High sensitivity and low-cost flavin luciferase (FLUX)-based reporter gene for mammalian cell expression.

Luciferase-based gene reporters generating bioluminescence signals are important tools for biomedical research. Amongst the luciferases, flavin-dependent enzymes use the most economical chemicals. However, their applications in mammalian cells are limited due to their low signals compared to other systems. Here, we constructed Flavin Luciferase from Vibrio campbellii (Vc) for Mammalian Cell Expression (FLUX) by engineering luciferase from V. campbellii (the most thermostable bacterial luciferase reported to date) and optimizing its expression and reporter assays in mammalian cells which can improve the bioluminescence light output by >400-fold as compared to the nonengineered version. We found that the FLUX reporter gene can be overexpressed in various cell lines and showed outstanding signal-to-background in HepG2 cells, significantly higher than that of firefly luciferase (Fluc). The combined use of FLUX/Fluc as target/control vectors gave the most stable signals, better than the standard set of Fluc(target)/Rluc(control). We also demonstrated that FLUX can be used for testing inhibitors of the NF-κB signaling pathway. Collectively, our results provide an optimized method for using the more economical flavin-dependent luciferase in mammalian cells.