title: CK1alpha plays a central role in mediating MDM2 control of p53 and E2F-1 protein stability.
abstract: The ubiquitin ligase murine double minute clone 2 (MDM2) mediates ubiquitination and degradation of the tumor suppressor p53. The activation and stabilization of p53 by contrast is maintained by enzymes catalyzing p53 phosphorylation and acetylation. Casein kinase 1 (CK1) is one such enzyme; it stimulates p53 after transforming growth factor-beta treatment, irradiation, or DNA virus infection. We analyzed whether CK1 regulates p53 protein stability in unstressed conditions. Depletion of CK1 using small interfering RNA or inhibition of CK1 using the kinase inhibitor (D4476) activated p53 and destabilized E2F-1, indicating that steady-state levels of these proteins are controlled by CK1. Co-immunoprecipitation of endogenous CK1 with MDM2 occurred in undamaged cells, indicating the existence of a stable multiprotein complex, and as such, we evaluated whether the MDM2 Nutlin had similar pharmacological properties to the CK1 inhibitor D4476. Indeed, D4476 or Nutlin treatments resulted in the same p53 and E2F-1 steady-state protein level changes, indicating that the MDM2 x CK1 complex is both a negative regulator of p53 and a positive regulator of E2F-1 in undamaged cells. Although the treatment of cells with D4476 resulted in a partial p53-dependent growth arrest, the induction of p53-independent apoptosis by D4476 suggested a critical role for the MDM2 x CK1 complex in maintaining E2F-1 anti-apoptotic signaling. These data highlighting a pharmacological similarity between MDM2 and CK1 small molecule inhibitors and the fact that CK1 and MDM2 form a stable complex suggest that the MDM2 x CK1 complex is a component of a genetic pathway that co-regulates the stability of the p53 and E2F-1 transcription factors.
authors.affiliation: Cancer Research UK p53 Signal Transduction Group, University of Edinburgh, Institute of Genetics and Molecular Medicine, Division of Cancer Biology, Crewe Road South, Edinburgh EH4 2XR, Scotland, United Kingdom.
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Huart
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: MacLaine
authors.forename: David W
authors.initials: DW
authors.lastname: Meek
authors.forename: Ted R
authors.initials: TR
authors.lastname: Hupp
mesh_terms: D017209:Apoptosis; D001549:Benzamides / Q000494:pharmacology; D047389:Casein Kinase I / Q000378:metabolism / Q000502:physiology*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D050687:E2F1 Transcription Factor / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008954:Models, Biological; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D020033:Protein Isoforms; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: C493177:4-(4-(2,3-dihydrobenzo(1,4)dioxin-6-yl)-5-pyridin-2-yl-1H-imidazol-2-yl)benzamide; D001549:Benzamides; D050687:E2F1 Transcription Factor; D007093:Imidazoles; D010879:Piperazines; D020033:Protein Isoforms; D034741:RNA, Small Interfering; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C482203:nutlin 1; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D047389:Casein Kinase I