DNA Interstrand Research Articles

The Colibactin Genotoxin Generates DNA Interstrand Cross-Links in Infected Cells.

ABSTRACTColibactins are hybrid polyketide-nonribosomal peptides produced by Escherichia coli, Klebsiella pneumoniae, and other Enterobacteriaceae harboring the pks genomic island. These genotoxic metabolites are produced by pks-encoded peptide-polyketide synthases as inactive prodrugs called precolibactins, which are then converted to colibactins by deacylation for DNA-damaging effects. Colibactins are bona fide virulence factors and are suspected of promoting colorectal carcinogenesis when produced by intestinal E. coli. Natural active colibactins have not been isolated, and how they induce DNA damage in the eukaryotic host cell is poorly characterized. Here, we show that DNA strands are cross-linked covalently when exposed to enterobacteria producing colibactins. DNA cross-linking is abrogated in a clbP mutant unable to deacetylate precolibactins or by adding the colibactin self-resistance protein ClbS, confirming the involvement of the mature forms of colibactins. A similar DNA-damaging mechanism is observed in cellulo, where interstrand cross-links are detected in the genomic DNA of cultured human cells exposed to colibactin-producing bacteria. The intoxicated cells exhibit replication stress, activation of ataxia-telangiectasia and Rad3-related kinase (ATR), and recruitment of the DNA cross-link repair Fanconi anemia protein D2 (FANCD2) protein. In contrast, inhibition of ATR or knockdown of FANCD2 reduces the survival of cells exposed to colibactin-producing bacteria. These findings demonstrate that DNA interstrand cross-linking is the critical mechanism of colibactin-induced DNA damage in infected cells.

Decapping protein EDC4 regulates DNA repair and phenocopies BRCA1

BRCA1 is a tumor suppressor that regulates DNA repair by homologous recombination. Germline mutations in BRCA1 are associated with increased risk of breast and ovarian cancer and BRCA1 deficient tumors are exquisitely sensitive to poly (ADP-ribose) polymerase (PARP) inhibitors. Therefore, uncovering additional components of this DNA repair pathway is of extreme importance for further understanding cancer development and therapeutic vulnerabilities. Here, we identify EDC4, a known component of processing-bodies and regulator of mRNA decapping, as a member of the BRCA1-BRIP1-TOPBP1 complex. EDC4 plays a key role in homologous recombination by stimulating end resection at double-strand breaks. EDC4 deficiency leads to genome instability and hypersensitivity to DNA interstrand cross-linking drugs and PARP inhibitors. Lack-of-function mutations in EDC4 were detected in BRCA1/2-mutation-negative breast cancer cases, suggesting a role in breast cancer susceptibility. Collectively, this study recognizes EDC4 with a dual role in decapping and DNA repair whose inactivation phenocopies BRCA1 deficiency.

Importance of homo-dimerization of Fanconi-associated nuclease 1 in DNA flap cleavage

Fanconi-associated nuclease 1 (FAN1) removes interstrand DNA crosslinks (ICLs) through its DNA flap endonuclease and exonuclease activities. Crystal structures of human and bacterial FAN1 bound to a DNA flap have been solved. The Pseudomonas aeruginosa bacterial FAN1 and human FAN1 (hFAN1) missing a flexible loop are monomeric, while intact hFAN1 is homo-dimeric in structure. Importantly, the monomeric and dimeric forms of FAN1 exhibit very different DNA binding modes. Here, we interrogate the functional differences between monomeric and dimeric forms of FAN1 and provide an explanation for the discrepancy in oligomeric state between the two hFAN1 structures. Specifically, we show that the flexible loop in question is needed for hFAN1 dimerization. While monomeric and dimeric bacterial or human FAN1 proteins cleave a short 5′ flap strand with similar efficiency, optimal cleavage of a long 5′ flap strand is contingent upon protein dimerization. Our study therefore furnishes biochemical evidence for a role of hFAN1 homodimerization in biological processes that involve 5′ DNA Flap cleavage.

Inhibition of non-homologous end joining in Fanconi Anemia cells results in rescue of survival after interstrand crosslinks but sensitization to replication associated double-strand breaks

When Fanconi Anemia (FA) proteins were depleted in human U2OS cells with integrated DNA repair reporters, we observed decreases in homologous recombination (HR), decreases in mutagenic non-homologous end joining (m-NHEJ) and increases in canonical NHEJ, which was independently confirmed by measuring V(D)J recombination. Furthermore, depletion of FA proteins resulted in reduced HR protein foci and increased NHEJ protein recruitment to replication-associated DSBs, consistent with our observation that the use of canonical NHEJ increases after depletion of FA proteins in cycling cells. FA-depleted cells and FA-mutant cells were exquisitely sensitive to a DNA-PKcs inhibitor (DNA-PKi) after sustaining replication-associated double strand breaks (DSBs). By contrast, after DNA interstrand crosslinks, DNA-PKi resulted in increased survival in FA-deficient cells, implying that NHEJ is contributing to lethality after crosslink repair. Our results suggest FA proteins inhibit NHEJ, since repair intermediates from crosslinks are rendered lethal by NHEJ. The implication is that bone marrow failure in FA could be triggered by naturally occurring DNA crosslinks, and DNA-PK inhibitors would be protective. Since some sporadic cancers have been shown to have deficiencies in the FA-pathway, these tumors should be vulnerable to NHEJ inhibitors with replication stress, but not with crosslinking agents, which could be tested in future clinical trials.

High-Resolution Locus-Specific Mapping of Chromatin Contacts using Two-Photon Photoactivated DNA Cross-Linking

Spatial organization of the genome remains an interesting and not fully understood area of nuclear architecture and gene regulation. Recently, there have been many technological and methodological developments towards this end from both imaging and genomic perspectives. Here we present a novel method to examine genomic contacts in vivo near a specific locus or nuclear region of interest. Using 3D localized two-photon excitation and a photoactivatable DNA crosslinker, the chromatin within a femtoliter volume around the region of interest can be labeled with an affinity tag. By carrying out this process on many cells using an automated microscope, we can then isolate the genomic DNA and pulldown the crosslinked DNA. While several DNA cross-linkers may be suitable for this method, we have initially focused on psoralen based compounds which are easily UV or two-photon photoactivated to form inter-strand DNA crosslinks preferentially at 5'-TpA dinucleotides in the genome. For photophysical optimization of the method, we use fluorescently labeled genomic loci where 200 copies of a transgene have been integrated at a single locus in U2OS cells. The DNA is extracted and purified using an affinity tag pull-down and the efficiency of crosslinking is quantified via qPCR. After the optimal photoactivation parameters are determined, the genomic locus will be irradiated and the crosslinked DNA extracted and sequenced as a proof-of-principle experiment. The long-term goal is to create a new method to bioinformatically map chromatin fragments at a nuclear region of interest, which can be performed before and after gene activation for any gene of interest.

Recent advances in understanding hematopoiesis in Fanconi Anemia.

Fanconi anemia is an inherited disease characterized by genomic instability, hypersensitivity to DNA cross-linking agents, bone marrow failure, short stature, skeletal abnormalities, and a high relative risk of myeloid leukemia and epithelial malignancies. The 21 Fanconi anemia genes encode proteins involved in multiple nuclear biochemical pathways that effect DNA interstrand crosslink repair. In the past, bone marrow failure was attributed solely to the failure of stem cells to repair DNA. Recently, non-canonical functions of many of the Fanconi anemia proteins have been described, including modulating responses to oxidative stress, viral infection, and inflammation as well as facilitating mitophagic responses and enhancing signals that promote stem cell function and survival. Some of these functions take place in non-nuclear sites and do not depend on the DNA damage response functions of the proteins. Dysfunctions of the canonical and non-canonical pathways that drive stem cell exhaustion and neoplastic clonal selection are reviewed, and the potential therapeutic importance of fully investigating the scope and interdependences of the canonical and non-canonical pathways is emphasized.

Novel N-mustard-benzimidazoles/benzothiazoles Hybrids, Synthesis and Anticancer Evaluation.

Bendamustine, an N-mustard-benzoimidazole hybrid conjugate, was recently approved for the treatment of chronic lymphocytic leukemia. However, the short half-life of bendamustine may limit its clinical applications. The purpose of this study is to design and synthesize compounds with a more favorable pharmacokinetic profile. We synthesized a series of hybrid molecules comprising a phenyl N-mustard moiety and benzothiazole or benzimidazole scaffold linked via a urea linker and evaluated their antitumor activity and plasma stability. We revealed that these agents exhibited significant cytotoxicity against a panel of human lymphoblastic leukemia and human solid tumor cells in culture. Human lymphoblastic leukemia CCRM-CEM cells were the most sensitive to the tested compounds. In general, the new hybrids were as potent as cisplatin, but significantly more cytotoxic than bendamustine. Phenyl N-mustard-benzothiazole compound 27d and phenyl N-mustardbenzimidaloe compound 32b possessed significant cytotoxicity and led to apoptotic death in the treated tumor cells. These two agents were able to induce DNA interstrand cross-linking and arrested cell cycle progression at the G2/M phase. Furthermore, we showed that these new hybrids were more chemically stable than bendamustine in rat plasma. Our results suggest that conjugation of phenyl N-mustard pharmacophore at C6 of benzimidazole or at C8 of the benzothiazole ring via a urea linker is likely an approach to increase the chemical stability and bioavailability. Highlights ⇒ Series of benzimidazoles and benzothiazoles linked to N-mustard were synthesized. ⇒ The newly synthesized derivatives induced DNA interstrand cross-links. ⇒ These derivatives induced cell cycle arrest in the G2/M phase and triggered apoptosis in H460 cells. ⇒ The new compounds are more cytotoxic than bendamustine. ⇒ The new compounds were chemically more stable than bendamustine in rat plasma.

Fanconi anemia with sun-sensitivity caused by a Xeroderma pigmentosum-associated missense mutation in XPF

BackgroundFanconi anemia (FA) is an inherited genomic instability disorder with congenital and developmental abnormalities, bone marrow failure and predisposition to cancer early in life, and cellular sensitivity to DNA interstrand crosslinks.Case presentationA fifty-one-year old female patient, initially diagnosed with FA in childhood on the basis of classic features and increased chromosomal breakage, and remarkable sun-sensitivity is described. She only ever had mild haematological abnormalities and no history of malignancy. To identify and characterise the genetic defect in this lady, who is one of the oldest reported FA patients, we used whole-exome sequencing for identification of causative mutations, and functionally characterized the cellular phenotype. Detection of the novel splice site mutation c.793-2A > G and the previously described missense mutation c.1765C > T (p.Arg589Trp) in XPF/ERCC4/FANCQ assign her as the third individual of complementation group FA-Q. Ectopic expression of wildtype, but not mutant, XPF/ERCC4/FANCQ, in patient-derived fibroblasts rescued cellular resistance to DNA interstrand-crosslinking agents. Patient derived FA-Q cells showed impaired nuclear excision repair capacity. However, mutated XPF/ERCC4/FANCQ protein in our patient’s cells, as in the two other patients with FA-Q, was detectable on chromatin, in contrast to XP-F cells, where missense-mutant protein failed to properly translocate to the nucleus.ConclusionsPatients with FA characteristics and UV sensitivity should be tested for mutations in XPF/ERCC4/FANCQ. The missense mutation p.Arg589Trp was previously detected in patients diagnosed with Xeroderma pigmentosum or Cockayne syndrome. Hence, phenotypic manifestations associated with this XPF/ERCC4/ FANCQ mutation are highly variable.

Expanding the FANCO/RAD51C associated phenotype: Cleft lip and palate and lobar holoprosencephaly, two rare findings in Fanconi anemia

Fanconi anemia is a rare chromosome instability disorder with a highly variable phenotype. In the antenatal and neonatal periods, the diagnosis is usually suggested by the presence of typical congenital abnormalities such as intrauterine growth retardation, microcephaly and radial ray defects. We report a newborn female with a prenatal diagnosis of Fanconi anemia, complementation group O (FANCO). Antenatal ultrasounds identified symmetrical intrauterine growth retardation, complex heart defect as well as brain anomalies, overlapping fingers and cleft lip and palate. Imperforate anus was detected after birth. Compound heterozygous RAD51C variants c. [571+5G > A]; [c.935G > A] were detected by prenatal whole exome sequencing and cellular hypersensitivity to DNA interstrand crosslinking agents (DEB, MMC) was confirmed after birth. With only one previously described homozygous RAD51C variant to date, our findings expand the phenotypic spectrum of FANCO and suggest it should be part of the antenatal differential diagnosis for trisomy 13 and 18, due to the presence of atypical findings such as cleft lip and palate, holoprosencephaly, growth restriction and overlapping fingers.

Reduced recruitment of 53BP1 during interstrand crosslink repair is associated with genetically inherited attenuation of mitomycin C sensitivity in a family with Fanconi anemia.

The Fanconi anemia (FA) pathway is implicated in the repair of DNA interstrand crosslinks (ICL). In this process, it has been shown that FA factors regulate the choice for DNA double strand break repair towards homologous recombination (HR). As this mechanism is impaired in FA deficient cells exposed to crosslinking agents, an inappropriate usage of non-homologous end joining (NHEJ) leads to the accumulation of toxic chromosomal abnormalities. We studied a family with two FANCG patients and found a genetically inherited attenuation of mitomycin C sensitivity resulting in-vitro in an attenuated phenotype for one patient or in increased resistance for two healthy relatives. A heterozygous mutation in ATM was identified in these 3 subjects but was not directly linked to the observed phenotype. However, the attenuation of ICL sensitivity was associated with a reduced recruitment of 53BP1 during the course of ICL repair, and increased HR levels. These results further demonstrate the importance of favoring HR over NHEJ for the survival of cells challenged with ICLs.

PAK4 Inhibition Impacts Growth and Survival, and Increases Sensitivity to DNA-Damaging Agents in Waldestrostom Macroglobulinemia

p21-activated kinases (PAKs) are effectors for the small GTPases Cdc42 and Rac that control a wide range of cellular processes including cytoskeleton reorganization, cell proliferation, survival and motility. Based on our initial results showing significant biological and functional role of PAK4 in plasma cell malignancies, we investigated its role in Waldenström macroglobulinemia (WM). We first confirmed high level of PAK4 expression and activity in WM cells. Both genetic depletion via stable lentiviral knock down and pharmacological inhibition of PAK4 via allosteric modulator KPT-9274 decreased tumor cell growth and survival in a dose and time dependent manner in a panel of WM cell lines. The growth inhibitory effect was associated with induction of apoptotic cell death, caspases activation and PARP cleavage as well as modulation of pro-apoptotic proteins such as PUMA. In addition, related-PAK4 biological processes such as migration, invasion and adhesion to bone marrow stromal cells (BMSCs) were significantly impacted by the inhibitor. A significant effect of KPT9274 was also observed in primary tumor cells from both newly diagnosed and relapse WM patients, including primary cells from ibrutinib resistant patients.To gain further insight into the consequences of PAK4 inhibition, we performed gene expression profile in WM cell lines treated with KPT-9274. Intriguingly we detected a significant impact on expression of Fanconi Anemia (FA)/BRCA pathway related genes, a DNA-damage response pathway essential for the repair of DNA interstrand crosslinks (ICLs) and regulation of cellular responses to replication stress. Since FA/BRCA deficient cells are defective in the formation of Rad51 foci, a crucial component of the homologous recombination (HR) repair machinery, we examined the effect of PAK4/NAMPT inhibition on Rad51 as well its impact on HR. We observed that, apart from inducing DNA damage, assessed by γH2AX expression, KPT-9274 specifically inhibited Rad51 and the double strand break repair by the homologous recombination pathway. Protein pull down analysis revealed the existence of a complex between nicotinamide phosphoribosyltransferase (NAMPT) and the conserved PAK binding domain; treatment with KPT-9274 disrupted this interaction and inhibited the enzymatic activity of NAMPT. NAD is necessary for PARP function especially with increasing DNA damage; and its depletion severely hamper DNA repair. Consistent with this, we observed that nicotinic acid supplementation rescued the effect of KPT-9274 on NAMPT inhibition as well as DNA damage and repair.As FA/BRCA pathway has been shown to affects sensitivity to alkylating agents, we next combined KPT-9274 with either melphalan or bendamustine in MM and WM cells. The combination treatment resulted in a synergistic time- and dose-dependent inhibition of cell survival and growth in cell lines and primary patient tumor cells. We observed a synergistic induction of apoptosis and activation of caspase-3/7, -8 and -9 following treatment with combined versus single-agent therapy. Similarly, in PAK4 knock-down WM cells bendamustine significantly increased the rate of early and late apoptotic cells (60%) compared to scrambled knockdown cells (37%).In summary, we report a significant anti-proliferative activity of dual PAK4-NAMPT inhibition in WM cells, with induction of apoptosis, DNA-damage response and FA/BRCA pathway disruption and a strong synergistic activity in combination with DNA damaging agents such as Bendamustine. Altogether, our data suggests dual PAK4-NAMPT inhibition represents a novel therapeutic strategies in WM. DisclosuresSenapedis:Karyopharm Therapeutics Inc: Employment, Equity Ownership. Baloglu:Karyopharm Therapeutics Inc: Employment, Equity Ownership. Oliva:Takeda: Honoraria; Celgene: Honoraria. Anderson:Oncopep: Other: scientific founder; C4 Therapeutics: Other: scientific founder; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees; Millenium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; MedImmune: Membership on an entity's Board of Directors or advisory committees. Treon:Pharmacyclics: Consultancy, Research Funding.

FANCI and FANCD2 have common as well as independent functions during the cellular replication stress response.

Fanconi anemia (FA) is an inherited cancer predisposition syndrome characterized by cellular hypersensitivity to DNA interstrand crosslinks (ICLs). To repair these lesions, the FA proteins act in a linear hierarchy: following ICL detection on chromatin, the FA core complex monoubiquitinates and recruits the central FANCI and FANCD2 proteins that subsequently coordinate ICL removal and repair of the ensuing DNA double-stranded break by homology-dependent repair (HDR). FANCD2 also functions during the replication stress response by mediating the restart of temporarily stalled replication forks thereby suppressing the firing of new replication origins. To address if FANCI is also involved in these FANCD2-dependent mechanisms, we generated isogenic FANCI-, FANCD2- and FANCI:FANCD2 double-null cells. We show that FANCI and FANCD2 are partially independent regarding their protein stability, nuclear localization and chromatin recruitment and contribute independently to cellular proliferation. Simultaneously, FANCD2—but not FANCI—plays a major role in HDR-mediated replication restart and in suppressing new origin firing. Consistent with this observation, deficiencies in HDR-mediated DNA DSB repair can be overcome by stabilizing RAD51 filament formation in cells lacking functional FANCD2. We propose that FANCI and FANCD2 have partially non-overlapping and possibly even opposing roles during the replication stress response.

Fanconi anemia FANCD2 and FANCI proteins regulate the nuclear dynamics of splicing factors.

Proteins disabled in the cancer-prone disorder Fanconi anemia (FA) ensure the maintenance of chromosomal stability during DNA replication. FA proteins regulate replication dynamics, coordinate replication-coupled repair of interstrand DNA cross-links, and mitigate conflicts between replication and transcription. Here we show that FANCI and FANCD2 associate with splicing factor 3B1 (SF3B1), a key spliceosomal protein of the U2 small nuclear ribonucleoprotein (U2 snRNP). FANCI is in close proximity to SF3B1 in the nucleoplasm of interphase and mitotic cells. Furthermore, we find that DNA replication stress induces the release of SF3B1 from nuclear speckles in a manner that depends on FANCI and on the activity of the checkpoint kinase ATR. In chromatin, both FANCD2 and FANCI associate with SF3B1, prevent accumulation of postcatalytic intron lariats, and contribute to the timely eviction of splicing factors. We propose that FANCD2 and FANCI contribute to the organization of functional domains in chromatin, ensuring the coordination of DNA replication and cotranscriptional processes.

Sensing and Processing of DNA Interstrand Crosslinks by the Mismatch Repair Pathway

DNA interstrand crosslinks (ICLs) that are repaired innon-dividing cells must be recognized independently of replication-associated DNA unwinding. Using cell-free extracts from Xenopus eggs that support neither replication nor transcription, we establish that ICLs are recognized and processed by the mismatch repair (MMR) machinery. We find that ICL repair requires MutSα (MSH2-MSH6) and the mismatch recognition FXE motif in MSH6, strongly suggesting that MutSα functions as an ICL sensor. MutSα recruits MutLα and EXO1 to ICL lesions, and the catalytic activity of both these nucleases isessential for ICL repair. As anticipated for a DNAunwinding-independent recognition process, we demonstrate that least distorting ICLs fail to berecognized and repaired by the MMR machinery.This establishes that ICL structure is a critical determinant of repair efficiency outside of DNA replication.

Fanconi-Anemia-Associated Mutations Destabilize RAD51 Filaments and Impair Replication Fork Protection

Fanconi anemia (FA) is a genetic disorder characterized by a defect in DNA interstrand crosslink (ICL) repair, chromosomal instability, and a predisposition to cancer. Recently, two RAD51 mutations were reported to cause an FA-like phenotype. Despite the tight association of FA/HR proteins with replication fork (RF) stabilization during normal replication, it remains unknown how FA-associated RAD51 mutations affect replication beyond ICL lesions. Here, we report that these mutations fail to protect nascent DNA from MRE11-mediated degradation during RF stalling in Xenopus laevis egg extracts. Reconstitution of DNA protection invitro revealed that the defect arises directly due to altered RAD51 properties. Both mutations induce pronounced structural changes and RAD51 filament destabilization that is not rescued by prevention of ATP hydrolysis due to aberrant ATP binding. Our results further interconnect the FA pathway with DNA replication and provide mechanistic insight into the role of RAD51 in recombination-independent mechanisms of genome maintenance.

Selective cytotoxicity of the anti-diabetic drug, metformin, in glucose-deprived chicken DT40 cells.

Metformin is a biguanide drug that is widely used in the treatment of diabetes. Epidemiological studies have indicated that metformin exhibits anti-cancer activity. However, the molecular mechanisms underlying this activity currently remain unclear. We hypothesized that metformin is cytotoxic in a tumor-specific environment such as glucose deprivation and/or low oxygen (O2) tension. We herein demonstrated that metformin was highly cytotoxic under glucose-depleted, but not hypoxic (2% O2) conditions. In order to elucidate the underlying mechanisms of this selective cytotoxicity, we treated exposed DNA repair-deficient chicken DT40 cells with metformin under glucose-depleted conditions and measured cellular sensitivity. Under glucose-depleted conditions, metformin specifically killed fancc and fancl cells that were deficient in FANCC and FANCL proteins, respectively, which are involved in DNA interstrand cross-link repair. An analysis of chromosomal aberrations in mitotic chromosome spreads revealed that a clinically relevant concentration of metformin induced DNA double-strand breaks (DSBs) in fancc and fancl cells under glucose-depleted conditions. In summary, metformin induced DNA damage under glucose-depleted conditions and selectively killed cells. This metformin-mediated selective toxicity may suppress the growth of malignant tumors that are intrinsically deprived of glucose.

The association of genetic variations in DNA repair pathways with severe toxicities in NSCLC patients undergoing platinum-based chemotherapy.

Genetic variations in genes involved in repairing platinum-induced DNA lesions may contribute to the toxicity of platinum-based chemotherapy. The role of single-nucleotide polymorphisms (SNPs) within DNA repair pathways in the occurrence of severe toxicity is not yet understood. Current studies prefer to do original works rather than analyze previously published data. Our study aimed to replicate associations between previously investigated SNPs and toxicities and to identify new genetic makers. We systematically examined the relevance of 97 SNPs in 54 candidate genes responsible for repairing DNA interstrand and intrastrand cross-links to severe toxicity in a discovery cohort of 437 NSCLC patients receiving platinum-based chemotherapy. Statistically significant SNPs were then assessed for replication in an independent validation cohort of 781 NSCLC patients. We found that 7 SNPs were significant at p < 0.01 (RRM1 rs12806698, XPC rs2228000, XPF rs1799801, hMLH1 rs1800734, PMS2 rs1062372, REV3L rs462779 and FANCC rs4647554) in the discovery cohort. Among them, two SNPs (RRM1 rs12806698 and hMLH1 rs1800734) remained significant after Bonferroni correction. XPC rs2228000 showed a significant relationship with severe gastrointestinal toxicity in the validation cohort. When the two cohorts were combined, XPC rs2228000 presented better tolerance of severe hematologic toxicity, gastrointestinal toxicity and leukopenia (OR = 0.677, 95% CI: 0.510-0.899, p = 0.007; OR = 0.565, 95% CI: 0.368-0.869, p = 0.009; OR = 0.628, 95% CI: 0.439-0.899, p = 0.011, respectively). Our findings can offer comprehensive pharmacogenetic information for platinum-induced toxicities.

Emerging functions of the Fanconi anemia pathway at a glance.

Fanconi anemia (FA) is a rare disease, in which homozygous or compound heterozygous inactivating mutations in any of 21 genes lead to genomic instability, early-onset bone marrow failure and increased cancer risk. The FA pathway is essential for DNA damage response (DDR) to DNA interstrand crosslinks. However, proteins of the FA pathway have additional cytoprotective functions that may be independent of DDR. We have shown that many FA proteins participate in the selective autophagy pathway that is required for the destruction of unwanted intracellular constituents. In this Cell Science at a Glance and the accompanying poster, we briefly review the role of the FA pathway in DDR and recent findings that link proteins of the FA pathway to selective autophagy of viruses and mitochondria. Finally, we discuss how perturbations in FA protein-mediated selective autophagy may contribute to inflammatory as well as genotoxic stress.

Corrigendum: Photoinduced DNA Interstrand Cross-Link Formation by Naphthalene Boronates via a Carbocation.

The authors learned of an error in the publication of their manuscript, where Figure 3 was duplicated and mistakenly placed in the position of Figure 1. This error was introduced during the final production and typesetting stage and was not the fault of the authors. The editorial office apologises for the oversight and for the inconvenience caused. The correct version of Figure 1 is provided below. > A) UV-induced DNA cross-link formation by 1 and 2 upon irradiation for 4 h. Lane 1: DNA only; lane 2: 200 μm 1; lane 3: 50 μm 1 (cross-linking yield 4.2 %); lane 4: 200 μm 1 (11.1 %); lane 5: 200 μm 2; lane 6: 50 μm 2 (3.2 %); lane 7: 200 μm 2 (7.1 %). B) H2O2-induced DNA cross-link formation by 1 and 2 at 37 °C for 24 h. Lane 8: DNA only; lane 9: H2O2 only; lane 10: 200 μm 1; lane 11: 50 μm 1 and 100 μm H2O2 (2.1 %); lane 12: 200 μm 1 and 400 μm H2O2 (4.1 %); lane 13: 200 μm 2 without H2O2; lane 14: 50 μm 2 and 100 μm H2O2 (1.1 %); lane 15: 200 μm 2 and 400 μm H2O2 (2.9 %).

Systematic analysis of DNA crosslink repair pathways during development and aging in Caenorhabditis elegans.

DNA interstrand crosslinks (ICLs) are generated by endogenous sources and chemotherapeutics, and pose a threat to genome stability and cell survival. Using Caenorhabditis elegans mutants, we identify DNA repair factors that protect against the genotoxicity of ICLs generated by trioxsalen/ultraviolet A (TMP/UVA) during development and aging. Mutations in nucleotide excision repair (NER) components (e.g. XPA-1 and XPF-1) imparted extreme sensitivity to TMP/UVA relative to wild-type animals, manifested as developmental arrest, defects in adult tissue morphology and functionality, and shortened lifespan. Compensatory roles for global-genome (XPC-1) and transcription-coupled (CSB-1) NER in ICL sensing were exposed. The analysis also revealed contributions of homologous recombination (BRC-1/BRCA1), the MUS-81, EXO-1, SLX-1 and FAN-1 nucleases, and the DOG-1 (FANCJ) helicase in ICL resolution, influenced by the replicative-status of the cell/tissue. No obvious or critical role in ICL repair was seen for non-homologous end-joining (cku-80) or base excision repair (nth-1, exo-3), the Fanconi-related proteins BRC-2 (BRCA2/FANCD1) and FCD-2 (FANCD2), the WRN-1 or HIM-6 (BLM) helicases, or the GEN-1 or MRT-1 (SNM1) nucleases. Our efforts uncover replication-dependent and -independent ICL repair networks, and establish nematodes as a model for investigating the repair and consequences of DNA crosslinks in metazoan development and in adult post-mitotic and proliferative germ cells.