The Experts below are selected from a list of 2577 Experts worldwide ranked by ideXlab platform
Mitchell S. Turker - One of the best experts on this subject based on the ideXlab platform.
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Atm Haploinsufficiency does not Affect Ionizing Radiation Mutagenesis in Solid Mouse Tissues
Radiation Research, 2006Co-Authors: Lanelle Connolly, Michael R. Lasarev, Robert Jordan, Jeffrey L. Schwartz, Mitchell S. TurkerAbstract:Abstract Connolly, L., Lasarev, M., Jordan, R., Schwartz, J. L. and Turker, M. S. Atm Haploinsufficiency does not Affect Ionizing Radiation Mutagenesis in Solid Mouse Tissues. Radiat. Res. 166, 39–46 (2006). Ataxia telangiectasia (AT) is a hereditary disease with autosomal recessive inheritance of ATM (ataxia telangiectasia mutation) alleles. AT is associated with severe sensitivity to ionizing Radiation and a strong predisposition to develop cancer. A modest increase in cancer, particularly for the breast, has been shown for ATM carriers (i.e. heterozygotes), and a modest increase in Radiation sensitivity has also been shown for those patients and their cells. However, the extent of these effects is unclear. Based on the well-established relationship between cancer and mutation, we used a mouse model for Atm haploinsufficiency to ask whether partial loss of Atm function could lead to an increased mutagenic response for solid tissues of mice exposed to Radiation. The autosomal mouse Aprt gene was used as ...
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Atm haploinsufficiency does not affect ionizing Radiation Mutagenesis in solid mouse tissues.
Radiation research, 2006Co-Authors: Lanelle Connolly, Michael R. Lasarev, Robert Jordan, Jeffrey L. Schwartz, Mitchell S. TurkerAbstract:Ataxia telangiectasia (AT) is a hereditary disease with autosomal recessive inheritance of ATM (ataxia telangiectasia mutation) alleles. AT is associated with severe sensitivity to ionizing Radiation and a strong predisposition to develop cancer. A modest increase in cancer, particularly for the breast, has been shown for ATM carriers (i.e. heterozygotes), and a modest increase in Radiation sensitivity has also been shown for those patients and their cells. However, the extent of these effects is unclear. Based on the well-established relationship between cancer and mutation, we used a mouse model for Atm haploinsufficiency to ask whether partial loss of Atm function could lead to an increased mutagenic response for solid tissues of mice exposed to Radiation. The autosomal mouse Aprt gene was used as the mutational target and kidney and ear as the target tissues in B6D2F1 hybrids. Although induction of autosomal mutations was readily demonstrated in both tissues, a comparison of these data with those from an identical study performed with B6D2F1 mice that were wild-type for Atm (Cancer Res. 62, 1518-1523, 2002) revealed that Atm haploinsufficiency did not alter the Radiation mutagenic response for the cells of either tissue. Moreover, no effect of Atm haploinsufficiency on reduced cellular viability due to Radiation exposure was observed. The results demonstrate that Atm haploinsufficiency does not alter the Radiation mutagenic response or decrease viability for normally quiescent cells in solid tissues of the mouse.
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Tissue-specific deletion and discontinuous loss of heterozygosity are signatures for the mutagenic effects of ionizing Radiation in solid tissues.
Cancer research, 2002Co-Authors: Olga N. Ponomareva, Michael R. Lasarev, Jennifer A. Rose, Janet S. Rasey, Mitchell S. TurkerAbstract:The mouse Aprt locus on chromosome 8 was used as the selectable target for the study of spontaneous and ionizing Radiation-induced mutations in kidney epithelia and ear fibroblasts. Fifty-two Aprt heterozygous mice were exposed to 7.5 Gy of 137Cs-γ Radiation on their right sides, and Aprt-deficient clones were isolated from enzymatically digested tissues at times ranging from 1 day to 14 months after irRadiation. A statistically significant increase in the mutant frequencies for the irradiated tissues was observed when compared with the spontaneous mutant frequencies for the nonirradiated tissues. A molecular analysis of spontaneous mutations observed for the nonirradiated tissues revealed tissue-specific differences; apparent chromosome loss was common in kidney mutants but infrequent in the ear mutants, whereas apparent deletions were common in the ear mutants but not detected in the kidney mutants. For the irradiated kidneys, apparent deletions were observed commonly demonstrating that these events are markers for ionizing Radiation Mutagenesis in this tissue. All of the loss of heterozygosity (LOH) tracts observed in the spontaneous mutants were continuous, but discontinuous LOH patterns were observed in 6–8% of ionizing Radiation-induced ear and kidney cell mutants. Work with kidney-derived cell lines showed that discontinuous LOH is a novel signature for delayed ionizing Radiation Mutagenesis. Considered together, these results suggest that ionizing Radiation-induced mutations in vivo can result from both direct and delayed mutagenic effects.
Howard L Liber - One of the best experts on this subject based on the ideXlab platform.
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Deficiencies of Double-Strand Break Repair Factors and Effects on Mutagenesis in Directly γ-Irradiated and Medium-Mediated Bystander Human Lymphoblastoid Cells
Radiation research, 2008Co-Authors: Ying Zhang, Junqing Zhou, Kathryn D. Held, Robert W. Redmond, Kevin M. Prise, Howard L LiberAbstract:Abstract Zhang, Y., Zhou, J., Held, K. D., Redmond, R. W., Prise, K. M. and Liber, H. L. Deficiencies of Double-Strand Break Repair Factors and Effects on Mutagenesis in Directly γ-Irradiated and Medium-Mediated Bystander Human Lymphoblastoid Cells. Radiat. Res. 169, 197–206 (2008). Using RNA interference techniques to knock down key proteins in two major double-strand break (DSB) repair pathways (DNA-PKcs for nonhomologous end joining, NHEJ, and Rad54 for homologous recombination, HR), we investigated the influence of DSB repair factors on Radiation Mutagenesis at the autosomal thymidine kinase (TK) locus both in directly irradiated cells and in unirradiated bystander cells. We also examined the role of p53 (TP53) in these processes by using cells of three human lymphoblastoid cell lines from the same donor but with differing p53 status (TK6 is p53 wild-type, NH32 is p53 null, and WTK1 is p53 mutant). Our results indicated that p53 status did not affect either the production of Radiation bystander mutage...
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partial deficiency of dna pkcs increases ionizing Radiation induced Mutagenesis and telomere instability in human cells
Cancer Letters, 2007Co-Authors: Ying Zhang, Chang U K Lim, Junqing Zhou, Qinming Zhang, Susan M Bailey, Xiaofan Cao, Robert L Ullrich, Howard L LiberAbstract:The correct repair of DNA double-strand breaks (DSBs) is essential to maintaining the integrity of the genome. Misrepair of DSBs is detrimental to cells and organisms, leading to gene mutation, chromosomal aberration, and cancer development. Nonhomologous end-joining (NHEJ) is one of the principal rejoining processes in most higher eukaryotic cells. NHEJ is facilitated by DNA-dependent protein kinase (DNA-PK), which is composed of a catalytic subunit, DNA-PKcs, and the heterodimeric DNA binding regulatory complex Ku70/86. Null mutation of DNA-PKcs leads to immunodeficiency, chromosomal aberration, gene mutation, telomeric end-capping failure, and cancer predisposition in animals and cells. However, it is unknown whether partial deficiency of DNA-PKcs as might occur in a fraction of the population (e.g., heterozygotes), influences cellular function. Using small interfering RNA (siRNA) transfection, we established partial deficiency of DNA-PKcs in human cells, ranging from 4 to 85% of control levels. Our results reveal for the first time, that partial deficiency of DNA-PKcs leads to increased ionizing Radiation (IR)-induced Mutagenesis, cell killing, and telomere dysfunction. Radiation Mutagenesis was increased inversely with DNA-PKcs protein level, with the most pronounced effect being observed in cells with protein levels below 50% of controls. A small but statistically significant increase in IR-induced cell killing was observed as DNA-PKcs levels decreased, over the entire range of protein levels. Frequencies of IR-induced telomere-DSB fusion was increased at levels of DNA-PKcs as low as ∼50%, similar to what would be expected in heterozygous individuals. Taken together, our results suggest that even partial deficiency of DNA repair proteins may represent a considerable risk to genomic stability.
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Partial deficiency of DNA-PKcs increases ionizing Radiation induced Mutagenesis and cell killing in human cells
Cancer Research, 2006Co-Authors: Ying Zhang, Junqing Zhou, Qinming Zhang, Susan M Bailey, Xiaofan Cao, Howard L LiberAbstract:4388 The repair of DNA double strand breaks is essential to maintain the integrity of genome. Misrepaired DNA DSBs are detrimental to cells by leading to gene mutation and cancer development. Nonhomologous end-joining (NHEJ) is one of the principal rejoining processes in most higher eukaryotic cells. NHEJ is facilitated by DNA dependent protein kinase (DNA-PK), which is composed of a catalytic subunit, DNA-PKcs, and the heterodimeric DNA binding regulatory complex Ku. Null mutation of DNA-PKcs leads to immunodeficiency, chromosomal translocation, cancer predisposition in mice, and gene mutation. However, it is unknown whether the partial deficiency of DNA-PKcs that is more likely to occur in a fraction of the population influences cellular function. Using small interfering RNA transfection, we established partial deficiency of DNA-PKcs in human cells, with a range of 4-85% of control. Our results reveal that partial deficiency of DNA-PKcs leads to an increased ionizing Radiation-induced Mutagenesis and cell killing. Radiation Mutagenesis was increased inversely with DNA-PKcs protein levels, with the most pronounced effect observed between 4 and 50% protein levels.
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nbs1 knockdown by small interfering rna increases ionizing Radiation Mutagenesis and telomere association in human cells
Cancer Research, 2005Co-Authors: Ying Zhang, Chang U K Lim, Eli S Williams, Junqing Zhou, Qinming Zhang, Michael H Fox, Susan M Bailey, Howard L LiberAbstract:Hypomorphic mutations which lead to decreased function of the NBS1 gene are responsible for Nijmegen breakage syndrome, a rare autosomal recessive hereditary disorder that imparts an increased predisposition to development of malignancy. The NBS1 protein is a component of the MRE11/RAD50/NBS1 complex that plays a critical role in cellular responses to DNA damage and the maintenance of chromosomal integrity. Using small interfering RNA transfection, we have knocked down NBS1 protein levels and analyzed relevant phenotypes in two closely related human lymphoblastoid cell lines with different p53 status, namely wild-type TK6 and mutated WTK1. Both TK6 and WTK1 cells showed an increased level of ionizing Radiation-induced mutation at the TK and HPRT loci, impaired phosphorylation of H2AX (gamma-H2AX), and impaired activation of the cell cycle checkpoint regulating kinase, Chk2. In TK6 cells, ionizing Radiation-induced accumulation of p53/p21 and apoptosis were reduced. There was a differential response to ionizing Radiation-induced cell killing between TK6 and WTK1 cells after NBS1 knockdown; TK6 cells were more resistant to killing, whereas WTK1 cells were more sensitive. NBS1 deficiency also resulted in a significant increase in telomere association that was independent of Radiation exposure and p53 status. Our results provide the first experimental evidence that NBS1 deficiency in human cells leads to hypermutability and telomere associations, phenotypes that may contribute to the cancer predisposition seen among patients with this disease.
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Effects of Cell Cycle Position on Ionizing Radiation Mutagenesis. I. Quantitative Assays of Two Genetic Loci in a Human Lymphoblastoid Cell Line
Radiation research, 1996Co-Authors: Yao-yu Chuang, Howard L LiberAbstract:Relatively little work has been done on the influence of the position of the cell in the cell cycle on ionizing Radiation-induced Mutagenesis. We synchronized WTK1 human lymphoblastoid cells with 200 μM lovastatin for 48 h ; under these conditions more than 80% of the cells were arrested in G 1 phase. Upon release, there was a 12-15-h lag followed by movement of a large fraction into S phase. We irradiated cells with either 1.5 Gy X rays at 1, 15, 18, 21 or 24 h or 1.5 Gy γ rays at 1, 5, 10, 15 or 24 h after release from lovastatin. We showed that WTK1 cells were most sensitive to ionizing Radiation-induced toxicity in G 1 and into S phase, and more resistant in mid to late S and G 2 /M phase. Somewhat surprisingly, we found that the two different gene loci had different sensitivities to Radiation-induced mutation through the cell cycle. Cells in late G 1 through mid-S phase were most sensitive to Radiation-induced mutations at the autosomal thymidine kinase (TK) locus, whereas G 1 phase was the most sensitive phase at the X-linked hypoxanthine guanine phosphoribosyl transferase (HPRT) locus.
Michael R. Lasarev - One of the best experts on this subject based on the ideXlab platform.
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Atm Haploinsufficiency does not Affect Ionizing Radiation Mutagenesis in Solid Mouse Tissues
Radiation Research, 2006Co-Authors: Lanelle Connolly, Michael R. Lasarev, Robert Jordan, Jeffrey L. Schwartz, Mitchell S. TurkerAbstract:Abstract Connolly, L., Lasarev, M., Jordan, R., Schwartz, J. L. and Turker, M. S. Atm Haploinsufficiency does not Affect Ionizing Radiation Mutagenesis in Solid Mouse Tissues. Radiat. Res. 166, 39–46 (2006). Ataxia telangiectasia (AT) is a hereditary disease with autosomal recessive inheritance of ATM (ataxia telangiectasia mutation) alleles. AT is associated with severe sensitivity to ionizing Radiation and a strong predisposition to develop cancer. A modest increase in cancer, particularly for the breast, has been shown for ATM carriers (i.e. heterozygotes), and a modest increase in Radiation sensitivity has also been shown for those patients and their cells. However, the extent of these effects is unclear. Based on the well-established relationship between cancer and mutation, we used a mouse model for Atm haploinsufficiency to ask whether partial loss of Atm function could lead to an increased mutagenic response for solid tissues of mice exposed to Radiation. The autosomal mouse Aprt gene was used as ...
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Atm haploinsufficiency does not affect ionizing Radiation Mutagenesis in solid mouse tissues.
Radiation research, 2006Co-Authors: Lanelle Connolly, Michael R. Lasarev, Robert Jordan, Jeffrey L. Schwartz, Mitchell S. TurkerAbstract:Ataxia telangiectasia (AT) is a hereditary disease with autosomal recessive inheritance of ATM (ataxia telangiectasia mutation) alleles. AT is associated with severe sensitivity to ionizing Radiation and a strong predisposition to develop cancer. A modest increase in cancer, particularly for the breast, has been shown for ATM carriers (i.e. heterozygotes), and a modest increase in Radiation sensitivity has also been shown for those patients and their cells. However, the extent of these effects is unclear. Based on the well-established relationship between cancer and mutation, we used a mouse model for Atm haploinsufficiency to ask whether partial loss of Atm function could lead to an increased mutagenic response for solid tissues of mice exposed to Radiation. The autosomal mouse Aprt gene was used as the mutational target and kidney and ear as the target tissues in B6D2F1 hybrids. Although induction of autosomal mutations was readily demonstrated in both tissues, a comparison of these data with those from an identical study performed with B6D2F1 mice that were wild-type for Atm (Cancer Res. 62, 1518-1523, 2002) revealed that Atm haploinsufficiency did not alter the Radiation mutagenic response for the cells of either tissue. Moreover, no effect of Atm haploinsufficiency on reduced cellular viability due to Radiation exposure was observed. The results demonstrate that Atm haploinsufficiency does not alter the Radiation mutagenic response or decrease viability for normally quiescent cells in solid tissues of the mouse.
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Tissue-specific deletion and discontinuous loss of heterozygosity are signatures for the mutagenic effects of ionizing Radiation in solid tissues.
Cancer research, 2002Co-Authors: Olga N. Ponomareva, Michael R. Lasarev, Jennifer A. Rose, Janet S. Rasey, Mitchell S. TurkerAbstract:The mouse Aprt locus on chromosome 8 was used as the selectable target for the study of spontaneous and ionizing Radiation-induced mutations in kidney epithelia and ear fibroblasts. Fifty-two Aprt heterozygous mice were exposed to 7.5 Gy of 137Cs-γ Radiation on their right sides, and Aprt-deficient clones were isolated from enzymatically digested tissues at times ranging from 1 day to 14 months after irRadiation. A statistically significant increase in the mutant frequencies for the irradiated tissues was observed when compared with the spontaneous mutant frequencies for the nonirradiated tissues. A molecular analysis of spontaneous mutations observed for the nonirradiated tissues revealed tissue-specific differences; apparent chromosome loss was common in kidney mutants but infrequent in the ear mutants, whereas apparent deletions were common in the ear mutants but not detected in the kidney mutants. For the irradiated kidneys, apparent deletions were observed commonly demonstrating that these events are markers for ionizing Radiation Mutagenesis in this tissue. All of the loss of heterozygosity (LOH) tracts observed in the spontaneous mutants were continuous, but discontinuous LOH patterns were observed in 6–8% of ionizing Radiation-induced ear and kidney cell mutants. Work with kidney-derived cell lines showed that discontinuous LOH is a novel signature for delayed ionizing Radiation Mutagenesis. Considered together, these results suggest that ionizing Radiation-induced mutations in vivo can result from both direct and delayed mutagenic effects.
Lanelle Connolly - One of the best experts on this subject based on the ideXlab platform.
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Atm Haploinsufficiency does not Affect Ionizing Radiation Mutagenesis in Solid Mouse Tissues
Radiation Research, 2006Co-Authors: Lanelle Connolly, Michael R. Lasarev, Robert Jordan, Jeffrey L. Schwartz, Mitchell S. TurkerAbstract:Abstract Connolly, L., Lasarev, M., Jordan, R., Schwartz, J. L. and Turker, M. S. Atm Haploinsufficiency does not Affect Ionizing Radiation Mutagenesis in Solid Mouse Tissues. Radiat. Res. 166, 39–46 (2006). Ataxia telangiectasia (AT) is a hereditary disease with autosomal recessive inheritance of ATM (ataxia telangiectasia mutation) alleles. AT is associated with severe sensitivity to ionizing Radiation and a strong predisposition to develop cancer. A modest increase in cancer, particularly for the breast, has been shown for ATM carriers (i.e. heterozygotes), and a modest increase in Radiation sensitivity has also been shown for those patients and their cells. However, the extent of these effects is unclear. Based on the well-established relationship between cancer and mutation, we used a mouse model for Atm haploinsufficiency to ask whether partial loss of Atm function could lead to an increased mutagenic response for solid tissues of mice exposed to Radiation. The autosomal mouse Aprt gene was used as ...
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Atm haploinsufficiency does not affect ionizing Radiation Mutagenesis in solid mouse tissues.
Radiation research, 2006Co-Authors: Lanelle Connolly, Michael R. Lasarev, Robert Jordan, Jeffrey L. Schwartz, Mitchell S. TurkerAbstract:Ataxia telangiectasia (AT) is a hereditary disease with autosomal recessive inheritance of ATM (ataxia telangiectasia mutation) alleles. AT is associated with severe sensitivity to ionizing Radiation and a strong predisposition to develop cancer. A modest increase in cancer, particularly for the breast, has been shown for ATM carriers (i.e. heterozygotes), and a modest increase in Radiation sensitivity has also been shown for those patients and their cells. However, the extent of these effects is unclear. Based on the well-established relationship between cancer and mutation, we used a mouse model for Atm haploinsufficiency to ask whether partial loss of Atm function could lead to an increased mutagenic response for solid tissues of mice exposed to Radiation. The autosomal mouse Aprt gene was used as the mutational target and kidney and ear as the target tissues in B6D2F1 hybrids. Although induction of autosomal mutations was readily demonstrated in both tissues, a comparison of these data with those from an identical study performed with B6D2F1 mice that were wild-type for Atm (Cancer Res. 62, 1518-1523, 2002) revealed that Atm haploinsufficiency did not alter the Radiation mutagenic response for the cells of either tissue. Moreover, no effect of Atm haploinsufficiency on reduced cellular viability due to Radiation exposure was observed. The results demonstrate that Atm haploinsufficiency does not alter the Radiation mutagenic response or decrease viability for normally quiescent cells in solid tissues of the mouse.
Ying Zhang - One of the best experts on this subject based on the ideXlab platform.
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Deficiencies of Double-Strand Break Repair Factors and Effects on Mutagenesis in Directly γ-Irradiated and Medium-Mediated Bystander Human Lymphoblastoid Cells
Radiation research, 2008Co-Authors: Ying Zhang, Junqing Zhou, Kathryn D. Held, Robert W. Redmond, Kevin M. Prise, Howard L LiberAbstract:Abstract Zhang, Y., Zhou, J., Held, K. D., Redmond, R. W., Prise, K. M. and Liber, H. L. Deficiencies of Double-Strand Break Repair Factors and Effects on Mutagenesis in Directly γ-Irradiated and Medium-Mediated Bystander Human Lymphoblastoid Cells. Radiat. Res. 169, 197–206 (2008). Using RNA interference techniques to knock down key proteins in two major double-strand break (DSB) repair pathways (DNA-PKcs for nonhomologous end joining, NHEJ, and Rad54 for homologous recombination, HR), we investigated the influence of DSB repair factors on Radiation Mutagenesis at the autosomal thymidine kinase (TK) locus both in directly irradiated cells and in unirradiated bystander cells. We also examined the role of p53 (TP53) in these processes by using cells of three human lymphoblastoid cell lines from the same donor but with differing p53 status (TK6 is p53 wild-type, NH32 is p53 null, and WTK1 is p53 mutant). Our results indicated that p53 status did not affect either the production of Radiation bystander mutage...
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partial deficiency of dna pkcs increases ionizing Radiation induced Mutagenesis and telomere instability in human cells
Cancer Letters, 2007Co-Authors: Ying Zhang, Chang U K Lim, Junqing Zhou, Qinming Zhang, Susan M Bailey, Xiaofan Cao, Robert L Ullrich, Howard L LiberAbstract:The correct repair of DNA double-strand breaks (DSBs) is essential to maintaining the integrity of the genome. Misrepair of DSBs is detrimental to cells and organisms, leading to gene mutation, chromosomal aberration, and cancer development. Nonhomologous end-joining (NHEJ) is one of the principal rejoining processes in most higher eukaryotic cells. NHEJ is facilitated by DNA-dependent protein kinase (DNA-PK), which is composed of a catalytic subunit, DNA-PKcs, and the heterodimeric DNA binding regulatory complex Ku70/86. Null mutation of DNA-PKcs leads to immunodeficiency, chromosomal aberration, gene mutation, telomeric end-capping failure, and cancer predisposition in animals and cells. However, it is unknown whether partial deficiency of DNA-PKcs as might occur in a fraction of the population (e.g., heterozygotes), influences cellular function. Using small interfering RNA (siRNA) transfection, we established partial deficiency of DNA-PKcs in human cells, ranging from 4 to 85% of control levels. Our results reveal for the first time, that partial deficiency of DNA-PKcs leads to increased ionizing Radiation (IR)-induced Mutagenesis, cell killing, and telomere dysfunction. Radiation Mutagenesis was increased inversely with DNA-PKcs protein level, with the most pronounced effect being observed in cells with protein levels below 50% of controls. A small but statistically significant increase in IR-induced cell killing was observed as DNA-PKcs levels decreased, over the entire range of protein levels. Frequencies of IR-induced telomere-DSB fusion was increased at levels of DNA-PKcs as low as ∼50%, similar to what would be expected in heterozygous individuals. Taken together, our results suggest that even partial deficiency of DNA repair proteins may represent a considerable risk to genomic stability.
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Partial deficiency of DNA-PKcs increases ionizing Radiation induced Mutagenesis and cell killing in human cells
Cancer Research, 2006Co-Authors: Ying Zhang, Junqing Zhou, Qinming Zhang, Susan M Bailey, Xiaofan Cao, Howard L LiberAbstract:4388 The repair of DNA double strand breaks is essential to maintain the integrity of genome. Misrepaired DNA DSBs are detrimental to cells by leading to gene mutation and cancer development. Nonhomologous end-joining (NHEJ) is one of the principal rejoining processes in most higher eukaryotic cells. NHEJ is facilitated by DNA dependent protein kinase (DNA-PK), which is composed of a catalytic subunit, DNA-PKcs, and the heterodimeric DNA binding regulatory complex Ku. Null mutation of DNA-PKcs leads to immunodeficiency, chromosomal translocation, cancer predisposition in mice, and gene mutation. However, it is unknown whether the partial deficiency of DNA-PKcs that is more likely to occur in a fraction of the population influences cellular function. Using small interfering RNA transfection, we established partial deficiency of DNA-PKcs in human cells, with a range of 4-85% of control. Our results reveal that partial deficiency of DNA-PKcs leads to an increased ionizing Radiation-induced Mutagenesis and cell killing. Radiation Mutagenesis was increased inversely with DNA-PKcs protein levels, with the most pronounced effect observed between 4 and 50% protein levels.
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nbs1 knockdown by small interfering rna increases ionizing Radiation Mutagenesis and telomere association in human cells
Cancer Research, 2005Co-Authors: Ying Zhang, Chang U K Lim, Eli S Williams, Junqing Zhou, Qinming Zhang, Michael H Fox, Susan M Bailey, Howard L LiberAbstract:Hypomorphic mutations which lead to decreased function of the NBS1 gene are responsible for Nijmegen breakage syndrome, a rare autosomal recessive hereditary disorder that imparts an increased predisposition to development of malignancy. The NBS1 protein is a component of the MRE11/RAD50/NBS1 complex that plays a critical role in cellular responses to DNA damage and the maintenance of chromosomal integrity. Using small interfering RNA transfection, we have knocked down NBS1 protein levels and analyzed relevant phenotypes in two closely related human lymphoblastoid cell lines with different p53 status, namely wild-type TK6 and mutated WTK1. Both TK6 and WTK1 cells showed an increased level of ionizing Radiation-induced mutation at the TK and HPRT loci, impaired phosphorylation of H2AX (gamma-H2AX), and impaired activation of the cell cycle checkpoint regulating kinase, Chk2. In TK6 cells, ionizing Radiation-induced accumulation of p53/p21 and apoptosis were reduced. There was a differential response to ionizing Radiation-induced cell killing between TK6 and WTK1 cells after NBS1 knockdown; TK6 cells were more resistant to killing, whereas WTK1 cells were more sensitive. NBS1 deficiency also resulted in a significant increase in telomere association that was independent of Radiation exposure and p53 status. Our results provide the first experimental evidence that NBS1 deficiency in human cells leads to hypermutability and telomere associations, phenotypes that may contribute to the cancer predisposition seen among patients with this disease.
