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Nor Azian Abdul Murad,
Jason K Cullen,
Matthew McKenzie,
Michael T Ryan,
David Thorburn, Nuri Gueven,
Junya Kobayashi,
Geoff Birrell,
Jian Yang,
Thilo Dörk,
Olivier Becherel,
Padraic Grattan-Smith,
Martin F Lavin
[show abstract]
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ABSTRACT: Defects in the recognition and/or repair of damage to DNA are responsible for a sub-group of autosomal recessive ataxias. Included in this group is a novel form of ataxia with oculomotor apraxia characterised by sensitivity to DNA damaging agents, a defect in p53 stabilisation, oxidative stress and resistance to apoptosis. We provide evidence here that the defect in this patient's cells is at the level of the mitochondrion. Mitochondrial membrane potential was markedly reduced in cells from the patient and ROS levels were elevated. This was accompanied by lipid peroxidation of mitochondrial proteins involved in electron transport and RNA synthesis. However, no gross changes or alteration in composition or activity of mitochondrial electron transport complexes was evident. Sequencing of mitochondrial DNA revealed a mutation, 1349T, in the mitochondrial cytochrome B gene. These results describe a patient with an apparently novel form of AOA characterised by a defect at the level of the mitochondrion.
Mitochondrion 11/2012; · 3.62 Impact Factor
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James A L Brown,
Tara L Roberts,
Renee Richards,
Rick Woods,
Geoff Birrell,
Y C Lim,
Shigeo Ohno,
Akio Yamashita,
Robert T Abraham, Nuri Gueven,
Martin F Lavin
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ABSTRACT: hSMG-1 is a member of the phosphoinositide 3 kinase-like kinase (PIKK) family with established roles in nonsense-mediated decay (NMD) of mRNA containing premature termination codons and in genotoxic stress responses to DNA damage. We report here a novel role for hSMG-1 in cytoplasmic stress granule (SG) formation. Exposure of cells to stress causing agents led to the localization of hSMG-1 to SG, identified by colocalization with TIA-1, G3BP1, and eIF4G. hSMG-1 small interfering RNA and the PIKK inhibitor wortmannin prevented formation of a subset of SG, while specific inhibitors of ATM, DNA-PK(cs), or mTOR had no effect. Exposure of cells to H(2)O(2) and sodium arsenite induced (S/T)Q phosphorylation of proteins. While Upf2 and Upf1, an essential substrate for hSMG-1 in NMD, were present in SG, NMD-specific Upf1 phosphorylation was not detected in SG, indicating hSMG-1's role in SG is separate from classical NMD. Thus, SG formation appears more complex than originally envisaged and hSMG-1 plays a central role in this process.
Molecular and cellular biology 09/2011; 31(22):4417-29. · 6.06 Impact Factor
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Magtouf Gatei,
Burkhard Jakob,
Philip Chen,
Amanda W. Kijas,
Olivier J. Becherel, Nuri Gueven,
Geoff Birrell,
Ji-Hoon Lee,
Tanya T. Paull,
Yaniv Lerenthal,
Shazrul Fazry,
Gisela Taucher-Scholz,
Reinhard Kalb,
Detlev Schindler,
Regina Waltes,
Thilo Dörk,
Martin F. Lavin
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ABSTRACT: The Mre11/Rad50/NBN complex plays a central role in coordinating the cellular response to DNA double-strand breaks. The importance
of Rad50 in that response is evident from the recent description of a patient with Rad50 deficiency characterized by chromosomal
instability and defective ATM-dependent signaling. We report here that ATM (defective in ataxia-telangiectasia) phosphorylates
Rad50 at a single site (Ser-635) that plays an important adaptor role in signaling for cell cycle control and DNA repair.
Although a Rad50 phosphosite-specific mutant (S635G) supported normal activation of ATM in Rad50-deficient cells, it was defective
in correcting DNA damage-induced signaling through the ATM-dependent substrate SMC1. This mutant also failed to correct radiosensitivity,
DNA double-strand break repair, and an S-phase checkpoint defect in Rad50-deficient cells. This was not due to disruption
of the Mre11/Rad50/NBN complex revealing for the first time that phosphorylation of Rad50 plays a key regulatory role as an
adaptor for specific ATM-dependent downstream signaling through SMC1 for DNA repair and cell cycle checkpoint control in the
maintenance of genome integrity.
Journal of Biological Chemistry 09/2011; 286(36):31542-31556. · 4.77 Impact Factor
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Magtouf Gatei,
Burkhard Jakob,
Philip Chen,
Amanda W Kijas,
Olivier J Becherel, Nuri Gueven,
Geoff Birrell,
Ji-Hoon Lee,
Tanya T Paull,
Yaniv Lerenthal,
Shazrul Fazry,
Gisela Taucher-Scholz,
Reinhard Kalb,
Detlev Schindler,
Regina Waltes,
Thilo Dörk,
Martin F Lavin
[show abstract]
[hide abstract]
ABSTRACT: The Mre11/Rad50/NBN complex plays a central role in coordinating the cellular response to DNA double-strand breaks. The importance of Rad50 in that response is evident from the recent description of a patient with Rad50 deficiency characterized by chromosomal instability and defective ATM-dependent signaling. We report here that ATM (defective in ataxia-telangiectasia) phosphorylates Rad50 at a single site (Ser-635) that plays an important adaptor role in signaling for cell cycle control and DNA repair. Although a Rad50 phosphosite-specific mutant (S635G) supported normal activation of ATM in Rad50-deficient cells, it was defective in correcting DNA damage-induced signaling through the ATM-dependent substrate SMC1. This mutant also failed to correct radiosensitivity, DNA double-strand break repair, and an S-phase checkpoint defect in Rad50-deficient cells. This was not due to disruption of the Mre11/Rad50/NBN complex revealing for the first time that phosphorylation of Rad50 plays a key regulatory role as an adaptor for specific ATM-dependent downstream signaling through SMC1 for DNA repair and cell cycle checkpoint control in the maintenance of genome integrity.
Journal of Biological Chemistry 07/2011; 286(36):31542-56. · 4.77 Impact Factor
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ABSTRACT: Changes to the redox status of biological systems have been implicated in the pathogenesis of a wide variety of disorders. Sensitive quantification of these changes has been developed using a novel fluorescent probe containing a redox-sensitive nitroxide moiety. As well as being able to selectively detect the superoxide radical in vitro, this method can measure overall changes to the cellular redox environment using flow cytometry on the basis of nitroxide reduction. The reversible nature of the probe's detection mechanism offers the unique advantage of being able to monitor redox changes in both oxidizing and reducing directions in real time.
Free radical biology & medicine 03/2010; 49(1):67-76. · 5.42 Impact Factor
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Olivier J Becherel,
Burkhard Jakob,
Amy L Cherry, Nuri Gueven,
Markus Fusser,
Amanda W Kijas,
Cheng Peng,
Sachin Katyal,
Peter J McKinnon,
Junjie Chen,
Bernd Epe,
Stephen J Smerdon,
Gisela Taucher-Scholz,
Martin F Lavin
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ABSTRACT: Aprataxin, defective in the neurodegenerative disorder ataxia oculomotor apraxia type 1, resolves abortive DNA ligation intermediates during DNA repair. Here, we demonstrate that aprataxin localizes at sites of DNA damage induced by high LET radiation and binds to mediator of DNA-damage checkpoint protein 1 (MDC1/NFBD1) through a phosphorylation-dependent interaction. This interaction is mediated via the aprataxin FHA domain and multiple casein kinase 2 di-phosphorylated S-D-T-D motifs in MDC1. X-ray structural and mutagenic analysis of aprataxin FHA domain, combined with modelling of the pSDpTD peptide interaction suggest an unusual FHA binding mechanism mediated by a cluster of basic residues at and around the canonical pT-docking site. Mutation of aprataxin FHA Arg29 prevented its interaction with MDC1 and recruitment to sites of DNA damage. These results indicate that aprataxin is involved not only in single strand break repair but also in the processing of a subset of double strand breaks presumably through its interaction with MDC1.
Nucleic Acids Research 12/2009; 38(5):1489-503. · 8.03 Impact Factor
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ABSTRACT: Failure to maintain the integrity of DNA/chromatin can result in genome instability and an increased risk of cancer. The description of a number of human genetic disorders characterised not only by cancer predisposition but by a broader phenotype including neurodegeneration suggests that maintaining genome stability is also important for preserving post-mitotic neurons. The identification of genes associated with other neurodegenerative disorders provides further evidence for the importance of DNA damage response and DNA repair genes in protecting against neurodegeneration. This theme is further developed in this review.
DNA Repair 08/2008; 7(7):1061-76. · 4.14 Impact Factor
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Amila Suraweera,
Olivier J Becherel,
Philip Chen,
Natalie Rundle,
Rick Woods,
Jun Nakamura,
Magtouf Gatei,
Chiara Criscuolo,
Alessandro Filla,
Luciana Chessa,
Markus Fusser,
Bernd Epe, Nuri Gueven,
Martin F Lavin
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ABSTRACT: A defective response to DNA damage is observed in several human autosomal recessive ataxias with oculomotor apraxia, including ataxia-telangiectasia. We report that senataxin, defective in ataxia oculomotor apraxia (AOA) type 2, is a nuclear protein involved in the DNA damage response. AOA2 cells are sensitive to H2O2, camptothecin, and mitomycin C, but not to ionizing radiation, and sensitivity was rescued with full-length SETX cDNA. AOA2 cells exhibited constitutive oxidative DNA damage and enhanced chromosomal instability in response to H2O2. Rejoining of H2O2-induced DNA double-strand breaks (DSBs) was significantly reduced in AOA2 cells compared to controls, and there was no evidence for a defect in DNA single-strand break repair. This defect in DSB repair was corrected by full-length SETX cDNA. These results provide evidence that an additional member of the autosomal recessive AOA is also characterized by a defective response to DNA damage, which may contribute to the neurodegeneration seen in this syndrome.
The Journal of Cell Biology 07/2007; 177(6):969-79. · 10.26 Impact Factor
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ABSTRACT: Ataxia-telangiectasia (A-T) is a rare autosomal recessive genetic disorder characterized by progressive neurodegeneration, a high risk of cancer and immunodeficiency. These patients are also hypersensitive to radiotherapy. The gene product defective in this syndrome, ATM (ataxia-telangiectasia mutated), normally recognizes DNA damage and signal to the DNA repair machinery and the cell cycle checkpoints to minimize the risk of genetic damage. No curative strategy for this disease exists. Treatment has focused on slowing the progress of the neurodegeneration; devising approaches for the treatment of tumours while minimizing side effects and treatment with immunoglobulin for the immunodeficiency. The most debilitating feature of this disorder is the progressive neurodegeneration due to loss of Purkinje cells in the cerebellum and malfunction of other neuronal cells. Correcting for the loss of Purkinje cells is technically very difficult and would require transplantation of embryonic stem cells. However, since it seems likely that oxidative stress may contribute to the neurodegeneration in A-T, potential therapies based on the use of antioxidants offer some hope. We describe the natural course of disease, some supportive therapeutic approaches already in use and those with potential based on our knowledge of molecular and cellular characteristics of this disorder.
British Medical Bulletin 02/2007; 81-82:129-47. · 4.54 Impact Factor
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ABSTRACT: Mutations in the ATM gene (mutated in ataxia telangiectasia) in both humans and mice predispose to lymphoid tumors. A defect in this gene also causes neurodegeneration in humans and a less severe neurological phenotype in mice. There is some evidence that oxidative stress contributes to these defects, suggesting that antioxidants could alleviate the phenotype. We demonstrate here that the antioxidant 5-carboxy-1,1,3,3-tetramethylisoindolin-2-yloxyl (CTMIO) dramatically delays the onset of thymic lymphomas in Atm(-/-) mice which is not due to an enhancement of apoptosis by CTMIO. We also show that this compound corrects neurobehavioral deficits in these mice and reduces oxidative damage to Purkinje cells. The likely mechanism of action of CTMIO is due to a reduction in oxidative stress, which is protective against both the tumor progression and the development of neurological abnormalities. These data suggest that antioxidant therapy has considerable potential in the management of ataxia telangiectasia and possibly other neurodegenerative disorders where oxidative stress is implicated.
Free Radical Biology and Medicine 10/2006; 41(6):992-1000. · 5.42 Impact Factor
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ABSTRACT: The APTX gene, mutated in patients with the neurological disorder ataxia with oculomotor apraxia type 1 (AOA1), encodes a novel protein aprataxin. We describe here, the interaction and interdependence between aprataxin and several nucleolar proteins, including nucleolin, nucleophosmin and upstream binding factor-1 (UBF-1), involved in ribosomal RNA (rRNA) synthesis and cellular stress signalling. Interaction between aprataxin and nucleolin occurred through their respective N-terminal regions. In AOA1 cells lacking aprataxin, the stability of nucleolin was significantly reduced. On the other hand, down-regulation of nucleolin by RNA interference did not affect aprataxin protein levels but abolished its nucleolar localization suggesting that the interaction with nucleolin is involved in its nucleolar targeting. GFP-aprataxin fusion protein co-localized with nucleolin, nucleophosmin and UBF-1 in nucleoli and inhibition of ribosomal DNA transcription altered the distribution of aprataxin in the nucleolus, suggesting that the nature of the nucleolar localization of aprataxin is also dependent on ongoing rRNA synthesis. In vivo rRNA synthesis analysis showed only a minor decrease in AOA1 cells when compared with controls cells. These results demonstrate a cross-dependence between aprataxin and nucleolin in the nucleolus and while aprataxin does not appear to be directly involved in rRNA synthesis its nucleolar localization is dependent on this synthesis.
Human Molecular Genetics 08/2006; 15(14):2239-49. · 7.64 Impact Factor
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ABSTRACT: Ataxia-telangiectasia mutated (ATM), the protein defective in ataxia-telangiectasia, plays a central role in DNA damage response and signaling to cell cycle checkpoints. We describe here a cell line from a patient with an ataxia-telangiectasia-like clinical phenotype defective in the p53 response to radiation but with normal ATM activation and efficient downstream phosphorylation of other ATM substrates. No mutations were detected in ATM cDNA. A normal level of interaction between p53 and peptidyl-prolyl-isomerase Pin1 suggests that posttranslational modification was intact in these cells but operating at reduced level. Defective p53 stabilization was accompanied by defective induction of p53 effector genes and failure to induce apoptosis in response to DNA-damaging agents. Continued association between p53 and murine double minute-2 (Mdm2) occurred in irradiated ATL2ABR cells in response to DNA damage, and incubation with Mdm2 antagonists, nutlins, increased the stabilization of p53 and its transcriptional activity but failed to induce apoptosis. These results suggest that ATM-dependent stabilization of p53 and induction of apoptosis by radiation involve an additional factor(s) that is defective in ATL2ABR cells.
Cancer Research 04/2006; 66(6):2907-12. · 7.86 Impact Factor
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ABSTRACT: While ATM, the protein defective in the human genetic disorder ataxia-telangiectasia (A-T), is primarily activated as a preexisting protein by radiation, there is also evidence that expression of the protein can be regulated at the transcriptional level. Activation of the ATM promoter by ionizing radiation has been reported only in quiescent cells in culture. To investigate how the Atm promoter is regulated in vivo, we generated transgenic mice that express the luciferase reporter gene under the control of the murine Atm promoter. Using a biophotonic imaging system luciferase activity was monitored in vivo. Strong promoter activity was detected throughout the transgenic animals with particularly high signals from the thymus, abdominal region, and reproductive organs. This activity further increased in response to both ionizing radiation and heat stress in a time dependent manner. Luciferase activity, measured in vitro in extracts from different tissues, showed highest activities in testes, ovaries, and cerebellum. Subjecting these mice to a single dose of 4 Gy total body radiation led to a time-dependent activation of the promoter with the strongest response observed in the peritoneal membrane, skin, and spleen. For most tissues tested, maximal promoter activity was reached 8 hr after radiation. The observed changes in promoter activity largely correlated with levels and activity of Atm protein in tissue extracts. These results demonstrate that, in addition to activation by autophosphorylation, Atm can also be regulated in vivo at the transcriptional level possibly ensuring a more sustained response to radiation and other stimuli.
Genes Chromosomes and Cancer 02/2006; 45(1):61-71. · 3.31 Impact Factor
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ABSTRACT: Treatment with the protein kinase C activator 12-O-tetradecanoylphorbol 12-acetate (TPA) enables radiation-resistant LNCaP human prostate cancer cells to undergo radiation-induced apoptosis, mediated via activation of the enzyme ceramide synthase (CS) and de novo synthesis of the sphingolipid ceramide (Garzotto, M., Haimovitz-Friedman, A., Liao, W. C., White-Jones, M., Huryk, R., Heston, D. W. W., Cardon-Cardo, C., Kolesnick, R., and Fuks, Z. (1999) Cancer Res. 59, 5194-5201). Here, we show that TPA functions to decrease the cellular level of the ATM (ataxia telangiectasia mutated) protein, known to repress CS activation (Liao, W.-C., Haimovitz-Friedman, A., Persaud, R., McLoughlin, M., Ehleiter, D., Zhang, N., Gatei, M., Lavin, M., Kolesnick, R., and Fuks, Z. (1999) J. Biol. Chem. 274, 17908-17917). Gel shift analysis in LNCaP and CWR22-Rv1 cells demonstrated a significant reduction in DNA binding of the Sp1 transcription factor to the ATM promoter, and quantitative reverse transcription-PCR showed a 50% reduction of ATM mRNA between 8 and 16 h of TPA treatment, indicating that TPA inhibits ATM transcription. Furthermore, treatment of LNCaP, CWR22-Rv1, PC-3, and DU-145 human prostate cells with antisense-ATM oligonucleotides, which markedly reduced cellular ATM levels, significantly enhanced radiation-induced CS activation and apoptosis, leading to apoptosis at doses as a low as 1 gray. These data suggest that the CS pathway initiates a generic mode of radiation-induced apoptosis in human prostate cancer cells, regulated by a suppressive function of ATM, and that ATM might represent a potential target for pharmacologic inactivation with potential clinical applications in human prostate cancer.
Journal of Biological Chemistry 07/2005; 280(24):23262-72. · 4.77 Impact Factor
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ABSTRACT: DNA double strand breaks represent the most threatening lesion to the integrity of the genome in cells exposed to ionizing radiation and radiomimetic chemicals. Those breaks are recognized, signaled to cell cycle checkpoints and repaired by protein complexes. The product of the gene (ATM) mutated in the human genetic disorder ataxia-telangiectasia (A-T) plays a central role in the recognition and signaling of DNA damage. ATM is one of an ever growing number of proteins which when mutated compromise the stability of the genome and predispose to tumour development. Mechanisms for recognising double strand breaks in DNA, maintaining genome stability and minimizing risk of cancer are discussed.
Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 02/2005; 569(1-2):123-32. · 2.85 Impact Factor
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Advances in experimental medicine and biology 02/2005; 570:457-76. · 1.09 Impact Factor
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Nuri Gueven,
Olivier J Becherel,
Amanda W Kijas,
Philip Chen,
Orla Howe,
Jeanette H Rudolph,
Richard Gatti,
Hidetoshi Date,
Osamu Onodera,
Gisela Taucher-Scholz,
Martin F Lavin
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ABSTRACT: Ataxia-oculomotor apraxia (AOA1) is a neurological disorder with symptoms that overlap those of ataxia-telangiectasia, a syndrome characterized by abnormal responses to double-strand DNA breaks and genome instability. The gene mutated in AOA1, APTX, is predicted to code for a protein called aprataxin that contains domains of homology with proteins involved in DNA damage signalling and repair. We demonstrate that aprataxin is a nuclear protein, present in both the nucleoplasm and the nucleolus. Mutations in the APTX gene destabilize the aprataxin protein, and fusion constructs of enhanced green fluorescent protein and aprataxin, representing deletions of putative functional domains, generate highly unstable products. Cells from AOA1 patients are characterized by enhanced sensitivity to agents that cause single-strand breaks in DNA but there is no evidence for a gross defect in single-strand break repair. Sensitivity to hydrogen peroxide and the resulting genome instability are corrected by transfection with full-length aprataxin cDNA. We also demonstrate that aprataxin interacts with the repair proteins XRCC1, PARP-1 and p53 and that it co-localizes with XRCC1 along charged particle tracks on chromatin. These results demonstrate that aprataxin influences the cellular response to genotoxic stress very likely by its capacity to interact with a number of proteins involved in DNA repair.
Human Molecular Genetics 06/2004; 13(10):1081-93. · 7.64 Impact Factor
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ABSTRACT: We describe here the cloning of full-length ataxia-telangiectasia mutated (ATM) cDNA and characterization of its activity. Full-length ATM cDNA is cloned into an inducible EBV-based vector (pMEP4) and its expression analyzed in a stably transfected cell line. ATM protein induction is monitored by immunoblotting with antibodies against both ATM and a FLAG sequence tag in the recombinant protein. Extracts from irradiated cells are immunoprecipitated with anti-ATM antibodies, and protein kinase activity is measured using p53(1-44)-specific substrate or by immunoblotting extracts with an anti-phosphoserine 15 p53-specific antibody. Missense mutations affecting ATM kinase activity are detected using in vitro mutagenesis of ATM cDNA followed by the procedures outlined above.
Methods in molecular biology (Clifton, N.J.) 02/2004; 281:163-78.
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ABSTRACT: Although ATM, the protein defective in ataxia-telangiectasia (A-T), is activated primarily by radiation, there is also evidence that expression of the protein can be regulated by both radiation and growth factors. Computer analysis of the ATM promoter proximal 700-bp sequence reveals a number of potentially important cis-regulatory sequences. Using nucleotide substitutions to delete putative functional elements in the promoter of ATM, we examined the importance of some of these sites for both the basal and the radiation-induced activity of the promoter. In lymphoblastoid cells, most of the mutations in transcription factor consensus sequences [Sp1(1), Sp1(2), Cre, Ets, Xre, gammaIre(2), a modified AP1 site (Fse), and GCF] reduced basal activity to various extents, whereas others [gammaIre(1), NF1, Myb] left basal activity unaffected. In human skin fibroblasts, results were generally the same, but the basal activity varied up to 8-fold in these and other cell lines. Radiation activated the promoter approximately 2.5-fold in serum-starved lymphoblastoid cells, reaching a maximum by 3 hr, and all mutated elements equally blocked this activation. Reduction in Sp1 and AP1 DNA binding activity by serum starvation was rapidly reversed by exposure of cells to radiation. This reduction was not evident in A-T cells, and the response to radiation was less marked. Data provided for interaction between ATM and Sp1 by protein binding and co-immunoprecipitation could explain the altered regulation of Sp1 in A-T cells. The data described here provide additional evidence that basal and radiation-induced regulation of the ATM promoter is under multifactorial control.
Genes Chromosomes and Cancer 11/2003; 38(2):157-67. · 3.31 Impact Factor
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ABSTRACT: Ataxia-telangiectasia Mutated (ATM), mutated in the human disorder ataxia-telangiectasia, is rapidly activated by DNA double strand breaks. The mechanism of activation remains unresolved, and it is uncertain whether autophosphorylation contributes to activation. We describe an in vitro immunoprecipitation system demonstrating activation of ATM kinase from unirradiated extracts by preincubation with ATP. Activation is both time- and ATP concentration-dependent, other nucleotides fail to activate ATM, and DNA is not required. ATP activation is specific for ATM since it is not observed with kinase-dead ATM, it requires Mn2+, and it is inhibited by wortmannin. Exposure of activated ATM to phosphatase abrogates activity, and repeat cycles of ATP and phosphatase treatment reveal a requirement for autophosphorylation in the activation process. Phosphopeptide mapping revealed similarities between the patterns of autophosphorylation for irradiated and ATP-treated ATM. Caffeine inhibited ATM kinase activity for substrates but did not interfere with ATM autophosphorylation. ATP failed to activate either A-T and rad3-related protein (ATR) or DNA-dependent protein kinase under these conditions, supporting the specificity for ATM. These data demonstrate that ATP can specifically induce activation of ATM by a mechanism involving autophosphorylation. The relationship of this activation to DNA damage activation remains unclear but represents a useful model for understanding in vivo activation.
Journal of Biological Chemistry 04/2003; 278(11):9309-17. · 4.77 Impact Factor