Stressful preconditioning and HSP70 overexpression attenuate proteotoxicity of cellular ATP depletion

Abstract

. Stressful preconditioning and HSP70 overexpression attenuate proteotoxicity of cellular ATP depletion. Am J Physiol Cell Physiol 283: C521-C534, 2002. First published March 27, 2002 10.1152/ ajpcell.00503.2001.-Rat H9c2 myoblasts were preconditioned by heat or metabolic stress followed by recovery under normal conditions. Cells were then subjected to severe ATP depletion, and stress-associated proteotoxicity was assessed on 1) the increase in a Triton X-100-insoluble component of total cellular protein and 2) the rate of inactivation and insolubilization of transfected luciferase with cytoplasmic or nuclear localization. Both heat and metabolic preconditioning elevated the intracellular heat shock protein 70 (HSP70) level and reduced cell death after sustained ATP depletion without affecting the rate and extent of ATP decrease. Each preconditioning attenuated the stress-induced insolubility among total cellular protein as well as the inactivation and insolubilization of cytoplasmic and nuclear luciferase. Transient overexpression of human HSP70 in cells also attenuated both the cytotoxic and proteotoxic effects of ATP depletion. Quercetin, a blocker of stress-responsive HSP expression, abolished the effects of stressful preconditioning but did not influence the effects of overexpressed HSP70. Analyses of the cellular fractions revealed that both the stress-preconditioned and HSP70-overexpressing cells retain the soluble pool of HSP70 longer during ATP depletion. Larger amounts of other proteins coimmunoprecipitated with excess HSP70 compared with control cells deprived of ATP. This is the first demonstration of positive correlation between chaperone activity within cells and their viability in the context of ischemia-like stress. chaperone; protein aggregation; metabolic stress; ischemic tolerance AT THE CELLULAR LEVEL, failing energy metabolism and ATP depletion are the earliest cell-damaging factors of ischemic insults. In vivo, severe depletion of ATP is a proteotoxic stress that leads to dysfunction, destabilization, and aggregation of many cellular proteins, including enzymes, ion pumps, and constituents of cytoskeletal and contractile structures (1,9,17,27). Sustained lack of ATP is obviously lethal for the cell.On the contrary, a transient (reversible) drop in cellular ATP can confer tolerance to the next energy-depriving exposure, with heat shock proteins (HSPs) being involved in such an adaptive response (reviewed in Ref. 17). The HSP-involving cellular response appears to contribute to delayed ischemic tolerance (the second window of protection) found after heat or ischemic preconditioning in the myocardium. Like high temperature, cellular ATP depletion activates the heat shock transcription factor 1 (HSF1) that afterward induces HSP expression in the recovering cells (4, 36). Most HSPs are molecular chaperones stabilizing protein molecules under heat shock conditions in vitro and in vivo, and the same chaperone activity may protect HSP-enriched cells in the case of other proteotoxic stresses, e.g....

Overexpression of the Cochaperone CHIP Enhances Hsp70-Dependent Folding Activity in Mammalian Cells

“…6). Similar results were obtained in H9c2 cells, which are also sensitive to ATP depletion by 2-deoxyglucose and CCCP (14). These data also indicate that the effects of CHIP cannot be explained by global effects such as, for example, increasing the free pool of Hsp70 available for stressrelated chaperone activities or altering the balance between degradative and refolding chaperone functions, since such global effects should result in to protective effects even under conditions of ATP depletion.…”

Preeclamptic placental stress and over expression of mitochondrial HSP70

“…Similarly a reduced ATP/ADP ratio was noted in preeclamptic mitochondria. Severe depletion of ATP is a proteotoxic stress that leads to dysfunction, destabilization and aggregation of many cellular proteins (42). The stress may serve as a signal to initiate and propagate inflammatory processes resulting in apoptosis of placental tissue.…”

Identification of microRNAs associated with hyperthermia-induced cellular stress response

“…A few well-characterized stressors include hyperthermia, hypoxia, ionizing and non-ionizing radiation, ATP depletion, oxidative stress, and pathogenic stimuli (Schreck et al 1992;Feder and Hofmann 1999;Kabakov et al 2002;Kultz 2005;Diller 2006;Miller 2006;Millenbaugh et al 2008). At the cellular level, stressors can inflict strain on intracellular biomolecules (e.g., lipids, proteins, and DNA, and if such strain is appreciable, these biomolecules can undergo structural modifications that can preclude them from functioning properly.…”