title: Adenovirus E1B 55-kilodalton oncoprotein binds to Daxx and eliminates enhancement of p53-dependent transcription by Daxx.
abstract: The adenovirus E1B 55-kDa protein impairs the p53 pathway and enhances transformation, although the underlying mechanisms remain to be defined. We found that Daxx binds to the E1B 55-kDa protein in a yeast two-hybrid screen. The two proteins interact through their C termini. Mutation of three potential phosphorylation sites (S489/490 and T494 to alanine) within the E1B 55-kDa protein did not affect its interaction with Daxx, although such mutations were previously shown to inhibit E1B's ability to repress p53-dependent transcription and to enhance transformation. In addition to their coimmunoprecipitation in 293 extracts, purified Daxx interacted with the E1B 55-kDa protein in vitro, indicating their direct interaction. In 293 cells, Daxx colocalized with the E1B 55-kDa protein within discrete nuclear dots, where p53 was also found. Such structures were distinct from PML (promyelocytic leukemia protein) bodies, and it appeared that Daxx was displaced from PML bodies. Thus, the Daxx concentration was diminished in dots with a prominent presence of PML and vice versa. Indeed, PML overexpression led to dramatic redistribution of Daxx from p53-E1B 55-kDa protein complexes to PML bodies. Additionally, expression of the E1B 55-kDa protein in Saos2 osteosarcoma cells reduced the number of PML bodies. Our data suggest that E1B and PML compete for available Daxx in the cell. Surprisingly, Daxx significantly augmented p53-mediated transcription and the E1B 55-kDa protein eliminated this effect. Thus, it is likely that the E1B 55-kDa protein sequesters Daxx and p53 in specific nuclear locations, where p53 cannot activate transcription. One consequence of the Daxx-E1B interaction might be an alteration of normal interactions of Daxx, PML, and p53, which may contribute to cell transformation.
authors.affiliation: Department of Anatomy and Cell Biology and Shands Cancer Center, University of Florida College of Medicine, Gainesville, Florida 32610-0235, USA
authors.forename: Lisa Y
authors.initials: LY
authors.lastname: Zhao
authors.forename: April L
authors.initials: AL
authors.lastname: Colosimo
authors.forename: Yue
authors.initials: Y
authors.lastname: Liu
authors.forename: Yanping
authors.initials: Y
authors.lastname: Wan
authors.forename: Daiqing
authors.initials: D
authors.lastname: Liao
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D017501:Adenovirus E1B Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D056970:Co-Repressor Proteins; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008856:Microscopy, Fluorescence; D018832:Molecular Chaperones; D009363:Neoplasm Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism*; D011233:Precipitin Tests; D000071156:Promyelocytic Leukemia Protein; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D025521:Tumor Suppressor Proteins; D020798:Two-Hybrid System Techniques
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D017501:Adenovirus E1B Proteins; D002352:Carrier Proteins; D056970:Co-Repressor Proteins; C106985:DAXX protein, human; D047908:Intracellular Signaling Peptides and Proteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C070576:PML protein, human