Lack of heat shock response triggers programmed cell death in a rat histiocytic cell line

Heat shock transcription factor HSF2 modulates the autophagy response through the BTG2-SOD2 axis

The heat shock transcription factor HSF1 regulates the inducible Hsp gene transcription, whereas HSF2 is involved in the constitutive transcription. HSFs can work for the non-heat shock genes transcription in a case-specific manner to facilitate normal cellular functions. Here, we demonstrate that HSF2 acts as an upstream regulator of heat shock-induced autophagy response in a rat histiocytoma. The heat-induced HSF2 transactivates the B-cell translocation gene-2 (BTG2) transcription, and the latter acts as a transcriptional coactivator for superoxide dismutase (SOD2). The altered HSF2 promoter occupancy on the BTG2 promoter enhances BTG2 transcription. Since SOD2 regulation is linked to mitochondrial redox sensing, HSF2 appears to act as a redox sensor in deciding the cell fate. The HSF2 shRNA or NFE2L2/BTG2 siRNA treatments have interfered with the autophagy response. We demonstrate that HSF2 is an upstream activator of autophagy response, and the HSF2-BTG2-SOD2 axis acts as a switch between the non-selective (micro/macro) and selective (chaperone-mediated) autophagy.

PBDE-47 exposure causes gender specific effects on apoptosis and heat shock protein expression in marine medaka, Oryzias melastigma

Marine medaka (Oryzias melastigma) was fed with a low and high dose of dietary 2,2',4,4'-tetra-bromodiphenyl ether (PBDE-47), over 21 days. Gender specific changes in caspases 3 and 8 in medaka were found as activities in male medaka were significantly increased in both liver and muscle at both low and high exposure levels whereas caspase activity in female medaka tissue remained unchanged. Results of HSP90 and HSP70 immunoassays also showed gender specific related changes as both HSP families were unchanged in liver and muscle of male medaka but significantly increased in liver and muscle of female medaka, following PBDE-47 exposure. The gender specific effects of PBDE-47 on HSP expression profiles could not be explained by inherent differences in the heat shock response of male and female marine medaka, as the HSP profiles in liver and muscle, induced by acute heat shock, were similar in both sexes. The findings from this study provide evidence that PBDE-47 can cause gender specific modulatory effects on mechanisms critical to the apoptotic cascade as well as HSP regulation and expression.

Hsp60 chaperonin acts as barrier to pharmacologically induced oxidative stress mediated apoptosis in tumor cells with differential stress response

Mitochondrial functions play a central role in energy metabolism and provide survival fitness to both normal and tumor cells. Mitochondrial chaperonin Hsp60 is involved in both pro- and anti-apoptotic functions, but how Hsp60 senses the mitochondria selective oxidative stress response is unknown. In this study, by using rotenone, an irreversible inhibitor of oxidative phosphorylation against IMR-32 and BC-8 tumor cells containing differential heat shock transcriptional machinery, we studied whether the oxidative stress response is related to Hsp60. The accelerated cytotoxicity in response to rotenone has been correlated with enhanced production of O2 (•-), H2O2, reactive oxygen species, and Hsp60 translocation from the mitochondria to the cytoplasm. The inability of cells to resist oxidative stress mediated Hsp60 translocation appeared to depend on mitochondrial oxyradical scavenging system and Bax translocation. A delayed oxidative stress response in hsp60 shRNA-treated cells was found to be due to increased mitochondrial translocation of Hsp60 on shRNA pre-sensitization. Overexpression of Hsp60 failed to protect cells from oxidative stress due to a lack of its mitochondrial retention upon post-rotenone treatment. These results also revealed that Hsp60 mitochondrial localization is indispensable for decreasing O2 (•-) levels, but not H2O2 and ROS levels. However, cycloheximide treatment alone induced Hsp60 translocation, while rotenone combination delayed this translocation. In contrast to oxidative stress, MG132 and 17AAG treatments showed mitochondrial retention of Hsp60; however, MG132 combination either with hsp60 shRNA or 17AAG induced its translocation. Additionally, overexpression of Huntingtin gene also resulted in Hsp60 mitochondrial accumulation. We suggest that Hsp60 may act as a barrier to pharmacological targeting of mitochondria.

Atypical heat shock response and acquisition of thermotolerance in P388D1 cells

Reports of atypical heat shock response in some tumour cell lines emphasize the possibilities of alternate stress response mechanisms. We demonstrate here that P388D1, a mouse macrophage tumour cell line, failed to induce heat shock proteins (HSPs) in response to either heat stress (42 °C, 1h) or to heavy metal stress induced by arsenic trioxide (5-20 μM). Heat shock transcriptional factor 1 (HSF1) that mediates transcriptional up regulation of HSPs during stress was found to be deficient in transactivation despite its binding to the promoter region of HSP genes. Interestingly, cells exhibited thermotolerance in the absence of induced HSPs. However, the tolerance was abrogated in cells treated with cycloheximide (250 ng/ml) suggested that thermotolerance was dependent on de novo protein synthesis.

17AAG Treatment Accelerates Doxorubicin Induced Cellular Senescence: Hsp90 Interferes with Enforced Senescence of Tumor Cells

Hsp90 chaperone has been identified as an attractive pharmacological target to combat cancer. However, some metastatic tumors either fail to respond to Hsp90 inhibition or show recovery necessitating irreversible therapeutic strategies. In response to this enforced senescence has been proposed as an alternate strategy. Here, we demonstrate that inhibiting Hsp90 with 17AAG sensitizes human neuroblastoma to DNA damage response mediated cellular senescence. Among individual and combination drug treatments, 17AAG pre-treatment followed by doxorubicin treatment exhibited senescence-like characteristics such as increased nucleus to cytoplasm ratio, cell cycle arrest, SA-β-gal staining and the perpetual increase in SAHF. Doxorubicin induced senescence signaling was mediated by p53-p21(CIP/WAF-1) and was accelerated in the absence of functional Hsp90. Sustained p16(INK4a) and H3K4me3 expressions correlating with unaffected telomerase activation annulled replicative senescence and appraised stress induced senescence. Despite increases in [(ROS)i] and [(Ca(2+))i], a concomitant increase in cellular antioxidant defense system suggested oxidation independent senescence activation. Sustained activation of survival (Akt) and proliferative (ERK1/2) kinases fosters robustness of cells. Invigorating senescent cells with growth factor or snooping with mTOR or PI3 kinase inhibitors compromised cell survival but not senescence. Intriguingly, senescence-associated secretory factors from the senescence cells manifested established senescence in neuroblastoma, which offers clinical advantage to our approach. Our study discusses tumor selective functions of Hsp90 and discusses irrefutable strategies of Hsp90 inhibition in anticancer treatments.

Time and dose dependence of pluronic bioactivity in hyperthermia-induced tumor cell death

Pluronic block copolymers have been shown to sensitize cancer cells resulting in an increased activity of antineoplastic agents. In the current study we examined a new application of Pluronic bioactivity in potentiating hyperthermia-induced cancer cell injury. DHD/K12/TRb rat adenocarcinoma cells were exposed to low-grade hyperthermia at 43 degrees C with or without Pluronic P85 or Pluronic L61. A range of Pluronic doses, pre-exposure and heat exposure durations were investigated, and the test conditions were optimized. Treatment efficacy was assessed by measurement of intracellular ATP and mitochondrial dehydrogenase activity. Both P85 and L61 in synergy with heat reduced cell viability appreciably compared to either heat or Pluronic alone. Under optimal conditions, P85 (10 mg/ml, 240 mins) combined with 15 mins heat reduced intracellular ATP to 60.1 +/- 3.5% of control, while heat alone and P85 without heat caused a negligible decrease in ATP of 1.2% and 3.8%, respectively. Similarly, cells receiving 120 mins pre-exposure of L61 (0.3 mg/ml) showed reduction in intracellular ATP to 14.1 +/- 2.1% of control. Again, heat or L61 pre-exposure alone caused a minor decrease in levels of intracellular ATP (1.5% and 4.4%, respectively). Comparable results were observed when viability was assessed by mitochondrial enzyme activity. Survival studies confirmed that the loss of viability translates to a long-term reduction in proliferative activity, particularly for L61 treated cells. Based on these results, we conclude that Pluronic is effective in improving hyperthermic cancer treatment in vitro by potentiating heat-induced cytotoxicity in a concentration and time dependent manner.

Heat shock transcription factors regulate heat induced cell death in a rat histiocytoma

Heat shock response is associated with the synthesis of heat shock proteins (Hsps) which is strictly regulated by different members of heat shock transcription factors (HSFs). We previously reported that a rat histiocytoma, BC-8 failed to synthesize Hsps when subjected to typical heat shock conditions (42 degrees C, 60 min). The lack of Hsp synthesis in these cells was due to a failure in HSF1 DNA binding activity. In the present study we report that BC-8 tumor cells when subjected to heat shock at higher temperature (43 degrees C, 60 min) or incubation for longer time at 42 degrees C, exhibited necrosis characteristics; however,under mild heat shock (42 degrees C, 30 min) conditions cells showed activation of autophagy. Mild heat shock treatment induced proteolysis of HSF1, and under similar conditions we observed an increase in HSF2 expression followed by its enhanced DNA binding activity. Inhibiting HSF1 proteolysis by reversible proteasome inhibition failed to inhibit heat shock induced autophagy. Compromising HSF2 expression but not HSF1 resulted in the inhibition of autophagy, suggesting HSF2 dependent activation of autophagy. We are reporting for the first time that HSF2 is heat inducible and functions in heat shock induced autophagic cell death in BC-8 tumor cells.

Cortisol can be pro- or anti-apoptotic in sea bream cells: potential role of HSP70 induction for cytoprotection

Cortisol, and heat shock protein 70 (HSP70) are known to perform key roles as part of the fish stress response. In the present study, two in vitro systems were used to investigate a possible cortisol-HSP70-apoptosis regulatory relationship. Using a developed silver sea bream fibroblast cell line (SSF), cortisol was found to induce HSP70 synthesis with a concomitant protection against camptothecin induced apoptosis. The induction of HSP70 synthesis using azetidine was also found to protect SSF against apoptosis. A primary culture of silver sea bream macrophages (SSM) displayed reduced HSP70, underwent apoptosis and displayed reduced phagocytic activity upon exposure to cortisol. The effect of cortisol on HSP70 expression in both SSF and SSM were blocked by the glucocorticoid antagonist, RU486. Treatment of SSM with azetidine protected against apoptosis and also enhanced phagocytic activity. The data from this study demonstrates for the first time that cortisol can be either anti- apoptotic or pro-apoptotic in different fish cells and such actions can be mediated via HSP70 induction or suppression respectively.

Pharmacological modulation of the heat shock response

Life presents a continuous series of stresses. Increasing the adaptation capacity of the organism is a long-term survival factor of various organisms and has become an attractive field of intensive therapeutic research. Induction of the heat shock response promotes survival after a wide variety of environmental stresses. Preclinical studies have proven that physiological and pharmacological chaperone inducers and co-inducers are an efficient therapeutic approach in different acute and chronic diseases. In this chapter, we summarize current knowledge of the current state of chaperone modulation and give a comprehensive list of the main drug candidates.

Validation of Drosophila melanogaster as an in vivo model for genotoxicity assessment using modified alkaline Comet assay

The single cell gel electrophoresis or Comet assay is one of the most popular techniques for genotoxicity assessment. The present study was undertaken to validate our previously modified version of the Comet assay for genotoxicity assessment in Drosophila melanogaster (Oregon R(+)) with four well-known mutagenic and carcinogenic alkylating agents, i.e. ethyl methanesulfonate (EMS), methyl methanesulfonate (MMS), N-ethyl-N-nitrosourea (ENU) and cyclophosphamide (CP). Third instar larvae (74 +/- 2 h) of D.melanogaster were fed different concentrations of EMS, MMS, ENU and CP (0.05, 0.5 and 1.0 mM) mixed standard Drosophila food for 24 h. At 98 +/- 2 h, the anterior midgut from control and treated larvae were dissected out, single-cell suspensions were prepared and Comet assay was performed. Our results show a dose-dependent increase in DNA damage with all the four alkylating agents, in comparison to control. The lower concentration (0.05 mM) of the test chemicals, except MMS, did not induce any DNA damage in the gut cells of the exposed larvae. When comparison of Comet parameters was made among the chemicals, MMS was found to be the most potent genotoxicant and ENU the least. The present study validated our previous observation and shows that D.melanogaster is a sensitive and suitable model for the in vivo assessment of genotoxicity using our modified alkaline Comet assay.

Heat shock proteins in the regulation of apoptosis: new strategies in tumor therapy: a comprehensive review

Heat shock proteins (Hsp) form the most ancient defense system in all living organisms on earth. These proteins act as molecular chaperones by helping in the refolding of misfolded proteins and assisting in their elimination if they become irreversibly damaged. Hsp interact with a number of cellular systems and form efficient cytoprotective mechanisms. However, in some cases, wherein it is better if the cell dies, there is no reason for any further defense. Programmed cell death is a widely conserved general phenomenon helping in many processes involving the reconstruction of multicellular organisms, as well as in the elimination of old or damaged cells. Here, we review some novel elements of the apoptotic process, such as its interrelationship with cellular senescence and necrosis, as well as bacterial apoptosis. We also give a survey of the most important elements of the apoptotic machinery and show the various modes of how Hsp interact with the apoptotic events in detail. We review caspase-independent apoptotic pathways and anoikis as well. Finally, we show the emerging variety of pharmacological interventions inhibiting or, just conversely, inducing Hsp and review the emergence of Hsp as novel therapeutic targets in anticancer protocols.

Protection conferred by Bcl-2 expression involves reduced oxidative stress and increased glutathione production during hypothermia-induced apoptosis in AK-5 tumor cells

Hypothermia is known to retard mammalian cell growth, however, BC-8 cells, which have originated from AK-5 tumor after single cell cloning, were triggered into apoptotic pathway when grown at 30 degrees C. Cell death process showed typical apoptotic features like DNA fragmentation, cytochrome c release, etc. Introduction of Bcl-2 gene in BC-8 cells inhibited hypothermia-induced apoptotic process, which is ascribed to reduced ROS generation and higher glutathione production. Thus, Bcl-2 seems to control the apoptotic induction process at the level of redox regulation, in addition to its known effects at the mitochondrial dysregulation. These observations suggest that tumors, which are low in Bcl-2 expression, are sensitive to hypothermic shock and make hypothermia an interesting inducer of apoptosis in tumor cells.

Effect of C-terminal deletion of P53 on heat induced CD95 expression and apoptosis in a rat histiocytoma

Tumor suppressor gene product p53 in its wild-type conformation, is an effector of apoptosis. A rat histiocytic tumor, AK-5 which has a rearranged and mutated p53 gene undergoes apoptosis upon heat shock through surface expression of CD95 receptor. DNA sequence analysis of p53 gene from tumor cells revealed a deletion of 'C' at nucleotide position 942 and an addition of 'A' at position 1055. Deletion of one nucleotide caused premature termination of p53 protein which resulted in shorter p53 protein with an altered sequence from amino acids 315 to 341. Altered p53 was unable to protect BC-8, a single cell clone of AK-5 cells from apoptosis upon heat shock. BC-8 cells transfected with a wild-type p53gene (3B4 cells) were resistant to heat induced apoptosis and did not show the expression CD95 death receptor. Inhibition of p53 expression by using antisense oligo induced apoptosis upon heat shock in 3B4 cells. Similarly, inhibition of CD95 expression by antisense oligo inhibited heat induced apoptosis in BC-8 cells. In addition, cell cycle regulatory molecules, cdc2 and cdk2 are differentially regulated in a non-cell cycle dependent manner in these tumor cells. These results, in view of lack of heat shock response in BC-8 cells suggest a complex interaction between p53, CD95 and hsp70 which determines the fate of the cell. In the absence of functional p53, CD95 appears to be an effector of apoptosis in BC-8 cells.

A cross talk between cellular signalling and cellular redox state during heat-induced apoptosis in a rat histiocytoma

Increasing evidence provides support for oxidative stress to be closely linked to apoptosis. Reactive oxygen species (ROS) are thought to be involved in many forms of programmed cell death. Though heat shock is a universal phenomenon, BC-8, a macrophage-like cell line failed to mount a typical heat shock response. In the absence of heat shock proteins and functional p53, BC-8 cells undergo apoptosis through CD95 signaling. In the present study, we have investigated the role of ROS in the regulation of apoptosis in these cells. We show that cells transfected with hsp70 and functional p53 are resistant to heat-induced apoptosis through inhibition of CD95 expression and ROS induction. Furthermore, apoptosis in BC-8 cells resulted in two bursts of ROS generation, one correlated with heat stress and intracellular depletion of GSH and the other with Bax overexpression and cytochrome c release. Antioxidants could not protect these cells from heat-induced apoptosis and the death pathway seems to be dependent on initial signaling cascade subsequently altering the intracellular redox. Hence, our data suggest that ROS generation in BC-8 cells upon heat shock is facultative but not obligatory for apoptosis.

Induction of stress response renders human tumor cell lines resistant to curcumin-mediated apoptosis: role of reactive oxygen intermediates

Curcumin, a well-known dietary pigment derived from Curcuma longa, has been shown to be a potent antiinflammatory, antioxidant, and anticarcinogenic compound. The present study was designed to investigate the cytotoxic potential of curcumin against a range of human tumor cell lines in an attempt to understand its mechanism of action, which may lead to its possible therapeutic applications. We have shown that different cancer cell lines differ in their sensitivity to curcumin. Cell lines established from malignancies like leukemia, breast, colon, hepatocellular, and ovarian carcinomas underwent apoptosis in the presence of curcumin, whereas cell lines from lung, kidney, prostate, cervix, CNS malignancies, and melanomas showed resistance to the cytotoxic effects of curcumin. Sensitivity of the cancer cell lines to curcumin correlated with the generation of superoxide radicals as determined by the reduction of ferricytochrome C. Curcumin-resistant tumor cell lines showed significantly higher production of Hsp70, thus mounting a stress response and protecting the cells from the apoptotic cell death. These observations yield clues toward understanding the regulation of the cell death machinery by the stress proteins. Interestingly, curcumin had no effect on nontransformed cell lines, which showed neither superoxide generation nor the induction of a stress response. These observations demonstrate that curcumin is an interesting molecule with varied actions, depending on the cell type.

Heat induced expression of CD95 and its correlation with the activation of apoptosis upon heat shock in rat histiocytic tumor cells

The heat shock response is a universal phenomenon and is among the most highly conserved cellular responses. However, BC-8, a rat histiocytoma, fails to mount a heat shock response unlike all other eukaryotic cells. In the absence of induction of heat shock proteins, apoptotic cell death is activated in BC-8 tumor cells upon heat shock. We demonstrate here that stable transformants of BC-8 tumor cells transfected with hsp70 cDNA constitutively express hsp70 protein and are transiently protected from heat induced apoptosis for 6-8 h. In addition heat stress induces CD95 gene expression in these tumor cells. There is a delay in CD95 expression in hsp70 transfected cells suggesting a correlation between the cell surface expression of CD95 and the time of induction of apoptosis in this tumor cell line. Also expression of CD95 antigen appears to inhibit the interaction between heat shock factors and heat shock elements in these cells resulting in the lack of heat shock response.