title: MdmX inhibits ARF mediated Mdm2 sumoylation.
abstract: Mdm2, by virtue of an intrinsic E3 ubiquitin ligase activity, is capable of autoubiquitination and the ubiquitination of the p53 tumor suppressor protein. Additionally, Hdm2 has been reported to undergo a p14ARF-dependent sumoylation with concurrent Hdm2 stabilization. In this present work, we report that MdmX can undergo ARF-mediated sumoylation similar to that reported for Mdm2. When coexpressed, MdmX overexpression results in a dose-dependent inhibition of Mdm2 sumoylation and a concurrent increase in Mdm2 ubiquitination. This switch from Mdm2 sumoylation to Mdm2 ubiquitination may explain the destablization of Mdm2 previously observed in cells overexpressing both ARF and MdmX. Given that MdmX can heterodimerize with Mdm2 and separately associate with ARF we employed a series of MdmX mutants to examine how MdmX blocks Mdm2 sumoylation. A MdmX miniprotein capable of binding to ARF, but not p53 or Mdm2 was able to competitively inhibit Mdm2 sumoylation and reverse ARF mediated activation of p53 transactivation. Taken together, these results demonstrate that MdmX can affect post-translational modification and stability of Mdm2 and p53 activity through interaction with ARF.
authors.affiliation: Department of Biochemistry and Molecular Biology, Wright State University, Dayton, Ohio 45435, USA.
authors.forename: Mithua
authors.initials: M
authors.lastname: Ghosh
authors.forename: Karen
authors.initials: K
authors.lastname: Weghorst
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Berberich
mesh_terms: D015153:Blotting, Western; D002453:Cell Cycle; D045744:Cell Line, Tumor; D019941:Cyclin-Dependent Kinase Inhibitor p16; D019281:Dimerization; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D016158:Genes, p53; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism* / Q000502:physiology*; D051785:Smad Proteins / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection; D025803:Tumor Suppressor Protein p14ARF / Q000737:chemistry*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025801:Ubiquitin / Q000737:chemistry
chemical_list: C417743:Cdkn2a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D051785:Smad Proteins; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; D008156:Luciferases; D051736:Proto-Oncogene Proteins c-mdm2