Inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase epsilon.The transcription factor NFκB is retained in the cytoplasm in an inactive form by the inhibitory protein IκB. Activation of NFκB requires that IκB be phosphorylated on specific serine residues, which results in targeted degra-dation of IκB. IκB kinase α(IKKα), previously designated CHUK, interacts with IκB-αand specifically phosphorylates IκB-αon the sites that trigger its degradation, serines 32 and 36. The functional IKK complex contains three subunits, IKKα, IKKbetaand IKKgamma(also designated NEMO), and each appear to make essential contributions to IκB phosphorylation. IKK-i is a serine/threonine kinase that shares homology with IKKαand IKKbeta. IKK-i is pri-marily expressed in immune cells and is induced by lipopolysaccharide and by proinflammatory cytokines including TNFα, IL-1 and IL-6. Overexpression of IKK-i was shown to result in phosphorylation of IκBαon Ser32 and Ser36, and in NFκB activation, suggesting that IKK-i may act as an IκB kinase in the immune system. |