title: MDM4/HIPK2/p53 cytoplasmic assembly uncovers coordinated repression of molecules with anti-apoptotic activity during early DNA damage response.
abstract: The p53 inhibitor, MDM4 (MDMX) is a cytoplasmic protein with p53-activating function under DNA damage conditions. Particularly, MDM4 promotes phosphorylation of p53 at Ser46, a modification that precedes different p53 activities. We investigated the mechanism by which MDM4 promotes this p53 modification and its consequences in untransformed mammary epithelial cells and tissues. In response to severe DNA damage, MDM4 stimulates p53Ser46(P) by binding and stabilizing serine-threonine kinase HIPK2. Under these conditions, the p53-inhibitory complex, MDM4/MDM2, dissociates and this allows MDM4 to promote p53/HIPK2 functional interaction. Comparative proteomic analysis of DNA damage-treated cells versus -untreated cells evidenced a diffuse downregulation of proteins with anti-apoptotic activity, some of which were targets of p53Ser46(P)/HIPK2 repressive activity. Importantly, MDM4 depletion abolishes the downregulation of these proteins indicating the requirement of MDM4 to promote p53-mediated transcriptional repression. Consistently, MDM4-mediated HIPK2/p53 activation precedes HIPK2/p53 nuclear translocation and activity. Noteworthy, repression of these proteins was evident also in mammary glands of mice subjected to γ-irradiation and was significantly enhanced in transgenic mice overexpressing MDM4. This study evidences the flexibility of MDM2/MDM4 heterodimer, which allows the development of a positive activity of cytoplasmic MDM4 towards p53-mediated transcriptional function. Noteworthy, this activity uncovers coordinated repression of molecules with shared anti-apoptotic function which precedes active cell apoptosis and that are frequently overexpressed and/or markers of tumour phenotype in human cancer.
authors.affiliation: Institute of Cell Biology and Neurobiology, National Research Council of Italy (CNR), Roma, Italy.|Department of Endocrinology and Metabolism, Catholic University of Roma, Roma, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Mancini
authors.affiliation: Proteomic and Metabolomic Laboratory, Fondazione Santa Lucia, Roma, Italy.|Department of Experimental Medicine and Surgery, University of Roma 'Tor Vergata', Roma, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Pieroni
authors.affiliation: Institute of Cell Biology and Neurobiology, National Research Council of Italy (CNR), Roma, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Monteleone
authors.affiliation: Institute of Cell Biology and Neurobiology, National Research Council of Italy (CNR), Roma, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Lucà
authors.affiliation: Institute of Cell Biology and Neurobiology, National Research Council of Italy (CNR), Roma, Italy.|Department of Obstetrics and Gynaecology, Catholic University of Roma, Roma, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Fici
authors.affiliation: Institute of Cell Biology and Neurobiology, National Research Council of Italy (CNR), Roma, Italy.|Department of Endocrinology and Metabolism, Catholic University of Roma, Roma, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Luca
authors.affiliation: Proteomic and Metabolomic Laboratory, Fondazione Santa Lucia, Roma, Italy.|Department of Experimental Medicine and Surgery, University of Roma 'Tor Vergata', Roma, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Urbani
authors.affiliation: Department of Genetics, M.D. Anderson Cancer Center, Houston, TX, USA.
authors.forename: S
authors.initials: S
authors.lastname: Xiong
authors.affiliation: Regina Elena National Cancer Institute, Roma, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Soddu
authors.affiliation: Department of Obstetrics and Gynaecology, Catholic University of Roma, Roma, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Masetti
authors.affiliation: Department of Genetics, M.D. Anderson Cancer Center, Houston, TX, USA.
authors.forename: G
authors.initials: G
authors.lastname: Lozano
authors.affiliation: Department of Endocrinology and Metabolism, Catholic University of Roma, Roma, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Pontecorvi
authors.affiliation: Institute of Cell Biology and Neurobiology, National Research Council of Italy (CNR), Roma, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Moretti
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D003593:Cytoplasm / Q000378:metabolism; D004249:DNA Damage / Q000502:physiology*; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D005260:Female; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D045325:HCT116 Cells; D006801:Humans; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C482775:MDM4 protein, human; C461497:Mdm4 protein, mouse; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D012694:Serine; D044767:Ubiquitin-Protein Ligases; C115114:HIPK2 protein, human; D017346:Protein Serine-Threonine Kinases