Nuclear-to-Cytoplasmic Signaling

Cellular genomes are constantly exposed to stress from both exogenous and endogenous genotoxic or DNA-damaging agents. To cope with these stresses, cells evolved orchestrated DNA damage response (DDR) pathways that modulate cell cycle progression, DNA repair, and the ultimate choice between life and death. The importance of appropriately managing genotoxic stress conditions is underscored by the many pathological conditions that may result from deficiencies in DDR components, such as premature ageing, neurodegeneration and predisposition to cancer development. NF-κB, a major stress-responsive transcription factor that is ubiquitously expressed in different cell types, is normally kept inactive in the cytoplasm but is also activated by DNA damage.  Activated NF-κB then migrates into the nucleus and modulates expression of an array of genes (such as survival genes) depending on the offending DNA lesions. Due to the spatial separation between the initiating event (DNA damage in the nucleus) and the signal target (inactive NF-κB in the cytoplasm), the concept of a nuclear-to-cytoplasmic NF-κB signaling pathway was proposed over two decades ago; however, its complete molecular definition still remains incompletely understood. Understanding this mechanism may allow us to develop animal models to investigate the physiological roles of this particular signaling event in normal and pathological processes.  Moreover, such an understanding may also help develop new therapeutics to increase the efficacy of anticancer agents (many of which cause DNA damage to kill cancer cells) since NF-κB activation in both cancer cells and surrounding normal cells is implicated in malignant progression of multiple human cancer types.