An autoregulatory feedback loop between nuclear receptor SHP and Mdm2 that controls Mdm2, SHP and p53 protein stability

Abstract

MethodsImmunoprecipitation, Western blots, in vitro ubiquitination assays, luciferase reporter assays, qPCR, ChIP assays, and apoptosis assays etc.ResultsMdm2 attenuates SHP expression by promoting SHP protein ubiquitination and downregulating SHP mRNA, and SHP in turn stabilizes Mdm2 protein by abrogating Mdm2 selfubiquitination. p53 reduces SHP protein through proteasome, but not phosphorylation and acetylation, mediated SHP degradation by Mdm2, and inhibits SHP mRNA by transcriptional repression. SHP destabilizes p53 by augmentation of Mdm2 ubiquitin ligase activity toward p53. Such cross‐regulation critically depends on the physical interaction of SHP with Mdm2 through the SHPK170 residue. Consequently, SHP antagonizes p53 dependent induction of apoptosis and inhibition of tumor growth by AHPN and 3‐Cl‐AHPC in colon cancer cells.ConclusionsThe Mdm2‐SHP‐p53 interplay represents a novel component of Mdm2/p53 crosstalk that dictates p53 activity and function.This work was supported by the National Institutes of Health (DK080440) to L.W.