Thermal Protein Denaturation and Protein Aggregation in Cells Made Thermotolerant by Various Chemicals: Role of Heat Shock Proteins

doi:10.1006/excr.1995.1262

Experimental Cell Research

Volume 219, Issue 2, August 1995, Pages 536-546

https://doi.org/10.1006/excr.1995.1262 Get rights and content

Abstract

Thermotolerance (TT) induced by sodium arsenite (A-TT: 100 μM, 1 h, 37°C), ethanol (E-TT: 6% (v/v), 25 min, 37°C), and diamide (D-TT: 300 μM, 1 h, 37°C) was compared to heat-induced thermotolerance (H-TT: 15 min, 44°C) using HeLa S3 cells. All four pretreatments led to comparable levels of thermotolerance and also induced resistance to arsenite-, ethanol-, and diamide-induced toxicity (clonogenic ability). Stress-induced expression of the major heat shock proteins (hsp27, hsc70_(p73), hsp70_(p72), and hsp90) was generally highest in H-TT cells and lowest in A-TT cells. Interestingly, the four types of TT cells showed distinct differences in certain aspects of resistance against thermal protein damage. Thermal protein denaturation and aggregation determined in isolated cellular membrane fractions was found to be attenuated when they were isolated from H-TT and A-TT cells but not when isolated from E-TT and D-TT cells. The heat resistance in the proteins of the membrane fraction corresponded with elevated levels of hsp70_(p72) associated with the isolated membrane fractions. In the nuclear fraction, only marginal (not significant) attenuation of the formation of protein aggregates (as determined by TX-100 (in)solubility) was observed. However, the postheat recovery from heat-induced protein aggregation in the nucleus was faster in H-TT, E-TT, and D-TT cells, but not in A-TT cells. Despite the fact that elevated levels of hsp27, hsp70_(p73), and hsp70_(p72) were found in the TX-100 insoluble nuclear fraction derived from all TT cells, no correlation was found with the degree of resistance in terms of the accelerated recovery from nuclear protein aggregation. The only correlation between accelerated recovery from nuclear protein aggregates was that with total cellular levels of hsp27. The data indicate that heat-induced loss of clonogenic ability may be a multitarget rather than a single target event. A threshold of damage may exist in cells after exposure to heat; multiple sets of proteins in (different compartments of) the cell need to be damaged before this threshold is exceeded and the cell dies. As a consequence, stabilization of only one of these sets of proteins is already sufficient to render cells thermotolerant at the clonogenic level.

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Related compensatory mechanisms may be the reason for the synergistic interaction between these two stressors: compensatory responses induced by temperature may have been associated with heightened tolerance to nitrate, or vice versa. Phenomena where protective responses against one stressor enable organisms to transiently increase tolerance to another form of stress are called cross-tolerance (Kampinga et al., 1995) and are known to occur in fish. Initial heat shock exposure (+12 °C) increased the survival of tidepool sculpins, Oligocottus maculosus, when subsequently exposed to osmotic and hypoxic stressors (Todgham et al., 2005).
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Regular ArticleThermal Protein Denaturation and Protein Aggregation in Cells Made Thermotolerant by Various Chemicals: Role of Heat Shock Proteins

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Regular Article
Thermal Protein Denaturation and Protein Aggregation in Cells Made Thermotolerant by Various Chemicals: Role of Heat Shock Proteins