We have a long-standing interest in polyamine biochemistry. Polyamine metabolism can be affected by environmental stress. Of particular note is the induction of ornithine decarboxylase gene expression in mammalian cells by hypotonic shock. As an initial effort, we have examined some of the earlier responses of cells to osmotic stress. We unexpectedly discovered that osmotic shock is a potent way to activate heat shock trans-acting factor (HSF) binding activity. The activation occurred within 10 min after osmotic shock, as rapid as the well known heat shock response. We also demonstrated that the activation is due to trimerization of HSTF. The signal transduction pathway which leads to the activation of HSTF is under intense study in many laboratories. Our finding provides an alternate model for investigating the mechanism of HSTF activation.
Hypo- and hyper-osmotic stresses represent two opposing physical forces in nature. Surprisingly, both stresses activate heat shock factor 1, a universal stress transcription factor present in all eukaryotes. What is the mechanism of activation? What is the physiological significance of this stress response?