Membrane-Associated Heat Shock Proteins in Oncology: From Basic Research to New Theranostic Targets

Heat shock proteins (HSPs) constitute a large family of conserved proteins acting as molecular chaperones that play a key role in intracellular protein homeostasis, regulation of apoptosis, and protection from various stress factors (including hypoxia, thermal stress, oxidative stress). Apart from their intracellular localization, members of different HSP families such as small HSPs, HSP40, HSP60, HSP70 and HSP90 have been found to be localized on the plasma membrane of malignantly transformed cells. In the current article, the role of membrane-associated molecular chaperones in normal and tumor cells is comprehensively reviewed with implications of these proteins as plausible targets for cancer therapy and diagnostics.

An inventory of interactors of the human HSP60/HSP10 chaperonin in the mitochondrial matrix space

The HSP60/HSP10 chaperonin assists folding of proteins in the mitochondrial matrix space by enclosing them in its central cavity. The chaperonin forms part of the mitochondrial protein quality control system. It is essential for cellular survival and mutations in its subunits are associated with rare neurological disorders. Here we present the first survey of interactors of the human mitochondrial HSP60/HSP10 chaperonin. Using a protocol involving metabolic labeling of HEK293 cells, cross-linking, and immunoprecipitation of HSP60, we identified 323 interacting proteins. As expected, the vast majority of these proteins are localized to the mitochondrial matrix space. We find that approximately half of the proteins annotated as mitochondrial matrix proteins interact with the HSP60/HSP10 chaperonin. They cover a broad spectrum of functions and metabolic pathways including the mitochondrial protein synthesis apparatus, the respiratory chain, and mitochondrial protein quality control. Many of the genes encoding HSP60 interactors are annotated as disease genes. There is a correlation between relative cellular abundance and relative abundance in the HSP60 immunoprecipitates. Nineteen abundant matrix proteins occupy more than 60% of the HSP60/HSP10 chaperonin capacity. The reported inventory of interactors can form the basis for interrogating which proteins are especially dependent on the chaperonin.

Heat Shock Protein 60 in Cardiovascular Physiology and Diseases

Heat shock protein 60 (HSP60) is a highly conserved protein abundantly expressed in both prokaryotic and eukaryotic cells. In mammals, HSP60 has been primarily considered to reside in the mitochondria, where HSP60 and HSP10 form a complex and facilitate mitochondrial protein folding. However, HSP60 is also observed in the cytoplasm, the plasma membrane, and the extracellular space. HSP60 regulates a broad spectrum of cellular events including protein trafficking, peptide hormone signaling, cell survival, cell proliferation, inflammation, and immunization. In the cardiovascular system, growing evidence indicates that HSP60 could not only play an important role under physiological conditions, but also regulate the initiation and progression of heart failure and atherosclerosis. In this review, we focus on recent progress in understanding the function of HSP60 in cardiomyocytes, endothelial cells, and vascular smooth muscle cells (VSMCs), respectively, and discuss the related signaling pathways that have been found in these cells, so as to illustrate the role of HSP60 in the development of cardiovascular disease.

The 60-kDa heat shock protein regulates energy rearrangement and protein synthesis to promote proliferation of multiple myeloma cells

To investigate the cellular mechanisms of multiple myeloma (MM), we used liquid chromatography-tandem mass spectrometry for proteomics analysis of CD138⁺ plasma cells from patients with MM and healthy controls. We found that the 60-kDa heat shock protein (HSP60, also known as HSPD1) was significantly upregulated in myeloma cells. HSP60 is an important chaperone protein that regulates the homeostasis of mitochondrial proteins and maintains mitochondrial function. Knockdown (KD) of HSP60 in myeloma cells resulted in inhibition of proliferation and reduced the quality of the mitochondria. Mitochondrial stress tests showed that HSP60 KD inhibited glycolysis and mitochondrial activity. Metabolomics showed a decrease in glycolysis and tricarboxylic acid cycle metabolites, and inhibited the formation of creatine and phosphocreatine by the reaction of S-adenosylmethionine (SAM) with amino acids mediated by demethyladenosine transferase 1, mitochondrial (TFB1M) and reduced energy storage substances. Moreover, HSP60 silencing influenced the synthesis of ribonucleotides and nicotinamide adenine dinucleotide phosphate (NADPH) by the pentose phosphate pathway to inhibit cell proliferation. HSP60 KD inhibited 5' adenosine monophosphate-activated protein kinase (AMPK), which inhibited the key enzyme 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), effecting the metabolism of fatty acids by inhibiting malonyl-coenzyme A. Our data suggest that reduced HSP60 expression alters metabolic reprogramming in MM, inhibits tumour progression and reduces mitochondrial-dependent biosynthesis, suggesting that HSP60 is a potential therapeutic target for MM treatment.

Comparison of the protein acetylome of endothelial cells upon shear flow and resveratrol treatment

BACKGROUND

Posttranslational acetylation/deacetylation known as the acetylome is important in regulating protein activity. Shear flow (SF) and resveratrol (RSV) are two stimuli that represent physical and chemical signal separately. The acetylome co-regulated by these two stimuli remain unclear.

METHODS

Human umbilical cord vein endothelial cells (HUVECs) were subjected to either SF of 12 dynes/cm² or 10 μM RSV. The purified acetylated peptides were labeled by isobaric tags for relative and absolute quantitation (iTRAQ) analysis. The signaling cascades of the identified acetylome were predicted by ingenuity pathway analysis (IPA). Co-immunoprecipitation was applied to confirm the acetylation status of proteins.

RESULTS

Five groups of proteins showed an increased acetylation upon SF and RSV treatment. After algorithm, 628 proteins with increased acetylation and 22 proteins with decreased acetylation were identified in the SF acetylome. For the acetylome regulated by RSV, 145 proteins with increased acetylation and 23 proteins with decreased acetylation were identified. Compared these two acetylomes, 129 proteins with increased acetylation and 2 proteins with decreased acetylation were co-regulated by both SF and RSV treatments. IPA analysis showed that this co-regulated acetylome was involved in heat shock response, and the signals of eNOS, STAT3, JAK/STAT and ERK/MAPK. Co-immunoprecipitation analysis further confirmed the acetylated status of mitochondrial HSP60 and mitochondrial citrate synthase.

CONCLUSIONS

This study indicated that physical signal is more complicated than chemical signal in the case of acetylome. The co-regulated proteins are worthy for further study in discussing synergetic effect between physical and chemical signal in cardioprotection.

Left ventricular hypertrophy is associated with overexpression of HSP60, TLR2, and TLR4 in the myocardium

Left ventricular hypertrophy is a common adaptive response to increased cardiac workload. Cardiomyocytes growth and increase in contractile force are conditioned by sufficient energy production, which implies appropriate mitochondrial function. The 60 kDa heat shock protein (HSP60) is a chaperone essential for mitochondrial proteostasis, but when translocates from mitochondria, it can also act as a potent inflammatory mediator binding to toll-like receptors (TLRs). In this study, we aimed to compare the expression pattern of HSP60, TLR2, and TLR4 in hypertrophic vs non-hypertrophic, normal human myocardium. We further examined whether HSP60 in situ binds to TLRs in hypertrophic myocardial tissue. In addition, expression of activated downstream targets of TLR 2/4 pathways was also evaluated.For this purpose, immunohistochemical expression analyses were performed on myocardial tissue samples obtained during the autopsy of human subjects in which left ventricular hypertrophy was the only cardiopathological finding and had died from sudden cardiac death, as well as from the subjects without any cardiac pathology, that died by unnatural death (accident or suicide). Double immunofluorescence was used to examine HSP60 translocation, while proximity ligation assay (PLA) was performed to assess HSP60 and TLRs interactions.Hypertrophic myocardium showed significantly higher expression of HSP60, TLR2, and TLR4 compared to normal myocardium. Furthermore, in hypertrophic cardiomyocytes, we found membrane translocation of HSP60 and signs of HSP60/TLR interactions.Conclusion: The obtained data point to an important supportive role of HSP60 in adaptive cardiomyocytes growth, while concomitant induction of TLR2 and TLR4 candidates HSP60-TLRs interactions as an early events during pathogenesis of secondary complications consequently to the left ventricular hypertrophy.

miR-382-5p promotes porcine reproductive and respiratory syndrome virus (PRRSV) replication by negatively regulating the induction of type I interferon

Previous studies have indicated that inhibition of type I interferon production may be an important reason for porcine reproductive and respiratory syndrome virus (PRRSV) to achieve immune escape, revealing the mechanism of inhibiting the production of type I interferon will help design novel strategies for controlling PRRS. Here, we found that PRRSV infection upregulated the expression of miR-382-5p, which in turn inhibited polyI:C-induced the production of type I interferon by targeting heat shock protein 60 (HSP60), thus facilitating PRRSV replication in MARC-145 cells. Furthermore, we found that HSP60 could interact with mitochondrial antiviral signaling protein (MAVS), an important signal transduction protein for inducing production of type I interferon, and promote polyI:C-mediated the production of type I interferon in a MAVS-dependent manner. Finally, we also found that HSP60 could inhibit PRRSV replication in a MAVS-dependent manner, which indicated that HSP60 was a novel antiviral protein against PRRSV replication. In conclusion, the study demonstrated that miR-382-5p was upregulated during PRRSV infection and may promote PRRSV replication by negatively regulating the production of type I interferon, which also indicated that miR-382-5p and HSP60 might be the potential therapeutic targets for anti-PRRSV.

Mitochondrial stress protein HSP60 regulates ER stress-induced hepatic lipogenesis

Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are associated with hepatic steatosis and insulin resistance. Molecular mechanisms underlying ER stress and/or mitochondrial dysfunction that cause metabolic disorders and hepatic steatosis remain to be fully understood. Here, we found that a high fat diet (HFD) or chemically induced ER stress can stimulate mitochondrial stress protein HSP60 expression, impair mitochondrial respiration, and decrease mitochondrial membrane potential in mouse hepatocytes. HSP60 overexpression promotes ER stress and hepatic lipogenic protein expression and impairs insulin signaling in mouse hepatocytes. Mechanistically, HSP60 regulates ER stress-induced hepatic lipogenesis via the mTORC1-SREBP1 signaling pathway. These results suggest that HSP60 is an important ER and mitochondrial stress cross-talking protein and may control ER stress-induced hepatic lipogenesis and insulin resistance.

Curcumin Affects HSP60 Folding Activity and Levels in Neuroblastoma Cells

The fundamental challenge in fighting cancer is the development of protective agents able to interfere with the classical pathways of malignant transformation, such as extracellular matrix remodeling, epithelial–mesenchymal transition and, alteration of protein homeostasis. In the tumors of the brain, proteotoxic stress represents one of the main triggering agents for cell transformation. Curcumin is a natural compound with anti-inflammatory and anti-cancer properties with promising potential for the development of therapeutic drugs for the treatment of cancer as well as neurodegenerative diseases. Among the mediators of cancer development, HSP60 is a key factor for the maintenance of protein homeostasis and cell survival. High HSP60 levels were correlated, in particular, with cancer development and progression, and for this reason, we investigated the ability of curcumin to affect HSP60 expression, localization, and post-translational modifications using a neuroblastoma cell line. We have also looked at the ability of curcumin to interfere with the HSP60/HSP10 folding machinery. The cells were treated with 6, 12.5, and 25 µM of curcumin for 24 h, and the flow cytometry analysis showed that the compound induced apoptosis in a dose-dependent manner with a higher percentage of apoptotic cells at 25 µM. This dose of curcumin-induced a decrease in HSP60 protein levels and an upregulation of HSP60 mRNA expression. Moreover, 25 µM of curcumin reduced HSP60 ubiquitination and nitration, and the chaperonin levels were higher in the culture media compared with the untreated cells. Furthermore, curcumin at the same dose was able to favor HSP60 folding activity. The reduction of HSP60 levels, together with the increase in its folding activity and the secretion in the media led to the supposition that curcumin might interfere with cancer progression with a protective mechanism involving the chaperonin.

Impact of thermal stress on expression dynamics of HSP60 in cardiac fibroblast cells of goat

The present study was aimed to determine the impact of thermal stress on expression dynamics of heat shock protein 60 (HSP60) mRNA in cultured cardiac fibroblast cells of the goat. The heart tissues (n = 6) from different goats were used for the culture study. The cardiac fibroblast cells were cultured and subjected to thermal stress at 42 °C for 0, 20, 60 and 100 min. The relative abundance of HSP60 mRNA was assessed by quantitative real-time PCR (qRT-PCR). The cardiac cells exposed to thermal stress at 42 °C for 0 min was taken as control. The relative abundance of HSP60 mRNA did not change at 20 min of thermal stress as compared to control. Thereafter, the relative abundance of HSP60 mRNA was significantly up-regulated (p < 0.05) at 60 min and 100 min of thermal stress. However, the highest mRNA expression of HSP60 was noticed at 100 min of thermal stress. The present study indicates that, thermal stress modulates the mRNA expression HSP60 in cultured caprine cardiac fibroblast cells.

Role of Heat Shock Proteins in Glaucoma

Glaucoma, one of the most common causes of blindness worldwide, is a multifactorial neurodegenerative disease characterized by damage of retinal ganglion cells and optic nerve degeneration. However, the exact mechanism leading to glaucoma is still not understood. Evidences suggest an immunological involvement in the pathogenesis. Among other immune responses, altered autoantibody patterns were found in glaucoma patients. Especially elevated antibody levels against heat shock proteins (HSPs), like HSP27 or HSP60, were identified. In an animal model, an immunization with these HSPs induced a pressure-independent retinal ganglion cell degeneration and axon loss, hence mimicking glaucoma-like damage. In addition, development of autoreactive antibodies, as well as a glia and T-cell activation, were described in these animals. Recently, we noted that intravitreal HSP27 injection likewise led to a degeneration of retinal ganglion cells and their axons. Therefore, HSP27 might have a direct damaging effect on retinal cells, and might play a key role in glaucoma.

Liquiritigenin and liquiritin alleviated monocrotaline-induced hepatic sinusoidal obstruction syndrome via inhibiting HSP60-induced inflammatory injury

Hepatic sinusoidal obstruction syndrome (HSOS) is a life-threatening liver disease caused by the damage to liver sinusoidal endothelial cells (LSECs). Liquiritigenin and liquiritin are two main compounds in Glycyrrhizae Radix et Rhizoma (Gan-cao). Our previous study has shown that both liquiritigenin and liquiritin alleviated monocrotaline (MCT)-induced HSOS in rats via inducing the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant signaling pathway. This study aims to further investigate whether inhibiting liver inflammatory injury also contributed to the liquiritigenin and liquiritin-provided alleviation on MCT-induced HSOS. The results of serum alanine/aspartate aminotransferases (ALT/AST) activities and total bilirubin (TBil) amount, liver histological evaluation, scanning electron microscope observation and hepatic metalloproteinase-9 (MMP9) expression showed that liquiritigenin and liquiritin both alleviated MCT-induced HSOS in rats. Liquiritigenin and liquiritin reduced the increased liver myeloperoxidase (MPO) activity, mRNA expression of pro-inflammatory factors, hepatic infiltration of immune cells, hepatic toll-like receptor 4 (TLR4) expression and nuclear factor κB (NFκB) nuclear accumulation induced by MCT in rats. Furthermore, liquiritigenin and liquiritin attenuated MCT-induced liver mitochondrial injury, increased the decreased Lon protein expression and reduced the release of heat shock protein 60 (HSP60). Moreover, liquiritigenin and liquiritin also reduced NFκB nuclear accumulation and decreased the elevated cellular mRNA expression of NFκB-downstream pro-inflammatory cytokines induced by HSP60 in macrophage RAW264.7 cells. In conclusion, our study revealed that both liquiritigenin and liquiritin alleviated MCT-induced HSOS by inhibiting hepatic inflammatory responses triggered by HSP60.

HSP60 silencing promotes Warburg-like phenotypes and switches the mitochondrial function from ATP production to biosynthesis in ccRCC cells

HSP60 is a major mitochondrial chaperone for maintaining mitochondrial proteostasis. Our previous studies showed that HSP60 was significantly downregulated in clear cell renal cell carcinoma (ccRCC), the most common type of kidney cancer characterized by the classic Warburg effect. Here, we analyzed datasets in The Cancer Genome Atlas and revealed that higher HSP60 expression correlated with better overall survival in ccRCC patients. We also stably knocked down or overexpressed HSP60 in ccRCC cells to investigate the effects of HSP60 expression on the transition between oxidative phosphorylation and glycolysis. We confirmed that HSP60 knockdown increased cell proliferation, whereas its overexpression decreased cell growth. Proteomics and metabolomics revealed that HSP60 knockdown promoted Warburg-like phenotypes with enhanced glycolysis and decreased mitochondrial activity. Consistent with this finding, isotope tracing showed that the metabolic flow from glycolysis to TCA was reduced. However, HSP60 silencing enhanced mitochondrial functions in glutamine-directed biosynthesis with increased flow in two parts of the TCA cycle: Gln→αKG→OAA→Asp and Gln→αKG→ISO→acetyl-CoA, resulting in elevated de novo nucleotide synthesis and lipid synthesis. Proteomic analysis indicated that HSP60 silencing activated NRF2-mediated oxidative stress responses, while glutamate generated from glutamine increased glutathione synthesis for quenching excessive reactive oxygen species (ROS) produced upon elevated cell growth. We further found that HSP60 silencing activated the MEK/ERK/c-Myc axis to promote glutamine addiction, and confirmed that ccRCC cells were susceptible to oxidative stress and glutaminase inhibition. Collectively, our data show that HSP60 knockdown drives metabolic reprogramming in ccRCC to promote tumor progression and enhances mitochondrial-dependent biosynthesis.

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Mitochondrial dysfunction is a hallmark of clear cell renal cell carcinoma.

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HSP60 silencing promotes ccRCC progression via the enhanced Warburg effect.

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HSP60 silencing renders dysfunctional mitochondria glutamine addictive for biosynthesis in rapid proliferating cells.

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High ROS levels are detrimental to ccRCC cells which can be quenched by glutamine derived glutathione.

Dual-targeting GroEL/ES chaperonin and protein tyrosine phosphatase B (PtpB) inhibitors: A polypharmacology strategy for treating Mycobacterium tuberculosis infections

Current treatments for Mycobacterium tuberculosis infections require long and complicated regimens that can lead to patient non-compliance, increasing incidences of antibiotic-resistant strains, and lack of efficacy against latent stages of disease. Thus, new therapeutics are needed to improve tuberculosis standard of care. One strategy is to target protein homeostasis pathways by inhibiting molecular chaperones such as GroEL/ES (HSP60/10) chaperonin systems. M. tuberculosis has two GroEL homologs: GroEL1 is not essential but is important for cytokine-dependent granuloma formation, while GroEL2 is essential for survival and likely functions as the canonical housekeeping chaperonin for folding proteins. Another strategy is to target the protein tyrosine phosphatase B (PtpB) virulence factor that M. tuberculosis secretes into host cells to help evade immune responses. In the present study, we have identified a series of GroEL/ES inhibitors that inhibit M. tuberculosis growth in liquid culture and biochemical function of PtpB in vitro. With further optimization, such dual-targeting GroEL/ES and PtpB inhibitors could be effective against all stages of tuberculosis - actively replicating bacteria, bacteria evading host cell immune responses, and granuloma formation in latent disease - which would be a significant advance to augment current therapeutics that primarily target actively replicating bacteria.

HSP60/10 chaperonin systems are inhibited by a variety of approved drugs, natural products, and known bioactive molecules

All living organisms contain a unique class of molecular chaperones called 60 kDa heat shock proteins (HSP60 - also known as GroEL in bacteria). While some organisms contain more than one HSP60 or GroEL isoform, at least one isoform has always proven to be essential. Because of this, we have been investigating targeting HSP60 and GroEL chaperonin systems as an antibiotic strategy. Our initial studies focused on applying this antibiotic strategy for treating African sleeping sickness (caused by Trypanosoma brucei parasites) and drug-resistant bacterial infections (in particular Methicillin-resistant Staphylococcus aureus - MRSA). Intriguingly, during our studies we found that three known antibiotics - suramin, closantel, and rafoxanide - were potent inhibitors of bacterial GroEL and human HSP60 chaperonin systems. These findings prompted us to explore what other approved drugs, natural products, and known bioactive molecules might also inhibit HSP60 and GroEL chaperonin systems. Initial high-throughput screening of 3680 approved drugs, natural products, and known bioactives identified 161 hit inhibitors of the Escherichia coli GroEL chaperonin system (4.3% hit rate). From a purchased subset of 60 hits, 29 compounds (48%) re-confirmed as selective GroEL inhibitors in our assays, all of which were nearly equipotent against human HSP60. These findings illuminate the notion that targeting chaperonin systems might be a more common occurrence than we previously appreciated. Future studies are needed to determine if the in vivo modes of action of these approved drugs, natural products, and known bioactive molecules are related to GroEL and HSP60 inhibition.

The bovine herpesvirus-1 major tegument protein, VP8, interacts with host HSP60 concomitant with deregulation of mitochondrial function

The U_L47 gene product, VP8, is a major tegument protein of BoHV-1. While VP8 is not essential for virus replication in cell culture, a U_L47-deleted virus exhibits a smaller tegument structure and is avirulent in cattle. To obtain pure VP8 protein for structural analysis, we expressed a N-terminally truncated version of VP8 in Eschericia coli. However, the recombinant VP8 was consistently co-purified with a tightly associated bacterial protein; this protein was identified by mass spectrometry as GroEL, which has considerable homology with mammalian heat shock protein-60 (HSP60), thus suggesting a new role for VP8 in virus-host interaction. A physical interaction of HSP60 and VP8 in both VP8-transfected and BoHV-1-infected cells was demonstrated by immunoprecipitation. Analysis of different truncated VP8 constructs revealed that amino acids 259-482 and 632-741 are involved in binding to HSP60. Full-length VP8 and VP8 219-741 (containing both interacting domains, 259-482 and 632-741) co-localized with HSP60 and mitochondria. VP8 was localized in the mitochondria from 2 to 14 h post infection in BoHV-1-infected cells. The mitochondrial membrane potential was reduced in both VP8-transfected and BoHV-1-infected cells and was further diminished by overexpression of HSP60 in the presence of VP8. In addition, VP8 expression decreased the ATP concentration during transfection, as well as BoHV-1 infection. Thus, VP8 may play a role in the deregulation of mitochondrial function through interaction with HSP60. This is consistent with the fact that BoHV-1 infection is known to promote mitochondrial dysfunction.

Acute heat stress induces changes in physiological and cellular responses in Saanen goats

The relationships between rectal temperatures and physiological and cellular responses to heat stress can improve the productivity of Saanen goats in tropical environments. In this context, this study evaluated the physiological responses and gene expression of heat shock proteins (HSP60, 70, and 90) and genes related to apoptosis (Bax, Bcl-2, and p53) of Saanen goats subjected to acute heat stress. Ten health Saanen goats were exposed to solar radiation during 3 consecutive days. The expression of HSP60, HSP70, HSP90, Bax, Bcl-2, and p53 genes in blood leukocytes, rectal and superficial temperatures, respiratory frequency, cortisol, triiodothyronine, and thyroxine was measured at 06:00, 13:00, and 18:00 h. In vitro, blood leukocytes were subjected to 38 °C and 40 °C for 3 h to measure the expression of the same target genes. The temperature humidity index, measured from 12:00 to 15:00, was greater than 80 and black globe temperatures were greater at 40 °C, indicating the intensity of the solar radiation. Although the solar radiation caused acute heat stress, increased cortisol release, and the expression of HSP60 and 70 in dry Saanen goats, the increased respiratory frequency and decreased T4 and T3 restored the homeothermy of the experimental goats. In vitro, the 40 °C increased the expression of p53 (pro-apoptotic protein), Bcl-2 (anti-apoptotic protein), HSP60, HSP70, and HSP90, suggesting that these genes have protective functions. However, further studies are necessary to understand the physiological and cellular responses to heat stress.

Heat shock proteins and cardiovascular disease

The development of stress drives a host of biological responses that include the overproduction of a family of proteins named heat shock proteins (HSPs), because they were initially studied after heat exposure. HSPs are evolutionarily preserved proteins with a high degree of interspecies homology. HSPs are intracellular proteins that also have extracellular expression. The primary role of HSPs is to protect cell function by preventing irreversible protein damage and facilitating molecular traffic through intracellular pathways. However, in addition to their chaperone role, HSPs are immunodominant molecules that stimulate natural as well as disease-related immune reactivity. The latter may be a consequence of molecular mimicry, generating cross-reactivity between human HSPs and the HSPs of infectious agents. Autoimmune reactivity driven by HSPs could also be the result of enhancement of the immune response to peptides generated during cellular injury and of their role in the delivery of peptides to the major histocompatibility complex in antigen-presenting cells. In humans, HSPs have been found to participate in the pathogenesis of a large number of diseases. This review is focused on the role of HSPs in atherosclerosis and essential hypertension.

HSP60 critically regulates endogenous IL-1β production in activated microglia by stimulating NLRP3 inflammasome pathway

Background

Interleukin-1β (IL-1β) is one of the most important cytokine secreted by activated microglia as it orchestrates the vicious cycle of inflammation by inducing the expression of various other pro-inflammatory cytokines along with its own production. Microglia-mediated IL-1β production is a tightly regulated mechanism which involves the activation of nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing 3 (NLRP3) inflammasome pathway. Our previous study suggests the critical role of heat shock protein 60 (HSP60) in IL-1β-induced inflammation in microglia through TLR4-p38 MAPK axis. However, whether HSP60 regulates endogenous IL-1β production is not known. Therefore, to probe the underlying mechanism, we elucidate the role of HSP60 in endogenous IL-1β production.

Methods

We used in vitro (N9 murine microglial cells) and in vivo (BALB/c mouse) models for our study. HSP60 overexpression and knockdown experiment was done to elucidate the role of HSP60 in endogenous IL-1β production by microglia. Western blotting and quantitative real-time PCR was performed using N9 cells and BALB/c mice brain, to analyze various proteins and transcript levels. Reactive oxygen species levels and mitochondrial membrane depolarization in N9 cells were analyzed by flow cytometry. We also performed caspase-1 activity assay and enzyme-linked immunosorbent assay to assess caspase-1 activity and IL-1β production, respectively.

Results

HSP60 induces the phosphorylation and nuclear localization of NF-κB both in vitro and in vivo. It also induces perturbation in mitochondrial membrane potential and enhances reactive oxygen species (ROS) generation in microglia. HSP60 further activates NLRP3 inflammasome by elevating NLRP3 expression both at RNA and protein levels. Furthermore, HSP60 enhances caspase-1 activity and increases IL-1β secretion by microglia. Knockdown of HSP60 reduces the IL-1β-induced production of IL-1β both in vitro and in vivo. Also, we have shown for the first time that knockdown of HSP60 leads to decreased IL-1β production during Japanese encephalitis virus (JEV) infection, which eventually leads to decreased inflammation and increased survival of JEV-infected mice.

Conclusion

HSP60 mediates microglial IL-1β production by regulating NLRP3 inflammasome pathway and reduction of HSP60 leads to reduction of inflammation in JEV infection.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1214-5) contains supplementary material, which is available to authorized users.

SLC35B4, an Inhibitor of Gluconeogenesis, Responds to Glucose Stimulation and Downregulates Hsp60 among Other Proteins in HepG2 Liver Cell Lines

SLC35B4, solute receptor for UDP-N-acetylglucosamine and UDP-xylose, is associated with diabetes and predisposing conditions. This study investigated the localization of SLC35B4 and compared the differential expression between a knockdown of SLC35B4 and controls in HepG2. Responsiveness to glucose, expression, and localization were assayed using Western blot and immunostaining. Localization was confirmed using a proximity ligation assay. Two-dimensional (2D) gel electrophoresis and MALDI-TOF were used to identify differentially expressed proteins and pathway analysis was performed. SLC35B4 was increased by 60% upon glucose stimulation and localized in Golgi apparatus and endoplasmic reticulum. Presence of SLC35B4 in the Golgi apparatus suggests its involvement in the biosynthesis of glycoconjugate proteins. Four proteins were markedly under-expressed (Hsp60, HspA8, TUBA1A, and ENO1) and linked to the pathogenesis of diabetes or post-translationally modified by O-GlcNAc. Glucose levels activate SLC35B4 expression. This triggers a downstream effect via Hsp60 and other proteins. We hypothesize that the downstream effect on the proteins is mediated via altering the glycosylation pattern inside liver cells. The downstream cascade ultimately alters the ability of cultured liver cells to inhibit endogenous glucose production, and this could play a role in the association of the above-listed genes with the pathogenesis of diabetes.

Stress proteins in the pathogenesis of spondyloarthritis

Spondyloarthritis is an autoinflammatory rheumatic disease in which arthritis and osteoproliferation lead the patients who suffer from it to chronic disability. This disease is associated with the expression of class I MHC molecule HLA-B27, which tends to be misfolded in the endoplasmic reticulum and, therefore, expressed in aberrant forms. This phenomena lead to endoplasmic reticulum stress, which in time, evokes a whole response to cellular injury. Under these conditions, the molecules involved in restoring cell homeostasis play a key role. Such is the case of the "heat-shock proteins", which usually regulate protein folding, but also have important immunomodulatory functions, as well as some roles in tissue modeling. In this review, we attempt to summarize the involvement of cell stress and heat-shock proteins in the homeostatic disturbances and pathological conditions associated with this disease.

Single-Ring Intermediates Are Essential for Some Chaperonins

Chaperonins are macromolecular complexes found throughout all kingdoms of life that assist unfolded proteins reach a biologically active state. Historically, chaperonins have been classified into two groups based on sequence, subunit structure, and the requirement for a co-chaperonin. Here, we present a brief review of chaperonins that can form double- and single-ring conformational intermediates in their protein-folding catalytic pathway. To date, the bacteriophage encoded chaperonins ϕ-EL and OBP, human mitochondrial chaperonin and most recently, the bacterial groEL/ES systems, have been reported to form single-ring intermediates as part of their normal protein-folding activity. These double-ring chaperonins separate into single-ring intermediates that have the ability to independently fold a protein. We discuss the structural and functional features along with the biological relevance of single-ring intermediates in cellular protein folding. Of special interest are the ϕ-EL and OBP chaperonins which demonstrate features of both group I and II chaperonins in addition to their ability to function via single-ring intermediates.

HSP60 and HSP90β from blunt snout bream, Megalobrama amblycephala: Molecular cloning, characterization, and comparative response to intermittent thermal stress and Aeromonas hydrophila infection

Heat shock proteins (HSPs) play critical roles in the process of anti-stress and immunity and are implicated in autoimmune diseases. In order to understand the comparative stress responses of HSP60 and HSP90β under intermittent thermal stress and Aeromonas hydrophila infection, we cloned their full-length cDNAs from Megalobrama amblycephala liver, predicted their secondary and tertiary structure, and examined their tissue-specific expression patterns. The full length of HSP60 and HSP90β cDNAs indicated that they included all signature sequences of corresponding protein families. They showed high homology to their counterparts in other species, and were consistent with the known classification of fishes based on phylogenetic analysis. HSP60 showed the highest expression in head-kidney, brain, and gill, while HSP90β presented higher in hindgut, liver, and brain. Significant mRNA expression differences were determined between HSP60 and HSP90β in tissues of bladder, liver, heart, and gill. During thermal stress and recovery phase, the highest expression of them were observed at the first recovery for 2 d and 1 d, respectively. The expression between them were extremely significant difference during the first recovery and second stress period. After A. hydrophila infection, their expressions were extremely significantly upregulated. The significant upregulation and rapid response indicated that they were sensitive to thermal stress and bacterial challenge. This study demonstrated that HSP60 and HSP90β might participate in innate immune and environmental responses of M. amblycephala. It indicated that they could be used as biomarkers to test the stress caused by local aquaculture environment.

Molecular characteristics of a novel HSP60 gene and its differential expression in Manila clams (Ruditapes philippinarum) under thermal and hypotonic stress

The Manila clam Ruditapes philippinarum inhabits the intertidal zone and must therefore tolerate broad fluctuations in water temperature and salinity. Heat shock protein 60 (HSP60) is an evolutionarily conserved, multi-functional protein that plays a significant role in protecting organisms from harmful stress conditions. We cloned the R. philippinarum HSP60 (RpHSP60) gene and analyzed its transcriptional responses to thermal and low-salinity stresses. The complete sequence of RpHSP60 cDNA was 1777 nucleotides, containing a 1728-bp open reading frame encoding a polypeptide of 576-amino acids, with a calculated molecular mass of 61.25 kDa and predicted isoelectric point of 5.08. Comparisons of amino acid sequences and three-dimensional structures of HSP60 revealed that RpHSP60 was highly conserved in the signature HSP60-family domains. RpHSP60 mRNA was detected in all the tested tissues of R. philippinarum, with the highest expression levels in hemocytes. We measured RpHSP60 mRNA levels in the gills under thermal and low-salinity stresses using quantitative real-time reverse transcription-polymerase chain reaction. Following the thermal challenge, RpHSP60 mRNA was significantly upregulated at 6 h, and then progressively downregulated under high-temperature stress (30 °C), while only slight fluctuations were observed under low-temperature stress (-1 °C). Under low-salinity (17 ppt) stress, RpHSP60 mRNA levels were significantly increased at 3, 72, and 96 h (P < 0.05). These results suggest that HSP60 of R. philippinarum may play important roles in responding to high-temperature and low-salinity stresses.

Physicochemical Properties of the Mammalian Molecular Chaperone HSP60

The E. coli GroEL/GroES chaperonin complex acts as a folding cage by producing a bullet-like asymmetric complex, and GroEL exists as double rings regardless of the presence of adenosine triphosphate (ATP). Its mammalian chaperonin homolog, heat shock protein, HSP60, and co-chaperonin, HSP10, play an essential role in protein folding by capturing unfolded proteins in the HSP60/HSP10 complex. However, the structural transition in ATPase-dependent reaction cycle has remained unclear. We found nucleotide-dependent association and dissociation of the HSP60/HSP10 complex using various analytical techniques under near physiological conditions. Our results showed that HSP60 exist as a significant number of double-ring complexes (football- and bullet-type complexes) and a small number of single-ring complexes in the presence of ATP and HSP10. HSP10 binds to HSP60 in the presence of ATP, which increased the HSP60 double-ring formation. After ATP is hydrolyzed to Adenosine diphosphate (ADP), HSP60 released the HSP10 and the dissociation of the double-ring to single-rings occurred. These results indicated that HSP60/HSP10 undergoes an ATP-dependent transition between the single- and double-rings in their system that is highly distinctive from the GroEL/GroES system particularly in the manner of complex formation and the roles of ATP binding and hydrolysis in the reaction cycle.

Downregulation of HSP60 disrupts mitochondrial proteostasis to promote tumorigenesis and progression in clear cell renal cell carcinoma

In the present study, we demonstrate that HSP60 is unequivocally downregulated in clear cell renal cell carcinoma (ccRCC) tissues compared to pericarcinous tissues. Overexpression of HSP60 in ccRCC cancer cells suppresses cell growth. HSP60 knockdown increases cell growth and proliferation in both cell culture and nude mice xenografts, and drives cells to undergo epithelial to mesenchymal transition (EMT). Our results propose that HSP60 silencing disrupts the integrity of the respiratory complex I and triggers the excessive ROS production, which promotes tumor progression in the following aspects: (1) ROS activates the AMPK pathway that promotes acquisition of the Warburg phenotype in HSP60-KN cells; (2) ROS generated by HSP60 knockdown or by rotenone inhibition drives cells to undergo EMT; and (3) the high level of ROS may also fragment the Fe-S clusters that up regulates ADHFe1 expression and the 2-hydroxygluterate (2-HG) production leading to changes in DNA methylation. These results suggest that the high level of ROS is needed for tumorigenesis and progression in tumors with the low HSP60 expression and HSP60 is a potential diagnostic biomarker as well as a therapeutic target in ccRCC.

The histone deacetylase inhibitor SAHA induces HSP60 nitration and its extracellular release by exosomal vesicles in human lung-derived carcinoma cells

HSP60 undergoes changes in quantity and distribution in some types of tumors suggesting a participation of the chaperonin in the mechanism of transformation and cancer progression. Suberoylanilide hydroxamic acid (SAHA), a member of a family of histone deacetylase inhibitors (HDACi), has anti-cancer potential but its interaction, if any, with HSP60 has not been elucidated. We investigated the effects of SAHA in a human lung-derived carcinoma cell line (H292). We analysed cell viability and cycle; oxidative stress markers; mitochondrial integrity; HSP60 protein and mRNA levels; and HSP60 post-translational modifications, and its secretion. We found that SAHA is cytotoxic for H292 cells, interrupting the cycle at the G2/M phase, which is followed by death; cytotoxicity is associated with oxidative stress, mitochondrial damage, and diminution of intracellular levels of HSP60; HSP60 undergoes a post-translational modification and becomes nitrated; and nitrated HSP60 is exported via exosomes. We propose that SAHA causes ROS overproduction and mitochondrial dysfunction, which leads to HSP60 nitration and release into the intercellular space and circulation to interact with the immune system. These successive steps might constitute the mechanism of the anti-tumor action of SAHA and provide a basis to design supplementary therapeutic strategies targeting HSP60, which would be more efficacious than the compound alone.

Heat Shock Proteins in Vascular Diabetic Complications: Review and Future Perspective

Heat shock proteins (HSPs) are a large family of proteins highly conserved throughout evolution because of their unique cytoprotective properties. Besides assisting protein refolding and regulating proteostasis under stressful conditions, HSPs also play an important role in protecting cells from oxidative stress, inflammation, and apoptosis. Therefore, HSPs are crucial in counteracting the deleterious effects of hyperglycemia in target organs of diabetes vascular complications. Changes in HSP expression have been demonstrated in diabetic complications and functionally related to hyperglycemia-induced cell injury. Moreover, associations between diabetic complications and altered circulating levels of both HSPs and anti-HSPs have been shown in clinical studies. HSPs thus represent an exciting therapeutic opportunity and might also be valuable as clinical biomarkers. However, this field of research is still in its infancy and further studies in both experimental diabetes and humans are required to gain a full understanding of HSP relevance. In this review, we summarize current knowledge and discuss future perspective.

Effects of oral and subcutaneous administration of HSP60 on myeloid-derived suppressor cells and atherosclerosis in ApoE-/- mice

HSP60 has been proved to be closely related to atherosclerosis due to its antigenicity. To determine this antigenicity effect, the ApoE-/- mice were fed with western-type diet and HSP60 was administrated orally or subcutaneously (SC) for potential vaccine against atherosclerosis. Here, we observed the ApoE-/- mice with oral HSP60 administration group showed a significant reduction in plaque size at the aortic root; accompanied by increased MSDCs (CD11b⁺Gr1⁺) in peripheral blood and spleen which was mostly composed of M-MDSCs (CD11b⁺LY6G^-LY6C^high), and increased plasma IL-10 and splenic Foxp3, Arg1, iNOS mRNA as well as decreased plasma IFN-γ and splenic T-bet mRNA compared to control group. Surprisingly, ApoE-/- mice with subcutaneous HSP60 administration group showed contrary results and their MDSCs were mostly composed of G-MDSCs (CD11b⁺LY6G⁺LY6C^low). As expected, both PBS-oral and PBS-SC groups showed no significant effects on both the immune response and atherosclerotic plaque formation. In contrast, subcutaneous administration of HSP60 causes the opposite response. Thus, we propose the proper method for administering HSP60 as a new immunologic agent for prevention and treatment of atherosclerosis.

HSP60 activity on human bronchial epithelial cells

HSP60 has been implicated in chronic inflammatory disease pathogenesis, including chronic obstructive pulmonary disease (COPD), but the mechanisms by which this chaperonin would act are poorly understood. A number of studies suggest a role for extracellular HSP60, since it can be secreted from cells and bind Toll-like receptors; however, the effects of this stimulation have never been extensively studied. We investigated the effects (pro- or anti-inflammatory) of HSP60 in human bronchial epithelial cells (16-HBE) alone and in comparison with oxidative, inflammatory, or bacterial challenges. 16-HBE cells were cultured for 1–4 h in the absence or presence of HSP60, H₂O₂, lipopolysaccharide (LPS), or cytomix. The cell response was evaluated by measuring the expression of IL-8 and IL-10, respectively, pro- and anti-inflammatory cytokines involved in COPD pathogenesis, as well as of pertinent TLR-4 pathway mediators. Stimulation with HSP60 up-regulated IL-8 at mRNA and protein levels and down-regulated IL-10 mRNA and protein. Likewise, CREB1 mRNA was up-regulated. H₂O₂ and LPS up-regulated IL-8. Experiments with an inhibitor for p38 showed that this mitogen-activated protein kinase could be involved in the HSP60-mediated pro-inflammatory effects. HSP60 showed pro-inflammatory properties in bronchial epithelial cells mediated by activation of TLR-4-related molecules. The results should prompt further studies on more complex ex-vivo or in-vivo models with the aim to elucidate further the role of those molecules in the pathogenesis of COPD.

Interaction of heat shock protein 60 (HSP60) with microRNA in Chinese mitten crab during Spiroplasma eriocheiris infection

Heat shock protein 60 from the Chinese mitten crab Eriocheir sinensis (EsHSP60) was previously identified in relation to Spiroplasma eriocheiris infection by isobaric tags for relative and absolute quantitation labelling followed by liquid chromatography-tandem mass spectrometry. In the present study, to validate the immune function of this protein, the cDNA of the EsHSP60 gene was cloned. Various crab tissues were assessed using real-time PCR, which showed that EsHSP60 transcription occurred in all tissues examined. The expression profiles of EsHSP60 in haemolymph at transcription and protein levels when infected with S. eriocheiris were investigated by real-time PCR and Western blot analysis, respectively. A significant increase of EsHSP60 transcription and protein expression appeared post-injection in response to S. eriocheiris infection when compared to the control group. The double-luciferase reporter gene assay showed that the microRNA PC-533-3p interacted with the 3'-untranslated region of EsHSP60 and inhibited the translation of EsHSP60. The expression profiles of PC-533-3p during S. eriocheiris infection were also investigated by real-time PCR. However, the change tendency of PC-533-3p was opposite to that of the EsHSP60 after S. eriocheiris challenge. These data indicate that the EsHSP60 proteins may play an important role in mediating the immune responses of E. sinensis to an S. eriocheiris challenge.

pylori Infection in Mongolian gerbils

Epitope-based vaccine is a promising strategy for therapeutic vaccination against Helicobacter pylori (H. pylori) infection. A multivalent subunit vaccine containing various antigens from H. pylori is superior to a univalent subunit vaccine. However, whether a multivalent epitope-based vaccine is superior to a univalent epitope-based vaccine in therapeutic vaccination against H. pylori, remains unclear. In this study, a multivalent epitope-based vaccine named CWAE against H. pylori urease, neutrophil-activating protein (NAP), heat shock protein 60 (HSP60) and H. pylori adhesin A (HpaA) was constructed based on mucosal adjuvant cholera toxin B subunit (CTB), Th1-type adjuvant NAP, multiple copies of selected B and Th cell epitopes (UreA_27–53, UreA_183–203, HpaA_132–141, and HSP60_189–203), and also the epitope-rich regions of urease B subunit (UreB_158–251 and UreB_321–385) predicted by bioinformatics. Immunological properties of CWAE vaccine were characterized in BALB/c mice model. Its therapeutic effect was evaluated in H. pylori-infected Mongolian gerbil model by comparing with a univalent epitope-based vaccine CTB-UE against H. pylori urease that was constructed in our previous studies. Both CWAE and CTB-UE could induce similar levels of specific antibodies against H. pylori urease, and had similar inhibition effect of H. pylori urease activity. However, only CWAE could induce high levels of specific antibodies to NAP, HSP60, HpaA, and also the synthetic peptides epitopes (UreB_158–172, UreB_181–195, UreB_211–225, UreB_349–363, HpaA_132–141, and HSP60_189–203). In addition, oral therapeutic immunization with CWAE significantly reduced the number of H. pylori colonies in the stomach of Mongolian gerbils, compared with oral immunization using CTB-UE or H. pylori urease. The protection of CWAE was associated with higher levels of mixed CD4⁺ T cell (Th cell) response, IgG, and secretory IgA (sIgA) antibodies to H. pylori. These results indic ate that a multivalent epitope-based vaccine including Th and B cell epitopes from various H. pylori antigens could be a promising candidate against H. pylori infection.

Probiotic supplementation promotes a reduction in T-cell activation, an increase in Th17 frequencies, and a recovery of intestinal epithelium integrity and mitochondrial morphology in ART-treated HIV-1-positive patients

Introduction

HIV infection is characterized by a persistent immune activation associated to a compromised gut barrier immunity and alterations in the profile of the fecal flora linked with the progression of inflammatory symptoms. The effects of high concentration multistrain probiotic (Vivomixx®, Viale del Policlinico 155, Rome, Italy in EU; Visbiome®, Dupont, Madison, Wisconsin in USA) on several aspects of intestinal immunity in ART‐experienced HIV‐1 patients was evaluated.

Methods

A sub‐study of a longitudinal pilot study was performed in HIV‐1 patients who received the probiotic supplement twice a day for 6 months (T6). T‐cell activation and CD4+ and CD8+ T‐cell subsets expressing IFNγ (Th1, Tc1) or IL‐17A (Th17, Tc17) were stained by cytoflorimetric analysis. Histological and immunohistochemical analyses were performed on intestinal biopsies while enterocytes apoptosis index was determined by TUNEL assay.

Results

A reduction in the frequencies of CD4⁺ and CD8⁺ T‐cell subsets, expressing CD38⁺, HLA‐DR⁺, or both, and an increase in the percentage of Th17 cell subsets, especially those with central or effector memory phenotype, was recorded in the peripheral blood and in gut‐associated lymphoid tissue (GALT) after probiotic intervention. Conversely, Tc1 and Tc17 levels remained substantially unchanged at T6, while Th1 cell subsets increase in the GALT. Probiotic supplementation was also associated to a recovery of the integrity of the gut epithelial barrier, a reduction of both intraepithelial lymphocytes density and enterocyte apoptosis and, an improvement of mitochondrial morphology sustained in part by a modulation of heat shock protein 60.

Conclusions

These findings highlight the potential beneficial effects of probiotic supplementation for the reconstitution of physical and immunological integrity of the mucosal intestinal barrier in ART‐treated HIV‐1‐positive patients.

In silico analyses of heat shock protein 60 and calreticulin to designing a novel vaccine shifting immune response toward T helper 2 in atherosclerosis

Recent experiments demonstrated that atherosclerosis is a Th1 dominant autoimmune condition, whereas Th2 cells are rarely detected within the atherosclerotic lesions. Several studies have indicated that Th2 type cytokines could be effective in the reduction and stabilization of atherosclerotic plaque. Therefore, the modulation of the adaptive immune response by shifting immune responses toward Th2 cells by a novel vaccine could represent a promising approach to prevent from progression and thromboembolic events in coronary artery disease. In the present study, an in silico approach was applied to design a novel multi-epitope vaccine to elicit a desirable immune response against atherosclerosis. Six novel IL-4 inducing epitopes were selected from HSP60 and calreticulin proteins. To enhance epitope presentation, IL-4 inducing epitopes were linked together by AAY and HEYGAEALERAG linkers. In addition, helper epitopes selected from Tetanus toxin fragment C (TTFrC) were applied to induce CD4+ helper T lymphocytes (HTLs) responses. Moreover, cholera toxin B (CTB) was employed as an adjuvant. A multi-epitope construct was designed based on predicted epitopes which was 320 residues in length. Then, the physico-chemical properties, secondary and tertiary structures, stability, intrinsic protein disorder, solubility and allergenicity of this chimeric protein were analyzed using bioinformatics tools and servers. Based on bioinformatics analysis, a soluble, and non-allergic protein with 35.405kDa molecular weight was designed. Expasy ProtParam classified this chimeric protein as a stable protein. In addition, predicted epitopes in the chimeric vaccine indicated strong potential to induce B-cell mediated immune response and shift immune responses toward protective Th2 immune response. Various in silico analyses indicate that this vaccine is a qualified candidate for improvement of atherosclerosis by inducing immune responses toward T helper 2.

Paying for the Tolls: The High Cost of the Innate Immune System for the Cardiac Myocyte

The cardiac myocyte differs strikingly from the specialized cells of the immune system, which has two different responses to invading organisms and tissue damage. Adaptive or acquired immunity generates highly specific antibodies in response to threats and is an essential component of immunity; however, adaptive immunity can take 4-7 days to mobilize, and a more primitive response, innate immunity, fills the gap. Innate immunity is expressed in complex and in primitive life forms. Specialized receptors, Toll-like receptors (TLRs), which are widely distributed throughout different tissues recognize danger signals and rapidly respond with the release of noxious substances, such as TNFα. The problem is that many endogenous molecules have been found to act as ligands for specific TLRs, and when these molecules are released into the extracellular environment, they can cause problems by activating innate immunity and an inflammatory response. In cardiac myocytes heat shock protein (HSP)60 can activate TLR4, as can HMGB1, and this type of response can amplify the response to ischemia/reperfusion leading to increased cell and tissue injury. Activation of TLRs can potentially amplify chronic, inflammatory diseases, such as ischemic heart failure. Thus, it is important to understand the regulation of the TLRs and their downstream effects. This chapter will focus on the TLRs and cardiac myocytes.

Genome-Wide Analysis of Alternative Splicing Provides Insights into Stress Adaptation of the Pacific Oyster

Alternative splicing (AS) is thought to enhance transcriptome diversity dramatically and play an important role in stress adaptation. While well studied in vertebrates, AS remains poorly understood in invertebrates. Here, we used high-throughput RNA-sequencing data to perform a genome-wide survey of AS in the Pacific oyster (Crassostrea gigas), an economically important mollusk that is cultivated worldwide. This analysis identified 8223 AS events corresponding to 4480 genes in the Pacific oyster, suggesting that about 16 % of oyster multiexonic genes undergo AS. We observed that a majority of the identified AS events were related to skipped exons (37.8 %). Then Gene Ontology analysis was conducted to analyze the function of the genes that undergo AS and the genes that produce more than five AS isoforms. After that, the expression of AS isoforms facing temperature, salinity, and air exposure challenge were examined. To validate our bioinformatic-predicted results and examine whether AS affects stress adaptation, we selected heat-shock protein 60 (HSP60) and HSP90 genes, both of which experience AS, for reverse transcription PCR (RT-PCR). We also performed quantitative real-time PCR (qRT-PCR) to determine the relative expression of each AS isoform among different stress adapted populations. Our study indicates that AS events are likely complex in the Pacific oyster and may be related to stress adaptation. These results will complement the predicted gene database of C. gigas and provide an invaluable resource for future functional genomic studies on molluscs.

Targeting the HSP60/10 chaperonin systems of Trypanosoma brucei as a strategy for treating African sleeping sickness

Trypanosoma brucei are protozoan parasites that cause African sleeping sickness in humans (also known as Human African Trypanosomiasis-HAT). Without treatment, T. brucei infections are fatal. There is an urgent need for new therapeutic strategies as current drugs are toxic, have complex treatment regimens, and are becoming less effective owing to rising antibiotic resistance in parasites. We hypothesize that targeting the HSP60/10 chaperonin systems in T. brucei is a viable anti-trypanosomal strategy as parasites rely on these stress response elements for their development and survival. We recently discovered several hundred inhibitors of the prototypical HSP60/10 chaperonin system from Escherichia coli, termed GroEL/ES. One of the most potent GroEL/ES inhibitors we discovered was compound 1. While examining the PubChem database, we found that a related analog, 2e-p, exhibited cytotoxicity to Leishmania major promastigotes, which are trypanosomatids highly related to Trypanosoma brucei. Through initial counter-screening, we found that compounds 1 and 2e-p were also cytotoxic to Trypanosoma brucei parasites (EC₅₀=7.9 and 3.1μM, respectively). These encouraging initial results prompted us to develop a library of inhibitor analogs and examine their anti-parasitic potential in vitro. Of the 49 new chaperonin inhibitors developed, 39% exhibit greater cytotoxicity to T. brucei parasites than parent compound 1. While many analogs exhibit moderate cytotoxicity to human liver and kidney cells, we identified molecular substructures to pursue for further medicinal chemistry optimization to increase the therapeutic windows of this novel class of chaperonin-targeting anti-parasitic candidates. An intriguing finding from this study is that suramin, the first-line drug for treating early stage T. brucei infections, is also a potent inhibitor of GroEL/ES and HSP60/10 chaperonin systems.

Fasting induces prominent proteomic changes in liver in very long chain Acyl-CoA dehydrogenase deficient mice

Very long chain acyl-CoA dehydrogenase (VLCAD) deficiency (VLCADD) is a clinically heterogeneous disorder of mitochondrial fatty acid β-oxidation usually identified through newborn screening. Genotype-phenotype correlations have been defined, but considerable clinical heterogeneity still exists. Symptoms are often induced by physiological stress such as fasting or intercurrent illness, setting it as an important example of environmental effects altering clinical course in an individual with a genetic disease. However, neither the cellular changes that predispose to this phenomenon nor the alterations it induces are well characterized. We examined the effects of fasting in a knockout mouse model to explore changes in global mitochondria protein profiles in liver and to investigate the physiologically relevant changes that lead to the clinical presentations. An isobaric tags for relative and absolute quantification (iTRAQ) labeling approach was employed to examine mitochondrial proteome changes in VLCAD deficient compared to wild type mice in the fed and fasted states. We identified numerous proteomic changes associated with the gene defect and fasting within relevant metabolic pathways. Few changes induced by fasting were shared between the VLCAD deficient and wild type mice, with more alterations found in the deficient mice on fasting. Particularly, fasting in the deficient mice could reverse the protective response in oxidative phosphorylation pathway seen in wild type animals. In addition, we found that changes in chaperone proteins including heat shock protein 60 (HSP60) and 10 (HSP10) during fasting differed between the two genotypes, highlighting the importance of these proteins in VLCAD deficiency. Finally, the effects on the liver proteome imposed by changes in fasted VLCAD deficient mice indicates that this environmental factor may be an inducer of both cellular and physiological changes.

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VLCAD deficient mice show significant changes in the proteome compared to wild type animals.

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Hypoglycemia induces different proteomic changes in VLCAD deficient mice than is seen in wild type animals.

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Multiple functional pathways are altered in VLCAD deficient animals.

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Proteomic changes in VLCAD deficient mice may help understand the physiologic ramifications of this deficiency in humans.

Disease-Associated Mutations in the HSPD1 Gene Encoding the Large Subunit of the Mitochondrial HSP60/HSP10 Chaperonin Complex

Heat shock protein 60 (HSP60) forms together with heat shock protein 10 (HSP10) double-barrel chaperonin complexes that are essential for folding to the native state of proteins in the mitochondrial matrix space. Two extremely rare monogenic disorders have been described that are caused by missense mutations in the HSPD1 gene that encodes the HSP60 subunit of the HSP60/HSP10 chaperonin complex. Investigations of the molecular mechanisms underlying these disorders have revealed that different degrees of reduced HSP60 function produce distinct neurological phenotypes. While mutations with deleterious or strong dominant negative effects are not compatible with life, HSPD1 gene variations found in the human population impair HSP60 function and depending on the mechanism and degree of HSP60 dys- and mal-function cause different phenotypes. We here summarize the knowledge on the effects of disturbances of the function of the HSP60/HSP10 chaperonin complex by disease-associated mutations.

APL-1, an altered peptide ligand derived from heat-shock protein, alone or combined with methotrexate attenuates murine collagen-induced arthritis

Induction of tolerance to autoantigens in vivo is a complex process that involves several mechanisms such as the induction of regulatory T cells and changes in the cytokine and chemokine profiles. This approach represents an attractive alternative for treatment of autoimmune diseases. APL-1 is an altered peptide ligand derived from a novel CD4 + T cell epitope of human heat-shock protein of 60 kDa (HSP60), an autoantigen involved in the pathogenesis of rheumatoid arthritis (RA). We have shown previously that this peptide efficiently inhibited the course of adjuvant-induced arthritis in Lewis rats and induced regulatory T cell (Treg) in ex vivo assay with PBMC isolated from RA patients. This study was undertaken to evaluate the therapeutic effect of APL-1 and its combination with methotrexate (MTX) in collagen-induced arthritis (CIA). CIA was induced in male DBA/1 mice at 8 weeks of age by immunization with chicken collagen. APL, MTX or both were administrated beginning from arthritis onset. Therapeutic effect was evaluated by arthritis and joint pathologic scores. In addition, TNFα and IL-10 in sera were measured by ELISA. Treg induction was assessed by FACS analysis. APL-1 inhibits efficiently the course of arthritis in CIA, similar to MTX. In addition, therapy with APL-1 plus MTX reduced CIA in mice, associated with an increase in Treg. These facts reinforce the therapeutic possibilities of APL-1 as a candidate drug for treatment of RA.

GroEL/ES inhibitors as potential antibiotics

We recently reported results from a high-throughput screening effort that identified 235 inhibitors of the Escherichia coli GroEL/ES chaperonin system [Bioorg. Med. Chem. Lett.2014, 24, 786]. As the GroEL/ES chaperonin system is essential for growth under all conditions, we reasoned that targeting GroEL/ES with small molecule inhibitors could be a viable antibacterial strategy. Extending from our initial screen, we report here the antibacterial activities of 22 GroEL/ES inhibitors against a panel of Gram-positive and Gram-negative bacteria, including E. coli, Bacillus subtilis, Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter cloacae. GroEL/ES inhibitors were more effective at blocking the proliferation of Gram-positive bacteria, in particular S. aureus, where lead compounds exhibited antibiotic effects from the low-μM to mid-nM range. While several compounds inhibited the human HSP60/10 refolding cycle, some were able to selectively target the bacterial GroEL/ES system. Despite inhibiting HSP60/10, many compounds exhibited low to no cytotoxicity against human liver and kidney cell lines. Two lead candidates emerged from the panel, compounds 8 and 18, that exhibit >50-fold selectivity for inhibiting S. aureus growth compared to liver or kidney cell cytotoxicity. Compounds 8 and 18 inhibited drug-sensitive and methicillin-resistant S. aureus strains with potencies comparable to vancomycin, daptomycin, and streptomycin, and are promising candidates to explore for validating the GroEL/ES chaperonin system as a viable antibiotic target.

MaxiK channel interactome reveals its interaction with GABA transporter 3 and heat shock protein 60 in the mammalian brain

Large conductance voltage and calcium-activated potassium (MaxiK) channels are activated by membrane depolarization and elevated cytosolic Ca(2+). In the brain, they localize to neurons and astrocytes, where they play roles such as resetting the membrane potential during an action potential, neurotransmitter release, and neurovascular coupling. MaxiK channels are known to associate with several modulatory proteins and accessory subunits, and each of these interactions can have distinct physiological consequences. To uncover new players in MaxiK channel brain physiology, we applied a directed proteomic approach and obtained MaxiK channel pore-forming α subunit brain interactome using specific antibodies. Controls included immunoprecipitations with rabbit immunoglobulin G (IgG) and with anti-MaxiK antibodies in wild type and MaxiK channel knockout mice (Kcnma1(-/-)), respectively. We have found known and unreported interactive partners that localize to the plasma membrane, extracellular space, cytosol and intracellular organelles including mitochondria, nucleus, endoplasmic reticulum and Golgi apparatus. Localization of MaxiK channel to mitochondria was further confirmed using purified brain mitochondria colabeled with MitoTracker. Independent proof of MaxiK channel interaction with previously unidentified partners is given for GABA transporter 3 (GAT3) and heat shock protein 60 (HSP60). In human embryonic kidney 293 cells containing SV40 T-antigen (HEK293T) cells, both GAT3 and HSP60 coimmunoprecipitated and colocalized with MaxiK channel; colabeling was observed mainly at the cell periphery with GAT3 and intracellularly with HSP60 with protein proximity indices of ∼ 0.6 and ∼ 0.4, respectively. In rat primary hippocampal neurons, colocalization index was identical for GAT3 (∼ 0.6) and slightly higher for HSP60 (∼ 0.5) association with MaxiK channel. The results of this study provide a complete interactome of MaxiK channel the mouse brain, further establish the localization of MaxiK channel in the mouse brain mitochondria and demonstrate the interaction of MaxiK channel with GAT3 and HSP60 in neurons. The interaction of MaxiK channel with GAT3 opens the possibility of a role of MaxiK channel in GABA homeostasis and signaling.

A potent multivalent vaccine for modulation of immune system in atherosclerosis: an in silico approach

Purpose

Atherosclerosis is classically defined as an immune-mediated disease characterized by accumulation of low-density lipoprotein cholesterol over intima in medium sized and large arteries. Recent studies have demonstrated that both innate and adaptive immune responses are involved in atherosclerosis. In addition, experimental and human models have recognized many autoantigens in pathophysiology of this disease. Oxidized low-density lipoproteins, β2 glycoprotein I (β-2-GPI), and heat shock protein 60 (HSP60) are the best studied of them which can represent promising approach to design worthwhile vaccines for modulation of atherosclerosis.

Materials and Methods

In silico approaches are the best tools for design and evaluation of the vaccines before initiating the experimental study. In this study, we identified immunogenic epitopes of HSP60, ApoB-100, and β-2-GPI as major antigens to construct a chimeric protein through bioinformatics tools. Additionally, we have evaluated physico-chemical properties, structures, stability, MHC binding properties, humoral and cellular immune responses, and allergenicity of this chimeric protein by means of bioinformatics tools and servers.

Results

Validation results indicated that 89.1% residues locate in favorite or additional allowed region of Ramachandran plot. Also, based on Ramachandran plot analysis this protein could be classified as a stable fusion protein. In addition, the epitopes in the chimeric protein had strong potential to induce both the B-cell and T-cell mediated immune responses.

Conclusion

Our results supported that this chimeric vaccine could be effectively utilized as a multivalent vaccine for prevention and modulation of atherosclerosis.

Antibodies against small heat-shock proteins in Alzheimer's disease as a part of natural human immune repertoire or activation of humoral response?

Characterization of autoantibodies specific for some disease-related proteins, would allow to better assess their role as diagnostic and prognostic markers. In the light of increasing evidence for both humoral and cellular adaptive immune responses in the pathophysiology of Alzheimer’s disease (AD), and data on the increased small heat-shock proteins (sHSP) expression in this disease, it seemed justified to assess humoral response against sHSP in AD patients. The aim of the study was to check whether AD has the ability to elicit immune response against small HSP, which could also serve as disease biomarkers. IgG and IgM autoantibodies against alpha B-crystallin and anti-HSP 60 IgG autoantibodies were assessed in 59 AD patients and 59 healthy subjects. Both IgM and IgG autoantibodies against alpha B-crystallin in AD patients were significantly higher compared to healthy controls (p < 0.05). No statistically significant differences were found between AD patients and healthy subjects were found in anti-HSP60 IgG autoantibody titers (p = 0.29). Anti-HSP60 antibodies present in AD patients may indeed belong to natural human immune repertoire, and chronic neurodegenerative process does not have significant inducing effect on the systemic immunoreactivity against HSP60. Increased titers of IgM and IgG autoantibodies against alpha B-crystallin in AD patients may reflect activation of humoral immune response in the course of this chronic disease, probably secondary to its increased expression. Further prospective studies, on larger group of AD patients and measuring a change in antibodies titers with disease progression are necessary to assess the exact role of these antibodies in AD.

Selective targeting of the stress chaperome as a therapeutic strategy

Normal cellular function is maintained by coordinated proteome machinery that performs a vast array of activities. Helping the proteome in such roles is the chaperome, a network of molecular chaperones and folding enzymes. The stressed cell contains, at any time, a complex mixture of chaperome complexes; a majority performs 'housekeeping functions' similarly to non-stressed, normal cells, but a finely-tuned fraction buffers the proteome altered by chronic stress. The stress chaperome is epigenetically distinct from its normal, housekeeping counterpart, providing a basis for its selective targeting by small molecules. We discuss here the development of chaperome inhibitors, and how agents targeting chaperome members in stressed cells are in fact being directed towards chaperome complexes, and their effect is therefore determined by their ability to sample and engage such complexes. A new approach is needed to target and implement chaperome modulators in the investigation of diseases, and we propose that the classical thinking in drug discovery needs adjustment when developing chaperome-targeting drugs.

GTP binding controls complex formation by the human ROCO protein MASL1

The human ROCO proteins are a family of multi-domain proteins sharing a conserved ROC-COR supra-domain. The family has four members: leucine-rich repeat kinase 1 (LRRK1), leucine-rich repeat kinase 2 (LRRK2), death-associated protein kinase 1 (DAPK1) and malignant fibrous histiocytoma amplified sequences with leucine-rich tandem repeats 1 (MASL1). Previous studies of LRRK1/2 and DAPK1 have shown that the ROC (Ras of complex proteins) domain can bind and hydrolyse GTP, but the cellular consequences of this activity are still unclear. Here, the first biochemical characterization of MASL1 and the impact of GTP binding on MASL1 complex formation are reported. The results demonstrate that MASL1, similar to other ROCO proteins, can bind guanosine nucleotides via its ROC domain. Furthermore, MASL1 exists in two distinct cellular complexes associated with heat shock protein 60, and the formation of a low molecular weight pool of MASL1 is modulated by GTP binding. Finally, loss of GTP enhances MASL1 toxicity in cells. Taken together, these data point to a central role for the ROC/GTPase domain of MASL1 in the regulation of its cellular function.

APL-1, an altered peptide ligand derived from human heat-shock protein 60, selectively induces apoptosis in activated CD4+ CD25+ T cells from peripheral blood of rheumatoid arthritis patients

Rheumatoid arthritis (RA) is a chronic T-cell mediated autoimmune disease that affects primarily the joints. The induction of immune tolerance through antigen-specific therapies for the blockade of pathogenic CD4+ T cells constitutes a current focus of research. In this focus it is attempted to simultaneously activate multiple regulatory mechanisms, such as: apoptosis and regulatory T cells (Tregs). APL-1 is an altered peptide ligand derived from a novel CD4+ T-cell epitope of human heat-shock protein of 60kDa, an autoantigen involved in the pathogenesis of RA. Previously, we have reported that APL-1 induces CD4+ CD25(high)Foxp3+ Tregs in several systems. Here, we investigated the ability of APL-1 in inducing apoptosis in PBMCs from RA patients, who were classified as active or inactive according to their DAS28 score. APL-1 decreased the viability of PBMCs from active but not from inactive patients. DNA fragmentation assays and typical morphological features clearly demonstrated that APL-1 induced apoptosis in these cells. Activated CD4+ CD25+ T cells but not resting CD4+ CD25- T cells were identified as targets of APL-1. Furthermore, CD4+ T-cell responses to APL-1 were found to be dependent on antigen presentation via the HLA-DR molecule. Thus, APL-1 is a regulatory CD4+ T cell epitope which might modulate inflammatory immune responses in PBMCs from RA patients by inducing CD4+ CD25(high)Foxp3+ Tregs and apoptosis in activated CD4+ T cells. These results support further investigation of this candidate drug for the treatment of RA.

Hyperglycaemia and oxidative stress upregulate HSP60 & HSP70 expression in HeLa cells

Heat Shock Proteins 60 & 70 (HSP60 & HSP70) are intracellular protein that has been shown to be present at elevated levels in systemic circulation in Type 2 Diabetes mellitus (T2DM) patients. Conditions that lead to its secretion, and the mechanism of its translocation from cells, have not yet been defined. The aim of this study was to determine if specific cell stressors associated with T2DM, namely hyperglycaemia and oxidative stress, result in the upregulation of HSP60 in human cells in vitro. Human HeLa cells were grown in media supplemented with 100 mM glucose, 200 μM hydrogen peroxide (H₂O₂), and 50 μM sodium azide. Initially, the effect of these treatments on cell growth rate was examined, with each treatment significantly inhibiting growth rate. LDH and MTT assays were also used to successfully demonstrate that these treatments do not significantly increase cell lysis, but do significantly impair mitochondrial dehydrogenase activity. To confirm this mitochondria specific form of inhibition, DCFDA assay were used to investigate any increases in intracellular reactive oxygen species (ROS) generation. All three treatments resulted in significantly increased ROS generation, with greater ROS production occurring with a greater exposure time. Interestingly, when the protein levels of HSP60 and HSP70 were measured after 3 and 7 days of exposure of the HeLa cells to 100 mM glucose, 200 μM H₂O₂, and 50 μM sodium azide significant induction of these two molecular stress proteins were observed ranging from 2.43-5.08 fold compared to untreated control cells.

Light activation of the insulin receptor regulates mitochondrial hexokinase. A possible mechanism of retinal neuroprotection

The serine/threonine kinase Akt has been shown to mediate the anti-apoptotic activity through hexokinase (HK)-mitochondria interaction. We previously reported that Akt activation in retinal rod photoreceptor cells is mediated through the light-dependent insulin receptor (IR)/PI3K pathway. Our data indicate that light-induced activation of IR/PI3K/Akt results in the translocation of HK-II to mitochondria. We also found that PHLPPL, a serine/threonine phosphatase, enhanced the binding of HK-II to mitochondria. We found a mitochondrial targeting signal in PHLPPL and our study suggests that Akt translocation to mitochondria could be mediated through PHLPPL. Our results suggest that the light-dependent IR/PI3K/Akt pathway regulates hexokinase-mitochondria interaction in photoreceptors. Down-regulation of IR signaling has been associated with ocular diseases of retinitis pigmentosa, diabetic retinopathy, and Leber Congenital Amaurosis-type 2, and agents that enhance the binding interaction between hexokinase and mitochondria may have therapeutic potential against these ocular diseases.