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Superoxide Dismutase Levels in Chinese Hamster Ovary Cells and Ovarian Carcinoma Cells after Hyperthermia or Exposure to Cycloheximide¹

Radiation Research Laboratory, Department of Radiology, University of Iowa, Iowa City, Iowa 52242 [D. P. L., L. W. O.], and Department of Radiation Therapy and Nuclear Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107 [D. B. L.]

Superoxide dismutase (SOD) activity in Chinese hamster ovary (CHO) and ovarian carcinoma (OvCa) cells was measured after exposure to hyperthermia and correlated with the development of thermotolerance. The SOD activity of each cell type was largely copper- and zinc-containing SOD activity. Both cell types had similar but low levels of SOD activity when the cells were grown at 37°C. After exposure for 2 h at 41.5°C, SOD activity of OvCa cells, but not of CHO cells, was increased. After exposure to 45°C for 15 min, SOD activity was also increased in the OvCa cells, but not in CHO cells. After 15 min at 45°C followed by 1 h incubation at 37°C, SOD activity was increased in OvCa and CHO cells; after an 8-h incubation at 37°C, SOD activity doubled in each cell type. Thermotolerance is maximal after 2 to 3 h of exposure at 41.5°C and after 8 to 10 h incubation at 37°C following exposure to 15 min at 45°C. The turnover of SOD activity in OvCa cells was estimated by the rate at which activity was lost following addition of cycloheximide (10 µg/ml). Twenty-four % of the activity was lost with a half-life of 10 min, and 76% was lost with a half-life of 4.5 h. Despite restriction of general protein synthesis 3 to 4 h after 45°C hyperthermia, SOD activity was increased at 1 and 8 h after exposure, presumably coincidental with heat shock protein synthesis and development of thermotolerance. These data suggest that SOD activity may be important in protecting cells exposed to heat and that it may play a role in the development of thermotolerance.

¹ Supported by Grants T32-CA09125 and PO1-CA11602 from the National Cancer Institute.

² Present address: Department of Radiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC.

³ To whom requests for reprints should be addressed.

Received 12/13/84. Revised 4/ 2/85. Accepted 4/ 3/85.

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