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.
Mesh Terms:
Amino Acid Sequence, 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
J. Biol. Chem.
Date: Aug. 27, 2004
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