NF-κB-dependent Signaling Pathway

NF-κB is a transcription factor that regulates expression of over 100 genes essential for immune and inflammatory responses. It controls crucial cellular functions including immune cell activation, cell adhesion, antimicrobial response, and cell cycle regulation. NF-κB also regulates cell proliferation, apoptosis, and plays diverse roles in the nervous system such as learning and memory.

In resting cells, NF-κB exists as a heterodimer bound to the inhibitory protein IκBα, which suppresses its transcriptional activity. IκBα masks the nuclear localization signals of NF-κB, keeping it inactive in the cytoplasm. This inhibitory mechanism prevents NF-κB from entering the nucleus and activating target genes until an appropriate signal is received.

The NF-κB pathway activates when ligands bind to cell-surface receptors, such as tumor necrosis factor-α binding to TNF receptor, interleukin-1 binding to IL1 receptor, or pathogens binding to toll-like receptors. These ligand-receptor interactions activate the IκB kinase complex, which phosphorylates IκBα, leading to its ubiquitination and proteasomal degradation, releasing NF-κB for nuclear translocation.

Once IκBα is degraded in the proteasome, the NF-κB dimer is released and free to translocate to the nucleus. In the nucleus, NF-κB acts as a transcriptional activator, binding to DNA and activating expression of target genes. This allows the cell to mount appropriate physiological responses to external stimuli such as pathogens or reactive oxygen species.

NF-κB activates the gene encoding IκBα protein as one of its target genes. Upon increased expression, newly synthesized IκBα binds to NF-κB in the nucleus, causing it to exit and return to the cytoplasm. This negative feedback loop prevents excessive NF-κB signaling and helps maintain cellular homeostasis by limiting the duration and intensity of the immune response.

Dysregulation of NF-κB can lead to various cancers and inflammatory diseases such as arthritis and asthma. Additionally, pathogens like HIV, HPV, and Yersinia pestis exploit or interfere with the NF-κB signaling pathway to evade host defense mechanisms. Because of its diverse roles in animals, the NF-κB signaling pathway and associated diseases make it an excellent therapeutic target.

NF-κB regulates expression of genes essential for both innate and adaptive immune responses as well as inflammatory stress responses. It controls activation of immune cells, antimicrobial defenses, and inflammatory signaling. Since its discovery in 1986, over three decades of research has revealed that NF-κB coordinates multiple aspects of immune defense, making it central to how animals respond to pathogens and cellular stress.