Prof Wojciech Niedzwiedz

Research Area: Cell and Molecular Biology
Scientific Themes: Genes, Genetics, Epigenetics & Genomics
Keywords: Fanconi anemia, DNA replication,, DNA repair, Homologous recombination and Cancer
Web Links:
Figure 1. (A) Cartoon depicts the DNA fiber labelling procedure. (B) Examples of various replication structures that can be visualised with this technique. (C) Representative images showing colocalisation of γH2AX (red) and CldU (green) foci in WT DT40 and ΔFANCM cells treated with CPT. (D) Representative images showing increased Rad51 foci formation in FANCM-depleted cells treated with HU.

Figure 1. (A) Cartoon depicts the DNA fiber labelling procedure. (B) Examples of various ...

DNA is continuously exposed to endogenous and exogenous agents that can create lesions disrupting duplication of the genome. Mounting evidence suggests that defects in DNA replication are the major source of spontaneous chromosome instability, a recognised causative factor in cancer. This is underscored by several genome instability and cancer predisposing human diseases, one of them being Fanconi Anaemia (FA).

FA is a rare childhood cancer predisposing syndrome, characterised by developmental defects and progressive bone marrow failure. As a consequence, children with FA often develop pancytopenia, and ultimately most FA patients die at a young age of haematological diseases.

The genes mutated in this syndrome encode a network of ‘caretaker’ proteins, which not only ensure that our DNA is accurately copied but also prevent replication failure and associated genomic instability. Consequently, a properly functioning FA pathway is important for normal development, haematopoiesis and suppression of solid tumours in everyone, and as such underscores the importance of research in this area. 

Interestingly, cells from FA patients are also hypersensitive to DNA damaging agents that link two strands of DNA together, forming interstrand crosslinks (ICLs) and blocking DNA replication. This implies that the FA pathway is critical for removal of such lesions. This is important, as ICL inducing agents are the most widely used drugs in cancer therapy. 

Despite the critical role of ICLs in anti-cancer therapy the mechanisms by which higher vertebrate cells overcome ICL-induced replication blocks remains to be fully understood.  The research interest of my group focuses on elucidating how the repair of damaged DNA is executed in the context of the replication fork, and how fork stability is achieved under stressful conditions. We are particularly interested in the molecular function of the FA proteins in these processes.  To address these questions we are employing different techniques to monitor aspects of DNA replication. Among these techniques, DNA fiber analysis allows the monitoring of DNA replication at the single molecule level (Figure 1). Using these approaches we aim to explain how the FA proteins promote DNA replication under stressful conditions, and whether dysfunctional replication-mediated DNA repair is a common signal that drives FA disease progression to leukemia. A long-term goal of our research is to elucidate the FA-dependent mechanism required to suppress devastating haematological and malignant conditions and translate our basic laboratory findings into the development of novel therapies for cancer.

Name Department Institution Country
Prof Stephen P Jackson The Gurdon Institute and Department of Biochemistry University of Cambridge United Kingdom
Dr Grant Stewart College of Medical and Dental Sciences University of Birmingham United Kingdom
Prof Andrew OM Wilkie FRS FMedSci FRCP Nuffield Division of Clinical Laboratory Sciences Oxford University, Weatherall Institute of Molecular Medicine United Kingdom
Prof Barbara Tudek Faculty of Biology Warsaw University Poland
Prof Mark Glover Biochemistry University of Alberta Canada
Dr Michael Lisby Department of Biology University of Copenhagen Denmark
Niedzwiedz W. 2016. Activating ATR, the devil's in the dETAA1l. Nat Cell Biol, 18 (11), pp. 1120-1122. | Show Abstract | Read more

Two studies now show that Ewing's tumour-associated antigen 1 (ETAA1) is recruited to sites of DNA replication stress through its interaction with replication protein A, where it stimulates the ATR kinase to promote efficient genome duplication. These findings provide exciting insight into the already very complex regulatory mechanism of the ATR activation cascade.

Nieminuszczy J, Broderick R, Niedzwiedz W. 2016. EXD2 - a new player joins the DSB resection team. Cell Cycle, 15 (12), pp. 1519-1520. | Read more

Fenwick AL, Kliszczak M, Cooper F, Murray J, Sanchez-Pulido L, Twigg SR, Goriely A, McGowan SJ, Miller KA, Taylor IB et al. 2016. Mutations in CDC45, Encoding an Essential Component of the Pre-initiation Complex, Cause Meier-Gorlin Syndrome and Craniosynostosis. Am J Hum Genet, 99 (1), pp. 125-138. | Show Abstract | Read more

DNA replication precisely duplicates the genome to ensure stable inheritance of genetic information. Impaired licensing of origins of replication during the G1 phase of the cell cycle has been implicated in Meier-Gorlin syndrome (MGS), a disorder defined by the triad of short stature, microtia, and a/hypoplastic patellae. Biallelic partial loss-of-function mutations in multiple components of the pre-replication complex (preRC; ORC1, ORC4, ORC6, CDT1, or CDC6) as well as de novo stabilizing mutations in the licensing inhibitor, GMNN, cause MGS. Here we report the identification of mutations in CDC45 in 15 affected individuals from 12 families with MGS and/or craniosynostosis. CDC45 encodes a component of both the pre-initiation (preIC) and CMG helicase complexes, required for initiation of DNA replication origin firing and ongoing DNA synthesis during S-phase itself, respectively, and hence is functionally distinct from previously identified MGS-associated genes. The phenotypes of affected individuals range from syndromic coronal craniosynostosis to severe growth restriction, fulfilling diagnostic criteria for Meier-Gorlin syndrome. All mutations identified were biallelic and included synonymous mutations altering splicing of physiological CDC45 transcripts, as well as amino acid substitutions expected to result in partial loss of function. Functionally, mutations reduce levels of full-length transcripts and protein in subject cells, consistent with partial loss of CDC45 function and a predicted limited rate of DNA replication and cell proliferation. Our findings therefore implicate the preIC as an additional protein complex involved in the etiology of MGS and connect the core cellular machinery of genome replication with growth, chondrogenesis, and cranial suture homeostasis.

Nieminuszczy J, Schwab RA, Niedzwiedz W. 2016. The DNA fibre technique - tracking helicases at work. Methods, 108 pp. 92-98. | Show Abstract | Read more

Faithful duplication of genetic material during every cell division is essential to ensure accurate transmission of genetic information to daughter cells. DNA helicases play a crucial role in promoting this process by facilitating almost all transactions occurring on DNA, including DNA replication and repair. They are responsible not only for DNA double helix unwinding ahead of progressing replication forks but also for resolution of secondary structures like G4 quadruplexes, HJ branch migration, double HJ dissolution, protein displacement, strand annealing and many more. Their importance in maintaining genome stability is underscored by the fact that many human disorders, including cancer, are associated with mutations in helicase genes. Here we outline how DNA fibre fluorography, a straightforward and inexpensive approach, can be employed to study the in vivo function of helicases in DNA replication and the maintenance of genome stability at a single molecule level. This approach directly visualizes the progression of individual replication forks within living cells and hence provides quantitative information on various aspects of DNA synthesis, such as replication fork processivity (replication speed), fork stalling, origin usage and fork termination.

Broderick R, Nieminuszczy J, Baddock HT, Deshpande R, Gileadi O, Paull TT, McHugh PJ, Niedzwiedz W. 2016. EXD2 promotes homologous recombination by facilitating DNA end resection. Nat Cell Biol, 18 (3), pp. 271-280. | Show Abstract | Read more

Repair of DNA double-strand breaks (DSBs) by homologous recombination (HR) is critical for survival and genome stability of individual cells and organisms, but also contributes to the genetic diversity of species. A vital step in HR is MRN-CtIP-dependent end resection, which generates the 3' single-stranded DNA overhangs required for the subsequent strand exchange reaction. Here, we identify EXD2 (also known as EXDL2) as an exonuclease essential for DSB resection and efficient HR. EXD2 is recruited to chromatin in a damage-dependent manner and confers resistance to DSB-inducing agents. EXD2 functionally interacts with the MRN complex to accelerate resection through its 3'-5' exonuclease activity, which efficiently processes double-stranded DNA substrates containing nicks. Finally, we establish that EXD2 stimulates both short- and long-range DSB resection, and thus, together with MRE11, is required for efficient HR. This establishes a key role for EXD2 in controlling the initial steps of chromosomal break repair.

Schwab RA, Nieminuszczy J, Shah F, Langton J, Lopez Martinez D, Liang CC, Cohn MA, Gibbons RJ, Deans AJ, Niedzwiedz W. 2015. The Fanconi Anemia Pathway Maintains Genome Stability by Coordinating Replication and Transcription. Mol Cell, 60 (3), pp. 351-361. | Show Abstract | Read more

DNA replication stress can cause chromosomal instability and tumor progression. One key pathway that counteracts replication stress and promotes faithful DNA replication consists of the Fanconi anemia (FA) proteins. However, how these proteins limit replication stress remains largely elusive. Here we show that conflicts between replication and transcription activate the FA pathway. Inhibition of transcription or enzymatic degradation of transcription-associated R-loops (DNA:RNA hybrids) suppresses replication fork arrest and DNA damage occurring in the absence of a functional FA pathway. Furthermore, we show that simple aldehydes, known to cause leukemia in FA-deficient mice, induce DNA:RNA hybrids in FA-depleted cells. Finally, we demonstrate that the molecular mechanism by which the FA pathway limits R-loop accumulation requires FANCM translocase activity. Failure to activate a response to physiologically occurring DNA:RNA hybrids may critically contribute to the heightened cancer predisposition and bone marrow failure of individuals with mutated FA proteins.

Broderick R, Niedzwiedz W. 2015. Sister chromatid decatenation: bridging the gaps in our knowledge. Cell Cycle, 14 (19), pp. 3040-3044. | Show Abstract | Read more

Faithful chromosome segregation is critical in preventing genome loss or damage during cell division. Failure to properly disentangle catenated sister chromatids can lead to the formation of bulky or ultrafine anaphase bridges, and ultimately genome instability. In this review we present an overview of the current state of knowledge of how sister chromatid decatenation is carried out, with particular focus on the role of TOP2A and TOPBP1 in this process.

Broderick R, Nieminuszczy J, Blackford AN, Winczura A, Niedzwiedz W. 2015. TOPBP1 recruits TOP2A to ultra-fine anaphase bridges to aid in their resolution. Nat Commun, 6 pp. 6572. | Show Abstract | Read more

During mitosis, sister chromatids must be faithfully segregated to ensure that daughter cells receive one copy of each chromosome. However, following replication they often remain entangled. Topoisomerase IIα (TOP2A) has been proposed to resolve such entanglements, but the mechanisms governing TOP2A recruitment to these structures remain poorly understood. Here, we identify TOPBP1 as a novel interactor of TOP2A, and reveal that it is required for TOP2A recruitment to ultra-fine anaphase bridges (UFBs) in mitosis. The C-terminal region of TOPBP1 interacts with TOP2A, and TOPBP1 recruitment to UFBs requires its BRCT domain 5. Depletion of TOPBP1 leads to accumulation of UFBs, the majority of which arise from centromeric loci. Accordingly, expression of a TOPBP1 mutant that is defective in TOP2A binding phenocopies TOP2A depletion. These findings provide new mechanistic insights into how TOP2A promotes resolution of UFBs during mitosis, and highlights a pivotal role for TOPBP1 in this process.

Blackford AN, Nieminuszczy J, Schwab RA, Galanty Y, Jackson SP, Niedzwiedz W. 2015. TopBP1 interacts with BLM to maintain genome stability but is dispensable for preventing BLM degradation. Mol Cell, 57 (6), pp. 1133-1141. | Show Abstract | Read more

The Bloom syndrome helicase BLM and topoisomerase-IIβ-binding protein 1 (TopBP1) are key regulators of genome stability. It was recently proposed that BLM phosphorylation on Ser338 mediates its interaction with TopBP1, to protect BLM from ubiquitylation and degradation (Wang et al., 2013). Here, we show that the BLM-TopBP1 interaction does not involve Ser338 but instead requires BLM phosphorylation on Ser304. Furthermore, we establish that disrupting this interaction does not markedly affect BLM stability. However, BLM-TopBP1 binding is important for maintaining genome integrity, because in its absence cells display increased sister chromatid exchanges, replication origin firing and chromosomal aberrations. Therefore, the BLM-TopBP1 interaction maintains genome stability not by controlling BLM protein levels, but via another as-yet undetermined mechanism. Finally, we identify critical residues that mediate interactions between TopBP1 and MDC1, and between BLM and TOP3A/RMI1/RMI2. Taken together, our findings provide molecular insights into a key tumor suppressor and genome stability network.

Higgs MR, Reynolds JJ, Winczura A, Blackford AN, Borel V, Miller ES, Zlatanou A, Nieminuszczy J, Ryan EL, Davies NJ et al. 2015. BOD1L Is Required to Suppress Deleterious Resection of Stressed Replication Forks. Mol Cell, 59 (3), pp. 462-477. | Show Abstract | Read more

Recognition and repair of damaged replication forks are essential to maintain genome stability and are coordinated by the combined action of the Fanconi anemia and homologous recombination pathways. These pathways are vital to protect stalled replication forks from uncontrolled nucleolytic activity, which otherwise causes irreparable genomic damage. Here, we identify BOD1L as a component of this fork protection pathway, which safeguards genome stability after replication stress. Loss of BOD1L confers exquisite cellular sensitivity to replication stress and uncontrolled resection of damaged replication forks, due to a failure to stabilize RAD51 at these forks. Blocking DNA2-dependent resection, or downregulation of the helicases BLM and FBH1, suppresses both catastrophic fork processing and the accumulation of chromosomal damage in BOD1L-deficient cells. Thus, our work implicates BOD1L as a critical regulator of genome integrity that restrains nucleolytic degradation of damaged replication forks.

Higgs MR, Reynolds JJ, Winczura A, Blackford AN, Borel V, Miller ES, Zlatanou A, Nieminuszczy J, Ryan EL, Davies NJ et al. 2015. BOD1L Is Required to Suppress Deleterious Resection of Stressed Replication Forks Molecular Cell, 59 (3), pp. 462-477. | Show Abstract | Read more

© 2015 Elsevier Inc. Recognition and repair of damaged replication forks are essential to maintain genome stability and are coordinated by the combined action of the Fanconi anemia and homologous recombination pathways. These pathways are vital to protect stalled replication forks from uncontrolled nucleolytic activity, which otherwise causes irreparable genomic damage. Here, we identify BOD1L as a component of this fork protection pathway, which safeguards genome stability after replication stress. Loss of BOD1L confers exquisite cellular sensitivity to replication stress and uncontrolled resection of damaged replication forks, due to a failure to stabilize RAD51 at these forks. Blocking DNA2-dependent resection, or downregulation of the helicases BLM and FBH1, suppresses both catastrophic fork processing and the accumulation of chromosomal damage in BOD1L-deficient cells. Thus, our work implicates BOD1L as a critical regulator of genome integrity that restrains nucleolytic degradation of damaged replication forks.

Yata K, Bleuyard JY, Nakato R, Ralf C, Katou Y, Schwab RA, Niedzwiedz W, Shirahige K, Esashi F. 2014. BRCA2 coordinates the activities of cell-cycle kinases to promote genome stability. Cell Rep, 7 (5), pp. 1547-1559. | Show Abstract | Read more

Numerous human genome instability syndromes, including cancer, are closely associated with events arising from malfunction of the essential recombinase Rad51. However, little is known about how Rad51 is dynamically regulated in human cells. Here, we show that the breast cancer susceptibility protein BRCA2, a key Rad51 binding partner, coordinates the activity of the central cell-cycle drivers CDKs and Plk1 to promote Rad51-mediated genome stability control. The soluble nuclear fraction of BRCA2 binds Plk1 directly in a cell-cycle- and CDK-dependent manner and acts as a molecular platform to facilitate Plk1-mediated Rad51 phosphorylation. This phosphorylation is important for enhancing the association of Rad51 with stressed replication forks, which in turn protects the genomic integrity of proliferating human cells. This study reveals an elaborate but highly organized molecular interplay between Rad51 regulators and has significant implications for understanding tumorigenesis and therapeutic resistance in patients with BRCA2 deficiency.

Schwab RA, Nieminuszczy J, Shin-ya K, Niedzwiedz W. 2013. FANCJ couples replication past natural fork barriers with maintenance of chromatin structure. J Cell Biol, 201 (1), pp. 33-48. | Show Abstract | Read more

Defective DNA repair causes Fanconi anemia (FA), a rare childhood cancer-predisposing syndrome. At least 15 genes are known to be mutated in FA; however, their role in DNA repair remains unclear. Here, we show that the FANCJ helicase promotes DNA replication in trans by counteracting fork stalling on replication barriers, such as G4 quadruplex structures. Accordingly, stabilization of G4 quadruplexes in ΔFANCJ cells restricts fork movements, uncouples leading- and lagging-strand synthesis and generates small single-stranded DNA gaps behind the fork. Unexpectedly, we also discovered that FANCJ suppresses heterochromatin spreading by coupling fork movement through replication barriers with maintenance of chromatin structure. We propose that FANCJ plays an essential role in counteracting chromatin compaction associated with unscheduled replication fork stalling and restart, and suppresses tumorigenesis, at least partially, in this replication-specific manner.

Blackford AN, Schwab RA, Nieminuszczy J, Deans AJ, West SC, Niedzwiedz W. 2012. The DNA translocase activity of FANCM protects stalled replication forks. Hum Mol Genet, 21 (9), pp. 2005-2016. | Show Abstract | Read more

FANCM is the most highly conserved protein within the Fanconi anaemia (FA) tumour suppressor pathway. However, although FANCM contains a helicase domain with translocase activity, this is not required for its role in activating the FA pathway. Instead, we show here that FANCM translocaseactivity is essential for promoting replication fork stability. We demonstrate that cells expressing translocase-defective FANCM show altered global replication dynamics due to increased accumulation of stalled forks that subsequently degenerate into DNA double-strand breaks, leading to ATM activation, CTBP-interacting protein (CTIP)-dependent end resection and homologous recombination repair. Accordingly, abrogation of ATM or CTIP function in FANCM-deficient cells results in decreased cell survival. We also found that FANCM translocase activity protects cells from accumulating 53BP1-OPT domains, which mark lesions resulting from problems arising during replication. Taken together, these data show that FANCM plays an essential role in maintaining chromosomal integrity by promoting the recovery of stalled replication forks and hence preventing tumourigenesis.

Schwab RA, Niedzwiedz W. 2011. Visualization of DNA replication in the vertebrate model system DT40 using the DNA fiber technique. J Vis Exp, (56), pp. e3255. | Show Abstract | Read more

Maintenance of replication fork stability is of utmost importance for dividing cells to preserve viability and prevent disease. The processes involved not only ensure faithful genome duplication in the face of endogenous and exogenous DNA damage but also prevent genomic instability, a recognized causative factor in tumor development. Here, we describe a simple and cost-effective fluorescence microscopy-based method to visualize DNA replication in the avian B-cell line DT40. This cell line provides a powerful tool to investigate protein function in vivo by reverse genetics in vertebrate cells(1). DNA fiber fluorography in DT40 cells lacking a specific gene allows one to elucidate the function of this gene product in DNA replication and genome stability. Traditional methods to analyze replication fork dynamics in vertebrate cells rely on measuring the overall rate of DNA synthesis in a population of pulse-labeled cells. This is a quantitative approach and does not allow for qualitative analysis of parameters that influence DNA synthesis. In contrast, the rate of movement of active forks can be followed directly when using the DNA fiber technique(2-4). In this approach, nascent DNA is labeled in vivo by incorporation of halogenated nucleotides (Fig 1A). Subsequently, individual fibers are stretched onto a microscope slide, and the labeled DNA replication tracts are stained with specific antibodies and visualized by fluorescence microscopy (Fig 1B). Initiation of replication as well as fork directionality is determined by the consecutive use of two differently modified analogues. Furthermore, the dual-labeling approach allows for quantitative analysis of parameters that influence DNA synthesis during the S-phase, i.e. replication structures such as ongoing and stalled forks, replication origin density as well as fork terminations. Finally, the experimental procedure can be accomplished within a day, and requires only general laboratory equipment and a fluorescence microscope.

Blackford AN, Schwab RA, Niedzwiedz W. 2010. A novel ATRibute of FANCM. Cell Cycle, 9 (8), pp. 1453-1455. | Read more

Schwab RA, Blackford AN, Niedzwiedz W. 2010. ATR activation and replication fork restart are defective in FANCM-deficient cells. EMBO J, 29 (4), pp. 806-818. | Show Abstract | Read more

Fanconi anaemia is a chromosomal instability disorder associated with cancer predisposition and bone marrow failure. Among the 13 identified FA gene products only one, the DNA translocase FANCM, has homologues in lower organisms, suggesting a conserved function in DNA metabolism. However, a precise role for FANCM in DNA repair remains elusive. Here, we show a novel function for FANCM that is distinct from its role in the FA pathway: promoting replication fork restart and simultaneously limiting the accumulation of RPA-ssDNA. We show that in DT40 cells this process is controlled by ATR and PLK1, and that in the absence of FANCM, stalled replication forks are unable to resume DNA synthesis and genome duplication is ensured by excess origin firing. Unexpectedly, we also uncover an early role for FANCM in ATR-mediated checkpoint signalling by promoting chromatin retention of TopBP1. Failure to retain TopBP1 on chromatin impacts on the ability of ATR to phosphorylate downstream molecular targets, including Chk1 and SMC1. Our data therefore indicate a fundamental role for FANCM in the maintenance of genome integrity during S phase.

Blackford AN, Schwab RA, Niedzwiedz W. 2010. A novel ATRibute of FANCM Cell Cycle, 9 (8), pp. 1453-1455.

Cited:

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Schwab RA, Blackford AN, Niedzwiedz W. 2010. ATR activation and replication fork restart are defective in FANCM-deficient cells EMBO Journal, 29 (4), pp. 806-818. | Show Abstract | Read more

Fanconi anaemia is a chromosomal instability disorder associated with cancer predisposition and bone marrow failure. Among the 13 identified FA gene products only one, the DNA translocase FANCM, has homologues in lower organisms, suggesting a conserved function in DNA metabolism. However, a precise role for FANCM in DNA repair remains elusive. Here, we show a novel function for FANCM that is distinct from its role in the FA pathway: promoting replication fork restart and simultaneously limiting the accumulation of RPA-ssDNA. We show that in DT40 cells this process is controlled by ATR and PLK1, and that in the absence of FANCM, stalled replication forks are unable to resume DNA synthesis and genome duplication is ensured by excess origin firing. Unexpectedly, we also uncover an early role for FANCM in ATR-mediated checkpoint signalling by promoting chromatin retention of TopBP1. Failure to retain TopBP1 on chromatin impacts on the ability of ATR to phosphorylate downstream molecular targets, including Chk1 and SMC1. Our data therefore indicate a fundamental role for FANCM in the maintenance of genome integrity during S phase. © 2010 European Molecular Biology Organization.

Rosado IV, Niedzwiedz W, Alpi AF, Patel KJ. 2009. The Walker B motif in avian FANCM is required to limit sister chromatid exchanges but is dispensable for DNA crosslink repair. Nucleic Acids Res, 37 (13), pp. 4360-4370. | Show Abstract | Read more

FANCM, the most highly conserved component of the Fanconi Anaemia (FA) pathway can resolve recombination intermediates and remodel synthetic replication forks. However, it is not known if these activities are relevant to how this conserved protein activates the FA pathway and promotes DNA crosslink repair. Here we use chicken DT40 cells to systematically dissect the function of the helicase and nuclease domains of FANCM. Our studies reveal that these domains contribute distinct roles in the tolerance of crosslinker, UV light and camptothecin-induced DNA damage. Although the complete helicase domain is critical for crosslink repair, a predicted inactivating mutation of the Walker B box domain has no impact on FA pathway associated functions. However, this mutation does result in elevated sister chromatid exchanges (SCE). Furthermore, our genetic dissection indicates that FANCM functions with the Blm helicase to suppress spontaneous SCE events. Overall our results lead us to reappraise the role of helicase domain associated activities of FANCM with respect to the activation of the FA pathway, crosslink repair and in the resolution of recombination intermediates.

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Rosado IV, Niedzwiedz W, Alpi AF, Patel KJ. 2009. The Walker B motif in avian FANCM is required to limit sister chromatid exchanges but is dispensible for DNA crosslink repair Nucleic Acids Research, 37 (13), pp. 4360-4370. | Show Abstract | Read more

FANCM, the most highly conserved component of the Fanconi Anaemia (FA) pathway can resolve recombination intermediates and remodel synthetic replication forks. However, it is not known if these activities are relevant to how this conserved protein activates the FA pathway and promotes DNA crosslink repair. Here we use chicken DT40 cells to systematically dissect the function of the helicase and nuclease domains of FANCM. Our studies reveal that these domains contribute distinct roles in the tolerance of crosslinker, UV light and camptothecininduced DNA damage. Although the complete helicase domain is critical for crosslink repair, a predicted inactivating mutation of the Walker B box domain has no impact on FA pathway associated functions. However, this mutation does result in elevated sister chromatid exchanges (SCE). Furthermore, our genetic dissection indicates that FANCM functions with the Blm helicase to suppress spontaneous SCE events. Overall our results lead us to reappraise the role of helicase domain associated activities of FANCM with respect to the activation of the FA pathway, crosslink repair and in the resolution of recombination intermediates.

Oestergaard VH, Langevin F, Kuiken HJ, Pace P, Niedzwiedz W, Simpson LJ, Ohzeki M, Takata M, Sale JE, Patel KJ. 2007. Deubiquitination of FANCD2 is required for DNA crosslink repair. Mol Cell, 28 (5), pp. 798-809. | Show Abstract | Read more

Monoubiquitination of FANCD2 and PCNA promotes DNA repair. It causes chromatin accumulation of FANCD2 and facilitates PCNA's recruitment of translesion polymerases to stalled replication. USP1, a protease that removes monoubiquitin from FANCD2 and PCNA, was thought to reverse the DNA damage response of these substrates. We disrupted USP1 in chicken cells to dissect its role in a stable genetic system. USP1 ablation increases FANCD2 and PCNA monoubiquitination but unexpectedly results in DNA crosslinker sensitivity. This defective DNA repair is associated with constitutively chromatin-bound, monoubiquitinated FANCD2. In contrast, persistent PCNA monoubiquitination has negligible impact on DNA repair or mutagenesis. USP1 was previously shown to autocleave after DNA damage. In DT40, USP1 autocleavage is not stimulated by DNA damage, and expressing a noncleavable mutant in the USP1 knockout strain partially rescues crosslinker sensitivity. We conclude that efficient DNA crosslink repair requires FANCD2 deubiquitination, whereas FANCD2 monoubiquitination is not dependent on USP1 autocleavage.

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Oestergaard VH, Langevin F, Kuiken HJ, Pace P, Niedzwiedz W, Simpson LJ, Ohzeki M, Takata M, Sale JE, Patel KJ. 2007. Deubiquitination of FANCD2 Is Required for DNA Crosslink Repair Molecular Cell, 28 (5), pp. 798-809. | Show Abstract | Read more

Monoubiquitination of FANCD2 and PCNA promotes DNA repair. It causes chromatin accumulation of FANCD2 and facilitates PCNA's recruitment of translesion polymerases to stalled replication. USP1, a protease that removes monoubiquitin from FANCD2 and PCNA, was thought to reverse the DNA damage response of these substrates. We disrupted USP1 in chicken cells to dissect its role in a stable genetic system. USP1 ablation increases FANCD2 and PCNA monoubiquitination but unexpectedly results in DNA crosslinker sensitivity. This defective DNA repair is associated with constitutively chromatin-bound, monoubiquitinated FANCD2. In contrast, persistent PCNA monoubiquitination has negligible impact on DNA repair or mutagenesis. USP1 was previously shown to autocleave after DNA damage. In DT40, USP1 autocleavage is not stimulated by DNA damage, and expressing a noncleavable mutant in the USP1 knockout strain partially rescues crosslinker sensitivity. We conclude that efficient DNA crosslink repair requires FANCD2 deubiquitination, whereas FANCD2 monoubiquitination is not dependent on USP1 autocleavage. © 2007 Elsevier Inc. All rights reserved.

Mosedale G, Niedzwiedz W, Alpi A, Perrina F, Pereira-Leal JB, Johnson M, Langevin F, Pace P, Patel KJ. 2005. The vertebrate Hef ortholog is a component of the Fanconi anemia tumor-suppressor pathway. Nat Struct Mol Biol, 12 (9), pp. 763-771. | Show Abstract | Read more

The helicase-associated endonuclease for fork-structured DNA (Hef) is an archaeabacterial protein that processes blocked replication forks. Here we have isolated the vertebrate Hef ortholog and investigated its molecular function. Disruption of this gene in chicken DT40 cells results in genomic instability and sensitivity to DNA cross-links. The similarity of this phenotype to that of cells lacking the Fanconi anemia-related (FA) tumor-suppressor genes led us to investigate whether Hef functions in this pathway. Indeed, we found a genetic interaction between the FANCC and Hef genes. In addition, Hef is a component of the FA nuclear protein complex that facilitates its DNA damage-inducible chromatin localization and the monoubiquitination of the FA protein FANCD2. Notably, Hef interacts directly with DNA structures that are intermediates in DNA replication. This discovery sheds light on the origins, regulation and molecular function of the FA tumor-suppressor pathway in the maintenance of genome stability.

Niedzwiedz W, Patel KJ. 2005. "Dub"bing a tumor suppressor pathway. Cancer Cell, 7 (2), pp. 114-115. | Show Abstract | Read more

The autosomal recessive disease Fanconi anemia (FA) causes bone marrow failure and a hugely increased propensity to develop cancer. Cells from FA patients are prone to chromosome breakage, indicating that FA gene products are required to ensure genomic integrity. Most of the identified FA proteins are components of a nuclear complex whose principal function is to activate FANCD2 by monoubiquitination. Monoubiquitinated FANCD2 accumulates at sites of genome damage, where it probably functions to facilitate DNA repair. A recent paper in Molecular Cell (Nijmanet al., 2005) reports the identification of an enzyme that is responsible for regulating the FA pathway by deactivating FANCD2.

Niedzwiedz W, Patel KJ. 2005. "Dub"bing a tumor suppressor pathway Cancer Cell, 7 (2), pp. 114-115. | Show Abstract | Read more

The autosomal recessive disease Fanconi anemia (FA) causes bone marrow failure and a hugely increased propensity to develop cancer. Cells from FA patients are prone to chromosome breakage, indicating that FA gene products are required to ensure genomic integrity. Most of the identified FA proteins are components of a nuclear complex whose principal function is to activate FANCD2 by monoubiquitination. Monoubiquitinated FANCD2 accumulates at sites of genome damage, where it probably functions to facilitate DNA repair. A recent paper in Molecular Cell (Nijman et al., 2005) reports the identification of an enzyme that is responsible for regulating the FA pathway by deactivating FANCD2.

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145

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Mosedale G, Niedzwiedz W, Alpi A, Perrina F, Pereira-Leal JB, Johnson M, Langevin F, Pace P, Patel KJ. 2005. The vertebrate Hef ortholog is a component of the Fanconi anemia tumor-suppressor pathway Nature Structural and Molecular Biology, 12 (9), pp. 763-771. | Show Abstract | Read more

The helicase-associated endonuclease for fork-structured DNA (Hef) is an archaeabacterial protein that processes blocked replication forks. Here we have isolated the vertebrate Hef ortholog and investigated its molecular function. Disruption of this gene in chicken DT40 cells results in genomic instability and sensitivity to DNA cross-links. The similarity of this phenotype to that of cells lacking the Fanconi anemia-related (FA) tumor-suppressor genes led us to investigate whether Hef functions in this pathway. Indeed, we found a genetic interaction between the FANCC and Hef genes. In addition, Hef is a component of the FA nuclear protein complex that facilitates its DNA damage-inducible chromatin localization and the monoubiquitination of the FA protein FANCD2. Notably, Hef interacts directly with DNA structures that are intermediates in DNA replication. This discovery sheds light on the origins, regulation and molecular function of the FA tumor-suppressor pathway in the maintenance of genome stability. © 2005 Nature Publishing Group.

Niedzwiedz W, Mosedale G, Johnson M, Ong CY, Pace P, Patel KJ. 2004. The Fanconi anaemia gene FANCC promotes homologous recombination and error-prone DNA repair. Mol Cell, 15 (4), pp. 607-620. | Show Abstract | Read more

The Fanconi anemia (FA) protein FANCC is essential for chromosome stability in vertebrate cells, a feature underscored by the extreme sensitivity of FANCC-deficient cells to agents that crosslink DNA. However, it is not known how this FA protein facilitates the repair of both endogenously acquired and mutagen-induced DNA damage. Here, we use the model vertebrate cell line DT40 to address this question. We discover that apart from functioning in homologous recombination, FANCC also promotes the mutational repair of endogenously generated abasic sites. Moreover in these vertebrate cells, the efficient repair of crosslinks requires the combined functions of FANCC, translesion synthesis, and homologous recombination. These studies reveal that the FA proteins cooperate with key mutagenesis and repair processes that enable replication of damaged DNA.

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Scopus

Niedzwiedz W, Mosedale G, Johnson M, Ong CY, Pace P, Patel KJ. 2004. The Fanconi anaemia gene FANCC promotes homologous recombination and error-prone DNA repair Molecular Cell, 15 (4), pp. 607-620. | Show Abstract | Read more

The Fanconi anemia (FA) protein FANCC is essential for chromosome stability in vertebrate cells, a feature underscored by the extreme sensitivity of FANCC-deficient cells to agents that crosslink DNA. However, it is not known how this FA protein facilitates the repair of both endogenously acquired and mutagen-induced DNA damage. Here, we use the model vertebrate cell line DT40 to address this question. We discover that apart from functioning in homologous recombination, FANCC also promotes the mutational repair of endogenously generated abasic sites. Moreover in these vertebrate cells, the efficient repair of crosslinks requires the combined functions of FANCC, translesion synthesis, and homologous recombination. These studies reveal that the FA proteins cooperate with key mutagenesis and repair processes that enable replication of damaged DNA.

Nieminuszczy J, Broderick R, Niedzwiedz W. 2016. EXD2 - a new player joins the DSB resection team. Cell Cycle, 15 (12), pp. 1519-1520. | Read more

Fenwick AL, Kliszczak M, Cooper F, Murray J, Sanchez-Pulido L, Twigg SR, Goriely A, McGowan SJ, Miller KA, Taylor IB et al. 2016. Mutations in CDC45, Encoding an Essential Component of the Pre-initiation Complex, Cause Meier-Gorlin Syndrome and Craniosynostosis. Am J Hum Genet, 99 (1), pp. 125-138. | Show Abstract | Read more

DNA replication precisely duplicates the genome to ensure stable inheritance of genetic information. Impaired licensing of origins of replication during the G1 phase of the cell cycle has been implicated in Meier-Gorlin syndrome (MGS), a disorder defined by the triad of short stature, microtia, and a/hypoplastic patellae. Biallelic partial loss-of-function mutations in multiple components of the pre-replication complex (preRC; ORC1, ORC4, ORC6, CDT1, or CDC6) as well as de novo stabilizing mutations in the licensing inhibitor, GMNN, cause MGS. Here we report the identification of mutations in CDC45 in 15 affected individuals from 12 families with MGS and/or craniosynostosis. CDC45 encodes a component of both the pre-initiation (preIC) and CMG helicase complexes, required for initiation of DNA replication origin firing and ongoing DNA synthesis during S-phase itself, respectively, and hence is functionally distinct from previously identified MGS-associated genes. The phenotypes of affected individuals range from syndromic coronal craniosynostosis to severe growth restriction, fulfilling diagnostic criteria for Meier-Gorlin syndrome. All mutations identified were biallelic and included synonymous mutations altering splicing of physiological CDC45 transcripts, as well as amino acid substitutions expected to result in partial loss of function. Functionally, mutations reduce levels of full-length transcripts and protein in subject cells, consistent with partial loss of CDC45 function and a predicted limited rate of DNA replication and cell proliferation. Our findings therefore implicate the preIC as an additional protein complex involved in the etiology of MGS and connect the core cellular machinery of genome replication with growth, chondrogenesis, and cranial suture homeostasis.

Nieminuszczy J, Schwab RA, Niedzwiedz W. 2016. The DNA fibre technique - tracking helicases at work. Methods, 108 pp. 92-98. | Show Abstract | Read more

Faithful duplication of genetic material during every cell division is essential to ensure accurate transmission of genetic information to daughter cells. DNA helicases play a crucial role in promoting this process by facilitating almost all transactions occurring on DNA, including DNA replication and repair. They are responsible not only for DNA double helix unwinding ahead of progressing replication forks but also for resolution of secondary structures like G4 quadruplexes, HJ branch migration, double HJ dissolution, protein displacement, strand annealing and many more. Their importance in maintaining genome stability is underscored by the fact that many human disorders, including cancer, are associated with mutations in helicase genes. Here we outline how DNA fibre fluorography, a straightforward and inexpensive approach, can be employed to study the in vivo function of helicases in DNA replication and the maintenance of genome stability at a single molecule level. This approach directly visualizes the progression of individual replication forks within living cells and hence provides quantitative information on various aspects of DNA synthesis, such as replication fork processivity (replication speed), fork stalling, origin usage and fork termination.

Broderick R, Nieminuszczy J, Baddock HT, Deshpande R, Gileadi O, Paull TT, McHugh PJ, Niedzwiedz W. 2016. EXD2 promotes homologous recombination by facilitating DNA end resection. Nat Cell Biol, 18 (3), pp. 271-280. | Show Abstract | Read more

Repair of DNA double-strand breaks (DSBs) by homologous recombination (HR) is critical for survival and genome stability of individual cells and organisms, but also contributes to the genetic diversity of species. A vital step in HR is MRN-CtIP-dependent end resection, which generates the 3' single-stranded DNA overhangs required for the subsequent strand exchange reaction. Here, we identify EXD2 (also known as EXDL2) as an exonuclease essential for DSB resection and efficient HR. EXD2 is recruited to chromatin in a damage-dependent manner and confers resistance to DSB-inducing agents. EXD2 functionally interacts with the MRN complex to accelerate resection through its 3'-5' exonuclease activity, which efficiently processes double-stranded DNA substrates containing nicks. Finally, we establish that EXD2 stimulates both short- and long-range DSB resection, and thus, together with MRE11, is required for efficient HR. This establishes a key role for EXD2 in controlling the initial steps of chromosomal break repair.

Schwab RA, Nieminuszczy J, Shah F, Langton J, Lopez Martinez D, Liang CC, Cohn MA, Gibbons RJ, Deans AJ, Niedzwiedz W. 2015. The Fanconi Anemia Pathway Maintains Genome Stability by Coordinating Replication and Transcription. Mol Cell, 60 (3), pp. 351-361. | Show Abstract | Read more

DNA replication stress can cause chromosomal instability and tumor progression. One key pathway that counteracts replication stress and promotes faithful DNA replication consists of the Fanconi anemia (FA) proteins. However, how these proteins limit replication stress remains largely elusive. Here we show that conflicts between replication and transcription activate the FA pathway. Inhibition of transcription or enzymatic degradation of transcription-associated R-loops (DNA:RNA hybrids) suppresses replication fork arrest and DNA damage occurring in the absence of a functional FA pathway. Furthermore, we show that simple aldehydes, known to cause leukemia in FA-deficient mice, induce DNA:RNA hybrids in FA-depleted cells. Finally, we demonstrate that the molecular mechanism by which the FA pathway limits R-loop accumulation requires FANCM translocase activity. Failure to activate a response to physiologically occurring DNA:RNA hybrids may critically contribute to the heightened cancer predisposition and bone marrow failure of individuals with mutated FA proteins.

Broderick R, Niedzwiedz W. 2015. Sister chromatid decatenation: bridging the gaps in our knowledge. Cell Cycle, 14 (19), pp. 3040-3044. | Show Abstract | Read more

Faithful chromosome segregation is critical in preventing genome loss or damage during cell division. Failure to properly disentangle catenated sister chromatids can lead to the formation of bulky or ultrafine anaphase bridges, and ultimately genome instability. In this review we present an overview of the current state of knowledge of how sister chromatid decatenation is carried out, with particular focus on the role of TOP2A and TOPBP1 in this process.

Broderick R, Nieminuszczy J, Blackford AN, Winczura A, Niedzwiedz W. 2015. TOPBP1 recruits TOP2A to ultra-fine anaphase bridges to aid in their resolution. Nat Commun, 6 pp. 6572. | Show Abstract | Read more

During mitosis, sister chromatids must be faithfully segregated to ensure that daughter cells receive one copy of each chromosome. However, following replication they often remain entangled. Topoisomerase IIα (TOP2A) has been proposed to resolve such entanglements, but the mechanisms governing TOP2A recruitment to these structures remain poorly understood. Here, we identify TOPBP1 as a novel interactor of TOP2A, and reveal that it is required for TOP2A recruitment to ultra-fine anaphase bridges (UFBs) in mitosis. The C-terminal region of TOPBP1 interacts with TOP2A, and TOPBP1 recruitment to UFBs requires its BRCT domain 5. Depletion of TOPBP1 leads to accumulation of UFBs, the majority of which arise from centromeric loci. Accordingly, expression of a TOPBP1 mutant that is defective in TOP2A binding phenocopies TOP2A depletion. These findings provide new mechanistic insights into how TOP2A promotes resolution of UFBs during mitosis, and highlights a pivotal role for TOPBP1 in this process.

Blackford AN, Nieminuszczy J, Schwab RA, Galanty Y, Jackson SP, Niedzwiedz W. 2015. TopBP1 interacts with BLM to maintain genome stability but is dispensable for preventing BLM degradation. Mol Cell, 57 (6), pp. 1133-1141. | Show Abstract | Read more

The Bloom syndrome helicase BLM and topoisomerase-IIβ-binding protein 1 (TopBP1) are key regulators of genome stability. It was recently proposed that BLM phosphorylation on Ser338 mediates its interaction with TopBP1, to protect BLM from ubiquitylation and degradation (Wang et al., 2013). Here, we show that the BLM-TopBP1 interaction does not involve Ser338 but instead requires BLM phosphorylation on Ser304. Furthermore, we establish that disrupting this interaction does not markedly affect BLM stability. However, BLM-TopBP1 binding is important for maintaining genome integrity, because in its absence cells display increased sister chromatid exchanges, replication origin firing and chromosomal aberrations. Therefore, the BLM-TopBP1 interaction maintains genome stability not by controlling BLM protein levels, but via another as-yet undetermined mechanism. Finally, we identify critical residues that mediate interactions between TopBP1 and MDC1, and between BLM and TOP3A/RMI1/RMI2. Taken together, our findings provide molecular insights into a key tumor suppressor and genome stability network.

Higgs MR, Reynolds JJ, Winczura A, Blackford AN, Borel V, Miller ES, Zlatanou A, Nieminuszczy J, Ryan EL, Davies NJ et al. 2015. BOD1L Is Required to Suppress Deleterious Resection of Stressed Replication Forks. Mol Cell, 59 (3), pp. 462-477. | Show Abstract | Read more

Recognition and repair of damaged replication forks are essential to maintain genome stability and are coordinated by the combined action of the Fanconi anemia and homologous recombination pathways. These pathways are vital to protect stalled replication forks from uncontrolled nucleolytic activity, which otherwise causes irreparable genomic damage. Here, we identify BOD1L as a component of this fork protection pathway, which safeguards genome stability after replication stress. Loss of BOD1L confers exquisite cellular sensitivity to replication stress and uncontrolled resection of damaged replication forks, due to a failure to stabilize RAD51 at these forks. Blocking DNA2-dependent resection, or downregulation of the helicases BLM and FBH1, suppresses both catastrophic fork processing and the accumulation of chromosomal damage in BOD1L-deficient cells. Thus, our work implicates BOD1L as a critical regulator of genome integrity that restrains nucleolytic degradation of damaged replication forks.

Yata K, Bleuyard JY, Nakato R, Ralf C, Katou Y, Schwab RA, Niedzwiedz W, Shirahige K, Esashi F. 2014. BRCA2 coordinates the activities of cell-cycle kinases to promote genome stability. Cell Rep, 7 (5), pp. 1547-1559. | Show Abstract | Read more

Numerous human genome instability syndromes, including cancer, are closely associated with events arising from malfunction of the essential recombinase Rad51. However, little is known about how Rad51 is dynamically regulated in human cells. Here, we show that the breast cancer susceptibility protein BRCA2, a key Rad51 binding partner, coordinates the activity of the central cell-cycle drivers CDKs and Plk1 to promote Rad51-mediated genome stability control. The soluble nuclear fraction of BRCA2 binds Plk1 directly in a cell-cycle- and CDK-dependent manner and acts as a molecular platform to facilitate Plk1-mediated Rad51 phosphorylation. This phosphorylation is important for enhancing the association of Rad51 with stressed replication forks, which in turn protects the genomic integrity of proliferating human cells. This study reveals an elaborate but highly organized molecular interplay between Rad51 regulators and has significant implications for understanding tumorigenesis and therapeutic resistance in patients with BRCA2 deficiency.

Schwab RA, Nieminuszczy J, Shin-ya K, Niedzwiedz W. 2013. FANCJ couples replication past natural fork barriers with maintenance of chromatin structure. J Cell Biol, 201 (1), pp. 33-48. | Show Abstract | Read more

Defective DNA repair causes Fanconi anemia (FA), a rare childhood cancer-predisposing syndrome. At least 15 genes are known to be mutated in FA; however, their role in DNA repair remains unclear. Here, we show that the FANCJ helicase promotes DNA replication in trans by counteracting fork stalling on replication barriers, such as G4 quadruplex structures. Accordingly, stabilization of G4 quadruplexes in ΔFANCJ cells restricts fork movements, uncouples leading- and lagging-strand synthesis and generates small single-stranded DNA gaps behind the fork. Unexpectedly, we also discovered that FANCJ suppresses heterochromatin spreading by coupling fork movement through replication barriers with maintenance of chromatin structure. We propose that FANCJ plays an essential role in counteracting chromatin compaction associated with unscheduled replication fork stalling and restart, and suppresses tumorigenesis, at least partially, in this replication-specific manner.

Blackford AN, Schwab RA, Nieminuszczy J, Deans AJ, West SC, Niedzwiedz W. 2012. The DNA translocase activity of FANCM protects stalled replication forks. Hum Mol Genet, 21 (9), pp. 2005-2016. | Show Abstract | Read more

FANCM is the most highly conserved protein within the Fanconi anaemia (FA) tumour suppressor pathway. However, although FANCM contains a helicase domain with translocase activity, this is not required for its role in activating the FA pathway. Instead, we show here that FANCM translocaseactivity is essential for promoting replication fork stability. We demonstrate that cells expressing translocase-defective FANCM show altered global replication dynamics due to increased accumulation of stalled forks that subsequently degenerate into DNA double-strand breaks, leading to ATM activation, CTBP-interacting protein (CTIP)-dependent end resection and homologous recombination repair. Accordingly, abrogation of ATM or CTIP function in FANCM-deficient cells results in decreased cell survival. We also found that FANCM translocase activity protects cells from accumulating 53BP1-OPT domains, which mark lesions resulting from problems arising during replication. Taken together, these data show that FANCM plays an essential role in maintaining chromosomal integrity by promoting the recovery of stalled replication forks and hence preventing tumourigenesis.

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