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Numerous DNA repair and signaling proteins function at DNA damage sites to protect the genome. Here, we show that fusion of the promiscuous biotin ligase BirAR118G with RAD18 leads to localized protein biotinylation at DNA damage sites, allowing identification of ZPET (zinc finger protein proximal to RAD eighteen)/ZNF280C as a potential DNA damage response (DDR) protein. ZPET binds ssDNA and localizes to DNA double-strand breaks (DSBs) and stalled replication forks. In vitro, ZPET inhibits MRE11 binding to ssDNA. In cells, ZPET delays MRE11 binding to chromatin after DSB formation and slows DNA end resection through binding ssDNA. ZPET hinders resection independently of 53BP1 and HELB. Cells lacking ZPET displayed enhanced homologous recombination (HR), accelerated replication forks under stress, and increased resistance to DSBs and PARP inhibition. These results not only reveal ZPET as an HR repressor but also suggest that localized protein biotinylation at DNA damage sites is a useful strategy to identify DDR proteins.

Summary: Refinement of risk stratification in Philadelphia chromosome (Ph)‐negative B‐cell acute lymphoblastic leukaemia (ALL) might aid the identification of patients who are likely to relapse. Abnormal S100 calcium binding protein A16 (S100A16) has been implicated in various cancers, but its function remains unclear. We found S100A16 transcript levels were higher in 130 adults with newly‐diagnosed Ph‐negative B‐cell ALL compared with 33 healthy controls. In 115 of 130 patients who achieved first complete remission, those with high S100A16 transcript levels displayed a lower 3‐year cumulative incidence of relapse (CIR; 34% [21, 47%] vs. 40% [48, 72%]; P = 0·012) and higher 3‐year relapse‐free survival (RFS; 65% [53, 78%] vs. 35% [23, 46%]; P = 0·012), especially when receiving chemotherapy only. In multivariate analysis a low S100A16 transcript level was independently‐associated with a higher CIR (Hazard ratio [HR] = 3·74 [1·01–13·82]; P = 0·048) and inferior RFS (HR = 5·78 [1·91, 17·84]; P < 0·001). Function analysis indicated that knockdown of S100A16 promoted proliferation and anti‐apoptosis and reduced chemosensitivity. S100A16 over‐expression revealed an opposite trend, especially in a xeno‐transplant mouse model. Western blotting analysis showed upregulation of PI3K/AKT and ERK1/2 in S100A16‐knockdown and S100A16‐overexpression B‐cell ALL cell lines respectively. Inhibition assays suggested these two signalling pathways participated in the S100A16‐mediated proliferation and survival effects in B‐cell ALL cell lines. Trial Registration: Registered in the Chinese Clinical Trial Registry [ChiCTR‐OCH‐10000940]; http://www.chictr.org.cn. [ABSTRACT FROM AUTHOR]

: During DNA double-strand break repair, two structure-specific DNA nucleases are controlled by the same regulator Pxd1, but in opposite manners. [ABSTRACT FROM AUTHOR]