Cell surface expression of heat shock proteins in dog neutrophils induced by mitochondrial benzodiazepine receptor ligands

Human HSP70-escort protein 1 (hHep1) interacts with negatively charged lipid bilayers and cell membranes

Human Hsp70-escort protein 1 (hHep1) is a cochaperone that assists in the function and stability of mitochondrial HSPA9. Similar to HSPA9, hHep1 is located outside the mitochondria and can interact with liposomes. In this study, we further investigated the structural and thermodynamic behavior of interactions between hHep1 and negatively charged liposomes, as well as interactions with cellular membranes. Our results showed that hHep1 interacts peripherally with liposomes formed by phosphatidylserine and cardiolipin and remains partially structured, exhibiting similar affinities for both. In addition, after being added to the cell membrane, recombinant hHep1 was incorporated by cells in a dose-dependent manner. Interestingly, the association of HSPA9 with hHep1 improved the incorporation of these proteins into the lipid bilayer. These results demonstrated that hHep1 can interact with lipids also present in the plasma membrane, indicating roles for this cochaperone outside of mitochondria.

Cell-surface Expression of Heat Shock proteins in Dog Neutrophils after Oxidative Stress

The effect of oxidative stress induced by different concentrations of hydrogen peroxide on dog neutrophils was studied. This effect was measured using dichlorofluorescein-diacetate (DCFH-DA) and by the cell surface membrane expression of heat shock protein (HSP) 27kDa, HSP 72kDa and HSP 90kDa families. Hydrogen peroxide induced a concentration-dependent increase in DCFH oxidation (from 10(-6)mto 10(-4)m), and an increase in the cell surface expression of HSPs families. At a concentration of 10(-4)m, the percentage of positive cells that showed an oxidation of DCFH was 94.7%+/-5.2 (n=3). Only vitamin E (but not vitamin C) at a concentration of 0.5mm was able to inhibit the intracellular oxidative stress induced by hydrogen peroxide. The percentage of positive cells that express these proteins after the treatment with hydrogen peroxide (10(-4)m) was: 74%+/-3.5 for HSP 27, 72%+/-2.6 for HSP 72 and 73%+/-1.2 for HSP 90 (n=3). This cell surface expression was not abolished by either vitamin C or vitamin E. Localization of HSPs in plasma membrane is of immunological interest because they have been implicated in autoimmune diseases.

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.

Small heat shock proteins associated with cerebral amyloid angiopathy of hereditary cerebral hemorrhage with amyloidosis (Dutch type) induce interleukin-6 secretion

In hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D), severe cerebral amyloid angiopathy (CAA) is associated with an inflammatory reaction. Small heat shock proteins (sHsps) are molecular chaperones and association of HspB8 with CAA in HCHWA-D has been observed. The aims of this study were to investigate (1) if other sHsps are associated with the pathological lesions in HCHWA-D brains, (2) if the amyloid-beta protein (A beta) increases production of sHsps in cultured cerebral cells and (3) if sHsps are involved in the cerebral inflammatory processes in both Alzheimer's disease (AD) and HCHWA-D. We conclude that Hsp20, HspB8 and HspB2 are present in CAA in HCHWA-D, and that A beta did not affect cellular sHsps expression in cultured human brain pericytes and astrocytes. In addition, we demonstrated that Hsp20, HspB2 and HspB8 induced interleukin-6 production in cultured pericytes and astrocytes, which could be antagonized by dexamethasone, whereas other sHsps and A beta were inactive, suggesting that sHsps may be among the key mediators of the local inflammatory response associated with HCHWA-D and AD lesions.

Small heat shock proteins inhibit amyloid-beta protein aggregation and cerebrovascular amyloid-beta protein toxicity

Small heat shock proteins Hsp20 and HspB2/B3 co-localize with Abeta deposition in senile plaques and cerebral amyloid angiopathy in Alzheimer's disease brains, respectively. It was the aim of our study to investigate if these and other sHsps bind to wild-type Abeta1-42 or the more toxic Abeta1-40 carrying the 'Dutch' mutation (22Glu-->Gln) (D-Abeta1-40), affect Abeta aggregation and thereby influence Abeta cytotoxicity. Binding affinity between sHsps and Abeta was investigated by surface plasmon resonance. Abeta aggregation was studied by using circular dichroism spectroscopy and electron microscopy. Furthermore, we used cultured cerebrovascular cells to investigate the effects of sHsps on Abeta-mediated cytotoxicity. Hsp20, Hsp27 and alphaB-crystallin, but not HspB2/B3, bound to Abeta (both D-Abeta1-40 and Abeta1-42) and reduced or completely inhibited aggregation of D-Abeta1-40 into mature fibrils but did not affect Abeta1-42 aggregation. Furthermore, these sHsps were effective inhibitors of the cerebrovascular toxicity of Abeta (both D-Abeta1-40 and Abeta1-42) in vitro. Binding affinity of the sHsps to D-Abeta1-40 correlated to the degree of inhibition of Abeta-mediated cytotoxicity and the potential to reduce Abeta beta-sheet and fibril formation. With Abeta1-42, a similar correlation between binding affinity and cytotoxicity was observed, but not with its aggregation state. In conclusion, sHsps may regulate Abeta aggregation and serve as antagonists of the biological action of Abeta, but the extent of their interaction depends on the type of sHsp and Abeta peptide.

Small heat shock protein HspB8: its distribution in Alzheimer's disease brains and its inhibition of amyloid-beta protein aggregation and cerebrovascular amyloid-beta toxicity

Alzheimer's disease (AD) is characterized by pathological lesions, such as senile plaques (SPs) and cerebral amyloid angiopathy (CAA), both predominantly consisting of a proteolytic cleavage product of the amyloid-beta precursor protein (APP), the amyloid-beta peptide (Abeta). CAA is also the major pathological lesion in hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D), caused by a mutation in the gene coding for the Abeta peptide. Several members of the small heat shock protein (sHsp) family, such as alphaB-crystallin, Hsp27, Hsp20 and HspB2, are associated with the pathological lesions of AD, and the direct interaction between sHsps and Abeta has been demonstrated in vitro. HspB8, also named Hsp22 of H11, is a recently discovered member of the sHsp family, which has chaperone activity and is observed in neuronal tissue. Furthermore, HspB8 affects protein aggregation, which has been shown by its ability to prevent formation of mutant huntingtin aggregates. The aim of this study was to investigate whether HspB8 is associated with the pathological lesions of AD and HCHWA-D and whether there are effects of HspB8 on Abeta aggregation and Abeta-mediated cytotoxicity. We observed the expression of HspB8 in classic SPs in AD brains. In addition, HspB8 was found in CAA in HCHWA-D brains, but not in AD brains. Direct interaction of HspB8 with Abeta(1-42), Abeta(1-40) and Abeta(1-40) with the Dutch mutation was demonstrated by surface plasmon resonance. Furthermore, co-incubation of HspB8 with D-Abeta(1-40) resulted in the complete inhibition of D-Abeta(1-40)-mediated death of cerebrovascular cells, likely mediated by a reduction in both the beta-sheet formation of D-Abeta(1-40) and its accumulation at the cell surface. In contrast, however, with Abeta(1-42), HspB8 neither affected beta-sheet formation nor Abeta-mediated cell death. We conclude that HspB8 might play an important role in regulating Abeta aggregation and, therefore, the development of classic SPs in AD and CAA in HCHWA-D.

Peripheral benzodiazepine receptor and its clinical targeting

Tumor cell targeted therapies, by induction or enhancement of apoptosis, constitute recent promising approaches achieving more specific anti-tumor efficacy. The peripheral benzodiazepine receptor (PBR), which belongs to the permeability transition pore (PTP), the central regulatory complex of apoptosis, is a potential target. A number of findings argue in favor of the development of PBR targeting approaches: (i) overexpression of PBR has been described in a large range of human cancers, (ii) PTP-mediated regulation of programmed cell death is an apoptotic-inducing factor-independent check-point that could be modulated by various conventional cancer therapies, and (iii) PBR ligation enhances apoptosis induction in many types of tumors and reverses Bcl-2 cytoprotective effects. Altogether, these observations support the use of PBR-directed drugs, particularly PBR ligands such as Ro5-4864, in the treatment of human cancers.

Material-dependent levels of heat-shock protein 70 (hsp70) in human plasma following contact of blood with artificial surfaces

Recently, it has been shown that heat-shock protein 70 (hsp70) functions in a dual role as a chaperone and a cytokine. However, no information is available on the occurrence of hsp70 in the extracellular milieu or on its ability to modulate cellular immune response. This study shows a material-dependent increase of hsp70 levels in plasma following contact of fresh heparinized whole human blood with three different biomaterials (PVC, heparin-coated PVC, Silicone). We report a previously unknown behavior of hsp70 to act as a plasma-adsorption protein. Further, high binding capacities for hsp70 to artificial surfaces (measured by Western blotting) and elevated hsp70 levels in plasma (measured by EIA) following contact with blood correspond with a reduced hemocompatibility. The degree of surface-induced activation of blood was determined by analysis of markers for coagulation, inflammation and complement activation. These findings indicate that the selective adsorption of hsp70 on artificial surfaces and the increased hsp70 levels in plasma may be important in directing host inflammatory and immune responses. We suggest that the levels of hsp70 in human plasma may represent a new prognostic factor or a diagnostic biomarker in hemostasis research.

Involvement of p38 mitogen-activated protein kinase in heat shock protein 27 induction in human neutrophils

We investigated whether tumor necrosis factor-alpha (TNF-alpha) stimulates the induction of heat shock protein 27 (HSP27) in human neutrophils and the mechanism underlying this induction. In intact neutrophils, almost no HSP27 was detected. Stimulation of neutrophils by TNF-alpha increased the levels of HSP27 in the presence, but not in the absence, of cycloheximide. Reverse transcription-polymerase chain reaction (RT-PCR) experiments showed that TNF-alpha also induced HSP27 mRNA in the presence of cycloheximide. TNF-alpha induced the phosphorylation of p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase. The HSP27 accumulation induced by TNF-alpha was significantly suppressed by 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole (SB203580) or 4-(4-fluorophenyl)-2-(4-nitrophenyl)-5-(4-pyridyl)-1H-imidazole (PD169316); both are specific inhibitors of p38 MAP kinase, but not by 2'-amino-3'-methoxyflavone (PD098059, a specific inhibitor of the upstream kinase that activates p44/p42 MAP kinase). The accumulation of HSP27 induced by TNF-alpha plus cycloheximide was also suppressed by pretreatment with a specific protein kinase C (PKC) inhibitor. Furthermore, phorbol myristate acetate (PMA), a PKC stimulant, but not dibutyryl cyclic AMP, a protein kinase A stimulant, stimulated the accumulation of HSP27. Interestingly, SB203580 did not inhibit PMA-stimulated HSP27 induction. These results strongly suggest that TNF-alpha may act as the regulator of HSP27 induction in neutrophils. p38 MAP kinase (but not p44/p42 MAP kinase) and PKC take part in TNF-alpha-stimulated HSP27 induction in human neutrophils.

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

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

Contribution of heat shock proteins to cell protection from complement-mediated lysis

The possible participation of hsc70 and hsp70 in cellular protection from complement damage was studied. Human erythroleukemia K562 cells were pretreated with reagents affecting hsc70 or hsp70, and cell sensitivity to lysis by antibody and human complement was examined. Treatment with deoxyspergualin, an hsc70 inhibitor, sensitized K562 cells to complement lysis, whereas treatment with ethanol, butanol or hemin, inducers of hsc70 synthesis, protected the cells from complement-mediated lysis. Incubation of K562 at either 42 degrees C or with the amino acid analogue L-azetidine-2-carboxylic acid induced synthesis of hsp70, but not of hsc70. The latter treatment also conferred elevated resistance to complement lysis on K562 cells. Pretreatment of K562 cells with sub-lethal doses of complement desensitizes them to lethal complement doses. No effect of sublytic complement on synthesis of hsc70 and hsp70 was found. However, the results demonstrated that complement stress causes translocation of hsc70 from the cytoplasm to the K562 cell surface. Two monoclonal and two polyclonal antibodies identified hsc70 on the surface of intact, viable complement-stressed cells, while antibodies directed to hsp70 did not bind to these cells. Altogether, the results suggest that the heat shock proteins hsc70 and hsp70 play a role in cell defense against complement.

Bcl-2 resistant mitochondrial toxicity mediated by the isoquinoline carboxamide PK11195 involves de novo generation of reactive oxygen species

Resistance to apoptosis is a major obstacle preventing effective therapy for malignancy. Mitochondria localized anti-death proteins of the Bcl-2 family play a central role in inhibiting apoptosis and therefore present valid targets for novel therapy. The peripheral benzodiazepine receptor (PBR) shares a close physical association with the permeability transition pore complex (PTPC), a pivotal regulator of cell death located at mitochondrial contact sites. In this study we investigated the cytotoxicity of the PBR ligand, PK11195, in the micromolar concentration range. PK11195 induced antioxidant inhibitable collapse of the inner mitochondrial membrane potential (DeltaPsi(m)) and mitochondrial swelling in HL60 human leukaemia cells, but not in SUDHL4 lymphoma cells (which exhibited a higher level of reduced glutathione and relative tolerance to chemotherapy or pro-oxidant induced DeltaPsi(m)dissipation). PK11195 induced the production of hydrogen peroxide that was not inhibited by Bcl-2 transfection, nor depletion of mitochondrial DNA. ROS production was however blocked by protonophore, implicating a requirement for DeltaPsi(m). Our findings suggest that PK11195-induced cytotoxicity relies upon Bcl-2 resistant generation of oxidative stress; a process only observed at concentrations several orders of magnitude higher that required to saturate its receptor.

The molecular chaperone alphaB-crystallin enhances amyloid beta neurotoxicity

Amyloid beta (Abeta) is a 40- to 42-residue peptide that is implicated in the pathogenesis of Alzheimer's Disease (AD). As a result of conformational changes, Abeta assembles into neurotoxic fibrils deposited as 'plaques' in the diseased brain. In AD brains, the small heat shock proteins (sHsps) alphaB-crystallin and Hsp27 occur at increased levels and colocalize with these plaques. In vitro, sHsps act as molecular chaperones that recognize unfolding peptides and prevent their aggregation. The presence of sHsps in AD brains may thus reflect an attempt to prevent amyloid fibril formation and toxicity. Here we report that alphaB-crystallin does indeed prevent in vitro fibril formation of Abeta(1-40). However, rather than protecting cultured neurons against Abeta(1-40) toxicity, alphaB-crystallin actually increases the toxic effect. This indicates that the interaction of alphaB-crystallin with conformationally altering Abeta(1-40) may keep the latter in a nonfibrillar, yet highly toxic form.

Peripheral-type benzodiazepine receptors in diagnostic subtypes of schizophrenic patients

The peripheral-type benzodiazepine receptor (pBZD-R; also called the omega-3 receptor or the mitochondrial benzodiazepine receptor) seems to play a critical role in the production of neurosteroids, which are able to alter the electrical properties of neuronal membranes and thus the firing patterns of neurons. Putative endogenous ligands are the diazepam-binding inhibitor and its processing products, as well as porphyrins, some of them, in the case of porphyria, are well known to give rise to certain aspects of neuropsychiatric disorders, such as schizophrenic-like symptoms. Previous findings of altered benzodiazepine binding sites in post-mortem brain samples and platelets from small samples of schizophrenic patients have been inconclusive. Therefore we investigated characteristic binding parameters (Bmax, Kd) of the granulocytic pBZD-R by using the selective ligand PK11.195 in 53 subjects, fulfilling ICD-10 and DSM-IV criteria of schizophrenia. The binding parameters in our total group of 53 schizophrenic patients did not differ from those in healthy subjects. However, Bmax values were significantly reduced in schizophrenic patients with predominantly negative symptoms (residual type) compared to schizophrenic patients with predominantly positive symptoms, i.e. paranoid (-50%) and catatonic subtype (-38%). Moreover, only residual type schizophrenics exhibited a significantly reduced binding capacity compared to healthy subjects (-38%). More studies are warranted to clarify the functional significance of this binding site in the pathogenesis of negative symptoms.

Determination of nitric oxide generation in mammalian neurons using dichlorofluorescin diacetate and flow cytometry

A method for the rapid detection of intracellular nitric oxide (NO) generation in dissociated cerebellar granule cells using dichlorofluorescin (DCFH) and flow cytometry was developed. DCFH can be oxidized specifically by NO and this was assessed by 1) the use of SIN-1 (10 nM-100 microM), an NO donor, that induced a concentration-dependent increase in dichlorofluorescein (DCF) fluorescence and 2) the use of hemoglobin (10 microM), an NO-scavenger, that totally inhibited the increase of fluorescence induced by SIN-1 (10 microM). This assay was used to determine the ability to kainate to stimulate NO production in dissociated cerebellar granule cells. Kainate (1 microM-10 mM) induced an increase in DCF fluorescence that was partially reduced by NG-nitro-L-arginine (1 nM-10 microM), a nitric oxide synthase inhibitor (61.9% +/- 9.1), or hemoglobin (10 microM) (55.0% +/- 4.1). The method described allows evaluation of the oxidation of DCFH to produce DCF as a parameter for measuring intracellular NO generation. The extent of DCFH oxidation by NO and ROS can be determined by using NO scavengers or NO synthase inhibitors.