Abrogation of Wip1 expression by RITA-activated p53 potentiates apoptosis induction via activation of ATM and inhibition of HdmX

Cell Death Differ. 2011 Nov;18(11):1736-45. doi: 10.1038/cdd.2011.45. Epub 2011 May 6.

Abstract

Inactivation of the p53 tumour suppressor, either by mutation or by overexpression of its inhibitors Hdm2 and HdmX is the most frequent event in cancer. Reactivation of p53 by targeting Hdm2 and HdmX is therefore a promising strategy for therapy. However, Hdm2 inhibitors do not prevent inhibition of p53 by HdmX, which impedes p53-mediated apoptosis. Here, we show that p53 reactivation by the small molecule RITA leads to efficient HdmX degradation in tumour cell lines of different origin and in xenograft tumours in vivo. Notably, HdmX degradation occurs selectively in cancer cells, but not in non-transformed cells. We identified the inhibition of the wild-type p53-induced phosphatase 1 (Wip1) as the major mechanism important for full engagement of p53 activity accomplished by restoration of the ataxia telangiectasia mutated (ATM) kinase-signalling cascade, which leads to HdmX degradation. In contrast to previously reported transactivation of Wip1 by p53, we observed p53-dependent repression of Wip1 expression, which disrupts the negative feedback loop conferred by Wip1. Our study reveals that the depletion of both HdmX and Wip1 potentiates cell death due to sustained activation of p53. Thus, RITA is an example of a p53-reactivating drug that not only blocks Hdm2, but also inhibits two important negative regulators of p53 - HdmX and Wip1, leading to efficient elimination of tumour cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects*
  • Ataxia Telangiectasia Mutated Proteins
  • Cell Cycle Proteins / metabolism*
  • Cell Line, Tumor
  • DNA-Binding Proteins / metabolism*
  • Down-Regulation
  • Furans / pharmacology*
  • Gene Expression Regulation / drug effects
  • Humans
  • Nuclear Proteins / metabolism
  • Phosphoprotein Phosphatases / genetics
  • Phosphoprotein Phosphatases / metabolism*
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Phosphatase 2C
  • Protein-Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-mdm2 / metabolism
  • Signal Transduction
  • Tumor Suppressor Protein p53 / antagonists & inhibitors
  • Tumor Suppressor Protein p53 / metabolism*
  • Tumor Suppressor Proteins / metabolism*

Substances

  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Furans
  • MDM4 protein, human
  • NSC 652287
  • Nuclear Proteins
  • Proto-Oncogene Proteins
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins
  • MDM2 protein, human
  • Proto-Oncogene Proteins c-mdm2
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • Protein-Serine-Threonine Kinases
  • PPM1D protein, human
  • Phosphoprotein Phosphatases
  • Protein Phosphatase 2C
  • Proteasome Endopeptidase Complex