The functional IKK complex contains three subunits, IKKα, IKKβ and IKKγ (also designated NEMO), and each appear to make essential contributions to IκB phosphorylation. IKK-i is a serine/threonine kinase that shares homology with IKKα and IKKβ. IKK-i is primarily 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 IκBα on Ser32 and Ser36, and in NFκB activation, suggesting that IKK-i may act as an IκB kinase in the immune system.
