Mitochondria-dependent signalling pathway are involved in the early process of radiation-induced bystander effects

Abstract

Bystander effects induced by cytoplasmic irradiation have been reported recently. However, the mechanism(s) underlying, such as the functional role of mitochondria, is not clear. In the present study, we used either mtDNA-depleted (r 0 ) A L or normal (r þ ) A L cells as irradiated donor cells and normal human skin fibroblasts as receptor cells in a series of medium transfer experiments to investigate the mitochondria-related signal process. Our results indicated that mtDNA-depleted cells or normal A L cells treated with mitochondrial respiratory chain function inhibitors had an attenuated g-H2AX induction, which indicates that mitochondria play a functional role in bystander effects. Moreover, it was found that treatment of normal A L donor cells with specific inhibitors of NOS, or inhibitor of mitochondrial calcium uptake (ruthenium red) significantly decreased g-H2AX induction and that radiation could stimulate cellular NO and O 2 KÀ production in irradiated r þ A L cells, but not in r 0 A L cells. These observations, together with the findings that ruthenium red treatment significantly reduced the NO and O 2 KÀ levels in irradiated r þ A L cells, suggest that radiationinduced NO derived from mitochondria might be an intracellular bystander factor and calcium-dependent mitochondrial NOS might play an essential role in the process.

Bystander effect in human lymphocytes incubated with irradiated mitochondrial DNA deficient yeast cells

“…3) clearly shows that irradiated rho + yeast cells induced BE is much stronger than the rho 0 cells. These results confirm the view that strength of bystander effect depends on existence of mitochondrial DNA and normally functioning mitochondria [4].…”

“…This phenomenon has been described in wide variety of vertebrate cell types, and to a lesser extent in other Metazoa cells and several unicellular organisms [2,3]. It was shown that BE is not cell-type dependent and can be induced in mixed cell cultures containing cells of different lines or cells derived from different species [4]. In addition, there is evidence for the existence of BE-like interactions in vivo in animals [5], in plants [6], as well as between cohabiting individuals of the same species [7,8].…”

“…al. reported that mtDNA-depleted cells have an attenuated BE induction [4]. The purpose of the present study was comparison of strength of bystander effect in human lymphocytes induction by rho 0 (complete loss of mitochondrial DNA) and rho + (with fully functional mtDNA) strains of S. cerevisiae.…”

Mitochondrial dysfunction resulting from loss of cytochrome c impairs radiation-induced bystander effect

“…This study, together with several other studies (Lyng et al, 2000(Lyng et al, , 2002Limoli et al, 2003;Maguire et al, 2005;Murphy et al, 2005;Nugent et al, 2007;Tartier et al, 2007;Chen et al, 2008), suggested that mitochondria represent the sensor of radiationinduced ionisation events. In this study, we showed that Cyt c-null cells can respond to radiation normally in ROS/NO generations as Cyt c-normal cells (Figures 2B and 3B).…”

“…The 4-amino-5-methylamino-2 0 ,7 0 -difluorofluorescein diacetate (DAF-FM diacetate) and 5-(and-6)-chloromethyl-2 0 ,7 0 -dichlorodihydrofluorescein diacetate, acetyl ester (CM-H 2 DCFDA) (Molecular Probes, Eugene, OR, USA) were used to quantify the level of NO and ROS, respectively, as described (Wan et al, 2005;Chen et al, 2008). In brief, cells at confluency were stained with 5 mM DAF-FM diacetate in Tyrode's solution or 2 mM CM-H 2 DCFDA in D-Hanks for 30 min in incubator, and then washed twice with the proper buffer respectively.…”