Figure 1.

The fluorescence emitted from HeLa-C3 cells changes from green to blue in response to induction of apoptosis. (a) HeLa-C3 cells grown on a cover-slip-based observation chamber were treated with three apoptotic inducers: 100 nM paclitaxel for 24 h, 10 ng ml⁻¹ TNF-α plus 10 μg ml⁻¹cycloheximide for 12 h and 12 h after UV-irradiation for 5 min. The phase images and fluorescent images of YFP and CFP were recorded from the same observation field in the green and blue channels, respectively. Merged color images of YFP (green) and CFP (blue) of HeLa-C3 cells show a significant increase in blue color exclusively in cells with cell shrinkage morphologies. The phase images show cell shrinkage and apoptotic bodies, which are significant indicators of apoptosis. Bar, 25 μm. (b) HeLa-C3 cells grown in a 96-well plate were treated with UV-irradiation (UV) for 5 min in the absence or presence of the pan caspase inhibitor Z-VAD-FMK (20 μM), or treated with 100 nM of paclitaxel (Tax) for 18 and 36 h. At the indicated time points, the fluorescence intensity was measured using a fluorescent plate reader. Data shown are means±s.d. from three experiments. (c) Caspase-3 activity was measured from HeLa-C3 cells using an in vitro assay described in Methods. The decrease in the Y/C emission ratio of the HeLa-C3 cells correlates well with the increase of caspase-3 activity during apoptosis. Data shown are means±s.d. from three experiments.