NFκB (Nuclear Factor kappa B) is a family of transcription factors with five members that includes Rel (c-Rel), RelA (p65), RelB, NFκB1 (p50 and its precursor p105), and NFκB2 (p52 and its precursor p100). NFκB members can exist as either homo- or heterodimers. NFκB dimers containing p65 are activators of transcription. In a majority of unstimulated cells, NFκB remains in its inactive form and is retained in the cytoplasm by the bound inhibitory IkB proteins. Upon stimulation by inducers such as TNFa, IL-1, or PMA, IkBa is phosphorylated and degraded. This results in the release of the NFκB complex from the IKK complex and the p105 subunit is cleaved into its active p50 form. Subsequently the p50/p65 translocates to the nucleus where it activates transcription of many genes, including its own inhibitor IκBα, causing an auto-regulatory mechanism of NFκB.
NFκB is known to regulate numerous genes that include cytokines, chemokines, adhesion targets, and acute phase proteins. These are involved in both cellular and physiological processes such as growth, development, apoptosis, immune and inflammatory response, and activation of various viral promoters.