A paracrine signal mediates the cell transformation response to low dose gamma radiation in JB6 cells

The carcinogenic response to radiation is complex and may involve adaptive cellular responses as well as a bystander effect mediated by paracrine or intercellular signaling activities. Using a newly developed co-culture model we have examined whether low dose gamma radiation induces the transformation of JB6 mouse epidermal cells as well as nonirradiated bystander cells. Cell transformation response is defined as the acquisition of anchorage-independent growth properties and is quantified by counting colonies on soft agar. Exposure of J136 cells to low dose (2-20 cGy) gamma radiation resulted in an approximate 1.9 +/- 0.1 and 2.8 +/- 0.5-fold increase in cell transformation response when cells were seeded at 1 X 10(4) or 1 X 10(5) cells/dish, relative to respective sham exposed controls. We developed a co-culture model where sham exposed or irradiated JB6 cells were mixed with non-irradiated JB6 cells that had been stably transfected with the enhanced yellow fluorescent protein (EYFP) to enable the distinction of fluorescent bystander-specific colonies. A significant increase in the number of bystander-specific colonies was observed in co-culture with 10 cGy irradiated JB6 cells (224 +/- 9), relative to the number of bystander-specific colonies arising in coculture with sham exposed JB6 cells (55 +/- 16). Our results indicate that low dose radiation induces the transformation of JB6 cells and that a soluble paracrine factor that is secreted by irradiated cells induces the transformation of nonirradiated bystander cells. (c) 2005 Wiley-Liss, Inc.