Detection of apoptosis using cyclic luciferase in living mammals.

Programmed cell death, apoptosis, is a crucial process involved in pathogenesis and progression of diseases, which is executed by cysteine aspartyl proteases (caspases). The caspase activities in living subjects and their regulation with small chemical compounds are of great interest for screening drug candidates or pathological agents. We describe a novel genetically encoded bioluminescent indicator for real-time imaging of caspase-3 activities in living cells and animals. The indicator is composed of an engineered firefly luciferase, of which the N- and C-terminal ends are linked with a substrate sequence of caspase-3 (Asp-Glu-Val-Asp). When activated caspase-3 digests the substrate sequence, the cyclized luciferase recovers its activity. The indicator provides a general means of evaluating effects of cytotoxic compounds or novel pharmacological chemicals and apoptosis.