Homology-directed Fanconi anemia pathway cross-link repair is dependent on DNA replication (original) (raw)
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Human Fanconi anemia monoubiquitination pathway promotes homologous DNA repair
Proceedings of The National Academy of Sciences, 2005
Fanconi anemia (FA) is a recessive disorder characterized by congenital abnormalities, progressive bone-marrow failure, and cancer susceptibility. Cells from FA patients are hypersensitive to agents that produce DNA crosslinks and, after treatment with these agents, have pronounced chromosome breakage and other cytogenetic abnormalities. Eight FANC genes have been cloned, and the encoded proteins interact in a common cellular pathway. DNA-damaging agents activate the monoubiquitination of FANCD2, resulting in its targeting to nuclear foci that also contain BRCA1 and BRCA2͞FANCD1, proteins involved in homologydirected DNA repair. Given the interaction of the FANC proteins with BRCA1 and BRCA2, we tested whether cells from FA patients (groups A, G, and D2) and mouse Fanca ؊/؊ cells with a targeted mutation are impaired for this repair pathway. We find that both the upstream (FANCA and FANCG) and downstream (FANCD2) FA pathway components promote homology-directed repair of chromosomal double-strand breaks (DSBs). The FANCD2 monoubiquitination site is critical for normal levels of repair, whereas the ATM phosphorylation site is not. The defect in these cells, however, is mild, differentiating them from BRCA1 and BRCA2 mutant cells. Surprisingly, we provide evidence that these proteins, like BRCA1 but unlike BRCA2, promote a second DSB repair pathway involving homology, i.e., single-strand annealing. These results suggest an early role for the FANC proteins in homologous DSB repair pathway choice.
The Fanconi anemia pathway and the DNA interstrand cross-links repair
Biochimie, 2003
Fanconi anemia (FA) is a genetic cancer-predisposition syndrome characterized by bone marrow failure and cellular and chromosomal hypersensitivity to DNA cross-linking agents. Seven FA genes have been isolated and their products associate to form a pathway that interacts functionally or physically with several DNA-damage response proteins involved in cell cycle checkpoints and/or DNA repair. These proteins include BLM, ATM, BRCA1, XPF and the MRE11/RAD50/NBS1 complex. In spite of several recent striking progresses in the biochemistry and the molecular biology of the disorder, the precise function(s) of the FA proteins remain(s) poorly determined. However, several recent data indicate that the FA pathway could be involved in the coordination of both cell cycle checkpoints and DNA repair.
Fanconi anemia proteins, DNA interstrand crosslink repair pathways, and cancer therapy
Current Cancer Drug Targets, 2009
DNA interstrand crosslinkers, a chemically diverse group of compounds which also induce alkylation of bases and DNA intrastrand crosslinks, are extensively utilized for cancer therapy. Understanding the cellular response to DNA damage induced by these agents is critical for more effective utilization of these compounds and for the identification of novel therapeutic targets. Importantly, the repair of DNA interstrand crosslinks (ICLs) involves many distinct DNA repair pathways, including nucleotide excision repair, translesion synthesis (TLS), and homologous recombination (HR). Additionally, proteins implicated in the pathophysiology of the multigenic disease Fanconi anemia (FA) have a role in the repair of ICLs that is not well understood. Cells from FA patients are hypersensitive to agents that induce ICLs, therefore FA proteins are potentially novel therapeutic targets. Here we will review current research directed at identifying FA genes and understanding the function of FA proteins in DNA damage responses. We will also examine interactions of FA proteins with other repair proteins and pathways, including signaling networks, which are potentially involved in ICL repair. Potential approaches to the modulation of FA protein function to enhance therapeutic outcome will be discussed. Also, mutation of many genes that encode proteins involved in ICL repair, including FA genes, increases susceptibility to cancer. A better understanding of these pathways is therefore critical for the design of individualized therapies tailored to the genetic profile of a particular malignancy. For this purpose, we will also review evidence for the association of mutation of FA genes with cancer in non-FA patients.
Molecular and cellular biology, 2005
Recent studies show overlap between Fanconi anemia (FA) proteins and those involved in DNA repair mediated by homologous recombination (HR). However, the mechanism by which FA proteins affect HR is unclear. FA proteins (FancA/C/E/F/G/L) form a multiprotein complex, which is responsible for DNA damage-induced FancD2 monoubiquitination, a key event for cellular resistance to DNA damage. Here, we show that FANCD2-disrupted DT40 chicken B-cell line is defective in HR-mediated DNA double-strand break (DSB) repair, as well as gene conversion at the immunoglobulin light-chain locus, an event also mediated by HR. Gene conversions occurring in mutant cells were associated with decreased nontemplated mutations. In contrast to these defects, we also found increased spontaneous sister chromatid exchange (SCE) and intact Rad51 foci formation after DNA damage. Thus, we propose that FancD2 promotes a subpathway of HR that normally mediates gene conversion by a mechanism that avoids crossing over a...
The Fanconi anaemia pathway orchestrates incisions at sites of crosslinked DNA
The Journal of Pathology, 2011
Fanconi anaemia (FA) is a rare, autosomal recessive, genetically complex, DNA repair deficiency syndrome in man. Patients with FA exhibit a heterogeneous spectrum of clinical features. The most significant and consistent phenotypic characteristics are stem cell loss, causing progressive bone marrow failure and sterility, diverse developmental abnormalities and a profound predisposition to neoplasia. To date, 15 genes have been indentified, biallelic disruption of any one of which results in this clinically defined syndrome. It is now apparent that all 15 gene products act in a common process to maintain genome stability. At the molecular level, a fundamental defect in DNA repair underlies this complex phenotype. Cells derived from FA patients spontaneously accumulate broken chromosomes and exhibit a marked sensitivity to DNA-damaging chemotherapeutic agents. Despite complementation analysis defining many components of the FA DNA repair pathway, no direct link to DNA metabolism was established until recently. First, it is now evident that the FA pathway is required to make incisions at the site of damaged DNA. Second, a specific component of the FA pathway has been identified that regulates nucleases previously implicated in DNA interstrand crosslink repair. Taken together, these data provide genetic and biochemical evidence that the FA pathway is a bona fide DNA repair pathway that directly mediates DNA repair transactions, thereby elucidating the specific molecular defect in human Fanconi anaemia.
How Fanconi anemia proteins promote the four Rs: Replication, recombination, repair, and recovery
Environmental and Molecular Mutagenesis, 2005
The genetically complex disease Fanconi anemia (FA) comprises cancer predisposition, developmental defects, and bone marrow failure due to elevated apoptosis. The FA cellular phenotype includes universal sensitivity to DNA crosslinking damage, symptoms of oxidative stress, and reduced mutability at the X-linked HPRT gene. In this review article, we present a new heuristic molecular model that accommodates these varied features of FA cells. In our view, the FANCA, -C, and -G proteins, which are both cytoplasmic and nuclear, have an integrated dual role in which they sense and convey information about cytoplasmic oxidative stress to the nucleus, where they participate in the further assembly and functionality of the nuclear core complex (NCC FA ¼ FANCA/B/C/E/F/G/L). In turn, NCC FA facilitates DNA replication at sites of base damage and strand breaks by performing the critical monoubiquitination of FANCD2, an event that somehow helps stabilize blocked and broken replication forks. This stabilization facilitates two kinds of processes: translesion synthesis at sites of blocking lesions (e.g., oxidative base damage), which produces point mutations by error-prone polymerases, and homologous recombination-mediated restart of broken forks, which arise spontaneously and when crosslinks are unhooked by the ERCC1-XPF endonuclease. In the absence of the critical FANCD2 monoubiquitination step, broken replication forks further lose chromatid continuity by collapsing into a configuration that is more difficult to restart through recombination and prone to aberrant repair through nonhomologous end joining. Thus, the FA regulatory pathway promotes chromosome integrity by monitoring oxidative stress and coping efficiently with the accompanying oxidative DNA damage during DNA replication. Environ. Mol. Mutagen. 45:128-142, 2005. Published 2005 Wiley-Liss, Inc.