HSF2 expression declines during mitosis in a cell type–specific manner, thus protecting cells against prolonged mitosis. (A–D) Representative immunoblots of HSF2 protein in unsynchronized (U) and mitotic (M) MCF7, HeLa, MDA-MB-231, and WI38 cells. Cells were synchronized into mitosis by a thymidine-nocodazole block and collected by mitotic shake-off. Cells were left untreated (C) or subjected to heat shock (HS; 30 min at 42°C, 1 h at 37°C). Immunoblotting was performed with the indicated antibodies. Tubulin serves as a loading control. <, HSF2; *, unspecific band. (left middle panels) Quantification of immunoblots (n = 3) showing HSF2 protein related to tubulin. (right middle panels) Quantification of immunoblots (n = 3) showing Hsp70 induction in unsynchronized and mitotic cells. Samples were analyzed as in Fig. 2 B. (A and C, right) qRT-PCR analysis of hsf2 mRNA in unsynchronized (U) and mitotic (M) cells (n = 3). Relative quantities of hsf2 mRNA were analyzed as in Fig. 1 B. (E) qRT-PCR analysis of hsp70 mRNA induction upon a 30-min heat shock at 42°C in unsynchronized (U) and mitotic (M) MCF7, HeLa, MDA-MB-231 (MDA), and WI38 cells. Relative quantities of hsp70 mRNA were analyzed as in Fig. 2 C. (n = 3). (F) Duration of mitosis was measured from rounding up of cells until the formation of two daughter cells in untreated (C) or heat-treated (pulse at 42°C or 30 min at 42°C) cells. At least 20 cells per treatment from five (MCF7 and MDA-MB-231) or two (HeLa and WI38) individual experiments were monitored. All values represent mean + SEM (error bars). n.s., not specific.