DNA-PKcs and ATM influence generation of ionizing radiation-induced bystander signals

Abstract

The phenomenon by which irradiated cells influence nonirradiated neighboring cells, referred to as the bystander effect (BSE), is not well understood in terms of the underlying pathways involved. We sought to enlighten connections between DNA damage repair and the BSE. Utilizing sister chromatid exchange (SCE) frequencies as a marker of the BSE, we performed cell transfer strategies that enabled us to distinguish between generation versus reception of a bystander signal. We find that DNAdependent Protein Kinase catalytic subunit (DNA-PKcs) and Ataxia Telangectasia Mutated (ATM) are necessary for the generation of such a bystander signal in normal human cells following gamma (c)-ray exposure, but are not required for its reception. Importantly, we also show that directly irradiated human cells do not respond to receipt of a bystander signal, helping to explain why the BSE is a low-dose phenomenon. These studies provide the first evidence for a role of the DNA damage response proteins DNA-PKcs and ATM specifically in the generation of a bystander signal and intercellular signaling.

Direct and Bystander Effect on Cervix Cancer Cells (SiHa) Exposed to High Dose-Rate Gamma Radiation Sourced from Ir 192 Used in Brachytherapy

“…Such a difference was more prominent, if the differences among the dose rates were in the order of 0.01-1Gy/min, and below this dose-rate range the survival curve changes a little in response to dose rate [33,34]. The results obtained in the present study had some difference in the frequencies of MN as well as the clonogenic ability at higher doses among the different dose-rates studies, were not significant.…”

“…Brachytherapy reduces doses on the surrounding cell compared to teletherapy due to its nature of tumour site directed therapy and reduced therapy time [33]. Therefore to investigate the non-targeted effects of HDR gamma radiation sourced from Ir 192 upon the unexposed tumor and normal cells, co-culture methodology was employed and the bystander effect was measured using MN assay.…”

DNA-PK phosphorylation of RPA32 Ser4/Ser8 regulates replication stress checkpoint activation, fork restart, homologous recombination and mitotic catastrophe

“…Metaphase chromosomes were prepared using standard cytogenetic techniques and SCE analysis performed using Fluorescence Plus Giemsa (FPG) staining [44]. Briefly, near confluent cells were treated with 5 mM HU or mock treated for 16 h, then transferred to media containing 10 μM BrdU and incubated for two cell cycles to enable harlequin staining.…”

Non-targeted effects of ionising radiation—Implications for low dose risk

“…The relevance of this work to low-dose risk in humans is unclear, but suggests, as with some others [31, 32], that bystander effects can act to increase rather than decrease risk. It has been reported that not all cell types produce bystander signals and not all cell types respond [139–141]. This variable expression of BE could be due to the presence of multiple pathways involved in the various bystander phenomena.…”

“…From these results and others, it is reasonable to propose that the biological consequences of such a wide range of responses can be both damaging (i.e., sister chromatid exchanges, gene mutation, and transformation in vitro , and in vivo induction of medullablastoma through the transmission of bystander signals from the back of the irradiated mice to the cerebellum) [137] and protective (i.e., apoptotic cell death in vivo and in vitro , as well as the enhancement of cell differentiation with loss of proliferation in tissue in vivo with either high- or low-LET radiation) [141, 152, 153]. …”