Loss of Ikkβ promotes migration and proliferation of mouse embryo fibroblast cells

The IκB kinase complex (IKK) is central to the activation of NF-κB, a critical transcription factor governing expression of genes involved in cell proliferation and anti-apoptotic responses. Mice with genetic disruptions of the Ikkβ or Ikkγ gene loci die during embryogenesis because of severe hepatic apoptosis. We now show that Ikkβ gene deficiency promotes migration and proliferation of mouse embryo fibroblast cells. Morphological analyses revealed an unusual protrusion of the cytoplasm in Ikkβ^-/- cells when cultured at a lower density. In a Boyden chamber assay, Ikkβ^-/- cells exhibited a high rate of invasion and migration. Enhanced formation of actin stress fibers was also observed in the Ikkβ^-/- cells. Mechanistic studies indicated that IKKβ affects the expression of proteins involved in the assembly of cytoskeleton and cell movement. Furthermore, re-expression of Ikkβ and antioxidant treatment in Ikkβ^-/- cells caused a reversal of protrusive phenotype and high motility, respectively. Furthermore, elimination of reactive oxygen species (ROS) blocked expression of snail and subsequently derepressed E-cadherin expression. Although the underlying mechanism is likely entangled and complicated, the data presented indicate that generation of ROS played a key role in the morphological and mobility changes in Ikkβ^-/- cells. These data thus suggest that IKKβ provides inhibitory signals for cell mobility and growth. Deficiency in the Ikkβ gene promotes cell mobilization, at least partially, through a ROS-dependent mechanism.