The Fanconi anaemia group G gene FANCG is identical with XRCC9

Oligogenic basis of premature ovarian insufficiency: an observational study

BACKGROUND

The etiology of premature ovarian insufficiency, that is, the loss of ovarian activity before 40 years of age, is complex. Studies suggest that genetic factors are involved in 20-25% of cases. The aim of this study was to explore the oligogenic basis of premature ovarian insufficiency.

RESULTS

Whole-exome sequencing of 93 patients with POI and whole-genome sequencing of 465 controls were performed. In the gene-burden analysis, multiple genetic variants, including those associated with DNA damage repair and meiosis, were more common in participants with premature ovarian insufficiency than in controls. The ORVAL-platform analysis confirmed the pathogenicity of the RAD52 and MSH6 combination.

CONCLUSIONS

The results of this study indicate that oligogenic inheritance is an important cause of premature ovarian insufficiency and provide insights into the biological mechanisms underlying premature ovarian insufficiency.

NTHL1 is a recessive cancer susceptibility gene

In search of novel breast cancer (BC) risk variants, we performed a whole-exome sequencing and variant analysis of 69 Finnish BC patients as well as analysed loss-of-function variants identified in DNA repair genes in the Finns from the Genome Aggregation Database. Additionally, we carried out a validation study of SERPINA3 c.918-1G>C, recently suggested for BC predisposition. We estimated the frequencies of 41 rare candidate variants in 38 genes by genotyping them in 2482-4101 BC patients and in 1273-3985 controls. We further evaluated all coding variants in the candidate genes in a dataset of 18,786 BC patients and 182,927 controls from FinnGen. None of the variants associated significantly with cancer risk in the primary BC series; however, in the FinnGen data, NTHL1 c.244C>T p.(Gln82Ter) associated with BC with a high risk for homozygous (OR = 44.7 [95% CI 6.90-290], P = 6.7 × 10-5) and a low risk for heterozygous women (OR = 1.39 [1.18-1.64], P = 7.8 × 10-5). Furthermore, the results suggested a high risk of colorectal, urinary tract, and basal-cell skin cancer for homozygous individuals, supporting NTHL1 as a recessive multi-tumour susceptibility gene. No significant association with BC risk was detected for SERPINA3 or any other evaluated gene.

A C57BL/6J Fancg-KO Mouse Model Generated by CRISPR/Cas9 Partially Captures the Human Phenotype

Fanconi anemia (FA) develops due to a mutation in one of the FANC genes that are involved in the repair of interstrand crosslinks (ICLs). FANCG, a member of the FA core complex, is essential for ICL repair. Previous FANCG-deficient mouse models were generated with drug-based selection cassettes in mixed mice backgrounds, leading to a disparity in the interpretation of genotype-related phenotype. We created a Fancg-KO (KO) mouse model using CRISPR/Cas9 to exclude these confounders. The entire Fancg locus was targeted and maintained on the immunological well-characterized C57BL/6J background. The intercrossing of heterozygous mice resulted in sub-Mendelian numbers of homozygous mice, suggesting the loss of FANCG can be embryonically lethal. KO mice displayed infertility and hypogonadism, but no other developmental problems. Bone marrow analysis revealed a defect in various hematopoietic stem and progenitor subsets with a bias towards myelopoiesis. Cell lines derived from Fancg-KO mice were hypersensitive to the crosslinking agents cisplatin and Mitomycin C, and Fancg-KO mouse embryonic fibroblasts (MEFs) displayed increased γ-H2AX upon cisplatin treatment. The reconstitution of these MEFs with Fancg cDNA corrected for the ICL hypersensitivity. This project provides a new, genetically, and immunologically well-defined Fancg-KO mouse model for further in vivo and in vitro studies on FANCG and ICL repair.

Inherited bone marrow failure in the pediatric patient

Inherited bone marrow (BM) failure syndromes are a diverse group of disorders characterized by BM failure, usually in association with ≥1 extrahematopoietic abnormalities. BM failure, which can involve ≥1 cell lineages, often presents in the pediatric age group. Furthermore, some children initially labeled as having idiopathic aplastic anemia or myelodysplasia represent cryptic cases of inherited BM failure. Significant advances in the genetics of these syndromes have been made, identifying more than 100 disease genes, giving insights into normal hematopoiesis and how it is disrupted in patients with BM failure. They have also provided important information on fundamental biological pathways, including DNA repair: Fanconi anemia (FA) genes; telomere maintenance: dyskeratosis congenita (DC) genes; and ribosome biogenesis: Shwachman-Diamond syndrome and Diamond-Blackfan anemia genes. In addition, because these disorders are usually associated with extrahematopoietic abnormalities and increased risk of cancer, they have provided insights into human development and cancer. In the clinic, genetic tests stemming from the recent advances facilitate diagnosis, especially when clinical features are insufficient to accurately classify a disorder. Hematopoietic stem cell transplantation using fludarabine-based protocols has significantly improved outcomes, particularly in patients with FA or DC. Management of some other complications, such as cancer, remains a challenge. Recent studies have suggested the possibility of new and potentially more efficacious therapies, including a renewed focus on hematopoietic gene therapy and drugs [transforming growth factor-β inhibitors for FA and PAPD5, a human poly(A) polymerase, inhibitors for DC] that target disease-specific defects.

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.

A never-ending story: the steadily growing family of the FA and FA-like genes

Among the chromosome fragility-associated human syndromes that present cancer predisposition, Fanconi anemia (FA) is unique due to its large genetic heterogeneity. To date, mutations in 21 genes have been associated with an FA or an FA-like clinical and cellular phenotype, whose hallmarks are bone marrow failure, predisposition to acute myeloid leukemia and a cellular and chromosomal hypersensitivity to DNA crosslinking agents exposure. The goal of this review is to trace the history of the identification of FA genes, a history that started in the eighties and is not yet over, as indicated by the cloning of a twenty-first FA gene in 2016.

Loss of heterozygosity in FANCG, FANCF and BRIP1 from head and neck squamous cell carcinoma of the oral cavity

Recent advances have been made in the understanding of Fanconi anemia (FA), a hereditary disease that increases the risk for head and neck squamous cell carcinomas (HNSCC) by 500- to 700-fold. FA patients harbour germline mutations in genes of cellular DNA repair pathways that are assumed to facilitate the accumulation of mutations during HNSCC development. Mutations in these FA genes may also contribute to HNSCC in general. In the present study, we analysed three FA genes; FANCF, FANCG and BRIP1, that are involved in the repair of DNA inter strand cross-links, in HNSCC and their potential role for patient survival. We measured loss of heterozygosity (LOH) mutations at eight microsatellite loci flanking three FA genes in 54 HNSCC of the oral cavity and corresponding blood samples. Survival analyses were carried out using mutational data and clinical variables. LOH was present in 17% (FANCF region), 41% (FANCG region) and 11% (BRIP1 region) of the patients. Kaplan-Meier survival curves and log-rank tests indicated strong clinical predictors (lymph node stages with decreased survival: p=2.69e-12; surgery with improved survival: p=0.0005). LOH in the FANCF region showed a weaker association with decreased overall survival (p=0.006), which however, did not hold in multivariate analyses. LOH may predominantly indicate copy number gains in FANCF and losses in FANCG and BRIP1. Integration of copy number data and gene expression proved difficult as the available sample sets did not overlap. In conclusion, LOH in FA genes appears to be a common feature of HNSCC development seen here in 57% of patients and other mutation types may increase this mutation frequency. We suggest larger patient cohorts would be needed to test the observed association of LOH in FANCF and patient survival comprehensively.

Characterization of two novel FANCG mutations in Indian Fanconi anemia patients

FA is a rare recessive genetic disorder with autosomal or X-linked mode of inheritance and is associated with 19 different FA complementation groups. We have studied three patients clinically diagnosed as FA. All three patients showed a high frequency chromosomal breakage in MMC induced blood cultures and FANCD2 non-monoubiquitination by western blotting. The molecular analysis using direct sequencing revealed two novel mutations in FANCG; 2 novel mutations c.1143+5G>C and c.883dupG, and a reported mutation c.1471_1473delAAAinsG. We have for the first time modeled FANCG protein with fold based template search using pGenthreader which revealed sequence fold identical to super helical TPR domain of O linked GLCNAC transferase and have studied the impact of mutations on the function and structure of FANCG. All three mutations are potential pathogenic molecular changes which can affect FANCG interactions required for FA pathway, homologous recombination repairs and unhooking step of the ICL repair process.

Metformin improves defective hematopoiesis and delays tumor formation in Fanconi anemia mice

Fanconi anemia (FA) is an inherited bone marrow failure disorder associated with a high incidence of leukemia and solid tumors. Bone marrow transplantation is currently the only curative therapy for the hematopoietic complications of this disorder. However, long-term morbidity and mortality remain very high, and new therapeutics are badly needed. Here we show that the widely used diabetes drug metformin improves hematopoiesis and delays tumor formation in Fancd2^-/- mice. Metformin is the first compound reported to improve both of these FA phenotypes. Importantly, the beneficial effects are specific to FA mice and are not seen in the wild-type controls. In this preclinical model of FA, metformin outperformed the current standard of care, oxymetholone, by improving peripheral blood counts in Fancd2^-/- mice significantly faster. Metformin increased the size of the hematopoietic stem cell compartment and enhanced quiescence in hematopoietic stem and progenitor cells. In tumor-prone Fancd2^-/-Trp53^+/- mice, metformin delayed the onset of tumors and significantly extended the tumor-free survival time. In addition, we found that metformin and the structurally related compound aminoguanidine reduced DNA damage and ameliorated spontaneous chromosome breakage and radials in human FA patient-derived cells. Our results also indicate that aldehyde detoxification might be one of the mechanisms by which metformin reduces DNA damage in FA cells.

Recent discoveries in the molecular pathogenesis of the inherited bone marrow failure syndrome Fanconi anemia

Fanconi anemia (FA) is a rare autosomal and X-linked genetic disease characterized by congenital abnormalities, progressive bone marrow failure (BMF), and increased cancer risk during early adulthood. The median lifespan for FA patients is approximately 33years. The proteins encoded by the FA genes function together in the FA-BRCA pathway to repair DNA damage and to maintain genome stability. Within the past two years, five new FA genes have been identified-RAD51/FANCR, BRCA1/FANCS, UBE2T/FANCT, XRCC2/FANCU, and REV7/FANCV-bringing the total number of disease-causing genes to 21. This review summarizes the discovery of these new FA genes and describes how these proteins integrate into the FA-BRCA pathway to maintain genome stability and critically prevent early-onset BMF and cancer.

Mechanisms of interstrand DNA crosslink repair and human disorders

Interstrand DNA crosslinks (ICLs) are the link between Watson-Crick strands of DNAs with the covalent bond and prevent separation of DNA strands. Since the ICL lesion affects both strands of the DNA, the ICL repair is not simple. So far, nucleotide excision repair (NER), structure-specific endonucleases, translesion DNA synthesis (TLS), homologous recombination (HR), and factors responsible for Fanconi anemia (FA) are identified to be involved in ICL repair. Since the presence of ICL lesions causes severe defects in transcription and DNA replication, mutations in these DNA repair pathways give rise to a various hereditary disorders. NER plays an important role for the ICL recognition and removal in quiescent cells, and defects of NER causes congential progeria syndrome, such as xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy. On the other hand, the ICL repair in S phase requires more complicated orchestration of multiple factors, including structure-specific endonucleases, and TLS, and HR. Disturbed this ICL repair orchestration in S phase causes genome instability resulting a cancer prone disease, Fanconi anemia. So far more than 30 factors in ICL repair have already identified. Recently, a new factor, UHRF1, was discovered as a sensor of ICLs. In addition to this, numbers of nucleases that are involved in the first incision, also called unhooking, of ICL lesions have also been identified. Here we summarize the recent studies of ICL associated disorders and repair mechanism, with emphasis in the first incision of ICLs.

Update of the human and mouse Fanconi anemia genes

Fanconi anemia (FA) is a recessively inherited disease manifesting developmental abnormalities, bone marrow failure, and increased risk of malignancies. Whereas FA has been studied for nearly 90 years, only in the last 20 years have increasing numbers of genes been implicated in the pathogenesis associated with this genetic disease. To date, 19 genes have been identified that encode Fanconi anemia complementation group proteins, all of which are named or aliased, using the root symbol “FANC.” Fanconi anemia subtype (FANC) proteins function in a common DNA repair pathway called “the FA pathway,” which is essential for maintaining genomic integrity. The various FANC mutant proteins contribute to distinct steps associated with FA pathogenesis. Herein, we provide a review update of the 19 human FANC and their mouse orthologs, an evolutionary perspective on the FANC genes, and the functional significance of the FA DNA repair pathway in association with clinical disorders. This is an example of a set of genes––known to exist in vertebrates, invertebrates, plants, and yeast––that are grouped together on the basis of shared biochemical and physiological functions, rather than evolutionary phylogeny, and have been named on this basis by the HUGO Gene Nomenclature Committee (HGNC).

AluY-mediated germline deletion, duplication and somatic stem cell reversion in UBE2T defines a new subtype of Fanconi anemia

Fanconi anemia (FA) is a rare inherited disorder clinically characterized by congenital malformations, progressive bone marrow failure and cancer susceptibility. At the cellular level, FA is associated with hypersensitivity to DNA-crosslinking genotoxins. Eight of 17 known FA genes assemble the FA E3 ligase complex, which catalyzes monoubiquitination of FANCD2 and is essential for replicative DNA crosslink repair. Here, we identify the first FA patient with biallelic germline mutations in the ubiquitin E2 conjugase UBE2T. Both mutations were aluY-mediated: a paternal deletion and maternal duplication of exons 2-6. These loss-of-function mutations in UBE2T induced a cellular phenotype similar to biallelic defects in early FA genes with the absence of FANCD2 monoubiquitination. The maternal duplication produced a mutant mRNA that could encode a functional protein but was degraded by nonsense-mediated mRNA decay. In the patient's hematopoietic stem cells, the maternal allele with the duplication of exons 2-6 spontaneously reverted to a wild-type allele by monoallelic recombination at the duplicated aluY repeat, thereby preventing bone marrow failure. Analysis of germline DNA of 814 normal individuals and 850 breast cancer patients for deletion or duplication of UBE2T exons 2-6 identified the deletion in only two controls, suggesting aluY-mediated recombinations within the UBE2T locus are rare and not associated with an increased breast cancer risk. Finally, a loss-of-function germline mutation in UBE2T was detected in a high-risk breast cancer patient with wild-type BRCA1/2. Cumulatively, we identified UBE2T as a bona fide FA gene (FANCT) that also may be a rare cancer susceptibility gene.

Coregulation of FANCA and BRCA1 in human cells

Fanconi anemia (FA) is a genetically heterogeneous syndrome associated with increased cancer predisposition. The underlying genes govern the FA pathway which functions to protect the genome during the S-phase of the cell cycle. While upregulation of FA genes has been linked to chemotherapy resistance, little is known about their regulation in response to proliferative stimuli. The purpose of this study was to examine how FA genes are regulated, especially in relation to the cell cycle, in order to reveal their possible participation in biochemical networks. Expression of 14 FA genes was monitored in two human cell-cycle models and in two RB1/E2F pathway-associated primary cancers, retinoblastoma and basal breast cancer. In silico studies were performed to further evaluate coregulation and identify connected networks and diseases. Only FANCA was consistently induced over 2-fold; FANCF failed to exhibit any regulatory fluctuations. Two tools exploiting public data sets indicated coregulation of FANCA with BRCA1. Upregulation of FANCA and BRCA1 correlated with upregulation of E2F3. Genes coregulated with both FANCA and BRCA1 were enriched for MeSH-Term id(s) genomic instability, microcephaly, and Bloom syndrome, and enriched for the cellular component centrosome. The regulation of FA genes appears highly divergent. In RB1-linked tumors, upregulation of FA network genes was associated with reduced expression of FANCF. FANCA and BRCA1 may jointly act in a subnetwork - supporting vital function(s) at the subcellular level (centrosome) as well as at the level of embryonic development (mechanisms controlling head circumference).

PALB2: the hub of a network of tumor suppressors involved in DNA damage responses

PALB2 was first identified as a partner of BRCA2 that mediates its recruitment to sites of DNA damage. PALB2 was subsequently found as a tumor suppressor gene. Inherited heterozygosity for this gene is associated with an increased risk of cancer of the breast and other sites. Additionally, biallelic mutation of PALB2 is linked to Fanconi anemia, which also has an increased risk of developing malignant disease. Recent work has identified numerous interactions of PALB2, suggesting that it functions in a network of proteins encoded by tumor suppressors. Notably, many of these tumor suppressors are related to the cellular response to DNA damage. The recruitment of PALB2 to DNA double-strand breaks at the head of this network is via a ubiquitin-dependent signaling pathway that involves the RAP80, Abraxas and BRCA1 tumor suppressors. Next, PALB2 interacts with BRCA2, which is a tumor suppressor, and with the RAD51 recombinase. These interactions promote DNA repair by homologous recombination (HR). More recently, PALB2 has been found to bind the RAD51 paralog, RAD51C, as well as the translesion polymerase pol η, both of which are tumor suppressors with functions in HR. Further, an interaction with MRG15, which is related to chromatin regulation, may facilitate DNA repair in damaged chromatin. Finally, PALB2 interacts with KEAP1, a regulator of the response to oxidative stress. The PALB2 network appears to mediate the maintenance of genome stability, may explain the association of many of the corresponding genes with similar spectra of tumors, and could present novel therapeutic opportunities.

TNF-α signaling in Fanconi anemia

Tumor necrosis factor-alpha (TNF-α) is a major pro-inflammatory cytokine involved in systemic inflammation and the acute phase reaction. Dysregulation of TNF production has been implicated in a variety of human diseases including Fanconi anemia (FA). FA is a genomic instability syndrome characterized by progressive bone marrow failure and cancer susceptibility. The patients with FA are often found overproducing TNF-α, which may directly affect hematopoietic stem cell (HSC) function by impairing HSC survival, homing and proliferation, or indirectly change the bone marrow microenvironment critical for HSC homeostasis and function, therefore contributing to disease progression in FA. In this brief review, we discuss the link between TNF-α signaling and FA pathway with emphasis on the implication of inflammation in the pathophysiology and abnormal hematopoiesis in FA.

A protein prioritization approach tailored for the FA/BRCA pathway

Fanconi anemia (FA) is a heterogeneous recessive disorder associated with a markedly elevated risk to develop cancer. To date sixteen FA genes have been identified, three of which predispose heterozygous mutation carriers to breast cancer. The FA proteins work together in a genome maintenance pathway, the so-called FA/BRCA pathway which is important during the S phase of the cell cycle. Since not all FA patients can be linked to (one of) the sixteen known complementation groups, new FA genes remain to be identified. In addition the complex FA network remains to be further unravelled. One of the FA genes, FANCI, has been identified via a combination of bioinformatic techniques exploiting FA protein properties and genetic linkage. The aim of this study was to develop a prioritization approach for proteins of the entire human proteome that potentially interact with the FA/BRCA pathway or are novel candidate FA genes. To this end, we combined the original bioinformatics approach based on the properties of the first thirteen FA proteins identified with publicly available tools for protein-protein interactions, literature mining (Nermal) and a protein function prediction tool (FuncNet). Importantly, the three newest FA proteins FANCO/RAD51C, FANCP/SLX4, and XRCC2 displayed scores in the range of the already known FA proteins. Likewise, a prime candidate FA gene based on next generation sequencing and having a very low score was subsequently disproven by functional studies for the FA phenotype. Furthermore, the approach strongly enriches for GO terms such as DNA repair, response to DNA damage stimulus, and cell cycle-regulated genes. Additionally, overlaying the top 150 with a haploinsufficiency probability score, renders the approach more tailored for identifying breast cancer related genes. This approach may be useful for prioritization of putative novel FA or breast cancer genes from next generation sequencing efforts.

The Fanconi anemia pathway: repairing the link between DNA damage and squamous cell carcinoma

Fanconi anemia (FA) is a rare inherited recessive disease caused by mutations in one of fifteen genes known to encode FA pathway components. In response to DNA damage, nuclear FA proteins associate into high molecular weight complexes through a cascade of post-translational modifications and physical interactions, followed by the repair of damaged DNA. Hematopoietic cells are particularly sensitive to the loss of these interactions, and bone marrow failure occurs almost universally in FA patients. FA as a disease is further characterized by cancer susceptibility, which highlights the importance of the FA pathway in tumor suppression, and will be the focus of this review. Acute myeloid leukemia is the most common cancer type, often subsequent to bone marrow failure. However, FA patients are also at an extreme risk of squamous cell carcinoma (SCC) of the head and neck and gynecological tract, with an even greater incidence in those individuals who have received a bone marrow transplant and recovered from hematopoietic disease. FA tumor suppression in hematopoietic versus epithelial compartments could be mechanistically similar or distinct. Definition of compartment specific FA activities is now critical to assess the effects of today's bone marrow failure treatments on tomorrow's solid tumor development. It is our hope that current therapies can then be optimized to decrease the risk of malignant transformation in both hematopoietic and epithelial cells. Here we review our current understanding of the mechanisms of action of the Fanconi anemia pathway as it contributes to stress responses, DNA repair and squamous cell carcinoma susceptibility.

Towards a molecular understanding of the fanconi anemia core complex

Fanconi Anemia (FA) is a genetic disorder characterized by the inability of patient cells to repair DNA damage caused by interstrand crosslinking agents. There are currently 14 verified FA genes, where mutation of any single gene prevents repair of DNA interstrand crosslinks (ICLs). The accumulation of ICL damage results in genome instability and patients having a high predisposition to cancers. The key event of the FA pathway is dependent on an eight-protein core complex (CC), required for the monoubiquitination of each member of the FANCD2-FANCI complex. Interestingly, the majority of patient mutations reside in the CC. The molecular mechanisms underlying the requirement for such a large complex to carry out a monoubiquitination event remain a mystery. This paper documents the extensive efforts of researchers so far to understand the molecular roles of the CC proteins with regard to its main function in the FA pathway, the monoubiquitination of FANCD2 and FANCI.

Fanconi anemia proteins and their interacting partners: a molecular puzzle

In recent years, Fanconi anemia (FA) has been the subject of intense investigations, primarily in the DNA repair research field. Many discoveries have led to the notion of a canonical pathway, termed the FA pathway, where all FA proteins function sequentially in different protein complexes to repair DNA cross-link damages. Although a detailed architecture of this DNA cross-link repair pathway is emerging, the question of how a defective DNA cross-link repair process translates into the disease phenotype is unresolved. Other areas of research including oxidative metabolism, cell cycle progression, apoptosis, and transcriptional regulation have been studied in the context of FA, and some of these areas were investigated before the fervent enthusiasm in the DNA repair field. These other molecular mechanisms may also play an important role in the pathogenesis of this disease. In addition, several FA-interacting proteins have been identified with roles in these “other” nonrepair molecular functions. Thus, the goal of this paper is to revisit old ideas and to discuss protein-protein interactions related to other FA-related molecular functions to try to give the reader a wider perspective of the FA molecular puzzle.

FANCP/SLX4: a Swiss army knife of DNA interstrand crosslink repair

Fanconi anemia (FA) is a rare genetic disease characterized by congenital abnormalities, bone marrow failure and heightened cancer susceptibility. The FA proteins are known to function in the cellular defense against DNA interstrand crosslinks (ICLs), a process that remains poorly understood. A recent spate of discoveries has led to the identification of one new FA gene, FANCP/SLX4, and two strong candidate FA genes, FAN1 and RAD51C. In this perspective we describe the discovery of FANCP/SLX4 and discuss how these new findings collectively refine our understanding of DNA ICL repair.

The role of Fanconi anemia/BRCA genes in zebrafish sex determination

Fanconi anemia (FA) is a human disease of bone marrow failure, leukemia, squamous cell carcinoma, and developmental anomalies, including hypogonadism and infertility. Bone marrow transplants improve hematopoietic phenotypes but do not prevent other cancers. FA arises from mutation in any of the 15 FANC genes that cooperate to repair double stranded DNA breaks by homologous recombination. Zebrafish has a single ortholog of each human FANC gene and unexpectedly, mutations in at least two of them (fancl and fancd1(brca2)) lead to female-to-male sex reversal. Investigations show that, as in human, zebrafish fanc genes are required for genome stability and for suppressing apoptosis in tissue culture cells, in embryos treated with DNA damaging agents, and in meiotic germ cells. The sex reversal phenotype requires the action of Tp53 (p53), an activator of apoptosis. These results suggest that in normal sex determination, zebrafish oocytes passing through meiosis signal the gonadal soma to maintain expression of aromatase, an enzyme that converts androgen to estrogen, thereby feminizing the gonad and the individual. According to this model, normal male and female zebrafish differ in genetic factors that control the strength of the late meiotic oocyte-derived signal, probably by regulating the number of meiotic oocytes, which environmental factors can also alter. Transcripts from fancd1(brca2) localize at the animal pole of the zebrafish oocyte cytoplasm and are required for normal oocyte nuclear architecture, for normal embryonic development, and for preventing ovarian tumors. Embryonic DNA repair and sex reversal phenotypes provide assays for the screening of small molecule libraries for therapeutic substances for FA.

Several tetratricopeptide repeat (TPR) motifs of FANCG are required for assembly of the BRCA2/D1-D2-G-X3 complex, FANCD2 monoubiquitylation and phleomycin resistance

The Fanconi anaemia (FA) FANCG protein is an integral component of the FA nuclear core complex that is required for monoubiquitylation of FANCD2. FANCG is also part of another protein complex termed D1-D2-G-X3 that contains FANCD2 and the homologous recombination repair proteins BRCA2 (FANCD1) and XRCC3. Formation of the D1-D2-G-X3 complex is mediated by serine-7 phosphorylation of FANCG and occurs independently of the FA core complex and FANCD2 monoubiquitylation. FANCG contains seven tetratricopeptide repeat (TPR) motifs that mediate protein-protein interactions and here we show that mutation of several of the TPR motifs at a conserved consensus residue ablates the in vivo binding activity of FANCG. Expression of mutated TPR1, TPR2, TPR5 and TPR6 in Chinese hamster fancg mutant NM3 fails to functionally complement its hypersensitivities to mitomycin C (MMC) and phleomycin and fails to restore FANCD2 monoubiquitylation. Using co-immunoprecipitation analysis, we demonstrate that these TPR-mutated FANCG proteins fail to interact with BRCA2, XRCC3, FANCA or FANCF. The interactions of other proteins in the D1-D2-G-X3 complex are also absent, including the interaction of BRCA2 with both the monoubiquitylated (FANCD2-L) and non-ubiquitylated (FANCD2-S) isoforms of FANCD2. Interestingly, a mutation of TPR7 (R563E), that complements the MMC and phleomycin hypersensitivity of human FA-G EUFA316 cells, fails to complement NM3, despite the mutated FANCG protein co-precipitating with FANCA, BRCA2 and XRCC3. Whilst interaction of TPR7-mutated FANCG with FANCF does appear to be reduced in NM3, FANCD2 is monoubiquitylated suggesting that sub-optimal interactions of FANCG in the core complex and the D1-D2-G-X3 complex are responsible for the observed MMC- and phleomycin-hypersensitivity, rather than a defect in FANCD2 monoubiquitylation. Our data demonstrate that FANCG functions as a mediator of protein-protein interactions and is vital for the assembly of multi-protein complexes including the FA core complex and the D1-D2-G-X3 complex.

The structure of the catalytic subunit FANCL of the Fanconi anemia core complex

The Fanconi Anemia pathway is activated in response to DNA damage, leading to monoubiquitination of the substrates FANCI and FANCD2 by the Fanconi Anemia core complex. Here we report the crystal structure of FANCL, the catalytic subunit of the Fanconi Anemia core complex at 3.2 Å. The structure reveals an architecture that is fundamentally different from previous sequence-based predictions. The molecule is composed of an N-terminal E2-like fold, which we term the ELF domain, a novel double-RWD (DRWD) domain, and a C-terminal RING domain predicted to facilitate E2 binding. Binding assays demonstrate that the DRWD domain, but not the ELF domain, is responsible for substrate binding.

Targeting the Fanconi anemia/BRCA pathway circumvents drug resistance in multiple myeloma

The Fanconi anemia/BRCA (FA/BRCA) DNA damage repair pathway plays a pivotal role in the cellular response to replicative stress induced by DNA alkylating agents and greatly influences drug response in cancer treatment. We recently reported that FA/BRCA genes are overexpressed and causative for drug resistance in human melphalan-resistant multiple myeloma cell lines. However, the transcriptional regulation of the FA/BRCA pathway is not understood. In this report, we describe for the first time a novel function of the NF-kappaB subunits, RelB/p50, as transcriptional activators of the FA/BRCA pathway. Specifically, our findings point to constitutive phosphorylation of IkappaB kinase alpha and subsequent alterations in FANCD2 expression and function as underlying events leading to melphalan resistance in repeatedly exposed multiple myeloma cells. Inhibiting NF-kappaB by small interfering RNA, blocking the IkappaB kinase complex with BMS-345541, or using the proteasome inhibitor bortezomib drastically reduced FA/BRCA gene expression and FANCD2 protein expression in myeloma cells, resulting in diminished DNA damage repair and enhanced melphalan sensitivity. Importantly, we also found that bortezomib decreases FA/BRCA gene expression in multiple myeloma patients. These results show for the first time that NF-kappaB transcriptionally regulates the FA/BRCA pathway and provide evidence for targeting Fanconi anemia-mediated DNA repair to enhance chemotherapeutic response and circumvent drug resistance in myeloma patients.

How the fanconi anemia pathway guards the genome

Fanconi Anemia (FA) is an inherited genomic instability disorder, caused by mutations in genes regulating replication-dependent removal of interstrand DNA crosslinks. The Fanconi Anemia pathway is thought to coordinate a complex mechanism that enlists elements of three classic DNA repair pathways, namely homologous recombination, nucleotide excision repair, and mutagenic translesion synthesis, in response to genotoxic insults. To this end, the Fanconi Anemia pathway employs a unique nuclear protein complex that ubiquitinates FANCD2 and FANCI, leading to formation of DNA repair structures. Lack of obvious enzymatic activities among most FA members has made it challenging to unravel its precise modus operandi. Here we review the current understanding of how the Fanconi Anemia pathway components participate in DNA repair and discuss the mechanisms that regulate this pathway to ensure timely, efficient, and correct restoration of chromosomal integrity.

The role of the Fanconi anemia network in the response to DNA replication stress

Fanconi anemia is a genetically heterogeneous disorder associated with chromosome instability and a highly elevated risk for developing cancer. The mutated genes encode proteins involved in the cellular response to DNA replication stress. Fanconi anemia proteins are extensively connected with DNA caretaker proteins, and appear to function as a hub for the coordination of DNA repair with DNA replication and cell cycle progression. At a molecular level, however, the raison d'être of Fanconi anemia proteins still remains largely elusive. The thirteen Fanconi anemia proteins identified to date have not been embraced into a single and defined biological process. To help put the Fanconi anemia puzzle into perspective, we begin this review with a summary of the strategies employed by prokaryotes and eukaryotes to tolerate obstacles to the progression of replication forks. We then summarize what we know about Fanconi anemia with an emphasis on biochemical aspects, and discuss how the Fanconi anemia network, a late acquisition in evolution, may function to permit the faithful and complete duplication of our very large vertebrate chromosomes.

The genetic and molecular basis of Fanconi anemia

The capacity to maintain genomic integrity is shared by all living organisms. Multiple pathways are distinguished that safeguard genomic stability, most of which have originated in primitive life forms. In human individuals, defects in these pathways are typically associated with cancer proneness. The Fanconi anemia pathway, one of these pathways, has evolved relatively late during evolution and exists - in its fully developed form - only in vertebrates. This pathway, in which thus far 13 distinct proteins have been shown to participate, appears essential for error-free DNA replication. Inactivating mutations in the corresponding genes underlie the recessive disease Fanconi anemia (FA). In the last decade the genetic basis of this disorder has been uncovered by a variety of approaches, including complementation cloning, genetic linkage analysis and protein association studies. Here we review these approaches, introduce the encoded proteins, and discuss their possible role in ensuring genomic integrity.

Cellular and molecular consequences of defective Fanconi anemia proteins in replication-coupled DNA repair: mechanistic insights

The Fanconi anemia (FA) molecular network consists of 15 "FANC" proteins, of which 13 are associated with mutations in patients with this cancer-prone chromosome instability disorder. Whereas historically the common phenotype associated with FA mutations is marked sensitivity to DNA interstrand crosslinking agents, the literature supports a more global role for FANC proteins in coping with diverse stresses encountered by replicative polymerases. We have attempted to reconcile and integrate numerous observations into a model in which FANC proteins coordinate the following physiological events during DNA crosslink repair: (a) activating a FANCM-ATR-dependent S-phase checkpoint, (b) mediating enzymatic replication-fork breakage and crosslink unhooking, (c) filling the resulting gap by translesion synthesis (TLS) by error-prone polymerase(s), and (d) restoring the resulting one-ended double-strand break by homologous recombination repair (HRR). The FANC core subcomplex (FANCA, B, C, E, F, G, L, FAAP100) promotes TLS for both crosslink and non-crosslink damage such as spontaneous oxidative base damage, UV-C photoproducts, and alkylated bases. TLS likely helps prevent stalled replication forks from breaking, thereby maintaining chromosome continuity. Diverse DNA damages and replication inhibitors result in monoubiquitination of the FANCD2-FANCI complex by the FANCL ubiquitin ligase activity of the core subcomplex upon its recruitment to chromatin by the FANCM-FAAP24 heterodimeric translocase. We speculate that this translocase activity acts as the primary damage sensor and helps remodel blocked replication forks to facilitate checkpoint activation and repair. Monoubiquitination of FANCD2-FANCI is needed for promoting HRR, in which the FANCD1/BRCA2 and FANCN/PALB2 proteins act at an early step. We conclude that the core subcomplex is required for both TLS and HRR occurring separately for non-crosslink damages and for both events during crosslink repair. The FANCJ/BRIP1/BACH1 helicase functions in association with BRCA1 and may remove structural barriers to replication, such as guanine quadruplex structures, and/or assist in crosslink unhooking.

The fanconi anemia core complex acts as a transcriptional co-regulator in hairy enhancer of split 1 signaling

Mutations in one of the 13 Fanconi anemia (FA) genes cause a progressive bone marrow failure disorder associated with developmental abnormalities and a predisposition to cancer. Although FA has been defined as a DNA repair disease based on the hypersensitivity of patient cells to DNA cross-linking agents, FA patients develop various developmental defects such as skeletal abnormalities, microphthalmia, and endocrine abnormalities that may be linked to transcriptional defects. Recently, we reported that the FA core complex interacts with the transcriptional repressor Hairy Enhancer of Split 1 (HES1) suggesting that the core complex plays a role in transcription. Here we show that the FA core complex contributes to transcriptional regulation of HES1-responsive genes, including HES1 and the cyclin-dependent kinase inhibitor p21(cip1/waf1). Chromatin immunoprecipitation studies show that the FA core complex interacts with the HES1 promoter but not the p21(cip1/waf1) promoter. Furthermore, we show that the FA core complex interferes with HES1 binding to the co-repressor transducin-like-Enhancer of Split, suggesting that the core complex affects transcription both directly and indirectly. Taken together these data suggest a novel function of the FA core complex in transcriptional regulation.

Differential p53 engagement in response to oxidative and oncogenic stresses in Fanconi anemia mice

Members of the Fanconi anemia (FA) protein family are involved in repair of genetic damage caused by DNA cross-linkers. It is not clear whether the FA proteins function in oxidative DNA damage and oncogenic stress response. Here, we report that deficiency in the Fanca gene in mice elicits a p53-dependent growth arrest and DNA damage response to oxidative DNA damage and oncogenic stress. Using a Fanca-/-Trp53-/- double knockout model and a functionally switchable p53 retrovirus, we define the kinetics, dependence, and persistence of p53-mediated response to oxidative and oncogenic stresses in Fanca-/- cells. Notably, oxidative stress induces persistent p53 response in Fanca-/- cells, likely due to accumulation of unrepaired DNA damage. On the other hand, whereas wild-type cells exhibit prolonged response to oncogene activation, the p53-activating signals induced by oncogenic ras are short-lived in Fanca-/- cells, suggesting that Fanca may be required for the cell to engage p53 during constitutive ras activation. We propose that the FA proteins protect cells from stress-induced proliferative arrest and tumor evolution by acting as a modulator of the signaling pathways that link FA to p53.

The Fanconi anemia/BRCA gene network in zebrafish: embryonic expression and comparative genomics

Fanconi anemia (FA) is a genetic disease resulting in bone marrow failure, high cancer risks, and infertility, and developmental anomalies including microphthalmia, microcephaly, hypoplastic radius and thumb. Here we present cDNA sequences, genetic mapping, and genomic analyses for the four previously undescribed zebrafish FA genes (fanci, fancj, fancm, and fancn), and show that they reverted to single copy after the teleost genome duplication. We tested the hypothesis that FA genes are expressed during embryonic development in tissues that are disrupted in human patients by investigating fanc gene expression patterns. We found fanc gene maternal message, which can provide Fanc proteins to repair DNA damage encountered in rapid cleavage divisions. Zygotic expression was broad but especially strong in eyes, central nervous system and hematopoietic tissues. In the pectoral fin bud at hatching, fanc genes were expressed specifically in the apical ectodermal ridge, a signaling center for fin/limb development that may be relevant to the radius/thumb anomaly of FA patients. Hatching embryos expressed fanc genes strongly in the oral epithelium, a site of squamous cell carcinomas in FA patients. Larval and adult zebrafish expressed fanc genes in proliferative regions of the brain, which may be related to microcephaly in FA. Mature ovaries and testes expressed fanc genes in specific stages of oocyte and spermatocyte development, which may be related to DNA repair during homologous recombination in meiosis and to infertility in human patients. The intestine strongly expressed some fanc genes specifically in proliferative zones. Our results show that zebrafish has a complete complement of fanc genes in single copy and that these genes are expressed in zebrafish embryos and adults in proliferative tissues that are often affected in FA patients. These results support the notion that zebrafish offers an attractive experimental system to help unravel mechanisms relevant not only to FA, but also to breast cancer, given the involvement of fancj (brip1), fancn (palb2) and fancd1 (brca2) in both conditions.

Oxidative stress in Fanconi anemia hematopoiesis and disease progression

Patients with the genomic instability syndrome Fanconi anemia (FA) commonly develop progressive bone marrow failure and have a high risk of cancer. The prominent role of the FA protein family involves DNA damage response and/or repair. Oxidative stress, defined as an imbalance between the production of reactive oxygen species and antioxidant defense, is considered to be an important pathogenic factor in leukemia-prone bone marrow diseases such as FA. Cellular responses inducing resistance to oxidative stress are important for cellular survival, organism lifespan, and cancer prevention, but until recently, mammalian factors regulating resistance to oxidative stress have not been well characterized. Significant evidence supports excessive apoptosis of hematopoietic stem/progenitor cells, induced by stresses, most significantly oxidative stress, as a critical factor in the pathogenesis of bone marrow failure and leukemia progression in FA. In this brief review, we discuss the functional link between FA proteins and oxidative DNA damage response/repair, with emphasis on the implication of oxidative stress in the pathophysiology and abnormal hematopoiesis in FA.

The ubiquitin system, disease, and drug discovery

The ubiquitin system of protein modification has emerged as a crucial mechanism involved in the regulation of a wide array of cellular processes. As our knowledge of the pathways in this system has grown, so have the ties between the protein ubiquitin and human disease. The power of the ubiquitin system for therapeutic benefit blossomed with the approval of the proteasome inhibitor Velcade in 2003 by the FDA. Current drug discovery activities in the ubiquitin system seek to (i) expand the development of new proteasome inhibitors with distinct mechanisms of action and improved bioavailability, and (ii) validate new targets. This review summarizes our current understanding of the role of the ubiquitin system in various human diseases ranging from cancer, viral infection and neurodegenerative disorders to muscle wasting, diabetes and inflammation. I provide an introduction to the ubiquitin system, highlight some emerging relationships between the ubiquitin system and disease, and discuss current and future efforts to harness aspects of this potentially powerful system for improving human health.

Republished from Current BioData's Targeted Proteins database (TPdb; ).

HES1 is a novel interactor of the Fanconi anemia core complex

Fanconi anemia (FA) proteins are thought to play a role in chromosome stability and repair of DNA cross-links; however, these functions may not fully explain the developmental abnormalities and bone marrow failure that are characteristic of FA individuals. Here we associate the FA proteins with the Notch1 developmental pathway through a direct protein-protein interaction between the FA core complex and the hairy enhancer of split 1 (HES1). HES1 interaction with FA core complex members is dependent on a functional FA pathway. Cells depleted of HES1 exhibit an FA-like phenotype that includes cellular hypersensitivity to mitomycin C (MMC) and lack of FANCD2 monoubiquitination and foci formation. HES1 is also required for proper nuclear localization or stability of some members of the core complex. Our results suggest that HES1 is a novel interacting protein of the FA core complex.

AMD3100 synergizes with G-CSF to mobilize repopulating stem cells in Fanconi anemia knockout mice

Fanconi anemia (FA) is a heterogeneous inherited disorder characterized by a progressive bone marrow (BM) failure and susceptibility to myeloid leukemia. Genetic correction using gene-transfer technology is one potential therapy. A major hurdle in applying this technology in FA patients is the inability of granulocyte colony-stimulating factor (G-CSF) to mobilize sufficient numbers of hematopoietic stem (HSC)/progenitor cells (HPC) from the BM to the peripheral blood. Whether the low number of CD34(+) cells is a result of BM hypoplasia or an inability of G-CSF to adequately mobilize FA HSC/HPC remains incompletely understood. Here we use competitive repopulation of lethally irradiated primary and secondary recipients to show that in two murine models of FA, AMD3100 synergizes with G-CSF resulting in a mobilization of HSC, whereas G-CSF alone fails to mobilize stem cells even in the absence of hypoplasia.

TNF-alpha induces leukemic clonal evolution ex vivo in Fanconi anemia group C murine stem cells

The molecular pathogenesis of the myeloid leukemias that frequently occur in patients with Fanconi anemia (FA) is not well defined. Hematopoietic stem cells bearing inactivating mutations of FA complementation group C (FANCC) are genetically unstable and hypersensitive to apoptotic cytokine cues including IFN-gamma and TNF-alpha, but neoplastic stem cell clones that arise frequently in vivo are resistant to these cytokines. Reasoning that the combination of genetic instability and cytokine hypersensitivity might create an environment supporting the emergence of leukemic stem cells, we tested the leukemia-promoting effects of TNF-alpha in murine stem cells. TNF-alpha exposure initially profoundly inhibited the growth of Fancc-/- stem cells. However, longer-term exposure of these cells promoted the outgrowth of cytogenetically abnormal clones that, upon transplantation into congenic WT mice, led to acute myelogenous leukemia. TNF-alpha induced ROS-dependent genetic instability in Fancc-/- but not in WT cells. The leukemic clones were TNF-alpha resistant but retained their characteristic hypersensitivity to mitomycin C and exhibited high levels of chromosomal instability. Expression of FANCC cDNA in Fancc-/- stem cells protected them from TNF-alpha-induced clonal evolution. We conclude that TNF-alpha exposure creates an environment in which somatically mutated preleukemic stem cell clones are selected and from which unaltered TNF-alpha-hypersensitive Fancc-/- stem cells are purged.

FANCG promotes formation of a newly identified protein complex containing BRCA2, FANCD2 and XRCC3

Fanconi anemia (FA) is a human disorder characterized by cancer susceptibility and cellular sensitivity to DNA crosslinks and other damages. Thirteen complementation groups and genes are identified, including BRCA2, which is defective in the FA-D1 group. Eight of the FA proteins, including FANCG, participate in a nuclear core complex that is required for the monoubiquitylation of FANCD2 and FANCI. FANCD2, like FANCD1/BRCA2, is not part of the core complex, and we previously showed direct BRCA2-FANCD2 interaction using yeast two-hybrid analysis. We now show in human and hamster cells that expression of FANCG protein, but not the other core complex proteins, is required for co-precipitation of BRCA2 and FANCD2. We also show that phosphorylation of FANCG serine 7 is required for its co-precipitation with BRCA2, XRCC3 and FANCD2, as well as the direct interaction of BRCA2-FANCD2. These results argue that FANCG has a role independent of the FA core complex, and we propose that phosphorylation of serine 7 is the signalling event required for forming a discrete complex comprising FANCD1/BRCA2-FANCD2-FANCG-XRCC3 (D1-D2-G-X3). Cells that fail to express either phospho-Ser7-FANCG, or full length BRCA2 protein, lack the interactions amongst the four component proteins. A role for D1-D2-G-X3 in homologous recombination repair (HRR) is supported by our finding that FANCG and the RAD51-paralog XRCC3 are epistatic for sensitivity to DNA crosslinking compounds in DT40 chicken cells. Our findings further define the intricate interface between FANC and HRR proteins in maintaining chromosome stability.

Emergence of a DNA-damage response network consisting of Fanconi anaemia and BRCA proteins

Fanconi anaemia (FA) has recently become an attractive model to study breast cancer susceptibility (BRCA) genes, as three FA genes, FANCD1, FANCN and FANCJ, are identical to the BRCA genes BRCA2, PALB2 and BRIP1. Increasing evidence shows that FA proteins function as signal transducers and DNA-processing molecules in a DNA-damage response network. This network consists of many proteins that maintain genome integrity, including ataxia telangiectasia and Rad3 related protein (ATR), Bloom syndrome protein (BLM), and BRCA1. Now that the gene that is defective in the thirteenth and last assigned FA complementation group (FANCI) has been identified, I discuss what is known about FA proteins and their interactive network, and what remains to be discovered.

Identification, developmental expression and regulation of the Xenopus ortholog of human FANCG/XRCC9

Fanconi anemia (FA) is associated with variable developmental abnormalities, bone marrow failure and cancer susceptibility. FANCG/XRCC9 is member of the FA core complex, a group of proteins that control the monoubiquitylation of FANCD2, an event that plays a critical role in maintaining genomic stability. Here we report the identification of the Xenopus laevis ortholog of human FANCG (xFANCG), its expression during development, and its molecular interactions with a partner protein, xFANCA. The xFANCG protein sequence is 47% similar to its human ortholog, with highest conservation in the two putative N-terminal leucine zippers and the tetratricopeptide repeat (TPR) motifs. xFANCG is maternally and zygotically transcribed. Prior to the midblastula stage, a single xFANCG transcript is observed but two additional alternatively spliced mRNAs are detected after the midblastula transition. One of the variants is predicted to encode a novel isoform of xFANCG lacking exon 2. The mutual association between FANCG and FANCA required for their nuclear import is conserved in Xenopus egg extracts. Our data demonstrate that interactions between FANCA and FANCG occur at the earliest stage of vertebrate development and raise the possibility that functionally different isoforms of xFANCG may play a role in early development.

Fanconi Anemia and Ubiquitination

Fanconi anemia (FA) is a rare recessive hereditary disease characterized clinically by congenital defects, progressive bone-marrow failure, and cancer predisposition. Cells from FA patients exhibit hypersensitivity to DNA cross-linking agents, such as mitomycin C (MMC). To date, at least 12 FA genes have been found deleted or mutated in FA cells, and 10 FA gene products form a core complex involved in FA/BRCA2 DNA repair pathway?FA pathway. The ubiquitin E3 ligase FANCL, an important factor of FA core complex, co-functions with a new ubiquitin conjugating enzyme UBE2T to catalyze the monoubiquitination of FANCD2. FANCD2-Ub binds BRCA2 to form a new complex located in chromatin foci and then take part in DNA repair process. The deubiquitylating enzyme USP1 removes the mono-ubiquitin from FANCD2-Ub following completion of the repair process, then restores the blocked cell cycle to normal order by shutting off the FA pathway. In a word, the FANCD2 activity adjusted exquisitely by ubiquitination and/or deubiquitination in vivo may co-regulate the FA pathway involving in variant DNA repair pathway.

Inflammatory reactive oxygen species-mediated hemopoietic suppression in Fancc-deficient mice

Patients with the genomic instability syndrome Fanconi anemia (FA) commonly develop progressive bone marrow (BM) failure and have a high risk of cancer. Certain manifestations of the disease suggest that the FA immune system is dysfunctional and may contribute to the pathogenesis of both BM failure and malignancies. In this study, we have investigated inflammation and innate immunity in FA hemopoietic cells using mice deficient in Fanconi complementation group C gene (Fancc). We demonstrate that Fancc-deficient mice exhibit enhanced inflammatory response and are hypersensitive to LPS-induced septic shock as a result of hemopoietic suppression. This exacerbated inflammatory phenotype is intrinsic to the hemopoietic system and can be corrected by the re-expression of a wild-type FANCC gene, suggesting a potential role of the FANCC protein in innate immunity. LPS-mediated hemopoietic suppression requires two major inflammatory agents, TNF-alpha and reactive oxygen species. In addition, LPS-induced excessive accumulation of reactive oxygen species in Fancc(-/-) BM cells overactivates the stress kinase p38 and requires prolonged activation of the JNK. Our data implicate a role of inflammation in pathogenesis of FA and BM failure diseases in general.

Targeting Fanconi anemia/BRCA2 pathway defects in cancer: the significance of preclinical pharmacogenomic models

Defects in the Fanconi anemia (FA) pathway occur in subsets of diverse human cancers. The hypersensitivity of FA pathway-deficient cells to DNA interstrand cross-linking and possibly other agents renders these genes attractive targets for a genotype-based, individualized anticancer therapy. A prerequisite before clinical trials is the validation and quantification of this hypersensitivity in suitable preclinical pharmacogenomic models. In addition, the effects of combinational therapy need to be evaluated and novel agents sought. We discuss here the pitfalls and limitations in the interpretation of common FA models when applied to the validation of FA gene defects as therapeutic targets. In general, all preclinical models are prone to certain artifacts and, thus, promising results in a single or few models rarely translate into clinical success. Nevertheless, the extraordinary robustness of FA pathway-deficient cells to interstrand cross-linking agents, which are observable in virtually any model independent of species, cell type, or technique used to engineer the gene defect, in various in vitro and in vivo settings, renders these gene defects particularly attractive for targeted therapy. Clinical trials are now under way.

Loss of expression of FANCD2 protein in sporadic and hereditary breast cancer

Fanconi anemia (FA) is a recessive disorder associated with progressive pancytopenia, multiple developmental defects, and marked predisposition to malignancies. FA is genetically heterogeneous, comprising at least 12 complementation groups (A–M). Activation of one of the FA proteins (FANCD2) by mono-ubiquitination is an essential step in DNA damage response. As FANCD2 interacts with BRCA1, is expressed in proliferating normal breast cells, and FANCD2 knockout mice develop breast tumors, we investigated the expression of FANCD2 in sporadic and hereditary invasive breast cancer patients to evaluate its possible role in breast carcinogenesis. Two tissue microarrays of 129 and 220 sporadic breast cancers and a tissue microarray containing 25 BRCA1 germline mutation-related invasive breast cancers were stained for FANCD2. Expression results were compared with several clinicopathological variables and tested for prognostic value. Eighteen of 96 (19%) sporadic breast cancers and two of 21 (10%) BRCA1-related breast cancers were completely FANCD2-negative, which, however, still showed proliferation. In the remaining cases, the percentage of FANCD2-expressing cells correlated strongly with mitotic index and percentage of cells positive for the proliferation markers Ki-67 and Cyclin A. In immunofluorescence double staining, coexpression of FANCD2 and Ki-67 was apparent. In survival analysis, high FANCD2 expression appeared to be prognostically unfavorable for overall survival (p = 0.03), independent from other major prognosticators (p = 0.026). In conclusion, FANCD2 expression is absent in 10–20% of sporadic and BRCA1-related breast cancers, indicating that somatic inactivating (epi)genetic events in FANCD2 may be important in both sporadic and hereditary breast carcinogenesis. FANCD2 is of independent prognostic value in sporadic breast cancer.