ACTIVATION OF HEAT-SHOCK TRANSCRIPTION FACTOR-1 BY HYPERTONIC SHOCK IN 3T3 CELLS

The exposure of 3T3 cells to a medium made hypertonic by the addition of NaCl induced activation of a heat-shock transcription factor (HSF). This activation, as monitored by gel-mobility-shift assays, occurred within 10 min of hypertonic shock and was dose-dependent in relation t o the osmotic strength of the medium up to 0.7 osM. Competition analys is indicated that the effect of hypertonic shock on HSF binding activi ty was specific. The magnitude of the heat-shock element (HSE)-HSF bin ding induced by incubating the cells in a 0.7 osM medium was comparabl e in intensity and time course with that induced by a 44 degrees C hea t shock. Following removal of the stressors, the decrease in HSF-HSE b inding was more rapid in hypertonicity-shocked than in heat-shocked ce lls. Treatment of the cells with cycloheximide did not inhibit HSF-HSE binding, indicating that the activation was independent of new protei n synthesis. By using a specifically directed polyclonal serum, HSF1 w as identified as the transcription factor involved in the hypertonicit y-induced activation. HSF was also activated when a membrane-impermeab le osmolyte such as sucrose was used to increase the osmolarity of the medium. However, no HSF-HSE binding was observed after addition of gl ycerol (a freely membrane-permeable osmolyte) in excess. There was a t emporal relationship between the hypertonicity-induced volume decrease , the increase in the intracellular K+ concentration and the induction of HSF-HSE binding. In contrast, an increase in the intracellular Na concentration was not required to induce HSF-HSE binding. However, un like the heat-shock response, the activation of HSF by hypertonic shoc k did not lead to elongation of the RNA transcript of heat-shock prote in 70.