53BP1 integrates DNA repair and p53-dependent cell fate decisions via distinct mechanisms. Homo sapiens

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 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 provides 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. Overall design: We evaluated the transcriptional profiles of two 53BP1Δ cell lines and included a positive (WT) and a negative (p53Δ) controls. These cell lines were treated with Nutlin-3, ionising radiation or mock treated. Three independent replicates were included for each independent condition generating a total of 36 samples.