hsp 70-like protein in rhesus erythrocyte cytosol and its interactions with membrane skeleton under heat and pathologic stress

Role of Heat Shock Proteins in Immune Modulation in Malaria

Malaria is one of the major parasitic killer diseases worldwide. Severe cases of malaria are mostly in children under the age of 5 years due to their naïve immune system and in pregnant women with weakened immune responses. Inflammatory immune responses against the parasite involve complement activation as well as the antibody and effector cell-mediated immune system. However, after an infection with Plasmodium falciparum (P. falciparum), the most dangerous malaria species, the host-derived immunity is often insufficient to completely inhibit the infection cycles of the parasite in red blood cells for yet unknown reasons. In the present chapter we aim to elucidate the role of the host's and the parasite's heat shock proteins (HSPs) in the development of a novel anti-malaria therapeutic approach.

Identification of human erythrocyte cytosolic proteins associated with plasma membrane during thermal stress

The influence of thermal stress on the association between human erythrocyte membranes and cytosolic proteins was studied by exposing erythrocyte suspensions and whole blood to different elevated temperatures. Membranes and cytosolic proteins from unheated and heat-stressed erythrocytes were analyzed by electrophoresis, followed by mass spectrometric identification. Four major (carbonic anhydrase I, carbonic anhydrase II, peroxiredoxin VI, flavin reductase) and some minor (heat shock protein 90α, heat shock protein 70, α-enolase, peptidylprolyl cis-trans isomerase A) cytosolic proteins were found to be associated with the erythrocyte membrane in response to in vitro thermal stress. Unlike the above proteins, catalase and peroxiredoxin II were associated with membranes from unheated erythrocytes, and their content increased in the membrane following heat stress. The heat-induced association of cytosolic proteins was restricted to the Triton shells (membrane skeleton/cytoskeleton). Similar results were observed when Triton shells derived from unheated erythrocyte membranes were incubated with an unheated erythrocyte cytosolic fraction at elevated temperatures. This is a first report on the association of cytosolic catalase, α-enolase, peroxiredoxin VI, peroxiredoxin II and peptidylprolyl cis-trans isomerase A to the membrane or membrane skeleton of erythrocytes under heat stress. From these results, it is concluded that specific cytosolic proteins are translocated to the membrane in human erythrocytes exposed to heat stress and they may play a novel role as erythrocyte membrane protectors under stress by stabilizing the membrane skeleton through their interactions with skeletal proteins.

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.

Red blood cell aging markers during storage in citrate-phosphate-dextrose-saline-adenine-glucose-mannitol

BACKGROUND

It has been suggested that red blood cell (RBC) senescence is accelerated under blood bank conditions, although neither protein profile of RBC aging nor the impact of additive solutions on it have been studied in detail.

STUDY DESIGN AND METHODS

RBCs and vesicles derived from RBCs in both citrate-phosphate-dextrose (CPD)-saline-adenine-glucose-mannitol (SAGM) and citrate-phosphate-dextrose-adenine (CPDA) were evaluated for the expression of cell senescence markers (vesiculation, protein aggregation, degradation, activation, oxidation, and topology) through immunoblotting technique and immunofluorescence or immunoelectron microscopy study.

RESULTS

A group of cellular stress proteins exhibited storage time- and storage medium-related changes in their membrane association and exocytosis. The extent, the rate, and the expression of protein oxidation, Fas oligomerization, caspase activation, and protein modifications in Band 3, hemoglobin, and immunoglobulin G were less conspicuous and/or exhibited significant time retardation under storage in CPD-SAGM, compared to the CPDA storage. There was evidence for the localization of activated caspases near to the membrane of both cells and vesicles.

CONCLUSIONS

We provide circumstantial evidence for a lower protein oxidative damage in CPD-SAGM-stored RBCs compared to the CPDA-stored cells. The different expression patterns of the senescence markers in the RBCs seem to be accordingly related to the oxidative stress management of the cells. We suggest that the storage of RBCs in CPD-SAGM might be more alike the in vivo RBC aging process, compared to storage in CPDA, since it is characterized by a slower stimulation of the recognition signaling pathways that are already known to trigger the erythrophagocytosis of senescent RBCs.

T-complex polypeptide-1 interacts with the erythrocyte cytoskeleton in response to elevated temperatures

Chaperonins are double ring complexes composed of highly conserved 60-kDa protein subunits that are divided into two subgroups. Group II chaperonins are found in archaea and the cytoplasm of eukarya and are believed to function like other chaperonins as part of a protein folding system. We report here that human erythrocytes contain the group II chaperonin T-complex polypeptide 1 (TCP-1) and that this complex translocates from the cytoplasm to the cytoskeleton in response to heat treatment in the absence of overt cell damage. Identification as TCP-1 was determined by immunodetection for TCP-1alpha and corroborated by mass spectroscopy peptide sequencing. Direct visualization by immunofluorescence confirmed peripherally localized TCP-1 in response to heat treatment. Temperatures ranging from 37-50 degrees C were demonstrated to have distinct kinetic profiles of induced translocation. Heat-induced binding was shown by Triton shell analysis to be specifically associated with the cytoskeletal proteins. Furthermore, the binding was reversible following removal of the stimulatory condition. A stabilizing process is hypothesized based on the known interactions of chaperonins.

Host chaperones are recruited in membrane-bound complexes by Plasmodium falciparum

The ability of malarial parasite to deploy proteins at the surface of infected erythrocytes is well known. After their synthesis within the parasite, the cargo proteins are exported from the parasite and carried across the erythrocyte cytoplasm to be delivered at the erythrocyte surface. Our knowledge about the mechanisms involved in this complex trafficking path is limited. We have addressed the involvement of chaperones in traffic across erythrocyte cytoplasm. Our analyses of the chaperones available to the parasite indicated that none of the reported chaperones of the parasite origin are present in the erythrocyte cytoplasm. The chaperones of the host (Hsp70, Hsp90, Hop60), on the other hand, were readily detected in the erythrocyte cytosol. Hypotonic lysis and detergent solubilization experiments indicated that unlike their soluble nature in normal erythrocytes, host chaperones are recruited in membrane-bound, detergent-resistant complexes in infected cells. The association of host-Hsp70 with detergent-resistant complexes was ATP-dependent. Importantly, host chaperones could be detected in knob-enriched fractions and could be cross-linked to the knob subunit, PfHRP1, in a large complex at the surface of the infected erythrocytes. Our results implicate host chaperones in the assembly of parasite proteins such as knob subunits at the erythrocyte surface.

Oxysterols from oxidized LDL are cytotoxic but fail to induce hsp70 expression in endothelial cells

Oxidized low density lipoprotein (OxLDL) possesses several proatherogenic characteristics, among which a marked cytotoxicity. In vitro, cytotoxicity of OxLDL to endothelial cells is associated with an increase in the expression of the inducible form of heat shock protein 70 (hsp70), generally regarded as a cytoprotective protein. Oxidized derivatives of cholesterol which form upon LDL oxidation are cytotoxic. Moreover, most of the OxLDL cytotoxicity is due to its lipid moiety, in particular to oxysterols. In this report we demonstrate that although oxysterols identified in OxLDL are cytotoxic, they cannot trigger the increase in hsp70 expression observed with intact oxidized lipoproteins. We speculate therefore that oxysterols may represent the most toxic form of oxidized lipids in LDL because they cannot activate a rescue mechanism (i.e. the hsp response) and may contribute significantly to cell death within atherosclerotic plaques.

Constitutive hsp70 attenuates hydrogen peroxide-induced membrane lipid peroxidation

Thermal pretreatment improves cardiac recovery from subsequent ischemia/reperfusion. Induction of heat shock proteins (hsps) may contribute to this protection. We have demonstrated that augmentation of the constitutive hsp70 (hsc70) in H9c2 heart myoblasts promotes oxidative resistance. We employed a model oxidant to explore potential target(s) of protection by hsc70. Upon exposure to 54 microM of hydrogen peroxide (H(2)O(2)), hsc70-overexpressing cells exhibited a lower lipid peroxidation than the sham-transfected control. Constitutive hsc70 overexpression, however, did not protect against H(2)O(2)-induced depletion of ATP and glutathione (GSH). Lipid protection also occurred in cells preconditioned at 39 degrees C (selectively induces hsc70) during H(2)O(2) exposure. Interestingly, the protection conferred by hsc70 was comparable in magnitude to that provided by alpha-tocopherol, and was followed with a reduced release of lactate dehydrogenase and a unaltered calcium uptake during H(2)O(2) challenge. Collectively, our observations suggest that hsc70 may preserve membrane function via attenuation of lipid peroxidation during oxidative insult.

Isolation, molecular characterization, and tissue-specific expression of ECP-51 and ECP-54 (TIP49), two homologous, interacting erythroid cytosolic proteins

We isolated two proteins, ECP-51 and ECP-54, from human erythrocyte cytosol by affinity chromatography using a peptide of the integral membrane protein stomatin as bait. Partial amino acid sequence information obtained by microsequencing allowed us to clone the respective cDNAs. Analysis of the nucleotide sequences revealed that ECP-51 and ECP-54 are homologous (44.2% amino acid identity) and contain ATP-binding sites. ECP-54 was identified as TIP49/RUVBL1/NMP238, which is a component of a large nuclear protein complex, possibly the RNA polymerase II holoenzyme; ECP-51 is a novel protein. Using the two-hybrid system, we showed that these proteins interact with each other. The interaction of ECP-51 and ECP-54 with the stomatin peptide and the localization to the nucleus and cytoplasm suggest an additional function for these proteins as chaperone components.

Response of Leishmania chagasi promastigotes to oxidant stress

At the onset of infection, Leishmania promastigotes are phagocytized by mammalian macrophages. They must survive despite exposure to toxic oxidants such as hydrogen peroxide (H2O2) and superoxide (.O2-) generated during phagocytosis. We investigated the effects of these oxidants on Leishmania chagasi promastigotes and promastigote mechanisms for oxidant resistance. According to spin trapping and electron paramagnetic resonance spectrometry, .O2- could be generated by exposure of promastigotes to the redox-cycling compound menadione. Incubation in either menadione or H2O2 caused a concentration-dependent loss of promastigote viability. However, incubation in sublethal concentrations of H2O2 or menadione caused a stress response in promastigotes. This oxidant-induced response was associated with an increase in the amount of heat shock protein hsp70. Induction of a stress response by exposure of promastigotes either to heat shock or to sublethal oxidants (H2O2 or menadione) caused promastigotes to become more resistant to H2O2 toxicity. Sublethal menadione also caused promastigotes to become more virulent in a BALB/c mouse model of leishmaniasis. We previously correlated H2O2 cytotoxicity for promastigotes with the formation of hydroxyl radical (.OH) from H2O2. However, according to electron paramagnetic resonance spectrometry, the increase in H2O2 resistance after exposure to sublethal oxidants was not associated with diminished generation (i.e., scavenging) of .OH. These data suggest that there is a cross-protective stress response that occurs after exposure of L. chagasi promastigotes to heat shock or to sublethal H2O2 or .O2-, exposures that also occur during natural infection. This response results in increased resistance to H2O2 toxicity and increased virulence for a mammalian host.