Fig. 5. Conditional activation of p53 causes decreased proliferation and increased apoptosis. (A) Ki-67 immunofluorescence of OSEC2 cells demonstrates that, on day 1, OSEC2 cells at 34°C had many positively stained nuclei (red), whereas OSEC2 cells at 39°C had decreased numbers of Ki-67-positive nuclei and, thus, had decreased proliferation. Ki-67 staining of non-ts IOSE 397 and WI38 cells did not show the same pattern: with the switch in temperature from 34 to 39°C, the number of Ki-67-positive nuclei in the IOSE 397 cultures increased, whereas the number of positive nuclei in WI38 cells remained unchanged. (B) Cell death detection ELISA to quantify levels of apoptosis of the cells demonstrated that the percentage of apoptotic OSEC2 cells at 39°C was significantly higher than at 34°C. Treatment of cells at 34°C with LY294002 also resulted in increased apoptosis.