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

Abstract

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 non-irradiated 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 JB6 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 co-culture 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 non-irradiated bystander cells.

Cellular dichotomy between anchorage‐independent growth responses to bFGF and TPA reflects molecular switch in commitment to carcinogenesis

“…We have previously demonstrated that ionizing radiation induces the transformation of JB6 mouse epidermal cells 6. As expected, a low dose of radiation (10 cGy) produces a small increase in cell transformation response (doubling–tripling of spontaneous background transformation frequency of ∼20 colonies/10 000 cells).…”

“…We examined endogenous murine DBP and HLF expression in colonies derived from irradiated JB6 cells 6 to determine whether central features of AIG regulation were conserved in colonies induced by low doses of radiation. Colonies spontaneously arising in control, 2 and 20 cGy irradiated dishes were isolated and established as cell lines.…”

Radiation-induced bystander effects and adaptive response in murine lymphocytes

“…Enhanced proliferation (14 -17%) has been reported following co-culture of unirradiated rat liver epithelial cells with cells exposed to 0.5 -10 Gy (Gerashchenko & Howell 2003). A significant increase in the number of bystander-specific colonies has also been observed when unirradiated JB6 cells were co-cultured with their low dose (10 cGy) irradiated counterparts as compared to that in cells co-cultured with sham exposed JB6 cells (Weber et al 2005). Increased proliferation response following co-culture of unirradiated neoplastic human salivary gland (HSG) cells with irradiated cells was related to the linear energy transfer (LET) as well as the radiation dose (Shao et al 2003).…”

Sesquiterpene lactones isolated from indigenous Middle Eastern plants inhibit tumor promoter-induced transformation of JB6 cells

“…Colony growth in soft agar is a well-established index of cell transformation [24]. Anchorage-independent growth was studied using the CytoSelect TM 96-Well Cell Transformation Assay kit (Cell Biolabs) according to manufacturer’s instructions.…”

“…In contrast to tumor initiation, tumor promotion is largely reversible, dependent on epigenetic mechanisms, and is a rate-limiting step in multi-stage carcinogenesis, making it an attractive target for anticancer drugs [20,21]. The JB6P + cells can be transformed to malignancy by tumor promoters, and hence, constitute an ideal model to identify anti-tumor promoting and chemopreventive agents and to decipher their mechanism of action [19,22-24]. …”