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Cell cycle progression during chronic hyperthermia in S phase CHO cells
1Radiation Oncology Research Laboratory, University of California, San Francisco 94143.
Summary
Chinese hamster ovary (CHO) cells heated at 41.5°C showed thermotolerance after exiting S phase. However, cells in S phase at 42°C continued to be killed, indicating S phase thermotolerance is not expressed.
Area of Science:
- Cell Biology
- Cancer Research
- Thermal Biology
Background:
- Cellular response to heat stress is crucial for understanding cancer therapies.
- Thermotolerance, a protective mechanism against heat, varies across the cell cycle.
- Investigating S phase sensitivity to heat is key for optimizing hyperthermia treatments.
Purpose of the Study:
- To determine if Chinese hamster ovary (CHO) cells in S phase develop thermotolerance during chronic heat exposure.
- To investigate the cell cycle progression and heat sensitivity of CHO cells under different temperatures.
- To elucidate the relationship between cell cycle phase and the expression of chronic thermotolerance.
Main Methods:
- Chronic heat exposure of CHO cells at 41.5°C and 42°C.
- Cell cycle analysis to monitor progression through S, G2, and mitosis.
- Tritium suicide experiments to assess clonogenic cell survival.
- Microscopy to observe nuclear morphology changes.
Main Results:
- At 41.5°C, cells progressed out of S phase, exhibiting thermotolerance in subsequent phases.
- At 42°C, prolonged S phase delay (8-10 h) and G2 accumulation occurred.
- Continuous cell killing was observed in S phase cells at 42°C, indicating lack of thermotolerance.
- Altered nuclear morphology and abnormal division were noted in cells heated at 41.5°C.
Conclusions:
- Chronic thermotolerance is not expressed by CHO cells while they are in S phase.
- Thermotolerance is acquired after cells progress out of S phase during continuous heating.
- Heat sensitivity and cell cycle progression are significantly influenced by temperature during chronic exposure.