Real-time imaging of ligand-induced IKK activation in intact cells and in living mice

The transcription factor NF-kappa B is a key regulator of cellular activation, proliferation and apoptosis. Defects in the NF-kappa B pathway contribute to a broad array of malignant, neurodegenerative and chronic inflammatory diseases. IKK-dependent I kappa B alpha degradation by the 26S proteasome is a critical NF-kappa B regulatory control point, which is emerging as an important target for drug development. To directly monitor regulation of IKK activation in intact organisms, we engineered an I kappa B alpha-firefly luciferase (I kappa B alpha-FLuc) fusion reporter. In cultured cells and living animals, the reporter provided a continuous, noninvasive readout of the kinetics of ligand-induced IKK activation and the pharmacodynamics of selective inhibitors of both IKK and the 26S proteasome. This I kappa B alpha-FLuc reporter now permits continuous readout of IKK activation in vivo, facilitates development and validation of target-specific therapeutics, and complements conventional NF-kappa B transcriptional reporters for more complete temporal and regional investigations of the NF-kappa B signaling pathway in health and disease.