title: Lack of spontaneous and radiation-induced chromosome breakage at interstitial telomeric sites in murine scid cells.
abstract: Interstitial telomeric sites (ITSs) in chromosomes from DNA repair-proficient mammalian cells are sensitive to both spontaneous and radiation-induced chromosome breakage. Exact mechanisms of this chromosome breakage sensitivity are not known. To investigate factors that predispose ITSs to chromosome breakage we used murine scid cells. These cells lack functional DNA-PKcs, an enzyme involved in the repair of DNA double-strand breaks. Interestingly, our results revealed lack of both spontaneous and radiation-induced chromosome breakage at ITSs found in scid chromosomes. Therefore, it is possible that increased sensitivity of ITSs to chromosome breakage is associated with the functional DNA double-strand break repair machinery. To investigate if this is the case we used scid cells in which DNA-PKcs deficiency was corrected. Our results revealed complete disappearance of ITSs in scid cells with functional DNA-PKcs, presumably through chromosome breakage at ITSs, but their unchanged frequency in positive and negative control cells. Therefore, our results indicate that the functional DNA double-strand break machinery is required for elevated sensitivity of ITSs to chromosome breakage. Interestingly, we observed significant differences in mitotic chromosome condensation between scid cells and their counterparts with restored DNA-PKcs activity suggesting that lack of functional DNA-PKcs may cause a defect in chromatin organization. Increased condensation of mitotic chromosomes in the scid background was also confirmed in vivo. Therefore, our results indicate a previously unanticipated role of DNA-PKcs in chromatin organisation, which could contribute to the lack of ITS sensitivity to chromosome breakage in murine scid cells.
authors.affiliation: Brunel Institute of Cancer Genetics and Pharmacogenomics, Brunel University, Uxbridge, UK.
authors.forename: H-P
authors.initials: HP
authors.lastname: Wong
authors.forename: H
authors.initials: H
authors.lastname: Mozdarani
authors.forename: C
authors.initials: C
authors.lastname: Finnegan
authors.forename: J
authors.initials: J
authors.lastname: McIlrath
authors.forename: P E
authors.initials: PE
authors.lastname: Bryant
authors.forename: P
authors.initials: P
authors.lastname: Slijepcevic
mesh_terms: D000818:Animals; D002478:Cells, Cultured / Q000528:radiation effects / Q000648:ultrastructure; D019457:Chromosome Breakage; D020223:Chromosome Painting; D002875:Chromosomes / Q000528:radiation effects / Q000648:ultrastructure; D002898:Chromosomes, Human, Pair 8 / Q000235:genetics; D004247:DNA / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D004260:DNA Repair / Q000235:genetics; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011836:Radiation Tolerance / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid / Q000528:radiation effects; D016511:Severe Combined Immunodeficiency / Q000235:genetics* / Q000473:pathology; D016615:Telomere / Q000528:radiation effects* / Q000648:ultrastructure
chemical_list: D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D004247:DNA; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases