title: MDMX stability is regulated by p53-induced caspase cleavage in NIH3T3 mouse fibroblasts.
abstract: MDMX is a p53 binding protein, which shares a high degree of homology with MDM2, a negative regulator of the tumor suppressor p53. MDMX has been shown to counteract MDM2-dependent p53 degradation and to stabilize p53 in its inactive form. In this study: we identify two MDMX proteolytic pathways that control its intracellular levels, and show that MDMX post-translational processing may be regulated by p53. Mouse MDMX is cleaved in vitro and in vivo by caspase activity, between aminoacids 358 and 361, producing a p54 minor form. In addition, MDMX is subjected to proteasome-mediated degradation, which concurs to MDMX proteolysis mainly through degradation of p54. A D361A-MDMX mutant, resistant to caspase cleavage, exhibits prolonged intracellular lifetime in comparison to wild-type protein, indicating that caspase cleavage affects stability of MDMX protein probably by modulating its further degradation. Overexpression of exogenous p53 increases the intracellular levels of p54 product. Similarly, activation of endogenous p53 by adriamycin enhances MDMX cleavage and produces a marked decrease of its intracellular levels, while not affecting the D361A-MDMX mutant. In addition, the D361A-MDMX mutant lacks the ability to inhibit p53 transactivation in respect to wild-type MDMX, suggesting that MDMX caspase cleavage play an important functional role. In conclusion, our results demonstrate that, in analogy to MDM2, MDMX may be subjected to proteolytic modifications that regulate its intracellular levels. Moreover, decrease of MDMX protein levels following p53 activation suggests a p53-dependent regulatory feedback of MDMX function.
authors.affiliation: Molecular Oncogenesis Laboratory, Regina Elena Cancer Institute, Via delle Messi D'Oro 156, 00158 Rome, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Gentiletti
authors.forename: Francesca
authors.initials: F
authors.lastname: Mancini
authors.forename: Marco
authors.initials: M
authors.lastname: D'Angelo
authors.forename: Ada
authors.initials: A
authors.lastname: Sacchi
authors.forename: Alfredo
authors.initials: A
authors.lastname: Pontecorvi
authors.forename: Aart G
authors.initials: AG
authors.lastname: Jochemsen
authors.forename: Fabiola
authors.initials: F
authors.lastname: Moretti
mesh_terms: D016475:3T3 Cells / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D020169:Caspases / Q000378:metabolism*; D002453:Cell Cycle; D016384:Consensus Sequence; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D004318:Doxycycline / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D005246:Feedback; D016158:Genes, p53; D006207:Half-Life; D006801:Humans; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D010446:Peptide Fragments / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D011993:Recombinant Fusion Proteins / Q000502:physiology; D013329:Structure-Activity Relationship; D015533:Transcriptional Activation; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D015853:Cysteine Proteinase Inhibitors; D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D010446:Peptide Fragments; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; D004317:Doxorubicin; C497206:MDM2 protein, human; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D004318:Doxycycline; D005033:Ethylmaleimide