title: The ubiquitin ligase COP1 is a critical negative regulator of p53.
abstract: COP1 (constitutively photomorphogenic 1) is a RING-finger-containing protein that functions to repress plant photomorphogenesis, the light-mediated programme of plant development. Mutants of COP1 are constitutively photomorphogenic, and this has been attributed to their inability to negatively regulate the proteins LAF1 (ref. 1) and HY5 (ref. 2). The role of COP1 in mammalian cells is less well characterized. Here we identify the tumour-suppressor protein p53 as a COP1-interacting protein. COP1 increases p53 turnover by targeting it for degradation by the proteasome in a ubiquitin-dependent fashion, independently of MDM2 or Pirh2, which are known to interact with and negatively regulate p53. Moreover, COP1 serves as an E3 ubiquitin ligase for p53 in vitro and in vivo, and inhibits p53-dependent transcription and apoptosis. Depletion of COP1 by short interfering RNA (siRNA) stabilizes p53 and arrests cells in the G1 phase of the cell cycle. Furthermore, we identify COP1 as a p53-inducible gene, and show that the depletion of COP1 and MDM2 by siRNA cooperatively sensitizes U2-OS cells to ionizing-radiation-induced cell death. Overall, these results indicate that COP1 is a critical negative regulator of p53 and represents a new pathway for maintaining p53 at low levels in unstressed cells.
authors.affiliation: Department of Molecular Oncology, Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, USA.
authors.forename: David
authors.initials: D
authors.lastname: Dornan
authors.forename: Ingrid
authors.initials: I
authors.lastname: Wertz
authors.forename: Harumi
authors.initials: H
authors.lastname: Shimizu
authors.forename: David
authors.initials: D
authors.lastname: Arnott
authors.forename: Gretchen D
authors.initials: GD
authors.lastname: Frantz
authors.forename: Patrick
authors.initials: P
authors.lastname: Dowd
authors.forename: Karen
authors.initials: K
authors.lastname: O'Rourke
authors.forename: Hartmut
authors.initials: H
authors.lastname: Koeppen
authors.forename: Vishva M
authors.initials: VM
authors.lastname: Dixit
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D003546:Cysteine Endopeptidases / Q000378:metabolism; D016193:G1 Phase; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; C471981:COP1 protein, human; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D044767:Ubiquitin-Protein Ligases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex