Signal transduction controls heterogeneous NF-κB dynamics and target gene expression through cytokine-specific refractory states

Cells respond dynamically to pulsatile cytokine stimulation. Here we report that single, or well-spaced pulses of TNF alpha (> 100 min apart) give a high probability of NF-kappa B activation. However, fewer cells respond to shorter pulse intervals (<100 min) suggesting a heterogeneous refractory state. This refractory state is established in the signal transduction network downstream of TNFR and upstream of IKK, and depends on the level of the NF-kappa B system negative feedback protein A20. If a second pulse within the refractory phase is IL-1 beta instead of TNF alpha, all of the cells respond. This suggests a mechanism by which two cytokines can synergistically activate an inflammatory response. Gene expression analyses show strong correlation between the cellular dynamic response and NF-kappa B-dependent target gene activation. These data suggest that refractory states in the NF-kappa B system constitute an inherent design motif of the inflammatory response and we suggest that this may avoid harmful homogenous cellular activation.