The Nucleolar Protein Myb-binding Protein 1A ( MYBBP1A) Enhances p53 Tetramerization and Acetylation in Response to Nucleolar Disruption*

Background: Nucleolar disruption is involved in cellular stress response and is sufficient for p53 activation. p53 tetramerization is crucial to exert its activity. Results: The nucleolar protein MYBBP1A enhanced p53 tetramerization by directly interacting with p53. Conclusion: p53 tetramerization by MYBBP1A is indispensable for activating p53 under nucleolar stress. Significance: This is the first report to describe the possible mechanism underlying p53 tetramerization in cells under nucleolar stress. Tetramerization of p53 is crucial to exert its biological activity, and nucleolar disruption is sufficient to activate p53. We previously demonstrated that nucleolar stress induces translocation of the nucleolar protein MYBBP1A from the nucleolus to the nucleoplasm and enhances p53 activity. However, whether and how MYBBP1A regulates p53 tetramerization in response to nucleolar stress remain unclear. In this study, we demonstrated that MYBBP1A enhances p53 tetramerization, followed by acetylation under nucleolar stress. We found that MYBBP1A has two regions that directly bind to lysine residues of the p53 C-terminal regulatory domain. MYBBP1A formed a self-assembled complex that provided a molecular platform for p53 tetramerization and enhanced p300-mediated acetylation of the p53 tetramer. Moreover, our results show that MYBBP1A functions to enhance p53 tetramerization that is necessary for p53 activation, followed by cell death with actinomycin D treatment. Thus, we suggest that MYBBP1A plays a pivotal role in the cellular stress response.