Project description:We used ChIP-seq to assess where p53 binds in the human genome and how that binding changes during the DNA double-strand break response. In particular, we considered the 1-Mb-wide window centered on the MYC locus. Contrary to previous reports, we found no evidence of p53 binding at the MYC promoter. Rather, we identified three locations downstream of MYC at which p53 was bound; binding at each of these regions increased during the DNA double-strand break response.
Project description:Recent observations show that the single-cell response of p53 to ionizing radiation (IR) is “digital” in that it is the number of oscillations rather than the amplitude of p53 that shows dependence on the radiation dose. We present a model of this phenomenon. In our model, double-strand break (DSB) sites induced by IR interact with a limiting pool of DNA repair proteins, forming DSB–protein complexes at DNA damage foci. The persisting complexes are sensed by ataxia telangiectasia mutated (ATM), a protein kinase that activates p53 once it is phosphorylated by DNA damage. The ATM-sensing module switches on or off the downstream p53 oscillator, consisting of a feedback loop formed by p53 and its negative regulator, Mdm2. In agreement with experiments, our simulations show that by assuming stochasticity in the initial number of DSBs and the DNA repair process, p53 and Mdm2 exhibit a coordinated oscillatory dynamics upon IR stimulation in single cells, with a stochastic number of oscillations whose mean increases with IR dose. The damped oscillations previously observed in cell populations can be explained as the aggregate behavior of single cell
Project description:SPO11-promoted DNA double-strand breaks (DSBs) formation is a crucial step for meiotic recombination, and it is indispensable to detect the broken DNA ends accurately for dissecting the molecular mechanisms behind. Here, we report a novel technique, named DEtail-seq (DNA End tailing followed by sequencing), that can directly and quantitatively capture the meiotic DSB 3’ overhang hotspots at single-nucleotide resolution.
Project description:In the bacterium Escherichia coli, RecG directs DNA synthesis during the repair of DNA double-strand breaks by homologous recombination. Examination of RecA binding during double-strand break repair in Escherichia coli in the presence and absence of RecG protein
Project description: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.
Project description:We used ATAC-seq to detect changes in chromatin accessibility and nucleosome positioning around the MYC gene during the DNA double-strand break response in human cells and the dependence of these changes on p53. We found that, in the region ~50 kb downstream of MYC where p53 binds strongly, chromatin accessibility as measured by ATAC-seq fragment density increased during the DNA DSB response, corresponding to the removal of a single nucleosome. These results are consistent with increased accessibility of a distal regulatory element at this locus that is dependent on DNA damage and p53 expression. At the MYC promoter region there is a p53-dependent decrease in chromatin accessibility in response to DSBs, even in the absence of a direct p53 binding site near the region. While both the P1 and P2 promoters of MYC are relatively free of nucleosomes in MCF-7 sh-p53 cells, both promoters are occluded in cells expressing WT levels of p53, with an increase of nucleosomal occlusion in response to DNA damage. This supports the hypothesis that MYC repression during the DNA DSB response results from nucleosomal occlusion of both the P1 and P2 promoters.
Project description:Measuring the effect of MYC on transcription during the DNA double-strand break response by RNA-seq of newly synthesized transcripts