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.     

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.     

Heat stress induced apoptosis in BC-8 cells derived from AK-5 tumor involves downregulation of Bcl-2 and generation of reactive oxygen species

BC-8, a rat histiocytoma undergoes apoptosis after heat shock, which is due to lack of an effective heat shock response. Heat shock induced generation of free radicals, which in turn are involved in the induction of apoptotic death in BC-8 cells. Treatment of BC-8 cells with N-acetylcysteine partially inhibited the heat induced apoptosis. Introduction of Bcl-2 gene in these cells did not protect them from apoptotic death, whereas transfection with hsp-70 gene did render these cells resistant to heat induced apoptosis transiently. Heat shock also downregulated the expression of Bcl-2 and p53 in these cells. These observations suggested that the heat shock induced apoptosis was mediated through reactive oxygen species and controlled upstream of Bcl-2 check point.     

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.     

Heat shock-induced apoptosis in preimplantation bovine embryos is a developmentally regulated phenomenon

Apoptosis is a form of cell death that can function to eliminate cells damaged by environmental stress. One stress that can compromise embryonic development is elevated temperature (i.e., heat shock). For the current studies, we hypothesized that heat shock induces apoptosis in bovine embryos in a developmentally regulated manner. Studies were performed to 1) determine whether heat shock can induce apoptosis in preimplantation embryos, 2) test whether heat-induced apoptosis is developmentally regulated, 3) evaluate whether heat shock-induced changes in caspase activity parallel patterns of apoptosis, and 4) ascertain whether exposure to a mild heat shock can protect embryos from heat-induced apoptosis. As determined by TUNEL reaction, exposure of bovine embryos > or =16 cells on Day 5 after insemination to 41 or 42 degrees C for 9 h increased the percentage of cells undergoing apoptosis. In addition, there was a duration-dependent increase in the proportion of blastomeres that were apoptotic when embryos were exposed to temperatures of 40 or 41 degrees C, which are more characteristic of temperatures experienced by heat-stressed cows. Heat shock also increased caspase activity in Day 5 embryos. However, heat shock did not induce apoptosis in 2- or 4-cell embryos, nor did it increase caspase activity in 2-cell embryos. The apoptotic response of 8- to 16-cell-stage bovine embryos to heat shock depended upon the day after insemination that heat shock occurred. When 8- to 16-cell embryos were collected on Day 3 after insemination, heat shock of 41 degrees C for 9 h did not induce apoptosis. In contrast, when 8- to 16-cell embryos were collected on Day 4 after insemination and exposed to heat shock, there was an increase in the percentage of cells undergoing apoptosis. Exposure of 8- to 16-cell embryos at Day 4 to a mild heat shock of 40 degrees C for 80 min blocked the apoptotic response to a subsequent, more-severe heat shock of 41 degrees C for 9 h. In conclusion, apoptosis is a developmentally acquired phenomenon that occurs in embryos exposed to elevated temperature, and it can be prevented by induced thermotolerance.     

Thermotolerance induced at a mild temperature of 40 degrees C protects cells against heat shock-induced apoptosis

Apoptosis constitutes a response of organisms to various physiological or pathological stimuli, and to different stresses. The ability of thermotolerance induced at a mild temperature of 40 degrees C to protect against activation of the apoptotic cascade by heat shock was investigated. When Chinese hamster ovary and human adenocarcinoma cervical cells were pretreated at 40 degrees C for 3 h, they were resistant to subsequent lethal heat shock at 43 degrees C. Induction of thermotolerance at 40 degrees C led to increased expression of heat shock proteins 27, 32, 72, and 90. Heat shock induced apoptotic events at the mitochondrial level, involving a decrease in membrane potential, translocation of Bax to mitochondria, and liberation of cytochrome c into the cytosol. These events were diminished in thermotolerant cells. Heat shock (42-45 degrees C) caused activation of initiator caspase-9 and effector caspases-3, -6, and -7, relative to controls at 37 degrees C. Activation of caspases was decreased in thermotolerant cells. Heat shock caused fragmentation of the caspase substrate, inhibitor of caspase-activated DNase. Fragmentation was diminished in thermotolerant cells. Thermotolerance afforded protection against heat shock-induced nuclear chromatin condensation, but not against necrosis.     

Role of glutathione and hsp 70 in the acquisition of thermotolerance in postimplantation rat embryos

Studies were initiated to determine the extent to which reduced glutathione (GSH) may be involved in the capacity of cultured rat embryos to develop heat-induced tolerance to the deleterious effects of exposure to high temperatures (heat shock). Investigations of the modulation of dysmorphogenic responses of embryos to heat shock (43 degrees C, 30 min) as well as to the expression of the hsp70 gene and subsequent formation of hsps indicated that the acquisition of thermotolerance by rat embryos could be significantly influenced by the inhibition of GSH synthesis. Treatment of conceptuses with L-buthionine-S,R-sulfoximine (BSO) reduced intracellular GSH concentrations and compromised the capacity of embryos to mount a thermotolerance response as assessed by alterations in indices of growth and development. Embryonic thermotolerance elicited by preexposure to 42 degrees C for 30 min was accompanied by increases in GSH to levels greater than those measured in control embryos at 37 degrees C just prior to the subsequent 43 degrees C heat exposure. Expression of hsp70 mRNA was detectable soon after elevation of the temperature to 42 degrees C and reached its highest level of accumulation 1.5 hr after the 43 degrees C heat shock. BSO treatment had little if any effect on hsp70 message levels or on the synthesis of hsp70. The fact that BSO-treatment attenuated the thermotolerance response but did not produce a decrease in hsp70 RNA or the synthesis of hsp70 suggests that hsp70 alone is not sufficient to confer thermotolerance upon cultured rat embryos.     

Patterns of protein synthesis in various cells after extreme heat shock

The analysis of proteins synthesized in rat thymocytes and mouse teratocarcinoma PCC-4 Aza 1 and myeloma Sp2/0 cells after 1 h of treatment at 42 or 44 degrees C was carried out. Shock at 42 degrees C reduced the total synthetic rate of proteins in all three cell lines and induced "classical" heat-shock protein with a mass of 70 kDa (hsp 70). Heat shock at 44 degrees C resulted in almost complete inhibition of protein synthesis; only a small amount of hsp 70 was synthesized. Meanwhile a new 48-kDa polypeptide (pI = 7.5) was found in the cells exposed to severe heat shock. This protein was compared by peptide mapping with other known polypeptides of the same size: heat-shock protein from chicken embryo cells and mitogen-stimulated polypeptide from human lymphoid cells. The peptide maps were not identical. It was also shown that after a shock at 44 degrees C teratocarcinoma cells were able to accumulate anomalous amounts of hsp 70 despite hsp 70 synthesis inhibition. The data show that reaction of various cells to extreme heat shock depends heavily on cell type.     

Induced thermotolerance to apoptosis in a human T lymphocyte cell line.

A brief exposure to elevated temperatures elicits, in all organisms, a transient state of increased heat resistance known as thermotolerance. The mechanism for this thermotolerant state is unknown primarily because it is not clear how mild hyperthermia leads to cell death. The realization that cell death can occur through an active process of self destruction, known as apoptosis, led us to consider whether thermotolerance provides protection against this mode of cell death. Apoptosis is a common and essential form of cell death that occurs under both physiological and pathological conditions. This mode of cell death requires the active participation of the dying cell and in this way differs mechanistically from the alternative mode of cell death, necrosis. Here we show that mild hyperthermia induces apoptosis in a human leukemic T cell line. This is evidenced by chromatin condensation, nuclear fragmentation and the cleavage of DNA into oligonucleosome size units. DNA fragmentation is a biochemical hallmark of apoptosis and requires the activation of an endogenous endonuclease. The extent of DNA fragmentation was proportional to the severity of heat stress for cells heated at 43 degrees C from 30 to 90 minutes. A brief conditioning heat treatment induced a resistance to apoptosis. This was evident as a resistance to DNA fragmentation and a reduction in the number of apoptotic cells after a heat challenge. Resistance to DNA fragmentation developed during a recovery period at 37 degrees C and was correlated with enhanced heat shock protein (hsp) synthesis. This heat-induced resistance to apoptosis suggests that thermotolerant cells have gained the capacity to prevent the onset of this pathway of self-destruction. An examination of this process in heated cells should provide new insights into the molecular basis of cellular thermotolerance.     

Heat shock affects cell cycling in the neural plate of cultured rat embryos: a flow cytometric study

The effects of heat shock on cell cycling in the mammalian neuroectoderm were determined by applying heat shocks to cultured rat embryos at the neural plate stage, as part of a study on the teratogenic effects of heat shock on neural development. The heat shocks had been characterized previously (Walsh et al.: Teratology 36:181-191, 1987) with respect to their effects on the gross morphological development of the rat embryos. The effects on cell cycling were observed in DNA histograms of neural plate cells recorded in a flow cytometer after staining with DAPI. The mild heat shock (42 degrees C for 10 min) arrested cells at entry to S phase. The teratogenic heat shock (43 degrees C for 7.5 min) arrested cells at entry to S phase also but for a longer time and inhibited cycling through S phase. After each arrest, a synchronized peak of cells later entered S phase and progressed through the cycle. The induced-thermotolerance heat shock, which was the mild heat shock followed after an interval by the teratogenic heat shock, showed that pre-treatment with the mild heat shock reduced the magnitude of the response to the teratogenic heat shock. The cell-cycle inhibitor ICRF 159 showed the effects on cycling rates of the heat-shock treatments. The arrest of cells at entry to S phase by heat shock may function to prevent cells entering DNA synthesis under non-optimal conditions. We report estimates of proportions of non-proliferative cells in the neural plate of the rat embryos.     

Heat-induced increases in endothelial NO synthase expression and activity and endothelial NO release

Endothelial nitric oxide (NO) synthase (eNOS) is regulated by heat shock protein 90 (HSP90), a heat-inducible protein; however, the effect of heat shock on eNOS expression and eNO release is unknown. Bovine aortic endothelial cells were incubated for 1 h at 37 degrees C, 42 degrees C, or 45 degrees C and cell lysates were evaluated with the use of Western blotting. We observed a 2.1 +/- 0.1-fold increase in eNOS protein content, but no change in HSP90 content, HSP70 content, or HSP90/eNOS association, 24 h after heat shock at 42 degrees C. We also observed a 7.7 +/- 1.5-fold increase in HSP70 protein content, but did not observe a change in eNOS or HSP90 24 h after heat shock at 45 degrees C. eNOS activity and maximal bradykinin-stimulated NO release was significantly increased 24 h after heat shock at 42 degrees C. Heat shock in rats (core temperature: 42 degrees C, 15 min) resulted in a significant increase in aortic eNOS, HSP90, and HSP70 protein content. The aorta from heat-shocked rats exhibited a decreased maximal contractile response to phenylephrine, which was abolished by preincubation with NG-nitro-l-arginine. We conclude that prior heat shock is a physical stimulus of increased eNOS expression and is associated with an increase in eNOS activity, agonist-stimulated NO release, and a decreased vasoconstrictor response.     

Cycloheximide can rescue heat-shocked L cells from death by blocking stress-induced apoptosis.

Cultured mouse L cells undergo apoptosis upon 1 h heat shock at 43 and 45 degrees C. Morphologically characteristic apoptotic cells begin to appear soon after the shock. Immunohistochemistry with anti-transglutaminase antibody shows that in most treated cells the enzyme is induced. Its activation results in the formation of highly cross-linked detergent-resistant apoptotic bodies during recovery. Cycloheximide added during hyperthermic stress inhibits the appearance of apoptotic bodies, showing that heat-shock-induced apoptosis is dependent on protein neosynthesis. The analysis of colony-forming ability of heat-shocked L cells shows a survival of 5% at 43 degrees C and less than 0.02% at 45 degrees C. When protein synthesis is inhibited during heat shock the fraction of surviving cells increases to 23% at 43 degrees C and 0.9% at 45 degrees C. This suggest that part of the cells that die upon heat shock are not heavily damaged and would have survived in the presence of a block in protein synthesis.     

Antitumour activity of Annona squamosa seed extracts is through the generation of free radicals and induction of apoptosis

The plant, Annona squamosa traditionally known as custard apple possesses potent bioactive principles in all its parts. The effect of aqueous and organic extracts from defatted seeds of A. squamosa was studied on a rat histiocytic tumour cell line, AK-5. Both the extracts caused significant apoptotic tumour cell death with enhanced caspase-3 activity, down regulation of antiapoptotic genes Bcl-2 and Bcl(XL), and enhanced the generation of intracellular ROS, which correlated well with the decreased levels of intracellular GSH. In addition, DNA fragmentation and annexin-V staining confirmed that the extracts induced apoptosis in tumour cells through the oxidative stress. Aqueous extracts of A. squamosa seeds possessed significant antitumor activity in vivo against AK-5 tumor.     

Anti-proliferative effects of heating on the human prostatic carcinoma cells in culture

Prostatic cancers are well-known to be sensitive to heat stress. However, the mechanism by which the cancer cells are killed by high temperature remains poorly understood. The present study was undertaken to determine the anti-proliferative effects of heat stress on the prostatic cancer cells in culture. Heat shock at 43 degrees C inhibited the cell growth of three different prostatic cell lines. Flow cytometrical analysis using BrdU and PI showed a decrease in the proportion of cells in an S phase, accompanied by cell accumulation in G1 and G2, in both JCA-1 and PC-3 but not in LNcap. Both JCA-1 and PC-3 presented a strong expression of hsp70 at 37 degrees C. The heat shock caused apparent enhancement of the expression of hsp70 through the cell cycle. A treatment at 43 degrees C for 8 hours resulted in not only an apparent increment of positive hsp70 cells, but cells with subdiploid DNA content in LNcap. Flow cytometrical analysis by FITC-labeled Annexin V showed increment of apoptotic cells at 43 degrees C for 8 hours in LNcap cells. The results suggest that apoptosis is an important pathway of heat-induced killing of these cells. In conclusion, the cell growth of prostatic cancers may be affected by the temperature through relationship of the cell cycle and hsp70.     

Structure and expression of the human gene encoding major heat shock protein HSP70.

We have cloned a human gene encoding the 70,000-dalton heat shock protein (HSP70) from a human genomic library, using the Drosophila HSP70 gene as a heterologous hybridization probe. The human recombinant clone hybridized to a 2.6-kilobase polyadenylated mRNA from HeLa cells exposed to 43 degrees C for 2 h. The 2.6-kilobase mRNA was shown to direct the translation in vitro of a 70,000-dalton protein similar in electrophoretic mobility to the HSP70 synthesized in vivo. From the analysis of S1 nuclease-resistant mRNA-DNA hybrids, the HSP70 gene appears to be transcribed as an uninterrupted mRNA of 2.3 kilobases. We show that the cloned HSP70 gene contains the sequences necessary for heat shock-induced expression by two criteria. First, hamster cells transfected with a subclone containing the HSP70 gene and flanking sequences synthesized a HSP70-like protein upon heat shock. Second, human cells transfected with a chimeric gene containing the 5' flanking sequences of the HSP70 gene and the coding sequences of the bacterial chloramphenicol acetyltransferase gene transcribed the chimeric gene upon heat shock. We show that the HSP70 mRNA transcribed in an adenovirus 5 transformed human cell line (293 cells) is identical to the HSP70 mRNA induced by heat shock.