LncRNAs in inflammasome regulation: Orchestrating cancer signaling and chemoresistance.

DNA ligases catalyse the joining of single and double-strand DNA breaks, which is an essential final step in DNA replication, recombination and repair. Mammalian cells have four DNA ligases, termed ligases I-IV. In contrast, other than a DNA ligase I homologue (encoded by CDC9), no other DNA ligases have hitherto been identified in Saccharomyces cerevisiae. Here, we report the identification and characterization of a novel gene, LIG4, which encodes a protein with strong homology to mammalian DNA ligase IV. Unlike CDC9, LIG4 is not essential for DNA replication, RAD52-dependent homologous recombination nor the repair of UV light-induced DNA damage. Instead, it encodes a crucial component of the non-homologous end-joining (NHEJ) apparatus, which repairs DNA double-strand breaks that are generated by ionizing radiation or restriction enzyme digestion: a function which cannot be complemented by CDC9. Lig4p acts in the same DNA repair pathway as the DNA end-binding protein Ku. However, unlike Ku, it does not function in telomere length homeostasis. These findings indicate diversification of function between different eukaryotic DNA ligases. Furthermore, they provide insights into mechanisms of DNA repair and suggest that the NHEJ pathway is highly conserved throughout the eukaryotic kingdom.

DNA repair and metabolic pathways are vital to maintain cellular homeostasis in normal human cells. Both of these pathways, however, undergo extensive changes during tumorigenesis, including modifications that promote rapid growth, genetic heterogeneity, and survival. While these two areas of research have remained relatively distinct, there is growing evidence that the pathways are interdependent and intrinsically linked. Therapeutic interventions that target metabolism or DNA repair systems have entered clinical practice in recent years, highlighting the potential of targeting these pathways in cancer. Further exploration of the links between metabolic and DNA repair pathways may open new therapeutic avenues in the future. Here, we discuss the dependence of DNA repair processes upon cellular metabolism; including the production of nucleotides required for repair, the necessity of metabolic pathways for the chromatin remodeling required for DNA repair, and the ways in which metabolism itself can induce and prevent DNA damage. We will also discuss the roles of metabolic proteins in DNA repair and, conversely, how DNA repair proteins can impact upon cell metabolism. Finally, we will discuss how further research may open therapeutic avenues in the treatment of cancer.

Cancer cells have genomic instability resulting from acquired defects in DNA repair. One DNA repair pathway_the Fanconi Anemia/BRCA homologous recombination pathway (Kennedy and D'Andrea, Genes&Development 19:2925, 2005) _ is defective in many human cancers, including breast, ovarian, pancreatic, and lung neoplasms. Disruption of the FA/BRCA Pathway results in the characteristic chromosome instability and radiation/crosslinker hypersensitivity of these tumors. In general, loss of one DNA repair pathway often leads to hyperdependence on another pathway for tumor cell survival. This hyperdependence offers a unique opportunity for the development of anticancer therapeutics. For instance, FA/BRCA pathway deficient tumors are hyperdependent on Base Excision Repair (BER) and, accordingly, these tumors are hypersensitive to single agent treatment with PARP1 inhibitors which block BER. Our laboratory efforts are focused on profiling the FA/BRCA pathway and the other five major DNA repair pathways in tumor cells (Kennedy and D'Andrea, JCO 24: 3799, 2006). Each DNA repair pathway has a characteristic protein biomarker and repairs a specific type of DNA lesion. By profiling these pathways in primary tumor samples with activation-specific antibodies to DNA repair proteins, we are developing methods (1) to predict the sensitivity of tumors to conventional chemotherapy and radiation (Personalized Medicine) (2) to subset tumors for their sensitivity to novel classes of DNA repair inhibitors, (i.e., PARP1, Chk1, and ATM inhibitors) and (3) to screen for new small molecule inhibitors of other DNA repair pathways. This combination of novel DNA repair inhibitors, conventional DNA damaging agents, and DNA repair biomarkers offers new opportunities for developing more effective anticancer therapy. The FA/BRCA pathway was elucidated through the systematic study of the rare inherited chromosome breakage disorder, Fanconi Anemia (Moldovan and D'Andrea, Ann Rev Genet 43:223, 2009). FA is an autosomal recessive disease characterized by bone marrow failure, congenital malformations, and cellular sensitivity to Cisplatin, Mitomycin C, and other DNA interstrand crosslinking agents. Patients with FA develop hematopoietic malignancies and squamous cell carcinomas. Based on somatic cell fusion studies, there are thirteen FA complementation groups (A, B, C, D1, D2, E, F, G, I, J, L, M, N), and the corresponding gene for each of these complementation groups has been identified. Interestingly, the thirteen FA proteins cooperate in a common cellular pathway in normal human cells, referred to as the Fannoni Anemia/BRCA pathway. Eight of the FA proteins (A, B, C, E, F, G, L, M) are assembled in a core complex (the FA core complex) which is an active ubiquitin E3 ligase. In response to DNA damage, the FA core complex modifies (monoubiquitinates) the downstream FANCD2 protein. Monoubiquitinated FANCD2 translocates to nuclear foci where it interacts with the FANCD1/BRCA2 protein and participates in the process of homologous recombination DNA repair. Additional FA proteins (namely, FANCJ/BRIP1 and FANCN/PALB2) function downstream of FANCD2 monoubiquitination. At least three of the FA genes (FANCD1, FANCJ, and FANCN) are inherited breast cancer susceptibility genes. Disruption of any step in the FA/BRCA pathway results in the common clinical and cellular phenotype of FA patients. Human tumor cells, derived from cancer patients from the general (non-FA) population, often exhibit genomic instability. Genomic instability of tumors has important clinical consequences. On the one hand, genomic instability gives the tumor the ability to break and fuse chromosomes, inactivate tumor suppressor genes, form novel oncogene fusions, and amplify drug resistance genes. Thus, the tumor with genomic instability may become more malignant and drug resistant over time. On the other hand, in order to achieve a state of genomic instability, a tumor cell must inactivate one of its major DNA repair pathways. This inactivation appears to account, at least in part, for the selective hypersensitivity of cancer cells to the cytotoxic effects of conventional anti-cancer radiation and chemotherapy. Recent studies indicate that some human tumors inactivate the FA/BRCA pathway. Pathway inactivation may result from somatic mutation of genes in the FA/BRCA pathway or by epigenetic silencing. For instance, methylation of one of the FA genes, FANCF, has been implicated as a mechanism for genomic instability in a wide variety of cancers, including ovarian, breast, lung, cervical, and head and neck squamous cell carcinomas. Somatic inactivation of the FA/BRCA pathway appears to account for the genomic instability and the cisplatin hypersensitivity of many of these cancers. A wide array of biomarkers is available for measuring the activity of the FA/BRCA pathway in human tumors, or for measuring the activity of the other human DNA repair pathways. Since many of the genes in the FA/BRCA pathway (i.e., the thirteen cloned FA genes) have been identified, tumors can be screened for germline or somatic mutations in these genes. Furthermore, tumors can be analyzed for function of the pathway by following various biochemical events in the pathway. For instance, the full function of the pathway requires monoubiquitination of the FANCD2 protein, ATR and CHK1 dependent phosphorylation of subunits of the pathway, and assembly of FANCD2 and FANCE nuclear foci. A tumor which has defects in any of these genetic or biochemical biomarkers has a defect in the FA/BRCA pathway and may therefore have a hypersensitivity to crosslinking drugs such as cisplatin. Thus, biochemical monitoring of DNA repair pathways may be a means for predicting drug sensitivity of individual tumors. Loss of DNA repair pathways can lead to hyperdependence on other survival pathways. Inhibition of these alternative pathways may represent a therapeutic approach which is selectively toxic to repair pathway deficient tumor cells. For instance, breast and ovarian tumor cells which are deficient in the homologous recombination (HR) pathway are hypersensitive to drugs (PARP1 inhibitors) which selectively inactivate a compensatory DNA Repair pathway, the Base Excision Repair (BER) pathway. We recently used a high throughput siRNA screening approach to identify DNA damage response genes that were critical for the survival of FA/BRCA pathway deficient tumor cells (Kennedy et al, J. Clin Invest 117:1440, 2007). Using this approach we identified the DNA damage response kinase, ATM, as being important for the survival of cells deficient in the FA pathway. Accordingly, we found that the Atm -/- Fancg -/- mouse genotype was deleterious when Fancg +/- Atm +/- mice were interbred. We also demonstrated constitutive activation of ATM in FA pathway deficient cells, which was abrogated by reconstitution of the pathway. Furthermore, inhibition of ATM using siRNA oligonucleotides or the specific ATM inhibitor KU55933 resulted DNA breakage and cell death specifically in cells with a non functioning FA pathway. These data suggest that ATM and the FA pathway function in parallel and compensatory roles following endogenous DNA Damage. Moreover, pharmaceutical inhibition of ATM may be selectively toxic to cancer cells that have lost function of the FA pathway. We are currently exploring other therapeutic strategies to selectively target tumors with a defect in the FA/BRCA pathway or with a defect in one of the other human DNA repair pathways. For instance, we recently determined that tumors which are deficient in the FA/BRCA pathway are hypersensitive to CHK1 inhibitors (Chen et al, Mol Cancer 8: 24, 2009). In my presentation, I will review the features of the six major DNA repair pathways in human cells, and how knowledge of the disruption of these pathways in cancers can lead to the prediction of drug response. Citation Format: Alan D. D'Andrea. Targeting DNA repair pathways in cancer therapy [abstract]. In: Proceedings of the AACR 101st Annual Meeting 2010; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr SY28-01

Prostate cancer (PCa) is the most frequent malignant tumour in males,1 it is essential to precisely identify the specific molecular features and judge potential clinical outcomes from the multi-omics aspect. Recently, we developed an R package "MOVICS" (https://xlucpu.github.io/MOVICS/MOVICS-VIGNETTE.html) for multi-omics integration and clustering, aim to stratify tumour molecular subtypes and facilitate precision medicine.2 In the current study, we firstly proposed the PCa multi-omics classification (PMOC) system derived from mRNA, microRNA, long noncoding RNA, DNA methylation, and somatic mutation, using 10 leading-edge clustering algorithms. We collected a total of 1192 PCa patients from five independent cohorts and an external AHMU-PC cohort from our own institute3 (Tables S1 and S2). The technical details are listed in Supporting Information. We identified three clusters independently from ten multi-omics integrative clustering algorithms (Figure 1A) referring to the clustering prediction index, Gaps-statistics analysis (Figure S1) and predefined PAM50 system,4 and further combined the clustering results via a consensus ensemble approach (Figure 1B). Multi-omics data in PMOCs was visualized in Figure 1C. Significantly, diverse clinical recurrence-free survival (RFS) outcomes were observed (all p < .001, Figure 1D). Most PMOC2 patients had a higher Gleason score than PMOC1 and PMOC3 (61.8% vs. 23.0% vs. 9.7%, p = .012), as well as the proportion of advanced pathology T stage (86.8% vs. 54.9% vs. 52.6%, p < 0.001, Table S3). The top 100 subtype-specific markers for each PMOC were selected for the reproduction of PMOCs in external validation cohorts (Table S4). We observed the significant activation of the G2M checkpoint, E2F target pathways in PMOC2 (Figure 2A). Specifically, the decreased phosphorylated protein levels of p-CHK1 and p-CHK2 in PMOC2 may weaken the inhibitory function of CDC25 components and increase CDK1 activation (Figure 2B). For PMOC1, we observed the activation of TNF-α signalling, IL6/JAK/STAT3 and IL2/STAT5 signalling, which were immune response relevant. PMOC3 presented activation of both immune-associated and oncogenic pathways; the phosphorylated mTOR and mTOR levels were activated and could further promote cell growth (Figure 2C). We further compared the activation status of metabolic pathways. The nicotinamide adenine dinucleotide biosynthesis and cyclooxygenase arachidonic acid metabolism pathways were activated in PMOC1, which were reported to be associated with tumour inflammation and immune-metabolic circuits.5 In PMOC2, we observed the activated pyrimidine metabolism and biosynthesis, biotin metabolism, and oxidative phosphorylation. Glycogen metabolism and amino acid metabolism-associated pathways were highly activated in PMOC3 (Figure 2D). PMOC3 had higher infiltration of immune-suppressed components, while PMOC1 tended to exhibit immune activated components, and higher expression of PD1, PDL1 and CTLA4 (Figure 2E,F), and was also associated with immune activated molecular subtype3 (Figure S2A). Genetic alteration contributed dramatically to shaping the subtypes. Specifically, the total tumour mutant burden was highest in PMOC2 (p < .001, Figure S3A). PMOC2 contained most patients with TP53 mutation (PMOC2: 23.6%, PMOC1: 8.6%, PMOC3: 5.8%, p < .001), and SPOP (PMOC2: 18.7%, PMOC1: 9.6%, PMOC3: 7.8%, p = .0138, Figure S3B, Table S5). The tumour suppressor APC protein is an antagonist of the Wnt signalling pathway.6 Mutant APC resulted in lower expression (p = .0026, Figure S3C) and led to an unfavourable clinical outcome (p = .013, Figure S3D). Both the lost and gained copy numbers were significantly increased in PMOC2 (Figure S4A). Interestingly, we observed that the gained copy number in PMOC2 was mostly located at the 8q24.21 region which was not amplified in either PMOC1 or PMOC3 (Figure S4B). The amplification and gain alteration of PVT1, an important gene located in the 8q24.21 region,7 occurred mostly in PMOC2 patients (p < .001, Figure S5A), PVT1 expression positively linked with its copy number alteration (p < .001, Figure S5B), and patients carried with PVT1 amplification suffered from the worst RFS (p = .003, Figure S5C). In the PAM50 system, LumB has the worst prognosis (Figure S6A). PMOC2 remarkably overlapped with LumB and demonstrates the worst outcome. LumB/PMOC2 patients had an unfavourable outcome compared with LumB/PMOC1+PMOC3 patients (Figure S6B), which may be affected by DNA repair and replication pathways (Figure S6C), LumB/PMOC2 also had higher infiltration of anti-inflammatory immunocytes (Figure S6D). TCGA research network reported a classifier of seven genetically distinct subtypes via the differential ERG/ETV1/ETV4/FLI1 fusion, or SPOP, FOXA1, IDH1 mutations.8 Of note, the PMOC system offered additional prognostic value to the existing classification scheme (Figure S2B,C). Transcriptome regulatory networks play important role in the genesis and progression of tumours, we, therefore, evaluated the activity of 23 regulons and 71 chromatin remodelling regulons.9 Patients with PMOC2 are likely regulated by the human Fox gene family, patients in the PMOC3 group attracted us by the activation of androgen receptor (AR), epidermal growth factor receptor (EGFR), and hypoxia inducible factor 1 subunit alpha (HIF1A) (Figure 3A). PMOC3 significantly enriched the AR-A score (p < .001, Figure 3B) and AR activation signature (p < .001, Figure 3C). In the androgen deprivation therapy (ADT)-treated Abida cohort,10 PMOC2 demonstrated the activation of cell cycle-associated pathways, and PMOC3 was linked with the activated androgen, estrogen and PI3K/AKT signalling pathways (Figure 3D). PMOC3 was more likely to respond to ADT therapy (response rate of 26.7% in PMOC3, Figure 3E), including bicalutamide (p = .089, Figure 3F). To further validate the differential activity of AR signalling, we represented the PMOC groups in the AHMU-PC cohort (Figure 3G) by nearest template prediction (NTP) using subtype-specific genes; we revealed that patients in PMOC3 from the AHMU-PC cohort contained the highest activation of AR signalling (p < .001, Figure 3H), and more sensitive to bicalutamide (p = .0036, Figure 3I). In-dept validations are warranted for the tight association between PMOC3 and anti-androgen therapy. In addition, we represented the separation of PMOCs in external independent cohorts (Figure S7). In GSE54460, GSE70770, MSKCC and GSE116918 cohorts, all patients belonging to PMOC2 presented the worst clinical outcomes (all p < .05, Figure 3J). Moreover, our PMOC system remained the independent prognostic factor after adjusting other major clinical features in all five PCa patient cohorts (all p < .05, Table 1). Tumour biological process is complex with the internal cross-talking between regulatory features from a different level, thus comprehensive data mining through multi-omics profile is essential to decipher the tumour heterogeneity. We harnessed ten algorithms to recognize the PMOC system by the consensus clustering, more algorithms included, more stable and convincing the system is. Taken together, the PMOC1 "tumour-inflammatory" subtype involves the activation of inflammation-associated metabolism pathways and a high level of immune checkpoint proteins. The PMOC2 "tumour-activated" subtype contains activated cell cycle and DNA repair pathways, a high rate of gene mutation, and 8q24.21 copy number amplification associated with poor prognosis. The PMOC3 "tumour-balanced" subtype represents the activation of both oncogenic and proinflammatory pathways, links with a favourable prognosis, the enrichment of the AR response resulted in the suitability of ARSI treatment. This multi-omics consensus PMOC system can further assist the precise and targeted clinical therapy for PCa patients. We greatly appreciate the patients and investigators who participated in the corresponding medical project for providing data. The authors declare that they have no conflict of interest. This work was supported by the National Natural Science Foundation of China (81630019, 81870519, 81802827 and 81973145), supporting project for Distinguished Young Scholar of Anhui Colleges (gxyqZD2019018), the National Key R&D Program of China (2019YFC1711000), the Key R&D Program of Jiangsu Province [Social Development] (BE2020694), the Scientific Research Foundation of the Institute for Translational Medicine of Anhui Province (2017ZHYX02), the Natural Science Foundation of Guangdong Province, China (2017A030313800), the Key project of provincial natural science research project of Anhui Colleges (KJ2019A0278), and 2017 Anhui Province special program for guiding local science and technology development by the central government (2017070802D148). Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Moreover, the metabolic alterations in cancer enable cancer cells drug resistance in cancer therapy [3]. Actually, metabolic factors have recently been suggested as one part of the important targets for the development of novel, combinatory drugs to overcome the resistance to chemotherapy, target therapy and immunotherapy [4]. In addition, host metabolic factors, such as metabolites derived from commensal gut microbiota, have also been recognized as modifiers of the cancer microenvironment and been targeted for therapeutic gain in cancer [5; 6].The metabolites derived from amino acid have been recognized as modifiers of the cancer microenvironment and targets for cancer therapeutics. As a non-essential amino acid, glutamine can be synthesized by cells. Glutamine metabolism contributes to the growth and proliferation of mammalian cells as well as tumor cells. Yang XJ et al. summarized the role of glutamine metabolism in ovarian cancer cell proliferation, invasion, and drug resistance. They also discussed the role of glutamine in protein synthesis and in the purine and pyrimidine synthesis as primary nitrogen donor. In addition, they collected the studies that glutamine-addicted tumor cells depend on glutamine for survival. Most interestingly, combining platinum-based chemotherapy with inhibition of glutamine metabolic pathways may be a new strategy for treating ovarian cancer, especially drug resistant ovarian cancer.Branched-chain amino acid metabolism affects systemic metabolism in cancer cells. Branched-chain amino acid transferase (BCAT) is an enzyme that catalyzes the transamination of three branched-chain amino acid to branched-chain keto acids.Nong XZ et al. reviewed the potential roles of BCAT in different cancer development and treatments. They also discussed the BCAT as the target of the proto-oncogene c-Myc. Furthermore, they emphasized that BCAT usually promotes cancer proliferation and invasion by activating the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin pathway as well as Wnt/β-Catenin signal transduction.Cornett K et al. summarized another well-known gene GAPDH involved in glycolysis. Recently, GAPDH is found to have diverse localizations and its role is largely dependent on its cellular location and interaction partners. They discussed the membrane-associated function of GAPDH in stimulating glucose uptake in neuroblastomaand the nuclear complex of GAPDH in DNA repair, which demonstrated its potential role in cancer metabolism, treatment and drug resistance.The perceptions of cancer metabolism are driven by technological and methodological advances in omics. Genome sequencing has been widely used in clinic cancer target therapeutics. Li CX et al. conducted next generation sequencing for a rare case of secondary tumor of the ovary from liver and identified BRCA2 mutation. Therefore, they treated the patient with poly adenosine diphosphate-ribose polymerase inhibitor olaparib after the administration of surgery. The patient has achieved nearly 2-year survival and lives a relatively normal life with good quality.Meanwhile, enormous amount of information is contained in the public cancer genomics database waiting for deep mining to provide clues for cancer therapeutics.To this end, Li K et al. analyzed the data from Genomics of Drug Sensitivity in Cancer (GDSC) database, and found that cuproptosis-related genes are associated with the development, tumor microenvironment, and prognosis of lung adenocarcinoma. They also provided a scoring system based on these cuproptosisrelated genes to predict the efficacy of targeted drugs and immune response. These findings may indicate the potential roles of copper metabolism in cancer biology and provide a new path for the assessment of cancer prognosis and therapeutics.Spatial metabolomics offers an opportunity to demonstrate the drug-resistant tumor profile with metabolic heterogeneity, and poses a data-mining challenge to reveal meaningful insights from high-dimensional spatial information. Zhang ZQ et al.discussed the latest progress, with the focus on currently available bulk, single-cell and spatial metabolomics technologies and their successful applications in cancer drug resistance. They summarized the underlying metabolic mechanisms including the Warburg effect, altered amino acid/lipid/drug metabolism, generation of drugresistant cancer stem cells, and immunosuppressive metabolism. The perspective of how the spatial metabolomics approach (integrating spatial metabolomics) could be further developed to improve the management of drug resistance in cancer patients is expounded.More recently, gut microbiome has demonstrated great influence on the cancer formation, prognosis and treatment via their metabolites. Huang JT et al. discussed the effects and the underlying mechanisms of gut microbiome and microbial-derived metabolites in cancer development and treatment. They reviewed the works of gut microbiome intervention of cancer patients by fecal microbiota transplantation from healthy ones, which can suppress the carcinogenesis, or augment therapeutic effect on the tumor through the related metabolites, suggesting targeting gut microbiome will be a new approach to improve the efficacy of tumor prevention and treatment.Overall, our research topic highlights the ongoing challenges in the field of the amino acid metabolism in cancer cells, the metabolites of microbes in the gut of host, and the methodology of omics in cancer metabolism. These knowledges will ultimately contribute to better understanding the role of metabolism in tumorigenesis and advance the translation of these findings to overcome drug resistance in cancer therapy.

SY11-01: Targeting the Fanconi anemia/BRCA pathway in cancer therapy

IA9: Targeting the Fanconi anemia/BRCA pathway in cancer therapy

CN05-02: Targeting the Fanconi anemia/BRCA pathway in cancer therapy.

Defects in DNA repair can result in oncogenic genomic instability. Cancers occurring from DNA repair defects were once thought to be limited to rare inherited mutations (such as BRCA1 or 2). It now appears that a clinically significant fraction of cancers have acquired DNA repair defects. DNA repair pathways operate in related networks, and cancers arising from loss of one DNA repair component typically become addicted to other repair pathways to survive and proliferate. Drug inhibition of the rescue repair pathway prevents the repair-deficient cancer cell from replicating, causing apoptosis (termed synthetic lethality). However, the selective pressure of inhibiting the rescue repair pathway can generate further mutations that confer resistance to the synthetic lethal drugs. Many such drugs currently in clinical use inhibit PARP1, a repair component to which cancers arising from inherited BRCA1 or 2 mutations become addicted. It is now clear that drugs inducing synthetic lethality may also be therapeutic in cancers with acquired DNA repair defects, which would markedly broaden their applicability beyond treatment of cancers with inherited DNA repair defects. Here we review how each DNA repair pathway can be attacked therapeutically and evaluate DNA repair components as potential drug targets to induce synthetic lethality. Clinical use of drugs targeting DNA repair will markedly increase when functional and genetic loss of repair components are consistently identified. In addition, future therapies will exploit artificial synthetic lethality, where complementary DNA repair pathways are targeted simultaneously in cancers without DNA repair defects.

Many proteins involved in DNA replication and repair undergo post-translational modifications such as phosphorylation and ubiquitylation. Proliferating cell nuclear antigen (PCNA; a homotrimeric protein that encircles double-stranded DNA to function as a sliding clamp for DNA polymerases) is monoubiquitylated by the RAD6-RAD18 complex and further polyubiquitylated by the RAD5-MMS2-UBC13 complex in response to various DNA-damaging agents. PCNA mono- and polyubiquitylation activate an error-prone translesion synthesis pathway and an error-free pathway of damage avoidance, respectively. Here we show that replication factor C (RFC; a heteropentameric protein complex that loads PCNA onto DNA) was also ubiquitylated in a RAD18-dependent manner in cells treated with alkylating agents or H(2)O(2). A mutant form of RFC2 with a D228A substitution (corresponding to a yeast Rfc4 mutation that reduces an interaction with replication protein A (RPA), a single-stranded DNA-binding protein) was heavily ubiquitylated in cells even in the absence of DNA damage. Furthermore RFC2 was ubiquitylated by the RAD6-RAD18 complex in vitro, and its modification was inhibited in the presence of RPA. The inhibitory effect of RPA on RFC2 ubiquitylation was relatively specific because RAD6-RAD18-mediated ubiquitylation of PCNA was RPA-insensitive. Our findings suggest that RPA plays a regulatory role in DNA damage responses via repression of RFC2 ubiquitylation in human cells.

To maintain genome stability, cells have evolved various DNA repair pathways to deal with oxidative DNA damage. DNA damage response (DDR) pathways, including ATM-Chk2 and ATR-Chk1 checkpoints, are also activated in oxidative stress to coordinate DNA repair, cell cycle progression, transcription, apoptosis, and senescence. Several studies demonstrate that DDR pathways can regulate DNA repair pathways. On the other hand, accumulating evidence suggests that DNA repair pathways may modulate DDR pathway activation as well. In this review, we summarize our current understanding of how various DNA repair and DDR pathways are activated in response to oxidative DNA damage primarily from studies in eukaryotes. In particular, we analyze the functional interplay between DNA repair and DDR pathways in oxidative stress. A better understanding of cellular response to oxidative stress may provide novel avenues of treating human diseases, such as cancer and neurodegenerative disorders.

Genetic polymorphisms in DNA repair and oxidative stress pathways may modify the association between body size and postmenopausal breast cancer

DAG-Lactone Radiosensitization of Human Prostate Cancer Cells Is Mediated by ATM Down-regulation But Not Due to Abnormal DNA Repair

Delayed-onset psoriasiform eruption secondary to a phosphoinositide 3-kinase inhibitor: A case report and literature review

DNA repair in neurons: So if they don’t divide what's to repair?