Fluorescence recovery after photobleaching reveals that LPS rapidly transfers from CD14 to hsp70 and hsp90 on the cell membrane

Diversity of extracellular HSP70 in cancer: advancing from a molecular biomarker to a novel therapeutic target

Heat shock protein 70 (HSP70) is a highly conserved protein functioning as a "molecular chaperone", which is integral to protein folding and maturation. In addition to its high expression within cells upon stressful challenges, HSP70 can be translocated to the cell membrane or released from cells in free form or within extracellular vesicles (EVs). Such trafficking of HSP70 is also present in cancer cells, as HSP70 is overexpressed in various types of patient samples across a range of common malignancies, signifying that extracellular HSP70 (eHSP70) can serve as a tumor biomarker. eHSP70 is involved in a broad range of cancer-related events, including cell proliferation and apoptosis, extracellular matrix (ECM) remodeling, epithelial-mesenchymal transition (EMT), angiogenesis, and immune response. eHSP70 can also induce cancer cell resistance to various treatments, such as chemotherapy, radiotherapy, and anti-programmed death-1 (PD-1) immunotherapy. Though the role of eHSP70 in tumors is contradictory, characterized by both pro-tumor and anti-tumor effects, eHSP70 serves as a promising target in cancer treatment. In this review, we comprehensively summarized the current knowledge about the role of eHSP70 in cancer progression and treatment resistance and discussed the feasibility of eHSP70 as a cancer biomarker and therapeutic target.

Expression of ectopic heat shock protein 90 in male and female primary afferent nociceptors regulates inflammatory pain

ABSTRACT

Heat shock protein 90 (Hsp90) is a ubiquitously expressed integral cellular protein essential for regulating proteomic stress. Previous research has shown that Hsp90 regulates critical signaling pathways underlying chronic pain and inflammation. Recent discovery of membrane bound ectopic Hsp90 (eHsp90) on tumor cells has shown that Hsp90 induction to the plasma membrane can stabilize disease-relevant proteins. Here, we characterize eHsp90 expression in a mouse model of inflammation and demonstrate its role in nociception and pain. We found that intraplantar complete Freund adjuvant (CFA) induced robust expression of eHsp90 on the cell membranes of primary afferent nociceptors located in the L3-L5 dorsal root ganglia (DRG), bilaterally, with minimal to no expression in other tissues. Complete Freund adjuvant-induced increases in eHsp90 expression on lumbar DRG were significantly greater in females compared with males. Furthermore, exogenous Hsp90 applied to primary Pirt-GCaMP3 nociceptors induced increases in calcium responses. Responses were estrogen-dependent such that greater activity was observed in female or estrogen-primed male nociceptors compared with unprimed male nociceptors. Treatment of mice with the selective eHsp90 inhibitor HS-131 (10 nmol) significantly reversed CFA-induced mechanical pain, thermal heat pain, and hind paw edema. Notably, a higher dose (20 nmol) of HS-131 was required to achieve analgesic and anti-inflammatory effects in females. Here, we provide the first demonstration that inflammation leads to an upregulation of eHsp90 on DRG nociceptors in a sex-dependent manner and that inhibition of eHsp90 reduces nociceptor activity, pain, and inflammation. Thus, eHsp90 represents a novel therapeutic axis for the development of gender-tailored treatments for inflammatory pain.

Lipid Droplets Embedded in a Model Cell Membrane Create a Phospholipid Diffusion Barrier

Lipid droplets (LDs) are ubiquitous, cytoplasmic fat storage organelles that originate from the endoplasmic reticulum (ER) membrane. They are composed of a core of neutral lipids surrounded by a phospholipid monolayer. Proteins embedded into this monolayer membrane adopt a monotopic topology and are crucial for regulated lipid storage and consumption. A key question is, which collective properties of protein-intrinsic and lipid-mediated features determine spatio-temporal protein partitioning between phospholipid bilayer and LD monolayer membranes. To address this question, a freestanding phospholipid bilayer with physiological lipidic composition is produced using microfluidics and micrometer-sized LDs are dispersed around the bilayer that spontaneously insert into the bilayer. Using confocal microscopy, the 3D geometry of the reconstituted LDs is determined with high spatial resolution. The micrometer-sized bilayer-embedded LDs present a characteristic lens shape that obeys predictions from equilibrium wetting theory. Fluorescence recovery after photobleaching measurements reveals the existence of a phospholipid diffusion barrier at the monolayer-bilayer interface. Coarse-grained molecular dynamics simulation reveals lipid specific density distributions along the pore rim, which may rationalize the diffusion barrier. The lipid diffusion barrier between the LD covering monolayer and the bilayer may be a key phenomenon influencing protein partitioning between the ER membrane and LDs in living cells.

Lateral diffusion of CD14 and TLR2 in macrophage plasma membrane assessed by raster image correlation spectroscopy and single particle tracking

The diffusion of membrane receptors is central to many biological processes, such as signal transduction, molecule translocation, and ion transport, among others; consequently, several advanced fluorescence microscopy techniques have been developed to measure membrane receptor mobility within live cells. The membrane-anchored receptor cluster of differentiation 14 (CD14) and the transmembrane toll-like receptor 2 (TLR2) are important receptors in the plasma membrane of macrophages that activate the intracellular signaling cascade in response to pathogenic stimuli. The aim of the present work was to compare the diffusion coefficients of CD14 and TLR2 on the apical and basal membranes of macrophages using two fluorescence-based methods: raster image correlation spectroscopy (RICS) and single particle tracking (SPT). In the basal membrane, the diffusion coefficients obtained from SPT and RICS were found to be comparable and revealed significantly faster diffusion of CD14 compared with TLR2. In addition, RICS showed that the diffusion of both receptors was significantly faster in the apical membrane than in the basal membrane, suggesting diffusion hindrance by the adhesion of the cells to the substrate. This finding highlights the importance of selecting the appropriate membrane (i.e., basal or apical) and corresponding method when measuring receptor diffusion in live cells. Accurately knowing the diffusion coefficient of two macrophage receptors involved in the response to pathogen insults will facilitate the study of changes that occur in signaling in these cells as a result of aging and disease.

Low incubation temperature during early development negatively affects survival and related innate immune processes in zebrafish larvae exposed to lipopolysaccharide

In many fish species, the immune system is significantly constrained by water temperature. In spite of its critical importance in protecting the host against pathogens, little is known about the influence of embryonic incubation temperature on the innate immunity of fish larvae. Zebrafish (Danio rerio) embryos were incubated at 24, 28 or 32 °C until first feeding. Larvae originating from each of these three temperature regimes were further distributed into three challenge temperatures and exposed to lipopolysaccharide (LPS) in a full factorial design (3 incubation × 3 challenge temperatures). At 24 h post LPS challenge, mortality of larvae incubated at 24 °C was 1.2 to 2.6-fold higher than those kept at 28 or 32 °C, regardless of the challenge temperature. LPS challenge at 24 °C stimulated similar immune-related processes but at different levels in larvae incubated at 24 or 32 °C, concomitantly with the down-regulation of some chemokine and lysozyme transcripts in the former group. Larvae incubated at 24 °C and LPS-challenged at 32 °C exhibited a limited immune response with up-regulation of hypoxia and oxidative stress processes. Annexin A2a, S100 calcium binding protein A10b and lymphocyte antigen-6, epidermis were identified as promising candidates for LPS recognition and signal transduction.

Role of the Native Outer-Membrane Environment on the Transporter BtuB

BtuB is a TonB-dependent transporter that permits the high-affinity binding and transport of cobalamin (CBL), or vitamin B₁₂, across the asymmetric outer membrane (OM) of Gram-negative bacteria. It has been shown that Ca²⁺ binding is necessary for high-affinity binding of CBL to BtuB, and earlier simulations suggested that calcium ions serve to stabilize key substrate-binding extracellular loops. However, those simulations did not account for the lipopolysaccharides in the OM. To illuminate the roles of both Ca²⁺ and lipopolysaccharides in protein functionality, we performed simulations of apo and Ca²⁺-loaded BtuB in symmetric and asymmetric bilayers. The simulations reveal that the oligosaccharides of LPS stabilize the extracellular loops to some degree, apparently obviating the need for Ca²⁺. However, it is shown that Ca²⁺ ions stabilize a key substrate-binding loop to an even greater degree, as well as reposition specific CBL-binding residues, bringing them closer to the organization found in the CBL-bound structure. These results indicate the importance of including realistic membrane models when simulating outer-membrane proteins.

Receptor cluster formation during activation by bacterial products

The recognition of bacterial products, such as lipopolysaccharide (LPS) by the innate immune system lead to a strong pro-inflammatory response that can eventually lead to fatal sepsis syndrome in humans. Although CD14 and TLR4 have been identified as the key molecules involved in LPSinduced signal transduction, accumulating evidence indicates that multiple receptors are also involved. Our group has recently identified a cluster of receptors, involving heat-shock proteins 70 and 90, chemokine receptor 4 as well as growth differentiation factor 5, that are formed following LPS stimulation. In addition, we present data demonstrating that these molecules associate with TLR4 and accumulate in membrane microdomains following LPS ligation. Our results suggest that the entire bacterial recognition is based around the recruitment of multiple signalling molecules, in addition to CD14 and TLRs, within the lipid rafts. We propose that different combinational associations of receptors within activation clusters determine the different responses to a variety of bacterial stimuli.

Retina-on-a-chip: a microfluidic platform for point access signaling studies

We report on a microfluidic platform for culture of whole organs or tissue slices with the capability of point access reagent delivery to probe the transport of signaling events. Whole mice retina were maintained for multiple days with negative pressure applied to tightly but gently bind the bottom of the retina to a thin poly-(dimethylsiloxane) membrane, through which twelve 100 μm diameter through-holes served as fluidic access points. Staining with toluidine blue, transport of locally applied cholera toxin beta, and transient response to lipopolysaccharide in the retina demonstrated the capability of the microfluidic platform. The point access fluidic delivery capability could enable new assays in the study of various kinds of excised tissues, including retina.

Bioinspired Hierarchical Surface Structures with Tunable Wettability for Regulating Bacteria Adhesion

To circumvent the influence from varied topographies, the systematic study of wettability regulated Gram-positive bacteria adhesion is carried out on bioinspired hierarchical structures duplicated from rose petal structures. With the process of tuning the interfacial chemical composition of the self-assembled films from supramolecular gelators, the varied wettable surfaces from superhydrophilicity to superhydrophobicity can be obtained. The investigation of Gram-positive bacteria adhesion on the hierarchical surfaces reveals that Gram-positive bacteria adhesion is crucially mediated by peptidoglycan due to its different interaction mechanisms with wettable surfaces. The study makes it possible to systematically study the influence mechanism of wettability regulated bacteria adhesion and provides a sight to make the bioinspired topographies in order to investigate wettability regulated bioadhesion.

Gedunin Binds to Myeloid Differentiation Protein 2 and Impairs Lipopolysaccharide-Induced Toll-Like Receptor 4 Signaling in Macrophages

Recognition of bacterial lipopolysaccharide (LPS) by innate immune system is mediated by the cluster of differentiation 14/Toll-like receptor 4/myeloid differentiation protein 2 (MD-2) complex. In this study, we investigated the modulatory effect of gedunin, a limonoid from species of the Meliaceae family described as a heat shock protein Hsp90 inhibitor, on LPS-induced response in immortalized murine macrophages. The pretreatment of wild-type (WT) macrophages with gedunin (0.01-100 µM, noncytotoxic concentrations) inhibited LPS (50 ng/ml)-induced calcium influx, tumor necrosis factor-α, and nitric oxide production in a concentration-dependent manner. The selective effect of gedunin on MyD88-adapter-like/myeloid differentiation primary response 88- and TRIF-related adaptor molecule/TIR domain-containing adapter-inducing interferon-β-dependent signaling pathways was further investigated. The pretreatment of WT, TIR domain-containing adapter-inducing interferon-β knockout, and MyD88 adapter-like knockout macrophages with gedunin (10 µM) significantly inhibited LPS (50 ng/ml)-induced tumor necrosis factor-α and interleukin-6 production, at 6 hours and 24 hours, suggesting that gedunin modulates a common event between both signaling pathways. Furthermore, gedunin (10 µM) inhibited LPS-induced prostaglandin E2 production, cyclooxygenase-2 expression, and nuclear factor κB translocation into the nucleus of WT macrophages, demonstrating a wide-range effect of this chemical compound. In addition to the ability to inhibit LPS-induced proinflammatory mediators, gedunin also triggered anti-inflammatory factors interleukin-10, heme oxygenase-1, and Hsp70 in macrophages stimulated or not with LPS. In silico modeling studies revealed that gedunin efficiently docked into the MD-2 LPS binding site, a phenomenon further confirmed by surface plasmon resonance. Our results reveal that, in addition to Hsp90 modulation, gedunin acts as a competitive inhibitor of LPS, blocking the formation of the Toll-like receptor 4/MD-2/LPS complex.

Investigation of Pathogenesis of H1N1 Influenza Virus and Swine Streptococcus suis Serotype 2 Co-Infection in Pigs by Microarray Analysis

Swine influenza virus and Streptococcus suis are two important contributors to the porcine respiratory disease complex, and both have significant economic impacts. Clinically, influenza virus and Streptococcus suis co-infections in pigs are very common, which often contribute to severe pneumonia and can increase the mortality. However, the co-infection pathogenesis in pigs is unclear. In the present study, co-infection experiments were performed using swine H1N1 influenza virus and Streptococcus suis serotype 2 (SS2). The H1N1-SS2 co-infected pigs exhibited more severe clinical symptoms, serious pathological changes, and robust apoptosis of lungs at 6 days post-infection compared with separate H1N1 and SS2 infections. A comprehensive gene expression profiling using a microarray approach was performed to investigate the global host responses of swine lungs against the swine H1N1 infection, SS2 infection, co-infection, and phosphate-buffered saline control. Results showed 457, 411, and 844 differentially expressed genes in the H1N1, SS2, and H1N1-SS2 groups, respectively, compared with the control. Noticeably, genes associated with the immune, inflammatory, and apoptosis responses were highly overexpressed in the co-infected group. Pathway analysis indicated that the cytokine–cytokine receptor interactions, MAPK, toll-like receptor, complement and coagulation cascades, antigen processing and presentation, and apoptosis pathway were significantly regulated in the co-infected group. However, the genes related to these were less regulated in the separate H1N1 and SS2 infection groups. This observation suggested that a certain level of synergy was induced by H1N1 and SS2 co-infection with significantly stronger inflammatory and apoptosis responses, which may lead to more serious respiratory disease syndrome and pulmonary pathological lesion.

Development of a strategy for the identification of surface proteins in the pathogenic microsporidian Nosema bombycis

Parasite–host interactions mediated by cell surface proteins have been implicated as a critical step in infections caused by the microsporidian Nosema bombycis. Such cell surface proteins are considered as promising diagnostic markers and targets for drug development. However, little research has specifically addressed surface proteome identification in microsporidia due to technical barriers. Here, a combined strategy was developed to separate and identify the surface proteins of N. bombycis. Briefly, following (1) biotinylation of the spore surface, (2) extraction of total proteins with an optimized method and (3) streptavidin affinity purification of biotinylated proteins, 22 proteins were identified based on LC-MS/MS analysis. Among them, 5 proteins were confirmed to be localized on the surface of N. bombycis. A total of 8 proteins were identified as hypothetical extracellular proteins, whereas 7 other hypothetical proteins had no available function annotation. Furthermore, a protein with a molecular weight of 18·5 kDa was localized on the spore surface by western blotting and immunofluorescence analysis, even though it was predicted to be a nuclear protein by bioinformatics. Collectively, our work provides an effective strategy for isolating microsporidian surface protein components for both drug target identification and further diagnostic research on microsporidian disease control.

Role of lipid microdomains in TLR-mediated signalling

Over the last twenty years, evidence has been provided that the plasma membrane is partitioned with microdomains, laterally mobile in the bilayer, providing the necessary microenvironment to specific membrane proteins for signalling pathways to be initiated. We discuss here the importance of such microdomains for Toll-like receptors (TLR) localization and function. First, lipid microdomains favour recruitment and clustering of the TLR machinery partners, i.e. receptors and co-receptors previously identified to be required for ligand recognition and signal transmission. Further, the presence of the so-called Cholesterol Recognition Amino-Acid Consensus (CRAC) sequences in the intracellular juxtamembrane domain of several Toll-like receptors suggests a direct role of cholesterol in the activation process. This article is part of a Special Issue entitled: Lipid-protein interactions.

HSP90 inhibition suppresses lipopolysaccharide-induced lung inflammation in vivo

Inflammation is an important component of cancer diathesis and treatment-refractory inflammation is a feature of many chronic degenerative lung diseases. HSP90 is a 90kDa protein which functions as an ATP-dependent molecular chaperone that regulates the signalling conformation and expression of multiple protein client proteins especially oncogenic mediators. HSP90 inhibitors are in clinical development as cancer therapies but the myeleosuppressive and neutropenic effect of first generation geldanamycin-class inhibitors has confounded studies on the effects on HSP90 inhibitors on inflammation. To address this we assessed the ability of Ganetespib, a non-geldanamycin HSP90 blocker, to suppress lipopolysaccharide (LPS)-induced cellular infiltrates, proteases and inflammatory mediator and transcriptional profiles. Ganetespib (10-100 mg/kg, i.v.) did not directly cause myelosuppression, as assessed by video micrography and basal blood cell count, but it strongly and dose-dependently suppressed LPS-induced neutrophil mobilization into blood and neutrophil- and mononuclear cell-rich steroid-refractory lung inflammation. Ganetespib also suppressed B cell and NK cell accumulation, inflammatory cytokine and chemokine induction and MMP9 levels. These data identify non-myelosuppresssive HSP90 inhibitors as potential therapies for inflammatory diseases refractory to conventional therapy, in particular those of the lung.

Ca(2+) released from calcium alginate gels can promote inflammatory responses in vitro and in vivo

In general, alginate hydrogels are considered to be biologically inert and are commonly used for biomedical purposes that require minimum inflammation. However, Ca(2+), which is commonly used to crosslink alginate, is a critical second messenger in immune cell signaling, and little has been done to understand its effect on immune cell fate when delivered as a component of alginate gels. We found that dendritic cells (DCs) encapsulated in Ca(2+)-crosslinked alginate (calcium alginate) secreted at least fivefold more of the inflammatory cytokine IL-1β when compared to DCs encapsulated in agarose and collagen gels, as well as DCs plated on tissue-culture polystyrene (TCPS). Plating cells on TCPS with the alginate polymer could not reproduce these results, whereas culturing DCs on TCPS with increasing concentrations of Ca(2+) increased IL-1β, MHC class II and CD86 expression in a dose-dependent manner. In agreement with these findings, calcium alginate gels induced greater maturation of encapsulated DCs compared to barium alginate gels. When injected subcutaneously in mice, calcium alginate gels significantly upregulated IL-1β secretion from surrounding tissue relative to barium alginate gels, and similarly, the inflammatory effects of LPS were enhanced when it was delivered from calcium alginate gels rather than barium alginate gels. These results confirm that the Ca(2+) used to crosslink alginate gels can be immunostimulatory and suggest that it is important to take into account Ca(2+)'s bioactive effects on all exposed cells (both immune and non-immune) when using calcium alginate gels for biomedical purposes. This work may strongly impact the way people use alginate gels in the future as well as provide insights into past work utilizing alginate gels.

Regulation of G protein signaling by the 70kDa heat shock protein

G protein-coupled receptors (GPCRs) transduce extracellular signals to the interior of the cell by activating membrane-bound guanine nucleotide-binding regulatory proteins (G proteins). An increasing number of proteins have been reported to bind to and regulate GPCRs. We report a novel regulation of the alpha(2A) adrenergic receptor (α(2A)-R) by the ubiquitous stress-inducible 70kDa heat shock protein, hsp70. Hsp70, but not hsp90, attenuated G protein-dependent high affinity agonist binding to the α(2A)-R in Sf9 membranes. Antagonist binding was unchanged, suggesting that hsp70 uncouples G proteins from the receptor. As hsp70 did not bind G proteins but complexed with the α(2A)-R in intact cells, a direct interaction with the receptor seems likely. In the presence of hsp70, α(2A)-R-catalyzed [(35)S]GTPγS binding was reduced by approximately 70%. In contrast, approximately 50-fold higher concentrations of hsp70 were required to reduce agonist binding to the stress-inducible 5-hydroxytryptamine(1A) receptor (5-HT(1A)-R). In heat-stressed CHO cells, the α(2A)-R was significantly uncoupled from G proteins, coincident with an increased localization of hsp70 at the membrane. The contrasting effect of hsp70 on the α(2A)-R compared to the 5-HT(1A)-R suggests that during stress, upregulation of hsp70 may attenuate signaling from specific GPCRs as part of the stress response to foster survival.

Proteotoxic stress and circulating cell stress proteins in the cardiovascular diseases

The cardiovasculature is one of the major body systems and probably the one most exposed to stress. There is clear evidence that increasing levels of cell stress proteins within the heart is cardioprotective. In addition, there is rapidly emerging evidence that secreted cell stress proteins play a role in the function of the cardiovascular tissues. Those secreted proteins have three potential functions: (1) as normal homeostatic cardiovascular signals (e.g. protein disulphide isomerase); (2) as anti-inflammatory molecules, which are able to inhibit cardiovascular pathology (e.g. Hsp27); and (iii) as pro-inflammatory signals that can induce and promote cardiovascular pathology (e.g. Hsp60). As all of these various proteins may be released-at different rates-and in different cardiovascular diseases-we need to consider the cohort of potential secreted cell stress proteins as a dynamic system (network) that can aid and/or damage the equally dynamic cardiovascular system.

Inhibition of heat shock protein (molecular weight 90 kDa) attenuates proinflammatory cytokines and prevents lipopolysaccharide-induced liver injury in mice

Endotoxin-mediated proinflammatory cytokines play a significant role in the pathogenesis of acute and chronic liver diseases. Heat shock protein 90 (molecular weight, 90 kDa) (hsp90) functions as an important chaperone of lipopolysaccharide (LPS) signaling and is required for the production of proinflammatory cytokines. We hypothesized that inhibition of hsp90 would prevent LPS-induced liver injury by decreasing proinflammatory cytokines. C57BL/6 mice were injected intraperitoneally with an hsp90 inhibitor, 17-dimethylamino-ethylamino-17-demethoxygeldanamycin (17-DMAG), and LPS. Parameters of liver injury, proinflammatory cytokines, and associated mechanisms were studied by in vivo and in vitro experiments. Inhibition of hsp90 by 17-DMAG prevented LPS-induced increases in serum alanine aminotransferase activity and significantly reduced serum tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) protein as well as messenger RNA (mRNA) in liver. Enhanced DNA-binding activity of heat shock transcription factor 1 (HSF1) and induction of target gene heat shock protein 70 (molecular weight, 70 kDa) confirmed hsp90 inhibition in liver. 17-DMAG treatment decreased cluster of differentiation 14 mRNA and LPS-induced nuclear factor kappa light-chain enhancer of activated B cells (NFκB) DNA binding without affecting Toll-like receptor 4 mRNA in liver. Mechanistic studies revealed that 17-DMAG-mediated inhibition of TNFα showed no effect on LPS-induced NFκB promoter-driven reporter activity, but significantly decreased TNFα promoter-driven reporter activity. Chromatin immunoprecipitation assays showed that 17-DMAG enhanced HSF1 binding to the TNFα promoter, but not the IL-6 promoter, suggesting HSF1 mediated direct inhibition of TNFα, but not IL-6. We show that HSF1 indirectly regulates IL-6 by the induction of another transcription factor, activating transcription factor 3. Inhibition of HSF1, using small interfering RNA, prevented 17-DMAG-mediated down-regulation of NFκB-binding activity, TNFα, and IL-6 induction, supporting a repressive role for HSF1 on proinflammatory cytokine genes during hsp90 inhibition.

CONCLUSION

Hsp90 inhibition in vivo reduces proinflammatory cytokines and prevents LPS-induced liver injury likely through repressive action of HSF1. Our results suggest a novel application for 17-DMAG in alleviating LPS-induced liver injury.

Chaperone gp96-independent inhibition of endotoxin response by chaperone-based peptide inhibitors

HSP90 chaperones a large number of proteins, and it plays essential roles in multiple signaling pathways to maintain protein homeostasis in the cytosol. In addition, HSP90 has been implicated in mediating recognition of lipopolysaccharide (LPS). However, no pharmacologic agents have been developed to interrogate this pathway. Herein we demonstrate that a peptide-based inhibitor that was previously reported to inhibit the master Toll-like receptor-chaperone gp96, an endoplasmic reticulum paralog of HSP90, in fact blocks HSP90-LPS interaction. It inhibited the binding of LPS to the cell surface of both wild type and gp96-null cells and thereby abrogated the cellular response to LPS but not to other Toll-like receptor ligands. We also generated a series of peptide derivatives (named peptide inhibitors of endotoxin responsiveness (PIERs)) from the N-terminal helix structure of HSP90 and demonstrated their effectiveness in blocking LPS activity. PIER inhibition of LPS signaling was partially reversed by CD14 expression. Moreover, we found that a cell-permeable PIER abrogated HSP90 function and caused degradation of multiple known HSP90 client proteins in cancer cells. Thus, targeting HSP90 is a promising modality for treatment of both LPS-mediated pathology and cancer.

A novel putative lipoprotein receptor (CasLpR) in the hemocytes of the blue crab, Callinectes sapidus: cloning and up-regulated expression after the injection of LPS and LTA

The full-length cDNA encoding a putative lipoprotein receptor (CasLpR) was isolated from the hemocytes of Callinectes sapidus using 5' and 3' RACEs. The open reading frame for CasLpR contains a precursor of putative CasLpR consisting of 1710 amino acid residues including 22 amino acid residues of the signal peptide (22 amino acids). Mature CasLpR (1688 amino acids with 5.6% of phosphorylation sites) has multiple, putative functional domains: five low-density lipoprotein receptor domains in the N-terminus, and a G-protein-coupled receptor proteolysis site domain and a 7 transmembrane receptor (secretin family) domain in the C-terminus. To date, there are no proteins with a similar domain structure in the GenBank. The expression pattern of CasLpR was exclusive in hemocytes among all tested tissues obtained from a juvenile female at intermolt stage: brain, eyestalk ganglia, pericardial organs, and thoracic ganglia complex (nervous system); hepatopancreas (digestive system); heart, artery and hemocytes (circulatory system); gill and antennal gland (excretory system), hypodermis; and Y-organ (endocrine organ). There was no CasLpR expression in the ovary of an adult female. A putative function of CasLpR was examined after challenges of lipopolysaccharides (LPS) and lipoteichoic acid (LTA) in vivo using qRT-PCR assays. Animals at 24 h after injection of LPS or LTA up-regulated the expression of CasLpR in hemocytes by ∼3.5 and 1.4 folds, respectively, compared to the controls that received saline injection. LPS challenge also caused the greatest increment (∼55 folds) of heat shock protein 90 (Hsp90) expression in these samples. These data indicate that putative CasLpR and CasHsp90 may be involved in the defense system or the stress response of C. sapidus.

Visualising PAMP-PRR interactions using nanoscale imaging

The innate immune system utilises a set of receptors, called pattern recognition receptors (PRRs), in order to recognise specific molecular patterns or motifs called pathogen-associated molecular patterns (PAMPs) on invading pathogens. The toll-like receptor (TLR) family of proteins is an integral part of the mammalian innate immune system. We are now beginning to decipher which TLRs are involved in the recognition of particular microbial patterns, but questions remain as to the homo- and heterotypic associations that TLRs form and how these associations affect their activation. Technical advances in fluorescence microscopy has enabled us to investigate the functional associations of TLRs and other PPRs in living cells in response to different pathogens using non-invasive fluorescence imaging methods. In this chapter, we will describe some of the fluorescent imaging techniques, such as FRET and FRAP, that we employ in order to study PAMP-PRR associations.

The soluble recombinant Neisseria meningitidis adhesin NadA(Δ351-405) stimulates human monocytes by binding to extracellular Hsp90

The adhesin NadA favors cell adhesion/invasion by hypervirulent Neisseria meningitidis B (MenB). Its recombinant form NadA(Δ351-405,) devoid of the outer membrane domain, is an immunogenic candidate for an anti-MenB vaccine able to stimulate monocytes, macrophages and dendritic cells. In this study we investigated the molecular mechanism of NadA(Δ351-405) cellular effects in monocytes. We show that NadA(Δ351-405) (against which we obtained polyclonal antibodies in rabbits), binds to hsp90, but not to other extracellular homologous heat shock proteins grp94 and hsp70, in vitro and on the surface of monocytes, in a temperature dependent way. Pre-incubation of monocytes with the MenB soluble adhesin interfered with the binding of anti-hsp90 and anti-hsp70 antibodies to hsp90 and hsp70 at 37°C, a condition in which specific cell-binding occurs, but not at 0°C, a condition in which specific cell-binding is very diminished. Conversely, pre-incubation of monocytes with anti-hsp90 and anti-hsp70 antibodies did not affected NadA(Δ351-405) cell binding in any temperature condition, indicating that it associates to another receptor on their plasma membrane and then laterally diffuses to encounter hsp90. Consistently, polymixin B interfered with NadA(Δ351-405) /hsp90 association, abrogated the decrease of anti-hsp90 antibodies binding to the cell surface due to NadA(Δ351-405) and inhibited adhesin-induced cytokine/chemokine secretion without affecting monocyte-adhesin binding. Co-stimulation of monocytes with anti-hsp90 antibodies and NadA(Δ351-405) determined a stronger but polymixin B insensitive cell activation. This indicated that the formation of a recombinant NadA/hsp90/hsp70 complex, although essential for full monocyte stimulation, can be replaced by anti-hsp90 antibody/hsp90 binding. Finally, the activation of monocytes by NadA(Δ351-405) alone or in the presence of anti-hsp90 antibodies were both inhibited by neutralizing anti-TLR4 antibodies, but not by anti-TLR2 antibodies. We propose that hsp90-dependent recruitment into an hsp90/hsp70/TLR4 transducing signal complex is necessary for the immune-stimulating activity of NadA(Δ351-405) anti-MenB vaccine candidate.

Measuring immune receptor mobility by fluorescence recovery after photobleaching

The coordinated effort of cells in the immune system relies heavily on surface receptor interactions. Immune receptor mobility provides vital information on the function and responses of immune cells, and these measurements shed light on their interactions with other membrane, cytosolic, and extracellular matrix proteins. These measurements can be obtained using the fluorescence recovery after photobleaching (FRAP) technique in living cells. We describe here general approaches for FRAP using green fluorescent protein fusion proteins.

Rapid decrease of CD16 (FcγRIII) expression on heat-shocked neutrophils and their recognition by macrophages

Accumulation of neutrophils in the site of inflammation is a typical mechanism of innate immunity. The accumulated neutrophils are exposed to stressogenic factors usually associated with inflammation. Here, we studied response of human peripheral blood neutrophils subjected to short, febrile-range heat stress. We show that 90 min heat stress slowed down the spontaneous apoptosis of neutrophils. In the absence of typical markers of apoptosis the heat-shocked neutrophils induced antiinflammatory effect in human monocyte-derived macrophages (hMDMs), yet without being engulfed. Importantly, the expression of FcγRIII (CD16) was sharply reduced. Surprisingly, concentration of the soluble CD16 did not change in heat-shocked neutrophil supernates indicating that the reduction of the cell surface CD16 was achieved mainly by inhibition of fresh CD16 delivery. Inhibitors of 90 kDa heat shock protein (HSP90), a molecular chaperone found in membrane platforms together with CD16 and CD11b, significantly increased the observed effects caused by heat shock. The presented data suggest a novel systemic aspect of increased temperature which relies on immediate modification by heat of a neutrophil molecular pattern. This effect precedes cell death and may be beneficial in the initial phase of inflammation providing a nonphlogistic signal to macrophages before it comes from apoptotic cells.

Emodin suppresses lipopolysaccharide-induced pro-inflammatory responses and NF-κB activation by disrupting lipid rafts in CD14-negative endothelial cells

BACKGROUND AND PURPOSE

Emodin [1,3,8-trihydroxy-6-methylanthraquinone] has been reported to exhibit vascular anti-inflammatory properties. However, the corresponding mechanisms are not well understood. The present study was designed to explore the molecular target(s) of emodin in modifying lipopolysaccharide (LPS)-associated signal transduction pathways in endothelial cells.

EXPERIMENTAL APPROACH

Cultured primary human umbilical vein endothelial cells (HUVECs; passages 3-5) were pre-incubated with emodin (1-50 µg·mL(-1) ). LPS-induced expression of pro-inflammatory cytokines [interleukin (IL)-1β, IL-6] and chemokines (IL-8; CCL2/MCP-1) were determined by reverse transcription-PCR and elisa. Nuclear factor-κB (NF-κB) activation, inhibitor of κB (IκB)α degradation and Toll-like receptor-4 (TLR-4) were detected by immunocytochemistry and Western blotting. Cholesterol depletion [by methyl β-cyclodextrin (MBCD), a specific cholesterol binding agent] and cholesterol replenishment were further used to investigate the roles of lipid rafts in activation of HUVECs.

KEY RESULTS

Emodin inhibited, concentration-dependently, the expression of LPS-induced pro-inflammatory cytokines (IL-1β, IL-6) and chemokines (IL-8, CCL2) and, in parallel, inhibited NF-κB activation and IκBα degradation in HUVECs. However, emodin did not inhibit the NF-κB activation and IκBα degradation induced by IL-1β. The cholesterol binding agent, MBCD, inhibited LPS-induced NF-κB activation in passaged HUVECs [which also lack the LPS receptor, membrane CD14 (mCD14)], showing that lipid rafts played a key role in LPS signalling in mCD14-negative HUVECs. Moreover, emodin disrupted the formation of lipid rafts in cell membranes by depleting cholesterol.

CONCLUSIONS AND IMPLICATIONS

Lipid rafts were crucial in facilitating inflammatory responses of mCD14-negative HUVECs to LPS. Emodin disrupted lipid rafts through depleting cholesterol and, consequently, inhibited inflammatory responses in endothelial cells.

Caught with their PAMPs down? The extracellular signalling actions of molecular chaperones are not due to microbial contaminants

In recent years, it has been hypothesised that a new signalling system may exist in vertebrates in which secreted molecular chaperones form a dynamic continuum between the cellular stress response and corresponding homeostatic physiological mechanisms. This hypothesis seems to be supported by the finding that many molecular chaperones are released from cells and act as extracellular signals for a range of cells. However, this nascent field of biological research seems to suffer from an excessive criticism that the biological activities of molecular chaperones are due to undefined components of the microbial expression hosts used to generate recombinant versions of these proteins. In this article, a number of the proponents of the cell signalling actions of molecular chaperones take this criticism head-on. They show that sufficient evidence exists to support fully the hypothesis that molecular chaperones have cell-cell signalling actions that are likely to be part of the homeostatic mechanism of the vertebrate.

Evidence for a role of heat shock protein-90 in toll like receptor 4 mediated pain enhancement in rats

Spinal cord microglial toll-like receptor 4 (TLR4) has been implicated in enhancing neuropathic pain and opposing morphine analgesia. The present study was initiated to explore TLR4-mediated pain modulation by intrathecal lipopolysaccharide, a classic TLR4 agonist. However, our initial study revealed that intrathecal lipopolysaccharide failed to induce low-threshold mechanical allodynia in naive rats, suggestive that TLR4 agonism may be insufficient to enhance pain. These studies explore the possibility that a second signal is required; namely, heat shock protein-90 (HSP90). This candidate was chosen for study given its known importance as a regulator of TLR4 signaling. A combination of in vitro TLR4 cell signaling and in vivo behavioral studies of pain modulation suggest that TLR4-enhancement of neuropathic pain and TLR4-suppression of morphine analgesia each likely require HSP90 as a cofactor for the effects observed. In vitro studies revealed that dimethyl sulfoxide (DMSO) enhances HSP90 release, suggestive that this may be a means by which DMSO enhances TLR4 signaling. While 2 and 100 microg lipopolysaccharide intrathecally did not induce mechanical allodynia across the time course tested, co-administration of 1 microg lipopolysaccharide with a drug that enhances HSP90-mediated TLR4 signaling now induced robust allodynia. In support of this allodynia being mediated via a TLR4/HSP90 pathway, it was prevented or reversed by intrathecal co-administration of a HSP90 inhibitor, a TLR4 inhibitor, a microglia/monocyte activation inhibitor (as monocyte-derived cells are the predominant cell type expressing TLR4), and interleukin-1 receptor antagonist (as this proinflammatory cytokine is a downstream consequence of TLR4 activation). Together, these results suggest for the first time that TLR4 activation is necessary but not sufficient to induce spinally mediated pain enhancement. Rather, the data suggest that TLR4-dependent pain phenomena may require contributions by multiple components of the TLR4 receptor complex.

Molecular or pharmacologic inhibition of the CD14 signaling pathway protects against burn-related myocardial inflammation and dysfunction

Signaling through toll-like receptor 4 (TLR4) plays an obligate role in burn-related myocardial dysfunction. We hypothesized that signaling through CD14, a cellular receptor for endotoxin that lacks a transmembrane domain but is coupled to TLR4, also plays a role in postburn myocardial inflammation and dysfunction. Burn covering 40% total body surface area (or sham burn for controls) was produced in wild-type (WT) and CD14 knockout (KO) as well as vehicle-treated and geldanamycin-treated WT mice (1 microg/g body weight) to inhibit CD14 signaling. Groups included (1) WT shams, (2) CD14 KO sham, (3) WT burns, (4) CD14 KO burns, (5) vehicle-treated WT shams, (6) geldanamycin-treated WT shams, (7) vehicle-treated WT burns, and (8) geldanamycin-treated WT burns. Twenty-four hours after burn, cardiac function (Langendorff) and cardiomyocyte secretion of inflammatory cytokines TNF-alpha, IL-1 beta, and IL-6 (in pg/mL; 5 x 10(4) myocytes) were studied in all groups. Relative to sham WT controls, burn trauma in increased cardiac myocyte secretion of inflammatory cytokines (TNF-alpha, IL-1 beta, and IL-6 rose from 59 +/- 10 to 171 +/- 8; 6 +/- 0.2 to 78 +/- 1; and 88 +/- 3 to 170 +/- 12 pg/mL, respectively; P < 0.05) and produced robust cardiac contractile dysfunction (left ventricular pressure and +dP/dt fell from 105 +/- 4 to 73 +/- 5 mmHg and 2,400 +/- 73 to 1,803 +/- 90 mmHg/s; P < 0.05). Inability to signal through the CD14/TLR4 pathway (induced by CD14/KO or inhibition of CD14 expression by administration of geldanamycin) attenuated TNF-alpha, IL-1 beta, and IL-6 production in response to burn injury and improved postburn myocardial contractile function. Our data suggest that signaling through the CD14 pathway plays an obligate role in cardiac inflammation/dysfunction which occurs after major burn injury.

A phosphatidylserine species inhibits a range of TLR- but not IL-1beta-induced inflammatory responses by disruption of membrane microdomains

TLRs detect conserved molecular patterns that are unique to microbes, enabling tailored responses to invading pathogens and modulating a multitude of immunopathological conditions. We investigated the ability of a naturally occurring stearoyl-arachidonoyl form of phosphatidylserine (SAPS) to inhibit the proinflammatory effects of TLR agonists in models of inflammation investigating the interaction of leukocytes with epithelial and endothelial cells. The responses to LPS of both epithelial and endothelial cells were highly amplified in the presence of PBMCs. Coincubation with SAPS markedly inhibited activation of cocultures by LPS, principally through inhibition of the TLR4 signaling pathway in PBMCs; however, this was not through downmodulation of TLR4 or coreceptor expression, nor was IL-1beta-induced cytokine release affected. SAPS also impaired Pam(3)CSK(4) (TLR2/1), Gardiquimod (TLR7/8), and Streptococcus pneumoniae-induced cytokine release, but had only modest effects on poly(I:C) (TLR3)-induced responses. Fluorescence resonance energy transfer analysis of molecular associations revealed that SAPS disrupted the association of both TLR4 and TLR2 with their respective membrane partners that are required for signaling. Thus, our data reinforce the existence and importance of cooperative networks of TLRs, tissue cells, and leukocytes in mediating innate immunity, and identify a novel disrupter of membrane microdomains, revealing the dependence of TLR signaling on localization within these domains.

Heat shock protein 70 (Hsp70): membrane location, export and immunological relevance

Stress or heat shock proteins (HSPs) are remarkably conserved in all living organisms. Their expression is induced in response to a variety of physiological and environmental insults. In the cytosol these proteins play an essential role as molecular chaperones by assisting the correct folding of nascent and stress-accumulated misfolded proteins, preventing protein aggregation, transport of proteins, and supporting antigen processing and presentation. Following stress, intracellularly located HSPs fulfill protective functions and thus prevent lethal damage. In contrast, membrane-bound or extracellularly located HSPs act as danger signals and elicit immune responses mediated either by the adaptive or innate immune system. Here, HSPs act as carriers for immunogenic peptides, induce cytokine release or provide recognition sites for natural killer (NK) cells. This article will discuss methods for the detection of membrane-bound and extracellular HSPs and methods for determining their immunological functions.

Mycobacterium tuberculosis heat-shock protein 70 impairs maturation of dendritic cells from bone marrow precursors, induces interleukin-10 production and inhibits T-cell proliferation in vitro

In different inflammatory disease models, heat-shock proteins (hsp) and hsp-derived peptides have been demonstrated to possess anti-inflammatory properties. While some studies have shown that hsp can directly interact with antigen-presenting cells, others report that bacterial hsp can induce specific T cells with regulatory phenotypes. Effective characterization of the immunomodulatory effects of hsp 70, however, has historically been confounded by lipopolysaccharide (LPS) contamination. In this study, we compared the effects of LPS-free Mycobacterial tuberculosis hsp 70 (TBhsp70) and its possible contaminants on dendritic cells (DC). We demonstrate herein that LPS-free TBhsp70 inhibits murine DC maturation in vitro, while LPS-contaminated TBhsp70 induces DC maturation. Mock recombinant preparations have no effect. In contrast to LPS, TBhsp70 does not induce tumour necrosis factor-alpha production by DC, but interleukin-10. In vivo, only LPS-contaminated TBhsp70 induces up-regulation of CD86 in splenic mature DC. Finally, TBhsp70 inhibited phytohaemagglutinin-induced T-cell proliferation. Our results support the hypothesis that TBhsp70 does not have inflammatory potential, but rather has immunosuppressive properties.

Microbial heat shock protein 70 stimulatory properties have different TLR requirements

Members of the HSP70 family have acquired special significance in immunity. Among other receptors, toll like receptor (TLR)-2 and TLR-4 have been suggested to be involved in HSP70-mediated signalling. We have previously shown that recombinant HSP70 from Trypanosoma cruzi and from Plasmodium falciparum function as adjuvants. In the present study, we have extended the study with other microbial HSPs (mHSPs) and considered of interest to assess the influence of TLR-2 and TLR-4 in mHSP-promoted responses. To test this, we evaluated the adjuvant effect of various mHSP molecules in TLR-2(-/-), TLR-4(-/-) and MyD88(-/-) mice. We show that all the mHSPs tested are strong adjuvants and induced IL-12 production by bone marrow macrophages. However, even within the same family, mHSPs induced different types of immune responses. Furthermore, the mHSPs tested, possess different requirements for signaling through TLRs. Interestingly, Tc70 was found to induce in vivo and in vitro responses in both TLR-2(-/-) and TLR-4(-/-) mice. Possible implications of our findings are taken up in the discussion section.

Ethanol suppresses LPS-induced Toll-like receptor 4 clustering, reorganization of the actin cytoskeleton, and associated TNF-alpha production

BACKGROUND

Ethanol (EtOH) suppresses cytokine responses induced through most Toll-like receptors (TLRs), but the mechanism of action is unclear. We recently found that acute EtOH alters lipopolysaccharide (LPS)-induced partitioning of CD14, a critical component of the LPS receptor complex, within lipid raft fractions in the macrophage-like cell line RAW264.7.

METHODS

Here we investigated the role of receptor clustering in alteration of the responses of cells to LPS caused by EtOH both in vitro and in vivo. The cellular distribution of CD14, TLR4, actin cytoskeleton, and tumor necrosis factor-alpha (TNF-alpha) were studied by confocal microscopy following exposure of cells to LPS with or without EtOH. TLR4 and CD14 were clustered into highly colocalized patches on the cell membrane accompanied by the reorganization of the actin cytoskeleton in some of the RAW264.7 cells as well as peritoneal cells following LPS treatment.

RESULTS

Addition of EtOH reduced the number of cells that had LPS-induced receptor patches and in which this reorganization occurred. Cells on which CD14 and TLR4 formed clusters or caps had substantially higher levels of membrane-bound TNF-alpha compared with cells without clustering or capping of these molecules. Interference with the actin cytoskeleton by cytochalasin D suppressed the production of TNF-alpha and receptor clustering, as EtOH did.

CONCLUSIONS

These data confirm our previous observations, suggest a novel mechanism of EtOH action that involves interference with receptor clustering, and indicate a potential role of actin filaments in the formation of receptor patches, subsequent activation of macrophages by LPS, and production of TNF-alpha.

Intracellular and extracellular functions of heat shock proteins: repercussions in cancer therapy

Stress or heat shock proteins (HSPs) are the most conserved proteins present in both prokaryotes and eukaryotes. Their expression is induced in response to a wide variety of physiological and environmental insults. These proteins play an essential role as molecular chaperones by assisting the correct folding of nascent and stress-accumulated misfolded proteins, and preventing their aggregation. HSPs have a dual function depending on their intracellular or extracellular location. Intracellular HSPs have a protective function. They allow the cells to survive lethal conditions. Various mechanisms have been proposed to account for the cytoprotective functions of HSPs. Several HSPs have also been demonstrated to directly interact with various components of the tightly regulated programmed cell death machinery, upstream and downstream of the mitochondrial events. On the other hand, extracellular located or membrane-bound HSPs mediate immunological functions. They can elicit an immune response modulated either by the adaptive or innate immune system. This review will focus on HSP27, HSP70, and HSP90. We will discuss the dual role of these HSPs, protective vs. immunogenic properties, making a special emphasis in their utility as targets in cancer therapy.

Fucoidan induces nitric oxide production via p38 mitogen-activated protein kinase and NF-kappaB-dependent signaling pathways through macrophage scavenger receptors

It has been reported that ligands of the macrophage scavenger receptor (MSR) induce a range of cellular responses including urokinase-type plasminogen activator and the production of inflammatory cytokines. Although nitric oxide (NO) is an important regulatory molecule in physiological functions such as vascular homeostasis, neurotransmission, and host defense, the effect of MSR ligands on NO production from macrophages was unknown. Here, we demonstrate that the MSR ligand, fucoidan, but neither oxidized low-density lipoprotein, acetylated LDL, maleylated bovine serum albumin nor dextran sulfate induces activation of inducible nitric oxide synthase (iNOS) promoter or NO production in RAW264.7 cells. Furthermore, we investigated the molecular mechanism by which fucoidan induces iNOS promoter activation. Using different inhibitors, we showed that the stimulation of fucoidan was mediated by both the p38 mitogen-activated protein kinase and the NF-kappaB-dependent pathways. Although these two pathways were independent, heat shock protein 90 (HSP90) played a significant role in both pathways. Our previous study showed that HSP90 directly interacts with the cytoplasmic domain of MSR. These results provide the evidence that HSP90 bound to the cytoplasmic domain of MSR is implicated in MSR-mediated signal transduction. Moreover, fucoidan-induced NO production by peritoneal macrophages from MSR-knockout (MSR-/-) mice significantly decreases compared with those from wild-type mice. This is the first indication that MSR transduces the signal of fucoidan to iNOS gene expression.

Stimulation of innate immune responses by malarial glycosylphosphatidylinositol via pattern recognition receptors

The glycosylphosphatidylinositol (GPI) anchor of Plasmodium falciparum is thought to function as a critical toxin that contributes to severe malarial pathogenesis by eliciting the production of proinflammatory responses by the innate immune system of mammalian hosts. Analysis of the fine structure of P. falciparum GPI suggests a requirement for the presence of both core glycan and lipid moieties in the recognition and signalling of parasite glycolipids by host immune cells. It has been demonstrated that GPI anchors of various parasitic protozoa can mediate cellular immune responses via members of the Toll-like family of pattern recognition receptors (TLRs). Recent studies indicate that GPI anchors of P. falciparum and other protozoa are preferentially recognized by TLR-2, involving the MyD88-dependent activation of specific signalling pathways that mediate the production of proinflammatory cytokines and nitric oxide from host macrophages in vitro. However, the contribution of malaria GPI toxin to severe disease syndromes and the role of specific TLRs or other pattern recognition receptors in innate immunity in vivo is only just beginning to be characterized. A better understanding of the molecular mechanisms underlying severe malarial pathogenesis may yet lead to substantial new insights with important implications for the development of novel therapeutics for malaria treatment.

Chaperon and adjuvant activity of hsp70: different natural killer requirement for cross-priming of chaperoned and bystander antigens

Heat shock proteins (HSP) convey both chaperoned propeptide and danger signal to dendritic cells (DC). However, few studies have compared the two activities. Using a murine inducible hsp70 secreted by cells distinct from those providing the tumor antigens, we showed that hsp70 exerts efficacious adjuvant effects toward DC cross-priming. Hsp70 induces DC maturation and phagocytosis of cellular debris both in vitro and in vivo, which are conducive to CTL response to chaperoned and nonchaperoned antigens. Whereas the ability of hsp70 to induce cross-presentation of chaperoned peptides is natural killer (NK) independent, the adjuvant activity requires NK cells at the site of DC-hsp70 interaction to induce CTL response and therapeutic effect against lung metastases. However, although bystander activity provides equal CTL induction, the best therapeutic efficacy rests on cell vaccine secreting hsp70 that combines chaperoned antigen and danger signal within the same cell.

Evidence that hsp90 is involved in the altered interactions of Acanthamoeba castellanii variants with bacteria

There are many similarities between the interactions of environmental protozoa with pathogenic bacterial species and those observed in mammalian macrophages. Since single-celled protozoa predate mammalian hosts, it is likely that interactions in environmental biofilms have selected for many of the bacterial virulence mechanisms responsible for human disease. In order to better understand bacterial-phagocyte interactions, we developed a selection for Acanthamoeba castellanii variants that are more resistant to killing by bacterial pathogens. We identified four amoebal clones that display decreased phagocytosis of bacteria but no difference in uptake of latex beads compared to wild-type amoebae. These amoebal variants display differences in cellular morphology, partial resistance to killing by bacteria, more bactericidal activity, and higher frequencies of lysosome fusion with the bacterial vacuole. Three proteins are present at lower levels in these variants than in wild-type amoebae, and matrix-assisted laser desorption ionization-time of flight mass spectrometry allowed identification of two of them as actin and hsp90. We found that specific inhibitors of hsp90 produce a similar phenotypic effect in macrophages. These data suggest that hsp90 plays a role in phagocytic and, possibly, bactericidal pathways that affect interactions of phagocytic cells with bacteria.

Activation of human meningeal cells is modulated by lipopolysaccharide (LPS) and non-LPS components of Neisseria meningitidis and is independent of Toll-like receptor (TLR)4 and TLR2 signalling

The interactions of Neisseria meningitidis with cells of the meninges are critical to progression of the acute, compartmentalized intracranial inflammatory response that is characteristic of meningococcal meningitis. An important virulence mechanism of the bacteria is the ability to shed outer membrane (OM) blebs containing lipopolysaccharide (LPS), which has been assumed to be the major pro-inflammatory molecule produced during meningitis. Comparison of cytokine induction by human meningeal cells following infection with wild-type meningococci, LPS-deficient meningococci or after treatment with OM isolated from both organisms, demonstrated the involvement of non-LPS bacterial components in cell activation. Significantly, recognition of LPS-replete OM did not depend on host cell expression of Toll-like receptor (TLR)4, the accessory protein MD-2 or CD14, or the recruitment of LPS-accessory surface proteins heat shock protein (HSP)70, HSP90alpha, chemokine receptor CXCR4 and growth differentiation factor (GDF)5. In addition, recognition of LPS-deficient OM was not associated with the expression of TLR2 or any of these other molecules. These data suggest that during meningococcal meningitis innate recognition of both LPS and non-LPS modulins is dependent on the expression of as yet uncharacterized pattern recognition receptors on cells of the meninges. Moreover, the biological consequences of cellular activation by non-LPS modulins suggest that clinical intervention strategies based solely on abrogating the effects of LPS are likely to be only partially effective.

Proteomic analysis of lipid microdomains from lipopolysaccharide-activated human endothelial cells

The endothelium plays a critical role in orchestrating the inflammatory response seen during sepsis. Many of the inflammatory effects of Gram-negative sepsis are elicited by lipopolysaccharide (LPS), a glycolipid component of bacterial cell walls. Lipid-rich microdomains have been shown to concentrate components of the LPS signaling system. However, much remains to be learned about which proteins are constituents of lipid microdomains, and how these are regulated following cell activation. Progress in this area would be accelerated by employing global proteomic analyses, but the hydrophobicity of membrane proteins presents an analytical barrier to the effective application of such approaches. Herein, we describe a method to isolate detergent-resistant membranes from endothelial cells, and prepare these samples for proteomic analysis in a way that is compatible with subsequent separations and mass spectrometric (MS) analysis. In the application of these sample preparation and MS analyses, 358 proteins from the lipid-rich microdomains of LPS-activated endothelial cell membranes have been identified of which half are classified as membrane proteins by Gene Ontology. We also demonstrate that the sample preparation method used for solubilization and trypsin digestion of lipid-rich microdomains renders the membrane spanning sequences of transmembrane proteins accessible for endoproteolytic hydrolysis. This analysis sets the analytical foundation for an in-depth probing of LPS signaling in endothelial cells.

Extracellular hsp70 levels in children with septic shock

OBJECTIVE

To determine whether hsp70 is elevated in the plasma of children with septic shock.

DESIGN

Cohort study.

SETTING

Two academic, tertiary pediatric intensive care units.

PATIENTS

Ninety-four children admitted to the pediatric intensive care unit with septic shock and 24 control children undergoing elective surgical procedures.

INTERVENTIONS

Venous or arterial blood sampling.

MEASUREMENTS AND MAIN RESULTS

Children admitted to the pediatric intensive care unit with a diagnosis of septic shock were enrolled in the study following written informed consent. The control group consisted of healthy children undergoing elective surgical procedures. Blood samples from children in the septic shock or control groups were obtained within 24 hrs of admission to the pediatric intensive care unit or during the preoperative visit. Samples were collected, centrifuged, and stored at -70 degrees C. The hsp70 levels were measured using a commercially available enzyme-linked immunosorbent assay. Results were analyzed by Wilcoxon's rank sum test. Extracellular hsp70 levels in children with septic shock were significantly elevated compared with control patients (51.6 ng/mL vs. 8.1 ng/mL, respectively, p = .0004).

CONCLUSIONS

Extracellular hsp70 levels are significantly elevated in children with septic shock compared with controls. Given the newly described cell signaling properties of hsp70, these data suggest that extracellular hsp70 may play a role in the host response during septic shock.

Lateral diffusion of Toll-like receptors reveals that they are transiently confined within lipid rafts on the plasma membrane

The innate immune system utilises pattern recognition receptors in order to recognise microbial conserved molecular patterns. The family of Toll-like receptors (TLRs) has been shown to act as the main pattern recognition receptors for the innate immune system. Using biochemical as well as fluorescence imaging techniques, TLR2 and TLR4 were found to be recruited within microdomains upon stimulation by bacterial products. Furthermore their lateral diffusion in the cell membrane as determined by fluorescence recovery after photobleaching revealed that upon stimulation by bacterial products TLRs encounter barriers to their lateral movement, thus supporting the notion that specialised domains on the plasma membrane facilitate the innate recognition.

Lipoteichoic Acid and Toll-like Receptor 2 Internalization and Targeting to the Golgi Are Lipid Raft-dependent

Lipoteichoic acid (LTA), a key cell wall component of Gram-positive bacteria, seems to function as an immune activator with characteristics very similar to lipopolysaccharide from Gram-negative bacteria. It has been shown that LTA binds CD14 and triggers activation via Toll-like receptor 2, but whether the activation occurs at the cell surface or internalization is required to trigger signaling has yet to be demonstrated. In this work we have investigated LTA binding and internalization and found that LTA and its receptor molecules accumulate in lipid rafts and are subsequently targeted rapidly to the Golgi apparatus. This internalization seems to be lipid raft-dependent because raft-disrupting drugs inhibited LTA/Toll-like receptor 2 colocalization in the Golgi. Similarly to lipopolysaccharide, LTA activation occurs at the cell surface, and the observed trafficking is independent of signaling.

Hsp90 invades the outside

Metalloproteases are required for the invasive nature of cancer cells. Surprisingly, the cytosolic molecular chaperone Hsp90 is now shown to promote maturation of the extracellular metalloprotease MMP2. This finding extends the multiplicity of roles assigned to the Hsp90 family to a new function outside the cell.