Heat shock proteins and thermotolerance; a comparison of induction kinetics

The hypothesis that the expression of heat shock proteins following a preliminary hyperthermic treatment is responsible for subsequent thermotolerance to a second heat treatment is examined. CHO cells were given a 12 min, 45 degrees C pretreatment and then incubated for varying intervals at 37 degrees C. The synthesis of certain intracellular proteins was monitored as a function of time post-incubation by using 35S-methionine incorporation as determined in SDS polyacrylamide gel electrophoresis. Cell survival was concurrently measured by challenging the cells with a second heat treatment (45 degrees C/27 min). Major heat shock proteins were observed at 68 000, 89 000 and 110 000 daltons. The synthesis of these proteins was significantly reduced in the presence of cyclohexamide. The total 35S-methionine incorporation into these proteins correlated well with the induction of survival resistance (thermotolerance). An approximate exponential relationship between survival and the amount of each of these proteins may occur. These and other heat shock proteins were also present, in a significantly reduced degree, in control (non-heat shocked) cells maintained under normal culture conditions at 37 degrees C. It is possible that heat shock proteins are responsible for the phenomenon of thermotolerance.