title: Nuclear accumulation of p53 following inhibition of transcription is not due to diminished levels of MDM2.
abstract: A common mechanism by which the tumor suppressor p53 accumulates in the nucleus following cellular stress is through the attenuation of its interaction with MDM2, a protein involved in the nuclear export and degradation of p53. This is accomplished by induced modifications of p53, MDM2 or both. We have previously found that the kinase and mRNA synthesis inhibitor DRB (5,6-dichloro-1-b-D-ribofuranosylbenzimidazole) induces the nuclear accumulation of p53 without concomitant phosphorylation of the ser15 site of p53, which is thought to be a modification important for the attenuation of p53-MDM2 interaction. It has been proposed that the mechanism by which p53 accumulates following blockage of transcription involves the downregulation of MDM2 expression. In this study, we tested this hypothesis and found that after DRB treatment, p53 accumulated despite the fact that MDM2 levels remained high in human cells. Furthermore, over expression of MDM2 did not prevent the accumulation of p53 following DRB treatment. In, addition, p53 accumulating in the nucleus after DRB treatment was able to interact with MDM2 and was ubiquitylated. These findings suggest that blockage of transcription induce the nuclear accumulation of p53 without breaking the p53-MDM2 regulation loop.
authors.affiliation: Program in Molecular and Cellular Biology, Department of Radiation Oncology, Division of Radiation and Cancer Biology, University of Michigan Medical School, Ann Arbor, MI 48109-0936, USA.
authors.forename: Heather M
authors.initials: HM
authors.lastname: O'Hagan
authors.forename: Mats
authors.initials: M
authors.lastname: Ljungman
mesh_terms: D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D004004:Dichlororibofuranosylbenzimidazole / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D014158:Transcription, Genetic / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D009687:Nuclear Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; D004004:Dichlororibofuranosylbenzimidazole; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2