Mutant human cells with constitutive activation of NF-kappaB.

We have used a genetic approach to generate eight different mutant human cell lines in which NF-kappaB is constitutively activated. These independent clones have different phenotypes and belong to several different genetic complementation groups. In one clone inhibitor of kappaB(IkappaB) kinase is constitutively active, but in the seven others it is not, despite the fact that IkappaB is degraded in all eight clones. Thus, IkappaB kinase-independent mechanisms of IkappaB degradation and NF-kappaB activation are predominant in these mutants. Biochemical analyses of the mutants revealed that they fall into at least five different categories, differing in the sets of upstream kinases that are activated, confirming multiple mechanisms of NF-kappaB activation. By introducing a retroviral cDNA library into the Ras C6 cell line, with constitutively active NF-kappaB, followed by selection for functional complementation, we isolated a cDNA encoding a C-terminal fragment of enolase 1 and identified it as negative regulator of NF-kappaB.