title: Mitochondrial mutagenesis induced by tumor-specific radiation bystander effects.
abstract: The radiation bystander effect is a cellular process whereby cells not directly exposed to radiation display cellular alterations similar to directly irradiated cells. Cellular targets including mitochondria have been postulated to play a significant role in this process. In this study, we utilized the Random Mutation Capture assay to quantify the levels of random mutations and deletions in the mitochondrial genome of bystander cells. A significant increase in the frequency of random mitochondrial mutations was found at 24 h in bystander cells exposed to conditioned media from irradiated tumor explants (p = 0.018). CG:TA mutations were the most abundant lesion induced. A transient increase in the frequency of random mitochondrial deletions was also detected in bystander cells exposed to conditioned media from tumor but not normal tissue at 24 h (p = 0.028). The increase in both point mutations and deletions was transient and not detected at 72 h. To further investigate mitochondrial dysfunction, mitochondrial membrane potential and reactive oxygen species were assessed in these bystander cells. There was a significant reduction in mitochondrial membrane potential and this was positively associated with the frequency of random point mutation and deletions in bystander cells treated with conditioned media from tumor tissue (r = 0.71, p = 0.02). This study has shown that mitochondrial genome alterations are an acute consequence of the radiation bystander effect secondary to mitochondrial dysfunction and suggests that this cannot be solely attributable to changes in ROS levels alone.
authors.affiliation: Centre for Colorectal Disease, St. Vincent's University Hospital, Elm Park, Dublin 4, Ireland.
authors.forename: Sheeona
authors.initials: S
authors.lastname: Gorman
authors.forename: Edward
authors.initials: E
authors.lastname: Fox
authors.forename: Diarmuid
authors.initials: D
authors.lastname: O'Donoghue
authors.forename: Kieran
authors.initials: K
authors.lastname: Sheahan
authors.forename: John
authors.initials: J
authors.lastname: Hyland
authors.forename: Hugh
authors.initials: H
authors.lastname: Mulcahy
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Loeb
authors.forename: Jacintha
authors.initials: J
authors.lastname: O'Sullivan
mesh_terms: D000368:Aged; D024201:Bystander Effect; D017077:Culture Media, Conditioned / Q000378:metabolism; D004272:DNA, Mitochondrial / Q000528:radiation effects*; D005260:Female; D005720:Gamma Rays; D006801:Humans; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000528:radiation effects; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects*; D009154:Mutation; D009369:Neoplasms / Q000378:metabolism*; D017354:Point Mutation; D017382:Reactive Oxygen Species / Q000378:metabolism; D017384:Sequence Deletion
chemical_list: D017077:Culture Media, Conditioned; D004272:DNA, Mitochondrial; D017382:Reactive Oxygen Species