Nuclear factor-B (NF-B) is an inducible cytoplasmic transcription factor that plays a role as a master regulator of airway mucosal inflammation. The prototypical ("canonical") NF-B pathway controls cytoplasmic to nuclear translocation in response to stimulation by the mononuclear cytokine, TNF. Despite intensive investigation, the spectrum of kinases involved in the canonical NF-B pathway has not yet been systematically determined. Here we have applied a high throughput siRNA-mediated loss-of-function screening assay to identify novel kinases important in TNF-induced NF-B signaling. Type II A549 epithelial cells stably expressing an IL-8/luciferase reporter gene optimized for high throughput siRNA format (Z score of 0.65) and siRNAs for 636 human kinases were reversetransfected and screened in the assay. 36 candidate genes were identified that inhibited TNF signaling with a Z score deviation of <؊1.3 in replicate plates. From this group, 11 kinases were selected for independent validation, of which eight were successfully silenced. Six kinases were validated, including ATM, CDK2, -5, and -7, CALM3, MAPAKP5, and MAP3K/MEKK3. The surprising function of ATM in TNF signaling was confirmed where reduced NF-B/RelA translocation and Ser-276 phosphorylation were seen in ATM ؊/؊ mouse embryo fibroblasts. These data indicate that ATM is a key regulatory kinase that may control global NF-B activation in the TNF-induced canonical pathway.Eukaryotic tissues respond to signals in their extracellular environment through the induction of long term phenotypic plasticity. An important mechanism for this plasticity is through the activation of cell surface receptors coupled to intracellular signal transduction networks, the activation of which, in turn, induces a reactive gene expression. One specific example occurs in airway mucosal surfaces that normally promote gas exchange, facilitate particulate matter clearance through the muco-ciliary escalator, and protect against oxidative damage (1). Within this surface, sentinel epithelial cells are responsible for activating the innate inflammatory response upon stimulation with macrophage-derived cytokines via the plasma membrane-anchored TNF/death receptor (TNFR) 2 superfamily (2, 3). Liganded TNFRs signal intracellularly through nuclear factor-B (NF-B), an inducible cytoplasmic transcription factor that temporally coordinates expression of gene networks, including interferon, cytokine, and anti-apoptotic genes (4 -6). As a result, the mucosal surface assumes a pathogen-resistant and proinflammatory phenotype. Because of its central role in airway inflammatory disease, the NF-B signaling pathway has been extensively investigated.Under resting conditions, NF-B is inhibited in the cytoplasm by binding to members of the IB family of inhibitory proteins, resulting in cytoplasmic retention and inactivation of its latent DNA binding activity. TNFR-ligand binding results in submembranous recruitment of death domains containing adapter molecules, including the TNF receptor-associated factors...