During the course of NF-κB dimer activation, IκB kinase(IKK) play a crucial role by phosphorylation of inhibitory κB(IκBs). There are lots of existing forms in cytoplasm about IKK complex, which activate IκBs through different ways. Generally, IKK has two catalytic subunits, IKK-α、IKK-β, which have 52% amino acids identity and similar construction, one regulatory subunit, IKK-γ. Both NF-κB-inducing kinase(NIK) and mitogen -activated protein kinase kinase kinase-1(MEKK₁) are upstream kinases of IKK. MEKK₁ preferentially activates IKK-β,whereas NIK efficiently phosphorylates both IKK-α Ser176 and IKK-β. Through cascade reaction, IκBs are phosphorylated by IKK and dissociated from IκB- NF-κB complex, NF-κB dimer enter the nucleus and activate a series of genes.