Regulates DNA Double-strand Break Repair Research Articles

The cGAS-Ku80 complex regulates the balance between two end joining subpathways.

As the major DNA sensor that activates the STING-TBK1 signaling cascade, cGAS is mainly present in the cytosol. A number of recent reports have indicated that cGAS also plays critical roles in the nucleus. Our previous work demonstrated for the first time that cGAS is translocated to the nucleus upon the occurrence of DNA damage and inhibits homologous recombination (HR), one of the two major pathways of DNA double strand break (DSB) repair. However, whether nuclear cGAS regulates the other DSB repair pathway, nonhomologous end joining (NHEJ), which can be further divided into the less error-prone canonical NHEJ (c-NHEJ) and more mutagenic alternative NHEJ (alt-NHEJ) subpathways, has not been characterized. Here, we demonstrated that cGAS tipped the balance of the two NHEJ subpathways toward c-NHEJ. Mechanistically, the cGAS-Ku80 complex enhanced the interaction between DNA-PKcs and the deubiquitinase USP7 to improve DNA-PKcs protein stability, thereby promoting c-NHEJ. In contrast, the cGAS-Ku80 complex suppressed alt-NHEJ by directly binding to the promoter of Polθ to suppress its transcription. Together, these findings reveal a novel function of nuclear cGAS in regulating DSB repair, suggesting that the presence of cGAS in the nucleus is also important in the maintenance of genome integrity.

Tolerance to colibactin correlates with homologous recombination proficiency and resistance to irinotecan in colorectal cancer cells

The bacterial genotoxin colibactin promotes colorectal cancer (CRC) tumorigenesis, but systematic assessment of its impact on DNA repair is lacking, and its effect on response to DNA-damaging chemotherapeutics is unknown. We find that CRC cell lines display differential response to colibactin on the basis of homologous recombination (HR) proficiency. Sensitivity to colibactin is induced by inhibition of ATM, which regulates DNA double-strand break repair, and blunted by HR reconstitution. Conversely, CRC cells chronically infected with colibactin develop a tolerant phenotype characterized by restored HR activity. Notably, sensitivity to colibactin correlates with response to irinotecan active metabolite SN38, in both cell lines and patient-derived organoids. Moreover, CRC cells that acquire colibactin tolerance develop cross-resistance to SN38, and a trend toward poorer response to irinotecan is observed in a retrospective cohort of CRCs harboring colibactin genomic island. Our results shed insight into colibactin activity and provide translational evidence on its chemoresistance-promoting role in CRC.

The fructose-bisphosphate, Aldolase A (ALDOA), facilitates DNA-PKcs and ATM kinase activity to regulate DNA double-strand break repair

Glucose metabolism and DNA repair are fundamental cellular processes frequently dysregulated in cancer. In this study, we define a direct role for the glycolytic Aldolase A (ALDOA) protein in DNA double-strand break (DSB) repair. ALDOA is a fructose biphosphate Aldolase that catalyses fructose-1,6-bisphosphate to glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP), during glycolysis. Here, we show that upon DNA damage induced by ionising radiation (IR), ALDOA translocates from the cytoplasm into the nucleus, where it partially co-localises with the DNA DSB marker γ-H2AX. DNA damage was shown to be elevated in ALDOA-depleted cells prior to IR and following IR the damage was repaired more slowly. Consistent with this, cells depleted of ALDOA exhibited decreased DNA DSB repair via non-homologous end-joining and homologous recombination. In support of the defective repair observed in its absence, ALDOA was found to associate with the major DSB repair effector kinases, DNA-dependent Protein Kinase (DNA-PK) and Ataxia Telangiectasia Mutated (ATM) and their autophosphorylation was decreased when ALDOA was depleted. Together, these data establish a role for an essential metabolic protein, ALDOA in DNA DSB repair and suggests that targeting ALDOA may enable the concurrent targeting of cancer metabolism and DNA repair to induce tumour cell death.

The HDAC6-RNF168 axis regulates H2A/H2A.X ubiquitination to enable double-strand break repair.

Histone deacetylase 6 (HDAC6) mediates DNA damage signaling by regulating the mismatch repair and nucleotide excision repair pathways. Whether HDAC6 also mediates DNA double-strand break (DSB) repair is unclear. Here, we report that HDAC6 negatively regulates DSB repair in an enzyme activity-independent manner. In unstressed cells, HDAC6 interacts with H2A/H2A.X to prevent its interaction with the E3 ligase RNF168. Upon sensing DSBs, RNF168 rapidly ubiquitinates HDAC6 at lysine 116, leading to HDAC6 proteasomal degradation and a restored interaction between RNF168 and H2A/H2A.X. H2A/H2A.X is ubiquitinated by RNF168, precipitating the recruitment of DSB repair factors (including 53BP1 and BRCA1) to chromatin and subsequent DNA repair. These findings reveal novel regulatory machinery based on an HDAC6-RNF168 axis that regulates the H2A/H2A.X ubiquitination status. Interfering with this axis might be leveraged to disrupt a key mechanism of cancer cell resistance to genotoxic damage and form a potential therapeutic strategy for cancer.

The ends in sight: Mre11-Rad50-Nbs1 complex structures come into focus

In this issue of Molecular Cell, Rotheneder etal.1 elucidate the eukaroytic Mre11-Rad50-Nbs1 (MRN) complex quaternary architecture, which together with cryo-EM structures of bacterial Mre11-Rad50-DNA complexes,2 resolves the basis for MRN assembly and its broad nuclease specificity regulating DNA double-strand break repair.

EP400NL is involved in PD-L1 gene activation by forming a transcriptional coactivator complex

EP400 is an ATP-dependent chromatin remodelling enzyme that regulates DNA double-strand break repair and transcription, including cMyc-dependent gene expression. We previously showed that the N-terminal domain of EP400 increases the efficacy of chemotherapeutic drugs against cancer cells. As the EP400 N-terminal-Like (EP400NL) gene resides next to the EP400 gene locus, this prompted us to investigate whether EP400NL plays a similar role in transcriptional regulation to the full-length EP400 protein. We found that EP400NL forms a human NuA4-like chromatin remodelling complex that lacks both the TIP60 histone acetyltransferase and EP400 ATPase. However, this EP400NL complex displays H2A.Z deposition activity on a chromatin template comparable to the human NuA4 complex, suggesting another associated ATPase such as BRG1 or RuvBL1/RuvBL2 catalyses the reaction. We demonstrated that the transcriptional coactivator function of EP400NL is required for serum and IFNγ-induced PD-L1 gene activation. Furthermore, transcriptome analysis indicates that EP400NL contributes to cMyc-responsive mitochondrial biogenesis. Taken together, our studies show that EP400NL plays a role as a transcription coactivator of PD-L1 gene regulation and provides a potential target to modulate cMyc functions in cancer therapy.

Screen identifies fasudil as a radioprotector on human fibroblasts.

Radioprotectors safeguard biological system exposed to ionizing radiation (IR) by protecting normal cells from radiation damage during radiotherapy. Due to the toxicity and limited clinical utility of the present radioprotectors, it prompts us to identify novel radioprotectors that could alleviate IR-induced cytotoxicity of normal tissues. To identify new radioprotectors, we screened a chemical molecular library comprising 253 compounds in normal human fibroblasts (HFs) or 16HBE cells upon IR by CCK-8 assays and clonogenic survival assays. Fasudil was identified as a potential effective radioprotector. The results indicated that Fasudil exerts radioprotective effects on HFs against IR-induced DNA double-strand breaks (DSBs) through the regulation of DSB repair. Fasudil increased homologous recombination (HR) repair by 45.24% and decreased non-homologous end-joining (NHEJ) by 63.88% compared with untreated cells, without affecting changes to cell cycle profile. We further found that fasudil significantly facilitated the expression and foci formation of HR core proteins such as Rad51 and BRCA1 upon IR, and decreased the expression of NHEJ-associated proteins such as DNA-PKcs at 24 h post-IR. Our study identified fasudil as a novel radioprotector that exert radioprotective effects on normal cells through regulation of DSB repair by promoting HR repair.

The Chromatin Landscape Channels DNA Double-Strand Breaks to Distinct Repair Pathways.

DNA double-strand breaks (DSBs), the most deleterious DNA lesions, are primarily repaired by two pathways, namely homologous recombination (HR) and non-homologous end joining (NHEJ), the choice of which is largely dependent on cell cycle phase and the local chromatin landscape. Recent studies have revealed that post-translational modifications on histones play pivotal roles in regulating DSB repair pathways including repair pathway choice. In this review, we present our current understanding of how these DSB repair pathways are employed in various chromatin landscapes to safeguard genomic integrity. We place an emphasis on the impact of different histone post-translational modifications, characteristic of euchromatin or heterochromatin regions, on DSB repair pathway choice. We discuss the potential roles of damage-induced chromatin modifications in the maintenance of genome and epigenome integrity. Finally, we discuss how RNA transcripts from the vicinity of DSBs at actively transcribed regions also regulate DSB repair pathway choice.

CHAMP1-POGZ counteracts the inhibitory effect of 53BP1 on homologous recombination and affects PARP inhibitor resistance

DNA double-strand break (DSB) repair-pathway choice regulated by 53BP1 and BRCA1 contributes to genome stability. 53BP1 cooperates with the REV7-Shieldin complex and inhibits DNA end resection to block homologous recombination (HR) and affects the sensitivity to inhibitors for poly (ADP-ribose) polymerases (PARPs) in BRCA1-deficient cells. Here, we show that a REV7 binding protein, CHAMP1 (chromosome alignment-maintaining phosphoprotein 1), has an opposite function of REV7 in DSB repair and promotes HR through DNA end resection together with POGZ (POGO transposable element with ZNF domain). CHAMP1 was recruited to laser-micro-irradiation-induced DSB sites and promotes HR, but not NHEJ. CHAMP1 depletion suppressed the recruitment of BRCA1, but not the recruitment of 53BP1, suggesting that CHAMP1 regulates DSB repair pathway in favor of HR. Depletion of either CHAMP1 or POGZ impaired the recruitment of phosphorylated RPA2 and CtIP (CtBP-interacting protein) at DSB sites, implying that CHAMP1, in complex with POGZ, promotes DNA end resection for HR. Furthermore, loss of CHAMP1 and POGZ restored the sensitivity to a PARP inhibitor in cells depleted of 53BP1 together with BRCA1. These data suggest that CHAMP1and POGZ counteract the inhibitory effect of 53BP1 on HR by promoting DNA end resection and affect the resistance to PARP inhibitors.

CDK2 phosphorylation of Werner protein (WRN) contributes to WRN's DNA double-strand break repair pathway choice.

Werner syndrome (WS) is an accelerated aging disorder characterized by genomic instability, which is caused by WRN protein deficiency. WRN participates in DNA metabolism including DNA repair. In a previous report, we showed that WRN protein is recruited to laser‐induced DNA double‐strand break (DSB) sites during various stages of the cell cycle with similar intensities, supporting that WRN participates in both non‐homologous end joining (NHEJ) and homologous recombination (HR). Here, we demonstrate that the phosphorylation of WRN by CDK2 on serine residue 426 is critical for WRN to make its DSB repair pathway choice between NHEJ and HR. Cells expressing WRN engineered to mimic the unphosphorylated or phosphorylation state at serine 426 showed abnormal DSB recruitment, altered RPA interaction, strand annealing, and DSB repair activities. The CDK2 phosphorylation on serine 426 stabilizes WRN’s affinity for RPA, likely increasing its long‐range resection at the end of DNA strands, which is a crucial step for HR. Collectively, the data shown here demonstrate that a CDK2‐dependent phosphorylation of WRN regulates DSB repair pathway choice and cell cycle participation.

USP37 regulates DNA damage response through stabilizing and deubiquitinating BLM.

The human RecQ helicase BLM is involved in the DNA damage response, DNA metabolism, and genetic stability. Loss of function mutations in BLM cause the genetic instability/cancer predisposition syndrome Bloom syndrome. However, the molecular mechanism underlying the regulation of BLM in cancers remains largely elusive. Here, we demonstrate that the deubiquitinating enzyme USP37 interacts with BLM and that USP37 deubiquitinates and stabilizes BLM, thereby sustaining the DNA damage response (DDR). Mechanistically, DNA double-strand breaks (DSB) promotes ATM phosphorylation of USP37 and enhances the binding between USP37 and BLM. Moreover, knockdown of USP37 increases BLM polyubiquitination, accelerates its proteolysis, and impairs its function in DNA damage response. This leads to enhanced DNA damage and sensitizes breast cancer cells to DNA-damaging agents in both cell culture and in vivo mouse models. Collectively, our results establish a novel molecular mechanism for the USP37–BLM axis in regulating DSB repair with an important role in chemotherapy and radiotherapy response in human cancers.

Abstract PO-029: USP14 is a potential target to improve the efficacy of radiotherapy in combination with immune-checkpoint inhibitors in non-small cell lung cancer

Abstract Non-small cell lung cancer (NSCLC) represents ~85% of lung cancer cases and has a 5-year survival rate of ~23%. Thus, research aimed at determining more effective treatment strategies is critical. Immune checkpoint inhibitors (ICis), e.g. anti-PD-L1 antibodies, have transformed cancer treatment in recent years. Clinical trial studies have indicated that radiotherapy enhances the curative effect of ICis. However, most patients do not respond to immune-radiotherapy combinations. While best known to induce DNA double strand break (DSB)-mediated cytotoxicity, ionizing radiation (IR) induces an increase of cytosolic DNA and activates the cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) signaling pathway that leads to the type 1 interferon (IFN) response, essential to achieve anti-tumor immunity in combination with ICis. Homologous recombination (HR) DNA repair deficiency is an important determinant of radiation response that can also increase the immune recognition of cancers by increasing the number of non-synonymous mutations, as well as by increasing the cGAS/STING-mediated type1 IFN response. We have shown an important role for ubiquitin specific protease (USP14) in regulating DNA repair (1, 2,3). Here, we identify a novel role of USP14 in regulating HR and the cGAS/STING pathway in response to IR in NSCLC. USP14 is a proteasomal deubiquitinase that we show to have a prominent role in NSCLC. Knockdown of USP14 (shUSP14) or its pharmacological inhibition (IU1 or VLX1570) led to: (i) radio-sensitization, as shown by reduced clonogenic survival in NSCLC cell lines, and delayed growth of NSCLC tumor xenografts in nude mice; increased (ii) HR-deficiency; (iii) chromosomal aberrations and micronuclei formation; as well as (iv) cGAS puncta in response to IR. Further, USP14 interacts with and deubiquitinates cGAS in IR-treated NSCLC cells. USP14-mediated deubiquitination of cGAS has been shown to inhibit cGAS protein turn-over and increase the levels of cGAS in response to virus infection. Unexpectedly, however, in response to IR shUSP14 NSCLC cells have significantly higher cytoplasmic cGAS puncta and type 1 IFN response. Overall, these findings identify USP14 as a potential target to enhance sensitization to immune-radiotherapy by both regulation of HR and direct regulation of cGAS ubiquitination, leading to type 1 IFN response. Understanding the mechanisms that regulate DSB repair and cGAS/STING pathways holds potential for developing strategies to enhance the effectiveness of immune-radiotherapy combinations in NSCLC.

Abstract PO-031: Aldolase A (ALDOA) is required for efficient DNA double-strand break (DSB) repair

Abstract Introduction: Metabolic reprogramming, known as the Warburg effect, is one of the universal differences between cancer cells and non-cancerous cells. Glucose metabolism and DNA repair are frequently dysregulated in cancer. Metabolic pathways provide cells with nucleic acids and energy required to repair DNA. However, the underlying mechanisms that promote crosstalk between these processes are unknown. ALDOA is a glycolytic enzyme that catalyses the conversion of fructose 1,6-bisphosphate to glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. ALDOA is overexpressed in several types of cancer. In this study, we demonstrate a novel mechanism through which ALDOA directly regulates DSB repair. Methods: ALDOA was depleted from cells using siRNA and single-shot quantitative proteomics were performed. Immunofluorescence was utilized to determine the localization of ALDOA. DSB repair reporter assays were used to measure DSB break repair. Gene expression was quantified by western blot and qPCR. Immunoprecipitations were used to detect protein:protein interactions. Statistical analysis: The experiments were at least n=3, and data are presented as the means ± SEM. Statistical significance was evaluated using Student’s t-test or one-way ANOVA. Results: In order to identify ALDOA-dependent pathways, we performed quantitative mass spectrometry on ALDOA depleted cells. In addition to the expected decrease in glycolysis pathways, we also observed a significant downregulation of DNA repair proteins in ALDOA depleted cells. Further analysis showed that the ALDOA protein responds to DNA damage (IR) and migrates from the cytosol to the nucleus, suggesting that it could be directly involved in DNA damage repair. Slower clearance of γ-H2AX foci (a DSB marker), and decreased clonogenicity following irradiation (IR) treatment were also observed, indicating dysfunctional DNA repair processes. Repair of DSBs is primarily though the NHEJ (non-homologous end-joining) or HR (homologous recombination) -mediated DNA repair pathways. Silencing ALDOA led to a decrease in both NHEJ- and HR-mediated DSB repair efficiency. This disruption was likely due to the significant reduction of both the mRNA and protein of the DNA repair effector kinases, DNA-Dependent Kinase (DNA-PK) and Ataxia and Telangiectasia Mutated (ATM) in ALDOA-depleted cells. In addition to regulating the expression of DNAPK and ATM we also found that ALDOA directly interacted with both kinases, suggesting that it may have a direct role in regulating their function. Here, we define a role for ALDOA in the repair of DNA DSBs, through the regulation of DNA repair effector kinase expression and function. Conclusion: These results identify crosstalk between metabolic and DNA repair pathways and have implications for cancer treatment and tumorigenesis. The role of ALDOA in DNA repair could promote therapeutic resistance in tumors and may be a future therapeutic target to sensitize tumors to DNA-damaging agents such as radiation. Citation Format: Amila Suraweera, Kenneth O’Byrne, Derek Richard, Emma Bolderson, Thais Sobanski. Aldolase A (ALDOA) is required for efficient DNA double-strand break (DSB) repair [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-031.

Phosphorylation of SMURF2 by ATM exerts a negative feedback control of DNA damage response

Timely repair of DNA double-strand breaks (DSBs) is essential to maintaining genomic integrity and preventing illnesses induced by genetic abnormalities. We previously demonstrated that the E3 ubiquitin ligase SMURF2 plays a critical tumor suppressing role via its interaction with RNF20 (ring finger protein 20) in shaping chromatin landscape and preserving genomic stability. However, the mechanism that mobilizes SMURF2 in response to DNA damage remains unclear. Using biochemical approaches and MS analysis, we show that upon the onset of the DNA-damage response, SMURF2 becomes phosphorylated at Ser384 by ataxia telangiectasia mutated (ATM) serine/threonine kinase, and this phosphorylation is required for its interaction with RNF20. We demonstrate that a SMURF2 mutant with an S384A substitution has reduced capacity to ubiquitinate RNF20 while promoting Smad3 ubiquitination unabatedly. More importantly, mouse embryonic fibroblasts expressing the SMURF2 S384A mutant show a weakened ability to sustain the DSB response compared with those expressing WT SMURF2 following etoposide treatment. These data indicate that SMURF2-mediated RNF20 ubiquitination and degradation controlled by ataxia telangiectasia mutated–induced phosphorylation at Ser384 constitutes a negative feedback loop that regulates DSB repair.

RB Regulates DNA Double Strand Break Repair Pathway Choice by Mediating CtIP Dependent End Resection.

Inactivation of the retinoblastoma tumor suppressor gene (RB1) leads to genome instability, and can be detected in retinoblastoma and other cancers. One damaging effect is causing DNA double strand breaks (DSB), which, however, can be repaired by homologous recombination (HR), classical non-homologous end joining (C-NHEJ), and micro-homology mediated end joining (MMEJ). We aimed to study the mechanistic roles of RB in regulating multiple DSB repair pathways. Here we show that HR and C-NHEJ are decreased, but MMEJ is elevated in RB-depleted cells. After inducing DSB by camptothecin, RB co-localizes with CtIP, which regulates DSB end resection. RB depletion leads to less RPA and native BrdU foci, which implies less end resection. In RB-depleted cells, less CtIP foci, and a lack of phosphorylation on CtIP Thr847, are observed. According to the synthetic lethality principle, based on the altered DSB repair pathway choice, after inducing DSBs by camptothecin, RB depleted cells are more sensitive to co-treatment with camptothecin and MMEJ blocker poly-ADP ribose polymerase 1 (PARP1) inhibitor. We propose a model whereby RB can regulate DSB repair pathway choice by mediating the CtIP dependent DNA end resection. The use of PARP1 inhibitor could potentially improve treatment outcomes for RB-deficient cancers.

Role of H3K9 demethylases in DNA double-strand break repair.

H3K9 demethylases can remove the repressive H3K9 methylation marks on histones to alter chromatin structure, gene transcription and epigenetic state of cells. By counteracting the function of H3K9 methyltransferases, H3K9 demethylases have been shown to play an important role in numerous biological processes, including diseases such as cancer. Recent evidence points to a key role for some H3K9 demethylases in the repair of DNA double-strand breaks (DSBs) via homologous recombination (HR) and/or non-homologous end joining (NHEJ) pathways. Mechanistically, H3K9 demethylases can upregulate the expression of DNA repair factors. They can also be recruited to the DNA damage sites and regulate the recruitment or function of DNA repair factors. Here, we will discuss the role and mechanisms of H3K9 demethylases in the regulation of DSB repair.

Depletion of DNA damage binding protein 2 sensitizes triple-negative breast cancer cells to poly ADP-ribose polymerase inhibition by destabilizing Rad51.

Poly ADP‐ribose polymerase inhibitors (PARPi) have shown promising therapeutic efficacy in triple‐negative breast cancer (TNBC) patients. However, resistance ultimately develops, preventing a curative effect from being attained. Extensive investigations have indicated the diversity in the mechanisms underlying the PARPi sensitivity of breast cancer. In this study, we found that DNA damage binding protein 2 (DDB2), a DNA damage‐recognition factor, could protect TNBC cells from PARPi by regulating DNA double‐strand break repair through the homologous recombination pathway, whereas the depletion of DDB2 sensitizes TNBC cells to PARPi. Furthermore, we found that DDB2 was able to stabilize Rad51 by physical association and disrupting its ubiquitination pathway‐induced proteasomal degradation. These findings highlight an essential role of DDB2 in modulating homologous recombination pathway activity and suggest a promising therapeutic target for TNBC.

The deubiquitinase OTUD5 regulates Ku80 stability and non-homologous end joining.

The ability of cells to repair DNA double-strand breaks (DSBs) is important for maintaining genome stability and eliminating oncogenic DNA lesions. Two distinct and complementary pathways, non-homologous end joining (NHEJ) and homologous recombination (HR), are employed by mammalian cells to repair DNA DSBs. Each pathway is tightly controlled in response to increased DSBs. The Ku heterodimer has been shown to play a regulatory role in NHEJ repair. Ku80 ubiquitination contributes to the selection of a DSB repair pathway by causing the removal of Ku heterodimers from DSB sites. However, whether Ku80 deubiquitination also plays a role in regulating DSB repair is unknown. To address this question, we performed a comprehensive study of the deubiquitinase specific for Ku80, and our study showed that the deubiquitinase OTUD5 serves as an important regulator of NHEJ repair by increasing the stability of Ku80. Further studies revealed that OTUD5 depletion impaired NHEJ repair, and hence reduced overall DSB repair. Furthermore, OTUD5-depleted cells displayed excess end resection; as a result, HR repair was facilitated by OTUD5 depletion during the S/G2 phase. In summary, our study demonstrates that OTUD5 is a specific deubiquitinase for Ku80 and establishes OTUD5 as an important and positive regulator of NHEJ repair.

DNA double-strand break repair pathway choice: the fork in the road

DNA double-strand breaks (DSBs) are cytotoxic lesions that will lead to genomic instability or even tumorigenesis if left unrepaired or misrepaired. To maintain homeostasis, cells have evolved two major repair pathways to counteract DSBs: classical non-homologous end joining (c-NHEJ) and homologous recombination (HR). Two other modes for repairing DSBs have been described: alternative non-homologous end joining (alt-NHEJ) and single-strand annealing (SSA). c-NHEJ ligates adjacent DSB ends directly with rapid kinetics throughout interphase, while HR meticulously initiates DNA-end resection in late S or G2 phase when sister chromatids are available as repair templates. Although partially sharing the DNA-end resection procedure with HR, alt-NHEJ and SSA often contribute to chromosomal translocation and genome rearrangement. Selection of the appropriate pathway to repair DSBs helps to maintain genome integrity. Here, we review current knowledge of the mechanisms regulating DSB repair pathway choice.

Putting phage to work in deubiquitinase ligand discovery

Inhibiting deubiquitinase (DUB) function is a promising strategy for the treatment of cancers and other human diseases. Of the hundreds of human DUBs, USP11 has emerged as an ideal therapeutic target, as it regulates DNA double-strand break repair by homologous recombination (HR) and other functions central to eukaryotic cell survival. A new study by Spiliotopoulos et al. cleverly uses next-generation phage display (NGPD) to identify peptide ligands that bind USP11 in a unique pocket that impacts HR. The study provides an important step toward novel DUB inhibitors that may reduce the resistance of some cancers to current treatment options.