title: Up-regulation of ROS by mitochondria-dependent bystander signaling contributes to genotoxicity of bystander effects.
abstract: Genomic instability can be observed in bystander cells. However, the underlying mechanism(s) is still relatively unclear. In a previous study, we found that irradiated cells released mitochondria-dependent intracellular factor(s) which could lead to bystander gamma-H2AX induction. In this paper, we used normal (rho(+)) and mtDNA-depleted (rho(0)) human-hamster hybrid cells to investigate mitochondrial effects on the genotoxicity in bystander effect through medium transfer experiments. Through the detection of DNA double-strand breaks with gamma-H2AX, we found that the fraction of gamma-H2AX positive cells changed with time when irradiation conditioned cell medium (ICCM) were harvested. ICCM harvested from irradiated rho(+) cells at 10 min post-irradiation (rho(+) ICCM(10 min)) caused larger increases of bystander gamma-H2AX induction comparing to rho(0) ICCM(10 min), which only caused a slight increase of bystander gamma-H2AX induction. The rho(+) ICCM(10 min) could also result in the up-regulation of ROS production (increased by 35% at 10 min), while there was no significant increase in cells treated with rho(0) ICCM(10 min). We treated cells with dimethyl sulfoxide (DMSO), the scavenger of ROS, and quenched gamma-H2AX induction by rho(+) ICCM. Furthermore, after the medium had been transferred and the cells were continuously cultured for 7 days, we found significantly increased CD59(-) gene loci mutation (increased by 45.9%) and delayed cell death in the progeny of rho(+) ICCM-treated bystander cells. In conclusion, the work presented here suggested that up-regulation of the mitochondria-dependent ROS might be very important in mediating genotoxicity of bystander effects.
authors.affiliation: Key Laboratory of Ion Beam Bioengineering, Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China.
authors.forename: Shaopeng
authors.initials: S
authors.lastname: Chen
authors.forename: Ye
authors.initials: Y
authors.lastname: Zhao
authors.forename: Guoping
authors.initials: G
authors.lastname: Zhao
authors.forename: Wei
authors.initials: W
authors.lastname: Han
authors.forename: Lingzhi
authors.initials: L
authors.lastname: Bao
authors.forename: K N
authors.initials: KN
authors.lastname: Yu
authors.forename: Lijun
authors.initials: L
authors.lastname: Wu
mesh_terms: D000818:Animals; D024201:Bystander Effect / Q000528:radiation effects*; D016466:CHO Cells; D016923:Cell Death; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage; D004272:DNA, Mitochondrial / Q000378:metabolism*; D006657:Histones / Q000378:metabolism*; D006801:Humans; D006822:Hybrid Cells / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000528:radiation effects*; D015398:Signal Transduction; D015854:Up-Regulation
chemical_list: D004272:DNA, Mitochondrial; C468783:H2AX protein, human; D006657:Histones; D017382:Reactive Oxygen Species