title: Ubiquitin over-expression promotes E6AP autodegradation and reactivation of the p53/MDM2 pathway in HeLa cells.
abstract: It has been established that intracellular ubiquitin pools are subject to regulatory constrains. Less certain is the mechanism by which the pool of conjugated ubiquitin shift in parallel with total ubiquitin, and how this type of regulation affects the flux of substrates through the pathway. In this study we demonstrate that ubiquitin over-expression promotes the destabilization of the ubiquitin protein ligase E6AP, by a mechanism involving self-ubiquitination, and the stabilization of p53. These results represent the very first evidence that the levels of a ubiquitin ligase can be regulated in vivo by ubiquitin abundance, supporting the idea that a strict interrelationship between pathway component activities and ubiquitin pool size exists. Interestingly, ubiquitin-induced p53 accumulation did not induce cell-cycle arrest, suggesting that although fluctuations of the intracellular ubiquitin content may actively modulate the level of regulatory proteins, this event is not per se sufficient to elicit a cellular response in terms of proliferation.
authors.affiliation: Istituto di Chimica Biologica G. Fornaini, Università degli Studi di Urbino Carlo Bo, via Saffi, 2, 61029 Urbino, PU, Italy. rita.crinelli@uniurb.it
authors.forename: Rita
authors.initials: R
authors.lastname: Crinelli
authors.forename: Marzia
authors.initials: M
authors.lastname: Bianchi
authors.forename: Michele
authors.initials: M
authors.lastname: Menotta
authors.forename: Elisa
authors.initials: E
authors.lastname: Carloni
authors.forename: Elisa
authors.initials: E
authors.lastname: Giacomini
authors.forename: Marzia
authors.initials: M
authors.lastname: Pennati
authors.forename: Mauro
authors.initials: M
authors.lastname: Magnani
mesh_terms: D020134:Catalytic Domain; D002453:Cell Cycle; D002467:Cell Nucleus / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D050505:Mutant Proteins / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism*; D013816:Thermodynamics; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; D050505:Mutant Proteins; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; C471639:UBE3A protein, human; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D044767:Ubiquitin-Protein Ligases