NF-κB is a transcriptional activator that can be activated by what?

• A. Growth factors
• B. Calcium ions
• C. The free radicals produced in contracting muscles
• D. Heat shock

Answer: (C)

NF-κB responds to cellular stress by moving into the nucleus to turn on genes involved in inflammation, protection, and remodeling. In contracting muscle, the reactive oxygen species that are produced act as a stress signal to kick this pathway into gear. These free radicals stimulate signaling that leads to the phosphorylation and degradation of IκB, the inhibitor that keeps NF-κB in the cytoplasm. Once IκB is removed, NF-κB can enter the nucleus and activate transcription.

That makes the free radicals produced in contracting muscles the best match. While growth factors can also activate NF-κB in some circumstances, and calcium signaling or heat shock influence other pathways, the scenario most directly linking to NF-κB activation in exercising muscle is the oxidative stress from ROS. Heat shock, in particular, activates a different transcriptional program via HSF1, not NF-κB.