Targeted cytoplasmic irradiation induces bystander responses.
The observation of radiation-induced bystander responses, in which cells respond to their neighbors being irradiated, has important implications for understanding mechanisms of radiation action particularly after low-dose exposure. Much of this questions the current dogma of direct DNA damage driving response in irradiated systems. In this study, we have used a charged-particle microbeam to target individual helium ions ((3)He(2+)) to individual cells within a population of radioresistant glioma cells cultured alone or in coculture with primary human fibroblasts. We found that even when a single cell within the glioma population was precisely traversed through its cytoplasm with one (3)He(2+) ion, bystander responses were induced in the neighboring nonirradiated glioma or fibroblasts so that the yield of micronuclei was increased by 36% for the glioma population and 78% for the bystander fibroblast population. Importantly, the yield of bystander-induced micronuclei was independent of whether the cytoplasm or nucleus of a cell was targeted. The bystander responses were fully eliminated when the populations were treated with 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide or filipin, which scavenge nitric oxide (NO) and disrupt membrane rafts, respectively. By using the probe 4-amino-5-methylamino-2',7'-difluorofluorescein, it was found that the NO level in the glioma population was increased by 15% after 1 or 10 cytoplasmic traversals, and this NO production was inhibited by filipin. This finding shows that direct DNA damage is not required for switching on of important cell-signaling mechanisms after low-dose irradiation and that, under these conditions, the whole cell should be considered a sensor of radiation exposure.
Shao
Chunlin
C
Gray Cancer Institute, P.O. Box 100, Mount Vernon Hospital, Northwood, Middlesex HA6 2JR, United Kingdom.
Folkard
Melvyn
M
Michael
Barry D
BD
Prise
Kevin M
KM
D001685:Biological Factors / Q000378:metabolism; D024201:Bystander Effect / Q000528:radiation effects*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism / Q000528:radiation effects*; D003593:Cytoplasm / Q000528:radiation effects*; D005347:Fibroblasts; D006801:Humans; D048629:Micronuclei, Chromosome-Defective / Q000528:radiation effects; D009569:Nitric Oxide / Q000378:metabolism; D015398:Signal Transduction / Q000528:radiation effects; D012995:Solubility
D001685:Biological Factors; D009569:Nitric Oxide