The Wip1 Phosphatase acts as a gatekeeper in the p53-Mdm2 autoregulatory loop.

The tumor suppressor p53 is a transcription factor that responds to cellular stresses by initiating cell cycle arrest or apoptosis. One transcriptional target of p53 is Mdm2, an E3 ubiquitin ligase that interacts with p53 to promote its proteasomal degradation in a negative feedback regulatory loop. Here we show that the wild-type p53-induced phosphatase 1 (Wip1), or PPM1D, downregulates p53 protein levels by stabilizing Mdm2 and facilitating its access to p53. Wip1 interacts with and dephosphorylates Mdm2 at serine 395, a site phosphorylated by the ATM kinase. Dephosphorylated Mdm2 has increased stability and affinity for p53, facilitating p53 ubiquitination and degradation. Thus, Wip1 acts as a gatekeeper in the Mdm2-p53 regulatory loop by stabilizing Mdm2 and promoting Mdm2-mediated proteolysis of p53.

[1]  G. Wahl,et al.  A New Twist in the Feedback Loop: Stress-Activated MDM2 Destabilization is Required for p53 Activation , 2005, Cell cycle.

[2]  U. Knippschild,et al.  Posttranslational modification of MDM2. , 2003, Molecular cancer research : MCR.

[3]  A. Levine,et al.  The p53 pathway: positive and negative feedback loops , 2005, Oncogene.

[4]  Masaaki Adachi,et al.  p53‐inducible Wip1 phosphatase mediates a negative feedback regulation of p38 MAPK‐p53 signaling in response to UV radiation , 2000, The EMBO journal.

[5]  Y Taya,et al.  Activation of the ATM kinase by ionizing radiation and phosphorylation of p53. , 1998, Science.

[6]  S. Elledge,et al.  DNA damage-induced activation of p53 by the checkpoint kinase Chk2. , 2000, Science.

[7]  Marie-Claude Marsolier-Kergoat,et al.  The Wip1 phosphatase (PPM1D) antagonizes activation of the Chk2 tumour suppressor kinase , 2007, Oncogene.

[8]  L. Donehower,et al.  The structure and expression of the murine wildtype p53-induced phosphatase 1 (Wip1) gene. , 2000, Genomics.

[9]  E. Appella,et al.  The role of the MKK6/p38 MAPK pathway in Wip1-dependent regulation of ErbB2-driven mammary gland tumorigenesis , 2007, Oncogene.

[10]  Axel Benner,et al.  Genomic and protein expression profiling identifies CDK6 as novel independent prognostic marker in medulloblastoma. , 2005, Journal of clinical oncology : official journal of the American Society of Clinical Oncology.

[11]  G. Wahl,et al.  Regulating the p53 pathway: in vitro hypotheses, in vivo veritas , 2006, Nature Reviews Cancer.

[12]  Alison L. Cuff,et al.  Integrating mutation data and structural analysis of the TP53 tumor‐suppressor protein , 2002, Human mutation.

[13]  F. Alt,et al.  Genetic interactions between ATM and the nonhomologous end-joining factors in genomic stability and development , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[14]  J. Inazawa,et al.  Association of 17q21-q24 gain in ovarian clear cell adenocarcinomas with poor prognosis and identification of PPM1D and APPBP2 as likely amplification targets. , 2003, Clinical cancer research : an official journal of the American Association for Cancer Research.

[15]  Albert J. Fornace,et al.  Amplification of PPM1D in human tumors abrogates p53 tumor-suppressor activity , 2002, Nature Genetics.

[16]  M. Oren,et al.  Cell Cycle Regulation and p53 Activation by Protein Phosphatase 2Cα* , 2003, The Journal of Biological Chemistry.

[17]  M. Fiscella,et al.  Wip1, a novel human protein phosphatase that is induced in response to ionizing radiation in a p53-dependent manner. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[18]  Zigang Dong,et al.  Post-translational modification of p53 in tumorigenesis , 2004, Nature Reviews Cancer.

[19]  L. Donehower,et al.  Reversal of the ATM/ATR-Mediated DNA Damage Response by the Oncogenic Phosphatase PPM1D , 2005, Cell cycle.

[20]  K. Vousden,et al.  Transcriptional activation by p53 correlates with suppression of growth but not transformation , 1994, Cell.

[21]  E. Appella,et al.  Post-translational modifications and activation of p53 by genotoxic stresses. , 2001, European journal of biochemistry.

[22]  A. Levine,et al.  Surfing the p53 network , 2000, Nature.

[23]  Albert J. Fornace,et al.  Chemical inhibition of Wip1 phosphatase contributes to suppression of tumorigenesis , 2005, Cancer biology & therapy.

[24]  G. Wahl,et al.  The tumorigenic potential and cell growth characteristics of p53-deficient cells are equivalent in the presence or absence of Mdm2. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[25]  Muyang Li,et al.  A dynamic role of HAUSP in the p53-Mdm2 pathway. , 2004, Molecular cell.

[26]  Akira Nakagawara,et al.  PPM1D is a potential target for 17q gain in neuroblastoma. , 2003, Cancer research.

[27]  K. Kohn,et al.  UCN-01 inhibits p53 up-regulation and abrogates gamma-radiation-induced G(2)-M checkpoint independently of p53 by targeting both of the checkpoint kinases, Chk2 and Chk1. , 2002, Cancer research.

[28]  S. T. Kim,et al.  ATM-dependent phosphorylation of Mdm2 on serine 395: role in p53 activation by DNA damage. , 2001, Genes & development.

[29]  L. Donehower,et al.  The p53-induced oncogenic phosphatase PPM1D interacts with uracil DNA glycosylase and suppresses base excision repair. , 2004, Molecular cell.

[30]  H. K. Sluss,et al.  Phosphorylation of Serine 18 Regulates Distinct p53 Functions in Mice , 2004, Molecular and Cellular Biology.

[31]  S. Durell,et al.  Development of a substrate-based cyclic phosphopeptide inhibitor of protein phosphatase 2Cdelta, Wip1. , 2006, Biochemistry.

[32]  L. Donehower,et al.  Inactivation of the Wip1 phosphatase inhibits mammary tumorigenesis through p38 MAPK–mediated activation of the p16Ink4a-p19Arf pathway , 2004, Nature Genetics.

[33]  Jeffrey R. Marks,et al.  Oncogenic properties of PPM1D located within a breast cancer amplification epicenter at 17q23 , 2002, Nature Genetics.

[34]  S. Thorgeirsson,et al.  Cyclin G recruits PP2A to dephosphorylate Mdm2. , 2002, Molecular cell.

[35]  Lawrence A. Donehower,et al.  Mice Deficient for the Wild-Type p53-Induced Phosphatase Gene (Wip1) Exhibit Defects in Reproductive Organs, Immune Function, and Cell Cycle Control , 2002, Molecular and Cellular Biology.

[36]  Y. Taya,et al.  A Role for the p38 Mitogen-activated Protein Kinase Pathway in the Transcriptional Activation of p53 on Genotoxic Stress by Chemotherapeutic Agents , 2000 .

[37]  N. Onishi,et al.  Regulation of the antioncogenic Chk2 kinase by the oncogenic Wip1 phosphatase , 2006, Cell Death and Differentiation.

[38]  M. Mumby,et al.  Protein serine/threonine phosphatases: structure, regulation, and functions in cell growth. , 1993, Physiological reviews.

[39]  Y Taya,et al.  A role for ATR in the DNA damage-induced phosphorylation of p53. , 1999, Genes & development.

[40]  L. Donehower,et al.  Augmented cancer resistance and DNA damage response phenotypes in PPM1D null mice , 2006, Molecular carcinogenesis.

[41]  J. Niland,et al.  The MDM2 gene amplification database. , 1998, Nucleic acids research.

[42]  Y. Shiloh.  ATM and related protein kinases: safeguarding genome integrity , 2003, Nature Reviews Cancer.

[43]  A. Levine,et al.  MDM2 is a central node in the p53 pathway: 12 years and counting. , 2005, Current cancer drug targets.

[44]  T. Halazonetis,et al.  Chk2/hCds1 functions as a DNA damage checkpoint in G(1) by stabilizing p53. , 2000, Genes & development.

[45]  N. Onishi,et al.  Intrinsic Kinase Activity and SQ/TQ Domain of Chk2 Kinase as Well as N-terminal Domain of Wip1 Phosphatase Are Required for Regulation of Chk2 by Wip1* , 2006, Journal of Biological Chemistry.

[46]  U. Moll,et al.  The MDM2-p53 interaction. , 2003, Molecular cancer research : MCR.

[47]  M. Oren,et al.  The p53-Mdm2 module and the ubiquitin system. , 2003, Seminars in cancer biology.

[48]  D. Lane,et al.  Exploiting the p53 pathway for the diagnosis and therapy of human cancer. , 2005, Cold Spring Harbor symposia on quantitative biology.

[49]  N. Gueven,et al.  The complexity of p53 stabilization and activation , 2006, Cell Death and Differentiation.

[50]  E. Appella,et al.  Wip1 phosphatase modulates ATM-dependent signaling pathways. , 2006, Molecular cell.

[51]  H. Ovaa,et al.  Loss of HAUSP-mediated deubiquitination contributes to DNA damage-induced destabilization of Hdmx and Hdm2. , 2005, Molecular cell.