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DNA double strand breaks (DSBs) are critical for the efficacy of radiotherapy as they lead to cell death if not repaired. DSBs caused by ionizing radiation (IR) initiate histone modifications and accumulate DNA repair proteins, including 53BP1, which forms distinct foci at damage sites and serves as a marker for DSBs. DSB repair primarily occurs through Non-Homologous End Joining (NHEJ) and Homologous Recombination (HR). NHEJ directly ligates DNA ends, employing proteins such as DNA-PKcs, while HR, involving proteins such as Rad54, uses a sister chromatid template for accurate repair and functions in the S and G2 phases of the cell cycle. Both pathways are crucial, as illustrated by the IR sensitivity in cells lacking DNA-PKcs or Rad54. We generated mouse embryonic stem (mES) cells which are knockout (KO) for DNA-PKcs and Rad54 to explore the combined role of HR and NHEJ in DSB repair. We found that cells lacking both DNA-PKcs and Rad54 are hypersensitive to X-ray radiation, coinciding with impaired 53BP1 focus resolution and a more persistent G2 phase cell cycle block. Additionally, mES cells deficient in DNA-PKcs or both DNA-PKcs and Rad54 exhibit an increased nuclear size approximately 18–24 h post-irradiation. To further explore the role of Rad54 in the absence of DNA-PKcs, we generated DNA-PKcs KO mES cells expressing GFP-tagged wild-type (WT) or ATPase-defective Rad54 to track the Rad54 foci over time post-irradiation. Cells lacking DNA-PKcs and expressing ATPase-defective Rad54 exhibited a similar phenotypic response to IR as those lacking both DNA-PKcs and Rad54. Despite a strong G2 phase arrest, live-cell imaging showed these cells eventually progress through mitosis, forming micronuclei. Additionally, mES cells lacking DNA-PKcs showed increased Rad54 foci over time post-irradiation, indicating an enhanced reliance on HR for DSB repair without DNA-PKcs. Our findings underscore the essential roles of HR and NHEJ in maintaining genomic stability post-IR in mES cells. The interplay between these pathways is crucial for effective DSB repair and cell cycle progression, highlighting potential targets for enhancing radiotherapy outcomes. [ABSTRACT FROM AUTHOR]

Background: Cardiac fibrosis is the hallmark of all forms of chronic heart disease. Activation and proliferation of cardiac fibroblasts are the prime mediators of cardiac fibrosis. Existing studies show that ROS and inflammatory cytokines produced during fibrosis not only signal proliferative stimuli but also contribute to DNA damage. Therefore, as a prerequisite to maintain sustained proliferation in fibroblasts, activation of distinct DNA repair mechanism is essential. Result: In this study, we report that TET3, a DNA demethylating enzyme, which has been shown to be reduced in cardiac fibrosis and to exert antifibrotic effects does so not only through its demethylating activity but also through maintaining genomic integrity by facilitating error-free homologous recombination (HR) repair of DNA damage. Using both in vitro and in vivo models of cardiac fibrosis as well as data from human heart tissue, we demonstrate that the loss of TET3 in cardiac fibroblasts leads to spontaneous DNA damage and in the presence of TGF-β to a shift from HR to the fast but more error-prone non-homologous end joining repair pathway. This shift contributes to increased fibroblast proliferation in a fibrotic environment. In vitro experiments showed TET3's recruitment to H2O2-induced DNA double-strand breaks (DSBs) in mouse cardiac fibroblasts, promoting HR repair. Overexpressing TET3 counteracted TGF-β-induced fibroblast proliferation and restored HR repair efficiency. Extending these findings to human cardiac fibrosis, we confirmed TET3 expression loss in fibrotic hearts and identified a negative correlation between TET3 levels, fibrosis markers, and DNA repair pathway alteration. Conclusion: Collectively, our findings demonstrate TET3's pivotal role in modulating DDR and fibroblast proliferation in cardiac fibrosis and further highlight TET3 as a potential therapeutic target. [ABSTRACT FROM AUTHOR]

Metabolic changes involving the tricarboxylic acid (TCA) cycle have been linked to different non-metabolic cell processes. Among them, apart from cancer and immunity, emerges the DNA damage response (DDR) and specifically DNA damage repair. The oncometabolites succinate, fumarate and 2-hydroxyglutarate (2HG) increase reactive oxygen species levels and create pseudohypoxia conditions that induce DNA damage and/or inhibit DNA repair. Additionally, by influencing DDR modulation, they establish direct relationships with DNA repair on at least four different pathways. The AlkB pathway deals with the removal of N-alkylation DNA and RNA damage that is inhibited by fumarate and 2HG. The MGMT pathway acts in the removal of O-alkylation DNA damage, and it is inhibited by the silencing of the MGMT gene promoter by 2HG and succinate. The other two pathways deal with the repair of double-strand breaks (DSBs) but with opposite effects: the FH pathway, which uses fumarate to help with the repair of this damage, and the chromatin remodeling pathway, in which oncometabolites inhibit its repair by impairing the homologous recombination repair (HRR) system. Since oncometabolites inhibit DNA repair, their removal from tumor cells will not always generate a positive response in cancer therapy. In fact, their presence contributes to longer survival and/or sensitization against tumor therapy in some cancer patients. [ABSTRACT FROM AUTHOR]

Despite the great advances in discovering cyclic peptides against protein targets, their reduced aqueous solubility, cell permeability, and activity of the cyclic peptide restrict its utilization in advanced biological research and therapeutic applications. Here we report on a novel approach of structural alternation of the exocyclic and linker parts that led to a new derivative with significantly improved cell activity allowing us to dissect its mode of action in detail. We have identified an effective cyclic peptide (CP7) that induces approximately a 9‐fold increase in DNA damage accumulation and a remarkable increase in apoptotic cancer cell death compared to the reported molecule. Notably, treating cells with CP7 leads to a dramatic decrease in the efficiency of non‐homologous end joining (NHEJ) repair of DNA double‐strand breaks (DSBs), which is accompanied by an increase in homologous recombination (HR) repair. Interestingly, treating BRCA1‐deficient cells with CP7 restores HR integrity, which is accompanied by increased resistance to CP7. Additionally, CP7 treatment increases the sensitivity of cancer cells to ionizing radiation. Collectively, our findings demonstrate that CP7 is a selective inhibitor of NHEJ, offering a potential strategy to enhance the effectiveness of radiation therapy. [ABSTRACT FROM AUTHOR]

Abstract Background Cardiac fibrosis is the hallmark of all forms of chronic heart disease. Activation and proliferation of cardiac fibroblasts are the prime mediators of cardiac fibrosis. Existing studies show that ROS and inflammatory cytokines produced during fibrosis not only signal proliferative stimuli but also contribute to DNA damage. Therefore, as a prerequisite to maintain sustained proliferation in fibroblasts, activation of distinct DNA repair mechanism is essential. Result In this study, we report that TET3, a DNA demethylating enzyme, which has been shown to be reduced in cardiac fibrosis and to exert antifibrotic effects does so not only through its demethylating activity but also through maintaining genomic integrity by facilitating error-free homologous recombination (HR) repair of DNA damage. Using both in vitro and in vivo models of cardiac fibrosis as well as data from human heart tissue, we demonstrate that the loss of TET3 in cardiac fibroblasts leads to spontaneous DNA damage and in the presence of TGF-β to a shift from HR to the fast but more error-prone non-homologous end joining repair pathway. This shift contributes to increased fibroblast proliferation in a fibrotic environment. In vitro experiments showed TET3’s recruitment to H2O2-induced DNA double-strand breaks (DSBs) in mouse cardiac fibroblasts, promoting HR repair. Overexpressing TET3 counteracted TGF-β-induced fibroblast proliferation and restored HR repair efficiency. Extending these findings to human cardiac fibrosis, we confirmed TET3 expression loss in fibrotic hearts and identified a negative correlation between TET3 levels, fibrosis markers, and DNA repair pathway alteration. Conclusion Collectively, our findings demonstrate TET3’s pivotal role in modulating DDR and fibroblast proliferation in cardiac fibrosis and further highlight TET3 as a potential therapeutic target. Graphical abstract Schematic representation illustrating the role of TET3 in modulating the DDR response in healthy and fibrotic fibroblasts.

Abstract Non-homologous end joining (NHEJ) and homology-directed repair (HDR) are two mechanisms in filamentous fungi to repair DNA damages. NHEJ is the dominant response pathway to rapidly join DNA double-strand breaks, but often leads to insertions or deletions. On the other hand, HDR is more precise and utilizes a homologous DNA template to restore the damaged sequence. Both types are exploited in genetic engineering approaches ranging from knock-out mutations to precise sequence modifications. In this study, we evaluated the efficiency of an HDR based gene integration system designed for the pyrG locus of Aspergillus niger. While gene integration was achieved at a rate of 91.4%, we also discovered a mixed-type repair (MTR) mechanism with simultaneous repair of a Cas9-mediated double-strand break by both NHEJ and HDR. In 20.3% of the analyzed transformants the donor DNA was integrated by NHEJ at the 3’ end and by HDR at the 5’ end of the double-strand break. Furthermore, sequencing of the locus revealed different DNA repair mechanisms at the site of the NHEJ event. Together, the results support the applicability of the genome integration system and a novel DNA repair type with implication on the diversity of genetic modifications in filamentous fungi.

Plants are often subjected to DNA damage due to a range of environmental and internal factors in the natural world. Among these factors, DNA double strand breaks（DSBs）have the most serious consequences to plants. If these DSBs are repaired improperly, which may result in genome instability, gene mutations, and even cell death. On one hand, plants have evolved a powerful and well-organized damage repair mechanism to ensure overall survival and normal reproduction. On the other hand, based on the fault-tolerance and mutagenicity of the repair process, a series of techniques such as T-DNA insertion, gene editing, and physical mutagenesis have been widely used for variety improvement in plants and animals. Compared with mammals, reports on DSBs repair pathways and their molecular mechanisms in plants are limited. In this paper, we review the responses of plants to DSBs damage and the main repair mechanisms, and we also focus on the recent advances in alternative end joining（Alt-EJ）, whose mechanism has not yet been fully revealed. In addition, we discuss the characteristics and multi-pathway options of DSBs repair in plants induced by heavy ion beams irradiation, and the progress of gene editing technology based on different DSBs repair pathways. This study aims to provide reference for understanding the molecular mechanism of plant DSBs damage response and developing efficient biological breeding technology. [ABSTRACT FROM AUTHOR]

The process of end-joining during nonhomologous repair of DNA double-strand breaks (DSBs) after radiation damage is considered. Experimental evidence has revealed that the dynamics of DSB ends exhibit subdiffusive motion rather than simple diffusion with rare directional movement. Traditional models often overlook the rare long-range directed motion. To address this limitation, we present a heterogeneous anomalous diffusion model consisting of subdiffusive fractional Brownian motion interchanged with short periods of long-range movement. Our model sheds light on the underlying mechanisms of heterogeneous diffusion in DSB repair and could be used to quantify the DSB dynamics on a time scale inaccessible to single particle tracking analysis. The model predicts that the long-range movement of DSB ends is responsible for the misrepair of DSBs in the form of dicentric chromosome lesions. [ABSTRACT FROM AUTHOR]

Histone H3 Lys36 (H3K36) methylation and its associated modifiers are crucial for DNA double-strand break (DSB) repair, but the mechanism governing whether and how different H3K36 methylation forms impact repair pathways is unclear. Here, we unveil the distinct roles of H3K36 dimethylation (H3K36me2) and H3K36 trimethylation (H3K36me3) in DSB repair via non-homologous end joining (NHEJ) or homologous recombination (HR). Yeast cells lacking H3K36me2 or H3K36me3 exhibit reduced NHEJ or HR efficiency. yKu70 and Rfa1 bind H3K36me2- or H3K36me3-modified peptides and chromatin, respectively. Disrupting these interactions impairs yKu70 and Rfa1 recruitment to damaged H3K36me2- or H3K36me3-rich loci, increasing DNA damage sensitivity and decreasing repair efficiency. Conversely, H3K36me2-enriched intergenic regions and H3K36me3-enriched gene bodies independently recruit yKu70 or Rfa1 under DSB stress. Importantly, human KU70 and RPA1, the homologs of yKu70 and Rfa1, exclusively associate with H3K36me2 and H3K36me3 in a conserved manner. These findings provide valuable insights into how H3K36me2 and H3K36me3 regulate distinct DSB repair pathways, highlighting H3K36 methylation as a critical element in the choice of DSB repair pathway. [ABSTRACT FROM AUTHOR]

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Background/Aim: Ewing sarcoma is an aggressive mesenchymal malignancy commonly affecting children and young adolescents. The molecular basis of this neoplasia is well reported with the formation of the EWSR1/FLI1 fusion gene being the most common genetic finding. However, this fusion gene has not been targeted therapeutically nor is being used as a prognostic marker. Its relevance regarding the molecular steps leading to Ewing sarcoma genesis are yet to be defined. The generation of the oncogenic EWSR1/FLI1 fusion gene, can be attributed to the simultaneous introduction of two DNA double-strand breaks (DSBs). The scope of this study is to detect any association between DNA repair deficiency and the clinicopathological aspects of Ewing's sarcoma disease. Patients and Methods: We have conducted an expression analysis of 35 patients diagnosed with Ewing sarcoma concerning the genes involved in nonhomologous end joining (NHEJ) and homologous recombination (HR) repair pathways. We have analyzed the expression levels of 6 genes involved in NHEJ (XRCC4, XRCC5, XRCC6, POLλ, POLμ) and 9 genes involved in HR (RAD51, RAD52, RAD54, BRCA1, BRCA2, FANCC, FANCD, DNTM1, BRIT1) using real time PCR. Age, sex, location of primary tumor, tumor size, KI67, mitotic count, invasion of adjacent tissues and treatment were the clinicopathological parameters included in the statistical analysis. Results: Our results show that both these DNA repair pathways are deregulated in Ewing sarcoma. In addition, low expression of the xrcc4 gene has been associated with better overall survival probability (p=0.032). Conclusion: Our results, even though retrospective and in a small number of patients, highlight the importance of DSBs repair and propose a potential therapeutic target for this type of sarcoma. [ABSTRACT FROM AUTHOR]

Abstract Background Genome-scale screening can be applied to efficiently mine for unknown genes with phenotypes of interest or special functions. It is also useful to identify new targets for engineering desirable properties of cell factories. Results Here, we designed a new approach for genome-scale transcription activation using non-homologous end joining (NHEJ)-mediated integration in Yarrowia lipolytica. We utilized this approach to screen for genes that, upon activation, confer phenotypes including improved acetic acid tolerance and xylose metabolism. The candidates were validated using gene overexpression, and functional changes including improved growth performance under multiple stressors and activated pentose metabolism were identified. Conclusions This study provides a simple and effective approach to randomly activate endogenous genes and mine for key targets associated with phenotypes of interest. The specific gene targets identified here will be useful for cell factory construction and biorefining lignocellulose.

We explore the possibility that defects in genes associated with the response and repair of DNA double strand breaks predispose oral potentially malignant disorders (OPMD) to undergo malignant transformation to oral squamous cell carcinoma (OSCC). Defects in the homologous recombination/Fanconi anemia (HR/FA), but not in the non-homologous end joining, causes the DNA repair pathway to appear to be consistent with features of familial conditions that are predisposed to OSCC (FA, Bloom's syndrome, Ataxia Telangiectasia); this is true for OSCC that occurs in young patients, sometimes with little/no exposure to classical risk factors. Even in Dyskeratosis Congenita, a disorder of the telomerase complex that is also predisposed to OSCC, attempts at maintaining telomere length involve a pathway with shared HR genes. Defects in the HR/FA pathway therefore appear to be pivotal in conditions that are predisposed to OSCC. There is also some evidence that abnormalities in the HR/FA pathway are associated with malignant transformation of sporadic cases OPMD and OSCC. We provide data showing overexpression of HR/FA genes in a cell-cycle-dependent manner in a series of OPMD-derived immortal keratinocyte cell lines compared to their mortal counterparts. The observations in this study argue strongly for an important role of the HA/FA DNA repair pathway in the development of OSCC. [ABSTRACT FROM AUTHOR]

Double-strand breaks (DSBs) are the most dangerous injuries for a genome. When unrepaired, death quickly ensues. In most bacterial systems, DSBs are repaired through homologous recombination. Nearly one-quarter of bacterial species harbor a second system, allowing direct ligation of broken ends, known as Non- Homologous End Joining (NHEJ). The relative role of both systems in DSBs repair in bacteria has been explored only in a few cases. To evaluate this in the bacterium Rhizobium etli, we used a modified version of the symbiotic plasmid (264kb), containing a single copy of the nifH gene. In this plasmid, we inserted an integrative plasmid harboring a modified nifH gene fragment containing an I-SceI site. DSBs were easily inflicted in vivo by conjugating a small, replicative plasmid that expresses the I-SceI nuclease into the appropriate strains. Repair of a DSB may be achieved through homologous recombination (either between adjacent or distant repeats) or NHEJ. Characterization of the derivatives that repaired DSB in different configurations, revealed that in most cases (74%), homologous recombination was the prevalent mechanism responsible for repair, with a relatively minor contribution of NHEJ (23%). Inactivation of the I-SceI gene was detected in 3% of the cases. Sequence analysis of repaired derivatives showed the operation of NHEJ. To enhance the number of derivatives repaired through NHEJ, we repeated these experiments in a recA mutant background. Derivatives showing NHEJ were readily obtained when the DSB occurred on a small, artificial plasmid in a recA mutant. However, attempts to deliver a DSB on the symbiotic plasmid in a recA background failed, due to the accumulation of mutations that inactivated the I-SceI gene. This result, coupled with the absence of derivatives that lost the nonessential symbiotic plasmid, may be due to an unusual stability of the symbiotic plasmid, possibly caused by the presence of multiple toxin-antitoxin modules. [ABSTRACT FROM AUTHOR]

Background: Genome-scale screening can be applied to efficiently mine for unknown genes with phenotypes of interest or special functions. It is also useful to identify new targets for engineering desirable properties of cell factories. Results: Here, we designed a new approach for genome-scale transcription activation using non-homologous end joining (NHEJ)-mediated integration in Yarrowia lipolytica. We utilized this approach to screen for genes that, upon activation, confer phenotypes including improved acetic acid tolerance and xylose metabolism. The candidates were validated using gene overexpression, and functional changes including improved growth performance under multiple stressors and activated pentose metabolism were identified. Conclusions: This study provides a simple and effective approach to randomly activate endogenous genes and mine for key targets associated with phenotypes of interest. The specific gene targets identified here will be useful for cell factory construction and biorefining lignocellulose. [ABSTRACT FROM AUTHOR]

Background: Although the incidence of anaplastic thyroid carcinoma (ATC) is low (2.5% of thyroid cancer cases), this cancer has a very poor prognosis (survival rates < 5 months) and accounts for 14-39% of deaths. Conventional therapies based on surgery in combination with radiotherapy or chemotherapy showed limited effectiveness primarily due to the robust and protective DNA damage response in thyroid cancer cells. Methods: We used single-cell transcriptomic data from patients with different subtypes of thyroid cancer to study expression of genes involved in homologous recombination (HR) and non-homologous end joining (NHEJ) pathways. Then, we investigated the mechanisms of DNA damage and repair in anaplastic (C643 and Hth74) and papillary (TPC-1) thyroid cancer cell lines. The effect of caffeine (inhibitor of ATM and ATR) and UCN-01 (CHK1 inhibitor) was evaluated in cell cycle progression of thyroid cancer cells after g-radiation or doxorubicin treatment. The DNA damage response was monitored after staining of phosphorylated g-H2AX and 53BP1. Reporter plasmids were used to determine the efficacy of double-strand DNA breaks (DSBs) repair by HR and NHEJ in thyroid cancer cells. We evaluated the combination of selective inhibition of the DNA ligase IV by SCR7 and doxorubicin on cellular apoptosis and tumor growth in xenograft murine models of anaplastic thyroid cancer. Results: Single-cell RNA-Seq showed that NHEJ- and HR-related genes are expressed in ATC and PTC patients. We showed that ATC cells undergo mitosis in the presence of unrepaired DNA damage caused by g-radiation and doxorubicin treatment. To proliferate and survive, these cells efficiently repair DNA lesions using homologous recombination (HR) and non-homologous end joining (NHEJ). The combination of SCR7 with doxorubicin, significantly increased apoptosis and impaired ATC tumor growth in a xenograft mouse model compared to doxorubicin monotherapy. Conclusion: This study shows the therapeutic value of the combination of a DNA ligase IV inhibitor and DNA-damaging agents (doxorubicin and/or g-radiation) for the treatment of anaplastic thyroid cancer. [ABSTRACT FROM AUTHOR]

The impending climate change is threatening the rice productivity of the Asian subcontinent as instances of crop failures due to adverse abiotic and biotic stress factors are becoming common occurrences. CRISPR-Cas9 mediated genome editing offers a potential solution for improving rice yield as well as its stress adaptation. This technology allows modification of plant's genetic elements and is not dependent on foreign DNA/gene insertion for incorporating a particular trait. In this review, we have discussed various CRISPR-Cas9 mediated genome editing tools for gene knockout, gene knock-in, simultaneously disrupting multiple genes by multiplexing, base editing and prime editing the genes. The review here also presents how these genome editing technologies have been employed to improve rice productivity by directly targeting the yield related genes or by indirectly manipulating various abiotic and biotic stress responsive genes. Lately, many countries treat genome-edited crops as non-GMOs because of the absence of foreign DNA in the final product. Thus, genome edited rice plants with improved yield attributes and stress resilience are expected to be accepted by the public and solve food crisis of a major portion of the globe. [ABSTRACT FROM AUTHOR]

This article discusses a strategy called the T-circle vector strategy that increases the frequency of site-specific integration (SSI) in soybean plants. The authors used a non-homologous end joining (NHEJ) repair pathway to insert the entire T-DNA into a specific target site in the soybean genome. They tested different vector designs and found that a vector with two target sites and a split selectable marker gene resulted in a higher frequency of SSI events. The T-circle vector strategy has the potential to reduce costs and improve the efficiency of plant production. [Extracted from the article]

Abstract Background Cancer-associated fibroblasts (CAFs) play pivotal roles in chemoresistance of pancreatic ductal adenocarcinoma (PDAC). However, the underlying mechanisms are poorly understood. Revealing the cross-talk network between tumor stroma and pancreatic cancer and developing effective strategies against oxaliplatin resistance are highly desired in the clinic. Methods High-throughput sequence was used to screened the key circRNAs transmitted by extracellular vesicles (EVs) from CAFs to pancreatic cancer cells. The associations between EV-packaged circBIRC6 and chemotherapy responsiveness were validated in a cohort of 82 cases of advanced PDAC patients. Then, the effects of EV-packaged circBIRC6 on CAF-induced oxaliplatin resistance were investigated by flow cytometry, colony formation, viability of pancreatic cancer organoids in vitro and by xenograft models in vivo. RNA pulldown, RNA immunoprecipitation, and sites mutation assays were used to reveal the underlying mechanism. Results We identified a circRNA, circBIRC6, is significantly upregulated in CAF-derived EVs and is positively associated with oxaliplatin-based chemoresistance. In vitro and in vivo functional assays showed that CAF-derived EV-packaged circBIRC6 enhance oxaliplatin resistance of pancreatic cancer cells and organoids via regulating the non-homologous end joining (NHEJ) dependent DNA repair. Mechanistically, circBIRC6 directly binds with XRCC4 and enhanced the interaction of XRCC4 with SUMO1 at the lysine 115 residue, which facilitated XRCC4 chromatin localization. XRCC4K115R mutation dramatically abrogated the EV-packaged circBIRC6 induced effect. Moreover, combination of antisense oligonucleotide inhibitors against circBIRC6 with Olaparib dramatically suppressed chemoresistance in patient-derived xenograft models. Conclusions Our study revealed that EV-packaged circBIRC6 confer oxaliplatin resistance in PDAC by mediating SUMOylation of XRCC4, introducing a promising predictive and therapeutic target for PDAC on oxaliplatin resistance.

Metabolic changes involving the tricarboxylic acid (TCA) cycle have been linked to different non-metabolic cell processes. Among them, apart from cancer and immunity, emerges the DNA damage response (DDR) and specifically DNA damage repair. The oncometabolites succinate, fumarate and 2-hydroxyglutarate (2HG) increase reactive oxygen species levels and create pseudohypoxia conditions that induce DNA damage and/or inhibit DNA repair. Additionally, by influencing DDR modulation, they establish direct relationships with DNA repair on at least four different pathways. The AlkB pathway deals with the removal of N-alkylation DNA and RNA damage that is inhibited by fumarate and 2HG. The MGMT pathway acts in the removal of O-alkylation DNA damage, and it is inhibited by the silencing of the MGMT gene promoter by 2HG and succinate. The other two pathways deal with the repair of double-strand breaks (DSBs) but with opposite effects: the FH pathway, which uses fumarate to help with the repair of this damage, and the chromatin remodeling pathway, in which oncometabolites inhibit its repair by impairing the homologous recombination repair (HRR) system. Since oncometabolites inhibit DNA repair, their removal from tumor cells will not always generate a positive response in cancer therapy. In fact, their presence contributes to longer survival and/or sensitization against tumor therapy in some cancer patients.

Background: Cancer is a highly heterogeneous disease, driven by frequent genetic alterations which have significant effects on radiosensitivity. However, radiotherapy for a given cancer type is typically given with a standard dose determined from population‐level trials. As a result, a proportion of patients are under‐ or over‐dosed, reducing the clinical benefit of radiotherapy. Biological optimization would not only allow individual dose prescription but also a more efficient allocation of limited resources, such as proton and carbon ion therapy. Proton and ion radiotherapy offer an advantage over photons due to their elevated Relative Biological Effectiveness (RBE) resulting from their elevated Linear Energy Transfer (LET). Despite significant interest in optimizing LET by tailoring radiotherapy plans, RBE's genetic dependence remains unclear. Purpose: The aim of this study is to better define the RBE/LET relationship in a panel of cell lines with different defects in DSB repair pathways, but otherwise identical biological features and genetic background to isolate these effects. Methods: Normal human cells (RPE1), genetically modified to introduce defects in DNA double‐strand break (DSB) repair genes, ATM, BRCA1, DCLRE1C, LIG4, PRKDC and TP53, were used to map the RBE‐LET relationship. Cell survival was measured with clonogenic assays after exposure to photons, protons (LET 1 and 12 keV/µm) and alpha particles (129 keV/µm). Gene knockout sensitizer enhancement ratio (SER) values were calculated as the ratio of the mean inactivation dose (MID) of wild‐type cells to repair‐deficient cells, and RBE values were calculated as the ratio of the MID of X‐ray and particle irradiated cells. 53BP1 foci were used to quantify radiation‐induced DSBs and their repair following irradiation. Results: Deletion of NHEJ genes had the greatest impact on photon sensitivity (ATM−/− SER = 2.0 and Lig4−/− SER = 1.8), with genes associated with HR having smaller effects (BRCA1−/− SER = 1.2). Wild‐type cells showed RBEs of 1.1, 1.3, 5.0 for low‐ and high‐LET protons and alpha particles respectively. SERs for different genes were independent of LET, apart from NHEJ knockouts which proved to be markedly hypersensitive across all tested LETs. Due to this hypersensitivity, the impact of high LET was reduced in cell models lacking the NHEJ repair pathway. HR‐defective cells had moderately increased sensitivity across all tested LETs, but, notably, the contribution of HR pathway to survival appeared independent of LET. Analysis of 53BP1 foci shows that NHEJ‐defective cells had the least DSB repair capacity after low LET exposure, and no visible repair after high LET exposure. HR‐defective cells also had slower repair kinetics, but the impact of HR defects is not as severe as NHEJ defects. Conclusions: DSB repair defects, particularly in NHEJ, conferred significant radiosensitivity across all LETs. This sensitization appeared independent of LET, suggesting that the contribution of different DNA repair pathways to survival does not depend on radiation quality. [ABSTRACT FROM AUTHOR]

Purpose: The transcription factor NF-E2-related factor 2 (NRF2) is a master regulator widely involved in essential cellular functions such as DNA repair. By clarifying the upstream and downstream links of NRF2 to DNA damage repair, we hope that attention will be drawn to the utilization of NRF2 as a target for cancer therapy. Methods: Query and summarize relevant literature on the role of NRF2 in direct repair, BER, NER, MMR, HR, and NHEJ in pubmed. Make pictures of Roles of NRF2 in DNA Damage Repair and tables of antioxidant response elements (AREs) of DNA repair genes. Analyze the mutation frequency of NFE2L2 in different types of cancer using cBioPortal online tools. By using TCGA, GTEx and GO databases, analyze the correlation between NFE2L2 mutations and DNA repair systems as well as the degree of changes in DNA repair systems as malignant tumors progress. Results: NRF2 plays roles in maintaining the integrity of the genome by repairing DNA damage, regulating the cell cycle, and acting as an antioxidant. And, it possibly plays roles in double stranded break (DSB) pathway selection following ionizing radiation (IR) damage. Whether pathways such as RNA modification, ncRNA, and protein post-translational modification affect the regulation of NRF2 on DNA repair is still to be determined. The overall mutation frequency of the NFE2L2 gene in esophageal carcinoma, lung cancer, and penile cancer is the highest. Genes (50 of 58) that are negatively correlated with clinical staging are positively correlated with NFE2L2 mutations or NFE2L2 expression levels. Conclusion: NRF2 participates in a variety of DNA repair pathways and plays important roles in maintaining genome stability. NRF2 is a potential target for cancer treatment. [ABSTRACT FROM AUTHOR]

Background: Cancer-associated fibroblasts (CAFs) play pivotal roles in chemoresistance of pancreatic ductal adenocarcinoma (PDAC). However, the underlying mechanisms are poorly understood. Revealing the cross-talk network between tumor stroma and pancreatic cancer and developing effective strategies against oxaliplatin resistance are highly desired in the clinic. Methods: High-throughput sequence was used to screened the key circRNAs transmitted by extracellular vesicles (EVs) from CAFs to pancreatic cancer cells. The associations between EV-packaged circBIRC6 and chemotherapy responsiveness were validated in a cohort of 82 cases of advanced PDAC patients. Then, the effects of EV-packaged circBIRC6 on CAF-induced oxaliplatin resistance were investigated by flow cytometry, colony formation, viability of pancreatic cancer organoids in vitro and by xenograft models in vivo. RNA pulldown, RNA immunoprecipitation, and sites mutation assays were used to reveal the underlying mechanism. Results: We identified a circRNA, circBIRC6, is significantly upregulated in CAF-derived EVs and is positively associated with oxaliplatin-based chemoresistance. In vitro and in vivo functional assays showed that CAF-derived EV-packaged circBIRC6 enhance oxaliplatin resistance of pancreatic cancer cells and organoids via regulating the non-homologous end joining (NHEJ) dependent DNA repair. Mechanistically, circBIRC6 directly binds with XRCC4 and enhanced the interaction of XRCC4 with SUMO1 at the lysine 115 residue, which facilitated XRCC4 chromatin localization. XRCC4K115R mutation dramatically abrogated the EV-packaged circBIRC6 induced effect. Moreover, combination of antisense oligonucleotide inhibitors against circBIRC6 with Olaparib dramatically suppressed chemoresistance in patient-derived xenograft models. Conclusions: Our study revealed that EV-packaged circBIRC6 confer oxaliplatin resistance in PDAC by mediating SUMOylation of XRCC4, introducing a promising predictive and therapeutic target for PDAC on oxaliplatin resistance. [ABSTRACT FROM AUTHOR]

Arsenic is a carcinogen that can cause skin, lung, and bladder cancer. While DNA double‐strand breaks (DSBs) have been implicated in arsenic‐induced carcinogenesis, the exact mechanism remains unclear. In this study, we performed genetic analysis to examine the impact of arsenic trioxide (As2O3) on four different DSB repair pathways using the human pre‐B cell line Nalm‐6. Random integration analysis showed that As2O3 does not negatively affect non‐homologous end joining or polymerase theta‐mediated end joining. In contrast, chromosomal DSB repair analysis revealed that As2O3 decreases the efficiency of homologous recombination (HR) and, less prominently, single‐strand annealing. Consistent with this finding, As2O3 decreased gene‐targeting efficiency, owing to a significant reduction in the frequency of HR‐mediated targeted integration. To further verify the inhibitory effect of arsenic on HR, we examined cellular sensitivity to olaparib and camptothecin, which induce one‐ended DSBs requiring HR for precise repair. Intriguingly, we found that As2O3 significantly enhances sensitivity to those anticancer agents in HR‐proficient cells. Our results suggest that arsenic‐induced genomic instability is attributed to HR suppression, providing valuable insights into arsenic‐associated carcinogenesis and therapeutic options. [ABSTRACT FROM AUTHOR]

To investigate the structural features of wild-type and phospho-mimicking mutated XRCC4 protein, a protein involved in DNA double-strand break repair. XRCC4 with a HisTag were expressed by E. coli harboring plasmid DNA and purified. Phospho-mimicking mutants in which one phosphorylation site was replaced with aspartic acid were also prepared in order to reproduce the negative charge resulting from phosphorylation. The proteins were separated into dimers and multimers by gel filtration chromatography. Circular dichroism (CD) spectroscopy was performed in the region from ultraviolet to vacuum-ultraviolet. The CD spectra were analyzed with two analysis programs to evaluate the secondary structures of the wild-type and phospho-mimicked dimers and multimers. The proportion of β-strand in the wild-type dimers was very low, particularly in their C-terminal region, including the five phosphorylation sites. The secondary structure of the phospho-mimic hardly changed in the dimeric form. In contrast, the β-strand content increased and the α-helix content decreased upon multimerization of the wild-type protein. The structural change of multimers slightly depended on the phospho-mimic site. These results suggest that the β-strand structure stabilizes the multimerization of XRCC4 and it is regulated by phosphorylation at the C-terminal site in living cells. An increase in the β-strand content in XRCC4 is essential for stabilization of the multimeric form through C-terminal phosphorylation, allowing the formation of the large double-strand break repair machinery. [ABSTRACT FROM AUTHOR]

Double-strand breaks (DSBs) are the most dangerous injuries for a genome. When unrepaired, death quickly ensues. In most bacterial systems, DSBs are repaired through homologous recombination. Nearly one-quarter of bacterial species harbor a second system, allowing direct ligation of broken ends, known as Non-Homologous End Joining (NHEJ). The relative role of both systems in DSBs repair in bacteria has been explored only in a few cases. To evaluate this in the bacterium Rhizobium etli, we used a modified version of the symbiotic plasmid (264 kb), containing a single copy of the nifH gene. In this plasmid, we inserted an integrative plasmid harboring a modified nifH gene fragment containing an I-SceI site. DSBs were easily inflicted in vivo by conjugating a small, replicative plasmid that expresses the I-SceI nuclease into the appropriate strains. Repair of a DSB may be achieved through homologous recombination (either between adjacent or distant repeats) or NHEJ. Characterization of the derivatives that repaired DSB in different configurations, revealed that in most cases (74%), homologous recombination was the prevalent mechanism responsible for repair, with a relatively minor contribution of NHEJ (23%). Inactivation of the I-SceI gene was detected in 3% of the cases. Sequence analysis of repaired derivatives showed the operation of NHEJ. To enhance the number of derivatives repaired through NHEJ, we repeated these experiments in a recA mutant background. Derivatives showing NHEJ were readily obtained when the DSB occurred on a small, artificial plasmid in a recA mutant. However, attempts to deliver a DSB on the symbiotic plasmid in a recA background failed, due to the accumulation of mutations that inactivated the I-SceI gene. This result, coupled with the absence of derivatives that lost the nonessential symbiotic plasmid, may be due to an unusual stability of the symbiotic plasmid, possibly caused by the presence of multiple toxin-antitoxin modules.

BackgroundAlthough the incidence of anaplastic thyroid carcinoma (ATC) is low (2.5% of thyroid cancer cases), this cancer has a very poor prognosis (survival rates < 5 months) and accounts for 14–39% of deaths. Conventional therapies based on surgery in combination with radiotherapy or chemotherapy showed limited effectiveness primarily due to the robust and protective DNA damage response in thyroid cancer cells.MethodsWe used single-cell transcriptomic data from patients with different subtypes of thyroid cancer to study expression of genes involved in homologous recombination (HR) and non-homologous end joining (NHEJ) pathways. Then, we investigated the mechanisms of DNA damage and repair in anaplastic (C643 and Hth74) and papillary (TPC-1) thyroid cancer cell lines. The effect of caffeine (inhibitor of ATM and ATR) and UCN-01 (CHK1 inhibitor) was evaluated in cell cycle progression of thyroid cancer cells after γ‐radiation or doxorubicin treatment. The DNA damage response was monitored after staining of phosphorylated γ-H2AX and 53BP1. Reporter plasmids were used to determine the efficacy of double-strand DNA breaks (DSBs) repair by HR and NHEJ in thyroid cancer cells. We evaluated the combination of selective inhibition of the DNA ligase IV by SCR7 and doxorubicin on cellular apoptosis and tumor growth in xenograft murine models of anaplastic thyroid cancer.ResultsSingle-cell RNA-Seq showed that NHEJ- and HR-related genes are expressed in ATC and PTC patients. We showed that ATC cells undergo mitosis in the presence of unrepaired DNA damage caused by γ‐radiation and doxorubicin treatment. To proliferate and survive, these cells efficiently repair DNA lesions using homologous recombination (HR) and non-homologous end joining (NHEJ). The combination of SCR7 with doxorubicin, significantly increased apoptosis and impaired ATC tumor growth in a xenograft mouse model compared to doxorubicin monotherapy.ConclusionThis study shows the therapeutic value of the combination of a DNA ligase IV inhibitor and DNA-damaging agents (doxorubicin and/or γ-radiation) for the treatment of anaplastic thyroid cancer.

Chromosomal translocations arising from aberrant repair of multiple DNA double-strand breaks (DSBs) are a defining characteristic of many cancers. DSBs are an essential part of physiological processes in antibody-producing B cells. The B cell environment is poised to generate genome instability leading to translocations relevant to the pathology of blood cancers. These are a diverse set of cancers, but limited data from under-represented groups have pointed to health disparities associated with each. We focus on the DSBs that occur in developing B cells and propose the most likely mechanism behind the formation of translocations. We also highlight specific cancers in which these rearrangements occur and address the growing concern of health disparities associated with them.

Background: Efficient gene editing technology is needed for successful knock-in. Homologous recombination (HR) is a major double-strand break repair pathway that can be utilized for accurately inserting foreign genes into the genome. HR occurs during the S/G2 phase, and the DNA mismatch repair (MMR) pathway is inextricably linked to HR to maintain HR fidelity. This study was conducted to investigate the effect of inhibiting MMR-related genes using CdCl2, an MMR-related gene inhibitor, on HR efficiency in HC11 cells. Methods: The mRNA and protein expression levels of MMR-related genes (Msh2, Msh3, Msh6, Mlh1, Pms2), the HR-related gene Rad51, and the NHEJ-related gene DNA Ligase IV were assessed in HC11 cells treated with 10 μM of CdCl2 for 48 hours. In addition, HC11 cells were transfected with a CRISPR/sgRNA expression vector and a knock-in vector targeting Exon3 of the mouse-beta casein locus, and treated with 10 μM cadmium for 48 hours. The knock-in efficiency was monitored through PCR. Results: The treatment of HC11 cells with a high-dose of CdCl2 decreased the mRNA expression of the HR-related gene Rad51 in HC11 cells. In addition, the inhibition of MMR-related genes through CdCl2 treatment did not lead to an increase in knock-in efficiency. Conclusions: The inhibition of MMR-related gene expression through high-dose CdCl2 treatment reduces the expression of the HR-related gene Rad51, which is active during recombination. Therefore, it was determined that CdCl2 is an inappropriate compound for improving HR efficiency.

Abstract Background Although the clinical application of PARP inhibitors has brought hope to ovarian cancer, the problem of its resistance has become increasingly prominent. Therefore, clinical experts have been focused on finding specific indicators and therapeutic targets that can be used for resistance monitoring of PARP inhibitors. Results By cfDNA detecting during Olaparib maintenance therapy in platinum-sensitive relapsed ovarian cancer, we found the presence of MRE11:p.K464R mutation was strongly associated with acquired Olaparib resistance. Structural analysis revealed that the MRE11:p.K464R mutation is situated at a critical site where the MRE11 protein interacts with other biomolecules, leading to potential structural and functional abnormalities of MRE11 protein. Functionally, MRE11:p.K464R mutation enhanced the tolerance of Olaparib by reducing the DNA damage. Mechanistically, MRE11:p.K464R mutation improved the efficiency of DNA damage repair and induce Olaparib resistance by enhancing its binding activity with the interacting proteins (including RAD50 and RPS3). Among them, the enhanced binding of MRE11:p.K464R mutation to RAD50/RPS3 facilitated non-homologous end joining (NHEJ) repair in tumor cells, thereby expanding the scope of research into acquired resistance to PARP inhibitors. Conclusions Our findings provide a theoretical basis for MRE11:p.K464R mutation as a specific indicator of resistance monitoring in Olaparib treatment, and the exploration of its resistance mechanism provides a novel insights for the formulation of combination ther therapies after Olaparib resistance.

The process of end-joining during nonhomologous repair of DNA double-strand breaks (DSBs) after radiation damage is considered. Experimental evidence has revealed that the dynamics of DSB ends exhibit subdiffusive motion rather than simple diffusion with rare directional movement. Traditional models often overlook the rare long-range directed motion. To address this limitation, we present a heterogeneous anomalous diffusion model consisting of subdiffusive fractional Brownian motion interchanged with short periods of long-range movement. Our model sheds light on the underlying mechanisms of heterogeneous diffusion in DSB repair and could be used to quantify the DSB dynamics on a time scale inaccessible to single particle tracking analysis. The model predicts that the long-range movement of DSB ends is responsible for the misrepair of DSBs in the form of dicentric chromosome lesions.

Abstract Premature ovarian insufficiency (POI) is a clinically heterogeneous disease that may seriously affect the physical and mental health of women of reproductive age. POI primarily manifests as ovarian function decline and endocrine disorders in women prior to age 40 and is an established cause of female infertility. It is crucial to elucidate the causative factors of POI, not only to expand the understanding of ovarian physiology, but also to provide genetic counselling and fertility guidance to affected patients. Factors leading to POI are multifaceted with genetic factors accounting for 7% to 30%. In recent years, an increasing number of DNA damage-repair-related genes have been linked with the occurrence of POI. Among them, DNA double-strand breaks (DSBs), one of the most damaging to DNA, and its main repair methods including homologous recombination (HR) and non-homologous end joining (NHEJ) are of particular interest. Numerous genes are known to be involved in the regulation of programmed DSB formation and damage repair. The abnormal expression of several genes have been shown to trigger defects in the overall repair pathway and induce POI and other diseases. This review summarises the DSB-related genes that may contribute to the development of POI and their potential regulatory mechanisms, which will help to further establish role of DSB in the pathogenesis of POI and provide theoretical guidance for the study of the pathogenesis and clinical treatment of this disease.

DNA double-strand break repair (DSBR) plays an important role in maintaining genome stability and cell survival. DSBR are predominately accomplished by two pathways: Homologous Recombination (HR) and Non-homologous End Joining (NHEJ), and both pathways are essential for the maintenance of physiological functions in neurons. Dysregulation of DSBR has been reported to be involved in multiple neurodegenerative diseases. Therefore, a deeper understanding of mechanisms in the DSBR will provide further insights into the pathogenesis of distinct neurodegenerative disease and help to develop effective therapeutics for these diseases. In this review, we provide a comprehensive overview of the common DSBR pathways, and summarize the latest involvement of DSBR in the pathogenic mechanisms of several common neurodegenerative diseases.

Abstract The filamentous fungus Trichoderma reesei (teleomorph Hypocrea jecorina, Ascomycota) is a well-known lignocellulolytic enzymes-producing strain in industry. To increase the fermentation titer of lignocellulolytic enzymes, random mutagenesis and rational genetic engineering in T. reesei were carried out since it was initially found in the Solomon Islands during the Second World War. Especially the continuous exploration of the underlying regulatory network during (hemi)cellulase gene expression in the post-genome era provided various strategies to develop an efficient fungal cell factory for these enzymes’ production. Meanwhile, T. reesei emerges competitiveness potential as a filamentous fungal chassis to produce proteins from other species (e.g., human albumin and interferon α-2b, SARS-CoV-2 N antigen) in virtue of the excellent expression and secretion system acquired during the studies about (hemi)cellulase production. However, all the achievements in high yield of (hemi)cellulases are impossible to finish without high-efficiency genetic strategies to analyze the proper functions of those genes involved in (hemi)cellulase gene expression or secretion. Here, we in detail summarize the current strategies employed to investigate gene functions in T. reesei. These strategies are supposed to be beneficial for extending the potential of T. reesei in prospective strain engineering.

Hepatocellular carcinoma (HCC) is one of the most common types of malignant tumors with increasing incidence rates and high mortality rates. The currently available methods for treating HCC include surgery, radiotherapy or chemotherapy, but all of them have limitations. Therefore, developing novel therapeutic methods for HCC is in great need. Here, in this study, we found that tanshinone I, a small molecule compound, inhibited the proliferation of HCC cells in a dose-dependent manner. We also observed that Tanshinone I destabilized genomes by inhibiting both NHEJ and HR repair pathways, which are responsible for repairing DNA double strand breaks (DSBs). Mechanistically, this compound suppressed the expression of 53BP1, and the recruitment of RPA2 to DNA damage sites. Importantly, we demonstrated that combining Tanshinone I with radiotherapy exhibited better therapeutic potential for treating HCC.

Introduction: The non-growing, meiotically-arrested oocytes housed within primordial follicles are exquisitely sensitive to genotoxic insults from endogenous and exogenous sources. Even a single DNA double-strand break (DSB) can trigger oocyte apoptosis, which can lead to accelerated depletion of the ovarian reserve, early loss of fertility and menopause. Therefore, repair of DNA damage is important for preserving the quality of oocytes to sustain fertility across the reproductive lifespan. This study aimed to evaluate the role of KU80 (encoded by the XRCC5 gene) - an essential component of the non-homologous end joining (NHEJ) pathway - in the repair of oocyte DNA DSBs during reproductive ageing, and following insult caused by the DNA-damaging chemotherapies cyclophosphamide and cisplatin. Methods: To investigate the importance of KU80 following endogenous and exogenous DNA damage, ovaries from conditional oocyte-specific Xrcc5 knockout (Xrcc5 cKO) and wildtype (WT) mice that were aged or exposed to DNA damage-inducing chemotherapy were compared. Ovarian follicles and oocytes were quantified, morphologically assessed and analysed via immunohistochemistry for markers of DNA damage and apoptosis. In addition, chemotherapy exposed mice were superovulated, and the numbers and quality of mature metaphase-II (MII) oocytes were assessed. Results: The number of healthy follicles, atretic (dying) follicles, and corpora lutea were similar in Xrcc5 cKO and WT mice at PN50, PN200 and PN300. Additionally, primordial follicle number and ovulation rates were similar in young adult Xrcc5 cKO and WT mice following treatment with cyclophosphamide (75mg/kg), cisplatin (4mg/kg), or vehicle control (saline). Furthermore, KU80 was not essential for the repair of exogenously induced DNA damage in primordial follicle oocytes. Discussion: These data indicate that KU80 is not required for maintenance of the ovarian reserve, follicle development, or ovulation during maternal ageing. Similarly, this study also indicates that KU80 is not required for the repair of exogenously induced DSBs in the prophase-arrested oocytes of primordial follicles. [ABSTRACT FROM AUTHOR]

SUMMARY: Non‐homologous end joining (NHEJ) plays a major role in repairing DNA double‐strand breaks and is key to genome stability and editing. The minimal core NHEJ proteins, namely Ku70, Ku80, DNA ligase IV and XRCC4, are conserved, but other factors vary in different eukaryote groups. In plants, the only known NHEJ proteins are the core factors, while the molecular mechanism of plant NHEJ remains unclear. Here, we report a previously unidentified plant ortholog of PAXX, the crystal structure of which showed a similar fold to human 'PAXX'. However, plant PAXX has similar molecular functions to human XLF, by directly interacting with Ku70/80 and XRCC4. This suggests that plant PAXX combines the roles of mammalian PAXX and XLF and that these functions merged into a single protein during evolution. This is consistent with a redundant function of PAXX and XLF in mammals. Significance Statement: Non‐homologous end joining (NHEJ) is a major pathway to repair DNA double‐strand breaks and therefore is important for genome maintenance and editing. Using an evolutional analysis, we identified a plant ortholog of an NHEJ protein PAXX and contributed to understanding the exact molecular mechanism of NHEJ in plants. [ABSTRACT FROM AUTHOR]

Variants in non-homologous end joining (NHEJ) DNA repair genes are associated with various human syndromes, including microcephaly, growth delay, Fanconi anemia, and different hereditary cancers. However, very little has been done previously to systematically record the underlying molecular consequences of NHEJ variants and their link to phenotypic outcomes. In this study, a list of over 2983 missense variants of the principal components of the NHEJ system, including DNA Ligase IV, DNA-PKcs, Ku70/80 and XRCC4, reported in the clinical literature, was initially collected. The molecular consequences of variants were evaluated using in silico biophysical tools to quantitatively assess their impact on protein folding, dynamics, stability, and interactions. Cancer-causing and population variants within these NHEJ factors were statistically analyzed to identify molecular drivers. A comprehensive catalog of NHEJ variants from genes known to be mutated in cancer was curated, providing a resource for better understanding their role and molecular mechanisms in diseases. The variant analysis highlighted different molecular drivers among the distinct proteins, where cancer-driving variants in anchor proteins, such as Ku70/80, were more likely to affect key protein–protein interactions, whilst those in the enzymatic components, such as DNA-PKcs, were likely to be found in intolerant regions undergoing purifying selection. We believe that the information acquired in our database will be a powerful resource to better understand the role of non-homologous end-joining DNA repair in genetic disorders, and will serve as a source to inspire other investigations to understand the disease further, vital for the development of improved therapeutic strategies. [ABSTRACT FROM AUTHOR]

Background: Although the clinical application of PARP inhibitors has brought hope to ovarian cancer, the problem of its resistance has become increasingly prominent. Therefore, clinical experts have been focused on finding specific indicators and therapeutic targets that can be used for resistance monitoring of PARP inhibitors. Results: By cfDNA detecting during Olaparib maintenance therapy in platinum-sensitive relapsed ovarian cancer, we found the presence of MRE11:p.K464R mutation was strongly associated with acquired Olaparib resistance. Structural analysis revealed that the MRE11:p.K464R mutation is situated at a critical site where the MRE11 protein interacts with other biomolecules, leading to potential structural and functional abnormalities of MRE11 protein. Functionally, MRE11:p.K464R mutation enhanced the tolerance of Olaparib by reducing the DNA damage. Mechanistically, MRE11:p.K464R mutation improved the efficiency of DNA damage repair and induce Olaparib resistance by enhancing its binding activity with the interacting proteins (including RAD50 and RPS3). Among them, the enhanced binding of MRE11:p.K464R mutation to RAD50/RPS3 facilitated non-homologous end joining (NHEJ) repair in tumor cells, thereby expanding the scope of research into acquired resistance to PARP inhibitors. Conclusions: Our findings provide a theoretical basis for MRE11:p.K464R mutation as a specific indicator of resistance monitoring in Olaparib treatment, and the exploration of its resistance mechanism provides a novel insights for the formulation of combination ther therapies after Olaparib resistance. [ABSTRACT FROM AUTHOR]

Mitotic slippage, which enables cancer cells to bypass cell death by transitioning from mitosis to the G1 phase without undergoing normal cytokinesis, is one likely mechanism of paclitaxel (PTX) resistance. DNA double-strand breaks (DSBs) in the G1 phase are mainly repaired through non-homologous end joining (NHEJ). Therefore, inhibiting NHEJ could augment the PTX-induced cytotoxicity by impeding the repair of PTX-induced DSBs during the G1 phase following mitotic slippage. We aimed to evaluate the effects of NHEJ inhibition on mitotic slippage after PTX treatment in non-small cell lung cancer (NSCLC). H1299, A549, H1975, and H520 NSCLC cell lines were employed. In addition, A-196 and JQ1 were used as NHEJ inhibitors. H1299 cells were PTX-resistant and exhibited an increased frequency of mitotic slippage upon PTX treatment. NHEJ inhibitors significantly augmented the PTX-induced cytotoxicity, DSBs, and apoptosis in H1299 cells. The newly generated PTX-resistant cells were even more prone to mitotic slippage following PTX treatment and susceptible to the combined therapy. Docetaxel further demonstrated synergistic effects with the NHEJ inhibitor in PTX-resistant cells. NHEJ inhibition may overcome intrinsic or acquired PTX resistance resulting from mitotic slippage by synergistically increasing the cytotoxic effects of antimitotic drugs in NSCLC. [ABSTRACT FROM AUTHOR]

In the non-homologous end-joining (NHEJ) of a DNA double-strand break, DNA ends are bound and protected by DNA-PK, which synapses across the break to tether the broken ends and initiate repair. There is little clarity surrounding the nature of the synaptic complex and the mechanism governing the transition to repair. We report an integrative structure of the synaptic complex at a precision of 13.5 Å, revealing a symmetric head-to-head arrangement with a large offset in the DNA ends and an extensive end-protection mechanism involving a previously uncharacterized plug domain. Hydrogen/deuterium exchange mass spectrometry identifies an allosteric pathway connecting DNA end-binding with the kinase domain that places DNA-PK under tension in the kinase-active state. We present a model for the transition from end-protection to repair, where the synaptic complex supports hierarchical processing of the ends and scaffold assembly, requiring displacement of the catalytic subunit and tension release through kinase activity.

Objective: Beta-thalassemia is a group of inherited hematologic. The most HBB gene variant among Iranianbeta-thalassemia patients is related to two mutations of IVSII-1 (G>A) and IVSI-5 (G>C). Therefore, our aim ofthis study is to use the knock in capability of CRISPR Cas9 system to investigate the correction of IVSII-1 (G>A)variant in Iran.Materials and Methods: In this experimental study, following bioinformatics studies, the vector containingPuromycin resistant gene (PX459) was cloned individually by designed RNA-guided nucleases (gRNAs), andcloning was confirmed by sequencing. Proliferation of TLS-12 was done. Then, the transfect was set up by thevector with GFP marker (PX458). The PX459 vectors carrying the designed gRNAs together with Single-strandedoligodeoxynucleotides (ssODNs) as healthy DNA pattern were transfected into TLS-12 cells. After taking the singlecell clones, molecular evaluations were performed on single clones. Sanger sequencing was then performed toinvestigate homology directed repair (HDR).Results: The sequencing results confirmed that all three gRNAs were successfully cloned into PX459 vector. In thetransfection phase, The TLS-12 containing PX459-gRNA/ssODN was selected. Molecular evaluations showed thatthe HBB gene was cleaved by the CRISPR/Cas9 system, that indicates that the performance of non-homologous endjoining (NHEJ) repair system. Sequencing in some clones cleaved by the T7E1 enzyme showed that HDR was notconfirmed in these clones.Conclusion: IVS-II-1 (G> A) mutation, which is the most common thalassemia mutation especially in Iran, the CRISPR/Cas9 system was able to specifically target the HBB gene sequence. This could even lead to a correction in themutation and efficiency of the HDR repair system in future research.

We explore the possibility that defects in genes associated with the response and repair of DNA double strand breaks predispose oral potentially malignant disorders (OPMD) to undergo malignant transformation to oral squamous cell carcinoma (OSCC). Defects in the homologous recombination/Fanconi anemia (HR/FA), but not in the non-homologous end joining, causes the DNA repair pathway to appear to be consistent with features of familial conditions that are predisposed to OSCC (FA, Bloom’s syndrome, Ataxia Telangiectasia); this is true for OSCC that occurs in young patients, sometimes with little/no exposure to classical risk factors. Even in Dyskeratosis Congenita, a disorder of the telomerase complex that is also predisposed to OSCC, attempts at maintaining telomere length involve a pathway with shared HR genes. Defects in the HR/FA pathway therefore appear to be pivotal in conditions that are predisposed to OSCC. There is also some evidence that abnormalities in the HR/FA pathway are associated with malignant transformation of sporadic cases OPMD and OSCC. We provide data showing overexpression of HR/FA genes in a cell-cycle-dependent manner in a series of OPMD-derived immortal keratinocyte cell lines compared to their mortal counterparts. The observations in this study argue strongly for an important role of the HA/FA DNA repair pathway in the development of OSCC.

IntroductionThe non-growing, meiotically-arrested oocytes housed within primordial follicles are exquisitely sensitive to genotoxic insults from endogenous and exogenous sources. Even a single DNA double-strand break (DSB) can trigger oocyte apoptosis, which can lead to accelerated depletion of the ovarian reserve, early loss of fertility and menopause. Therefore, repair of DNA damage is important for preserving the quality of oocytes to sustain fertility across the reproductive lifespan. This study aimed to evaluate the role of KU80 (encoded by the XRCC5 gene) – an essential component of the non-homologous end joining (NHEJ) pathway – in the repair of oocyte DNA DSBs during reproductive ageing, and following insult caused by the DNA-damaging chemotherapies cyclophosphamide and cisplatin.MethodsTo investigate the importance of KU80 following endogenous and exogenous DNA damage, ovaries from conditional oocyte-specific Xrcc5 knockout (Xrcc5 cKO) and wildtype (WT) mice that were aged or exposed to DNA damage-inducing chemotherapy were compared. Ovarian follicles and oocytes were quantified, morphologically assessed and analysed via immunohistochemistry for markers of DNA damage and apoptosis. In addition, chemotherapy exposed mice were superovulated, and the numbers and quality of mature metaphase- II (MII) oocytes were assessed.ResultsThe number of healthy follicles, atretic (dying) follicles, and corpora lutea were similar in Xrcc5 cKO and WT mice at PN50, PN200 and PN300. Additionally, primordial follicle number and ovulation rates were similar in young adult Xrcc5 cKO and WT mice following treatment with cyclophosphamide (75mg/kg), cisplatin (4mg/kg), or vehicle control (saline). Furthermore, KU80 was not essential for the repair of exogenously induced DNA damage in primordial follicle oocytes.DiscussionThese data indicate that KU80 is not required for maintenance of the ovarian reserve, follicle development, or ovulation during maternal ageing. Similarly, this study also indicates that KU80 is not required for the repair of exogenously induced DSBs in the prophase-arrested oocytes of primordial follicles.

Premature ovarian insufficiency (POI) is a clinically heterogeneous disease that may seriously affect the physical and mental health of women of reproductive age. POI primarily manifests as ovarian function decline and endocrine disorders in women prior to age 40 and is an established cause of female infertility. It is crucial to elucidate the causative factors of POI, not only to expand the understanding of ovarian physiology, but also to provide genetic counselling and fertility guidance to affected patients. Factors leading to POI are multifaceted with genetic factors accounting for 7% to 30%. In recent years, an increasing number of DNA damage-repair-related genes have been linked with the occurrence of POI. Among them, DNA double-strand breaks (DSBs), one of the most damaging to DNA, and its main repair methods including homologous recombination (HR) and non-homologous end joining (NHEJ) are of particular interest. Numerous genes are known to be involved in the regulation of programmed DSB formation and damage repair. The abnormal expression of several genes have been shown to trigger defects in the overall repair pathway and induce POI and other diseases. This review summarises the DSB-related genes that may contribute to the development of POI and their potential regulatory mechanisms, which will help to further establish role of DSB in the pathogenesis of POI and provide theoretical guidance for the study of the pathogenesis and clinical treatment of this disease. [ABSTRACT FROM AUTHOR]

The filamentous fungus Trichoderma reesei (teleomorph Hypocrea jecorina, Ascomycota) is a well-known lignocellulolytic enzymes-producing strain in industry. To increase the fermentation titer of lignocellulolytic enzymes, random mutagenesis and rational genetic engineering in T. reesei were carried out since it was initially found in the Solomon Islands during the Second World War. Especially the continuous exploration of the underlying regulatory network during (hemi)cellulase gene expression in the post-genome era provided various strategies to develop an efficient fungal cell factory for these enzymes' production. Meanwhile, T. reesei emerges competitiveness potential as a filamentous fungal chassis to produce proteins from other species (e.g., human albumin and interferon α-2b, SARS-CoV-2 N antigen) in virtue of the excellent expression and secretion system acquired during the studies about (hemi)cellulase production. However, all the achievements in high yield of (hemi)cellulases are impossible to finish without high-efficiency genetic strategies to analyze the proper functions of those genes involved in (hemi)cellulase gene expression or secretion. Here, we in detail summarize the current strategies employed to investigate gene functions in T. reesei. These strategies are supposed to be beneficial for extending the potential of T. reesei in prospective strain engineering. [ABSTRACT FROM AUTHOR]

Recombinant adeno-associated virus (rAAV) vectors have been developed for therapeutic treatment of genetic diseases. Current rAAV vectors administered to affected individuals often contain vector DNA-related contaminants. Here we present a thorough molecular analysis of the configuration of non-standard AAV genomes generated during rAAV production using single-molecule sequencing. In addition to the sub-vector genomic-size particles containing incomplete AAV genomes, our results showed that rAAV preparations were contaminated with multiple categories of subgenomic particles with a snapback genome (SBG) configuration or a vector genome with deletions. Through CRISPR and nuclease-based modeling in tissue culture cells, we identified that a potential mechanism leading to formation of non-canonical genome particles occurred through non-homologous end joining of fragmented vector genomes caused by genome lesions or DNA breaks present in the host cells. The results of this study advance our understanding of AAV vectors and provide new clues for improving vector efficiency and safety profiles for use in human gene therapy.