The Effects of Hyperthermia on the Protein-to-DNA Ratio of Isolated HeLa Cell Chromatin

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Abstract
HeLa [human cervical cancer] cells were heated for a fixed time interval (30 min) at various temperatures from 40-48.degree. C, or heated at a fixed temperature (45.degree. C) for various times between 7.5 and 90 min. After heating, chromatin was isolated and a heat-dependent increase in the protein to DNA ratio of the chromatin was found. After 30 min of heat at 45.degree. C, the protien to DNA ratio increased 1.57 .+-. 0.08-fold relative to control. No significant DNA degradation was found with these heat treatments. The increase in protein content was biphasic with increasing time at 45.degree. C or increasing temperature. If cells were incubated at 37.degree. C following hyperthermia at 45.degree. C or 15 or 30 min, the protein to DNA ratio of control cells was restored to normal within 3 h following 15 min of heat or 15 h following 30 min of heat. During the heating and recovery periods, there was no measurable increase in fraction of trypan blue stainable cells. To determine if these additional proteins in isolated chromatin were present in situ, double-label mixing experiment was done. The protein from heated cells apparently binds to chromatin more effectively than do proteins from control cells.

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