The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform

Alan S. B. Khoo - One of the best experts on this subject based on the ideXlab platform.

  • Oxidative stress-induced Chromosome breaks within the ABL gene: a model for Chromosome Rearrangement in nasopharyngeal carcinoma.
    Human Genomics, 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim, Alan S. B. Khoo
    Abstract:

    The mechanism underlying Chromosome Rearrangement in nasopharyngeal carcinoma (NPC) remains elusive. It is known that most of the aetiological factors of NPC trigger oxidative stress. Oxidative stress is a potent apoptotic inducer. During apoptosis, chromatin cleavage and DNA fragmentation occur. However, cells may undergo DNA repair and survive apoptosis. Non-homologous end joining (NHEJ) pathway has been known as the primary DNA repair system in human cells. The NHEJ process may repair DNA ends without any homology, although region of microhomology (a few nucleotides) is usually utilised by this DNA repair system. Cells that evade apoptosis via erroneous DNA repair may carry chromosomal aberration. Apoptotic nuclease was found to be associated with nuclear matrix during apoptosis. Matrix association region/scaffold attachment region (MAR/SAR) is the binding site of the chromosomal DNA loop structure to the nuclear matrix. When apoptotic nuclease is associated with nuclear matrix during apoptosis, it potentially cleaves at MAR/SAR. Cells that survive apoptosis via compromised DNA repair may carry Chromosome Rearrangement contributing to NPC tumourigenesis. The Abelson murine leukaemia (ABL) gene at 9q34 was targeted in this study as 9q34 is a common region of loss in NPC. This study aimed to identify the Chromosome breakages and/or Rearrangements in the ABL gene in cells undergoing oxidative stress-induced apoptosis. In the present study, in silico prediction of MAR/SAR was performed in the ABL gene. More than 80% of the predicted MAR/SAR sites are closely associated with previously reported patient breakpoint cluster regions (BCR). By using inverse polymerase chain reaction (IPCR), we demonstrated that hydrogen peroxide (H2O2)-induced apoptosis in normal nasopharyngeal epithelial and NPC cells led to chromosomal breakages within the ABL BCR that contains a MAR/SAR. Intriguingly, we detected two translocations in H2O2-treated cells. Region of microhomology was found at the translocation junctions. This observation is consistent with the operation of microhomology-mediated NHEJ. Our findings suggested that oxidative stress-induced apoptosis may participate in Chromosome Rearrangements of NPC. A revised model for oxidative stress-induced apoptosis mediating Chromosome Rearrangement in NPC is proposed.

  • Oxidative stress-induced Chromosome breaks within the ABL gene: a model for Chromosome Rearrangement in nasopharyngeal carcinoma
    Human Genomics, 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim, Alan S. B. Khoo
    Abstract:

    Background The mechanism underlying Chromosome Rearrangement in nasopharyngeal carcinoma (NPC) remains elusive. It is known that most of the aetiological factors of NPC trigger oxidative stress. Oxidative stress is a potent apoptotic inducer. During apoptosis, chromatin cleavage and DNA fragmentation occur. However, cells may undergo DNA repair and survive apoptosis. Non-homologous end joining (NHEJ) pathway has been known as the primary DNA repair system in human cells. The NHEJ process may repair DNA ends without any homology, although region of microhomology (a few nucleotides) is usually utilised by this DNA repair system. Cells that evade apoptosis via erroneous DNA repair may carry chromosomal aberration. Apoptotic nuclease was found to be associated with nuclear matrix during apoptosis. Matrix association region/scaffold attachment region (MAR/SAR) is the binding site of the chromosomal DNA loop structure to the nuclear matrix. When apoptotic nuclease is associated with nuclear matrix during apoptosis, it potentially cleaves at MAR/SAR. Cells that survive apoptosis via compromised DNA repair may carry Chromosome Rearrangement contributing to NPC tumourigenesis. The Abelson murine leukaemia ( ABL) gene at 9q34 was targeted in this study as 9q34 is a common region of loss in NPC. This study aimed to identify the Chromosome breakages and/or Rearrangements in the ABL gene in cells undergoing oxidative stress-induced apoptosis. Results In the present study, in silico prediction of MAR/SAR was performed in the ABL gene. More than 80% of the predicted MAR/SAR sites are closely associated with previously reported patient breakpoint cluster regions (BCR). By using inverse polymerase chain reaction (IPCR), we demonstrated that hydrogen peroxide (H_2O_2)-induced apoptosis in normal nasopharyngeal epithelial and NPC cells led to chromosomal breakages within the ABL BCR that contains a MAR/SAR. Intriguingly, we detected two translocations in H_2O_2-treated cells. Region of microhomology was found at the translocation junctions. This observation is consistent with the operation of microhomology-mediated NHEJ. Conclusions Our findings suggested that oxidative stress-induced apoptosis may participate in Chromosome Rearrangements of NPC. A revised model for oxidative stress-induced apoptosis mediating Chromosome Rearrangement in NPC is proposed.

Philippe Jonveaux - One of the best experts on this subject based on the ideXlab platform.

  • de novo complex x Chromosome Rearrangement unmasking maternally inherited csf2ra deletion in a girl with pulmonary alveolar proteinosis
    American Journal of Medical Genetics Part A, 2013
    Co-Authors: Julie Auger, Celine Bonnet, Mylene Valduga, Christophe Philippe, Emmanuelle Bertolohouriez, Mylene Beridexheimer, Cyril Schweitzer, Bruno Leheup, Philippe Jonveaux
    Abstract:

    We report on a 3-year-old girl with a de novo complex X Chromosome Rearrangement associated with congenital pulmonary alveolar proteinosis (PAP) and short stature. Array comparative genome hybridization and FISH analyses contributed to characterize the complex Rearrangement consisting of a 7.37 Mb terminal deletion of Xp22.33p22.2, a 17.3 Mb interstitial inverted duplication of Xp22.2p21.3, and a 10.14 Mb duplication of Xq27.3q28. PCR analysis of microsatellite markers supported a paternal origin of the X Chromosome Rearrangement. A pre-meiotic two-step mechanism may explain the occurrence of this complex X Rearrangement: an inverted duplication deletion event on Xp, and duplication of the Xq27.3qter region through a telomere capture event stabilizing the broken Chromosome Xp end. The girl has also inherited from her healthy mother an X Chromosome with a colony stimulating factor 2 receptor, alpha (CSF2RA) gene deletion. Consistent with the recessive mode of inheritance, the de novo paternal Xp22.33p22.2 deletion combined to the maternally inherited CSF2RA gene deletion led to homozygous deletion of CSF2RA and PAP diagnosis in the girl. The Xp deletion encompasses the pseudoautosomal region 1 (PAR1) which contains genes that escape X inactivation. Short stature homeobox (SHOX) haploinsufficiency explains growth retardation. Absence of other symptoms in relation to the X deletion/amplification is most probably due to skewed X inactivation. Finally, inherited deletions may unmask rare pathogenic genomic Rearrangement and contribute to clinical phenotypes by a recessive mode of gene action. © 2013 Wiley Periodicals, Inc.

  • De novo complex X Chromosome Rearrangement unmasking maternally inherited CSF2RA deletion in a girl with pulmonary alveolar proteinosis
    American Journal of Medical Genetics Part A, 2013
    Co-Authors: Julie Auger, Celine Bonnet, Mylene Valduga, Christophe Philippe, Cyril Schweitzer, Bruno Leheup, Emmanuelle Bertolo-houriez, Mylène Beri-dexheimer, Philippe Jonveaux
    Abstract:

    We report on a 3-year-old girl with a de novo complex X Chromosome Rearrangement associated with congenital pulmonary alveolar proteinosis (PAP) and short stature. Array comparative genome hybridization and FISH analyses contributed to characterize the complex Rearrangement consisting of a 7.37 Mb terminal deletion of Xp22.33p22.2, a 17.3 Mb interstitial inverted duplication of Xp22.2p21.3, and a 10.14 Mb duplication of Xq27.3q28. PCR analysis of microsatellite markers supported a paternal origin of the X Chromosome Rearrangement. A pre-meiotic two-step mechanism may explain the occurrence of this complex X Rearrangement: an inverted duplication deletion event on Xp, and duplication of the Xq27.3qter region through a telomere capture event stabilizing the broken Chromosome Xp end. The girl has also inherited from her healthy mother an X Chromosome with a colony stimulating factor 2 receptor, alpha (CSF2RA) gene deletion. Consistent with the recessive mode of inheritance, the de novo paternal Xp22.33p22.2 deletion combined to the maternally inherited CSF2RA gene deletion led to homozygous deletion of CSF2RA and PAP diagnosis in the girl. The Xp deletion encompasses the pseudoautosomal region 1 (PAR1) which contains genes that escape X inactivation. Short stature homeobox (SHOX) haploinsufficiency explains growth retardation. Absence of other symptoms in relation to the X deletion/amplification is most probably due to skewed X inactivation. Finally, inherited deletions may unmask rare pathogenic genomic Rearrangement and contribute to clinical phenotypes by a recessive mode of gene action.

Mary D Stephenson - One of the best experts on this subject based on the ideXlab platform.

  • information rich reproductive outcomes in carriers of a structural Chromosome Rearrangement ascertained on the basis of recurrent pregnancy loss
    Fertility and Sterility, 2012
    Co-Authors: Michelle K Desjardins, Mary D Stephenson
    Abstract:

    Objective To determine whether evaluation and management of concomitant recurrent pregnancy loss (RPL) factors, followed by close monitoring in the first trimester, improved subsequent live birth rate, in carriers of a structural Chromosome Rearrangement ascertained on the basis of RPL. Design Prospective tabulation and analysis of subsequent pregnancy outcomes. Setting Academic medical center. Patient(s) Carriers of a structural Chromosome Rearrangement with a history of RPL, defined as two or more pregnancy losses at any gestational age. Intervention(s) Evaluation and treatment for concomitant factors and close monitoring in the first trimester. Main Outcome Measure(s) Live birth rate, defined as term, preterm, and ongoing pregnancies. Secondary outcomes include number of cycles to conception, and miscarriage Chromosome results. Result(s) Live birth rate was 6.7% before evaluation and 63% subsequent. The proportion of women with at least one live birth increased significantly from 25%–90%. The mean number of cycles to conception was 1.7 (SD 1.3). Miscarriage Chromosome results revealed that 13% were unbalanced structural Chromosome Rearrangements. Conclusion(s) This study provides further evidence that evaluation and treatment of concomitant RPL factors and close monitoring in the first trimester leads to a high subsequent live birth rate in carriers of a structural Chromosome Rearrangement ascertained on the basis of RPL. The number of cycles needed to conceive was less than two, indicating that infertility is not associated with carrier status. The low percentage of miscarriages or ongoing pregnancies with an unbalanced structural Chromosome Rearrangement suggests that there is natural selection against an unbalanced Rearrangement.

  • reproductive outcomes in recurrent pregnancy loss associated with a parental carrier of a structural Chromosome Rearrangement
    Human Reproduction, 2006
    Co-Authors: Mary D Stephenson, Sony Sierra
    Abstract:

    BACKGROUND: Reproductive outcome studies of couples with a history of recurrent pregnancy loss (RPL) associated with a maternal or paternal carrier of a structural Chromosome Rearrangement are limited. Correlation of carrier status and cytogenetics of miscarriage specimens is critical to estimate subsequent pregnancy outcome. METHODS: Couples found to have a structural Chromosome Rearrangement were followed prospectively in a tertiary academic centre. Descriptive analysis and subsequent pregnancy outcomes were tabulated and compared to historic controls. RESULTS: In 1893 RPL couples, 51 carriers of a structural Chromosome Rearrangement were identified (2.7%). Overall, this cohort had a total of 273 documented pregnancies. Prior to evaluation, the mean maternal age at the time of delivery or miscarriage was 29.8 years and the live birth rate was 15%. Following evaluation and treatment of concomitant factors, there were 58 monitored pregnancies, with a live birth rate of 71%. Amniocentesis was performed on 22% of the ongoing pregnancies; all were diploid or balanced structural Chromosome Rearrangements. Thirty-six per cent of the miscarriages were found to have an unbalanced structural Chromosome Rearrangement. CONCLUSIONS: Following evaluation and management of RPL, the live birth rate for carriers of a structural Chromosome Rearrangement is highly encouraging at 71%, without the addition of assisted reproductive technology.

Sang-nee Tan - One of the best experts on this subject based on the ideXlab platform.

  • Oxidative stress-induced Chromosome breaks within the ABL gene: a model for Chromosome Rearrangement in nasopharyngeal carcinoma.
    Human Genomics, 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim, Alan S. B. Khoo
    Abstract:

    The mechanism underlying Chromosome Rearrangement in nasopharyngeal carcinoma (NPC) remains elusive. It is known that most of the aetiological factors of NPC trigger oxidative stress. Oxidative stress is a potent apoptotic inducer. During apoptosis, chromatin cleavage and DNA fragmentation occur. However, cells may undergo DNA repair and survive apoptosis. Non-homologous end joining (NHEJ) pathway has been known as the primary DNA repair system in human cells. The NHEJ process may repair DNA ends without any homology, although region of microhomology (a few nucleotides) is usually utilised by this DNA repair system. Cells that evade apoptosis via erroneous DNA repair may carry chromosomal aberration. Apoptotic nuclease was found to be associated with nuclear matrix during apoptosis. Matrix association region/scaffold attachment region (MAR/SAR) is the binding site of the chromosomal DNA loop structure to the nuclear matrix. When apoptotic nuclease is associated with nuclear matrix during apoptosis, it potentially cleaves at MAR/SAR. Cells that survive apoptosis via compromised DNA repair may carry Chromosome Rearrangement contributing to NPC tumourigenesis. The Abelson murine leukaemia (ABL) gene at 9q34 was targeted in this study as 9q34 is a common region of loss in NPC. This study aimed to identify the Chromosome breakages and/or Rearrangements in the ABL gene in cells undergoing oxidative stress-induced apoptosis. In the present study, in silico prediction of MAR/SAR was performed in the ABL gene. More than 80% of the predicted MAR/SAR sites are closely associated with previously reported patient breakpoint cluster regions (BCR). By using inverse polymerase chain reaction (IPCR), we demonstrated that hydrogen peroxide (H2O2)-induced apoptosis in normal nasopharyngeal epithelial and NPC cells led to chromosomal breakages within the ABL BCR that contains a MAR/SAR. Intriguingly, we detected two translocations in H2O2-treated cells. Region of microhomology was found at the translocation junctions. This observation is consistent with the operation of microhomology-mediated NHEJ. Our findings suggested that oxidative stress-induced apoptosis may participate in Chromosome Rearrangements of NPC. A revised model for oxidative stress-induced apoptosis mediating Chromosome Rearrangement in NPC is proposed.

  • Oxidative stress-induced Chromosome breaks within the ABL gene: a model for Chromosome Rearrangement in nasopharyngeal carcinoma
    Human Genomics, 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim, Alan S. B. Khoo
    Abstract:

    Background The mechanism underlying Chromosome Rearrangement in nasopharyngeal carcinoma (NPC) remains elusive. It is known that most of the aetiological factors of NPC trigger oxidative stress. Oxidative stress is a potent apoptotic inducer. During apoptosis, chromatin cleavage and DNA fragmentation occur. However, cells may undergo DNA repair and survive apoptosis. Non-homologous end joining (NHEJ) pathway has been known as the primary DNA repair system in human cells. The NHEJ process may repair DNA ends without any homology, although region of microhomology (a few nucleotides) is usually utilised by this DNA repair system. Cells that evade apoptosis via erroneous DNA repair may carry chromosomal aberration. Apoptotic nuclease was found to be associated with nuclear matrix during apoptosis. Matrix association region/scaffold attachment region (MAR/SAR) is the binding site of the chromosomal DNA loop structure to the nuclear matrix. When apoptotic nuclease is associated with nuclear matrix during apoptosis, it potentially cleaves at MAR/SAR. Cells that survive apoptosis via compromised DNA repair may carry Chromosome Rearrangement contributing to NPC tumourigenesis. The Abelson murine leukaemia ( ABL) gene at 9q34 was targeted in this study as 9q34 is a common region of loss in NPC. This study aimed to identify the Chromosome breakages and/or Rearrangements in the ABL gene in cells undergoing oxidative stress-induced apoptosis. Results In the present study, in silico prediction of MAR/SAR was performed in the ABL gene. More than 80% of the predicted MAR/SAR sites are closely associated with previously reported patient breakpoint cluster regions (BCR). By using inverse polymerase chain reaction (IPCR), we demonstrated that hydrogen peroxide (H_2O_2)-induced apoptosis in normal nasopharyngeal epithelial and NPC cells led to chromosomal breakages within the ABL BCR that contains a MAR/SAR. Intriguingly, we detected two translocations in H_2O_2-treated cells. Region of microhomology was found at the translocation junctions. This observation is consistent with the operation of microhomology-mediated NHEJ. Conclusions Our findings suggested that oxidative stress-induced apoptosis may participate in Chromosome Rearrangements of NPC. A revised model for oxidative stress-induced apoptosis mediating Chromosome Rearrangement in NPC is proposed.

  • Bile acids at neutral and acidic pH induce apoptosis and gene cleavages in nasopharyngeal epithelial cells: implications in Chromosome Rearrangement
    BMC cancer, 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim
    Abstract:

    Chronic rhinosinusitis (CRS) increases the risk of developing nasopharyngeal carcinoma (NPC) while nasopharyngeal reflux is known to be one of the major aetiological factors of CRS. Bile acid (BA), the component of gastric duodenal contents, has been recognised as a carcinogen. BA-induced apoptosis was suggested to be involved in human malignancies. Cells have the potential and tendency to survive apoptosis. However, cells that evade apoptosis upon erroneous DNA repair may carry Chromosome Rearrangements. Apoptotic nuclease, caspase-activated deoxyribonuclease (CAD) has been implicated in mediating translocation in leukaemia. We hypothesised that BA-induced apoptosis may cause Chromosome breaks mediated by CAD leading to Chromosome Rearrangement in NPC. This study targeted the AF9 gene located at 9p22 because 9p22 is one of the most common deletion sites in NPC. We tested the ability of BA at neutral and acidic pH in inducing phosphatidylserine (PS) externalisation, reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP) disruption, and caspase 3/7 activity in normal nasopharyngeal epithelial (NP69) and NPC (TWO4) cells. Inverse-PCR (IPCR) was employed to detect AF9 gene cleavages. To investigate the role of CAD in mediating these cleavages, caspase inhibition was performed. IPCR bands representing AF9 cleaved fragments were sequenced. BA-treated cells showed higher levels of PS externalisation, ROS production, MMP loss and caspase 3/7 activity than untreated control cells. The effect of BA in the induction of these intracellular events was enhanced by acid. BA at neutral and acidic pH also induced significant cleavage of the AF9 gene. These BA-induced gene cleavages were inhibited by Z-DEVD-FMK, a caspase-3 inhibitor. Intriguingly, a few Chromosome breaks were identified within the AF9 region that was previously reported to participate in reciprocal translocation between the mixed lineage leukaemia (MLL) and AF9 genes in an acute lymphoblastic leukaemia (ALL) patient. These findings suggest a role for BA-induced apoptosis in mediating Chromosome Rearrangements in NPC. In addition, CAD may be a key player in Chromosome cleavages mediated by BA-induced apoptosis. Persistent exposure of sinonasal tract to gastric duodenal refluxate may increase genomic instability in surviving cells.

  • Bile acids at neutral and acidic pH induce apoptosis and gene cleavages in nasopharyngeal epithelial cells : implications in Chromosome Rearrangement
    'Springer Science and Business Media LLC', 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim
    Abstract:

    Background: Chronic rhinosinusitis (CRS) increases the risk of developing nasopharyngeal carcinoma (NPC) while nasopharyngeal reflux is known to be one of the major aetiological factors of CRS. Bile acid (BA), the component of gastric duodenal contents, has been recognised as a carcinogen. BA-induced apoptosis was suggested to be involved in human malignancies. Cells have the potential and tendency to survive apoptosis. However, cells that evade apoptosis upon erroneous DNA repair may carry Chromosome Rearrangements. Apoptotic nuclease, caspase-activated deoxyribonuclease (CAD) has been implicated in mediating translocation in leukaemia. We hypothesised that BA-induced apoptosis may cause Chromosome breaks mediated by CAD leading to Chromosome Rearrangement in NPC. This study targeted the AF9 gene located at 9p22 because 9p22 is one of the most common deletion sites in NPC. Methods: We tested the ability of BA at neutral and acidic pH in inducing phosphatidylserine (PS) externalisation, reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP) disruption, and caspase 3/7 activity in normal nasopharyngeal epithelial (NP69) and NPC (TWO4) cells. Inverse-PCR (IPCR) was employed to detect AF9 gene cleavages. To investigate the role of CAD in mediating these cleavages, caspase inhibition was performed. IPCR bands representing AF9 cleaved fragments were sequenced. Results: BA-treated cells showed higher levels of PS externalisation, ROS production, MMP loss and caspase 3/7 activity than untreated control cells. The effect of BA in the induction of these intracellular events was enhanced by acid. BA at neutral and acidic pH also induced significant cleavage of the AF9 gene. These BA-induced gene cleavages were inhibited by Z-DEVD-FMK, a caspase-3 inhibitor. Intriguingly, a few Chromosome breaks were identified within the AF9 region that was previously reported to participate in reciprocal translocation between the mixed lineage leukaemia (MLL) and AF9 genes in an acute lymphoblastic leukaemia (ALL) patient. Conclusions: These findings suggest a role for BA-induced apoptosis in mediating Chromosome Rearrangements in NPC. In addition, CAD may be a key player in Chromosome cleavages mediated by BA-induced apoptosis. Persistent exposure of sinonasal tract to gastric duodenal refluxate may increase genomic instability in surviving cells

Sai-peng Sim - One of the best experts on this subject based on the ideXlab platform.

  • Oxidative stress-induced Chromosome breaks within the ABL gene: a model for Chromosome Rearrangement in nasopharyngeal carcinoma.
    Human Genomics, 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim, Alan S. B. Khoo
    Abstract:

    The mechanism underlying Chromosome Rearrangement in nasopharyngeal carcinoma (NPC) remains elusive. It is known that most of the aetiological factors of NPC trigger oxidative stress. Oxidative stress is a potent apoptotic inducer. During apoptosis, chromatin cleavage and DNA fragmentation occur. However, cells may undergo DNA repair and survive apoptosis. Non-homologous end joining (NHEJ) pathway has been known as the primary DNA repair system in human cells. The NHEJ process may repair DNA ends without any homology, although region of microhomology (a few nucleotides) is usually utilised by this DNA repair system. Cells that evade apoptosis via erroneous DNA repair may carry chromosomal aberration. Apoptotic nuclease was found to be associated with nuclear matrix during apoptosis. Matrix association region/scaffold attachment region (MAR/SAR) is the binding site of the chromosomal DNA loop structure to the nuclear matrix. When apoptotic nuclease is associated with nuclear matrix during apoptosis, it potentially cleaves at MAR/SAR. Cells that survive apoptosis via compromised DNA repair may carry Chromosome Rearrangement contributing to NPC tumourigenesis. The Abelson murine leukaemia (ABL) gene at 9q34 was targeted in this study as 9q34 is a common region of loss in NPC. This study aimed to identify the Chromosome breakages and/or Rearrangements in the ABL gene in cells undergoing oxidative stress-induced apoptosis. In the present study, in silico prediction of MAR/SAR was performed in the ABL gene. More than 80% of the predicted MAR/SAR sites are closely associated with previously reported patient breakpoint cluster regions (BCR). By using inverse polymerase chain reaction (IPCR), we demonstrated that hydrogen peroxide (H2O2)-induced apoptosis in normal nasopharyngeal epithelial and NPC cells led to chromosomal breakages within the ABL BCR that contains a MAR/SAR. Intriguingly, we detected two translocations in H2O2-treated cells. Region of microhomology was found at the translocation junctions. This observation is consistent with the operation of microhomology-mediated NHEJ. Our findings suggested that oxidative stress-induced apoptosis may participate in Chromosome Rearrangements of NPC. A revised model for oxidative stress-induced apoptosis mediating Chromosome Rearrangement in NPC is proposed.

  • Oxidative stress-induced Chromosome breaks within the ABL gene: a model for Chromosome Rearrangement in nasopharyngeal carcinoma
    Human Genomics, 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim, Alan S. B. Khoo
    Abstract:

    Background The mechanism underlying Chromosome Rearrangement in nasopharyngeal carcinoma (NPC) remains elusive. It is known that most of the aetiological factors of NPC trigger oxidative stress. Oxidative stress is a potent apoptotic inducer. During apoptosis, chromatin cleavage and DNA fragmentation occur. However, cells may undergo DNA repair and survive apoptosis. Non-homologous end joining (NHEJ) pathway has been known as the primary DNA repair system in human cells. The NHEJ process may repair DNA ends without any homology, although region of microhomology (a few nucleotides) is usually utilised by this DNA repair system. Cells that evade apoptosis via erroneous DNA repair may carry chromosomal aberration. Apoptotic nuclease was found to be associated with nuclear matrix during apoptosis. Matrix association region/scaffold attachment region (MAR/SAR) is the binding site of the chromosomal DNA loop structure to the nuclear matrix. When apoptotic nuclease is associated with nuclear matrix during apoptosis, it potentially cleaves at MAR/SAR. Cells that survive apoptosis via compromised DNA repair may carry Chromosome Rearrangement contributing to NPC tumourigenesis. The Abelson murine leukaemia ( ABL) gene at 9q34 was targeted in this study as 9q34 is a common region of loss in NPC. This study aimed to identify the Chromosome breakages and/or Rearrangements in the ABL gene in cells undergoing oxidative stress-induced apoptosis. Results In the present study, in silico prediction of MAR/SAR was performed in the ABL gene. More than 80% of the predicted MAR/SAR sites are closely associated with previously reported patient breakpoint cluster regions (BCR). By using inverse polymerase chain reaction (IPCR), we demonstrated that hydrogen peroxide (H_2O_2)-induced apoptosis in normal nasopharyngeal epithelial and NPC cells led to chromosomal breakages within the ABL BCR that contains a MAR/SAR. Intriguingly, we detected two translocations in H_2O_2-treated cells. Region of microhomology was found at the translocation junctions. This observation is consistent with the operation of microhomology-mediated NHEJ. Conclusions Our findings suggested that oxidative stress-induced apoptosis may participate in Chromosome Rearrangements of NPC. A revised model for oxidative stress-induced apoptosis mediating Chromosome Rearrangement in NPC is proposed.

  • Bile acids at neutral and acidic pH induce apoptosis and gene cleavages in nasopharyngeal epithelial cells: implications in Chromosome Rearrangement
    BMC cancer, 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim
    Abstract:

    Chronic rhinosinusitis (CRS) increases the risk of developing nasopharyngeal carcinoma (NPC) while nasopharyngeal reflux is known to be one of the major aetiological factors of CRS. Bile acid (BA), the component of gastric duodenal contents, has been recognised as a carcinogen. BA-induced apoptosis was suggested to be involved in human malignancies. Cells have the potential and tendency to survive apoptosis. However, cells that evade apoptosis upon erroneous DNA repair may carry Chromosome Rearrangements. Apoptotic nuclease, caspase-activated deoxyribonuclease (CAD) has been implicated in mediating translocation in leukaemia. We hypothesised that BA-induced apoptosis may cause Chromosome breaks mediated by CAD leading to Chromosome Rearrangement in NPC. This study targeted the AF9 gene located at 9p22 because 9p22 is one of the most common deletion sites in NPC. We tested the ability of BA at neutral and acidic pH in inducing phosphatidylserine (PS) externalisation, reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP) disruption, and caspase 3/7 activity in normal nasopharyngeal epithelial (NP69) and NPC (TWO4) cells. Inverse-PCR (IPCR) was employed to detect AF9 gene cleavages. To investigate the role of CAD in mediating these cleavages, caspase inhibition was performed. IPCR bands representing AF9 cleaved fragments were sequenced. BA-treated cells showed higher levels of PS externalisation, ROS production, MMP loss and caspase 3/7 activity than untreated control cells. The effect of BA in the induction of these intracellular events was enhanced by acid. BA at neutral and acidic pH also induced significant cleavage of the AF9 gene. These BA-induced gene cleavages were inhibited by Z-DEVD-FMK, a caspase-3 inhibitor. Intriguingly, a few Chromosome breaks were identified within the AF9 region that was previously reported to participate in reciprocal translocation between the mixed lineage leukaemia (MLL) and AF9 genes in an acute lymphoblastic leukaemia (ALL) patient. These findings suggest a role for BA-induced apoptosis in mediating Chromosome Rearrangements in NPC. In addition, CAD may be a key player in Chromosome cleavages mediated by BA-induced apoptosis. Persistent exposure of sinonasal tract to gastric duodenal refluxate may increase genomic instability in surviving cells.

  • Bile acids at neutral and acidic pH induce apoptosis and gene cleavages in nasopharyngeal epithelial cells : implications in Chromosome Rearrangement
    'Springer Science and Business Media LLC', 2018
    Co-Authors: Sang-nee Tan, Sai-peng Sim
    Abstract:

    Background: Chronic rhinosinusitis (CRS) increases the risk of developing nasopharyngeal carcinoma (NPC) while nasopharyngeal reflux is known to be one of the major aetiological factors of CRS. Bile acid (BA), the component of gastric duodenal contents, has been recognised as a carcinogen. BA-induced apoptosis was suggested to be involved in human malignancies. Cells have the potential and tendency to survive apoptosis. However, cells that evade apoptosis upon erroneous DNA repair may carry Chromosome Rearrangements. Apoptotic nuclease, caspase-activated deoxyribonuclease (CAD) has been implicated in mediating translocation in leukaemia. We hypothesised that BA-induced apoptosis may cause Chromosome breaks mediated by CAD leading to Chromosome Rearrangement in NPC. This study targeted the AF9 gene located at 9p22 because 9p22 is one of the most common deletion sites in NPC. Methods: We tested the ability of BA at neutral and acidic pH in inducing phosphatidylserine (PS) externalisation, reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP) disruption, and caspase 3/7 activity in normal nasopharyngeal epithelial (NP69) and NPC (TWO4) cells. Inverse-PCR (IPCR) was employed to detect AF9 gene cleavages. To investigate the role of CAD in mediating these cleavages, caspase inhibition was performed. IPCR bands representing AF9 cleaved fragments were sequenced. Results: BA-treated cells showed higher levels of PS externalisation, ROS production, MMP loss and caspase 3/7 activity than untreated control cells. The effect of BA in the induction of these intracellular events was enhanced by acid. BA at neutral and acidic pH also induced significant cleavage of the AF9 gene. These BA-induced gene cleavages were inhibited by Z-DEVD-FMK, a caspase-3 inhibitor. Intriguingly, a few Chromosome breaks were identified within the AF9 region that was previously reported to participate in reciprocal translocation between the mixed lineage leukaemia (MLL) and AF9 genes in an acute lymphoblastic leukaemia (ALL) patient. Conclusions: These findings suggest a role for BA-induced apoptosis in mediating Chromosome Rearrangements in NPC. In addition, CAD may be a key player in Chromosome cleavages mediated by BA-induced apoptosis. Persistent exposure of sinonasal tract to gastric duodenal refluxate may increase genomic instability in surviving cells