Fig. 4

Transactivation activity of HSF1 is required for cell proliferation, AIG, and assembly of mitotic spindles. a Depletion of HSF1 attenuated cell proliferation. Cells were transduced with various volumes of virions containing HSF1 shRNAs or not, and then cell proliferation was analyzed daily by the trypan blue exclusion assay. b Immunoblot analysis of the levels of endogenous HSF1 in CGL2 cells and the FLAG-tagged wild-type and mutant HSF1 in HSF1-depleted cells. Red asterisk indicates the position of each HSF1 expressed in the cells. c and d Depletion of HSF1 suppressed AIG and induced spindle abnormalities. Overexpression of HSF1 isoforms lacking transactivation activity could not rescue HSF1 depletion-induced AIG suppression and spindle defects. HSF1-depleted cells were transduced with virions containing cDNAs of FALG-tagged wild-type (wt) HSF1 or mutant HSF1 for 50 h and then collected for immunoblotting analysis (b), AIG (c), or spindle abnormalities (d). e and f Overexpression of HSP70 reduced the cell death and rescued the spindle defects induced by HSF1 depletion. The means ± SD from at least three independent experiments are shown. *p < 0.01 by Student’s t test