title: MDM2 binding induces a conformational change in p53 that is opposed by heat-shock protein 90 and precedes p53 proteasomal degradation.
abstract: p53 protein conformation is an important determinant of its localization and activity. Changes in p53 conformation can be monitored by reactivity with wild-type conformation-specific (pAb-1620) or mutant conformation-specific (pAb-240) p53 antibodies. Wild-type p53 accumulated in a mutant (pAb-240 reactive) form when its proteasome-dependent degradation was blocked during recovery from stress treatment and in cells co-expressing p53 and MDM2. This suggests that conformational change precedes wild-type p53 degradation by the proteasome. MDM2 binding to the p53 N terminus could induce a conformational change in wild-type p53. Interestingly, this conformational change was opposed by heat-shock protein 90 and did not require the MDM2 RING-finger domain and p53 ubiquitination. Finally, ubiquitinated p53 accumulated in a pAb-240 reactive form when p53 degradation was blocked by proteasome inhibition, and a p53-ubiquitin fusion protein displayed a mutant-only conformation in MDM2-null cells. These results support a model in which MDM2 binding induces a conformational change that is opposed by heat-shock protein 90 and precedes p53 ubiquitination. The covalent attachment of ubiquitin may "lock" p53 in a mutant conformation in the absence of MDM2-binding and prior to its degradation by the proteasome.
authors.affiliation: Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Sasaki
authors.forename: Linghu
authors.initials: L
authors.lastname: Nie
authors.forename: Carl G
authors.initials: CG
authors.lastname: Maki
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D001859:Bone Neoplasms / Q000378:metabolism / Q000473:pathology; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008113:Liver Neoplasms / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D012516:Osteosarcoma / Q000378:metabolism / Q000473:pathology; D011485:Protein Binding; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D018841:HSP90 Heat-Shock Proteins; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2