FIG. 5.

Expression of Hsp90 and induced thermotolerance in HSF1-null cells. (A) Expression of heat shock proteins, including Hsp90, in three independently generated cHSF1-null clones (33, 47, and 59). Wild-type, HSF1-null, and HSF3-null cells were incubated at 43.5°C for 24 h. Accumulations of Hsp90α and Hsp90β mRNAs were examined by Northern blot analysis. Accumulations of Hsp90, Hsp70, and Hsp25 proteins were determined by Western blot analysis. (B) cHSF1-null cells acquire induced thermotolerance. cHSF1-null cells (HSF1^−/−/− 59) and cHSF1-restored cells (D2) as well as wild-type cells (wt) grown at 37°C were incubated at a lethal 46°C temperature for the indicated periods. The numbers of surviving cells were counted by a colony formation assay, and percent survival is shown. Some cells were treated at a sublethal 43°C for 30 min and then allowed to recover for 2 h before lethal heat shock (wt:TT, HSF1^−/−/− 59:TT, and D2:TT). Means of three independent experiments are shown.