Heat shock proteins and protection of proliferation and translation in mammalian cells.

The characteristics of heat shock protein(s) (HSP) and thermotolerance induction were examined in Chinese hamster ovary cells following two diverse nonlethal heat shocks: a continuous 41 degree exposure and a 45 degree, 5-min exposure. While induction of both HSP and thermotolerance were observed to initially develop simultaneously, a significant period was observed during which HSP induction was not accompanied by any further increase in the cells' ability to survive a thermal stress. Conversely, the achievement of the full tolerant state, as measured by colony survival, correlates in these instances with the moment at which development of the induction of HSP either ceased or began to be repressed. When a 99% lethal 45 degree, 22-min heat shock was examined, HSP and a thermal resistance were again observed to develop synchronously, despite the fact that the tolerance was measured in only 1% of the cell population. In this instance, a new protein of molecular weight 66,000 was observed which was not visibly induced by either of the two nonlethal treatments. Finally, the ability of heat-shocked thermotolerant cells to translate proteins following a second heat challenge (protection of translation) was investigated as an alternative measure of thermotolerance. While a protection of translation which encompassed several normal cellular proteins was observed, the phenomenon paralleled the induction and repression phases of HSP synthesis and was therefore not related to thermotolerance.