the ability to induce or attenuate the level of particular heat shock proteins.

Spontaneous apoptosis and expression of cell surface heat-shock proteins in cultured EL-4 lymphoma cells

The expression of heat-shock proteins (HSPs) is enhanced in stressed cells and can protect cells from stress-induced injury. However, existing data about the relationship between apoptosis and HSP expression is contradictory. In this paper, a mouse lymphoma cell death model system is used to detect simultaneously both the process of apoptosis and the level of HSP expression. The model was established after discovering that spontaneous apoptosis and spontaneous cell surface HSP expression occurs in EL-4 mouse lymphoma cells during normal optimal culture conditions. The data show that apoptotic EL-4 cells had higher levels of hsp25, hsp60, hsp70 and hsp90 exposed on the plasma membrane surface than viable cells. The level of surface HSPs was found to increase through several stages of early and late apoptotic death as measured by flow cytometry, with the highest levels observed during the loss of cell membrane phospholipid asymmetry. Heat shock and actinomycin D significantly increased the proportion of apoptotic cells in culture. However, hyperthermia only stimulated a weak and temporary increase in surface HSP expression, whereas actinomycin D strongly elevated the level of surface and intracellular HSPs, particularly in live cells. These results show an associative relationship between apoptosis and HSP expression. The relationship between the progression of cell death and HSP expression suggests a role for membrane HSP expression in programmed cell death.

Membrane regulation of the stress response from prokaryotic models to mammalian cells

"Membrane regulation" of stress responses in various systems is widely studied. In poikilotherms, membrane rigidification could be the first reaction to cold perception: reducing membrane fluidity of membranes at physiological temperatures is coupled with enhanced cold inducibility of a number of genes, including desaturases (see J.L. Harwood's article in this Proceedings volume). A similar role of changes in membrane physical state in heat (oxidative stress, etc.) sensing- and signaling gained support recently from prokaryotes to mammalian cells. Stress-induced remodeling of membrane lipids could influence generation, transduction, and deactivation of stress signals, either through global effects on the fluidity of the membrane matrix, or by specific interactions of boundary (or raft) lipids with receptor proteins, lipases, ion channels, etc. Our data point to membranes not only as targets of stress, but also as sensors in activating a stress response.

Hyperfluidization-coupled membrane microdomain reorganization is linked to activation of the heat shock response in a murine melanoma cell line

Targeting of the Hsp function in tumor cells is currently being assessed as potential anticancer therapy. An improved understanding of the molecular signals that trigger or attenuate the stress protein response is essential for advances to be made in this field. The present study provides evidence that the membrane fluidizer benzyl alcohol (BA), a documented nondenaturant, acts as a chaperone inducer in B16(F10) melanoma cells. It is demonstrated that this effect relies basically on heat shock transcription factor 1 (HSF1) activation. Under the conditions tested, the BA-induced Hsp response involves the up-regulation of a subset of hsp genes. It is shown that the same level of membrane fluidization (estimated in the core membrane region) attained with the closely analogous phenethyl alcohol (PhA) does not generate a stress protein signal. BA, at a concentration that activates heat shock genes, exerts a profound effect on the melting of raft-like cholesterol-sphingomyelin domains in vitro, whereas PhA, at a concentration equipotent with BA in membrane fluidization, has no such effect. Furthermore, through the in vivo labeling of melanoma cells with a fluorescein labeled probe that inserts into the cholesterol-rich membrane domains [fluorescein ester of polyethylene glycol-derivatized cholesterol (fPEG-Chol)], we found that, similarly to heat stress per se, BA, but not PhA, initiates profound alterations in the plasma membrane microdomain structure. We suggest that, apart from membrane hyperfluidization in the deep hydrophobic region, a distinct reorganization of cholesterol-rich microdomains may also be required for the generation and transmission of stress signals to activate hsp genes.

Modulation of endothelial cell damages by anti-Hsp60 autoantibodies in systemic autoimmune diseases

Heat-shock protein (Hsp) family is made up of heterogeneous proteins of which Hsp60 members are the most studied. It is now generally admitted that Hsp60 is not only a mitochondrial component but can be localized on the membrane cell surface. Considered as a signal danger following infections, Hsp60 can induce the production of anti-Hsp60 antibodies as defense mechanisms against pathogens. However, endogenous Hsp60 is also a target of autoantibodies in autoimmune disorders, atherosclerosis and vascular diseases, in which anti-endothelial cell antibodies (AECA) are generated. Hsp60 is one of the endothelial cell autoantigens able to trigger cytotoxic and apoptotic responses when recognized by the related autoantibodies. Depending on the Hsp60 epitope specificity, it appears that AECA with Hsp60 reactivity may differ in their functional effects. These observations suggest that new therapeutic approach to avoid endothelial cell damages due to anti-Hsp60 autoantibodies would be successful provided that specific Hsp60 epitopes would have been precisely characterized.

Chaperones as parts of cellular networks

The most important interactions between cellular molecules have a high affinity, are unique and specific, and require a network approach for a detailed description. Molecular chaperones usually have many first and second neighbors in protein-protein interaction networks and they play a prominent role in signaling and transcriptional regulatory networks of the cell. Chaperones may uncouple protein, signaling, membranous, organellar and transcriptional networks during stress, which gives an additional protection for the cell at the network-level. Recent advances uncovered that chaperones act as genetic buffers stabilizing the phenotype of various cells and organisms. This chaperone effect on the emergent properties of cellular networks may be generalized to proteins having a specific, central position and low affinity, weak links in protein networks. Cellular networks are preferentially remodeled in various diseases and aging, which may help us to design novel therapeutic and anti-aging strategies.

Heat Shock Proteins and the Resolution of Inflammation by Lymphocytes

Depletion of phagocytes that infiltrate host organs like the lungs reduces inflammatory damage to tissues. Understanding the mechanisms by which this process occurs could lead to new therapeutic approaches to limit the detrimental effects of inflammation. The lungs, gastrointestinal tract, and skin are particularly prone to infection. Specialized immune cells protect these organs from tissue damage by eliminating phagocytes from inflamed tissues by recognizing signals produced by the phagocytes. One such signal is heat shock proteins (HSP) expressed on the cell surface of phagocytes. These HSP closely resemble their microbial equivalents, and therefore phagocytes that are labeled by HSP are recognized as target cells. T lymphocytes bearing γδT cell receptor (TCR) elicit fast responses to invading pathogens. Since the γδTCR has limited germline-encoded diversity, HSP are an ideal target for recognition by these cells. γδT cells exert cytotoxic actions towards macrophages and neutrophils that express Hsp60 or Hsp70, respectively, on their cell surface. Through the recognition of HSP on the cell surface of inflamed cells, γδT cells eliminate phagocytes from inflammatory sites, thereby preventing host tissue damage

Environmental stress response in wine lactic acid bacteria: beyond Bacillus subtilis

Lactic acid bacteria (LAB) constitute a heterogeneous group of bacteria that are traditionally used to produce fermented foods. The industrialization of food transformations has increased the economical importance of LAB, as they play a crucial role in the development of the organoleptic and hygienic quality of fermented products. However, the strains selected for industrial purposes, should tolerate adverse conditions encountered in industrial processes, either during starter handling and storage (freeze-drying, freezing, or spray-drying) or during food processing in which abiotic stresses such as heat, cold, acidity, and high concentration of NaCl or ethanol are common. Wine LAB have to deal with several stresses including an acidic pH, a high alcoholic content, non optimal growth temperatures, and growth-inhibitory compounds such as fatty acids and tannins, originated from yeast and bacteria metabolism. Wine LAB have developed several mechanisms to escape or to tolerate wine conditions. They carry out a malolactic fermentation in this stressful environment. In addition to the regulation of the expression of specific genes, bacteria have evolved adaptive networks to face the challenges of a changing environment and to survive under conditions of stress. The so called Global Regulatory Systems control the simultaneous expression of a large number of genes in response to a variety of environmental stress factors. CIRCE sequences able to bind the HrcA repressor, sigma(B) dependent promoters and CtsR regulatory elements have been observed in several genes identified from wine LAB. Improved knowledge of regulators and a better understanding of LAB stress responses could constitute a basis of comparison with the well known model microorganisms, Escherichia coli and Bacillus subtilis. Moreover, it can provide an important insight into improving current industrial starter strains.

Surface expression of HSP72 by LPS-stimulated neutrophils facilitates gammadeltaT cell-mediated killing

During inflammation and sepsis, accumulation of activated neutrophils causes lung tissue damage and organ failure. Effective clearance of neutrophils reduces the risk of organ failure; however, its mechanisms are poorly understood. Because lungs are rich in gammadeltaT cells, we investigated the physiological role of these cells in the protection of lung tissue from infiltrating neutrophils. In a mouse model of sepsis, we found that the lungs of survivors contained significantly higher numbers of gammadeltaT cells than those of mice that died from sepsis. The number of gammadeltaT cells correlated inversely with the number of neutrophils in the lungs and with the degree of lung tissue damage. LPS rapidly elicited the expression of heat shock protein (HSP) 72 on the surface of human neutrophils. Inhibitors of transcription, protein synthesis, and intracellular protein transport blocked HSP72 expression, indicating that de novo synthesis is required. gammadeltaT cells targeted and rapidly killed LPS-treated neutrophils through direct cell-to-cell contact. Pre-treatment with neutralizing antibodies to HSP72 diminished neutrophil killing. Our data indicate that HSP72 expression on the cell surface predisposes inflamed neutrophils to killing by gammadeltaT cells. This intercellular exchange may allow gammadeltaT cells to resolve inflammation and limit host tissue damage during sepsis.

Analytical assays of human HSP27 and thermal-stress survival of Escherichia coli cells that overexpress it

HSP27 is a small heat-shock protein (sHSP). Such proteins are produced in all organisms. These small HSPs exhibit chaperone-like activity that can bind to unfolded polypeptides and prevent uncontrolled protein aggregation in vitro. Cellular anti-apoptosis function and enhanced cell survival are correlated with increased expression of HSPs. This study presents a thermal-stress survival model for cells using the Escherichia coli expression system for which human HSP27, a recombinant protein, is inducible. Results show that E. coli cells overexpressing human HSP27 have enhanced tolerance to 50 degrees C thermal stress.

Development-dependent differences in intracellular localization of stress proteins (hsps) in rainbow trout, Oncorhynchus mykiss, following heat shock

Using antibodies specific for salmonid fish, we have determined the intracellular localization of hsp70, hsc70 and hsp90 before and after an acute heat shock in juvenile and mature rainbow trout. We found that both hsp70 and hsp90 were primarily located outside the nucleus in both the liver and the heart of juvenile and mature fish and heat shock resulted in an increase in these proteins in all cellular fractions examined. In mature fish, liver hsp70 was predominantly found in the membranes and organelles after heat shock, while in juvenile fish, hsp70 was mostly cytoplasmic. Hsc70 was found in all cellular compartments examined both before and after heat shock in the livers and hearts of juvenile and mature fish. Heat shock resulted in a significant induction of hsp90 in the liver tissue of both juvenile and mature fish; however, in juvenile fish, this increase was seen in the membranes and organelles whereas in mature fish, hsp90 increased in the nucleus and cytoplasm. Hsp90 was only induced in the hearts of mature fish with heat shock, where it increased in both the nucleus and the cytoplasm. These results indicate that the cells of juvenile and mature fish respond differently to acute temperature stress. While the nucleus appears to be an important target for hsp protection following heat shock, the presence of hsps in all subcellular fractions examined suggests multifunctional roles for these proteins in the cellular response to temperature stress in fish.

Immobilization induces alterations in the outer membrane protein pattern of Yersinia ruckeri

We compared the outer membrane protein (OMP) pattern of 2-day-old immobilized Yersinia ruckericells (IC) with that of early (FC24) and late (FC48) stationary-phase planktonic counterparts. Fifty-five OMPs were identified. Principal component analysis discriminated between the protein maps of FC and IC. Some OMPs involved in bacterial adaptation were accumulated by both FC48 and IC but the expression of other proteins was controlled by the sessile mode of growth.

The hyperfluidization of mammalian cell membranes acts as a signal to initiate the heat shock protein response

The concentrations of two structurally distinct membrane fluidizers, the local anesthetic benzyl alcohol (BA) and heptanol (HE), were used at concentrations so that their addition to K562 cells caused identical increases in the level of plasma membrane fluidity as tested by 1,6-diphenyl-1,3,5-hexatriene (DPH) anisotropy. The level of membrane fluidization induced by the chemical agents on isolated membranes at such concentrations corresponded to the membrane fluidity increase seen during a thermal shift up to 42 degrees C. The formation of isofluid membrane states in response to the administration of BA or HE resulted in almost identical downshifts in the temperature thresholds of the heat shock response, accompanied by increases in the expression of genes for stress proteins such as heat shock protein (HSP)-70 at the physiological temperature. Similarly to thermal stress, the exposure of the cells to these membrane fluidizers elicited nearly identical increases of cytosolic Ca2+ concentration in both Ca2+-containing and Ca2+-free media and also closely similar extents of increase in mitochondrial hyperpolarization. We obtained no evidence that the activation of heat shock protein expression by membrane fluidizers is induced by a protein-unfolding signal. We suggest, that the increase of fluidity in specific membrane domains, together with subsequent alterations in key cellular events are converted into signal(s) leading to activation of heat shock genes.

Chaperones and proteases: cellular fold-controlling factors of proteins in neurodegenerative diseases and aging

The formation of toxic protein aggregates is a common denominator to many neurodegenerative diseases and aging. Accumulation of toxic, possibly infectious protein aggregates induces a cascade of events, such as excessive inflammation, the production of reactive oxygen species, apoptosis and neuronal loss. A network of highly conserved molecular chaperones and of chaperone-related proteases controls the fold-quality of proteins in the cell. Most molecular chaperones can passively prevent protein aggregation by binding misfolding intermediates. Some molecular chaperones and chaperone-related proteases, such as the proteasome, can also hydrolyse ATP to forcefully convert stable harmful protein aggregates into harmless natively refoldable, or protease-degradable, polypeptides. Molecular chaperones and chaperone-related proteases thus control the delicate balance between natively folded functional proteins and aggregation-prone misfolded proteins, which may form during the lifetime and lead to cell death. Abundant data now point at the molecular chaperones and the proteases as major clearance mechanisms to remove toxic protein aggregates from cells, delaying the onset and the outcome of protein-misfolding diseases. Therapeutic approaches include treatments and drugs that can specifically induce and sustain a strong chaperone and protease activity in cells and tissues prone to toxic protein aggregations.

A small HSP, Lo18, interacts with the cell membrane and modulates lipid physical state under heat shock conditions in a lactic acid bacterium

The small heat shock proteins (sHSP) are characterized by a chaperone activity to prevent irreversible protein denaturation. This study deals with the sHSP Lo18 induced by multiple stresses in Oenococcus oeni, a lactic acid bacterium. Using in situ immunocytochemistry and cellular fractionation experiments, we demonstrated the association of Lo18 with the membrane in O. oeni cells submitted to heat shock. The same result was obtained after exposure of cells to ethanol or benzyl alcohol, agents known to have an influence on membranes. For the different stresses, the protein was located on the periphery of the cell at membrane level and was also found within the cytoplasm. In order to determine if Lo18 could interact with the phospholipids, we used model membranes made of lipids extracted from O. oeni cells. Using fluorescence anisotropy of diphenylhexatriene (DPH) and generalized polarization of Laurdan, we showed that purified Lo18 interacts with these liposomes, and increases the molecular order of the lipid bilayer in these membranes when the temperature reaches 33.8 degrees C. All these data suggest that Lo18 could be involved in an adaptive response allowing the maintenance of membrane integrity during stress conditions in O. oeni cells.