Thermotolerance induced by heat, sodium arsenite, or puromycin: Its inhibition and differences between 43°C and 45°C

Abstract

AbstractWhen CHO cells were treated either for 10 min at 45–45.5°C or for 1 hr with 100 μM sodium arsenite (ARS) or for 2 hr with 20 μg/ml puromycin (PUR‐20), they became thermotolerant to a heat treatment at 45–45.5°C administered 4–14 hr later, with thermotolerance ratios at 10−3 isosurvival of 4–6, 2–3.2, and 1.7, respectively. These treatments caused an increase in synthesis of HSP families (70, 87, and 110 kDa) relative to total protein synthesis. However, for a given amount of thermotolerance, the ARS and PUR‐20 treatments induced 4 times more synthesis than the heat treatment. This decreased effectiveness of the ARS treatment may occur because ARS has been reported to stimulate minimal redistribution of HSP‐70 to the nucleus and nucleolus. Inhibiting protein synthesis with cycloheximide (CHM, 10 μg/ml) or PUR (100 μg/ml) after the initial treatments greatly inhibited thermotolerance to 45–45.5°C in all cases. However, for a challenge at 43°C, thermotolerance was inhibited only for the ARS and PUR‐20 treatments. CHM did not suppress heat‐induced thermotolerance to 43°C, which was the same as heat protection observed when CHM was added before and during heating at 43°C without the initial heat treatment. These differences between the initial treatments and between 43 and 45°C may possibly be explained by reports that show that heat causes more redistribution of HSP‐70 to the nucleus and nucleolus than ARS and that redistribution of HSP‐70 can occur during heating at 42°C with or without the presence of CHM. Heating cells at 43°C for 5 hr after thermotolerance had developed induced additional thermotolerance, as measured with a challenge at 45°C immediately after heating at 43°C. Compared to the nonthermotolerant cells, thermotolerance ratios were 10 for the ARS treatment and 8.5 for the initial heat treatment. Adding CHM (10 μg/ml) or PUR (100 μg/ml) to inhibit protein synthesis during heating at 43°C did not greatly reduce this additional thermotolerance. If, however, protein synthesis was inhibited between the initial heat treatment and heating at 43°C, protein synthesis was required during 43°C for the development of additional thermotolerance to 45°C. These data suggest that if a considerable amount of synthesis of HSP families occurred after the initial treatment before heating at 43°C, redistribution during 43°C of the previously synthesized HSP families could lead to the additional thermotolerance to 45°C.