Long lasting heat shock stimulation of TRAIL-induced apoptosis in transformed T lymphocytes

Clinical effectiveness of combined whole body hyperthermia and external beam radiation therapy (EBRT) versus EBRT alone in patients with painful bony metastases: A phase III clinical trial study

PURPOSE

To evaluate the response rate, pain relief duration, and time it took for pain to decline or resolve after radiation therapy (RT) with or without fever-range Whole Body Hyperthermia (WBH) in bony metastatic patients with mainly primary tumor of prostate and breast cancer leading to bone pain.

MATERIALS & METHODS

Bony metastatic patients with pain score ≥4 on the Brief Pain Inventory (BPI) underwent RT of 30 Gy in 10 fractions in combination with WBH with nursing care under medical supervision versus RT-alone. WBH application time was 3-4 h in three fractions with at least 48-h intervals. All patients were stratified primary site, breast or prostate cancer vs others, BPI score, and exclusion criteria. The primary endpoint was complete response (CR) (BPI equal to zero with no increase of analgesics) within two months of follow-up.

RESULTS

Based on this study, the RT-alone group showed the worst pain. The study was terminated after the enrollment of a total of 61 patients, 5 years after the first enrollment (April 2016 to February 2021). Finally, the CR rate in RT + WBH revealed the most significant difference with RT-alone, 47.4% versus 5.3% respectively within 2 months post-treatment (P-value <0.05). The time of complete pain relief was 10 days for RT + WBH, while the endpoint was not reached during the RT-alone arm. Pain progression or stable disease was observed in half of the patients in RT-alone group within 4 weeks after treatment. However, this score was near zero in RT + WBHT patients in two months post-treatment.

CONCLUSIONS

WBH plus RT showed significant increases in pain relief and shorter response time in comparison with RT-alone for patients with bone metastatic lesions.

A comparative study of effects of curcumin and its nanoparticles on the growth, immunity and heat stress resistance of Nile tilapia (Oreochromis niloticus)

This study evaluated the effects of dietary supplementation with free- or nano-curcumin on the growth performance, immune status and heat stress resistance of Nile tilapia (Oreochromis niloticus). Seven isonitrogenous (28% protein) and isocaloric (445 kcal/100 g DM) diets were prepared. Six diets were supplemented with three levels of nano-curcumin (50 (CN50), 100 (CN100), 200 (CN200) mg kg-1 diet) or free-curcumin (50 (C50), 100 (C100), 200 (C200) mg kg-1 diet), and the control diet was left without an additive (CON). Fish (13.54 ± 0.32 g) (mean ± SD) fed the experimental diets for 65 days. Following the feeding trial, the fish were exposed to the acute heat stress by gradually raising the water temperature from 25 to 40 °C within 3 h. The fish were then exposed to 40 °C for 4 h. Results revealed the superiority of nano-curcumin over its free-form in enhancing the growth performance, with the highest results obtained at CN100, followed by CN200. Only heat stress, not the experimental diets, increased the platelets, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), leukocytes and neutrophils count, while lymphocytes decreased. The CN50 and CN100 groups showed lower activity of liver enzymes (alanine aminotransferase (ALT) and aspartate aminotransferase (AST)) than the other treatments, while C200 gave the highest activity of these enzymes. The highest immunoglobulin (IgM) levels were detected in CN100, CN200, C100 and C200, followed by CN50. The C200 group showed higher levels of complement 3 and complement 4 (C3 and C4, respectively) than the other treatments. The C50 and CON groups gave the lowest values of IgM, C3 and C4. Cortisol levels were significantly lower in the CN50 and CN100 groups compared to the other groups. After the heat stress, ALT, AST, IgM, C3, C4, cortisol and glucose increased. Thus, nano-curcumin is more effective than its free-form in enhancing the resistance to heat stress, inducing innate immunity, lowering the stress indicators and promoting growth performance of Nile tilapia with the best concentration at 100 mg kg-1 diet.

Mild hyperthermia by MR-guided focused ultrasound in an ex vivo model of osteolytic bone tumour: optimization of the spatio-temporal control of the delivered temperature

BACKGROUND

Magnetic resonance guided focused ultrasound was suggested for the induction of deep localized hyperthermia adjuvant to radiation- or chemotherapy. In this study we are aiming to validate an experimental model for the induction of uniform temperature elevation in osteolytic bone tumours, using the natural acoustic window provided by the cortical breakthrough.

MATERIALS AND METHODS

Experiments were conducted on ex vivo lamb shank by mimicking osteolytic bone tumours. The cortical breakthrough was exploited to induce hyperthermia inside the medullar cavity by delivering acoustic energy from a phased array HIFU transducer. MR thermometry data was acquired intra-operatory using the proton resonance frequency shift (PRFS) method. Active temperature control was achieved via a closed-loop predictive controller set at 6 °C above the baseline. Several beam geometries with respect to the cortical breakthrough were investigated. Numerical simulations were used to further explain the observed phenomena. Thermal safety of bone heating was assessed by cross-correlating MR thermometry data with the measurements from a fluoroptic temperature sensor inserted in the cortical bone.

RESULTS

Numerical simulations and MR thermometry confirmed the feasibility of spatio-temporal uniform hyperthermia (± 0.5 °C) inside the medullar cavity using a fixed focal point sonication. This result was obtained by the combination of several factors: an optimal positioning of the focal spot in the plane of the cortical breakthrough, the direct absorption of the HIFU beam at the focal spot, the "acoustic oven effect" yielded by the beam interaction with the bone, and a predictive temperature controller. The fluoroptical sensor data revealed no heating risks for the bone and adjacent tissues and were in good agreement with the PRFS thermometry from measurable voxels adjacent to the periosteum.

CONCLUSION

To our knowledge, this is the first study demonstrating the feasibility of MR-guided focused ultrasound hyperthermia inside the medullar cavity of bones affected by osteolytic tumours. Our results are considered a promising step for combining adjuvant mild hyperthermia to external beam radiation therapy for sustained pain relief in patients with symptomatic bone metastases.

Evaluating the effectiveness of combined radiotherapy and hyperthermia for the treatment response of patients with painful bony metastases: A phase 2 clinical trial

INTRODUCTION

Since the survival time of patients with bony metastases has noticeably improved in recent years, these patients are at high risk of complications associated with this metastasis. Hence, the appropriate choice of treatment modality or combination of therapeutic approaches can lead to increasing bone pain relief, improving quality of life, etc. This study is aimed to evaluate the effectiveness of combined radiotherapy and hyperthermia for the treatment response of patients with painful bony metastases.

PATIENTS AND METHODS

In a single-arm clinical trial, 23 eligible patients (14 female and 9 male) with the mean age of 67 years old and suffering from bony metastases were enrolled in the study. Two hours after radiotherapy, the patients underwent hyperthermia for 1 h in the supine position. All the patients completed the brief pain inventory (BPI) assessment tool and quality of life questionnaire (QLQ-C30) from the European Organization for Research and Treatment of Cancer (EORTC) at the baseline, end of the treatment and 1, 2 and 3 months thereafter. The response to the treatment was assessed as the zero score (complete response) or two or more than two-point drop of the worst pain within the preceding 24 h (partial response) during the 3-month posttreatment.

RESULTS

All the pain intensity and interference scores, except the pain interference with the enjoyment of life score, significantly decreased. A total of 18 out of 23 patients (78%) achieved complete or partial response. The number of patients using pain relief medications decreased from 74% (n=17) at the baseline to 48% (n=11) 3 months later. Moreover, except for nausea and vomiting, appetite loss, diarrhea and financial impact problems, the patients' quality of life improved significantly in all the functional scales and symptoms within 3 months.

CONCLUSION

This study showed that using hyperthermia in combination with radiotherapy significantly ameliorated bone pain among the patients suffering from cancer with painful bony metastases.

Effects of fermented Chinese herbal medicines on milk performance and immune function in late-lactation cows under heat stress conditions

Heat stress (HS) causes significant economic losses and has become a continual challenge in the dairy industry worldwide. The objective of this study was to evaluate the effects of a dietary supplement on milk performance and immune function in late-lactation cows under HS conditions. The supplement was a fermented Chinese herbal medicines (CHMs) mixture consisting of 18 herbs. Forty lactating Holstein cows (560 ± 51.0 kg of initial BW, 230 ± 10.0 DIM, 16 ± 3.0 kg of milk per day) were randomly assigned into 4 treatment groups (10 cows per group). Each group was fed a dietary supplemented with 0, 25, 50, or 100 g CHMs per cow per day. Cows were housed at high ambient temperature-humidity index (average 74.5) for an experimental period of 42 d during the summer months. Milk yield, composition, immune responses involving blood lymphocyte apoptosis rate, serum biochemical parameters, and genes expression in lymphocytes were evaluated on days 14, 28, and 42, respectively. Results showed that milk yield, milk fat, and protein content were greater (all P < 0.05) for 50 or 100 g/d CHMs compared with the group without CHMs supplements throughout the experimental period. On the other hand, increasing CHMs dose demonstrated a greater lymphocyte or leukocyte count (P < 0.01). By flow cytometry analysis, early or late apoptosis rate of the lymphocytes was decreased (P < 0.05) by CHMs supplements. The immunity-related biochemistry and genes transcript responses involving cytokines (IL-1, IL-2, IL-6, and IL-12), apoptosis (Bak, Mcl-1, Bax, Bcl-2, Bcl-xl, and P53), and immunoglobulins (IgA, IgG, and IgM) were investigated. Compared with the unsupplemented group, the serum IL-2 and IL-6 levels, as well as IL-2 mRNA expression, increased (P < 0.05) for 100 g/d. However, the serum IL-1 level tended to decrease (P = 0.08) with increasing CHMs dose, and IL-1 mRNA expression was down-regulated (P = 0.02) by up to 24% for 100 g/d. Additionally, the serum Bax level decreased (P < 0.01) and Bcl-2 level increased (P = 0.01) for 100 g/d. Bax and Bak mRNA expressions were down-regulated (P < 0.05), and Bcl-2 and Bcl-xl expression were up-regulated (P < 0.05) for 50 or 100 g/d. The mRNA expressions of P53 and Mcl-1 were not affected by CHMs (P > 0.10). Besides, serum IgG levels were greater (P < 0.01) for 50 or 100 g/d, compared with unsupplemented group. In conclusion, CHMs supplements may improve milk performance and immune function in dairy cows under HS conditions.

MicroRNA-216b inhibits heat stress-induced cell apoptosis by targeting Fas in bovine mammary epithelial cells

Heat stress affects milk yield and quality in lactating dairy cows in summer. Bovine mammary epithelial cells (bMECs) play a key role in milk secretion, and microRNAs (miRNAs) regulate numerous functions of bMEC. Previous reports have verified that miR-216b regulated cell apoptosis through repressing target genes in several cancer cells. So, our purpose was to explore the potential involvement of miR-216b in heat stress-induced cell apoptosis in bMECs. Firstly, the heat stress model was constructed and we found that apoptotic rates of bMECs significantly increased under heat stress. The expression of miR-216b, Bax mRNA, and caspase-3 mRNA was upregulated. However, Bcl-2 mRNA level was detected to differentially downregulated. Overexpression of miR-216b remarkably downregulated the expression of caspase-3 and Bax mRNA and protein, and the mRNA and protein level of Bcl-2 was increased. Inhibition of miR-216b increased the activity of caspase-3 and Bax, and the level of Bcl-2 was inhibited. Moreover, Fas was identified as a target gene of miR-216b through bioinformatic analysis and dual-luciferase reporter assay. Fas activity was significantly inhibited and enhanced respectively after transfecting miRNA mimics and inhibitor. Finally, inhibition of Fas via the small interfering RNA (siRNA) also inhibited cell apoptosis induced by heat stress. Taken together, our results indicated that miR-216b exerted as an anti-apoptotic effect under heat stress in bMECs by targeting Fas.

Heat stress prevents lipopolysaccharide-induced apoptosis in pulmonary microvascular endothelial cells by blocking calpain/p38 MAPK signalling

Pulmonary microvascular endothelial cells (PMECs) injury including apoptosis plays an important role in the pathogenesis of acute lung injury during sepsis. Our recent study has demonstrated that calpain activation contributes to apoptosis in PMECs under septic conditions. This study investigated how calpain activation mediated apoptosis and whether heat stress regulated calpain activation in lipopolysaccharides (LPS)-stimulated PMECs. In cultured mouse primary PMECs, incubation with LPS (1 μg/ml, 24 h) increased active caspase-3 fragments and DNA fragmentation, indicative of apoptosis. These effects of LPS were abrogated by pre-treatment with heat stress (43 °C for 2 h). LPS also induced calpain activation and increased phosphorylation of p38 MAPK. Inhibition of calpain and p38 MAPK prevented apoptosis induced by LPS. Furthermore, inhibition of calpain blocked p38 MAPK phosphorylation in LPS-stimulated PMECs. Notably, heat stress decreased the protein levels of calpain-1/2 and calpain activities, and blocked p38 MAPK phosphorylation in response to LPS. Additionally, forced up-regulation of calpain-1 or calpain-2 sufficiently induced p38 MAPK phosphorylation and apoptosis in PMECs, both of which were inhibited by heat stress. In conclusion, heat stress prevents LPS-induced apoptosis in PMECs. This effect of heat stress is associated with down-regulation of calpain expression and activation, and subsequent blockage of p38 MAPK activation in response to LPS. Thus, blocking calpain/p38 MAPK pathway may be a novel mechanism underlying heat stress-mediated inhibition of apoptosis in LPS-stimulated endothelial cells.

Liver transcriptome response to hyperthermic stress in three distinct chicken lines

Background

High ambient temperatures cause stress in poultry, especially for broiler lines, which are genetically selected for rapid muscle growth. RNA-seq technology provides powerful insights into environmental response from a highly metabolic tissue, the liver. We investigated the effects of acute (3 h, 35 °C) and chronic (7d of 35 °C for 7 h/d) heat stress on the liver transcriptome of 3-week-old chicks of a heat-susceptible broiler line, a heat-resistant Fayoumi line, and their advanced intercross line (AIL).

Results

Transcriptome sequencing of 48 male chickens using Illumina HiSeq 2500 technology yielded an average of 33.9 million, 100 base-pair, single-end reads per sample. There were 8 times more differentially expressed genes (DEGs) (FDR < 0.05) in broilers (n = 627) than Fayoumis (n = 78) when comparing the acute-heat samples to the control (25 °C) samples. Contrasting genetic lines under similar heat treatments, the highest number of DEGs appeared between Fayoumi and broiler lines. Principal component analysis of gene expression and analysis of the number of DEGs suggested that the AIL had a transcriptomic response more similar to the Fayoumi than the broiler line during acute heat stress. The number of DEGs also suggested that acute heat stress had greater impact on the broiler liver transcriptome than chronic heat stress. The angiopoietin-like 4 (ANGPTL4) gene was identified as differentially expressed among all 6 contrasts. Ingenuity Pathway Analysis (IPA) created a novel network that combines the heat shock protein family with immune response genes.

Conclusions

This study extends our understanding of the liver transcriptome response to different heat exposure treatments in distinct genetic chicken lines and provides information necessary for breeding birds to be more resilient to the negative impacts of heat. The data strongly suggest ANGPTL4 as a candidate gene for improvement of heat tolerance in chickens.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3291-0) contains supplementary material, which is available to authorized users.

Heat stress pretreatment decreases lipopolysaccharide-induced apoptosis via the p38 signaling pathway in human umbilical vein endothelial cells

The present study aimed to investigate vascular endothelial apoptosis, and the regulatory molecules involved in the condition of heatstroke caused by direct hyperthermia due to high core temperature and gut‑derived endotoxemia. Human umbilical vascular endothelial cells (HUVECs) were isolated and treated with heat stress (43˚C for 1 h), lipopolysaccharide (LPS; 1 µg/ml), or a combination of heat stress pretreatment followed by LPS. Caspase‑3 activity, DNA fragmentation, and cell viability, determined using a 3‑(4, 5‑dimethyl thiazol‑2‑yl)‑2,5‑diphenyl tetrazolium bromide assay, were measured to examine cellular apoptosis. Changes in the expression levels of heat shock protein (HSP) 27, HSP90 and B‑cell lymphoma 2 (Bcl‑2), and the phosphorylation of p38 were detected using Western blot assays. The specific inhibitor of p38, SB203580, was also used. LPS induced endothelial apoptosis, as indicated by increased caspase‑3 activity, a high level of DNA fragmentation and low cell viability. LPS also increased p38 phosphorylation and decreased the expression levels of HSP27, HSP90 and Bcl‑2. Heat stress pretreatment inhibited LPS‑induced cellular apoptosis, increased the phosphorylation of p38, and increased the expression levels of HSP27, HSP90 and Bcl‑2. Pretreatment with SB203580 had effects similar to those of heat stress in the amelioration of LPS‑induced effects. These findings demonstrated that heat stress pretreatment decreased LPS‑induced Bcl‑2‑associated apoptosis in HUVECs by attenuating p38 activation, thereby increasing the expression levels of HSP27 and HSP90.

Hyperthermia restores apoptosis induced by death receptors through aggregation-induced c-FLIP cytosolic depletion

TRAIL is involved in immune tumor surveillance and is considered a promising anti-cancer agent owing to its limited side effects on healthy cells. However, some cancer cells display resistance, or become resistant to TRAIL-induced cell death. Hyperthermia can enhance sensitivity to TRAIL-induced cell death in various resistant cancer cell lines, including lung, breast, colon or prostate carcinomas. Mild heat shock treatment has been proposed to restore Fas ligand or TRAIL-induced apoptosis through c-FLIP degradation or the mitochondrial pathway. We demonstrate here that neither the mitochondria nor c-FLIP degradation are required for TRAIL-induced cell death restoration during hyperthermia. Our data provide evidence that insolubilization of c-FLIP, alone, is sufficient to enhance apoptosis induced by death receptors. Hyperthermia induced c-FLIP depletion from the cytosolic fraction, without apparent degradation, thereby preventing c-FLIP recruitment to the TRAIL DISC and allowing efficient caspase-8 cleavage and apoptosis. Hyperthermia-induced c-FLIP depletion was independent of c-FLIP DED2 FL chain assembly motif or ubiquitination-mediated c-FLIP degradation, as assessed using c-FLIP point mutants on lysine 167 and 195 or threonine 166, a phosphorylation site known to regulate ubiquitination of c-FLIP. Rather, c-FLIP depletion was associated with aggregation, because addition of glycerol not only prevented the loss of c-FLIP from the cytosol but also enabled c-FLIP recruitment within the TRAIL DISC, thus inhibiting TRAIL-induced apoptosis during hyperthermia. Altogether our results demonstrate that c-FLIP is a thermosensitive protein whose targeting by hyperthermia allows restoration of apoptosis induced by TNF ligands, including TRAIL. Our findings suggest that combining TRAIL agonists with whole-body or localized hyperthermia may be an interesting approach in cancer therapy.

Heat stress induces apoptosis through transcription-independent p53-mediated mitochondrial pathways in human umbilical vein endothelial cell

Cells apoptosis induced by intense heat stress is the prominent feature of heat-related illness. However, little is known about the biological effects of heat stress on cells apoptosis. Herein, we presented evidence that intense heat stress could induce early apoptosis of HUVEC cells through activating mitochondrial pathway with changes in mitochondrial membrane potential(ΔΨm), release of cytochrome c, and activation of caspase-9 and -3. We further revealed that p53 played a crucial role in heat stress-induced early apoptosis, with p53 protein rapidly translocated into mitochondria. Using pifithrin-α(PFT), a p53's mitochondrial translocation inhibitor, we found that pretreated with PFT, heat stress induced mitochondrial p53 translocation was significantly suppressed, accompanied by a significant alleviation in the loss of ΔΨm, cytochrome c release and caspase-9 activation. Furthermore, we also found that generation of reactive oxygen species (ROS) was a critical mediator in heat stress-induced apoptosis. In addition, the antioxidant MnTMPyP significantly decreased the heat stress-induced p53's mitochondrial translocation, followed by the loss of ΔΨm, cytochrome c release, caspase-9 activation and heat stress-mediated apoptosis. Conclusively, these findings indicate the contribution of the transcription-independent mitochondrial p53 pathway to early apoptosis in HUVEC cells induced by oxidative stress in response to intense heat stress.

Mechanisms of heat shock response in mammals

Heat shock (HS) is one of the best-studied exogenous cellular stresses. The cellular response to HS utilizes ancient molecular networks that are based primarily on the action of stress-induced heat shock proteins and HS factors. However, in one way or another, all cellular compartments and metabolic processes are involved in such a response. In this review, we aimed to summarize the experimental data concerning all aspects of the HS response in mammalian cells, such as HS-induced structural and functional alterations of cell membranes, the cytoskeleton and cellular organelles; the associated pathways that result in different modes of cell death and cell cycle arrest; and the effects of HS on transcription, splicing, translation, DNA repair, and replication.

Knock down of heat shock protein 27 (HspB1) induces degradation of several putative client proteins

Hsp27 belongs to the heat shock protein family and displays chaperone properties in stress conditions by holding unfolded polypeptides, hence avoiding their inclination to aggregate. Hsp27 is often referenced as an anti-cancer therapeutic target, but apart from its well-described ability to interfere with different stresses and apoptotic processes, its role in non-stressed conditions is still not well defined. In the present study we report that three polypeptides (histone deacetylase HDAC6, transcription factor STAT2 and procaspase-3) were degraded in human cancerous cells displaying genetically decreased levels of Hsp27. In addition, these proteins interacted with Hsp27 complexes of different native size. Altogether, these findings suggest that HDAC6, STAT2 and procaspase-3 are client proteins of Hsp27. Hence, in non stressed cancerous cells, the structural organization of Hsp27 appears to be a key parameter in the regulation by this chaperone of the level of specific polypeptides through client-chaperone type of interactions.

Death receptors mediate the adverse effects of febrile-range hyperthermia on the outcome of lipopolysaccharide-induced lung injury

We have shown that febrile-range hyperthermia enhances lung injury and mortality in mice exposed to inhaled LPS and is associated with increased TNF-α receptor activity, suppression of NF-κB activity in vitro, and increased apoptosis of alveolar epithelial cells in vivo. We hypothesized that hyperthermia enhances lung injury and mortality in vivo by a mechanism dependent on TNF receptor signaling. To test this, we exposed mice lacking the TNF-receptor family members TNFR1/R2 or Fas (TNFR1/R2(-/-) and lpr) to inhaled LPS with or without febrile-range hyperthermia. For comparison, we studied mice lacking IL-1 receptor activity (IL-1R(-/-)) to determine the role of inflammation on the effect of hyperthermia in vivo. TNFR1/R2(-/-) and lpr mice were protected from augmented alveolar permeability and mortality associated with hyperthermia, whereas IL-1R(-/-) mice were susceptible to augmented alveolar permeability but protected from mortality associated with hyperthermia. Hyperthermia decreased pulmonary concentrations of TNF-α and keratinocyte-derived chemokine after LPS in C57BL/6 mice and did not affect pulmonary inflammation but enhanced circulating markers of oxidative injury and nitric oxide metabolites. The data suggest that hyperthermia enhances lung injury by a mechanism that requires death receptor activity and is not directly associated with changes in inflammation mediated by hyperthermia. In addition, hyperthermia appears to enhance mortality by generating a systemic inflammatory response and not by a mechanism directly associated with respiratory failure. Finally, we observed that exposure to febrile-range hyperthermia converts a modest, survivable model of lung injury into a fatal syndrome associated with oxidative and nitrosative stress, similar to the systemic inflammatory response syndrome.

Heat Shock Protein translocation induced by membrane fluidization increases tumor-cell sensitivity to chemotherapeutic drugs

Treatment of chronic lymphocytic leukemia (CLL) remains a challenge due to the frequency of drug resistance amongst patients. Improving the delivery of chemotherapeutic agents while reducing the expression of anti-apoptotic Heat Shock Proteins (HSPs) within the cancer cells may facilitate in overcoming this drug resistance. We demonstrate for the first time that sub-lethal doses of chemotherapeutic agents can be combined with membrane fluidizing treatments to produce a significant increase in drug efficacy and apoptosis in vitro. We show that fluidizers result in a transient decrease in intracellular HSPs, resulting in increased tumor-cell sensitivity and a membrane-associated induction of HSP gene expression.

Caspases activation in hyperthermia-induced stimulation of TRAIL apoptosis

In leukemia cells, hyperthermia enhances tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. The phenomenon is caspase-dependent and results in membrane changes leading to an increased recognition of TRAIL death receptors by TRAIL. Because either caspase-2 or an apical proteolytic event has been recently proposed to act as an initiator of the cell death mechanism induced by heat shock, we have investigated the hierarchy of caspase activation in cells exposed to the combined heat shock plus TRAIL treatment. We report here that caspases-2, -3, and -8 were the first caspases to be activated. As expected, caspase-8 is required and indispensable during the initiation of this death signaling. Caspase-2 may also participate in the phenomenon but, in contrast to caspase-8, its presence appears dispensable because its depletion by small interfering RNA is devoid of effects. Our observations also suggest a role of caspase-3 and of a particular cleaved form of this caspase during the early signals of heat shock plus TRAIL-induced apoptosis.

Potential roles of membrane fluidity and ceramide in hyperthermia and alcohol stimulation of TRAIL apoptosis

We recently reported that a mild heat shock induces a long lasting stimulation of TRAIL-induced apoptosis of leukemic T-lymphocytes and myeloid cell lines, but not normal T-lymphocytes, which correlates with an enhanced ability of TRAIL to recognize its receptors. As shown here, this phenomenon could be inhibited by the xanthogenate agent D609, a sphingomyelin/ceramide pathway inhibitor. A caspase-dependent and D609-sensitive two-fold increase in ceramide level was elicited by heat shock plus TRAIL combined treatment. One day after heat shock, a similar increase in ceramide was induced by TRAIL. Sphingolipids/ceramides are known to regulate membrane integrity, and heat shock increases membrane fluidity. In this regard, the heat shock plus TRAIL combined treatment resulted in a D609-sensitive membrane fluidization which was far more intense than that induced by heat shock only. We also report that membrane fluidizers, that mimic the effect of heat shock, such benzyl alcohol and ethanol, potently stimulated TRAIL-induced apoptosis. As heat shock, these alcohols increased, in a D609-sensitive manner, membrane fluidity in the presence of TRAIL, the recognition of TRAIL death receptors, and ceramide levels. These results suggest that stress agents that trigger ceramide production and an overall increase in membrane fluidity are stimulators of TRAIL apoptosis.

Sensitization of chronic lymphocytic leukemia cells to TRAIL-induced apoptosis by hyperthermia

We recently reported that, in cultured leukemic T lymphocytes and promyelocytic cells, a mild heat shock treatment (1 h at 42 degrees C) induced a long lasting stimulation of the apoptosis induced by TNF-related apoptosis inducing ligand (TRAIL). On the opposite, no effects were recorded toward normal human T lymphocytes. The apoptogenic efficiency of TRAIL in leukemic lymphocytes is linked to the long lasting increased ability of TRAIL to recognize and bind DR4 and DR5 receptors during hyperthermia. Here, we have analyzed whether this new apoptotic co-treatment could be relevant toward primary cells from patients suffering of chronic lymphocytic leukemia. Analysis of samples from 24 patients with different ages, sex and disease stages revealed that half of them had lymphocytes that, once isolated and analyzed in vitro, positively responded (increase of cell death) to the heat shock plus TRAIL co-treatment. Analysis of the level of expression of various anti-apoptotic proteins in the cell samples revealed a great heterogeneity between patients and no clear relationships could be drawn. Nevertheless, most cell samples that were sensitive to TRAIL plus heat shock induced apoptosis displayed a higher level of cell surface DR4 and DR5 receptors than the non-sensitive counterparts. Hence, analysis of the level of TRAIL surface receptors is a prerequisite for future clinical applications based on this protocol.

Sensitization of Mesothelioma Cells to Tumor Necrosis Factor–Related Apoptosis–Inducing Ligand–Induced Apoptosis by Heat Stress via the Inhibition of the 3-Phosphoinositide-Dependent Kinase 1/Akt Pathway

Heat stress may enhance the effect of apoptosis-inducing agents in resistant tumor cells. One such agent is the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which has attracted intense interest for its ability to induce apoptosis in tumors without affecting nonmalignant cells. We therefore tested whether heat stress potentiates TRAIL-induced apoptosis in mesothelioma cells, its cell type being resistant to TRAIL alone. We found that heat stress enhanced the apoptosis caused by TRAIL but not by chemotherapy. To explain this potentiation, we found that heat stress decreased Akt phosphorylation via the dissociation of heat shock protein 90 (Hsp90) from its client protein 3-phosphoinositide-dependent kinase 1 (PDK-1), a major Akt kinase. The role of Hsp90 and the Akt pathway was confirmed by showing that inhibitors of Hsp90 and the phosphatidyilinositol-3 kinase/Akt pathway reproduced the effect of heat stress on TRAIL-induced apoptosis and that the effect of inhibiting Hsp90 on TRAIL-induced apoptosis could be overcome by activating the Akt pathway with a constitutively active construct of the Akt kinase PDK-1. The effect of heat stress involved multiple steps of the apoptotic machinery. Heat stress potentiated the death receptor pathway, as shown by an increase in TRAIL-induced caspase 8 cleavage. Nonetheless, knockdown of Bid, the main intermediary molecule from the death receptor pathway to the mitochondria, inhibited the effect of heat stress, showing that mitochondrial amplification was required for potentiation by heat stress. In summary, these results support the novel concept that heat stress inhibits the Akt pathway by dissociating PDK-1 from its chaperone Hsp90, leading to potentiation of TRAIL-induced apoptosis in resistant malignant cells.

Redox control of apoptosis: an update

The redox environment of the cell is currently thought to be extremely important to control cell growth, differentiation, and apoptosis as many redox-sensitive proteins characterize these networks. A recent, widely accepted theory is that free radicals are not only dangerous species but, at low concentration, they have been designed by evolution to participate in the maintenance of cellular redox (reduction/oxidation) homeostasis. This notion derives from the evidence that cells constantly generate free radicals both as waste products of aerobic metabolism and in response to a large variety of stimuli. Free radicals, once produced, provoked cellular responses (redox regulation) against oxidative stress transducing the signals to maintain the cellular redox balance. Growing evidence suggests that in many instances the production of radical species is tightly regulated and their downstream targets are very specific, indicating that reactive oxygen species and reactive nitrogen species actively participate in several cell-signalling pathways as physiological "second messengers." In this review, we provide a general overview and novel insights into the redox-dependent pathways involved in programmed cell death.