Increase of epidermal growth factor-stimulated cell-cycle progression and induction of thermotolerance by heat shock: Temperature and time relationship

When quiescent confluent cultures were incubated at increased temperature and then incubated at 37°C prior to a second increase of temperature (46°C) it appeared that heat-induced morphological alteration and ability to proliferate could be influenced by the previous thermal history of the cells. Incubations for 20 min in a temperature range of 41–46°C caused cells to develop thermotolerance within 3 h of incubation at 37°C.Confluent quiescent Swiss mouse 3T3 cells were incubated at 41.8, 43.7 or 45.6°C and then reincubated at 37°C to determine the effects of heat shock on the mitogenic effects of epidermal growth factor (EGF). Preincubation at 43.7°C or 45.6°C enhanced stimulation of G1-S progression by EGF. Preincubation at 43.7°C markedly increased the rate at which cells enter the S phase without changing the length of the lag phase. A comparison of the duration of incubation at 43.7°C for potentiation of EGF-induced DNA synthesis and that for induction of thermotolerance showed that a similar time interval for induction of effect could be implied.