We carried out live imaging of PC12 cells expressing SCAT3, a caspase-3 cleavage peptide sequence linking two fluorescent proteins, ECFP and Venus, which function respectively as the donor and acceptor for FRET. Live imaging of SCAT3-expressing cells was performed from 60 to 300min after exposure to sodium arsenite (NaAsO2: 0, 1, 5, or 10μM) was initiated. We then measured the emission ratio of ECFP to Venus to monitor the activity of caspase-3 and found that the ratio was temporally and dose-dependently increased by NaAsO2. The mean ECFP/Venus emission ratio between 200 and 300min after exposure to NaAsO2 at a dose of 5 or 10μM, but not at 1μM, was significantly higher than that in the control group. We showed by other methods that NaAsO2 significantly increased the amount and activity of mature caspase-3 and the amount of nucleosomes generated from DNA fragmentation, and decreased cell viability. However, methods other than live imaging required a longer time and higher doses of NaAsO2 than did live imaging to detect significant effects. This result suggests that live imaging using SCAT3 is a useful method for the screening of chemical toxicities and for improving the efficiency of toxicity evaluation.
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