Keynote Talk: Measurement, Manipulation and Consequences of NF-kB Dynamics

The NF-κB system controls inflammatory responses to pathogens and participates in cell fate decision-making. Aberrant NF-κB signalling is linked to inflammatory disease and cancer. We showed that NF-κB can oscillate between the cytoplasm and nucleus in single cells (from cell lines and primary cells from reporter transgenic mice). These oscillations have a typical 90–100 minute period, but this can alter in different cellular contexts. We investigated factors including cytokine pulse frequency, drug treatment and temperature that alter NF-κB dynamics and downstream gene expression.

Temperature change within the physiological range (34–40^oC) affected NF-κB dynamics, causing a substantial change in the frequency of nuclear/cytoplasmic NF-κB oscillations. Higher temperatures increasing oscillation frequency A mathematical model of the NF-κB system could not predict the observed temperature sensitivity and analyses of the transcription data and model predictions suggested that there might be an A20-dependent mechanism, involving a temperature-dependent delay in the activation of A20 transcription.

RNAi knock-down of A20 led to a substantially longer period of NF-κB oscillations. Remarkably, when A20 was knocked down there was no change in oscillation frequency between 37 and 40^oC. The change in temperature led to tightly controlled temperature and TNFα-dependent changes in expression of an immunologically-relevant set of NF-κB target genes. A key set of immediate genes showed temperature control of the timing of their response, but many genes did not show significant control of their cytokine-induced expression (i.e. they were temperature compensated). We have analysed functional networks of these altered genes and find that they participate in cross-talk with MAPK, Wnt and p53-dependent pathways. These data suggest the hypothesis that temperature in the fever range may subtly regulate the NF-κB system to modulate the cellular immune response to pathogens.

I will discuss the implications of this work for our understanding of the function of NF-κB dynamics.