Heat shock response by cells treated with azetidine-2-carboxylic acid

The purpose of this study is to reinvestigate the heat shock response in ce lls treated with the antimetabolite azetidine-2-carboxylic acid (azetidine) , an analogue of proline. Previous studies could not clearly discriminate b etween the progressive thermosensitization caused by amino acid analogues a nd a parallel induction of thermotolerance by heat shock. Incubation of H35 cells with 2.5 mm azetidine causes an increasing thermosensitization which achieves a maximum after approximately 18-22 h. At this point, azetidine d oes not prevent the development of acute thermotolerance following a heat s hock at 42.5 degrees C, or the simultaneous induction of chronic thermotole rance during mild hyperthermia at 38-41 degrees C. However, for both the ac ute and chronic heating conditions thermotolerance levels are reduced in pr oportion with azetidine-thermosensitization. Incorporation of azetidine cau ses an apparent downward temperature shift of approximately 1 degrees C rel ative to the time-temperature relationships for normal, or following heat s hocks, for thermotolerant cells. After 18 h of incubation with azetidine, p rotein synthesis is reduced by a factor of 4 and cells show a preferential synthesis of heat shock proteins (hsp). A heat shock then, although inducin g thermotolerance, is not followed by any noticeable effect on the synthesi s of hsps. It is shown that the combination of prolonged azetidine treatmen t and heat shock causes a persistent inhibition of protein synthesis. This is hypothesized to result in the development of hsp synthesis independent t hermotolerance. Additional treatment following heat shock in azetidine-trea ted cells with the protein synthesis inhibitor cycloheximide does not affec t the induction of thermotolerance. In contrast to the heat shock response, no thermotolerance induction is observed in azetidine-treated cells after an exposure to sodium arsenite.