Thermotolerance induced by heat, sodium arsenite, or puromycin: its inhibition and differences between 43 degrees C and 45 degrees C.
When CHO cells were treated either for 10 min at 45-45.5 degrees C or for 1 hr with 100 microM sodium arsenite (ARS) or for 2 hr with 20 micrograms/ml puromycin (PUR-20), they became thermotolerant to a heat treatment at 45-45.5 degrees 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 micrograms/ml) or PUR (100 micrograms/ml) after the initial treatments greatly inhibited thermotolerance to 45-45.5 degrees C in all cases. However, for a challenge at 43 degrees C, thermotolerance was inhibited only for the ARS and PUR-20 treatments. CHM did not suppress heat-induced thermotolerance to 43 degrees C, which was the same as heat protection observed when CHM was added before and during heating at 43 degrees C without the initial heat treatment. These differences between the initial treatments and between 43 and 45 degrees 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 degrees C with or without the presence of CHM. Heating cells at 43 degrees C for 5 hr after thermotolerance had developed induced additional thermotolerance, as measured with a challenge at 45 degrees C immediately after heating at 43 degrees 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 micrograms/ml) or PUR (100 micrograms/ml) to inhibit protein synthesis during heating at 43 degrees C did not greatly reduce this additional thermotolerance. If, however, protein synthesis was inhibited between the initial heat treatment and heating at 43 degrees C, protein synthesis was required during 43 degrees C for the development of additional thermotolerance to 45 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)