title: Topors functions as an E3 ubiquitin ligase with specific E2 enzymes and ubiquitinates p53.
abstract: 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.
authors.affiliation: Department of Pharmacology, The Cancer Institute of New Jersey, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, New Brunswick, NJ 08901, USA.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Rajendra
authors.forename: Diptee
authors.initials: D
authors.lastname: Malegaonkar
authors.forename: Pooja
authors.initials: P
authors.lastname: Pungaliya
authors.forename: Henderson
authors.initials: H
authors.lastname: Marshall
authors.forename: Zeshaan
authors.initials: Z
authors.lastname: Rasheed
authors.forename: James
authors.initials: J
authors.lastname: Brownell
authors.forename: Leroy F
authors.initials: LF
authors.lastname: Liu
authors.forename: Stuart
authors.initials: S
authors.lastname: Lutzker
authors.forename: Ahamed
authors.initials: A
authors.lastname: Saleem
authors.forename: Eric H
authors.initials: EH
authors.lastname: Rubin
mesh_terms: D000595:Amino Acid Sequence; D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D045744:Cell Line, Tumor; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D004330:Drosophila; D004591:Electrophoresis, Polyacrylamide Gel; D005982:Glutathione Transferase / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism; D015151:Immunoblotting; D033862:Iron-Binding Proteins / Q000737:chemistry; D008164:Luminescent Proteins / Q000378:metabolism; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D009363:Neoplasm Proteins; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D010957:Plasmids / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D016622:Silver Staining; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D014162:Transfection; D014364:Tryptophan / Q000737:chemistry; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000737:chemistry; D043743:Ubiquitin-Protein Ligase Complexes / Q000096:biosynthesis; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D017874:Immediate-Early Proteins; D033862:Iron-Binding Proteins; D008164:Luminescent Proteins; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; D049452:Green Fluorescent Proteins; D014364:Tryptophan; C577447:CDC34 protein, human; C097308:UBE2D1 protein, human; C097310:UBE2D3 protein, human; C086376:UBE2H protein, human; C079437:UBE2L3 protein, human; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; C120157:TOPORS protein, human; D044767:Ubiquitin-Protein Ligases; C051804:Vmw110 protein, Human herpesvirus 1; D005982:Glutathione Transferase; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex