Supplementary Components1. factors RIF1 and PTIP. Depletion of FOXK1 impairs DNA restoration and induces jeopardized cell survival upon DNA damage. Overexpression of FOXK1 diminishes 53BP1 foci formation, that leads to level of resistance to PARPis and elevation of HR in BRCA1-lacking cells and reduced telomere fusion in TRF2-depleted cells. Collectively, our results demonstrate that FOXK1 adversely regulates 53BP1 function by inhibiting 53BP1 localization to sites of DNA harm, which alters the DSB-induced protein complexes centering on 53BP1 and influences DNA fix choice therefore. In Short 53BP1 plays a crucial part in DNA double-strand break restoration choice. Tang et al. record that FOXK1 functions as well as 53BP1 and participates in appropriate DNA restoration pathway choice during various cell cycle phases. Graphical Abstract INTRODUCTION Chromosomes are under constant assault as cells encounter endogenous lesions or Methasulfocarb are exposed to various DNA-damaging agents. Among all of the DNA lesions, DNA double-strand breaks (DSBs) are considered the most genotoxic because unrepaired DSBs prevent the completion of DNA replication and transcription. Cells respond to DSBs by blocking cell cycle progression and initiating DNA repair. Usually, DSBs can be repaired via two major pathways: non-homologous end joining (NHEJ) (Lieber, 2010) and homologous recombination (HR) (Heyer et al., 2010). 53BP1 is a key regulator of DNA damage response and is required for DNA repair and tumor suppression (Schultz et al., 2000; Ward et al., 2003). 53BP1 plays critical roles in the regulation of class-switch recombination in B lymphocytes (Manis et al., 2004; Ward et al., 2004), end joining of dysfunctional telomeres in TRF2-depleted cells (Dimitrova et al., 2008), and sensitivity to poly(ADP-ribose) polymerase inhibitors (PARPis) in BRCA1-deficient cancers (Bouwman et al., 2010; Bunting et al., 2010). Upon DSB induction, 53BP1 can rapidly form damage-induced foci near DNA lesions. The minimal region in 53BP1 that controls its localization to DSBs contains an oligomerization domain (Zgheib et al., 2009), TNFRSF10C a tandem Tudor domain that recognizes histone H4 Lys 20 dimethylation (H4K20me2) (Charier et al., 2004), and a Methasulfocarb ubiquitin-dependent recruitment (UDR) motif that recognizes histone H2A(X) Lys-15 ubiquitination (H2AK15ub) (Fradet-Turcotte et al., 2013). 53BP1 coordinates the two major DSB repair pathways; while it promotes NHEJ repair, it inhibits HR repair (Bunting et al., 2010). In the G1 phase, ATM-mediated 53BP1 phosphorylation recruits the downstream factors RIF1 and PTIP to sites of DNA damage to suppress BRCA1-mediated 5-to-3 DNA end resection; in the S/G2 phase, BRCA1 can antagonize 53BP1 signaling to promote HR repair and inhibit NHEJ by inhibiting 53BP1 phosphorylation and preventing the translocation of RIF1 to DSBs (Chapman et al., 2013; Daley and Sung, 2013; Di Virgilio et al., 2013; Escribano-Daz et al., 2013; Feng et al., 2013; Munoz et al., 2007; Wang et al., 2010). The role of 53BP1 in dictating DNA repair choice between NHEJ and HR is critically important for the treatment of BRCA1-deficient breast and ovarian cancers. BRCA1- and BRCA2-mutated cancers, which are deficient in HR repair, are hypersensitive to PARPis through the mechanism of synthetic lethality (Farmer et al., Methasulfocarb 2005; Helleday et al., 2005). Recent studies demonstrated that BRCA1-deficient tumors may acquire resistance to PARPis by partially restoring HR repair, either through reversion mutations in BRCA1 or through synthetic viability due to a loss of 53BP1 or 53BP1-related proteins (Bunting et al., 2010; Cao et al., 2009). These results reveal that 53BP1 might play a significant part in identifying the results of PARPi-based tumor therapy, that is becoming used within the center for the treating breasts quickly, ovarian, prostate, along with other cancers which have defects within the HR pathway. Therefore, identification of book 53BP1 regulators would help us better understand the rules of 53BP1 function in DSB restoration choice and style better anticancer strategies. To this final end, we utilized CRISPR-Cas9 Methasulfocarb technology to put in a tag in the C terminus of 53BP1 at its genomic loci and examined endogenous 53BP1-connected proteins utilizing a tandem affinity purification (Faucet) approach..