Examination of KNK437- and quercetin-mediated inhibition of heat shock-induced heat shock protein gene expression in Xenopus laevis cultured cells

Mode of Action of Heat Shock Protein (HSP) Inhibitors against Viruses through Host HSP and Virus Interactions

Misfolded proteins after stress-induced denaturation can regain their functions through correct re-folding with the aid of molecular chaperones. As a molecular chaperone, heat shock proteins (HSPs) can help client proteins fold correctly. During viral infection, HSPs are involved with replication, movement, assembly, disassembly, subcellular localization, and transport of the virus via the formation of macromolecular protein complexes, such as the viral replicase complex. Recent studies have indicated that HSP inhibitors can inhibit viral replication by interfering with the interaction of the virus with the HSP. In this review, we describe the function and classification of HSPs, the transcriptional mechanism of HSPs promoted by heat shock factors (HSFs), discuss the interaction between HSPs and viruses, and the mode of action of HSP inhibitors at two aspects of inhibiting the expression of HSPs and targeting the HSPs, and elaborate their potential use as antiviral agents.

A flavonoid, quercetin, is capable of enhancing long-term memory formation if encountered at different times in the learning, memory formation, and memory recall continuum

A major extrinsic factor influencing memory and neuro-cognitive performances across taxa is diet. Studies from vertebrates have shown the effects of a flavonoid rich diet on cognitive performance, but the mechanism underlying this action is still poorly understood. A common and abundant flavonoid present in numerous food substances is quercetin (Q). The present study provides the first support for Q-modulated enhancement of cognitive function in an invertebrate model, the pond snail Lymnaea stagnalis, after an operant conditioning procedure. We found that when snails were exposed to Q 3 h before or after a single 0.5 h training session, which typically results in memory lasting ~ 3 h, they formed a long-term memory (LTM) lasting for at least 24 h. Additionally, we assessed the effects of the combined presentation of a single reinforcing stimulus (at 24 h post-training or 24 h before training) and Q-exposure on both LTM formation and reconsolidation. That is, when applied within 3 h of critical periods of memory, Q regulates four different phases: (1) acquisition (i.e., a learning event), (2) consolidation processes after acquisition, (3) memory recall, and (4) memory reconsolidation. In all these phases Q-exposure enhanced LTM persistence.

To eat or not to eat: a Garcia effect in pond snails (Lymnaea stagnalis)

Taste aversion learning is universal. In animals, a single presentation of a novel food substance followed hours later by visceral illness causes animals to avoid that taste. This is known as bait-shyness or the Garcia effect. Humans demonstrate this by avoiding a certain food following the development of nausea after ingesting that food ('Sauce Bearnaise effect'). Here, we show that the pond snail Lymnaea stagnalis is capable of the Garcia effect. A single 'pairing' of a novel taste, a carrot slurry followed hours later by a heat shock stressor (HS) is sufficient to suppress feeding response elicited by carrot for at least 24 h. Other food tastes are not suppressed. If snails had previously been exposed to carrot as their food source, the Garcia-like effect does not occur when carrot is 'paired' with the HS. The HS up-regulates two heat shock proteins (HSPs), HSP70 and HSP40. Blocking the up-regulation of the HSPs by a flavonoid, quercetin, before the heat shock, prevented the Garcia effect in the snails. Finally, we found that snails exhibit Garcia effect following a period of food deprivation but the long-term memory (LTM) phenotype can be observed only if the animals are tested in a food satiated state.

Cytoprotective effect of eupatilin against indomethacin-induced damage in feline esophageal epithelial cells: relevance of HSP27 and HSP70

Indomethacin is a non-steroidal anti-inflammatory drug with clearly known side effects on the gastrointestinal tract. The purpose of the present study was to investigate whether eupatilin inhibit cell injury induced by indomethacin in cultured feline esophageal epithelial cells (EECs). EECs were used to investigate the ability of eupatilin to induce the expression of heat shock proteins (HSP27 and HSP70) and analyze its cytoprotective effect against indomethacin-induced damage. The treatment of EECs with indomethacin for 8 h decreased cell viability. Western blot analysis showed that the levels of HSPs gradually decreased in cells treated with indomethacin, while eupatilin treatment increased the levels of HSPs. When treated with both indomethacin and eupatilin, the levels of HSPs increased rapidly, and were maintained at 130-140%. In addition, treatment with the specific inhibitors of PTK, PKC, PLC, p38 MAPK, JNKs, and PI3K attenuated the eupatilin-induced expression of HSPs. Pretreatment of EECs with the inhibitors of protein synthesis, actinomycin D or cycloheximide, attenuated the cytoprotective effect of eupatilin on indomethacin-induced cell damage. Reactive oxygen species production was upregulated by indomethacin, but downregulated by eupatilin. Taken together, it was suggested that HSPs were partly responsible for the eupatilin-mediated cytoprotective activity against the indomethacin-induced damage in EECs.

Role of MAPKs in HSP70's Protection against Heat Stress-Induced Injury in Rat Small Intestine

Aim

To evaluate the role of heat shock protein 70 (HSP70) on the MAPK pathway activation with quercetin treatment and its protection against small intestine impairments of heat stressed rats.

Methods

Forty-eight male Sprague-Dawley rats aged 6 weeks were randomized to three groups (n=16/group), namely, control (CON), heat stress (HS), and heat stress + quercetin (HQ). The experiment lasted for 14 days with daily 50 min of heat stress treatment (43°C) for the HS and HQ groups. Rats of HQ group were intragastrically given 0.5 ml quercetin solution (50 mg/kg body weight) before the heat stress treatment. Half of the animals were sacrificed on day 7 and the rest on day 14 for tissue sampling. Intestinal morphology, small intestine morphology and permeability, protein expression of HSP70, phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), and caspase-3 activity were examined.

Results

Heat stress caused morphological damage to the small intestine and increased intestinal permeability. HSP70 expression and MAPK activity in the small intestine were increased by heat stress. Inhibition of HSP70 by quercetin did not change intestinal permeability compared with the HS group but aggravated intestinal injury and affected the activation of MAPKs and caspase-3.

Conclusions

HSP70 may modulate stress-activated signaling and acts in a protective manner via MAPK signaling. Affecting HSP70 protective mechanisms could be useful for protection against heat stress-induced injury in rat small intestine.

Effect of isothiocyanates, BITC and PEITC, on stress protein accumulation, protein aggregation and aggresome-like structure formation in Xenopus A6 kidney epithelial cells

Numerous studies have elucidated the health benefits of organosulfur compounds, known as isothiocyanates (ITCs), derived from cruciferous vegetables. As electrophiles, ITCs have the ability to directly bind and modify thiol-containing compounds such as glutathione and cellular protein, including tubulin. While the biochemical effects of ITCs have been well characterized, less information is available regarding their effects on the accumulation of stress-inducible heme oxygenase-1 (HO-1), heat shock proteins (HSPs) and the possible formation of aggregated protein due to thiol modification. The present study has examined the effect of the ITCs, benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC), on the accumulation of HO-1, HSP70 and HSP30 in Xenopus laevis A6 kidney epithelial cells. Immunoblot analysis revealed that both BITC and PEITC induced the accumulation of HO-1 and HSP70 whereas HSP30 levels were enhanced only in cells treated with BITC. Immunocytochemistry determined that ITC treatment induced F-actin disorganization and membrane ruffling and enhanced accumulation of HO-1 in the cytoplasm. Additionally, BITC induced enhanced levels of ubiquitinated protein, aggregated protein, and the collapse and fragmentation of microtubules. In comparison, treatment of cells with the proteasomal inhibitor, MG132, induced the accumulation of all three stress proteins, aggregated protein and aggresome-like structures. Finally, cells pretreated with BITC inhibited the formation of MG132-induced aggresome-like structures in the perinuclear region. This latter finding suggests that BITC-induced microtubule fragmentation may impede the movement of aggregated protein via microtubules and their subsequent coalescence into aggresome-like structures in the perinuclear region.

Heat shock response and shape regulation during newt tail regeneration

Regenerating newt tail has recently been found to react to hypergravity in a stable and reproducible way - by curving downwards. Such morphogenetic effect of non-specific physical factor applied to a complex structure of an adult animal is a rare phenomenon with unknown molecular basis. For the first steps of unraveling this basis we've chosen heat shock proteins (HSPs) as promising candidates. Morphometrical analysis of tail regeneration was performed in aquarium (control), on substrate (relative hypergravity) and in aquarium under weekly application of heat shock. HSPs were inhibited pharmacologically during regeneration in aquarium and on substrate. Hsp70, 90 gene expression and protein localization were analyzed in the studied conditions. Weekly application of heat shock to newts regenerating tails in otherwise normal conditions led to development of curved tails (both upwards and downwards), suggesting that similar mechanisms are at play in both hypergravity-altered and heat shock-altered morphogenesis. Heat shock protein inhibitor KNK437 didn't affect tail shape during normal regeneration, but prevented the formation of tail curve in appropriate conditions. It was shown that HSP70 and HSP90 proteins are present in muscle and connective tissue of intact tails as well as regenerates, but only appear in epidermis in hypergravity-altered regenerates and heated tails. Based on our data, we hypothesize, that different external factors (e.g. hypergravity and heat shock) are received, analyzed and transmitted further to affect morphogenesis by similar mechanisms that utilize a set of HSP in epidermal cells.

Effect of varicocelectomy treatment on spermatogenesis and apoptosis via the induction of heat shock protein 70 in varicocele‑induced rats

In the current study, the hypothesis that testicular varicocelectomy improves spermatogenesis and attenuates apoptosis via the induction of heat shock protein 70 (Hsp70) in a rat model of varicocele was investigated. Adult male Wistar rats (n=75) were randomly divided into 5 groups of 15 each: Control, sham, varicocele, varicocelectomy, and varicocelectomy plus Quercetin. A total of 6 weeks after the varicocelectomy, the left testis of all rats was removed for subsequent examination. Histological changes were compared between the groups. The expression of Hsp70 and apoptosis‑associated indicators were evaluated based on immunohistochemical, western blot and mRNA expression analyses. Compared with the varicocele group, the varicocelectomy group exhibited a markedly reduced Bcl‑2‑associated X protein/B‑cell lymphoma 2 (Bax/Bcl‑2) ratio, and had a decreased expression of caspase‑9, cytochrome c (cyt c) and caspase‑3 through the intrinsic signal transduction pathways. Quercetin treatment inhibited the protective effects of varicocelectomy. The expression of Hsp70 was increased in the varicocele group which was further elevated by the varicocelectomy. These results indicated that varicocelectomy can reduce the Bax/Bcl‑2 ratio, and decrease the levels of caspase‑9, cyt c and caspase‑3 via the mitochondrial signal transduction pathway. Such protective effects on left testis spermatogenesis and against apoptosis may be due to the induction of Hsp70. The findings of the present study suggested that varicocelectomy has a clear advantage in protecting testicular function and ameliorating spermatogenic cells apoptosis.

Characterization of cadmium chloride-induced BiP accumulation in Xenopus laevis A6 kidney epithelial cells

Endoplasmic reticulum (ER) stress can result in the accumulation of unfolded/misfolded protein in the ER lumen, which can trigger the unfolded protein response (UPR) resulting in the activation of various genes including immunoglobulin-binding protein (BiP; also known as glucose-regulated protein 78 or HSPA5). BiP, an ER heat shock protein 70 (HSP70) family member, binds to unfolded protein, inhibits their aggregation and re-folds them in an ATP-dependent manner. While cadmium, an environmental contaminant, was shown to induce the accumulation of HSP70 in vertebrate cells, less information is available regarding the effect of this metal on BiP accumulation or function. In this study, cadmium chloride treatment of Xenopus laevis A6 kidney epithelial cells induced a dose- and time-dependent increase in BiP, HSP70 and heme oxygenase-1 (HO-1) accumulation. Exposure of cells to a relatively low cadmium concentration at a mild heat shock temperature of 30°C greatly enhanced BiP and HSP70 accumulation compared to cadmium at 22°C. Treatment of cells with the glutathione synthesis inhibitor, buthionine sulfoximine, enhanced cadmium-induced BiP and HSP70 accumulation. Immunocytochemistry revealed that cadmium-induced BiP accumulation occurred in a punctate pattern in the perinuclear region. In some cells treated with cadmium chloride or the proteasomal inhibitor, MG132, large BiP complexes were observed that co-localized with aggregated protein or aggresome-like structures. These BiP/aggresome-like structures were also observed in cells treated simultaneously with cadmium at 30°C or in the presence of buthionine sulfoximine. In amphibians, the association of BiP with unfolded protein and its possible role in aggresome function may be vital in the maintenance of cellular proteostasis.

The expression and function of hsp30-like small heat shock protein genes in amphibians, birds, fish, and reptiles

Small heat shock proteins (sHSPs) are a superfamily of molecular chaperones with important roles in protein homeostasis and other cellular functions. Amphibians, reptiles, fish and birds have a shsp gene called hsp30, which was also referred to as hspb11 or hsp25 in some fish and bird species. Hsp30 genes, which are not found in mammals, are transcribed in response to heat shock or other stresses by means of the heat shock factor that is activated in response to an accumulation of unfolded protein. Amino acid sequence analysis revealed that representative HSP30s from different classes of non-mammalian vertebrates were distinct from other sHSPs including HSPB1/HSP27. Studies with amphibian and fish recombinant HSP30 determined that they were molecular chaperones since they inhibited heat- or chemically-induced aggregation of unfolded protein. During non-mammalian vertebrate development, hsp30 genes were differentially expressed in selected tissues. Also, heat shock-induced stage-specific expression of hsp30 genes in frog embryos was regulated at the level of chromatin structure. In adults and/or tissue culture cells, hsp30 gene expression was induced by heat shock, arsenite, cadmium or proteasomal inhibitors, all of which enhanced the production of unfolded/damaged protein. Finally, immunocytochemical analysis of frog and chicken tissue culture cells revealed that proteotoxic stress-induced HSP30 accumulation co-localized with aggresome-like inclusion bodies. The congregation of damaged protein in aggresomes minimizes the toxic effect of aggregated protein dispersed throughout the cell. The current availability of probes to detect the presence of hsp30 mRNA or encoded protein has resulted in the increased use of hsp30 gene expression as a marker of proteotoxic stress in non-mammalian vertebrates.

Heat shock protein inhibitor, quercetin, as a novel adjuvant agent to improve radiofrequency ablation-induced tumor destruction and its molecular mechanism

BACKGROUND

We investigated the effect of a small molecular inhibitor of heat shock protein (HSP), quercetin, on tumor radiofrequency (RF) ablation, and explored the underlying molecular mechanisms.

METHODS

In in vivo study, rats with R3230 breast adenocarcinoma were sacrificed 24 h post-treatment and gross coagulation areas were compared, and next, randomized into four treatment arms (control, quercetin alone, RF alone, and combination) for Kaplan-Meier analysis of defined endpoint survival. Then the distribution and expression levels of heat shock protein 70 (HSP70), cleaved caspase-3 and heat shock factor 1 (HSF1) were analyzed after different treatments. In in vitro study, we used quercetin to promote SK-HEP-1 (hepatic) and MCF-7 (breast) cancer cell apoptosis in heat shock cell model, and siRNA was used to block c-Jun and to explore the role of activating protein-1 (AP-1) signaling pathways.

RESULTS

We found the effects of quercetin plus RFA resulted in increase on the tumor destruction/endpoint survival (26.5±3.4 d) in vivo, compared with RF alone (17.6±2.5 d) and quercetin alone (15.7±3.1 d). Most importantly, quercetin-induced cancer cell death required the presence of HSF1 in animal model. Furthermore, quercetin directly down-regulated expression of HSF1 in vitro, which our findings have revealed, required the activation of AP-1 signaling pathways by loss-of-function analysis using siRNA mediated targeting of c-Jun.

CONCLUSIONS

These results indicated a protective role of quercetin in tumor ablation and highlighted a novel mechanism involving HSP70 with HSF1 pathway in thermal ablation of solid tumors.

Baculovirus IE2 Stimulates the Expression of Heat Shock Proteins in Insect and Mammalian Cells to Facilitate Its Proper Functioning

Baculoviruses have gained popularity as pest control agents and for protein production in insect systems. These viruses are also becoming popular for gene expression, tissue engineering and gene therapy in mammalian systems. Baculovirus infection triggers a heat shock response, and this response is crucial for its successful infection of host insect cells. However, the viral protein(s) or factor(s) that trigger this response are not yet clear. Previously, we revealed that IE2-an early gene product of the baculovirus-could form unique nuclear bodies for the strong trans-activation of various promoters in mammalian cells. Here, we purified IE2 nuclear bodies from Vero E6 cells and investigated the associated proteins by using mass spectrometry. Heat shock proteins (HSPs) were found to be one of the major IE2-associated proteins. Our experiments show that HSPs are greatly induced by IE2 and are crucial for the trans-activation function of IE2. Interestingly, blocking both heat shock protein expression and the proteasome pathway preserved the IE2 protein and its nuclear body structure, and revived its function. These observations reveal that HSPs do not function directly to assist the formation of the nuclear body structure, but may rather protect IE2 from proteasome degradation. Aside from functional studies in mammalian cells, we also show that HSPs were stimulated and required to determine IE2 protein levels, in insect cells infected with baculovirus. Upon inhibiting the expression of heat shock proteins, baculovirus IE2 was substantially suppressed, resulting in a significantly suppressed viral titer. Thus, we demonstrate a unique feature in that IE2 can function in both insect and non-host mammalian cells to stimulate HSPs, which may be associated with IE2 stabilization and lead to the protection of the its strong gene activation function in mammalian cells. On the other hand, during viral infection in insect cells, IE2 could also strongly stimulate HSPs and ultimately affect viral replication.

Unraveling Main Limiting Sites of Photosynthesis under Below- and Above-Ground Heat Stress in Cucumber and the Alleviatory Role of Luffa Rootstock

Photosynthesis is one of the most thermo-sensitive processes in plants. Although the severity of heat stress could be attenuated by grafting approach, the primary damaged site of photosynthesis system under heat stress and the regulatory mechanism of rootstock-mediated heat tolerance are poorly understood. In the current study, cucumber plants grafted onto their own roots and heat-tolerant luffa roots were exposed to root-zone heat (25/40°C) and aerial heat (40/25°C) individually and in combination (40/40°C) to understand the response of photosynthetic process by investigating energy absorption and distribution, electron transport in photosystem (PS) II and I, and CO2 assimilation. According to the results, root-zone heat stress inhibited photosynthesis mainly through decreasing Rubisco activity, while aerial heat stress mainly through inhibiting PSII acceptor side. The imbalance in light absorption and utilization resulted in accumulation of reactive oxygen species that caused damage to photosynthetic apparatus, forming a vicious cycle. On the contrary, grafting cucumber onto heat-tolerant luffa rootstock alleviated heat-induced photosynthetic inhibition and oxidative stress by maintaining higher root vitality, HSP70 accumulation, and antioxidant potential.

An in vitro model to consider the effect of 2 mM glutamine and KNK437 on endotoxin-stimulated release of heat shock protein 70 and inflammatory mediators

OBJECTIVE

Glutamine has been shown to promote the release of heat shock protein 70 (HSP70) both within experimental in vitro models of sepsis and in adults with septic shock. This study aimed to investigate the effects of 2 mM glutamine and an inhibitor of HSP70 (KNK437) on the release of HSP70 and inflammatory mediators in healthy adult volunteers.

METHODS

An in vitro whole blood endotoxin stimulation assay was used.

RESULTS

The addition of 2 mM glutamine significantly increased HSP70 levels over time (P < 0.05). HSP70 release had a positive correlation at 4 h with IL-1 β (r = 0.51, P = 0.03) and an inverse correlation with TNF-α (r = -0.56, P = 0.02) and IL-8 levels (r = -0.52, P = 0.03), and there were no significant correlations between HSP70 and IL6 or IL-10 or glutamine. Glutamine supplementation significantly (P < 0.05) attenuated the release of IL-10 at 4 h and IL-8 at 24 h, compared with conditions without glutamine. In endotoxin-stimulated blood there were no significant differences in the release of IL-6, TNF-α, and IL-1 β with glutamine supplementation at 4 and 24 h. However, glutamine supplementation (2 mM) appeared to attenuate the release of inflammatory mediators (IL-1 β, IL-6, TNF-α), although this effect was not statistically significant. The addition of KNK437, a HSP70 inhibitor, significantly diminished HSP70 release, which resulted in lower levels of inflammatory mediators (P < 0.05).

CONCLUSION

Glutamine supplementation promotes HSP70 release in an experimental model of sepsis. After the addition of KNK437, the effects of glutamine on HSP70 and inflammatory mediator release appear to be lost, suggesting that HSP70 in part orchestrates the inflammatory mediator response to sepsis. The clinical implications require further investigation.

Expression profile of heat shock response factors during hookworm larval activation and parasitic development

When organisms are exposed to an increase in temperature, they undergo a heat shock response (HSR) regulated by the transcription factor heat shock factor 1 (HSF-1). The heat shock response includes the rapid changes in gene expression initiated by binding of HSF-1 to response elements in the promoters of heat shock genes. Heat shock proteins function as molecular chaperones to protect proteins during periods of elevated temperature and other stress. During infection, hookworm infective third stage larvae (L3) undergo a temperature shift from ambient to host temperature. This increased temperature is required for the resumption of feeding and activation of L3, but whether this increase initiates a heat shock response is unknown. To investigate the role of the heat shock in hookworm L3 activation and parasitic development, we identified and characterized the expression profile of several components of the heat shock response in the hookworm Ancylostoma caninum. We cloned DNAs encoding an hsp70 family member (Aca-hsp-1) and an hsp90 family member (Aca-daf-21). Exposure to a heat shock of 42°C for one hour caused significant up-regulation of both genes, which slowly returned to near baseline levels following one hour attenuation at 22°C. Neither gene was up-regulated in response to host temperature (37°C). Conversely, levels of hsf-1 remained unchanged during heat shock, but increased in response to incubation at 37°C. During activation, both hsp-1 and daf-21 are down regulated early, although daf-21 levels increase significantly in non-activated control larvae after 12h, and slightly in activated larvae by 24h incubation. The heat shock response modulators celastrol and KNK437 were tested for their effects on gene expression during heat shock and activation. Pre-incubation with celastrol, an HSP90 inhibitor that promotes heat shock gene expression, slightly up-regulated expression of both hsp-1 and daf-21 during heat shock. KNK437, an inhibitor of heat shock protein expression, slightly down regulated both genes under similar conditions. Both modulators inhibited activation-associated feeding, but neither had an effect on hsp-1 levels in activated L3 at 16h. Both celastrol and KNK437 prevent the up-regulation of daf-21 and hsf-1 seen in non-activated control larvae during activation, and significantly down regulated expression of the HSF-1 negative regulator Aca-hsb-1 in activated larvae. Expression levels of heat shock response factors were examined in developing Ancylostoma ceylanicum larvae recovered from infected hosts and found to differ significantly from the expression profile of activated L3, suggesting that feeding during in vitro activation is regulated differently than parasitic development. Our results indicate that a classical heat shock response is not induced at host temperature and is suppressed during larval recovery and parasitic development in the host, but a partial heat shock response is induced after extended incubation at host temperature in the absence of a developmental signal, possibly to protect against heat stress.

Ischemic postconditioning prevents renal ischemia reperfusion injury through the induction of heat shock proteins in rats

Ischemic postconditioning (IPo) attenuates ischemia-reperfusion injuries (IRI) in various organs, of both animals and humans. This study tested the hypothesis that IPo attenuates renal IRI through the upregulation of heat shock protein (HSP)70, HSP27 and heme oxygenase-1 (HO-1, also known as HSP 32) expression. Adult Sprague Dawley rats were subjected to bilateral renal ischemia for 45 min followed by reperfusion for up to 48 h. One group of rats received IPo prior to restoring full perfusion. Another group was administered 100 mg/kg HSP inhibitor quercetin, injected intraperitoneally 1 h prior to ischemia. Control rats received sham operations. Renal IR resulted in severe morphological and pathological changes, with increased serum creatinine and blood urea nitrogen concentrations. IR resulted in increased inflammation by inducing plasma tumor necrosis factor-α and renal nuclear factor kappa-light-chain-enhancer of activated B cells expression. IR also increased lipid peroxidation, as indicated by elevated malondialdehyde content, reduced superoxide dismutase activity and increased renal apoptosis. Renal HSP70, HSP27 and HO-1 mRNA and protein levels were increased by IR and further elevated by IPo. IPo attenuated these changes observed in pathology, lipid peroxidation, apoptosis and inflammation. Quercetin treatment abolished all the protective effects of IPo. In conclusion, this study showed that IPo can attenuate lipid peroxidation, apoptosis and inflammation as well as renal IRI by upregulating the expression of HSP70, HSP27 and HO-1.

Heat shock protein 70 induction by valproic acid delays photoreceptor cell death by N-methyl-N-nitrosourea in mice

Retinal degenerative diseases (RDs) are a group of inherited diseases characterized by the loss of photoreceptor cells. Selective photoreceptor loss can be induced in mice by an intraperitoneal injection of N-methyl-N-nitrosourea (MNU) and, because of its selectivity, this model is widely used to study the mechanism of RDs. Although it is known that calcium-calpain activation and lipid peroxidation are involved in the initiation of cell death, the precise mechanisms of this process remain unknown. Heat shock protein 70 (HSP70) has been shown to function as a chaperone molecule to protect cells against environmental and physiological stresses. In this study, we investigated the role of HSP70 on photoreceptor cell death in mice. HSP70 induction by valproic acid, a histone deacetylase inhibitor, attenuated the photoreceptor cell death by MNU through inhibition of apoptotic caspase signals. Furthermore, HSP70 itself was rapidly and calpain-dependently cleaved after MNU treatment. Therefore, HSP70 induction by valproic acid was dually effective against MNU-induced photoreceptor cell loss as a result of its anti-apoptotic actions and its ability to prevent HSP70 degradation. These findings might help lead us to a better understanding of the pathogenic mechanism of RDs. Retinal degenerative diseases are characterized by the loss of photoreceptor cells. We proposed the following cascade for N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell death: MNU gives rise to cleavage of heat shock protein 70 (HSP70); HSP70 induction by valproic acid (VPA) is dually effective against MNU-induced photoreceptor cell loss because of its anti-apoptotic actions and its ability to prevent HSP70 degradation. We hope that the present study heralds a new era in developing therapeutic tools against retinal degenerative diseases.

Enhanced HSP30 and HSP70 accumulation in Xenopus cells subjected to concurrent sodium arsenite and cadmium chloride stress

Heat shock proteins (HSPs) are molecular chaperones that aid in protein folding, translocation and in preventing stress-induced protein aggregation. The present study examined the effect of simultaneous sodium arsenite and cadmium chloride treatment on the pattern of HSP30 and HSP70 accumulation in A6 kidney epithelial cells of the frog, Xenopus laevis. Immunoblot analysis revealed that HSP30 and HSP70 accumulation in concurrent stressor treatments were significantly higher than the sum of HSP30 or HSP70 accumulation in individual treatments. This finding suggested a synergistic action between sodium arsenite and cadmium chloride. KNK437 inhibitor studies indicated that the combined stressor-induced accumulation of HSPs may be regulated, at least in part, at the level of transcription. Immunocytochemistry revealed that simultaneous treatment of cells with the two stressors induced HSP30 accumulation primarily in the cytoplasm in a punctate pattern with some dysregulation of F-actin structure. Increased ubiquitinated protein accumulation was observed with combined sodium arsenite and cadmium chloride treatment compared to individual stressors suggesting an impairment of the ubiquitin proteasome degradation system. The addition of a mild heat shock further enhanced the accumulation of HSP30 and HSP70 in response to relatively low concentrations of sodium arsenite plus cadmium chloride.

Recruitment of the host plant heat shock protein 70 by Tomato yellow leaf curl virus coat protein is required for virus infection

A functional capsid protein (CP) is essential for host plant infection and insect transmission of Tomato yellow leaf curl virus (TYLCV) and other monopartite begomoviruses. We have previously shown that TYLCV CP specifically interacts with the heat shock protein 70 (HSP70) of the virus insect vector, Bemisia tabaci. Here we demonstrate that during the development of tomato plant infection with TYLCV, a significant amount of HSP70 shifts from a soluble form into insoluble aggregates. CP and HSP70 co-localize in these aggregates, first in the cytoplasm, then in the nucleus of cells associated with the vascular system. CP-HSP70 interaction was demonstrated by co-immunopreciptation in cytoplasmic - but not in nuclear extracts from leaf and stem. Inhibition of HSP70 expression by quercetin caused a decrease in the amount of nuclear CP aggregates and a re-localization of a GFP-CP fusion protein from the nucleus to the cytoplasm. HSP70 inactivation resulted in a decrease of TYLCV DNA levels, demonstrating the role of HSP70 in TYLCV multiplication in planta. The current study reveals for the first time the involvement of plant HSP70 in TYLCV CP intracellular movement. As described earlier, nuclear aggregates contained TYLCV DNA-CP complexes and infectious virions. Showing that HSP70 localizes in these large nuclear aggregates infers that these structures operate as nuclear virus factories.

Withaferin A induces proteasome inhibition, endoplasmic reticulum stress, the heat shock response and acquisition of thermotolerance

In the present study, withaferin A (WA), a steroidal lactone with anti-inflammatory and anti-tumor properties, inhibited proteasome activity and induced endoplasmic reticulum (ER) and cytoplasmic HSP accumulation in Xenopus laevis A6 kidney epithelial cells. Proteasomal inhibition by WA was indicated by an accumulation of ubiquitinated protein and a decrease in chymotrypsin-like activity. Additionally, immunoblot analysis revealed that treatment of cells with WA induced the accumulation of HSPs including ER chaperones, BiP and GRP94, as well as cytoplasmic/nuclear HSPs, HSP70 and HSP30. Furthermore, WA-induced an increase in the relative levels of the protein kinase, Akt, while the levels of actin were unchanged compared to control. Northern blot experiments determined that WA induced an accumulation in bip, hsp70 and hsp30 mRNA but not eIF-1α mRNA. Interestingly, WA acted synergistically with mild heat shock to enhance HSP70 and HSP30 accumulation to a greater extent than the sum of both stressors individually. This latter phenomenon was not observed with BiP or GRP94. Immunocytochemical analysis indicated that WA-induced BiP accumulation occurred mainly in the perinuclear region in a punctate pattern, while HSP30 accumulation occurred primarily in a granular pattern in the cytoplasm with some staining in the nucleus. Prolonged exposure to WA resulted in disorganization of the F-actin cytoskeleton as well as the production of relatively large HSP30 staining structures that co-localized with F-actin. Finally, prior exposure of cells to WA treatment, which induced the accumulation of HSPs conferred a state of thermal protection since it protected the F-actin cytoskeleton against a subsequent cytotoxic thermal challenge.

Sodium arsenite and cadmium chloride induction of proteasomal inhibition and HSP accumulation in Xenopus laevis A6 kidney epithelial cells

Sodium arsenite (NA) and cadmium chloride (CdCl(2)) are relatively abundant environmental toxicants that have multiple toxic effects including carcinogenesis, dysfunction of gene regulation and DNA and protein damage. In the present study, treatment of Xenopus laevis A6 kidney epithelial cells with concentrations of NA (20-30 μM) or CdCl(2) (100-200 μM) that induced HSP30 and HSP70 accumulation also produced an increase in the relative levels of ubiquitinated protein. Actin protein levels were unchanged in these experiments. In time course experiments, the levels of ubiquitinated protein and HSPs increased over a 24h exposure to NA or CdCl(2). Furthermore, treatment of cells with NA or CdCl(2) reduced the relative levels of proteasome chymotrypsin (CT)-like activity compared to control. Interestingly, pretreatment of cells with the HSP accumulation inhibitor, KNK437, prior to NA or CdCl(2) exposure decreased the relative levels of ubiquitinated protein as well as HSP30 and HSP70. A similar finding was made with ubiquitinated protein induced by proteasomal inhibitors, MG132 and celastrol, known to induce HSP accumulation in A6 cells. However, the NA- or CdCl(2)-induced decrease in proteasome CT-like activity was not altered by KNK437 pretreatment. This study has shown for the first time in poikilothermic vertebrates that NA and CdCl(2) can inhibit proteasomal activity and that there is a possible association between HSP accumulation and the mechanism of protein ubiquitination.

Proteasome inhibition induces hsp30 and hsp70 gene expression as well as the acquisition of thermotolerance in Xenopus laevis A6 cells

Previous studies have shown that inhibiting the activity of the proteasome leads to the accumulation of damaged or unfolded proteins within the cell. In this study, we report that proteasome inhibitors, lactacystin and carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG132), induced the accumulation of ubiquitinated proteins as well as a dose- and time-dependent increase in the relative levels of heat shock protein (HSP)30 and HSP70 and their respective mRNAs in Xenopus laevis A6 kidney epithelial cells. In A6 cells recovering from MG132 exposure, HSP30 and HSP70 levels were still elevated after 24 h but decreased substantially after 48 h. The activation of heat shock factor 1 (HSF1) may be involved in MG132-induced hsp gene expression in A6 cells since KNK437, a HSF1 inhibitor, repressed the accumulation of HSP30 and HSP70. Exposing A6 cells to simultaneous MG132 and mild heat shock enhanced the accumulation of HSP30 and HSP70 to a much greater extent than with each stressor alone. Immunocytochemical studies determined that HSP30 was localized primarily in the cytoplasm of lactacystin- or MG132-treated cells. In some cells treated with higher concentrations of MG132 or lactacystin, we observed in the cortical cytoplasm (1) relatively large HSP30 staining structures, (2) colocalization of actin and HSP30, and (3) cytoplasmic areas that were devoid of HSP30. Lastly, MG132 treatment of A6 cells conferred a state of thermotolerance such that they were able to survive a subsequent thermal challenge.

The interface between generating renal tubules and a polyester fleece in comparison to the interstitium of the developing kidney

An increasing number of investigations is dealing with the repair of acute and chronic renal failure by the application of stem/progenitor cells. However, accurate data concerning the cell biological mechanisms controlling the process of regeneration are scarce. For that reason new implantation techniques, advanced biomaterials and morphogens supporting regeneration of renal parenchyma are under research. Special focus is directed to structural and functional features of the interface between generating tubules and the surrounding interstitial space. The aim of the present experiments was to investigate structural features of the interstitium during generation of tubules. Stem/progenitor cells were isolated from neonatal rabbit kidney and mounted between layers of a polyester fleece to create an artificial interstitium. Perfusion culture was performed for 13 days in chemically defined Iscove's Modified Dulbecco's Medium containing aldosterone (1 x 10(-7) M) as tubulogenic factor. Recordings of the artificial interstitium in comparison to the developing kidney were performed by morphometric analysis, scanning and transmission electron microscopy. The degree of differentiation was registered by immunohistochemistry. The data reveal that generated tubules are embedded in a complex network of fibers consisting of newly synthesized extracellular matrix proteins. Morphometric analysis further shows that the majority of tubules within the artificial interstitium develops in a surprisingly close distance between 5 and 25 mum to each other. The abundance of synthesized extracellular matrix acts obviously as a spacer keeping generated tubules in distance. For comparison, the same principle of construction is found in the developing parenchyma of the neonatal kidney. Most astonishingly, scanning electron microscopy reveals that the composition of interstitial matrix is not homogeneous but differs along a cortico-medullary axis of proceeding tubule development.

A key role for heat shock protein 70 in the localization and insertion of tombusvirus replication proteins to intracellular membranes

Plus-stranded RNA viruses coopt host proteins to promote their robust replication in infected hosts. Tomato bushy stunt tombusvirus (TBSV) is a model virus that can replicate a small replicon RNA in Saccharomyces cerevisiae and in plants. The tombusvirus replicase complex contains heat shock protein 70 (Hsp70), an abundant cytosolic chaperone, which is required for TBSV replication. To dissect the function of Hsp70 in TBSV replication, in this paper we use an Hsp70 mutant (ssa1 ssa2) yeast strain that supports a low level of TBSV replication. Using confocal laser microscopy and cellular fractionation experiments, we find that the localization of the viral replication proteins changes to the cytosol in the mutant cells from the peroxisomal membranes in wild-type cells. An in vitro membrane insertion assay shows that Hsp70 promotes the integration of the viral replication proteins into subcellular membranes. This step seems to be critical for the assembly of the viral replicase complex. Using a gene-silencing approach and quercetin as a chemical inhibitor to downregulate Hsp70 levels, we also confirm the significance of cytosolic Hsp70 in the replication of TBSV and other plant viruses in a plant host. Taken together, our results suggest that cytosolic Hsp70 plays multiple roles in TBSV replication, such as affecting the subcellular localization and membrane insertion of the viral replication proteins as well as the assembly of the viral replicase.

Comparison of the effect of heat shock factor inhibitor, KNK437, on heat shock- and chemical stress-induced hsp30 gene expression in Xenopus laevis A6 cells

In this study, we compared the effect of KNK437 (N-formyl-3, 4-methylenedioxy-benzylidene-gamma-butyrolactam), a benzylidene lactam compound, on heat shock and chemical stressor-induced hsp30 gene expression in Xenopus laevis A6 kidney epithelial cells. Previously, KNK437 was shown to inhibit HSE-HSF1 binding activity and heat-induced hsp gene expression. In the present study, Northern and Western blot analysis revealed that pretreatment of A6 cells with KNK437 inhibited hsp30 mRNA and HSP30 and HSP70 protein accumulation induced by chemical stressors including sodium arsenite, cadmium chloride and herbimycin A. In A6 cells subjected to sodium arsenite, cadmium chloride, herbimycin A or a 33 degrees C heat shock treatment, immunocytochemistry and confocal microscopy revealed that HSP30 accumulated primarily in the cytoplasm. However, incubation of A6 cells at 35 degrees C resulted in enhanced HSP30 accumulation in the nucleus. Pre-treatment with 100 microM KNK437 completely inhibited HSP30 accumulation in A6 cells heat shocked at 33 or 35 degrees C as well as cells treated with 10 microM sodium arsenite, 100 microM cadmium chloride or 1 microg/mL herbimycin A. These results show that KNK437 is effective at inhibiting both heat shock- and chemical stress-induced hsp gene expression in amphibian cells.