title: ATM and Chk2-dependent phosphorylation of MDMX contribute to p53 activation after DNA damage.
abstract: The p53 tumor suppressor is activated after DNA damage to maintain genomic stability and prevent transformation. Rapid activation of p53 by ionizing radiation is dependent on signaling by the ATM kinase. MDM2 and MDMX are important p53 regulators and logical targets for stress signals. We found that DNA damage induces ATM-dependent phosphorylation and degradation of MDMX. Phosphorylated MDMX is selectively bound and degraded by MDM2 preceding p53 accumulation and activation. Reduction of MDMX level by RNAi enhances p53 response to DNA damage. Loss of ATM prevents MDMX degradation and p53 stabilization after DNA damage. Phosphorylation of MDMX on S342, S367, and S403 were detected by mass spectrometric analysis, with the first two sites confirmed by phosphopeptide-specific antibodies. Mutation of MDMX on S342, S367, and S403 each confers partial resistance to MDM2-mediated ubiquitination and degradation. Phosphorylation of S342 and S367 in vivo require the Chk2 kinase. Chk2 also stimulates MDMX ubiquitination and degradation by MDM2. Therefore, the E3 ligase activity of MDM2 is redirected to MDMX after DNA damage and contributes to p53 activation.
authors.affiliation: Molecular Oncology Program, H Lee Moffitt Comprehensive Cancer Center and Research Institute, Tampa, FL 33612, USA.
authors.forename: Lihong
authors.initials: L
authors.lastname: Chen
authors.forename: Daniele M
authors.initials: DM
authors.lastname: Gilkes
authors.forename: Yu
authors.initials: Y
authors.lastname: Pan
authors.forename: William S
authors.initials: WS
authors.lastname: Lane
authors.forename: Jiandong
authors.initials: J
authors.lastname: Chen
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D064447:Checkpoint Kinase 2; D002851:Chromatography, High Pressure Liquid; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation; D006801:Humans; D047468:Immunoprecipitation; D013058:Mass Spectrometry; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C482775:MDM4 protein, human; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases