FIG. 6.

Suppression of JNK activation and cell death in fibroblasts subjected to severe heat shock correlates with Hsp72 accumulation. (A) Suppression of JNK activation in response to severe heat shock correlates with Hsp72 accumulation after mild heat shock. Cells were pretreated with mild heat shock (45°C, 30 min), incubated for different time periods at 37°C, and then subjected to severe heat shock (45°C, 75 min). JNK activity (upper panel) was measured using c-Jun as the substrate. JNK activity in nonpreheated cells (−) after severe heat shock is also shown. The Hsp72 level (lower panel) was measured by immunoblotting with antibodies to inducible Hsp72 as described for Fig. 1A and B. (B) Increase in viability of cells subjected to severe heat shock correlates with JNK suppression. Cells were treated as explained for panel A, and their viability was measured 24 h later as explained for Fig. 1C. JNK activity and Hsp72 accumulation were measured as explained for panel A. This experiment was reproduced three times. Data shown here represent a typical experiment.