The deubiquitinating enzyme USP2a regulates the p53 pathway by targeting Mdm2

Abstract

Mdm2 is an E3 ubiquitin ligase that promotes its own ubiquitination and also ubiquitination of the p53 tumour suppressor. In a bacterial two-hybrid screen, using Mdm2 as bait, we identified an Mdm2-interacting peptide that bears sequence similarity to the deubiquitinating enzyme USP2a. We have established that full-length USP2a associates with Mdm2 in cells where it can deubiquitinate Mdm2 while demonstrating no deubiquitinating activity towards p53. Ectopic expression of USP2a causes accumulation of Mdm2 in a dose-dependent manner and consequently promotes Mdm2-mediated p53 degradation. This differs from the behaviour of HAUSP, which deubiquitinates p53 in addition to Mdm2 and thus protects p53 from Mdm2-mediated degradation. We further demonstrate that suppression of endogenous USP2a destabilises Mdm2 and causes accumulation of p53 protein and activation of p53. Our data identify the deubiquitinating enzyme USP2a as a novel regulator of the p53 pathway that acts through its ability to selectively target Mdm2.

MdmX is a substrate for the deubiquitinating enzyme USP2a

“…Ectopic expression of USP2a results in elevated levels of Mdm2 and an increase in degradation of p53 (Stevenson et al, 2007). To determine the effect of USP2a on Mdm2-mediated degradation of MdmX, H1299 cells (p53 null) were co-transfected with plasmids expressing MdmX, Mdm2 and increasing amounts of plasmidexpressing USP2a.…”

“…These data indicate that there are at least two binding sites for MdmX in USP2a: one between amino acids 1-200 in its N-terminal extension and one between amino acids 403-503 in its catalytic core. Similarly, deletion of both the N and C-terminus of USP2a was required to prevent its binding to Mdm2 (Stevenson et al, 2007).…”

“…However, the balance of activity of endogenous HAUSP is such that its knockdown or knockout results in destabilization of Mdm2 and MdmX and stabilization of p53 (Li et al, 2002(Li et al, , 2004Cummins et al, 2004;Meulmeester et al, 2005). We have previously shown that USP2a can deubiquitinate Mdm2 without reversing Mdm2-mediated p53 ubiquitination (Stevenson et al, 2007). USP2a has oncogenic properties and its overexpression can prevent apoptosis induced by chemotherapeutic agents (Graner et al, 2004;Priolo et al, 2006).…”

“…USP2a has oncogenic properties and its overexpression can prevent apoptosis induced by chemotherapeutic agents (Graner et al, 2004;Priolo et al, 2006). USP2a knockdown results in increased p53 protein expression and upregulation of p53 target genes (Priolo et al, 2006;Stevenson et al, 2007). USP2a mRNA is expressed in a range of normal tissues, the highest level of expression being in the testis (Lin et al, 2001;Park et al, 2002;Gousseva and Baker, 2003).…”

Updates on p53: modulation of p53 degradation as a therapeutic approach

“…More recently, USP2a (ubiquitin-specific protease 2a) has been identified as a novel DUB that selectively targets Mdm2, unlike HAUSP, and thereby offers another potential approach of therapeutic intervention to reactivate WT p53 (Stevenson et al, 2007). Future studies will further address the importance of these DUBs as clinical targets and also the selectivity of their use based on tumour subtypes.…”