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BRCA1 Is Required for Maintenance of Phospho-Chk1 and G2/M Arrest during DNA Cross-Link Repair in DT40 Cells. Mol Cell Biol 2015; 35:3829-40. [PMID: 26324327 PMCID: PMC4609749 DOI: 10.1128/mcb.01497-14] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 08/14/2015] [Indexed: 12/16/2022] Open
Abstract
The Fanconi anemia DNA repair pathway is pivotal for the efficient repair of DNA interstrand cross-links. Here, we show that FA-defective (Fancc−) DT40 cells arrest in G2 phase following cross-link damage and trigger apoptosis. Strikingly, cell death was reduced in Fancc− cells by additional deletion of the BRCA1 tumor suppressor, resulting in elevated clonogenic survival. Increased resistance to cross-link damage was not due to loss of toxic BRCA1-mediated homologous recombination but rather through the loss of a G2 checkpoint. This proapoptotic role also required the BRCA1-A complex member ABRAXAS (FAM175A). Finally, we show that BRCA1 promotes G2 arrest and cell death by prolonging phosphorylation of Chk1 on serine 345 after DNA damage to sustain arrest. Our data imply that DNA-induced cross-link death in cells defective in the FA pathway is dependent on the ability of BRCA1 to prolong cell cycle arrest in G2 phase.
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Molina B, Marchetti F, Gómez L, Ramos S, Torres L, Ortiz R, Altamirano-Lozano M, Carnevale A, Frias S. Hydroxyurea induces chromosomal damage in G2 and enhances the clastogenic effect of mitomycin C in Fanconi anemia cells. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2015; 56:457-467. [PMID: 25663157 DOI: 10.1002/em.21938] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Accepted: 01/05/2015] [Indexed: 06/04/2023]
Abstract
Fanconi's anemia (FA) is a recessive disease; 16 genes are currently recognized in FA. FA proteins participate in the FA/BRCA pathway that plays a crucial role in the repair of DNA damage induced by crosslinking compounds. Hydroxyurea (HU) is an agent that induces replicative stress by inhibiting ribonucleotide reductase (RNR), which synthesizes deoxyribonucleotide triphosphates (dNTPs) necessary for DNA replication and repair. HU is known to activate the FA pathway; however, its clastogenic effects are not well characterized. We have investigated the effects of HU treatment alone or in sequential combination with mitomycin-C (MMC) on FA patient-derived lymphoblastoid cell lines from groups FA-A, B, C, D1/BRCA2, and E and on lymphocytes from two unclassified FA patients. All FA cells showed a significant increase (P < 0.05) in chromosomal aberrations following treatment with HU during the last 3 h before mitosis. Furthermore, when FA cells previously exposed to MMC were treated with HU, we observed an increase of MMC-induced DNA damage that was characterized by high occurrence of DNA breaks and a reduction in rejoined chromosomal aberrations. These findings show that exposure to HU during G2 induces chromosomal aberrations by a mechanism that is independent of its well-known role in replication fork stalling during S-phase and that HU interfered mainly with the rejoining process of DNA damage. We suggest that impaired oxidative stress response, lack of an adequate amount of dNTPs for DNA repair due to RNR inhibition, and interference with cell cycle control checkpoints underlie the clastogenic activity of HU in FA cells. Environ. Mol. Mutagen. 56:457-467, 2015. © 2015 Wiley Periodicals, Inc.
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Affiliation(s)
- Bertha Molina
- Laboratorio de Citogenética, Instituto Nacional de Pediatría, México
| | | | - Laura Gómez
- Laboratorio de Citogenética, Instituto Nacional de Pediatría, México
| | - Sandra Ramos
- Laboratorio de Citogenética, Instituto Nacional de Pediatría, México
| | - Leda Torres
- Laboratorio de Citogenética, Instituto Nacional de Pediatría, México
| | - Rocio Ortiz
- Laboratorio de Citometría de Flujo, Universidad Autónoma Metropolitana, Iztapalapa, Mexico
| | | | - Alessandra Carnevale
- Subdirección de Genómica Poblacional, Instituto Nacional de Medicina Genómica, México
| | - Sara Frias
- Laboratorio de Citogenética, Instituto Nacional de Pediatría, México
- Departamento de Medicina, Genómica y Toxicología Ambiental, Instituto de Investigaciones Biomédicas, UNAM, México
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Thompson LH, Hinz JM. Cellular and molecular consequences of defective Fanconi anemia proteins in replication-coupled DNA repair: mechanistic insights. Mutat Res 2009; 668:54-72. [PMID: 19622404 PMCID: PMC2714807 DOI: 10.1016/j.mrfmmm.2009.02.003] [Citation(s) in RCA: 122] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Revised: 01/20/2009] [Accepted: 02/10/2009] [Indexed: 12/13/2022]
Abstract
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.
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Affiliation(s)
- Larry H Thompson
- Biology and Biotechnology Division, L452, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-0808, United States.
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Neveling K, Endt D, Hoehn H, Schindler D. Genotype-phenotype correlations in Fanconi anemia. Mutat Res 2009; 668:73-91. [PMID: 19464302 DOI: 10.1016/j.mrfmmm.2009.05.006] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Revised: 03/30/2009] [Accepted: 05/12/2009] [Indexed: 11/30/2022]
Abstract
Although still incomplete, we now have a remarkably detailed and nuanced picture of both phenotypic and genotypic components of the FA spectrum. Initially described as a combination of pancytopenia with a limited number of physical anomalies, it was later recognized that additional features were compatible with the FA phenotype, including a form without detectable malformations (Estren-Dameshek variant). The discovery of somatic mosaicism extended the boundaries of the FA phenotype to cases even without any overt hematological manifestations. This clinical heterogeneity was augmented by new conceptualizations. There was the realization of a constant risk for the development of myelodysplasia and certain malignancies, including acute myelogenous leukemia and squamous cell carcinoma, and there was the emergence of a distinctive cellular phenotype. A striking degree of genetic heterogeneity became apparent with the delineation of at least 12 complementation groups and the identification of their underlying genes. Although functional genetic insights have fostered the interpretation of many phenotypic features, surprisingly few stringent genotype-phenotype connections have emerged. In addition to myriad genetic alterations, less predictable influences are likely to modulate the FA phenotype, including modifier genes, environmental factors and chance effects. In reviewing the current status of genotype-phenotype correlations, we arrive at a unifying hypothesis to explain the remarkably wide range of FA phenotypes. Given the large body of evidence that genomic instability is a major underlying mechanism of accelerated ageing phenotypes, we propose that the numerous FA variants can be viewed as differential modulations and compression in time of intrinsic biological ageing.
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Affiliation(s)
- Kornelia Neveling
- Department of Human and Medical Genetics, University of Wurzburg, Biozentrum, Am Hubland, Wurzburg D-97074, Germany
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Abstract
Inherited defects in DNA repair or the processing of DNA damage can lead to disease. Both autosomal recessive and autosomal dominant modes of inheritance are represented. The diseases as a group are characterized by genomic instability, with eventual appearance of cancer. The inherited defects frequently have a specific DNA damage sensitivity, with cells from affected individuals showing normal resistance to other genotoxic agents. The known defects are subtle alterations in transcription, replication, or recombination, with alternate pathways of processing permitting cellular viability. Distinct diseases may arise from different mutations in one gene; thus, clinical phenotypes may reflect the loss of different partial functions of a gene. The findings indicate that partial defects in transcription or recombination lead to genomic instability, cancer, and characteristic disease phenotypes.
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Affiliation(s)
- R E Moses
- Department of Molecular and Medical Genetics, Oregon Health Sciences University, Portland, Oregon 97201, USA.
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Akkari YM, Bateman RL, Reifsteck CA, D'Andrea AD, Olson SB, Grompe M. The 4N cell cycle delay in Fanconi anemia reflects growth arrest in late S phase. Mol Genet Metab 2001; 74:403-12. [PMID: 11749045 DOI: 10.1006/mgme.2001.3259] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Fanconi anemia (FA) is a human genetic disorder characterized by hypersensitivity to DNA crosslinking agents. Its cellular phenotypes include increased chromosome breakage and a marked cell-cycle delay with 4N DNA content after introduction of interstrand DNA crosslinks (ICL). To further understand the nature of this delay previously described as a G2/M arrest, we introduced ICL specifically during G2 and monitored the cells for passage into mitosis. Our results showed that, even at the highest doses, postreplication ICL produced neither G2/M arrest nor chromosome breakage in FA-A or FA-C cells. This suggests that, similar to wild-type cells, DNA replication is required to trigger both responses. Therefore, the 4N cell DNA content observed in FA cells after ICL treatment also represents incomplete DNA replication and arrest in late S phase. FA fibroblasts from complementation groups A and C were able to recover from the ICL-induced cell-cycle arrest, but took approximately 3 times longer than controls. These results indicate that the FA pathway is required for the efficient resolution of ICL-induced S-phase arrest.
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Affiliation(s)
- Y M Akkari
- Department of Molecular and Medical Genetics, Oregon Health Sciences University, 3181 SW Sam Jackson Park Road L103, Portland, Oregon 97201, USA.
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Sala-Trepat M, Rouillard D, Escarceller M, Laquerbe A, Moustacchi E, Papadopoulo D. Arrest of S-phase progression is impaired in Fanconi anemia cells. Exp Cell Res 2000; 260:208-15. [PMID: 11035915 DOI: 10.1006/excr.2000.4994] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Fanconi anemia (FA) is an inherited cancer-susceptibility disorder, characterized by genomic instability, hypersensitivity to DNA cross-linking agents, and a prolonged G2 phase of the cell cycle. We observed a marked dose-dependent accumulation of FA cells in the G2 compartment after treatment with 4,5',8-trimethylpsoralen (Me(3)Pso) in combination with 365 nm irradiation. Using bivariate DNA distribution methodology, we determined the proportion of replicating and arresting S-phase cells and observed that, whereas normal cells arrested DNA replication in the presence of Me(3)Pso cross-links and monoadducts, FA lymphoblasts failed to arrest DNA synthesis. Taken together, the above data suggest that, in response to damage induced by DNA cross-linking agents, the S-phase checkpoint is inefficient in FA cells. This would lead to accumulation of secondary lesions, such as single- and double-strand breaks and gaps. The prolonged time in G2 phase seen in FA cells therefore exists in order to allow the cells to remove lesions which accumulated during the preceding abnormal S phase.
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Centurion SA, Kuo HR, Lambert WC. Damage-resistant DNA synthesis in Fanconi anemia cells treated with a DNA cross-linking agent. Exp Cell Res 2000; 260:216-21. [PMID: 11035916 DOI: 10.1006/excr.2000.4995] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Fanconi anemia (FA) is a recessive disorder associated with diverse congenital anomalies, progressive bone marrow failure, and a marked predisposition to develop cancer. At the cellular level, FA is characterized by a prolonged G(2) phase in proliferating cells and a marked hypersensitivity to both the cytotoxic and the clastogenic effects of agents which produce DNA interstrand cross-links. Treatment with these agents leads to even further prolongation of the G(2) phase in FA cells. We now show that FA cells, from four different complementation groups, fail to decrease their rates of replicative DNA synthesis, as do normal cells, following treatment with a DNA cross-linking agent. This may be responsible for the prolongation of the G2 phase seen in these cells, and suggests that the fundamental defect in response of FA cells to DNA cross-linking agents may be in the S phase, rather than the G(2) phase, of the cell cycle.
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Affiliation(s)
- S A Centurion
- Department of Pathology and Laboratory Medicine, UMDNJ-New Jersey Medical School, Newark, New Jersey, 07103-2714, USA
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9
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Abstract
Cancer is a multi-step process evolving as the result of the accumulation of a number of mutational events. The growing body of evidence implicating genetic instability as a key feature of this evolutionary process and the risk of malignancy associated with chromosomal instability syndromes highlight the importance of understanding the mechanisms that cells use to maintain the integrity of their genomes. Classic examples of inherited chromosomal instability with cancer predisposition are Bloom's syndrome, ataxia telangiectasia, and Fanconi anaemia, although the mechanisms involved are far from understood. Selected features of these inherited disorders are reviewed to provide a background to the more recently discovered inducible chromosomal instability, a phenotype in which apparently normal cells that have survived ionizing radiation and certain chemical insults may produce descendants exhibiting a high frequency of de novo chromosome aberrations and gene mutations. The phenotype is induced at frequencies considerably greater than conventional mutation frequencies but little is understood of the underlying mechanism(s). To date, chromosomal instability induced by ionizing radiation has been the most extensively studied phenotype and it is evident that the expression of inducible instability has a strong dependence on the type of radiation exposure, the cell type irradiated, and the genetic 'predisposition' of the irradiated cell.
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Affiliation(s)
- E G Wright
- Radiation and Genome Stability Unit, Medical Research Council, Harwell, Oxfordshire, U.K.
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10
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DNA Cross-Linker–Induced G2/M Arrest in Group C Fanconi Anemia Lymphoblasts Reflects Normal Checkpoint Function. Blood 1998. [DOI: 10.1182/blood.v91.1.275.275_275_287] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cells from individuals with Fanconi anemia (FA) arrest excessively in the G2/M cell cycle compartment after exposure to low doses of DNA cross-linking agents. The relationship of this abnormality to the fundamental genetic defect in such cells is unknown, but many investigators have speculated that the various FA genes directly regulate cell cycle checkpoints. We tested the hypothesis that the protein encoded by the FA group C complementing gene (FAC) functions to control a cell cycle checkpoint and that cells from group C patients (FA[C]) have abnormalities of cell cycle regulation directly related to the genetic mutation. We found that retroviral transduction of FA(C) lymphoblasts with wild-type FAC cDNA resulted in normalization of the cell cycle response to low-dose mitomycin C (MMC). However, when DNA damage was quantified in terms of cytogenetic damage or cellular cytotoxicity, we found similar degrees of G2/M arrest in response to equitoxic amounts of MMC in FA(C) cells as well as in normal lymphoblasts. Similar results were obtained using isogenic pairs of uncorrected, FAC- or mock-corrected (neo only) FA(C) cell lines. To test the function of other checkpoints we examined the effects of hydroxyurea (HU) and ionizing radiation on cell cycle kinetics of FA(C) and normal lymphoblasts as well as with isogenic pairs of uncorrected, FAC-corrected, or mock-corrected FA(C) cell lines. In all cases the cell cycle response of FA(C) and normal lymphoblasts to these two agents were identical. Based on these studies we conclude that the aberrant G2/M arrest that typifies the response of FA(C) cells to low doses of cross-linking agents does not represent an abnormal cell cycle response but instead represents a normal cellular response to the excessive DNA damage that results in FA(C) cells following exposure to low doses of cross-linking agents.
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11
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DNA Cross-Linker–Induced G2/M Arrest in Group C Fanconi Anemia Lymphoblasts Reflects Normal Checkpoint Function. Blood 1998. [DOI: 10.1182/blood.v91.1.275] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AbstractCells from individuals with Fanconi anemia (FA) arrest excessively in the G2/M cell cycle compartment after exposure to low doses of DNA cross-linking agents. The relationship of this abnormality to the fundamental genetic defect in such cells is unknown, but many investigators have speculated that the various FA genes directly regulate cell cycle checkpoints. We tested the hypothesis that the protein encoded by the FA group C complementing gene (FAC) functions to control a cell cycle checkpoint and that cells from group C patients (FA[C]) have abnormalities of cell cycle regulation directly related to the genetic mutation. We found that retroviral transduction of FA(C) lymphoblasts with wild-type FAC cDNA resulted in normalization of the cell cycle response to low-dose mitomycin C (MMC). However, when DNA damage was quantified in terms of cytogenetic damage or cellular cytotoxicity, we found similar degrees of G2/M arrest in response to equitoxic amounts of MMC in FA(C) cells as well as in normal lymphoblasts. Similar results were obtained using isogenic pairs of uncorrected, FAC- or mock-corrected (neo only) FA(C) cell lines. To test the function of other checkpoints we examined the effects of hydroxyurea (HU) and ionizing radiation on cell cycle kinetics of FA(C) and normal lymphoblasts as well as with isogenic pairs of uncorrected, FAC-corrected, or mock-corrected FA(C) cell lines. In all cases the cell cycle response of FA(C) and normal lymphoblasts to these two agents were identical. Based on these studies we conclude that the aberrant G2/M arrest that typifies the response of FA(C) cells to low doses of cross-linking agents does not represent an abnormal cell cycle response but instead represents a normal cellular response to the excessive DNA damage that results in FA(C) cells following exposure to low doses of cross-linking agents.
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Abstract
Fanconi anemia (FA) is a rare, autosomal recessive disease characterized by multiple congenital abnormalities, bone marrow failure, and cancer susceptibility. Although traditionally described as a classic clinical syndrome, as more is discovered regarding its basic molecular and cell biology, FA is emerging as a true premalignant syndrome. Two of the genes of the five known complementation groups have been cloned, and work to understand their function is underway. Further understanding of these gene products has lent new ideas concerning modes of novel therapy, including gene therapy. The impact of molecular biology on our understanding of basic biology and the clinical care of FA patients is discussed.
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Affiliation(s)
- G M Kupfer
- Division of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA
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Johnstone P, Reifsteck C, Kohler S, Worland P, Olson S, Moses RE. Fanconi anemia group A and D cell lines respond normally to inhibitors of cell cycle regulation. SOMATIC CELL AND MOLECULAR GENETICS 1997; 23:371-7. [PMID: 9661700 DOI: 10.1007/bf02673747] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Cells from patients with Fanconi anemia (FA) show decreased viability and decreased chromosome stability after treatment with DNA cross-linking agents, compared to normal cells. FA cells also show a relative accumulation at the G2/M transition after such treatment. This has suggested a possible checkpoint abnormality. In the studies presented here, treatment with hydroxyurea, caffeine or inhibitors of cell cycle kinases did not reveal abnormalities in survival or chromosome stability in FA-A or FA-D cells. Chromosomal breaks introduced by hydrogen peroxide or methyl methanesulfonate accumulated to the same extent in FA-A or FA-D cells as in normal cells. We conclude that FA-A and FA-D cells respond normally to agents known to alter the cell cycle or introduce DNA strand breaks. FA cells process strand breaks and a variety of DNA monoadducts normally. Our results are compatible with repair of DNA crosslinks being slower in FA than in normal cells and FA cells having normal cell cycle checkpoints.
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Affiliation(s)
- P Johnstone
- Department of Molecular and Medical Genetics, Oregon Health Sciences University, Portland 97201, USA
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Abstract
AbstractFanconi anemia (FA) is an autosomal recessive disorder characterized by developmental defects, bone marrow failure, and cancer susceptibility. Cells derived from FA patients are sensitive to crosslinking agents and have a prolonged G2 phase, suggesting a cell cycle abnormality. Although transfection of type-C FA cells with the FAC cDNA corrects these cellular abnormalities, the molecular function of the FAC polypeptide remains unknown. In the current study we show that expression of the FAC polypeptide is regulated during cell cycle progression. In synchronized HeLa cells, FAC protein expression increased during S phase, was maximal at the G2 /M transition, and declined during M phase. In addition, the FAC protein coimmunoprecipitated with the cyclin-dependent kinase, cdc2. We next tested various mutant forms of the FAC polypeptide for binding to cdc2. A patient-derived mutant FAC polypeptide, containing a point mutation at L554P, failed to bind to cdc2. The FAC/cdc2 binding interaction therefore correlated with the functional activity of the FAC protein. Moreover, binding of FAC to cdc2 was mediated by the carboxyl-terminal 50 amino acids of FAC in a region of the protein required for FAC function. Taken together, our results suggest that the binding of FAC and cdc2 is required for normal G2 /M progression in mammalian cells. Absence of a functional interaction between FAC and cdc2 in FA cells may underlie the cell cycle abnormality and clinical abnormalities of FA.
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Abstract
Fanconi anemia (FA) is an autosomal recessive disorder characterized by developmental defects, bone marrow failure, and cancer susceptibility. Cells derived from FA patients are sensitive to crosslinking agents and have a prolonged G2 phase, suggesting a cell cycle abnormality. Although transfection of type-C FA cells with the FAC cDNA corrects these cellular abnormalities, the molecular function of the FAC polypeptide remains unknown. In the current study we show that expression of the FAC polypeptide is regulated during cell cycle progression. In synchronized HeLa cells, FAC protein expression increased during S phase, was maximal at the G2 /M transition, and declined during M phase. In addition, the FAC protein coimmunoprecipitated with the cyclin-dependent kinase, cdc2. We next tested various mutant forms of the FAC polypeptide for binding to cdc2. A patient-derived mutant FAC polypeptide, containing a point mutation at L554P, failed to bind to cdc2. The FAC/cdc2 binding interaction therefore correlated with the functional activity of the FAC protein. Moreover, binding of FAC to cdc2 was mediated by the carboxyl-terminal 50 amino acids of FAC in a region of the protein required for FAC function. Taken together, our results suggest that the binding of FAC and cdc2 is required for normal G2 /M progression in mammalian cells. Absence of a functional interaction between FAC and cdc2 in FA cells may underlie the cell cycle abnormality and clinical abnormalities of FA.
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Affiliation(s)
- M S Meyn
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06510, USA
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