Phosphorylation of p53 by IκB kinase 2 promotes its degradation by β-TrCP

Abstract

Functional inactivation of p53 and constitutive activation of the NF-κB pathway has been associated with several human cancers. In this study, we show that IκB kinase 2 (IKK2/IKKβ), which is critical for NF-κB activation, also phosphorylates p53. Phosphorylation of p53 at serines 362 and 366 by IKK2 leads to its recruitment to and ubiquitination by β-TrCP1. Degradation of ubiquitinated p53 is independent of Mdm2, because it occurs in both wild-type and Mdm2^−/− cells. SiRNA-mediated reduction in the levels of β-TrCP1 and other members of the SCF^β−TrCP1E3 ubiquitin ligase complex or overexpression of a dominant negative form of β-TrCP1 enhances p53 stability. Substitutions at Ser-362 and 366 of p53 by alanines (p53 AA) result in reduced phosphorylation of p53 by IKK2, decreased association with β-TrCP1, and thus increased stability of p53 and expression of p53 target genes such as p21, altering the G1 phase of the cell cycle. Our results identify IKK2 and β-TrCP1 as novel regulators of the p53 pathway and suggest that blocking of IKK2 and β-TrCP1 could be a means of regulating p53 stability and thereby modulating its biological activity.