Role of HSF activation for resistance to heat, cold and high-temperature knock-down.

Regulation of heat shock proteins (Hsps) by the heat shock factor (HSF) and the importance of these proteins for resistance to heat stress is well documented. Less characterized is the importance of Hsps for cold stress resistance although Hsp70 is known to be induced following long-term cold exposure in Drosophila melanogaster. In this study, a temperature-sensitive HSF mutant line was used to investigate the role of HSF activation following heat hardening, rapid cold hardening (RCH) and long-term cold acclimation (LTCA) on heat and cold resistance, and this was correlated with Hsp70 expression. In addition, the effect of HSF activation on high-temperature knock-down resistance was evaluated. We found a significantly decreased HSF activation in the mutant line as compared to a corresponding control line following heat hardening, and this was correlated with decreased heat resistance of the mutant line. However, we did not find this difference in HSF activity to be important for resistance to cold stress or high-temperature knock-down. The findings indicate that induction of stress genes regulated by HSF, such as Hsps, although occurring following LTCA, are not of major importance for cold stress resistance and neither for RCH nor high-temperature knock-down resistance in D. melanogaster.