Antioxidant-mediated inhibition of the heat shock response leads to apoptosis (original) (raw)
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FEBS Letters, 1999
We tested the hypothesis that heat shock protein (Hsp) induction and cell death are mutually exclusive responses to stress. Despite activation of heat shock transcription factor 1 at temperatures ranging from 40 to 46 degrees C, Hsp72 and Hsp27 were not induced above 42 degrees C. Moreover, cells underwent apoptosis at 44 degrees C and necrosis at 46 degrees C, with mitochondrial cytochrome c release at both temperatures. However, only apoptosis was associated with caspase activation. Treatment of cells with z-VAD-fmk prior to heat shock at 44 degrees C failed to restore Hsp induction despite inhibition of heat-induced apoptosis. Furthermore, accumulation of Hsps after incubation at 42 degrees C rendered the cells resistant to apoptosis. These results suggest that lack of Hsp induction is the cause rather than the consequence of cell death.
Role of the human heat shock protein hsp70 in protection against stress-induced apoptosis
Molecular and Cellular Biology, 1997
Resistance to stress-induced apoptosis was examined in cells in which the expression of hsp70 was either constitutively elevated or inducible by a tetracycline-regulated transactivator. Heat-induced apoptosis was blocked in hsp70-expressing cells, and this was associated with reduced cleavage of the common death substrate protein poly(ADP-ribose) polymerase (PARP). Heat-induced cell death was correlated with the activation of the stress-activated protein kinase SAPK/JNK (c-Jun N-terminal kinase). Activation of SAPK/JNK was strongly inhibited in cells in which hsp70 was induced to a high level, indicating that hsp70 is able to block apoptosis by inhibiting signaling events upstream of SAPK/JNK activation. In contrast, SAPK/JNK activation was not inhibited by heat shock in cells with constitutively elevated levels of hsp70. Cells that constitutively overexpress hsp70 resist apoptosis induced by ceramide, a lipid signaling molecule that is generated by apoptosis-inducing treatments and...
Heat Shock Proteins Increase Resistance to Apoptosis
Experimental Cell Research, 1996
Heat shock treatment of cells increases their survival and resistance to apoptosis. The kinetics of development of this resistance correlates with the kinetics of synthesis of heat shock proteins (hsps). U937 and Wehi-s cells were cultured for 1 h at 42 degrees C, conditions which induced the synthesis of heat shock proteins 27, 70, and 90. The cells were subsequently permitted to recover for a 2-h period, prior to exposure to the apoptosis inducing agents actinomycin-D (5 micrograms/ml), camptothecin (5 micrograms/ml), and etoposide (25 micrograms/ml). Apoptosis was determined by both DNA fragmentation and flow cytometric analysis. Heat-shocked cultures had a smaller number of apoptotic compared to control cultures when both were exposed to apoptosis inducing stimuli. Transfected Wehi-s cells constitutively overexpressing human hsp 70 or 27 were then examined for their resistance to apoptosis inducing by these drugs. Using the MTT assay, hsp 27 and 70 overexpressing cells exhibited an increased resistance to cell death when compared to the parental line. The parental line demonstrated features of apoptosis, that is, cell shrinkage and single- and double-strand DNA breaks. Taken together these results demonstrate that an increase in cellular levels of hsp 27 or 70, either by a mild heat shock treatment or by stable transfection, increases the resistance of U937 and Wehi-s cells to apoptotic cell death.
Free Radical Biology and Medicine, 2002
Hyperthermia is used in cancer treatment and potentiates the cytotoxicity of radiation and certain chemotherapy drugs. The mechanism(s) of heat killing and those involved in heat potentiation of cytotoxic modalities are not understood. This study examines whether heat shock causes a redox imbalance, leading to oxidative changes in Chinese hamster ovary cells. Decreases in the GSH/GSSG ratio reflected an oxidative imbalance in heated (42°C) and in H 2 O 2 -challenged cells. Glucose provided protection against these changes. Glucose also protected cells against cytotoxicity of H 2 O 2 and/or hyperthermia (42 to 43°C). Glucose appears to protect cells against H 2 O 2 and heat shock by providing NADPH through its metabolism via the pentose phosphate cycle (PC). When cells were deprived of glucose, there was a marked decrease in the GSH/GSSG ratio and in NADPH levels, indicating a severe redox imbalance. Glucose deprivation caused cell death, which was consistent with increased accumulation of H 2 O 2 , since three distinct H 2 O 2 -detoxifying systems (N-acetyl-L-cysteine, sodium pyruvate, and catalase) rescued cells against cytotoxicity. Nontoxic levels of H 2 O 2 stimulated a corresponding increase in both PC activity and NADPH levels. NADPH levels and basal activity of the PC increased at 42°C. However, the oxidant-stimulated increases in PC activity and NADPH levels were lost in heated cells. Therefore, heat shock inactivates an important cellular defense mechanism against oxidants. These findings suggest that heat shock may enhance the cytotoxicity of oxidants by inhibiting increases in PC activity following oxidative stress. These data are potentially relevant to understanding the potentiation of cytotoxicity of radiation and oxidant-generating drugs by heat shock, used in combined modality cancer treatment.
Cancer research, 1993
When cells are exposed to heat shock, heavy metals, amino acid analogues, and other stresses, the heat shock transcription factor (HSF) is activated. The HSF then binds to the promoter of the heat shock genes, stimulating transcription of the heat shock proteins. Here, we demonstrate that exposure of NIH-3T3 cells to oxidants (H2O2 or menadione) also causes activation of the HSF. This activation is not blocked by inhibitors of protein synthesis (cycloheximide) or by inhibitors of protein kinases (2-aminopurine or genistein). In addition, the oxidant activated HSF is located in the nucleus of the cells. However, oxidant activation of the HSF does not result in the accumulation of hsp70 mRNA or of heat shock proteins. This is in contrast to the accumulation of heat shock proteins seen after heat shock activation of the HSF. This suggests that oxidant induced activation of HSF binding may have a function different from that of heat induced activation of HSF binding.
Plant, cell & environment, 2008
Exposure to adverse temperature conditions is a common stress factor for plants. In order to cope with heat stress, plants activate several defence mechanisms responsible for the control of reactive oxygen species (ROS) and redox homeostasis. Specific heat shocks (HSs) are also able to activate programmed cell death (PCD). In this paper, the alteration of several oxidative markers and ROS scavenging enzymes were studied after subjecting cells to two different HSs. Our results suggest that, under moderate HS, the redox homeostasis is mainly guaranteed by an increase in glutathione (GSH) content and in the ascorbate peroxidase (APX) and catalase (CAT) activities. These two enzymes undergo different regulatory mechanisms. On the other hand, the HS-induced PCD determines an increase in the activity of the enzymes recycling the ascorbate- and GSH-oxidized forms and a reduction of APX; whereas, CAT decreases only after a transient rise of its activity, which occurs in spite of the decreas...
Free Radical Biology and Medicine, 2002
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.