Heat protectors and heat-induced preferential redistribution of 26 and 70 kDa proteins in Chinese hamster ovary cells.

An overall increase of 40% in nuclear-associated protein has been shown to be one of the sequellae of exposure of eukaryotic cells to elevated temperatures. Several investigators have shown that the increased protein/DNA ratios correlated well with the degree of cytotoxicity. In previous investigations, we have shown that cycloheximide, which protects the cell from the killing effects of heat, produces a dramatic reduction of the bulk nuclear-associated proteins after heating. In this investigation, we studied a previously unobserved efflux of a 26 kDa protein after heat shock and the preferential accumulation of the 70 kDa protein. The 26 kDa protein was shown not to be a member of previously described heat shock protein families. Preferential reduction of a 26 kDa protein and accumulation of a 70 kDa protein was observed in nuclei isolated from Chinese hamster ovary cells after heating at 43 degrees C. After heat treatment, the 26 kDa protein in the nucleus was decreased to a level 0.1-0.3 times the original amount in unheated cells, and the 70 kDa protein in the nucleus increased by a factor of 1.6-1.8. The normal levels of these two proteins were restored when cells were incubated at 37 degrees C following heat shock. Cells treated with heat protectors, cycloheximide and histidinol, demonstrated approximately the same redistribution in nuclear 26 and 70 kDa proteins immediately after heating as those not exposed to these drugs. On the other hand, restoration to control levels was much faster in the protector-treated cells, suggesting that "repair" of heat-induced damage is an important factor in the cells ability to survive this insult. Return to normal protein levels did not require new protein synthesis.