Correlation between redistribution of a 26 kDa protein and development of chronic thermotolerance in various mammalian cell lines

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Abstract
Previous studies suggested that a 26 kDa protein might play an important role in protein synthesis‐independent thermotolerance development in CHO cells. To determine if this phenomenon was universal, four mammalian cell lines, viz., CHO, HA‐1, murine Swiss 3T3, and human HeLa, were studied. Cells were heated at 42°C, and the level of 26 kDa protein in the nucleus was measured, together with clonogenic survival and protein synthesis. The results demonstrated that (1) the 26 kDa protein was present in the four different cell lines, and (2) the level of the 26 kDa protein in their nuclei was decreased by 30–70% after heating at 42°C for 1 hr. However, restoration of this protein occurred along with development of chronic thermotolerance. The protein synthesis inhibitor cycloheximide (10 μg/ml) neither inhibited the development of chronic thermotolerance nor affected the restoration of the 26 kDa protein in the nucleus. In fact, this drug protected cells from hyperthermic killing and heat‐induced reduction of 26 kDa protein in the nucleus. Heat sensitizers, quercetin (0.1 mM), 3,3′‐dipentyloxacarbocyanine iodide (DiOC5[3]: 5 μg/ml), and stepdown heating (45°C‐10 min→42°C), potentiated hyperthermic killing and inhibited or delayed the restoration of the 26 kDa protein to the nucleus. These results support a correlated, perhaps causal relationship between the restoration of the 26 kDa protein and chronic thermotolerance development in four different mammalian cell lines.