IκB stands for Inhibitor of kappa B. It is a regulatory protein that binds to NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) and prevents it from entering the nucleus, where it would otherwise activate genes related to inflammation, immunity, and cell survival.
🔐 Key Role of IκB:
- In the resting state, IκB is bound to NF-κB in the cytoplasm.
- This masks NF-κB’s nuclear localization signal, keeping it inactive and outside the nucleus.
- It acts like a brake, holding NF-κB in check until it’s truly needed (e.g., during infection or injury).
🔄 Activation Process:
- A signal (like cytokines, infection, or stress) activates the IKK complex (IκB kinase).
- IKK phosphorylates IκB, tagging it for degradation.
- IκB is broken down by the proteasome.
- This frees NF-κB, which then enters the nucleus.
- NF-κB activates gene expression for inflammation, immune defense, and cell survival.
🔁 Negative Feedback Loop:
Interestingly, one of the genes NF-κB activates is IκBα — a form of IκB. This means:
- After NF-κB does its job, new IκB is made to re-bind and turn off NF-κB, completing a self-regulating loop.
📌 Summary:
IκB is the key inhibitor that keeps NF-κB in check under normal conditions. When a signal disrupts this inhibition, NF-κB is freed to trigger inflammation or immune responses. IκB plays a vital role in balancing defense and overreaction — and when this balance breaks, chronic inflammation or disease can follow.