Nuclear factor kappa B (NF-kappaB) is a ubiquitous transcription factor and an essential mediator of gene expression during activation of immune and inflammatory responses. NF-kappaB mediates the expression of a great variety of genes in response to extracellular stimuli including IL-1, TNFalpha, LPS and mitogens. A serine/threonine protein kinase which mediates NF-kappaB activation by IL-1, TNFalpha and CD95 was identified recently and designated NIK (for NF-kappaB inducing kinase) . NIK is an activator of IkappaB kinase alpha and beta (IKKalpha and IKKbeta). Therefore, NIK is a key molecule in the NF-kappaB signaling pathway leading to the induction of a variety of gene expression in response to proinflammatory cytokines and bacteria products.Synonyms: Mitogen-activated protein kinase kinase kinase 14, NF-kappa beta-inducing kinase, Serine/threonine-protein kinase NIK