The NF-κB pathway is important in the control of the immune and inflammatory response. One of the critical events in the activation of this pathway is the stimulation of the IκB kinases (IKKs) by cytokines such as tumor necrosis factor-α and interleukin-1. Although the mechanisms that modulate IKK activation have been studied in detail, much less is known about the processes that down-regulate its activity following cytokine treatment. In this study, we utilized biochemical fractionation and mass spectrometry to demonstrate that protein phosphatase 2Cβ (PP2Cβ) can associate with the IKK complex. PP2Cβ association with the IKK complex led to the dephosphorylation of IKKβ and decreased its kinase activity. The binding of PP2Cβ to IKKβ was decreased at early times post-tumor necrosis factor-α treatment and was restored at later times following treatment with this cytokine. Experiments utilizing siRNA directed against PP2Cβ demonstrated an in vivo role for this phosphatase in decreasing IKK activity at late times following cytokine treatment. These studies are consistent with the ability of PP2Cβ to down-regulate cytokine-induced NF-κB activation by altering IKK activity.
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