Heat-shock proteins

The dimeric structure of the Cpn60.2 chaperonin of Mycobacterium tuberculosis at 2.8 Å reveals possible modes of function

Mycobacterium tuberculosis expresses two proteins (Cpn60.1 and Cpn60.2) that belong to the chaperonin (Cpn) family of heat shock proteins. Studies have shown that the two proteins have different functional roles in the bacterial life cycle and that Cpn60.2 is essential for cell viability and may be involved in M. tuberculosis pathogenicity. Cpn60.2 does not form a tetradecameric double ring, which is typical of other Cpns. We have determined the crystal structure of recombinant Cpn60.2 to 2.8 Å resolution by molecular replacement; the asymmetric unit (AU) contains a dimer, which is consistent with size-exclusion high-performance liquid chromatography and dynamic light-scattering measurements of the soluble recombinant protein. However, we suggest that the actual Cpn60.2 dimer may be different from that identified within the AU on the basis of surface contact stability, solvation free-energy gain, and functional aspects. Unlike the dimer found in the AU, which is formed through apical domain interactions, the dimeric form we propose here provides a free apical domain that is required for normal chaperone activity and may be involved in M. tuberculosis association with macrophages and arthrosclerosis plaque formation. Here we describe in detail the structural aspects that lead to Cpn60.2 dimer formation and prevent the formation of heptameric rings and tetradecameric double rings.

HSP70 decreases receptor-dependent phosphorylation of Smad2 and blocks TGF-β-induced epithelial-mesenchymal transition

Smad2 and Smad3, the intracellular mediators of transforming growth factor β (TGF-β) signaling, are directly phosphorylated by the activated type I receptor kinase, and then shuttle from the cytoplasm into the nucleus to regulate target gene expression. Here, we report that the 70-kDa heat-shock protein (HSP70) interacts with Smad2 and decreases TGF-β signal transduction. Ectopic expression of HSP70 prevents receptor-dependent phosphorylation and nuclear translocation of Smad2, and blocks TGF-β-induced epithelial-mesenchymal transition (EMT) in HaCat cells. Our findings reveal an essential role of HSP70 in TGF-β-induced epithelial-mesenchymal transition (EMT) by impeding Smad2 phosphorylation.

Effect of cigarette smoke and dexamethasone on Hsp72 system of alveolar epithelial cells

Smoking is the leading risk factor of chronic obstructive pulmonary disease (COPD) and lung cancer. Corticosteroids are abundantly used in these patients; however, the interaction of smoking and steroid treatment is not fully understood. Heat shock proteins (Hsps) play a central role in the maintenance of cell integrity, apoptosis and cellular steroid action. To better understand cigarette smoke-steroid interaction, we examined the effect of cigarette smoke extract (CSE) and/or dexamethasone (DEX) on changes of intracellular heat shock protein-72 (Hsp72) in lung cells. Alveolar epithelial cells (A549) were exposed to increasing doses (0; 0.1; 1; and 10 μM/μl) of DEX in the medium in the absence(C) and presence of CSE. Apoptosis, necrosis, Hsp72 messenger-ribonucleic acid (mRNA) and protein expression of cells were measured, and the role of Hsp72 on steroid effect examined. CSE reduced the number of viable cells by significantly increasing the number of apoptotic and necrotic cells. DEX dose-dependently decreased the ratio of apoptosis when CSE was administered, without change in necrosis. CSE - DEX co-treatment dose-dependently increased Hsp72 mRNA and protein expression, with the highest level measured in CSE + DEX (10) cells, while significantly lower levels were noted in all respective C groups. Pretreatment with Hsp72 silencing RNA confirmed that increased survival observed following DEX administration in CSE-treated cells was mainly mediated via the Hsp72 system. CSE significantly decreases cell survival by inducing apoptosis and necrosis. DEX significantly increases Hsp72 mRNA and protein expression only in the presence of CSE resulting in increased cellular protection and survival. DEX exerts its cell protective effects by decreasing apoptotic cell death via the Hsp72 system in CSE-treated alveolar epithelial cells.

Validation of housekeeping genes for gene expression studies in Symbiodinium exposed to thermal and light stress

Unicellular photosynthetic algae (dinoflagellate) from the genus Symbiodinium live in mutualistic symbiosis with reef-building corals. Cultured Symbiodinium sp. (clade C) were exposed to a range of environmental stresses that included elevated temperatures (29°C and 32°C) under high (100 μmol quanta m(-2) s(-1) Photosynthetic Active Radiation) and low (10 μmol quanta m(-2) s(-1)) irradiances. Using real-time RT-PCR the stability of expression for the nine selected putative housekeeping genes (HKGs) was tested. The most stable expression pattern was identified for cyclophilin and S-adenosyl methionine synthetase (SAM) followed by S4 ribosomal protein (Rp-S4), Calmodulin (Cal), and Cytochrome oxidase subunit 1 (Cox), respectively. Thermal stress alone resulted in the highest expression stability for Rp-S4 and SAM, with a minimum of two reference genes required for data normalization. For Symbiodinium exposed to both, light and thermal stresses, at least five reference genes were recommended by geNorm analysis. In parallel, the expression of Hsp90 for Symbiodinium in culture and in symbiosis within coral host (Acropora millepora) was evaluated using the most stable HKGs. Our results revealed a drop in Hsp90 expression after an 18 h-period and a 24 h-period of exposure to elevated temperatures indicating the similar Hsp90 expression profile in symbiotic and non-symbiotic environments. This study provides the first list of the HKGs and will provide a useful reference in future gene expression studies in symbiotic dinoflagellates.

Presence of tissue transglutaminase in granular endoplasmic reticulum is characteristic of melanized neurons in Parkinson's disease brain

Parkinson's disease (PD) is characterized by the accumulation of α-synuclein aggregates and degeneration of melanized neurons. The tissue transglutaminase (tTG) enzyme catalyzes molecular protein cross-linking. In PD brain, tTG-induced cross-links have been identified in α-synuclein monomers, oligomers and α-synuclein aggregates. However, whether tTG and α-synuclein occur together in PD affected neurons remains to be established. Interestingly, using immunohistochemistry, we observed a granular distribution pattern of tTG, characteristic of melanized neurons in PD brain. Apart from tTG, these granules were also positive for typical endoplasmic reticulum (ER)-resident chaperones, that is, protein disulphide isomerase, ERp57 and calreticulin, suggesting a direct link to the ER. Additionally, we observed the presence of phosphorylated pancreatic ER kinase (pPERK), a classical ER stress marker, in tTG granule positive neurons in PD brain, although no subcellular colocalization of tTG and pPERK was found. Our data therefore suggest that tTG localization to granular ER compartments is specific for stressed melanized neurons in PD brain. Moreover, as also α-synuclein aggregates were observed in tTG granule positive neurons, these results provide a clue to the cellular site of interaction between α-synuclein and tTG.

Histoplasma capsulatum heat-shock 60 orchestrates the adaptation of the fungus to temperature stress

Heat shock proteins (Hsps) are among the most widely distributed and evolutionary conserved proteins. Hsps are essential regulators of diverse constitutive metabolic processes and are markedly upregulated during stress. A 62 kDa Hsp (Hsp60) of Histoplasma capsulatum (Hc) is an immunodominant antigen and the major surface ligand to CR3 receptors on macrophages. However little is known about the function of this protein within the fungus. We characterized Hc Hsp60-protein interactions under different temperature to gain insights of its additional functions oncell wall dynamism, heat stress and pathogenesis. We conducted co-immunoprecipitations with antibodies to Hc Hsp60 using cytoplasmic and cell wall extracts. Interacting proteins were identified by shotgun proteomics. For the cell wall, 84 common interactions were identified among the 3 growth conditions, including proteins involved in heat-shock response, sugar and amino acid/protein metabolism and cell signaling. Unique interactions were found at each temperature [30°C (81 proteins), 37°C (14) and 37/40°C (47)]. There were fewer unique interactions in cytoplasm [30°C (6), 37°C (25) and 37/40°C (39)] and four common interactions, including additional Hsps and other known virulence factors. These results show the complexity of Hsp60 function and provide insights into Hc biology, which may lead to new avenues for the management of histoplasmosis.

Gene expression profiles of cytosolic heat shock proteins Hsp70 and Hsp90 from symbiotic dinoflagellates in response to thermal stress: possible implications for coral bleaching

Unicellular photosynthetic dinoflagellates of the genus Symbiodinium are the most common endosymbionts of reef-building scleractinian corals, living in a symbiotic partnership known to be highly susceptible to environmental changes such as hyperthermic stress. In this study, we identified members of two major heat shock proteins (HSPs) families, Hsp70 and Hsp90, in Symbiodinium sp. (clade C) with full-length sequences that showed the highest similarity and evolutionary relationship with other known HSPs from dinoflagellate protists. Regulation of HSPs gene expression was examined in samples of the scleractinian coral Acropora millepora subjected to elevated temperatures progressively over 18 h (fast) and 120 h (gradual thermal stress). Moderate to severe heat stress at 26°C and 29°C (+3°C and +6°C above average sea temperature) resulted in an increase in algal Hsp70 gene expression from 39% to 57%, while extreme heat stress (+9°C) reduced Hsp70 transcript abundance by 60% (after 18 h) and 70% (after 120 h). Elevated temperatures decreased an Hsp90 expression under both rapid and gradual heat stress scenarios. Comparable Hsp70 and Hsp90 gene expression patterns were observed in Symbiodinium cultures and in hospite, indicating their independent regulation from the host. Differential gene expression profiles observed for Hsp70 and Hsp90 suggests diverse roles of these molecular chaperones during heat stress response. Reduced expression of the Hsp90 gene under heat stress can indicate a reduced role in inhibiting the heat shock transcription factor which may lead to activation of heat-inducible genes and heat acclimation.

Beneficial effects of mild stress (hormetic effects): dietary restriction and health

Hormesis is defined as a dose-response phenomenon characterized by low-dose stimulation and high-dose inhibition, and has been recognized as representing an overcompensation for mild environmental stress. The beneficial effects of mild stress on aging and longevity have been studied for many years. In experimental animals, mild dietary stress (dietary restriction, DR) without malnutrition delays most age-related physiological changes, and extends maximum and average lifespan. Animal studies have also demonstrated that DR can prevent or lessen the severity of cancer, stroke, coronary heart disease, autoimmune disease, allergy, Parkinson's disease and Alzheimer's disease. The effects of DR are considered to result from hormetic mechanisms. These effects were reported by means of various DR regimens, such as caloric restriction, total-nutrient restriction, alternate-day fasting, and short-term fasting. Mild dietary stress, including restriction of amount or frequency of intake, is the essence of DR. For more than 99% of their history, humans lived as hunter-gatherers and adapted to restrictions in their food supply. On the other hand, an oversufficiency of food for many today has resulted in the current global epidemic of obesity and obesity-related diseases. DR may be used, therefore, as a novel approach for therapeutic intervention in several diseases, when detailed information about effects of mild dietary stress on human health is obtained from clinical trials.

Quercetin suppresses HeLa cell viability via AMPK-induced HSP70 and EGFR down-regulation

Quercetin, an anti-oxidant flavonoid that is widely distributed in the plant kingdom, has been suggested to have chemopreventive effects on cancer cells, although the mechanism is not completely understood. In this study, we found that quercetin increased the phosphorylation of AMP-activated protein kinase (AMPK) and downstream acetyl-CoA carboxylase (ACC) and suppressed the viability of HeLa cells. AICAR, an AMPK activator, and quercetin down-regulated heat shock protein (HSP)70 and increased the activity of the pro-apoptotic effector, caspase 3. Knock-down of AMPK blocked quercetin-mediated HSP70 down-regulation. Moreover, knock-down of HSP70 enhanced quercetin-mediated caspase 3 activation. Furthermore, quercetin sustained epidermal growth factor receptor (EGFR) activation by suppressing the phosphatases, PP2a and SHP-2. Finally, quercetin increased the interaction between EGFR and Cbl, and also induced the tyrosine phosphorylation of Cbl. Together, these results suggest that quercetin may have anti-tumor effects on HeLa cells via AMPK-induced HSP70 and down-regulation of EGFR.

Circulating heat shock protein 70 (HSPA1A) in normal and pathological pregnancies

Heat shock proteins (Hsps) are ubiquitous and phylogenetically conserved molecules. They are usually considered to be intracellular proteins with molecular chaperone and cytoprotective functions. However, Hsp70 (HSPA1A) is present in the peripheral circulation of healthy nonpregnant and pregnant individuals. In normal pregnancy, circulating Hsp70 levels are decreased, and show a positive correlation with gestational age and an inverse correlation with maternal age. The capacity of extracellular Hsp70 to elicit innate and adaptive proinflammatory (Th1-type) immune responses might be harmful in pregnancy and may lead to the maternal immune rejection of the fetus. Decreased circulating Hsp70 level, consequently, may promote the maintenance of immunological tolerance to the fetus. Indeed, elevated circulating Hsp70 concentrations are associated with an increased risk of several pregnancy complications. Elevated Hsp70 levels in healthy pregnant women at term might also have an effect on the onset of labor. In preeclampsia, serum Hsp70 levels are increased, and reflect systemic inflammation, oxidative stress and hepatocellular injury. Furthermore, serum Hsp70 levels are significantly higher in patients with the syndrome of hemolysis, elevated liver enzymes, and low platelet count (HELLP syndrome) than in severely preeclamptic patients without HELLP syndrome. In HELLP syndrome, elevated serum Hsp70 level indicates tissue damage (hemolysis and hepatocellular injury) and disease severity. Increased circulating Hsp70 level may not only be a marker of these conditions, but might also play a role in their pathogenesis. Extracellular Hsp70 derived from stressed and damaged, necrotic cells can elicit a proinflammatory (Th1) immune response, which might be involved in the development of the maternal systemic inflammatory response and resultant endothelial damage in preeclampsia and HELLP syndrome. Circulating Hsp70 level is also elevated in preterm delivery high-risk patients, particularly in treatment-resistant cases, and may be a useful marker for evaluating the curative effects of treatment for preterm delivery. In addition, increased circulating Hsp70 levels observed in asthmatic pregnant patients might play a connecting role in the pathomechanism of asthmatic inflammation and obstetrical/perinatal complications. Nevertheless, a prospective study should be undertaken to determine whether elevated serum Hsp70 level precedes the development of any pregnancy complication, and thus can help to predict adverse maternal or perinatal pregnancy outcome. Moreover, the role of circulating Hsp70 in normal and pathological pregnancies is not fully known, and further studies are warranted to address this important issue.

Housekeeping genes in prostate tumorigenesis

Housekeeping (HK) genes are involved in basic cellular functions and tend to be constitutively expressed across various tissues and conditions. A number of studies have analyzed the value of HK genes as an internal standard for assessing gene expression, but the role of HK genes in cancer development has never been specifically addressed. In this study, we sought to evaluate the expression of HK genes during prostate tumorigenesis. We performed a meta-analysis of gene expression during the transition from normal prostate (NP) to localized prostate cancer (LPC) (i.e., NP > LPC) and from localized to metastatic prostate cancer (MPC) (i.e., LPC > MPC). We found that HK genes are more likely to be differentially expressed during prostate tumorigenesis than is the average gene in the human genome, suggesting that prostate tumorigenesis is driven by modulation of the expression of HK genes. Cell-cycle genes and proliferation markers were up-regulated in both NP > LPC and LPC > MPC transitions. We also found that the genes encoding ribosomal proteins were up-regulated in the NP > LPC and down-regulated in the LPC > MPC transition. The expression of heat shock proteins was up-regulated during the LPC > MPC transition, suggesting that in its advanced stages, prostate tumor is under cellular stress. The results of these analyses suggest that during prostate tumorigenesis, there is a period when the tumor is under cellular stress and, therefore, may be the most vulnerable and responsive to treatment.

Adenosine receptors interacting proteins (ARIPs): Behind the biology of adenosine signaling

Adenosine is a well known neuromodulator in the central nervous system. As a consequence, adenosine can be beneficial in certain disorders and adenosine receptors will be potential targets for therapy in a variety of diseases. Adenosine receptors are G protein-coupled receptors, and are also expressed in a large variety of cells and tissues. Using these receptors as a paradigm of G protein-coupled receptors, the present review focus on how protein-protein interactions might contribute to neurotransmitter/neuromodulator regulation, based on the fact that accessory proteins impinge on the receptor/G protein interaction and therefore modulate receptor functioning. Besides affecting receptor signaling, these accessory components also play a key role in receptor trafficking, internalization and desensitization, as it will be reviewed here. In conclusion, the finding of an increasing number of adenosine receptors interacting proteins, and specially the molecular and functional integration of these accessory proteins into receptorsomes, will open new perspectives in the understanding of particular disorders where these receptors have been proved to be involved.

Co-ordinated stage-dependent enhancement of Plasmodium falciparum antioxidant enzymes and heat shock protein expression in parasites growing in oxidatively stressed or G6PD-deficient red blood cells

Background

Plasmodium falciparum-parasitized red blood cells (RBCs) are equipped with protective antioxidant enzymes and heat shock proteins (HSPs). The latter are only considered to protect against thermal stress. Important issues are poorly explored: first, it is insufficiently known how both systems are expressed in relation to the parasite developmental stage; secondly, it is unknown whether P. falciparum HSPs are redox-responsive, in view of redox sensitivity of HSP in eukaryotic cells; thirdly, it is poorly known how the antioxidant defense machinery would respond to increased oxidative stress or inhibited antioxidant defense. Those issues are interesting as several antimalarials increase the oxidative stress or block antioxidant defense in the parasitized RBC. In addition, numerous inhibitors of HSPs are currently developed for cancer therapy and might be tested as anti-malarials. Thus, the joint disruption of the parasite antioxidant enzymes/HSP system would interfere with parasite growth and open new perspectives for anti-malaria therapy.

Methods

Stage-dependent mRNA expression of ten representative P. falciparum antioxidant enzymes and hsp60/70–2/70–3/75/90 was studied by quantitative real-time RT-PCR in parasites growing in normal RBCs, in RBCs oxidatively-stressed by moderate H2O2 generation and in G6PD-deficient RBCs. Protein expression of antioxidant enzymes was assayed by Western blotting. The pentosephosphate-pathway flux was measured in isolated parasites after Sendai-virus lysis of RBC membrane.

Results

In parasites growing in normal RBCs, mRNA expression of antioxidant enzymes and HSPs displayed co-ordinated stage-dependent modulation, being low at ring, highest at early trophozoite and again very low at schizont stage. Additional exogenous oxidative stress or growth in antioxidant blunted G6PD-deficient RBCs indicated remarkable flexibility of both systems, manifested by enhanced, co-ordinated mRNA expression of antioxidant enzymes and HSPs. Protein expression of antioxidant enzymes was also increased in oxidatively-stressed trophozoites.

Conclusion

Results indicated that mRNA expression of parasite antioxidant enzymes and HSPs was co-ordinated and stage-dependent. Secondly, both systems were redox-responsive and showed remarkably increased and co-ordinated expression in oxidatively-stressed parasites and in parasites growing in antioxidant blunted G6PD-deficient RBCs. Lastly, as important anti-malarials either increase oxidant stress or impair antioxidant defense, results may encourage the inclusion of anti-HSP molecules in anti-malarial combined drugs.

The expression pattern of the 70-kDa heat shock protein Hspa2 in mouse tissues

The highest expression level of a 70-kDa heat shock protein family member Hspa2 is detected specifically in meiotic and post-meiotic male germ cells, which is reflected by original name of this protein, i.e., testis-specific Hsp70. However, this chaperon protein could be also detected in certain somatic tissues. Here, the extra-testicular expression pattern of mouse Hspa2 was analyzed. We found expression of Hspa2 in various epithelial cells including lining of bronchioles and oviduct, columnar epithelium of endometrium, epithelial reticular cells of thymus, transitional epithelium of the urinary bladder, or ependymal cells covering walls of the ventricular system of the brain. Surprisingly, Hspa2 was a putative secretory protein in intestine, endometrial glands and subcommissural organ. Hspa2 was detected in central and peripheral nervous system: in neuron's bodies and fiber tracts, in the subventricular zone of the lateral ventricles, in the dentate gyrus of the hippocampus, in enteric ganglia of the gastrointestinal tract. Hspa2 was also expressed in smooth muscles and at low level in immune system (in germinal centers associated with B-lymphocyte production). In addition to somatic tissues listed above, Hspa2 was detected in oocytes arrested at diplotene of the first meiotic division.

Molecular cloning and characterization of heat shock protein 70 from Trichinella spiralis

A cDNA encoding heat shock protein 70 of Trichinella spiralis (Ts-Hsp70) was identified by immunoscreening the adult T. spiralis cDNA library with rabbit antisera against T. spiralis adult extracts. The open reading frame of Ts-Hsp70 cDNA encoded a 623-amino acid peptide with a predicted molecular weight of 68.7kDa, which shares a high degree of sequence conservation with HSP70s from other parasites. Recombinant Ts-Hsp70 was expressed in Escherichia coli and purified with nickel column chromatography. Western blot analysis showed that recombinant Ts-Hsp70 could be recognized not only by trichinellosis patient sera, but also by T. spiralis-infected sera from rabbits, swine, and mice. Mice vaccinated with recombinant Ts-Hsp70 formulated with Freund's adjuvant exhibited strong humoral immune responses indicated by high titer of IgG antibody and significant muscle larval reduction (37%) after being challenged with T. spiralis larvae. The present results indicate that Ts-Hsp70 is a possible candidate vaccine against T. spiralis infection.

Hyperthermia on immune regulation: a temperature's story

Over the last decade the linkage between hyperthermia, heat shock proteins and fever with the body's immune system has been well investigated. The immunomodulatory function of hyperthermia has been found to be quite sensitively regulated by temperature, as different levels of heating can bring different modulatory effect on different sensitive targets. Understanding these intrinsic mechanisms could bring new inspirations on the design of clinical trials combining local tumor hyperthermia with immunotherapy in cancer patients. This review will attempt to tell the story about the effect of temperature on immune regulation, with special emphasis on the clinical application of hyperthermia and the feasibility of combining it with immunotherapy in the clinic.