IkB is an inhibitory protein that sequesters NF-kB in the cytoplasm, by masking a nuclear localization signal, located just at the C-terminal end in each of the NF-kB subunits. A key event in NF-kB activation involves phosphorylation of IkB by an IkB kinase (IKK). NGF stimulates the activity of the IkB kinase IKK-beta, and, possibly, IKK-alpha as well. Once IkB is phosphorylated, the IkB:NF-kB complex dissociates.