Modification of the heat response and thermotolerance by cycloheximide, hydroxyurea, and lucanthone in CHO cells

Exposure of Chinese hamster ovary cells to cycloheximide for 2 hr immediately prior to 450C hyperthemia increased cell survival by a factor of 1.8. The increase in cell survival was independent of the heating time for heat treatments longer than 10 min at 450C and was similar with cycloheximide concentrations of 1 and 10 μg/ml. Thermotolerance was induced by an initial treatment of 10 min at 450C (conditioning), developed during a 7-hr incubation period at 370C, and was defined by the hyperthermia dose response with a second 450C heat treatment. When cycloheximide (1μg/ml) was added to the medium after heat conditioning and removed prior to the second heat treatment, the degree of thermotolerance was 50% less than that in medium controls. A 3-hr exposure to 10 μg/ml cycloheximide at 370C by itself did not result in the progressive development of thermotolerance which occurs after a conditioning heat treatment. In contrast to the effects of cycloheximide, hydroxyurea (1 mM) and lucanthone (5 μg/ml) showed little effect on the heat sensitivity and the development of thermotolerance after heat conditioning. Although the results can be interpreted that the development of thermotolerance requires the synthesis of new proteins, but not that of DNA and RNA, alternate interpretations are possible based on known cycloheximide effects aside from its primary inhibition of protein synthesis