title: Functional analysis and consequences of Mdm2 E3 ligase inhibition in human tumor cells.
abstract: Mdm2 is the major negative regulator of p53 tumor-suppressor activity. This oncoprotein is overexpressed in many human tumors that retain the wild-type p53 allele. As such, targeted inhibition of Mdm2 is being considered as a therapeutic anticancer strategy. The N-terminal hydrophobic pocket of Mdm2 binds to p53 and thereby inhibits the transcription of p53 target genes. Additionally, the C-terminus of Mdm2 contains a RING domain with intrinsic ubiquitin E3 ligase activity. By recruiting E2 ubiquitin-conjugating enzyme(s), Mdm2 acts as a molecular scaffold to facilitate p53 ubiquitination and proteasome-dependent degradation. Mdmx (Mdm4), an Mdm2 homolog, also has a RING domain and hetero-oligomerizes with Mdm2 to stimulate its E3 ligase activity. Recent studies have shown that C-terminal residues adjacent to the RING domain of both Mdm2 and Mdmx contribute to Mdm2 E3 ligase activity. However, the molecular mechanisms mediating this process remain unclear, and the biological consequences of inhibiting Mdm2/Mdmx co-operation or blocking Mdm2 ligase function are relatively unexplored. This study presents biochemical and cell biological data that further elucidate the mechanisms by which Mdm2 and Mdmx co-operate to regulate p53 level and activity. We use chemical and genetic approaches to demonstrate that functional inhibition of Mdm2 ubiquitin ligase activity is insufficient for p53 activation. This unexpected result suggests that concomitant treatment with Mdm2/Mdmx antagonists may be needed to achieve therapeutic benefit.
authors.affiliation: Gene Expression Laboratory, Salk Institute for Biological Studies, La Jolla, CA, USA. mark.wade@iit.it
authors.forename: M
authors.initials: M
authors.lastname: Wade
authors.forename: Y C
authors.initials: YC
authors.lastname: Li
authors.forename: A S
authors.initials: AS
authors.lastname: Matani
authors.forename: S M G
authors.initials: SM
authors.lastname: Braun
authors.forename: F
authors.initials: F
authors.lastname: Milanesi
authors.forename: L W
authors.initials: LW
authors.lastname: Rodewald
authors.forename: G M
authors.initials: GM
authors.lastname: Wahl
mesh_terms: D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D015870:Gene Expression; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D009154:Mutation; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D018797:Cell Cycle Proteins; D007093:Imidazoles; C482775:MDM4 protein, human; D009687:Nuclear Proteins; D010879:Piperazines; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; C482205:nutlin 3; D051736:Proto-Oncogene Proteins c-mdm2