RESUMEN
Identifying new molecular targets for novel anticancer treatments is a major challenge in clinical cancer research. We have shown that cytidine deaminase (CDA) expression is downregulated in about 60% of cancer cells and tissues. In this study, we aimed to develop a new anticancer treatment specifically inhibiting the growth of CDA-deficient tumor cells. High-throughput screening of a chemical library led to the identification of a naphthol derivative, X55, targeting CDA-deficient tumor cells preferentially, without affecting the growth of non-tumoral cells regardless of CDA expression status. Metabolomic profiling revealed that CDA-deficient HeLa cells differed markedly from control HeLa cells. X55 treatment had a moderate effect on control cells, but greatly disturbed the metabolome of CDA-deficient HeLa cells, worsening the deregulation of many metabolites. In particular, the levels of the three oncometabolites, fumarate, succinate and 2-hydroxyglutarate, were significantly lower in CDA-depleted cells, and this decrease in levels was exacerbated by X55 treatment, revealing an unexpected link between CDA deficiency, mitochondrial function and X55 response. Finally, we identified strong downregulation of MAPT (encoding Tau, a microtubule associated protein) expression as a reliable predictive marker for tumor cell X55 sensitivity.
Asunto(s)
Citidina Desaminasa , Naftoles , Citidina Desaminasa/genética , Citidina Desaminasa/metabolismo , Células HeLa , HumanosRESUMEN
Cytidine deaminase (CDA) deficiency induces an excess of cellular dCTP, which reduces basal PARP-1 activity, thereby compromising complete DNA replication, leading to ultrafine anaphase bridge (UFB) formation. CDA dysfunction has pathological implications, notably in cancer and in Bloom syndrome. It remains unknown how reduced levels of PARP-1 activity and pyrimidine pool imbalance lead to the accumulation of unreplicated DNA during mitosis. We report that a decrease in PARP-1 activity in CDA-deficient cells impairs DNA-damage-induced Chk1 activation, and, thus, the downstream checkpoints. Chemical inhibition of the ATR-Chk1 pathway leads to UFB accumulation, and we found that this pathway was compromised in CDA-deficient cells. Our data demonstrate that ATR-Chk1 acts downstream from PARP-1, preventing the accumulation of unreplicated DNA in mitosis, and, thus, UFB formation. Finally, delaying entry into mitosis is sufficient to prevent UFB formation in both CDA-deficient and CDA-proficient cells, suggesting that both physiological and pathological UFBs are derived from unreplicated DNA. Our findings demonstrate an unsuspected requirement for a balanced nucleotide pool for optimal Chk1 activation both in unchallenged cells and in response to genotoxic stress.
Asunto(s)
Anafase , Quinasa 1 Reguladora del Ciclo Celular (Checkpoint 1)/metabolismo , Pirimidinas/metabolismo , Proteínas de la Ataxia Telangiectasia Mutada/metabolismo , Puntos de Control del Ciclo Celular , Citidina Desaminasa/metabolismo , Daño del ADN , Replicación del ADN , Activación Enzimática , Células HeLa , Humanos , Modelos Biológicos , Poli(ADP-Ribosa) Polimerasas/metabolismo , Fase SRESUMEN
Genome stability is jeopardized by imbalances of the dNTP pool; such imbalances affect the rate of fork progression. For example, cytidine deaminase (CDA) deficiency leads to an excess of dCTP, slowing the replication fork. We describe here a novel mechanism by which pyrimidine pool disequilibrium compromises the completion of replication and chromosome segregation: the intracellular accumulation of dCTP inhibits PARP-1 activity. CDA deficiency results in incomplete DNA replication when cells enter mitosis, leading to the formation of ultrafine anaphase bridges between sister-chromatids at "difficult-to-replicate" sites such as centromeres and fragile sites. Using molecular combing, electron microscopy and a sensitive assay involving cell imaging to quantify steady-state PAR levels, we found that DNA replication was unsuccessful due to the partial inhibition of basal PARP-1 activity, rather than slower fork speed. The stimulation of PARP-1 activity in CDA-deficient cells restores replication and, thus, chromosome segregation. Moreover, increasing intracellular dCTP levels generates under-replication-induced sister-chromatid bridges as efficiently as PARP-1 knockdown. These results have direct implications for Bloom syndrome (BS), a rare genetic disease combining susceptibility to cancer and genomic instability. BS results from mutation of the BLM gene, encoding BLM, a RecQ 3'-5' DNA helicase, a deficiency of which leads to CDA downregulation. BS cells thus have a CDA defect, resulting in a high frequency of ultrafine anaphase bridges due entirely to dCTP-dependent PARP-1 inhibition and independent of BLM status. Our study describes previously unknown pathological consequences of the distortion of dNTP pools and reveals an unexpected role for PARP-1 in preventing DNA under-replication and chromosome segregation defects.
Asunto(s)
Síndrome de Bloom/genética , Citidina Desaminasa/genética , Poli(ADP-Ribosa) Polimerasas/genética , Pirimidinas/metabolismo , Síndrome de Bloom/patología , Línea Celular , Centrómero/genética , Sitios Frágiles del Cromosoma/genética , Segregación Cromosómica/genética , Citidina Desaminasa/deficiencia , Replicación del ADN/genética , Inestabilidad Genómica , Humanos , Mitosis/genética , Poli(ADP-Ribosa) Polimerasa-1 , Poli(ADP-Ribosa) Polimerasas/biosíntesis , RecQ Helicasas/genética , Intercambio de Cromátides Hermanas/genéticaRESUMEN
Cytidine deaminase (CDA) catalyzes the deamination of cytidine (C) and deoxycytidine (dC) to uridine and deoxyuridine, respectively. We recently showed that CDA deficiency leads to genomic instability, a hallmark of cancers. We therefore investigated whether constitutive CDA inactivation conferred a predisposition to cancer development. We developed a novel mouse model of Cda deficiency by generating Cda-knockout mice. Cda+/+ and Cda-/- mice did not differ in lifetime phenotypic or behavioral characteristics, or in the frequency or type of spontaneous cancers. However, the frequency of chemically induced tumors in the colon was significantly lower in Cda-/- mice. An analysis of primary kidney cells from Cda-/- mice revealed an excess of C and dC associated with significantly higher frequencies of sister chromatid exchange and ultrafine anaphase bridges and lower Parp-1 activity than in Cda+/+ cells. Our results suggest that, despite inducing genetic instability, an absence of Cda limits the number of chemically induced tumors. These results raise questions about whether a decrease in basal Parp-1 activity can protect against inflammation-driven tumorigenesis; we discuss our findings in light of published data for the Parp-1-deficient mouse model.
Asunto(s)
Neoplasias del Colon , Citidina Desaminasa , Animales , Ratones , Citidina Desaminasa/genética , Inhibidores de Poli(ADP-Ribosa) Polimerasas , Inestabilidad Genómica , Neoplasias del Colon/inducido químicamente , Neoplasias del Colon/genéticaRESUMEN
Cytidine deaminase (CDA), an enzyme of the pyrimidine salvage pathway, deaminates cytidine, deoxycytidine and analogs, such as gemcitabine. Constitutive low levels of CDA activity have been reported in the blood of patients with hematological malignancies or suffering from gemcitabine toxicity. We previously reported that cellular CDA deficiency leads to genetic instability. We therefore hypothesized that constitutive CDA deficiency might confer a predisposition to cancer. We analyzed CDA activity and expression in blood samples from breast cancer (BC) patients with a suspected predisposition to the disease, and in healthy controls. Contrary to our hypothesis, we found that both CDA activity and mRNA levels were higher in blood samples from BC patients than in those from controls, and that this difference was not due to excess neutrophils. CDA activity levels were significantly higher in the serum samples of BC patients treated by radiotherapy (RT) than in those of untreated healthy controls, and hormone therapy in RT-treated BC patients was associated with significantly lower levels of CDA activity. A preliminary analysis of CDA activity in the serum of the very few BC patients who had undergone no treatment other than surgery suggested that the increase in CDA activity might be due to the breast cancer itself. Our findings raise important questions, which should lead to studies to elucidate the origin and significance of the increase in CDA activity in the serum of BC patients, and the impact of hormone therapy.
Asunto(s)
Neoplasias de la Mama , Citidina Desaminasa/metabolismo , Susceptibilidad a Enfermedades , Femenino , Genotipo , Hormonas , HumanosRESUMEN
Topoisomerase IIα (Topo IIα), a well-conserved double-stranded DNA (dsDNA)-specific decatenase, processes dsDNA catenanes resulting from DNA replication during mitosis. Topo IIα defects lead to an accumulation of ultrafine anaphase bridges (UFBs), a type of chromosome non-disjunction. Topo IIα has been reported to resolve DNA anaphase threads, possibly accounting for the increase in UFB frequency upon Topo IIα inhibition. We hypothesized that the excess UFBs might also result, at least in part, from an impairment of the prevention of UFB formation by Topo IIα. We found that Topo IIα inhibition promotes UFB formation without affecting the global disappearance of UFBs during mitosis, but leads to an aberrant UFB resolution generating DNA damage within the next G1. Moreover, we demonstrated that Topo IIα inhibition promotes the formation of two types of UFBs depending on cell cycle phase. Topo IIα inhibition during S-phase compromises complete DNA replication, leading to the formation of UFB-containing unreplicated DNA, whereas Topo IIα inhibition during mitosis impedes DNA decatenation at metaphase-anaphase transition, leading to the formation of UFB-containing DNA catenanes. Thus, Topo IIα activity is essential to prevent UFB formation in a cell-cycle-dependent manner and to promote DNA damage-free resolution of UFBs.
Asunto(s)
ADN-Topoisomerasas de Tipo II/metabolismo , Proteínas de Unión a Poli-ADP-Ribosa/metabolismo , Razoxano/farmacología , Anafase , Segregación Cromosómica , Daño del ADN , Replicación del ADN/efectos de los fármacos , Células HeLa , Humanos , No Disyunción Genética , Proteínas de Unión a Poli-ADP-Ribosa/antagonistas & inhibidoresRESUMEN
Cytidine deaminase (CDA) deficiency causes pyrimidine pool disequilibrium. We previously reported that the excess cellular dC and dCTP resulting from CDA deficiency jeopardizes genome stability, decreasing basal poly(ADP-ribose) polymerase 1 (PARP-1) activity and increasing ultrafine anaphase bridge (UFB) formation. Here, we investigated the mechanism underlying the decrease in PARP-1 activity in CDA-deficient cells. PARP-1 activity is dependent on intracellular NAD+ concentration. We therefore hypothesized that defects of the NAD+ salvage pathway might result in decreases in PARP-1 activity. We found that the inhibition or depletion of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the NAD+ salvage biosynthesis pathway, mimicked CDA deficiency, resulting in a decrease in basal PARP-1 activity, regardless of NAD+ levels. Furthermore, the expression of exogenous wild-type NAMPT fully restored basal PARP-1 activity and prevented the increase in UFB frequency in CDA-deficient cells. No such effect was observed with the catalytic mutant. Our findings demonstrate that (1) the inhibition of NAMPT activity in CDA-proficient cells lowers basal PARP-1 activity, and (2) the expression of exogenous wild-type NAMPT, but not of the catalytic mutant, fully restores basal PARP-1 activity in CDA-deficient cells; these results strongly suggest that basal PARP-1 activity in CDA-deficient cells decreases due to a reduction of NAMPT activity.
Asunto(s)
Citidina Desaminasa/deficiencia , NAD/metabolismo , Poli(ADP-Ribosa) Polimerasa-1/metabolismo , Citidina Desaminasa/metabolismo , Citocinas/antagonistas & inhibidores , Citocinas/genética , Citocinas/metabolismo , Células HeLa , Humanos , Mutación/genética , Niacinamida/metabolismo , Nicotinamida Fosforribosiltransferasa/antagonistas & inhibidores , Nicotinamida Fosforribosiltransferasa/genética , Nicotinamida Fosforribosiltransferasa/metabolismoRESUMEN
Bloom Syndrome (BS) is a rare genetic disease characterized by high levels of chromosomal instability and an increase in cancer risk. Cytidine deaminase (CDA) expression is downregulated in BS cells, leading to an excess of cellular dC and dCTP that reduces basal PARP-1 activity, compromising optimal Chk1 activation and reducing the efficiency of downstream checkpoints. This process leads to the accumulation of unreplicated DNA during mitosis and, ultimately, ultrafine anaphase bridge (UFB) formation. BS cells also display incomplete sister chromatid disjunction when depleted of cohesin. Using a combination of fluorescence in situ hybridization and chromosome spreads, we investigated the possible role of CDA deficiency in the incomplete sister chromatid disjunction in cohesin-depleted BS cells. The decrease in basal PARP-1 activity in CDA-deficient cells compromised sister chromatid disjunction in cohesin-depleted cells, regardless of BLM expression status. The observed incomplete sister chromatid disjunction may be due to the accumulation of unreplicated DNA during mitosis in CDA-deficient cells, as reflected in the changes in centromeric DNA structure associated with the decrease in basal PARP-1 activity. Our findings reveal a new function of PARP-1 in sister chromatid disjunction during mitosis.
Asunto(s)
Cromátides/metabolismo , Citidina Desaminasa/deficiencia , No Disyunción Genética , Poli(ADP-Ribosa) Polimerasas/metabolismo , Intercambio de Cromátides Hermanas , Proteínas de Ciclo Celular , Centrómero/metabolismo , Citidina Desaminasa/metabolismo , ADN/química , Proteínas de Unión al ADN , Células HeLa , Humanos , Metafase , Modelos Biológicos , Proteínas Nucleares/metabolismo , Fosfoproteínas/metabolismoRESUMEN
Cells from Bloom's syndrome patients display genome instability due to a defective BLM and the downregulation of cytidine deaminase. Here, we use a genome-wide RNAi-synthetic lethal screen and transcriptomic profiling to identify genes enabling BLM-deficient and/or cytidine deaminase-deficient cells to tolerate constitutive DNA damage and replication stress. We found a synthetic lethal interaction between cytidine deaminase and microtubule-associated protein Tau deficiencies. Tau is overexpressed in cytidine deaminase-deficient cells, and its depletion worsens genome instability, compromising cell survival. Tau is recruited, along with upstream-binding factor, to ribosomal DNA loci. Tau downregulation decreases upstream binding factor recruitment, ribosomal RNA synthesis, ribonucleotide levels, and affects ribosomal DNA stability, leading to the formation of a new subclass of human ribosomal ultrafine anaphase bridges. We describe here Tau functions in maintaining survival of cytidine deaminase-deficient cells, and ribosomal DNA transcription and stability. Moreover, our findings for cancer tissues presenting concomitant cytidine deaminase underexpression and Tau upregulation open up new possibilities for anti-cancer treatment.Cytidine deaminase (CDA) deficiency leads to genome instability. Here the authors find a synthetic lethal interaction between CDA and the microtubule-associated protein Tau deficiencies, and report that Tau depletion affects rRNA synthesis, ribonucleotide pool balance, and rDNA stability.
Asunto(s)
Síndrome de Bloom/genética , ADN Ribosómico/metabolismo , Proteínas tau/fisiología , Síndrome de Bloom/patología , Supervivencia Celular , Citidina Desaminasa/deficiencia , Regulación hacia Abajo , Inestabilidad Genómica , Células HeLa , Humanos , RecQ Helicasas/genética , Regulación hacia Arriba , Proteínas tau/genética , Proteínas tau/metabolismoRESUMEN
Purpose: One of the main challenges in cancer therapy is the identification of molecular mechanisms mediating resistance or sensitivity to treatment. Cytidine deaminase (CDA) was reported to be downregulated in cells derived from patients with Bloom syndrome, a genetic disease associated with a strong predisposition to a wide range of cancers. The purpose of this study was to determine whether CDA deficiency could be associated with tumors from the general population and could constitute a predictive marker of susceptibility to antitumor drugs.Experimental Design: We analyzed CDA expression in silico, in large datasets for cancer cell lines and tumors and in various cancer cell lines and primary tumor tissues using IHC, PDXs, qRT-PCR, and Western blotting. We also studied the mechanism underlying CDA silencing and searched for molecules that might target specifically CDA-deficient tumor cells using in silico analysis coupled to classical cellular experimental approaches.Results: We found that CDA expression is downregulated in about 60% of cancer cells and tissues. We demonstrate that DNA methylation is a prevalent mechanism of CDA silencing in tumors. Finally, we show that CDA-deficient tumor cells can be specifically targeted with epigenetic treatments and with the anticancer drug aminoflavone.Conclusions: CDA expression status identifies new subgroups of cancers, and CDA deficiency appears to be a novel and relevant predictive marker of susceptibility to antitumor drugs, opening up new possibilities for treating cancer. Clin Cancer Res; 23(8); 2116-26. ©2016 AACR.
Asunto(s)
Biomarcadores de Tumor/análisis , Citidina Desaminasa/deficiencia , Neoplasias/enzimología , Animales , Western Blotting , Línea Celular Tumoral , Resistencia a Antineoplásicos/fisiología , Humanos , Inmunohistoquímica , Ratones , Reacción en Cadena en Tiempo Real de la Polimerasa , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
The absence of Tsa1, a key peroxiredoxin that scavenges H2O2 in Saccharomyces cerevisiae, causes the accumulation of a broad spectrum of mutations. Deletion of TSA1 also causes synthetic lethality in combination with mutations in RAD51 or several key genes involved in DNA double-strand break repair. In the present study, we propose that the accumulation of reactive oxygen species (ROS) is the primary cause of genome instability of tsa1Δ cells. In searching for spontaneous suppressors of synthetic lethality of tsa1Δ rad51Δ double mutants, we identified that the loss of thioredoxin reductase Trr1 rescues their viability. The trr1Δ mutant displayed a Can(R) mutation rate 5-fold lower than wild-type cells. Additional deletion of TRR1 in tsa1Δ mutant reduced substantially the Can(R) mutation rate of tsa1Δ strain (33-fold), and to a lesser extent, of rad51Δ strain (4-fold). Loss of Trr1 induced Yap1 nuclear accumulation and over-expression of a set of Yap1-regulated oxido-reductases with antioxidant properties that ultimately re-equilibrate intracellular redox environment, reducing substantially ROS-associated DNA damages. This trr1Δ -induced effect was largely thioredoxin-dependent, probably mediated by oxidized forms of thioredoxins, the primary substrates of Trr1. Thioredoxin Trx1 and Trx2 were constitutively and strongly oxidized in the absence of Trr1. In trx1Δ trx2Δ cells, Yap1 was only moderately activated; consistently, the trx1Δ trx2Δ double deletion failed to efficiently rescue the viability of tsa1Δ rad51Δ. Finally, we showed that modulation of the dNTP pool size also influences the formation of spontaneous mutation in trr1Δ and trx1Δ trx2Δ strains. We present a tentative model that helps to estimate the respective impact of ROS level and dNTP concentration in the generation of spontaneous mutations.
Asunto(s)
Inestabilidad Genómica , Mutación , Peroxidasas/genética , Proteínas de Saccharomyces cerevisiae/genética , Tiorredoxina Reductasa 1/genética , Daño del ADN/genética , Reparación del ADN/genética , Peroxidasas/metabolismo , Recombinasa Rad51/genética , Recombinasa Rad51/metabolismo , Especies Reactivas de Oxígeno/metabolismo , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Tiorredoxina Reductasa 1/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Centromeres are specialized chromosome domains that control chromosome segregation during mitosis, but little is known about the mechanisms underlying the maintenance of their integrity. Centromeric ultrafine anaphase bridges are physiological DNA structures thought to contain unresolved DNA catenations between the centromeres separating during anaphase. BLM and PICH helicases colocalize at these ultrafine anaphase bridges and promote their resolution. As PICH is detectable at centromeres from prometaphase onwards, we hypothesized that BLM might also be located at centromeres and that the two proteins might cooperate to resolve DNA catenations before the onset of anaphase. Using immunofluorescence analyses, we demonstrated the recruitment of BLM to centromeres from G2 phase to mitosis. With a combination of fluorescence in situ hybridization, electron microscopy, RNA interference, chromosome spreads and chromatin immunoprecipitation, we showed that both BLM-deficient and PICH-deficient prometaphase cells displayed changes in centromere structure. These cells also had a higher frequency of centromeric non disjunction in the absence of cohesin, suggesting the persistence of catenations. Both proteins were required for the correct recruitment to the centromere of active topoisomerase IIα, an enzyme specialized in the catenation/decatenation process. These observations reveal the existence of a functional relationship between BLM, PICH and topoisomerase IIα in the centromere decatenation process. They indicate that the higher frequency of centromeric ultrafine anaphase bridges in BLM-deficient cells and in cells treated with topoisomerase IIα inhibitors is probably due not only to unresolved physiological ultrafine anaphase bridges, but also to newly formed ultrafine anaphase bridges. We suggest that BLM and PICH cooperate in rendering centromeric catenates accessible to topoisomerase IIα, thereby facilitating correct centromere disjunction and preventing the formation of supernumerary centromeric ultrafine anaphase bridges.
Asunto(s)
Antígenos de Neoplasias/metabolismo , Centrómero/metabolismo , ADN Helicasas/metabolismo , ADN-Topoisomerasas de Tipo II/metabolismo , Proteínas de Unión al ADN/metabolismo , RecQ Helicasas/metabolismo , Anafase , Proteínas de Ciclo Celular/metabolismo , Centrómero/química , Centrómero/enzimología , Proteínas Cromosómicas no Histona/metabolismo , Cromosomas/metabolismo , ADN Helicasas/antagonistas & inhibidores , ADN Helicasas/genética , ADN Encadenado/metabolismo , Fase G2 , Células HeLa , Humanos , Mitosis , Mutagénesis Sitio-Dirigida , Prometafase , Interferencia de ARN , ARN Interferente Pequeño/metabolismo , RecQ Helicasas/antagonistas & inhibidores , RecQ Helicasas/genética , CohesinasRESUMEN
Defects in DNA replication are associated with genetic instability and cancer development, as illustrated in Bloom syndrome. Features of this syndrome include a slowdown in replication speed, defective fork reactivation and high rates of sister chromatid exchange, with a general predisposition to cancer. Bloom syndrome is caused by mutations in the BLM gene encoding a RecQ helicase. Here we report that BLM deficiency is associated with a strong cytidine deaminase defect, leading to pyrimidine pool disequilibrium. In BLM-deficient cells, pyrimidine pool normalization leads to reduction of sister chromatid exchange frequency and is sufficient for full restoration of replication fork velocity but not the fork restart defect, thus identifying the part of the Bloom syndrome phenotype because of pyrimidine pool imbalance. This study provides new insights into the molecular basis of control of replication speed and the genetic instability associated with Bloom syndrome. Nucleotide pool disequilibrium could be a general phenomenon in a large spectrum of precancerous and cancer cells.
Asunto(s)
Síndrome de Bloom/genética , Replicación del ADN/genética , Inestabilidad Genómica/genética , Pirimidinas/metabolismo , RecQ Helicasas/deficiencia , Western Blotting , Línea Celular , Citidina Desaminasa/metabolismo , Cartilla de ADN/genética , Humanos , Análisis por Micromatrices , Mutagénesis Sitio-Dirigida , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Intercambio de Cromátides Hermanas/genética , Estadísticas no ParamétricasRESUMEN
Bloom's syndrome (BS) displays one of the strongest known correlations between chromosomal instability and a high risk of cancer at an early age. BS cells combine a reduced average fork velocity with constitutive endogenous replication stress. However, the response of BS cells to replication stress induced by hydroxyurea (HU), which strongly slows the progression of replication forks, remains unclear due to publication of conflicting results. Using two different cellular models of BS, we showed that BLM deficiency is not associated with sensitivity to HU, in terms of clonogenic survival, DSB generation, and SCE induction. We suggest that surviving BLM-deficient cells are selected on the basis of their ability to deal with an endogenous replication stress induced by replication fork slowing, resulting in insensitivity to HU-induced replication stress.
RESUMEN
Little is known about the functional interaction between the Bloom's syndrome protein (BLM) and the recombinase RAD51 within cells. Using RNA interference technology, we provide the first demonstration that RAD51 acts upstream from BLM to prevent anaphase bridge formation. RAD51 downregulation was associated with an increase in the frequency of BLM-positive anaphase bridges, but not of BLM-associated ultrafine bridges. Time-lapse live microscopy analysis of anaphase bridge cells revealed that BLM promoted cell survival in the absence of Rad51. Our results directly implicate BLM in limiting the lethality associated with RAD51 deficiency through the processing of anaphase bridges resulting from the RAD51 defect. These findings provide insight into the molecular basis of some cancers possibly associated with variants of the RAD51 gene family.