Figure 4: Activation of transcription factors by external and internal stress reponses (NF-κB). External stimuli such as environmental toxicants and oxidative stress activate IKK which phosphorylates IkB, targeting it for proteosomal degradation. The release of the inhibitory IkB allows for the NF-κB complex (RelA/p50) to enter the nucleus and initiate transcription. Interestingly, one of the genes transcribed following NF-κB activation is IkBa, which can in turn inhibit NF-κB.