title: HIPK2 inhibits both MDM2 gene and protein by, respectively, p53-dependent and independent regulations.
abstract: We address here the involvement of the homeodomain-interacting protein kinase 2 (HIPK2)/p53 complex on MDM2 regulation following apoptotic DNA damage. Our results provide a plausible transcriptional (p53-dependent) and posttranscriptional (p53-independent) double mechanism by which HIPK2 accomplishes MDM2 downmodulation. First, in wtp53-carrying cells HIPK2-dependent p53Ser46 phosphorylation selectively inhibits MDM2 at transcriptional level. Secondly, HIPK2 interacts with MDM2 in vitro and in vivo and promotes MDM2 nuclear export and proteasomal degradation, in p53-null cellular context. This p53-independent effect is likely mediated by HIPK2 catalytic activity and we found that HIPK2 phosphorylates MDM2 in vitro. In response to DNA damage, depletion of HIPK2 by RNA-interference abolishes MDM2 protein degradation. We propose that HIPK2 contributes to drug-induced modulation of MDM2 activity at transcriptional (through p53Ser46 phosphorylation) and posttranscriptional (through p53-independent subcellular re-localization and proteasomal degradation) levels.
authors.affiliation: Department of Experimental Oncology, Molecular Oncogenesis Laboratory, Regina Elena Cancer Institute, Rome, Italy.
authors.forename: Valeria
authors.initials: V
authors.lastname: Di Stefano
authors.forename: Marina
authors.initials: M
authors.lastname: Mattiussi
authors.forename: Ada
authors.initials: A
authors.lastname: Sacchi
authors.forename: Gabriella
authors.initials: G
authors.lastname: D'Orazi
mesh_terms: D021581:Active Transport, Cell Nucleus; D017209:Apoptosis; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D004249:DNA Damage; D005786:Gene Expression Regulation; D006801:Humans; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D034622:RNA Interference; D012694:Serine / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D016159:Tumor Suppressor Protein p53; D012694:Serine; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; C115114:HIPK2 protein, human; D017346:Protein Serine-Threonine Kinases; D046988:Proteasome Endopeptidase Complex