Stress response of Tetrahymena pyriformis to arsenite and heat shock: differences and similarities.

Molecular and cellular events associated with the response of Tetrahymena pyriformis to stress induced by sodium meta-arsenite, have been examined by pulse-labelling experiments. This stress agent induces the synthesis of two main groups of proteins, with molecular masses in the ranges 70-75 kDa and 25-29 kDa, together with other proteins of molecular masses 92, 83, 46, 42 (two species), 36 and 35 kDa. Comparison of the results with those of a previous study concerning the response of T. pyriformis to heat-shock, shows that the two main groups of proteins, as well as the 92-kDa and 35-kDa species, which seem to be similarly induced by both types of stress, display similar or identical peptide maps. Other stress proteins seem to be either heat-shock-specific or arsenite-specific. Studies using actinomycin D suggest that the response to arsenite is controlled mainly at the transcriptional level, for the 70-75-kDa group and 92-kDa proteins, but it seems that the other arsenite-induced proteins are subjected to transcriptional/translational control. In fact, results obtained by northern blotting, show that the mRNA coding for the 70-kDa stress protein is present only in stressed cells, whereas the 27-kDa-coding mRNA is present both in stressed and in unstressed cells. Inhibition of translation by cycloheximide has shown that heat-shock-induced-messengers are conserved under heat to be immediately translated upon removal of that inhibitor. Qualitatively similar results are obtained after prolonged treatments of T. pyriformis with arsenite and cycloheximide. The most striking difference between the responses of T. pyriformis to these two stress conditions is that arsenite does not repress normal protein synthesis so drastically as heat shock. In addition, our results suggest that some arsenite-induced messengers may be more stable than the corresponding heat-shock-induced messengers.