Induced Thermal Tolerance and Heat Shock Protein Synthesis in Chinese Hamster Ovary Cells

We have performed experiments to determine the kinetics of induction of thermal tolerance in Chinese hamster HA-1 cells, and the effects of heat treatments on the recovery of protein synthesis, with particular attention to whether heat induces specific proteins, perhaps the heat shock proteins (HSP). The kinetics of the development of thermal tolerance were measured by increases in cellular survival. In parallel experiments, the effects of heat treatment on the recovery of protein synthesis in HA-1 cells were examined. After heating (45 degrees, 20 minutes), some of these cells were immediately labeled with 35S-methionine (10 microCi/ml) for 1 hour at 37 degrees, while the others were incubated at 37 degrees for 1-8 hours and then labeled. The cell samples were prepared for electrophoresis on a gradient SDS gel. The incorporation of label into HA-1 cell proteins was drastically inhibited by the 45 degrees heat treatment, but recovered gradually during the 8-hour incubation period at 37 degrees C. A comparison of the proteins synthesized following heat shock with those synthesized by non-heated cells showed that the levels of synthesis of certain proteins were greatly enhanced following the 45 degrees treatment. By 8 hours, it was qualitatively apparent that three proteins, with molecular weights of 59K, 70K and 87K, were synthesized in greater amounts than in untreated cells. The kinetics of HSP synthesis were compared to the kinetics of thermal tolerance; these showed good correlation. Overall protein synthesis also increased during this time, although at a rate slower than the synthesis of the HSP. The question of whether the HSP play a causative role in the development of thermal tolerance and if so, what role might be, has not been answered.