Topors functions as an E3 ubiquitin ligase with specific E2 enzymes and ubiquitinates p53.
The human topoisomerase I- and p53-binding protein topors contains a highly conserved, N-terminal C3HC4-type RING domain that is homologous to the RING domains of known E3 ubiquitin ligases. We demonstrate that topors functions in vitro as a RING-dependent E3 ubiquitin ligase with the E2 enzymes UbcH5a, UbcH5c, and UbcH6 but not with UbcH7, CDC34, or UbcH2b. Additional studies indicate that a conserved tryptophan within the topors RING domain is required for ubiquitination activity. Furthermore, both in vitro and cellular studies implicate p53 as a ubiquitination substrate for topors. Similar to MDM2, overexpression of topors results in a proteasome-dependent decrease in p53 protein expression in a human osteosarcoma cell line. These results are similar to the recent finding that a Drosophila topors orthologue ubiquitinates the Hairy transcriptional repressor and suggest that topors functions as a ubiquitin ligase for multiple transcription factors.
Pubmed ID: 15247280 RIS Download
Amino Acid Sequence | Anaphase-Promoting Complex-Cyclosome | Animals | Carrier Proteins | Cell Line, Tumor | Cysteine Endopeptidases | DNA-Binding Proteins | Drosophila | Electrophoresis, Polyacrylamide Gel | Glutathione Transferase | Green Fluorescent Proteins | Humans | Immediate-Early Proteins | Immunoblotting | Iron-Binding Proteins | Luminescent Proteins | Mass Spectrometry | Molecular Sequence Data | Multienzyme Complexes | Neoplasm Proteins | Nuclear Proteins | Plasmids | Proteasome Endopeptidase Complex | Protein Structure, Tertiary | Proto-Oncogene Proteins | Proto-Oncogene Proteins c-mdm2 | Recombinant Proteins | Sequence Homology, Amino Acid | Silver Staining | Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization | Transcription Factors | Transcription, Genetic | Transfection | Tryptophan | Tumor Suppressor Protein p53 | Ubiquitin | Ubiquitin-Conjugating Enzymes | Ubiquitin-Protein Ligase Complexes | Ubiquitin-Protein Ligases