The Co-Recessive Inheritance Model: A Paradigm for Fanconi Anemia and Other Bone Marrow Failure Syndromes.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 3760-3760
Author(s):  
W. Clark Lambert ◽  
Monique M. Brown ◽  
Santiago A. Centurion
Keyword(s):  
Bone Marrow ◽  
Dna Repair ◽  
Fanconi Anemia ◽  
Normal Population ◽  
Bone Marrow Failure ◽  
Significant Proportion ◽  
Complementation Group ◽  
Recessive Model ◽  
Compound Heterozygous ◽  
Recessive Inheritance

Abstract One of us (WCL) has previously proposed a mathematical model, Co-Recessive Inheritance, for inherited diseases associated with DNA repair deficiencies (Lambert WC, Lambert MW: Mutat. Res., 1985;145:227–234; Lambert WC: Keynote Address, 21st Anniversary Celebration, MRC Cell Mutation Unit, University of Sussex, UK. Mutat. Res., 1992;273:179–102). The model is also applicable to diseases associated with defective cell cycle modulation following specific types of DNA damage, such as Fanconi Anemia, with or without additional defects in DNA repair. The model proposes that in some complementation groups of these diseases defective alleles at more than one locus are required for the disease phenotype to be expressed. It follows from the model (A readily understandable derivation will be presented.) that the carrier frequencies of the genes involved are very much higher than would be predicted based on classical population genetics. This may impact on recent observations of higher than expected co-inheritance of defective alleles of Fanconi Anemia and Bloom Syndrome genes along with BRCA genes in certain populations (e.g., Koren-Michowitz, M, et al.: Am. J. Hematol., 2005;78:203–206), and provides an explanation for the lower than expected incidence of cancer in these individuals. It also provides an explanation for finding biallelic defects in the same DNA repair genes in more than one complementation group of Fanconi Anemia (Howlett NG, et al.: Science, 2002;297:606–609). The Co-Recessive Model predicts that other findings of this nature are to be expected, and provides some guidelines that may be helpful in the process of gene discovery in Fanconi Anemia. Among the more important of these are 1) that the search for defective genes in each complementation group should not cease when one such gene is found, even if one or more patients in the group is homozygous or compound heterozygous for defective alleles of that gene, and 2) that carrier frequencies for some Fanconi Anemia genes may be much higher than would otherwise be anticipated, with a significant proportion of the normal population being carriers. If the latter hypothesis is correct, it follows that the relevance of these rare diseases and their associated genes to disease, including bone marrow failure, in the general population is dramatically greater than has been generally believed.

Clonal chromosomal aberrations in bone marrow cells of Fanconi anemia patients: gains of the chromosomal segment 3q26q29 as an adverse risk factor

Blood ◽  
2003 ◽  
Vol 101 (10) ◽  
pp. 3872-3874 ◽  
Author(s):  
Holger Tönnies ◽  
Stefanie Huber ◽  
Jörn-Sven Kühl ◽  
Antje Gerlach ◽  
Wolfram Ebell ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Risk Factor ◽  
Fanconi Anemia ◽  
Bone Marrow Cells ◽  
Bone Marrow Failure ◽  
Molecular Cytogenetics ◽  
Complementation Group ◽  
Significant Survival ◽  
High Incidence ◽  
Marrow Cells

Abstract Fanconi anemia (FA) is a condition that induces susceptibility to bone marrow failure, myelodysplastic syndrome (MDS), and leukemia. We report on a high incidence of expanding clonal aberrations with partial trisomies and tetrasomies of chromosome 3q in bone marrow cells of 18 of 53 FA patients analyzed, detected by conventional and molecular cytogenetics. To determine the clinical relevance of these findings, we compared the cytogenetic data, the morphologic features of the bone marrow, and the clinical course of these patients with those of 35 FA patients without clonal aberrations of 3q. The 2 groups did not differ significantly with respect to age, sex, or complementation group. There was a significant survival advantage of patients without abnormalities of chromosome 3q. Even more pronounced was the risk assessment of patients with gains of 3q material with respect to the development of morphologic MDS and acute myeloid leukemia (AML). Thus, our data from 18 patients with 3q aberrations reveal that gains of 3q are strongly associated with a poor prognosis and represent an adverse risk factor in FA.

scholarly journals Clinical severity in Fanconi anemia correlates with residual function of FANCB missense variants

2019 ◽  
Author(s):  
Moonjung Jung ◽  
Ramanagouda Ramanagoudr-Bhojappa ◽  
Sylvie van Twest ◽  
Rasim Ozgur Rosti ◽  
Vincent Murphy ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Fanconi Anemia ◽  
Congenital Abnormalities ◽  
Bone Marrow Failure ◽  
Complementation Group ◽  
Clinical Severity ◽  
List Type ◽  
Missense Variants ◽  
Pathogenic Variants ◽  
Fancd2 Monoubiquitination

ABSTRACTFanconi anemia (FA) is the most common genetic cause of bone marrow failure, and is caused by inherited pathogenic variants in any of 22 genes. Of these, only FANCB is X-linked. We describe a cohort of 19 children with FANCB variants, from 16 families of the International Fanconi Anemia Registry (IFAR). Those with FANCB deletion or truncation demonstrate earlier than average onset of bone marrow failure, and more severe congenital abnormalities compared to a large series of FA individuals in the published reports. This reflects the indispensable role of FANCB protein in the enzymatic activation of FANCD2 monoubiquitination, an essential step in the repair of DNA interstrand crosslinks. For FANCB missense variants, more variable severity is associated with the extent of residual FANCD2 monoubiquitination activity. We used transcript analysis, genetic complementation, and biochemical reconstitution of FANCD2 monoubiquitination to determine the pathogenicity of each variant. Aberrant splicing and transcript destabilization was associated with two missence variants. Individuals carrying missense variants with drastically reduced FANCD2 monoubiquitination in biochemical and/or cell-based assays showed earlier onset of hematologic disease and shorter survival. Conversely, variants with near-normal FANCD2 monoubiquitination were associated with more favorable outcome. Our study reveals a genotype-phenotype correlation within the FA-B complementation group of FA, where severity is linked to the extent of residual FANCD2 monoubiquitination.KEY POINTSX-linked FANCB pathogenic variants predominantly cause acute, early onset bone marrow failure and severe congenital abnormalitiesBiochemical and cell-based assays with patient variants reveal functional properties of FANCB that associate with clinical severity

Israeli Fanconi Anemia Registry

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 4125-4125
Author(s):  
Hannah Tamary ◽  
Blanche P. Alter ◽  
Daniella Nishri ◽  
Philip S Rosenberg
Keyword(s):  
Bone Marrow ◽  
Solid Tumors ◽  
Fanconi Anemia ◽  
Congenital Abnormality ◽  
Bone Marrow Failure ◽  
Epidemiological Data ◽  
Quantitative Model ◽  
Complementation Group ◽  
Adverse Outcomes ◽  
Complementation Groups

Abstract Using epidemiological data from retrospective cohorts of patients with Fanconi Anemia (FA) in North America and Germany a quantitative model to estimate bone marrow failure (BMF) and cancer risk was previously generated. To evaluate generalizability to another population, and to determine the risks for adverse outcomes in Israel, we created an Israeli FA registry and used the model to evaluate complications. We reviewed patient charts of 66 patients with FA diagnosed in Israel between 1964–2005. The data base included demographic information, as well as data describing the congenital abnormalities, FA complementation groups, BMT course and malignancies. Thirty six (36) patients were of Jewish origin [Ashkenzi 7, Sephardic 23, mixed 6] and 30 of Arabic origin. The first adverse event was bone marrow failure (BMF) in 35 patients (53%), hematological malignancy in 7 (11%) and 2 solid tumors in each of 3 patients (5%). The cause-specific hazard of BMF peaked at 10.5%/year at age 10 years (95% CI: 6.7–14.1%/year). The hazard of AML/ALL and MDS were stable at 0.9%/year (95% CI: 0.42–1.85%/year) and 1.4%/year (95% CI: 0.76–2.49%/year) respectively. The cumulative incidence of each outcome to age 32 was 70% for BMF, 13% for AML/ALL, and 17% for solid tumor. A five item congenital abnormality score was significantly associated with the risk of BMF (P = 0.009). The ratio of observed to expected cancer was 71 for all cancers [50 for solid tumors, 175 for leukemia] and >11,000 for myelodysplastic syndrome. Significantly elevated ratios of observed to expected cancers were observed for head and neck squamous cell carcinoma in 2 patients (986-fold), tumor of larynx (13,238-fold), vulva (3,701-fold), cervix (244-fold) and breast (88-fold). The complementation group was known in 41 patients [A 25 (63%), C 9 (22%), G 6 (15%), and D1 1 (2%)]. However, associations between complementation groups and specific outcomes were not significant. Despite the different ethnic background and the smaller number of FA patients in the Israeli cohort the risk estimates compared with the US and German cohorts were similar. As previously suggested the congenital abnormality score was significantly associated with the risk of BMF; an extraordinary risk of developing AML/MDS and later specific solid tumors was also found.

scholarly journals Association of clinical severity with FANCB variant type in Fanconi anemia

Blood ◽  
2020 ◽  
Vol 135 (18) ◽  
pp. 1588-1602 ◽  
Author(s):  
Moonjung Jung ◽  
Ramanagouda Ramanagoudr-Bhojappa ◽  
Sylvie van Twest ◽  
Rasim Ozgur Rosti ◽  
Vincent Murphy ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Fanconi Anemia ◽  
Bone Marrow Failure ◽  
Complementation Group ◽  
Clinical Severity ◽  
Missense Variants ◽  
Interstrand Crosslinks ◽  
Pathogenic Variants ◽  
Enzymatic Activation ◽  
Fancd2 Monoubiquitination

Abstract Fanconi anemia (FA) is the most common genetic cause of bone marrow failure and is caused by inherited pathogenic variants in any of 22 genes. Of these, only FANCB is X-linked. We describe a cohort of 19 children with FANCB variants, from 16 families of the International Fanconi Anemia Registry. Those with FANCB deletion or truncation demonstrate earlier-than-average onset of bone marrow failure and more severe congenital abnormalities compared with a large series of FA individuals in published reports. This reflects the indispensable role of FANCB protein in the enzymatic activation of FANCD2 monoubiquitination, an essential step in the repair of DNA interstrand crosslinks. For FANCB missense variants, more variable severity is associated with the extent of residual FANCD2 monoubiquitination activity. We used transcript analysis, genetic complementation, and biochemical reconstitution of FANCD2 monoubiquitination to determine the pathogenicity of each variant. Aberrant splicing and transcript destabilization were associated with 2 missense variants. Individuals carrying missense variants with drastically reduced FANCD2 monoubiquitination in biochemical and/or cell-based assays tended to show earlier onset of hematologic disease and shorter survival. Conversely, variants with near-normal FANCD2 monoubiquitination were associated with more favorable outcome. Our study reveals a genotype-phenotype correlation within the FA-B complementation group of FA, where severity is associated with level of residual FANCD2 monoubiquitination.

Cytokinesis Failure in Fanconi Anemia Pathway Deficient Murine Hematopoietic Stem Cells.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 495-495
Author(s):  
Patrizia Vinciguerra ◽  
Susana Godinho ◽  
Kalindi Parmar ◽  
David Pellman ◽  
Alan D'Andrea
Keyword(s):  
Cell Cycle ◽  
Stem Cells ◽  
Bone Marrow ◽  
Dna Repair ◽  
Hematopoietic Stem Cells ◽  
Fanconi Anemia ◽  
Bone Marrow Failure ◽  
Hematopoietic Stem ◽  
Cell Biol ◽  
Normal Mitosis

Abstract Abstract 495 Fanconi Anemia (FA) is a rare recessive chromosomal-instability disorder characterized by congenital malformations, a high predisposition to cancer, and progressive bone marrow failure. FA is genetically heterogeneous and, to date, thirteen FA genes have been identified (FANCA, -B, -C, -D1, -D2, -E, -F, -G, -I, -J, -L, -M, -N). The thirteen encoded FA proteins cooperate in a common DNA repair pathway active during the Synthesis (S) phase of the cell cycle. DNA damage detected during replication results in the monoubiquitination of two FA proteins, FANCD2 and FANCI, that translocate into chromatin-associated DNA repair foci where they colocalize with downstream components of the pathway. Partial colocalization with BLM, the RecQ helicase mutated in Bloom's syndrome, has also been described. How disruption of this pathway leads to bone marrow failure is a critical unanswered question. Interestingly, FA cells also have abnormalities that suggest a defect in mitosis, including micronuclei and multinucleation. The objectives of this study were to 1) investigate the role of the FA pathway in normal mitosis and 2) determine whether defects in this function underlie the bone marrow failure of FA patients. For this study, we used HeLa cells transiently or stably knocked down for FA genes, FA patient derived cell lines and hematopoietic stem cells from Fanconi mice models generated in our laboratory (Fancd2-/- and Fancg-/-). First, a polyclonal antibody was raised against FANCI and, together with an anti-FANCD2 antibody, used to investigate the localization of the FANCD2-I complex throughout the cell cycle by immunostaining. FANCI and FANCD2 colocalized to discrete foci on condensed chromosomes in a population of cells in Mitosis (M) phase, consistent with results of Chan et al. (Replication stress induces sister-chromatid bridging at fragile site loci in mitosis. Nat Cell Biol. 2009;11:753-760), Naim and Rosselli (The FANC pathway and BLM collaborate during mitosis to prevent micro-nucleation and chromosome abnormalities. Nat Cell Biol. 2009;11:761-768). These foci were dependent on an intact FA pathway, but did not localize at centromeres and did not increase when the spindle assembly checkpoint was challenged. By immunofluorescence, we showed an increase in the presence of Hoechst positive DNA bridges and PICH positive / BLM positive DNA bridges (Hoechst positive and negative) in anaphase and telophase of FA deficient cells compared to FA proficient cells. This increase of DNA bridges between separating sister chromatids in FA deficient cells correlated with an increase of multinucleated cells. Multinuclearity, scored by immunostaining for microtubules and Hoechst staining for DNA, was the result of cytokinesis failure as observed by live cell imaging. Furthermore, inhibition of apoptosis increased the number of binucleated cells, suggesting that cytokinesis failure led to apoptosis. Importantly, an increase in binucleated cells was also observed in the hematopoietic stem cells population from Fancd2-/- and Fancg-/- mice, compared to wild-type sibling mice, and this increase correlated with elevated apoptosis in those cells. Based on these new findings, we conclude that the Fanconi pathway is required for normal mitosis and hypothesize that apoptosis induced by cytokinesis failure of hematopoietic stem cells may cause the bone marrow failure commonly found in FA patients. Disclosures: No relevant conflicts of interest to declare.

scholarly journals A Dutch Fanconi AnemiaFANCCFounder Mutation in Canadian Manitoba Mennonites

Anemia ◽  
2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Yne de Vries ◽  
Nikki Lwiwski ◽  
Marieke Levitus ◽  
Bertus Kuyt ◽  
Sara J. Israels ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Fanconi Anemia ◽  
Bone Marrow Failure ◽  
Complementation Group ◽  
Cross Linking ◽  
Founder Mutations ◽  
Developmental Abnormalities ◽  
Dna Instability ◽  
Common Founder ◽  
Complementation Groups

Fanconi anemia (FA) is a recessive DNA instability disorder associated with developmental abnormalities, bone marrow failure, and a predisposition to cancer. Based on their sensitivity to DNA cross-linking agents, FA cells have been assigned to 15 complementation groups, and the associated genes have been identified. Founder mutations have been found in different FA genes in several populations. The majority of Dutch FA patients belongs to complementation group FA-C. Here, we report 15 patients of Dutch ancestry and a large Canadian Manitoba Mennonite kindred carrying theFANCCc.67delG mutation. Genealogical investigation into the ancestors of the Dutch patients shows that these ancestors lived in four distinct areas in The Netherlands. We also show that the Dutch and Manitoba MennoniteFANCCc.67delG patients share the same haplotype surrounding this mutation, indicating a common founder.

scholarly journals Fanconi Anemia: A Paradigm for Understanding DNA Repair During Replication.

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. SCI-32-SCI-32 ◽  
Author(s):  
Agata Smogorzewska
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Dna Damage ◽  
Dna Repair ◽  
Hematopoietic Stem Cells ◽  
Fanconi Anemia ◽  
Bone Marrow Failure ◽  
Chromosome Breakage ◽  
Dna Lesions ◽  
Hematopoietic Stem

Fanconi anemia, the most common hereditary bone marrow failure disorder, results from defective repair of DNA interstrand crosslinks (ICLs), which covalently link complementary DNA strands causing replication stalling. Mutations in 22 different genes (FANCA-FANCW) have been shown to result in Fanconi anemia. Their protein products work at different stages of DNA repair leading to considerable heterogeneity in human phenotypes. The majority of the FANC gene mutations are recessively inherited with the exceptions of FANCB and FANCR/RAD51. FANCB is X-linked, and all FANCR/RAD51 mutations arise de novo, affect only one allele, and the mutant protein acts as a dominant negative against the wild type protein. Despite advances in the molecular diagnosis of Fanconi anemia, if Fanconi anemia is suspected, chromosome breakage (DEB or MMC) testing on patient cells is essential. We have seen a number of patients referred to the International Fanconi Anemia Registry (http://lab.rockefeller.edu/smogorzewska/ifar/) who are misdiagnosed with Fanconi anemia based solely on the presence of a FANC gene variant in gene panel or whole exome sequencing. Conversely, blood mosaicism may lead to a negative blood chromosome breakage test. If there is a high suspicion of Fanconi anemia, but blood breakage results are negative, breakage test on patient fibroblasts should be performed. Diagnosis of Fanconi anemia should also be entertained in young adults presenting with squamous cell carcinoma of the aerodigestive tract, since this may be their initial presentation of Fanconi anemia and conventional chemotherapy dose would precipitate bone marrow failure in these patients. In my talk, I will discuss the mechanism of the Fanconi anemia repair pathway during DNA replication. Then, I will concentrate on the mechanism of bone marrow failure and tumorigenesis in Fanconi anemia. I will explore the hypothesis that the endogenously produced aldehydes including some that are still unknown, contribute to disease development. Fanconi anemia-deficient hematopoietic stem cells have an autonomous DNA repair defect. Accumulation of DNA damage leads to apoptosis due to the activation of p53. If cells escape death, mutagenesis may lead to the development of leukemia. The sources of endogenous DNA damage are poorly understood. Cell cycle induction of Fanconi anemia pathway-deficientmouse hematopoietic stem cells results in DNA damage and bone marrow failure, which implies that the DNA lesions encountered during replication are the culprit. There is mounting evidence that the endogenous aldehydes, including acetaldehyde and formaldehyde,may cause those DNA lesions. To identify other metabolites that may induce bone marrow failure in Fanconi anemia, we used a library of CRISPR guides to target Cas9 to metabolic genes to screen for and identify synthetic lethality with Fanconi anemia deficiency. We have identifiedALDH9A1as the most significantly depleted gene in FANCD2-/- cells. The synthetically lethal interaction was validated using single gene editing in human umbilical cord-derived hematopoietic stem progenitor cells. We propose a model in which aldehydes that are metabolized by ALDH9A1 accumulate in the absence of this enzyme and cause DNA damage that requires the Fanconi anemia pathway proteins for repair, survival, and suppression of tumorigenesis. We are testing this model using Fanca-/-Aldh9a1-/-mice. Disclosures No relevant conflicts of interest to declare.

The DNA Synthesis Inhibitor, Hydroxyurea, as a Potential Novel Therapeutic Approach for Fanconi Anemia: Further Studies in Complementation Group D1.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 4214-4214
Author(s):  
W. Clark Lambert ◽  
Monique M Brown
Keyword(s):  
Bone Marrow ◽  
Dna Synthesis ◽  
Effective Treatment ◽  
Sickle Cell ◽  
Fanconi Anemia ◽  
Sickle Cell Anemia ◽  
Bone Marrow Failure ◽  
Complementation Group ◽  
Lymphoblastoid Cells ◽  
Complementation Groups

Abstract Abstract 4214 Fanconi anemia (FA) is an inherited, cancer-prone bone marrow failure disease. FA is heterogeneous, with 13 complementation groups, but all groups have in common hypersensitivity to agents that produce DNA interstrand cross links (DISCLs), with associated increased clastogenicity, as a diagnostic hallmark. Although progress has been made in treating FA, particularly using bone marrow transplantation (BMT) to prevent bone marrow failure and leukemogenesis, BMT is not a trivial procedure, and treatment remains challenging. Head and neck cancers, which occur in high frequency in FA, are a particular problem that is not well remedied by BMT. Lymphoblastoid cells from normal subjects and from patients with FA were treated in culture with psoralen plus ultraviolet A radiation (PUVA) in a regimen shown to produce DISCLs. Following this, cells were treated with hydroxyurea, 5-fluorouracil, or high dose thymidine, in doses we have shown to produce a marked decrease in rate of DNA synthesis, for 24 hours. We have previously shown that clastogenicity and cytotoxicity, measured as trypan blue exclusion as well as colony forming ability (CFA), are markedly increased in FA cells, complementation groups A, B, C, and E, associated with deficiencies in their corresponding FA core proteins, but these increases are not observed in these FA cells subsequently treated with any of these other, DNA synthesis retarding agents, which effectively correct the FA phenotype in culture. FA A and C cells genetically corrected for the FANC A and G gene, respectively, display normal clastogenicity and cytotoxicity following PUVA, and do not show this correction following subsequent treatment with hydroxyurea, 5-fluorouracil, or high dose thymidine. We now report similar results for short term cell viability, and similar, although less marked, results for clastogenicity in FA complementation group D1 cells, associated with a deficiency in BRCA2. When all drugs were removed after these treatments and the cells cultured for 10 days without any drug in CFA assays, the FA group D1 cells resembled normals, however, and did not show this correction. We propose that the mechanism in FA A, B, C and G cells is related to a decrease in the rate of DNA synthesis, which we have shown occurs in normal but not FA cells following PUVA, and which is also produced by these other agents in the concentrations used here. The partial correction observed in FA group D1 cells may be due to this or a different mechanism. Partial or complete correction appears to apply to multiple FA complementation groups. Hydroxyurea has been used for many years as a safe and effective treatment for sickle cell anemia and other diseases. It is now proposed as a possible treatment for FA to delay or even prevent development of bone marrow failure and/or other complications, including leukemogenesis and carcinogenesis, with or without prior BMT. In some cases it may serve as a viable alternative where BMT is not fungible. Alternatively it may obviate the need for BMT altogether in responsive patients, or be effectively used in combination with other modalities. Complementation group may be important in determining which patients may be less responsive or require modified regimens. Disclosures: Off Label Use: We have obtained laboratory results which show partial or complete restoration of cytotoxicity and clastogenicity, as well as colony forming ability in the absence of drug in FA A, B, C, and G but not D1 cells, following treatment with a DNA cross-linking agent, in Fanconi anemia lymphoblastoid cells, by subsequent application of hydroxyurea, to normal levels. Hydroxyurea has been used for many years as a safe and effective treatment for sickle cell anemia. It is now proposed as a possible treatment for Fanconi anemia to delay or even prevent development of bone marrow failure and/or other complications, including leukemogenesis and carcinogenesis. It may be less effective in FA complementation group D1. Disclosures: Off Label Use: We have obtained laboratory results which show partial or complete restoration of cytotoxicity and clastogenicity, as well as colony forming ability in the absence of drug, following treatment with a DNA cross-linking agent, in Fanconi anemia lymphoblastoid cells, by subsequent application of hydroxyurea, to normal levels. Hydroxyurea has been used for many years as a safe and effective treatment for sickle cell anemia. It is now proposed as a possible treatment for Fanconi anemia to delay or even prevent development of bone marrow failure and/or other complications, including leukemogenesis and carcinogenesis..

Bone Marrow Failure in Fanconi Anemia from Hyperactive TGF-β Signaling

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 356-356
Author(s):  
Haojian Zhang ◽  
David Kozono ◽  
Kevin O'Connor ◽  
Sofia Vidal-Cardenas ◽  
Abigail Hamilton ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Dna Repair ◽  
Signaling Pathway ◽  
Fanconi Anemia ◽  
Bone Marrow Failure ◽  
Genotoxic Stress ◽  
Cellular Growth ◽  
Cross Linking ◽  
Repair Pathway ◽  
Growth Defects

Abstract Fanconi anemia (FA) is the most common inherited bone marrow failure syndrome. FA patients develop bone marrow failure during the first decade of life due to attrition of hematopoietic stem and progenitor cells (HSPCs). FA patients also develop other hematologic manifestations, including myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) due to clonal evolution. FA is caused by biallelic mutants in one of sixteen FANC genes, the products of which cooperate in the FA/BRCA DNA repair pathway and regulate cellular resistance to DNA cross-linking agents. Bone marrow failure in FA may result, directly or indirectly, from hyperactivation of cell autonomous or microenvironmental growth suppressive pathways induced due to genotoxic stress. Recent studies suggest that one suppressive pathway may be the hyperactive p53 response observed in HSPCs from FA patients. In order to further identify suppressive mechanisms accounting for bone marrow failure in FA, we performed a whole genome-wide shRNA screen in FA cells. Specifically, we screened for candidate genes whose knockdown would rescue cellular growth inhibition and genotoxic stress induced by a DNA cross-linking agent mitomycin C (MMC). We transduced a FA-deficient human fibroblast line with pools of shRNAs and screened for rescue of MMC-inhibited growth. Selected shRNA inserts were identified by next generation sequencing. The top hits in the screen were shRNAs directed against multiple components of the TGF-β signaling pathway. Consistent with this, disruption of the TGF-β signaling pathway by shRNA/sgRNA-mediated knockdown of SMAD3 or TGFR1 (downstream components of the TGF- β pathway) rescued growth of multiple cell lines from several FA complementation groups in presence of genotoxic agents (e.g. MMC or acetaldehyde). Pharmacologic inhibition of the TGF- β pathway using small molecule inhibitors resulted in improved survival of FA-deficient lymphoblast cells in presence of MMC or acetaldehyde, suggesting that a hyperactive, TGF-β-mediated, suppression pathway may account, at least in part, for reduced FA cell growth. Interestingly, genes encoding TGF-β pathway signaling components were highly expressed in the bone marrow from FA patients and FA mice. Moreover, disruption of the TGF- β pathway by shRNA-mediated knockdown of SMAD3 rescued the growth defects of primary HSPCs from FA-deficient murine bone marrow. To further implicate the TGF-β pathway, we established primary stromal cell lines from the bone marrow of FA-deficient mice as well as human FA patients. We confirmed that TGF-β signaling was hyperactive in these stroma cells resulting in growth suppression and elevated phospho-ERK levels due to non-canonical signaling of the pathway. Inhibitors of TGF-β signaling partially rescued the growth defects and reduced phospho-ERK levels in these FA stroma cells. The deficiency of FA DNA repair pathway leads to cellular defects in homologous recombination (HR) repair and hyperactivation of toxic non-homologous end joining (NHEJ)-mediated repair. We therefore tested whether inhibition of the TGF-β pathway in FA cells could rescue HR defects and account for the improvement of FA cellular growth. Interestingly, disruption of the TGF-β signaling pathway caused a decrease in NHEJ activity. Disruption of the TGF-β pathway also resulted in reduced MMC-mediated DNA damage and increased HR. Taken together, our results demonstrate that primary FA hematopoietic and bone marrow stromal cells exhibit hyperactive TGF-β signaling accounting at least in part for the bone marrow failure in FA. Inhibitors of the TGF-β signaling pathway may therefore be useful in the clinical treatment of patients with bone marrow failure and Fanconi anemia. Disclosures No relevant conflicts of interest to declare.

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