Nuclear translocation of green fluorescent protein‐nuclear factor κB with a distinct lag time in living cells

Abstract
A highly fluorescent mutant form of the green fluorescent protein (GFP) has been fused to the human nuclear factor κB (NF-κB) p50 and p105 (p50/IκBγ), a precursor protein of NF-κB p50. GFP-p50 and GFP-p105 were expressed in monkey COS-7 cells and human HeLa cells. Translocation of these chimeric proteins was observed by confocal laser scanning microscopy. GFP-p50 (without IκBγ) in the transfected cells resided in the nucleus. On the other hand, GFP-p105 (GFP-p50 with IκBγ) localized only in the cytoplasm before stimulation and translocated to the nucleus with stimulant specificity similar to that of native NF-κB/IκB. In addition, the translocation of NF-κB to the nucleus had a distinct lag time (a quiescent time) in the target cells. The lag time lasted 10–20 min after stimulation with hydrogen peroxide or tumor necrosis factor α. It was suggested that this might be due to the existence of a limiting step where NF-κB is released from NF-κB/IκB by the proteasome.