The tumor suppressor protein 53BP1, a pivotal regulator of DNA double-strand break (DSB) repair, was first identified as a p53-interacting protein over two decades ago. However, its direct contributions to p53-dependent cellular activities remain undefined. Here, we reveal that 53BP1 stimulates genome-wide p53-dependent gene transactivation and repression events in response to ionizing radiation (IR) and synthetic p53 activation. 53BP1-dependent p53 modulation requires both auto-oligomerization and tandem-BRCT domain-mediated bivalent interactions with p53 and the ubiquitin-specific protease USP28. Loss of these activities results in inefficient p53-dependent cell-cycle checkpoint and exit responses. Furthermore, we demonstrate 53BP1-USP28 cooperation to be essential for normal p53-promoter element interactions and gene transactivation-associated events, yet dispensable for 53BP1-dependent DSB repair regulation. Collectively, our data provide a mechanistic explanation for 53BP1-p53 cooperation in controlling anti-tumorigenic cell-fate decisions and reveal these activities to be distinct and separable from 53BP1's regulation of DNA double-strand break repair pathway choice.
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Bacterial Proteins, Base Sequence, Binding Sites, CRISPR-Associated Protein 9, Clustered Regularly Interspaced Short Palindromic Repeats, DNA Breaks, Double-Stranded, DNA Repair, Endonucleases, Gamma Rays, Gene Editing, Gene Expression Regulation, Humans, MCF-7 Cells, Promoter Regions, Genetic, Protein Binding, Protein Conformation, alpha-Helical, Protein Conformation, beta-Strand, Protein Interaction Domains and Motifs, Protein Multimerization, RNA, Guide, Signal Transduction, Tumor Suppressor Protein p53, Tumor Suppressor p53-Binding Protein 1, Ubiquitin Thiolesterase