The effect of extracellular Ca2+ and temperature on the induction of the heat-shock and glucose-regulated proteins in hamster fibroblasts.

The expression of two stress-inducible protein families was examined in hamster fibroblast cells. These are the heat-shock and glucose-regulated proteins which have been shown to be highly inducible by heat and glucose-starvation, respectively. Our studies here demonstrate that the two sets of proteins can be induced simultaneously or separately. The enhanced synthesis of one set of proteins apparently does not affect the level of expression of the other set. We further show that pre-incubation of these fibroblast cells in calcium-free medium does not inhibit the synthesis of the 70 and 72-kilodalton heat-shock proteins at the elevated temperature. While extracellular calcium is apparently not involved in the activation of the heat-shock protein synthesis, its removal from the culture medium has a modest stimulative effect on the synthesis of the glucose-regulated proteins. Our results are consistent with the hypothesis that the expression of these two sets of proteins are regulated by separate control mechanisms.