title: MAGE-A Cancer/Testis Antigens Inhibit MDM2 Ubiquitylation Function and Promote Increased Levels of MDM4.
abstract: Melanoma antigen A (MAGE-A) proteins comprise a structurally and biochemically similar sub-family of Cancer/Testis antigens that are expressed in many cancer types and are thought to contribute actively to malignancy. MAGE-A proteins are established regulators of certain cancer-associated transcription factors, including p53, and are activators of several RING finger-dependent ubiquitin E3 ligases. Here, we show that MAGE-A2 associates with MDM2, a ubiquitin E3 ligase that mediates ubiquitylation of more than 20 substrates including mainly p53, MDM2 itself, and MDM4, a potent p53 inhibitor and MDM2 partner that is structurally related to MDM2. We find that MAGE-A2 interacts with MDM2 via the N-terminal p53-binding pocket and the RING finger domain of MDM2 that is required for homo/hetero-dimerization and for E2 ligase interaction. Consistent with these data, we show that MAGE-A2 is a potent inhibitor of the E3 ubiquitin ligase activity of MDM2, yet it does not have any significant effect on p53 turnover mediated by MDM2. Strikingly, however, increased MAGE-A2 expression leads to reduced ubiquitylation and increased levels of MDM4. Similarly, silencing of endogenous MAGE-A expression diminishes MDM4 levels in a manner that can be rescued by the proteasomal inhibitor, bortezomid, and permits increased MDM2/MDM4 association. These data suggest that MAGE-A proteins can: (i) uncouple the ubiquitin ligase and degradation functions of MDM2; (ii) act as potent inhibitors of E3 ligase function; and (iii) regulate the turnover of MDM4. We also find an association between the presence of MAGE-A and increased MDM4 levels in primary breast cancer, suggesting that MAGE-A-dependent control of MDM4 levels has relevance to cancer clinically.
authors.affiliation: Division of Cancer Research, University of Dundee, Clinical Research Centre and Jacqui Wood Cancer Centre, Ninewells Hospital, James Arrott Drive, Dundee, United Kingdom.
authors.forename: Lynnette
authors.initials: L
authors.lastname: Marcar
authors.affiliation: Division of Cancer Research, University of Dundee, Clinical Research Centre and Jacqui Wood Cancer Centre, Ninewells Hospital, James Arrott Drive, Dundee, United Kingdom.
authors.forename: Bianca
authors.initials: B
authors.lastname: Ihrig
authors.affiliation: Division of Cancer Research, University of Dundee, Clinical Research Centre and Jacqui Wood Cancer Centre, Ninewells Hospital, James Arrott Drive, Dundee, United Kingdom.
authors.forename: John
authors.initials: J
authors.lastname: Hourihan
authors.affiliation: Division of Cancer Research, University of Dundee, Clinical Research Centre and Jacqui Wood Cancer Centre, Ninewells Hospital, James Arrott Drive, Dundee, United Kingdom.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Bray
authors.affiliation: School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington Campus, Leicestershire, United Kingdom; School of Computer Science, University of Nottingham, Jubilee Campus, Nottingham, United Kingdom; Advanced Data Analysis Centre, University of Nottingham, Nottingham, United Kingdom.
authors.forename: Philip R
authors.initials: PR
authors.lastname: Quinlan
authors.affiliation: Division of Cancer Research, University of Dundee, Clinical Research Centre and Jacqui Wood Cancer Centre, Ninewells Hospital, James Arrott Drive, Dundee, United Kingdom.
authors.forename: Lee B
authors.initials: LB
authors.lastname: Jordan
authors.affiliation: M. D. Anderson Cancer Center, University of Texas, 1400 Pressler Drive, Unit 1484, Houston, United States of America.
authors.forename: Alastair M
authors.initials: AM
authors.lastname: Thompson
authors.affiliation: p53 Signal Transduction Laboratory, Edinburgh Cancer Research UK Centre, The University of Edinburgh, Crewe Road South, Edinburgh, United Kingdom.
authors.forename: Ted R
authors.initials: TR
authors.lastname: Hupp
authors.affiliation: Division of Cancer Research, University of Dundee, Clinical Research Centre and Jacqui Wood Cancer Centre, Ninewells Hospital, James Arrott Drive, Dundee, United Kingdom.
authors.forename: David W
authors.initials: DW
authors.lastname: Meek
mesh_terms: D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D000951:Antigens, Neoplasm; D018797:Cell Cycle Proteins; C482775:MDM4 protein, human; C420909:Mage-a2 antigen; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D025801:Ubiquitin; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2